publicationDate,title,abstract,id
2024/1/15,Calculating Magnetic Properties of Two-Dimensional Materials for Memory Applications,"Calculating magnetic properties of two-dimensional materials is crucial for
implementing memory devices (like USB drive, RAM, hard disk drive of computers)
having reduced size. Two dimensional materials can be implemented as a thin
film which can reduce the size of memory devices. These materials as well as
devices made with magnetic two-dimensional materials are of current research
interest in industry and academia. From the materials project database, crystal
structure file of 30 two dimensional materials have been downloaded to
calculate their magnetic properties. BURAI Quantum espresso software has been
used to extract magnetic properties of 30 two dimensional (2D) materials. These
30 materials have magnetic Fe, Ni, Co, Mn, and Cr atoms in their molecular
structure. Magnetic materials play a key and vital role in today's modern-day
technology. There are five different types of magnetic materials. The
classification magnetic materials are diamagnetism, paramagnetic,
ferromagnetism, ferrimagnetism, and anti-ferromagnetism. Total energy of
different magnetic configurations has been calculated to find the most stable
magnetic configurations of these materials.",2401.07980v1
2011/3/5,Physics and measurements of magnetic materials,"Magnetic materials, both hard and soft, are used extensively in several
components of particle accelerators. Magnetically soft iron-nickel alloys are
used as shields for the vacuum chambers of accelerator injection and extraction
septa; Fe-based material is widely employed for cores of accelerator and
experiment magnets; soft spinel ferrites are used in collimators to damp
trapped modes; innovative materials such as amorphous or nanocrystalline core
materials are envisaged in transformers for high-frequency polyphase resonant
convertors for application to the International Linear Collider (ILC). In the
field of fusion, for induction cores of the linac of heavy-ion inertial fusion
energy accelerators, based on induction accelerators requiring some 107 kg of
magnetic materials, nanocrystalline materials would show the best performance
in terms of core losses for magnetization rates as high as 105 T/s to 107 T/s.
After a review of the magnetic properties of materials and the different types
of magnetic behaviour, this paper deals with metallurgical aspects of
magnetism. The influence of the metallurgy and metalworking processes of
materials on their microstructure and magnetic properties is studied for
different categories of soft magnetic materials relevant for accelerator
technology. Their metallurgy is extensively treated. Innovative materials such
as iron powder core materials, amorphous and nanocrystalline materials are also
studied. A section considers the measurement, both destructive and
non-destructive, of magnetic properties. Finally, a section discusses magnetic
lag effects.",1103.1069v1
2020/8/25,Recent advancements in the study of intrinsic magnetic topological insulators and magnetic Weyl semimetals,"The studies of topological insulators and topological semimetals have been at
frontiers of condensed matter physics and material science. Both classes of
materials are characterized by robust surface states created by the topology of
the bulk band structures and exhibit exotic transport properties. When
magnetism is present in topological materials and breaks the time-reversal
symmetry, more exotic quantum phenomena can be generated, e.g. quantum
anomalous Hall effect, axion insulator, large intrinsic anomalous Hall effect,
etc. In this research update, we briefly summarize the recent research
progresses in magnetic topological materials, including intrinsic magnetic
topological insulators and magnetic Weyl semimetals.",2008.10770v1
2015/1/28,Experimental Characterization of Magnetic Materials for the Magnetic Shielding of Cryomodules in Particle Accelerators,"The magnetic properties of two important passive magnetic shielding materials
(A4K and Amumetal) for accelerator applications, subjected to various
processing and heat treatment conditions are studied comprehensively over a
wide range of temperatures: from Cryogenic to room temperature. We analyze the
effect of processing on the extent of degradation of the magnetic properties of
both materials and investigate the possibility of restoring these properties by
re-annealing.",1501.07312v1
2023/8/3,Magnetic interactions in IV-VI diluted magnetic semiconductors,"Diluted magnetic semiconductors (DMS) are interesting because of the
interplay between the electronic and magnetic subsystems. We describe selected
magnetic properties of IV-VI diluted magnetic semiconductors, looking at the
similarities and differences between magnetic properties of II-VI, IV-VI, and
III-V DMS. We focus on the influence of the crystalline and electronic
structure of the material on its magnetic properties, especially on the
exchange interactions among magnetic ions. We describe methods of determination
of the exchange parameters by using different experimental techniques, such as
measurements of magnetic susceptibility, magnetization, and specific heat. We
follow the development in the material technology from bulk crystals to thin
films and nanostructures.",2308.01780v1
2017/2/28,Chemical Responsive Single Crystal Organic Magnet,"Materials that change their magnetic properties in response to the external
stimuli have long been of interest for their potential applicability in
magnetic storage device, spintronics and smart magnetic materials. Organic
materials are suitable candidates for such materials due to their chemical
diversity, flexibility and designablity. However, most methods used for
changing magnetism are inefficient or destructive to the magnetic material.
Hence there is a need for innovation in this field. Here we report
high-performance magnetic control of a gas-responsive single-molecule magnet
(SMM). The results exhibit that the magnetic properties of the SMM can be
significantly changed according to the gas environment it is in and some of the
magnetic states can be reversibly transformed or coexistent in the SMM through
artificial control. More importantly, the monocrystalline structure of the SMM
remains unchanged during the transformation process except for slight change of
the lattice constant. Thus, this work opens up new insights into the
stimuli-responsive magnetic materials which have great prospects for
application in artificial design magnetic network and also highlight their
potential as smart materials.",1703.00006v2
2015/6/5,On the magnetization process of ferromagnetic materials,"The present article concludes that a ferromagnetic sample could be considered
like a paramagnetic system where the role of magnetic moments plays magnetic
domains. Based on this conclusion and taking into account presence of an
anisotropic field the formula which describes magnetization dependence on the
external magnetic field is derived. Expressions for a remanent magnetization
and a coercive force are presented. The new parameter to characterize a
magnetic stiffness of a material is introduced. A physical expression for a
dynamic magnetic susceptibility as a function of material's characteristics,
external magnetic field, and a temperature is given.",1506.01805v3
2023/12/26,Magnetic vortex control with current-induced axial magnetization in centrosymmetric Weyl materials,"We consider magnetic Weyl metals as a platform to achieve current control of
magnetization textures with transport currents, utilizing their underlying band
geometry. We show that the transport current in a Weyl semimetal produces an
axial magnetization due to orbital magnetic moments of the Weyl electrons. The
associated axial magnetization can generate a torque acting on the localized
magnetic moments. For the case of a magnetic vortex in a nanodisk of Weyl
materials, this current-induced torque can be used to reverse its circulation
and polarity. We discuss the axial magnetization torques in Weyl metals on
general symmetry grounds, and compare their strength to current-induced torques
in more conventional materials.",2312.16122v1
2005/6/23,"Magnetic phase diagram copper metaborate CuB_2O_4 in magnetic field parallel c-axis: resonant, magnetic and magnetoelastic investigations","The magnetic phase diagram in a single crystal of copper metaborate CuB_2O_4
in a magnetic field parallel to a tetragonal axis $c$ has been investigated.
  From the resonant, magnetic and magnetostrictive data the phase diagram of
CuB_2O_4 on a plane ``temperature - magnetic field'' is constructed. The
magnetic incommensurate-commensurate phase transition is caused by the
saturation of weak subsystem of copper ions in the strong magnetic field
$H\|c$.",0506596v1
2020/4/1,Theoretical investigation on magnetic property of monolayer CrI3 from microscale to macroscale,"Magnetic two-dimensional (2D) materials have received tremendous attention
recently due to its potential application in spintronics and other magnetism
related fields. To our knowledge, five kinds of 2D materials with intrinsic
magnetism have been synthesized in experiment. They are CrI3, Cr2Ge2Te6, FePS3,
Fe3GeTe2 and VSe2. Apart from the above intrinsic magnetic 2D materials, many
strategies have also been proposed to induce magnetism in normal 2D materials
such as atomic modification, spin valve and proximity effect. Various devices
have also been designed to fulfill the basic functions of spintronics: inducing
spin, manipulating spin and detecting spin.",2004.00468v1
2019/7/11,Improving the Signal-to-noise Ratio for Heat-Assisted Magnetic Recording by Optimizing a High/Low Tc bilayer structure,"We optimize the recording medium for heat-assisted magnetic recording by
using a high/low $T_{\mathrm{c}}$ bilayer structure to reduce AC and DC noise.
Compared to a former work, small Gilbert damping $\alpha=0.02$ is considered
for the FePt like hard magnetic material. Atomistic simulations are performed
for a cylindrical recording grain with diameter $d=5\,$nm and height $h=8\,$nm.
Different soft magnetic material compositions are tested and the amount of hard
and soft magnetic material is optimized. The results show that for a soft
magnetic material with $\alpha_{\mathrm{SM}}=0.1$ and
$J_{ij,\mathrm{SM}}=7.72\times 10^{-21}\,$J/link a composition with $50\%$ hard
and $50\%$ soft magnetic material leads to the best results. Additionally, we
analyse how much the areal density can be improved by using the optimized
bilayer structure compared to the pure hard magnetic recording material. It
turns out that the optimized bilayer design allows an areal density that is
$1\,$Tb/in$^2$ higher than that of the pure hard magnetic material while
obtaining the same SNR.",1907.05027v1
2023/12/22,Magnetic Materials via High-Pressure Torsion of Powders,"Magnets are key materials for the electrification of mobility and also for
the generation and transformation of electric energy. Research and development
in recent decades lead to high performance magnets, which require a finely
tuned microstructure to serve applications with ever increasing requirements.
Besides optimizing already known materials and the search on novel material
combinations, an increasing interest in unconventional processing techniques
and the utilization of magnetic concepts is apparent. Severe plastic
deformation (SPD), in particular by high-pressure torsion (HPT) is a versatile
and suitable method to manufacture microstructures not attained so far, but
entitling different magnetic coupling mechanisms fostering magnetic properties.
In this work, we review recent achievements obtained by HPT on soft and hard
magnetic materials, focusing on powder as starting materials. Furthermore, we
give specific attention to the formation of magnetic composites and highlight
the opportunities of powder starting materials for HPT to exploit magnetic
interaction mechanism.",2312.14582v1
2009/6/26,Relaxation Mechanism for Ordered Magnetic Materials,"We have formulated a relaxation mechanism for ferrites and ferromagnetic
metals whereby the coupling between the magnetic motion and lattice is based
purely on continuum arguments concerning magnetostriction. This theoretical
approach contrasts with previous mechanisms based on microscopic formulations
of spin-phonon interactions employing a discrete lattice. Our model explains
for the first time the scaling of the intrinsic FMR linewidth with frequency,
and 1/M temperature dependence and the anisotropic nature of magnetic
relaxation in ordered magnetic materials, where M is the magnetization. Without
introducing adjustable parameters our model is in reasonable quantitative
agreement with experimental measurements of the intrinsic magnetic resonance
linewidths of important class of ordered magnetic materials, insulator or
metals.",0906.4979v1
2020/2/28,High-throughput calculations of magnetic topological materials,"The discoveries of intrinsically magnetic topological materials, including
semimetals with a large anomalous Hall effect and axion insulators, have
directed fundamental research in solid-state materials. Topological quantum
chemistry has enabled the understanding of and the search for paramagnetic
topological materials. Using magnetic topological indices obtained from
magnetic topological quantum chemistry (MTQC), here we perform a
high-throughput search for magnetic topological materials based on
first-principles calculations. We use as our starting point the Magnetic
Materials Database on the Bilbao Crystallographic Server, which contains more
than 549 magnetic compounds with magnetic structures deduced from
neutron-scattering experiments, and identify 130 enforced semimetals (for which
the band crossings are implied by symmetry eigenvalues), and topological
insulators. For each compound, we perform complete electronic structure
calculations, which include complete topological phase diagrams using different
values of the Hubbard potential. Using a custom code to find the magnetic
co-representations of all bands in all magnetic space groups, we generate data
to be fed into the algorithm of MTQC to determine the topology of each magnetic
material. Several of these materials display previously unknown topological
phases, including symmetry-indicated magnetic semimetals, three-dimensional
anomalous Hall insulators and higher-order magnetic semimetals. We analyse
topological trends in the materials under varying interactions: 60 per cent of
the 130 topological materials have topologies sensitive to interactions, and
the others have stable topologies under varying interactions. We provide a
materials database for future experimental studies and open-source code for
diagnosing topologies of magnetic materials.",2003.00012v2
2020/8/29,High-throughput Design of Magnetic Materials,"Materials design based on density functional theory (DFT) calculations is an
emergent field of great potential to accelerate the development and employment
of novel materials. Magnetic materials play an essential role in green energy
applications as they provide efficient ways of harvesting, converting, and
utilizing energy. In this review, after a brief introduction to the major
functionalities of magnetic materials, we demonstrated the fundamental
properties which can be tackled via high-throughput DFT calculations, with a
particular focus on the current challenges and feasible solutions. Successful
case studies are summarized on several classes of magnetic materials, followed
by bird-view perspectives for the future.",2008.12907v1
2020/1/9,Two-dimensional magnetic nanoelectromechanical resonators,"Two-dimensional (2D) layered materials possess outstanding mechanical,
electronic and optical properties, making them ideal materials for
nanoelectromechanical applications. The recent discovery of 2D magnetic
materials has promised a new class of magnetically active nanoelectromechanical
systems (NEMS). Here we demonstrate resonators made of 2D CrI3, whose
mechanical resonances depend on the magnetic state of the material. We quantify
the underlining effects of exchange and anisotropy magnetostriction by
measuring the field dependence of the resonance frequency under a magnetic
field parallel and perpendicular to the easy axis, respectively. Furthermore,
we show efficient strain tuning of magnetism in 2D CrI3 as a result of the
inverse magnetostrictive effect using the NEMS platform. Our results establish
the basis for mechanical detection of magnetism and magnetic phase transitions
in 2D layered magnetic materials. The new magnetic NEMS may also find
applications in magnetic actuation and sensing.",2001.03153v1
2009/8/10,Tunnel magnetoresistance of magnetic junctions with cubic symmetry of the layers,"A tunnel magnetic junction is considered with magnetic hard and magnetic soft
layers of cubic symmetry. The magnetic switching is analyzed of the layers by a
magnetic field perpendicular to the initial magnetizations. In such a
situation, an additional peak of the TMR ratio appears at the magnetic field
value lower substantially than the anisotropy energy of the soft layer.",0908.1278v1
2022/8/7,Mixels: Fabricating Interfaces using Programmable Magnetic Pixels,"In this paper, we present Mixels, programmable magnetic pixels that can be
rapidly fabricated using an electromagnetic printhead mounted on an
off-the-shelve 3-axis CNC machine. The ability to program magnetic material
pixel-wise with varying magnetic force enables Mixels to create new tangible,
tactile, and haptic interfaces. To facilitate the creation of interactive
objects with Mixels, we provide a user interface that lets users specify the
high-level magnetic behavior and that then computes the underlying magnetic
pixel assignments and fabrication instructions to program the magnetic surface.
Our custom hardware add-on based on an electromagnetic printhead and hall
effect sensor clips onto a standard 3-axis CNC machine and can both write and
read magnetic pixel values from magnetic material. Our evaluation shows that
our system can reliably program and read magnetic pixels of various strengths,
that we can predict the behavior of two interacting magnetic surfaces before
programming them, that our electromagnet is strong enough to create pixels that
utilize the maximum magnetic strength of the material being programmed, and
that this material remains magnetized when removed from the magnetic plotter.",2208.03804v1
2013/7/18,Interaction effect detected by compared of the irreversible and remanent initial magnetization curves in Ni-Cu-Zn ferrites,"A new technique for estimation of magnetic interaction effects of initial
magnetization curves has been proposed. It deals with remanence, and initial
irreversible magnetization, curves. The method is applied for single-phase
polycrystalline Ni0.85-xCu0.15ZnxFe2O4, (x = 0, 0.2, 0.4 and 0.6), which were
synthesized by a standard ceramic technology. A study of the initial reversible
and irreversible magnetization processes in ferrite materials was carried out.
The field dependence of the irreversible, and reversible, magnetizations was
determined by magnetic losses of minor hysteresis loops obtained from different
points of an initial magnetization curve. The influence of Zn-substitutions in
Ni-Cu ferrites over irreversible magnetization processes and interactions in
magnetic systems has been analyzed.",1307.4881v1
2021/10/16,A stretched exponential-based approach for the magnetic properties of spin glasses,"The spin glasses show intriguing characteristic features that are not well
understood yet, as for instance its aging, rejuvenation and memory effects.
Here a model based on a stretched exponential decay of its magnetization is
proposed, which can describe the main magnetic features of spin glasses
observed in experiments as the time-decay of thermoremament magnetization, the
relaxation of zero field cooled magnetization, the ac and dc magnetization as a
function of temperature and others. In principle, the here proposed model could
be adapted to describe other glassy systems.",2110.08625v2
2020/9/3,Coincidence inelastic neutron scattering for detection of two-spin magnetic correlations,"Inelastic neutron scattering (INS) is one powerful technique to study the
low-energy single-spin dynamics of magnetic materials. A variety of quantum
magnets show novel magnetic correlations such as quantum spin liquids. These
novel magnetic correlations are beyond the direct detection of INS. In this
paper we propose a coincidence technique, coincidence inelastic neutron
scattering (cINS), which can detect the two-spin magnetic correlations of the
magnetic materials. In cINS there are two neutron sources and two neutron
detectors with an additional coincidence detector. Two neutrons from the two
neutron sources are incident on the target magnetic material, and they are
scattered by the electron spins of the magnetic material. The two scattered
neutrons are detected by the two neutron detectors in coincidence with the
coincidence probability described by a two-spin Bethe-Salpeter wave function.
Since the two-spin Bethe-Salpeter wave function defines the momentum-resolved
dynamical wave function with two spins excited, cINS can explicitly detect the
two-spin magnetic correlations of the magnetic material. Thus, it can be
introduced to study the various spin valence bond states of the quantum
magnets.",2009.01680v2
2004/9/8,Magnetic and electronic phase transformations in (Sm0.65Sr0.35)MnO3 induced by temperature and magnetic field,"Temperature (4.2-260 K) and magnetic field (0-50 kOe) dependencies of the dc
electrical resistance, dc magnetization, and ac magnetic susceptibility of
(Sm0.65Sr0.35)MnO3 prepared from high purity components have been studied.",0409213v1
2022/3/18,Prediction of novel two-dimensional rare-earth material with room-temperature ferromagnetism and large perpendicular magnetic anisotropy,"Novel 2D ferromagnets with high Curie temperature and large perpendicular
magnetic anisotropy are especially attractive owing to the future promising
application in modern spintronics, but meanwhile the 2D ferromagnetic materials
with high Curie temperature and large perpendicular magnetic anisotropy are
rarely reported. Based on density functional theory (DFT) calculations, we
predict a new kind of 2D ferromagnetic materials - GdB2N2, which possesses
large magnetic moment, high Curie temperature (335 K) and large perpendicular
magnetic anisotropy (10.38 meV/f.u.). Biaxial strain ranging from -0.5% to 5%
and different concentrations of charge-carrier doping are applied to reveal the
influence on the Curie temperature and magnetic anisotropy energy (MAE).
Besides, magnetic coupling process within GdB2N2 is found to be via a
Ruderman-Kittel-Kasuya-Yosida (RKKY) mechanism. In summary, our work here
predicts a novel 2D rare-earth material GdB2N2, which not only enriches the
category of 2D room-temperature ferromagnets, but also proposes a new
possibility of combining traditional 2D materials and rare-earth materials to
achieve more intriguing magnetic properties, finally it carves out the path for
the next-generation spintronic devices and sensors.",2203.10969v1
2014/10/23,Determining the minimum mass and cost of a magnetic refrigerator,"An expression is determined for the mass of the magnet and magnetocaloric
material needed for a magnetic refrigerator and these are determined using
numerical modeling for both parallel plate and packed sphere bed regenerators
as function of temperature span and cooling power. As magnetocaloric material
Gd or a model material with a constant adiabatic temperature change,
representing a infinitely linearly graded refrigeration device, is used. For
the magnet a maximum figure of merit magnet or a Halbach cylinder is used. For
a cost of \$40 and \$20 per kg for the magnet and magnetocaloric material,
respectively, the cheapest 100 W parallel plate refrigerator with a temperature
span of 20 K using Gd and a Halbach magnet has 0.8 kg of magnet, 0.3 kg of Gd
and a cost of \$35. Using the constant material reduces this cost to \$25. A
packed sphere bed refrigerator with the constant material costs \$7. It is also
shown that increasing the operation frequency reduces the cost. Finally, the
lowest cost is also found as a function of the cost of the magnet and
magnetocaloric material.",1410.6248v1
2023/7/18,Yu-Shiba-Rusinov tips: imaging spins at the atomic scale with full magnetic sensitivity,"Measurements of magnetic properties at the atomic scale require probes
capable of combining high spatial resolution with spin sensitivity.
Spin-polarized scanning tunneling microscopy (SP-STM) fulfills these conditions
by using atomically sharp magnetic tips. The imaging of spin structures results
from the tunneling magneto-conductance that depends on the imbalance in the
local density of spin-up and spin-down electrons. Spin-sensitive tips are
generally formed from bulk materials or by coating non-magnetic tips with a
thin magnetic layer. However, ferromagnetic materials generate stray magnetic
fields which can influence the magnetic structure of the probed system, while
the magnetization of antiferromagnetic materials is difficult to set tip by
externally applied magnetic fields. Here, we use functionalized
Yu-Shiba-Rusinov (YSR) tips prepared by attaching magnetic adatoms at the apex
of a superconducting cluster to image magnetic interactions at the atomic
scale. We demonstrate that YSR tips are capable of sensing different
magnetization directions, conferring them full magnetic sensitivity. We
additionally show that the finite size of the tip superconducting cluster makes
it robust against relatively strong magnetic fields, making YSR tips capable of
visualizing magnetic field driven transitions of the spin texture.",2307.09534v1
2011/7/8,Antimagnets: Controlling magnetic fields with superconductor-metamaterial hybrids,"Magnetism is very important in science and technology, from magnetic
recording to energy generation to trapping cold atoms. Physicists have managed
to master magnetism - to create and manipulate magnetic fields- almost at will.
Surprisingly, there is at least one property which until now has been elusive:
how to 'switch off' the magnetic interaction of a magnetic material with
existing magnetic fields without modifying them. Here we introduce the
antimagnet, a design to conceal the magnetic response of a given volume from
its exterior, without altering the external magnetic fields, somehow analogous
to the recent theoretical proposals for cloaking electromagnetic waves with
metamaterials. However, different from these devices requiring extreme material
properties, our device is feasible and needs only two kinds of available
materials: superconductors and isotropic magnetic materials. Antimagnets may
have applications in magnetic-based medical techniques such as MRI or in
reducing the magnetic signature of vessels or planes.",1107.1647v1
2018/6/20,Data-driven studies of magnetic two-dimensional materials,"We use a data-driven approach to study the magnetic and thermodynamic
properties of van der Waals (vdW) layered materials. We investigate monolayers
of the form A$_2$B$_2$X$_6$, based on the known material Cr$_2$Ge$_2$Te$_6$,
using density functional theory (DFT) calculations and machine learning methods
to determine their magnetic properties, such as magnetic order and magnetic
moment. We also examine formation energies and use them as a proxy for chemical
stability. We show that machine learning tools, combined with DFT calculations,
can provide a computationally efficient means to predict properties of such
two-dimensional (2D) magnetic materials. Our data analytics approach provides
insights into the microscopic origins of magnetic ordering in these systems.
For instance, we find that the X site strongly affects the magnetic coupling
between neighboring A sites, which drives the magnetic ordering. Our approach
opens new ways for rapid discovery of chemically stable vdW materials that
exhibit magnetic behavior.",1806.07989v1
2020/6/1,High-throughput search for magnetic and topological order in transition metal oxides,"The discovery of intrinsic magnetic topological order in $\rm MnBi_2Te_4$ has
invigorated the search for materials with coexisting magnetic and topological
phases. These multi-order quantum materials are expected to exhibit new
topological phases that can be tuned with magnetic fields, but the search for
such materials is stymied by difficulties in predicting magnetic structure and
stability. Here, we compute over 27,000 unique magnetic orderings for over
3,000 transition metal oxides in the Materials Project database to determine
their magnetic ground states and estimate their effective exchange parameters
and critical temperatures. We perform a high-throughput band topology analysis
of centrosymmetric magnetic materials, calculate topological invariants, and
identify 18 new candidate ferromagnetic topological semimetals, axion
insulators, and antiferromagnetic topological insulators. To accelerate future
efforts, machine learning classifiers are trained to predict both magnetic
ground states and magnetic topological order without requiring first-principles
calculations.",2006.01075v1
2016/9/27,The magnetic properties of the hollow cylindrical ideal remanence magnet,"We consider the magnetic properties of the hollow cylindrical ideal remanence
magnet. This magnet is the cylindrical permanent magnet that generates a
uniform field in the cylinder bore, using the least amount of magnetic energy
to do so. The remanence distribution of this magnet is derived and the
generated field is compared to that of a Halbach cylinder of equal dimensions.
The ideal remanence magnet is shown in most cases to generate a significantly
lower field than the equivalent Halbach cylinder, although the field is
generated with higher efficiency. The most efficient Halbach cylinder is shown
to generate a field exactly twice as large as the equivalent ideal remanence
magnet.",1609.08548v1
2019/1/31,"Anisotropic ferromagnetism and structure stability in $4f$-$3d$ intermetallics: ab initio structure optimization and magnetic anisotropy for RCo$_5$ (R=Ce, La, and Y)","Electronic mechanism in the interplay between ferromagnetism and structure
stability of $4f$-$3d$ intermetallics in the main phase of rare-earth permanent
magnets is investigated from first principles. We present a case study with an
archetypical materials family RCo$_5$ (R=Ce, La, Y), which was a part of the
earliest rare-earth permanent magnets and from which other representative
main-phase compounds can be regarded as a derived type. Comparison with the
champion magnet materials family R$_2$T$_{14}$B and recently revisited
materials family RT$_{12}$ (T=Co and Fe) points to a direction leading to a
mid-class magnet for the possible next generation materials.",1901.11498v1
2008/9/9,Magnetic Properties of Ni-Fe Nanowire Arrays: Effect of Template Material and Deposition Conditions,"The objective of this work is to study the magnetic properties of arrays of
Ni-Fe nanowires electrodeposited in different template materials such as porous
silicon, polycarbonate and alumina. Magnetic properties were studied as a
function of template material, applied magnetic field (parallel and
perpendicular) during deposition, wire length, as well as magnetic field
orientation during measurement. The results show that application of magnetic
field during deposition strongly influences the c-axis preferred orientation
growth of Ni-Fe nanowires. The samples with magnetic field perpendicular to
template plane during deposition exhibits strong perpendicular anisotropy with
greatly enhanced coercivity and squareness ratio, particularly in Ni-Fe
nanowires deposited in polycarbonate templates. In case of polycarbonate
template, as magnetic field during deposition increases, both coercivity and
squareness ratio also increase. The wire length dependence was also measured
for polycarbonate templates. As wire length increases, coercivity and
squareness ratio decrease, but saturation field increases. Such magnetic
behavior (dependence on template material, magnetic field, wire length) can be
qualitatively explained by preferential growth phenomena, dipolar interactio",0809.1657v1
1999/4/7,Perpendicular transport and magnetization processes in magnetic multilayers with strongly and weakly coupled magnetic layers,"Within the framework of a two-band tight-binding model, we have performed
calculations of giant magnetoresistance, exchange coupling and thermoelectric
power (TEP) for a system consisting of three magnetic layers separated by two
non-magnetic spacers with the first two magnetic layers strongly
antiferromagnetically exchange-coupled. We have shown how does the GMR relate
with the corresponding regions of magnetic structure phase diagrams and
computed some relevant hysteresis loops, too. The GMR may take negative values
for specific layers thicknesses, and the TEP reveals quite pronounced
oscillations around a negative bias.",9904086v1
2011/3/8,Permanent magnets including undulators and wigglers,"After a few historic remarks on magnetic materials we introduce the basic
definitions related to permanent magnets. The magnetic properties of the most
common materials are reviewed and the production processes are described.
Measurement techniques for the characterization of macroscopic and microscopic
properties of permanent magnets are presented. Field simulation techniques for
permanent magnet devices are discussed. Today, permanent magnets are used in
many fields. This article concentrates on the applications of permanent magnets
in accelerators starting from dipoles and quadrupoles on to wigglers and
undulators.",1103.1573v1
2018/6/8,Real-Space Magnetic Imaging of the Multiferroic Spinels MnV2O4 and Mn3O4,"Controlling multiferroic behavior in materials will enable the development of
a wide variety of technological applications. However, the exact mechanisms
driving multiferroic behavior are not well understood in most materials. Two
such materials are the spinels MnV2O4 and Mn3O4, where mechanical strain is
thought to play a role in determining magnetic behavior. Bulk studies of MnV2O4
have yielded conflicting and inconclusive results, due in part to the presence
of mesoscale magnetic inhomogeneity, which complicates the interpretation of
bulk measurements. To study the sub-micron-scale magnetic properties of
Mn-based spinel materials, we performed magnetic force microscopy (MFM) on
MnV2O4 samples subject to different levels of mechanical strain. We also used a
crystal grain mapping technique to perform spatially registered MFM on Mn3O4.
These local investigations revealed 100-nm-scale ""stripe"" modulations in the
magnetic structure of both materials. In MnV2O4, the magnetization of these
stripes is estimated to be Mz $\approx$ 105 A/m, which is on the order of the
saturation magnetization reported previously. Cooling in a strong magnetic
field eliminated the stripe patterning only in the low-strain sample of MnV2O4.
The discovery of nanoscale magnetostructural inhomogeneity that is highly
susceptible to magnetic field control in these materials necessitates both a
revision of theoretical proposals and a reinterpretation of experimental data
regarding the low-temperature phases and magnetic-field-tunable properties of
these Mn-based spinels.",1806.03148v1
2010/12/17,Phenomenology of magnetically active superconductors,"The thermodynamical phenomenological theory of magnetically active
superconducting materials and magnetic-superconducting heterostructures is
presented. The materials may exhibit arbitrarily strong anisotropy, parametric
or structural. Exact anisotropic similarity transformations are found for both
the continuum and layered hybrid systems.",1012.3869v1
2016/1/4,Mechanically Stimulated Domain Re-arrangement in Cryogenic Magnetic Shielding Materials,"Room temperature properties and behavior of several types of cryogenic
magnetic shielding materials are measured and reported here. Large changes in
the effective relative permeability are observed when the materials are
perturbed with a relatively small mechanical stimulation. The change in
permeability is a reversible effect.",1601.00592v1
2014/8/5,Tunable asymmetric magnetoimpedance effect in ferromagnetic NiFe/Cu/Co films,"We investigate the magnetization dynamics through the magnetoimpedance effect
in ferromagnetic NiFe/Cu/Co films. We observe that the magnetoimpedance
response is dependent on the thickness of the non-magnetic Cu spacer material,
a fact associated to the kind of the magnetic interaction between the
ferromagnetic layers. Thus, we present an experimental study on asymmetric
magnetoimpedance in ferromagnetic films with biphase magnetic behavior and
explore the possibility of tuning the linear region of the magnetoimpedance
curves around zero magnetic field by varying the thickness of the non-magnetic
spacer material, and probe current frequency. We discuss the experimental
magnetoimpedance results in terms of the different mechanisms governing the
magnetization dynamics at distinct frequency ranges, quasi-static magnetic
properties, thickness of the non-magnetic spacer material, and the kind of the
magnetic interaction between the ferromagnetic layers. The results place
ferromagnetic films with biphase magnetic behavior exhibiting asymmetric
magnetoimpedance effect as a very attractive candidate for application as probe
element in the development of auto-biased linear magnetic field sensors.",1408.0992v1
2018/5/7,Single-shot multi-level all-optical magnetization switching mediated by spin-polarized hot electron transport,"All-optical ultrafast magnetization switching in magnetic material thin film
without the assistance of an applied external magnetic field is being explored
for future ultrafast and energy-efficient magnetic storage and memories. It has
been shown that femto-second light pulses induce magnetization reversal in a
large variety of magnetic materials. However, so far, only GdFeCo-based
ferrimagnetic thin films exhibit magnetization switching via a single optical
pulse. Here we demonstrate the single-pulse switching of Co/Pt multilayers
within a magnetic spin-valve structure ([Co/Pt] / Cu / GdFeCo) and further show
that the four possible magnetic configurations of the spin valve can be
accessed using a sequence of single femto-second light pulses. Our experimental
study reveals that the magnetization final state of the ferromagnetic [Co/Pt]
layer is determined by spin-polarized hot electrons generated by the light
pulse interactions with the GdFeCo layer. This work provides a new approach to
deterministically switch ferromagnetic layers and a pathway to engineering
materials for opto-magnetic multi-bit recording.",1805.02432v1
2023/11/10,Exchange stiffness proportional to power of magnetization in permalloy co-doped with Mo and Cu,"The exchange stiffness of magnetic materials is one of the essential
parameters governing magnetic texture and its dynamics in magnetic devices. The
effect of single-element doping on exchange stiffness has been investigated for
several doping elements for permalloy (NiFe alloy), a soft magnetic material
whose soft magnetic properties can be controlled by doping. However, the impact
of more practical multi-element doping on the exchange stiffness of permalloy
is unknown. This study investigates the typical magnetic properties, including
exchange stiffness, of permalloy systematically co-doped with Mo and Cu using
broadband ferromagnetic resonance spectroscopy. We find that the exchange
stiffness, which decreases with increasing doping levels, is proportional to a
power of magnetization, which also decreases with increasing doping levels. The
magnetization, $M_{\rm s}$, dependence of the exchange stiffness constant, $A$,
of all the investigated samples, irrespective of the doping levels of each
element, lies on a single curve expressed as $A\propto M_{\rm s}^n$ with
exponent $n$ close to 2. This empirical power-law relationship provides a
guideline for predicting unknown exchange stiffness in non-magnetic
element-doped permalloy systems.",2311.05852v2
2021/3/10,Search and Structural Featurization of Magnetically Frustrated Kagomé Lattices,"We have searched nearly 40,000 inorganic solids in the Inorganic Crystal
Structural Database to identify compounds containing a transition metal or rare
earth kagom\'e sublattice, a geometrically magnetically frustrated lattice,
ultimately identifying $\sim$500 materials. A broad analysis of the chemical
and structural trends of these materials shows three types of kagom\'e sheet
stacking and several classes of magnetic complexity. Following the search and
classification, we rapidly screen the magnetic properties of a subset of the
materials using density functional theory to eliminate those that are unlikely
to exhibit magnetic frustration. From the results of our computational
screening, we rediscover six materials that have previously been explored for
their low temperature magnetic behavior, albeit showing symmetry breaking
distortions, spin glass behavior, or magnetic ordering. However, all are
materials with antiferromagnetic behavior, which we correctly predict. Finally,
we also report three materials that appear to be unexplored for their magnetic
properties.",2103.06187v1
2024/1/11,GPTArticleExtractor: An Automated Workflow for Magnetic Material Database Construction,"A comprehensive database of magnetic materials is valuable for researching
the properties of magnetic materials and discovering new ones. This article
introduces a novel workflow that leverages large language models for extracting
key information from scientific literature. From 22,120 articles in the Journal
of Magnetism and Magnetic Materials, a database containing 2,035 magnetic
materials was automatically generated, with ferromagnetic materials
constituting 76% of the total. Each entry in the database includes the
material's chemical compounds, as well as related structures (space group,
crystal structure) and magnetic temperatures (Curie, N'eel, and other
transitional temperatures). To ensure data accuracy, we meticulously compared
each entry in the database against the original literature, verifying the
precision and reliability of each entry.",2401.05875v1
2014/3/4,All-optical control of ferromagnetic thin films and nanostructures,"The interplay of light and magnetism has been a topic of interest since the
original observations of Faraday and Kerr where magnetic materials affect the
light polarization. While these effects have historically been exploited to use
light as a probe of magnetic materials there is increasing research on using
polarized light to alter or manipulate magnetism. For instance deterministic
magnetic switching without any applied magnetic fields using laser pulses of
the circular polarized light has been observed for specific ferrimagnetic
materials. Here we demonstrate, for the first time, optical control of
ferromagnetic materials ranging from magnetic thin films to multilayers and
even granular films being explored for ultra-high-density magnetic recording.
Our finding shows that optical control of magnetic materials is a much more
general phenomenon than previously assumed. These results challenge the current
theoretical understanding and will have a major impact on data memory and
storage industries via the integration of optical control of ferromagnetic
bits.",1403.0784v1
2022/1/10,A theory for anisotropic magnetoresistance in materials with two vector order parameters,"Anisotropic magnetoresistance (AMR) and related planar Hall resistance (PHR)
are ubiquitous phenomena of magnetic materials. Although the universal angular
dependences of AMR and PHR in magnetic polycrystalline materials with one order
parameter are well known, no similar universal relation for other class of
magnetic materials are known to date. Here I present a general theory of
galvanomagnetic effects in magnetic materials with two vector order parameters,
such as magnetic single crystals with a dominated crystalline axis or
polycrystalline non-collinear ferrimagnetic materials. It is shown that AMR and
PHR have a universal angular dependence. In general, both longitudinal and
transverse resistivity are non-reciprocal in the absence of inversion symmetry:
Resistivity takes different value when the current is reversed. Different from
simple magnetic polycrystalline materials where AMR and PHR have the same
magnitude, and $\pi/4$ out of phase, the magnitude of AMR and PHR of materials
with two vector order parameters are not the same in general, and the phase
difference is not $\pi/4$. Instead of $\pi$ periodicity of the usual AMR and
PHR, the periodicities of materials with two order parameters are $2\pi$.",2201.03316v1
2020/3/30,Tunable interlayer magnetism and band topology in van der Waals heterostructures of MnBi2Te4-family materials,"Manipulating the interlayer magnetic coupling in van der Waals magnetic
materials and heterostructures is the key to tailoring their magnetic and
electronic properties for various electronic applications and fundamental
studies in condensed matter physics. By utilizing the MnBi2Te4-family compounds
and their heterostructures as a model system, we systematically studied the
dependence of the sign and strength of interlayer magnetic coupling on
constituent elements by using first-principles calculations. It was found that
the coupling is a long-range superexchange interaction mediated by the chains
of p orbitals between the magnetic atoms of neighboring septuple-layers. The
interlayer exchange is always antiferromagnetic in the pure compounds, but can
be tuned to ferromagnetic in some combinations of heterostructures, dictated by
d orbital occupations. Strong interlayer magnetic coupling can be realized if
the medial p electrons are delocalized and the d bands of magnetic atoms are
near the Fermi level. The knowledge on the interlayer coupling mechanism
enables us to engineer magnetic and topological properties of MnBi2Te4-family
materials as well as many other insulating van der Waals magnetic materials and
heterostructures.",2003.13485v1
2022/1/29,Machine Learning Study of the Magnetic Ordering in 2D Materials,"Magnetic materials have been applied in a large variety of technologies, from
data storage to quantum devices. The development of 2D materials has opened new
arenas for magnetic compounds, even when classical theories discourage their
examination. Here we propose a machine-learning-based strategy to predict and
understand magnetic ordering in 2D materials. This strategy couples the
prediction of the existence of magnetism in 2D materials using random forest
and the SHAP method with material maps defined by atomic features predicting
the magnetic ordering (ferromagnetic or antiferromagnetic). While the random
forest model predicts magnetism with an accuracy of 86%, the material maps
obtained by the SISSO method have an accuracy of about 90% in predicting the
magnetic ordering. Our model indicates that 3d transition metals, halides, and
structural clusters with regular transition metals sublattices have a positive
contribution in the total weight deciding the existence of magnetism in 2D
compounds. This behavior is associated with the competition between crystal
field and exchange splitting. The machine learning model also indicates that
the atomic SOC is a determinant feature for the identification of the patterns
separating ferro- from antiferro-magnetic order. The proposed strategy is used
to identify novel 2D magnetic compounds which, together with the fundamental
trends in the chemical and structural space, paves novel routes for
experimental exploration.",2201.12630v1
2022/9/22,Stacking and Layer dependence of magnetic properties in Ti\textsubscript{2}C and Fe\textsubscript{2}C,"Magnetic MXenes are turning out to be an important family of materials for
exploring 2D magnetism. However, investigations into the inter-dependence of
layer thickness, stacking patterns and magnetism in these materials, from a
microscopic point of view, is still lacking. In this work, we have used Density
Functional Theory (DFT) based calculations to understand the effects of layer
thickness and stacking on the magnetic properties in two magnetic MXenes,
Ti$_{2}$C and Fe$_{2}$C in their monolayer and bilayer forms. The ground state
magnetic structures, magnetic moments, magnetic exchange interactions, magnetic
transition temperatures and magnetic anisotropy energies are calculated and
analysed using their electronic structures and standardised models. We find
that in both systems increase in layer thickness (monolayer to bilayer) affects
the ground state magnetic configuration which is driven by the changes in the
magnetic exchange interactions. While the effects of stacking pattern is rather
weak in Ti$_{2}$C, they are substantial, both qualitatively and quantitatively
in Fe$_{2}$C. The computed results are analysed from their electronic
structures. The results suggest that fascinating physical effects can be
obtained in Fe$_{2}$C by tuning the layer thickness and stacking patterns,
making it more suitable for device applications.",2209.10765v1
2023/4/23,Magnetism and Fermiology of Kagome Magnet YMn6Sn4Ge2,"Kagome lattice magnets are an interesting class of materials as they can host
topological properties in their magnetic and electronic structures. YMn6Sn6 is
one such compound in which a series of competing magnetic phases is stabilized
by an applied magnetic field, and both an enigmatic topological Hall effect and
a Dirac crossing close to the Fermi energy have been realized. This material
also shows a magnetization-induced Lifshitz transition and evidence of a unique
charge spin coupling in one of the magnetic phases, namely the fan-like phase.
Tuning the magnetism, and thus the interplay with the electronic states, opens
new avenues for precise control of these novel properties. Here, we demonstrate
the extreme sensitivity of the magnetic phases in YMn6Sn4Ge2 through the
investigation of structural, magnetic, and transport properties. The high
sensitivity to small doping provides great potential for engineering the
magnetic phases and associated electronic properties in this family of
rare-earth kagome magnets.",2304.11502v1
2020/1/27,Non-exponential magnetic relaxation in magnetic nanoparticles for hyperthermia,"Magnetic nanoparticle based hyperthermia emerged as a potential tool for
treating malignant tumours. The efficiency of the method relies on the
knowledge of magnetic properties of the samples; in particular, knowledge of
the frequency dependent complex magnetic susceptibility is vital to optimize
the irradiation conditions and to provide feedback for material science
developments. We study the frequency-dependent magnetic susceptibility of an
aqueous ferrite suspension for the first time using non-resonant and resonant
radiofrequency reflectometry. We identify the optimal measurement conditions
using a standard solenoid coil, which is capable of providing the complex
magnetic susceptibility up to 150 MHz. The result matches those obtained from a
radiofrequency resonator for a few discrete frequencies. The agreement between
the two different methods validates our approach. Surprisingly, the dynamic
magnetic susceptibility cannot be explained by an exponential magnetic
relaxation behavior even when we consider a particle size-dependent
distribution of the relaxation parameter.",2001.09774v1
2021/9/23,Tuning magnetic antiskyrmion stability in tetragonal inverse Heusler alloys,"The identification of materials supporting complex, tunable magnetic order at
ambient temperatures is foundational to the development of new magnetic device
architectures. We report the design of Mn2XY tetragonal inverse Heusler alloys
that are capable of hosting magnetic antiskyrmions whose stability is sensitive
to elastic strain. We first construct a universal magnetic Hamiltonian
capturing the short- and long- range magnetic order which can be expected in
these materials. This model reveals critical combinations of magnetic
interactions that are necessary to approach a magnetic phase boundary, where
the magnetic structure is highly susceptible to small perturbations such as
elastic strain. We then computationally search for quaternary Mn2(X1,X2)Y
alloys where these critical interactions may be realized and which are likely
to be synthesizable in the inverse Heusler structure. We identify the
Mn2Pt(1-z)X(z)Ga family of materials with X=Au, Ir, Ni as an ideal system for
accessing all possible magnetic phases, with several critical compositions
where magnetic phase transitions may be actuated mechanically.",2109.11423v1
2007/11/13,Magnetic nanowires as permanent magnet materials,"We present the fabrication of metallic magnetic nanowires using a low
temperature chemical process. We show that pressed powders and magnetically
oriented samples exhibit a very high coercivity (6.5 kOe at 140 K and 4.8 kOe
at 300 K). We discuss the magnetic properties of these metamaterials and show
that they have the suitable properties to realize ""high temperature magnets""
competitive with AlNiCo or SmCo permanent magnets. They could also be used as
recording media for high density magnetic recording.",0711.1978v1
2021/2/26,Distinctive magnetic properties of CrI3 and CrBr3 monolayers caused by spin-orbit coupling,"After the discovery of magnetism in monolayer CrI3, the magnetic properties
of different 2D materials from the chromium-trihalide family are intuitively
assumed to be similar, yielding magnetic anisotropy from the spin-orbit
coupling on halide ligands. Here we reveal significant differences between the
CrI3 and CrBr3 magnetic monolayers in their magnetic anisotropy, resulting
Curie temperature, hysteresis in external magnetic field, and evolution of
magnetism with strain, all predominantly attributed to distinctly different
interplay of atomic contributions to spin-orbit coupling in two materials.",2102.13325v1
2022/10/6,MagNet: machine learning enhanced three-dimensional magnetic reconstruction,"Three-dimensional (3D) magnetic reconstruction is vital to the study of novel
magnetic materials for 3D spintronics. Vector field electron tomography (VFET)
is a major in house tool to achieve that. However, conventional VFET
reconstruction exhibits significant artefacts due to the unavoidable presence
of missing wedges. In this article, we propose a deep-learning enhanced VFET
method to address this issue. A magnetic textures library is built by
micromagnetic simulations. MagNet, an U-shaped convolutional neural network, is
trained and tested with dataset generated from the library. We demonstrate that
MagNet outperforms conventional VFET under missing wedge. Quality of
reconstructed magnetic induction fields is significantly improved.",2210.03066v1
2022/10/30,Controlling magnetic anisotropy in amplitude expansion of phase field crystal model,"The amplitude expansion for a magnetic phase-field-crystal (magnetic APFC)
model enables a convenient coarse-grained description of crystalline structures
under the influence of magnetic fields. Considering higher-order magnetic
coupling terms, we demonstrate the possibility of tuning the magnetic
anisotropy in these models. This allows for reproducing the easy and hard
direction of magnetization. Such a result can be achieved without increasing
the computational cost, enabling simulations of the manipulation of dislocation
networks and microstructures in ferromagnetic materials. As a demonstration, we
report on the simulation of the shrinkage of a spherical grain with the
magnetic anisotropy of Fe.",2210.16855v1
1999/5/14,Magnetic Domain Walls in Double Exchange Materials,"We study magnetic domain walls in double exchange materials. The domain wall
width is proportional to the square root of the stiffness. In the double
exchange model the stiffness has two terms: the kinetic energy and the Hartree
term. The kinetic energy term comes from the decrease of the tunneling
amplitude in the domain wall region. The Hartree term appears only in double
exchange materials and it comes from the connection between band-width and
magnetization. We also calculate the low-field magnetoresistance associated
with the existence of magnetic domains. We find a magnetoresistance of 1-2%.
The magnetoresistance c an be considerably larger in magnetically constrained
nanocontacts.",9905209v1
2017/2/27,Basics of the magnetocaloric effect,"This chapter reviews the basic physics and thermodynamics that govern
magnetocaloric materials. The thermodynamics of magnetic materials is discussed
by introducing relevant free energy terms together with their microscopic
origin leading to a discussion of the sources of entropy that can change in an
applied magnetic field. Such entropies account for measurable magnetocaloric
effects, especially in the vicinity of magnetic phase transitions. Particular
attention is devoted to first order magnetic transitions that involve the
coupling of spin, lattice, electronic and anisotropic magneto-crystalline
degrees of freedom. The problem of irreversibility and hysteresis, present in
magnetocaloric materials with first order phase transitions is discussed in the
context of out-of-equilibrium thermodynamics and hysteresis modeling.",1702.08347v1
2018/3/21,Magnetic illusion: transforming a magnetic object into another object by negative permeability,"We theoretically predict and experimentally verify the illusion of
transforming the magnetic signature of a 3D object into that of another
arbitrary object. This is done by employing negative-permeability materials,
which we demonstrate that can be emulated by tailored sets of currents. The
experimental transformation of the magnetic response of a ferromagnet into that
of its antagonistic material, a superconductor, is presented to confirm the
theory. The emulation of negative-permeability materials by currents provides a
new pathway for designing devices for controlling magnetic fields in
unprecedented ways.",1803.08009v1
2022/11/22,Atomic-resolution imaging of magnetism via ptychographic phase retrieval,"Atomic-scale characterization of spin textures in solids is essential for
understanding and tuning properties of magnetic materials and devices. While
high-energy electrons are employed for atomic-scale imaging of materials, they
are insensitive to the spin textures. In general, the magnetic contribution to
the phase of high-energy electron wave is 1000 times weaker than the
electrostatic potential. Via accurate phase retrieval through electron
ptychography, here we show that the magnetic phase can be separated from the
electrostatic one, opening the door to atomic-resolution characterization of
spin textures in magnetic materials and spintronic devices.",2211.12008v2
2024/2/19,Multistep severe plastic deformation to achieve non-rare earth bulk magnets with high α-MnBi phase content,"The ferromagnetic {\alpha}-MnBi phase as non-rare earth magnetic material has
gained increasing interest, but fabrication of large volumes containing a
significant amount of {\alpha}-MnBi is still challenging. Targeting successful
processing strategies, we apply multistep severe plastic deformation with
intermediate magnetic field assisted annealing. The subsequent severe plastic
deformation renewed the high amount of material defects and lead to
microstructural refinement of the previously formed {\alpha}-MnBi phase. Thus,
{\alpha}-MnBi phase content is enhanced during final annealing. Secondly, the
magnetic coercivity increases. These results suggest that further optimization
will pave the way towards non-rare-earth bulk magnetic materials with enhanced
{\alpha}-MnBi phase content.",2402.11859v1
2010/6/17,Recent progress in exploring magnetocaloric materials,"Magnetic refrigeration based on the magnetocaloric effect (MCE) of materials
is a potential technique that has prominet advantages over the currently used
gas compression-expansion technique in the sense of its high efficiency and
environment friendship. In this article, our recent progress in explorating
effective MCE materials is reviewed with the emphasis on the MCE in the
LaFe13-xSix-based alloys with a first order magnetic transition discovered by
us. These alloys show large entropy changes in a wide temperature range near
room temperature. Effects of magnetic rare-earth doping, interstitial atom, and
high pressure on the MCE have been systematically studied. Special issues such
as appropriate approaches to determining the MCE associated with the
first-order magnetic transition, the depression of magnetic and thermal
hystereses, and the key factors determining the magnetic exchange in alloys of
this kind are discussed. The applicability of the giant MCE materials to the
magnetic refrigeration near ambient temperature is evaluated. A brief review of
other materials with significant MCE is also presented in the article.",1006.3415v1
2021/2/8,Transverse thermoelectric generation using magnetic materials,"The transverse thermoelectric effect refers to the conversion of a
temperature gradient into a transverse charge current, or vice versa, which
appears in a conductor under a magnetic field or in a magnetic material with
spontaneous magnetization. Among such phenomena, the anomalous Nernst effect in
magnetic materials has been receiving increased attention from the viewpoints
of fundamental physics and thermoelectric applications owing to the rapid
development of spin caloritronics and topological materials science. In this
research trend, a conceptually different transverse thermoelectric conversion
phenomenon appearing in thermoelectric/magnetic hybrid materials has been
demonstrated, enabling the generation of a large transverse thermopower. Here,
we review the recent progress in fundamental and applied studies on the
transverse thermoelectric generation using magnetic materials. We anticipate
that this perspective will further stimulate research activities on the
transverse thermoelectric generation and lead to the development of
next-generation thermal energy harvesting and heat-flux sensing technologies.",2102.04183v2
2014/2/3,A Physical Model of a Smart Magneto-Composite Material and the Methodology of Research of the Elastic Properties of Nano Magnetic Composite Materials,"In this study, we show that any system consisting of magnetic dipoles forming
ordered or disordered configurations can be simplified to a form mathematically
equivalent to a system consisting of two magnetic dipoles. It is shown that the
energy of all kinds of magnetic dipole systems can be written as
$E=\frac{\beta}{\alpha^3}$, where $\alpha$ is the nearest distance between the
dipoles and $\beta$ is a certain constant depending on the magnetic moments of
dipoles and configuration. Using this fact we model any nano-magnetic composite
material by a simple two-magnetic dipole system. Then we experimentaly and
theoreticaly show that under certain conditions the elastic properties of the
composite material can be changed using exernal magnetic field which leads to
creation of smart composite materials.",1402.0540v1
2021/4/26,Highly sensitive spin-flop transition in antiferromagnetic van-der Waals material MPS3 (M = Ni and Mn),"Recent developments in two-dimensional (2D) magnetism have motivated the
search for novel van-der Waals (vdWs) magnetic materials to explore new
magnetic phenomenon in the 2D limit. Metal thiophosphates, MPX3, is a class of
magnetic vdWs materials with antiferromagnetic (AFM) ordering persisting down
to the atomically thin limit. The magnetism in this material family has been
found to be highly dependent on the choice of transition metal M. In this work,
we have synthesized the intermediate compounds Ni1-xMnxPS3 (0 < x < 1) and
investigated their magnetic properties. Our study reveals that the variation of
Ni and Mn content in Ni1-xMnxPS3 can efficiently tune the spin-flop transition,
likely due to the modulation of the magnetic anisotropy. Such effective tunning
offers a promising candidate to engineer 2D magnetism for future device
applications.",2104.12334v1
2019/5/25,Magnetic 2D electron liquid at the surface of Heusler semiconductors,"Conducting and magnetic properties of a material often change in some
confined geometries. However, a situation where a non-magnetic semiconductor
becomes both metallic and magnetic at the surface is quite rare, and to the
best of our knowledge has never been observed in experiment. In this work, we
employ first-principles electronic structure theory to predict that such a
peculiar magnetic state emerges in a family of quaternary Heusler compounds. We
investigate magnetic and electronic properties of CoCrTiP, FeMnTiP and CoMnVAl.
For the latter material, we also analyse the magnetic exchange interactions and
use them for parametrizing an effective spin Hamiltonian. According to our
results, magnetism in this material should persist at temperatures at least as
high as 155 K.",1905.10541v1
2020/2/4,Accelerated design of Fe-based soft magnetic materials using machine learning and stochastic optimization,"Machine learning was utilized to efficiently boost the development of soft
magnetic materials. The design process includes building a database composed of
published experimental results, applying machine learning methods on the
database, identifying the trends of magnetic properties in soft magnetic
materials, and accelerating the design of next-generation soft magnetic
nanocrystalline materials through the use of numerical optimization. Machine
learning regression models were trained to predict magnetic saturation ($B_S$),
coercivity ($H_C$) and magnetostriction ($\lambda$), with a stochastic
optimization framework being used to further optimize the corresponding
magnetic properties. To verify the feasibility of the machine learning model,
several optimized soft magnetic materials -- specified in terms of compositions
and thermomechanical treatments -- have been predicted and then prepared and
tested, showing good agreement between predictions and experiments, proving the
reliability of the designed model. Two rounds of optimization-testing
iterations were conducted to search for better properties.",2002.05225v2
2022/11/23,An ultra-low field SQUID magnetometer for measuring antiferromagnetic and weakly remanent magnetic materials at low temperatures,"A novel setup for the measurement of magnetic fields external to certain
antiferromagnets and generally weakly remanent magnetic materials is presented.
The setup features a highly sensitive Super Conducting Quantum Interference
Device (SQUID) magnetometer with a magnetic field resolution of approx. 10 fT,
non-electric thermalization of the sample space for a temperature range of 1.5
- 65 K with a non-electric sample movement drive and optical position encoding.
To minimize magnetic susceptibility effects, the setup components are degaussed
and realized with plastic materials in sample proximity. Running the setup in
magnetically shielded rooms allows for a well-defined ultra low magnetic
background field well below 150 nT in situ. The setup enables studies of
inherently weak magnetic materials which cannot be measured with high field
susceptibility setups, optical methods or neutron scattering techniques, giving
new opportunities for the research on e.g. spin-spiral multiferroics, skyrmion
materials and spin ices.",2211.12894v1
2024/3/23,Engineering the electronic and magnetic properties of monolayer TiS$_2$ through systematic transition-metal doping,"Layered materials that exhibit magnetic ordering in their pristine form are
very rare. Several standard approaches, such as adsorption of atoms,
introduction of point defects, and edge engineering, have been developed to
induce magnetism in two-dimensional materials. In this way, we investigate the
electronic and magnetic properties of monolayer TiS$_2$ doped with 3$d$
transition metals (TMs) atoms in both octahedral 1T and trigonal prismatic 1H
structures using first-principles calculations. In its pristine form, TiS$_2$
is a non-magnetic semiconductor. The bands near the Fermi energy primarily
exhibit $d$ orbital characters, and due to the presence of ideal octahedral and
trigonal arrangements, they are well separated from other bands with $p$
character. Upon substituting 3$d$-TM atoms in both structures, a variety of
electronic and magnetic phases emerge, including magnetic semiconductor,
magnetic half-metal, non-magnetic metal, and magnetic metal. Chromium exhibits
the largest magnetic moment in both the 1T and 1H structures. The 1T structure
shows a slightly higher magnetic moment of 3.419 $\mu_B$ compared to the 1H
structure 3.138 $\mu_B$, attributed to the distorted octahedral structure of
the 1T structure. Unlike pristine TiS$_2$, the deficiency in saturation of
neighboring S atoms in the presence of impurities leads to the proximity of
energy levels of $d$ and $p$ states, resulting in unexpectedly sizable magnetic
moments. Another interesting case is Cobalt, which leads to a magnetic moment
of approximately 0.805 $\mu_B$ in the 1H structure, while the Co exhibits a
non-magnetic state in the 1H structure. These materials demonstrate a high
degree of tunability and can be optimized for various magnetic applications.",2403.15850v1
2023/8/25,Coexistence of non-trivial van der Waals magnetic orders enable field-free spin-orbit torque switching at room temperature,"The discovery of van der Waals (vdW) materials exhibiting non-trivial and
tunable magnetic interactions at room temperature can give rise to exotic
magnetic states, which are not readily attainable with conventional materials.
Such vdW magnets can provide a unique platform for studying new magnetic
phenomena and realising magnetization dynamics for energy-efficient and
non-volatile spintronic memory and logic technologies. Recent developments in
vdW magnets have revealed their potential to enable spin-orbit torque (SOT)
induced magnetization dynamics. However, the deterministic and field-free SOT
switching of vdW magnets at room temperature has been lacking, prohibiting
their potential applications. Here, we demonstrate magnetic field-free and
deterministic SOT switching of a vdW magnet (Co0.5Fe0.5)5GeTe2 (CFGT) at room
temperature, capitalizing on its non-trivial intrinsic magnetic ordering. We
discover a coexistence of ferromagnetic and antiferromagnetic orders in CFGT at
room temperature, inducing an intrinsic exchange bias and canted perpendicular
magnetism. The resulting canted perpendicular magnetization of CFGT introduces
symmetry breaking, facilitating successful magnetic field-free magnetization
switching in the CFGT/Pt heterostructure devices. Furthermore, the SOT-induced
magnetization dynamics and their efficiency are evaluated using 2nd harmonic
Hall measurements. This advancement opens new avenues for investigating tunable
magnetic phenomena in vdW material heterostructures and realizing field-free
SOT-based spintronic technologies.",2308.13408v1
2017/9/12,Noise reduction in heat-assisted magnetic recording by optimizing a high/low Tc bilayer structure,"It is assumed that heat-assisted magnetic recording (HAMR) is the recording
technique of the future. For pure hard magnetic grains in high density media
with an average diameter of $5$nm and a height of $10$nm the switching
probability is not sufficiently high for the use in bit-patterned media. Using
a bilayer structure with 50$\%$ hard magnetic material with low Curie
temperature and 50$\%$ soft magnetic material with high Curie temperature to
obtain more than 99.2$\%$ switching probability, leads to very large jitter. We
propose an optimized material composition to reach a switching probability of
$P_{\mathrm{switch}}>99.2\%$ and simultaneously achieve the narrow transition
jitter of pure hard magnetic material. Simulations with a continuous laser spot
were performed with the atomistic simulation program VAMPIRE for a single
cylindrical recording grain with a diameter of 5nm and a height of 10nm.
Different configurations of soft magnetic material and different amounts of
hard and soft magnetic material were tested and discussed. Within our analysis,
a composition with 20$\%$ soft magnetic and $80\%$ hard magnetic material
reaches the best results with a switching probability
$P_{\mathrm{switch}}>99.2\%$, an off-track jitter parameter
$\sigma_{\mathrm{off},80/20}=14.2$K and a down-track jitter parameter
$\sigma_{\mathrm{down},80/20}=0.49$nm.",1709.03764v1
2019/7/29,Controlling Magnetization of Gr/Ni Composite for Application in High Performance Magnetic Sensors,"Graphene (Gr), a well-known 2D material, has been under intensive
investigation in the last decade due to its high potential applications in
industry and advanced technological elements. The Gr, while composed with
magnetic materials, has opened new opportunities for further developments of
magnetic based devices. Here, we report a mass production of Gr/Ni composite
powders using electrochemical exfoliation/deposition method with different
magnetic strengths of the final composite material. We applied the magnetic
composite materials in a magnetoimpedance (MI) based sensor and observed
significant enhancement in the MI effect and its field sensitivity. Such
magnetic composites with controlled magnetization strengths are coated on the
MI-ribbon sensor surface and different MI responses are observed. The MI
response of a ribbon coated with a Gr/Ni layer is theoretically determined
based on an electrodynamic model with a qualitative consistency between the
experimental results and the theoretical model. Our comprehensive study can be
applied in high performance functionalized MI based magnetic sensors and
devices.",1907.12249v1
2021/6/25,Long-Time Magnetic Relaxation in Antiferromagnetic Topological Material EuCd$_2$As$_2$,"Magnetic topological materials have attracted much attention due to the
correlation between topology and magnetism. Recent studies suggest that
EuCd$_2$As$_2$ is an antiferromagnetic topological material. Here by carrying
out thorough magnetic, electrical and thermodynamic property measurements, we
discover a long time relaxation of the magnetic susceptibility in
EuCd$_2$As$_2$. The (001) in-plane magnetic susceptibility at 5 K is found to
continuously increase up to $\sim$10% over the time of $\sim$14 hours. The
magnetic relaxation is anisotropic and strongly depends on the temperature and
the applied magnetic field. These results will stimulate further theoretical
and experimental studies to understand the origin of the relaxation process and
its effect on the electronic structure and physical properties of the magnetic
topological materials.",2106.13678v1
2001/8/29,Theoretical investigation on the possibility of preparing left-handed materials in metallic magnetic granular composites,"We investigate the possibility of preparing left-handed materials in metallic
magnetic granular composites. Based on the effective medium approximation, we
show that by incorporating metallic magnetic nanoparticles into an appropriate
insulating matrix and controlling the directions of magnetization of metallic
magnetic components and their volume fraction, it may be possible to prepare a
composite medium of low eddy current loss which is left-handed for
electromagnetic waves propagating in some special direction and polarization in
a frequency region near the ferromagnetic resonance frequency. This composite
may be easier to make on an industrial scale. In addition, its physical
properties may be easily tuned by rotating the magnetization locally.",0108503v1
2007/5/12,"Comment on six papers published by M.A. El-Hakiem and his co-workers in International Communications in Heat and Mass Transfer, Journal of Magnetism and Magnetic Materials and Heat and Mass Transfer","Comment on six papers published by M.A. El-Hakiem and his co-workers in
International Communications in Heat and Mass Transfer, Journal of Magnetism
and Magnetic Materials and Heat and Mass Transfer",0705.1803v1
2010/3/26,Temperature effects on the magnetization of quasi-one-dimensional Peierls distorted materials,"It is shown that temperature acts to disrupt the magnetization of Peierls
distorted quasi-one-dimensional materials (Q1DM). The mean-field finite
temperature phase diagram for the field theory model employed is obtained by
considering both homogeneous and inhomogeneous condensates. The tricritical
points of the second order transition lines of the gap parameter and
magnetization are explicitly calculated. It is also shown that in the absence
of an external static magnetic field the magnetization is always zero, at any
temperature. As expected, temperature does not induce any magnetization effect
on Peierls distorted Q1DM.",1003.5242v1
2014/6/12,A Simple Apparatus for the Direct Measurement of Magnetic Forces and Magnetic Properties of Materials,"In this paper, we describe a simple apparatus consisting of a scale, capable
of a one milligram resolution, and a commonly obtainable magnet to measure
magnetic forces. This simple apparatus is capable of measuring magnetic
properties of materials in either a research or an instructional laboratory. We
illustrate the capability of this apparatus by the measurement of the force of
iron samples exerted on the magnet, the force of a paramagnetic sample, that by
a current carrying wire, and the force of a high temperature superconductor.",1406.3341v3
2017/8/16,Copper Tellurium Oxides - A Playground for Magnetism,"A variety of copper tellurium oxide minerals are known, and many of them
exhibit either unusual forms of magnetism, or potentially novel spin liquid
behavior. Here, I review a number of the more interesting materials with a
focus on their crystalline symmetry and, if known, the nature of their
magnetism. Many of these exist (so far) in mineral form only, and most have yet
to have their magnetic properties studied. This means a largely unexplored
space of materials awaits our exploration.",1708.05100v1
2023/4/25,Magnetization Switching in van der Waals Systems by Spin-Orbit Torque,"Electrical switching of magnetization via spin-orbit torque (SOT) is of great
potential in fast, dense, energy-efficient nonvolatile magnetic memory and
logic technologies. Recently, enormous efforts have been stimulated to
investigate switching of perpendicular magnetization in van der Waals systems
that have unique, strong tunability and spin-orbit coupling effect compared to
conventional metals. In this review, we first give a brief, generalized
introduction to the spin-orbit torque and van der Waals materials. We will then
discuss the recent advances in magnetization switching by the spin current
generated from van der Waals materials and summary the progress in the
switching of Van der Waals magnetization by the spin current.",2304.12632v1
2023/6/13,Unraveling Magnetic Anisotropy Energy in Ferromagnetic Monolayer on Ferroelectric ABO$_3$ via DFT and Machine Learning,"Spin-based devices have attracted attention as an alternative to CMOS-based
technology. However, one of the challenges in spintronics devices is reducing
the spin-switching energy in ferromagnetic (FM) materials. To address this, we
considered ferroelectric (FE) materials, which may affect the magnetic
properties of FM materials. We explored various oxide perovskites ABO$_3$ as FE
materials, onto which a Fe monolayer was placed as the FM material. We
evaluated the magnetic anisotropy energy (MAE) of the Fe monolayer while
varying the polarization of ABO$_3$. Our analysis showed that the MAE depends
on the magnetic dipole moment induced in the FE material at the interface
between the FE and FM materials due to structural modifications. Machine
learning techniques were also employed to identify universal behaviors of the
MAE in the presence of FE layers, confirming the importance of magnetic moments
near the interface in explaining the dependence of the MAE on FE materials.",2306.07953v1
2011/5/19,Ultra-fast spin avalanches in crystals of molecular magnets in terms of magnetic detonation,"Recent experiments (Decelle et al., Phys. Rev. Lett. 102, 027203 (2009))
discovered an ultra-fast regime of spin avalanches in crystals of magnetic
magnets, which was three orders of magnitude faster than the traditionally
studied magnetic deflagration. The new regime has been hypothetically
identified as magnetic detonation. Here we demonstrate the possibility of
magnetic detonation in the crystals, as a front consisting of a leading shock
and a zone of Zeeman energy release. We study the dependence of the magnetic
detonation parameters on the applied magnetic field. We find that the magnetic
detonation speed only slightly exceeds the sound speed in agreement with the
experimental observations.",1105.3962v1
2017/9/11,Magnetic order and phase transition in the iron oxysulfide La2O2Fe2OS2,"The Mott-insulating iron oxychalcogenides exhibit complex magnetic behaviour
and we report here a neutron diffraction investigation into the magnetic
ordering in La2O2Fe2OS2. This quaternary oxysulfide adopts the
anti-Sr2MnO2Sb2-type structure and orders antiferromagnetically below TN = 105
K. We consider both its long-range magnetic structure and its magnetic
microstructure, and the onset of magnetic order. It adopts the multi-k vector
""2k"" magnetic structure (k = (0.5 0 0.5) and k = (0 0.5 0.5) and has
similarities with related iron oxychalcogenides, illustrating the robust nature
of the ""2k"" magnetic structure.",1709.03323v1
2015/4/20,Recent Progress in the thermodynamics of ferrotoroidic materials,"Recent theoretical and experimental progress on the study of ferrotoroidic
materials is reviewed. The basic field equations are first described and then
the expressions for magnetic toroidal moment and toroidization are derived.
Relevant materials and experimental observation of magnetic toroidal moment and
toroidal domains are summarized next. The thermodynamics of such magnetic
materials is discussed in detail with examples of ferrorotoidic phase
transition studied using Landau modelling. Specifically, an example of
application of Landau modelling to the study of toroidocaloric effect is also
provided. Recent results of polar nanostructures with electrical toroidal
moment are finally reviewed.",1504.04958v1
2000/4/26,Magnetic relaxation and magnetization field dependence measurements in La0.5Ca0.5MnO3,"We reported a systematic change in the average magnetic relaxation rate,
after the application and removal of a 5 T magnetic field, in a polycrystalline
sample of La0.5Ca0.5MnO3. Magnetic relaxation measurements and magnetization
versus field curves were taken from 10 K to 160 K. The long time behavior of
the relaxation curves was approximately logarithmic in all cases. Keywords:
Charge Ordering, Relaxation, Magnetic measurements",0004460v2
2014/10/10,Comparison of adjustable permanent magnetic field sources,"A permanent magnet assembly in which the flux density can be altered by a
mechanical operation is often significantly smaller than comparable
electromagnets and also requires no electrical power to operate. In this paper
five permanent magnet designs in which the magnetic flux density can be altered
are analyzed using numerical simulations, and compared based on the generated
magnetic flux density in a sample volume and the amount of magnet material
used. The designs are the concentric Halbach cylinder, the two half Halbach
cylinders, the two linear Halbach arrays and the four and six rod mangle. The
concentric Halbach cylinder design is found to be the best performing design,
i.e. the design that provides the most magnetic flux density using the least
amount of magnet material. A concentric Halbach cylinder has been constructed
and the magnetic flux density, the homogeneity and the direction of the
magnetic field are measured and compared with numerical simulation and a good
agreement is found.",1410.2681v1
2014/11/25,Computing with spins and magnets,"The possible use of spin and magnets in place of charge and capacitors to
store and process information is well known. Magnetic tunnel junctions are
being widely investigated and developed for magnetic random access memories.
These are two terminal devices that change their resistance based on switchable
magnetization of magnetic materials. They utilize the interaction between
electron spin and magnets to read information from the magnets and write onto
them. Such advances in memory devices could also translate into a new class of
logic devices that offer the advantage of nonvolatile and reconfigurable
information processing over transistors. Logic devices having a transistor-like
gain and directionality could be used to build integrated circuits without the
need for transistor-based amplifiers and clocks at every stage. We review
device characteristics and basic logic gates that compute with spins and
magnets from the mesoscopic to the atomic scale, as well as materials,
integration, and fabrication challenges and methods.",1411.6960v1
2020/6/3,Structural and magnetic properties of small symmetrical and asymmetrical sized fullerene dimers,"Magnetism in carbon nanostructures is of high scientific interest, which
could lead to novel magnetic materials. The magnetic properties of symmetrical
and asymmetrical sized small fullerene dimers have been investigated using spin
polarized density functional theory. The interaction energies depict that small
fullerene cages form stable dimer structures and symmetrical sized fullerene
dimers are found more stable than asymmetrical sized dimers. The dimerization
of fullerene cages in different modes leads to change in their magnetic
properties. The non-magnetic fullerene cages become magnetic after formation of
dimer (C20-C20, C24-C24, C32-C32, C40-C40, C20-C24, C40-C44 and
C44-C50),whereas the magnetism of magnetic fullerenes is enhanced or lowered
after dimerization (C28-C28 C36-C36, C24-C28, C28-C32, C32-C36 and C36-C40).
The individual cages of dimer structures show ferromagnetic interactions
amongst them and resultant magnetic moment strongly depends on the type of
inter-connecting bonds. The magnetism may also be explained based on distortion
of carbon cages and change in the density of states (DOS) in dimer
configuration. The calculations presented show strong possibility of
experimental synthesis of small fullerene based magnetic dimers.",2006.02233v1
2021/12/21,Tunable room temperature magnetic skyrmions in centrosymmetric kagome magnet Mn$_4$Ga$_2$Sn,"The successful realization of skyrmion-based spintronic devices depends on
the easy manipulation of underlying magnetic interactions in the
skyrmion-hosting materials. Although the mechanism of skyrmion formation in
non-centrosymmetric magnets is comprehensively established, the stabilization
process of different skyrmion-like magnetic textures in centrosymmetric magnets
needs further investigation. Here, we utilize Lorentz transmission electron
microscopy study to report the finding of a tunable skyrmion lattice up to room
temperature in a centrosymmetric kagome ferromagnet Mn$_4$Ga$_2$Sn. We
demonstrate that a controlled switching between the topological skyrmions and
non-topological type-II magnetic bubbles can be realized at the optimal
magnetic anisotropy. We find that the topological skyrmions are the
energetically most stable magnetic objects in the centrosymmetric hexagonal
magnets, whereas application of in-plane magnetic field stabilizes type-II
magnetic bubbles as an excited state. The present study is a significant step
towards understanding of the skyrmion stabilization mechanism in
centrosymmetric materials for their future applications.",2112.11259v2
2023/2/22,Controllable CVD-Growth of 2D Cr5Te8 Nanosheets with Thickness-Dependent Magnetic Domains,"As a typical 2D magnetic material with self-intercalated structure, Cr5Te8
exhibits many fascinating magnetic properties. Although the ferromagnetism of
2D Cr5Te8 has been reported, the study of its magnetic domain is still blank.
Herein, we successfully fabricated 2D Cr5Te8 nanosheets with controlled
thickness and lateral size by chemical vapor deposition (CVD). Then magnetic
property measurement system suggested Cr5Te8 nanosheets possessing intense
out-of-plane ferromagnetism with the Curie temperature of 179 K. Most
importantly, we found magnetic bubbles and thickness-dependent maze-like
magnetic domains by cryogenic magnetic force microscopy (MFM) for the first
time. The domain width of the maze-like magnetic domains increases rapidly with
decreasing sample thickness, while domain contrast decreases. This indicates
dipolar interaction is the dominant role over exchange interaction and magnetic
anisotropy. Our work not only paves a way for the controllable growth of 2D
magnetic materials, but also suggests new directions for controlling magnetic
phases and systematically adjusting domain properties.",2302.11422v2
2004/9/3,Helicoidal ordering in iron perovskites,"We consider magnetic ordering in materials with negative charge transfer
energy, such as iron perovskite oxides. We show that for a large weight of
oxygen holes in conduction bands, the double exchange mechanism favors a
helicoidal rather than ferromagnetic spin ordering both in metals, e.g. SrFeO_3
and insulators with a small gap, e.g. CaFeO_3. We discuss the magnetic
excitation spectrum and effects of pressure on magnetic ordering in these
materials.",0409068v1
2014/5/21,Magnetoresistance peculiarities and magnetization of materials with two kinds of superconducting inclusions,"Low-temperature properties of a crystal containing superconducting inclusions
of two different materials have been studied. In the approximation that the
size of inclusions is much smaller than the coherence length/penetration depth
of the magnetic field the theory for magnetoresistance of a crystal containing
spherical superconducting inclusions of two different materials has been
developed, and magnetization of crystals has been calculated.",1405.5420v1
2014/11/15,"Orbital-selective behavior in Y5Mo2O12 and (Cd,Zn)V2O4","We present two examples of the real materials, which show orbital-selective
behavior. In both compounds a part of the electrons is localized on the
molecular orbitals, which lead to a significant reduction of the magnetic
moment on the transition metal ion.",1411.4147v2
2019/11/3,Spin and Magnetism in 2D Materials,"We review recent progress on spins and magnetism in 2D materials including
graphene, transition metal dichalcogenides, and 2D magnets. We also discuss
challenges and prospects for the future of spintronics with 2D van der Waals
heterostructures.",1911.00894v2
2002/11/3,Magnetically induced signatures in a thin film superconductor,"We study the interaction between a one dimensional magnetic nanostructure and
a thin film superconductor. It is shown that different magnetic distributions
produce characteristic magnetic field signatures. Moreover, the magnetic
structure can induce a weak link in the superconducting film, or be positioned
directly above a predefined nonsuperconducting weak link. We estimate the
magnetic flux associated with such a structure, and discuss a general
expression for the energy calculated within the London model.",0211043v1
2005/10/26,Ferroelectricity in spiral magnets,"It was recently observed that materials showing most striking multiferroic
phenomena are frustrated spin-density-wave magnets. We present a simple
phenomenological theory, which describes the orientation of the induced
electric polarization for various incommensurate magnetic states, its
dependence on temperature and magnetic field, and anomalies of dielectric
susceptibility at magnetic transitions. We show that electric polarization can
be induced at domain walls and that magnetic vortices carry electric charge.",0510692v1
2008/5/18,Effect of spin diffusion on spin torque in magnetic nanopillars,"We present systematic magnetoelectronic measurements of magnetic nanopillars
with different structures of polarizing magnetic layers. The magnetic reversal
at small magnetic field, the onset of magnetic dynamics at larger field, and
the magnetoresistance exhibit a significant dependence on the type of the
polarizing layer. We performed detailed quantitative modeling showing that the
differences can be explained by the effects of spin-dependent electron
diffusion.",0805.2706v1
2024/4/2,Local spin structure in the layered van der Waals materials MnPS$_{x}$Se$_{3-x}$,"Two-dimensional (2D) layered materials, whether in bulk form or reduced to
just a single layer, have potential applications in spintronics and capacity
for advanced quantum phenomena. A prerequisite for harnessing these
opportunities lies in gaining a comprehensive understanding of the spin
behavior in 2D materials. The low dimensionality motivates an understanding of
the spin correlations over a wide length scale, from local to long range order.
In this context, we focus on the magnetism in bulk \MPSe ~and \MPS, 2D layered
van der Waals antiferromagnetic semiconductors. These materials have similar
honeycomb Mn layers and magnetic ordering temperatures, but distinct spin
orientations and exchange interactions. We utilize neutron scattering to gain
deeper insights into the local magnetic structures and spin correlations in the
paramagnetic and ordered phases by systematically investigating a
MnPS$_{x}$Se$_{3-x}$ ($x$ = 0, 1, 1.5, 2, 3) series of powder samples using
total neutron scattering measurements. By employing magnetic pair distribution
function (mPDF) analysis, we unraveled the short-range magnetic correlations in
these materials and explored how the non-magnetic anion S/Se mixing impacts the
magnetic correlations. The results reveal that the magnetism can be gradually
tuned through alteration of the non-magnetic S/Se content, which tunes the
atomic structure. The change in magnetic structure is also accompanied by a
control of the magnetic correlation length within the 2D honeycomb layers.
Complimentary inelastic neutron scattering measurements allowed a
quantification of the change in the magnetic exchange interactions for the
series and further highlighted the gradual evolution of spin interactions in
the series MnPS$_{x}$Se$_{3-x}$.",2404.02328v1
2008/5/21,Energetic Analysis of Magnetic Transitions in Ultra-small Nanoscopic Magnetic Rings,"In this article, we report on experimental and theoretical investigations of
magnetic transitions in cobalt rings of size (diameter, width and thickness)
comparable to the exchange length of cobalt. Magnetization measurements were
performed for two sets of magnetic ring arrays: ultra-small magnetic rings
(outer diameter 13 nm, inner diameter 5nm and thickness 5 nm) and small
thin-walled magnetic rings (outer diameter 150 nm, width 5 nm and thickness 5
nm). This is the first report on the fabrication and magnetic properties of
such small rings. Our calculations suggest that if the magnetic ring's sizes
are comparable to, or smaller than, the exchange length of the magnetic
material, then only two magnetic states are important - the pure single domain
state and the flux closure vortex state. The onion-shape magnetic state does
not arise. Theoretical calculations are based on an energetic analysis of pure
and slightly distorted single domain and flux closure vortex magnetic states.
Based on the analytical calculations, a phase diagram is also derived for
ultra-small ring structures exhibiting the region for vortex magnetic state
formations as a function of material parameter.",0805.3191v2
2019/11/8,Magnetic glassy state at low spin state of Co3+ in EuBaCo2O5+δ (δ = 0.47) cobaltite,"The magnetic glassy state is a fascinating phenomenon, which results from the
kinetic arrest of the first order magnetic phase transition. Interesting
properties, such as metastable magnetization and nonequilibrium magnetic
phases, are naturally developed in the magnetic glassy state. Here, we report
magnetic glass property in the low spin state of Co3+ in EuBaCo2O5+{\delta}
({\delta} = 0.47) cobaltite at low temperature (T < 60 K). The measurements of
magnetization under the cooling and heating in unequal fields, magnetization
relaxation and thermal cycling of magnetization show the kinetic arrest of low
magnetization state below 60 K. The kinetically arrested low temperature
magnetic phase is further supported through the study of isothermal magnetic
entropy, which shows the significant entropy change. The present results will
open a new window to search the microscopic relation between the spin state
transitions and the kinetic arrest induced magnetic glassy phenomena in complex
materials.",1911.03258v1
2014/10/10,Improving magnet designs with high and low field regions,"A general scheme for increasing the difference in magnetic flux density
between a high and a low magnetic field region by removing unnecessary magnet
material is presented. This is important in, e.g., magnetic refrigeration where
magnet arrays has to deliver high field regions in close proximity to low field
regions. Also, a general way to replace magnet material with a high
permeability soft magnetic material where appropriate is discussed. As an
example these schemes are applied to a two dimensional concentric Halbach
cylinder design resulting in a reduction of the amount of magnet material used
by 42% while increasing the difference in flux density between a high and a low
field region by 45%.",1410.2679v1
2018/3/8,Hard magnetic properties in nanoflake van der Waals Fe3GeTe2,"Two dimensional (2D) van der Waals (vdW) materials have demonstrated
fascinating optical, electrical and thickness-dependent characteristics. These
have been explored by numerous authors but reports on magnetic properties and
spintronic applications of 2D vdW materials are scarce by comparison. By
performing anomalous Hall effect transport measurements, we have characterised
the thickness dependent magnetic properties of single crystalline vdW Fe3GeTe2.
The nanoflakes of this vdW metallic material exhibit a single hard magnetic
phase with a near square-shaped magnetic loop, large coercivity (up to 550 mT
at 2 K), a Curie temperature near 200 K and strong perpendicular magnetic
anisotropy. Using criticality analysis, we confirmed the existence of magnetic
coupling between vdW atomic layers and obtained an estimated coupling length of
~ 5 vdW layers in Fe3GeTe2. Furthermore, the hard magnetic behaviour of
Fe3GeTe2 can be well described by a proposed model. The magnetic properties of
Fe3GeTe2 highlight its potential for integration into vdW magnetic
heterostructures, paving the way for spintronic research and applications based
on these devices.",1803.02934v1
2019/10/2,Magnetic Scattering Chapter,"The present chapter reviews current neutron and x-ray scattering techniques
employed to elucidate the magnetic structures and spin dynamics of magnetic
materials. Both techniques provide measurements as a function of the energy and
the momentum transferred from the spin system to the probe particles, in terms
of five-dimensional data sets as a function of various thermodynamic fields at
the control of the experimenter. These scattering techniques yield fundamental
information about the equal-time correlations such the magnetic configuration
and symmetry, as well as the dynamics that determine the exchange interactions
for prototypical systems that behave as linear, planar, or three-dimensional
systems. Historically, neutron scattering has been the magnetic scattering
technique of choice for such investigations, but the extraordinary advances in
resonant x-ray scattering techniques have enable new types of magnetic
scattering measurements. The type of information obtained with the two
techniques is largely complementary and depends on the interests of the
investigators. We discuss these possibilities and provide numerous examples of
the techniques applied to different classes of magnetic systems.",1910.01218v1
2020/1/13,Gate-tunable spin waves in antiferromagnetic atomic bilayers,"The emergence of two-dimensional (2D) layered magnetic materials has opened
an exciting playground for both fundamental studies of magnetism in 2D and
explorations of spinbased applications. Remarkable properties, including spin
filtering in magnetic tunnel junctions and gate control of magnetic states,
have recently been demonstrated in 2D magnetic materials. While these studies
focus on the static properties, dynamic magnetic properties such as excitation
and control of spin waves have remained elusive. Here we excite spin waves and
probe their dynamics in antiferromagnetic CrI3 bilayers by employing an
ultrafast optical pump/magneto-optical Kerr probe technique. We identify
sub-terahertz magnetic resonances under an in-plane magnetic field, from which
we determine the anisotropy and interlayer exchange fields and the spin damping
rates. We further show tuning of antiferromagnetic resonances by tens of
gigahertz through electrostatic gating. Our results shed light on magnetic
excitations and spin dynamics in 2D magnetic materials, and demonstrate their
unique potential for applications in ultrafast data storage and processing.",2001.04044v1
2020/7/8,Nanoscale Magnetic Domain Memory,"Magnetic domain memory (MDM) is the ability exhibited by certain magnetic
materials to reproduce the exact same nanoscale magnetic domain pattern, even
after it has been completely erased by an external magnetic field. In this
chapter, we review the various circumstances under which this unusual
phenomenon occurs. We explain how partial MDM was first observed in rough Co/Pt
multilayers with perpendicular magnetization as a result of structural defects.
We then show how 100 % MDM was achieved, even in smooth ferromagnetic films, by
coupling Co/Pd multilayers to an antiferromagnetic IrMn template via exchange
interactions. We describe how high MDM, extending through-out nearly the
entirety of the magnetization process, is obtained when zero-field-cooling the
material below its blocking temperature where exchange couplings occur. We also
review the persistence of MDM through field cycling and while warming the
material all the way up to the blocking temperature. Additionally, we discuss
the spatial dependence of MDM, highlighting intriguing oscillatory behaviors
suggesting magnetic correlations and rotational symmetries at the nanoscopic
scales. Finally, we review the dependence of MDM on cooling conditions,
revealing how MDM can be fully controlled, turned on and off, by adjusting the
magnitude of the cooling field.",2007.04984v1
2021/12/11,Macroscopic Magnetic Monopoles in a 3D-Printed Mechano-Magnet,"The notion of magnetic monopoles has puzzled physicists since the
introduction of Maxwell's Equations and famously Dirac had hypothesized them in
the context of quantum mechanics. While they have proved experimentally elusive
as elementary particles, the concept has come to describe excitations or
topological defects in various material systems, from liquid crystals, to Hall
systems, skyrmion lattices, and Bose-Einstein condensate. Perhaps the most
versatile manifestation of magnetic monopoles as quasiparticles in matter has
been in so-called spin ice materials. There, they represent violations of the
ice rule, carry a magnetic charge, and can move freely unbound. Spin ice
emergent magnetic monopoles appear at the atomic scale in rare earth
pyrochlores or at the nano-scale in artificial spin ices systems. Here we
demonstrate for the first time that the notion of magnetic monopoles can be
transported at the macroscopic scale. We have built a mechano-magnet realized
via 3D-printing, that consists of mechanical rotors on which macroscopic
magnets can pivot. By controlling the relative height of the rotors we can
achieve different regimes for magnetic monopoles, including the free monopole
state. We then explore their driven dynamics under field. In the future,
integration of our proof of principle in an elastic matrix can lead to novel
macroscopic mechano-magnetic materials, to explore unusual piezomagnetism and
magnetostriction, with applications to actuators and soft-robotics.",2112.06058v2
2021/3/14,Toward a systematic discovery of artificial functional magnetic materials,"Although ferromagnets are found in all kinds of technological applications,
only few substances are known to be intrinsically ferromagnetic at room
temperature. In the past twenty years, a plethora of new artificial
ferromagnetic materials have been found by introducing defects into
non-magnetic host materials. In contrast to the intrinsic ferromagnetic
materials, they offer an outstanding degree of material engineering freedom,
provided one finds a type of defect to functionalize every possible host
material to add magnetism to its intrinsic properties. Still, one controversial
question remains: Are these materials really technologically relevant
ferromagnets? To answer this question, in this work the emergence of a
ferromagnetic phase upon ion irradiation is systematically investigated both
theoretically and experimentally. Quantitative predictions are validated
against experimental data from the literature of SiC hosts irradiated with high
energy Ne ions and own experiments on low energy Ar ion irradiation of TiO$_2$
hosts. In the high energy regime, a bulk magnetic phase emerges, which is
limited by host lattice amorphization, whereas at low ion energies an ultrathin
magnetic layer forms at the surface and evolves into full magnetic percolation.
Lowering the ion energy, the magnetic layer thickness reduces down to a
bilayer, where a perpendicular magnetic anisotropy appears due to magnetic
surface states.",2103.08045v3
2019/8/2,An accelerating approach of designing ferromagnetic materials via machine learning modeling of magnetic ground state and Curie temperature,"Magnetic materials have a plethora of applications ranging from informatics
to energy harvesting and conversion. However, such functionalities are limited
by the magnetic ordering temperature. In this work, we performed machine
learning on the magnetic ground state and the Curie temperature (TC), using
generic chemical and crystal structural descriptors. Based on a database of
2805 known intermetallic compounds, a random forest model is trained to
classify ferromagnetic and antiferromagnetic compounds and to do regression on
the TC for the ferromagnets. The resulting accuracy is about 86% for
classification and 92% for regression (with a mean absolute error of 58K).
Composition based features are sufficient for both classification and
regression, whereas structural descriptors improve the performance. Finally, we
predict the magnetic ordering and TC for all the intermetallic magnetic
materials in the Materials Project. Our work paves the way to accelerate the
development of magnetic materials for technological applications.",1908.00926v2
2014/1/9,Persistent Optically Induced Magnetism in Oxygen-Deficient Strontium Titanate,"Strontium titanate (SrTiO$_3$) is a foundational material in the emerging
field of complex oxide electronics. While its electronic and optical properties
have been studied for decades, SrTiO$_3$ has recently become a renewed
materials research focus catalyzed in part by the discovery of magnetism and
superconductivity at interfaces between SrTiO$_3$ and other oxides. The
formation and distribution of oxygen vacancies may play an essential but
as-yet-incompletely understood role in these effects. Moreover, recent
signatures of magnetization in gated SrTiO$_3$ have further galvanized interest
in the emergent properties of this nominally nonmagnetic material. Here we
observe an optically induced and persistent magnetization in oxygen-deficient
SrTiO$_{3-\delta}$ using magnetic circular dichroism (MCD) spectroscopy and
SQUID magnetometry. This zero-field magnetization appears below ~18K, persists
for hours below 10K, and is tunable via the polarization and wavelength of
sub-bandgap (400-500nm) light. These effects occur only in oxygen-deficient
samples, revealing the detailed interplay between magnetism, lattice defects,
and light in an archetypal oxide material.",1401.1871v1
2016/8/26,Optimization of nanocomposite materials for permanent magnets by micromagnetic simulations: effect of the intergrain exchange and the hard grains shape,"In this paper we perform the detailed numerical analysis of remagnetization
processes in nanocomposite magnetic materials consisting of magnetically hard
grains (i.e. grains made of a material with a high magnetocrystalline
anisotropy) embedded into a magnetically soft phase. Such materials are widely
used for the production of permanent magnets, because they combine the high
remanence with the large coercivity. We perform simulations of nanocomposites
with Sr-ferrite as the hard phase and Fe or Ni as the soft phase, concentrating
our efforts on analyzing the effects of ({\it i}) the imperfect intergrain
exchange and ({\it ii}) the non-spherical shape of hard grains. We demonstrate
that - in contrast to the common belief - the maximal energy product is
achieved not for systems with the perfect intergrain exchange, but for
materials where this exchange is substantially weakened. We also show that the
main parameters of the hysteresis loop - remanence, coercivity and the energy
product - exhibit non-trivial dependencies on the shape of hard grains, and
provide detailed explanations for our results. Simulation predictions obtained
in this work open new ways for the optimization of materials for permanent
magnets.",1608.07429v1
2022/1/19,Controlling magnetic frustration in 1T-TaS$_2$ via Coulomb engineered long-range interactions,"Magnetic frustrations in two-dimensional materials provide a rich playground
to engineer unconventional phenomena such as non-collinear magnetic order and
quantum spin-liquid behavior. However, despite intense efforts, a realization
of tunable frustrated magnetic order in two-dimensional materials remains an
open challenge. Here we propose Coulomb engineering as a versatile strategy to
tailor magnetic ground states in layered materials. Using the proximal quantum
spin-liquid candidate 1T-TaS$_2$ as an example, we show how long-range Coulomb
interactions renormalize the low energy nearly flat band structure, leading to
a Heisenberg model which decisively depends on the Coulomb interactions. Based
on this, we show that superexchange couplings in the material can be precisely
tailored by means of environmental dielectric screening, ultimately allowing to
externally drive the material towards the quantum spin-liquid regime. Our
results put forward Coulomb engineering as a powerful tool to manipulate
magnetic properties of van der Waals materials.",2201.07826v2
2006/9/21,High Temperature Superconductivity - Magnetic Mechanisms,"A brief history is offered concerning the relation of magnetism to
superconductivity, and the possibility that magnetic correlations are
responsible for certain types of superconductors. A central focus is on high
temperature cuprate superconductivity and the important question of whether its
d-wave pairing is caused by antiferromagnetic or singlet correlations.
Connected with this question is the much debated relation of the pseudogap
phase to the superconducting phase, and whether lattice degrees of freedom are
relevant or not.",0609559v1
2008/9/11,Ferromagnetic ordering in dilute magnetic dielectrics with and without free carriers,"The state of art in the theoretical and experimental studies of transition
metal doped oxides (dilute magnetic dielectrics) is reviewed. The available
data show that the generic non-equilibrium state of oxide films doped with
magnetic impurities may either favor ferromagnetism with high Curie temperature
or result in highly inhomogeneous state without long-range magnetic order. In
both case concomitant defects (vacancies, interstitial ions play crucial part.",0809.2005v1
2009/1/19,Toroidal moments as indicator for magneto-electric coupling: the case of BiFeO_3 versus FeTiO_3,"In this paper we present an analysis of the magnetic toroidal moment and its
relation to the various structural modes in R3c-distorted perovskites with
magnetic cations on either the perovskite A or B site. We evaluate the toroidal
moment in the limit of localized magnetic moments and show that the full
magnetic symmetry can be taken into account by considering small induced
magnetic moments on the oxygen sites. Our results give a transparent picture of
the possible coupling between magnetization, electric polarization, and
toroidal moment, thereby highlighting the different roles played by the various
structural distortions in multiferroic BiFeO_3 and in the recently discussed
isostructural material FeTiO_3, which has been predicted to exhibit electric
field-induced magnetization switching.",0901.2812v1
2013/7/19,X-ray diffraction by magnetic charges (monopoles),"Magnetic charges, or magnetic monopoles, may form in the electronic structure
of magnetic materials where ions are deprived of symmetry with respect to
spatial inversion. Predicted in 2009, the strange magnetic, pseudoscalars have
recently been found different from zero in simulations of electronic structures
of some magnetically ordered, orthorhombic, lithium orthophosphates (LiMPO4).
We prove that magnetic charges in lithium orthophosphates diffract x-rays tuned
in energy to an atomic resonance, and to guide future experiments we calculate
appropriate unit-cell structure factors for monoclinic LiCoPO4 and orthorhombic
LiNiPO4.",1307.5164v1
2014/5/22,Magnetic phases of erbium orthochromite,"Erbium orthochromite, ErCrO3, is a distorted-perovskite which has
antiferromagnetic ground state below 10 K while Cr3+ magnetic moments order at
133 K. The temperature dependence of magnetization is studied across different
magnetic phases for ErCrO3 and different magnetization isotherms are analyzed.
In the presence of external magnetic field, polycrystalline ErCrO3 develops
weak ferromagnetism from antiferromagnetic ground state. These magnetic phase
transitions are observed to be of first order which is justified by thermal
hysteresis and Arrott-plots.",1405.5636v1
2022/12/29,Magnetically enhanced thin film coarsening by a magnetic XPFC model allowing to decouple magnetic anisotropy and magnetostriction,"External magnetic fields provide a macroscopic control mechanism to influence
the microstructure of polycrystalline materials. We model the influence of
strong magnetic fields on grain growth in thin films with a magnetic extended
phase field crystal (XPFC) model. The magneto-structural effects are
incorporated into the correlation function in reciprocal space. With this
approach magnetic anisotropy, magnetostriction and mobility of grain boundary
can be controlled and a variety of geometrical and topological properties
consistent with experimental results can be determined.",2212.14416v1
2023/4/27,Effective Tight-Binding Model of Compensated Ferrimagnetic Weyl Semimetal with Spontaneous Orbital Magnetization,"The effective tight-binding model with compensated ferrimagnetic
inverse-Heusler lattice Ti$_{2}$MnAl, candidate material of magnetic Weyl
semimetal, is proposed. The energy spectrum near the Fermi level, the
configurations of the Weyl points, and the anomalous Hall conductivity are
calculated. We found that the orbital magnetization is finite, while the total
spin magnetization vanishes, at the energy of the Weyl points. The magnetic
moments at each site are correlated with the orbital magnetization, and can be
controlled by the external magnetic field.",2304.14009v1
2019/3/27,High throughput computational screening for 2D ferromagnetic materials: the critical role of anisotropy and local correlations,"The recent observation of ferromagnetic order in two-dimensional (2D)
materials has initiated a booming interest in the subject of 2D magnetism. In
contrast to bulk materials, 2D materials can only exhibit magnetic order in the
presence of magnetic anisotropy. In the present work we have used the
Computational 2D Materials Database (C2DB) to search for new ferromagnetic 2D
materials using the spinwave gap as a simple descriptor that accounts for the
role of magnetic anisotropy. In addition to known compounds we find 12 novel
insulating materials that exhibit magnetic order at finite temperatures. For
these we evaluate the critical temperatures from classical Monte Carlo
simulations of a Heisenberg model with exchange and anisotropy parameters
obtained from first principles. Starting from 150 stable ferromagnetic 2D
materials we find five candidates that are predicted to have critical
temperatures exceeding that of CrI3. We also study the effect of Hubbard
corrections in the framework of DFT+U and find that the value of U can have a
crucial influence on the prediction of magnetic properties. Our work provides
new insight into 2D magnetism and identifies a new set of promising monolayers
for experimental investigation.",1903.11466v2
2021/4/23,Interesting magnetic response of the nuclear fuel material UO2,"Magnetic response of uranium dioxide (UO2) has been investigated through
temperature and magnetic field dependent dc magnetization measurements. UO2 is
a paramagnet at room temperature. The magnetic susceptibility, however,
deviates from Curie-Weiss (CW) like paramagnetic behavior below T = 280 K.
Further down the temperature UO2 undergoes phase transition to an
antiferromagnetic state below TN = 30.6 K. The zero field cooled (ZFC) and
field cooled (FC) magnetizations exhibit some distinct thermomagnetic
irreversibility below TN. The temperature dependence of the FC magnetization is
more like a ferromagnet, whereas ZFC magnetization exhibits distinct structures
not usually observed in the antiferromagnets. In low applied magnetic field
this thermomagnetic irreversibility in magnetization exists in a subtle way
even in the paramagnetic regime above TN up to a fairly high temperature, but
vanishes in high applied magnetic fields. Deviation from CW law and
irreversibility between ZFC and FC magnetization indicate that the paramagnetic
state above TN is not a trivial one. Magnetic response below TN changes
significantly with the increase in the applied magnetic field. Thermomagnetic
irreversibility in magnetization initially increases with the increase in the
strength of applied magnetic field, but then gets reduced in the high applied
fields. A subtle signature of a magnetic field induced phase transition is also
observed in the isothermal magnetic field vartaion of magnetization. All these
experimetal results highlight the non-trivial nature of the antiferromagnetic
state in UO2",2104.11412v1
2015/4/17,Model for the FC and ZFC Ferrimagnetic Spinel,"There are two methods of preparation of ferrimagnetic spinel. If, during the
preparation, an external magnetic field as high as 300 O\""{e} is applied upon
cooling the material is named field-cooled (FC). If the applied field is about
1O\""{e} the material is zero-field cooled (ZFC). To explore the magnetic and
thermodynamic properties of these materials we consider two-sublattice spin
system, defined on the bcc lattice, with spin-$s^A$ operators $\bf{S_{i}^A}$ at
the sublattice $A$ site and spin-$s^B$ operators $\bf{S_{i}^B}$ at the
sublattice $B$ site, where $s^A>s^B$. The subtle point is the exchange between
sublattice A and B spins, which is antiferromanetic. Applying magnetic field
along the sublattice A magnetization, during preparation of the material, one
compensates the Zeeman splitting, due to the exchange, of sublattice B
electrons. This effectively leads to a decrease of the $s^B$ spin. We consider
a model with $s^B$ varying parameter which accounts for the applied, during the
preparation, magnetic field.
  It is shown that the model agrees well with the observed
magnetization-temperature curves of zero field cooled (ZFC) and non-zero field
cooled (FC) spinel ferrimagnetic spinel and explains the anomalous temperature
dependence of the specific heat.",1504.04547v1
2019/9/29,Magnetic Shape Memory Polymers with Integrated Multifunctional Shape Manipulations,"Shape-programmable soft materials that exhibit integrated multifunctional
shape manipulations, including reprogrammable, untethered, fast, and reversible
shape transformation and locking, are highly desirable for a plethora of
applications, including soft robotics, morphing structures, and biomedical
devices. Despite recent progress, it remains challenging to achieve multiple
shape manipulations in one material system. Here, we report a novel magnetic
shape memory polymer composite to achieve this. The composite consists of two
types of magnetic particles in an amorphous shape memory polymer matrix. The
matrix softens via magnetic inductive heating of low-coercivity particles, and
high-remanence particles with reprogrammable magnetization profiles drive the
rapid and reversible shape change under actuation magnetic fields. Once cooled,
the actuated shape can be locked. Additionally, varying the particle loadings
for heating enables sequential actuation. The integrated multifunctional shape
manipulations are further exploited for applications including soft magnetic
grippers with large grabbing force, sequential logic for computing, and
reconfigurable antennas.
  Keyword: shape memory polymers, soft active materials, magnetic soft
material, soft robotics, soft material computing",1909.13171v1
2019/7/24,Understanding Magnetic Properties of Actinide-Based Compounds from Machine Learning,"Actinide and lanthanide-based materials display exotic properties that
originate from the presence of itinerant or localized f-electrons and include
unconventional superconductivity and magnetism, hidden order; and heavy fermion
behavior. Due to the strongly correlated nature of the 5f electrons, magnetic
properties of these compounds depend sensitively on applied magnetic field and
pressure, as well as on chemical doping. However, precise connection between
the structure and magnetism in actinide-based materials is currently unclear.
In this investigation, we established such structure-property links by
assembling and mining two datasets that aggregate, respectively, the results of
high-throughput DFT simulations and experimental measurements for the families
of uranium and neptunium based binary compounds. Various regression algorithms
were utilized to identify correlations among accessible attributes (features or
descriptors) of the material systems and predict their cation magnetic moments
and general forms of magnetic ordering. Descriptors representing compound
structural parameters and cation f-subshell occupation numbers were identified
as most important for accurate predictions. The best machine learning model
developed employs the Random Forest Regression algorithm and can predict
magnetic moment sizes and ordering forms in actinide-based systems with 10-20%
of root mean square error.",1907.10587v1
2021/12/18,Quantum Imaging of Magnetic Phase Transitions and Spin Fluctuations in Intrinsic Magnetic Topological Nanoflakes,"Topological materials featuring exotic band structures, unconventional
current flow patterns, and emergent organizing principles offer attractive
platforms for the development of next-generation transformative quantum
electronic technologies. The family of MnBi2Te4 (Bi2Te3)n materials is
naturally relevant in this context due to their nontrivial band topology,
tunable magnetism, and recently discovered extraordinary quantum transport
behaviors. Despite numerous pioneering studies, to date, the local magnetic
properties of MnBi2Te4 (Bi2Te3)n remain an open question, hindering a
comprehensive understanding of their fundamental material properties.
Exploiting nitrogen-vacancy (NV) centers in diamond, we report nanoscale
quantum imaging of magnetic phase transitions and spin fluctuations in
exfoliated MnBi2Te4 (Bi2Te3)n flakes, revealing the underlying spin transport
physics and magnetic domains at the nanoscale. Our results highlight the unique
advantage of NV centers in exploring the magnetic properties of emergent
quantum materials, opening new opportunities for investigating the interplay
between topology and magnetism.",2112.09863v1
2022/2/28,Magnetic Interactions of the Centrosymmetric Skyrmion Material Gd2PdSi3,"The experimental realization of magnetic skyrmions in centrosymmetric
materials has been driven by theoretical understanding of how a delicate
balance of anisotropy and frustration can stabilize topological spin structures
in applied magnetic fields. Recently, the centrosymmetric material
Gd$_{2}$PdSi$_{3}$ was shown to host a field-induced skyrmion phase, but the
skyrmion stabilization mechanism remains unclear. Here, we employ
neutron-scattering measurements on an isotopically-enriched polycrystalline
Gd$_{2}$PdSi$_{3}$ sample to quantify the interactions that drive skyrmion
formation. Our analysis reveals spatially-extended interactions in triangular
planes that are consistent with an RKKY mechanism, and large ferromagnetic
inter-planar magnetic interactions that are modulated by the Pd/Si
superstructure. The skyrmion phase emerges from a zero-field helical magnetic
order with magnetic moments perpendicular to the magnetic propagation vector,
indicating that the magnetic dipolar interaction plays a significant role. Our
experimental results establish an interaction space that can promote skyrmion
formation, facilitating identification and design of centrosymmetric skyrmion
materials.",2203.00066v1
2022/11/18,Angstrom-Scale Imaging of Magnetization in Antiferromagnetic Fe$_2$As via 4D-STEM,"We demonstrate a combination of computational tools and experimental 4D-STEM
methods to image the local magnetic moment in antiferromagnetic Fe$_2$As with 6
angstrom spatial resolution. Our techniques utilize magnetic diffraction peaks,
common in antiferromagnetic materials, to create imaging modes that directly
visualize the magnetic lattice. Using this approach, we show that
center-of-mass analysis can determine the local magnetization component in the
plane perpendicular to the path of the electron beam. Moreover, we develop
Magnstem, a quantum mechanical electron scattering simulation code, to model
electron scattering of an angstrom-scale probe from magnetic materials. Using
these tools, we identify optimal experimental conditions for separating weak
magnetic signals from the much stronger interactions of an angstrom-scale probe
with electrostatic potentials. Our techniques should be useful for
characterizing the local magnetic order in systems such in thin films,
interfaces, and domain boundaries of antiferromagnetic materials, which are
difficult to probe with existing methods.",2211.10423v1
2023/3/20,2D Magnetic Semiconductors via Substitutional Doping of Transition Metal Dichalcogenides,"Transition metal dichalcogenides (TMDs) are two-dimensional (2D) materials
with remarkable electrical, optical and chemical properties. One promising
strategy to tailor TMD properties of TMDs is to create alloys through
dopant-induced modification. Dopants can introduce additional states within the
bandgap of TMDs, leading to changes in their optical, electronic, and magnetic
properties. This paper overviews chemical vapor deposition (CVD) methods to
introduce dopants into TMD monolayers. The advantages and limitations and their
impacts on the doped TMDs' structural, electrical, optical, and magnetic
properties are discussed. The dopants in TMDs modify the density and type of
carriers in the material, thereby influencing the optical properties of the
materials. The TMDs' magnetic moment and circular dichroism are also strongly
affected by doping, which enhances the magnetic signal in the material.
Finally, we highlight the different doping-induced magnetic properties of TMDs,
including superexchange-induced ferromagnetism and valley Zeeman shift.
Overall, this review paper provides a comprehensive summary of magnetic TMDs
synthesized via CVD, which can guide future research on doped TMDs for various
applications, such as spintronics, optoelectronics, and magnetic memory
devices.",2303.11173v1
2013/3/30,Defect-Induced Magnetism in Solids,"In the last years the number of nominally non-magnetic solids showing
magnetic order induced by some kind of defects has increased continuously. From
the single element material graphite to several covalently bonded non-magnetic
compounds, the influence of defects like vacancies and/or non-magnetic ad-atoms
on triggering magnetic order has attracted the interest of experimentalists and
theoreticians. We review and discuss the main theoretical approach as well as
recently obtained experimental evidence based on different experimental methods
that supports the existence of defect-induced magnetism (DIM) in non-magnetic
as well as in magnetic materials.",1304.0137v1
2014/8/6,Permanent magnet with MgB2 bulk superconductor,"Superconductors with persistent zero-resistance currents serve as permanent
magnets for high-field applications requiring a strong and stable magnetic
field, such as magnetic resonance imaging (MRI). The recent global helium
shortage has quickened research into high-temperature superconductors (HTSs)
materials that can be used without conventional liquid-helium cooling to 4.2 K.
Herein, we demonstrate that 40-K-class metallic HTS magnesium diboride (MgB2)
makes an excellent permanent bulk magnet, maintaining 3 T at 20 K for 1 week
with an extremely high stability (<0.1 ppm/h). The magnetic field trapped in
this magnet is uniformly distributed, as for single-crystalline
neodymium-iron-boron. Magnetic hysteresis loop of the MgB2 permanent bulk
magnet was detrmined. Because MgB2 is a simple-binary-line compound that does
not contain rare-earth metals, polycrystalline bulk material can be
industrially fabricated at low cost and with high yield to serve as strong
magnets that are compatible with conventional compact cryocoolers, making MgB2
bulks promising for the next generation of Tesla-class permanent-magnet
applications.",1408.1277v1
2019/1/10,Ultrafast magnetization dynamics in uniaxial ferrimagnets with compensation point. GdFeCo,"We derive an effective Lagrangian in the quasi-antiferromagnetic
approximation that allows to describe the magnetization dynamics for uniaxial
f-d (rare-earth - transition metal) ferrimagnet near the magnetization
compensation point in the presence of external magnetic field. We perform
calculations for the parameters of GdFeCo, a metallic ferrimagnet with
compensation point that is one of the most promising materials in ultrafast
magnetism. Using the developed approach, we find the torque that acts on the
magnetization due to ultrafast demagnetization pulse that can be caused either
by ultrashort laser or electrical current pulse. We show that the torque is
non-zero only in the non-collinear magnetic phase that can be acquired by
applying external magnetic field to the material. The coherent response of
magnetization dynamics amplitude and its timescale exhibits critical behavior
near certain values of the magnetic field corresponding to a spin-flop like
phase transition. Understanding the underlying mechanisms for these effects
opens the way to efficient control of the amplitude and the timescales of the
spin dynamics, which is one of the central problems in the field of ultrafast
magnetism.",1901.03072v2
2019/12/16,3D printing of polymer-bonded anisotropic magnets in an external magnetic field and by a modified production process,"The possibility of producing polymer-bonded magnets with the aid of additive
processes, such as 3D printing, opens up a multitude of new areas of
application. Almost any structures and prototypes can be produced
cost-effectively in small quantities. Extending the 3D printing process allows
the manufacturing of anisotropic magnetic structures by aligning the magnetic
easy axis of ferromagnetic particles inside a paste-like compound material
along an external magnetic field. This is achieved by two different approaches:
First, the magnetic field for aligning the particles is provided by a permanent
magnet. Secondly, the 3D printing process itselfs generates an anisotropic
behavior of the structures. An inexpensive and customizable end-user fused
filament fabrication 3D printer is used to print the magnetic samples. The
magnetical properties of different magnetic anisotropic Sr ferrite and SmFeN
materials are investigated and discussed.",1912.07374v1
2023/3/10,New Research Trends in Electrically Tunable 2D van der Waals Magnetic Materials,"The recent discovery of two-dimensional (2D) van der Waals (vdW) magnetic
materials has provided new, unprecedented opportunities for both fundamental
science and technological applications. Unlike three-dimensional (3D) magnetic
systems, the electric manipulation of vdW magnetism (e.g., magnetization state,
magnetic anisotropy, magnetic ordering temperature) down to the monolayer limit
at ambient conditions enables high efficiency operation and low energy
consumption, which has the potential to revolutionize the fields of
spintronics, spin-caloritronics, and valleytronics. This article provides an
in-depth analysis of the recent progress, emerging opportunities, and technical
challenges in the electric manipulation of magnetic functionalities of a wide
variety of 2D vdW magnetic systems ranging from metals to semiconductors and
heterostructures. The state-of-the-art understanding of the mechanisms behind
the electric modulation of magnetism in these 2D vdW magnetic systems will
drive future research towards novel applications in spintronics,
spin-caloritronics, valleytronics, and quantum computation.",2303.05748v1
2012/11/22,Hydrogenated Bilayer Wurtzite SiC Nanofilms: A Two-Dimensional Bipolar Magnetic Semiconductor Material,"Recently, a new kind of spintronics materials, bipolar magnetic semiconductor
(BMS), has been proposed. The spin polarization of BMS can be conveniently
controlled by a gate voltage, which makes it very attractive in device
engineering. Now, the main challenge is finding more BMS materials. In this
article, we propose that hydrogenated wurtzite SiC nanofilm is a
two-dimensional BMS material. Its BMS character is very robust under the effect
of strain, substrate, or even a strong electric field. The proposed
two-dimensional BMS material paves the way to use this promising new material
in an integrated circuit.",1211.5187v1
2011/10/6,Giant Magnetoresistance Effect in Organic Material and Its Potential for Magnetic Sensor,"Giant magnetoresistance (GMR) material has great potential as next generation
magnetic field sensing devices, have magnetic properties and high electrical
potential to be developed into various applications such as: magnetic field
sensor measurements, current measurements, linear and rotational position
sensor, data storage, head recording, and non-volatile magnetic random access
memory (MRAM). Today, the new GMR materials based on organic material obtained
after allowing for Organic Magnetoresistance (OMAR) was found in OLEDs (organic
light-emitting diodes). This organic material is used as a spacer layer in GMR
devices with spin-valve structures. Traditionally, metals and semiconductors
are used as a spacer layer in spin-valve. However, several factors such as spin
scattering caused by large atoms of the spacer material and the interface
scattering of ferromagnetic with a spacer, will limit the efficiency of
spin-valve. In this paper, we describe a new GMR materials based on organic
material that we have developed.",1110.1123v1
2008/5/26,Magnetic field induced incommensurate resonance in cuprate superconductors,"The influence of a uniform external magnetic field on the dynamical spin
response of cuprate superconductors in the superconducting state is studied
based on the kinetic energy driven superconducting mechanism. It is shown that
the magnetic scattering around low and intermediate energies is dramatically
changed with a modest external magnetic field. With increasing the external
magnetic field, although the incommensurate magnetic scattering from both low
and high energies is rather robust, the commensurate magnetic resonance
scattering peak is broadened. The part of the spin excitation dispersion seems
to be an hourglass-like dispersion, which breaks down at the heavily low energy
regime. The theory also predicts that the commensurate resonance scattering at
zero external magnetic field is induced into the incommensurate resonance
scattering by applying an external magnetic field large enough.",0805.3922v2
2014/9/29,Review and comparison of magnet designs for magnetic refrigeration,"One of the key issues in magnetic refrigeration is generating the magnetic
field that the magnetocaloric material must be subjected to. The magnet
constitutes a major part of the expense of a complete magnetic refrigeration
system and a large effort should therefore be invested in improving the magnet
design. A detailed analysis of the efficiency of different published permanent
magnet designs used in magnetic refrigeration applications is presented in this
paper. Each design is analyzed based on the generated magnetic flux density,
the volume of the region where this flux is generated and the amount of magnet
material used. This is done by characterizing each design by a figure of merit
magnet design efficiency parameter, $\Lambda_\mathrm{cool}$. The designs are
then compared and the best design found. Finally recommendations for designing
the ideal magnet design are presented based on the analysis of the reviewed
designs.",1409.8046v1
2020/4/24,Observation of magnetic domains in uniaxial magnets via small-angle electron diffraction and Foucault imaging,"Observation of magnetic domains is important in understanding the magnetic
properties of magnetic materials and devices. In this study, we report that the
magnetic domains of M-type hexaferrites with uniaxial anisotropy can be
visualized via small-angle electron diffraction and Foucault imaging. The
position of the diffraction pattern spots has the same period as that of
magnetic domains in a Sc-substituted hexaferrite
(BaFe$_{12-x-\delta}$Sc$_x$Mg$_\delta$O$_{19}$). Conversely, the spots were
observed four times longer than the period of magnetic domains in hexaferrite
without substitution (BaFe$_{12}$O$_{19}$), demonstrating the long-range order
of the Bloch walls. When the specimen was tilted, the magnetic deflection
effect, as well as the periodic spots of magnetic domains, occurred. Thus, we
were able to visualize the magnetic domains with different magnetization
directions and domain orientations by selecting deflection spots. The results
indicate that the technique utilized in this study is useful in observing the
magnetic materials with uniaxial anisotropy.",2004.11589v1
2019/3/28,Micromagnetics of rare-earth efficient permanent magnets,"The development of permanent magnets containing less or no rare-earth
elements is linked to profound knowledge of the coercivity mechanism.
Prerequisites for a promising permanent magnet material are a high spontaneous
magnetization and a sufficiently high magnetic anisotropy. In addition to the
intrinsic magnetic properties the microstructure of the magnet plays a
significant role in establishing coercivity. The influence of the
microstructure on coercivity, remanence, and energy density product can be
understood by {using} micromagnetic simulations. With advances in computer
hardware and numerical methods, hysteresis curves of magnets can be computed
quickly so that the simulations can readily provide guidance for the
development of permanent magnets. The potential of rare-earth reduced and free
permanent magnets is investigated using micromagnetic simulations. The results
show excellent hard magnetic properties can be achieved in grain boundary
engineered NdFeB, rare-earth magnets with a ThMn12 structure, Co-based
nano-wires, and L10-FeNi provided that the magnet's microstructure is
optimized.",1903.11922v1
2024/2/15,Understanding and tuning magnetism in layered Ising-type antiferromagnet FePSe3 for potential 2D magnet,"Recent development in two-dimensional (2D) magnetic materials have motivated
the search for new van der Waals magnetic materials, especially Ising-type
magnets with strong magnetic anisotropy. Fe-based MPX3 (M = transition metal, X
= chalcogen) compounds such as FePS3 and FePSe3 both exhibit an Ising-type
magnetic order, but FePSe3 receives much less attention compared to FePS3. This
work focuses on establishing the strategy to engineer magnetic anisotropy and
exchange interactions in this less-explored compound. Through chalcogen and
metal substitutions, the magnetic anisotropy is found to be immune against S
substitution for Se whereas tunable only with heavy Mn substitution for Fe. In
particular, Mn substitution leads to a continuous rotation of magnetic moments
from the out-of-plane direction towards in-plane. Furthermore, the magnetic
ordering temperature displays non-monotonic doping dependence for both
chalcogen and metal substitutions but due to different mechanisms. These
findings provide deeper insight into the Ising-type magnetism in this important
van der Waals material, shedding light on the study of other Ising-type
magnetic systems as well as discovering novel 2D magnets for potential
applications in spintronics.",2402.10155v1
2014/7/8,Competing magnetic phases and field-induced dynamics in DyRuAsO,"Analysis of neutron diffraction, dc magnetization, ac magnetic
susceptibility, heat capacity, and electrical resistivity for DyRuAsO in an
applied magnetic field are presented at temperatures near and below those at
which the structural distortion (T_S = 25 K) and subsequent magnetic ordering
(T_N = 10.5 K) take place. Powder neutron diffraction is used to determine the
antiferromagnetic order of Dy moments of magnitude 7.6(1) mu_B in the absence
of a magnetic field, and demonstrate the reorientation of the moments into a
ferromagnetic configuration upon application of a magnetic field. Dy magnetism
is identified as the driving force for the structural distortion. The magnetic
structure of analogous TbRuAsO is also reported. Competition between the two
magnetically ordered states in DyRuAsO is found to produce unusual physical
properties in applied magnetic fields at low temperature. An additional phase
transition near T* = 3 K is observed in heat capacity and other properties in
fields greater than about 3 T. Magnetic fields of this magnitude also induce
spin-glass-like behavior including thermal and magnetic hysteresis, divergence
of zero-field-cooled and field-cooled magnetization, frequency dependent
anomalies in ac magnetic susceptibility, and slow relaxation of the
magnetization. This is remarkable since DyRuAsO is a stoichiometric material
with no disorder detected by neutron diffraction, and suggests analogies with
spin-ice compounds and related materials with strong geometric frustration.",1407.2184v1
2006/8/14,Thermal relaxation of magnetic clusters in amorphous Hf_{57}Fe_{43} alloy,"The magnetization processes in binary magnetic/nonmagnetic amorphous alloy
Hf_{57}Fe_{43} are investigated by the detailed measurements of magnetic
hysteresis loops, temperature dependence of magnetization, relaxation of
magnetization and magnetic ac susceptibility, including a nonlinear term.
Blocking of magnetic moments at lower temperatures is accompanied with the slow
relaxation of magnetization and magnetic hysteresis loops. All of the observed
properties are explained with the superparamagnetic behaviour of the single
domain magnetic clusters inside the nonmagnetic host, their blocking by the
anisotropy barriers and thermal fluctuation over the barriers accompanied by
relaxation of magnetization. From magnetic viscosity analysis based on thermal
relaxation over the anisotropy barriers it is found out that magnetic clusters
occupy the characteristic volume from 25 up to 200 nm3 . The validity of the
superparamagnetic model of Hf_{57}Fe_{43} is based on the concentration of iron
in the Hf_{100-x}Fe_{43} system that is just below the threshold for the long
range magnetic ordering. This work throws more light on magnetic behaviour of
other amorphous alloys, too.",0608307v3
2013/11/18,"Fabrication, properties, and applications of flexible magnetic films","Flexible magnetic devices, i.e., magnetic devices fabricated on flexible
substrates, are very attractive in application of detecting magnetic field in
arbitrary surface, non-contact actuators, and microwave devices due to the
stretchable, biocompatible, light-weight, portable, and low cost properties.
Flexible magnetic films are essential for the realization of various
functionalities of flexible magnetic devices. To give a comprehensive
understanding for flexible magnetic films and related devices, we have reviewed
recent advances in the studies of flexible magnetic films including fabrication
methods, magnetic and transport properties of flexible magnetic films, and
their applications in magnetic sensors, actuators, and microwave devices. Three
typical methods were introduced to prepare the flexible magnetic films.
Stretching or bending the flexible magnetic films offers a good way to apply
mechanical strain on magnetic films, so that magnetic anisotropy, exchanged
bias, coercivity, and magnetoresistance can be effectively manipulated.
Finally, a series of examples were shown to demonstrate the great potential of
flexible magnetic films for future applications.",1311.4318v1
2021/10/31,Shape Programmable Magnetic Pixel Soft Robot,"Magnetic response soft robot realizes programmable shape regulation with the
help of magnetic field and produces various actions. The shape control of
magnetic soft robot is based on the magnetic anisotropy caused by the orderly
distribution of magnetic particles in the elastic matrix. In the previous
technologies, magnetic programming is coupled with the manufacturing process,
and the orientation of magnetic particles cannot be modified, which brings
restrictions to the design and use of magnetic soft robot. This paper presents
a magnetic pixel robot with shape programmable function. By encapsulating
NdFeB/gallium composites into silicone shell, a thermo-magnetic response
functional film with lattice structure are fabricated. Basing on
thermal-assisted magnetization technique, we realized the discrete
magnetization region distribution on the film. Therefore, we proposed a
magnetic coding technique to realize the mathematical response action design of
software robot. Using these methods, we prepared several magnetic soft robots
based on origami structure. The experiments show that the behavior mode of
robot can be flexibly and repeatedly regulated by magnetic encoding technique.
This work provides a basis for the programmed shape regulation and motion
design of soft robot.",2111.00422v2
2022/10/6,Current-induced perpendicular effective magnetic field in magnetic heterostructures,"Generation of perpendicular effective magnetic field or perpendicular spins
({\sigma}z) is central for the development of energy-efficient, scalable, and
external-magnetic-field-free spintronic memory and computing technologies.
Here, we report the first identification and the profound impacts of a
significant effective perpendicular magnetic field that can arise from
asymmetric current spreading within magnetic microstrips and Hall bars. This
effective perpendicular magnetic field can exhibit all the three
characteristics that have been widely assumed in the literature to ""signify""
the presence of a flow of {\sigma}z, i.e., external-magnetic-field-free current
switching of uniform perpendicular magnetization, a sin2{\phi}-dependent
contribution in spin-torque ferromagnetic resonance signal of in-plane
magnetization ({\phi} is the angle of the external magnetic field with respect
to the current, and a {\phi}-independent but field-dependent contribution in
the second harmonic Hall voltage of in-plane magnetization. This finding
suggests that it is critical to include current spreading effects in the
analyses of various spin polarizations and spin-orbit torques in magnetic
heterostructure. Technologically, our results provide perpendicular effective
magnetic field induced by asymmetric current spreading as a novel, universally
accessible mechanism for efficient, scalable, and external-magnetic-field-free
magnetization switching in memory and computing technologies.",2210.02916v1
1999/3/20,Magnetism Controlled Vortex Matter,"We discuss a new class of phenomena based on strong interaction between
magnetic superstructures and vortices in superconductors in combined
heterogeneous structures. An inhomogeneous magnetization can pin vortices or
create them spontaneously changing drastically properties of the
superconductor. On the other hand, the interaction between magnetic moments
mediated by vortices can result in specific types of magnetic ordering. The
same interaction can create coupled magnetic-superconducting defects. We
discuss possible experimental observation of magnetism controlled vortex matter
in superconducting films with magnetic nanoscale dots or stripes and layered
systems with alternating superconducting and magnetic layers.",9903312v1
2009/9/25,Probing punctual magnetic singularities during magnetization process in FePd films,"We report the use of Lorentz microscopy to observe the domain wall structure
during the magnetization process in FePd thin foils. We have focused on the
magnetic structure of domain walls of bubble-shaped magnetic domains near
saturation. Regions are found along the domain walls where the magnetization
abruptly reverses. Multiscale magnetic simulations shown that these regions are
vertical Bloch lines (VBL) and the different bubble shapes observed are then
related to the inner structure of the VBLs. We were thus able to probe the
presence of magnetic singularities as small as Bloch points in the inner
magnetization of the domain walls.",0909.4645v1
2010/6/21,Dynamics of magnetic charges in artificial spin ice,"Artificial spin ice has been recently implemented in two-dimensional arrays
of mesoscopic magnetic wires. We propose a theoretical model of magnetization
dynamics in artificial spin ice under the action of an applied magnetic field.
Magnetization reversal is mediated by domain walls carrying two units of
magnetic charge. They are emitted by lattice junctions when the the local field
exceeds a critical value $H_c$ required to pull apart magnetic charges of
opposite sign. Positive feedback from Coulomb interactions between magnetic
charges induces avalanches in magnetization reversal.",1006.4075v2
2013/2/20,Non-magnetic doping induced magnetism in Li doped SnO2 nanoparticles,"We address the possibility of non-magnetic doping induced magnetism, in Li
doped SnO2 nano-particles. The compounds have been prepared by solid state
route at equilibrium and were found to be crystallized in single rutile phase.
The magnetization measurements have shown that Li-doping induces magnetism in
SnO2 for a particular range of Li concentration. However, for other Li
concentrations, including pure SnO2, the samples exhibit diamagnetism. To
investigate the possible origin of the induced magnetism, we have studied the
variation of the magnetization as a function of the average nano-particle
radius. Possible scenarios for the appearance of magnetism in these compounds
are discussed.",1302.4869v1
2023/8/24,Non-reciprocal coherent all-optical switching between magnetic multi-states,"We present experimental and computational findings of the laser-induced
non-reciprocal motion of magnetization during ultrafast photo-magnetic
switching in garnets. We found distinct coherent magnetization precession
trajectories and switching times between four magnetization states, depending
on both directions of the light linear polarization and initial magnetic state.
As a fingerprint of the topological symmetry, the choice of the switching
trajectory is governed by an interplay of the photo-magnetic torque and
magnetic anisotropy. Our results open a plethora of possibilities for designing
energy-efficient magnetization switching routes at arbitrary energy landscapes.",2308.12771v1
2005/8/26,Ferroelectricity in Incommensurate Magnets,"We review the phenomenology of coupled magnetic and electric order parameters
for systems in which ferroelectric and incommensurate magnetic order occur
simultaneously. We discuss the role that such materials might play in
fabricating novel magnetoelectric devices. Then we briefly review the
mean-field description of ferroelectricity and modulated magnetic ordering as a
preliminary to analyzing the symmetry of the interaction between the
spontaneous polarization and the order parameters describing long-range
modulated magnetic ordering. As illustration we show how this formulation
provides a phenomenological explanation for the observed phase transitions in
Ni$_3$V$_2$O$_8$ and TbMnO$_3$ in which ferroelectric and magnetic order
parameters simultaneously become nonzero at a single phase transition. In
addition, this approach explains the fact that the spontaneous polarization
only appears along a specific crystallographic direction. We analyze the
symmetry of the strain dependence of the exchange tensor and show that it is
consistent with the macroscopic symmetry analysis. We conclude with a brief
discussion of how our approach might be relevant in understanding other systems
with coupled magnetic and ferroelectric order, and more importantly, how these
principles relate to the search for materials with larger magnetoelectric
couplings at room temperature.",0508617v1
2016/4/26,Compensation temperatures and exchange bias in La1.5Ca0.5CoIrO6,"We report on the study of magnetic properties of the La1.5Ca0.5CoIrO6 double
perovskite. Via ac magnetic susceptibility we have observed evidence of weak
ferromagnetism and reentrant spin glass behavior on an antiferromagnetic
matrix. Regarding the magnetic behavior as a function of temperature, we have
found that the material displays up to three inversions of its magnetization,
depending on the appropriate choice of the applied magnetic field. At low
temperature the material exhibit exchange bias effect when it is cooled in the
presence of a magnetic field. Also, our results indicate that this effect may
be observed even when the system is cooled at zero field. Supported by other
measurements and also by electronic structure calculations, we discuss the
magnetic reversals and spontaneous exchange bias effect in terms of magnetic
phase separation and magnetic frustration of Ir4+ ions located between the
antiferromagnetically coupled Co ions.",1604.07804v2
2017/10/20,Anisotropic magnetic properties of the triangular plane lattice material TmMgGaO4,"The crystal growth, structure, and basic magnetic properties of TmMgGaO4 are
reported. The Tm ions are located in a planar triangular lattice consisting of
distorted TmO6 octahedra, while the Mg and Ga atoms randomly occupy
intermediary bilayers of M-O triangular bipyramids. The Tm ions are
positionally disordered. The material displays an antiferromagnetic Curie Weiss
theta of ~ -20 -25 K, with no clear ordering visible in the magnetic
susceptibility down to 1.8 K; the structure and magnetic properties suggest
that ordering of the magnetic moments is frustrated by both structural disorder
and the triangular magnetic motif. Single crystal magnetization measurements
indicate that the magnetic properties are highly anisotropic, with large
moments measured perpendicular to the triangular planes. At 2 K, a broad
step-like feature is seen in the field-dependent magnetization perpendicular to
the plane on applied field near 2 Tesla.",1710.07707v1
2008/11/21,Grounded Uniaxial Material Slabs as Magnetic Conductors,"The objective of this paper is all-angle artificial magnetic conductor, i.e.
artificial magnetic conductor that has stable magnetic-wall effect with respect
to the incidence angle. Furthermore, we seek for a design that would be easy
for manufacturing. In order to achieve this we use grounded uniaxial material
slabs and we do not constrict ourselves to naturally available materials.
Instead, we assume that the desired parameters can be synthesized using the
emerging artificial electromagnetic materials. It is found that it is possible
to have an all-angle magnetic-wall effect for both TE and TM polarization.
Especially for the TM fields the structure would be easily manufacturable. The
proposed structure has similar appearance as more well-known artificial
impedance surfaces, but the design parameters and the physical properties
behind the magnetic wall effect are novel. The performance of the proposed
artificial magnetic conductor is verified with numerical simulations. This
paper introduces a new approach how to obtain a magnetic-wall effect. It is
possible to use this this approach also together with other ways of obtaining
the magnetic-wall effect for dual-band operation.",0811.3493v2
2021/3/16,Complete mapping of magnetic anisotropy for prototype Ising van der Waals FePS$_3$,"Several Ising-type magnetic van der Waals (vdW) materials exhibit stable
magnetic ground states. Despite these clear experimental demonstrations, a
complete theoretical and microscopic understanding of their magnetic anisotropy
is still lacking. In particular, the validity limit of identifying their
one-dimensional (1-D) Ising nature has remained uninvestigated in a
quantitative way. Here we performed the complete mapping of magnetic anisotropy
for a prototypical Ising vdW magnet FePS$_3$ for the first time. Combining
torque magnetometry measurements with their magnetostatic model analysis and
the relativistic density functional total energy calculations, we successfully
constructed the three-dimensional (3-D) mappings of the magnetic anisotropy in
terms of magnetic torque and energy. The results not only quantitatively
confirm that the easy axis is perpendicular to the $ab$ plane, but also reveal
the anisotropies within the $ab$, $ac$, and $bc$ planes. Our approach can be
applied to the detailed quantitative study of magnetism in vdW materials.",2103.09029v1
2021/9/9,Unraveling the magnetic softness in Fe-Ni-B based nanocrystalline material by magnetic small-angle neutron scattering,"We employ magnetic small-angle neutron scattering to investigate the magnetic
interactions in $(Fe_{0.7}Ni_{0.3})_{86}B_{14}$ alloy, a HiB-NANOPERM-type soft
magnetic nanocrystalline material, which exhibits an ultrafine microstructure
with an average grain size below 10 nm. The neutron data reveal a significant
spin-misalignment scattering, which is mainly related to the jump of the
longitudinal magnetization at internal particle-matrix interfaces. The field
dependence of the neutron data can be well described by the micromagnetic
small-angle neutron scattering theory. In particular, the theory explains the
'clover-leaf-type' angular anisotropy observed in the purely magnetic neutron
scattering cross section. The presented neutron-data analysis also provides
access to the magnetic interaction parameters, such as the exchange-stiffness
constant, which plays a crucial role towards the optimization of the magnetic
softness of Fe-based nanocrystalline materials.",2109.04107v2
2022/2/20,Magneto-optical Spectroscopy with RAMBO: A Table-Top 30 T Magnet,"Optically probing materials in high magnetic fields can provide enlightening
insight into field-modified electronic states and phases, while optically
driving materials in high magnetic fields can induce novel nonequilibrium
many-body dynamics of spin and charge carriers. While there are high-field
magnets compatible with standard optical spectroscopy methods, they are
generally bulky and have limited optical access, which prohibit performing
state-of-the-art ultrafast and/or nonlinear optical experiments. The Rice
Advanced Magnet with Broadband Optics (RAMBO), a unique 30-T pulsed mini-coil
magnet system with direct optical access, has enabled previously challenging
experiments using femtosecond optical pulses, including time-domain terahertz
spectroscopy, in cutting-edge materials placed in strong magnetic fields. Here,
we review recent experimental advances made possible by the first-generation
RAMBO setup. After summarizing technological aspects of combining optical
spectroscopic techniques with the mini-coil magnet, we describe results of
magneto-optical studies of a wide variety of materials, providing new insight
into the states and dynamics of four types of quasiparticles in solids -
excitons, plasmons, magnons, and phonons - in high magnetic fields.",2202.09732v1
2024/1/24,Progress and Prospects in Two-Dimensional Magnetism of van der Waals Materials,"Two-dimensional (2D) magnetism in van der Waals (vdW) atomic crystals and
moir\'e superlattices has emerged as a topic of tremendous interest in the
fields of condensed matter physics and materials science within the past
half-decade since its first experimental discovery in 2016 - 2017. It has not
only served as a powerful platform for investigating phase transitions in the
2D limit and exploring new phases of matter, but also provided new
opportunities for applications in microelectronics, spintronics, magnonics,
optomagnetics, and so on. Despite the flourishing developments in 2D magnetism
over this short period of time, further efforts are welcome in multiple
forefronts of 2D magnetism research for achieving the ultimate goal of
routinely implementing 2D magnets as quantum electronic components. In this
review article, we will start with basic concepts and properties of 2D
magnetism, followed by a brief overview of historical efforts in 2D magnetism
research and then a comprehensive review of vdW material-based 2D magnetism. We
will conclude with discussions on potential future research directions for this
growing field of 2D vdW magnetism.",2401.13781v1
2024/2/7,Equivariant Neural Network Force Fields for Magnetic Materials,"Neural network force fields have significantly advanced ab initio atomistic
simulations across diverse fields. However, their application in the realm of
magnetic materials is still in its early stage due to challenges posed by the
subtle magnetic energy landscape and the difficulty of obtaining training data.
Here we introduce a data-efficient neural network architecture to represent
density functional theory total energy, atomic forces, and magnetic forces as
functions of atomic and magnetic structures. Our approach incorporates the
principle of equivariance under the three-dimensional Euclidean group into the
neural network model. Through systematic experiments on various systems,
including monolayer magnets, curved nanotube magnets, and moir\'e-twisted
bilayer magnets of $\text{CrI}_{3}$, we showcase the method's high efficiency
and accuracy, as well as exceptional generalization ability. The work creates
opportunities for exploring magnetic phenomena in large-scale materials
systems.",2402.04864v1
2010/3/17,On effective electromagnetic parameters of artificial nanostructured magnetic materials,"In this paper we discuss effective material parameter description of new
nanostructures designed to perform as artificial magnetic materials for vis-
ible light. Among these structures there are various split-ring resonators,
dual-bar structures, fishnet layers and other geometries. Artificial magnetic
response in these structures appears due to weak spatial dispersion effects,
and it is important to study the conditions under which the magnetic re- sponse
can be adequately measured with effective permeability tensor. On the examples
of dual bars and split rings we show that this is possible only under some
quite restrictive conditions. In the general case, more compli- cated
constitutive relations with more effective material parameters need to be
developed.",1003.3309v1
2010/7/20,Inhomogeneous Magnetoelectric Effect on Defect in Multiferroic Material: Symmetry Prediction,"Inhomogeneous magnetoelectric effect in magnetization distribution
heterogeneities (0-degree domain walls) appeared on crystal lattice defect of
the multiferroic material has been investigated. Magnetic symmetry based
predictions of kind of electrical polarization distribution in their volumes
were used. It was found that magnetization distribution heterogeneity with any
symmetry produces electrical polarization. Results were systemized in scope of
micromagnetic structure chirality. It was shown that all 0-degree domain walls
with time-noninvariant chirality have identical type of spatial distribution of
the magnetization and polarization.",1007.3531v3
2011/11/10,Magnonic band structure of a two-dimensional magnetic superlattice,"The frequencies and linewidths of spin waves in a two-dimensional periodic
superlattice of magnetic materials are found, using the Landau-Lifshitz-Gilbert
equations. The form of the exchange field from a surface-torque-free boundary
between magnetic materials is derived, and magnetic-material combinations are
identified which produce gaps in the magnonic spectrum across the entire
superlattice Brillouin zone for hexagonal and square-symmetry superlattices.",1111.2506v1
2012/11/14,Giant third-order magneto-optical rotation in ferromagnetic EuO,"A magnetization-induced rotation in the third-order nonlinear optical
response is observed in out-of-plane-magnetized epitaxial EuO films. We discuss
the relation of this nonlinear magneto-optical rotation to the linear Faraday
rotation. It is allowed in all materials but, in contrast to the linear Faraday
rotation, not affected by the reduction of the thickness of the material. Thus,
the third-order magneto-optical rotation is particularly suitable for probing
the magnetization of functional magnetic materials such as ultra-thin films and
multilayers.",1211.3252v1
2023/8/1,Overview of superconductivity in field-cooled magnetic materials,"Considerable experimental skills have been accumulated in the preparation of
field-cooled (FC) magnetic materials. This stimulates the search for FC
magnetic materials that are superconductors.
  The article overviews the recent proposed mechanism of superconductivity in
field-cooled magnetic materials.
  It is based on previously published results for magnon-induced
superconductivity in field-cooled spin-1/2 antiferromagnets $[PRB96,214409]$
(arXiv:1712.02983), Sequence of superconducting states in field cooled
$FeCr_2S_4$ $[JPCM33,495604]$
  (arXiv:2111.02765) and Partial order induced superconductivity in $Fe^{2+}$
iron. $[EPL126,47001]$ (arXiv:1902.02290).",2308.00470v1
2022/11/23,Raman scattering signatures of the strong spin-phonon coupling in the bulk magnetic van der Waals material CrSBr,"Magnetic excitations in layered magnetic materials that can be thinned down
the two-dimensional (2D) monolayer limit are of high interest from a
fundamental point of view and for applications perspectives. Raman scattering
has played a crucial role in exploring the properties of magnetic layered
materials and, even-though it is essentially a probe of lattice vibrations, it
can reflect magnetic ordering in solids through the spin-phonon interaction or
through the observation of magnon excitations. In bulk CrSBr, a layered A type
antiferromagnet (AF), we show that the magnetic ordering can be directly
observed in the temperature dependence of the Raman scattering response i)
through the variations of the scattered intensities, ii) through the activation
of new phonon lines reflecting the change of symmetry with the appearance of
the additional magnetic periodicity, and iii) through the observation, below
the Neel temperature (TN) of second order Raman scattering processes. We
additionally show that the three different magnetic phases encountered in
CrSBr, including the recently identified low temperature phase, have a
particular Raman scattering signature. This work demonstrates that magnetic
ordering can be observed directly in the Raman scattering response of bulk
CrSBr with in-plane magnetization, and that it can provide a unique insight
into the magnetic phases encountered in magnetic layered materials.",2211.12939v1
2021/2/7,Recent progress and challenges in magnetic tunnel junctions with 2D materials for spintronic applications,"As Moore's law is gradually losing its effectiveness, developing alternative
high-speed and low-energy-consuming information technology with post-silicon
advanced materials is urgently needed. The successful application of tunneling
magnetoresistance (TMR) in magnetic tunnel junctions (MTJs) has given rise to a
tremendous economic impact on magnetic informatics, including MRAM,
radio-frequency sensors, microwave generators and neuromorphic computing
networks. The emergence of two-dimensional (2D) materials brings opportunities
for MTJs based on 2D materials which have many attractive characters and
advantages. Especially, the recently discovered intrinsic 2D ferromagnetic
materials with high spin-polarization hold the promise for next-generation
nanoscale MTJs. With the development of advanced 2D materials, many efforts on
MTJs with 2D materials have been made both theoretically and experimentally.
Various 2D materials, such as semi-metallic graphene, insulating h-BN,
semiconducting MoS2, magnetic semiconducting CrI3, magnetic metallic Fe3GeTe2
and some other recently emerged 2D materials are discussed as the electrodes
and/or central scattering materials of MTJs in this review. We discuss the
fundamental and main issues facing MTJs, and review the current progress made
with 2D MTJs, briefly comment on work with some specific 2D materials, and
highlight how they address the current challenges in MTJs, and finally offer an
outlook and perspective of 2D MTJs.",2102.03791v1
2023/4/13,High-performance descriptor for magnetic materials: Accurate discrimination of magnetic structure,"The magnetic structure is crucial in determining the physical properties
inherent in magnetic compounds. We present an adequate descriptor for magnetic
structure with proper magnetic symmetry and high discrimination performance,
which does not depend on artificial choices for coordinate origin, axis, and
magnetic unit cell in crystal. We extend the formalism called ``smooth overlap
of atomic positions'' (SOAP), providing a numerical representation of atomic
configurations to that of magnetic moment configurations. We introduce the
descriptor in terms of the vector spherical harmonics to describe a magnetic
moment configuration and partial spectra from the expansion coefficients. We
discuss that the lowest-order partial spectrum is insufficient to discriminate
the magnetic structures with different magnetic anisotropy, and a higher-order
partial spectrum is required in general to differentiate detailed magnetic
structures on the same atomic configuration. We then introduce the fourth-order
partial spectrum and evaluate the discrimination performance for different
magnetic structures, mainly focusing on the difference in magnetic symmetry.
The modified partial spectra that are defined not to reflect the difference of
magnetic anisotropy are also useful in evaluating magnetic structures obtained
from the first-principles calculations performed without spin-orbit coupling.
We apply the present method to the symmetry-classified magnetic structures for
the crystals of Mn$_3$Ir and Mn$_3$Sn, which are known to exhibit anomalous
transport under the antiferromagnetic order, and examine the discrimination
performance of the descriptor for different magnetic structures on the same
crystal.",2304.06282v2
1996/10/6,Improved Magnetic Information Storage using Return-Point Memory,"The traditional magnetic storage mechanisms (both analog and digital) apply
an external field signal H(t) to a hysteretic magnetic material, and read the
remanent magnetization M(t), which is (roughly) proportional to H(t). We
propose a new analog method of recovering the signal from the magnetic
material, making use of the shape of the hysteresis loop M(H). The field H,
``stored'' in a region with N domains or particles, can be recovered with
fluctuations of order 1/N using the new method - much superior to the 1/sqrt{N}
fluctuations in traditional analog storage.",9610036v1
1999/10/25,Propagation of solitons of the magnetization in magnetic nano-particle arrays,"It is clarified for the first time that solitons originating from the dipolar
interaction in ferromagnetic nano-particle arrays are stably created. The
characteristics can be well controlled by the strength of the dipolar
interaction between particles and the shape anisotropy of the particle. The
soliton can propagate from a particle to a neighbor particle at a clock
frequency even faster than 100 GHz using materials with a large magnetization.
Such arrays of nano-particles might be feasible in an application as a signal
transmission line.",9910389v1
2006/11/30,Heavy Fermions: electrons at the edge of magnetism,"An introduction to the physics of heavy fermion compounds is presented,
attempting to highlight the conceptual developments and emphasize the mysteries
and open questions that persist in this active field of research.",0612006v3
2008/8/28,Inhomogeneous ferrimagnetic-like behavior in Gd2/3Ca1/3MnO3 single crystals,"We present a study of the magnetic properties of Gd2/3Ca1/3MnO3 single
crystals at low temperatures. We show that this material behave as an
inhomogeneous ferrimagnet. In addition to small saturation magnetization at 5
K, we have found history dependent effects in the magnetization and the
presence of exchange bias. These features are compatible with microscopic phase
separation in the clean Gd2/3Ca1/3MnO3 system studied.",0808.3922v1
2011/8/10,A route towards finding large magnetic anisotropy in nano-composites: application to a W$_{1-x}$Re$_x$/Fe multilayer,"We suggest here a novel nano-laminate, 5[Fe]/2[W$_x$Re$_{1-x}$] (x=0.6-0.8),
with enhanced magnetic hardness in combination with a large saturation moment.
The calculated magnetic anisotropy of this material reaches values of 5.3-7.0
MJ/m$^3$, depending on alloying conditions. We also propose a recipe in how to
identify other novel magnetic materials, such as nano-laminates and
multilayers, with large magnetic anisotropy in combination with a high
saturation moment.",1108.2105v1
2012/6/13,Saturation Magnetization of Inorganic/polymer Nanocomposites Higher than That of Their Inorganic Magnetic Component,"Herein, some magnetic nanoparticles (MNP)/clay/polymer nanocomposites have
been prepared, whose saturation magnetization is higher than that of pure oleic
acid coated MNP component. The existence of unique 'nano-network' structure and
tight three-phase nano-interface in the nanocomposites contribute to the
surprising saturation magnetization.",1206.2805v1
2015/6/18,Dynamical systems study in single-phase multiferroic materials,"Electric field induced magnetization switching in single-phase multiferroic
materials is intriguing for both fundamental studies and potential
technological applications. Here we develop a framework to study the switching
dynamics of coupled polarization and magnetization in such multiferroic
materials. With the coupling term between the polarization and magnetization as
an invariant dictated by the Dzyaloshinsky-Moriya vector, the dynamical systems
study reveals switching failures and oscillatory mode of magnetization if the
polarization and magnetization relax slowly during switching.",1506.07864v1
2015/9/14,Torsional chiral magnetic effect in Weyl semimetal with topological defect,"We propose a torsional response raised by lattice dislocation in Weyl
semimetals akin to chiral magnetic effect; i.e. a fictitious magnetic field
arising from screw or edge dislocation induces charge current. We demonstrate
that, in sharp contrast to the usual chiral magnetic effect which vanishes in
real solid state materials, the torsional chiral magnetic effect exists even
for realistic lattice models, which implies the experimental detection of the
effect via SQUID or nonlocal resistivity measurements in Weyl semimetal
materials.",1509.03981v3
2018/9/26,Resonant magnetic induction tomography of a magnetized sphere,"We demonstrate the structural imaging of magnetostatic spin-wave modes hosted
in a millimeter-sized ferromagnetic sphere. Unlike for low-dimensional magnetic
materials, there is no prior technique to image these modes in bulk magnetized
solid of revolution. Based on resonant magnetic induction tomography in the
microwave range, our approach ensures the robust identification of these
non-trivial spin-wave modes by establishing their azimuthal and polar
dependences, starting point of magnonic fundamental studies and hybrid systems
with complex spin textures well beyond the uniform precession mode.",1809.09785v2
2021/5/10,Model studies of topological phase transitions in materials with two types of magnetic atoms,"We study the topological phase transitions induced by Coulomb engineering in
three triangular-lattice Hubbard models $AB_2$, $AC_3$ and $B_2C_3$, each of
which consists of two types of magnetic atoms with opposite magnetic moments.
The energy bands are calculated using the Schwinger boson method. We find that
a topological phase transition can be triggered by the second-order
(three-site) virtual processes between the two types of magnetic atoms, the
strengths of which are controlled by the on-site Coulomb interaction $U$. This
new class of topological phase transitions have been rarely studied and may be
realized in a variety of real magnetic materials.",2105.04523v1
2021/3/25,Enhancement of polarization and magnetization in polycrystalline magnetoelectric composite,"Electrical control of magnetization or magnetic control of polarization
offers an extra degree of freedom in materials possessing both electric and
magnetic dipole moments viz., magnetoelectric multiferroics. Microstructure
with polycrystalline configurations that enhances the overall
polarization/magnetization and that outperform single crystalline
configurations are identified. The characterization of local fields
corresponding to the polycrystal configuration underlines nontrivial role
played by randomness in better cross-coupling mediated by anisotropic and
asymmetric strains.",2103.13738v2
2023/11/4,On implicit interpolation models for nonlinear anisotropic magnetic material behavior,"Implicit models for magnetic coenergy have been proposed by Pera et al. to
describe the anisotropic nonlinear material behavior of electrical steel
sheets. This approach aims at predicting magnetic response for any direction of
excitation by interpolating measured of B--H curves in the rolling and
transverse directions. In an analogous manner, an implicit model for magnetic
energy is proposed. We highlight some mathematical properties of these implicit
models and discuss their numerical realization, outline the computation of
magnetic material laws via implicit differentiation, and discuss the potential
use for finite element analysis in the context of nonlinear magnetostatics.",2311.02380v1
2004/3/18,Low Losses Left Handed Materials Using Metallic Magnetic Cylinders,"We discuss materials based on arrays of metallic magnetic cylindrical
structures near ferromagnetic resonance with applied magnetic fields at
microwave frequencies. We have found that the materials have a negative
refraction index when the appropriate structure is chosen. Numerical FDTD
simulations were performed, after a very large number of geometries were swept.
The simulations reveal that only ferromagnetic cylinders, with diameters of 0.1
cm and 0.5 cm apart, and with periodic or random configurations, are
left-handed materials with very small losses; i.e. with transmitivity
practically unity or no losses.",0403479v1
2004/5/14,Non-magnetic left-handed material,"We develop a new approach to build a material with negative refraction index.
In contrast to conventional designs which make use of a resonant behavior to
achieve a non-zero magnetic response, our material is intrinsically
non-magnetic and relies on an anisotropic dielectric constant to provide a
left-handed response in waveguide geometry. We demonstrate that the proposed
material can support surface (polariton) waves, and show the connection between
polaritons and the enhancement of evanescent fields, also referred to as
super-lensing.",0405077v1
2013/8/30,Scaling in Modeling of Core Losses in Soft Magnetic Materials Exposed to Nonsinusoidal Flux Waveforms and DC Bias,"Assuming that core loss data of Soft Magnetic Materials obey scaling
relations, models describing the power losses in materials exposed to
non-sinusoidal flux waveforms and DC Bias conditions have been derived. In
order to test these models, the measurement data for two materials have been
collected and the core losses calculated. Agreement between the experimental
data and the model predictions is satisfactory.",1309.0022v1
2016/4/29,Viewpoint: Opportunities and challenges of two-dimensional magnetic van der Waals materials: magnetic graphene?,"There has been a huge increase of interests in two-dimensional van der Waals
materials over the past ten years or so with the conspicuous absence of one
particular class of materials: magnetic van der Waals systems. In this
Viewpoint, we point it out and illustrate how we might be able to benefit from
exploring these so-far neglected materials.",1604.08833v1
2020/1/6,Metamaterials and Cesàro convergence,"In this paper, we show that the linear dielectrics and magnetic materials in
matter obey a special kind of mathematical property known as Ces\`{a}ro
convergence. Then, we also show that the analytical continuation of the linear
permittivity \& permeability to a complex plane in terms of Riemann zeta
function. The metamaterials are fabricated materials with a negative refractive
index. These materials, in turn, depend on permittivity \& permeability of the
linear dielectrics and magnetic materials. Therefore, the Ces\`{a}ro
convergence property of the linear dielectrics and magnetic materials may be
used to fabricate the metamaterials.",2001.10935v1
2020/2/26,"Chern number and orbital magnetization in ribbons, polymers, and layered materials","The modern theory of orbital magnetization addresses crystalline materials at
the noninteracting level: therein the observable is the k-space integral of a
geometrical integrand. Alternatively, magnetization admits a local
representation in r space, i.e. a ""density"" which may address noncrystalline
and/or inhomogeneous materials as well; the Chern number admits an analogous
density. Here we provide the formulation for ribbons, polymers, and layered
materials, where both k-space and r-space integrations enter the definition of
the two observables.",2002.11595v1
2021/6/25,Bias-tunable two-dimensional magnetic and topological materials,"Searching for novel two-dimensional (2D) materials is crucial for the
development of the next generation technologies such as electronics,
optoelectronics, electrochemistry and biomedicine. In this work, we designed a
series of 2D materials based on endohedral fullerenes, and revealed that many
of them integrate different functions in a single system, such as
ferroelectricity with large electric dipole moments, multiple magnetic phases
with both strong magnetic anisotropy and high Curie temperature, quantum spin
Hall effect or quantum anomalous Hall effect with robust topologically
protected edge states. We further proposed a new style topological field-effect
transistor. These findings provide a strategy of using fullerenes as building
blocks for the synthesis of novel 2D materials which can be easily controlled
with a local electric field.",2106.13912v1
2003/11/6,A new condition to identify isotropic dielectric-magnetic materials displaying negative phase velocity,"The derivation of a new condition for characterizing isotropic
dielectric-magnetic materials exhibiting negative phase velocity, and the
equivalence of that condition with previously derived conditions, are
presented.",0311029v1
2017/6/6,Designing magnetism in Fe-based Heusler alloys: a machine learning approach,"Combining material informatics and high-throughput electronic structure
calculations offers the possibility of a rapid characterization of complex
magnetic materials. Here we demonstrate that datasets of electronic properties
calculated at the ab initio level can be effectively used to identify and
understand physical trends in magnetic materials, thus opening new avenues for
accelerated materials discovery. Following a data-centric approach, we utilize
a database of Heusler alloys calculated at the density functional theory level
to identify the ideal ions neighbouring Fe in the $X_2$Fe$Z$ Heusler prototype.
The hybridization of Fe with the nearest neighbour $X$ ion is found to cause
redistribution of the on-site Fe charge and a net increase of its magnetic
moment proportional to the valence of $X$. Thus, late transition metals are
ideal Fe neighbours for producing high-moment Fe-based Heusler magnets. At the
same time a thermodynamic stability analysis is found to restrict $Z$ to main
group elements. Machine learning regressors, trained to predict magnetic moment
and volume of Heusler alloys, are used to determine the magnetization for all
materials belonging to the proposed prototype. We find that Co$_2$Fe$Z$ alloys,
and in particular Co$_2$FeSi, maximize the magnetization, which reaches values
up to 1.2T. This is in good agreement with both ab initio and experimental
data. Furthermore, we identify the Cu$_2$Fe$Z$ family to be a cost-effective
materials class, offering a magnetization of approximately 0.65T.",1706.01840v1
2023/4/19,Deep Learning Illuminates Spin and Lattice Interaction in Magnetic Materials,"Atomistic simulations hold significant value in clarifying crucial phenomena
such as phase transitions and energy transport in materials science. Their
success stems from the presence of potential energy functions capable of
accurately depicting the relationship between system energy and lattice
changes. In magnetic materials, two atomic scale degrees of freedom come into
play: the lattice and the spin. However, accurately tracing the simultaneous
evolution of both lattice and spin in magnetic materials at an atomic scale is
a substantial challenge. This is largely due to the complexity involved in
depicting the interaction energy precisely, and its influence on lattice and
spin-driving forces, such as atomic force and magnetic torque, which continues
to be a daunting task in computational science. Addressing this deficit, we
present DeepSPIN, a versatile approach that generates high-precision predictive
models of energy, atomic forces, and magnetic torque in magnetic systems. This
is achieved by integrating first-principles calculations of magnetic excited
states with deep learning techniques via active learning. We thoroughly explore
the methodology, accuracy, and scalability of our proposed model in this paper.
Our technique adeptly connects first-principles computations and atomic-scale
simulations of magnetic materials. This synergy presents opportunities to
utilize these calculations in devising and tackling theoretical and practical
obstacles concerning magnetic materials.",2304.09606v3
2015/9/30,Roadmap for Emerging Materials for Spintronic Device Applications,"The Technical Committee of the IEEE Magnetics Society has selected 7 research
topics to develop their roadmaps, where major developments should be listed
alongside expected timelines; (i) hard disk drives, (ii) magnetic random access
memories, (iii) domain-wall devices, (iv) permanent magnets, (v) sensors and
actuators, (vi) magnetic materials and (vii) organic devices. Among them,
magnetic materials for spintronic devices have been surveyed as the first
exercise. In this roadmap exercise, we have targeted magnetic tunnel and
spin-valve junctions as spintronic devices. These can be used for example as a
cell for a magnetic random access memory and spin-torque oscillator in their
vertical form as well as a spin transistor and a spin Hall device in their
lateral form. In these devices, the critical role of magnetic materials is to
inject spin-polarised electrons efficiently into a non-magnet. We have
accordingly identified 2 key properties to be achieved by developing new
magnetic materials for future spintronic devices: (1) Half-metallicity at room
temperature (RT); (2) Perpendicular anisotropy in nano-scale devices at RT. For
the first property, 5 major magnetic materials are selected for their
evaluation for future magnetic/spintronic device applications: Heusler alloys,
ferrites, rutiles, perovskites and dilute magnetic semiconductors. These alloys
have been reported or predicted to be half-metallic ferromagnets at RT. They
possess a bandgap at the Fermi level EF only for its minority spins, achieving
100% spin polarisation at EF. We have also evaluated L10-alloys and
D022-Mn-alloys for the development of a perpendicularly anisotropic ferromagnet
with large spin polarisation. We have listed several key milestones for each
material on their functionality improvements, property achievements, device
implementations and interdisciplinary applications within 35 years time scale.",1509.08997v1
2023/3/1,Proton-fluence dependent magnetic properties of exfoliable quasi-2D van der Waals Cr2Si2Te6 magnet,"The discovery of long-range magnetic ordering in atomically thin materials
catapulted the van der Waals (vdW) family of compounds into an unprecedented
popularity. In particular, with a current push in space exploration, it is
beneficial to study how the properties of such materials evolve under proton
irradiation. Owing to their robust intra-layer stability and sensitivity to
external perturbations, these materials provide excellent opportunities for
studying proton irradiation as a non-destructive tool for controlling their
magnetic properties. Specifically, the exfoliable Cr2Si2Te6 (CST) is a
ferromagnetic semiconductor with the Curie temperature (TC) of ~32 K. Here, we
have investigated the magnetic properties of CST upon proton irradiation as a
function of fluence (1 x 1015, 5 x 1015, 1 x 1016, 5 x 1016, and 1 x 1018
H+/cm2) by employing variable-temperature, variable-field magnetization
measurements coupled with electron paramagnetic resonance (EPR) spectroscopy
and detail how the magnetization, magnetic anisotropy and EPR spectral
parameters vary as a function of proton fluence across the magnetic phase
transition. While the TC remains constant as a function of proton fluence, we
observed that the saturation magnetization and magnetic anisotropy diverge at
the proton fluence of 5 x 1016 H+/cm2, which is prominent in the ferromagnetic
phase, in particular. This work demonstrates that proton irradiation is a
feasible method for modifying the magnetic properties and local magnetic
interactions of vdWs crystals, which represents a significant step forward in
the design of future spintronic and magneto-electronic applications.",2303.00824v1
2018/2/27,Computational study on microstructure evolution and magnetic property of laser additively manufactured magnetic materials,"Additive manufacturing (AM) offers an unprecedented opportunity for the quick
production of complex shaped parts directly from a powder precursor. But its
application to functional materials in general and magnetic materials in
particular is still at the very beginning. Here we present the first attempt to
computationally study the microstructure evolution and magnetic properties of
magnetic materials (e.g. Fe-Ni alloys) processed by selective laser melting
(SLM). SLM process induced thermal history and thus the residual stress
distribution in Fe-Ni alloys are calculated by finite element analysis (FEA).
The evolution and distribution of the $\gamma$-Fe-Ni and FeNi$_3$ phase
fractions were predicted by using the temperature information from FEA and the
output from CALculation of PHAse Diagrams (CALPHAD). Based on the relation
between residual stress and magnetoelastic energy, magnetic properties of SLM
processed Fe-Ni alloys (magnetic coercivity, remanent magnetization, and
magnetic domain structure) are examined by micromagnetic simulations. The
calculated coercivity is found to be in line with the experimentally measured
values of SLM-processed Fe-Ni alloys. This computation study demonstrates a
feasible approach for the simulation of additively manufactured magnetic
materials by integrating FEA, CALPHAD, and micromagnetics.",1802.09821v2
2023/10/3,Magnetic phenomena in equiatomic ternary rare earth compounds,"The chapter discusses the structural and magnetic properties of equiatomic
ternary RTX compounds, where R represents rare earth, T is transition metal,
and X belongs to the p block elements. RTX compounds exhibit a variety of
crystal structures, which leads to a range of magnetic phenomenon ranging from
long range antiferromagnetic-ferromagnetic ordering, unconventional
superconductivity, magnetic frustration to spin ices. Coexistence of various
magnetic phenomenon result in many exotic properties, which make these
materials promising for next generation technological applications. In RTX
family of compounds, most transition metals, except manganese, Mn do not
contribute significantly to the magnetic moment and behave as non-magnetic. The
lack of magnetic behaviour in the transition metal sublattices of these ternary
compounds may be attributed to hybridization between p electron states of X
atom and d electron states of the transition metal, resulting in the filling of
the d band. The dominant interaction in these compounds is of Ruderman Kittel
Kasuya Yosida type due to the localized nature of the 4f electrons in the rare
earths. The magnetic transition temperature in these materials varies from
ultra-low to high temperatures, making them suitable for integration into
devices operating at room temperature. The RTX series discussed here
encompasses all rare earth elements, a range of transition metals, and various
p-block elements such as Al, Ga, In, Si, Ge, Sn, Sb, and Bi. Most of the
materials studied are arc melted polycrystalline materials with some in the
form of single crystal or thin films.",2310.02103v1
2004/3/29,Quantum Tunneling of the Magnetization in the Ising Chain Compound Ca3Co2O6,"The magnetic behavior of the Ca3Co2O6 spin chain compound is characterized by
a large Ising-like character of its ferromagnetic chains, set on triangular
lattice, that are antiferromagnetically coupled. At low temperature, T < 7K,
the 3D antiferromagnetic state evolves towards a spin frozen state. In this
temperature range, magnetic field driven magnetization of single crystals
(H//chains) exhibits stepped variations. The occurrence of these steps at
regular intervals of the applied magnetic field, Hstep=1.2T, is reminiscent of
the quantum tunneling of the magnetization (QTM) of molecular based magnets.
Magnetization relaxation experiments also strongly support the occurrence of
this quantum phenomenon. This first observation of QTM in a magnetic oxide
belonging to the large family of the A3BBO6 compounds opens new opportunities
to study a quantum effect in a very different class of materials from molecular
magnets.",0403695v1
2009/4/28,Magnetically-induced electric polarization in an organo-metallic magnet,"The coupling between magnetic order and ferroelectricity has been under
intense investigation in a wide range of transition-metal oxides. The strongest
coupling is obtained in so-called magnetically-induced multiferroics where
ferroelectricity arises directly from magnetic order that breaks inversion
symmetry. However, it has been difficult to find non-oxide based materials in
which these effects occur. Here we present a study of copper dimethyl sulfoxide
dichloride (CDC), an organo-metallic quantum magnet containing $S = 1/2$ Cu
spins, in which electric polarization arises from non-collinear magnetic order.
We show that the electric polarization can be switched in a stunning hysteretic
fashion. Because the magnetic order in CDC is mediated by large organic
molecules, our study shows that magnetoelectric interactions can exist in this
important class of materials, opening the road to designing magnetoelectrics
and multiferroics using large molecules as building blocks. Further, we
demonstrate that CDC undergoes a magnetoelectric quantum phase transition where
both ferroelectric and magnetic order emerge simultaneously as a function of
magnetic field at very low temperatures.",0904.4490v1
2009/6/29,A Magnetization Sensitive Potential at Garnet-Metal Interfaces,"We investigate a magnetization-dependent voltage that appears at the
interface between garnets and various metals. The voltage is even in the
applied magnetic field and is dependent on the surface roughness and the
pressure holding the surfaces together. Large variations in the size, sign and
magnetic dependence are observed between different metal surfaces. Some
patterns have been identified in the measured voltages and a simple model is
described that can accommodate the gross features. The bulk magnetoelectric
response of one of our polycrystalline YIG samples is measured and is found to
be consistent with a term in the free energy that is quadratic in both the
electric and magnetic fields. However, the presence of such a term does not
fully explain the complex magnetization dependence of the measured voltages.",0906.5340v2
2010/1/8,Self-organized synthesis of patterned magnetic nanostructures with in-plane and perpendicular to the plane magnetization,"Patterned arrays of ferromagnetic nanoparticles of Co, Ni, and Fe_{\text{50}}
Co_{\text{50}} have been synthesized from their ultrathin metal films on
SiO_{\text{2}} substrate by nanosecond laser-induced self-organization. The
morphology, nanostructure, and magnetic behavior of the nanoparticle arrays
were investigated by a combination of electron, atomic force, and magnetic
force microscopy techniques. Transmission electron microscopy investigations
revealed a granular polycrystalline nanostructure, with the number of grains
inside the nanoparticle increasing with their diameter. Magnetic force
measurements showed that the magnetization direction of the Co and Ni
nanoparticles was predominantly out-of-plane while those for the
Fe_{\text{50}}Co_{\text{50}} alloy was in the plane of the substrate. This
difference in behavior is due to the dominating influence of magnetostrictive
energy on the magnetization as a result of residual thermal strain following
fast laser processing. Since the magnetostriction coefficient is negative for
polycrystalline Co and Ni, and positive for Fe_{\text{50}}Co_{\text{50}}, the
tensile residual strain forces the magnetization direction of the negative
magnetostriction materials out-of-plane and the positive magnetostriction
materials in-plane. This demonstrates a cost-effective non-epitaxial technique
for the fabrication of patterned arrays of magnetic nanoparticles with tailored
magnetization orientations.",1001.1328v1
2011/6/15,Monte Carlo simulation of magnetic phase transitions in Mn doped ZnO,"The magnetic properties of Mn-doped ZnO semi-conductor have been investigated
using the Monte Carlo method within the Ising model. The temperature
dependences of the spontaneous magnetization, specific heat and magnetic
susceptibility have been constructed for different concentrations of magnetic
dopant Mn and different carrier concentrations. The exact values of Mn
concentration and carrier concentration at which high temperature transition
occurs are determined. An alternative for the explanation of some controversies
concerning the existence and the nature of magnetism in Mn diluted in ZnO
systems is given. Other features are also studied.",1106.3009v1
2008/11/23,New Samarium and Neodymium based admixed ferromagnets with near zero net magnetization and tunable exchange bias field,"Rare earth based intermetallics, SmScGe and NdScGe, are shown to exhibit near
zero net magnetization with substitutions of 6 to 9 atomic percent of Nd and 25
atomic percent of Gd, respectively. The notion of magnetic compensation in them
is also elucidated by the crossover of zero magnetization axis at low magnetic
fields (less than 103 Oe) and field-induced reversal in the orientation of the
magnetic moments of the dissimilar rare earth ions at higher magnetic fields.
These magnetically ordered materials with no net magnetization and appreciable
conduction electron polarization display an attribute of an exchange bias
field, which can be tuned. The attractively high magnetic ordering temperatures
of about 270 K, underscore the importance of these materials for potential
applications in spintronics.",0811.3728v1
2020/9/8,Electrical detection of magnetic circular dichroism: application to magnetic microscopy in ultra-thin ferromagnetic films,"Imaging the magnetic configuration of thin-films has been a long-standing
area of research. Since a few years, the emergence of two-dimensional
ferromagnetic materials calls for innovation in the field of magnetic imaging.
As the magnetic moments are extremely small, standard techniques like SQUID,
torque magnetometry, magnetic force microscopy and Kerr effect microscopy are
challenging and often lead to the detection of parasitic magnetic contributions
or spurious effects. In this work, we report a new magnetic microscopy
technique based on the combination of magnetic circular dichroism and Seebeck
effect in semiconductor/ferromagnet bilayers. We implement this method with
perpendicularly magnetized (Co/Pt) multilayers sputtered on Ge (111). We
further show that the electrical detection of MCD is more sensitive than the
Kerr magnetometry, especially in the ultra-thin film regime, which makes it
particularly promising for the study of emergent two-dimensional ferromagnetic
materials.",2009.03982v1
2021/6/5,On the anomalous low-resistance state and exceptional Hall component in hard-magnetic Weyl nanoflakes,"Magnetic topological materials, which combine magnetism and topology, are
expected to host emerging topological states and exotic quantum phenomena. In
this study, with the aid of greatly enhanced coercive fields in high-quality
nanoflakes of the magnetic Weyl semimetal Co3Sn2S2, we investigate anomalous
electronic transport properties that are difficult to reveal in bulk Co3Sn2S2
or other magnetic materials. When the magnetization is antiparallel to the
applied magnetic field, the low longitudinal resistance state occurs, which is
in sharp contrast to the high resistance state for the parallel case.
Meanwhile, an exceptional Hall component that can be up to three times larger
than conventional anomalous Hall resistivity is also observed for transverse
transport. These anomalous transport behaviors can be further understood by
considering nonlinear magnetic textures and the chiral magnetic field
associated with Weyl fermions, extending the longitudinal and transverse
transport physics and providing novel degrees of freedom in the spintronic
applications of emerging topological magnets.",2106.02906v1
2021/11/6,Tuning the electronic band structure in a kagome ferromagnetic metal via magnetization,"Materials with zero energy band gap display intriguing properties including
high sensitivity of the electronic band structure to external stimulus such as
pressure or magnetic field. An interesting candidate for zero energy band gap
are Weyl nodes at the Fermi level EF. A prerequisite for the existence of Weyl
nodes is to either have inversion or time reversal symmetry broken. Weyl nodes
in systems with broken time reversal symmetry are ideal to realize the
tunability of the electronic band structure by magnetic field. Theoretically,
it has been shown that in ferromagnetic Weyl materials, the band structure is
dependent upon the magnetization direction and thus the electronic bands can be
tuned by controlling the magnetization direction. Here, we demonstrate tuning
of the band structure in a kagome Weyl ferromagnetic metal Fe3Sn2 with
magnetization and magnetic field. Owing to spin-orbit coupling, we observe
changes in the band structure depending on the magnetization direction that
amount to a decrease in the carrier density by a factor of four when the
magnetization lies in the kagome plane as compared to when the magnetization is
along the c axis. Our discovery opens a way for tuning the carrier density in
ferromagnetic materials.",2111.03826v1
2022/2/15,Spin orbital reorientation transitions induced by magnetic field,"Here we report on a new effect similar to the spin reorientation transition
(SRT) that takes place at two magnetic fields of $B_{SORT1}$ and $B_{SORT2}$.
The effect is observed in the magnetization curves of small Mn$^{3+}$ magnetic
clusters in the wurtzite GaN (being in a paramagnetic state) calculated using
crystal field model approach. The obtained results suggest that the computed
magnetic anisotropy (MA) reverses its sign on increasing $B$ across $B_{SORT}$.
Detailed analysis show however that MA is unchanged for high magnetic fields.
We show that the observed effect arises from the interplay of the crystalline
environment and the spin-orbit coupling $\lambda \hat{\textbf{S}}
\hat{\textbf{L}}$, therefore we name it spin orbital reorientation transition
(SORT). The value of $B_{SORT1}$ depends on the crystal field model parameters
and the number of ions $N$ in a given cluster, whereas $B_{SORT2}$ is
controlled mostly by the magnitude of the spin-orbit coupling $\lambda$. The
explanation of SORT is given in terms of the spin $M_S$ and orbital momentum
$M_L$ contributions to the total magnetization $M = M_S + M_L$. The similar
effect should also be present in other materials with not completely quenched
(non zero) orbital angular momentum $L$, a uniaxial magnetic anisotropy and the
positive value of $\lambda$.",2202.07443v1
2022/7/13,Boosting spin-orbit torque efficiency in spin-current generator/magnet/oxide superlattices,"Efficient manipulation of magnetic materials is essential for spintronics. In
spin-current generator/magnet bilayers, the efficiency of spin-orbit torques
per magnetic layer thickness scales inversely with the magnetic layer
thickness, leading to considerable power increase in applications with large
magnetic layer thickness. Here, we develop a 3D spin-orbit material scheme in
which the spin torque efficiency can be remarkably boosted up by stacking
[spin-current generator/magnet/oxide]n superlattices, with the oxide layers
breaking the inversion symmetry. In contrast, the spin torque diminishes in
[spin-current generator/magnet]n superlattices lacking inversion symmetry
breaking. These results advances the understanding of spin-orbit torques in
magnetic multilayers and establishes spin-current generator/magnet/oxide
superlattices as advantageous bricks for development of high energy-efficiency,
high-endurance, and high-density spintronic memory and computing.",2207.05968v2
2023/1/9,X-ray detected ferromagnetic resonance techniques for the study of magnetization dynamics,"Element-specific spectroscopies using synchrotron-radiation can provide
unique insights into materials properties. The recently developed technique of
X-ray detected ferromagnetic resonance (XFMR) allows studying the magnetization
dynamics of magnetic spin structures. Magnetic sensitivity in XFMR is obtained
from the X-ray magnetic circular dichroism (XMCD) effect, where the phase of
the magnetization precession of each magnetic layer with respect to the
exciting radio frequency is obtained using stroboscopic probing of the spin
precession. Measurement of both amplitude and phase response in the magnetic
layers as a function of bias field can give a clear signature of spin-transfer
torque (STT) coupling between ferromagnetic layers due to spin pumping. Over
the last few years, there have been new developments utilizing X-ray scattering
techniques to reveal the precessional magnetization dynamics of ordered spin
structures in the GHz frequency range. The techniques of diffraction and
reflectometry ferromagnetic resonance (DFMR and RFMR) provide novel ways for
the probing of the dynamics of chiral and multilayered magnetic materials,
thereby opening up new pathways for the development of high-density and
low-energy consumption data processing solutions.",2301.03256v1
2023/5/17,Material Parameters for Faster Ballistic Switching of an In-plane Magnetized Nanomagnet,"High-speed magnetization switching of a nanomagnet is necessary for faster
information processing. The ballistic switching by a pulsed magnetic filed is a
promising candidate for the high-speed switching. It is known that the
switching speed of the ballistic switching can be increased by increasing the
magnitude of the pulsed magnetic field. However it is difficult to generate a
strong and short magnetic field pulse in a small device. Here we explore
another direction to achieve the high-speed ballistic switching by designing
material parameters such as anisotropy constant, saturation magnetization, and
the Gilbert damping constant. We perform the macrospin simulations for the
ballistic switching of in-plane magnetized nano magnets with varying material
parameters. The results are analyzed based on the switching dynamics on the
energy density contour. We show that the pulse width required for the ballistic
switching can be reduced by increasing the magnetic anisotropy constant or by
decreasing the saturation magnetization. We also show that there exists an
optimal value of the Gilbert damping constant that minimizes the pulse width
required for the ballistic switching.",2305.10111v1
2024/2/29,Searching for magnetically hard monoborides (and finding a few): A first-principles investigation,"New hard magnetic materials with zero or low rare earth content are in demand
due to the high prices of the rare earth metals. Among the candidates for such
materials, we consider MnB, FeB and their alloys, because previous experiments
suggest that FeB has a relatively high magnetic hardness of about 0.83 at room
temperature. Using first-principles calculations, we examine the full range of
alloys from CrB, through MnB, FeB, to CoB. Furthrmore, we consider alloys of
MnB and FeB with substitutions of 3$d$, 4$d$ and 5$d$ transition metals. For
the above ninety compositions, we determine magnetic moment, magnetocrystalline
anisotropy energy and magnetic hardness. For (Fe-Co)B alloys, the calculated
values of magnetic hardness exceed five, which is an exceptionally high. While
these values are inflated by the virtual crystal approximation used, we still
expect actual magnetic hardnesses well above unity. Furthermore, we classify
considered MnB alloys substituted with transition metals as magnetically soft
or semi-hard and FeB alloys with Sc, Ti, V, Zr, Nb, Mo, Hf, Ta or W as
magnetically hard (with magnetic hardness exceeding unity).",2403.00138v1
2008/2/20,Anomalous Magnetic Properties of Sr2YRuO6,"Anomalous magnetic properties of the double perovskite ruthenates compound
Sr2YRuO6 are reported here. Magnetization measurements as a function of
temperature in low magnetic fields show clear evidence for two components of
magnetic order (TM1 ~ 32K and TM2 ~ 27K) aligned opposite to each other with
respect to the magnetic field direction even though only Ru5+moments can order
magnetically in this compound. The second component of the magnetic order at
TM2 ~ 27K results only in a magnetization reversal, and not in the negative
magnetization when the magnetization is measured in the field cooled (FC) mode.
Isothermal magnetization (M-H) measurements show hysteresis with maximum
coercivity (Hc) and remnant magnetization (Mr) at T ~ 27 K, corroborating the
presence of the two oppositely aligned magnetic moments, each with a
ferromagnetic component. The two components of magnetic ordering are further
confirmed by the double peak structure in the heat capacity measurements. These
anomalous properties have significance to some of the earlier results obtained
for the Cu-substituted superconducting Sr2YRu1-xCuxO6 compounds.",0802.2953v2
2014/9/5,"Analysis of the magnetic field, force, and torque for two-dimensional Halbach cylinders","The Halbach cylinder is a construction of permanent magnets used in
applications such as nuclear magnetic resonance apparatus, accelerator magnets
and magnetic cooling devices. In this paper the analytical expression for the
magnetic vector potential, magnetic flux density and magnetic field for a two
dimensional Halbach cylinder are derived. The remanent flux density of a
Halbach magnet is characterized by the integer $p$. For a number of
applications the force and torque between two concentric Halbach cylinders are
important. These quantities are calculated and the force is shown to be zero
except for the case where $p$ for the inner magnet is one minus $p$ for the
outer magnet. Also the force is shown never to be balancing. The torque is
shown to be zero unless the inner magnet $p$ is equal to minus the outer magnet
$p$. Thus there can never be a force and a torque in the same system.",1409.1712v1
2020/9/14,Voltage-driven Magnetization Switching via Dirac Magnetic Anisotropy and Spin--orbit Torque in Topological-insulator-based Magnetic Heterostructures,"Electric-field control of magnetization dynamics is fundamentally and
technologically important for future spintronic devices. Here, based on
electric-field control of both magnetic anisotropy and spin--orbit torque, two
distinct methods are presented for switching the magnetization in topological
insulator (TI)/magnetic-TI hybrid systems. The magnetic anisotropy energy in
magnetic TIs is formulated analytically as a function of the Fermi energy, and
it is confirmed that the out-of-plane magnetization is always favored for the
partially occupied surface band. Also proposed is a transistor-like device with
the functionality of a nonvolatile magnetic memory that uses voltage-driven
writing and the (quantum) anomalous Hall effect for readout. For the
magnetization reversal, by using parameters of Cr-doped
Bi_{1-x}Sb_{x})_{2}Te_{3}, the estimated source-drain current density and gate
voltage are of the orders of $10^4$--$10^5$~A/cm$^2$ and 0.1~V, respectively,
below 20~K and the writing requires no external magnetic field. Also discussed
is the possibility of magnetization switching by the proposed method in
TI/ferromagnetic-insulator bilayers with the magnetic proximity effect.",2009.06187v1
2022/8/31,Second-order phase transition of silicon from a band insulator to metal induced by strong magnetic fields,"We present the second-order phase transition from a band insulator to metal
that is induced by a strong magnetic field. The magnetic-field dependences of
the magnetization and energy band gap of a crystalline silicon immersed in a
magnetic field are investigated by means of the nonperturbative
magnetic-field-containing relativistic tight-binding approximation method
[Phys. Rev. B 97, 195135 (2018)]. It is shown that the energy band gap
disappears at the critical magnetic field of 2.22x$10^4$ (T). At the critical
magnetic field, the magnetic-field dependence of the magnetization exhibits a
kink behavior, which means that this phenomenon is the second-order phase
transition from a band insulator to metal. It is found that in strong magnetic
fields above the critical magnetic field, namely in the metallic phase, the
oscillation of the magnetization appears. It is shown that this magnetic
oscillation comes from the energy bands in the magnetic Brillouin zone that
change from the occupied states to unoccupied states or vice vasa.",2208.14690v1
2007/2/8,Clausius-Mossotti approximation in the theory of polar materials,"Clausius-Mossotti approximation is extended to describe the measured magnetic
moment of an ellipsoidal sample containing magnetic or nonmagnetic ellipsoidal
inclusions and magnetic or nonmagnetic matrix. The magnetic field in the matrix
and inclusions is calculated. The magnetic energy of a system is calculated
also. The equilibrium shape of a pore in a ferromagnetic sample is
investigated. The phenomenon of cavitation in porous ferromagnetic samples is
described. The model is applied to calculate magnetic properties of granular
superconductors. The effective electric conductivity of a sample of a composite
material, containing an arbitrary number of differently ordered distributions
of ellipsoidal inclusions is calculated. Effective conductivity of a composite
material, consisting of fibers of high conductivity and a matrix of low
conductivity is discussed. Concentrated electric field in the vicinity of the
ends of a conductive nanofiber in a composite material is calculated. The high
quantity of this field is of an extreme importance to provide the proper
functioning of monitors, based on conductive nanofibers in dielectric media.",0702222v2
2016/4/22,Theoretical methods for understanding advanced magnetic materials: the case of frustrated thin films,"Materials science has been intensively developed during the last 30 years.
This is due, on the one hand, to an increasing demand of new materials for new
applications and, on the other hand, to technological progress which allows for
the synthesis of materials of desired characteristics and to investigate their
properties with sophisticated experimental apparatus. Among these advanced
materials, magnetic materials at nanometric scale such as ultra thin films or
ultra fine aggregates are no doubt among the most important for electronic
devices.In this review, we show advanced theoretical methods and solved
examples that help understand microscopic mechanisms leading to experimental
observations in magnetic thin films. Attention is paid to the case of
magnetically frustrated systems in which two or more magnetic interactions are
present and competing. The interplay between spin frustration and surface
effects is the origin of spectacular phenomena which often occur at boundaries
of phases with different symmetries: reentrance, disorder lines, coexistence of
order and disorder at equilibrium. These phenomena are shown and explained
using of some exact methods, the Green's function and Monte Carlo simulation.
We show in particular how to calculate surface spin-wave modes, surface
magnetization, surface reorientation transition and spin transport.",1604.06546v1
2018/12/13,Orbital magnetic moments of phonons,"In ionic materials, circularly polarized phonons carry orbital magnetic
moments that arise from circular motions of the ions, and which interact with
other magnetic moments or fields. Here, we calculate the orbital magnetic
moments of phonons in 35 different materials using density functional theory,
and we identify the factors that lead to, and materials that show, large
responses. We compute the resulting macroscopic orbital magnetic moments that
can be induced by the excitation of coherent phonons using mid-infrared laser
pulses, and we evaluate the magnitudes of the phonon Zeeman effect in a strong
magnetic field. Finally, we apply our formalism to chiral phonons, in which the
motions of the ions are intrinsically circular. The zoology presented here may
serve as a guide to finding materials for phonon and spin-phonon driven
phenomena.",1812.05379v1
2021/7/14,Evolving Devil's staircase magnetization from tunable charge density waves in nonsymmorphic Dirac semimetals,"While several magnetic topological semimetals have been discovered in recent
years, their band structures are far from ideal, often obscured by trivial
bands at the Fermi energy. Square-net materials with clean, linearly dispersing
bands show potential to circumvent this issue. CeSbTe, a square-net material,
features multiple magnetic field-controllable topological phases. Here, it is
shown that in this material, even higher degrees of tunability can be achieved
by changing the electron count at the square-net motif. Increased electron
filling results in structural distortion and formation of charge density waves
(CDWs). The modulation wave-vector evolves continuously leading to a region of
multiple discrete CDWs and a corresponding complex ""Devil's staircase"" magnetic
ground state. A series of fractionally quantized magnetization plateaus are
observed, which implies direct coupling between CDW and a collective
spin-excitation. It is further shown that the CDW creates a robust idealized
non-symmorphic Dirac semimetal, thus providing access to topological systems
with rich magnetism.",2107.06883v1
2023/3/19,Modulation of skyrmionic magnetic textures in two-dimensional vdW materials and their heterostructures,"The intrinsic magnetism observed in two-dimensional (2D) van der Waals (vdW)
materials provides a unique opportunity for exploring the 2D topological
magnetic textures, in particular skyrmionic magnetic textures (SMTs) including
skyrmion and its topological equivalents. Since the experimental discovery of
skyrmions in the 2D vdW materials and their heterostructures, a critical
challenge lies in the control of these SMTs to translate their intriguing
features into spintronic applications. Here, we review the recent experimental
and theoretical progresses on the modulations of SMTs in 2D vdW monolayer
materials and their heterostructures. Besides well-established basic modulation
factors including temperature, magnetic field and sample thickness, we present
the experimental realization of mobility and transition driven by electric
current, and the theoretical prediction of diverse magnetoelectric modulations
by electric field. Considering the 2D character of vdW layered materials,
strain and stacking style are also efficient approaches to tune the magnetic
textures.",2303.11335v1
1999/1/29,Gravimetric Measurement of Magnetic Field Gradient Spatial Distribution,"Magnetic interaction between a weighing sample and an external magnetic field
allows to measure characteristics of magnetic field (a sample with known
magnetic characteristics), as well as the magnetic properties of a sample (a
known magnetic field). Measurement of materials magnetic permeability is a well
known application of this method. In this paper we restrict ourselves to the
measurement of magnetic field spatial distribution, which was achieved by
scanning of samples from known materials along the vertical axis. Field
measurements by Hall detector were done to calibrate obtained data. Such
measurements are of great interest in some branches of physics, in particular,
in accelerator physics, where the quality of magnetic system parts eventually
determine the quality of accelerated bunches. Development of a simple and cheep
device for measurement of magnetic field spatial distribution is an urgent
problem. The developed system for gravimetric measurement of magnetic field
gradients partially solves this problem.",9901058v1
2021/4/2,Highly Complex Magnetic Structures Resulting From Hierarchical Phase Separation in AlCo(Cr)FeNi High Entropy Alloys,"Magnetic high entropy alloys (HEAs) are a new category of high-performance
magnetic materials, with multi-component concentrated compositions and complex
multi-phase structures. Although there have been numerous reports of their
interesting magnetic properties, there is very limited understanding about the
interplay between their hierarchical multi-phase structures and their local
magnetic structures. By employing high spatial resolution correlative magnetic,
structural and chemical studies, we reveal the influence of a hierarchically
decomposed B2 + A2 structure in an AlCo0.5Cr0.5FeNi HEA on the formation of
magnetic vortex states within individual A2 (disordered BCC) precipitates,
which are distributed in an ordered B2 matrix that is weakly ferromagnetic.
Non-magnetic or weakly ferromagnetic B2 precipitates in large magnetic domains
of the A2 phase, and strongly magnetic Fe-Co-rich interphase A2 regions, are
also observed. These results provide important insight into the origin of
coercivity in this HEA, which can be attributed to a complex magnetization
process that includes the successive reversal of magnetic vortices.",2104.00943v1
2020/5/2,Optically driven ultrafast magnetic order transitions in two-dimensional ferrimagnets,"Laser-induced switching and manipulation of the spins in magnetic materials
are of great interest to revolutionize future magnetic storage technology and
spintronics with fastest speed and least power dissipative. Inspired by the
recent discovery of intrinsic two-dimensional (2D) magnets, which provide
unique platform to explore the new phenomenon for light-control magnetism in
the 2D limit, we propose to realize light can efficiently tune magnetic
properties of 2D ferrimagnets in early time. Here, using the 2D ferrimagnetic
MXenes as prototype systems, our real-time density functional theory (TDDFT)
simulation show that laser pulses can directly induce ultrafast spin-selective
charge transfer between two magnetic sublattices on a few femtoseconds, and
further generate dramatic changes in the magnetic structure of these MXenes,
including a magnetic order transition from ferrimagnetic (FiM) to transient
ferromagnetic (FM). The microscopic mechanism underpinning this ultrafast
switching of magnetic order in MXenes is governed by optically induced
inter-site spin transfer (OISTR) effect, which theoretically enables the
ultrafast direct optical manipulation of the magnetic state in MXenes-based
materials. Our results open new opportunities to optically manipulate the spin
in 2D magnets.",2005.00871v1
2020/12/9,Optimization of a NdFeB permanent magnet configuration for in-vivo drug delivery experiments,"We propose a new concept of magnetic focusing for targeting and accumulation
of functionalized superparamagnetic nanoparticles in living organs through
composite configurations of different permanent magnets. The proposed setups
fulfill two fundamental requirements for in vivo experiments: 1) reduced size
of the magnets to best focusing on small areas representing the targeted organs
of mice and rats and 2) maximization of the magnetic driving force acting on
the magnetic nanoparticles dispersed in blood. To this aim, several
configurations of permanent magnets organized with different degrees of
symmetry have been tested. The product B*grad(B) proportional to the magnetic
force has been experimentally measured, over a wide area (20x20 mm^2), at a
distance corresponding to the hypothetical distance of the mouse organ from the
magnets. A non-symmetric configuration of mixed shape permanent magnets
resulted in particularly promising to achieve the best performances for further
in vivo experiments.",2012.05059v1
2022/5/8,Two-dimensional characterization of three-dimensional magnetic bubbles in Fe$_3$Sn$_2$ nanostructures,"We report differential phase contrast scanning transmission electron
microscopy (TEM) of nanoscale magnetic objects in Kagome ferromagnet
Fe$_3$Sn$_2$ nanostructures. This technique can directly detect the deflection
angle of a focused electron beam, thus allowing clear identification of the
real magnetic structures of two magnetic objects including three-ring and
complex arch-shaped vortices in Fe$_3$Sn$_2$ by Lorentz transmission electron
microscopy imaging. Numerical calculations based on real material-specific
parameters well reproduced the experimental results, showing that the magnetic
objects can be attributed to integral magnetizations of two types of complex
three-dimensional (3D) magnetic skyrmion bubbles with depth-modulated spin
twisting. Magnetic configurations obtained using the high-resolution TEM are
generally considered as two-dimensional (2D) magnetic objects previously. Our
results imply the importance of the integral magnetizations of underestimated
3D magnetic structures in 2D TEM magnetic characterizations.",2205.03751v2
2022/5/9,"Controlling magnetic exchange and anisotropy by non-magnetic ligand substitution in layered MPX3 (M = Ni, Mn; X = S, Se)","Recent discoveries in two-dimensional (2D) magnetism have intensified the
investigation of van der Waals (vdW) magnetic materials and further improved
our ability to tune their magnetic properties. Tunable magnetism has been
widely studied in antiferromagnetic metal thiophosphates MPX3. Substitution of
metal ions M has been adopted as an important technique to engineer the
magnetism in MPX3. In this work, we have studied the previously unexplored
chalcogen X substitutions in MPX3 (M = Mn/Ni; X = S/Se). We synthesized the
single crystals of MnPS3-xSex (0 < x < 3) and NiPS3-xSex (0 < x < 1.3) and
investigated the systematic evolution of the magnetism with varying x. Our
study reveals the effective tuning of magnetic interactions and anisotropies in
both MnPS3 and NiPS3 upon Se substitution. Such efficient engineering of the
magnetism provides a suitable platform to understand the low-dimensional
magnetism and develop future magnetic devices.",2205.04585v1
2022/11/28,Algorithms for magnetic symmetry operation search and identification of magnetic space group from magnetic crystal structure,"A crystal symmetry search is crucial for computational crystallography and
materials science. Although algorithms and implementations for the crystal
symmetry search have been developed, their extension to magnetic space groups
(MSGs) remains limited. In this paper, algorithms for determining magnetic
symmetry operations of magnetic crystal structures, identifying magnetic
space-group types of given MSGs, searching for transformations to a BNS
setting, and symmetrizing the magnetic crystal structures using the MSGs are
presented. The determination of magnetic symmetry operations is numerically
stable and is implemented with minimal modifications from the existing crystal
symmetry search. Magnetic space-group types and transformations to the BNS
setting are identified by a two-step approach combining space-group type
identification and the use of affine normalizers. Point coordinates and
magnetic moments of the magnetic crystal structures are symmetrized by
projection operators for the MSGs. An implementation is distributed with a
permissive free software license in spglib v2.0.2:
https://github.com/spglib/spglib.",2211.15008v2
2007/9/10,Reducing the magnetic susceptibility of parts in a magnetic gradiometer,"In this paper we report a detailed investigation of a number of different
materials commonly used in precision instrumentation in the view of using them
as critical components in the magnetic gradiometer. The materials requirement
inside a magnetic gradiometer is stringent because the presence of magnetic
susceptible material will introduce intrinsic errors into the device. Many
commercial grade non-magnetic materials still have unacceptably high levels of
volume magnetic susceptibility between 0.001 and 0.0001. It is shown here that
machining with steel tools can further increase the susceptibility by up to an
order of magnitude. The ability of an acid wash to remove this contamination is
also reported. Washing in acid is shown to reduce the variation of volume
susceptibility in several commercial grade plastics which already have low
values of susceptibility.",0709.1323v2
2018/1/10,The hidden magnetization in ferromagnetic material: Miamagnetism,"This paper presents the hidden magnetization features of ferromagnetic
materials: called miamagnetism. As we know, we have several forms of
magnetization: the diamagnetism, the paramagnetism, the ferromagnetism etc. The
main character of the diamagnetism is that its magnetic susceptibility is
negative (from -1e-9 for gas and -1e-6 for liquid and solid to -1 for
superconducting materials of type I) and it is not less than -1 unless for
special materials like metamaterials at high frequencies. The miamagnetism has
the character that the magnetic susceptibility can reach at low frequencies a
negative value of -155 of magnitude leading to a negative permeability. We can
not see it because it is hidden by the ferromagnetic character which has a high
positive magnetic susceptibility. We use the discrete Fourier transform to
illustrate this hidden character and the hysteresis model can be represented
only by harmonics of (2n+1)f0 of magnitude. This magnetization follows a
Boltzmann distribution for the modulus of theses harmonics.",1801.03479v1
2018/6/7,Composite Skyrmion bags in two-dimensional materials,"Skyrmions are particle-like topological excitations, studied in various
condensed matter systems and models of high-energy physics (HEP). They occur as
stable spin textures in certain planar magnetic materials and as configurations
in chiral nematic liquid crystals, having been originally proposed as model of
atomic nuclei. Since magnetic Skyrmions can be accelerated with a current, they
have the potential to encode bits in low-power magnetic storage devices.
Drawing on techniques from HEP, we demonstrate that magnetic and liquid crystal
Skyrmions interact like orientation dependent, localised particles, explaining
previously observed Skyrmion behaviour. This interaction motivates the
construction of Skyrmion bags: textures of high topological degree which we
realise experimentally in liquid crystals, and in magnetic materials by
computer simulations. These Skyrmion bags configurations are nested multiple
Skyrmions, which act like single Skyrmions in pairwise interaction, and under
the influence of a current in magnetic materials. These results emphasize
equivalent Skyrmion behaviour in different physical systems, and suggest new,
high-density magnetic memory storage devices based on Skyrmion bags.",1806.02576v1
2020/9/7,Releasing latent chirality in magnetic two-dimensional materials,"Dzyaloshinskii-Moriya interaction is at heart of chiral magnetism and causes
emergence of rich non-collinear and unique topological spin textures in
magnetic materials, including cycloids, helices, skyrmions and other. Here we
show that strong intrinsic DMI lives in recently discovered van der Waals
magnetic two-dimensional materials, due to the sizeable spin-orbit coupling on
the non-magnetic ions. In a perfect crystal, this intrinsic DMI remains hidden,
but is released with any break of point-inversion symmetry between magnetic
ions, unavoidable at the sample edges, at ever present structural defects, with
any buckling of the material, or with non-uniform strain on an uneven
substrate. We demonstrate such release of latent chirality on an archetypal
magnetic monolayer - CrI3, and discuss the plethora of realizable DMI patterns,
their control by nanoengineering and tuning by external electric field, thereby
opening novel routes in 2D magnetoelectronics.",2009.03421v1
2021/8/16,Flavors of Magnetic Noise in Quantum Materials,"The complexity of electronic band structures in quantum materials offers new
charge-neutral degrees of freedom stable for transport, a promising example
being the valley (axial) degree of freedom in Weyl semimetals (WSMs). A
noninvasive probe of their transport properties is possible by exploiting the
frequency dependence of the magnetic noise generated in the vicinity of the
material. In this work, we investigate the magnetic noise generically
associated with diffusive transport using a systematic Langevin approach.
Taking a minimal model of magnetic WSMs for demonstration, we show that thermal
fluctuations of the charge current, the valley current, and the magnetic order
can give rise to magnetic noise with distinctively different spectral
characters, which provide a theoretical guidance to separate their
contributions. Our approach is extendable to the study of magnetic noise and
its spectral features arising from other transport degrees of freedom in
quantum materials.",2108.07305v3
2021/9/13,Gradient soft magnetic materials produced by additive manufacturing from non-magnetic powders,"Additive manufacturing (AM) allows printing parts of complex geometries that
cannot be produced by standard technologies. Besides, AM provides the
possibility to create gradient materials with different structural and physical
properties. We, for the first time, printed gradient soft magnetic materials
from paramagnetic powders (316L steel and Cu-12Al-2Fe (in wt.%) aluminium
bronze)). The magnetic properties can be adjusted during the in-situ printing
process. The saturated magnetization value of alloys reaches 49 emu g^{-1}. The
changes in the magnetic properties have been attributed to the formation of the
BCC phase after mixing two FCC-dominated powders. Moreover, the phase
composition of the obtained gradient materials can be predicted with reasonable
accuracy by the CALPHAD approach, thus providing efficient optimization of the
performance. The obtained results provide new prospects for printing gradient
magnetic alloys.",2109.05947v1
2023/2/27,Evolution of topological states in magnetic materials by symmetry-breaking,"The magnetism-controllable band topology renders magnetic topological
materials as one of the most promising candidates for next-generation
electronic devices. Here we first construct three datasets allowing
ascertaining the evolutions of topological states (with all enforced band
crossings identified) using symmetry-indicators in the 1651 magnetic space
groups. We then perform high-throughput investigations based on 1267
stoichiometric magnetic materials ever-experimentally synthesized and the three
datasets to reveal a hierarchy of topological states by symmetry-breaking,
along all ergodic and continuous paths of symmetry-breaking (preserving the
translation symmetry) from the parent magnetic space group to the trivial
group. The results are expected to aid experimentalists in selecting feasible
and appropriate means to tune topological states towards realistic applications
in new paradigm of memory device by topological state switching.",2302.13622v1
2023/4/1,Magnetic proximity effect at the interface of two-dimensional materials and magnetic oxide insulators,"Two-dimensional (2D) materials provide a platform for developing novel
spintronic devices and circuits for low-power electronics. In particular,
inducing magnetism and injecting spins in graphene have promised the emerging
field of graphene spintronics. This review focuses on the magnetic proximity
effect at the interface of 2D materials and magnetic oxide insulators. We
highlight the unique spin-related phenomena arising from magnetic exchange
interaction and spin-orbital coupling in 2D materials coupled with magnetic
oxides. We also describe the fabrication of multifunctional hybrid devices
based on spin transport. We conclude with a perspective of the field and
highlight challenges for the design and fabrication of 2D spintronic devices
and their potential applications in information storage and logic devices.",2304.00356v1
2023/6/1,CrTe$_2$ as a two-dimensional material for topological magnetism in complex heterobilayers,"The discovery of two-dimensional (2D) van der Waals magnetic materials and
their heterostructures provided an exciting platform for emerging phenomena
with intriguing implications in information technology. Here, based on a
multiscale modelling approach that combines first-principles calculations and a
Heisenberg model, we demonstrate that interfacing a CrTe$_2$ layer with various
Te-based layers enables the control of the magnetic exchange and
Dzyaloshinskii-Moriya interactions as well as the magnetic anisotropy energy of
the whole heterobilayer, and thereby the emergence of topological magnetic
phases such as skyrmions and antiferromagnetic Neel merons. The latter are
novel particles in the world of topological magnetism since they arise in a
frustrated Neel magnetic environment and manifest as multiples of intertwined
hexamer-textures. Our findings pave a promising road for proximity-induced
engineering of both ferromagnetic and long-sought antiferromagnetic chiral
objects in the very same 2D material, which is appealing for new information
technology devices employing quantum materials.",2306.00448v1
2022/4/4,Hole-doping induced ferromagnetism in 2D materials,"Two-dimensional (2D) ferromagnetic materials are considered as promising
candidates for the future generations of spintronic devices. Yet, 2D materials
with intrinsic ferromagnetism are scarce. High-throughput first-principles
simulations are performed in order to screen 2D materials that present a
non-magnetic to a ferromagnetic transition upon hole doping. A global
evolutionary search is subsequently performed, in order to identify alternative
possible atomic structures of the eligible candidates, and 122 materials
exhibiting a hole-doping induced ferromagnetism are identified. Their energetic
and dynamic stability, as well as their magnetic properties under hole doping
are investigated systematically. Half of these 2D materials are metal halides,
followed by chalcogenides, oxides and nitrides, some of them having predicted
Curie temperatures above 300 K. The exchange interactions responsible for the
ferromagnetic order in these 2D materials are also discussed. This work not
only provides theoretical insights into hole-doped 2D ferromagnetic materials,
but also enriches the family of 2D magnetic materials for possible spintronic
applications.",2204.01551v2
2020/12/18,Frustrated Magnetism in Fluoride and Chalcogenide Pyrochlore Lattice Materials,"Pyrochlore lattices, which are found in two important classes of materials --
the $A_2B_2X_7$ pyrochlore family and the $AB_2X_4$ spinel family -- are the
quintessential 3-dimensional frustrated lattice architecture. While
historically oxides ($X =$~O) have played the starring role in this field, the
past decade has seen materials synthesis breakthroughs that have lead to the
emergence of fluoride ($X =$~F) and chalcogenide ($X =$~S, Se) pyrochlore
lattice materials. In this Research Update, we summarize recent progress in
understanding the magnetically frustrated ground states in three families of
non-oxide pyrochlore lattice materials: (i) $3d$-transition metal fluoride
pyrochlores, (ii) rare earth chalcogenide spinels, and (iii) chromium
chalcogenide spinels with a breathing pyrochlore lattice. We highlight how the
change of anion can modify the single ion spin anisotropy due to crystal
electric field effects, stabilize the incorporation of new magnetic elements,
and dramatically alter the exchange pathways and thereby lead to new magnetic
ground states. We also consider a range of future directions -- materials with
the potential to define the next decade of research in frustrated magnetism.",2012.10060v2
2021/1/30,"High-throughput search for magnetic topological materials using spin-orbit spillage, machine-learning and experiments","Magnetic topological insulators and semi-metals have a variety of properties
that make them attractive for applications including spintronics and quantum
computation, but very few high-quality candidate materials are known. In this
work, we use systematic high-throughput density functional theory calculations
to identify magnetic topological materials from 40000 three-dimensional
materials in the JARVIS-DFT database (https://jarvis.nist.gov/jarvisdft).
First, we screen materials with net magnetic moment > 0.5 {\mu}B and spin-orbit
spillage > 0.25, resulting in 25 insulating and 564 metallic candidates. The
spillage acts as a signature of spin-orbit induced band-inversion. Then, we
carry out calculations of Wannier charge centers, Chern numbers, anomalous Hall
conductivities, surface bandstructures, and Fermi-surfaces to determine
interesting topological characteristics of the screened compounds. We also
train machine learning models for predicting the spillage, bandgaps, and
magnetic moments of new compounds, to further accelerate the screening process.
We experimentally synthesize and characterize a few candidate materials to
support our theoretical predictions.",2102.00237v2
2021/12/21,A family tree of two-dimensional magnetic materials with tunable topological properties,"Two-dimensional (2D) magnetic materials empowered with nontrivial band
topology may lead to the emergence of exotic quantum states with significant
application potentials. Here we predict a family tree of 2D magnetic materials
with tunable topological properties, starting from the parental materials of
CrI3 and CrBr3. The underlying design principle is that, by substituting the
alternating sites of the Cr honeycomb lattice sandwiched between the halogen
layers with V or Mn, the parental materials of trivial ferromagnetic insulators
are ripe to be converted into topological systems. Specifically, our
first-principles calculations show that, due to the elegant interplay between
bandgap narrowing and spin-orbital coupling, CrI3 branches into
high-temperature quantum anomalous Hall insulators of CrVI6 and CrMnI6 with
different topological invariants, while CrBr3 branches into topological
half-metals of CrVBr6 and CrMnBr6. Those novel 2D magnets are also shown to be
easily exfoliated from their bulk counterparts. The present study is thus
geared to advance the field of 2D magnetic materials into the topologically
nontrivial realm.",2112.10924v1
2022/4/29,"Realization of the electric-field driven ""one-material""-based magnetic tunnel junction using van der Waals antiferromagnetic MnPX3 (X: S, Se)","Presently a lot of efforts are devoted to the investigation of new
two-dimensional magnetic materials, which are considered as promising for the
realization of the future electronics and spintronics devices. However, the
utilization of these materials in different junctions requires complicated
processing that in many cases leads to unwanted parasitic effects influencing
the performance of the junctions. Here, we propose the new elegant approach for
the realization of the ""one-material""-based magnetic tunnel junction. The
several layers of 2D van der Waals MnPX3 (X: S, Se), which is insulating
antiferromagnet in its ground state, are used and the effect of the applied
external electric filed leads to the half-metallic ferromagnetic states for the
outermost layers of the MnPX3 stack. The rich states diagram of such magnetic
tunnel junction permits to precisely control its tunneling conductivity. The
realized ""one-material""-based magnetic tunnel junction allows to avoid all
effects connected with the lattice mismatches and carriers scattering effects
at the materials interfaces, giving high perspectives for the application of
such systems in electronics and spintronics.",2204.14262v1
2002/1/14,Polaron percolation in diluted magnetic semiconductors,"We theoretically study the development of spontaneous magnetization in
diluted magnetic semiconductors as arising from a percolation of bound magnetic
polarons. Within the framework of a generalized percolation theory we derive
analytic expressions for the Curie temperature and the magnetization, obtaining
excellent quantitative agreement with Monte Carlo simulation results and good
qualitative agreement with experimental results.",0201229v1
2003/7/11,Magnetic and transport percolation in diluted magnetic semiconductors,"The ferromagnetic transition in a diluted magnetic semiconductor with
localized charge carriers is inevitably a percolation transition. In this work
we theoretically study the correlation between this magnetic percolation and
transport properties of the sample, including the possibility of a simultaneous
transport percolation. We find nontrivial signatures of the percolating
magnetic clusters in the transport properties of the system, including
interesting non-monotonic temperature dependence of the system resistivity.",0307294v1
2003/9/24,Non conservation of the magnetization current across magnetic hetero-structures,"We show that when the magnetizations on opposite sides of a junction are not
collinear, the magnetization current is not conserved as the junction is
crossed. Thus the usual treatment of this problem needs to be modified. We
argue that this is due to an implicit assumption of an external torque that is
required to clamp the magnetization in place. The physical consequence of this
is explored.",0309555v1
2005/11/21,Magnetization reversal in the anisotropy-dominated regime using time-dependent magnetic fields,"We study magnetization reversal using various r.f. magnetic pulses. We show
numerically that switching is possible with simple sinusoidal pulses; however
the optimum approach is to use a frequency-swept (chirped) r.f. magnetic pulse,
the shape of which can be derived analytically. Switching times of the order of
nanoseconds can be achieved with relatively small r.f. fields, independent of
the anisotropy's strength.",0511497v1
2007/11/7,Magnetic properties of bi-phase micro- and nanotubes,"The magnetic configurations of bi-phase micro- and nanotubes consisting of a
ferromagnetic internal tube, an intermediate non-magnetic spacer, and an
external magnetic shell are investigated as a function of their geometry. Based
on a continuum approach we obtained analytical expressions for the energy which
lead us to obtain phase diagrams giving the relative stability of
characteristic internal magnetic configurations of the bi-phase tubes.",0711.1101v1
2012/12/20,Magnetic properties of the RbNd(WO4)2 single crystal,"The magnetic investigations as a function of temperature and magnetic field
for the rubidium neodymium double tungstate RbNd(WO4)2 single crystal have been
performed. The magnetization was measured in the temperature range from 4.2 to
100 K and for the magnetic field up to 1.5 T. The crystal field and exchange
parameters were found.",1212.4997v1
2014/6/14,Computer Simulations on Barkhausen effects and Magnetizations in Fe Nano-Structure Systems,"The magnetization processes in Fe nano-systems are investigated using the
numerical simulations based on classical magnetic dipole moment interactions.
The domain energies are calculated from moment-moment interactions over whole
systems using large scale computing resources. The results directly show most
of basic magnetization phenomena. The Barkhausen effects are represented with
jumps and terraces of magnetization steps induced from external field changes
of {\Delta}H.",1406.3688v1
2015/8/11,Transport between metals and magnetic insulators,"We derive the Onsager response matrix of fluctuation-mediated spin-collinear
transport through a ferromagnetic insulator and normal metal interface driven
by a temperature difference, spin accumulation, or magnetic field. We predict
magnon-squeezing spin currents, magnetic field-induced cooling (magnon Peltier
effect), temperature induced magnetization (thermal magnetic field) as well as
universal spin Seebeck/Peltier coefficients.",1508.02486v2
2021/11/16,Effect of a weak magnetic field on ductile-brittle transition in micro-cutting of single-crystal calcium fluoride,"Magneto-plasticity occurs when a weak magnetic field alters material
plasticity and offers a viable solution to enhance ductile-mode cutting of
brittle materials. This study demonstrates the susceptibility of non-magnetic
single-crystal calcium fluoride (CaF2) to the magneto-plastic effect. The
influence of magneto-plasticity on CaF2 was confirmed in micro-deformation
tests under a weak magnetic field of 20 mT. The surface pile-up effect was
weakened by 10-15 nm along with an enlarged plastic zone and suppressed crack
propagation under the influence of the magnetic field. Micro-cutting tests
along different crystal orientations on the (111) plane of CaF2 revealed an
increase in the ductile-brittle transition of the machined surface with the aid
of magneto-plasticity where the largest increase in ductile-brittle transition
occurred along the [11-2] orientation from 512 nm to a range of 664-806 nm.
Meanwhile, the subsurface damage layer was concurrently thinner under magnetic
influence. An anisotropic influence of the magnetic field relative to the
single-crystal orientation and the cutting direction was also observed. An
analytical model was derived to determine an orientation factor M that
successfully describes the anisotropy while considering the single-crystal
dislocation behaviour, material fracture toughness, and the orientation of the
magnetic field. Previously suggested theoretical mechanism of
magneto-plasticity via formation of non-singlet electronic states in defected
configurations was confirmed with density functional theory calculations. The
successful findings on the influence of a weak magnetic field on plasticity
present an opportunity for the adoption of magnetic-assisted micro-cutting of
non-magnetic materials.",2111.08187v1
2023/9/18,The contribution and FIP bias of three types of materials inside ICMEs associated with different flare intensities,"The studies on the origination and generation mechanisms of ICME materials
are crucial for understanding the connection between CMEs and flares. The
materials inside ICMEs can be classified into three types, coming from corona
directly (corona-materials), heated by magnetic reconnection in corona
(heated-corona-materials), and generated by chromospheric evaporation
(chromospheric-evaporation-materials). Here, the contribution and First
Ionization Potential (FIP) bias of three types of materials inside ICMEs
associated with different flare intensities are analyzed and compared. We find
that the speeds and scales of near-Earth ICMEs both increase with flare
intensities. The proportions of heated-corona-materials are nearly constant
with flare intensities. The contributions of corona-materials
(chromospheric-evaporation-materials) are significantly decreased (increased)
with flare intensities. More than two-thirds of materials are
chromospheric-evaporation-materials for ICMEs associated with strong flares.
The FIP bias of corona-materials and heated-corona-materials is almost the
same. The FIP bias of chromospheric-evaporation-materials is significantly
higher than that of corona-materials and heated-corona-materials, and it is
increased with flare intensities. The above characteristics of FIP bias can be
explained reasonably by the origination and generation mechanisms of three
types of ICME materials. The present study demonstrates that the origination
and generation mechanisms of ICME materials are significantly influenced by
flare intensities. The reasons for the elevation of FIP bias, if ICMEs are
regarded as a whole, are that the FIP bias of
chromospheric-evaporation-materials is much higher, and the
chromospheric-evaporation-materials contributed significantly to the ICMEs
which associated with strong flares.",2309.09434v1
2001/5/29,Study of magnetic and specific heat measurements at low temperatures in Nd0.5Sr0.5MnO3 and Nd0.5Ca0.5MnO3,"The magnetization at low temperatures for Nd0.5Sr0.5MnO3 and Nd0.5Ca0.5MnO3
samples showed a rapid increase with decreasing temperatures, contrary to a
La0.5Ca0.5MnO3 sample. Specific heat measurement at low temperatures showed a
Schottky-like anomaly for the first two samples. However, there is not a
straight forward correlation between the intrinsic magnetic moment of the Nd3+
ions and the Schottky-like anomaly.",0105571v1
2001/7/5,Magnetization in quasiperiodic magnetic multilayers with biquadratic exchange and uniaxial anisotropy,"A theoretical study is made of the magnetization versus applied field curves
of ferromagnetic/nonmagnetic multilayers constructed according to a Fibonacci
quasiperiodic sequence. The ferromagnetic films are assumed to have uniaxial
anisotropy and are coupled by both bilinear and biquadratic effective exchange.
The effects of quasiperiodicity in the magnetic phases are illustrated
numerically for Fe/Cr systems.",0107127v1
2005/10/5,Magnetization dynamics using ultrashort magnetic field pulses,"Very short and well shaped magnetic field pulses can be generated using
ultra-relativistic electron bunches at Stanford Linear Accelerator. These
fields of several Tesla with duration of several picoseconds are used to study
the response of magnetic materials to a very short excitation. Precession of a
magnetic moment by 90 degrees in a field of 1 Tesla takes about 10 picoseconds,
so we explore the range of fast switching of the magnetization by precession.",0510121v2
2005/11/25,Decoupled magnetic and electrical switching in manganite trilayer,"We report magnetic and electrical transport studies of an epitaxially grown
trilayer thin film structure comprising La0.59Ca0.41MnO3 sandwiched between
La0.67Ca0.33MnO3 electrodes. Since La0.59Ca0.41MnO3 lies at the edge of the
thin film ferromagnetic metallic phase field, phase separation effects are
expected. These effects can explain the observed magnetic isotropy of the
middle layer. By contrast, the electrode material is magnetically uniaxial.
Easy axis magnetic field sweeps of the trilayer produce two sharp magnetic
transitions, but only one sharp transition in current-in-plane resistance
measurements.",0511632v1
2006/7/17,Magnetic transition and magnetic structure of Sr4Ru3O10,"We have investigated the magnetic transition and magnetic structure of
triple-layered ruthenate Sr4Ru3O10 directly using neutron scattering
techniques. Only one ferromagnetic phase is observed, and previously proposed
antiferromagnetic phase transitions are ruled out. The complex anisotropic
magnetotransport, magnetization and in-plane metamagnetic behaviors of this
quasi two-dimensional (2D) material are most likely due to magnetic domain
processes with strong magnetocrystalline anisotropy and a strongly anisotropic
demagnetization factor.",0607428v1
2009/8/21,Quantitative Observation of Magnetic Flux Distribution in New Magnetic Films for Future High Density Recording Media,"Off-axis electron holography was used to observe and quantify the magnetic
microstructure of a perpendicular magnetic anisotropic (PMA) recording media.
Thin foils of PMA materials exhibit an interesting up and down domain
configuration. These domains are found to be very stable and were observed at
the same time with their stray field, closing magnetic flux in the vacuum. The
magnetic moment can thus be determined locally in a volume as small as few tens
of cubic nanometers.",0908.3153v1
2010/8/5,Anisotropic magnetocaloric effect in all-ferromagnetic (La0.7Sr0.3MnO3/SrRuO3) superlattices,"We exploit the magnetic interlayer coupling in La0.7Sr0.3MnO3/SrRuO3
superlattices to realize a crossover between inverse and conventional magnetic
entropy changes. Our data reveal a strong anisotropic nature of the
magnetocaloric effect due to the magnetic anisotropy of the superlattice.
Therefore, artificial superlattices built from ferromagnetic materials that can
be used to alter the magnetic structure as well as the magnetic anisotropy,
could also be utilized for tuning the magnetocaloric properties, which may open
a constructive approach for magnetic refrigeration applications.",1008.1041v1
2013/1/7,Magnetic domain pattern in hierarchically twinned epitaxial Ni-Mn-Ga films,"Magnetic shape memory alloys exhibit a hierarchically twinned microstructure,
which has been well examined in epitaxial Ni-Mn-Ga films. Here we analyze
consequences of this twin within twins microstructure on the magnetic domain
pattern. Atomic and magnetic force microscopy are used to probe the correlation
between the martensitic microstructure and magnetic domains. We examine
consequences of different twin boundary orientations with respect to the
substrate normal as well as variant boundaries between differently aligned
twinned laminates. A detailed micromagnetic analysis is given which describes
the influence of the finite film thickness on the formation of magnetic band
domains in these multiferroic materials.",1301.1200v1
2013/9/9,Strain-induced magnetism in MoS2 monolayer with defects,"The strain-induced magnetism is observed in single-layer MoS2 with atomic
single vacancies from density functional calculations. Calculated magnetic
moment is no less than 2muB per vacancy defect. The straininduced band gap
closure is concurrent with the occurrence of the magnetism. Possible physical
mechanism of the emergence of strain-induced magnetism is illustrated. We also
demonstrate the possibility to test the predicted magnetism in experiment. Our
study may provide an opportunity for the design of new type of memory-switching
or logic devices by using earth-rich nonmagnetic materials MoS2.",1309.2066v2
2014/6/14,Numerical Analysis of Magnetic Domain Energy System in Nano-scale Fe,"Magnetic materials generally construct magnetic domains in external field H.
These domain structures are changed with the field changes {\Delta}H
accompanying the Barkhausen effects. These phenomena are shown using Fe domain
energy systems composed of classical magnetic dipole moment interactions. The
magnetization curves are created with terraces and jumps, where the flux
structure changes produce the Barkhausen noise. The terraces indicate the
delays of the magnetization processes for the field H. These numerical
simulations are performed in Fe nano-scale regular lattice systems of rods and
belts, which directly show the evidences of these basic phenomena.",1406.3690v1
2015/9/2,Elastic scattering of electron vortex beams in magnetic matter,"Elastic scattering of electron vortex beams on magnetic materials leads to a
weak magnetic contrast due to Zeeman interaction of orbital angular momentum of
the beam with magnetic fields in the sample. The magnetic signal manifests
itself as a redistribution of intensity in diffraction patterns due to a change
of sign of the orbital angular moment. While in the atomic resolution regime
the magnetic signal is most likely under the detection limits of present
transmission electron microscopes, for electron probes with high orbital
angular momenta, and correspondingly larger spatial extent, its detection is
predicted to be feasible.",1509.00744v2
2016/4/29,Ferroelectrics Manipulate Magnetic Bloch Skyrmions in a Composite Bilayer,"Theoretical investigation demonstrates that the composite bilayer (i.e.,
chiral-magnetic/ferroelectric bilayer) offers the possibility of
electric-induced magnetic Skyrmions [Phys. Rev. B \textbf{94}, 014311 (2016)].
In this Article, we propose a micromagnetic model to physically manipulate
magnetic Bloch Skyrmions propagating in a chiral-magnetic thin film with a
polarized ferroelectric essential to drive the system through the converse
magnetoelectric effect. Effects caused by different velocities of the
propagation, sizes of the thin film, and strength of the magnetoelectric
couplings strongly impact on quality and quantity of the magnetic Skyrmions.",1604.08780v2
2018/6/11,Crystal fields and Kondo effect: Magnetic susceptibility of Cerium ions in axial crystal fields,"The thermodynamic Bethe ansatz equations of the Coqblin-Schrieffer model have
been solved numerically. The full N=6 (J=5/2) degeneracy of the Hund's rule
ionic ground state of Ce is taken into account. Results for the temperature
dependent magnetic susceptibility parallel and perpendicular to the crystal
axis are presented. The deviations, due to the Kondo effect, to the
non-interacting ion results are pointed out.",1806.04177v2
2018/7/21,Quantum oscillations of the Stoner susceptibility: theory,"Oscillatory effects in magnetic susceptibility of free electrons in a strong
magnetic field is well known phenomenon and is well captured by
Lifshitz-Kosevich formula. In this paper we point out similar oscillatory
effects in Stoner susceptibility which makes the system to oscillate between
paramagnetic phase and ferromagnetic phase alternatively as a function of
external magnetic field strength. This effect can happen in a material which is
tuned near to its magnetic instability. We suggest an experimental set-up to
observe this effect. We also suggest that our result can be exploited to
control a quantum critical system around its quantum critical point to study
its thermodynamical or transport properties.",1807.08128v1
2018/10/29,A Spin Glass State in Ba3TiRu2O9,"The magnetic properties of Ba3TiRu2O9 , whose crystal structure is based on
stacked triangular planar lattices of MO6 dimers and single MO6 octahedra, are
reported. The system is magnetically disturbed by a substantial amount of Ti/Ru
chemical disorder. The Weiss temperature and effective magnetic moment were
found to be -29.5 K and 1.82 {\mu}B/f.u. respectively, and a bifurcation in the
zero field cooled and field cooled magnetic susceptibility is observed below
4.7 K, suggesting that this is a compositionally-disordered spin-glass system.
The material is a semiconductor with an activation energy for charge transport
of approximately 0.14 eV.",1810.12151v1
2019/9/6,Families of magnetic semiconductors -- an overview,"The interplay of magnetic and semiconducting properties has been in the focus
since more than a half of the century. In this introductory article we briefly
review the key properties and functionalities of various magnetic semiconductor
families, including europium chalcogenides, chromium spinels, dilute magnetic
semiconductors, dilute ferromagnetic semiconductors and insulators, mentioning
also sources of non-uniformities in the magnetization distribution, accounting
for an apparent high Curie temperature ferromagnetism in many systems. Our
survey is carried out from today's perspective of ferromagnetic and
antiferromagnetic spintronics as well as of the emerging fields of magnetic
topological materials and atomically thin 2D layers.",1909.02999v1
2021/5/20,MagneticTB: A package for tight-binding model of magnetic and non-magnetic materials,"We present a Mathematica program package MagneticTB, which can generate the
tight-binding model for arbitrary magnetic space group. The only input
parameters in MagneticTB are the (magnetic) space group number and the orbital
information in each Wyckoff positions. Some useful functions including getting
the matrix expression for symmetry operators, manipulating the energy band
structure by parameters and interfacing with other software are also developed.
MagneticTB can help to investigate the physical properties in both magnetic and
non-magnetic system, especially for topological properties.",2105.09504v1
2019/11/8,Magnetic i-MXene: a new class of multifunctional two-dimensional materials,"Based on density functional theory calculations, we investigated the
two-dimensional in-plane ordered MXene (i-MXenes), focusing particularly on the
magnetic properties. It is observed that robust two-dimensional magnetism can
be achieved by alloying nonmagnetic MXene with magnetic transition metal atoms.
Moreover, both the magnetic ground states and the magnetocrystalline anisotropy
energy of the i-MXenes can be effectively manipulated by strain, indicating
strong piezomagnetic effect. Further studies on the transport properties reveal
that i-MXenes provide an interesting playground to realize large thermoelectric
response, antiferromagnetic topological insulator, and spin-gapless
semiconductors. Thus, i-MXenes are a new class of multifunctional
two-dimensional magnetic materials which are promising for future spintronic
applications.",1911.03470v1
2019/11/29,Magnetic orders induced by RKKY interaction in Tsai-type quasicrystalline approximant Au-Al-Gd,"Recent experimental study on Tsai-type quasicrystalline approximant Au-Al-Gd
has revealed the presence of magnetic orders and phase transitions with
changing the Au/Al concentration. Motivated by the experiment, we theoretically
investigate whether a successive change of magnetic orders occurs in a minimal
magnetic model including the RKKY interaction only. We find that the model
induces multifarious magnetic orders depending on the Fermi wavenumber and
gives a good starting point for understanding the experimental observation. In
addition, we predict the presence of an undiscovered novel magnetic order
called cuboc order at large Fermi wavenumber region.",1911.12952v1
2023/5/4,Electric-field-induced formation and annihilation of skyrmions in two-dimensional magnet,"Electric manipulation of skyrmions in 2D magnetic materials has garnered
significant attention due to the potential in energy-efficient spintronic
devices. In this work, using first-principles calculations and Monte Carlo
simulations, we report the electric-field-tunable magnetic skyrmions in
MnIn2Te4 monolayer. By adjusting the magnetic parameters, including the
Heisenberg exchange interaction, DMI, and MAE, through applying an electric
field, the formation or annihilation of skyrmions can be achieved. Our work
suggests a platform for experimental realization of the electric-field-tunable
magnetic skyrmions in 2D magnets.",2305.02520v1
2023/11/22,Nonrelaxational FMR peak broadening in spatially inhomogeneous films,"The modification of magnetic properties in spatially inhomogeneous epitaxial
films of magnetic shape memory alloys in martensitic state with the temperature
variation has been studied. The proposed theoretical model is based on Landau
theory of martensitic transformation and statistical model of martensitic
state. It was shown that that spatial inhomogeneity of the material leads to
the dispersion of local martensitic transformation temperatures resulting in
the variation of local magnetic anisotropy values. This model allows describing
the dramatic ferromagnetic resonance line broadening observed in the
experiments in epitaxial films of magnetic shape memory alloys at low
temperatures.",2311.13733v1
2004/1/9,Thermal Spin Valves,"The ability of an insulating solid to conduct heat is rarely effected by the
application of a magnetic field. We have found, however, that the low
temperature heat conduction of some solids increases by more than a factor of
two with the application of a modest magnetic field. The effect occurs in
low-dimensional magnetically ordered materials when a small gap, \delta, in the
acoustic magnon (spin wave) spectra is closed using a magnetic field H >
\delta/g\mu_B. Since all magnetically ordered materials must have a gap in the
magnon spectra for magnons with k = 0, this may be a very general effect. Extra
heat is carried through the solid only when the magentic field exceeds the
critical value (H > \delta/g\mu_B). At this critical field the tiny atomic
magnets in the solid abruptly change the direction they point which results in
more heat flowing through the material. The magnetic field thus acts as a heat
switch. We have observed this effect in three quite different magnetically
ordered materials: K_2V_3O_8, Nd_2CuO_4 and Pr_2CuO_4. Several possible
explanations for these effects will be discussed.",0401154v1
2005/4/18,Epitaxial self-organization: from surfaces to magnetic materials,"Self-organization of magnetic materials is an emerging and active field. An
overview of the use of self-organization for magnetic purposes is given, with a
view to illustrate aspects that cannot be covered by lithography. A first set
of issues concerns the quantitative study of low-dimensional magnetic phenomena
(1D and 0D). Such effects also occur in microstructured and
lithographically-patterned materials but cannot be studied in these because of
the complexity of such materials. This includes magnetic ordering, magnetic
anisotropy and superparamagnetism. A second set of issues concerns the
possibility to directly use self-organization in devices. Two sets of examples
are given: first, how superparamagnetism can be fought by fabricating thick
self-organized structures, and second, what new or improved functionalities can
be expected from self-organized magnetic systems, like the tailoring of
magnetic anisotropy or controlled dispersion of properties.",0504424v1
2007/8/10,"Structural Characterization of Magnetic Nano-particles Suspensions, Using Magnetic Measurements","The paper describes some characteristics of the ""P"" curves for structural
characterization of magnetic nano-particles suspensions (complex fluids,
complex powders, complex composite materials, or living biological materials
having magnetic properties). In the case of these materials, the magnetic
properties are conferred to various carrier liquids by artificially integrating
in their structure ferromagnetic particles of different sizes. The magnetic
properties are usually shown by the hysteresis curve. The structure can be seen
on (electronic) micrography. The P curves offer another possibility to
determine the structure of the magnetic component of a complex fluid by
numerical analysis of the magnetization curve experimentally obtained. The
paper presents a detailed approach of the P curves and some limitations in
their use.",0708.1462v1
2014/6/24,Magnetomechanical response of bilayered magnetic elastomers,"Magnetic elastomers are appealing materials from an application point of
view: they combine the mechanical softness and deformability of polymeric
substances with the addressability by external magnetic fields. In this way,
mechanical deformations can be reversibly induced and elastic moduli can be
reversibly adjusted from outside. So far, mainly the behavior of
single-component magnetic elastomers and ferrogels has been studied. Here, we
go one step further and analyze the magnetoelastic response of a bilayered
material composed of two different magnetic elastomers. It turns out that,
under appropriate conditions, the bilayered magnetic elastomer can show a
strongly amplified deformational response in comparison to a single-component
material. Furthermore, a qualitatively opposite response can be obtained, i.e.\
a contraction along the magnetic field direction (as opposed to an elongation
in the single-component case). We hope that our results will further stimulate
experimental and theoretical investigations directly on bilayered magnetic
elastomers, or, in a further hierarchical step, on bilayered units embedded in
yet another polymeric matrix.",1406.6412v1
2015/1/4,Effect of the double-counting functional on the electronic and magnetic properties of half-metallic magnets using the GGA+U method,"Methods based on the combination of the usual density functional theory (DFT)
codes with the Hubbard models are widely used to investigate the properties of
strongly correlated materials. Using first-principle calculations we study the
electronic and magnetic properties of 20 half-metallic magnets performing
self-consistent GGA+U calculations using both the atomic-limit (AL) and
around-mean-field (AMF) functionals for the double counting term, used to
subtract the correlation part from the DFT total energy, and compare these
results to the usual generalized-gradient-approximation (GGA) calculations.
Overall the use of AMF produces results similar to the GGA calculations. On the
other hand the effect of AL is diversified depending on the studied material.
In general the AL functional produces a stronger tendency towards magnetism
leading in some cases to unphysical electronic and magnetic properties. Thus
the choice of the adequate double-counting functional is crucial for the
results obtained using the GGA+U method.",1501.00732v1
2016/10/3,"Synthesis, structure and magnetism of the new $S=\frac{1}{2}$ kagome magnet NH$_4$Cu$_{2.5}$V$_2$O$_7$(OH)$_2$.H$_2$O","The study of quantum spin-liquid states (QSL) with lattice dimension $>1$ has
proven an enduring problem in solid state physics. Key candidate materials are
the $S=\frac{1}{2}$ kagome magnets due to their ability to host quantum
fluctuations within the high degeneracy of their frustrated geometries. Studies
of an increasing library of known $S=\frac{1}{2}$ kagome magnetic materials has
challenged our understanding of the possible QSL states, for example, the
recent discovery of a chiral spin-liquid ground state in kapellasite showed
that even magnets with ferromagnetic nearest-neighbour exchange are not
necessarily trivial and that QSL states beyond the superposition of simple
singlet are possible.
  Here, we outline the synthesis, structure and preliminary magnetic
characterisation of a candidate QSL material, the $S=\frac{1}{2}$ kagome magnet
NH$_4$Cu$_{2.5}$V$_2$O$_7$(OH)$_2$.H$_2$O. The crystal structure of
NH$_4$Cu$_{2.5}$V$_2$O$_7$(OH)$_2$.H$_2$O has the 3-fold symmetry of a
geometrically `perfect' kagome lattice while the magnetism shows a competition
between ferromagnetic and antiferromagnetic characters reminiscent of
kapellasite.",1610.00498v1
2017/3/8,"Interplay of Dirac electrons and magnetism in AMnBi2 (A=Ca, Sr)","Dirac materials exhibit intriguing low-energy carrier dynamics that offer a
fertile ground for novel physics discovery. Of particular interest is the
interplay of Dirac carriers with other quantum phenomena, such as magnetism.
Here we report on a two-magnon Raman scattering study of AMnBi2 (A=Ca, Sr), a
prototypical magnetic Dirac system comprising alternating Dirac-carrier and
magnetic layers. We present the first accurate determination of the exchange
energies in these compounds and, by comparison to the reference compound
BaMn2Bi2, we show that the Dirac-carrier layers in AMnBi2 significantly enhance
the exchange coupling between the magnetic layers, which in turn drives a
charge-gap opening along the Dirac locus. Our findings break new grounds in
unveiling the fundamental physics of magnetic Dirac materials, which offer a
novel platform for probing a distinct type of spin-Fermion interaction. The
outstanding properties of these materials allow a delicate manipulation of the
interaction between the Dirac carriers and magnetic moments, thus holding great
promise for applications in magnetic Dirac devices.",1703.02712v1
2018/2/20,Controlling magnetism in 2D CrI3 by electrostatic doping,"The atomic thickness of two-dimensional (2D) materials provides a unique
opportunity to control material properties and engineer new functionalities by
electrostatic doping. Electrostatic doping has been demonstrated to tune the
electrical and optical properties of 2D materials in a wide range, as well as
to drive the electronic phase transitions. The recent discovery of atomically
thin magnetic insulators has opened up the prospect of electrical control of
magnetism and new devices with unprecedented performance. Here we demonstrate
control of the magnetic properties of monolayer and bilayer CrI3 by
electrostatic doping using a dual-gate field-effect device structure. In
monolayer CrI3, doping significantly modifies the saturation magnetization,
coercive force and Curie temperature, showing strengthened (weakened) magnetic
order with hole (electron) doping. Remarkably, in bilayer CrI3 doping
drastically changes the interlayer magnetic order, causing a transition from an
antiferromagnetic ground state in the pristine form to a ferromagnetic ground
state above a critical electron density. The result reveals a strongly
doping-dependent interlayer exchange coupling, which enables robust switching
of magnetization in bilayer CrI3 by small gate voltages.",1802.07355v1
2019/11/7,"Additive manufactured isotropic NdFeB magnets by stereolithography, fused filament fabrication, and selective laser sintering","Magnetic isotropic NdFeB powder is processed by the following additive
manufacturing methods: (i) stereolithography (SLA), (ii) fused filament
fabrication (FFF), and (iii) selective laser sintering (SLS). For the first
time, a stereolithography based method is used to 3D print hard magnetic
materials. FFF and SLA use a polymer matrix material as binder, SLS sinters the
powder directly. All methods use the same hard magnetic NdFeB powder material.
Complex magnets with small feature sizes in a superior surface quality can be
printed with SLA. The magnetic properties for the processed samples are
investigated and compared. SLA can print magnets with a remanence of 388 mT and
a coercivity of 0.923 T. A complex magnetic design for speed wheel sensing
applications is presented and printed with all methods.",1911.02881v1
2020/5/21,Antiferromagnet-semiconductor van der Waals heterostructures: interlayer interplay of exciton with magnetic ordering,"Van der Waals (vdW) heterostructures have attracted great interest because of
their rich material combinations.The discovery of two-dimensional magnets has
provided a new platform for magnetic vdW heterointerfaces; however, research on
magnetic vdW heterointerfaces has been limited to those with ferromagnetic
surfaces. Here we report a magnetic vdW heterointerface using layered
intralayer-antiferromagnetic MPSe3 (M=Mn, Fe) and monolayer transition metal
dichalcogenides (TMDs). We found an anomalous upshift of the excitonic peak in
monolayer TMDs below the antiferromagnetic transition temperature in the MPSe3,
capturing a signature of the interlayer exciton-magnon coupling. This is a
concept extended from single materials to heterointerfaces. Moreover, this
coupling strongly depends on the in-plane magnetic structure and stacking
direction, showing its sensitivity to their magnetic interfaces. Our finding
offers an opportunity to investigate interactions between elementary
excitations in different materials across interfaces and to search for new
functions of magnetic vdW heterointerfaces.",2005.10727v1
2021/7/10,Multi-Material Topology Optimization with Continuous Magnetization Direction for Permanent Magnet Synchronous Reluctance Motors,"Permanent magnet-assisted synchronous reluctance motors (PMSynRM) have a
significantly higher average torque than synchronous reluctance motors. Thus,
determining an optimal design results in a multi-material topology optimization
problem, where one seeks to distribute ferromagnetic material, air and
permanent magnets within the rotor in an optimal manner. This study proposed a
novel density-based distribution scheme, which allows for continuous
magnetization direction instead of a finite set of angles. Thus, an
interpolation scheme is established between properties pertaining to magnets
and non-linear materials. This allows for new designs to emerge without
introducing complex geometric parameterization or relying on the user's biases
and intuitions. Toward reducing computation time, Nitsche-type mortaring is
applied, allowing for free rotation of the rotor mesh relative to the stator
mesh. The average torque is approximated using only four-point static
positions. This study investigates several interpolation schemes and presents a
new one inspired by the topological derivative. We propose to filter the final
design for the magnetization angle using K-mean clustering accounting for
technical feasibility constraints of magnets. Finally, the design of the
electrical motor is proposed to maximize torque value.",2107.04825v1
2022/1/10,Soft Magnetic Properties of Ultra-Strong and Nanocrystalline Pearlitic Wires,"The paper describes the capability of magnetic softening of a coarse grained
bulk material by a severe deformation technique. Connecting the microstructure
with magnetic properties, the coercive field decreases dramatically for grains
smaller than the magnetic exchange length. This makes the investigation of soft
magnetic properties of severely drawn pearlitic wires very interesting. With
the help of the starting two phase microstructure, it is possible to
substantially refine the material, which allows the investigation of magnetic
properties for nanocrystalline bulk material. Compared to the coarse grained
initial, pearlitic state, the coercivities of the highly deformed wires
decrease while the saturation magnetization values increase, even beyond the
value expectable from the individual constituents. The lowest coercivity in the
drawn state is found to be 520 A m for a wire of 24 um thickness and an
annealing treatment has a further positive effect on it. The decreasing
coercivity is discussed in the framework of two opposing models: grain
refinement on the one hand and dissolution of cementite on the other hand.
Auxiliary measurements give a clear indication for the latter model, delivering
a sufficient description of the observed evolution of magnetic properties.",2201.03302v1
2022/12/18,Intrinsic Magnetic Topological Materials,"Topological states of matter possess bulk electronic structures categorized
by topological invariants and edge/surface states due to the bulk-boundary
correspondence. Topological materials hold great potential in the development
of dissipationless spintronics, information storage, and quantum computation,
particularly if combined with magnetic order intrinsically or extrinsically.
Here, we review the recent progress in the exploration of intrinsic magnetic
topological materials, including but not limited to magnetic topological
insulators, magnetic topological metals, and magnetic Weyl semimetals. We pay
special attention to their characteristic band features such as the gap of
topological surface state, gapped Dirac cone induced by magnetization (either
bulk or surface), Weyl nodal point/line, and Fermi arc, as well as the exotic
transport responses resulting from such band features. We conclude with a brief
envision for experimental explorations of new physics or effects by
incorporating other orders in intrinsic magnetic topological materials.",2212.09057v1
2023/2/4,Tailoring magnetic hysteresis of Fe-Ni permalloy by additive manufacturing: Multiphysics-multiscale simulations of process-property relationships,"Designing the microstructure of Fe-Ni permalloy by additive manufacturing
(AM) opens new avenues to tailor the materials' magnetic properties. Yet,
AM-produced parts suffer from spatially inhomogeneous thermal-mechanical and
magnetic responses, which are less investigated in terms of process simulation
and modeling schemes. Here we present a powder-resolved multiphysics-multiscale
simulation scheme for describing magnetic hysteresis in materials produced via
AM. The underlying physical processes are explicitly considered, including the
coupled thermal-structural evolution, chemical order-disorder transitions, and
associated thermo-elasto-plastic behaviors. The residual stress is identified
as the key thread in connecting the physical processes and in-process phenomena
across scales. By employing this scheme, we investigate the dependence of the
fusion zone size, the residual stress and plastic strain, and the magnetic
hysteresis of AM-produced Fe21.5Ni78.5 permalloy on beam power and scan speed.
Simulation results also suggest a phenomenological relation between magnetic
coercivity and average residual stress, which can guide the magnetic hysteresis
design of soft magnetic materials by choosing appropriate AM-process
parameters.",2302.02217v1
2023/3/16,"Magnetic Electrides: High-Throughput Material Screening, Intriguing Properties, and Applications","Electrides are a unique class of electron-rich materials where excess
electrons are localized in interstitial lattice sites as anions, leading to a
range of unique properties and applications. While hundreds of electrides have
been discovered in recent years, magnetic electrides have received limited
attention, with few investigations into their fundamental physics and practical
applications. In this work, 51 magnetic electrides (12 antiferromagnetic, 13
ferromagnetic, and 26 interstitial-magnetic) were identified using
high-throughput computational screening methods and the latest Material Project
database. Based on their compositions, these magnetic electrides can be
classified as magnetic semiconductors, metals, or half-metals, each with unique
topological states and excellent catalytic performance for N2 fixation due to
their low work functions and excess electrons. The novel properties of magnetic
electrides suggest potential applications in spintronics, topological
electronics, electron emission, and as high-performance catalysts. This work
marks the beginning of a new era in the identification, investigation, and
practical applications of magnetic electrides.",2303.09226v1
2023/8/21,Coupling Between Magnetic and Transport Properties in Magnetic Layered Material Mn2-xZnxSb,"We synthesized single crystals for Mn2-xZnxSb and studied their magnetic and
electronic transport properties. This material system displays rich magnetic
phase tunable with temperature and Zn composition. In addition, two groups of
distinct magnetic and electronic properties, separated by a critical Zn
composition of x = 0.6, are discovered. The Zn-less samples are metallic and
characterized by a resistivity jump at the magnetic ordering temperature, while
the Zn-rich samples lose metallicity and show a metal-to-insulator
transition-like feature tunable by magnetic field. Our findings establish
Mn2-xZnxSb as a promising material platform that offers opportunities to study
how the coupling of spin, charge, and lattice degrees of freedom governs
interesting transport properties in 2D magnets, which is currently a topic of
broad interest.",2308.10764v1
2023/8/24,Highly efficient room-temperature nonvolatile magnetic switching by current in Fe3GaTe2 thin flakes,"Effectively tuning magnetic state by using current is essential for novel
spintronic devices. Magnetic van der Waals (vdW) materials have shown superior
properties for the applications of magnetic information storage based on the
efficient spin torque effect. However, for most of known vdW ferromagnets, the
ferromagnetic transition temperatures lower than room temperature strongly
impede their applications and the room-temperature vdW spintronic device with
low energy consumption is still a long-sought goal. Here, we realize the highly
efficient room-temperature nonvolatile magnetic switching by current in a
single-material device based on vdW ferromagnet Fe3GaTe2. Moreover, the
switching current density and power dissipation are about 300 and 60000 times
smaller than conventional spin-orbit-torque devices of magnet/heavymetal
heterostructures. These findings make an important progress on the applications
of magnetic vdW materials in the fields of spintronics and magnetic information
storage.",2308.12710v1
2023/8/28,Linearizing Anhysteretic Magnetization Curves: A Novel Algorithm for Finding Simulation Parameters and Magnetic Moments,"This paper proposes a new method for determining the simulation parameters of
the Jiles-Atherton Model used to simulate the first magnetization curve and
hysteresis loop in ferromagnetic materials. The Jiles-Atherton Model is an
important tool in engineering applications due to its relatively simple
differential formulation. However, determining the simulation parameters for
the anhysteretic curve is challenging. Several methods have been proposed,
primarily based on mathematical aspects of the anhysteretic and first
magnetization curves and hysteresis loops. This paper focuses on finding the
magnetic moments of the material, which are used to define the simulation
parameters for its anhysteretic curve. The proposed method involves using the
susceptibility of the material and a linear approximation of a paramagnet to
find the magnetic moments. The simulation parameters can then be found based on
the magnetic moments. The method is validated theoretically and experimentally
and offers a more physical approach to finding simulation parameters for the
anhysteretic curve and a simplified way of determining the magnetic moments of
the material.",2308.14573v1
2023/8/29,Layer-dependent magnetism and spin fluctuations in atomically thin van der Waals magnet CrPS4,"van der Waals (vdW) magnets, an emerging family of two-dimensional (2D)
materials, have received tremendous attention due to their rich fundamental
physics and significant potential for cutting-edge technological applications.
In contrast to the conventional bulk counterparts, vdW magnets exhibit
significant tunability of local material properties, such as stacking
engineered interlayer coupling and layer-number dependent magnetic and
electronic interactions, which promise to deliver previously unavailable merits
to develop multifunctional microelectronic devices. As a further ingredient of
this emerging topic, here we report nanoscale quantum sensing and imaging of
atomically thin vdW magnet chromium thiophosphate CrPS4, revealing its
characteristic layer-dependent 2D static magnetism and dynamic spin
fluctuations. We also show a large tunneling magnetoresistance in CrPS4-based
spin filter vdW heterostructures. The excellent material stability, robust
strategy against environmental degradation, in combination with tailored
magnetic properties highlight the potential of CrPS4 in developing
state-of-the-art 2D spintronic devices for next-generation information
technologies.",2308.15396v1
2023/10/30,Computational Design of Magnetic Soft Shape-Forming Catheters using the Material Point Method,"Magnetic Soft Catheters (MSCs) are capable of miniaturization due to the use
of an external magnetic field for actuation. Through careful design of the
magnetic elements within the MSC and the external magnetic field, the shape
along the full length of the catheter can be precisely controlled. However,
modeling of the magnetic-soft material is challenging due to the complex
relationship between magnetic and elastic stresses within the material.
Approaches based on traditional Finite Element Methods (FEM) lead to high
computation time and rely on proprietary implementations. In this work, we
showcase the use of our recently presented open-source simulation framework
based on the Material Point Method (MPM) for the computational design of
magnetic soft catheters to realize arbitrary shapes in 3D, and to facilitate
follow-the-leader shape-forming insertion.",2310.19983v1
2023/1/21,Hard Ferromagnets as a New Perspective on Materials for Thermomagnetic Power Generation Cycles,"We consider the ways in which magnetically hard materials can be used as the
working materials in thermomagnetic power generation (TMG) cycles in order to
expand the area in the magnetisation vs. applied field ($M-H$) plane available
for energy conversion. There are 3 parts to this Perspective. First,
experiments on commercially available hard ferrites reveal that, while these
materials are not yet good TMG candidates, hard ferromagnets with higher
thermal conductivity and a greater change of magnetization with temperature
could outperform existing TMG materials. Second, computational results indicate
that biasing a soft magnet with a hard ferromagnet is essentially equivalent to
shifting the $M-H$ loop by an amount proportional to the field of the biasing
magnet. Work outputs under biased conditions show a substantial improvement
over unbiased cycles, but experimental verification is needed. Third, we
discuss the rationale for exploring artificial spin reorientation materials as
novel TMG working materials.",2301.08854v1
2006/5/19,Correlation length and negative phase velocity in isotropic dielectric-magnetic materials,"A composite material comprising randomly distributed spherical particles of
two different isotropic dielectric-magnetic materials is homogenized using the
second-order strong-property-fluctuation theory in the long-wavelength
approximation. Whereas neither of the two constituent materials by itself
supports planewave propagation with negative phase velocity (NPV), the
homogenized composite material (HCM) can. The propensity of the HCM to support
NPV propagation is sensitive to the distributional statistics of the
constituent material particles, as characterized by a two--point covariance
function and its associated correlation length. The scope for NPV propagation
diminishes as the correlation length increases.",0605166v1
1998/2/25,Magnetization Controlled Superconductivity in a Film with Magnetic Dots,"We consider a superconducting film with Magnetic Dots Array (MDA) placed on
it. Magnetic moments of these dots are supposed to be normal to the film and
strong enough to create vortices in the superconducting film. Magnetic
interaction between dots is negligible. Below the superconducting transition
temperature of the film in zero magnetic field the MDA with randomly magnetized
dots produces resistive state of the film. Paradoxically, in a finite magnetic
field the film with MDA is superconductive.",9802276v1
2003/7/8,Asymmetric Lineshape due to Inhomogeneous Broadening of the Crystal-Field Transitions in Mn12ac Single Crystals,"The lineshape of crystal-field transitions in single crystals of Mn12ac
molecular magnets is determined by the magnetic history. The absorption lines
are symmetric and Gaussian for the non-magnetized state obtained by zero-field
cooling (zfc). In the magnetized state which is reached when the sample is
cooled in a magnetic field (fc), however, they are asymmetric even in the
absence of an external magnetic field. These observations are quantitatively
explained by inhomogeneous symmetrical (Gaussian) broadening of the
crystal-field transitions combined with a contribution of off-diagonal
components of the magnetic susceptibility to the effective magnetic
permeability.",0307164v1
2005/1/17,Frustration effects in magnetic molecules,"By means of exact diagonalization we study the ground-state and the
low-temperature physics of the Heisenberg antiferromagnet on the cuboctahedron
and the icosidodecahedron. Both are frustrated magnetic polytopes and
correspond to the arrangement of magnetic atoms in the magnetic molecules
Cu12La8 and Mo72Fe30. The interplay of strong quantum fluctuations and
frustration influences the ground state spin correlations drastically and leads
to an interesting magnetization process at low temperatures. Furthermore the
frustration yields low-lying non-magnetic excitations resulting in an extra
low-temperature peak in the specific heat.",0501376v1
2005/10/18,Local field of magnetic islands: role of their shape,"I analyze in details distribution of local magnetic field induced by micro-
and nano-magnets. I consider three kinds of elongated magnetic islands:
ellipse-, diamond- and rectangular shaped islands which were magnetized
uniformly along long axis. This report concentrates on the role of their shape
upon distribution of the field. Calculations show that unlike
rectangular-shaped magnet, ellipse-shaped and diamond-shaped ones produce much
more localized field in proximity of its magnetic poles. Additionally in the
case of ellipse-shaped islands the magnitude of induced field is large. This
two facts favor arrays of ellipse-shaped magnetic islands to build
zero-dimensional spin traps in a hybrid based on Ferromagnet/Semiconductor
structure.",0510486v1
2006/4/1,Magnetization reversal through synchronization with a microwave,"Based on the Landau-Lifshitz-Gilbert equation, it can be shown that a
circularly-polarized microwave can reverse the magnetization of a Stoner
particle through synchronization. In comparison with magnetization reversal
induced by a static magnetic field, it can be shown that when a proper
microwave frequency is used the minimal switching field is much smaller than
that of precessional magnetization reversal. A microwave needs only to overcome
the energy dissipation of a Stoner particle in order to reverse magnetization
unlike the conventional method with a static magnetic field where the switching
field must be of the order of magnetic anisotropy.",0604013v1
2006/5/1,Possible magnetic-field-induced voltage and thermopower in diluted magnetic semiconductors,"In diluted magnetic semiconductors, the carrier concentration and the
magnetization of local moments are strongly coupled, since the magnetic
interaction is mediated by the carriers. It is predicted that this coupling
leads to an electric polarization due to an applied magnetic-field gradient and
to the appearance of a magnetic-field-dependent voltage. An expression for this
voltage is derived within Landau theory and its magnitude is estimated for
(Ga,Mn)As. Furthermore, a large contribution to the thermopower based on the
same mechanism is predicted. The role of fluctuations is also discussed. These
predictions hold both if the magnetization is uniform and if it shows
stripe-like modulations, which are possible at lower temperatures.",0605043v1
2012/1/4,Origin of training effect of exchange bias in Co/CoO due to irreversible thermoremanent magnetization of the magnetically diluted antiferromagnet,"The irreversible thermoremanent magnetization of a sole, magnetically diluted
epitaxial antiferromagnetic Co$_{1-y}$O(100) layer is determined by the mean of
its thermoremanent magnetizations at positive and negative remanence. During
hysteresis-loop field cycling, thermoremanent magnetization exhibits successive
reductions, consistent with the training effect (TE) of the exchange bias
measured for the corresponding Co$_{1-y}$O(100)/Co bilayer. The TE of exchange
bias is shown to have its microscopic origin in the TE of the irreversible
thermoremanent magnetization of the magnetically diluted AFM.",1201.0831v1
2012/7/10,Micromagnetic simulation of magnetic small-angle neutron scattering from two-phase nanocomposites,"The recent development of a micromagnetic simulation methodology - suitable
for multiphase magnetic nanocomposites - permits the computation of the
magnetic microstructure and of the associated magnetic small-angle neutron
scattering (SANS) cross section of these materials. In this review article we
summarize results on the micromagnetic simulation of magnetic SANS from
two-phase nanocomposites. The decisive advantage of this approach resides in
the possibility to srutinize the individual magnetization Fourier contributions
to the total magnetic SANS cross section, rather than their sum, which is
generally obtained from experiment. The procedure furnishes unique and
fundamental information regarding magnetic neutron scattering from nanomagnets.",1207.2331v1
2013/4/10,A proposed new route to d0 magnetism in semiconductors,"Here we propose to induce magnetism in semiconductor utilizing the unique
properties of the interstitial defect to act as the magnetic impurity within
the alpha-PbO crystal structure. The Pbi interstitial generates the p-localized
state with two on-site electrons to obey the Hund's rule for their ordering. It
is demonstrated that instead of Pb interstitial other non-magnetic impurities
of s^2p^{x} outer shell configuration can be applied to induce d0 magnetism
with possibility to tune the local magnetic moments mu_B by varying a number of
electrons 1< x< 3. The magnetic coupling between such defects is found to be
driven by the long-range order interactions that in combination with high
defect solubility promises the magnetic percolation to remain above the room
temperature.",1304.2945v1
2013/10/23,Magnetization Characteristic of Ferromagnetic Thin Strip by Measuring Anisotropic Magnetoresistance and Ferromagnetic Resonance,"The magnetization characteristic in a permalloy thin strip is investigated by
electrically measuring the anisotropic magnetoresistance and ferromagnetic
resonance in in-plane and out-of-plane configurations. Our results indicate
that the magnetization vector can rotate in the film plane as well as out of
the film plane by changing the intensity of external magnetic field of certain
direction. The magnetization characteristic can be explained by considering
demagnetization and magnetic anisotropy. Our method can be used to obtain the
demagnetization factor, saturated magnetic moment and the magnetic anisotropy.",1310.6117v1
2015/5/13,Optical detection of magnetic orders in HgCr$_2$O$_4$ frustrated spin magnet under pulsed high magnetic fields,"A magneto-optical survey was conducted for HgCr$_2$O$_4$ powder samples under
pulsed high magnetic fields of up to 55 T. Intensity changes in magnetic fields
observed for the exciton-magnon-phonon optical transition spectra coincide well
with those of magnetization, lattice distortion from X-ray diffraction, and
electron-magnetic resonances. The last-ordered phase was detected prior to the
fully polarized magnetic phase, similarly to the other chromium spinel oxide,
ZnCr$_2$O$_4$ and CdCr$_2$O$_4$.",1505.03216v1
2018/1/9,Magneto-electric effect in doped magnetic ferroelectrics,"We propose a model of magneto-electric effect in doped magnetic
ferroelectrics. This magneto-electric effect does not involve the spin-orbit
coupling and is based purely on the Coulomb interaction. We calculate magnetic
phase diagram of doped magnetic ferroelectrics. We show that magneto-electric
coupling is pronounced only for ferroelectrics with low dielectric constant. We
find that magneto-electric coupling leads to modification of magnetization
temperature dependence in the vicinity of ferroelectric phase transition. A
peak of magnetization appears. We find that magnetization of doped magnetic
ferroelectrics strongly depends on applied electric field.",1801.03114v1
2018/3/3,Long Range Magnetic order stabilized by acceptors,"Tuning magnetic order in magnetic semiconductors is a long sought goal. A
proper concentration of acceptors can dramatically suppress local magnetic
order in favor of the long one. Using Mn and an acceptor codoped LiZnAs as an
example, we demonstrate, by first-principles calculation, the emergence of a
long-range magnetic order. This intriguing phenomenon can be understood from an
interplay between an acceptor-free magnetism and a band coupling magnetism. Our
observation thus lays the ground for a precise control of the magnetic order in
future spintronic devices.",1803.01179v1
2018/5/24,Searching the weakest link: Demagnetizing fields and magnetization reversal in permanent magnets,"Magnetization reversal in permanent magnets occurs by the nucleation and
expansion of reversed domains. Micromagnetic theory offers the possibility to
localize the spots within the complex structure of the magnet where
magnetization reversal starts. We compute maps of the local nucleation field in
a Nd2Fe14B permanent magnet using a model order reduction approach. Considering
thermal fluctuations in numerical micromagnetics we can also quantify the
reduction of the coercive field due to thermal activation. However, the major
reduction of the coercive field is caused by the soft magnetic grain boundary
phases and misorientation if there is no surface damage.",1805.09798v1
2021/6/1,Impact of magnetic domains on magnetic flux concentrators,"The impact of magnetic domains in magnetic flux concentrators is studied
using the simulation software MuMax3. First, the simulation parameters are
validated using experimental results from magnetic force microscopy; second the
simulation output is benchmarked with the one obtained using Comsol
Multiphysics. Finally, the impact of magnetic domain is assessed, showing how
micromagnetic effects can become relevant, if not dominant, when scaling the
gap between the MFC and the sensor.",2106.00370v2
2019/1/7,Unconventional magnetization textures and domain-wall pinning in Sm-Co magnets,"The most powerful magnets for high temperature applications are Sm-Co-based
alloys with a microstructure that combines magnetically soft and hard regions.
The microstructure consists of a dense domain-wall-pinning network that endows
the material with remarkable magnetic hardness. A precise understanding of the
coupling between magnetism and microstructure is essential for enhancing the
performance of Sm-Co magnets, but experiments and theory have not yet converged
to a unified model. Here, we combine transmission electron microscopy, atom
probe tomography, and nanometer-resolution off-axis electron holography with
micromagnetic simulations to show that the magnetization processes in Sm-Co
magnets result from an interplay between curling instabilities and pinning
effects at the intersections between magnetically soft and hard regions. We
also find that topologically non-trivial magnetic domains separated by a
complex network of domain walls play a key role in the magnetic state. Our
findings reveal a previously hidden aspect of magnetism and provide insight
into the full potential of high-performance magnetic materials.",1901.01922v3
2022/7/14,UI$_3$ -- 5f-electron magnetic van der Waals material,"We grew high-quality single crystals of the 5f electron van der Waals
compound UI$_3$ and investigated them by measurements of specific heat and
magnetization as functions of temperature and magnetic field. UI$_3$ behaves as
an antiferromagnet with a first-order magnetic phase transition at the Ne\'el
temperature $T_N$ = 2.65 K. It is characterized by a sharp symmetric
specific-heat peak which is gradually shifted to lower temperatures by
increasing magnetic field applied along either the a- or b-axis. The behavior
in magnetic fields reveals orthorhombic magnetocrystalline anisotropy with the
hard magnetization direction along the c-axis. The 2-K a- and b-axis
magnetization curves exhibit a metamagnetic transition at the critical field
$H_c$ = 3 T and 1.8 T, respectively. In higher fields, when the long-range
antiferromagnetism is suppressed by a metamagnetic transition, signs of
short-range magnetic ordering of antiferromagnetic correlations in the
paramagnetic state show up both in specific heat and magnetization. The
anomalous S-shape field dependence of a-axis magnetization well above $H_c$ can
be understood as the crossover from the correlated paramagnetic regime to the
high-field polarized paramagnet. The magnetic phase diagrams for the magnetic
field applied along the a- and b-axis, respectively, designed using the
mentioned experimental results are presented. We have also found that the
UI$_3$ crystals are easily cleavable which predisposes this material for direct
investigation of 5f electron magnetism in the 2D limit on exfoliated atomically
thin samples.",2207.06880v1
2023/6/13,Imaging magnetism evolution of magnetite to megabar pressure range with quantum sensors in diamond anvil cell,"High-pressure diamond anvil cells have been widely used to create novel
states of matter. Nevertheless, the lack of universal in-situ magnetic
measurement techniques at megabar pressures makes it difficult to understand
the underlying physics of materials' behavior at extreme conditions, such as
high-temperature superconductivity of hydrides and the formation or destruction
of the local magnetic moments in magnetic systems, etc. Here we break through
the limitations of pressure on quantum sensors and develop the in-situ magnetic
detection technique at megabar pressures with high sensitivity
(~1{\mu}T/Hz^(1\2)) and sub-microscale spatial resolution. By directly imaging
the magnetic field and the evolution of magnetic domains, we observe the
macroscopic magnetic transition of Fe3O4 in the megabar pressure range from
strong ferromagnetism ({\alpha}-Fe3O4) to weak ferromagnetism ({\beta}-Fe3O4)
and finally to non-magnetism ({\gamma}-Fe3O4). The scenarios for magnetic
changes in Fe3O4 characterized here shed light on the direct magnetic
microstructure observation in bulk materials at high pressure and contribute to
understanding the mechanism of magnetic moment suppression related to spin
crossover. The presented method can potentially investigate the spin-orbital
coupling and magnetism-superconductivity competition in magnetic systems.",2306.07840v1
2022/5/12,Remarkably strong magnetic response in molecules with polar groups,"For more than a century, electricity and magnetism have been believed to
always exhibit inextricable link due to the symmetry in electromagnetism. At
the interface, polar groups that have polar charges, are indispensable to be
considered, which interact directly with other polar charges/external
charges/external electric fields. However, there is no report on the
corresponding magnetic properties on these polar groups. Clearly, such
asymmetry, that is, only the interaction between the polar groups and charges,
is out of bounds. Here we show that those molecules with considerable polar
groups, such as cellulose acetate (CA) and other cellulose derivatives with
different polar groups, can have strong magnetic response, indicating that they
are strongly paramagnetic. Density functional theory (DFT) calculation shows
that the polarity greatly reduces the excitation energy from the state without
net spin (singlet) to the state with net spin (triplet), making the
considerable existence of magnetic moments on the polar groups. We note that
the hydrophobic groups in these molecules have no magnetic moments, however,
they make the molecules aggregate to amply the magnetic effect of the magnetic
moments in the polar groups, so that these magnetic moments can induce the
strong paramagnetism. Our observations suggest a recovery of the symmetry with
inextricable link between the electricity and magnetism at the interface. The
findings leave many imaginations of the role of the magnetic interaction in
biological systems as well as other magnetic applications considering that many
of those polar materials are biological materials, pharmaceutical materials,
chemical raw materials, and even an essential hormone in agricultural
production.",2205.05917v1
2022/4/22,"Magnetic band representations, Fu-Kane-like symmetry indicators and magnetic topological materials","To realize novel topological phases and to pursue potential applications in
low-energy consumption spintronics, the study of magnetic topological materials
is of great interest. Starting from the theory of nonmagnetic topological
quantum chemistry [Bradlyn et al., Nature 547, 298 (2017)], we have obtained
irreducible (co)representations and compatibility relations (CRs) in momentum
space, and we constructed a complete list of magnetic band (co)representations
(MBRs) in real space for other MSGs with anti-unitary symmetries (i.e. type-III
and type-IV MSGs). The results are consistent with the magnetic topological
quantum chemistry [Elcoro et al., Nat. Comm. 12, 5965 (2021)]. Using the CRs
and MBRs, we reproduce the symmetry-based classifications for MSGs, and we
obtain a set of Fu-Kane-like formulas of symmetry indicators (SIs) in both
spinless (bosonic) and spinful (fermionic) systems, which are implemented in an
automatic code - TopMat - to diagnose topological magnetic materials. The
magnetic topological materials, whose occupied states can not be decomposed
into a sum of MBRs, are consistent with nonzero SIs. Lastly, using our online
code, we have performed spin-polarized calculations for magnetic compounds in
the materials database and find many magnetic topological candidates.",2204.10556v2
2007/10/22,Observation of magnetization reversal and negative magnetization in a double perovskite compound Sr2YbRuO6,"Detailed magnetic properties of the compound Sr2YbRuO6 are presented here.
The compound belongs to the family of double perovskites forming a monoclinic
structure. Magnetization meas-urements reveal clear evidence for two components
of magnetic ordering aligned opposite to each other, leading to a magnetization
reversal, compensation temperature (T* = 34 K) and neg-ative magnetization at
low temperatures and low magnetic fields. Heat capacity measurements
corroborate the presence of two components in the magnetic ordering and a
noticeable third anomaly at low temperatures (~15 K) which cannot be attributed
the Schottky effect. The calcu-lated magnetic entropy is substantially lower
than that expected for the ground states of the or-dered moments of Ru5+ and
Yb3+, indicating the presence of large crystal field effects and/ or
in-complete magnetic ordering and/or magnetic frustrations well above the
magnetic ordering. An attempt is made to explain the magnetization reversal
within the frameworks of available models.",0710.4043v3
2014/10/8,An optimized magnet for magnetic refrigeration,"A magnet designed for use in a magnetic refrigeration device is presented.
The magnet is designed by applying two general schemes for improving a magnet
design to a concentric Halbach cylinder magnet design and dimensioning and
segmenting this design in an optimum way followed by the construction of the
actual magnet. The final design generates a peak value of 1.24 T, an average
flux density of 0.9 T in a volume of 2 L using only 7.3 L of magnet, and has an
average low flux density of 0.08 T also in a 2 L volume. The working point of
all the permanent magnet blocks in the design is very close to the maximum
energy density. The final design is characterized in terms of a performance
parameter, and it is shown that it is one of the best performing magnet designs
published for magnetic refrigeration.",1410.1987v1
2016/12/28,"Magnetic structure of Cu2MnBO5 ludwigite: thermodynamic, magnetic properties and neutron diffraction study","We report on the thermodynamic, magnetic properties and the magnetic
structure of ludwigite-type Cu2MnBO5. The specific heat, the low-field
magnetization and the paramagnetic susceptibility were studied on a single
crystal and combined with powder neutron diffraction data. The temperature
dependence of the specific heat and the neutron diffraction pattern reveal a
single magnetic phase transition at T=92 K, which corresponds to the magnetic
ordering into a ferromagnetic phase. The cation distribution and the values and
directions of magnetic moments of ions in different crystallographic sites are
established. The magnetic moments of Cu2+ and Mn3+ ions occupying different
magnetic sites in the ferrimagnetic phase are pairwise antiparallel and their
directions do not coincide with the directions of the principal
crystallographic axes.The small value of the magnetic moment of copper ions
occupying site 2a is indicative of partial disordering of the magnetic moments
on this site. The magnetization measurements show a strong temperature
hysteresis of magnetization, which evidences for field-dependent transitions
below the phase transition temperature.",1612.08805v1
2017/12/18,Magnetic and universal magnetocaloric behavior of rare-earth substituted DyFe0.5Cr0.5O3,"We report the effect of partial substitution of Dy-site by rare-earths (R=Gd,
Er and La)on the magnetic and magnetocaloric behavior of a mixed metal oxide
DyFe0.5Cr0.5O3.Structural studies reveal that substitution of Dy by R has a
minimal influence on the crystal structure. Magnetic and heat capacity studies
show that the magnetic transition around 121 K observed for DyFe0.5Cr0.5O3
remains unchanged with rare-earth substitution, whereas the lower magnetic
transition temperature is suppressed/enhanced by magnetic/non-magnetic
substitution. In all these compounds, the second order nature of magnetic
transition is confirmed by Arrott plots. As compared to DyFe0.5Cr0.5O3, the
values of magnetic entropy change and relative cooling power are increased with
magnetic rare-earth substitution while it decreases with non-magnetic
rare-earth substitution. In all these compounds, magnetic entropy change
follows the power law dependence of magnetic field and the value of the
exponent n indicate the presence of ferromagnetic correlation in an
antiferromagnetic state. A phenomenological universal master curve is also
constructed for all the compounds by normalizing the entropy change with
rescaled temperature using a single reference temperature. This master curve
also reiterates the second order nature of the magnetic phase transition in
such mixed metal oxides.",1712.06396v1
2019/5/22,"Effect of doping of Co, Ni and Ga on magnetic and dielectric properties of layered perovskite multiferroic YBaCuFeO5","YBaCuFeO5 is one of the interesting multiferroic compounds, which exhibits
magnetic ordering and dielectric anomaly above 200 K. Partial substitution of
Fe with other magnetic and non-magnetic ion affects the magnetic and the
structural properties of the system. We report detailed investigation of
structural, magnetic and dielectric properties of YBaCuFe0.85M0.15O5 (M=Co, Ni
and Ga). We observed that the partial replacement of Ni and Co in place of Fe,
results in magnetic dilution and broadening of the magnetic transition and
shifting towards lower temperature. The replacement of Fe with non-magnetic Ga
also results in shifting of the magnetic transition to the lower temperature
side. The observed dielectric relaxation behavior in these compounds is due to
the charge carrier hoping. This study highlights the impacts of magnetic and
non-magnetic doping at the magnetic site on magnetic and dielectric properties
in layered perovskite compound YBaCuFeO5.",1905.08982v2
2022/9/7,Atypical magnetic behavior in the incommensurate $[CH_3NH_3][Ni(HCOO)_3]$ hybrid perovskite,"A plethora of temperature induced phase transitions have been observed in
$[CH_3NH_3][M(HCOO)_3]$ compounds, where M is Co(II) or Ni(II). Among them, the
nickel compound exhibits a combination of magnetic and nuclear
incommensurabil-ity below N\'eel temperature. Despite the fact that the
zero-field behavior has been previously addressed, here we study in depth the
macroscopic magnetic behavior of this compound to unveil the origin of the
atypical magnetic response found in it and in its parent family of formate
perovskites. In particular, they show a puzzling magnetization reversal in the
curves measured starting from low temperatures, after cooling under zero field.
The first atypical phenomena is the im-possibility of reaching zero
magnetization, even by nullifying the applied external field and even
compensating it for the influence earth's magnetic field. Relatively large
magnetic fields are needed to switch the magnetization from negative to
positive values or vice versa, which is compatible with a soft-ferromagnetic
system. The atypical path found in its first magnetization curve and hysteresis
loop at low temperatures is the most noticeable feature. The magnetization
curve switches from more than 1200 Oe from the first magnetization loop to the
subsequent magnetization loops. A feature that cannot be explained using a
model based on unbalanced pair of domains. As a result, we decipher this
behavior in light of the incommensurate structure of this material. We propose,
in particular, that the applied magnetic field induces a mag-netic phase
transition from a magnetically incommensurate structure to a magnetically
commensurate structure.",2209.03093v1
2002/11/21,Temperature-dependent magnetization in diluted magnetic semiconductors,"We calculate magnetization in magnetically doped semiconductors assuming a
local exchange model of carrier-mediated ferromagnetic mechanism and using a
number of complementary theoretical approaches. In general, we find that the
results of our mean-field calculations, particularly the dynamical mean field
theory results, give excellent qualitative agreement with the experimentally
observed magnetization in systems with itinerant charge carriers, such as
Ga_{1-x}Mn_xAs with 0.03 < x < 0.07, whereas our percolation-theory-based
calculations agree well with the existing data in strongly insulating
materials, such as Ge_{1-x}Mn_x. We comment on the issue of non-mean-field like
magnetization curves and on the observed incomplete saturation magnetization
values in diluted magnetic semiconductors from our theoretical perspective. In
agreement with experimental observations, we find the carrier density to be the
crucial parameter determining the magnetization behavior. Our calculated
dependence of magnetization on external magnetic field is also in excellent
agreement with the existing experimental data.",0211496v1
2012/6/2,Electric dipoles on magnetic monopoles in spin ice,"The close connection of electricity and magnetism is one of the cornerstones
of modern physics. This connection plays crucial role from the fundamental
point of view and in practical applications, including spintronics and
multiferroic materials. A breakthrough was a recent proposal that in magnetic
materials called spin ice the elementary excitations have a magnetic charge and
behave as magnetic monopoles. I show that, besides magnetic charge, there
should be an electric dipole attached to each magnetic monopole. This opens new
possibilities to study and to control such monopoles by electric field. Thus
the electric--magnetic analogy goes even further than usually assumed: whereas
electrons have electric charge and magnetic dipole (spin), magnetic monopoles
in spin ice, while having magnetic charge, also have electric dipole.",1206.0402v1
2012/2/15,Ferroelectricity induced by interatomic magnetic exchange interaction,"Multiferroics, where two or more ferroic order parameters coexist, is one of
the hottest fields in condensed matter physics and materials science[1-9].
However, the coexistence of magnetism and conventional ferroelectricity is
physically unfavoured[10]. Recently several remedies have been proposed, e.g.,
improper ferroelectricity induced by specific magnetic[6] or charge orders[2].
Guiding by these theories, currently most research is focused on frustrated
magnets, which usually have complicated magnetic structure and low magnetic
ordering temperature, consequently far from the practical application. Simple
collinear magnets, which can have high magnetic transition temperature, have
never been considered seriously as the candidates for multiferroics. Here, we
argue that actually simple interatomic magnetic exchange interaction already
contains a driving force for ferroelectricity, thus providing a new microscopic
mechanism for the coexistence and strong coupling between ferroelectricity and
magnetism. We demonstrate this mechanism by showing that even the simplest
antiferromagnetic (AFM) insulator MnO, can display a magnetically induced
ferroelectricity under a biaxial strain.",1202.3381v2
2018/2/8,Manipulating Anomalous Hall Antiferromagnets with Magnetic Fields,"The symmetry considerations that imply a non-zero anomalous Hall effect (AHE)
in certain non-collinear antiferromagnets also imply both non-zero orbital
magnetization and a net spin magnetization. We have explicitly evaluated the
orbital magnetizations of several anomalous Hall effect antiferromagnets and
find that they tend to dominate over spin magnetizations, especially so when
spin-orbit interactions are weak. Because of the greater relative importance of
orbital magnetization the coupling between magnetic order and an external
magnetic field is unusual. We explain how magnetic fields can be used to
manipulate magnetic configurations in these systems, pointing in particular to
the important role played by the response of orbital magnetization to the
Zeeman-like spin exchange fields.",1802.03044v2
2018/5/30,Nonequilibrium Magnetic Oscillation with Cylindrical Vector Beams,"Magnetic oscillation is a generic property of electronic conductors under
magnetic fields and widely appreciated as a useful probe of their electronic
band structure, i.e., the Fermi surface geometry. However, the usage of the
strong static magnetic field makes the measurement insensitive to the magnetic
order of the target material. That is, the magnetic order is anyhow turned into
a forced ferromagnetic one. Here we theoretically propose an experimental
method of measuring the magnetic oscillation in a magnetic-order-resolved way
by using the azimuthal cylindrical vector (CV) beam, an example of topological
lightwaves. The azimuthal CV beam is unique in that when focused tightly, it
develops a pure longitudinal magnetic field. We argue that this characteristic
focusing property and the discrepancy in the relaxation timescale between
conduction electrons and localized magnetic moments allow us to develop the
nonequilibrium analog of the magnetic oscillation measurement. Our optical
method would be also applicable to metals the under ultra-high pressure of
diamond anvil cells.",1805.11831v2
2019/4/22,Strain-Induced Reversible Manipulation of Orbital Magnetic Moments in Ni/Cu Multilayers on Ferroelectric BaTiO3,"Controlling magnetic anisotropy by orbital magnetic moments related to
interfacial strains has considerable potential for the development of future
devices using spins and orbitals. For the fundamental physics, the relationship
between strain and orbital magnetic moment is still unknown, because there are
few tools to probe changes of orbital magnetic moment. In this study, we
developed an electric-field- (E)-induced X-ray magnetic circular dichroism
(EXMCD) technique to apply E to a ferroelectric BaTiO3 substrate. We reversibly
tuned the interfacial lattice constants of Ni/Cu multilayers on BaTiO3 using
this technique. As the domain structures in BaTiO3 are modulated by E, EXMCD
measurements reveal that the changes in the magnetic anisotropy of Ni/Cu films
are induced through the modulation of orbital magnetic moments in Ni with
magneto-elastic contributions. The strained Ni layer that induces the
perpendicular magnetic anisotropy without E is released at E = 8 kV/cm, and
in-plane magnetization also occurs. We observed that EXMCD measurements
clarified the origin of the reversible changes in perpendicular magnetic
anisotropy and established the relationship between macroscopic inverse
magnetostriction effects and microscopic orbital moment anisotropy.",1904.09719v1
2019/4/25,Magnetic-field-induced quantized anomalous Hall effect in intrinsic magnetic topological insulator MnBi$_2$Te$_4$,"In a magnetic topological insulator, nontrivial band topology conspires with
magnetic order to produce exotic states of matter that are best exemplified by
quantum anomalous Hall (QAH) insulators and axion insulators. Up till now, such
magnetic topological insulators are obtained by doping topological insulators
with magnetic atoms. The random magnetic dopants, however, inevitably introduce
disorders that hinder further exploration of quantum effects in the material.
Here, we resolve this dilemma by probing quantum transport in MnBi$_2$Te$_4$
thin flake - a topological insulator with intrinsic magnetic order. In this
layered van der Waals crystal, the ferromagnetic layers couple anti-parallel to
each other, so MnBi$_2$Te$_4$ is an antiferromagnet. A magnetic field, however,
aligns all the layers and induces an interlayer ferromagnetic order; we show
that a quantized anomalous Hall response emerges in atomically thin
MnBi$_2$Te$_4$ under a moderate magnetic field. MnBi$_2$Te$_4$ therefore
becomes the first intrinsic magnetic topological insulator exhibiting quantized
anomalous Hall effect. The result establishes MnBi$_2$Te$_4$ as an ideal arena
for further exploring various topological phenomena.",1904.11468v1
2020/10/6,An ultra-stable 1.5 tesla permanent magnet assembly for qubit experiments at cryogenic temperatures,"Magnetic fields are a standard tool in the toolbox of every physicist, and
are required for the characterization of materials, as well as the polarization
of spins in nuclear magnetic resonance or electron paramagnetic resonance
experiments. Quite often a static magnetic field of sufficiently large, but
fixed magnitude is suitable for these tasks. Here we present a permanent magnet
assembly that can achieve magnetic field strengths of up to 1.5T over an air
gap length of 7mm. The assembly is based on a Halbach array of neodymium
(NdFeB) magnets, with the inclusion of the soft magnetic material Supermendur
to boost the magnetic field strength inside the air gap. We present the design,
simulation and characterization of the permanent magnet assembly, measuring an
outstanding magnetic field stability with a drift rate of |D| < 2.8 ppb/h. Our
measurements demonstrate that this assembly can be used for spin qubit
experiments inside a dilution refrigerator, successfully replacing the more
expensive and bulky superconducting solenoids.",2010.02455v2
2023/4/3,Bloch-type magnetic skyrmions in two-dimensional lattice,"Magnetic skyrmions in two-dimensional lattice are a prominent topic of
condensed matter physics and material science. Current research efforts in this
field are exclusively constrained to Neel-type and antiskyrmion, while
Bloch-type magnetic skyrmions are rarely explored. Here, we report the
discovery of Bloch-type magnetic skyrmions in two-dimensional lattice of
MnInP2Te6, using firstprinciples calculations and Monte-Carlo simulations.
Arising from the joint effect of broken inversion symmetry and strong
spin-orbit coupling, monolayer MnInP2Te6 presents large Dzyaloshinskii-Moriya
interaction. This, along with ferromagnetic exchange interaction and
out-ofplane magnetic anisotropy, gives rise to skyrmion physics in monolayer
MnInP2Te6, without needing magnetic field. Remarkably, different from all
previous works on two-dimensional lattice,the resultant magnetic skyrmions
feature Bloch-type, which is protected by D3 symmetry.Furthermore, the
Bloch-type magnetic bimerons are also identified in monolayer MnTlP2Te6. The
phase diagrams of these Bloch-type topological magnetisms under magnetic field,
temperature and strain are mapped out. Our results greatly enrich the research
on magnetic skyrmions in twodimensional lattice.",2304.00671v1
2023/9/7,Magnetization reversal in Fe(001) films grown by magnetic field assisted molecular beam epitaxy,"We studied the influence of a magnetic field (MF) on epitaxial growth and
magnetic properties of Fe(001) films deposited on MgO(001). Thanks to modular
sample holders and a specialized manipulator in our multi-chamber ultrahigh
vacuum system, the films could be deposited and annealed in an in-plane MF of
100 mT. In situ scanning tunnelling microscopy showed that MF had a strong
influence on the film morphology, and, in particular, on the structure of
surface steps. The magnetic properties were studied ex situ using magneto-optic
Kerr effect (MOKE) magnetometry and microscopy. We showed that the moderate
in-plane magnetic field applied during growth has the visible impact on the
magnetic properties. The observed angular dependence of the MOKE loops and
domain structures were discussed based on a magnetization reversal model. In
particular we found that magnetization reversal occurs via 90{\deg} domains and
the reversal differs for the no-field and in-field grown samples, in
correlation with the film morphology.",2309.03583v1
2023/9/26,Soft X-ray phase nano-microscopy of micrometre-thick magnets,"Imaging of nanoscale magnetic textures within extended material systems is of
critical importance both to fundamental research and technological
applications. Whilst high resolution magnetic imaging of thin nanoscale samples
is well-established with electron and soft X-ray microscopy, the extension to
micrometer-thick systems with hard X-rays currently limits high resolution
imaging to rare-earth magnets. Here we overcome this limitation by establishing
soft X-ray magnetic imaging of micrometer-thick systems using the pre-edge
phase X-ray Magnetic Circular Dichroism signal, thus making possible the study
of a wide range of magnetic materials. By performing dichroic
spectro-ptychography, we demonstrate high spatial resolution imaging of
magnetic samples up to 1.7 {\mu}m thick, an order of magnitude higher than
conventionally possible with absorption-based techniques. This new regime of
magnetic imaging makes possible the study of extended non rare-earth systems
that have until now been inaccessible, from magnetic textures for future
spintronic applications to non-rare-earth permanent magnets.",2309.14969v1
2023/10/3,Permanent Magnets Based on Hard Ferrite Ceramics,"Permanent magnets are integral components in many of the modern technologies
that are critical for the transition to a sustainable society. However, most of
the high-performance (BHmax > 100 kJ/m3) permanent magnets that are currently
employed contain rare earth elements (REE), which have long been classified as
critical materials with a high supply risk and concerns regarding pollution in
their mining. Therefore, suitable REE-lean/free magnets must be developed in
order to ensure the sustainability of clean energy generation and electric
mobility. The REE-free hexagonal ferrites (or hexaferrites) are the most used
permanent magnets across all applications, with an 85 wt.% pie of the permanent
magnet market. They are the dominant lower-grade option (BHmax < 25 kJ/m3) due
to their relatively good hard magnetic properties, high Curie temperature (>700
K), low cost and good chemical stability. In recent years, the hexaferrites
have also emerged as candidates for substituting REE-based permanent magnets in
applications requiring intermediate magnetic performance (25-100 kJ/m3), due to
considerable performance improvements achieved through chemical tuning,
nanostructuring and compaction/sintering optimization. This chapter reviews the
state-of-the-art sintering strategies being investigated with the aim of
manufacturing hexaferrite magnets with optimized magnetic properties,
identifying key challenges and highlighting the natural future steps to be
followed.",2310.02106v1
2023/10/25,Phase Change Induced Magnetic Switching through Metal-insulator Transition in VO2/TbFeCo Films,"The ability to manipulate spins in magnetic materials is essential in
designing spintronics devices. One method for magnetic switching is through
strain. In VO2 on TiO2 thin films, while VO2 remains rutile across the
metal-insulator transition, the in-plane lattice area expands going from low
temperature insulating phase to high temperature conducting phase. In a
VO2/TbFeCo bilayer, the expansion of the VO2 lattice area exerts tension on the
amorphous TbFeCo layer. Through the strain effect, magnetic properties,
including the magnetic anisotropy and magnetization, of TbFeCo can be changed.
In this work, the changes in magnetic properties of TbFeCo on VO2/TiO2(011) are
demonstrated using anomalous Hall effect measurements. Across the
metal-insulator transition, TbFeCo loses perpendicular magnetic anisotropy, and
the magnetization in TbFeCo turns from out-of-plane to in-plane. Using
atomistic simulations, we confirm these tunable magnetic properties originating
from the metal-insulator transition of VO2. This study provides the groundwork
for controlling magnetic properties through a phase transition.",2310.17045v1
2024/4/1,"Harnessing Interlayer Magnetic Coupling for Efficient, Field-Free Current-Induced Magnetization Switching in a Magnetic Insulator","Owing to the unique features of low Gilbert damping, long spin-diffusion
lengths and zero Ohmic losses, magnetic insulators are promising candidate
materials for next-generation spintronic applications. However, due to the
localized magnetic moments and the complex metal-oxide interface between
magnetic insulators and heavy metals, spin-functional Dzyaloshinskii-Moriya
interactions or spin Hall and Edelstein effects are weak, which diminishes the
performance of these typical building blocks for spintronic devices. Here, we
exploit the exchange coupling between metallic and insulating magnets for
efficient electrical manipulation of heavy metal/magnetic insulator
heterostructures. By inserting a thin Co layer, we enhance the spin-orbit
torque efficiency by more than 20 times, which significantly reduces the
switching current density. Moreover, we demonstrate field-free current-induced
magnetization switching caused by a symmetry-breaking non-collinear magnetic
texture. Our work launches magnetic insulators as an alternative platform for
low-power spintronic devices.",2404.00845v1
2008/3/18,Magnetic Graphene Nanohole Superlattices,"We investigate the magnetic properties of nano-holes (NHs) patterned in
graphene using first principles calculations. We show that superlattices
consisting of a periodic array of NHs form a new family of 2D crystalline
""bulk"" magnets whose collective magnetic behavior is governed by inter-NH
spin-spin interaction. They exhibit long-range magnetic order well above room
temperature. Furthermore, magnetic semiconductors can be made by doping
magnetic NHs into semiconducting NH superlattices. Our findings offer a new
material system for fundamental studies of spin-spin interaction and magnetic
ordering in low dimensions, and open up the exciting opportunities of making
engineered magnetic materials for storage media and spintronics applications.",0803.2660v1
2011/8/9,Proximal magnetometry of monolayers of magnetic moments,"We present a method to measure the magnetic properties of monolayers and
ultra-thin films of magnetic material. The method is based on low energy muon
spin rotation and $\beta$-detected nuclear magnetic resonance measurements. A
spin probe is used as a ""proximal"" magnetometer by implanting it in the
substrate, just below the magnetic material. We calculate the expected magnetic
field distribution sensed by the probe and discuss its temperature and
implantation depth dependencies. This method is highly suitable for measuring
the magnetic properties of monolayers of single molecule magnets, but can also
be extended to ultra-thin magnetic films.",1108.1990v1
2012/6/8,Room temperature magnetic entropy change and magnetoresistance in La_{0.70}(Ca_{0.30-x}Sr_x)MnO_3:Ag 10% (x = 0.0-0.10),"The magnetic and magnetocaloric properties of polycrystalline
La0.70(Ca0.30-xSrx)MnO3:Ag 10% manganite have been investigated. All the
compositions are crystallized in single phase orthorhombic Pbnm space group.
Both, the Insulator-Metal transition temperature (TIM) and Curie temperature
(Tc) are observed at 298 K for x = 0.10 composition. Though both TIM and Tc are
nearly unchanged with Ag addition, the MR is slightly improved. The MR at 300 K
is found to be as large as 31% with magnetic field change of 1Tesla, whereas it
reaches up to 49% at magnetic field of 3Tesla for La0.70Ca0.20Sr0.10MnO3:Ag0.10
sample. The maximum entropy change (\DeltaSMmax) is 7.6 J.Kg-1.K-1 upon the
magnetic field change of 5Tesla, near its Tc (300.5 K). The
La0.70Ca0.20Sr0.10MnO3:Ag0.10 sample having good MR (31%1Tesla, 49%3Tesla) and
reasonable change in magnetic entropy (7.6 J.Kg-1.K-1, 5 Tesla) at 300 K can be
a potential magnetic refrigerant material at ambient temperatures.",1206.1699v1
2013/8/28,Static magnetic field concentration and enhancement using magnetic materials with positive permeability,"In this paper a novel compressor for static magnetic fields is proposed based
on finite embedded transformation optics. When the DC magnetic field passes
through the designed device, the magnetic field can be compressed inside the
device. After it passes through the device, one can obtain an enhanced static
magnetic field behind the output surface of the device (in a free space
region). We can also combine our compressor with some other structures to get a
higher static magnetic field enhancement in a free space region. In contrast
with other devices based on transformation optics for enhancing static magnetic
fields, our device is not a closed structure and thus has some special
applications (e.g., for controlling magnetic nano-particles for gene and drag
delivery). The designed compressor can be constructed by using currently
available materials or DC meta-materials with positive permeability. Numerical
simulation verifies good performance of our device.",1308.6078v1
2013/10/22,Evidence for Multiferroic Characteristics in NdCrTiO5,"We report NdCrTiO5 to be an unusual multiferroic material with large magnetic
field dependent electric polarization. While magneto-electric coupling in this
two magnetic sub-lattice oxide is well established, the purpose of this study
is to look for spontaneous symmetry breaking at the magnetic transition. The
conclusions are based on extensive magnetization, dielectric and polarization
measurements around its antiferromagnetic ordering temperature of 18K. Room
temperature X-ray diffraction pattern of NdCrTiO5 reveals that the sample is
single phase with an orthorhombic crystal structure that allows linear
magneto-electric coupling. DC magnetization measurement shows magnetization
downturn at 11K together with a small kink corresponding to the Co+3
sub-lattice ordering at ~18K. An anomaly in dielectric constant is observed
around the magnetic ordering temperature that increases substantially with
increasing magnetic field. Through detailed pyroelectric current measurements
at zero magnetic field, particularly as a function of thermal cycling, we
establish that NdCrTiO5 is a genuine multiferroic material that is possibly
driven by collinear magneto-striction.",1310.5803v1
2016/4/12,Accumulative magnetic switching of ultra-high-density recording media by circularly polarized light,"Manipulation of the magnetization by external energies other than magnetic
field, such as spin-polarized current1-4, electric voltage5,6 and circularly
polarized light7-11 gives a paradigm shift in magnetic nanodevices.
Magnetization control of ferromagnetic materials only by circularly polarized
light has received increasing attention both as a fundamental probe of the
interactions of light and magnetism but also for future high-density magnetic
recording technologies. Here we show that for granular FePt films, designed for
ultrahigh-density recording, the optical magnetic switching by circularly
polarized light is an accumulative effect from multiple optical pulses. We
further show that deterministic switching of high anisotropy materials by the
combination of circularly polarized light and modest external magnetic fields,
thus revealing a pathway towards technological implementation.",1604.03488v1
2017/5/29,Magnetic hexadecapole order and magnetopiezoelectric metal in Ba$_{1-x}$K$_x$Mn$_2$As$_2$,"We study an odd-parity magnetic multipole order in
Ba$_{1-x}$K$_x$Mn$_2$As$_2$ and related materials. Although BaMn$_2$As$_2$ is a
seemingly conventional Mott insulator with G-type antiferromagnetic order, we
identify the ground state as a magnetic hexadecapole ordered state accompanied
by simultaneous time-reversal and space-inversion symmetry breaking. A symmetry
argument and microscopic calculations reveal the ferroic ordering of leading
magnetic hexadecapole moment and admixed magnetic quadrupole moment.
Furthermore, we clarify electromagnetic responses characterizing the magnetic
hexadecapole state of semiconducting BaMn$_2$As$_2$ and doped metallic systems.
A magnetoelectric effect and antiferromagnetic Edelstein effect are shown.
Interestingly, a counter-intuitive currentinduced nematic order occurs in the
metallic state. The electric current along the \textit{z}-axis induces the
\textit{xy}-plane nematicity in sharp contrast to the spontaneous nematic order
in superconducting Febased 122-compounds. Thus, the magnetic hexadecapole state
of doped BaMn$_2$As$_2$ is regarded as a magnetopiezoelectric metal. The
anomalous responses stem from the peculiar symmetry of the parity-violating
magnetic order. Other candidate materials for magnetic hexadecapole order are
proposed.",1705.10349v3
2016/8/11,Chiral magnetic excitations in FeGe films,"Although chiral magnetic materials have emerged as a potential ingredient in
future spintronic memory devices, there are few comprehensive studies of
magnetic properties in scalably-grown thin films. We present growth, systematic
physical and magnetic characterization, and microwave absorption spectroscopy
of B20 FeGe thin films. We also perform micromagnetic simulations and
analytical theory to understand the dynamical magnetic behavior of this
material. We find magnetic resonance features in both the helical and
field-polarized magnetic states that are well explained by micromagnetic
simulations and analytical calculations. In particular, we show the resonant
enhancement of spin waves along the FeGe film thickness that has a wave vector
matching the helical vector. Using our analytic model, we also describe the
resonance frequency of a helical magnetic state, which depends solely on its
untwisting field. Our results pave the way for understanding and manipulating
high frequency spin waves in thin-film chiral-magnet FeGe near room
temperature.",1608.03582v1
2017/3/24,Phase Diagram of $α$-RuCl$_3$ in an in-plane Magnetic Field,"The low-temperature magnetic phases in the layered honeycomb lattice material
$\alpha$-RuCl$_3$ have been studied as a function of in-plane magnetic field.
In zero field this material orders magnetically below 7 K with so-called zigzag
order within the honeycomb planes. Neutron diffraction data show that a
relatively small applied field of 2 T is sufficient to suppress the population
of the magnetic domain in which the zigzag chains run along the field
direction. We found that the intensity of the magnetic peaks due to zigzag
order is continuously suppressed with increasing field until their
disappearance at $\mu_o$H$_c$=8 T. At still higher fields (above 8 T) the
zigzag order is destroyed, while bulk magnetization and heat capacity
measurements suggest that the material enters a state with gapped magnetic
excitations. We discuss the magnetic phase diagram obtained in our study in the
context of a quantum phase transition.",1703.08431v1
2014/4/29,The AC multi-harmonic magnetic susceptibility measurement setup at the LNF-INFN,"The AC magnetic susceptibility is a fundamental method in materials science,
which allows to probe the dynamic magnetic response of magnetic materials and
superconductors. The LAMPS laboratory at the Laboratori Nazionali di Frascati
of the INFN hosts an AC multi-harmonic magnetometer that allows performing
experiments with an AC magnetic field ranging from 0.1 to 20 Gauss and in the
frequency range from 17 to 2070 Hz. A DC magnetic field from 0 to 8 T produced
by a superconducting magnet can be applied, while data may be collected in the
temperature range 4.2-300 K using a liquid He cryostat under different
temperature cycles setups. The first seven AC magnetic multi-harmonic
susceptibility components can be measured with a magnetic sensitivity of 1x10-6
emu and a temperature precision of 0.01 K. Here we will describe in detail
about schematic of the magnetometer, special attention will be dedicated to the
instruments control, data acquisition framework and the user-friendly
LabVIEW-based software platform.",1404.7389v1
2016/12/8,Synthesis and pressure and field dependent magnetic properties of the Kagome-bilayer spin liquid Ca$_{10}$Cr$_7$O$_{28}$,"We report synthesis of polycrystalline samples of the recently discovered
spin liquid material Ca$_{10}$Cr$_7$O$_{28}$ and present measurements of the
ambient and high pressure magnetic susceptibility $\chi$ versus temperature
$T$, magnetization $M$ versus magnetic field $H$ at various $T$, and heat
capacity $C$ versus $T$ at various $H$. The ambient pressure magnetic
measurements indicate the presence of both ferromagnetic and antiferromagnetic
exchange interactions with dominant ferromagnetic interactions and with the
largest magnetic energy scale $\sim 10$~K\@. The $\chi(T)$ measurements under
externally applied pressure of up to $P \approx 1$~GPa indicate the robust
nature of the spin-liquid state despite relative increase in the ferromagnetic
exchanges. $C(T)$ shows a broad anomaly at $T\approx 2.5$~K which moves to
higher temperatures in a magnetic field. The evolution of the low temperature
$C(T,H)$ and the magnetic entropy is consistent with frustrated magnetism in
Ca$_{10}$Cr$_7$O$_{28}$.",1612.02692v2
2019/3/27,Real-space imaging and flux noise spectroscopy of magnetic dynamics in Ho$_2$Ti$_2$O$_7$,"Holmium titanate (Ho$_2$Ti$_2$O$_7$) is a rare earth pyrochlore and a
canonical example of a classical spin ice material. Despite the success of
magnetic monopole models, a full understanding of the energetics and relaxation
rates in this material has remained elusive, while recent studies have shown
that defects play a central role in the magnetic dynamics. We used a scanning
superconducting quantum interference device (SQUID) microscope to study the
spatial and temporal magnetic fluctuations in three regions with different
defect densities from a Ho$_2$Ti$_2$O$_7$ single crystal as a function of
temperature. We found that the magnetic flux noise power spectra are not
determined by simple thermally-activated behavior and observed evidence of
magnetic screening that is qualitatively consistent with Debye-like screening
due to a dilute gas of low-mobility magnetic monopoles. This work establishes
magnetic flux spectroscopy as a powerful tool for studying materials with
complex magnetic dynamics, including frustrated correlated spin systems.",1903.11465v1
2019/5/30,Evolution of Magnetic Order from the Localized to the Itinerant Limit,"Quantum materials that feature magnetic long-range order often reveal complex
phase diagrams when localized electrons become mobile. In many materials
magnetism is rapidly suppressed as electronic charges dissolve into the
conduction band. In materials where magnetism persists, it is unclear how the
magnetic properties are affected. Here we study the evolution of the magnetic
structure in Nd(1-x)Ce(x)CoIn(5) from the localized to the highly itinerant
limit. We observe two magnetic ground states inside a heavy-fermion phase that
are detached from unconventional superconductivity. The presence of two
different magnetic phases provides evidence that increasing charge
delocalization affects the magnetic interactions via anisotropic band
hybridization.",1905.13219v2
2022/5/13,Micromagnetics of magnetic chemical modulations in soft-magnetic cylindrical nanowires,"We analyze the micromagnetics of short longitudinal modulations of a
high-magnetization material in cylindrical nanowires made of a soft-magnetic
material of lower magnetization such as permalloy, combining magnetic
microscopy, analytical modeling, and micromagnetic simulations. The mismatch of
magnetization induces curling of magnetization around the axis in the
modulations, in an attempt to screen the interfacial magnetic charges. The
curling angle increases with modulation length, until a plateau is reached with
nearly full charge screening for a specific length scale~$\Delta_\mathrm{mod}$,
larger than the dipolar exchange length of any of the two materials. The
curling circulation can be switched by the Oersted field arising from a charge
current with typical magnitude $10^{12} A/m^{2}$ for a diameter of $\sim$100
nm, and reaching a maximum for $\Delta_\mathrm{mod}$.",2205.06705v2
2022/9/6,Magnetization controlled by crystallization in soft magnetic Fe-Si-B-P-Cu alloys,"Soft magnetic materials have low coercive fields and high permeability.
Recently, nanocrystalline alloys obtained using annealing amorphous alloys have
attracted much interest since nanocrystalline alloys with small grain sizes of
tens of nanometers exhibit low coercive fields comparable to that of amorphous
alloys. Since nanocrystalline soft magnetic materials attain remarkable soft
magnetic properties by controlling the grain size, the crystal grains'
microstructure has a substantial influence on the soft magnetic properties. In
this research, we examined the magnetic properties of Fe-Si-B-P-Cu
nanocrystalline soft magnetic alloys obtained by annealing amorphous alloys.
During crystallization, the observation findings reveal the correlation between
the generated microstructures and soft magnetic properties.",2209.02225v1
2023/4/20,"Magnetic behavior of cubic Dy4RhAl with respect to isostructural Dy4PtAl, revealing a novel 4f d-band interaction","We have investigated for the first time the magnetic behaviour of an
intermetallic compound, Dy4RhAl, crystallizing in Gd4RhIn type cubic structure
containing 3 sites for rare-earth (R), by several bulk measurements down to 1.8
K. This work is motivated by the fact that the isostructural Dy compound in the
R4PtAl family surprisingly orders ferromagnetically unlike other members of
this series, which order antiferromagnetically. The results reveal that the
title compound undergoes antiferromagnetic order at about 18 K, similar to
other heavy R members of R4RhAl family, unlike its Pt counterpart, indicating a
subtle difference in the role of conduction electrons to decide magnetism of
these compounds. Besides, spin-glass features coexisting with antiferromagnetic
order could be observed, which could mean cluster antiferromagnetism. The
electrical resistivity and magnetoresistance behaviours in the magnetically
ordered state are typical of magnetic materials exhibiting antiferromagnetic
gap. Features attributable to spin-reorientation as a function of temperature
and magnetic field can be seen in the magnetization data.",2304.10122v1
2011/10/26,Nanostructured exchange coupled hard / soft composites: from the local magnetization profile to an extended 3D simple model,"In nanocomposite magnetic materials the exchange coupling between phases
plays a central role in the determination of the extrinsic magnetic properties
of the material: coercive field, remanence magnetization. Exchange coupling is
therefore of crucial importance in composite systems made of magnetically hard
and soft grains or in partially crystallized media including nanosized
crystallites in a soft matrix. It has been shown also to be a key point in the
control of stratified hard / soft media coercive field in the research for
optimized recording media. A signature of the exchange coupling due to the
nanostructure is generally obtained on the magnetization curve $M(H)$ with a
plateau characteristic of the domain wall compression at the hard/soft
interface ending at the depinning of the wall inside the hard phase. This
compression / depinning behavior is clearly evidenced through one dimensional
description of the interface, which is rigorously possible only in stratified
media. Starting from a local description of the hard/soft interface in a model
for nanocomposite system we show that one can extend this kind of behavior for
system of hard crystallites embedded in a soft matrix.",1110.5737v1
2021/7/29,Magnetic frustration in a van der Waals metal CeSiI,"The realization of magnetic frustration in a metallic van der Waals (vdW)
coupled material has been sought as a promising platform to explore novel
phenomena both in bulk matter and in exfoliated devices. However, a suitable
material platform has been lacking so far. Here, we demonstrate that CeSiI
hosts itinerant electrons coexisting with exotic magnetism. In CeSiI, the
magnetic cerium atoms form a triangular bilayer structure sandwiched by van der
Waals stacked iodine layers. From resistivity and magnetometry measurements, we
confirm the coexistence of itinerant electrons with magnetism with dominant
antiferromagnetic exchange between the strongly Ising-like Ce moments below 7
K. Neutron diffraction directly confirms magnetic order with an incommensurate
propagation vector k ~ (0.28, 0, 0.19) at 1.6 K, which points to the importance
of further neighbor magnetic interactions in this system. The presence of a
two-step magnetic-field-induced phase transition along c axis further suggests
magnetic frustration in the ground state. Our findings provide a novel material
platform hosting a coexistence of itinerant electron and frustrated magnetism
in a vdW system, where exotic phenomena arising from rich interplay between
spin, charge and lattice in low dimension can be explored.",2107.13810v1
2023/11/2,Accelerated Data-Driven Discovery and Screening of Two-Dimensional Magnets Using Graph Neural Networks,"In this study, we employ Graph Neural Networks (GNNs) to accelerate the
discovery of novel 2D magnetic materials which have transformative potential in
spintronics applications. Using data from the Materials Project database and
the Computational 2D materials database (C2DB), we train three GNN
architectures on a dataset of 1190 magnetic monolayers with energy above the
convex hull ($E_{\text{hull}}$) less than 0.3 eV/atom. Our Crystal Diffusion
Variational Auto Encoder (CDVAE) generates 11,100 candidate crystals.
Subsequent training on two Atomistic Line Graph Neural Networks (ALIGNN)
achieves a 93$\%$ accuracy in predicting magnetic monolayers and a mean average
error of 0.039 eV/atom for $E_{\text{hull}}$ predictions. After narrowing down
candidates based on magnetic likelihood and predicted energy, constraining the
atom count in the monolayers to five or fewer, and performing dimensionality
checks, we identify 190 candidates. These are validated using
Density-Functional Theory (DFT) to confirm their magnetic and energetic
favorability resulting in 167 magnetic monolayers with $E_{\text{hull}} < 0.3$
eV/atom and a total magnetization of $\geq$ $0.5 \mu_{B}$. Our methodology
offers a way to accelerate exploring and predicting potential 2D magnetic
materials, contributing to the ongoing computational and experimental efforts
aimed at the discovery of new 2D magnets.",2311.00939v2
2004/7/26,Magnetic transition in Ni-Pt alloy Systems : Experiment and Theory,"We report here the preparation and measurements on the susceptibility, sound
velocity and internal friction for Ni-Pt systems. We then compare these
experimental results with the first principle theoretical predictions and show
that there is reasonable agreement with experiment and theory.",0407661v1
2004/11/11,Metal-coated carbon nanotube tips for Magnetic Force Microscopy,"We fabricated cantilevers for magnetic force microscopy with carbon nanotube
tips coated with magnetic material. Images of a custom hard drive demonstrated
20 nm lateral resolution, with prospects for further improvements.",0411289v1
1995/8/1,Interlayer Coupling in Magnetic/Pd Multilayers,"The Anderson model of local-state conduction electron mixing is applied to
the p roblem of interlayer magnetic coupling in metallic multilayered
structures with palladium (Pd) spacer layers. An oscillation period of $5$
spacer monolayers and the tendency towards ferromag netic bias of the
interlayer magnetic coupling that we obtain are consistent with the
experimental data.",9508002v1
2006/7/12,Magnetic domain-walls and the relaxation method,"The relaxation method used to solve boundary value problems is applied to
study the variation of the magnetization orientation in several types of domain
walls that occur in ferromagnetic materials. The algorithm is explained and
applied to several cases: the Bloch wall in bulk magnetic systems, the radial
wall in cylindrical wires and the N\'eel wall in thin films",0607119v1
2007/12/8,Polar Behavior in a Magnetic Perovskite Via A-Site Disorder,"We elucidate a mechanism for obtaining polar behavior in magnetic perovskites
based on A-site disorder and demonstrate this mechanism by density functional
calculations for the double perovskite (La,Lu)MnNiO$_6$ with Lu concentrations
at and below 50%. We show that this material combines polar behavior and
ferromagnetism. The mechanism is quite general and may be applicable to a wide
range of magnetic perovskites.",0712.1281v1
2016/2/2,Magnetic Field Tunable Capacitive Dielectric:Ionic-liquid Sandwich Composites,"We examined the tunability of the capacitance for GaFeO3-ionic liquid-GaFeO3
composite material by external magnetic and electric field. Up to 1.6 folds of
capacitance tunability could be achieved at 957kHz with voltage 4v and magnetic
field 0.02T applied. We show that the capacitance enhancement is due to the
polarization coupling between dielectric layer and ionic liquid layer.",1602.01134v1
2019/5/6,Vapor Pressure in a Paramagnetic Solid?,"In this paper, we obtain an analytical expression for the vapor pressure of a
paramagnetic solid for high temperatures. We have considered the behavior of
magnetic materials in the presence of an external magnetic field using the
thermodynamical analysis and the elements of statistical mechanics in
microscopic systems. We found that the vapor pressure depends on the magnetic
susceptibility of material and the external field applied.",1905.02587v1
2023/6/25,Discovering two-dimensional magnetic topological insulators by machine learning,"Topological materials with unconventional electronic properties have been
investigated intensively for both fundamental and practical interests.
Thousands of topological materials have been identified by symmetry-based
analysis and ab initio calculations. However, the predicted magnetic
topological insulators with genuine full band gaps are rare. Here we employ
this database and supervisedly train neural networks to develop a heuristic
chemical rule for electronic topology diagnosis. The learned rule is
interpretable and diagnoses with a high accuracy whether a material is
topological using only its chemical formula and Hubbard $U$ parameter. We next
evaluate the model performance in several different regimes of materials.
Finally, we integrate machine-learned rule with ab initio calculations to
high-throughput screen for magnetic topological insulators in 2D material
database. We discover 6 new classes (15 materials) of Chern insulators, among
which 4 classes (7 materials) have full band gaps and may motivate for
experimental observation. We anticipate the machine-learned rule here can be
used as a guiding principle for inverse design and discovery of new topological
materials.",2306.14155v2
2006/3/30,Single-pulse and two-pulse echoes at multipulse excitation mode in multidomain magnetic materials,"Properties of single-pulse and two-pulse echoes and their secondary echo
signals as well as the role of reversible relaxation in the observed decays of
echo signals at the multipulse excitation mode in a number of multidomain
magnetic materials were studied.",0603810v2
2005/5/3,Strongly anisotropic media: the THz perspectives of left-handed materials,"We demonstrate that non-magnetic ($\mu \equiv 1$) left-handed materials can
be effectively used for waveguide imaging systems. We also propose a specific
THz realization of the non-magnetic left-handed material based on homogeneous,
naturally-occurring media.",0505024v1
2022/11/15,Experimental Observation of a Magnetic Interfacial Effect,"We observed a magnetic interfacial effect due to the coupling between two
interfaces of different materials. The interface is compoust of an
antiferromagnetic and other quasi-ferromagnetic material. This effect we
measured through the ferromagnetic resonance technique without and with
electric current.",2211.08130v1
2022/3/22,Dynamic Magnetic Crossover at the Origin of the Hidden-Order in van der Waals Antiferromagnet CrSBr,"The van der Waals material CrSBr stands out as a promising two-dimensional
magnet. Especially, its high magnetic ordering temperature and versatile
magneto-transport properties make CrSBr an important candidate for new devices
in the emergent field of two-dimensional magnetic materials. To date, the
magnetic and structural properties of CrSBr have not been fully elucidated.
Here, we report on the detailed temperature-dependent magnetic and structural
properties of this material, by comprehensively combining neutron scattering,
muon spin relaxation spectroscopy, synchrotron X-ray diffraction, and
magnetization measurements. We evidence that this material undergoes a
transition to an A-type antiferromagnetic state below $T_{\rm N} \approx$ 140
K, with a pronounced two-dimensional character as deduced from the determined
critical exponent of $\beta \approx $ 0.18. In our analysis of the
field-induced metamagnetic transition, we find that the ferromagnetic
correlations within the monolayers persist clearly above the N\'eel temperature
in this material. Furthermore, we unravel the low-temperature (i.e. $T < T_{\rm
N}$) magnetic hidden order within the long-range magnetically ordered state. We
find that it is associated to a slowing down of the magnetic fluctuations,
accompanied by a continuous reorientation of the internal magnetic field. These
take place upon cooling below $T_s$ $\approx$ 100 K, until a spin freezing
process occurs at $T$* $\approx$ 40 K. We argue this complex dynamic behavior
to reflect a magnetic crossover driven by the in-plane uniaxial anisotropy,
which is ultimately caused by the mixed-anion character of the material. Our
findings indicate that the magnetic and structural properties of CrSBr widen
its potential application as a component for spin-based electronic devices.",2203.11785v1
2017/8/9,Weyl magnons in pyrochlore antiferromagnets with all-in-all-out orders,"We investigate novel topological magnon band crossings of pyrochlore
antiferromagnets with all-in-all-out (AIAO) magnetic order. By general symmetry
analysis and spin-wave theory, we show that pyrochlore materials with AIAO
orders can host Weyl magnons under external magnetic fields or uniaxial
strains. Under a small magnetic field, the magnon bands of the pyrochlore with
AIAO background can feature two opposite-charged Weyl points, which is the
minimal number of Weyl points realizable in quantum materials and has not be
experimentally observed so far. We further show that breathing pyrochlores with
AIAO orders can exhibit Weyl magnons upon uniaxial strains. These findings
apply to any pyrochlore material supporting AIAO orders, irrespective of the
forms of interactions. Specifically, we show that the Weyl magnons are robust
against direct (positive) Dzyaloshinskii-Moriya interactions. Because of the
ubiquitous AIAO orders in pyrochlore magnets including R$_2$Ir$_2$O$_7$, and
experimentally achievable external strain and magnetic field, our predictions
provide promising arena to witness the Weyl magnons in quantum magnets.",1708.02948v2
2019/10/8,Magnetic 2D materials and heterostructures,"The family of 2D materials grows day by day, drastically expanding the scope
of possible phenomena to be explored in two dimensions, as well as the possible
van der Waals heterostructures that one can create. Such 2D materials currently
cover a vast range of properties. Until recently, this family has been missing
one crucial member - 2D magnets. The situation has changed over the last two
years with the introduction of a variety of atomically-thin magnetic crystals.
Here we will discuss the difference between magnetic states in 2D materials and
in bulk crystals and present an overview of the 2D magnets that have been
explored recently. We will focus, in particular, on the case of the two most
studied systems - semiconducting CrI$_3$ and metallic Fe$_3$GeTe$_2$ - and
illustrate the physical phenomena that have been observed. Special attention
will be given to the range of novel van der Waals heterostructures that became
possible with the appearance of 2D magnets, offering new perspectives in this
rapidly expanding field.",1910.03425v1
2019/7/15,Study of CoFe2O4/CoFe2 nanostructured powder,"We report an experimental study of the CoFe2O4/CoFe2 nanocomposite, a
nanostructured material formed by hard (CoFe2O4) and soft (CoFe2) magnetic
materials. The precursor material, cobalt ferrite (CoFe2O4), was prepared using
the conventional stoichiometric gel-combustion method. The nanocomposite
material was obtained by reducing partially the precursor material using
activated charcoal as reducing agent in air and argon atmospheres, at 800 and
900 C respectively. The magnetic hysteresis loops demonstrate that, in general,
prepared nanocomposite samples display single magnetic behavior, indicating
exchange coupling between the soft and hard magnetic phases. However, for
nanocomposite samples prepared at higher temperatures, the hysteresis
measurements show steps typical of two-phase magnetic behavior, suggesting the
existence of two non-coupled magnetic phases. The studied nanocomposites
presented coercivity (HC) of about 0.7 kOe, which is considerably lower than
the expected value for cobalt ferrite. A huge increase in HC (>440%) and
maximum energy product (about 240%) was obtained for the nanocomposite after
high energy milling processing.",1907.06758v1
2023/1/18,Experimental Evidence for the Spiral Spin Liquid in LiYbO$_2$,"Spiral spin liquids are an exotic class of correlated paramagnets with an
enigmatic magnetic ground state composed of a degenerate manifold of
fluctuating spin spirals. Experimental realisations of the spiral spin liquid
are scarce, mainly due to the prominence of structural distortions in candidate
materials that can trigger order-by-disorder transitions to more conventionally
ordered magnetic ground states. Expanding the pool of candidate materials that
may host a spiral spin liquid is therefore crucial to realising this novel
magnetic ground state and understanding its robustness against perturbations
that arise in real materials. Here, we show that the material LiYbO$_2$ is the
first experimental realisation of a spiral spin liquid predicted to emerge from
the $J_1$-$J_2$ Heisenberg model on an elongated diamond lattice. Through a
complementary combination of high-resolution and diffuse neutron magnetic
scattering studies on a polycrystalline sample, we demonstrate that LiYbO$_2$
fulfils the requirements for the experimental realisation of the spiral spin
liquid and reconstruct single-crystal diffuse neutron magnetic scattering maps
that reveal continuous spiral spin contours -- a characteristic experimental
hallmark of this exotic magnetic phase.",2301.07559v2
2009/2/1,Neutron Studies of the Iron-based Family of High TC Magnetic Superconductors,"We review neutron scattering investigations of the crystal structures,
magnetic structures, and spin dynamics of the iron-based RFe(As,P)O (R=La, Ce,
Pr, Nd), (Ba,Sr,Ca)Fe2As2, and Fe1+x(Te-Se) systems. On cooling from room
temperature all the undoped materials exhibit universal behavior, where a
tetragonal-to-orthorhombic/monoclinic structural transition occurs, below which
the systems become antiferromagnets. For the first two classes of materials the
magnetic structure within the a-b plane consists of chains of parallel Fe spins
that are coupled antiferromagnetically in the orthogonal direction, with an
ordered moment typically less than one Bohr magneton. Hence these are itinerant
electron magnets, with a spin structure that is consistent with Fermi-surface
nesting and a very energetic spin wave bandwidth ~0.2 eV. With doping, the
structural and magnetic transitions are suppressed in favor of
superconductivity. Magnetic correlations are observed in the superconducting
regime, with a magnetic resonance that follows the superconducting order
parameter just like the cuprates. The rare-earth moments order
antiferromagnetically at low T like conventional magnetic-superconductors.
Pressure in CaFe2As2 transforms the system from a magnetically ordered
orthorhombic material to a collapsed non-magnetic tetragonal system. Tetragonal
Fe1+xTe transforms to a low T monoclinic structure at small x that changes to
orthorhombic at larger x, which is accompanied by a crossover from commensurate
to incommensurate magnetic order. Se doping suppresses the magnetic order.",0902.0091v2
2019/9/2,Magnetically induced/enhanced coarsening in thin films,"External magnetic fields influence the microstructure of polycrystalline
materials. We explore the influence of strong external magnetic fields on the
long time scaling of grain size during coarsening in thin films with an
extended phase-field-crystal model. Additionally, the change of various
geometrical and topological properties is studied. In a situation which leads
to stagnation, an applied external magnetic field can induce further grain
growth. The induced driving force due to the magnetic anisotropy defines the
magnetic influence of the external magnetic field. Different scaling regimes
are identified dependent on the magnetization. At the beginning, the scaling
exponent increases with the strength of the magnetization. Later, when the
texture becomes dominated by grains preferably aligned with the external
magnetic field, the scaling exponent becomes independent of the strength of the
magnetization or stagnation occurs. We discuss how the magnetic influence
change the effect of retarding or pinning forces, which are known to influence
the scaling exponent. We further study the influence of the magnetic field on
the grain size distribution (GSD), next neighbor distribution (NND) as well as
grain shape and orientation. If possible, we compare our predictions with
experimental findings.",1909.00527v5
2013/11/23,Universal Scaling Law to Predict the Efficiency of Magnetic Nanoparticles as MRI T2-Contrast Agents,"Magnetic particles are very efficient Magnetic Resonance Imaging (MRI)
contrast agents. In the recent years, chemists have unleashed their imagination
to design multi-functional nanoprobes for biomedical applications including MRI
contrast enhancement. This study is focused on the direct relationship between
the size and magnetization of the particles and their nuclear magnetic
resonance relaxation properties, which condition their efficiency. Experimental
relaxation results with maghemite particles exhibiting a wide range of sizes
and magnetizations are compared to previously published data and to
well-established relaxation theories with a good agreement. This allows
deriving the experimental master curve of the transverse relaxivity versus
particle size and to predict the MRI contrast efficiency of any type of
magnetic nanoparticles. This prediction only requires the knowledge of the size
of the particles impermeable to water protons and the saturation magnetization
of the corresponding volume. To predict the T2 relaxation efficiency of
magnetic single crystals, the crystal size and magnetization obtained through a
single Langevin fit of a magnetization curve is the only information needed.
For contrast agents made of several magnetic cores assembled into various
geometries (dilute fractal aggregates, dense spherical clusters, core-shell
micelles, hollow vesicles), one needs to know a third parameter, namely the
intra-aggregate volume fraction occupied by the magnetic materials relatively
to the whole (hydrodynamic) sphere. Finally a calculation of the maximum
achievable relaxation effect and the size needed to reach this maximum is
performed for different cases: maghemite single crystals and dense clusters,
core-shell particles (oxide layer around a metallic core) and zinc manganese
ferrite crystals.",1311.6022v1
2013/2/27,When metal organic frameworks turn into linear magnets,"We investigate the existence of linear magnetism in the metal organic
framework materials MOF-74-Fe, MOF-74-Co, and MOF-74-Ni, using first-principles
density functional theory. MOF-74 displays regular quasi-linear chains of
open-shell transition metal atoms, which are well separated. Our results show
that within these chains-for all three materials-ferromagnetic coupling of
significant strength occurs. In addition, the coupling in-between chains is at
least one order of magnitude smaller, making these materials almost perfect 1D
magnets at low temperature. The inter-chain coupling is found to be
anti-ferromagnetic, in agreement with experiments. While some quasi-1D
materials exist that exhibit linear magnetism-mostly complex oxides, polymers,
and a few other rare material-they are typically very difficult to synthesize.
The significance of our finding is that MOF-74 is very easy to synthesize and
it is likely the simplest realization of the 1D Ising model in nature. MOF-74
could thus be used in future experiments to study 1D magnetism at low
temperature.",1302.6886v1
2018/3/21,Negative permeability in magnetostatics and its experimental demonstration,"The control of magnetic fields, essential for our science and technology, is
currently achieved by magnetic materials with positive permeability, including
ferromagnetic, paramagnetic, and diamagnetic types. Here we introduce materials
with negative static permeability as a new paradigm for manipulating magnetic
fields. As a first step, we extend the solutions of Maxwell magnetostatic
equations to include negative-permeability values. The understanding of these
new solutions allow us to devise a negative-permeability material as a suitably
tailored set of currents arranged in space, overcoming the fact that passive
materials with negative permeability do no exist in magnetostatics. We confirm
the theory by experimentally creating a spherical shell that emulates a
negative-permeability material in a uniform magnetic field. Our results open
new possibilities for creating and manipulating magnetic fields, which can be
useful for practical applications.",1803.08013v1
2021/8/24,Spin-orbit torque: Moving towards two-dimensional van der Waals heterostructures,"The manipulation of magnetic properties using either electrical currents or
gate bias is the key of future high-impact nanospintronics applications such as
spin-valve read heads, non-volatile logic, and random-access memories. The
current technology for magnetic switching with spin-transfer torque requires
high current densities, whereas gate-tunable magnetic materials such as
ferromagnetic semiconductors and multiferroic materials are still far from
practical applications. Recently, magnetic switching induced by pure spin
currents using the spin Hall and Rashba effects in heavy metals, called
spin-orbit torque (SOT), has emerged as a candidate for designing
next-generation magnetic memory with low current densities. The recent
discovery of topological materials and two-dimensional (2D) van der Waals (vdW)
materials provides opportunities to explore versatile 3D-2D and 2D-2D
heterostructures with interesting characteristics. In this review, we introduce
the emerging approaches to realizing SOT nanodevices including techniques to
evaluate the SOT efficiency as well as the opportunities and challenges of
using 2D topological materials and vdW materials in such applications.",2108.10622v1
2001/10/22,"Crystal structures, magnetic and superconducting properties of the RuSr_2NdCu_2O_x and RuSr_2GdCu_2O_y compounds","We report the magnetization and the susceptibility measurements of the
RuSr_2GdCu_2O_y and RuSr_2NdCu_2O_x perovskite materials. We find that
RuSr_2GdCu_2O_y compound exhibits a magnetic transition at Tn=135 K followed by
a superconducting one with an onset Tc=35 K. Samples of RuSr_2NdCu_2O_x
material have shown neither superconductivity nor magnetic transition. XRD
measurements show that in RuSr_2NdCu_2O_x the Nd ions tend to substitute to Sr
ions in very high percentages. The relevance of this phenomenon on the absence
of superconductivity in RuSr_2NdCu_2O_x is discussed.",0110482v1
2005/8/17,Magnetic Composites: Magnonic Excitations vs. Three-Dimensional Structural Periodicity,"This study deals with the spin wave spectrum in magnetic macrostructure
(composed of two ferromagnetic materials) showing a 3D periodicity: spherical
ferromagnetic grains disposed in the nodes of a simple cubic crystal lattice
are embedded in a matrix with different ferromagnetic properties. It is shown
that the \textit{magnonic spectrum} of this composite structure exhibits
frequency regions \textit{forbidden} for magnon propagation, and the energy
gaps are found to be sensitive to the exchange contrast between the constituent
materials as well as to the magnetization contrast. The widths of the
respective magnonic gaps are studied as functions of parameters characterizing
the magnetic structure.",0508390v1
2006/2/6,Studies on Magnetic-field induced first-order transitions,"We shall discuss magnetization and transport measurements in materials
exhibiting a broad first-order transition. The phase transitions would be
caused by varying magnetic field as well as by varying temperature, and we
concentrate on ferromagnetic to antiferromagnetic transitions in magnetic
materials. We distinguish between metastable supercooled phases and metastable
glassy phase.",0602128v1
2006/10/17,"Comment on: ""Ferroelectricity in spiral magnets""","There is much interest in the physics of materials that show a strong
coupling between magnetic and electric degrees of freedom. In a recent paper by
Mostovoy a theory is presented that is based on symmetry arguments and leads to
quite general claims which we feel merit some further analysis. In particular,
Mostovoy concludes that ""spiral magnets are, in general, ferroelectric"". We
argue that this conclusion is not generally valid, and that the symmetry of the
unit cell has to be taken into account by any symmetry-based magneto-electric
coupling theory. In an attempt to avoid further confusion in the search of new
multiferroic materials, we identify in this Comment some of the necessary
symmetry properties of spiral magnets that can lead to ferroelectricity.",0610471v1
2009/12/14,Magnetic Faraday rotation in lossy photonic structures,"Magnetic Faraday rotation is widely used in optics and MW. In uniform
magneto-optical materials, this effect is very weak. One way to enhance it is
to incorporate the magnetic material into a high-Q optical resonator. One
problem with magneto-optical resonators is that along with Faraday rotation,
the absorption and linear birefringence can also increase dramatically,
compromising the device performance. Another problem is strong ellipticity of
the output light. We discuss how the above problems can be addressed in the
cases of optical microcavities and a slow wave resonators. We show that a slow
wave resonator has a fundamental advantage when it comes to Faraday rotation
enhancement in lossy magnetic materials.",0912.2612v1
2013/9/25,Prediction of half metallic properties in Ti\raisebox{-.2ex}{\scriptsize 2}CoSi Heusler alloy based on density functional theory,"The electronic and magnetic properties of Ti\raisebox{-.2ex}{\scriptsize
2}CoSi Heusler compound are investigated using density functional calculations.
The optimized lattice constant is found to be 6.030 A. The compound is a
half-metallic ferromagnet with an energy gap in minority spin channel of 0.652
eV at equilibrium lattice constant, which leads to a 100% spin-polarization.
The obtained total magnetic moment from spin-polarized calculations is 3.0
$\mu_{B}$ for values of lattice constants higher than 5.941 A. The
half-metallicity is spoiled for a compressed volume of 4%, suggesting a
possible application as pressure sensitive material.",1309.6427v1
2016/1/8,Extreme Sensitivity of Magnetic Properties on the Synthesis Routes in La$_{0.7}$Sr$_{0.3}$MnO$_3$,"La$_{0.7}$Sr$_{0.3}$MnO$_3$ polycrystalline samples have been prepared using
different synthesis routes. X-ray Diffraction (XRD) confirms that the samples
are of single phase with R$\bar{3}$c space group. The surface morphology and
particle size has been measured using Field Emission Scanning Electron
Microscopy (FESEM). Magnetic measurement shows that the magnetization in the
materials are affected by low crystallite size which destroys the spin ordering
due to strain at grain boundaries and in turn also lead to reduction in
magnetization as well as an enhanced coercivity in the material.",1601.01805v1
2016/1/31,Topological Excitations in Magnetic Materials,"In this work we propose a new route to describe topological excitations in
magnetic systems through a single real scalar field. We show here that
spherically symmetric structures in two spatial dimensions, which map helical
excitations in magnetic materials, admit this formulation and can be used to
model skyrmion-like structures in magnetic materials.",1602.00262v2
2016/10/13,Electronic control of magnonic and spintronic devices,"Nanometric magnonic and spintronic devices need magnetic field control in
addition to conventional electronic control. In this work we review ways to
replace magnetic field control by an electronic one in order to circumvent
appearance of stray magnetic fields or the difficulty of creating large
magnetic fields over nanometric distances. Voltage control is compared to
current control and corresponding devices are compared from their energetic
efficiency point of view.",1610.04011v1
2016/11/25,"Magnetism in the KBaRE(BO3)2 (RE=Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) series: materials with a triangular rare earth lattice","We report the magnetic properties of compounds in the KBaRE(BO3)2 family (RE=
Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb), materials with a planar triangular lattice
composed of rare earth ions. The samples were analyzed by x-ray diffraction and
crystallize in the space group R-3m. Physical property measurements indicate
the compounds display predominantly antiferromagnetic interactions between
spins without any signs of magnetic ordering above 1.8 K. The ideal 2D rare
earth triangular layers in this structure type make it a potential model system
for investigating magnetic frustration in rare-earth-based materials.",1611.08548v1
2018/7/24,Pushing the limits of magnetic anisotropy in the Sm-Co system,"Materials based on the Sm-Co system exhibit remarkable magnetic performance
due to their high Curie temperature, large saturation magnetization, and strong
magnetic anisotropy, which are the result of the electronic structure in Co and
Sm and their arrangement in the hexagonal lattice. In this paper we show, using
first-principles calculations, mean-field theory, and atomistic Monte Carlo
simulations that slight modifications of the SmCo5 crystal structure, induced
by strain or partial substitution of Sm by Ce, change the exchange interaction
energy and increase the magnetocrystalline anisotropy energy drastically. This
finding shows how small changes in local-structure environments lead to
substantial changes in macroscopic properties and enables the optimization of
high-performance materials at the atomic level.",1807.09257v1
2016/3/29,Generic aspects of skyrmion lattices in chiral magnets,"Magnetic skyrmions are topologically non-trivial spin whirls that may not be
transformed continuously into topologically trivial states such as
ferromagnetic spin alignment. In recent years lattice structures composed of
skyrmions have been discovered in certain bulk chiral magnets with
non-centrosymmetric crystal structures. The magnetic phase diagrams of these
materials share remarkable similarities despite great variations of the
characteristic temperature, field, and length scales and regardless whether the
underlying electronic state is that of a metal, semiconductor, or insulator.",1603.08730v1
2020/8/17,"Synthesis, Engineering, and Theory of 2D van der Waals Magnets","Spontaneous magnetic order is a routine instance in three-dimensional (3D)
materials but for a long time, it remained elusive in the 2D world. Recently,
the first examples of (stand-alone) 2D van der Waals (vdW) crystals with
magnetic order, either antiferromagnetic or ferromagnetic, have been reported.
In this review, we describe the state of the art of the nascent field of
magnetic 2D materials focusing on synthesis, engineering, and theory aspects.
We also discuss challenges and some of the many different promising directions
for future work.",2008.07666v1
2019/4/17,Two-orbital effective model for magnetic Weyl semimetal in Kagome-lattice shandite,"We construct a two-orbital effective model for a ferromagnetic Kagome-lattice
shandite, $\rm{{Co}_3{Sn}_2{S}_2}$, a candidate material of magnetic Weyl
semimetals, by considering one $d$ orbital from Co, and one $p$ orbital from
interlayer Sn. The energy spectrum near the Fermi level, and the configurations
of the Weyl points, computed by using our model, are similar to those obtained
by first principle calculations. We show also that nodal rings appear even with
spin-orbit coupling when the magnetization points in-plane direction.
Additionally, magnetic properties of $\rm{{Co}_3{Sn}_2{S}_2}$ and other
shandite materials are discussed.",1904.08148v1
2022/2/22,Skyrmions in magnetic materials,"Skyrmions are vortex-like textures of magnetic moments found in some
magnetically ordered materials. Here we describe the origin of the skyrmion and
discuss the experimental realization of skyrmions in magnetic materials, the
dynamic properties of the skyrmion and the potentially useful interaction of
skyrmions with electrons. Our discussion is based on the physics of fields and
allows us to touch on notions from field theory and topology that illustrate
how skyrmions can be understood as part of a family of defects in an ordered
field, and hint at other topological objects that await our discovery.",2202.11019v1
2024/3/14,Toroidal orders and related phenomena in nonmagnetic and magnetic materials,"In this short article, we overview a concept of electronic toroidal
multipoles, and their ordering with associated physical properties in
non-magnetic and magnetic materials. The toroidal multipoles are introduced as
microscopic electronic variables in view of symmetry and connection to Dirac
theory. They are classified according to crystallographic and magnetic point
groups, which allows us to discuss various possible cross correlations in a
transparent and unified manner. The representative examples of toroidal orders
and related phenomena, and the mutual relationship between these orders are
given, with focusing on monopoles and dipoles. The concept of toroidal
multipoles would promote future studies toward observations and identifications
of unknown electronic phases and their related physical phenomena.",2403.09492v1
2017/7/13,Electric field controlled magnetic exchange bias and magnetic state switching at room temperature in Ga doped α-Fe2O3 oxide,"We have developed a new magnetoelectric material based on Ga doped
{\alpha}-Fe2O3 in rhombohedral phase. The material is a canted ferromagnet at
room temperature and showing magneto-electric properties. The experimental
results of electric field controlled magnetic state provided a direct evidence
of room temperature magnetoelectric coupling in Ga doped {\alpha}-Fe2O3 system.
Interestingly, (un-doped) {\alpha}-Fe2O3 system does not exhibit any electric
field controlled magnetic exchange bias shift, but Ga doped {\alpha}-Fe2O3
system has shown an extremely high electric field induced magnetic exchange
bias shift up to the value of 1120 Oe (positive). On the other hand, in a first
time, we report the electric field controlled magnetic state switching both in
{\alpha}-Fe2O3 and in Ga doped {\alpha}-Fe2O3 systems. The switching of
magnetic state is highly sensitive to ON and OFF modes, as well as to the
change of polarity of applied electric voltage during in-field magnetic
relaxation experiments. The switching of magnetic state to upper level for
positive electric field and to down level for negative electric field indicates
that electric and magnetic orders are coupled in the Ga doped hematite system.
Such material is of increasing demand in today for multifunctional applications
in next generation magnetic sensor, switching, non-volatile memory and
spintronic devices.",1707.04496v1
2019/11/27,"Synthesis, magnetization and heat capacity of triangular lattice materials NaErSe$_2$ and KErSe$_2$","In this paper we report the synthesis, magnetization and heat capacity of the
frustrated magnets \emph{A}ErSe$_2$(\emph{A}=Na,K) which contain perfect
triangular lattices of Er$^{3+}$. The magnetization data suggests no long-range
magnetic order exists in \emph{A}ErSe$_2$(\emph{A}=Na,K), which is consistent
with the heat capacity measurements. Large anisotropy is observed between the
magnetization within the \emph{ab} plane and along the \emph{c} axis of both
compounds. When the magnetic field is applied along \emph{ab} plane, anomalies
are observed at 1.8 $\mu_B$ in NaErSe$_2$ at 0.2 T and 2.1 $\mu_B$ in KErSe$_2$
at 0.18 T. Unlike NaErSe$_2$, a plateau-like field-induced metamagnetic
transition is observed for H$\|$\emph{c} below 1 K in KErSe$_2$. Two broad
peaks are observed in the heat capacity below 10 K indicating possible crystal
electric field(CEF) effects and magnetic entropy released under different
magnetic fields. All results indicate that \emph{A}ErSe$_2$ are strongly
anisotropic, frustrated magnets with field-induced transition at low
temperature. The lack of signatures for long-range magnetic order implies that
these materials are candidates for hosting a quantum spin liquid ground state.",1911.12268v1
2020/11/9,Quantum-torque-induced breaking of magnetic interfaces in ultracold gases,"A rich variety of physical effects in spin dynamics arises at the interface
between different magnetic materials. Engineered systems with interlaced
magnetic structures have been used to implement spin transistors, memories and
other spintronic devices. However, experiments in solid state systems can be
difficult to interpret because of disorder and losses. Here, we realize
analogues of magnetic junctions using a coherently-coupled mixture of ultracold
bosonic gases. The spatial inhomogeneity of the atomic gas makes the system
change its behavior from regions with oscillating magnetization -- resembling a
magnetic material in the presence of an external transverse field -- to regions
with a defined magnetization, as in magnetic materials with a ferromagnetic
anisotropy stronger than external fields. Starting from a far-from-equilibrium
fully polarized state, magnetic interfaces rapidly form. At the interfaces, we
observe the formation of short-wavelength magnetic waves. They are generated by
a quantum torque contribution to the spin current and produce strong spatial
anticorrelations in the magnetization. Our results establish ultracold gases as
a platform for the study of far-from-equilibrium spin dynamics in regimes that
are not easily accessible in solid-state systems.",2011.04271v2
2021/12/8,Modification of unconventional Hall effect with doping at the non-magnetic site in a 2D van der Waals ferromagnet,"Two-dimensional (2D) van der Waals (vdW) magnetic materials have garnered
considerable attention owing to the existence of magnetic order down to atomic
dimensions and flexibility towards interface engineering, offering an
attractive platform to explore novel spintronic phenomena and functionalities.
Understanding of the magnetoresistive properties and their correlation to the
underlying magnetic configurations is essential for 2D vdW-based spintronic or
quantum information devices. Among the promising candidates, vdW ferromagnet
(FM) Fe3GeTe2 shows an unusual magnetotransport behavior, tunable by doping at
the magnetic (Fe) site, and tentatively arising from complicated underlying
spin texture configurations. Here, we explore an alternative route towards
manipulation of magnetotransport properties of a vdW FM without directly
affecting the magnetic site i.e., by doping at the non-magnetic (Ge) site of
Fe3(Ge,As)Te2. Interestingly, doping at the non-magnetic (Ge) site results in
an unconventional Hall effect whose strength was considerably modified by
increasing As concentration, possibly arising from emergent electromagnetic
behavior from underlying complicated spin configurations. The present results
provide a possible route to understand the intricate role played by the
non-magnetic (Ge) atom towards magnetic properties of vdW FMs, and shows a
novel direction towards tailoring of underlying interactions responsible for
the stabilization of non trivial spin textures in 2D magnetic vdW materials.",2112.04425v1
2023/7/3,Nitrogen-vacancy magnetometry of CrSBr by diamond membrane transfer,"Magnetic imaging using nitrogen-vacancy (NV) spins in diamonds is a powerful
technique for acquiring quantitative information about sub-micron scale
magnetic order. A major challenge for its application in the research on
two-dimensional (2D) magnets is the positioning of the NV centers at a
well-defined, nanoscale distance to the target material required for detecting
the small magnetic fields generated by magnetic monolayers. Here, we develop a
diamond 'dry-transfer' technique, akin to the state-of-the-art 2D-materials
assembly methods, and use it to place a diamond micro-membrane in direct
contact with the 2D interlayer antiferromagnet CrSBr. We harness the resulting
NV-sample proximity to spatially resolve the magnetic stray fields generated by
the CrSBr, present only where the CrSBr thickness changes by an odd number of
layers. From the magnetic stray field of a single uncompensated ferromagnetic
layer in the CrSBr, we extract a monolayer magnetization of $M_\mathrm{CSB}$ =
0.46(2) T, without the need for exfoliation of monolayer crystals or applying
large external magnetic fields. The ability to deterministically place
NV-ensemble sensors into contact with target materials and detect ferromagnetic
monolayer magnetizations paves the way for quantitative analysis of a wide
range of 2D magnets assembled on arbitrary target substrates.",2307.01129v1
2023/11/14,Visualizing thickness-dependent magnetic textures in few-layer $\text{Cr}_2\text{Ge}_2\text{Te}_6$,"Magnetic ordering in two-dimensional (2D) materials has recently emerged as a
promising platform for data storage, computing, and sensing. To advance these
developments, it is vital to gain a detailed understanding of how the magnetic
order evolves on the nanometer-scale as a function of the number of atomic
layers and applied magnetic field. Here, we image few-layer
$\text{Cr}_2\text{Ge}_2\text{Te}_6$ using a combined scanning superconducting
quantum interference device and atomic force microscopy probe. Maps of the
material's stray magnetic field as a function of applied magnetic field reveal
its magnetization per layer as well as the thickness-dependent magnetic
texture. Using a micromagnetic model, we correlate measured stray-field
patterns with the underlying magnetization configurations, including labyrinth
domains and skyrmionic bubbles. Comparison between real-space images and
simulations demonstrates that the layer dependence of the material's magnetic
texture is a result of the thickness-dependent balance between crystalline and
shape anisotropy. These findings represent an important step towards 2D
spintronic devices with engineered spin configurations and controlled
dependence on external magnetic fields.",2311.08529v1
2009/12/30,Voltage induced control and magnetoresistance of noncollinear frustrated magnets,"Noncollinear frustrated magnets are proposed as a new class of spintronic
materials with high magnetoresistance which can be controlled with relatively
small applied voltages. It is demonstrated that their magnetic configuration
strongly depends on position of the Fermi energy and applied voltage. The
voltage induced control of noncollinear frustrated materials (VCFM) can be seen
as a way to intrinsic control of colossal magnetoresistance (CMR) and is the
bulk material counterpart of spin transfer torque concept used to control giant
magnetoresistance in layered spin-valve structures.",0912.5487v1
2011/11/23,Converse Magnetoelectric Experiments on a Room Temperature Spirally Ordered Hexaferrite,"Experiments have been performed to measure magnetoelectric properties of room
temperature spirally ordered Sr3Co2Fe24O41 hexaferrite slabs. The measured
properties include the magnetic permeability, the magnetization and the strain
all as a function of the electric field E and the magnetic intensity H. The
material hexaferrite Sr3Co2Fe24O41 exhibits broken symmetries for both time
reversal and parity. The product of the two symmetries remains unbroken. This
is the central feature of these magnetoelectric materials. A simple physical
model is proposed to explain the magnetoelectric effect in these materials.",1111.5636v1
2015/6/8,Approximate solution of wave propagation in transverse magnetic mode through a graded interface positive-negative using asymptotic iteration method,"We investigate the propagation of electromagnetic waves in transverse
magnetic (TM) mode through the structure of materials interface that have
permittivity or permeability profile graded positive-negative using asymptotic
iteration method (AIM). As the optical character of materials, the permittivity
and the permeability profiles have been designed from constant or hyperbolic
functions. In this work we show the approximate solution of magnetic field
distribution and the eight models of wave vector of materials or interface
positive-negative gradation.",1506.02346v1
2010/4/6,Frontiers of Condensed Matter Physics Explored with High-Field Specific Heat,"Production of very high magnetic fields in the laboratory has relentlessly
increased in quantity and quality over the last five decades, and a shift
occurred from research focused in magnet technology to studies of the
fundamental physics of novel materials in high fields. New strategies designed
to understand microscopic mechanisms at play in materials surfaced, with
methods to extract fundamental energy scales and thermodynamic properties from
thermal probes up to 60 Tesla. Here we summarize developments in the area of
specific heat of materials in high magnetic fields, with focus in the original
study of the Kondo Insulator system Ce3Bi4Pt3.",1004.0972v1
2007/7/5,The current spin on manganites,"In a material, the existence and coexistence of phases with very different
magnetic and electronic properties is both unusual and surprising. Manganites
in particular capture the imagination because they demonstrate a complexity
that belies their chemically single-phase nature. This complexity arises
because the magnetic, electronic and crystal structures interact with one
another to deliver exotic magnetic and electronic phases that coexist. This
coexistence is self-organized and yet readily susceptible to external
perturbations, permitting subtle and imaginative experiments of the type that
we describe here. Moreover, these experiments reveal that each competing phase
itself remains an incompletely solved mystery.",0707.0746v1
2020/11/13,Metal-organic Frameworks: Possible New Two-Dimensional Magnetic and Topological materials,"Finding new two-dimensional (2D) materials with novel quantum properties is
highly desirable for technological innovations. In this work, we studied a
series of metal-organic frameworks (MOFs) with different metal cores and
discovered various attractive properties, such as room-temperature magnetic
ordering, strong perpendicular magnetic anisotropy, huge topological band gap
(>200meV), and excellent spin-filtering performance. As many MOFs have been
successfully synthesized in experiments, our results suggest realistic new 2D
functional materials for the design of spintronic nanodevices.",2011.07088v1
2020/1/19,Disentangling magnetic and grain contrast in polycrystalline FeGe thin films using four-dimensional Lorentz scanning transmission electron microscopy,"The study of nanoscale chiral magnetic order in polycrystalline materials
with a strong Dzyaloshinkii-Moriya interaction (DMI) is interesting for the
observation of magnetic phenomena at grain boundaries and interfaces. One such
material is sputter-deposited B20 FeGe on Si, which has been actively
investigated as the basis for low-power, high-density magnetic memory
technology in a scalable material platform. Although conventional Lorentz
electron microscopy provides the requisite spatial resolution to probe chiral
magnetic textures in single-crystal FeGe, probing the magnetism of sputtered
B20 FeGe is more challenging because the sub-micron crystal grains add
confounding contrast. We address the challenge of disentangling magnetic and
grain contrast by applying 4-dimensional Lorentz scanning transmission electron
microscopy using an electron microscope pixel array detector. Supported by
analytical and numerical models, we find that the most important parameter for
imaging magnetic materials with polycrystalline grains is the ability for the
detector to sustain large electron doses, where having a high-dynamic range
detector becomes extremely important. Despite the small grain size in sputtered
B20 FeGe on Si, using this approach we are still able to observe helicity
switching of skyrmions and magnetic helices across two adjacent grains as they
thread through neighboring grains. We reproduce this effect using micromagnetic
simulations by assuming that the grains have distinct orientation and magnetic
chirality and find that magnetic helicity couples to crystal chirality. Our
methodology for imaging magnetic textures is applicable to other thin-film
magnets used for spintronics and memory applications, where an understanding of
how magnetic order is accommodated in polycrystalline materials is important.",2001.06900v3
2004/7/12,Stable room temperature magnetic graphite,"Carbon materials are attracting increasing attention due to the novelty of
the associated physical properties and the potential applications in high-tech
devices. The possibility to achieve outstanding properties in macroscopic
carbon materials opens up a profusion of new striking applications. Magnetic
properties induced by defects on graphite structures, such as pores, edges of
the planes and topological defects, have been theoretically predicted. The
possible coexistence of sp3 and sp2 bonds have been also invoked to predict
this behavior (for a review, see ref. 1). Some reports have proved the
existence of weak ferromagnetic-like magnetization loops in highly-oriented
pyrolytic graphite (HOPG) (ref. 2-3). Very recently two reports showed that the
existence of ferromagnetism in pure carbon is unambiguously possible (ref.
4-5). Here we report on a novel and inexpensive chemical route consistent in a
controlled etching on the graphite structure to obtain macroscopic amounts of
magnetic pure graphite. This material has a strong magnetic response even at
room temperature where it can be attracted by a commercial magnet and would be
the experimental confirmation for the defect induced magnetism previously
predicted.",0407303v1
2012/5/15,Probing the Interplay between Quantum Charge Fluctuations and Magnetic Ordering in LuFe2O4,"Ferroelectric and ferromagnetic materials possess spontaneous electric and
magnetic order, respectively, which can be switched by the corresponding
applied electric and magnetic fields. Multiferroics combine these properties in
a single material, providing an avenue for controlling electric polarization
with a magnetic field and magnetism with an electric field. These materials
have been intensively studied in recent years, both for their fundamental
scientific interest as well as their potential applications in a broad range of
magnetoelectric devices [1, 2, 3, 4]. However, the microscopic origins of
magnetism and ferroelectricity are quite different, and the mechanisms
producing strong coupling between them are not always well understood. Hence,
gaining a deeper understanding of magnetoelectric coupling in these materials
is the key to their rational design. Here, we use ultrafast optical
spectroscopy to show that quantum charge fluctuations can govern the interplay
between electric polarization and magnetic ordering in the charge-ordered
multiferroic LuFe2O4.",1205.3528v3
2012/6/22,Reversible Control of Magnetic Interactions by Electric Field in a Single Phase Material,"Intrinsic magnetoelectric coupling describes the interaction between magnetic
and electric polarization through an inherent microscopic mechanism in a single
phase material. This phenomenon has the potential to control the magnetic state
of a material with an electric field, an enticing prospect for device
engineering. We demonstrate 'giant' magnetoelectric cross-field control in a
single phase rare earth titanate film. In bulk form, EuTiO3 is
antiferromagnetic. However, both anti and ferromagnetic interactions coexist
between different nearest neighbor europium ions. In thin epitaxial films,
strain can be used to alter the relative strength of the magnetic exchange
constants. Here, we not only show that moderate biaxial compression
precipitates local magnetic competition, but also demonstrate that the
application of an electric field at this strain state, switches the magnetic
ground state. Using first principles density functional theory, we resolve the
underlying microscopic mechanism resulting in the EuTiO3 G-type magnetic
structure and illustrate how it is responsible for the 'giant' cross-field
magnetoelectric effect.",1206.5181v1
2012/8/7,Temperature-controlled interlayer exchange coupling in strong/weak ferromagnetic multilayers: a thermo-magnetic Curie-switch,"We investigate a novel type of interlayer exchange coupling based on driving
a strong/weak/strong ferromagnetic tri-layer through the Curie point of the
weakly ferromagnetic spacer, with the exchange coupling between the strongly
ferromagnetic outer layers that can be switched, on and off, or varied
continuously in magnitude by controlling the temperature of the material. We
use Ni-Cu alloy of varied composition as the spacer material and model the
effects of proximity-induced magnetism and the interlayer exchange coupling
through the spacer from first principles, taking into account not only thermal
spin-disorder but also the dependence of the atomic moment of Ni on the
nearest-neighbor concentration of the non-magnetic Cu. We propose and
demonstrate a gradient-composition spacer, with a lower Ni-concentration at the
interfaces, for greatly improved effective-exchange uniformity and
significantly improved thermo-magnetic switching in the structure. The reported
magnetic multilayer materials can form the base for a variety of novel magnetic
devices, such as sensors, oscillators, and memory elements based on
thermo-magnetic Curie-switching in the device.",1208.1493v1
2014/2/14,Coupling of (ferro)electricity and magnetism through Coulomb blockade in Composite Multiferroics,"Composite multiferroics are materials exhibiting the interplay of
ferroelectricity, magnetism, and strong electron correlations. Typical example
--- magnetic nano grains embedded in a ferroelectric matrix. Coupling of
ferroelectric and ferromagnetic degrees of freedom in these materials is due to
the influence of ferroelectric matrix on the exchange coupling constant via
screening of the intragrain and intergrain Coulomb interaction. Cooling typical
magnetic materials the ordered state appears at lower temperatures than the
disordered state. We show that in composite multiferroics the ordered magnetic
phase may appear at higher temperatures than the magnetically disordered phase.
In non-magnetic materials such a behavior is known as inverse phase transition.",1402.3565v2
2017/6/10,Magnetic properties of photosynthetic materials - a nano scale study,"Photosynthetic materials form the basis of quantum biology. An important
attribute of quantum biology is correlation and coherence of spin states. Such
correlated spin states are targets of static magnetic field. In this paper, we
report magnetic properties and spectroscopically realizable static magnetic
field effect in photosynthetic materials. Two classes of nano-scale assembly of
chlorophyll (NC) are used for such a study. Magnetic measurements are made
using a superconducting quantum interference device (SQUID). Both ferromagnetic
and superparamagnetic states are observed in NC along with a blocking
temperature around 250 K. Low temperature quantum (liquid nitrogen)
spectroscopy is employed to see how optical transitions are affected in
presence of static magnetic field. Plausible practical application aspects of
magnetic properties of this optically active material are discussed in the
text.",1706.08861v1
2009/7/6,Magnetic Charge Transport,"It has recently been predicted that certain magnetic materials contain mobile
magnetic charges or `monopoles'. Here we address the question of whether these
magnetic charges and their associated currents (`magnetricity') can be directly
measured in experiment, without recourse to any material-specific theory. By
mapping the problem onto Onsager's theory of weak electrolytes, we show that
this is possible, and devise an appropriate method. Then, using muon spin
rotation as a convenient local probe, we apply the method to a real material:
the spin ice Dy2Ti2O7. Our experimental measurements prove that magnetic
charges exist in this material, interact via a Coulomb interaction, and have
measurable currents. We further characterise deviations from Ohm's Law, and
determine the elementary unit of magnetic charge to be 5 muB per Angstrom,
which is equal to that predicted by Castelnovo, Moessner and Sondhi using the
microscopic theory of spin ice. Our demonstration of magnetic charge transport
has both conceptual and technological implications.",0907.0956v1
2017/12/10,Switching of magnons by electric and magnetic fields in multiferroic borates,"Electric manipulation of magnetic properties is a key problem of materials
research. To fulfil the requirements of modern electronics, these processes
must be shifted to high frequencies. In multiferroic materials this may be
achieved by electric and magnetic control of their fundamental excitations.
Here we identify magnetic vibrations in multiferroic iron-borates which are
simultaneously sensitive to external electric and magnetic fields. Nearly 100%
modulation of the terahertz radiation in an external field is demonstrated for
SmFe3(BO3)4. High sensitivity can be explained by a modification of the spin
orientation which controls the excitation conditions in multiferroic borates.
These experiments demonstrate the possibility to alter terahertz magnetic
properties of materials independently by external electric and magnetic fields.",1712.03501v1
2017/12/29,Multiphase Magnetic Systems: Measurement and Simulation,"Multiphase magnetic systems are common in nature and are increasingly being
recognized in technical applications. One characterization method which has
shown great promise for determining separate and collective effects of
multiphase magnetic systems is first order reversal curves (FORCs). Several
examples are given of FORC patterns which provide distinguishing evidence of
multiple phases. In parallel, a visualization method for understanding
multiphase magnetic interaction is given, which allocates Preisach magnetic
elements as an input 'Preisach hysteron distribution pattern' (PHDP) to enable
simulation of different 'wasp-waisted' magnetic behaviors. These simulated
systems allow reproduction of different major hysteresis loop, FORC pattern,
and switching field distributions of real systems and parameterized theoretical
systems. The experimental FORC measurements and FORC diagrams of four
commercially obtained magnetic materials, particularly those sold as
nanopowders, shows that these materials are often not phase pure. They exhibit
complex hysteresis behaviors that are not predictable based on relative phase
fraction obtained by characterization methods such as diffraction. These
multiphase materials, consisting of various fractions of BaFe12O19,
epsilon-Fe2O3, and gamma-Fe2O3, are discussed.",1712.10283v1
2019/2/3,Long range antiferromagnetic order in a rocksalt high entropy oxide,"We report for the first time the magnetic structure of the high entropy oxide
$(Mg_{0.2}Co_{0.2}Ni_{0.2}Cu_{0.2}Zn_{0.2})O$ using neutron powder diffraction.
This material exhibits a sluggish magnetic transition but possesses a
long-range ordered antiferromagnetic ground state, as revealed by DC and AC
magnetic susceptibility, elastic and inelastic neutron scattering measurements.
The magnetic propagation wavevector is k=(1/2, 1/2, 1/2) based on the cubic
structure Fm-3m, and the magnetic structure consists of ferromagnetic sheets in
the (111) planes with spins antiparallel between two neighboring planes.
Inelastic neutron scattering reveals strong magnetic excitations at 100 K that
survive up to room temperature. This work demonstrates that entropy-stabilized
oxides represent a unique platform to study long range magnetic order with
extreme chemical disorder.",1902.00833v1
2020/1/23,Magnetic oscillations induced by phonons in non-magnetic materials,"An unexpected finding two decades ago demonstrated that Shockley electron
states in noble metal surfaces are spin-polarized, forming a circulating spin
texture in reciprocal space. The fundamental role played by the spin degree of
freedom was then revealed, even for a non-magnetic system, whenever the
spin-orbit coupling was present with some strength. Here we demonstrate that
similarly to electrons in the presence of spin-orbit coupling, the propagating
vibrational modes are also accompanied by a well-defined magnetic oscillation
even in non-magnetic materials. Although this effect is illustrated by
considering a single layer of the WSe2 dichalogenide, the phenomenon is
completely general and valid for any non-magnetic material with spin-orbit
coupling. The emerging phonon-induced magnetic oscillation acts as an
additional effective flipping mechanism for the electron spin and its
implications in the transport and scattering properties of the material are
evident and profound.",2001.08629v1
2022/3/6,Progress and prospects in magnetic topological materials,"Magnetic topological materials represent a class of compounds whose
properties are strongly influenced by the topology of the electronic
wavefunctions coupled with the magnetic spin configuration. Such materials can
support chiral electronic channels of perfect conduction, and can be used for
an array of applications from information storage and control to
dissipationless spin and charge transport. Here, we review the theoretical and
experimental progress achieved in the field of magnetic topological materials
beginning with the theoretical prediction of the Quantum Anomalous Hall Effect
without Landau levels, and leading to the recent discoveries of magnetic Weyl
semimetals and antiferromagnetic topological insulators. We outline the recent
theoretical progress that resulted in the tabulation, for the first time, of
all magnetic symmetry group representations and topology. We describe several
experiments realizing Chern insulators, Weyl and Dirac magnetic semimetals, and
an array of axionic and higher-order topological phases of matter as well as
survey future perspectives.",2203.02890v1
2022/9/23,Mapping AC Susceptibility with Quantum Diamond Microscope,"We present a novel technique for determining the microscale AC susceptibility
of magnetic materials. We use magnetic field sensing properties of
nitrogen-vacancy (\ce{NV-}) centers in diamond to gather quantitative data
about the magnetic state of the magnetic material under investigation. In order
to achieve the requisite speed in imaging, a lock-in camera is used to perform
pixel-by-pixel lock-in detection of \ce{NV-} photo-luminescence. In addition, a
secondary sensor is employed to isolate the effect of the excitation field from
fields arising from magnetic structures on \ce{NV-} centers. We demonstrate our
experimental technique by measuring the AC susceptibility of soft permalloy
micro-magnets at excitation frequencies of up to \SI{20}{\hertz} with a spatial
resolution of \SI{1.2}{\micro \meter} and a field of view of \SI{100}{\um}. Our
work paves the way for microscopic measurement of AC susceptibilities of
magnetic materials relevant to physical, biological, and material sciences.",2209.11610v1
2023/4/3,Switching of Perpendicular Magnetization by Spin-Orbit Torque,"Magnetic materials with strong perpendicular magnetic anisotropy are of great
interest for the development of nonvolatile magnetic memory and computing
technologies due to their high stabilities at the nanoscale. However,
electrical switching of such perpendicular magnetization in an
energy-efficient, deterministic, scalable manner has remained a big challenge.
This problem has recently attracted enormous efforts in the field of
spintronics. Here, I review recent advances and challenges in the understanding
of the electrical generation of spin currents, the switching mechanisms and the
switching strategies of perpendicular magnetization, the switching current
density by spin-orbit torque of transverse spins, the choice of perpendicular
magnetic materials, and summarize the progress in prototype perpendicular SOT
memory and logic devices toward the goal of energy-efficient, dense, fast
perpendicular spin-orbit torque applications.",2304.00683v1
2023/6/25,Current-induced deterministic switching of van der Waals ferromagnet at room temperature,"Recent discovery of emergent magnetism in van der Waals magnetic materials
(vdWMM) has broadened the material space for developing spintronic devices for
energy-efficient computation. While there has been appreciable progress in
vdWMM discovery, with strong perpendicular magnetic anisotropy (PMA) and Curie
temperatures exceeding room temperature, a solution for non-volatile,
deterministic switching of vdWMMs at room temperature has been missing,
limiting the prospects of their adoption into commercial spintronic devices.
Here, we report the first demonstration of current-controlled non-volatile,
deterministic magnetization switching in a vdW magnetic material at room
temperature. We have achieved spin-orbit torque (SOT) switching of the PMA vdW
magnet Fe3GaTe2 using a Pt spin-Hall layer up to 320 K, with a threshold
switching current density as low as $J_{sw} = 1.69\times10^6 A/cm^2$ at room
temperature. We have also quantitatively estimated the anti-damping-like SOT
efficiency of our Fe3GaTe2/Pt bilayer system to be $\xi_{DL}$ = 0.093, using
second harmonic Hall voltage measurement technique. These results mark a
crucial step in making vdW magnetic materials a viable choice for the
development of scalable, future spintronic devices.",2306.14355v1
2023/7/3,"On the magnetic structures of 1:1:1 stoichiometric topological phases LnSbTe (Ln = Pr, Nd, Dy and Er)","LnSbTe (Ln - lanthanide) group of materials, belonging to ZrSiS/PbFCl
(P4/nmm) structure type, is a platform to study the phenomena originating from
the interplay between the electronic correlations, magnetism, structural
instabilities and topological electronic structure. Here we report a systematic
study of magnetic properties and magnetic structures of LnSbTe materials. The
studied materials undergo antiferromagnetic ordering at TN = 2.1 K (Ln = Er),
6.7 K (Ln = Dy), 3.1 K (Ln = Nd). Neutron powder diffraction reveals ordering
with k1 = (1/2 + d 0 0) in ErSbTe, k2 = (1/2 0 1/4) in NdSbTe. DySbTe features
two propagation vectors k2 and k4 = (0 0 1/2). No long-range magnetic order is
observed in PrSbTe down to 1.8 K. We propose the most probable models of
magnetic structures, discuss their symmetry and possible relation between the
electronic structure and magnetic ordering.",2307.00838v2
2024/2/1,Nonlinear electrodynamics for the vacuum of Dirac materials. Photon magnetic properties and radiation pressures,"We investigate the magnetic properties of photons propagating through Dirac
materials in the presence of a magnetic field, taking into account both medium
and vacuum contributions. The vacuum photon propagation properties are obtained
through a second-order expansion of nonlinear Euler-Heisenberg electrodynamics
considering Dirac material parameters (effective structure constant, band gap
and Fermi velocity, respectively). Total magnetization and effective magnetic
moment are obtained. Observables such as energy density, radiation pressure,
and Poynting vector are getting by an average of components of the
energy-momentum tensor. All these quantities are expressed in terms of
Lagrangian derivatives and are valid for arbitrary values of the external
magnetic field. The weak and strong field limits are recovered for all the
quantities. We discuss some ideas of experiments that may contribute to testing
in Dirac materials the phenomenology of the strong magnetic field in the
Quantum Electrodynamic's vacuum",2402.01042v6
2024/2/7,Antiferromagnetism in two-dimensional materials: progress and computational challenges,"We present a perspective on the status of antiferromagnetism in
two-dimensional (2D) materials. Various types of spin-compensated orders are
discussed and include non-collinear order, spin spirals and altermagnetism.
Spin-orbit effects ultimately determine, whether compounds exhibit long range
order, Kosterlitz-Thouless physics, or multiferroic properties and we discuss
the basic magnetic prototypes that may arise in 2D materials depending on the
magnetic anisotropy and ordering vector. A summary of 2D antiferromagnets that
have been characterized experimentally is provided - with particular emphasis
on magnetic anisotropies and Neel temperatures. We then outline the ingredients
needed to describe the magnetic properties using density functional theory. In
particular, the systematic determination of magnetic ground states from the
generalized Bloch theorem and the magnetic force theorem, which may be used to
calculate magnetic excitations from the Heisenberg model with parameters
determined from first principles. The methods are exemplified by application to
the monolayer helimagnet NiBr$_2$. Finally, we present a summary of predicted
and prospective 2D antiferromagnets and discuss the challenges associated with
the prediction of N\'eel temperatures from first principles.",2402.05313v1
2024/4/4,Direct visualization of local magnetic domain dynamics in a 2D Van der Walls material/ferromagnet interface,"Exploring new strategies for controlling the magnetic domain propagation is
the key to realize ultrafast, high-density domain wall-based memory and logic
devices for next generation computing. These strategies include strain
modulation in multiferroic devices, geometric confinement and area-selective
pinning of domain wall. 2D Van der Waals materials introduce localized
modifications to the interfacial magnetic order, enabling control over the
propagation of magnetic domains. Here, using Lorentz-Transmission Electron
Microscopy (L-TEM) along with the Modified Transport of Intensity equations
(MTIE), we demonstrate controlled domain expansion with in-situ magnetic field
in a ferromagnet (Permalloy, NiFe) interfacing with a 2D Van der Waals material
Graphene (Gr). The Gr/NiFe interface exhibits distinctive domain expansion rate
with magnetic field selectively near the interface which is further analyzed
using micromagnetic simulations. Our findings are crucial for comprehending
direct visualization of interface controlled magnetic domain expansion,
offering insights for developing future domain wall-based technology.",2404.03177v1
2024/4/4,Giant and controllable nonlinear magneto-optical effects in two-dimensional magnets,"The interplay of polarization and magnetism in materials with light can
create rich nonlinear magneto-optical (NLMO) effects, and the recent discovery
of two-dimensional (2D) van der Waals magnets provides remarkable control over
NLMO effects due to their superb tunability. Here, based on first-principles
calculations, we reported giant NLMO effects in CrI3-based 2D magnets,
including a dramatic change of second-harmonics generation (SHG) polarization
direction (90 degrees) and intensity (on/off switch) under magnetization
reversal, and a 100% SHG circular dichroism effect. We further revealed that
these effects could not only be used to design ultra-thin multifunctional
optical devices, but also to detect subtle magnetic orderings. Remarkably, we
analytically derived conditions to achieve giant NLMO effects and propose
general strategies to realize them in 2D magnets. Our work not only uncovers a
series of intriguing NLMO phenomena, but also paves the way for both
fundamental research and device applications of ultra-thin NLMO materials.",2404.03203v1
2015/4/29,The formation of regular interarm magnetic fields in spiral galaxies,"Observations of regular magnetic fields in several nearby galaxies reveal
magnetic arms situated between the material arms. The nature of these magnetic
arms is a topic of active debate. Previously we found a hint that taking into
account the effects of injections of small-scale magnetic fields generated,
e.g., by turbulent dynamo action, into the large-scale galactic dynamo can
result in magnetic arm formation. We now investigate the joint roles of an
arm/interarm turbulent diffusivity contrast and injections of small-scale
magnetic field on the formation of large-scale magnetic field (""magnetic arms"")
in the interarm region. We use the relatively simple ""no-$z$"" model for the
galactic dynamo. This involves projection on to the galactic equatorial plane
of the azimuthal and radial magnetic field components; the field component
orthogonal to the galactic plane is estimated from the solenoidality condition.
We find that addition of diffusivity gradients to the effect of magnetic field
injections makes the magnetic arms much more pronounced. In particular, the
regular magnetic field component becomes larger in the interarm space compared
to that within the material arms.The joint action of the turbulent diffusivity
contrast and small-scale magnetic field injections (with the possible
participation of other effects previously suggested) appears to be a plausible
explanation for the phenomenon of magnetic arms.",1504.07824v3
2018/1/30,Open Material Property Library With Native Simulation Tool Integrations -- MASTO,"Reliable material property data is crucial for trustworthy simulations
throughout different areas of engineering. Special care must be taken when
materials at extreme conditions are under study. Superconductors and devices
assembled from superconductors and other materials, like superconducting
magnets, are often operated at such extreme conditions: at low temperatures
under high magnetic fields and stresses. Typically, some library or database is
used for getting the data. We have started to develop a database for storing
all kind of material property data online called Open Material Property Library
With Native Simulation Tool Integrations -- MASTO. The data that can be
imported includes, but is not limited to, anisotropic critical current surfaces
for high temperature superconducting materials, electrical resistivities as a
function of temperature, RRR and magnetic field, general fits for describing
material behaviour etc. Data can also depend on other data and it can be
versioned to guarantee permanent access. The guiding idea in MASTO is to build
easy-to-use integration for various programming languages, modelling frameworks
and simulation software. Currently, a full-fledged integration is built for
MATLAB to allow users to fetch and use data with one-liners. In this paper we
briefly review some of the material property databases commonly used in
superconductor modelling, present a case study showing how selection of the
material property data can influence the simulation results, and introduce the
principal ideas behind MASTO. This work serves as the reference document for
citing MASTO when it is used in simulations.",1801.09897v1
2020/1/30,Computational Search for Magnetic and Non-magnetic 2D Topological Materials using Unified Spin-orbit Spillage Screening,"Two-dimensional topological materials (TMs) have a variety of properties that
make them attractive for applications including spintronics and quantum
computation. However, there are only a few such experimentally known materials.
To help discover new 2D TMs, we develop a unified and computationally
inexpensive approach to identify magnetic and non-magnetic 2D TMs, including
gapped and semi-metallic topological classifications, in a high-throughput way
using density functional theory-based spin-orbit spillage,
Wannier-interpolation, and related techniques. We first compute the spin-orbit
spillage for the ~1000 2D materials in the JARVIS-DFT dataset
(https://www.ctcms.nist.gov/~knc6/JVASP.html ), resulting in 122 materials with
high-spillage values. Then, we use Wannier-interpolation to carry-out Z2,
Chern-number, anomalous Hall conductivity, Curie temperature, and edge state
calculations to further support the predictions. We identify various
topologically non-trivial classes such as quantum spin-hall insulators (QSHI),
quantum anomalous-hall insulators (QAHI), and semimetals. For a few predicted
materials, we run G0W0+SOC and DFT+U calculations. We find that as we introduce
many-body effects, only a few materials retain non-trivial band-topology,
suggesting the importance of high-level DFT methods in predicting 2D
topological materials. However, as an initial step, the automated spillage
screening and Wannier-approach provide useful predictions for finding new
topological materials and to narrow down candidates for experimental synthesis
and characterization.",2001.11389v2
2023/11/22,"MagGen: A graph aided deep generative model for inverse design of stable, permanent magnets","A significant development towards inverse design of materials with
well-defined target properties is reported. A deep generative model based on
variational autoencoder (VAE), conditioned simultaneously by two target
properties, is developed to inverse design stable magnetic materials. Structure
of the physics informed, property embedded latent space of the model is
analyzed using graph theory, based on the idea of similarity index. The graph
idea is shown to be useful for generating new materials that are likely to
satisfy target properties. An impressive ~96% of the generated materials is
found to satisfy the target properties as per predictions from the target
learning branches. This is a huge improvement over approaches that do not
condition the VAE latent space by target properties, or do not consider
connectivity of the parent materials perturbing which the new materials are
generated. In such models, the fraction of materials satisfying targets can be
as low as ~5%. This impressive feat is achieved using a simple real-space only
representation called Invertible Real-space Crystallographic Representation
(IRCR), that can be directly read from material cif files. Model predictions
are finally validated by performing DFT calculations on a randomly chosen
subset of materials. Performance of the present model using IRCR is comparable
or superior to that of the models reported earlier. This model for magnetic
material generation, MagGen, is applied to the problem of designing rare earth
free permanent magnets with promising results.",2311.13328v1
2019/7/3,Spin wave excitations of magnetic metalorganic materials,"The Organic Materials Database (OMDB) is an open database hosting about
22,000 electronic band structures, density of states and other properties for
stable and previously synthesized 3-dimensional organic crystals. The web
interface of the OMDB offers various search tools for the identification of
novel functional materials such as band structure pattern matching and density
of states similarity search. In this work the OMDB is extended to include
magnetic excitation properties. For inelastic neutron scattering we focus on
the dynamical structure factor $S(\mathbf{q},\omega)$ which contains
information on the excitation modes of the material. We introduce a new dataset
containing atomic magnetic moments and Heisenberg exchange parameters for which
we calculate the spin wave spectra and dynamic structure factor with linear
spin wave theory and atomistic spin dynamics. We thus develop the materials
informatics tools to identify novel functional organic and metalorganic
magnets.",1907.01817v2
2021/11/9,Design of soft magnetic materials,"We present a strategy for the design of ferromagnetic materials with
exceptionally low magnetic hysteresis, quantified by coercivity. In this
strategy, we use a micromagnetic algorithm that we have developed in previous
research and which has been validated by its success in solving the ""Permalloy
Problem"" -- the well-known difficulty of predicting the composition 78.5% Ni of
lowest coercivity in the Fe-Ni system -- and by the insight, it provides into
the ""Coercivity Paradox"" of W. F. Brown. Unexpectedly, the design strategy
predicts that cubic materials with large saturation magnetization $m_s$ and
large magnetocrystalline anisotropy constant $\kappa_1$ will have low
coercivity on the order of that of Permalloy, as long as the magnetostriction
constants $\lambda_{100}, \lambda_{111}$ are tuned to special values. The
explicit prediction for a cubic material with low coercivity is the
dimensionless number $(c_{11}-c_{12}) \lambda_{100}^2/\kappa_1 = 81$ for
$\langle 100 \rangle$ easy axes. The results would seem to have a broad
potential application, especially to magnetic materials of interest in energy
research.",2111.05456v1
2024/1/23,Ruddlesden-Popper and perovskite phases as a material platform for altermagnetism,"The subclass of collinear antiferromagnets where spin Kramers degeneracy is
broken -- so that they can display ferromagnetic-like properties -- stimulates
a new perspective in magnetism. However, the material base for these so-called
altermagnets is still relatively limited. We show that Ruddlesden-Popper and
perovskite phases generically host altermagnetic materials. In particular, we
analyze prototypical nickel-based systems via first-principles calculations and
identify additional materials from their crystal structure and magnetic orders.
These materials span both insulating/semiconducting and metallic conduction
types and the computed values of the nonrelativistic spin splittings reach
250~meV. Our analysis also indicates some formal inconsistencies that may
appear within the traditional classification of magnetically ordered materials,
which can easily be resolved from the altermagnetic perspective. In addition,
we indicate the possibility of having altermagnetic behavior in systems beyond
collinear antiferromagnets with perfectly compensated magnetization.",2401.12910v1
2007/10/16,A generalization of Snoek's law to ferromagnetic films and composites,"The present paper establishes characteristics of the relative magnetic
permeability spectrum $\mu$(f) of magnetic materials at microwave frequencies.
The integral of the imaginary part of $\mu$(f) multiplied with the frequency f
gives remarkable properties. A generalisation of Snoek's law consists in this
quantity being bounded by the square of the saturation magnetization multiplied
with a constant. While previous results have been obtained in the case of
non-conductive materials, this work is a generalization to ferromagnetic
materials and ferromagnetic-based composites with significant skin effect. The
influence of truncating the summation to finite upper frequencies is
investigated, and estimates associated to the finite summation are provided. It
is established that, in practice, the integral does not depend on the damping
model under consideration. Numerical experiments are performed in the exactly
solvable case of ferromagnetic thin films with uniform magnetization, and these
numerical experiments are found to confirm our theoretical results. Microwave
permeability measurements on soft amorphous films are reported. The relation
between the integral and the saturation magnetization is verified
experimentally, and some practical applications of the theoretical results are
introduced. The integral can be used to determine the average magnetization
orientation in materials with complex configurations of the magnetization, and
furthermore to demonstrate the accuracy of microwave measurement systems. For
certain applications, such as electromagnetic compatibility or radar absorbing
materials, the relations established herein provide useful indications for the
design of efficient materials, and simple figures of merit to compare the
properties measured on various materials.",0710.2980v2
2012/6/29,Enhancement of critical current density in superconducting/magnetic multi-layers with slow magnetic relaxation dynamics and large magnetic susceptibility,"We propose to use superconductor-magnet multi-layer structure to achieve high
critical current density by invoking polaronic mechanism of pinning. The
magnetic layers should have large magnetic susceptibility to enhance the
coupling between vortices and magnetization in magnetic layers. The relaxation
of the magnetization should be slow. When the velocity of vortices is low, they
are dressed by nonuniform magnetization and move as polarons. In this case, the
viscosity of vortices proportional to the magnetic relaxation time is enhanced
significantly. As velocity increases, the polarons dissociate and the viscosity
drops to the usual Bardeen-Stephen one, resulting in a jump in the I-V curve.
Experimentally the jump shows up as a depinning transition and the
corresponding current at the jump is the depinning current. For Nb and proper
magnet multi-layer structure, we estimate the critical current density $J_c\sim
10^{9}\ \rm{A/m^2}$ at magnetic field $B\approx 1$ T.",1206.6929v2
2013/3/7,Complex Magnetic Phase Diagram of a Geometrically Frustrated Sm Lattice: SmPd2Al3 case,"Magnetism in SmPd2Al3 was investigated on a single crystal by magnetometry
and neutron diffraction. SmPd2Al3 represents a distinctive example of the Sm
magnetism exhibiting complex magnetic behavior at low temperatures with four
consecutive magnetic phase transitions at 3.4, 3.9, 4.3 and 12.5 K. The rich
magnetic phase diagram of this compound reflects the specific features of the
Sm3+ ion, namely the energy nearness of the ground-state multiplet J = 5/2 and
the first excited multiplet J = 7/2 in conjunction with strong crystal field
influence. Consequently, a significantly reduced Sm magnetic moment in
comparison with the theoretical Sm3+ free-ion value is observed. Despite the
strong neutron absorption by natural samarium and the small Sm magnetic moment
(~ 0.2 {\mu}B) we have successfully determined the magnetic k-vector (1/3, 1/3,
0) of the phase existing in the temperature interval 12.5 - 4.3 K. This
observation classifies the SmPd2Al3 compound as a magnetically frustrated
system. The complex magnetic behavior of this material is further illustrated
by kinetic effects of the magnetization inducing rather complicated magnetic
structure with various metastable states.",1303.1607v1
2014/3/11,Piezo-Voltage Manipulation of the Magnetization and Magnetic Reversal in Thin Fe Film,"We carefully investigated the in-plane magnetic reversal and corresponding
magnetic domain structures in Fe/GaAs/piezo-transducer heterostructure using
longitudinal magneto-optical Kerr microscopy. The coexistence of the <100>
cubic magnetic anisotropy and uniaxial magnetic anisotropy was observed in our
Fe thin film grown on GaAs. The induced deformation along [110] orientation can
effectively manipulate the magnetic reversal with magnetic field applied along
magnetic uniaxial hard [110] axes. The control of two-jump magnetization
switching to one-jump magnetization switching during the magnetic reversal was
achieved by piezo-voltages with magnetic field applied in [100] direction. The
additional uniaxial anisotropy induced by piezo-voltages at -75 /75V are
-1.400/1400 J/m3 .",1403.2469v1
2017/2/24,Angle-dependence and optimal design for magnetic bubblecade with maximum speed,"Unidirectional magnetic domain-wall motion is a key concept underlying
next-generation application devices. Such motion has been recently demonstrated
by applying an alternating magnetic field, resulting in the coherent
unidirectional motion of magnetic bubbles. Here we report the optimal
configuration of applied magnetic field for the magnetic bubblecade, the
coherent unidirectional motion of magnetic bubbles, driven by a tilted
alternating magnetic field. The tilted alternating magnetic field induces
asymmetric expansion and shrinkage of the magnetic bubbles under the influence
of the Dzyaloshinskii-Moriya interaction, resulting in continuous shift of the
bubbles in time. By realizing the magnetic bubblecade in PtCoPt films, we find
that the bubblecade speed is sensitive to the tilt angle with a maximum at an
angle, which can be explained well by a simple analytical form within the
context of the domain-wall creep theory. A simplified analytic formula for the
angle for maximum speed is then given as a function of the amplitude of the
alternating magnetic field. The present observation provides a practical design
rule for memory and logic devices based on the magnetic bubblecade.",1702.07439v1
2021/5/2,Magnetic textures in a hexaferrite thin film and their response to magnetic fields revealed by phase microscopy,"We investigated magnetic textures in a Sc-doped hexaferrite film by means of
phase microscopy (PM) with a hole-free phase plate in a transmission electron
microscope. In a zero magnetic field, the stripe-shaped magnetic domains
coexist with magnetic bubbles. The magnetization in both magnetic domains was
oriented perpendicular to the film and the domain walls have an in-plane
magnetization. In the remnant state at 9.2 mT, several magnetic bubbles were
formed with the formation of stripe-shaped magnetic domains, and the
out-of-plane component in the stripe-shaped domains gradually appeared as the
film thickness increased. As the film thickness increases further, the magnetic
bubbles with clockwise or counter-clockwise spin helicities formed a triangular
lattice. These results in the remnant state suggest that the domain wall energy
in the magnetic bubble domains is lower in the thicker region.",2105.00396v1
2023/6/2,Accelerating the electronic-structure calculation of magnetic systems by equivariant neural networks,"Complex spin-spin interactions in magnets can often lead to magnetic
superlattices with complex local magnetic arrangements, and many of the
magnetic superlattices have been found to possess non-trivial topological
electronic properties. Due to the huge size and complex magnetic moment
arrangement of the magnetic superlattices, it is a great challenge to perform a
direct DFT calculation on them. In this work, an equivariant deep learning
framework is designed to accelerate the electronic calculation of magnetic
systems by exploiting both the equivariant constraints of the magnetic
Hamiltonian matrix and the physical rules of spin-spin interactions. This
framework can bypass the costly self-consistent iterations and build a direct
mapping from a magnetic configuration to the ab initio Hamiltonian matrix.
After training on the magnets with random magnetic configurations, our model
achieved high accuracy on the test structures outside the training set, such as
spin spiral and non-collinear antiferromagnetic configurations. The trained
model is also used to predict the energy bands of a skyrmion configuration of
NiBrI containing thousands of atoms, showing the high efficiency of our model
on large magnetic superlattices.",2306.01558v1
2008/12/16,Evidence for reversible control of magnetization in a ferromagnetic material via spin-orbit magnetic field,"Conventional computer electronics creates a dichotomy between how information
is processed and how it is stored. Silicon chips process information by
controlling the flow of charge through a network of logic gates. This
information is then stored, most commonly, by encoding it in the orientation of
magnetic domains of a computer hard disk. The key obstacle to a more intimate
integration of magnetic materials into devices and circuit processing
information is a lack of efficient means to control their magnetization. This
is usually achieved with an external magnetic field or by the injection of
spin-polarized currents. The latter can be significantly enhanced in materials
whose ferromagnetic properties are mediated by charge carriers. Among these
materials, conductors lacking spatial inversion symmetry couple charge currents
to spin by intrinsic spin-orbit (SO) interactions, inducing nonequilibrium spin
polarization tunable by local electric fields. Here we show that magnetization
of a ferromagnet can be reversibly manipulated by the SO-induced polarization
of carrier spins generated by unpolarized currents. Specifically, we
demonstrate domain rotation and hysteretic switching of magnetization between
two orthogonal easy axes in a model ferromagnetic semiconductor.",0812.3160v2
2020/7/8,Magnetoelectric effect arising from a field-induced pseudo Jahn-Teller distortion in a rare earth magnet,"Magnetoelectric materials are attractive for several applications, including
actuators, switches, and magnetic field sensors. Typical mechanisms for
achieving a strong magnetoelectric coupling are rooted in transition metal
magnetism. In sharp contrast, here we identify CsEr(MoO4)2 as a magnetoelectric
material without magnetic transition metal ions, thus ensuring that the Er ions
play a key role in achieving this interesting property. Our detailed study
includes measurements of the structural, magnetic, and electric properties of
this material. Bulk characterization and neutron powder diffraction show no
evidence for structural phase transitions down to 0.3 K and therefore
CsEr(MoO4)2 maintains the room temperature P2/c space group over a wide
temperature range without external magnetic field. These same measurements also
identify collinear antiferromagnetic ordering of the Er3+ moments below TN =
0.87 K. Complementary dielectric constant and pyroelectric current measurements
reveal that a ferroelectric phase (P ~ 0.5 nC/cm2) emerges when applying a
modest external magnetic field, which indicates that this material has a strong
magnetoelectric coupling. We argue that the magnetoelectric coupling in this
system arises from a pseudo Jahn-Teller distortion induced by the magnetic
field.",2007.04274v1
2023/8/28,Magnetic kagome materials RETi3Bi4 family with weak interlayer interactions,"Kagome materials have attracted a surge of research interest recently,
especially for the ones combining with magnetism, and the ones with weak
interlayer interactions which can fabricate thin devices. However, kagome
materials combining both characters of magnetism and weak interlayer
interactions are rare. Here we investigate a new family of titanium based
kagome materials RETi3Bi4 (RE = Eu, Gd and Sm). The flakes of nanometer
thickness of RETi3Bi4 can be obtained by exfoliation due to the weak interlayer
interactions. According to magnetic measurements, out-of-plane ferromagnetism,
out-of-plane anti-ferromagnetism, and in-plane ferromagnetism are formed for RE
= Eu, Gd, and Sm respectively. The magnetic orders are simple and the
saturation magnetizations can be relatively large since the rare earth elements
solely provide the magnetic moments. Further by angle-resolved photoemission
spectroscopy (ARPES) and first-principles calculations, the electronic
structures of RETi3Bi4 are investigated. The ARPES results are consistent with
the calculations, indicating the bands characteristic with kagome sublattice in
RETi3Bi4. We expect these materials to be promising candidates for observation
of the exotic magnetic topological phases and the related topological quantum
transport studies.",2308.14509v1
2023/9/21,Magnetic order in the computational 2D materials database (C2DB) from high throughput spin spiral calculations,"We report a detailed investigation of the magnetic order in 192 stable
magnetic two-dimensional materials from the Computational 2D Materials Database
having one magnetic atom in the unit cell. The calculations are based on a
systematic workflow that employs spin spiral calculations and yields the
magnetic order in terms of a two-dimensional ordering vector $\mathbf{Q}$. We
then include spin-orbit coupling to extract the easy and hard axes for
collinear structures and the orientation of spiral planes in non-collinear
structures. Finally, for all predicted ferromagnets we compute the
Dzyaloshinskii-Moriya interactions and determine whether or not these are
strong enough to overcome the magnetic anisotropy and stabilise a chiral spin
spiral ground state. These steps completely determines the ground state order
within the spiralling ansatz. We find 58 ferromagnets, 21 collinear
anti-ferromagnets, and 85 non-collinear ground states of which 15 are chiral
spin spirals driven by Dzyaloshinskii-Moriya interactions. The results show
that non-collinear order is in fact as common as collinear order in these
materials and emphasise the need for detailed investigation of the magnetic
ground state when reporting magnetic properties of new materials. Furthermore,
non-collinear order typically breaks symmetries inherent to the lattice and may
give rise to emergent properties such as multiferroicity, magnetoelectricity or
second order optical effects that would be predicted as absent based on a
collinear assumption.",2309.11945v1
2019/4/4,Band engineering of a magnetic thin film rare earth monopnictide,"Realizing quantum materials in few atomic layer morphologies is a key to both
observing and controlling a wide variety of exotic quantum phenomena. This
includes topological electronic materials, where the tunability and
dimensionality of few layer materials have enabled the detection of $Z_2$,
Chern, and Majorana phases. Here, we report the development of a platform for
thin film correlated, topological states in the magnetic rare-earth
monopnictide ($RX$) system GdBi synthesized by molecular beam epitaxy. This
material is known from bulk single crystal studies to be semimetallic
antiferromagnets with Neel temperature $T_N =$ 28 K and is the magnetic analog
of the non-$f$-electron containing system LaBi proposed to have topological
surface states. Our transport and magnetization studies of thin films grown
epitaxially on BaF$_2$ reveal that semimetallicity is lifted below
approximately 8 crystallographic unit cells while magnetic order is maintained
down to our minimum thickness of 5 crystallographic unit cells.
First-principles calculations show that the non-trivial topology is preserved
down to the monolayer limit, where quantum confinement and the lattice symmetry
give rise to a $C=2$ Chern insulator phase. We further demonstrate the
stabilization of these films against atmospheric degradation using a
combination of air-free buffer and capping procedures. These results together
identify thin film $RX$ materials as potential platforms for engineering
topological electronic bands in correlated magnetic materials.",1904.02582v1
2021/11/29,Prediction of Large Magnetic Moment Materials With Graph Neural Networks and Random Forests,"Magnetic materials are crucial components of many technologies that could
drive the ecological transition, including electric motors, wind turbine
generators and magnetic refrigeration systems. Discovering materials with large
magnetic moments is therefore an increasing priority. Here, using
state-of-the-art machine learning methods, we scan the Inorganic Crystal
Structure Database (ICSD) of hundreds of thousands of existing materials to
find those that are ferromagnetic and have large magnetic moments. Crystal
graph convolutional neural networks (CGCNN), materials graph network (MEGNet)
and random forests are trained on the Materials Project database that contains
the results of high-throughput DFT predictions. For random forests, we use a
stochastic method to select nearly one hundred relevant descriptors based on
chemical composition and crystal structure. This gives results that are
comparable to those of neural networks. The comparison between these different
machine learning approaches gives an estimate of the errors for our predictions
on the ICSD database. Validating our final predictions by comparisons with
available experimental data, we found 15 materials that are likely to have
large magnetic moments and have not been yet studied experimentally.",2111.14712v4
2020/6/25,In-plane magnetic domains and Néel-like domain walls in thin flakes of the room temperature CrTe$_2$ van der Waals ferromagnet,"The recent discovery of magnetic van der Waals materials has triggered a
wealth of investigations in materials science, and now offers genuinely new
prospects for both fundamental and applied research. Although the catalogue of
van der Waals ferromagnets is rapidly expanding, most of them have a Curie
temperature below 300 K, a notable disadvantage for potential applications.
Combining element-selective x-ray magnetic imaging and magnetic force
microscopy, we resolve at room temperature the magnetic domains and domains
walls in micron-sized flakes of the CrTe$_2$ van der Waals ferromagnet.
Flux-closure magnetic patterns suggesting in-plane six-fold symmetry are
observed. Upon annealing the material above its Curie point (315 K), the
magnetic domains disappear. By cooling back down the sample, a different
magnetic domain distribution is obtained, indicating material stability and
lack of magnetic memory upon thermal cycling. The domain walls presumably have
N\'eel texture, are preferentially oriented along directions separated by 120
degrees, and have a width of several tens of nanometers. Besides microscopic
mapping of magnetic domains and domain walls, the coercivity of the material is
found to be of a few mT only, showing that the CrTe$_2$ compound is
magnetically soft. The coercivity is found to increase as the volume of the
material decreases.",2006.14339v1
2019/11/14,Real time observation of a stationary magneton,"The magnetic dipole field geometry of subatomic elementary particles like the
electron differs from the classical macroscopic field imprint of a bar magnet.
It resembles more like an eight figure or else joint double quantum-dots
instead of the classical, spherical more uniform field of a bar magnet. This
actual subatomic quantum magnetic field of an electron at rest, is called
Quantum Magnet or else a Magneton. Normally, a macroscale bar magnet should
behave like a relative giant Quantum Magnet with identical magnetic dipole
field imprint since all of its individual magnetons collectively inside the
material, dipole moments are uniformly aligned forming the total net field of
the magnet. However due to Quantum Decoherence (QDE) phenomenon at the
macroscale and macroscopic magnetic field imaging sensors limitations which
cannot pickup these rapid quantum magnetization fluctuations, this field is
masked and not visible at the macroscale. By using the relative inexpensive
submicron resolution Ferrolens quantum magnetic optical sensor and method, we
can actually make this net magneton field visible on macroscale magnets. We
call this net total field herein, Quantum Field of Magnet (QFM) differentiating
it therefore from the field of the single subatomic magneton thus quantum
magnet. Additionally, the unique potential of the Ferrolens device to display
also the magnetic flux lines of this macroscopically projected giant Magenton
gives us the unique opportunity to study the individual magnetic flux lines
geometrical pattern that of a single subatomic magneton. We describe this
particular magnetic flux of the magneton observed, quantum magnetic flux.
Therefore a novel observation has been made that the QFM of the Magnet-Magneton
consists of a dipole vortex shaped magnetic flux geometrical pattern
responsible for creating the classical macroscopic N-S field of the magnet.",1911.05735v1
2005/8/4,On Rapidly Rotating Magnetic Core-Collapse Supernovae,"We have analyzed the magnetic effects that may occur in rapidly rotating core
collapse supernovae. We consider effects from both magnetic turbulence and the
formation of magnetic bubbles. For magnetic turbulence we have made a
perturbative analysis for our spherically symmetric core-collapse supernova
model that incorporates the build up of magnetic field energy in the matter
accreting onto the proto-neutron star shortly after collapse and bounce. This
significantly modifies the pressure profile and increases the heating of the
material above the proto-neutron star resulting in an explosion even in
rotating stars that would not explode otherwise. Regarding magnetic bubbles we
show that a model with a modest initial uniform magnetic field and uniform
angular velocity of ~0.1 rad/s can form magnetic bubbles due to the very non
homologous nature of the collapse. It is estimated that the buoyancy of the
bubbles causes matter in the proto-neutron star to rise, carrying neutrino-rich
material to the neutron-star surface. This increases the neutrino luminosity
sufficiently at early times to achieve a successful neutrino-driven explosion.
Both magnetic mechanisms thus provide new means for initiating a Type II
core-collapse supernova.",0508146v1
2001/10/4,Dynamics of Magnetization Reversal in Models of Magnetic Nanoparticles and Ultrathin Films,"We discuss numerical and theoretical results for models of magnetization
switching in nanoparticles and ultrathin films. The models and computational
methods include kinetic Ising and classical Heisenberg models of highly
anisotropic magnets which are simulated by dynamic Monte Carlo methods, and
micromagnetics models of continuum-spin systems that are studied by
finite-temperature Langevin simulations. The theoretical analysis builds on the
fact that a magnetic particle or film that is magnetized in a direction
antiparallel to the applied field is in a metastable state. Nucleation theory
is therefore used to analyze magnetization reversal as the decay of this
metastable phase to equilibrium. We present numerical results on magnetization
reversal in models of nanoparticles and films, and on hysteresis in magnets
driven by oscillating external fields.",0110103v1
2006/7/12,The Stoner-Wohlfarth model of Ferromagnetism: Static properties,"Recent advances in high-density magnetic storage and spin electronics are
based on the use of magnetic materials along with conventional microelectronic
materials (metals, insulators and semiconductors). The unit information (bit)
is stored as a magnetization state in some ferromagnetic ma rial (FM) and
controlled with an external field altering the magnetization state. As device
size is shrinking steadily toward the nanometer and the need to incr se its
bandwidth prevails, racing toward higher frequencies is getting even more cha
enging. In magnetic systems, denser storage leads to finer magnetic grains and
small size leads to single magnetic domain physics. The Stoner-Wohlfarth model
is the simplest model that describes adequately the physics of fine magnetic
grains containing single domains and where magnetization state changes by
rotation or switching (abrupt reversal). The SW model is reviewed and discussed
with its consequences and potential app cations in the physics of magnetism and
spin electronics.",0607117v3
2011/11/29,Low magnetic field reversal of electric polarization in a Y-type hexaferrite,"Magnetoelectric multiferroics in which ferroelectricity and magnetism coexist
have attracted extensive attention because they provide great opportunities for
the mutual control of electric polarization by magnetic fields and
magnetization by electric fields. From a practical point view, the main
challenge in this field is to find proper multiferroic materials with a high
operating temperature and great magnetoelectric sensitivity. Here we report on
the magnetically tunable ferroelectricity and the giant magnetoelectric
sensitivity up to 250 K in a Y-type hexaferrite, BaSrCoZnFe11AlO22. Not only
the magnitude but also the sign of electric polarization can be effectively
controlled by applying low magnetic fields (a few hundreds of Oe) that modifies
the spiral magnetic structures. The magnetically induced ferroelectricity is
stabilized even in zero magnetic field. Decayless reproducible flipping of
electric polarization by oscillating low magnetic fields is shown. The maximum
linear magnetoelectric coefficient reaches a high value of ~ 3.0\times10^3 ps/m
at 200 K.",1111.6753v2
2012/3/17,Magnetic domain structure of epitaxial Ni-Mn-Ga films,"For the magnetic shape memory effect, knowledge about the interaction between
martensitic and magnetic domain structure is essential. In the case of Ni-Mn-Ga
bulk material and foils, a staircase-like magnetic domain structure with
90{\deg}- and 180{\deg}-domain walls is known for modulated martensite. In the
present paper we show that the magnetic domain pattern of thin epitaxial films
is fundamentally different. Here we analyze epitaxial Ni-Mn-Ga films by atomic
and magnetic force microscopy to investigate the correlation between the
twinned martensitic variants and the magnetic stripe domains. The observed
band-like domains with partially perpendicular outof-plane magnetization run
perpendicular to the microstructure domains defined by twinning variants. These
features can be explained by the finite film thickness, resulting in an
equilibrium twinning period much smaller than the domain period. This does not
allow the formation of a staircase domain patter. Instead the energies of the
magnetic and martensitic microstructures are minimized independently by
aligning both patterns perpendicularly to each other. By analyzing a thickness
series we can show that the observed magnetic domain pattern can be
quantitatively described by an adapted band domain model of Kittel.",1203.3840v1
2012/3/30,Field induced changes in cycloidal spin ordering and coincidence between magnetic and electric anomalies in BiFeO3 multiferroic,"The ZFC and FC magnetization dependence on temperature was measured for
BiFeO3 ceramics at the applied magnetic field up to H=10T in 2K-1000K range.
The antiferromagnetic order was detected from the hysteresis loops below the
Neel temperature TN=646K. In the low magnetic field range there is an anomaly
in M(H), probably due to the field-induced transition from circular cycloid to
the anharmonic cycloid. At high field limit we observe the field-induced
transition to the homogeneous spin order. From the M(H) dependence we deduce
that above the field Ha the spin cycloid becomes anharmonic which causes
nonlinear magnetization, and above the field Hc the cycloid vanishes and the
system again exhibits linear magnetization M(H). The anomalies in the electric
properties, which are manifested within the 640K-680K range, coincide to the
anomaly in the magnetization M(T) dependence, which occurs in the vicinity of
TN. We propose to ascribe this coincidence to the critical behaviour of the
chemical potential, related to the magnetic phase transition.",1203.6886v1
2013/2/7,"Crystal Structure and Magnetic Properties of the Ba3TeCo3P2O14, Pb3TeCo3P2O14, and Pb3TeCo3V2O14 Langasites","We report the structural and magnetic characterizations of Ba3TeCo3P2O14,
Pb3TeCo3P2O14, and Pb3TeCo3V2O14, compounds that are based on the mineral
Dugganite, which is isostructural to Langasites. The magnetic part of the
structure consists of layers of Co2+ triangles. Nuclear and magnetic structures
were determined through a co-refinement of synchrotron and neutron powder
diffraction data. In contrast to the undistorted P321 Langasite structure of
Ba3TeCo3P2O14, a complex structural distortion yielding a large supercell is
found for both Pb3TeCo3P2O14 and Pb3TeCo3V2O14. Comparison of the three
compounds studied along with the zinc analog Pb3TeZn3P2O14, also characterized
here, suggests that the distortion is driven by Pb2+ lone pairs; as such, the
Pb compounds crystallize in a pyroelectric space group, P2. Magnetic
susceptibility, magnetization, and heat capacity measurements were performed to
characterize the magnetic behavior. All three compounds become
antiferromagnetic with N\'eel temperatures TN ~ 21 K (Ba3TeCo3P2O14), ~ 13 K
(Pb3TeCo3P2O14), and ~ 8 K (Pb3TeCo3V2O14), and they exhibit magnetic
transitions at high applied magnetic fields, suggesting intrinsically complex
magnetic behavior for tetrahedrally coordinated d7 Co2+ in this structure type.",1302.1636v1
2013/3/21,"Co monolayers and adatoms on Pd(100), Pd(111) and Pd(110): Anisotropy of magnetic properties","We investigate to what extent the magnetic properties of deposited
nanostructures can be influenced by selecting as a support different surfaces
of the same substrate material. Fully relativistic ab initio calculations were
performed for Co monolayers and adatoms on Pd(100), Pd(111), and Pd(110)
surfaces. Changing the crystallographic orientation of the surface has a
moderate effect on the spin magnetic moment and on the number of holes in the d
band, a larger effect on the orbital magnetic moment but sometimes a dramatic
effect on the magnetocrystalline anisotropy energy (MAE) and on the magnetic
dipole term T_alpha. The dependence of T_alpha on the magnetization direction
alpha can lead to a strong apparent anisotropy of the spin magnetic moment as
deduced from the X-ray magnetic circular dichroism (XMCD) sum rules. For
systems in which the spin-orbit coupling is not very strong, the T_alpha term
can be understood as arising from the differences between components of the
spin magnetic moment associated with different magnetic quantum numbers m.",1303.5262v1
2013/3/27,Possible valence-bond condensation in the frustrated cluster magnet LiZn2Mo3O8,"The emergence of complex electronic behaviour from simple ingredients has
resulted in the discovery of numerous states of matter. Many examples are found
in systems exhibiting geometric magnetic frustration, which prevents
simultaneous satisfaction of all magnetic interactions. This frustration gives
rise to complex magnetic properties such as chiral spin structures
orbitally-driven magnetism, spin-ice behavior exhibiting Dirac strings with
magnetic monopoles, valence bond solids, and spin liquids. Here we report the
synthesis and characterization of LiZn2Mo3O8, a geometrically frustrated
antiferromagnet in which the magnetic moments are localized on small transition
metal clusters rather than individual ions. By doing so, first order
Jahn-Teller instabilities and orbital ordering are prevented, allowing the
strongly interacting magnetic clusters in LiZn2Mo3O8 to probably give rise to
an exotic condensed valence-bond ground state reminiscent of the proposed
resonating valence bond state. Our results also link magnetism on clusters to
geometric magnetic frustration in extended solids, demonstrating a new approach
for unparalleled chemical control and tunability in the search for collective,
emergent electronic states of matter.",1303.6986v1
2013/4/23,Interfacial tuning of perpendicular magnetic anisotropy and spin magnetic moment in CoFe/Pd multilayers,"We report on a strong perpendicular magnetic anisotropy in [CoFe 0.4nm/Pd t]6
(t = 1.0-2.0 nm) multilayers fabricated by DC sputtering in a ultrahigh vacuum
chamber. Saturation magnetization, $M_s$, and uniaxial anisotropy, $K_u$, of
the multilayers decrease with increasing the spacing thickness, with a $M_s$ of
155 emu/cc and a $K_u$ of 1.14$\times 10^5$ J/m$^3$ at a spacing thickness of t
= 2 nm. X-ray absorption spectroscopy and X-ray magnetic circular dichroism
measurements reveal that spin and orbital magnetic moments of Co and Fe in CoFe
film decrease as function of Pd thickness, indicating the major contribution of
surface/interfacial magnetism to the magnetic properties of the film.",1304.6156v2
2013/6/27,Amorphous GdFeCo Films Exhibiting Large and Tunable Perpendicular Magnetic Anisotropy,"We report the compositional and temperature dependence of magnetic
compensation in amorphous GdFeCo films. Magnetic compensation is attributed to
the competition between antiferromagnetic coupling of rare-earth with
transition-metal (TM) ions and ferromagnetic interaction between the TM ions.
The low-Gd region from 20 to 34 at. % was found to exhibit compensation
phenomena characterized by a low saturation magnetization and perpendicular
magnetic anisotropy (PMA) near the compensation temperature. Compensation
temperature was not observed in previously unreported high-Gd region from 52 to
59 at. %, in qualitative agreement with results from recent model calculations.
However, low magnetization was achieved at room temperature, accompanied by a
large PMA with coercivity reaching ~6.6 kOe. The observed perpendicular
magnetic anisotropy of amorphous GdFeCo films probably has a structural origin
consistent with certain aspects of the atomic-scale anisotropy. Our findings
have broadened the composition range of transition metal-rare earth alloys for
designing PMA films, making it attractive for tunable magnetic anisotropy in
nanoscale devices.",1306.6451v1
2013/9/2,Recent progress in perpendicularly magnetized Mn-based binary alloy films,"In this article, we review the recent progress in growth, structural
characterization, magnetic properties and related spintronic devices of
tetragonal MnxGa and MnxAl thin films with perpendicular magnetic anisotropy.
In the first part of this review, we present a brief introduction to the
demands for perpendicularly magnetized materials in spintronics, magnetic
recording and permanent magnets applications, and the most promising candidates
of tetragonal MnxGa and MnxAl with strong perpendicular anisotropy. Then, in
the second and third parts, we focus on the recent progress of perpendicularly
magnetized MnxGa and MnxAl, respectively, including their lattice structures,
bulk synthesis, epitaxial growth, structural chracterizations, magnetic and
other spin-dependent properties, and spintronic devices like magnetic tunneling
junctions, spin valves and spin injector into semiconductors. Finally, we give
a summary and a perspective of these perpendicularly magnetized Mn-based binary
alloy films for future applications.",1309.0298v2
2014/12/2,Third-order effect in magnetic small-angle neutron scattering by a spatially inhomogeneous medium,"Magnetic small-angle neutron scattering (SANS) is a powerful tool for
investigating nonuniform magnetization structures inside magnetic materials.
Here, considering a ferromagnetic medium with weakly inhomogeneous uniaxial
magnetic anisotropy, saturation magnetization, and exchange stiffness, we
derive the second-order (in the amplitude of the inhomogeneities) micromagnetic
solutions for the equilibrium magnetization textures and compute the
corresponding magnetic SANS cross sections up to the next, third order. We find
that in the case of perpendicular scattering (the incident neutron beam is
perpendicular to the applied magnetic field) if twice the cross section along
the direction orthogonal to both the field and the neutron beam is subtracted
from the cross section along the field direction, the result has only a
third-order contribution (the lower-order terms are canceled). This difference
does not depend on the amplitude of the exchange inhomogeneities and provides a
separate gateway for a deeper analysis of the sample's magnetic structure. We
derive and analyze analytical expressions for the dependence of this
combination on the scattering-vector magnitude for the case of spherical
Gaussian inhomogeneities.",1412.1059v1
2015/7/16,Coherent radiation by magnets with exchange interactions,"A wide class of materials acquires magnetic properties due to particle
interactions through exchange forces. These can be atoms and molecules
composing the system itself, as in the case of numerous magnetic substances. Or
these could be different defects, as in the case of graphene, graphite, carbon
nanotubes, and related materials. The theory is suggested describing fast
magnetization reversal in magnetic systems, whose magnetism is caused by
exchange interactions. The effect is based on the coupling of a magnetic sample
with an electric circuit producing a feedback magnetic field. This method can
find various applications in spintronics. The magnetization reversal can be
self-organized, producing spin superradiance. A part of radiation is absorbed
by a resonator magnetic coil. But an essential part of radiation can also be
emitted through the coil sides.",1507.04560v1
2017/8/26,Scaling of Memories and Crossover in Glassy Magnets,"Glassiness is ubiquitous and diverse in characteristics in nature.
Understanding their differences and classification remains a major scientific
challenge. Here, we show that scaling of magnetic memories with time can be
used to classify magnetic glassy materials into two distinct classes. The
systems studied are high-temperature superconductor-related materials,
spin-orbit Mott insulators, frustrated magnets, and dilute magnetic alloys. Our
bulk magnetization measurements reveal that most densely populated magnets
exhibit similar memory behavior characterized by a relaxation exponent of 1-n ~
0.6(1). This exponent is different from 1-n ~ 1/3 of dilute magnetic alloys
that was ascribed to their hierarchical and fractal energy landscape and is
also different from 1-n=1 of the conventional Debye relaxation expected for a
spin solid, a state with long range order. Furthermore, our systematic study on
dilute magnetic alloys with varying magnetic concentration exhibits crossovers
among the two glassy states and spin solid.",1708.07974v1
2018/4/10,Engineering and improving the magnetic properties of thin Fe layers through exchange coupling with hard magnetic Dysprosium layers,"We report on a comprehensive study of the magnetic coupling between soft
magnetic Fe layers and hard magnetic Dysprosium (Dy) layers at low temperatures
(4.2 - 120K). For our experiments we prepared thin films of Fe and Dy and
multilayers of Fe/Dy by ultra-high vacuum sputtering. The magnetic properties
of each material were determined with a superconducting quantum interference
device. Furthermore, we performed magnetoresistance measurements with similarly
grown, microstructured devices, where the anisotropic magnetoresistance (AMR)
effect was used to identify the magnetization state of the samples. By
analyzing and comparing the corresponding data of Fe and Dy, we show that the
presence of a Dy layer on top of the Fe layer significantly influences its
magnetic properties and makes it magnetically harder. We perform a systematic
evaluation of this effect and its dependence on temperature and on the
thickness of the soft magnetic layer. All experimental results can consistently
be explained with exchange coupling at the interface between the Fe and the Dy
layer. Our experiments also yield a negative sign of the AMR effect of thin Dy
films, and an increase of the Dy films' Curie temperature, which is due to
growth conditions.",1804.03609v1
2012/11/19,Magnetically controlled accretion onto a black hole,"An accretion scenario in which the material captured by a black hole from its
environment is assumed to be magnetized (\beta ~ 1) is discussed. We show that
the accretion picture in this case is strongly affected by the magnetic field
of the flow itself. The accretion power within this Magnetically Controlled
Accretion (MCA) scenario is converted predominantly into the magnetic energy of
the accretion flow. The rapidly amplified field prevents the accretion flow
from forming a homogeneous Keplerian disk. Instead, the flow is decelerated by
its own magnetic field at a large distance (Shvartsman radius) from the black
hole and switches into a non-Keplerian dense magnetized slab. The material in
the slab is confined by the magnetic field and moves towards the black hole on
the time scale of the magnetic field annihilation. The basic parameters of the
slab are evaluated. Interchange instabilities in the slab may lead to a
formation of Z-pinch type configuration of the magnetic field over the slab in
which the accretion power can be converted into jets and high-energy radiation.",1211.4400v1
2017/6/16,Observation of Various and Spontaneous Magnetic Skyrmionic Bubbles at Room-Temperature in a Frustrated Kagome Magnet with Uniaxial Magnetic Anisotropy,"Various and spontaneous magnetic skyrmionic bubbles are experimentally
observed for the first time, at room temperature in a frustrated kagome magnet
Fe3Sn2 with unixial magnetic anisotropy. The magnetization dynamics were
investigated using in-situ Lorentz transmission electron microscopy, revealing
that the transformation between different magnetic bubbles and domains are via
the motion of Bloch lines driven by applied external magnetic field. The
results demonstrate that Fe3Sn2 facilitates a unique magnetic control of
topological spin textures at room temperature, making it a promising candidate
for further skyrmion-based spintronic devices.",1706.05177v1
2020/3/12,Designing Magnetic Topological van der Waals Heterostructure,"We demonstrate a new method of designing 2D functional magnetic topological
heterostructure (HS) by exploiting the vdw heterostructure (vdw-HS) through
combining 2D magnet CrI$_3$ and 2D materials (Ge/Sb) to realize new 2D
topological system with nonzero Chern number (C=1) and chiral edge state. The
nontrivial topology originates primarily from the CrI$_3$ layer while the
non-magnetic element induces the charge transfer process and proximity enhanced
spin-orbit coupling. Due to these unique properties, our topological magnetic
vdw-HS overcomes the weak magnetization via proximity effect in previous
designs since the magnetization and topology coexist in the same magnetic
layer. Specifically, our systems of bilayer CrI$_3$/Sb and trilayer
CrI$_3$/Sb/CrI$_3$ exhibit different topological ground state ranging from
antiferromagnetic topological crystalline insulator (C$_M$= 2) to a QAHE. These
nontrivial topological transition is shown to be switchable in a trilayer
configuration due to the magnetic switching from antiferromagnetism to
ferromangetism in the presence an external perpendicular electric field with
value as small as 0.05 eV/A. Thus our study proposes a realistic system to
design switchable magnetic topological device with electric field.",2003.05840v1
2016/12/19,Sensitivity of Fields Generated within Magnetically Shielded Volumes to Changes in Magnetic Permeability,"Future experiments seeking to measure the neutron electric dipole moment
(nEDM) require stable and homogeneous magnetic fields. Normally these
experiments use a coil internal to a passively magnetically shielded volume to
generate the magnetic field. The stability of the magnetic field generated by
the coil within the magnetically shielded volume may be influenced by a number
of factors. The factor studied here is the dependence of the internally
generated field on the magnetic permeability $\mu$ of the shield material. We
provide measurements of the temperature-dependence of the permeability of the
material used in a set of prototype magnetic shields, using experimental
parameters nearer to those of nEDM experiments than previously reported in the
literature. Our measurements imply a range of $\frac{1}{\mu}\frac{d\mu}{dT}$
from 0-2.7\%/K. Assuming typical nEDM experiment coil and shield parameters
gives $\frac{\mu}{B_0}\frac{dB_0}{d\mu}=0.01$, resulting in a temperature
dependence of the magnetic field in a typical nEDM experiment of
$\frac{dB_0}{dT}=0-270$~pT/K for $B_0=1~\mu$T. The results are useful for
estimating the necessary level of temperature control in nEDM experiments.",1612.06047v2
2017/7/11,Magnetophononics: ultrafast spin control through the lattice,"Using a combination of first-principles and magnetization-dynamics
calculations, we study the effect of the intense optical excitation of phonons
on the magnetic behavior in insulating magnetic materials. Taking the
prototypical magnetoelectric \CrO\ as our model system, we show that excitation
of a polar mode at 17 THz causes a pronounced modification of the magnetic
exchange interactions through a change in the average Cr-Cr distance. In
particular, the quasi-static deformation induced by nonlinear phononic coupling
yields a structure with a modified magnetic state, which persists for the
duration of the phonon excitation. In addition, our time-dependent
magnetization dynamics computations show that systematic modulation of the
magnetic exchange interaction by the phonon excitation modifies the
magnetization dynamics. This temporal modulation of the magnetic exchange
interaction strengths using phonons provides a new route to creating
non-equilibrium magnetic states and suggests new avenues for fast manipulation
of spin arrangements and dynamics.",1707.03216v3
2018/11/9,Giant Exchange Bias in the Single-layered Ruddlesden-Popper Perovskite SrLaCo0.5Mn0.5O4,"Exchange bias (EB) as large as ~5.5 kOe is observed in SrLaCo0.5Mn0.5O4 which
is the highest ever found in any layered transition metal oxides including
Ruddlesden-Popper series. Neutron diffraction measurement rules out long-range
magnetic ordering and together with dc magnetic measurements suggest formation
of short-range magnetic domains. AC magnetic susceptibility, magnetic memory
effect and magnetic training effect confirm the system to be a cluster spin
glass. By carrying out density functional calculations on several model
configurations, we propose that EB is originated at the boundary between
Mn-rich antiferromagnetic and Co-rich ferromagnetic domains at the
sub-nanoscale. Reversal of magnetization axis on the Co-side alters the
magnetic coupling between the interfacial Mn and Co spins which leads to EB.
Our analysis infers that the presence of competing magnetic interactions is
sufficient to induce exchange bias and thereby a wide range of materials
exhibiting giant EB can be engineered for designing novel magnetic memory
devices.",1811.03960v1
2019/3/28,Computational Design of the Rare-Earth Reduced Permanent Magnets,"Multiscale simulation is a key research tool for the quest for new permanent
magnets. Starting with first principles methods, a sequence of simulation
methods can be applied to calculate the maximum possible coercive field and
expected energy density product of a magnet made from a novel magnetic material
composition. Fe-rich magnetic phases suitable for permanent magnets can be
found by adaptive genetic algorithms. The intrinsic properties computed by ab
initio simulations are used as input for micromagnetic simulations of the
hysteresis properties of permanent magnets with realistic structure. Using
machine learning techniques, the magnet's structure can be optimized so that
the upper limits for coercivity and energy density product for a given phase
can be estimated. Structure property relations of synthetic permanent magnets
were computed for several candidate hard magnetic phases. The following pairs
(coercive field (T), energy density product (kJ/m3)) were obtained for
Fe3Sn0.75Sb0.25: (0.49, 290), L10 FeNi: (1, 400), CoFe6Ta: (0.87, 425), and
MnAl: (0.53, 80).",1903.11995v1
2019/5/21,Commensurate to incommensurate magnetic phase transition in Honeycomb-lattice pyrovanadate Mn2V2O7,"We have synthesized single crystalline sample of Mn$_2$V$_2$O$_7$ using
floating zone technique and investigated the ground state using magnetic
susceptibility, heat capacity and neutron diffraction. Our magnetic
susceptibility and heat capacity reveal two successive magnetic transitions at
$T_{N1} =$ 19 K and $T_{N2} =$ 11.8 K indicating two distinct magnetically
ordered phases. The single crystal neutron diffraction study shows that in the
temperature ($T$) range 11.8 K $\le T \le$ 19 K the magnetic structure is
commensurate with propagation vector $k_1 = (0, 0.5, 0)$, while upon lowering
temperature below $T_{N2} =$ 11.8 K an incommensurate magnetic order emerges
with $k_2 = (0.38, 0.48, 0.5)$ and the magnetic structure can be represented by
cycloidal modulation of the Mn spin in $ac-$plane. We are reporting this
commensurate to incommensurate transition for the first time. We discuss the
role of the magnetic exchange interactions and spin-orbital coupling on the
stability of the observed magnetic phase transitions.",1905.08722v1
2019/12/28,Manipulating magnetic fields in inaccessible regions by negative magnetic permeability,"The control of magnetic fields underpins a wide variety of cutting-edge
technologies, ranging from the guiding of micro-robots for medical applications
to the trapping of atoms for quantum experiments. Relying on different
arrangements of coils, these technologies demand advances in the manipulation
of magnetic fields at a distance from the sources that generate them. Here, we
present a strategy for remotely shaping magnetic fields based on active
magnetic metamaterials with negative permeability and we theoretically and
experimentally demonstrate the possibility of emulating and cancelling magnetic
sources at distance. Our strategy provides magnetic field focusing deep into
physically inaccessible volumes where neither sources of magnetic field nor
magnetic materials can be placed.",1912.12477v1
2020/5/19,New Way of Generating Electromagnetic Waves,"This paper presents a new method for generating low-frequency electromagnetic
waves for navigation and communication in challenging environments, such as
underwater and underground. The main idea is to store magnetic energy in two
different spaces using the interaction between a permanent magnet and a
magnetic material. The magnetic reluctance of the medium around the permanent
magnet is modulated to change the magnetic flux path. The nonlinear properties
of magnetic material as a critical phenomenon are used for effective
modulation. As a result, a time-variant field is generated by the modulation of
the permanent magnet flux. This non-resonant time-variant characterization
means that the transmitter is not bound to the fundamental limits of the
antennas and can transmit higher data rates. A prototype transmitter as a
prove-of-concept is designed and tested based on the proposed idea. Compared to
the rotating magnet, the prototyped transmitter can modulate $50\%$ of the
stored energy of the permanent magnet with much lower power consumption.",2005.09707v1
2020/9/15,A new class of intrinsic magnet: two-dimensional yttrium sulphur selenide,"Exploring and controlling magnetism in two-dimensional (2D) layered magnetic
crystals, as well as their inclusion in heterogeneous assemblies, provide an
unprecedented opportunity for fundamental science and technology. To date,
however, there are only a few known intrinsic 2D magnets. Here we predict a
novel 2D intrinsic magnet, yttrium sulfur selenide (YSSe), using
first-principles calculations. The magnetism of this transition metal
dichalcogenide originates from the partially-filled $3p$- and $4p$-orbitals of
the chalcogens, unlike other known intrinsic magnets where magnetism arises
from the partially-filled $3d$- and $4f$-orbitals. The unconventional magnetism
in YSSe is a result of a unique combination of its structural and electronic
properties. We further show that a lack of mirror symmetry results in
piezoelectric properties, while the broken space- and time-symmetry ensures
valley polarization. YSSe is a rare magnetic-piezoelectric material that can
enable novel spintronics, valleytronics, and quantum technologies.",2009.07232v1
2020/12/8,Intrinsic magnetic topological insulators,"Introducing magnetism into topological insulators breaks time-reversal
symmetry, and the magnetic exchange interaction can open a gap in the otherwise
gapless topological surface states. This allows various novel topological
quantum states to be generated, including the quantum anomalous Hall effect
(QAHE) and axion insulator states. Magnetic doping and magnetic proximity are
viewed as being useful means of exploring the interaction between topology and
magnetism. However, the inhomogeneity of magnetic doping leads to complicated
magnetic ordering and small exchange gaps, and consequently the observed QAHE
appears only at ultralow temperatures. Therefore, intrinsic magnetic
topological insulators are highly desired for increasing the QAHE working
temperature and for investigating topological quantum phenomena further. The
realization and characterization of such systems are essential for both
fundamental physics and potential technical revolutions. This review summarizes
recent research progress in intrinsic magnetic topological insulators, focusing
mainly on the antiferromagnetic topological insulator MnBi2Te4 and its family
of materials.",2012.04258v3
2021/6/13,Investigation of physical dose enhancement in core-shell magnetic gold nanoparticles with TOPAS simulation,"The application of metal nanoparticles as sensitization materials is a common
strategy that is used to study dose enhancement in radiotherapy. Recent in
vitro tests have revealed that magnetic gold nanoparticles can be used in
cancer therapy under a magnetic field to enhance the synergistic efficiency in
radiotherapy and photothermal therapy. However, magnetic gold nanoparticles
have rarely been studied as sensitization materials. In this study, we obtained
further results of the sensitization properties of magnetic gold nanoparticles
using the Monte Carlo method TOPAS and TOPAS-nBio. We analyzed the properties
of magnetic gold nanoparticles in monoenergetic photons and brachytherapy, and
we investigated whether the magnetic field contributes to the sensitization
process. Our results demonstrated that the dose enhancement factor of the
magnetic gold nanoparticles was 16.7% lower than that of gold nanoparticles in
a single particle irradiated by monoenergetic photons. In the cell model, the
difference was less than 8.1% in the cytoplasm. We revealed that the magnetic
field has no detrimental effect on radiosensitization. Moreover, the
sensitization properties of magnetic gold nanoparticles in a clinical
brachytherapy source have been revealed for the first time.",2106.06941v1
2021/10/21,Magnetic hysteresis of individual Janus particles with hemispherical exchange-biased caps,"We use sensitive dynamic cantilever magnetometry to measure the magnetic
hysteresis of individual magnetic Janus particles. These particles consist of
hemispherical caps of magnetic material deposited on micrometer-scale silica
spheres. The measurements, combined with corresponding micromagnetic
simulations, reveal the magnetic configurations present in these individual
curved magnets. In remanence, ferromagnetic Janus particles are found to host a
global vortex state with vanishing magnetic moment. In contrast, a remanent
onion state with significant moment is recovered by imposing an exchange bias
to the system via an additional antiferromagnetic layer in the cap. A robust
remanent magnetic moment is crucial for most applications of magnetic Janus
particles, in which an external magnetic field actuates their motion.",2110.11158v1
2022/1/31,Observation of magnetization surface textures of the van der Waals antiferromagnet FePS3 by spin Hall magnetoresistance,"Van der Waals materials are a new platform to study two-dimensional systems,
including magnetic order. Since the number of spins is relatively small,
measuring the magnetization is challenging. Here we report spin Hall
magnetoresistance (SMR) up to room temperature caused by the magnetic surface
texture of exfoliated flakes of magnetic van der Waals materials. For the
antiferromagnet FePS3 the SMR amounts to 0.1 % for an applied magnetic field of
7 T at 5 K which implies a substantial canting of the magnetic moments relative
to the colinear antiferromagnetic order. The canting is substantial even for a
magnetic field along the N\'eel vector, which illustrates the unique power of
the SMR to detect magnetic surface textures in van der Waals magnets.",2201.13241v1
2022/6/17,Theory of ultrafast magnetization of non-magnetic semiconductors with localized conduction bands,"The magnetization of a non-magnetic semiconductor by femtosecond light pulses
is crucial to achieve an all-optical control of the spin dynamics in materials
and to develop faster memory devices. However, the conditions for its detection
are largely unknown. In this work we identify the criteria for the observation
of ultrafast magnetization and critically discuss the difficulties hindering
its experimental detection. We show that ultrafast magnetization of a non
magnetic semiconductor can be observed in compounds with very localized
conduction band states and more delocalized valence bands, such as in the case
of a p-d charge transfer gap. By using constrained and time dependent density
functional theory simulations, we demonstrate that a transient ferrimagnetic
state can be induced in diamagnetic semiconductor V2O5 via ultrafast pulses at
realistic fluences. The ferrimagnetic state has opposite magnetic moments on
vanadium (conduction) and oxygen (valence) states. Our methodology outruns the
case of V2O5 as it identifies the key requirements for a computational
screening of ultrafast magnetism in non-magnetic semiconductors.",2206.08624v1
2023/2/23,In-situ Growth of Ultrathin Magnetic Films and Tuning the Magnetic Properties by Ion-sculpting,"Magnetic anisotropy is a key parameter of magnetic materials as it decides
the response in the presence of an external magnetic field. The artificial
tailoring of magnetic anisotropy by manipulating surface and interface
morphology is attracting widespread interest for its application in spintronic
and magnetic memory devices. In this perspective, the primary focus of this
thesis has been inducing and tailoring magnetic anisotropy in thin film-based
systems via the engineering of structure and surface/interfacial morphology.
For this purpose, instead of multistep, expensive lithographic techniques, we
have utilized low-energy IBE as a handy, cost-effective, and useful tool for
producing magnetic nanostructures and tailoring its surface structure,
morphology and magnetic anisotropy. Furthermore, we have also proposed various
new and unconventional methods (oblique angle deposition on the rippled
substrate, sequential deposition-erosion) for enhancement of UMA and proved its
effectiveness via experiments. We have performed most of the present thesis
work in-situ utilizing a UHV chamber to get genuine characteristics and
understand their interdependencies. However, advanced synchrotron-based
techniques such as GISAXS and NFS were also utilized to complement the in-situ
observations.",2302.11941v1
2023/6/11,Jahn-Teller magnets,"A wide class of materials with different crystal and electronic structures
from quasi-two-dimensional unconventional superconductors (cuprates,
nickelates, ferropnictides/chalcogenides, ruthenate SrRuO$_4$), 3D systems as
manganites RMnO$_3$, ferrates (CaSr)FeO$_3$, nickelates RNiO$_3$, to silver
oxide AgO are based on Jahn-Teller $3d$ and $4d$ ions. These unusual materials
called Jahn-Teller (JT) magnets are characterized by an extremely rich variety
of phase states from non-magnetic and magnetic insulators to unusual metallic
and superconducting states. The unconventional properties of the JT-magnets can
be related to the instability of their highly symmetric Jahn-Teller
""progenitors"" with the ground orbital $E$-state to charge transfer with
anti-Jahn-Teller $d$-$d$ disproportionation and the formation of a system of
effective local composite spin-singlet or spin-triplet, electronic or hole
$S$-type bosons moving in a non-magnetic or magnetic lattice. We consider
specific features of the anti-JT-disproportionation reaction, properties of the
electron-hole dimers, possible phase states of JT-magnets, effective
Hamiltonians for single- and two-band JT-magnets, and present a short overview
of physical properties for actual JT-magnets.",2306.06612v1
2015/10/2,Magnetic and gaseous spiral arms in M83,"Isotropic and anisotropic wavelet transforms are used to decompose the images
of the spiral galaxy M83 in various tracers to quantify structures in a range
of scales from 0.2 to 10 kpc. We used radio polarization observations at
{\lambda}6 cm and 13 cm obtained with the VLA, Effelsberg and ATCA telescopes
and APEX sub-mm observations at 870 {\mu}m, which are first published here,
together with maps of the emission of warm dust, ionized gas, molecular gas,
and atomic gas. The spatial power spectra are similar for the tracers of dust,
gas, and total magnetic field, while the spectra of the ordered magnetic field
are significantly different. The wavelet cross-correlation between all material
tracers and total magnetic field is high, while the structures of the ordered
magnetic field are poorly correlated with those of other tracers. -- The
magnetic field configuration in M83 contains pronounced magnetic arms. Some of
them are displaced from the corresponding material arms, while others overlap
with the material arms. The magnetic field vectors at {\lambda}6 cm are aligned
with the outer material arms, while significant deviations occur in the inner
arms and in the bar region, possibly due to non-axisymmetric gas flows. Outside
the bar region, the typical pitch angles of the material and magnetic spiral
arms are very close to each other at about 10{\deg}. The typical pitch angle of
the magnetic field vectors is about 20{\deg} larger than that of the material
spiral arms. One of the main magnetic arms in M83 is displaced from the gaseous
arms, while the other main arm overlaps a gaseous arm. We propose that a
regular spiral magnetic field generated by a mean-field dynamo is compressed in
material arms and partly aligned with them. The interaction of galactic dynamo
action with a transient spiral pattern is a promising mechanism for producing
such complicated spiral patterns as in M83.",1510.00746v3
2013/9/28,Synthetic Multiferroic Interconnects for Magnetic Logic Circuits,"In this work, we consider the possibility of using synthetic multiferroics
comprising piezoelectric and magnetostrictive materials as an interconnect for
nano magnetic logic circuits. The proposed interconnect resembles a parallel
plate capacitor filled with a piezoelectric, where one of the plates is made of
a magnetoelastic material. The operation of the interconnect is based on the
effect of stress-mediated anisotropy modulation, where an electric field
applied across the piezoelectric material produces stress, which, in turn,
affects the anisotropy field in the magnetostrictive material. We present the
results of numerical modeling illustrating signal propagation through the
interconnect. The model combines electric and magnetic parts, where the
electric part describes the distribution of an electric field through the
piezoelectric and the magnetic part describes the change of magnetization in
the magnetoelastic layer. The model is based on the Landau-Lifshitz-Gilbert
equation with the electric field dependent anisotropy term included. The
utilization of the electro-magnetic coupling makes it possible to amplify
magnetic signal during its propagation via energy conversion from the electric
to magnetic domains. Potentially, synthetic multiferroic interconnects can be
implemented in a variety of spin-based devices ensuring reliable and low-energy
consuming data transmission. According to the estimates, the group velocity of
magnetic signals may be up to 100 km/s with energy dissipation less than aJ per
bit per 100nm. The fundamental limits and practical shortcoming of the proposed
approach are also discussed.",1309.7399v1
2016/5/9,The lifetime cost of a magnetic refrigerator,"The total cost of a 25 W average load magnetic refrigerator using commercial
grade Gd is calculated using a numerical model. The price of magnetocaloric
material, magnet material and cost of operation are considered, and all
influence the total cost. The lowest combined total cost with a device lifetime
of 15 years is found to be in the range \$150-\$400 depending on the price of
the magnetocaloric and magnet material. The cost of the magnet is largest,
followed closely by the cost of operation, while the cost of the magnetocaloric
material is almost negligible. For the lowest cost device, the optimal magnetic
field is about 1.4 T, the particle size is 0.23 mm, the length of the
regenerator is 40-50 mm and the utilization is about 0.2, for all device
lifetimes and material and magnet prices, while the operating frequency vary as
function of device lifetime. The considered performance characteristics are
based on the performance of a conventional A$^{+++}$ refrigeration unit. In a
rough life time cost comparison between the magnetic refrigeration device and
such a unit we find similar costs, the former being slightly cheaper, assuming
the cost of the magnet can be recuperated at end of life.",1605.02524v1
2023/2/1,Temperature-independent ferromagnetic resonance shift in Bi-doped YIG garnets through magnetic anisotropy tuning,"Thin garnet films are becoming central for magnon-spintronics and
spin-orbitronics devices as they show versatile magnetic properties together
with low magnetic losses. These fields would benefit from materials in which
heat does not affect the magnetization dynamics, an effect known as the
non-linear thermal frequency shift. In this study, low damping Bi substituted
Iron garnet (Bi:YIG) ultra-thin films have been grown using Pulsed Laser
Deposition. Through a fine tuning of the growth parameters, the precise control
of the perpendicular magnetic anisotropy allows to achieve a full compensation
of the dipolar magnetic anisotropy. Strikingly, once the growth conditions are
optimized, varying the growth temperature from 405 {\deg}C to 475 {\deg}C as
the only tuning parameter induces the easy-axis to go from out-of-plane to
in-plane. For films that are close to the dipolar compensation, Ferromagnetic
Resonance measurements yield an effective magnetization $\mu _{0}M_{eff} (T)$
that has almost no temperature dependence over a large temperature range (260 K
to 400 K) resulting in an anisotropy temperature exponent of 2. These findings
put Bi:YIG system among the very few materials in which the temperature
dependence of the magnetic anisotropy varies at the same rate than the
saturation magnetization. This interesting behavior is ascribed
phenomenologically to the sizable orbital moment of $Bi^{3+}$.",2302.00585v1
2023/2/22,Exchange bias in molecule/Fe3GeTe2 van der Waals heterostructures via spinterface effects,"The exfoliation of layered magnetic materials generates atomically thin
flakes characterized by an ultrahigh surface sensitivity, which makes their
magnetic properties tunable via external stimuli, such as electrostatic gating
and proximity effects. Another powerful approach to tailor magnetic materials
is molecular functionalization, which leads to hybrid interface states with
peculiar magnetic properties, called spinterfaces. However, spinterface effects
have not yet been explored on layered magnetic materials. Here, we demonstrate
the emergence of spinterface effects at the interface between flakes of the
prototypical layered magnetic metal Fe3GeTe2 and thin films of paramagnetic
Co-phthalocyanine. Magnetotransport measurements show that the molecular layer
induces a magnetic exchange bias in Fe3GeTe2, indicating that the unpaired
spins in Co-phthalocyanine develop antiferromagnetic ordering by proximity and
pin the magnetization reversal of Fe3GeTe2. The effect is strongest for a
Fe3GeTe2 thickness of 20 nm, for which the exchange bias field reaches -840 Oe
and is measurable up to approximately 110 K. This value compares very favorably
with previous exchange bias fields reported for Fe3GeTe2 in all-inorganic van
der Waals heterostructures, demonstrating the potential of molecular
functionalization to tailor the magnetism of van der Waals layered materials.",2302.11071v2
2023/9/15,"Emergence of partially disordered antiferromagnetism and isothermal magnetization plateau due to geometrical frustration in a metallic compound, Er2RhSi3","Partially disordered antiferro (PDA) magnetism (in which one of the three
magnetic ions in a triangular network remains magnetically disordered), has
been known commonly among geometrically frustrated insulating materials. The
one-third plateau in isothermal magnetization (M) of such materials has been of
great theoretical interest. Here, we report these properties in a
AlB2-structure derived metallic material, Er2RhSi3 in which Er sublattice has
triangular networks. The presence of a well-defined lamda anomaly in the
temperature (T) dependence of heat capacity and its magnetic-field (H)
dependence, and the loss of spin-disorder contribution in electrical
resistivity (rho) confirm antiferromagnetic order below (TN=) 5 K. On the other
hand, the separation of zero-field-cooled and field-cooled dc magnetic
susceptibility (chi) curves, decay of isothermal remnant magnetization and the
frequency dependence of real and imaginary components of ac chi suggest the
onset of spin-glass freezing concomitant with the antiferromagnetic order. In
addition, interestingly, we observe one-third plateau in M(H) below 20 kOe for
T less than TN. The change in rho as a function of H at a given temperature
well below TN is also revealing, with this compound exhibiting a plateau below
20 kOe, with complexities at higher fields. Therefore, this compound serves as
a prototype for theoretical understanding of transport behavior across
one-third plateau due to PDA magnetism in a metal without any interference from
the 4f delocalization phenomena.",2309.08176v1
1999/7/7,Exotic structures on magnetic multilayers,"To characterize the possible magnetic structures created on magnetic
multilayers a model has been formulated and studied. The interlayer
inhomogeneous structures found indicate either (i) a regular periodic, (ii) a
quasiperiodic change in the magnetization or (iii) spatially chaotic glass
states. The magnetic structures created depend mainly on the ratio of the
magnetic anisotropy constant to the exchange constant.
  With the increase of this ratio the periodic structures first transform into
the quasiperiodic and then into the chaotic glass states. The same tendency
arises with the depolarization of the magnetic moments of the first layer
deposited on the substrate.",9907099v1
2000/5/17,Conversion of free magnetic polaron into vortex lattice in diluted magnetic semiconductors in quantizing magnetic fields,"We show that in strong (quantizing) magnetic fields ""ordinary"" free magnetic
polaron in diluted magnetic semiconductors (of type $A^2MeB^6$, where Me=Fe,
Mn) exists in the form of vortex lattice quite similar to that in type II
superconductors (Abricosov vortex lattice). The region of external parameters
(like external magnetic field and temperature), where such lattice exists, is
determined from the condition that lattice dimension is less or equal to
polaron localization radius.",0005285v1
2000/10/26,Magnetic storage device with improved temporal stability,"The current efforts to fabricate non-volatile magnetic recording media with a
high areal density is deteriorated by the increasing temporal instability of
the stored information. If the stored energy per magnetic particle competes
with the thermal energy, spontaneous magnetic reversal processes may occur.
Deposition of the magnetic particles on top of an antiferromagnetic substrate
will increase its energy barrier due to the exchange coupling between the two
subsystems. For this the magnetic moments of the antiferromagnet in the
vicinity of the magnetic particle have to deviate from their undisturbed
arrangement. This disturbation vanishes within a few lattice constants. In the
framework of a classical spin model we calculate the spin arrangements and the
resulting energy barriers for typical systems.",0010420v1
2000/12/15,Effective Interaction Hamiltonian of Polaron Pairs in Diluted Magnetic Semiconductors,"The magnetic interaction of a pair of bound magnetic polarons (BMP) in
diluted magnetic semiconductors (DMS) is analyzed via a generalized
Hubbard-type Hamiltonian for two carriers in the presence of effective magnetic
fields arising from the magnetic polarization of their respective polarons. For
the case where the magnetic fields at the two sites have equal magnitude but
are allowed to have arbitrary directions, it is shown that the energy of the
two polarons is minimized for a ferromagnetic configuration of the carrier
spins (in contrast to the case of hydrogenic centers in nonmagnetic
semiconductors) if polaron fields are strong enough. A modified Heisenberg-type
Hamiltonian is constructed to describe the low energy states of the resulting
system.",0012279v1
2003/5/28,Magnetic light,"In this paper we report on the observation of novel and highly unusual
magnetic state of light. It appears that in small holes light quanta behave as
small magnets so that light propagation through such holes may be affected by
magnetic field. When arrays of such holes are made, magnetic light of the
individual holes forms novel and highly unusual two-dimensional magnetic light
material. Magnetic light may soon become a great new tool for quantum
communication and computing.",0305661v1
2003/12/11,Current-Driven Switching in Magnetic Multilayer Nanopillars,"We summarize our recent findings on how the current-driven magnetization
switching in nanofabricated magnetic multilayers is affected by an applied
magnetic field, changes of temperature, magnetic coupling between the
ferromagnetic layers, variations in the multilayer structure, and the relative
rotation of the layers' magnetizations. We show how these results can be
interpreted with a model describing current-driven excitations as an effective
current-dependent magnetic temperature.",0312287v1
2003/12/22,Microscopic origin of the adiabatic change of magnetization in molecular magnets,"A microscopic model of the molecular magnet V15 is used to study mechanisms
for the adiabatic change of the magnetization in time-dependent magnetic
fields. Effects of the Dzyaloshinskii-Moriya interaction, the most plausible
source for the energy-level repulsions that lead to adiabatic changes of the
magnetization, are studied in detail. We find that the energy-level repulsions
that result from this interaction exhibit a strong dependence on the direction
of the applied field. We also discuss the role of magnetic anisotropy in the
molecule Mn12 -acetate.",0312581v1
2004/7/1,Propagation of a magnetic domain wall in magnetic wires with asymmetric notches,"The propagation of a magnetic domain wall (DW) in a submicron magnetic wire
consisting of a magnetic/nonmagnetic/magnetic trilayered structure with
asymmetric notches was investigated by utilizing the giant magnetoresistance
effect. The propagation direction of a DW was controlled by a pulsed local
magnetic field, which nucleates the DW at one of the two ends of the wire. It
was found that the depinning field of the DW from the notch depends on the
propagation direction of the DW.",0407006v1
2004/9/3,Manipulating Current-Induced Magnetization Switching,"We summarize our recent findings on how current-driven magnetization
switching and magnetoresistance in nanofabricated magnetic multilayers are
affected by varying the spin-scattering properties of the non-magnetic spacers,
the relative orientations of the magnetic layers, and spin-dependent scattering
properties of the interfaces and the bulk of the magnetic layers. We show how
our data are explained in terms of current-dependent effective magnetic
temperature.",0409085v1
2004/12/15,"Magnetic behavior of the spin-chain compounds,Ca3CuIrO6 and Ca3CuRhO6","The spin-chain compounds, Ca3CuIrO6 and Ca3CuRhO6, crystallizing in a
K4CdCl6-derived monoclinic structure, are investigated by ac and dc
magnetization, isothermal remnant magnetization as well as heat capacity
measurements. The results reveal the existence of a magnetic ordering in the
vicinity of 15 K for both the compounds, but the transition appears to be of a
complex nature. The existence of a spin-glass component is strongly indicated
by the results. We propose that topological effects play a role on magnetism of
these compounds. The magnetic properties for these two compounds are
interestingly similar as though isoelectronic chemical substitution at the
octahedral coordination site does not significantly interfere in the magnetic
exchange process.",0412386v1
2004/12/17,Hysteresis loops of magnetic thin films with perpendicular anisotropy,"We model the magnetization of quasi two-dimensional systems with easy
perpendicular (z-)axis anisotropy upon change of external magnetic field along
z. The model is derived from the Landau-Lifshitz-Gilbert equation for
magnetization evolution, written in closed form in terms of the z component of
the magnetization only. The model includes--in addition to the external
field--magnetic exchange, dipolar interactions and structural disorder. The
phase diagram in the disorder/interaction strength plane is presented, and the
different qualitative regimes are analyzed. The results compare very well with
observed experimental hysteresis loops and spatial magnetization patterns, as
for instance for the case of Co-Pt multilayers.",0412461v1
2005/1/19,Anisotropic magnetization of RuEu1.5Ce0.5Sr2Cu2O10 (Ru-1222) thin films,"A dc magnetic study is reported on c-axis oriented epitaxial thin films of
EuSr2Eu1.5Ce0.5Cu2O10 (Ru-1222) on (100) SrTiO3 wafers. Magnetic measurements
on 200 and 500 nm thick films were performed with the magnetic field either
parallel or perpendicular to the wafer. We found that the films order
magnetically at 180 K. The easy axis of the magnetization is in the basal plane
and the Ru5+ ions are in their high-spin state, as deduced from the isothermal
magnetization curves at low temperatures. The anisotropy ratio was found to be
7.5. The observed results are compared to data of the Ru-1222 ceramic material.",0501454v1
2005/3/31,Boundary conditions for magnetization in magnetic nano-elements,"We show that the dynamic magnetization at the edges of a thin magnetic
element with finite lateral size can be described by new effective boundary
conditions that take into account inhomogeneous demagnetizing fields near the
element edges. These fields play a dominant role in the effective pinning of
the dynamic magnetization at the boundaries of mesoscopic and nano-sized
magnetic elements. The derived effective boundary conditions generalize
well-known Rado-Weertman boundary conditions and are reduced to them in the
limiting case of a very thin magnetic element.",0503745v1
2005/8/26,Kinetic arrest of the first order ferromagnetic to antiferromagnetic transition in Ce(Fe$_{0.96}$Ru$_{0.04}$)$_2$ : formation of a magnetic-glass,"We present results of dc magnetization and magnetic relaxation study showing
the kinetic arrest of a first order ferromagnetic to antiferromagnetic
transition in Ce(Fe$_{0.96}$Ru$_{0.04}$)$_2$. This leads to the formation of a
non-ergodic glass-like magnetic state. The onset of the magnetic-glass
transformation is tracked through the slowing down of the magnetization
dynamics. This glassy state is formed with the assistance of an external
magnetic field and this is distinctly different from the well known
'spin-glass' state.",0508625v1
2005/9/26,Charge and Magnetization Inhomogeneities in Diluted Magnetic Semiconductors,"It is predicted that III-V diluted magnetic semiconductors can exhibit
stripe-like modulations of magnetization and carrier concentration. This
inhomogeneity results from the strong dependence of the magnetization on the
carrier concentration. Within Landau theory, a characteristic temperature T*
below the Curie temperature is found so that below T* the equilibrium
magnetization shows modulations, which are strongly anharmonic. Wavelength and
amplitude of the modulation rise for decreasing temperature, starting from zero
at T*. Above T* the equilibrium state is homogeneous, but the coupling between
charge and magnetization leads to the appearance of an electrically charged
layer in domain walls.",0509653v2
2005/11/5,Ratchet Effect in Magnetization Reversal of Stoner Particles,"A new strategy is proposed aimed at substantially reducing the minimal
magnetization switching field for a Stoner particle. Unlike the normal method
of applying a static magnetic field which must be larger than the magnetic
anisotropy, a much weaker field, proportional to the damping constant in the
weak damping regime, can be used to switch the magnetization from one state to
another if the field is along the motion of the magnetization. The concept is
to constantly supply energy to the particle from the time-dependent magnetic
field to allow the particle to climb over the potential barrier between the
initial and the target states.",0511135v1
2006/1/17,Electric field control of magnetization dynamics in ZnMnSe/ZnBeSe diluted-magnetic-semiconductor heterostructures,"We show that the magnetization dynamics in diluted magnetic semiconductors
can be controlled separately from the static magnetization by means of an
electric field. The spin-lattice relaxation (SLR) time of magnetic Mn2+ ions
was tuned by two orders of magnitude by a gate voltage applied to n-type
modulation-doped (Zn,Mn)Se/(Zn,Be)Se quantum wells. The effect is based on
providing an additional channel for SLR by a two-dimensional electron gas
(2DEG). The static magnetization responsible for the giant Zeeman spin
splitting of excitons was not influenced by the 2DEG density.",0601383v1
2006/2/3,X-ray magnetic circular dichroism study of Re 5d magnetism in Sr2CrReO6,"We have measured Re 5d spin and orbital magnetic moments in the ferrimagnetic
double perovskite Sr2CrReO6 by X-ray magnetic circular dichroism at the L_{2,3}
edges. In fair agreement with recent band-structure calculations [Vaitheeswaran
et. al., Ref 1], at the Re site a large 5d spin magnetic moment of -0.68 mu_B
and a considerable orbital moment of +0.25 mu_B have been detected. We found
that the Curie temperature of the double perovskites A2BB'O6 scales with the
spin magnetic moment of the 'non-magnetic' B' ion.",0602071v1
2006/7/5,Instabilities of switching processes in synthetic antiferromagnets,"It is shown that magnetic states and field-driven reorientation transitions
in synthetic antiferromagnets crucially depend on contributions of higher-order
anisotropies. A phenomenological macrospin model is derived to describe the
magnetic states of two antiferromagnetically coupled magnetic thin film
elements. The calculated phase diagrams show that magnetic states with
out-of-plane magnetization, symmetric escaped spin-flop phases, exist in a
broad range of the applied magnetic field. Due to the formation of such states
and concomitant multidomain patterns, the switching processes in toggle
magnetic random access memory devices (MRAM) can radically deviate from
predictions within oversimplified models.",0607124v1
2007/2/7,Vacuum fluctuations and the spin current in mesoscopic structures with collinear magnetic order,"We show that in magnetic nanostructures with a homogeneous magnetic order,
the equilibrium spin current can be nonzero. For example, this is the case of a
wide magnetic ring with the magnetization along the ring axis. The physical
reason of this effect is a variation of the orientation of anisotropy axis
inducing a spin torque acting on the magnetic ions. The mechanism of the spin
current generation is related to the quantum vacuum fluctuations in the
magnetic system.",0702168v2
2007/11/19,Room Temperature Magnetocaloric Effect in Ni-Mn-In,"We have studied the effect of magnetic field on a non-stoichiometric Heusler
alloy Ni$_{50}$Mn$_{35}$In$_{15}$ that undergoes a martensitic as well as a
magnetic transition near room temperature. Temperature dependent magnetization
measurements demonstrate the influence of magnetic field on the structural
phase transition temperature. From the study of magnetization as a function of
applied field, we show the occurrence of inverse-magnetocaloric effect
associated with this magneto-structural transition. The magnetic entropy change
attains a value as high as 25 J/kg-K (at 5 T field) at room temperature as the
alloy transforms from the austenitic to martensitic phase with a concomitant
magnetic ordering.",0711.2896v1
2008/3/26,The commensurate phase of multiferroic HoMn2O5 studied by X-ray magnetic scattering,"The commensurate phase of multiferroic HoMn2O5 was studied by X-ray magnetic
scattering, both off resonance and in resonant conditions at the Ho-L3 edge.
Below 40 K, magnetic ordering at the Ho sites is induced by the main Mn
magnetic order parameter, and its temperature dependence is well accounted for
by a simple Curie-Weiss susceptibility model. A lattice distortion of
periodicity twice that of the magnetic order is also evidenced. Azimuthal scans
confirm the model of the magnetic structure recently refined from neutron
diffraction data for both Mn and Ho sites, indicating that the two sublattices
interact via magnetic superexchange.",0803.3779v1
2008/10/29,Contrasting the magnetic response between magnetic-glass and reentrant spin-glass,"Magnetic-glass is a recently identified phenomenon in various classes of
magnetic systems undergoing a first order magnetic phase transition. We shall
highlight here a few experimentally determined characteristics of
magnetic-glass and the relevant set of experiments, which will enable to
distinguish a magnetic-glass unequivocally from the well known phenomena of
spin-glass and reentrant spin-glass.",0810.5215v2
2009/2/3,Tuning Magnetic Avalanches in Mn12-ac,"Using micron-sized Hall sensor arrays to obtain time-resolved measurements of
the local magnetization, we report a systematic study in the molecular magnet
Mn$_{12}$-acetate of magnetic avalanches controllably triggered in different
fixed external magnetic fields and for different values of the initial
magnetization. The speeds of propagation of the spin-reversal fronts are in
good overall agreement with the theory of magnetic deflagration of Garanin and
Chudnovsky \cite{Garanin}.",0902.0531v2
2009/4/7,Unconventional magnetism in small gold organic molecules,"We present a theoretical study of the magnetic properties of
dicyclopentadienyl metallocene and phthalocyanine molecules, that contain the
transition metal atoms M = Fe, Co, Ni, Cu, Zn, Ir, Pt and Au. Our most
important prediction is that gold and copper molecules are magnetic. We find
that the magnetism of these molecules is fairly unconventional: the gold atom
itself is weakly magnetic or even non-magnetic. Its role is rather to induce
magnetism in the surrounding carbon and nitrogen atoms, producing a sort of
spin density wave.",0904.1138v1
2009/5/2,Voltage-assisted Magnetization Switching in Ultrathin Fe80Co20 Alloy Layers,"Growing demands for the voltage-driven spintronic applications with
ultralow-power consumption have led to new interest in exploring the
voltage-induced magnetization switching in ferromagnetic metals. In this study,
we observed a large perpendicular magnetic anisotropy change in Au(001) /
ultrathin Fe80Co20(001) / MgO(001) / Polyimide / ITO junctions, and succeeded
in realizing a clear switching of magnetic easy axis between in-plane and
perpendicular directions. Furthermore, employing a perpendicularly magnetized
film, voltage-induced magnetization switching in the perpendicular direction
under the assistance of magnetic fields was demonstrated. These pioneering
results may open a new window of electric-field controlled spintronics devices.",0905.0185v1
2010/5/15,Thermodynamics of strongly frustrated magnet in a field: Ising antiferromagnet on triangular Husimi lattice,"Some strongly frustrated magnets such as the ""spin-ice"" compounds fail to
produce any magnetic order at finite temperatures even in the presence of
magnetic field. Still they have very unusual low-temperature thermodynamic
properties related to the field-induced ground state transitions. Here we show
that general qualitative picture of such peculiar thermodynamics can be
obtained in the antiferromagnetic Ising model on the triangular Husimi lattice.
The analytical results for this model show magnetic plateaus, entropy spikes,
crossing points and peculiarities in magnetic susceptibility and specific heat
behavior reflecting the existence of ground state transitions. These signatures
of strong frustration may help in search of new frustrated magnets and in the
interpretation of experimental data.",1005.2650v1
2010/7/2,Spin-polarizing properties of heterostructures with magnetic nano elements,"The problem of electron resonant and non-resonant scatterings on two
magnetized barriers is studied in the one-dimension. The transfer-matrix is
built up to exactly calculate the coefficient of the electron transmittance
through the system of two magnetic barriers with non-collinear magnetizations.
The polarization of the transmitted electron wave for resonance and
non-resonance transmittances is calculated. The transmittance coefficient and
spin polarization can be drastically enhanced and controlled by the angle
between the barrier magnetizations",1007.0421v1
2010/11/18,Possibility of exchange switching ferromagnet - antiferromagnet junctions,"Current flowing is studied in magnetic junctions consisting of a
ferromagnetic metal (FM), antiferromagnetic conductor (AFM) and a nonmagnetic
metal closing the electric circuit. The FM layer with high anisotropy and
pinned spins of the magnetic atoms in the lattice acts as a spin injector
relative to the AFM layer. To obtain resulting magnetization in the AFM layer,
magnetic field is applied, which may be varied to control the magnetization.
The spin-polarized current from the FM layer creates a torque and makes it
possible to switch the magnetization. A possibility is shown to lower the
threshold current density by the orders of magnitude by means of the magnetic
field.",1011.4303v1
2011/6/12,Anomalies in the Multicritical Behavior of Staggered Magnetic and Direct Magnetic Susceptibilities of Iron Group Dihalides,"In this study, the temperature dependencies of magnetic response functions of
the anhydrous dihalides of iron-group elements are examined in the neighborhood
of multi-critical points (tricritical, critical end point, double critical end
point) and first order transition temperatures within molecular field
approximation. Our findings reveal the fact that metamagnetic Ising system
exhibits anomalies in the temperature dependence of the magnetic response
functions for r<0.3. In addition, we extensively investigated how an inter- and
intra-layer exchange interaction ratio can influence magnetic response
properties of these systems. Finally, a comparison is made with related works.",1106.2308v1
2011/11/1,Measurement of magnetic permeability of steel laminations of Booster gradient magnets,"New experiments at Fermilab require higher beam intensities at Booster,
resulting in higher influence of magnet steel on the beam. In order to
carefully take these effects into account it is necessary to know geometric and
material properties of magnets. This work is dedicated to the measurement of
magnetic permeability of steel laminations of Booster gradient magnets as a
complex function of frequency in the frequency range from several megahertz up
to 1 GHz. The magnetic permeability is estimated by analyzing S-parameters of
microstrip lines made up from laminated steel.",1111.0247v3
2012/5/14,Effects of the randomly distributed magnetic field on the phase diagrams of the Ising Nanowire I: discrete distributions,"The effect of the random magnetic field distribution on the phase diagrams
and ground state magnetizations of the Ising nanowire is investigated with
effective field theory with correlations. Trimodal distribution chosen as a
random magnetic field distribution. The variation of the phase diagrams with
that distribution parameters obtained and some interesting results found such
as reentrant behavior. Also for the trimodal distribution, ground state
magnetizations for different distribution parameters determined which can be
regarded as separate partially ordered phases of the system.",1205.3219v1
2012/6/6,Magnetic field dependent impact ionization in InSb,"Carrier generation by impact ionization and subsequent recombination under
the influence of magnetic field has been studied for InSb slab. A simple
analytic expression for threshold electric field as a function of magnetic
field is proposed. Impact ionization is suppressed by magnetic field. However,
surface recombination is dependent on the polarity of magnetic field:
strengthened in one direction and suppressed on the opposite direction. The
former contributes quadratic increase to threshold electric field, and the
latter gives additional linear dependence on magnetic field. Based on this
study, electrical switching devices driven by magnetic field can be designed.",1206.1094v1
2012/12/5,"Influence of Magnetic Anisotropy on Laser-induced Precession of Magnetization in Ferromagnetic Semiconductor (Ga,Mn)As","The laser-induced precession of magnetization in (Ga,Mn)As samples with
different magnetic anisotropy was studied by the time-resolved magneto-optical
method. We observed that the dependence of the precession amplitude on the
external magnetic field depends strongly on the magnetic anisotropy of
(Ga,Mn)As and we explain this phenomenon in terms of competing cubic and
uniaxial anisotropies. We also show that the corresponding anisotropy fields
can be deduced from the magnetic field dependence of the precession frequency.",1212.0962v1
2013/6/13,Temperature- and Magnetic-Field-Tuning of Magnetic Phases in Multiferroic NdFe3(BO3)4,"We report the low-temperature coexistence in NdFe3(BO3)4 of an incommensurate
magnetic phase with a strained commensurate magnetic phase that is primarily at
the surface of the crystal. Increasing the temperature or magnetic field
decreases the incommensurability and stabilizes the commensurate magnetic phase
above Tic ~14 K or Hic = 0.9 T. A comparison to published studies indicates the
onset of longitudinal magnetostriction and electric polarization at the
magnetic-field-induced transition, which may arise due to a basal plane
spin-flop and canting of the moments along the field direction.",1306.3152v1
2013/7/10,Spintronic Oscillator Based on Magnetic Field Feedback,"We present a circuit design of a spintronic oscillator based on magnetic
tunnel junction. In this design, a dc current is passed through a magnetic
tunnel junction which is connected to a feed-back wire below it. Any
fluctuation in the magnetization direction of the free layer of MTJ, drives a
fluctuating current through the feed-back wire, which exerts a magnetic field
on the free layer. This in turn can amplify the magnetization fluctuations of
the free layer. If the dc current passing through the MTJ is more than a
critical value, continuous precessing states of the magnetization are possible.",1307.2744v1
2014/2/25,Magnetic field control of ferroelectric polarization and magnetization of LiCu2O2 compound,"A spin model of LiCu2O2 compound with ground state of ellipsoidal helical
structure has been adopted. Taking into account the interchain coupling and
exchange anisotropy, we focus on the magnetoelectric properties in a rotating
magnetic field and perform the Monte Carlo simulation on a two-dimensional
lattice. A prominent anisotropic response is observed in the magnetization and
polarization curves, qualitatively coinciding with the behaviors that detected
in the experiment. In addition, the influences of the magnetic field with
various magnitudes are also explored and analyzed in detail. As the magnetic
field increases, a much smoother polarization of angle dependence is exhibited,
indicating the strong correlation between the magnetic and ferroelectric
orders.",1402.6648v1
2014/5/16,Magnetoelectric surface acoustic wave resonator with ultrahigh magnetic field sensitivity,"A magnetoelectric surface acoustic wave (MESAW) type device based on
piezoelectric/magnetostrictive heterostructure was proposed to use as weak
magnetic field sensor. Unlike conventional magnetoelectric bulk laminates or
film stacks collecting magnetic field induced electrical charge, the MESAW
detects the shift of the center frequency, which highly depends on the magnetic
field due to the giant delta E effect and the phase velocity dispersion. The
magnetic field sensitivity can reach 10^(-11) Tesla in consideration of 100 Hz
frequency accuracy. Additionally, the unique working mechanism of MESAW allows
a broadband detection of weak magnetic field even with no bias magnetic field.",1405.4076v2
2014/6/18,Spin-lattice coupling induced weak dynamical magnetism in EuTiO_3 at high temperatures,"EuTiO_3, which is a G-type antiferromagnet below T_N = 5.5 K, has some
fascinating properties at high temperatures, suggesting that macroscopically
hidden dynamically fluctuating weak magnetism exists at high temperatures. This
conjecture is substantiated by magnetic field dependent magnetization
measurements, which exhibit pronounced anomalies below 200 K becoming more
distinctive with increasing magnetic field strength. Additional results from
muon spin rotation (${\mu}$SR) experiments provide evidence for weak
fluctuating bulk magnetism induced by spin-lattice coupling which is strongly
supported in increasing magnetic field.",1406.4915v1
2015/10/27,Evidence for a re-entrant character of magnetism of sigma-phase Fe-Mo alloys: non-linear susceptibilities,"Non-linear ac magnetic susceptibility terms viz. quadratic, chi2, and cubic,
chi3, were measured versus temperature and frequency for a series of the
sigma-phase Fe(100-x)Mo(x) (47<x<53) compounds. Clear evidence was found that
the ground magnetic state of the samples is mixed i.e. constituted by two
phases: a spin glass (SG) and a ferromagnet (FM), hence the magnetism of the
investigated samples can be regarded as re-entrant (RSG). Based on the present
data, previously reported magnetic phase diagram has been upgraded [J.
Przewoznik, S. M. Dubiel,J. Alloy. Comp., 630 (2015) 222].",1510.07811v1
2017/1/1,Electrical Transport of perpendicularly magnetized L10-MnGa and MnAl films,"Ferromagnetic films of L10-ordered MnGa and MnAl that exhibit giant
perpendicular magnetic anisotropy and great controllability in the magnetism
and structural disorders show promise not only in the applications in magnetic
recording, permanent magnets and spintronics, but also in controllable studies
of disorder-relevant electrical transport phenomena. In this article, we review
the intriguing experimental observations of the orbital two-channel Kondo
effect and anomalous Hall effect in L10-ordered MnGa and MnAl thin films with
perpendicular magnetic anisotropy. We also give a perspective with regards to
the future technological and fundamental applications of these perpendicularly
magnetized Mn-based binary alloy films.",1701.00191v1
2012/11/6,Spin Wave Scattering in Ferromagnetic Cross,"Spin wave scattering in the right angle ferromagnetic cross was measured.
Shape anisotropy defined magnetization ground states at zero biasing magnetic
fields. Scattering of the spin waves in the center of ferromagnetic cross is
strongly dependent on the amplitude and angle of the biasing magnetic field.
Micromagnetic simulations indicate that low in-plane biasing magnetic fields
rotate the magnetization of the cross center while the arms stay axially
magnetized due to the shape anisotropy. We discuss effect of biasing magnetic
fields on the spin wave scattering and approaches to an effective spin wave
switch based on the fabricated structure.",1211.1259v1
2017/6/5,Generalized magnetic mirrors,"We propose generalized magnetic mirrors that can be achieved by excitations
of sole electric resonances. Conventional approaches to obtain magnetic mirrors
rely heavily on exciting the fundamental magnetic dipoles, whereas here we
reveal that besides magnetic resonances, electric resonances of higher orders
can be also employed to obtain highly efficient magnetic mirrors. Based on the
electromagnetic duality, it is also shown that electric mirrors can be achieved
by exciting magnetic resonances. We provide direct demonstrations of the
generalized mirrors proposed in a simple system of one-dimensional periodic
array of all-dielectric wires, which may shed new light to many advanced fields
of photonics related to resonant multipolar excitations and interferences.",1706.01398v2
2012/9/17,Size and polydispersity effect on the magnetization of densely packed magnetic nanoparticles,"The magnetic properties of densely packed magnetic nanoparticles (MNP)
assemblies are investigated from Monte Carlo simulations. The case of iron
oxide nanoparticles is considered as a typical example of MNP. The main focus
is put on particle size and size polydispersity influences on the magnetization
curve. The particles are modeled as uniformly magnetized spheres isolated one
from each other by a non magnetic layer representing the organic coating. A
comparison with recent experimental results on $\gamma-$Fe$_2$O$_3$ powder
samples differing by their size is given.",1209.3566v1
2018/12/20,Self-Organized Criticality of Domain Walls and Magnetization Curve,"We propose a kind of Ginzburg--Landau equation with quenched randomness.
There is a pinning--depinning transition in the system when the external
magnetic force is changed. The transition is self-organized when the external
magnetic field is slowly changed under the demagnetizing effect. The total
magnetization increases stepwise and the probability distribution of the
increase in the total magnetization approximately obeys a power law. A
hysteresis loop is obtained when the external magnetic field is changed
reciprocally. In our model, the coercivity in the magnetization curve is
expressed as the critical value for the pinning-depinning transition.",1812.08344v1
2018/12/26,Probing the Relationship between Anisotropic Magnetoresistance and Magnetization of ferromagnetic films,"The anisotropic magnetoresistance (AMR) in thin permalloy strips was
calculated at each steps during magnetization by the finite element method. The
magnetization at equilibrium under different external fields was obtained by
micromagnetic simulations, while the resistance with different magnetization
was obtained by solving the Poisson equations iteratively until
self-consistence. We find that the relation between magnetization and AMR
deviates from the Stoner-Wohlfarth prediction when the magnetization is reduced
from saturation. The reason is that the demagnetization is not necessarily from
coherent rotation of the magnetic moment. We conclude that it is necessary to
use numeric simulations to optimize the responses of AMR sensors.",1812.10294v1
2016/3/29,Switching local magnetization by electric-field-induced domain wall motion,"Electric field effect on magnetism is an appealing technique for manipulating
the magnetization at a low cost of energy. Here, we show that the local
magnetization of the ultra-thin Co film can be switched by just applying a gate
electric field without an assist of any external magnetic field or current
flow. The local magnetization switching is explained by the nucleation and
annihilation of the magnetic domain through the domain wall motion induced by
the electric field. Our results lead to external field free and ultra-low
energy spintronic applications.",1603.08688v1
2019/7/30,Graphical Magnetogranulometry of EMG909,"The magnetization curve of the ferrofluid EMG909 is measured. It can
adequately be described by a superposition of four Langevin terms. The
effective dipole strength of the magnetic particles in this fluid is
subsequently obtained by a graphical rectification of the magnetization curve
based on the inverse Langevin function. The method yields the arithmetic and
the harmonic mean of the magnetic moment distribution function, and a guess for
the geometric mean and the relative standard deviation. It has the advantage
that it does not require a prejudiced guess of the distribution function of the
poly-disperse suspension of magnetic particles.",1907.12779v2
2020/12/23,Magnetic Moment Tensor Potentials for collinear spin-polarized materials reproduce different magnetic states of bcc Fe,"We present the magnetic Moment Tensor Potentials (mMTPs), a class of
machine-learning interatomic potentials, accurately reproducing both
vibrational and magnetic degrees of freedom as provided, e.g., from
first-principles calculations. The accuracy is achieved by a two-step
minimization scheme that coarse-grains the atomic and the spin space. The
performance of the mMTPs is demonstrated for the prototype magnetic system bcc
iron, with applications to phonon calculations for different magnetic states,
and molecular dynamics simulations with fluctuating magnetic moments.",2012.12763v2
2022/4/15,Energy Extraction via Magnetic Reconnection in the Ergosphere of a rotating non-Kerr Black Hole,"Magnetic reconnection process in the ergosphere is investigated for a
relativistic plasma around a rotating non-Kerr black hole. For a rotating
non-Kerr black hole immersed in magnetic field generated by an externally
material, anti-parallel magnetic field line could form in the ergosphere due to
the frame dragging. Therefore, magnetic reconnection could occur in the
ergosphere. Such magnetic reconnection may generate negative energy at infinity
by redistributing the angular momentum during the process. The results show
that, with the effect of the deformed parameter, extraction of energy from a
rotating non-Kerr black hole by magnetic reconnection could be enhanced in the
presence of a positive deformed parameter.",2204.07338v1
2022/9/9,Quantum Stoner-Wohlfarth model of two-dimensional single domain magnets,"The Stoner-Wohlfarth (SW) model is a classical model for magnetic hysteresis
of single-domain particles. For two-dimensional magnets at finite temperature,
the SW model must be extended to include intrinsic strong spin fluctuations. We
predict several fundamentally different hysteresis properties between 2D and 3D
magnets. The magnetization switching diagram known as the Asteroid figure in
the conventional SW model becomes highly temperature dependent and asymmetric
with respect to the transverse and longitudinal magnetic fields. Our results
provide new insights for 2D magnetic materials based spintronics applications.",2209.04479v1
2022/10/16,On the angular anisotropy of the randomly-averaged magnetic neutron scattering cross section of nanoparticles,"We calculate the magnetic SANS cross section of dilute ensembles of uniformly
magnetized and randomly-oriented Stoner-Wohlfarth particles using the
Landau-Lifshitz equation. The focus of our study is on the angular anisotropy
of the magnetic SANS signal as it can be seen on a two-dimensional
position-sensitive detector. Depending on the symmetry of the magnetic
anisotropy of the particles (e.g. uniaxial, cubic), an anisotropic magnetic
SANS pattern may result, even in the demagnetized state or at the coercive
field. The case of inhomogeneously magnetized particles and the effects of a
particle-size distribution and interparticle correlations are discussed.",2210.08406v1
2023/2/26,Low-temperature thermal Hall conductivity of Pr2Zr2O7 single crystal,"To probe the peculiar excitations spinons and magnetic monopoles in the
quantum spin ice candidate Pr2Zr2O7, we studied the low-temperature thermal
Hall conductivity (\k{appa}xy) and thermal conductivity (\k{appa}xx) of
Pr2Zr2O7 single crystal with magnetic fields applied along the [111] axis. The
magnetic field dependencies of \k{appa}xx suggest the roles of magnetic
excitations in thermal conductivity, that is, the emergent magnetic monopoles
can transport heat at T > 1.4 K and spinons mainly scatter phonons at lower
temperatures. The finite \k{appa}xy was observed at low fields of several Tesla
and was discussed to be related to the magnetic excitations, including magnetic
monopoles as well as spinons.",2302.13300v1
2023/7/4,Phonon-induced magnetization dynamics in Co-doped iron garnets,"The developing field of strain-induced magnetization dynamics offers a
promising path toward efficiently controlling spins and phase transitions.
Understanding the underlying mechanisms is crucial in finding the optimal
parameters supporting the phononic switching of magnetization. Here, we present
an experimental and numerical study of time-resolved magnetization dynamics
driven by the resonant excitation of an optical phonon mode in iron garnets.
Upon pumping the latter with an infrared pulse obtained from a free-electron
laser, we observe spatially-varying magnetization precession, with its phase
depending on the direction of an external magnetic field. Our micromagnetic
simulations effectively describe the magnetization precession and switching in
terms of laser-induced changes in the crystal's magneto-elastic energy.",2307.01907v1
2023/10/5,Exotic rare earth-based materials for emerging spintronic technology,"The progress in materials science has always been associated with the
development of functional materials systems, which enables us to design
proof-of-concept devices. To advance further, theoretical predictions of new
novel materials and their experimental realization is very important. This
chapter reviews the intriguing properties of rare earth-based materials and
their applications in spintronics. Spintronics is an emerging technology, which
exploits spin degree of freedom of an electron along with its charge property.
Discovery of various physical phenomena and their industrial applications in
the field of magnetic sensors, magnetic recording and non-volatile memories
such as magnetic random access memory (MRAM) and spin-transfer torque (STT)
MRAM opens several new directions in this field. Materials with large spin
polarization, strong spin-orbit coupling, and tunable electronic and magnetic
properties offer an excellent platform for the spintronics technology.
Combination of rare earths with other elements such as transition metals show
broad range of structural, electronic, and magnetic properties which make them
excellent candidates for various spintronic applications. This chapter
discusses many such materials ranging from Heusler alloys, topological
insulators to two-dimensional ferromagnets and their potential applications.
The review gives an insight of how rare-earth materials can play a key role in
emerging future technology and have great potential in many new spintronic
related applications.",2310.03541v1
1998/6/5,Magnetic Particles,"We present an overview of the subject of Magnetic Particles, starting at a
level suitable for advanced high-school students and ending at a level suitable
for current practitioners in the field. The sub-topics covered include: Types
of Magnetic Materials, Relationships Between the Vector Fields, Magnetic
Energies, Dynamics of Magnetic Particles, and Magnetocaloric Effects.",9806082v1
1999/6/29,Quantitative Model of Large Magnetostrain Effect in Ferromagnetic Shape Memory Alloys,"A quantitative model describing large magnetostrain effect observed in
several ferromagnetic shape memory alloys such as Ni2MnGa is briefly
reported.The paper contains an exact thermodynamic consideration of the
mechanical and magnetic properties for a similar type materials. As a result,
the basic mechanical state equation including magnetic field effect is directly
derived from a general Poisson's rule. It is shown that the magnetic field
induced deformation effect is directly connected with the strain dependence of
magnetization. A simple model of magnetization and its dependence on the strain
is considered and applied to explain the results of experimental study of large
magnetostrain effects in Ni2MnGa.",9906433v1
2002/12/16,Magnetic phase diagram of Ca_1-xMn_xO,"Alternating current susceptibility and direct current magnetization have been
studied for polycrystalline Ca$_{1-x}$Mn$_x$O. On increasing the Mn content,
magnetic ordering changes from spin-glass behavior for $0.25 \leqslant x
\leqslant 0.4$ to antiferromagnetic order. The paramagnetic/antiferromagnetic
transition is of second order for $0.5 \leqslant x \leqslant 0.65$ and of first
order for $x \geqslant 0.7$. For low Mn concentrations, the high-temperature
alternating current susceptibility can be described by a diluted Heisenberg
magnet model developed for diluted magnetic semiconductors.",0212378v1
2003/5/21,From Bubble to Skyrmion: Dynamic Transformation Mediated by a Strong Magnetic Tip,"Skyrmions in thin metallic ferromagnetic films are stable due to competition
between the RKKY interaction and uniaxial magnetic anisotropy. We mimic the
RKKY interaction by the next-nearest-neighbors ferromagnetic and
antiferromagnetic exchange interactions. We demonstrate analytically and
numerically dissipative transformation of a bubble created by a strong
cylindrical magnetic tip into a stable Skyrmion.",0305487v1
2005/10/28,Irreversible susceptibility of initial magnetization curve,"A method for estimation of reversible and irreversible susceptibilities of
initial magnetization curves has been developed. It deals only with the energy
necessary for magnetizing and demagnetizing the sample, not with the nature of
the magnetization processes neither with a specific type of anisotropy, so it
could be applied for a wide variety of real materials. A set of minor
hysteresis loops of an initially demagnetized sample, plotted with
progressively increasing maximum magnetic field, has been used. The obtained
results showed an excellent coincidence with those calculated by the remanence
curve method for a Stoner-Wohlfarth model system.",0510776v1
2005/11/18,Investigation of Co$_2$FeSi: The Heusler compound with Highest Curie Temperature and Magnetic Moment,"This work reports on structural and magnetic investigations of the Heusler
compound Co$_2$FeSi. X-Ray diffraction and M\""o\ss bauer spectrometry indicate
an ordered $L2_1$ structure. Magnetic measurements by means of X-ray magnetic
circular dichroism and magnetometry revealed that this compound is, currently,
the material with the highest magnetic moment ($6 \mu_B$) and Curie-temperature
(1100K) in the classes of Heusler compounds as well as half-metallic
ferromagnets.",0511462v1
2006/11/2,Study of the Magnetic Film Materials by Horizontal Scanning Mode for the Magnetic Force Microscopy in Magnetostatic and ac Regimes,"The magnetic force microscopy inverse problem for the case of horizontal
scanning of a tip on a linear magnetic film is introduced. We show the
possibility to recover the magnetic permeability of the material from the
experimental data by using the Hankel (Fourier-Bessel) transform inverse method
(HIM). This method is applied to the case of a layered slab film as well. The
inverse problem related to the ac MFM is introduced.",0611060v1
2007/8/8,Janus particles with coupled electric and magnetic moments make a disordered magneto-electric medium,"We demonstrate that by combining permanent electric and magnetic moments in
particles, it is possible to realize a new type of medium that allows for a
cross-correlation between electric and magnetic properties of matter, known as
magnetoelectric coupling. Magnetoelectric materials have so far been restricted
to systems that exhibit long-range order in their electric and magnetic
moments. Here, we show that a room-temperature, switchable magnetoelectric can
be realized that is naturally disordered. The building blocks are Tellegen
particles that orient in either an electric or a magnetic field.",0708.1126v1
2007/8/29,"Tuning the Competing magnetic interactions in RTiGe (R = Tb, Er) Compounds and tailoring the Magnetocaloric effect","The tetragonal layered compounds TbTiGe and ErTiGe order
antiferromagnetically at 276 K and 39 K, respectively. Partial substitution of
Mo for Ti in these two compounds modifies the magnetic interactions giving rise
to a ferromagnetic ground state which results in an enhanced magnetocaloric
effect. The magnetic entropy change in ErTi0.85Mo0.15Ge for a magnetic field
change of 5 T is ~10.5 J/kg/K against ~0.8 J/kg/K for ErTiGe in the vicinity of
the magnetic transition. Thus, magnetocaloric properties of such layered
materials may be tunable by suitable chemical substitutions.",0708.3887v1
2007/11/21,Anomalous Hall effect in a two dimensional electron gas with magnetic impurities,"Magnetic impurities play an important role in many spintronics-related
materials. Motivated by this fact, we study the anomalous Hall effect in the
presence of magnetic impurities, focusing on two-dimensional electron systems
with Rashba spin-orbit coupling. We find a highly nonlinear dependence on the
impurity polarization, including possible sign changes. At small impurity
magnetizations, this is a consequence of the remarkable result that the linear
term is independent of the spin-orbit coupling strength. Near saturation of the
impurity spins, the anomalous Hall conductivity can be resonantly enhanced, due
to interference between potential and magnetic scattering.",0711.3415v1
2008/7/23,Magnetocapacitance in non-magnetic inhomogeneous media,"The dielectric response in a magnetic field is routinely used to probe the
existence of coupled magnetic and elastic order in the multiferroics. However,
here we demonstrate that magnetism is not necessary to produce a
magnetocapacitance when the material is inhomogeneous. By considering a
two-dimensional, two-component composite medium, we find a characteristic
dielectric resonance that depends on magnetic field. We propose this as a
possible signature of inhomogeneities and we argue that this behavior has
already been observed in nanoporous silicon and some manganites.",0807.3625v1
2010/7/9,Polarization and magnetization dynamics of a field-driven multiferroic structure,"We consider a multiferroic chain with a linear magnetoelectric coupling
induced by the electrostatic screening at the ferroelectric/ferromagnet
interface. We study theoretically the dynamic ferroelectric and magnetic
response to external magnetic and electric fields by utilizing an approach
based on coupled Landau- Khalatnikov and finite-temperature
Landau-Lifshitz-Gilbert equations. Additionally, we compare with Monte Carlo
calculations. It is demonstrated that for material parameters corresponding to
BaTiO3/Fe the polarization and the magnetization are controllable by external
magnetic and electric fields respectively.",1007.1543v1
2012/12/4,Magnetization switching by ultrashort acoustic pulses,"It is shown theoretically that a single a few picoseconds long acoustic pulse
can reverse magnetization in a magneto-strictive material Terfenol-D. Following
giant magneto-elastic changes of free energy density the magnetization vector
is kicked out of a local in-plane energy mininum and decays into another
minimum. For acoustic pulse duration significantly shorter than magnetization
precession period $\tau_{ac}$<<$T_{prec}$, the switching threshold is
determined by the {\it acoustic pulse area}, i.e. pulse integral in time
domain, similar to coherent phenomena in optics. Simulation results are
summarized in a magneto-acoustic switching diagram and discussed in the context
of all-optical magnetization switching by circularly polarized light pulses.",1212.0669v1
2013/1/9,Onset of a Propagating Self-Sustained Spin Reversal Front in a Magnetic System,"The energy released in a magnetic material by reversing spins as they relax
toward equilibrium can lead to a dynamical instability that ignites
self-sustained rapid relaxation along a deflagration front that propagates at a
constant subsonic speed. Using a trigger heat pulse and transverse and
longitudinal magnetic fields, we investigate and control the crossover between
thermally driven magnetic relaxation and magnetic deflagration in single
crystals of Mn$_{12}$-acetate.",1301.1900v2
2013/1/17,Electric-field control of domain wall nucleation and pinning in a metallic ferromagnet,"The electric (E) field control of magnetic properties opens the prospects of
an alternative to magnetic field or electric current activation to control
magnetization. Multilayers with perpendicular magnetic anisotropy (PMA) have
proven to be particularly sensitive to the influence of an E-field due to the
interfacial origin of their anisotropy. In these systems, E-field effects have
been recently applied to assist magnetization switching and control domain wall
(DW) velocity. Here we report on two new applications of the E-field in a
similar material : controlling DW nucleation and stopping DW propagation at the
edge of the electrode.",1301.4007v1
2013/3/22,"Magnetic and Magnetocaloric Exploration of Fe rich (Mn,Fe)2(P,Ge)","We explored the Fe rich side of the (Mn,Fe)2(P,Ge) magnetocaloric system. The
transition temperature of this system is extremely easy to tune with careful
manipulation of Fe and Ge content as well as stoichiometrical proportions,
which gives rise to the real possibility of lowering the price of this compound
and thus make it economically viable for practical magnetocaloric applications.
Novel and unexpected magnetic properties observed in this system suggest an
exciting potential for permanent magnet application in a limited concentration
range.",1303.5620v1
2013/10/1,Magnetization plateaus in generalized Shastry-Sutherland models,"We study an anisotropic Heisenberg antiferromagnet with ferromagnetic
transverse spin exchange using exact quantum Monte Carlo methods. Such a model
is relevant to a class of rare earth tetraboride materials that display a range
of magnetization plateaus under applied magnetic field. The layered arrangement
of magnetic ions in these materials is topologically equivalent to the
Shastry-Sutherland lattice. In this frustrated geometry, we study the interplay
of next-nearest neighbor interactions in stabilizing a plateau at half the
saturation magnetization (or 1/2 plateau). We also show hysteresis-like
behavior at the onset of the 1/3 plateau.",1310.0135v1
2013/12/17,Itinerant magnetism in doped semiconducting beta-FeSi2 and CrSi2,"Novel or unusual magnetism is a subject of considerable interest,
particularly in metals and degenerate semiconductors. In such materials the
interplay of magnetism, transport and other Fermi liquid properties can lead to
fascinating physical behavior. One example is in magnetic semiconductors, where
spin polarized currents may be controlled and used. We report density
functional calculations predicting magnetism in doped semiconducting beta-FeSi2
and CrSi2 at relatively low doping levels particularly for n-type. In this
case, there is a rapid cross-over to a half-metallic state as a function of
doping level. The results are discussed in relation to the electronic structure
and other properties of these compounds.",1312.4773v1
2014/9/23,Guidelines for understanding cubic manganese-rich Heusler compounds,"Manganese-rich Heusler compounds are attracting much interest in the context
of spin transfer torque and rare-earth free hard magnets. Here we give a
comprehensive overview of the magnetic properties of non-centrosymmetric cubic
Mn$_2$-based Heusler materials, which are characterized by an antiparallel
coupling of magnetic moments on Mn atoms. Such a ferrimagnetic order leads to
the emergence of new properties that are absent in ferromagnetic
centrosymmetric Heusler structures. In terms of the band structure
calculations, we explain the formation of this magnetic order and the Curie
temperatures. This overview is intended to establish guidelines for a basic
understanding of magnetism in Mn2 -based Heusler compounds.",1409.6532v1
2015/4/22,Microwave magnetochiral effect in Cu2OSeO3,"We theoretically find that in a multiferroic chiral magnet Cu2OSeO3, resonant
magnetic excitations are coupled to collective oscillation of electric
polarization, and thereby attain simultaneous activity to ac magnetic field and
ac electric field. Because of interference between these magnetic and electric
activation processes, this material hosts gigantic magnetochiral dichroism on
microwaves, that is, the directional dichroism at gigahertz frequencies in
Faraday geometry. The absorption intensity of microwave differs by as much as
30% depending on whether its propagation direction is parallel or antiparallel
to the external magnetic field.",1504.05864v1
2016/4/21,Non-equilibrium magnetic fields in ab initio spin dynamics,"Starting from the continuity equation for the magnetization in time-dependent
spin-density functional theory, we derive an expression for the effective
time-dependent magnetic fields driving the out-of-equilibrium spin dynamics in
magnetic systems. We evaluate these, so called, kinetic magnetic fields in the
ultrafast demagnetization response to optical pulse excitations of
ferromagnetic iron-based materials, namely Fe$_6$ cluster and bulk bcc Fe. We
identify spatial ""hot spots"" where the demagnetization is particularly enhanced
as a result of the increased kinetic torque.",1604.06262v2
2018/4/19,Damping of magnetization dynamics by phonon pumping,"We theoretically investigate pumping of phonons by the dynamics of a magnetic
film into a non-magnetic contact. The enhanced damping due to the loss of
energy and angular momentum shows interference patterns as a function of
resonance frequency and magnetic film thickness that cannot be described by
viscous (""Gilbert"") damping. The phonon pumping depends on magnetization
direction as well as geometrical and material parameters and is observable,
e.g., in thin films of yttrium iron garnet on a thick dielectric substrate.",1804.07080v2
2019/6/2,Structural and Magnetic Properties of Er3Fe5-xAlxO12 Garnets,"Er3Fe5-xAlxO12 (0.0 < x < 0.8) garnets were prepared by ball milling and
sintering at 1300 C. Rietveld refinement of the samples revealed a garnet
structure with Ia3d symmetry. The lattice parameter, cell volume, X-ray density
and magnetization of the prepared garnets decreased with the increase of Al
content (x). The coercivity of the garnets increased with x, but remained
generally low, being below 20 Oe. Low temperature magnetic measurements versus
temperature indicated that the magnetization of x = 0.0 exhibited a
compensation temperature at -186 C, however, x = 0.8 exhibited a minimum at a
higher temperature of -134 C.",1906.00405v1
2012/10/27,"Structural, magnetic, magnetocaloric and magneto-transport properties in Ge doped Ni-Mn-Sb Heusler Alloys","The effect of Ge substitution on the magnetic, magnetocaloric and transport
properties of Ni45Co5Mn38Sb12-xGex (x=0-3) has been investigated. The decrease
in the exchange interaction brought by Ge substitution can be seen from the
reduction in the magnetization of austenite phase and the increase in the
martensitic transition temperature. Large magnetocaloric effect and
magnetoresistance have been observed at room temperature, making it a potential
material system for various applications.",1210.7297v2
2018/3/30,Magnetism in amorphous carbon,"We investigate magnetism in amorphous carbon as suggested by the recently
reported ferromagnetism in a new form of amorphous carbon. We use spin
constrained first-principles simulations to obtain amorphous carbon structures
with the desired magnetization. We show that the existence of $sp^2$-like
3-fold coordinated carbon atoms plays an important role in obtaining magnetism
in amorphous carbon. The detailed geometries of 3-fold carbon atoms induce the
magnetic order in amorphous carbon.",1803.11336v1
2018/12/10,Configurational Entropy for Skyrmion-like Magnetic Structures,"In this work we explore the relationship between two ideas recently
introduced in the literature. The first one deals with a quantity related to
the informational contents of solutions of spatially localized structures, and
the second consists of obtaining analytical solutions to describe skyrmion-like
structures in magnetic materials. In particular, we use the topological charge
density to extract information on the configurational entropy of the magnetic
structure.",1812.04950v1
2020/8/11,Robust atomic orbital in the cluster magnet LiMoO2,"In this study, we present a rutile-related material, LiMoO2, that becomes a
cluster magnet and exhibits a spin singlet formation on a preformed molybdenum
dimer upon cooling. Unlike ordinary cluster magnets, the atomic dyz orbital
robustly survives despite the formation of molecular orbitals, thereby
affecting the magnetic properties of the selected material. Such hybrid cluster
magnets with the characters of molecular and atomic orbitals realize multiple
independent spins on an isolated cluster, leading to an ideal platform to study
the isolated spin dimers physics.",2008.04457v1
2013/11/1,An alternative formulation of the magnetostatic boundary value problem,"We present an alternative formulation of the magnetostatic boundary value
problem which is useful for calculating the magnetic field around a magnetic
material placed in the vicinity of steady currents. The formulation differs
from the standard approach in that a single-valued scalar potential, plus a
vector field that depends on the given currents but not on the magnetic
material, are used to obtain the total magnetic field instead of a magnetic
vector potential. We illustrate the method by a few sample computations.",1311.0315v1
2015/2/9,Hard magnet coercivity,"Based on a critical analysis of the experimental coercive properties, general
considerations on the reversal mechanisms in RFeB magnets are recalled. By
plotting together the experimental parameters obtained in various magnets,
common features of the reversal processes are demonstrated. Modeling provides
an almost quantitative description of coercivity in these materials and permits
connecting the defect characteristic properties to reversal mechanisms.",1502.02491v1
2017/12/10,Visible evidence to magnetism of graphene oxide,"Graphene oxide continues to amaze scientific community for multiple
potentials in a broad span of applications such as catalysts, adsorbents,
oxidants, etc., determined by constant unveiling of its fantastic natures. Of
them, magnetism is not ultimately identified and directly observed by naked
eyes. Herein, we report graphene oxide directionally migrated and deposited
together simply under external magnetic field from common Nd-Fe-B magnet,
whereas the ferromagnetism of graphene oxide did not exhibit that strong as
iron. Therefore, we illustrated this interesting pathway to keep close to such
2D carbon materials and potentially promoted magnetic-oriented applications.",1712.03570v4
2021/8/11,"Higher-order, quantum magnetic inductions in chiral topological materials","The classic magnetic induction effect is usually considered in electric
circuits or conductor coils. In this work, we propose quantum induction effects
induced by the Berry curvature in homogenous solids. Two different types of
quantum inductions are identified in the higher order of a magnetic field. They
are closely related to the magnetic-field-induced anomalous velocity
proportional to the Berry curvature so that both quantum inductions become
significantly enhanced near Weyl points. Further, we propose an
ac-magnetic-field measurement to detect quantum induction effects and
distinguish them from classical induction.",2108.05403v2
2021/10/18,Self-consistent Analysis of Doping Effect for Magnetic Ordering in Stacked-Kagome Weyl System,"We theoretically study the carrier doping effect for magnetism in a
stacked-kagome system $\rm{{Co}_3{Sn}_2{S}_2}$ based on an effective model and
the Hartree-Fock method. We show the electron filling and temperature
dependences of the magnetic order parameter. The perpendicular ferromagnetic
ordering is suppressed by hole doping, wheres undoped $\rm{{Co}_3{Sn}_2{S}_2}$
shows magnetic Weyl semimetal state. Additionally, in the electron-doped
regime, we find a non-collinear antiferromagnetic ordering. Especially, in the
non-collinear antiferromagnetic state, by considering a certain spin-orbit
coupling, the finite orbital magnetization and the anomalous Hall conductivity
are obtained.",2110.09459v1
2022/4/30,Piezoelectric ferromagnetism in two dimensional FeCl$_2$,"We predict that monolayer FeCl$_2$ is a two-dimensional piezoelectric
ferromagnet (PFM) with easy-axis magnetism and a Curie temperature of 260 K.
Our ab-initio calculations combined with data mining reveal 2H-FeCl$_2$ as the
only easy-axis 2D monolayer PFM, and that its magnetic anisotropy increases
many-fold with moderate hole doping. We develop an analysis based on magnetic
anisotropy energy densities that explain the magnetic and doping-dependent
behavior of FeCl$_2$, as well as VSe$_2$ and CrI$_3$, and can enable the design
of future 2D magnetically ordered materials.",2205.00300v1
2022/6/20,Magnetic ground states of honeycomb lattice Wigner crystals,"Lattice Wigner crystal states stabilized by long-range Coulomb interactions
have recently been realized in two-dimensional moir\'e materials. We employ
large-scale unrestricted Hartree-Fock techniques to unveil the magnetic phase
diagrams of honeycomb lattice Wigner crystals. For the three lattice filling
factors with the largest charge gaps, n = 2/3, 1/2, 1/3, the magnetic phase
diagrams contain multiple phases, including ones with non-collinear and
non-coplanar spin arrangements. We discuss magnetization evolution with
external magnetic field, which has potential as an experimental signature of
exotic spin states. Our theoretical results could potentially be validated in
moir\'e materials formed from group VI transition metal dichalcogenide twisted
homobilayers.",2206.10024v1
2004/5/25,Ferroelectric properties controlled by magnetic fields in DyMn2O5,"Cross-correlation between magnetic and dielectric properties has been
attracting renewed interest because of the fundamental as well as technological
importance of controlling the electric (magnetic) polarization by an external
magnetic (electric) field. Here, we report the novel phenomenon that an
external magnetic field induces and/or modifies ferroelectric states in a
magnetic material, DyMn2O5. Measurements of temperature dependence of
hysteretic polarization curves, pyroelectric current, specific heat, optical
second harmonic generation, and x-ray superlattice peaks have revealed
successive phase transitions between 43 K and 4 K, accompanying three
ferroelectric phases. The zero-field lowest-temperature phase (<8 K) induced by
the Dy-moment ordering is a reentrant paraelectric state, but is turned to a
ferroelectric state with increasing the magnetic field. The phenomenon is
closely related to the metamagnetic transitions of the Dy f-moment, indicating
that all the ferroelectric phases of this material are strongly tied to the
antiferromagnetic Mn spin structure affected by the f-d exchange interaction.
The electric phase diagram for DyMn2O5 is presented in the plane of temperature
and magnetic field.",0405571v1
2004/7/29,Temperature dependent magnetic anisotropy in metallic magnets from an ab-initio electronic structure theory: L1_0-ordered FePt,"On the basis of a first-principles, relativistic electronic structure theory
of finite temperature metallic magnetism, we investigate the variation of
magnetic anisotropy, K, with magnetisation, M, in metallic ferromagnets. We
apply the theory to the high magnetic anisotropy material, L1_0-ordered FePt,
and find its uniaxial K consistent with a magnetic easy axis perpendicular to
the Fe/Pt layering for all M and to be proportional to M^2 for a broad range of
values of M. For small M, near the Curie temperature, the calculations pick out
the easy axis for the onset of magnetic order. Our results are in good
agreement with recent experimental measurements on this important magnetic
material.",0407774v1
2004/10/22,Magnetostriction in an array of spin chains under magnetic field,"We consider an array of XX spin-1/2 chains coupled to acoustic phonons and
placed in a magnetic field. Treating the phonons in the mean field
approximation, we show that this system presents a first order transition as a
function of the magnetic field between a partially magnetized distorted state
and the fully polarized undistorted state at low temperature. This behavior
results from the magnetostriction of the coupled chain system. A dip in the
elastic constant of the material near the saturation field along with an
anomaly in the magnetic susceptibility is predicted. We also predict the
contraction of the material as the magnetic field is reduced (positive
magnetostriction) and the reciprocal effect i.e. a decrease of magnetization
under applied pressure. At higher temperature, the first order transition is
replaced by a crossover. However, the anomalies in the susceptibilities in the
system near the saturation field are still present. We discuss the relevance of
our analysis in relation to recent experiments on spin-1/2 chain and ladder
materials in strong magnetic fields.",0410571v2
2012/6/7,"Hybridization of electromagnetic, spin and acoustic waves in magnetic having conical spiral ferromagnetic order","The spectrum of hybrid electromagnetic-spin-acoustic waves for magnetic
having conical spiral ferromagnetic structure defined by heterogeneous exchange
and relativistic interactions have been received. The possibility of resonant
interaction of spin, electromagnetic and acoustic waves has been shown. The
electromagnetic waves reflectance from the half-infinity layer of magnetic
having conical spiral ferromagnetic order has been calculated for different
values of external magnetic field (angle of spiral). The acoustic Faradey
effect has been considered.",1206.1421v2
2013/6/27,Exchange interaction and its tuning in magnetic binary chalcogenides,"Using a first-principles Green's function approach we study magnetic
properties of the magnetic binary chalcogenides Bi2Te3, Bi2Se3, and Sb2Te3. The
magnetic coupling between transition-metal impurities is long-range, extends
beyond a quintuple layer, and decreases with increasing number of d electrons
per 3d atom. We find two main mechanisms for the magnetic interaction in these
materials: the indirect exchange interaction mediated by free carriers and the
indirect interaction between magnetic moments via chalcogen atoms. The
calculated Curie temperatures of these systems are in good agreement with
available experimental data. Our results provide deep insight into magnetic
interactions in magnetic binary chalcogenides and open a way to design new
materials for promising applications.",1306.6590v1
2015/3/24,Magnetically-induced ferroelectricity in the (ND4)2[FeCl5(D2O)] molecular compound,"The number of magnetoelectric multiferroic materials reported to date is
scarce, as magnetic structures that break inversion symmetry and induce an
improper ferroelectric polarization typically arise through subtle competition
between different magnetic interactions. The (NH4)2[FeCl5(H2O)] compound is a
rare case where such improper ferroelectricity has been observed in a molecular
material. We have used single crystal and powder neutron diffraction to obtain
detailed solutions for the crystal and magnetic structures of
(NH4)2[FeCl5(H2O)], from which we determined the mechanism of multiferroicity.
From the crystal structure analysis, we observed an order-disorder phase
transition related to the ordering of the ammonium counterion. We have
determined the magnetic structure below TN, at 2K and zero magnetic field,
which corresponds to a cycloidal spin arrangement with magnetic moments
contained in the ac-plane, propagating parallel to the c-axis. The observed
ferroelectricity can be explained, from the obtained magnetic structure, via
the inverse Dzyaloshinskii-Moriya mechanism.",1503.07130v1
2015/5/27,Dopant-mediated structural and magnetic properties of TbMnO3,"Structural and magnetic properties of the doped terbium manganites (Tb,A)MnO3
(A = Gd, Dy and Ho) have been investigated using first-principles calculations
and further confirmed by subse- quent experimental studies. Both computational
and experimental studies suggest that compared to the parent material, namely,
TbMnO3 (with a magnetic moment of 9.7 /muB for Tb3+) Dy- and Ho- ion
substituted TbMnO3 results in an increase in the magnetic moment (< 10.6/muB
for Dy3+ and Ho3+). The observed spiral-spin AFM order in TbMnO3 is stable with
respect to the dopant substitutions, which modify the Mn-O-Mn bond angles and
lead to stronger the ferromagnetic component of the magnetic moment. Given the
fact that magnetic ordering in TbMnO3 causes the ferroelectricity, this is an
important step in the field of the magnetically driven ferroelectricity in the
class of magnetoelectric multiferroics, which traditionally have low magnetic
moments due to the predominantly antiferromagnetic order. In addition, the
present study reveals important insights on the phenomenological coupling
mechanism in detail, which is essential in order to design new materials with
enhanced magneto-electric effects at higher temperatures.",1505.07182v1
2016/11/23,Dynamics of magnetic nano-flake vortices in Newtonian fluids,"We study the rotational motion of nano-flake ferromagnetic discs suspended in
a Newtonian fluid, as a potential material owing the vortex-like magnetic
configuration. Using analytical expressions for hydrodynamic, magnetic and
Brownian torques, the stochastic angular momentum equation is determined in the
dilute limit conditions under applied magnetic field. Results are compared
against experimental ones and excellent agreement is observed. We also estimate
the uncertainty in the orientation of the discs due to the Brownian torque when
an external magnetic field aligns them. Interestingly, this uncertainty is
roughly proportional to the ratio of thermal energy of fluid to the magnetic
energy stored in the discs. Our approach can be implemented in many practical
applications including biotechnology and multi-functional fluidics.",1611.07680v1
2017/5/28,Chiral magnetic effect of light,"We study a photonic analog of the chiral magnetic (vortical) effect. We
discuss that the vector component of magnetoelectric tensors plays a role of
""vector potential,"" and its rotation is understood as ""magnetic field"" of a
light. Using the geometrical optics approximation, we show that ""magnetic
fields"" cause an anomalous shift of a wave packet of a light through an
interplay with the Berry curvature of photons. The mechanism is the same as
that of the chiral magnetic (vortical) effect of a chiral fermion, so that we
term the anomalous shift ""chiral magnetic effect of a light."" We further study
the chiral magnetic effect of a light beyond geometric optics by directly
solving the transmission problem of a wave packet at a surface of a
magnetoelectric material. We show that the experimental signal of the chiral
magnetic effect of a light is the nonvanishing of transverse displacements for
the beam normally incident to a magnetoelectric material.",1705.09926v3
2017/10/13,Low-dimensional quantum magnetism in Cu(NCS)$_2$: A molecular framework material,"Low-dimensional magnetic materials with spin-$\frac{1}{2}$ moments can host a
range of exotic magnetic phenomena due to the intrinsic importance of quantum
fluctuations to their behavior. Here, we report the structure, magnetic
structure and magnetic properties of copper(II) thiocyanate, Cu(NCS)$_2$, a
one-dimensional coordination polymer which displays low-dimensional quantum
magnetism. Magnetic susceptibility, electron paramagnetic resonance (EPR)
spectroscopy, $^{13}$C magic-angle spinning nuclear magnetic resonance (MASNMR)
spectroscopy, and density functional theory (DFT) investigations indicate that
Cu(NCS)$_2$ behaves as a two-dimensional array of weakly coupled
antiferromagnetic spin chains ($J_2 = 133(1)$ K, $\alpha = J_1/J_2 = 0.08$).
Powder neutron-diffraction measurements confirm that Cu(NCS)$_2$ orders as a
commensurate antiferromagnet below $T_\mathrm{N} = 12$ K, with a strongly
reduced ordered moment (0.3 $\mu_\mathrm{B}$) due to quantum fluctuations.",1710.04889v3
2019/9/26,The study of magnetic topological semimetals by first principles calculations,"Magnetic topological semimetals (TSMs) are topological quantum materials with
broken time-reversal symmetry (TRS) and isolated nodal points or lines near the
Fermi level. Their topological properties would typically reveal from the
bulk-edge correspondence principle as nontrivial surface states such as Fermi
arcs or drumhead states, etc. Depending on the degeneracies and distribution of
the nodes in the crystal momentum space, TSMs are usually classified into Weyl
semimetals (WSMs), Dirac semimetals (DSMs), nodal-line semimetals (NLSMs),
triple-point semimetals (TPSMs), etc. In this review article, we present the
recent advances of magnetic TSMs from a computational perspective. We first
review the early predicted magnetic WSMs such as pyrochlore iridates and
HgCr2Se4, as well as the recently proposed Heusler, Kagome layers, and
honeycomb lattice WSMs. Then we discuss the recent developments of magnetic
DSMs, especially CuMnAs in Type-III and EuCd2As2 in Type-IV magnetic space
groups (MSGs). Then we introduce some magnetic NLSMs that are robust against
spin-orbit coupling (SOC), namely Fe3GeTe2 and LaCl (LaBr). Finally, we discuss
the prospects of magnetic TSMs and the interesting directions for future
research.",1909.11999v1
2021/4/20,Investigation of the magnetic ground state of GaV$_4$S$_8$ using powder neutron diffraction,"The magnetic ground state of polycrystalline N\'eel skyrmion hosting material
GaV$_4$S$_8$ has been investigated using ac susceptibility and powder neutron
diffraction. In the absence of an applied magnetic field GaV$_4$S$_8$ undergoes
a transition from a paramagnetic to a cycloidal state below 13~K and then to a
ferromagnetic-like state below 6~K. With evidence from ac susceptibility and
powder neutron diffraction, we have identified the commensurate magnetic
structure at 1.5 K, with ordered magnetic moments of $0.23(2)~\mu_{\mathrm{B}}$
on the V1 sites and $0.22(1)~\mu_{\mathrm{B}}$ on the V2 sites. These moments
have ferromagnetic-like alignment but with a 39(8)$^{\circ}$ canting of the
magnetic moments on the V2 sites away from the V$_4$ cluster. In the
incommensurate magnetic phase that exists between 6 and 13 K, we provide a
thorough and careful analysis of the cycloidal magnetic structure exhibited by
this material using powder neutron diffraction.",2104.09912v1
2021/5/25,Epitaxial Growth and Domain Structure Imaging of Kagome Magnet Fe$_3$Sn$_2$,"Magnetic materials with kagome crystal structure exhibit rich physics such as
frustrated magnetism, skyrmion formation, topological flat bands, and
Dirac/Weyl points. Until recently, most studies on kagome magnets have been
performed on bulk crystals or polycrystalline films. Here we report the
synthesis of high-quality epitaxial films of topological kagome magnet
Fe$_3$Sn$_2$ by atomic layer molecular beam epitaxy. Structural and magnetic
characterization of Fe$_3$Sn$_2$ on epitaxial Pt(111) identifies highly ordered
films with c-plane orientation and an in-plane magnetic easy axis. Studies of
the local magnetic structure by anomalous Nernst effect imaging reveals
in-plane oriented micrometer size domains. The realization of high-quality
films by atomic layer molecular beam epitaxy opens the door to explore the rich
physics of this system and investigate novel spintronic phenomena by
interfacing Fe$_3$Sn$_2$ with other materials.",2105.12203v1
2017/7/6,Structure and Topology of Band Structures in the 1651 Magnetic Space Groups,"The properties of electrons in magnetically ordered crystals are of interest
both from the viewpoint of realizing novel topological phases, such as magnetic
Weyl semimetals, and from the applications perspective of creating
energy-efficient memories. A systematic study of symmetry and topology in
magnetic materials has been challenging given that there are 1651 magnetic
space groups (MSGs). Here, by using an efficient representation of allowed band
structures, we obtain a systematic description of several basic properties of
free electrons in all MSGs in three dimensions as well as in the 528 magnetic
layer groups relevant to two dimensional magnetic materials. We compute
constraints on electron fillings and band connectivity compatible with
insulating behavior. Also, by contrasting with atomic insulators, we identify
band topology entailed by the symmetry transformation of bands, as determined
by the MSG alone. We give an application of our results to identifying
topological semimetals arising in periodic arrangements of hedgehog-like
magnetic textures.",1707.01903v2
2017/7/12,Magneto-optical response enhanced by Mie resonances in nanoantennas,"Control of light by an external magnetic field is one of the important
methods for modulation of its intensity and polarisation. Magneto-optical
effects at the nanoscale are usually observed in magnetophotonic crystals,
nanostructured hybrid materials or magnetoplasmonic crystals. An indirect
action of an external magnetic field (e.g. through the Faraday effect) is
explained by the fact that natural materials exhibit negligible magnetism at
optical frequencies. However, the concept of metamaterials overcome this
limitation imposed by nature by designing artificial subwavelength meta-atoms
that support a strong magnetic response, usually termed as optical magnetism,
even when they are made of nonmagnetic materials. The fundamental question is
what would be the effect of the interaction between an external magnetic field
and an optically-induced magnetic response of metamaterial structures. Here we
make the first step toward answering this fundamental question and demonstrate
the multifold enhancement of the magneto-optical response of nanoantenna
lattices due to the optical magnetism.",1707.03799v1
2017/12/8,Magnon-induced superconductivity in field-cooled spin-1/2 antiferromagnets,"If, during the preparation, an external magnetic field is applied upon
cooling we say it has been field cooled. A novel mechanism for insulator-metal
transition and superconductivity in field-cooled spin-$1/2$ antiferromagnets on
bcc lattice is discussed. Applying a magnetic field along the sublattice B
magnetization, we change the magnetic and transport properties of the material.
There is a critical value $H_{cr1}$. When the magnetic field is below the
critical one $H<H_{cr1}$ the prepared material is a spin$-1/2$
antiferromagnetic insulator. When $H>H_{cr1}$ the sublattice A electrons are
delocalized and the material is metal. There is a second critical value
$H_{cr2}>H_{cr1}$. When $H=H_{cr2}$, it is shown that the Zeeman splitting of
the sublattice A electrons is zero and they do not contribute to the
magnetization of the system. At this quantum partial order point (QPOP) the
sublattice B transversal spin fluctuations (magnons) interact with sublattice A
electrons inducing spin anti-parallel \emph{p}-wave superconductivity which
coexists with magnetism. At zero temperature the magnetic moment of sublattice
B electrons is maximal. Below the N\'{e}el temperature $(T_N)$ the gap is
approximately constant with a small increase when the system approaches $T_N$.
It abruptly falls down to zero at temperatures above $T_N$.",1712.02983v1
2018/2/19,Borderline Magnetism: How Does Adding Magnesium to Paramagnetic CeCo$_3$ Make a 450 K Ferromagnet with Large Magnetic Anisotropy?,"A recent experimental study (Phys. Rev. Appl. 9, 024023, 2018) on
paramagnetic CeCo$_3$ finds that Magnesium alloying induces a ferromagnetic
transition with intrinsic properties large enough for permanent magnet
applications. Here we explain these surprising results \textit{via} a first
principles study of the electronic structure and magnetism of Magnesium-alloyed
CeCo$_3$. We find the origin of this Magnesium-induced ferromagnetic transition
to be Stoner physics - the substantial increase in the Fermi-level
density-of-states $N(E_F)$ with Mg alloying. Our calculations suggest that both
Ce and Co atoms are important for generating large magnetic anisotropy
suggesting the viability of Co-3$d$, and Ce-4$f$ interaction for the generation
of magnetic anisotropy in magnetic materials. These results offer a new route
to the discovery of ferromagnetic materials and provide fundamental insight
into the magnetic properties of these alloys",1802.06747v2
2019/12/3,Large Resistance Change on Magnetic Tunnel Junction based Molecular Spintronics Devices,"Molecular bridges covalently bonded to two ferromagnetic electrodes can
transform ferromagnetic materials and produce intriguing spin transport
characteristics. This paper discusses the impact of molecule induced strong
coupling on spin transport. To study the molecular coupling effect
organometallic molecular complex (OMC) was bridged between two ferromagnetic
electrodes of a magnetic tunnel junction (Ta/Co/NiFe/AlOx/NiFe/Ta) along the
exposed side edges. OMCs induced strong iter-ferromagnetic electrode coupling
to yield drastic changes in transport properties of the magnetic tunnel
junction testbed at the room temperature. These OMCs also transformed the
magnetic properties of magnetic tunnel junctions. SQUID and ferromagnetic
resonance studies provided insightful data to explain transport studies on the
magnetic tunnel junction based molecular spintronics devices.",1912.01305v1
2020/2/24,Metal-free magnetism in chemically doped covalent organic frameworks,"Organic and molecule-based magnets are not easily attainable, because to
introduce stable paramagnetic centers to pure organic systems is challenging.
Crystalline covalent organic frameworks (COFs) with high designability and
chemical diversity constitute ideal platforms to access intriguing magnetic
phenomena of organic materials. In this work, we proposed a general approach to
attain unpaired electron spin and metal-free magnetism in narrow-band COFs by
chemical doping. By using density functional theory calculations, we found that
dopants with energy-matched frontier orbitals to COFs not only inject charges
to them but also further localize the charges through orbital hybridization and
formation of supramolecular charge-transfer complex. The localized states
enable stable paramagnetic centers introduced to nonmagnetic COFs. Based on
this discovery, we designed two new COFs with narrow valence band, which show
prospective magnetism after doping with iodine. Further, we unraveled magnetic
anisotropy in two-dimensional COFs and showed that both spin-conduction and
magnetic interactions can be modulated by manipulating the building blocks of
COFs. Our work highlights a practical scenario to attain magnetism in COFs and
other organic materials, which hold great promise for applications in organic
spintronic devices.",2002.10216v2
2021/6/17,Computational Optimization of MnBi to Enhance Energy Product,"High energy density magnets are preferred over induction magnets for many
applications, including electric motors used in flying rovers, electric
vehicles, and wind turbines. However, several issues related to cost and supply
with state-of-the-art rare-earth-based magnet necessities development of
high-flux magnets containing low cost, earth-abundant materials. Here, we
demonstrate the possibility of tuning magnetization and magnetocrystalline
anisotropy of one of the candidate materials, MnBi, by alloying it with foreign
elements. By using the density functional theory in the high-throughput
fashion, we consider the possibility of alloying MnBi with all possible metal
and non-metal elements in the periodic table and found that MnBi-based alloys
with Pd, Pt, Rh, Li, and O are stable against decomposition to constituent
elements and have larger magnetization, energy product compared and magnetic
anisotropy compared to MnBi We consider the possibility of these elements
occupying half and all of the available empty sites. Combined with other
favorable properties of MnBi, such as high Curie temperature and earth
abundancy of constituents elements, we envision the possibility of MnBi-based
high-energy-density magnets.",2106.09631v1
2021/6/18,Magnetic transitions in the 1-D chain compounds NdPd5Ge3 and NdPt5Ge3,"We present the structural and initial magnetic characterization of the
previously unreported materials NdPd5Ge3 and NdPd5Ge3. These materials, with
1-dimensional Nd chains, crystallize in the orthorhombic YNi5Si3-type structure
in space group Pnma. Magnetic ordering is observed for both compounds at ~ 2.2
K for NdPd5Ge3 and ~ 3.0 K for NdPt5Ge3. A magnetic-field-induced transition is
clearly observed for NdPd5Ge3 below 2K, at an applied magnetic field of around
1.6 Tesla. The heat capacity data reveals that essentially all the available
magnetic entropy is released at the magnetic ordering transition for NdPd5Ge3
but that only 29% is seen for NdPt5Ge3 at temperatures down to 1.5 K, the data
implying that a second magnetic transition can be expected at lower
temperatures.",2106.10325v2
2021/7/6,Static and dynamic magnetic properties of K3CrO4,"We report on the magnetic properties of geometrically frustrated K3CrO4, in
which Cr5+ cations are arranged on a distorted pyrochlore lattice. The crystal
structure, static and dynamic magnetic properties of the compound are
investigated in detail. A combination of DC and AC magnetic susceptibility
measurements together with thermoremanent magnetization decay measurements
reveal several magnetic transitions: the onset of glassy canted
antiferromagnetic order occurs at 36 K, followed by the appearance of
ferromagnetic/ferrimagnetic cluster glass behavior below the freezing
temperature of 20 K. Further field-induced, temperature-dependent transitions
are observed in the range 3-10 K. The frequency dependence of the freezing
temperature for the cluster glass state is analyzed on the basis of dynamic
scaling laws including the critical slowing down formula and the Vogel-Fulcher
law.",2107.02878v1
2022/8/27,Magnetic bond-order potential for iron-cobalt alloys,"For large-scale atomistic simulations of magnetic materials, the interplay of
atomic and magnetic degrees of freedom needs to be described with high
computational efficiency. Here we present an analytic bond-order potential
(BOP) for iron-cobalt, an interatomic potential based on a coarse-grained
description of the electronic structure. We fitted BOP parameters to magnetic
and non-magnetic density-functional theory (DFT) calculations of Fe, Co, and
Fe-Co bulk phases. Our BOP captures the electronic structure of magnetic and
non-magnetic Fe-Co phases. It provides accurate predictions of structural
stability, elastic constants, phonons, point and planar defects, and structural
transformations. It also reproduces the DFT-predicted sequence of stable
ordered phases peculiar to Fe-Co and the stabilization of B2 against disordered
phases by magnetism. Our Fe-Co BOP is suitable for atomistic simulations with
thousands and millions of atoms.",2208.12973v2
2022/10/17,Spinteract: A Program to Refine Magnetic Interactions to Diffuse Scattering Data,"Magnetic diffuse scattering -- the broad magnetic scattering features
observed in neutron-diffraction data above a material's magnetic ordering
temperature -- provides a rich source of information about the material's
magnetic Hamiltonian. However, this information has often remained
under-utilised due to a lack of available computer software that can fit values
of magnetic interaction parameters to such data. Here, an open-source computer
program, Spinteract, is presented, which enables straightforward refinement of
magnetic interaction parameters to powder and single-crystal magnetic diffuse
scattering data. The theory and implementation of this approach are summarised.
Examples are presented of refinements to published experimental
diffuse-scattering data sets for the canonical antiferromagnet MnO and the
highly-frustrated classical spin liquid Gd3Ga5O12. Guidelines for data
collection and refinement are outlined, and possible developments of the
approach are discussed.",2210.09016v1
2023/2/19,Magnetic bulk photovoltaic effect as a probe of magnetic structures of $EuSn_2As_2$,"The bulk photovoltaic effect (BPVE) is a second-order optical process in
noncentrosymmetric materials that converts the light into DC currents. BPVE is
classified into shift current and injection current according to the generation
mechanisms, whose dependence on the polarization of light is sensitive to the
spatial and time-reversal symmetry of materials. In this work, we present a
comprehensive study on the BPVE response of $EuSn_2As_2$ with different
magnetic structures through symmetry analysis and first-principles calculation.
We demonstrate that the interlayer antiferromagnetic (AFM) $EuSn_2As_2$ of
even-layer breaks the inversion symmetry and has the second-order optical
responses. Moreover, the bilayer AFM $EuSn_2As_2$ not only displays distinct
BPVE responses when magnetic moments align in different directions, but also
shows symmetry-related responses in two phases which have mutually
perpendicular in-plane magnetic moments. Due to the dependence of BPVE
responses on the polarization of light and magnetic symmetry, these magnetic
structures can be distinguished by the circular polarized light with
well-designed experiments. Our work demonstrates the feasibility of the BPVE
response as a tool to probe the magnetic structure.",2302.09514v1
2023/6/20,Giant effective magnetic moments of chiral phonons from orbit-lattice coupling,"Circularly polarized lattice vibrations carry angular momentum and lead to
magnetic responses in applied magnetic fields or when resonantly driven with
ultrashort laser pulses. Recent measurements have found responses that are
orders of magnitude larger than those calculated in prior theoretical studies.
Here, we present a microscopic model for the effective magnetic moments of
chiral phonons in magnetic materials that is able to reproduce the
experimentally measured magnitudes and that allows us to make quantitative
predictions for materials with giant magnetic responses using microscopic
parameters. Our model is based on orbit-lattice couplings that hybridize
optical phonons with orbital electronic transitions. We apply our model to two
types of materials: $4f$ rare-earth halide paramagnets and $3d$
transition-metal oxide magnets. In both cases, we find that chiral phonons can
carry giant effective magnetic moments of the order of a Bohr magneton, orders
of magnitude larger than previous predictions.",2306.11630v1
2023/8/10,Exciton localization on a magnetic domain wall in MoSe$_2$-CrI$_3$ heterostructure,"The existence of spontaneous magnetization that fingerprints a ground-state
ferromagnetic order was recently observed in two-dimensional (2D) van der Waals
materials. Despite progress in the fabrication and manipulation of the
atom-thick magnets, investigation of nanoscale magnetization properties is
still challenging due to the concomitant technical issues. We propose a
promising approach for a direct visualization of the domain walls formed in 2D
magnetic materials. By interfacing 2D magnet with a transition metal
dichalcogenide (TMD) monolayer, the strong proximity effects enable pinning the
TMD excitons on the domain wall. The emergent localization stems from the
proximity-induced exchange mixing between spin-dark and spin-bright TMD
excitons due to the local in-plane magnetization characteristic of the domain
wall in the magnetic monolayer.",2308.05531v2
2023/12/13,Defect-sensitive High-frequency Modes in a Three-Dimensional Artificial Magnetic Crystal,"Modern three-dimensional nanofabrication methods make it possible to generate
arbitrarily shaped nanomagnets, including periodic networks of interconnected
magnetic nanowires. Structurally similar to optical or acoustic metamaterials,
these arrays could represent magnetic variants of such artificial materials.
Using micromagnetic simulations, we investigate a three-dimensional array of
interconnected magnetic nanowires with intersection points corresponding to
atomic positions of a diamond lattice. The high-frequency excitation spectrum
of this artificial magnetic crystal (AMC) is governed by its microstructure
and, to a lesser extent, by the magnetic configuration. The magnetic system
displays characteristics of three-dimensional artificial spin ice. It can
contain Dirac-type magnetic defect structures, which modify the magnonic
spectrum of the AMC similarly as defect sites in a natural diamond crystal
influence optical absorption spectra. Our study opens new perspectives for
applying such materials in high-density magnonic devices and shows that AMCs
represent a promising category of magnonic materials with tunable properties.",2312.08415v1
2024/2/22,Barium hexaferrite-based nanocomposites as Random Magnets for microwave absorption H,"The present work reports experimental evidence of random magnetic behavior
observed in modified barium hexagonal ferrites. A significant transition in the
magnetic properties of this system is observed when divalent cations (Ni2+,
Cu2+, Mn2+) are introduced in the structure and give rise to a magnetic
nanocomposite. Such introduction takes place in a random manner throughout each
sample and creates the conditions for such materials to behave as random
magnets. We verify the occurrence of such behavior in our samples by fitting
the magnetization in approaching saturation to the corresponding theoretical
model. We therefore analyze the microwave absorption capacities of random
magnets in the GHz range and predict large and broad absorption signals under
certain conditions. The findings presented here postulate, for the first time,
ceramic materials as promising random magnets and underline their potential as
microwave absorbers, in good agreement with recent theoretical models.",2402.14324v1
2024/3/13,Simultaneous mapping of magnetic and atomic structure for direct visualization of nanoscale magnetoelastic coupling,"Achieving a correlative measurement of both magnetic and atomic structures at
the nanoscale is imperative to understand the fundamental magnetism of matters
and for fostering the development of new magnetic nanomaterials. Conventional
microscopy methods fall short in providing the two information simultaneously.
Here, we develop a new approach to simultaneously map the magnetic field and
atomic structure at the nanoscale using Lorentz 4-dimensional scanning
transmission electron microscopy (Ltz-4D-STEM). This method enables precise
measurement of the characteristic atomic and magnetic structures across an
extensive field of view, a critical aspect for investigating real-world
ferromagnetic materials. It offers a comprehensive visualization and
statistical evaluation of the different structural information at a
pixel-by-pixel correlation. The new method allows to directly visualize the
magnetoelastic coupling and the resulting complex magnetization arrangement as
well as the competition between magnetoelastic and magnetostatic energy. This
approach opens new avenues for in-depth studying the structure-property
correlation of nanoscale magnetic materials.",2403.08582v1
1998/8/25,General Green's function formalism for transport calculations with spd-Hamiltonians and giant magnetoresistance in Co and Ni based magnetic multilayers,"A novel, general Green's function technique for elastic spin-dependent
transport calculations is presented, which (i) scales linearly with system size
and (ii) allows straightforward application to general tight-binding
Hamiltonians (spd in the present work). The method is applied to studies of
conductance and giant magnetoresistance (GMR) of magnetic multilayers in CPP
(current perpendicular to planes) geometry in the limit of large coherence
length. The magnetic materials considered are Co and Ni, with various
non-magnetic materials from the 3d, 4d, and 5d transition metal series.
Realistic tight-binding models for them have been constructed with the use of
density functional calculations. We have identified three qualitatively
different cases which depend on whether or not the bands (densities of states)
of a non-magnetic metal (i) form an almost perfect match with one of spin
sub-bands of the magnetic metal (as in Cu/Co spin valves); (ii) have almost
pure sp character at the Fermi level (e.g. Ag); (iii) have almost pure d
character at the Fermi energy (e.g. Pd, Pt). The key parameters which give rise
to a large GMR ratio turn out to be (i) a strong spin polarization of the
magnetic metal, (ii) a large energy offset between the conduction band of the
non-magnetic metal and one of spin sub-bands of the magnetic metal, and (iii)
strong interband scattering in one of spin sub-bands of a magnetic metal. The
present results show that GMR oscillates with variation of the thickness of
either non-magnetic or magnetic layers, as observed experimentally.",9808282v1
2013/8/4,Effect of Magnetic Misalignment on Protobinary Evolution,"The majority of solar-type stars reside in multiple systems, especially
binaries. They form in dense cores of molecular clouds that are observed to be
significantly magnetized. Our previous study shows that magnetic braking can
tighten the binary separation during the protostellar mass accretion phase by
removing the angular momentum of the accreting material. Recent numerical
calculations of single star formation have shown that misalignment between the
magnetic field and rotation axis may weaken both magnetic braking and the
associated magnetically driven outflows. These two effects allow for disk
formation even in strongly magnetized cores. Here we investigate the effects of
magnetic field misalignment on the properties of protobinaries. Somewhat
surprisingly, the misaligned magnetic field is more efficient at tightening the
binary orbit compared to the aligned field. The main reason is that the
misalignment weakens the magnetically-driven outflow, which allows more
material to accrete onto the binary. Even though the specific angular momentum
of this inner material is higher than in the aligned case, it is insufficient
to compensate for the additional mass. A corollary of this result is that a
weaker field is required to achieve the same degree of inward migration when
the field is tilted relative to the rotation axis. Large field misalignment
also helps to produce rotationally-supported circumbinary disks even for
relatively strong magnetic fields, by weakening the magnetically-dominated
structure close to the binary. Our result may provide an explanation for the
circumbinary disks detected in recent SMA and ALMA observations.",1308.0830v1
2018/1/15,"Reversal magnetization, spin reorientation and exchange bias in YCrO$_3$ doped with praseodymium","Crystal structure, thermal and magnetic properties were systematically
studied in the Y$_{1-x}$Pr$_x$CrO$_3$ with $0 \leq x \leq 0.3$ compositions.
Magnetic susceptibility and specific heat measurements show an increase of the
antiferromagnetic transition temperature ($T_N$) as Pr is substituted in the Y
sites and notable magnetic features are observed below $T_N$. Strong coupling
between magnetic and crystalline parameters is observed in a small range of Pr
compositions. A small perturbation in the lattice parameters by Pr ion is
sufficient to induce a spin reorientation transition followed by magnetization
reversal, to finally induce exchange bias effect. The spin reorientation
temperature ($T_{SR}$) is increased from 35 K to 149 K for $0.025 \leq x \leq
0.1$ compositions. It is found that the Cr spins sublattice rotates
continuously from $T_{SR}$ to a new spin configuration a lower temperature. In
addition, magnetization reversal is observed at $T^* \sim 35$ K for x= 0.05 up
to $T^* \sim 63$ K for x = 0.20 composition. The $M-H$ curves show negative
exchange bias effect induced by Pr ions, which are observed below of 100 K and
being more intense at 5 K. At 10 K, the magnetic contribution of the specific
heat, as well as the ZFC magnetization, show the rise of a peak with increasing
Pr content. The magnetic anomaly could be associated with the freezing of the
Pr magnetic moment randomly distributed at the 4c crystallographic site. A
clear correspondence between spin reorientation, magnetization reversal and
exchange bias anisotropy with the tilting and octahedral distortion is also
discussed.",1801.04967v1
2019/1/21,Evolutionary optimization of all-dielectric magnetic nanoantennas,"Magnetic light and matter interactions are generally too weak to be detected,
studied and applied technologically. However, if one can increase the magnetic
power density of light by several orders of magnitude, the coupling between
magnetic light and matter could become of the same order of magnitude as the
coupling with its electric counterpart. For that purpose, photonic nanoantennas
have been proposed, and in particular dielectric nanostructures, to engineer
strong local magnetic field and therefore increase the probability of magnetic
interactions. Unfortunately, dielectric designs suffer from physical
limitations that confine the magnetic hot spot in the core of the material
itself, preventing experimental and technological implementations. Here, we
demonstrate that evolutionary algorithms can overcome such limitations by
designing new dielectric photonic nanoantennas, able to increase and extract
the optical magnetic field from high refractive index materials. We also
demonstrate that the magnetic power density in an evolutionary optimized
dielectric nanostructure can be increased by a factor 5 compared to state of
the art dielectric nanoantennas. In addition, we show that the fine details of
the nanostructure are not critical in reaching these aforementioned features,
as long as the general shape of the motif is maintained. This advocates for the
feasibility of nanofabricating the optimized antennas experimentally and their
subsequent application. By designing all dielectric magnetic antennas that
feature local magnetic hot-spots outside of high refractive index materials,
this work highlights the potential of evolutionary methods to fill the gap
between electric and magnetic light-matter interactions, opening up new
possibilities in many research fields.",1901.06913v1
2016/12/15,Magnetic and Thermal Transport Properties of Permanent Magnets with Anisotropic Grain Structure,"Nanostructured permanent magnets are gaining increasing interest and
importance for applications such as generators and motors. Thermal management
is a key concern since performance of permanent magnets decreases with
temperature. We investigated the magnetic and thermal transport properties of
rare-earth free nanostructured SrFe12O19 magnets produced by the current
activated pressure assisted densification. The synthesized magnets have aligned
grains such that their magnetic easy axis is perpendicular to their largest
surface area to maximize their magnetic performance. The SrFe12O19 magnets have
fine grain sizes in the cross-plane direction and substantially larger grain
sizes in the in-plane direction. It was found that this microstructure results
in approximately a factor of two higher thermal conductivity in the in-plane
direction, providing an opportunity for effective cooling. The phonons are the
dominant heat carriers in this type of permanent magnets near room temperature.
Temperature and direction dependent thermal conductivity measurements indicate
that both Umklapp and grain boundary scattering are important in the in-plane
direction, where the characteristic grain size is relatively large, while grain
boundary scattering dominates the cross-plane thermal transport. The
investigated nano/microstructural design strategy should translate well to
other material systems and thus have important implications for thermal
management of nanostructured permanent magnets.",1612.05174v1
2003/9/11,Left-handed materials in metallic magnetic granular composites,"There is recently interests in the ``left-handed '' materials. In these
materials the direction of the wave vector of electromagnetic radiation is
opposite to the direction of the energy flow. We present simple arguments that
suggests that magnetic composites can also be left-handed materials. However,
the physics involved seems to be different from the original argument. In our
argument, the imaginary part of the dielectric constant is much larger than the
real part, opposite to the original argument.",0309290v1
2004/3/5,Toward creating wide-band uniaxial left-handed materials with small losses,"In this work a possible realizations of a uniaxial variant of left-handed
material (LHM) at microwaves is considered. The meta-material has some features
of the known structure studied by the group of D. Smith in 2001, however in the
present structure a lattice of parallel wires and a lattice of artificial
magnetic resonators (MRs) are unified and the MRs are not split-ring
resonators. The optimizing of MRs allows significantly decrease the magnetic
losses and broaden the band within which the meta-material becomes a LHM.",0403176v1
2008/4/15,Interface-driven magnetocapacitance in a broad range of materials,"Triggered by the revival of multiferroic materials, a lot of effort is
presently undergoing as to find a coupling between a capacitance and a magnetic
field. We show in this report that interfaces are the right way of increasing
such a coupling provided free charges are localized on these two-dimensional
defects. Starting from commercial diodes at room temperature and going to grain
boundaries in giant permittivity materials and to ferroelectric domain walls, a
clear magnetocapacitance is reported which is all the time more than a few
percent for a magnetic field of 90kOe. The only tuning parameter for such
strong coupling to arise is the dielectric relaxation time which is reached on
tuning the operating frequency and the temperature in many different materials.",0804.2416v1
2017/11/8,Effective uniaxial anisotropy in easy-plane materials through nanostructuring,"Permanent magnet materials require a high uniaxial magneto-crystalline
anisotropy. Exchange coupling between small crystallites with easy-plane
anisotropy induces an effective uniaxial anisotropy if arranged accordingly.
Nanostructuring of materials with easy-plane anisotropy is an alternative way
to create hard-magnetic materials. The coercivity increases with decreasing
feature size. The resulting coercive field is about 12 percent of the
anisotropy field for a crystal size of 3.4 times the Bloch parameter.",1711.03144v1
2012/11/26,Vector spherical wavefunctions for orthorhombic dielectric-magnetic material with gyrotropic-like magnetoelectric properties,"Vector spherical wavefunctions were derived in closed-form to represent
time-harmonic electromagnetic fields in an orthorhombic dielectric-magnetic
material with gyrotropic-like magnetoelectric properties. These wavefunctions
were used to formulate the T matrix for scattering by a three-dimensional
object composed of the chosen material. Furthermore, a closed-form,
coordinate-free expression of the dyadic Green function for the chosen material
was derived. Expressions ascertained for the singularity behavior will be
useful for formulating volume integral equations for scattering inside the
chosen material. A bilinear expansion of the dyadic Green function was obtained
in terms of the derived vector spherical wavefunctions.",1211.5894v1
2023/9/29,Micromagnetics of ferromagnetic/antiferromagnetic nanocomposite materials. Part I: Towards the mesoscopic approach,"In the first of two articles, we present here a novel mesoscopic
micromagnetic approach for simulating materials composed of ferromagnetic and
antiferromagnetic phases. Starting with the atomistic modeling of quasi
one-dimensional systems, we explicitly show how the material parameters for the
mesoscopic model of an antiferromagnet can be derived. The comparison between
magnetization profiles obtained in atomistic and mesoscopic calculations (using
a Heusler alloy as an example) proves the validity of our method. This approach
opens up the possibility to recover the details of the magnetization
distribution in ferromagnetic/antiferromagnetic materials with the resolution
of a few nanometers covering length scales up to several hundreds of
nanometers.",2309.17131v1
2006/12/13,A Model for Predicting Magnetic Targeting of Multifunctional Particles in the Microvasculature,"A mathematical model is presented for predicting magnetic targeting of
multifunctional carrier particles that are designed to deliver therapeutic
agents to malignant tissue in vivo. These particles consist of a nonmagnetic
core material that contains embedded magnetic nanoparticles and therapeutic
agents such as photodynamic sensitizers. For in vivo therapy, the particles are
injected into the vascular system upstream from malignant tissue, and captured
at the tumor using an applied magnetic field. The applied field couples to the
magnetic nanoparticles inside the carrier particle and produces a force that
attracts the particle to the tumor. In noninvasive therapy the applied field is
produced by a permanent magnet positioned outside the body. In this paper a
mathematical model is developed for predicting noninvasive magnetic targeting
of therapeutic carrier particles in the microvasculature. The model takes into
account the dominant magnetic and fluidic forces on the particles and leads to
an analytical expression for predicting their trajectory. An analytical
expression is also derived for predicting the volume fraction of embedded
magnetic nanoparticles required to ensure capture of the carrier particle at
the tumor. The model enables rapid parametric analysis of magnetic targeting as
a function of key variables including the size of the carrier particle, the
properties and volume fraction of the embedded magnetic nanoparticles, the
properties of the magnet, the microvessel, the hematocrit of the blood and its
flow rate.",0612116v1
2013/4/11,Field induced phase transitions and phase diagrams in BiFeO_3-like multiferroics,"The incommensurate magnetic structures and phase diagrams of multiferroics
has been explored on the basis of accurate micromagnetic analysis taking into
account the spin flexoelecric interaction (Lifshitz invariant). The objects of
the study are BiFeO_3-like single crystals and epitaxial films grown on the
<111> substrates. The main control parameters are the magnetic field, the
magnetic anisotropy, and the epitaxial strain in the case of films. We predict
novel quasi-cycloidal structures induced by external magnetic field or by
epitaxial strain in the BiFeO_3-films. Phase diagrams representing the regions
of homogeneous magnetic states and incommensurate structures stability are
constructed for the two essential geometries of magnetic field (magnetic field
oriented parallel to the principal crystal axis C_3 and perpendicular to this
direction C_3). It is shown that the direction of applied magnetic field
substantially affects a set of magnetic phases, properties of incommensurate
structures, character of phase transitions. Novel conical type of cycloidal
ordering is revealed during the transition from incommensurate cycloidal
structure into homogeneous magnetic state. Elaborated phase diagrams allow
estimate appropriate combination of control parameters (magnetic field,
magnetic anisotropy, exchange stiffness) required to the destruction of
cycloidal ordering corresponding to the transition into homogeneous structure.
The results show that the magnitude of critical magnetic field suppressing
cycloid is lowered in multiferroics films comparing to single crystals, it can
be also lowered by the selection of orientation of magnetic field. Our results
can be useful for strain engineering of new multiferroic functional materials
on demand.",1304.3204v1
2021/5/10,Parameterization of magnetic vector potentials and fields for efficient multislice calculations of elastic electron scattering,"The multislice method, which simulates the propagation of the incident
electron wavefunction through a crystal, is a well-established method for
analyzing the multiple scattering effects that an electron beam may undergo.
The inclusion of magnetic effects into this method proves crucial towards
simulating magnetic differential phase contrast images at atomic resolution,
enhanced magnetic interaction of vortex beams with magnetic materials,
calculating magnetic Bragg spots, or searching for magnon signatures, to name a
few examples. Inclusion of magnetism poses novel challenges to the efficiency
of the multislice method for larger systems, especially regarding the
consistent computation of magnetic vector potentials and magnetic fields over
large supercells. We present in this work a tabulation of parameterized
magnetic values for the first three rows of transition metal elements computed
from atomic density functional theory calculations, allowing for the efficient
computation of approximate magnetic vector fields across large crystals using
only structural and magnetic moment size and direction information.
Ferromagnetic bcc Fe and tetragonal FePt are chosen as examples in this work to
showcase the performance of the parameterization versus directly obtaining
magnetic vector fields from the unit cell spin density by density functional
theory calculations, both for the quantities themselves and the resulting
magnetic signal from their respective use in multislice calculations.",2105.04195v1
2022/1/3,Exchange Bias and Interface-related Effects in Two-dimensional van der Waals Magnetic Heterostructures: Open Questions and Perspectives,"The exchange bias (EB) effect is known as a fundamentally and technologically
important magnetic property of a magnetic bilayer film. It is manifested as a
horizontal shift in a magnetic hysteresis loop of a film subject to cooling in
the presence of a magnetic field. The EB effect in van der Waals (vdW)
heterostructures offers a novel approach for tuning the magnetic properties of
the newly discovered single-layer magnets, as well as adds a new impetus to
magnetic vdW heterostructures. Indeed, intriguing EB effects have recently been
reported in a variety of low-dimensional vdW magnetic systems ranging from a
weakly interlayer-coupled vdW magnet (e.g., Fe3GeTe2) to a bilayer composed of
two different magnetic vdW materials (e.g., Fe3GeTe2/CrCl3, Fe3GeTe2/FePS3,
Fe3GeTe2/MnPS3), to bilayers of two different vdW defective magnets (e.g.,
VSe2/MoS2), or to metallic ferromagnet/vdW defective magnet interfaces (e.g.,
Fe/MoS2). Despite their huge potential in spintronic device applications, the
physical origins of the observed EB effects have remained elusive to
researchers. We present here a critical review of the EB effect and associated
phenomena such as magnetic proximity (MP) in various vdW heterostructure
systems and propose approaches to addressing some of the emerging fundamental
questions.",2201.00479v1
2022/7/27,Effective and asymptotic criticality of structurally disordered magnets,"Changes in magnetic critical behaviour of quenched structurally-disordered
magnets are usually exemplified in experiments and in MC simulations by diluted
systems consisting of magnetic and non-magnetic components. By our study we aim
to show, that similar effects can be observed not only for diluted magnets with
non-magnetic impurities, but may be implemented, e.g., by presence of two (and
more) chemically different magnetic components as well. To this end, we
consider a model of the structurally-disordered quenched magnet where all
lattice sites are occupied by Ising-like spins of different length $L$. In such
random spin length Ising model the length $L$ of each spin is a random variable
governed by the distribution function $p(L)$. We show that this model belongs
to the universality class of the site-diluted Ising model. This proves that
both models are described by the same values of asymptotic critical exponents.
However, their effective critical behaviour differs. As a case study we
consider a quenched mixture of two different magnets, with values of elementary
magnetic moments $L_1=1$ and $L_2=s$, and of concentration $c$ and $1-c$,
correspondingly. We apply field-theoretical renormalization group approach to
analyze the renormalization group flow for different initial conditions,
triggered by $s$ and $c$, and to calculate effective critical exponents further
away from the fixed points of the renormalization group transformation. We show
how the effective exponents are governed by difference in properties of the
magnetic components.",2207.13655v1
2024/1/24,Magnetic nanoparticles: from the nanostructure to the physical properties,"Some of the synthesis methods and physical properties of iron-oxide based
magnetic nanoparticles such as Fe3-xO4 and CoxFe3-xO4 are reviewed because of
their interest in health, environmental applications, and ultra-high-density
magnetic recording. Unlike high crystalline quality nanoparticles larger than a
few nanometers that show bulk-like magnetic and electronic properties,
nanostructures with increasing structural defects yield a progressive worsening
of their general performance due to frozen magnetic disorder and local breaking
of their crystalline symmetry. Thus, it is shown that single-crystal,
monophasic nanoparticles do not exhibit significant surface or finite-size
effects, such as spin canting, reduced saturation magnetization, high closure
magnetic fields, hysteresis-loop shift or dead magnetic layer features which
are mostly associated with crystallographic defective systems. Besides, the key
role of the nanoparticle coating, surface anisotropy, and inter-particle
interactions are discussed. Finally, the results of some single particle
techniques -- magnetic force microscopy, X-ray photoemission electron
microscopy, and electron magnetic chiral dichroism -- that allow studying
individual nanoparticles down to sub-nanometer resolution with element, valence
and magnetic selectivity, are presented. All in all, the intimate, fundamental
correlation of the nanostructure (crystalline, chemical, magnetic) to the
physical properties of the nanoparticles is ascertained.",2401.13422v1
2018/4/2,Collective Coordinate Descriptions of Magnetic Domain Wall Motion in Perpendicularly Magnetized Nanostructures under the Application of In-plane Fields,"Manipulation of magnetic domain walls can be used to improve the capabilities
of the next generation of memory and sensing devices. Materials of recent
interest for such devices include heterostructures of ultrathin ferromagnets
sandwiched between a heavy metal and an oxide, where spin-orbit coupling and
broken inversion symmetry give rise to the Dzyaloshinskii-Moriya interaction
(DMI), stabilizing chiral domain walls. The efficiency of the motion of these
chiral domain walls may be controlled using in-plane magnetic fields. This
property has been used for measurement of DMI strength. While micromagnetic
simulations are able to accurately predict domain wall motion under in-plane
fields in these materials, collective coordinate models such as the $q-\phi$
and $q-\phi-\chi$ models fail to reproduce the micromagnetic results. In this
theoretical work, we present a set of extended collective coordinate models
including canting in the domains, which better reproduce micromagnetic results,
and helps us better understand the effect of in-plane fields on magnetic domain
walls. These models are used in conjunction with micromagnetic simulations to
identify critical points observed in the motion of the domain walls driven by
out-of-plane magnetic fields, and electric current under magnetic in-plane
fields. Our new models and results help in the development of future domain
wall based devices based on perpendicularly magnetized materials.",1804.00569v3
2018/3/23,Observation of hedgehog skyrmions in sub-100 nm soft magnetic nanodots,"Magnetic skyrmions are nanometric spin textures of outstanding potential for
spintronic applications due to unique features governed by their non-trivial
topology. It is well known that skyrmions of definite chirality are stabilized
by the Dzyaloshinskii-Moriya exchange interaction (DMI) in bulk
non-centrosimmetric materials or ultrathin films with strong spin-orbit
coupling in the interface. In this work, we report on the detection of magnetic
hedgehog-skyrmions at room temperature in confined systems with neither DMI nor
perpendicular magnetic anisotropy. We show that soft magnetic (permalloy)
nanodots are able to host non- chiral hedgehog skyrmions that can be further
stabilized by the magnetic field arising from the Magnetic Force Microscopy
probe. Analytical calculations and micromagnetic simulations confirmed the
existence of metastable N\'eel skyrmions in permalloy nanodots even without
external stimuli in a certain size range. Our work implies the existence of a
new degree of freedom to create and manipulate skyrmions in soft nanodots. The
stabilization of skyrmions in soft magnetic materials opens a possibility to
study the skymion magnetization dynamics otherwise limited due to the large
damping constant coming from the high spin-orbit coupling in materials with
high magnetic anisotropy.",1803.08768v1
2021/8/6,Interplay of magnetism and dimerization in pressurized Kitaev material $β$-Li$_2$IrO$_3$,"We present magnetization measurements on polycrystalline
$\beta$-Li$_2$IrO$_3$ under hydrostatic pressures up to 3~GPa and construct the
temperature-pressure phase diagram of this material. Our data confirm that
magnetic order breaks down in a first-order phase transition at $p_{\rm{c}}$
$\approx$ 1.4~GPa and additionally reveal a step-like feature -- magnetic
signature of structural dimerization -- that appears at $p_{\rm{c}}$ and shifts
to higher temperatures upon further compression. Following the structural study
by L. S. I. Veiga et al. [Phys. Rev. B 100, 064104 (2019)], we suggest that a
partially dimerized phase with a mixture of magnetic and non-magnetic Ir$^{4+}$
sites develops above $p_{\rm{c}}$. This phase is thermodynamically stable
between 1.7 and 2.7~GPa according to our ab initio calculations. It confines
the magnetic Ir$^{4+}$ sites to weakly coupled tetramers with a singlet ground
state and no long-range magnetic order. Our results rule out the formation of a
pressure-induced spin-liquid phase in $\beta$-Li$_2$IrO$_3$ and reveal
peculiarities of the magnetism collapse transition in a Kitaev material. We
also show that a compressive strain imposed by the pressure treatment of
$\beta$-Li$_2$IrO$_3$ enhances signatures of the 100~K magnetic anomaly at
ambient pressure.",2108.03118v2
2021/12/23,DyOCl: a rare-earth based two-dimensional van der Waals material with strong magnetic anisotropy,"Comparing with the widely known transitional metal based van der Waals (vdW)
materials, rare-earth based ones are rarely explored in the research of
intrinsic two-dimensional (2D) magnetism. In this work, we report the physical
properties of DyOCl, a rare-earth based vdW magnetic insulator with direct band
gap of $\sim 5.72~eV$. The magnetic order of bulk DyOCl is determined by
neutron scattering as the $A$-type antiferromagnetic structure below the
N\'{e}el temperature $T_N=10~$K. The large magnetic moment near 10.1 $ \mu_{B}
$/Dy lies parallel to the $a$-axis with strong uniaxial magnetic anisotropy. At
$2~K$, a moderate magnetic field ($\sim 2~T$) applied along the easy axis
generates spin-flip transitions and polarizes DyOCl to a ferromagnetic state.
Density functional theory calculations reveal an extremely large magnetic
anisotropy energy ($-5850~\mu eV/Dy$) for DyOCl, indicating the great
potentials to realize magnetism in 2D limit. Furthermore, the mechanical
exfoliation of bulk DyOCl single crystals down to seven layers is demonstrated.
Our findings suggest DyOCl is a promising material playground to investigate 2D
$f$-electron magnetism and spintronic applications at the nanoscale.",2112.12556v1
2022/11/16,Continuous Electrical Manipulation of Magnetic Anisotropy and Spin Flopping in van der Waals Ferromagnetic Devices,"Controlling the magnetic anisotropy of ferromagnetic materials plays a key
role in magnetic switching devices and spintronic applications. Examples of
spin-orbit torque devices with different magnetic anisotropy geometries
(in-plane or out-of-plane directions) have been demonstrated with novel
magnetization switching mechanisms for extended device functionalities.
Normally, the intrinsic magnetic anisotropy in ferromagnetic materials is
unchanged within a fixed direction, and thus, it is difficult to realize
multifunctionality devices. Therefore, continuous modulation of magnetic
anisotropy in ferromagnetic materials is highly desired but remains
challenging. Here, we demonstrate a gate-tunable magnetic anisotropy transition
from out-of-plane to canted and finally to in-plane in layered Fe$_5$GeTe$_2$
by combining the measurements of the angle-dependent anomalous Hall effect and
magneto-optical Kerr effect with quantitative Stoner-Wohlfarth analysis. The
magnetic easy axis continuously rotates in a spin-flop pathway by gating or
temperature modulation. Such observations offer a new avenue for exploring
magnetization switching mechanisms and realizing new spintronic
functionalities.",2211.08909v1
2022/11/17,On universal butterfly and antisymmetric magnetoresistances,"Butterfly magnetoresistance (BMR) and antisymmetric magnetoresistance (ASMR)
are about a butterfly-cross curve and a curve with one peak and one valley when
a magnetic field is swept up and down along a fixed direction. Other than the
parallelogram-shaped magnetoresistance-curve (MR-curve) often observed in
magnetic memory devices, BMR and ASMR are two ubiquitous types of MR-curves
observed in diversified magnetic systems, including van der Waals materials,
strongly correlated systems, and traditional magnets. Here, we reveal the
general principles and the picture behind the BMR and the ASMR that do not
depend on the detailed mechanisms of magnetoresistance: 1) The systems exhibit
hysteresis loops, common for most magnetic materials with coercivities. 2) The
magnetoresistance of the magnetic structures in a large positive magnetic field
and in a large negative magnetic field is approximately the same. With the
generalized Ohm's law in magnetic materials, these principles explain why most
BMR appears in the longitudinal resistance measurements and is very rare in the
Hall resistance measurements. Simple toy models, in which the
Landau-Lifshitz-Gilbert equation governs magnetization, are used to demonstrate
the principles and explain the appearance and disappearance of BMR in various
experiments. Our finding provides a simple picture to understand
magnetoresistance-related experiments.",2211.09369v1
2023/12/8,Low Noise Inverse Magnetoelectric Magnetic Field Sensor,"In the development of any type of magnetic field sensor based on magnetic
films, special consideration must be given to the magnetic layer component. The
presented work investigates the use of flux closing magnetostrictive
multilayers for inverse magnetoelectric sensors. In such a type of magnetic
field sensor, highly sensitive AC and DC field detection relies on strong
excitation of the incorporated magnetic layers by piezoelectrically driven
cantilever oscillation at mechanical resonances. The provoked periodic flux
change is influenced by the magnetic field to be measured and is picked up by a
coil, which generates the measured output. The effect of the magnetic
multilayer on linearity, noise behavior, and detection limit of DC and AC
signals is investigated. This study demonstrates the next step for inverse
magnetoelectric thin film sensors, which achieve one order of magnitude
improved detection limits with less than $8 pT/Hz^{1/2}$ at $10 Hz$ and $18
pT/Hz^{1/2}$ at $DC$ using exchange bias stabilized magnetic multilayers for
obtaining flux closure.",2312.04988v1
2024/2/2,Emerging topological states in EuMn$_2$Bi$_2$: A first principles prediction,"New materials with magnetic order driven topological phases are hugely sought
after for their immense application potential. In this work, we propose a new
compound EuMn$_2$Bi$_2$ from our first principles density functional theory
calculations to host novel topological phases such as Dirac/Weyl semimetal and
topological insulator in its different magnetic states which are energetically
close to one another. We started with an isostructural compound EuMn$_2$As$_2$
where the magnetic structure has been studied experimentally. From our
calculations we could explain the nature of two magnetic transitions observed
experimentally in this system and could also establish the correct magnetic
ground state. Our electronic structure calculations reveal the insulating
nature of the ground state consistent with the experiments. By replacing all As
by Bi in EuMn$_2$As$_2$ and by optimizing the new structure, we obtained the
new compound EuMn$_2$Bi$_2$. We observe this compound to be dynamically stable
from our phonon calculations supporting its experimental preparation in future.
By comparing the total energies of various possible magnetic structures we
identified the ground state. Though the magnetic ground state is found to be
insulating in nature with tiny band gap which is an order of magnitude less
than the same in EuMn$_2$As$_2$, there were other magnetic states energetically
very close to the ground state which display remarkable non-trivial band
topology such as Dirac/Weyl points close to the Fermi level and topological
insulator state. The energetic proximity of these magnetic order driven
topological phases makes them tunable via external handle which indicates that
the proposed new material EuMn$_2$Bi$_2$ would be a very versatile magnetic
topological material.",2402.01328v1
2000/10/7,Local magnetic properties of periodic nonuniform spin-1/2 XX chains,"Using the Jordan-Wigner fermionization, Green function approach and continued
fractions we examine rigorously the local magnetizations and the local static
susceptibilities of the spin-1/2 XX chain in a transverse field with regularly
varying exchange interactions. We discuss our findings from a viewpoint of the
strong-coupling approach.",0010120v1
2002/4/8,Determining the Saddle Point in Micromagnetic Models of Magnetization Switching,"A numerical model of single-domain nanoscale iron magnets fabricated using
scanning-microscope-assisted chemical vapor deposition is simulated using
finite-temperature micromagnetics. A Projective-dynamics method is used to
determine the magnetization at the saddle point as a function of temperature.
This magnetization is found to decrease linearly as the temperature is raised.",0204180v1
2002/11/19,Current induced magnetization switching in magnetic tunnel junctions,"A new mechanism different from the spin accumulation picture is proposed for
the current induced magnetization switching in magnetic tunnel junctions by
taking into account the effect of the electron electron interaction. We found
in tunnel structures the possibility of an enhanced spin switching effect that,
when normalized with respect to the current, is much bigger than that in
multilayers. Some recent experimental results show evidence for the present
picture.",0211414v1
2003/4/18,Superradiation from Crystals of High-Spin Molecular Nanomagnets,"Phenomenological theory of superradiation from crystals of high-spin
molecules is suggested. We show that radiation friction can cause a
superradiation pulse and investigate the role of magnetic anisotropy, external
magnetic field and dipole-dipole interactions. Depending on the contribution of
all these factors at low temperature, several regimes of magnetization of
crystal sample are described. Very fast switch of magnetization's direction for
some sets of parameters is predicted.",0304424v1
2004/1/26,Emerging Magnetism in Platinum Nanowires,"We have investigated infinitely long, monostrand Pt nanowires theoretically,
and found that they exhibit Hund's rule magnetism. We find a spin moment of 0.6
Bohr magnetons per atom, at the equilibrium bond length. Its magnetic moment
increases with stretching. The origin of the wire magnetism is analyzed and its
effect on the conductance through the wire is discussed.",0401524v1
2004/9/27,Electronic Structure and Magnetic Properties of Solids,"We review basic computational techniques for simulations of various magnetic
properties of solids. Several applications to compute magnetic anisotropy
energy, spin wave spectra, magnetic susceptibilities and temperature dependent
magnetisations for a number of real systems are presented for illustrative
purposes.",0409704v1
2004/11/5,Magnetic tuning of tunnel conductivity,"Using the simplest two-subband Stoner model, it is shown that the variation
of the Fermi energy under applied magnetic field is inverse proportional to the
spontaneous magnetization and hence most pronounced close to the critical
Stoner condition, that is to the quantum critical point of ferromagnetic
transition. The perspectives of this result for magnetic tuning of tunnel
conductivity in spintronics devices is discussed.",0411150v1
2006/6/26,Magnetic and electric phase control in epitaxial EuTiO$_3$ from first principles,"We propose a design strategy - based on the coupling of spins, optical
phonons, and strain - for systems in which magnetic (electric) phase control
can be achieved by an applied electric (magnetic) field. Using first-principles
density-functional theory calculations, we present a realization of this
strategy for the magnetic perovskite EuTiO$_3$.",0606664v2
2006/8/30,Magnetic memory and current amplification devices using moving domain walls,"A moving magnetic domain wall produces an electromotive force (emf). It is
therefore possible to read the state of a magnetic memory device via the emf it
produces when subject to an interrogation pulse. It is also possible to amplify
currents in pulse circuits, opening up the possibility of all magnetic logic
circuits.",0608666v1
2008/12/7,Current-induced reversal in magnetic nanopillars passivated by silicon,"We demonstrate that magnetic multilayer nanopillars can be efficiently
protected from oxidation by coating with silicon. Both the protected and the
oxidized nanopillars exhibit an increase of reversal current at cryogenic
temperatures. However the magnetic excitation onset current increases only in
the oxidized samples. We show that oxidized nanopillars exhibit anomalous
switching statistics at low temperature, providing a simple test for the
quality of magnetic nanodevices.",0812.1381v1
2009/5/23,Influence of a Transport Current on Magnetic Anisotropy in Gyrotropic Ferromagnets,"Current-induced torques are commonly used to manipulate non-collinear
magnetization configurations. In this article we discuss current-induced
torques present in a certain class of collinear magnetic systems, relating them
to current-induced changes in magnetic anisotropy energy. We present a
quantitative estimate of their characteristics in uniform strained
ferromagnetic (Ga,Mn)As.",0905.3856v1
2009/11/11,Wavelets spectra of magnetization dynamics in geometry driven magnetic thin layers,"Squared cobalt thin layers of different thickness and width were investigated
by numerical simulations. Using zero-valued externally applied magnetic field
(geometry driven regime) and different initial conditions the magnetization
dynamics were examined. The wavelet-based spectral analysis was applied.
Transient states of different types were identified.",0911.1994v1
2010/7/22,Switching magnetic junction by joint action of current pulse and magnetic field: Numerical simulation,"The results are presented of a numerical simulation of the switching magnetic
junction by a spin-polarized current pulse under applied magnetic field with
the current density and field below the threshold values. A possibility is
shown of the switching with controllable time delay relative to the current
pulse.",1007.3889v1
2014/11/27,The critical relaxation of the model of iron-vanadium magnetic superlattice,"The critical relaxation of iron-vanadium magnetic superlattice in case of the
equality between interlayer and intralayer exchange interactions is
investigated. The dynamic and static critical exponents of the model are
calculated. A value of the critical temperature is evaluated.",1411.7505v1
2015/5/25,Magnetic Vortex Guide,"A concept of magnetic vortex guide is proposed and numerically studied.
Similar to the waveguides of electromagnetic waves, a magnetic vortex guide
allows a vortex domain wall to move along a nanostrip without annihilation at
the strip edges. It is shown by micromagnetic simulations that a magnetic
nanostrip of a properly designed superlattice structure or bilayered structure
can serve as vortex guides.",1505.06574v1
2015/12/6,Magnetic properties of bismuth-cobalt oxides doped by erbium,"We synthesized bismuth - cobalt oxide doped by erbium with general formula
Bi3-xErxCoO3-y. Compound has structure of delta-form bismuth oxide. Magnetic
properties of the compound were measured by Faraday's method using quartz
scales in the temperature range of 80-500 K. The magnetic susceptibility and
effective magnetic moment were calculated.",1512.01782v1
2020/3/12,MagGene: A genetic evolution program for magnetic structure prediction,"We have developed a software MagGene to predict magnetic structures by using
genetic algorithm. Starting from an atom structure, MagGene repeatedly
generates new magnetic structures and calls first-principles calculation engine
to get the most stable structure. This software is applicable to both collinear
and noncollinear systems. It is particularly convenient for predicting the
magnetic structures of atomic systems with strong spin-orbit couplings and/or
strong spin frustrations.",2003.05650v1
2020/4/16,Simulations of black hole accretion torus in various magnetic field configurations,"Using axisymetric general relativistic magnetohydrodynamics simulations we
study evolution of accretion torus around black hole endowed with different
initial magnetic field configurations. Due to accretion of material onto black
hole, parabolic magnetic field will develop in accretion torus funnel around
vertical axis, for any initial magnetic field configuration.",2004.07535v1
2015/2/27,Magnetic field at the center of a vortex: a new criterion for the classification of the superconductors,"Magnetic response of a superconductor depends on the thermodynamic stability
of vortex in the material. Here we show that the vortex stability has a close
relation with the ratio of the magnetic field at the vortex core center to the
thermodynamic critical field. This finding provides a new criterion for the
classification of the superconductors according to their magnetic responses.",1502.07894v1
2022/7/25,Spin Coulomb drag by non-equilibrium magnetic textures,"Interaction between local magnetization and conduction electrons is
responsible for a variety of phenomena in magnetic materials. We have shown
that the spin-dependent motive force induced by magnetization dynamics in a
conducting ferromagnet lead to the spin Coulomb drag effect. The spin Coulomb
drag an intrinsic friction mechanism which operates whenever the average
velocities of up-spin and down-spin electrons differ.",2207.11978v1
2014/5/5,The magnetic shielding for the neutron decay spectrometer aSPECT,"Many experiments in nuclear and neutron physics are confronted with the
problem that they use a superconducting magnetic spectrometer which potentially
affects other experiments by their stray magnetic field. The retardation
spectrometer aSPECT consists, inter alia, of a superconducting magnet system
that produces a strong longitudinal magnetic field of up to 6.2T. In order not
to disturb other experiments in the vicinity of aSPECT, we had to develop a
magnetic field return yoke for the magnet system. While the return yoke must
reduce the stray magnetic field, the internal magnetic field and its
homogeneity should not be affected. As in many cases, the magnetic shielding
for aSPECT must manage with limited space. In addition, we must ensure that the
additional magnetic forces on the magnet coils are not destructive. In order to
determine the most suitable geometry for the magnetic shielding for aSPECT, we
simulated a variety of possible geometries and combinations of shielding
materials of non-linear permeability. The results of our simulations were
checked through magnetic field measurements both with Hall and nuclear magnetic
resonance probes. The experimental data are in good agreement with the
simulated values: The mean deviation from the simulated exterior magnetic field
is (-1.7+/-4.8)%. However, in the two critical regions, the internal magnetic
field deviates by 0.2% respectively <1E-4 from the simulated values.",1405.0957v1
2014/7/15,Magnetic nanoparticle traveling in external magnetic field,"A set of equations describing the motion of a free magnetic nanoparticle in
an external magnetic field in a vacuum, or in a medium with negligibly small
friction forces is postulated. The conservation of the total particle momentum,
i.e. the sum of the mechanical and the total spin momentum of the nanoparticle
is taken into account explicitly. It is shown that for the motion of a
nanoparticle in uniform magnetic field there are three different modes of
precession of the unit magnetization vector and the director that is parallel
the particle easy anisotropy axis. These modes differ significantly in the
precession frequency. For the high-frequency mode the director points
approximately along the external magnetic field, whereas the frequency and the
characteristic relaxation time of the precession of the unit magnetization
vector are close to the corresponding values for conventional ferromagnetic
resonance. On the other hand, for the low-frequency modes the unit
magnetization vector and the director are nearly parallel and rotate in unison
around the external magnetic field. The characteristic relaxation time for the
low-frequency modes is remarkably long. This means that in a rare assembly of
magnetic nanoparticles there is a possibility of additional resonant absorption
of the energy of alternating magnetic field at a frequency that is much smaller
compared to conventional ferromagnetic resonance frequency. The scattering of a
beam of magnetic nanoparticles in a vacuum in a non-uniform external magnetic
field is also considered taking into account the precession of the unit
magnetization vector and director.",1407.3964v1
2012/11/20,Magnetic Cluster Excitations,"Magnetic clusters, i.e., assemblies of a finite number (between two or three
and several hundred) of interacting spin centers which are magnetically
decoupled from their environment, can be found in many materials ranging from
inorganic compounds, magnetic molecules, artificial metal structures formed on
surfaces to metalloproteins. The magnetic excitation spectra in them are
determined by the nature of the spin centers, the nature of the magnetic
interactions, and the particular arrangement of the mutual interaction paths
between the spin centers. Small clusters of up to four magnetic ions are ideal
model systems to examine the fundamental magnetic interactions which are
usually dominated by Heisenberg exchange, but often complemented by anisotropic
and/or higher-order interactions. In large magnetic clusters which may
potentially deal with a dozen or more spin centers, the possibility of novel
many-body quantum states and quantum phenomena are in focus. In this review the
necessary theoretical concepts and experimental techniques to study the
magnetic cluster excitations and the resulting characteristic magnetic
properties are introduced, followed by examples of small clusters demonstrating
the enormous amount of detailed physical information which can be retrieved.
The current understanding of the excitations and their physical interpretation
in the molecular nanomagnets which represent large magnetic clusters is then
presented, with an own section devoted to the subclass of the single-molecule
magnets which are distinguished by displaying quantum tunneling of the
magnetization. Finally, some quantum many-body states are summarized which
evolve in magnetic insulators characterized by built-in or field-induced
magnetic clusters. The review concludes addressing future perspectives in the
field of magnetic cluster excitations.",1211.4688v1
2020/1/8,Non-equilibrium spin dynamics in the temperature and magnetic field dependence of magnetization curves of ferrimagnetic Co$_{1.75}$Fe$_{1.25}$O$_4$ and its composite with BaTiO$_3$,"A comparative study of the non-equilibrium magnetic phenomena (magnetic
blocking, memory, exchange bias and aging effect) has been presented for
ferrimagnetic Co$_{1.75}$Fe$_{1.25}$O$_4$ (CFO) and its composite with
non-magnetic BaTiO$_3$ (BTO). Synchrotron X-Ray diffraction patterns have
confirmed coexistence of CFO and BTO structures in composite, but magnetic spin
dynamics have been remarkably modified. The blocking phenomenon of
ferrimagnetic domains below the room temperature has been studied by different
modes of (zero field cooled and field cooled) magnetic measurements in
collaboration with magnetic fields ON and OFF modes and time dependent
magnetization. The applications of unconventional protocols during time
dependent magnetization measurement at different stages of the temperature and
field dependence of the magnetization curves have been useful to reveal the
non-equilibrium dynamics of magnetic spin order. The applying of off-field
relaxation experiments has made possible to tune the magnetic state and
coercivity of the systems. The role of interfacial coupling between magnetic
and non-magnetic particles has been understood on different magnetic phenomena
(meta-stable magnetic state, exchange bias and memory effect) by comparing the
experimental results of Co$_{1.75}$Fe$_{1.25}$O$_4$ spinel oxide and its
composite with BaTiO$_3$ particles.",2001.02602v2
2021/9/24,Fluidic Endogenous Magnetism and Magnetic Monopole Clues from Liquid Metal Droplet Machine,"Magnetism and magnetic monopole are classical issues in basic physics.
Conventional magnets are generally composed of rigid materials with shapes and
structures unchangeable which may face challenges sometimes to answer the above
questions. Here, from an alternative other than rigid magnet, we disclosed an
unconventional way to generate endogenous magnetism and then construct magnetic
monopole through tuning liquid metal machine. Through theoretical
interpretation and conceptual experiments, we illustrated that when gallium
base liquid metal in solution rotates under actuation of an external electric
field, it forms an endogenous magnetic field inside which well explains the
phenomenon that two such discrete metal droplets could easily fuse together,
indicating their reciprocal attraction via N and S poles. Further, we conceived
that the self-driving liquid metal motor was also an endogenous magnet owning
the electromagnetic homology. When liquid metal in solution swallowed aluminum
inside, it formed a spin motor and dynamically variable charge distribution
which produced an endogenous magnetic field. This finding explains the
phenomena that there often happened reflection collision and attraction fusion
between running liquid metal motors which were just caused by the dynamic
adjustment of their N and S polarities. Finally, we conceived that such
endogenous magnet could lead to magnetic monopole and four technical routes
were suggested as: 1. Matching the interior flow field of liquid metal
machines; 2. Superposition between external electric effect and magnetic field;
3. Composite construction between magnetic particles and liquid metal motor; 4.
Chemical ways such as via galvanic cell reaction. Overall, the fluidic
endogenous magnet and the promising magnetic monopole it enabled may lead to
unconventional magnetoelectric devices and applications in the near future.",2111.02867v1
2022/5/13,Isotropic orbital magnetic moments in magnetically anisotropic SrRuO3 films,"Epitaxially strained SrRuO3 films have been a model system for understanding
the magnetic anisotropy in metallic oxides. In this paper, we investigate the
anisotropy of the Ru 4d and O 2p electronic structure and magnetic properties
using high-quality epitaxially strained (compressive and tensile) SrRuO3 films
grown by machine-learning-assisted molecular beam epitaxy. The element-specific
magnetic properties and the hybridization between the Ru 4d and O 2p orbitals
were characterized by Ru M2,3-edge and O K-edge soft X-ray absorption
spectroscopy and X-ray magnetic circular dichroism measurements. The
magnetization curves for the Ru 4d and O 2p magnetic moments are identical,
irrespective of the strain type, indicating the strong magnetic coupling
between the Ru and O ions. The electronic structure and the orbital magnetic
moment relative to the spin magnetic moment are isotropic despite the
perpendicular and in-plane magnetic anisotropy in the compressive-strained and
tensile-strained SrRuO3 films; i.e., the orbital magnetic moments have a
negligibly small contribution to the magnetic anisotropy. This result
contradicts Bruno model, where magnetic anisotropy arises from the difference
in the orbital magnetic moment between the perpendicular and in-plane
directions. Contributions of strain-induced electric quadrupole moments to the
magnetic anisotropy are discussed, too.",2205.06563v1
2024/1/9,2024 Roadmap on Magnetic Microscopy Techniques and Their Applications in Materials Science,"Considering the growing interest in magnetic materials for unconventional
computing, data storage, and sensor applications, there is active research not
only on material synthesis but also characterisation of their properties. In
addition to structural and integral magnetic characterisations, imaging of
magnetization patterns, current distributions and magnetic fields at nano- and
microscale is of major importance to understand the material responses and
qualify them for specific applications. In this roadmap, we aim to cover a
broad portfolio of techniques to perform nano- and microscale magnetic imaging
using SQUIDs, spin center and Hall effect magnetometries, scanning probe
microscopies, x-ray- and electron-based methods as well as magnetooptics and
nanoMRI. The roadmap is aimed as a single access point of information for
experts in the field as well as the young generation of students outlining
prospects of the development of magnetic imaging technologies for the upcoming
decade with a focus on physics, materials science, and chemistry of planar, 3D
and geometrically curved objects of different material classes including 2D
materials, complex oxides, semi-metals, multiferroics, skyrmions,
antiferromagnets, frustrated magnets, magnetic molecules/nanoparticles, ionic
conductors, superconductors, spintronic and spinorbitronic materials.",2401.04793v1
2022/2/9,Field-Dependent Magnetic Domain Behavior in van der Waals Fe$_3$GeTe$_2$,"Two-dimensional magnetic van der Waals (vdW) materials can show a variety of
topological nontrivial spin textures, such as Bloch- or N\'eel-type stripe,
skyrmion or bubble domains under certain external stimuli. It is critical to
understand the magnetic domain behavior in vdW materials in order to control
their size, and density in response to external stimuli such as electric and
magnetic fields. Here we examine the magnetic field dependence of topologically
non-trivial magnetization spin textures in vdW Fe$_3$GeTe$_2$. N\'eel-type
stripe domains and skyrmions are formed depending on the magnetic field-cooling
protocol used during in-situ Lorentz transmission electron microscopy (LTEM)
experiments. Use of quantitative reconstruction of magnetic induction maps, and
micromagnetic simulations, allow for understanding the LTEM results of
N\'eel-type stripe domains as well as skyrmions. In addition, the deformation
of skyrmion contrast is observed as a result of the introduction of an in-plane
magnetic field. We demonstrate the stability of the stripe domains and
skyrmions in response to externally applied magnetic field due to energy
barrier for domain wall annihilation. Our results establish an understanding of
the energy landscape that governs the behavior of the topologically non-trivial
spin textures in vdW materials which can be harnessed for spintronic
applications.",2202.04248v1
2022/5/31,Magnetic hourglass fermions: from exhaustive symmetry conditions to high-throughput materials predictions,"Many topological band crossings (BCs) have been predicted efficiently
utilizing the symmetry properties of wave-functions at high-symmetry points.
Among various BCs, the so-called hourglass BCs (with the low-energy excitations
dubbed as hourglass fermions) are fascinating since they can be guaranteed to
exist under specific symmetry conditions even without realistic calculations.
Such novel property renders the theoretical prediction on magnetic topological
metals with hourglass BC (being Weyl point, Dirac point, lying in nodal loop,
and so on) independent on the calculation methods and only determined by the
symmetry of crystal and magnetic structure, namely, the magnetic space group
(MSG). To date, there have no magnetic material verified with hourglass
fermions. Here we first list all symmetry conditions that allow hourglass BCs
in the 1651 MSGs and 528 magnetic layer groups (MLGs) with spin-orbital
coupling (SOC): Only 331 MSGs and 53 MLGs can host hourglass BCs. Among these
results, the essential hourglass BCs are highlighted, whose MSGs are then
applied to predict hundreds of magnetic materials from the MAGNDATA magnetic
materials database and first-principles calculations in the frame of LDA+SOC+U
verify the hourglass BCs for different values of $U$. We take CsMn$_2$F$_6$,
synthesized recently with a distorted pyrochlore structure to illustrate the
hourglass band structure in detail which is very clear around the Fermi level
and the topologically protected surface drumhead states of (100) surface are
found to spread over more than one half surface Brillouin zone and only appear
in a narrow energy window ($\sim 30$ meV), which could induce intriguing
stability by prominent electronic correlation.",2206.00078v2
2018/12/20,Ab initio theory of the Gibbs free energy and a hierarchy of local moment correlation functions in itinerant electron systems: The magnetism of Mn$_3$A materials class,"We present an \textit{ab-initio} disordered local moment theory for the Gibbs
free energy of a magnetic material. Two central objects are calculated: the
lattice Fourier transform of the direct local moment - local moment correlation
functions in the paramagnetic state and local internal magnetic fields as
functions of magnetic order. We identify the potentially most stable magnetic
phases from the first, which can include non-collinear and long-period states
in complex multi-atom unit cells, and extract higher order correlations among
the local moments from the second. We propose that these latter entities
produce a picture of effective multi-site magnetic interactions depending on
the state and extent of magnetic order and discuss its relation to other
approaches. We show how magnetic phase diagrams for temperature, magnetic
field, and lattice structure and also magnetocaloric and mechanocaloric effects
can be obtained from this approach. The theory accurately predicts the order of
transitions and quantifies contributions to first-order and order-order
magnetic phase transitions from both purely electronic sources and
magnetoelastic effects. Our case study is the apparently frustrated magnetism
of the Mn$_3$A class of materials in all its cubic, hexagonal, and tetragonal
structures. The theory produces magnetic phases and transition temperatures in
good agreement with experiment. We explain the first-order triangular
antiferromagnetic to collinear antiferromagnetic transition in cubic Mn$_3$Pt
as a magnetovolume driven effect, and its absence for A=Ir and Rh. We also
construct the magnetic phase diagram of Mn$_3$Pt and explore its potential as a
barocaloric material. Finally, we prepare the groundwork for future fully
relativistic studies of the temperature dependence of the magnetism of Mn$_3$A,
including Mn$_3$Sn, Mn$_3$Ga, and Mn$_3$Ge.",1812.08653v2
2005/4/23,New Method to Calculate the Sign and Relative Strength of Magnetic Interactions in Low-Dimensional Systems on the Basis of Structural Data,"The connection of strength of magnetic interactions and type ordering the
magnetic moments with crystal chemical characteristics in low-dimensional
magnets is investigated. The new method to calculate the sign and relative
strength of magnetic interactions in low-dimensional systems on the basis of
the structural data is proposed. This method allows to estimate magnetic
interactions not only inside low-dimensional fragments but also between them,
and also to predict the possibility of the occurrence of magnetic phase
transitions and anomalies of the magnetic interactions. Moreover, it can be
used for search of low-dimensional magnets among the compounds whose crystal
structures are known. The possibilities of the method are illustrated in an
example of research of magnetic interactions in familiar low-dimensional
magnets SrCu2(BO3)2, CaCuGe2O6, CaV4O9, Cu2Te2O5Cl2, Cu2Te2O5Br2, BaCu2Si2O7,
BaCu2Ge2O7, BaCuSi2O6, LiCu2O2, and NaCu2O2.",0504599v3
2005/10/21,Magnetostrictive hysteresis of TbCo/CoFe multilayers and magnetic domains,"Magnetic and magnetostrictive hysteresis loops of TbCo/CoFe multilayers under
field applied along the hard magnetization axis are studied using vectorial
magnetization measurements, optical deflectometry and magneto optical Kerr
microscopy. Even a very small angle misalignment between hard axis and magnetic
field direction is shown to drastically change the shape of magnetization and
magnetostrictive torsion hysteresis loops. Two kinds of magnetic domains are
revealed during the magnetization: big regions with opposite rotation of
spontaneous magnetization vector and spontaneous magnetic domains which appear
in a narrow field interval and provide an inversion of this rotation.
  We show that the details of the hysteresis loops of our exchange-coupled
films can be described using the classical model of homogeneous magnetization
rotation of single uniaxial films and the configuration of observed domains.
The understanding of these features is crucial for applications (for MEMS or
microactuators) which benefit from the greatly enhanced sensitivity near the
point of magnetic saturation at the transverse applied field.",0510568v1
2019/10/17,Magnetic textures and dynamics in magnetic Weyl semimetals,"Recent theoretical and experimental attemps have been successful in finding
magnetic Weyl semimetal phases, which show both nodal-point structure in the
electronic bands and magnetic orders. Beyond uniform ferromagnetic or
antiferromagnetic orders, nonuniform magnetic textures, such as domain walls
and skyrmions, may even more enrich the properties of the Weyl electrons in
such materials. This article gives a topical review on interplay between Weyl
electrons and magnetic textures in those magnetic Weyl semimetals. The basics
of magnetic textures in non-topological magnetic metals are reviewed first, and
then the effect of magnetic textures in Weyl semimetals is discussed, regarding
the recent theoretical and experimental progress therein. The idea of the
fictitious ""axial gauge fields"" is pointed out, which effectively describes the
effect of magnetic textures on the Weyl electrons and can well account for the
properties of the electrons localized around magnetic domain walls.",1910.07774v1
2020/4/25,Pulse-assisted magnetization switching in magnetic nanowires at picosecond and nanosecond timescales with low energy,"Detailed understanding of spin dynamics in magnetic nanomaterials is
necessary for developing ultrafast, low-energy and high-density spintronic
logic and memory. Here, we develop micromagnetic models and analytical
solutions to elucidate the effect of increasing damping and uniaxial anisotropy
on magnetic field pulse-assisted switching time, energy and field requirements
of nanowires with perpendicular magnetic anisotropy and yttrium iron
garnet-like spin transport properties. A nanowire is initially magnetized using
an external magnetic field pulse (write) and self-relaxation. Next, magnetic
moments exhibit deterministic switching upon receiving 2.5 ns-long external
magnetic pulses in both vertical polarities. Favorable damping
({\alpha}~0.1-0.5) and anisotropy energies (10^4-10^5 J m^-3) allow for as low
as picosecond magnetization switching times. Magnetization reversal with fields
below coercivity was observed using spin precession instabilities. A
competition or a nanomagnetic trilemma arises among the switching rate, energy
cost and external field required. Developing magnetic nanowires with optimized
damping and effective anisotropy could reduce the switching energy barrier down
to 3163kBT at room temperature. Thus, pulse-assisted picosecond and low energy
switching in nanomagnets could enable ultrafast nanomagnetic logic and cellular
automata.",2004.12243v1
2019/4/12,The magnetic structure factor of correlated moments in small-angle neutron scattering,"The interplay between structural and magnetic properties of nanostructured
magnetic materials allows to realize unconventional magnetic effects, which
results in a demand for experimental techniques to determine the magnetization
profile with nanoscale resolution. Magnetic small-angle neutron scattering
(SANS) probes both the chemical and magnetic nanostructure and is thus a
powerful technique e.g. for the characterization of magnetic nanoparticles.
Here, we show that the conventionally used particle-matrix approach to describe
SANS of magnetic particle assemblies, however, leads to a flawed
interpretation. As remedy, we provide general expressions for the
field-dependent 2D magnetic SANS cross-section of correlated moments. It is
shown that for structurally disordered ensembles the magnetic structure factor
is in general, and contrary to common assumptions, (i) anisotropic also in zero
field, and (ii) that even in saturation the magnetic structure factor deviates
from the nuclear one. These theoretical predictions explain qualitatively the
intriguing experimental, polarized SANS data of an ensemble of dipolar-coupled
iron oxide nanoparticles.",1904.06243v3
2019/12/3,Magnetic Force Microscopy Revealing Molecule Impact on Magnetic Tunnel Junction Based Molecular Devices at Room Temperature,"Commercially successful magnetic tunnel junction can harness the unmatched
capabilities of molecular device elements by solving decade-old fabrication
issues. Utilization of magnetic tunnel junction as a testbed for molecules also
enables unprecedented magnetic studies of molecular spintronics devices. This
paper utilizes magnetic force microscopy (MFM) to vividly show that
organometallic molecules when bridged between two ferromagnetic electrodes
along the magnetic tunnel junction edges, transformed the magnetic electrodes
itself. Molecules impacted several hundred-micron areas of ferromagnetic
electrodes at room temperature. Complementary, magnetic resonance and
magnetometer studies supported the dramatic MFM results. Molecule induced
changes in the magnetic electrodes impacted the transport of the magnetic
tunnel junction and stabilized as much as six orders smaller current at room
temperature. Magnetic tunnel junction based molecular devices can be a gateway
to a vast range of commercially viable futuristic logic and memory devices that
are controlled by the molecular quantum states near room temperature.",1912.01316v1
2020/10/19,Magnetic texture based magnonics,"The spontaneous magnetic orders arising in ferro-, ferri- and
antiferromagnets stem from various magnetic interactions. Depending on the
interplay and competition among the Heisenberg exchange interaction,
Dzyaloshinskii-Moriya exchange interaction, magnetic dipolar interaction and
crystal anisotropies, a great variety of magnetic textures may be stabilized,
such as magnetic domain walls, vortices, Skyrmions and spiral helical
structures. While each of these spin textures responds to external forces in a
specific manner with characteristic resonance frequencies, they also interact
with magnons, the fundamental collective excitation of the magnetic order,
which can propagate in magnetic materials free of charge transport and
therefore with low energy dissipation. Recent theories and experiments found
that the interplay between spin waves and magnetic textures is particularly
interesting and rich in physics. In this review, we introduce and discuss the
theoretical framework of magnons living on a magnetic texture background, as
well as recent experimental progress in the manipulation of magnons via
magnetic textures. The flexibility and reconfigurability of magnetic textures
are discussed regarding the potential for applications in information
processing schemes based on magnons.",2010.09180v1
2022/4/26,Slow spin dynamics and quantum tunneling of magnetization in the dipolar antiferromagnet DyScO$_3$,"We present a comprehensive study of static and dynamic magnetic properties in
the Ising-like dipolar antiferromagnet (AFM) DyScO$_3$\ by means of DC and AC
magnetization measurements supported by classical Monte-Carlo calculations. Our
AC-susceptibility data show that the magnetic dynamics exhibit a clear
crossover from an Arrhenius-like regime to quantum tunneling of magnetization
(QTM) at $T^* = 10$ K. Below $T_{\mathrm{N}} = 3.2$ K DyScO$_3$ orders in an
antiferromagnetic $GxAy$-type magnetic structure and the magnetization dynamics
slow down to the minute timescale. The low-temperature magnetization curves
exhibit complex hysteretic behavior, which depends strongly on the magnetic
field sweep rate. We demonstrate that the low-field anomalies on the
magnetization curve are related to the metamagnetic transition, while the
hysteresis at higher fields is induced by a strong magnetocaloric effect. Our
theoretical calculations, which take into account dipolar interaction between
Dy$^{3+}$ moments, reproduce essential features of the magnetic behavior of
DyScO$_3$. We demonstrate that DyScO$_3$ represents a rare example of inorganic
compound, which exhibits QTM at a single-ion level and magnetic order due to
classical dipolar interaction.",2204.12398v1
2022/5/28,Finite element simulation for validation of multi-dipole line cusp magnetic field configuration for MPD,"A Multi-dipole line cusp configured Plasma Device (MPD) having six
electromagnets with embedded Vacoflux-50 as a core material has been operated
with a capability to experimentally control the field-free region, the radial
profile of magnetic field, and pole magnetic field by changing magnet current.
For the validation of multi-dipole line cusp magnetic field (MMF) configuration
in a 3-D geometry, a finite element simulation has been performed using COMSOL
software. This paper presents 3-D magnetic field simulation results of
multi-pole line cusp magnetic field configuration performed over the 1.2m
length and 40cm diameter chamber in the vacuum condition. The simulation
results show good agreement with the experimentally measured magnetic field
profile. The performed magnetic field simulation results clearly capture that
this configuration has full control over a null region (nearly field-free
region) as well is capable to change the magnetic field values and radial
variation of the magnetic field. Moreover, the magnetic field profiles over the
end cross-section of the device have been discussed.",2205.14381v1
2023/7/6,Plasmon-enhanced optical control of magnetism at the nanoscale via the inverse Faraday effect,"The relationship between magnetization and light has been the subject of
intensive research for the past century, focusing on the impact of magnetic
moments on light polarization. Conversely, the manipulation of magnetism
through polarized light is being investigated to achieve all-optical control of
magnetism in spintronics. While remarkable discoveries such as single pulse
all-optical switching of the magnetization in thin films and sub-micrometer
structures have been reported, the demonstration of local optical control of
magnetism at the nanoscale has remained elusive. Here, we show that exciting
gold nanodiscs with circularly polarized femtosecond laser pulses leads to the
generation of sizeable local magnetic fields that enable ultrafast local
control of the magnetization of an adjacent magnetic film. In addition, we find
that the highest magnetic fields are generated when exciting the sample at a
wavelength larger than that of the actual plasmonic resonance of the gold
nanodiscs, so avoiding undesired heating effects due to absorption. Our study
paves the way for light-driven control in nanoscale spintronic devices and
provides important insights into the generation of magnetic fields in plasmonic
nanostructures.",2307.03326v1
2004/12/13,Magneto-controlled nonlinear optical materials,"We exploit theoretically a magneto-controlled nonlinear optical material
which contains ferromagnetic nanoparticles with a non-magnetic metallic
nonlinear shell in a host fluid. Such an optical material can have anisotropic
linear and nonlinear optical properties and a giant enhancement of
nonlinearity, as well as an attractive figure of merit.",0412332v1
2004/1/9,Tailoring ferromagnetic chalcopyrites,"If magnetic semiconductors are ever to find wide application in real
spintronic devices, their magnetic and electronic properties will require
tailoring in much the same way that band gaps are engineered in conventional
semiconductors. Unfortunately, no systematic understanding yet exists of how,
or even whether, properties such as Curie temperatures and band gaps are
related in magnetic semiconductors. Here we explore theoretically these and
other relationships within 64 members of a single materials class, the Mn-doped
II-IV-V2 chalcopyrites, three of which are already known experimentally to be
ferromagnetic semiconductors. Our first-principles results reveal a variation
of magnetic properties across different materials that cannot be explained by
either of the two dominant models of ferromagnetism in semiconductors. Based on
our results for structural, electronic, and magnetic properties, we identify a
small number of new stable chalcopyrites with excellent prospects for
ferromagnetism.",0401157v2
2004/8/19,Fabrication and physical properties of stable room temperature bulk ferromagnetic graphite,"The search for macroscopic magnetic ordering phenomena in organic materials,
in particular in pure graphite, has been one of the more exciting scientific
activities working in the frontiers of physics, chemistry, and materials
science. In this Letter we report on a novel chemical route leading to
undoubtedly obtain macroscopic quantities of magnetic graphite. This material
has a stable and strong ferromagnetic response even at room temperature where
it can be attracted by a commercial magnet. We have obtained this magnetic
graphite by a vapor reaction consisting of a controlled etching on the graphite
structure. This behavior has been previously predicted and postulated to be
associated to micro-structural characteristics breaking the continuity of the
delocalized p-electron clouds of the graphitic material, thus allowing the
existence of magnetic centers related to the topology.",0408441v1
2008/4/9,Multiferroic materials for spin-based logic devices,"Logical devices based on spin waves offer the potential to avoid dissipation
mechanisms that limit devices based on either the charge or spin of mobile
electrons. Multiferroic magnetoelectrics, which are materials that combine
ferroelectric and magnetic order, allow direct switching of magnetic order and
thence of spin-wave properties using an applied electric field. The intrinsic
coupling between polarization and magnetic moments, generated by strong
electronic correlations in these multiferroic materials, is argued to provide
new approaches to spin-wave injection and spin-wave switching using applied
voltages with no external magnetic field. These effects are shown to arise in a
phenomenological Landau theory of coupled electronic and magnetic orders in
multiferroic BiFeO3, and found to depend subtly on differences between the
crystalline and film states of this material.",0804.1539v1
2012/12/13,Material Targets for Scaling All Spin Logic,"All-spin logic devices are promising candidates to augment and complement
beyond-CMOS integrated circuit computing due to non-volatility, ultra-low
operating voltages, higher logical efficiency, and high density integration.
However, the path to reach lower energy-delay product performance compared to
CMOS transistors currently is not clear. We show that scaling and engineering
the nanoscale magnetic materials and interfaces is the key to realizing spin
logic devices that can surpass energy-delay performance of CMOS transistors.
With validated stochastic nano-magnetic and vector spin transport numerical
models, we derive the target material and interface properties for the
nanomagnets and channels. We identified promising new directions for material
engineering/discovery focusing on systematic scaling of magnetic anisotropy
(Hk) with saturation magnetization (Ms), use of perpendicular magnetic
anisotropy, and interface spin mixing conductance of ferromagnet/spin channel
interface (Gmix). We provide systematic targets for scaling spin logic
energy-delay product toward a 2 aJ.ns energy-delay product, comprehending the
stochastic noise for nanomagnets.",1212.3362v1
2017/9/20,Static Magnetization Properties Of AL800 Garnet Material,"A second harmonic tunable RF cavity is being developed for the Fermilab
Booster. This device, which promises reduction of the particle beam loss at the
injection, transition, and extraction stages, employs perpendicularly biased
garnet material for frequency tuning. The required range of the tuning is
significantly wider than in previously built and tested tunable RF devices. As
a result, the magnetic field in the garnet comes fairly close to the
gyromagnetic resonance line at the lower end of the frequency range. The chosen
design concept of a tuner for the cavity cannot ensure uniform magnetic field
in the garnet material; thus, it is important to know the static magnetic
properties of the material to avoid significant increase in the local RF loss
power density. This report summarizes studies performed at Fermilab to
understand variations in the magnetic properties of the AL800 garnet material
used to build the tuner of the cavity.",1709.07050v1
2019/11/3,Curie Temperature of Emerging Two-Dimensional Magnetic Structures,"Recent realizations of intrinsic, long-range magnetic orders in
two-dimensional (2D) van der Waals materials have ignited tremendous research
interests. In this work, we employ the XXZ Heisenberg model and Monte Carlo
simulations to study a fundamental property of these emerging 2D magnetic
materials, the Curie temperature (Tc). By including both onsite and neighbor
couplings extracted from first-principles simulations, we have calculated Tc of
monolayer chromium trihalides and Cr2Ge2Te6, which are of broad interests
currently, and the simulation results agree with available measurements. We
also clarify the roles played by anisotropic and isotropic interactions in
deciding Tc of magnetic orders. Particularly, we find a universal, linear
dependence between Tc and magnetic interactions within the parameter space of
realistic materials. With this linear dependence, we can predict Tc of general
2D lattice structures, omitting the Monte Carlo simulations. Compared with the
widely used Ising model, mean-field theory, and spin-wave theory, this work
provides a convenient and quantitative estimation of Tc, giving hope to
speeding up the search for novel 2D materials with higher Curie temperatures.",1911.00973v1
2020/10/31,P-orbital magnetic topological states on square lattice,"Honeycomb or triangular lattices were extensively studied and thought to be
proper platforms for realizing quantum anomalous Hall effect (QAHE), where
magnetism is usually caused by d orbitals of transition metals. Here we propose
that square lattice can host three magnetic topological states, including the
fully spin polarized nodal loop semimetal, QAHE and topologically trivial
ferromagnetic semiconductor, in terms of the symmetry and k$\cdot$p model
analyses that are materials-independent. A phase diagram is presented. We
further show that the above three magnetic topological states can be indeed
implemented in two-dimensional (2D) materials ScLiCl5, LiScZ5 (Z=Cl, Br), and
ScLiBr5, respectively. The ferromagnetism in these 2D materials is
microscopically revealed from p electrons of halogen atoms. This present study
opens a door to explore the exotic topological states as well as quantum
magnetism from p-orbital electrons by means of the materials-independent
approach.",2011.00161v2
2021/3/11,Stimuli-responsive assembly of iron oxide nanoparticles into magnetic flexible filaments,"The combination of multiple functionalities in a single material is an
appealing strategy for the de-velopment of smart materials with unique
features. In this work, we present the preparation of thermoresponsive magnetic
nanoparticles and their one-dimensional assembly into transient
micro-filaments. The material is based on 9.4 nm iron oxide nanoparticles
grafted with poly(N-n-propylacrylamide) via multiphosphonic acid anchoring
sites. The hybrid nanoparticles present a low critical solution temperature
(LCST) transition between 21 {\deg}C and 28 {\deg}C, depending on the pH and
the ionic strength. When heated above the LCST in defined conditions, the
nanoparticles ag-gregate and respond to an external magnetic field. An
intrinsic characteristic of the thermorespon-sive particles is an asymmetric
transition between cooling and heating cycles, that was favorably exploited to
build one-dimensional permanent microstructures, such as magnetic
microfilaments and cilia. In summary, we present the development of a
nanoplatform responsive to multiple stimu-li, including temperature, magnetic
field, pH and ionic strength and its transformation into magneti-cally active
microfilaments that could find potential applications in remotely controlled
devices.",2103.06837v1
2021/10/26,Basic formulation and first-principles implementation of nonlinear magneto-optical effects,"First-principles calculation of nonlinear magneto-optical effects has become
an indispensable tool to reveal the geometric and topological nature of
electronic states and to understand light-matter interactions. While
intriguingly rich physics could emerge in magnetic materials, further
methodological developments are required to deal with time-reversal symmetry
breaking, due to the degeneracy and gauge problems caused by symmetry and the
low-frequency divergence problem in the existing calculation formalism. Here we
present a gauge-covariant and low-frequency convergent formalism for the
first-principles computation. Remarkably, this formalism generally works for
both non-magnetic and magnetic materials with or without band degeneracy.
Reliability and capability of our method are demonstrated by studying example
materials (i.e., bilayers of MnBi$_2$Te$_4$ and CrI$_3$) and comparing with
published results. Moreover, an importance correction term that ensures gauge
covariance of degenerate states is derived, whose influence on physical
responses is systematically checked. Our method enables computation of
nonlinear magneto-optical effects in magnetic materials and paves the way for
exploring rich physics created by the interplay of light and magnetism.",2110.13415v1
2022/10/31,Finite temperature tensor network algorithm for frustrated two-dimensional quantum materials,"Aimed at a more realistic classical description of natural quantum systems,
we present a two-dimensional tensor network algorithm to study finite
temperature properties of frustrated model quantum systems and real quantum
materials. For this purpose, we introduce the infinite projected entangled
simplex operator ansatz to study thermodynamic properties. To obtain
state-of-the-art benchmarking results, we explore the highly challenging
spin-1/2 Heisenberg anti-ferromagnet on the Kagome lattice, a system for which
we investigate the melting of the magnetization plateaus at finite magnetic
field and temperature. Making close connection to actual experimental data of
real quantum materials, we go on to studying the finite temperature properties
of Ca$_{10}$Cr$_7$O$_{28}$. We compare the magnetization curve of this material
in the presence of an external magnetic field at finite temperature with
classically simulated data. As a first theoretical tool that incorporates both
thermal fluctuations as well as quantum correlations in the study of this
material, our work contributes to settling the existing controversy between the
experimental data and previous theoretical works on the magnetization process.",2211.00121v1
2023/6/30,"Giant magnetocaloric effect in the (Mn,Fe)NiSi-system","The search for energy-efficient and environmentally friendly cooling
technologies is a key driver for the development of magnetic refrigeration
based on the magnetocaloric effect (MCE). This phenomenon arises from the
interplay between magnetic and lattice degrees of freedom that is strong in
certain materials, leading to a change in temperature upon application or
removal of a magnetic field. Here we report on a new material,
Mn$_{1-x}$Fe$_x$NiSi$_{0.95}$Al$_{0.05}$, with an exceptionally large
isothermal entropy at room temperature. By combining experimental and
theoretical methods we outline the microscopic mechanism behind the large MCE
in this material. It is demonstrated that the competition between the
Ni$_2$In-type hexagonal phase and the MnNiSi-type orthorhombic phase, that
coexist in this system, combined with the distinctly different magnetic
properties of these phases, is a key parameter for the functionality of this
material for magnetic cooling.",2307.00128v1
2023/10/10,Non-relativistic torque and Edelstein effect in noncollinear magnets,"The Edelstein effect is the origin of the spin-orbit torque: a
current-induced torque that is used for the electrical control of ferromagnetic
and antiferromagnetic materials. This effect originates from the relativistic
spin-orbit coupling, which necessitates utilizing materials with heavy
elements. Here we show that in magnetic materials with non-collinear magnetic
order, the Edelstein effect and consequently also a current-induced torque can
exist even in the absence of the spin-orbit coupling. Using group symmetry
analysis, model calculations, and realistic simulations on selected compounds,
we identify large classes of non-collinear magnet candidates and demonstrate
that the current-driven torque is of similar magnitude as the celebrated
spin-orbit torque in conventional transition metal structures. We also show
that this torque can exist in an insulating material, which could allow for
highly efficient electrical control of magnetic order.",2310.06499v1
2024/1/11,Room-temperature Magnetic Thermal Switching by Suppressing Phonon-Magnon Scattering,"Thermal switching materials, whose thermal conductivity can be controlled
externally, show great potential in contemporary thermal management.
Manipulating thermal transport properties through magnetic fields has been
accomplished in materials that exhibit a high magnetoresistance. However, it is
generally understood that the lattice thermal conductivity attributed to
phonons is not significantly impacted by the magnetic fields. In this study, we
experimentally demonstrate the significant impact of phonon-magnon scattering
on the thermal conductivity of the rare-earth metal gadolinium near room
temperature, which can be controlled by a magnetic field to realize thermal
switching. Using first-principles lattice dynamics and spin-lattice dynamics
simulations, we attribute the observed change in phononic thermal conductivity
to field-suppressed phonon-magnon scattering. This research suggests that
phonon-magnon scattering in ferromagnetic materials is crucial for determining
their thermal conductivity, opening the door to innovative
magnetic-field-controlled thermal switching materials.",2401.05607v1
2024/1/26,First-principles Methodology for studying magnetotransport in magnetic materials,"Unusual magnetotransport behaviors such as temperature dependent negative
magnetoresistance(MR) and bowtie-shaped MR have puzzled us for a long time.
Although several mechanisms have been proposed to explain them, the absence of
comprehensive quantitative calculations has made these explanations less
convincing. In our work, we introduce a methodology to study the
magnetotransport behaviors in magnetic materials. This approach integrates
anomalous Hall conductivity induced by Berry curvature, with a multi-band
ordinary conductivity tensor, employing a combination of first-principles
calculations and semi-classical Boltzmann transport theory. Our method
incorporates both the temperature dependency of relaxation time and anomalous
Hall conductivity, as well as the field dependency of anomalous Hall
conductivity. We initially test this approach on two-band models and then apply
it to a Weyl semimetal \CSS. The results, which align well with experimental
observations in terms of magnetic field and temperature dependencies,
demonstrate the efficacy of our approach. Additionally, we have investigated
the distinct behaviors of magnetoresistance (MR) and Hall resistivities across
various types of magnetic materials. This methodology provides a comprehensive
and efficient means to understand the underlying mechanisms of the unusual
behaviors observed in magneto-transport measurements in magnetic materials.",2401.15146v1
2024/2/25,Topological skyrmions in monolayer multiferroic MoPtGe2S6,"Two-dimensional (2D) multiferroic materials with coexisting ferroelectricity
and ferromagnetism have garnered substantial attention for their intriguing
physical properties and diverse promising applications in spintronics. For
example, multiferroic materials with electronically controlled broken central
symmetry provide a versatile platform for designing and manipulating
topological skyrmions and diverse spintronic applications. Here, we investigate
the complex magnetic properties of room-temerature multiferroic material
MoPtGe2S6 and its electrical control of topological skyrmions using
first-principles calculations and atomistic micromagnetic simulations. A
sizable Dzyaloshinskii-Moriya interaction (DMI) (2.1 meV) is found in the
multiferroic material MoPtGe2S6 with an electrically polarized ground state.
The magnetic skyrmions can be stabilized in monolayer MoPtGe2S6 under zero
magnetic field, and the chirality of skyrmions can be reversed with electric
field-induced flipping of electrical polarization due to the reversed chirality
of the DMI. Furthermore, an external magnetic fielc can reverse the
magnetization direction and topological charge of the skyrmions as well as tune
the size of skyrmions. These results demonstrate that the monolayer MoPtGe2S6
can enrich the 2D skyrmion community and pave the way for electronically
controlled spintronic devices.",2402.15983v1
2024/3/2,"Coexisting Magnetism, Ferroelectric, and Ferrovalley Multiferroic in Stacking-Dependent Two-Dimensional Materials","The two-dimensional (2D) multiferroic materials have widespread of
application prospects in facilitating the integration and miniaturization of
nanodevices. However, it is rarely coupling between the magnetic,
ferroelectric, and ferrovalley in one 2D material. Here, we propose a mechanism
for manipulating magnetism, ferroelectric, and valley polarization by
interlayer sliding in 2D bilayer material. Monolayer GdI2 exhibits a
ferromagnetic semiconductor with the valley polarization up to 155.5 meV. More
interestingly, the magnetism and valley polarization of bilayer GdI2 can be
strongly coupled by sliding ferroelectricity, appearing these tunable and
reversible. In addition, we uncover the microscopic mechanism of magnetic phase
transition by spin Hamiltonian and electron hopping between layers. Our
findings offer a new direction for investigating 2D multiferroic in the
implication for next-generation electronic, valleytronic, and spintronic
devices.",2403.01070v1
2024/3/29,Piezomagnetism in the Ising ferromagnet URhGe,"Piezomagnetism, linear response between strain and magnetic field, is
relatively unexplored cross-correlation but has promising potential as a novel
probe of time-reversal-symmetry breaking in various classes of materials.
Interestingly, there has been no report of piezomagnetism in ferromagnets, most
archetypal time-reversal-symmetry-broken materials. This half-century absence
of piezomagnetic ferromagnets is attributable to complications originating from
multiple-domain states, as well as from changes in the magnetic point group by
rotation of magnetic moment. Here, we report characteristic V-shaped
magnetostriction in the Ising itinerant ferromagnet URhGe, observed by
simultaneous multi-axis strain measurement technique utilizing optical fiber
Bragg grating sensors. This novel magnetostriction occurs only under fields
along the c axis and does not scale with the square of magnetization. Such
unconventional feature indicates piezomagnetism as its origin. Our observation,
marking the first report of piezomagnetism in ferromagnets, is owing to the
mono-domain switching and the Ising magnetization. The obtained piezomagnetic
coefficients are fairly large, implying that Ising ferromagnets are promising
frontiers when seeking for materials with large piezomagnetic responses.",2403.19998v1
2016/8/9,Compensated ferrimagnetic tetragonal Heusler thin films for antiferromagnetic spintronics,"In recent years, antiferromagnetic spintronics has received much attention
since ideal antiferromagnets do not produce stray fields and are much more
stable to external magnetic fields compared to materials with net
magnetization. Akin to antiferromagnets, compensated ferrimagnets have zero net
magnetization but have the potential for large spin-polarization and strong out
of plane magnetic anisotropy, and, hence, are ideal candidates for high density
memory applications. Here, we demonstrate that a fully compensated magnetic
state with a tunable magnetic anisotropy is realized in Mn-Pt-Ga based
tetragonal Heusler thin films. Furthermore, we show that a bilayer formed from
a fully compensated and a partially compensated Mn-Pt-Ga layer, exhibits a
large interfacial exchange bias up to room temperature. The present work
establishes a novel design principle for spintronic devices that are formed
from materials with similar elemental compositions and nearly identical crystal
and electronic structures. Such devices are of significant practical value due
to their improved properties such as thermal stability. The flexible nature of
Heusler materials to achieve tunable magnetizations, and anisotropies within
closely matched materials provides a new direction to the growing field of
antiferromagnetic spintronics.",1608.02887v1
2020/3/31,Robust spin liquid state against magnetic-dilution in the bi-layer Kagome material Ca$_{10}$Cr$_7$O$_{28}$,"Recently, the bi-layer Kagome lattice material Ca$_{10}$Cr$_7$O$_{28}$ has
been shown to be a quasi-two-dimensional quantum spin liquid (QSL) where the
frustration arises from a balance between competing ferromagnetic and
antiferromagnetic exchange within a bi-layer. In an attempt to understand what
happens when this balance is disturbed, we present a magnetic dilution study.
Specifically, we have synthesized Ca$_{10}$(Cr$_{1-x}$V$_x$)$_7$O$_{28}$ (0
$\leq$ x $\leq$ 0.5) where magnetic Cr$^{5+}$ ($S = 1/2$) is partially replaced
by non-magnetic V$^{5+}$ ($S = 0$). We also synthesized the fully non-magnetic
isostructural material Ca$_{10}$V$_7$O$_{27.5}$. We report a detailed
structural, magnetic and heat capacity study on these materials. A monotonic
increase in the unit cell parameters is found for the
Ca$_{10}$(Cr$_{1-x}$V$_x$)$_7$O$_{28}$ materials with increasing $x$. An order
of magnitude decrease in the Curie-Weiss temperature from $4$ to $0.5$~ K is
found for the partial V substituted samples, which indicates a relative
increase in antiferromagnetic exchange with increase in V content. However,
despite this change in the relative balance in the exchange interactions and
the large disorder introduced, no magnetic ordering or spin-glass state is
observed down to $2$~K in the V substituted samples. The QSL state of the
parent compound thus seems surprisingly robust against these large
perturbations.",2003.13957v1
2017/12/13,Nanoscale Magnetic Behavior Localization in Exchange Strength Modulated Ferromagnets,"Although ferromagnetism is in general a long-range collective phenomenon, it
is possible to induce local spatial variations of magnetic properties in
ferromagnetic materials. For example, systematic variation of the exchange
coupling strength can be used to create systems that behave as if they are
comprised of virtually independent segments that exhibit ""local"" Curie
temperatures. Such localization of thermodynamic behavior leads to boundaries
between strongly and weakly magnetized regions that can be controllably moved
within the material with temperature. The utility of this interesting
functionality is largely dependent on the inherent spatial resolution of
magnetic properties - specifically the distance over which the exchange
strength and corresponding properties behave locally. To test the degree to
which this type of localization can be realized in materials, we have
fabricated epitaxial films of Co[1-x]Ru[x] alloy featuring a nanometer scale
triangular wave-like concentration depth profile. Continuous nanoscale
modulation of the local Curie temperature was observed using polarized neutron
reflectometry. These results are consistent with mean-field simulations of spin
systems that encompass the possibility of delocalized exchange coupling, and
show that composition grading can be used to localize magnetic properties in
films down to the nanometer level. Since this is demonstrated here for an
itinerant metal, we assert that for virtually any modulated magnetic material
system, collective effects can be suppressed to length scales smaller than
about 3 nm, so that magnetic behavior overall can be well described in terms of
local material properties.",1712.04998v2
2018/5/25,Room Temperature Magnetic Order in Air-Stable Ultra-Thin Iron Oxide,"Certain two-dimensional (2D) materials exhibit intriguing properties such as
valley polarization, ferroelectricity, superconductivity and charge-density
waves. Many of these materials can be manually assembled into atomic-scale
multilayer devices under ambient conditions, owing to their exceptional
chemical stability. Efforts have been made to add a magnetic degree of freedom
to these 2D materials via defects, but only local magnetism has been achieved.
Only with the recent discoveries of 2D materials supporting intrinsic
ferromagnetism have stacked spintronic devices become realistic. Assembling 2D
multilayer devices with these ferromagnets under ambient conditions remains
challenging due to their sensitivity to environmental degradation, and magnetic
order at room temperature is rare in van der Waals materials. Here, we report
the growth of air-stable ultra-thin epsilon-phase iron oxide crystals that
exhibit magnetic order at room temperature. These crystals require no
passivation and can be prepared in large quantity by cost-effective chemical
vapor deposition (CVD). We find that the epsilon phase, which is energetically
unfavorable and does not form in bulk, can be easily made in 2D down to a seven
unit-cell thickness. Magneto-optical Kerr effect (MOKE) magnetometry of
individual crystals shows that even at this ultrathin limit the epsilon phase
exhibits robust magnetism with coercive fields of hundreds of mT. These
measurements highlight the advantages of ultrathin iron oxide as a promising
candidate towards air-stable 2D magnetism and integration into 2D spintronic
devices.",1805.10372v1
2020/6/21,"Crystal Structure, Magnetism, and Electronic Properties of New Rare-Earth-Free Ferromagnetic MnPt5As","The design and synthesis of targeted functional materials have been a
long-term goal for material scientists. Although a universal design strategy is
difficult to generate for all types of materials, however, it is still helpful
for a typical family of materials to have such design rules. Herein, we
incorporated several significant chemical and physical factors regarding
magnetism, such as structure type, atom distance, spin-orbit coupling, and
successfully synthesized a new rare-earth-free ferromagnet, MnPt5As, for the
first time. MnPt5As can be prepared by using high-temperature pellet methods.
According to X-ray diffraction results, MnPt5As crystallizes in a tetragonal
unit cell with the space group P4/mmm (Pearson symbol tP7). Magnetic
measurements on MnPt5As confirm ferromagnetism in this phase with a Curie
temperature of ~301 K and a saturated moment of 3.5 uB per formula. Evaluation
by applying the Stoner Criterion also indicates that MnPt5As is susceptible to
ferromagnetism. Electronic structure calculations using the WIEN2k program with
local spin density approximation imply that the spontaneous magnetization of
this phase arises primarily from the hybridization of d orbitals on both Mn and
Pt atoms. The theoretical assessments are consistent with the experimental
results. Moreover, the spin-orbit coupling effects heavily influence on
magnetic moments in MnPt5As. MnPt5As is the first high-performance magnetic
material in this structure type. The discovery of MnPt5As offers a platform to
study the interplay between magnetism and structure.",2006.11897v1
2020/12/16,A tool to predict coercivity in magnetic materials,"Magnetic coercivity is often viewed to be lower in alloys with negligible (or
zero) values of the anisotropy constant. However, this explains little about
the dramatic drop in coercivity in FeNi alloys at a non-zero anisotropy value.
Here, we develop a theoretical and computational tool to investigate the
fundamental interplay between material constants that govern coercivity in bulk
magnetic alloys. The two distinguishing features of our coercivity tool are
that: (a) we introduce a large localized disturbance, such as a spike-like
magnetic domain, that provides a nucleation barrier for magnetization reversal;
and (b) we account for magneto-elastic energy -- however small -- in addition
to the anisotropy and magnetostatic energy terms. We apply this coercivity tool
to show that the interactions between local instabilities and material
constants, such as anisotropy and magnetostriction constants, are key factors
that govern magnetic coercivity in bulk alloys. Using our model, we show that
coercivity is minimum at the permalloy composition (Fe-21.5Ni-78.5) at which
the alloy's anisotropy constant is not zero. We systematically vary the values
of the anisotropy and magnetostriction constants, around the permalloy
composition, and identify new combinations of material constants at which
coercivity is small. More broadly, our coercivity tool provides a theoretical
framework to potentially discover novel magnetic materials with low coercivity.",2012.09320v1
2023/7/19,Enumeration and representation of spin space groups,"Those fundamental properties, such as phase transitions, Weyl fermions and
spin excitation, in all magnetic ordered materials was ultimately believed to
rely on the symmetry theory of magnetic space groups. Recently, it has come to
light that a more comprehensive group, known as the spin space group (SSG),
which combines separate spin and spatial operations, is necessary to fully
characterize the geometry and physical properties of magnetic ordered materials
such as altermagnets. However, the basic theory of SSG has been seldomly
developed. In this work, we present a systematic study of the enumeration and
the representation theory of SSG. Starting from the 230 crystallographic space
groups and finite translational groups with a maximum order of 8, we establish
an extensive collection of over 80,000 SSGs under a four-segment nomenclature.
We then identify inequivalent SSGs specifically applicable to collinear,
coplanar, and noncoplanar magnetic configurations. Moreover, we derive the
irreducible co-representations of the little group in momentum space within the
SSG framework. Finally, we illustrate the SSGs and band degeneracies resulting
from SSG symmetries through several representative material examples, including
a well-known altermagnet RuO2, and a spiral magnet CeAuAl3. Our work advances
the field of group theory in describing magnetic ordered materials, opening up
avenues for deeper comprehension and further exploration of emergent phenomena
in magnetic materials.",2307.10369v2
2018/8/24,Topological axion states in magnetic insulator MnBi$_2$Te$_4$ with the quantized magnetoelectric effect,"Topological states of quantum matter have attracted great attention in
condensed matter physics and materials science. The study of
time-reversal-invariant (TRI) topological states in quantum materials has made
tremendous progress in both theories and experiments. As a great success,
thousands of TRI topological materials are predicted through sweeping search.
Richer exotic phenomena are expected to appear in magnetic topological
materials because of varied magnetic configurations, but this study falls much
behind due to the complex magnetic structures and transitions. Here, we predict
the tetradymite-type compound MnBi$_2$Te$_4$ and its related materials host
interesting magnetic topological states. The magnetic ground state of
MnBi$_2$Te$_4$ is an antiferromagnetic phase which leads to an antiferromagetic
topological insulator state with a large topologically non-trivial energy gap
($\sim$0.2~eV). It is the parent state for the axion state, which has gapped
bulk and surface states, and quantized topological magnetoelectric effect. The
ferromagnetic phase of MnBi$_2$Te$_4$ leads to an ideal minimal type-II Weyl
semimetal with two Weyl points accompanied by one hole-type and one
electron-type Fermi pocket at the Fermi level, which has never been discovered
elsewhere. We further present a simple and unified continuum model to capture
the salient topological features of this kind of materials.",1808.08014v5
2019/3/7,High mobility in a van der Waals layered antiferromagnetic metal,"Magnetic van der Waals (vdW) materials have been heavily pursued for
fundamental physics as well as for device design. Despite the rapid advances,
so far magnetic vdW materials are mainly insulating or semiconducting, and none
of them possesses a high electronic mobility - a property that is rare in
layered vdW materials in general. The realization of a magnetic high-mobility
vdW material would open the possibility for novel magnetic twistronic or
spintronic devices. Here we report very high carrier mobility in the layered
vdW antiferromagnet GdTe3. The electron mobility is beyond 60,000 cm2 V-1 s-1,
which is the highest among all known layered magnetic materials, to the best of
our knowledge. Among all known vdW materials, the mobility of bulk GdTe3 is
comparable to that of black phosphorus, and is only surpassed by graphite. By
mechanical exfoliation, we further demonstrate that GdTe3 can be exfoliated to
ultrathin flakes of three monolayers, and that the magnetic order and
relatively high mobility is retained in approximately 20-nm-thin flakes.",1903.03111v2
2020/6/17,Tuning Magnetic Order in the van der Waals Metal Fe5GeTe2 by Cobalt Substitution,"Fe5-xGeTe2 is a van der Waals material with one of the highest reported bulk
Curie temperatures, $T_C$ ~ 310K. In this study, theoretical calculations and
experiments are utilized to demonstrate that the magnetic ground state is
highly sensitive to local atomic arrangements and the interlayer stacking.
Cobalt substitution is found to be an effective way to manipulate the magnetic
properties while also increasing the ordering temperature. In particular,
cobalt substitution up to 30% enhances $T_C$ and changes the magnetic
anisotropy, while approximately 50% cobalt substitution yields an
antiferromagnetic state. Single crystal x-ray diffraction evidences a
structural change upon increasing the cobalt concentration, with a rhombohedral
cell observed in the parent material and a primitive cell observed for ~46%
cobalt content relative to iron. First principles calculations demonstrate that
it is a combination of high cobalt content and the concomitant change to
primitive layer stacking that produces antiferromagnetic order. These results
illustrate the sensitivity of magnetism in Fe5-xGeTe2 to composition and
structure, and emphasize the important role of structural order/disorder and
layer stacking in cleavable magnetic materials.",2006.10116v2
2005/8/12,Group theoretical description of artificial magnetic metamaterials utilized for negative index of refraction,"Group theoretical methods are used to determine the electromagnetic
properties of artificial magnetic meta-materials, based solely upon the
symmetries of the underlying constituent particles. Point groups for such
materials are determined. From the transformation properties of an
electromagnetic (EM) basis under symmetries of the particles, it is possible to
determine, (i) the EM modes of the particles, (ii) the form of constitutive
relations (iii) magneto-optical response of a meta-material or lack thereof.
These methods are shown to be useful for determination of the isotropic or
bi-anisotropic nature of artificial magnetic particles. The results for several
artificial magnetic metamaterials are given. Based upon these methods, we
predict an ideal planar artificial meta-material, which eliminates an
undesirable electric resonance while still exhibiting a magnetic response.
Further we determine the subset of point groups of which particles must belong
to in order to yield an isotropic 3D magnetic response, and we show an example.",0508307v1
2006/11/7,"Calculated electronic and magnetic properties of the half-metallic, transition metal based Heusler compounds","In this work, results of {\it ab-initio} band structure calculations for
$A_2BC$ Heusler compounds that have $A$ and $B$ sites occupied by transition
metals and $C$ by a main group element are presented. This class of materials
includes some interesting half-metallic and ferromagnetic properties. The
calculations have been performed in order to understand the properties of the
minority band gap and the peculiar magnetic behavior found in these materials.
Among the interesting aspects of the electronic structure of the materials are
the contributions from both $A$ and $B$ atoms to states near the Fermi energy
and to the total magnetic moment. The magnitude of the total magnetic moment,
which depends as well on the kind of $C$ atoms, shows a trend consistent with
the Slater-Pauling type behavior in several classes of these compounds. The
localized moment in these magnetic compounds resides at the $B$ site. Other
than in the classical Cu$_2$-based Heusler compounds, the $A$ atoms in Co$_2$,
Fe$_2$, and Mn$_2$ based compounds may contribute pronounced to the total
magnetic moment.",0611179v1
2009/11/9,The effect of transverse magnetic correlations on a coupled order parameter: shifted transition temperatures and thermal hysteresis,"We use a Green's function method with Random Phase Approximation to show how
magnetic correlations may affect electric polarization in multiferroic
materials with magnetic-exchange-type magnetoelectric coupling. We use a model
spin 1/2 ferromagnetic ferroelectric system but our results are expected to
apply to multiferroic materials with more complex magnetic structures. In
particular, we find that transverse magnetic correlations result in a change in
the free energy of the ferroelectric solutions leading to the possibility for
thermal hysteresis of the electric polarization above the magnetic Curie
temperature. Although we are motivated by multiferroic materials, this problem
represents a more general calculation of the effect of fluctuations on coupled
order parameters.",0911.1600v1
2010/1/29,Dipole-Dipole Interactions of Charged Magnetic Grains,"The interaction between dust grains is an important process in fields as
diverse as planetesimal formation or the plasma processing of silicon wafers
into computer chips. This interaction depends in large part on the material
properties of the grains, for example whether the grains are conducting,
non-conducting, ferrous or non-ferrous. This work considers the effects that
electrostatic and magnetic forces, alone or in combination, can have on the
coagulation of dust in various environments. A numerical model is used to
simulate the coagulation of charged, charged-magnetic and magnetic dust
aggregates formed from ferrous material and the results are compared to each
other as well as to those from uncharged, non-magnetic material. The
interactions between extended dust aggregates are also examined, specifically
looking at how the arrangement of charge over the aggregate surface or the
inclusion of magnetic material produces dipole-dipole interactions. It will be
shown that these dipole-dipole interactions can affect the orientation and
structural formation of aggregates as they collide and stick. Analysis of the
resulting dust populations will also demonstrate the impact that grain
composition and/or charge can have on the structure of the aggregate as
characterized by the resulting fractal dimension.",1001.5442v1
2013/8/20,Intrinsic Magnetism of Grain Boundaries in Two-dimensional Metal Dichalcogenides,"Grain boundaries (GBs) are structural imperfections that typically degrade
the performance of materials. Here we show that dislocations and GBs in
two-dimensional (2D) metal dichalcogenides MX2 (M = Mo, W; X = S, Se) can
actually improve the material by giving it a qualitatively new physical
property: magnetism. The dislocations studied all have a substantial magnetic
moment of ~1 Bohr magneton. In contrast, dislocations in other well-studied 2D
materials are typically non-magnetic. GBs composed of pentagon-heptagon pairs
interact ferromagnetically and transition from semiconductor to half-metal or
metal as a function of tilt angle and/or doping level. When the tilt angle
exceeds 47{\deg} the structural energetics favor square-octagon pairs and the
GB becomes an antiferromagnetic semiconductor. These exceptional magnetic
properties arise from an interplay of dislocation-induced localized states,
doping, and locally unbalanced stoichiometry. Purposeful engineering of
topological GBs may be able to convert MX2 into a promising 2D magnetic
semiconductor.",1308.4355v1
2014/6/16,Heat transport of the spin-ice materials Ho$_2$Ti$_2$O$_7$ and Dy$_2$Ti$_2$O$_7$,"The elementary excitations of the spin-ice materials Ho$_2$Ti$_2$O$_7$ and
Dy$_2$Ti$_2$O$_7$ in zero field can be described as independent magnetic
monopoles. We investigate the influence of these exotic excitations on the heat
transport by measuring the magnetic-field dependent thermal conductivity
$\kappa $. Additional measurements on the highly dilute reference compounds
HoYTi$_2$O$_7$ and DyYTi$_2$O$_7$ enable us to separate $\kappa $ into a sum of
phononic ($\kappa_{ph}$) and magnetic ($\kappa_{mag}$) contributions. For both
spin-ice materials, we derive significant zero-field contributions
$\kappa_{mag}$, which are rapidly suppressed in finite magnetic fields.
Moreover, $\kappa_{mag}$ sensitively depends on the scattering of phonons by
magnetic excitations, which is rather different for the Ho- and the Dy-based
materials and, as a further consequence, the respective magnetic-field
dependent changes $\kappa_{ph}(B)$ are even of opposite signs.",1406.4037v1
2014/9/17,Birefringence of silica hydrogels prepared under high magnetic fields reinvestigated,"Birefringence is an indicator of structural anisotropy of materials. We
measured the birefringence of Pb(II)-doped silica hydrogels prepared under a
high magnetic field of various strengths. Because the silica is diamagnetic,
one does not expect the structural anisotropy induced by a magnetic field. In
previous work [Mori A, Kaito T, Furukawa H 2008 Mater. Lett. 62 3459-3461], we
prepared samples in cylindrical cells made of borosilicate glass and obtained a
preliminary result indicating a negative birefringence for samples prepared at
5T with the direction of the magnetic field being the optic axis. We have
measured the birefringence of Pn(II)-doped silica hydrogels prepared in square
cross-sectional cells made of quartz and reverted the previous conclusion.
Interestingly, the magnetic-influenced silica hydrogels measured have been
classified into four classes: two positive birefringent ones, no birefringent
one, and negative birefringent one. Proportionality between birefringence and
the strength of magnetic field is seen for the former two.",1409.4846v1
2015/7/2,Macroscopic Simulation of Isotropic Permanent Magnets,"Accurate simulations of isotropic permanent magnets require to take the
magnetization process into account and consider the anisotropic, nonlinear, and
hysteretic material behaviour near the saturation configuration. An efficient
method for the solution of the magnetostatic Maxwell equations including the
description of isotropic permanent magnets is presented. The algorithm can
easily be implemented on top of existing finite element methods and does not
require a full characterization of the hysteresis of the magnetic material.
Strayfield measurements of an isotropic permanent magnet and simulation results
are in good agreement and highlight the importance of a proper description of
the isotropic material.",1507.00450v1
2017/10/5,"Magnetic properties of monoclinic lanthanide orthoborates, $Ln$BO$_3$, $Ln$ = Gd, Tb, Dy, Ho, Er, Yb","The lanthanide orthoborates, $Ln$BO$_3$, $Ln$ = Gd, Tb, Dy, Ho, Er, Yb
crystallise in a monoclinic structure with the magnetic $Ln^{3+}$ forming an
edge-sharing triangular lattice. The triangles are scalene, however all
deviations from the ideal equilateral geometry are less than 1.5%. The bulk
magnetic properties are studied using magnetic susceptibility, specific heat
and isothermal magnetisation measurements. Heat capacity measurements show
ordering features at $T \leq$ 2 K for $Ln$ = Gd, Tb, Dy, Er. No ordering is
observed for YbBO$_3$ at $T \geq$ 0.4 K and HoBO$_3$ is proposed to have a
non-magnetic singlet state. Isothermal magnetisation measurements indicate
isotropic Gd$^{3+}$ spins and strong single-ion anisotropy for the other
$Ln^{3+}$. The change in magnetic entropy has been evaluated to determine the
magnetocaloric effect in these materials. GdBO$_3$ and DyBO$_3$ are found to be
competitive magnetocaloric materials in the liquid helium temperature regime.",1710.01980v2
2017/10/23,Designing hysteresis with dipolar chains,"Materials that have a hysteretic response to an external field are essential
in modern information storage and processing technologies. The magnetization
curves of several natural and artificial materials have previously been
measured and explained in terms of the Neel model, Preisach phenomenological
model, the creation, propagation, and annihilation of topological defects, or
by resonant quantum tunnelling of the magnetization in single molecule magnets.
However, a simple way to design the magnetic response of a material is missing.
Here, we propose and experimentally realize an elementary method to engineer
hysteresis loops in metamaterials built out of dipolar chains. We show that by
tuning the system's interactions and geometry we can induce magnetic responses
with or without remanence at will. Our findings pave the way for the rational
design of hysteretical responses in a variety of physical systems such as
dipolar cold atoms, ferroelectrics, or artificial magnetic lattices, among
others.",1710.08391v2
2018/4/4,Direct observation of the magnetic proximity effect in amorphous exchange-spring magnets by neutron reflectometry,"In this letter we report a direct observation of a magnetic proximity effect
in an amorphous thin film exchange-spring magnet by the use of neutron
reflectometry. The exchange-spring magnet is a trilayer consisting of two
ferromagnetic layers with high $T_c$'s separated by a ferromagnetic layer,
which is engineered to have a significantly lower $T_c$ than the embedding
layers. This enables us to measure magnetization depth profiles at which the
low $T_c$ material is in a ferromagnetic or paramagnetic state, while the
embedding layers are ferromagnetic. A clear proximity effect is observed 7 K
above the $T_c$ of the embedded layer, with a range extending 50
$\unicode{xC5}$.",1804.01479v2
2017/9/29,Non-local Gilbert damping tensor within the torque-torque correlation model,"An essential property of magnetic devices is the relaxation rate in magnetic
switching which depends strongly on the damping in the magnetisation dynamics.
It was recently measured that damping depends on the magnetic texture and,
consequently, is a non-local quantity. The damping enters the
Landau-Lifshitz-Gilbert equation as the phenomenological Gilbert damping
parameter $\alpha$, that does not, in a straight forward formulation, account
for non-locality. Efforts were spent recently to obtain Gilbert damping from
first principles for magnons of wave vector $\mathbf{q}$. However, to the best
of our knowledge, there is no report about real space non-local Gilbert damping
$\alpha_{ij}$. Here, a torque-torque correlation model based on a tight binding
approach is applied to the bulk elemental itinerant magnets and it predicts
significant off-site Gilbert damping contributions, that could be also
negative. Supported by atomistic magnetisation dynamics simulations we reveal
the importance of the non-local Gilbert damping in atomistic magnetisation
dynamics. This study gives a deeper understanding of the dynamics of the
magnetic moments and dissipation processes in real magnetic materials. Ways of
manipulating non-local damping are explored, either by temperature, material's
doping or strain.",1709.10365v1
2018/3/8,Compositional optimization of hard-magnetic phases with machine-learning models,"Machine Learning (ML) plays an increasingly important role in the discovery
and design of new materials. In this paper, we demonstrate the potential of ML
for materials research using hard-magnetic phases as an illustrative case. We
build kernel-based ML models to predict optimal chemical compositions for new
permanent magnets, which are key components in many green-energy technologies.
The magnetic-property data used for training and testing the ML models are
obtained from a combinatorial high-throughput screening based on
density-functional theory calculations. Our straightforward choice of
describing the different configurations enables the subsequent use of the ML
models for compositional optimization and thereby the prediction of promising
substitutes of state-of-the-art magnetic materials like Nd$_2$Fe$_{14}$B with
similar intrinsic hard-magnetic properties but a lower amount of critical
rare-earth elements.",1803.03073v2
2016/3/24,Role of Berry phase theory for describing orbital magnetism: From magnetic heterostructures to topological orbital ferromagnets,"We address the importance of the modern theory of orbital magnetization for
spintronics. Based on an all-electron first-principles approach, we demonstrate
that the predictive power of the routinely employed ""atom-centered""
approximation is limited to materials like elemental bulk ferromagnets, while
the application of the modern theory of orbital magnetization is crucial in
chemically or structurally inhomogeneous systems such as magnetic thin films,
and materials exhibiting non-trivial topology in reciprocal and real
space,~e.g.,~Chern insulators or non-collinear systems. We find that the modern
theory is particularly crucial for describing magnetism in a class of materials
that we suggest here $-$ topological orbital ferromagnets.",1603.07683v2
2017/3/1,Towards understanding of magnetization reversal in Nd$-$Fe$-$B nanocomposites: Analysis by high-throughput micromagnetic simulations,"We demonstrate how micromagnetic simulations can be employed in order to
characterize and analyze the magnetic microstructure of nanocomposites. For the
example of nanocrystalline Nd$-$Fe$-$B, which is a potential material for
future permanent-magnet applications, we have compared three different models
for the micromagnetic analysis of this material class: (i) a description of the
nanocomposite microstructure in terms of Stoner-Wohlfarth particles with and
without the magnetodipolar interaction; (ii) a model based on the core-shell
representation of the nanograins; (iii) the latter model including a
contribution of superparamagnetic clusters. The relevant parameter spaces have
been systematically scanned with the aim to establish which micromagnetic
approach can most adequately describe experimental data for this material.
According to our results, only the last, most sophisticated model is able to
provide an excellent agreement with the measured hysteresis loop. The presented
methodology is generally applicable to multiphase magnetic nanocomposites and
it highligths the complex interrelationship between the microstructure,
magnetic interactions, and the macroscopic magnetic properties.",1703.00288v2
2009/7/1,Dipole-Dipole Interactions of Charged-Magnetic Grains,"The interaction between dust grains is an important process in fields as
diverse as planetesimal formation or the plasma processing of silicon wafers
into computer chips. This interaction depends in large part on the material
properties of the grains, for example whether the grains are conducting,
non-conducting, ferrous or non-ferrous. This work considers the effects that
electrostatic and magnetic forces, alone or in combination, can have on the
coagulation of dust in various environments. A numerical model is used to
simulate the coagulation of charged, charged-magnetic and magnetic dust
aggregates formed from ferrous material and the results are compared to each
other as well as to those from uncharged, non-magnetic material. The
interactions between extended dust aggregates are also examined, specifically
looking at how the arrangement of charge over the aggregate surface or the
inclusion of magnetic material produces dipole-dipole interactions. It will be
shown that these dipole-dipole interactions can affect the orientation and
structural formation of aggregates as they collide and stick. Analysis of the
resulting dust populations will also demonstrate the impact that grain
composition and/or charge can have on the structure of the aggregate as
characterized by the resulting fractal dimension.",0907.0242v1
2009/7/6,Experimental Proof of a Magnetic Coulomb Phase,"Spin ice materials are magnetic substances in which the spin directions map
onto hydrogen positions in water ice. Recently this analogy has been elevated
to an electromagnetic equivalence, indicating that the spin ice state is a
Coulomb phase, with magnetic monopole excitations analogous to ice's mobile
ionic defects. No Coulomb phase has yet been proved in a real magnetic
material, as the key experimental signature is difficult to resolve in most
systems. Here we measure the scattering of polarised neutrons from the
prototypical spin ice Ho2Ti2O7. This enables us to separate different
contributions to the magnetic correlations to clearly demonstrate the existence
of an almost perfect Coulomb phase in this material. The temperature dependence
of the scattering is consistent with the existence of deconfined magnetic
monopoles connected by Dirac strings of divergent length.",0907.0954v1
2015/2/12,Towards a scale-bridging description of ferrogels and magnetic elastomers,"Ferrogels and magnetic elastomers differentiate themselves from other
materials by their unique capability of reversibly changing shape and
mechanical properties under the influence of an external magnetic field. A
crucial issue in the study of these outstanding materials is the interaction
between the mesoscopic magnetic particles and the polymer matrix in which they
are embedded. Here we analyze interactions between two such particles connected
by a polymer chain, a situation representative for particle-crosslinked
magnetic gels. To make a first step towards a scale-bridging description of the
materials, effective potentials for mesoscopic configurational changes are
specified using microscopic input obtained from simulations. Furthermore, the
impact of the presence of magnetic interactions on the probability
distributions and thermodynamic quantities of the system is considered. The
resulting mesoscopic model potentials can be used to economically model the
system on the particle length scales. This first coarse-graining step is
important to realize simplified but realistic scale-bridging models for these
promising materials.",1502.03707v2
2016/12/21,Giant ferroelectric polarization and electric reversal of strong spontaneous magnetization in multiferroic Bi2FeMoO6,"BiFeO$_3$ is the most famous multiferroic material, but it has no strong
spontaneous magnetization due to its antiferromagnetism. Here we show that
giant ferroelectric polarization and strong spontaneous magnetization can be
both realized in double perovskite Bi$_2$FeMoO$_6$ with R3 (\#146) space group
based on BiFeO$_3$. Our first-principles phonon spectra establishes that this
multiferroic R3 phase is stable. Our systematic calculations show that it is a
spin-polarized semiconductor with gap reaching to 0.54 eV and has a strong
ferroelectric polarization of 85$\mu$C/cm$^2$. This ferroelctricity is
comparable with that of BiFeO$_3$, but here obtained is a strong ferrimagnetism
with net magnetic moment of 2$\mu_B$ per formula unit and Curie temperature of
650 K. Both ferroelectric polarization and magnetic easy axis are shown to be
in pseudocubic [111] orientation. Our further analysis shows that the
macroscopic spontaneous magnetization can be deterministically reversed through
a three-step path by external electric field. Therefore, we believe that this
Bi$_2$FeMoO$_6$ material can be used to design new multifunctional materials
and achieve high-performance devices.",1612.07124v1
2018/2/28,Magnetocaloric effect in some magnetic materials in alternating magnetic fields up to 22 Hz,"Direct measurements of the magnetocaloric effect (MCE) in different materials
(Gd, Fe48Rh52, Ni43Mn37.9In12.1Co7 and Ni2.07Co0.09Mn0.84Ga) in alternating
magnetic fields with frequencies f < 22 Hz and an amplitude deltaH = 6.2 kOe
are carried out. The MCE in Gd shows inconsiderable changes with field
frequency. Near paramagnetic-ferromagnetic phase transition in
Ni43Mn37.9In12.1Co7 Heusler alloy a slight reduction of MCE with frequency is
observed. In weak alternating fields in materials with AFM-FM
magneto-structural phase transitions (Fe48Rh52, Ni43Mn37.9In12.1Co7) it is not
possible to get a structural contribution to overall MCE because of
irreversibility of the transitions in these fields. Near magneto-structural
phase transitions the MCE in these alloys has only magnetic contribution, and
does not show a significant dependence on the magnetic field frequency. In
Ni2.07Co0.09Mn0.84Ga Heusler alloy the MCE vanishes at frequencies about 20 Hz.
The obtained results show the increase of frequencies of operating cycles is
one of the powerful methods to improve the efficiency of magnetic refrigerators
in case of Gd as a refrigerant.",1802.10391v1
2019/4/29,Multifold nodal points in magnetic materials,"We describe the symmetry protected nodal points that can exist in magnetic
space groups and show that only 3-, 6-, and 8-fold degeneracies are possible
(in addition to the 2- and 4-fold degeneracies that have already been studied.)
The 3- and 6-fold degeneracies are derived from ""spin-1"" Weyl fermions. The
8-fold degeneracies come in different flavors. In particular, we distinguish
between 8-fold fermions that realize non-chiral ""Rarita-Schwinger fermions"" and
those that can be described as four degenerate Weyl fermions. We list the
(magnetic and non-magnetic) space groups where these exotic fermions can be
found. We further show that in several cases, a magnetic translation symmetry
pins the Hamiltonian of the multifold fermion to an idealized exactly solvable
point that is not achievable in non-magnetic crystals without fine-tuning.
Finally, we present known compounds that may host these fermions and methods
for systematically finding more candidate materials.",1904.12867v2
2019/5/2,Magnetically Controllable Topological Quantum Phase Transitions in Antiferromagnetic Topological Insulator MnBi$_2$Te$_4$,"The recent discovery of antiferromagnetic (AFM) topological insulator (TI)
MnBi$_2$Te$_4$ has triggered great research efforts on exploring novel magnetic
topological physics. Based on first-principles calculations, we find that the
manipulation of magnetic orientation and order not only significantly affects
material symmetries and orbital hybridizations, but also results in variant new
magnetic topological phases in MnBi$_2$Te$_4$. We thus predict a series of
unusual topological quantum phase transitions that are magnetically
controllable in the material, including phase transitions from AFM TI to AFM
mirror topological crystalline insulator, from type-II to type-I topological
Weyl semimetal, and from axion insulator to Chern insulator. The findings open
new opportunities for future research and applications of magnetic topological
materials.",1905.00642v2
2020/6/15,The Pair Approximation method for the ferromagnetic Heisenberg model with spin $S=1$ and arbitrary range of interactions. Application for the magnetic semiconductor CrIAs,"The Pair Approximation method has been formulated for the isotropic
ferromagnetic Heisenberg model with spin $S=1$. The exchange interactions of
arbitrary range have been taken into account. The single-ion anisotropy has
been considered as well as the external magnetic field. Within the method, the
Gibbs free-energy has been derived, from which all thermodynamic properties can
be self-consistently obtained. In order to illustrate the developed formalism,
the numerical calculations have been performed for CrIAs planar magnetic
semiconductor, a hypothetical material whose existence has been recently
predicted by the Density Functional Theory-based calculations. For this model
material, all the relevant thermodynamic magnetic properties have been studied.
The numerical results have been presented in the figures and discussed.",2006.08318v2
2020/9/28,Thermal Magnetic Fluctuations of a Ferroelectric Quantum Critical Point,"Entanglement of two different quantum orders is of an interest of the modern
condensed matter physics. One of the examples is the dynamical multiferroicity,
where fluctuations of electric dipoles lead to magnetization. We investigate
this effect at finite temperature and demonstrate an elevated magnetic response
of a ferroelectric near the ferroelectric quantum critical point (FE QCP). We
calculate the magnetic susceptibility of a bulk sample on the paraelectric side
of the FE QCP at finite temperature and find enhanced magnetic susceptibility
near the FE QCP. We propose quantum paraelectric strontium titanate (STO) as a
candidate material to search for dynamic multiferroicity. We estimate the
magnitude of the magnetic susceptibility for this material and find that it is
detectable experimentally.",2009.12995v1
2020/11/25,Complex magnetic phases enriched by charge density waves in topological semimetals GdSb_xTe_{2-x-δ},"The interplay of crystal symmetry, magnetism, band topology and electronic
correlation can be the origin of quantum phase transitions in condensed matter.
Particularly, square-lattice materials have been serving as a versatile
platform to study the rich phenomena resulting from that interplay. In this
work, we report a detailed magnetic study on the square-lattice based magnetic
topological semimetals GdSb_{x}Te_{2-x-{\delta}}. We report the H-T magnetic
phase diagrams along three crystallographic orientations and show that, for
those materials where a charge density wave distortion is known to exist, many
different magnetic phases are identified. In addition, the data provides a clue
to the existence of an antiferromagnetic skyrmion phase, which has been
theoretically predicted but not experimentally confirmed in a bulk material
yet.",2011.12952v1
2021/6/5,Superconducting materials: Challenges and opportunities for large-scale applications,"Superconducting materials hold great potential to bring radical changes for
electric power and high-field magnet technology , enabling high-efficiency
electric power generation, high-capacity lossless electric power transmission,
small light-weighted electrical equipment, high-speed maglev transportation,
ultra-strong magnetic field generation for high-resolution magnetic resonance
imaging (MRI) systems, nuclear magnetic resonance (NMR) systems, the future
advanced high energy particle accelerators, nuclear fusion reactors and so on.
The performance, economy and operating parameters (temperatures and magnetic
fields) of these applications strongly depend on the electromagnetic and
mechanical properties, as well as manufacturing and material cost of
superconductors. This perspective examines the basic properties relevant to
practical applications and key issues of wire fabrication for practical
superconducting materials, and describes their challenges and current state in
practical applications. Finally, future perspectives for their opportunities
and development in the applications of superconducting power and magnetic
technologies are given.",2106.02825v1
2021/6/23,Spin-glass state induced by Mn-doping into a moderate gap layered semiconductor SnSe$_2$,"Various types of magnetism can appear in emerging quantum materials such as
van der Waals layered ones. Here, we report the successful doping of manganese
atoms into a post-transition metal dichalcogenide semiconductor: SnSe$_2$. We
synthesized a single crystal Sn$_{1-x}$Mn$_x$Se$_{2}$ with $\textit{x}$ = 0.04
by the chemical vapor transport (CVT) method and characterized it by x-ray
diffraction (XRD) and energy-dispersive x-ray spectroscopy (EDS). The magnetic
properties indicated a competition between coexisting ferromagnetic and
antiferromagnetic interactions, from the temperature dependence of the
magnetization, together with magnetic hysteresis loops. This means that
magnetic clusters having ferromagnetic interaction within a cluster form and
the short-range antiferromagnetic interaction works between the clusters; a
spin-glass state appears below ~ 60 K. Furthermore, we confirmed by $\textit{ab
initio}$ calculations that the ferromagnetic interaction comes from the
3$\textit{d}$ electrons of the manganese dopant. Our results offer a new
material platform to understand and utilize the magnetism in the van der Waals
layered materials.",2106.12334v1
2022/1/12,Photo-magnetization in two-dimensional sliding ferroelectrics,"Light-matter interaction is one of the key routes to understanding and
manipulating geometric and electronic behaviors of materials, especially
two-dimensional materials which are optically accessible owing to their high
surface to volume ratio. In the current work we focus on the recently
discovered two-dimensional sliding ferroelectric materials, in which the
out-of-plane electric polarization can be switched with a small horizontal
translation in one layer. Combining symmetry analysis and first-principles
calculations, we predict that light illumination could inject non-equilibrium
magnetic moments into the sliding ferroelectrics. Such magnetic moment is
composed of both spin and orbital degrees of freedom contributions. We use
$\mathrm{ZrI}_2$, $\mathrm{WTe}_2$, and $\mathrm{MoS}_2$ bilayer ferroelectrics
to illustrate our theory. Under intermediate light illumination, one can yield
non-equilibrium magnetic moments on the order of $0.1-1$ $\mu_B$ in these
systems, which also depends on the polarization nature of incident light.
Furthermore, we show that such photo-injected magnetism changes its sign when
the sliding dipole moment switches. This photo-magnetization can be detected by
magneto-optical methods (such as Kerr or Faraday effect), which serves as an
indicator of sliding ferroelectricity. Hence, one can use an all-optical pump
and probe setup to measure and detect the subtle sliding ferroelectric phase.",2201.04367v1
2022/2/23,Ab initio calculation of the magnetic Gibbs free energy of materials using magnetically constrained supercells,"We present a first-principles approach for the computation of the magnetic
Gibbs free energy of materials using magnetically constrained supercell
calculations. Our approach is based on an adiabatic approximation of slowly
varying local moment orientations, the so-called finite-temperature disordered
local moment picture. It describes magnetic phase transitions and how
electronic and/or magnetostructural mechanisms generate a discontinuous
(first-order) character. We demonstrate that the statistical mechanics of the
local moment orientations can be described by an affordable number of supercell
calculations containing noncollinear magnetic configurations. The applicability
of our approach is illustrated by firstly studying the ferromagnetic state in
bcc Fe. We then investigate the temperature-dependent properties of a
triangular antiferromagnetic state stabilizing in two antiperovskite systems
Mn$_3$AN (A = Ga, Ni). Our calculations provide the negative volume expansion
of these materials as well as the ab initio origin of the discontinuous
character of the phase transitions, electronic and/or magnetostructural, in
good agreement with experiment.",2202.11492v1
2022/3/22,Weak ferromagnetism linked to the high-temperature spiral phase of YBaCuFeO5,"The layered perovskite YBaCuFeO5 is a rare example of cycloidal spiral magnet
whose ordering temperature Tspiral can be tuned far beyond room temperature by
adjusting the degree of Cu2+/Fe3+ chemical disorder in the structure. This
unusual property qualifies this material as one of the most promising
spin-driven multiferroic candidates. However, very little is known about the
response of the spiral to magnetic fields, crucial for magnetoelectric
cross-control applications. Using bulk magnetization and neutron powder
diffraction measurements under magnetic fields up to 9 T we report here the
first temperature-magnetic field phase diagram of this material. Besides
revealing a strong stability of the spiral state, our data uncover the presence
of weak ferromagnetism coexisting with the spiral modulation. Since
ferromagnets can be easily manipulated with magnetic fields, this observation
opens new perspectives for the control of the spiral orientation, directly
linked to the polarization direction, as well as for a possible future use of
this material in technological applications.",2203.11767v1
2022/4/25,Magnetocaloric particles of the Laves phase compound HoAl2 prepared by electrode induction melting gas atomization,"Processing magnetocaloric materials into magnetic refrigerant particles is an
essential issue in developing high-performance magnetic refrigerators. Here, we
succeed in stably producing magnetocaloric particles of the promising material
HoAl2 by a newly devised method based on electrode induction melting gas
atomization process. The particle size range is on the order of submillimeter,
which is suitable for practical refrigeration systems. The resulting particles
with less contamination have good morphological, magnetic, and magnetocaloric
properties: (i) almost spherical shapes with few internal pores, (ii) a sharp
ferromagnetic transition around 30 K, and (iii) a large magnetocaloric effect
comparable to the bulk counterpart. These features suggest the HoAl$_{2}$
gas-atomized particles have the potential of use as a magnetic refrigerant. The
presented method can be applied not only to HoAl2 but also to other brittle
magnetocaloric materials with high melting points, facilitating the production
of various magnetic refrigerants needed to develop magnetic refrigerators for
hydrogen liquefaction.",2204.11480v1
2022/5/9,Multifunctional Two-dimensional van der Waals Janus Magnet Cr-based Dichalcogenide Halides,"Two-dimensional van der Waals Janus materials and their heterostructures
offer fertile platforms for designing fascinating functionalities. Here, by
means of systematic first-principles studies on van der Waals Janus monolayer
Cr-based dichalcogenide halides CrYX (Y=S, Se, Te; X=Cl, Br, I), we find that
CrSX (X=Cl, Br, I) are the very desirable high TC ferromagnetic semiconductors
with an out-of-plane magnetization. Excitingly, by the benefit of the large
magnetic moments on ligand S2- anions, the sought-after large-gap quantum
anomalous Hall effect and sizable valley splitting can be achieved through the
magnetic proximity effect in van der Waals heterostructures CrSBr/Bi2Se3/CrSBr
and MoTe2/CrSBr, respectively. Additionally, we show that large
Dzyaloshinskii-Moriya interactions give rise to skyrmion states in CrTeX (X=Cl,
Br, I) under external magnetic fields. Our work reveals that two-dimensional
Janus magnet Cr-based dichalcogenide halides have appealing
multifunctionalities in the applications of topological electronic and
valleytronic devices.",2205.04053v1
2023/6/13,Reduced energies for thin ferromagnetic films with perpendicular anisotropy,"We derive four reduced two-dimensional models that describe, at
  different spatial scales, the micromagnetics of ultrathin
  ferromagnetic materials of finite spatial extent featuring
  perpendicular magnetic anisotropy and interfacial
  Dzyaloshinskii-Moriya interaction. Starting with a microscopic model
  that regularizes the stray field near the material's lateral edges,
  we carry out an asymptotic analysis of the energy by means of
  $\Gamma$-convergence. Depending on the scaling assumptions on the
  size of the material domain vs. the strength of dipolar interaction,
  we obtain a hierarchy of the limit energies that exhibit
  progressively stronger stray field effects of the material
  edges. These limit energies feature, respectively, a renormalization
  of the out-of-plane anisotropy, an additional local boundary penalty
  term forcing out-of-plane alignment of the magnetization at the
  edge, a pinned magnetization at the edge, and, finally, a pinned
  magnetization and an additional field-like term that blows up at the
  edge, as the sample's lateral size is increased. The pinning of the
  magnetization at the edge restores the topological protection and
  enables the existence of magnetic skyrmions in bounded samples.",2306.07634v2
2023/10/11,Magnetic State Control of Non-van der Waals 2D Materials by Hydrogenation,"Controlling the magnetic state of two-dimensional (2D) materials is crucial
for spintronic applications. By employing data-mining and autonomous density
functional theory calculations, we demonstrate the switching of magnetic
properties of 2D non-van der Waals materials upon hydrogen passivation. The
magnetic configurations are tuned to states with flipped and enhanced moments.
For 2D CdTiO$_3$ - a nonmagnetic compound in the pristine case - we observe an
onset of ferromagnetism upon hydrogenation. Further investigation of the
magnetization density of the pristine and passivated systems provides a
detailed analysis of modified local spin symmetries and the emergence of
ferromagnetism. Our results indicate that selective surface passivation is a
powerful tool for tailoring magnetic properties of nanomaterials such as
non-vdW 2D compounds.",2310.07329v1
2010/11/15,Light-induced size changes in BiFeO3 crystals,"Multifunctional oxides are promising materials because of their fundamental
physical properties as well as their potential in applications1. Among these
materials, multiferroics exhibiting ferroelectricity and magnetism are good
candidates for spin electronic applications using the magnetoelectric effect,
which couples magnetism and ferroelecticity. Furthermore, because
ferroelectrics are insulators with a reasonable bandgap, photons can
efficiently interact with electrons leading to photoconduction or photovoltaic
effects. However, until now, coupling of light with mechanical degrees of
freedom has been elusive, although ferroelasticity is a well-known property of
these materials. Here, we report on the observation, for the first time, of a
substantial visiblelight- induced change in the dimensions of BiFeO3 crystals
at room temperature. The relative light-induced photostrictive effect is of the
order of 10e-5 with response times below 0.1s. It depends on the polarization
of incident light as well as applied magnetic fields. This opens the
perspective of combining mechanical, magnetic, electric and optical
functionalities in future generations of remote switchable devices.",1011.3398v1
2020/7/28,Electron correlation effects on exchange interactions and spin excitations in 2D van der Waals materials,"Despite serious effort, the nature of the magnetic interactions and the role
of electron-correlation effects in magnetic two-dimensional (2D) van der Waals
materials remain elusive. Using CrI$_3$ as a model system, we show that the
calculated electronic structure including nonlocal electron correlations yields
spin excitations consistent with inelastic neutron scattering measurements.
Remarkably, this approach identifies an unreported correlation-enhanced
interlayer super-superexchange, which rotates the magnon Dirac lines off, and
introduces a gap along, the high-symmetry $\Gamma$-$K$-$M$ path. This discovery
provides a different perspective on the gap opening mechanism observed in
CrI$_3$, which was previously associated with spin-orbit coupling through the
Dzyaloshinskii-Moriya interaction or Kitaev interaction. Our observation
elucidates the critical role of electron correlations on the spin ordering and
spin dynamics in magnetic van der Waals materials and demonstrates the
necessity of explicit treatment of electron correlations in the broad family of
2D magnetic materials.",2007.14518v2
2021/3/17,Identification of materials with strong magneto-structural coupling using computational high-throughput screening,"Important phenomena such as magnetostriction, magnetocaloric, and
magnetoelectric effects arise from, or could be enhanced by, the coupling of
magnetic and structural degrees of freedom. The coupling of spin and lattice
also influence transport and structural properties in magnetic materials in
particular around phase transitions. In this paper we propose a method for
screening materials for a strong magneto-structural coupling by assessing the
effect of the local magnetic configuration on the atomic forces using density
functional theory (DFT). We have employed the disordered local moment approach
in a supercell formulation to probe different magnetic local configurations and
their forces and performed a high-throughput search on binary and ternary
compounds available in the Crystallographic Open Database. We identify a list
of materials with a strong spin-lattice coupling out of which several are
already known to display magneto-lattice coupling-phenomena like Fe3O4 and CrN.
Others, such as Mn2CrO4 and CaFe7O11 have been less studied and are yet to
reveal their potentials in experiments and applications.",2103.09652v1
2021/12/10,Enhanced Planar Antenna Efficiency Through Magnetic Thin-Films,"This work proposes to use magnetic material as the substrate of planar
antennas to overcome the platform effect caused by the conducting ground plane.
The upper bound of the radiation efficiency of an electric-current-driven
low-profile antenna is theoretically derived, which is inversely proportional
to the Gilbert damping factor of the magnetic material. Meanwhile, the
improvement of radiation due to the use of magnetic material is demonstrated by
a three-dimensional (3D) multiphysics and multiscale time-domain model. The
simulation results match the theoretical derivation, showing 25% radiation
efficiency from a planar antenna backed by a FeGaB thin film with 2.56 um
thickness. Furthermore, for conductive ferromagnetic materials, it is shown
that the eddy current loss can be well suppressed by laminating the thin film
into multiple layers. The radiation efficiency of the modeled antenna with a
conductive ferromagnetic substrate is improved from 2.2% to 11.8% by dividing
the substrate into 10 layers, with a ferromagnetic material fill factor of 93%.",2201.04932v1
2022/4/25,Evolution of Electronic and Magnetic Properties in Topological Semimetal SmSbxTe2-x,"The ZrSiS-type materials have attracted intensive attention due to the
existence of various topological fermions. The magnetic version of the
ZrSiS-type materials, LnSbTe (Ln = lanthanides), is an ideal candidate to
explore novel exotic states due to the interaction between magnetism and
topology. In this work, we report the experimental study on structural,
magnetic, thermodynamic, and electronic properties for SmSbxTe2-x with various
Sb content. The revealed evolutions of these properties with tuning the
compositions would provide useful insights for the fundamental topological
physics and the future applications.",2204.11812v1
2023/1/3,Monolayer-to-mesoscale modulation of the optical properties in 2D CrI3 mapped by hyperspectral microscopy,"Magnetic 2D materials hold promise to change the miniaturization paradigm of
unidirectional photonic components. However, the integration of these materials
in devices hinges on the accurate determination of the optical properties down
to the monolayer limit, which is still missing. By using hyperspectral
wide-field imaging we reveal a non-monotonic thickness dependence of the
complex optical dielectric function in the archetypal magnetic 2D material CrI3
extending across different length scales: onsetting at the mesoscale, peaking
at the nanoscale and decreasing again down to the single layer. These results
portray a modification of the electronic properties of the material and align
with the layer-dependent magnetism in CrI3, shedding light into the
long-standing structural conundrum in this material. The unique modulation of
the complex dielectric function from the monolayer up to more than 100 layers
will be instrumental for understanding and manipulating the magneto-optical
effects of magnetic 2D materials.",2301.01002v1
2023/1/26,Cubic Double Perovskites Host Noncoplanar Spin Textures,"Magnetic materials with noncoplanar magnetic structures can show unusual
physical properties driven by nontrivial topology. Topologically-active states
are often multi-q structures, which are challenging to stabilize in models and
to identify in materials. Here, we use inelastic neutron-scattering experiments
to show that the insulating double perovskites Ba2YRuO6 and Ba2LuRuO6 host a
noncoplanar 3-q structure on the face-centered cubic lattice. Quantitative
analysis of our neutron-scattering data reveals that these 3-q states are
stabilized by biquadratic interactions. Our study identifies double perovskites
as a highly promising class of materials to realize topological magnetism,
elucidates the stabilization mechanism of the 3-q state in these materials, and
establishes neutron spectroscopy on powder samples as a valuable technique to
distinguish multi-q from single-q states, facilitating the discovery of
topologically-nontrivial magnetic materials.",2301.11395v1
2024/1/5,Integrated ab initio modelling of atomic order and magnetic anisotropy for rare-earth-free magnet design: effects of alloying additions in $\mathrm{L}1_0$ FeNi,"We describe an integrated modelling approach to accelerate the search for
novel, single-phase, multicomponent materials with high magnetocrystalline
anisotropy (MCA). For a given system we predict the nature of atomic ordering,
its dependence on the magnetic state, and then proceed to describe the
consequent MCA. Crucially, within our modelling framework, the same ab initio
description of the material's electronic structure determines both aspects. We
demonstrate this holistic method by studying the effects of alloying additions
in FeNi, examining systems with the general stoichiometry Fe$_4$Ni$_3X$,
including $X = $ Pt, Pd, Al, and Co. The atomic ordering behaviour predicted on
adding these elements, fundamental for determining a material's MCA, is rich
and varied. Equiatomic FeNi has been reported to require ferromagnetic order to
establish the tetragonal $\mathrm{L}1_0$ order suited for significant MCA. Our
results show that when alloying additions are included in this material,
annealing in an applied magnetic field and/or below a material's Curie
temperature may also promote tetragonal order, along with an appreciable effect
on the predicted MCA.",2401.02809v1
2021/11/23,Magnetism in Metastable and Annealed Compositionally Complex Alloys,"Compositionally complex materials (CCMs) present a potential paradigm shift
in the design of magnetic materials. These alloys exhibit long-range structural
order coupled with limited or no chemical order. As a result, extreme local
environments exist with a large opposing magnetic energy term, which can
manifest large changes in the magnetic behavior. In the current work, the
magnetic properties of (Cr, Mn, Fe, Ni) alloys are presented. These materials
were prepared by room-temperature combinatorial sputtering, resulting in a
range of compositions with a single BCC structural phase and no chemical
ordering. The combinatorial growth technique allows CCMs to be prepared outside
of their thermodynamically stable phase, enabling the exploration of otherwise
inaccessible order. The mixed ferromagnetic and antiferromagnetic interactions
in these alloys causes frustrated magnetic behavior, which results in an
extremely low coercivity (<1 mT), which increases rapidly at 50 K. At low
temperatures, the coercivity achieves values of nearly 500 mT, which is
comparable to some high-anisotropy magnetic materials. Commensurate with the
divergent coercivity is an atypical drop in the temperature dependent
magnetization. These effects are explained by a mixed magnetic phase model,
consisting of ferro-, antiferro , and frustrated magnetic regions, and are
rationalized by simulations. A machine-learning algorithm is employed to
visualize the parameter space and inform the development of subsequent
compositions. Annealing the samples at 600 {\deg}C orders the sample, more-than
doubling the Curie temperature and increasing the saturation magnetization by
as much as 5x. Simultaneously, the large coercivities are suppressed, resulting
in magnetic behavior that is largely temperature independent over a range of
350 K.",2111.12188v1
2009/8/31,Emergence of local magnetic moments in doped graphene-related materials,"Motivated by recent studies reporting the formation of localized magnetic
moments in doped graphene, we investigate the energetic cost for spin
polarizing isolated impurities embedded in this material. When a well-known
criterion for the formation of local magnetic moments in metals is applied to
graphene we are able to predict the existence of magnetic moments in cases that
are in clear contrast to previously reported Density Functional Theory (DFT)
results. When generalized to periodically repeated impurities, a geometry so
commonly used in most DFT-calculations, this criterion shows that the energy
balance involved in such calculations contains unavoidable contributions from
the long-ranged pairwise magnetic interactions between all impurities. This
proves the fundamental inadequacy of the DFT-assumption of independent unit
cells in the case of magnetically doped low-dimensional graphene-based
materials. We show that this can be circumvented if more than one impurity per
unit cell is considered, in which case the DFT results agree perfectly well
with the criterion-based predictions for the onset of localized magnetic
moments in graphene. Furthermore, the existence of such a criterion determining
whether or not a magnetic moment is likely to arise within graphene will be
instrumental for predicting the ideal materials for future carbon-based
spintronic applications.",0908.4516v1
2012/3/2,Mixed Magnetism for Refrigeration and Energy Conversion,"The efficient coupling between lattice degrees of freedom and spin degrees of
freedom in magnetic materials can be used for refrigeration and energy
conversion. This coupling is enhanced in materials exhibiting the giant
magnetocaloric effect. First principle electronic structure calculations on
hexagonal MnFe(P, Si) reveal a new form of magnetism: the coexistence of strong
and weak magnetism in alternate atomic layers. The weak magnetism of Fe layers
(disappearance of local magnetic moments at the Curie temperature) is
responsible for a strong coupling with the crystal lattice while the strong
magnetism in adjacent Mn-layers ensures Curie temperatures high enough to
enable operation at and above room temperature. Varying the composition on
these magnetic sublattices gives a handle to tune the working temperature and
to achieve a strong reduction of the undesired thermal hysteresis. In this way
we design novel materials based on abundantly available elements with
properties matched to the requirements of an efficient refrigeration or
energy-conversion cycle.",1203.0556v2
2016/11/15,Optimization of the magnetic properties of aligned Co nanowires/polymer composites for the fabrication of permanent magnets,"We aim at combining high coercivity magnetic nanowires in a polymer matrix in
a view to fabricate rare--earth free bonded magnets. In particular, our aim is
to fabricate anisotropic materials by aligning the wires in the polymer matrix.
We have explored the different parameters of the fabrication process in order
to produce a material with the best possible magnetic properties. We show that
the choice of a proper solvent allows obtaining stable nanowire suspensions.
The length and the type of the polymer chains play also an important role.
Smaller chains ($M_w < 10000$) provide better magnetization results. The
magnetic field applied during the casting of the material plays also a role and
should be of the order of a fraction of a tesla. The local order of the
nanowires in the matrix has been characterized by TEM and Small Angle Neutron
Scattering. The correlation between the local order of the wires and the
magnetic properties is discussed. Materials with coercivity $\mu_0 H_c$ up to
0.70 $T$ at room temperature have been obtained.",1611.04735v1
2019/1/15,Anomalous Hall Conductivity of a Non-Collinear Magnetic Antiperovskite,"The anomalous Hall effect (AHE) is a well-known fundamental property of
ferromagnetic metals, commonly associated with the presence of a net
magnetization. Recently, an AHE has been discovered in non-collinear
antiferromagnetic (AFM) metals. Driven by non-vanishing Berry curvature of AFM
materials with certain magnetic space group symmetry, anomalous Hall
conductivity (AHC) is very sensitive to the specific type of magnetic ordering.
Here, we investigate the appearance of AHC in antiperovskite GaNMn$_{3}$ as a
representative of broader materials family ANMn$_{3}$ (A is a main group
element), where different types of non-collinear magnetic ordering can emerge.
Using symmetry analyses and first-principles density-functional theory
calculations, we show that with almost identical band structure, the nearly
degenerate non-collinear AFM $\Gamma_{5g}$ and $\Gamma_{4g}$ phases of
GaNMn$_{3}$ have zero and finite AHC, respectively. In a non-collinear
ferrimagnetic $M$-1 phase, GaNMn$_{3}$ exhibits a large AHC due to the presence
of a sizable net magnetic moment. In the non-collinear antiperovskite magnets,
transitions between different magnetic phases, exhibiting different AHC states,
can be produced by doping, strain, or spin transfer torque, which makes these
materials promising for novel spintronic applications.",1901.05040v1
2019/2/14,Database of novel magnetic materials for high-performance permanent magnet development,"This paper describes the open Novamag database that has been developed for
the design of novel Rare-Earth free/lean permanent magnets. The database
software technologies, its friendly graphical user interface, advanced search
tools and available data are explained in detail. Following the philosophy and
standards of Materials Genome Initiative, it contains significant results of
novel magnetic phases with high magnetocrystalline anisotropy obtained by three
computational high-throughput screening approaches based on a crystal structure
prediction method using an Adaptive Genetic Algorithm, tetragonally distortion
of cubic phases and tuning known phases by doping. Additionally, it also
includes theoretical and experimental data about fundamental magnetic material
properties such as magnetic moments, magnetocrystalline anisotropy energy,
exchange parameters, Curie temperature, domain wall width, exchange stiffness,
coercivity and maximum energy product, that can be used in the study and design
of new promising high-performance Rare-Earth free/lean permanent magnets. The
results therein contained might provide some insights into the ongoing debate
about the theoretical performance limits beyond Rare-Earth based magnets.
Finally, some general strategies are discussed to design possible experimental
routes for exploring most promising theoretical novel materials found in the
database.",1902.05241v1
2023/7/20,Stray magnetic field imaging of thin exfoliated iron halides flakes,"Magnetic van der Waals materials are often proposed for use in future
spintronic devices, aiming to leverage the combination of long-range magnetic
order and near-atomic thinness to produce energy-efficient components. One
class of material that has been discussed in this context are the iron halides
FeCl$_2$ and FeBr$_2$, which are A-type antiferromagnets with strong uniaxial
magnetocrystalline anisotropy. However, despite characterization of the bulk
materials, the possibility for sustaining the magnetic behaviors that would
underpin such applications in thin flakes has not been investigated. In this
work, we use nitrogen-vacancy (NV) center microscopy to quantitatively image
magnetism in individual exfoliated flakes of these iron halides, revealing the
absence of magnetic remanence, a weak induced magnetization under bias field
and variable behavior versus temperature. We show that our results are
consistent with the antiferromagnetic behavior of the bulk material with a soft
ferromagnetic uncompensated layer, indicating that extended ($>1~\mu$m)
ferromagnetic domains are not sustained even at low temperatures (down to 4 K).
Finally, we find that the magnetic order is strongly affected by the sample
preparation, with a surprising diamagnetic order observed in a thin, hydrated
sample.",2307.10561v1
2023/12/26,The nature of low-temperature spin-freezing in frustrated Kitaev magnets,"The subtle interplay between competing degrees of freedom, anisotropy, and
spin correlations in frustrated Kitaev quantum materials offer an ideal
platform to host myriads of non-trivial quantum states with exotic fractional
excitations. The signature of spin-freezing behavior of these spin-orbit driven
frustrated magnets is characterized by a bifurcation of zero-field-cooled and
field-cooled magnetic susceptibility at low temperatures much below the
characteristic interaction energy scale. The magnetic-specific heat exhibits a
T^2 dependence below the freezing temperature. The field-independent behavior
of magnetic-specific heat below the freezing temperature implies the presence
of exotic low-energy excitations. The aging and memory effect experiments in
the Kitaev magnets suggest the non-hierarchical free energy distribution, which
differs from the hierarchical organization of conventional spin-freezing.
Furthermore, NMR spin-lattice relaxation rate follows a power law behavior
below the spin-freezing temperature suggesting the persistence of
unconventional spin excitation spectra. Herein, we demonstrate that the
observed low-temperature spin-freezing phenomena in a few representative Kitaev
quantum materials can be effectively explained by the Halperin and Saslow (HS)
hydrodynamic modes relevant for non-trivial spin glass materials. The linearly
dispersive HS modes are hypothesized to account for instigating non-abelian
defect propagation, thereby inducing a spin jam state in the low-temperature
regime in frustrated Kitaev magnets. Our investigation reveals that HS modes
capture the essence of unconventional spin-freezing ascribed to topological
origin in two-dimensional (2D) Kitaev magnets decorated on a honeycomb lattice
and its 3D analog hyperhoneycomb that offers a viable ground to extend this
framework to a large class of frustrated quantum materials.",2312.16096v1
2000/9/11,Magnetic properties of the S=1/2 quasi-one-dimensional antiferromagnet CaCu2O3,"We report single crystal growth and magnetic susceptibility and neutron
diffraction studies of the S=1/2 quasi-1D antiferromagnet CaCu2O3. The
structure of this material is similar to that of the prototype two-leg
spin-ladder compound SrCu2O3. However, the Cu-O-Cu bond angle in the ladder
rungs in CaCu2O3 is equal to 123 deg, and therefore the magnetic interaction
along the rungs is expected to be much weaker in this material. At high
temperatures, the magnetic susceptibility of CaCu2O3 can be decomposed into a
contribution from 1D antiferromagnetic chains of finite-size chain segments
together with a weak Curie contribution. The intrachain magnetic exchange
constant, determined from the magnetic susceptibility measurements, is 2000 K.
CaCu2O3 undergoes a Neel transition at T_N=25 K with ordering wavevector of
(0.429(5), 0.5, 0.5). The magnetic structure is incommensurate in the direction
of the frustrated interchain interaction. Weak commensurate (0.5, 0.5, 0.5)
magnetic peaks are also observed below T_N. Application of a magnetic field
induces a metamagnetic transition at which the incommensurability of the
magnetic structure is substantially reduced. The material possesses only
short-range magnetic order above the transition field.",0009158v1
2001/3/3,Magnetic properties of magnetically textured Bi-2212 ceramics,"This paper aims at reporting magnetic properties of bulk polycrystalline
Bi2Sr2Ca0.8Dy0.2Cu2O8-y samples textured under a magnetic field. The
microstructure of these materials is highly anisotropic and exhibits particular
features needed to be taken into account in order to interpret their magnetic
and electrical properties. First the AC magnetic susceptibility c = c ' - j c""
has been measured for several magnetic fields (H // ab and H // c) and compared
to the electrical resistivity data. The structure of the c"" peak is shown to be
related to the chemical content distribution of the superconducting grains.
Next, the magnetic flux profiles have been extracted from the magnetic
measurements using the Campbell - Rollins procedure. The anisotropy of the flux
profiles and their peculiar curvature behaviour for H // c point out the role
of both grain platelet structure and the presence of secondary phases. From
these results, we conclude that the magnetic properties of such magnetically
textured materials do not allow for a reliable extraction of the critical
current density Jc but essentially probe geometric effects. Such effects have
to be taken into account for improving the manufacture of attractive high-Tc
materials.",0103081v2
2009/4/28,Magnetic characterization of undoped and 15%F doped LaFeAsO and SmFeAsO compounds,"In this paper the magnetic behaviour of undoped and 15% F doped SmFeAsO
(Sm-1111) and LaFeAsO (La-1111) samples is presented and discussed.
Magnetization measurements are not a simple tool to use for the
characterisation of the new family of Fe-based superconductors because magnetic
impurities can be easily formed during the preparation procedure and may affect
the magnetic signal. In spite of this problem bulk magnetization measurements,
properly treated, may give very useful information. In the undoped samples we
gathered the main aspects of the physical behavior of the 1111 phase, i.e. the
onset of the Spin Density Wave (SDW), the antiferromagnetic ordering at the Sm
sublattice and the susceptibility increase with increasing temperature above
the SDW temperature, and, in addition, we were able to estimate the Pauli
contribution to susceptibility and therein the Wilson ratio both for LaFeAsO
and SmFeAsO compounds, and the amplitude of the jump at the SDW temperature. In
the doped samples, while the presence of magnetic signals due to impurities is
dominating in the normal state, the superconducting behavior may be clearly
observed and studied. In particular, in the Sm-1111 superconducting sample the
coexistence-competition between superconductivity and antiferromagnetic
ordering of the Sm ions was clearly observed.",0904.4348v1
2014/2/26,Giant magnetic anisotropy and tunnelling of the magnetization in Li2(Li_{1-x}Fe_x)N,"Large magnetic anisotropy and coercivity are key properties of functional
magnetic materials and are generally associated with rare earth elements. Here
we show an extreme, uniaxial magnetic anisotropy and the emergence of magnetic
hysteresis in Li2(Li1-xFex)N. An extrapolated, magnetic anisotropy field of 220
Tesla and a coercivity field of over 11 Tesla at 2 Kelvin outperform all known
hard-ferromagnets and single-molecule magnets (SMMs). Steps in the hysteresis
loops and relaxation phenomena in striking similarity to SMMs are particularly
pronounced for x << 1 and indicate the presence of nano-scale magnetic centres.
Quantum tunnelling, in form of temperature-independent relaxation and
coercivity, deviation from Arrhenius behaviour and blocking of the relaxation,
dominates the magnetic properties up to 10 Kelvin. The simple crystal
structure, the availability of large single crystals, and the ability to vary
the Fe concentration make Li2(Li1-xFex)N (i) an ideal model system to study
macroscopic quantum effects at elevated temperatures and (ii) a basis for novel
functional magnetic materials.",1402.6626v1
2014/8/8,Stable Magnetic Droplet Solitons in Spin Transfer Nanocontacts,"Magnetic thin films with perpendicular magnetic anisotropy (PMA) have
localized excitations that correspond to reversed dynamically precessing
magnetic moments, known as magnetic droplet solitons. Fundamentally, these
excitations are associated with an attractive interaction between elementary
spin-excitations (i.e., magnons) and were predicted to occur in PMA materials
in the absence of damping [1,2]. While damping, present in all magnetic
materials, suppresses these excitations, it is now possible to compensate
damping by spin transfer torques through electrical current flow in nanometer
scale contacts to ferromagnetic thin films [3,4]. A theory predicts the
appearance of magnetic droplet solitons at a threshold current in nanocontacts
[5] and, recently, experimental signatures of droplet nucleation have been
reported [6]. However, thus far, they have been observed to be nearly
reversible excitations, with only partially reversed magnetization and to be
subject to instabilities that cause them to drift away from the nanocontacts
(i.e., drift instabilities) [6]. Here we show that magnetic droplet solitons
can be stabilized in a spin transfer nanocontact. Further, they exhibit a
strong hysteretic response to fields and currents and a nearly fully reversed
magnetization in the contact. These observations, in addition to their
fundamental interest, open up new applications for magnetic droplet solitons as
multi-state high frequency current and field tunable oscillators.",1408.1902v1
2016/5/20,Two-dimensional terahertz magnetic resonance spectroscopy of collective spin waves,"Nonlinear manipulation of nuclear and electron spins is the basis for all
advanced methods in magnetic resonance including multidimensional nuclear
magnetic and electron spin resonance spectroscopies, magnetic resonance
imaging, and in recent years, quantum control over individual spins. The
methodology is facilitated by the ease with which the regime of strong coupling
can be reached between radiofrequency or microwave magnetic fields and nuclear
or electron spins respectively, typified by sequences of magnetic pulses that
control the magnetic moment directions. The capabilities meet a bottleneck,
however, for far-infrared magnetic resonances characteristic of correlated
electron materials, molecular magnets, and proteins that contain high-spin
transition metal ions. Here we report the development of two-dimensional
terahertz magnetic resonance spectroscopy and its use for direct observation of
the nonlinear responses of collective spin waves (magnons). The spectra show
magnon spin echoes and 2-quantum signals that reveal pairwise correlations
between magnons at the Brillouin zone center. They also show resonance-enhanced
second-harmonic and difference-frequency signals. Our methods are readily
generalizable to multidimensional magnetic resonance spectroscopy and nonlinear
coherent control of terahertz-frequency spin systems in molecular complexes,
biomolecules, and materials.",1605.06476v3
2017/6/6,"Magnetic Behavior and Spin-Lattice Coupling in Cleavable, van der Waals Layered CrCl3 Crystals","CrCl3 is a layered insulator that undergoes a crystallographic phase
transition below room temperature and orders antiferromagnetically at low
temperature. Weak van der Waals bonding between the layers and ferromagnetic
in-plane magnetic order make it a promising material for obtaining atomically
thin magnets and creating van der Waals heterostructures. In this work we have
grown crystals of CrCl3, revisited the structural and thermodynamic properties
of the bulk material, and explored mechanical exfoliation of the crystals. We
find two distinct anomalies in the heat capacity at 14 and 17 K confirming that
the magnetic order develops in two stages on cooling, with ferromagnetic
correlations forming before long range antiferromagnetic order develops between
them. This scenario is supported by magnetization data. A magnetic phase
diagram is constructed from the heat capacity and magnetization results. We
also find an anomaly in the magnetic susceptibility at the crystallographic
phase transition, indicating some coupling between the magnetism and the
lattice. First principles calculations accounting for van der Waals
interactions also indicate spin-lattice coupling, and find multiple nearly
degenerate crystallographic and magnetic structures consistent with the
experimental observations. Finally, we demonstrate that monolayer and few-layer
CrCl3 specimens can be produced from the bulk crystals by exfoliation,
providing a path for the study of heterostructures and magnetism in ultrathin
crystals down to the monolayer limit.",1706.01796v1
2016/3/14,Magnetic properties of restacked 2D spin $\frac{1}{2}$ honeycomb RuCl$_3$ nanosheets,"Spin $\frac{1}{2}$ honeycomb materials have gained substantial interest due
to their exotic magnetism and possible application in quantum computing.
However, in all current materials out-of-plane interactions are interfering
with the in-plane order, hence a true 2D magnetic honeycomb system is still of
demand. Here, we report the exfoliation of the magnetic semiconductor
$\alpha$-RuCl$_3$ into the first halide monolayers and the magnetic
characterization of the spin $\frac{1}{2}$ honeycomb arrangement of
turbostratically stacked RuCl$_3$ monolayers. The exfoliation is based on a
reductive lithiation/hydration approach, which gives rise to a loss of
cooperative magnetism due to the disruption of the spin $\frac{1}{2}$ state by
electron injection into the layers. After an oxidative treatment, cooperative
magnetism similar to the bulk is restored. The oxidized pellets of restacked
single layers feature a magnetic transition at T$_N$ = 7 K in the in-plane
direction, while the magnetic properties in the out-of-plane direction vastly
differ from bulk $\alpha$-RuCl$_3$. The macroscopic pellets of RuCl$_3$
therefore behave like a stack of monolayers without any symmetry relation in
the stacking direction. The deliberate introduction of turbostratic disorder to
manipulate the spin structure of RuCl$_3$ is of interest for research in
frustrated magnetism and complex magnetic order as predicted by the
Kitaev-Heisenberg model.",1603.04463v2
2016/6/29,Dynamic Elastic Moduli in Magnetic Gels: Normal Modes and Linear Response,"In the perspective of developing smart hybrid materials with customized
features, ferrogels and magnetorheological elastomers allow a synergy of
elasticity and magnetism. The interplay between elastic and magnetic properties
gives rise to a unique reversible control of the material behavior by applying
an external magnetic field. Albeit few works have been performed on the
time-dependent properties so far, understanding the dynamic behavior is the key
to model many practical situations, e.g. applications as vibration absorbers.
Here we present a way to calculate the frequency-dependent elastic moduli based
on the decomposition of the linear response to an external stress in normal
modes. We use a minimal three-dimensional dipole-spring model to theoretically
describe the magnetic and elastic interactions on the mesoscopic level.
Specifically, the magnetic particles carry permanent magnetic dipole moments
and are spatially arranged in a prescribed way, before they are linked by
elastic springs. An external magnetic field aligns the magnetic moments. On the
one hand, we study regular lattice-like particle arrangements to compare with
previous results in the literature. On the other hand, we calculate the dynamic
elastic moduli for irregular, more realistic particle distributions. Our
approach measures the tunability of the linear dynamic response as a function
of the particle arrangement, the system orientation with respect to the
external magnetic field, as well as the magnitude of the magnetic interaction
between the particles. The strength of the present approach is that it
explicitly connects the relaxational modes of the system with the rheological
properties as well as with the internal rearrangement of the particles in the
sample, providing new insight into the dynamics of these remarkable materials.",1606.09104v2
2019/12/10,Magnetic properties of thin epitaxial Pd$_{1-x}$Fe$_x$ alloy films,"In the paper we present the results of extensive studies of palladium-rich
Pd1-xFex alloy films epitaxially grown on MgO single-crystal substrate. In a
composition range of x = 0.01-0.07 these materials are soft ferromagnets, the
saturation magnetization and magnetic anisotropy of which can be tuned by its
composition. Vibrating sample magnetometry was used to study temperature
dependences of spontaneous magnetic moment and to establish the temperature of
magnetic ordering (Curie temperature). Ferromagnetic resonance (FMR)
measurements at low temperatures in the in-plane and out-of-plane geometries
revealed the four-fold in-plane magnetic anisotropy with the easy directions
along the <110> axes of the substrate. The modelling of the angular dependence
of the field for resonance allowed to extract the cubic and tetragonal
contributions to the magnetic anisotropy of the films and establish their
dependence on the concentration of iron in the alloy. Experimental data are
discussed in the framework of existing theories of dilute magnetic alloys.
Using the anisotropy constants established from FMR, the magnetic hysteresis
loops are reproduced utilizing the Stoner-Wohlfarth model thus indicating the
predominant coherent magnetic moment rotation at low temperatures. The obtained
results compile a database of magnetic properties of a palladium-iron alloy
considered as a material for superconducting spintronics.",1912.04852v1
2020/11/16,Magnetic Dynamic Polymers for Modular Assembling and Reconfigurable Morphing Architectures,"Shape morphing magnetic soft materials, composed of magnetic particles in a
soft polymer matrix, can transform shapes reversibly, remotely, and rapidly,
finding diverse applications in actuators, soft robotics, and biomedical
devices. To achieve on-demand and sophisticated shape morphing, the
manufacturing of structures with complex geometry and magnetization
distribution is highly desired. Here, we report a magnetic dynamic polymer
composite composed of hard-magnetic microparticles in a dynamic polymer network
with thermal-responsive reversible linkages, which permit functionalities
including targeted welding, magnetization reprogramming, and structural
reconfiguration. These functions not only provide highly desirable structural
and material programmability and reprogrammability but also enable the
manufacturing of structures with complex geometry and magnetization
distribution. The targeted welding is exploited for modular assembling of
fundamental building modules with specific logics for complex actuation. The
magnetization reprogramming enables altering the morphing mode of the
manufactured structures. The shape reconfiguration under magnetic actuation is
coupled with network plasticity to remotely transform two-dimensional
tessellations into complex three-dimensional architectures, providing a new
strategy of manufacturing functional soft architected materials such as
three-dimensional kirigami. We anticipate that the reported magnetic dynamic
polymer provides a new paradigm for the design and manufacturing of future
multifunctional assemblies and reconfigurable morphing architectures and
devices.",2011.07736v1
2021/2/4,Magnetic properties of nickel electrodeposited on porous GaN substrates with infiltrated and laminated connectivity,"We studied the magnetic properties of ferromagnetic-semiconductor composites
based on nickel and porous-GaN, motivated by the effort to couple magnetic and
semiconductor functionality. Nickel-infiltrated and nickel-coated (laminated
thin-film) porous GaN structures were fabricated by electrodeposition, and
their magnetic properties were subsequently examined collectively, by vibrating
sample magnetometry and on the nanoscale, by magnetic force microscopy. We
successfully demonstrated the ability to realize nickel infiltrated porous GaN,
where the magnetic properties were dominated by the infiltrated material
without a measurable surface contribution. We found that the structure and
magnetization of electrodeposited porous-GaN/Ni composites depended on GaN
degree of porosity and the amount of deposited nickel. The magnetization
evolves from a nearly isotropic response in the infiltrated structures, to a
shape-anisotropy controlled magnetic thin-film behaviour. Furthermore, both
infiltrated and thin-film nickel electrodeposited on porous GaN were found to
have low (< 0.1%) strain and corresponding low coercivity: < 6.4 and < 2.4 kA/m
for infiltrated and thin-film, correspondingly. The most likely cause for the
lowered strain is increased compliance of the porous GaN compared to bulk.
These results encourage deeper investigation of magnetic nanostructure property
tuning and of magnetic property coupling to GaN and similar materials.",2102.02904v4
2021/3/30,Magnetic Texture in Insulating Single Crystal High Entropy Oxide Spinel Films,"Magnetic insulators are important materials for a range of next generation
memory and spintronic applications. Structural constraints in this class of
devices generally require a clean heterointerface that allows effective
magnetic coupling between the insulating layer and the conducting layer.
However, there are relatively few examples of magnetic insulators which can be
synthesized with surface qualities that would allow these smooth interfaces and
precisely tuned interfacial magnetic exchange coupling which might be
applicable at room temperature. In this work, we demonstrate an example of how
the configurational complexity in the magnetic insulator layer can be used to
realize these properties. The entropy-assisted synthesis is used to create
single crystal (Mg0.2Ni0.2Fe0.2Co0.2Cu0.2)Fe2O4 films on substrates spanning a
range of strain states. These films show smooth surfaces, high resistivity, and
strong magnetic responses at room temperature. Local and global magnetic
measurements further demonstrate how strain can be used to manipulate magnetic
texture and anisotropy. These findings provide insight into how precise
magnetic responses can be designed using compositionally complex materials that
may find application in next generation magnetic devices.",2103.16722v1
2023/9/9,Intrinsic magnetic properties of the layered antiferromagnet CrSBr,"Van der Waals magnetic materials are an ideal platform to study
low-dimensional magnetism. Opposed to other members of this family, the
magnetic semiconductor CrSBr is highly resistant to degradation in air, which,
besides its exceptional optical, electronic, and magnetic properties, is the
reason the compound is receiving considerable attention at the moment. For many
years, its magnetic phase diagram seemed to be well-understood. Recently,
however, several groups observed a magnetic transition in magnetometry
measurements at temperatures of around 40 K that is not expected from
theoretical considerations, causing a debate about the intrinsic magnetic
properties of the material. In this letter, we report the absence of this
particular transition in magnetization measurements conducted on high-quality
CrSBr crystals, attesting to the extrinsic nature of the low-temperature
magnetic phase observed in other works. Our magnetometry results obtained from
large bulk crystals are in very good agreement with the magnetic phase diagram
of CrSBr previously predicted by the mean-field theory; A-type
antiferromagnetic order is the only phase observed below the N\'eel temperature
at TN = 131 K. Moreover, numerical fits based on the Curie-Weiss law confirm
that strong ferromagnetic correlations are present within individual layers
even at temperatures much larger than TN.",2309.04778v1
2024/1/10,Quantum magnetism in the frustrated square lattice oxyhalides YbBi2IO4 and YbBi2ClO4,"Square-lattice systems offer a direct route for realizing 2D quantum
magnetism with frustration induced by competing interactions. In this work, the
square-lattice materials YbBi2IO4 and YbBi2ClO4 were investigated using a
combination of magnetization and specific heat measurements on polycrystalline
samples. Specific heat measurements provide evidence for long-range magnetic
order below TN = 0.21 K (0.25 K) for YbBi2IO4 (YbBi2ClO4). On the other hand, a
rather broad maximum is found in the temperature-dependent magnetic
susceptibility, located at Tmax = 0.33 K (0.38 K) in YbBi2IO4 (YbBi2ClO4),
consistent with the quasi-2D magnetism expected for the large separation
between the magnetic layers. Estimation of the magnetic entropy supports the
expected Kramers' doublet ground state for Yb3+ and the observed paramagnetic
behavior is consistent with a well-isolated doublet. Roughly two-thirds of the
entropy is consumed above TN, due to a combination of the quasi-2D behavior and
magnetic frustration. The impact of frustration is examined from the viewpoint
of a simplified J1-J2 square lattice model, which is frustrated for
antiferromagnetic interactions. Specifically, a high-temperature series
expansion analysis of the temperature-dependent specific heat and magnetization
data yields J2/J1 = 0.30 (0.23) for YbBi2IO4 (YbBi2ClO4). This simplified
analysis suggests strong frustration that should promote significant quantum
fluctuations in these compounds, and thus motivates future work on the static
and dynamic magnetic properties of these materials.",2401.05283v1
2005/7/1,Resistivity memory effect in La(1-x)Sr(x)MnO(3),"During the study of magnetoresistivity in La(1-x)Ca(x)MnO(3) it was found
that after cycling of the magnetic field, some kind of magnetic field memory
effect was observed. For La0.5Ca0.5MnO3 after cycling of the magnetic field to
13T and back to zero, ""frozen"" magnetoresistivity decreases about 20 times
comparing to zero field value, while for La(0.47)Ca(0.53)MnO(3) it is already
about four orders of magnitude. This effect can be observed only for
concentration region 0.45 < x < 0.55. In zero magnetic field, temperature
dependence of resistivity ro(T) shows semiconducting-like behavior, while after
magnetic field cycling it becomes metal-like. So it looks as we are dealing
with magnetic field induced semiconductor (or dielectric) to metal transition.
Such effect can be explained within phase-separation picture. In zero magnetic
field material consists of antiferromagnetic matrix (insulating phase) and
coexisting ferromagnetic, conducting phase. Magnetic field application causes
ferromagnetic phase to form some kind of conducting channels which shunts
semiconducting matrix phase. Such structure is preserved after reduction of
magnetic field, leaving the material conducting.",0507018v2
2006/6/8,An ab-initio theory for the temperature dependence of magnetic anisotropy,"We present a first-principles theory of the variation of magnetic anisotropy,
K, with temperature, T, in metallic ferromagnets. It is based on relativistic
electronic structure theory and calculation of magnetic torque. Thermally
induced `local moment' magnetic fluctuations are described within the
relativistic generalisation of the `disordered local moment' (R-DLM) theory
from which the T dependence of the magnetisation, m, is found. We apply the
theory to a uniaxial magnetic material with tetragonal crystal symmetry,
L1_0-ordered FePd, and find its uniaxial K consistent with a magnetic easy axis
perpendicular to the Fe/Pd layers for all m and proportional to m squared for a
broad range of values of m. This is the same trend that we have previously
found in L1_0-ordered FePt and which agrees with experiment. This account,
however, differs qualitatively from that extracted from a single ion anisotropy
model. We also study the magnetically soft cubic magnet, the Fe(50)Pt(50) solid
solution, and find that its small magnetic anisotropy constant K_1 rapidly
diminishes from 8 micro-eV to zero. K evolves from being proportional to the
seventh power of m at low T to the fourth power near the Curie temperature.",0606219v1
2007/5/27,Influence of pulsed magnetic field on single- and two-pulse nuclear spin echoes in multidomain magnets,"By the method of additional pulsed magnetic field influence in different
magnetic materials (half metals, manganites, lithium ferrite, cobalt) it is
established the analogy of time diagrams of magnetic pulse influence on single-
and two pulse echoes in magnets when the distortion mechanism of single-pulse
echo formation is effective, and the absence of such analogy in the case of
lithium ferrite where the multipulse mechanism of single-pulse echo formation
is effective.
  It is shown also that the timing and frequency diagrams of magnetic pulse
influence on the two-pulse echo signals, corresponding to the symmetric and
asymmetric magnetic pulse applications in the studied magnets, are defined by
their domain walls parameters and could serve for their qualitative and
quantitative characterization.",0705.3979v1
2010/12/6,Magnetic and electronic properties of nitrogen-doped lanthanum sesquioxide La2O3 as predicted from first principles,"Using the ab initio FLAPW-GGA method we examine the electronic and magnetic
properties of nitrogen-doped non-magnetic sesquioxide La2O3 emphasizing the
role of doping sites in the occurrence of d0-magnetism. We predict the
magnetization of La2O3 induced by nitrogen impurity in both octahedral and
tetrahedral sites of the oxygen sublattice. The most interesting results are
that (i) the total magnetic moments (about 1 {\mu}B per supercells) are
independent of the doping site, whereas (ii) the electronic spectra of these
systems differ drastically: La2O3:N with six-fold coordinated nitrogen behaves
as a narrow-band-gap magnetic semiconductor, whereas with four-fold coordinated
nitrogen is predicted to be a magnetic half-metal. This effect is explained
taking into account the differences in N-2pz versus N-2px,y orbital splitting
for various doping sites. Thus, the type of the doping site is one of the
essential factors for designing of new d0-magnetic materials with promising
properties.",1012.1108v1
2011/7/28,Domain walls in helical magnets,"The structure of domain walls determines to a large extent the properties of
magnetic materials, in particular their hardness and switching behavior, it
represents an essential ingredient of spintronics. Common domain walls are of
Bloch and Neel types in which the magnetization rotates around a fixed axis,
giving rise to a one-dimensional magnetization profile. Domain walls in helical
magnets, most relevant in multiferroics, were never studied systematically.
Here we show that domain walls in helical magnets are fundamentally different
from Bloch and Neel walls. They are generically characterized by a
two-dimensional pattern formed by a regular lattice of vortex singularities. In
conical phases vortices carry Berry phase flux giving rise to the anomalous
Hall effect. In multiferroics vortices are charged, allowing to manipulate
magnetic domain walls by electric fields. Our theory allows the interpretation
of magnetic textures observed in helical magnetic structures.",1107.5753v2
2013/3/6,Change in the Magnetic Domain Alignment Process at the Onset of a Frustrated Magnetic State in Ferrimagnetic La2Ni(Ni1/3Sb2/3)O6 Double Perovskite,"We have performed a combined study of magnetization hysteresis loops and time
dependence of the magnetization in a broad temperature range for the
ferrimagnetic La2Ni(Ni1/3Sb2/3)O6 double perovskite. This material has a
ferrimagnetic order transition at ~100 K and at lower temperatures (~ 20 K)
shows the signature of a frustrated state due to the presence of two competing
magnetic exchange interactions. The temperature dependence of the coercive
field shows an important upturn below the point where the frustrated state sets
in. The use of the magnetization vs. applied magnetic field hysteresis data,
together with the magnetization vs. time data provides a unique opportunity to
distinguish between different scenarios for the low temperature regime. From
our analysis, a strong domain wall pinning results the best scenario for the
low temperature regime. For temperatures larger than 20K the adequate scenario
seems to correspond to a weak domain wall pinning.",1303.1372v1
2013/7/27,Formation of metallic magnetic clusters in a Kondo-lattice metal: Evidence from an optical study,"Magnetic materials are usually divided into two classes: those with localised
magnetic moments, and those with itinerant charge carriers. We present a
comprehensive experimental (spectroscopic ellipsomerty) and theoretical study
to demonstrate that these two types of magnetism do not only coexist but
complement each other in the Kondo-lattice metal, Tb2PdSi3. In this material
the itinerant charge carriers interact with large localised magnetic moments of
Tb(4f) states, forming complex magnetic lattices at low temperatures, which we
associate with self-organisation of magnetic clusters. The formation of
magnetic clusters results in low-energy optical spectral weight shifts, which
correspond to opening of the pseudogap in the conduction band of the itinerant
charge carriers and development of the low- and high-spin intersite electronic
transitions. This phenomenon, driven by self-trapping of electrons by magnetic
fluctuations, could be common in correlated metals, including besides
Kondo-lattice metals, Fe-based and cuprate superconductors.",1307.7243v1
2014/8/1,Unconventional magnetic order on the hyperhoneycomb Kitaev lattice in $β$-Li2IrO3: full solution via magnetic resonant x-ray diffraction,"The recently-synthesized iridate $\beta$-Li$_2$IrO$_3$ has been proposed as a
candidate to display novel magnetic behavior stabilized by frustration effects
from bond-dependent, anisotropic interactions (Kitaev model) on a
three-dimensional ""hyperhoneycomb"" lattice. Here we report a combined study
using neutron powder diffraction and magnetic resonant x-ray diffraction to
solve the complete magnetic structure. We find a complex, incommensurate
magnetic order with non-coplanar and counter-rotating Ir moments, which
surprisingly shares many of its features with the related structural polytype
""stripyhoneycomb"" $\gamma$-Li$_2$IrO$_3$, where dominant Kitaev interactions
have been invoked to explain the stability of the observed magnetic structure.
The similarities of behavior between those two structural polytypes, which have
different global lattice topologies but the same local connectivity, is
strongly suggestive that the same magnetic interactions and the same underlying
mechanism governs the stability of the magnetic order in both materials,
indicating that both $\beta$- and $\gamma$-Li$_2$IrO$_3$ are strong candidates
to realize dominant Kitaev interactions in a solid state material.",1408.0246v1
2015/1/5,Interfacial deformation and jetting of a magnetic fluid,"An attractive technique for forming and collecting aggregates of magnetic
material at a liquid--air interface by an applied magnetic field gradient was
recently addressed theoretically and experimentally [Soft Matter, (9) 2013,
8600-8608]: when the magnetic field is weak, the deflection of the liquid--air
interface has a steady shape, while for sufficiently strong fields, the
interface destabilizes and forms a jet that extracts magnetic material.
Motivated by this work, we develop a numerical model for the closely related
problem of solving two-phase Navier--Stokes equations coupled with the static
Maxwell equations. We computationally model the forces generated by a magnetic
field gradient produced by a permanent magnet and so determine the interfacial
deflection of a magnetic fluid (a pure ferrofluid system) and the transition
into a jet. We analyze the shape of the liquid--air interface during the
deformation stage and the critical magnet distance for which the static
interface transitions into a jet. We draw conclusions on the ability of our
numerical model to predict the large interfacial deformation and the consequent
jetting, free of any fitting parameter.",1501.01000v1
2015/11/24,Magnetic domain walls in nanostrips of single-crystalline $\mathrm{Fe}_4\mathrm{N}(001)$ thin films with fourfold in-plane magnetic anisotropy,"We investigated head-to-head domain walls in nanostrips of epitaxial
$\mathrm{Fe}_4\mathrm{N}(001)$ thin films, displaying a fourfold magnetic
anisotropy. Magnetic force microscopy and micromagnetic simulations show that
the domain walls have specific properties, compared to soft magnetic materials.
In particular, strips aligned along a hard axis of magnetization are wrapped by
partial flux-closure concertina domains below a critical width, while
progressively transforming to zigzag walls for wider strips. Transverse walls
are favored upon initial application of a magnetic field transverse to the
strip, while transformation to a vortex walls is favored upon motion under a
longitudinal magnetic field. In all cases the magnetization texture of such
fourfold anisotropy domain walls exhibits narrow micro-domain walls, which may
give rise to peculiar spin-transfer features.",1511.07520v1
2017/2/7,Topology Optimized and 3D Printed Polymer Bonded Permanent Magnets for a Predefined External Field,"Topology optimization offers great opportunities to design permanent magnetic
systems that have specific external field characteristics. Additive
manufacturing of polymer bonded magnets with an end-user 3D printer can be used
to manufacture permanent magnets with structures that have been difficult or
impossible to manufacture previously. This work combines these two powerful
methods to design and manufacture permanent magnetic system with specific
properties. The topology optimization framework is simple, fast, and accurate.
It can be also used for reverse engineering of permanent magnets in order to
find the topology from field measurements. Furthermore, a magnetic system that
generate a linear external field above the magnet is presented. With a volume
constraint the amount of magnetic material can be minimized without losing
performance. Simulations and measurements of the printed system show a very
good agreement.",1702.01968v1
2017/8/23,Spin-orbit torques induced by interface-generated spin currents,"Magnetic torques generated through spin-orbit coupling promise
energy-efficient spintronic devices. It is important for applications to
control these torques so that they switch films with perpendicular
magnetizations without an external magnetic field. One suggested approach uses
magnetic trilayers in which the torque on the top magnetic layer can be
manipulated by changing the magnetization of the bottom layer. Spin currents
generated in the bottom magnetic layer or its interfaces transit the spacer
layer and exert a torque on the top magnetization. Here we demonstrate
field-free switching in such structures and attribute it to a novel spin
current generated at the interface between the bottom layer and the spacer
layer. The measured torque has a distinct dependence on the bottom layer
magnetization which is consistent with this interface-generated spin current
but not the anticipated bulk effects. This other interface-generated spin-orbit
torque will enable energy-efficient control of spintronic devices.",1708.06864v1
2019/8/13,Converting Faraday rotation into magnetization in europium chalcogenides,"We present a simple semiclassical model to sustain that in europium
chalcogenides (EuX), Faraday rotation (FR) in the transparency gap is
proportional to the magnetization of the sample, irrespective of the material's
magnetic phase, temperature, or applied magnetic field. The model is validated
by FR and magnetization measurements in EuSe in the temperature interval
1.7-300K, covering all EuSe magnetic phases (paramagnetic, antiferromagnetic
type I or type II, ferrimagnetic and ferromagnetic). Furthermore, by combining
the semiclassical model with the explicit electronic energy structure of EuX,
the proportionality coefficient between magnetization and FR is shown to be
dependent only on the wavelength and the band gap. Due to its simplicity, the
model has didactic value, moreover, it provides a working tool for converting
FR into magnetization in EuX. Possible extension of the model to other
intrinsic magnetic semiconductors is discussed.",1908.04444v1
2019/8/14,"Rivalry of diffusion, external field and gravity in micro-convection of magnetic colloids","Magnetic fields and magnetic materials have promising microfluidic
applications. For example, magnetic micro-convection can enhance mixing
considerably. However, previous studies have not explained increased effective
diffusion during this phenomenon. Here we show that enhanced interface smearing
comes from a gravity induced convective motion within a thin microfluidic
channel, caused by a small density difference between miscible magnetic and
non-magnetic fluids. This motion resembles diffusive behavior and can be
described with an effective diffusion coefficient. We explain this with a
theoretical model, based on a dimensionless gravitational Rayleigh number, and
verify it by numerical simulations and experiments with different cell
thicknesses. Results indicate the applicability and limitations for
microfluidic applications of other colloidal systems. Residual magnetic
micro-convection follows earlier predictions.",1908.05011v2
2016/3/11,High Resolution Hard X-ray Magnetic Imaging with Dichroic Ptychography,"Imaging the magnetic structure of a material is essential to understanding
the influence of the physical and chemical microstructure on its magnetic
properties. Magnetic imaging techniques, however, have up to now been unable to
probe 3D micrometer-sized systems with nanoscale resolution. Here we present
the imaging of the magnetic domain configuration of a micrometre-thick FeGd
multilayer with hard X-ray dichroic ptychography at energies spanning both the
Gd L3 edge and the Fe K edge, providing a high spatial resolution spectroscopic
analysis of the complex X-ray magnetic circular dichroism. With a spatial
resolution reaching 45 nm, this advance in hard X-ray magnetic imaging is the
first step towards the investigation of buried magnetic structures and extended
three-dimensional magnetic systems at the nanoscale.",1603.03588v3
2016/3/27,High resolution Kerr microscopy study of exchange bias phenomena in FePt/Fe exchange spring magnets,"Magnetization and magnetic microstructure of top soft magnetic layer (Fe),
which is exchange spring coupled to bottom hard magnetic layer ($L1_0$ FePt) is
studied using high resolution Kerr microscopy. When the sample (FePt/Fe) is at
remanent condition of hard magnetic layer, considerable shifting of Fe layer
hysteresis loop from centre i.e., exchange bias phenomena is observed. It is
observed that one can tune the magnitude of exchange bias shift by reaching the
remanent state from different saturating fields ($H_{SAT}$) and also by varying
the angle between measuring field and $H_{SAT}$. The M-H loops and domain
images of top soft Fe layer demonstrates unambiguously that soft magnetic layer
at remanent state in such exchange coupled system is having unidirectional
anisotropy. An analogy is drawn and the observations are explained in terms of
the mostly accepted models of exchange bias phenomena exhibited by bilayers
consisting of ferromagnetic(FM) and anti-ferromagnetic (AFM) layers, when the
AFM layer is field cooled across $N\acute{e}el$ transition temperature.",1603.08164v1
2019/8/31,Magnetocaloric properties of V6 molecular magnet,"The paper presents a theoretical study of magnetocaloric properties of
polyoxovanadate molecular magnet V6 containing 6 vanadium ions carrying quantum
spins $S = 1/2$. The characteristic property of such structure is the presence
of two weakly interacting spin triangles with all-antiferromagnetic couplings.
The properties of the system are described using the exact numerical
diagonalization approach applied to the quantum Heisenberg model and utilizing
a field ensemble formalism. The dependence of the magnetic entropy and magnetic
specific heat on the temperature and external magnetic field is calculated and
extensively discussed. The magnetocaloric properties are quantified by
isothermal entropy change and entropy derivative over the magnetic field. An
interesting behaviour of isothermal entropy change is found, with high degree
of tunability of the magnetocaloric effect with the initial and final magnetic
field values.",1909.00242v2
2019/9/2,Performances of a Compact Shielded Superconducting Magnet for Continuous Nuclear Demagnetization Refrigerator,"We have successfully developed and tested a compact shielded superconducting
(SSC) magnet with a FeCoV magnetic shield. This was developed for the PrNi$_5$
based nuclear demagnetization refrigerator which can keep temperatures below 1
mK continuously (CNDR) [Toda $\it{et~al}$., J. Phys.: Conf. Ser. $\bf{969}$,
012093 (2018)]. The clear bore diameter, outer diameter, and total length of
the SSC magnet are 22, 42 and 169 mm, respectively, and it produces the maximum
field of 1.38 T at an electric current of 6 A. In order to realize both the
compactness and the high shielding performance, we carefully chose material and
optimized design of the magnetic shield by numerical simulations of the field
distribution based on measured magnetization curves of several candidate
materials with high permeability. We also measured a heat generated by sweeping
the SSC magnet in vacuum to be 230 mJ per field cycle. This value agrees very
well with an estimation from the measured magnetic hysteresis of the
superconducting wire used to wind the magnet.",1909.00567v1
2019/9/28,Size-Dependent Structural and Magnetic Properties of Disordered Co2FeAl Heusler Alloy Nanoparticles,"Co2FeAl (CFA) nanoparticles (NPs) of different sizes were synthesized by
chemical route. The effect of the size of NPs upon the structure and
magnetization compared to its bulk counterpart was investigated. The structure
and composition were determined from X-ray diffraction (XRD) and electron
microscopy. XRD analysis shows that the samples are having single (A2-type)
disordered phase. Magnetization measurements suggest that the samples are soft
ferromagnetic in nature with very low coercivity. Enhanced magnetic properties
like saturation magnetization, coercive force, retentivity, and
Curie-temperature are observed with a decrease in particle size. The effect of
particle size on hysteresis losses is also discussed. The smallest particles of
size 16 nm exhibited the highest saturation magnetization and transition
temperature of 180.73 emu/g and 1261 K, respectively. The origin of enhancement
in the magnetization of Co2FeAl nano-alloy is attributed to the strong Co-Co
exchange interaction due to disorder present in the systems.",1909.13088v1
2019/10/25,Local magnetic anisotropy by polarized neutron powder diffraction: application of magnetically induced preferred crystallite orientation,"Polarized neutron diffraction allows to determine the local susceptibility
tensor on the magnetic site both in single crystals and powders. It is widely
used in the studies of single crystals, but it is still hardly applicable to a
number of highly interesting powder materials, like molecular magnets or
nanoscale systems because of the low luminosity of existing instruments and the
absence of an appropriate data analysis software. We show that these
difficulties can be overcome by using a large area detector in combination with
the two-dimensional Rietveld method and powder samples with magnetically
induced preferred crystallite orientation. This is demonstrated by revisiting
two test powder compounds, namely, low anisotropy (soft) ferrimagnetic compound
Fe3O4 and spin-ice compound Ho2Ti2O7 with high local anisotropy. The values of
magnetic moments in Fe3O4 and the susceptibility tensors of Ho2Ti2O7 at various
temperatures and fields were found in perfect agreement with these found
earlier in single crystal experiments. The magnetically induced preferred
crystallite orientation was used to study the local susceptibility of a
single-molecule magnet Co([(CH3)2N]2CS)2Cl2. Hence, the studies of local
magnetic anisotropy in powder systems might now become accessible.",1910.11822v1
2020/3/26,Spin textures in chiral magnetic monolayers with suppressed nearest-neighbor exchange,"High tunability of two dimensional magnetic materials (by strain, gating,
heterostructuring or otherwise) provides unique conditions for studying
versatile magnetic properties and controlling emergent magnetic phases.
Expanding the scope of achievable magnetic phenomena in such materials is
important for both fundamental and technological advances. Here we perform
atomistic spin-dynamics simulations to explore the (chiral) magnetic phases of
atomic monolayers in the limit of suppressed first-neighbors exchange
interaction. We report the rich phase diagram of exotic magnetic
configurations, obtained for both square and honeycomb lattice symmetries,
comprising coexistence of ferromagnetic and antiferromagnetic spin-cycloids, as
well as multiple types of magnetic skyrmions. We perform a minimum-energy path
analysis for the skyrmion collapse to evaluate the stability of such
topological objects, and reveal that magnetic monolayers could be good
candidates to host the antiferromagnetic skyrmions that are experimentally
evasive to date.",2003.11933v1
2020/8/31,Benchmark for Ab Initio Prediction of Magnetic Structures based on Cluster-Multipole Theory,"The cluster multipole (CMP) expansion for magnetic structures provides a
scheme to systematically generate candidate magnetic structures specifically
including noncollinear magnetic configurations adapted to the crystal symmetry
of a given material. A comparison with the experimental data collected on
MAGNDATA shows that the most stable magnetic configurations in nature are
linear combinations of only few CMPs. Furthermore, a high-throughput
calculation for all candidate magnetic structures is performed in the framework
of spin-density functional theory (SDFT). We benchmark the predictive power of
CMP+SDFT with $2935$ calculations, which show that (i) the CMP expansion
administers an exhaustive list of candidate magnetic structures, (ii) CMP+SDFT
can narrow down the possible magnetic configurations to a handful of computed
configurations, and (iii) SDFT reproduces the experimental magnetic
configurations with an accuracy of $\pm0.5\,\mu_\text{B}$. For a subset the
impact of on-site Coulomb repulsion $U$ is investigated by means of $1545$
CMP+SDFT+U calculations revealing no further improvement on the predictive
power.",2008.13669v2
2021/4/13,Crystallographic and magnetic structure of UNi$_4$$^{11}$B,"We present an extensive powder and single-crystal neutron scattering
investigation of the crystallographic structure and magnetic order of the
frustrated metallic $f$-electron magnet UNi$_4$B. We carry out a full
refinement of the crystallographic structure and conclude that the
low-temperature lattice symmetry is orthorhombic (space group Pmm2; cell
parameters: $a = 6.963(4)~\r{A}$ , $b = 14.793(9)~\r{A}$ , $c =
17.126(8)~\r{A}$). We determine the magnetically ordered structure, concluding
that below $T_\mathrm{N} = 19.5~\mathrm{K}$ the material undergoes a transition
into a partially ordered antiferromagnetic state. The magnetic structure is
consistent with the existence of toroidal order in this material. We further
test the proposal of a second magnetic transition occurring at
$330~\mathrm{mK}$, concluding that the thermodynamic anomalies observed at
these temperatures do not reflect modifications of the magnetic structure. Our
study provides a consistent picture of the interrelationship of structural and
magnetic properties in the frustrated magnet UNi$_4$B previously unresolved.",2104.06119v2
2021/5/4,Magnetic properties and magnetocaloric effect of $\mathrm{Tb_2Rh_3Ge}$,"We report the structural, magnetic properties, and magnetocaloric effect of a
new polycrystalline compound of $\mathrm{Tb_2Rh_3Ge}$. This present compound
crystallizes with $\mathrm{Mg_2Ni_3Si}$-type of rhombohedral Laves phases
(space group $R\overline{3}m$, hR18). The magnetic properties and
magnetocaloric effect of the $\mathrm{Tb_2Rh_3Ge}$ is explored through
dc-magnetization measurements. Temperature dependence of magnetization revealed
that the compound exhibits ferromagnetic behavior with $T_C$$=$56 K. The field
dependence of magnetization indicates that $\mathrm{Tb_2Rh_3Ge}$ is a soft
ferromagnet. The obtained isothermal magnetic entropy changes ($\Delta S_m$),
and refrigeration capacity (relative power cooling) for a change of magnetic
field 0-9 T are 12.74 J/kg-K, and 497(680) J/kg respectively. The Arrott plots
and universal curve of normalized $\Delta S_m$ indicate that this compound
undergoes second order ferromagnetic phase transition",2105.01364v2
2016/6/12,Electromagnetic signatures of the chiral anomaly in Weyl semimetals,"Weyl semimetals are predicted to realize the three-dimensional axial anomaly
first discussed in particle physics. The anomaly leads to unusual transport
phenomena such as the chiral magnetic effect in which an applied magnetic field
induces a current parallel to the field. Here we investigate diagnostics of the
axial anomaly based on the fundamental equations of axion electrodynamics. We
find that materials with Weyl nodes of opposite chirality and finite energy
separation immersed in a uniform magnetic field exhibit an anomaly-induced
oscillatory magnetic field with a period set by the chemical potential
difference of the nodes. In the case where a chemical potential imbalance is
created by applying parallel electric and magnetic fields, we find a
suppression of the magnetic field component parallel to the electric field
inside the material for rectangular samples, suggesting that the chiral
magnetic current opposes this imbalance. For cylindrical geometries, we instead
find an enhancement of this magnetic field component along with an
anomaly-induced azimuthal component. We propose experiments to detect such
magnetic signatures of the axial anomaly.",1606.03739v2
2018/1/30,Circumventing Magnetic Reciprocity: a Diode for Magnetic Fields,"Lorentz reciprocity establishes a stringent relation between electromagnetic
fields and their sources. For static magnetic fields, a relation between
magnetic sources and fields can be drawn in analogy to the Green's reciprocity
principle for electrostatics. Here we theoretically and experimentally show
that a linear and isotropic electrically conductive material moving with
constant velocity is able to circumvent the magnetic reciprocity principle and
realize a diode for magnetic fields. This result is demonstrated by measuring
an extremely asymmetric magnetic coupling between two coils that are located
near a moving conductor. The possibility to generate controlled unidirectional
magnetic couplings breaks down one of the most deeply-established relations in
classical electromagnetism, namely that mutual inductances are symmetric. This
result might provide novel possibilities for applications and technologies
based on magnetically coupled elements.",1802.00832v3
2018/2/24,Non-saturating Quantum Magnetization in Weyl semimetal TaAs,"Detecting the spectroscopic signatures of Dirac-like quasiparticles in
emergent topological materials is crucial for searching their potential
applications. Magnetometry is a powerful tool for fathoming electrons in
solids, yet its ability for discerning Dirac-like quasiparticles has not been
recognized. Adopting the probes of magnetic torque and parallel magnetization
for the archetype Weyl semimetal TaAs in strong magnetic field, we observed a
quasi-linear field dependent effective transverse magnetization and a strongly
enhanced parallel magnetization when the system is in the quantum limit.
Distinct from the saturating magnetic responses for massive carriers, the
non-saturating signals of TaAs in strong field is consistent with our newly
developed magnetization calculation for a Weyl fermion system in an arbitrary
angle. Our results for the first time establish a thermodynamic criterion for
detecting the unique magnetic response of 3D massless Weyl fermions in the
quantum limit.",1802.08801v1
2019/4/24,Ultra-low-power orbital-controlled magnetization switching using a ferromagnetic oxide interface,"A major challenge in spin-based electronics is reducing power consumption for
magnetization switching of ferromagnets, which is being implemented by
injecting a large spin-polarized current. The alternative approach is to
control the magnetic anisotropy (MA) of the ferromagnet by an electric field.
However, the voltage-induced MA is too weak to deterministically switch the
magnetization without an assisting magnetic field, and the strategy towards
this goal remains elusive. Here, we demonstrate a new scheme of
orbital-controlled magnetization switching (OCMS): A sharp change in the MA is
induced when the Fermi level is moved between energy bands with different
orbital symmetries. Using a ferromagnetic oxide interface, we show that OCMS
can be used to achieve a deterministic and magnetic-field-free 90
degree-magnetization switching solely by applying an extremely small electric
field of 0.05 V/nm with a negligibly small current density of 10^-2 A/cm^2. Our
results highlight the huge potential of band engineering in ferromagnetic
materials for efficient magnetization control.",1904.10599v1
2020/6/22,Magnetic structure and exchange interactions in the layered semiconductor CrPS4,"Compounds with two-dimensional (2D) layers of magnetic ions weakly connected
by van der Waals bonding offer routes to enhance quantum behavior, stimulating
both fundamental and applied interest. CrPS4 is one such magnetic van der Waals
material, however, it has undergone only limited investigation. Here we present
a comprehensive series of neutron scattering measurements to determine the
magnetic structure and exchange interactions. The observed magnetic excitations
allow a high degree of constraint on the model parameters not normally
associated with measurements on a powder sample. The results demonstrate the 2D
nature of the magnetic interactions, while also revealing the importance of
interactions along 1D chains within the layers. The subtle role of competing
interactions is observed, which manifest in a non-trivial magnetic transition
and a tunable magnetic structure in a small applied magnetic field through a
spin-flop transition. Our results on the bulk compound provide insights that
can be applied to an understanding of the behavior of reduced layer CrPS4.",2006.12539v1
2020/7/15,Magnetic Charge Propagation upon a 3D Artificial Spin-ice,"Magnetic charge propagation in bulk frustrated materials has yielded a
paradigm-shift in science, allowing the symmetry between electricity and
magnetism to be studied. Recent work is now suggesting magnetic charge dynamics
upon the spin-ice surface may have important implications in determining the
ordering and associated phase space. Here we detail a 3D artificial spin-ice, a
3D nanostructured array of magnetic islands which captures the exact geometry
of bulk systems, allowing field-driven dynamics of magnetic charge to be
directly visualized upon the surface. Using magnetic microscopy, we observe
vastly different magnetic charge dynamics along two principle directions. These
striking differences are found to be due to the surface-termination and
associated coordination which yields different energetics and interaction
strengths for magnetic charges upon the surface.",2007.07618v2
2021/8/11,Enhancement of in-plane anisotropy in MoS2/CoFeB bilayers,"Transition metal dichalcogenides (TMD) possess novel properties which makes
them potential candidates for various spintronic applications. Heterostructures
of TMD with magnetic thin film have been extensively considered for
spin-orbital torque, enhancement of perpendicular magnetic anisotropy etc.
However, the effect of TMD on magnetic anisotropy in heterostructures of
in-plane magnetization has not been studied so far. Further the effect of the
TMD on the domain structure and magnetization reversal of the ferromagnetic
system is another important aspect to be understood. In this context we study
the effect of MoS2, a well-studied TMD material, on magnetic properties of
CoFeB in MoS2/CoFeB heterostructures. The reference CoFeB film possess a weak
in-plane anisotropy. However, when the CoFeB is deposited on MoS2 the in-plane
anisotropy is enhanced as observed from magneto optic Kerr effect (MOKE)
microscopy as well as ferromagnetic resonance (FMR). Magnetic domain structure
and magnetization reversal have also been significantly modified for the
MoS2/CoFeB bilayer as compared to the reference CoFeB layer. Frequency and
angle dependent FMR measurement show that the magnetic anisotropy of CoFeB
increases with increase in thickness of MoS2 in the MoS2/CoFeB
heterostructures.",2108.05130v1
2021/9/15,Magnetic Compton profile in non-magnetic ferroelectrics,"Magnetic Compton scattering is an established tool for probing magnetism in
ferromagnetic or ferrimagnetic materials with a net spin polarization. Here we
show that, counterintuitively, {\it non-magnetic} systems can also have a
non-zero magnetic Compton profile, provided that space-inversion symmetry is
broken. The magnetic Compton profile is antisymmetric in momentum and, if the
inversion symmetry is broken by an electric-field switchable ferroelectric
distortion, can be reversed using an electric field. We show that the
underlying physics of the magnetic Compton profile and its electrical control
are conveniently described in terms of $k$-space magnetoelectric multipoles,
which are reciprocal to the real-space charge dipoles associated with the
broken inversion symmetry. Using the prototypical ferroelectric lead titanate,
PbTiO$_3$, as an example, we show that the ferroelectric polarization
introduces a spin asymmetry in momentum space that corresponds to a pure
$k$-space magnetoelectric toroidal moment. This in turn manifests in an
antisymmetric magnetic Compton profile which can be reversed using an electric
field. Our work suggests an experimental route to directly measuring and tuning
hidden $k$-space magnetoelectric multipoles via their magnetic Compton profile.",2109.07315v1
2021/11/6,Phase transition in the 5d1 double perovskite Ba2CaReO6 induced by high magnetic field,"Magnetic properties of an antiferromagnetic double perovskite oxide
Ba2CaReO6, where Re6+ (5d1) ions with large spin-orbit coupling are arranged on
the face-centered-cubic lattice, are investigated using pulsed high magnetic
field up to 66 T. Magnetization and magnetostriction measurements have revealed
a magnetic field induced phase transition at around 50 T. The phase transition
accompanies a jump of magnetization and longitudinal magnetostriction of
approximately 2 10^(-4) with the change of power law behavior, indicating
sizable coupling between the electronic degrees of freedom and the lattice. The
high field phase exhibits a magnetic moment approximately 0.2 {\mu}B, which is
close to the values observed in 5d1 double perovskite oxides with non-collinear
magnetic structure. We argue that Ba2CaReO6 is an antiferromagnet that sits
close to the phase boundary between the collinear and non-collinear phases,
providing the target material for investigating the interplay between
spin-orbital entangled electrons and magnetic field.",2111.03807v1
2021/11/28,Liquid-metal/NdFeB/Sillicone Composite Elastomer with Reprogrammable Magnetization and Modulus,"Magnetic programming soft machines has great development prospects in the
fields of minimally invasive medicine, wearable device and soft robot. However,
unrepeatable magnetization and low modulus limits their applications. So far,
there are few techniques that can make magnetic soft robots have adjustable
functions, mechanical and electrical properties. This paper presented a
magnetic functional elastomer based on liquid metal-NdFeB-Silicone composite
materials. This magnetoelastomer uses the phase transition characteristics of
liquid-metal and magnetic guided rotation of micro ferromagnetic particles to
realize reprogrammable magnetization and modulus. The elastomer's fabrication
method was given and the basic programmable properties were tested. Some robot
prototypes have also been manufactured to show how to respond to different
mission requirements by programming magnetization and modulus. Our research
provides a new path for the design and large-scale manufacturing of magnetic
soft robot.",2111.14170v1
2022/2/15,Optically-induced magnetization switching in NiCo2O4 thin films using ultrafast lasers,"Recently, all-optical magnetization control has been garnering considerable
attention in realizing next-generation ultrafast magnetic information devices.
Here, employing a magneto-optical Kerr effect (MOKE) microscope, we observed
the laser-induced magnetization switching of ferrimagnetic oxide NiCo2O4 (NCO)
epitaxial thin films with perpendicular magnetic anisotropy, where the sample
was pumped at 1030-nm laser pulses, and magnetic domain images were acquired
via the MOKE microscope with a white light emitting diode. Laser pulses
irradiated an NCO thin film at various temperatures from 300 K to 400 K while
altering the parameters of pulse interval, fluence, and the number of pulses
with the absence of the external magnetic field. We observed accumulative
all-optical switching at 380 K and above. Our observation of oxide NCO thin
films facilitates the realization of chemically stable magnetization switching
using ultrafast lasers, and without applying a magnetic field.",2202.07257v1
2022/2/18,Modulated non-collinear magnetic structure of (Co$_{0.97}$$^{57}$Fe$_{0.03}$)$_{4}$Nb$_{2}$O$_{9}$ as revealed by Mössbauer spectroscopy,"In this work, we present detailed $^{57}$Fe M\""ossbauer spectroscopy
investigations of (Co$_{0.97}$$^{57}$Fe$_{0.03}$)$_{4}$Nb$_{2}$O$_{9}$ compound
to study its possible magnetic structures. We have shown that the previously
reported magnetic structures can not satisfactorily describe our low
temperature M\""ossbauer spectra. Therefore, in combination with theoretical
calculations, we have proposed a modulated helicoidal magnetic structure that
can be used to simulate the whole series of our low temperature M\""ossbauer
spectra. Our results suggest that the combination of previously reported
different magnetic structures are only approximations of the average magnetic
structure from our modulated helicoidal model. We anticipate that the proposed
modulated non-collinear magnetic structure might shed light on the
understanding of the complex magnetoelectric effects observed in this system.",2202.09012v2
2022/5/11,Violation of the Rule of Parsimony: Mixed Local Moment and Itinerant Fe Magnetism in Fe$_{3}$GeN,"Ternary iron nitrides are of considerable interest due to their diverse
magnetic properties. We find, based on first principles calculations, that the
relatively minor structural distortion from the cubic antiperovskite structure
in Fe$_3$GeN leads to unusual magnetic behavior. In particular, there is a
separation into Fe sites with very different magnetic behaviors, specifically a
site with Fe atoms having a stable local moment and a site where the Fe shows
characteristics of much more itinerant behavior. This shows a remarkable
flexibility of the Fe magnetic behavior in these nitrides and points towards
the possibility of systems where minor structural and chemical changes can lead
to dramatic changes in magnetic properties. The results suggest that,
analogously to oxide perovskite materials, modulation of magnetic properties
via chemical or strain control of octahedral rotation may be feasible. This may
then lead to approaches for tuning magnetism to realize properties of interest,
for example tuning magnetic transitions to quantum critical regimes or to
proximity to metamagnetic transitions of interest for devices.",2205.05506v2
2022/8/8,"Magnetic, thermal, and magnetocaloric properties of the holmium trialuminide HoAl$_{3}$ with polytypic phases","We investigate the magnetic, thermal, and magnetocaloric properties of the
intermetallic HoAl$_{3}$ compounds with two different crystal structures. The
room-temperature equilibrium trigonal phase HoAl$_{3}$ undergoes an
antiferromagnetic (AFM) transition at the Neel temperature $T^{\rm tri}_{\rm N}
=$ 9.8 K. The AFM ordering of the compound is strong against the magnetic
field, so that inverse magnetocaloric effect (MCE) is found even under a
magnetic field change of 0-50 kOe. The high-pressure cubic phase HoAl3,
prepared by a rapid-solidification process, is antiferromagnetically ordered
below $T^{\rm cub}_{\rm N} =$ 15 K. Magnetic and specific heat measurements
reveal that this long-range AFM state becomes unstable as the temperature drops
and then it is replaced by a magnetic glassy state below a spin freezing
temperature $T_{\rm f} =$ 11 K. The successive changes in magnetic state result
in complicated temperature and field dependence of the MCE at low temperatures.",2208.04027v1
2022/10/11,New Gd-based magnetic compound GdPt$_2$B with a chiral crystal structure,"Herein, we report the discovery of a novel Gd-based magnetic compound
GdPt$_2$B with a chiral crystal structure. X-ray diffraction and chemical
composition analyses reveal a CePt$_2$B-type crystal structure (space group:
$P6_422$) for GdPt$_2$B. Moreover, we successfully grew single crystals of
GdPt$_2$B using the Czochralski method. Magnetization measurements and the
Curie$-$Weiss analysis demonstrate that the ferromagnetic interaction is
dominant in GdPt$_2$B. A clear transition is observed in the temperature
dependence of electrical resistivity, magnetic susceptibility, and specific
heat at $T_{\rm O}$ = 87 K. The magnetic phase diagram of GdPt$_2$B, which
consists of a field-polarized ferromagnetic region and a magnetically ordered
region, resembles those of known chiral helimagnets. Furthermore, magnetic
susceptibility measurements reveal a possible spin reorientation within the
magnetically ordered phase in magnetic fields perpendicular to the screw axis.
The results demonstrate that GdPt$_2$B is a suitable platform for investigating
the competing effects of ferromagnetic and antisymmetric exchange interactions
in rare-earth-based chiral compounds.",2210.05099v1
2023/1/13,Multistep magnetization switching in orthogonally twisted ferromagnetic monolayers,"The advent of twist-engineering in two-dimensional (2D) crystals enables the
design of van der Waals (vdW) heterostructures exhibiting emergent properties.
In the case of magnets, this approach can afford artificial antiferromagnets
with tailored spin arrangements. Here, we fabricate an orthogonally-twisted
bilayer by twisting 90 degrees two CrSBr ferromagnetic monolayers with an
easy-axis in-plane anisotropy. The magneto-transport properties reveal
multistep magnetization switching with a magnetic hysteresis opening, that is
absent in the pristine case. By tuning the magnetic field, we modulate the
remanent state and coercivity and select between hysteretic and non-hysteretic
magneto-resistance scenarios. This complexity pinpoints spin anisotropy as a
key aspect in twisted magnetic superlattices. Our results highlight the control
over the magnetic properties in vdW heterostructures, leading to a variety of
field-induced phenomena and opening a fruitful playground for creating desired
magnetic symmetries and manipulating non-collinear magnetic configurations.",2301.05647v2
2023/4/4,Topological Surface Magnetism and Neel Vector Control in a Magnetoelectric Antiferromagnet,"Antiferromagnetic states with no stray magnetic fields can enable
high-density ultra-fast spintronic technologies. However, the detection and
control of antiferromagnetic Neel vectors remain challenging. Linear
magnetoelectric antiferromagnets (LMAs) may provide new pathways, but applying
simultaneous electric and magnetic fields, necessary to control Neel vectors in
LMAs, is cumbersome and impractical for most applications. Herein, we show that
Cr2O3, a prototypical room-temperature LMA, carries a topologically-protected
surface magnetism in all surfaces, which stems from intrinsic surface electric
fields due to band bending, combined with the bulk linear magnetoelectricity.
Consequently, bulk Neel vectors with zero bulk magnetization can be simply
tuned by magnetic fields through controlling the magnetizations associated with
the surface magnetism. Our results imply that the surface magnetizations
discovered in Cr2O3 should be also present in all LMAs.",2304.01513v1
2023/5/24,Non-collinear Magnetic Atomic Cluster Expansion for Iron,"The Atomic Cluster Expansion (ACE) provides a formally complete basis for the
local atomic environment. ACE is not limited to representing energies as a
function of atomic positions and chemical species, but can be generalized to
vectorial or tensorial properties and to incorporate further degrees of freedom
(DOF). This is crucial for magnetic materials with potential energy surfaces
that depend on atomic positions and atomic magnetic moments simultaneously. In
this work, we employ the ACE formalism to develop a non-collinear magnetic ACE
parametrization for the prototypical magnetic element Fe. The model is trained
on a broad range of collinear and non-collinear magnetic structures calculated
using spin density functional theory. We demonstrate that the non-collinear
magnetic ACE is able to reproduce not only ground state properties of various
magnetic phases of Fe but also the magnetic and lattice excitations that are
essential for a correct description of the finite temperature behavior and
properties of crystal defects.",2305.15137v1
2023/6/2,Interplay of magnetic field and magnetic impurities in Ising superconductors,"Phonon-driven $s$-wave superconductivity is fundamentally antagonistic to
uniform magnetism, and field-induced suppression of the critical temperature is
one of its canonical signatures. Examples of the opposite are unique and
require fortuitous cancellations and very fine parameter tuning. The recently
discovered Ising superconductors violate this rule: an external magnetic field
applied in a certain direction does not suppress superconductivity in an ideal,
impurity-free material. We propose a simple and experimentally accessible
system where the effects of spin-conserving and spin-flip scattering can be
studied in a controlled way, namely NbSe$_2$ monolayers dozed with magnetic
$3d$ atoms. We predict that the critical temperature is slightly increased by
an in-plane magnetic field in NbSe$_2$ dozed with Cr. Due to the band spin
splitting, magnetic spin-flip scattering requires a finite momentum transfer,
while spin-conserving scattering does not. If the magnetic anisotropy is
easy-axis, an in-plane field reorients the impurity spins and transforms
spin-conserving scattering into spin-flip. The critical temperature is enhanced
if the induced magnetization of NbSe$_2$ has a substantial long-range
component, as is the case for Cr ions.",2306.01700v1
2023/9/8,Measurement of the magnetic octupole susceptibility of PrV2Al20,"In the electromagnetic multipole expansion, magnetic octupoles are the
subsequent order of magnetic multipoles allowed in centrosymmetric systems,
following the more commonly observed magnetic dipoles. As order parameters in
condensed matter systems, magnetic octupoles have been experimentally elusive.
In particular, the lack of simple external fields that directly couple to them
makes their experimental detection challenging. Here, we demonstrate a
methodology for probing the magnetic octupole susceptibility using a product of
magnetic field $H_i$ and shear strain $\epsilon_{jk}$ to couple to the
octupolar fluctuations, while using an adiabatic elastocaloric effect to probe
the response to this composite effective field. We observe a Curie-Weiss
behavior in the obtained octupolar susceptibility of \ce{PrV2Al20} up to
temperatures approximately forty times the putative octupole ordering
temperature. Our results demonstrate the presence of magnetic octupole
fluctuations in the particular material system, and more broadly highlight how
anisotropic strain can be combined with magnetic fields to formulate a
versatile probe to observe otherwise elusive emergent `hidden' electronic
orders.",2309.04633v1
2023/9/27,On the potential of hard ferrite ceramics for permanent magnet technology -- a review on sintering strategies,"A plethora of modern technologies rely on permanent magnets for their
operation, including many related to the transition towards a sustainable
future, such as wind turbines or electric vehicles. Despite the overwhelming
superiority of magnets based on rare-earth elements in terms of the magnetic
performance, the harmful environmental impact of the mining of these raw
materials, their uneven distribution on Earth and various political conflicts
among countries leave no option but seeking for rare-earth-free alternatives.
The family of the hexagonal ferrites or hexaferrites, and in particular the
barium and strontium M-type ferrites (BaFe12O19 and SrFe12O19), are strong
candidates for a partial rare-earth magnets substitution, and they are indeed
successfully implemented in multiple applications. The manufacturing of
hexaferrites into dense pieces (i.e. magnets) meeting the requirements of the
specific application (e.g. magnetic and mechanical properties, shape) is not
always straightforward, which has in many cases hampered the actual
substitution at the industrial level. Here, past and on-going research on
hexaferrites sintering is reviewed with a historical perspective, focusing on
the challenges encountered and the solutions explored, and correlating the
sintering approaches with the magnetic performance of the resulting ceramic
magnet.",2309.15680v1
2023/10/20,Multiferroic kinks and spin-flop transition in Ni$_{2}$InSbO$_6$ from first principles,"Magnetoelectric multiferroics are key materials for next-generation devices
due to their entangled magnetic and ferroelectric properties. Spiral
multiferroics induce ferroelectric polarization and are particularly promising
for electric control of magnetism and magnetic control of ferroelectricity. In
this work, we uncover long-period incommensurate states characterized by unique
multiferroic kinks in corundum nickelate Ni$_{2}$InSbO$_6$. Utilizing a
2-orbital $S=1$ model, we derive formulas for Heisenberg and anisotropic
magnetic exchanges and magnetically-induced polarization, enabling their
calculations from first principles. Our theory reproduces experimentally
observed magnetic structures and polarization dependence on the magnetic field
and predicts a three-step magnetic phase transition (flat spiral $\rightarrow$
conical spiral $\rightarrow$ spin-flop $\rightarrow$ ferromagnet) under
external magnetic fields. Kinks in the spiral phases repel each other through a
Yukawa-like potential arising from exchange of massive magnons. Furthermore,
our continuum theory predicts that an electric field directed one way
stabilizes the ferromagnetic state, while the opposite direction stabilizes the
spiral layer state. Our findings open a new pathway to predictive
first-principles modelling of multiferroics and may lead to technological
applications based on multiferroic kinks.",2310.13301v1
2024/2/16,Nonlinear optics driven magnetism reorientation in semiconductors,"Based on nonlinear optics, we develop a band theory to elucidate how light
could manipulate magnetization, which is rooted by the quantum geometric
structure and topological nature of electronic wavefunctions. Their existence
are determined by the light polarization and specific material symmetry, based
on the magnetic group theory. In general, both circularly and linearly
polarized light could exert an effective magnetic field and torque effect, to
reorient the magnetization. They are contributed by spin and orbital angular
momenta simultaneously. Aided by group theory and first-principles
calculations, we illustrate this theory using a showcase example of monolayer
NiCl2, showing that light irradiation effectively generates an out-of-plane
effective magnetic torque, which lifts its in-plane easy magnetization.
According to magnetic dynamic simulations, the in-plane magnetization could be
switched to the out-of-plane direction in a few nanoseconds under a modest
light intensity, demonstrating its ultrafast nature desirable for quantum
manipulation.",2402.10518v1
2021/4/13,Pseudo-gauge Fields in Dirac and Weyl Materials,"Electrons in low-temperature solids are governed by the non-relativistic
Schr$\ddot{o}$dinger equation, since the electron velocities are much slower
than the speed of light. Remarkably, the low-energy quasi-particles given by
electrons in various materials can behave as relativistic Dirac/Weyl fermions
that obey the relativistic Dirac/Weyl equation. These materials are called
""Dirac/Weyl materials"", which provide a tunable platform to test relativistic
quantum phenomena in table-top experiments. More interestingly, different types
of physical fields in these Weyl/Dirac materials, such as magnetic
fluctuations, lattice vibration, strain, and material inhomogeneity, can couple
to the ""relativistic"" quasi-particles in a similar way as the $U(1)$ gauge
coupling. As these fields do not have gauge-invariant dynamics in general, we
refer to them as ""pseudo-gauge fields"". In this chapter, we overview the
concept and the physical consequences of pseudo-gauge fields in Weyl/Dirac
materials. In particular, we will demonstrate that pseudo-gauge fields can
provide a unified understanding of a variety of physical phenomena, including
chiral zero modes inside a magnetic vortex core of magnetic Weyl semimetals, a
giant current response at magnetic resonance in magnetic topological
insulators, and piezo-electromagnetic response in time-reversal invariant
systems. These phenomena are deeply related to various concepts in high-energy
physics, such as chiral anomaly and axion electrodynamics.",2104.06382v3
2016/11/10,Magnetism and ultra-fast magnetization dynamics of Co and CoMn alloys at finite temperature,"Temperature-dependent magnetic experiments like pump-probe measurements
generated by a pulsed laser have become a crucial technique for switching the
magnetization in the picosecond time scale. Apart from having practical
implications on the magnetic storage technology, the research field of
ultrafast magnetization poses also fundamental physical questions. To correctly
describe the time evolution of the atomic magnetic moments under the influence
of a temperature-dependent laser pulse, it remains crucial to know if the
magnetic material under investigation has magnetic excitation spectrum that is
more or less dependent on the magnetic configuration, e.g. as reflected by the
temperature dependence of the exchange interactions. In this article, we
demonstrate from first-principles theory that the magnetic excitation spectra
in Co with fcc, bcc and hcp structures are nearly identical in a wide range of
non-collinear magnetic configurations. This is a curious result of a balance
between the size of the magnetic moments and the strength of the Heisenberg
exchange interactions, that in themselves vary with configuration, but put
together in an effective spin Hamiltonian results in a configuration
independent effective model. We have used such a Hamiltonian, together with
ab-initio calculated damping parameters, to investigate the magnon dispersion
relationship as well as the ultrafast magnetisation dynamics of Co and Co-rich
CoMn alloys.",1611.03541v2
2016/11/21,Self-consistent model of a solid for the description of lattice and magnetic properties,"In the paper a self-consistent theoretical description of the lattice and
magnetic properties of a model system with magnetoelastic interaction is
presented. The dependence of magnetic exchange integrals on the distance
between interacting spins is assumed, which couples the magnetic and the
lattice subsystem. The framework is based on summation of the Gibbs free
energies for the lattice subsystem and magnetic subsystem. On the basis of
minimization principle for the Gibbs energy, a set of equations of state for
the system is derived. These equations of state combine the parameters
describing the elastic properties (relative volume deformation) and the
magnetic properties (magnetization changes).
  The formalism is extensively illustrated with the numerical calculations
performed for a system of ferromagnetically coupled spins $S$=1/2 localized at
the sites of simple cubic lattice. In particular, the significant influence of
the magnetic subsystem on the elastic properties is demonstrated. It manifests
itself in significant modification of such quantities as the relative volume
deformation, thermal expansion coefficient or isothermal compressibility, in
particular, in the vicinity of the magnetic phase transition. On the other
hand, the influence of lattice subsystem on the magnetic one is also evident.
It takes, for example, the form of dependence of the critical (Curie)
temperature and magnetization itself on the external pressure, which is
thoroughly investigated.",1611.06941v2
2021/4/5,Efficient determination of the true magnetic structure in a high-throughput ab initio screening: the MDMC method,"Finding the true magnetic structure at given external conditions is crucial
for describing magnetic materials and predicting their properties. This is
especially important for high-throughput screening of potentially good magnets
that without adequate description of the magnetic structure may result in an
enormous waste of computational resources. I introduce a method, which
accurately and efficiently treats magnetic ordering in the course of standard
first-principles calculations. The method is suitable for all temperatures and
is based on Monte Carlo (MC) technique. At high temperatures MC is coupled to
ab initio molecular dynamics, therefore treating atomic vibrations and magnetic
ordering simultaneously. The method takes care of the convergence to the true
ground-state magnetic structure at 0 K, coupling between spins and atomic
vibrations at high temperatures, and spin-spin interactions in non-Heisenberg
systems, i.e. it naturally goes beyond the usual pair-like effective exchange
interactions at all temperatures. I show that the method nicely reproduces the
magnetic structures at low and high temperatures even on relatively small
supercells and provides a ground for truly ab initio calculations of magnetic
systems in high-throughput studies. In its general formulation the MDMC method
deals with non-collinear magnetism, but its collinear version may be more
suitable for fast high-throughput calculations. The examples of the application
of the MDMC method addressed in this paper are $\alpha$-Mn; body-centered cubic
Fe, which is ferromagnetic at low and paramagnetic at high temperatures; and
MnB$_2$W$_2$, a new magnetic compound with non-trivial magnetism.",2104.02106v1
2021/4/7,Hysteresis in Two Dimensional Arrays of Magnetic Nanoparticles,"We perform computer simulations to probe the magnetic hysteresis in a
two-dimensional ($L^{}_x\times L^{}_y$) assembly of magnetic nanoparticles as a
function of dipolar interaction strength $h^{}_d$, temperature $T$, aspect
ratio $A^{}_r=L^{}_y/L^{}_x$, and the applied alternating magnetic field's
direction. In the absence of magnetic interaction ($h^{}_d\approx0$) and
thermal fluctuations ($T=0$ K), the hysteresis follows the Stoner and Wohlfarth
model, as expected. For weak dipolar interaction and substantial temperature,
the hysteresis has the dominance of superparamagnetic behaviour, irrespective
of the applied magnetic field's direction and $A^{}_r$. Interestingly, the
hysteresis curve has all the characteristics of antiferromagnetic interaction
dominance for $A^{}_r\leq6$ and considerable dipolar interaction strength
($h^{}_d>0.2)$, which is independent of applied magnetic direction. When the
magnetic field is applied along the system's shorter axis ($x$-direction), a
non-hysteresis straight line is observed with large $h^{}_d$. In the case of
the magnetic field applied along the long axis of the sample ($y$-direction),
ferromagnetic interaction dominates the hysteresis for large $h^{}_d$ and
$A^{}_r>6$. Irrespective of $h^{}_d$ and applied magnetic field's direction,
the coercive field $\mu^{}_oH^{}_c$ and remanence $M^{}_r$ are minimal for
$A^{}_r\leq6$ and significant temperature. They are found to increase with
$h^{}_d$ when $A^{}_r$ is enormous. Remarkably, the variation of hysteresis
loop area $E^{}_H$ as a function of these parameters is the same as that of the
coercive field variation. We believe that the concepts presented in this work
are relevant in various technological applications such as spintronics and
magnetic hyperthermia, in which such self-assembled nanoparticle arrays are
ubiquitous.",2104.02961v1
2019/5/1,Observation of a mesoscopic magnetic modulation in chiral Mn1/3NbS2,"We have investigated the structural, magnetic, thermodynamic, and charge
transport properties of Mn1/3NbS2 single crystals through x-ray and neutron
diffraction, magnetization, specific heat, magnetoresistance, and Hall effect
measurements. Mn1/3NbS2 displays a magnetic transition at TC ~ 45 K with highly
anisotropic behavior expected for a hexagonal structured material. Below TC,
neutron diffraction reveals increased scattering near the structural Bragg
peaks having a wider Q-dependence along the c-axis than the nuclear Bragg
peaks. This indicates helimagnetism with a long pitch length of ~250 nm (or a
wavevector q~0.0025 {\AA}-1) along the c-axis. This q is substantially smaller
than that found for the helimagnetic state in isostructural Cr1/3NbS2 (0.015
{\AA}-1). Specific heat capacity measurements confirm a second-order magnetic
phase transition with a substantial magnetic contribution that persists to low
temperature. The large low-temperature specific heat capacity is consistent
with a large density of low-lying magnetic excitations that are likely
associated with topologically interesting magnetic modes. Changes to the
magnetoresistance, the magnetization, and the magnetic neutron diffraction,
which become more apparent below 20 K, imply a modification in the character of
the magnetic ordering corresponding to the magnetic contribution to the
specific heat capacity. These observations signify a more complex magnetic
structure both at zero and finite fields for Mn1/3NbS2 than for the
well-investigated Cr1/3NbS2.",1905.00452v1
2020/9/24,Tunable layered-magnetism-assisted magneto-Raman effect in a two-dimensional magnet $\mathrm{CrI_3}$,"We use a combination of polarized Raman spectroscopy experiment and model
magnetism-phonon coupling calculations to study the rich magneto-Raman effect
in the two-dimensional (2D) magnet $\mathrm{CrI_3}$. We reveal a novel
layered-magnetism-assisted phonon scattering mechanism below the magnetic onset
temperature, whose Raman excitation breaks time-reversal symmetry, has an
antisymmetric Raman tensor, and follows the magnetic phase transitions across
critical magnetic fields, on top of the presence of the conventional phonon
scattering with symmetric Raman tensors in $N$-layer $\mathrm{CrI_3}$. We
resolve in data and by calculations that the 1st-order $A_g$ phonon of
monolayer splits into a $N$-fold multiplet in $N$-layer $\mathrm{CrI_3}$ due to
the interlayer coupling ($N$>=2) and that the phonons with the multiple show
distinct magnetic field dependence because of their different
layered-magnetism-phonon coupling. We further find that such a
layered-magnetism-phonon coupled Raman scattering mechanism extends beyond
1st-order to higher-order multi-phonon scattering processes. Our results on
magneto-Raman effect of the 1st-order phonons in the multiplet and the
higher-order multi-phonons in $N$-layer $\mathrm{CrI_3}$ demonstrate the rich
and strong behavior of emergent magneto-optical effects in 2D magnets and
underlines the unique opportunities of new spin-phonon physics in van der Waals
layered magnets.",2009.11470v1
2023/4/18,Multiple Incommensurate Magnetic States in the Kagome Antiferromagnet Na2Mn3Cl8,"The kagome lattice can host exotic magnetic phases arising from frustrated
and competing magnetic interactions. However, relatively few insulating kagome
materials exhibit incommensurate magnetic ordering. Here, we present a study of
the magnetic structures and interactions of antiferromagnetic
Na$_2$Mn$_3$Cl$_8$ with an undistorted Mn$^{2+}$ kagome network. Using
neutron-diffraction and bulk magnetic measurements, we show that
Na$_2$Mn$_3$Cl$_8$ hosts two different incommensurate magnetic states, which
develop at $T_{N1} = 1.6$ K and $T_{N2} = 0.6$ K. Magnetic Rietveld refinements
indicate magnetic propagation vectors of the form $\mathbf{q} =
(q_{x},q_{y},\frac{3}{2})$, and our neutron-diffraction data can be well
described by cycloidal magnetic structures. By optimizing exchange parameters
against magnetic diffuse-scattering data, we show that the spin Hamiltonian
contains ferromagnetic nearest-neighbor and antiferromagnetic third-neighbor
Heisenberg interactions, with a significant contribution from long-ranged
dipolar coupling. This experimentally-determined interaction model is compared
with density-functional-theory simulations. Using classical Monte Carlo
simulations, we show that these competing interactions explain the experimental
observation of multiple incommensurate magnetic phases and may stabilize
multi-$\mathbf{q}$ states. Our results expand the known range of magnetic
behavior on the kagome lattice.",2304.08680v1
2022/5/27,Self-supervised graph neural networks for accurate prediction of Néel temperature,"Antiferromagnetic materials are exciting quantum materials with rich physics
and great potential for applications. It is highly demanded of the accurate and
efficient theoretical method for determining the critical transition
temperatures, N\'{e}el temperatures, of antiferromagnetic materials. The
powerful graph neural networks (GNN) that succeed in predicting material
properties lose their advantage in predicting magnetic properties due to the
small dataset of magnetic materials, while conventional machine learning models
heavily depend on the quality of material descriptors. We propose a new
strategy to extract high-level material representations by utilizing
self-supervised training of GNN on large-scale unlabeled datasets. According to
the dimensional reduction analysis, we find that the learned knowledge about
elements and magnetism transfers to the generated atomic vector
representations. Compared with popular manually constructed descriptors and
crystal graph convolutional neural networks, self-supervised material
representations can help us obtain a more accurate and efficient model for
N\'{e}el temperatures, and the trained model can successfully predict high
N\'{e}el temperature antiferromagnetic materials. Our self-supervised GNN may
serve as a universal pre-training framework for various material properties.",2206.04109v1
2013/9/17,Strongly Correlated Materials,"Strongly correlated materials are profoundly affected by the repulsive
electron-electron interaction. This stands in contrast to many commonly used
materials such as silicon and aluminum, whose properties are comparatively
unaffected by the Coulomb repulsion. Correlated materials often have remarkable
properties and transitions between distinct, competing phases with dramatically
different electronic and magnetic orders. These rich phenomena are fascinating
from the basic science perspective and offer possibilities for technological
applications. This article looks at these materials through the lens of
research performed at Rice University. Topics examined include: Quantum phase
transitions and quantum criticality in ""heavy fermion"" materials and the iron
pnictide high temperature superconductors; computational ab initio methods to
examine strongly correlated materials and their interface with analytical
theory techniques; layered dichalcogenides as example correlated materials with
rich phases (charge density waves, superconductivity, hard ferromagnetism) that
may be tuned by composition, pressure, and magnetic field; and nanostructure
methods applied to the correlated oxides VO2 and Fe3O4, where metal-insulator
transitions can be manipulated by doping at the nanoscale or driving the system
out of equilibrium. We conclude with a discussion of the exciting prospects for
this class of materials.",1309.4473v1
2018/5/21,Proximitized Materials,"Advances in scaling down heterostructures and having an improved interface
quality together with atomically-thin two-dimensional materials suggest a novel
approach to systematically design materials. A given material can be
transformed through proximity effects whereby it acquires properties of its
neighbors, for example, becoming superconducting, magnetic, topologically
nontrivial, or with an enhanced spin-orbit coupling. Such proximity effects not
only complement the conventional methods of designing materials by doping or
functionalization, but can also overcome their various limitations. In
proximitized materials it is possible to realize properties that are not
present in any constituent region of the considered heterostructure. While the
focus is on magnetic and spin-orbit proximity effects with their applications
in spintronics, the outlined principles provide also a broader framework for
employing other proximity effects to tailor materials and realize novel
phenomena.",1805.07942v1
2020/6/10,Hexagonal Perovskites as Quantum Materials,"Hexagonal oxide perovskites, in contrast to the more familiar perovskites,
allow for face-sharing of metal-oxygen octahedra or trigonal prisms within
their structural frameworks. This results in dimers, trimers, tetramers, or
longer fragments of chains of face-sharing octahedra in the crystal structures,
and consequently in much shorter metal-metal distances and lower
metal-oxygen-metal bond angles than are seen in the more familiar perovskites.
The presence of the face-sharing octahedra can have a dramatic impact on
magnetic properties of these compounds, and dimer-based materials, in
particular, have been the subjects of many quantum-materials-directed studies
in materials physics. Hexagonal oxide perovskites are of contemporary interest
due to their potential for geometrical frustration of the ordering of magnetic
moments or orbital occupancies at low temperatures, which is especially
relevant to their significance as quantum materials. As such, several hexagonal
oxide perovskites have been identified as potential candidates for hosting the
quantum spin liquid state at low temperatures. In our view, hexagonal oxide
perovskites are fertile ground for finding new quantum materials. This review
briefly describes the solid state chemistry of many of these materials.",2006.05864v1
2023/10/16,Creation of flexible spin-caloritronic material with giant transverse thermoelectric conversion by nanostructure engineering,"Functional materials such as magnetic, thermoelectric, and battery materials
have been revolutionized through nanostructure engineering. However, spin
caloritronics, an advancing field based on spintronics and thermoelectrics with
fundamental physics studies, has focused only on uniform materials without
complex microstructures. Here, we show how nanostructure engineering enables
transforming simple magnetic alloys into spin-caloritronic materials displaying
significantly large transverse thermoelectric conversion properties. The
anomalous Nernst effect (ANE), a promising transverse thermoelectric phenomenon
for energy harvesting and heat sensing, has been challenging to utilize due to
the scarcity of materials with large anomalous Nernst coefficients. We
demonstrate a remarkable improvement in the anomalous Nernst coefficients in
flexible Fe-based amorphous materials through nanostructural engineering,
without altering their composition. This surpasses all reported amorphous
alloys and is comparable to single crystals showing large ANE. The enhancement
is attributed to Cu nano-clustering, facilitating efficient transverse
thermoelectric conversion. This discovery advances the materials science of
spin caloritronics, opening new avenues for designing high-performance
transverse thermoelectric devices for practical applications.",2310.10233v1
2017/5/17,Magnetic Transport in Spin Antiferromagnets for Spintronics Applications,"Had magnetic monopoles been ubiquitous as electrons are, we would probably
have had a different form of matter, and power plants based on currents of
these magnetic charges would have been a familiar scene of modern technology.
Magnetic dipoles do exist, however, and in principle one could wonder if we can
use them to generate magnetic currents. In the present work, we address the
issue of generating magnetic currents and magnetic thermal currents in
electrically-insulating low-dimensional Heisenberg antiferromagnets by invoking
the (broken) electricity-magnetism duality symmetry. The ground state of these
materials is a spin-liquid state that can be described well via~the
Jordan--Wigner fermions, which permit an easy definition of the magnetic
particle and thermal currents. The magnetic and magnetic thermal conductivities
are calculated in the present work using the bond--mean field theory. The
spin-liquid states in these antiferromagnets are either gapless or gapped
liquids of spinless fermions whose flow defines a current just as the one
defined for electrons in a Fermi liquid. The driving force for the magnetic
current is a magnetic field with a gradient along the magnetic conductor. We
predict the generation of a magneto-motive force and realization of magnetic
circuits using low-dimensional Heisenberg antiferromagnets. The present work is
also about claiming that what the experiments in spintronics attempt to do is
trying to treat the magnetic degrees of freedoms on the same footing as the
electronic ones.",1705.06318v2
2013/7/4,The relation between magnetic and material arms in models for spiral galaxies,"Context. Observations of polarized radio emission show that large-scale
(regular) magnetic fields in spiral galaxies are not axisymmetric, but
generally stronger in interarm regions. In some nearby galaxies such as NGC
6946 they are organized in narrow magnetic arms situated between the material
spiral arms. Aims. The phenomenon of magnetic arms and their relation to the
optical spiral arms (the material arms) call for an explanation in the
framework of galactic dynamo theory. Several possibilities have been suggested
but are not completely satisfactory; here we attempt a consistent
investigation. Methods. We use a 2D mean-field dynamo model in the no-z
approximation and add injections of small-scale magnetic field, taken to result
from supernova explosions, to represent the effects of dynamo action on smaller
scales. This injection of small scale field is situated along the spiral arms,
where star-formation mostly occurs. Results. A straightforward explanation of
magnetic arms as a result of modulation of the dynamo mechanism by material
arms struggles to produce pronounced magnetic arms, at least with realistic
parameters, without introducing new effects such as a time lag between Coriolis
force and {\alpha}-effect. In contrast, by taking into account explicitly the
small-scale magnetic field that is injected into the arms by the action of the
star forming regions that are concentrated there, we can obtain dynamo models
with magnetic structures of various forms that can be compared with magnetic
arms. (abbrev). Conclusions. We conclude that magnetic arms can be considered
as coherent magnetic structures generated by large-scale dynamo action, and
associated with spatially modulated small-scale magnetic fluctuations, caused
by enhanced star formation rates within the material arms.",1307.1258v1
2006/8/14,Nitrogen based magnetic semiconductors,"We describe a possible pathway to new magnetic materials with no conventional
magnetic elements present. The substitution of Nitrogen for Oxygen in simple
non magnetic oxides leads to holes in N 2$p$ states which form local magnetic
moments. Because of the very large Hund's rule coupling of Nitrogen and O 2$p$
electrons and the rather extended spatial extend of the wave functions these
materials are predicted to be ferromagnetic metals or small band gap
insulators. Experimental studies support the theoretical calculations with
regard to the basic electronic structure and the formation of local magnetic
moments. It remains to be seen if these materials are magnetically ordered and
if so below what temperature.",0608313v1
2007/3/1,Magnetic effects at the interface between nonmagnetic oxides,"The electronic reconstruction at the interface between two insulating oxides
can give rise to a highly-conductive interface. In analogy to this remarkable
interface-induced conductivity we show how, additionally, magnetism can be
induced at the interface between the otherwise nonmagnetic insulating
perovskites SrTiO3 and LaAlO3. A large negative magnetoresistance of the
interface is found, together with a logarithmic temperature dependence of the
sheet resistance. At low temperatures, the sheet resistance reveals magnetic
hysteresis. Magnetic ordering is a key issue in solid-state science and its
underlying mechanisms are still the subject of intense research. In particular,
the interplay between localized magnetic moments and the spin of itinerant
conduction electrons in a solid gives rise to intriguing many-body effects such
as Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions, the Kondo effect, and
carrier-induced ferromagnetism in diluted magnetic semiconductors. The
conducting oxide interface now provides a versatile system to induce and
manipulate magnetic moments in otherwise nonmagnetic materials.",0703028v2
2000/10/2,Dipole Septum Magnet in the Fast Kicker System for Multi-Axis Advanced Radiography,"Here we present designs for a static septum magnet with two adjacent
apertures where ideally one aperture has a uniform dipole field and the other
zero field. Two designs are considered. One is a true septum magnet with a thin
layer of coils and materials separating the dipole field region from the null
field region. During the beam switching process, the intense electron beam will
spray across this material septum leading to concerns on beam control, vacuum
quality, radiation damage, etc. due to the lost particles. Therefore, another
configuration without a material septum is also considered. With this
configuration it is more difficult to achieve high field quality near the
transition region. Shaped shims are designed to limit the degradation of beam
quality (emittance growth). This approach is closely related to a previous
septum magnet design with two oppositely oriented dipole field regions
presented by the authors [1]. Simulations are performed to obtain the magnetic
field profile in both designs. A PIC simulation is used to transport a beam
slice consisting of several thousand particles through the magnet to estimate
emittance growth in the magnet due to field non-uniformity.",0010005v1
2008/1/28,GaMnAs-based hybrid multiferroic memory device,"A rapidly developing field of spintronics is based on the premise that
substituting charge with spin as a carrier of information can lead to new
devices with lower power consumption, non-volatility and high operational
speed. Despite efficient magnetization detection, magnetization manipulation is
primarily performed by current-generated local magnetic fields and is very
inefficient. Here we report a novel non-volatile hybrid multiferroic memory
cell with electrostatic control of magnetization based on strain-coupled GaMnAs
ferromagnetic semiconductor and a piezoelectric material. We use the
crystalline anisotropy of GaMnAs to store information in the orientation of the
magnetization along one of the two easy axes, which is monitored via transverse
anisotropic magnetoresistance. The magnetization orientation is switched by
applying voltage to the piezoelectric material and tuning magnetic anisotropy
of GaMnAs via the resulting stress field.",0801.4191v1
2008/1/31,Impurity-Ion pair induced high-temperature ferromagnetism in Co-doped ZnO,"Magnetic 3d-ions doped into wide-gap oxides show signatures of room
temperature ferromagnetism, although their concentration is two orders of
magnitude smaller than that in conventional magnets. The prototype of these
exceptional materials is Co-doped ZnO, for which an explanation of the room
temperature ferromagnetism is still elusive. Here we demonstrate that magnetism
originates from Co2+ oxygen-vacancy pairs with a partially filled level close
to the ZnO conduction band minimum. The magnetic interaction between these
pairs is sufficiently long-ranged to cause percolation at moderate
concentrations. However, magnetically correlated clusters large enough to show
hysteresis at room temperature already form below the percolation threshold and
explain the current experimental findings. Our work demonstrates that the
magnetism in ZnO:Co is entirely governed by intrinsic defects and a phase
diagram is presented. This suggests a recipe for tailoring the magnetic
properties of spintronics materials by controlling their intrinsic defects.",0801.4945v1
2008/5/5,Molecular Thin Films: a New Type of Magnetic Switch,"The design and fabrication of materials that exhibit both semiconducting and
magnetic properties for spintronics and quantum computing has proven difficult.
Important starting points are high-purity thin films as well as fundamental
theoretical understanding of the magnetism. Here we show that small molecules
have great potential in this area, due to ease of insertion of localised spins
in organic frameworks and both chemical and structural purity. In particular,
we demonstrate that archetypal molecular semiconductors, namely the metal
phthalocyanines (Pc), can be readily fabricated as thin film quantum
antiferromagnets, important precursors to a solid state quantum computer. Their
magnetic state can be switched via fabrication steps which modify the film
structure, offering practical routes into information processing. Theoretical
calculations show that a new mechanism, which is the molecular analogue of the
interactions between magnetic ions in metals, is responsible for the magnetic
states. Our combination of theory and experiments opens the field of organic
thin film magnetic engineering.",0805.0460v1
2009/2/4,Magnetic cooling at Risoe DTU,"Magnetic refrigeration at room temperature is of great interest due to a
long-term goal of making refrigeration more energy-efficient, less noisy and
free of any environmentally hostile materials. A refrigerator utilizing an
active magnetic regenerator (AMR) is based on the magnetocaloric effect, which
manifests itself as a temperature change in magnetic materials when subjected
to a varying magnetic field. In this work we present the current state of
magnetic refrigeration research at Risoe DTU with emphasis on the numerical
modeling of an existing AMR test machine. A 2D numerical heat-transfer and
fluid-flow model that represents the experimental setup is presented.
Experimental data of both no-heat load and heat load situations are compared to
the model. Moreover, results from the numerical modeling of the permanent
magnet design used in the system are presented.",0902.0812v1
2009/4/9,Magnetic field control of charge structures in the magnetically disordered phase of the multiferroic LuFe$_2$O$_4$,"Using neutron diffraction, we have studied the magnetic field effect on
charge structures in the charge-ordered multiferroic material LuFe$_2$O$_4$. An
external magnetic field is able to change the magnitude and correlation lengths
of the charge valence order even before the magnetic order sets in. This
affects the dielectric and ferroelectric properties of the material and induces
a giant magneto-electric effect. Our results suggest that the magneto-electric
coupling in LuFe$_2$O$_4$ is likely due to magnetic field effect on local
spins, in clear contrast to the case in most other known multiferroic systems
where the bulk magnetic order is important.",0904.1561v2
2010/7/14,Origin of ferroelectricity in high $T_c$ magnetic ferroelectric CuO,"""Magnetic ferroelectric"" has been found in a wide range of spiral magnets.
However, these materials all suffer from low critical temperatures, which are
usually below 40 K, due to strong spin frustration. Recently, CuO has been
found to be multiferroic at much higher ordering temperature ($\sim$ 230K). To
clarify the origin of the high ordering temperature in CuO, we investigate the
structural, electronic and magnetic properties of CuO via first-principles
methods. We find that CuO has very special nearly commensurate spiral magnetic
structure, which is stabilized via the Dzyaloshinskii-Moriya interaction. The
spin frustration in CuO is relatively weak, which is one of the main reasons
that the compound have high ordering temperature. We propose that high $T_c$
magnetic ferroelectric materials can be found in double sublattices of magnetic
structures similar to that of CuO.",1007.2274v4
2010/8/2,First-Principles Prediction of Novel Magnetic Materials Based on ZrCuSiAs-like Semiconducting Pnictide-Oxides,"We assumed that significant enlargement of the functional properties of the
family of quaternary ZrCuSiAs-like pnictide-oxides, often called also as 1111
phases, which are known now first of all as parent phases for new FeAs
superconductors, may be achieved by replacement of nonmagnetic ions by magnetic
ions in semiconducting ZrCuSiAs-like phases. We checked this assumption by
means of first-principles FLAPW-GGA calculations using a wide-band-gap
semiconductor YZnAsO doped with Mn, Fe, and Co as an example. Our main finding
is that substitution of Mn, Fe, and Co for Zn leads to drastic transformations
of electronic and magnetic properties of the parent material: as distinct from
the non-magnetic YZnAsO, the examined doped phases YZn0.89Mn0.11AsO,
YZn0.89Fe0.11AsO, and YZn0.89Co0.11AsO behave as a magnetic semiconductor, a
magnetic half-metal or as a magnetic gapless semi-metal, respectively.",1008.0250v1
2011/3/30,Giant coercivity of dense nanostructured spark plasma sintered barium hexaferrite,"Due to the limited rare-earth elements resources, ferrite magnets need to be
improved drastically. Ideally, for a true hard magnet, the coercive field
should be larger than the saturation magnetization, which is not yet realized
for ferrites. Thus, an alternative can be found in making very fine grain
ferrite magnets, but it is usually impossible to get small grains and dense
material together. In this paper, it is shown that the spark plasma sintering
method is able to produce approximately 80% of dense material with crystallites
smaller than 100 nm. The as-prepared bulk sintered anisotropic magnets exhibits
coercive field of 0.5 T which is approximately 60% of the theoretical limit and
only a few percentage below that of loose nanopowders. As a result, the magnets
behave nearly ideal (-1.18 slope in the BH plane second quadrant) and the
energy product reaches 8.8 kJ m-3, the highest value achieved in the isotropic
ferrite magnet to our knowledge.",1103.5840v1
2014/9/30,Predicting a Ferrimagnetic Phase of Zn2FeOsO6 with Strong Magnetoelectric Coupling,"Multiferroic materials, in which ferroelectric and magnetic ordering coexist,
are of fundamental interest for the development of novel memory devices that
allow for electrical writing and non-destructive magnetic readout operation.
The great challenge is to create room temperature multiferroic materials with
strongly coupled ferroelectric and ferromagnetic (or ferrimagnetic) orderings.
BiFeO3 has been the most heavily investigated single-phase multiferroic to date
due to the coexistence of its magnetic order and ferroelectric order at room
temperature. However, there is no net magnetic moment in the cycloidal
(antiferromagnetic-like) magnetic state of bulk BiFeO3, which severely limits
its realistic applications in electric field controlled spintronic devices.
Here, we predict that double perovskite Zn2FeOsO6 is a new multiferroic with
properties superior to BiFeO3. First, there are strong ferroelectricity and
strong ferrimagnetism at room temperature in Zn2FeOsO6. Second, the easy-plane
of the spontaneous magnetization can be switched by an external electric field,
evidencing the strong magnetoelectric coupling existing in this system. Our
results suggest that ferrimagnetic 3d-5d double perovskite may therefore be
used to achieve voltage control of magnetism in future spintronic devices.",1409.8430v2
2015/9/17,Antiferromagnetic spintronics,"Antiferromagnetic materials are magnetic inside, however, the direction of
their ordered microscopic moments alternates between individual atomic sites.
The resulting zero net magnetic moment makes magnetism in antiferromagnets
invisible on the outside. It also implies that if information was stored in
antiferromagnetic moments it would be insensitive to disturbing external
magnetic fields, and the antiferromagnetic element would not affect
magnetically its neighbors no matter how densely the elements were arranged in
a device. The intrinsic high frequencies of antiferromagnetic dynamics
represent another property that makes antiferromagnets distinct from
ferromagnets. The outstanding question is how to efficiently manipulate and
detect the magnetic state of an antiferromagnet. In this article we give an
overview of recent works addressing this question. We also review studies
looking at merits of antiferromagnetic spintronics from a more general
perspective of spin-ransport, magnetization dynamics, and materials research,
and give a brief outlook of future research and applications of
antiferromagnetic spintronics.",1509.05296v1
2015/11/25,"Three possible mechanisms of capacitance enhancement under magnetic field: charge density gradient modulation, electron gas excitation and oscillatory magnetization- polarization coupling","Three mechanisms of capacitance enhance-ment by a magnetic field have been
analyz-ed. Through semiclassical description of charge movement under a
magnetic field, it can be shown that the charge density gradient, a term
coupled with magnetic field strength, could be used to augment the
magnetocapacitance. Also a magnetic field could enhance capacitance on the
polarized metallic material surface due to the electron gas excitation.
Finally, a magnetic field could produce oscillation in the capacitance when
relating the polarization with the magnetization through the modification of
standard free energy model. By deriving these three mechanisms, it can be seen
that three approaches are of potential for exploring tunable dielectric
materials.",1511.07937v1
2016/4/5,Ab Initio Theory of Coherent Laser-Induced Magnetization in Metals,"We present the first materials specific ab initio theory of the magnetization
induced by circularly polarized laser light in metals. Our calculations are
based on non-linear density matrix theory and include the effect of absorption.
We show that the induced magnetization, commonly referred to as inverse Faraday
effect, is strongly materials and frequency dependent, and demonstrate the
existence of both spin and orbital induced magnetizations which exhibit a
surprisingly different behavior. We show that for nonmagnetic metals (as Cu,
Au, Pd, Pt) and antiferromagnetic metals the induced magnetization is
antisymmetric in the light's helicity, whereas for ferromagnetic metals (Fe,
Co, Ni, FePt) the imparted magnetization is only asymmetric in the helicity. We
compute effective optomagnetic fields that correspond to the induced
magnetizations and provide guidelines for achieving all-optical
helicity-dependent switching.",1604.01188v2
2017/1/12,Training-induced inversion of spontaneous exchange bias field on La1.5Ca0.5CoMnO6,"In this work we report the synthesis and structural, electronic and magnetic
properties of La1.5Ca0.5CoMnO6 double-perovskite. This is a re-entrant spin
cluster material which exhibits a non-negligible negative exchange bias effect
when it is cooled in zero magnetic field from an unmagnetized state down to low
temperature. X-ray powder diffraction, X-ray photoelectron spectroscopy and
magnetometry results indicate mixed valence state at Co site, leading to
competing magnetic phases and uncompensated spins at the magnetic interfaces.
We compare the results for this Ca-doped material with those reported for the
resemblant compound La1.5Sr0.5CoMnO6, and discuss the much smaller spontaneous
exchange bias effect observed for the former in terms of its structural and
magnetic particularities. For La1.5Ca0.5CoMnO6, when successive magnetization
loops are carried, the spontaneous exchange bias field inverts its sign from
negative to positive from the first to the second measurement. We discuss this
behavior based on the disorder at the magnetic interfaces, related to the
presence of a glassy phase. This compound also exhibits a large conventional
exchange bias, for which there is no sign inversion of the exchange bias field
for consecutive cycles.",1701.03496v1
2017/2/2,Parameterisation of non-collinear energy landscapes in itinerant magnets,"The magnetic force theorem provides convenient ways to study exchange
interactions in magnetic systems. However, it is well known that short range
interactions in itinerant magnetic systems are poorly described with the
conventional use of the theorem and numerous strategies have been developed
over the years to overcome this deficiency. In this study, we discuss this
issue in the context of the frozen magnon method and find that a
self-consistent approach is in general preferable. Moreover, an extended
Heisenberg model is suggested in order to better describe finite deviations
from the magnetic ground state and is shown through cross-validation to give a
superior description of the interactions in non-collinear magnetic
configurations compared to the regular Heisenberg model. The present study thus
supplies a fully self-consistent method for systematic investigations of
exchange interactions beyond the standard Heisenberg model. This may prove
relevant to high-throughput computational materials science, e.g., in
developing high moment materials for the magnetic storage industry.",1702.00599v3
2018/1/31,How to manipulate magnetic states of antiferromagnets,"Antiferromagnetic materials, which have drawn considerable attention
recently, have fascinating features: they are robust against perturbation,
produce no stray fields, and exhibit ultrafast dynamics. Discerning how to
efficiently manipulate the magnetic state of an antiferromagnet is key to the
development of antiferromagnetic spintronics. In this review, we introduce four
main methods (magnetic, strain, electrical, and optical) to mediate the
magnetic states and elaborate on intrinsic origins of different
antiferromagnetic materials. Magnetic control includes a strong magnetic field,
exchange bias, and field cooling, which are traditional and basic. Strain
control involves the magnetic anisotropy effect or metamagnetic transition.
Electrical control can be divided into two parts, electric field and electric
current, both of which are convenient for practical applications. Optical
control includes thermal and electronic excitation, an inertia-driven
mechanism, and terahertz laser control, with the potential for ultrafast
antiferromagnetic manipulation. This review sheds light on effective usage of
antiferromagnets and provides a new perspective on antiferromagnetic
spintronics.",1801.10332v1
2018/4/4,Magnetic properties of isolated Re ion and Re-Re complex in ZnO studied by GGA +U approach,"Magnetic properties of Re substituting for the divalent Zn ions and impurity
pairs in wurtzite and zinc blende ZnO are analyzed by employing the Generalized
Gradient Approximation with the +U corrections. The +U term applied to d(Zn),
p(O), and d(Re) orbitals stabilizes spin polarization of Re. Re impurity
introduces a defect level located in the band gap, and Re2+ generates the local
spin 5/2 in both wurtzite and zinc blende structures. Magnetic coupling of
Re-Re pairs as a function of distance between the defects, their relative
orientation, and the charge state was calculated. All magnetic coupling between
impurities is antiferromagnetic and due to an intermediate O atom via strong
d(Re)-p(O) hybridization between Re and O states. The defect states and
magnetic moments come from d(Re) with a contribution of p(O) orbitals of the O
nearest neighbors of Re. The results show that the Re-doped wurtzite ZnO may be
a new type of magneto-optical materials with a great promise.",1804.01332v1
2019/8/9,Modeling Spin Dynamics in the Singlet Ground State Garnet Ho3Ga5O12,"Materials containing non-Kramers magnetic ions can show unusual quantum
excitations because of the exact mapping of the two-singlet crystal-field
ground state to a quantum model of Ising spins in a transverse magnetic field.
Here, we model the magnetic excitation spectrum of garnet-structured Ho3Ga5O12,
which has a two-singlet crystal-field ground state. We use a reaction-field
approximation to explain published inelastic neutron-scattering data [Zhou et
al., Phys. Rev. B 78, 140406(R) (2008)] using a three-parameter model
containing the magnetic dipolar interaction, the two-singlet crystal-field
splitting, and the nuclear hyperfine coupling. Our study clarifies the magnetic
Hamiltonian of Ho3Ga5O12, reveals that the nuclear hyperfine interaction drives
magnetic ordering in this system, and provides a framework for quantitative
analysis of magnetic excitation spectra of materials with singlet crystal-field
ground states.",1908.03530v1
2012/11/11,Magnetic phase transitions in Gd64Sc36 studied using non-contact ultrasonics,"The speed and attenuation of ultrasound propagation can be used to determine
material properties and identify phase transitions. Standard ultrasonic contact
techniques are not always convenient due to the necessity of using couplant,
however, recently reliable non-contact ultrasonic techniques involving
electromagnetic generation and detection of ultrasound with electromagnetic
acoustic transducers (EMATs) have been developed for use on electrically
conducting and/or magnetic materials. We present a detailed study of magnetic
phase transitions in a single crystal sample of Gd64Sc36 magnetic alloy using
contact and non-contact ultrasonic techniques for two orientations of external
magnetic field. Phase diagrams are constructed based on measurements of elastic
constant, the attenuation, and the efficiency of generation when using an EMAT.
The EMATs are shown to provide additional information related to the magnetic
phase transitions in the studied sample, and results identify a conical helix
phase in Gd64Sc36 in the magnetic field orientation H||c.",1211.2471v1
2017/9/14,Towards diluted magnetism in TaAs,"Magnetism in Weyl semimetals is desired to investigate the interaction
between the magnetic moments and Weyl fermions, e.g. to explore anomalous
quantum Hall phenomena. Here we demonstrate that proton irradiation is an
effective tool to induce ferromagnetism in the Weyl semimetal TaAs. The
intrinsic magnetism is observed with a transition temperature above room
temperature. The magnetic moments from d states are found to be localized
around Ta atoms. Further, the first-principles calculations indicate that the d
states localized on the nearest-neighbor Ta atoms of As vacancy sites are
responsible for the observed magnetic moments and the long-ranged magnetic
order. The results show the feasibility of inducing ferromagnetism in Weyl
semimetals so that they may facilitate the applications of this material in
spintronics.",1709.04605v2
2018/10/3,"Nuclear and Magnetic Structures of the Frustrated Quantum Antiferromagnet Barlowite, Cu$_{4}$(OH)$_{6}$FBr","Barlowite, Cu$_{4}$(OH)$_{6}$FBr, has attracted much attention as the parent
compound of a new series of quantum spin liquid candidates,
Zn$_{x}$Cu$_{4-x}$(OH)$_{6}$FBr. While it is known to undergo a magnetic phase
transition to a long-range ordered state at $T_{N} = 15$ K, there is still no
consensus over either its nuclear or magnetic structures. Here, we use
comprehensive powder neutron diffraction studies on deuterated samples of
barlowite to demonstrate that the only space group consistent with the observed
nuclear and magnetic diffraction at low-temperatures is the orthorhombic $Pnma$
space group. We furthermore conclude that the magnetic intensity at $T < T_{N}$
is correctly described by the $Pn^\prime m^\prime a$ magnetic space group,
which crucially allows the ferromagnetic component observed in previous
single-crystal and powder magnetisation measurements. As such, the magnetic
structure of barlowite resembles that of the related material clinoatacamite,
Cu$_{4}$(OH)$_{6}$Cl$_{2}$, the parent compound of the well-known quantum spin
liquid candidate hebertsmithite, ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$.",1810.01684v1
2015/12/8,Development of magnetic liquid metal suspensions for magnetohydrodynamics,"A new class of materials is developed that is a liquid with both high
conductivity and magnetic susceptibility for magnetohydrodynamic (MHD)
applications. We develop a general method for making such suspensions and
demonstrate that various magnetic and non-magnetic metal particles, from 40 nm
- 500 microns in diameter, can be suspended in liquid gallium and its alloys.
The method uses an acid solution to prevent oxidation of the liquid metal and
metallic particles, which allows wetting and thus suspending. We can increase
the magnetic permeability by a factor of 5.0 by controlling the packing
fraction of magnetic particles, which gives these materials the potential to
exhibit strong MHD effects on the laboratory scale that are usually only
observable in the cores of planets and stars. We can independently tune the
viscosity by a factor of 230 by adding non-magnetic particles, which would
allow independent control of MHD effects from turbulence.",1512.02575v4
2016/3/4,Switching of both local ferroelectric and magnetic domains in multiferroic Bi0.9La0.1FeO3 thin film by mechanical force,"Cross-coupling of ordering parameters in multiferroic materials by multiple
external stimuli other than electric field and magnetic field is highly
desirable from both practical application and fundamental study points of view.
Recently, mechanical force has attracted great attention in switching of
ferroic ordering parameters via electro-elastic coupling in ferroelectric
materials. In this work, mechanical force induced polarization and
magnetization switching were investigated in a polycrystalline multiferroic
Bi0.9La0.1FeO3 thin film using a scanning probe microscopy system. The
piezoresponse force microscopy and magnetic force microscopy responses suggest
that both the ferroelectric domains and the magnetic domains in Bi0.9La0.1FeO3
film could be switched by mechanical force as well as electric field. High
strain gradient created by mechanical force is demonstrated as able to induce
ferroelastic switching and thus induce both ferroelectric dipole and magnetic
spin flipping in our thin film, as a consequence of electro-elastic coupling
and magneto-electric coupling. The demonstration of mechanical force control of
both the ferroelectric and the magnetic domains at room temperature provides a
new freedom for manipulation of multiferroics and could result in devices with
novel functionalities.",1603.01323v1
2020/4/12,Topological phase transition and nontrivial thermal Hall signatures in honeycomb lattice magnets,"We investigate spinon band topology and engineering from the interplay
between long-ranged magnetic order and fractionalized spinons, as well as
Zeeman coupling under external magnetic fields, in honeycomb lattice magnets.
The synergism of N\'eel order and magnetic fields could reconstruct the spinon
bands and drive a topological phase transition from the coexisting phase of
long-ranged order and chiral spin liquid with semion topological order to the
conventional magnetic order. Our prediction can be immediately tested through
thermal Hall transport measurements among the honeycomb lattice magnets that
are tuned to be proximate to the quantum critical point. Our theory should also
shed light on the critical behavior of honeycomb Kitaev materials with emergent
Majorana fermion bands. We suggest a possible relevance to the spin-1/2
honeycomb spin liquid candidate material In$_3$Cu$_2$VO$_9$.",2004.05633v1
2018/2/6,New magnetic phase of the chiral skyrmion material Cu2OSeO3,"The lack of inversion symmetry in the crystal lattice of magnetic materials
gives rise to complex non-collinear spin orders through interactions of
relativistic nature, resulting in interesting physical phenomena, such as
emergent electromagnetism. Studies of cubic chiral magnets revealed a universal
magnetic phase diagram, composed of helical spiral, conical spiral and skyrmion
crystal phases. Here, we report a remarkable deviation from this universal
behavior. By combining neutron diffraction with magnetization measurements we
observe a new multi-domain state in Cu2OSeO3. Just below the upper critical
field at which the conical spiral state disappears, the spiral wave vector
rotates away from the magnetic field direction. This transition gives rise to
large magnetic fluctuations. We clarify physical origin of the new state and
discuss its multiferroic properties.",1802.02070v2
2018/2/12,Dynamics and morphology of chiral magnetic bubbles in perpendicularly magnetized ultra-thin films,"We study bubble domain wall dynamics using micromagnetic simulations in
perpendicularly magnetized ultra-thin films with disorder and
Dzyaloshinskii-Moriya interaction. Disorder is incorporated into the material
as grains with randomly distributed sizes and varying exchange constant at the
edges. As expected, magnetic bubbles expand asymmetrically along the axis of
the in-plane field under the simultaneous application of out-of-plane and
in-plane fields. Remarkably, the shape of the bubble has a ripple-like part
which causes a kink-like (steep decrease) feature in the velocity versus
in-plane field curve. We show that these ripples originate due to the
nucleation and interaction of vertical Bloch lines. Furthermore, we show that
the Dzyaloshinskii-Moriya interaction field is not constant but rather depends
on the in-plane field. We also extend the collective coordinate model for
domain wall motion to a magnetic bubble and compare it with the results of
micromagnetic simulations.",1802.04215v1
2018/11/8,Magnetically-driven orbital-selective insulator-metal transition in double perovskite oxides,"Interaction-driven metal-insulator transitions or Mott transitions
  are widely observed in condensed-matter systems. In multi-orbital
  systems, many-body physics is richer in which an orbital-selective
  metal-insulator transition is an intriguing and unique
  phenomenon. Here we use first-principles calculations to show that a
  magnetic transition (from paramagnetic to long-range magnetically
  ordered) can simultaneously induce an orbital-selective
  insulator-metal transition in rock-salt ordered double perovskite
  oxides $A_2BB'$O$_6$ where $B$ is a non-magnetic ion (Y$^{3+}$ and
  Sc$^{3+}$) and $B'$ a
  magnetic ion with a $d^3$ electronic configuration (Ru$^{5+}$ and
  Os$^{5+}$). The orbital selectivity originates from
  geometrical frustration of a face-centered-cubic lattice on which
  the magnetic ions $B'$ reside. Including realistic structural
  distortions and spin-orbit interaction do
  not affect the transition. The predicted orbital-selective transition
  naturally explains the anomaly observed in the electric resistivity
  of Sr$_2$YRuO$_6$. Implications of other available experimental data
  are also discussed. Our work shows that by exploiting
  geometrical frustration on non-bipartite lattices, novel
  electronic/magnetic/orbital-coupled phase transitions can occur in
  correlated materials that are in the vicinity of metal-insulator phase
  boundary.",1811.03465v1
2019/2/13,Magnon transport in quasi-two-dimensional van der Waals antiferromagnets,"The recent emergence of 2D van der Waals magnets down to atomic layer
thickness provides an exciting platform for exploring quantum magnetism and
spintronics applications. The van der Waals nature stabilizes the long-range
ferromagnetic order as a result of magnetic anisotropy. Furthermore, giant
tunneling magnetoresistance and electrical control of magnetism have been
reported. However, the potential of 2D van der Waals magnets for magnonics,
magnon-based spintronics, has not been explored yet. Here, we report the
experimental observation of long-distance magnon transport in
quasi-twodimensional van der Waals antiferromagnet MnPS3, which demonstrates
the 2D magnets as promising material candidates for magnonics. As the 2D MnPS3
thickness decreases, a shorter magnon diffusion length is observed, which could
be attributed to the surface-impurity-induced magnon scattering. Our results
could pave the way for exploring quantum magnonics phenomena and designing
future magnonics devices based on 2D van der Waals magnets.",1902.04719v1
2019/5/28,RMATE: A device to test radiation-induced effects under controlled magnetic field and temperature,"This study shows the development and performance assessment of a novel set-up
that enables the research of structural materials for fusion reactors, by
making possible simultaneous application of temperature (up to 450$^{\circ}$C)
and magnetic field (close to 0.6 T) during irradiation experiments. These
aspects become critical as structural materials in fusion reactors are exposed
to intense radiation levels under the presence of strong magnetic fields.
Moreover, material microstructural could be modified by radiation-induce
propagating defects, which are thought to be sensitive to magnetic field. The
device has three main components: magnetic closure, sample holder with
integrated heater, and radiation shield. It is provided with a thermal shield
to prevent other elements of the device to heat up and fail. A mapping of the
magnetic flux in the region where sample and heater are located has been
modeled by finite elements simulation software and correlated with magnetic
measurements",1905.11988v1
2019/5/31,Intrinsic magnetism in monolayer transition metal trihalides: a comparative study,"Two dimensional magnetic materials, with tunable electronic properties could
lead to new spintronic, magnetic and magneto-optic applications. Here, we
explore intrinsic magnetic ordering in two dimensional monolayers of transition
metal tri-halides (MX$_3$, M = V, Cr, Mn, Fe and Ni, and X = F, Cl, Br and I),
using density functional theory. We find that other than FeX$_3$ family which
has an anti-ferromagnetic ground state, rest of the trihalides are
ferromagnetic. Amongst these the VX$_3$ and NiX$_3$ family are found to have
the highest magnetic transition temperature, beyond the room temperature. In
terms of electronic properties, the tri-halides of Mn and Ni are either half
metals or Dirac half metals, while the tri-halides of V, Fe and Cr are
insulators. Among all the trihalides studied in this paper, we find the
existence of very clean spin polarized Dirac half metallic state in MnF$_3$,
MnCl$_3$, MnBr$_3$, NiF$_3$ and NiCl$_3$. These spin polarized Dirac half
metals will be immensely useful for spin-current generation and other
spintronic applications.",1905.13677v1
2019/11/17,"Unconventional Spin-Glass-Like State in AgCo2V3O10, the Novel Magnetically Frustrated Material","Single crystals of a new silver and-cobalt based vanadate AgCo2V3O10 were
grown from a melted mixture. The crystal structure determination reveals that
this new vanadate crystallizes in triclinic system with space group P-1. The
structure of the titled compound is constructed from CoO6octahedra and VO4
tetrahedra sharing edges and vertices leading to an open three-dimensional
framework delimiting tunnels along [001], where the Ag cations are located. The
bands observed in Raman spectrum were assigned to corresponding vibrations of
the VO4 groups. DC and AC magnetization (susceptibility) measurements revealed
the spin-glass (SG) -type transition below a frequency-independent temperature
Tf(H) that is nearly independent on the applied magnetic field. Magnetic field
H> 10 kOe induces the spin glass antiferromagnet. These observations brings
AgCo2V3O10 into the class of geometrically frustrated magnetic systems.",1911.07175v1
2019/11/27,Large topological Hall effect in a geometrically frustrated kagome magnet Fe$_3$Sn$_2$,"We report on the observation of a large topological Hall effect (THE) over a
wide temperature region in a geometrically frustrated Fe3Sn2 magnet with a
kagome-bilayer structure. We found that the magnitude of the THE resistivity
increases with temperature and reaches -0.875 {\mu}{\Omega}.cm at 380 K.
Moreover, the critical magnetic fields with the change of THE are consistent
with the magnetic structure transformation, which indicates that the real-space
fictitious magnetic field is proportional to the formation of magnetic
skyrmions in Fe3Sn2. The results strongly suggest that the large THE originates
from the topological magnetic spin textures and may open up further research
opportunities in exploring emergent phenomena in kagome materials.",1911.12214v1
2020/2/18,The Launching of Cold Clouds by Galaxy Outflows III: The Influence of Magnetic Fields,"Motivated by observations of outflowing galaxies, we investigate the combined
impact of magnetic fields and radiative cooling on the evolution of cold clouds
embedded in a hot wind. We perform a collection of three-dimensional adaptive
mesh refinement, magnetohydrodynamical simulations that span two resolutions,
and include fields that are aligned and transverse to the oncoming,
super-Alfv\'enic material. Aligned fields have little impact on the overall
lifetime of the clouds over the non-magnetized case, although they do increase
the mixing between the wind and cloud material by a factor of $\approx 3.$
Transverse fields lead to magnetic draping, which isolates the clouds, but they
also squeeze material in the direction perpendicular to the field lines, which
leads to rapid mass loss. A resolution study suggests that the magnetized
simulations have somewhat better convergence properties than non-magnetized
simulations, and that a resolution of 64 zones per cloud radius is sufficient
to accurately describe these interactions. We conclude that the combined
effects of radiative cooling and magnetic fields are dependent on field
orientation, but are unlikely to enhance cloud lifetimes beyond the effect of
radiative cooling alone.",2002.07804v1
2020/7/28,"Data Assimilation Method for Experimental and First-Principles Data: Finite-Temperature Magnetization of (Nd,Pr,La,Ce)$_{2}$(Fe,Co,Ni)$_{14}$B","We propose a data-assimilation method for evaluating the finite-temperature
magnetization of a permanent magnet over a high-dimensional composition space.
Based on a general framework for constructing a predictor from two data sets
including missing values, a practical scheme for magnetic materials is
formulated in which a small number of experimental data in limited composition
space are integrated with a larger number of first-principles calculation data.
We apply the scheme to
(Nd$_{1-\alpha-\beta-\gamma}$Pr$_{\alpha}$La$_{\beta}$Ce$_{\gamma}$)$_{2}$(Fe$_{1-\delta-\zeta}$Co$_{\delta}$Ni$_{\zeta}$)$_{14}$B.
The magnetization in the whole $(\alpha, \beta, \gamma, \delta, \zeta)$ space
at arbitrary temperature is obtained. It is shown that the Co doping does not
enhance the magnetization at low temperatures, whereas the magnetization
increases with increasing $\delta$ above 320 K.",2007.14101v1
2020/10/29,Collective spin dynamics under dissipative spin Hall torque,"Current-induced spin torques in layered magnetic heterostructures have many
commonalities across broad classes of magnetic materials. These include not
only collinear ferromagnets, ferrimagnets, and antiferromagnets, but also more
complex noncollinear spin systems. We develop a general Lagrangian-Rayleigh
approach for studying the role of dissipative torques, which can pump energy
into long-wavelength magnetic dynamics, causing dynamic instabilities. While
the Rayleigh structure of such torques is similar for different magnetic
materials, their consequences depend sensitively on the nature of the order
and, in particular, on whether there is a net magnetic moment. The latter
endows the system with a unipolar switching capability, while magnetically
compensated materials tend to evolve towards limit cycles, at large torques,
with chirality dependent on the torque sign. Apart from the ferromagnetic and
antiferromagnetic cases, we discuss ferrimagnets, which display an intricate
competition between switching and limit cycles. As a simple case for
compensated noncollinear order, we consider isotropic spin glasses, as well as
a scenario of their coexistence with a collinear magnetic order.",2010.15994v1
2020/11/29,Analogy between the magnetic dipole moment at the surface of a magnetoelectric and the electric charge at the surface of a ferroelectric,"In honor of Igor Dzyaloshinskii on his 90th birthday, we revisit his
pioneering work on the linear magnetoelectric effect in light of the modern
theory of ferroelectric polarization. We show that the surface magnetic dipole
moment associated with magnetoelectric materials is analogous to the bound
surface charge in ferroelectrics, in that it can be conveniently described in
terms of a bulk magnetoelectric multipolization that is analogous to the
ferroelectric polarization. We define the intrinsic surface magnetization to be
this surface magnetic dipole moment per unit area, and provide a convenient
recipe for extracting it for any surface plane, from knowledge of the bulk
magnetic order. We demonstrate the procedure for the prototypical
magnetoelectric material, Cr$_2$O$_3$, in which Dzyaloshinskii first identified
the linear magnetoelectric effect, and compare the value of the intrinsic
surface magnetization to recent experimental measurements. Finally, we argue
that non-magnetoelectric antiferromagnets whose multipolization lattices do not
contain zero should have an intrinsic surface magnetization, in the same way
that non-polar insulators whose polarization lattices do not contain zero have
an intrinsic surface charge.",2011.14351v2
2021/1/18,Angle-dependent thermodynamics of $α$-RuCl$_3$,"Thermodynamics of the Kitaev honeycomb magnet $\alpha$-RuCl$_3$ is studied
for different directions of in-plane magnetic field using measurements of the
magnetic Gr\""uneisen parameter $\Gamma_B$ and specific heat $C$. We identify
two critical fields $B_c^{\rm AF1}$ and $B_c^{\rm AF2}$ corresponding,
respectively, to a transition between two magnetically ordered states and the
loss of magnetic order toward a quantum paramagnetic state. The $B_c^{AF2}$
phase boundary reveals a narrow region of magnetic fields where inverse melting
of the ordered phase may occur. No additional transitions are detected above
$B_c^{\rm AF2}$ for any direction of the in-plane field, although a shoulder
anomaly in $\Gamma_B$ is observed systematically at $8-10$ T. Large
field-induced entropy effects imply additional low-energy excitations at low
fields and/or strongly field-dependent phonon entropies. Our results establish
universal features of $\alpha$-RuCl$_3$ in high magnetic fields and challenge
the presence of a field-induced Kitaev spin liquid in this material.",2101.07275v1
2021/3/2,Magnetic slip casting: a review of current achievements and issues,"Ceramic materials are ubiquitous in technologies operating under high
mechanical, thermal or chemical constrains. Research in ceramic processing aims
at creating ceramics with properties that are still challenging to obtain, such
as toughness, transparency, conductivity, among others. Magnetic slip casting
is a ceramic process where an external magnetic field is used to align the
ceramic grains along preferential crystallographic directions, thereby creating
controlled texture. Over the past 20 years of research on magnetic slip
casting, ceramics of multiple chemistry were found to exhibit enhanced
properties as a result from the texturation. This paper reviews the progress in
the field of magnetic slip casting, details the processing parameters, the
textures obtained for a diverse range of ceramic materials. The achieved
mechanical and functional properties of the magnetically textured parts are
presented. This overview of the magnetic slip casting process allows to
identify critical directions for future advancement in advanced technical
ceramics",2103.01440v1
2021/8/2,Spin Wave Computing using pre-recorded magnetization patterns,"We propose a novel type of a spin wave computing device, based on a bilayer
structure which includes a bias layer, made from a hard magnetic material and a
propagation layer, made from a magnetic material with low damping, for example,
Yttrium Garnet (YiG) or Permalloy. The bias layer maintains a stable
pre-recorded magnetization pattern, generating a bias field with a desired
spatial dependence, which in turn sets the equilibrium magnetization inside the
propagation layer. When an external source applies an RF field or spinwave to
the propagation layer, excited spin waves scatter on the magnetization's
inhomogenuities, resulting in a complex interference behavior. One thus has the
ability to adjust spin wave propagation properties simply by altering the
magnetization in the bias layer. We demonstrate that the phenomenon can be
utilized to perform a variety of computational operations, including Fourier
Transform, Vector-Matrix multiplication and Grover search algorithm, with the
operational parameters exceeding conventional designs by orders of magnitude.",2108.00909v1
2021/8/3,Phonon spectrum of Pr$_2$Zr$_2$O$_7$ and Pr$_2$Ir$_2$O$_7$ as an evidence of coupling of the lattice with electronic and magnetic degrees of freedom,"Magnetic materials with pyrochlore crystal structure form exotic magnetic
states due to the high lattice frustration. In this work we follow the effects
of coupling of the lattice and electronic and magnetic degrees of freedom in
two Praseodymium-based pyrochlores Pr$_2$Zr$_2$O$_7$ and Pr$_2$Ir$_2$O$_7$. In
both materials the presence of magnetic interactions does not lead to
magnetically ordered low temperature states, however their electronic
properties are different. A comparison of Raman phonon spectra of
Pr$_2$Zr$_2$O$_7$ and Pr$_2$Ir$_2$O$_7$ allows us to identify magneto-elastic
coupling in Pr$_2$Zr$_2$O$_7$ that elucidates its magnetic properties at
intermediate temperatures, and allows us to characterize phonon-electron
coupling in the semimetallic Pr$_2$Ir$_2$O$_7$. We also show that the effects
of random disorder on the Raman phonon spectra is small.",2108.01664v2
2021/8/14,Voltage-controlled magnetism enabled by resistive switching,"The discovery of new mechanisms of controlling magnetic properties by
electric fields or currents furthers the fundamental understanding of magnetism
and has important implications for practical use. Here, we present a novel
approach of utilizing resistive switching to control magnetic anisotropy. We
study a ferromagnetic oxide that exhibits an electrically triggered
metal-to-insulator phase transition producing a volatile resistive switching.
This switching occurs in a characteristic spatial pattern: the formation of a
transverse insulating barrier inside a metallic matrix resulting in an unusual
ferromagnetic/paramagnetic/ferromagnetic configuration. We found that the
formation of this voltage-driven paramagnetic insulating barrier is accompanied
by the emergence of a strong uniaxial magnetic anisotropy that overpowers the
intrinsic material anisotropy. Our results demonstrate that resistive switching
is an effective tool for manipulating magnetic properties. Because resistive
switching can be induced in a very broad range of materials, our findings could
enable a new class of voltage-controlled magnetism systems.",2108.06445v1
2022/1/25,Quantum paramagnetism in the hyperhoneycomb Kitaev magnet $β$-ZnIrO$_3$,"A polycrystalline sample of the hyperhoneycomb iridate $\beta$-ZnIrO$_3$ was
synthesized via a topochemical reaction, and its structural, magnetic, and
thermodynamic properties were investigated. The magnetization and heat capacity
data show the absence of long-range magnetic order at least down to 2 K. A
positive Curie-Weiss temperature $\theta_W \sim 45$ K probed by the temperature
dependence of magnetic susceptibility indicates that a Kitaev interaction is
dominant. These observations suggest that a quantum spin liquid may have been
realized. Furthermore, the observation of linear temperature-dependent
contribution to the heat capacity with no magnetic field effect evidences
gapless excitation. These facts are surprisingly contrary to the chemical
disorder evidenced by the crystallographic analysis. By discussing the
differences in the size effect of Z$_2$-fluxes in 2D and 3D Kitaev magnets, we
propose that there is a hidden mechanism to protect the quantum spin liquid
state from chemical disorder.",2201.10119v1
2022/2/8,"Electronic, Magnetic and Vibrational Properties of Single Layer Aluminum Oxide","The structural, magnetic, vibrational and electronic properties of single
layer aluminum oxide (AlO2) are investigated by performing state-of-the-art
first-principles calculations. Total energy optimization and phonon
calculations reveal that aluminum oxide forms a distorted octahedral structure
(1T'-AlO2) in its single layer limit. It is also shown that surfaces of
1T'-AlO2 display magnetic behavior originating from the O atoms. While the
ferromagnetic (FM) state is the most favorable magnetic order for 1T'-AlO2,
transformation to a dynamically stable antiferromagnetic (AFM) state upon a
slight distortion in the crystal structure is also possible. It is also shown
that Raman activities (350-400 cm^-1) obtained from the vibrational spectrum
can be utilized to distinguish the possible magnetic phases of the crystal
structure. Electronically, both FM and the AFM phases are semiconductors with
an indirect band gap and they can form a type-III vdW heterojunction with
graphene-like ultra-thin materials. Moreover, it is predicted that presence of
oxygen defects that inevitably occur during synthesis and production do not
alter the magnetic state, even at high vacancy density. Apparently, ultra-thin
1T'-AlO2 with its stable crystal structure, semiconducting nature and robust
magnetic state is a quite promising material for nanoscale device applications.",2202.04144v1
2022/3/18,Plasmonic dichroism and all-optical magnetization switching in nanophotonic structures with GdFeCo,"We report on a phenomenon of plasmonic dichroism observed in magnetic
materials with the transverse magnetization under the excitation of the surface
plasmon polariton waves. The effect originates from the interplay of the two
magnetization-dependent contributions to the material absorption, both of which
are enhanced under plasmon excitation. Similar to the recently discovered
effect of a all-optical helicity-dependent magnetization switching, this effect
provides a possibility to perform a deterministic magnetization switching to
the desired state. We show by electromagnetic modeling that laser pulses
exciting counter-propagating plasmons can be used to write +M or -M state in a
deterministic way independent on the initial magnetization state. The presented
approach applies to various ferrimagnetic materials exhibiting the phenomenon
of all-optical switching of thermal nature and broadens the horizons of their
applications in data storage devices.",2203.09956v1
2022/5/13,Magnetic skyrmion lattices in a novel two-dimensional twisted bilayer magnet,"Magnetic skyrmions are topologically protected spin swirling vertices, which
are promising in device applications due to their particle-like nature and
excellent controlability. Magnetic skyrmions have been extensively studied in a
variety of materials and were proposed to exist in the extreme two-dimensional
limit, i.e., in twisted bilayer CrI$_3$ (TBCI). Unfortunately, the magnetic
states of TBCIs with small twist angles are disorderly distributed
ferromagnetic (FM) and antiferromagnetic (AFM) domains in recent experiments,
and thus the method to get rid of disorders in TBCIs is highly desirable. Here
we use intralayer exchange interactions up to the third nearest neighbors
without empirical parameters and very accurate interlayer exchange interactions
to study the magnetic states of TBCIs. We propose the functions of interlayer
exchange interactions obtained using first-principles calculations and stored
in symmetry-adapted artificial neural networks. Based on them, the subsequent
Landau-Lifshitz-Gillbert equation calculations explain the disorderly
distributed FM-AFM domains in TBCIs with small twist angles and predict the
orderly distributed skyrmions in TBCIs with large twist angles. This novel
twisted two-dimensional bilayer magnet can be used to design memory devices,
monochromatic spin wave generators and many kinds of skyrmion lattices.",2205.06438v2
2022/5/14,Tutorial: A Beginner's Guide to Interpreting Magnetic Susceptibility Data with the Curie-Weiss Law,"Magnetic susceptibility measurements are often the first characterization
tool that researchers turn to when beginning to assess the magnetic nature of a
newly discovered material. Breakthroughs in instrumentation have made the
collection of high quality magnetic susceptibility data more accessible than
ever before. However, the analysis of susceptibility data remains a common
challenge for newcomers to the field of magnetism. While a comprehensive
treatment of the theoretical aspects of magnetism are found in numerous
excellent textbooks, there is a gap at the point of practical application. We
were inspired by this obstacle to put together this guide to the analysis and
interpretation of magnetic susceptibility data, with an emphasis on materials
that exhibit Curie-Weiss paramagnetism.",2205.07107v1
2022/5/21,"Spin Seebeck Effect: Sensitive Probe for Elementary Excitation, Spin Correlation, Transport, Magnetic Order, and Domains in Solids","The spin Seebeck effect (SSE) refers to the generation of a spin current as a
result of a temperature gradient in a magnetic material, which can be detected
electrically via the inverse spin Hall effect in a metallic contact. Since the
discovery of SSE in 2008, intensive studies on SSE have been conducted to
elucidate its origin. SSEs appear in a wide range of magnetic materials
including ferro-, ferri-, and antiferro-magnets and also paramagnets with
classical or quantum spin fluctuation. SSE voltage reflects fundamental
properties of a magnet, such as elementary excitation, static magnetic order,
spin correlation, and spin transport. In this article, we review recent
progress on SSEs in various systems, with particular emphasis on its emerging
role as a probe of these magnetic properties in solids. We also briefly discuss
the recently-discovered nuclear SSE.",2205.10509v2
2022/6/7,Hydrogen-impurity induced unconventional magnetism in semiconducting molybdenum ditelluride,"Layered transition-metal dichalcogenides are proposed as building blocks for
van der Waals (vdW) heterostructures due to their graphene-like two dimensional
structure. For this purpose, a magnetic semiconductor could represent an
invaluable component for various spintronics and topotronics devices. Here, we
combine different local magnetic probe spectroscopies with angle-resolved
photoemission and density-functional theory calculations to show that 2H-MoTe2
is on the verge of becoming magnetic. Our results present clear evidence that
the magnetism can be ""switched on"" by a hydrogen-like impurity. We also show
that this magnetic state survives up to the free surface region, demonstrating
the material's potential applicability as a magnetic component for thin-film
heterostructures.",2206.03051v1
2022/6/30,Strain engineering of the magnetic anisotropy and magnetic moment in NdFeO3 epitaxial thin films,"Strain engineering is a powerful mean for tuning the various functionalities
of ABO3 perovskite oxide thin films. Rare-earth orthoferrite RFeO3 materials
such as NdFeO3 (NFO) are of prime interest because of their intriguing magnetic
properties as well as their technological potential applications especially as
thin films. Here, using a large set of complementary and advanced techniques,
we show that NFO epitaxial thin films, successfully grown by pulsed laser
deposition on (001)-SrTiO3, show a strong magnetic anisotropy below a critical
thickness tc of 54 nm, associated with the occurrence of structural
modifications related to symmetry and domain pattern changes. By varying the
tensile misfit strain through the decrease of film thickness below tc, the
amplitudes of in and out-of-plane magnetization can be continuously tuned while
their ratio stays constant. Furthermore, different low-temperature magnetic
behaviors are evidenced for strained and relaxed films, suggesting that the
strain-induced structural state impacts the magnetic phase stability.",2206.15071v1
2022/8/11,Electron magnetic moment of transient chiral phonons in KTaO$_3$,"High intensity THz lasers allow for the coherent excitation of individual
phonon modes. The ultrafast control of emergent magnetism by means of phonons
opens up new tuning mechanisms for functional materials. While theoretically
predicted phonon magnetic moments are tiny, recent experiments hint towards a
significant magnetization in various materials. To explain these phenomena, we
derive a coupling mechanism between the phonon angular momentum and the
electron spin. This coupling introduces the transient level-splitting of
spin-up and spin-down channels and a resulting magnetization. We estimate this
magnetization on the example of the lowest infrared active mode in the
perovskite KTaO$_3$. Our results show an electronic magnetic moment of $\approx
10^{-1}$ $\mu_B$ per unit cell, depending on the doping level and electron
temperature.",2208.05746v2
2022/8/23,Anomalous electrical transport and magnetic skyrmions in Mn-tuned Co9Zn9Mn2 single crystals,"\b{eta}-Mn-type CoxZnyMnz (x + y + z = 20) alloys have recently attracted
increasing attention as a new class of chiral magnets with skyrmions at and
above room temperature. However, experimental studies on the transport
properties of this material are scarce. In this work, we report the successful
growth of the \b{eta}-Mn-type Co9.24Zn9.25Mn1.51 and Co9.02Zn9.18Mn1.80 single
crystals and a systematic study on their magnetic and transport properties. The
skyrmion phase was found in a small temperature range just below the Curie
temperature. The isothermal ac susceptibility and dc magnetization as a
function of magnetic field confirm the existence of the skyrmion phase. A
negative linear magnetoresistance over a wide temperature range from 2 K to 380
K is observed and attributed to the suppression of the magnetic ordering
fluctuation under high fields. Both the magnetization and electrical
resistivity are almost isotropic. The quantitative analysis of the Hall
resistance suggests that the anomalous Hall effect of Co9.24Zn9.25Mn1.51 and
Co9.02Zn9.18Mn1.80 single crystals is dominated by the intrinsic mechanism. Our
findings contribute to a deeper understanding of the properties of CoxZnyMnz (x
+ y + z = 20) alloys material and advance their application in spintronic
devices.",2208.10955v1
2022/11/19,Deep-learning electronic-structure calculation of magnetic superstructures,"Ab initio study of magnetic superstructures (e.g., magnetic skyrmion) is
indispensable to the research of novel materials but bottlenecked by its
formidable computational cost. For solving the bottleneck problem, we develop a
deep equivariant neural network method (named xDeepH) to represent density
functional theory Hamiltonian $H_\text{DFT}$ as a function of atomic and
magnetic structures and apply neural networks for efficient electronic
structure calculation. Intelligence of neural networks is optimized by
incorporating a priori knowledge about the important locality and symmetry
properties into the method. Particularly, we design a neural-network
architecture fully preserving all equivalent requirements on $H_\text{DFT}$ by
the Euclidean and time-reversal symmetries ($E(3) \times \{I, T\}$), which is
essential to improve method performance. High accuracy (sub-meV error) and good
transferability of xDeepH are shown by systematic experiments on nanotube,
spin-spiral, and Moir\'{e} magnets, and the capability of studying magnetic
skyrmion is also demonstrated. The method could find promising applications in
magnetic materials research and inspire development of deep-learning ab initio
methods.",2211.10604v1
2023/1/7,Crucial role of Fe in determining the hard magnetic properties of Nd$_2$Fe$_{14}$B,"Nd$_2$Fe$_{14}$B's unsurpassed, hard magnetic properties for a wide range of
temperatures result from a combination of a large volume magnetization from Fe
and a strong single-ion anisotropy from Nd. Here, using finite temperature
first-principles calculations, we focus on the other crucial roles played by
the Fe atoms in maintaining the magnetic order on the Nd sublattices, and hence
the large magnetic anisotropy, and directly generating significant uniaxial
anisotropy at high temperatures. We identify effective spins for atomistic
modelling from the material's interacting electrons and {quantify pairwise and
higher order, non-pairwise magnetic interactions among them. We find the Nd
spins couple most strongly to spins on sites belonging to two specific Fe
sublattices, 8$j_1$, 8$j_2$. Moreover the Fe 8$j_1$ sublattice also provides
the electronic origin of the unusual, nonmonotonic temperature dependence of
the anisotropy of Y$_2$Fe$_{14}$B.} Our work provides atomic-level resolution
of the properties of this fascinating magnetic material.",2301.02868v1
2023/4/24,Gate-tunable ferromagnetism in a van der Waals magnetic semimetal,"Magnetic semimetals form an attractive class of materials because of the
non-trivial contributions of itinerant electrons to magnetism. Due to their
relatively low-carrier-density nature, a doping level of those materials could
be largely tuned by a gating technique. Here we demonstrate gate-tunable
ferromagnetism in an emergent van der Waals magnetic semimetal Cr3Te4 based on
an ion-gating technique. Upon doping electrons into the system, the Curie
temperature (TC) sharply increases, approaching near to room temperature, then
decreases to some extent. Interestingly, this non-monotonous variation of TC
accompanies the switching of the magnetic anisotropy. Furthermore, such
evolutions of TC and anisotropy occur synchronously with the sigh changes of
the ordinary and anomalous Hall effects. Those results clearly elucidate that
the magnetism in Cr3Te4 should be governed by its semimetallic band nature,
where the band crossing points play a crucial role both for the
magneto-transport properties and magnetism itself.",2304.11890v1
2023/7/14,"Frustration-induced magnetic bimerons in transition metal halide CoX2 (X = Cl, Br) monolayers","With the field of two-dimensional (2D) magnetic materials expanding rapidly,
noncollinear topological magnetic textures in 2D materials are attracting
growing interest recently. As the in-plane counterpart of magnetic skyrmions,
magnetic bimerons have the same topological advantages, but are rarely observed
in experiments. Employing first-principles calculations and Monte Carlo
simulations, we predict that the centrosymmetric transition metal halide CoX2
(X = Cl, Br) monolayers can be promising candidates for observing the
frustration-induced bimerons. These bimerons crystallize into stable triangular
lattice under an appropriate magnetic field. Compared to the skyrmions driven
by the Dzyaloshinskii-Moriya interaction or the long-ranged magnetic
dipole-dipole interactions, these frustration-induced bimerons have much
smaller size and flexible tunability. Furthermore, the biaxial strain provides
an effective method to tune the frustration and thereby to tune the bimeron
lattice. In detail, for CoCl2 monolayer, tensile strain can be applied to
generate bimeron lattice, further shrink bimeron size and increase the density
of bimerons. For CoBr2 monolayer with inherent bimeron lattice state, a unique
orientation rotation of bimeron lattice controlled by compressive strain is
predicted.",2307.07253v1
2023/9/29,Magnetic order in the two-dimensional metal-organic framework manganese pyrazinecarboxylate with Mn-Mn dimers,"The magnetic properties of [Mn(pyrazinecarboxylate)2]n (Mn-pyrazine),
empirical formula C10H6MnN4O4, are investigated through susceptibility, heat
capacity and neutron scattering measurements. The structure of Mn-pyrazine
consists of Mn-Mn dimers linked on a distorted 2D hexagonal structure. The weak
out of plane interactions create a quasi-2D magnetic material within the larger
three dimensional metal organic framework (MOF) structure. We show that this
material undergoes a two stage magnetic transition, related to the low
dimensionality of the Mn lattice. First at 5 K, which is assigned to the
initial development of short range order in the 2D layers. This is followed by
long range order at 3.3 K. Applied field measurements reveal the potential to
induce magnetic transitions in moderately small fields of 2 T. Neutron powder
diffraction enabled the determination of a unique magnetic space group P21'/c
(#14.77) at 1.5 K. This magnetic structure consists of antiferromagnetically
coupled Mn-Mn dimers with spins principally along the out of plane a-axis.",2310.00083v1
2023/10/2,Adiabatic demagnetization refrigeration to mK temperatures with the distorted square lattice magnet NaYbGeO$_{4}$,"We report the synthesis, characterization, low-temperature magnetic, and
thermodynamic measurements of the novel milli-Kelvin adiabatic demagnetization
refrigeration (mK-ADR) candidate material NaYbGeO$_4$ which exhibits a
distorted square lattice arrangement of YbO$_{6}$ magnetic units. Magnetization
and specific heat indicate weakly interacting effective spin-1/2 moments below
10~K, with a Curie-Weiss temperature of only 15~mK, that can be polarized by
magnetic fields of order 1~T. For the ADR performance test, we start the
demagnetization from 5~T at a temperature of $\sim 2$~K and reach a minimum
temperature of 150~mK at zero field. The warming curve indicates a sharp
magnetic transition in the heat capacity at 210~mK, implying only weak magnetic
frustration. The entropy density of $S_{\rm GS}\simeq 101$ mJ K$
^{-1}$cm$^{-3}$ and hold time below 2~K of 220~min are competitive while the
minimal temperature is higher compared to frustrated Ytterbium-oxide ADR
materials studied under similar conditions.",2310.00961v1
2023/10/6,Turning non-magnetic two-dimensional molybdenum disulfide into room temperature magnets by the synergistic effect of strain engineering and charge injection,"The development of two-dimensional (2D) room temperature magnets is of great
significance to the practical application of spintronic devices. However, the
number of synthesized intrinsic 2D magnets is limited and the performances of
them are not satisfactory, e.g. typically with low Curie temperature and poor
environmental stability. Magnetic modulation based on developed 2D materials,
especially non-magnetic 2D materials, can bring us new breakthroughs. Herein,
we report room temperature ferromagnetism in halogenated MoS2 monolayer under
the synergistic effect of strain engineering and charge injection, and the
combined implementation of these two processes is based on the halogenation of
MoS2. The adsorbed halogen atoms X (X = F, Cl, and Br) on the surface leads to
lattice superstretching and hole injection, resulting in MoS2 monolayer
exhibiting half-metallic properties, with one spin channel being gapless in the
band structure. The Curie temperature of halogenated MoS2 monolayer is 513~615
K, which is much higher than the room temperature. In addition, large magnetic
anisotropy energy and good environmental stability make halogenated MoS2
display great advantages in practical spintronic nanodevices.",2310.03995v2
2023/12/13,Ultrafast light-induced magnetization in non-magnetic films: from orbital and spin Hall phenomena to the inverse Faraday effect,"The field of orbitronics has emerged with great potential to impact
information technology by enabling environmentally friendly electronic devices.
The main electronic degree of freedom at play is the orbital angular momentum,
which can give rise to a myriad of phenomena such as the orbital Hall effect
(OHE), torques and orbital magnetoelectric effects. Here, we explore via
realistic time-dependent electronic structure simulations the magnetic response
of a non-magnetic material, an ultrathin Pt film, to ultrafast laser pulses of
different polarizatons and helicities. We demonstrate the generation of
significant orbital and spin magnetizations and identify the underlying
mechanisms consisting of the interplay of the OHE, inverse Faraday effect and
spin-orbit interaction. Our discoveries advocate for the prospect of encoding
magnetic information using light in materials that are not inherently magnetic.",2312.07888v1
2024/1/1,Calculation of Gilbert damping and magnetic moment of inertia using torque-torque correlation model within ab initio Wannier framework,"Magnetization dynamics in magnetic materials are well described by the
modified semiclassical Landau-Lifshitz-Gilbert (LLG) equation, which includes
the magnetic damping $\alpha$ and the magnetic moment of inertia $\mathrm{I}$
tensors as key parameters. Both parameters are material-specific and physically
represent the time scales of damping of precession and nutation in
magnetization dynamics. $\alpha$ and $\mathrm{I}$ can be calculated quantum
mechanically within the framework of the torque-torque correlation model. The
quantities required for the calculation are torque matrix elements, the real
and imaginary parts of the Green's function and its derivatives. Here, we
calculate these parameters for the elemental magnets such as Fe, Co and Ni in
an ab initio framework using density functional theory and Wannier functions.
We also propose a method to calculate the torque matrix elements within the
Wannier framework. We demonstrate the effectiveness of the method by comparing
it with the experiments and the previous ab initio and empirical studies and
show its potential to improve our understanding of spin dynamics and to
facilitate the design of spintronic devices.",2401.00714v1
2011/7/12,Magnetic superspace groups and symmetry constraints in incommensurate magnetic phases,"Although superspace formalism has become the standard approach for the
analysis of structurally modulated crystals, it has remained during the last
thirty years almost unexplored as a practical tool to deal with magnetic
incommensurate structures. This situation has recently changed with the
development of new computer tools for magnetic phases based on this formalism.
In this context we show here that, as in the case of nonmagnetic incommensurate
systems, the concept of superspace symmetry provides a simple, efficient and
systematic way to characterize the symmetry and rationalize the structural and
physical properties of incommensurate magnetic materials. The method introduces
significant advantages over the most commonly employed method of representation
analysis for the description of the magnetic structure of a crystal. But, more
importantly, in contrast with that method, it consistently yields and
classifies all degrees of freedom of the system. The knowledge of the
superspace group of an incommensurate magnetic material allows to predict its
crystal tensor properties and to rationalize its phase diagram, previous to any
appeal to microscopic models or mechanisms. This is especially relevant when
the properties of incommensurate multiferroics are being studied. We present
first a summary of the superspace method under a very practical viewpoint
particularized to magnetic modulations. Its relation with the usual
representation analysis is then analyzed in detail, with the derivation of
important general rules for magnetic modulations with a single propagation
vector. The power and efficiency of the formalism is illustrated with various
selected examples, including some multiferroic materials.",1107.2358v2
2012/12/5,"High Precision Magnetic Linear Dichroism Measurements in (Ga,Mn)As","Investigation of magnetic materials using the first-order magneto-optical
Kerr effects (MOKE) is well established and is frequently used in the
literature. On the other hand, the utilization of the second-order (or
quadratic) magneto-optical (MO) effects for the material research is rather
rare. This is due to the small magnitude of quadratic MO signals and the fact
that the signals are even in magnetization (i.e., they do not change a sign
when the magnetization orientation is flipped), which makes it difficult to
separate second-order MO signals from various experimental artifacts. In 2005 a
giant quadratic MO effect - magnetic linear dichroism (MLD) - was observed in
the ferromagnetic semiconductor (Ga,Mn)As. This discovery not only provided a
new experimental tool for the investigation of in-plane magnetization dynamics
in (Ga,Mn)As using light at normal incidence, but it also motivated the
development of experimental techniques for the measurement of second-order MO
effects in general. In this paper we compare four different experimental
techniques that can be used to measure MLD and to separate it from experimental
artifacts. We show that the most reliable results are obtained when the
harmonic dependence of MLD on a mutual orientation of magnetization and light
polarization plane is used together with the in-situ rotation of the sample
followed by the magnetic field-induced rotation of magnetization. Using this
technique we measure the MLD spectra of (Ga,Mn)As in a broad spectral range
from 0.1 eV to 2.7 eV and we observe that MLD has a comparable magnitude as
polar MOKE signals in this material.",1212.0956v1
2013/3/22,Unconventional and Exotic Magnetism in Carbon-Based Structures and Related Materials,"The detailed analysis of the problem of possible magnetic behavior of the
carbon-based structures was fulfilled to elucidate and resolve (at least
partially) some unclear issues. It was the purpose of the present paper to look
somewhat more critically into some conjectures which have been made and to the
peculiar and contradictory experimental results in this rather indistinct and
disputable field. Firstly the basic physics of magnetism was briefly addressed.
Then a few basic questions were thoroughly analyzed and critically reconsidered
to elucidate the possible relevant mechanism (if any) which may be responsible
for observed peculiarities of the ""magnetic"" behavior in these systems. The
arguments supporting the existence of the intrinsic magnetism in carbon-based
materials, including pure graphene were analyzed critically. It was concluded
that recently published works have shown clearly that the results of the
previous studies, where the ""ferromagnetism"" was detected in pure graphene,
were incorrect. Rather, graphene is strongly diamagnetic, similar to graphite.
Thus the possible traces of a quasi-magnetic behavior which some authors
observed in their samples may be attributed rather to induced magnetism due to
the impurities, defects, etc. On the basis of the present analysis the
conclusion was made that the thorough and detailed experimental studies of
these problems only may shed light on the very complicated problem of the
magnetism of carbon-based materials. Lastly the peculiarities of the magnetic
behavior of some related materials and the trends for future developments were
mentioned.",1303.6233v1
2014/9/24,Field tunable spin density wave phases in Sr3Ru2O7,"The conduction electrons in a metal experience competing interactions with
each other and the atomic nuclei. This competition can lead to many types of
magnetic order in metals. For example, in chromium the electrons order to form
a spin-density-wave (SDW) antiferromagnetic state. A magnetic field may be used
to perturb or tune materials with delicately balanced electronic interactions.
Here we show that the application of a magnetic field can induce SDW magnetic
order in a metal, where none exists in the absence of the field. We use
magnetic neutron scattering to show that the application of a large (~8T)
magnetic field to the metamagnetic perovskite metal Sr3Ru2O7 can be used to
tune the material through two magnetically-ordered SDW states. The ordered
states exist over relatively small ranges in field (<0.4T) suggesting that
their origin is due to a new mechanism related to the electronic fine structure
near the Fermi energy, possibly combined with the stabilising effect of
magnetic fluctuations. The magnetic field direction is shown to control the SDW
domain populations which naturally explains the strong resistivity anisotropy
or electronic nematic behaviour observed in this material.",1409.7054v2
2016/2/25,Silicide Induced Surface Defects in FePt nanoParticle fcc-to-fct Thermally Activated Phase Transition,"Magnetic nanoparticles (MnPs) are relevant to a wide range of applications
including high density information storage and magnetic resonance imaging to
name but a few. Among the materials available to prepare MnPs, FePt is
attracting growing attention. However, to harvest the strongest magnetic
properties of FePt MnPs, a thermal annealing is often required to convert
face-centered cubic as synthesized nPs into its tetragonal phase. Rarely
addressed are the potential side effects of such treatments on the magnetic
properties. In this study, we focus on the impact of silica shells often used
in strategies aiming at overcoming MnP coalescence during the thermal
annealing. While we show that this shell does prevent sintering, and that
fcc-to-fct conversion does occur, we also reveal the formation of silicide,
which can prevent the stronger magnetic properties of fct-FePt MnPs from being
fully realised. This report therefore sheds lights on poorly investigated and
understood interfacial phenomena occurring during the thermal annealing of MnPs
and, by doing so, also highlights the benefits of developing new strategies to
avoid silicide formation.",1602.07804v3
2019/6/9,Antiferromagnetic ordering in van der Waals two-dimensional magnetic material MnPS3 probed by Raman spectroscopy,"Magnetic ordering in the two-dimensional limit has been one of the most
important issues in condensed matter physics for the past several decades. The
recent discovery of new magnetic van der Waals materials heralds a much-needed
easy route for the studies of two-dimensional magnetism: the thickness
dependence of the magnetic ordering has been examined by using Ising- and
XXZ-type magnetic van der Waals materials. Here, we investigated the magnetic
ordering of MnPS3, a two-dimensional antiferromagnetic material of
Heisenberg-type, by Raman spectroscopy from bulk all the way down to bilayer.
The phonon modes that involve the vibrations of Mn ions exhibit characteristic
changes as the temperature gets lowered through the N\'eel temperature. In bulk
MnPS3, the Raman peak at ~155 cm-1 becomes considerably broadened near the
N\'eel temperature and upon further cooling is subsequently red-shifted. The
measured peak positions and polarization dependences of the Raman spectra are
in excellent agreement with our first-principles calculations. In few-layer
MnPS3, the peak at ~155 cm-1 exhibits the characteristic red-shift at low
temperatures down to the bilayer, indicating that the magnetic ordering is
surprisingly stable at such a thin limit. Our work sheds light on the hitherto
unexplored magnetic ordering in the Heisenberg-type antiferromagnetic systems
in the atomic-layer limit.",1906.05802v1
2019/8/6,The complex non-collinear magnetic orderings in Ba2YOsO6: A new approach to tuning spin-lattice interactions and controlling magnetic orderings in frustrated complex oxides,"Frustrated magnets are one class of fascinating materials that host many
intriguing phases such as spin ice, spin liquid and complex long-range magnetic
orderings at low temperatures. In this work we use first-principles
calculations to find that in a wide range of magnetically frustrated oxides, at
zero temperature a number of non-collinear magnetic orderings are more stable
than the type-I collinear ordering that is observed at finite temperatures. The
emergence of non-collinear orderings in those complex oxides is due to
higher-order exchange interactions that originate from second-row and third-row
transition metal elements. This implies a collinear-to-noncollinear spin
transition at sufficiently low temperatures in those frustrated complex oxides.
Furthermore, we find that in a particular oxide Ba$_2$YOsO$_6$, experimentally
feasible uniaxial strain can tune the material between two different
non-collinear magnetic orderings. Our work predicts new non-collinear magnetic
orderings in frustrated complex oxides at very low temperatures and provides a
mechanical route to tuning complex non-collinear magnetic orderings in those
materials.",1908.01916v1
2020/3/22,An electron-counting rule to determine the interlayer magnetic coupling of the van der Waals materials,"In layered magnetic materials, the magnetic coupling between neighboring van
der Waals layers is challenging to understand and anticipate, although the
exchange interaction inside a layer can be well rationalized for example by the
superexchange mechanism. In this work, we elucidate the interlayer exchange
mechanism and propose an electron-counting rule to determine the interlayer
magnetic order between van der Waals layers, based on counting the $d$-orbital
occupation ($d^n$, where $n$ is the number of $d$-electrons at the magnetic
cation). With this rule, we classify magnetic monolayers into two groups,
type-I ($n<5$) and type-II ($n\geq5$), and derive three types of interlayer
magnetic coupling for both insulators and metals. The coupling between two
type-II layers prefers the antiferromagnetic (AFM) order, while type-I and
type-II interfaces favor the ferromagnetic (FM) way. However, for two type-I
layers, they display competition between FM and AFM orders and even lead to the
stacking dependent magnetism. Additionally, metallic layers can also be
incorporated into this rule with a minor correction from the free carrier
hopping. Therefore, this rule provides simple guidance to understand the
interlayer exchange and further design van der Waals junctions with desired
magnetic orders.",2003.09942v2
2019/12/20,Picosecond spin-orbit torque switching of ferrimagnets,"Spintronics provides an efficient platform for realizing non-volatile memory
and logic devices. In these systems, data is stored in the magnetization of
magnetic materials, and magnetization is switched in the writing process. In
conventional spintronic devices, ferromagnetic materials are used which have a
magnetization dynamics timescale of around the nanoseconds, setting a limit for
the switching speed. Increasing the magnetization switching speed has been one
of the challenges in spintronic research. In this work we take advantage of the
ultrafast magnetization dynamics in ferrimagnetic materials instead of
ferromagnets, and we use femtosecond laser pulses and a photoconductive Auston
switch to create picosecond current pulses for switching the ferrimagnet. By
anomalous Hall and magneto-optic Kerr (MOKE) measurement, we demonstrate the
robust picosecond SOT driven magnetization switching of ferrimagnetic GdFeCo.
The time-resolved MOKE shows more than 50 GHz magnetic resonance frequency of
GdFeCo, indicating faster than 20 ps spin dynamics and tens of picosecond SOT
switching speed. Our work provides a promising route to realize picosecond
operation speed for non-volatile magnetic memory and logic applications.",1912.10129v1
2020/5/29,Electron spin resonance and ferromagnetic resonance spectroscopy in the high-field phase of the van der Waals magnet CrCl$_3$,"We report a comprehensive high-field/high-frequency electron spin resonance
(ESR) study on single crystals of the van der Waals magnet CrCl$_3$. This
material, although being known for quite a while, has received recent
significant attention in a context of the use of van der Waals magnets in novel
spintronic devices. Temperature-dependent measurements of the resonance fields
were performed between 4 and 175 K and with the external magnetic field applied
parallel and perpendicular to the honeycomb planes of the crystal structure.
These investigations reveal that the resonance line shifts from the
paramagnetic resonance position already at temperatures well above the
transition into a magnetically ordered state. Thereby the existence of
ferromagnetic short-range correlations above the transition is established and
the intrinsically two-dimensional nature of the magnetism in the title compound
is proven. To study details of the magnetic anisotropies in the field-induced
effectively ferromagnetic state at low temperatures, frequency-dependent
ferromagnetic resonance (FMR) measurements were conducted at 4 K. The observed
anisotropy between the two magnetic-field orientations is analyzed by means of
numerical simulations based on a phenomenological theory of FMR. These
simulations are in excellent agreement with measured data if the shape
anisotropy of the studied crystal is taken into account, while the
magnetocrystalline anisotropy is found to be negligible in CrCl$_3$. The
absence of a significant intrinsic anisotropy thus renders this material as a
practically ideal isotropic Heisenberg magnet.",2005.14559v1
2020/12/18,Complex magnetic phases in polar tetragonal intermetallic NdCoGe$_3$,"Polar materials can host a variety of topologically significant magnetic
phases, which often emerge from a modulated magnetic ground state. Relatively
few noncentrosymmetric tetragonal materials have been shown to host topological
spin textures and new candidate materials are necessary to expand the current
theoretical models. This manuscript reports on the anisotropic magnetism in the
polar, tetragonal material NdCoGe$_3$ via thermodynamic and neutron diffraction
measurements. The previously reported $H$-$T$ phase diagram is updated to
include several additional phases, which exist for both $H$ = 0 and with an
applied field H$\perp$ c. Neutron diffraction data reveal that the magnetic
structures below $T_{N1}$ = 3.70 K and $T_{N2}$ = 3.50 K are incommensurate,
with a ground state magnetic order that is incommensurate in all directions
with the propagation vector $\vec{k}$ = (0.494, 0.0044, 0.385) at 1.8 K. A
unique magnetic structure solution is not achievable, but the possible single
and multi-$\vec{k}$ spin models are discussed. These results demonstrate that
NdCoGe3 hosts complicated magnetic order derived from modulated magnetic
moments.",2012.10499v1
2020/12/21,Recent Progress in Proximity Coupling of Magnetism to Topological Insulators,"Inducing long-range magnetic order in three-dimensional topological
insulators can gap the Diraclike metallic surface states, leading to exotic new
phases such as the quantum anomalous Hall effect or the axion insulator state.
These magnetic topological phases can host robust, dissipationless charge and
spin currents or unique magnetoelectric behavior, which can be exploited in
low-energy electronics and spintronics applications. Although several different
strategies have been successfully implemented to realize these states, to date
these phenomena have been confined to temperatures below a few Kelvin. In this
review, we focus on one strategy, inducing magnetic order in topological
insulators by proximity of magnetic materials, which has the capability for
room temperature operation, unlocking the potential of magnetic topological
phases for applications. We discuss the unique advantages of this strategy, the
important physical mechanisms facilitating magnetic proximity effect, and the
recent progress to achieve, understand, and harness proximity-coupled magnetic
order in topological insulators. We also highlight some emerging new phenomena
and applications enabled by proximity coupling of magnetism and topological
materials, such as skyrmions and the topological Hall effect, and we conclude
with an outlook on remaining challenges and opportunities in the field.",2012.11248v1
2022/3/24,Effect of vacancy defects on geometrically frustrated magnets,"Quenched disorder may prevent the formation of the widely sought
quantum-spin-liquid states (QSLs) or mask their signatures by inducing a
spin-glass state, which is why considerable experimental efforts are directed
at purifying materials that may host QSLs. However, in geometrically frustrated
(GF) magnets, the largest class of materials in which QSLs are sought, the
glass-transition temperature $T_g$ grows with decreasing the density of vacancy
defects, accompanied by a simultaneous growth of the magnetic susceptibility.
In this paper, we develop a phenomenological theory of glass transitions and
magnetic susceptibility in 3D geometrically frustrated (GF) magnetic materials.
We consider a model of a GF magnet in which the glass transition occurs in the
absence of vacancies, e.g., due to other types of quenched disorder. We show
that disorder that creates weak local perturbations, e.g. weak random strain,
leads to the growth of the transition temperature $T_g$. By contrast, vacancies
reduce $T_g$ for small vacancy concentrations. Another consequence of the
presence of vacancies is the creation of quasispins, effective magnetic moments
localised near the vacancies, that contribute to the magnetic susceptibility of
the system together with the bulk spins. We show that increasing the vacancy
density leads to an increase of the total magnetic susceptibility.",2203.13330v2
2022/5/11,Hybrid ab initio method for examining thermal properties in magnetic materials,"A hybrid ab initio theoretical approach for examining thermal properties in
magnetic systems of unknown entropy is presented. Commonly used theoretical
approaches interrogate thermal properties from Gibbs/Helmholtz free energies,
which require an accurate model of magnetic interactions. The present approach
avoids this requirement by instead calculating system pressure from thermally
disordered microstates that properly incorporate vibrational and spin
subsystems at each temperature as well as the coupling between these
subsystems. In place of a specific model for magnetic interactions, the
approach integrates measurements of temperature dependent magnetization of the
studied material. We apply the approach to calculate phonon modes and to
investigate the anomalously low thermal expansion of the classical Invar alloy,
Fe_0.65Ni_0.35. The calculated phonon dispersions for Invar are in excellent
agreement with measured data. The Invar thermal expansion is shown to remain
small between 50 K and room temperature, consistent with the experimentally
observed low thermal expansion value in this same temperature range. This
anomalously small thermal expansion is directly connected to a small positive
contribution from lattice thermal disorder that is nearly canceled by a large
negative magnetic disorder contribution. By contrast, calculations for bcc Fe
show a much larger thermal expansion, consistent with experiment, which is
dominated by a large contribution from lattice thermal disorder that is reduced
only slightly by a small negative contribution from that of magnetism. These
findings give insights into the unusual nature of magnetism and spin-lattice
coupling in Invar and Fe, and they support the presented new methodology as a
complementary way to investigate thermal properties of magnetic materials.",2205.05788v1
2022/11/8,Classification of second harmonic generation effect in magnetically ordered materials,"The relationship between magnetic order and the second harmonic generation
(SHG) effect is a fundamental area of study in condensed matter physics with
significant practical implications. In order to gain a clearer understanding of
this intricate relation, this study presents a comprehensive classification
scheme for the SHG effect in magnetically ordered materials. This framework
offers a straightforward approach to connect magnetic order and SHG effect. The
characteristics of the SHG tensors in all magnetic point groups are studied
using the isomorphic group method, followed by a comprehensive SHG effect
classification scheme that includes seven types based on the symmetries of the
magnetic phases and their corresponding parent phases. In addition, a tensor
dictionary containing the SHG and linear magneto-optic (LMO) effect is
established. Furthermore, an extensive SHG database of magnetically ordered
materials is also built up. This classification strategy exposes an anomalous
SHG effect with even characteristic under time-reversal symmetry, which is
solely contributed by magnetic structure. Moreover, the proposed classification
scheme facilitates the determination of magnetic structures through SHG effect.",2211.04354v3
2022/11/15,Tunable magnetic and magnetocaloric properties by thermal annealing in ErCo2 atomized particles,"Processing magnetocaloric materials into magnetic refrigerants with
appropriate shapes is essential for the development of magnetic refrigeration
systems. In this context, the impact of processing on the physical properties
of magnetocaloric materials is one of the important issues. Here, we
investigate the crystallographic, magnetic, and magnetocaloric properties of
gas-atomized particles of the intermetallic compound ErCo$_{2}$, a giant
magnetocaloric material for low-temperature applications. The results
demonstrate that the physical properties of ErCo$_{2}$ are significantly
changed by atomization and subsequent thermal annealing. In the as-atomized
particles, the magnetic transition temperature increases from 34 to 56 K and
the phase transition changes from first order to second order. The thermal
annealing shifts the transition temperature back to the original one and
restores the first-order phase transition characteristic. The changes in
magnetic properties are closely related to those in crystallographic
properties, suggesting the importance of the magneto-structural coupling. The
magnetic entropy change $-\Delta S_{M}$ of the particles can be tuned in size,
shape, and peak temperature depending on the annealing conditions. The peak
value of $-\Delta S_{M}$ varies in the range of 9--33 J kg$^{-1}$ K$^{-1}$ for
a magnetic field change of 0--5 T. All the ErCo$_{2}$ atomized particles have
magnetocaloric properties comparable or superior to other promising candidates
for low-temperature magnetic refrigerants.",2211.08069v1
2023/9/18,Computational Exploration of Magnetic Saturation and Anisotropy Energy for Nonstoichiometric Ferrite Compositions,"A grand challenge in materials research is identifying the relationship
between composition and performance. Herein, we explore this relationship for
magnetic properties, specifically magnetic saturation (M$_s$) and magnetic
anisotropy energy (MAE) of ferrites. Ferrites are materials derived from
magnetite (which has the chemical formulae Fe$_3$O$_4$) that comprise metallic
elements in some combination such as Fe, Mn, Ni, Co, Cu and Zn. They are used
in a variety of applications such as electromagnetism, magnetic hyperthermia,
and magnetic imaging. Experimentally, synthesis and characterization of
magnetic materials is time consuming. In order to create insight to help guide
synthesis, we compute the relationship between ferrite composition and magnetic
properties using density functional theory (DFT). Specifically, we compute
M$_s$ and MAE for 571 ferrite structures with the formulae
M1$_x$M2$_y$Fe$_{3-x-y}$O$_4$, where M1 and M2 can be Mn, Ni, Co, Cu and/or Zn
and 0 $\le$ x $\le$ 1 and y = 1 - x. By varying composition, we were able to
vary calculated values of M$_s$ and MAE by up to 9.6$\times$10$^5$ A m$^{-1}$
and 14.1$\times$10$^5$ J m$^{-3}$, respectively. Our results suggest that
composition can be used to optimize magnetic properties for applications in
heating, imaging, and recording. This is mainly achieved by varying M$_s$, as
these applications are more sensitive to variation in M$_s$ than MAE.",2309.09754v1
2023/10/23,Lead-free Magnetic Double Perovskites for Photovoltaic and Photocatalysis Applications,"The magnetic spin degrees of freedom in magnetic materials serve as
additional capability to tune materials properties, thereby invoking
magneto-optical response. Herein, we report the magneto-optoelectronic
properties of a family of lead-free magnetic double perovskites Cs_{2}AgTX_{6}
(T = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu; X=Cl, Br, I). This turns out to provide
an extremely fertile series, giving rise to potential candidate materials for
photovoltaic(PV) applications. In conjunction with high absorption coefficient
and high simulated power conversion efficiency for PV applications, few
compounds in this series exhibit novel magnetic character useful for spintronic
applications. The interaction between magnetism and light can have far-reaching
results on the photovoltaic properties as a consequence of the shift in the
defect energy levels due to Zeeman effect. This subsequently affects the
recombination rate of minority carriers, and hence the photoconversion
efficiency. Moreover, the distinct ferromagnetic and anti-ferromagnetic
ordering driven by hybridization and super-exchange mechanism can play a
significant role to break the time-reversal and/or inversion symmetry. Such a
coalescence of magnetism and efficient optoelectronic response has the
potential to trigger magnetic/spin anomalous photovoltaic (non-linear Optical)
effect in this Cs$_{2}$AgTX$_{6}$ family. These insights can thus channelize
the advancement of lead-free double perovskites in magnetic/spin anomalous
photovoltaic field as well.",2310.15309v1
2023/11/9,Optically Induced Ferromagnetic Order in a Ferrimagnet,"The parallel or antiparallel arrangement of electron spins plays a pivotal
role in determining the properties of a physical system. To meet the demands
for innovative technological solutions, extensive efforts have been dedicated
to exploring effective methods for controlling and manipulating this
arrangement [1]. Among various techniques, ultrashort laser pulses have emerged
as an exceptionally efficient tool to influence magnetic order. Ultrafast
suppression of the magnetic order [2,3], all-optical magnetization switching
[4, 5, 6, 7], and light-induced magnetic phase transitions [8] are just a few
notable examples. However, the transient nature of light-induced changes in the
magnetic state has been a significant limitation, hindering their practical
implementation. In this study, we demonstrate that infrared ultrashort laser
pulses can induce a ferromagnetic arrangement of magnetic moments in an
amorphous TbCo alloy, a material that exhibits ferrimagnetism under equilibrium
conditions. Strikingly, the observed changes in the magnetic properties persist
for significantly longer durations than any previously reported findings. Our
results reveal that ultrashort optical pulses can generate materials with
identical chemical composition and structural state but entirely distinct
magnetic arrangements, leading to unique magnetic properties. This breakthrough
discovery marks a new era in light-driven control of matter, offering the
exciting potential to create materials with properties that were once
considered unattainable.",2311.05507v2
2019/9/20,Spin-orbitronic materials with record spin-charge conversion from high-throughput ab initio calculations,"The spin Hall effect (SHE) is an important spintronics phenomenon, which
allows transforming a charge current into a spin current and vice versa without
the use of magnetic materials or magnetic fields. To gain new insight into the
physics of the SHE and to identify materials with a substantial spin Hall
conductivities (SHC), we performed high-precision, high-throughput ab initio
electronic structure calculations of the intrinsic SHC for over 20,000
non-magnetic crystals. The calculations reveal a strong and unexpected relation
of the magnitude of the SHC with the crystalline symmetry, which we show exists
because large SHC is typically associated with mirror symmetry protected nodal
lines in the band structure. From the new developed database, we identify new
promising materials. This includes eleven materials with a SHC comparable or
even larger than that the up to now record Pt as well as materials with
different types of spin currents, which could allow for new types of
spin-obitronics devices.",1909.09605v2
2019/11/19,Magnetic and electronic phase transitions probed by nanomechanical resonance,"Two-dimensional (2D) materials enable new types of magnetic and electronic
phases mediated by their reduced dimensionality like magic-angle induced phase
transitions, 2D Ising antiferromagnets and ferromagnetism in 2D atomic layers
and heterostructures. However, only a few methods are available to study these
phase transitions, which for example is particularly challenging for
antiferromagnetic materials. Here, we demonstrate that these phases can be
probed by the mechanical motion: the temperature dependent resonance frequency
and quality factor of multilayer 2D material membranes show clear anomalies
near the phase transition temperature, which are correlated to anomalies in the
specific heat of the materials. The observed coupling of mechanical degrees of
freedom to magnetic and electronic order is attributed to thermodynamic
relations that are not restricted to van der Waals materials. Nanomechanical
resonators, therefore, offer the potential to characterize phase transitions in
a wide variety of materials, including those that are antiferromagnetic,
insulating or so thin that conventional bulk characterization methods become
unsuitable.",1911.08537v1
2022/5/28,High-throughput computation and structure prototype analysis for two-dimensional ferromagnetic materials,"We perform high-throughput first-principles computations to search the high
Curie temperature ($T_{\rm C}$) two-dimensional ferromagnetic (2DFM) materials.
We identify 79 2DFM materials and calculate their $T_{\rm C}$, in which
Co$_2$F$_2$ has the highest $T_{\rm C}$=541K, well above the room temperature.
The 79 2DFM materials are classified into different structural prototypes
according to their structural similarity. We perform sure independence
screening and sparsifying operator (SISSO) analysis to explore the relation
between $T_{\rm C}$ and the material structures. The results suggest that the
2DFM materials with shorter distance between the magnetic atoms, larger local
magnetic moments and more neighboring magnetic atoms are more likely to have
higher $T_{\rm C}$.",2205.14286v1
2023/9/14,Theoretical study on spintronic and optical property prediction of doped magnetic Borophene,"Two dimensional materials are attracting new research for optoelectronics and
spintronics due to their unique physical properties. A wide range of emerging
spintronic devices are achieved from parent and doped two dimensional
materials. First-principles electronic structure calculations of a
two-dimensional monolayer of borophene in its P6/mmm form is explored in this
study. The electronic, magnetic, and optical properties of doped borophene are
analyzed for doping with lithium, sodium, and magnesium. Density functional
theory calculations advocate their good dynamical and thermal stability.
Spin-polarized electronic properties of these materials are observed to be
useful for predicting new spintronic materials. Additionally optical analysis
exhibits the absorption peaks in monolayers along the in-plane direction. These
properties of doped magnetic borophene suggest the material to be a suitable
candidate for designing optoelectronic devices. The most competent spintronic
material among three different doped borophenes is lithium doping that can
imply a promising avenue for the fast-growing electronics industry.",2309.07546v1
2015/6/30,Materials with low DC magnetic susceptibility for sensitive magnetic measurements,"Materials with very low DC magnetic susceptibility have many scientific
applications. To our knowledge however, relatively little research has been
conducted with the goal to produce a totally nonmagnetic material. This phrase
in our case means after spatially averaging over macroscopic volumes, it
possesses an average zero DC magnetic susceptibility. We report measurements of
the DC magnetic susceptibility of three different types of nonmagnetic
materials at room temperature: (I) solutions of paramagnetic salts and
diamagnetic liquids, (II) liquid gallium-indium alloys and (III) pressed powder
mixtures of tungsten and bismuth. The lowest measured magnetic susceptibility
among these candidate materials is in the order of 10^-9 cgs volume
susceptibility units, about two orders of magnitude smaller than distilled
water. In all cases, the measured concentration dependence of the magnetic
susceptibility is consistent with that expected for the weighted sum of the
susceptibilities of the separate components within experimental error. These
results verify the Wiedemann additivity law and thereby realize the ability to
produce materials with small but tunable magnetic susceptibility. For our
particular scientific application, we are also looking for materials with the
largest possible number of neutrons and protons per unit volume. The
gallium-indium alloys fabricated and measured in this work possess to our
knowledge the smallest ratio of volume magnetic susceptibility to nucleon
number density per unit volume for a room temperature liquid, and the
tungsten-bismuth pressed powder mixtures possess to our knowledge the smallest
ratio of volume magnetic susceptibility to nucleon number density per unit
volume for a room temperature solid. This ratio is a figure of merit for a
certain class of precision experiments that search for possible exotic
spin-dependent forces of Nature.",1506.09199v1
2002/11/21,Magnetic levitation force between a superconducting bulk magnet and a permanent magnet,"The current density in a disk-shaped superconducting bulk magnet and the
magnetic levitation force exerted on the superconducting bulk magnet by a
cylindrical permanent magnet are calculated from first principles. The effect
of the superconducting parameters of the superconducting bulk is taken into
account by assuming the voltage-current law and the material law. The magnetic
levitation force is dominated by the remnant current density, which is induced
by switching off the applied magnetizing field. High critical current density
and flux creep exponent may increase the magnetic levitation force. Large
volume and high aspect ratio of the superconducting bulk can enhance the
magnetic levitation force further.",0211470v1
2006/12/4,Magnetic-dipole induced appearance of vortices in a bilayered superconductor/soft-magnet heterostructure,"The penetration of the magnetic field of an infinitesimal magnetic dipole
into a bilayered type-II superconductor/soft-magnet heterostructure is studied
on the basis of the classical London approach. The critical values of the
dipole moment for the first appearance of a single magnetic vortex and,
respectively, a magnetic vortex-antivortex pair in the superconductor
constituent are obtained, when the magnetic dipole faces the superconductor or
the soft-magnet constituent. This reveals that the soft-magnet constituent
inhibits penetration of vortices into the superconductor constituent, when the
dipole faces the soft-magnet constituent.",0612083v1
2007/9/7,Frustration-driven successive metamagnetic transitions in TbB4,"Resonant magnetic x-ray diffraction experiments on the Shastry-Sutherland
lattice TbB$_4$ were carried out under strong pulsed magnetic fields up to 30
T. TbB$_4$ exhibits a multi-step magnetization process above 16 T when magnetic
fields are applied along the c-axis. We examined the intensity of the 010
magnetic reflection as a function of magnetic field and found that the
magnetization plateau phases are accompanied by large XY components of magnetic
moments, in contrast to normal fractional magnetization plateau phases. The
magnetization was calculated using a simple spin model deduced from the above
result. Finally we propose that frustration is the key to understanding the
observed multi-step magnetization.",0709.0977v2
2011/11/27,A first-order magnetic phase transition near 15 K with novel magnetic-field-induced effects in Er5Si3,"We present magnetic characterization of a binary rare-earth intermetallic
compound Er5Si3, crystallizing in Mn5Si3-type hexagonal structure, through
magnetization, heat-capacity, electrical resistivity, and magnetoresistance
measurements. Our investigations confirm that the compound exhibits two
magnetic transitions with decreasing temperature, first one at 35 K and the
second one at 15 K. The present results reveal that the second magnetic
transition is a disorder-broadened first-order transition, as shown by thermal
hysteresis in the measured data. Another important finding is that, below 15 K,
there is a magnetic-field-induced transition with a hysteretic effect with the
electrical resistance getting unusually enhanced at this transition and the
magnetorsistance (MR) is found to exhibit intriguing magnetic-field dependence
indicating novel magnetic phase-co-existence phenomenon. It thus appears that
this compound is characterized by interesting magnetic anomalies in the
temperature-magnetic-field phase diagram.",1111.6240v1
2012/6/30,On conservation of the of crystal lattice symmetry in transition at Curie point in exchange magnets,"We show that symmetry of the crystal lattice of exchange magnets (containing
only 3d magneto-active elements) does not change at the Curie point; only the
magnetic symmetry of the crystal is decreasing in the transition point. In the
non-exchange magnets (containing only rare-earth magneto-active elements), on
the contrary, both the magnetic and crystal-chemical symmetry decrease at the
Curie point. There is isotropic magnetic phase in exchange magnets; and their
magnetic symmetry is described by color groups of magnetic symmetry of P-type.
Non-exchange magnets do not have isotropic phase; their symmetry is described
by color groups of magnetic symmetry of Q-type.",1207.0049v1
2013/10/30,Passive Magnetic Shielding in Gradient Fields,"The effect of passive magnetic shielding on dc magnetic field gradients
imposed by both external and internal sources is studied. It is found that for
concentric cylindrical or spherical shells of high permeability material,
higher order multipoles in the magnetic field are shielded progressively
better, by a factor related to the order of the multipole. In regard to the
design of internal coil systems for the generation of uniform internal fields,
we show how one can take advantage of the coupling of the coils to the
innermost magnetic shield to further optimize the uniformity of the field.
These results demonstrate quantitatively a phenomenon that was previously
well-known qualitatively: that the resultant magnetic field within a passively
magnetically shielded region can be much more uniform than the applied magnetic
field itself. Furthermore we provide formulae relevant to active magnetic
compensation systems which attempt to stabilize the interior fields by sensing
and cancelling the exterior fields close to the outermost magnetic shielding
layer. Overall this work provides a comprehensive framework needed to analyze
and optimize dc magnetic shields, serving as a theoretical and conceptual
design guide as well as a starting point and benchmark for finite-element
analysis.",1310.8242v1
2013/12/4,Quantum s = 1/2 Antiferromagnets on Archimedean Lattices: The Route from Semiclassical Magnetic Order to Nonmagnetic Quantum States,"We investigate ground states of $s$=1/2 Heisenberg antiferromagnets on the
eleven two-dimensional (2D) Archimedian lattices by using the coupled cluster
method. Magnetic interactions and quantum fluctuations play against each other
subtly in 2D quantum magnets and the magnetic ordering is thus sensitive to the
features of lattice topology. Archimedean lattices are those lattices that have
2D arrangements of regular polygons and they often build the underlying
magnetic lattices of insulating quasi-two-dimensional quantum magnetic
materials. Hence they allow a systematic study of the relationship between
lattice topology and magnetic ordering. We find that the Archimedian lattices
fall into three groups: those with semiclassical magnetic ground-state
long-range order, those with a magnetically disordered (cooperative quantum
paramagnetic) ground state, and those with a fragile magnetic order. The most
relevant parameters affecting the magnetic ordering are the coordination number
and the degree of frustration present.",1312.1203v1
2015/1/27,Magnetic behavior of the metal organic framework solid: [(CH3)2NH2][Co(HCOO)3],"In this study we examine the phase transitions in single crystals of
[(CH3)2NH2]Co(HCOO)3], using magnetization and specific heat measurements as a
function of temperature and magnetic field. Magnetisation measurements indicate
a transition at 15 K that is associated with an antiferromagnetic transition.
The results of the isothermal magnetization versus magnetic field curves
demonstrate the presence of a single-ion magnet phase, coexisting with
antiferromagnetism. A peak in specific heat is seen at 15 K, corresponding to
the magnetic transition. The enthalpy of the transition evaluated from the area
under the specific heat peak decreases with the application of magnetic field
of upto8 T. This is suggestive of long range antiferromagnetic magnetic order,
giving way to single-ion magnetic behavior under external field. In experiments
at high temperatures, corresponding to the well-known structural transition in
this system, the specific heat measurements, shows a peak at ~155K, that is
insensitive to applied magnetic field. The magnetisation in this temperature
range, while it exhibits a paramagnetic behavior, shows a distinct jump that
has been attributed to a spin-state transition of Co2+ associated with the
structural transition.",1501.06651v1
2015/6/3,Proximity-induced magnetism in transition-metal substituted graphene,"We investigate the interactions between two identical magnetic impurities
substituted into a graphene superlattice. Using a first-principles approach, we
calculate the electronic and magnetic properties for transition-metal
substituted graphene systems with varying spatial separation. These
calculations are compared for three different magnetic impurities, manganese,
chromium, and vanadium. We determine the electronic band structure, density of
states, and Millikan populations (magnetic moment) for each atom, as well as
calculate the exchange parameter between the two magnetic atoms as a function
of spatial separation. We find that the presence of magnetic impurities
establishes a distinct magnetic moment in the graphene lattice, where the
interactions are highly dependent on the spatial and magnetic characteristic
between the magnetic atoms and the carbon atoms, which leads to either
ferromagnetic or antiferromagnetic behavior. Furthermore, through an analysis
of the calculated exchange energies and partial density of states, it is
determined that interactions between the magnetic atoms can be classified as an
RKKY interaction.",1506.01319v1
2015/10/16,Enhanced orbital magnetic moments in magnetic heterostructures with interface perpendicular magnetic anisotropy,"We have studied the magnetic layer thickness dependence of the orbital
magnetic moment in magnetic heterostructures to identify contributions from
interfaces. Three different heterostructures, Ta/CoFeB/MgO, Pt/Co/AlO$_x$ and
Pt/Co/Pt, which possess significant interface contribution to the perpendicular
magnetic anisotropy, are studied as model systems. X-ray magnetic circular
dichroism spectroscopy is used to evaluate the relative orbital moment, i.e.
the ratio of the orbital to spin moments, of the magnetic elements constituting
the heterostructures. We find that the relative orbital moment of Co in
Pt/Co/Pt remains constant against its thickness whereas the moment increases
with decreasing Co layer thickness for Pt/Co/AlO$_x$, suggesting that a
non-zero interface orbital moment exists for the latter system. For
Ta/CoFeB/MgO, a non-zero interface orbital moment is found only for Fe. X-ray
absorption spectra shows that a particular oxidized Co state in Pt/Co/AlO$_x$,
absent in other heterosturctures, may give rise to the interface orbital moment
in this system. These results show element specific contributions to the
interface orbital magnetic moments in ultrathin magnetic heterostructures.",1510.04756v1
2016/1/21,Vortex Dynamics-Mediated Low-Field Magnetization Switching in an Exchange-Coupled System,"A magnetic vortex has attracted significant attention since it is a
topologically stable magnetic structure in a soft magnetic nanodisk. Many
studies have been devoted to understanding the nature of magnetic vortex in
isolated systems. Here we show a new aspect of a magnetic vortex the dynamics
of which strongly affects the magnetic structures of environment. We exploit a
nanodot of an exchange-coupled bilayer with a soft magnetic Ni81Fe19
(permalloy; Py) having a magnetic vortex and a perpendicularly magnetized
L10-FePt exhibiting a large switching field (Hsw). The vortex dynamics with
azimuthal spin waves makes the excess energy accumulate in the Py, which
triggers the reversed-domain nucleation in the L10-FePt at a low magnetic
field. Our results shed light on the non-local mechanism of a reversed-domain
nucleation, and provide with a route for efficient Hsw reduction that is needed
for ultralow-power spintronic devices.",1601.05521v1
2016/9/12,Induced magnetism at the interfaces of a Fe/V superlattice investigated by resonant magnetic x-ray scattering,"The induced magnetic moments in the V 3d electronic states of interface
atomic layers in a Fe(6ML)/V(7ML) superlattice was investigated by x-ray
resonant magnetic scattering. The first V atomic layer next to Fe was found to
be strongly antiferromagnetically polarized relatively to Fe and the magnetic
moments of the next few atomic layers in the interior V region decay
exponentially with increasing distance from the interface, while the magnetic
moments of the Fe atomic layers largely remain bulk-like. The induced V moments
decay more rapidly as observed by x-ray magnetic scattering than in standard
x-ray magnetic circular dichroism. The theoretical description of the induced
magnetic atomic layer profile in V was found to strongly rely on the interface
roughness within the superlattice period. These results provide new insight
into interface magnetism by taking advantage of the enhanced depth sensitivity
to the magnetic profile over a certain resonant energy bandwidth in the
vicinity of the Bragg angles.",1609.03486v1
2016/3/17,Trends in magnetism of free Rh clusters via relativistic ab-initio calculations,"A fully relativistic ab-initio study on free Rh clusters of 13-135 atoms is
performed to identify general trends concerning their magnetism and to check
whether concepts which proved to be useful in interpreting magnetism of 3d
metals are applicable to magnetism of 4d systems. We found that there is no
systematic relation between local magnetic moments and coordination numbers. On
the other hand, the Stoner model appears well-suited both as a criterion for
the onset of magnetism and as a guide for the dependence of local magnetic
moments on the site-resolved density of states at the Fermi level. Large
orbital magnetic moments antiparallel to spin magnetic moments were found for
some sites. The intra-atomic magnetic dipole Tz term can be quite large at
certain sites but as a whole it is unlikely to affect the interpretation of
x-ray magnetic circular dichroism experiments based on the sum rules.",1603.05394v1
2020/3/18,Thermally induced generation and annihilation of magnetic chiral skyrmion bubbles and achiral bubbles in Mn-Ni-Ga Magnets,"Magnetic chiral skyrmion bubbles and achiral bubbles are two independent
magnetic domain structures, in which the former with equivalent winding number
to skyrmions offers great promise as information carriers for further
spintronic devices. Here, in this work, we experimentally investigate the
generation and annihilation of magnetic chiral skyrmion bubbles and achiral
bubbles in the Mn-Ni-Ga thin plate by using the Lorentz transmission electron
microscopy (L-TEM). The two independent magnetic domain structures can be
directly controlled after the field cooling manipulation by varying the titled
angles of external magnetic fields. By imaging the magnetization reversal with
increasing temperature, we found an extraordinary annihilation mode of magnetic
chiral skyrmion bubbles and a non-linear frequency for the winding number
reversal. Quantitative analysis of such dynamics was performed by using L-TEM
to directly determine the barrier energy for the magnetization reversal of
magnetic chiral skyrmion bubbles.",2003.08035v1
2020/8/4,Magnetism and anomalous transport in the Weyl semimetal PrAlGe: Possible route to axial gauge fields,"In magnetic Weyl semimetals, where magnetism breaks time-reversal symmetry,
large magnetically sensitive anomalous transport responses are anticipated that
could be useful for topological spintronics. The identification of new magnetic
Weyl semimetals is therefore in high demand, particularly since in these
systems Weyl node configurations may be easily modified using magnetic fields.
Here we explore experimentally the magnetic semimetal PrAlGe, and unveil a
direct correspondence between easy-axis Pr ferromagnetism and anomalous Hall
and Nernst effects. With sizes of both the anomalous Hall conductivity and
Nernst effect in good quantitative agreement with first principles
calculations, we identify PrAlGe as a system where magnetic fields can connect
directly to Weyl nodes via the Pr magnetization. Furthermore, we find the
predominantly easy-axis ferromagnetic ground state co-exists with a low density
of nanoscale textured magnetic domain walls. We describe how such nanoscale
magnetic textures could serve as a local platform for tunable axial gauge
fields of Weyl fermions.",2008.01476v1
2021/5/9,"Degenerate magnetic ground state and metastable state on trihexagonal Co-sublattices in Co3Sn2(S,Se)2 single crystals","A trihexagonal lattice has been predicted to retain a degenerate magnetic
state which enriches physical properties. Especially, Co3Sn2S2, possessing
trihexagonal Co-sublattices, has been observed to own topological quantum
properties. Experimentally, Co3Sn2S2 has been reported to have hidden magnetic
phases due to magnetic anomalies. To clarify the hidden magnetic phase, we
fabricated high-quality single crystals of Co3Sn2S2-xSex (x = 0, 0.26, & 0.86).
The Se-substitution is intended to broaden the distance between Co atoms. For
each Se-composition, magnetizations of single-crystalline Co3Sn2S2-xSex
implicate that the magnetic ground state consists of the out-of-plane
ferromagnetism and the in-plane antiferromagnetism: Being degenerate.
Meanwhile, along out-of-plane, remanent magnetizations of Co3Sn2S2-xSex have a
first-order phase transition, so Co3Sn2S2-xSex owns an excited magnetic state,
denoted as the metastable state. Consequently, we have provided semiclassical
magnetic structures of the degenerate ground state and the metastable state via
both magnetic symmetries and experimental constraints. Moreover, we have
discovered mechanisms raising degeneracy and metastability.",2105.03892v1
2013/11/12,Magnetic and Dielectric Properties in Multiferroic Cu3Mo2O9 under High Magnetic Fields,"The magnetic and dielectric properties under high magnetic fields are studied
in the single crystal of Cu3Mo2O9. This multiferroic compound has distorted
tetrahedral spin chains. The effects of the quasi-one dimensionality and the
geometrical spin frustration are expected to appear simultaneously. We measure
the magnetoelectric current and the differential magnetization under the pulsed
magnetic field up to 74 T. We also measure the electric polarization versus the
electric field curve/loop under the static field up to 23 T. Dielectric
properties change at the magnetic fields where the magnetization jumps are
observed in the magnetization curve. Moreover, the magnetization plateaus are
found at high magnetic fields.",1311.2706v1
2014/1/27,Topological magnetic crystalline insulators and co-representation theory,"Gapless surface states of time reversal invariant topological insulators are
protected by the anti-unitary nature of the time reversal operation. Very
recently, this idea was generalized to magnetic structures, in which time
reversal symmetry is explicitly broken, but there is still an anti-unitary
symmetry operation combining time reversal symmetry and crystalline symmetry.
These topological phases in magnetic structures are dubbed ""topological
magnetic crystalline insulators"". In this work, we present a general theory of
topological magnetic crystalline insulators in different types of magnetic
crystals based on the co-representation theory of magnetic crystalline symmetry
groups. We construct two concrete tight-binding models of topological magnetic
crystalline insulators, the $\hat{C}_4\Theta$ model and the $\hat{\bf
\tau}\Theta$ model, in which topological surface states and topological
invariants are calculated explicitly. Moreover, we check different types of
anti-unitary operators in magnetic systems and find that the systems with
$\hat{C}_4\Theta$, $\hat{C}_6\Theta$ and $\hat{\bf \tau}\Theta$ symmetry are
able to protect gapless surface states. Our work will pave the way to search
for topological magnetic crystalline insulators in realistic magnetic
materials.",1401.6922v1
2018/2/1,An analytical computation of magnetic field generated from a cylinder ferromagnet,"An analytical formulation to compute a magnetic field generated from an
uniformly magnetized cylinder ferromagnet is developed. Exact solutions of the
magnetic field generated from the magnetization pointing in an arbitrary
direction are derived, which are applicable both inside and outside the
ferromagnet. The validities of the present formulas are confirmed by comparing
them with demagnetization coefficients estimated in earlier works. The results
will be useful for designing practical applications, such as high-density
magnetic recording and microwave generators, where nanostructured ferromagnets
are coupled to each other through the dipole interactions and show cooperative
phenomena such as synchronization. As an example, the magnetic field generated
from a spin torque oscillator for magnetic recording based on microwave
assisted magnetization reversal is studied.",1802.00384v1
2019/2/21,Self-induced Magnetic Flux Structure in the Magnetic Superconductor RbEuFe$_4$As$_4$,"We report an unusual enhancement of the magnetic induction in single crystals
of the magnetic superconductor RbEuFe$_4$As$_4$ , highlighting the interplay
between superconducting and magnetic subsystems in this material. Contrary to
the conventional Meissner expulsion of magnetic flux below the superconducting
transition temperature, we observe a substantial boost of the magnetic flux
density upon approaching the magnetic transition temperature, Tm. Direct
imaging of the flux evolution with a magneto-optical technique, shows that the
magnetic subsystem serves as an internal magnetic flux pump, drawing Abrikosov
vortices from the surface, while the superconducting subsystem controls their
conveyance into the bulk of the magnetic superconductor via a peculiar
self-organized critical state.",1902.08125v1
2019/5/22,Reduced Exchange Interactions in Magnetic Tunnel Junction Free Layers with Insertion Layers,"Perpendicularly magnetized CoFeB layers with ultra-thin non-magnetic
insertion layers are very widely used as the electrodes in magnetic tunnel
junctions for spin transfer magnetic random access memory devices. Exchange
interactions play a critical role in determining the thermal stability of
magnetic states in such devices and their spin torque switching efficiency.
Here the exchange constant of free layers incorporated in full magnetic tunnel
junction layer stacks, specifically CoFeB free layers with W insertion layers
is determined by magnetization measurements in a broad temperature range. A
significant finding is that the exchange constant decreases significantly and
abruptly with W insertion layer thickness. The perpendicular magnetic
anisotropy shows the opposite trend; it initially increases with W insertion
layer thickness and shows a broad maximum for approximately one monolayer (0.3
nm) of W. These results highlight the interdependencies of magnetic
characteristics required to optimize the performance of magnetic tunnel
junction devices.",1905.09329v1
2019/7/24,Electron doping induced magnetic glassy state in phase separated YBaCo$_2$O$_{5.5-δ}$,"The structural, magnetic and transport properties of the layered
RBaCo$_2$O$_{5.5}$ cobaltites are sensitive to the oxygen stoichiometry. In
this present study, we report the presence of a low-temperature magnetic glassy
state in electron-doped polycrystalline YBaCo$_2$O$_{5.5}$ cobaltite. The ac
magnetization studies show the absence of conventional spin glass features,
while the various dc magnetization studies demonstrate the presence of
non-equilibrium magnetic glassy state at low temperature. The magnetic glassy
state of this sample results from the kinetic arrest of the first order ferro
(or ferri) to antiferromagnetic transition. The role of electron doping in the
occurrence of magnetic glassy phenomena is discussed in terms of magnetic phase
separation involving the Co3+/Co2+ clusters of the ferrimagnetic phase in the
Co3+/Co3+ antiferromagnetic matrix.",1907.10248v1
2019/12/3,Nanoscale Tantalum Layer Controlling the Magnetic Coupling between Two Ferromagnetic Electrodes via Insulator of a Magnetic Tunnel Junction,"Ability to tailor the nature of the magnetic coupling between two
ferromagnetic electrodes can enable the realization of new spintronics device
systems. This paper discusses our finding that deposition of an ultrathin
tantalum (Ta) on the NiFe top electrode reversed the nature of
inter-ferromagnetic electrode coupling. We observed that the deposition of ~ 5
nm Ta on the top of a magnetic tunnel junction with Ta( 2 nm)/Co(5 nm)/NiFe (5
nm)/AlOx( 2 nm)/NiFe (10-15 nm) configuration changed the magnetic coupling
between two ferromagnetic electrodes from antiferromagnetic to ferromagnetic.
We investigated Ta effect using multiple magnetic characterizations like
ferromagnetic resonance, magnetometry, and polarized neutron reflectometry.
Ferromagnetic resonance characterization was very sensitive for detecting the
changes in magnetic coupling via the insulating spacer. This simple approach of
adding Ta film to alter the magnetic coupling can impact the other burgeoning
areas like molecular spintronics. We found that preexisting magnetic coupling
between two ferromagnetic electrodes impacted the resultant magnetic properties
of magnetic tunnel junctions based molecular spintronics devices.",1912.01331v1
2020/2/25,Noncollinear magnetic structure and magnetoelectric coupling in buckled honeycomb Co$_4$Nb$_2$O$_9$:A single crystal neutron diffraction study,"Through analysis of single crystal neutron diffraction data, we present the
magnetic structures of magnetoelectric Co4Nb2O9 under various magnetic fields.
In zero-field, neutron diffraction experiments below TN=27 K reveal that the
Co2+ moments order primarily along the a* direction without any spin canting
along the c axis, manifested by the magnetic symmetry C2/c'. The moments of
nearest neighbor Co atoms order ferromagnetically with a small cant away from
the next nearest neighbor Co moments along the c axis. In the applied magnetic
field H//a, three magnetic domains were aligned with their major magnetic
moments perpendicular to the magnetic field with no indication of magnetic
phase transitions. The influences of magnetic fields on the magnetic structures
associated with the observed magnetoelectric coupling are discussed.",2002.10599v1
2020/7/28,Magnetic bubbles in an M-type hexagonal ferrite observed by hollow-cone Foucault imaging and small-angle electron diffraction,"We report hollow-cone imaging and small-angle electron diffraction of
nanoscale magnetic textures such as magnetic-striped domains and magnetic
bubbles of M-type hexagonal ferrite
BaFe$_{10.35}$Sc$_{1.6}$Mg$_{0.05}$O$_{19}$. The advantage of the hollow-cone
Foucault method is that magnetic domains with various directions of
magnetization can be visualized under an infocus condition. Moreover, the
contrast of magnetic domain walls in magnetic bubbles depends on the
inclination angle of the illumination beam. The combination of small-angle
electron diffraction and hollow-cone Foucault imaging proves that magnetization
at domain walls exhibits in-plane directions in the magnetic-striped domains
and magnetic bubbles.",2007.13994v1
2020/9/24,Magnetic Field Induced Phase Transition in Spinel GeNi2O4,"Cubic spinel GeNi2O4 exhibits intriguing magnetic properties with two
successive antiferromagnetic phase transitions (TN1 12.1 and TN2 11.4 K) with
the absence of any structural transition. We have performed detailed heat
capacity and magnetic measurements in different crystallographic orientations.
A new magnetic phase in presence of magnetic field (H > 4 T) along the [111]
direction is revealed, which is not observed when the magnetic field is applied
along the [100] and [110] directions. High field neutron powder diffraction
measurements confirm such a change in magnetic phase, which could be ascribed
to a spin reorientation in the presence of magnetic field. A strong magnetic
anisotropy and competing magnetic interactions play a crucial role on the
complex magnetic behavior in this cubic system.",2009.11960v1
2021/1/26,Understanding Magnetism in Double Double Perovskites: A Complex Multiple Magnetic Sublattice System,"Understanding magnetism in multiple magnetic sublattice system, driven by the
interplay of varied nature of magnetic exchanges, is on one hand challenging
and on other hand intriguing. Motivated by the recent synthesis of AA'BB'O_6
double double perovskites with multiple magnetic ions both at A- and B-sites,
we investigate the mechanism of magnetic behavior in these interesting class of
compounds. We find that the magnetism in such multiple sublattice compounds is
governed by the interplay and delicate balance between two distinct mechanisms,
a) kinetic energy-driven multiple sublattice double exchange mechanism and b)
the conventional super-exchange mechanism. The derived spin Hamiltonian based
on first-principles calculations is solved by the classical Monte Carlo
technique which reproduces the observed magnetic properties. Finally, the
influence of off-stoichiometry, as in experimental samples, is discussed. Some
of these double double perovskite compounds are found to possess large total
magnetic moment and also are found to be half-metallic, which raises the hope
of future applications of these large magnetic moment half-metallic oxides in
spintronics and memory devices.",2101.10822v1
2021/3/16,Efficient field-free perpendicular magnetization switching by a magnetic spin Hall effect,"Current induced spin-orbit torques driven by the conventional spin Hall
effect are widely used to manipulate the magnetization. This approach, however,
is nondeterministic and inefficient for the switching of magnets with
perpendicular magnetic anisotropy that are demanded by the high-density
magnetic storage and memory devices. Here, we demonstrate that this limitation
can be overcome by exploiting a magnetic spin Hall effect in noncollinear
antiferromagnets, such as Mn3Sn. The magnetic group symmetry of Mn3Sn allows
generation of the out-of-plane spin current carrying spin polarization induced
by an in-plane charge current. This spin current drives an out-of-plane
anti-damping torque providing deterministic switching of perpendicular
magnetization of an adjacent Ni/Co multilayer. Compared to the conventional
spin-orbit torque devices, the observed switching does not need any external
magnetic field and requires much lower current density. Our results demonstrate
great prospects of exploiting the magnetic spin Hall effect in noncollinear
antiferromagnets for low-power spintronics.",2103.09011v1
2021/10/29,Two types of magnetic bubbles in MnNiGa observed via Lorentz microscopy,"Magnetic bubbles are remarkable spin structures that developed in uniaxial
magnets with strong magnetocrystalline anisotropy. Several contradictory
reports have been published concerning the magnetic bubble structure in a
metallic magnet MnNiGa: Biskyrmions or type-II bubbles. Lorentz microscopy in
polycrystalline MnNiGa was used to explain the magnetic bubble structure.
Depending on the connection between the magnetic easy axis and the observation
plane, two types of magnetic bubbles were formed. Magnetic bubbles with
180{\deg} domains were formed if the easy axis was away from the direction
perpendicular to the observation plane. The contrast of biskyrmion is
reproduced by this form of a magnetic bubble. When the easy axis was
approximately perpendicular to the observing plane, type-II bubbles were
observed in the same specimen. The findings will fill a knowledge gap between
prior reports on magnetic bubbles in MnNiGa.",2110.15507v1
2022/1/1,"Nanomagnetism in porous amorphous palladium, a sequel. A possible light-weight magnet","Magnetism is a very relevant subject that permeates our everyday lives.
However, magnetism keeps taking us from surprise to surprise which seems to
indicate that it is a phenomenon not well understood. For example, we found
that bulk amorphous palladium becomes magnetic; so, naturally one should ask,
could defective palladium develop magnetism? In particular, would amorphous
porous palladium become magnetic? Here we show that the answer to that question
is affirmative, this defective topology of Pd is magnetic, with a magnetism
that depends on the amount of sample porosity and on the topology of their
structures. Clearly, if magnetism exists in porous amorphous palladium, this
indicates the possibility of developing light-weight magnets, useful when a
maximized magnetism/weight ratio is demanded, well suited for space and
aeronautical applications.",2201.00086v1
2022/6/14,Frustration and ordering in Ising chain in an external magnetic field with third-neighbor interactions,"In this paper, the frustration properties of the Ising model on a
one-dimensional monoatomic equidistant lattice in an external magnetic field
are investigated, taking into account the exchange interactions of atomic spins
at the sites of the first, second, and third neighbors. Exact analytical
expressions for the thermodynamic functions of the system are obtained by the
Kramers--Wannier transfer-matrix method. A magnetic phase diagram of the ground
state of such a spin system is constructed and studied thoroughly. The points
and lines of frustrations of the system depending on the values and signs of
exchange interactions and on an external magnetic field are found. The criteria
for the occurrence of magnetic frustrations in the presence of competition
between the energies of exchange interactions and an external magnetic field
are formulated. The peculiar features are investigated and the values of
entropy and magnetization of the ground state of this model are obtained in the
frustration regime and beyond it. Various types of behavior of entropy,
magnetization, and magnetic susceptibility depending on the model parameters
are revealed.",2206.06753v1
2022/10/6,Field and temperature tuning of magnetic diode in permalloy honeycomb lattice,"The observation of magnetic diode behavior with ultra-low forward voltage of
5 mV renders new venue for energetically efficient spintronic device research
in the unconventional system of two-dimensional permalloy honeycomb lattice.
Detailed understanding of temperature and magnetic field tuning of diode
behavior is imperative to any practical application. Here, we report a
comprehensive study in this regard by performing electrical measurements on
magnetic diode sample as functions of temperature and magnetic field. Magnetic
diode is found to persist across the broad temperature range. Magnetic field
application unveils a peculiar reentrant characteristic where diode behavior is
suppressed in remnant field but reappears after warming to room temperature.
Analysis of I-V data suggests a modest energy gap, 0.03-0.1 eV, which is
comparable to magnetic Coulomb's interaction energy between emergent magnetic
charges on honeycomb vertices in the reverse biased state. It affirms the role
of magnetic charge correlation in unidirectional conduction in 2D honeycomb
lattice. The experimental results are expected to pave way for the utilization
of magnetic diode in next generation spintronic device applications.",2210.03184v1
2023/9/22,Electric control of optically-induced magnetization dynamics in a van der Waals ferromagnetic semiconductor,"Electric control of magnetization dynamics in two-dimensional (2D) magnetic
materials is an essential step for the development of novel spintronic
nanodevices. Electrostatic gating has been shown to greatly affect the static
magnetic properties of some van der Waals magnets, but the control over their
magnetization dynamics is still largely unexplored. Here we show that the
optically-induced magnetization dynamics in the van der Waals ferromagnet
Cr$_2$Ge$_2$Te$_6$ can be effectively controlled by electrostatic gates, with a
one order of magnitude change in the precession amplitude and over 10% change
in the internal effective field. In contrast to the purely thermally-induced
mechanisms previously reported for 2D magnets, we find that coherent
opto-magnetic phenomena play a major role in the excitation of magnetization
dynamics in Cr$_2$Ge$_2$Te$_6$. Our work sets the first steps towards electric
control over the magnetization dynamics in 2D ferromagnetic semiconductors,
demonstrating their potential for applications in ultrafast opto-magnonic
devices.",2309.12776v1
2023/12/5,THz-Driven Coherent Magnetization Dynamics in a Labyrinth Domain State,"Terahertz (THz) light pulses can be used for an ultrafast coherent
manipulation of the magnetization. Driving the magnetization at THz frequencies
is currently the fastest way of writing magnetic information in ferromagnets.
Using time-resolved resonant magnetic scattering, we gain new insights to the
THz-driven coherent magnetization dynamics on nanometer length scales. We
observe ultrafast demagnetization and coherent magnetization oscillations that
are governed by a time-dependent damping. This damping is determined by the
interplay of lattice heating and magnetic anisotropy reduction revealing an
upper speed limit for THz-induced magnetization switching. We show that in the
presence of nanometer-sized magnetic domains, the ultrafast magnetization
oscillations are associated with a correlated beating of the domain walls. The
overall domain structure thereby remains largely unaffected which highlights
the applicability of THz-induced switching on the nanoscale.",2312.02654v1
2023/12/18,Doping-control of excitons and magnetism in few-layer CrSBr,"Magnetism in two-dimensional materials reveals phenomena distinct from bulk
magnetic crystals, with sensitivity to charge doping and electric fields in
monolayer and bilayer van der Waals magnet CrI3. Within the class of layered
magnets, semiconducting CrSBr stands out by featuring stability under ambient
conditions, correlating excitons with magnetic order and thus providing strong
magnon-exciton coupling, and exhibiting peculiar magneto-optics of
exciton-polaritons. Here, we demonstrate that both exciton and magnetic
transitions in bilayer and trilayer CrSBr are sensitive to voltage-controlled
field-effect charging, exhibiting bound exciton-charge complexes and
doping-induced metamagnetic transitions. Moreover, we demonstrate how these
unique properties enable optical probes of local magnetic order, visualizing
magnetic domains of competing phases across metamagnetic transitions induced by
magnetic field or electrostatic doping. Our work identifies few-layer CrSBr as
a rich platform for exploring collaborative effects of charge, optical
excitations, and magnetism.",2312.11041v1
1998/8/20,Barkhausen noise in soft amorphous magnetic materials under applied stress,"We report experimental measurements of Barkhausen noise on
Fe_{64}Co_{21}B_{15} amorphous alloy under tensile stress. We interpret the
scaling behavior of the noise distributions in terms of the depinning
transition of the domain walls. We show that stress induced anisotropy enhance
the effect of short-range elastic interactions that dominate over long-range
dipolar interactions. The universality class is thus different from the one
usually observed in Barkhausen noise measurements and is characterized by the
exponents \tau = 1.3 and \alpha = 1.5, for the decay of the distributions of
jump sizes and durations.",9808224v1
2003/5/7,Voltage-Controlled Spin Selection in a Magnetic Resonant Tunnelling Diode,"We have fabricated all II-VI semiconductor resonant tunneling diodes based on
the (Zn,Mn,Be)Se material system, containing dilute magnetic material in the
quantum well, and studied their current-voltage characteristics. When subjected
to an external magnetic field the resulting spin splitting of the levels in the
quantum well leads to a splitting of the transmission resonance into two
separate peaks. This is interpreted as evidence of tunneling transport through
spin polarized levels, and could be the first step towards a voltage controlled
spin filter.",0305124v1
2003/5/13,"Electronic structure and magnetism in X_xW_{1-x}O_3 (X=Nb,V,Re) from supercell calculations","Some doped semiconductors have recently been shown to display
superconductivity or weak ferromagnetism. Here we investigate the electronic
structure and conditions for magnetism in a supercells of cubic XW_{26}O_{81},
where X=Nb,V and Re.
  The undoped material is an insulator, and although the slightly doped
material is a metal, it is far from the Stoner criterion of magnetism. The
conditions of a localized density-of-states which varies rapidly with the
energy, resemble those of doped hexaborides. The virtual crystal approximation
is used to vary the doping level. A small moment appears if the Fermi energy
coincides with a large derivative of the DOS.",0305282v1
2004/4/12,Magnetization measurements on Li2Pd3B superconductor,"Magnetization in DC magnetic fields and at different temperatures have been
measured on the Li2Pd3B compound. This material was recently found to show
superconductivity at 7-8K. Critical fields Hc1(0) and Hc2(0) have been
determined to be 135Oe and 4T, respectively. Critical current density, scaling
of the pinning force within the Kramer model and the irreversibility field data
are presented. Several superconductivity parameters were deduced: x(csi)=9.1
nm, l(lamda)=194nm and k=21. The material resembles other boride
superconductors from the investigated points of view.",0404257v1
2006/9/1,Thermally excited spin-current in metals with embedded ferromagnetic nanoclusters,"We show that a thermally excited spin-current naturally appears in metals
with embedded ferromagnetic nanoclusters. When such materials are subjected to
a magnetic field, a spin current can be generated by a temperature gradient
across the sample as a signature of electron-hole symmetry breaking in a metal
due to the electron spin-flip scattering from polarised magnetic moments. Such
a spin current can be observed via a giant magneto-thermopower which tracks the
polarisation state of the magnetic subsystem and is proportional to the
magnetoresistance. Our theory explains the recent experiment on Co clusters in
copper by S. Serrano-Guisan \textit{et al} [Nature Materials AOP,
doi:10.1038/nmat1713 (2006)]",0609012v1
2004/9/13,Size-Dependent Bruggeman Approach for Dielectric-Magnetic Composite Materials,"Expressions arising from the Bruggeman approach for the homogenization of
dielectric-magnetic composite materials, without ignoring the sizes of the
spherical particles, are presented. These expressions exhibit the proper limit
behavior. The incorporation of size dependence is directly responsible for the
emergence of dielectric-magnetic coupling in the estimated relative
permittivity and permeability of the homogenized composite material.",0409059v1
2005/6/27,Non-magnetic nano-composites for optical and infrared negative refraction index media,"We develop an approach to use nanostructured plasmonic materials as a
non-magnetic negative-refractive index system at optical and near-infrared
frequencies. In contrast to conventional negative refraction materials, our
design does not require periodicity and thus is highly tolerant to fabrication
defects. Moreover, since the proposed materials are intrinsically non-magnetic,
their performance is not limited to proximity of a resonance so that the
resulting structure has relatively low loss. We develop the analytical
description of the relevant electromagnetic phenomena and justify our analytic
results via numerical solutions of Maxwell equations.",0506196v1
2009/11/21,Thermal Casimir Force between Magnetic Materials,"We investigate the Casimir pressure between two parallel plates made of
magnetic materials at nonzero temperature. It is shown that for real
magnetodielectric materials only the magnetic properties of ferromagnets can
influence the Casimir pressure. This influence is accomplished through the
contribution of the zero-frequency term of the Lifshitz formula. The
possibility of the Casimir repulsion through the vacuum gap is analyzed
depending on the model used for the description of the dielectric properties of
the metal plates.",0911.4175v1
2010/7/22,Neutron magnetic form factor in strongly correlated materials,"We introduce a formalism to compute the neutron magnetic form factor Fm(q)
within a first-principles Density Functional Theory (DFT) + Dynamical Mean
Field Theory (DMFT). The approach treats spin and orbital interactions on the
same footing and reduces to earlier methods in the fully localized or the fully
itinerant limit. We test the method on various actinides of current interest
NpCoGa5, PuSb and PuCoGa5; we show that PuCoGa5 is in mixed valent state, which
naturally explains the measured magnetic form factor.",1007.3997v2
2011/10/26,Spherical sample holders to improve the susceptibility measurement of superparamagnetic materials,"The design of two custom sample holders with a spherical cavity for
commercial vibrating sample magnetometer systems is described. For such
cavities the magnetization M and the internal magnetic field Hi of a sample are
both homogeneous. Consequently, the material parameter M(Hi) of a sample can be
determined even for liquids and powders with a high magnetic susceptibility.",1110.5739v2
2015/4/10,Electronic structure and the origin of the high ordering temperature in SrRu2O6,"SrRu2O6 is a layered honeycomb lattice material with an extraordinarily high
magnetic ordering temperature. We investigated this material using density
functional calculations. We find that the energy scales for moment formation
and ordering are similar and high. Additionally, we find that the magnetic
anisotropy is high and favors moments oriented along the $c$-axis. This
provides an explanation for the exceptionally high ordering temperature.
Finally, the compound is found to be semiconducting at the bare density
functional level, even without magnetic order. Experimental consequences of
this scenario for the high ordering temperature are discussed.",1504.02745v1
2015/5/4,Magnetomechanical effects in the elastic polymer composites containing different volume fraction of ferromagnetic powder particles,"In the present work a detailed thermodynamic consideration for the magnetic
free energy of the composite material consisting of the ferromagnetic powder
particles embedded into a polymer matrix is given. We estimate their
magnetostatic interaction energy and its dependence on the microscopic
distribution of the magnetization and the magnetic field in the composite
material. We also define the hydrostatic component of the mechanical force
developed and the volume change effect caused by the magnetostatic interactions
in such composites.",1505.00795v1
2020/8/20,Clausius-Mossotti Relation Revisited: Media with Electric and Magnetic Response,"A reexamination of the Clausius-Mossotti relation in which material with both
electric and magnetic responses yields surprising results. Materials with
indices near zero and with real parts less than zero, that is the real part of
both the permeability and permittivity are negative, are found to emerge from
the interaction of electric and magnetic responses in a self-consistent theory.
The new results point the way to artificial and natural materials with exotic
responses. A simulation with 10^10 particles shows good agreement with the
analytical results.",2008.09178v4
2021/5/5,"Magnetic Properties of NbSi2N4, VSi2N4, and VSi2P4 Monolayers","The recent demonstration of MoSi2N4 and its exceptional stability to air,
water, acid, and heat has generated intense interest in this family of
two-dimensional (2D) materials. Among these materials, NbSi2N4, VSi2N4, and
VSi2P4 are semiconducting, easy-plane ferromagnets with negligible in-plane
magnetic anisotropy. They thus satisfy a necessary condition for exhibiting a
dissipationless spin superfluid mode. The Curie temperatures of monolayer
VSi2P4 and VSi2N4 are determined to be above room temperature based on Monte
Carlo and density functional theory calculations. The magnetic moments of
VSi2N4 can be switched from in-plane to out-of-plane by applying tensile
biaxial strain or electron doping.",2105.01857v2
2019/12/17,Negative longitudinal magnetoconductance at weak fields in Weyl semimetals,"Weyl semimetals are topological materials that provide a condensed-matter
realization of the chiral anomaly. A positive longitudinal magnetoconductance
quadratic in magnetic field has been promoted as a diagnostic for this anomaly.
By solving the Boltzmann equation analytically, we show that the
magnetoconductance can become negative in the experimentally relevant
semiclassical regime of weak magnetic fields. This effect is due to the
simultaneous presence of the Berry phase and the orbital magnetic moment of
carriers and occurs for sufficiently strong intervalley scattering.",1912.07852v3
2020/1/2,Sub-Wavelength Passive Optical Isolators Using Photonic Structures Based on Weyl Semimetals,"We design sub-wavelength high-performing non-reciprocal optical devices using
recently discovered magnetic Weyl semimetals. These passive bulk topological
materials exhibit anomalous Hall effect which results in magnetooptical effects
that are orders of magnitude higher than those in conventional materials,
without the need of any external magnetic bias. We design two optical isolators
of both Faraday and Voigt geometries. These isolators have dimensions that are
reduced by three orders of magnitude compared to conventional magneto-optical
configurations. Our results indicate that the magnetic Weyl semimetals may open
up new avenues in photonics for the design of various nonreciprocal components.",2001.00371v1
2023/4/8,Integral Absorption of Microwave Power by Random-Anisotropy Magnets,"We study analytically and numerically on lattices containing $10^5$ spins,
the integral absorption of microwaves by a random-anisotropy magnet, $\int
d\omega P(\omega)$. It scales as $D^2_R/J$ on the random-anisotropy strength
$D_R$ and the strength of the ferromagnetic exchange $J$ in low-anisotropy
amorphous magnetic materials. At high anisotropy and in low-anisotropy
materials sintered of sufficiently large ferromagnetic grains, the integral
power scales linearly on $D_R$. The maximum bandwidth, combined with the
maximum absorption power, is achieved when the amorphous structure factor, or
grain size, is of an order of the domain wall thickness in a conventional
ferromagnet that is of the order of $(J/D_R)^{1/2}$ lattice spacings.",2304.04121v1
2003/10/28,On magnetic field generation in Kolmogorov turbulence,"We analyze the initial, kinematic stage of magnetic field evolution in an
isotropic and homogeneous turbulent conducting fluid with a rough velocity
field, v(l) ~ l^alpha, alpha<1. We propose that in the limit of small magnetic
Prandtl number, i.e. when ohmic resistivity is much larger than viscosity, the
smaller the roughness exponent, alpha, the larger the magnetic Reynolds number
that is needed to excite magnetic fluctuations. This implies that numerical or
experimental investigations of magnetohydrodynamic turbulence with small
Prandtl numbers need to achieve extremely high resolution in order to describe
magnetic phenomena adequately.",0310780v2
1998/1/29,Symmetry of Magnetically Ordered Quasicrystals,"The notion of magnetic symmetry is reexamined in light of the recent
observation of long range magnetic order in icosahedral quasicrystals [Charrier
et al., Phys. Rev. Lett. 78, 4637 (1997)]. The relation between the symmetry of
a magnetically-ordered (periodic or quasiperiodic) crystal, given in terms of a
``spin space group,'' and its neutron diffraction diagram is established. In
doing so, an outline of a symmetry classification scheme for magnetically
ordered quasiperiodic crystals is provided. Predictions are given for the
expected diffraction patterns of magnetically ordered icosahedral crystals,
provided their symmetry is well described by icosahedral spin space groups.",9801296v1
1999/4/17,Tunneling Via Individual Electronic States in Ferromagnetic Nanoparticles,"We measure electron tunneling via discrete energy levels in ferromagnetic
cobalt particles less than 4 nm in diameter, using non-magnetic electrodes. Due
to magnetic anisotropy, the energy of each tunneling resonance shifts as an
applied magnetic field rotates the particle's magnetic moment. We see both
spin-increasing and decreasing tunneling transitions, but we do not observe the
spin degeneracy at small magnetic fields seen previously in non-magnetic
materials. The tunneling spectrum is denser than predicted for independent
electrons, possibly due to spin-wave excitations.",9904248v2
1999/6/10,Magnetic Roughness and Domain Correlations in Antiferromagnetically Coupled Multilayers,"The in-plane correlation lengths and magnetic disorder of magnetic domains in
a transition metal multilayer have been studied using neutron scattering
techniques. A new theoretical framework is presented connecting the observed
scattering to the in-plane correlation length and the dispersion of the local
magnetization vector about the mean macroscopic direction. The results
unambiguously show the highly correlated nature of the antiferromagnetically
coupled domain structure vertically throughout the multilayer. We are easily
able to relate the neutron determined magnetic dispersion and domain
correlations to magnetization and magnetotransport experiments.",9906145v1
2000/4/13,Large Magnetic-Field-Induced Strains in Ni-Mn-Ga Alloys due to Redistribution of Martensite Variants,"A polycrystalline and single-crystal samples of near-stoichiometric Ni2MnGa
alloys have been investigated. It was confirmed that martensite short
crystallographic axis (c-axis) is the easy axis of magnetization. The
reversible reorientation of the easy magnetization direction of martensite
samples after 5% compression is found. The same reversible reorientation of the
easy magnetization direction under applied magnetic field occurs in the
single-crystal samples. The field-induced reorientation of the easy
magnetization direction is accompanied with more than 4% of sample's dimension
change. About the same value of the field-induced strains can be obtained for
polycrystalline samples after appropriate thermo-mechanical treatment.",0004211v1
2001/11/3,"Mean-field approach to ferromagnetism in (III,Mn)V diluted magnetic semiconductors at low carrier densities","We present a detailed study, within the mean-field approximation, of an
impurity band model for III-V diluted magnetic semiconductors. Such a model
should be relevant at low carrier densities, below and near the metal-insulator
transition. Positional disorder of the magnetic impurities inside the host
semiconductor is shown to have observable consequences for the shape of the
magnetization curve. Below the critical temperature the magnetization is
spatially inhomogeneous, leading to very unusual temperature dependence of the
average magnetization as well as specific heat. Disorder is also found to
enhance the ferromagnetic transition temperature. Unusual spin and charge
transport is implied.",0111045v1
2001/11/25,Tip effects in scanning tunnelling microscopy of atomic-scale magnetic structures,"The spin-polarized scanning tunnelling microscope (STM) can in principle
resolve not only the electronic, but also the magnetic surface structure. We
model recent STM measurements achieving magnetic resolution on the atomic scale
by a first-principles method. It is shown that the signature of a specific
magnetic or non-magnetic STM tip can unambiguously be identified. It is also
established that the model of Tersoff and Hamann would yield an electronic as
well as magnetic contrast of the surface which is well below STM resolution.",0111477v1
2002/1/3,Quantum computing of molecular magnet Mn$_{12}$,"Quantum computation in molecular magnets is studied by solving the
time-dependent Schr\""{o}dinger equation numerically. Following Leuenberger and
Loss (Nature (London) 410, 789(2001)), an external oscillating magnetic field
is applied to populate and manipulate the spin coherent states in molecular
magnet Mn$_{12}$. The conditions to realize parallel recording and reading data
bases of Grover algorithsm in molecular magnets are discussed in details. It is
found that an accurate duration time of magnetic pulse as well as the
amplitudes are required to design the device of quantum computing.",0201023v1
2003/1/31,Non-collinear magnetism in iron at high pressures,"Using a first principles based, magnetic tight-binding total energy model,
the magnetization energy and moments are computed for various ordered spin
configurations in the high pressure polymorphs of iron (fcc, or $\gamma$-Fe,
and hcp, or $\epsilon$-Fe), as well ferromagnetic bcc iron ($\alpha$-Fe). For
hcp, a non-collinear, antiferromagnetic, spin configuration that minimizes
unfavorable ferromagnetic nearest neighbor ordering is the lowest energy state
and is more stable than non-magnetic $\epsilon$ iron up to about 75 GPa.
Accounting for non-collinear magnetism yields better agreement with the
experimental equation of state, in contrast to the non-magnetic equation of
state, which is in poor agreement with experiment below 50 GPa.",0301615v1
2003/4/28,Effect of annealing on magnetic and magnetotransport properties of Ga1-xMnxAs epilayers,"High-field magnetic measurements performed with the use of magnetooptical
Kerr effect (MOKE) in the polar configuration as well as high-field and
low-field magnetotransport studies were carried out on Ga1-xMnxAs epilayers
grown by low temperature molecular beam epitaxy, and subsequently annealed
under various conditions. The structural investigations by means of high
resolution XRD were also performed. We observe significant changes in
magnetoresistivity curves, magnetization and strain introduced by the
annealing.",0304622v1
2003/5/29,Magnetic Interactions in Transition-Metal Oxides,"This a review article, which presents a general framework for the analysis of
interatomic magnetic interactions in the spin-density-functional theory, which
is based on the magnetic force theorem, make a link with the models for
transition-metal oxides, and gives several examples of how this strategy can be
used for the analysis of magnetic properties of colossal-magnetoresistive
perovskite manganites, double perovskite and pyrochlore compounds.",0305668v1
2003/6/30,Magnetic fluctuations in frustrated Laves hydrides R(Mn_{1-x}Al_{x})_{2}H_{y},"By neutron scattering, we have studied the spin correlations and spin
fluctuations in frustrated Laves hydrides, where magnetic disorder sets in the
topologically frustrated Mn lattice. Below the transition towards short range
magnetic order, static spin clusters coexist with fluctuating and alsmost
uncorrelated spins. The magnetic response shows a complexe lineshape, connected
with the presence of the magnetic inhomogeneities. Its analysis shows the
existence of two different processes, relaxation and local excitations, for the
spin fluctuations below the transition. The paramagnetic fluctuations are
discussed in comparison with classical spin glasses, cluster glasses, and non
Fermi liquid itinerant magnets.",0306743v1
2003/7/11,Evidence of spontaneous spin polarized transport in magnetic nanowires,"The exploitation of the spin in charge-based systems is opening revolutionary
opportunities for device architecture. Surprisingly, room temperature
electrical transport through magnetic nanowires is still an unresolved issue.
Here, we show that ferromagnetic (Co) suspended atom chains spontaneously
display an electron transport of half a conductance quantum, as expected for a
fully polarized conduction channel. Similar behavior has been observed for Pd
(a quasi-magnetic 4d metal) and Pt (a non-magnetic 5d metal). These results
suggest that the nanowire low dimensionality reinforces or induces magnetic
behavior, lifting off spin degeneracy even at room temperature and zero
external magnetic field.",0307284v1
2003/9/8,Switching Current vs. Magnetoresistance in Magnetic Multilayer Nanopillars,"We study current-driven magnetization switching in nanofabricated magnetic
trilayers, varying the magnetoresistance in three different ways. First, we
insert a strongly spin-scattering layer between the magnetic trilayer and one
of the electrodes, giving increased magnetoresistance. Second, we insert a
spacer with a short spin-diffusion length between the magnetic layers,
decreasing the magnetoresistance. Third, we vary the angle between layer
magnetizations. In all cases, we find an approximately linear dependence
between magnetoresistance and inverse switching current. We give a qualitative
explanation for the observed behaviors, and suggest some ways in which the
switching currents may be reduced.",0309191v1
2004/4/28,"Current-induced magnetization reversal in a (Ga,Mn)As-based magnetic tunnel junction","We report current-induced magnetization reversal in a ferromagnetic
semiconductor-based magnetic tunnel junction (Ga,Mn)As/AlAs/(Ga,Mn)As prepared
by molecular beam epitaxy on a p-GaAs(001) substrate. A change in
magneto-resistance that is asymmetric with respect to the current direction is
found with the excitation current of 10^6 A/cm^2. Contributions of both
unpolarized and spin-polarized components are examined, and we conclude that
the partial magnetization reversal occurs in the (Ga,Mn)As layer of smaller
magnetization with the spin-polarized tunneling current of 10^5 A/cm^2.",0404663v1
2004/8/18,Half-magnetization plateau stabilized by structural distortion in the antiferromagnetic Heisenberg model on a pyrochlore lattice,"Magnetization plateaus, visible as anomalies in magnetic susceptibility at
low temperatures, are one of the hallmarks of frustrated magnetism. We show how
an extremely robust half-magnetization plateau can arise from coupling between
spin and lattice degrees of freedom in a pyrochlore antiferromagnet, and
develop a detailed symmetry of analysis of the simplest possible scenario for
such a plateau state. The application of this theory to the spinel oxides
CdCr2O4 and HgCr2O4, where a robust half magnetization plateau has been
observed, is discussed.",0408397v1
2005/2/9,Evidence for a smooth superconductor to normal state transition for nonzero applied magnetic field in RbOs2O6,"The effect of the magnetic field on the critical behavior of RbOs2O6 is
investigated. We present and analyze magnetization data, revealing remarkable
consistency with a magnetic field induced finye size effect. It is traced back
that at temperatures Tp(H) smaller than Tc the correlation length cannot grow
beyond the limiting length scale set by the magnetic field. Thus, for nonzero H
the transition from the superconducting to the normal state turns out to be
smooth and the apropriately scaled magnetization data fall on a single curve.",0502232v1
2005/6/16,Fabrication of uniform half-shell magnetic nanoparticles and microspheres with applications as magnetically modulated optical nanoprobes,"Magnetically Modulated Optical Nanoprobes (MagMOONs) are magnetic particles
that indicate their angular orientation by emitting varying intensities of
light for different orientations and have shown promise for a variety of
applications. In this letter we describe a new method to fabricate uniform
magnetic half-shell particles that can be used as MagMOONs. Cobalt was
deposited onto commercially made polystyrene nanospheres and microspheres,
using ultrahigh vacuum vapor deposition, producing particles with uniform size,
shape and magnetic content. Additionally, the coercivity of the cobalt
deposited on the nanospheres was enhanced compared to its bulk value.",0506418v1
2005/11/3,Non-equilibrium Magnetic Properties of Single Crystalline La0.7Ca0.3CoO3,"Magnetic and electric properties of a single crystal of La0.7Ca0.3CoO3 have
been experimentally studied. The system attains a ferromagnetic spontaneous
moment below 170 K and exhibits a re-entrant spin-glass phase below 100 K. In
the ordered and the re-entrant phases, the low field magnetic properties are
strongly direction dependent, showing considerably higher magnetization values
perpendicular than parallel to the c-axis. Magnetic relaxation experiments show
that both the ferromagnetic and the re-entrant spin-glass phases are
non-equilibrium states, where the system exhibits magnetic aging characteristic
of spin-glasses and disordered and frustrated ferromagnets.",0511066v1
2005/12/8,Physics of Complex Magnetic Materials: Quasiparticle Many-Body Dynamics,"A brief survey of the author's works on the quantum theory of magnetism.
Theoretical foundation and applications of the generalized spin-fermion (sp-d)
exchange lattice model to various magnetic systems, e.g., rare-earth metals and
compounds, and magnetic and diluted magnetic semiconductors are discussed
briefly. The main emphasis is put on the dynamic behavior of two interacting
subsystems, the localized spins and spin density of itinerant carriers. A
nonperturbative many-body approach was used to describe the quasiparticle
dynamics. The approach permits to investigate and clarify the role of various
interactions and disorder effects in combined quantum models of magnetism in
unified and coherent fashion.",0512183v1
2006/1/4,Tunable temperature induced magnetization jump in a GdVO3 single crystal,"We report a novel feature of the temperature induced magnetization jump
observed along the a-axis of the GdVO3 single crystal at temperature TM = 0.8
K. Below TM, the compound shows no coercivity and remanent magnetization
indicating a homogenous antiferromagnetic structure. However, we will
demonstrate that the magnetic state below TM is indeed history dependent and it
shows up in different jumps in the magnetization only when warming the sample
through TM. Such a magnetic memory effect is highly unusual and suggesting
different domain arrangements in the supposedly homogenous antiferromagnetic
phase of the compound.",0601066v1
2006/6/16,Remanence and switching sensitivity in nanodot magnetic arrays,"New results are reported of the computer simulations on the magnetic
behaviour of magnetic arrays of nanoscopic dots, placed in cells of the square
lattice. We show that the remanence magnetization $M_r$ decreases with the
array size. For arrays 50x50, we investigate also the stability of the magnetic
structure of an array in an oscillating magnetic field. The damage spreading
technique reveals that this stability increases with the standard deviation
$\sigma$ of the switching field of individual elements of the array. On the
other hand, $M_r$ decreases with $\sigma$. An optimalization of the system
(large $M_r$ and large stability) can then be reached at some intermediate
value of $\sigma$.",0606456v1
2006/12/7,"Magnetism, spin-wave relaxation and spiral exchange in a trilayer magnetic junction","We study the non-collinear exchange coupling across a trilayer magnetic
junction consisting of two ferromagnets separated by a thin dilute magnetic
semiconductor containing itinerant carriers with finite spin relaxation. It is
remarkable that, by increasing the spin relaxation, the critical temperature is
substantially enhanced and the shape of the magnetization curve becomes more
mean-field like. We attribute these interesting changes to the broken
time-reversal symmetry which suppresses the oscillatory
Ruderman-Kittel-Kasuya-Yosida interaction. Our argument is further strengthened
by the emergence of the non-collinear spiral exchange coupling across the
trilayer magnetic junction with finite spin relaxation.",0612177v1
2006/12/13,Tuning alloy disorder in diluted magnetic semiconductors in high fields to 89 T,"Alloy disorder in II-VI diluted magnetic semiconductors (DMS) is typically
reduced when the local magnetic spins align in an applied magnetic field. An
important and untested expectation of current models of alloy disorder,
however, is that alloy fluctuations in many DMS compounds should increase again
in very large magnetic fields of order 100 tesla. Here we measure the disorder
potential in a Zn$_{.70}$Cd$_{.22}$Mn$_{.08}$Se quantum well via the low
temperature photoluminescence linewidth, using a new magnet system to 89 T.
Above 70 T, the linewidth is observed to increase again, in accord with a
simple model of alloy disorder.",0612332v1
2007/2/8,Canonical band theory of non-collinear magnetism,"A canonical band theory of non-collinear magnetism is developed and applied
to the close packed fcc and bcc crystal structures. Several examples of
non-collinear magnetism in the periodic table are seen to be canonical in
origin. This is a parameter free theory where the crystal and magnetic
symmetry, and exchange splitting, uniquely determine the electronic bands. The
only contribution to the determination of magnetic stability is the change in
band energy due to hybridisation resulting from spin mixing, and on this basis
we are able to analyse the origin of the stability of non-collinear magnetic
structures, and the instability of the FM state towards non-collinear ordering.",0702202v1
2007/2/22,Quantum mechanical motion of off-center ion in external magnetic field,"We consider the magnetostatic response to an external magnetic field of a
crystal containing off-center ions, such as Li^+ in KCl and KBr or the apical
oxygens O(A) in the LaSCO family of layered perovskites. Magnetic dipoles are
deduced from the matrix elements of the energy operator of a spinning particle
in a magnetic field which particle also satisfies the nonlinear Mathieu
equation. The magnetic moments are found to increase in magnitude as the system
goes from the lowest energy ground state to the higher lying excited states.
Our conclusions are in concert with earlier studies of magnetic dipoles from
circular currents based on Ampere's theorem.",0702533v1
2007/3/11,Resonant switching using spin valves,"Using micromagnetics we demonstrate that the r.f. field produced by a spin
valve can be used to reverse the magnetization in a magnetic nanoparticle. The
r.f. field is generated using a current that specifically excites a uniform
spin wave in the spin valve. This current is swept such that the
chirped-frequency generated by the valve matches the angular dependent resonant
frequency of the anisotropy-dominated magnetic nanoparticle, as a result of
which the magnetization reversal occurs. The switching is fast, requires
currents similar to those used in recent experiments with spin valves, and is
stable with respect to small perturbations. This phenomenon can potentially be
employed in magnetic information storage devices or recently discussed magnetic
computing schemes.",0703271v1
2007/6/6,Peculiar Ferrimagnetism Associated with Charge Order in Layered Perovskite GdBaMn2O5,"The magnetic properties of GdBaMn_{2}O_{5.0}, which exhibits charge ordering,
are studied from 2 to 400 K using single crystals. In a small magnetic field
applied along the easy axis, the magnetization M shows a temperature-induced
reversal which is sometimes found in ferrimagnets. In a large magnetic field,
on the other hand, a sharp change in the slope of M(T) coming from an unusual
turnabout of the magnetization of the Mn sublattices is observed. Those
observations are essentially explained by a molecular field theory which
highlights the role of delicate magnetic interactions between Gd^{3+} ions and
the antiferromagnetically coupled Mn^{2+}/Mn^{3+} sublattices.",0706.0749v1
2007/11/26,Electric field control of magnetic phase transitions in Ni3V2O8,"We report on the electric field control of magnetic phase transition
temperatures in multiferroic Ni3V2O8 thin films. Using magnetization
measurements, we find that the phase transition temperature to the canted
antiferromagnetic state is suppressed by 0.2 K in an electric field of 30 MV/m,
as compared to the unbiased sample. Dielectric measurements show that the
transition temperature into the magnetic state associated with ferroelectric
order increases by 0.2 K when the sample is biased at 25 MV/m. This electric
field control of the magnetic transitions can be qualitatively understood using
a mean field model incorporating a tri-linear coupling between the magnetic
order parameters and spontaneous polarization.",0711.4137v1
2008/5/23,Geometric Control Over the Motion of Magnetic Domain Walls,"We propose a method, which enables precise control of magnetic patterns,
relying only on the fundamental properties of the wire and the choice of the
path in the controlled parameter space but not on the rate of motion along this
path. Possible experimental realizations of this mechanism are discussed. In
particular, we show that the domain walls in magnetic nanowires can be
translated by rotation of the magnetic easy axis, or by applying pulses of
magnetic field directed transverse to the magnetic easy axis.",0805.3709v1
2008/6/29,Dynamical Regimes Induced by Spin Transfer in Magnetic Nanopillars,"We demonstrate the predicted out-of-plane precession induced by spin transfer
in magnetic nanostructures with in-plane magnetic field. We show that other
magnetic excitations have a significant effect on the stability of the out-of
plane precession, making it extremely sensitive to the orientation of the
applied magnetic field. The data are supported with micromagnetic simulations.
Our results elucidate the relation between the excitation spectrum and the
specific dynamical behaviors of nanoscale magnets.",0806.4731v2
2008/9/3,Imaging the antiparallel magnetic alignment of adjacent Fe and MnAs thin films,"The magnetic coupling between iron and alpha - MnAs in the epitaxial system
Fe/MnAs/GaAs(001) has been studied at the sub-micron scale, using element
selective x-ray photoemission electron microscopy. At room temperature, MnAs
layers display ridges and grooves, alternating alpha (magnetic) and beta
(non-magnetic) phases. The self-organised microstructure of MnAs and the stray
fields that it generates govern the local alignment between the Fe and alpha -
MnAs magnetization directions, which is mostly antiparallel with a marked
dependence upon the magnetic domain size.",0809.0620v1
2008/10/19,Magnetic anisotropy of single 3d spins on CuN surface,"First-principles calculations of the magnetic anisotropy energy for Mn- and
Fe-atoms on CuN/Cu(001) surface are performed making use of the torque method.
The easy magnetization direction is found to be different for Mn and Fe atoms
in accord with the experiment. It is shown the magnetic anisotropy has a
single-ion character and mainly originates from the local magnetic moment of
Mn- and Fe-atoms. The uniaxial magnetic anisotropy constants are calculated in
reasonable agreement with the experiment.",0810.3389v1
2009/1/19,Local magnetic anisotropy controlled by a surface nano-modulation,"A topological modulation of magnetic thin films can induce a magnetic
anisotropy of magnetostatic origin. In this letter, we report on the magnetic
properties of NiFe layers deposited on wavy shaped Si substrates. Without any
modulation, our films always present an intrinsic anisotropy. We show
unambiguously that patterning the substrate can overcome this anisotropy and
even impose a different easy axis of magnetization. This allows the definition
of two orthogonal easy axes at different places on the same substrate. This
control of anisotropy both in direction and intensity paves the way to the
realization of high precision bidimensional magnetic sensors.",0901.2617v1
2009/1/18,Probing Magnetic Configurations in Co/Cu Multilayered Nanowires,"Magnetic configurations in heterostructures are often difficult to probe when
the magnetic entities are buried inside. In this study we have captured
magnetic and magnetoresistance ""fingerprints"" of Co nanodiscs embedded in Co/Cu
multilayered nanowires using a first-order reversal curve method. In 200nm
diameter nanowires, the magnetic configurations can be tuned by adjusting the
Co nanodisc aspect ratio. Nanowires with the thinnest Co nanodiscs exhibit
single domain behavior, while those with thicker Co reverse via vortex states.
A superposition of giant and anisotropic magnetoresistance is observed, which
corresponds to the different magnetic configurations of the Co nanodiscs.",0901.2745v1
2009/2/11,Skyrmion Lattice in a Chiral Magnet,"Skyrmions represent topologically stable field configurations with
particle-like properties. We used neutron scattering to observe the spontaneous
formation of a two-dimensional lattice of skyrmion lines, a type of magnetic
vortices, in the chiral itinerant-electron magnet MnSi. The skyrmion lattice
stabilizes at the border between paramagnetism and long-range helimagnetic
order perpendicular to a small applied magnetic field regardless of the
direction of the magnetic field relative to the atomic lattice. Our study
experimentally establishes magnetic materials lacking inversion symmetry as an
arena for new forms of crystalline order composed of topologically stable spin
states.",0902.1968v1
2009/3/10,Magnetic properties of nanosized diluted magnetic semiconductors with band splitting,"The continual model of the nonuniform magnetism in thin films and wires of a
diluted magnetic semiconductor is considered with taking into account the
finite spin polarization of carriers responsible for the indirect interaction
of magnetic impurities (e.g. via RKKY mechanism). Spatial distributions (across
the film thickness or the wire radius) of the magnetizaton and carrier
concentrations of different spin orientations, as well as the temperature
dependence of the average magnetization are determined as the solution of the
nonlinear integral equation.",0903.1728v1
2009/4/3,Electrical Control of Magnetization in Charge-ordered Multiferroic LuFe2O4,"LuFe2O4 exhibits multiferroicity due to charge order on a frustrated
triangular lattice. We find that the magnetization of LuFe2O4 in the
multiferroic state can be electrically controlled by applying voltage pulses.
Depending on with or without magnetic fields, the magnetization can be
electrically switched up or down. We have excluded thermal heating effect and
attributed this electrical control of magnetization to an intrinsic
magnetoelectric coupling in response to the electrical breakdown of charge
ordering. Our findings open up a new route toward electrical control of
magnetization.",0904.0520v1
2009/4/17,Novel magnetic properties of graphene: Presence of both ferromagnetic and antiferromagnetic features and other aspects,"Investigations of the magnetic properties of graphenes prepared by different
methods reveal that dominant ferromagnetic interactions coexist along with
antiferromagnetic interactions in all the samples. Thus, all the graphene
samples exhibit room-temperature magnetic hysteresis. The magnetic properties
depend on the number of layers and the sample area, small values of both
favoring larger magnetization. Molecular charge-transfer affects the magnetic
properties of graphene, interaction with a donor molecule such as
tetrathiafulvalene having greater effect than an electron-withdrawing molecule
such as tetracyanoethylene",0904.2739v1
2009/9/18,Multipartite Entanglement in a Discrete Magnetic Bands Magnetic Lattice,"Using magneto-optical materials, an asymmetric multi-quantum state magnetic
lattice is proposed to host an entangled multipartite system formed by using a
quantum degenerate gas of ultracold atoms in a Bose Einstein Condensate (BEC).
The discrete magnetic bands magnetic lattice is devised to locate a
controllable long-range entanglement of a many harmonic oscillator system well
separated in space. The confinement of the coupled magnetic quantum well (CMQW)
system may significantly improve the condition for the long-range entanglement
of the multipartite (multi-qubits) to be used in quantum information
processors.",0909.3433v1
2009/10/27,Molecular spintronics using noncollinear magnetic molecules,"We investigate the spin transport through strongly anisotropic noncollinear
magnetic molecules and find that the noncollinear magnetization acts as a
spin-switching device for the current. Moreover, spin currents are shown to
offer a viable route to selectively prepare the molecular device in one of two
degenerate noncollinear magnetic states. Spin-currents can be also used to
create a non-zero density of toroidal magnetization in a recently characterized
Dy_3 noncollinear magnet.",0910.5235v3
2010/1/1,Magnetic Response in Mesoscopic Rings and Moebius Strips: A Theoretical Study,"We investigate magnetic response in mesoscopic rings and moebius strips
penetrated by magnetic flux $\phi$. Based on a simple tight-binding framework
all the calculations are performed numerically which describe persistent
current and low-field magnetic susceptibility as functions of magnetic flux
$\phi$, total number of electrons $N_e$, system size $N$ and disorder strength
$W$. Our exact analysis may provide some important signatures to study magnetic
response in nano-scale loop geometries.",1001.0243v1
2010/7/20,Finite-temperature magnetism in bcc Fe under compression,"We investigate the contributions of finite-temperature magnetic fluctuations
to the thermodynamic properties of bcc Fe as a function of pressure. First, we
apply a tight-binding total-energy model parameterized to first-principles
linearized augmented planewave computations to examine various ferromagnetic,
anti-ferromagnetic, and noncollinear spin spiral states at zero temperature.
The tight-binding data are fit to a generalized Heisenberg Hamiltonian to
describe the magnetic energy functional based on local moments. We then use
Monte Carlo simulations to compute the magnetic susceptibility, the Curie
temperature, heat capacity, and magnetic free energy. Including the
finite-temperature magnetism improves the agreement with experiment for the
calculated thermal expansion coefficients.",1007.3422v1
2010/10/15,Theory of I-V Characteristics of Magnetic Josephson Junctions,"We analyze the electrical characteristics of a circuit consisting of a free
thin-film magnetic layer and source and drain electrodes that have opposite
magnetization orientations along the free magnet's two hard directions. We find
that when the circuit's current exceeds a critical value there is a sudden
resistance increase which can be large in relative terms if the currents to
source or drain are strongly spin polarized and the free magnet is thin. This
behavior can be partly understood in terms of a close analogy between the
magnetic circuit and a Josephson junction.",1010.3073v1
2010/10/22,Magnetization asymmetry of type-II superconductors in high magnetic fields,"Inhomogeneous distribution of the pinning force in superconductor results in
a magnetization asymmetry. A model considering the field distribution in
superconductor was developed and symmetric and asymmetric magnetization loops
of porous and textured Bi_{1.8}Pb_{0.3}Sr_{1.9}Ca_{2}Cu_{3}O_{x} were fitted.
It is found that the thermal equilibrium magnetization realizes in crystals
smaller than some size depending on temperature and magnetic field.",1010.4650v1
2010/11/21,Magnetoelectric studies on polycrystalline FeVO4,"We report the magnetic, dielectric and ferroelectric properties of
polycrystalline iron vanadate(FeVO4), which has been recently found to exhibit
multiferroicity in low temperature with noncollinear magnetic orderings. The
influence of external magnetic field up to 9T on these properties is
systematically investigated. Besides the suppressing effect on the original
ferroelectric transition, the strong magnetic field seems to induce a secondary
ferroelectric transition at a slight lower temperature. And the corresponding
magnetization measurement reveals a field-induced metamagnetic transition at
low temperatures. Our results will help to clarify the complex magnetic
structure and microscopic mechanism of multiferroicity in FeVO4.",1011.4677v2
2010/12/6,Local electrical characterization of resonant magnetization motion in a single ferromagnetic sub-micrometer particle in lateral geometry,"In this article a detailed characterization of a magnetization motion in a
single sub-micrometer and multi-terminal ferromagnetic structure in lateral
geometry is performed in a GHz regime using direct DC characterization
technique. We have shown applicability of the Stoner-Wohlfarth model to the
magnetic nano-structure with large length to with ratio. Applying the model to
experimental data we are able to extract relevant magnetization motion
parameters and show a correlation between high frequency inductive currents and
local magnetization. Additionally, DC voltage generated over the structure at
the resonance, with external magnetic field under an angle to the shape
anisotropy axis, is explained by the model.",1012.1266v1
2010/12/18,Tunnel magnetoresistance of Fe3O4/MgO/Fe nanostructures,"A magnetic tunnel junction Fe3O4/MgO/Fe with (001) layer orientation is
considered. The junction magnetic energy is analyzed as a function of the angle
between the layer magnetization vectors under various magnetic fields. The
tunnel magnetoresistance is calculated as a function of the external magnetic
field. In contrast with junctions with unidirectional anisotropy, a
substantially lower magnetic field is required for the junction switching.",1012.4089v1
2011/2/17,Critical magnetization behaviors of the triangular and Kagome lattice quantum antiferromagnets,"We investigate the $S=1/2$ quantum spin antiferromagnets on the triangular
and Kagome lattices in magnetic field, using the numerical exact
diagonalization. Particularly we focus on an anomalous magnetization behavior
of each system at 1/3 of the saturation magnetization. The critical exponent
analyses suggest that it is a conventional magnetization plateau on the
triangular lattice, while an unconventional phenomenon, called the
magnetization ramp, on the Kagome lattice.",1102.3486v1
2011/4/17,Drops deformation and magnetic permeability of a ferrofluid emulsion,"In the paper the novel soft magnetic composite system is investigated. A
ferrofluid emulsion studied demonstrates the strong magnetic properties which
are atypical for commonly known emulsions. Interaction of ferrofluid emulsions
with a magnetic field is considered. Structural transformations in these media,
such as deformation of emulsion microdroplets and emulsion inversion, are
studied. The changes in the relative permeability of emulsion associated with
structural transformations are investigated. The theory of the observed
phenomena is developed, and the feasibility of effectively controlling the
magnetic properties of ferrofluid emulsions by applying a magnetic field is
demonstrated.",1104.3289v1
2011/8/12,Magnetic noise induced by dc current in a micron-size magnetic wire,"The magnetic noise spectra induced by direct-current (dc) current flowing
through a micron-scale ferromagnetic wire have been investigated. We have
observed the noise spectra with a resonance frequency. Under the application of
the magnetic field in the plane, the magnetic field dependences of the
resonance frequency and amplitude were well interpreted by the analytical
calculation based on the stochastic model. The noise spectra are attributable
to the resistance oscillation reflecting the uniform magnetization precession
which is produced by the Joule heating due to the dc current.",1108.2548v1
2011/9/9,Theoretical Investigation of the Magnetic Order in FeAs,"The magnetic structure of the iron monoarsenide FeAs is studied using
first-principles calculations. We consider the collinear and non-collinear
(spin-spiral wave) magnetic ordering and magnetic anisotropy. It is
analitically shown that a magnetic triaxial anisotropy results in a sum of two
spin-spiral waves with opposite directions of wave vectors and different spin
amplitudes, so that the magnetic moments in two perpendicular directions do not
equal each other.",1109.1924v1
2012/4/23,Heavy fermions in high magnetic field,"We give an overview on experimental studies performed in the last 25 years on
heavy-fermion systems in high magnetic field. The properties of field-induced
magnetic transitions in heavy-fermion materials close to a quantum
antiferromagnetic-to-paramagnetic instability are presented. Effects of a high
magnetic field to the Fermi surface, in particular the splitting of spin-up and
spin-down bands, are also considered. Finally, we review on recent advances on
the study of non-centrosymmetric compounds and ferromagnetic superconductors in
a high magnetic field.",1204.5128v2
2012/12/1,Ab initio calculation of the local magnetic moment in titanium doped zinc oxide with a corrected-band-gap scheme,"The local magnetic moment of Ti:ZnO is calculated from first principles by
using the corrected-band-gap scheme (CBGS). The results shows that the system
is magnetic with the magnetization of 0.699 $\mu_B$ per dopant. The origin of
the local magnetic moment is considered to be the impurity band partially
occupied by the donor electrons in the conduction band. Further, the impacts of
applying Hubbard U to Ti-d orbital on the magnetic moment have been
investigated.",1212.0066v1
2013/4/4,Numerical calculation of magnetic form factors of complex shape nano-particles coupled with micromagnetic simulations,"We investigate the calculation of the magnetic form factors of nano-objects
with complex geometrical shapes and non homogeneous magnetization
distributions. We describe a numerical procedure which allows to calculate the
3D magnetic form factor of nano-objects from realistic magnetization
distributions obtained by micromagnetic calculations. This is illustrated in
the canonical cases of spheres, rods and platelets. This work is a first step
towards a 3D vectorial reconstruction of the magnetization at the nanometric
scale using neutron scattering techniques.",1304.1308v1
2013/12/13,A generalized magnetic refrigeration scheme,"We have investigated the magnetocaloric effects in antiferromagnets and
compared them with those in ferromagnets using Monte Carlo simulations. In
antiferromagnets, the magnetic entropy reaches a maximum value at a finite
magnetic field when the temperature is fixed below the N\'eel temperature.
Using the fact, we proposed a protocol for applying magnetic fields to achieve
the maximum efficiency for magnetic refrigeration in antiferromagnets. In
particular, we found that at low temperatures, antiferromagnets are more useful
for magnetic refrigeration than ferromagnets.",1312.3716v2
2013/12/13,"Quantum states, symmetry and dynamics in degenerate spin s=1 magnets","The article deals with spin s=1 magnets. The symmetry conditions for normal
and degenerate equilibrium states are defined and types of magnetic ordering
found out. For each type of symmetry breaking the structure of source in the
Gibbs statistical operator has been obtained and additional thermodynamic
parameters introduced. The algebra of Poisson bracket for magnetic degrees of
freedom has been established and nonlinear dynamic equations have been derived.
Using the models of the exchange interaction, we have calculated the spectra of
collective excitations for two degenerate states whose order parameters have
digerent signature under the time reversal transformation.",1312.3799v2
2014/12/12,"Structure, magnetic order and excitations in the 245 family of Fe-based superconductors","Elastic neutron scattering simultaneously probes both the crystal structure
and magnetic order in a material. Inelastic neutron scattering measures phonons
and magnetic excitations. Here, we review the average composition, crystal
structure and magnetic order in the 245 family of Fe-based superconductors and
in related insulating compounds from neutron diffraction works. A
three-dimensional phase-diagram summarizes various structural, magnetic and
electronic properties as a function of the sample composition. A high pressure
phase diagram for the superconductor is also provided. Magnetic excitations and
the theoretic Heisenberg Hamiltonian are provided for the superconductor.
Issues for future works are discussed.",1412.3995v1
2014/12/17,Revealing the role of orbital magnetism in ultrafast laser-induced demagnetization in multisublattice metallic magnets by terahertz spectroscopy,"Simultaneous detection of THz emission and transient magneto-optical response
is employed to study ultrafast laser-induced magnetization dynamics in
multisublattice magnets NdFeCo and GdFeCo amorphous alloys with in-plane
magnetic anisotropy. A satisfactory quantitative agreement between the dynamics
revealed with the help of these two techniques is obtained for GdFeCo. For
NdFeCo the THz emission reveals faster dynamics than the magneto-optical
response. This indicates that in addition to spin dynamics of Fe ultrafast
laser excitation triggers faster magnetization dynamics of Nd.",1412.5396v1
2015/5/29,Coherent Sub-Nanosecond Switching of Perpendicular Magnetization by the Field-like Spin-Orbit Torque without an External Magnetic Field,"We theoretically study the influence of a predominant field-like spin-orbit
torque on the magnetization switching of small devices with a uniform
magnetization. We show that for a certain range of ratios (0.23-0.55) of the
Slonczewski to the field-like torques, it is possible to deterministically
switch the magnetization without requiring any external assist field. A precise
control of the pulse length is not necessary, but the pulse edge sharpness is
critical. The proposed switching scheme is numerically verified to be effective
in devices by micromagnetic simulations. Switching without any external assist
field is of great interest for the application of spin-orbit torques to
magnetic memories.",1505.07939v1
2015/8/17,Generation of flat-top pulsed magnetic fields with feedback control approach,"We describe the construction of a simple, compact, and cost-effective
feedback system that produces flat-top field profiles in pulsed magnetic
fields. This system is designed for use in conjunction with a typical
capacitor-bank driven pulsed magnet, and was tested using a 60-T pulsed magnet.
With the developed feedback controller, we have demonstrated flat-top magnetic
fields as high as 60.64 T with an excellent field stability of +-0.005 T. The
result indicates that the flat-top pulsed magnetic field produced features high
field stability and an accessible field strength. These features make this
system useful for improving the resolution of data with signal averaging.",1508.04045v1
2017/2/16,Domain wall nucleation in ferromagnetic nanowire with perpendicular magnetization stimulated by stray field of V-shaped magnetic particle,"We report the results of micromagnetic simulations of domain wall (DW)
nucleation and pinning/depinning processes in ferromagnetic planar structure
consisting of nanowire (NW) with perpendicular anisotropy and special V-shaped
nanoparticle (NP) with in-plane anisotropy located on top of NW. The
magnetization reversal features of this system in an external magnetic field
are investigated depending on the direction of particle magnetic moment.
Possible variants of magnetic logic cells (LCs) based on such system are
discussed.",1702.05416v1
2017/5/3,Spin Resonance and Magnetic Order in an Unconventional Superconductor,"Unconventional superconductivity in many materials is believed to be mediated
by magnetic fluctuations. It is an open question how magnetic order can emerge
from a superconducting condensate and how it competes with the magnetic spin
resonance in unconventional superconductors. Here we study a model d-wave
superconductor that develops spin-density wave order, and find that the spin
resonance is unaffected by the onset of static magnetic order. This result
suggests a scenario, in which the resonance in Nd0.05Ce0.95CoIn5 is a
longitudinal mode with fluctuating moments along the ordered magnetic moments.",1705.01255v2
2017/5/23,Spin-filter effect at the interface of magnetic/non-magnetic homojunctions in Li doped ZnO nanostructures,"After more than a decade of extensive research on the magnetic order
triggered by lattice defects in a wide range of nominally non-magnetic
materials, we report its application in a spintronic device. This device is
based on a spin-filter phenomenon we discovered at the interfaces between
defect-induced magnetic and non-magnetic regions, produced at the surface of a
Li doped ZnO microwire by low-energy proton implantation. Positive
magnetoresistance is observed at 300~K and scales with the number of interfaces
introduced along the wire.",1705.08124v2
2018/1/24,Voltage-induced precessional switching at zero-bias magnetic field in a conically magnetized free layer,"Voltage-induced magnetization dynamics in a conically magnetized free layer
with an elliptic cylinder shape is theoretically studied on the basis of the
macrospin model. It is found that an application of voltage pulse can induce
the precessional switching of magnetization even at zero-bias magnetic field,
which is of substantial importance for device applications such as
voltage-controlled nonvolatile memory. Analytical expressions of the conditions
for precessional switching are derived.",1801.07842v1
2017/4/10,Probing the Nanoskyrmion Lattice on Fe/Ir(111) with Magnetic Exchange Force Microscopy,"We demonstrate that the magnetic nanoskyrmion lattice on the Fe monolayer on
Ir(111) and the positions of the Fe atoms can be resolved simultaneously using
magnetic exchange force microscopy. Thus, the relation between magnetic and
atomic structure can be determined straightforwardly by evaluating the Fourier
transformation of the real space image data. We further show that the magnetic
contrast can be mapped on a Heisenberg-like magnetic interaction between tip
and sample spins. Since our imaging technique is based on measuring forces, our
observation paves the way to study skyrmions or other complex spin textures on
insulating sample systems with atomic resolution.",1704.02857v1
2017/4/18,Quantitative analysis of the influence of keV He ion bombardment on exchange bias layer systems,"The mechanism of ion bombardment induced magnetic patterning of exchange bias
layer systems for creating engineered magnetic stray field landscapes is still
unclear. We compare results from vectorial magneto-optic Kerr effect
measurements to a recently proposed model with time dependent rotatable
magnetic anisotropy. Results show massive reduction of rotational magnetic
anisotropy compared to all other magnetic anisotropies. We disprove the
assumption of comparable weakening of all magnetic anisotropies and show that
ion bombardment mainly influences smaller grains in the antiferromagnet.",1704.05487v1
2018/3/15,On identifying magnetized anomalies using geomagnetic monitoring,"We propose and investigate the inverse problem of identifying magnetized
anomalies beneath the Earth using the geomagnetic monitoring. Suppose a
collection of magnetized anomalies presented in the shell of the Earth. The
presence of the anomalies interrupts the magnetic field of the Earth, monitored
above the Earth. Using the difference of the magnetic fields before and after
the presence of the magnetized anomalies, we show that one can uniquely recover
the locations as well as their material parameters of the anomalies. Our study
provides a rigorous mathematical theory to the geomagnetic detection technology
that has been used in practice.",1803.05613v1
2012/9/24,Control of the magnetism and magnetic anisotropy of a single-molecule magnet with an electric field,"Through systematics density functional calculations, the mechanism of the
substrate induced spin reorientation transition in FePc/O-Cu(110) was explained
in terms of charge transfer and rearrangement of Fe-d orbitals. Moreover, we
found giant magnetoelectric effects in this system, manifested by the sensitive
dependences of its magnetic moment and magnetic anisotropy energy on external
electric field. In particular, the direction of magnetization of FePc/O-Cu(110)
is switchable between in-plane and perpendicular axes, simply by applying an
external electric field of 0.5 eV/{\AA} along the surface normal.",1209.5453v3
2008/11/6,Magnetic exchange interaction between rare-earth and Mn ions in multiferroic hexagonal manganites,"We report a study of magnetic dynamics in multiferroic hexagonal manganite
HoMnO3 by far-infrared spectroscopy. Low-temperature magnetic excitation
spectrum of HoMnO3 consists of magnetic-dipole transitions of Ho ions within
the crystal-field split J=8 manifold and of the triangular antiferromagnetic
resonance of Mn ions. We determine the effective spin Hamiltonian for the Ho
ion ground state. The magnetic-field splitting of the Mn antiferromagnetic
resonance allows us to measure the magnetic exchange coupling between the
rare-earth and Mn ions.",0811.0999v1
2018/9/19,Generation of magnetic skyrmions through pinning effect,"Based on analytical estimation and lattice simulation, a proposal is made
that magnetic skyrmions can be generated through the pinning effect in 2D
chiral magnetic materials, in absence of an external magnetic field or magnetic
anisotropy. In our simulation, stable magnetic skyrmions can be generated in
the pinning areas. The properties of the skyrmions are studied for various
values of ferromagnetic exchange strength and the Dzyaloshinskii-Moriya
interaction strength.",1809.07149v2
2021/4/1,Spin relaxation in diluted magnetic semiconductors. GaMnAs as example,"We report on study of magnetic impurities spin relaxation in diluted magnetic
semiconductors above Curie temperature. Systems with a high concentration of
magnetic impurities where magnetic correlations take place were studied. The
developed theory assumes that main channel of spin relaxation is mobile
carriers providing indirect interactions between magnetic impurities. Our
theoretical model is supported by experimental measurements of manganese spin
relaxation time in GaMnAs by means of spin-flip Raman scattering. It is found
that with temperature increase spin relaxation rate of ferromagnetic samples
increases and tends to that measured in paramagnetic sample.",2104.00417v1
2021/4/28,All optical resonant magnetization switching in $\text{CrI}_3$ monolayers,"Efficient control of a magnetization without an application of the external
magnetic fields is the ultimate goal of spintronics. We demonstrate, that in
monolayers of $\text{CrI}_3$, magnetization can be switched all optically, by
application of the resonant pulses of circularly polarized light. This happens
because of the efficient coupling of the lattice magnetization with bright
excitonic transition. $\text{CrI}_3$ is thus perspective functional material
with high potential for applications in the domains of spintronics and
ultra-fast magnetic memory.",2104.13956v1
2007/7/18,Piezomagnetic Quantum Dots,"We study the influence of deformations on magnetic ordering in quantum dots
doped with magnetic impurities. The reduction of symmetry and the associated
deformation from circular to elliptical quantum confinement lead to the
formation of piezomagnetic quantum dots. The strength of elliptical deformation
can be controlled by the gate voltage to change the magnitude of magnetization,
at a fixed number of carriers and in the absence of applied magnetic field. We
reveal a reentrant magnetic ordering with the increase of elliptical
deformation and suggest that the piezomagnetic quantum dots can be used as
nanoscale magnetic switches.",0707.2805v1
2009/7/25,Magnetic Nanoparticle Assemblies,"This chapter provides an introduction to the fundamental physical ideas and
models relevant to the phenomenon of magnetic hysteresis in nanoparticle
assemblies. The concepts of single-domain particles and superparamagnetism are
discussed. The mechanisms of magnetization by coherent rotation and the role of
temperature in the gradual decay of magnetization are analyzed in the framework
of simple analytical models. Modern numerical techniques (Monte Carlo
simulations, Magnetization Dynamics) used to study dense nanoparticle
assemblies are presented. An overview of the most common experimental
techniques used to measure the magnetic hysteresis effect in nanoparticle
assemblies are presented and the underlying principles are exposed.",0907.4417v2
2009/7/27,Para-ortho transition of artificial H$_2$ molecule in lateral quantum dots doped with magnetic impurities,"We present the magnetic phase diagram of artificial H$_2$ molecule in lateral
quantum dots doped with magnetic impurities as a function of external magnetic
field and plunger gate voltage. The onset of Mn-Mn
antiferromagnetic-ferromagnetic transition follows the electron spin
singlet-triplet transition. We deploy a configuration-interaction method to
exactly diagonalize the electron-Mn Hamiltonian and map it to an effective
Mn-Mn Heisenberg Hamiltonian. We find that Mn-Mn exchange coupling can be
described by RKKY-interaction/magnetic-polaron in weak/strong electron-Mn
coupling at low/high magnetic fields.",0907.4726v2
2009/7/28,Universal magnetic structure of the half-magnetization phase in Cr-based spinels,"Using an elastic neutron scattering technique under a pulsed magnetic field
up to 30 T, we determined the magnetic structure in the half-magnetization
plateau phase in the spinel CdCr$_2$O$_4$. The magnetic structure has a cubic
$P4_3$32 symmetry, which is the same as that observed in HgCr$_2$O$_4$. This
suggests that there is a universal field induced spin-lattice coupling
mechanism at work in the Cr-based spinels.",0907.4835v1
2012/2/18,Measuring spectrum of spin wave using vortex dynamics,"We propose to measure the spectrum of magnetic excitation in magnetic
materials using motion of vortex lattice driven by both ac and dc current in
superconductors. When the motion of vortex lattice is resonant with oscillation
of magnetic moments, the voltage decreases at a given current. From transport
measurement, one can obtain frequency of the magnetic excitation with the wave
number determined by vortex lattice constant. By changing the lattice constant
through applied magnetic fields, one can obtains the spectrum of the magnetic
excitation up to a wave vector of order $10\rm{\ nm^{-1}}$.",1202.4048v1
2013/12/31,Tuning Magnetic Properties Polycrystalline of PtCo Alloys Films with Pt,"We experimentally investigated disordered PtxCo1-x (here x: 0.4, 0.5 and 0.6)
alloy thin films magnetic properties which depended on Pt content. The magnetic
properties of PtCo films were described with two effects, one of them is the
hybridization between Co 3d and Pt 5d energy levels and it causes Pt magnetic
polarization. The second one is the high spin orbit coupling constant of Pt
which increases the ratio of magnetic orbital moment to spin moment. We
investigated magnetic properties considering these effects by vibrating sample
magnetometer (VSM) and ferromagnetic resonance (FMR) techniques.",1401.0227v2
2015/2/5,DFT calculations of magnetic anisotropy energy for GeMnTe ferromagnetic semiconductor,"Density functional theory (DFT) calculations of the energy of magnetic
anisotropy for diluted ferromagnetic semiconductor GeMnTe were performed using
using OpenMX package with fully relativistic pseudopotentials. The influence of
hole concentration and magnetic ion neighborhood on magnetic anisotropy energy
is presented. Analysis of microscopic mechanism of magnetic anisotropy is
provided, in particular the role of spin-orbit coupling, spin polarization and
spatial changes of electron density are discussed. The calculations are in
accordance with the experimental observation of perpendicular magnetic
anisotropy in rhombohedral GeMnTe (111) thin layers.",1502.01715v3
2016/12/21,Critical current density of a spin-torque oscillator with an in-plane magnetized free layer and an out-of-plane magnetized polarizer,"Spin-torque induced magnetization dynamics in a spin-torque oscillator with
an in-plane (IP) magnetized free layer and an out-of-plane (OP) magnetized
polarizer under IP shape-anisotropy field ($H_{\rm k}$) and applied IP magnetic
field ($H_{\rm a}$) was theoretically studied based on the macrospin model. The
rigorous analytical expression of the critical current density ($J_{\rm c1}$)
for the OP precession was obtained. The obtained expression successfully
reproduces the experimentally obtained $H_{\rm a}$-dependence of $J_{\rm c1}$
reported in [D. Houssameddine $et$ $al$., Nat. Mater. 6, 447 (2007)].",1612.06951v1
2019/3/12,Quantum Anomalous Parity Hall Effect in Magnetically Disordered Topological Insulator Films,"In magnetically doped thin-film topological insulators, aligning the magnetic
moments generates a quantum anomalous Hall phase supporting a single chiral
edge state. We show that as the system de-magnetizes, disorder from randomly
oriented magnetic moments can produce a `quantum anomalous parity Hall' phase
with \emph{helical} edge modes protected by a unitary reflection symmetry. We
further show that introducing superconductivity, combined with selective
breaking of reflection symmetry by a gate, allows for creation and manipulation
of Majorana zero modes via purely electrical means and at zero applied magnetic
field.",1903.05089v2
2020/5/18,Theory of universal differential conductance of magnetic Weyl type -II junctions,"We study the transport properties of junctions of normal and superconducting
Weyl semi-metal with tilted dispersion, in the presence of magnetization
induced by magnetic strips. The sub gap tunnelling conductance shows robust
signatures in the presence of different orientation and strength of
magnetization of the magnetic strips. We obtain the analytical results for the
normal-magnetic-superconducting junction in the thin barrier limit and
demonstrate that these results have no analogues to their conventional
counterparts and junctions with Dirac electrons in two-dimensions. We discuss
possible experimental setups to test our theoretical predictions.",2005.09094v1
2020/10/1,Spin fluctuations in quantized transport of magnetic topological insulators,"In magnetic topological insulators, quantized electronic transport is
interwined with spontaneous magnetic ordering, as magnetization controls band
gaps, hence band topology, through the exchange interaction. We show that
considering the exchange gaps at the mean-field level is inadequate to predict
phase transitions between electronic states of distinct topology. Thermal spin
fluctuations disturbing the magnetization can act as frozen disorders that
strongly scatter electrons, reducing the onset temperature of quantized
transport appreciably even in the absence of structural impurities. This
effect, which has hitherto been overlooked, provides an alternative explanation
of recent experiments on intrinsic magnetic topological insulators.",2010.00570v1
2020/10/12,Magnetization steps of $J_{1}$ quintets in the hcp lattice,"The magnetization steps of quintets, consisting of five identical magnetic
ions coupled by isotropic nearest neighbors antiferromagnetic exchange
interaction, in the hcp lattice, have been investigated. In that model there
are 17 types of quintets. The values of the magnetic field of the magnetization
steps of the quintets have been determined by numerical diagonalization of the
spin Hamiltonian, which is composed by the isotropic exchange and the Zeeman
interactions. The quintets are composed of individual spin $S$ = 1/2, 3/2 and
5/2. The contribution of the quintets for the effective concentration (or
technical saturation) as a function of the magnetic ions concentration was also
calculated.",2010.06051v1
2021/1/14,The magnetic field induced ferromagnetism in EuPd$_2$Sn$_4$ novel compound,"We report on crystal structure, magnetic and thermal physical properties of
EuPd$_2$Sn$_4$ stannide. From the magnetic susceptibility measurements a
divalent state of Eu rare earth element was determined together with an
antiferromagnetic (AFM) order at 11 K. By applying magnetic field, the magnetic
behavior variation reveals a complex magnetic structure. Above a critical field
Bc a ferromagnetic (FM)-like character starts to prevail. AFM and FM regimes
are separated by a metamagnetic region. Heat capacity measurements confirm this
behavior.",2101.05854v1
2021/2/2,Macroscopic magnetization in uniform magnetic fields,"The finding of a new formulation of the magnetization vector of a quantum
system interacting with a static uniform magnetic field\cite{Selenu1} is
reported. There a gauge invariant form of its divergence is shown being
expressed as a function of the electronic current per state coupled with the
Berry curvature of the quantum system. A Fourier analysis of the magnetization
vector and magnetization density is reported as an application of the presented
formula it could be applied in the context of computational
modelling\cite{Martin} of quantum matter.",2102.01513v1
2021/7/23,Surface-induced reduction of the switching field in nanomagnets,"Magnetization reversal in a many-spin nanomagnet subjected to an rf magnetic
field, on top of a DC magnetic field, is studied by numerically solving the
system of coupled (damped) Landau-Lifshitz equations. It is demonstrated that
spin-misalignment induced by surface anisotropy favors switching with a DC
magnetic field weaker than the Stoner-Wohlfarth switching field, for optimal
intensities and frequencies of the rf field.",2107.11407v3
2021/10/2,Quantum Anomalous Hall Effect in Perfectly Compensated Collinear Antiferromagnetic Thin Films,"We show that the quantum anomalous Hall effect almost always occurs in
magnetic topological insulator thin films whenever the top and bottom surface
layer magnetizations are parallel, independent of the interior layer
magnetization configuration. Using this criteria we identify structures that
have a quantum anomalous Hall effect even though they have collinear magnetic
structures with no net magnetization, and discuss strategies for realizing
these interesting magnetic states experimentally.",2110.00890v1
2022/5/16,Magnetic neutron scattering from spherical nanoparticles with Neel surface anisotropy: Atomistic simulations,"We consider a dilute ensemble of randomly-oriented noninteracting spherical
nanomagnets and investigate its magnetization structure and ensuing
neutron-scattering response by numerically solving the Landau-Lifshitz
equation. Taking into account the isotropic exchange interaction, an external
magnetic field, a uniaxial magnetic anisotropy for the particle core, and in
particular the Neel surface anisotropy, we compute the magnetic small-angle
neutron scattering cross section and pair-distance distribution function from
the obtained equilibrium spin structures. The numerical results are compared to
the well-known analytical expressions for uniformly magnetized particles and
provide guidance to the experimentalist. Moreover, the effect of a
particle-size distribution function is modeled.",2205.07552v1
2022/8/12,From Vertices to Vortices in magnetic nanoislands,"Recent studies in magnetic nanolithography show that a variety of complex
magnetic states emerge as a function of a single magnetic island's aspect
ratio. We propose a model which, in addition to fitting experiments, predicts
magnetic states with continuous symmetry at particular aspect ratios and
reveals a duality between vortex and vertex states. Our model then opens new
means of engineering novel types of artificial spin systems, and their
application to complex magnetic textures in devices and computing.",2208.06391v1
2022/8/25,Single crystal synthesis and magnetic properties of a Shastry-Sutherland lattice compound BaNd2ZnS5,"Single crystals of a Shastry-Sutherland magnetic semiconductor, BaNd2ZnS5,
were synthesized through a high-temperature solution growth technique. Physical
properties were characterized by powder and single crystal x-ray diffraction,
temperature- and field-dependent magnetization, and temperature-dependent
specific heat measurements. BaNd2ZnS5 orders antiferromagnetically at 2.9 K,
with magnetic moments primarily aligned within the ab-plane. Magnetic
isothermal measurements show metamagnetic transitions at ~ 15 kOe for the [110]
direction and ~ 21 kOe for the [100] direction. Estimated magnetic entropy
suggests a double ground state for each Nd ion.",2208.12180v1
2022/9/28,Numerical Study of S=1/2 Heisenberg Antiferromagnet on the Floret Pentagonal Lattice,"The $S=1/2$ Heisenberg antiferromagnet on the floret-pentagonal lattice with
two kinds of interaction strength is studied by the numerical-diagonalization
method. It is known that, near the five-ninth of the saturation magnetization,
this system shows a magnetization jump that is not accompanied by magnetization
plateaux. We focus our attention on the behavior of this system around the
five-ninth of the saturation magnetization; the changes of the magnetization
jump and plateau at and around this magnetization are clarified from the
diagonalization data for finite-size systems up to 45 sites.",2209.13887v1
2022/10/8,Analyzing the magnetic influence on magneto-optical interactions,"Here, we study the magneto-optical interactions in magnetic structures
considering the dependence of the interactions with the magnetic field. We
perform numerical simulations in a structure of magnetic nanowires, considering
them as one chain of strongly interacting single-domain particles. Robustly, we
obtain a quantitative value for the interactions, which allows us to classify
them into two magnetic states: demagnetized and magnetized.",2210.03997v2
2022/12/22,Planar Magnetic Paul Traps for Ferromagnetic Particles,"We present a study on the trapping of hard ferromagnetic particles using
alternating magnetic fields, with a focus on planar trap geometries. First, we
realize and characterize a magnetic Paul trap design for millimeter-size
magnets based on a rotating magnetic potential. Employing a physically rotating
platform with two pairs of permanent magnets with opposite poles, we show
stable trapping of hard ferromagnets a centimeter above the trap and
demonstrate that the particle shape plays a critical role in the trapping.
Finally, we propose a chip trap design that will open a path to studies of
gyromagnetic effects with ferromagnetic micro-particles.",2212.11622v1
2023/8/22,Topological analog of the magnetic bit within the Su-Schrieffer-Heeger-Holstein model,"In magnetic memories, the state of a ferromagnet is encoded in the
orientation of its magnetization. The energy of the system is minimized when
the magnetization is parallel or antiparallel to a preferred (easy) axis. These
two stable directions define the logical bit. Under an external perturbation,
the direction of magnetization can be controllably reversed and thus the bit
flipped. Here, we theoretically design a topological analogue of the magnetic
bit in the Su-Schrieffer-Heeger (SSH)-Holstein model, where we show that a
transient external perturbation can lead to a permanent change in the
electronic band topology.",2308.11099v2
2023/9/27,Regulating spin dynamics in magnetic nanomaterials,"Magnetic nanomaterials can be used in the construction of devices for
information processing and memory storage. For this purpose, they have to enjoy
two contradictory properties, from one side being able of keeping for long time
magnetization frozen, hence information stored, and from the other side
allowing for quick change of magnetization required for fast erasing of memory
and rewriting new information. Methods of resolving this dilemma are suggested
based on triggering resonance, dynamic resonance tuning, and on quadratic
Zeeman effect. These methods make it possible to realize effective regulation
of spin dynamics in such materials as magnetic nanomolecules and magnetic
nanoclusters.",2309.15568v1
2021/12/24,Visualizing Atomically-Layered Magnetism in CrSBr,"Two-dimensional (2D) materials can host stable, long-range magnetic phases in
the presence of underlying magnetic anisotropy. The ability to realize the full
potential of 2D magnets necessitates systematic investigation of the role of
individual atomic layers and nanoscale inhomogeneity ($\textit{i.e.}$, strain)
on the emergence and stability of both intra- and interlayer magnetic phases.
Here, we report multifaceted spatial-dependent magnetism in few-layer CrSBr
using magnetic force microscopy (MFM) and Monte Carlo-based magnetic
simulations. We perform nanoscale visualization of the magnetic sheet
susceptibility from raw MFM data and force-distance curves, revealing a
characteristic onset of both intra- and interlayer magnetic correlations as a
function of temperature and layer-thickness. We demonstrate that the presence
of a single uncompensated layer in odd-layer terraces significantly reduces the
stability of the low-temperature antiferromagnetic (AFM) phase and gives rise
to multiple coexisting magnetic ground states at temperatures close to the bulk
N\'eel temperature ($\textit{T}$$_N$). Furthermore, the AFM phase can be
reliably suppressed using modest fields (~300 Oe) from the MFM probe, behaving
as a nanoscale magnetic switch. Our prototypical study of few-layer CrSBr
demonstrates the critical role of layer parity on field-tunable 2D magnetism
and provides vital design criteria for future nanoscale magnetic devices.
Moreover, we provide a roadmap for using MFM for nano-magnetometry of 2D
materials, despite the ubiquitous absence of bulk zero-field magnetism in
magnetized sheets.",2112.12903v1
2023/6/11,"Surface Magnetization in Antiferromagnets: Classification, example materials, and relation to magnetoelectric responses","We use symmetry analysis and density functional theory to characterize
antiferromagnetic (AFM) materials which have a finite equilibrium magnetization
density on particular surface terminations. A nonzero magnetic dipole moment
per unit area or ""surface magnetization"" can arise on particular surfaces of
many AFMs due to the bulk magnetic symmetries. Such surface magnetization plays
an essential role in numerous device applications, from random-access
magnetoelectric (ME) memory to exchange bias. However, at this point a
universal description of AFM surface magnetization is lacking. We first
introduce a classification system based on whether the surface magnetization is
sensitive or robust to roughness, and on whether the surface of interest is
magnetically compensated or uncompensated in the bulk magnetic ground state. We
show that uncompensated surface magnetization can be conveniently described in
terms of ME multipoles at the local-moment, unit cell level, and demonstrate
that the symmetry of the multivalued ""multipolization lattice"" distinguishes
between roughness-robust and roughness-sensitive surface magnetization. We then
demonstrate that magnetization on bulk-compensated surfaces arises due to ME
multipoles (in addition to higher-order magnetic terms) at the atomic site
level. These can further be understood in terms of bulk ME responses, arising
from the effective electric field resulting from the surface termination. We
also show with density functional calculations that nominally compensated
surfaces in Cr2O3 and FeF2 develop a finite magnetization density at the
surface, in agreement with our predictions based on both group theory and the
linear and higher-order ME response tensors. Our analysis provides a
comprehensive basis for understanding the surface magnetic properties in AFMs,
and has important implications for phenomena such as exchange bias coupling.",2306.06631v1
2006/7/24,Calculation of material properties and ray tracing in transformation media,"Complex and interesting electromagnetic behavior can be found in spaces with
non-flat topology. When considering the properties of an electromagnetic medium
under an arbitrary coordinate transformation an alternative interpretation
presents itself. The transformed material property tensors may be interpreted
as a different set of material properties in a flat, Cartesian space. We
describe the calculation of these material properties for coordinate
transformations that describe spaces with spherical or cylindrical holes in
them. The resulting material properties can then implement invisibility cloaks
in flat space. We also describe a method for performing geometric ray tracing
in these materials which are both inhomogeneous and anisotropic in their
electric permittivity and magnetic permeability.",0607205v1
2011/2/28,Introduction to bulk metallic glass composite and its recent applications,"Bulk metallic glass (BMG) materials are hot topics in recent years, not to
mention BMG matrix composites, which further improve the magnetic and
mechanical properties of BMG materials. BMG and BMG matrix materials are fast
developing and promising materials in modern industry due to their
extraordinary properties such as high strength, low density, excellent
resistibility to high temperature and corrosion. In this paper, I reviewed
processing and application of several recently developed BMG and BMG matrix
materials.",1102.5758v1
2011/8/18,Half-Metallic Antiferromagnet as a Prospective Material for Spintronics,"Spintronics is expected as the next-generation technology based on the novel
notch of spin degree of freedom of electrons. Half metals, a class of materials
which behave as a metal in one spin direction and an insulator in the opposite
spin direction, are ideal for spintronic applications. Half metallic
antiferromagnets as a subclass of half metals are characterized further by
totally compensated spin moments in a unit cell, and have the advantage of
being able to generate fully spin-polarized current while exhibiting zero
macroscopic magnetization. Considerable efforts have been devoted to the search
for this novel material, from which we may get useful hints for prospective
material exploration.",1108.3645v1
2020/3/15,New quantum phases of matter: Topological Materials,"In this article, we provide an overview of the basic concepts of novel
topological materials. This new class of materials developed by combining the
Weyl/Dirac fermionic electron states and magnetism, provide a materials-science
platform to test predictions of the laws of topological physics. Owing to their
dissipationless transport, these materials hold high promises for technological
applications in quantum computing and spintronics devices.",2003.06835v1
2017/7/29,"Reply to the correspondence: ""On the fracture toughness of bioinspired ceramic materials""","This is a reply to the correspondence of Prof. Robert Ritchie: ""On the
fracture toughness of bioinspired ceramic materials"", submitted to Nature
Materials, which discusses the fracture toughness values of the following
papers: Bouville, F., Maire, E., Meille, S., Van de Moort\`ele, B., Stevenson,
A. J., & Deville, S. (2014). Strong, tough and stiff bioinspired ceramics from
brittle constituents. Nature Materials, 13(5), 508-514 and Le Ferrand, H.,
Bouville, F., Niebel, T. P., & Studart, A. R. (2015). Magnetically assisted
slip casting of bioinspired heterogeneous composites. Nature Materials, 14(11),
1172-1172.",1707.09528v1
2013/4/24,Supramolecular Spin Valves,"Magnetic molecules possess a high potential as building blocks for the design
of spintronic devices. Moreover, the use of molecular materials opens the way
for the controlled use of bottom-up, e.g. supramolecular, processing techniques
combining massively parallel self-fabrication with conventional top-down
nanostructuring techniques. The development of solid state spintronic devices
based on the giant magnetoresistance (GMR), tunnel magnetoresistance (TMR), and
spin valve effects has revolutionized the field of magnetic memory
applications. Recently, organic semiconductors were inserted into nanometer
sized tunnel junctions allowing enhancement of spin reversal, giant
magneto-resistance behaviour was observed in single non-magnetic molecules
coupled to magnetic electrodes, and the use of the quantum tunnelling
properties of single-molecule magnets (SMMs) in hybrid devices was proposed.
Herein, we present an original device in which a non-magnetic molecular quantum
dot, made of a single-wall carbon nanotube (SWCNT) contacted with non-magnetic
electrodes, is laterally coupled via supramolecular interactions to a TbPc2-SMM
(Pc = phthalocyanine), which provides a localized magnetic moment. The
conductance through the SWCNT is modulated by sweeping the magnetic field,
exhibiting magnetoresistance ratios up to 300% between fully polarized and
non-polarized SMMs below 1 K. We thus demonstrate the functionality of a
supramolecular spin valve without magnetic leads. Our results open up prospects
of circuit-integration and implementation of new device capabilities.",1304.6543v1
2017/1/7,Polarizability of electrically induced magnetic vortex plasma,"Electric field control of magnetic structures, particularly topological
defects in magnetoelectric materials, draws a great attention in recent years,
which has led to experimental success in creation and manipulation by electric
field of single magnetic defects, such as domain walls and skyrmions. In this
work we explore a scenario of electric field creation of another type of
topological defects -- magnetic vortices and antivortices, which are
characteristic for materials with easy plane (XY) symmetry. Each magnetic
(anti)vortex in magnetoelectric materials (such as type-II multiferroics)
possesses a quantized magnetic and an electric charge, where the former is
responsible for interaction between vortices and the latter couples the
vortices to electric field. This property of magnetic vortices opens a peculiar
possibility of creation of magnetic vortex plasma by non-uniform electric
fields. We show that the electric field, created by a cantilever tip, produces
a ""magnetic atom"" with a localized spatially ordered spot of vortices
(""nucleus"" of the atom) surrounded by antivortices (""electronic shells""). We
analytically find the vortex density distribution profile and temperature
dependence of polarizability of this structure and confirm it numerically. We
show that electric polarizability of the ""magnetic atom"" depends on temperature
as $\alpha \sim 1/T^{1-\eta}$ ($\eta>0$), which is consistent with Euclidean
random matrix theory prediction.",1701.01842v2
2012/10/7,Tailoring Magnetism of Perpendicularly Magnetized MnxGa Epitaxial Films on GaAs for Practical Applications,"MnxGa films with high perpendicular anisotropy, coercivity and energy product
have great application potential in ultrahigh-density perpendicular recording,
permanent magnets, spin-transfer-torque memory and oscillators,
magneto-resistance sensors and ferromagnetic metal/semiconductor
heterostructure devices. Here we present a comprehensive diagram of effective
magnetism-tailoring of perpendicularly magnetized MnxGa films grown on III-V
semiconductor GaAs by using molecular-beam epitaxy for the first time, by
systematically investigating the wide-range composition and detailed
post-growth annealing effects. We show that the (001)-orientated MnxGa films
with L10 or D022 ordering could be crystallized on GaAs in a very wide
composition range from x=0.76 to 2.6. L10-ordered MnxGa films show robust
magnetization, high remanent ratio, giant perpendicular anisotropy, high
intrinsic and extrinsic coercivity, and large energy product, which make this
kind of material favorable for perpendicular magnetic recording,
high-performance spintronic devices and permanent magnet applications. In
contrast, D022-ordered films exhibit lower perpendicular anisotropy and weaker
magnetism. Post-growth annealing MnxGa films studies reveal high
thermal-stability up to 450 oC, and effective tailoring of magnetic properties
can be realized by prolonging annealing at 450 oC. These results would be
helpful for understanding this kind of material and designing new spintronic
devices for specific practical applications.",1210.2062v3
2017/4/13,Extreme Magnetoresistance in Magnetic Rare Earth Monopnictides,"The acute sensitivity of the electrical resistance of certain systems to
magnetic fields known as extreme magnetoresistance (XMR) has recently been
explored in a new materials context with topological semimetals. Exemplified by
WTe$_{2}$ and rare earth monopnictide La(Sb,Bi), these systems tend to be
non-magnetic, nearly compensated semimetals and represent a platform for large
magnetoresistance driven by intrinsic electronic structure. Here we explore
electronic transport in magnetic members of the latter family of semimetals and
find that XMR is strongly modulated by magnetic order. In particular, CeSb
exhibits XMR in excess of $1.6 \times 10^{6}$ % at fields of 9 T while the
magnetoresistance itself is non-monotonic across the various magnetic phases
and shows a transition from negative magnetoresistance to XMR with field above
magnetic ordering temperature $T_{N}$. The magnitude of the XMR is larger than
in other rare earth monopnictides including the non-magnetic members and
follows an non-saturating power law to fields above 30 T. We show that the
overall response can be understood as the modulation of conductivity by the Ce
orbital state and for intermediate temperatures can be characterized by an
effective medium model. Comparison to the orbitally quenched compound GdBi
supports the correlation of XMR with the onset of magnetic ordering and
compensation and highlights the unique combination of orbital inversion and
type-I magnetic ordering in CeSb in determining its large response. These
findings suggest a paradigm for magneto-orbital control of XMR and are relevant
to the understanding of rare earth-based correlated topological materials.",1704.04226v1
2019/10/11,Magnetization governed magnetoresistance anisotropy in topological semimetal CeBi,"Magnetic topological semimetals, the latest member of topological quantum
materials, are attracting extensive attention as they may lead to
topologically-driven spintronics. Currently, magnetotransport investigations on
these materials are focused on anomalous Hall effect. Here, we report on the
magnetoresistance anisotropy of topological semimetal CeBi, which has tunable
magnetic structures arising from localized Ce 4f electrons and exhibits both
negative and positive magnetoresistances, depending on the temperature. We
found that the angle dependence of the negative magnetoresistance, regardless
of its large variation with the magnitude of the magnetic field and with
temperature, is solely dictated by the field-induced magnetization that is
orientated along a primary crystalline axis and flops under the influence of a
rotating magnetic field. The results reveal the strong interaction between
conduction electrons and magnetization in CeBi. They also indicate that
magnetoresistance anisotropy can be used to uncover the magnetic behavior and
the correlation between transport phenomena and magnetism in magnetic
topological semimetals.",1910.05247v1
2017/7/21,"Sensitivity of magnetic properties to chemical pressure in lanthanide garnets $Ln_3A_2X_3\text{O}_{12}$, $Ln$ = Gd, Tb, Dy, Ho, $A$ = Ga, Sc, In, Te, $X$ = Ga, Al, Li","A systematic study of the structural and magnetic properties of
three-dimensionally frustrated lanthanide garnets $Ln_3A_2X_3\text{O}_{12}$,
$Ln$ = Gd, Tb, Dy, Ho, $A$ = Ga, Sc, In, Te, $X$ = Ga, Al, Li is presented.
Garnets with $Ln$ = Gd show magnetic behaviour consistent with isotropic
Gd$^{3+}$ spins; no magnetic ordering is observed for T $\geq$ 0.4 K. Magnetic
ordering features are seen for garnets with $Ln$ = Tb, Dy, Ho in the
temperature range 0.4 < T < 2.5 K, however the nature of the magnetic ordering
varies for the different $Ln$ as well as for different combinations of $A$ and
$X$. The changes in magnetic behaviour can be explained by tuning of the
magnetic interactions and changes in the single-ion anisotropy. The change in
magnetic entropy is evaluated from isothermal magnetisation measurements to
characterise the magnetocaloric effect in these materials. Among the Gd
garnets, the maximum change in magnetic entropy per mole (15.45 J K$^{-1}$
mol$_{\text{Gd}}^{-1}$) is observed for Gd$_3$Sc$_2$Ga$_3$O$_{12}$ at 2 K, in a
field of 9 T. The performance of Dy$_3$Ga$_5$O$_{12}$ as a magnetocaloric
material surpasses the other garnets with $Ln$ = Tb, Dy, Ho.",1707.06730v1
2021/3/6,Observation of inverse magnetocaloric effect in magnetic-field-induced austenite phase of Heusler Alloys Ni50-xCoxMn31.5Ga18.5 (x = 9 and 9.7),"Magnetocaloric effect (MCE), magnetization, specific heat, and
magnetostriction measurements were performed in both pulsed and steady high
magnetic fields to investigate the magnetocaloric properties of Heusler alloys
Ni50-xCoxMn31.5Ga18.5 (x = 9 and 9.7). From direct MCE measurements for
Ni41Co9Mn31.5Ga18.5 up to 56 T, a steep temperature drop was observed for
magnetic-field-induced martensitic transformation (MFIMT), designated as
inverse MCE. Remarkably, this inverse MCE is apparent not only with MFIMT, but
also in the magnetic-field-induced austenite phase. Specific heat measurements
under steady high magnetic fields revealed that the magnetic field variation of
the electronic entropy plays a dominant role in the unconventional
magnetocaloric properties of these materials. First-principles based
calculations performed for Ni41Co9Mn31.5Ga18.5 and Ni45Co5Mn36.7In13.3 revealed
that the magnetic-field-induced austenite phase of Ni41Co9Mn31.5Ga18.5 is more
unstable than that of Ni45Co5Mn36.7In13.3 and that it is sensitive to slight
tetragonal distortion. We conclude that the inverse MCE in the
magnetic-field-induced austenite phase is realized by marked change in the
electronic entropy through tetragonal distortion induced by the externally
applied magnetic field.",2103.04143v1
2021/11/5,Quadrupolar magnetic excitations in an isotropic spin-1 antiferromagnet,"The microscopic origins of emergent behaviours in condensed matter systems
are encoded in their excitations. In ordinary magnetic materials, single
spin-flips give rise to collective dipolar magnetic excitations called magnons.
Likewise, multiple spin-flips can give rise to multipolar magnetic excitations
in magnetic materials with spin $\mathbf{S} \boldsymbol{\ge} \mathbf{1}$.
Unfortunately, since most experimental probes are governed by dipolar selection
rules, collective multipolar excitations have generally remained elusive. For
instance, only dipolar magnetic excitations have been observed in isotropic
$\mathbf{S}\boldsymbol{=}\mathbf{1}$ Haldane spin systems. Here, we unveil a
hidden quadrupolar constituent of the spin dynamics in antiferromagnetic
$\mathbf{S}\boldsymbol{=}\mathbf{1}$ Haldane chain material
Y$_\mathbf{2}$BaNiO$_\mathbf{5}$ using Ni $\mathbf{L_3}$-edge resonant
inelastic x-ray scattering. Our results demonstrate that pure quadrupolar
magnetic excitations can be probed without direct interactions with dipolar
excitations or anisotropic perturbations. Originating from on-site double
spin-flip processes, the quadrupolar magnetic excitations in
Y$_\mathbf{2}$BaNiO$_\mathbf{5}$ show a remarkable dual nature of collective
dispersion. While one component propagates as non-interacting entities, the
other behaves as a bound quadrupolar magnetic wave. This result highlights the
rich and largely unexplored physics of higher-order magnetic excitations.",2111.03625v1
2019/1/30,Comparative Study of the Surface Potential of Magnetic and Non-magnetic Spherical Objects in a Magnetized RF Discharge Plasma,"We report measurements of the time-averaged surface floating potential of
magnetic and non-magnetic spherical probes (or large dust particles) immersed
in a magnetized capacitively coupled discharge. In this study, the size of the
spherical probes is taken greater than the Debye length. The surface potential
of a spherical probe first increases, i.e. becomes more negative at low
magnetic field (B $<$ 0.05 T), attains a maximum value and decreases with
further increase of the magnetic field strength (B $>$ 0.05 T). The rate of
change of the surface potential in the presence of a B-field mainly depends on
the background plasma and types of material of the objects. The results show
that the surface potential of the magnetic sphere is higher (more negative)
compared to the non-magnetic spherical probe. Hence, the smaller magnetic
sphere collects more negative charges on its surface than a bigger non-magnetic
sphere in a magnetized plasma. The different sized spherical probes have nearly
the same surface potential above a threshold magnetic field (B $>$ 0.03 T),
implicating a smaller role of size dependence on the surface potential of
spherical objects. The variation of the surface potential of the spherical
probes is understood on the basis of a modification of the collection currents
to their surface due to charge confinement and cross-field diffusion in the
presence of an external magnetic field.",1901.10955v4
2020/6/12,Odd-even layer-number effect and layer-dependent magnetic phase diagrams in MnBi2Te4,"The intrinsic magnetic layered topological insulator MnBi2Te4 with nontrivial
topological properties and magnetic order has become a promising system for
exploring exotic quantum phenomena such as quantum anomalous Hall effect.
However, the layer-dependent magnetism of MnBi2Te4, which is fundamental and
crucial for further exploration of quantum phenomena in this system, remains
elusive. Here, we use polar reflective magnetic circular dichroism
spectroscopy, combined with theoretical calculations, to obtain an in-depth
understanding of the layer-dependent magnetic properties in MnBi2Te4. The
magnetic behavior of MnBi2Te4 exhibits evident odd-even layer-number effect,
i.e. the oscillations of the coercivity of the hysteresis loop (at {\mu}0Hc)
and the spin-flop transition (at {\mu}0H1), concerning the Zeeman energy and
magnetic anisotropy energy. In the even-number septuple layers, an anomalous
magnetic hysteresis loop is observed, which is attributed to the
thickness-independent surface-related magnetization. Through the linear-chain
model, we can clarify the odd-even effect of the spin-flop field and determine
the evolution of magnetic states under the external magnetic field. The
mean-field method also allows us to trace the experimentally observed magnetic
phase diagrams to the magnetic fields, layer numbers and especially,
temperature. Overall, by harnessing the unusual layer-dependent magnetic
properties, our work paves the way for further study of quantum properties of
MnBi2Te4.",2006.07216v1
2021/11/3,Anisotropic magnetocaloric effect of CrI$_{3}$: A theoretical study,"CrI$_{3}$ is considered to be a promising candidate for spintronic devices
and data storage. We derived the Heisenberg Hamiltonian for CrI$_{3}$ from
density functional calculations using the Liechtenstein formula. Moreover, the
Monte--Carlo simulations with the Sucksmith--Thompson method were performed to
analyze the effect of magnetic anisotropy energy on the thermodynamic
properties. Our method successfully reproduced the negative sign of isothermal
magnetic entropy changes when a magnetic field was applied along the hard
plane. We found that the temperature dependence of the magnetocrystalline
anisotropy energy is not negligible at temperatures slightly above the Curie
temperature. We clarified that the origin of this phenomenon is attributed to
anisotropic magnetic susceptibility and magnetization anisotropy. The
difference between the entropy change of the easy axis and the hard plane is
proportional to the temperature dependence of the magnetic anisotropy energy,
implying that the anisotropic entropy term is the main source of the
temperature dependence of the free energy difference when magnetizing in a
specific direction other than the easy axis. We also investigated the magnetic
susceptibility that can be used for the characterization of the negative sign
of the entropy change in the case of a hard plane. The competition of
magnetocrystalline anisotropy energy and external magnetic field at low
temperature and low magnetic field region causes a high magnetic susceptibility
as the fluctuation of magnetization. Meanwhile, the anisotropy energy is
suppressed at a sufficient magnetic field applied along the hard axis, the
magnetization is fully rotated to the direction of the external magnetic field.",2111.02063v1
2018/9/20,Electronic and Magnetic Properties of double-perovskites La$_2$MnRuO$_6$ and Hole-Doped La$_2$MnFeO$_6$ and their Potential for Magnetic Refrigeration,"Magnetic refrigeration at room-temperature is a technology that could
potentially be more environmentally-friendly, efficient and affordable than
traditional refrigeration. The search for suitable materials for magnetocaloric
refrigeration led to the study of double-perovskites La$_2$MnNiO$_6$,
La$_2$MnCoO$_6$ and La$_2$MnFeO$_6$. While La$_2$MnNiO$_6$ and La$_2$MnCoO$_6$
are ferromagnets with near room-temperature $T_C$s, previous theoretical study
of double-perovskite La$_2$MnFeO$_6$ revealed that this material is a
ferrimagnet due to strong electronic interactions in Fe-$d$ orbitals. Here, we
investigate the double-perovskites La$_2$MnRuO$_6$ and LaA''MnFeO$_6$ (A'' =
Ba, Ca and Sr) with density functional theory (DFT) as materials that can
counteract the effects the strong repulsion present in the in Fe-$d$ shells of
La$_2$MnFeO$_6$ and lead to a ferromagnetic state. Our study reaveals that
while La$_2$MnRuO$_6$ is also a ferrimagnet, but with a higher net magnetic
moment per formula than La$_2$MnFeO$_6$, doubly-ordered LaA''MnFeO$_6$ are
ferromagnets. By mapping the total energy of the LaA''MnFeO$_6$ compounds
obtained from DFT calculations to the Ising model, we also calculate their
magnetic exchange couplings. This allows us to estimate the trend in $T_C$ of
the three doped La$_2$MnFeO$_6$ materials with classical Monte-Carlo
calculations and predict that doubly-ordered LaBaMnFeO$_6$ and LaSrMnFeO$_6$
could be suitable materials for room-temperature magnetic refrigeration.",1809.07813v2
2021/11/23,"TaCo$_{2}$Te$_{2}$: An air-stable, magnetic van der Waals material with high mobility","Van der Waals (vdW) materials are an indispensable part of functional device
technology due to their versatile physical properties and ease of exfoliating
to the low-dimensional limit. Among all the compounds investigated so far, the
search for magnetic vdW materials has intensified in recent years, fueled by
the realization of magnetism in two dimensions (2D). However, metallic magnetic
vdW systems are still uncommon. In addition, they rarely host high-mobility
charge carriers, which is an essential requirement for high-speed electronic
applications. Another shortcoming of 2D magnets is that they are highly air
sensitive. Using chemical reasoning, we introduce TaCo2Te2 as an air-stable,
high-mobility, magnetic vdW material. It has a layered structure, which
consists of Peierls distorted Co chains and a large vdW gap between the layers.
We find that the bulk crystals can be easily exfoliated and the obtained thin
flakes are robust to ambient conditions after four months of monitoring using
an optical microscope. We also observe signatures of canted antiferromagntic
behavior at low-temperature. TaCo2Te2 shows a metallic character and a large,
non-saturating, anisotropic magnetoresistance. Furthermore, our Hall data and
quantum oscillation measurements reveal the presence of both electron- and
hole-type carriers and their high mobility.",2111.12079v1
2023/9/18,Extrinsic nonlinear Kerr rotation in topological materials under a magnetic field,"Topological properties in quantum materials are often governed by symmetry
and tuned by crystal structure and external fields, and hence
symmetry-sensitive nonlinear optical measurements in a magnetic field are a
valuable probe. Here we report nonlinear magneto-optical second harmonic
generation (SHG) studies of non-magnetic topological materials including
bilayer WTe2, monolayer WSe2 and bulk TaAs. The polarization-resolved patterns
of optical SHG under magnetic field show nonlinear Kerr rotation in these
time-reversal symmetric materials. For materials with three-fold rotational
symmetric lattice structure, the SHG polarization pattern rotates just slightly
in a magnetic field, whereas in those with mirror or two-fold rotational
symmetry the SHG polarization pattern rotates greatly and distorts. These
different magneto-SHG characters can be understood by considering the
superposition of the magnetic field-induced time-noninvariant nonlinear optical
tensor and the crystal-structure-based time-invariant counterpart. The
situation is further clarified by scrutinizing the Faraday rotation, whose
subtle interplay with crystal symmetry accounts for the diverse behavior of the
extrinsic nonlinear Kerr rotation in different materials. Our work illustrates
the application of magneto-SHG techniques to directly probe nontrivial
topological properties, and underlines the importance of minimizing extrinsic
nonlinear Kerr rotation in polarization-resolved magneto-optical studies.",2309.09512v1
2004/2/2,Giant magnetic enhancement in Fe/Pd films and its influence on the magnetic interlayer coupling,"The magnetic properties of thin Pd fcc(001) films with embedded monolayers of
Fe are investigated by means of first principles density functional theory. The
induced spin polarization in Pd is calculated and analyzed in terms of quantum
interference within the Fe/Pd/Fe bilayer system. An investigation of the
magnetic enhancement effects on the spin polarization is carried out and its
consequences for the magnetic interlayer coupling are discussed. In contrast to
{\it e.g.} the Co/Cu fcc(001) system we find a large effect on the magnetic
interlayer coupling due to magnetic enhancement in the spacer material. In the
case of a single embedded Fe monolayer we find aninduced Pd magnetization
decaying with distance $n$ from the magnetic layer as ~$n^{-\alpha}$ with
$\alpha \approx 2.4$. For the bilayer system we find a giant magnetic
enhancement (GME) that oscillates strongly due to interference effects. This
results in a strongly modified magnetic interlayer coupling, both in phase and
magnitude, which may not be described in the pure
Ruderman-Kittel-Kasuya-Yoshida (RKKY) picture. No anti-ferromagnetic coupling
was found and by comparison with magnetically constrained calculations we show
that the overall ferromagnetic coupling can be understood from the strong
polarization of the Pd spacer.",0402043v1
2007/12/14,Electric self inductance of quasi-2D magnetic-dipolar-mode ferrite disks,"An electric current flowing around a loop produces a magnetic field and hence
a magnetic flux through the loop. The ratio of the magnetic flux to the
electric current is called the (magnetic) self inductance. Can there be a dual
situation with a magnetic current flowing around a loop and producing an
electric field and hence an electric flux through the loop? Following the
classical electrodynamics laws an answer to this question should be negative.
Nevertheless special spectral properties of magnetic dipolar modes in a
quasi-2D ferrite disk show there are the double-valued-function loop magnetic
currents which may produce eigen electric fields and hence eigen electric
fluxes through the loop. In this case one can definitely introduce the notion
of the electric self inductance as the ratio of the electric flux to the
magnetic current. In this paper we show experimentally that in the
magnetic-dipolar-mode ferrite disks there exist eigen electric fluxes. These
fluxes are very sensitive to permittivity parameters of materials abutting to
the ferrite disk. Dielectric samples above a ferrite disk with a higher
permittivity than air confine the electric field closely outside the ferrite,
thereby changing the loop magnetic currents and thus transforming the
magnetic-dipolar-mode oscillating spectrum.",0712.2305v1
2018/6/28,Readout of field induced magnetic anisotropy in a magnetoactive elastomer,"It is shown that in external magnetic fields, a uniaxial magnetic anisotropy
comes into being in a magnetoactive elastomer (MAE). The magnitude of the
induced uniaxial anisotropy grows with the increasing external magnetic field.
The filler particles are immobilized in the matrix if the MAE sample is cooled
below 220 K, where the anisotropy can be read out. The cooling of the sample is
considered as an alternative methodological approach to the experimental
investigation of the magnetized state of MAEs. The appearance of magnetic
anisotropy in MAE is associated with restructuring of the filler during
magnetization, which leads to an additional effective field felt by the
magnetization. It is found that the magnitude of the effective magnetic
anisotropy constant of the MAE is approximately two times larger than its
effective shear modulus in the absence of magnetic field. It is proposed that
the experimentally observed large (about 40) ratio of the magnetic anisotropy
constant of the filler to the shear modulus of the matrix deserves attention
for the explanation of magnetic and magnetoelastic properties of MAEs. It may
lead to additional rigidity of the elastic subsystem increasing the shear
modulus of the composite material through the magnetomechanical coupling.",1806.11014v1
2016/12/19,Evidence of room temperature magnetoelectric properties in α-Fe1.6Ga0.4O3 oxide by magnetic field controlled electric properties and electric field controlled magnetism,"We have stabilized the {\alpha}-Fe1.6Ga0.4O3 (Ga doped {\alpha}-Fe2O3) system
in rhombohedral structure. The system has shown magnetically canted
ferromagnetic state and ferroelectric properties at room temperature. In first
time, we confirm the existence of magneto-electric coupling and
multiferro-electric properties at room temperature in the Ga doped
{\alpha}-Fe2O3 system based on the experimental observation of magnetic field
controlled electric polarization and electric field controlled magnetization.
The {\alpha}-Fe2O3 system does not exhibit electric field controlled magnetic
exchange bias effect, where as Ga doped {\alpha}-Fe2O3 showed exchange bias
shift up to the value of 370 Oe. We have recorded the response of
current-voltage characteristics and in-field magnetic relaxation of the system
under the simultaneous application of magnetic and electric fields. The
magnetization of the system is found highly sensitive to the ON and OFF modes,
as well as change of the polarity of external electric field. The system is a
new addition in the list of non-traditional
magneto-electrics/multi-ferroelectrics so far reported in literature. Such
novel materials, where magnetization and electric polarization can be
controlled by simultaneous application of magnetic and electric fields, is in
the increasing demand for potential applications in the field of next
generation magnetic sensor, switching, non-volatile memory and spintronic
devices.",1612.06049v1
2019/7/12,New method for characterization of magnetic nanoparticles by scanning magnetic microscopy,"In this paper, we present a new method for the magnetic characterization of
bulk materials, microstructures, and nanostructures. We investigated the
magnetic and morphological properties of two colloidal dispersions of iron
oxide (Fe3O4) magnetic nanoparticles (MNPs), synthesized by chemical
precipitation (co-precipitation) and pulsed laser ablation (PLA) in liquid, by
scanning magnetic microscopy (SMM) applied to a small sample with mass on the
order of tens of {\mu}g. We evaluated the performance of this technique by
comparing magnetization curves and measurements obtained with commercial
magnetometers, considered standard. The errors obtained for the saturation and
remanent magnetization were approximately 0.18 Am2/kg and 0.6 Am2/kg,
respectively. The average size distribution of the NPs estimated from the
magnetization curve measurements is consistent with the results obtained by
traditional transmission electron microscopy (TEM). The technique can be
extended to measure and analyze magnetization curves (hysteresis loops), thus
enabling an even more accurate estimation of overall NP sizes.",1907.05908v1
2022/7/6,Sensing the local magnetic environment through optically active defects in a layered magnetic semiconductor,"Atomic-level defects in van der Waals (vdW) materials are essential building
blocks for quantum technologies and quantum sensing applications. The layered
magnetic semiconductor CrSBr is an outstanding candidate for exploring
optically active defects owing to a direct gap in addition to a rich magnetic
phase diagram including a recently hypothesized defect-induced magnetic order
at low temperature. Here, we show optically active defects in CrSBr that are
probes of the local magnetic environment. We observe spectrally narrow (1 meV)
defect emission in CrSBr that is correlated with both the bulk magnetic order
and an additional low temperature defect-induced magnetic order. We elucidate
the origin of this magnetic order in the context of local and non-local
exchange coupling effects. Our work establishes vdW magnets like CrSBr as an
exceptional platform to optically study defects that are correlated with the
magnetic lattice. We anticipate that controlled defect creation allows for
tailor-made complex magnetic textures and phases with the unique ingredient of
direct optical access.",2207.02884v1
2022/11/28,Magnetic interactions and possible structural distortion in kagome FeGe from first-principles study and symmetry analysis,"Based on density functional theory and symmetry analysis, we present a
comprehensive investigation of electronic structure, magnetic properties and
possible structural distortion of magnetic kagome metal FeGe. We estimate the
magnetic parameters including Heisenberg and Dzyaloshinskii-Moriya (DM)
interactions, and find that the ferromagnetic nearest-neighbor $J_{1}$
dominates over the others, while the magnetic interactions between nearest
kagome layers favors antiferromagnetic. The N\'{e}el temperature $T_{N}$ and
Curie-Weiss temperature $\theta _{CW}$ are successfully reproduced, and the
calculated magnetic anisotropy energy is also in consistent with the
experiment. However, these reasonable Heisenberg interactions and magnetic
anisotropy cannot explain the double cone magnetic transition, and the DM
interactions, which even exist in the centrosymmetric materials, can result in
this small magnetic cone angle. Unfortunately, due to the crystal symmetry of
the high-temperature structure, the net contribution of DM interactions to
double cone magnetic structure is absent. Based on the experimental $2\times
2\times 2$ supercell, we thus explore the subgroups of the parent phase. Group
theoretical analysis reveals that there are 68 different distortions, and only
four of them (space group $P622$ or $P6_{3}22$) without inversion and mirror
symmetry thus can explain the low-temperature magnetic structure. Furthermore,
we suggest that these four proposed CDW phases can be identified by using Raman
spectroscopy. Since DM interactions are very sensitive to small atomic
displacements and symmetry restrictions, we believe that symmetry analysis is
an effective method to reveal the interplay of delicate structural distortions
and complex magnetic configurations.",2211.15545v1
2023/1/23,Signatures of a magnetic superstructure phase induced by ultrahigh magnetic fields in a breathing pyrochlore antiferromagnet,"The mutual coupling of spin and lattice degrees of freedom is ubiquitous in
magnetic materials and potentially creates exotic magnetic states in response
to the external magnetic field. Particularly, geometrically frustrated magnets
serve as a fertile playground for realizing magnetic superstructure phases.
Here, we observe an unconventional two-step magnetostructural transition prior
to a half-magnetization plateau in a breathing pyrochlore chromium spinel by
means of state-of-the-art magnetization and magnetostriction measurements in
ultrahigh magnetic fields available up to 600 T. Considering a microscopic
magnetoelastic theory, the intermediate-field phase can be assigned to a
magnetic superstructure with a three-dimensional periodic array of 3-up-1-down
and canted 2-up-2-down spin molecules. We attribute the emergence of the
magnetic superstructure to a unique combination of the strong spin-lattice
coupling and large breathing anisotropy.",2301.09509v3
2023/4/18,Transient non-collinear magnetic state for all-optical magnetization switching,"Resonant absorption of a photon by bound electrons in a solid can promote an
electron to another orbital state or transfer it to a neighboring atomic site.
Such a transition in a magnetically ordered material could affect the magnetic
order. While this process is an obvious road map for optical control of
magnetization, experimental demonstration of such a process remains
challenging. Exciting a significant fraction of magnetic ions requires a very
intense incoming light beam, as orbital resonances are often weak compared to
above-band-gap excitations. In the latter case, a sizeable reduction of the
magnetization occurs as the absorbed energy increases the spin temperature,
masking the non-thermal optical effects. Here, using ultrafast x-ray
spectroscopy, we were able to resolve changes in the magnetization state
induced by resonant absorption of infrared photons in Co-doped yttrium iron
garnet, with negligible thermal effects. We found that the optical excitation
of the Co ions affects the two distinct magnetic Fe sublattices differently,
resulting in a transient non-collinear magnetic state. The present results
indicate that the all-optical magnetization switching most likely occurs due to
the creation of a transient, non-collinear magnetic state followed by coherent
spin rotations of the Fe moments.",2304.08890v1
2023/8/3,Unconventional Metallic Magnetism: Non-analyticity and Sign-changing Behavior of Orbital Magnetization in ABC Trilayer Graphene,"We study an unique form of metallic ferromagnetism in which orbital moments
surpasses the role of spin moments in shaping the overall magnetization. This
system emerges naturally upon doping a topologically non-trivial Chern band in
the recently identified quarter metal phase of rhombohedral trilayer graphene.
Our comprehensive scan of the density-interlayer potential parameter space
reveals an unexpected landscape of orbital magnetization marked by two sign
changes and a line of singularities. The sign change originates from an intense
Berry curvature concentrated close to the band-edge, and the singularity arises
from a topological Lifshitz transition that transform a simply connected Fermi
sea into an annular Fermi sea. Importantly, these variations occur while the
groundstate order-parameter (i.e. valley and spin polarization) remains
unchanged. This unconventional relationship between the order parameter and
magnetization markedly contrasts traditional spin ferromagnets, where spin
magnetization is simply proportional to the groundstate spin polarization via
the gyromagnetic ratio. We compute energy and magnetization curves as functions
of collective valley rotation to shed light on magnetization dynamics and to
expand the Stoner-Wohlfarth magnetization reversal model. We provide
predictions on the magnetic coercive field that can be readily tested in
experiments. Our results challenge established perceptions of magnetism,
emphasising the important role of orbital moments in two-dimensional materials
such as graphene and transition metal dichalcogenides, and in turn, expand our
understanding and potential manipulation of magnetic behaviors in these
systems.",2308.01996v2
2015/10/21,Electromagnetic-Magnetoelectric Duality for Waveguides,"We develop a theory for waveguides that respects the duality of
electromagnetism, namely the symmetry of the equations arising through
inclusion of magnetic monopoles in addition to including electrons (electric
monopoles). The term magnetoelectric potential is sometimes used to signify the
magnetic-monopole induced dual to the usual electromagnetic potential. To this
end, we introduce a general theory for describing modes and characteristics of
waveguides based on mixed-monopole materials, with both electric and magnetic
responses. Our theory accommodates exotic media such as double-negative,
near-zero and zero-index materials, and we demonstrate that our general theory
exhibits the electromagnetic duality that would arise if we were to incorporate
magnetic monopoles into the media. We consider linear, homogeneous, isotropic
waveguide materials with slab and cylindrical geometries. To ensure manifest
electromagnetic duality, we construct generic electromagnetic susceptibilities
that are dual in both electric charges and magnetic monopoles using a
generalized Drude-Lorentz model that manifests this duality. Our model reduces
to standard cases in appropriate limits. We consider metamaterials and
metamaterial waveguides, as well as metal guides, as examples of waveguides
constructed of mixed-monopole materials, to show the generality of our
waveguide theory. In particular, we show that, in slab and cylindrical
waveguides, exchanging electric and magnetic material properties leads to the
exchange of transverse magnetic and transverse electric modes and dispersion
equations, which suggests a good test of the potential duality of waveguides.
This theory has the capability to predict waveguide behavior under an exchange
of electromagnetic parameters from the dual waveguide.",1510.06458v1
2016/2/4,Ba2YIrO6: A cubic double perovskite material with Ir5+ ions,"Materials with a 5d4 electronic configuration are generally considered to
have a nonmagnetic ground state (J=0). Interestingly, Sr2YIrO6 (Ir5+ having 5d4
electronic configuration) was recently reported to exhibit long-range magnetic
order at low temperature and the distorted IrO6 octahedra were discussed to
cause the magnetism in this material. Hence, a comparison of structurally
distorted Sr2YIrO6 with cubic Ba2YIrO6 may shed light on the source of
magnetism in such Ir5+ materials with 5d4 configuration. Besides, Ir5+
materials having 5d4 are also interesting in the context of recently predicted
excitonic types of magnetism. Here we report a single-crystal-based analysis of
the structural, magnetic, and thermodynamic properties of Ba2YIrO6. We observe
that in Ba2YIrO6 for temperatures down to 0.4 K, long-range magnetic order is
absent but at the same time correlated magnetic moments are present. We show
that these moments are absent in fully relativistic ab initio band-structure
calculations; hence, their origin is presently unclear.",1602.01670v1
2016/10/17,Thickness-Dependent and Magnetic-Field-Driven Suppression of Antiferromagnetic Order in Thin V$_{5}$S$_{8}$ Single Crystals,"With materials approaching the 2d limit yielding many exciting systems with
intriguing physical properties and promising technological functionalities,
understanding and engineering magnetic order in nanoscale, layered materials is
generating keen interest. One such material is V$_{5}$S$_{8}$, a metal with an
antiferromagnetic ground state below the N\'eel temperature $T_{N} \sim$ 32 K
and a prominent spin-flop signature in the magnetoresistance (MR) when $H||c
\sim$ 4.2 T. Here we study nanoscale-thickness single crystals of
V$_{5}$S$_{8}$, focusing on temperatures close to $T_{N}$ and the evolution of
material properties in response to systematic reduction in crystal thickness.
Transport measurements just below $T_{N}$ reveal magnetic hysteresis that we
ascribe to a metamagnetic transition, the first-order magnetic field-driven
breakdown of the ordered state. The reduction of crystal thickness to $\sim$ 10
nm coincides with systematic changes in the magnetic response: $T_{N}$ falls,
implying that antiferromagnetism is suppressed; and while the spin-flop
signature remains, the hysteresis disappears, implying that the metamagnetic
transition becomes second order as the thickness approaches the 2d limit. This
work demonstrates that single crystals of magnetic materials with nanometer
thicknesses are promising systems for future studies of magnetism in reduced
dimensionality and quantum phase transitions.",1610.05124v1
2017/2/10,Tunable Half-metallic Magnetism in Atom-thin Holey Two-dimensional C$_2$N Monolayer,"Exploring two-dimensional (2D) materials with magnetic ordering is a focus of
current research. It remains a challenge to achieve tunable magnetism in a
material of one-atom-thickness without introducing extrinsic magnetic atoms or
defects. Here, based on first-principles calculations, we propose that tunable
ferromagnetism can be realized in the recently synthesized holey 2D C$_2$N
($h$2D-C$_2$N) monolayer via purely electron doping that can be readily
achieved by gating. We show that owing to the prominent van Hove singularity in
the band structure, the material exhibits ferromagnetism even at a small doping
level. Remarkably, over a wide doping range of 4$\times$10$^{13}$/cm$^2$ to
8$\times$10$^{13}$/cm$^2$, the system becomes half-metallic, with carriers
fully spin-polarized. The estimated Curie temperature can be up to 320 K.
Besides gating, we find that the magnetism can also be effectively tuned by
lattice strain. Our result identifies $h$2D-C$_2$N as the first material with
single-atom-thickness that can host gate-tunable room-temperature half-metallic
magnetism, suggesting it as a promising platform to explore nanoscale magnetism
and flexible spintronic devices.",1702.03022v2
2018/8/20,Calculating critical temperatures for ferromagnetic order in two-dimensional materials,"Magnetic order in two-dimensional (2D) materials is intimately coupled to
magnetic anisotropy (MA) since the Mermin-Wagner theorem implies that
rotational symmetry cannot be spontaneously broken at finite temperatures in
2D. Large MA thus comprises a key ingredient in the search for magnetic 2D
materials that retains the magnetic order above room temperature. Magnetic
interactions are typically modeled in terms of Heisenberg models and the
temperature dependence on magnetic properties can be obtained with the Random
Phase Approximation (RPA), which treats magnon interactions at the mean-field
level. In the present work we show that large MA gives rise to strong
magnon-magnon interactions that leads to a drastic failure of the RPA. We then
demonstrate that classical Monte Carlo (MC) simulations correctly describe the
critical temperatures in the large MA limit and agree with RPA when the MA
becomes small. A fit of the MC results leads to a simple expression for the
critical temperatures as a function of MA and exchange coupling constants,
which significantly simplifies the theoretical search for new 2D magnetic
materials with high critical temperatures. The expression is tested on a
monolayer of CrI$_3$, which were recently observed to exhibit ferromagnetic
order below 45 K and we find excellent agreement with the experimental value.",1808.06400v3
2020/6/24,Giant nonlinear photocurrent in $\mathcal{PT}$-symmetric magnetic topological quantum materials,"Nonlinear photocurrent in time-reversal invariant noncentrosymmetric systems
have attracted substantial interest. Here we propose two new types of
second-order nonlinear direct photocurrent as the counterpart of normal shift
photocurrent (NSC) and normal injection photocurrent (NIC), namely magnetic
shift photocurrent (MSC) and magnetic injection photocurrent (MIC) in
time-reversal symmetry and inversion symmetry broken system. We show that MSC
is mainly governed by shift vector and interband Berry curvature, and MIC is
dominated by absorption strength and asymmetry of the group velocity difference
at time-reversed $\pm$$\textbf{k}$ points. MSC and MIC can be induced by
circularly and linearly polarized light, respectively, in
$\mathcal{PT}$-symmetric systems with $\mathcal{P}$ and $\mathcal{T}$ being
individually broken. Taking $\mathcal{PT}$-symmetric magnetic topological
quantum material bilayer antiferromagnetic (AFM) MnBi$_2$Te$_4$ as an example,
we predict the presence of large MIC in the terahertz frequency regime which
can be magnetically switched between two AFM states with time-reversed spin
orderings. While NSC vanishes in $\mathcal{T}$-symmetric systems, external
electric field breaks $\mathcal{PT}$ symmetry and enables large NSC response
which can be electrically switched. MIC and NSC are perpendicular to each other
upon linearly $x$/$y$-polarized light, and are highly tunable under electric
field, resulting in giant nonlinear photocurrent response down to a few THz
regime. It suggests bilayer AFM MnBi$_2$Te$_4$ as a tunable platform with rich
THz and magneto-optoelectronic applications. The present work reveals that
nonlinear photocurrent provides a powerful tool for deciphering magnetic
structures and interactions, particularly fruitful for probing and
understanding magnetic topological quantum materials.",2006.13573v1
2023/8/8,Room temperature reversible colossal volto-magnetic effect in all-oxide metallicmagnet/topotactic-phase-transition material heterostructures,"Multiferroic materials have undergone extensive research in the past two
decades in an effort to produce a sizable room-temperature magneto-electric
(ME) effect in either exclusive or composite materials for use in a variety of
electronic or spintronic devices. These studies have looked into the ME effect
by switching the electric polarization by the magnetic field or switching the
magnetism by the electric field. Here, an innovative way is developed to knot
the functional properties based on the tremendous modulation of electronics and
magnetization by the electric field of the topotactic phase transitions (TPT)
in heterostructures composed of metallic-magnet/TPT-material. It is divulged
that application of a nominal potential difference of 2-3 Volts induces
gigantic changes in magnetization by 100-250% leading to colossal Voltomagnetic
effect, which would be tremendously beneficial for low-power consumption
applications in spintronics. Switching electronics and magnetism by inducing
TPT through applying an electric field requires much less energy, making such
TPT-based systems promising for energy-efficient memory and logic applications
as well as opening a plethora of tremendous opportunities for applications in
different domains.",2308.04324v1
1997/10/22,Muon spin rotation and relaxation in magnetic materials,"A review of the muon spin rotation and relaxation ($\mu$SR) studies on
magnetic materials published from July 1993 is presented. It covers the
investigation of magnetic phase diagrams, of spin dynamics and the analysis of
the magnetic properties of superconductors. We have chosen to focus on selected
experimental works in these different topics. In addition, a list of published
works is provided.",9710235v1
1999/9/18,Magnetic quasicrystals: What can we expect to see in their neutron diffraction data?,"The theory of magnetic symmetry in quasicrystals is used to characterize the
nature of magnetic peaks, expected in elastic neutron diffraction experiments.
It is established that there is no symmetry-based argument which forbids the
existence of quasiperiodic long-range magnetic order. Suggestions are offered
as to where one should look for the simplest kinds of antiferromagnetic
quasicrystals.",9909272v1
2001/7/30,Spin Torques in Ferromagnetic/Normal Metal Structures,"Recent theories of spin-current-induced magnetization reversal are formulated
in terms of a spin-mixing conductance $G^{mix}$. We evaluate $G^{mix}$ from
first-principles for a number of (dis)ordered interfaces between magnetic and
non-magnetic materials. In multi-terminal devices, the magnetization direction
of a one side of a tunnel junction or a ferromagnetic insulator can ideally be
switched with negligible charge current dissipation.",0107589v1
2001/10/25,Multiscale nature of hysteretic phenomena: Application to CoPt-type magnets,"We suggest a workable approach for the description of multiscale
magnetization reversal phenomena in nanoscale magnets and apply it to CoPt-type
alloys. We show that their hysteretic properties are governed by two effects
originating at different length scales: a peculiar splitting of domain walls
and their strong pinning at antiphase boundaries. We emphasize that such
multiscale nature of hysteretic phenomena is a generic feature of nanoscale
magnetic materials.",0110526v2
2002/1/4,Magnon modes for thin circular vortex state magnetic dot,"The magnetization in a magnetic microdot made from soft magnetic materials
can have a vortex-like ground state structure resulting from competition
between the exchange and dipolar interactions. Normal mode magnon frequencies
for such dots are calculated taking into account both exchange and
magnetostatic effects. The presence of a low-lying mode as well as doublet
structure with small splitting is demonstrated. Estimates of the mode
frequencies for permalloy dots are obtained, and the possibility of
experimental detection of such modes is discussed.",0201050v1
2002/1/23,"Correlated defects, metal-insulator transition, and magnetic order in ferromagnetic semiconductors","The effect of disorder on transport and magnetization in ferromagnetic III-V
semiconductors, in particular (Ga,Mn)As, is studied theoretically. We show that
Coulomb-induced correlations of the defect positions are crucial for the
transport and magnetic properties of these highly compensated materials. We
employ Monte Carlo simulations to obtain the correlated defect distributions.
Exact diagonalization gives reasonable results for the spectrum of valence-band
holes and the metal-insulator transition only for correlated disorder. Finally,
we show that the mean-field magnetization also depends crucially on defect
correlations.",0201411v2
2003/1/9,Soft X-ray Magnetic Circular Dichroism of c(2x2) CuMn Ordered Surface Alloy,"Mn 2p soft X-ray absorption (XAS) spectroscopy excited with circularly
polarized synchrotron radiation has been applied to a new class of material,
c(2x2)CuMn/Cu(001) two-dimensional ordered surface alloy. A significant X-ray
magnetic circular dichroism (XMCD) signal has been clearly observed at T=25K,
indicating the existence of the ferromagnetic state under the external magnetic
field of 1.4 Tesla. The lineshape analyses of the XAS and XMCD spectra clearly
show that the Mn 3d state is rather localized and has a high spin magnetic
moment due to its half-filled character.",0301114v1
2003/2/20,Prediction of a surface magnetic moment in alpha-uranium,"Recently, there has been an increased interest in first-principles
calculations of the actinides as well as in finding the new materials which
display surface magnetism. We predict the existence of a magnetic moment on the
uranium (001) surface by performing density functional calculations for a slab
geometry in the generalized gradient and local spin density approximations with
included spin orbit coupling. The ferromagnetic phase is energetically favored
for all geometries. The calculated total magnetic moment, $0.65{\mu_{B}}$, is
stable on films of different thickness and it should be observable
experimentally.",0302423v1
2003/5/27,Clustered States as a New Paradigm of Condensed Matter Physics,"We argue that several materials of much current interest in condensed matter
physics share common phenomenological aspects that only very recent
investigations are unveiling. The list includes colossal magnetoresistance
manganites, high temperature superconducting cuprates, diluted magnetic
semiconductors, and others. The common aspect is the relevance of intrinsic
inhomogeneities in the form of ""clustered states"", as explained in the text.",0305628v2
2003/7/12,"Magnetic and microwave properties of (Ni,Co)Fe2O4-ferroelectric and (La,Ca,Sr)MnO3-ferroelectric multilayer structures","Structural, magnetic and ferromagnetic resonance characterization studies
have been performed on lay-ered ferromagnetic-ferroelectric oxides that show
strong magnetoelectric coupling. The samples contained thick films of ferrites
or substituted lanthanum manganites for the ferromagnetic phase and lead
zirconate titanate for the ferroelectric phase, and were sintered high
temperatures. Results indicate defect free ferrites, but deterioration of
manganite parameters due to diffusion at the interface and accounts for poor
magnetoelectric coupling in manganite-PZT samples.",0307302v1
2003/9/9,Finite-Temperature Micromagnetics of Hysterisis for Misaligned Single Iron Nanopillars,"We present micromagnetic results for the hysterisis of a single magnetic
nanopillar which is misaligned with respect to the applied magnetic field. We
provide results for both a one dimensional stack of magnetic rotors and of full
micromagnetic simulations. The results are compared to the Stoner-Wohlfarth
model.",0309237v1
2004/6/24,Exact diagonalization studies of doped Heisenberg spin rings,"Motivated by magnetization studies of the ""telephon number compound""
Sr_14Cu_24O_41 we investigate doped Heisenberg spin rings by means of complete
numerical diagonalization of a Heisenberg Hamiltonian that depends
parametrically on hole positions. A comparison with experimental magnetization
data reveals rather accurate information about the screened electrostatic
interaction between the charged holes on the ring which appears to be
astonishingly strong.",0406592v1
2004/9/12,Inhomogeneous magnetic behavior of Pr0.7Ca0.3CoO3 and Nd0.7Ca0.3CoO3,"Unlike La0.7Ca0.3CoO2.97, Pr0.7Ca0.3CoO3 and Nd0.7Ca0.3CoO2.95 do not show
distinct ferromagnetic transitions, but instead they exhibit very low magnetic
moments down to 50 K. A detail study of magnetic properties of Pr0.7Ca0.3CoO3
and Nd0.7Ca0.3CoO2.95 shows that the materials are inhomogeneous, exhibiting
properties similar to those of frustrated magnetic systems. In both these
cobaltates, small ferromagnetic clusters seem to be present in an
antiferromagnetic host.",0409297v1
2005/1/6,Magnetism in BN nanotubes induced by Carbon Substitution,"We performed ab initio calculation on the pristine and carbon-doped (5,5) and
(9,0) BN nanotubes. It was found that Carbon substitution for either boron or
nitrogen in BN nanotubes can induce spontaneous magnetization. Calculations
based on density functional theory with the local-spin-density-approximation on
the electronic band structure revealed a spin polarized, dispersionless band
near the Fermi energy. The magnetization can be attributed to the carbon 2p
electron. Compared to other theoretical models of light-element or metal-free
magnetic materials, the Carbon-doped BN nanotubes are more experimentally
accessible and can be potentially useful.",0501104v1
2005/10/13,Frustration-induced exotic properties of magnetic molecules,"Geometric frustration of interacting spin systems is the driving force of a
variety of fascinating phenomena in low-dimensional magnetism. In this
contribution I will review recent results on frustration-induced effects in
magnetic molecules, i.e. zero-dimensional magnetic systems, as well as in a
recently synthesized frustrated molecule-based spin tube, i.e. a
one-dimensional spin system.",0510355v1
2006/11/9,Chiral scattering in complex magnets,"General properties of the chiral scattering of polarized neutrons are
considered for two possible axial vector interactions: Zeeman energy and
non-alternating Dzyaloshinskii-Moriya interaction. Behavior in magnetic field
of helical magnetic structures is discussed for $Mn Si$ and magneto-electric
materials. The dynamical chiral fluctuations in magnetic field are considered
briefly. The chiral fluctuations in materials with the Dzyaloshinskii-Moriya
interaction are discussed and an assumption is made that above the transition
temperature they have to be incommensurate.",0611244v1
2007/2/17,Magnetic Anisotropy of Co2+ as Signature of Intrinsic Ferromagnetism in ZnO:Co,"We report on the magnetic properties of thoroughly characterized Zn1-xCoxO
epitaxial thin films, with low Co concentration, x=0.003-0.005. Magnetic and
EPR measurements, combined with crystal field theory, reveal that isolated Co2+
ions in ZnO possess a strong single ion anisotropy which leads to an ""easy
plane"" ferromagnetic state when the ferromagnetic Co-Co interaction is
considered. We suggest that the peculiarities of the magnetization process of
this state can be viewed as a signature of intrinsic ferromagnetism in ZnO:Co
materials.",0702410v1
1994/11/16,Three-dimensional electronic instabilities in polymerized solid A1C60,"The low-temperature structure of A1C60 (A=K, Rb) is an ordered array of
polymerized C60 chains, with magnetic properties that suggest a non-metallic
ground state. We study the paramagnetic state of this phase using
first-principles electronic-structure methods, and examine the magnetic
fluctuations around this state using a model Hamiltonian. The electronic and
magnetic properties of even this polymerized phase remain strongly three
dimensional, and the magnetic fluctuations favor an unusual three-dimensional
antiferromagnetically ordered structure with a semi-metallic electronic
spectrum.",9411004v1
1994/12/2,Commensurate and modulated magnetic phases in orthorhombic A1C60,"Competing magnetically ordered structures in polymerized orthorhombic A1C60
are studied. A mean-field theory for the equilibrium phases is developed using
an Ising model and a classical Heisenberg model to describe the competition
between inter- and intra-chain magnetic order in the solid. In the Ising model,
the limiting commensurate one-dimensional and three-dimensional phases are
separated by a commensurate three-sublattice state and by two sectors
containing higher-order commensurate phases. For the Heisenberg model the
quasi-1D phase is never the equilibrium state; instead the 3D commensurate
phases exhibits a transition to a continuum of coplanar spiral magnetic phases.",9412002v1
2007/5/7,Microscopic origin of Magnetic Ferroelectrics in Nonlinear Multiferroics,"A simple but general microscopic mechanism to understand the interplay
between the electric and magnetic degrees of freedom is developed. Within this
mechanism, the magnetic structure generates an electric current which induce an
counterbalance electric current from the spin orbital coupling. When the
magnetic structure is described by a single order parameter, the electric
polarization is determined by the single spin orbital coupling parameter, and
the material is predicted to be a half insulator. This mechanism provides a
simple estimation of the value of ferroelectricity and sets a physical
limitation as well.",0705.0955v3
2007/6/12,Temperature dependence of magnetic anisotropy in bulk and nanoparticles of Pr_0.5Sr_0.5MnO_3,"Nanoparticles (size 20, 40 and 60 nm) of Pr_0.5Sr_0.5MnO_3 are prepared by
sol-gel technique and their magnetic properties are studied using ferromagnetic
resonance and magnetization measurements. A comparison with the properties of
the bulk material shows that the ferromagnetic transition at 265 K remains
unaffected but the anti-ferromagnetic transition at T_N = 150 K disappears in
the nanoparticles. Further, the temperature dependence of magnetic anisotropy
shows a complex behavior, being higher in the nanoparticles at high
temperatures and lower at lower temperatures in comparison with the bulk.",0706.1662v1
2007/10/1,Friedel oscillations in one-dimensional metals: from Luttinger's theorem to the Luttinger liquid,"Charge density and magnetization density profiles of one-dimensional metals
are investigated by two complementary many-body methods: numerically exact
(Lanczos) diagonalization, and the Bethe-Ansatz local-density approximation
with and without a simple self-interaction correction. Depending on the
magnetization of the system, local approximations reproduce different Fourier
components of the exact Friedel oscillations.",0710.0358v1
2007/11/2,Origin and control of ferromagnetism in dilute magnetic semiconductors and oxides,"The author reviews the present understanding of the hole-mediated
ferromagnetism in magnetically doped semiconductors and oxides as well as the
origin of high temperature ferromagnetism in materials containing no valence
band holes. It is argued that in these systems spinodal decomposition into
regions with a large and a small concentration of magnetic component takes
place. This self-organized assembling of magnetic nanocrystals can be
controlled by co-doping and growth conditions. Functionalities of these
multicomponent systems are described together with prospects for their
applications in spintronics, nanoelectronics, photonics, plasmonics, and
thermoelectrics.",0711.0343v1
2008/2/20,Magnetic field induced ferroelectric loop in Bi0.75Sr0.25FeO3,"Magnetic field induced ferroelectric hysteresis loop observed in
Bi0.75Sr0.25FeO3-delta is of prime importance. The coexistence of
antiferromagnetism and weak ferromagnetism is responsible for the original
magnetoelastic and magnetoferroelectric properties. Upon external magnetic
field application, the existence of a magnetostrictive effect supports a
structural transition towards a homogeneous antiferromagnetic and ferroelectric
phase. The magnetic field induced polarization is among the highest reported
for BiFeO3 based systems in either thin film or bulk forms (Pr=96 microC/cm2 at
10T) while the ferroelectric coercive field is among the lowest reported
(Hc=661(V/cm) at 10T). These properties make this material very attractive for
technical applications.",0802.2877v1
2008/3/5,Distribution of magnetic domain pinning fields in GaMnAs ferromagnetic films,"Using the angular dependence of the planar Hall effect in GaMnAs
ferromagnetic films, we were able to determine the distribution of magnetic
domain pinning fields in this material. Interestingly, there is a major
difference between the pinning field distribution in as-grown and in annealed
films, the former showing a strikingly narrower distribution than the latter.
This conspicuous difference can be attributed to the degree of non-uniformity
of magnetic anisotropy in both types of films. This finding provides a better
understanding of the magnetic domain landscape in GaMnAs that has been the
subject of intense debate.",0803.0714v1
2008/4/21,Controlled aggregation of magnetic ions in a semiconductor. Experimental demonstration,"The control on the distribution of magnetic ions into a semiconducting host
is crucial for the functionality of magnetically doped semiconductors. Through
a structural analysis at the nanoscale, we give experimental evidence that the
aggregation of Fe ions in (Ga,Fe)N and consequently the magnetic response of
the material are affected by growth rate and co-doping with shallow impurities.",0804.3324v1
2008/4/26,Spin-torque oscillator based on tilted magnetization of the fixed layer,"The spin torque oscillator (STO), where the magnetization of the fixed layer
is tilted out of the film plane, is capable of strong microwave signal
generation in zero magnetic field. Through numerical simulations of the
Landau-Lifshitz-Gilbert-Slonczewski equations, within a macro-spin
approximation, we study the microwave signal generation as a function of drive
current for two realistic tilt angles. The tilt magnetization of the fixed
layer can be achieved by using a material with high out-of-plane
magnetocrystalline anisotropy, such as L10 FePt.",0804.4213v1
2008/5/3,Kramers degeneracy in a magnetic field and Zeeman spin-orbit coupling in antiferromagnetic conductors,"In this article, I study magnetic response of electron wavefunctions in a
commensurate collinear antiferromagnet. I show that, at a special set of
momenta, hidden anti-unitary symmetry protects Kramers degeneracy of Bloch
eigenstates against a magnetic field, pointing transversely to staggered
magnetization. Hence a substantial momentum dependence of the transverse
g-factor in the Zeeman term, turning the latter into a spin-orbit coupling,
that may be present in materials from chromium to borocarbides, cuprates,
pnictides, as well as organic and heavy fermion conductors.",0805.0378v2
2008/5/15,Dynamical Theory of Artificial Optical Magnetism Produced by Rings of Plasmonic Nanoparticles,"We present a detailed analytical theory for the plasmonic nanoring
configuration first proposed in [A. Alu, A. Salandrino, N. Engheta, Opt. Expr.
14, 1557 (2006)], which is shown to provide negative magnetic permeability and
negative index of refraction at infrared and optical frequencies. We show
analytically how the nanoring configuration may provide superior performance
when compared to some other solutions for optical negative index materials,
offering a more 'pure' magnetic response at these high frequencies, which is
necessary for lowering the effects of radiation losses and absorption.
Sensitivity to losses and the bandwidth of operation of this magnetic inclusion
are also investigated in details and compared with other available setups.",0805.2329v1
2008/7/11,Magnetism in Graphene Systems,"Graphene has attracted a great interest in material science due to its novel
electronic structrues. Recently, magnetism discovered in graphene based systems
opens the possibility of their spintronics application. This paper provides a
comprehensive review on the magnetic behaviors and electronic structures of
graphene systems, including 2-dimensional graphene, 1-dimensional graphene
nanoribbons, and 0-dimensional graphene nanoclusters. Theoretical research
suggests that such metal-free magnetism mainly comes from the localized states
or edges states. By applying external electric field, or by chemical
modification, we can turn the zigzag nanoribbon systems to half metal, thus
obtain a perfect spin filter.",0807.1791v1
2008/10/31,Defect-induced ferromagnetism in graphite,"We demonstrate direct evidence for ferromagnetic order at defect structures
in highly oriented pyrolytic graphite with magnetic force microscopy at room
temperature. Magnetic impurities have been excluded as the origin of the
magnetic signal after careful analysis supporting an intrinsic magnetic
behavior of carbon-based materials. The observed ferromagnetism has been
attributed to originate from unpaired electron spins localized at grain
boundaries. Scanning tunneling spectroscopy of grain boundaries showed intense
localized states and enhanced charge density compared to bare graphite.",0810.5657v1
2008/12/3,Correlation between magnetism and spin-dependent transport in CoFeB alloys,"We report a correlation between the spin polarization of the tunneling
electrons (TSP) and the magnetic moment of amorphous CoFeB alloys. Such a
correlation is surprising since the TSP involves s-like electrons close to the
Fermi level (EF), while the magnetic moment mainly arises due to all
d-electrons below EF. We show that probing the s and d-bands individually
provides clear and crucial evidence for such a correlation to exist through s-d
hybridization, and demonstrate the tuneability of the electronic and magnetic
properties of CoFeB alloys.",0812.0679v1
2009/9/25,The magnetic properties of the Garnet and glass forms of Mn3Al2Si3O12,"The magnetic susceptibilities and specific heats of the crystalline garnet
and glass forms of Mn3Al2Si3O12 are reported. This allows a direct comparison
of the degree of magnetic frustration of the triangle-based garnet lattice and
the structurally disordered solid at the same composition for isotropic spin
5/2 Mn^2+ (3d^5). The results show that the glass phase shows more pronounced
signs of magnetic frustration than the crystalline phase. Through comparison of
the specific heats of Ca3Al2Si3O12 (grossular) and Mn3Al2Si3O12 (spessartine)
garnets, information is provided concerning the anomalous extra specific heat
in the latter material.",0909.4720v1
2010/5/28,Density functional theory calculations on magnetic properties of actinide compounds,"We have performed a detailed analysis of the magnetic (collinear and
noncollinear) order and atomic and the electron structures of UO2, PuO2 and UN
on the basis of density functional theory with the Hubbard electron correlation
correction (DFT+U). We have shown that the 3-k magnetic structure of UO2 is the
lowest in energy for the Hubbard parameter value of U=4.6 eV (and J=0.5 eV)
consistent with experiments when Dudarev's formalism is used. In contrast to
UO2, UN and PuO2 show no trend for a distortion towards rhombohedral structure
and, thus, no complex 3-k magnetic structure is to be anticipated in these
materials.",1005.5369v1
2011/2/13,Long wavelength magnetic and magnetoelectric excitations in the ferroelectric antiferromagnet BiFeO3,"We present a terahertz spectroscopic study of magnetic excitations in
ferroelectric antiferromagnet BiFeO3. We interpret the observed spectrum of
long-wavelength magnetic resonance modes in terms of the normal modes of the
material's cycloidal antiferromagnetic structure. We find that the modulated
Dzyaloshinski-Moriya interaction leads to a splitting of the out-of-plane
resonance modes. We also assign one of the observed absorption lines to an
electromagnon excitation that results from the magnetoelectric coupling between
the ferroelectric polarization and the cycloidal magnetic structure of BiFeO3.",1102.2552v1
2011/6/7,Tailoring the magnetic properties of Fe asymmetric nanodots,"Asymmetric dots as a function of their geometry have been investigated using
three-dimensional (3D) object oriented micromagnetic framework (OOMMF) code.
The effect of shape asymmetry of the disk on coercivity and remanence is
studied. Angular dependence of the remanence and coercivity is also addressed.
Asymmetric dots are found to reverse their magnetization by nucleation and
propagation of a vortex, when the field is applied parallel to the direction of
asymmetry. However, complex reversal modes appear when the angle at which the
external field is applied is varied, leading to a non monotonic behavior of the
coercivity and remanence.",1106.1407v1
2011/7/29,Coexistence of Ferromagnetism and Superconductivity in Noncentrosymmetric Materials with Cubic Symmetry,"This is a model study for the emergence of superconductivity in
ferromagnetically ordered phases of cubic materials whose crystal structure
lacks inversion symmetry. A Ginzburg-Landau-type theory is used to find the
ferromagnetic state and to determine the coupling of magnetic order to
superconductivity. It is found that noncentrosymmetricity evokes a helical
magnetic phase. If the wavelength of the magnetic order is long enough, it
gives rise to modulations of the order parameter of superconductivity, both in
modulus and complex phase. At magnetic domain walls the nucleation of
superconductivity is found to be suppressed as compared to the interior of
ferromagnetic domains.",1107.5954v2
2011/12/6,Instability in magnetic materials with dynamical axion field,"It has been pointed out that the axion electrodynamics exhibits instability
in the presence of a background electric field. We show that the instability
leads to a complete screening of an applied electric field above a certain
critical value and the excess energy is converted into a magnetic field. We
clarify the physical origin of the screening effect and discuss its possible
experimental realization in magnetic materials where magnetic fluctuations play
the role of the dynamical axion field.",1112.1414v2
2012/7/2,Application of the finite-temperature Lanczos method for the evaluation of magnetocaloric properties of large magnetic molecules,"We discuss the magnetocaloric properties of gadolinium containing magnetic
molecules which potentially could be used for sub-Kelvin cooling. We show that
a degeneracy of a singlet ground state could be advantageous in order to
support adiabatic processes to low temperatures and simultaneously minimize
disturbing dipolar interactions. Since the Hilbert spaces of such spin systems
assume very large dimensions we evaluate the necessary thermodynamic
observables by means of the Finite-Temperature Lanczos Method.",1207.0299v1
2012/12/9,Surface-confined molecular coolers for cryogenics,"An excellent molecule-based cryogenic magnetic refrigerant, gadolinium
acetate tetrahydrate, is here used to decorate selected portions of silicon
substrate. By quantitative magnetic force microscopy for variable applied
magnetic field near liquid-helium temperature, we demonstrate that the
molecules hold intact their magnetic properties, and therefore their cooling
functionality, after their deposition. Our result represents a step forward
towards the realization of a molecule-based microrefrigerating device for very
low temperatures.",1212.1880v1
2012/12/17,Cavity equations for a positive or negative refraction index material with electric and magnetic non-linearities,"We study evolution equations for electric and magnetic field amplitudes in a
ring cavity with plane mirrors. The cavity is filled with a positive or
negative refraction index material with third order effective electric and
magnetic non-linearities. Two coupled non-linear equations for the electric and
magnetic amplitudes are obtained. We prove that the description can be reduced
to one Lugiato Lefever equation with generalized coefficients. A stability
analysis of the homogeneous solution, complemented with numerical integration,
shows that any combination of the parameters should correspond to one of three
characteristic behaviors.",1212.3974v1
2013/1/16,"Magnetic, magnetocaloric and transport properties of HoRuSi compound","Magnetic, thermal, magnetocaloric and transport properties of polycrystalline
HoRuSi have been studied. It was found that the compound shows magnetic
transitions at T1=18 K and T2=8 K. Magnetization data reveal that the
ferromagnetic ordering is dominant in this compound. Magnetocaloric effect has
been estimated from M-H-T data and the -{\Delta}SM has been found to be 12.8
J/kg K for field of 50 kOe, which is comparable to some potential refrigerant
materials in same temperature regime.",1301.3670v1
2013/6/29,Perpendicular magnetization of Co20Fe50Ge30 films induced by MgO interface,"Epitaxial growth of Co20Fe50Ge30 thin film on single crystal MgO (001)
substrate is reported. Structure characterization revealed (001)-oriented B2
order of CoFeGe well lattice matched with the MgO barrier. Perpendicular
magnetic anisotropy (PMA) was achieved in the MgO/CoFeGe/MgO structure with an
optimized magnetic anisotropy energy density (K) of 3 106 erg/cm3. The magnetic
anisotropy is found to depend strongly on the thickness of the MgO and CoFeGe
layers, indicating that the PMA of CoFeGe is contributed by the interfacial
anisotropy between CoFeGe and MgO. With reported low damping constant, CoFeGe
films are promising spintronic materials for achieving low switching current.",1307.0104v1
2013/9/27,Morphology and magnetic properties of Fe3O4-alginic acid nanocomposites,"Morphology, structure and magnetic properties of nanocomposites of magnetite
(Fe3O4) nanoparticles and alginic acid (AA) are studied. Magnetite Fe3O4
nanoparticles and the nanoparticles capped with alginic acid exhibit very
distinct properties. The chemical bonding between alginic acid and surface of
magnetite nanoparticles results in recovery of surface magnetization. On the
other hand, it also leads to enhanced surface spin disorder and unconventional
behavior of magnetization observed in Fe3O4-AA nanocomposites at low
temperatures.",1309.7216v1
2013/12/6,Anomalous magneto-structural behavior of MnBi explained: a path towards an improved permanent magnet,"Low-temperature MnBi (hexagonal NiAs phase) exhibits anomalies in the lattice
constants (a, c) and bulk elastic modulus (B) below 100 K, spin reorientation
and magnetic susceptibility maximum near 90 K, and, importantly for
high-temperature magnetic applications, an increasing coercivity (unique to
MnBi) above 180 K. We calculate the total energy and magneto-anisotropy energy
(MAE) versus (a, c) using DFT+U methods. We reproduce and explain all the above
anomalies. We predict that coercivity and MAE increase due to increasing a,
suggesting means to improve MnBi permanent magnets.",1312.1988v2
2015/1/13,Spin crossover in ferropericlase from first-principles molecular dynamics,"Ferropericlase, (Mg,Fe)O, is the second-most abundant mineral of the Earth's
lower mantle. With increasing pressure, the Fe ions in the material begin to
collapse from a magnetic to non-magnetic spin state. We present a
finite-temperature first-principles phase diagram of this spin crossover,
finding a broad pressure range with coexisting magnetic and non-magnetic ions
due to favorable enthalpy of mixing of the two. Furthermore, we find the
electrical conductivity of the mineral to reach semi-metallic values inside the
Earth.",1501.02902v1
2015/4/2,Interplay between Magnetism and Na concentration in $Na_xCoO_2$,"Through comprehensive density functional calculations, the crystallographic,
magnetic and electronic properties of $Na_xCoO_2$ ($x$ = 1, 0.875, 0.75, 0.625
and 0.50) were investigated. We found that all Na ions in $NaCoO_2$ and
$Na_{0.875}CoO_2$ share the basal coordinates with O ions. However, as $x$
decreases, some of Na ions move within the basal plane in order to reduce the
in-plane Na$-$Na electrostatic repulsion. Magnetically, there was strong
tendency for type A antiferromagnetism in the $Na_{0.75}CoO_2$ system, while
all other Na deficient systems had a weaker ferromagnetic tendency. The results
on magnetism were in excellent agreement with the experiments.",1504.00456v2
2015/11/17,Neutron methods for the direct determination of the magnetic induction in thick films,"We review different neutron methods which allow extracting directly the value
of the magnetic induction in thick films: Larmor precession, Zeeman spatial
beam-splitting and neutron spin resonance. Resulting parameters obtained by the
neutron methods and standard magnetometry technique are presented and compared.
The possibilities and specificities of the neutron methods are discussed.",1511.05421v2
2015/11/23,Creation of Skyrmions by Electric Field on Chiral-Lattice Magnetic Insulators,"We theoretically propose that magnetic skyrmion, nanometric spin vortex
characterized by a quantized topological number, can be electrically created on
a thin-film specimen of chiral-lattice magnetic insulator within a few
nanoseconds by applying an electric field via an electrode tip taking advantage
of coupling between noncollinear skyrmion spins and electric polarizations.
This finding will pave a route to utilizing multiferroic skyrmions as
information carriers for low-energy-consuming magnetic storage devices without
Joule-heating energy losses.",1511.07123v1
2016/4/16,Beyond the upper limit of magnetic anisotropy in two-dimensional transition metal dichalcogenides,"Exploring an upper limit of magnetic anisotropy in two-dimensional materials,
such as graphene and transition metal dichalcogenides, is at the heart of
spintronics research. Herein, an atomic-scale perpendicular magnetic anisotropy
up to an order of 100 meV per atom, which is far beyond the ordinarily obtained
value in graphene and pristine transition metal dichalcogenides, is
demonstrated in individual ruthenium and osmium adatoms at a monosulfur vacancy
in molybdenum disulfide. We further propose a phenomenological model where a
spin state transition that involves hybridization between molybdenum a1 and
adatomic e' orbitals is a possible mechanism for magnetization reorientation.",1604.04708v1
2016/4/24,Dispersion regions overlapping for bulk and surface polaritons in a magnetic-semiconductor superlattice,"Extraordinary dispersion features of both bulk and surface polaritons in a
finely-stratified magnetic-semiconductor structure which is under an action of
an external static magnetic field in the Voigt geometry are discussed in this
letter. It is shown that the conditions for total overlapping dispersion
regions of simultaneous existence of bulk and surface polaritons can be reached
providing a conscious choice of the constitutive parameters and material
fractions for both magnetic and semiconductor subsystems.",1604.07392v1
2016/9/7,Thermally induced magnon accumulation in two-sublattice magnets,"We present a temperature dependent study of the thermal excitation of
magnonic spin currents in two-sublattice magnetic materials. Using atomistic
spin model simulations, we study the local magnetization profiles in the
vicinity of a temperature step in antiferromagnets, as well as in ferrimagnets.
It is shown that the strength of the excitation of the spin currents in these
systems scales with the derivative of the magnetization with respect to the
temperature.",1609.02161v1
2017/2/2,Magnon Condensation and Spin Superfluidity,"We consider the phenomenon of Bose-Einstein condensation of quasi-equilibrium
magnons which leads to a spin superfluidity, the coherent quantum transfer of
magnetization in magnetic materials. These phenomena are beyond the classical
Landau-Lifshitz-Gilbert paradigm. The critical conditions for excited magnon
density for ferro- and antiferromagnets, bulk and thin films are estimated and
discussed. The BEC should occur in the antiferromagnetic hematite at much lower
excited magnon density compared to the ferromagnetic YIG.",1702.00846v2
2018/6/21,"Magnetic Properties of Lithium-Containing Rare Earth Garnets Li3RE3Te2O12 (RE = Y, Pr, Nd, Sm-Lu)","The synthesis, structural description, temperature dependent magnetic
susceptibilities and field dependent magnetizations of a series of rare earth
garnets of the form Li3RE3Te2O12 (RE = Y, La, Pr, Nd, Sm-Lu) are reported. The
structure of Li3Dy3Te2O12 is refined from powder X-ray diffraction data. The
field dependent magnetizations saturate for some of the members by 9 Tesla at 2
K. Of particular interest for further study in this family is the behavior of
the Pr, Tb, Dy and Yb garnets.",1806.08399v1
2019/8/19,Amorphous Ferrimagnets: an Ideal Host for Ultra-Small Skyrmions at Room Temperature,"Recently, magnetic skyrmion has emerged as an active topic of fundamental
study and applications in magnetic materials research. Magnetic skyrmions are
vortex-like spin excitations with topological protection and therefore are more
robust to pinning compared with magnetic domain walls. We employ atomistic
simulations to create room-temperature ultra-small Neel skyrmions in amorphous
ferrimagnet. The fast propagation and low-dissipation dynamics of ultra-small
ferrimagnetic skyrmions make them attractive for utilization as an alternative
to domain walls in spin-based memory and logic devices.",1908.07003v2
2018/3/13,Ultrafast light switching of ferromagnetism in EuSe,"We demonstrate that light resonant with the bandgap forces the
antiferromagnetic semiconducor EuSe to enter ferromagnetic alignment in the
picosecond time scale. A photon generates an electron-hole pair, whose electron
forms a supergiant spin polaron of magnetic moment of nearly 6,000 Bohr
magnetons. By increasing the light intensity, the whole of the sample can be
fully magnetized. The key to the novel large photoinduced magnetization
mechanism is the huge enhancement of the magnetic susceptibility when both
antiferromagnetic and ferromagnetic interactions are present in the material,
and are of nearly equal magnitude, as is the case in EuSe.",1803.05038v1
2018/12/10,FDTD simulation algorithm of magnetized plasma media,"A technique of magnetized plasma simulation have been implemented into a well
known FDTD solver MEEP as a child class of ""susceptibility"" class. Magnetized
plasma posses gyrotrophic properties, polarization vector is being rotated
while the wave propagates through the material. Solid state plasma can be found
in semiconductor materials which rises a question of using gyrotrophic
properties of plasma in modern photonic development. To test the software, a
circular polarized wave propagation through 9mm layer of magnetized plasma has
been simulated and compared to the analytical solution.",1812.03779v1
2018/12/13,Tailoring the magnetic properties of nanocrystalline Cu-Co alloys prepared by high-pressure torsion and isothermal annealing,"In this study, severe plastic deformation by high pressure torsion is used as
a fabrication method for nanocrystalline magnetic CuCo alloys in bulk
quantities. By subsequent isothermal annealing, phase separation of the
supersaturated solid solutions can be obtained. The magnetic properties of the
as-processed and annealed materials have been studied systemically and
correlated to the evolving nanostructures investigated in detail by
transmission electron microscopy and atom probe tomography. By additional high
pressure torsion deformation at liquid nitrogen temperature the magnetic
properties of the Cu74Co26 alloy can be further tuned.",1812.05387v1
2017/3/17,Quantum Oscillations in the Chiral Magnetic Conductivity,"In strong magnetic field the longitudinal magnetoconductivity in 3D chiral
materials is shown to exhibit a new type of quantum oscillations arising from
the chiral magnetic effect (CME). These quantum CME oscillations are predicted
to dominate over the Shubnikov-de Haas (SdH) ones in chiral materials with an
approximately conserved chirality of quasiparticles at strong magnetic fields.
The phase of quantum CME oscillations differs from the phase of the
conventional SdH oscillations by $\pi/2$.",1703.05865v1
2020/4/23,Covalency a Pathway for Achieving High Magnetisation in $TMFe_2O_4$ Compounds,"The interplay between covalency and magnetism is non-trivial and can be
harnessed for designing new functional magnetic materials. Based on a survey
using density functional calculations, we show that $TM\unicode{x2013}O$ bond
covalency can increase the total magnetic moment of spinel compounds of
$TMFe_2O_4$ composition ($TM = V-Ni, Nb-Pd$) which are isomorphic to the
much-researched magnetite. Accordingly, $PdFe_2O_4$ was found to exhibit the
highest magnetic moment of 7.809 ${\mu}_B$ per formula unit which is
approximately twice that of $Fe_3O_4$ with $T_c$ predicted to be well above
ambient. We further propose a practical method for synthesising $PdFe_2O_4$.",2004.10948v1
2016/12/13,Magnetic Bloch Skyrmion Transport by Electric Fields in a Composite Bilayer,"We investigate a mechanical method to manipulate magnetic Bloch Skyrmions by
applying an electric field in a composite chiral-magnetic (CM)/ferroelectric
(FE) bilayer. The magnetoelectric coupling at the interface allows the electric
field to stimulate magnetic ordering. Therefore it offers the possibility to
generate Skyrmions [Phys. Rev. B 94, 014311 (2016)]. Here, we design a movable
and localized electric field source to drive skyrmion transport along the
bilayer. A traveling velocity of the electric field source must be carefully
chosen to show the stability and effciency of this process. The effects of high
speed operation will be discussed.",1612.03995v1
2019/2/17,The role of magnetic order in VOCl,"VOCl and other transition metal oxychlorides are candidate materials for
next-generation rechargeable batteries. We have investigated the influence of
the underlying magnetic order on the crystallographic and electronic structure
by means of density functional theory. Our study shows that antiferromagnetic
ordering explains the observed low-temperature monoclinic distortion of the
lattice, which leads to a decreased distance between antiferromagnetically
coupled V-V nearest neighbors. We also show that the existence of a local
magnetic moment removes the previously suggested degeneracy of the occupied
levels, in agreement with experiments. To describe the electronic structure, it
turns out crucial to take the correct magnetic ordering into account,
especially at elevated temperature.",1902.06217v1
2019/12/24,Parameterization of the Stoner-Wohlfarth model of magnetic hysteresis,"The Stoner-Wohlfarth is the most used model of magnetic hysteresis, but its
computation is time-consuming. We use machine learning to approximate piecewise
this model by easy-to-compute analytic functions. Our parametrization is
suitable for fast quantitative evaluations and fitting experimental data, which
we exemplify.",1912.11553v1
2020/6/17,"Magnetic properties of two-dimensional M$_2$N$_3$ (M-metal, N=S,Se,Te) compounds","Using \textit{ab-initio} methods we study structural, electronic and magnetic
properties of two dimensional compounds with stoichiometry M$_2$N$_3$ (M-metal,
N=S,Se,Te). Our study shows that structures with Cr, Ti, and Mn are stable,
with significant binding energy. Also, such structures are semiconductors with
narrow band gaps. We also show that Cr$_2$Se$_3$, Cr$_2$Te$_3$ and Mn$_2$Te$_3$
have considerable magnetic moments. The negative values of magnetic anisotropy
energy suggest, that these materials can maintain ferromagnetic ordering in
non-zero temperatures with estimated Curie temperatures in the range of 30-55
K.",2006.09757v1
2020/7/8,Complex magnetic structure in Ba5Ru3O12 with isolated Ru3O12-trimer,"We report detailed magnetic, transport, heat-capacity, and neutron
diffraction measurements of Ba5Ru3O12, a compound consisting of isolated Ru3O12
trimers. We show that this system develops long-range antiferromagnetic
ordering at 60 K (TN) without structural distortion and metal-insulator-type
transition, which is in sharp contrast to other Barium Ruthenate trimer systems
such as 9R-BaRuO3 and Ba4Ru3O10. A complex magnetic structure is revealed which
is attributable to the magnetic frustration due to competing exchange
interactions between Ru ions on different crystallographic sites within the
Ru3O12 trimer.",2007.03854v2
2021/2/25,Topological classification and diagnosis in magnetically ordered electronic materials,"We show that compositions of time-reversal and spatial symmetries, also known
as the magnetic-space-group symmetries, protect topological invariants as well
as surface states that are distinct from those of all preceding topological
states. We obtain, by explicit and exhaustive construction, the topological
classification of electronic band insulators that are magnetically ordered for
each one of the 1421 magnetic space groups in three dimensions. We have also
computed the symmetry-based indicators for each nontrivial class, and, by doing
so, establish the complete mapping from symmetry representations to topological
invariants.",2102.12645v1
2022/1/18,Uniaxial polarization analysis of bulk ferromagnets: Theory and first experimental Results,"Based on Brown's static equations of micromagnetics, we compute the uniaxial
polarization of the scattered neutron beam of a bulk magnetic material. The
theoretical expressions are compared to experimental data on a soft magnetic
nanocrystalline alloy. The micromagnetic SANS theory provides a general
framework for polarized real-space neutron methods, and it opens up a new
avenue for magnetic neutron data analysis on magnetic microstructures.",2201.06802v1
2022/5/30,Non-Abelian Vortices in Magnets,"We show that non-Abelian vortices can exist in magnetic materials. These are
singularity-free textures, are described by spin-lattice and field theory
models, and we demonstrate that typical magnetic materials can be quite
suitable for their realization and observation. We give a topological
classification of these vortices and reveal their connection with Abelian
topological structures, such as usual vortices, merons and skyrmions. We also
describe how non-Abelian magnetic vortices can carry topologically protected
information and present reasons for the advantage of such information carriers,
as compared to Abelian entities.",2205.15264v1
2023/3/23,Neutron Reflectometry: a technique for revealing emergent phenomena at interfaces in heterostructures,"Neutron reflectometry (NR) has emerged as a unique technique for the
investigation of structure and magnetism of thin films of both biologically
relevant and magnetic materials. The advantage of NR with respect to many other
surface-sensitive techniques is its sub-nanometer resolution that enables
structural characterizations at the molecular level. While in the case of
bio-relevant samples, NR can be used to probe thin films at buried interfaces,
non-destructively, even adopting a complex sample environment. Whereas the
polarized version of NR is best suited for revealing the interface magnetism
with a sub-nanometer depth resolution. In this article, I will briefly describe
the basic principle of NR with some applications of NR to both bio-relevant
samples and magnetic heterostructures.",2303.13028v1
2023/4/6,Electrically-excited Motion of Topological Defects in Multiferroic Materials,"Topological magnetic defects in multiferroic materials acquire an electric
charge or dipole moment due to the inverse Dzyaloshinskii-Moriya mechanism.
This magnetoelectric coupling makes possible to excite large-amplitude
collective motion of topological magnetic textures with an oscillating electric
field. Here, I discuss electric excitation of a polar optical mode in a
vortex-antivortex crystal and the electrically-induced spin precession in a
magnetic skyrmion, which gives rise to rotation of skyrmions around each other
and a translational motion of skyrmion-antiskyrmion pairs. The electric
manipulation of magnetic topological defects in Mott insulators can find
applications in magnetoelectric memory and logical devices.",2304.03111v1
2023/7/18,Flat-band spin density wave in twisted bilayer materials,"Twisting is a novel technique for creating strongly correlated effects in
two-dimensional bilayered materials, and can tunably generate nontrivial
topological properties, magnetism, and superconductivity. Magnetism is
particularly significant as it can both compete with superconductivity and lead
to the emergence of nontrivial topological states. However, the origin of
magnetism in twisted structures remains a subject of controversy. Using
self-developed large-scale electronic structure calculations, we propose the
magnetism in these twisted bilayer systems originates from spin splitting
induced by the enhanced ratio of the exchange interaction to band dispersion.",2307.09506v1
2023/8/28,Laser-enhanced magnetism in SmFeO$_3$,"To coherently enhance inherent weak magnetic interactions in rare-earth
orthoferrite SmFeO$_3$ as a functional material for spintronic applications, we
simulate the dissipative spin dynamics that are linearly and quadratically
coupled to laser-driven infrared-active phonons. When linear coupling
dominates, we discover a magnetophononic dynamical first-order phase transition
in the nonequilibrium steady state which can inhibit strong enhancement of
magnetic interactions. By contrast, when quadratic spin-phonon coupling
dominates, no phase transition exists at experimentally relevant parameters. By
utilizing a chirp protocol, the phase transition can be engineered, enabling
stronger magnetic interactions. We also discuss the route for experimental
observation of our results.",2308.14939v2
2023/9/24,Unraveling the Effect of Circularly Polarized Light on Reciprocal Media: Breaking Time Reversal Symmetry with Non-Maxwellian Magnetic-esque Fields,"Optical rectification of intense, circularly polarized light penetrating a
material generates a static magnetic field aligned with the light's direction
and proportional to its intensity. Recent experiments have unveiled a
substantial, orders-of-magnitude gap between the observed magnetization and
theoretical predictions. In this study, we demonstrate that circularly
polarized light creates large non-Maxwellian fields that disrupt time-reversal
symmetry, effectively mimicking authentic magnetic fields within the material
while eluding detection externally. These unconventional fields give rise to
Faraday-rotation-like phenomena, which are a high-frequency manifestation of
Berry's curvature.",2309.13622v2
2023/10/10,Video recognition by physical reservoir computing in magnetic materials,"Nonlinear spin dynamics in magnetic materials offers a promising avenue for
implementing physical reservoir computing, one of the most accomplished
brain-inspired frameworks for information processing. In this study, we
investigate the practical utility of magnetic physical reservoirs by assessing
their performance in a video recognition task. Leveraging a recently developed
spatiotemporal parallelization scheme, our reservoir achieves accurate
classifications of previously provided images. Our findings pave the way for
the development of visual sensors based on the magnetic physical reservoir
computing.",2310.06497v1
2023/12/8,Phase Shift in AC Magnetocaloric Effect Measurements as an Indicator of the Order of Magnetic Phase Transitions,"It is shown that the phase shift between an applied weak alternating magnetic
field and the magnetocaloric response signal of the magnetic material is
drastically sensitive to the order of phase transition. Namely, at the
second-order phase transition, the phase shift does not depend on the magnetic
field magnitude, while in the first-order phase transition this one depends
significantly on the field strength. We have shown that this effect follows
from the general critical dynamics theory.",2312.04979v1
2023/12/11,Experimental verification of the inverse Anomalous spin Hall effect with perpendicular magnetic anisotropy Materials,"In this work, the spin pumping technique was employed to investigate the
anomalous inverse spin Hall effect in BIG/NiO/Fe samples where
BIG[(Bi,Tm)3(Fe,Ga)5O12] exhibits perpendicular magnetic anisotropy. Our
results reveal an intriguing phenomenon: when the magnetizations of both
ferromagnetic layers align perpendicularly, a distinct spin-to-charge current
conversion mechanism occurs. This conversion is intricately linked to the
magnetization of the converting layer, spin polarization, and the spin current
orientation.",2312.06819v1
2019/10/1,Giant spontaneous exchange bias in an antiperovskite structure driven by a canted triangular magnetic structure,"Exchange bias (EB) refers to a shift of the hysteresis loop along the field
axis in materials consisting of ferromagnetic (FM) and antiferromagnetic (AFM)
layers, generally after a cooling procedure in high magnetic field. This effect
is highly desirable for technological applications ranging from spintronics to
magnetic recording. Achieving giant EB effect near room temperature in a small
cooling field is thus an on-going technologically relevant challenge for the
materials science community. In this work, we present the experimental
realization of such a fundamental goal by demonstrating the existence of giant
EB after a zero field cooled (ZFC) procedure in antiperovskite Mn3.5Co0.5N
below 256 K. We found that it exhibits an EB field of 0.28 T at 50 K after a
ZFC procedure accompanied by a large vertical magnetization shift (VMS).
Interestingly, this EB field can be elevated up to 1.2 T after a cooling
procedure with a small applied field of just 500 Oe. Mn3:5Co0:5N bears the
first intermetallic material showing a strong correlation between EB and VMS.We
attribute the observed EB effect to a completely new canted triangular magnetic
structure determined by neutron diffraction experiment. Finally, we discuss the
striking effect of Co substitution on the physical properties of antiperovskite
materials and put forward a new strategy for antiperovskite lattice to exploit
new single phase materials showing large EB effect at room temperature.",1910.00616v1
2019/3/22,The microscopic origin of DMI in magnetic bilayers and prediction of giant DMI in new bilayers,"Skyrmions are widely regarded as promising candidates for emergent spintronic
devices. Dzyaloshinskii-Moriya interaction (DMI) is often critical to the
generation and manipulation of skyrmions. However, there is a fundamental lack
of understanding of the origin of DMI or the mechanism by which DMI generates
skyrmions in magnetic bilayers. Very little is known of the material parameters
that determine the value of DMI. This knowledge is vital for rational design of
skyrmion materials and further development of skyrmion technology. To address
this important problem, we investigate DMI in magnetic bilayers using
first-principles. We present a new theoretical model that explains the
microscopic origin of DMI in magnetic bilayers. We demonstrate that DMI depends
on two parameters, interfacial hybridization and orbital contributions of the
heavy metal. Using these parameters, we explain the trend of DMI observed. We
also report four new materials systems with giant DMI and new designs for
magnetic multilayers that are expected to outperform the best materials known
so far. Our results present a notably new understanding of DMI, uncover highly
promising materials and put forth novel pathways for the controlled generation
of skyrmions.",1903.09345v3
2020/5/12,Machine Learning Guided Discovery of Gigantic Magnetocaloric Effect in HoB$_{2}$ Near Hydrogen Liquefaction Temperature,"Magnetic refrigeration exploits the magnetocaloric effect which is the
entropy change upon application and removal of magnetic fields in materials,
providing an alternate path for refrigeration other than the conventional gas
cycles. While intensive research has uncovered a vast number of magnetic
materials which exhibits large magnetocaloric effect, these properties for a
large number of compounds still remain unknown. To explore new functional
materials in this unknown space, machine learning is used as a guide for
selecting materials which could exhibit large magnetocaloric effect. By this
approach, HoB$_{2}$ is singled out, synthesized and its magnetocaloric
properties are evaluated, leading to the experimental discovery of gigantic
magnetic entropy change 40.1 J kg$^{-1}$ K$^{-1}$ (0.35 J cm$^{-3}$ K$^{-1}$)
for a field change of 5 T in the vicinity of a ferromagnetic second-order phase
transition with a Curie temperature of 15 K. This is the highest value reported
so far, to our knowledge, near the hydrogen liquefaction temperature thus it is
a highly suitable material for hydrogen liquefaction and low temperature
magnetic cooling applications.",2005.05618v1
2020/7/21,Magnetic Order and Symmetry in the 2D Semiconductor CrSBr,"The recent discovery of two-dimensional (2D) magnets offers unique
opportunities for the experimental exploration of low-dimensional magnetism4
and the magnetic proximity effects, and for the development of novel
magnetoelectric, magnetooptic and spintronic devices. These advancements call
for 2D materials with diverse magnetic structures as well as effective probes
for their magnetic symmetries, which is key to understanding intralayer
magnetic order and interlayer magnetic coupling. Here we apply second harmonic
generation (SHG), a technique acutely sensitive to symmetry breaking, to probe
the magnetic structure of a new 2D magnetic semiconductor, CrSBr. We find that
CrSBr monolayers are ferromagnetically ordered below 146 K, an observation
enabled by the discovery of a giant magnetic dipole SHG effect in the
centrosymmetric 2D structure. In multilayers, the ferromagnetic monolayers are
coupled antiferromagnetically, with the N\'eel temperature notably increasing
with decreasing layer number. The magnetic structure of CrSBr, comprising spins
co-aligned in-plane with rectangular unit cell, differs markedly from the
prototypical 2D hexagonal magnets CrI3 and Cr2Ge2Te6 with out-of-plane moments.
Moreover, our SHG analysis suggests that the order parameters of the
ferromagnetic monolayer and the antiferromagnetic bilayer are the magnetic
dipole and the magnetic toroidal moments, respectively. These findings
establish CrSBr as an exciting 2D magnetic semiconductor and SHG as a powerful
tool to probe 2D magnetic symmetry, opening the door to the exploration of
coupling between magnetic order and excitonic/electronic properties, as well as
the magnetic toroidal moment, in a broad range of applications.",2007.10715v1
2005/9/5,CeMnNi4: A soft ferromagnet with a high degree of transport spin polarization,"In this letter we introduce a new soft ferromagnetic compound, i.e. CeMnNi4,
which exhibits a large moment (~4.95mu_B/Mn) and high degree of spin
polarization. The system has a ferromagnetic transition temperature of 148K.
Isothermal magnetization measurements at 5K reveal that the material is a soft
ferromagnet with a magnetization saturating at about 500Oe and a coercive field
of < 5 Oe. We determine the transport spin polarization of this material from
Point Contact Andreev Reflection measurements to be 66% thereby making this
material potentially important for spintronic applications.",0509101v2
2005/10/10,"A One-Dimensional Coordination Polymer, BBDTA-InCl4; Possible Spin-Peierls Transition with High Critical Temperature of 108 K","We have studied the crystal structure and magnetic properties of the organic
radical cation salt, BBDTA-InCl4. This material formed a one-dimensional
coordination polymer, whose structure was characteristic of inorganic
spin-Peierls materials. Magnetic measurements indicated the spin-Peierls
transition like behavior at 108 K, which was higher than those typically
observed for the other organic spin-Peierls materials. The structural aspects
of the lattice distortion from X-ray diffraction measurements at 50 K have been
discussed.",0510231v1
2006/2/28,Collective pinning of imperfect vortex lattices by material line defects in extreme type-II superconductors,"The critical current density shown by a superconductor at the extreme type-II
limit is predicted to follow an inverse square-root power law with external
magnetic field if the vortex lattice is weakly pinned by material line defects.
It acquires an additional inverse dependence with thickness along the line
direction once pinning of the interstitial vortex lines by material point
defects is included. Moderate quantitative agreement with the critical current
density shown by second-generation wires of high-temperature superconductors in
kG magnetic fields is achieved at liquid-nitrogen temperature.",0602651v1
2009/5/14,MgN: a new promising material for spintronic applications,"Density functional theory calculations demonstrate that rocksalt MgN is a
magnetic material at the verge of half-metallicity, with an electronic
structure robust against strong correlations and spin-orbit interaction.
Furthermore the calculated heat of formation describes the compound as
metastable and suggests that it can be fabricated by tuning the relative Mg and
N abundance during growth. Intriguingly the equilibrium lattice constant is
close to that of MgO, so that MgN is likely to form as an inclusion during the
fabrication of N-doped MgO. We then speculate that the MgO/MgN system may
represent a unique materials platform for magnetic tunnel junctions not
incorporating any transition metals.",0905.2387v1
2015/9/23,One-dimensional domain walls in thin ferromagnetic films with fourfold anisotropy,"We study the properties of domain walls and domain patterns in ultrathin
epitaxial magnetic films with two orthogonal in-plane easy axes, which we call
fourfold materials. In these materials, the magnetization vector is constrained
to lie entirely in the film plane and has four preferred directions dictated by
the easy axes. We prove the existence of $90^\circ$ and $180^\circ$ domain
walls in these materials as minimizers of a nonlocal one-dimensional energy
functional. Further, we investigate numerically the role of the considered
domain wall solutions for pattern formation in a rectangular sample.",1509.06977v2
2016/10/4,First-principles calculation method and its applications for two-dimensional materials,"We present details of our effective computational methods based on the
real-space finite-difference formalism to elucidate electronic and magnetic
properties of the two-dimensional (2D) materials within the framework of the
density functional theory. The real-space finite-difference formalism enables
us to treat truly 2D computational models by imposing individual boundary
condition on each direction. The formulae for practical computations under the
boundary conditions specific to the 2D materials are derived and the electronic
band structures of 2D materials are demonstrated using the proposed method.
Additionally, we introduce other first-principles works on the MoS2 monolayer
focusing on the modulation of electronic and magnetic properties originating
from lattice defects.",1610.00940v1
2019/9/20,Quantum Diffusive Magneto-transport in Massive Dirac Materials with Chiral Symmetry Breaking,"Massive Dirac fermions break the chiral symmetry explicitly and also make the
Berry curvature of the band structure non-Abelian. By utilizing the Green's
function technique, we develop a microscopic theory to establish a set of
quantum diffusive equations for massive Dirac materials in the presence of
electric and magnetic fields. It is found that the longitudinal
magnetoresistance is always negative and quadratic in the magnetic field, and
decays quickly with the mass. The theory is applicable to the systems with
non-Abelian Berry curvature and resolves the puzzles of anomalous
magnetotransport properties measured in topological materials.",1909.09297v1
2021/4/6,Magnetic Tilting in Nematic Liquid Crystals driven by Self-Assembly,"Self-assembly is one of the crucial mechanisms allowing to design
multifunctional materials. Soft hybrid materials contain components of
different nature and exhibit competitive interactions which drive
self-organisation into structures of a particular function. Here we demonstrate
a novel type of a magnetic hybrid material where the molecular tilt can be
manipulated through a delicate balance between the topologically-assisted
colloidal self-assembly of \rev{magnetic nanoparticles} and the anisotropic
molecular interactions in a liquid crystal matrix.",2104.02404v1
2021/5/24,Eshelby-twisted 3D moire superlattices,"Twisted bilayers of van der Waals materials have recently attracted great
attention due to their tunable strongly correlated phenomena. Here, we
investigate the chirality-specific physics in 3D moir\'e superlattices induced
by Eshelby twist. Our direct DFT calculations reveal helical rotation leads to
optical circular dichroism, and chirality-specific nonlinear Hall effect, even
though there is no magnetization or magnetic field. Both these phenomena can be
reversed by changing the structural chirality. This provides a way to
constructing chirality-specific materials.",2105.11125v1
2009/7/13,Choosing Dielectric or Magnetic Material to Optimize the Bandwidth of Miniaturized Resonant Antennas,"We address the question of the optimal choice of loading material for antenna
miniaturization. A new approach to identify the optimal loading material,
dielectric or magnetic, is presented for resonant antennas. Instead of
equivalent resonance circuits or transmission-line models, we use the analysis
of radiation to identify the fields contributing mostly to the stored energy.
This helps to determine the beneficial material type. The formulated principle
is qualitatively illustrated using three antenna types. Guidelines for
different antenna types are presented.",0907.2132v1
2020/12/23,Two-Dimensional Multifunctional Materials from Endohedral Fullerenes,"A new multifunctional 2D material is theoretically predicted based on
systematic ab-initio calculations and model simulations for the honeycomb
lattice of endohedral fullerene W@C28 molecules. It has structural bistability,
ferroelectricity, multiple magnetic phases, and excellent valley characters and
can be easily functionalized by the proximity effect with magnetic isolators
such as MnTiO3. Furthermore, we may also manipulate the valley Hall and spin
transport properties by selectively switch a few W@C28 molecules to the
metastable phase. These findings pave a new way in integrate different
functions in a single 2D material for technological innovations.",2012.12855v2
2022/11/17,Polycrystalline MnBi as a transverse thermoelectric material,"To assess the potential of polycrystalline MnBi as a transverse
thermoelectric material, we have experimentally investigated its anomalous
Nernst effect (ANE) by means of the heat flux method. We prepared MnBi samples
by powder metallurgy; this technique allows the preparation of samples in
arbitrary shapes with the possibility to tailor their magnetic properties. In
the material exhibiting the highest remanent magnetization, we found a value of
the ANE thermopower of -1.1 $\mu$V/K at 1 T, after the compensation of the
ordinary Nernst effect from pure bismuth present inside the polycrystalline
sample. This value is comparable with those reported in the literature for
single crystals.",2211.09553v1
2006/10/16,Internal magnetic field effect on magnetoelectricity in orthorhombic $RMnO_3$ crystals,"We have investigated the role of the 4$f$ moment on the magnetoelectric (ME)
effect of orthorhombic $R$MnO$_{3}$ ($R$=rare earth ions). In order to clarify
the role of the 4$f$ moment, we prepared three samples: (Eu,Y)MnO$_{3}$ without
the 4$f$ moment, TbMnO$_{3}$ with the anisotropic 4$f$ moment, and
(Gd,Y)MnO$_{3}$ with the isotropic 4$f$ moment. The ferroelectric behaviors of
these samples are different from each other in a zero magnetic field.
(Eu,Y)MnO$_{3}$ and (Gd,Y)MnO$_{3}$ show the ferroelectric polarization along
the a axis in the ground state, while TbMnO$_{3}$ shows it along the c axis.
Such difference may arise from the influence of the anisotropic Tb$^{3+}$ 4$f$
moment. The direction of the ferroelectric polarization of $R$MnO$_{3}$ is
determined by the internal magnetic field arising from the 4$f$ moment.",0610421v1
2006/12/23,Magnetic phase diagram of Ce2Fe17,"Rare-earth-based permanent-magnet materials rich in iron have relatively low
ferromagnetic ordering temperatures. This is believed to be due to the presence
of antiferromagnetic exchange interactions, besides the ferromagnetic
interactions responsible for the magnetic order. The magnetic properties of
Ce2Fe17 are anomalous. Instead of ferromagnetic, it is antiferromagnetic, and
instead of one ordering temperature, it shows two, at the Neel temperature TN ~
208 K and at TT ~ 124 K. Ce2Fe17, doped by 0.5% Ta, also shows two ordering
temperatures, one to an antiferromagnetic phase, at TN ~ 214 K, and one to a
ferromagnetic phase, at T0 ~ 75 K. In order to clarify this behavior,
single-crystalline samples were prepared by solution growth, and characterized
by electron microscopy, single crystal x-ray diffraction, temperature-dependent
specific heat, and magnetic field and temperature-dependent electrical
resistivity and magnetization. From these measurements, magnetic H-T phase
diagrams were determined for both Ta-doped Ce2Fe17 and undoped Ce2Fe17. These
phase diagrams can be very well described in terms of a theory that gives
magnetic phase diagrams of systems with competing antiferro- and
ferromagnetism.",0612603v1
2001/1/9,Hysteresis in layered spring magnets,"This article addresses a problem of micromagnetics: the reversal of magnetic
moments in layered spring magnets. A one-dimensional model is used of a film
consisting of several atomic layers of a soft material on top of several atomic
layers of a hard material. Each atomic layer is taken to be uniformly
magnetized, and spatial inhomogeneities within an atomic layer are neglected.
The state of such a system is described by a chain of magnetic spin vectors.
Each spin vector behaves like a spinning top driven locally by the effective
magnetic field and subject to damping (Landau-Lifshitz-Gilbert equation). A
numerical integration scheme for the LLG equation is presented that is
unconditionally stable and preserves the magnitude of the magnetization vector
at all times. The results of numerical investigations for a bilayer in a
rotating in-plane magnetic field show hysteresis with a basic period of $2\pi$
at moderate fields and hysteresis with a basic period of $\pi$ at strong
fields.",0101077v1
2010/10/21,Van der Waals torque induced by external magnetic fields,"We present a method for inducing and controlling van der Waals torques
between two parallel slabs using a constant magnetic field. The torque is
calculated using the Barash theory of dispersive torques. In III-IV
semiconductors such as $InSb$, the effect of an external magnetic field is to
induce an optical anisotropy, in an otherwise isotropic material, that will in
turn induce a torque.
  The calculations of the torque are done in the Voigt configuration, with the
magnetic field parallel to the surface of the slabs. As a case study we
consider a slab made of calcite and a second slab made of $InSb$. In the
absence of magnetic field there is no torque. As the magnetic field increases,
the optical anisotropy of $InSb$ increases and the torque becomes different
from zero, increasing with the magnetic field. The resulting torque is of the
same order of magnitude as that calculated using permanent anisotropic
materials when the magnetic fields is close to 1 T.",1010.4553v1
2011/10/31,Magnetic switching by spin torque from the spin Hall effect,"The spin Hall effect (SHE) generates spin currents within nonmagnetic
materials. Previously, studies of the SHE have been motivated primarily to
understand its fundamental origin and magnitude. Here we demonstrate, using
measurement and modeling, that in a Pt/Co bilayer with perpendicular magnetic
anisotropy the SHE can produce a spin transfer torque that is strong enough to
efficiently rotate and reversibly switch the Co magnetization, thereby
providing a new strategy both to understand the SHE and to manipulate magnets.
We suggest that the SHE torque can have a similarly strong influence on
current-driven magnetic domain wall motion in Pt/ferromagnet multilayers. We
estimate that in optimized devices the SHE torque can switch magnetic moments
using currents comparable to those in magnetic tunnel junctions operated by
conventional spin-torque switching, meaning that the SHE can enable magnetic
memory and logic devices with similar performance but simpler architecture than
the current state of the art.",1110.6846v2
2012/1/5,Direct measurement of the three dimensional magnetization vector trajectory in GaMnAs by a magneto-optical pump-and-probe method,"We report on a quantitative experimental determination of the
three-dimensional magnetization vector trajectory in GaMnAs by means of the
static and time-resolved pump-and-probe magneto-optical measurements. The
experiments are performed in a normal incidence geometry and the time evolution
of the magnetization vector is obtained without any numerical modeling of
magnetization dynamics. Our experimental method utilizes different polarization
dependences of the polar Kerr effect and magnetic linear dichroism to
disentangle the pump-induced out-of-plane and in-plane motions of
magnetization, respectively. We demonstrate that the method is sensitive enough
to allow for the determination of small angle excitations of the magnetization
in GaMnAs. The method is readily applicable to other magnetic materials with
sufficiently strong circular and linear magneto-optical effects.",1201.1213v1
2013/5/9,Origin of interface magnetism in BiMnO3/SrTiO3 and LaAlO3/SrTiO3 heterostructures,"Possible ferromagnetism induced in otherwise non-magnetic materials has been
motivating intense research in complex oxide heterostructures. Here we show
that a confined magnetism is realized at the interface between SrTiO3 and two
insulating polar oxides, BiMnO3 and LaAlO3. By using polarization dependent
x-ray absorption spectroscopy, we find that in both cases the magnetic order is
stabilized by a negative exchange interaction between the electrons transferred
to the interface and local magnetic moments. These local magnetic moments are
associated to Ti3+ ions at the interface itself for LaAlO3/SrTiO3 and to Mn3+
ions in the overlayer for BiMnO3/SrTiO3. In LaAlO3/SrTiO3 the induced magnetic
moments are quenched by annealing in oxygen, suggesting a decisive role of
oxygen vacancies in the stabilization of interfacial magnetism.",1305.2226v2
2014/10/13,"Kinetic arrest, and ubiquity of interrupted 1st order magnetic transitions","Phase transitions are caused by varying temperature, or pressure, or magnetic
field. The observation of 1st order magneto-structural transitions has created
application possibilities based on magnetoresistance, magnetocaloric effect,
magnetic shape memory effect, and magneto-dielectric effect. Magnetic field
induced transitions, and phase coexistence of competing magnetic phases down to
the lowest temperature, gained prominence over a decade ago with theoretical
models suggesting that the ground state is not homogeneous. Researchers at
Indore pushed an alternative view that this phase coexistence could be due to
glasslike kinetic arrest of a disorder-broadened first-order magnetic
transition between two states with long-range magnetic order, resulting in
phase coexistence down to the lowest temperatures. The CHUF (cooling and
heating in unequal field) protocol created at Indore allows the observation of
devitrification, followed by melting. I show examples of measurements
establishing kinetic arrest in various materials, emphasizing that glasslike
arrest of 1st order magnetic transitions may be as ubiquitous as glass
formation following the arrest of 1st order structural transitions.",1410.3254v2
2015/1/12,Ab initio construction of magnetic phase diagrams in alloys: The case of Fe$_{1-x}$Mn$_x$Pt,"A first-principles approach to the construction of concentration-temperature
magnetic phase diagrams of metallic alloys is presented. The method employs
self-consistent total energy calculations based on the coherent potential
approximation for partially ordered and noncollinear magnetic states and is
able to account for competing interactions and multiple magnetic phases.
Application to the Fe$_{1-x}$Mn$_x$Pt ""magnetic chameleon"" system yields the
sequence of magnetic phases at T=0 and the c-T magnetic phase diagram in good
agreement with experiment, and a new low-temperature phase is predicted at the
Mn-rich end. The importance of non-Heisenberg interactions for the description
of the magnetic phase diagram is demonstrated.",1501.02794v2
2015/7/12,"Non-equilibrium behavior of the magnetization in the helimagnetic phases of the rare earth alloys R_{1-x}Y_{x} (R = Gd, Tb, Dy)","We have performed DC and AC magnetization measurements for the rare-earth
magnetic alloy systems Gd_{0.62}Y_{0.38}, Tb_{0.86}Y_{0.14}, and
Dy_{0.97}Y_{0.03}. These materials commonly exhibit a proper helical magnetic
structure, and ferromagnetic structure at lower temperatures.In all of these
materials, a difference between zero-field-cooled (ZFC) magnetization and
field-cooled (FC) magnetization and a hysteresis loop in the M-H curve have
been observed in the helimagnetic phases. The non-equilibrium behavior is
possibly caused by a common nature, e. g., chiral domain structures. In
addition to the above behavior, strong non-linearity of the magnetization and
slow spin dynamics have been observed around the N'eel temperature only in
Gd$_{0.62}$Y$_{0.38}$. The spin-glass like behavior observed in
Gd_{0.62}Y_{0.38} could be related to a novel glassy state such as a
helical-glass state.",1507.03202v3
2015/8/7,Evolution of competing magnetic order in the Jeff=1/2 insulating state of Sr2Ir1-xRuxO4,"We investigate the magnetic properties of the series Sr2Ir1-xRuxO4 with
neutron, resonant x-ray and magnetization measurements. The results indicate an
evolution and coexistence of magnetic structures via a spin flop transition
from ab-plane to c-axis collinear order as the 5d Ir4+ ions are replaced with
an increasing concentration of 4d Ru4+ ions. The magnetic structures within the
ordered regime of the phase diagram (x<0.3) are reported. Despite the changes
in magnetic structure no alteration of the Jeff=1/2 ground state is observed.
The behavior of Sr2Ir1-xRuxO4 is consistent with electronic phase separation
and diverges from a standard scenario of hole doping. The role of lattice
alterations with doping on the magnetic and insulating behavior is considered.
The results presented here provide insight into the magnetic insulating states
in strong spin-orbit coupled materials and the role perturbations play in
altering the behavior.",1508.01807v1
2016/1/6,Strain-assisted magnetization reversal in Co/Ni multilayers with perpendicular magnetic anisotropy,"Multifunctional materials composed of ultrathin magnetic films with
perpendicular magnetic anisotropy combined with ferroelectric substrates
represent a new approach toward low power, fast, high density spintronics. Here
we demonstrate Co/Ni multilayered films with tunable saturation magnetization
and perpendicular anisotropy grown directly on ferroelectric PZT
[Pb(Zr_xTi_1-x)O_3] substrate plates. Electric fields up to +/- 2 MV/m expand
the PZT by 0.1% and generate at least 0.02% in-plane compression in the Co/Ni
multilayered film. Modifying the strain with a voltage can reduce the coercive
field by over 30%. We also demonstrate that alternating in-plane tensile and
compressive strains (less than 0.01%) can be used to propagate magnetic domain
walls. This ability to manipulate high anisotropy magnetic thin films could
prove useful for lowering the switching energy for magnetic elements in future
voltage-controlled spintronic devices.",1601.01349v1
2016/1/29,Switching of chiral magnetic skyrmions by picosecond magnetic field pulses via transient topological states,"Magnetic chiral skyrmions are vortex like spin structures that appear as
stable or meta-stable states in magnetic materials due to the interplay between
the symmetric and antisymmetric exchange interactions, applied magnetic field
and/or uniaxial anisotropy. Their small size and internal stability make them
prospective objects for data storage but for this, the controlled switching
between skyrmion states of opposite polarity and topological charge is
essential. Here we present a study of magnetic skyrmion switching by an applied
magnetic field pulse based on a discrete model of classical spins and atomistic
spin dynamics. We found a finite range of coupling parameters corresponding to
the coexistence of two degenerate isolated skyrmions characterized by mutually
inverted spin structures with opposite polarity and topological charge. We
demonstrate how for a wide range of material parameters a short inclined
magnetic field pulse can initiate the reliable switching between these states
at GHz rates. Detailed analysis of the switching mechanism revealed the complex
path of the system accompanied with the excitation of a chiral-achiral meron
pair and the formation of an achiral skyrmion.",1601.08212v1
2016/2/10,Temperature dependence of the threshold magnetic field for nucleation and domain wall propagation in an inhomogeneous structure with grain boundary,"In order to study the dependence of the coercive force of sintered magnets on
temperature, nucleation and domain wall propagation at the grain boundary are
studied as rate-determining processes of the magnetization reversal phenomena
in magnets consisting of bulk hard magnetic grains contacting via grain
boundaries of a soft magnetic material. These systems have been studied
analytically for a continuum model at zero temperature (A. Sakuma, et al. J.
Mag. Mag. Mat. {\bf 84} 52 (1990)). In the present study, the temperature
dependence is studied by making use of the stochastic Landau-Lifshitz-Gilbert
equation at finite temperatures. In particular, the threshold fields for
nucleation and domain wall propagation are obtained as functions of ratios of
magnetic interactions and anisotropies of the soft and hard magnets for various
temperatures. It was found that the threshold field for domain wall propagation
is robust against thermal fluctuations, while that for nucleation is fragile.
The microscopic mechanisms of the observed temperature dependence are
discussed.",1602.03285v2
2016/4/26,Electric polarization observed in single crystals of multiferroic Lu2MnCoO6,"We report electric polarization and magnetization measurements in single
crystals of double perovskite Lu2MnCoO6 using pulsed magnetic fields and
optical second harmonic generation (SHG) in DC magnetic fields. we observe
well-resolved magnetic field-induced changes in the electric polarization in
single crystals and thereby resolve the question about whether multiferroic
behavior is intrinsic to these materials or an extrinsic feature of
polycrystals. We find electric polarization along the crystalline b-axis, that
is suppressed by applying a magnetic fields along c-axis and advance a model
for the origin of magnetoelectric coupling. We furthermore map the phase
diagram using both capacitance and electric polarization to identify regions of
ordering and regions of magnetoelectric hysteresis. This compound is a rare
example of coupled hysteretic behavior in the magnetic and electric properties.
The ferromagnetic-like magnetic hysteresis loop that couples to hysteretic
polarization can be attributed not to ordinary ferromagnetic domains, but to
the rich physics of magnetic frustration of Ising-like spins in the axial
next-nearest neighbor interaction model.",1604.07802v1
2016/7/5,Magnetic moment of inertia within the breathing model,"An essential property of magnetic devices is the relaxation rate in magnetic
switching which strongly depends on the energy dissipation and magnetic inertia
of the magnetization dynamics. Both parameters are commonly taken as a
phenomenological entities. However very recently, a large effort has been
dedicated to obtain Gilbert damping from first principles. In contrast, there
is no ab initio study that so far has reproduced measured data of magnetic
inertia in magnetic materials. In this letter, we present and elaborate on a
theoretical model for calculating the magnetic moment of inertia based on the
torque-torque correlation model. Particularly, the method has been applied to
bulk bcc Fe, fcc Co and fcc Ni in the framework of the tight-binding
approximation and the numerical values are comparable with recent experimental
measurements. The theoretical results elucidate the physical origin of the
moment of inertia based on the electronic structure. Even though the moment of
inertia and damping are produced by the spin-orbit coupling, our analysis shows
that they are caused by undergo different electronic structure mechanisms.",1607.01307v1
2016/10/28,Spin-Orbit Torque Efficiency in Compensated Ferrimagnetic Cobalt-Terbium Alloys,"Despite the potential advantages of information storage in
antiferromagnetically coupled materials, it remains unclear whether one can
control the magnetic moment orientation efficiently because of the cancelled
magnetic moment. Here, we report spin-orbit torque induced magnetization
switching of ferrimagnetic Co1-xTbx films with perpendicular magnetic
anisotropy. Current induced switching is demonstrated in all of the studied
film compositions, including those near the magnetization compensation point.
The spin-orbit torque induced effective field is further quantified in the
domain wall motion regime. A divergent behavior that scales with the inverse of
magnetic moment is confirmed close to the compensation point, which is
consistent with angular momentum conservation. Moreover, we also quantify the
Dzyaloshinskii-Moriya interaction energy in the Ta/Co1-xTbx system and we find
that the energy density increases as a function of the Tb concentration. The
demonstrated spin-orbit torque switching, in combination with the fast magnetic
dynamics and minimal net magnetization of ferrimagnetic alloys, promises
spintronic devices that are faster and with higher density than traditional
ferromagnetic systems.",1610.09200v1
2017/2/3,"Evolution of structure, magnetism and electronic transport in doped pyrochlore iridate Y$_2$Ir$_{2-x}$Ru$_{x}$O$_7$","The interplay between spin-orbit coupling (SOC) and electron correlation
($U$) is considered for many exotic phenomena in iridium oxides. We have
investigated the evolution of structural, magnetic and electronic properties in
pyrochlore iridate Y$_2$Ir$_{2-x}$Ru$_{x}$O$_7$ where the substitution of Ru
has been aimed to tune this interplay. The Ru substitution does not introduce
any structural phase transition, however, we do observe an evolution of lattice
parameters with the doping level $x$. X-ray photoemission spectroscopy (XPS)
study indicates Ru adopts charge state of Ru$^{4+}$ and replaces the Ir$^{4+}$
accordingly. Magnetization data reveal both the onset of magnetic
irreversibility and the magnetic moment decreases with progressive substitution
of Ru. These materials show non-equilibrium low temperature magnetic state as
revealed by magnetic relaxation data. Interestingly, we find magnetic
relaxation rate increases with substitution of Ru. The electrical resistivity
shows an insulating behavior in whole temperature range, however, resistivity
decreases with substitution of Ru. Nature of electronic conduction has been
found to follow power-law behavior for all the materials.",1702.01023v1
2018/1/24,Very Large Tunneling Magnetoresistance in Layered Magnetic Semiconductor CrI$_3$,"Magnetic layered van der Waals crystals are an emerging class of materials
giving access to new physical phenomena, as illustrated by the recent
observation of 2D ferromagnetism in Cr2Ge2Te6 and CrI3. Of particular interest
in semiconductors is the interplay between magnetism and transport, which has
remained unexplored. Here we report first magneto-transport measurements on
exfoliated CrI3 crystals. We find that tunneling conduction in the direction
perpendicular to the crystalline planes exhibits a magnetoresistance as large
as 10 000 %. The evolution of the magnetoresistance with magnetic field and
temperature reveals that the phenomenon originates from multiple transitions to
different magnetic states, whose possible microscopic nature is discussed on
the basis of all existing experimental observations. This observed dependence
of the conductance of a tunnel barrier on its magnetic state is a new
phenomenon that demonstrates the presence of a strong coupling between
transport and magnetism in magnetic van der Waals semiconductors.",1801.08188v2
2018/4/14,Calculating magnetic interactions in organic electrides,"We present our calculation results for organic magnetic electrides. In order
to identify the `cavity' electrons, we use maximally-localized Wannier
functions and `empty atom' technique. The estimation of magnetic coupling is
then performed based on magnetic force linear response theory. Both short- and
long-range magnetic interactions are calculated with a single self-consistent
calculation of a primitive cell. With this scheme we investigate four different
organic electrides whose magnetic properties have been partly unknown or under
debate. Our calculation results unveil the nature of magnetic moment and their
interactions, and justify or defy the validity of preassumed spin models. Our
work not only provides useful insight to understand magnetic electrides but
also suggests a new paradigm to study the related materials.",1804.05244v2
2019/6/6,Charactering the magnetic properties of the copper chalcopyrite semiconductor CuGaSe2 via Monte Carlo simulations,"This manuscript presents a model and simulation of the copper chalcopyrite
semiconductor CuGaSe2 in order to predict its magnetic properties. In the
semiconductor material CuGaSe2 (CGS), the atom Cu is the only magnetic element
with a magnetic moment value S = 1/2. We propose a Hamiltonian to calculate the
energies corresponding to different configurations of the system. In a first
step, we presented the magnetization behavior by using the Monte Carlo
simulations (MCS). The magnetizations as a function of the temperature, the
exchange coupling have been studied and discussed. We have also deduced and
studied the magnetic susceptibilities. To complete this study, we have
established and discussed the magnetic hysteresis loops of the studied
compound. Also we have calculated the corresponding critical exponents and
compared them with the standard 3D Ising model.",1906.02542v1
2012/10/18,Magnetic excitation spectra in pyrochlore iridates,"Metal-insulator transitions in pyrochlore iridates (A2Ir2O7) are believed to
occur due to subtle interplay of spin-orbit coupling, geometric frustration,
and electron interactions. In particular, the nature of magnetic ordering of
iridium ions in the insulating phase is crucial for understanding of several
exotic phases recently proposed for these materials. We study the spectrum of
magnetic excitations in the intermediate-coupling regime for the so-called
all-in/all-out magnetic state in pyrochlore iridates with non-magnetic A-site
ions (A=Eu,Y), which is found to be preferred in previous theoretical studies.
We find that the effect of charge fluctuations on the spin-waves in this regime
leads to strong departure from the lowest-order spin-wave calculations based on
models obtained in strong-coupling calculations. We discuss the characteristic
features of the magnetic excitation spectrum that can lead to conclusive
identification of the magnetic order in future resonant inelastic x-ray (or
neutron) scattering experiments. Knowledge of the nature of magnetic order and
its low-energy features may also provide useful information on the accompanying
metal-insulator transition.",1210.5242v2
2012/11/6,"Spin dynamics of hard-soft magnetic multi-layer systems: Effect of Exchange, Dipolar and Dzyaloshinski-Moriya interactions","We investigate the effect of coupling (intensity and nature), applied field,
and anisotropy on the spin dynamics of a multi-layer system composed of a hard
magnetic slab coupled to a soft magnetic slab through a nonmagnetic spacer. The
soft slab is modeled as a stack of several atomic layers while the hard layer,
of a different material, is either considered as a pinned macroscopic magnetic
moment or as an atomic multi-layer system. We compute the magnetization profile
and hysteresis loop of the multi-layer system by solving the Landau-Lifshitz
equations for the net magnetic moment of each (atomic) layer. We study the
competition between the intra-layer anisotropy and exchange interaction,
applied magnetic field, and the inter-slab exchange, dipolar or
Dzyaloshinski-Moriya interaction. Comparing the effects on the magnetization
profile of the three couplings shows that despite the strong effect of the
exchange coupling, the dipolar and Dzyaloshinski-Moriya interactions induce a
slight (but non negligible) deviation in either the polar or azimuthal
direction thus providing more degrees of freedom for adjusting the spin
configuration in the multi-layer system.",1211.1217v1
2012/11/11,Electric polarization of magnetic textures: new horizons of micromagnetism,"A common scenario of magnetoelectric coupling in multiferroics is the
electric polarization induced by spatially modulated spin structures. It is
shown in this paper that the same mechanism works in magnetic dielectrics with
inhomogeneous magnetization distribution: the domain walls and magnetic
vortexes can be the sources of electric polarization. The electric field driven
magnetic domain wall motion is observed in iron garnet films. The electric
field induced nucleation of vortex state of magnetic nanodots is theoretically
predicted and numerically simulated. From the practical point of view the
electric field control of micromagnetic structures is promising for
applications in low-power-consumption spintronic and magnonic devices.",1211.2403v1
2017/6/7,Coupled multiferroic domain switching in the canted conical spin spiral system Mn$_{2}$GeO$_{4}$,"Despite remarkable progress in developing multifunctional materials,
spin-driven ferroelectrics featuring both spontaneous magnetization and
electric polarization are still rare. Among such ferromagnetic ferroelectrics
are conical spin spiral magnets with a simultaneous reversal of magnetization
and electric polarization that is still little understood. Such materials can
feature various multiferroic domains that complicates their study. Here we
study the multiferroic domains in ferromagnetic ferroelectric Mn$_{2}$GeO$_{4}$
using neutron diffraction, and show that it features a double-Q conical
magnetic structure that, apart from trivial 180 degree commensurate magnetic
domains, can be described by ferromagnetic and ferroelectric domains only. We
show unconventional magnetoelectric couplings such as the magnetic-field-driven
reversal of ferroelectric polarization with no change of spin-helicity, and
present a phenomenological theory that successfully explains the
magnetoelectric coupling. Our measurements establish Mn$_{2}$GeO$_{4}$ as a
conceptually simple multiferroic in which the magnetic-field-driven flop of
conical spin spirals leads to the simultaneous reversal of magnetization and
electric polarization.",1706.02363v1
2019/1/17,"Influences of interfacial oxidization on surface magnetic energy, magnetic damping and spin-orbit-torques in Pt / ferromagnet / capping structures","We investigate the effect of capping layer (CAP) on the interfacial magnetic
anisotropy energy density (K_S), magnetic damping ({\alpha}), and spin-orbit
torques (SOTs) in heavy-metal (Pt) / ferromagnet (Co or Py) / CAP (MgO/Ta,
HfOx, or TaN). At room temperature (RT) the CAP materials influence the
effective magnitude of K_S, which is associated with a formation of interfacial
magnetic oxides. The dynamical dissipation parameters of Co are considerably
influenced by the CAP (especially MgO) while those of Py are not. This is
possibly due to an extra magnetic damping via spin-pumping process across the
Co/CoO interface and incoherent magnon generation (spin fluctuation) in the
interfacial CoO. It is also observed that both anti-damping and field-like SOT
efficiencies vary marginally with the CAP in the thickness ranges we examined.
Our results reveal the crucial role of interfacial oxides on the perpendicular
magnetic anisotropy, magnetic damping, and SOTs.",1901.05777v1
2016/8/11,Tuning magnetic spirals beyond room temperature with chemical disorder,"In the past years, magnetism-driven ferroelectricity and gigantic
magnetoelectric effects have been reported for a number of frustrated magnets
with spiral magnetic orders. Such materials are of high current interest due to
their potential for spintronics and low-power magnetoelectric devices. However,
their low magnetic order temperatures (typically <100K) greatly restrict their
fields of application. Here we demonstrate that the stability domain of the
spiral phase in the perovskite YBaCuFeO5 can be enlarged by more than 150K
through a controlled manipulation of the Fe/Cu chemical disorder. Moreover we
show that this novel mechanism can stabilize the magnetic spiral state of
YBaCuFeO5 above the symbolic value of 25{\deg}C at zero magnetic field. Our
findings demonstrate that the properties of a magnetic spiral, including its
wavelength and stability range, can be engineered through the control of
chemical disorder, offering a great potential for the design of materials with
magnetoelectric properties beyond room temperature.",1608.03372v2
2016/8/21,A streamlined approach to mapping the magnetic induction of skyrmionic materials,"Recently, Lorentz transmission electron microscopy (LTEM) has helped
researchers advance the emerging field of magnetic skyrmions. These magnetic
quasi-particles, composed of topologically non-trivial magnetization textures,
have a large potential for application as information carriers in low-power
memory and logic devices. LTEM is one of a very few techniques for direct real
space imaging of magnetic features at the nanoscale. For Fresnel-contrast LTEM,
the transport of intensity equation (TIE) is the tool of choice for
quantitative reconstruction of the local magnetic induction through the sample
thickness. Typically this analysis requires collection of at least three
images.Here we show that for uniform thin magnetic films which includes many
skyrmionic samples, the magnetic induction can be quantitatively determined
from a single defocused image using a simplified TIE approach.",1608.06000v2
2016/8/26,New Evidence for a Low-Temperature Magnetic Ground State in Double-Perovskite Iridates with Ir5+(5d4) Ions,"We report an unusual magnetic ground state in single-crystal,
double-perovskite Ba2YIrO6 and Sr doped Ba2YIrO6 with Ir5+(5d4) ions.
Long-range magnetic order below 1.7 K is confirmed by DC magnetization, AC
magnetic susceptibility and heat capacity measurements. The observed magnetic
order is extraordinarily delicate and cannot be explained in terms of either a
low-spin S=1 state, or a singlet Jeff=0 state imposed by the spin-orbit
interactions (SOI). Alternatively, the magnetic ground state appears consistent
with a SOI that competes with comparable Hund's rule coupling and inherently
large electron hopping, which cannot stabilize the singlet Jeff=0 ground state.
However, this picture is controversial, and conflicting magnetic behavior for
these materials is reported in both experimental and theoretical studies, which
highlights the intricate interplay of interactions that determine the ground
state of materials with strong SOI.",1608.07624v3
2018/12/6,Realisation of a Frustrated 3D Magnetic Nanowire Lattice,"Patterning nanomagnets in three-dimensions presents a new paradigm in
condensed matter physics and allows access to a plethora of fundamental
phenomena including robust spin textures, magnetic metamaterials that are home
to defects carrying magnetic charge and ultrahigh density devices that store
information in three-dimensions. However, the nanostructuring of functional
magnetic materials into complex three-dimensional geometries has thus far
proven to be a formidable challenge. Here we show magnetic nanowires can be
arranged into 3D frustrated magnetic nanowire lattices by using a combination
of 3D polymer nanoprinting and metallic deposition. The fabricated nanowires
are single domain and they switch via nucleation and propagation of domain
walls. Deep nanoscale magnetic imaging and finite element simulations elucidate
the spin texture present on the 3D nanostructured lattice. Our study
demonstrates a generic platform for the production of 3D nanostructured
magnetic materials allowing the realisation of racetrack memory devices and 3D
nanostructured systems that mimic bulk frustrated crystals.",1812.02442v1
2016/3/3,Cloaking the magnons,"We propose two approaches to cloak the spin waves (magnons) by investigating
magnetization dynamics. One approach is based on a spatially inhomogeneous
anisotropic magnetic moment tensor. The other mechanism is using a spatially
inhomogeneous anisotropic gyromagnetic factor tensor and an inhomogeneous
external magnetic field. For both approaches, the damping tensor is also
inhomogeneous and anisotropic. The magnetic characteristic functions of the
magnetic materials have been theoretically derived for both mechanisms. A
non-magnetic core, which prevents magnons from entering and consequently
distorts the spin wave propagation, can be cloaked by a structured magnetic
shell to redirect the spin wave around the core using the above design
mechanisms. We discuss the feasibility of the proposed mechanisms in an
ensemble of quantum dot molecules and magnetic semiconductors. The proposed
approaches shed light on transformation magnonics, and can be utilized for
future spin-wave lenses, concentrators, low back-scattering waveguides, and
ultimately quantum computing.",1603.01000v1
2016/3/24,Interplay between magnetism and energetics in FeCr alloys from a predictive non-collinear magnetic tight-binding model,"Magnetism is a key driving force controlling several thermodynamic and
kinetic properties of Fe-Cr systems. We present a newly-developed TB model for
Fe-Cr, where magnetism is treated beyond the usual collinear approcimation. A
major advantage of this model consists in a rather simple fitting procedure. In
particular, no specific properties of the binary system is explicitly required
in the fitting database. The present model is proved to be accurate and highly
transfer-able for electronic, magnetic and energetic properties of a large
variety of structural and chemical environments: surfaces, interfaces, embedded
clusters, and the whole compositional range of the binary alloy. The occurence
of non-collinear magnetic configurations caused by magnetic frustrations is
successfully predicted. The present TB approach can apply for other binary
magnetic transition-metal alloys. It is expected to be particularly promissing
if the size difference between the alloying elements is rather small and the
electronic properties prevail.",1603.07482v1
2017/3/3,Nanoscale Magnetic Compasses,"We have synthesized nanoscale magnetic compasses with high yield. These
ferromagnetic iron carbide nano-particles, which are encapsulated in a pair of
parallel carbon needles, change their direction in response to an external
magnetic field. Electron holography reveals magnetic fields confined to the
vicinity of the bicone-shaped particles, which are composed of few
ferromagnetic domains. Aligned magnetically and encapsulated in an acrylate
polymer matrix, these nanocompasses exhibit anisotropic bulk magnetic
permeability with an easy axis normal to the needle direction, that can be
understood as a result of the anisotropic demagnetizing field of a nonspherical
single-domain particle. This novel material with orthogonal magnetic and
structural axes could be highly useful as magnetic components in
electromagnetic wave absorbent materials and magnetorheological fluids.",1703.01316v1
2019/10/18,Weak-field induced nonmagnetic state in a Co-based honeycomb,"Layered honeycomb magnets are of interest as potential realizations of the
Kitaev quantum spin liquid (KQSL), a quantum state with long-range spin
entanglement and an exactly solvable Hamiltonian. Conventional magnetically
ordered states are present for all currently known candidate materials,
however, because non-Kitaev terms in the Hamiltonians obscure the Kitaev
physics. Current experimental studies of the KQSL are focused on 4d- or
5d-transition-metal-based honeycombs, in which strong spin-orbit coupling can
be expected, yielding Kitaev interaction that dominate in an applied magnetic
field. In contrast, for 3d-based layered honeycomb magnets, spin orbit coupling
is weak and thus Kitaev-physics should be substantially less accessible. Here
we report our studies on BaCo2(AsO4)2, for which we find that the magnetic
order associated with the non-Kitaev interactions can be fully suppressed by a
relatively low magnetic field, yielding a non-magnetic material and implying
the presence of strong magnetic frustration and weak non-Kitaev interactions.",1910.08577v1
2009/7/22,Circularly polarized resonant soft x-ray diffraction study of helical magnetism in hexaferrite,"Magnetic spiral structures can exhibit ferroelectric moments as recently
demonstrated in various multiferroic materials. In such cases the helicity of
the magnetic spiral is directly correlated with the direction of the
ferroelectric moment and measurement of the helicity of magnetic structures is
of current interest. Soft x-ray resonant diffraction is particularly
advantageous because it combines element selectivity with a large magnetic
cross-section. We calculate the polarization dependence of the resonant
magnetic x-ray cross-section (electric dipole transition) for the basal plane
magnetic spiral in hexaferrite Ba0.8Sr1.2Zn2Fe12O22 and deduce its domain
population using circular polarized incident radiation. We demonstrate there is
a direct correlation between the diffracted radiation and the helicity of the
magnetic spiral.",0907.3852v2
2012/2/9,Magnetic ordering and multiferroicity in MnI$_2$,"Density-functional calculations are carried out to investigate incommensurate
magnetic structures and ferroelectric polarization in newly discovered
multiferroic material MnI$_2$. The exchange interactions among local moments on
Mn are parameterized by mapping the mean-field Heisenberg model on to total
energy difference of several magnetic ordering states. The experimentally
observed noncollinear magnetic states are well reproduced by using this model
and exchange interaction parameters. The direction of polarization
experimentally measured is also consistent with the result derived from the
symmetry analysis of the magnetically ordered state. In particular, we find
that the inter-plane magnetic exchange coupling is pivotal to the emergence of
the spiral magnetic structure. This noncollinear magnetic structure, combined
with spin-orbit coupling mainly from I ions, is responsible for the appearance
of ferroelectric polarization.",1202.1884v2
2015/2/27,Skyrmions at room temperature : From magnetic thin films to magnetic multilayers,"Facing the ever-growing demand for data storage will most probably require a
new paradigm. Magnetic skyrmions are anticipated to solve this issue as they
are arguably the smallest spin textures in magnetic thin films in nature. We
designed cobalt-based multilayered thin films where the cobalt layer is
sandwiched between two heavy metals providing additive interfacial
Dzyaloshinskii-Moriya interactions, which reach about 2 mJ/m2 in the case of
the Ir/Co/Pt multilayers. Using a magnetization-sensitive scanning x-ray
transmission microscopy technique, we imaged magnetic bubble-like domains in
these multilayers. The study of their behavir in magnetic field allows us to
conclude that they are actually magnetic skyrmions stabilized by the
Dzyaloshinsskii-Moriya interaction. This discoevry of stable skyrmions at room
temperature in a technologically relevant material opens the way for device
applications in a near future.",1502.07853v1
2019/1/31,Coupling phenomena and collective effects in resonant meta-molecules supporting plasmonic and magnetic functionalities: a review,"We review both the fundamental aspects and the applications of functional
magneto-optic and opto-magnetic metamaterials displaying collective and
coupling effects on the nanoscale, where the concepts of optics and magnetism
merge to produce unconventional phenomena. The use of magnetic materials
instead of the usual noble metals allows for an additional degree of freedom
for the control of electromagnetic field properties, as well as it allows light
to interact with the spins of the electrons and to actively manipulate the
magnetic properties of such nanomaterials. In this context, we explore the
concepts of near-field coupling of plasmon modes in magnetic meta-molecules, as
well as the effect of excitation of surface lattice resonances in
magneto-plasmonic crystals. Moreover, we discuss how these coupling effects can
be exploited to artificially enhance optical magnetism in plasmonic
meta-molecules and crystals. Finally, we highlight some of the present
challenges and provide a perspective on future directions of the research
towards photon-driven fast and efficient nanotechnologies bridging magnetism
and optics beyond current limits.",1902.00042v1
2019/2/21,Magnetic force theory combined with quasi-particle self-consistent GW method,"We report a successful combination of magnetic force linear response theory
with quasiparticle self-consistent GW method. The self-consistently determined
wavefunctions and eigenvalues can just be used for the conventional magnetic
force calculations. While its formulation is straightforward, this combination
provides a way to investigate the effect of GW self-energy on the magnetic
interactions which can hardly be quantified due to the limitation of current GW
methodology in calculating the total energy difference in between different
magnetic phases. In ferromagnetic $3d$ elements, GW self-energy slightly
reduces the $d$ bandwidth and enhances the interactions while the same
long-range feature is maintained. In antiferromagnetic transition-metal
monoxides, QSGW significantly reduces the interaction strengths by enlarging
the gap. Orbital-dependent magnetic force calculations show that the coupling
between $e_g$ and the nominally-empty $4s$ orbital is noticeably large in MnO
which is reminiscent of the discussion for cuprates regarding the role of
Cu-$4s$ state. This combination of magnetic force theory with quasiparticle
self-consistent GW can be a useful tool to study various magnetic materials.",1902.08292v1
2019/2/27,Emergence of Flat-Band Magnetism and Half-Metallicity in Twisted Bilayer Graphene,"Evidence of flat-band magnetism and half-metallicity in compressed twisted
bilayer graphene is provided with first-principles calculations. We show that
dynamic band-structure engineering in twisted bilayer graphene is possible by
controlling the chemical composition with extrinsic doping, the interlayer
coupling strength with pressure, and the magnetic ordering with external
electric field. By varying the rotational order and reducing the interlayer
separation an unbalanced distribution of charge density resulting in the
spontaneous apparition of localized magnetic moments without disrupting the
structural integrity of the bilayer. Weak exchange correlation between magnetic
moments is estimated in large unit cells. External electric field switches the
local magnetic ordering from ferromagnetic to anti-ferromagnetic.
Substitutional doping shifts the chemical potential of one spin distribution
and leads to half-metallicity. Flakes of compressed twisted bilayer graphene
exhibit spontaneous magnetization, demonstrating that correlation between
magnetic moments is not a necessary condition for their formation.",1902.10287v2
2019/3/14,Magnetically Switchable Light-Matter Interaction in the Two-Dimensional Magnet CrI3,"Coupling different physical properties is a fascinating subject of physics.
Already well-known are the multiferroics which show properties of
ferroelectrics and magnets. But ferroelectricity by itself also entails the
bulk photovoltaic effect, a light-matter interaction which generates dc
currents. Here we propose a magnetic photogalvanic effect that couples the
magnetism to the light-matter interaction. This phenomenon emerges from the
$\mathbf{k}$ to $\mathbf{-k}$ symmetry-breaking in the band structure and does
not require a static polarization. It is distinct from other known bulk
photovoltaic mechanisms such as the shift current. We demonstrate such
phenomena in a newly discovered layered magnetic insulator CrI$_3$. A record
photoconductivity response (more than 200 $\mu A V^{-2} $) is generated under
the irradiation of a visible light in the antiferromagnetic phase. The current
can be reversed and switched by controllable magnetic phase transitions. Our
work paves a new route for photovoltaic and optoelectronic devices and provides
a sensitive probe for the magnetic transition.",1903.06264v2
2019/7/10,Magnetic-field control of topological electronic response near room temperature in correlated Kagome magnets,"Strongly correlated Kagome magnets are promising candidates for achieving
controllable topological devices owing to the rich interplay between inherent
Dirac fermions and correlation-driven magnetism. Here we report tunable local
magnetism and its intriguing control of topological electronic response near
room temperature in the Kagome magnet Fe3Sn2 using small angle neutron
scattering, muon spin rotation, and magnetoresistivity measurement techniques.
The average bulk spin direction and magnetic domain texture can be tuned
effectively by small magnetic fields. Magnetoresistivity, in response, exhibits
a measurable degree of anisotropic weak localization behavior, which allows the
direct control of Dirac fermions with strong electron correlations. Our work
points to a novel platform for manipulating emergent phenomena in
strongly-correlated topological materials relevant to future applications.",1907.04948v1
2019/7/23,Tunable Magnetic Transition to a Singlet Ground State in a 2D Van der Waals Layered Trimerized Kagomé Magnet,"Incorporating magnetism into two dimensional (2D) van der Waals (VdW)
heterostrutures is crucial for the development of functional electronic and
magnetic devices. Here we show that Nb3X8 (X = Cl, Br) is a family of 2D
layered trimerized kagom\'e magnets that are paramagnetic at high temperatures
and undergo a first order phase transition on cooling to a singlet magnetic
state. X-ray diffraction shows that a rearrangement of the VdW stacking
accompanies the magnetic transition, with high and low temperature phases
consistent with STEM images of the end members {\alpha}-Nb3Cl8 and
\b{eta}-Nb3Br8. The temperature of this transition is systematically varied
across the solid solution Nb3Cl8-xBrx (x = 0-8), with x = 6 having transitions
near room temperature. The solid solution also varies the optical properties,
which are further modulated by the phase transition. As such, they provide a
platform on which to understand and exploit the interplay between
dimensionality, magnetism, and optoelectronic behavior in VdW materials.",1907.10108v1
2019/11/27,A Class of Compounds Featuring Frustrated Triangular Magnetic Lattice CsRESe$_2$ (RE=La-Lu): Quantum Spin-Liquid Candidates,"A triangular lattice selenide series of rare earth (RE), CsRESe2, were
synthesized as large single crystals using a flux growth method. This series
stabilized in either trigonal (R-3m) or hexagonal (P63/mmc) crystal systems.
Physical properties of CsRESe2 were explored by magnetic susceptibility and
heat capacity measurements down to 0.4 K. Antiferromagnetic interaction was
observed in all magnetic compounds, while no long-range magnetic order was
found, indicating the frustrated magnetism. CsDySe2 presents spin freezing at
0.7 K, revealing a spin-glass state. CsCeSe2 and CsYbSe2 present broad peaks at
0.7 K and 1.5 K in the magnetization, respectively, suggesting the short-range
interactions between magnetic rare earth ions. The lack of signature for
long-range magnetic order and spin freezing down to 0.4 K in these compounds
(RE = Ce, Yb) implies their candidacy for quantum spin liquid state.",1911.12278v1
2019/11/30,Phono-magnetic analogs to opto-magnetic effects,"The magneto-optical and opto-magnetic effects describe the interaction of
light with a magnetic medium. The most prominent examples are the Faraday and
Cotton-Mouton effects that modify the transmission of light through a medium,
and the inverse Faraday and inverse Cotton-Mouton effects that produce
effective magnetic fields for the spin in the material. Here, we introduce the
phenomenology of the analogous magneto-phononic and phono-magnetic effects, in
which vibrational quanta take the place of the light quanta. We show, using a
combination of first-principles calculations and phenomenological modeling,
that the effective magnetic fields exerted by the phonon analogs of the inverse
Faraday and inverse Cotton-Mouton effects on the spins of antiferromagnetic
nickel oxide yield magnitudes comparable to and potentially larger than those
of the opto-magnetic originals.",1912.00129v2
2020/1/8,Magnetic correlations in the disordered ferromagnetic alloy Ni-V revealed with small angle neutron scattering,"We present small angle neutron scattering (SANS) data collected on
polycrystalline Ni$_{1-x}$V$_x$ samples with $x\geq0.10$ with confirmed random
atomic distribution. We aim to determine the relevant length scales of magnetic
correlations in ferromagnetic samples with low critical temperatures $T_c$ that
show signs of magnetic inhomogeneities in magnetization and $\mu$SR data. The
SANS study reveals signatures of long-range order and coexistence of
short-range magnetic correlations in this randomly disordered ferromagnetic
alloy. We show the advantages of a polarization analysis in identifying the
main magnetic contributions from the dominating nuclear scattering.",2001.02706v1
2020/1/29,Perpendicularly Magnetized Ni / Pt (001) Epitaxial Superlattice,"A perpendicularly magnetized ferromagnetic layer is an important building
block for recent/future highdensity spintronic memory applications. This paper
reports on the fabrication of perpendicularly magnetized Ni / Pt superlattices
and the characterization of their structures and magnetic properties. The
optimization of film growth conditions allowed us to grow epitaxial Ni / Pt
(001) superlattices on SrTiO$_{3}$ (001) single crystal substrates. We
investigated their structural parameters and magnetic properties as a function
of the Ni layer thickness, and obtained a high uniaxial magnetic anisotropy
energy of 1.9 x 10$^{6}$ erg/cm$^{3}$ for a [Ni (4.0 nm) / Pt (1.0 nm)]
superlattice. In order to elucidate the detailed mechanism on perpendicular
magnetic anisotropy for the Ni / Pt (001) superlattices, the experimental
results were compared with the first-principles calculations. It has been found
that the strain effect is a prime source of the emergence of perpendicular
magnetic anisotropy.",2001.11127v1
2020/2/17,Monte Carlo study of the magnetic properties of the spinel ZnFe$_2$O$_4$ compound,"In this work, a study of the magnetic behavior of the spinel ZnFe2O4 is
presented by using the Monte Carlo simulations (MCS). The iron atoms provide
the magnetism in this material. In fact, the magnetic spin of moment of the
Fe3+ ions is S=5/2. In this context, we propose a Hamiltonian describing and
modeling this compound. Firstly, at zero temperature we have studied the ground
state phase diagrams of the system in order to find the more stable
configurations. On the other hand, for a non-null temperature values, we
obtained the results of the Monte Carlo simulations, namely: the magnetizations
and the susceptibilities as a function of temperature. The behavior of those
physical parameters shows an anti-ferromagnetic behavior with a
Neel-temperature of about TN=12 K. This value is found to be in good agreement
with the literature. Moreover, the effect of varying the crystal field, the
exchange coupling interactions and the external magnetic field is studied and
discussed on the behavior of the magnetizations. To complete this study, we
presented the magnetic hysteresis loops deducing the antiferromagnetic behavior
of the ZnFe2O4 compound.",2002.06889v1
2020/5/12,Anisometric mesoscale nuclear and magnetic texture in sintered Nd-Fe-B magnets,"By means of temperature and wavelength-dependent small-angle neutron
scattering (SANS) experiments on sintered isotropic and textured Nd-Fe-B
magnets we provide evidence for the existence of an anisometric structure in
the microstructure of the textured magnets. This conclusion is reached by
observing a characteristic cross-shaped angular anisotropy in the total
unpolarized SANS cross section at temperatures well above the Curie
temperature. Comparison of the experimental SANS data to a microstructural
model based on the superquadrics form factor allows us to estimate the shape
and lower bounds for the size of the structure. Subtraction of the scattering
cross section in the paramagnetic regime from data taken at room temperature
provides the magnetic SANS cross section. Surprisingly, the anisotropy of the
magnetic scattering is very similar to the nuclear SANS signal, suggesting that
the nuclear structure is decorated by the magnetic moments via spin-orbit
coupling. Based on the computation of the two-dimensional correlation function
we estimate lower bounds for the longitudinal and transversal magnetic
correlation lengths.",2005.05648v1
2020/5/13,Interplay between magnetism and charge instabilities in layered NbSe$_{2}$,"Using ab initio methods based on density functional theory, the electronic
and magnetic structure of layered hexagonal NbSe$_{2}$ is studied. In the case
of single-layer NbSe$_{2}$ it is found that, for all the functionals
considered, the magnetic solution is lower in energy than the non-magnetic
solution. The magnetic ground-state is ferrimagnetic with a magnetic moment of
1.09 $\mu_{B}$ at the Nb atoms and a magnetic moment of 0.05 $\mu_{B}$, in the
opposite direction, at the Se atoms. Our calculations show that single-layer
NbSe$_{2}$ does not display a charge density wave instability unless a graphene
layer is considered as a substrate. Then, two kinds of 3$\times$3 charge
density waves are found, which are observed in our STM experiments. This
suggest that the driving force of charge instabilities in NbSe$_{2}$ differ in
bulk and in the single-layer limit. Our work sets magnetism into play in this
highly-correlated 2D material, which is crucial to understand the formation
mechanisms of 2D superconductivity and charge density wave order.",2005.06210v1
2020/6/22,Towards skyrmion-superconductor hybrid systems,"Spin-polarized scanning tunneling microscopy is used to identify the magnetic
state of different thin films on a Re(0001) substrate, which becomes
superconducting below 1.7 K. All magnetic films contain an Fe/Ir interface,
which is known to facilitate the emergence of non-collinear magnetic order. For
Fe monolayers on ultra-thin Ir films of different thickness we find several
different atomic-scale magnetic states. For Pd/Fe bilayers we find nano-scale
spin spirals as magnetic ground states for Ir thicknesses of three and four
atomic layers. In applied magnetic fields skyrmions emerge, and in remanence
non-trivial magnetic textures survive. This demonstrates the possibility to
prepare skryrmion-hosting magnetic films on superconducting substrates.",2006.12035v1
2020/7/16,Crystal and Magnetic Structure of Polar Oxide HoCrWO$_6$,"Polar magnetic oxide HoCrWO$_6$ is synthesized and its crystal structure,
magnetic structure, and thermodynamic properties are investigated. HoCrWO$_6$
forms the polar crystal structure (space group Pna2$_1$ (#33)) due to the
cation ordering of W$^{6+}$ and Cr$^{3+}$. There is an antiferromagnetic
transition at TN = 24.5 K along with the magnetic entropy change (~5
J.Kg.$^{-1}$K$^{-1}$ at 70 kOe). Neutron diffraction measurement indicates that
both Cr and Ho sublattices are ordered with the moment of 2.32(5)$\mu_B$ and
8.7(4)$\mu_B$ at 2 K, respectively. While Cr forms A-type collinear
antiferromagnetic (AFM) structure with magnetic moment along the $b$ axis, Ho
sublattice orders in a non-coplanar AFM arrangement. A comparison with
isostructural DyFeWO$_6$ and DyCrWO$_6$ indicates that the magnetic structure
of this family of compounds is controlled by the presence or absence of eg
electrons in the transition metal sublattice.",2007.08581v1
2020/9/29,Dimensional Crossover Tuned by Pressure in Layered Magnetic NiPS3,"Layered magnetic transition-metal thiophosphate NiPS3 has unique
two-dimensional (2D) magnetic properties and electronic behavior. The
electronic band structure and corresponding magnetic state are expected to
sensitive to the interlayer interaction, which can be tuned by external
pressure. Here, we report an insulator-metal transition accompanied with
magnetism collapse during the 2D-3D crossover in structure induced by
hydrostatic pressure. A two-stage phase transition from monoclinic (C2=m) to
trigonal (P-31m) lattice is identified by ab initio simulation and confirmed by
high-pressure XRD and Raman data, corresponding to a layer by layer slip
mechanism along the a-axis. Temperature dependence resistance measurements and
room temperature infrared spectroscopy show that the insulator-metal transition
occurs near 20 GPa as well as magnetism collapse, which is further confirmed by
low temperature Raman measurement and theoretical calculation. These results
establish a strong correlation among the structural change, electric transport,
and magnetic phase transition and expand our understandings about the layered
magnetic materials.",2009.14051v1
2020/10/9,Inplane spin orbit torque magnetization switching and its detection using the spin rectification effect at sub-GHz frequencies,"Inplane magnetization reversal of a permalloy/platinum bilayer was detected
using the spin rectification effect. Using a sub GHz microwave frequency to
excite spin torque ferromagnetic resonance (ST FMR) in the bilayer induces two
discrete DC voltages around an external static magnetic field of 0 mT. These
discrete voltages depend on the magnetization directions of the permalloy and
enable detection of the inplane magnetization reversal. The threshold current
density for the magnetization reversal is from 10 to 20 MA/cm^2, the same order
as for known spin orbit torque (SOT) switching with in-plane magnetization
materials. The magnitude of the signal is the same or larger than that of the
typical ST FMR signal; that is, detection of magnetization switching is highly
sensitive in spite of deviation from the optimal ST-FMR condition. The proposed
method is applicable to a simple device structure even for a small
ferromagnetic electrode with a width of 100 nm.",2010.04435v1
2020/10/14,Spin-orbit torque as a method for field-free detection of in-plane magnetization switching,"We proposed and demonstrated a simple method for detection of in-plane
magnetization switching by spin-orbit torque (SOT) in bilayers of non-magnetic
/ magnetic materials. In our method, SOT is used not only for magnetization
switching but also for detection. Our method can detect arbitrary Mx and My
component without an external magnetic field, which is useful for fast
characterization of type-X, type-Y, and type-XY SOT magnetization switching.
Our SOT detection scheme can be utilized not only for fast characterization of
SOT switching in bilayers, but also for electrical detection of in-plane
magnetic domains in race-track memory.",2010.06826v2
2020/11/20,A phenomenological theory of the optical magnetization reversal,"All-optical switching of the magnetization in magnetic nanostructures by
femtosecond circularly polarized laser pulses has been demonstrated in several
systems. We present a Landau-Lifshitz-Lambda (LLL) model which describes the
magnetization dynamics using three density states: two ferromagnetic grounds
states and an excited optical state. One of the ferromagnetic ground states is
optically excited by circularly polarized light to a spin reversed state, which
is then ""Coulomb collapsed"" to the magnetization reversed ground state. The
time evolution of the optically excited states is described by a Lindblad
master equation, in which the optical excitation is introduced via the
Hamiltonian. Dissipation terms are introduced via Lindblad operators. The LLL
model combines the precessional motion of the magnetization described by the
Landau-Lifshitz theory, with the response of the three level Lambda system. The
optical excitation lasts for the duration of the laser pulse and the system
relaxes at a fast rate due to the electron-electron interaction. We study the
solution of the eigenvalues problem of the optical equation of motion for the
magnetization and identify a coherent and incoherent regimes and derive an LLL
model that can be integrated with existing micromagnetic codes to describe
optical excitation of magnetic materials.",2011.10247v1
2021/6/2,Topological Magnons: A Review,"At sufficiently low temperatures magnetic materials often enter a correlated
phase hosting collective, coherent magnetic excitations such as magnons or
triplons. Drawing on the enormous progress on topological materials of the last
few years, recent research has led to new insights into the geometry and
topology of these magnetic excitations. Berry phases associated to magnetic
dynamics can lead to observable consequences in heat and spin transport while
analogues of topological insulators and semimetals can arise within magnon band
structures from natural magnetic couplings. Magnetic excitations offer a
platform to explore the interplay of magnetic symmetries and topology, to drive
topological transitions using magnetic fields. examine the effects of
interactions on topological bands and to generate topologically protected spin
currents at interfaces. In this review, we survey progress on all these topics,
highlighting aspects of topological matter that are unique to magnon systems
and the avenues yet to be fully investigated.",2106.01430v1
2021/7/15,Tailoring topological Hall effect in SrRuO3/SrTiO3 superlattices,"Investigating the effects of the complex magnetic interactions on the
formation of nontrivial magnetic phases enables a better understanding of
magnetic materials. Moreover, an effective method to systematically control
those interactions and phases could be extensively utilized in spintronic
devices. SrRuO3 heterostructures function as a suitable material system to
investigate the complex magnetic interactions and the resultant formation of
topological magnetic phases, as the heterostructuring approach provides an
accessible controllability to modulate the magnetic interactions. In this
study, we have observed that the Hall effect of SrRuO3/SrTiO3 superlattices
varies nonmonotonically with the repetition number (z). Using Monte Carlo
simulations, we identify a possible origin of this experimental observation:
the interplay between the Dzyaloshinskii-Moriya interaction and dipole-dipole
interaction, which have differing z-dependence, might result in a z-dependent
modulation of topological magnetic phases. This approach provides not only a
collective understanding of the magnetic interactions in artificial
heterostructures but also a facile control over the skyrmion phases.",2107.07144v1
2021/7/28,Multiple magnetism controlled topological states in EuAgAs,"The interplay between magnetism and band topology is a focus of current
research on magnetic topological systems. Based on first-principle calculations
and symmetry analysis, we reveal multiple intriguing topological states can be
realized in a single system EuAgAs, controlled by the magnetic ordering. The
material is Dirac semimetal in the paramagnetic state, with a pair of
accidental Dirac points. Under different magnetic configurations, the Dirac
points can evolve into magnetic triply-degenerate points, magnetic linear and
double Weyl points, or being gapped out and making the system a topological
mirror semimetal characterized by mirror Chern numbers. The change in bulk
topology is also manifested in the surface states, including the surface Fermi
arcs and surface Dirac cones. In addition, the antiferromagnetic states also
feature a nontrivial Z4 index, implying a higher order topology. These results
deepen our understanding of magnetic topological states and provide new
perspectives for spintronic applications.",2107.13345v2
2021/8/9,Phase diagram of CeSb$_2$ from magnetostriction and magnetization measurements: Evidence for ferrimagnetic and antiferromagnetic states,"Cerium diantimonide (CeSb$_2$) is one of a family of rare earth based
magnetic materials that exhibit metamagnetism, enabling control of the magnetic
ground state through an applied magnetic field. At low temperatures, CeSb$_2$
hosts a rich phase diagram with multiple magnetically ordered phases for many
of which the order parameter is only poorly understood. In this paper, we
report a study of its metamagnetic properties by Scanning Tunneling Microscopy
(STM) and magnetization measurements. We use STM measurements to characterize
the sample magnetostriction with sub-picometer resolution from magnetic field
and temperature sweeps. This allows us to directly assess the bulk phase
diagram as a function of field and temperature and relate spectroscopic
features from tunneling spectroscopy to bulk phases. Our magnetostriction and
magnetisation measurements indicate that the low temperature ground state at
zero field is ferrimagnetic. Quasiparticle interference mapping shows evidence
for a reconstruction of the electronic structure close to the Fermi energy upon
entering the magnetically ordered phase.",2108.04245v1
2021/10/29,Double-helix magnetic order in CrAs with Pnma space group,"The transition metal pnictide CrAs exhibits superconductivity in the vicinity
of a helimagnetic phase, where it has been found that the propagation vector is
parallel to the c axis and the magnetic moments lie in the ab plane. Here we
use ab initio calculations to study the magnetic interactions in the material.
Mapping onto a Heisenberg Hamiltonian, we calculate the magnetic exchanges by
using LDA+U calculations and we unveil the origin of the magnetic frustration.
Finally, we reproduce the double helix magnetic order with a propagation vector
Q = (0, 0, 0.456) and we obtain the magnetic transition temperature TN through
Monte-Carlo simulations of the specific heat. Due to the limitations of the use
of the Heisenberg Hamiltonian for itinerant magnetic systems, the theoretical
TN underestimated the experimental value of the pure CrAs. However, our results
are in good agreement with those found for the alloy CrAs0.5Sb0.5 belonging to
the same space group, showing that our result can describe this material class.",2110.15631v1
2021/10/31,Thermally induced all-optical ferromagnetic resonance in thin YIG films,"All-optical ferromagnetic resonance (AO-FMR) is a powerful tool for local
detection of micromagnetic parameters, such as magnetic anisotropy, Gilbert
damping or spin stiffness. In this work we demonstrate that the AO-FMR method
can be used in thin films of Yttrium Iron Garnet (YIG) if a metallic capping
layer (Au, Pt) is deposited on top of the film. Magnetization precession is
triggered by heating of the metallic layer with femtosecond laser pulses. The
heating modifies the magneto-crystalline anisotropy of the YIG film and shifts
the quasi-equilibrium orientation of magnetization, which results in
precessional magnetization dynamics. The laser-induced magnetization precession
corresponds to a uniform (Kittel) magnon mode, with the precession frequency
determined by the magnetic anisotropy of the material as well as the external
magnetic field, and the damping time set by a Gilbert damping parameter. The
AO-FMR method thus enables measuring local magnetic properties, with spatial
resolution given only by the laser spot size.",2111.00586v1
2021/11/10,Dependence of magnetic domain patterns on plasma-induced differential oxidation of CoPd thin films,"We demonstrate the evolution of the micro-patterned magnetic domains in CoPd
thin films pretreated with e-beam lithography and O2 plasma. During the
days-long oxidation, significantly different behaviors of the patterned
magnetic domains under magnetization reversal are observed via magneto-optic
Kerr effect microscopy on different days. The evolution of the magnetic
behaviors indicate critical changes in the local magnetic anisotropy energies
due to the Co oxides that evolve into different oxide forms, which are
characterized by micro-area X-ray absorption spectroscopy and X-ray
photoelectron spectroscopy. The coercive field of the area pre-exposed to
plasma can decrease to a value 10 Oe smaller than that unexposed to plasma,
whereas after a longer duration of oxidation the coercive field can instead
become larger in the area pre-exposed to plasma than that unexposed, leading to
an opposite magnetic pattern. Various forms of oxidation can therefore provide
an additional dimension for magnetic-domain engineering to the current
conventional lithographies.",2111.05767v1
2022/1/18,In-situ alignment of anisotropic hard magnets of 3D printed magnets,"Within this work, we demonstrate in-situ easy-axis alignment of
single-crystal magnetic particles inside a polymer matrix using fused filament
fabrication. Two different magnetic materials are investigated: (i) Strontium
hexaferrite inside a PA6 matrix, fill grade: 49 vol% and (ii) Samarium iron
nitride inside a PA12 matrix, fill grade: 44 vol%. In the presence of the
external alignment field, the strontium hexaferrite particles inside the PA6
matrix can be well aligned with a ratio of remanent magnetization to saturation
magnetization of 0.7. No significant alignment for samarium iron nitride could
be achieved. The results show the feasibility to fabricate magnets with
arbitrary and locally defined easy axis using fused filament fabrication since
the permanent magnets used for the alignment (or alternatively an
electromagnet) can be mounted on a rotatable platform.",2201.07111v1
2022/2/2,Defect Controlled Ferromagnetic Ordering in Au Implanted TiSe$_2$ Nanocrystals,"Layered transition metal dichalcogenides (TMDs) are attracting increasing
attention because they exhibit unconventional magnetic properties due to
crystal imperfections in their usually non-magnetic 2D structure. This work
aims to investigate the magnetic response of self-engineered Se deficient
TiSe$_2$ thin films, synthesized using chemical vapour deposition. We
demonstrate tunability of the ferromagnetic order with the introduction of Au
atoms using low energy Au ion implantation, which works as a controlling knob
to vary the stoichiometry of Se in TiSe$_{2-x}$. The corresponding isothermal
field-magnetization curves fit well with a modified Brillouin J function with J
value of 1.5 for Ti$^{3+}$, and 4 for Au$^{3+}$, accounting for the
diamagnetism that arises from Au implantation. We propose a qualitative model
for the experimentally observed magnetization as a function of ion fluence,
corroborated with high-resolution transmission electron microscopy. Depending
on the Au nanoparticle size in the implanted samples, magnetization saturates
faster at a much lower applied magnetic field than the pristine sample. Our
findings hold potential to expand the range of 2D ferromagnetic materials for
spintronics and magnetic sensing applications.",2202.01152v1
2022/3/30,Origin of Perpendicular Magnetic Anisotropy in Co$_x$Fe$_{3-x}$O$_{4+δ}$ Thin Films Studied by X-ray Magnetic Circular and Linear Dichroisms,"We investigate the element-specific spin and orbital states and their roles
on magnetic anisotropy in the Co-ferrite (Co$_x$Fe$_{3-x}$O$_{4+\delta}$ (001))
thin films which exhibit perpendicular magnetic anisotropy (PMA). The origin of
PMA in the low $x$ region ($x$ $<$ 1) can be mainly explained by the large
perpendicular orbital magnetic moments in the Co$^{2+}$ (3$d^7$) states
detected by X-ray magnetic circular and linear dichroisms (XMCD/XMLD). The XMLD
for a PMA film ($x=0.2$) with square hysteresis curve shows the oblate charge
distribution in the Co$^{2+}$ site, which is consistent with the change in
local nearest neighbor distance in Co detected by extended X-ray absorption
fine structure analysis. Our finding reveals that the microscopic origin of PMA
in Co-ferrite comes from the enhanced orbital magnetic moments along
out-of-plane [001] direction through in-plane charge distribution by tensile
strain, which adds the material functionalities in spinel ferrite thin films
from the viewpoint of strain and orbital magnetic moments.",2203.16061v1
2022/4/8,Electrically tunable moiré magnetism in twisted double bilayer antiferromagnets,"The introduction of moir\'e superlattices to electronic materials can
dramatically alter electronic properties, promising emergent correlated and
topological phenomena. Its first demonstration in van der Waals magnets
exhibited noncollinear states and domain structures with, however, limited
manipulation. Here, we fabricated twisted double antiferromagnetic bilayer
CrI3, and by magneto-optical Kerr effect microscopy demonstrate the coexistence
of antiferromagnetic and ferromagnetic orders with nonzero net magnetization,
which is the hallmark of moir\'e magnetism. Such magnetic state exhibits
nonmonotonic temperature dependence and extends over a wide range of twist
angles with transitions at ~0{\deg} and above 20{\deg}. We further demonstrate
voltage-assisted magnetic switching and the linear magnetoelectric effect. The
observed nontrivial magnetic states and unprecedented control by twist angle,
temperature and electrical gating are supported by the simulated phase diagram
of the moir\'e magnetism. Our results illustrate the rich behaviors of twisted
antiferromagnets and the control over them.",2204.03837v2
2022/4/13,Influence of Co and Mn on Electronic and Magnetic properties of Ni2MnGa Heusler alloy,"The ferromagnetic Heusler alloy $Ni_2MnGa$ had been of major interest in the
past few years because of its magnetic properties which can be easily tuned.
The $Ni_2MnGa$ Heusler alloys are intermetallic alloy with $L2_1$ structure.
Here we report a detailed investigation of the effect of doping of Co and Mn in
Ni2MnGa. Magnetic properties and electronic structure of
$Ni_{2-x}Co_xMnGa_{1-y}Mn_y$ Heusler alloys have been studied by using Green's
function-based KKR-CPA method based DFT calculations. We will show the
magnetization can be tuned depending on the Co and Mn occumencies. We will also
discuss the critical temperature, magnetic interactions and magnetic stability
of the systems.",2204.06140v4
2022/4/22,Emerging research landscape of altermagnetism,"Magnetism is one of the largest, most fundamental, and technologically most
relevant fields of condensed-matter physics. Traditionally, two basic magnetic
phases have been considered -- ferromagnetism and antiferromagnetism. The
breaking of the time-reversal symmetry and spin splitting of the electronic
states by the magnetization in ferromagnets underpins a range of macroscopic
responses in this extensively explored and exploited type of magnets. By
comparison, antiferromagnets have vanishing net magnetization. This Perspective
reflects on recent observations of materials hosting an intriguing
ferromagnetic-antiferromagnetic dichotomy, in which spin-split spectra and
macroscopic observables, akin to ferromagnets, are accompanied by antiparallel
magnetic order with vanishing magnetization, typical of antiferromagnets. An
unconventional non-relativistic symmetry-group formalism offers a resolution of
this apparent contradiction by delimiting a third basic magnetic phase, dubbed
altermagnetism. Our Perspective starts with an overview of the still emerging
unique phenomenology of the phase, and of the wide array of altermagnetic
material candidates. In the main part of the article, we illustrate how
altermagnetism can enrich our understanding of overarching condensed-matter
physics concepts, and have impact on prominent condensed-matter research areas.",2204.10844v1
2022/5/10,The spontaneous exchange bias effect in La2-xCaxCoMnO6 series,"Structural, electronic and magnetic properties of polycrystalline
La2-xCaxCoMnO6 (0 $\leq$ x $\leq$ 0.75) compounds are investigated by x-ray
diffraction and magnetometry. All the samples have an orthorhombic structure
and show a slight decrease in the unit cell with Ca-doping.
Temperature-dependent magnetization measurements reveal a complex magnetic
behavior with two ferromagnetic transitions. These transitions are ascribed to
Co2+--Mn4+ and Co3+--Mn3+ couplings and suggest the presence of additional
antiferromagnetic couplings in these disordered compounds. Field-dependent
magnetization curves, measured after cooling the samples in a zero external
magnetic field, reveal the spontaneous exchange bias (SEB) effect for the
Ca-doped samples. The strengthening of the uncompensated magnetic coupling at
the interfaces, caused by the increased antiferromagnetic phase, explains the
increase of SEB with increasing the Ca-content.",2205.04772v1
2022/5/10,Anisotropic Dzyaloshinskii-Moriya interaction and topological magnetism in two-dimensional magnets protected by P4-m2 crystal symmetry,"As a fundamental magnetic parameter, Dzyaloshinskii-Moriya interaction (DMI),
has gained a great deal of attention in the last two decades due to its
critical role in formation of magnetic skyrmions. Recent discoveries of
two-dimensional (2D) van der Waals (vdW) magnets has also gained a great deal
of attention due to appealing physical properties, such as gate tunability,
flexibility and miniaturization. Intensive studies have shown that isotropic
DMI stabilizes ferromagnetic (FM) topological spin textures in 2D magnets or
their corresponding heterostructures. However, the investigation of anisotropic
DMI and antiferromagnetic (AFM) topological spin configurations remains
elusive. Here, we propose and demonstrate that a family of 2D magnets with
P4-m2 symmetry-protected anisotropic DMI. More interestingly, various
topological spin configurations, including FM/AFM antiskyrmion and AFM
vortex-antivortex pair, emerge in this family. These results give a general
method to design anisotropic DMI and pave the way towards topological magnetism
in 2D materials using crystal symmetry.",2205.04976v1
2022/8/4,Characterizing and Overcoming Surface Paramagnetism in Magnetoelectric Antiferromagnets,"We use a combination of density functional theory and Monte Carlo
calculations to calculate the surface magnetization in magnetoelectric
$\mathrm{Cr_2O_3}$ at finite temperatures. Such antiferromagnets, lacking both
inversion and time-reversal symmetries, are required by symmetry to posses an
uncompensated magnetization density on particular surface terminations. Here,
we first show that the uppermost layer of magnetic moments on the $(001)$
surface remain paramagnetic at the bulk N\'{e}el temperature, bringing the
theoretical estimate of surface magnetization density in line with experiment.
We demonstrate that the lower surface ordering temperature compared to bulk is
a generic feature of surface magnetization when the termination reduces the
effective Heisenberg coupling. We then propose two methods by which the surface
magnetization in $\mathrm{Cr_2O_3}$ could be stabilised at higher temperatures.
Specifically, we show that the effective coupling of surface magnetic ions can
be drastically increased either by a different choice of surface Miller plane,
or by $\mathrm{Fe}$ doping. Our findings provide an improved understanding of
surface magnetization properties in AFMs.",2208.02701v1
2022/9/23,Magnetostatics of Room Temperature Compensated Co/Gd/Co/Gd-based Synthetic Ferrimagnets,"Flexibility for interface engineering, and access to all-optical switching of
the magnetization, make synthetic ferrimagnets an interesting candidate for
advanced opto-spintronic devices. Moreover, due to their layered structure and
disordered interfaces they also bear promise for the emerging field of graded
magnetic materials. The fastest and most efficient spin-orbit torque driven
manipulation of the magnetic order in this material system generally takes
place at compensation. Here, we present a systematic experimental and modeling
study of the conditions for magnetization compensation and perpendicular
magnetic anisotropy in the synthetic ferrimagnetic Co/Gd/Co/Gd system. A model
based on partial intermixing at the Co/Gd interfaces of this system has been
developed which explains the experiments well, and provides a new tool to
understand its magnetic characteristics. More specifically, this work provides
new insight in the decay of the Co proximity-induced magnetization in the Gd,
and the role the capping layer plays in the Gd magnetization.",2209.11562v1
2022/10/11,Multiple Topological Magnetism in van der Waals Heterostructure of MnTe2/ZrS2,"Topological magnetism in low-dimensional systems is of fundamental and
practical importance in condensed-matter physics and material science. Here,
using first-principles and Monte-Carlo simulations, we present that multiple
topological magnetism (i.e., skyrmion and bimeron) can survive in van der Waals
Heterostructure of MnTe2ZrS2. Arising from interlayer coupling, MnTe2ZrS2 can
harbor a large Dzyaloshinskii-Moriya interaction. This, combined with
ferromagnetic exchange interaction, yields an intriguing skyrmion phase
consisting of sub-10 nm magnetic skyrmions under a tiny magnetic field of 75
mT. Meanwhile, upon harnessing a small electric field, magnetic bimeron can be
observed in MnTe2ZrS2 as well, suggesting the existence of multiple topological
magnetism. Through interlayer sliding, both topological spin textures can be
switched on-off, suggesting their stacking-dependent character. In addition,
the impacts of d and Keff on these spin textures are revealed, and a
dimensionless parameter is utilized to describe their joint effect. These
explored phenomena and insights not only are useful for fundamental research in
topological magnetism, but also enable novel applications in nanodevices.",2210.05065v1
2022/11/7,Determining Perpendicular Magnetic Anisotropy in Fe/MgO/Fe Magnetic Tunnel Junction: A DFT-Based Spin-Orbit Torque Method,"In our JunPy package, we have combined the first-principles calculated
self-consistent Hamiltonian with divide-and-conquer technique to successfully
determine the magnetic anisotropy (MA) in an Fe/MgO/Fe magnetic tunnel junction
(MTJ). We propose a comprehensive analytical derivation to clarify the crucial
roles of spin-orbit coupling that mediates the exchange and spin-orbit
components of spin torque, and the kinetic and spin-orbit components of spin
current accumulation. The angular dependence of cumulative spin-orbit torque
(SOT) indicates a uniaxial MA corresponding to the out-of-plane rotations of
magnetic moments of the free Fe layers. Different from the conventional MA
energy calculation and the phenomenological theory for a whole MTJ, our results
provide insight into the orbital-resolved SOT for atomistic spin dynamics
simulation in emergency complex magnetic heterojunctions.",2211.03603v3
2022/11/17,Tremendous tunneling magnetoresistance effects based on van der Waals room-temperature ferromagnet Fe$_3$GaTe$_2$ with highly spin-polarized Fermi surfaces,"Recently, van der Waals (vdW) magnetic heterostructures have received
increasing research attention in spintronics. However, the lack of
room-temperature magnetic order of vdW material has largely impedes its
development in practical spintronics devices. Inspired by the recently
discovered vdW ferromagnet Fe3GaTe2, which has been shown to have magnetic
order above room temperature and sizable perpendicular magnetic anisotropy, we
investigate the basic electronic structure and magnetic properties of Fe3GaTe2
as well as tunneling magnetoresistance effect in magnetic tunnel junctions
(MTJs) with structure of Fe3GaTe2/Insulator/Fe3GaTe2 by using first-principles
calculations. It is found that Fe3GaTe2 with highly spin-polarized Fermi
surface ensures that such magnetic tunnel junctions may have prominent
tunneling magnetoresistance effect at room temperature even comparable to
existing conventional AlOx and MgO-based MTJs. Our results suggest that
Fe3GaTe2-based MTJs may be the promising candidate for realizing long-waiting
full magnetic vdW spintronic devices.",2211.09484v1
2022/11/28,Superfluid-like spin transport in the dynamic states of easy-axis magnets,"The existing proposals for superfluid-like spin transport have been based on
easy-plane magnets where the U(1) spin-rotational symmetry is spontaneously
broken in equilibrium, and this has been limiting material choices for
realizing superfluid-like spin transport to restricted class of magnets. In
this work, we lift this limitation by showing that superfluid-like spin
transport can also be realized based on easy-axis magnets, where the U(1)
spin-rotational symmetry is intact in equilibrium but can be broken in
non-equilibrium. Specifically, we find the condition to engender a
non-equilibrium easy-cone state by applying a spin torque to easy-axis magnets,
which dynamically induces the spontaneous breaking of the U(1) spin-rotational
symmetry and thereby can support superfluid-like spin transport. By exploiting
this dynamic easy-cone state, we show theoretically that superfluid-like spin
transport can be achieved in easy-axis magnets under suitable conditions and
confirmed the prediction by micromagnetic simulations. We envision that our
work broadens material library for realizing superfluid-like spin transport,
showing the potential utility of dynamic states of magnets as venue to look for
spin-transport phenomena that do not occur in static magnetic backgrounds.",2211.15091v1
2022/12/2,Coherent magnon-induced domain wall motion in a magnetic insulator channel,"Advancing the development of spin-wave devices requires high-quality
low-damping magnetic materials where magnon spin currents can propagate
efficiently and interact effectively with local magnetic textures. We show that
magnetic domain walls (DW) can modulate spin-wave transport in perpendicularly
magnetized channels of Bi-doped yttrium-iron-garnet (BiYIG). Conversely, we
demonstrate that the magnon spin current can drive DW motion in the BiYIG
channel device by means of magnon spin-transfer torque. The DW can be reliably
moved over 15 um distances at zero applied magnetic field by a magnon spin
current excited by an RF pulse as short as 1 ns. The required energy for
driving DW motion is orders of magnitude smaller than those reported for
metallic systems. These results facilitate low-switching-energy magnonic
devices and circuits where magnetic domains can be efficiently reconfigured by
magnon spin currents flowing within magnetic channels.",2212.01408v1
2022/12/29,Magnetic oxides,"In this article we give a general survey of the main properties of magnetic
oxides - mostly the oxides of transition metals, but sometime also containing
rare earths ions. This is a very rich class of materials, among which there are
insulators and metals, systems with insulator-metal transitions, and there are
among them even high-temperature superconductors. One of the main features of
these compounds, which attract to them special attention and which serve as a
basis of many applications, are their rich magnetic properties. In this article
we discuss the main physical effects determining their behaviour, and describe
in detail especially their magnetic properties, but not only. After shortly
discussing the basic structure of isolated magnetic ions, we concentrate on the
collective effects depending on the interaction between sites, especially
exchange interaction, giving rise to different magnetic properties: different
types of magnetic ordering in conventional systems, but also more exotic states
such as spin liquid states in frustrated systems. We also cover related
phenomena in magnetic oxides, such as magnetoelectric and multiferroic
behaviour, and discuss at the end their diverse useful properties serving as a
basis of many applications.",2212.14176v1
2023/1/13,Magnetic phase diagram of the breathing-kagome antiferromagnet Nd$_3$BWO$_9$,"The highly-frustrated rare-earth based magnet Nd$_3$BWO$_9$ is a promising
candidate in the search for proximate spin liquid physics. We present a
thorough investigation on single crystals of this material using bulk and
microscopic techniques. Magnetization data reveal a fractional magnetization
plateau for three different investigated field directions. The magnetic phase
diagram is mapped out from calorimetric data and exhibits several domes of
magnetic order below 0.3 K. Propagation vectors for all ordered phases are
presented. The results suggest complex ordering in this material, and unveil
the existence of a commensuration transition of the propagation vector at zero
magnetic field. A scenario where interplane exchange interactions are essential
to a magnetic model of Nd$_3$BWO$_9$ is discussed.",2301.05555v1
2023/1/27,"Magnetic Amplification at Yb3+ ""Designer Defects"" in the van der Waals Ferromagnet, CrI3","The two-dimensional (2D) van der Waals ferromagnet CrI3 has been doped with
the magnetic optical impurity Yb3+ to yield materials that display sharp
multi-line Yb3+ photoluminescence (PL) controlled by the magnetism of CrI3.
Magneto-PL shows that Yb3+ magnetization is pinned to the magnetization of
CrI3. An effective internal field of ~10 T at Yb3+ is estimated, attributed to
strong in-plane Yb3+-Cr3+ superexchange coupling. The anomalously low energy of
Yb3+ PL in CrI3 reflects relatively high Yb3+-I- covalency, contributing to
Yb3+-Cr3+ superexchange coupling. The Yb3+ PL energy and linewidth both reveal
the effects of spontaneous zero-field CrI3 magnetic ordering within 2D layers
below TC, despite the absence of net magnetization in multilayer samples. These
results illustrate the use of optical impurities as ""designer defects"" to
introduce unique functionality to 2D magnets.",2301.11949v1
2023/3/28,Giant magnetocaloric effect in magnets down to the monolayer limit,"Two-dimensional magnets could potentially revolutionize information
technology, but their potential application to cooling technology and
magnetocaloric effect (MCE) in a material down to the monolayer limit remain
unexplored. Herein, we reveal through multiscale calculations the existence of
giant MCE and its strain tunability in monolayer magnets such as CrX$_3$ (X=F,
Cl, Br, I), CrAX (A=O, S, Se; X=F, Cl, Br, I), and Fe$_3$GeTe$_2$. The maximum
adiabatic temperature change ($\Delta T_\text{ad}^\text{max}$), maximum
isothermal magnetic entropy change, and specific cooling power in monolayer
CrF$_3$ are found as high as 11 K, 35 $\mu$Jm$^{-2}$K$^{-1}$, and 3.5
nWcm$^{-2}$ under a magnetic field of 5 T, respectively. A 2% biaxial and 5%
$a$-axis uniaxial compressive strain can remarkably increase $\Delta
T_\text{ad}^\text{max}$ of CrCl$_3$ and CrOF by 230% and 37% (up to 15.3 and
6.0 K), respectively. It is found that large net magnetic moment per unit area
favors improved MCE. These findings advocate the giant-MCE monolayer magnets,
opening new opportunities for magnetic cooling at nanoscale.",2303.15722v1
2023/5/31,Magnetization dynamics in a three-dimensional interconnected nanowire array,"Three-dimensional magnetic nanostructures have recently emerged as artificial
magnetic material types with unique properties bearing potential for
applications, including magnonic devices. Interconnected magnetic nanowires are
a sub-category within this class of materials that is attracting particular
interest. We investigate the high-frequency magnetization dynamics in a cubic
array of cylindrical magnetic nanowires through micromagnetic simulations based
on a frequency-domain formulation of the linearized Landau-Lifshitz-Gilbert
equation. The small-angle high-frequency magnetization dynamics excited by an
external oscillatory field displays clear resonances at distinct frequencies.
These resonances are identified as oscillations connected to specific geometric
features and micromagnetic configurations. The geometry- and
configuration-dependence of the nanowire array's absorption spectrum
demonstrates the potential of such magnetic systems for tuneable and
reprogrammable magnonic applications.",2306.00174v1
2023/6/26,Controllable magnetic domains in twisted trilayer magnets,"The use of moir\'e patterns to manipulate two-dimensional materials has
facilitated new possibilities for controlling material properties. The moir\'e
patterns in the two-dimensional magnets can cause peculiar spin texture, as
shown by previous studies focused on twisted bilayer systems. In our study, we
develop a theoretical model to investigate the magnetic structure of twisted
trilayer magnets. Unlike the twisted bilayer, the twisted trilayer magnet has
four different local stacking structures distinguished by the interlayer
couplings between the three layers. Our results show that the complex
interlayer coupling effects in the moir\'e superlattice can lead to the
stabilization of rich magnetic domain structures; these structures can be
significantly manipulated by adjusting the twist angle. Additionally, external
magnetic fields can easily manipulate these domain structures, indicating
potential applications in spintronics devices.",2306.14423v1
2023/8/31,Supercell Altermagnets,"Altermagnets are compensated magnets with unconventional $d$, $g$, and
$i$-wave spin order in reciprocal space. So far the search for new
altermagnetic candidates has been focused on materials in which the magnetic
unit cell is identical to the non-magnetic one, i.e. magnetic structures with
zero propagation vector. Here, we substantially broaden the family of
altermagnetic candidates by predicting supercell altermagnets. Their magnetic
unit cell is constructed by enlarging the nonmagnetic primitive unit cell,
resulting in a non-zero propagation vector for the magnetic structure. This
connection of the magnetic configuration to the ordering of sublattices gives
an extra degree of freedom to supercell altermagnets, which can allow for the
control over the order parameter spatial orientation. We identify realistic
candidates MnSe$_2$ with a $d$-wave order, and RbCoBr$_3$, CsCoCr$_3$, and
BaMnO$_3$ with $g$-wave order. We demonstrate the reorientation of the order
parameter in MnSe$_2$, which has two different magnetic configurations, whose
energy difference is only 5 meV, opening the possibility of controlling the
orientation of the altermagnetic order parameter by external perturbations.",2308.16662v2
2023/10/9,Micromagnetic textures in exchange coupled-ferromagnetic multiferroic films,"The development of new computing technologies has given a new stimulus in the
study of multiferroics. The use of multiferroics allows the realization of
competitive energy efficient scalable logic and storage devices. The low-power
consumption in Magneto Electric-Spin Orbital logics and Magnetic Random Access
Memory components is provided by magnetoelectric switching in multiferroic
based systems using a low-energy electric field. Our work concerns the
modelling of the Magneto Electric-Spin Orbital elements with an emphasis on the
magnetoelectric component and simulation of magnetization reversal processes in
a model system. The use of the proposed approach makes it possible to analyze
the influence of dimensional factors (film thicknesses, transverse dimensions,
sample shape) affecting the magnetic states of multiferroic nanoelements;
taking into interfacial interactions (magnetic anisotropy and interlayer
exchange); energy-efficient external influences that allow switching magnetic
states using magnetic and electric fields.",2310.05438v1
2023/10/18,"First-principles study of the magnetic anisotropy of ultrathin B-, C-, and N-doped FeCo films","Iron-based layered systems are of great interest because of their ability to
tune effective material parameters such as magnetic anisotropy energy (MAE).
The influence of the crystallographic structure of Fe, its thickness, and the
presence of other layers above and below the Fe layer on magnetic parameters,
such as the MAE of the studied system, is an intriguing and important topic
from an application point of view. Here, we present a density functional theory
(DFT) study of the magnetic anisotropy of nine-monolayer Fe, FeCo, and FeCo
films with B, C, and N dopants placed in octahedral interstitial positions. The
theoretical study is based on calculations using the full-potential
local-orbital code FPLO and the generalized gradient approximation. The
chemical disorder in the FeCo layers was modeled using the virtual crystal
approximation. The structures of the layers were subjected to optimization of
the geometry of the interlayer spacings and the neighborhood of the dopant
sites. We determined the local magnetic moments and the excess charge at each
layer position. We also identified the influence of dopant atoms on the
magnetic properties of FeCo layers, such as magnetization and magnetic
anisotropy.",2310.12242v1
2023/11/15,Exotic magnetic anisotropy near digitized dimensional Mott boundary,"The magnetic anisotropy of low-dimensional Mott systems exhibits unexpected
magnetotransport behavior useful for spin-based quantum electronics. Yet, the
anisotropy of natural materials is inherently determined by the crystal
structure, highly limiting its engineering. We demonstrate the magnetic
anisotropy modulation near a digitized dimensional Mott boundary in artificial
superlattices composed of a correlated magnetic monolayer SrRuO3 and
nonmagnetic SrTiO3. The magnetic anisotropy is initially engineered by
modulating the interlayer coupling strength between the magnetic monolayers.
Interestingly, when the interlayer coupling strength is maximized, a nearly
degenerate state is realized, in which the anisotropic magnetotransport is
strongly influenced by both the thermal and magnetic energy scales. Our results
offer a new digitized control for magnetic anisotropy in low-dimensional Mott
systems, inspiring promising integration of Mottronics and spintronics.",2311.09322v1
2023/12/1,Unravelling spontaneous Bloch-type skyrmion in centrosymmetric two-dimensional magnets,"The realization of magnetic skyrmions in two-dimensional (2D) magnets holds
great promise for both fundamental research and device applications. Despite
recent progress, two-dimensional skyrmion hosts are still limited, due to the
fact that most 2D magnets are centrosymmetric and thus lack
Dzyaloshinskii-Moriya interaction (DMI). We show here, using a general analysis
based on symmetry, that Bloch-type skyrmions can, in fact, be stabilized in 2D
magnets, due to the interplay between in-plane component (dx) of second
nearest-neighbor DMI and magnetic anisotropy. Its validity is demonstrated in
the Cr2Ge2Te6 monolayer, which is also verified by recent experiments. Our work
gives a clear direction for experimental studies of 2D magnetic materials to
stabilize skyrmions and should greatly enrich the research on magnetic
skyrmions in 2D lattices.",2312.00423v1
2023/12/7,Automatic Calculation of the Transition Temperatures for two-dimensional Heisenberg type Magnets,"Theoretical prediction of the 2nd-order magnetic transition temperature (TM)
used to be arduous. Here, we develop a first principle-based, fully automatic
structure-to-TM method for two-dimensional (2D) magnets whose effective
Hamiltonians follow the Heisenberg model. The Heisenberg exchanges, which can
be calculated to an arbitrary shell, are transferred into the Monte Carlo
calculation. Using Cr-based magnets as the showcases, we show that our method
is a powerful tool to study the 2D magnets in two aspects. First, considering
long-range exchanges enables us to identify the spin frustration in the
suspended CrTe2 monolayer, whereas the heterostructure calculations reveal that
the ferromagnetism can be recovered if the monolayer CrTe2 is grown onto
various 2D substrates. Second, we realize a high-throughput screening of novel
magnets discovered by random structure searches. Six 2D Cr chalcogenides are
selected to have high TM. Our work provides a new insight for the study of 2D
magnets and helps accelerate the pace of magnetic materials data-mining.",2312.04497v1
2023/12/28,Anomalous exchange bias effect in ferromagnetic VI3 flakes,"The exchange bias (EB) effect, pivotal in magnetic data storage and sensing
devices, has been observed not only in interfacial regions but also in
intrinsic ferromagnetic materials. Here, we've uncovered a robust and stable
exchange bias effect within the layered van der Waals (vdW) ferromagnet VI3
employing magnetic circular dichroism microscopy. At 10 K, we observed a
significant exchange field of approximately 0.1 T, accompanied by random shifts
(positive or negative relative to zero magnetic field) after zero-field
cooling. Notably, this effect is effectively controllable after field cooling,
with shift direction opposing the applied magnetic field. The presence of
strong magnetic anisotropic energy within VI3 results in larger
coercivity-bound magnetic domains. These domains dictate the neighboring
ferromagnetic alignment and induce shifts in the hysteresis loop. Our study not
only contributes to comprehending fundamental nanoscale magnetic interactions
but also sheds light on emergent phenomena within layered van der Waals
magnets.",2312.16899v1
2024/2/20,Magnetic transitions of biphenylene network layers induced by external perturbations,"We present a comprehensive investigation of the magnetic ordering in
biphenylene network (BPN) layers, employing density functional theory (DFT)
calculations under external perturbations, including uniaxial strains and hole
doping. We compute fully relaxed structures, energy bands, and magnetic states
by performing DFT calculations augmented with extended Hubbard interactions,
encompassing both on-site and inter-site interactions, to accurately capture
electron correlations. We emphasize the importance of the extended Hubbard
forces by contrasting BPN layers with and without the forces. Our results
reveal that in their fully relaxed structures, both BPN monolayer and bilayer
are non-magnetic. We exploit external perturbations to induce magnetic
ordering. The application of uniaxial strains induces magnetic phase
transitions, leading to ferrimagnetic and antiferromagnetic states in BPN
monolayer and bilayer, respectively. Additionally, we investigate hole doping
as an alternative mechanism for inducing magnetic transitions. Our findings
shed light on the tunability of magnetic properties in BPN layers through
external perturbations, demonstrating the promise of low-dimensional materials
in future spintronics and nanoelectronic applications.",2402.13129v1
2000/5/2,Magnetoelastic coupling in epitaxial magnetic films: An ab-initio study,"A method is developed which allows to determine the first-order and the
second-order magnetoelastic coefficients of a magnetic bulk material from the
ab-initio calculation of the magnetocrystalline anisotropy energy as function
of a prestrain. Excplicit results are given for bcc Fe, and they agree well
with experimental data obtained from the magnetostrictive stress measurements
for epitaxial Fe films.",0005053v1
2000/12/28,Unipolar spin diodes and transistors,"Unipolar devices constructed from ferromagnetic semiconducting materials with
variable magnetization direction are shown theoretically to behave very
similarly to nonmagnetic bipolar devices such as the p-n diode and the bipolar
(junction) transistor. Such devices may be applicable for magnetic sensing,
nonvolatile memory, and reprogrammable logic.",0012484v1
2002/7/15,Origin of spin-glass behavior of Zn_1-xMn_xO,"ac susceptibility has been studied for polycrystalline Zn$_{1-x}$Mn$_x$O.
Stoichiometric samples demonstrate Curie-Weiss behavior, which indicates mostly
antiferromagnetic interactions. Magnetic susceptibility can be described by a
diluted Heisenberg magnet model developed for semimagnetic semiconductors.
High-pressure oxygen annealing induces spin-glass like behavior in
Zn$_{1-x}$Mn$_x$O by precipitation of ZnMnO$_3$ in the paramagnetic matrix.",0207349v1
2002/7/15,Magnetism of carbon-based materials,"We present a collection of experimental evidence on UFOs: Unidentified
Ferromagnetic Organic structures. Five types of carbon magnets have been
obtained experimentally: 1. Chains of interacting radicals 2. Carbonaceous
substances with a mixture of sp2 and sp3 coordinated atoms 3. Amorphous carbon
structures containing trivalent elements like P, N. B. 4. Nanographite and bulk
graphite, nanodiamond, carbon nanofoam 5. Fullerenes.",0207368v1
2003/7/23,Spin order manipulations in nanostructures of II-VI ferromagnetic semiconductors,"An overview of recent studies on ferromagnetism in Cr- and Mn-based II-VI
diluted magnetic semiconductors is presented emphasizing differences in
underlying exchange mechanisms. Examples of manipulations with spin ordering by
carrier density, dimensionality, light, and electric field are given.",0307573v1
1996/4/28,Magnetic susceptibility of insulators from first principles,"We present an {\it ab initio} approach for the computation of the magnetic
susceptibility $\chi$ of insulators. The approach is applied to compute $\chi$
in diamond and in solid neon using density functional theory in the local
density approximation, obtaining good agreement with experimental data. In
solid neon, we predict an observable dependence of $\chi$ upon pressure.",9604008v1
2007/8/10,"Nanostructures, Magnetic Semiconductors and Spinelectronics","A short overview is given of recent advances in the field of
nanosemiconductors, which are suitable as materials for spin polarized
transport of charge carriers. On the basis of last theoretical and experimental
achievements it is shown that development of diluted and wide forbidden zone
semiconductors with controlled disorders as well as their molecular structures
is the very prospective way for magnetic semiconductors preparation.",0708.1445v1
2008/12/31,"Synthesis of DNA Templated Tri-functional Electrically Conducting, Optical and Magnetic nanochain of Nicore-Aushell for Bio-device","Synthesis of tri functional electrically conducting, optical and magnetic
nano-chain of Nicore-Aushell has been discussed here. Our Investigation
indicates that such material attached with biomolecule DNA in chain form will
have great potentiality in medical instrument and bio computer device.",0901.0087v1
2010/6/29,Magnetostatics of synthetic ferrimagnet elements,"We calculate the magnetostatic energy of synthetic ferrimagnet (SyF)
elements, consisting of two thin ferromagnetic layers coupled
antiferromagnetically through RKKY coupling. We calculate exact formulas as
well as approximate yet accurate ones, which can be used to easily derive
energy barriers and anisotropy fields of SyF. These can be used to evaluate
coercivity, thermal stability and other useful quantities.",1006.5531v2
2010/8/24,Electronic and magnetic properties of the graphene-ferromagnet interface,"The article presents the work on the investigation of the surface structure
as well as electronic and magnetic properties of graphene layer on a lattice
matched surface of a ferromagnetic material, Ni(111).",1008.3975v1
2012/1/21,Non-magnetic negative-refraction systems for terahertz and far-infrared frequencies,"We demonstrate that homogeneous naturally-occurring materials can form
non-magnetic negative refractive index systems, and present specific
realizations of the proposed approach for the THz and far-IR frequencies. The
proposed structure operates away from resonance, thereby promising the capacity
for low-loss devices.",1201.4514v2
2014/11/19,"Elastic, electronic and magnetic properties of new oxide perovskite BaVO3: a first-principles study","The structural, elastic, magnetic properties, as well as electronic structure
and chemical bonding picture of new oxide 3d1-perovskite BaVO3, recently
synthesized, were systematically investigated involving the first-principles
FLAPW-GGA calculations. The obtained results are discussed in comparison with
available experimental data, as well as with those obtained before for
isostructural and isoelectronic SrVO3 perovskite.",1411.5128v1
2009/7/15,Barnett Effect in Thin Magnetic Films and Nanostructures,"The Barnett effect refers to the magnetization induced by rotation of a
demagnetized ferromagnet. We describe the location and stability of stationary
states in rotating nanostructures using the Landau-Lifshitz-Gilbert equation.
The conditions for an experimental observation of the Barnett effect in
different materials and sample geometries are discussed.",0907.2648v1
2014/4/9,Novel non-magnetic hard boride Co5B16 synthesized under high pressure,"A first cobalt boride with the Co:B ratio below 1:1, Co5B16, was synthesized
under high-pressure high-temperature conditions. It has a unique orthorhombic
structure (space group Pmma, a = 19.1736(12), b = 2.9329(1), and c = 5.4886(2)
{\AA}, R1 (all data) = 0.037). The material is hard, paramagnetic, with a weak
temperature dependence of magnetic susceptibility.",1404.2575v1
2022/4/26,Unusually strong electronic correlation and field-induced ordered phase in YbCo$_2$,"We report the first study of electrical resistivity, magnetization, and
specific heat on YbCo$_2$. The measurements on a single-phased sample of
YbCo$_2$ bring no evidence of magnetic ordering down to 0.3 K in a zero
magnetic field. The manifestations of low Kondo temperature are observed. The
specific heat value divided by temperature, C/T, keeps increasing
logarithmically beyond 7 J/mol.K2 with decreasing temperature down to 0.3 K
without no sign of magnetic ordering, suggesting a very large electronic
specific heat. Analysis of the magnetic specific heat indicates that the large
portion of the low-temperature specific heat is not explained simply by the low
Kondo temperature but is due to the strong intersite magnetic correlation in
both the 3d and 4f electrons. Temperature-dependent measurements under static
magnetic fields up to 7 T are carried out, which show the evolution of
field-induced transition above 2 T. The transition temperature increases with
increasing field, pointing to a ferromagnetic character. The extrapolation of
the transition temperature to zero field suggests that YbCo$_2$ is in the very
proximity of the quantum critical point. These results indicate that in the
unique case of YbCo$_2$, the itinerant electron magnetism of Co 3d-electrons
and the Kondo effect within the vicinity of quantum criticality of Yb 4f-local
moments can both play a role.",2204.12025v2
2023/12/7,The Er doping of ZnCr2O4,"Magnetic Er3+ is doped into the well-studied frustrated normal spinel
ZnCr2O4. Various spectroscopies are employed to prove that Er3+ successfully
enters the spinel to form ZnCr2-xErxO4 for x less than 0.005. The low levels of
Er3+ doping possible nonetheless have a significant effect on the frustrated
magnetism and the ordering that is seen near 12 K in the undoped material.",2312.04376v1
1999/10/7,Study of the connection between hysteresis and thermal relaxation in magnetic materials,"The connection between hysteresis and thermal relaxation in magnetic
materials is studied from both the experimental and the theoretical viewpoint.
Hysteresis and viscosity effects are measured in Finemet-type nanocrystalline
materials above the Curie temperature of the amorphous phase, where the system
consists of ferromagnetic nanograins imbedded in a paramagnetic matrix. The
hysteresis loop dependence on field rate, the magnetization time decay at
different constant fields and the magnetization curve shape after field
reversal are all consistent with a single value of the fluctuation field Hf =
8A/m (at 430 C). In addition, it is shown that all data collapse onto a single
curve M(Hath), when magnetization is plotted as a function of a properly
defined field Hath, dependent on time and field rate. Experimental data are
interpreted by assuming that the system consists of an assembly of elementary
bistable units, distributed in energy levels and energy barriers. The
approximations under which one predicts data collapse onto a single curve
M(Hath) are discussed.",9910108v1
2004/6/25,X-ray magneto-optics of lanthanide materials: principles and applications,"Lanthanide metals are a particular class of magnetic materials in which the
magnetic moments are carried mainly by the localized electrons of the 4f shell.
They are frequently found in technically relevant systems, to achieve, e.g.,
high magnetic anisotropy. Magneto-optical methods in the x-ray range are well
suited to study complex magnetic materials in an element-specific way. In this
work, we report on recent progress on the quantitative determination of
magneto-optical constants of several lanthanides in the soft x-ray region and
we show some examples of applications of magneto-optics to hard-magnetic
interfaces and exchange-coupled layered structures containing lanthanide
elements.",0406643v2
2006/3/8,Magnetic and Electronic Properties of the New Ferrimagnet Sr8CaRe3Cu4O24,"Magnetic and electronic properties of the recently-discovered material
Sr8CaRe3Cu4O24 were investigated by means of a quantum Monte Carlo simulation,
the Green function method and the LSDA+U (local spin-density approximation plus
the Hubbard-U term) method. The LSDA+U calculation shows that the ground state
is an insulator with magnetic moment M=1.01\muB/f.u., which is consistent with
experimental results. The magnetic sites were specified and an effective model
for the magnetic properties of this compound derived. The resultant effective
model is a three-dimensional Heisenberg model with spin-alternation.
Finite-temperature properties of this effective model are investigated by the
quantum Monte Carlo method (continuous-time loop algorithm) and the Green
function method. The numerical results are consistent with experimental
results, indicating that the model is suitable for this material. Using the
analysis of the effective model, some predictions for the material are made.",0603194v1
2008/6/17,Resonance enhancement of magnetic Faraday rotation,"Magnetic Faraday rotation is widely used in optics. In natural transparent
materials, this effect is very weak. One way to enhance it is to incorporate
the magnetic material into a periodic layered structure displaying a high-Q
resonance. One problem with such magneto-optical resonators is that a
significant enhancement of Faraday rotation is inevitably accompanied by strong
ellipticity of the transmitted light. More importantly, along with the Faraday
rotation, the resonator also enhances linear birefringence and absorption
associated with the magnetic material. The latter side effect can put severe
limitations on the device performance. From this perspective, we carry out a
comparative analysis of optical microcavity and a slow wave resonator. We show
that slow wave resonator has a fundamental advantage when it comes to Faraday
rotation enhancement in lossy magnetic materials.",0806.2884v1
2011/4/8,Magnetic nanocomposites at microwave frequencies,"Most conventional magnetic materials used in the electronic devices are
ferrites, which are composed of micrometer-size grains. But ferrites have small
saturation magnetization, therefore the performance at GHz frequencies is
rather poor. That is why functionalized nanocomposites comprising magnetic
nanoparticles (e.g. Fe, Co) with dimensions ranging from a few nm to 100 nm,
and embedded in dielectric matrices (e.g. silicon oxide, aluminium oxide) have
a significant potential for the electronics industry. When the size of the
nanoparticles is smaller than the critical size for multidomain formation,
these nanocomposites can be regarded as an ensemble of particles in
single-domain states and the losses (due for example to eddy currents) are
expected to be relatively small. Here we review the theory of magnetism in such
materials, and we present a novel measurement method used for the
characterization of the electromagnetic properties of composites with
nanomagnetic insertions. We also present a few experimental results obtained on
composites consisting of iron nanoparticles in a dielectric matrix.",1104.1535v1
2012/8/6,Coupling of magnetic and ferroelectric hysteresis by a multi-component magnetic structure in Mn2GeO4,"The olivine compound Mn2GeO4 is shown to feature both a ferroelectric
polarization and a ferromagnetic magnetization that are directly coupled and
point along the same direction. We show that a spin spiral generates
ferroelectricity (FE), and a canted commensurate order leads to weak
ferromagnetism (FM). Symmetry suggests that the direct coupling between the FM
and FE is mediated by Dzyaloshinskii-Moriya interactions that exist only in the
ferroelectric phase, controlling both the sense of the spiral rotation and the
canting of the commensurate structure. Our study demonstrates how
multi-component magnetic structures found in magnetically-frustrated materials
like Mn2GeO4 provide a new route towards functional materials that exhibit
coupled FM and FE.",1208.1128v1
2012/12/31,Effects of lateral device size and material properties on the ferromagnetic resonance response of spinwave eigen-modes in magnetic devices,"We analyze the effects of lateral device size and magnetic material
parameters on the ferromagnetic resonance (FMR) response. Results presented are
directly relevant to widely used FMR experimental techniques for extracting
magnetic parameters from thin films, the results of which are often assumed to
carry over to corresponding nanometer-sized patterned devices. We show that
there can be significant variation in the FMR response with device size, and
that the extent of the variation depends on the magnetic material properties.
This explains, for example, why different experiments along these lines have
yielded different size-dependent trends from damping measurements. Observed
trends with increasing size and different material parameters are explained
through the evolution of three distinct eigen-modes, demonstrating the
respective roles of demagnetization and exchange. It is also shown that there
is a crossover of dominant eigen-modes in the response signal, accompanied by
conjugating edge-type modes, leading to evident effects in measured linewidth
and damping. Among the sizes considered, in higher saturation magnetization, we
observe as much as a 40% increase in apparent damping, due solely to device
size variation.",1212.6835v1
2015/7/23,Ba{0.4}Rb{0.6}Mn2As2: A Prototype Half-Metallic Ferromagnet,"Half-metallic ferromagnetism (FM) in single-crystal
Ba{0.39(1)}Rb{0.61(1)}Mn2As2 below its Curie temperature TC = 103(2) K is
reported. The magnetization M versus applied magnetic field H isotherm data at
1.8 K show complete polarization of the itinerant doped-hole magnetic moments
that are introduced by substituting Rb for Ba. The material exhibits extremely
soft FM, with unobservably small remanent magnetization and coercive field.
Surprisingly, and contrary to typical itinerant FMs, the M(H) data follow the
Arrott-plot paradigm that is based on a mean-field theory of local-moment FMs.
The in-plane electrical resistivity data are fitted well by an activated-T^2
expression for T < TC, whereas the data sharply deviate from this model for T >
TC. Hence the activated-T^2 resistivity model is an excellent diagnostic for
determining the onset of half-metallic FM in this compound, which in turn
demonstrates the presence of a strong correlation between the electronic
transport and magnetic properties of the material. Together with previous data
on 40% hole-doped Ba{0.6}K{0.4}Mn2As2, these measurements establish 61%-doped
Ba{0.39}Rb{0.61}Mn2As2 as a prototype for a new class of half-metallic
ferromagnets in which all the itinerant carriers in the material are
ferromagnetic.",1507.06679v1
2015/8/4,Tailoring superelasticity of soft magnetic materials,"Embedding magnetic colloidal particles in an elastic polymer matrix leads to
smart soft materials that can reversibly be addressed from outside by external
magnetic fields. We discover a pronounced nonlinear superelastic stress-strain
behavior of such materials using numerical simulations. This behavior results
from a combination of two stress-induced mechanisms: a detachment mechanism of
embedded particle aggregates as well as a reorientation mechanism of magnetic
moments. The superelastic regime can be reversibly tuned or even be switched on
and off by external magnetic fields and thus be tailored during operation.
Similarities to the superelastic behavior of shape-memory alloys suggest
analogous applications, with the additional benefit of reversible switchability
and a higher biocompatibility of soft materials.",1508.00770v2
2015/8/10,Tunable multiple Fano resonances in magnetic single-layered core-shell particles,"We investigate multiple Fano, comblike scattering resonances in
single-layered, concentric core-shell nanoparticles composed of magnetic
materials. Using the Lorenz-Mie theory, we derive, in the long-wavelength
limit, an analytical condition for the occurrence of comblike resonances in the
single scattering by coated spheres. This condition establishes that comblike
scattering response uniquely depends on material parameters and thickness of
the shell, provided that it is magnetic and thin compared to the scatterer
radius. We also demonstrate that comblike scattering response shows up beyond
the long-wavelength limit and it is robust against absorption. Since multiple
Fano resonances are shown to depend explicitly on the magnetic permeability of
the shell, we argue that both the position and profile of the comblike,
morphology-dependent resonances could be externally tuned by exploiting the
properties of engineered magnetic materials.",1508.02255v1
2015/9/9,"Large magneto-optical Kerr effect in noncollinear antiferromagnets Mn$_{3}X$ ($X$ = Rh, Ir, or Pt)","Magneto-optical Kerr effect, normally found in magnetic materials with
nonzero magnetization such as ferromagnets and ferrimagnets, has been known for
more than a century. Here, using first-principles density functional theory, we
demonstrate large magneto-optical Kerr effect in high temperature noncollinear
antiferromagnets Mn$_{3}X$ ($X$ = Rh, Ir, or Pt), in contrast to usual wisdom.
The calculated Kerr rotation angles are large, being comparable to that of
transition metal magnets such as bcc Fe. The large Kerr rotation angles and
ellipticities are found to originate from the lifting of the band
double-degeneracy due to the absence of spatial symmetry in the Mn$_{3}X$
noncollinear antiferromagnets which together with the time-reversal symmetry
would preserve the Kramers theorem. Our results indicate that Mn$_{3}X$ would
provide a rare material platform for exploration of subtle magneto-optical
phenomena in noncollinear magnetic materials without net magnetization.",1509.02865v1
2015/10/13,"Review paper: Magnetocaloric effects in RTX intermetallic compounds (R = Gd~Tm, T = Fe~Cu and Pd, X = Al and Si)","The ternary intermetallic RTX compounds (R = rare earth, T = transitional
metal, X = p-block metal) have been investigated extensively in the past few
decades due to their interesting physical properties. Recently, much attention
has been paid to the magnetocaloric effect (MCE) of these RTX compounds,
especially the ones with heavy rare-earth, for their potential application in
low temperature magnetic refrigeration. In this paper, we review the MCE of
RTSi and RTAl systems with R = Gd~Tm, T = Fe~Cu and Pd, which are widely
investigated in recent years. It is found that these RTX compounds exhibit
various crystal structures and magnetic properties, which then result in
different MCE. Large MCE has been observed not only in the typical
ferromagnetic materials but also in the antiferromagnetic materials. The
magnetic properties have been studied in detail to discuss the physical
mechanism of large MCE in RTX compounds. Particularly, some RTX compounds, such
as ErFeSi, HoCuSi, HoCuAl, etc, exhibit large reversible MCE under low magnetic
field change, which suggests that these compounds could be promising materials
for magnetic refrigeration in low temperature range.",1510.03503v1
2015/11/25,Giant magnetic pumping of photovoltage and photocurrent using dielectric lossy material,"The enhancement of photovoltage and photocurrent of material is fundamentally
significant owing to the many interesting phenomena found and the potential
applications. However, vast altering of magnitude-orders of photoelectricity
has been technologically challenging. Here we report two dielectric materials
Li2ZnSiO4 and Li2SiO3 showing high photovoltage and photocurrent tunability.
When magnetic field increasing from 0.00015T up to 0.44T,it is found that 3850%
of photovoltage tunability and 3841 % of photocurrent tunability in Li2ZnSiO4 ,
and 132.8% of photovoltage tunability and 132.5% of photocurrent tunability in
Li2SiO3. A simple model that considers the effects of spin mixing/interaction
and magnetically-tunable charge gradient is used to explain this interaction
between magnetic field and the photoelectricity. This result indicates a
magnetic approach can be potentially used for energy efficiency.",1511.07936v1
2016/5/20,A centrosymmetric hexagonal magnet with superstable biskyrmion magnetic nanodomains in a wide temperature range of 100K to 340K,"Here, we report on the experimental discovery of biskyrmion magnetic
nanodomains at RT and the observation of a biskyrmion-derived topological Hall
effect (THE) in the centrosymmetric hexagonal MnNiGa magnet. Using a phase
reconstruction technique based on a transport-of-intensity equation (TIE), we
established the texture of the biskyrmion spin. Results from Lorentz
transmission electron microscopy (TEM) and the topological Hall effect revealed
that the biskyrmion phase is stable over a much wider temperature range (100 K
to ~340K) and a larger magnetic field range in our material than in
skyrmion-hosting bulk crystals reported previously[1-3,6]. The super-wide
operating temperature and the broad range of material options indicate
important progress toward the realization of skyrmion-based spintronic devices.",1605.06186v1
2016/9/7,Classification of materials with divergent magnetic Grüneisen parameter,"At any quantum critical point (QCP) with a critical magnetic field $H_c$, the
magnetic Gr\""uneisen parameter $\Gamma_{\rm H}$, which equals the adiabatic
magnetocaloric effect, is predicted to show characteristic signatures such as a
divergence, sign change and $T/(H-H_c)^\epsilon$ scaling. We categorize
thirteen materials, ranging from heavy fermion metals to frustrated magnets,
where such experimental signatures have been found. Remarkably, seven
stoichiometric materials at ambient pressure show $H_c=0$. However, additional
thermodynamic and magnetic experiments suggest that most of them do not show a
zero-field QCP. While the existence of a pressure insensitive ""strange metal""
state is one possibility, for some of the materials $\Gamma_{\rm H}$ seems
influenced by impurities or a fraction of moments which are not participating
in a frozen state. To unambiguously prove zero-field and pressure sensitive
quantum criticality, a $\Gamma_{\rm H}$ divergence is insufficient and also the
Gr\""uneisen ratio of thermal expansion to specific heat must diverge.",1609.02013v1
2017/2/13,Collective spin excitations of helices and magnetic skyrmions: review and perspectives of magnonics in non-centrosymmetric magnets,"Magnetic materials hosting correlated electrons play an important role for
information technology and signal processing. The currently used ferro-, ferri-
and antiferromagnetic materials provide microscopic moments (spins) that are
mainly collinear. Recently more complex spin structures such as spin helices
and cycloids have regained a lot of interest. The interest has been initiated
by the discovery of the skyrmion lattice phase in non-centrosymmetric helical
magnets. In this review we address how spin helices and skyrmion lattices
enrich the microwave characteristics of magnetic materials. When discussing
perspectives for microwave electronics and magnonics we focus particularly on
insulating materials as they avoid eddy current losses, offer low spin-wave
damping, and might allow for electric field control of collective spin
excitations. Thereby, they further fuel the vision of magnonics operated at low
energy consumption.",1702.03668v1
2019/8/7,Tunability of Room Temperature Ferromagnetism in Spintronic Semiconductors through Non-magnetic Atoms,"The implementation and control of room temperature ferromagnetism (RTFM) by
adding magnetic atoms to a semiconductor's lattice has been one of the most
important problems in solid state state physics in the last decade. Herein we
report for the first time, to our knowledge, on the mechanism that allows RTFM
to be tuned by the inclusion of \emph{non-magnetic} aluminum in nickel ferrite.
This material, NiFe$_{2-x}$Al$_x$O$_4$ (x=0, 0.5, 1.5), has already shown much
promise for magnetic semiconductor technologies, and we are able to add to its
versatility technological viability with our results. The site occupancies and
valencies of Fe atoms (Fe$^{3+}$ T$_d$, Fe$^{2+}$ O$_h$, and Fe$^{3+}$ O$_h$)
can be methodically controlled by including aluminum. Using the fact that
aluminum strongly prefers a 3+ octahedral environment, we can selectively fill
iron sites with aluminum atoms, and hence specifically tune the magnetic
contributions for each of the iron sites, and therefore the bulk material as
well. Interestingly, the influence of the aluminum is weak on the electronic
structure (supplemental material), allowing one to retain the desirable
electronic properties while achieving desirable magnetic properties.",1908.02610v1
2019/8/29,Theory and simulations of critical temperatures in CrI3 and other 2D materials: Easy-axis magnetic order and easy-plane Kosterlitz-Thouless transitions,"The recent observations of ferromagnetic order in several two-dimensional
(2D) materials have generated an enormous interest in the physical mechanisms
underlying 2D magnetism. In the present prospective article we show that
Density Functional Theory (DFT) combined with either classical Monte Carlo
simulations or renormalized spin-wave theory can predict Curie temperatures for
ferromagnetic insulators that are in quantitative agreement with experiment.
The case of materials with in-plane anisotropy is then discussed and it is
argued that finite size effects may lead to observable magnetic order in
macroscopic samples even if long range magnetic order is forbidden by the
Mermin-Wagner theorem.",1908.11115v1
2010/4/6,A Cu2+ (S = 1/2) Kagomé Antiferromagnet: MgxCu4-x(OH)6Cl2,"Spin-frustrated systems are one avenue for inducing macroscopic quantum
states in materials. However, experimental realization of this goal has been
difficult because of the lack of simple materials and, if available, the
separation of the unusual magnetic properties arising from exotic magnetic
states from behavior associated with chemical disorder, such as site mixing.
Here we report the synthesis and magnetic properties of a new series of
magnetically frustrated materials, MgxCu4-x(OH)6Cl2. Because of the
substantially different ligand-field chemistry of Mg2+ and Cu2+, site disorder
within the kagom\'e layers is minimized, as directly measured by X-ray
diffraction. Our results reveal that many of the properties of these materials
and related systems are not due to disorder of the magnetic lattice but rather
reflect an unusual ground state.",1004.0941v1
2016/3/24,Multi-layered chalcogenides with potential for magnetism and superconductivity,"Layered thallium copper chalcogenides can form single, double, or triple
layers of Cu-Ch separated by Tl sheets. Here we report on the preparation and
properties of Tl-based materials of TlCu2Se2, TlCu4S3, TlCu4Se3 and TlCu6S4,
and compare to reports on layered ACu2nChn+1 materials with A = Ba, K, Rb, and
Cs, and Ch = S, Se. Having no long-range magnetism for these materials is quite
surprising considering the possibilities of inter- and intra-layer exchange
interactions through Cu 3d, and we measure by magnetic susceptibility and
confirm by neutron diffraction. First principles density-functional theory
calculations for both the single-layer TlCu2Se2 (isostructural to the 122
iron-based superconductors) and the double-layer TlCu4Se3 suggest a lack of
Fermi-level spectral weight that is needed to drive a magnetic or
superconducting instability. The electronic structure calculations show a much
greater likelihood of magnetism for multiple structural layers with Fe.",1603.07698v1
2018/9/12,Screening magnetic two-dimensional atomic crystals with nontrivial electronic topology,"To date only a few two-dimensional (2D) magnetic crystals were experimentally
confirmed, such as CrI3 and CrGeTe3, all with very low Curie temperatures (TC).
High-throughput first-principles screening over a large set of materials yields
89 magnetic monolayers including 56 ferromagnetic (FM) and 33 antiferromagnetic
compounds. Among them, 24 FM monolayers are promising candidates possessing TC
higher than that of CrI3. High TC monolayers with fascinating electronic phases
are identified: (i) quantum anomalous and valley Hall effects coexist in a
single material RuCl3 or VCl3, leading to a valley-polarized quantum anomalous
Hall state; (ii) TiBr3, Co2NiO6 and V2H3O5 are revealed to be half-metals. More
importantly, a new type of fermion dubbed type-II Weyl ring is discovered in
ScCl. Our work provides a database of 2D magnetic materials, which could guide
experimental realization of high-temperature magnetic monolayers with exotic
electronic states for future spintronics and quantum computing applications.",1809.04223v1
2020/3/2,A comparison of computed and experimental neutron diffraction intensity at large momentum for MnO and NiO,"Magnetic neutron scattering measures spin-spin correlations giving
information about the long-range spin order as well as the shape of the spin
density in magnetic materials. Similarly, detailed first principles
calculations directly compute the spin density in materials. In this work, the
authors carefully compare experimentally measured magnetic neutron intensities
to three levels of theory: density functional theory in two approximations, and
fixed-node diffusion Monte Carlo. While each theory performs similarly for the
simple antiferromagnet MnO, there are significant differences between density
functional theory and diffusion Monte Carlo in NiO. For both materials,
fixed-node diffusion Monte Carlo shows the lowest RMS error with respect to
experiment for the form factor and the intensity. Through connection of the
intensities and form factors to the real-space spin densities, it is shown that
diffusion Monte Carlo spin density becomes more diffuse by spreading spin away
from the bond directions. This benchmark is of importance when considering the
efficacy of an ab initio calculation in capturing both the long-range magnetic
correlations and the microscopic spin details of magnetic systems.",2003.01183v1
2020/3/17,"Structure, magnetic and dielectric properties in nano-crystalline Yb$_2$CoMnO$_6$","Structural, magnetic and dielectric properties have been studied for
Yb$_2$CoMnO$_6$. Nano-crystalline sample of Yb$_2$CoMnO$_6$ synthesized by
sol-gel method and structural analysis shows that the sample crystallizes in
monoclinic crystal structure with \textit{P2$_1$/n} phase group. To understand
the charge state of Co, Mn and Yb we have performed the XPS study. Magnetic
study shows that the sample undergoes a paramagnetic to ferromagnetic phase
transition around $T_c$ $\sim$56 K and an additional magnetic ordering at a
lower temperature around 14 K due to ordering of Yb$^{3+}$ magnetic ions.
Temperature dependent Raman study reveals that spin-phonon interaction is
present in this material. Further, we have studied the dielectric properties of
this material. We observed that the material shows a relaxation behavior that
obeys the thermally activated relaxation mechanism. Impedance spectroscopy
reveals that the material shows non-Debye's behavior. AC conductivity study is
performed to understand the conduction mechanics which involve the quantum
mechanical tunneling phenomenon.",2003.07872v1
2017/7/13,Valley Magnetoelectricity in Single-Layer MoS2,"Magnetoelectric (ME) effect, the phenomenon of inducing magnetization by
application of an electric field or vice versa, holds great promise for
magnetic sensing and switching applications. Studies of the ME effect have so
far focused on the control of the electron spin degree of freedom (DOF) in
materials such as multiferroics and conventional semiconductors. Here, we
report a new form of the ME effect based on the valley DOF in two-dimensional
(2D) Dirac materials. By breaking the three-fold rotational symmetry in
single-layer MoS2 via a uniaxial stress, we have demonstrated the pure
electrical generation of valley magnetization in this material, and its direct
imaging by Kerr rotation microscopy. The observed out-of-plane magnetization is
independent of in-plane magnetic field, linearly proportional to the in-plane
current density, and optimized when the current is orthogonal to the
strain-induced piezoelectric field. These results are fully consistent with a
theoretical model of valley magnetoelectricity driven by Berry curvature
effects. Furthermore, the effect persists at room temperature, opening
possibilities for practical valleytronic devices.",1707.03999v1
2019/3/26,Theoretical method for calculation of effective properties of composite materials with reconfigurable microstructure: electric and magnetic phenomena,"We propose a theoretical approach for calculating effective electric and
magnetic properties of composites with field-dependent restructuring of the
filler. The theory combines the Bruggeman-Landauer approximation extended to a
field-dependent (variable) percolation threshold with the approximate treatment
of nonlinearity of material properties. Theoretical results are compared with
experiments on magnetorheological elastomers, which in the context of
investigated phenomena are often called magnetoactive elastomers (MAEs). In
MAEs with soft polymer matrices, the mutual arrangement of inclusions changes
in an applied magnetic field. This reorganization of the microstructure leads
to unconventionally large changes of electrical and magnetic properties.
Obtained theoretical results describe observed phenomena in MAEs well.
Qualitative agreement between theory and experiment is demonstrated for the
magnetodielectric effect. In the case of magnetic permeability, quantitative
agreement is achieved. The theoretical approach presented can be useful for
development of field-controlled smart materials and design of smart structures
on their basis, because the field dependence of physical properties can be
predicted.",1903.11031v1
2020/9/2,Controlling ligand-mediated exchange interactions in periodically driven magnetic materials,"A periodic drive could alter the effective exchange interactions in magnetic
materials. Here, we explore how exchange pathways affect the effective
interactions of periodically driven magnetic materials. Aiming to apply Floquet
engineering methods to two-dimensional magnetic materials, we consider
realistic models and discuss the effect of a periodic drive on ligand-mediated
exchange interactions. We show that depending on bond angles and the number of
ligand ions involved in the exchange process, drive-induced changes can be very
different from those calculated from direct-hopping models considered earlier.
We study these effects and find that the presence of ligand ions must be taken
into account, especially for TMTCs where ligand ion mediated next-neighbor
interactions play a crucial role in determining the magnetic ground state of
the system.",2009.00813v1
2020/9/23,Thickness dependence of antiferromagnetic phase transition in Heisenberg-type MnPS3,"The behavior of 2-dimensional (2D) van der Waals (vdW) layered magnetic
materials in the 2D limit of the few-layer thickness is an important
fundamental issue for the understanding of the magnetic ordering in lower
dimensions. The antiferromagnetic transition temperature TN of the
Heisenberg-type 2D magnetic vdW material MnPS3 was estimated as a function of
the number of layers. The antiferromagnetic transition was identified by
temperature-dependent Raman spectroscopy, from the broadening of a phonon peak
at 155 cm-1, accompanied by an abrupt redshift and an increase of its spectral
weight. TN is found to decrease only slightly from ~78 K for bulk to ~ 66 K for
3L. The small reduction of TN in thin MnPS3 approaching the 2D limit implies
that the interlayer vdW interaction is playing an important role in stabilizing
magnetic ordering in layered magnetic materials.",2009.10964v1
2021/1/12,Tuning the Magnetic and Electronic Properties of Monolayer VI3 by 3d Transition Metal Doping: A First-Principles Study,"Two-dimensional (2D) materials with robust magnetism have drawn immense
attention for their promising applications in spintronics. Recently, intrinsic
ferromagnetic vanadium triiodide (VI3) has been synthesized experimentally. To
enhance its spintronic property, we modified VI3 by interstitial doping with 3d
transition metals (TM) and used first-principles calculations to investigate
the geometric structure, formation energy, electronic property, and magnetism
of pristine VI3 and 3d TM-doped VI3 monolayer. Among eight transition metal
(Sc-, Ti-, V-, Cr-, Mn-, Fe-, Co-, and Ni-) doped VI3 materials, four of them
(Ti-, V-, Mn-, and Ni-doped VI3) show robust magnetism with full spin
polarization near the Fermi energy. Our research demonstrates that Ti-doped VI3
results in half-metallic semiconductor properties (HMS), while V-doped VI3 and
Ni-doped VI3 result in half-semiconductor properties (HSC). Surprisingly,
Mn-doped VI3 exhibits an unusual bipolar magnetic semiconductor property (BMS).
This unique combination of strong ferromagnetism and 100% spin polarization
with a half-metallic, half-semiconductor, or bipolar semiconductor property
renders 3d TM-doped VI3 as potential candidates for next generation
semiconductor spintronic applications. These spin-polarized materials will be
extremely useful for spin-current generation and other spintronic applications.",2101.05071v2
2021/7/23,Reduced magnetocrystalline anisotropy of CoFe$_2$O$_4$ thin films studied by angle-dependent x-ray magnetic circular dichroism,"Spinel-type CoFe$_2$O$_4$ is a ferrimagnetic insulator with the N\'eel
temperature exceeding 790 K, and shows a strong cubic magnetocrystalline
anisotropy (MCA) in bulk materials. However, when a CoFe$_2$O$_4$ film is grown
on other materials, its magnetic properties are degraded so that so-called
magnetically dead layers are expected to be formed in the interfacial region.
We investigate how the magnetic anisotropy of CoFe$_2$O$_4$ is modified at the
interface of CoFe$_2$O$_4$/Al$_2$O$_3$ bilayers grown on Si(111) using x-ray
magnetic circular dichroism (XMCD). We find that the thinner CoFe$_2$O$_4$
films have significantly smaller MCA values than bulk materials. The reduction
of MCA is explained by the reduced number of Co$^{2+}$ ions at the $O_h$ site
reported by a previous study [Y. K. Wakabayashi $\textit{et al.}$, Phys. Rev. B
$\textbf{96}$, 104410 (2017)].",2107.11204v1
2021/12/2,Strain Engineering of Magnetic Anisotropy in Epitaxial Films of Cobalt Ferrite,"Perpendicular magnetic anisotropy (PMA) energy up to
$K_{\mathrm{u}}=6.1\pm0.8$ MJ m$^{-3}$ is demonstrated in this study by
inducing large lattice-distortion exceeding 3% at room temperature in
epitaxially distorted cobalt ferrite Co$ _{x} $Fe$ _{3-x} $O$ _{4} $ (x = 0.72)
(001) thin films. Although the thin film materials include no rare-earth
elements or noble metals, the observed $ K_{u} $ is larger than that of the
neodymium-iron-boron compounds for high-performance permanent magnets. The
large PMA is attributed to the significantly enhanced magneto-elastic effects,
which are pronounced in distorted films with epitaxial lattice structures upon
introducing a distortion control layer of composition Mg$ _{2-x} $Sn$_{1+x}$O$
_{4} $. Surprisingly, the induced $ K_{u} $ can be quantitatively explained in
terms of the agreement between the local crystal field of Co$ ^{2+} $ and the
phenomenological magneto-elastic model, indicating that the linear response of
induced $K_u$ is sufficiently valid even under lattice distortions as large as
3.2%. Controlling tetragonal lattice deformation using a non-magnetic spinel
layer for ferrites could be a promising protocol for developing materials with
large magnetic anisotropies.",2112.00916v1
2022/2/1,Machine-learning-enhanced quantum sensors for accurate magnetic field imaging,"Local detection of magnetic fields is crucial for characterizing nano- and
micro-materials and has been implemented using various scanning techniques or
even diamond quantum sensors. Diamond nanoparticles (nanodiamonds) offer an
attractive opportunity to chieve high spatial resolution because they can
easily be close to the target within a few 10 nm simply by attaching them to
its surface. A physical model for such a randomly oriented nanodiamond ensemble
(NDE) is available, but the complexity of actual experimental conditions still
limits the accuracy of deducing magnetic fields. Here, we demonstrate magnetic
field imaging with high accuracy of 1.8 $\mu$T combining NDE and machine
learning without any physical models. We also discover the field direction
dependence of the NDE signal, suggesting the potential application for vector
magnetometry and improvement of the existing model. Our method further enriches
the performance of NDE to achieve the accuracy to visualize mesoscopic current
and magnetism in atomic-layer materials and to expand the applicability in
arbitrarily shaped materials, including living organisms. This achievement will
bridge machine learning and quantum sensing for accurate measurements.",2202.00380v1
2022/2/9,First-principles calculations for transient absorption of laser-excited magnetic materials,"We investigate the modification in the optical properties of laser-excited
bulk cobalt and nickel using the time-dependent density functional theory at a
finite electron temperature. As a result of the first-principles simulation, a
complex change in the photoabsorption of the magnetic materials is observed
around the $M_{2,3}$ absorption edge. Based on the microscopic analysis, we
clarify that this complex absorption change consists of the two following
components: (i) the decrease in the photoabsorption in a narrow energy range
around the $M_{2,3}$ edge, which reflects the blue shift of the absorption edge
due to the light-induced demagnetization, and (ii) the increase in the
photoabsorption in a wider range around the $M_{2,3}$ edge, which reflects the
modification in the local-field effect due to the light-induced electron
localization. The relation between the transient optical and magnetic
properties may open a way to monitor ultrafast (de)magnetization and spin
dynamics in magnetic materials via transient absorption spectroscopy.",2202.04226v1
2022/7/21,A micropolar shell model for hard-magnetic soft materials,"Hard-magnetic soft materials (HMSMs) are particulate composites that consist
of a soft matrix embedded with particles of high remnant magnetic induction.
Since the application of an external magnetic flux induces a body couple in
HMSMs, the Cauchy stress tensor in these materials is asymmetric, in general.
Therefore, the micropolar continuum theory can be employed to capture the
deformation of these materials. On the other hand, the geometries and
structures made of HMSMs often possess small thickness compared to the overall
dimensions of the body. Accordingly, in the present contribution, a
10-parameter micropolar shell formulation to model the finite elastic
deformation of thin structures made of HMSMs and subject to magnetic stimuli is
developed. The present shell formulation allows for using three-dimensional
constitutive laws without any need for modification to apply the plane stress
assumption in thin structures. Due to the highly nonlinear nature of the
governing equations, a nonlinear finite element formulation for numerical
simulations is also developed. To circumvent locking at large distortions, an
enhanced assumed strain formulation is adopted. The performance of the
developed formulation is examined in several numerical examples. It is shown
that the proposed formulation is an effective tool for simulating the
deformation of thin bodies made of HMSMs.",2207.10480v2
2023/11/11,Single-Phase L1$_{0}$-Ordered High Entropy Thin Films with High Magnetic Anisotropy,"The vast high entropy alloy (HEA) composition space is promising for
discovery of new material phases with unique properties. We explore the
potential to achieve rare-earth-free high magnetic anisotropy materials in
single-phase HEA thin films. Thin films of FeCoNiMnCu sputtered on thermally
oxidized Si/SiO$_{2}$ substrates at room temperature are magnetically soft,
with a coercivity on the order of 10 Oe. After post-deposition rapid thermal
annealing (RTA), the films exhibit a single face-centered-cubic (fcc) phase,
with an almost 40-fold increase in coercivity. Inclusion of 50 at.% Pt in the
film leads to ordering of a single L1$_{0}$ high entropy intermetallic phase
after RTA, along with high magnetic anisotropy and a 3 orders of magnitude
coercivity increase. These results demonstrate a promising HEA approach to
achieve high magnetic anisotropy materials using RTA.",2311.06618v2
2023/12/4,"Electronic and topological characters of the ideal magnetic topological materials EuAuX with X = P, As, Sb, and Bi","Ideal magnetic topological materials have great significance in both
fundamental physics and technical applications, due to their abundant exotic
quantum properties and facilitation of control. Using first-principles
calculations, we find several ideal magnetic topological materials in EuTX (T =
Cu, Ag, and Au; X= P, As, Sb, and Bi) family. Particularly, EuAuP is the
ferromagnetic Weyl semimetal, and EuAuX (X=As, Sb, and Bi) in their ground
state with in-plane moments are the antiferromagnetic semimetals hosting the
topological gap near the Fermi level. By tuning the magnetic moments to z-axis,
EuAuX (X=As, Sb, and Bi) could further evolve into triple degenerate nodal
points (TDNPs) semimetal states. The main characteristics of antiferromagnetic
TDNP semimetal, including the Fermi arcs, and tangent Fermi surfaces with
opposite spin winding numbers, are also studied. Our work provides a promising
platform to modulate the magnetism, topological electronic structures and
emergent quantum states.",2312.01922v1
2024/1/16,"Influence of temperature, doping, and amorphization on the electronic structure and magnetic damping of iron","Hybrid magnonic quantum systems have drawn increased attention in recent
years for coherent quantum information processing, but too large magnetic
damping is a persistent concern when metallic magnets are used. Their intrinsic
damping is largely determined by electron-magnon scattering induced by
spin-orbit interactions. In the low scattering limit, damping is dominated by
intra-band electronic transitions, which has been theoretically shown to be
proportional to the electronic density of states at the Fermi level. In this
work, we focus on body-centered-cubic iron as a paradigmatic ferromagnetic
material. We comprehensively study its electronic structure using
first-principles density functional theory simulations and account for finite
lattice temperature, boron (B) doping, and structure amorphization. Our results
indicate that temperature induced atomic disorder and amorphous atomic
geometries only have a minor influence. Instead, boron doping noticeably
decreases the density of states near the Fermi level with an optimal doping
level of 6.25%. In addition, we show that this reduction varies significantly
for different atomic geometries and report that the highest reduction
correlates with a large magnetization of the material. This may suggest
materials growth under external magnetic fields as a route to explore in
experiment.",2401.08076v1
2004/4/7,Large Anomalous Hall effect in a silicon-based magnetic semiconductor,"Magnetic semiconductors are attracting high interest because of their
potential use for spintronics, a new technology which merges electronics and
manipulation of conduction electron spins. (GaMn)As and (GaMn)N have recently
emerged as the most popular materials for this new technology. While Curie
temperatures are rising towards room temperature, these materials can only be
fabricated in thin film form, are heavily defective, and are not obviously
compatible with Si. We show here that it is productive to consider transition
metal monosilicides as potential alternatives. In particular, we report the
discovery that the bulk metallic magnets derived from doping the narrow gap
insulator FeSi with Co share the very high anomalous Hall conductance of
(GaMn)As, while displaying Curie temperatures as high as 53 K. Our work opens
up a new arena for spintronics, involving a bulk material based only on
transition metals and Si, and which we have proven to display a variety of
large magnetic field effects on easily measured electrical properties.",0404185v1
2008/8/26,Magnetothermodynamics of the Ising Antiferromagnet Dy2Ge2O7,"We report systematic low temperature measurements of the DC magnetization, AC
susceptibility, and heat capacity of dysprosium pyrogermanate (Dy2Ge2O7) single
crystal and powder samples. Our results confirm that Dy2Ge2O7 is an anisotropic
antiferromagnet. The isothermal field dependent magnetization and the
integrated magnetic entropy both indicate that the Dy3+ ions behave as
Ising-like spins, analogous to those in the pyrochlore spin ice materials. Both
single-spin and collective spin relaxation phenomena appear to lead to spin
freezing in this material, again in analogy to observations in the spin ice
materials, suggesting that such phenomena may be generic to a broader class of
magnetic materials.",0808.3596v1
2014/7/23,Effect of Eu magnetism on the electronic properties of the candidate Dirac material EuMnBi2,"The crystal structure and physical properties of the layered material EuMnBi2
have been characterized by measurements on single crystals. EuMnBi2 is
isostructural with the Dirac material SrMnBi2 based on single crystal x-ray
diffraction, crystallizing in the I4/mmm space group (No. 139). Magnetic
susceptibility measurements suggest antiferromagnetic (AFM) ordering of moments
on divalent Eu ions near T_N=22K. For low fields, the ordered Eu moments are
aligned along the c-axis, and a spin-flop is observed near 5.4T at 5K. The
moment is not saturated in an applied field of 13T at 5K, which is uncommon for
compounds containing Eu^{2+}. The magnetic behavior suggests an anisotropy
enhancement via interaction between Eu and the Mn moments that appear to be
order antiferromagnetically below approximately 310K. A large increase in the
magnetoresistance is observed across the spin-flop, with absolute
magnetoresistance reaching approximately 650% at 5K and 12T. Hall effect
measurements reveal a decrease in the carrier density below T_N, which implies
a manipulation of the Fermi surface by magnetism on the sites surrounding the
Bi square nets that lead to Dirac cones in this family of materials.",1407.6203v1
2016/4/28,The chiral anomaly factory: Creating Weyl fermions with a magnetic field,"Weyl fermions can be created in materials with both time reversal and
inversion symmetry by applying a magnetic field, as evidenced by recent
measurements of anomalous negative magnetoresistance. Here, we do a thorough
analysis of the Weyl points in these materials: by enforcing crystal
symmetries, we classify the location and monopole charges of Weyl points
created by fields aligned with high-symmetry axes. The analysis applies
generally to materials with band inversion in the $T_d$, $D_{4h}$ and $D_{6h}$
point groups. For the $T_d$ point group, we find that Weyl nodes persist for
all directions of the magnetic field. Further, we compute the anomalous
magnetoresistance of field-created Weyl fermions in the semiclassical regime.
We find that the magnetoresistance can scale non-quadratically with magnetic
field, in contrast to materials with intrinsic Weyl nodes. Our results are
relevant to future experiments in the semi-classical regime.",1604.08601v3
2018/12/20,Size-dependent bistability in multiferroic nanoparticles,"Most multiferroic materials with coexisting ferroelectric and magnetic order
exhibit cycloidal antiferromagnetism with wavelength of several nanometers. The
prototypical example is bismuth ferrite (BiFeO$_3$ or BFO), a room-temperature
multiferroic considered for a number of technological applications. While most
applications require small sizes such as nanoparticles, little is known about
the state of these materials when their sizes are comparable to the cycloid
wavelength. This work describes a microscopic theory of cycloidal magnetism in
nanoparticles based on Hamiltonian calculations. It is demonstrated that
magnetic anisotropy close to the surface has a huge impact on the multiferroic
ground state. For certain nanoparticle sizes the modulus of the ferromagnetic
and ferroelectric moments are bistable, an effect that may be used in the
design of ideal memory bits that can be switched electrically and read out
magnetically.",1812.08297v4
2020/4/29,High throughput computational screening for two-dimensional magnetic materials based on experimental databases of three-dimensional compounds,"We perform a computational screening for two-dimensional magnetic materials
based on experimental bulk compounds present in the Inorganic Crystal Structure
Database and Crystallography Open Database. A recently proposed geometric
descriptor is used to extract materials that are exfoliable into
two-dimensional derivatives and we find 85 ferromagnetic and 61
anti-ferromagnetic materials for which we obtain magnetic exchange and
anisotropy parameters using density functional theory. For the easy-axis
ferromagnetic insulators we calculate the Curie temperature based on classical
Monte Carlo simulations of anisotropic Heisenberg models. We find good
agreement with the experimentally reported Curie temperatures of known 2D
ferromagnets and identify 10 potentially exfoliable two-dimensional
ferromagnets that have not been reported previously. In addition, we find 18
easy-axis anti-ferromagnetic insulators with several compounds exhibiting very
strong exchange coupling and magnetic anisotropy.",2004.14460v1
2018/2/14,Moderate Magnetic Field Induced Large Exchange Bias Effect in Ferrimagnetic 314-Sr3YCo4O10.5 Material,"Herein, we report the appearance of a large exchange bias (EB) effect in a
moderate cooling field (cooling field, H$_{FC}$ = 1 kOe) for the
314-Sr3YCo4O10.5 material. The exchange bias has started to appear near room
temperature and reaches a maximum value of 5.5 kOe at 4 K. The existence of
ferrimagnetic clusters in the compensated host in this layered structure
originates the large exchange anisotropy. Remarkably, the observed value of
moderate magnetic field induced exchange bias field is extremely large in
comparison with material systems which are recognized to exhibit giant exchange
bias effect. In combination with the feasibility of room temperature
application, the appearance of large exchange bias in a moderate cooling field
exemplifying the present material system as a promising class of compounds for
designing coherent magnetic materials with huge exchange bias in low/moderate
magnetic field.",1802.05194v1
2022/3/25,Magnetic domain walls of the van der Waals material Fe$_3$GeTe$_2$,"Among two-dimensional materials, Fe$_3$GeTe$_2$ has come to occupy a very
important place owing to its ferromagnetic nature with one of the highest Curie
temperatures among known van der Waals materials and the potential for hosting
skyrmions. In this combined experimental and theoretical work, we investigate
the magnetic bubble domains as well as the microscopic domain wall profile
using spin-polarized scanning tunneling microscopy in combination with
atomistic spin-dynamics simulations performed with parameters from density
functional theory calculations. We find a weak magneto-electric effect
influencing the domain wall width by the electric field in the tunneling
junction and determine the critical magnetic field for the collapse of the
bubble domains. Our findings shed light on the origins of complex magnetism
that Fe$_3$GeTe$_2$ exhibits.",2203.13562v1
2022/10/5,"Ln2(SeO3)2(SO4)(H2O)2 (Ln = Sm, Dy, Yb): A Mixed-Ligand Pathway to New Lathanide (III) Multifunctional Materials Featuring Nonlinear Optical and Magnetic Anisotropy Properties","Bottom-up assembly of optically nonlinear and magnetically anisotropic
lanthanide materials involving precisely placed spin carriers and optimized
metal-ligand coordination offers a potential route to developing electronic
architectures for coherent radiation generation and spin-based technologies,
but the chemical design historically has been extremely hard to achieve. To
address this, we developed a worthwhile avenue for creating new
noncentrosymmetric chiral Ln3+ materials Ln2(SeO3)2(SO4)(H2O)2 (Ln = Sm, Dy,
Yb) by mixed-ligand design. The materials exhibit phase-matching nonlinear
optical responses, elucidating the feasibility of the heteroanionic strategy.
Ln2(SeO3)2(SO4)(H2O)2 displays paramagnetic property with strong magnetic
anisotropy facilitated by large spin-orbit coupling. This study demonstrates a
new chemical pathway for creating previously unknown polar chiral magnets with
multiple functionalities.",2210.02342v1
2022/12/25,Tunable Quantum Anomalous Hall Effects in Ferromagnetic van der Waals Heterostructures,"The quantum anomalous Hall effect (QAHE) has unique advantages in topotronic
applications, but it is still challenging to realize the QAHE with tunable
magnetic and topological properties for building functional devices. Through
systematic first-principles calculations, we predict that the in-plane
magnetization induced QAHE with Chern numbers C = $\pm$1 and the out-of-plane
magnetization induced QAHE with high Chern numbers C = $\pm$3 can be realized
in a single material candidate, which is composed of van der Waals (vdW)
coupled Bi and MnBi$_2$Te$_4$ monolayers. The switching between different
phases of QAHE can be controllable by multiple ways, such as applying strain or
(weak) magnetic field or twisting the vdW materials. The prediction of an
experimentally available material system hosting robust, highly tunable QAHE
will stimulate great research interest in the field. Our work opens a new
avenue for the realization of tunable QAHE and provides a practical material
platform for the development of topological electronics.",2212.12905v2
2022/12/29,Non-volatile Electric Control of Magnetic and Topological Properties of MnBi2Te4 Thin Films,"In this letter, we propose a mechanism to control the magnetic properties of
topological quantum material (TQM) by using magnetoelectric coupling: this
mechanism uses a heterostructure of TQM with two-dimensional (2D) ferroelectric
material, which can dynamically control the magnetic order by changing the
polarization of the ferroelectric material and induce possible topological
phase transitions. This concept is demonstrated using the example of the
bilayer MnBi2Te4 on ferroelectric In2Se3 or In2Te3, where the polarization
direction of the 2D ferroelectrics determines the interfacial band alignment
and consequently the direction of the charge transfer. This charge transfer, in
turn, enhances the stability of the ferromagnetic state of MnBi2Te4 and leads
to a possible topological phase transition between the quantum anomalous Hall
(QAH) effect and the zero plateau QAH. Our work provides a route to dynamically
alter the magnetic ordering of TQMs and could lead to the discovery of new
multifunctional topological heterostructures.",2212.14331v1
2023/3/16,Magnetic Real Chern Insulator in 2D Metal-Organic Frameworks,"Real Chern insulators have attracted great interest, but so far, their
material realization is limited to nonmagnetic crystals and to systems without
spin-orbit coupling. Here, we reveal magnetic real Chern insulator (MRCI) state
in a recently synthesized metal-organic framework material Co3(HITP)2. Its
ground state with in-plane ferromagnetic ordering hosts a nontrivial real Chern
number, enabled by the C2zT symmetry and robust against spin-orbit coupling.
Distinct from previous nonmagnetic examples, the topological corner zero-modes
of MRCI are spin-polarized. Furthermore, under small tensile strains, the
material undergoes a topological phase transition from MRCI to a magnetic
double-Weyl semimetal phase, via a pseudospin-1 critical state. Similar physics
can also be found in closely related materials Mn3(HITP)2 and Fe3(HITP)2, which
are also existing. Possible experimental detections and implications of an
emerging magnetic flat band in the system are discussed.",2303.09218v1
2023/8/28,Multiferroicity in plastically deformed SrTiO$_3$,"A major challenge in the development of quantum technologies is to induce
additional types of ferroic orders into materials that exhibit other useful
quantum properties. Various techniques have been applied to this end, such as
elastically straining, doping, or interfacing a compound with other materials.
Plastic deformation introduces permanent topological defects and large local
strains into a material, which can give rise to qualitatively new
functionality. Here we show via local magnetic imaging that plastic deformation
induces robust magnetism in the quantum paraelectric SrTiO3, in both conducting
and insulating samples. Our analysis indicates that the magnetic order is
localized along dislocation walls and coexists with polar order along the
walls. The magnetic signals can be switched on and off in a controllable manner
with external stress, which demonstrates that plastically deformed SrTiO3 is a
quantum multiferroic. These results establish plastic deformation as a
versatile platform for quantum materials engineering.",2308.14801v1
2023/10/4,Current-driven magnetic resistance in van der Waals spin-filter antiferromagnetic tunnel junctions with MnBi$_2$Te$_4$,"The field of 2D magnetic materials has paved the way for the development of
spintronics and nanodevices with new functionalities. Utilizing
antiferromagnetic materials, in addition to layered van der Waals (vdW)
ferromagnetic materials, has garnered significant interest. In this work, we
present a theoretical investigation of the behavior of MnBi$_2$Te$_4$ devices
based on the non-equilibrium Green's function method. Our results show that the
current-voltage (I-V) characteristics can be influenced significantly by
controlling the length of the device and bias voltage and thus allow us to
manipulate the tunneling magneto-resistance (TMR) with an external bias
voltage. This can be further influenced by the presence of the boron nitride
layer which shows significantly enhanced TMR by selectively suppressing
specific spin channels for different magnetic configurations. By exploiting
this mechanism, the observed TMR value reaches up to 3690\%, which can be
attributed to the spin-polarized transmission channel and the projected local
density of states. Our findings on the influence of structural and magnetic
configurations on the spin-polarized transport properties and TMR ratios give
the potential implementation of antiferromagnetic vdW layered materials in
ultrathin spintronics.",2310.02830v1
2023/10/12,From electronic structure to magnetism and skyrmions (Topical review),"Solid state theory, density functional theory and its generalizations for
correlated systems together with numerical simulations on supercomputers allow
nowadays to model magnetic systems realistically and in detail and can be even
used to predict new materials, paving the way for more rapid material
development for applications in energy storage and conversion, information
technologies, sensors, actuators etc. Modelling magnets on different length
scales (between a few \r{A}ngstr\""om and several micrometers) requires,
however, approaches with very different mathematical formulations. Parameters
defining the material in each formulation can be determined either by fitting
experimental data or from theoretical calculations and there exists a
well-established approach for obtaining model parameters for each length scale
using the information from the smaller length scale. In this review, this
approach will be explained step-by-step in textbook style with examples of
successful multiscale modelling of different classes of magnetic materials from
the research literature as well as based on results newly obtained for this
review.",2310.08628v1
2020/3/5,Quantum anomalous Hall effect in two-dimensional magnetic insulator heterojunctions,"Recent years have witnessed tremendous success in the discovery of
topological states of matter. Particularly, sophisticated theoretical methods
in time-reversal-invariant topological phases have been developed, leading to
the comprehensive search of crystal database and the prediction of thousands of
new topological materials. In contrast, the discovery of magnetic topological
phases that break time reversal is still limited to several exemplary materials
because the coexistence of magnetism and topological electronic band structure
is rare in a single compound. To overcome this challenge, we propose an
alternative approach to realize the quantum anomalous Hall (QAH) effect, a
typical example of magnetic topological phase, via engineering two-dimensional
(2D) magnetic van der Waals heterojunctions. Instead of a single magnetic
topological material, we search for the combinations of two 2D (typically
trivial) magnetic insulator compounds with specific band alignment so that they
can together form a type-III heterojunction with topologically non-trivial band
structure. By combining the data-driven materials search, first principles
calculations, and the symmetry-based analytical models, we identify 8 type-III
heterojunctions consisting of 2D ferromagnetic insulator materials from a
family of 2D monolayer MXY compounds (M = metal atoms, X = S, Se, Te, Y = F,
Cl, Br, I) as a set of candidates for the QAH effect. In particular, we
directly calculate the topological invariant (Chern number) and chiral edge
states in the MnNF/MnNCl heterojunction with ferromagnetic stacking. This work
illustrates how data-driven material science can be combined with
symmetry-based physical principles to guide the search for novel
heterojunction-based quantum materials hosting the QAH effect and other exotic
quantum states in general.",2003.02470v1
1998/7/1,Magnetic Dipole Microwave Emission from Dust Grains,"Thermal fluctuations in the magnetization of interstellar grains will produce
magnetic dipole emission at frequencies below ~100 GHz. We show how to
calculate absorption and emission from small particles composed of magnetic
materials. The Kramers-Kronig relations for a dusty medium are generalized to
include the possibility of magnetic grains. The frequency-dependent magnetic
permeability is discussed for candidate grain materials, including iron and
magnetite.
  We calculate emission spectra for various interstellar grain candidates.
While paramagnetic grains or magnetite grains cannot account for the observed
""anomalous"" emission from dust in the 14-90 GHz range, stronger magnetic dipole
emission will result if a fraction of the grain material is ferromagnetic, as
could be the case given the high Fe content of interstellar dust. The observed
emission from dust near 90 GHz implies that not more than 5% of interstellar Fe
is in the form of metallic iron grains or inclusions (e.g., in ""GEMS"").
However, we show that if most interstellar Fe is in a moderately ferromagnetic
material, it could contribute a substantial fraction of the observed 14-90 GHz
emission, perhaps comparable to the contribution from spinning ultrasmall dust
grains. The two emission mechanisms can be distinguished by measuring the
emission from dark clouds. The expected polarization of magnetic dipole
emission is discussed",9807009v1
1998/2/25,On the T-dependence of the magnetic penetration depth in unconventional superconductors at low temperatures: can it be linear?,"We present a thermodynamics argument against a strictly linear temperature
dependence of the magnetic penetration depth, which applies to superconductors
with arbitrary pairing symmetry at low temperatures.",9802264v1
2001/6/21,"Comment on ""Novel Convective Instabilities in a Magnetic Fluid""","Comment on the paper ""Novel Convective Instabilities in a Magnetic Fluid"" by
W. Luo, T. Du, and J. Huang, Phys. Rev. Lett., v.82, p.4134 (1999).",0106440v1
2004/7/28,"Comment on ""Exchange interaction parameters and adiabatic spin-wave spectra of ferromagnets: A 'renormalized magnetic force theorem'""","This is a comment on publication in Phys. Rev. Lett. 90, 087205 (2003):
``Exchange interaction parameters and adiabatic spin-wave spectra of
ferromagnets: A `renormalized magnetic force theorem'''",0407739v1
2004/9/17,Magnetism in Carbon Structures,"We discuss different magnetic phenomena observed in carbon-based structures,
in particular the diamagnetism, paramagnetism and ferromagnetism observed in
graphite, disordered carbon, fullerenes and irradiated carbon structures.",0409443v1
2005/11/21,"Micromagnetic simulations of absoption spectra in magnetic nanodots, r.f. field perpendicular to the samples' plane","Recently developed eigenvalue method is being used to calculate absorption
spectra in magnetic square nanodots and nanodisks. Obtained results are being
compared with both theoretical and experimental results obtained previously for
such structures.",0511502v1
2006/4/4,Quantum State of Neutrons in Magnetic Thin Films and Superlattices,"An experiment which describes the quantum states of neutrons in magnetic thin
films and superlattices is reviewed.",0604091v1
2008/7/28,Nature of Magnetic Interactions and Inelastic Neutron Scattering as a Probe of Magnetic Excitations in Iron-Pnictide Superconductors,"This submission has been withdrawn by the arXiv admins because it is an
abstract only, which is against arXiv policy.",0807.4351v2
2009/1/23,Chemical reactivity and magnetism of graphene,"The basic problem of weak interaction between odd electrons in graphene is
considered within the framework of broken spin-symmetry approach. The latter
exhibits the peculiarities of the odd electron behavior via both enhanced
chemical reactivity and magnetism.",0901.3757v1
2011/11/23,Siphon flow in a cool magnetic loop,"We investigate the properties of a structure in the solar chromosphere in an
active region to find out whether the feature is consistent with a siphon flow
in a magnetic loop filled with chromospheric material.",1111.5564v1
2014/10/16,Changing the type of superconductivity by magnetic and potential scattering,"By evaluating the upper and thermodynamic critical fields, $H_{c2}$ and
$H_c$, and their ratio $H_{c2}/H_c $ at arbitrary temperatures, we argue that
situations are possible when a type-II material is transformed to type-I by
adding magnetic impurities.",1410.4605v1
2012/10/23,Numerical Simulations of Laser Induced Magnetic Bloch Oscillations,"We propose to use a laser to generate magnetic Bloch oscillations in one
dimensional easy-axis ferromagnets at low temperatures. This proposal is
investigated numerically in details for material parameters relevant for
CoCl2*2H2O.",1210.6200v1
2017/6/13,Novel Exotic Magnetic Spin-order in Co5Ge3 Nano-size Materials,"The Cobalt-germanium (Co-Ge) is a fascinating complex alloy system that has
unique structure and exhibit range of interesting magnetic properties which
would change when reduce to nanoscale dimension. At this experimental work, the
high-aspect-ratio Co5Ge3 nanoparticle with average size of 8nm was synthesized
by gas aggregation-type cluster-deposition technology. The nanostructure
morphology of the as-made binary Co5Ge3 nanoparticles demonstrate excellent
single-crystalline hexagonal structure with mostly preferable growth along
(110) and (102) directions. In contrast the bulk possess Pauli paramagnetic
spin-order at all range of temperature, here we discover size-driven new
magnetic ordering of as-synthesized Co5Ge3 nanoparticles exhibiting
ferromagnetism at room temperature with saturation magnetization of Ms = 32.2
emu/cm3. This is first report of observing such new magnetic spin ordering in
this kind of material at nano-size which the magnetization has lower
sensitivity to thermal energy fluctuation and exhibit high Curie temperature
close to 850 K. This ferromagnetic behavior along with higher Curie temperature
at Co5Ge3 nanoparticles are attributes to low-dimension and quantum-confinement
effect which imposes strong spin coupling and provides a new set of size-driven
spin structures in Co5Ge3 nanoparticle which no such magnetic behavior being
present in the bulk of same material. This fundamental scientific study
provides important insights into the formation, structural, and the magnetic
property of sub 10nm Co5Ge3 nanostructure which shall lead to promising
practical versatile applications for magneto- germanide based nano-devices.",1706.04271v2
2018/8/14,Magnetic nanowires and nanotubes,"We propose a review of the current knowledge about the synthesis, magnetic
properties and applications of magnetic cylindrical nanowires and nanotubes. By
""nano"" we consider diameters reasonably smaller than a micrometer. At this
scale, comparable to micromagnetic and transport length scales, novel
properties appear. At the same time, this makes the underlying physics easier
to understand due to the limiter number of degrees of freedom involved. The
three-dimensional nature and the curvature of these objects contribute also to
their specific properties, compared to patterns flat elements. While the topic
of nanowires and later nanotubes started now decades ago, it is nevertheless
flourishing, thanks to the progress of synthesis, theory and characterization
tools. These give access to ever more complex and thus functional structures,
and also shifting the focus from material-type measurements of large
assemblies, to single-object investigations. We first provide an overview of
common fabrication methods yielding nanowires, nanotubes and structures
engineered in geometry~(change in diameter, shape) or material (segments,
core-shell structures), shape or core-shell. We then review their magnetic
properties: global measurements, magnetization states and switching, single
domain wall statics and dynamics, and spin waves. For each aspect, both theory
and experiments are surveyed. We also mention standard characterization
techniques useful for these. We finally mention emerging applications of
magnetic nanowires and nanotubes, along with the foreseen perspectives in the
topic.",1808.04656v1
2012/8/31,Magnetic symmetry of the plain domain walls in the plates of cubic ferro- and ferrimagnets,"Magnetic symmetry of possible plane domain walls in arbitrary oriented plates
of the crystal of hexoctahedral crystallographic class is considered. The
symmetry classification is applied for ferro- and ferrimagnets.",1209.0004v1
2012/2/16,Symmetry Analysis of Multiferroic Co_3TeO_6,"A phenomenological explanation of the magnetoelectric behavior of Co_3TeO_6
is developed. We explain the second harmonic generation data and the magnetic
field induced spontaneous polarization in the magnetically ordered phase below
20K.",1202.3631v1
2020/9/17,Magnetoelectric near fields,"We consider near field topological singularities originated from magnetic
dipolar mode oscillations in ferrite disk particles.",2009.08084v1
2020/12/22,Field-free deterministic switching of a perpendicularly polarized magnet using unconventional spin-orbit torques in WTe2,"Spin-orbit torque (SOT) driven deterministic control of the magnetization
state of a magnet with perpendicular magnetic anisotropy (PMA) is key to next
generation spintronic applications including non-volatile, ultrafast, and
energy efficient data storage devices. But, field-free deterministic switching
of perpendicular magnetization remains a challenge because it requires an
out-of-plane anti-damping torque, which is not allowed in conventional spin
source materials such as heavy metals (HM) and topological insulators due to
the system's symmetry. The exploitation of low-crystal symmetries in emergent
quantum materials offers a unique approach to achieve SOTs with unconventional
forms. Here, we report the first experimental realization of field-free
deterministic magnetic switching of a perpendicularly polarized van der Waals
(vdW) magnet employing an out-of-plane anti-damping SOT generated in layered
WTe2 which is a low-crystal symmetry quantum material. The numerical
simulations confirm that out-of-plane antidamping torque in WTe2 is responsible
for the observed magnetization switching in the perpendicular direction.",2012.12388v1
2021/8/9,"Spin and Orbital Effects on Asymmetric Exchange Interaction in Polar Magnets: M(IO3)2 (M = Cu, Mn)","We study how spin and orbital effects influence the capability of promoting
Dzyaloshinskii-Moriya (DM) interaction by studying the two magnetic polar
materials, Cu(IO3)2 (S = 1/2 with orbital contribution) and Mn(IO3)2 (S = 5/2
with quenched orbital magnetism) and connecting their electronic and magnetic
properties with their structures. The chemically controlled low-temperature
synthesis of these complexes resulted in pure polycrystalline samples,
providing a viable pathway to prepare bulk forms of transition-metal io-dates.
Rietveld refinements of the powder synchrotron X-ray diffraction data reveal
that these materials exhibit different crystal structures but crystallize in
the same polar and chiral P21 space group, giving rise to an electric
polarization along the b-axis direction. The presence and absence of an evident
phase transition to a possible topologically distinct state observed in
Cu(IO3)2 and Mn(IO3)2, respectively, implies the important role of spin-orbit
coupling. Neutron diffraction experiments reveal helpful insights into the
magnetic ground state of these materials. While the long-wavelength
incommensurability of Cu(IO3)2 is in harmony with orbital effects and
anisotropic magnetic exchange, the commensurate stripe AFM ground state of
Mn(IO3)2 is attributed to quenched orbital angular momentum and isotropic
magnetic coupling. The work demonstrates connections between combined spin and
orbital effects, magnetic coupling dimensionality and DM exchange, providing a
worthwhile approach for tuning asymmetric interaction which promotes evolution
of topologically distinct spin phases.",2108.04290v2
2022/2/6,A semi-empirical analysis of the paramagnetic susceptibility of solid state magnetic clusters,"Recent developments in the synthesis of new magnetic materials lead to the
discovery of new quantum paramagnets. Many of these materials, such as the
perovskites Ba$_{4}$LnMn$_{4}$O$_{12}$ (Ln = Sc or Nb),
Ba$_{3}$Mn$_{2}$O$_{8}$, and Sr$_{3}$Cr$_{2}$O$_{8}$ present isolated magnetic
clusters with strong intracluster interactions but weak intercluster
interactions, which delays the onset of order to lower temperatures ($T$). This
offset between the local energy scale and the magnetic ordering temperature is
the hallmark of magnetic frustration. At sufficient high-$T$, the paramagnetic
susceptibility ($\chi$) of frustrated cluster magnets can be fit to a
Curie-Weiss law, but the derived microscopic parameters cannot in general be
reconciled with those obtained from other methods. In this work, we present an
analytical microscopic theory to obtain $\chi$ of dimer and trimer cluster
magnets, the two most commonly found in literature, making use of suitable
Heisenberg-type Hamiltonians. We also add intercluster interactions in a
mean-field level, thus obtaining an expression to the critical temperature of
the system and defining a new effective frustration parameter $f_{\text{eff}}$.
Our method is exemplified by treating the $\chi$ data of some selected
materials.",2202.02792v1
2022/3/15,Atomic Layer Epitaxy of Kagome Magnet Fe${_3}$Sn${_2}$ and Sn-modulated Heterostructures,"Magnetic materials with kagome crystal structure exhibit rich physics such as
frustrated magnetism, skyrmion formation, topological flat bands, and
Dirac/Weyl points. Until recently, most studies on kagome magnets have been
performed on bulk crystals or polycrystalline films. Here we report the atomic
layer molecular beam epitaxy synthesis of high-quality thin films of
topological kagome magnet Fe${_3}$Sn${_2}$. Structural and magnetic
characterization of Fe${_3}$Sn${_2}$ on epitaxial Pt(111) identifies highly
ordered films with c-plane orientation and an in-plane magnetic easy axis.
Studies of the local magnetic structure by anomalous Nernst effect imaging
reveals in-plane oriented micrometer size domains. Superlattice structures
consisting of Fe${_3}$Sn${_2}$ and Fe${_3}$Sn are also synthesized by atomic
layer molecular beam epitaxy, demonstrating the ability to modulate the sample
structure at the atomic level. The realization of high-quality films by atomic
layer molecular beam epitaxy opens the door to explore the rich physics of this
system and investigate novel spintronic phenomena by interfacing
Fe${_3}$Sn${_2}$ with other materials.",2203.08092v1
2022/5/23,Identifying magnetic antiskyrmions while they form with convolutional neural networks,"Chiral magnets have attracted a large amount of research interest in recent
years because they support a variety of topological defects, such as skyrmions
and bimerons, and allow for their observation and manipulation through several
techniques. They also have a wide range of applications in the field of
spintronics, particularly in developing new technologies for memory storage
devices. However, the vast amount of data generated in these experimental and
theoretical studies requires adequate tools, among which machine learning is
crucial. We use a Convolutional Neural Network (CNN) to identify the relevant
features in the thermodynamical phases of chiral magnets, including
(anti-)skyrmions, bimerons, and helical and ferromagnetic states. We use a
flexible multi-label classification framework that can correctly classify
states in which different features and phases are mixed. We then train the CNN
to predict the features of the final state from snapshots of intermediate
states of a lattice Monte Carlo simulation. The trained model allows
identifying the different phases reliably and early in the formation process.
Thus, the CNN can significantly speed up the large-scale simulations for 3D
materials that have been the bottleneck for quantitative studies so far.
Moreover, this approach can be applied to the identification of mixed states
and emerging features in real-world images of chiral magnets.",2205.11535v2
2022/6/3,Anisotropic Laser-Pulse-Induced Magnetization Dynamics in van der Waals Magnet Fe$_3$GeTe$_2$,"Femtosecond laser-pulse excitation provides an energy efficient and fast way
to control magnetization at the nanoscale, providing great potential for
ultrafast next-generation data manipulation and nonvolatile storage devices.
Ferromagnetic van der Waals materials have garnered much attention over the
past few years due to their low dimensionality, excellent magnetic properties,
and large response to external stimuli. Nonetheless, their behaviour upon fs
laser-pulse excitation remains largely unexplored. Here, we investigate the
ultrafast magnetization dynamics of a thin flake of Fe$_3$GeTe$_2$ (FGT) and
extract its intrinsic magnetic properties using a microscopic framework. We
find that our data is well described by our modelling, with FGT undergoing a
slow two-step demagnetization, and we experimentally extract the
spin-relaxation timescale as a function of temperature, magnetic field and
excitation fluence. Our observations indicate a large spin-flip probability in
agreement with a theoretically expected large spin-orbit coupling, as well as a
weak interlayer exchange coupling. The spin-flip probability is found to
increase when the magnetization is pulled away from its quantization axis,
opening doors to an external control over the spins in this material. Our
results provide a deeper understanding of the dynamics van der Waals materials
upon fs laser-pulse excitation, paving the way towards two-dimensional
materials-based ultrafast spintronics.",2206.01452v1
2022/11/24,A Simplified Method of the Assessment of Magnetic Anisotropy of Commonly Used Sapphire Substrates in SQUID Magnetometers,"Solid state wafers are indispensable components in material science as
substrates for epitaxial homo- or hetero-structures or carriers for
two-dimensional materials. However, a reliable determination of magnetic
properties of nanomaterials in volume magnetometry is frequently affected by
unexpectedly rich magnetism of these substrates, including significant magnetic
anisotropy. Here, we describe a simplified experimental routine of magnetic
anisotropy assessment, which we exemplify and validate for epi-ready sapphire
wafers from various sources. Both the strength and the sign of magnetic
anisotropy is obtained from carefully designed temperature dependent
measurements, which mitigate all known pitfalls of volume SQUID magnetometry
and are substantially faster than traditional approaches. Our measurements
indicate that in all the samples two types of net paramagnetic contributions
coexists with diamagnetism. The first one can be as strong as 10% of the base
diamagnetism of sapphire [-3.7(1) x 10-7 emu/gOe], and, when exceeds 2% mark,
it exhibits pronounced magnetic anisotropy with the easy axis oriented
perpendicularly to the face of c-plane wafers. The other is much weaker but
exhibit ferromagnetic-like appearance. These findings form an important message
that non-standard magnetism of common substrates can significantly influence
the results of precise magnetometry of nanoscale materials and its existence
must be taken for granted by both industry and academia.",2211.13690v1
2023/1/25,Gate-controlled Magnetotransport and Electrostatic Modulation of Magnetism in 2D magnetic semiconductor CrPS$_4$,"Using field-effect transistors (FETs) to explore atomically thin magnetic
semiconductors with transport measurements is difficult, because the very
narrow bands of most 2D magnetic semiconductors cause carrier localization,
preventing transistor operation. Here, we show that exfoliated layers of
CrPS$_4$ -- a 2D layered antiferromagnetic semiconductor whose bandwidth
approaches 1 eV -- allow the realization of FETs that operate properly down to
cryogenic temperature. Using these devices, we perform conductance measurements
as a function of temperature and magnetic field, to determine the full magnetic
phase diagram, which includes a spin-flop and a spin-flip phase. We find that
the magnetoconductance depends strongly on gate voltage, reaching values as
high as 5000 % near the threshold for electron conduction. The gate voltage
also allows the magnetic states to be tuned, despite the relatively large
thickness of the CrPS$_4$ multilayers employed in our study. Our results show
the need to employ 2D magnetic semiconductors with sufficiently large bandwidth
to realize properly functioning transistors, and identify a candidate material
to realize a fully gate-tunable half-metallic conductor.",2301.10535v2
2023/4/29,Evolution of medium-range order and its correlation with magnetic nanodomains in Fe-Dy-B-Nb bulk metallic glasses,"Fe-based metallic glasses are promising functional materials for advanced
magnetism and sensor fields. Tailoring magnetic performance in amorphous
materials requires a thorough knowledge of the correlation between structural
disorder and magnetic order, which remains ambiguous. Two practical
difficulties remain: the first is directly observing subtle magnetic structural
changes on multiple scales, and the second is precisely regulating the various
amorphous states. Here we propose a novel approach to tailor the amorphous
structure through the liquid liquid phase transition. In-situ synchrotron
diffraction has unraveled a medium-range ordering process dominated by
edge-sharing cluster connectivity during the liquid-liquid phase transition.
Moreover, nanodomains with topological order have been found to exist in
composition with liquid-liquid phase transition, manifesting as hexagonal
patterns in small-angle neutron scattering profiles. The liquid-liquid phase
transition can induce the nanodomains to be more locally ordered, generating
stronger exchange interactions due to the reduced Fe-Fe bond and the enhanced
structural order, leading to the increment of saturation magnetization.
Furthermore, the increased local heterogeneity in the medium range scale
enhances the magnetic anisotropy, promoting the permeability response under
applied stress and leading to a better stress-impedance effect. These
experimental results pave the way to tailor the magnetic structure and
performance through the liquid-liquid phase transition.",2305.00274v1
2023/10/23,Experimental signatures of quantum and topological states in frustrated magnetism,"Frustration in magnetic materials arising from competing exchange
interactions can prevent the system from adopting long-range magnetic order and
can instead lead to a diverse range of novel quantum and topological states
with exotic quasiparticle excitations. Here, we review prominent examples of
such emergent phenomena, including magnetically-disordered and extensively
degenerate spin ices, which feature emergent magnetic monopole excitations,
highly-entangled quantum spin liquids with fractional spinon excitations,
topological order and emergent gauge fields, as well as complex particle-like
topological spin textures known as skyrmions. We provide an overview of recent
advances in the search for magnetically-disordered candidate materials on the
three-dimensional pyrochlore lattice and two-dimensional triangular, kagome and
honeycomb lattices, the latter with bond-dependent Kitaev interactions, and on
lattices supporting topological magnetism. We highlight experimental signatures
of these often elusive phenomena and single out the most suitable experimental
techniques that can be used to detect them. Our review also aims at providing a
comprehensive guide for designing and investigating novel frustrated magnetic
materials, with the potential of addressing some important open questions in
contemporary condensed matter physics.",2310.15071v2
2019/1/16,Discovery of Hidden Classes of Layered Electrides by Extensive High-throughput Materials Screening,"Despite their extraordinary properties, electrides are still a relatively
unexplored class of materials with only a few compounds grown experimentally.
Especially for layered electrides, the current researches mainly focus on
several isostructures of Ca2N with similar interlayer two-dimensional (2D)
anionic electrons. An extensive screening for different layered electrides is
still missing. Here, by screening materials with anionic electrons for the
structures in Materials Project, we uncover 12 existing materials as new
layered electrides. Remarkably, these layered electrides demonstrate completely
different properties from Ca2N. For example, unusual fully spin-polarized
zero-dimensional (0D) anionic electrons are shown in metal halides with
MoS2-like structures; unique one-dimensional (1D) anionic electrons are
confined within the tubes of the quasi-1D structures; a coexistence of magnetic
and non-magnetic anionic electrons is found in ZrCl-like structures and a new
ternary Ba2LiN with both 0D and 1D anionic electrons. These materials not only
significantly increase the pool of experimentally synthesizable layered
electrides but also are promising to be exfoliated into advanced 2D materials.",1901.05121v1
2018/5/2,Cold prominence materials detected within magnetic clouds during 1998-2007,"Coronal mass ejections (CMEs) are intense solar explosive eruptions, and they
are frequently correlated with prominence eruptions. Previous observations show
that about $70\%$ of CMEs are associated with prominence eruptions. However,
there are only a handful of reported observations of prominence plasma
materials within interplanetary CMEs (ICMEs), which are the interplanetary
manifestations of CMEs. Moreover, approximately $4\%$ of ICMEs exhibit the
presence of prominence materials, and approximately $12\%$ of magnetic clouds
(MCs) contain prominence materials. We aim to comprehensively search for cold
prominence materials in MCs observed by the Advanced Composition Explorer (ACE)
spacecraft during 1998-2007. Using the criteria of unusual $O^{5+}$ and (or)
$Fe^{6+}$ abundances, we examined 76 MCs observed by ACE during 1998-2007 to
search for cold prominence materials. Our results revealed that out of the 76
MCs, 27 ($36\%$) events contained prominence material regions with
low-charge-state signatures. Although the fraction is still lower than the
approximately $70\%$ of CMEs associated with prominence eruptions, it is much
higher than $12\%$. The unusual $O^{5+}$ and (or) $Fe^{6+}$ abundances may be
simple and reliable criteria to investigate prominence materials in the
interplanetary medium.",1805.01057v1
2020/11/1,First-principles discovery of novel quantum physics and materials: From theory to experiment,"Modern material science has been revolutionized by the discovery of novel
topological states of quantum matter, which sheds new lights on solving
long-standing scientific challenges. However, the exotic quantum phenomena are
typically observable only in rare material systems under extreme experimental
conditions. The search of suitable candidate materials that are able to work at
ambient conditions is thus of crucial importance to both fundamental research
and practical applications. Here we review our recent efforts on
first-principles exploration of novel quantum physics and materials, focusing
on emergent quantum phenomena induced by spin-orbit coupling and its interplay
with magnetism, topology and superconductivity. The first-principles material
design guided by fundamental theory enables the discoveries of several key
quantum materials, including next-generation magnetic topological insulators,
high-temperature quantum anomalous Hall and quantum spin Hall insulators, and
unconventional superconductors. A close collaboration with experiment not only
successfully confirmed most of our theoretical predictions, but also led to
surprising findings for further investigations, which greatly promotes
development of the research field.",2011.00411v1
2023/1/24,Seebeck-driven transverse thermoelectric generation in magnetic hybrid bulk materials,"The Seebeck-driven transverse thermoelectric generation in
magnetic/thermoelectric hybrid materials (STTG) has been investigated in
all-bulk hybrid materials. The transverse thermopower in a ferromagnetic
Co$_2$MnGa/thermoelectric $n$-type Si hybrid bulk material with the adjusted
dimensions reaches 16.0 $\mu$V/K at room temperature with the aid of the STTG
contribution, which is much larger than the anomalous Nernst coefficient of the
Co$_2$MnGa slab (6.8 $\mu$V/K). Although this transverse thermopower is smaller
than the value for previously reported thin-film-based hybrid materials, the
hybrid bulk materials exhibit much larger electrical power owing to their small
internal resistance. This demonstration confirms the validity of STTG in bulk
materials and clarifies its potential as a thermal energy harvester.",2301.09903v1
2023/9/30,Quantum Materials Group Annual Report 2022,"The Quantum Materials group at Indian Institute of Technology Patna is
working on a range of topics relating to nanoelectronics, spintronics, clean
energy and memory design etc. The PI has past experiences of working
extensively with superconducting systems like cuprates [1, 2], ruthanate [3],
pnictide [4, 5], thin film heterostructures [6, 7] etc and magnetic recording
media [8, 9] etc. In this report, we have summarised the ongoing works in our
group. We explored a range of functional materials like two-dimensional
materials, oxides. topological insulators, organic materials etc. using a
combination of experimnetal and computational tools. Some of the useful
highlights are as follows: (a) tuning and control of the magnetic and
electronic state of 2D magentic materials with rapid enhancement in the Curie
temperature, (b) Design and detection of single electron transistor based
nanosensors for the detection of biological species with single molecular
resolution, (c) Observation of non-volatile memory behaviour in the hybrid
structures made of perovskite materials and 2D hybrids. The results offer
useful insight in the design of nanoelectronic architecrures for diverse
applications.",2310.00456v2
2011/9/28,To use or not to use cool superconductors?,"The high critical temperature and magnetic field in cuprates and Fe-based
superconductors are not enough to assure applications at higher temperatures.
Making these superconductors useful involves complex and expensive technologies
to address many conflicting physics and materials requirements.",1109.6307v1
2021/4/6,Noncollinear topological textures in two-dimensional van der Waals materials: From magnetic to polar systems,"In recent years, noncollinear topological textures have long gained
increasing research attentions for their high values of both fundamental
researches and potential applications. The recent discovery of intrinsic orders
in magnetic and polar two-dimensional van der Waals materials provides a new
ideal platform for the investigation of noncollinear topological textures.
Here, we review the theoretical and experimental progresses on noncollinear
topological textures in two-dimensional van der Waals materials in very recent
years. During these years, magnetic skyrmions of both Bloch and N\'eel types
have been observed experimentally in a few two-dimensional van der Waals
materials and related heterostructures. Concurrently, more theoretic
predictions basing on various mechanisms have been reported about different
noncollinear topological textures in two-dimensional van der Waals materials,
such as skyrmions, bimerons, anti-biskyrmions and skyrmionium, which are still
waiting to be confirmed in experiments. Besides, noncollinear topological
electric dipole orders have also been predicted in two-dimensional van der
Waals materials. Taking advantage of the intrinsic two-dimensional nature and
high integratability, the two-dimensional van der Waals materials will play an
important role in the investigation on noncollinear topological textures in
both magnetic and polar systems.",2104.02208v1
2022/11/30,Anomalous magneto-thermoelectric behavior in massive Dirac materials,"Extensive studies of electron transport in Dirac materials have shown
positive magneto-resistance (MR) and positive magneto-thermopower (MTP) in a
magnetic field perpendicular to the excitation current or thermal gradient. In
contrast, measurements of electron transport often show a negative longitudinal
MR and negative MTP for a magnetic field oriented along the excitation current
or thermal gradient; this is attributed to the chiral anomaly in Dirac
materials. Here, we report a very different magneto-thermoelectric transport
behavior in the massive Dirac material ZrTe5. Although thin flakes show a
commonly observed positive MR in a perpendicular magnetic field, distinct from
other Dirac materials, we observe a sharp negative MTP. In a parallel magnetic
field, we still observe a negative longitudinal MR, however, a remarkable
positive MTP is observed for the fields parallel to the thermal gradients. Our
theoretical calculations suggest that this anomalous magneto-thermoelectric
behavior can be attributed to the screened Coulomb scattering. This work
demonstrates the significance of impurity scattering in the electron transport
of topological materials and provides deep insight into the novel
magneto-transport phenomena in Dirac materials.",2211.17027v1
2024/1/8,Ferromagnetic Materials for Josephson π Junctions,"The past two decades have seen an explosion of work on Josephson junctions
containing ferromagnetic materials. Such junctions are under consideration for
applications in digital superconducting logic and memory. In the presence of
the exchange field, spin-singlet Cooper pairs from conventional superconductors
undergo rapid oscillations in phase as they propagate through a ferromagnetic
material. As a result, the ground-state phase difference across a ferromagnetic
Josephson junction oscillates between 0 and $\pi$ as a function of the
thickness of the ferromagnetic material. $\pi$-junctions have been proposed as
circuit elements in superconducting digital logic and in certain qubit designs
for quantum computing. If a junction contains two or more ferromagnetic layers
whose relative magnetization directions can be controlled by a small applied
magnetic field, then the junction can serve as the foundation for a memory
cell. Success in all of those applications requires careful choices of
ferromagnetic materials. Often, materials that optimize magnetic properties do
not optimize supercurrent propagation, and vice versa. In this review we
discuss the significant progress that has been made in identifying and testing
a wide range of ferromagnetic materials in Josephson junctions over the past
two decades. The review concentrates on ferromagnetic metals, partly because
eventual industrial applications of ferromagnetic Josephson junctions will most
likely start with metallic ferromagnets (either in all metal junctions or
junctions containing also an insulating layer). We will briefly mention work on
non-metallic barriers, including ferromagnetic insulators, and some of the
exciting work on spin-triplet supercurrent in junctions containing noncollinear
magnetic inhomogeneity.",2401.04219v2
2019/10/17,"Tunable magnetic order in low-symmetry SeO$_3$ ligand linked $TM_3$(SeO$_3$)$_3$H$_2$O ($TM$ = Mn, Co and Ni) compounds","Generally, one has two strategies to achieve magnetic frustration: through
geometric means or interactions with different length scales. As the former
leads to much simpler theoretical treatments it is favored and so magnetic
sublattices with geometric frustration are sought after. One approach to
finding such lattices is to design them chemically by using non-magnetic linker
ligands. Here we report on the magnetic properties of one such family of
materials, the transition metal ($TM$) selenite hydrate compounds chemical
formula $TM_3$(SeO$_3$)$_3$H$_2$O . These materials link highly distorted
$TM$O$_6$ octahedra via non-magnetic [SeO$_3$]$^{2+}$ linkers. Using $TM$ = Mn,
Co and Ni we report on the structural effects of changing the $TM$ site and how
they may influence the magnetic structure. Using magnetic susceptibility and
neutron powder diffraction we identify low temperature magnetic transitions for
all three compounds characterized by the onset of long-range AFM order with
moderate frustration indexes. Consideration of the magnetic structures reveal
that the magnetic order is sensitive to the $TM$ site ion and is tunable as it
is changed - especially from Mn to Co - with changes in both the moment
direction and the ordering vector. Field dependent susceptibility and heat
capacity measurements reveal metamagnetic transitions in both
Mn$_3$(SeO$_3$)$_3$H$_2$O and Co$_3$(SeO$_3$)$_3$H$_2$O indicating nearby
magnetic ground states accessible under relatively small applied fields.
Density functional theory calculations broadly confirm these results, showing
both a sensitivity of the magnetic structure to the $TM$ and its local
environment. Although no spin liquid behavior is achieved, these results
suggest the fruitfulness of such synthesis philosophies and encourage future
work to engender higher frustration in these materials via doping, field,
pressure or larger linker ligands.",1910.08175v1
2012/7/26,Galactic spiral patterns and dynamo action I: A new twist on magnetic arms,"We generalise the theory of mean-field galactic dynamos by allowing for
temporal non-locality in the mean electromotive force (emf). This arises in
random flows due to a finite response time of the mean emf to changes in the
mean magnetic field, and leads to the telegraph equation for the mean field.
The resulting dynamo model also includes the nonlinear dynamo effects arising
from magnetic helicity balance. Within this framework, coherent large-scale
magnetic spiral arms superimposed on the dominant axially symmetric magnetic
structure are considered. A non-axisymmetric forcing of the mean-field dynamo
by a spiral pattern (either stationary or transient) is invoked, with the aim
of explaining the phenomenon of magnetic arms. For a stationary dynamo forcing
by a rigidly rotating material spiral, we find corotating non-axisymmetric
magnetic modes enslaved to the axisymmetric modes and strongly peaked around
the corotation radius. For a forcing by transient material arms wound up by the
galactic differential rotation, the magnetic spiral is able to adjust to the
winding so that it resembles the material spiral at all times. There are
profound effects associated with the temporal non-locality, i.e. finite `dynamo
relaxation time'. For the case of a rigidly rotating spiral, a finite
relaxation time causes each magnetic arm to mostly lag the corresponding
material arm with respect to the rotation. For a transient material spiral that
winds up, the finite dynamo relaxation time leads to a large, negative (in the
sense of the rotation) phase shift between the magnetic and material arms,
similar to that observed in NGC 6946 and other galaxies. We confirm that
sufficiently strong random seed fields can lead to global reversals of the
regular field along the radius whose long-term survival depends on specific
features of a given galaxy.",1207.6239v2
1999/10/28,Determination of the magnetization scaling exponent for single crystal La$_{0.8}$Sr$_{0.2}$MnO$_3$ by broadband microwave surface impedance measurements,"Employing a broadband microwave reflection configuration, we have measured
the complex surface impedance, $Z_S(\omega,T)$, of single crystal
La$_{0.8}$Sr$_{0.2}$MnO$_3$, as a function of frequency (0.045-45 GHz) and
temperature (250-325 K). Through the dependence of the microwave surface
impedance on the magnetic permeability, $\hat\mu(\omega,T)$, we have studied
the local magnetic behavior of this material, and have extracted the
spontaneous magnetization, $M_0(T)$, in {\em zero applied field}. The broadband
nature of these measurements and the fact that no external field is applied to
the material provide a unique opportunity to analyze the critical behavior of
the spontaneous magnetization at temperatures very close to the ferromagnetic
phase transition. We find a Curie temperature $T_C=305.5\pm 0.5$ K and scaling
exponent $\beta=0.45\pm 0.05$, in agreement with the prediction of mean-field
theory. We also discuss other recent determinations of the magnetization
critical exponent in this and similar materials and show why our results are
more definitive.",9910481v1
2001/10/1,Stability of magnetic vortex in soft magnetic nano-sized circular cylinder,"Stability of magnetic vortex with respect to displacement of its center in a
nano-scale circular cylinder made of soft ferromagnetic material is studied
theoretically. The mode of vortex displacement producing no magnetic charges on
the cylinder side is proposed and the corresponding absolute single-domain
radius of the cylinder is calculated as a function of its thickness and the
exchange length of the material. In cylinders with the radii less than the
single-domain radius the vortex state is unstable and is absolutely prohibited
(except if pinned by material imperfections), so that the distribution of the
magnetization vector in such cylinders in no applied magnetic field is uniform
(or quasi-uniform). The phase diagram of nano-scale cylinders including the
stability line and the metastability region obtained here is presented.",0110037v1
2006/4/28,Magnetic neutron scattering in hole doped cuprate superconductors,"A review is presented of the static and dynamic magnetic properties of
hole-doped cuprate superconductors measured with neutron scattering. A wide
variety of experiments are described with emphasis on the monolayer
La_{2-x}(Sr,Ba)_{x}CuO_{4} and bilayer YBa_{2}Cu_{3}O_{6+x} cuprates. At zero
hole doping, both classes of materials are antiferromagnetic insulators with
large superexchange constants of J > 100 meV. For increasing hole doping, the
cuprates become superconducting at a critical hole concentration of
x_{c}=0.055. The development of new instrumentation at neutron beam sources
coupled with the improvement in materials has lead to a better understanding of
these materials and the underlying spin dynamics over a broad range of hole
dopings. We will describe how the spin dispersion changes across the insulating
to superconducting boundary as well as the static magnetic properties which are
directly coupled with the superconductivity. Experiments directly probing the
competing magnetic and superconducting order parameters involving magnetic
fields, impurity doping, and structural order will be examined. Correlations
between superconductivity and magnetism will also be discussed.",0604667v1
2007/10/3,Theory of stripe domains in magnetic shape memory alloys,"The evolution of multivariant patterns in thin plates of magnetic shape
memory materials with an applied magnetic field was studied theoretically. A
geometrical domain-model is considered composed of straight stripe-like
martensite variants with constant internal magnetization (high anisotropy
limit) and magnetic domain wall orientation fixed by the twin boundaries.
Through integral transforms of the demagnetization energy, the micromagnetic
energy is cast into a form convenient for direct numerical evaluation and
analytical calculations. The equilibrium geometrical parameters of multivariant
patterns with straight and oblique twin boundaries have been derived as
functions of the applied field and the material parameters of a plate. It is
shown that the oblique multivariant states exist only in plates with
thicknesses L larger than a certain critical value L_0. In samples with L < L_0
a magnetic-field-driven transformation occurs directly between single variant
states.",0710.0840v2
2007/10/31,Circular polarimetry reveals helical magnetic fields in the young stellar object HH 135-136,"Magnetic fields are believed to have a vital role in regulating and shaping
the flow of material onto and away from protostars during their initial mass
accretion phase. It is becoming increasingly accepted that bipolar outflows are
generated and collimated as material is driven along magnetic field lines and
centrifugally accelerated off a rotating accretion disk. However, the precise
role of the magnetic field is poorly understood and evidence for its shape and
structure has not been forthcoming. Here we report imaging circular polarimetry
in the near-infrared and Monte Carlo modelling showing that the magnetic field
along the bipolar outflow of the HH 135-136 young stellar object is helical.
The field retains this shape for large distances along the outflow, so the
field structure can also provide the necessary magnetic pressure for
collimation of the outflow. This result lends further weight to the hypothesis
- central to any theory of star formation - that the outflow is an important
instrument for the removal of high-angular-momentum material from the accretion
disk, thereby allowing the central protostar to increase its mass.",0710.5927v1
2007/11/2,Origin of ferromagnetic response in diluted magnetic semiconductors and oxides,"This paper reviews the present understanding of the origin of ferromagnetic
response of diluted magnetic semiconductors and diluted magnetic oxides as well
as in some nominally magnetically undoped materials. It is argued that these
systems can be grouped into four classes. To the first belong composite
materials in which precipitations of a known ferromagnetic, ferrimagnetic or
antiferromagnetic compound account for magnetic characteristics at high
temperatures. The second class forms alloys showing chemical nano-scale phase
separation into the regions with small and large concentrations of the magnetic
constituent. To the third class belong (Ga,Mn)As, heavily doped p-(Zn,Mn)Te,
and related semiconductors. In these solid solutions the theory built on p-d
Zener's model of hole-mediated ferromagnetism and on either the Kohn-Luttinger
kp theory or the multi-orbital tight-binding approach describes qualitatively,
and often quantitatively many relevant properties. Finally, in a number of
carrier-doped DMS and DMO a competition between long-range ferromagnetic and
short-range antiferromagnetic interactions and/or the proximity of the
localisation boundary lead to an electronic nano-scale phase separation.",0711.0340v1
2008/8/13,Magnetic flux penetration and AC loss in a composite superconducting wire with ferromagnetic parts,"The current distribution and the AC loss in a composite superconducting tape
containing a layer from magnetic material is calculated and compared with
experiments, showing a very good agreement. The situations of an alternating
uniform applied field or a transport current are studied. The newly developed
numerical model is an approximation to the critical state model, adapted for
the applicability to commercial finite elements codes that solve the vector
potential. Substantial feature of this procedure is that it can be carried out
in the case when the critical current density in superconductor depends on the
magnetic field and the magnetic layer material is non- linear. Additionally,
the hysteresis loss in the magnetic material is estimated, based on its
measured magnetization loops. Measurements on Bi-2223 multifilamentary tapes
covered on edges by nickel confirmed our predictions, showing a substantial ac
loss reduction in both the investigated regimes.",0808.1790v1
2008/8/21,Theory of the Ordered Phase in A-site Antiferromagnetic Spinels,"Insulating spinel materials, with the chemical formula $AB_2X_4$, behave as
diamond lattice antiferromagnets when only the A-site atom is magnetic. Many
exhibit classic signatures of frustration, induced not geometrically but by
competing first and second neighbor exchange interactions. In this paper, we
further develop a theory of the magnetism of these materials, focusing on the
physics observable within the ordered state. We derive a phenomenological
Landau theory that predicts the orientation of the spins within incommensurate
spiral ordered states. It also describes how the spins reorient in a magnetic
field, and how they may undergo a low temperature ""lock-in"" transition to a
commensurate state. We discuss microscopic mechanisms for these magnetic
anisotropy effects. The reduction of the ordered moment by quantum fluctuations
is shown to be enhanced due to frustration. Our results are compared to
experiments on MnSc_2S_4, the best characterized of such A-site spinels, and
more general implications are discussed. One prediction is that
magnetically-induced ferroelectricity is generic in these materials, and a
detailed description of the relation of the electric polarization to the
magnetism is given.",0808.3010v1
2009/5/29,Ferromagnetic resonance linewidth in ultrathin films with perpendicular magnetic anisotropy,"Transition metal ferromagnetic films with perpendicular magnetic anisotropy
(PMA) have ferromagnetic resonance (FMR) linewidths that are one order of
magnitude larger than soft magnetic materials, such as pure iron (Fe) and
permalloy (NiFe) thin films. A broadband FMR setup has been used to investigate
the origin of the enhanced linewidth in Ni$|$Co multilayer films with PMA. The
FMR linewidth depends linearly on frequency for perpendicular applied fields
and increases significantly when the magnetization is rotated into the film
plane. Irradiation of the film with Helium ions decreases the PMA and the
distribution of PMA parameters. This leads to a great reduction of the FMR
linewidth for in-plane magnetization. These results suggest that fluctuations
in PMA lead to a large two magnon scattering contribution to the linewidth for
in-plane magnetization and establish that the Gilbert damping is enhanced in
such materials ($\alpha \approx 0.04$, compared to $\alpha \approx 0.002$ for
pure Fe).",0905.4779v2
2009/10/16,Heavy fermion material: Ce versus Yb case,"Heavy fermion compounds are complex systems but excellent materials to study
quantum criticality with the switch of different ground states. Here a special
attention is given on the interplay between magnetic and valence instabilities
which can be crossed or approached by tuning the system by pressure or magnetic
field. By contrast to conventional rare earth magnetism or classical s wave
superconductivity, strong couplings may occur with drastic changes in spin or
charge dynamics. Measurements on Ce materials give already a sound basis with
clear key factors; they have pointed out that close to a magnetic or a valence
criticality unexpected phenomena such as unconventional superconductivity, non
Fermi liquid behaviour and the possibility of re-entrance phenomena under
magnetic field. Recent progresses in the growth of Yb heavy fermion compounds
give the perspectives of clear interplays between valence and magnetic
fluctuations and also the possibility to enter in new situations such as
valence transitions inside a sole doublet crystal field ground state.",0910.3110v2
2010/3/1,Switchable Hardening of a Ferromagnet at Fixed Temperature,"The intended use of a magnetic material, from information storage to power
conversion, depends crucially on its domain structure, traditionally crafted
during materials synthesis. By contrast, we show that an external magnetic
field applied transverse to the preferred magnetization of a model disordered
uniaxial ferromagnet is an isothermal regulator of domain pinning. At elevated
temperatures, near the transition into the paramagnet, modest transverse fields
increase the pinning, stabilize the domain structure, and harden the magnet,
until a point where the field induces quantum tunneling of the domain walls and
softens the magnet. At low temperatures, tunneling completely dominates the
domain dynamics and provides an interpretation of the quantum phase transition
in highly disordered magnets as a localization/delocalization transition for
domain walls. While the energy scales of the rare earth ferromagnet studied
here restrict the effects to cryogenic temperatures, the principles discovered
are general and should be applicable to existing classes of highly anisotropic
ferromagnets with ordering at room temperature or above.",1003.0369v1
2010/5/29,Strong magnetic response of submicron Silicon particles in the infrared,"High-permittivity dielectric particles with resonant magnetic properties are
being explored as constitutive elements of new metamaterials and devices in the
microwave regime. Magnetic properties of low-loss dielectric nanoparticles in
the visible or infrared are not expected due to intrinsic low refractive index
of optical materials in these regimes. Here we analyze the dipolar electric and
magnetic response of loss-less dielectric spheres made of moderate permittivity
materials. For low material refractive index there are no sharp resonances due
to strong overlapping between different multipole contributions. However, we
find that Silicon particles with refractive index 3.5 and radius approx. 200nm
present a dipolar and strong magnetic resonant response in telecom and
near-infrared frequencies, (i.e. at wavelengths approx. 1.2-2 micrometer).
Moreover, the light scattered by these Si particles can be perfectly described
by dipolar electric and magnetic fields, quadrupolar and higher order
contributions being negligible.",1005.5446v1
2011/5/26,On the Free Energy of the Flexomagnetoelectric Interactions,"It was shown that free energy density of the local flexomagnetoelectric
effect is determined by the four phenomenological constants in case of the
cubic (hexoctahedral) crystal. The well-known single-constant Lifshitz
invariant term is correct only when fixed electric polarization induces the
inhomogeneity of the magnetization. Proposed phenomenological theory was
applied to the magnetic domain walls. The domain wall structure has been
investigated in details. The four-constant phenomenological theory conforms to
the symmetry based predictions (V.G. Bar'yakhtar et al., 1984). The proposed
experimental verification of the four-constant flexomagnetoelectric
phenomenology is a detection of the shift of the N\'eel domain walls under the
strong homogeneous electric field.",1105.5300v1
2011/9/14,Dipolar interactions in magnetic nanowires aggregates,"We investigate the role of dipolar interactions on the magnetic properties of
nanowires aggregates. Micromagnetic simulations show that dipolar interactions
between wires are not detrimental to the high coercivity properties of magnetic
nanowires composites even in very dense aggregates. This is confirmed by
experimental magnetization measurements and Henkel plots which show that the
dipolar interactions are small. Indeed, we show that misalignment of the
nanowires in aggregates leads to a coercivity reduction of only 30%. Direct
dipolar interactions between nanowires, even as close as 2 nm, have small
effects (maximum coercivity reduction of ~15%) and are very sensitive to the
detailed geometrical arrangement of wires. These results strenghten the
potential of magnetic composite materials based on elongated single domain
particles for the fabrication of permanent magnetic materials.",1109.3174v1
2011/10/17,Investigation of the magnetic phase transition and magnetocaloric properties of the Mn$_2$FeSbO$_6$ ilmenite,"The magnetic phase transition and magnetocaloric properties of mineral and
synthetic melanostibite Mn$_2$FeSbO$_6$ with ilmenite-type structure have been
studied. Mn$_2$FeSbO$_6$ orders ferrimagnetically below 270 K and is found to
undergo a second-order magnetic phase transition. The associated magnetic
entropy change amounts to 1.7 J/kgK for the mineral and 1.8 J/kgK synthetic
melanostibite for 5 T field change. For the synthetic Mn$_2$FeSbO$_6$ the
adiabatic temperature change was estimated from magnetic- and specific heat
measurements and amounts to 0.2 K in 1 T field change. Perspectives of the
promising functional properties of Mn$_2$FeSbO$_6$-based materials are
discussed.",1110.3624v2
2013/10/24,Towards wafer scale inductive determination of magnetostatic and dynamic parameters of magnetic thin films and multilayers,"We investigate an inductive probe head suitable for non-invasive
characterization of the magnetostatic and dynamic parameters of magnetic thin
films and multilayers on the wafer scale. The probe is based on a planar
waveguide with rearward high frequency connectors that can be brought in close
contact to the wafer surface. Inductive characterization of the magnetic
material is carried out by vector network analyzer ferromagnetic resonance.
Analysis of the field dispersion of the resonance allows the determination of
key material parameters such as the saturation magnetization MS or the
effective damping parameter Meff. Three waveguide designs are tested. The
broadband frequency response is characterized and the suitability for inductive
determination of MS and Meff is compared. Integration of such probes in a wafer
prober could in the future allow wafer scale in-line testing of magnetostatic
and dynamic key material parameters of magnetic thin films and multilayers.",1310.6578v1
2014/6/26,Tunable dynamic response of magnetic gels: impact of structural properties and magnetic fields,"Ferrogels and magnetic elastomers feature mechanical properties that can be
reversibly tuned from outside through magnetic fields. Here we concentrate on
the question how their dynamic response can be adjusted. The influence of three
factors on the dynamic behavior is demonstrated using appropriate minimal
models: first, the orientational memory imprinted into one class of the
materials during their synthesis; second, the structural arrangement of the
magnetic particles in the materials; and third, the strength of an external
magnetic field. To illustrate the latter point, structural data are extracted
from a real experimental sample and analyzed. Understanding how internal
structural properties and external influences impact the dominant dynamical
properties helps to design materials that optimize the requested behavior.",1406.6979v2
2014/7/14,Thermal noise induced stochastic resonance in self organizing Fe nanoparticle system,"The natural world is replete with examples of multistable systems, known to
respond to periodic modulations and produce a signal, which exhibits resonance
with noise amplitude. This is a concept not demonstrated in pure materials,
which involve a measured physical property. In a thermoremanent magnetization
experiment with a common magnetic material, Fe, in the nanoparticulate form, we
establish how magnetization in a system of dilute spins during dissipation of
stored magnetic energy, breaks up into spontaneous oscillatory behavior.
Starting at 175 K and aided by temperature (stochastic noise) the oscillation
amplitude goes through a maximum, reminiscent of stochastic resonance. Our
observation of thermal noise induced coherent resonance is due to intrinsic
self-organizing magnetic dynamics of the Fe nanoperticle system without
applying any external periodic force. These results yield new possibilities in
design of magnetic materials and a platform to understand stochastic
interference and phase synchronization in neural activity, as models for neural
communication.",1407.3579v1
2015/1/28,Spin Amplification by Controlled Symmetry Breaking for Spin-Based Logic,"Spin amplification is one of the most critical challenges for spintronics and
spin-based logic in order to achieve spintronic circuits with fan-out. We
propose a new concept for spin amplification that will allow a small spin
current in a non-magnetic spin channel to control the magnetization of an
attached ferromagnet. The key step is to bring the ferromagnet into an unstable
symmetric state (USS), so that a small spin transfer torque from a small spin
current can provide a magnetic bias to control the spontaneous symmetry
breaking and select the final magnetization direction of the ferromagnet. Two
proposed methods for achieving the USS configuration are voltage-controlled
Curie temperature (VC-TC) and voltage-controlled magnetic anisotropy (VC-MA).
We believe the development of new 2D magnetic materials with greater tunability
of VC-TC and VC-MA will be needed for practical applications. A successful
realization of spin amplification by controlled symmetry breaking will be
important for the implementation of existing spin-logic proposals (e.g. ""All
Spin Logic"") and could inspire alternative ideas for spintronic circuits and
devices.",1501.07125v2
2015/3/27,Magnetic properties of defect-free and oxygen-deficient cubic SrCoO$_{3-δ}$,"We investigated theoretically electronic and magnetic properties of the
perovskite material SrCoO$_{3-\delta}$ with $\delta\leq 0.15$ using a
projector-augmented plane-wave method and a Green's function method. This
material is known from various experiments to be ferromagnetic with a Curie
temperature of 260$\,$K to 305$\,$K and a magnetic moment of
1.5${\,\mu_\text{B}}$ to 3.0${\,\mu_\text{B}}$. Applying the magnetic force
theorem as it is formulated within Green's function method, we calculated for
SrCoO$_{3-\delta}$ the magnetic exchange parameters and estimated the Curie
temperature. Including correlation effects by an effective $U$ parameter within
the GGA$+U$ approach and verifying this by hybrid functional calculations, we
obtained the Curie temperatures in dependence of the oxygen deficiency close to
the experimental values.",1503.08009v2
2015/4/25,Relevance of $4f$-$3d$ exchange to finite-temperature magnetism of rare-earth permanent magnets: an ab-initio-based spin model approach for NdFe$_{12}$N,"A classical spin model derived ab initio for rare-earth-based permanent
magnet compounds is presented. Our target compound, NdFe$_{12}$N, is a material
that goes beyond today's champion magnet compound Nd$_{2}$Fe$_{14}$B in its
intrinsic magnetic properties with a simpler crystal structure. Calculated
temperature dependence of the magnetization and the anisotropy field agree with
the latest experimental results in the leading order. Having put the realistic
observables under our numerical control, we propose that engineering
$5d$-electron-mediated indirect exchange coupling between $4f$-electrons in Nd
and $3d$-electrons from Fe would most critically help to enhance the material's
utility over the operation-temperature range.",1504.06697v2
2015/4/30,Theory of neutron scattering by electrons in magnetic materials,"A theory of neutron scattering by magnetic materials is reviewed with
emphasis on the use of electronic multipoles that have universal appeal,
because they are amenable to calculation and appear in theories of many other
experimental techniques. The conventional theory of magnetic neutron
scattering, which dates back to Schwinger (1937) and Trammell (1953), yields an
approximation for the scattering amplitude in terms of magnetic dipoles formed
with the spin (S) and orbital angular momentum (L) of valence electrons. The
so-called dipole-approximation has been widely adopted by researchers during
the past few decades that has seen neutron scattering develop to its present
status as the method of choice for investigations of magnetic structure and
excitations. Looking beyond the dipole-approximation, however, reveals a wealth
of additional information about electronic degrees of freedom conveniently
encapsulated in magnetic multipoles. In this language, the dipole-approximation
retains electronic axial dipoles, S and L. At the same level of approximation
are polar dipoles - called anapoles or toroidal dipoles - allowed in the
absence of a centre of inversion symmetry. Anapoles are examples of
magneto-electric multipoles, time-odd and parity-odd irreducible tensors, that
have come to the fore as signatures of electronic complexity in materials.",1504.08184v1
2015/7/2,Magnetically Responsive PDMS with aligned nickel coated carbon fibres,"We detail a technique to produce actuators able to bear large strain and
respond to an external magnetic field. The material used is PDMS reinforced
with nickel coated carbon fibres. Thanks to the nickel functionalisation, the
fibre orientation can be achieved by embedding the viscous solution into a low
external magnetic field ($<0.2$~T). It is shown that both mechanical and
magnetic properties can be controlled by tailoring the material anisotropy
through properly orientating the reinforcing fibres in the pre-curing phase.
The large strain behaviour is investigated by tensile testing up to 60 % of
deformation and shows a strong dependence on the fibre orientation. The
magnetic properties are investigated by placing beam-like specimens into a
uniform magnetic field. The results show a multistable behaviour with a
transition from a bending-only deformed configuration for the 0$^\circ$ fibres
specimen, to a twisting only configuration, achieved for fibres at 90$^\circ$
whereas all the intermediate angles show both bending and twisting. This
behaviour is accurately captured by the large rotations beam model introduced.
Such an actuator can be used in all applications which require fast response
times and large strain.",1507.00485v1
2015/9/3,Interfacial Magnetism in Complex Oxide Heterostructures Probed by Neutrons and X-rays,"Magnetic complex-oxide heterostructures are of keen interest because a wealth
of phenomena at the interface of dissimilar materials can give rise to
fundamentally new physics and potentially valuable functionalities. Altered
magnetization, novel magnetic coupling and emergent interfacial magnetism at
the epitaxial layered-oxide interfaces are under intensive investigation, which
shapes our understanding on how to utilize those materials, particularly for
spintronics. Neutron and x-ray based techniques have played a decisive role in
characterizing interfacial magnetic structures and clarifying the underlying
physics in this rapidly developing field. Here we review some recent
experimental results, with an emphasis on those studied via polarized neutron
reflectometery and polarized x-ray absorption spectroscopy. We conclude with
some perspectives.",1509.00912v1
2016/9/20,Positive Exchange Bias between Permalloy and Twined (10-10)-Cr2O3 Films,"We report the discovery of a positive exchange bias between Ni80Fe20 (Py) and
twined (10-10)-Cr2O3 film near its blocking temperature (TB) when it is cooled
in an in-plane magnetic field applied along 45 degrees from the two spin
configurations of the Cr atoms. This is an abnormal behavior compared to the
negative exchange bias at all temperatures below TB when the cooling and
measuring magnetic fields are applied along one of the two spin configurations
of the Cr atoms. We speculate these results could be related to the exchange
interactions between the twined structure of the (10-10)-Cr2O3 film epitaxially
grown on the rutile (001)-TiO2 substrate.",1609.06216v1
2017/10/18,Empirical correlation between the interfacial Dzyaloshinskii Moriya interaction and work function in metallic magnetic trilayers,"The Dzyaloshinskii Moriya interaction (DMI) generates intriguing chiral
magnetic objects such as magnetic skyrmions and chiral domain walls that can be
used as building blocks in emerging magnetic nanodevices. To achieve better
stability and functionality of these chiral objects, it is essential to achieve
a larger DMI. In this paper, we report an experimental observation that in
magnetic trilayer films, the DMI strength is mainly determined by the work
functions of the nonmagnetic layers interfaced with the magnetic layer. The
clear correlation with the intrinsic material parameters provides a guideline
for material selection to engineer the DMI strength.",1710.06588v1
2019/8/23,Massively parallel atomistic simulation of ultrafast thermal spin dynamics of a permalloy vortex,"Ultrafast magnetization dynamics probes the most fundamental properties of
magnetic materials, exploring questions about the fundamental interactions
responsible for magnetic phenomena. Thermal effects are known to be extremely
important for laser-induced dynamics in metallic systems, but the dynamics of
topological magnetic structures are little understood. Here we apply a
massively parallel atomistic spin dynamics simulation to study the response of
a permalloy vortex to a 50 fs laser pulse. We find that macroscopically the
short timescale dynamics are indistinguishable from the bulk, but that strong
edge spin waves lead to a complex time evolution of the magnetic structure and
long-lived oscillations on the nanosecond timescale. In the near future such
simulations will provide unprecedented insight into the dynamics of magnetic
materials and devices beyond the approximations of continuum micromagnetics.",1908.08885v1
2012/10/13,To the problem of the intrinsic magnetism in carbon-based systems: pro et contra,"The arguments supporting the existence of the intrinsic magnetism in
carbon-based materials including pure graphene were analyzed critically
together with the numerous experimental evidences denying the magnetism in
these materials. The crucial experiment of Sepioni et al (Phys.Rev.Lett., v.105
p.207205 (2010)) showed clearly that no ferromagnetism was detected in pure
graphene at any temperature down to 2 K. Neither do they found strong
paramagnetism expected due to the massive amount of edge defects. Rather,
graphene is strongly diamagnetic, similar to graphite. Thus the possible traces
of a quasi-magnetic behavior which some authors observed in their samples may
be attributed rather to induced magnetism due to the impurities, defects, etc.
On the basis of the present analysis the conclusion was made that the thorough
and detailed experimental studies of these problems only may shed light on the
very complicated problem of the magnetism of carbon-based materials.",1210.3687v1
2012/10/24,Magnetic phase diagram of CePt3B1-xSix,"We present a study of the main bulk properties (susceptibility,
magnetization, resistivity and specific heat) of CePt_3B_(1-x)Si-x, an alloying
system that crystallizes in a noncentrosymmetric lattice, and derive the
magnetic phase diagram. The materials at the end point of the alloying series
have previously been studied, with CePt_3B established as a material with two
different magnetic phases at low temperatures (antiferromagnetic below T_N =
7.8 K, weakly ferromagnetic below T_C ~ 5 K), while CePt3Si is a heavy fermion
superconductor (T_c = 0.75 K) coexisting with antiferromagnetism (T_N = 2.2 K).
From our experiments we conclude that the magnetic phase diagram is divided
into two regions. In the region of low Si content (up to x ~ 0.7) the material
properties resemble those of CePt3B. Upon increasing the Si concentration
further the magnetic ground state continuously transforms into that of CePt3Si.
In essence, we argue that CePt_3B can be understood as a low pressure variant
of CePt3Si.",1210.6489v3
2017/9/14,Imaging the magnetic states in an actinide ferromagnet UMn$_2$Ge$_2$,"We present studies of the magnetic domain structure of UMn$_2$Ge$_2$ single
crystals using a home-built low temperature magnetic force microscope. The
material has two distinct magnetic ordering temperatures, originating from the
Mn and U moments. At room temperature, where the Mn moments dominate, there are
flower-like domain patterns similar to those observed in uniaxial ferromagnets.
After exposing the sample to a one-tesla magnetic field near 40 K, the
evolution of the magnetic domains are imaged through zero-field warming up to
200 K. Near the ordering temperature of the uranium moments a clear change in
the domain wall motion is observed. The domain size analysis of the flower-like
pattern reveals that the domain structure is consistent with a model of
branching domains.",1709.05007v4
2018/3/22,Large Perpendicular Magnetocrystalline Anisotropy at Fe/Pb(001) interface,"Search for ultrathin magnetic film with large perpendicular
magnetocrystalline anisotropy (PMA) has been inspired for years by the
continuous miniaturization of magnetic units in spintronics devices. The common
magnetic materials used in research and applications are based on Fe because
the pure Fe metal is the best yet simple magnetic material from nature. Through
systematic first-principles calculations, we explored the possibility to
produce large PMA with ultrathin Fe on non-noble and non-magnetic Pb(001)
substrate. Interestingly, huge magnetocrystalline anisotropy energy (MAE) of
7.6 meV was found in Pb/Fe/Pb(001) sandwich structure with only half monolayer
Fe. Analysis of electronic structures reveals that the magnetic proximity
effect at the interface is responsible for this significant enhancement of MAE.
The MAE further increases to 13.6 meV with triply repeated capping Pb and
intermediate Fe layers. Furthermore, the MAE can be tuned conveniently by
charge injection.",1803.08219v1
2018/12/5,Quantum mechanics basis of quality control in hard metals,"Non-destructive and reliable quality control methods are a key aspect to
designing, developing and manufacturing new materials for industrial
applications and new technologies. The measurement of the magnetic saturation
is one of such methods and it is conventionally employed in the cemented
carbides industry. We present a general quantum mechanics based relation
between the magnetic saturation and the components of the binder phase of
cemented carbides, which can be directly employed as a quality control. To
illustrate our results, we calculate the magnetic saturation of a binder phase,
85Ni15Fe binary alloy, using ab-initio methods and compare the theoretical
predictions to the magnetic saturation measurements. We also analyse interface
and segregation effects on the magnetic saturation by studying the electronic
structure of the binder phase. The excellent agreement between calculations and
measurements demonstrates the applicability of our method to any binder phase.
Since the magnetic saturation is employed to ensure the quality of cemented
carbides, the present method allows us to explore new materials for alternative
binder phases efficiently",1812.01960v1
2018/12/18,Twists in Ferromagnetic Monolayers With Trigonal Prismatic Symmetry,"Two-dimensional materials such as graphene or hexagonal boron nitride are
indispensable in industry. The recently discovered 2D ferromagnetic materials
also promise to be vital for applications. In this work, we develop a
phenomenological description of non-centrosymmetric 2D ferromagnets with
trigonal prismatic crystal structure. We chose to study this special symmetry
group since these materials do break inversion symmetry and therefore, in
principle, allow for chiral spin structures such as magnetic helices and
skyrmions. However, unlike all non-centrosymmetric magnets known so far, we
show that the symmetry of magnetic trigonal prismatic monolayers neither allow
for an internal relativistic Dzyaloshinskii-Moriya interaction (DMI) nor a
reactive spin-orbit torque. We demonstrate that the DMI only becomes important
at the boundaries, where it modifies the boundary conditions of the
magnetization and leads to a helical equilibrium state with a helical
wavevector that is inherently linked to the internal spin orientation.
Furthermore, we find that the helical wavevector can be electrically
manipulated via dissipative spin-torque mechanisms. Our results reveal that 2D
magnets offer a large potential for unexplored magnetic effects.",1812.07361v1
2008/11/7,Sources of experimental errors in the observation of nanoscale magnetism,"It has been recently reported that some non-magnetic materials in bulk state,
exhibit magnetic behavior at the nanscale due to surface and size effects. The
experimental observation of these effects is based on the measurement of very
small magnetic signals. Thus, some spurious effects that are not critical for
bulk materials with large magnetic signals may become important when measuring
small signals (typically below 0.0001 emu). Here, we summarize some sources of
these small magnetic signals that should be considered when studying this new
nanomagnetism",0811.1127v3
2010/4/12,Emergence of magnetism in graphene materials and nanostructures,"Magnetic materials and nanostructures based on carbon offer unique
opportunities for future technological applications such as spintronics. This
article reviews graphene-derived systems in which magnetic correlations emerge
as a result of reduced dimensions, disorder and other possible scenarios. In
particular, zero-dimensional graphene nanofragments, one-dimensional graphene
nanoribbons, and defect-induced magnetism in graphene and graphite are covered.
Possible physical mechanisms of the emergence of magnetism in these systems are
illustrated with the help of computational examples based on simple model
Hamiltonians. In addition, this review covers spin transport properties,
proposed designs of graphene-based spintronic devices, magnetic ordering at
finite temperatures as well as the most recent experimental achievements.",1004.2034v1
2010/4/21,Robust isothermal electric switching of interface magnetization: A route to voltage-controlled spintronics,"Roughness-insensitive and electrically controllable magnetization at the
(0001) surface of antiferromagnetic chromia is observed using magnetometry and
spin-resolved photoemission measurements and explained by the interplay of
surface termination and magnetic ordering. Further, this surface in placed in
proximity with a ferromagnetic Co/Pd multilayer film. Exchange coupling across
the interface between chromia and Co/Pd induces an electrically controllable
exchange bias in the Co/Pd film, which enables a reversible isothermal (at room
temperature) shift of the global magnetic hysteresis loop of the Co/Pd film
along the magnetic field axis between negative and positive values. These
results reveal the potential of magnetoelectric chromia for spintronic
applications requiring non-volatile electric control of magnetization.",1004.3763v1
2017/3/13,Artificial control of the bias-voltage dependence of tunnelling anisotropic magnetoresistance using quantization in a single-crystal ferromagnet,"A major issue in the development of spintronic memory devices is the
reduction of the power consumption for the magnetization reversal. For this
purpose, the artificial control of the magnetic anisotropy of ferromagnetic
materials is of great importance. Here, we demonstrate the control of the
carrier-energy dependence of the magnetic anisotropy of the density of states
(DOS) using the quantum size effect in a single-crystal ferromagnetic material,
GaMnAs. We show that the mainly two-fold symmetry of the magnetic anisotropy of
DOS, which is attributed to the impurity band, is changed to a four-fold
symmetry by enhancing the quantum size effect in the valence band of the GaMnAs
quantum wells. By combination with the gate-electric field control technique,
our concept of the usage of the quantum size effect for the control of the
magnetism will pave the way for the ultra-low-power manipulation of
magnetization in future spintronic devices.",1703.04294v1
2017/3/15,Domain engineering of the metastable domains in the 4f-uniaxial-ferromagnet CeRu$_2$Ga$_2$B,"In search of novel, improved materials for magnetic data storage and
spintronic devices, compounds that allow a tailoring of magnetic domain shapes
and sizes are essential. Good candidates are materials with intrinsic
anisotropies or competing interactions, as they are prone to host various
domain phases that can be easily and precisely selected by external tuning
parameters such as temperature and magnetic field. Here, we utilize vector
magnetic fields to visualize directly the magnetic anisotropy in the uniaxial
ferromagnet CeRu$_2$Ga$_2$B. We demonstrate a feasible control both globally
and locally of domain shapes and sizes by the external field as well as a
smooth transition from single stripe to bubble domains, which opens the door to
future applications based on magnetic domain tailoring.",1703.05228v1
2017/3/25,$d^0$ half-metallic ferromagnetism in CaN and CaAs pnictides: An ab initio study,"Conventional magnetism occurs in systems which contain transition metals or
rare earth ions with partially filled $d$ or $f$ shells. It is theoretically
predicted that compounds of groups IA and IIA with IV and V, in some structural
phases, are ferromagnetic half-metals which made them new candidates for
spintronics applications. Employing density functional theory (DFT) we
investigate magnetism in binary compounds CaN and CaAs. Regarding the structure
of analogous magnetic materials and experimental results of CaAs synthesis, we
have considered two cubic structures: rocksalt (RS) and zincblende (ZB), and
four hexagonal structures: NiAs, wurtzite (WZ), anti-NiAs, and NaO. The
calculated results show that CaN in cubic, NiAs, and wurtzite structures, and
CaAs only in zincblende phase have ferromagnetic ground states with a magnetic
moment of $1\mu _B$. Electronic structure analysis of these materials indicates
that magnetism originates from anion $p$ states. Existence of flat $p$ bands
and consequently high density of states at the Fermi level of magnetic
structures gives rise to Stoner spin splitting and spontaneous ferromagnetism.",1703.08691v1
2018/9/13,Spin Model for Nontrivial Magnetic Orders in the Inverse-Perovskite Antiferromagnets,"Nontrivial magnetic orders in the inverse-perovskite manganese nitrides are
theoretically studied by constructing a classical spin model describing the
magnetic anisotropy and frustrated exchange interactions inherent in specific
crystal and electronic structures of these materials. With a replica-exchange
Monte-Carlo technique, a theoretical analysis of this model reproduces the
experimentally observed triangular \Gamma^{5g} and \Gamma^{4g} spin ordered
patterns and the systematic evolution of magnetic orders. Our work solves a
40-year-old problem of nontrivial magnetism for the inverse-perovskite
manganese nitrides and provides a firm basis for clarifying the
magnetism-driven negative thermal expansion phenomenon discovered in this class
of materials.",1809.04740v1
2018/9/17,Electric-Field Control of Magnetic Order: From FeRh to Topological Antiferromagnetic Spintronics,"Using an electric field instead of an electric current (or a magnetic field)
to tailor the electronic properties of magnetic materials is promising for
realizing ultralow energy-consuming memory devices because of the suppression
of Joule heating, especially when the devices are scaled to the nanoscale. In
the review, we summarize recent results on the giant magnetization and
resistivity modulation in a metamagnetic intermetallic alloy - FeRh, which is
achieved by electric-field-controlled magnetic phase transitions in
multiferroic heterostructures. Furthermore, the approach is extended to
topological antiferromagnetic spintronics, which is currently receiving
attention in the magnetic society, and the antiferromagnetic order parameter
has been able to switch back and forth by a small electric field. In the end,
we envision the possibility of manipulating exotic physical phenomena in the
emerging topological antiferromagnetic spintronics field via the electric-field
approach.",1809.06011v1
2020/8/2,Photoinduced Bidirectional Magnetism against Monodirectional Electronics in Square-Antiprismatic Octacyanometalates,"Irradiating ${\rm Cu}_2{\rm Mo}({\rm CN})_8\cdot 8{\rm H}_2{\rm O}$ with blue
light induces a global magnetization, whereas succeeding irradiations with red
or longer-wavelength light demagnetize this material. We solve the
time-dependent Schr\""odinger equation for an extended Hubbard model to
reproduce the photoreversible magnetism. Monitoring the photoinduced
optical-conductivity and angle-resolved-photoemission spectra, we reveal that
the magnetic round trip by way of ferromagnetism is far from a return in terms
of electronics. While visible-light-induced magnetization has never been
observed in the tungsten analog ${\rm Cu}_2{\rm W}({\rm CN})_8\cdot 5{\rm
H}_2{\rm O}$, infrared-light irradiation may magnetize this material as well.",2008.00411v1
2021/4/28,Effect of biaxial strain and hydrostatic pressure on the magnetic properties of bilayer CrI3,"Two-dimensional van der Waals magnetic materials are intriguing for
applications in the future spintronics devices, so it is crucial to explore
strategy to control the magnetic properties. Here, we carried out
first-principles calculations and Monte Carlo simulations to investigate the
effect of biaxial strain and hydrostatic pressure on the magnetic properties of
the bilayer CrI3. We found that the magnetic anisotropy, intralayer and
interlayer exchange interactions, and Curie temperature can be tuned by biaxial
strain and hydrostatic pressure. Large compressive biaxial strain may induce a
ferromagnetic-to-antiferromagnetic transition of both CrI3 layers. The
hydrostatic pressure could enhance the intralayer exchange interaction
significantly and hence largely boost the Curie temperature. The effect of the
biaxial strain and hydrostatic pressure revealed in the bilayer CrI3 may be
generalized to other two-dimensional magnetic materials.",2104.13525v2
2021/5/3,Light-Induced Control of Magnetic Phases in Kitaev Quantum Magnets,"Leveraging coherent light-matter interaction in solids is a promising new
direction towards control and functionalization of quantum materials, to
potentially realize regimes inaccessible in equilibrium and stabilize new or
useful states of matter. We show how driving the strongly spin-orbit coupled
proximal Kitaev magnet $\alpha$-RuCl$_3$ with circularly-polarized light can
give rise to a novel ligand-mediated magneto-electric effect that both
photo-induces a large dynamical effective magnetic field and dramatically
alters the interplay of competing isotropic and anisotropic exchange
interactions. We propose that tailored light pulses can nudge the material
towards the elusive Kitaev quantum spin liquid as well as probe competing
magnetic instabilities far from equilibrium, and predict that the transient
competition of magnetic exchange processes can be readily observed via
pump-probe spectroscopy.",2105.01062v2
2013/11/15,Electric-field-induced strain-mediated magnetoelectric effect in CoFeB-MgO magnetic tunnel junctions,"Magnetoelectric coupling between magnetic and electric dipoles is one of the
cornerstones of modern physics towards developing the most energy-efficient
magnetic data storage. Conventionally, magnetoelectric coupling is achieved in
single-phase multiferroics or in magnetoelectric composite nanostructures
consisting of ferromagnetic and ferroelectric/piezoelectric materials. Here, we
demonstrate an electric-field-induced strain-mediated magnetoelectric effect in
ultrathin CoFeB/MgO magnetic tunnel junction employing non-piezoelectric
material, which is a vitally important structure for spintronic devices, by
using dynamical magnetoelectric and piezoresponse force microscopy measurement
techniques. We show that the applied electric-field induces strain in a few
atomic layers of dielectric MgO which is transferred to magnetostrictive CoFeB
layer, resulting in a magnetoelectric effect of magnitude up to 80.8 V cm-1
Oe-1 under -0.5 V. The demonstrated strain-mediated magnetoelectric effect with
an electric field in magnetic tunnel junctions is a significant step towards
exploring magnetoelectrically controlled spintronic devices for low-power and
high density magnetic data storage applications.",1311.3794v1
2015/2/3,Possible magnetic-polaron-switched positive and negative magnetoresistance in the GdSi single crystal,"Magnetoresistance (MR) has attracted tremendous attention for possible
technological applications. Understanding the role of magnetism in manipulating
MR may in turn steer the searching for new applicable MR materials. Here we
show that antiferromagnetic (AFM) GdSi metal displays an anisotropic positive
MR value (PMRV), up to $\sim$ 415%, accompanied by a large negative thermal
volume expansion (NTVE). Around $T_\text{N}$ the PMRV translates to negative,
down to $\sim$ -10.5%. Their theory-breaking magnetic-field dependencies [PMRV:
dominantly linear; negative MR value (NMRV): quadratic] and the unusual NTVE
indicate that PMRV is induced by the formation of magnetic polarons in 5$d$
bands, whereas NMRV is possibly due to abated electron-spin scattering
resulting from magnetic-field-aligned local 4$f$ spins. Our results may open up
a new avenue of searching for giant MR materials by suppressing the AFM
transition temperature, opposite the case in manganites, and provide a
promising approach to novel magnetic and electric devices.",1502.00774v1
2015/2/12,A new material for probing spin-orbit coupling in Iridates,"We report the structure and magnetic properties of a new iridate compound,
SrxLa11-xIr4O24, where the d-electron count of Ir and therefore its number of
unpaired electrons can be tuned continuously from 5d5 Ir4+ to 5d4 Ir5+, i.e.
from SrLa10Ir4O24 to Sr5La6Ir4O24. The IrO6 octahedra in SrxLa11-xIr4O24 are
isolated from each other and from other transition elements, minimizing band
effects, and the doping is on the framework sites, not the Ir sites, minimizing
the effects of disorder. Measurements of the temperature dependent magnetic
susceptibility are employed to determine the evolution of the Ir magnetic
moment on progressing from 5d5 Ir4+ to 5d4 Ir5+, and are clearly best described
by a transition from a J=1/2 to a J=0 Ir magnetic state; that is, the evolution
of the magnetic susceptibility shows the dominance of spin-orbit coupling in
determining the magnetic properties of a material with highly isolated IrO6
octahedra.",1502.03833v2
2017/12/10,Magnetic field gradient driven dynamics of isolated skyrmions and antiskyrmions in frustrated magnets,"The study of skyrmion/antiskyrmion motion in magnetic materials is very
important in particular for the spintronics applications. In this work, we
study the dynamics of isolated skyrmions and antiskyrmions in frustrated
magnets driven by magnetic field gradient, using the Landau-Lifshitz-Gilbert
simulations on the frustrated classical Heisenberg model on the triangular
lattice. A Hall-like motion induced by the gradient is revealed in bulk system,
similar to that in the well-studied chiral magnets. More interestingly, our
work suggests that the lateral confinement in nano-stripes of the frustrated
system can completely suppress the Hall motion and significantly speed up the
motion along the gradient direction. The simulated results are well explained
by the Thiele theory. It is demonstrated that the acceleration of the motion is
mainly determined by the Gilbert damping constant, which provides useful
information for finding potential materials for skyrmion-based spintronics.",1712.03550v1
2018/11/8,Giant anomalous Nernst effect in the magnetic Weyl semimetal Co3Sn2S2,"In ferromagnetic solids, even in absence of magnetic field, a transverse
voltage can be generated by a longitudinal temperature gradient. This
thermoelectric counterpart of the Anomalous Hall effect (AHE) is dubbed the
Anomalous Nernst effect (ANE). Expected to scale with spontaneous
magnetization, both these effects arise because of the Berry curvature at the
Fermi energy. Here, we report the observation of a giant ANE in a
newly-discovered magnetic Weyl semimetal Co$_3$Sn$_2$S$_2$ crystal. Hall
resistivity and Nernst signal both show sharp jumps at a threshold field and
exhibit a clear hysteresis loop below the ferromagnetic transition temperature.
The ANE signal peaks a maximum value of about 5 miuV/K which is comparable to
the largest seen in any magnetic material. Moreover, the anomalous transverse
thermoelectric conductivity becomes as large as about 10 A/K.m at 70 K, the
largest in known semimetals. The observed ANE signal is much larger than what
is expected according to the magnetization.",1811.03485v2
2019/3/29,Emergence of magnetism in bulk amorphous palladium,"Magnetism in palladium has been the subject of much work and speculation.
Bulk crystalline palladium is paramagnetic with a high magnetic susceptibility.
Palladium under pressure and palladium nanoclusters have generated interest to
scrutinize its magnetic properties. Here we report another possibility:
Palladium may become an itinerant ferromagnet in the amorphous bulk phase at
atmospheric pressure. Atomic palladium is a d$^{10}$ element, whereas bulk
crystalline Pd is a d$^{10-x}$(sp)$^{x}$ material; this, together with the
possible presence of 'unsaturated bonds' in amorphous materials, may explain
the remnant magnetism reported herein. This work presents and discusses
magnetic effects in bulk amorphous palladium.",1904.09166v3
2019/11/6,Surfing multiple conformation-property landscapes via machine learning: Designing magnetic anisotropy,"The advent of computational statistical disciplines, such as machine
learning, is leading to a paradigm shift in the way we conceive the design of
new compounds. Today computational science does not only provide a sound
understanding of experiments, but also can directly design the best compound
for specific applications. This approach, known as reverse engineering,
requires the construction of models able to efficiently predict continuous
structure-property maps. Here we show that reverse engineering can be used to
tune the magnetic properties of a single-ion molecular magnet in an automated
intelligent fashion. We design a machine learning model to predict both the
energy and magnetic properties as function of the chemical structure. Then, a
particle-swarm optimization algorithm is used to explore the conformational
landscapes in the search for new molecular structures leading to an enhanced
magnetic anisotropy. We find that a 5% change in one of the coordination angles
leads to a 50% increase in the anisotropy. Our approach paves the way for a
machine-learning-driven exploration of the chemical space of general classes of
magnetic materials. Most importantly, it can be applied to any
structure-property relation and offers an effective way to automatically
generate new materials with target properties starting from the knowledge of
previously synthesized ones.",1911.02263v1
2020/2/7,Half-magnetization plateau and the origin of threefold symmetry breaking in an electrically-switchable triangular antiferromagnet,"We perform high-field magnetization measurements on the triangular lattice
antiferromagnet Fe$_{1/3}$NbS$_2$. We observe a plateau in the magnetization
centered at approximately half the saturation magnetization over a wide range
of temperature and magnetic field. From density functional theory calculations,
we determine a likely set of magnetic exchange constants. Incorporating these
constants into a minimal Hamiltonian model of our material, we find that the
plateau and of the $Z_3$ symmetry breaking ground state both arise from
interplane and intraplane antiferromagnetic interactions acting in competition.
These findings are pertinent to the magneto-electric properties of
Fe$_{1/3}$NbS$_2$, which allow electrical switching of antiferromagnetic
textures at relatively low current densities.",2002.02960v2
2020/5/6,Robust Magnetoelectric Effect in Decorated Graphene/In2Se3 Heterostructure,"Magnetoelectric effect is a fundamental physics phenomenon that synergizes
electric and magnetic degrees of freedom to generate distinct material
responses like electrically tuned magnetism, which serves as a key foundation
of the emerging field of spintronics. Here, we show by first-principles studies
that ferroelectric (FE) polarization of an In2Se3 monolayer can modulate the
magnetism of an adjacent transition-metal (TM) decorated graphene layer via an
FE induced electronic transition. The TM nonbonding d-orbital shifts downward
and hybridizes with carbon p states near the Fermi level, suppressing the
magnetic moment, under one FE polarization, but on reversed FE polarization
this TM d-orbital moves upward, restoring the original magnetic moment. This
finding of robust magnetoelectric effect in TM decorated graphene/In2Se3
heterostructure offers powerful insights and a promising avenue for
experimental exploration of FE controlled magnetism in 2D materials.",2005.02663v1
2020/5/26,K$_2$CoS$_2$: A new two-dimensional in-plane antiferromagnetic insulator,"The recent discovery of two-dimensional (2D) magnetic materials has brought
magnetism to the flatland. This has opened up exciting opportunities for the
exploration of fundamental physics as well as for novel device applications.
Here, we predict a new thermodynamically stable 2D magnetic material,
K$_2$CoS$_2$, which retains its in-plane anti-ferromagnetic order down to the
monolayer and bilayer limits. We find that the magnetic moments ($2.5
\mu_B/$Co) are aligned along the intra-Co chains, from monolayer to bulk. The
non-magnetic electronic spectrum of both the monolayer and bilayer films is
found to host flat bands and van-Hove singularities, which in instrumental in
giving rise to the the magnetic ground state. Based on classical Monte-Carlo
simulations, we estimate the Neel temperature for the antiferromagnetic
monolayer to be $\approx 15$K. Our study thus establishes that K$_2$CoS$_2$
hosts a robust antiferromagnetic state which persists from the monolayer limit
to the bulk material.",2005.12868v2
2020/6/17,Magnon Polarons induced by a magnetic field gradient,"In this work, we report the theoretical possibility of generating magnon
polaron excitations through a space-varying magnetic field. The spatial
dependence of the magnetic field in the Zeeman interaction gives rise to a
magnon-phonon coupling when a magnetic field gradient is applied, and such a
coupling depends directly on the strength of the gradient. It is also predicted
that the direction of the magnetic field gradient allows control over which
phonon polarization couples to the magnons in the material. Here we develop the
calculations of the magnon-phonon coupling for an arbitrary (anti)ferromagnet,
which are later used to numerically study its consequences. These results are
compared to the ones obtained with the phenomenological magnetoelastic coupling
in YIG, where we show that the magnon polaron bandgap seen in YIG can be also
obtained with a magnetic field gradient of $\sim 0.1$T/m which can be achieved
with the current experimental techniques. Our results propose a new way of
controlling the magnetoelastic coupling in an arbitrary material and open a new
route to exploit the magnon-phonon interaction in magnonic and spintronic
devices.",2006.09839v1
2020/6/19,Room Temperature Magnetocaloric effect in CrTe1-xSbx Alloys,"We investigate the magnetocaloric effect (MCE), relative cooling power (RCP)
and crystalline structure in Sb substituted CrTe_{1-x}Sb_{x} (0 \leq x \leq
0.2) alloy. The Rietveld refinement of the XRD pattern of CrTe1-xSbx showed the
emerging of pure hexagonal NiAs structure with P63/mmc (194) space group with
increasing Sb substitution. We detect a slight increase in the basal plane
a-lattice parameter, with a much larger reduction in the c-axis. Magnetic
isotherms were measured in the temperature range of 50-400K. The results
revealed an increase in the maximum entropy change |S_{M}(T,H)| with
Sb-substitutions in the temperature range (~285-325K). Moreover, The RCP values
increased by about 33% with 20% Sb substitutions. These findings suggest that
CrTe_{1-x}Sb_{x} alloys can be used in room temperature magnetic cooling at
fraction of the coast of pure Gd element the porotype magnetic material for
magnetic refrigeration.",2006.11059v2
2020/9/30,Designing of Magnetic MAB Phases for Energy Applications,"Based on high-throughput density functional theory calculations, we performed
screening for stable magnetic MAB compounds and predicted potential strong
magnets for permanent magnet and magnetocaloric applications. The
thermodynamical, mechanical, and dynamical stabilities are systematically
evaluated, resulting in 21 unreported compounds on the convex hull, and 434
materials being metastable considering convex hull tolerance to be 100
meV/atom. Analysis based on the Hume-Rothery rules revealed that the valence
electron concentration and size factor difference are of significant importance
in determining the stability, with good correspondence with the local atomic
bonding. We found 71 compounds with the absolute value of magneto-crystalline
anisotropy energy above 1.0 MJ/m$^3$ and 23 compounds with a uniaxial
anisotropy greater than 0.4 MJ/m$^3$, which are potential gap magnets. Based on
the magnetic deformation proxy, 99 compounds were identified as potential
materials with interesting magnetocaloric performance.",2009.14543v1
2020/10/3,Vector Potential and Surface Magnetic Field in Magnetoelectric Antiferromagnetic Materials,"A general formula for the average vector potential of bulk periodic systems
is proposed and shown to set the boundary conditions at magnetic interfaces.
For antiferromagnetic materials, the study reveals a unique relation between
the macroscopic potential and the orientation-dependent magnetic quadrupole, as
a result of the different crystalline and magnetic symmetries. In particular,
at surfaces and interfaces of a truncated bulk without inversion and
time-reversal symmetries, the average vector potential exhibits a
discontinuity, which results in an interfacial magnetic field. In general,
however, due to the surface and interface electronic and atomic relaxations,
additional magnetization may result. For the experimentally-observed
magnetoelectric antiferromagnets, in particular, our symmetry analysis suggest
that the relaxation effects could well be a system response to the presence of
such a potential discontinuity.",2010.01372v2
2020/10/18,Light-Induced Static Magnetization: Nonlinear Edelstein Effect,"We theoretically and computationally demonstrate that static magnetization
can be generated under light illumination via nonlinear Edelstein effect
(NLEE). NLEE is applicable to semiconductors under both linearly and circularly
polarized light, and there are no constraints from either spatial inversion or
time-reversal symmetry. Remarkably, magnetization can be induced under linearly
polarized light in nonmagnetic materials. With ab initio calculations, we
reveal several prominent features of NLEE. We find that the orbital
contributions can be significantly greater than the spin contributions. And
magnetization with various orderings, including anti-ferromagnetic,
ferromagnetic, etc., are all realizable with NLEE, which may facilitate many
applications, such as unveiling hidden physical effects, creating a spatially
varying magnetization, or manipulating the magnetization of anti-ferromagnetic
materials. The relationship between NLEE and other magneto-optic effects,
including the inverse Faraday effect and inverse Cotton-Mouton effect, is also
discussed.",2010.09143v2
2020/11/5,Engineering the ligand states by surface functionalization: A new way to enhance the ferromagnetism of CrI3,"The newly discovered 2D magnetic materials provide new opportunities for
basic physics and device applications. However, their low Curie temperature
(TC) is a common weakness. In this paper, by combining magnetic Hamiltonian,
Wannier functions and first-principle calculations, we systematically study the
magnetic properties of monolayer CrI3 functionalized by halogen. The magnetic
exchange coupling (EX) and magnetic anisotropy (MA) are found to increase
significantly by X (X=F, Cl and Br) atom adsorption, and increase along with
the coverage of X atom. In the frame work of superexchange theory, the enhanced
EX can be ascribed to the reduced energy difference and increased hopping
strength between Cr d and I p orbitals, due to the states of I ligand are
engineered by X adatom. Besides, the X adatom may provide additional
ferromagnetic superexchange channel. Finally, the CrI3 that one side is fully
adsorbed by F atoms is found to be a room temperature ferromagnetic
semiconductor with TC=650 K. Our results not only give an insightful
understanding for the enhancement of ferromagnetism of CrI3 by atom adsorption,
but also propose a promising way to improve the ferromagnetism of 2D magnetic
materials.",2011.02775v1
2020/11/11,Characterization of room-temperature in-plane magnetization in thin flakes of CrTe$_2$ with a single spin magnetometer,"We demonstrate room-temperature ferromagnetism with in-plane magnetic
anisotropy in thin flakes of the CrTe$_2$ van der Waals ferromagnet. Using
quantitative magnetic imaging with a single spin magnetometer based on a
nitrogen-vacancy defect in diamond, we infer a room-temperature in-plane
magnetization in the range of $M\sim 27$ kA/m for flakes with thicknesses down
to $20$ nm. In addition, our measurements indicate that the orientation of the
magnetization is not determined solely by shape anisotropy in micron-sized
CrTe$_2$ flakes, which suggest the existence of a non-negligible
magnetocrystalline anisotropy. These results make CrTe$_2$ a unique system in
the growing family of van der Waals ferromagnets, as it is the only material
platform known to date which offers an intrinsic in-plane magnetization and a
Curie temperature above $300$ K in thin flakes.",2011.05722v2
2021/1/29,Magnetization Reversal Mechanism in Exchange-Biased Spring-like Thin-Film Composite,"Development of modern spintronic devices requires materials exhibiting
specific magnetic effects. In this paper, we investigate a magnetization
reversal mechanism in a [Co/Pdx]7/CoO/[Co/Pdy]7 thin-film composite where an
antiferromagnet is sandwiched between a hard and a soft ferromagnets with
different coercivities. The antiferromagnet/ferromagnet interfaces give rise to
the exchange bias effect. The application of soft and hard ferromagnetic films
causes exchange-spring-like behavior while the choice of the Co/Pd multilayers
provides large out-of-plane magnetic anisotropy. We observed that the magnitude
and the sign of the exchange bias anisotropy field are related to the
arrangement of the magnetic moments in the antiferromagnetic layer. This
ordering is induced by the spin orientation present in neighboring
ferromagnetic films which is, in turn, dependent on the orientation and
strength of the external magnetic field.",2101.12495v1
2021/3/1,Frustrated magnet for adiabatic demagnetization cooling to milli-Kelvin temperatures,"Generation of very low temperatures has been crucially important for
applications and fundamental research, as low-temperature quantum coherence
enables operation of quantum computers and formation of exotic quantum states,
such as superfluidity and superconductivity. One of the major techniques to
reach milli-Kelvin temperatures is adiabatic demagnetization refrigeration
(ADR). This method uses almost non-interacting magnetic moments of paramagnetic
salts where large distances suppress interactions between the magnetic ions.
The large spatial separations are facilitated by water molecules, with a
drawback of reduced stability of the material. Here, we show that an
H$_2$O-free frustrated magnet KBaYb(BO$_3$)$_2$ can be ideal refrigerant for
ADR, achieving at least 22\,mK upon demagnetization under adiabatic conditions.
Compared to conventional refrigerants, KBaYb(BO$_3)_2$ does not degrade even
under high temperatures and ultra-high vacuum conditions. Further, its
frustrated magnetic network and structural randomness enable cooling to
temperatures several times lower than the energy scale of magnetic
interactions, which is the main limiting factor for the base temperature of
conventional refrigerants.",2103.00765v1
2021/7/1,New type of half-metallic fully compensated ferrimagnet,"Half-metallic fully compensated ferrimagnets (HM-FCFMs), a special class of
half-metals exhibiting zero magnetization at absolute zero, are promising
candidates for next-generation spintronics applications. For over 25 years,
theoretical studies have been conducted to realize HM-FCFM materials for
practical applications. Herein, we experimentally demonstrate a NiAs-type
hexagonal-structured (CrFe)S compound that could serve as an HM-FCFM material.
It has a half-metallic nature, with 100% spin-polarized Fermi surfaces and zero
magnetization. Further, the magnetization shows a linear behavior as a function
of the magnetic field below the compensation temperature of around 200 K, with
high magnetic coercivity of 38 kOe at 300 K. These magnetic features are
expected to contribute to a quantum leap in the application of HM-FCFM layers
in spintronics devices.",2107.00258v1
2021/11/9,Anomalous response in the orbital magnetic susceptibility of 2D topological systems,"Two-dimensional compounds with non-zero Berry curvature are ideal systems to
study exotic and technologically favourable thermoelectric and magnetoelectric
properties. Within this class of materials, the topological trivial and
non-trivial regimes had to present very different behaviours which are encoded
for the orbital susceptibility and magnetization. In order to try to reveal
them, we have found that it was necessary to introduce a k-dependent mass term
in the relativistic formalism of these materials. Thus, while a topologically
trivial insulator is predicted to have a very limited response, in the
non-trivial regime we unveil a singular contribution to the orbital magnetic
susceptibility which is inversely proportional to the square of the quantum
magnetic flux. In this emergent scenario, besides determining the measurement
conditions we also find a new route for enhancing the intrinsic orbital
magnetism of topological materials widening the range of temperatures and
magnetic fields without involving tiny band gaps.",2111.05021v1
2021/11/30,Spin-voltage-driven efficient terahertz spin currents from the magnetic Weyl semimetals Co$_2$MnGa and Co$_2$MnAl,"Magnetic Weyl semimetals are an emerging material class that combines
magnetic order and a topologically non-trivial band structure. Here, we study
ultrafast optically driven spin injection from thin films of the magnetic Weyl
semimetals Co$_2$MnGa and Co$_2$MnAl into an adjacent Pt layer by means of
terahertz emission spectroscopy. We find that (i) Co$_2$MnGa and Co$_2$MnAl are
efficient terahertz spin-current generators reaching efficiencies of typical
3d-transition-metal ferromagnets such as Fe. (ii) The relaxation of the spin
current provides an estimate of the electron-spin relaxation time of Co$_2$MnGa
(165 fs) and Co$_2$MnAl (102 fs), which is comparable to Fe (92 fs). Both
observations are consistent with a simple analytical model and highlight the
large potential of magnetic Weyl semimetals as spin-current sources in
terahertz spintronic devices. Finally, our results provide a strategy to
identify magnetic materials that provide maximum spin current amplitudes for a
given deposited optical energy density.",2111.15599v1
2022/4/4,Manufacturing of Textured Bulk Fe-SmCo$_{5}$ Magnets by Severe Plastic Deformation,"Exchange-coupling between soft- and hard-magnetic phases plays an important
role in the engineering of novel magnetic materials. To achieve exchange
coupling, a two-phase microstructure is necessary. This interface effect is
further enhanced if both phase dimensions are reduced to the nanometer scale.
At the same time, it is challenging to obtain large sample dimensions. In this
study, powder blends and ball-milled powder blends of Fe-SmCo$_{5}$ are
consolidated and are deformed by high-pressure torsion (HPT), as this technique
allows us to produce bulk magnetic materials of reasonable sizes. Additionally,
the effect of severe deformation by ball-milling and severe plastic deformation
by HPT on exchange coupling in Fe-SmCo$_{5}$ composites is investigated. Due to
the applied shear deformation, it is possible to obtain a texture in both
phases, resulting in an anisotropic magnetic behavior and an improved magnetic
performance.",2204.01383v1
2022/8/25,Computational studies on magnetism and ferroelectricity,"Magnetics, ferroelectrics and multiferroics have attracted great attentions
because they are not only extremely important for investigating fundamental
physics, but also have important applications in information technology. Here,
recent computational studies on magnetism and ferroelectricity are reviewed. We
first give a brief introduction to magnets, ferroelectrics, and multiferroics.
Then, theoretical models and corresponding computational methods for
investigating these materials are presented. In particular, a new method for
computing the linear magnetoelectric coupling tensor without applying an
external field in the first principle calculations is proposed for the first
time. The functionalities of our homemade Property Analysis and Simulation
Package for materials (PASP) and its applications in the field of magnetism and
ferroelectricity are discussed. Finally, we summarize this review and give a
perspective on possible directions of future computational studies on magnetism
and ferroelectricity.",2208.11886v1
2022/9/23,Ferroelectricity controlled chiral spin textures and anomalous valley Hall effect in the Janus magnet-based multiferroic heterostructure,"Realizing effective manipulation and explicit identification of topological
spin textures are two crucial ingredients to make them as information carrier
in spintronic devices with high storage density, high data handling speed and
low energy consumption. Electric-field manipulation of magnetism has been
achieved as a dissipationless method compared with traditional regulations.
However, the magnetization is normally insensitive to the electric field since
it does not break time-reversal symmetry directly, and distribution of
topological magnetic quasiparticles is difficult to maintain due to the drift
arising from external fluctuation, which could result in ambiguous recognition
between quasiparticles and uniform magnetic background. Here, we demonstrate
that electric polarization-driven skyrmionic and uniform ferromagnetic states
can be easily and explicitly distinguished by transverse voltage arising from
anomalous valley Hall effect in the Janus magnet-based multiferroic
heterostructure LaClBr/In2Se3. Our work provides an alternative approach for
data encoding, in which data are encoded by combing topological spin textures
with detectable electronic transport.",2209.11394v1
2022/10/20,A setup for direct measurement of the adiabatic temperature change in magnetocaloric materials,"In order to find a highly efficient, environment-friendly magnetic
refrigerant, direct measurements of the adiabatic temperature change $\Delta
T_{adb}$ is required. Here, in this work, a simple setup for the $\Delta
T_{adb}$ measurement is presented. Using a permanent magnet Halbach array with
a maximum magnetic field of $1.8$ T and a rate of magnetic field change of $5$
T/s, accurate determination of $\Delta T_{adb}$ is possible in this system. The
operating temperature range of the system is from $100$ K to $400$ K, designed
for the characterization of materials with potential for room temperature
magnetic refrigeration applications. Using the setup, the $\Delta T_{adb}$ of a
first-order and a second-order compound have been studied. Results from the
direct measurement for the first-order compound have been compared with $\Delta
T_{adb}$ calculated from the temperature and magnetic field dependent specific
heat data. By comparing results from direct and indirect measurements, it is
concluded that for a reliable characterization of the magnetocaloric effect,
direct measurement of $\Delta T_{adb}$ should be adopted.",2210.11509v1
2022/11/3,Magnetism in Two-Dimensional Ilmenenes: Intrinsic Order and Strong Anisotropy,"Iron ilmenene is a new two-dimensional material that has recently been
exfoliated from the naturally-occurring iron titanate found in ilmenite ore, a
material that is abundant on earth surface. In this work, we theoretically
investigate the structural, electronic and magnetic properties of 2D
transition-metal-based ilmenene-like titanates. The study of magnetic order
reveals that these ilmenenes usually present intrinsic antiferromagnetic
coupling between the 3d magnetic metals decorating both sides of the Ti-O
layer. Furthermore, the ilmenenes based on late 3d brass metals, such as
CuTiO$_3$ and ZnTiO$_3$, become ferromagnetic and spin compensated,
respectively. Our calculations including spin-orbit coupling reveal that the
magnetic ilmenenes have large magnetocrystalline anisotropy energies when the
3d shell departs from being either filled or half-filled, with their spin
orientation being out-of-plane for elements below half-filling of 3d states and
in-plane above. These interesting magnetic properties of ilmenenes make them
useful for future spintronic applications because they could be synthesized as
already realized in the iron case.",2211.01732v1
2022/11/30,Magnetic ground state of the Kitaev Na$_2$Co$_2$TeO$_6$ spin liquid candidate,"As a candidate Kitaev material, Na$_2$Co$_2$TeO$_6$ exhibits intriguing
magnetism on a honeycomb lattice that is believed to be $C_3$-symmetric. Here
we report a neutron diffraction study of high quality single crystals under
$a$-axis magnetic fields. Our data support the less common notion of a magnetic
ground state that corresponds to a triple-$\mathbf{q}$ magnetic structure with
$C_3$ symmetry, rather than the multi-domain zigzag structure typically assumed
in prototype Kitaev spin liquid candidates. In particular, we find that the
field is unable to repopulate the supposed zigzag domains, where the only
alternative explanation is that the domains are strongly pinned by hitherto
unidentified structural reasons. If the triple-$\mathbf{q}$ structure is
correct then this requires reevaluation of many candidate Kitaev materials. We
also find that fields beyond about 10 Tesla suppress the long range
antiferromagnetic order, allowing new magnetic behavior to emerge different
from that expected for a spin liquid.",2211.16941v1
2022/12/16,"Unraveling effects of electron correlation in two-dimensional Fe$_{n}$GeTe$_{2}$ (n=3, 4, 5) by dynamical mean field theory","The Fe$_{n}$GeTe$_{2}$ systems are newly discovered two-dimensional
van-der-Waals materials, exhibiting magnetism at room temperature. The
sub-systems belonging to Fe$_{n}$GeTe$_{2}$ class are special because they show
site-dependent magnetic behavior. We focus on the critical evaluation of
magnetic properties and electron correlation effects in Fe$_{n}$GeTe$_{2}$
($n$= 3, 4, 5) (FGT) systems performing first-principles calculations. Three
different ab-initio approaches have been used, viz., i) standard density
functional theory (DFT), ii) incorporating static electron correlation (DFT+U)
and iii) inclusion of dynamic electron correlation effect (DFT+DMFT). Our
results show that DFT+DMFT is the most accurate technique to correctly
reproduce the magnetic interactions and experimentally observed transition
temperatures. The inaccurate values of structural parameters, magnetic moments
and exchange interactions obtained from DFT+U make this method inapplicable for
the FGT family. Correct determination of magnetic properties for this class of
materials is important since they are promising candidates for spin transport
and spintronic applications at room temperature.",2212.08552v1
2023/1/25,Discovery of spin glass in maple-leaf lattice Na2Mn3O7,"Geometrically frustrated magnetism is commonly studied in triangular and
Kagome lattices. A rare lattice which exhibits frustration is obtained by
depleting 1/7 of the sites from a triangular lattice and is called a maple-leaf
lattice. We report the magnetic properties of an oxide material with a
maple-leaf lattice: Na2Mn3O7. Structural studies suggest slight lattice
distortion and density functional theory predicts energetic near-degeneracy
between ferromagnetism and antiferromagnetic phases which points towards
competing magnetic orderings at low temperatures. In addition, from our
magnetic studies, we discovered a non-equilibrium spin state below ~50 K. The
bifurcation of field-cooled and zero-field-cooled magnetization curves,
hysteresis of ~16 kOe at 2 K, and time-dependent magnetization response is
consistent with a spin glass state. To our knowledge this is the first report
of such a state in materials with a MLL. This is a promising discovery towards
using spin glass to transport angular momentum or spins for applications low
power spintronics.",2301.10399v1
2023/2/6,Landau theory for ferro-paramagnetic phase transition in finitely-strained viscoelastic magnets,"The thermodynamic model of visco-elastic deformable magnetic materials at
finite strains is formulated in a fully Eulerian way in rates. The Landau
theory applies for ferro-to-para-magnetic phase transition, the gradient theory
(leading exchange energy) for magnetization with general mechanically dependent
coefficient, hysteresis in magnetization evolution by Landau-Lifshitz-Gilbert
equation involving objective corotational time derivative of magnetization, and
demagnetizing field are considered in the model. The Kelvin-Voigt viscoelastic
rheology with a higher-order viscosity (exploiting the concept of multipolar
materials) is used, allowing for physically relevant frame-indifferent stored
energies and for local invertibility of deformation. The model complies with
energy conservation and Clausius-Duhem entropy inequality. Existence and a
certain regularity of weak solutions is proved by a Faedo-Galerkin
semi-discretization and a suitable regularization.",2302.02850v1
2023/3/10,Giant periodic pseudo-magnetic fields in strained kagome magnet FeSn epitaxial films on SrTiO$_3$(111) substrate,"Quantum materials, particularly Dirac materials with linearly dispersing
bands, can be effectively tuned by strain-induced lattice distortions leading
to a pseudo-magnetic field that strongly modulates their electronic properties.
Here, we grow kagome magnet FeSn films, consisting of alternatingly stacked
Sn$_2$ honeycomb (stanene) and Fe$_3$Sn kagome layers, on SrTiO$_3$(111)
substrates by molecular beam epitaxy. Using scanning tunneling
microscopy/spectroscopy, we show that the Sn honeycomb layer can be
periodically deformed by epitaxial strain for film thickness below 10 nm,
resulting in differential conductance peaks consistent with Landau levels
generated by a pseudo-magnetic field greater than 1000 T. Our findings
demonstrate the feasibility of strain engineering the electronic properties of
topological magnets at the nanoscale.",2303.05664v1
2023/4/22,Gate-tunable phonon magnetic moment in bilayer graphene,"We develop a first-principles quantum scheme to calculate the phonon magnetic
moment in solids. As a showcase example, we apply our method to study gated
bilayer graphene, a material with strong covalent bonds. According to the
classical theory based on the Born effective charge, the phonon magnetic moment
in this system should vanish, yet our quantum mechanical calculations find
significant phonon magnetic moments. Furthermore, the magnetic moment is highly
tunable by changing the gate voltage. Our results firmly establish the
necessity of the quantum mechanical treatment, and identify small-gap covalent
materials as a promising platform for studying tunable phonon magnetic moment.",2304.11283v1
2023/5/3,Generation of long-ranged spin-triplet pairs across a two-dimensional superconductor/helimagnet van der Waals interface,"The combination of a superconductor with a magnetically inhomogeneous
material has been established as an efficient mechanism for the generation of
long-ranged spin-polarized (spin-triplet) Cooper pairs. Evidence for this
mechanism, however, has been established based on studies done on
three-dimensional systems, where the strong bonds existing at the interface
between the superconductor and the magnetic material should in principle
enhance proximity effects and strengthen any electronic correlations. Here, we
fabricate devices based on van der Waals stacks of flakes of the
two-dimensional superconductor NbS2 combined with flakes of Cr1/3NbS2, which
has a built-in magnetic inhomogeneity due to its helimagnetic spin texture at
low temperatures. We find that the critical temperature of these vdW bilayers
is strongly dependent on the magnetic state of Cr1/3NbS2, whose degree of
magnetic inhomogeneity can be controlled via an applied magnetic field. Our
results demonstrate evidence for the generation of long-ranged spin-triplet
pairs across the Cr1/3NbS2/NbS2 vdW interface.",2305.02216v1
2023/12/15,Hyperbolic Bloch points in ferrimagnetic exchange spring,"Bloch points in magnetic materials are attractive entities in view of
magnetic information transport. Here, Bloch point configuration has been
investigated and experimentally determined in a magnetic trilayer
($Gd_{12}Co_{88}/Nd_{17}Co_{83}/Gd_{24}Co_{76}$) with carefully adjusted
composition within the ferrimagnetic $Gd_{x}Co_{1-x}$ alloys in order to
engineer saturation magnetization, exchange length, and interlayer couplings
(ferromagnetic vs antiferromagnetic). X-ray vector magnetic tomography has
allowed us to determine experimentally Bloch point polarity (related to
topological charge) and Bloch point helicity ${\gamma}$ (determined by
magnetostatic energy). At the bottom layer (close to the ferromagnetic
interface), Bloch points adopt a standard circulating configuration with
helicity ${\gamma}$ close to ${\pi}/2$. Within the top layer (with much lower
saturation magnetization), Bloch points nucleate within a Neel-like exchange
spring domain wall created by the antiferromagnetic coupling and adopt an
uncommon hyperbolic configuration, characterized by much larger helicity
angles. Our results indicate a path for Bloch point engineering in future
applications adjusting material parameters and domain wall characteristics.",2312.09836v1
2024/2/3,Ultrafast magneto-volume effect in transient reflectivity measurements of the chiral magnet MnSi,"Transient reflectivity measurements are an invaluable tool to study ultrafast
thermal processes and contribute to the understanding of electron-lattice
interactions and thermal diffusion, providing key information for the numerical
modeling of thermally-excited ultrafast magnetic phenomena. Accurately
extracting the material's temperature response from transient reflectivity
requires a precise understanding of ultrafast processes influencing
reflectivity, which is challenging in magnetic materials due to the intricate
interplay of electron, charge, and spin degree of freedom. Here, we report
transient reflectivity measurements on MnSi, an archetypical chiral magnet with
strong magnetoelastic coupling. We find unipolar response in the paramagnetic
state and bipolar response in states exhibiting magnetic long-range order.
Comparison with thermal expansion data from literature suggests that the
bipolar response originates in the ultrafast magneto-volume effect due to
magnetoelastic coupling, which enables the extraction of characteristic
timescales of this effect from transient reflectivity. These findings highlight
that magnetoelastic coupling needs to be taken into account for accurately
interpreting the transient reflectivity of magnetic materials, extending the
standard picture of transient reflectivity.",2402.02174v1
2024/2/28,Plasma-induced magnetic phase in 3D $\mathrm{Mn^{II}-Nb^{IV}}$ octacyanidometalate with magnetic sponge behavior,"A new magnetic phase with $T_C = 72 \ \mathrm K$ was obtained by exposing the
three-dimensional $\mathrm{\{ [Mn^{II}(H_2O)_2]_2[Nb^{IV}(CN)_8] \cdot 4H_2O \}
_n}$ coordination ferrimagnet ($T_C = 49 \ \mathrm K$) to air, oxygen,
nitrogen, and argon-based plasma. The X-ray powder diffraction pattern revealed
that the unit cell shrank after plasma treatment, leading to a 20% enhancement
of the superexchange couplings, as estimated from the mean-field approximation
(MFA) model. Although no stable dehydrated form was found in the
thermogravimetric analysis, the observed changes are attributed to the removal
of crystallization water molecules. The plasma-induced magnetic phase could not
be obtained by exposing the studied material to 0% relative humidity during
dynamic vapor sorption. Instead, the material underwent a major structural
reorganization after dehydration, necessitating an extended MFA model to
reproduce the magnetic susceptibility. These findings demonstrate that
plasma-induced changes can create unique magnetic phases in molecule-based
systems that are otherwise unobtainable.",2402.18195v1
2024/3/12,Ferrimagnetic Heusler tunnel junctions with fast spin-transfer torque switching enabled by low magnetization,"Magnetic random access memory that uses magnetic tunnel junction memory cells
is a high performance, non-volatile memory technology that goes beyond
traditional charge-based memories. Today its speed is limited by the high
magnetization of the memory storage layer. Here we show that fast and highly
reliable switching is possible using a very low magnetization ferrimagnetic
Heusler alloy, Mn3Ge. Moreover, the tunneling magnetoresistance is the highest
yet achieved for a ferrimagnetic material at ambient temperature. Furthermore,
the devices were prepared on technologically relevant amorphous substrates
using a novel combination of a nitride seed layer and a chemical templating
layer. These results show a clear path to the lowering of switching currents
using ferrimagnetic Heusler materials and, therefore, to the scaling of high
performance magnetic random access memories beyond those nodes possible with
ferromagnetic devices.",2403.08112v1
2024/4/3,Enhancing Phase Stability and Coercivity of MnAl $τ$-L$1_0$ with Fe and Ni Substitutions: \textit{ab initio} and Micromagnetic Modeling,"The binary manganese aluminium (MnAl) alloy with L$1_0$ crystal structure,
which exhibits exceptional magnetic properties, is a promising rare earth
element free permanent magnet material. However, according to experimental
reports, synthesizing it in a stable bulk form is extremely challenging. Here,
we propose and theoretically verify an alternative method of stabilizing the
material by partially substituting Mn and Al sites by Fe and Ni and identify
its stability, electronic structure, and magnetic properties from density
functional theory (DFT) calculations. When considering a fixed ($50\%$)-Ni, the
magnetic anisotropy increases with the increasing Fe content, but the trend is
opposite in terms of formation energy. The calculated formation energies
demonstrate that all the binary and quaternary compositions are stable. Through
the analysis of calculated elastic constants and phonon frequencies, we confirm
that all compositions are mechanically and dynamically stable. Most
importantly, both magnetic moment and magnetic anisotropy constant in $50\%$-Fe
substituted composition (equiatomic phase) increases significantly as compared
to the MnAl. Predicted coercivity of equiatomic phase is larger than parent
compound obtained by combining DFT computed parameters with micromagnetic
simulations.",2404.03051v1
2001/4/26,A hysteresis model with dipole interaction: one more devil-staircase,"Magnetic properties of 2D systems of magnetic nanoobjects (2D regular
lattices of the magnetic nanoparticles or magnetic nanostripes) are considered.
The analytical calculation of the hysteresis curve of the system with
interaction between nanoobjects is provided. It is shown that during the
magnetization reversal system passes through a number of metastable states. The
kinetic problem of the magnetization reversal was solved for three models. The
following results have been obtained. 1) For 1D system (T=0) with the
long-range interaction with the energy proportional to $r^{-p}$, the
staircase-like shape of the magnetization curve has self-similar character. The
nature of the steps is determined by interplay of the interparticle interaction
and coercivity of the single nanoparticle. 2) The influence of the thermal
fluctuations on the kinetic process was examined in the framework of the
nearest-neighbor interaction model. The thermal fluctuations lead to the
additional splitting of the steps on the magnetization curve. 3) The
magnetization curve for system with interaction and coercivity dispersion was
calculated in mean field approximation. The simple method to experimentally
distinguish the influence of interaction and coercivity dispersion on the
magnetization curve is suggested.",0104507v1
2001/6/20,Convective Instability of Magnetized Ferrofluids: Influence of Magnetophoresis and Soret Effect,"Convective instability in a ferrofluid layer heated from below or from above
in the presence of a uniform vertical magnetic field is investigated
theoretically. Convection is caused by a magnetic mechanism based on the
temperature and concentration dependence of magnetization. An imposed
temperature gradient establishes (by the Soret effect) a concentration gradient
of magnetic particles of which the ferrofluid is composed. Both these gradients
cause a spatial variation in magnetization, which induces a gradient of
magnetic field intensity within the fluid layer. The field gradient induces in
its turn an additional redistribution of magnetic grains due to
magnetophoresis. Resulting self-consistent magnetic force tries to mix the
fluid. A linear stability analysis predicts oscillatory instability in a
certain region of the magnetic field strength and the fluid parameters. The
instability owes magneto- and thermophoresis its origin: were the particle
diffusion not operative, then only stationary instability would occur. A
discovery of predicted convective oscillations is expected in ferrofluid layers
about 1 mm thick, where the buoyancy mechanism is negligible and the
characteristic diffusion time is not too long.",0106413v1
2002/4/14,Large nonzero-moment magnetic strings in antiferromagnetic crystals of the manganite type,"The magnetic strings in antiferromagnetic crystals with the spin $S = 1 /2$
differ from the magnetic polarons (ferrons) by the absence of the additional
magnetic moment. We show that in the $S > 1 /2$ double exchange crystals with
the antiferromagnetic $s-d$ exchange, a new type of magnetic strings appears,
which possesses a magnetic moment. It is concentrated at the center of the
string, and the magnetized string is, in its essence, the state intermediate
between the string and the ferron. In antiferromagnetic manganites, this moment
is by an order of magnitude larger than that of a magnetic atom. Unlike the
conventional ferrons, the magnetization of the strings exists at any parameters
of the crystals under consideration. We argue that this new type of magnetic
state can be relevant to some doped antiferromagnets including manganites.",0204308v1
1999/9/9,Thermodynamics of Magnets,"Thermodynamics of magnetic materials is discussed in practical, lab-oriented
terms. In the common experimental configuration in which the external magnetic
field comes from a solenoidal coil connected to a power supply, magnetic work
is identified unambiguously as the flow of electromagnetic field energy from
the power supply into the system via the connecting wires. A simple algebraic
expression is derived for the ""magnetic energy"" of microscopic dipoles which
interact with the magnetic fields produced by each other, by an external coil,
or by a permanent magnet. The discussion delineates the important distinction
between induced magnetic moments, which are diamagnetic, and permanent
microscopic moments, which are paramagnetic. The practicality of these ideas is
illustrated by calculations of the magnetic properties of several idealized
magnetic solids via minimization of the appropriate free energy.",9909018v2
2007/10/3,Magnetic and Electric Excitations in Split Ring Resonators,"We studied the electric and magnetic resonance of U-shaped SRRs. We showed
that higher order excitation modes exist in both of the electric and magnetic
resonances. The nodes in the current distribution were found for all the
resonance modes. It turns out that the magnetic resonances are the modes with
odd-number of half-wavelength of the current wave, i.e. 1/2, 3/2 and 5/2
wavelengths modes, and the electric resonances are modes with integer number of
whole-wavelength of current wave, i.e. 1, 2 and 3 wavelengths modes. We
discussed the electric moment and magnetic moment of the electric and magnetic
resonances, and their dependence to the length of two parallel side arms. We
show that the magnetic moment of magnetic resonance vanishes as the length side
arms of the SRR reduces to zero, i.e. a rod does not give any magnetic moment
or magnetic resonance.",0710.0812v2
2008/10/1,Lattice disorder and Ferromagnetism in La0.67Ca0.33MnO3 nanoparticle,"We study the ferromagnetism of La0.67Ca0.33MnO3 in bulk polycrystalline,
nanocrystalline and amorphous phase. The structural change from crystalline
phase to amorphous phase exhibited a systematic decrease of TC(paramagnetic to
ferromagnetic transition temperature) and spontaneous magnetization (MS). The
experimental results suggested few more features, e.g., appearance of large
magnetic irreversibility in the temperature dependence of magnetization, lack
of magnetic saturation at high magnetic field, blocking of magnetization below
TB, and enhancement of coercivity. In addition, the magnetic phase transition
near to TC has changed from first order character in bulk sample to second
order character in nanocrystalline and amorphous samples. We understand the
observed magnetic features as the effects of decreasing particle size and
increasing magnetic (spin- lattice) disorder. We noted that magnetic dynamics
of amorphous samples is distinctly different from the nanocrystalline samples.
The ferromagnetism of amorphous samples are comparable with the properties of
reported amorphous ferromagnetic nanoparticles. We also demonstrate the effect
of disorder shell in controlling the dynamics of ferromagnetic cores.",0810.0090v1
2008/10/10,Anomalous Magnetic Properties in Ni50Mn35In15,"We present here a comprehensive investigation of the magnetic ordering in
Ni50Mn35In15 composition. A concomitant first order martensitic transition and
the magnetic ordering occurring in this off-stoichiometric Heusler compound at
room temperature signifies the multifunctional character of this magnetic shape
memory alloy. Unusual features are observed in the dependence of the
magnetization on temperature that can be ascribed to a frustrated magnetic
order. It is compelling to ascribe these features to the cluster type
description that may arise due to inhomogeneity in the distribution of magnetic
atoms. However, evidences are presented from our ac susceptibility, electrical
resistivity and dc magnetization studies that there exists a competing
ferromagnetic and antiferromagnetic order within crystal structure of this
system. We show that excess Mn atoms that substitute the In atoms have a
crucial bearing on the magnetic order of this compound. These excess Mn atoms
are antiferromagnetically aligned to the other Mn, which explains the peculiar
dependence of magnetization on temperature.",0810.1850v1
2009/1/14,Effect of the applied magnetic field on formation of complex polyaniline films,"Formation of complex polyaniline (PANI) films with diamagnetic TCNQ and
paramagnetic metal ion impurities cast under applied magnetic field was
studied. It has been found that the applied magnetic field affects interaction
of PANI chains with the impurities and induces formation of magnetically
ordered regions in the complex film doped by paramagnetic metal ions in
contrast to the reference film of the same composition but prepared under
ambient conditions. The magnetically ordered regions have been observed
directly by scanning magnetic force microscopy. It was found a correlation in
distribution of the magnetically ordered regions and peculiarities of the
surface relief of a film. Electronic absorption spectra and conductivity
measurements showed that an applied stationary magnetic field can suppress the
interaction of PANI chains and paramagnetic metal ions and lowers conductivity
of the resulting complex film up to one order of magnitude as compared with the
reference film. An alternating magnetic field was found to improve interaction
of PANI and diamagnetic TCNQ molecules. The mechanisms of the magnetic field
influence on the complex film formation are discussed.",0901.2028v1
2009/2/23,High-field muSR studies of superconducting and magnetic correlations in cuprates above Tc,"The advent of high transverse-field muon spin rotation (TF-muSR) has led to
recent muSR investigations of the magnetic-field response of cuprates above the
superconducting transition temperature T_c. Here the results of such
experiments on hole-doped cuprates are reviewed. Although these investigations
are currently ongoing, it is clear that the effects of high field on the
internal magnetic field distribution of these materials is dependent upon a
competition between superconductivity and magnetism. In La_{2-x}Sr_xCuO_4 the
response to the external field above Tc is dominated by heterogeneous spin
magnetism. However, the magnetism that dominates the observed inhomogeneous
line broadening below x ~ 0.19 is overwhelmed by the emergence of a completely
different kind of magnetism in the heavily overdoped regime. The origin of the
magnetism above x ~ 0.19 is currently unknown, but its presence hints at a
competition between superconductivity and magnetism that is reminiscent of the
underdoped regime. In contrast, the width of the internal field distribution of
underdoped YBa_2Cu_3O_y above Tc is observed to track Tc and the density of
superconducting carriers. This observation suggests that the magnetic response
above Tc is not dominated by electronic moments, but rather inhomogeneous
fluctuating superconductivity.",0902.4006v2
2009/9/30,Phase diagram of magnetic configurations for soft magnetic nanodots of circular and elliptical shape obtained by micromagnetic simulation,"Magnetic disks or dots of soft magnetic material of sub-micron dimensions may
have as the lowest energy magnetic configuration a single-domain structure,
with magnetization either perpendicular of parallel to the plane, or else may
form magnetic vortices. The properties of these vortices may be used to encode
data bits, in magnetic memory applications. In the present work the OOMMF code
was used to compute by micromagnetic simulation the energy and the
magnetization of circular and elliptical nanodots of permalloy. For the
elliptical magnetic dots the analysis was made for variable thickness and
length of major axis, keeping a 2:1 axis ratio. From the simulations, a phase
diagram was constructed, where the ground state configurations of the nanodots
are represented in a diagram of nanodot height versus length of the major axis
$2a$ of the ellipse. The phase diagram obtained includes regions with one and
two vortices; it is similar, but more complex than that derived using a
numerical scaling approach, since it includes configurations with lateral
vortices. These diagrams are useful as guides for the choice of dimensions of
elliptical nanodots for practical applications.",0909.5686v1
2013/4/11,Theory of magnetic small-angle neutron scattering of two-phase ferromagnets,"Based on micromagnetic theory we have derived analytical expressions for the
magnetic small-angle neutron scattering (SANS) cross section of a two-phase
particle-matrix-type ferromagnet. The approach---valid close to magnetic
saturation---provides access to several features of the spin structure such as
perturbing magnetic anisotropy and magnetostatic fields. Depending on the
applied magnetic field and on the magnitude $H_p$ of the magnetic anisotropy
field relative to the magnitude $\Delta M$ of the jump in the longitudinal
magnetization at the particle-matrix interface, we observe a variety of angular
anisotropies in the magnetic SANS cross section. In particular, the model
explains the ""clover-leaf""-shaped angular anisotropy which was previously
observed for several nanostructured magnetic materials, and it provides access
to the magnetic interaction parameters such as the average exchange-stiffness
constant. It is also shown that the ratio $H_p / \Delta M$ decisively
determines the asymptotic power-law exponent and the range of spin-misalignment
correlations.",1304.3214v1
2014/3/27,Theoretical model for torque differential magnetometry of single domain magnets,"We present a generic theoretical model for torque differential magnetometry
(TDM) - an experimental method for determining the magnetic properties of a
magnetic specimen by recording the resonance frequency of a mechanical
oscillator, on which the magnetic specimen has been mounted, as a function of
the applied magnetic field. The effective stiffness change, and hence the
resonance frequency shift, of the oscillator due to the magnetic torque on the
specimen is calculated, treating the magnetic specimen as a single magnetic
domain. Our model can deal with an arbitrary magnetic free energy density
characterizing the specimen, as well as any relative orientation of the applied
magnetic field, the specimen and the oscillator. Our calculations agree well
with published experimental data. The theoretical model presented here allows
to take full advantage of TDM as an efficient magnetometry method.",1403.7103v2
2014/9/1,Correlation Effects and Non-Collinear Magnetism in the Doped Hubbard Model,"The ground--state magnetic phase diagram is investigated for the two-- and
three--dimensional $t$--$t'$ Hubbard model. We take into account commensurate
ferro--, antiferromagnetic, and incommensurate (spiral) magnetic phases, as
well as phase separation into magnetic phases of different types, which was
often missed in previous investigations. We trace the influence of correlation
effects on the stability of both spiral and collinear magnetic order by
comparing the results of employing both the generalized non-correlated
mean--field (Hartree--Fock) approximation and generalized slave boson approach
by Kotliar and Ruckenstein with correlation effects included. We found that the
spiral states and especially ferromagnetism are generally strongly suppressed
up to non-realistic large Hubbard $U$, if the correlation effects are taken
into account. The electronic phase separation plays an important role in the
formation of magnetic states and corresponding regions are wide, especially in
the vicinity of half--filling. The details of magnetic ordering for different
cubic lattices are discussed.",1409.0320v2
2015/3/26,Quantitative analysis of magnetic spin and orbital moments from an oxidized iron (1 1 0) surface using electron magnetic circular dichroism,"Understanding the ramifications of reduced crystalline symmetry on magnetic
behavior is a critical step in improving our understanding of nanoscale and
interfacial magnetism. However, investigations of such effects are often
controversial largely due to the challenges inherent in directly correlating
nanoscale stoichiometry and structure to magnetic behavior. Here, we describe
how to use Transmission Electron Microscope (TEM) to obtain Electron Magnetic
Circular Dichroism (EMCD) signals as a function of scattering angle to locally
probe the magnetic behavior of thin oxide layers grown on an Fe (1 1 0)
surface. Experiments and simulations both reveal a strong dependence of the
magnetic orbital to spin ratio on its scattering vector in reciprocal space. We
exploit this variation to extract the magnetic properties of the oxide cladding
layer, showing that it locally may exhibit an enhanced orbital to spin moment
ratio. This finding is supported here by both spatially and angularly resolved
EMCD measurements, opening up the way for compelling investigations into how
magnetic properties are affected by nanoscale features.",1503.07681v2
2015/8/31,Skyrmionic magnetization configurations at chiral magnet/ferromagnet heterostructures,"We consider magnetization configurations at chiral magnet (CM)/ferromagnet
(FM) heterostructures. In the CM, magnetic skyrmions and spin helices emerge
due to the Dzyaloshinskii-Moriya interaction, which then penetrate into the
adjacent FM. However, because the non-uniform magnetization structures are
energetically unfavorable in the FM, the penetrated magnetization structures
are deformed, resulting in exotic three-dimensional configurations, such as
skyrmion cones, sideways skyrmions, and twisted helices and skyrmions. We
discuss the stability of possible magnetization configurations at the CM/FM and
CM/FM/CM hybrid structures within the framework of the variational method, and
find that various magnetization configurations appear in the ground state, some
of which cause nontrivial emergent magnetic field.",1508.07665v1
2015/10/15,Magnetization process of spin-1/2 Heisenberg antiferromagnets on a layered triangular lattice,"We study the magnetization process of the spin-1/2 antiferromagnetic
Heisenberg model on a layered triangular lattice by means of a numerical
cluster mean-field method with a scaling scheme (CMF+S). It has been known that
antiferromagnetic spins on a two-dimensional (2D) triangular lattice with
quantum fluctuations exhibit a one-third magnetization plateau in the
magnetization curve under magnetic field. We demonstrate that the CMF+S
quantitatively reproduces the magnetization curve including the stabilization
of the plateau. {We also discuss the effects of a finite interlayer coupling,
which is unavoidable in real quasi-2D materials. It has been recently argued
for a model of the layered-triangular-lattice compound Ba3CoSb2O9 that such
interlayer coupling can induce an additional first-order transition at a strong
field. We present the detailed CMF+S results for the magnetization and
susceptibility curves of the fundamental Heisenberg Hamiltonian in the presence
of magnetic field and weak antiferromagnetic interlayer coupling. The extra
first-order transition appears as a quite small jump in the magnetization curve
and a divergence in the susceptibility at a strong magnetic field ~ 0.712 of
the saturation field.",1510.04402v1
2016/5/15,Chiral Magnetic Effect due to Inhomogeneous Magnetic Fields in Noncentrosymmetric Weyl Semimetals,"The chiral magnetic effect is a phenomenon where an electromagnetic current
is generated along a magnetic field. Recently, in nonequilibrium systems,
negative longitudinal magnetoresistance has been observed experimentally in
Dirac/Weyl semimetals, which provides evidence for the chiral magnetic effect
as a nonequilibrium current. On the other hand, the emergence of the chiral
magnetic effect as an equilibrium current is still controversial. We propose a
possible realization of the chiral magnetic effect as an equilibrium current
using inhomogeneous magnetic fields. By employing tight-binding calculations
and linear response theory, we demonstrate that a finite current density is
generated by inhomogeneous magnetic fields, while the spatial integration of
the current is equal to zero, which is consistent with the so-called ""no-go
theorem"" of the chiral magnetic effect in real lattice systems. Moreover, we
propose an experimental setup to detect the effect in Weyl semimetal materials.",1605.04567v3
2016/7/5,Magnetic Effects in the Paraxial Regime of Elastic Electron Scattering,"Based on a recent claim [Phys. Rev. Lett. 116, 127203 (2016)] that electron
vortex can be used to image magnetism at the nanoscale in elastic scattering
experiments, using transmission electron microscopy, a comprehensive
computational study is performed to study magnetic effects in the paraxial
regime of elastic electron scattering in magnetic solids. Magnetic interactions
from electron vortex beams, spin polarized electron beams and beams with phase
aberrations are considered, as they pass through ferromagnetic FePt or
antiferromagnetic LaMnAsO. The magnetic signals are obtained by comparing the
intensity over a disk in the diffraction plane for beams with opposite angular
momentum or aberrations. The strongest magnetic signals are obtained from
vortex beams with large orbital angular momentum, where relative magnetic
signals above $10^{-3}$ are indicated for $10\hbar$ orbital angular momentum,
meaning that relative signals of one percent could be expected with the even
larger orbital angular momenta, which have been produced in experimental
setups. All results indicate that beams with low acceleration voltage and small
convergence angles yield stronger magnetic signals, which is unfortunately
problematic for the possibility of high spatial resolution imaging.
Nevertheless, under atomic resolution conditions, relative magnetic signals in
the order of $10^{-4}$ are demonstrated, corresponding to an increase with one
order of magnitude compared to previous work.",1607.01230v1
2016/7/14,Magnetic phase diagrams in the H-T plane of the magnetically strongest sigma-phase Fe-V compounds,"Magnetization measurements were performed on two sigma-phase samples of
Fe(100-x)V(x) (x=35.5, 34.1) vs. temperature, T, and in DC magnetic field, of
various amplitudes. Using three characteristic temperatures, magnetic phase
diagrams in the H-T plane have been designed testifying to a re-entrant
character of magnetism. The ground magnetic state, a spin glass (SG), was
evidenced to be composed of two sub phases: one with a weak irreversibility and
the other with a strong irreversibility. Two critical lines were reconstructed
within the SG state. Both of them show a crossover from the Gabay-Toulouse
behavior (low field) to a linear and/or quasi-Almeida-Touless behavior. A
strong difference in the effect of the applied magnetic field on the SG phase
in the two samples was revealed.",1607.04112v2
2016/7/16,Scanning tunneling spectroscopy as a probe of multi-Q magnetic states of itinerant magnets,"The combination of electronic correlations and Fermi surfaces with multiple
nesting vectors can lead to the appearance of complex multi-Q magnetic ground
states, hosting unusual states such as chiral density-waves and quantum Hall
insulators. Distinguishing single-Q and multi-Q magnetic phases is however a
notoriously difficult experimental problem. Here we propose theoretically that
the local density of states near a magnetic impurity, whose orientation may be
controlled by an external magnetic field, can be used to map out the detailed
magnetic configuration of an itinerant system and distinguish unambiguously
between single-Q and multi-Q phases. We demonstrate this concept by computing
and contrasting the LDOS near a magnetic impurity embedded in three different
magnetic ground states relevant to iron-based superconductors -- one single-Q
and two double-Q phases. Our results open a promising avenue to investigate
complex magnetic configurations in itinerant systems via standard scanning
tunneling spectroscopy, without requiring spin-resolved capability.",1607.04711v1
2016/7/18,Magnetic Behavior of Superatom-Fullerene Assemblies,"It has recently been possible to synthesize ordered assemblies composed of
magnetic superatomic clusters Ni9Te6(PEt3)8 separated by C60 and study their
magnetic behavior. We have carried out theoretical studies on model systems
consisting of magnetic superatoms separated by non-magnetic species to examine
the evolution in magnetic response as the nature of the magnetic superatom
(directions of spin quantization), the strength of isotropic and anisotropic
interactions, the magnetic anisotropy energy, and the size of the assembly are
varied. We have examined square planar configurations consisting 16, 24 and 48
sites with 8, 12 and 24 magnetic superatoms respectively. The magnetic atoms
are allowed 2 or 5 orientations. The model Hamiltonian includes isotropic
exchange interactions with second nearest neighbor ferromagnetic and nearest
neighbor antiferromagnetic couplings and anisotropic Dzyaloshinskii-Moriya
interactions. It is shown that the inclusion of Dzyaloshinskii-Moriya
interaction that cause spin canting is necessary to get qualitative response as
observed in experiments.",1607.05349v1
2016/10/7,Performance Evaluation of Klystron Beam Focusing System with Anisotropic Ferrite Magnet,"A klystron beam focusing system using permanent magnets, which increases
reliability in comparison with electromagnet focusing system, is reported. A
prototype model has been designed and fabricated for a 1.3 GHz, 800 kW klystron
for evaluation of the feasibility of the focusing system with permanent
magnets. In order to decrease the production cost and to mitigate complex
tuning processes of the magnetic field, anisotropic ferrite magnet is adopted
as the magnetic material. As the result of a power test, 798 kW peak output
power was successfully achieved with the prototype focusing system. Considering
a power consumption of the electromagnet focusing system, the required
wall-plug power to produce nominal 800 kW output power with the permanent
magnet system is less than that with electromagnet. However, the power
conversion efficiency of the klystron with the permanent magnet system was
found to be limited by transverse multipole magnetic fields. By decreasing
transverse multipole magnetic field components, especially the dipole and the
quadrupole, the power conversion efficiency would approach to that with
electromagnets.",1610.02130v1
2017/5/9,The origin of fine structure in magnetization curve of $α$-CoV$_2$O$_6$,"Multiple field-induced plateaus in $\alpha$-CoV$_2$O$_6$ at low temperatures
were revealed earlier by M. Lenertz et al. [J. Phys. Chem. C 115, 17190 (2011)]
and carefully investigated recently by M. Nandi and P. Mandal [J. Appl. Phys.
119, 133904 (2016)]. Four equidistant steps were observed in the magnetization
curve. We present a model to describe this phenomenon. A magnetic structure of
this substance is formed by highly anisotropic triangular lattice of Ising
chains running along the $\bf{b}$ axis. Due to a three-fold degeneracy of
three-sublattice magnetic ordering, domain boundaries appear. Their
transformation under magnetic field variation leads to two additional steps in
the 1/3 magnetization plateau and gives rise to complex magnetic behavior
observed experimentally. The domain structure in $\alpha$-CoV$_2$O$_6$ occurs
to be strongly anisotropic because a lifetime of the metastable states depends
greatly on the configuration orientation. A strong dependence of the
magnetization curve on magnetic field sweep time is predicted.",1705.03234v2
2017/11/8,Magnetization measurements on as prepared and annealed Fe3-xMnxSi alloys,"The magnetic properties of the alloy system Fe3-xMnxSi have been studied by
measuring magnetization for samples with x = 0, 0.1, 0.25, 0.5, and by thermal
scanning techniques for samples with x = 0, 0.1. The results reveal that the
system is ferromagnetic in this composition range. Zero field cooling and field
cooling magnetization measurements indicate a similar magnetic ordering and
magnetic anisotropy in all samples. The saturation magnetization for the
annealed samples was higher than that for as prepared samples. This is
attributed to the reduction of magnetic domain boundaries rather than to
improving magnetic order as a result of annealing. Further, TC values
determined from thermal DSC measurements are in good agreement with previously
reported results based on magnetic measurements.",1711.03052v1
2017/11/9,"Magnetization, specific heat, and thermal conductivity of hexagonal ErMnO$_3$ single crystals","We report a study of magnetism and magnetic transitions of hexagonal
ErMnO$_3$ single crystals by magnetization, specific heat and heat transport
measurements. Magnetization data show that the $c$-axis magnetic field induces
three magnetic transitions at 0.8, 12 and 28 T. The specific heat shows a peak
at 2.2 K, which is due to a magnetic transition of Er$^{3+}$ moments. For
low-$T$ thermal conductivity ($\kappa$), a clear dip-like feature appears in
$\kappa(H)$ isotherm at 1--1.25 T for $H \parallel ab$; while in the case of $H
\parallel c$, a step-like increase is observed at 0.5--0.8 T. The transition
fields in $\kappa(H)$ are in good agreement with those obtained from
magnetization, and the anomaly of $\kappa$ can be understood by a spin-phonon
scattering scenario. The natures of magnetic structures and corresponding
field-induced transitions at low temperatures are discussed.",1711.03562v1
2018/1/10,Quantum Theory of Rare-Earth Magnets,"Strong permanent magnets mainly consist of rare earths ($R$) and transition
metals ($T$). The main phase of the neodymium magnet, which is the strongest
magnet, is Nd$_2$Fe$_{14}$B. Sm$_{2}$Fe$_{17}$N$_{3}$ is another magnet
compound having excellent magnetic properties comparable to those of
Nd$_{2}$Fe$_{14}$B. Their large saturation magnetization, strong
magnetocrystalline anisotropy, and high Curie temperature originate from the
interaction between the $T$-3d electrons and $R$-4f electrons. This article
discusses the magnetism of rare-earth magnet compounds. The basic theory and
first-principles calculation approaches for quantitative description of the
magnetic properties are presented, together with applications to typical
compounds such as Nd$_2$Fe$_{14}$B, Sm$_{2}$Fe$_{17}$N$_{3}$, and the recently
synthesized NdFe$_{12}$N.",1801.03455v1
2018/4/3,Adjustable current-induced magnetization switching utilizing interlayer exchange coupling,"Electrical current-induced deterministic magnetization switching in a
magnetic multilayer structure without external magnetic field is realized by
utilizing interlayer exchange coupling. Two ferromagnetic Co layers, with
in-plane and out-of-plane anisotropy respectively, are separated by a spacer Ta
layer, which plays a dual role of inducing antiferromagnetic interlayer
coupling, and contributing to the current-induced effective magnetic field
through the spin Hall effect. The current-induced magnetization switching
behavior can be tuned by pre-magnetizing the in-plane Co layer. The
antiferromagnetic exchange coupling field increases with decreasing thickness
of the Ta layer, reaching 630+-5 Oe for a Ta thickness of 1.5nm. The magnitude
of the current-induced perpendicular effective magnetic field from spin-orbit
torque is 9.2 Oe/(107Acm-2). The large spin Hall angle of Ta, opposite in sign
to that of Pt, results in a low critical current density of 9*10^6A/cm^2. This
approach is promising for the electrical switching of magnetic memory elements
without external magnetic field.",1804.00798v1
2018/7/3,Importance of Paramagnetic Background Subtraction for Determining the Magnetic Moment in Epitaxially Grown Monolayer and Few-Layer van der Waals Magnets,"Due to the atomically thin nature of monolayer and few-layer van der Waals
magnets, the undesired background signal from the substrate can have
significant contribution when characterizing their magnetic properties. This
brings challenges in accurately determining the magnitude of the magnetic
moment of the epitaxially grown van der Waals magnets on bulk substrates. In
this paper, we discuss the impact of the background subtraction method for
accurately determining the magnetic moments in such systems. Using the recently
reported intrinsic two-dimensional (2D) van der Waals ferromagnet MnSe${_2}$ as
an example, we show that a normal diamagnetic background subtraction method in
analyzing the bulk magnetometry measurement will result in an unexpectedly
large magnetic moment (greater than ~10 {\mu}${_B}$ per formula unit). Through
our systematic growth study, we identify an additional paramagnetic signal due
to unintentional Mn doping of the substrate. To extract the correct magnetic
moment, a paramagnetic background should also be considered. This yields a
total magnetic moment of ~4 {\mu}${_B}$ per formula unit in monolayer
MnSe${_2}$, which is in close agreement to the theoretically predicted value.",1807.01348v1
2018/7/24,Impact of magnetic moment and anisotropy of Co$_\textrm{1-x}$Fe$_\textrm{x}$ thin films on the magnetic proximity effect of Pt,"We present a systematic study of the magnetic proximity effect in Pt,
depending on the magnetic moment and anisotropy of adjacent metallic
ferromagnets. Element-selective x-ray resonant magnetic reflectivity
measurements at the Pt absorption edge (11565$\,$eV) are carried out to
investigate the spin polarization of Pt in Pt/Co$_\textrm{1-x}$Fe$_\textrm{x}$
bilayers. We observe the largest magnetic moment of (0.72$\,\pm\,$0.03)$\,
\mu_\textrm{B}$ per spin polarized Pt atom in
Pt/Co$_\textrm{33}$Fe$_\textrm{67}$, following the Slater-Pauling curve of
magnetic moments in Co-Fe alloys. In general, a clear linear dependence is
observed between the Pt moment and the moment of the adjacent ferromagnet.
Further, we study the magnetic anisotropy of the magnetized Pt which clearly
adopts the magnetic anisotropy of the ferromagnet below. This is depicted for
Pt on Fe(001) and on Co$_\textrm{50}$Fe$_\textrm{50}$(001), which have a
45$^{\circ}$ relative rotation of the fourfold magnetocrystalline anisotropy.",1807.09032v2
2012/11/29,The magnetic structure of bixbyite a-Mn2O3: a combined density functional theory DFT+U and neutron diffraction study,"First principles density functional theory DFT+U calculations and
experimental neutron diffraction structure analyses were used to determine the
low-temperature crystallographic and magnetic structure of bixbyite Mn2O3. The
energies of various magnetic arrangements, calculated from first principles,
were fit to a cluster-expansion model using a Bayesian method that overcomes a
problem of underfitting caused by the limited number of input magnetic
configurations. The model was used to predict the lowest-energy magnetic
states. Experimental determination of magnetic structure benefited from
optimized sample synthesis, which produced crystallite sizes large enough to
yield a clear splitting of peaks in the neutron powder diffraction patterns,
thereby enabling magnetic-structure refinements under the correct orthorhombic
symmetry. The refinements employed group theory to constrain magnetic models.
Computational and experimental analyses independently converged to similar
ground states, with identical antiferromagnetic ordering along a principal
magnetic axis and secondary ordering along a single orthogonal axis, differing
only by a phase factor in the modulation patterns. The lowest-energy magnetic
states are compromise solutions to frustrated antiferromagnetic interactions
between certain corner-sharing MnO6 octahedra.",1211.6960v1
2017/4/12,Ultra-fast magnetization manipulation using single femtosecond light and hot-electrons pulse,"Current induced magnetization manipulation is a key issue for spintronic
application. Therefore, deterministic switching of the magnetization at the
picoseconds timescale with a single electronic pulse represents a major step
towards the future developments of ultrafast spintronic. Here, we have studied
the ultrafast magnetization dynamics in engineered Gdx[FeCo]1-x based structure
to compare the effect of femtosecond laser and hot-electrons pulses. We
demonstrate that a single femtosecond hot-electrons pulse allows a
deterministic magnetization reversal in either Gd-rich and FeCo-rich alloys
similarly to a femtosecond laser pulse. In addition, we show that the limiting
factor of such manipulation for perpendicular magnetized films arises from the
multi-domain formation due to dipolar interaction. By performing time resolved
measurements under various field, we demonstrate that the same magnetization
dynamics is observed for both light and hot-electrons excitation and that the
full magnetization reversal take place within 5 ps. The energy efficiency of
the ultra-fast current induced magnetization manipulation is optimized thanks
to the ballistic transport of hot-electrons before reaching the GdFeCo magnetic
layer.",1704.03749v1
2018/3/23,Magnetization distribution in a spin ladder-shaped quantum nanomagnet,"The quantum nanomagnets show interesting site-dependent magnetic properties
as a function of the temperature and the external magnetic field. In the paper
we present the results of calculations for a finite quantum spin ladder with
two legs, consisting of 12 spins $S=1/2$. We describe our system with isotropic
quantum Heisenberg model and perform exact numerical diagonalization of the
Hamiltonian to use canonical ensemble approach. Our analysis focuses on the
site-dependent magnetization in the system, presenting magnetization
distributions for various interaction parameters. We discuss extensively the
temperature and magnetic field dependences of individual site magnetizations.
The interesting behaviour, with pronounced non-uniformity of magnetization
across the ladder, is found.",1803.08835v2
2018/8/28,Metastable magnetic bubble in [Co/Pd]4/Py multilayers,"Magnetic bubbles are topologically spin textures that offering the
interesting physics and great promise for next-generation information storage
technologies. The main obstacles so far are that magnetic bubbles are generated
with no field stimuli in new material systems at room temperature. Here, we
report the observation of individual magnetic bubbles and its high frequency
measurement at room temperature in an exchange-coupled [Co/Pd]4/Py multilayers.
We demonstrate that the emergence of magnetic bubbles at remanence can be tuned
by the in-plane tilted magnetic field (roughly 3{\deg}) along the film plane at
room temperature. High frequency results indicate that the presence of magnetic
bubbles leads to broadening of the magnetic permeability spectrum lines (due to
the non-uniformity of the magnetic moments). Our findings open the door to the
bubble-based spintronics at room temperature in exchange-coupled magnetic
multilayers.",1808.09215v2
2012/9/13,Spontaneous magnetization in presence of nanoscale inhomogeneities in diluted magnetic systems,"The presence of nanoscale inhomogeneities has been experimentally evidenced
in several diluted magnetic systems, which in turn often leads to interesting
physical phenomena. However, a proper theoretical understanding of the
underlying physics is lacking in most of the cases. Here we present a detailed
and comprehensive theoretical study of the effects of nanoscale inhomogeneities
on the temperature dependent spontaneous magnetization in diluted magnetic
systems, which is found to exhibit an unusual and unconventional behavior. The
effects of impurity clustering on the magnetization response have hardly been
studied until now. We show that nanosized clusters of magnetic impurities can
lead to drastic effects on the magnetization compared to that of homogeneously
diluted compounds. The anomalous nature of the magnetization curves strongly
depends on the relative concentration of the inhomogeneities as well as the
effective range of the exchange interactions. In addition we also provide a
systematic discussion of the nature of the distributions of the local
magnetization.",1209.2927v2
2008/11/12,Magnetic Response of NiFe2O4 nanoparticles in polymer matrix,"We report the magnetic properties of magnetic nano-composite, consisting of
different quantity of NiFe2O4 nanoparticles in polymer matrix. The
nanoparticles exhibited a typical magnetization blocking, which is sensitive on
the variation of magnetic field, mode of zero field cooled/field cooled
experiments and particle quantity in the matrix. The samples with lower
particle quantity showed an upturn of magnetization down to 5 K, whereas the
blocking of magnetization dominates at lower temperatures as the particle
quantity increases in the polymer. We examine such magnetic behaviour in terms
of the competitive magnetic ordering between core and surface spins of
nanoparticles, taking into account the effect of inter-particle (dipole-dipole)
interactions on nanoparticle magnetic dynamics.",0811.1838v1
2021/5/20,Impact of magnetism on screw dislocations in body-centered cubic chromium,"The influence of magnetism on the properties of screw dislocations in
body-centered cubic chromium is investigated by means of ab initio
calculations. Screw dislocations having Burgers vectors 1/2 111 and 100 are
considered, following experimental observations showing activity for both slip
systems. At low temperature, chromium has a magnetic order close to
antiferromagnetism along 100 directions, for which 1/2 111 is not a periodicity
vector. Hence, dislocations with Burgers vectors 1/2 111 generate magnetic
faults when shearing the crystal, which constrain them to coexist and move
pairwise, leading to dissociated 111 super-dislocations. On the other side, 100
is a periodicity vector of the magnetic order of chromium, and no such magnetic
fault are generated when 100 dislocations glide. Dislocation properties are
computed in the magnetically ordered and non magnetic phases of chromium for
comparison purposes. We report a marginal impact of magnetism on the structural
properties and energies of dislocations for both slip systems. The Peierls
energy barrier opposing dislocation glide in {110} planes is comparable for
both 1/2 111 {110} and 100 {110} slip systems, with lower Peierls stresses in
the magnetically ordered phase of chromium.",2105.09651v1
2017/7/24,"Magnetic properties of monoclinic lanthanide metaborates, $Ln$(BO$_2$)$_3$, $Ln$ = Pr, Nd, Gd, Tb","The bulk magnetic properties of the lanthanide metaborates, $Ln$(BO$_2$)$_3$,
$Ln$ = Pr, Nd, Gd, Tb are studied using magnetic susceptibility, heat capacity
and isothermal magnetisation measurements. They crystallise in a monoclinic
structure containing chains of magnetic $Ln^{3+}$ and could therefore exhibit
features of low-dimensional magnetism and frustration. Pr(BO$_2$)$_3$ is found
to have a non-magnetic singlet ground state. No magnetic ordering is observed
down to 0.4 K for Nd(BO$_2$)$_3$. Gd(BO$_2$)$_3$ exhibits a sharp magnetic
transition at 1.1 K, corresponding to three-dimensional magnetic ordering.
Tb(BO$_2$)$_3$ shows two magnetic ordering features at 1.05 K and 1.95 K. A
magnetisation plateau at a third of the saturation magnetisation is seen at 2 K
for both Nd(BO$_2$)$_3$ and Tb(BO$_2$)$_3$ which persists in an applied field
of 14 T. This is proposed to be a signature of quasi one-dimensional behaviour
in Nd(BO$_2$)$_3$ and Tb(BO$_2$)$_3$.",1707.07485v1
2017/12/5,Inducing and Manipulating Magnetization in Two-Dimensional ZnO by Strain and External Gating,"Two-dimensional structures that exhibit intriguing magnetic phenomena such as
perpendicular magnetic anisotropy and switchable magnetization are of great
interests in spintronics research. Herein, the density-functional theory
studies reveal the critical impacts of strain and external gating on
vacancy-induced magnetism and its spin direction in a graphene-like single
layer of zinc oxide (ZnO). In contrast to the pristine and defective ZnO with
an O-vacancy, the presence of a Zn-vacancy induces significant magnetic moments
to its first neighboring O and Zn atoms due to the charge deficit. We further
predict that the direction of magnetization easy axis reverses from an in-plane
to perpendicular orientation under a practically achieved biaxial compressive
strain of $\sim$1--2\% or applying an electric-field by means of the charge
density modulation. This magnetization reversal is driven by the strain- and
electric-field-induced changes in the spin-orbit coupled \emph{d} states of the
first-neighbor Zn atom to the Zn-vacancy. These findings open interesting
prospects for exploiting strain and electric-field engineering to manipulate
magnetism and magnetization orientation of two-dimensional materials.",1712.01578v1
2019/4/19,Prediction of Stoner-Type Magnetism in Low-Dimensional Electrides,"Electrides are special ionic solids with excess cavity-trapped electrons
serving as anions. Despite the extensive studies on electrides, the interplay
between electrides and magnetism is not well understood due to the lack of
stable magnetic electrides, particularly the lack of inorganic magnetic
electrides. Here, based on the mechanism of Stoner-type magnetic instability,
we propose that in certain electrides the low-dimensionality can facilitate the
formation of magnetic ground state because of the enhanced density of states
near the Fermi level. To be specific, A5B3 (A = Ca, Sr, Ba; B = As, Sb, Bi)
(1D), Sr11Mg2Si10 (0D), Ba7Al10 (0D) and Ba4Al5 (0D) have been identified as
stable magnetic electrides with spin-polarization energies of tens to hundreds
of meV per formula unit. Especially for Ba5As3, the spin-polarization energy
can reach up to 220 meV. Furthermore, we demonstrate that the magnetic moment
and spin density mainly derive from the interstitial anionic electrons near the
Fermi level. Our work paves a way to the searching of stable magnetic
electrides and further exploration of the magnetic properties and related
applications in electrides.",1904.09050v1
2019/7/19,Direct observations of chiral spin textures in van der Waals magnet Fe3GeTe2 nanolayers,"In two-dimensional van der Waals (vdW) magnets, the presence of magnetic
orders, strong spin-orbit coupling and asymmetry at interfaces is the key
ingredient for hosting chiral spin textures. However, experimental evidences
for chiral magnetism in vdW magnets remain elusive. Here we demonstrate
unambiguously the formation of chiral spin textures in thin Fe3GeTe2 nanoflakes
using advanced magnetic electron microscopy and first-principles calculations.
Specifically, electron holography analyses reveal the spin configurations of
N\'eel-type, zero-field-stabilized skyrmions in 20-nm-thick Fe3GeTe2 nanoflakes
at cryogenic temperature. In situ Lorentz transmission electron microscopy
measurements further provide detailed magnetic phase diagrams of chiral spin
textures including spirals and skyrmions in Fe3GeTe2 as a function of
temperature, applied magnetic field and specimen thickness. First-principles
calculations unveil a finite interfacial Dzyaloshinskii-Moriya interaction in
the Te/Fe3Ge/Te slabs that induces the spin chirality in Fe3GeTe2. Our
discovery of spin chirality in the prototypical vdW Fe3GeTe2 opens up new
opportunities for studying chiral magnetism in two-dimensional vdW magnets from
both fundamental and applied perspectives.",1907.08382v1
2019/12/11,Magnetic Skyrmions are Quasi-Magnetic Monopoles in Two-Dimensional Magnetic Materials,"Using $su(N)$ Cartan subalgebra local bases parametrization of density
operator $\rho$, we prove that the Wu-Yang potentials of a general $N$-level
quantum system are completely expressed by $SU(N)$ gauge transformation. By
taking the $SU(2)$ Cartan subalgebra local basis as a local normalized
magnetization vector, we find that magnetic skyrmion and Wu-Yang magnetic
monopole have the same algebraic structure. Moreover, by taking the adiabatic
unitary evolution of magnetization as local gauge transformation, we verify
that the Wu-Yang potential of magnetic skyrmions is proportional to the Berry
connection, this means that magnetic skyrmion is quasi-magnetic monopole. The
exact relation between Wu-Yang potentials and Berry connection is discussed in
detail for the general $SU(N)$ case, i.e. the Berry connection for the pure or
mixed state is the weighted average of the $(N-1)$ Wu-Yang potentials.",1912.05085v1
2020/7/9,Shaping nanoscale magnetic domain memory in exchange-coupled ferromagnets by field cooling,"The advance of magnetic nanotechnologies relies on detailed understanding of
nanoscale magnetic mechanisms in materials. Magnetic domain memory (MDM), i.e.,
the tendency for magnetic domains to repeat the same pattern during
field-cycling, is important to many technologies including magnetic recording
developments. We show coherent x-ray magnetic scattering studies unveiling MDM
in [Co/Pd]/IrMn films. When illuminated by coherent x-rays, the magnetic
domains in the [Co/Pd] multilayer produce a speckle pattern unique to their
specific nanoscale configuration. By cross-correlating such speckle patterns
throughout the magnetization loop, we measure the MDM. When cooled below its
blocking temperature, the film exhibits up to 100% MDM, induced by
exchange-couplings with the IrMn layer. Furthermore, the degree of MDM
drastically depends on cooling conditions. If the film is cooled under moderate
fields, MDM is high throughout the entire magnetization loop. If the film is
cooled under nearly saturating field, MDM vanishes, except at nucleation and
saturation",2007.04930v1
2020/10/9,Skew scattering and side jump of spin wave across magnetic texture,"Spin wave and magnetic texture are two elementary excitations in magnetic
systems, and their interaction leads to rich magnetic phenomena. By describing
the spin wave and the magnetic texture using their own collective coordinates,
we find that they interact as classical particles traveling in mutual
electromagnetic fields. Based on this unified collective coordinate model, we
find that both skew scattering and side jump may occur as spin wave passing
through magnetic textures. The skew scattering is associated with the magnetic
topology of the texture, while the side jump is correlated to the total
magnetization of the texture. We illustrate the concepts of skew scattering and
side jump by investigating the spin wave trajectories across the topological
magnetic Skyrmion and the topologically trivial magnetic bubble respectively.",2010.04626v1
2021/3/15,Interplay between breathing-mode distortions and magnetic order in rare-earth nickelates from $ab$ $initio$ magnetic models,"We use density-functional theory calculations to explore the magnetic
properties of perovskite rare-earth nickelates, $\mathcal{R}$NiO$_3$, by
constructing microscopic magnetic models containing all relevant exchange
interactions via Wannierization and Green's function techniques. These models
elucidate the mechanism behind the formation of antiferromagnetic order with
the experimentally observed propagation vector, and explain the reason previous
DFT plus Hubbard $U$ calculations favored ferromagnetic order. We perform
calculations of magnetic moments and exchange-coupling parameters for different
amplitudes of the $R_1^+$ breathing mode distortion, which results in expanded
and compressed NiO$_6$ octahedra. We find that the magnetic moment vanishes for
the ""short bond"" nickels, i.e., the ones in the compressed octahedra. The
inclusion of spin-orbit coupling demonstrates that the magnetic anisotropy is
very small, while the magnetic moment of the short bond nickel atoms tend to
zero even for the noncollinear case. Our results provide a clear picture of the
trends of the magnetic order across the nickelate series and give insights into
the coupling between magnetic order and structural distortions.",2103.08412v1
2021/10/10,Photon correlation spectroscopy with heterodyne mixing based on soft-x-ray magnetic circular dichroism,"Many magnetic equilibrium states and phase transitions are characterized by
fluctuations. Such magnetic fluctuation can in principle be detected with
scattering-based x-ray photon correlation spectroscopy (XPCS). However, in the
established approach of XPCS, the magnetic scattering signal is quadratic in
the magnetic scattering cross section, which results not only in often
prohibitively small signals but also in a fundamental inability to detect
negative correlations (anticorrelations). Here, we propose to exploit the
possibility of heterodyne mixing of the magnetic signal with static charge
scattering to reconstruct the first-order (linear) magnetic correlation
function. We show that the first-order magnetic scattering signal reconstructed
from heterodyne scattering now directly represents the underlying magnetization
texture. Moreover, we suggest a practical implementation based on an absorption
mask rigidly connected to the sample, which not only produces a static charge
scattering signal but also eliminates the problem of drift-induced artificial
decay of the correlation functions. Our method thereby significantly broadens
the range of scientific questions accessible by magnetic x-ray photon
correlation spectroscopy.",2110.04790v2
2021/12/6,Engineering of Intrinsic Chiral Torques in Magnetic Thin Films Based on the Dzyaloshinskii-Moriya Interaction,"The establishment of chiral coupling in thin magnetic films with
inhomogeneous anisotropy has led to the development of artificial systems of
fundamental and technological interest. The chiral coupling itself is enabled
by the Dzyaloshinskii-Moriya interaction (DMI) enforced by the patterned
noncollinear magnetization. Here, we create a domain wall track with
out-of-plane magnetization coupled on each side to a narrow parallel strip with
in-plane magnetization. With this we show that the chiral torques emerging from
the DMI at the boundary between the regions of noncollinear magnetization in a
single magnetic layer can be used to bias the domain wall velocity. To tune the
chiral torques, the design of the magnetic racetracks can be modified by
varying the width of the tracks or the width of the transition region between
noncollinear magnetizations, reaching effective chiral magnetic fields of up to
7.8 mT. Furthermore, we show how the magnitude of the chiral torques can be
estimated by measuring asymmetric domain wall velocities, and demonstrate
spontaneous domain wall motion propelled by intrinsic torques even in the
absence of any external driving force.",2112.03017v1
2022/2/16,Orbit-transfer torque driven field-free switching of perpendicular magnetization,"The reversal of perpendicular magnetization (PM) by electric control is
crucial for high-density integration of low-power magnetic random-access memory
(MRAM). Although the spin-transfer torque (STT) and spin-orbit torque (SOT)
technologies have been used to switch the magnetization of a free layer with
perpendicular magnetic anisotropy, the former has limited endurance because of
the high current density directly through the junction, while the latter
requires an external magnetic field or unconventional configuration to break
the symmetry. Here we propose and realize the orbit-transfer torque (OTT), that
is, exerting torque on the magnetization using the orbital magnetic moments,
and thus demonstrate a new strategy for current-driven PM reversal without
external magnetic field. The perpendicular polarization of orbital magnetic
moments is generated by a direct current in a few-layer WTe2 due to the
existence of nonzero Berry curvature dipole, and the polarization direction can
be switched by changing the current polarity. Guided by this principle, we
construct the WTe2/Fe3GeTe2 heterostructures, where the OTT driven field-free
deterministic switching of PM is achieved.",2202.07840v1
2022/3/23,Magnetic properties of the noncentrosymmetric tetragonal antiferromagnet EuPtSi$_{3}$,"We report a comprehensive study of single crystals of the noncentrosymmetric
rare-earth compound EuPtSi$_{3}$ grown by the optical floating-zone technique.
Measurements of the magnetization, ac susceptibility, and specific heat
consistently establish antiferromagnetic order of localized Eu$^{2+}$ moments
below the N\'{e}el temperature $T_{\mathrm{N}} = 17~\mathrm{K}$, followed by a
second magnetic transition at $T_{\mathrm{N1}} = 16~\mathrm{K}$. For a magnetic
field along the easy $[001]$ axis, the magnetic phase diagram is composed of
these two phases. For fields applied in the magnetically hard basal plane, two
additional phases emerge under magnetic field, where the in-plane anisotropy is
weak with $[100]$ being the hardest axis. At the phase transitions, the
magnetic properties exhibit hysteresis and discrepancies between differential
and ac susceptibility, suggesting slow reorientation processes of mesoscale
magnetic textures. Consistently, powder and single-crystal neutron diffraction
in zero field identify magnetic textures that are modulated on a length scale
of the order of $100~\textrm{\r{A}}$, most likely in the form of N\'{e}el-type
antiferromagnetic cycloids.",2203.12453v1
2022/8/2,Melting of spin ice state and development of fifth order susceptibility with magnetic field in pyrochlore Tb2Sn2O7,"Pyrochlores offer an ideal playground to investigate the magnetic ground
state of frustrated magnetic systems. In this class of materials, competition
between various magnetic interactions remains frustrated and prevents an
ordered magnetic state at low temperatures. Tb2Sn2O7 has recently attracted
significant attention due to its ordered spin-ice state. Additionally, in such
systems, application of external magnetic field might result in exotic magnetic
states. Our current investigation on Tb2Sn2O7 reveal the presence of a new
phase associated with fifth order susceptibility at low temperatures and high
magnetic fields. In this compound, at zero fields, for a stabilized spin-ice
state, the singlet-singlet state separated by {\delta} play an imperative role.
Under magnetic fields, {\delta} increases and the Zeeman energy associated with
the magnetic anisotropy is believed to get enhanced; which can be the key
ingredient for evolution of higher-order moments, above 10 kOe, in this
compound.",2208.01279v1
2022/8/2,Emergence of low temperature glassy dynamics in Ru substituted non magnetic insulator CaHfO3,"Non magnetic insulators/semiconductors with induced magnetism introduced via
transition metal substitution are one of the promising materials in the field
of spintronic, magnetoelectronics and magneto optical devices. In this context,
here, we focus on magnetism induced in a non magnetic insulator CaHfO3, by the
substitution of 4d element Ru, at Hf site. Structural investigations indicate
that substitution of Ru4+ (up to 50%) does not affect the original crystal
structure of the parent compound. Magnetic studies divulge a crossover from a
diamagnetic to paramagnetic state with 20% Ru substitution. Further replacement
of Hf results in a glassy magnetic state in CaHf1-xRuxO3 (0.3 < x < 0.5). The
nature of the low temperature glassiness (below 20 K) in these compositions is
confirmed through Vogel Fulcher and Power law, along with, magnetic memory
effect and relaxation dynamics. The observed glassiness is explained through
the phenomenological hierarchical model. Our studies indicate that the presence
of competing short range interactions among randomly arranged Ru cations in non
magnetic insulator CaHfO3 are responsible for the observed low temperature
magnetic state in this series with compositions > 0.25.",2208.01282v1
2022/9/15,Nanoscale imaging of antiferromagnetic domains in epitaxial films of Cr2O3 via scanning diamond magnetic probe microscopy,"We report direct imaging of boundary magnetization associated with
antiferromagnetic domains in magnetoelectric epitaxial Cr2O3 thin films using
diamond nitrogen vacancy microscopy. We found a correlation between magnetic
domain size and structural grain size which we associate with the domain
formation process. We performed field cooling, i.e., cooling from above to
below the N\'eel temperature in the presence of magnetic field, which resulted
in the selection of one of the two otherwise degenerate 180 degree domains.
Lifting of such a degeneracy is achievable with a magnetic field alone due to
the Zeeman energy of a weak parasitic magnetic moment in Cr2O3 films that
originates from defects and the imbalance of the boundary magnetization of
opposing interfaces. This boundary magnetization couples to the
antiferromagnetic order parameter enabling selection of its orientation.
Nanostructuring the Cr2O3 film with mesa structures revealed reversible edge
magnetic states with the direction of magnetic field during field cooling.",2209.07476v2
2022/11/18,Skew scattering by magnetic monopoles and anomalous Hall effect in spin-orbit coupled systems,"Magnetic textures like skyrmions and domain walls coupled to itinerant
electrons give rise to rich transport phenomena such as anomalous Hall effect
and nonreciprocal current. An interesting case is when the transport
coefficient is related to the global (or topological) property of the magnetic
texture, e.g., skyrmion and domain wall numbers. Such phenomena are also
interesting from applications, in which the transport phenomena are potential
probes for electrically detecting magnetic textures in nano-scale devices.
Here, we show that an anomalous Hall effect proportional to the net magnetic
monopole charge occurs from skew scattering when the magnetic texture couples
to itinerant electrons in a non-centrosymmetric system with spin-orbit
interaction. This mechanism gives rise to a finite anomalous Hall effect in a
ferromagnetic domain wall whose spins rotate in the $xy$ plane, despite no
out-of-plane magnetic moment. We also discuss the relation between the magnetic
texture contributing to the anomalous Hall effect and the crystal symmetry. The
results demonstrate rich features arising from the interplay of spin-orbit
interaction and magnetic textures and their potential for detecting various
magnetic textures in nanoscale devices.",2211.10180v1
2023/6/2,Bloch point nanospheres for the design of magnetic traps,"Through micromagnetic simulations, this work analyzes the stability of Bloch
points in magnetic nanospheres and the possibility of using an array of such
particles to compose a system with the features of a magnetic trap. We show
that a BP can be nucleated as a metastable configuration in a relatively wide
range of the nanosphere radius compared to a quasi-uniform and vortex state. We
also show that the stabilized Bloch point generates a quadrupolar magnetic
field outside it, from which we analyze the field profile of different arrays
of these nanospheres to show that the obtained magnetic field shares the
features of magnetic traps. Some of the highlights of the proposed magnetic
traps rely on the magnetic field gradients achieved, which are orders of
magnitude higher than standard magnetic traps, and allow three-dimensional
trapping. Our results could be useful in trapping particles through the
intrinsic magnetization of ferromagnetic nanoparticles while avoiding the
commonly used mechanisms associated with Joule heating.",2306.01680v1
2023/8/24,Coercivity Mechanisms of Single-Molecule Magnets,"Magnetic hysteresis has become a crucial aspect for characterizing
single-molecule magnets, but the comprehension of the coercivity mechanism is
still a challenge. By using analytical derivation and quantum dynamical
simulations, we reveal fundamental rules that govern magnetic relaxation of
single molecule magnets under the influence of external magnetic fields, which
in turn dictates the hysteresis behavior. Specifically, we find that energy
level crossing induced by magnetic fields can drastically increase the
relaxation rate and set a coercivity limit. The activation of
optical-phonon-mediated quantum tunneling accelerates the relaxation and
largely determines the coercivity. Intra-molecular exchange interaction in
multi-ion compounds may enhance the coercivity by suppressing key relaxation
processes. Unpaired bonding electrons in mixed-valence complexes bear a
pre-spin-flip process, which may facilitate magnetization reversal. Underlying
these properties are magnetic relaxation processes modulated by the interplay
of magnetic fields, phonon spectrum and spin state configuration, which also
proposes a fresh perspective for the nearly centurial coercive paradox.",2308.12616v2
2023/11/6,Chiral magnetic phases in Moire bilayers of magnetic dipoles,"In magnetic insulators, the sense of rotation of the magnetization is
associated with novel phases of matter and exotic transport phenomena. Aimed to
find new sources of chiral magnetism rooted in intrinsic fields and geometry,
twisted square bilayers of magnetic dipoles with easy plane anisotropy are
studied. For no twist, each lattice settles in the zig-zag magnetic state and
orders antiferromagnetically to the other layer. The moire patterns that result
from the mutual rotation of the two square lattices influence such zig-zag
order, giving rise to several phases that depict non-collinear magnetic
textures with chiral motifs that break both time and inversion symmetry. For
certain moire angles, helical and toroidal magnetic orders arise. Changing the
vertical distance between layers can further manipulate these novel phases. It
is shown that the dipolar interlayer interaction induces an emergent
twist-dependent chiral magnetic field orthogonal to the direction of the
zig-zag chains, which is responsible for the internal torques conjugated to the
toroidal orders.",2311.03519v2
2023/11/15,"Ba6RE2Ti4O17 (RE= Nd, Sm,Gd, Dy-Yb): A family of Rare-earth based layered triangular lattice magnets","Rare-earth-based triangular-lattice magnets provide the fertile ground to
explore the exotic quantum magnetic state. Herein, we report a new family of
RE-based triangular-lattice magnets Ba6RE2Ti4O17(RE= rare earth ions)
crystallized into the hexagonal structure with space group of P63 mmc, where
magnetic rare earth ions form an ideal triangular lattice within the ab-plane
and stack in an AA -type fashion along the c-axis. The low-temperature magnetic
susceptibility results reveal all the serial compounds have the dominant
antiferromagnetic interactions and an absence of magnetic ordering down to 1.8
K. The magnetization and electron spin resonance results indicate distinct
magnetic anisotropy for the compounds with different RE ions. Moreover,
Ba6Nd2Ti4O17 single crystal is successfully grown and it exhibits strong Ising
like anisotropy with magnetic easy-axis perpendicular to the triangle-lattice
plane, being a candidate to explore quantum spin liquid state with dominant
Ising-type interaction.",2311.08937v2
2023/12/10,Universal patterns of skyrmion magnetizations unveiled by defect implantation,"Skyrmions are spin-swirling textures hosting wonderful properties with
potential implications in information technology. Such magnetic particles carry
a magnetization, whose amplitude is crucial to establish them as robust
magnetic bits, while their topological nature gives rise to a plethora of
exquisite features such as topological protection, the skyrmion and topological
Hall effects as well as the topological orbital moment. These effects are all
induced by an emergent magnetic field directly proportional to the three-spin
scalar chirality, $\chi= (\mathbf{S}_i\times\mathbf{S}_j)\cdot \mathbf{S}_k$,
and shaped by the peculiar spatial dependence of the magnetization. Here, we
demonstrate the existence of novel chiral magnetizations emerging from the
interplay of spin-orbit interaction and either $\chi$ or the two-spin vector
chirality $\boldsymbol{\kappa} = \mathbf{S}_i\times\mathbf{S}_j$. By
scrutinizing correlations among the spin, orbital (trivial and chiral)
magnetizations, we unveil from ab-initio universal patterns, quantify the rich
set of magnetizations carried by single skyrmions generated in PdFe bilayer on
Ir(111) surface and demonstrate the ability to engineer their magnitude via
controlled implantation of impurities. We anticipate that our findings can
guide the design of disruptive storage devices based on skyrmionic bits by
encoding the desired magnetization with strategic seeding of defects.",2312.05903v1
2024/1/3,Local distortion driven magnetic phase switching in pyrochlore $Yb_2(Ti_{1-x}Sn_x)_2O_7$,"While it is commonly accepted that the disorder induced by magnetic ion
doping in quantum magnets usually generates a rugged free-energy landscape
resulting in slow or glassy spin dynamics, the disorder/distortion effects
associated with non-magnetic ion sites doping are still illusive. Here, using
AC susceptibility measurements, we show that the mixture of Sn/Ti on the
non-magnetic ion sites of pyrochlore $Yb_2(Ti_{1-x}Sn_x)_2O_7$ induces an
antiferromagnetic ground state despite both parent compounds, $Yb_2Ti_2O_7$,
and $Yb_2Sn_2O_7$, order ferromagnetically. Local structure studies through
neutron total scattering reveals the local distortion in the non-magnetic ion
sites and its strong correlation with the magnetic phase switching. Our study,
for the first time, demonstrates the local distortion as induced by the
non-magnetic ion site mixture could be a new path to achieve magnetic phase
switching, which has been traditionally obtained by external stimuli such as
temperature, magnetic field, pressure, strain, light, etc.",2401.01807v1
2024/1/15,"Generation of intense, polarization-controlled magnetic fields with non-paraxial structured laser beams","The ability to spatially separate the electric and magnetic fields of a light
beam enables the inspection of laser-matter interactions driven solely by
optical magnetic fields. However, magnetic field excitations are commonly
orders of magnitude weaker than those driven by the electric field. Several
studies have already demonstrated the isolation of an intense, linearly
polarized magnetic field using structured light. In this work, we report the
generation of isolated high intensity magnetic fields with controlled
polarization state in the non-paraxial regime using structured laser beams. Our
theoretical findings highlight a significant enhancement in the amplitude of
the longitudinal magnetic field carried by an azimuthally polarized laser under
tight-focusing conditions. Furthermore, by implementing a multiple-beam
configuration, we achieve precise control over the polarization state and
amplitude of the spatially isolated magnetic field. We report the generation of
polarization-controlled magnetic fields reaching up to tens of Tesla, even from
moderately intense laser beams of $\sim 10^{12} \, \mathrm{W}/\mathrm{cm}^2$.
Our study paves the way for ultraintense interactions with circularly polarized
magnetic fields from a feasible experimental setup point of view, particularly
interesting to probe ferromagnetic materials and chiral media.",2401.07649v1
2024/2/5,Bifurcation to complex dynamics in largely modulated voltage-controlled parametric oscillator,"An experimental demonstration of a parametric oscillation of a magnetization
in a ferromagnet was performed recently by applying a microwave voltage,
indicating the potential to be applied in a switching method in non-volatile
memories. In the previous works, the modulation of a perpendicular magnetic
anisotropy field produced by the microwave voltage was small compared with an
external magnetic field pointing in an in-plane direction. A recent trend is,
however, opposite, where an efficiency of the voltage controlled magnetic
anisotropy (VCMA) effect is increased significantly by material research and
thus, the modulated magnetic anisotropy field can be larger than the external
magnetic field. Here, we solved the Landau-Lifshitz-Gilbert equation
numerically and investigated the magnetization dynamics driven under a wide
range of the microwave VCMA effect. We evaluated bifurcation diagrams, which
summarize local maxima of the magnetization dynamics. For low modulation
amplitudes, the local maximum is a single point because the dynamics is the
periodic parametric oscillation. The bifurcation diagrams show distributions of
the local maxima when the microwave magnetic anisotropy field becomes larger
than the external magnetic field. The appearance of this broadened distribution
indicates complex dynamics such as chaotic and transient-chaotic behaviors,
which were confirmed from an analysis of temporal dynamics.",2402.02742v1
2024/3/9,Switching intrinsic magnetic skyrmions with controllable magnetic anisotropy in van der Waals multiferroic heterostructures,"Magnetic skyrmions, topologically nontrivial whirling spin textures at
nanometer scales, have emerged as potential information carriers for spintronic
devices. The ability to efficiently create and erase magnetic skyrmions is
vital yet challenging for such applications. Based on first-principles studies,
we find that switching between intrinsic magnetic skyrmion and high-temperature
ferromagnetic states can be achieved in two-dimensional van der Waals (vdW)
multiferroic heterostructure CrSeI/In2Te3 by reversing the ferroelectric
polarization of In2Te3. The core mechanism of this switching is traced to the
controllable magnetic anisotropy of CrSeI influenced by the ferroelectric
polarization of In2Te3. We propose a useful descriptor linking the presence of
magnetic skyrmions to magnetic parameters, and validate this connection through
studies of a variety of similar vdW multiferroic heterostructures. Our work
demonstrates that manipulating magnetic skyrmions via tunable magnetic
anisotropies in vdW multiferroic heterostructures represents a highly promising
and energy-efficient strategy for future development of spintronics.",2403.05747v1
2008/10/27,Hybrid resonant phenomenon in a metamaterial structure with integrated resonant magnetic material,"We explore the hybridization of fundamental material resonances with the
artificial resonances of metamaterials. A hybrid structure is presented in the
waveguide environment that consists of a resonant magnetic material with a
characteristic tuneable gyromagnetic response that is integrated into a
complementary split ring resonator (CSRR) metamaterial structure. The combined
structure exhibits a distinct hybrid resonance in which each natural resonance
of the CSRR is split into a lower and upper resonance that straddle the
frequency for which the magnetic material's permeability is zero. We provide an
analytical understanding of this hybrid resonance and define an effective
medium theory for the combined structure that demonstrates good agreement with
numerical electromagnetic simulations. The designed structure demonstrates the
potential for using a ferrimagnetic or ferromagnetic material as a means of
creating a tunable metamaterial structure.",0810.4871v1
2018/3/31,Ultra-low-field magneto-elastocaloric cooling in a multiferroic composite device,"The advent of caloric materials for magnetocaloric, elastocaloric, and
electrocaloric cooling is changing the landscape of solid state cooling
technologies with potentials for high-efficiency and environmentally-friendly
residential and commercial cooling as well as heating applications. Given that
caloric materials are ferroic materials which undergo first (or second) order
transitions near room temperature, they open up intriguing possibilities for
novel multiferroic devices with hitherto unexplored functionalities coupling
their thermal properties with different fields (magnetic, electric, and stress)
through composite configurations. Here, we demonstrate a composite
magneto-elastocaloric effect with ultra-low magnetic field (0.16 T) in a
compact geometry to generate a cooling temperature change as large as 4 K using
a magnetostriction/superelastic alloy composite. Such composite systems can be
used to circumvent shortcomings of existing technologies such as the need for
high-stress actuation mechanism for elastocaloric materials and the high
magnetic-field requirement of magnetocaloric materials, while enabling new
applications such as compact remote cooling devices.",1804.00196v1
2020/12/15,Advanced materials for magnetic cooling:fundamentals and practical aspects,"Over the last two decades, the research activities on magnetocalorics have
been exponentially increased leading to the discovery of a wide category of
materials including intermetallics and oxides. Even though the reported
materials were found to show excellent magnetocaloric properties on laboratory
scale, only a restricted family among them could be upscaled toward industrial
levels and implemented as refrigerants in magnetic cooling devices. On the
other hand, in the most of reported reviews, the magnetocaloric materials are
usually discussed in terms of their adiabatic temperature and entropy changes,
which is not enough to get more insight about their large scale applicability.
In this review, not only the fundamental properties of recently reported
magnetocaloric materials are discussed but also their thermodynamic performance
in functional devices. The reviewed families particularly include Gd1-xRx
alloys, LaFe13-xSix, MnFeP1-xAsx and R1-xAxMnO3 based compounds. Other relevant
practical aspects such as mechanical stability, synthesis and corrosion issues
are discussed. In addition, the intrinsic and extrinsic parameters that play a
crucial role in the control of magnetic and magnetocaloric properties are
regarded. In order to reproduce the needed magnetocaloric parameters, some
practical models are proposed. Finally, the concepts of the rotating
magnetocaloric effect and multilayered magnetocalorics are introduced.",2012.08176v1
2022/3/3,Achieving high-temperature ferromagnetism by means of magnetic ions dimerization,"Magnetic two-dimensional materials have potential application in
next-generation electronic devices and have stimulated extensive interest in
condensed matter physics and material fields. However, how to realize
high-temperature ferromagnetism in two-dimensional materials remains a great
challenge in physics.
  Herein, we propose an effective approach that the dimerization of magnetic
ions in two-dimensional materials can enhance the exchange coupling and
stabilize the ferromagnetism.
  Manganese carbonitride Mn$_2$N$_6$C$_6$ with a planar monolayer structure is
taken as an example to clarify the method, in which two Mn atoms are gathered
together to form a ferromagnetic dimer of Mn atoms and further these dimers are
coupled together to form the overall ferromagnetism of the two-dimensional
material.
  In Mn$_2$N$_6$C$_6$ monolayer, the near-room-temperature ferromagnetism with
the Curie temperature of 272.3 K is determined by solving Heisenberg model
using Monte Carlo simulations method.",2203.01775v3
2022/11/8,Extraordinary magnetometry -- a review on extraordinary magnetoresistance,"Extraordinary magnetoresistance (EMR) is a geometric magnetoresistance effect
occurring in hybrid devices consisting of a high-mobility material joined by a
metal. The change in resistance can exceed 107% at room temperature when a
magnetic field of 5 T is applied. Magnetic field sensors based on EMR hold the
potential formeasuring weak magnetic fields with an unprecedented sensitivity,
yet, to date this potential is largely unmet. In this work, we provide an
extensive review of the current state-of-the-art in EMR sensors with a focus on
the hybrid device geometries, the constituent material properties and
applications of EMR. We present a direct comparison of the best devices in
literature across magnetoresistance, sensitivity and noise equivalent field for
different materials and geometric designs. The compilation of studies collected
in this review illustrates the extremely rich possibilities for tuning the
magnetoresistive behavior varying the device geometry and material properties.
In addition, we aim to improve the understanding of the EMR effect and its
interplay with geometry and material properties. Finally, we discuss recent
trends in the field and future perspectives for EMR.",2211.04308v1
2024/2/5,Ab initio property characterisation of thousands of previously unknown 2D materials,"We perform extensive density functional theory (DFT) calculations to
determine the stability and elementary properties of 4249 previously unexplored
monolayer crystals. The monolayers comprise the most stable subset (energy
within 0.1 eV/atom of the convex hull) of a larger portfolio of two-dimensional
(2D) materials recently discovered using a deep generative model and systematic
lattice decoration schemes. The relaxed 2D structures are run through the basic
property workflow of the Computational 2D Materials Database (C2DB) to evaluate
the dynamical stability and obtain the stiffness tensor, piezoelectric tensor,
deformation potentials, Born and Bader charges, electronic band structure,
effective masses, plasma frequency, Fermi surface, projected density of states,
magnetic moments, magnetic exchange couplings, magnetic anisotropy, topological
indices, optical- and infrared polarisability. We provide statistical overviews
of the property data and highlight a few specific examples of interesting
materials. Our work exposes previously unknown parts of the 2D chemical space
and provides a basis for the discovery of 2D materials with specific
properties. All data is available in the C2DB.",2402.02783v1
2023/5/4,Laser Powder Bed Fusion of anisotropic Nd-Fe-B bonded magnets utilizing an in situ mechanical alignment approach,"Nd-Fe-B bonded magnets are an important class of permanent magnets, employed
in many technological sectors. The Additive Manufacturing (AM) processes
enables the fabrication of net-shape bonded magnets with complex geometries,
allowing to tailor their magnetic stray field specifically for a given
application. A crucial challenge to be addressed concerning AM of bonded
magnets is the production of magnetically anisotropic components. The common
approaches presented in the literature up to now, required a post-printing
procedure or the complex integration of a magnetic field source into the AM
process. Here, we present a technique to fabricate anisotropic bonded magnets
via Laser Powder Bed Fusion (LPBF) by utilizing the mechanical alignment of
anisotropic particles in a single step, without the need for a magnetic field
source. Anisotropic bonded magnets were fabricated using a mixture of
anisotropic Nd-Fe-B powder (MQA-38-14) and polyamide-12 (PA12). This magnetic
powder consists of ellipsoidal particles, where the easy magnetization axis is
distributed perpendicular to their longest side, which can be exploited to
generate magnetic texture. Depending on the particle size used as feedstock,
the degree of alignment (<cos$(\theta)$>) can be tailored to a maximum of
<cos$(\theta)$> = 0.78. The fabricated anisotropic bonded magnets exhibited a
maximum remanence of Jr = 377 mT and an energy product of (BH)max = 28.6 kJ/m3,
respectively.",2305.02867v2
2008/8/27,Magnetic phase evolution in the spinel compounds Zn$_{1-x}$Co$_x$Cr$_2$O$_4$,"We present the magnetic properties of complete solid solutions of
ZnCr$_2$O$_4$ and CoCr$_2$O$_4$: two well-studied oxide spinels with very
different magnetic ground states. ZnCr$_2$O$_4$, with non-magnetic $d^{10}$
cations occupying the A site and magnetic $d^3$ cations on the B site, is a
highly frustrated antiferromagnet. CoCr$_2$O$_4$, with magnetic $d^7$ cations
(three unpaired electrons) on the A site as well, exhibits both N\'eel
ferrimagnetism as well as commensurate and incommensurate non-collinear
magnetic order. More recently, CoCr$_2$O$_4$ has been studied extensively for
its polar behavior which arises from conical magnetic ordering. Gradually
introducing magnetism on the A site of ZnCr$_2$O$_4$ results in a transition
from frustrated antiferromagnetism to glassy magnetism at low concentrations of
Co, and eventually to ferrimagnetic and conical ground states at higher
concentrations. Real-space Monte-Carlo simulations of the magnetic
susceptibility suggest that the first magnetic ordering transition and features
of the susceptibility across $x$ are captured by near-neighbor self- and
cross-couplings between the magnetic A and B atoms. We present as a part of
this study, a method for displaying the temperature dependence of magnetic
susceptibility in a manner which helps distinguish between compounds possessing
purely antiferromagnetic interactions from compounds where other kinds of
ordering are present.",0808.3789v3
2012/3/1,Magnetic properties of carbon nanodisk and nanocone powders,"We have investigated the magnetic properties of carbon powders which consist
of nanodisks, nanocones, and a small fraction of carbon-black particles.
Magnetization measurements were carried out using a superconducting quantum
interference device in magnetic fields $-5<\mu_{0}H<5\:\mathrm{T}$ for
temperatures in the range $2\leq T<350\:\mathrm{K}$. Measurements of the
magnetization $M$ versus temperature $T$ and magnetic field $\mu_{0}H$ for
these carbon samples show diamagnetism and paramagetism with an additional
ferromagnetic contribution. The ferromagnetic magnetization is in agreement
with the calculated magnetization from Fe impurities as determined by the
particle-induced x-ray emission method ($<75\:\mu\mathrm{g/g}$). Magnetization
measurements in weak magnetic fields show thermal hysteresis, and for strong
fields the magnetization $M$ decreases as $M\sim aT^{-\alpha}$ with $\alpha<1$,
which is slower than the Curie law ($\alpha=1$), when the temperature
increases. The magnetization $M$ versus magnetic field $\mu_{0}H$ shows
paramagnetic free-spin $S=\frac{1}{2}$ and $\frac{3}{2}$ behaviors for
temperatures $T=2\:\mathrm{K}$ and $15\leq T\leq50\:\mathrm{K}$, respectively.
A tendency for localization of electrons was found by electron spin resonance
when the temperature $T$ decreases ($2<T<40\:\mathrm{K}$). The magnetic
properties in these carbon cone and disk powder samples are more complex than a
free-spin model predicts, which is apparently valid only for the temperature
$T=2\:\mathrm{K}$.",1203.0284v3
2013/1/21,Increase of magnetic hyperthermia efficiency due to dipolar interactions in low anisotropy magnetic nanoparticles : theoretical and experimental results,"When magnetic nanoparticles (MNPs) are single-domain and magnetically
independent, their magnetic properties and the conditions to optimize their
efficiency in magnetic hyperthermia applications are now well-understood.
However, the influence of magnetic interactions on magnetic hyperthermia
properties is still unclear. Here, we report hyperthermia and high-frequency
hysteresis loop measurements on a model system consisting of MNPs with the same
size but a varying anisotropy, which is an interesting way to tune the relative
strength of magnetic interactions. A clear correlation between the MNP
anisotropy and the squareness of their hysteresis loop in colloidal solution is
observed : the larger the anisotropy, the smaller the squareness. Since low
anisotropy MNPs display a squareness higher than the one of magnetically
independent nanoparticles, magnetic interactions enhance their heating power in
this case. Hysteresis loop calculations of independent and coupled MNPs are
compared to experimental results. It is shown that the observed features are a
natural consequence of the formation of chains and columns of MNPs during
hyperthermia experiments: in these structures, when the MNP magnetocristalline
anisotropy is small enough to be dominated by magnetic interactions, the
hysteresis loop shape tends to be rectangular, which enhance their efficiency.
On the contrary, when MNPs do not form chains and columns, magnetic
interactions reduces the hysteresis loop squareness and the efficiency of MNPs
compared to independent ones. The present work should improve the understanding
and interpretation of magnetic hyperthermia experiments.",1301.5590v1
2021/5/2,Tunable Néel-Bloch magnetic twists in Fe3GeTe2 with van der Waals structure,"The advent of ferromagnetism in two-dimensional (2D) van der Waals (vdW)
magnets has stimulated high interest in exploring topological magnetic
textures, such as skyrmions for use in future skyrmion-based spintronic
devices. To engineer skyrmions in vdW magnets by transforming Bloch-type
magnetic bubbles into N\'eel-type skyrmions, the heterostructure of heavy
metal/vdW magnetic thin film has been made to induce interfacial
Dzyaloshinskii-Moriya interaction (DMI). However, the unambiguous
identification of the magnetic textures inherent to vdW magnets, e.g., whether
the magnetic twists (skyrmions/domain walls) are N\'eel- or Bloch-type, is
unclear. Here we demonstrate that the N\'eel- or Bloch-type magnetic twists can
be tuned in the vdW magnet Fe3GeTe2 (FGT) with/without interfacial DMI. We use
an in-plane magnetic field to align the modulation wavevector q of the
magnetizations in order to distinguish the N\'eel- or Bloch-type magnetic
twists. We observe that q is perpendicular to the in-plane field in the
heterostructure (Pt/oxidized-FGT/FGT/oxidized-FGT), while q aligns at a rotated
angle with respect to the field direction in the thin plate by thinning bulk
FGT. We find that the aligned domain wall twists hold fan-like modulations,
coinciding qualitatively with our computational results.",2105.00468v1
2017/12/20,Optical Manipulation of Magnetic Vortex Visualized in situ by 4D Electron Microscopy,"Understanding the fundamental dynamics of topological vortex and antivortex
naturally formed in micro/nanoscale ferromagnetic building blocks under
external perturbations is crucial to magnetic vortex based information
processing and spintronic devices. All previous studies have focused on
magnetic vortex-core switching via external magnetic fields, spin-polarized
currents, or spin waves, which have largely prohibited the investigation of
novel spin configurations that could emerge from the ground states in
ferromagnetic disks and their underlying dynamics. Here, we report in situ
visualization of femtosecond laser quenching induced magnetic vortex change in
various symmetric ferromagnetic Permalloy disks by Lorentz phase imaging using
4D electron microscopy. Besides the switching of magnetic vortex chirality and
polarity, we observed with distinct occurrence frequencies a plenitude of
complex magnetic structures that have never been observed by magnetic field or
current assisted switching. These complex magnetic structures consist of a
number of newly created topological magnetic defects (vortex and antivortex)
strictly conserving the topological winding number, demonstrating the direct
impact of topological invariant on the magnetization dynamics in ferromagnetic
disks. Their spin configurations show mirror or rotation symmetry due to the
geometrical confinement of the disks. Combined micromagnetic simulations with
the experimental observations reveal the underlying magnetization dynamics and
formation mechanism of the optical quenching induced complex magnetic
structures. Their distinct occurrence rates are pertinent to their
formation-growth energetics and pinning effects at the disk edge. Based on
these findings, we propose a paradigm of optical-quenching-assisted fast
switching of vortex cores for the control of magnetic vortex based information
recording and spintronic devices.",1712.07280v1
2018/11/21,"Exploring interfacial exchange coupling and sublattice effect in heavy metal/ferrimagnetic insulator heterostructures using Hall measurements, x-ray magnetic circular dichroism, and neutron reflectometry","We use temperature-dependent Hall measurements to identify contributions of
spin Hall, magnetic proximity, and sublattice effects to the anomalous Hall
signal in heavy metal/ferrimagnetic insulator heterostructures with
perpendicular magnetic anisotropy. This approach enables detection of both the
magnetic proximity effect onset temperature and the magnetization compensation
temperature and provides essential information regarding the interfacial
exchange coupling. Onset of a magnetic proximity effect yields a local extremum
in the temperature-dependent anomalous Hall signal, which occurs at higher
temperature as magnetic insulator thickness increases. This magnetic proximity
effect onset occurs at much higher temperature in Pt than W. The magnetization
compensation point is identified by a sharp anomalous Hall sign change and
divergent coercive field. We directly probe the magnetic proximity effect using
x-ray magnetic circular dichroism and polarized neutron reflectometry, which
reveal an antiferromagnetic coupling between W and the magnetic insulator.
Finally, we summarize the exchange-coupling configurations and the anomalous
Hall-effect sign of the magnetized heavy metal in various heavy metal/magnetic
insulator heterostructures.",1811.08574v2
2019/11/14,Suspensions of magnetic nanogels at zero field: equilibrium structural properties,"Magnetic nanogels represent a cutting edge of magnetic soft matter research
due to their numerous potential applications. Here, using Langevin dynamics
simulations, we analyse the influence of magnetic nanogel concentration and
embedded magnetic particle interactions on the self-assembly of magnetic
nanogels at zero field. For this, we calculated radial distribution functions
and structure factors for nanogels and magnetic particles within them. We found
that, in comparison to suspensions of free magnetic nanoparticles, where the
self-assembly is already observed if the interparticle interaction strength
exceeds the thermal fluctuations by approximately a factor of three,
self-assembly of magnetic nanogels only takes place by increasing such ratio
above six. This magnetic nanogel self-assembly is realised by means of
favourable close contacts between magnetic nanoparticles from different
nanogels. It turns out that for high values of interparticle interactions,
corresponding to the formation of internal rings in isolated nanogels, in their
suspensions larger magnetic particle clusters with lower elastic penalty can be
formed by involving different nanogels. Finally, we show that when the
self-assembly of these nanogels takes place, it has a drastic effect on the
structural properties even if the volume fraction of magnetic nanoparticles is
low.",1911.06031v1
2020/1/19,Impact of the magnetic proximity effect in Pt on the total magnetic moment of Pt/Co/Ta trilayers studied by x-ray resonant magnetic reflectivity,"In this work, we study the influence of the magnetic proximity effect (MPE)
in Pt on the total magnetic moment of thin film trilayer systems consisting of
the ferromagnet (FM) Co adjacent to the heavy metals (HMs) Pt and Ta. We
investigate the trilayer systems HM1/FM/HM2 with different stacking order as
well as a reference bilayer without any MPE. X-ray resonant magnetic
reflectivity (XRMR) is a powerful tool to probe induced magnetism, especially
when buried at interfaces in a multilayer. By using XRMR, we are able to obtain
magnetic depth profiles of the structural, optical and magnetic parameters. By
fitting the experimental data with a Gaussian-like magnetooptic profile taking
the structural roughness at the interface into account, we can extract the
magnetic moment of the spin-polarized layer. Comparing the obtained moments to
the measured total moment of the sample, we can determine the impact of the MPE
on the total magnetic moment of the system. Such information can be critical
for analyzing spin transport experiments, including spin-orbit torque and spin
Hall angle measurements, where the saturation magnetization $M_s$ has to be
taken into account. Therefore, by combining magnetization measurements and XRMR
methods we were able to get a complete picture of the magnetic moment
distribution in these trilayer systems containing spin-polarized Pt.",2001.06857v1
2020/2/13,"A new family of disorder-free Rare-Earth-based kagomé lattice magnets: structure and magnetic characterizations of RE3BWO9 (RE=Pr, Nd, Gd-Ho) Boratotungstates","Exploration of rare-earth (RE)-based Kagome lattice magnets with spin-orbital
entangled jeff=1/2 moments will provide new platform for investigating the
exotic magnetic phases. Here, we report a new family of RE3BWO9
(RE=Pr,Nd,Gd-Ho) boratotungstates with magnetic RE3+ ions arranged on Kagome
lattice, and perform its structure and magnetic characterizations. This serial
compounds crystallize in hexagonal coordinated structure with space group P63
(No.173), where magnetic RE3+ ions have distorted Kagom\'e lattice connections
within the ab plane and stacked in a AB-type fashion along c axis. The
interlayer RE-RE separation is comparable with that of intralayer distance,
forming 3-dimensional (3D) exchange coupled magnetic framework of RE3+ ions.
The magnetic susceptibility data of RE3BWO9 (RE=Pr, Nd, Gd-Ho) reveal dominant
antiferromagnetic interactions between magnetic RE3+ ions, but without visible
magnetic ordering down to 2 K. The magnetization analyses for different RE3+
ions show diverse anisotropic behaviors, make RE3BWO9 as an appealing
Kagome-lattice antiferromagnet to explore exotic magnetic phases.",2002.05420v1
2020/5/19,Numerical Analysis of the Screening Current-Induced Magnetic Field in the HTS Insert Dipole Magnet Feather-M2.1-2,"Screening currents are field-induced dynamic phenomena which occur in
superconducting materials, leading to persistent magnetization. Such currents
are of importance in ReBCO tapes, where the large size of the superconducting
filaments gives rise to strong magnetization phenomena. In consequence,
superconducting accelerator magnets based on ReBCO tapes might experience a
relevant degradation of the magnetic field quality in the magnet aperture,
eventually leading to particle beam instabilities. Thus, persistent
magnetization phenomena need to be accurately evaluated. In this paper, the 2D
finite element model of the Feather-M2.1-2 magnet is presented. The model is
used to analyze the influence of the screening current-induced magnetic field
on the field quality in the magnet aperture. The model relies on a coupled
field formulation for eddy current problems in time-domain. The formulation is
introduced and verified against theoretical references. Then, the numerical
model of the Feather-M2.1-2 magnet is detailed, highlighting the key
assumptions and simplifications. The numerical results are discussed and
validated with available magnetic measurements. A satisfactory agreement is
found, showing the capability of the numerical tool in providing accurate
analysis of the dynamic behavior of the Feather-M2.1-2 magnet.",2005.09467v2
2021/6/9,Unraveling the role of the magnetic anisotropy on thermoelectric response: a theoretical and experimental approach,"Magnetic anisotropies have key role to taylor magnetic behavior in
ferromagnetic systems. Further, they are also essential elements to manipulate
the thermoelectric response in Anomalous Nernst (ANE) and Longitudinal Spin
Seebeck systems (LSSE). We propose here a theoretical approach and explore the
role of magnetic anisotropies on the magnetization and thermoelectric response
of noninteracting multidomain ferromagnetic systems. The magnetic behavior and
the thermoelectric curves are calculated from a modified Stoner Wohlfarth model
for an isotropic system, a uniaxial magnetic one, as well as for a system
having a mixture of uniaxial and cubic magnetocrystalline magnetic
anisotropies. It is verified remarkable modifications of the magnetic behavior
with the anisotropy and it is shown that the thermoelectric response is
strongly affected by these changes. Further, the fingerprints of the energy
contributions to the thermoelectric response are disclosed. To test the
robustness of our theoretical approach, we engineer films having the specific
magnetic properties and compare directly experimental data with theoretical
results. Thus, experimental evidence is provided to confirm the validity of our
theoretical approach. The results go beyond the traditional reports focusing on
magnetically saturated films and show how the thermoelectric effect behaves
during the whole magnetization curve. Our findings reveal a promising way to
explore the ANE and LSSE effects as a powerful tool to study magnetic
anisotropies, as well as to employ systems with magnetic anisotropy as sensing
or elements in technological applications.",2106.05063v1
2023/9/19,Field Orientation Dependent Magnetic Phases In Weyl Semimetal Co3Sn2S2,"Magnetism plays a key role in the emergence of topological phenomena in the
Weyl semimetal Co3Sn2S2, which exhibits a ferromagnetic (FM) interactions along
the c-axis of the crystal and an antiferromagnetic (AFM) interactions within
the ab plane. Extensive studies on the temperature dependence of the magnetism
with the magnetic field along the c-axis have uncovered a number of magnetic
phases. Currently, the nature and origins of the reported magnetic phases are
under debate. Here we report on magnetic field orientation effects on the
magnetism in Co3Sn2S2. The shape of the hysteresis loop of the Hall resistance
at a fixed temperature is found to change from rectangular to bow-tie-like as
the magnetic field is tilted from the c-axis towards the ab plane, resembling
that reported for magnetic fields along the c-axis as the temperature
approaches the Curie temperature from below. Unlike their temperature-dependent
counterparts, the newly observed bow-tie-like hysteresis loops show exchange
bias. Our results showcase the contribution of the in-plane AFM interactions to
the magnetism in Co3Sn2S2 and demonstrate a new way to tune its magnetic
phases. They also shed light on the temperature-dependent magnetic phases
occurring in the magnetic field along the c-axis of the crystal.",2309.10221v1
2024/3/24,Strongly asymmetric magnetization switching and programmable complete Boolean logic enabled by long-range intralayer Dzyaloshinskii-Moriya interaction,"Electrical switching of magnetization is central to spintronics. Despite the
enormous efforts on the spin torques and the Dzyaloshinskii-Moriya interaction
(DMI) effects, some fundamental physics for electrical switching of
magnetization is still missing as indicated by a number of remarkable
long-standing puzzles. Here, we report the discovery of the long-range
intralayer DMI effect widely existing in magnetic heterostructure, which is
distinct from the yet-known DMI effects as it describes the chiral coupling of
two orthogonal magnetic domains within the same magnetic layer via the
mediation of an adjacent heavy metal layer. The long-range intralayer DMI
generates a strong perpendicular effective magnetic field (H_DMI^z) on the
perpendicular magnetization. Characteristically, H_DMI^z varies with the
sign/magnitude of the interfacial DMI constant, the applied in-plane magnetic
fields, and the distribution of the perpendicular magnetic anisotropy. The
long-range intralayer DMI results in striking consequences including the
strongly asymmetric current/field switching of perpendicular magnetization,
hysteresis loop shift of perpendicular magnetization in the absence of in-plane
direct current, and sharp, complete switching of perpendicular magnetization
purely by an in-plane magnetic field. Utilizing the long-range intralayer DMI
effect, we demonstrate programable, complete Boolean logic operations (i.e.,
AND, NAND, NOT, OR, and NOR) within a single spin-orbit torque device. These
results will stimulate the investigation of the long-range intralayer DMI
effect and its impacts on a variety of spintronic devices.",2403.16035v1
2004/4/26,Giant Single-Molecule Magnets: A Mn84 Torus and its Supramolecular Nanotubes,"The discovery a decade ago that individual molecules can function as
magnetizable magnets provided a new, 'bottom-up' approach to nanoscale magnetic
materials, and such molecules have since been called single-molecule magnets
(SMMs). Each molecule functions as a nanoscale, single-domain magnetic particle
that, below its blocking temperature (TB), exhibits the classical macroscale
property of a magnet, namely magnetization hysteresis. In addition, they
straddle the classical/quantum interface in also displaying quantum tunnelling
of magnetization (QTM) and quantum phase interference, the properties of the
atomic or microscale. SMMs have a number of potential applications, including
very high density information storage, where each bit would be stored as the
magnetization orientation of an individual molecule, and as quantum bits for
quantum computing, taking advantage of the quantum superposition of states
provided by the QTM. To facilitate development of techniques for addressing
individual SMMs for such applications, and other reasons, it has been of
interest to us to explore whether very large examples (by molecular standards)
could be synthesized. In effect, can the molecular (or 'bottom-up') approach
reach the size regime of the classical (or 'top-down') approach to nanoscale
magnetic materials? Indeed, here we sure that a giant Mn84 SMM can be prepared
with a torus structure of 4 nm dimensions, that it displays both magnetization
hysteresis and QTM, and that it crystallizes as highly ordered, supramolecular
nanotubes.",0404625v1
2015/4/14,Magnetization induced local electric dipoles and multiferroic properties of Ba2CoGe2O7,"Ba2CoGe2O7, crystallizing in the noncentrosymmetric but nonpolar structure,
belongs to a special class of multiferroic materials, whose properties are
predetermined by the rotoinversion symmetry. Unlike inversion, the
rotoinversion symmetry can be easily destroyed by the magnetization. Moreover,
due to specific structural pattern, the magnetic structure of Ba2CoGe2O7 is
relatively soft. Altogether, this leads to the rich variety of multiferroic
properties, where the magnetic structure can be easily deformed by the magnetic
field, inducing the electric polarization in the direction, which depends on
the direction of the magnetic field. In this paper, we show that all these
properties can be successfully explained on the basis of realistic low-energy
model, derived from the first-principles electronic structure calculations for
the magnetically active Co 3d bands, and the Berry-phase theory of electric
polarization. Particularly, we argue that the magnetization induced electric
polarization in Ba2CoGe2O7 is essentially local and expressed via the
expectation values of some dipole matrices, calculated in the Wannier basis of
the model, and the site-diagonal density matrices of the magnetic Co sites.
Thus, the basic aspects of the behavior of Ba2CoGe2O7 can be understood already
in the atomic limit, where both magnetic anisotropy and magnetoelectric
coupling are specified by density matrix. Then, the macroscopic polarization
can be found as a superposition of electric dipoles of the individual Co sites.
We discuss the behavior of interatomic magnetic interactions, main
contributions to the magnetocrystalline anisotropy and the spin canting, as
well as the similarities and differences of the proposed picture from the
phenomenological model of spin-dependent p-d hybridization.",1504.03540v1
2012/9/19,Orbital and spin magnetic moments of transforming 1D iron inside metallic and semiconducting carbon nanotubes,"The orbital and spin magnetic properties of iron inside transforming metallic
and semiconducting 1D carbon nanotube hybrids are studied by means of local
x-ray magnetic circular dichroism (XMCD) and bulk superconducting quantum
interference device (SQUID) measurements. Nanotube hybrids are initially
ferrocene filled single-walled carbon nanotubes (SWCNT) of different
metallicities. After a high temperature nanochemical reaction ferrocene
molecules react with each other to form iron nano clusters. We show that the
ferrocenes molecular orbitals interact differently with the SWCNT of different
metallicities without significant XMCD response. This XMCD at various
temperatures and magnetic fields reveals that the orbital and/or spin magnetic
moments of the encapsulated iron are altered drastically as the transformation
to 1D Fe nanoclusters takes place. The orbital and spin magnetic moments are
both found to be larger in filled semiconducting nanotubes than in the metallic
sample. This could mean that the magnetic polarizations of the encapsulated
material is dependent on the metallicity of the tubes. From a comparison
between the iron 3d magnetic moments and the bulk magnetism measured by SQUID,
we conclude that the delocalized magnetisms dictate the magnetic properties of
these 1D hybrid nanostructures.",1209.4265v1
2020/4/15,Synthesis optimization of Zn-Mn ferrites for magnetic fluid aplications,"Mn-Zn ferrite nanoparticles have been subject of increasing research due to
their desired properties for a wide range of applications. These properties
include nanometer particle size control, tunable magnetic properties and low
toxicity, providing these ferrites with the necessary requirements for cancer
treatment via magnetic hyperthermia. During this master thesis, powders of
Mn1-xZnxFe2O4 (x=0; 0.5; 0.8; 1) were synthesized via the sol-gel
autocombustion and hydrothermal methods, aiming to optimize their structural
and magnetic properties for further application in a ferrofluid. Samples were
characterized by XRD, SQUID, SEM, TEM and magnetic induction heating (MIH)
techniques. The XRD diffractograms of hydrothermally produced samples present
spinel crystal structure with high single-phase percentage (>88%). Rietveld
refinement and Williamson-Hall analysis reveal a decrease of lattice constant
and crystallite size with increase of Zn/Mn ratio. TEM images reveal narrow
particle size distributions and decrease of the mean particle size with
increase of Zn/Mn. SQUID results show that the increase of Zn results in a
decrease of saturation magnetization and remnant magnetization. More
noticeably, the M(T) curves present a shift in the samples magnetic ordering
temperature towards lower temperatures with the increase of Zn content, from
~556 to ~284 K. The MIH experiment also unveil a decrease in the heating rate
with the increase of Zn. Nanocrystals of Mn-Zn ferrite produced by hydrothermal
method present better crystallinity and magnetic properties than the sol-gel
auto-combustion samples. The hydrothermally synthesized samples revealed
dependence of its structural and magnetic properties with Mn/Zn ratio.The
magnetic ordering temperature of these ferrites can be used as a
self-controlled mechanism of heating, raising these ferrites to a class of
smart materials.",2004.07006v2
2019/2/25,Strong anisotropy in the mixed antiferromagnetic system Mn$_{1-x}$Fe$_{x}$PSe$_3$,"We report the magnetic phase diagram of Mn$_{1-x}$Fe$_{x}$PSe$_3$ which
represents a random magnet system of two antiferromagnetic systems with mixed
spin, mixed spin anisotropies, mixed nearest neighbor magnetic interactions and
mixed periodicities in their respective antiferromagnetic structure. Bulk
samples of Mn$_{1-x}$Fe$_{x}$PSe$_3$ have been prepared and characterized phase
pure by powder X-ray and neutron diffraction and X-ray fluorescence. Nature and
extent of magnetically ordered state has been established using powder neutron
diffraction, dc magnetic susceptibility and heat capacity. Long-range magnetic
ordering exists between $x = 0.0$ and 0.25 (MnPSe$_3$-type) and between $x =
0.875$ and $1$ (FePSe$_3$-type). A short-range magnetic order with existence of
both MnPSe$_3$- and FePSe$_3$-type nano-clusters has been established between
$x = 0.25$ and $0.875$. Irreversibility in dc magnetization measurements, also
characterized by isothermal and thermoremanent magnetization measurements
suggest similarities to magnetic nanoparticles where uncompensated surface
spins result in a non-zero TRM and IRM response, further reinforcing existence
of magnetic nano-clusters or domains. A spin glass state, observed in analogous
Mn$_{1-x}$Fe$_x$PS$_3$, has been ruled out and formation of nano-clusters
exhibiting both ordering types results from unusually high anisotropy values.
The effect of ligand contributions to the spin-orbit interactions has been
suggested as a possible explanation for high $D$ values in these compounds.",1902.09655v2
2019/3/2,Microwave excitations and hysteretic magnetization dynamics of stripe domain films,"FeNi films with the stripe domain (SD) pattern are prepared by
electrodeposition and sputtering methods. The magnetic domain, static magnetic
parameters, and quality factor, as well as dynamic properties of the two films,
are respectively performed. The results show the magnetizations of the film
were dependent on the direction of SD, and the rotation of the SD is lagging
behind the magnetization reversal. The microwave properties of the SD emerge
dynamic hysteresis before the saturation magnetic field. These microwave
properties are selectively excited with acoustic mode, optical mode, and
spin-wave mode. The frequency and intensity of different resonance modes of
stripe domain are determined by the local magnetization. The magnetization
variations and the rotation of SD of different modes are further illuminated by
the micromagnetic simulation. The magnetic anisotropy and the resonance
intensity of permeability of different modes were finally described by the
modified resonance equations.",1903.00656v2
2019/4/5,Tailoring anomalous Nernst effect in stressed magnetostrictive film grown onto flexible substrate,"The anomalous Nernst effect in nanostructured magnetic materials is a key
phenomenon to optimally control and employ the internal energy dissipated in
electronic devices, being dependent on for instance the magnetic anisotropy of
the active element. Thereby, here we report a theoretical and experimental
investigation of the magnetic properties and anomalous Nernst effect in a
flexible magnetostrictive film with induced uniaxial magnetic anisotropy and
under external stress. Specifically, we calculate the magnetization behavior
and the thermoelectric voltage response from a theoretical approach for a
planar geometry and with a magnetic free energy density which takes into
account the induced uniaxial and magnetoelastic anisotropy contributions.
Experimentally, we verify modifications of the effective magnetic anisotropy
and thermoelectric voltage with the stress and explore the possibility of
tailoring the anomalous Nernst effect in a flexible magnetostrictive film by
modifying both, the magnetic field and external stress. We find quantitative
agreement between experiment and numerical calculations, thus elucidating the
magnetic and thermoelectric voltage behaviors, as well as providing evidence to
confirm the validity of the theoretical approach to describe the magnetic
properties and anomalous Nernst effect in ferromagnetic magnetostrictive films
having uniaxial magnetic anisotropy and submitted to external stress. Hence,
the results place flexible magnetostrictive systems as a promising candidate
for active elements in functionalized touch electronic devices.",1904.03125v1
2019/11/11,Gate Tunable Magnetism and Giant Magnetoresistance in ABC-stacked Few-Layer Graphene,"Magnetism is a prototypical phenomenon of quantum collective state, and has
found ubiquitous applications in semiconductor technologies such as dynamic
random access memory (DRAM). In conventional materials, it typically arises
from the strong exchange interaction among the magnetic moments of d- or
f-shell electrons. Magnetism, however, can also emerge in perfect lattices from
non-magnetic elements. For instance, flat band systems with high density of
states (DOS) may develop spontaneous magnetic ordering, as exemplified by the
Stoner criterion. Here we report tunable magnetism in rhombohedral-stacked
few-layer graphene (r-FLG). At small but finite doping (n~10^11 cm-2), we
observe prominent conductance hysteresis and giant magnetoconductance that
exceeds 1000% as a function of magnetic fields. Both phenomena are tunable by
density and temperature, and disappears for n>10^12 cm-2 or T>5K. These results
are confirmed by first principles calculations, which indicate the formation of
a half-metallic state in doped r-FLG, in which the magnetization is tunable by
electric field. Our combined experimental and theoretical work demonstrate that
magnetism and spin polarization, arising from the strong electronic
interactions in flat bands, emerge in a system composed entirely of carbon
atoms. The electric field tunability of magnetism provides promise for
spintronics and low energy device engineering.",1911.04450v1
2020/7/9,Magnetic Immunoassays: A Review of Virus and Pathogen Detection Before and Amidst the Coronavirus Disease-19 (COVID-19),"The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which
causes coronavirus disease 2019 (COVID-19), is a threat to the global
healthcare system and economic security. As of July 2020, no specific drugs or
vaccines are yet available for COVID-19, fast and accurate diagnosis for
SARS-CoV-2 is essential in slowing down the spread of COVID-19 and for
efficient implementation of control and containment strategies. Magnetic
immunoassay is a novel and emerging topic representing the frontiers of current
biosensing and magnetics areas. The past decade has seen rapid growth in
applying magnetic tools for biological and biomedical applications. Recent
advances in magnetic materials and nanotechnologies have transformed current
diagnostic methods to nanoscale and pushed the detection limit to early stage
disease diagnosis. Herein, this review covers the literatures of magnetic
immunoassay platforms for virus and pathogen detections, before COVID-19. We
reviewed the popular magnetic immunoassay platforms including magnetoresistance
(MR) sensors, magnetic particle spectroscopy (MPS), and nuclear magnetic
resonance (NMR). Magnetic Point-of-Care (POC) diagnostic kits are also reviewed
aiming at developing plug-and-play diagnostics to manage the SARS-CoV-2
outbreak as well as preventing future epidemics. In addition, other platforms
that use magnetic materials as auxiliary tools for enhanced pathogen and virus
detections are also covered. The goal of this review is to inform the
researchers of diagnostic and surveillance platforms for SARS-CoV-2 and their
performances.",2007.04809v1
2020/12/8,Hidden momentum in continuous media and the Abraham-Minkowski debate,"We perform a detailed study of the connection between hidden momentum and the
Abraham-Minkowski debate about the electromagnetic momentum density in material
media. The results of a previous work on the subject [P. L. Saldanha and J. S.
Oliveira Filho, Phys. Rev. A 95, 043804 (2017)] are extended to the continuous
medium limit, where some subtleties arise. We consider a polarized and
magnetized continuous medium with applied electric and magnetic static fields,
where the medium polarization can be due to either an electric charge density
or a hypothetical magnetic current density and the medium magnetization can be
due to either an electric current density or a hypothetical magnetic charge
density. Each model leads to a different expression for the system material
hidden momentum and for the electromagnetic momentum density in the medium. We
show that the main results of the cited reference are sustained in the
continuous medium limit: Abraham momentum is compatible with a model for the
medium where the polarization is due to electric charges and the magnetization
is due to magnetic charges, Minkowski momentum is compatible to a model where
the polarization is due to magnetic currents and the magnetization is due to
electric currents, and the expression $\varepsilon_0\mathbf{E}\times\mathbf{B}$
is compatible with a model where the polarization is due to electric charges
and the magnetization is due to electric currents, which is the natural model.
These results are illustrated with the example of a uniformly polarized and
magnetized sphere.",2012.04574v1
2021/2/24,Unusual direction-dependent magnetic orbital moment obtained from X-ray magnetic circular dichroism in a multiferroic oxide system,"The electric-field control of $d$-electron magnetism in multiferroic
transition metal oxides is attracting widespread interest for the underlying
fundamental physics and for next generation spintronic devices. Here, we report
an extensive study of the $3d$ magnetism in magnetoelectric
Ga$_{0.6}$Fe$_{1.4}$O$_3$ (GFO) epitaxial films by polarization dependent x-ray
absorption spectroscopy. We found a non-zero integral of the x-ray magnetic
circular dichroism, with a sign depending upon the relative orientation between
the external magnetic field and the crystallographic axes. %By reliably
enlarging the limit of the spin and orbital sum rules, which usually holds for
materials where the magnetic ions exhibit a unique crystal field symmetry This
finding translates in a sign-reversal between the average Fe magnetic orbital
and spin moments. Large Fe-displacements, among some of the octahedral sites,
lower the symmetry of the system producing anisotropic paths for the Fe-O
bondings giving rise to a large orbital-lattice interaction akin to a
preferential crystallographic direction for the magnetic orbital moment. The
latter may lead to a partial re-orientation of the magnetic orbital moment
under an external magnetic field that, combined to the ferrimagnetic nature of
the GFO, can qualitatively explain the observed sign-reversal of the XMCD
integral. The results suggest that a control over the local symmetry of the
oxygen octahedra in transition metal oxides can offer a suitable leverage over
the manipulation of the effective orbital and spin moments in magnetoelectric
systems.",2102.12118v2
2021/10/21,Shaping Magnetic Fields with Zero-Magnetic-Permeability Media,"Some of the most important technological challenges of today's society, such
as fusion reactors for future clean unlimited energy or the next generation of
medical imaging techniques, require precise spatial shapes of strong magnetic
fields. Achieving these high fields is currently hindered by limitations such
as large forces damaging the wires in coils or the saturation of ferromagnets
at high fields. Here we demonstrate a novel paradigm for creating magnetic
landscapes. By enclosing magnetic sources within zero-magnetic-permeability
(ZMP) media, a set of novel properties is unveiled. The magnetic field shape
directly results from the contour of the outer surface of the ZMP enclosure,
which allows the realization of basically any imaginable field landscape. Also,
currents embedded in ZMP media can be fully magnetically isolated, which
eliminates the forces in the wires, one of the main factors that currently
impedes achieving very high magnetic fields. We confirm these properties,
rooted in fundamental laws of electromagnetism, by numerical simulations and by
proof-of-principle experiments using conventional high-temperature
superconductors as ZMP materials, which showcase the practical applicability of
our ideas. The freedom in the design of magnetic fields provided by ZMP media
enables to concentrate and homogenize magnetic fields with unprecedented
precision, as needed in medical imaging techniques and particle-physics
experiments, and to realize devices like perfect electromagnetic absorbers of
mechanical vibrations.",2110.11257v1
2022/2/15,Investigation of the magnetoelastic coupling anisotropy in the Kitaev material $α$-RuCl$_3$,"The Kitaev material $\alpha$-RuCl$_3$ is among the most prominent candidates
to host a quantum spin-liquid state endowed with fractionalized excitations.
Recent experimental and theoretical investigations have separately revealed the
importance of both the magnetoelastic coupling and the magnetic anisotropy, in
dependence of the applied magnetic field direction. In this combined
theoretical and experimental research, we investigate the anisotropic magnetic
and magnetoelastic properties for magnetic fields applied along the main
crystallographic axes as well as for fields canted out of the honeycomb plane.
We found that the magnetostriction anisotropy is unusually large compared to
the anisotropy of the magnetization, which is related to the strong
magnetoelastic $\widetilde{\Gamma'}$-type coupling in our \textit{ab-initio}
derived model. We observed large, non-symmetric magnetic anisotropy for
magnetic fields canted out of the honeycomb $ab$-plane in opposite directions,
namely towards the $+c^*$ or $-c^*$ axes, respectively. The observed
directional anisotropy is explained by considering the relative orientation of
the magnetic field with respect to the co-aligned RuCl$_6$ octahedra.
Magnetostriction measurements in canted fields support this non-symmetric
magnetic anisotropy, however these experiments are affected by magnetic torque
effects. Comparison of theoretical predictions with experimental findings allow
us to recognize the significant contribution of torque effects in experimental
setups where $\alpha$-RuCl$_3$ is placed in canted magnetic fields.",2202.07102v1
2022/6/6,"Anisotropic magnetic property of single crystals $R$V$_6$Sn$_6$ ($R$ = Y, Gd - Tm, Lu)","$R$V${_6}$Sn${_6}$ ($R$ = Y, Gd - Tm, Lu) single crystals are synthesized by
Sn-flux method and their physical properties are characterized by
magnetization, resistivity, and specific heat measurements. Powder X-ray
diffraction patterns of all samples can be well indexed with the hexagonal
HfFe$_6$Ge$_6$-type structure, where rare-earth atoms form hexagonal layers and
vanadium atoms form Kagome layers. At high temperatures, magnetic
susceptibility measurements of moment bearing rare-earths ($R$ = Gd - Tm)
follow Curie-Weiss behavior. Effective moments estimated from the
polycrystalline average of magnetic susceptibility curves are consistent with
the values for free $R^{3+}$ ion. Strong magnetic anisotropy due to crystalline
electric field effects is observed for moment bearing rare-earths, except
GdV$_6$Sn$_6$. The easy magnetization direction is determined to be $c$-axis
for $R$ = Tb - Ho and $ab$-plane for $R$ = Er, and Tm. The vanadium ions in
$R$V${_6}$Sn${_6}$ possess no magnetic moment. The compounds for $R$ = Y and Lu
exhibit typical characteristics of paramagnetic metals. At low temperatures,
the magnetic ordering is confirmed from magnetization, specific heat, and
resistivity: the highest $T_{N} = 4.9$~K for GdV$_6$Sn$_6$ and the lowest
$T_{N} = 2.3$~K for HoV$_6$Sn$_6$. No magnetic ordering is observed down to
1.8~K for $R$ = Er and Tm. A slight deviation of the magnetic ordering
temperature from the de Gennes scaling suggests the dominant
Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interaction between rare-earth
moments in metallic $R$V${_6}$Sn${_6}$ compounds.",2206.02924v1
2022/10/19,"Unveiling the anisotropic fractal magnetic domain structure in bulk crystal of antiskyrmion-host (Fe,Ni,Pd)$_3$P by small-angle neutron scattering","Intermetallic Pd-doped (Fe,Ni)$_3$P, that crystalizes in a
non-centrosymmetric tetragonal structure with $S_4$ symmetry, has recently been
discovered to host magnetic antiskyrmions, antivortex-like topological spin
textures. In this material, uniaxial magnetic anisotropy and dipolar
interactions play a significant role, giving rise to finely branched magnetic
domain patterns near the surface of bulk crystals, as revealed by a previous
magnetic force microscopy (MFM) measurement. However, small-angle neutron
scattering (SANS) is a more suitable method for characterizing bulk properties
and fractal structures at the mesoscopic length scale. In this study, using
SANS and MFM, we quantitatively investigate the magnetic domain structure in
bulk single crystals of (Fe$_{0.63}$Ni$_{0.30}$Pd$_{0.07}$)$_3$P. The SANS
results demonstrate that the magnetic domain structure exhibits anisotropic
fractal character on the length scale down to the width of the magnetic domain
walls. The fractal features are gradually lost in magnetic fields, and
different field dependences are observed at 300 K and 2 K due to a
temperature-dependent anisotropy. This study quantifies the fractality of the
highly anisotropic magnetic domain structures in an antiskyrmion material, and
highlights the versatility of SANS for the study of fractal structures in
magnetic systems.",2210.10274v1
2023/11/27,Spin order dependent skyrmion stabilization in MnFeCoGe hexagonal magnets,"Topological magnetic skyrmions in centrosymmetric systems exhibit a higher
degrees of freedom in their helicity, hence possess a great potential in the
advanced spintronics including skyrmion based quantum computation. However, the
centrosymmetric magnets also display non-topological trivial bubbles along with
the topological skyrmions. Hence it is utmost priority to investigate the
impact of different magnetic ground states and their underlying interactions on
the stabilization of magnetic skyrmions in cetrosymmetric magnets. Here, we
present a combined theoretical and experimental study on the role of
non-collinear magnetic ground state on the skyrmion stabilization in a series
of exchange frustrated non-collinear ferromagnetic system MnFe1-xCoxGe. With
the help of neutron diffraction (ND) and Lorentz transmission electron
microscopy (LTEM) studies, we show that hexagonal skyrmions lattice emerges as
a stable field driven state only when the underlying magnetic ground state is
collinear with easy-axis anisotropy. In contrast, non-topological type-II
bubbles are found to be stable state in the case of non-collinear magnetic
ordering with partial in-plane anisotropy. Furthermore, we also find that the
skyrmions transform to the non-topological bubbles when the system undergoes a
spin reorientation transition from the easy-axis to easy-cone ferromagnetic
phase. Our results categorically establish the significant role of in-plane
magnetic moment/anisotropy that hinders the stability of skyrmion both in the
case of collinear and non-collinear magnets. Thus, the present study offers a
wide range of opportunities to manipulate the stability of dipolar skyrmions by
changing the intrinsic characteristics of the materials.",2311.15823v1
2003/10/7,Magnetic Spin-Up of Line-Driven Winds,"We summarize recent 2D MHD simulations of line-driven stellar winds from
rotating hot-stars with a dipole magnetic field aligned to the star's rotation
axis. For moderate to strong fields, much wind outflow is initially along
closed magnetic loops that nearly corotate as a solid body with the underlying
star, thus providing a torque that results in an effective angular momentum
spin-up of the outflowing material. But instead of forming the ``magnetically
torqued disk'' (MTD) postulated in previous phenemenological analyses, the
dynamical simulations here show that material trapped near the tops of such
closed loops tends either to fall back or break out, depending on whether it is
below or above the Keplerian corotation radius. Overall the results raise
serious questions about whether magnetic torquing of a wind outflow could
naturally result in a Keplerian circumstellar disk. However, for very strong
fields, it does still seem possible to form a %``magnetically confined,
centrifugally supported, rigid-body disk'', centrifugally supported,
``magnetically rigid disk'' (MRD), in which the field not only forces material
to maintain a rigid-body rotation, but for some extended period also holds it
down against the outward centrifugal force at the loop tops. We argue that such
rigid-body disks seem ill-suited to explain the disk emission from Be stars,
but could provide a quite attractive paradigm for circumstellar emission from
the magnetically strong Bp and Ap stars.",0310179v1
2006/1/9,Centrifugal Breakout of Magnetically Confined Line-Driven Stellar Winds,"We present 2D MHD simulations of the radiatively driven outflow from a
rotating hot star with a dipole magnetic field aligned with the star's rotation
axis. We focus primarily on a model with moderately rapid rotation (half the
critical value), and also a large magnetic confinement parameter, $\eta_{\ast}
\equiv B_{\ast}^2 R_{\ast}^{2} / \dot{M} V_{\infty} = 600$. The magnetic field
channels and torques the wind outflow into an equatorial, rigidly rotating disk
extending from near the Kepler corotation radius outwards. Even with
fine-tuning at lower magnetic confinement, none of the MHD models produce a
stable Keplerian disk. Instead, material below the Kepler radius falls back on
to the stellar surface, while the strong centrifugal force on material beyond
the corotation escape radius stretches the magnetic loops outwards, leading to
episodic breakout of mass when the field reconnects. The associated dissipation
of magnetic energy heats material to temperatures of nearly $10^{8}$K, high
enough to emit hard (several keV) X-rays. Such \emph{centrifugal mass ejection}
represents a novel mechanism for driving magnetic reconnection, and seems a
very promising basis for modeling X-ray flares recently observed in rotating
magnetic Bp stars like $\sigma$ Ori E.",0601193v2
2013/3/18,On the Support of Solar Prominence Material by the Dips of a Coronal Flux Tube,"The dense prominence material is believed to be supported against gravity
through the magnetic tension of dipped coronal magnetic field. For quiescent
prominences, which exhibit many gravity-driven flows, hydrodynamic forces are
likely to play an important role in the determination of both the large and
small scale magnetic field distributions. In this study, we present the first
steps toward creating three-dimensional magneto-hydrostatic prominence model
where the prominence is formed in the dips of a coronal flux tube. Here 2.5D
equilibria are created by adding mass to an initially force-free magnetic
field, then performing a secondary magnetohydrodynamic relaxation. Two inverse
polarity magnetic field configurations are studied in detail, a simple o-point
configuration with a ratio of the horizontal field (B_x) to the axial field
(B_y) of 1:2 and a more complex model that also has an x-point with a ratio of
1:11. The models show that support against gravity is either by total pressure
or tension, with only tension support resembling observed quiescent
prominences. The o-point of the coronal flux tube was pulled down by the
prominence material, leading to compression of the magnetic field at the base
of the prominence. Therefore tension support comes from the small curvature of
the compressed magnetic field at the bottom and the larger curvature of the
stretched magnetic field at the top of the prominence. It was found that this
method does not guarantee convergence to a prominence-like equilibrium in the
case where an x-point exists below the prominence flux tube. The results imply
that a plasma beta of ~ 0.1 is necessary to support prominences through
magnetic tension.",1303.4130v1
2016/1/16,"Lattice specific heat for the RMIn$_5$ (R = Gd, La, Y, M = Co, Rh) compounds: non-magnetic contribution subtraction","We analyze theoretically a common experimental process used to obtain the
magnetic contribution to the specific heat of a given magnetic material. In the
procedure, the specific heat of a non-magnetic analog is measured and used to
subtract the non-magnetic contributions, which are generally dominated by the
lattice degrees of freedom in a wide range of temperatures. We calculate the
lattice contribution to the specific heat for the magnetic compounds GdMIn$_5$
(M = Co, Rh) and for the non-magnetic YMIn$_5$ and LaMIn$_5$ (M = Co, Rh),
using density functional theory based methods. We find that the best
non-magnetic analog for the subtraction depends on the magnetic material and on
the range of temperatures. While the phonon specific heat contribution of
YRhIn$_5$ is an excellent approximation to the one of GdCoIn$_5$ in the full
temperature range, for GdRhIn$_5$ we find a better agreement with LaCoIn$_5$,
in both cases, as a result of an optimum compensation effect between masses and
volumes. We present measurements of the specific heat of the compounds
GdMIn$_5$ (M = Co, Rh) up to room temperature where it surpasses the value
expected from the Dulong-Petit law. We obtain a good agreement between theory
and experiment when we include anharmonic effects in the calculations.",1601.04214v1
2016/5/2,Electrical Detection of Magnetization Dynamics via Spin Rectification Effects,"The purpose of this article is to review the current status of a frontier in
dynamic spintronics and contemporary magnetism, in which much progress has been
made in the past decade, based on the creation of a variety of micro- and
nano-structured devices that enable electrical detection of magnetization
dynamics. The primary focus is on the physics of spin rectification effects,
which are well suited for studying magnetization dynamics and spin transport in
a variety of magnetic materials and spintronic devices. Intended to be
intelligible to a broad audience, the paper begins with a pedagogical
introduction, comparing the methods of electrical detection of charge and spin
dynamics in semiconductors and magnetic materials respectively. After that it
provides a comprehensive account of the theoretical study of both the angular
dependence and line shape of electrically detected ferromagnetic resonance
(FMR), which is summarized in a handbook formate easy to be used for analyzing
experimental data. We then review and examine the similarity and differences of
various spin rectification effects found in ferromagnetic films, magnetic
bilayers and magnetic tunnel junctions, including a discussion of how to
properly distinguish spin rectification from the spin pumping/inverse spin Hall
effect generated voltage. After this we review the broad applications of
rectification effects for studying spin waves, nonlinear dynamics, domain wall
dynamics, spin current, and microwave imaging. We also discuss spin
rectification in ferromagnetic semiconductors. The paper concludes with both
historical and future perspectives, by summarizing and comparing three
generations of FMR spectroscopy which have been developed for studying
magnetization dynamics.",1605.00710v2
2018/6/14,Rare-earth/transition-metal magnets at finite temperature: Self-interaction-corrected relativistic density functional theory in the disordered local moment picture,"Atomic-scale computational modeling of technologically relevant permanent
magnetic materials faces two key challenges. First, a material's magnetic
properties depend sensitively on temperature, so the calculations must account
for thermally induced magnetic disorder. Second, the most widely-used permanent
magnets are based on rare-earth elements, whose highly localized 4$f$ electrons
are poorly described by standard electronic structure methods. Here, we take
two established theories, the disordered local moment picture of thermally
induced magnetic disorder and self-interaction-corrected density functional
theory, and devise a computational framework to overcome these challenges.
Using the new approach, we calculate magnetic moments and Curie temperatures of
the rare-earth cobalt (RECo$_5$) family for RE=Y--Lu. The calculations
correctly reproduce the experimentally measured trends across the series and
confirm that, apart from the hypothetical compound EuCo$_5$, SmCo$_5$ has the
strongest magnetic properties at high temperature. An order-parameter analysis
demonstrates that varying the RE has a surprisingly strong effect on the Co--Co
magnetic interactions determining the Curie temperature, even when the lattice
parameters are kept fixed. We propose the origin of this behavior is a small
contribution to the density from $f$-character electrons located close to the
Fermi level.",1806.05646v1
2018/9/19,Structural distortion and incommensurate noncollinear magnetism in EuAg4As2,"Layered pnictide materials have provided a fruitful platform to study various
emergent phenomena, including superconductivity, magnetism, charge density
waves, etc. Here we report the observation of structural distortion and
noncollinear magnetism in layered pnictide EuAg$_4$As$_2$ via transport,
magnetization, single crystal X-ray and neutron diffraction data.
EuAg$_4$As$_2$ single crystal shows a structural distortion at 120 K, where two
sets of superlattice peaks with the propagation vectors of $q_1=\pm$(0, 0.25,
0.5) and $q_2=\pm$(0.25, 0, 1) emerge. Between 9 K to 15 K, the hexagonal
Eu$^{2+}$ sub-lattice enters an unpinned state, with magnetic Bragg reflections
pictured as circular-sectors. Below 9 K, it orders in an incommensurate
noncollinear antiferromagnetic state with a well-defined propagation wavevector
of (0, 0.1, 0.12), where the magnetic structure is helical along the $c$ axis
and cycloidal along the $b$ axis with a moment of 6.4 $\mu_B$/Eu$^{2+}$.
Furthermore, rich magnetic phases under magnetic fields, large
magnetoresistance, and strong coupling between charge carriers and magnetism in
EuAg$_4$As$_2$ are revealed.",1809.07317v4
2020/4/23,Temperature-dependent Magnetic Transitions in CoCrPt-Ru-CoCrPt Synthetic Ferrimagnets,"The magnetic orientations and switching fields of a CoCrPt-Ru-CoCrPt
synthetic ferrimagnet with perpendicular magnetic anisotropy have been studied
in the temperature range from 2 K to 300 K. It was found that two sets of
magnetic transitions occur in the CoCrPt-Ru-CoCrPt ferrimagnet across this
temperature range. The first set exhibits three magnetic transitions in the 50
K - 370 K range, whereas the second involves only two transitions in the 2 K
and 50 K range. The observed magnetic hysteresis curves of the synthetic
ferrimagnet are explained using the energy diagram technique framework
pioneered by Koplak et al. [1] which accurately describes the competition
between interlayer exchange coupling energy, Zeeman energy, and anisotropy
energy in the system. In this work we expand the framework to include synthetic
ferrimagnets (SFMs) comprising higher perpendicular magnetic anisotropy
materials and large (4X) interlayer exchange coupling energies which are
promising for the development of ultrafast (ps) magnetic switching free layers
in MTJ structures. Furthermore, we apply the analysis to predict SFM magnetic
hysteresis curves in a temperature regime that includes temperature extrema
that a synthetic ferrimagnet would be expected to reliably operate at, were it
to be utilized as a free layer in a memory or sensor spintronic device.",2004.11406v2
2021/5/1,Anisotropy and Current Control of Magnetization in SrRuO$_3$ SrTiO$_3$ Heterostructures for Spin-Memristors,"Spintronics-based nonvolatile components in neuromorphic circuits offer the
possibility of realizing novel functionalities at low power. Current-controlled
electrical switching of magnetization is actively researched in this context.
Complex oxide heterostructures with perpendicular magnetic anisotropy (PMA),
consisting of SrRuO$_3$ (SRO) grown on SrTiO$_3$ (STO) are strong material
contenders. Utilizing the crystal orientation, magnetic anisotropy in such
simple heterostructures can be tuned to either exhibit a perfect or slightly
tilted PMA. Here, we investigate current-induced magnetization modulation in
such tailored ferromagnetic layers with a material with strong spin-orbit
coupling (Pt), exploiting the spin Hall effect. We find significant differences
in the magnetic anisotropy between the SRO/STO heterostructures, as manifested
in the first and second harmonic magnetoresistance measurements.
Current-induced magnetization switching can be realized with spin-orbit
torques, but for systems with perfect PMA this switching is probabilistic as a
result of the high symmetry. Slight tilting of the PMA can break this symmetry
and allow the realization of deterministic switching. Control over the magnetic
anisotropy of our heterostructures therefore provides control over the manner
of switching. Based on our findings, we propose a three-terminal spintronic
memristor, with a magnetic tunnel junction design, that shows several resistive
states controlled by electric charge. Non-volatile states can be written
through SOT by applying an in-plane current, and read out as a tunnel current
by applying a small out-of-plane current. Depending on the anisotropy of the
SRO layer, the writing mechanism is either deterministic or probabilistic
allowing for different functionalities to emerge. We envisage that the
probabilistic MTJs could be used as synapses while the deterministic devices
can emulate neurons",2105.00269v1
2019/11/27,Field-induced magnetic transition and spin fluctuation in quantum spin liquid candidate CsYbSe$_2$,"Two-dimensional triangular-lattice materials with spin-1/2 are perfect
platforms for investigating quantum frustrated physics with spin fluctuations.
Here we report the structure, magnetization, heat capacity and inelastic
neutron scattering (INS) results on cesium ytterbium diselenide, CsYbSe$_2$.
There is no long-range magnetic order down to 0.4 K at zero field. The
temperature dependent magnetization, $M(T)$, reveals an easy-plane magnetic
anisotropy. A maximum is found in $M(T)$ around \emph{T}$\sim$1.5 K when
magnetic field $H$ is applied in the $ab$ plane, indicating the short-range
interaction. The low-temperature isothermal magnetization $M(H)$ shows a
one-third plateau of the estimated saturation moment, that is characteristic of
a two-dimensional frustrated triangular lattice. Heat capacity shows
field-induced long-range magnetic order for both $H||c$ and $H||ab$ directions.
The broad peak in heat capacity and highly damped INS magnetic excitation at
$T$=2 K suggests strong spin fluctuations. The dispersive in-plane INS,
centered at the (1/3 1/3 0) point, and the absence of dispersion along $c$
direction suggests 120$^{\circ}$ non-collinear 2D-like spin correlations. All
these results indicate that the two-dimensional frustrated material CsYbSe$_2$
can be in proximity to the triangular-lattice quantum spin liquid. We propose
an experimental low-temperature $H$-$T$ phase diagram for CsYbSe$_2$.",1911.12286v1
2020/11/19,Giant anisotropy of the magnetocaloric effect in the orthovanadate TbVO4 single crystals,"It is known that the Zircon-type orthovanadates RVO4 show promise in many
different applications as catalysts and optical materials. In this work, we
demonstrate that the TbVO4 compound can be also used as magnetic refrigerant in
efficient and ecofriendly cryocoolers due to its strong magnetocaloric effect
at low temperature regime. The application of a relatively low magnetic field
of 2 T along the easy magnetization axis (a) gives rise to a maximum entropy
change of about 20 J/kg K at 4 K. More interestingly, under sufficiently high
magnetic fields, the isothermal entropy change -{\Delta}ST remains
approximately constant over a wide temperature range which is highly
appreciated from a practical point of view. In the magnetic field change of 7
T, -{\Delta}ST that reaches roughly 22 J/kg K remains practically unchanged
between 0 and 34 K leading to an outstanding refrigerant capacity of about 823
J/kg. On the other hand, the lowering of crystallographic symmetry from the
tetragonal to the orthorhombic structure occurring close to 33 K as confirmed
by Raman scattering data results in a strong magnetic anisotropy. Accordingly,
strong thermal effects can be also obtained simply by spinning the TbVO4 single
crystals between their hard and easy orientations in constant magnetic fields
instead the standard magnetization-demagnetization process. Such rotating
magnetocaloric effects would open the way for the implementation of TbVO4 in a
new generation of compact and simplified magnetic refrigerators that can be
dedicated to the liquefaction of hydrogen and helium.",2011.09798v1
2020/12/3,"Polar magneto-optical Kerr effect in antiferromagnetic M$_2$As (M=Cr, Mn, Fe) under an external magnetic field","Antiferromagnetic metals attract tremendous interest for memory applications
due to their expected fast response dynamics in the terahertz frequency regime.
Reading from and writing information into these materials is not easily
achievable using magnetic fields, due to weak high-order magneto-optical
signals and robustness of the magnetic structure against external magnetic
fields. Polarized electromagnetic radiation is a promising alternative for
probing their response, however, when ideal antiferromagnetic symmetry is
present, this response vanishes. Hence, in this work we combine
first-principles simulations with measurements of the polar magneto-optical
Kerr effect under external magnetic fields, to study magneto-optical response
of antiferromagnetic M$_2$As (M=Cr, Mn, and Fe). We devise a computational
scheme to compute the magnetic susceptibility from total-energy changes using
constraints on magnetic-moment tilting. Our predictions of the spectral
dependence of polar magneto-optical Kerr rotation and ellipticity allow us to
attribute these effects to breaking of the magnetic symmetry. We show that
tilting affects the exchange interaction, while the spin-orbit interaction
remains unaffected as the tilting angle changes. Our work provides
understanding of the polar magneto-optical Kerr effect on a band structure
level and underscores the importance of the magnetic susceptibility when
searching for materials with large magneto-optical response.",2012.02090v1
2020/12/31,Neutron diffraction study of magnetism in van der Waals layered MnBi$_{2n}$Te$_{3n+1}$,"Two-dimensional van der Waals MnBi$_{2n}$Te$_{3n+1}$ (n = 1, 2, 3, 4)
compounds have been recently found to be intrinsic magnetic topological
insulators rendering quantum anomalous Hall effect and diverse topological
states. Here, we summarize and compare the crystal and magnetic structures of
this family, and discuss the effects of chemical composition on their
magnetism. We found that a considerable fraction of Bi occupies at the Mn sites
in MnBi$_{2n}$Te$_{3n+1}$ (n = 1, 2, 3, 4) while Mn is no detectable at the
non-magnetic atomic sites within the resolution of neutron diffraction
experiments. The occupancy of Mn monotonically decreases with the increase of
n. The polarized neutron diffraction on the representative MnBi$_{4}$Te$_{7}$
reveals that its magnetization density is exclusively accumulated at the Mn
site, in good agreement with the results from the unpolarized neutron
diffraction. The defects of Bi at the Mn site naturally explain the
continuously reduced saturated magnetic moments from n = 1 to n = 4. The
experimentally estimated critical exponents of all the compounds generally
suggest a three-dimensional character of magnetism. Our work provides
material-specified structural parameters that may be useful for band structure
calculations to understand the observed topological surface states and for
designing quantum magnetic materials through chemical doping.",2012.15415v2
2021/3/18,Technical Review: Imaging weak magnetic field patterns on the nanometer-scale and its application to 2D materials,"Nanometer-scale imaging of magnetization and current density is the key to
deciphering the mechanisms behind a variety of new and poorly understood
condensed matter phenomena. The recently discovered correlated states hosted in
atomically layered materials such as twisted bilayer graphene or van der Waals
heterostructures are noteworthy examples. Manifestations of these states range
from superconductivity, to highly insulating states, to magnetism. Their
fragility and susceptibility to spatial inhomogeneities limits their
macroscopic manifestation and complicates conventional transport or
magnetization measurements, which integrate over an entire sample. In contrast,
techniques for imaging weak magnetic field patterns with high spatial
resolution overcome inhomogeneity by measuring the local fields produced by
magnetization and current density. Already, such imaging techniques have shown
the vulnerability of correlated states in twisted bilayer graphene to
twist-angle disorder and revealed the complex current flows in quantum Hall
edge states. Here, we review the state-of-the-art techniques most amenable to
the investigation of such systems, because they combine the highest magnetic
field sensitivity with the highest spatial resolution and are minimally
invasive: magnetic force microscopy, scanning superconducting quantum
interference device microscopy, and scanning nitrogen-vacancy center
microscopy. We compare the capabilities of these techniques, their required
operating conditions, and assess their suitability to different types of source
contrast, in particular magnetization and current density. Finally, we focus on
the prospects for improving each technique and speculate on its potential
impact, especially in the rapidly growing field of two-dimensional (2D)
materials.",2103.10382v1
2021/8/27,Gigantic current control of coercive field and magnetic memory based on nm-thin ferromagnetic van der Waals Fe3GeTe2,"Controlling magnetic states by a small current is essential for the
next-generation of energy-efficient spintronic devices. However, it invariably
requires considerable energy to change a magnetic ground state of intrinsically
quantum nature governed by fundamental Hamiltonian, once stabilized below a
phase transition temperature. We report that surprisingly an in-plane current
can tune the magnetic state of nm-thin van der Waals ferromagnet Fe3GeTe2 from
a hard magnetic state to a soft magnetic state. It is the direct demonstration
of the current-induced substantial reduction of the coercive field. This
surprising finding is possible because the in-plane current produces a highly
unusual type of gigantic spin-orbit torque for Fe3GeTe2. And we further
demonstrate a working model of a new nonvolatile magnetic memory based on the
principle of our discovery in Fe3GeTe2, controlled by a tiny current. Our
findings open up a new window of exciting opportunities for magnetic van der
Waals materials with potentially huge impacts on the future development of
spintronic and magnetic memory.",2108.12111v2
2021/11/17,Chiral Spin Bobbers in Exchange-Coupled Hard-Soft Magnetic Bilayers,"The spin structure of exchange-coupled MnBi:Co-Fe bilayers is investigated by
X-ray magnetic circular dichroism (XMCD), polarized neutron reflectometry
(PNR), and micromagnetic simu-lations. The purpose of the present research is
two-fold. First, the current search for new permanent-magnet materials includes
hard-soft nanocomposites, and the analysis of coercivity mechanisms in these
structures is an important aspect of this quest. Second, topological
micro-magnetic structures such as skyrmions have recently become of intense
fundamental and applied research, for example in the context of spin-based
electronics. We find that the magnetization reversal of the MnBi:Co-Fe bilayer
structure involves a curling-type twisting of the magnetization in the film
plane. This curling in the exchange-coupled hard-soft magnetic bilayers is
reminiscent of chiral spin structures known as bobbers and, in fact,
establishes a new type of skyrmionic spin structure.",2111.09183v2
2021/12/30,Non-uniform magnetization profile in ferromagnetic heterostructures leading to topological Hall effect like signatures,"Anomalous Hall effect (AHE), which arises when a current is passed through a
ferromagnetic material subjected to a perpendicular magnetic field, is
proportional to the magnetization of the sample.Additional hump-like features
in AHE are often attributed to the presence of non trivial spin textures
leading to topological Hall effect (THE). However, several recent reports have
emphasized in context of ferromagnetic SrRuO$_3$ based heterostructures that
the sample inhomogeneity can also result in THE-like features. In order to
investigate this issue in general for any ferromagnetic heterostructure, we
have considered a phenomenological model to calculate the changes in the shape
of hysteresis loop due to various interfacial effects. These changes in the
magnetization have been accounted for by considering that the interdomain
magnetic coupling parameter ($\alpha$) varies exponentially with the distance
from the interface along the growth direction of the heterostructure. In case
of symmetric interfaces on both sides of a ferromagnet, we have considered the
variation of $\alpha$ as a Gaussian function. We have found that the additional
AHE contribution due to the net change in magnetization in such cases are akin
to experimentally observed THE, even though we have not considered any
topological quantity explicitly in our model. Thus, we propose another
situation with nonuniform magnetization profile that may be used to explain
additional features in AHE, which might not necessarily be intrinsic THE.",2112.15020v1
2022/5/23,Surface-Driven Evolution of the Anomalous Hall Effect in Magnetic Topological Insulator MnBi2Te4 Thin Films,"Understanding the effects of interfacial modification to the functional
properties of magnetic topological insulator thin films is crucial for
developing novel technological applications from spintronics to quantum
computing. Here, we report that a large electronic and magnetic response is
induced in the intrinsic magnetic topological insulator MnBi2Te4 by controlling
the propagation of surface oxidation. We show that the formation of the surface
oxide layer is confined to the top 1-2 unit cells but drives large changes in
the overall magnetic response. Specifically, we observe a dramatic reversal of
the sign of the anomalous Hall effect driven by finite thickness magnetism,
which indicates that the film splits into distinct magnetic layers each with a
unique electronic signature. These data reveal a delicate dependence of the
overall magnetic and electronic response of MnBi2Te4 on the stoichiometry of
the top layers. Our study suggests that perturbations resulting from surface
oxidation may play a non-trivial role in the stabilization of the quantum
anomalous Hall effect in this system and that understanding targeted
modifications to the surface may open new routes for engineering novel
topological and magnetic responses in this fascinating material.",2205.10991v1
2022/8/25,"Incommensurate magnetic modulation in K-rich cryptomelane, K$_x$Mn$_8$O$_{16}$ ($x\approx1.46$)","Cryptomelane is a hollandite-like material consisting of K$^+$ cations in an
$\alpha$-MnO$_2$ tunnel-like crystallographic motif. A sample with
stoichiometry K$_{1.461(4)}$Mn$_8$O$_{16}$ has been synthesised and its
magnetic properties investigated using variable-temperature magnetic
susceptibility, heat capacity, and neutron powder diffraction. Three distinct
magnetic transitions at $184$\,K, $54.5$\,K, and $24$\,K are assigned to
K$_{1.461(4)}$Mn$_8$O$_{16}$. Magnetic Bragg peaks emerge below $54.5$\,K, and
from their positions they indicate a modulated magnetic structure which is
incommensurate with the crystallographic nuclear structure. The model
consistent with the data is a dual-$\vec{k}_\mathrm{mag}$ structure with a
canted ferrimagnetic $\vec{k}_\mathrm{mag}=0$ component and an incommensurate
$\vec{k}_\mathrm{mag}=(0,0,k_z)$ [$k_z=0.36902(15)$] component, with the latter
most likely to be of the helical type formerly proposed for this material.
Below 24\,K, there is a magnetic transition, which gives rise to a different
set of magnetic Bragg peaks indicative of a highly complex magnetic structure.",2208.12197v1
2023/3/1,"Interplay between magnetism and short-range order in medium- and high-entropy alloys: CrCoNi, CrFeCoNi, and CrMnFeCoNi","The impact of magnetism on predicted atomic short-range order in three
medium- and high-entropy alloys is studied using a first-principles,
all-electron, Landau-type linear response theory, coupled with lattice-based
atomistic modelling. We perform two sets of linear-response calculations: one
in which the paramagnetic state is modelled within the disordered local moment
picture, and one in which systems are modelled in a magnetically ordered state,
which is ferrimagnetic for the alloys considered in this work. We show that the
treatment of magnetism can have significant impact both on the predicted
temperature of atomic ordering and also the nature of atomic order itself. In
CrCoNi, we find that the nature of atomic order changes from being
$\mathrm{L}1_2$-like when modelled in the paramagnetic state to MoPt$_2$-like
when modelled assuming the system has magnetically ordered. In CrFeCoNi, atomic
correlations between Fe and the other elements present are dramatically
strengthened when we switch from treating the system as magnetically disordered
to magnetically ordered. Our results show it is necessary to consider the
magnetic state when modelling multicomponent alloys containing mid- to
late-$3d$ elements. Further, we suggest that there may be high-entropy alloy
compositions containing $3d$ transition metals that will exhibit specific
atomic short-range order when thermally treated in an applied magnetic field.
This has the potential to provide a route for tuning physical and mechanical
properties in this class of materials.",2303.00641v2
2023/10/19,Correlation Driven Magnetic Frustration and Insulating Behavior of TiF$_3$,"We investigate the halide perovskite TiF$_3$, renowned for its intricate
interplay between structure, electronic correlations, magnetism, and thermal
expansion. Despite its simple structure, understanding its low-temperature
magnetic behavior has been a challenge. Previous theories proposed
antiferromagnetic ordering. In contrast, experimental signatures for an ordered
magnetic state are absent down to 10~K. Our current study has successfully
reevaluated the theoretical modeling of TiF$_3$, unveiling the significance of
strong electronic correlations as the key driver for its insulating behavior
and magnetic frustration. In addition, our frequency-dependent optical
reflectivity measurements exhibit clear signs of an insulating state. Analysis
of the calculated magnetic data gives an antiferromagnetic exchange coupling
with a net Weiss temperature of order 25~K as well as a magnetic response
consistent with a $S$=1/2 local moment per Ti$^{3+}$. Yet, the system shows no
susceptibility peak at this temperature scale and appears free of long-range
antiferromagnetic order down to 1~K. Extending ab initio modeling of the
material to larger unit cells shows a tendency for relaxing into a
non-collinear magnetic ordering, with a shallow energy landscape between
several magnetic ground states, promoting the status of this simple, nearly
cubic perovskite structured material as a candidate spin liquid.",2310.12645v1
2014/3/7,Multifunctional Magnetoelectric Materials for Device Applications,"Mutiferroics are a novel class of next generation multifunctional materials,
which display simultaneous magnetic spin, electric dipole, and ferroelastic
ordering, and have drawn increasing interest due to their multi-functionality
for a variety of device applications. Since single-phase materials exist rarely
in nature with such cross-coupling properties, an intensive research activity
is being pursued towards the discovery of new single-phase multiferroic
materials and the design of new engineered materials with strong
magneto-electric (ME) coupling. This review article summarizes the development
of different kinds of multiferroic material: single-phase and composite
ceramic, laminated composite, and nanostructured thin films. Thin-film
nanostructures have higher magnitude direct ME coupling values and clear
evidence of indirect ME coupling compared with bulk materials. Promising ME
coupling coefficients have been reported in laminated composite materials in
which signal to noise ratio is good for device fabrication. We describe the
possible applications of these materials.",1403.1838v1
2023/7/13,Machine Learning Predictions of High-Curie-Temperature Materials,"Technologies that function at room temperature often require magnets with a
high Curie temperature, $T_\mathrm{C}$, and can be improved with better
materials. Discovering magnetic materials with a substantial $T_\mathrm{C}$ is
challenging because of the large number of candidates and the cost of
fabricating and testing them. Using the two largest known data sets of
experimental Curie temperatures, we develop machine-learning models to make
rapid $T_\mathrm{C}$ predictions solely based on the chemical composition of a
material. We train a random forest model and a $k$-NN one and predict on an
initial dataset of over 2,500 materials and then validate the model on a new
dataset containing over 3,000 entries. The accuracy is compared for multiple
compounds' representations (""descriptors"") and regression approaches. A random
forest model provides the most accurate predictions and is not improved by
dimensionality reduction or by using more complex descriptors based on atomic
properties. A random forest model trained on a combination of both datasets
shows that cobalt-rich and iron-rich materials have the highest Curie
temperatures for all binary and ternary compounds. An analysis of the model
reveals systematic error that causes the model to over-predict
low-$T_\mathrm{C}$ materials and under-predict high-$T_\mathrm{C}$ materials.
For exhaustive searches to find new high-$T_\mathrm{C}$ materials, analysis of
the learning rate suggests either that much more data is needed or that more
efficient descriptors are necessary.",2307.06879v1
1999/3/23,Magnetism and magnetic asphericity in NiFe alloys,"We here study magnetic properties of Ni$_{x}$Fe$_{1-x}$ using Augmented space
recursion technique coupled with tight-binding linearized muffin tin orbital
method. Also the spectral properties of this alloy has been studied here.",9903348v1
1999/7/13,Phase separation and enhanced charge-spin coupling near magnetic transitions,"The generic changes of the electronic compressibility in systems which show
magnetic instabilities is studied. It is shown that, when going into the
ordered phase, the compressibility is reduced by an amount comparable to the
its original value, making charge instabilities also possible. We discuss,
within this framework, the tendency towards phase separation of the double
exchange systems, the pyrochlores, and other magnetic materials.",9907184v1
2000/5/1,Nonexponential Relaxation of Magnetization at the Resonant Tunneling Point under a Fluctuating Random Noise,"Nonexponential relaxation of magnetization at resonant tunneling points of
nanoscale molecular magnets is interpreted to be an effect of fluctuating
random field around the applied field. We demonstrate such relaxation in
Langevin equation analysis and clarify how the initial relaxation (square-root
time) changes to the exponential decay. The scaling properties of the
relaxation are also discussed.",0005013v1
2000/6/20,Field induced long-range-ordering in an S=1 quasi-one-dimensional Heisenberg antiferromagnet,"We have measured the heat capacity and magnetization of the spin one
one-dimensional Heisenberg antiferromagnet NDMAP and constructed a magnetic
field versus temperature phase diagram. We found a field induced long-range
magnetic ordering. We have been successful in explaining the phase diagram
theoretically.",0006295v1
2001/11/29,Tensor form of magnetization damping,"A tensor form of phenomenological damping is derived for small magnetization
motions. This form reflects basic physical relaxation processes for a general
uniformly magnetized particle or film. Scalar Landau-Lifshitz damping is found
to occur only for two special cases of system symmetry.",0111566v1
2002/2/21,Mechanisms of spin-polarized current-driven magnetization switching,"The mechanisms of the magnetization switching of magnetic multilayers driven
by a current are studied by including exchange interaction between local
moments and spin accumulation of conduction electrons. It is found that this
exchange interaction leads to two additional terms in the
Landau-Lifshitz-Gilbert equation: an effective field and a spin torque. Both
terms are proportional to the transverse spin accumulation and have comparable
magnitudes.",0202363v1
2003/4/4,On the fundamental conceptual problems in magnetism,"An extensive survey of misinterpretations and misconceptions concerning
presentation of the hysteresis loop for ferromagnetic materials occurring in
undergraduate textbooks as well as in recent magnetism literature has been
carried out. This survey has also revealed a number of intricacies and
conceptual problems concerning the fundamental aspect of magnetism. This note
provides a critical analysis of these problems aimed at clarification of the
intricacies and preventing further proliferation of the confusion in question.",0304099v1
2003/4/25,Structural order parameter and itinerant electron magnetism in Cd2Re2O7,"We describe the low temperature behaviour of the magnetic susceptibility of
Cd2Re2O7 in terms of a Landau theory of structural phase transitions. We
calculate the zero temperature Pauli susceptibility using a tight-binding
approach to reveal the mechanism of coupling between the structural order
parameter and itinerant magnetism.",0304582v1
2003/7/6,Equilibrium current temperature quasi-oscillations in a ferromagnetic loop,"Equilibrium persistent current carried by a small ferromagnet-metal loop is
considered. This current is shown to be quasi periodic in temperature at low
temperatures. The quasi period is determined mainly by the temperature
dependence of the magnetization.",0307128v1
2003/9/5,Induced Magnetic Ordering by Proton Irradiation in Graphite,"We provide evidence that proton irradiation of energy 2.25 MeV on
highly-oriented pyrolytic graphite samples triggers ferro- or ferrimagnetism.
Measurements performed with a superconducting quantum interferometer device
(SQUID) and magnetic force microscopy (MFM) reveal that the magnetic ordering
is stable at room temperature.",0309128v1
2003/12/10,Spin Gain Transistor in Ferromagnetic Semiconductors: the Semiconductor Bloch Equations Approach,"Scheme and principle of operation of a spin gain transistor are proposed: a
large unmagnetized current creates density sufficient for the ferromagnetic
transition; a small magnetized current initiates spontaneous magnetization;
large magnetized current is extracted. Therefore spin gain of more than 1000 is
predicted. Collective dynamics of spins under Coulomb exchange interaction is
described via Semiconductor Bloch Equations.",0312243v1
2004/2/9,Evidence of large anisotropy in the magnetization of Na0.35CoO2.1.3H2O quasi-single-crystal superconductors,"Quasi-single crystals (up to 2x2x1 mm3) of Na0.35CoO2.1.3H2O-superconductor
have been grown. Magnetization M(H, T) and M(T, H) curves with magnetic field
approximately parallel and perpendicular to c-axis indicates on large
anisotropy, comparable with Bi-based high-temperature superconducting (HTS)
phases.",0402235v1
2004/6/16,Collective electromagnetic relaxation in crystals of molecular magnets,"We study the magnetization reversal and electromagnetic radiation due to
collective Landau-Zener relaxation in a crystal of molecular magnets.
Analytical and numerical solutions for the time dependence of the relaxation
process are obtained. The power of the radiation and the total emitted energy
are computed as functions of the crystal parameters and the field sweep rate.",0406361v1
2004/7/21,Orbital magnetism in the half-metallic Heusler alloys,"Using the fully-relativistic screened Korringa-Kohn-Rostoker method I study
the orbital magnetism in the half-metallic Heusler alloys. Orbital moments are
almost completely quenched and they are negligible with respect to the spin
moments. The change in the atomic-resolved orbital moments can be easily
explained in terms of the spin-orbit strength and hybridization effects.
Finally I discuss the orbital and spin moments derived from X-ray magnetic
circular dichroism experiments.",0407560v1
2005/5/12,Incipient magnetism in the cubic perovskites MgCNi3 and YBRh3: A comparison,"Using density-functional-based methods, we have studied the effects of
incipient magnetism in the cubic perovskites MgCNi_{3} and YBRh_{3} . Our
results show that (i) at the equilibrium volume, both MgCNi_{3} and YBRh_{3}
alloys remain paramagnetic and (ii) at expanded volumes, only YBRh_{3} shows
the possibility of a ferromagnetic phase with a local magnetic moment larger
than 0.25 mu_{B} per Rh atom.",0505310v1
2005/10/15,Current-driven domain wall motion in magnetic wires with asymmetric notches,"Current-driven domain wall (DW) motion in magnetic wires with asymmetric
notches was investigated by means of magnetic force microscopy. It was found
that the critical current density necessary for the current-driven DW motion
depended on the propagation direction of the DW. The DW moved more easily in
the direction along which the slope of the asymmetric notch was less inclined.",0510404v1
2005/10/30,Domain instability during precessional magnetization reversal,"Spin wave equations in the non-equilibrium precessing state of a
ferromagnetic system are found. They show a spin-wave instability towards
growing domains of stable magnetization. Precession of the uniform
magnetization mode is described by the Landau Lifshitz equation with the
exponentially growing in time effective Gilbert dissipation constant that could
have both signs. On the developed stages of the domain instability a
non-stationary picture of domain chaos is observed.",0510817v1
2006/2/17,Quasi-Two Dimensional Diluted Magnetic Semiconductors with Arbitrary Carrier Degeneracy,"In the framework of the generalized mean field theory, conditions for arising
the ferromagnetic state in a two-dimensional diluted magnetic semiconductor and
the features of that state are defined. RKKY-interaction of magnetic impurities
is supposed. The spatial disorder of their arrangement and temperature
alteration of the carrier degeneracy are taken into account.",0602416v2
2006/3/31,Half-metallic diluted antiferromagnetic semiconductors,"The possibility of half-metallic antiferromagnetism, a special case of
ferrimagnetism with a compensated magnetization, in the diluted magnetic
semiconductors is highlighted on the basis of the first principles electronic
structure calculation. As typical examples, the electrical and magnetic
properties of II-VI compound semiconductors doped with 3d transition metal ion
pairs--(V, Co) and (Fe, Cr)--are discussed.",0603846v1
2006/12/11,Magnetic properties and EPR spectrum of CsPr(MoO4)2,"The temperature dependencies of magnetic susceptibility in temperature range
4.2-250 K along the principal magnetic axes as well as frequency-field
dependence EPR spectrum at helium temperature in basic plane was studied. It is
found that ground state of CsPr(MoO4)2, is the quasi-doublet. The experimental
values of g-factors gc=1.54; ga<0.1; gb<0.1 and energy gap 0,2 cm-1 was
determined",0612246v1
2006/12/24,Self-focusing and envelope pulse generation in nonlinear magnetic metamaterials,"The self-modulation of waves propagating in nonlinear magnetic metamaterials
is investigated. Considering the propagation of a modulated amplitude magnetic
field in such a medium, we show that the self-modulation of the carrier wave
leads to a spontaneous energy localization via the generation of localized
envelope structures (envelope solitons), whose form and properties are
discussed. These results are also supported by numerical calculations.",0612615v1
2007/3/11,Time-dependent fields and anisotropy dominated magnetic media,"We use a single dipole approximation to analyze the behavior of
anisotropy-dominated magnetic nanoparticles subjected to an external r.f.
field. We identify the steady state oscillations and analyze their stability.
We also analyze the case when the external r.f. field has a time-dependent
frequency which insures the most effective switching of the magnetization.",0703272v1
2007/3/23,"Quantum Chemistry, Magnetism and Lasers","Using highly correlational quantum chemistry we compute from first principles
the contributions of the electric dipoles and quadupoles, and magnetic dipoles
to the nonlinear optics of NiO. The material is modeled as a doubly embedded
cluster and all magnetic intragap d-character states are calculated, thus
explaining the experimental results.",0703601v1
2007/3/24,Critical exponents of small one-dimensional ising magnetic,"Within the framework of a generalized Ising model, a one-dimensional magnetic
of a finite length with free ends is considered. The correlation length
exponent, dynamic critical exponent z of the magnet is calculated taking into
account the next nearest neighbor interactions and the external field.",0703639v1
2008/3/11,Magnetic field induced 3D to 1D crossover in type II superconductors,"We review and analyze magnetization and specific heat investigations on
type-II superconductors which uncover remarkable evidence for the magnetic
field induced fnite size effect and the associated 3D to 1D crossover which
enhances thermal fluctuations.",0803.1560v2
2008/3/18,Magnetism and structure at a vacancy in graphene,"The electronic structure, bonding and magnetism in graphene containing
vacancies are studied using density-functional methods. The single-vacancy
graphene ground state is spin polarized and structurally flat. The unpolarized
state is non planar only for finite segments. Systems containing periodic
arrays of vacancies displays magnetic transitions and metal-insulator
transitions.",0803.2730v1
2008/9/21,Quantized Conductance of a Single Magnetic Atom,"A single Co atom adsorbed on Cu(111) or on ferromagnetic Co islands is
contacted with non-magnetic W or ferromagnetic Ni tips in a scanning tunneling
microscope. When the Co atom bridges two non-magnetic electrodes conductances
of 2e^2/h are found. With two ferromagnetic electrodes a conductance of e^2/h
is observed which may indicate fully spin-polarized transport.",0809.3567v1
2008/10/21,"Coherent manipulation of magnetization precession in ferromagnetic semiconductor (Ga,Mn)As with successive optical pumping","We report dynamic control of magnetization precession by light alone. A
ferromagnetic (Ga,Mn)As epilayer was used for experiments. Amplitude of
precession was modulated to a large extent by tuning the time interval between
two successive optical pump pulses which induced torques on magnetization
through a non-thermal process. Nonlinear effect in precession motion was also
discussed.",0810.3728v1
2009/3/30,Lower current-driven exchange switching threshold in noncollinear magnetic junctions under high spin injection,"Current-induced switching is considered in a magnetic junction. The junction
includes pinned and free ferromagnetic layers which work in the regime of the
high spin injection. It is shown that in such a regime the exchange
magnetization reversal threshold can be lowered up to two times when the axes
of the layers are noncollinear.",0903.5131v1
2009/6/3,The Binary History and the Magnetic Field of Neutron Star,"There has been strong observational evidence suggesting a causal connection
between the binary history of neutron stars and the evolution of their magnetic
field. In this article we discuss one of the plausible mechanisms proposed for
the evolution of the surface magnetic field, that of the diamagnetic screening
of the field by accreted material.",0906.0682v1
2009/8/20,"Magnetism, Superconductivity and Stoichiometry in Single Crystals of Fe1+y(Te1-xSx)z","We report synthesis of high quality Fe1+y(Te1-xSx)z single crystals and a
comprehensive study of structural, magnetic and transport properties. There is
high sensitivity to material stoichiometry which includes vacancies on the
Te(S) site. Our results reveal competition and coexistence of magnetic order
and percolative superconductivity for x >= 0.03, while zero resistivity is
acheived for x >= 0.1.",0908.3011v1
2009/11/24,The hybrid magnet with a logarithmic in time field deviation,"The pulsed-field magnetization of hybrid magnet (soft ferromagnetic and
melt-grown superconductor Y-Ba-Cu-O) was investigated at T = 78K. It is shown
that choosing the pulse amplitude one can create a logarithmic in time field
deviation near the specified value.",0911.4588v1
2010/7/6,Effects of chemical substitution on transport properties of Bi-based high temperature superconductors,"This report describes some transport and magnetic properties of doped Bi2212
and Bi2223 superconducting whiskers. These materials have advantages over
polycrystalline sample as well as large bulk crystals in that they provide
narrow transitions in resistance versus temperature as well as in magnetization
versus temperature curves. In addition they are easy to grow and and have short
oxygen annealing times. Here Data on transport and magnetic properties of these
superconducting whiskers are presented.",1007.0971v1
2013/2/8,Investigation on the critical dynamics of real magnetics models by computational physics methods,"The critical dynamics of classical 3D Heisenberg model and complex model of
the real antiferromagnetic Cr2O3 is investigated with use of the method of
molecular dynamics. The dynamic critical exponent z are determined for these
models on the basis of the theory dynamic finite-size scaling.",1302.1964v1
2013/7/9,Magnetic monopoles and unusual transport effects in magnetoelectrics,"It is argued that in magnetoelectrics with diagonal magnetoelectric coupling
there should be a monopole-like distribution of magnetization around electric
charge. It may lead to nontrivial transport properties of such materials, to
understand which the picture of magnetic monopoles attached to electric charges
may be very useful.",1307.2327v1
2013/7/29,Instability of the ferrofluid layer on a magnetizable substrate in a perpendicular magnetic field,"The paper presents an experimental study of the instability of a magnetic
fluid layer of finite thickness covering a magnetizable metal plate exposed to
a perpendicular magnetic field. The critical field strength and the instability
wave number have been measured.",1307.7481v1
2013/9/25,A report on the magnetic order of transition-metal $δ$-doped cubic ZnO,"Preliminary results on the properties of transition-metal (Ti, V, Cr, Mn, Fe,
Co, Ni) $\delta$-doped ZnO are reported. Using \emph{ab-initio} electronic
structure calculations the magnetic order is studied assuming both the cubic
rock-salt and zinc-blende structures for ZnO. The ground state magnetic order
is found to depend strongly on the transition-metal atom.",1309.6462v1
2014/2/18,Synthesis and Magnetic Properties of Ferroelectric GdCrO3 nanoparticles,"Homogeneous single phase GdCrO3 nanoparticles are synthesized by a
modified-hydrothermal synthesis. The sample shows a compensation temperature at
128 K, below which the DC magnetization becomes negative and positive at low
temperatures due to the competition between the two sublattice magnetization.
At N\'eel temperature (168K), the line width and the intensity show an abrupt
transition, revealed from electron paramagnetic resonance spectroscopy.",1402.4260v1
2014/6/3,Phase coexistence and interrupted 1st order transition in magnetic shape memory alloys,"Current theoretical studies on structural and magnetic properties of
functional Ni-Mn-Z (Z = Ga, In, Sn) Heusler alloys address the origin of the
structural transition from the austenite to martensite, and also address the
dominant contribution to the latent heat associated with this
magneto-structural transition. This should help understand the origin of
kinetic arrest of 1st order magnetic transitions.",1406.0627v1
2014/7/17,Magnetic Properties of Bismuth Ferrite Nanopowder Obtained by Mechanochemical Synthesis,"Multiferroic bismuth ferrite (BiFeO3) nanopowders have been obtained in room
temperature by mechanical synthesis. Depending on the post-synthesis processing
the nanopowders have exhibited differences in the mean sizes, presence of
amorphous layer and/or secondary phases. Extended magnetic study performed for
fresh, annealed and hot-pressed nanopowders have revealed substantial
improvement of the magnetic properties in the as-prepared powder.",1407.4657v1
2015/10/17,Coupled electricity and magnetism in solids: multiferroics and beyond,"The interplay of electricity and magnetism, one of the cornerstones of modern
physics, takes a special form in solids in such phenomena as magnetoelectricity
and the possibility of multiferroic behaviour. In this paper I give a short
survey of the main notions of this field, paying special attention to
microscopic aspects. Some related phenomena, such as electric activity of
magnetic domain walls, etc., are also shortly discussed.",1510.05174v2
2016/1/29,Neutron Zeeman beam-splitting for the investigation of magnetic nanostructures,"The Zeeman spatial splitting of a neutron beam takes place during a neutron
spin-flip in magnetically non-collinear systems at grazing incidence geometry.
We apply the neutron beam-splitting method for the investigation of
magnetically non-collinear clusters of submicron size in a thin film. The
experimental results are compared with ones obtained by other methods.",1601.08080v1
2012/11/21,Electronic and magnetic properties of two-dimensional Li$_{3}$N,"Using first-principles plane-wave calculations study of electronic and
magnetic properties of hypothetical two-dimensional structure of Li$_{2}$N
compound have been conducted. Calculations show, that electronic properties of
this this structure can be inflenced by hydrogenation, which may change the
system from wide-gap semiconductor to metal. Also, non-zero magnetic moment,
equal to 1 $\mu_{B}$ can be generated by intruduction of H vacanies in
hydrogenated structure.",1211.5005v1
2018/9/29,Proposal for a three-dimensional magnetic measurement method with nanometer-scale depth resolution,"We propose a magnetic measurement method based on combining depth sectioning
and electron magnetic circular dichroism in scanning transmission electron
microscopy. Electron vortex beams with large convergence angles, as those
achievable in current state-of-the-art aberration correctors, could produce
atomic lateral resolution and depth resolution below 2~nm.",1810.00187v1
2012/8/31,Magnetic symmetry of the plain domain walls in ferro- and ferrimagnets,"Magnetic symmetry of all possible plane domain walls in ferro- and
ferrimagnets is considered. Magnetic symmetry classes of non 180 degree
(including 0 degree) domain walls are obtained. The domain walls degeneracy is
investigated. The symmetry classification is applied for research of all
possible plane domain walls in crystals of the hexoctahedral crystallographic
class.",1209.0003v1
2016/3/28,Electric-field modulation of exchange stiffness in MgO/CoFeB with perpendicular anisotropy,"We observe magnetic domain structures of MgO/CoFeB with a perpendicular
magnetic easy axis under an electric field. The domain structure shows a maze
pattern with electric-field dependent isotropic period. We find that the
electric-field modulation of the period is explained by considering the
electric-field modulation of the exchange stiffness constant in addition to the
known magnetic anisotropy modulation.",1603.08280v1
2007/7/31,From the Magnetization Profile to the Stray Field of Bistable Wires,"We present new analytical calculations of the spatial dependence of the stray
field of a bistable magnetic wire from the magnetization profile of the wire.
Contributions from the outer shell and from the wire ends are neglected. The
results qualitatively agree with experimental data, taken from literature.",0707.4666v1
2019/11/5,Magnetic ordering in metal-free radical thin films,"Molecular systems are materials that intersect with many different promising
fields such as organic/molecular electronics and spintronics, organic magnetism
and quantum computing1-7. Particularly, magnetism in organic materials is very
intriguing: the possibility to realize long-range magnetic order in completely
metal-free systems means that magnetic moments are coupled to useful properties
of organic materials, such as optical transparency, low-cost fabrication, and
flexible chemical design. Magnetic ordering in light elements, such as nitrogen
and carbon, has been studied in magnetic-edged graphene nanoribbons8 and
bilayers9, and polymers10 while in organic thin films most of the
investigations show this effect as due to the proximity of light atoms to heavy
metals, impurities, or vacancies11. Purely organic radicals are molecules that
carry one unpaired electron giving rise to a permanent magnetic moment, in the
complete absence of metal ions.12-14 Inspired by their tremendous potential,
here we investigate thin films of an exceptionally chemically stable Blatter
radical derivative15 by using X-ray magnetic circular dichroism (XMCD)16-18.
Here we observe XMCD at the nitrogen K-edge. Our results show a magnetic
ordering different than in the single crystals and calculations indicate,
although weak, a long-range intermolecular coupling. We anticipate our work to
be a starting point for investigating and modelling magnetic behaviour in
purely organic thin films. The tuning of the magnetic properties by the
molecular arrangement in organic films is an exciting perspective towards
revealing new properties and applications.",1911.02082v3
2021/2/6,Topological invariants of electronic currents in magnetic fields,"In this article it is reported a formulation of the solenoidal nature of
quantum electronic currents at the nanoscale whose divergence is expressed as
the coupling of a magnetic field, interacting with a quantum body, and a
weighted Cern invariant vector making then a direct topological interpretation
of this quantum magnetic phenomenon. Also a Fourier analysis of the signaling
of electronic waves is reported in an ab initio formalism from first
pinciples\cite{Martin}.",2102.03605v1
2022/3/15,"Comment on ""Using Dipole Interaction to Achieve Nonvolatile Voltage Control of Magnetism in Multiferroic Heterostructures"" [Adv. Mater., 2021, 2105902]","In a recent article, A. Chen et al. claimed that they have switched (rotated
by ~90 degrees) the magnetization of the soft layer of a magnetic tunnel
junction (MTJ) in a non-volatile way with volatile strain by exploiting dipole
interaction with the hard layer. I show that dipole interaction cannot cause
this effect and the authors' explanation cannot be correct. An alternate
explanation is offered.",2203.08236v1
2022/6/12,Exchange-enhancement of the ultrafast magnetic order dynamics in antiferromagnets,"We theoretically demonstrate that the ultrafast magnetic order dynamics in
antiferromagnets is exchange-enhanced in comparison to their ferromagnetic
counterparts. We provide an equation of motion for the magnetic order dynamics
validated by computer simulations using atomistic spin dynamics methods. The
exchange of angular momentum between sublattices speeds up the dynamics in
antiferromagnets, a process absent in ferromagnets.",2206.05783v1
2023/3/22,Surface barrier of holes drilled in a type-II superconductor,"Holes drilled in a type-II superconductor trap the magnetic flux. Following
Clem's flux pinning model, we consider surface pinning as a mechanism for
compressing the magnetic flux in the holes. Estimations of the trapped magnetic
flux demonstrate that the holes with the diameter up to 2 mm are advantageous
for bulk single-crystal REBCO samples. The REBCO films and tapes can be
improved by the holes with diameter smaller than 10 $\mu$m.",2303.12315v1
2023/11/1,Engineering of Chern number of topological bands in bilayer graphene by in-plane magnetic field and electrical bias,"Based on the full Hamiltonian of bilayer graphene, phase transitions are
realized by the change of the in-plane magnetic field and the electrical bias
in bilayer graphene. We show that the engineering of Chern numbers of four
bands is possible by an applied in-plane magnetic field and an electrical bias
in bilayer graphene. Our results are promising for the exploration of new
topological phenomena in 2D materials.",2311.00331v1
2020/1/22,Spintronic superconductor in a bulk layered material with natural spin-valve structure,"Multi-layered materials provide fascinating platforms to realize various
functional properties, possibly leading to future electronic devices controlled
by external fields. In particular, layered magnets coupled with conducting
layers have been extensively studied recently for possible control of their
transport properties via the spin structure. Successful control of
quantum-transport properties in the materials with antiferromagnetic (AFM)
layers, so-called natural spin-valve structure, has been reported for the Dirac
Fermion and topological/axion materials. However, a bulk crystal in which
magnetic and superconducting layers are alternately stacked has not been
realized until now, and the search for functional properties in it is an
interesting yet unexplored field in material science. Here, we discover
superconductivity providing such an ideal platform in EuSn2As2 with the van der
Waals stacking of magnetic Eu layers and superconducting Sn-As layers, and
present the first demonstration of a natural spin-valve effect on the
superconducting current. Below the superconducting transition temperature (Tc),
the electrical resistivity becomes zero in the in-plane direction. In contrast,
it, surprisingly, remains finite down to the lowest temperature in the
out-of-plane direction, mostly due to the structure of intrinsic magnetic
Josephson junctions in EuSn2As2. The magnetic order of the Eu layers (or
natural spin-valve) is observed to be extremely soft, allowing one to easy
control of the out-of-plane to in-plane resistivities ratio from 1 to infinity
by weak external magnetic fields. The concept of multi-functional materials
with stacked magnetic-superconducting layers will open a new pathway to develop
novel spintronic devices with magnetically controllable superconductivity.",2001.07991v1
2014/6/6,High speed photospheric material flow observed at the polarity inversion line of a delta-type sunspot producing an X5.4 flare on 7 March 2012,"Solar flares abruptly release the free energy stored as a non-potential
magnetic field in the corona and may be accompanied by eruptions of the coronal
plasma. Formation of a non-potential magnetic field and the mechanisms for
triggering the onset of flares are still poorly understood. In particular,
photospheric dynamics observed near those polarity inversion lines that are
sites of major flare production have not been well observed with high spatial
resolution spectro-polarimetry. This paper reports on a remarkable high-speed
material flow observed along the polarity inversion line located between flare
ribbons at the main energy release side of an X5.4 flare on 7 March 2012.
Observations were carried out by the spectro-polarimeter of the Solar Optical
Telescope onboard Hinode. The high-speed material flow was observed in the
horizontally-oriented magnetic field formed nearly parallel to the polarity
inversion line. This flow persisted from at least 6 hours before the onset of
the flare, and continued for at least several hours after the onset of the
flare. Observations suggest that the observed material flow represents neither
the emergence nor convergence of the magnetic flux. Rather, it may be
considered to be material flow working both to increase the magnetic shear
along the polarity inversion line and to develop magnetic structures favorable
for the onset of the eruptive flare.",1406.1617v1
2015/5/28,Giant directional birefringence in multiferroic ferroborate,"Many technological applications are based on electric or magnetic order of
materials, for instance magnetic memory. Multiferroics are materials which
exhibit electric and magnetic order simultaneously. Due to the coupling of
electric and magnetic effects, these materials show a strong potential to
control electricity and magnetism and, more generally, the properties and
propagation of light. One of the most fascinating and counter-intuitive recent
results in multiferroics is directional anisotropy, the asymmetry of light
propagation with respect to the direction of propagation. The absorption in the
material can be different for forward and backward propagation of light, which
in extreme case may lead to complete suppression of absorption in one
direction. Another remarkable effect in multiferroics is directional
birefringence, i.e. different velocities of light for different directions of
propagation. In this paper, we demonstrate giant directional birefringence in a
multiferroic samarium ferroborate. The effect is easily observed for linear
polarization of light in the range of millimeter-wavelengths, and survives down
to very low frequencies. The dispersion and absorption close to the
electromagnon resonance can be controlled and fully suppressed in one
direction. Therefore, samarium ferroborate is a universal tool for optical
control: with a magnetic field as an external parameter it allows switching
between two functionalities: polarization rotation and directional anisotropy.",1505.07813v2
2017/2/27,Single shot ultrafast all optical magnetization switching of ferromagnetic Co/Pt multilayers,"In a number of recent experiments, it has been shown that femtosecond laser
pulses can control magnetization on picosecond timescales, which is at least an
order of magnitude faster compared to conventional magnetization dynamics.
Among these demonstrations, one material system (GdFeCo ferromagnetic films) is
particularly interesting, as deterministic toggle-switching of the magnetic
order has been achieved without the need of any symmetry breaking magnetic
field. This phenomenon is often referred to as all optical switching (AOS).
However, so far, GdFeCo remains the only material system where such
deterministic switching has been observed. When extended to ferromagnetic
systems, which are of greater interest in many technological applications, only
a partial effect can be achieved, which in turn requires repeated laser pulses
for full switching. However, such repeated pulsing is not only energy hungry,
it also negates the speed advantage of AOS. Motivated by this problem, we have
developed a general method for single-shot, picosecond timescale, complete all
optical switching of ferromagnetic materials. We demonstrate that in
exchange-coupled layers of Co/Pt and GdFeCo, single shot, switching of the
ferromagnetic Co/Pt layer is achieved within 7 picoseconds after irradiation by
a femtosecond laser pulse. We believe that this approach will greatly expand
the range of materials and applications for ultrafast magnetic switching.",1702.08491v3
2017/6/1,Quantifying Confidence in Density Functional Theory Predicted Magnetic Ground States,"The success of descriptor-based material design relies on eliminating bad
candidates and keeping good candidates for further investigation. While DFT has
been widely successfully for the former, often times good candidates are lost
due to the uncertainty associated with the DFT-predicted material properties.
Uncertainty associated with DFT predictions has gained prominence and has led
to the development of exchange correlation functionals that have built-in error
estimation capability. In this work, we demonstrate the use of built-in error
estimation capabilities within the BEEF-vdW exchange correlation functional for
quantifying the uncertainty associated with the magnetic ground state of
solids. We demonstrate this approach by calculating the uncertainty estimate
for the energy difference between the different magnetic states of solids and
compare them against a range of GGA exchange correlation functionals as is done
in many first principles calculations of materials. We show that this estimate
reasonably bounds the range of values obtained with the different GGA
functionals. The estimate is determined as a post-processing step and thus
provides a computationally robust and systematic approach to estimating
uncertainty associated with predictions of magnetic ground states. We define a
confidence value (c-value) that incorporates all calculated magnetic states in
order to quantify the concurrence of the prediction at the GGA level and argue
that predictions of magnetic ground states from GGA level DFT is incomplete
without an accompanying c-value. We demonstrate the utility of this method
using a case study of Li and Na-ion cathode materials and the c-value metric
correctly identifies that GGA level DFT will have low predictability for
NaFePO$_4$F.",1706.00416v1
2018/8/3,Giant magnetocaloric effect driven by indirect exchange in magnetic multilayers,"Indirect exchange coupling in magnetic multilayers, also known as the
Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, is known to be highly
effective in controlling the interlayer alignment of the magnetization. This
coupling is typically fixed at the stage of the multilayer fabrication and does
not allow ex-situ control needed for device applications. It is highly
desirable, in addition to the orientational control, to also control the
magnitude of the intralayer magnetization, ideally switch it on/off by
switching the relevant RKKY coupling. Here we demonstrate a magnetic multilayer
material, incorporating thermally -- as well as field-controlled RKKY exchange,
focused on to a dilute ferromagnetic alloy layer and driving it though it's
Curie transition. Such on/off magnetization switching of a thin ferromagnet,
performed repeatably and fully reproducibly within a low-field sweep, results
in a giant magnetocaloric effect, with the estimated isothermal entropy change
of -10 mJ/K cm^3 under an external field of ~10 mT, which greatly exceeds the
performance of the best rare-earth based materials used in the
adiabatic-demagnetization refrigeration systems.",1808.01291v3
2019/10/23,Giant room temperature anomalous Hall effect and magnetically tuned topology in the ferromagnetic Weyl semimetal Co2MnAl,"Weyl semimetals (WSM) have been extensively studied due to their exotic
properties such as topological surface states and anomalous transport
phenomena. Their band structure topology is usually predetermined by material
parameters and can hardly be manipulated once the material is formed. Their
unique transport properties appear usually at very low temperature, which sets
challenges for practical device applications. In this work, we demonstrate a
way to modify the band topology via a weak magnetic field in a ferromagnetic
topological semimetal, Co2MnAl, at room temperature. We observe a tunable,
giant anomalous Hall effect, which is induced by the transition between Weyl
points and nodal rings as rotating the magnetization axis. The anomalous Hall
conductivity is as large as that of a 3D quantum anomalous Hall effect (QAHE),
with the Hall angle reaching a record value (21%) at the room temperature among
magnetic conductors. Furthermore, we propose a material recipe to generate the
giant anomalous Hall effect by gaping nodal rings without requiring the
existence of Weyl points. Our work reveals an ideal intrinsically magnetic
platform to explore the interplay between magnetic dynamics and topological
physics for the development of a new generation of spintronic devices.",1910.10378v1
2017/12/15,"Tunable polymorphism of epitaxial iron oxides in the four-in-one ferroic-on-GaN system with magnetically ordered α-, γ-, ε-Fe2O3 and Fe3O4 layers","Hybridization of semiconducting and magnetic materials into a single
heterostructure is believed to be potentially applicable to the design of novel
functional spintronic devices. In the present work we report epitaxial
stabilization of four magnetically ordered iron oxide phases (Fe3O4,
{\gamma}-Fe2O3, {\alpha}-Fe2O3 and most exotic metastable {\epsilon}-Fe2O3) in
the form of nanometer sized single crystalline films on GaN(0001) surface. The
epitaxial growth of as many as four distinctly different iron oxide phases is
demonstrated within the same single-target Laser MBE technological process on a
GaN semiconductor substrate widely used for electronic device fabrication. The
discussed iron oxides belong to a family of simple formula magnetic materials
exhibiting a rich variety of outstanding physical properties including peculiar
Verwey and Morin phase transitions in Fe3O4 and {\alpha}-Fe2O3 and multiferroic
behavior in metastable magnetically hard {\epsilon}-Fe2O3 ferrite. The physical
reasons standing behind the nucleation of a particular phase in an epitaxial
growth process deserve interest from the fundamental point of view. The
practical side of the presented study is to exploit the tunable polymorphism of
iron oxides for creation of ferroic-on-semiconductor heterostructures usable in
novel spintronic devices. By application of a wide range of experimental
techniques the surface morphology, crystalline structure, electronic and
magnetic properties of the single phase iron oxide epitaxial films on GaN have
been studied. A comprehensive comparison has been made to the properties of the
same ferrite materials in the bulk and nanostructured form reported by other
research groups.",1712.05632v1
2020/11/2,Layer-dependent mechanical properties and enhanced plasticity in the van der Waals chromium trihalide magnets,"The mechanical properties of magnetic materials are instrumental for the
development of the magnetoelastic theory and the optimization of
strain-modulated magnetic devices. In particular, two-dimensional (2D) magnets
hold promise to enlarge these concepts into the realm of low-dimensional
physics and ultrathin devices. However, no experimental study on the intrinsic
mechanical properties of the archetypal 2D magnet family of the chromium
trihalides has thus far been performed. Here, we report the room temperature
layer-dependent mechanical properties of atomically thin CrI3 and CrCl3,
finding that bilayers of CrI3 and CrCl3 have Young's moduli of 62.1 GPa and
43.4 GPa, with the highest sustained strain of 6.09% and 6.49% and breaking
strengths of 3.6 GPa and 2.2 GPa, respectively. Both the elasticity and
strength of the two materials decrease with increased thickness, which is
attributed to a weak interlayer interaction that enables interlayer sliding
under low levels of applied load. The mechanical properties observed in the
few-layer chromium trihalide crystals provide evidence of outstanding
plasticity in these materials, which is qualitatively demonstrated in their
bulk counterparts. This study will contribute to various applications of the
van der Waals magnetic materials, especially for their use in magnetostrictive
and flexible devices.",2011.00942v2
2021/7/24,Chemical design and magnetic ordering in thin layers of 2D MOFs,"Through rational chemical design, and thanks to the hybrid nature of
metal-organic frameworks (MOFs), it is possible to prepare molecule-based 2D
magnetic materials stable at ambient conditions. Here, we illustrate the
versatility of this approach by changing both the metallic nodes and the
ligands in a family of layered MOFs that allows the tuning of their magnetic
properties. Specifically, the reaction of benzimidazole-type ligands with
different metal centres (MII = Fe, Co, Mn, Zn) in a solvent-free synthesis
produces a family of crystalline materials, denoted as MUV-1(M), which order
antiferromagnetically with critical temperatures that depend on M. Furthermore,
the incorporation of additional substituents in the ligand results in a novel
system, denoted as MUV-8, formed by covalently bound magnetic double-layers
interconnected by van der Waals interactions, a topology that is very rare in
the field of 2D materials and unprecedented for 2D magnets. These layered
materials are robust enough to be mechanically exfoliated down to a few layers
with large lateral dimensions. Finally, the robustness and crystallinity of
these layered MOFs allow the fabrication of nanomechanical resonators that can
be used to detect -- through laser interferometry -- the magnetic order in thin
layers of these 2D molecule-based antiferromagnets.",2107.11569v1
2022/2/1,1T-FeS$_2$$:$ a new type of two-dimensional metallic ferromagnet,"Discovery of intrinsic two-dimensional (2D) magnetic materials is crucial for
understanding the fundamentals of 2D magnetism and realizing next-generation
magnetoelectronic and magneto-optical devices. Although significant efforts
have been devoted to identifying 2D magnetism by exfoliating bulk magnetic
layered materials, seldom studies are performed to synthesize ultra-thin
magnetic materials directly for non-layered magnetic materials. Here, we report
the successful synthesis of a new type of theoretically proposed 2D metallic
ferromagnet 1T FeS2, through the molten-salt-assisted chemical vapor deposition
(CVD) method. The long-range 2D ferromagnetic order is confirmed by the
observation of a large anomalous Hall effect (AHE) and a hysteretic
magnetoresistance. The experimentally detected out-of-plane ferromagnetic
ordering is theoretically suported with Stoner criterion. Our findings open up
new possibilities to search novel 2D ferromagnets in non-layered compounds and
render opportunities for realizing realistic ultra-thin spintronic devices.",2202.00252v1
2022/11/10,Magnetic Proximity Evoked Colossal Bulk Photovoltaics in Crystalline Symmetric Layers,"Bulk photovoltaic (BPV) effect, a second order nonlinear process that
generates static current under light irradiation, requires centrosymmetric
broken systems as its application platform. In order to realize measurable BPV
photocurrent in spatially centrosymmetric materials, various schemes such as
chemical doping, structural deformation, or electric bias have been developed.
In the current work, we suggest that magnetic proximity effect via van der
Waals interfacial interaction, a contact-free strategy, also breaks the
centrosymmetry and generate large BPV photocurrents. Using the Bi2Te3 quintuple
layer as an exemplary material, we show that magnetic proximity from MnBi2Te4
septuple layers yield finite and tunable shift and injection photocurrents. We
apply group analysis and first-principles calculations to evaluate the
layer-specific shift and injection current generations under linearly polarized
light irradiation. We find that the magnetic injection photoconductivity that
localized on the Bi2Te3 layer can reach over 70*108 A/(V2s), so that a 1D
linear current density on the order of 0.1 mA/nm can be achieved under an
intermediate intensity light. In addition to charge current, we also extend our
discussions into spin BPV current, giving pure photo-generated spin current.
The vertical propagation direction between the charge and spin photocurrents
suggest that they can be used individually in a single material. Compared with
previously reported methods, the magnetic proximity effect via van der Waals
interface does not significantly alter the intrinsic feature of the
centrosymmetric material (e.g., Bi2Te3), and its manipulation can be easily
achieved by the proximate magnetic configurations (of MnBi2Te4), interlayer
distance, and light polarization.",2211.05348v1
2023/6/29,Phonon thermal transport shaped by strong spin-phonon scattering in a Kitaev material Na$_2$Co$_2$TeO$_6$,"The recent report of a half-quantized thermal Hall effect in the Kitaev
material $\alpha$-RuCl$_3$ has sparked a strong debate on whether it is
generated by Majorana fermion edge currents or whether other more conventional
mechanisms involving magnons or phonons are at its origin. A more direct
evidence for Majorana fermions which could be expected to arise from a
contribution to the longitudinal heat conductivity $\kappa_{xx}$ at
$T\rightarrow0$ is elusive due to a very complex magnetic field dependence of
$\kappa_{xx}$. Here, we report very low temperature (below 1~K) thermal
conductivity ($\kappa$) of another candidate Kitaev material,
Na$_2$Co$_2$TeO$_6$. The application of a magnetic field along different
principal axes of the crystal reveals a strong directional-dependent
magnetic-field ($\bf B$) impact on $\kappa$. We show that no evidence for
mobile quasiparticles except phonons can be concluded at any field from 0~T to
the field polarized state. In particular, severely scattered phonon transport
is observed across the $B-T$ phase diagram, which is attributed to prominent
magnetic fluctuations. Cascades of phase transitions are uncovered for all $\bf
B$ directions by probing the strength of magnetic fluctuations via a precise
record of $\kappa$($B$). Our results thus rule out recent proposals for
itinerant magnetic excitations in Na$_2$Co$_2$TeO$_6$, and emphasise the
importance of discriminating true spin liquid transport properties from
scattered phonons in candidate materials.",2306.16963v1
2023/8/17,Specular Inverse Faraday Effect in Transition Metals,"The inverse Faraday effect is an opto-magnetic phenomenon that describes the
ability of circularly polarized light to induce magnetism in solids. The
capability of light to control magnetic order in solid state materials and
devices is of interest for a variety of applications, such as magnetic
recording, quantum computation and spintronic technologies. However,
significant gaps in understanding about the effect persist, such as what
material properties govern the magnitude of the effect in metals. In this work,
we report time-resolved measurements of the specular inverse Faraday effect in
non-magnetic metals, i.e., the magneto-optic Kerr effect induced by circularly
polarized light. We measure this specular inverse Faraday effect in Cu, Pd, Pt,
W, Ta, and Au at a laser wavelength of 783 nm. For Ta and W, we investigate
both {\alpha} and \{beta} phases. We observe that excitation of these metals
with circularly polarized light induces significant circular dichroism. This
nonlinear magneto-optical response to circularly polarized light is an order of
magnitude larger in {\alpha}-W than other metals, e.g., Pt, Au, and is greater
than nearly all other reported values for IFE in other materials. Our results
benchmark the range of IFE that can be observed in non-magnetic metals and
provide insight into what material properties govern the inverse Faraday effect
in metals.",2308.09150v2
2018/1/25,Stable 3D FDTD Method for arbitrary Fully Electric and Magnetic Anisotropic Maxwell Equations,"We have developed a new fully anisotropic 3D FDTD Maxwell solver for
arbitrary electrically and magnetically anisotropic media for piecewise
constant electric and magnetic materials that are co-located over the primary
computational cells. Two numerical methods were developed that are called
non-averaged and averaged methods, respectively. The non-averaged method is
first order accurate, while the averaged method is second order accurate for
smoothly-varying materials and reduces to first order for discontinuous
material distributions. For the standard FDTD field locations with the
co-location of the electric and magnetic materials at the primary computational
cells, the averaged method require development of the different inversion
algorithms of the constitutive relations for the electric and magnetic fields.
We provide a mathematically rigorous stability proof followed by extensive
numerical testing that includes long-time integration, eigenvalue analysis,
tests with extreme, randomly placed material parameters, and various boundary
conditions. For accuracy evaluation we have constructed a test case with an
explicit analytic solution. Using transformation optics, we have constructed
complex, spatially inhomogeneous geometrical object with fully anisotropic
materials and a large dynamic range of $\underline{\epsilon}$ and
$\underline{\mu}$, such that a plane wave incident on the object is perfectly
reconstructed downstream. In our implementation, the considerable increase in
accuracy of the averaged method only increases the computational run time by
20%.",1801.08506v2
2018/2/11,"Heusler, Weyl, and Berry","Heusler materials, initially discovered by Fritz Heusler more than a century
ago, have grown into a family of more than 1000 compounds, synthesized from
combinations of more than 40 elements. These materials show a wide range of
properties, but new properties are constantly being found. Most recently, by
incorporating heavy elements that can give rise to strong spin-orbit coupling
(SOC), non-trivial topological phases of matter, such as topological insulators
(TIs), have been discovered in Heusler materials. Moreover, the interplay of
symmetry, SOC and magnetic structure allows for the realization of a wide
variety of topological phases through Berry curvature design. Weyl points and
nodal lines can be manipulated by various external perturbations, which results
in exotic properties such as the chiral anomaly, and large anomalous spin and
topological Hall effects. The combination of a non-collinear magnetic structure
and Berry curvature gives rise a non-zero anomalous Hall effect, which was
first observed in the antiferromagnets Mn3Sn and Mn3Ge. Besides this k-space
Berry curvature, Heusler compounds with non-collinear magnetic structures also
possess real-space topological states in the form of magnetic antiskyrmions,
which have not yet been observed in other materials. The possibility of
directly manipulating the Berry curvature shows the importance of understanding
both the electronic and magnetic structures of Heusler compounds. Together,
with the new topological viewpoint and the high tunability, novel physical
properties and phenomena await discovery in Heusler compounds.",1802.03771v1
2022/6/13,An efficient material search for room temperature topological magnons,"Topologically protected magnon surface states are highly desirable as an
ideal platform to engineer low-dissipation spintronics devices. However,
theoretical prediction of topological magnons in strongly correlated materials
proves to be challenging because the ab initio density functional theory
calculations fail to reliably predict magnetic interactions in correlated
materials. Here, we present a symmetry-based approach, which predicts
topological magnons in magnetically ordered crystals, upon applying external
perturbations such as magnetic/electric fields and/or mechanical strains. We
apply this approach to carry out an efficient search for magnetic materials in
the Bilbao Crystallographic Server, where, among 198 compounds with an over
300-K transition temperature, we identify 12 magnetic insulators that support
room-temperature topological magnons. They feature Weyl magnons with surface
magnon arcs and magnon axion insulators with either chiral surface or hinge
magnon modes, offering a route to realize energy-efficient devices based on
protected surface magnons.",2206.06248v2
2024/3/5,Orbital torque switching in perpendicularly magnetized materials,"The orbital Hall effect in light materials has attracted considerable
attention for developing novel orbitronic devices. Here we investigate the
orbital torque efficiency and demonstrate the switching of the perpendicularly
magnetized materials through the orbital Hall material (OHM), i.e., Zirconium
(Zr). The orbital torque efficiency of approximately 0.78 is achieved in the Zr
OHM with the perpendicularly magnetized [Co/Pt]3 sample, which significantly
surpasses that of the perpendicularly magnetized CoFeB/Gd/CoFeB sample
(approximately 0.04). Such notable difference is attributed to the different
spin-orbit correlation strength between the [Co/Pt]3 sample and the
CoFeB/Gd/CoFeB sample, which has been confirmed through the theoretical
calculations. Furthermore, the full magnetization switching of the [Co/Pt]3
sample with a switching current density of approximately 2.6x106 A/cm2 has been
realized through Zr, which even outperforms that of the W spin Hall material.
Our finding provides a guideline to understand orbital torque efficiency and
paves the way to develop energy-efficient orbitronic devices.",2403.03043v1
2024/3/28,"Kitaev Interactions Through an Extended Superexchange Pathway in the jeff = 1/2 Ru3+ Honeycomb Magnet, RuP3SiO11","Magnetic materials are composed of the simple building blocks of magnetic
moments on a crystal lattice that interact via short-range magnetic exchange
interactions. Yet from these simple building blocks emerges a remarkable
diversity of magnetic states. Some of these, such as ferromagnetism, are
familiar in our everyday lives, while others reveal the deep quantum mechanical
origins of magnetism. A prime example of the latter are quantum spin liquid
(QSL) states in which -- unlike in a ferromagnet where magnetic moments are
driven by their exchange interactions to adopt long-range order -- magnetic
moments remain disordered at low temperatures but are simultaneously correlated
over long length scales through quantum entanglement. A particularly promising
theoretical model of a QSL is the Kitaev model, composed of unusual
bond-dependent exchange interactions between magnetic moments on a honeycomb
lattice. However, the Kitaev QSL is extremely challenging to realise
experimentally as it is unstable to competing exchange interactions and crystal
lattice perturbations that inevitably arise in real materials. This makes it
essential to understand the relationship between the structure and interactions
that may give rise to Kitaev interactions in new candidate materials. Here we
show that the material requirements for the Kitaev QSL survive for an extended
pseudo-edge-sharing superexchange pathway of Ru3+ 4d5 octahedra within the
honeycomb layers of the inorganic framework solid, RuP3SiO11. Through materials
synthesis and structural characterisation, resonant inelastic X-ray and neutron
scattering experiments, we confirm the requisite jeff = 1/2 state of Ru3+ in
RuP3SiO11 and resolve the hierarchy of exchange interactions that provide
experimental access to an otherwise unexplored region of the extended Kitaev
phase diagram.",2403.19406v1
1997/8/22,Estimation of the Doping Dependence of Antiferromagnetism in the Copper Oxide Material,"Within the $t$-$J$ model, we study the doping dependence of
antiferromagnetism in the copper oxide materials by considering quantum
fluctuations of spinons in the random-phase-approximation. The staggered
magnetization vanishes around doping $\delta=5%$ for a reasonable parameter
value $t/J=5$, which is in agreement with the experiments on copper oxide
materials.",9708176v1
2006/3/14,Magnetothermal properties of molecule-based materials,"We critically review recent results obtained by studying the low-temperature
specific heat of some of the most popular molecular magnets. Perspectives of
this field are discussed as well.",0603368v1
2002/8/2,Spectral response of Cantor multilayers made of materials with negative refractive index,"Whereas Cantor multilayers made of an isotropic dielectric-magnetic material
with positive refractive index will show power-law characteristics, low-order
Cantor multilayers made of materials with negative refractive index will not
exhibit the power-law nature. A reason for this anomalous behavior is
presented.",0208011v1
2007/8/10,Prediction for new magnetoelectric fluorides,"We use symmetry considerations in order to predict new magnetoelectric
fluorides. In addition to these magnetoelectric properties, we discuss among
these fluorides the ones susceptible to present multiferroic properties. We
emphasize that several materials present ferromagnetic properties. This
ferromagnetism should enhance the interplay between magnetic and dielectric
properties in these materials.",0708.1475v1
2008/11/30,On the inapplicability of a negative-phase-velocity condition as a negative-refraction condition for active materials,"A negative-phase-velocity condition derived by Depine and Lakhtakia
[Microwave Opt Technol Lett 41 (2004) 315] for isotropic, homogeneous, passive,
dielectric-magnetic materials is inapplicable as a negative-refraction
condition for active materials.",0812.0171v2
2018/12/18,Interpretation of experimental evidence of the topological Hall effect,"The topological Hall effect in magnetic materials is considered the ultimate
trademark of the skyrmion phase. The phenomenon is identified by distinct
non-monotonic features in the Hall effect signal presumed to be the evidence of
the topological origin. It is demonstrated here that similar features,
unrelated to the skyrmion physics, arise in heterogeneous ferromagnets when
components of the material exhibit the extraordinary Hall effect with opposite
polarities. Relevance of this mechanism to the published data is discussed.",1812.07433v1
2003/4/23,"Magnetic frustration in a stoichiometric spin-chain compound, Ca$_3$CoIrO$_6$","The temperature dependent ac and dc magnetization and heat capacity data of
Ca$_3$CoIrO$_6$, a spin-chain compound crystallizing in a K$_4$CdCl$_6$-derived
rhombohedral structure, show the features due to magnetic ordering of a
frustrated-type below about 30 K, however without exhibiting the signatures of
the so-called ""partially disordered antiferromagnetic structure"" encountered in
the isostructural compounds, Ca$_3$Co$_2$O$_6$ and Ca$_3$CoRhO$_6$. This class
of compounds thus provides a variety for probing the consequences of magnetic
frustration due to topological reasons in stoichiometric spin-chain materials,
presumably arising from subtle differences in the interchain and intrachain
magnetic coupling strengths. This compound presents additional interesting
situations in the sense that, ac susceptibility exhibits a large frequency
dependence in the vicinity of 30 K uncharacteristic of conventional
spin-glasses, with this frustrated magnetic state being robust to the
application of external magnetic fields.",0304518v1
2004/8/31,Handedness of magnetic-dipolar modes in ferrite disks,"For magnetic-dipolar modes in a ferrite, components of the magnetic flux
density in a helical coordinate system are dependent on both an orientation of
a gyration vector and a sign of a pitch. It gives four types of helical
harmonics for magnetostatic-potential wave functions in a ferrite disk. Because
of the reflection symmetry breaking, coupling between certain types of helical
harmonics takes place in the reflection points. The reflection feature leads to
exhibition of two types of resonances: the ""right"" and ""left"" resonances. These
resonances become coupled for a ferrite disk placed in a homogeneous tangential
RF magnetic field. One also observes such resonance coupling for a ferrite disk
with a symmetrically oriented linear surface electrode, when this ferrite
particle is placed in a homogeneous tangential RF electric field. In a
cylindrical coordinate system handedness of magnetic-dipolar modes in a ferrite
disk is described by spinor wave functions.",0408682v2
2004/11/24,"Nature of magnetism in the spin-chain compound, Ca3CuRuO6","A quasi one-dimensional compound, Ca3CuRuO6, has been synthesized by
solid-state reaction method and studied using magnetization (M) and heat
capacity (C) measurements. This compound undergoes magnetic ordering (T_o)
around 40 K, as evidenced by the dc magnetic susceptibility (chi) behavior.
However, the magnitude of the paramagnetic
  Curie temperature (theta_p) obtained from the high temperature linear region
is large (-277 K, with the negative sign indicating antiferromagnetic
interaction). The reduction of T_o, compared to theta_p, is attributed to
geometrical frustration effect arising from the triangular arrangement of
antiferromagnetically coupled magnetic chains. The absence of a feature in ac
chi around 40 K rules out possible spin-glass freezing. However, we find that
the peak in C(T) around 40 K is weak, with the entropy change associated with
the transition being negligible, typical of a disordered magnetism. We infer
that this material thus exhibits inhomogeneous magnetism, despite being
stoichiometric, presumably due to an interplay between disorder in the Cu-Ru
chain.",0411601v1
2005/5/3,The effect of a weak ferromagnetic matrix on a system of nanomagnetic particles,"The study of system of magnetic nano-particle has received increasing
attention recently both because of the novel physical concepts involved and
also because of their vast potential for application. The influence of
background material (the substrate coating) on magnetic properties of such
systems is a relatively open topic and often a full understanding is missing.
In the present work we discuss our experiments and interpretation for two
systems: Ni nanoparticles coated with graphitic carbon and Ni nanoparticles
coated with Au. While the latter system exibits behavior typical of
superparamagnetic particle systems the former shows several puzzling results
such as extremely high blocking temperature ($T_{B}$), very fast relaxation
time well below $T_{B}$, temperature independent field-cooled magnetization and
very small coercivity and remanent magnetization. We interpret these findings
as being a result of weak ferromagnetism, characteristic of the graphitic
carbon. This induces strong magnetic interactions between the Ni particles in
the presence of small magnetic fields. Such systems give rise to a dramatic
difference in blocking temperature between measurements performed at zero field
and those performed at very small magnetic fields.",0505054v1
2005/5/30,Spin Disorder and Magnetic Anisotropy in Fe3O4 Nanoparticles,"We have studied the magnetic behavior of dextran-coated magnetite
(Fe$_3$O$_4$) nanoparticles with median particle size $\left<d\right>=8$ $nm$.
Magnetization curves and in-field M\""ossbauer spectroscopy measurements showed
that the magnetic moment $M_S$ of the particles was much smaller than the bulk
material. However, we found no evidence of magnetic irreversibility or
non-saturating behavior at high fields, usually associated to spin canting. The
values of magnetic anisotropy $K_{eff}$ from different techniques indicate that
surface or shape contributions are negligible. It is proposed that these
particles have bulk-like ferrimagnetic structure with ordered A and B
sublattices, but nearly compensated magnetic moments. The dependence of the
blocking temperature with frequency and applied fields, $T_B(H,\omega)$,
suggests that the observed non-monotonic behavior is governed by the strength
of interparticle interactions.",0505682v5
2005/11/19,"Transport, thermal and magnetic properties of RuSr_2(Gd_{1.5}Ce_{0.5})Cu_2O_{10-δ}, a magnetic superconductor","Resistivity, thermoelectric power, heat capacity and magnetization for
samples of RuSr_2(Gd_{1.5}Ce_{0.5})Cu_{2}O_{10-\delta} were investigated in the
temperature range 1.8-300 K with a magnetic field up to 8 T. The resistive
transitions to the superconducting state are found to be determined by the
inhomogeneous (granular) structure, characterized by the intragranular, T_{c0},
and intergranular, T_{cg}, transition temperatures. Heat capacity, C(T), shows
a jump at the superconducting transition temperature T_{c0}\approx 37.5 K. A
Schottky-like anomaly is found in C(T) below 20 K. This low temperature anomaly
can be attributed to splitting of the ground term $^{8}S_{7/2}$ of paramagnetic
Gd^{3+} ions by internal and external magnetic fields.",0511489v1
2006/2/2,Positive and negative magnetocapacitance in magnetic nanoparticle systems,"The dielectric properties of MnFe$_2$O$_4$ and $\gamma$-Fe$_2$O$_3$ magnetic
nanoparticles embedded in insulating matrices were investigated. The samples
showed frequency dependent dielectric anomalies coincident with the magnetic
blocking temperature and significant magnetocapacitance above this blocking
temperature, as large as 0.4% at H = 10kOe. For both samples the magnetic field
induced change in dielectric constant was proportional to the square of the
sample magnetization. These measurements suggest that the dielectric properties
of magnetic nanoparticles are closely related to the disposition of magnetic
moments in the system. As neither bulk gamma-Fe2O3 nor MnFe2O3 are
magnetoelectric materials, this magnetodielectric coupling is believed to arise
from extrinsic effects which are discussed in light of recent work relating
magnetoresistive and magnetocapacitive behavior.",0602057v1
2006/3/8,Anomalous Spontaneous Reversal in Magnetic Heterostructures,"We observe a thermally induced spontaneous magnetization reversal of
epitaxial ferromagnet/antiferromagnet heterostructures under a constant applied
magnetic field. Unlike any other magnetic system, the magnetization
spontaneously reverses, aligning anti-parallel to an applied field with
decreasing temperature. We show that this unusual phenomenon is caused by the
interfacial antiferromagnetic coupling overcoming the Zeeman energy of the
ferromagnet. A significant temperature hysteresis exists, whose height and
width can be tuned by the field applied during thermal cycling. The hysteresis
originates from the intrinsic magnetic anisotropy in the system. The
observation of this phenomenon leads to open questions in the general
understanding of magnetic heterostructures. Moreover, this shows that in
general heterogeneous nanostructured materials may exhibit unexpected phenomena
absent in the bulk.",0603224v1
2007/12/12,Reentrant spin glass transition in LuFe2O4,"We have carried out a comprehensive investigation of magnetic properties of
LuFe$_2$O$_4$, using AC susceptibility, DC magnetization and specific heat. A
magnetic phase transition around $\sim$236 K was observed with DC magnetization
and specific heat measurements, which is identified as a paramagnetic to
ferrimagnetic transition based on the nonlinear susceptibility data. Upon
further cooling below this temperature, we also observed highly relaxational
magnetic behavior: the DC magnetization exhibits history and time dependence,
and the real and imaginary part of the AC susceptibility shows large frequency
dependence. Dynamic scaling of the AC susceptibility data suggests that this
low temperature phase can be described as a reentrant spin glass phase. We also
discuss magnetic field dependence of the spin glass transition and aging,
memory and rejuvenation effect below the glass transition temperature around
228 K.",0712.1975v1
2008/6/10,Magnetic circular dichroism from the impurity band in III-V diluted magnetic semiconductors,"The magnetic circular dichroism of III-V diluted magnetic semiconductors,
calculated within a theoretical framework suitable for highly disordered
materials, is shown to be dominated by optical transitions between the bulk
bands and an impurity band formed from magnetic dopant states. The theoretical
framework incorporates real-space Green's functions to properly incorporate
spatial correlations in the disordered conduction band and valence band
electronic structure, and includes extended and localized electronic states on
an equal basis. Our findings reconcile unusual trends in the experimental
magnetic circular dichroism in III-V DMSs with the antiferromagnetic p-d
exchange interaction between a magnetic dopant spin and its host.",0806.1753v1
2008/6/11,The challenge of unravelling magnetic properties in LaFeAsO,"First principles calculations of magnetic and, to a lesser extent, electronic
properties of the novel LaFeAsO-based superconductors show substantial apparent
controversy, as opposed to most weakly or strongly correlated materials. Not
only do different reports disagree about quantitative values, there is also a
schism in terms of interpreting the basic physics of the magnetic interactions
in this system. In this paper, we present a systematic analysis using four
different first principles methods and show that while there is an unusual
sensitivity to computational details, well-converged full-potential
all-electron results are fully consistent among themselves. What makes results
so sensitive and the system so different from simple local magnetic moments
interacting via basic superexchange mechanisms is the itinerant character of
the calculated magnetic ground state, where very soft magnetic moments and
long-range interactions are characterized by a particular structure in the
reciprocal (as opposed to real) space. Therefore, unravelling the magnetic
interactions in their full richness remains a challenging, but utterly
important task.",0806.1869v2
2009/3/27,Magnetization in uniaxial spherical nanoparticles: consequence on the interparticle interaction,"We investigate the interaction between spherical magnetic nanoparticles which
present either a single domain or a vortex structure. First the magnetic
structure of a uniaxial soft sphere is revisited, and then the interaction
energy is calculated from a micromagnetic simulation. In the vortex regime the
orientation of the vortex relative to the easy axis depends on both the
particle size and the anisotropy constant. We show that the leading term of the
interaction is the dipolar interaction energy between the magnetic moments. For
particles presenting a vortex structure, we show that the polarization due to
the dipolar field must be included. The parameters entering in the dipolar
interaction are deduced from the magnetic behavior of the isolated particle.",0903.4924v1
2010/2/23,Crystal and magnetic structure of the oxypnictide superconductor LaO(1-x)FxFeAs: evidence for magnetoelastic coupling,"High-resolution and high-flux neutron as well as X-ray powder-diffraction
experiments were performed on the oxypnictide series LaO(1-x)FxFeAs with
0<x<0.15 in order to study the crystal and magnetic structure. The magnetic
symmetry of the undoped compound corresponds to those reported for ReOFeAs
(with Re a rare earth) and for AFe2As2 (A=Ba, Sr) materials. We find an ordered
magnetic moment of 0.63(1)muB at 2 K in LaOFeAs, which is significantly larger
than the values previously reported for this compound. A sizable ordered
magnetic moment is observed up to a F-doping of 4.5% whereas there is no
magnetic order for a sample with a F concentration of x=0.06. In the undoped
sample, several interatomic distances and FeAs4 tetrahedra angles exhibit
pronounced anomalies connected with the broad structural transition and with
the onset of magnetism supporting the idea of strong magneto-elastic coupling
in this material.",1002.4326v1
2010/11/4,Dirac Strings and Magnetic Monopoles in Spin Ice Dy2Ti2O7,"While sources of magnetic fields - magnetic monopoles - have so far proven
elusive as elementary particles, several scenarios have been proposed recently
in condensed matter physics of emergent quasiparticles resembling monopoles. A
particularly simple proposition pertains to spin ice on the highly frustrated
pyrochlore lattice. The spin ice state is argued to be well-described by
networks of aligned dipoles resembling solenoidal tubes - classical, and
observable, versions of a Dirac string. Where these tubes end, the resulting
defect looks like a magnetic monopole. We demonstrate, by diffuse neutron
scattering, the presence of such strings in the spin-ice Dy2Ti2O7. This is
achieved by applying a symmetry-breaking magnetic field with which we can
manipulate density and orientation of the strings. In turn, heat capacity is
described by a gas of magnetic monopoles interacting via a magnetic Coulomb
interaction.",1011.1174v1
2011/9/7,A theoretical analysis of inertia-like switching in magnets: applications to a synthetic antiferromagnet,"The magnetization dynamics of a synthetic antiferromagnet subject to a short
magnetic field pulse, has been studied by using a combination of
first-principles and atomistic spin dynamics simulations. We observe switching
phenomena on the time scale of tens of picoseconds, and inertia-like behavior
in the magnetization dynamics. We explain the latter in terms of a dynamic
redistribution of magnetic energy from the applied field pulse to other
possible energy terms, such as the exchange interaction and the magnetic
anisotropy, without invoking concepts such as inertia of an antiferromagnetic
vector. We also demonstrate that such dynamics can also be observed in a
ferromagnetic material where the incident field pulse pumps energy to the
magnetic anisotropy.",1109.1414v1
2011/10/10,Direct evidence for the magnetic ordering of Nd ions in NdMn$_2$Si$_2$ and NdMn$_2$Ge$_2$ by high resolution inelastic neutron scattering,"We have investigated the low energy nuclear spin excitations in
NdMn$_2$Si$_2$ and NdMn$_2$Ge$_2$ by high resolution inelastic neutron
scattering. Previous neutron diffraction investigations gave ambiguous results
about Nd magnetic ordering at low temperatures. The present element-specific
technique gave direct evidence for the magnetic ordering of Nd ions. We found
considerable difference in the process of the Nd magnetic ordering at low
temperature in NdMn$_2$Si$_2$ and NdMn$_2$Ge$_2$. Our results are consistent
with those of magnetization and recent neutron diffraction measurements.",1110.1954v1
2012/4/26,Peculiarities of timing and spectral diagrams of magnetic video-pulse excitation influence on NMR spin-echo in magnets,"We present the first systematic study of timing and spectral diagrams of
magnetic video-pulse influence on the NMR two-pulse echo in a number of magnets
(ferromagnets, ferrites, half metals, intermetals). It is shown that the timing
diagrams showing the dependence of two-pulse echo intensity on the temporal
location of a magnetic video-pulse in respect to radio-frequency pulses and the
spectral diagrams of this influence are defined mainly by the local hyperfine
field anisotropy and domain walls mobility. These diagrams could be used for
the identification of the nature of NMR spectra in multidomain magnetic
materials and to improve the resolution capacity of the NMR method in magnets.",1204.5844v1
2012/8/13,Magnetic Dipole and Electric Quadrupole Transitions in the Trivalent Lanthanide Series: Calculated Emission Rates and Oscillator Strengths,"Given growing interest in optical-frequency magnetic dipole transitions, we
use intermediate coupling calculations to identify strong magnetic dipole
emission lines that are well suited for experimental study. The energy levels
for all trivalent lanthanide ions in the 4fn configuration are calculated using
a detailed free ion Hamiltonian, including electrostatic and spin-orbit terms
as well as two-body, three-body, spin-spin, spin-other-orbit, and
electrostatically correlated spin-orbit interactions. These free ion energy
levels and eigenstates are then used to calculate the oscillator strengths for
all ground-state magnetic dipole absorption lines and the spontaneous emission
rates for all magnetic dipole emission lines including transitions between
excited states. A large number of strong magnetic dipole transitions are
predicted throughout the visible and near-infrared spectrum, including many at
longer wavelengths that would be ideal for experimental investigation of
magnetic light-matter interactions with optical metamaterials and plasmonic
antennas.",1208.2642v2
2013/3/11,"Crystals, magnetic and electronic properties of a new ThCr2Si2-type BaMn2Bi2 and K-doped compositions","This is a report on the new 122 ternary transition-metal pnictide of
BaMn2Bi2, which is crystallized from bismuth flux. BaMn2Bi2 adopts
ThCr2Si2-type structure (I4/mmm) with a = 4.4902(3) {\AA} and c = 14.687(1)
{\AA}; it is antiferromagnetic with anisotropic magnetic susceptibility and
semiconducting with a band gap of Eg = 6 meV. Heat capacity result confirms the
insulating ground state in BaMn2Bi2 with the electronic residual Sommerfeld
coefficient of {\gamma} ~ 0. The high temperature magnetization results show
that magnetic ordering temperature is TN ~ 400 K. Hole-doping in BaMn2Bi2 via
potassium in Ba1-xKxMn2Bi2 results in metallic behavior for x = 0.10(1),
0.32(1) and 0.36(1). With K-doping, more magnetically anisotropic behavior is
observed. Although there is a downturn in electrical resistivity and low-field
magnetization data below 4 K in > 30%-doped crystals, there is no sign of zero
resistance or diamagnetism. This manuscript is a report on new materials of
BaMn2Bi2 and Ba1-xKxMn2Bi2 (0 < x < 0.4). Results from powder X-ray
diffraction, anisotropic temperature- and field-dependent magnetization,
temperature-and field-dependent electrical resistivity, and heat capacity are
presented.",1303.2695v2
2013/4/4,Magnetic proximity effect at the 3D topological insulator/magnetic insulator interface,"The magnetic proximity effect is a fundamental feature of heterostructures
composed of layers of topological insulators and magnetic materials since it
underlies many potential applications in devices with novel quantum
functionality. Within density functional theory we study magnetic proximity
effect at the 3D topological insulator/magnetic insulator (TI/MI) interface in
Bi$_2$Se$_3$/MnSe(111) system as an example. We demonstrate that a gapped
ordinary bound state which spectrum depends on the interface potential arises
in the immediate region of the interface. The gapped topological Dirac state
also arises in the system owing to relocation to deeper atomic layers of
topological insulator. The gap in the Dirac cone is originated from an
overlapping of the topological and ordinary interfacial states. This result
being also corroborated by the analytic model, is a key aspect of the magnetic
proximity effect mechanism in the TI/MI structures.",1304.1275v1
2013/8/8,Domain wall tilting in the presence of the Dzyaloshinskii-Moriya interaction in out-of-plane magnetized magnetic nanotracks,"We show that the Dzyaloshinskii-Moriya interaction (DMI) can lead to a
tilting of the domain wall (DW) surface in perpendicularly magnetized magnetic
nanotracks when DW dynamics is driven by an easy axis magnetic field or a spin
polarized current. The DW tilting affects the DW dynamics for large DMI and the
tilting relaxation time can be very large as it scales with the square of the
track width. The results are well explained by an analytical model based on a
Lagrangian approach where the DMI and the DW tilting are included. We propose a
simple way to estimate the DMI in a magnetic multilayers by measuring the
dependence of the DW tilt angle on a transverse static magnetic field. Our
results shed light on the current induced DW tilting observed recently in Co/Ni
multilayers with inversion asymmetry, and further support the presence of DMI
in these systems.",1308.1824v1
2013/10/18,Ultrafast thermally induced magnetic switching in synthetic ferrimagnets,"Synthetic ferrimagnets are composite magnetic structures formed from two or
more anti- ferromagnetically coupled magnetic sublattices with different
magnetic moments. Here we report on atomistic spin simulations of the
laser-induced magnetization dynamics on such synthetic ferrimag- nets, and
demonstrate that the application of ultrashort laser pulses leads to
sub-picoscond magnetization dynamics and all-optical switching in a similar
manner as in ferrimagnetic alloys. Moreover, we present the essential material
properties for successful laser-induced switching, demonstrating the
feasibility of using a synthetic ferrimagnet as a high density magnetic storage
element without the need of a write field.",1310.5170v2
2013/12/4,Rashba Spin-Orbit Anisotropy and the Electric Field Control of Magnetism,"The control of the magnetism of ultra-thin ferromagnetic layers using an
electric field rather than a current, if large enough, would lead to many
technologically important applications. To date, while it is usually assumed
the changes in the magnetic anisotropy, leading to such a control, arises from
surface charge doping of the magnetic layer, a number of key experiments cannot
be understood within such a scenario. Much studied is the fact that, for
non-magnetic metals or semi-conductors, a large surface electric field gives
rise to a Rashba spin-orbit coupling which leads to a spin-splitting of the
conduction electrons. For a magnet, this splitting is modified by the exchange
field resulting in a large magnetic anisotropy energy via the
Dzyaloshinskii-Moriya mechanism. This different, yet traditional, path to an
electrically induced anisotropy energy can explain the electric field,
thickness, and material dependence reported in many experiments.",1312.1021v1
2014/6/4,A new soft X-ray magnetic circular dichroism facility at the BSRF beamline 4B7B,"X-ray magnetic circular dichroism (XMCD) has become an important and powerful
tool because it allows the study of material properties in combination with
elemental specificity, chemical state specificity, and magnetic specificity. A
new soft X-ray magnetic circular dichroism apparatus has been developed at the
Beijing Synchrotron Radiation Facility (BSRF). The apparatus combines three
experimental conditions: ultra-high-vacuum environment, moderate magnetic
fields and in-situ sample preparation to measure the absorption signal. We
designed a C type dipole electromagnet that provides magnetic fields up to 0.5T
in parallel (or anti-parallel) direction relative to the incoming X-ray beam.
The performances of the electromagnet are measured and the results show good
agreement with the simulation ones. Following film grown in situ by evaporation
methods, XMCD measurements are performed. Combined polarization corrections,
the magnetic moments of the Fe and Co films determined by sum rules are
consistent with other theoretical predictions and experimental measurements.",1406.0960v1
2014/6/25,Magnetic ordered structure dependence of magnetic refrigeration efficiency,"We have investigated the relation between magnetic ordered structure and
magnetic refrigeration efficiency in the Ising model on a simple cubic lattice
using Monte Carlo simulations. The magnetic entropy behaviors indicate that the
protocol, which was first proposed in [Appl. Phys. Lett. {\bf 104}, 052415
(2014).], can produce the maximum isothermal magnetic entropy change and the
maximum adiabatic temperature change in antiferromagnets. Furthermore, the
total amount of heat transfer under the proposed protocol reaches a maximum.
The relation between measurable physical quantities and magnetic refrigeration
efficiency is also discussed.",1406.6462v2
2014/7/21,All-in/all-out magnetic domains: X-ray diffraction imaging and magnetic field control,"Long-range non-collinear all-in/all-out magnetic order has been directly
observed for the first time in real space in the pyrochlore Cd$_2$Os$_2$O$_7$
using resonant magnetic microdiffraction at the Os L$_3$ edge. Two different
antiferromagnetic domains related by time-reversal symmetry could be
distinguished and have been mapped within the same single crystal. The two
types of domains are akin to magnetic twins and were expected - yet unobserved
so far - in the all-in/all-out model. Even though the magnetic domains are
antiferromagnetic, we show that their distribution can be controlled using a
magnetic field-cooling procedure.",1407.5401v1
2014/7/27,Ordered arrays of magnetic nanowires investigated by polarized small-angle neutron scattering,"Polarized small-angle neutron scattering (PSANS) experimental results
obtained on arrays of ferromagnetic Co nanowires ($\phi\approx13$ nm) embedded
in self-organized alumina (Al$_{2}$O$_{3}$) porous matrices are reported. The
triangular array of aligned nanowires is investigated as a function of the
external magnetic field with a view to determine experimentally the real space
magnetization $\vec{M}(\vec{r})$ distribution inside the material during the
magnetic hysteresis cycle. The observation of field-dependentSANSintensities
allows us to characterize the influence of magnetostatic fields. The PSANS
experimental data are compared to magnetostatic simulations. These results
evidence that PSANS is a technique able to address real-space magnetization
distributions in nanostructured magnetic systems. We show that beyond
structural information (shape of the objects, two-dimensional organization)
already accessible with nonpolarized SANS, using polarized neutrons as the
incident beam provides information on the magnetic form factor and stray fields
\textgreek{m}0Hd distribution in between nanowires.",1407.7193v1
2014/8/12,"Mechano-sysntesis and structural, magnetic and thermal characterization of $α$-Fe nanoparticles embedded in a Wüstite matrix","Magnetic materials for specific applications require an accurate control and
complete comprehension of their magnetic properties. In particular,
nanoparticles embedded in a polycrystalline matrix emerge as good candidates
for applications due to the possibility of tuning the magnetic properties
through interface interaction effects. Here, iron/w\""ustite composite is
prepared using high energy mechanical milling from iron powder and water. The
sample is analyzed by X-ray diffraction, dynamic laser light scattering,
M\""ossbauer spectroscopy, field cooling and zero field cooling curves,
magnetization curves, and magnetic hyperthermia. Based on the results, we
identify that the produced sample is like Fe nanoparticles embedded in a
w\""ustite matrix, with high stability in time, and shows noticeable features
such as exchange bias effect at low temperatures and promising temperatures
reached in a short time interval when considered magnetic hyperthermia, $\sim
46\,^\circ$C, becoming an interesting candidate for biological applications,
such as the one employed for cancer therapy.",1408.2703v1
2014/10/15,Orientation-dependent magnetism and orbital structure of strained YTiO$_3$ films on LaAlO$_3$ substrates,"The strain tuned magnetism of YTiO$_3$ film grown on the LaAlO$_3$ ($110$)
substrate is studied by the method of the first principles, and compared with
that of the ($001$)-oriented one. The obtained magnetism is totally different,
which is ferromagnetic for the film on the ($110$) substrate but A-type
antiferromagnetic on the ($001$) one. This orientation-dependent magnetism is
attributed to the subtle orbital ordering of YTiO$_3$ film. The
$d_{xz}$/$d_{yz}$-type orbital ordering is predominant for the ($001$) one, but
for the ($110$) case, the $d_{xy}$ orbital is mostly occupied plus a few
contribution from the $d_{xz}$/$d_{yz}$ orbital. Moreover, the lattice mismatch
is modest for the ($110$) case but more serious for the ($001$) one, which is
also responsible for this contrasting magnetism.",1410.3939v1
2014/12/14,Graphene nanoflakes in external electric and magnetic in-plane fields,"The paper discusses the influence of the external in-plane electric and
magnetic field on the ground state spin phase diagram of selected monolayer
graphene nanostructures. The calculations are performed for triangular graphene
nanoflakes with armchair edges as well as for short pieces of armchair graphene
nanoribbons with zigzag terminations. The Mean Field Approximation (MFA) is
employed to solve the Hubbard model. The total spin for both classes of
nanostructures is discussed as a function of external fields for various
structure sizes, for charge neutrality conditions as well as for weak charge
doping. The variety of nonzero spin states is found and their stability ranges
are determined. For some structures, the presence of antiferromagnetic
orderings is predicted within the zero-spin phase. The process of magnetization
of nanoflakes with magnetic field at constant electric field is also
investigated, showing opposite effect of electric field at low and at high
magnetic fields.",1412.4387v3
2014/12/28,Tunable Transient Decay Times in Nonlinear Systems: Application to Magnetic Precession,"The dynamical motion of the magnetization plays a key role in the properties
of magnetic materials. If the magnetization is initially away from the
equilibrium direction in a magnetic nanoparticle, it will precess at a natural
frequency and, with some damping present, will decay to the equilibrium
position in a short lifetime. Here we investigate a simple but important
situation where a magnetic nanoparticle is driven non-resonantly by an
oscillating magnetic field, not at the natural frequency. We find a surprising
result that the lifetime of the transient motion is strongly tunable, by
factors of over 10,000, by varying the amplitude of the driving field.",1412.8224v3
2014/12/30,Reversible control of Co magnetism by voltage induced oxidation,"We demonstrate that magnetic properties of ultra-thin Co films adjacent to
Gd2O3 gate oxides can be directly manipulated by voltage. The Co films can be
reversibly changed from an optimally-oxidized state with a strong perpendicular
magnetic anisotropy to a metallic state with an in-plane magnetic anisotropy,
or to an oxidized state with nearly zero magnetization, depending on the
polarity and time duration of the applied electric fields. Consequently, an
unprecedentedly large change of magnetic anisotropy energy up to 0.73 erg/cm2
has been realized in a nonvolatile manner using gate voltages of only a few
volts. These results open a new route to achieve ultra-low energy magnetization
manipulation in spintronic devices.",1412.8668v1
2015/3/4,Structural and magnetic properties of MnCo1-xFexSi alloys,"The crystal structures, martensitic structural transitions and magnetic
properties of MnCo1-xFexSi (0 <= x <= 0.50) alloys were studied by differential
scanning calorimetry (DSC), x-ray powder diffraction (XRD) and magnetic
measurements. In high-temperature paramagnetic state, the alloys undergo a
martensitic structural transitions from the Ni2In-type hexagonal parent phase
to the TiNiSi-type orthorhombic martensite. Both the martensitic transition
temperature (TM) and Curie temperatures of martensite (T_C^M) decrease with
increasing Fe content. The introduced Fe atoms establish ferromagnetic (FM)
coupling between Fe-Mn atoms and destroy the double spiral antiferromagnetic
(AFM) coupling in MnCoSi compound, resulting in a magnetic change in the
martensite phase from a spiral AFM state to a FM state. For the alloys with x =
0.10, 0.15 and 0.20, a metamagnetic transition was observed in between the two
magnetic states. A magnetostructural phase diagram of MnCo1-xFexSi (0 <= x <=
0.50) alloys was proposed.",1503.01226v1
2015/3/19,A new class of chiral materials hosting magnetic skyrmions beyond room temperature,"Skyrmions, topologically protected vortex-like nanometric spin textures in
magnets, have been attracting increasing attention for emergent electromagnetic
responses and possible technological applications for spintronics. In
particular, metallic magnets with chiral and cubic/tetragonal crystal structure
may have high potential to host skyrmions that can be driven by low electrical
current excitation. However, experimental observations of skyrmions have so far
been limited to below room temperature for the metallic chiral magnets,
specifically for the MnSi-type B20 compounds. Toward technological
applications, it is crucial to transcend this limitation. Here we demonstrate
the formation of skyrmions with unique spin helicity both at and above room
temperature in a family of cubic chiral magnets: beta-Mn-type Co-Zn-Mn alloys
with a different chiral space group from that of B20 compounds. Lorentz
transmission electron microscopy (LTEM), magnetization, and small angle neutron
scattering (SANS) measurements unambiguously reveal the formation of a skyrmion
crystal under the application of magnetic field (H<~1 kOe) in both thin- plate
(thickness<150 nm) and bulk forms.",1503.05651v1
2015/6/10,The magnetic ground state properties of non-centrosymmetric CePt$_3$B$_{1-x}$Si$_x$,"We present a study of the alloying series of the non-centrosymmetric
$f$-electron intermetallic CePt$_3$B$_{1-x}$Si$_x$ by means of muon spin
rotation and relaxation measurements. In addition, we include a high pressure
magnetization investigation of the stoichiometric parent compound CePt$_3$B.
From our data we establish the nature of the magnetic ground state properties
of the series, derive the ordered magnetic moment as function of stoichiometry
and gain insight into the evolution of the symmetry of the ordered magnetic
state with $x$. We thus can verify the notion that the behavior of the sample
series can essentially be understood within the framework of the Doniach phase
diagram. Further, our findings raise the issue of the role the
Dzyaloshinskii-Moriya magnetic interaction plays in correlated electron
materials, and its effect on magnetic fluctuations in such materials.",1506.03419v1
2015/6/17,The terahertz frontier for ultrafast coherent magnetic switching: Terahertz-induced demagnetization in ferromagnets,"The transition frequency between nonthermal coherent magnetic precessions and
ultrafast demagnetization is arguably the most sought after answer in magnetism
science and technology nowadays. So far, it is believed to be in the terahertz
(THz) range. Here, using an ultra-intense low frequency THz bullet, and thin
magnetic layers, we report on experimental evidences that fully coherent
nonthermal THz magnetic switching may never be reachable in conventional
ferromagnetic thin films. At high excitation intensities, while the spins still
coherently precess with the THz magnetic field, the deposited THz energy
initiates ultrafast demagnetization and ultimately material damage. These
series of phenomena are found to take place simultaneously. The reported
experiments set fundamental limits and raise questions on the coupling between
electronic and magnetic systems and the associated structural dynamics on the
ultrafast time scale.",1506.05397v1
2015/6/26,Observation of Valley-polarized Landau Levels in Strained Graphene,"In strained graphene, lattice deformation can create pseudo-magnetic fields
and result in zero-field Landau level-like quantization. In the presence of an
external magnetic field, valley-polarized Landau levels are predicted to be
observed because the pseudo-magnetic fields are of opposite directions in the K
and K' valleys of graphene. Here, we present experimental spectroscopic
measurements by scanning tunneling microscopy of strained graphene on Rh foil.
We direct observed valley splitting of the Landau level induced by the
coexistence of the pseudo-magnetic fields and external magnetic fields. The
observed result paves the way to exploit novel electronic properties in
graphene through the combination of the pseudo-magnetic fields and the external
magnetic fields.",1506.07965v1
2015/7/17,Quantum Hall States Stabilized in Semi-magnetic Bilayers of Topological Insulators,"By breaking the time-reversal-symmetry in three-dimensional topological
insulators with introduction of spontaneous magnetization or application of
magnetic field, the surface states become gapped, leading to quantum anomalous
Hall effect or quantum Hall effect, when the chemical potential locates inside
the gap. Further breaking of inversion symmetry is possible by employing
magnetic topological insulator heterostructures that host nondegenerate top and
bottom surface states. Here, we demonstrate the tailored-material approach for
the realization of robust quantum Hall states in the bilayer system, in which
the cooperative or cancelling combination of the anomalous and ordinary Hall
responses from the respective magnetic and non-magnetic layers is exemplified.
The appearance of quantum Hall states at filling factor 0 and +1 can be
understood by the relationship of energy band diagrams for the two independent
surface states. The designable heterostructures of magnetic topological
insulator may explore a new arena for intriguing topological transport and
functionality.",1507.05001v1
2015/9/15,Magnetization reversal of giant perpendicular magnetic anisotropy at the magnetic-phase transition in FeRh films on MgO,"Phenomena originated from spin-orbit interaction, such as magnetic anisotropy
(MA), Rashba-type interactions, or topological insulators, have drawn huge
attention for its intriguing physics. In particular, the search for a novel
antiferromagnetic material, with potentially large perpendicular MA (PMA), has
been becoming very intensive for next-generation high density memory
applications. Here, we propose that substitutions of transition metals Ru and
Ir, neighboring and same group elements in the periodic table, for the Rh site
in the vicinity of surface can induce a substantially large PMA, up to an order
of magnitude of 20 erg/cm2, in FeRh films on MgO. The main driving mechanism
for this huge PMA is the interplay between the dxy and dx2-y2 states of strong
spin-orbit 4d and 5d orbitals. Further investigations demonstrate that
magnetization direction of PMA undergoes a transition into an in-plane
magnetization at the antiferromagnetic-to-ferromagnetic phase transition, which
provides a viable route for achieving large and switchable PMA associated with
the magnetic-phase transition in antiferromagnetic spintronics.",1509.04361v2
2015/9/29,Field-free magnetization reversal by spin-Hall effect and exchange bias,"Magnetic random-access memory (MRAM) driven by spin-transfer torque (STT) is
a major contender for future memory applications. The energy dissipation
involved in writing remains problematic, even with the advent of more efficient
perpendicular magnetic anisotropy (PMA) devices. A promising alternative
switching mechanism employs spin-orbit torques and the spin-Hall effect (SHE)
in particular, but additional symmetry breaking is required to achieve
deterministic switching in PMA devices. Currently used methods rely on in-plane
magnetic fields or anisotropy gradients, which are not suitable for practical
applications. Here, we interface the magnetic layer with an anti-ferromagnetic
material. An in-plane exchange bias (EB) is created, and shown to enable
field-free SHE-driven magnetization reversal of a perpendicularly magnetized
Pt/Co/IrMn structure. Aside from the potential technological implications, our
experiment provides additional insight into the local spin structure at the
ferromagnetic/anti-ferromagnetic interface.",1509.08752v2
2015/10/7,Gyrotropic magnetic effect and the magnetic moment on the Fermi surface,"The current density ${\bf j}^{\rm{\bf B}}$ induced in a clean metal by a
slowly-varying magnetic field ${\bf B}$ is formulated as the low-frequency
limit of natural optical activity, or natural gyrotropy. Working with a
multiband Pauli Hamiltonian, we obtain from the Kubo formula a simple
expression for $\alpha^{\rm gme}_{ij}=j^{\rm{\bf B}}_i/B_j$ in terms of the
intrinsic magnetic moment (orbital plus spin) of the Bloch electrons on the
Fermi surface. An alternate semiclassical derivation provides an intuitive
picture of the effect, and takes into account the influence of scattering
processes in dirty metals. This ""gyrotropic magnetic effect"" is fundamentally
different from the chiral magnetic effect driven by the chiral anomaly and
governed by the Berry curvature on the Fermi surface, and the two effects are
compared for a minimal model of a Weyl semimetal. Like the Berry curvature, the
intrinsic magnetic moment should be regarded as a basic ingredient in the
Fermi-liquid description of transport in broken-symmetry metals.",1510.02167v3
2015/11/6,Self-organized magnetic particles to tune the mechanical behaviour of a granular system,"Above a certain density a granular material jams. This property can be
controlled by either tuning a global property, such as the packing fraction or
by applying shear strain, or at the micro-scale by tuning grain shape,
inter-particle friction or externally controlled organization. Here, we
introduce a novel way to change a local granular property by adding a weak
anisotropic magnetic interaction between particles. We measure the evolution of
the pressure, $P$, and coordination number, $Z$, for a packing of 2D
photo-elastic disks, subject to uniaxial compression. Some of the particles
have embedded cuboidal magnets. The strength of the magnetic interactions
between particles are too weak to have a strong direct effect on $P$ or $Z$
when the system is jammed. However, the magnetic interactions play an important
role in the evolution of latent force networks when systems containing a large
enough fraction of the particles with magnets are driven through unjammed
states. In this case, a statistically stable network of magnetic chains
self-organizes and overlaps with force chains, strengthening the granular
medium. We believe this property can be used to reversibly control mechanical
properties of granular materials.",1511.02219v1
2016/1/18,Magnetoelectric effect and phase transitions in CuO in external magnetic fields,"Apart from being so far the only known binary multiferroic compound, CuO has
a much higher transition temperature into the multiferroic state, 230 K, than
any other known material in which the electric polarization is induced by
spontaneous magnetic order, typically lower than 100 K. Although the
magnetically induced ferroelectricity of CuO is firmly established, no
magnetoelectric effect has been observed so far as direct crosstalk between
bulk magnetization and electric polarization counterparts. Here we demonstrate
that high magnetic fields of about 50 T are able to suppress the helical
modulation of the spins in the multiferroic phase and dramatically affect the
electric polarization. Furthermore, just below the spontaneous transition from
commensurate (paraelectric) to incommensurate (ferroelectric) structures at 213
K, even modest magnetic fields induce a transition into the incommensurate
structure and then suppress it at higher field. Thus, remarkable hidden
magnetoelectric features are uncovered, establishing CuO as prototype
multiferroic with abundance of competitive magnetic interactions.",1601.04607v1
2016/5/17,Direct observation of dynamic modes excited in a magnetic insulator by pure spin current,"Excitation of magnetization dynamics by pure spin currents has been recently
recognized as an enabling mechanism for spintronics and magnonics, which allows
implementation of spin-torque devices based on low-damping insulating magnetic
materials. Here we report the first spatially-resolved study of the dynamic
modes excited by pure spin current in nanometer-thick microscopic insulating
Yttrium Iron Garnet disks. We show that these modes exhibit nonlinear
self-broadening preventing the formation of the self-localized magnetic bullet,
which plays a crucial role in the stabilization of the single-mode
magnetization oscillations in all-metallic systems. This peculiarity associated
with the efficient nonlinear mode coupling in low-damping materials can be
among the main factors governing the interaction of pure spin currents with the
dynamic magnetization in high-quality magnetic insulators.",1605.05211v1
2016/10/5,"Orbital frustration in the S = 1/2 kagome magnet vesignieite, BaCu3V2O8(OD)2","Here we report crystallographic and magnetic studies on high quality samples
of the magnetically frustrated S = 1/2 kagome antiferromagnet vesignieite,
BaCu3V2O8(OD)2. Powder neutron diffraction data collected from samples obtained
by a new hydrothermal synthetic route reveal a previously unobserved trigonal
P3121 structure, similar to the isoelectronic mineral SrCu3V2O8(OH)2. The
refined structure is consistent with orbital frustration of the eg d-orbitals
in a sublattice of the Cu2+ kagome network due to a dynamic Jahn-Teller effect,
which persists below the magnetic transition at TN = 9K and makes the material
an interesting candidate for exploring concomitant spin and orbital
frustration. A combination of crystallographic strain analysis and
magnetisation measurements indicate strong magnetostructural coupling which may
explain the varied magnetic behaviour between samples of vesignieite in the
literature. The revised orbital structure is similar to that found in
volborthite, rather than the quantum spin liquid herbertsmithite, and provides
a convincing argument for the differing magnetic properties found in these
frustrated magnets.",1610.01436v1
2017/2/17,Magnetic anisotropy in Permalloy: hidden quantum mechanical features,"By means of relativistic, first principles calculations, we investigate the
microscopic origin of the vanishingly low magnetic anisotropy of Permalloy,
here proposed to be intrinsically related to the local symmetries of the alloy.
It is shown that the local magnetic anisotropy of individual atoms in Permalloy
can be several orders of magnitude larger than that of the bulk sample, and
5-10 times larger than that of elemental Fe or Ni. We, furthermore, show that
locally there are several easy axis directions that are favored, depending on
local composition. The results are discussed in the context of perturbation
theory, applying the relation between magnetic anisotropy and orbital moment.
Permalloy keeps its strong ferromagnetic nature due to the exchange energy to
be larger than the magnetocrystalline anisotropy. Our results shine light on
the magnetic anisotropy of permalloy and of magnetic materials in general, and
in addition enhance the understanding of pump-probe measurements and ultrafast
magnetization dynamics.",1702.05414v1
2017/8/12,Ground state magnetization of conduction electrons in graphene with Zeeman effect,"In this work we address the ground state magnetization in graphene,
considering the Zeeman effect and taking into account the conduction electrons
in the long wavelength approximation. We obtain analytical expressions for the
magnetization at T=0 K, where the oscillations given by the de Haas van Alphen
(dHvA) effect are present. We find that the Zeeman effect modifies the
magnetization by introducing new peaks associated with the spin splitting of
the Landau levels. These peaks are very small for typical carrier densities in
graphene, but become more important for higher densities. The obtained results
provide insight of the way in which the Zeeman effect modifies the
magnetization, which can be useful to control and manipulate the spin degrees
of freedom.",1708.03827v1
2017/11/3,THz-driven demagnetization with Perpendicular Magnetic Anisotropy: Towards ultrafast ballistic switching,"We study THz-driven spin dynamics in thin CoPt films with perpendicular
magnetic anisotropy. Femtosecond magneto-optical Kerr effect measurements show
that demagnetization amplitude of about $1\%$ can be achieved with a peak THz
electric field of $300$~kV/cm, and a corresponding peak magnetic field of
$0.1$~T. The effect is more than an order of magnitude larger than observed in
samples with easy-plane anisotropy irradiated with the same field strength. We
also utilize finite-element simulations to design a meta-material structure
that can enhance the THz magnetic field by more than an order of magnitude,
over an area of several tens of square micrometers. Magnetic fields exceeding
$1$~Tesla, generated in such meta-materials with the available laser-based THz
sources, are expected to produce full magnetization reversal via ultrafast
ballistic precession driven by the THz radiation. Our results demonstrate the
possibility of table-top ultrafast magnetization reversal induced by THz
radiation.",1711.01234v2
2017/11/18,Inducing skyrmions in ultrathin Fe films by hydrogen exposure,"Magnetic skyrmions are localized nanometer-sized spin configurations with
particle_like properties, which are envisioned to be used as bits in
next_generation information technology. An essential step towards future
skyrmion-based applications is to engineer key magnetic parameters for
developing and stabilizing individual magnetic skyrmions. Here we demonstrate
the tuning of the non_collinear magnetic state of an Fe double layer on an
Ir111 substrate by loading the sample with atomic hydrogen. By using
spin_polarized scanning tunneling microscopy, we discover that the hydrogenated
system supports the formation of skyrmions in external magnetic fields, while
the pristine Fe double layer does not. Based on ab initio calculations, we
attribute this effect to the tuning of the Heisenberg exchange and the
Dzyaloshinsky_Moriya interactions due to hydrogenation. In addition to
interface engineering, hydrogenation of thin magnetic films offers a unique
pathway to design and optimize the skyrmionic states in low_dimensional
magnetic materials.",1711.06784v1
2018/4/9,Canted antiferromagnetism in phase-pure CuMnSb,"We report the low-temperature properties of phase-pure single crystals of the
half-Heusler compound CuMnSb grown by means of optical float-zoning. The
magnetization, specific heat, electrical resistivity, and Hall effect of our
single crystals exhibit an antiferromagnetic transition at $T_{\mathrm{N}} =
55~\mathrm{K}$ and a second anomaly at a temperature $T^{*} \approx
34~\mathrm{K}$. Powder and single-crystal neutron diffraction establish an
ordered magnetic moment of $(3.9\pm0.1)~\mu_{\mathrm{B}}/\mathrm{f.u.}$,
consistent with the effective moment inferred from the Curie-Weiss dependence
of the susceptibility. Below $T_{\mathrm{N}}$, the Mn sublattice displays
commensurate type-II antiferromagnetic order with propagation vectors and
magnetic moments along $\langle111\rangle$ (magnetic space group $R[I]3c$).
Surprisingly, below $T^{*}$, the moments tilt away from $\langle111\rangle$ by
a finite angle $\delta \approx 11^{\circ}$, forming a canted antiferromagnetic
structure without uniform magnetization consistent with magnetic space group
$C[B]c$. Our results establish that type-II antiferromagnetism is not the
zero-temperature magnetic ground state of CuMnSb as may be expected of the
face-centered cubic Mn sublattice.",1804.03223v1
2018/7/12,Preferred magnetic excitations in Sr$_{1-x}$Na$_x$Fe$_2$As$_2$,"We have used inelastic neutron scattering to determine magnetic excitations
in a single-crystal sample of Sr$_{1-x}$Na$_x$Fe$_2$As$_2$. The material's two
magnetic phases, which differ in their orthorhombic and tetragonal lattice
symmetries, share very similar strengths of magnetic interactions as seen from
the high-energy excitations. At low energies, excitations polarized along the
$c$ axis are suppressed in the tetragonal magnetic phase, in accordance with
the associated reorientation of the ordered moments. Although excitations
perpendicular to the $c$ axis are still prominent, only the weak $c$-axis
response exhibits a spin resonant mode in the superconducting state. Our result
suggests that $c$-axis polarized magnetic excitations are important for the
formation of the superconductivity, and naturally explains why the critical
temperature is suppressed in the tetragonal magnetic phase.",1807.04462v1
2012/11/29,"Phase diagram, ferromagnetic martensitic transformation and magnetoresponsive properties of Fe-doped MnCoGe alloys","The crystal structure and magnetoresponsive properties of Fe-doped MnCoGe
alloys have been investigated using x-ray diffraction (XRD) and magnetic
measurements. By alloying the Fe-containing isostructure compounds into MnCoGe,
a magnetostructural transition from paramagnetic austenite to ferromagnetic
martensite with large magnetization difference can be realized in a temperature
window between the Curie temperatures of the austenite and martensite,
resulting in magnetic-field-induced martensitic transformations and large
magnetic-entropy changes. A structural and magnetic phase diagram of Fe-doped
MnCoGe alloys has been proposed.",1211.6815v1
2017/6/19,Electrical signature of individual magnetic skyrmions in multilayered systems,"Magnetic skyrmions are topologically protected whirling spin textures that
can be stabilized in magnetic materials in which a chiral interaction is
present. Their limited size together with their robustness against the external
perturbations promote them as the ultimate magnetic storage bit in a novel
generation of memory and logic devices. Despite many examples of the signature
of magnetic skyrmions in the electrical signal, only low temperature
measurements, mainly in magnetic materials with B20 crystal structure, have
demonstrated the skyrmions contribution to the electrical transport properties.
Using the combination of Magnetic Force Microscopy (MFM) and Hall resistivity
measurements, we demonstrate the electrical detection of sub-100 nm skyrmions
in multilayered thin film at room temperature (RT). We furthermore analyse the
room temperature Hall signal of a single skyrmion which contribution is mainly
dominated by anomalous Hall effect.",1706.05809v1
2018/3/9,Strong anomalous Nernst effect in collinear magnetic Weyl semimetals without net magnetic moments,"We predict a large anomalous Nernst effect in the inverse Heusler compensated
ferrimagnets Ti$_2$Mn$X$ ($X$=Al,Ga,In) with vanishing net magnetic moments.
Though the net magnetic moment is zero, the Weyl points in these systems lead
to a large anomalous Nernst conductivity (ANC) due to the lack of a magnetic
sublattice that inverses the sign of the Berry curvature. In comparison to the
noncollinear antiferromagnets Mn$_3$Sn and Mn$_3$Ge, the high ANC stems almost
entirely from the Weyl points in this class of compounds, and thus, it is
topologically protected. This work shows for the first time a large ANC with
zero net magnetic moments in collinear systems, which is helpful for
comprehensive understanding of the thermoelectric effect in zero-moment
magnetic materials and its further applications.",1803.03439v3
2018/3/20,Electric-field switching of two-dimensional van der Waals magnets,"Controlling magnetism by purely electrical means is a key challenge to better
information technology1. A variety of material systems, including ferromagnetic
(FM) metals2,3,4, FM semiconductors5, multiferroics6,7,8 and magnetoelectric
(ME) materials9,10, have been explored for the electric-field control of
magnetism. The recent discovery of two-dimensional (2D) van der Waals
magnets11,12 has opened a new door for the electrical control of magnetism at
the nanometre scale through a van der Waals heterostructure device platform13.
Here we demonstrate the control of magnetism in bilayer CrI3, an
antiferromagnetic (AFM) semiconductor in its ground state12, by the application
of small gate voltages in field-effect devices and the detection of
magnetization using magnetic circular dichroism (MCD) microscopy. The applied
electric field creates an interlayer potential difference, which results in a
large linear ME effect, whose sign depends on the interlayer AFM order. We also
achieve a complete and reversible electrical switching between the interlayer
AFM and FM states in the vicinity of the interlayer spin-flip transition. The
effect originates from the electric-field dependence of the interlayer exchange
bias.",1803.07272v1
2018/10/14,Tunable Magnetism of Transition Metal Nanostructures by Hydrogenated Graphene,"Controlling magnetism of transition metal atoms by pairing with $\pi$
electronic states of graphene is intriguing. Herein, through first - principle
computation we explore the possibility of switching magnetization by forming
the tetrahedral $sp^3$ - metallic $d$ hybrid bonds. Graphene multilayers capped
by single - layer cobalt atoms can transform into the $sp^3$ - bonded diamond
films upon the hydrogenation of the bottom surface. While the conversion is
favored by hybridization between the $sp^3$ dangling bonds and metallic
$d_{z^2}$ states, such a strong hybridization can lead to the reorientation of
magnetization easy axis of cobalt adatoms in plane to perpendicular. The
further investigations identify that this anisotropic magnetization even can be
modulated upon the change in charge carrier density, suggesting the possibility
of an electric - field control of magnetization reorientation. These results
provide a novel alternative that would represent tailoring magnetism by means
of degree of the interlayer hybrid bonds in the layered materials.",1810.05946v1
2010/4/20,"Mapping the B,T phase diagram of frustrated metamagnet CuFeO2","The magnetic phase diagram of CuFeO2 as a function of applied magnetic field
and temperature is thoroughly explored and expanded, both for magnetic fields
applied parallel and perpendicular to the material's c-axis. Pulsed field
magnetization measurements extend the typical magnetic staircase of CuFeO2 at
various temperatures, demonstrating the persistence of the recently discovered
high field metamagnetic transition up to Tn2 ~ 11 K in both field
configurations. An extension of the previously introduced phenomenological spin
model used to describe the high field magnetization process (Phys. Rev. B, 80,
012406 (2009)) is applied to each of the consecutive low-field commensurate
spin structures, yielding a semi-quantitative simulation and intuitive
description of the entire experimental magnetization process in both relevant
field directions with a single set of parameters.",1004.3554v1
2019/9/18,Ferromagnetic resonance with magnetic phase selectivity by means of resonant elastic x-ray scattering on a chiral magnet,"Cubic chiral magnets, such as Cu$_{2}$OSeO$_{3}$, exhibit a variety of
non-collinear spin textures, including a trigonal lattice of spin whirls,
so-called skyrmions. Using magnetic resonant elastic x-ray scattering (REXS) on
a crystalline Bragg peak and its magnetic satellites while exciting the sample
with magnetic fields at GHz frequencies, we probe the ferromagnetic resonance
modes of these spin textures by means of the scattered intensity. Most notably,
the three eigenmodes of the skyrmion lattice are detected with large
sensitivity. As this novel technique, which we label REXS-FMR, is carried out
at distinct positions in reciprocal space, it allows to distinguish
contributions originating from different magnetic states, providing information
on the precise character, weight and mode mixing as a prerequisite of tailored
excitations for applications.",1909.08293v2
2019/10/16,Magnetic Nanoparticle Chains in Gelatin Ferrogels: Bioinspiration from Magnetotactic Bacteria,"Inspired by chains of ferrimagnetic nanocrystals (NCs) in magnetotactic
bacteria (MTB), the synthesis and detailed characterization of ferrimagnetic
magnetite NC chain-like assemblies is reported. An easy green synthesis route
in a thermoreversible gelatin hydrogel matrix is used. The structure of these
magnetite chains prepared with and without gelatin is characterized by means of
transmission electron microscopy, including electron tomography (ET). These
structures indeed bear resemblance to the magnetite assemblies found in MTB,
known for their mechanical flexibility and outstanding magnetic properties and
known to crystallographically align their magnetite NCs along the strongest
<111> magnetization easy axis. Using electron holography (EH) and angular
dependent magnetic measurements, the magnetic interaction between the NCs and
the generation of a magnetically anisotropic material can be shown. The
electro- and magnetostatic modeling demonstrates that in order to precisely
determine the magnetization (by means of EH) inside chain-like NCs assemblies,
their exact shape, arrangement and stray-fields have to be considered (ideally
obtained using ET).",1910.07293v1
2020/4/2,Mechanical orientation of fine magnetic particles in powders by an external magnetic field: simulation-based optimization,"We present a numerical algorithm for predicting the optimal conditions for
the effective alignment of magnetic particles in dense powders during the
compactization process using an externally applied field. This task is
especially important for the permanent magnets development due to the fact that
alignment of anisotropy axes of nanocomposite grains increases both remanence
and coercivity of magnetic materials. In contrast to previously known methods
where magnetic moment of each particle was assumed to be 'fixed' with respect
to the particle itself, our approach takes into account the (field-dependent)
deviation of this moment from the particle anisotropy axis that occurs even for
magnetically 'hard' particles possessing a strong mechanical contact. We show,
that this deviation leads to the existence of the optimal value of the applied
field for which the particle orientation (or alignment) time is minimal. The
influence of the external pressure and internal mechanical friction on the
details of the compactization/orientation process is also studied.",2004.00868v1
2020/4/21,Hopf solitons in helical and conical backgrounds of chiral magnetic solids,"Three-dimensional topological solitons attract a great deal of interest in
fields ranging from particle physics to cosmology but remain experimentally
elusive in solid-state magnets. Here we numerically predict magnetic
heliknotons, an embodiment of such nonzero-Hopf-index solitons localized in all
spatial dimensions while embedded in a helical or conical background of chiral
magnets. We describe conditions under which heliknotons emerge as metastable or
ground-state localized nonsingular structures with fascinating knots of
magnetization field in widely studied materials. We demonstrate magnetic
control of three-dimensional spatial positions of such solitons, as well as
show how they interact to form molecule-like clusters and possibly even
crystalline phases comprising three-dimensional lattices of such solitons with
both orientational and positional order. Finally, we discuss both fundamental
importance and potential technological utility of magnetic heliknotons.",2004.10109v2
2020/8/20,Engineering the magnetic and magnetocaloric properties of PrVO3 epitaxial oxide thin films by strain effects,"Combining multiple degrees of freedom in strongly-correlated materials such
as transition-metal oxides would lead to fascinating magnetic and
magnetocaloric features. Herein, the strain effects are used to markedly tailor
the magnetic and magnetocaloric properties of PrVO3 thin films. The selection
of appropriate thickness and substrate enables us to dramatically decrease the
coercive magnetic field from 2.4 T previously observed in sintered PVO3 bulk to
0.05 T for compressive thin films making from the PrVO3 compound a nearly soft
magnet. This is associated with a marked enhancement of the magnetic moment and
the magnetocaloric effect that reach unusual maximum values of roughly 4.86 uB
and 56.8 J/kg K in the magnetic field change of 6 T applied in the sample plane
at the cryogenic temperature range (3 K), respectively. This work strongly
suggests that taking advantage of different degrees of freedom and the
exploitation of multiple instabilities in a nanoscale regime is a promising
strategy for unveiling unexpected phases accompanied by a large magnetocaloric
effect in oxides.",2008.09193v1
2020/8/28,Tunnel magnetoresistance in scandium nitride magnetic tunnel junctions using first principles,"The magnetic tunnel junction is a cornerstone of spintronic devices and
circuits, providing the main way to convert between magnetic and electrical
information. In state-of-the-art magnetic tunnel junctions, magnesium oxide is
used as the tunnel barrier between magnetic electrodes, providing a uniquely
large tunnel magnetoresistance at room temperature. However, the wide bandgap
and band alignment of magnesium oxide-iron systems increases the
resistance-area product and causes challenges of device-to-device variability
and tunnel barrier degradation under high current. Here, we study using first
principles narrower-bandgap scandium nitride tunneling properties and transport
in magnetic tunnel junctions in comparison to magnesium oxide. These
simulations demonstrate a high tunnel magnetoresistance in Fe/ScN/Fe MTJs via
{\Delta}_1 and {\Delta}_2' symmetry filtering with low wavefunction decay
rates, allowing a low resistance-area product. The results show that scandium
nitride could be a new tunnel barrier material for magnetic tunnel junction
devices to overcome variability and current-injection challenges.",2008.12770v1
2007/7/19,Map of metastable states for thin circular magnetic nano-cylinders,"Nano-magnetic systems of artificially shaped ferromagnetic islands, recently
became a popular subject due to their current and potential applications in
spintronics, magneto-photonics and superconductivity. When the island size is
close to the exchange length of magnetic material (around 15 nm), its magnetic
structure becomes markedly different. It determines both static and dynamic
magnetic properties of elements, but strongly depends on their shape and size.
Here we map this dependence for circular cylindrical islands of a few exchange
lengths in size. We outline the region of metastability of ""C""-type magnetic
states, proving that they are indeed genuine and not a result of pinning on
particle imperfections. A way to create the smallest particles with guaranteed
magnetic vortex state at zero field becomes evident. It is expected that the
map will help focus the efforts in planning of experiments and devices.",0707.2938v2
2009/7/3,Compaction dynamics of a magnetized powder,"We have investigated experimentally the influence of a magnetic interaction
between the grains on the compaction dynamics of a granular pile submitted to a
series of taps. The granular material used to perform this study is a mixture
of metallic and glass grains. The packing is immersed in an homogeneous
external magnetic field. The magnetic field induces an interaction between the
metallic grains that constitutes the tunable cohesion. The compaction
characteristic time and the asymptotic packing fraction have been measured as a
function of the Bond number which is the ratio between the cohesive magnetic
force and the grain weight. These measurements have been performed for
different fractions of metallic beads in the pile. When the pile is only made
of metallic grains, the characteristic compaction time increases as the square
root of the Bond number. While the asymptotic packing fraction decreases as the
inverse of the Bond number. For mixtures, when the fraction of magnetized
grains in the pile is increased, the characteristic time increases while the
asymptotic packing fraction decreases. A simple mesoscopic model based on the
formation of granular chains along the magnetic field direction is proposed to
explain the observed macroscopic properties of the packings.",0907.0646v1
2014/4/4,Evolution of magnetic dynamics in an artificially frustrated Fe nanoparticle system,"Frustrated lattices1-3, characterized by minor breakdown in local order in an
otherwise periodic lattice, lead to simultaneous possibilities of several
ground states which can trigger unique physical properties, in condensed matter
systems. In magnetic materials with atomic spins, frustration takes another
shape with added possibilities to construct various topological arrangements of
spins, whereby magnetic order is disturbed2,4. We have achieved a new approach
to introduce positional atomic disorder inside a Fe nanoparticle lattice,
forming domains without boundaries to study magnetic dynamics of the
constituent spins. This magnetism overrides the exchange bias derived magnetic
enhancement, appears only at temperatures around 200 K and is characterized by
a dynamic polarity, p = +/-1 (positive or negative) with a precise frequency.
The material otherwise behaves like a superparamagnet with characteristic
magnetization behaviour at room temperature and 2 K.",1404.1163v1
2016/6/4,Superconducting $π$-ring metamaterials,"We develop the concept of fractal metamaterials which consist of arrays of
nano and micron sized rings containing Josephson junctions which play the role
of ""atoms"" in such artificial materials. We show that if some of the junctions
have $\pi$-shifts in the Josephson phases that the ""atoms"" become magnetic and
their arrays can have tuned positive or negative permeabilty. Each individual
""$\pi$-ring"" - the Josephson ring with one $\pi$-junction - can be in one of
two energetically degenerate magnetic states in which the supercurrent flows in
the clockwise or counter-clockwise direction. This results in magnetic moments
that point downwards or upwards, respectively. The value of the total
magnetization of such a metamaterial may display fractal features. We describe
the magnetic properties of such superconducting metamaterials, including the
magnetic field distribution in them (i.e. in the network that is made up of
these rings). We also describe the way that the magnetic flux penetrates into
the Josephson network and how it is strongly dependent on the geometry of the
system.",1606.01413v1
2016/12/29,Manipulating exchange bias using all-optical helicity-dependent switching,"Deterministic all-optical control of magnetization without an applied
magnetic field has been reported for different materials such as ferrimagnetic
and ferromagnetic thin films and granular recording media. These findings have
challenged the understanding of all-optical helicity-dependent switching of
magnetization and opened many potential applications for future magnetic
information, memory and storage technologies. Here we demonstrate optical
control of an antiferromagnetic layer through the exchange bias interaction
using the helicity of a femtosecond pulsed laser on IrMn/[Co/Pt]xN
antiferromagnetic/ ferromagnetic heterostructures. We show controlled switching
of the sign of the exchange bias field without any applied field, only by
changing the helicity of the light, and quantify the influence of the laser
fluence and the number of light pulses on the exchange bias control. We also
present the combined effect of laser pulses and applied magnetic field. This
study opens applications in spintronic devices where the exchange bias
phenomenon is routinely used to fix the magnetization orientation of a magnetic
layer in one direction.",1612.09338v1
2018/2/27,Low lying magnetic states of the mixed valence cobalt ludwigite,"There are two interpretations offered for the different structural and
magnetic properties of the mixed valence homo-metallic ludwigites, Co3O2BO3 and
Fe3O2BO3. One of them associates the physical behavior to charge ordering
processes among the cations, as is well known in simpler oxides. The other
attributes the effects to local pairwise magnetic interactions. Recently first
principles calculations in the iron ludwigite have shown that the structural
cation dimerization is due to the formation of strong magnetic dyads supporting
the second model. Here we confirm the dominance of magnetic interactions to
explain the absence of dimerization in the cobalt compound. Density functional
non-collinear spin calculations are carried out on Co3O2BO3 to determine its
low temperature magnetic order. Low spin is found on tri-valent cobalt sites,
thus preventing the formation of the ferromagnetic dyad, the mechanism which
favors dimerization in Fe3O2BO3. We conclude that the difference between high
spin Fe3+ and low spin Co3+ pairwise interactions is responsible for the
observed differences between the two compounds. The pairwise magnetic
interactions also explain the difference between the existence of low
temperature bulk AF state in the Fe ludwigite and its absence in the Co
material.",1802.10063v2
2019/2/17,Experimental realization of a non-magnetic one-way spin switch,"Controlling magnetism through non-magnetic means is highly desirable for
future electronic devices, as such means typically have ultra-low power
requirements and can provide coherent control. In recent years, great
experimental progress has been made in the field of electrical manipulation of
magnetism in numerous material systems. These studies generally do not consider
the directionality of the applied non-magnetic potentials and/or magnetism
switching. Here, we theoretically conceive and experimentally demonstrate a
non-magnetic one-way spin switch device using a spin-orbit coupled
Bose-Einstein condensate subjected to a moving spin-independent dipole
potential. The physical foundation of this unidirectional device is based on
the breakdown of Galilean invariance in the presence of spin-orbit coupling.
Such a one-way spin switch opens an avenue for designing novel quantum devices
with unique functionalities and may facilitate further experimental
investigations of other one-way spintronic and atomtronic devices.",1902.06321v1
2019/3/26,Nuclear spin assisted quantum tunnelling of magnetic monopoles in spin ice,"Extensive work on single molecule magnets has identified a fundamental mode
of relaxation arising from the nuclear-spin assisted quantum tunnelling of
nearly independent and quasi-classical magnetic dipoles. Here we show that
nuclear-spin assisted quantum tunnelling can also control the dynamics of
purely emergent excitations: magnetic monopoles in spin ice. Our low
temperature experiments were conducted on canonical spin ice materials with a
broad range of nuclear spin values. By measuring the magnetic relaxation, or
monopole current, we demonstrate strong evidence that dynamical coupling with
the hyperfine fields bring the electronic spins associated with magnetic
monopoles to resonance, allowing the monopoles to hop and transport magnetic
charge. Our result shows how the coupling of electronic spins with nuclear
spins may be used to control the monopole current. It broadens the relevance of
the assisted quantum tunnelling mechanism from single molecular spins to
emergent excitations in a strongly correlated system.",1903.11122v1
2019/4/18,Suppression of long range magnetic ordering and electrical conduction in Y$_{1.7}$Bi$_{0.3}$Ir$_2$O$_7$ thin film,"We find that the long-range magnetic ordering is absent and electrical
conduction suppressed in Y$_{1.7}$Bi$_{0.3}$Ir$_2$O$_7$/YSZ(100) thin film
prepared by pulsed laser deposition. The sharp down-turn of inverse magnetic
susceptibility X-1(T) from the conventional Curie-Weiss behaviour below T* ~
168K suggests an inhomogeneous ferromagnetic Griffiths like phase. The
transport and magnetic properties are explained on the basis of the coexistence
of mixed oxidation states of Ir, (i.e. Ir4+ and Ir3+) leading to non-magnetic
defects and reduction in t2g density of states at the Fermi level.",1904.08615v1
2019/4/23,Current-induced switching of YIG/Pt bilayers with in-plane magnetization due to Oersted fields,"We report on the switching of the in-plane magnetization of thin yttrium iron
garnet (YIG)/Pt bilayers induced by an electrical current. The switching is
either field-induced and assisted by a dc current, or current-induced and
assisted by a static magnetic field. The reversal of the magnetization occurs
at a current density as low as $10^5$~A/cm$^{2}$ and magnetic fields of $\sim
40$~$\mu$T, two orders of magnitude smaller than in ferromagnetic metals,
consistently with the weak uniaxial anisotropy of the YIG layers. We use the
transverse component of the spin Hall magnetoresistance to sense the magnetic
orientation of YIG while sweeping the current. Our measurements and simulations
reveal that the current-induced effective field responsible for switching is
due to the Oersted field generated by the current flowing in the Pt layer
rather than by spin-orbit torques, and that the switching efficiency is
influenced by pinning of the magnetic domains.",1904.10517v1
2019/5/7,Natural van der Waals heterostructural single crystals with both magnetic and topological properties,"Heterostructures having both magnetism and topology are promising materials
for the realization of exotic topological quantum states while challenging in
synthesis and engineering. Here, we report natural magnetic van der Waals
heterostructures of (MnBi2Te4)m(Bi2Te3)n that exhibit controllable magnetic
properties while maintaining their topological surface states. The interlayer
antiferromagnetic exchange coupling is gradually weakened as the separation of
magnetic layers increases, and an anomalous Hall effect that is well coupled
with magnetization and shows ferromagnetic hysteresis was observed below 5 K.
The obtained homogeneous heterostructure with atomically sharp interface and
intrinsic magnetic properties will be an ideal platform for studying the
quantum anomalous Hall effect, axion insulator states, and the topological
magnetoelectric effect.",1905.02385v2
2019/7/19,Exchange-correlation magnetic fields in spin-density-functional theory,"In spin-density-functional theory for noncollinear magnetic materials, the
Kohn-Sham system features exchange-correlation (xc) scalar potentials and
magnetic fields. The significance of the xc magnetic fields is not very well
explored; in particular, they can give rise to local torques on the
magnetization, which are absent in standard local and semilocal approximations.
We obtain exact benchmark solutions for two electrons on four-site extended
Hubbard lattices over a wide range of interaction strengths, and compare exact
xc potentials and magnetic fields with approximations obtained from
orbital-dependent xc functionals. The xc magnetic fields turn out to play an
increasingly important role as systems becomes more and more correlated and the
electrons begin to localize; the effects of the xc torques, however, remain
relatively minor. The approximate xc functionals perform overall quite well,
but tend to favor symmetry-broken solutions for strong interactions.",1907.08724v1
2020/1/1,Magnetic entropy change of ErAl2 magnetocaloric wires fabricated by a powder-in-tube method,"We report the fabrication of ErAl2 magnetocaloric wires by a powder-in-tube
method (PIT) and the evaluation of magnetic entropy change through
magnetization measurements. The magnetic entropy change of ErAl2 PIT wires
exhibits similar behavior to the bulk counterpart, while its magnitude is
reduced by the decrease in the volume fraction of ErAl2 due to the surrounding
non-magnetic sheaths. We find that another effect reduces the magnetic entropy
change of the ErAl2 PIT wires around the Curie temperature, and discuss its
possible origin in terms of a correlation between magnetic properties of ErAl2
and mechanical properties of sheath material.",2001.00174v1
2020/1/30,Evolutionary Algorithm Guided Voxel-Encoding Printing of Functional Hard-Magnetic Soft Active Materials,"Hard-magnetic soft active materials (hmSAMs) have attracted a great amount of
research interests due to their fast-transforming, untethered control, as well
as excellent programmability. However, the current direct-ink-write (DIW)
printing-based fabrication of hmSAM parts and structures only permits
programmable magnetic direction with a constant magnetic density. Also, the
existing designs rely on the brute-force approach to generate the assignment of
magnetization direction distribution, which can only produce intuitional
deformations. These two factors greatly limit the design space and the
application potentials of hmSAMs. In this work, we introduce a voxel-encoding
DIW printing method to program both the magnetic density and direction
distributions during the hmSAM printing. The voxel-encoding DIW printing is
then integrated with an evolutionary algorithm (EA)-based design strategy to
achieve the desired magnetic actuation and motion with complex geometry
variations and curvature distributions. With the new EA-guided voxel-encoding
DIW printing technique, we demonstrate the functional hmSAMs that produce
complicated shape morphing with desired curvature distributions for advanced
applications such as biomimetic motions. These demonstrations indicate that the
proposed EA-guided voxel-encoding DIW printing method can significantly broaden
the application potentials of the hmSAMs.",2001.11189v1
2020/2/26,Extreme narrow magnetic domain walls in U ferromagnets: The UCoGa case,"Surface magnetic domains of a UCoGa single crystal during
magnetization/demagnetization processes in increasing/decreasing magnetic
fields were investigated by means of magnetic-force-microscopy (MFM) images at
low temperatures. The observed domain structure is typical for a ferromagnet
with strong uniaxial anisotropy. The evolution of magnetic domains during
cooling of the crystal below TC has also been manifested by MFM images.
Analysis of the available data reveals that the high uniaxial
magnetocrystalline energy in combination with the relatively small
ferromagnetic exchange interaction in UCoGa gives rise to the formation of very
narrow domain walls formed by the pairs of the nearest U neighbor ions with
antiparallel magnetic moments within the basal plane. Since the very high
anisotropy energy is a common feature of the majority of the uniaxial U
ferromagnets, analogous domain-wall properties are expected for all these
materials.",2002.11517v1
2020/6/2,Intrinsically weak magnetic anisotropy of cerium in potential hard-magnetic intermetallics,"Cerium-based intermetallics are currently attracting much interest as a
possible alternative to existing high-performance magnets containing scarce
heavy rare-earth elements. However, the intrinsic magnetic properties of Ce in
these systems are poorly understood due to the difficulty of a quantitative
description of the Kondo effect, a many-body phenomenon where conduction
electrons screen out the Ce-4f moment. Here, we show that the Ce-4f shell in
Ce-Fe intermetallics is partially Kondo screened. The Kondo scale is
dramatically enhanced by nitrogen interstitials completely suppressing the
Ce-4f contribution to the magnetic anisotropy, in striking contrast to the
effect of nitrogenation in isostructural intermetallics containing other
rare-earth elements. We determine the full temperature dependence of the Ce-4f
single-ion anisotropy and show that even unscreened Ce-4f moments contribute
little to the room-temperature intrinsic magnetic hardness. Our study thus
establishes fundamental constraints on the potential of cerium-based permanent
magnet intermetallics.",2006.01792v2
2020/7/20,Stacking Domain Wall Magnons in Twisted van der Waals Magnets,"Using bilayer CrI$_3$ as an example, we demonstrate that stacking domain
walls in van der Waals magnets can host one dimensional (1D) magnon channels,
which have lower energies than bulk magnons. Interestingly, some magnon
channels are hidden in magnetically homogeneous background and can only be
inferred with the knowledge of stacking domain walls. Compared to 1D magnons
confined in magnetic domain walls, 1D magnons in stacking domain walls are more
stable against external perturbations. We show that the relaxed moir\'e
superlattices of small-angle twisted bilayer CrI$_3$ is a natural realization
of stacking domain walls and host interconnected moir\'e magnon network. Our
work reveals the importance of stacking domain walls in understanding magnetic
properties of van der Waals magnets, and extends the scope of stacking
engineering to magnetic dynamics.",2007.10398v2
2020/9/7,Magnetic vortex liquid and anomalous thermal Hall conductivity in frustrated magnets with bond-dependent interactions,"Recently, the observation of large thermal Hall conductivities in correlated
insulators with no apparent broken symmetry have generated immense interest and
debates on the underlying ground states. Here, considering frustrated magnets
with bond-dependent interactions, which are realized in the so-called Kitaev
materials, we theoretically demonstrate that a large thermal Hall conductivity
can originate from a classical ground state without any magnetic order. We
discover a novel liquid state of magnetic vortices, which are inhomogeneous
spin textures embedded in the background of polarized spins, under out-of-plane
magnetic fields. In the classical regime, different configurations of vortices
form a degenerate manifold. We study the static and dynamical properties of the
magnetic vortex liquid state at zero and finite temperatures. In particular, we
show that the spin excitation spectrum resembles a continuum of nearly flat
Chern bands, which ultimately leads to a large thermal Hall conductivity.
Possible connections to experiments are discussed.",2009.03332v1
2020/10/27,Defect-induced $4p$-magnetism in layered platinum diselenide,"Platinum diselenide (PtSe$_{2}$) is a recently-discovered extrinsic magnet,
with its magnetism attributed to the presence of Pt-vacancies. The host
material to these defects itself displays interesting structural and electronic
properties, some of which stem from an unusually strong interaction between its
layers. To date, it is not clear how the unique intrinsic properties of
PtSe$_2$ will affect its induced magnetism. In this theoretical work, we show
that the defect-induced magnetism in PtSe$_{2}$ thin films is highly sensitive
to: (i) the layer-thickness (ii) defect density, and (iii) substrate choice.
These different factors dramatically modify all magnetic properties, including
the magnitude of local moments, strength of the coupling, and even nature of
the coupling between the moments. We further show that the strong inter-layer
interactions are key to understanding these effects. A better understanding of
the various influences on magnetism, can enable controllable tuning of the
magnetic properties in Pt-based dichalcogenides, which can be used to design
novel devices for magnetoelectric and magneto-optic applications.",2010.13985v2
2020/11/4,Imaging damage in steel using a diamond magnetometer,"We demonstrate a simple, robust and contactless method for non-destructive
testing of magnetic materials such as steel. This uses a fiber-coupled magnetic
sensor based on nitrogen vacancy centers (NVC) in diamond without magnetic
shielding. Previous NVC magnetometry has sought a homogeneous bias magnetic
field, but in our design we deliberately applied an inhomogeneous magnetic
field. As a consequence of our experimental set-up we achieve a high spatial
resolution: 1~mm in the plane parallel and 0.1~mm in the plane perpendicular to
the surface of the steel. Structural damage in the steel distorts this
inhomogeneous magnetic field and by detecting this distortion we reconstruct
the damage profile through quantifying the shifts in the NVC Zeeman splitting.
This works even when the steel is covered by a non-magnetic material. The
lift-off distance of our sensor head from the surface of 316 stainless steel is
up to 3~mm.",2011.02459v1
2020/12/1,Gate-controlled magnetic phase transition in a van der Waals magnet Fe$_5$GeTe$_2$,"Magnetic van der Waals (vdW) materials, including ferromagnets (FM) and
antiferromagnets (AFM), have given access to the investigation of magnetism in
two-dimensional (2D) limit and attracted broad interests recently. However,
most of them are semiconducting or insulating and the vdW itinerant magnets,
especially vdW itinerant AFM, are very rare. Here, we studied the anomalous
Hall effect of a vdW itinerant magnet Fe$_5$GeTe$_2$ (F5GT) with various
thicknesses down to 6.8 nm (two unit cells). Despite the robust ferromagnetic
ground state in thin-layer F5GT, however, we show that the electron doping
implemented by a protonic gate can eventually induce a magnetic phase
transition from FM to AFM. Realization of an antiferromagnetic phase in F5GT
highlights its promising applications in high-temperature antiferromagnetic vdW
devices and heterostructures.",2012.00891v1
2020/12/5,Superconductivity versus magnetism in the palladium 'ides': Pd$_{1-c}$(H/D/T)$_{c}$,"In general, conventional superconductivity and magnetism are competing
phenomena. In some alloys this competition is a function of the concentration
of the elements. Here we show that in the palladium alloys
Pd$_{1-c}$(H/D/T)$_{c}$ (Pd-ides) the increase in the concentration $c$ of the
ides: hydrogen, deuterium, tritium (H/D/T), lowers the predicted magnetism of
amorphous palladium ($a$-Pd) gradually, allowing superconductivity to appear
for $ c \approx 40\%$. This magnetism explains why superconductivity does not
manifest for smaller values of $c$ ($c \leq 40\%$) in these Pd alloys. Also,
these results validate indirectly our predicted magnetism in the
amorphous/porous palladium ($a/p$-Pd). The understanding of the interplay
between magnetism and superconductivity may contribute to the comprehension of
the magnetic behavior in materials, especially in high $T_{c}$ superconductors,
with the corresponding implications.",2012.02934v2
2020/12/6,Properties and dynamics of meron topological spin textures in the two-dimensional magnet CrCl3,"Merons are nontrivial topological spin textures highly relevant for many
phenomena in solid state physics. Despite their importance, direct observation
of such vortex quasiparticles is scarce and has been limited to a few complex
materials. Here we show the emergence of merons and antimerons in recently
discovered two-dimensional (2D) CrCl3 at zero magnetic field. We show their
entire evolution from pair creation, their diffusion over metastable domain
walls, and collision leading to large magnetic monodomains. Both quasiparticles
are stabilized spontaneously during cooling at regions where in-plane magnetic
frustration takes place. Their dynamics is determined by the interplay between
the strong in-plane dipolar interactions and the weak out-of-plane magnetic
anisotropy stabilising a vortex core within a radius of 8-10 nm. Our results
push the boundary to what is currently known about non-trivial spin structures
in 2D magnets and open exciting opportunities to control magnetic domains via
topological quasiparticles.",2012.03296v2
2021/1/13,Current-induced magnetization switching in a chemically disordered A1 CoPt single layer,"We report the first demonstration of the current-induced magnetization
switching in a perpendicularly magnetized A1 CoPt single layer. We show that
good perpendicular magnetic anisotropy can be obtained in a wide composition
range of the A1 Co1-xPtx single layers, which allows to fabricate
perpendicularly magnetized CoPt single layer with composition gradient to break
the inversion symmetry of the structure. By fabricating the gradient CoPt
single layer, we have evaluated the SOT efficiency and successfully realized
the SOT-induced magnetization switching. Our study provides an approach to
realize the current-induced magnetization in the ferromagnetic single layers
without attaching SOT source materials.",2101.04832v1
2021/1/29,Magnetic higher-order nodal lines,"Nodal lines, as one-dimensional band degeneracies in momentum space, usually
feature a linear energy splitting. Here, we propose the concept of magnetic
higher-order nodal lines, which are nodal lines with higher-order energy
splitting and realized in magnetic systems with broken time reversal symmetry.
We provide sufficient symmetry conditions for stabilizing magnetic quadratic
and cubic nodal lines, based on which concrete lattice models are constructed
to demonstrate their existence. Unlike its counterpart in nonmagnetic systems,
the magnetic quadratic nodal line can exist as the only band degeneracy at the
Fermi level. We show that these nodal lines can be accompanied by torus surface
states, which form a surface band that span over the whole surface Brillouin
zone. Under symmetry breaking, these magnetic nodal lines can be transformed
into a variety of interesting topological states, such as three-dimensional
quantum anomalous Hall insulator, multiple linear nodal lines, and magnetic
triple-Weyl semimetal. The three-dimensional quantum anomalous Hall insulator
features a Hall conductivity $\sigma_{xy}$ quantized in unit of $e^2/(hd)$
where $d$ is the lattice constant normal to the $x$-$y$ plane. Our work reveals
previously unknown topological states, and offers guidance to search for them
in realistic material systems.",2101.12477v1
2021/2/11,Defect-driven ferrimagnetism and hidden magnetization in MnBi$_2$Te$_4$,"MnBi$_2$Te$_4$ (MBT) materials are promising antiferromagnetic topological
insulators where field driven ferromagnetism is predicted to cause a transition
between axion insulator and Weyl semimetallic states. However, the presence of
antiferromagnetic coupling between Mn/Bi antisite defects and the main Mn layer
can reduce the low-field magnetization, and it has been shown that such defects
are more prevalent in the structurally identical trivial magnetic insulator
MnSb$_2$Te$_4$ (MST). We use high-field magnetization measurements to show that
the magnetization of MBT and MST occur in stages and full saturation requires
fields of~$\sim$~60 Tesla. As a consequence, the low-field magnetization
plateau state in MBT, where many determinations of quantum anomalous Hall state
are studied, actually consists of ferrimagnetic septuple blocks containing both
a uniform and staggered magnetization component.",2102.05797v2
2021/3/4,Strange electrical transport: Colossal magnetoresistance via avoiding fully polarized magnetization in ferrimagnetic insulator Mn3Si2Te6,"Colossal magnetoresistance is of great fundamental and technological
significance and exists mostly in the manganites and a few other materials.
Here we report colossal magnetoresistance that is starkly different from that
in all other materials. The stoichiometric Mn3Si2Te6 is an insulator featuring
a ferrimagnetic transition at 78 K. The resistivity drops by 7 orders of
magnitude with an applied magnetic field above 9 Tesla, leading to an
insulator-metal transition at up to 130 K. However, the colossal
magnetoresistance occurs only when the magnetic field is applied along the
magnetic hard axis and is surprisingly absent when the magnetic field is
applied along the magnetic easy axis where magnetization is fully saturated.
The anisotropy field separating the easy and hard axes is 13 Tesla, unexpected
for the Mn ions with nominally negligible orbital momentum and spin-orbit
interactions. Double exchange and Jahn-Teller distortions that drive the
hole-doped manganites do not exist in Mn3Si2Te6. The phenomena fit no existing
models, suggesting a unique, intriguing type of electrical transport.",2103.02764v1
2021/6/15,Thickness Dependent Magnetic Transition in Few Layer 1T Phase CrTe2,"Room temperature two-dimensional (2D) ferromagnetism is highly desired in
practical spintronics applications. Recently, 1T phase CrTe2 (1T-CrTe2)
nanosheets with five and thicker layers have been successfully synthesized,
which all exhibit the properties of ferromagnetic (FM) metals with Curie
temperatures around 305 K. However, whether the ferromagnetism therein can be
maintained when continuously reducing the nanosheet's thickness to monolayer
limit remains unknown. Here, through first-principles calculations, we explore
the evolution of magnetic properties of 1 to 6 layers CrTe2 nanosheets and
several interesting points are found: First, unexpectedly, monolayer CrTe2
prefers a zigzag antiferromagnetic (AFM) state with its energy much lower than
that of FM state. Second, in 2 to 4 layers CrTe2, both the intralayer and
interlayer magnetic coupling are AFM. Last, when the number of layers is equal
to or greater than five, the intralayer and interlayer magnetic coupling become
FM. Theoretical analysis reveals that the in-plane lattice contraction of few
layer CrTe2 compared to bulk is the main factor producing intralayer AFM-FM
magnetic transition. At the same time, as long as the intralayer coupling gets
FM, the interlayer coupling will concomitantly switch from AFM to FM. Such
highly thickness dependent magnetism provides a new perspective to control the
magnetic properties of 2D materials.",2106.07960v1
2021/7/11,Magnetic instabilities in quasi-one-dimensional Cr-based material,"The magnetic response of a K2Cr3As3 sample has been studied by means of dc
magnetization measurements as a function of magnetic field (H) at different
temperatures ranging from 5 K up to 300 K. Looking at the magnetic hysteresis
loops m(H), a diamagnetic behavior of the sample has been inferred at
temperatures higher than 60 K, whereas at lower temperatures the sample shows a
hysteresis loop compatible with the presence of ferrimagnetism. Moreover,
several spike-like magnetization jumps, both positive and negative, have been
observed at certain fields in the range -1000 Oe < H < 1000 Oe, regardless of
the temperature considered. The field position of the magnetization jumps has
been studied at different temperatures, and their distribution can be described
by a Lorentzian curve.",2107.05032v1
2021/9/8,Ground and Applied-Field-Driven Magnetic States of Antiferromagnets,"As discussed in this chapter, we develop a mean-field mathematical method to
calculate the ground states of antiferromagnets and better understand the
applied magnetic-field induced exotic properties. Within antiferromagnetic
materials competitive and cooperative interactions exist leading to substance
extraordinary magnetic states. Our calculations predict that applying a
magnetic field to antiferromagnets can switch it from one magnetic state to
another. These include antiferromagnetic ground state, spin-flop transition,
spin-flopped state, spin-flip transition and spin-flipped state. Our framework
successfully demonstrates these phase changes. With this, a map of all
equilibrium magnetic ground states, as well as the respective equilibrium phase
conditions, are derived. Our study provides insight into the origins of the
various magnetic states.",2109.03485v1
2021/10/2,Complex Spin Hamiltonian Represented by Artificial Neural Network,"The effective spin Hamiltonian method is widely adopted to simulate and
understand the behavior of magnetism. However, the magnetic interactions of
some systems, such as itinerant magnets, are too complex to be described by any
explicit function, which prevents an accurate description of magnetism in such
systems. Here, we put forward a machine learning (ML) approach, applying an
artificial neural network (ANN) and a local spin descriptor to develop
effective spin potentials for any form of interaction. The constructed
Hamiltonians include an explicit Heisenberg part and an implicit non-linear ANN
part. Such a method successfully reproduces artificially constructed models and
also sufficiently describe the itinerant magnetism of bulk Fe3GeTe2. Our work
paves a new way for investigating complex magnetic phenomena (e.g., skyrmions)
of magnetic materials.",2110.00724v1
2021/11/30,Dimension reduction induced anisotropic magnetic thermal conductivity in hematite nanowire,"The thermophysical properties near the magnetic phase transition point is of
great importance in the study of critical phenomenon. Low-dimensional materials
are suggested to hold different thermophysical properties comparing to their
bulk counterpart due to the dimension induced quantum confinement and
anisotropy. In this work, we measured the thermal conductivity of
$\alpha$-Fe$_2$O$_3$ nanowires along [110] direction (growing direction) with
temperature from 100K to 150K and found a dip of thermal conductivity near the
Morin temperature. We found the thermal conductivity near Morin temperature
varies with the angle between magnetic field and [110] direction of nanowire.
More specifically, an angular-dependent thermal conductivity is observed, due
to the magnetic field induced movement of magnetic domain wall. The angle
corresponding to the maximum of thermal conductivity varies near the Morin
transition temperature, due to the different magnetic easy axis as suggested by
our calculation based on magnetic anisotropy energy. This angular dependence of
thermal conductivity indicates that the easy axis of $\alpha$-Fe$_2$O$_3$
nanowires is different from bulk $\alpha$-Fe$_2$O$_3$ due to the geometric
anisotropy.",2111.15137v1
2022/1/13,Spin Seebeck effect in quantum magnet Pb2V3O9,"Spin Seebeck effect (SSE), the generation of spin current from heat, has been
extensively studied in a large variety of magnetic materials, including
ferromagnets, antiferromagnets, paramagnets, and quantum spin liquids. In this
paper, we report the study of the SSE in the single crystalline Pb2V3O9, a
spin-gapped quantum magnet candidate with quasi-one-dimensional spin-1/2 chain.
Detailed temperature and magnetic field dependences of the SSE are
investigated, and the temperature-dependent critical magnetic fields show a
strong correlation to the Bose-Einstein condensation phase of the quantum
magnet Pb2V3O9. This work shows the potential of using spin current as a probe
to study the spin correlation and phase transition properties in quantum
magnets.",2201.04759v1
2022/1/28,Hydrostatic pressure effect on Co-based honeycomb magnet BaCo2(AsO4)2,"The honeycomb antiferromagnet BaCo2(AsO4)2, in which small in-plane magnetic
fields (H1 = 0.26 T and H2 = 0.52 T at T = 1.8 K < TN = 5.4 K) induce two
magnetic phase transitions, has attracted attention as a possible candidate
material for the realization of Kitaev physics based on the 3d element Co2+.
Here, we report on the change of the transition temperature TN and the critical
fields H1 and H2 of BaCo2(AsO4)2 with hydrostatic pressure up to ~ 20 kbar, as
determined from magnetization and specific heat measurements. Within this
pressure range, a marginal increase of the magnetic ordering temperature is
observed. At the same time, the critical fields are changed significantly (up
to ~ 25-35 %). Specifically, we find that H1 is increased with hydrostatic
pressure, i.e., the antiferromagnetic state is stabilized with hydrostatic
pressure, whereas H2, which was previously associated with a transition into a
proposed Kitaev spin liquid state, decreases with increasing pressure. These
results put constraints on the magnetic models that are used to describe the
low-temperature magnetic properties of BaCo2(AsO4)2.",2201.12233v1
2022/2/24,Magnetic-field Induced Topological Transitions and Thermal Conductivity in a Generalized Kitaev Model,"Recent experiments on Kitaev spin liquid candidate materials reported
non-monotonic behavior of thermal conductivity as a function of magnetic field,
which lead to conflicting interpretations of its origin. Motivated by this
development, we study the magnetic field dependence of thermal conductivity of
a generalized Kitaev model, which allows the phase transitions between
different flux sectors as a function of the magnetic field. The thermal
conductivity due to Majorana fermions shows dip-bump structures as the magnetic
field increases, which is caused by either the transitions between different
flux sectors of Kitaev spin liquids or the topological transitions that change
the Majorana Chern number within the same flux sector. It is shown that the
change of Chern number is closely related to the four-Majorana-fermion
interaction induced by the magnetic field. The non-monotonic behavior in
thermal conductivity emerges at finite temperature, and it becomes weaker when
temperature decreases towards zero. Our model provides a generic mechanism for
the Kitaev spin liquids to develop non-monotonic magnetic-field dependence of
thermal conductivity while the detailed comparison to realistic materials
remains an open question for future investigation.",2202.12315v2
2022/3/3,Magnetism on the stretched diamond lattice in lanthanide orthotantalates,"The magnetic Ln$^{3+}$ ions in the fergusonite and scheelite crystal
structures form a distorted or stretched diamond lattice which is predicted to
host exotic magnetic ground states. In this study, polycrystalline samples of
the fergusonite orthotantalates $M$-LnTaO$_4$ (Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho,
Er) are synthesized and then characterized using powder diffraction and bulk
magnetometry and heat capacity. TbTaO$_4$ orders antiferromagnetically at 2.25
K into a commensurate magnetic cell with $\vec{k}=0$, magnetic space group
14.77 ($P2_1$$'/c$) and Tb moments parallel to the $a$-axis. No magnetic order
was observed in the other materials studied, leaving open the possibility of
exotic magnetic states at $T<2$ K.",2203.01658v2
2022/5/10,"Structural, electronic and magnetic properties of La$_{1.5}$Ca$_{0.5}$(Co$_{0.5}$Fe$_{0.5}$)IrO$_6$ double perovskite","In this work, we report the synthesis and investigation of structural,
electronic, and magnetic properties of
La$_{1.5}$Ca$_{0.5}$(Co$_{0.5}$Fe$_{0.5}$)IrO$_6$. Our polycrystalline sample
forms as a single-phase double perovskite in monoclinic $P2_{1}/n$ space group.
Co and Ir are most likely in bivalent and tetravalent oxidation states,
respectively, while Mossbauer spectroscopy indicates that Fe is in a trivalent
state. The ac and dc magnetization data suggest a ferrimagnetic behavior
resulting from the presence of two antiferromagnetic sublattices at Co/Fe and
Ir sites. The large coercive field H_C $\simeq$ 32 kOe observed at 10 K,
comparable to that of other double perovskites of interest for hard magnets, is
discussed in terms of the structural distortion and the spin and orbital
magnetic moments of the transition metal ions.",2205.04778v1
2022/8/17,Polarized neutron scattering study on the centrosymmetric skyrmion host material Gd2PdSi3,"We have investigated magnetic structures of the centrosymmetrric skyrmion
material Gd2PdSi3 by means of polarized neutron scattering near zero field with
an isotope-160Gd-enriched single crystal. In a previous study, magnetic
structures in Gd2PdSi3 at low temperatures were studied by resonant X-ray
scattering measurements [T. Kurumaji et al. Science 365, 914 (2019)]. The
present polarized neutron results confirm that the magnetic structure in zero
field has elliptic screw-type magnetic modulation with a propagation vector of
(q, 0, 0) with q ~ 0.14 and its equivalents. As the temperature increases, the
system undergoes a magnetic phase transition while keeping the incommensurate
q-vector of (q,0,0). We found that the thermally-induced phase has sinusoidal
magnetic modulations with magnetic moments perpendicular both to the c axis and
to the q-vector. We also investigate the spin-helicity degree of freedom in the
ground state by polarized neutrons, revealing that the system contains equal
fractions of the left-handed and right-handed screw-type orders as expected
from the centrosymmetric crystal structure.",2208.08188v1
2022/10/3,The effect of vanadium substitution on the structural and magnetic properties of (Fe$_{1-x}$V$_{x}$)$_{3}$Ga$_{4}$,"Fe$_{3}$Ga$_{4}$ displays a complex magnetic phase diagram that is sensitive
and tunable with both electronic and crystallographic structure changes. In
order to explore this tunability, vanadium-doped
(Fe$_{1-x}$V$_{x}$)$_{3}$Ga$_{4}$ has been synthesized and characterized.
High-resolution synchrotron X-ray diffraction and Rietveld refinement show that
samples up to 20\% V-doping remain isostructural to Fe$_{3}$Ga$_{4}$ and
display a linear increase in unit cell volume as doping is increased. Magnetic
measurements reveal a suppression of the antiferromagnetic helical spin-density
wave (SDW) with V-doping, revealed by changes in both the low-temperature
ferromagnetic-antiferromagentic (FM-AFM) transition (T$_{1}$) and
high-temperature AFM-FM transition (T$_{2}$). At 7.5\% V-doping, the
metamagnetic behavior of the helical AFM SDW phase is no longer observed. These
results offer an avenue to effective tuning of the magnetic order in
Fe$_{3}$Ga$_{4}$ for devices, as well as increased understanding of the
magnetism in this system.",2210.01039v1
2022/10/27,Current-induced quasiparticle magnetic multipole moments,"Magnetic ordering beyond the standard dipolar order has attracted significant
attention in recent years, but it remains an open question how to effectively
manipulate such nontrivial order parameters using external perturbations. In
this context, we present a theory for Cartesian magnetic multipole moments and
their currents created by electric currents based on a general gauge-invariant
formula for arbitrary-order spin magnetic multipole moments of Bloch wave
packets. As a concrete example, we point out that the low-energy quasiparticles
in phosphorene subject to a perpendicular electric field have a valley
structure that hosts magnetic octupole moments. The quasiparticle magnetic
octupole moments can be exhibited by an in-plane electric current and lead to
accumulation of staggered spin densities at the corners of a rectangular-shaped
sample. A current carrying the octupole moments can further be induced through
nonlinear response. Our work paves the way to systematically searching for and
utilizing quasiparticles with higher-order magnetic multipole moments in
crystal materials.",2210.15753v1
2023/1/10,Minimal time of magnetization switching in small ferromagnetic ellipsoidal samples,"In this paper, we consider a ferromagnetic material of ellipsoidal shape. The
associated magnetic moment then has two asymptotically stable opposite
equilibria, of the form $\pm\overline{m}$. In order to use these materials for
memory storage purposes, it is necessary to know how to control the magnetic
moment. We use as a control variable a spatially uniform external magnetic
field and consider the question of flipping the magnetic moment, i.e., changing
it from the $+\overline{m}$ configuration to the $-\overline{m}$ one, in
minimal time. Of course, it is necessary to impose restrictions on the external
magnetic field used. We therefore include a constraint on the $L^\infty$ norm
of the controls, assumed to be less than a threshold value $U$. We show that,
generically with respect to the dimensions of the ellipsoid, there is a minimal
value of $U$ for this problem to have a solution. We then characterize it
precisely. Finally, we investigate some particular configurations associated to
geometries enjoying symmetries properties and show that in this case the
magnetic moment can be controlled in minimal time without imposing a threshold
condition on $U$.",2301.03839v1
2023/2/21,"Giant Magneto-Optical Schäfer-Hubert Effect in Two-Dimensional van der Waals Antiferromagnets \textit{M}PS$_3$ (\textit{M}=Mn, Fe, Ni)","The recent discovery of long-range magnetic order in atomically thin films
has triggered particular interest in two-dimensional (2D) van der Waals (vdW)
magnetic materials. In this paper, we perform a systematic theoretical study of
the magneto-optical Sch\""{a}fer-Hubert effect (MOSHE) in 2D vdW
antiferromagnetic \textit{M}PS$_3$ (\textit{M} = Mn, Fe, Ni) with multifold
intralayer and interlayer magnetic orders. The formula for evaluating the MOSHE
in 2D magnets is derived by considering the influence of a non-magnetic
substrate. The MOSHE of monolayer and bilayer \textit{M}PS$_3$ are considerably
large ($>2^{\circ}$), originating from the strong anisotropy of in-plane
optical conductivity. The Sch\""{a}fer-Hubert rotation angles are surprisingly
insensitive to the orientations of the N\'{e}el vector, while the
Sch\""{a}fer-Hubert ellipticities are identified to be a good criterion to
distinguish different interlayer magnetic orders. Our work establishes a
theoretical framework for exploring novel 2D vdW magnets and facilitates the
promising applications of the 2D \textit{M}PS$_3$ family in antiferromagnetic
nanophotonic devices.",2302.10606v1
2023/3/21,Revealing Emergent Magnetic Charge in an Antiferromagnet with Diamond Quantum Magnetometry,"Whirling topological textures play a key role in exotic phases of magnetic
materials and offer promise for logic and memory applications. In
antiferromagnets, these textures exhibit enhanced stability and faster dynamics
with respect to ferromagnetic counterparts, but they are also difficult to
study due to their vanishing net magnetic moment. One technique that meets the
demand of highly sensitive vectorial magnetic field sensing with negligible
backaction is diamond quantum magnetometry. Here, we show that the archetypal
antiferromagnet, hematite, hosts a rich tapestry of monopolar, dipolar and
quadrupolar emergent magnetic charge distributions. The direct readout of the
previously inaccessible vorticity of an antiferromagnetic spin texture provides
the crucial connection to its magnetic charge through a duality relation. Our
work defines a novel paradigmatic class of magnetic systems to explore
two-dimensional monopolar physics, and highlights the transformative role that
diamond quantum magnetometry could play in exploring emergent phenomena in
quantum materials.",2303.12125v1
2023/4/27,"Room Temperature Ferrimagnetism, Magnetodielectric and Exchange Bias Effect in CoFeRhO$_4$","Geometrically frustrated structures combined with competing exchange
interactions that have different magnitudes are known ingredients for achieving
exotic properties. Herein, we studied detailed structural, magnetic, thermal
(specific heat), magneto-dielectric, and magnetic exchange bias properties of a
mixed 3d - 4d spinel oxide with composition CoFeRhO$_4$. Detailed
magnetization, heat capacity, and neutron powder diffraction studies (NPD)
highlight long-range ferrimagnetic ordering with an onset at 355 K. The
magnetic structure is established using a ferrimagnetic model (collinear-type)
that has a propagation vector k = 0, 0, 0. The magneto-dielectric effect
appears below the magnetic ordering temperature, and the exchange bias (EB)
effect is observed in field cooled (FC) conditions below 355 K. The
magneto-dielectric coupling in CoFeRhO$_4$ originates due to the frustration in
the structure, collinear ferrimagnetic ordering, and uncompensated magnetic
moments. The unidirectional anisotropy resulting from the uncompensated
magnetic moments causes the room-temperature exchange bias effect. Remarkably,
the appearance of technologically important properties (ferromagnetism,
magnetodielectric effect, and EB) at room temperature in CoFeRhO$_4$ indicates
its potential use in sensors or spintronics.",2304.13983v1
2023/4/27,Magnetism and exchange bias properties in Ba$_{2}$ScRuO$_{6}$,"This paper presents structural, detailed magnetic, and exchange bias studies
in polycrystalline Ba$_{2}$ScRuO$_{6}$ synthesized at ambient pressure. In
contrast to its strontium analogue, this material crystallizes in a 6L
hexagonal structure with the space group P$\overline{3}$m1. The Rietveld
refinement using the room-temperature powder X-ray diffraction pattern suggests
a Ru-Sc disorder in the structure. The temperature variation of the
dc-electrical resistivity highlights a semiconducting behaviour with the
electron conduction corresponding to the Mott 3D-VRH model. Detailed
magnetization measurements show that Ba$_{2}$ScRuO$_{6}$ develops
antiferromagnetic ordering at T$_{N}$ $\approx$ 9 K. Interestingly, below 9 K
(T$_{N}$), the field cooled (FC) magnetic field variation of the magnetization
curves highlights exchange bias effect in the sample. The exchange bias field
reaches a maximum value of 1.24 kOe at 2 K. The exchange bias effect below the
magnetic ordering temperature can be attributed to inhomogeneous magnetic
correlations owing to the disorder in the structure.",2304.13992v1
2023/5/18,Nanoscale magnetic domains in polycrystalline Mn3Sn films imaged by a scanning single-spin magnetometer,"Noncollinear antiferromagnets with novel magnetic orders, vanishingly small
net magnetization and exotic spin related properties hold enormous promise for
developing next-generation, transformative spintronic applications. A major
ongoing research focus of this community is to explore, control, and harness
unconventional magnetic phases of this emergent material system to deliver
state-of-the-art functionalities for modern microelectronics. Here we report
direct imaging of magnetic domains of polycrystalline Mn3Sn films, a
prototypical noncollinear antiferromagnet, using nitrogen-vacancy-based
single-spin scanning microscopy. Nanoscale evolution of local stray field
patterns of Mn3Sn samples are systematically investigated in response to
external driving forces, revealing the characteristic ""heterogeneous"" magnetic
switching behaviors in polycrystalline textured Mn3Sn films. Our results
contribute to a comprehensive understanding of inhomogeneous magnetic orders of
noncollinear antiferromagnets, highlighting the potential of nitrogen-vacancy
centers to study microscopic spin properties of a broad range of emergent
condensed matter systems.",2305.11343v1
2023/5/27,Effects of Chemical and magnetic disorder on the electrochemical properties of V$_{2-x}$Mn$_{x}$CO$_{2}$} MXene electrodes,"Investigation of structure-property relations in chemically and magnetically
disordered materials can give rise to interesting physical phenomena. The
potential of two-dimensional MXenes as electrodes in supercapacitor
applications have been studied extensively. However, the role of chemical and
magnetic disorder on their electrochemical parameters like the capacitance have
not been explored yet. In this work, we have systematically addressed this for
V$_{2-x}$Mn$_{x}$CO$_{2}$ MXene solid solutions with an analysis based upon
results from first-principles electronic structure calculations. We find that
the variations in the total capacitance over a voltage window depends upon the
degree of chemical and magnetic disorder. In course of our investigation, we
also found out that the magnetic structure on the surface can substantially
influence the redox charge transfer, an yet unexplored phenomenon. A
significantly large charge transfer and thus a large capacitance can be
obtained by manipulating the chemical composition and the magnetic order of the
surfaces.These findings can be useful in designing operational supercapacitor
electrodes with magnetic constituents.",2305.17462v1
2023/6/5,Critical Phenomena Study of 3D Heisenberg Magnet,"Recent discovery of several van der waals magnetic material and moire magnet
introduce to us an extremely challenging and revolutionary era of 2D magnetism
and correlated phenomena for low dimensional material.More often the simplest
spin models which is based on inter-atomic exchange and spin-orbit
coupling(SOC) potentially able to capture and explain the critical phenomena of
extremely complicated correlated magnetic material.In this work we have
attempted to simulate 3D Heisenberg magnet using classical Monte Carlo
simulation.Our goal is to establish a new and simplest spin simulation
technique which can help us to understand those van der waals magnet from its
microscopic length scale.Here we have been proposing a completely new
methodology of classical Monte Carlo simulation of Heisenberg spin which is
based on single spin flipping Metropolis algorithm.Our state of art simulation
technique potentially able to study the phase transition of isotropic XY(O(2))
and XYZ(O(3))spin model very efficiently.With this simulation technique we
overcome the barrier of critical slowing down during the phase transition in a
effective way and able to predict the transition temperature($T_c$) very
accurately.",2306.02566v1
2023/6/6,Large effective magnetic fields from chiral phonons in rare-earth halides,"Time-reversal symmetry (TRS) is pivotal for materials optical, magnetic,
topological, and transport properties. Chiral phonons, characterized by atoms
rotating unidirectionally around their equilibrium positions, generate dynamic
lattice structures that break TRS. Here we report that coherent chiral phonons,
driven by circularly polarized terahertz light pulses, can polarize the
paramagnetic spins in CeF3 like a quasi-static magnetic field on the order of 1
Tesla. Through time-resolved Faraday rotation and Kerr ellipticity, we found
the transient magnetization is only excited by pulses resonant with phonons,
proportional to the angular momentum of the phonons, and growing with magnetic
susceptibility at cryogenic temperatures, as expected from the spin-phonon
coupling model. The time-dependent effective magnetic field quantitatively
agrees with that calculated from phonon dynamics. Our results may open a new
route to directly investigate mode-specific spin-phonon interaction in
ultrafast magnetism, energy-efficient spintronics, and non-equilibrium phases
of matter with broken TRS.",2306.03852v1
2023/6/15,Exploring Magnetism of Lead-free Halide Double Perovskites: A High-Throughput First-Principles Study,"We have performed a comprehensive, first-principles high-throughput study of
the magnetic properties of halide double perovskites, $Cs_2BB^\prime Cl_6$,
with magnetic ions occupying one or both B and B$^\prime$ sites. Our findings
indicate a general tendency for these materials to exhibit antiferromagnetic
ordering with low N\'eel temperatures. At the same time, we reveal a few
potential candidates that predicted to be ferromagnetic with relatively high
Curie temperatures. Achieving ferromagnetic coupling might be feasible via
simultaneously alloying at B and B$^\prime$ sites with magnetic 3d and
non-magnetic 5d ions. With this approach, we discover that $Cs_2HgCrCl_6$,
$Cs_2AgNiCl_6$ and $Cs_2AuNiCl_6$ have high Curie temperatures relative to
their peers, with the latter two exhibiting half metallic behaviour. Further,
this study illuminates the underpinning mechanism of magnetic exchange
interactions in halide double perovskites, enabling a deeper understanding of
their magnetic behaviour. Our findings, especially the discovery of the
compounds with robust half-metallic properties and high Curie temperatures
holds promise for potential applications in the field of spintronics.",2306.09300v1
2023/7/13,Zero-field magnetic structure and metamagnetic phase transitions of the cobalt chain compound Li$_2$CoCl$_4$,"Exploring the uncharacterized magnetic phases of Co$^{2+}$ chain compounds is
critical for finding new low-dimensional magnets hosting quantized excitations.
We map the unexplored magnetic phases of the Co$^{2+}$ chain compound
Li$_2$CoCl$_4$. Magnetometry reveals magnetic ordering below 7 K with a
metamagnetic transition near 16.5 kOe and a gradual transition to a
field-aligned paramagnetic state above 31 kOe. Curie-Weiss fits to the high
temperature susceptibility reveal a high-spin (spin-$\frac{3}{2}$) state for
cobalt. Heat capacity data, though, give a magnetic entropy change of 5.46
J/mol, consistent with cobalt effective spin-$\frac{1}{2}$ systems. To
characterize the zero-field antiferromagnetic ordering, we separately
calculated the energy of proposed magnetic structures with density functional
theory and collected 3.5 K neutron diffraction data, finding that
Li$_2$CoCl$_4$ has ferromagnetic chains with antiferromagnetic interactions
between them. Increasing field rotates these spin chains, producing the
antiferromagnetic to intermediate to paramagnetic transition sequence.",2307.06899v1
2023/7/14,Signature of geometry modulation on interface magnetism emerged in isomeric IrO2-CoFe2O4 heterostructures,"The interface composed of magnets and strong spin-orbit coupling (SOC)
materials forms an important platform for spintronic devices and intriguing
magnetic phenomena, such as the chiral spin textures and magnetic proximity
effect (MPE). The interface exchange interaction and Dzyaloshinskii-Moriya
interaction (DMI) have been discussed in a wide range of heterostructures,
while the crystal stacking geometry modulation on these interface interactions
has rarely been considered. Here, we show a pronounced geometry modulation on
the interface magnetism through comparing a rutile and an anatase IrO2 capping
on a ferrimagnetic CoFe2O4. The rutile heterostructure with a high-symmetry
interface shows a conventional anomalous Hall effect (AHE) profile due to the
MPE. In contrast, the anatase one with a low-symmetry interface exhibits a
topological-like AHE even at zero-field, suggesting the emergence of
non-coplanar magnetic order at the interface. Our results suggest that the
influence of DMI at the interface can be more accentuated by forming a
low-symmetry interface and raises a new means of designing interface magnetism
via the geometry modulation.",2307.07169v2
2023/9/22,Laser-induced real-space topology control of spin wave resonances,"Femtosecond laser excitation of materials that exhibit magnetic spin textures
promises advanced magnetic control via the generation of ultrafast and
non-equilibrium spin dynamics. We explore such possibilities in ferrimagnetic
[Fe(0.35 nm)/Gd(0.40 nm)]$_{160}$ multilayers, which host a rich diversity of
magnetic textures from stripe domains at low magnetic fields, a dense
bubble/skyrmion lattice at intermediate fields, and a single domain state for
high magnetic fields. Using femtosecond magneto-optics, we observe distinct
coherent spin wave dynamics in response to a weak laser excitation allowing us
to unambiguously identify the different magnetic spin textures. Moreover,
employing strong laser excitation we show that we achieve versatile control of
the coherent spin dynamics via non-equilibrium and ultrafast transformation of
magnetic spin textures by both creating and annihilating bubbles/skyrmions. We
corroborate our findings by micromagnetic simulations and by Lorentz
transmission electron microscopy before and after laser exposure.",2309.12956v1
2023/9/24,Expanding the tunability and applicability of exchange-coupled/decoupled magnetic nanocomposites,"CoFe2O4/Co-Fe magnetic composites are usually prepared through partial
reduction of CoFe2O4, which often yields monoxides (i.e., FeO, CoO) as
secondary phases. Since these compounds are paramagnetic at ambient conditions,
the presence of a small amount of monoxide is generally downplayed in the
literature, and the possible effects on the magnetic properties are simply
ignored. However, the present study shows that even a low concentration of
monoxide results in decoupling of the soft and hard magnetic phases, which
inevitably leads to a deterioration of the magnetic properties. Additionally,
it is confirmed that a partial reduction of CoFe2O4 is a suitable method to
produce CoFe2O4/Co-Fe nanocomposites, provided that the treatment is well
controlled with respect to duration, temperature and flow of reductant. A
monoxide-free nanocomposite was produced and its magnetic properties evaluated
both at room and low temperature. Our model system exemplifies the potential of
exchange-coupling (and decoupling) as a tool to tune the magnetic properties of
a material within a relatively wide range of values, thus widening its spectrum
of potential applications.",2309.13725v1
2023/10/6,Magnetic Instability of Pr3Ru4Sn13,"We report on the quantum criticality of Pr$_3$Ru$_4$Sn$_{13}$ revealed by our
new material research. Pr$_3$Ru$_4$Sn$_{13}$ has been synthesized by flux
growth and characterized by single X-ray, powder X-ray, and powder neutron
diffraction measurements. The compound adopts a Yb$_3$Rh$_4$Sn$_{13}$-type
structure with a cubic Pm$\bar{3}$n. From the magnetization at 1 T, the
effective magnetic moment was estimated to be 3.58 $\mu _B$ per Pr$^{3+}$,
suggesting that the magnetism is mainly contributed by Pr$^{3+}$ ions. The
specific heat and magnetization show an anomaly at $T_{N} = 7.5$ ~ K owing to
the phase transition. The muon spin rotation and relaxation ($\mu$SR) time
spectra exhibit clear oscillations below $T_N$. This suggests that the phase is
magnetically ordered. The volume fraction of the magnetic phase estimated from
the initial asymmetry is around ten percent. In addition, spin fluctuations
were observed at low temperatures. These results provide microscopic evidence
that the material is closest to the antiferromagnetically quantum critical
point with a partial order among Pr$_3$$T_4$Sn$_{13}$ ($T= $ Co, Ru, Rh).",2310.04049v1
2023/11/21,Influence of interlayer exchange coupling on ultrafast laser-induced magnetization reversal in ferromagnetic spin valves,"In this study, we explore the influence of interlayer exchange coupling on
magnetization reversal triggered by femtosecond laser pulses in ferromagnetic
spin valves. Our experiments, focused on femtosecond laser-induced
magnetization reversal, methodically vary the thickness of the copper (Cu)
spacer layer. We identify a critical Cu thickness threshold at 2.32 nm. Above
this threshold, a stable reversed magnetic domain is consistently generated
upon exposure to a single laser pulse. Conversely, with a Cu spacer thinner
than 2.32 nm, the observed magnetization reversal from parallel (P) to
anti-parallel (AP) states occurs only under continuous laser irradiation. Once
the laser is stopped, the magnetic configuration relaxes back to its initial P
state, influenced by ferromagnetic exchange coupling. This research enhances
our understanding of the mechanisms that drive optically induced ultrafast
magnetization reversal in ferromagnetic spin valves.",2311.12753v2
2024/2/2,THz spin-wave excitations in the transverse conical phase of BiFeO$_3$,"Although BiFeO$_3$ is one of the most studied multiferroic materials, recent
magnetization and neutron scattering studies have revealed a new magnetic phase
in this compound - the transverse conical phase. To study the collective spin
excitations of this phase, we performed THz spectroscopy in magnetic fields up
to 17 T at and above room temperature. We observed five spin-wave branches in
the magnetic phase with long wavelength conical modulation. Using a numerical
spin dynamics model we found two kinds of excitations with magnetic moments
oscillating either along or perpendicular to the static fields. Remarkably, we
detected strong directional dichroism, an optical manifestation of the
magnetoelectric effect, for two spin-wave modes of the conical phase. According
to our experiments, the stability of the conical state is sensitive to the
magnetic field history and it can become (meta)stable at or close to zero
magnetic field, which may allow exploiting its magnetoelectric properties at
room temperature.",2402.01417v1
2024/2/15,"Insights into the magnetocaloric effect of Gadolinium: A DFT Exploration of Structural, Electronic, and Magnetic Features in Bulk and Film configurations","Gadolinium stand as the favored choice among magnetic refrigerant materials
for numerous active magnetic regenerator (AMR) prototypes due to its remarkable
ability to exhibit a substantial change in magnetic entropy. This unique
characteristic arises from its status as one of the elemental ferromagnets with
a high Curie temperature, closely aligning with room temperature conditions,
and undergoing a second-order magnetic phase transition. In this comprehensive
study, we employ density functional theory (DFT) calculations to explore the
structural, electronic, and magnetic properties of both Gadolinium bulk and
film configurations. Our primary objective is to gain a deeper understanding of
the intricate physics underlying the intriguing magnetocaloric features
observed in Gadolinium. This investigation provides valuable insights into the
potential applications and the broader implications of Gadolinium in the realm
of magnetic refrigeration technology.",2402.09979v1
2024/4/4,Temperature-dependent optical and magneto-optical spectra of ferromagnetic BCC Fe,"Optical and magneto-optical properties of magnetic materials have been widely
exploited to characterize magnetic structures and phenomena, however, their
temperature dependence is not well understood. This study implements the
supercell approach with thermal lattice and magnetic disorders to obtain
optical and magneto-optical spectra at finite temperatures based on
Williams-Lax theory. Our results show that large optical spectrum signals are
generated at photon energies below 1 eV, originating from the phonon- and
magnon-assisted intraband transitions as lattice and magnetic temperatures
increase. In addition, the prominent peak near 2.7 eV is redshifted
proportionally to magnetic temperature but depends much less on lattice
temperature. By analyzing unfolded bands, we show that the reduction of
exchange splitting due to the thermal demagnetization causes this redshift. Our
unfolded electronic band structure with magnetic disorder shows band kinks,
which are characteristic evidence of the coupling between electrons and
magnetic excitations. First-order magneto-optical spectra at finite temperature
are also predicted, but due to their small magnitude suffer more from sampling
errors. We discuss the effect of zero-point vibrations and the connection of
these simulations to the Drude model for intraband transitions.",2404.03545v1
1997/7/21,Magnetically-Driven Winds from Protostellar Disks,"Angular momentum transport in protostellar disks can be achieved by the
action of a large scale magnetic field that runs vertically through the disk.
The magnetic field centrifugally drives material from the disk surfaces into a
wind, initiating a bipolar outflow. One apparent difficulty for this model is
that the conductivity of the disk is extremely low in the inner 0.1--10 AU of
the disk, where grains are the dominant charge carriers. Near the midplane,
charged grains are unable to drift through the neutral gas and there is
negligible coupling between the magnetic field and the disk material. However,
the removal of angular momentum and acceleration of a wind by a magnetic field
can still take place in the surface layers of the disk where the gas
conductivity increases dramatically. Solutions to the multifluid MHD equations
for the vertical structure of a disk at a particular radius are presented. Most
of the disk material sits in hydrostatic equilibrium and does not interact with
the magnetic field running vertically through it. Near the disk surfaces, the
coupling between the magnetic field and disk material is sufficient to initiate
an outflow from the disk surface.",9707228v2
2008/8/30,Assessment of the RE(OH)3 Ising-like Magnetic Materials as Possible Candidates for the Study of Transverse-Field-Induced Quantum Phase Transitions,"The LiHo$_x$Y$_{1-x}$F$_4$ Ising magnetic material subject to a magnetic
field, $B_x$, perpendicular to the Ho$^{3+}$ Ising direction has shown over the
past twenty years to be a host of very interesting thermodynamic and magnetic
phenomena. Unfortunately, the availability of other magnetic materials other
than LiHo$_x$Y$_{1-x}$F$_4$ that may be described by a transverse field Ising
model remains very much limited. It is in this context that we use here
mean-field theory to investigate the suitability of the Ho(OH)$_{3}$,
Dy(OH)$_{3}$ and Tb(OH)$_3$ insulating hexagonal dipolar Ising-like
ferromagnets for the study of the quantum phase transition induced by a
magnetic field, $B_x$, applied perpendicular to the Ising spin direction. From
our calculations we estimate the critical transverse field, $B_{x}^{c}$, to
destroy ferromagnetic order at zero temperature to be $B_{x}^{c}=$4.35 T,
$B_{x}^{c}=$5.03 T and $B_{x}^{c}=$54.81 T for Ho(OH)$_{3}$, Dy(OH)$_{3}$ and
Tb(OH)$_{3}$, respectively. We conclude from our calculations that Ho(OH)$_{3}$
and Dy(OH)$_{3}$, and their Y$^{3+}$ diamagnetically diluted variants,
Ho$_{x}$Y$_{1-x}$(OH)$_{3}$ and Dy$_{x}$Y$_{1-x}$(OH)$_{3}$, are potentially
interesting systems to study transverse-field induced quantum fluctuations
effects in hard axis (Ising-like) magnetic materials.",0809.0059v1
2012/1/13,Preisach images of a simple mechanical system,"This work is an an early stage of a larger project aiming at answering the
question whether or not the Preisach map is really fingerprinting magnetic
materials. More precisely, we are interested whether Preisach model of magnetic
hysteresis indeed contains any physics or is just a convenient modeling tool.
To this extent we study a very simple mechanical system, thus fully tractable,
subjected to the external force. Despite of its simplicity, our model captures
all the fundamental features of real magnetic materials, namely their
hysteretic behavior, coercivity, remanent magnetization and saturation at high
fields. Both the overall shape of major hysteresis loop as well as First Order
Reversal Curves (FORC's) are reproduced quite correctly; they are very similar
to those observed in magnetic materials. The model essentially consists of a
single, spring loaded, rigid and rotative bar with non-zero friction torque.
The length of a projection of this bar onto the direction of an external force
is identified with magnetization. The friction torque and the spring constant
are the only freely adjustable parameters of our model. Here we investigate,
and present, their influence on the inferred Preisach maps.",1201.2811v1
2013/4/30,Power factor for layered thermoelectric materials with a closed Fermi surface in a quantizing magnetic field,"The field dependence of power factor for a layered thermoelectric material
with a closed Fermi surface in a quantizing magnetic field and at helium
temperatures has been studied in the geometry where the temperature gradient
and the magnetic field are perpendicular to the material lasyers. The
calculations are carried out in the constant relaxation time approximation. In
weak magnetic fields,the layered structure effects are shown to manifest
themselves in a phase retardation of power factor oscillations,increase of
their relativeb contribution, and certain reduction of the power factor in
whole.In highmagnetic fields,there exists an optimal range,where the power
factor reaches its maximum,with the corresponding value calculated for the
chosen parameters of the problem in the effective mass approximation being by
12%higher than that for real layered crystals.Despite low temperatures,the
power factor maximum obtained with those parameters in a magnetic field of 1T
has a value characteristic of cuprate thermoelectric materials at 1000K. For
this phenomenon to take place, it is necessary that the ratio between the free
path of charge carriers and interlayer distance should be equal to or larger
than 30000. However,in ultraquantum magnetic fields, the power factor
drastically decreases following the dependence P propto T^-3B^-6.The main
reason for this reduction is a squeeze of the Fermi surface along the magnetic
field in the ultraquantum limit owing the condensation of charge carriers on
the bottom of a single filled Landau subband.",1304.8054v1
2015/11/16,Plasmon Weyl Degeneracies in Magnetized Plasma,"In this letter, we report the presence of novel type of plasmon Weyl points
in a naturally existing material - magnetized plasma. In such a medium,
conventional, purely longitudinal bulk plasma oscillations exists only along
the direction of applied magnetic field (z direction). With strong enough
magnetic field, there exist helical propagating modes along z direction with
circular polarizations. The orthogonality between the longitudinal bulk plasmon
mode and the transverse helical propagating modes guarantees their crossing at
the bulk plasmon frequency. These crossing points, embedded in the bulk plasmon
dispersion line, serve as monopoles in the k space - the so called Weyl points.
These Weyl points lead to salient observable features. These include the highly
intriguing observation that, at a magnetized plasma surface which is parallel
to the applied magnetic field, reflection of an electromagnetic wave with
in-plane wave-vector close to the Weyl points exhibits chiral behavior only in
half of the k plane, which is bounded by the projection of the bulk plasmon
dispersion line. We also verify the presence of 'Fermi arcs' connecting the two
Weyl points with opposite chiralities when magnetized plasma interfaces with
trivial photonic materials. Our study introduces the concept of Weyl photonics
into homogeneous strongly dispersive photonic materials, which could pave way
for realizing new topological photonic devices.",1511.04875v1
2016/2/19,Magnetic effects in sulfur-decorated graphene,"The interaction between two different materials can present novel phenomena
that are quite different from the physical properties observed when each
material stands alone. Strong electronic correlations, such as magnetism and
superconductivity, can be produced as the result of enhanced Coulomb
interactions between electrons. Two-dimensional materials are powerful
candidates to search for the novel phenomena because of the easiness of
arranging them and modifying their properties accordingly. In this work, we
report magnetic effects of graphene, a prototypical non-magnetic
two-dimensional semi-metal, in the proximity with sulfur, a diamagnetic
insulator. In contrast to the well-defined metallic behaviour of clean
graphene, an energy gap develops at the Fermi energy for the graphene/sulfur
compound with decreasing temperature. This is accompanied by a steep increase
of the resistance, a sign change of the slope in the magneto-resistance between
high and low fields, and magnetic hysteresis. A possible origin of the observed
electronic and magnetic responses is discussed in terms of the onset of
low-temperature magnetic ordering. These results provide intriguing insights on
the search for novel quantum phases in graphene-based compounds.",1602.06214v2
2017/10/9,Huge magnetoresistance and ultra-sharp metamagnetic transition in polycrystalline ${Sm_{0.5}Ca_{0.25}Sr_{0.25}MnO_3}$,"Large magnetoresistive materials are of immense interest for a number of
spintronic applications by developing high density magnetic memory devices,
magnetic sensors and magnetic switches. Colossal magnetoresistance, for which
resistivity changes several order of magnitude (${\sim10^4 \%}$) in an external
magnetic field, occurs mainly in phase separated oxide materials, namely
manganites, due to the phase competition between the ferromagnetic metallic and
the antiferromagnetic insulating regions. Can one further enhance the
magnetoresistance by tuning the volume fraction of the two phases? In this
work, we report a huge colossal magnetoresistance along with the ultra-sharp
metamagnetic transition in half doped ${Sm_{0.5}Ca_{0.25}Sr_{0.25}MnO_3}$
manganite compound by suitably tuning the volume fraction of the competing
phases. The obtained magnetoresistance value at 10 K is as large as
$\sim10^{13}\%$ in a 30 kOe external magnetic field and $\sim10^{15}\%$ in 90
kOe external magnetic field and is several orders of magnitude higher than any
other observed magnetoresistance value reported so far. Using model Hamiltonian
calculations we have shown that the inhomogeneous disorder, deduced from
tunneling electron microscopy, suppresses the CE-type phase and seeds the
ferromagnetic metal in an external magnetic field.",1710.03007v2
2017/6/19,Spin order and dynamics in the diamond-lattice Heisenberg antiferromagnets CuRh2O4 and CoRh2O4,"Antiferromagnetic insulators on the diamond lattice are candidate materials
to host exotic magnetic phenomena ranging from spin-orbital entanglement to
degenerate spiral ground-states and topological paramagnetism. Compared to
other three-dimensional networks of magnetic ions, such as the geometrically
frustrated pyrochlore lattice, the investigation of diamond-lattice magnetism
in real materials is less mature. In this work, we characterize the magnetic
properties of model A-site spinels CoRh2O4 (cobalt rhodite) and CuRh2O4 (copper
rhodite) by means of thermo-magnetic and neutron scattering measurements and
perform group theory analysis, Rietveld refinement, mean-field theory, and spin
wave theory calculations to analyze the experimental results. Our investigation
reveals that cubic CoRh2O4 is a canonical S=3/2 diamond-lattice Heisenberg
antiferromagnet with a nearest neighbor exchange J = 0.63 meV and a Neel
ordered ground-state below a temperature of 25 K. In tetragonally distorted
CuRh2O4, competiting exchange interactions between up to third nearest-neighbor
spins lead to the development of an incommensurate spin helix at 24 K with a
magnetic propagation vector k = (0,0,0.79). Strong reduction of the ordered
moment is observed for the S=1/2 spins in CuRh2O4 and captured by our 1/S
corrections to the staggered magnetization. Our work identifies CoRh2O4 and
CuRh2O4 as reference materials to guide future work searching for exotic
quantum behavior in diamond-lattice antiferromagnets.",1706.05881v1
2019/1/11,"A Piezoelectric, Strain-Controlled Antiferromagnetic Memory Insensitive to Magnetic Fields","Spintronic devices based on antiferromagnetic (AFM) materials hold the
promise of fast switching speeds and robustness against magnetic fields.
Different device concepts have been predicted and experimentally demonstrated,
such as low-temperature AFM tunnel junctions that operate as spin-valves, or
room-temperature AFM memory, for which either thermal heating in combination
with magnetic fields, or N\'eel spin-orbit torque is used for the information
writing process. On the other hand, piezoelectric materials were employed to
control magnetism by electric fields in multiferroic heterostructures, which
suppresses Joule heating caused by switching currents and may enable low
energy-consuming electronic devices. Here, we combine the two material classes
to explore changes of the resistance of the high-N\'eel-temperature
antiferromagnet MnPt induced by piezoelectric strain. We find two non-volatile
resistance states at room temperature and zero electric field, which are stable
in magnetic fields up to 60 T. Furthermore, the strain-induced resistance
switching process is insensitive to magnetic fields. Integration in a tunnel
junction can further amplify the electroresistance. The tunneling anisotropic
magnetoresistance reaches ~11.2% at room temperature. Overall, we demonstrate a
piezoelectric, strain-controlled AFM memory which is fully operational in
strong magnetic fields and has potential for low-energy and high-density memory
applications.",1901.03551v1
2018/9/21,Experimental realization of an intrinsic magnetic topological insulator,"Intrinsic magnetic topological insulator (TI) is a stoichiometric magnetic
compound possessing both inherent magnetic order and topological electronic
states. Such a material can provide a shortcut to various novel topological
quantum effects but remains elusive experimentally so far. Here, we report the
experimental realization of high-quality thin films of an intrinsic magnetic
TI---MnBi$_2$Te$_4$---by alternate growth of a Bi$_2$Te$_3$ quintuple-layer and
a MnTe bilayer with molecular beam epitaxy. The material shows the archetypical
Dirac surface states in angle-resolved photoemission spectroscopy and is
demonstrated to be an antiferromagnetic topological insulator with
ferromagnetic surfaces by magnetic and transport measurements as well as
first-principles calculations. The unique magnetic and topological electronic
structures and their interplays enable the material to embody rich quantum
phases such as quantum anomalous Hall insulators and axion insulators in a
well-controlled way.",1809.07926v1
2019/10/23,Complex Transport and Magnetism in Inhomogeneous Mixed Valence Ce$_3$Ir$_4$Ge$_{13}$,"We report the discovery of Ce$_3$Ir$_4$Ge$_{13}$, a new Remeika phase
compound with a complex array of structural, electronic, and magnetic
properties. Our single crystal x-ray diffraction measurements show that
Ce$_3$Ir$_4$Ge$_{13}$ forms in the tetragonally distorted $I4_1/amd$ space
group. The electrical resistivity is almost temperature independent over three
decades in temperature, from 0.4 K to 400 K, while the Hall coefficient
measurements are consistent with a low-carrier semimetal. Magnetic
susceptibility measurements reveal an effective moment of
$\mu^{\text{exp}}_{\text{eff}} = 1.87 \mu_B$/Ce, suggesting that this material
has a mixture of magnetic Ce$^{3+}$ and non-magnetic Ce$^{4+}$. Upon cooling,
Ce$_3$Ir$_4$Ge$_{13}$ first enters a short range magnetically ordered state
below $T_{\text{SRO}}=10$ K, marked by a deviation from Curie-Weiss behavior in
susceptibility and a broad field-independent heat capacity anomaly. At lower
temperatures, we observe a second, sharper peak in the heat capacity at $T^* =
1.7$ K, concurrent with a splitting of the field-cooled and zero-field-cooled
susceptibilities. A small resistivity drop at $T^*$ suggests a loss of spin
disorder scattering consistent with a magnetic ordering or spin freezing
transition. Ce$_3$Ir$_4$Ge$_{13}$ is therefore a rare example of an
inhomogeneous mixed valence compound with a complex array of thermodynamic and
transport properties.",1910.10764v1
2019/10/29,"XFe4Ge2 (X = Y, Lu) and Mn3Pt: Filling-enforced magnetic topological metals","Magnetism, coupled with nontrivial band topology, can bring about many
interesting and exotic phenomena, so that magnetic topological materials have
attracted persistent research interest. However, compared with non-magnetic
topological materials (TMs), the magnetic TMs are less studied, since their
magnetic structures and topological phase transitions are usually complex and
the first-principles predictions are usually sensitive on the effect of Coulomb
interaction. In this work, we present a comprehensive investigation of XFe4Ge2
(X = Y, Lu) and Mn3Pt, and find these materials to be filling-enforced magnetic
topological metals. Our first-principles calculations show that XFe4Ge2 (X = Y,
Lu) host Dirac points near the Fermi level at high symmetry point S. These
Dirac points are protected by PT symmetry (P and T are inversion and
time-reversal transformations, respectively) and a 2-fold screw rotation
symmetry. Moreover, through breaking PT symmetry, the Dirac points would split
into Weyl nodes. Mn3Pt is found to host 4-fold degenerate band crossings in the
whole high symmetry path of A-Z. We also utilize the GGA+U scheme to take into
account the effect of Coulomb repulsion and find that the filling-enforced
topological properties are naturally insensitive on U.",1910.13383v1
2021/4/1,Crystallographic and magnetic structures of the VI$_3$ and LiVI$_3$ van der Waals compounds,"Two-dimensional (2D) layered magnetic materials are generating a great amount
of interest for the next generation of electronic devices thanks to their
remarkable properties associated to spin dynamics. The recently discovered
layered VI$_3$ ferromagnetic phase belongs to this family, although a full
understanding of its properties is limited by an ill-defined crystallographic
structure. This is not any longer true. Here, we investigate the VI$_3$ crystal
structure upon cooling using both synchrotron X-ray and neutron powder
diffraction and provide structural models for the two structural transitions
occurring at 76 K and 32 K. Moreover, we confirm by magnetic measurements that
VI$_3$ becomes ferromagnetic at 50 K and discuss the difficulty of solving its
full magnetic structure by neutrons. We equally determined the magnetic
properties of our recently reported LiVI$_3$ phase, which is alike the
well-known CrI$_3$ ferromagnetic phase in terms of electronic and
crystallographic structures and found to our surprise an antiferromagnetic
behavior with a N\'eel temperature of 12 K. Such a finding provides extra clues
for a better understanding of magnetism in these low dimension compounds.
Finally, the easiness of preparing novel Li-based 2D magnetic materials by
chemical/electrochemical means opens wide the opportunity to design materials
with exotic properties.",2104.00457v1
2021/5/17,AC susceptometry of 2D van der Waals magnets enabled by the coherent control of quantum sensors,"Precision magnetometry is fundamental to the development of novel magnetic
materials and devices. Recently, the nitrogen-vacancy (NV) center in diamond
has emerged as a promising probe for static magnetism in 2D van der Waals
materials, capable of quantitative imaging with nanoscale spatial resolution.
However, the dynamic character of magnetism, crucial for understanding the
magnetic phase transition and achieving technological applications, has rarely
been experimentally accessible in single 2D crystals. Here, we coherently
control the NV center's spin precession to achieve ultra-sensitive,
quantitative ac susceptometry of a 2D ferromagnet. Combining dc hysteresis with
ac susceptibility measurements varying temperature, field, and frequency, we
illuminate the formation, mobility, and consolidation of magnetic domain walls
in few-layer CrBr3. We show that domain wall mobility is enhanced in ultrathin
CrBr3, with minimal decrease for excitation frequencies exceeding hundreds of
kilohertz, and is influenced by the domain morphology and local pinning of the
flake. Our technique extends NV magnetometry to the multi-functional ac and dc
magnetic characterization of wide-ranging spintronic materials at the
nanoscale.",2105.08030v1
2020/2/6,Temperature scaling of two-ion anisotropy in pure and mixed anisotropy systems,"Magnetic anisotropy plays an essential role in information technology
applications of magnetic materials, providing a means to retain the long-term
stability of a magnetic state in the presence of thermal fluctuations.
Anisotropy consists of a single-ion contribution stemming from the crystal
structure and two-ion terms attributed to the exchange interactions between
magnetic atoms. A lack of robust theory crucially limits the understanding of
the temperature dependence of the anisotropy in pure two-ion and mixed
single-ion and two-ion systems. Here, we use Green's function theory and
atomistic Monte Carlo simulations to determine the temperature scaling of the
effective anisotropy in ferromagnets in these pure and mixed cases, from
saturated to vanishing magnetization. At low temperature, we find that the pure
two-ion anisotropy scales with the reduced magnetization as $k(m) \sim
m^{2.28}$, while the mixed scenario describes the diversity of the temperature
dependence of the anisotropy observed in real materials. The temperature
dependence of the mixed anisotropy determined here is expected to considerably
contribute to the understanding and the control of the thermal properties of
magnetic materials.",2002.02548v2
2020/9/29,Magnetic proximity effect on excitonic spin states in Mn-doped layered hybrid perovskites,"Materials combining the optoelectronic functionalities of semiconductors with
control of the spin degree of freedom are highly sought after for the
advancement of quantum technology devices. Here, we report the paramagnetic
Ruddlesden-Popper hybrid perovskite Mn:(PEA)2PbI4 (PEA = phenethylammonium) in
which the interaction of isolated Mn2+ ions with magnetically brightened
excitons leads to circularly polarized photoluminescence. Using a combination
of superconducting quantum interference device (SQUID) magnetometry and
magneto-optical experiments, we find that the Brillouin-shaped polarization
curve of the photoluminescence follows the magnetization of the material. This
indicates coupling between localized manganese magnetic moments and exciton
spins via a magnetic proximity effect. The saturation polarization of 15% at 4
K and 6 T indicates a highly imbalanced spin population and demonstrates that
manganese doping enables efficient control of excitonic spin states in
Ruddlesden-Popper perovskites. Our finding constitutes the first example of
polarization control in magnetically doped hybrid perovskites and will
stimulate research on this highly tuneable material platform that promises
tailored interactions between magnetic moments and electronic states.",2009.13867v1
2021/7/27,"Pressure-induced anomalies in the magnetic transitions of the exotic multiferroic material, Tb2BaNiO5","We have studied the influence of external pressure up to 1 GPa on the
magnetic transitions of the orthorhombic Haldane-spin chain compound Tb2BaNiO5
an exotic multiferroic material. This parent compound is known to undergo
N\'eel ordering at TN1= 63 K and another magnetic transition at TN2= 25K at
which ferroelectricity sets in, however, without any change in the magnetic
symmetry, but with only a sharp change in the canting angle of Tb 4f and Ni 3d
magnetic moments. There is a subtle difference in the antiferromagnetic state
above and below TN2, which is supported by the fact that there is a
metamagnetic transition below TN2only (for 5 K, at about 60 kOe). We report
here that, with the application of external pressure, there is an upward shift
of TN1, while TN2 shifts towards lower temperatures. It is interesting that the
two magnetic transitions in the same compound behave differently under pressure
and the opposite behavior at TN2 is attributed to local distortion leading to
ferroelectricity. The results are augmented by temperature dependent x-ray
diffraction and positive chemical pressure studies. The chemical pressure
caused by the isoelectronic doping at Ba site by Sr reduces both the transition
temperatures. Clearly, the external pressure favors antiferromagnetic coupling
(that is, leading to TN1 enhancement), whereas the chemical pressure reduces
TN1, suggesting important role of the changes in local hybridization induced by
doping on magnetism in this material.",2107.12729v1
2022/2/7,Pressure-induced magnetic and topological transitions in non-centrosymmetric MnIn$_{2}$Te$_{4}$,"The discovery of time-reversal-invariant topological states has drawn great
attention in recent decades. However, despite the potential of displaying a
variety of exotic physics, the study of magnetic topological phases lags behind
due to underlying added complexity of magnetism. In this work, we predict the
interplay of magnetism and topology in the non-centrosymmetric ternary
manganese compound MnIn$_2$Te$_4$, using first-principles calculations. At
ambient pressure, the ground state of the system is an antiferromagnetic
insulator. With the application of small hydrostatic pressure ($\sim$0.50 GPa),
it undergoes a magnetic transition and the ferromagnetic state becomes
energetically favourable. At $\sim$2.92 GPa, the system undergoes a transition
into a Weyl semimetallic phase, which hosts multiple Weyl points in the bulk
and is associated with non-trivial surface Fermi arcs. Remarkably, we discover
that the number of Weyl points in this system can be controlled by pressure and
that these manifest in an anomalous Hall conductivity (AHC). In addition to
proposing a new candidate magnetic topological material, our work demonstrates
that pressure can be an effective way to induce and control topological phases,
as well as AHC, in magnetic materials. These properties may allow our proposed
material to be used as a novel pressure-controlled Hall switch.",2202.03317v2
2022/7/13,Role of Dy on the magnetic properties of orthorhombic DyFeO3,"Orthoferrites are a class of magnetic materials with a magnetic ordering
temperature above 600 K, predominant G-type antiferromagnetic ordering of the
Fe-spin system and, depending on the rare-earth ion, a spin reorientation of
the Fe spin taking place at lower temperatures. DyFeO3 is of particular
interest since the spin reorientation is classified as a Morin transition with
the transition temperature depending strongly on the Dy-Fe interaction. Here,
we report a detailed study of the magnetic and structural properties of
microcrystalline DyFeO3 powder and bulk single crystal using neutron
diffraction and magnetometry between 1.5 and 450 K. We find that, while the
magnetic properties of the single crystal are largely as expected, the powder
shows strongly modified magnetic properties, including a modified spin
reorientation and a smaller Dy-Fe interaction energy of the order of 10
{\mu}eV. Subtle structural differences between powder and single crystal show
that they belong to distinct magnetic space groups. In addition, the Dy
ordering at 2 K in the powder is incommensurate, with a modulation vector of
0.0173(5) c*, corresponding to a periodicity of ~58 unit cells.",2207.06013v1
2023/2/10,Correlation-driven topological transition in Janus VSiGeP2As2,"The appearance of intrinsic ferromagnetism in 2D materials opens the
possibility of investigating the interplay between magnetism and topology. The
magnetic anisotropy energy (MAE) describing the easy axis for magnetization in
a particular direction is an important yardstick for nanoscale applications.
Here, the first-principles approach is used to investigate the electronic band
structures, the strain dependence of MAE in pristine VSi2Z4 (Z=P, As) and its
Janus phase VSiGeP2As2 and the evolution of the topology as a function of the
Coulomb interaction. In the Janus phase the compound presents a breaking of the
mirror symmetry, which is equivalent to having an electric field, and the
system can be piezoelectric. It is revealed that all three monolayers exhibit
ferromagnetic ground state ordering, which is robust even under biaxial
strains. A large value of coupling J is obtained, and this, together with the
magnetocrystalline anisotropy, will produce a large critical temperature. We
found an out-of-plane (in-plane) magnetization for VSi2P4 (VSi2As4), while
in-plane magnetization for VSiGeP2As2. Furthermore, we observed a
correlation-driven topological transition in the Janus VSiGeP2As2. Our analysis
of these emerging pristine and Janus-phased magnetic semiconductors opens
prospects for studying the interplay between magnetism and topology in
two-dimensional materials.",2302.05146v2
2023/3/24,"A multi-stage, first-order phase transition in LaFe11.8Si1.2: interplay between the structural, magnetic and electronic degrees of freedom","Alloys with a first-order magnetic transition are central to solid-state
refrigeration technology, sensors and actuators, or spintronic devices. The
discontinuous nature of the transition in these materials is a consequence of
the coupling between the magnetic, electronic and structural subsystems, but in
a real experiment, it is difficult to observe and analyze the simultaneous
evolution of all the subsystems. As a result, it is very hard to determine the
main mechanisms of the transition and purposefully develop these advanced
magnetic materials. To resolve this issue, we changed the existing paradigm and
conducted simultaneous measurements of the macroscopic properties -
magnetization, temperature change of the sample, longitudinal and transversal
magnetostrictions - to reveal the rich details of the magneto-structural,
first-order transition occurring in the prototypical alloy LaFe11.8Si1.2. We
complement these findings with experiments on the atomistic scale, i.e., x-ray
absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD) and
M\""ossbauer spectroscopy, and then combine them with first-principles
calculations to reveal the full complexity and two-stage nature of the
transition. This new approach can be successfully extended to a large class of
advanced magnetic materials that exhibit analogous transformations.",2303.13836v2
2023/5/4,Angle-resolved photoemission spectroscopy with an $\textit{in situ}$ tunable magnetic field,"Angle-resolved photoemission spectroscopy (ARPES) is a powerful tool for
probing the momentum-resolved single-particle spectral function of materials.
Historically, $\textit{in situ}$ magnetic fields have been carefully avoided as
they are detrimental to the control of photoelectron trajectory during the
photoelectron detection process. However, magnetic field is an important
experimental knob for both probing and tuning symmetry-breaking phases and
electronic topology in quantum materials. In this paper, we introduce an easily
implementable method for realizing an $\textit{in situ}$ tunable magnetic field
at the sample position in an ARPES experiment and analyze magnetic field
induced artifacts in ARPES data. Specifically, we identified and quantified
three distinct extrinsic effects of a magnetic field: Fermi surface rotation,
momentum shrinking, and momentum broadening. We examined these effects in three
prototypical quantum materials, i.e., a topological insulator (Bi$_2$Se$_3$),
an iron-based superconductor (LiFeAs), and a cuprate superconductor
(Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$), and demonstrate the feasibility of ARPES
measurements in the presence of a controllable magnetic field. Our studies lay
the foundation for the future development of the technique and interpretation
of ARPES measurements of field-tunable quantum phases.",2305.02625v1
2023/8/31,On the local aspect of valleytronics,"Valley magnetic moments play a crucial role in valleytronics in 2D hexagonal
materials. Traditionally, based on studies of quantum states in homogeneous
bulks, it is widely believed that only materials with broken structural
inversion symmetry can exhibit nonvanishing valley magnetic moments. Such
constraint excludes from relevant applications those with inversion symmetry,
as specifically exemplified by gapless monolayer graphene despite its
technological advantage in routine growth and production. This work revisits
valley-derived magnetic moments in a broad context covering inhomogeneous
structures as well. It generalizes the notion of valley magnetic moment for a
state from an integrated total quantity to the local field called ""local valley
magnetic moment"" with space-varying distribution. In suitable
inversion-symmetric structures with inhomogeneity, e.g., zigzag nanoribbons of
gapless monolayer graphene, it is shown that the local moment of a state can be
nonvanishing with sizable magnitude, while the corresponding total moment is
subject to the broken symmetry constraint. Moreover, it is demonstrated that
such local moment can interact with space-dependent electric and magnetic
fields manifesting pronounced field effects and making possible a local valley
control with external fields. Overall, a path to ""local valleytronics"" is
illustrated which exploits local valley magnetic moments for device
applications, relaxes the broken symmetry constraint on materials, and expands
flexibility in the implementation of valleytronics.",2309.00091v1
2023/9/12,Proximity-induced interfacial room-temperature ferromagnetism in semiconducting Fe3GeTe2,"The discoveries of two-dimensional ferromagnetism and magnetic semiconductors
highly enrich the magnetic material family for constructing spin-based
electronic devices but with an acknowledged challenge that the Curie
temperature (Tc) is usually far below room temperature. Many efforts such as
voltage control and magnetic ion doping are currently underway to enhance the
functional temperature, in which the involvement of additional electrodes or
extra magnetic ions limits their plenty of applications in practical devices.
Here we demonstrate that the magnetic proximity, a robust effect but with
elusive mechanisms, can induce room-temperature ferromagnetism at the interface
between sputtered Pt and semiconducting Fe3GeTe2, both of which do not show
ferromagnetism at 300 K. The independent electrical and magnetization
measurements, structure analysis, and control samples with Ta highlighting the
role of Pt confirm that the ferromagnetism with the Tc of above 400 K arises
from the Fe3GeTe2/Pt interfaces, rather than Fe aggregation or other artificial
effects. Moreover, contrary to conventional ferromagnet/Pt structures, the spin
current generated by the Pt layer is enhanced more than two times at the
Fe3GeTe2/Pt interfaces, indicating the potential applications of the unique
proximity effect in building high-efficient spintronic devices. These results
may pave a new avenue to create room-temperature functional spin devices based
on low-Tc materials and provide clear evidences of magnetic proximity effects
by using non-ferromagnetic materials.",2309.06204v1
2016/4/28,Large difference between the magnetic properties of Ba and Ti co-doped BiFeO$_3$ bulk materials and their corresponding nanoparticles prepared by ultrasonication,"The ceramic pellets of the nominal compositions
Bi$_{0.7}$Ba$_{0.3}$Fe$_{1-x}$Ti$_x$O$_3$ (x = 0.00-0.20) were prepared
initially by standard solid state reaction technique. The pellets were then
ground into micrometer-sized powders and mixed with isopropanol in an
ultrasonic bath to prepare nanoparticles. The X-ray diffraction patterns
demonstrate the presence of a significant number of impurity phases in bulk
powder materials. Interestingly, these secondary phases were completely removed
due to the sonication of these bulk powder materials for 60 minutes. The field
and temperature dependent magnetization measurements exhibited significant
difference between the magnetic properties of the bulk materials and their
corresponding nanoparticles. We anticipate that the large difference in the
magnetic behavior may be associated with the presence and absence of secondary
impurity phases in the bulk materials and their corresponding nanoparticles,
respectively. The leakage current density of the bulk materials was also found
to suppress in the ultrasonically prepared nanoparticles compared to that of
bulk counterparts.",1604.08520v1
2021/1/30,Determination of the Dzyaloshinskii-Moriya interaction using pattern recognition and machine learning,"Machine learning is applied to a large number of modern devices that are
essential in building energy efficient smart society. Audio and face
recognition are among the most well-known technologies that make use of such
artificial intelligence. In materials research, machine learning is adapted to
predict materials with certain functionalities, an approach often referred to
as materials informatics. Here we show that machine learning can be used to
extract material parameters from a single image obtained in experiments. The
Dzyaloshinskii-Moriya (DM) interaction and the magnetic anisotropy distribution
of thin film heterostructures, parameters that are critical in developing next
generation storage class magnetic memory technologies, are estimated from a
magnetic domain image. Micromagnetic simulation is used to generate thousands
of random images for training and model validation. A convolutional neural
network system is employed as the learning tool. The DM exchange constant of
typical Co-based thin film heterostructures is studied using the trained
system: the estimated values are in good agreement with experiments. Moreover,
we show that the system can independently determine the magnetic anisotropy
distribution, demonstrating the potential of pattern recognition. This approach
can considerably simplify experimental processes and broaden the scope of
materials research.",2102.00173v1
2021/10/20,Materials and possible mechanisms of extremely large magnetoresistance: A review,"Magnetoresistance (MR) is a characteristic that the resistance of a substance
changes with the external magnetic field, reflecting various physical origins
and microstructures of the substance. A large MR, namely a huge response to a
low external field, has always been a useful functional feature in industrial
technology and a core goal pursued by physicists and materials scientists.
Conventional large MR materials are mainly manganites, whose colossal MR (CMR)
can be as high as -90%. The dominant mechanism is attributed to spin
configuration aligned by the external field, which reduces magnetic scattering
and thus resistance. In recent years, some new systems have shown an extremely
large unsaturated MR (XMR). Unlike ordinary metals, the positive MR of these
systems can reach 103-108% and is persistent under super high magnetic fields.
The XMR materials are mainly metals or semimetals, distributed in high-mobility
topological or non-topological systems, and some are magnetic, which suggests a
wide range of application scenarios. Various mechanisms have been proposed for
the potential physical origin of XMR, including electron-hole compensation,
steep band, ultrahigh mobility, high residual resistance ratio, topological
fermions, etc. It turns out that some mechanisms play a leading role in certain
systems, while more are far from clearly defined. In addition, the researches
on XMR are largely overlapped or closely correlated with other recently rising
physics and materials researches, such as topological matters and
two-dimensional (2D) materials, which makes elucidating the mechanism of XMR
even more important. Moreover, the disclosed novel properties will lay a broad
and solid foundation for the design and development of functional devices. In
this review, we will discuss several aspects in the following order: ...",2110.10454v1
1997/9/16,A Critique of Current Magnetic-Accretion Models for Classical T-Tauri Stars,"Current magnetic-accretion models for classical T-Tauri stars rely on a
strong, dipolar magnetic field of stellar origin to funnel the disk material
onto the star, and assume a steady-state. In this paper, I critically examine
the physical basis of these models in light of the observational evidence and
our knowledge of magnetic fields in low-mass stars, and find it lacking.
  I also argue that magnetic accretion onto these stars is inherently a
time-dependent problem, and that a steady-state is not warranted.
  Finally, directions for future work towards fully-consistent models are
pointed out.",9709158v1
2005/9/29,Mixing zones in magnetized differentially rotating stars,"We study the secular instability of magnetized differentially rotating
radiative zones taking account of viscosity and magnetic and thermal
diffusivities. The considered instability generalizes the well-known
Goldreich-Schubert-Fricke instability for the case of a sufficiently strong
magnetic field. In magnetized stars, instability can lead to a formation of
non-spherical unstable zones where weak turbulence mixes the material between
the surface and interiors. Such unstable zones can manifest themselves by a
non-spherical distribution of abundance anormalies on the stellar surface.",0509877v1
1997/12/10,Magnetic imaging of the paramagnetic Meissner effect in the granular high-Tc superconductor Bi2Sr2CaCu2Ox,"We have imaged the spatial distribution of magnetic flux on a granular sample
of the high-temperature superconductor Bi2Sr2CaCu2Ox using a scanning SQUID
microscope. Our results establish the presence of spontaneous orbital magnetic
moments which were suggested to be the origin of the paramagnetic response of
these materials. The signature of the orbital magnetic moments is a rather
broad distribution of local magnetic fields at the surface of the sample. A
simple model for the distribution is presented.",9712113v1
1998/3/2,Anomalous magnetic response of the spin-one-half Falicov-Kimball model,"The infinite-dimensional spin one-half Falicov-Kimball model in an external
magnetic field is solved exactly. We calculate the magnetic susceptibility in
zero field, and the magnetization as a function of the field strength. The
model shows an anomalous magnetic response from thermally excited local moments
that disappear as the temperature is lowered. We describe possible real
materials that may exhibit this kind of anomalous behavior.",9803027v1
1998/4/19,Switching dynamics between metastable ordered magnetic state and nonmagnetic ground state - A possible mechanism for photoinduced ferromagnetism -,"By studying the dynamics of the metastable magnetization of a statistical
mechanical model we propose a switching mechanism of photoinduced
magnetization. The equilibrium and nonequilibrium properties of the Blume-Capel
(BC) model, which is a typical model exhibiting metastability, are studied by
mean field theory and Monte Carlo simulation. We demonstrate reversible changes
of magnetization in a sequence of changes of system parameters, which would
model the reversible photoinduced magnetization. Implications of the calculated
results are discussed in relation to the recent experimental results for
prussian blue analogs.",9804203v3
1999/10/14,Cauchy magnetic field component and magnitude distribution studied by the zero-field muon spin relaxation technique,"Zero-field muon spin relaxation (ZF-$\mu $SR) data for dilute spin magnetic
systems have been widely interpreted with what is called a Kubo-Toyabe form
based on a Lorentzian distribution of local field components. We derive here
the proper magnetic field \textit{magnitude} distribution using independent and
uncorrelated \textit{component} distributions. Our result is then compared to
the previously accepted formula for ZF-$\mu $SR. We discuss the origins of the
magnetic field component and magnitude distributions. Further we found that
after rescaling the magnetic field, the differences that are amenable to
experimental examination are quite small, although the interpretations behind
them are quite different.",9910215v1
2000/1/17,Orbital Structure and Magnetic Ordering in Layered Manganites: Universal Correlation and Its Mechanism,"Correlation between orbital structure and magnetic ordering in bilayered
manganites is examined. A level separation between the $3d_{3z^2-r^2}$ and
$3d_{x^2-y^2}$ orbitals in a Mn ion is calculated in the ionic model for a
large number of the compounds. It is found that the relative stability of the
orbitals dominates the magnetic transition temperatures as well as the magnetic
structures. A mechanism of the correlation between orbital and magnetism is
investigated based on the theoretical model with the two $e_g$ orbitals under
strong electron correlation.",0001221v1
2000/3/13,Effect of short range order on electronic and magnetic properties of disordered Co based alloys,"We here study electronic structure and magnetic properties of disordered CoPd
and CoPt alloys using Augmented Space Recursion technique coupled with the
tight-binding linearized muffin tin orbital (TB-LMTO) method. Effect of short
range ordering present in disordered phase of alloys on electronic and magnetic
properties has been discussed. We present results for magnetic moments, Curie
temperatures and electronic band energies with varying degrees of short range
order for different concentrations of Co and try to understand and compare the
magnetic properties and ordering phenomena in these systems.",0003206v1
2000/4/4,Magnetic Foehn Effect in Nonadiabatic Transition,"The magnetization curves as a response of sweeping magnetic field in the
thermal environment are investigated using the quantum master equation. In a
slow velocity region where the system almost behaves adiabatically, the
magnetic plateau appears which has been observed in the recent experiment of
V$_{15}$ [ Phys. Rev. Lett. (2000)]. We investigate its mechanism and propose
that this phenomenon is quite universal in the quasi-adiabatic transition with
small inflow of the heat, and we call it 'Magnetic Foehn Effect'. We observe
the crossover between this mechanism and the Landau-Zener-St\""{u}ckelberg
mechanism changing the velocity. Some experiment is proposed to clarify the
inherent mechanism of this effect.",0004027v1
2000/4/19,Statistical coarse-graining as an approach to multiscale problems in magnetism,"Multiscale phenomena which include several processes occuring simultaneously
at different length scales and exchanging energy with each other, are
widespread in magnetism. These phenomena often govern the magnetization
reversal dynamics, and their correct modeling is important. In the present
paper, we propose an approach to multiscale modeling of magnets, applying the
ideas of coarse graining. We have analyzed the choice of the weighting function
used in coarse graining, and propose an optimal form for this function. Simple
tests provide evidence that this approach may be useful for modeling of
realistic magnetic systems.",0004338v1
2000/6/28,Quantum Coherence and Decoherence in Magnetic Nanostructures,"The prospect of developing magnetic qubits is discussed. The first part of
the article makes suggestions on how to achieve the coherent quantum
superposition of spin states in small ferromagnetic clusters, weakly
uncompensated antiferromagnetic clusters, and magnetic molecules. The second
part of the article deals with mechanisms of decoherence expected in magnetic
systems. Main decohering effects are coming from nuclear spins and magnetic
fields. They can be reduced by isotopic purification and superconducting
shielding. In that case the time reversal symmetry of spin Hamiltonians makes
spin-phonon coupling ineffective in destroying quantum coherence.",0006442v1
2000/11/13,Spin Excitations in Localized and Itinerant Magnets,"Collective excitations in magnetic materials can be investigated by means of
inelastic neutron scattering. We show that this experimental method gives
access to the complete spectrum of magnetic fluctuations through the energy-
and momentum-dependence of the dynamical susceptibility. We focus on the
dynamical properties of magnets with localized spin densities and of metals.
  From such studies, microscopic parameters like exchange integrals, spin-wave
stiffness and relaxation times can be determined. This is of great help to test
current theories in magnetism.",0011220v1
2000/11/22,Giant and time-dependent magnetocaloric effect in high-spin molecular magnets,"We have measured and calculated the magnetocaloric effect in macroscopic
samples of oriented high-spin molecular clusters like Mn12 and Fe8 as a
function of the temperature and both the intensity and the sweeping rate of the
applied magnetic field. We have observed a high magnetic entropy variation
around the blocking temperature of the magnetic moment of molecules and
calculated the shift of the entropy variation and cooling temperature, with the
sweeping rate of the magnetic field.",0011384v1
2001/3/9,Magnetic Phase Diagram of Ca2-xSrxRuO4 Governed by Structural Distortions,"We constructed, by the first-principles calculations, a magnetic phase
diagram of Sr$_{2}$RuO$_4$ in the space spanned by structural distortions. Our
phase diagram can qualitatively explain the experimental one for
Ca$_{2-x}$Sr$_x$RuO$_4$. We found that the rotation and the tilting of RuO$_6$
octahedron are responsible for the ferro- and antiferro-magnetism,
respectively, while the flattening of RuO$_6$ is the key factor to stabilize
those magnetic ground states. Our results imply that the magnetic and the
structural instabilities in Sr$_2$RuO$_4$ are closely correlated cooperatively
rather than competitively.",0103223v1
2001/3/16,Hole-hole correlation effects on magnetic properties of Mn$_x$III$_{1-x}$V diluted magnetic semiconductors,"The mean-field theory represents a useful starting point for studying
carrier-induced ferromagnetism in Mn$_x$III$_{1-x}$V diluted magnetic
semiconductors. A detail description of these systems requires to include
correlations in the many-body hole system. We discuss the effects of
correlations among itinerant carriers on magnetic properties of bulk
Mn$_x$III$_{1-x}$V and magnetic semiconductor quantum wells. Presented results
were obtained using parabolic band approximation and we also derive a many-body
perturbation technique that allows to account for hole-hole correlations in
realistic semiconductor valence bands.",0103340v1
2001/3/16,Mean-field theory of magnetic properties of Mn$_x$III$_{1-x}$V semiconductors,"We present a mean-field theory of carrier-induced ferromagnetism in
Mn$_x$III$_{1-x}$V diluted magnetic semiconductors with a special emphasis
placed on the magnetic anisotropy. The valence band holes are described using
the six band Kohn-Luttinger model. We find that the magnetic anisotropy is a
complicated function of sample parameters such as hole density or strain.
Results of our numerical simulations are in agreement with magnetic anisotropy
measurements on samples with both compressive and tensile strains.",0103341v1
2001/3/26,Reorientation phase transitions in thin magnetic films: a review of the classical vector spin model within the mean field approach,"The ground state and the finite temperature phase diagrams with respect to
magnetic configurations are studied systematically for thin magnetic films in
terms of a classical Heisenberg model including magnetic dipole-dipole
interaction and uniaxial anisotropy. Simple relations are derived for the
occurrence of the various phase boundaries between the different regions of the
magnetic orientations. In particular, the range of the first and second order
reorientation phase transitions are determined for bi- and trilayers.",0103539v1
2001/5/3,Two-dimensional topological solitons in rectangular magnetic dots,"A general approach allowing to find the analytical expressions for
equilibrium magnetic structures in small and flat magnetic nano-sized cylinders
of arbitrary shape made of soft magnetic material is presented. The resulting
magnetization distributions are two-dimensional topological solitons and have a
non-zero topological charge. The approach is illustrated here on an example of
a thin rectangular particle.",0105072v1
2001/6/30,Magnetic domains in III-V magnetic semiconductors,"Recent progress in theoretical understanding of magnetic anisotropy and
stiffness in III-V magnetic semiconductors is exploited for predictions of
magnetic domain characteristics and methods of their tuning. We evaluate the
width and the energy of domain walls as well as the period of stripe domains in
perpendicular films. The computed stripe width d = 1.1 um for
Ga_0.957Mn_0.043As/In_0.16Ga_0.84As compares favorably to the experimental
value 1.5 um, as determined by Shono et al. [Appl. Phys. Lett. 77, 1363
(2000)].",0107009v2
2001/8/1,Conformal lattice of magnetic bubble domains in garnet film,"We report experimental observations of magnetic bubble domain arrays with no
apparent translational symmetry. Additionally the results of comparative
numerical studies are discussed. Our goal is to present experimental evidence
for natural occurence of conformal structures.",0108009v1
2001/9/4,Spin-parity dependent tunneling of magnetization in single-molecule magnets,"Single-molecule magnets facilitate the study of quantum tunneling of
magnetization at the mesoscopic level. The spin-parity effect is among the
fundamental predictions that have yet to be clearly observed. It is predicted
that quantum tunneling is suppressed at zero transverse field if the total spin
of the magnetic system is half-integer (Kramers degeneracy) but is allowed in
integer spin systems. The Landau-Zener method is used to measure the tunnel
splitting as a function of transverse field. Spin-parity dependent tunneling is
established by comparing the transverse field dependence of the tunnel
splitting of integer and half-integer spin systems.",0109067v1
2001/11/19,A magnetization and $^{11}$B NMR study of Mg$_{1-x}$Al$_x$B$_2$ superconductors,"We demonstrate for the first time the magnetic field distribution of the pure
vortex state in lightly doped Mg$_{1-x}$Al$_x$B$_2$ ($x\leq 0.025$) powder
samples, by using $^{11}$B NMR in magnetic fields of 23.5 and 47 kOe. The
magnetic field distribution at T=5 K is Al-doping dependent, revealing a
considerable decrease of anisotropy in respect to pure MgB$_2$. This result
correlates nicely with magnetization measurements and is consistent with
$\sigma$-band hole driven superconductivity for MgB$_2$.",0111351v1
2001/12/19,Interesting magnetic properties of Fe$_{1-x}$Co$_x$Si alloys,"Solid solution between nonmagnetic narrow gap semiconductor FeSi and
diamagnetic semi-metal CoSi gives rise to interesting metallic alloys with
long-range helical magnetic ordering, for a wide range of intermediate
concentration. We report various interesting magnetic properties of these
alloys, including low temperature re-entrant spin-glass like behaviour and a
novel inverted magnetic hysteresis loop. Role of Dzyaloshinski-Moriya
interaction in the magnetic response of these non-centrosymmetric alloys is
discussed.",0112346v1
2002/1/15,Determining surface magnetization and local magnetic moments with atomic scale resolution,"We propose a method to determine the direction of surface magnetization and
local magnetic moments on the atomic scale. The method comprises high
resolution scanning tunneling microscope experiments in conjunction with first
principles simulations of the tunneling current. The potential of the method is
demonstrated on a model system, antiferromagnetic Mn overlayers on W(110). We
expect that it will ultimately allow to study the detailed changes of magnetic
surface structures in the vicinity of dopants or impurities.",0201241v1
2002/1/28,Magnetic Properties of the Novel Low-Dimensional Cuprate Na5RbCu4(AsO4)4Cl2,"The magnetic properties of a new compound, Na5RbCu4(AsO4)4Cl2 are reported.
The material has a layered structure comprised of square Cu4O4 tetramers. The
Cu ions are divalent and the system behaves as a low-dimensional S=1/2
antiferromagnet. Spin exchange in Na5RbCu4(AsO4)4Cl2 appears to be
quasi-two-dimensional and non-frustrated. Measurements of the bulk magnetic
susceptibility and heat capacity are consistent with low-dimensional magnetism.
The compound has an interesting, low-entropy, magnetic transition at T = 17 K.",0201522v2
2002/2/21,Interlayer Exchange Coupling in Semiconductor Magnetic/Nonmagnetic Superlattices,"The interlayer spin correlations in the magnetic/non-magnetic semiconductor
superlattices are reviewed. The experimental evidences of interlayer exchange
coupling in different all-semiconductor structures, based on neutronographic
and magnetic studies, are presented. A tight-binding model is used to explain
interaction transfer across the non-magnetic block without the assistance of
carriers in ferromagnetic EuS/PbS and antiferromagnetic EuTe/PbTe systems.",0202377v1
2002/3/4,Simulation of Magnetization Switching in Nanoparticle Systems,"Magnetization reversal in magnetic nanostructures is investigated numerically
over time-scales ranging from fast switching processes on a picosecond scale to
thermally activated reversal on a microsecond time-scale. A simulation of the
stochastic Landau-Lifshitz equation of motion is used as well as a time
quantified Monte Carlo method for the simulation of classical spin systems
modeling magnetic Co nanoparticles. For field pulses larger than the
Stoner-Wohlfarth limit spin precession effects govern the reversal behavior of
the particle while for lower fields a magnetization reversal is only possible
when it is assisted by thermal fluctuations.",0203054v1
2002/9/4,Correlation Effects on Magnetic Anisotropy in Fe and Ni,"We calculate magnetic anisotropy energy of Fe and Ni by taking into account
the effects of strong electronic correlations, spin-orbit coupling, and
non-collinearity of intra-atomic magnetization. The LDA+U method is used and
its equivalence to dynamical mean-field theory in the static limit is derived.
The effects of strong correlations are studied along several paths in $(U,J)$
parameter space. Both experimental magnitude of MAE and direction of
magnetization are predicted correctly near $U=1.9 eV$, $J=1.2 eV$ for Ni and
$U=1.2 eV$, $J=0.8 eV$ for Fe. The modified one-electron spectra by strong
correlations are emphasized in conjunction with magnetic anisotropy.",0209073v1
2002/9/25,Magnetic properties of Ni2.18Mn0.82Ga Heusler alloys with a coupled magnetostructural transition,"Polycrystalline Ni2.18Mn0.82Ga Heusler alloys with a coupled
magnetostructural transition are studied by differential scanning calorimetry,
magnetic and resistivity measurements. Coupling of the magnetic and structural
subsystems results in unusual magnetic features of the alloy. These uncommon
magnetic properties of Ni2.18Mn0.82Ga are attributed to the first-order
structural transition from a tetragonal ferromagnetic to a cubic paramagnetic
phase.",0209574v1
2002/11/28,Spin diffusion at finite electric and magnetic fields,"Spin transport properties at finite electric and magnetic fields are studied
by using the generalized semiclassical Boltzmann equation. It is found that the
spin diffusion equation for non-equilibrium spin density and spin currents
involves a number of length scales that explicitly depend on the electric and
magnetic fields. The set of macroscopic equations can be used to address a
broad range of the spin transport problems in magnetic multilayers as well as
in semiconductor heterostructure. A specific example of spin injection into
semiconductors at arbitrary electric and magnetic fields is illustrated.",0211674v1
2002/12/9,On the hyperfine interaction in rare-earth Van Vleck paramagnets at high magnetic fields,"An influence of high magnetic fields on hyperfine interaction in the
rare-earth ions with non-magnetic ground state (Van Vleck ions) is
theoretically investigated for the case of $Tm^{3+}$ ion in axial symmetrical
crystal electric field (ethylsulphate crystal). It is shown that magnetic-field
induced distortions of $4f$-electron shell lead to essential changes in
hyperfine magnetic field at the nucleus. The proposed theoretical model is in
agreement with recent experimental data.",0212171v1
2003/3/31,DFT calculation of the intermolecular exchange interaction in the magnetic Mn$_4$ dimer,"The dimeric form of the single-molecule magnet
[Mn$_4$O$_3$Cl$_4$(O$_2$CEt)$_3$(py)$_3$]$_2$ recently revealed interesting
phenomena: no quantum tunneling at zero field and tunneling before magnetic
field reversal. This is attributed to substantial antiferromagnetic exchange
interaction between different monomers. The intermolecular exchange
interaction, electronic structure and magnetic properties of this molecular
magnet are calculated using density-functional theory within
generalized-gradient approximation. Calculations are in good agreement with
experiment.",0303645v1
2003/8/15,Current-Driven Magnetization Dynamics in Magnetic Multilayers,"We develop a quantum analog of the classical spin-torque model for
current-driven magnetic dynamics. The current-driven magnetic excitation at
finite field becomes significantly incoherent. This excitation is described by
an effective magnetic temperature rather than a coherent precession as in the
spin-torque model. However, both the spin-torque and effective temperature
approximations give qualitatively similar switching diagrams in the
current-field coordinates, showing the need for detailed experiments to
establish the proper physical model for current-driven dynamics.",0308320v2
2003/10/22,Topological Hall effect and Berry phase in magnetic nanostructures,"We discuss the anomalous Hall effect in a two-dimensional electron gas
subject to a spatially varying magnetization. This topological Hall effect
(THE) does not require any spin-orbit coupling, and arises solely from Berry
phase acquired by an electron moving in a smoothly varying magnetization. We
propose an experiment with a structure containing 2D electrons or holes of
diluted magnetic semiconductor subject to the stray field of a lattice of
magnetic nanocylinders. The striking behavior predicted for such a system (of
which all relevant parameters are well known) allows to observe unambiguously
the THE and to distinguish it from other mechanisms.",0310522v1
2003/10/26,Double Rosensweig instability in a ferrofluid sandwich structure,"We consider a horizontal ferrofluid layer sandwiched between two layers of
immiscible non-magnetic fluids. In a sufficiently strong vertical magnetic
field the flat interfaces between magnetic and non-magnetic fluids become
unstable to the formation of peaks. We theoretically investigate the interplay
between these two instabilities for different combinations of the parameters of
the fluids and analyze the evolving interfacial patterns. We also estimate the
critical magnetic field strength at which thin layers disintegrate into an
ordered array of individual drops.",0310611v3
2003/11/20,Suppression of the Magnetic Phase Transition in Manganites Close to the Metal-Insulator Crossover,"We report the suppression of the magnetic phase transition in La1-xCaxMnO3
close to the localized-to-itinerant electronic transition, i.e. at x = 0.2 and
x = 0.5. A new crossover temperature Tf can be defined for these compositions
instead of TC. Unlike in common continuous magnetic phase transition the
susceptibility does not diverge at Tf and a spontaneous magnetization cannot be
defined below it. We propose that the proximity to the doping-induced
metal-insulator transition introduces a random field which breaks up the
electronic/magnetic homogeneity of the system and explains these effects.",0311476v1
2004/3/3,Current-Induced Nanomagnet Dynamics for Magnetic Fields Perpendicular to the Sample Plane,"We present electrical measurements of high-frequency magnetic dynamics
excited by spin-polarized currents in Co/Cu/Ni80Fe20 nanopillar devices, with a
magnetic field applied perpendicular to the sample layers. As a function of
current and magnetic field, the dynamical phase diagram contains several
distinguishable precessional modes and also static magnetic states. Using
detailed comparisons with numerical simulations, we provide rigorous tests of
the theory of spin-transfer torques.",0403100v1
2004/4/21,Reversible 300K Ferromagnetic Ordering in a Diluted Magnetic Semiconductor,"The discovery of reversible 300 K ferromagnetic ordering in a diluted
magnetic semiconductor is reported. Switching of room-temperature
ferromagnetism between ""on"" and ""off"" states is achieved in Co2+:ZnO by lattice
incorporation and removal of the native n-type defect, interstitial Zn.
Spectroscopic and magnetic data implicate a double-exchange mechanism for
ferromagnetism. These results demonstrate for the first time reversible
room-temperature ferromagnetic ordering in a diluted magnetic semiconductor,
and present new opportunities for integrating magnetism and conductivity in
semiconductor sensor or spin-based electronics devices.",0404518v1
2004/5/13,Precessional dynamics of elemental moments in a ferromagnetic alloy,"We demonstrate an element-specific measurement of magnetization precession in
a metallic ferromagnetic alloy, separating Ni and Fe moment motion in Ni81Fe19.
Pump-probe X-ray magnetic circular dichroism (XMCD), synchronized with short
magnetic field pulses, is used to measure free magnetization oscillations up to
2.6 GHz with elemental specificity and a rotational resolution of < 2 deg.
Magnetic moments residing on Ni sites and Fe sites in a Ni81Fe19(50nm) thin
film are found to precess together at all frequencies, coupled in phase within
instrumental resolution of 90 ps.",0405295v1
2004/5/22,"Oxygen stoichiometry, crystal structure, and magnetism in La$_{0.5}$Sr$_{0.5}$CoO$_{3-δ}$","We have prepared a series of polycrystalline samples
La$_{0.5}$Sr$_{0.5}$CoO$_{3-\delta}$} with $0 < \delta \le 0.21$ and
characterized their oxygen content, crystal structure, and magnetic properties.
While the fully oxygenated samples are good ferromagnets, samples with larger
$\delta$ values display increasingly broad magnetic transitions. The saturation
magnetization at 5 K falls rapidly as $\delta$ increases. First principles
electronic structure calculations provide insights into the magnetic behavior
of the fully oxygenated compound, and the manner in which ferromagnetic
ordering is affected by increasing oxygen non-stoichiometry.",0405535v2
2004/7/7,Roles of non-equilibrium conduction electrons on magnetization dynamics of ferromagnets,"The mutual dependence of spin-dependent conduction and magnetization dynamics
of ferromagnets provides the key mechanisms in various spin-dependent
phenomena. We compute the response of the conduction electron spins to a
spatial and time varying magnetization ${\bf M} ({\bf r},t)$ within the
time-dependent semiclassical transport theory. We show that the induced
non-equilibrium conduction spin density in turn generates four spin torques
acting on the magnetization--with each torque playing different roles in
magnetization dynamics. By comparing with recent theoretical models, we find
that one of these torques that has not been previously identified is crucial to
consistently interpret experimental data on domain wall motion.",0407174v2
2004/8/27,Tunable magnetization damping in transition metal ternary alloys,"We show that magnetization damping in Permalloy, Ni80Fe20 (``Py''), can be
enhanced sufficiently to reduce post-switching magnetization precession to an
acceptable level by alloying with the transition metal osmium (Os). The damping
increases monotonically upon raising the Os-concentration in Py, at least up to
9% of Os. Other effects of alloying with Os are suppression of magnetization
and enhancement of in-plane anisotropy. Magnetization damping also increases
significantly upon alloying with the five other transition metals included in
this study (4d-elements: Nb, Ru, Rh; 5d-elements: Ta, Pt) but never as strongly
as with Os.",0408608v1
2004/9/1,Mesoscopic quantized properties of magnetic-dipolar-mode oscillations in disk ferromagnetic particles,"Magnetic dipolar mode or magnetostatic (MS) oscillations in ferrite samples
have the wavelength much smaller than the electromagnetic wavelength at the
same frequency and, at the same time, much larger than the exchange interaction
spin wavelength. This intermediate position between the electromagnetic and
spin wave (exchange interaction) processes reveals very special behaviors of
the geometrical effects. It was shown recently that magnetic dipolar mode
oscillations in a normally magnetized ferromagnetic disk are characterized by
discrete energy levels resulting from the structural confinement. In this
article we give results of the energy spectra in MS wave ferrite disks taking
into account nonhomogeneity of the internal DC magnetic field.",0409023v1
2004/9/30,Scaling theory of magneto-resistance in disordered local moment ferromagnets,"We present a scaling theory of magneto-transport in Anderson-localized
disordered ferromagnets. Within our framework a pronounced
magnetic-field-sensitive resistance peak emerges naturally for temperatures
near the magnetic phase transition. We find that the resistance anomaly is a
direct consequence of the change in localization length caused by the magnetic
transition. For increasing values of the external magnetic field, the
resistance peak is gradually depleted and pushed towards higher temperatures.
Our results are in good agreement with magneto-resistance measurements on a
variety of disordered magnets.",0410003v2
2004/10/11,Superconducting Nanocomposites: Enhancement of Bulk Pinning and Improvement of Intergrain Coupling,"Heterogeneous sonochemical method was applied for synthesis of novel
superconducting nanocomposites consisting of magnetic (and/or nonmagnetic)
nanoparticles embedded into the bulk of ceramic superconductors. In addition to
in-situ production of the efficient pinning centers, this synthesis method
considerably improves the interbrain coupling. Significant enhancement of the
magnetic irreversibility is reported for Fe2O3 nanoparticles embedded into the
bulk of MgB2 superconductor. Nonmagnetic Mo2O5 nanoparticles also increase
pinning strength, but less than magnetic Fe2O3. Detailed magnetization and
electron microscopy characterization is presented. Theory of bulk magnetic
pinning due to ferromagnetic nanoparticles of finite size embedded into the
superconducting matrix is developed.",0410266v1
2004/10/12,Ab-initio prediction of a new multiferroic with large polarization and magnetization,"We describe the design of a new magnetic ferroelectric with large spontaneous
magnetization and polarization using first-principles density functional
theory. The usual difficulties associated with the production of
robustly-insulating ferromagnets are circumvented by incorporating the
magnetism through {\it ferri-}magnetic behavior. We show that the the ordered
perovskite \BFCO will have a polarization of $\sim$80 $\mu$C/cm$^2$, a
piezoelectric coefficient of 283 $\mu$C/cm$^{2}$, and a magnetization of
$\sim$160 emu/cm$^3$ (2 $\mu_B$ per formula unit), far exceeding the properties
of any known multiferroic.",0410268v1
2004/12/22,Magnetization-induced optical third-harmonic generation in Co and Fe nanostructures,"Magnetization-induced optical third-harmonic generation (MTHG) is observed in
magnetic nanostructures: Co and Fe nanolayers and granular films containing Co
nanoparticles. Magnetization-induced variations of the MTHG characteristics in
these nanostructures exceed the typical values of linear magneto-optical Kerr
effect by at least an order of magnitude: the maximum of magnetic contrast in
the MTHG intensity is up to 0.2, the angle of polarization rotation for MTHG is
10 deg. and the relative phase shift is up to 100 deg.",0412616v1
2005/2/8,Microwave spectroscopy on magnetization reversal dynamics of nanomagnets with electronic detection,"We demonstrate a detection method for microwave spectroscopy on magnetization
reversal dynamics of nanomagnets. Measurement of the nanomagnet anisotropic
magnetoresistance was used for probing how magnetization reversal is resonantly
enhanced by microwave magnetic fields. We used Co strips of 2 um x 130 nm x 40
nm, and microwave fields were applied via an on-chip coplanar wave guide. The
method was applied for demonstrating single domain-wall resonance, and studying
the role of resonant domain-wall dynamics in magnetization reversal.",0502197v2
2005/2/24,Tailoring Fe/Ag Superparamagnetic Composites by Multilayer Deposition,"The magnetic properties of Fe/Ag granular multilayers were examined by SQUID
magnetization and Mossbauer spectroscopy measurements. Very thin (0.2 nm)
discontinuous Fe layers show superparamagnetic properties that can be tailored
by the thickness of both the magnetic and the spacer layers. The role of
magnetic interactions was studied in novel heterostructures of
superparamagnetic and ferromagnetic layers and the specific contribution of the
ferromagnetic layers to the low field magnetic susceptibility was identified.",0502578v1
2005/5/13,Magnetization Reversal in Elongated Fe Nanoparticles,"Magnetization reversal of individual, isolated high-aspect-ratio Fe
nanoparticles with diameters comparable to the magnetic exchange length is
studied by high-sensitivity submicron Hall magnetometry. For a Fe nanoparticle
with diameter of 5 nm, the magnetization reversal is found to be an incoherent
process with localized nucleation assisted by thermal activation, even though
the particle has a single-domain static state. For a larger elongated Fe
nanoparticle with a diameter greater than 10 nm, the inhomogeneous magnetic
structure of the particle plays important role in the reversal process.",0505356v1
2005/5/24,"Magnetic scattering of spin polarized carriers in (In,Mn)Sb dilute magnetic semiconductor","Magnetoresistance measurements on the magnetic semiconductor (In,Mn)Sb
suggest that magnetic scattering in this material is dominated by isolated
Mn$^{2+}$ ions located outside the ferromagnetically-ordered regions when the
system is below $T_{c}$. A model is proposed, based on the $p$-$d$ exchange
between spin-polarized charge carriers and localized Mn$^{2+}$ ions, which
accounts for the observed behavior both below and above the ferromagnetic phase
transition. The suggested picture is further verified by high-pressure
experiments, in which the degree of magnetic interaction can be varied in a
controlled way.",0505582v1
2005/5/30,Dynamical Symmetry Breaking in Quasistatic Magnetic Oscillations,"Recent microwave experiments demonstrate the anapole-moment and
magnetoelectric properties in quasi-2D ferrite particles with
magnetic-dipolar-wave oscillating spectra. The theory developed in this paper
shows that there are the macroscopically quantum topological effects. Quantum
coherence for macroscopic systems refers to circumstances when large numbers of
particles can collectively cooperate in a single quantum state. These effects
are rarely observed through macroscopic measurements because statistical
averaging over many states usually masks all evidence of quantum discreteness.
Magnetic-dipolar oscillating modes in normally magnetized ferrite disks
demonstrate properties of a Hamiltonian system. The purpose of this paper is to
show that because of the adiabatic motion process for such a Hamiltonian system
one has macroscopic quantum effects of symmetry breaking, magnetic currents,
and eigen electric moments.",0505717v1
2005/8/23,Switching magnetization of nano-scale ferromagnetic particle using non-local spin injection,"We have performed non-local spin injection into a nano-scale ferromagnetic
particle configured in a lateral spin valve structure to switch its
magnetization only by spin current. The non-local spin injection aligns the
magnetization of the particle parallel to the magnetization of the spin
injector. The responsible spin current for switching is estimated from the
experiment to be about 200 $\mu$A, which is reasonable compared with the values
obtained for conventional pillar structures. Interestingly the switching always
occurs from anti-parallel to parallel in the particle/injector magnetic
configurations, whereas no opposite switching is observed. Possible reasons for
this discrepancy are discussed.",0508559v1
2005/9/12,Quantum nucleation in a single-chain magnet,"The field sweep rate (v=dH/dt) and temperature (T) dependence of the
magnetization reversal of a single-chain magnet (SCM) is studied at low
temperatures. As expected for a thermally activated process, the nucleation
field (H_n) increases with decreasing T and increasing v. The set of H_n(T,v)
data is analyzed with a model of thermally activated nucleation of
magnetization reversal. Below 1 K, H_n becomes temperature independent but
remains strongly sweep rate dependent. In this temperature range, the reversal
of the magnetization is induced by a quantum nucleation of a domain wall that
then propagates due to the applied field.",0509309v1
2005/9/22,Magnetism and half-metallicity at the O surfaces of ceramic oxides,"The occurence of spin-polarization at ZrO$_{2}$, Al$_{2}$O$_{3}$ and MgO
surfaces is proved by means of \textit{ab-initio} calculations within the
density functional theory. Large spin moments, as high as 1.56 $\mu_B$, develop
at O-ended polar terminations, transforming the non-magnetic insulator into a
half-metal. The magnetic moments mainly reside in the surface oxygen atoms and
their origin is related to the existence of $2p$ holes of well-defined spin
polarization at the valence band of the ionic oxide. The direct relation
between magnetization and local loss of donor charge makes possible to extend
the magnetization mechanism beyond surface properties.",0509578v1
2005/10/2,Giant Magneto-Oscillations of Electric-Field-Induced Spin Polarization in 2DEG,"We consider a disordered two-dimensional electron gas with spin-orbit
coupling placed in a perpendicular magnetic field and calculate the magnitude
and direction of the electric-field-induced spin polarization. We find that in
strong magnetic fields the polarization becomes an oscillatory function of the
magnetic field and that the amplitude of these oscillations is parametrically
larger than the polarization at zero magnetic field. We show that the enhanced
amplitude of the polarization is a consequence of strong electron-hole
asymmetry in a quantizing magnetic field.",0510024v1
2005/10/11,Non-damping magnetization oscillations in a single-domain ferromagnet,"Non-damped oscillations of the magnetization vector of a ferromagnetic system
subject to a spin polarized current and an external magnetic field are studied
theoretically by solving the Landau-Lifshitz-Gilbert equation. It is shown that
the frequency and amplitude of such oscillations can be controlled by means of
an applied magnetic field and a spin current. The possibility of injection of
the oscillating spin current into a non-magnetic system is also discussed.",0510280v1
2005/11/3,Step-like magnetization in a spin-chain system: Ca3Co2O6,"Due to a ferromagnetic in-chain coupling between Co$^{3+}$ ions at trigonal
sites, chains Co$_2$O$_6$ are considered as large rigid spin moments. The
antiferromagnetic Ising model on the triangular lattice is applied to describe
an interchain ordering. An evolution of metastable states in a sweeping
magnetic field is investigated by the single-flip technique. At the first
approximation two steps in the magnetization curve and a plateau at 1/3 of the
saturation magnetization are found. Four steps in magnetization are determined
in high-order approximations in agreement with experimental results.",0511087v1
2006/1/19,Magnetic field effect on the superconducting magnetic gap of Nd{1.85}Ce{0.15}CuO4,"Inelastic neutron scattering measurements on the archetypical electron-doped
material Nd{1.85}Ce{0.15}CuO4 up to high relative magnetic field strength,
H/Hc2 ~ 50%, reveal a simple linear magnetic-field effect on the
superconducting magnetic gap and the absence of field-induced in-gap states.
The extrapolated gap-closing field value is consistent with the upper critical
field Hc2, and the high-field response resembles that of the paramagnetic
normal state.",0601424v2
2006/3/13,Phase transitions in random magnetic bilayer,"The influence of random interlayer exchange on the phase states of the
simplest magnetic heterostructure consisting of two ferromagnetic Ising layers
with large interaction radius is studied. It is shown that such system can
exist in three magnetic phases: ferromagnetic, antiferromagnetic and
ferrimagnetic. The possible phase diagrams and temperature dependencies of
thermodynamic parameters are described. The regions of existence of the
magnetic phases in external magnetic field are determined at zero temperature.",0603347v3
2006/4/7,Dark States and Coherent Control of Spin States in Molecular Magnets,"We propose a scheme to realize coherent control of spin states of molecule
magnet, Ni$_4$. We introduce transverse magnetic fields with special
frequencies. When the frequencies of transverse magnetic fields match in some
conditions, we obtain dark states in Ni$_4$ molecules. Through adjusting the
magnitude of magnetic fields, we can obtain any arbitrary superposition of the
two ground spin states of Ni$_4$ molecules.",0604189v1
2006/6/14,Observation of magnetism in Au thin films,"Direct magnetization measurements of thin gold films are presented. These
measurements integrate the signal from the thin film under study and the
magnetic contribution of the film's interface with the substrate. The
diamagnetic contribution to the signal from the bulk substrate is of the same
order as the noise level. we find that thin gold films can exhibit positive
magnetization. The character of their magnetic behavior is strongly substrate
dependent.",0606375v1
2006/6/21,Current-excited magnetization dynamics in narrow ferromagnetic wires,"We investigate the current-excited magnetization dynamics in a narrow
ferromagnetic Permalloy wire by means of Lorentz microscopy, together with the
results of simultaneous transport measurements. A detailed structural evolution
of the magnetization is presented as a function of the applied current density.
Local structural deformation, bidirectional displacement, and magnetization
reversal are found below the Curie temperature with increasing the current
density. We discuss probable mechanisms of observed features of the
current-excited magnetization dynamics.",0606547v1
2006/9/1,Calculations of Magnetic Exchange Interactions in Mott--Hubbard Systems,"An efficient method to compute magnetic exchange interactions in systems with
strong correlations is introduced. It is based on a magnetic force theorem
which evaluates linear response due to rotations of magnetic moments and uses a
novel spectral density functional framework combining our exact diagonalization
based dynamical mean field and local density functional theories. Applications
to spin waves and magnetic transition temperatures of 3d metal mono--oxides as
well as high--T_{c} superconductors are in good agreement with experiment.",0609006v1
2006/10/31,Magnetic anisotropies of late transition metal atomic clusters,"We analyze the impact of the magnetic anisotropy on the geometric structure
and magnetic ordering of small atomic clusters of palladium, iridium, platinum
and gold, using Density Functional Theory. Our results highlight the absolute
need to include self-consistently the spin orbit interaction in any simulation
of the magnetic properties of small atomic clusters, and a complete lack of
universality in the magnetic anisotropy of small-sized atomic clusters.",0610879v2
2006/11/26,Strong magnetic scattering from TiO$_{x}$ adhesion layers,"Electronic phase coherence in normal metals is incredibly sensitive to
magnetic scattering. As a result, the weak localization magnetoresistance and
time-dependent universal conductance fluctuations are powerful probes of
magnetic impurities. We report measurements of these effects in Au and Ag
nanowires with a 1.5 nm thick Ti adhesion layer underneath the deposited metal.
The results indicate an anomalously large magnetic impurity concentration due
to the Ti layer. Results suggest that this magnetic scattering and its
evolution are related to the oxidation state of the Ti.",0611633v1
2006/12/1,Vortex motion in chilarity-controlled pair of magnetic disks,"We investigate the influence of the vortex chirality on the magnetization
processes of a magnetostatically coupled pair of magnetic disks. The magnetic
vortices with opposite chiralities are realized by introducing asymmetry into
the disks. The motion of the paired vortices are studied by measuring the
magnetoresistance with lock-in resistance bridge technique. The vortex
annihilation process is found to depend on the moving directions of the
magnetic vorticies. The experimental results are well reproduced by the
micromagnetic simulation.",0612023v1
2006/12/13,"Sampling the two-dimensional density of states g(E,M) of a giant magnetic molecule using the Wang-Landau method","The Wang-Landau method is used to study the magnetic properties of the giant
paramagnetic molecule Mo_72Fe_30 in which 30 Fe3+ ions are coupled via
antiferromagnetic exchange. The two-dimensional density of states g(E,M) in
energy and magnetization space is calculated using a self-adaptive version of
the Wang-Landau method. From g(E,M) the magnetization and magnetic
susceptibility can be calculated for any temperature and external field.",0612320v1
2007/2/21,Magnetic Anisotropy of Deposited Transition Metal Clusters,"We present results of magnetic torque calculations using the fully
relativistic spin-polarized Korringa-Kohn-Rostoker approach applied to small Co
and Fe clusters deposited on the Pt(111) surface. From the magnetic torque one
can derive among others the magnetic anisotropy energy (MAE). It was found that
this approach is numerically much more stable and also computationally less
demanding than using the magnetic force theorem that allows to calculate the
MAE directly. Although structural relaxation effects were not included our
results correspond reasonably well to recent experimental data.",0702483v1
2007/3/13,Effect of symmetry on the electronic structure of spheroidal fullerenes in a weak uniform magnetic field,"The effect of a weak uniform magnetic field on the electronic structure of
slightly deformed fullerene molecules is studied within the continuum
field-theory model. It is shown that fine structure of the electronic energy
spectrum is very sensitive to the orientation of the magnetic field. In
particular, we found that the magnetic field pointed in the x direction does
not influence the first electronic level whereas it causes a splitting of the
second energy level. This behavior differs markedly from the case of the
magnetic field pointed in the z direction.",0703336v1
2007/3/28,Crystalline electric fields and the magnetic ground state of the novel Heusler intermetallic YbRh$_{2}$Pb,"We have synthesized a new intermetallic compound with a distorted Heusler
structure, YbRh$_{2}$Pb. We present a study of the magnetic, thermal, and
transport properties. Heat capacity measurements revealed that YbRh$_{2}$Pb
orders magnetically below T$_{N}$=0.57 K from a paramagnetic state with
substantial crystal electric field splitting. Magnetic field further splits the
ground state, which leads to the suppression of magnetic order in YbRh$_{2}$Pb.",0703765v2
2007/6/18,Magnetic Excitations in NpCoGa5,"We report the results of inelastic neutron scattering experiments on
NpCoGa$_{5}$, an isostructural analogue of the PuCoGa$_{5}$ superconductor. Two
energy scales characterize the magnetic response in the antiferromagnetic
phase. One is related to a non-dispersive excitation between two crystal field
levels. The other at lower energies corresponds to dispersive fluctuations
emanating from the magnetic zone center. The fluctuations persist in the
paramagnetic phase also, although weaker in intensity. This supports the
possibility that magnetic fluctuations are present in PuCoGa$_{5}$, where
unconventional d-wave superconductivity is achieved in the absence of magnetic
order.",0706.2524v1
2007/8/17,Observation of Ferromagnetic Clusters in Bi0.125Ca0.875MnO3,"The electron doped manganite system, Bi0.125Ca0.875MnO3, exhibits large bulk
magnetization of unknown origin. To select amongst possible magnetic ordering
models, we have conducted temperature and magnetic field dependent small-angle
neutron scattering measurements. Nontrivial spin structure has been revealed.
Ferromagnetic spin clusters form in the antiferromagnetic background when
temperature is decreased to Tc~108K. With a further reduction in temperature or
the application of external magnetic field, the clusters begin to form in
larger numbers, which gives an overall enhancement of magnetization below Tc.",0708.2300v1
2007/9/6,The formation and ordering of local magnetic moments in Fe-Al alloys,"With density functional theory, studied are the local magnetic moments in
Fe-Al alloys depending on concentration and Fe nearest environment. At zero
temperature, the system can be in different states: ferromagnetic,
antiferromagnetic and spin-spiral waves (SSW) which has a minimum energy. Both
SSW and negative moment of Fe atoms with many Al atoms around them agree with
experiments. Magnetization curves taken from literature are analysed.
Assumption on percolation character of size distribution of magnetic clusters
describes well the experimental superparamagnetic behaviour above 150 K.",0709.0793v1
2007/10/30,Angular dependence of coercivity in magnetic nanotubes,"The nucleation field for infinite magnetic nanotubes, in the case of a
magnetic field applied parallel to the long axis of the tubes, is calculated as
a function of their geometric parameters and compared with those produced
inside the pores of anodic alumina membranes by atomic layer deposition. We
also extended this result to the case of an angular dependence. We observed a
transition from curling-mode rotation to coherent-mode rotation as a function
of the angle in which the external magnetic field is applied. Finally, we
observed that the internal radii of the tubes favors the magnetization curling
reversal.",0710.5710v1
2007/11/5,Magnetization easy-axis in martensitic Heusler alloys estimated by strain measurements under magnetic-field,"We study the temperature dependence of strain under constant magnetic-fields
in Ni-Mn based ferromagnetic Heusler alloys in the form Ni-Mn-$X$ ($X$: Ga, In,
Sn, Sb) which undergo a martensitic transformation. We discuss the influence of
the applied magnetic-field on the nucleation of ferromagnetic martensite and
extract information on the easy-axis of magnetization in the martensitic state.",0711.0639v1
2007/12/7,"Magnetocaloric effect in R2Ti3Ge4 (R = Gd, Tb and Er) Compounds","Heat capacity of polycrystalline R2Ti3Ge4 (R = Gd, Tb and Er) compounds
(Orthorhombic, Sm5Ge4-type, Space group Pnma) has been studied in the
temperature range of 1.8 K to 300 K in various applied magnetic fields. The
compounds with magnetic lanthanide elements show interesting low field
magnetism intrigued by possible presence of competing antiferromagnetic and
ferromagnetic interactions. The magnetocaloric effect in these compounds is
estimated from the field dependent heat capacity data. The magnetic entropy
change and the adiabatic temperature change in the vicinity of the magnetic
transition are found to be significant.",0712.1095v1
2008/1/23,Effects of Intrinsic Spin-Relaxation in Molecular Magnets on Current-Induced Magnetic Switching,"Current-induced magnetic switching of a single magnetic molecule attached to
two ferromagnetic contacts is considered theoretically, with the main emphasis
put on the role of intrinsic spin relaxation processes. It is shown that
spin-polarized current can switch magnetic moment of the molecule, despite of
the intrinsic spin relaxation in the molecule. The latter processes increase
the threshold voltage (current) above which the switching takes place.",0801.3655v1
2008/2/6,The Suppression and Recovery of the Ferroelectric Phase in Multiferroic $MnWO_4$,"We report the discovery of a complete suppression of ferroelectricity in
$MnWO_4$ by 10 % iron substitution and its restoration in external magnetic
fields. The spontaneous polarization in $Mn_{0.9}Fe_{0.1}WO_4$ arises below 12
K in external fields above 4 T. The magnetic/ferroelectric phase diagram is
constructed from the anomalies of the dielectric constant, polarization,
magnetization, and heat capacity. The observations are qualitatively described
by a mean field model with competing interactions and strong anisotropy. We
propose that the magnetic field induces a non-collinear inversion symmetry
breaking magnetic structure in $Mn_{0.9}Fe_{0.1}WO_4$.",0802.0839v1
2008/2/15,Magnetocapacitive La0.6Sr0.4MnO3 0.7Pb(Mg0.33Nb0.67)O3 0.3PbTiO3 epitaxial heterostructures,"Epitaxial heterostructures of La0.6Sr0.4MnO3 0.7Pb(Mg0.33Nb0.67)O3 0.3PbTiO3
were fabricated on LaNiO3 coated LaAlO3 (100) substrates by pulsed laser
ablation. Ferromagnetic and ferroelectric hysteresis established their
biferroic nature. Dielectric behviour studied under different magnetic fields
over a wide range of frequency and temperatures revealed that the capacitance
in these heterostructures varies with the applied magnetic field. Appearance of
magnetocapacitance and its dependence on magnetic fields, magnetic layer
thickness, temperature and frequency indicated a combined contribution of
strain mediated magnetoelectric coupling, magnetoresistance of the magnetic
layer and Maxwell Wagner effect on the observed properties.",0802.2141v2
2008/3/13,Magnetic states and spin-glass properties in Bi0.67Ca0.33MnO3: macroscopic ac measurements and neutron scattering,"We report on the magnetic properties of the manganite Bi_{1-x}Ca_{x}MnO_3
(x=0.33) at low temperature. The analysis of the field expansion of the ac
susceptibility and the observation of aging properties make clear that a spin
glass phase appears below T = 39K, in the presence of magnetic order. Neutron
scattering shows both magnetic Bragg scattering and magnetic diffusion at small
angles, and confirms this coexistence. In contrast to Pr_{1-x}Ca_{x}MnO_3
(x=0.3-0.33) which exhibits a mesoscopic phase separation responsible for a
field driven percolation, the glassy and short range ferromagnetic order
observed here does not cause colossal magnetoresistance (CMR).",0803.2016v1
2008/3/24,Nonvolatile Static Random Access Memory (NV-SRAM) Using Magnetic Tunnel Junctions with Current-Induced Magnetization Switching Architecture,"We propose and computationally analyze a nonvolatile static random access
memory (NV-SRAM) cell using magnetic tunnel junctions (MTJs) with
magnetic-field-free current-induced magnetization switching (CIMS)
architecture. A pair of MTJs connected to the storage nodes of a standard SRAM
cell with CIMS architecture enables fully electrical store and restore
operations for nonvolatile logic information. The proposed NV-SRAM is expected
to be a key component of next-generation power-gating logic systems with
extremely low static-power dissipation.",0803.3370v2
2008/4/18,The nature of Ho magnetism in multiferroic HoMnO3,"Using x-ray resonant magnetic scattering and x-ray magnetic circular
dichroism, techniques that are element specific, we have elucidated the role of
Ho3+ in multiferroic HoMnO3. In zero field, Ho3+ orders antiferromagnetically
with moments aligned along the hexagonal c direction below 40 K, and undergoes
a transition to another magnetic structure below 4.5 K. In applied electric
fields of up to 1x10^7 V/m, the magnetic structure of Ho3+ remains unchanged.",0804.2921v1
2008/4/22,Effects of current on nanoscale ring-shaped magnetic tunnel junctions,"We report the observation and micromagnetic analysis of current-driven
magnetization switching in nanoscale ring-shaped magnetic tunnel junctions.
When the electric current density exceeds a critical value of the order of
$6\times 10^{6}$A/cm$^2$, the magnetization of the two magnetic rings can be
switched back and forth between parallel and antiparallel onion states.
Theoretical analysis and micromagnetic simulation show that the dominant
mechanism for the observed current-driven switching is the spin torque rather
than the current-induced circular Oersted field.",0804.3524v1
2008/5/2,Spatial characterization of the magnetic field profile of a probe tip used in magnetic resonance force microscopy,"We have developed the experimental approach to characterize spatial
distribution of the magnetic field produced by cantilever tips used in magnetic
resonance force microscopy (MRFM). We performed MRFM measurements on a well
characterized diphenyl-picrylhydrazyl (DPPH) film and mapped the 3D field
profile produced by a Nd2Fe14B probe tip. Using our technique field profiles of
arbitrarily shaped probe magnets can be imaged.",0805.0243v1
2008/5/5,Tuning of energy levels and optical properties of graphene quantum dots,"We investigate theoretically the magnetic levels and optical properties of
zigzag- and armchair-edged hexagonal graphene quantum dots (GQDs) utilizing the
tight-binding method. A new bound edge state at zero energy appears for the
zigzag GQDs in the absence of a magnetic field. The magnetic levels of GQDs
exhibit a Hofstadter-butterfly spectrum and approach the Landau levels of
two-dimensional graphene as the magnetic field increases. The optical
properties are tuned by the size, the type of the edge, and the external
magnetic field.",0805.0454v1
2008/6/25,A Neutron diffraction study of multiferroics RMn2O5,"The magnetic properties of RMn2O5 multiferrroics as obtained by unpolarized
and polarized neutron diffraction experiments are reviewed. We discuss the
qualitative features of the magnetic phase diagram both in zero magnetic field
and in field and analyze the commensurate magnetic structure and its coupling
to an applied electric field. The origin of ferrolectricity is discussed based
on calculations of the ferroelectric polarization predicted by different
microscopic coupling mechanisms (exchange striction and cycloidal spin-orbit
models). A minimal model containing a small set of parameters is also presented
in order to understand the propagation of the magnetic structure along the
c-direction.",0806.4128v1
2008/8/20,Conditions for the spin-spiral state in itinerant magnets,"The spin-spiral (SS) type of magnetization is studied with the Hubbard model.
Consideration of noncollinearity of the magnetic moments results in a phase
diagram which consists of regions of the SS and paramagnetic states depending
on the number of electrons and the parameter U/t (U is the Hubbard repulsion,
and t is an overlap integral). A possibility of stabilization of the SS state
with three nonzero components of magnetic moment is considered.",0808.2768v1
2008/8/26,Magnetic anisotropy and reversal in epitaxial Fe/MgO(001) films revisited,"We investigate the magnetization reversal in Fe/MgO(001) films with fourfold
in-plane magnetic anisotropy and an additional uniaxial anisotropy whose
orientation and strength are tuned using different growth geometries and post
growth treatments. The previously adopted mechanism of 180^{o} domain wall
nucleation clearly fails to explain the observed 180^{o} magnetization
reversal. A new reversal mechanism with two successive domain wall nucleations
consistently predicts the switching fields for all field orientations. Our
results are relevant for a correct interpretation of magnetization reversal in
many other epitaxial metallic and semiconducting thin films.",0808.3543v2
2008/9/24,Structure and Magnetism in Mn Doped Zirconia: Density-functional Theory Studies,"Using the first-principles density-functional theory plan-wave
pseudopotential method, we investigate the structure and magnetism in 25% Mn
substitutive and interstitial doped monoclinic, tetragonal and cubic ZrO2
systematically. Our studies show that the introduction of Mn impurities into
ZrO2 not only stabilizes the high temperature phase, but also endows ZrO2 with
magnetism. Based on the simple crystal field theory (CFT), we discuss the
origination of magnetism in Mn doped ZrO2. Moreover, we discuss the effect of
electron donor on magnetic semiconductors, and the possibility as electronic
structure modulator.",0809.4127v2
2008/12/2,Independent magnetization behavior of a ferromagnetic metal/semiconductor hybrid system,"We report the discovery of an effect where two ferromagnetic materials, one
semiconductor ((Ga,Mn)As) and one metal (permalloy), can be directly deposited
on each other and still switch their magnetization independently. We use this
independent magnetization behavior to create various resistance states
dependent on the magnetization direction of the individual layers. At zero
magnetic field a two layer device can reach up to four non-volatile resistance
states.",0812.0455v1
2008/12/30,Magnetically tunable rf wave absorption in polycrystalline La0.67Ba0.33MnO3,"We investigated temperature and magnetic field dependent radio-frequency
electromagnetic absorption in La0.67Ba0.33MnO3 by monitoring changes in
resonance frequency (fr) and current (II) through a LC resonant circuit powered
by an integrated chip oscillator. The ferromagnetic to paramagnetic transition
at Tc in zero external magnetic field is accompanied by an abrupt increase in
fr and I and they are tunable by small external magnetic field. We observed
fractional changes as much as 46% in delfr/fr and 23% in delI/I around Tc under
H = 0.1 T that can be exploited for low magnetic field sensors and other
applications.",0812.5000v1
2009/1/5,Excess specific heat and evidence of zero point entropy in magnetic glassy state of half-doped manganites,"We show that specific heat C$_p$ has non-Debye behavior for glassy states in
half-doped manganites. Irrespective of the magnetic order or electronic states,
these magnetic glasses have higher C$_p$ compared to their equilibrium
counterparts. The excess C$_p$ contributed by the glassy state varies linearly
with temperature similar to conventional glasses indicating tunneling in the
two-level systems. These glassy states show signature of zero point entropy.
Magnetic glasses can be produced simply by different field cooling protocols
and may be considered ideal magnetic counterpart of the conventional glass.",0901.0432v2
2009/2/22,Athermal All-Optical Femtosecond Magnetization Reversal in GdFeCo,"Magnetization reversal in GdFeCo by circularly polarized light is shown to
occur at the femtosecond time scale. In contrast to the well known
laser-assisted magnetization reversal based on the laser heating, we here
demonstrate that this femtosecond all-optical magnetization reversal is more
efficient at lower temperatures. The lower the temperatures, the smaller the
laser fluence required for the switching. This switching is in agreement with a
more recent theoretical prediction $[ \text{Phys. Lett. A \textbf{372}, 1915
(2008)} ] $ and demonstrates the feasibility of the femtosecond athermal
magnetization reversal.",0902.3800v1
2009/2/25,Electron doping and magnetic moment formation in N- and C-doped MgO,"The formation of the magnetic moment in C- and N-doped MgO is the result of a
delicate interplay between Hund's coupling, hybridization and Jahn-Teller
distortion. The balance depends on a number of environmental variables
including electron doping. We investigate such a dependence by self-interaction
corrected density functional theory and we find that the moment formation is
robust with respect to electron doping. In contrast, the local symmetry around
the dopant is more fragile and two different geometries can be stabilized.
Crucially the magnetic moment is always extremely localized, making any carrier
mediated picture of magnetism in d^0 magnets unlikely.",0902.4471v2
2009/3/10,Amplification of the induced ferromagnetism in diluted magnetic semiconductor,"Magnetic properties of the planar structure consisting of a ferromagnetic
metal and the diluted magnetic semiconductor are considered (by the example of
the structure Fe/Ga(Mn)As, experimentally studied in [F. Maccherozzi, e.a.,
Phys. Rev. Lett., 101, 267201 (2008)]). In the framework of the mean field
theory, we demonstrate the presence of the significant amplification of the
ferromagnetism, induced by the ferromagnetic metal in the near-interface
semiconductor area, due to the indirect interaction of magnetic impurities.
This results in the substantial expansion of the temperature range where the
magnetization in the boundary semiconductor region exists, that might be
important for possible practical applications.",0903.1726v1
2009/3/12,Self-organized patterns of macroscopic quantum tunneling in molecular magnets,"We study low temperature resonant spin tunneling in molecular magnets induced
by a field sweep with account of dipole-dipole interactions. Numerical
simulations uncovered formation of self-organized patterns of the magnetization
and of the ensuing dipolar field that provide resonant condition inside a
finite volume of the crystal. This effect is robust with respect to disorder
and should be relevant to the dynamics of the magnetization steps observed in
molecular magnets.",0903.2247v1
2009/4/17,Variation of T$_g$ with magnetic field in a magnetic glass,"Glass-like arrest has recently been reported in various magnetic materials.
As in structural glasses, the kinetics of a first-order transformation is
arrested while retaining the higher-entropy phase as a non-ergodic state. We
show visual mesoscopic evidence of the irreversible devitrification of the
arrested antiferromagnetic-insulating phase in
$Pr_{0.5}Ca_{0.5}Mn_{0.975}Al_{0.025}O_3$ to its equilibrium
ferromagnetic-metallic phase with isothermal increase of magnetic field,
similar to its iso-field devitrification on warming. The slope of $T_g$ vs
magnetic field in half-doped manganites is shown to have a sign governed by Le
Chatelier's Principle.",0904.2635v1
2009/4/17,Electronic properties of superconducting Sr4V2Fe2As2O6 versus Sr4Sc2Fe2As2O6,"First principle FLAPW-GGA calculations have been performed with the purpose
to understand the peculiarities of band structure and Fermi surface topology
for recently discovered superconductor: Sr4V2Fe2As2O - in comparison with
isostructural phase Sr4Sc2Fe2As2O6. Our main finding is that the replacement of
Sc on vanadium leads to drastic transformation of electronic, magnetic and
conductive properties of these materials: as against non-magnetic
Sr4Sc2Fe2As2O6 which is formed from non-magnetic conducting [Fe2As2] and
insulating [Sr4Sc2O6] blocks, Sr4V2Fe2As2O6 consists from non-magnetic
conducting [Fe2As2] blocks and [Sr4V2O6] blocks which exhibit magnetic
half-metallic properties.",0904.2671v1
2009/4/24,"Itinerant magnetic multipole moments of rank five, triakontadipoles, as the hidden order in URu$_{2}$Si$_{2}$","A broken symmetry ground state without any magnetic moments has been
calculated by means of local-density-approximation to density functional theory
plus a local exchange term, the so-called LDA+$U$ approach, for
URu$_{2}$Si$_{2}$. The solution is analysed in terms of a multipole tensor
expansion of the itinerant density matrix and is found to be a non-trivial
magnetic multipole. Analysis and further calculations show that this type of
multipole enters naturally in time reversal breaking in presence of large
effective spin-orbit coupling and co-exists with magnetic moments for most
magnetic actinides",0904.3883v1
2009/6/4,Structures and magnetic properties of ZnO nanoislands,"Using first-principles calculations, we systematically study the atomic
structures and electronic properties for two dimensional triangular ZnO
nanoislands that are graphite-like with monolayer and bilayer thickness. We
find that the monolayer ZnO nanoisland with O terminated zigzag edges is
magnetic at its ground state, with the magnetism coming from the O edge states.
The other monolayer and bilayer ZnO nanoislands with different edge structures
are all nonmagnetic at their ground states. It is further revealed that for
different ZnO nanoislands, their magnetic properties are quite dependent on
their sizes, with larger nanoislands having larger magnetic moments.",0906.0813v2
2009/10/9,Suppression of electron relaxation and dephasing rates in quantum dots caused by external magnetic fields,"An external magnetic field has been applied in laterally coupled dots (QDs)
and we have studied the QD properties related to charge decoherence. The
significance of the applied magnetic field to the suppression of
electron-phonon relaxation and dephasing rates has been explored. The coupled
QDs have been studied by varing the magnetic field and the interdot distance as
other system parameters. Our numerical results show that the electron
scattering rates are strongly dependent on the applied external magnetic field
and the details of the double QD configuration.",0910.1696v1
2009/10/19,Magnetic bubbles in FePd thin films near saturation,"The structure of domain walls delimiting magnetic bubbles in L10 FePd thin
layers is described on the basis of Lorentz transmission electron microscopy
(LTEM) and multiscale magnetic simulations. Images obtained by high resolution
LTEM show the existence of magnetization reversal areas inside domain walls,
called vertical Bloch lines (VBLs). Combining these observations and multiscale
simulations on various geometries, we can identify the structure of these VBLs,
notably the presence or not of magnetic singularities.",0910.3551v1
2009/11/30,Magnetization reversal in amorphous Fe/Dy multilayers: a Monte Carlo study,"The Monte Carlo method in the canonical ensemble is used to investigate
magnetization reversal in amorphous transition metal - rare earth multilayers.
Our study is based on a model containing diluted clusters which exhibit an
effective uniaxial anisotropy in competition with random magnetic anisotropy in
the matrix. We simulate hysteresis loops for an abrupt profile and a diffuse
one obtained from atom probe tomography analyses. Our results evidence that the
atom probe tomography profile favors perpendicular magnetic anisotropy in
agreement with magnetic measurements. Moreover, the hysteresis loops calculated
at several temperatures qualitatively agree with the experimental ones.",0911.5653v1
2009/12/7,Vector magnetic field microscopy using nitrogen vacancy centers in diamond,"The localized spin triplet ground state of a nitrogen vacancy (NV) center in
diamond can be used in atomic-scale detection of local magnetic fields. Here we
present a technique using these defects in diamond to image fields around
magnetic structures. We extract the local magnetic field vector by probing
resonant transitions of the four fixed tetrahedral NV orientations. In
combination with confocal microscopy techniques, we construct a 2-dimensional
image of the local magnetic field vectors. Measurements are done in external
fields less than 50 G and under ambient conditions.",0912.1355v1
2009/12/29,"Synthesis, characterization and magnetic properties of room-temperature nanofluid ferromagnetic graphite","We report the chemical synthesis route, structural characterization, and
physical properties of nanofluid magnetic graphite (NFMG) obtained from the
previously synthesized bulk organic magnetic graphite (MG) by stabilizing the
aqueous ferrofluid suspension with an addition of active cationic surfactant.
The measured magnetization-field hysteresis curves along with the temperature
dependence of magnetization confirmed room-temperature ferromagnetism in both
MG and NFMG samples.",0912.5344v1
2010/3/17,Calculated Magnetic and Electronic Properties of Pyrochlore Iridates,"Using density functional theory and LDA+U method, we investigate magnetic and
electronic structure of Y$_{2}$Ir$_{2}$O$_{7}$ and rare-earth based pyrochlore
iridates. Our study reveals that the ground state is a non-collinear magnetic
insulating state. Due to strong spin-orbit coupling in Ir 5\textit{d}, there is
an unusual correlation between the bands near Fermi level and the magnetization
direction, resulting in a possibility of insulator-to-metal transition under
applied magnetic field. This makes pyrochlore iridates a good candidate for
possible magnetoressitance and magnetooptical applications.",1003.3414v1
2010/5/13,Graphene spin capacitor for magnetic field sensing,"An analysis of a novel magnetic field sensor based on a graphene spin
capacitor is presented. The proposed device consists of graphene nanoribbons on
top of an insulator material connected to a ferromagnetic source/drain. The
time evolution of spin polarized electrons injected into the capacitor can be
used for an accurate determination at room temperature of external magnetic
fields. Assuming a spin relaxation time of 100 ns, magnetic fields on the order
of $\sim 10$ mOe may be detected at room temperature. The observational
accuracy of this device depends on the density of magnetic defects and spin
relaxation time that can be achieved.",1005.2423v1
2010/6/1,Geometric signature of reversal modes in ferromagnetic nanowires,"Magnetic nanowires are a good platform to study fundamental processes in
Magnetism and have many attractive applications in recording such as
perpendicular storage and in spintronics such as non-volatile magnetic memory
devices (MRAM) and magnetic logic devices. In this work, nanowires are used to
study magnetization reversal processes through a novel geometric approach.
Reversal modes imprint a definite signature on a parametric curve representing
the locus of the critical switching field. We show how the different modes
affect the geometry of this curve depending on the nature of the anisotropy
(uniaxial or cubic anisotropy), demagnetization and exchange effects. The
samples we use are electrochemically grown Nickel and Cobalt nanowires.",1006.0105v1
2010/6/30,New magnetic phase in rb3c60 fullerene in normal state observed in torque experiments,"For the first time, magnetic properties of fullerides have been studied using
a torque technique. Rb3C60 single crystal has been investigated in these
experiments. It was shown that this method is sensitive to the structural phase
transition from s.c. to f.c.c. structure. A rearrangement of magnetic system in
this material was observed at temperature T ~ 200 - 250 K. Our results clearly
show, that this effect is a crossover to an ordered magnetic phase related to
interaction of magnetic dipoles and is related to the distorted T' site. The
effect is discussed in terms of cooperative Jahn-Teller effect.",1006.5817v1
2010/10/28,Theory of magnetic switching of ferroelectricity in spiral magnets,"We propose a microscopic theory for magnetic switching of electric
polarization (P) in the spin-spiral multiferroics by taking TbMnO3 and DyMnO3
as examples. We reproduce their phase diagrams under a magnetic field H_ex by
Monte-Carlo simulation of an accurate spin model and reveal that competition
among the Dzyaloshinskii-Moriya interaction, spin anisotropy, and spin exchange
is controlled by the applied H_ex, resulting in magnetic transitions
accompanied by reorientation or vanishing of P. We also discuss the relevance
of the proposed mechanisms to many other multiferroics such as LiCu2O2, MnWO4,
and Ni3V2O4",1010.5970v1
2010/11/16,Magnetic field dependence of pairing interaction in ferromagnetic superconductors with triplet pairing,"It is developed a microscopic description of superconductivity in
ferromagnetic materials with triplet pairing triggered by the exchange of
magnetic fluctuations. Instead widely used paramagnon model we work with
phenomenological spectrum of fluctuations in the orthorhombic ferromagnet with
strong magnetic anisotropy. Depending of the field orientation parallel or
perpendicular to the direction of spontaneous magnetization the effective
amplitude of pairing interaction proves to be decreasing or increasing function
of magnetic field that allows to explain the drastic difference in magnitudes
of upper critical field in these directions.",1011.3753v1
2011/2/26,Superparamagnetism induced by polar nanoregions in relaxor ferroelectric (1$-$$x$)BiFeO$_{3}$-$x$BaTiO$_{3}$,"A new class of superparamagnetism was found in relaxor ferroelectric
2/3BiFeO$_{3}$-1/3BaTiO$_{3}$. The size of the magnetic particle, estimated
from the superparamagnetic magnetization curve, coincides with the size of the
polar nanoregion (PNR), which governs the relaxor ferroelectric property. This
suggests that the magnetic domain is identical to the PNR. The temperature
variations in the sizes of the magnetic domains and PNRs estimated by our
neutron diffraction measurements support this picture. Since the same domain
provides both electric and magnetic properties, strong coupling between the two
properties through the domain size is expected.",1102.5383v1
2011/4/15,Weak ferromagnetism of antiferromagnetic domains in graphene with defects,"Magnetic properties of graphene with randomly distributed magnetic
defects/vacancies are studied in terms of the Kondo Hamiltonian in the mean
field approximation. It has been shown that graphene with defects undergoes a
magnetic phase transition from a paramagnetic to a antiferromagnetic (AFM)
phase once the temperature reaches the critical point $T_{N}$. The defect
straggling is taken into account as an assignable cause of multiple nucleation
into AFM domains. Since each domain is characterized by partial compensating
magnetization of the defects associated with different sublattices, together
they reveal a super-paramagnetic behavior in a magnetic field. Theory
qualitatively describe the experimental data provided the temperature
dependence of the AFM domain structure.",1104.3101v1
2011/5/1,Possible magnetic states in buckybowl molecules,"Possible magnetic properties are studied in the buckybowl molecules: the
sumanene and a part of C_60. The Hubbard model is applied to the systems. We
find that the molecular structure determines the magnetism in the sumanene. On
the other hand, the edge state is found along the zigzag edge of a part of
C_60. Therefore, the novel property, transition from molecular magnetism to the
magnetism like in nanographene, is found.",1105.0145v3
2011/6/7,Magnetostatic fields in tubular nanostructures,"The non-uniform magnetostatic field produced by the equilibrium and non
equilibrium magnetic states of magnetic nanotubes has been investigated
theoretically. We consider magnetic fields produced by actual equilibrium
states and transverse and vortex domain walls confined within the
nanostructure. Our calculations allow us to understand the importance of the
magnetostatic field in nanomagnetism, which is frequently considered as a
uniform field. Moreover, our results can be used as a basis for future research
of others properties, such as the investigation of spin waves when domain walls
are present, or the motion of a magnetic particle near a magnetic field.",1106.1461v1
2011/6/10,Stress controlled magnetic properties of Cobalt nanowires,"We investigate the magnetic properties of a composite comprising of
ferromagnetic Cobalt nanowires embedded in nanoporous anodized alumina
template. We observe unusual increase in, the saturation magnetization and the
coercive field, of the nanowires below 100 K. We also report the appearance of
an unusual exchange bias effect in nanowires below 100 K. We argue our results
can be understood on the basis of a competition between different magnetic
energy scales induced by significant stresses acting on the nanowires at low
temperatures. The composite behaves as an effective medium in which the
magnetic anisotropy of nanowires can be conveniently controlled via stress on
the nanowires.",1106.1965v1
2011/6/13,Magnetostatic bias in multilayer microwires: theory and experiments,"The hysteresis curves of multilayer microwires consisting of a soft magnetic
nucleus, intermediate non-magnetic layers, and an external hard magnetic layer
are investigated. The magnetostatic interaction between magnetic layers is
proved to give rise to an antiferromagnetic-like coupling resulting in a
magnetostatic bias in the hysteresis curves of the soft nucleus. This
magnetostatic biasing effect is investigated in terms of the microwire
geometry. The experimental results are interpreted considering an analytical
model taking into account the magnetostatic interaction between the magnetic
layers.",1106.2366v1
2011/6/17,Current effect on magnetization oscillations in a ferromagnet - antiferromagnet junction,"Spin-polarized current effect is studied on the static and dynamic
magnetization of the antiferromagnet in a ferromagnet - antiferromagnet
junction. The macrospin approximation is generalized to antiferromagnets.
Canted antiferromagnetic configuration and resulting magnetic moment are
induced by an external magnetic field. The resonance frequency and damping are
calculated, as well as the threshold current density corresponding to
instability appearance. A possibility is shown of generating low-damping
magnetization oscillations in terahertz range. The fluctuation effect is
discussed on the canted antiferromagnetic configuration.",1106.3519v1
2011/7/13,Magnetism of cobalt nanoclusters on graphene on iridium,"The structure and magnetic properties of Co clusters, comprising from 26 to
2700 atoms, self-organized or not on the graphene/Ir(111) moir\'e, were studied
in situ with the help of scanning tunneling microscopy and X-ray magnetic
circular dichroism. Surprisingly the small clusters have almost no magnetic
anisotropy. We find indication for a magnetic coupling between the clusters.
Experiments have to be performed carefully so as to avoid cluster damage by the
soft X-rays.",1107.2571v1
2011/8/16,"All-optical four-state magnetization reversal in (Ga,Mn)As ferromagnetic semiconductors","Using density matrix equations of motion and a tight-binding band
calculation, we predict all-optical switching between four metastable magnetic
states of (III,Mn)As ferromagnets. This switching is initiated non-thermally
within 100fs, during nonlinear coherent photoexcitation. For a single optical
pulse, magnetization reversal is completed after $\sim$100 ps and controlled by
the coherent femtosecond photoexcitation. Our predicted switching comes from
magnetic nonlinearities triggered by a femtosecond magnetization tilt that is
sensitive to un--adiabatic light--induced spin interactions.",1108.3193v1
2011/12/15,Large magnetodielectric response in Pr0.6Ca0.4MnO3/ polyvinylidene fluoride nanocomposites,"We have studied the magnetic field effect on low frequency dielectric
properties of Pr0.6Ca0.4MnO3/polyvinylidene fluoride nanocomposite with 22.5%
volume fraction of Pr0.6Ca0.4MnO3 nanoparticles. A strong magnetodielectric
response was observed below 120 K where Pr0.6Ca0.4MnO3 nanoparticles show the
magnetic phase transition indicating a direct correlation between magnetism and
dielectric properties. A large change of the dielectric permittivity ~ 30% has
been observed in a magnetic field of 4.6 T with loss as low as 0.17 at 70 K.
The observed magnetodielectric response has been attributed to the decrement of
polaron activation barrier of Pr0.6Ca0.4MnO3 nanoparticles with the increase of
magnetic field.",1112.3579v1
2012/1/19,Measurement of the coupling between applied stress and magnetism in a manganite thin film,"We measured the magnetization depth profile of a (La1-xPrx)1-yCayMnO3 (x =
0.60\pm0.04, y = 0.20\pm0.03) film as a function of applied bending stress
using polarized neutron reflectometry. From these measurements we obtained a
coupling coefficient relating strain to the depth dependent magnetization. We
found application of compressive (tensile) bending stress along the magnetic
easy axis increases (decreases) the magnetization of the film.",1201.4001v1
2012/1/25,Evolution of Magnetic Glass on Partial Crystallization of a Bulk Metallic Glass: Tb36Sm20Al24Co20,"A comparative study on as cast and annealed rare earth bulk metallic glass
(BMG) with composition Tb36Sm20Al24Co20 has been carried out by magnetization
measurements. The as cast amorphous sample shows non-ergodic magnetization but
does not show the behavior expected from magnetic glass. After annealing, the
partially crystallized BMG shows this magnetic glass behavior. This is
confirmed by the established measurement protocol of cooling and heating in
unequal fields (CHUF).",1201.5255v1
2012/3/25,Magnetic and quantum entanglement properties of the distorted diamond chain model for azurite,"We present the results of magnetic properties and entanglement of the
distorted diamond chain model for azurite using pure quantum exchange
interactions. The magnetic properties and concurrence as a measure of pairwise
thermal entanglement have been studied by means of variational mean-field like
treatment based on Gibbs-Bogoliubov inequality. Such a system can be considered
as an approximation of the natural material azurite, Cu3(CO3)2(OH)2. For values
of exchange parameters, which are taken from experimental results, we study the
thermodynamic properties, such as azurite specific heat and magnetic
susceptibility. We also have studied the thermal entanglement properties and
magnetization plateau of the distorted diamond chain model for azurite.",1203.5518v1
2012/5/24,High Performance Calculation of Magnetic Properties and Simulation of Nonequilibrium Phenomena in nanofilms,"Images of surface topography of ultrathin magnetic films have been used for
Monte Carlo simulations in the framework of the ferromagnetic Ising model to
study the hysteresis and thermal properties of nanomaterials. For high
performance calculations was used super-scalable parallel algorithm for the
finding of the equilibrium configuration. The changing of a distribution of
spins on the surface during the reversal of the magnetization and the dynamics
of nanodomain structure of thin magnetic films under the influence of changing
external magnetic field was investigated.",1205.5588v1
2012/7/13,Abnormal Magnetic Behaviors in Unique Square alpha-MnO2 Nanotubes,"Systematic magnetic measurements have been performed in unique$\alpha -
MnO_2$ square nanotubes synthesized by a facile hydrothermal method with
microwave-assisted procedures. Unusual magnetic phenomena (abnormal
magnetization verse temperature (M - T) behaviour, large and abnormal
magnetization hysteresis loop horizontal shift (HHS) verse cooling field (HFC)
behaviours (HHS - HFC) has been observed in these square nanotubes. These
suggest the observation of large unfrozen orbital moment which also is the
micro -original of observed large and abnormal horizontal shift (HHS). The
findings demonstrated that engineering layered structures in nanoscale would
create many unique nanostructures and unusual physicochemical behaviours.",1207.3350v1
2012/8/3,Oscillatory tilt effect in a metal in a weak magnetic field,"The oscillatory tilt effect in a normal metal at external magnetic field is
discovered. The oscillatory tilt effect is characterized by the oscillations of
ultrasound attenuation in a metal at external magnetic field as predicted in
[1]. The dimension of the non-central cross-section of the Fermi surface and
the velocity of electrons in a high pure Gallium single crystal at external
magnetic field are found. At the low frequencies of ultrasonic signal, the
""inverse"" oscillatory tilt effect in a high pure Gallium single crystal at the
external magnetic field is observed.",1208.0724v1
2012/8/17,Observation of magnetocapacitance in ferromagnetic nanowires,"The authors have investigated magnetic domain wall induced capacitance
variation as a tool for the detection of magnetic reversal in magnetic
nanowires for in-plane (NiFe) and out-of-plane (Co/Pd) magnetization
configurations. The switching fields in the capacitance measurements match with
that of the magnetoresistance measurements in the opposite sense. The origin of
the magnetocapacitance has been attributed to magnetoresistance. This
magnetocapacitance detection technique can be useful for magnetic domain wall
studies.",1208.3526v1
2013/2/19,Slater-Pauling behavior in half-metallic magnets,"We review the appearance of Slater-Pauling rules in half-metallic magnets.
These rules have been derived using ab-initio electronic structure calculations
and directly connect the electronic properties (existence of minority-spin
energy gap) to the magnetic properties (total spin magnetic moment) in these
compounds. Their exact formulation depends on the half-metallic family under
study and they can be easily derived if the hybridization of the orbitals at
various sites is taken into account.",1302.4699v1
2013/3/28,Thermally assisted current-induced magnetization reversal in SrRuO3,"We inject a sequence of 1 ms current pulses into uniformly magnetized
patterns of the itinerant ferromagnet SrRuO3 until a magnetization reversal is
detected. We detect the effective temperature during the pulse and find that
the cumulative pulse time required to induce magnetization reversal depends
exponentially on 1/T. In addition, we find that the cumulative pulse time also
depends exponentially on the current amplitude. These observations indicate
current-induced magnetization reversal assisted by thermal fluctuations.",1303.7067v1
2013/4/5,Magnetic properties of double exchange biased diluted magnetic alloy/ferromagnet/antiferromagnet trilayers,"The magnetic properties of trilayers consisting of a diluted magnetic alloy,
CuMn (Cu0.99Mn0.01), a soft ferromagnet, Py(Ni0.8Fe0.2), and an
antiferromagnet, alpha-Fe2O3, were investigated. The samples, grown by UHV
magnetron sputtering, were magnetically characterized in the temperature range
T = 3-100 K. Typical exchange bias features, namely clear hysteresis cycle
shifts and coercivity enhancements, were observed. Moreover the presence of an
inverse bias, which had been already reported for spin glass-based structures,
was also obtained in a well defined range of temperatures and CuMn thicknesses.",1304.1707v1
2013/5/21,Switching of a single ferromagnetic layer driven by spin Hall effect,"The magnetization switching of a thin ferromagnetic layer placed on top of a
heavy metal (such as Pt, Ta or W) driven by an in-plane current has been
observed in recent experiments. The magnetization dynamics of these processes
is studied in a full micromagnetic framework which takes into account the
transfer-torque from spin Hall effect due to the spin-orbit coupling.
Simulations indicate that the reversal occurs via nucleation of complex
magnetization patterns. In particular, magnetic bubbles appear during the
reversal of the magnetization in the perpendicular configuration while for the
in-plane configuration, nucleation of vortexes are observed.",1305.4806v1
2013/7/2,"Density Functional Theory Study of the Entangled Crystal, Magnetic, and Electronic Structures of PuGa3","Systematically studying the crystal, magnetic, and electronic structures of
PuGa3 with density functional theory (DFT) reveals the entanglement of the
three types of structure. Magnetic structure affects the energy more strongly
than crystal structure. For DFT to correctly order the crystal structures in
agreement with experiment requires special treatment of the electronic
correlation in the 5f states, exemplified here by the GGA+U approach. The upper
and lower Hubbard bands change with increasing U in very dissimilar ways for
the two most different crystal structures. The results suggest the
effectiveness of using magnetic structure to simulate correlation effects in
the actinides depends on both the magnetic and the crystal structure.",1307.0762v1
2013/7/10,Current Leads for Superconducting Magnets of ADS Injector I,"In ADS Injector I, there are six superconducting magnets in each cryomodule.
Each superconducting magnet contains a solenoid magnet, a horizontal dipole
corrector (HDC) and a vertical dipole corrector (VDC). Six current leads will
be required for powering the electrical circuits, from room temperature to the
2.1K liquid helium bath. Two leads carry 100A current for the solenoid magnet
while the other four carry 12A for the HDC and the VDC. This paper presents the
principle for current lead optimization, which includes the cooling methods,
the choice of material and structure, and the issues for current lead
integration as well.",1307.2731v1
2013/8/1,Control of magnetization reversal in oriented Strontium Ferrite thin films,"Oriented Strontium Ferrite films with the c axis orientation were deposited
with varying oxygen partial pressure on Al2O3(0001) substrate using PLD
technique. The angle dependent magnetic hysteresis, remanent coercivity and
temperature dependent coercivity had been employed to understand the
magnetization reversal of these films. It was found that the Strontium Ferrite
thin film grown at lower (higher) oxygen partial pressure shows
Stoner-Wohlfarth type (Kondorsky like) reversal. The relative importance of
pinning and nucleation processes during magnetization reversal is used to
explain the type of the magnetization reversal with different oxygen partial
pressure during growth.",1308.0171v1
2013/10/25,Spontaneous tensor properties for multiferroic phases,"We have constructed dichromatic matrices of property coefficients for all
1601 Aizu species. This involves 122 non-magnetic Aizu species and extends the
work to the 773 species of phase transitions from disordered magnetic
prototypic (parent) phases and the 616 species from ordered magnetic prototypic
phases. In addition to coefficients describing the non-magnetic effects we have
included the coefficients of pyromagnetic, magnetoelectric, piezomagnetic
effects, and magnetic susceptibility. All components of these property tensors
are displayed in 13 by 13 matrices; non-zero components of the prototypic phase
are given in black and the spontaneous coefficients, that are non-zero in the
ferroic phase and zero in the prototypic phase, are given in red.",1310.7824v1
2013/10/30,Spin torque ferromagnetic resonance with magnetic field modulation,"We demonstrate a technique of broadband spin torque ferromagnetic resonance
(ST-FMR) with magnetic field modulation for measurements of spin wave
properties in magnetic nanostructures. This technique gives great improvement
in sensitivity over the conventional ST-FMR measurements, and application of
this technique to nanoscale magnetic tunnel junctions (MTJs) reveals a rich
spectrum of standing spin wave eigenmodes. Comparison of the ST-FMR
measurements with micromagnetic simulations of the spin wave spectrum allows us
to explain the character of low-frequency magnetic excitations in nanoscale
MTJs.",1310.7996v1
2013/10/30,Investigation of MoS2 and Graphene Nanosheets by Magnetic Force Microscopy,"For the first time, the magnetic force microscopy (MFM) is used to
characterize the mechanically-exfoliated single- and few-layer MoS2 and
graphene nanosheets. By analysis of the phase and amplitude shifts, the
magnetic response of MoS2 and graphene nanosheets exhibits the dependence on
their layer number. However, the solution-processed single-layer MoS2 nanosheet
shows the reverse magnetic signal to the mechanically-exfoliated one, and the
graphene oxide nanosheet has not shown any detectable magnetic signal.
Importantly, graphene and MoS2 flakes become nonmagnetic when they exceed a
certain thickness.",1310.8172v1
2014/2/3,Magnetism and Magnetic Anisotropy of Transition Metal-Phthalocyanine Molecules,"Search for single-molecule magnets (SMMs) with high blocking temperature (TB)
is urgent for practical applications in magnetic recording, molecular
spintronics and quantum computing. Based on the First-principles calculations,
magnetic anisotropy energies (MAE) of the transition metal-Phthalocyanine
(TM-Pc) molecules are investigated and the mechanism that determines the MAE of
TM-Pc molecules is established. In particular, colossal MAE > 100 meV can be
obtained by adding an Os atom on RuPc and OsPc, so these molecules may offer
ultrahigh thermal stability in devices.",1402.0278v1
2014/2/5,Non-collinear magnetism induced by frustration in transition-metal nanostructures deposited on surfaces,"How does magnetism behave when the physical dimension is reduced to the size
of nanostructures? The multiplicity of magnetic states in these systems can be
very rich, in that their properties depend on the atomic species, the cluster
size, shape and symmetry or choice of the substrate. Small variations of the
cluster parameters may change the properties dramatically. Research in this
field has gained much by the many novel experimental methods and techniques
exhibiting atomic resolution. Here I review the ab-initio approach, focusing on
recent calculations on magnetic frustration and occurrence of non-collinear
magnetism in antiferromagnetic nanostructures deposited on surfaces.",1402.1163v1
2014/3/3,Magnetic entropy change and critical exponents in double perovskite Y2NiMnO6,"We report on the magnetic entropy change and the critical exponents in the
double perovskite manganite Y2NiMnO6 with a ferromagnetic to paramagnetic
transition TC=85K. For a magnetic field change of 80kOe, a maximum magnetic
entropy change -6.57 J /kg K is recorded around TC. The corresponding relative
cooling power (134 J / kg) is appreciable towards potential application as a
magnetic refrigerant. The critical exponents, beta and gamma satisfy well to
values derived for a 3D Heisenberg ferromagnet.",1403.0453v1
2014/3/4,Low-temperature magnetism in the honeycomb systems SrLn2O4,"Recent progress in the understanding of the complex magnetic properties of
the family of rare-earth strontium oxides, SrLn2O4, is reviewed. These
compounds consisting of hexagons and triangles are affected by geometrical
frustration and therefore exhibit its characteristic features, such as a
significant reduction of magnetic ordering temperatures and complex phase
diagrams in an applied field. Some of the observed features appear to be rather
remarkable even in the context of the unusual behavior associated with
geometrically frustrated magnetic systems. Of particular interest is the
coexistence at the lowest temperature of different magnetic structures
(exhibiting either long or short-range order) characterized by different
propagation vectors in materials without significant chemical or structural
disorder.",1403.0877v1
2014/3/10,Magnetic compensation phenomenon by Nd doping in spin surplus Sm based ferromagnetic intermetallic SmScGe,"The magnetization compensation phenomenon is observed for Sm1-xNdxScGe at x =
0.09 at a temperature near 90 K in a small applied magnetic field, which
establishes the spin surplus status of magnetic moment of Sm in the host
matrix. We also noted that the sample profiles in QD SQUID magnetometer become
asymmetric in some situations indicating significant contributions from
multiple moments higher than the dipole moment. We have successfully accounted
for them using a fitting procedure involving the higher order magnetic moments.",1403.2359v1
2014/3/14,Magnetic Phases and Specific Heat of Ultra-Thin Holmium Films,"We report model calculations of the magnetic phases of very thin Ho films in
the temperature interval between 20K and 132K, and show that slab size, surface
effects and magnetic field due to spin ordering may impact significantly the
magnetic phase diagram. There is a relevant reduction of the external field
strength required to saturate the magnetization and for ultra-thin films the
helical state does not form. We explore the heat capacity and the
susceptibility as auxiliary tools to discuss the nature of the phase
transitions.",1403.3589v1
2014/3/26,Driving ferromagnets into a critical region of a magnetic phase diagram,"Exciting a ferromagnetic sample with an ultrashort laser pulse leads to a
quenching of the magne- tization on a subpicosecond timescale. On the basis of
the equilibration of intensive thermodynamic variables we establish a powerful
model to describe the demagnetization dynamics. We demonstrate that the
magnetization dynamics is mainly driven by the equilibration of chemical
potentials. The minimum of magnetization is revealed as a transient electronic
equilibrium state. Our method iden- tifies the slowing down of ultrafast
magnetization dynamics by a critical region within a magnetic phase diagram.",1403.6885v2
2014/6/16,Applications of exchange coupled bi-magnetic hard/soft and soft/hard magnetic core/shell nanoparticles,"The applications of exchange coupled bi-magnetic hard/soft and soft/hard
ferromagnetic core/shell nanoparticles are reviewed. After a brief description
of the main synthesis approaches and the core/shell structural-morphological
characterization, the basic static and dynamic magnetic properties are
presented. Five different types of perspective applications, based on diverse
patents and research articles, are described: permanent magnets, recording
media, microwave absorption, biomedical applications and other applications.
Both the advantages of the core/shell morphology and some of the remaining
challenges are discussed.",1406.3966v2
2014/6/24,Atomistic calculation of the thickness and temperature dependence of exchange coupling through a dilute magnetic oxide,"The exchange coupling of two magnetic layers via a diffuse oxide interlayer
is studied with an atomistic spin model. We investigate the effect of magnetic
concentration and oxide layer thickness on the effective exchange coupling
strength and find an exponential dependence of the coupling strength on the
oxide thickness without the need for magnetic pinholes. Furthermore we show
that exchange coupling has a strong temperature dependence which is significant
for the reversal dynamics during heat assisted magnetic recording.",1406.6214v1
2014/7/24,"Change in the magnetic structure of (Bi,Sm)FeO3 thin films at the morphotropic phase boundary probed by neutron diffraction","We report on the evolution of the magnetic structure of BiFeO3 thin films
grown on SrTiO3 substrates as a function of Sm doping. We determined the
magnetic structure using neutron diffraction. We found that as Sm increases,
the magnetic structure evolves from a cycloid to a G-type antiferromagnet at
the morphotropic phase boundary, where there is a large piezoelectric response
due to an electric-field induced structural transition. The occurrence of the
magnetic structural transition at the morphotropic phase boundary offers
another route towards room temperature multiferroic devices.",1407.6418v1
2014/8/27,Room temperature multiferroicity in orthorhombic LuFeO$_3$,"From the measurement of dielectric, ferroelectric, and magnetic properties we
observe simultaneous ferroelectric and magnetic transitions around $\sim$600 K
in orthorhombic LuFeO$_3$. We also observe suppression of the remanent
polarization by $\sim$95\% under a magnetic field of $\sim$15 kOe at room
temperature. The extent of suppression of the polarization under magnetic field
increases monotonically with the field. These results show that even the
orthorhombic LuFeO$_3$ is a room temperature multiferroic of type-II variety
exhibiting quite a strong coupling between magnetization and polarization.",1408.6392v1
2014/9/15,Ferroelectric Control of Magnetism and Transport in Oxide Heterostructures,"Magnetism and transport are two key functional ingredients in modern
electronic devices. In oxide heterostructures, ferroelectricity can provide a
new route to control these two properties via electrical operations, which is
scientifically interesting and technologically important. In this Brief Review,
we will introduce recent progresses on this fast developing research field.
Several subtopics will be covered. First, the ferroelectric polarization tuning
of interfacial magnetism will be introduced, which includes the tuning of
magnetization, easy axis, magnetic phases, as well as exchange bias. Second,
the ferroelectric polarization tuning of transverse and tunneling transport
will be reviewed.",1409.4125v1
2014/9/16,"Magnetisms in $p$-type monolayer gallium chalcogenides (GaSe, GaS)","Magnetisms in $p$-type monolayer GaX (X=S,Se) is investigated by performing
density-functional calculations. Due to the large density of states near the
valence band edge, these monolayer semiconductors are ferromagnetic within a
small range of hole doping. The intrinsic Ga vacancies can promote local
magnetic moment while Se vacancies cannot. Magnetic coupling between
vacancy-induced local moments is ferromagnetic and surprisingly long-range. The
results indicate that magnetization can be induced by hole doping and can be
tuned by controlled defect generation.",1409.4733v2
2014/11/10,Magnetism of sigma-phase Fe-Mo alloys: its revealing and characterization,"A low-temperature magnetism was revealed in a series of sigma-Fe(100-x)Mo(x)
alloys (x=45-53). Its characterization has been done using vibrating sample
magnetometry, M\""ossbauer spectroscopy, and ac magnetic susceptibility. The
magnetic ordering temperature was determined to lie in the range of 46 K for
x=45 and 22K for x=53, and the ground magnetic state was found to be typical of
a spin-glass.",1411.2446v1
2015/1/17,Magnetic and Magnetocaloric Study of the Ferromagnetically Coupled GdF3: The Best Cryogenic Magnetic Coolant Ever,"The magnetic susceptibility and isothermal magnetization for GdF3 were
measured, and the isothermal entropy change was evaluated up to 9 T. Combining
the large isotropic spin of Gd3+, the dense structure and the weak
ferromagnetic interaction, an extremely large -(delta)Sm for GdF3 was observed
up to 528 mJ cm-3 K-1 for (delta)H = 9 T, proving itself to be the best
cryogenic magnetic coolant ever.",1501.04180v1
2015/1/24,Magnetic Coupling in Ferromagnetic Semiconductor GaMnAs/AlGaMnAs Bilayer Devices,"We carefully investigated the ferromagnetic coupling in the as-grown and
annealed ferromagnetic semiconductor GaMnAs/AlGaMnAs bilayer devices. We
observed that the magnetic interaction between the two layers strongly affects
the magnetoresistance of the GaMnAs layer with applying out of plane magnetic
field. After low temperature annealing, the magnetic easy axis of the AlGaMnAs
layer switches from out of plane into in-plane and the interlayer coupling
efficiency is reduced from up to 0.6 to less than 0.4. However, the magnetic
coupling penetration depth for the annealed device is twice that of the
as-grown bilayer device.",1501.05993v1
2015/7/2,Coexistence of incommensurate magnetism and superconductivity in the two-dimensional Hubbard model,"We analyze the competition of magnetism and superconductivity in the
two-dimensional Hubbard model with a moderate interaction strength, including
the possibility of incommensurate spiral magnetic order. Using an unbiased
renormalization group approach, we compute magnetic and superconducting order
parameters in the ground state. In addition to previously established regions
of Neel order coexisting with d-wave superconductivity, the calculations reveal
further coexistence regions where superconductivity is accompanied by
incommensurate magnetic order.",1507.00560v2
2015/9/9,Inertial terms to magnetization dynamics in ferromagnetic thin films,"Inertial magnetization dynamics have been predicted at ultrahigh speeds, or
frequencies approaching the energy relaxation scale of electrons, in
ferromagnetic metals. Here we identify inertial terms to magnetization dynamics
in thin Ni$_{79}$Fe$_{21}$ and Co films near room temperature. Effective
magnetic fields measured in high-frequency ferromagnetic resonance (115-345
GHz) show an additional stiffening term which is quadratic in frequency and
$\sim$ 80 mT at the high frequency limit of our experiment. Our results extend
understanding of magnetization dynamics at sub-picosecond time scales.",1509.02836v1
2015/9/11,Finite temperature magnetism of FeRh compounds,"The temperature dependent stability of the magnetic phases of FeRh were
investigated by means of total energy calculations with magnetic disorder
treated within the uncompensated disordered local moment (uDLM) approach. In
addition, Monte Carlo simulations based on the extended Heisenberg model have
been performed, using exchange coupling parameters obtained rom first
principles. The crucial role and interplay of two factors in the metamagnetic
transition in FeRh has been revealed, namely the dependence of the Fe-Fe
exchange coupling parameters on the temperature-governed degree of magnetic
disorder in the system and the stabilizing nature of the induced magnetic
moment on Rh-sites. An important observation is the temperature dependence of
these two competing factors.",1509.03581v1
2015/9/29,Structural and Magnetic Characterization of Ni2MnBO5 ludwigite,"Single crystals of ludwigite Ni2MnBO5 were synthesized by flux growth
technique. The detailed structural and magnetic characterizations of the
synthesized samples have been carried out. The cations composition of the
studied crystal was determined using X-ray diffraction and EXAFS technique, the
resulting composition is differ from the content of the initial Mn2O3 - CuO
components of flux. Magnetic susceptibility measurements and the calculations
of the exchange integrals in frameworks of indirect coupling model revealed
strong antiferromagnetic interactions and appearance of magnetic ordering phase
at the temperature T=85 K. The hypothesis of the existence of several magnetic
subsystems was supposed.",1509.08656v1
2016/2/1,Universal transport and resonant current from chiral magnetic effect,"For relativistic Weyl fermions in 3+1 dimensions, an electric current
proportional to the external magnetic field is predicted. This remarkable
phenomenon is called Chiral Magnetic Effect (CME). Here we show that actual
transports in Weyl semimetals supporting CME cannot be discussed without proper
consideration of the law of electromagnetism. First, even in the absence of an
external magnetic field, CME leads to a material-independent, universal
effective capacitance. Moreover, the induced current by a time-dependent
external magnetic field can be resonantly enhanced reflecting a formation of
electromagnetic standing waves.",1602.00687v1
2016/2/26,Microscopic mechanism of the giant magnetocaloric effect in MnCoGe alloys probed by XMCD,"One important aspect of the magneto-structural transition in MnCoGe and
related materials is the reduction in saturation magnetization from the
orthorhombic to the hexagonal phase. Here, by combining an element specific
magnetization probe such as x-ray magnetic circular dichroism and band
structure calculations, we show that the magnetic moment instability between
orthorhombic and hexagonal structures originates from a reduction in the Mn
sub-lattice magnetization. The consequences of the moment instability for the
magnetocaloric effect are discussed.",1602.08263v1
2016/7/25,Spin-orbit-coupling-induced magnetic heterostructure in the bilayer Bose-Hubbard system,"We investigate magnetic phase in the bilayer system of ultra-cold bosons in
an optical lattice, which is involved with Raman-induced spin-orbit (SO)
coupling and laser-assisted interlayer tunneling. It is shown that there exit a
rich of spin textures such as hetero ferromagnet, heterochiral magnet, chiral
magnet with interlayer antiferromagnet. In particular, heterochiral magnet
induced by SO coupling occurs extremely rarely in real solid-state materials.
We present detailed experimental setup of realizing such a model in cold atom
system.",1607.07336v1
2017/1/8,Separate magnetization switching of hexagonal Co/BN/Co junctions grown epitaxially on c-sapphire,"Magnetic tunnel junctions (MTJ) have been grown by using molecular beam
epitaxy on c-plane Al2O3 substrates. The MTJ stacks consist of two
ferromagnetic hcp-Co layers separated by a thin insulating h-BN barrier. The
samples have been grown in a single run revealing single crystalline epitaxial
structures with sharp interfaces as observed by applying transmission electron
microscopy. The in-plane magnetization experiments have revealed separate
magnetization switching of a thin top Co (soft) layer and a thick bottom Co
(hard) layer. At zero magnetic field the two Co layers are found in an
antiparallel state.",1701.02027v1
2017/2/8,Temperature-dependent phonon spectra of magnetic random solid solutions,"A first-principles-based method for computing phonons of magnetic random
solid solutions including thermal magnetic fluctuations is developed. The
method takes fluctuations of force constants (FCs) due to magnetic excitations
as well as due to chemical disorder into account. The developed approach
correctly predicts the experimentally observed unusual phonon hardening of a
transverse acoustic mode in Fe-Pd an Fe-Pt Invar alloys with increasing
temperature. This peculiar behavior, which cannot be explained within a
conventional, harmonic picture, turns out to be a consequence of thermal
magnetic fluctuations.",1702.02389v1
2017/8/29,Prediction of a new efficient permanent magnet SmCoNiFe3,"We propose a new efficient permanent magnet, SmCoNiFe3, that is a
breakthrough development of the well-known SmCo5 prototype. More modern
neodymium magnets of the Nd-Fe-B type have an advantage over SmCo5 because of
their greater maximum energy products due to their iron-rich stoichiometry. Our
new magnet, however, removes most of this disadvantage of SmCo5 while
preserving its superior high-temperature efficiency over the neodymium magnets.",1708.08957v1
2017/11/8,Plasmon-induced demagnetization and magnetic switching in nickel nanoparticle arrays,"We report on the manipulation of magnetization by femtosecond laser pulses in
a periodic array of cylindrical nickel nanoparticles. By performing experiments
at different wavelength, we show that the excitation of collective surface
plasmon resonances triggers demagnetization in zero field or magnetic switching
in a small perpendicular field. Both magnetic effects are explained by
plasmon-induced heating of the nickel nanoparticles to their Curie temperature.
Model calculations confirm the strong correlation between the excitation of
surface plasmon modes and laser-induced changes in magnetization.",1711.02943v1
2018/6/17,Hopfions in chiral magnets,"A magnetic Hopfion is a three-dimensional topological soliton that consists
of a closed loop of a twisted magnetic Skyrmion string. The results of
numerical simulations are presented that demonstrate the existence of a stable
Hopfion in a nanocylinder of a chiral magnet and an explicit analytic
expression is shown to provide a reasonable approximation to the numerically
computed Hopfion. A mechanism is suggested to create the Hopfion from a target
Skyrmion by introducing an interfacial perpendicular magnetic anisotropy.",1806.06458v2
2019/6/2,Intermediate statistics in the Landau diamagnetism problem,"In the present study we investigate how the magnetization and other
thermodynamic quantities in the Landau diamagnetism problem depend on the
deforming parameter of two model developing intermediate statistics:
$q$-fermions and F-anyons (F-type systems). An important observation in the
present study is the fact that for F-anyons statistics the magnetization shows
a more strong response with respect to magnetic fields in relation to
magnetization for $q$-fermions statistics in the same range of field. This may
be verified experimentally, for instance, in superconductors which are perfect
diamagnetic materials with strong magnetic susceptibility, by adjusting
impurities or pressure if one assumes that the deforming parameter relates with
such tuning quantities.",1906.00340v1
2012/11/19,Magnetic anisotropy of La0.7Sr0.3MnO3 nanopowders,"The magnetic anisotropy of La0.7Sr0.3MnO3 nanopowders was measured as a
function of temperature by the modified singular point detection technique. In
this method singularities indicating the anisotropy field were determined
analyzing ac susceptibility data. The observed relationship between temperature
dependence of anisotropy constant and temperature dependence of magnetization
was used to deduce the origin of magnetic anisotropy in the nanopowders. It was
shown that magnetic anisotropy of La0.7Sr0.3MnO3 nanopowder is determined by
two-ion (dipolar or pseudodipolar) and single-ion mechanisms.",1211.4355v1
2017/6/1,Anomalous Magnetism for Dirac Electrons in Two Dimensional Rashba Systems,"Spin-spin correlation function response in the low electronic density regime
and externally applied electric field is evaluated for 2D metallic crystals
under Rashba-type coupling, fixed number of particles and two-fold energy band
structure. Intrinsic Zeeman-like effect on electron spin polarization, density
of states, Fermi surface topology and transverse magnetic susceptibility are
analyzed in the zero temperature limit. A possible magnetic state for Dirac
electrons depending on the zero field band gap magnitude under this conditions
is found.",1706.00277v2
2017/6/19,Chiral and Topological Orbital Magnetism of Spin Textures,"Using a semiclassical Green's function formalism, we discover the emergence
of chiral and topological orbital magnetism in two-dimensional chiral spin
textures by explicitly finding the corrections to the orbital magnetization,
proportional to the powers of the gradients of the texture. We show that in the
absence of spin-orbit coupling, the resulting orbital moment can be understood
as the electronic response to the emergent magnetic field associated with the
real-space Berry curvature. By referring to the Rashba model, we demonstrate
that by tuning the parameters of surface systems the engineering of emergent
orbital magnetism in spin textures can pave the way to novel concepts in
orbitronics.",1706.06068v1
2018/8/20,Stacking-Dependent Magnetism in Bilayer CrI$_3$,"We report the connection between the stacking order and magnetic properties
of bilayer CrI$_3$ using first-principles calculations. We show that the
stacking order defines the magnetic ground state. By changing the interlayer
stacking order one can tune the interlayer exchange interaction between
antiferromagnetic and ferromagnetic. To measure the predicted
stacking-dependent magnetism, we propose using linear magnetoelectric effect.
Our results not only gives a possible explanation for the observed
antiferromagnetism in bilayer CrI$_3$ but also have direct implications in
heterostructures made of two-dimensional magnets.",1808.06559v2
2018/10/4,Domain wall dynamics in easy-cone magnets,"We theoretically and numerically investigate magnetic domain wall dynamics in
a nanowire of easy-cone magnet. The easy-cone domain wall exhibits several
distinguishing dynamic features in comparison to the easy-axis domain wall. The
features of easy-cone domain wall are related to the generation of additional
chiral spin textures due to the domain wall precession, which is common for
various driving sources such as magnetic fields and spin-transfer torques. The
unique easy-cone domain wall dynamics could enrich magnetic domain wall study
and find use in device applications based on easy-cone domain walls.",1810.02216v1
2018/10/15,Small magnetic charges and monopoles in non-associative quantum mechanics,"Weak magnetic monopoles with a continuum of charges less than the minimum
implied by Dirac's quantization condition may be possible in non-associative
quantum mechanics. If a weakly magnetically charged proton in a hydrogen atom
perturbs the standard energy spectrum only slightly, magnetic charges could
have escaped detection. Testing this hypothesis requires entirely new methods
to compute energy spectra in non-associative quantum mechanics. Such methods
are presented here, and evaluated for upper bounds on the magnetic charge of
elementary particles.",1810.06540v1
2012/9/4,Magnetic oscillations driven by the spin Hall effect in 3-terminal magnetic tunnel junction devices,"We show that direct current in a tantalum microstrip can induce steady-state
magnetic oscillations in an adjacent nanomagnet through spin torque from the
spin Hall effect (SHE). The oscillations are detected electrically via a
magnetic tunnel junction (MTJ) contacting the nanomagnet. The oscillation
frequency can be controlled using the MTJ bias to tune the magnetic anisotropy.
In this 3-terminal device the SHE torque and the MTJ bias therefore provide
independent controls of the oscillation amplitude and frequency, enabling new
approaches for developing tunable spin torque nano-oscillators.",1209.0655v1
2016/8/28,Magnetic susceptibility of topological nodal semimetals,"Magnetic susceptibility of the topological Weyl, type-II Weyl, Dirac, and
line node semimetals is theoretically investigated. Dependences of this
susceptibility on the chemical potential, temperature, direction and magnitude
of the magnetic field are found. The obtained results show that magnetic
measurements can be very useful in investigating these semimetals. As an
example, we calculate magnetic susceptibility of Cd$_3$As$_2$, Na$_3$Bi, and
Ca$_3$P$_2$.",1608.07822v2
2010/4/22,Equilibrium magnetization at the boundary of a magnetoelectric antiferromagnet,"Symmetry arguments are used to show that a boundary of a magnetoelectric
antiferromagnet has an equilibrium magnetization. This magnetization is coupled
to the bulk antiferromagnetic order parameter and can be switched along with it
by a combination of E and B fields. As a result, the antiferromagnetic domain
state of a magnetoelectric can be used as a non-volatile switchable state
variable in nanoelectronic device applications. Mechanisms affecting the
boundary magnetization and its temperature dependence are classified. The
boundary magnetization can be especially large if the boundary breaks the
equivalence of the antiferromagnetic sublattices.",1004.3974v2
2010/4/24,An upper bound for the magnetic force gradient in graphite,"Cervenka et al. have recently reported ferromagnetism along graphite steps.
We present Magnetic Force microscopy (MFM) data showing that the signal along
the steps is independent of an external magnetic field. Moreover, by combining
Kelvin Probe Force Microscopy (KPFM) and MFM, we are able to separate the
electrostatic and magnetic interactions along the steps obtaining an upper
bound for the magnetic force gradient of about16 microN/m, a figure six times
lower than the lowest theoretical bound reported by Cervenka et al. Our
experiments suggest absence of MFM signal in graphite at room temperature.",1004.4266v1
2010/9/4,Magnetization Reversal by Electric-Field Decoupling of Magnetic and Ferroelectric Domains Walls in Multiferroic-Based Heterostructures,"We demonstrate that the magnetization of a ferromagnet in contact with an
antiferromagnetic multiferroic (LuMnO3) can be speedily reversed by electric
field pulsing, and the sign of the magnetic exchange bias can switch and
recover isothermally. As LuMnO3 is not ferroelastic, our data conclusively show
that this switching is not mediated by strain effects but is a unique
electric-field driven decoupling of the ferroelectric and ferromagnetic domains
walls. Their distinct dynamics are essential for the observed magnetic
switching.",1009.0820v1
2010/9/17,Mixing in two magnetic OB stars discovered by the MiMeS collaboration,"Recent observational and theoretical arguments suggest that magnetic OB stars
may suffer more mixing than their non magnetic analogs. We present the results
of an NLTE abundance study revealing a lack of CN-cycled material at the
surface of two magnetic stars discovered by the MiMeS project (NGC2244 #201 and
HD 57682). The existence of a strong magnetic field is therefore not a
sufficient condition for deep mixing in main-sequence OB stars.",1009.3433v1
2016/3/23,"Nucleation, imaging and motion of magnetic domain walls in cylindrical nanowires","We report several procedures for the robust nucleation of magnetic domain
walls in cylindrical permalloy nanowires. Specific features of the magnetic
force microscopy contrast of such soft wires are discussed, with a view to
avoid the misinterpretation of the magnetization states. The domain walls could
be moved under quasistatic magnetic fields in the range 0.1--10 mT.",1603.07240v1
2017/3/6,Controlling topological superconductivity by magnetization dynamics,"We study theoretically a chain of precessing classical magnetic impurities in
an $s$-wave superconductor. Utilizing a rotating wave description, we derive an
effective Hamiltonian that describes the emergent Shiba band. We find that this
Hamiltonian shows non-trivial topological properties, and we obtain the
corresponding topological phase diagrams both numerically and analytically. We
show that changing the precession frequency offers a control over topological
phase transitions and the emergence of Majorana bound states. We propose
driving the magnetic impurities or magnetic texture into precession by means of
spin-transfer torque in a spin-Hall setup, and manipulate it using spin
superfluidity in the case of planar magnetic order.",1703.01870v1
2017/3/11,Susceptibility effects in nuclear magnetic resonance imaging,"The properties of dephasing and the resulting relaxation of the magnetization
are the basic principle on which all magnetic resonance imaging methods are
based. The signal obtained from the gyrating spins is essentially determined by
the properties of the considered tissue. Especially the susceptibility
differences caused by magnetized materials (for example, deoxygenated blood,
BOLD-effect) or magnetic nanoparticles are becoming more important for
biomedical imaging. In the present work, the influence of such field
inhomogeneities on the NMR-signal is analyzed.",1703.04003v1
2019/10/23,Effect of Demagnetization Method on Remnance Magnetization States in Metallic Ferromagnets,"Parametric plots of the remagnetization versus demagnetization remnances were
found for four metallic ferromagnets -- nickel wire, two types of AlNiCo, and
samarium cobalt 2:17. These plots, known as Henkel plots, were compared to
Wohlfarth's model for noninteracting magnetic particles and several Preisach
models. The remagnetization data were taken with a variety of paths to the net
zero magnetization state. The resulting Henkel plots exhibit similarities to
independent Monte Carlo simulations. The differences can be mostly explained by
considering that the magnetization in the metallic ferromagnets occur by domain
wall motion.",1910.10648v1
2020/4/27,Nonreciprocal directional dichroism induced by a temperature gradient as a probe for mobile spin dynamics in quantum magnets,"Novel states of matter in quantum magnets like quantum spin liquids attract
considerable interest recently. Despite the existence of a plenty of candidate
materials, there is no confirmed quantum spin liquid, largely due to the lack
of proper experimental probes. For instance, spectrosocopy experiments like
neutron scattering receive contributions from disorder-induced local modes,
while thermal transport experiments receive contributions from phonons. Here we
propose a thermo-optic experiment which directly probes the mobile magnetic
excitations in spatial-inversion symmetric and/or time-reversal symmetric Mott
insulators: the temperature-gradient-induced nonreciprocal directional
dichroism (TNDD) spectroscopy. Unlike traditional probes, TNDD directly detects
mobile magnetic excitations and decouples from phonons and local magnetic
modes.",2004.13047v1
2007/7/22,Magnetic State Modification Induced by Superconducting Response in Ferromagnet/Superconductor Hybrids,"Magnetization measurements in superconductor/ferromagnet Nb/Co superlattices
show a complex behavior as a function of temperature, applied field and sample
history. In base to a simple model it is shown that this behavior is due to an
interplay between the superconductor magnetization temperature dependence, the
ferromagnet magnetization time dependence, and the stray fields of both
materials. It is also shown that the magnetic state of the Co layers is
modified by the Nb superconducting response, implying that the problem of a
superconductor/ferromagnetic heterogeneous sample has to be solved in a
self-consistent manner.",0707.3265v1
2012/2/14,Magnetic anisotropies of quantum dots,"Magnetic anisotropies in quantum dots (QDs) doped with magnetic ions are
discussed in terms of two frameworks: anisotropic $g$-factors and
magnetocrystalline anisotropy energy. It is shown that even a simple model of
zinc-blende p-doped QDs displays a rich diagram of magnetic anisotropies in the
QD parameter space. Tuning the confinement allows to control magnetic easy axes
in QDs in ways not available for the better-studied bulk.",1202.3145v1
2013/11/15,Switching of the Magnetic Vortex Core in a Pac-man Disk using a Single Field-Pulse,"We report on the switching of the magnetic vortex core in a Pac-man disk
using a magnetic field pulse, investigated via micromagnetic simulations. The
minimum core switching field is reduced by 72 % compared to that of a circular
disk with the same diameter and thickness. However, the core switches
irregularly with respect to both the field pulse amplitude and duration. This
irregularity is induced by magnetization oscillations which arise due to
excitation of the spin waves when the core annihilates. We show that the core
switching can be controlled with the assist magnetic field and by changing the
waveform.",1311.3782v1
2013/11/22,Reversible magnetism switching in graphene-based systems via the decoration of photochromic molecules,"By first principles calculations, we demonstrate that when decorated with
photochromic molecules, it is possible to use light to reversibly control the
magnetic properties of a nanoscale magnetic system. The combination of a
graphene-based magnetic system and a photochromic azobenzene molecule is chosen
as a model system. The {\it trans} and {\it cis} isomers of the azobenzene
molecule that can be converted between each other by means of photoexcitations
are found to have drastically different effects on the magnetic properties of
the system. The results may pave the way for the future design of light
controllable molecular-scale spintronic devices.",1311.5682v1
2013/11/27,Effects of Surface Anisotropy on Magnetic Vortex Core,"The vortex core shape in the three dimensional Heisenberg magnet is
essentially influenced by a surface anisotropy. We predict that depending of
the surface anisotropy type there appears barrel- or pillow-shaped deformation
of the vortex core along the magnet thickness. Our theoretical study is well
confirmed by spin-lattice simulations.",1311.6882v1
2014/1/22,Disentangling defect-induced ferromagnetism in SiC,"We present a detailed investigation of the magnetic properties in SiC single
crystals bombarded with neon ions. Through careful measuring of the
magnetization of virgin and irradiated SiC, we decompose the magnetization of
SiC into paramagnetic, superparamagnetic, and ferromagnetic contributions. The
ferromagnetic contribution persists well above room temperature and exhibits a
pronounced magnetic anisotropy. We qualitatively explain the magnetic
properties as a result of the intrinsic clustering tendency of defects.",1401.5576v1
2014/4/2,Perpendicular magnetic anisotropy of cobalt films intercalated under graphene,"Magnetic properties of nanometer thick Co films intercalated at the
graphene/Ir(111) interface are investigated using spin-polarized low-energy
electron microscopy (SPLEEM) and Auger electron spectroscopy. We show that the
graphene top layer promotes perpendicular magnetic anisotropy in the Co film
underneath, even for relatively thick intercalated deposits. The magnetic
anisotropy energy is significantly larger for the graphene/Co interface than
for the free Co surface. Hybridization of the graphene and Co electron orbitals
is believed to be at the origin of the observed perpendicular magnetic
anisotropy.",1404.0705v1
2015/2/4,Instability of a ferrimagnetic state of a frustrated S=1/2 Heisenberg antiferromagnet in two dimensions,"To clarify the instability of the ferrimagnetism which is the fundamental
magnetism of ferrite, numerical-diagonalization study is carried out for the
two-dimensional S=1/2 Heisenberg antiferromagnet with frustration. We find that
the ferrimagnetic ground state has the spontaneous magnetization in small
frustration; due to a frustrating interaction above a specific strength, the
spontaneous magnetization discontinuously vanishes so that the ferrimagnetic
state appears only under some magnetic fields. We also find that, when the
interaction is increased further, the ferrimagnetism disappears even under
magnetic field.",1502.01071v1
2016/6/9,Nanocomposite RE-Ba-Cu-O bulk superconductors,"Nanocomposite oxide high-temperature bulk superconductors can be used as
quasi-magnets. Thanks to the recent progress of material processing,
quasi-magnet with 26 mm diameter can generate a large field of 17.6 T at 26 K.
These results are highly attractive for applications, involving levitation of
permanent magnets on the bulk superconductors. Indeed, several other
applications such as motors and magnetic resonance microscope using bulk
superconductors have been proposed and demonstrated. In this chapter, we
describe several techniques to improve the magnetic properties for bulk
superconductors together with some basics such as phase diagrams and
solidifications.",1606.02872v1
2017/7/5,Controlling the magnetism of oxygen surface vacancies in strontium titanate $\mathrm{(SrTiO_3\!)}$ through charging,"We discuss, based on first principles calculations, the possibility to tune
the magnetism of oxygen vacancies at the (001) surface of strontium titanate
$(\mathrm{SrTiO_3}\!)$. The magnetic moment of single and clustered vacancies
stemming from Ti-O broken bonds can be both quenched and stabilized
controllably by chemical potential adjustment associated with doping the system
with electrons or holes. We discuss to what extent this route to magnetization
state control is robust against other external influences like chemical doping,
mechanical action and electric field. Such control of vacancy state and
magnetization can conceivably be achieved experimentally by using local probe
tips.",1707.01449v2
2017/7/17,Magnetic properties of the intermetallic compound HoCuBi,"We present an investigation on the intermetallic compound formed by HoCuBi
which has a monoclinic crystalline P2 structure with lattice parameters; a =
9:8012(26)A, b = 6:0647(6)A, c = 6:1663(13)A. In this report we performed an
extensive analysis of the magnetic characteristics, specific heat at low
temperature mainly close to the region of the observed antiferromagnetic
transition with Neel temperature about 7 K, and to the field induced
spin-crossover; the metamagnetic transition typically observed in
antiferromagnetic systems by measurements of M-H, (Magnetization - Magnetic
Field) at low temperatures.",1707.06086v1
2017/7/29,Thermodynamics of the SmCo5 compound doped with Fe and Ni: an ab initio study,"SmCo5 permanent magnets exhibit enormous uniaxial magnetocrystalline
anisotropy energy and have a high Curie temperature. However, a low energy
product presents a significant drawback in the performance of SmCo5 permanent
magnets. In order to increase the energy product in SmCo5, we propose
substituting fixed amount of cobalt with iron in a new magnet, SmFe3CoNi, where
inclusion of nickel metal makes this magnet thermodynamically stable. We
further discuss some basic theoretical magnetic properties of the SmCo5
compound.",1707.09447v1
2018/11/20,Direct observation of anapoles by neutron diffraction,"The scope of magnetic neutron scattering has been expanded by the observation
of electronic Dirac dipoles (anapoles) that are polar (parity-odd) and magnetic
(time-odd). A zero-magnetization ferromagnet Sm0.976Gd0.024Al2 with a
diamond-type structure presents Dirac multipoles at basis-forbidden reflections
that include the standard (2, 2, 2) reflection. Magnetic amplitudes measured at
four such reflections are in full accord with a structure factor calculated
from the appropriate magnetic space group.",1811.08407v1
2019/3/22,Learning magnetization dynamics,"Deep neural networks are used to model the magnetization dynamics in magnetic
thin film elements. The magnetic states of a thin film element can be
represented in a low dimensional space. With convolutional autoencoders a
compression ratio of 1024:1 was achieved. Time integration can be performed in
the latent space with a second network which was trained by solutions of the
Landau-Lifshitz-Gilbert equation. Thus the magnetic response to an external
field can be computed quickly.",1903.09499v1
2019/3/28,Magnetic susceptibility of topological semimetals,"We give a review of theoretical and experimental results concerning the
magnetic susceptibility of the Weyl, Dirac, and nodal-line semimetals. In
particular, dependences of the susceptibility on the chemical potential,
temperature, and magnitude of the magnetic field are discussed. The presented
results show that the specific features of the magnetic susceptibility can
serve as a hallmark of the topological semimetals, and hence magnetic
measurements can be useful in investigating these materials.",1903.12208v2
2019/5/10,Orbital Floquet Engineering of Exchange Interactions in Magnetic Materials,"We present a new scheme to control the spin exchange interactions between two
magnetic ions by manipulating the orbital degrees of freedom using a periodic
drive. We discuss two different protocols for orbital Floquet engineering. In
one case, we modify the properties of the ligand orbitals which mediate
magnetic interactions between two transition metal ions. While in the other
case, we mix the d orbitals on each magnetic ion. In contrast to previous works
on Floquet engineering of magnetic properties, the present scheme makes use of
the AC Stark shift of the states involved in the exchange process.",1905.03921v1
2019/5/10,Lagrangian formulation for emergent elastic waves in magnetic emergent crystals,"Magnetic emergent crystals are periodic alignment of ""particle-like"" spin
textures that emerge in magnets. Instead of focusing on an individual spin or a
macroscopic magnetization field, we analyze the dynamical behaviors of these
novel states by taking a solid-state point of view. Based on variational
principles, the basic equations for lattice dynamics of any emergent
crystalline states appearing in magnetic materials is established. For small
amplitude emergent elastic waves propagating in emergent crystals, the basic
equations reduce to an eigenvalue problem, from which the dispersion relation
and vibrational patterns for all emergent phonons are determined at the long
wavelength limit.",1905.03991v1
2019/5/28,Piezospintronic effect in antiperovskite Mn$_3$GaN,"Based on first-principles calculations, we investigated the topological
transport properties of Mn$_3$GaN with coplanar noncollinear magnetic
structures. The intrinsic anomalous Hall conductivity (IAHC) displays a
significant dependence with respect to the in-plane magnetization direction
between the $\Gamma_{5g}$ and $\Gamma_{4g}$ magnetic configurations, where
large anomalous Nernst effect (ANE) can be induced by tailoring the
magnetization direction. Moreover, we observed strong piezospintronic effect in
Mn$_3$GaN, where large IAHC can be induced by moderate epitaxial strain.
Symmetry analysis reveals that for both cases, the nonzero IAHC is originated
from the spin-orbit coupling instead of the noncollinear magnetic
configurations",1905.11798v1
2019/7/11,Valley-Contrasting Orbital Magnetic Moment Induced Negative Magnetoresistance,"The valley-contrasting orbital magnetic moment of Bloch electrons allows the
lifting of valley degeneracy by an out-of-plane magnetic field. We demonstrate
that this leads to negative magnetoresistance, utilizing a gapped
two-dimensional multi-valley model as an example. An intuitive physical picture
in terms of the increased carrier density from a magnetic gating effect is
proposed for this negative magnetoresistance. In particular, giant negative
magnetoresistance is achieved after one of the two valleys is depleted by the
magnetic field. This new mechanism of negative magnetoresistance is argued to
be relevant in ionic-liquid gated gapped graphene with small effective mass.",1907.04992v1
2019/11/7,Magnetic monopoles and toroidal moments in LuFeO$_3$ and related compounds,"Magnetic monopoles and toroidal order are compelling features that have long
been theorized but remain elusive in real materials. Multiferroic hexagonal
ferrites are an interesting realization of frustrated triangular lattice, where
magnetic order is coupled to ferroelectricity and trimerization. Here we
propose a mechanism, through which magnetic monopolar and toroidal orders
emerge from the combination of 120$^\circ$ antiferromagnetism and
trimerization, present in hexagonal manganites and ferrites. The experimentally
observable signatures of magnetic monopolar and toroidal orders are identified
in the inelastic neutron scattering cross section, simulated from a microscopic
model of LuFeO3. The non-reciprocal magnon propagation is demonstrated.",1911.02704v1
2020/1/31,Electric field control of interfacial Dzyaloshinskii-Moriya interaction in Pt/Co/AlO$_x$ thin films,"We studied electric field modification of magnetic properties in a
Pt/Co/AlO$_x$ trilayer via magneto-optical Kerr microscopy. We observed the
spontaneous formation of labyrinthine magnetic domain structure due to
thermally activated domain nucleation and propagation under zero applied
magnetic field. A variation of the period of the labyrinthine structure under
electric field is observed as well as saturation magnetization and magnetic
anisotropy variations. Using an analytical formula of the stripe equilibrium
width we estimate the variation of the interfacial Dzyaloshinskii-Moriya
interaction under electric field as function of the exchange stiffness
constant.",2001.11982v1
2020/10/7,Probing topological spin structures using light-polarization and magnetic microscopy,"We present an imaging modality that enables detection of magnetic moments and
their resulting stray magnetic fields. We use wide-field magnetic imaging that
employs a diamond-based magnetometer and has combined magneto-optic detection
(e.g. magneto-optic Kerr effect) capabilities. We employ such an instrument to
image magnetic (stripe) domains in multilayered ferromagnetic structures.",2010.03452v1
2020/12/2,Effects of exchange distortions in the magnetic Kagome lattice,"This study examines the effect of distorted triangular magnetic interactions
in the Kagome lattice. Using a Holstein-Primakoff expansion, we determine the
analytical solutions for classical energies and the spin-wave modes for various
magnetic configurations. By understanding the magnetic phase diagram, we
characterize the changes in the spin waves and examine the spin distortions of
the ferromagnetic (FM), Antiferrimagnetic (AfM), and 120$^{\circ}$ phases that
are produced by variable exchange interactions and lead to various
non-collinear phases, which provides a deeper understanding of the magnetic
fingerprints of these configurations for experimental characterization and
identification.",2012.00910v1
2021/1/15,Spin dynamics from a constrained magnetic Tight-Binding model,"A dynamics of the precession of coupled atomic moments in the tight-binding
(TB) approximation is presented. By implementing an angular penalty functional
in the energy that captures the magnetic effective fields self-consistently,
the motion of the orientation of the local magnetic moments is observed faster
than the variation of their magnitudes. This allows the computation of the
effective atomic magnetic fields that are found consistent with the
Heisenberg's exchange interaction, by comparison with classical atomistic spin
dynamics on Fe, Co and Ni magnetic clusters.",2101.06121v2
2021/1/19,Direct evidence of ferromagnetism in MnSb2Te4,"We report the magnetic imaging of ferromagnetic domains in the van der Waals
single crystal MnSb2Te4 from two different sources using cryogenic magnetic
force microscopy. The magnetic field dependence of the domains reveals very
weak pinning of domain walls in MnSb2Te4, resulting in a negligibly small
magnetic hysteresis loop. The temperature dependence of the domain contrast
reveals a mean field like behavior, in good agreement with that of bulk
magnetization measurements.",2101.07892v1
2021/6/16,Topological-chiral magnetic interactions in ultrathin films at surfaces,"We demonstrate that topological-chiral magnetic interactions can play a key
role for magnetic ground states in ultrathin films at surfaces. Based on
density functional theory we show that significant chiral-chiral interactions
occur in hexagonal Mn monolayers due to large topological orbital moments which
interact with the emergent magnetic field. Due to the competition with
higher-order exchange interactions superposition states of spin spirals such as
the 2Q state or a distorted 3Q state arise. Simulations of spin-polarized
scanning tunneling microscopy images suggest that the distorted 3Q state could
be the magnetic ground state of a Mn monolayer on Re(0001).",2106.08622v1
2021/11/12,Micromagnetic modeling of magnetization distribution caused by internal twin microstructure of NiMnGa ferromagnetic shape memory alloys,"In our present publication we will continue studying the effects of the
magnetostatic energy on the magnetization behavior of FMSMAs recently started
in some our publications. Our method is based on the direct minimization of our
new micromagnetic free energy model of FMSMAs taking into account both the
magnetic anisotropy energy and the magnetostatic energy contributions
associated with the laminated two-variant twin microstructure. Here, our
special interest is to investigate a distribution of local magnetizations
within both twin variants, their orientation and their dependence on the
external magnetic field and their volume fractions, as well.",2111.06605v1
2022/1/18,Magnetic slowdown of topological edge states,"We study the propagation of wavepackets along curved interfaces between
topological, magnetic materials. Our Hamiltonian is a massive Dirac operator
with a magnetic potential. We construct semiclassical wavepackets propagating
along the curved interface as adiabatic modulations of straight edge states
under constant magnetic fields. While in the magnetic-free case, the
wavepackets propagate coherently at speed one, here they experience slowdown,
dispersion, and Aharonov - Bohm effects. Several numerical simulations
illustrate our results.",2201.07133v1
2022/6/24,Meridional composite pulses for low-field magnetic resonance,"We discuss procedures for error-tolerant spin control in environments that
permit transient, large-angle reorientation of magnetic bias field. Short
sequences of pulsed, non-resonant magnetic field pulses in a laboratory-frame
meridional plane are derived. These are shown to have band-pass excitation
properties comparable to established amplitude-modulated, resonant pulses used
in high, static-field magnetic resonance. Using these meridional pulses, we
demonstrate robust $z$ inversion in proton ($^{1}$H) nuclear magnetic resonance
near earth's field.",2206.12025v1
2023/5/1,Theory of magnetic vortex crystals induced by electric dipole interactions,"Recent Lorentz transmission electron microscopy experiments have revealed a
variety of noncollinear spin textures including topological magnetisms such as
skyrmions, biskyrmions and multiple skyrmions in thin-plate magnetic samples of
e.g., perovskite manganites and hexaferrites whose crystal structures
originally have spatial inversion symmety. Motivated by these experiments, we
investigate a spin-lattice coupled model involving both magnetic and electric
dipole interactions by the Monte Carlo technique based on the stochastic
cut-off method and propose a physical mechanism for realizing topological spin
textures in which the electric dipole interaction plays a key role. This
mechanism is ubiquitous that stabilizes noncollinear and topological spin
textures in thin-plate samples of magnetic materials.",2305.00751v1
2023/5/2,Modeling the induced voltage of a disk magnet in free fall,"We drop a circular disk magnet through a thin coil of wire, record the
induced voltage, and compare the results to an analytic model based on the
dipole approximation and Faraday's law, which predicts that the difference
between the voltage peak magnitudes corresponding to the entry and exit of the
magnet should be in proportion to $z_0^{-1/2}$, where $z_0$ is the initial
height of the magnet above the center of the coil. Agreement between the model
and experimental data are excellent. This easily-reproduced experiment provides
an opportunity for students at a range of levels to quantitatively explore the
effects of magnetic induction.",2305.01813v1
2023/7/21,Thermomechanics of ferri-antiferromagnetic phase transition in finitely-strained rocks towards paleomagnetism,"The thermodynamic model of visco-elastic deformable magnetic materials at
finite strains is formulated in a fully Eulerian way in rates with the aim to
describe thermoremanent paleomagnetism in crustal rocks. The Landau theory
applied to a ferro-to-para-magnetic phase transition, the gradient theory for
magnetization (leading to exchange energy) with general mechanically dependent
coefficient, hysteresis in magnetization evolution by Gilbert equation
involving objective corotational time derivative of magnetization, and
demagnetizing field are considered in the model. The Jeffreys viscoelastic
rheology is used with temperature-dependent creep to model solidification or
melting transition. The model complies with energy conservation and the
Clausius-Duhem entropy inequality.",2307.11826v2
2023/9/13,Magnetic flux trapping in porous superconductors,"The magnetization of superconducting samples is influenced by their porosity.
In addition to structural modifications and improved cooling, the presence of
pores also plays a role in trapping magnetic flux. Pores have an impact on the
irreversibility field, the full penetration field, and the remnant
magnetization. Generally, as porosity increases, these parameters tend to
decrease. However, in the case of mesoscopic samples or samples with low
critical current densities, increased porosity can actually enhance the
trapping of magnetic flux.",2309.06839v1
2023/11/1,Topological transport of vorticity on curved magnetic membranes,"In this work, we study the transport of vorticity on curved dynamical
two-dimensional magnetic membranes. We find that topological transport can be
controlled by geometrically reducing symmetries, which enables processes that
are not present in flat magnetic systems. To this end, we construct a vorticity
3-current which obeys a continuity equation. This continuity equation is immune
to local fluctuations of the magnetic texture as well as spatiotemporal
fluctuations of the membrane. We show how electric current can manipulate
vortex transport in geometrically nontrivial magnetic systems. As an
illustrative example, we propose a minimal setup that realizes an
experimentally feasible energy storage device.",2311.00323v1
2023/12/14,Scaling analysis of two-dimensional random singlet state in magnetic field,"Quenched randomness strongly affects properties of magnetic materials.
Two-dimensional (2D) random singlet (RS) states emerge in random $J$-$Q$ model
by destroying valence bond solid order with spatial randomness. We examine the
2D RS state in magnetic field with quantum Monte Carlo simulations. The
magnetization and susceptibilities show power-law scaling with magnetic field
at low temperature. Moreover, they show one-parameter scaling behavior with
$B/T$, and the scaling functions are remarkably consistent with a
phenomenological model of random spin pairs with a singular distribution of
interactions. These universal scaling functions can be used to diagnose 2D RS
states in experiments.",2312.08919v1
2021/1/26,Data-driven design of a new class of rare-earth free permanent magnets,"A new class of rare-earth-free permanent magnets is proposed. The parent
compound of this class is Co$_3$Mn$_2$Ge, and its discovery is the result of
first principles theory combined with experimental synthesis and
characterisation. The theory is based on a high-throughput/data-mining search
among materials listed in the ICSD database. From ab-initio theory of the
defect free material it is predicted that the saturation magnetization is 1.71
T, the uniaxial magnetocrystalline anisotropy is 1.44 MJ/m$^3$, and the Curie
temperature is 700 K. Co$_3$Mn$_2$Ge samples were then synthesized and
characterised with respect to structure and magnetism. The crystal structure
was found to be the MgZn$_2$-type, with partial disorder of Co and Ge on the
crystallographic lattice sites. From magnetization measurements a saturation
polarization of 0.86 T at 10 K was detected, together with a uniaxial
magnetocrystalline anisotropy constant of 1.18 MJ/m$^3$, and the Curie
temperature of $T_{\rm C}$ = 359 K. These magnetic properties make
Co$_3$Mn$_2$Ge a very promising material as a rare-earth free permanent magnet,
and since we can demonstrate that magnetism depends critically on the amount of
disorder of the Co and Ge atoms, a further improvement of the magnetism is
possible. From the theoretical works, a substitution of Ge by neighboring
elements suggest two other promising materials - Co$_3$Mn$_2$Al and
Co$_3$Mn$_2$Ga. We demonstrate here that the class of compounds based on
$T_3$Mn$_2$X (T = Co or alloys between Fe and Ni; X=Ge, Al or Ga) in the
MgZn$_2$ structure type, form a new class of rare-earth free permanent magnets
with very promising performance.",2101.10773v1
2023/12/26,Perspective on nanoscale magnetic sensors using giant anomalous Hall effect in topological magnetic materials for read head application in magnetic recording,"Recent advances in the study of materials with topological electronic band
structures have revealed magnetic materials exhibiting giant anomalous Hall
effects (AHE). The giant AHE has not only attracted the research interest in
its mechanism but also opened up the possibility of practical application in
magnetic sensors. In this article, we describe simulation-based investigations
of AHE magnetic sensors for the applications to read head sensors (readers) of
hard disk drives. With the shrinking of magnetic recording patterns, the reader
technology, which currently uses multilayer-based tunnel magnetoresistance
(TMR) devices, is associated with fundamental challenges, such as insufficient
spatial resolution and signal-to-noise ratio (SNR) in sensors with dimensions
below 20 nm. The structure of an AHE-based device composed of a single
ferromagnetic material is advantageous for magnetic sensors with nanoscale
dimensions. We found that AHE readers using topological ferromagnets with giant
AHE, such as Co2MnGa, can achieve a higher SNR than current TMR readers. The
higher SNR originates from the large output signal of the giant AHE as well as
from the reduced thermal magnetic noise, which is the dominant noise in TMR
readers. We highlight a major challenge in the development of AHE readers: the
reduction in the output signal due to the shunting of the bias current and the
leakage of the Hall voltage through the soft magnetic shields surrounding the
AHE reader. We propose reader structures that overcome this challenge. Finally,
we discuss the scope for future research to realize AHE readers.",2312.15977v2
2008/2/9,^{7}Li NMR Study of Heavy Fermion LiV2O4 Containing Magnetic Defects,"We present a systematic study of the variations of the ^{7}Li NMR properties
versus magnetic defect concentration up to 0.83 mol% within the spinel
structure of polycrystalline powder samples and a collection of small single
crystals of LiV2O4 in the temperature range from 0.5 to 4.2 K. We also report
static magnetization measurements and ac magnetic susceptibility measurements
at 14 MHz on the samples at low temperatures. Both the NMR spectrum and nuclear
spin-lattice relaxation rate are inhomogeneous in the presence of the magnetic
defects. The NMR data for the powders are well explained by assuming that (i)
there is a random distribution of magnetic point defects, (ii) the same heavy
Fermi liquid is present in the samples containing the magnetic defects as in
magnetically pure LiV2O4, and (iii) the influences of the magnetic defects and
of the Fermi liquid on the magnetization and NMR properties are separable. In
the single crystals, somewhat different behaviors are observed. Remarkably, the
magnetic defects in the powder samples show evidence of spin freezing below T ~
1.0 K, whereas in the single crystals with similar magnetic defect
concentration no spin freezing was found down to 0.5 K. Thus different types of
magnetic defects and/or interactions between them appear to arise in the
powders versus the crystals, possibly due to the substantially different
synthesis conditions of the powders and crystals.",0802.1236v1
2009/6/8,"Enhanced magnetism, memory and aging in Gold-Iron oxide nanoparticle composites","In this report we present systematic magnetic studies of pure iron oxide
nanoparticles and gold iron oxide nanocomposite with increasing Au particle
size/content. For the magnetic studies of these samples we have measured: (1)
zero field cooled (ZFC) and field cooled (FC) magnetization, (2) ac
susceptibility, (3) magnetization vs field at various temperatures, (4)
thermoremanant magnetization relaxation (TRM) and zero field cooled
magnetization relaxation (ZFCM) at fixed temperature for various wait times tw
for studying the aging effect, (5) magnetization memory effect and (6) exchange
bias as a function of cooling field. The detailed magnetic measurement analysis
indicates that the pure Fe3O4 nanoparticles sample behaves like a
superparamagnet and on incorporation of gold (Au) nanoparticles the
nanocomposite system slowly evolves from superparamagnetic to superspin glass
state. The memory and aging effect enhances with the increase of the Au
nanoparticle size/content. The most important observation in this study is the
enhancement of magnetization with the incorporation of Au nanoparticles. The
enhancement increases with the increase in the Au content in the nanocomposite.
We have explained the cause of this enhancement of magnetization as due to
large orbital magnetic moment formation at the Au/magnetic particle interface.",0906.1497v2
2009/9/28,Magnetic properties and spin dynamics in single molecule paramagnets Cu6Fe and Cu6Co,"The magnetic properties and the spin dynamics of two molecular magnets have
been investigated by magnetization and d.c. susceptibility measurements,
Electron Paramagnetic Resonance (EPR) and proton Nuclear Magnetic Resonance
(NMR) over a wide range of temperature (1.6-300K) at applied magnetic fields,
H=0.5 and 1.5 Tesla. The two molecular magnets consist of
CuII(saldmen)(H2O)}6{FeIII(CN)6}](ClO4)38H2O in short Cu6Fe and the analog
compound with cobalt, Cu6Co. It is found that in Cu6Fe whose magnetic core is
constituted by six Cu2+ ions and one Fe3+ ion all with s=1/2, a weak
ferromagnetic interaction between Cu2+ moments through the central Fe3+ ion
with J = 0.14 K is present, while in Cu6Co the Co3+ ion is diamagnetic and the
weak interaction is antiferromagnetic with J = -1.12 K. The NMR spectra show
the presence of non equivalent groups of protons with a measurable contact
hyperfine interaction consistent with a small admixture of s-wave function with
the d-function of the magnetic ion. The NMR relaxation results are explained in
terms of a single ion (Cu2+, Fe3+, Co3+) uncorrelated spin dynamics with an
almost temperature independent correlation time due to the weak magnetic
exchange interaction. We conclude that the two molecular magnets studied here
behave as single molecule paramagnets with a very weak intramolecular
interaction, almost of the order of the dipolar intermolecular interaction.
Thus they represent a new class of molecular magnets which differ from the
single molecule magnets investigated up to now, where the intramolecular
interaction is much larger than the intermolecular one.",0909.5063v1
2011/7/26,Magnetic Behaviour of Disordered Ising Ferrimagnet in High Magnetic Field,"The magnetic behaviour of a disordered ferrimagnetic system Ap B1-p where
both A and B represent the magnetic atoms with respective spin SA = 1/2 and SB
= 1 in presence of high magnetic field is treated theoretically.Assuming the
magnetic interaction can be described through Ising Hamiltonian the approximate
free energy is obtained using the cluster-variational method. The field
dependence of the magnetization is then obtained for different concentration p
and exchange parameters (JAA, JBB and JAB). For p = 0.5,the magnetization M in
ferrimagnetic state and in absence of compensation temperature Tcm vanishes at
TC.Field induced reversal of M is found at switching temperature TS (<TC) which
is decreasing function of field H.A maximum in M is found above TS and the
maximum value of M increases with field.In ferrimagnetic state M increases
almost linearly at high H region. For system with large ferromagnetic JAA,the
compensation temperature Tcm is increasing function of JBB and JAB .The
decrease in compensation temperature is linear at small field and tends to
saturate at higher field.The sharpness of the magnetization reversal is
increased with H.For fully compensated state of the system with p = 2/3,the
magnetization in presence of H also exhibits switching behaviour at TS .For p =
0.2 the field induced reversal of magnetization occurs more sharply.The
orientational switching of the sublattice magnetization MA and MB with field
increases the Zeeman energy and is the origin of magnetization reversal at Ts",1107.5225v1
2013/12/9,High magnetic field evolution of ferroelectricity in CuCrO2,"CuCrO2 offers insights into the different types of spiral magnetic orderings
that can form spontaneously due to frustration in triangular-lattice
antiferromagnets. We explore the magnetic phase diagram up to 65 T along all
the principle axes, and also use electric polarization to probe changes in the
spiral order at high magnetic fields. It is known that at zero magnetic field a
proper-screw spiral of the Cr S = 3/2 spins forms that in turn induces electric
polarization with six possible orientations ab-plane. Applied magnetic fields
in the (hard) ab-plane have been shown to induce a transition to cycloidal
spiral magnetic order above 5.3 T in those domains that have spins
perpendicular to the applied magnetic field. We show that the cycloidal order
remains unchanged all the way up to 65 T, which is one quarter of the
extrapolated saturation magnetization. On the other hand for magnetic fields
along the (easy) c-axis, we observe a transition in the electric polarization
near 45 T, and it is followed by a series of steps and/or oscillations in the
electric polarization. The data is consistent with the a
proper-screw-to-cycloidal transition that is pushed from 5.3 to 45 T by
easy-axis anisotropy, and is in turn followed by stretching of the magnetic
spiral through commensurate and incommensurate wave vectors. This work also
highlights the ability of the magnetically-induced electric polarization to
probe complex magnetic orders in regimes of phase space that are difficult to
reach with neutron diffraction.",1312.2548v1
2014/11/24,Manipulating Femtosecond Spin--Orbit Torques with Laser Pulse Sequences to Control Magnetic Memory States and Ringing,"Femtosecond (fs) coherent control of collective order parameters is important
for non--equilibrium phase dynamics in correlated materials. Here we propose a
possible scheme for fs control of a ferromagnetic order parameter based on
non--adiabatic optical manipulation of electron--hole ($e$--$h$)
photoexcitations between spin--orbit--coupled bands that are exchange--split by
magnetic interaction with local spins. We photoexcite fs carrier spin--pulses
with controllable direction and time profile without using
circularly--polarized light, via time--reversal symmetry--breaking by
non--perturbative interplay between spin--orbit and magnetic exchange coupling
of coherent photocarriers. We manipulate photoexcited {\em fs spin--orbit
torques} to control complex switching pathways of the magnetization between
multiple magnetic memory states. We calculate the photoinduced fs magnetic
anisotropy in the time domain by using density matrix equations of motion
rather than the quasi--equilibrium free energy. By comparing to pump--probe
experiments, we identify a ""sudden"" magnetization canting induced by laser
excitation, which displays magnetic hysteresis absent in static
magneto--optical measurements and agrees with switchings measured by Hall
magnetoresistivity. The fs magnetization canting switches direction with
magnetic state and laser frequency, which distinguishes it from nonlinear
optical and demagnetization longitudinal effects. By shaping two--color
laser--pulse sequences analogous to multi--dimensional Nuclear Magnetic
Resonance (NMR) spectroscopy, we show that sequences of clockwise or
counter--clockwise fs spin--orbit torques can enhance or suppress magnetic
ringing and switching rotation at any desired time. We propose protocols that
can provide controlled access to four magnetic states via consequative 90$^{o}$
switchings.",1411.6662v1
2014/12/1,Quantifying magnetic anisotropy dispersion: Theoretical and experimental study of the magnetic properties of anisotropic FeCuNbSiB ferromagnetic films,"The Stoner-Wohlfarth model is a traditional and efficient tool to calculate
magnetization curves and it can provides further insights on the fundamental
physics associated to the magnetic properties and magnetization dynamics. Here,
we perform a theoretical and experimental investigation of the quasi-static
magnetic properties of anisotropic systems. We consider a theoretical approach
which corresponds to a modified version of the Stoner-Wohlfarth model to
describe anisotropic systems and a distribution function to express the
magnetic anistropy dispersion. We propose a procedure to calculate the magnetic
properties for the anisotropic case of the SW model from experimental results
of the quadrature of magnetization curves, thus quantifying the magnetic
anisotropy dispersion. To test the robustness of the approach, we apply the
theoretical model to describe the quasi-static magnetic properties of amorphous
FeCuNbSiB ferromagnetic films. We perform calculations and directly compare
theoretical results with longitudinal and transverse magnetization curves
measured for the films. Thus, our results provide experimental evidence to
confirm the validity of the theoretical approach to describe the magnetic
properties of anisotropic amorphous ferromagnetic films, revealed by the
excellent agreement between numerical calculation and experimental results.",1412.0563v1
2009/7/9,Annular Spin-Transfer Memory Element,"An annular magnetic memory that uses a spin-polarized current to switch the
magnetization direction or helicity of a magnetic region is proposed. The
device has magnetic materials in the shape of a ring (1 to 5 nm in thickness,
20 to 250 nm in mean radius and 8 to 100 nm in width), comprising a reference
magnetic layer with a fixed magnetic helicity and a free magnetic layer with a
changeable magnetic helicity. These are separated by a thin non-magnetic layer.
Information is written using a current flowing perpendicular to the layers,
inducing a spin-transfer torque that alters the magnetic state of the free
layer. The resistance, which depends on the magnetic state of the device, is
used to read out the stored information. This device offers several important
advantages compared to conventional spin-transfer magnetic random access memory
(MRAM) devices. First, the ring geometry offers stable magnetization states,
which are, nonetheless, easily altered with short current pulses. Second, the
ring geometry naturally solves a major challenge of spin-transfer devices:
writing requires relatively high currents and a low impedance circuit, whereas
readout demands a larger impedance and magnetoresistance. The annular device
accommodates these conflicting requirements by performing reading and writing
operations at separate read and write contacts placed at different locations on
the ring.",0907.1600v1
2017/12/1,Spin reorientation and disordered rare earth magnetism in Ho$_2$FeCoO$_6$,"We report the experimental observation of spin reorientation in the double
perovskite Ho$_2$FeCoO$_6$. The magnetic phase transitions in this compound are
characterized and studied through magnetization and specific heat, and the
magnetic structures are elucidated by neutron powder diffraction. Two magnetic
phase transitions are observed in this compound - one at $T_\mathrm{N1}
\approx$ 250~K, from paramagnetic to antiferromagnetic, and the other at
$T_\mathrm{N2} \approx$ 45~K, from a phase with mixed magnetic structures to a
single phase through a spin reorientation process. The magnetic structure in
the temperature range 200~K - 45~K is a mixed phase of the irreducible
representations $\Gamma_1$ and $\Gamma_3$, both of which are antiferromagnetic.
The phase with mixed magnetic structures that exists in Ho$_2$FeCoO$_6$ gives
rise to a large thermal hysteresis in magnetization that extends from 200~K
down to the spin reorientation temperature. At $T_\mathrm{N2}$, the magnetic
structure transforms to $\Gamma_1$. Though long-range magnetic order is
established in the transition metal lattice, it is seen that only short-range
magnetic order prevails in Ho$^{3+}$ - lattice. Our results should motivate
further detailed studies on single crystals in order to explore spin
reorientation process, spin switching and the possibility of anisotropic
magnetic interactions giving rise to electric polarization in Ho$_2$FeCoO$_6$.",1712.00177v1
2020/9/28,Magnetic domains and domain wall pinning in two-dimensional ferromagnets revealed by nanoscale imaging,"Magnetic-domain structure and dynamics play an important role in
understanding and controlling the magnetic properties of two-dimensional
magnets, which are of interest to both fundamental studies and
applications[1-5]. However, the probe methods based on the spin-dependent
optical permeability[1,2,6] and electrical conductivity[7-10] can neither
provide quantitative information of the magnetization nor achieve nanoscale
spatial resolution. These capabilities are essential to image and understand
the rich properties of magnetic domains. Here, we employ cryogenic scanning
magnetometry using a single-electron spin of a nitrogen-vacancy center in a
diamond probe to unambiguously prove the existence of magnetic domains and
study their dynamics in atomically thin CrBr$_3$. The high spatial resolution
of this technique enables imaging of magnetic domains and allows to resolve
domain walls pinned by defects. By controlling the magnetic domain evolution as
a function of magnetic field, we find that the pinning effect is a dominant
coercivity mechanism with a saturation magnetization of about 26~$\mu_B$/nm$^2$
for bilayer CrBr$_3$. The magnetic-domain structure and pinning-effect
dominated domain reversal process are verified by micromagnetic simulation. Our
work highlights scanning nitrogen-vacancy center magnetometry as a quantitative
probe to explore two-dimensional magnetism at the nanoscale.",2009.13440v1
2021/3/30,Soft X-ray absorption spectroscopy and magnetic circular dichroism under pulsed high magnetic field of Ni-Co-Mn-In metamagnetic shape memory alloy,"In this study, X-ray absorption spectroscopy (XAS) experiments for
Ni45Co5Mn36.7In13.3 metamagnetic shape memory alloy were performed under high
magnetic fields up to 12 T using a pulsed magnet. Field-induced reverse
transformation to austenite phase caused considerable changes in the magnetic
circular dichroism (MCD) signals and the magnetic moments of the ferromagnetic
coupling between Mn, Ni, and Co were determined. The spin magnetic moment,
Mspin, and orbital magnetic moment, Morb, of Mn atom in the induced austenite
ferromagnetic phase, estimated based on the magneto-optical sum rule, were 3.2
and 0.13 {\mu}B, respectively, resulting in an Morb / Mspin ratio of 0.04. In
the element-specific magnetization curves recorded at 150 K, metamagnetic
behavior associated with the field-induced reverse transformation is clearly
observed and reverse transformation finishing magnetic field and martensitic
transformation starting magnetic field are detected. There was almost no
difference in the magnetically averaged XAS spectrum for Mn-L2,3 edges between
in the martensite and in the magnetic field-induced austenite phases, however,
it was visible for Ni, indicating that Ni 3d-electrons mainly contribute to
martensitic transformation.",2103.16296v3
2022/1/20,"Correlation strength, orbital-selective incoherence, and local moments formation in the magnetic MAX-phase Mn$_2$GaC","We perform a theoretical study of the electronic structure and magnetic
properties of the prototypical magnetic MAX-phase Mn$_2$GaC with the main focus
given to the origin of magnetic interactions in this system. Using the density
functional theory+dynamical mean-field theory (DFT+DMFT) method we explore the
effects of electron-electron interactions and magnetic correlations on the
electronic properties, magnetic state, and spectral weight coherence of
paramagnetic and magnetically-ordered phases of Mn$_2$GaC. We also benchmark
the DFT-based disordered local moment approach for this system by comparing the
obtained electronic and magnetic properties with that of the DFT+DMFT method.
  Our results reveal a complex magnetic behavior characterized by a near
degeneracy of the ferro- and antiferromagnetic configurations of Mn$_2$GaC,
implying a high sensitivity of its magnetic state to fine details of the
crystal structure and unit-cell volume, consistent with experimental
observations.
  We observe robust local-moment behavior and orbital-selective incoherence of
the spectral properties of Mn$_2$GaC, implying the importance of
orbital-dependent localization of the Mn $3d$ states.
  We find that Mn$_2$GaC can be described in terms of local magnetic moments,
which may be modeled by DFT with disordered local moments. However, the
magnetic properties are dictated by the proximity to the regime of formation of
local magnetic moments, in which the localization is in fact driven by the
Hund's exchange interaction, and not the Coulomb interaction.",2201.07995v1
2022/11/24,Crustal magnetic fields do not lead to large magnetic-field amplifications in binary neutron-star mergers,"The amplification of magnetic fields plays an important role in explaining
numerous astrophysical phenomena associated with binary neutron-star mergers,
such as mass ejection and the powering of short gamma-ray bursts. Magnetic
fields in isolated neutron stars are often assumed to be confined to a small
region near the stellar surface, while they are normally taken to fill the
whole stars in the numerical modelling. By performing high-resolution, global,
and high-order general-relativistic magnetohydrodynamic simulations we
investigate the impact of a purely crustal magnetic field and contrast it with
the standard configuration consisting of a dipolar magnetic field with the same
magnetic energy but filling the whole star. While the crust-configurations are
very effective in generating strong magnetic fields during the
Kelvin-Helmholtz-instability stage, they fail to achieve the same level of
magnetic-field amplification of the full-star configurations. This is due to
the lack of magnetized material in the neutron-star interiors to be used for
further turbulent amplification and to the surface losses of highly magnetized
matter in the crust-configurations. Hence, the final magnetic energies in the
two configurations differ by more than one order of magnitude. We briefly
discuss the impact of these results on astrophysical observables and how they
can be employed to deduce the magnetic topology in merging binaries.",2211.13661v2
2023/3/26,The effect of the magnetically dead layer on the magnetization and the magnetic anisotropy of the dextran coated magnetite nanoparticles,"We present a study on the magnetic behavior of dextran-coated magnetite
nanoparticles (DM NPs) with sizes between 3 and 19 nm, synthesized by
hydrothermal-assisted co-precipitation method. The decrease of saturation
magnetization ($M_s$) with decreasing particle size has been modeled by
assuming the existence of a spin-disordered layer at the particle surface,
which is magnetically dead. Based on this core-shell model and taking into
account the weight contribution of the non-magnetic coating layer (dextran) to
the whole magnetization, the dead layer thickness ($t$) and saturation
magnetization $M_s$ of the magnetic cores in our samples were estimated to be
$t = 6.8~\mathrm{\AA}$ and $M_s = 98.8~\mathrm{emu/g}$, respectively. The data
of $M_s$ were analyzed using a law of approach to saturation, indicating an
increase in effective magnetic anisotropy ($K_{eff}$) with decreasing particle
size as expected from the increased surface/volume ratio in small MNPs. The
obtained $K_{eff}$ values were successfully modeled by including an extra
contribution of dipolar interactions due to the formation of chain-like
clusters of MNPs. The surface magnetic anisotropy ($K_s$) was estimated to be
about $K_s = 1.04\times10^5~\mathrm{J/m^3}$. Our method provides a simple and
accurate way to obtain the $M_s$ core values in surface-disordered MNPs, a
relevant parameter required for magnetic modeling in many applications.",2303.14654v1
2023/7/20,Fast Current Regulation and Persistent Current Maintenance of High-Temperature Superconducting Magnets with Contact Power Supply and Flux Pump,"Due to the properties of high temperature superconducting (HTS) materials,
current attenuation is inevitable during the closed-loop operation of HTS
magnets. When a contact DC power supply is used to supplement this attenuation,
it inevitably creates a huge thermal burden on the cryogenic system. The flux
pump is a revolutionary new power source that can charge closed-loop HTS magnet
wirelessly. However, for HTS magnets with a large inductance, such as particle
accelerator magnets and magnetic confinement magnet in Tokamak devices, the
flux pump cannot fast adjust the DC current of the magnet, due to its small DC
output voltage. Here, we present a method to fast regulate the current in a
closed-loop HTS magnet using a contact DC power supply and persistent current
switch (PCS). After current regulation, the HTS magnet is operated in the
persistent current mode (PCM) with a flux pump. By applying the ""four-quadrant""
control theory of the flux pump allows, the current in HTS magnet is controlled
with high stability. This study provide a power strategy for the fast current
regulation and maintenance of persistent current in the HTS magnet, enabling
the industrial applications of flux pumps for HTS magnets with large
inductance.",2307.10557v1
2023/12/14,Nanoscale magnetism and magnetic phase transitions in atomically thin CrSBr,"Since their first observation in 2017, atomically thin van der Waals (vdW)
magnets have attracted significant fundamental, and application-driven
attention. However, their low ordering temperatures, $T_c$, sensitivity to
atmospheric conditions and difficulties in preparing clean large-area samples
still present major limitations to further progress. The remarkably stable
high-$T_c$ vdW magnet CrSBr has the potential to overcome these key
shortcomings, but its nanoscale properties and rich magnetic phase diagram
remain poorly understood. Here we use single spin magnetometry to
quantitatively characterise saturation magnetization, magnetic anisotropy
constants, and magnetic phase transitions in few-layer CrSBr by direct magnetic
imaging. We show pristine magnetic phases, devoid of defects on micron
length-scales, and demonstrate remarkable air-stability down the monolayer
limit. We address the spin-flip transition in bilayer CrSBr by direct imaging
of the emerging antiferromagnetic (AFM) to ferromagnetic (FM) phase wall and
elucidate the magnetic properties of CrSBr around its ordering temperature. Our
work will enable the engineering of exotic electronic and magnetic phases in
CrSBr and the realisation of novel nanomagnetic devices based on this highly
promising vdW magnet.",2312.09279v1
2024/3/15,Spontaneous spin chirality reversal and competing phases in the topological magnet EuAl$_4$,"We demonstrate the spontaneous reversal of spin chirality in a single crystal
sample of the intermetallic magnet EuAl$_4$. We solve the nanoscopic nature of
each of the four magnetically phases of EuAl$_4$ using resonant magnetic x-ray
scattering, and demonstrate all four phases order with single-k incommensurate
magnetic modulation vectors. Below 15.4 K the system forms a spin density
modulated spin structure where the spins are orientated in the ab plane
perpendicular to the orientation of the magnetic propagation vector. Below 13.2
K a second spin density wave orders with moments aligned parallel to the
c-axis, such that the two spin density wave orders coexist. Below 12.2 K a
magnetic helix of a single chirality is stabilised across the entire sample.
Below 10 K the chirality of the magnetic helix reverses, and the sample remains
a single chiral domain. Concomitant with the establishment of the helical
magnetic ordering is the lowering of the crystal symmetry to monoclinic, as
evidenced the formation of uniaxial charge and spin strip domains. A group
theoretical analysis demonstrates that below 12.2 K the symmetry lowers to
polar monoclinic, which is necessary to explain the observed asymmetry in the
chiral states of the magnetic helix and the spin chiral reversal. We find that
in every magnetically ordered phase of EuAl4 the in-plane moment is
perpendicular to the orientation of the magnetic propagation vector, which we
demonstrate is favoured by magnetic dipolar interactions.",2403.10159v1
2002/6/25,"Zero Permeability Materials (ZmuM): A way out of the ""Left Handed Materials"" trap","Recently it has been shown that due to losses the claims on observation of
negative refraction using metamaterials are questionable. In this paper we
discus an interesting case that is based in almost zero permeability at a given
frequency: zero permeability materials. This represents a way out of the
problem of left handed materials, and constitutes a material that acts a band
pass filter with a very narrow band. The metamaterials claimed to present
negative refraction are just showing this effect. However, absorption can be
diminished in those metamaterials by using thicker wires. Materials based in
quasi metallic magnetic structures are proposed with ferromagnetic resonance at
microwave frequencies under applied magnetic fields. These materials, as well
as the zero permitivity in thin films, open a new ground for a new set of
optical devices.",0206476v1
2019/11/27,Computational screening of magnetocaloric alloys,"An exciting development over the past few decades has been the use of
high-throughput computational screening as a means of identifying promising
candidate materials for a variety of structural or functional properties.
Experimentally, it is often found that the highest-performing materials contain
substantial atomic site disorder. These are frequently overlooked in
high-throughput computational searches however, due to difficulties in dealing
with materials that do not possess simple, well-defined crystallographic unit
cells. Here we demonstrate that the screening of magnetocaloric materials with
the help of the density functional theory-based magnetic deformation proxy can
be extended to systems with atomic site disorder. This is accomplished by
thermodynamic averaging of the magnetic deformation for ordered supercells
across a solid solution. We show that the highly non-monotonic magnetocaloric
properties of the disordered solid solutions Mn(Co$_{1-x}$Fe$_x$)Ge and
(Mn$_{1-x}$Ni$_x$)CoGe are successfully captured using this method.",1911.12218v3
2020/2/10,Magnetic Field Simulation with Data-Driven Material Modeling,"This paper developes a data-driven magnetostatic finite-element (FE) solver
which directly exploits measured material data instead of a material curve
constructed from it. The distances between the field solution and the
measurement points are minimized while enforcing Maxwell's equations. The
minimization problem is solved by employing the Lagrange multiplier approach.
The procedure wraps the FE method within an outer data-driven iteration. The
method is capable of considering anisotropic materials and is adapted to deal
with models featuring a combination of exact material knowledge and measured
material data. Thereto, three approaches with an increasing level of
intrusivity according to the FE formulation are proposed. The numerical results
for a quadrupole-magnet model show that data-driven field simulation is
feasible and affordable and overcomes the need of modeling the material law.",2002.03715v2
2020/6/2,"Fabrication of magnetocaloric La(Fe,Si)$_{13}$ thick films","La(Fe,Si)$_{13}$-based compounds are considered to be very promising
magnetocaloric materials for magnetic refrigeration applications. Many studies
have focused on this material family but only in bulk form. In this paper, we
report the fabrication of thick films of La(Fe,Si)$_{13}$, both with and
without post-hydriding. These films exhibit magnetic and structural properties
comparable to those of bulk materials. We also observe that the ferromagnetic
phase transition has a negative thermal hysteresis, a phenomenon not previously
found in this material but which may have its origins in the availability of a
strain energy reservoir, as in the cases of other materials in which negative
thermal hysteresis has been found. Here, it appears that the substrate acts to
store strain energy. Our exploratory study demonstrates the viability of thick
films of the La(Fe,Si)$_{13}$ phase and motivates further work in the area,
while showing that additional perspectives can be gained from reducing the
dimensionality of magnetocaloric materials in which the magneto-volume effect
is large.",2006.01656v1
2023/7/7,Dynamic Nuclear Polarization in Battery Materials,"The increasing need for portable and large-scale energy storage systems
requires development of new, long lasting and highly efficient battery systems.
Solid state NMR spectroscopy has emerged as an excellent method for
characterizing battery materials. Yet, it is limited when it comes to probing
thin interfacial layers which play a central role in the performance and
lifetime of battery cells. Here we review how Dynamic Nuclear Polarization
(DNP) can lift the sensitivity limitation and enable detection of the
electrode-electrolyte interface, as well as the bulk of some electrode and
electrolyte systems. We describe the current challenges from the point of view
of materials development; considering how the unique electronic, magnetic and
chemical properties differentiate battery materials from other applications of
DNP in materials science. We review the current applications of exogenous and
endogenous DNP from radicals, conduction electrons and paramagnetic metal ions.
Finally, we provide our perspective on the opportunities and directions where
battery materials can benefit from current DNP methodologies as well as project
on future developments that will enable NMR investigation of battery materials
with sensitivity and selectivity under ambient conditions.",2307.03495v1
2023/8/27,How to produce spin-splitting in antiferromagnetic materials,"Antiferromagnetic (AFM) materials have potential advantages for spintronics
due to their robustness, ultrafast dynamics, and magnetotransport effects.
However, the missing spontaneous polarization and magnetization hinders the
efficient utilization of electronic spin in these AFM materials. Here, we
propose a simple way to produce spin-splitting in AFM materials by making the
magnetic atoms with opposite spin polarization locating in the different
environment (surrounding atomic arrangement), which does not necessarily
require the presence of spin-orbital coupling (SOC). We confirm our proposal by
four different types of two-dimensional (2D) AFM materials within the
first-principles calculations. Our works provide a intuitional design principle
to find or produce spin-splitting in AFM materials.",2308.14097v1
2023/12/29,Machine-learned models for magnetic materials,"We present a general framework for modeling materials using deep neural
networks. Material represented by multidimensional characteristics (that mimic
measurements) is used to train the neural autoencoder model in an unsupervised
manner. The encoder is trying to predict the material parameters of a
theoretical model, which is then used in a decoder part. The decoder, using the
predicted parameters, reconstructs the input characteristics. The neural model
is trained to capture a synthetically generated set of characteristics that can
cover a broad range of material behaviors, leading to a model that can
generalize on the underlying physics rather than just optimize the model
parameters for a single measurement. After setting up the model we prove its
usefulness in the complex problem of modeling magnetic materials in the
frequency and current (out-of-linear range) domains simultaneously.",2401.00072v1
2004/1/28,The influence of complex material coverings on the bandwidth of antennas,"The influence of material coverings on the antenna bandwidth is investigated
for antennas formed by thin electric or magnetic line sources. It is shown that
uniform thin layers of arbitrary passive materials (including Veselago,
left-handed, or double-negative materials) cannot help to overcome the
bandwidth limitations imposed by the amount of energy stored in the antenna
reactive field. Alternative possibilities offered by complex composite
materials in the antenna design are identified.",0401144v1
2007/11/26,Ab initio prediction on ferrotoroidic olivine Li4MnFeCoNiP4O16,"First-principles calculation predict that olivine Li4MnFeCoNiP4O16 has
ferrotoroidic characteristic and ferrimagnetic configuration with magnetic
moment of 1.56 \muB per formula unit. The ferrotoroidicity of this material
makes it a potential candidate for magnetoelectric materials . Based on the
orbital-resolved density of states for the transtion-metal ions in
Li4MnFeCoNiP4O16, the spin configuration for Mn2+,Fe3+,Co2+, and Ni2+ is
t2g3eg2, t2g3eg2,t2g1t2g3eg1eg2, and t2g2t2g3eg1eg2, respectively. Density
functional theory plus U (DFT+U) shows a indirect band gap of 1.25 eV in this
predicted material, which is not simply related to the electronic conductivity
in terms of being used as cathode material in rechargeable Li-ion batteries.",0711.3904v1
2012/3/7,Anisotropic Curie temperature materials,"Existence of anisotropic Curie temperature materials [E. R. Callen, Phys.
Rev. 124, 1373 (1961)] is a longstanding prediction - materials that become
paramagnetic along certain crystal directions at a lower temperature while
remaining magnetically ordered in other directions up to a higher temperature.
Validating Callen's theory, we show that all directions within the basal plane
of monoclinic Fe7S8 single crystals remain ordered up to 603 K while the hard
c-axis becomes paramagnetic at 225 K. Materials with such a large directional
dependence of Curie temperature opens the possibility of uniquely new devices
and phenomena.",1203.1475v1
2018/12/13,"A comment on ""The Computational 2D Materials Database: high-throughput modeling and discovery of atomically thin crystals""","Recently, Sten Haastrup, Mikkel Strange, Mohnish Pandey, Thorsten Deilmann,
Per S Schmidt, Nicki F Hinsche, Morten N Gjerding, Daniele Torelli, Peter M
Larsen, Anders C Riis-Jensen, Jakob Gath, Karsten W Jacobsen, Jens Jrgen
Mortensen, Thomas Olsen and Kristian S Thygesen [2D Mater. 5 (2018) 042002]
introduced the Computational 2D Materials Database (C2DB), which organises a
variety of structural, thermodynamic, elastic, electronic, magnetic, and
optical properties of around 1500 two-dimensional materials distributed over
more than 30 different crystal structures. Unfortunately, the work contains
serious and fundamental flaws in the field of elasticity and mechanical
stability tests what makes it unreliable.",1812.05372v2
2009/9/21,How many bits may fit in a single magnetic dot? XMCD-PEEM evidences the switching of Néel caps inside Bloch domain walls,"Data storage relies on the handling of two states, called bits. The market of
mass storage is currently still dominated by magnetic technology, hard disk
drives for the broad public and tapes for massive archiving. In these devices
each bit is stored in the form of the direction of magnetization of nanosized
magnetic domains, i.e. areas of ferromagnetic materials displaying a uniform
magnetization. While miniaturization is the conventional way to fuel the
continuous increase of device density, disruptive solutions are also sought. To
these pertain in recent years many fundamental studies no longer considering
the magnetic domains themselves, but the manipulation of the domain walls (DWs)
that separate such domains. Concepts of storage and logic based on the
propagation of DWs along lithographically-patterned stripes have been patented,
while many fundamental aspects of DW propagation deeply related to condensed
matter physics are still hotly debated. If one now considers magnetic dots of
submicrometer dimensions, the magnetization has a tendency to curl along the
outer edges of the nanostructure to close its magnetic flux and thereby reduce
its magnetostatic energy. Then both domains and DWs of well-defined geometries
arise, whose combined manipulation has been proposed as a multilevel magnetic
storage scheme...",0909.3731v1
2010/12/10,Anion vacancy driven magnetism in incipient ferroelectric SrTiO3 and KTaO3 nanoparticles,"Based on our analytical results [http://arxiv.org/abs/1006.3670], we predict
that undoped nanoparticles (size <10-100nm) of incipient ferroelectrics without
any magnetic ions can become ferromagnetic even at room temperatures due to the
inherent presence of a new type of magnetic defects with spin S=1, namely
oxygen vacancies, where the magnetic triplet state is the ground state in the
vicinity of the surface (magnetic shell), while the nonmagnetic singlet is the
ground state in the bulk material (nonmagnetic core). Consideration of randomly
distributed magnetic spins (S=1) had shown that magnetic properties of
incipient ferroelectric nanoparticles are strongly size and temperature
dependent due to the size and temperature dependence of their dielectric
permittivity and the effective Bohr radius proportional to permittivity. The
phase diagrams in coordinates temperature - particle radius are considered. In
particular, for particle radii less that the critical radius ferromagnetic
long-range order appears in a shell region of thickness 5 - 50 nm once the
concentration of magnetic defects exceeds the magnetic percolation threshold.
The critical radius is calculated in the mean field theory from the condition
of the magnetic defects exchange energy equality to thermal energy. For
particle radii higher than critical value only the paramagnetic phase is
possible. The conditions of the super-paramagnetic state appearance in the
assembly of nanoparticles with narrow distribution function of their sizes are
discussed also.",1012.2400v1
2013/4/9,Magnetocaloric effect and its implementation in critical behavior study of Mn4FeGe3-xSix intermetallic compounds,"Magnetocaloric effect in Mn4FeGe3-xSix compounds has been studied by dc
magnetization measurements. For the parent compound Mn4FeGe3, the paramagnetic
to ferromagnetic transition temperature TC is above room temperature (320 K),
which initially remains constant for small Si substitution at the Ge site and
then decreases marginally with an increase in Si concentration. A large change
in magnetic entropy at the TC, under a magnetic field variation of 50 kOe, with
typical values of 5.9, 6.5, 5.9 and 4.4 J kg-1 K-1 for x = 0, 0.2, 0.6, and 1
samples, respectively, along with a broad operating temperature range and a
negligible hysteresis make Mn4FeGe3-xSix series a promising candidate for
magnetic refrigerant material around room temperature. Mn4FeGe3-xSix series is
found to undergo a second-order magnetic phase transition. The field dependence
of the magnetic entropy change has been brought out and implemented it to
deduce the critical exponents. The critical behavior study shows that the
magnetic interactions for x = 0 and 0.2 samples have two different behaviors
below and above TC. Below TC, it follows the mean field theory with long-range
magnetic interaction and above TC it follows the Heisenberg three-dimensional
model with short-range or local magnetic interaction. The magnetic exchange
interactions for the x = 0.6 and 1 samples follow the mean-field theory.",1304.2465v1
2013/8/28,"Magnetic properties of a long, thin-walled ferromagnetic nanotube","We consider magnetic properties of a long, thin-walled ferromagnetic
nanotube. We assume that the tube consists of isotropic homogeneous magnet
whose spins interact via the exchange energy, the dipole-dipole interaction
energy, and also interact with an external field via Zeeman energy. Possible
stable states are the parallel state with the magnetization along the axis of
the tube, and the vortex state with the magnetization along azimuthal
direction. For a given material, which of them has lower energy depends on the
value \gamma=R^2d/(L \lambda_x^2), where R is the radius of the tube, d is its
thickness, L is its length and \lambda_x is an intrinsic scale of length
characterizing the ration of exchange and dipolar interaction. At \gamma<1 the
parallel state wins, otherwise the vortex state is stable. A domain wall in the
middle of the tube is always energy unfavorable, but it can exist as a
metastable structure. Near the ends of a tube magnetized parallel to the axis a
half-domain structure transforming gradually the parallel magnetization to a
vortex just at the edge of the tube is energy favorable. We also consider the
equilibrium magnetization textures in an external magnetic field either
parallel or perpendicular to the tube. Finally, magnetic fields produced by a
nanotube and an array of tubes is analyzed.",1308.6233v1
2013/10/10,"Magnetization non-rational quasi-plateau and spatially modulated spin order in the model of the single-chain magnet, [{(CuL)_2 Dy}{Mo(CN)_8}] 2CH_3CN H_2O","Using the exact solution in terms of the generalized classical transfer
matrix method we presented a detailed analysis of the magnetic properties and
ground state structure of the simplified model of the single-chain magnet,
trimetallic coordination polymer compound, [{(CuL)_2 Dy}{Mo(CN)_8}] 2CH_3CN
H_2O is N,N'-propylenebis(3-methoxysalicylideneiminato). Due to appearance of
highly anisotropic Dy3+ ion this material is an unique example of the
one-dimensional magnets with Ising and Heisenberg bonds, allowing exact
statistical-mechanical treatment. We found two zero-temperature ground states
corresponding to different part of the magnetization curve of the material. The
zero-filed ground state is shown to be an antiferromagnetic configuration with
spatial modulation of the local Dy3+(which is proven to posses well defined
Ising like properties due two large anisotropy of g-factors) and composite
S=1/2 spin of the quantum spin trimer Cu-Mo-Cu in the form
""up""-""down""-""down""-""up"". Another important feature of this compound is the
appearance of the quasi-plateau at non rational value of magnetization due to
difference of the g-factors of the Cu- and Mo-ion in quantum spin trimers. The
quasi-plateau is an almost horizontal part of the magnetization curve where the
corresponding zero-temperature ground state of the chain demonstrate slow but
monotonous dependence of the magnetization on the external magnetic field,
while the $z$-projection of the total spin is constant.",1310.2811v2
2014/8/27,Short-range magnetic correlations in the highly-correlated electron compound CeCu$_{4}Ga,"We present experimental results for the heavy-electron compound CeCu$_{4}$Ga
which show that it possesses short-range magnetic correlations down to a
temperature of $T = 0.1$ K. Our neutron scattering data show no evidence of
long-range magnetic order occurring despite a peak in the specific heat at
$T^{*} =1.2$ K. Rather, magnetic diffuse scattering occurs which corresponds to
short-range magnetic correlations occurring across two unit cells. The specific
heat remains large as $T\sim0$ K resulting in a Sommerfeld coefficient of
$\gamma_{0} = 1.44(2)$ J/mol-K$^{2}$, and, below $T^{*}$, the resistivity
follows $T^{2}$ behavior and the ac magnetic susceptibility becomes temperature
independent. A magnetic peak centered at an energy transfer of
$E_{\rm{c}}=0.24(1)$ meV is seen in inelastic neutron scattering data which
shifts to higher energies and broadens under a magnetic field. We discuss the
coexistence of large specific heat, magnetic fluctuations, and short-range
magnetic correlations at low temperatures and compare our results to those for
materials possessing spin-liquid behavior.",1408.6576v2
2015/11/24,Dynamical magnetoelectric phenomena of multiferroic skyrmions,"Magnetic skyrmions, vortex-like swirling spin textures characterized by a
quantized topological invariant, realized in chiral-lattice magnets are
currently attracting intense research interest. In particular, their dynamics
under external fields is an issue of vital importance both for fundamental
science and for technical application. Whereas observations of magnetic
skyrmions had been limited to metallic magnets so far, their realization was
discovered also in a chiral-lattice insulating magnet Cu2OSeO3 in 2012.
Skyrmions in the insulator turned out to exhibit multiferroic nature with
spin-induced ferroelectricity. Strong magnetoelectric coupling between
noncollinear skyrmion spins and electric polarizations mediated by relativistic
spin-orbit interaction enables us to drive motion and oscillation of magnetic
skyrmions by application of electric fields instead of injection of electric
currents. Insulating materials also provide an environment suitable for
detection of pure spin dynamics through spectroscopic measurements owing to
absence of appreciable charge excitations. In this article, we review recent
theoretical and experimental studies on multiferroic properties and dynamical
magnetoelectric phenomena of magnetic skyrmions in insulators. We argue that
multiferroic skyrmions show unique coupled oscillation modes of magnetizations
and polarizations, so-called electromagnon excitations, which are both
magnetically and electrically active, and interference between the electric and
magnetic activation processes leads to peculiar magnetoelectric effects in a
microwave frequency regime.",1511.07761v1
2016/11/2,Anomalous Hall effect and magnetic orderings in nanothick V$_5$S$_8$,"The rise of graphene marks the advent of two-dimensional atomic crystals,
which have exhibited a cornucopia of intriguing properties, such as the integer
and fractional quantum Hall effects, valley Hall effect, charge density waves
and superconductivity, to name a few. Yet, magnetism, a property of extreme
importance in both science and technology, remains elusive. There is a
paramount need for magnetic two-dimensional crystals. With the availability of
many magnetic materials consisting of van der Waals coupled two-dimensional
layers, it thus boils down to the question of how the magnetic order will
evolve with reducing thickness. Here we investigate the effect of thickness on
the magnetic ordering in nanothick V$_5$S$_8$. We uncover an anomalous Hall
effect, by which the magnetic ordering in V$_5$S$_8$ down to 3.2 nm is probed.
With decreasing thickness, a breakdown of antiferromagnetism is evident,
followed by a spin-glass-like state. For thinnest samples, a weak ferromagnetic
ordering emerges. The results not only show an interesting effect of reducing
thickness on the magnetic ordering in a potential candidate for magnetic
two-dimensional crystals, but demonstrate the anomalous Hall effect as a useful
characterization tool for magnetic orderings in two-dimensional systems.",1611.00584v3
2018/7/22,Electrical switching of perpendicular magnetization in L10 FePt single layer,"Electrical manipulation of magnetization is essential for integration of
magnetic functionalities such as magnetic memories and magnetic logic devices
into electronic circuits. The current induced spin-orbit torque (SOT) in heavy
metal/ferromagnet (HM/FM) bilayers via the spin Hall effect in the HM and/or
the Rashba effect at the interfaces provides an efficient way to switch the
magnetization. In the meantime, current induced SOT has also been used to
switch the in-plane magnetization in single layers such as ferromagnetic
semiconductor (Ga,Mn)As and antiferromagnetic metal CuMnAs with globally or
locally broken inversion symmetry. Here we demonstrate the current induced
perpendicular magnetization switching in L10 FePt single layer. The current
induced spin-orbit effective fields in L10 FePt increase with the chemical
ordering parameter (S). In 20 nm FePt films with high S, we observe a large
charge-to-spin conversion efficiency and a switching current density as low as
7.0E6 A/cm2. We anticipate our findings may stimulate the exploration of the
spin-orbit torques in bulk perpendicular magnetic anisotropic materials and the
application of high-efficient perpendicular magnetization switching in single
FM layer.",1807.08244v1
2018/8/9,Blocking of iron magnetic moments and Spin density wave in FeTi2S4 and Fe2TiS4,"Iron-titanium sulfides FeTi2S4 and Fe2TiS4 have been structurally and
magnetically characterized using powder X Ray Diffraction with Rietveld
refinement method and 57Fe M\""ossbauer spectroscopy at variable temperature.
Both sulfides have the same crystallographic phase, based on the monoclinic
Cr3S4 type structure and vary in atomic coordinates; FeTi2S4 retains the ideal
atomic positions proposed for the Cr3S4 phase, while in Fe2TiS4 the metal
displacements from ideal sites are noticeable. M\""ossbauer spectra reveal
different magnetic behaviors; in FeTi2S4 there is a transition from
paramagnetic to magnetic ordering at temperature Tc = 145 K, giving rise to
unusually low hyperfine magnetic field of 2.5 T (at 77 K) if compared with
values of iron magnetic moments reported previously, this behavior is explained
on the basis of blocking Fe localized magnetic moments by the Spin density wave
(SDW) originated from 3d Ti atoms. In Fe2TiS4 a transition from paramagnetic to
(SDW) arises at Tc = 290 K, the SDW is spread in both Fe and Ti metals through
[101] crystallographic plane and undergoes a transition of first order from
Incommensurate SDW (ISWD) to Commensurate SDW (CSDW) at TIC = 255 K. The atomic
positions in the unit cell are correlated to the magnetic behavior in both
sulfides.",1808.03362v1
2019/10/16,Ultra-high frequency magnetic resonance through strain-spin coupling in perpendicular magnetic multi-layers,"The interaction between strain and spin has received intensive attention in
the scientific community due to its abundant physical phenomena and huge
technological impact. Until now, there is no experimental report on ultra-high
frequency magnetic resonance through the strain-spin coupling for any
technologically relevant perpendicular magnetic material. Here we report the
experimental detection of the acoustic strain waves that have a response time
on the order of 10 picoseconds in perpendicular magnetic [Co/Pd]n multilayers
via a femtosecond laser pulse excitation. Through direct measurements of
acoustic strain waves, we observe an ultra-high frequency magnetic resonance up
to 60 GHz in [Co/Pd]n multilayers. We further report a theoretical model of the
strain-spin interaction. Our model reveals that the energy could be transferred
efficiently from the strain to the spins and well explains the existence of a
steady resonance state through exciting the spin system. The physical origins
of the resonance between strain waves and magnetic precession and the requested
conditions for obtaining magnetic resonance within thin magnetic films have
also been discussed after thorough analysis. These combined results point out a
potential pathway to enable an extremely high frequency (EHF) magnetic
resonance through the strain-spin coupling.",1910.07147v2
2018/2/15,Hunting Down Magnetic Monopoles in 2D Topological Insulators,"Contrary to the electric charge that generates the electric field, magnetic
charge (namely magnetic monopoles) does not exist in the elementary
electromagnetism. Consequently, magnetic flux lines only form loops and cannot
have a source or a sink in nature. It is thus extraordinary to find that
magnetic monopoles can be pictured conceptually in topological materials.
Specifically in the 2D topological insulators, the topological invariant
corresponds to the total flux of an effective magnetic field (the Berry
curvature) over the reciprocal space.It is thus tempting to wrap the 2D
reciprocal space into a compact manifold--a torus, and imagine the total flux
to originate from magnetic monopoles inside the torus with a quantized total
charge. However, such a physically appealing picture has not been realized
quantitatively: other than their existence in a toy (actually misleading)
picture, the properties of the magnetic monopoles remain unknown. Here, we will
address this long-standing problem by hunting down the magnetic monopoles in
the reciprocal $k$-space. We will show that a simple and physically useful
picture will arrive upon analytically continuing the system to a third
imaginary momentum space. We then illustrate the evolution of the magnetic
monopoles across the topological phase transition and use it to provide natural
explanations on: 1) discontinuous jump of integer topological invariants, 2)
the semi-metallic nature on the phase boundary, and 3) how a change of global
topology can be induced via a local change in reciprocal space.",1802.05624v2
2018/5/26,Distinct spin-lattice and spin-phonon interactions in monolayer magnetic CrI$_3$,"We apply the density-functional theory to study various phases (including
non-magnetic (NM), anti-ferromagnetic (AFM), and ferromagnetic (FM)) in
monolayer magnetic chromium triiodide (CrI$_3$), a recently fabricated 2D
magnetic material. It is found that: (1) the introduction of magnetism in
monolayer CrI$_3$ gives rise to metal-to-semiconductor transition; (2) the
electronic band topologies as well as the nature of direct and indirect band
gaps in either AFM or FM phases exhibit delicate dependence on the magnetic
ordering and spin-orbit coupling; and (3)the phonon modes involving Cr atoms
are particularly sensitive to the magnetic ordering, highlighting distinct
spin-lattice and spin-phonon coupling in this magnet. First-principles
simulations of the Raman spectra demonstrate that both frequencies and
intensities of the Raman peaks strongly depend on the magnetic ordering. The
polarization dependent $A_{1g}$ modes at 77 cm$^{-1}$ and 130 cm$^{-1}$ along
with the $E_g$ mode at about 50 cm$^{-1}$ in the FM phase may offer a useful
fingerprint to characterize this material. Our results not only provide a
detailed guiding map for experimental characterization of CrI$_3$, but also
reveal how the evolution of magnetism can be tracked by its lattice dynamics
and Raman response.",1805.10479v2
2019/5/14,Versatile Hall magnetometer with variable sensitivity assembly for characterization of the magnetic properties of nanoparticles,"A Hall magnetometer with variable sensitivity is constructed to measure the
magnetic properties of magnetic nanoparticles manufactured by different
methods. This novel magnetometer can also be used to measure bulk materials and
samples in liquids. The magnetometer is constructed with two commercial
Hall-effect sensors in an acrylic structure, which serves as the support for a
micrometer and the circuit board with the sensors. For operation, the
magnetometer it acquires a complete magnetization curve in a few minutes. If
has a magnetic moment sensitivity of 1.3*10-9 Am2 to sensitivity of 493 mV/mT,
the sensitivity can be adjustable in the range of 10 to 493 mV/mT. Its
performance is tested with magnetic nanoparticles. As an application example,
we estimate the mean diameter of the nanoparticles using the magnetic curves.
The results are compared with those obtained by other techniques, such as
transmission electron microscopy (TEM), X-ray diffraction (XRD) and dynamic
light scattering (DLS). The magnetization results are also compared with those
obtained by independent commercial magnetometers, which reveals errors of
approximately 0.31 Am2/kg (i.e., 0.6%) in the saturation region.",1905.05741v2
2020/2/18,Magnetic and all-optical switching properties of amorphous Tb$_x$Co$_{100-x}$ alloys,"Amorphous Tb$_{x}$Co$_{100-x}$ magnetic alloys exhibit a list of intriguing
properties, such as perpendicular magnetic anisotropy, high magneto-optical
activity and magnetization switching using ultrashort optical pulses. Varying
the Tb:Co ratio in these alloys allows for tuning properties such as the
saturation magnetic moment, coercive field and the performance of the
light-induced magnetization switching. In this work, we investigate the
magnetic, optical and magneto-optical properties of various
Tb$_{x}$Co$_{100-x}$ thin film alloy compositions. We report on the effect the
choice of different seeding layers has on the structural and magnetic
properties of Tb$_{x}$Co$_{100-x}$ layers. We also demonstrate that for a range
of alloys, deposited on fused silica substrates, with Tb content of 24-30
at.$\%$, helicity dependent all-optical switching of magnetization can be
achieved, albeit in a multi-shot framework. We explain this property to arise
from the helicity-dependent laser induced magnetization on the Co sublattice
due to the inverse Faraday effect. Our study provides an insight into material
aspects for future potential hybrid magneto-plasmonic TbCo-based architectures.",2002.07544v3
2020/11/19,Critical bending and magnetic shape memory effect in magnetoactive elastomers,"The results of a study of magnetoactive elastomers (MAEs) consisting of an
elastomer matrix with embedded ferromagnetic particles are presented. A
continuous critical bending induced by the magnetic field, characterized by a
critical exponent for the bending magnitude, and the derivative of which has a
singularity in the critical region is reported for the first time. The
mechanical stability loss and the symmetry reduction of the magnetic state,
which are interrelated with each other, take place at the critical point. The
magnetization in the high-symmetric state (below the critical point) is
directed along the magnetic field and the torque is absent. Above the critical
point, the magnetization and the magnetic field are noncollinear and there
arises a torque, which is self-consistent with the bending. The magnetic field
dependence of the MAE bending was found to have a hysteresis, which is
associated with the magneto-rheological effect. The shape memory effect was
also obtained for the MAE bending in a cycle consisting of magnetization,
cooling (at H=/0), and heating (at H=0). The influence of the critical glass
transition temperature of the matrix, as well as its melting/solidification
temperature, on the magnetic shape memory effect was studied.",2011.09689v1
2020/12/30,Magnetically Ejected Disks: Equatorial Outflows Near Vertically Magnetized Black Hole,"Black holes attract gaseous material from the surrounding environment. Cosmic
plasma is largely ionized and magnetized because of electric currents flowing
in the highly conductive environment near black holes; the process of accretion
then carries the magnetic flux onto the event horizon, $r\simeq R_+$. On the
other hand, magnetic pressure acts against accretion. It can not only arrest
the inflow but it can even push the plasma away from the black hole if the
magnetic repulsion prevails. The black hole does not hold the magnetic field by
itself.
  In this contribution we show an example of an equatorial outflow driven by a
large scale magnetic field. We initiate our computations with a spherically
symmetric distribution of gas, which flows onto the domain from a large
distance, $r\gg R_+$. After the flow settles in a steady (Bondi) solution, we
impose an axially symmetric configuration of a uniform (Wald) magnetic field
aligned with the rotation axis of the black hole. Then we evolve the initial
configuration numerically by employing the MHD code that approaches the
force-free limit of a perfectly conducting fluid.
  We observe how the magnetic lines of force start accreting with the plasma
while an equatorial intermittent outflow develops and goes on ejecting some
material away from the black hole.",2012.15105v1
2021/1/1,"Structure and magnetic properties of melilite-type compounds RE2Be2GeO7 (RE = Pr, Nd, Gd-Yb) with Rare-Earth ions on Shastry-Sutherland lattice","Rare-earth (RE) based frustrated magnets as typical systems of combining
strong spin-orbit coupling, geometric frustration and anisotropic exchange
interactions, can give rise to diverse exotic magnetic ground states such as
quantum spin liquid (QSL). The discovery of new RE-based frustrated materials
is crucial for exploring the exotic magnetic phases. Herein, we report the
synthesis, structure and magnetic properties of a family of melilite-type
RE2Be2GeO7 (RE = Pr, Nd, Gd-Yb) compounds crystallized in a tetragonal
structure, where magnetic RE3+ ions lay out on Shastry-Sutherland lattice (SSL)
within ab-plane and are well separated by nonmagnetic GeBe2O7 polyhedrons along
c-axis. Temperature-dependent susceptibilities and isothermal magnetization
M(H) measurements reveal that most RE2Be2GeO7 compounds except RE=Tb show no
magnetic ordering down to 2 K despite the dominant antiferromagnetic (AFM)
interactions, where Tb2Be2GeO7 undergoes AFM transition with Neel temperature
TN~ 2.5 K and field-induced spin flop behaviors (T< TN). In addition, the
calculated magnetic entropy change from the isothermal M(H) curves reveal a
viable magnetocaloric effect (MCE) for RE2Be2GeO7 (RE =Gd, Dy) in liquid helium
temperature regimes, Gd2Be2GeO7 shows maximum Sm up to 54.8 J K-1 Kg-1 at H= 7
T and Dy2Be2GeO7 has largest value Sm=16.1 J K-1 kg-1 at H= 2 T in this family.
More excitingly, rich diversity of RE ions in this family enables an archetype
for exploring exotic quantum magnetic phenomena with large variability of spin
located on SSL lattice.",2101.00156v1
2021/3/16,Complex magnetism of the two-dimensional antiferromagnetic Ge2F: from a Néel spin-texture to a potential antiferromagnetic skyrmion,"Based on density functional theory combined with low-energy models, we
explore the magnetic properties of a hybrid atomic-thick two-dimensional (2D)
material made of Germanene doped with fluorine atoms in a half-fluorinated
configuration (Ge2F). The Fluorine atoms are highly electronegative, which
induce magnetism and break inversion symmetry, triggering thereby a finite and
strong Dzyaloshinskii-Moriya interaction (DMI). The magnetic exchange
interactions is of antiferromagnetic nature among the first, second and third
neighbors, which leads to magnetic frustration. The N\'eel state is found to be
the most stable state, with magnetic moments lying in the surface plane. This
results from the out-of-plane component of the DMI vector, which seems to
induce an effective in-plane magnetic anisotropy. Upon application of a
magnetic field, spin-spirals and antiferromagnetic skyrmions can be stabilized.
We conjecture that this can be realized via magnetic exchange fields induced by
a magnetic substrate. To complete our characterization, we computed the
spin-wave excitations and the resulting spectra, which could be probed via
electron energy loss spectroscopy, magneto-Raman spectroscopy or scanning
tunneling spectroscopy.",2103.08964v1
2021/6/29,A Kirchhoff-like theory for hard magnetic rods under geometrically nonlinear deformation in three dimensions,"Magneto-rheological elastomers (MREs) are functional materials that can be
actuated by applying an external magnetic field. MREs comprise a composite of
hard magnetic particles dispersed into a nonmagnetic elastomeric matrix. By
applying a strong magnetic field, one can magnetize the structure to program
its deformation under the subsequent application of an external field. Hard
MREs, whose coercivities are large, have been receiving particular attention
because the programmed magnetization remains unchanged upon actuation. Hence,
once a structure made of a hard MRE is magnetized, it can be regarded as
magnetized permanently. Motivated by a new realm of applications, there have
been significant theoretical developments in the continuum description of hard
MREs. By reducing the 3D description into 1D or 2D via dimensional reduction,
several theories of hard magnetic slender structures such as linear beams,
elastica, and shells have been recently proposed. In this paper, we derive an
effective theory for MRE rods under geometrically nonlinear 3D deformation. Our
theory is based on reducing the 3D magneto-elastic energy functional for the
hard MREs into a 1D Kirchhoff-like description. Restricting the theory to 2D,
we reproduce previous works on planar deformations. For further validation in
the general case of 3D deformation, we perform precision experiments with both
naturally straight and curved rods under either constant or constant-gradient
magnetic fields. Our theoretical predictions are in excellent agreement with
both discrete simulations and precision-model experiments. Finally, we discuss
some limitations of our framework, as highlighted by the experiments, where
long-range dipole interactions, which are neglected in the theory, can play a
role.",2106.15189v1
2021/7/6,Magnetic Twists of Solar Filaments,"Solar filaments are cold and dense materials situated in magnetic dips, which
show distinct radiation characteristics compared to the surrounding coronal
plasma. They are associated with coronal sheared and twisted magnetic field
lines. However, the exact magnetic configuration supporting a filament material
is not easy to be ascertained because of the absence of routine observations of
the magnetic field inside filaments. Since many filaments lie above weak-field
regions, it is nearly impossible to extrapolate their coronal magnetic
structures by applying the traditional methods to noisy photospheric
magnetograms, in particular the horizontal components. In this paper, we
construct magnetic structures for some filaments with the regularized
Biot--Savart laws and calculate their magnetic twists. Moreover, we make a
parameter survey for the flux ropes of the Titov-Demoulin-modified model to
explore the factors affecting the twist of a force-free magnetic flux rope. It
is found that the twist of a force-free flux rope is proportional to its axial
length to minor radius ratio, and is basically independent of the overlying
background magnetic field strength. Thus, we infer that long quiescent
filaments are likely to be supported by more twisted flux ropes than short
active-region filaments, which is consistent with observations.",2107.02580v1
2021/8/12,Optically controllable magnetism in atomically thin semiconductors,"Electronic states in two-dimensional layered materials can exhibit a
remarkable variety of correlated phases including Wigner-crystals, Mott
insulators, charge density waves, and superconductivity. Recent experimental
and theoretical research has indicated that ferromagnetic phases can exist in
electronically-doped transition metal dichalcogenide (TMD) semiconductors, but
a stable magnetic state at zero magnetic field has eluded detection. Here, we
experimentally demonstrate that mesoscopic ferromagnetic order can be generated
and controlled by local optical pumping in monolayer WSe2 at zero applied
magnetic field. In a spatially resolved pump-probe experiment, we use
polarization-resolved reflectivity from excitonic states as a probe of
charge-carrier spin polarization. When the sample is electron-doped at density
$n_e = 10^{12} cm^{-2}$, we observe that a local, circularly-polarized,
microwatt-power optical pump breaks the symmetry between equivalent
ferromagnetic spin configurations and creates magnetic order which extends over
mesoscopic regions as large as 8 um x 5 um, bounded by sample edges and folds
in the 2D semiconductor. The experimental signature of magnetic order is
circular dichroism (CD) in reflectivity from the excitonic states, with
magnitude exceeding 20% at resonant wavelengths. The helicity of the pump
determines the orientation of the magnetic state, which can be aligned along
the two principle out-of-plane axes. In contrast to previous studies in 2D
materials that have required non-local, slowly varying magnetic fields to
manipulate magnetic phases, the demonstrated capability to control long-range
magnetism and corresponding strong CD with local and tunable optical pumps is
highly versatile. This discovery will unlock new TMD-based spin and optical
technologies and enable sophisticated control of correlated electron phases in
two-dimensional electron gases (2DEGs).",2108.05931v1
2021/11/22,Magnetization Reversal in Two-dimensional Ensemble of Nanoparticles with Positional Defects,"We study relaxation behaviour in the two-dimensional assembly of magnetic
nanoparticles (MNPs) with aligned anisotropy axes and positional defects. The
anisotropy axes orientation and disorder strength is changed by varying
$\alpha$ and $\Delta$, respectively. The magnetization decay does not depend on
the aspect ratio $A^{}_r$ of the system and $\Delta$ for small dipolar
interaction strength $h^{}_d=0.2$. Remarkably, the magnetization decays rapidly
for considerable $h^{}_d$ with negligible $\Delta$ and $A_r=1.0$. The dipolar
interaction of enough strength promotes antiferromagnetic coupling in square
ensembles of MNPs. There is a prolonged magnetization decay for large $\Delta$
because of enhancement in ferromagnetic coupling. Notably, magnetization
relaxes slowly for $\alpha<\alpha^\star$ even with moderate $h^{}_d$ and a
significant $A^{}_r$. Interestingly, the slowing down of the magnetic
relaxation shifts to a lower $\alpha^{\star}$ with $h^{}_d=1.0$. The
magnetization ceases to relax for $\alpha\leq60^\circ$ and $h^{}_d\leq0.6$ due
to large shape anisotropy with $A^{}_r=400.0$. Remarkably, a majority of the
magnetic moment reverses its direction by $180^\circ$ for $\alpha>60^\circ$ and
large $h^{}_d$, resulting in the negative magnetization. The effective N\'eel
relaxation time $\tau^{}_N$ also depends strongly on these parameters.
$\tau^{}_N$ depends weakly on $\alpha$ and $\Delta$ for $h^{}_d\leq0.2$,
irrespective of $A^{}_r$. On the other hand, $\tau^{}_N$ decreases with
$\alpha$ for significant $h^{}_d$ provided $\alpha$ is greater than $45^\circ$
because of antiferromagnetic coupling dominance. In a highly anisotropic
system, there is an enhancement in $\tau^{}_N$ with $\alpha$ ($\leq30^\circ$)
even with moderate $h^{}_d$. While for $\alpha>30^\circ$, $\tau^{}_N$ decreases
with $\alpha$. These observations are useful in novel materials, spintronics
based applications, etc.",2111.11034v1
2022/4/8,"Plane wave implementation of the magnetic force theorem for magnetic exchange constants: Application to bulk Fe, Co and Ni","We present a plane wave implementation of the magnetic force theorem, which
provides a first principles framework for extracting exchange constants
parameterizing a classical Heisenberg model description of magnetic materials.
It is shown that the full microscopic exchange tensor may be expressed in terms
of the static Kohn-Sham susceptibility tensor and the exchange-correlation
magnetic field. This formulation allows one to define arbitrary magnetic sites
localized to predefined spatial regions, hence rendering the problem of finding
Heisenberg parameters independent of any orbital decomposition of the problem.
The susceptibility is calculated in a plane wave basis, which allows for
systematic convergence with respect to unoccupied bands and spatial
representation. We then apply the method to the well-studied problem of
calculating adiabatic spin wave spectra for bulk Fe, Co and Ni, finding good
agreement with previous calculations. In particular, we utilize the freedom of
defining magnetic sites to show that the calculated Heisenberg parameters are
robust towards changes in the definition of magnetic sites. This demonstrates
that the magnetic sites can be regarded as well-defined and thus asserts the
relevance of the Heisenberg model description despite the itinerant nature of
the magnetic state.",2204.04169v2
2022/9/12,High-temperature kinetic magnetism in triangular lattices,"We study kinetic magnetism for the Fermi-Hubbard models in triangular type
lattices, including a zigzag ladder, four- and six-legged triangular cylinders
and a full two-dimensional triangular lattice. We focus on the regime of strong
interactions, $U\gg t$ and filling factors around one electron per site. For
temperatures well above the hopping strength, the Curie-Weiss form of the
magnetic susceptibility suggests effective antiferromagnetic correlations for
systems that are hole doped with respect to $\nu=1$, and ferromagnetic
correlations for systems with electron dopings. We show that these correlations
arise from magnetic polaron dressing of charge carrier propagating in a spin
incoherent Mott insulator. Effective interactions corresponding to these
correlations can strongly exceed the magnetic super-exchange energy. In the
case of hole doping, antiferromagnetic polarons originate from kinetic
frustration of individual holes in a triangular lattice. In the case of
electron doping, Nagaoka type ferromagnetic correlations are induced by
propagating doublons. These results provide a theoretical explanation of recent
experimental results in moire TMDC materials. To understand many-body states
arising from antiferromagentic polarons at low temperatures, we study hole
doped systems in finite magnetic fields. At low dopings and intermediate
magnetic fields we find a magnetic polaron phase, separated from the fully
polarized state by a metamagnetic transition. With decreasing magnetic field
the system shows a tendency to phase separate, with hole rich regions forming
antiferromagnetic spinbags. We demonstrate that direct observations of magnetic
polarons in triangular lattices can be achieved in experiments with ultracold
atoms, which allow measurements of three point hole-spin-spin correlations.",2209.05398v1
2022/11/2,Density functional approach to elastic properties of three-dimensional dipole-spring models for magnetic gels,"Magnetic gels are composite materials, consisting of a polymer matrix and
embedded magnetic particles. Those are mechanically coupled to each other,
giving rise to the magnetostrictive effects as well as to a controllable
overall elasticity responsive to external magnetic fields. Due to their
inherent composite and thereby multiscale nature, a theoretical framework
bridging different levels of description is indispensable for understanding the
magnetomechanical properties of magnetic gels. In this study, we extend a
recently developed density functional approach from two spatial dimensions to
more realistic three-dimensional systems. Along these lines, we connect a
mesoscopic characterization resolving the discrete structure of the magnetic
particles, to macroscopic continuum parameters of magnetic gels. In particular,
we incorporate the long-range nature of the magnetic dipole-dipole interaction,
and consider the approximate incompressibility of the embedding media, and
relative rotations with respect to an external magnetic field breaking
rotational symmetry. We then probe the shape of the model system in its
reference state, confirming the dependence of magnetostrictive effects on the
configuration of the magnetic particles and on the shape of the considered
sample. Moreover, calculating the elastic and rotational coefficients on the
basis of our mesoscopic approach, we examine how the macroscopic types of
behavior are related to the mesoscopic properties. Implications for real
systems of random particle configurations are also discussed.",2211.01219v1
2022/11/16,Synchrotron emitting Komissarov torus with magnetic polarization around Kerr black holes,"Magnetic fields in black hole accretion disks are associated with processes
of mass accretion and energy amplification. The contribution of the magnetic
field due to the magnetic polarization of the material induces effects on the
physical properties of the medium that have repercussions on the radiation
coming from the accretion disks. Hence, from observations, it could be possible
to infer the ""fingerprint"" left by the magnetic polarization of the material
and establish the properties of the spacetime itself. As the first step in this
purpose, we use numerical simulations to systematically analyze the possible
observable effects produced by the magnetic properties of an accretion disk
around a Kerr black hole. We found that under the synchrotron radiation
power-law model the effects of the magnetic polarization are negligible when
the plasma is gas pressure-dominated. Nevertheless, as beta-plasma decreases,
the emission becomes more intense for magnetic pressure-dominated disks. In
particular, we found that paramagnetic disks emit the highest intensity value
independent of the beta-plasma parameter in this regime. By contrast, the
emitted flux decreases with the increase of beta-plasma due to the dependence
of the magnetic field on the emission and absorption coefficients. Moreover,
the disk morphology changes with the magnetic susceptibility: paramagnetic
disks are more compact than diamagnetic ones. This fact leads to diamagnetic
disks emitting a greater flux because each photon has a more optical path to
travel inside the disk.",2211.08912v1
2022/11/29,Spin Torque Oscillator and Magnetization Switching in double barrier Rashba Zeeman Magnetic Tunnel Junction,"In this letter, we have studied the spin torque based magnetization
oscillations and switching in presence of Rashba - Zeeman (RZ), Ruderman -
Kittel - Kasuya - Yoside (RKKY) and Dzyaloshinskii - Moriya (DM) interactions
in a double barrier RZ$|$Heavy Metal (HM)$|$RZ magnetic tunnel junction (MTJ).
The system has stable magnetization oscillations and can work as an oscillator
or a switcher for a significant difference in the strength of RKKY and DM
interaction under suitable spin transfer torque (STT). For the proposed system
with same order of RKKY and DM interaction, a nonlinear characteristic of the
magnetization oscillation is observed. However, this nonlinearity of
oscillations can be reduced by an external magnetic field or considering a
material with suitable RZ interaction. In addition to this, our study reveals
the magnetization switching can be tuned by using suitable STT. A dependence of
switching time on layer thickness is also observed. Also, the switching speed
increases with the thickness for systems having either same order of RKKY and
DM interaction or dominated by RKKY interaction. An opposite characteristic is
seen when DM interaction dominates over RKKY interaction.",2211.16127v2
2022/12/13,How to Build the Optimal Magnet Assembly for Magnetocaloric Cooling: Structural Optimization with Isogeometric Analysis,"In the search for more efficient and less environmentally harmful cooling
technologies, the field of magnetocalorics is considered a promising
alternative. To generate cooling spans, rotating permanent magnet assemblies
are used to cyclically magnetize and demagnetize magnetocaloric materials,
which change their temperature under the application of a magnetic field. In
this work, an axial rotary permanent magnet assembly, aimed for
commercialization, is computationally designed using topology and shape
optimization. This is efficiently facilitated in an isogeometric analysis
framework, where harmonic mortaring is applied to couple the rotating
rotor-stator system of the multipatch model. Inner, outer and co-rotating
assemblies are compared and optimized designs for different magnet masses are
determined. These simulations are used to homogenize the magnetic flux density
in the magnetocaloric material. The resulting torque is analyzed for different
geometric parameters. Additionally, the influence of anisotropy in the active
magnetic regenerators is studied in order to guide the magnetic flux. Different
examples are analyzed and classified to find an optimal magnet assembly for
magnetocaloric cooling.",2212.06580v2
2023/2/21,Exploring the magnetic properties of individual barcode nanowires using wide-field diamond microscopy,"Barcode magnetic nanowires typically comprise a multilayer magnetic structure
in a single body with more than one segment type. Interestingly, owing to
selective functionalization and novel interactions between the layers, barcode
magnetic nanowires have attracted significant attention, particularly in the
field of bioengineering. However, an analysis of their magnetic properties at
the individual nanowire level remains challenging. With this background,
herein, we investigated the characterization of magnetic nanowires at room
temperature under ambient conditions based on magnetic images obtained via
wide-field quantum microscopy with nitrogen-vacancy centers in diamond.
Consequently, we could extract critical magnetic properties, such as the
saturation magnetization and coercivity, of single nanowires by comparing the
experimental results with those of micromagnetic simulations. This study opens
up the possibility for a versatile characterization method suited to individual
magnetic nanowires.",2302.10547v1
2023/3/15,"Effect of X-Ray Irradiation on Magnetocaloric Material, (MnNiSi)1-x(Fe2Ge)x","(MnNiSi)1-(Fe2Ge)x composition (x=0.34) alloy was prepared by arc melting,
crushed, and sieved to approximately <32 microns. They were utilized in
examining the possible magnetic and structural changes when exposed to a dosage
of a continuous sweeping rate of ~>120 Gy/min and an absorbed dose of 35 kGy of
X-ray radiation. This study reports observable trends in X-ray diffraction and
magnetic measurements. Magnetization in the magnetization vs. temperature (both
heating and cooling) measurements showed an increase from 2.72 emu/g to 4.01
emu/g in the irradiated sample. The Magnetization vs. magnetic field loops
exhibited irradiation-induced magnetic hysteresis. The irradiated sample also
exhibited an observable change in its coercivity of {\Delta}Hc = 14.7% at 200
K. A maximum entropy change {\Delta}Smag of ~ 11.139 J/kg*K and a Tave peak of
317.5 K was achieved for the pristine sample in comparison to {\Delta}Smag of ~
11.349 J/kg*K and a Tave peak of 312.5 K for the irradiated sample. These
presented results provided deeper insights into tuning the effect of
irradiation to the magnetic properties of (MnNiSi)1-(Fe2Ge)x for composition
(x=0.34) that can be utilized in a wide range of magnetocaloric applications in
high-energy radiation environments. The irradiation applied to the sample did
not induce any structural or magnetic phase changes in the selected composition
but modified the magnetic properties marginally.",2303.08369v1
2023/8/20,Room temperature magnetic phase transition in an electrically-tuned van der Waals ferromagnet,"Finding tunable van der Waals (vdW) ferromagnets that operate at above room
temperature is an important research focus in physics and materials science.
Most vdW magnets are only intrinsically magnetic far below room temperature and
magnetism with square-shaped hysteresis at room-temperature has yet to be
observed. Here, we report magnetism in a quasi-2D magnet Cr1.2Te2 observed at
room temperature (290 K). This magnetism was tuned via a protonic gate with an
electron doping concentration up to 3.8 * 10^21 cm^-3. We observed
non-monotonic evolutions in both coercivity and anomalous Hall resistivity.
Under increased electron doping, the coercivities and anomalous Hall effects
(AHEs) vanished, indicating a doping-induced magnetic phase transition. This
occurred up to room temperature. DFT calculations showed the formation of an
antiferromagnetic (AFM) phase caused by the intercalation of protons which
induced significant electron doping in the Cr1.2Te2. The tunability of the
magnetic properties and phase in room temperature magnetic vdW Cr1.2Te2 is a
significant step towards practical spintronic devices.",2308.10324v2
2023/8/25,Helical magnetic state in the vicinity of the pressure-induced superconducting phase in MnP,"MnP is a metal that shows successive magnetic transitions from paramagnetic
to ferromagnetic and helical magnetic phases at ambient pressure with
decreasing temperature. With applied pressure, the magnetic transition
temperatures decrease and superconductivity appears around 8 GPa where the
magnetic order is fully suppressed and the quantum critical behavior is
observed. These results suggest that MnP is an unconventional superconductor in
which magnetic fluctuations may be relevant to the superconducting pairing
mechanism. In order to elucidate the magnetic ground state adjacent to the
superconducting phase first discovered in Mn-based materials, high-pressure
neutron diffraction measurements have been performed in hydrostatic pressure up
to 7.5 GPa. The helical magnetic structure with the propagation vector along
the $b$ axis, reported previously at 3.8 GPa, was found to be robust up to 7.5
GPa. First principles and classical Monte Carlo calculations have also been
performed to understand how the pressure-driven magnetic phase transitions are
coupled with change of the exchange interactions. The calculations, which
qualitatively reproduce the magnetic structures as a function of pressure,
suggest that the exchange interactions change drastically with applied pressure
and the further-neighbor interactions become more influential at high
pressures. Combining the experimental and theoretical results, we describe the
detail of exchange interactions in the vicinity of the superconducting phase
which is critical to understand the pairing mechanism of the unconventional
superconductivity in MnP.",2308.13634v1
2023/9/24,FeCo Nanowire-Strontium Ferrite Powder Composites for Permanent Magnets with High-Energy Products,"Due to the issues associated with rare-earth elements, there arises a strong
need for magnets with properties between those of ferrites and rare-earth
magnets that could substitute the latter in selected applications. Here, we
produce a high remanent magnetization composite bonded magnet by mixing FeCo
nanowire powders with hexaferrite particles. In the first step, metallic
nanowires with diameters between 30 and 100 nm and length of at least 2 {\mu}m
are fabricated by electrodeposition. The oriented as-synthesized nanowires show
remanence ratios above 0.76 and coercivities above 199 kA/m and resist core
oxidation up to 300 {\deg}C due to the existence of a > 8 nm thin oxide
passivating shell. In the second step, a composite powder is fabricated by
mixing the nanowires with hexaferrite particles. After the optimal nanowire
diameter and composite composition are selected, a bonded magnet is produced.
The resulting magnet presents a 20% increase in remanence and an enhancement of
the energy product of 48% with respect to a pure hexaferrite (strontium
ferrite) magnet. These results put nanowire-ferrite composites at the forefront
as candidate materials for alternative magnets for substitution of rare earths
in applications that operate with moderate magnet performance.",2309.13724v1
2024/1/23,Revisiting magnetic exchange interactions in transition metal doped Bi$_2$Se$_3$ using DFT+MFT,"Topological insulators doped with magnetic impurities has become a promising
candidate for Quantum Anomalous Hall Effect (QAHE) in the dilute doping limit.
The crucial factor in realizing the QAHE in these systems is the spontaneous
Ferromagnetic (FM) ordering between the doped magnetic atoms. Hence,
understanding the magnetic exchange interaction between the magnetic atoms
becomes essential. In this work, we use the Density functional theory (DFT) and
Magnetic force theorem (MFT) to calculate the magnetic exchange interaction
between magnetic impurities (V, Cr, Mn, Fe) in the host Bi2Se3. Through an
orbital decomposition of the calculated exchange, we can identify the nature
and origin of the exchange mechanism that depends on the type of magnetic
atoms, doping concentration, host material etc. Our results show that Cr doping
results in an insulating state, a prerequisite for the QAHE, that remains
robust against doping concentration and local correlation. In this case, the
short-ranged superexchange and long-ranged exchange via the p-orbitals of the
host results in an FM order. For other doped systems (V, Mn and Fe doped),
their electronic configuration and local octahedral environment open the
possibility of finite carrier density at the Fermi energy. Depending on the
type of this carrier (electron/hole) and their localized/delocalized nature, a
short-ranged double exchange / long-ranged RKKY mechanism could occur between
the magnetic atoms.",2401.12514v1
2024/1/24,Magnetic structure and Ising-like antiferromagnetism in the bilayer triangular lattice compound NdZnPO,"The complex interplay of spin frustration and quantum fluctuations in
low-dimensional quantum materials leads to a variety of intriguing phenomena.
This research focuses on a detailed analysis of the magnetic behavior exhibited
by NdZnPO, a bilayer spin-1/2 triangular lattice antiferromagnet. The
investigation employs magnetization, specific heat, and powder neutron
scattering measurements. At zero field, a long-range magnetic order is observed
at $T_{\rm N}=1.64~\rm K$. Powder neutron diffraction experiments show the
Ising-like magnetic moments along the $c$-axis, revealing a stripe-like
magnetic structure with three equivalent magnetic propagation vectors.
Application of a magnetic field along the $c$-axis suppresses the
antiferromagnetic order, leading to a fully polarized ferromagnetic state above
$B_{\rm c}=4.5~\rm T$. This transition is accompanied by notable enhancements
in the nuclear Schottky contribution. Moreover, the absence of spin frustration
and expected field-induced plateau-like phases are remarkable observations.
Detailed calculations of magnetic dipolar interactions revealed complex
couplings reminiscent of a honeycomb lattice, suggesting the potential
emergence of Kitaev-like physics within this system. This comprehensive study
of the magnetic properties of NdZnPO highlights unresolved intricacies,
underscoring the imperative for further exploration to unveil the underlying
governing mechanisms.",2401.13318v1
2024/3/7,The magnetic structure of Ce$_3$TiBi$_5$ and its relation to current-induced magnetization,"The control of magnetization using electric fields has been extensively
studied in magnetoelectric multiferroic insulator materials. Changes in
magnetization in bulk metals caused by electric currents have attracted less
attention. The recently discovered metallic magnet Ce$_3$TiBi$_5$ has been
reported to exhibit current-induced magnetization. Here we determined the
magnetic structure of Ce$_3$TiBi$_5$ using neutron diffraction, aiming to
understand the microscopic origin of this magnetoelectric phenomenon in a
metal. We established that the antiferromagnetic order emerging below $T_N=5$ K
is a cycloid order described by $P6_3/mcm.1'(0,0,g)00sss$ with small moment
sizes of $0.50(2)~\mu_B$ and propagation vector ${\bf k}=(0,0,0.386)$.
Surprisingly, the symmetry of this magnetic structure is inconsistent with the
presence of current-induced magnetization and potential origins of this
inconsistency with previous results are discussed. Additionally, our results
suggest that moments order along their hard magnetic direction in
Ce$_3$TiBi$_5$, a phenomenon which has been observed in other Kondo systems.",2403.04896v1
1995/8/9,Kinetic Ising Systems as Models of Magnetization Switching in Submicron Ferromagnets,"Recently experimental techniques, such as magnetic force microscopy (MFM),
have enabled the magnetic state of individual sub-micron particles to be
resolved. Motivated by these experimental developments, we use Monte Carlo
simulations of two-dimensional kinetic Ising ferromagnets to study the magnetic
relaxation in a negative applied field of a grain with an initial magnetization
$m_0 = +1$. The magnetostatic dipole-dipole interactions are treated to lowest
order by adding to the Hamiltonian a term proportional to the square of the
magnetization. We use droplet theory to predict the functional forms for some
quantities observed by MFM, such as the probability that the magnetization is
positive. Our simulations are in excellent agreement with droplet-theoretical
predictions. The qualitative agreement between experiments and our simulations
of switching in individual single-domain ferromagnets indicates that the
switching mechanism in such particles may involve local nucleation and
subsequent growth of droplets of the stable phase.",9508031v1
2001/2/27,Substrate-effect on the magnetic microstructure of La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ thin films studied by magnetic force microscopy,"Colossal magnetoresistive (CMR) La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ (LSMO) thin
films have been grown under tensile strains on (100)-SrTiO$_{3}$ substrates and
compressive strains on (100)-LaAlO$_{3}$ and (110)-NdGaO$_{3}$ substrates by
pulsed laser deposition.
  Using magnetic force microscopy (MFM), a ""feather-like"" magnetic pattern,
characteristic of films with an in-plane magnetization, is observed for films
deposited on both SrTiO$_{3}$ and NdGaO$_{3}$ while a ""bubble"" magnetic
pattern, typical of films with an out-of plane magnetization, is recorded for
LaAlO$_{3}$. We show that the shape of the magnetic pattern imaged by MFM is
fully correlated to the easy direction of the magnetization in the film.",0102496v1
2002/6/15,Magnetic structures and reorientation transitions in noncentrosymmetric uniaxial antiferromagnets,"A phenomenological theory of magnetic states in noncentrosymmetric tetragonal
antiferromagnets is developed, which has to include homogeneous and
inhomogeneous terms (Lifshitz-invariants) derived from Dzyaloshinskii-Moriya
couplings. Magnetic properties of this class of antiferromagnets with low
crystal symmetry are discussed in relation to its first known members, the
recently detected compounds Ba2CuGe2O7 and K2V3O8. Crystallographic symmetry
and magnetic ordering in these systems allow the simultaneous occurrence of
chiral inhomogeneous magnetic structures and weak ferromagnetism. New types of
incommensurate magnetic structures are possible, namely, chiral helices with
rotation of staggered magnetization and oscillations of the total
magnetization. Field-induced reorientation transitions into modulated states
have been studied and corresponding phase diagrams are constructed. Structures
of magnetic defects (domain-walls and vortices) are discussed. In particular,
vortices, i.e. localized non-singular line defects, are stabilized by the
inhomogeneous Dzyaloshinskii-Moriya interactions in uniaxial noncentrosymmetric
antiferromagnets.",0206291v1
2002/9/30,Investigation of a ring single molecular magnet Mn$_6$R$_6$ in megagauss fields,"The dependence of the magnetic susceptibility on the magnetic field is
investigated for the single molecular magnet [Mn(hfac)$_2$NITPh]$_6$. The
spikes of the susceptibility detected in a magnetic field ranging from 90 T to
285 T are interpreted as a manifestation of magnetic quantum jumps under spins
reorientation from ferrimagnetic to ferromagnetic structure. The characteristic
feature of the single molecular magnet Mn$_6$ R$_6$ is a deficiency of pair
Heisenberg exchange interactions for the description of its magnetic properties
in high magnetic fields. The comparison of the experimental data with the
results of theoretical calculations allows us to prove the existence of strong
three-spin interaction in this molecular cluster and to determine the values of
exchange constants. For the calculation of the ground state spin structure the
modified Lanczos method is used.",0209670v1
2002/10/20,Trapped magnetic field in a superconducting disk magnetized by uniform field,"The distribution of the current density and the profile of the trapped
magnetic field of a superconducting disk magnetized by uniform field are
calculated from first principles. The effect of the superconducting parameters
is taken into account by assuming the voltage-current law and the material law.
The sample volume, the critical current density and the flux creep exponent
dominate the strength of the trapped magnetic field. The flux creep exponent
determines the decay rate of the trapped magnetic field. The aspect ratio of
the sample influences the shape of the trapped magnetic flux lines. We conclude
that higher trapped magnetic field cannot always be obtained by increasing the
applied magnetic field.",0210431v1
2003/10/8,Neutron scattering evidence for magnetic field driven abrupt magnetic and structural transitions in a phase separated manganite,"Substitutions at the Mn-site of the charge-ordered Pr0.5Ca0.5MnO3 manganite
is an effective way to induce abrupt jumps on the magnetic field driven
magnetization curve. In order to get new insights into the origin of this
remarkable feature, the Pr0.5Ca0.5Mn0.97Ga0.03O3 perovskite manganite has been
studied by neutron diffraction, versus temperature and at 2.5K in an applied
magnetic field up to 6 Tesla. A weak and complex antiferromagnetic order is
found for the low temperature ground-state. Magnetic transitions, associated
with structural ones, are evidenced for certain strengths of magnetic field,
which gives rise to the step-like behavior corresponding to the magnetization
curve. Small angle neutron scattering provides evidence for a nucleation
process of micron size ferromagnetic domains which follows the magnetization
behavior.",0310167v2
2003/10/29,Magnetic nanoparticles as many-spin systems,"We present a review of recent advances in the study of many-body effects in
magnetic nanoparticles. Considering classical spins on a lattice coupled by the
exchange interaction in the presence of the bulk and surface anisotropy, we
investigate the effects of finite size, free boundaries, and surface anisotropy
on the average and local magnetization for zero and finite temperatures and
magnetic fields. Superparamagnetism of magnetic particles necessitates
introducing two different, induced and intrinsic, magnetizations. We check the
validity of the much used relation between them within different theoretical
models. We show that the competition between the exchange and surface
anisotropy leads to spin canting dependent on the orientation of the average
magnetization with respect to the crystallographic axes and thus to a
second-order effective anisotropy of the particle. We have also investigated
the switching mechanism of the magnetization upon varying the surface
anisotropy constant. Some cases of more realistic particles are also dealt
with.",0310694v1
2004/9/20,Switching of magnetization by non-linear resonance studied in single nanoparticles,"Magnetization reversal in magnetic particles is one of the fundamental issues
in magnetic data storage. Technological improvements require the understanding
of dynamical magnetization reversal processes at nanosecond time scales. New
strategies are needed to overcome current limitations. For example, the problem
of thermal stability of the magnetization state (superparamagnetic limit) can
be pushed down to smaller particle sizes by increasing the magnetic anisotropy.
High fields are then needed to reverse the magnetization that are difficult to
achieve in current devices. Here we propose a new method to overcome this
limitation. A constant applied field, well below the switching field, combined
with a radio-frequency (RF) field pulse can reverse the magnetization of a
nanoparticle. The efficiency of this method is demonstrated on a 20 nm cobalt
particle by using the micro-SQUID technique. Other applications of this method
might be nucleation or depinning of domain walls.",0409502v1
2005/2/5,Observation of magnetization reversal in epitaxial Gd0.67Ca0.33MnO3 thin films,"High quality epitaxial thin films of Gd0.67Ca0.33MnO3 have been deposited
onto (100) SrTiO3 substrates by pulsed-laser deposition. Enhanced properties in
comparison with bulk samples were observed. The magnetic transition temperature
(Tc) of the as-grown films is much higher than the corresponding bulk values.
Most interestingly, magnetization measurements performed under small applied
fields, exhibit magnetization reversals below Tc, no matter whether the film is
field-cooled (FC) or zero-field-cooled (ZFC). A rapid magnetization reversal
occurs at 7 K when field cooled, while as for the ZFC process the magnetization
decreases gradually with increasing temperatures, taking negative values above
7 K and changing to positive values again, above 83 K. In higher magnetic
fields the magnetization does not change sign. The reversal mechanism is
discussed in terms of a negative exchange f-d interaction and magnetic
anisotropy, this later enhanced by strain effects induced by the lattice
mismatch between the film and the substrate.",0502145v1
2005/5/6,Relaxation of thermo-remanent magnetization in Fe-Cr GMR multilayers,"The time decay of the thermo-remanent magnetization (TRM) in Fe-Cr giant
magnetoresistive (GMR) multilayers has been investigated. The magnetization in
these multilayers relaxes as a function of time after being cooled in a small
magnetic field of 100 Oe to a low temperature and then the magnetic field is
switched off. Low-field ($<$ 500 Oe) magnetization studies of these samples
have shown hysteresis. This spin-glass-like behavior may originate from
structural imperfections at the interfaces and in the bulk. We find that the
magnetization relaxation is logarithmic. Here the magnetic viscosity is found
to increase first with increasing temperature, then it reaches a maximum around
T$_g$, and then it decreases with increasing temperature. This behavior is
different from that of conventional spin glasses where the logarithmic creep
rate is observed to increase with temperature. Power law also gives good fits
and it is better than the logarithmic fit at higher temperatures. The dynamical
effects of these multilayers are related to the relaxation of thermally blocked
superparamagnetic grains and magnetic domains in the film layers.",0505145v1
2005/7/19,A permanent magnetic film atom chip for Bose-Einstein condensation,"We present a hybrid atom chip which combines a permanent magnetic film with a
micromachined current-carrying structure used to realize a Bose-Einstein
condensate. A novel TbGdFeCo material with large perpendicular magnetization
has been tailored to allow small scale, stable magnetic potentials for
ultracold atoms. We are able to produce 87Rb Bose-Einstein condensates in a
magnetic trap based on either the permanent magnetic film or the
current-carrying structure. Using the condensate as a magnetic field probe we
perform cold atom magnetometry to profile both the field magnitude and gradient
as a function of distance from the magnetic film surface. Finally we discuss
future directions for our permanent magnetic film atom chip.",0507435v1
2007/2/20,Scattering by Atomic Spins and Magnetoresistance in Dilute Magnetic Semiconductors,"We studied electrical transport in magnetic semiconductors, which is
determined by scattering of free carriers off localized magnetic moments. We
calculated the scattering time and the mobility of the majority and
minority-spin carriers with both the effects of thermal spin fluctuations and
of spatial disorder of magnetic atoms taken into account. These are responsible
for the magnetic-field dependence of electrical resistivity. Namely, the
application of the external magnetic field suppresses the thermodynamic spin
fluctuations thus promoting negative magnetoresistance. Simultaneously,
scattering off the built-in spatial fluctuations of the atomic spin
concentrations may increase with the magnetic field. The latter effect is due
to the growth of the magnitude of random local Zeeman splittings with the
magnetic field. It promotes positive magnetoresistance. We discuss the role of
the above effects on magnetoresistance of non-degenerate semiconductors where
magnetic impurities are electrically active or neutral.",0702474v1
2007/6/6,Magnetic dead layers in La2/3Ca1/3MnO3 thin films probed by X-ray magnetic circular dichroism in reflection,"Surface magnetic properties of perovskite manganites have been a recurrent
topic during last years since they play a major role in the implementation of
magnetoelectronic devices. Magneto-optical techniques, such as X-ray magnetic
circular dichroism, turn out to be a very efficient tool to study surface
magnetism due to their sensitivity to magnetic and chemical variations across
the sample depth. Nevertheless, the application of the sum rules for the
determination of the spin magnetic moment might lead to uncertainties as large
as 40% in case of Mn ions. To overcome this problem we present an alternative
approach consisting of using X-ray magnetic circular dichroism in reflection
geometry. Fit of the data by using a computer code based in a 4X4 matrix
formalism leads to realistic results. In particular, we show that surface and
interface roughness are of major relevance for a proper description of the
experimental data and a correct interpretation of the results. By using such an
approach we demonstrate the presence of a narrow surface region with strongly
depressed magnetic properties in La2/3Ca1/3MnO3 thin films.",0706.0821v1
2007/8/1,Ignition and Propagation of Magnetic Avalanches in Mn$_{12}$-Acetate: the effect of quantum tunneling,"Using a wire heater to ignite magnetic avalanches in fixed magnetic field
applied along the easy axis of single crystals of the molecular magnet
Mn$_{12}$-acetate, we report fast local measurements of the temperature and
time-resolved measurements of the local magnetization as a function of magnetic
field. In addition to confirming maxima in the velocity of propagation, we find
that avalanches trigger at a threshold temperature which exhibits pronounced
minima at resonant magnetic fields, demonstrating that thermally assisted
quantum tunneling plays an important role in the ignition as well as the
propagation of magnetic avalanches in molecular magnets.",0708.0222v2
2007/9/11,Magnetic Behavior of Single La$_{0.67}$Ca$_{0.33}$MnO$_3$ Nanotubes: Surface and Shape Effects,"We report magnetization experiments in two magnetically isolated
ferromagnetic nanotubes of perovskite La$_{0.67}$Ca$_{0.33}$MnO$_3$. The
results show that the magnetic anisotropy is determined by the sample shape
although the coercive field is reduced by incoherent magnetization reversal
modes. The temperature dependence of the magnetization reveals that the
magnetic behavior is dominated by grain surface properties. These measurements
were acquired using a Silicon micro-mechanical oscillator working in its
resonant mode. The sensitivity was enough to measure the magnetic properties of
these two samples with a mass lower than 14 picograms and to obtain for the
first time the magnetization loop for one isolated nanotube.",0709.1707v2
2007/9/17,Calculation of Magnetic Field Noise from High-Permeability Magnetic Shields and Conducting Objects with Simple Geometry,"High-permeability magnetic shields generate magnetic field noise that can
limit the sensitivity of modern precision measurements. We show that
calculations based on the fluctuation-dissipation theorem allow quantitative
evaluation of magnetic field noise, either from current or magnetization
fluctuations, inside enclosures made of high-permeability materials. Explicit
analytical formulas for the noise are derived for a few axially symmetric
geometries, which are compared with results of numerical finite element
analysis. Comparison is made between noises caused by current and magnetization
fluctuations inside a high-permeability shield and also between
current-fluctuation-induced noises inside magnetic and non-magnetic conducting
shells. A simple model is suggested to predict power-law decay of noise spectra
beyond quasi-static regime. Our results can be used to assess noise from
existing shields and to guide design of new shields for precision measurements.",0709.2543v1
2007/10/30,Remanence of Ni nanowire arrays: Influence of size and labyrinth magnetic structure,"The influence of the macroscopic size of the Ni nanowire array system on
their remanence state has been investigated. A simple magnetic phenomenological
model has been developed to obtain the remanence as a function of the
magnetostatic interactions in the array. We observe that, due to the long range
of the dipolar interactions between the wires, the size of the sample strongly
influence the remanence of the array. On the other hand, the magnetic state of
nanowires has been studied by variable field magnetic force microscopy for
different remanent states. The distribution of nanowires with the magnetization
in up or down directions and the subsequent remanent magnetization has been
deduced from the magnetic images. The existence of two short-range magnetic
orderings with similar energies can explain the typical labyrinth pattern
observed in magnetic force microscopy images of the nanowire arrays.",0710.5757v1
2007/12/13,Euler equation of the optimal trajectory for the fastest magnetization reversal of nano-magnetic structures,"Based on the modified Landau-Lifshitz-Gilbert equation for an arbitrary
Stoner particle under an external magnetic field and a spin-polarized electric
current, differential equations for the optimal reversal trajectory, along
which the magnetization reversal is the fastest one among all possible reversal
routes, are obtained. We show that this is a Euler-Lagrange problem with
constrains. The Euler equation of the optimal trajectory is useful in designing
a magnetic field pulse and/or a polarized electric current pulse in
magnetization reversal for two reasons. 1) It is straightforward to obtain the
solution of the Euler equation, at least numerically, for a given magnetic
nano-structure characterized by its magnetic anisotropy energy. 2) After
obtaining the optimal reversal trajectory for a given magnetic nano-structure,
finding a proper field/current pulse is an algebraic problem instead of the
original nonlinear differential equation.",0712.2101v1
2008/2/14,Vacancy induced magnetism in graphene and graphene ribbons,"We address the electronic structure and magnetic properties of vacancies and
voids both in graphene and graphene ribbons. Using a mean field Hubbard model,
we study the appearance of magnetic textures associated to removing a single
atom (vacancy) and multiple adjacent atoms (voids) as well as the magnetic
interactions between them. A simple set of rules, based upon Lieb theorem, link
the atomic structure and the spatial arrangement of the defects to the emerging
magnetic order. The total spin $S$ of a given defect depends on its sublattice
imbalance, but some defects with S=0 can still have local magnetic moments. The
sublattice imbalance also determines whether the defects interact
ferromagnetically or antiferromagnetically with one another and the range of
these magnetic interactions is studied in some simple cases. We find that in
semiconducting armchair ribbons and two-dimensional graphene without global
sublattice imbalance there is maximum defect density above which local
magnetization disappears. Interestingly, the electronic properties of
semiconducting graphene ribbons with uncoupled local moments are very similar
to those of diluted magnetic semiconductors, presenting giant Zeeman splitting.",0802.2029v1
2008/6/18,Selective Heating Mechanism of Magnetic Metal Oxides by Alternating Magnetic Field in Microwave Sintering Process,"The mechanism of rapid and selective heating of magnetic metal oxides under
the magnetic field of microwaves which continues beyond the Curie temperature $
T_{c} $ is identified by using the Heisenberg model. Monte Carlo calculations
based on the energy principle show that such heating is caused by non-resonant
response of electron spins in the unfilled 3d shell to the wave magnetic field.
Small spin reorientation thus generated leads to a large internal energy change
through the exchange interactions between spins, which becomes maximal around $
T_{c} $ for magnetite $ {\rm Fe}_{3}{\rm O}_{4} $. The dissipative spin
dynamics simulation yields the imaginary part of the magnetic susceptibility,
which becomes largest around $ T_{c} $ and for the microwave frequency around 2
GHz. Hematite $ {\rm Fe}_{2}{\rm O}_{3} $ with weak spontaneous magnetization
responds much less to microwaves as observed in experiments. The heating of
titanium oxide by microwave magnetic field only when oxygen defects are present
is also explained by our theory in terms of the absence of spontaneous
magnetization.",0806.3055v3
2008/6/26,Debye relaxation in high magnetic fields,"Dielectric relaxation is universal in characterizing polar liquids and
solids, insulators, and semiconductors, and the theoretical models are well
developed. However, in high magnetic fields, previously unknown aspects of
dielectric relaxation can be revealed and exploited. Here, we report low
temperature dielectric relaxation measurements in lightly doped silicon in high
dc magnetic fields B both parallel and perpendicular to the applied ac electric
field E. For B//E, we observe a temperature and magnetic field dependent
dielectric dispersion e(w)characteristic of conventional Debye relaxation where
the free carrier concentration is dependent on thermal dopant ionization,
magnetic freeze-out, and/or magnetic localization effects. However, for BperpE,
anomalous dispersion emerges in e(w) with increasing magnetic field. It is
shown that the Debye formalism can be simply extended by adding the Lorentz
force to describe the general response of a dielectric in crossed magnetic and
electric fields. Moreover, we predict and observe a new transverse dielectric
response EH perp B perp E not previously described in magneto-dielectric
measurements. The new formalism allows the determination of the mobility and
the ability to discriminate between magnetic localization/freeze out and
Lorentz force effects in the magneto-dielectric response.",0806.4402v1
2009/3/8,Spherical magnetic nanoparticles: magnetic structure and interparticle interaction,"The interaction between spherical magnetic nanoparticles is investigated from
micromagnetic simulations and ananlysed in terms of the leading dipolar
interaction energy between magnetic dipoles. We focus mainly on the case where
the particles present a vortex structure. In a first step the local magnetic
structure in the isolated particle is revisited. For particles bearing a
uniaxial magnetocrystaline anisotropy, it is shown that the vortex core
orientation relative to the easy axis depends on both the particle size and the
anisotropy constant. When the particles magnetization present a vortex
structure, it is shown that the polarization of the particles by the dipolar
field of the other one must be taken into account in the interaction. An
analytic form is deduced for the interaction which involves the vortex core
magnetization and the magnetic susceptibility which are obtained from the
magnetic properties of the isolated particle.",0903.1423v2
2009/8/13,Anomalous phase of MnP at very low field,"Manganese phosphide MnP has been investigated for decades because of its rich
magnetic phase diagram. It is well known that the MnP exhibits the
ferromagnetic phase transition at $\Tc=292$ K and the helical magnetic phase
below $\TN=47$ K at zero field. Recently, a novel magnetic phase transition was
observed at $T^* = 282$ K when the magnetic field is lower than 5 Oe. However,
the nature of the new phase has not been illuminated yet. In order to reveal
it, we performed the AC and the DC magnetization measurements for a single
crystal MnP at very low field. A divergent behavior of the real and the
imaginary part of the AC susceptibility and a sharp increase of the DC
magnetization was observed at $T^*$, indicating the magnetic phase transition
at $T^*$. Furthermore a peculiar temperature hysteresis was observed: namely,
the magnetization depends on whether cooling sample to the temperature lower
than $\TN$ or not before the measurements. This hysteresis phenomenon suggests
the complicated nature of the new phase and a strong relation between the
magnetic state of the new phase and the helical structure.",0908.1934v1
2010/1/15,Control of the chirality and polarity of magnetic vortices in triangular nanodots,"Magnetic vortex dynamics in lithographically prepared nanodots is currently a
subject of intensive research, particularly after recent demonstration that the
vortex polarity can be controlled by in-plane magnetic field. This has
stimulated the proposals of non-volatile vortex magnetic random access
memories. In this work, we demonstrate that triangular nanodots offer a real
alternative where vortex chirality, in addition to polarity, can be controlled.
In the static regime, we show that vortex chirality can be tailored by applying
in-plane magnetic field, which is experimentally imaged by means of
Variable-Field Magnetic Force Microscopy. In addition, the polarity can be also
controlled by applying a suitable out-of-plane magnetic field component. The
experiment and simulations show that to control the vortex polarity, the
out-of-plane field component, in this particular case, should be higher than
the in-plane nucleation field. Micromagnetic simulations in the dynamical
regime show that the magnetic vortex polarity can be changed with
short-duration magnetic field pulses, while longer pulses change the vortex
chirality.",1001.2682v1
2010/2/7,Collective modes for an array of magnetic dots with perpendicular magnetization,"The dispersion relations of collective oscillations of the magnetic moment of
magnetic dots arranged in square-planar arrays and having magnetic moments
perpendicular to the array plane are calculated. The presence of the external
magnetic field perpendicular to the plane of array, as well as the uniaxial
anisotropy for single dot are taken into account. The ferromagnetic state with
all the magnetic moments parallel, and chessboard antiferromagnetic state are
considered. The dispersion relation yields information about the stability of
different states of the array. There is a critical magnetic field below which
the ferromagnetic state is unstable. The antiferromagnetic state is stable for
small enough magnetic fields. The dispersion relation is non-analytic as the
value of the wave vector approaches zero. Non-trivial Van Hove anomalies are
also found for both ferromagnetic and antiferromagnetic states.",1002.1477v1
2010/8/23,Finite-temperature magnetism of Fe$_x$Pd$_{1-x}$ and Co$_x$Pt$_{1-x}$ alloys,"The finite-temperature magnetic properties of Fe$_x$Pd$_{1-x}$ and
Co$_x$Pt$_{1-x}$ alloys have been investigated. It is shown that the
temperature-dependent magnetic behaviour of alloys, composed of originally
magnetic and non-magnetic elements, cannot be described properly unless the
coupling between magnetic moments at magnetic atoms (Fe,Co) mediated through
the interactions with induced magnetic moments of non-magnetic atoms (Pd,Pt) is
included. A scheme for the calculation of the Curie temperature ($T_C$) for
this type of systems is presented which is based on the extended Heisenberg
Hamiltonian with the appropriate exchange parameters $J_{ij}$ obtained from
{\em ab-initio} electronic structure calculations. Within the present study the
KKR Green's function method has been used to calculate the $J_{ij}$ parameters.
A comparison of the obtained Curie temperatures for Fe$_x$Pd$_{1-x}$ and
Co$_x$Pt$_{1-x}$ alloys with experimental data shows rather good agreement.",1008.3784v1
2010/10/26,Single domain to multi-domain transition due to in-plane magnetic anisotropy in phase separated (La$_{0.4}$Pr$_{0.6}$)$_{0.67}$Ca$_{0.33}$MnO$_{3}$ thin films,"Phase separated perovskite manganites have competing phases with different
crystal structures, magnetic and electronic properties. Hence, strain effects
play a critical role in determining the magnetic properties of manganite thin
films. Here we report the effect of anisotropic stress on the magnetic
properties of the phase separated manganite
(La$_{0.4}$Pr$_{0.6}$)$_{0.67}$Ca$_{0.33}$MnO$_{3}$. Thin films of
(La$_{0.4}$Pr$_{0.6}$)$_{0.67}$Ca$_{0.33}$MnO$_{3}$ grown under anisotropic
in-plane stress on (110) NdGaO$_{3}$ substrates display in-plane mangetic
anisotropy and single domain to multidomain transition as a function of
temperature. Angle dependent magnetization measurements also show that the
magnetization reversal occurs mainly through the nucleation $&$ propagation
mechanism. By comparing the results with
(La$_{0.4}$Pr$_{0.6}$)$_{0.67}$Ca$_{0.33}$MnO$_{3}$ thin films grown on (001)
SrLaGaO$_{4}$ substrates, we have confirmed that the magnetic anisotropy is
mainly due to substrate induced anisotropic stress. Our results suggest novel
avenues for storing magnetic information in nanoscale magnetic media.",1010.5482v1
2010/11/1,Quantitative magnetic force microscopy on permalloy dots using an iron filled carbon nanotube probe,"We have characterized a new Magnetic Force Microscopy (MFM) probe based on an
iron filled carbon nanotube (FeCNT) using MFM imaging on permalloy (Py) disks
saturated in a high magnetic field perpendicular to the disk plane. The
experimental data are accurately modeled by describing the FeCNT probe as
having a single magnetic monopole at its tip whose effective magnetic charge is
determined by the diameter of the iron wire enclosed in the carbon nanotube and
its saturation magnetization 4 \pi M_s ~ 2.2 x 10^4 G. A magnetic monopole
probe enables quantitative measurements of the magnetic field gradient close to
the sample surface. The lateral resolution is defined by the diameter of the
iron wire ~15 nm and the probe-sample separation. As a demonstration, the
magnetic field gradients close to the surface of a Py dot in domain and vortex
states were imaged.",1011.0389v1
2011/3/29,Current induced rotational torques in the skyrmion lattice phase of chiral magnets,"In chiral magnets without inversion symmetry, the magnetic structure can form
a lattice of magnetic whirl lines, a two-dimensional skyrmion lattice,
stabilized by spin-orbit interactions in a small range of temperatures and
magnetic fields. The twist of the magnetization within this phase gives rise to
an efficient coupling of macroscopic magnetic domains to spin currents. We
analyze the resulting spin-transfer effects, and, in particular, focus on the
current induced rotation of the magnetic texture by an angle. Such a rotation
can arise from macroscopic temperature gradients in the system as has recently
been shown experimentally and theoretically. Here we investigate an alternative
mechanism, where small distortions of the skyrmion lattice and the transfer of
angular momentum to the underlying atomic lattice play the key role. We employ
the Landau-Lifshitz-Gilbert equation and adapt the Thiele method to derive an
effective equation of motion for the rotational degree of freedom. We discuss
the dependence of the rotation angle on the orientation of the applied magnetic
field and the distance to the phase transition.",1103.5548v2
2011/3/31,Anisotropy of magnetic emulsions induced by magnetic and electric fields,"The anisotropy of magnetic emulsions induced by simultaneously acting
electric and magnetic fields is theoretically and experimentally investigated.
Due to the anisotropy, the electric conductivity and magnetic permeability of a
magnetic emulsion are no longer scalar coefficients, but are tensors. The
electric conductivity and magnetic permeability tensors of sufficiently diluted
emulsions in sufficiently weak electric and magnetic fields are found as
functions of the electric and magnetic intensity vectors. The theoretically
predicted induced anisotropy was verified experimentally. The experimental data
are analyzed and compared with theoretical predictions. The results of the
analysis and comparison are discussed.",1103.6251v2
2011/4/5,Photoemission Spectroscopy of Magnetic and Non-magnetic Impurities on the Surface of the Bi$_2$Se$_3$ Topological Insulator,"Dirac-like surface states on surfaces of topological insulators have a chiral
spin structure that suppresses back-scattering and protects the coherence of
these states in the presence of non-magnetic scatterers. In contrast, magnetic
scatterers should open the back- scattering channel via the spin-flip processes
and degrade the state's coherence. We present angle-resolved photoemission
spectroscopy studies of the electronic structure and the scattering rates upon
adsorption of various magnetic and non-magnetic impurities on the surface of
Bi$_2$Se$_3$, a model topological insulator. We reveal a remarkable
insensitivity of the topological surface state to both non-magnetic and
magnetic impurities in the low impurity concentration regime. Scattering
channels open up with the emergence of hexagonal warping in the high-doping
regime, irrespective of the impurity's magnetic moment.",1104.0966v2
2011/6/6,Empirical Magnetic Structure of Frustrated Spin Systems,"Frustrated magnetism plays a central role in the phenomenology of exotic
quantum states. However, because the magnetic structures of frustrated systems
are aperiodic, there has always been the problem that they cannot be determined
using traditional crystallographic techniques. Here we show that the magnetic
component of powder neutron scattering data is actually sufficiently
information-rich to drive magnetic structure solution for frustrated systems,
including spin ices, spin liquids, and molecular magnets. Consequently,
single-crystal samples are not prerequisite for detailed characterisation of
exotic magnetic states. Our methodology employs ab initio reverse Monte Carlo
refinement, making informed use of an additional constraint that minimises
variance in local spin environments. By refining atomistic spin configurations,
we obtain at once (i) a magnetic structure ""solution"" - i.e. the orientation of
classical spin vectors - (ii) the spin correlation functions, and (iii) the
full three-dimensional magnetic scattering pattern.",1106.1133v1
2012/1/9,Ground states and magnetization process for an triangular lattice array of magnetic dots with perpendicular anisotropy,"We analyzed the ground state of the array of magnetic particles (magnetic
dots) which form a two-dimensional triangular lattice, and magnetic moment of
which is perpendicular to the plane of the lattice, in the presence of external
magnetic field. In the small fields long range dipole-dipole interaction leads
to the specific antiferromagnetic order, where two out of six nearest neighbors
of the particle have the same direction of magnetization moment and four - the
opposite one. It is shown that magnetization process in such array of particles
as opposed to the rectangular lattices results from the formation of the
magnetized topological defects (dislocations) in the shape of the domain walls.",1201.1747v1
2012/3/21,The Nature of Magnetic Ordering in Magnetically Doped Topological Insulator Bi$_{2-x}$Fe$_x$Se$_3$,"We present a detailed investigation of the magnetic and structural properties
of magnetically doped 3D topological insulator Bi2Se3. From muon spin
relaxation measurements in zero magnetic field, we find that even 5% Fe doping
on the Bi site turns the full volume of the sample magnetic at temperatures as
high as ~250 K. This is also confirmed by magnetization measurements. Two
magnetic ""phases"" are identified; the first is observed between ~10-250 K while
the second appears below ~10 K. These cannot be attributed to impurity phases
in the samples. We discuss the nature and details of the observed magnetism and
its dependence on doping level.",1203.4850v1
2012/7/2,Evolution of the magnetism of Tb(Co_{x}Ni_{1-x})_{2}B_{2}C,"The magnetic properties of polycrystalline Tb(Co_{x}Ni_{1-x})_{2}B_{2}C
(x=0.2,0.4,0.6,0.8) samples were probed by magnetization, specific heat, ac
susceptibility, and resistivity techniques. For x{\neq}0.4, the obtained curves
are consistent with the features expected for the corresponding magnetic modes,
namely k_{1}=(0.55,0,0) at x=0;
k_{2}=([nicefrac]\nicefrac{1}{2}</LaTeX>,0,[nicefrac]<LaTeX>\nicefrac{1}{2}) at
x= 0.2; k_{3}=(0,0,[nicefrac]\nicefrac{1}{3}) at x= 0.6, and k_{4}=(0,0,0) at
x= 0.8 and 1. For x=0.4, even though the neutron diffraction indicates a k_{2}
mode, but with a reduced magnetic moment, the magnetization, the ac
susceptibility, and resistivity indicate two magnetic events; furthermore,
deviation from Curie-Weiss behavior is observed below 150 K for this sample.
These features, together with the evolution of both magnetic moment and
critical temperature, are attributed to an interplay between competing magnetic
couplings; for the particular x=0.4 case, additional factors such as
crystalline electric field effects may be in operation.",1207.0519v1
2012/7/17,Prediction of the bias voltage dependent magnetic contrast in spin-polarized scanning tunneling microscopy,"This work is concerned with the theoretical description of the contrast,
i.e., the apparent height difference between two lateral surface positions on
constant current spin-polarized scanning tunneling microscopy (SP-STM) images.
We propose a method to predict the bias voltage dependent magnetic contrast
from single point tunneling current or differential conductance measurements,
without the need of scanning large areas of the surface. Depending on the
number of single point measurements, the bias positions of magnetic contrast
reversals and of the maximally achievable magnetic contrast can be determined.
We validate this proposal by simulating SP-STM images on a complex magnetic
surface employing a recently developed approach based on atomic superposition.
Furthermore, we show evidence that the tip electronic structure and magnetic
orientation have a major effect on the magnetic contrast. Our theoretical
prediction is expected to inspire experimentalists to considerably reduce
measurement efforts for determining the bias dependent magnetic contrast on
magnetic surfaces.",1207.3995v2
2012/12/20,Magnetic stripe domain pinning and reduction of in plane magnet order due to periodic defects in thin magnetic films,"In thin magnetic films with strong perpendicular anisotropy and strong
demagnetizing field two ordered phases are possible. At low temperatures,
perpendicularly oriented magnetic domains form a striped pattern. As
temperature is increased the system can undergo a spin reorientation transition
into a state with in-plane magnetization. Here we present Monte Carlo
simulations of such a magnetic film containing a periodic array of non-magnetic
defects. We find that the presence of defects stabilizes parallel orientation
of stripes against thermal fluctuations at low temperatures. Above the spin
reorientation temperature we find that defects favor perpendicular spin
alignment and disrupt long range ordering of spin components parallel to the
sample. This increases cone angle and reduces in plane correlations, leading to
a reduction in the spontaneous magnetization.",1212.4938v1
2013/1/15,Low temperature high magnetic field $^{57}Fe$ M$\ddot{o}$ssbauer study of kinetic arrest in $Hf_{0.77}Ta_{0.23}Fe_2$,"Low temperature high magnetic field $^{57}Fe$ M$\ddot{o}$ssbauer measurements
were carried out on inter-metallic $Hf_{0.77}Ta_{0.23}Fe_2$ compound by
following novel paths in H-T space. The ferromagnetic (FM) fraction at 5K and
zero magnetic field is shown to depend on cooling field i.e., higher the field
higher is the FM fraction. M$\ddot{o}$ssbauer spectra collected in the presence
of 4 Tesla magnetic field shows that the antiferromagnetic (AFM) spins cant
with respect to the applied magnetic field and hence, contribute to the total
bulk magnetization in this compound. The data also show induced magnetic moment
even at the 2a site of AFM phase. M$\ddot{o}$ssbauer spectra collected using
CHUF (cooling and heating in un-equal magnetic fields) protocol shows
re-entrant transition when sample is cooled in zero field and measured during
warming in 4 Tesla showing FM state as the equilibrium state. The present work
is the first microscopic experimental evidence for the de-vitrification of
kinetically arrested magnetic state.",1301.3313v1
2013/2/14,Atomistic Coupling between Magnetization and Lattice Dynamics from First Principles,"We formulate a new scheme to study the combined magnetization and lattice
dynamics in magnets, so-called magnetoelastics. The coupling between
magnetization and lattice are considered through an expansion of
electron-phonon coupling, while the magnetization is coupled to electrons
through sd-like interaction. We show the that the time-scale of the
magnetization dynamics due to coupling between magnetic degrees of freedom and
electronic degrees of freedom can be transferred to lattice degrees of freedom
and therefore can give rise to lattice dynamics on the same time-scale. This
opens a new route to understand and treat ultrafast lattice dynamics induced by
magnetization dynamics. We also show that all the parameters necessary to
simulate this coupled lattice and magnetization dynamics can be obtained from
first-principles.",1302.3333v2
2013/2/20,Magnetic Avalanches in Molecular Magnets,"The reversal of the magnetization of crystals of molecular magnets that have
a large spin and high anisotropy barrier generally proceeds below the blocking
temperature by quantum tunneling. This is manifested as a series of controlled
steps in the hysteresis loops at resonant values of the magnetic field where
energy levels on opposite sides of the barrier cross. An abrupt reversal of the
magnetic moment of the entire crystal can occur instead by a process commonly
referred to as a magnetic avalanche, where the molecular spins reverse along a
deflagration front that travels through the sample at subsonic speed. In this
chapter, we review experimental results obtained to date for magnetic
deflagration in molecular nanomagnets.",1302.5100v1
2013/2/25,Anisotropic Monopole Heat Transport in the Spin-Ice Compound Dy$_2$Ti$_2$O$_7$,"We report a study of the thermal conductivity $\kappa$ of the spin-ice
material Dy$_2$Ti$_2$O$_7$. From the anisotropic magnetic-field dependence of
\kappa$ and by additional measurements on the phononic reference compounds
Y$_2$Ti$_2$O$_7$ and DyYTi$_2$O$_7$, we are able to separate the phononic and
the magnetic contributions to the total heat transport, i.e. $\kappa_{ph}$ and
$\kappa_{mag}$, respectively, which both depend on the magnetic field. The
field dependent $\kappa_{ph}$ arises from lattice distortions due to
magnetic-field induced torques on the non-collinear magnetic moments of the Dy
ions. For $\kappa_{mag}$, we observe a highly anisotropic magnetic-field
dependence, which correlates with the corresponding magnetization data
reflecting the different magnetic-field induced spin-ice ground states. The
magnitude of $\kappa_{mag}$ increases with the degree of the ground-state
degeneracy. This anisotropic field dependence as well as various hysteresis
effects suggest that $\kappa_{mag}$ is essentially determined by the mobility
of the magnetic monopole excitations in spin ice.",1302.6114v1
2013/7/2,Overlap Technique for End-Cap Seals on Cylindrical Magnetic Shields,"We present results from studies of the effectiveness of an overlap technique
for forming a magnetic seal across a gap at the boundary between a cylindrical
magnetic shield and an end-cap. In this technique a thin foil of magnetic
material overlaps the two surfaces, thereby spanning the gap across the
cylinder and the end-cap, with the magnetic seal then formed by clamping the
thin magnetic foil to the surfaces of the cylindrical shield and the end-cap on
both sides of the gap. In studies with a prototype 31-cm diameter, 91-cm long,
0.16-cm thick cylindrical magnetic shield and flared end-cap, the magnetic
shielding performance of our overlap technique is comparable to that obtained
with the conventional method in which the end-cap is placed in direct lapped
contact with the cylindrical shield via through bolts or screws.",1307.0866v1
2013/8/10,Electronic orbital angular momentum and magnetism of graphene,"Orbital angular momentum (OAM) of graphene electrons in a perpendicular
magnetic field is calculated and corresponding magnetic moment is used to
investigate the magnetism of perfect graphene. Variation in magnetization
demonstrates its decrease with carrier-doping, plateaus in a large field, and
de Haas-van Alphen oscillation. Regulation of magnetism by a parallel electric
field is presented. The OAM originates from atomic-scale electronic motion in
graphene lattice, and vector hopping interaction between carbon atomic orbitals
is the building element. A comparison between OAM of graphene electrons, OAM of
Dirac fermions, and total angular momentum of the latter demonstrates their
different roles in magnetism of graphene. Applicability and relation to
experiments of the results are discussed.",1308.2287v3
2013/9/27,Constrained non-collinear magnetism in disordered Fe and Fe-Cr alloys,"The development of quantitative models for radiation damage effects in iron,
iron alloys and steels, particularly for the high temperature properties of the
alloys, requires understanding of magnetic interactions, which control the
phase stability of ferritic-martensitic, ferritic, and austenitic steels. In
this work, disordered magnetic configurations of pure iron and Fe-Cr alloys are
investigated using Density Functional Theory (DFT) formalism, in the form of
constrained non-collinear magnetic calculations, with the objective of creating
a database of atomic magnetic moments and forces acting between the atoms. From
a given disordered atomic configuration of either pure Fe or Fe-Cr alloy, a
penalty contribution to the usual spin-polarized DFT total energy has been
calculated by constraining the magnitude and direction of magnetic moments. An
extensive database of non-collinear magnetic moment and force components for
various atomic configurations has been generated and used for interpolating the
spatially-dependent magnetic interaction parameters, for applications in
large-scale spin-lattice dynamics and magnetic Monte-Carlo simulations.",1309.7183v1
2013/12/12,Influence of the structure defects on the magnetic properties of the FePt/Fe bilayer,"Thin magnetic multilayered films containing FePt have attracted a lot of
attention recently due to their possible usage in ultra-high density magnetic
storage. Although structure defects play a dramatic role in the magnetization
process and influence magnetic properties in general this dependence haven't
been studied thoroughly. The main aim of this work was to perform theoretical
investigation of the magnetic properties of FePt and Fe/FePt thin films with
high coercivity with respect to the structure defects such as anisotropy
constant, magnetization saturation, exchange constant fluctuations and easy
axis deviation. For selected defect patterns the coercive field dependence on
layer thicknesses was analysed. Numerical study of the bilayer with hard
magnetic layer having the planar anisotropy was carried on using micromagnetic
calculations. Values of layers thickness have been found optimal for
perspective applications, the dependence of the hysteresis loop shape upon the
magnetization process has been shown and analysed.",1312.3541v1
2014/5/9,Magnetization dynamics and damping due to electron-phonon scattering in a ferrimagnetic exchange model,"We present a microscopic calculation of magnetization damping for a magnetic
""toy model."" The magnetic system consists of itinerant carriers coupled
antiferromagnetically to a dispersionless band of localized spins, and the
magnetization damping is due to coupling of the itinerant carriers to a phonon
bath in the presence of spin-orbit coupling. Using a mean-field approximation
for the kinetic exchange model and assuming the spin-orbit coupling to be of
the Rashba form, we derive Boltzmann scattering integrals for the distributions
and spin coherences in the case of an antiferromagnetic exchange splitting,
including a careful analysis of the connection between lifetime broadening and
the magnetic gap. For the Elliott-Yafet type itinerant spin dynamics we extract
dephasing and magnetization times T_1 and T_2 from initial conditions
corresponding to a tilt of the magnetization vector, and draw a comparison to
phenomenological equations such as the Landau-Lifshitz or the Gilbert damping.
We also analyze magnetization precession and damping for this system including
an anisotropy field and find a carrier mediated dephasing of the localized spin
via the mean-field coupling.",1405.2347v1
2014/6/26,Spinmotive force due to motion of magnetic bubble arrays driven by magnetic field gradient,"Interaction between local magnetization and conduction electrons is
responsible for a variety of phenomena in magnetic materials. It has been
recently shown that spin current and associated electric voltage can be induced
by magnetization that depends on both time and space. This effect, called
spinmotive force, provides for a powerful tool for exploring the dynamics and
the nature of magnetic textures, as well as a new source for electromotive
force. Here we theoretically demonstrate the generation of electric voltages in
magnetic bubble array systems subjected to a magnetic field gradient. It is
shown by deriving expressions for the electric voltages that the present system
offers a direct measure of phenomenological parameter that describes
non-adiabaticity in the current induced magnetization dynamics. This spinmotive
force opens a door for new types of spintronic devices that exploit the
field-gradient.",1406.6964v2
2014/7/15,Revealing Optically Induced Magnetization in SrTiO$_3$ using Optically Coupled SQUID Magnetometry and Magnetic Circular Dichroism,"In this work, we study the time- and temperature-dependence of optically
induced magnetization in bulk crystals of slightly oxygen-deficient
SrTiO$_{3-\delta}$ using an optically coupled SQUID magnetometer. We find that
a weak ($\sim$5$\times$10$^{-7}$~emu) but extremely long-lived (hours) magnetic
moment can be induced in SrTiO$_{3-\delta}$ at zero magnetic field by
circular-polarized sub-bandgap light. We utilize this effect to demonstrate
that SrTiO$_{3-\delta}$ crystals can be used as an optically addressable
magnetic memory by writing and subsequently reading magnetic patterns with
light. The induced magnetization is consistent with that of a polarized
ensemble of independent oxygen-vacancy-related complexes, rather than from
collective or long-range magnetic order.",1407.4157v1
2014/9/30,Possible Existence of Partially Disordered Sm Ions in Magnetically Ordered State of Ising Magnet SmPt2Si2: a Single Crystal Study,"We have succeeded in growing single crystals of SmPt2Si2 and have performed
electrical resistivity, magnetization and specific heat measurements. The
magnetic susceptibility shows that SmPt2Si2 is an Ising magnet with the
crystalline-electric-field ground state of Jz=+-3/2. We have found the
existence of two magnetically ordered states, i.e., an antiferromagnetically
(AFM) ordered phase (I) setting in at TN=5.1 K and a field-induced
magnetization plateau phase (II). In the phase I, unlike the usual AFM states,
a pronounced Curie-Weiss contribution remains in magnetic susceptibility,
indicating the existence of ""partially disordered"" Sm ions. Largely enhanced
Sommerfeld-coefficient (350 mJ/K2mol) in the phase I can be attributed to
formation of Kondo sublattice with heavy quasiparticles in the partially
disordered Sm ions. These findings may reflect substantial magnetic
frustrations inherent in SmPt2Si2.",1409.8474v1
2014/10/16,Magneto-Optical Imaging of Vortex Domain Deformation in Pinning Sites,"We use a sensitive magneto-optical microscopy technique to image the
magnetization response of micron-scale ferromagnetic disks to changes in
applied magnetic field. This differential technique relies on a modulated
applied magnetic field which allows us to measure changes in magnetization <1%
with sub-micron resolution. The disks are magnetized in single vortex domains,
with defects in the material serving to pin the vortex core at particular
positions. By applying a small AC magnetic field, we measure the deformation of
the magnetization while the core remains pinned. We can also characterize the
strength of the pinning site by increasing the AC magnetic field to unpin the
vortex core. While pinned, we find that the magnetization away from the core
reorients slightly to better align with an applied field. Additionally, an
applied field causes the pinned core itself to tilt in the direction of the
field. Once the field is large enough to unpin the core, this tilt disappears,
and the core instead translates across the disk.",1410.4518v1
2014/10/16,Spin-transfer torque switching in nanopillar superconducting-magnetic hybrid Josephson junctions,"The combination of superconducting and magnetic materials to create novel
superconducting devices has been motivated by the discovery of Josephson
critical current (Ics) oscillations as a function of magnetic layer thickness
and the demonstration of devices with switchable critical currents. However,
none of the hybrid devices have shown any spintronic effects, such as
spin-transfer torque, which are currently used in room-temperature magnetic
devices, including spin-transfer torque random-access memory and spin-torque
nano-oscillators. We have developed nanopillar Josephson junctions with a
minimum feature size of 50 nm and magnetic barriers exhibiting magnetic
pseudo-spin-valve behavior at 4 K. These devices allow current-induced
magnetization switching that results in 20-fold changes in Ics. The
current-induced magnetic switching is consistent with spin-transfer torque
models for room-temperature magnetic devices. Our work demonstrates that
devices that combine superconducting and spintronic functions show promise for
the development of a nanoscale, nonvolatile, cryogenic memory technology.",1410.4529v1
2014/12/1,Stabilization of helical magnetic structures in thin multilayers,"Based on micromagnetic simulations, we report on a novel helical magnetic
structure in a soft magnetic film that is sandwiched between and
exchange-coupled to two hard magnetic layers. Confined between antiparallel
hard magnetic moments, a helix with a turn of 180$^{\circ}$ is stable without
the presence of an external magnetic field. The magnetic stability is
determined by the energy minimization and is a result of an internal field
created by exchange interaction and anisotropy. Since the internal field stores
magnetic energy, the helix can serve as an energy-storing element in spin-based
nanodevices. Due to the significantly different magnetic resonance frequencies,
the ferromagnetic and helical ground states are easy to distinguish in a
broadband ferromagnetic resonance experiment.",1412.1379v1
2015/1/29,Minimizing magnetic fields for precision experiments,"An increasing number of measurements in fundamental and applied physics rely
on magnetically shielded environments with sub nano-Tesla residual magnetic
fields. State of the art magnetically shielded rooms (MSRs) consist of up to
seven layers of high permeability materials in combination with highly
conductive shields. Proper magnetic equilibration is crucial to obtain such low
magnetic fields with small gradients in any MSR. Here we report on a scheme to
magnetically equilibrate MSRs with a 10 times reduced duration of the magnetic
equilibration sequence and a significantly lower magnetic field with improved
homogeneity. For the search of the neutron's electric dipole moment, our
finding corresponds to a linear improvement in the systematic reach and a 40 %
improvement of the statistical reach of the measurement. However, this
versatile procedure can improve the performance of any MSR for any application.",1501.07408v1
2015/3/4,Electric Contributions to Magnetic Force Microscopy Response from Graphene and MoS2 Nanosheets,"Magnetic force microscopy (MFM) signals have recently been detected from
whole pieces of mechanically exfoliated graphene and molybdenum disulfide
(MoS2) nanosheets and magnetism of the two nanomaterials was claimed based on
these observations. However, non-magnetic interactions or artefacts are
commonly associated with MFM signals, which makes the interpretation of MFM
signals not straightforward. A systematic investigation has been done to
examine possible sources of the MFM signals from graphene and MoS2 nanosheets
and whether the MFM signals can be correlated with magnetism. It is found that
the MFM signals have significant non-magnetic contributions due to capacitive
and electrostatic interactions between the nanosheets and conductive cantilever
tip, as demonstrated by electric force microscopy (EFM) and scanning Kevin
probe microscopy (SKPM) analyses. In addition, the MFM signals of graphene and
MoS2 nanosheets are not responsive to reversed magnetic field of the magnetic
cantilever tip. Therefore, the observed MFM response is mainly from electric
artefacts and not compelling enough to correlate with magnetism of graphene and
MoS2 nanosheets.",1503.01292v1
2015/4/22,Detection of defect-induced magnetism in low-dimensional ZnO structures by Magnetophotocurrent,"The detection of defect-induced magnetic order in single low-dimensional
oxide structures is in general difficult because of the relatively small yield
of magnetically ordered regions. In this work we have studied the effect of an
external magnetic field on the transient photocurrent measured after light
irradiation on different ZnO samples at room temperature. We found that a
magnetic field produces a change in the relaxation rate of the transient
photocurrent only in magnetically ordered ZnO samples. This rate can decrease
or increase with field depending whether the magnetic order region is in the
bulk or only at the surface of the ZnO sample. The phenomenon reported here is
of importance for the development of magneto-optical low-dimensional oxides
devices and provide a new guideline for the detection of magnetic order in
low-dimensional magnetic semiconductors.",1504.05828v1
2015/5/26,Vacancy defects and monopole dynamics in oxygen-deficient pyrochlores,"The idea of magnetic monopoles in spin ice has enjoyed much success at
intermediate temperatures, but at low temperatures a description in terms of
monopole dynamics alone is insufficient. Recently, numerical simulations were
used to argue that magnetic impurities account for this discrepancy by
introducing a magnetic equivalent of residual resistance in the system. Here we
propose that oxygen deficiency is the leading cause of magnetic impurities in
as-grown samples, and we determine the defect structure and magnetism in
Y2Ti2O(7-\delta) using diffuse neutron scattering and magnetization
measurements. These defects are eliminated by oxygen annealing. The
introduction of oxygen vacancies causes Ti4+ to transform to magnetic Ti3+ with
quenched orbital magnetism, but the concentration is anomalously low. In the
spin-ice material Dy2Ti2O7 we find that the same oxygen-vacancy defects
suppress moments on neighbouring rare-earth sites, and that these magnetic
distortions dramatically slow down the long-time monopole dynamics at
sub-Kelvin temperatures.",1505.07035v1
2015/6/1,Electrical detection of magnetization reversal without auxiliary magnets,"First-generation magnetic random access memories based on anisotropic
magnetoresistance required magnetic fields for both writing and reading. Modern
all-electrical read/write memories use instead non-relativistic spin-transport
connecting the storing magnetic layer with a reference ferromagnet. Recent
studies have focused on electrical manipulation of magnetic moments by
relativistic spin-torques requiring no reference ferromagnet. Here we report
the observation of a counterpart magnetoresistance effect in such a
relativistic system which allows us to electrically detect the sign of the
magnetization without an auxiliary magnetic field or ferromagnet. We observe
the effect in a geometry in which the magnetization of a uniaxial (Ga,Mn)As
epilayer is set either parallel or antiparallel to a current-induced
non-equilibrium spin polarization of carriers. In our structure, this
linear-in-current magnetoresistance reaches 0.2\% at current density of $10^6$
A cm$^{-2}$.",1506.00400v1
2015/7/8,Enhancement of artificial magnetism via resonant bianisotropy,"All-dielectric ""magnetic light"" nanophotonics based on high refractive index
nanoparticles allows controlling magnetic component of light at nanoscale
without having high dissipative losses. The artificial magnetic optical
response of such nanoparticles originates from circular displacement currents
excited inside those structures and strongly depends on geometry and dispersion
of optical materials. Here a new approach for increasing magnetic response via
resonant bianisotropy effect is proposed and analyzed. The key mechanism of
enhancement is based on electric-magnetic interaction between two electrically
and magnetically resonant nanoparticles of all-dielectric dimer nanoantenna. It
was shown that proper geometrical arrangement of the dimer in respect to the
incident illumination direction allows flexible control over all vectorial
components of magnetic polarizability, tailoring the later in the dynamical
range of 100 % and enhancement up to 36 % relative to performances of
standalone spherical particles. The proposed approach provides pathways for
designs of all-dielectric metamaterials and metasurfaces with strong magnetic
response.",1507.02098v1
2015/7/13,Direct surface charging and alkali-metal doping for tuning the interlayer magnetic order in planar nanostructures,"The continuous reduction of magnetic units to ultra small length scales
inspires efforts to look for a suitable means of controlling magnetic states.
In this study we show two surface charge alteration techniques for tuning the
interlayer exchange coupling (IEC) of ferromagnetic layers separated by
paramagnetic spacers. Our study reveals that already a modest amount of extra
charge can switch the mutual alignment of the magnetization from
anti-ferromagnetic to ferromagnetic or vice verse. We also propose adsorption
of alkali metals as an alternative way of varying the electronic and chemical
properties of magnetic surfaces. Clear evidence is found that the interlayer
magnetic order can be reversed by adsorbing alkali metals on the magnetic
layer. Moreover, alkali metal overlayers strongly enhance the perpendicular
magnetic anisotropy in FePt thin films. These findings combined with atomistic
spin model calculations suggest that electronic or ionic way of surface
charging can have a crucial role for magnetic hardening and spin state control.",1507.03365v1
2015/8/29,"Magnetic properties of Gd$T_2$Zn$_{20}$ (T = Fe, Co) investigated by X-ray diffraction and spectroscopy","We investigate the magnetic and electronic properties of the Gd$T_2$Zn$_{20}$
($T$ = Fe and Co) compounds using X-ray resonant magnetic scattering (XRMS),
X-ray absorption near-edge structure (XANES) and X-ray magnetic circular
dichroism (XMCD) techniques. The XRMS measurements reveal that the
GdCo$_2$Zn$_{20}$ compound has a commensurate antiferromagnetic spin structure
with a magnetic propagation vector $\vec{\tau}$ =
$(\frac{1}{2},\frac{1}{2},\frac{1}{2})$ below the N\'eel temperature ($T_N
\sim$ 5.7 K). Only the Gd ions carry a magnetic moment forming an
antiferromagnetic structure with magnetic representation $\Gamma_6$. For the
ferromagnetic GdFe$_2$Zn$_{20}$ compound, an extensive investigation was
performed at low temperature and under magnetic field using XANES and XMCD
techniques. A strong XMCD signal of about 12.5 $\%$ and 9.7 $\%$ is observed
below the Curie temperature ($T_C \sim$ 85 K) at the Gd-$L_2$ and $L_3$ edges,
respectively. In addition, a small magnetic signal of about 0.06 $\%$ of the
jump is recorded at the Zn $K$-edge suggesting that the Zn 4$p$ states are spin
polarized by the Gd 5$d$ extended orbitals.",1508.07495v1
2015/9/8,Magnetic and structural properties of ferromagnetic Fe5PB2 and Fe5SiB2 and effects of Co and Mn substitutions,"Crystallographic and magnetic properties of Fe5PB2, Fe4CoPB2, Fe4MnPB2,
Fe5SiB2, Fe4CoSiB2, and Fe4MnSiB2 are reported. All adopt the tetragonal Cr5B3
structure-type and are ferromagnetic at room temperature with easy axis of
magnetization along the c-axis. The spin reorientation in Fe5SiB2 is observed
as an anomaly in the magnetization near 170 K, and is suppressed by
substitution of Co or Mn for Fe. The silicides are found to generally have
larger magnetic moments than the phosphides, but the data suggests smaller
magnetic anisotropy in the silicides. Cobalt substitution reduces the Curie
temperatures by more than 100 K and ordered magnetic moments by 16-20%, while
manganese substitution has a much smaller effect. This suggests Mn moments
align ferromagnetically with the Fe and that Co does not have an ordered moment
in these structures. Anisotropic thermal expansion is observed in Fe5PB2 and
Fe5SiB2, with negative thermal expansion seen along the c-axis of Fe5SiB2.
First principles calculations of the magnetic properties of Fe5SiB2 and
Fe4MnSiB2 are reported. The results, including the magnetic moment and
anisotropy, and are in good agreement with experiment.",1509.02544v1
2015/9/18,Simulation of Stacks of High Temperature Superconducting Coated Conductors Magnetized by Pulsed Field Magnetization Using Controlled Magnetic Density Distribution Coils,"High temperature superconducting (HTS) stacks of coated conductors (CCs) can
work as strong trapped field magnets (TFMs) and show potential in electrical
applications. Pulsed field magnetization (PFM) is a practical method to
magnetize such TFMs, but due to heat generation during the dynamic process, it
cannot achieve a trapped field as high as field cooling can. In this work, we
construct a 2D electromagnetic-thermal coupled model to simulate stacks of HTS
CCs with realistic laminated structures magnetized by PFM. The model considers
temperature and anisotropic magnetic field dependent Jc of HTS and other
temperature dependent thermal and electrical material properties. Based on the
model, a configuration of controlled magnetic density distribution coils is
suggested to improve the trapped field compared to that obtained by ordinary
solenoids.",1509.05541v1
2015/10/28,An analytical algorithm for 3D magnetic field mapping of a watt balance magnet,"A yoke-based permanent magnet, which has been employed in many watt balances
at national metrology institutes, is supposed to generate strong and uniform
magnetic field in an air gap in the radial direction. However, in reality the
fringe effect due to the finite height of the air gap will introduce an
undesired vertical magnetic component to the air gap, which should either be
measured or modeled towards some optimizations of the watt balance. A recent
publication, i.e., {\it Metrologia} 52(4) 445 [1], presented a full field
mapping method, which in theory will supply useful information for profile
characterization and misalignment analysis. This article is an additional
material of [1], which develops a different analytical algorithm to represent
the 3D magnetic field of a watt balance magnet based on only one measurement
for the radial magnetic flux density along the vertical direction, $B_r(z)$.
The new algorithm is based on the electromagnetic nature of the magnet, which
has a much better accuracy.",1510.08206v1
2015/11/11,Electric-field Controlled Magnetization Switching in Co/Pt thin-Film Ferromagnets,"A study of dynamic and reversible voltage controlled magnetization switching
in ferromagnetic Co/Pt thin film with perpendicular magnetic anisotropy at room
temperature is presented. The change in the magnetic properties of the system
is observed in a relatively thick film of 15 nm. A surface charge is induced by
the formation of electrochemical double layer between the metallic thin film
and non-aqueous lithium LiClO4 electrolyte to manipulate the magnetism. The
change in the magnetic properties occurred by the application of an external
electric field. As the negative voltage was increased, the coercivity and the
switching magnetic field decreased thus activating magnetization switching. The
results are envisaged to lead to faster and ultra-low power magnetization
switching as compared to spin-transfer torque (STT) switching in spintronic
devices.",1511.03717v1
2016/4/1,Interlayer exchange coupling -- a general scheme turning chiral magnets into magnetic multilayers carrying atomic-scale skyrmions,"We report on a general principle using the interlayer exchange coupling to
extend the regime of chiral magnetic films in which stable or metastable
magnetic skyrmions can appear at zero magnetic field. We verify this concept on
the basis of a first-principles model for a Mn monolayer on W(001) substrate, a
prototype chiral magnet for which the atomic-scale magnetic texture is
determined by the frustration of exchange interactions, impossible to unwind by
laboratory magnetic fields. By means of \textit{ab initio} calculations for the
Mn/W$_m$/Co$_n$/Pt/W(001) multilayer system we show that for certain
thicknesses $m$ of the W spacer and $n$ of the Co reference layer, the
effective field of the reference layer fully substitutes the required magnetic
field for skyrmion formation.",1604.00250v1
2016/4/3,Spin relaxation signature of colossal magnetic anisotropy in platinum atomic chains,"Recent experimental data demonstrate emerging magnetic order in platinum
atomically thin nanowires. Furthermore, an unusual form of magnetic anisotropy
-- colossal magnetic anisotropy (CMA) -- was earlier predicted to exist in
atomically thin platinum nanowires. Using spin dynamics simulations based on
first-principles calculations, we here explore the spin dynamics of atomically
thin platinum wires to reveal the spin relaxation signature of colossal
magnetic anisotropy, comparing it with other types of anisotropy such as
uniaxial magnetic anisotropy (UMA). We find that the CMA alters the spin
relaxation process distinctly and, most importantly, causes a large speed-up of
the magnetic relaxation compared to uniaxial magnetic anisotropy. The magnetic
behavior of the nanowire exhibiting CMA should be possible to identify
experimentally at the nanosecond time scale for temperatures below 5 K. This
time-scale is accessible in e.g., soft x-ray free electron laser experiments.",1604.00626v1
2016/8/7,Ultrafast photo-magnetic recording in transparent medium,"Finding a conceptually new way to control the magnetic state of media with
the lowest possible production of heat and simultaneously at the fastest
possible time-scale is a new challenge in fundamental magnetism [1-4] as well
as an increasingly important issue in modern information technology [5]. Recent
results demonstrate that exclusively in metals it is possible to switch
magnetization between metastable states by femtosecond circularly polarized
laser pulses [6-8]. However, despite the record breaking speed of the
switching, the mechanisms in these materials are directly related to strong
optical absorption and laser-induced heating close to the Curie temperature
[9-12]. Here we report about ultrafast all-optical photo-magnetic recording in
transparent dielectrics. In ferrimagnetic garnet film a single linearly
polarized femtosecond laser pulse breaks the degeneracy between metastable
magnetic states and promotes switching of spins between them. Changing the
polarization of the laser pulse we deterministically steer the net
magnetization in the garnet, write ""0"" and ""1"" magnetic bits at will. This
mechanism operates at room temperature and allows ever fastest write-read
magnetic recording event (< 20 ps) accompanied by unprecedentedly low heat load
(< 6 J/cm3).",1609.05223v1
2016/10/14,Magnetic resonances of multiferroic TbFe$_3$(BO$_3$)$_4$,"Low-energy magnetic excitations of the easy-axis antiferromagnet
TbFe$_3$(BO$_3$)$_4$ are investigated by far-infrared absorption and reflection
spectroscopy in high magnetic fields up to 30 T. The observed field dependence
of the resonance frequencies and the magnetization are reproduced by a
mean-field spin model for magnetic fields applied both along and perpendicular
to the easy axis. Based on this model we determined the full set of magnetic
interactions, including Fe-Fe and Fe-Tb exchange interactions, single-ion
anisotropy for Tb ions and $g$-factors, which describe the ground-state spin
texture and the low-energy spin excitations of TbFe$_3$(BO$_3$)$_4$. Compared
to earlier studies we allow a small canting of the nearly Ising-like Tb moments
to achieve a quantitative agreement with the magnetic susceptibility
measurements. The additional high energy magnetic resonance lines observed,
besides the two resonances expected for a two-sublattice antiferromagnet,
suggest a more complex six-sublattice magnetic ground state for
TbFe$_3$(BO$_3$)$_4$.",1610.04455v1
2017/2/23,Spin-Orbit Coupling of Conduction Electrons in Magnetization Switching,"Strong magnetic field pulses associated with a relativistic electron bunch
can imprint switching patterns in magnetic thin films that have uniaxial
in-plane anisotropy. In experiments with Fe and FeCo alloy films the pattern
shape reveals an additional torque acting on magnetization during the short (in
the 100fs time scale) magnetic field pulse. The magnitude of the torque is as
high as 15% of the torque from the magnetic field. The torque symmetry is that
of a uniaxial anisotropy along the direction of the eddy current screening the
magnetic field. Spin-orbit interaction acting on the conduction electrons can
produce such a torque with the required symmetry and magnitude. The same
interaction causes the anomalous Hall current to be spin-polarized, exerting a
back reaction on magnetization direction. Such a mechanism may be at work in
all-optical laser switching of magnetic materials.",1702.07153v1
2017/5/9,Large magnetic anisotropy in $Fe_xTaS_2$ single crystals,"In intercalated transition metal dichalcogenide $Fe_xTaS_2$ (0.2 $\leq$ x
$\leq$ 0.4) single crystals, large magnetic anisotropy is observed. Transport
property measurements indicate that heavy Fe-doping leads to a large anisotropy
of resistivity ($\rho$$_{c}$/$\rho$$_{ab}$). A sharp M-H hysteresis curve is
observed with magnetic field along c-axis, while a linear magnetization appears
with magnetic field applied in the ab-plane. The angular dependent magnetic
susceptibility from in-plane to out-of-plane indicates that magnetic moments
are strongly pinned along the c-axis in an unconventional manner and the
coercive field reaches as large as 6 T at T = 5 K. First-principles calculation
clearly suggests that the strong spin-orbital coupling give rise to such a
large anisotropy of magnetism. The strong pinning effect of magnetic moments
along c-axis makes this material a very promising candidate for the development
of spin-aligner in spintronics devices.",1705.03139v1
2017/10/11,Probing short-range magnetic order in a geometrically frustrated magnet by spin Seebeck effect,"Competing magnetic interactions in geometrically frustrated magnets give rise
to new forms of correlated matter, such as spin liquids and spin ices.
Characterizing the magnetic structure of these states has been difficult due to
the absence of long-range order. Here, we demonstrate that the spin Seebeck
effect (SSE) is a sensitive probe of magnetic short-range order (SRO) in
geometrically frustrated magnets. In low temperature (2 - 5 K) SSE measurements
on a model frustrated magnet \mathrm{Gd_{3}Ga_{5}O_{12}}, we observe
modulations in the spin current on top of a smooth background. By comparing to
existing neutron diffraction data, we find that these modulations arise from
field-induced magnetic ordering that is short-range in nature. The observed SRO
is anisotropic with the direction of applied field, which is verified by
theoretical calculation.",1710.04269v2
2017/10/20,Deterministic switching of perpendicularly magnetic layers by spin orbital torque through stray field engineering,"We proposed a novel multilayer structure to realize the deterministic
switching of perpendicularly magnetized layers by spin orbital torque from the
spin Hall effect through stray field engineering. In our design, a pinned
magnetic layer is introduced under the heave metal separated by an insulator,
generating an in-plane stray field in the perpendicularly magnetized layer. We
have confirmed the deterministic switching of perpendicularly magnetized layers
through micromagnetic simulation and theoretical analysis. The in-plane stray
field accounts for the deterministic switching exhibited in the structure and
the reversal ultimate state of the magnetic layer is predictable when the
applied spin current density is above the critical spin current density.
Moreover, the stray field is easily tunable in a wide range by adjusting the
saturation magnetization and dimensions of the pinned layer, and can
accommodate different perpendicularly magnetized materials without any external
magnetic field.",1710.08282v1
2018/4/2,Magnetism and high-magnetic field magnetization in alkali superoxide CsO2,"Alkali superoxide CsO2 is one of candidates for the spin-1/2 one-dimensional
(1D) antiferromagnet, which may be sequentially caused by an ordering of the
pi-orbital of O2- molecule below TS ~ 70 K. Here, we report on the magnetism in
powder CsO2 and high-magnetic field magnetization measurements in
pulsed-magnetic fields of up to 60 T. We obtained the low temperature phase
diagram around the antiferromagnetic ordering temperature TN = 9.6 K under the
magnetic field. At 1.3 K, remarkable up-turn curvature in the magnetization
around a saturation field of ~ 60 T is found, which corresponds to the
spin-1/2. We will compare it with the theoretical calculation.",1804.00377v1
2018/4/6,Model-free reconstruction of magnetic correlations in frustrated magnets,"Frustrated magnetic systems exhibit extraordinary physical properties but
quantification of their magnetic correlations poses a serious challenge to
experiment and theory. Current insight into frustrated magnetic correlations
relies on modelling techniques such as reverse Monte Carlo methods, which
require knowledge about the exact ordered atomic structure. Here we present a
method for direct reconstruction of magnetic correlations in frustrated magnets
by three-dimensional difference pair distribution function analysis of neutron
total scattering data. The methodology is applied to the disordered frustrated
magnet bixbyite, (Mn1-xFex)2O3, which reveals nearest-neighbor
antiferromagnetic correlations for the metal sites up to a range of
approximately 15 {\AA}. Importantly, this technique allows for magnetic
correlations to be determined directly from the experimental data without any
assumption about the atomic structure.",1804.02303v1
2018/4/16,Triple Exponential Relaxation Dynamics in a Metallacrown-Based {$Dy^{III}Cu^{II}_5$} 3d-4f Single-Molecule Magnet,"The interplay of strong single-ion anisotropy and magnetic interactions often
give rise to novel magnetic behavior and can provide additional routes for
controlling magnetization dynamics. However, novel effects arising from
interactions between lanthanide and transition-metal ions are nowadays rarely
observed. Herein, a {$Dy^{III}Cu^{II}_5$} 3d-4f single-molecule magnet (SMM) is
constructed as a rigid and planar [15-MC-5] metallacrown (MC), where the
$Dy^{III}$ ion is trapped in the central pseudo-$D_{5h}$ pocket. A strong axial
crystal field (CF) imbues the $Dy^{III}$ ion with large Ising-type magnetic
anisotropy, and we are able to observe and model the magnetic interactions
between the $Cu^{II}-Cu^{II}$ and $Dy^{III}-Cu^{II}$ pairs. Butterfly-shaped
magnetic hysteresis shows clear steps at $\pm$0.4 T, coincident with level
crossings in our model exchange Hamiltonian between the {$Cu^{II}_5$} and
$Dy^{III}$ spin systems. Most intriguingly, this air-stable SMM exhibits three
distinct regimes in its magnetic relaxation dynamics, all clearly displaying an
exponential dependence on temperature.",1804.05818v1
2018/6/12,Emergent c-axis magnetic helix in manganite-nickelate superlattices,"The nature of the magnetic order in (La2/3Sr1/3MnO3)9/(LaNiO3)3 superlattices
is investigated using x-ray resonant magnetic reflectometry. We observe a new
c-axis magnetic helix state in the (LaNiO3)3 layers that had never been
reported in nickelates, and which mediates the ~130deg magnetic coupling
between the ferromagnetic (La2/3Sr1/3MnO3)9 layers, illustrating the power of
x-rays for discovering the magnetic state of complex oxide interfaces. Resonant
inelastic x-ray scattering and x-ray absorption spectroscopy show that Ni-O
ligand hole states from bulk LaNiO3 are mostly filled due to interfacial
electron transfer from Mn, driving the Ni orbitals closer to an atomic-like 3d8
configuration. We discuss the constraints imposed by this electronic
configuration to the microscopic origin of the observed magnetic structure. The
presence of a magnetic helix in (La2/3Sr1/3MnO3)9/(LaNiO3)3 is crucial for
modeling the potential spintronic functionality of this system and may be
important for designing emergent magnetism in novel devices in general.",1806.04775v1
2018/7/17,Magnetic ordering with an XY-like anisotropy in the honeycomb lattice iridates ZnIrO$_3$ and MgIrO$_3$ synthesized via a metathesis reaction,"We have successfully synthesized the novel antiferromagnets with Ir$^{4+}$
honeycomb lattice ZnIrO$_3$ and MgIrO$_3$ and investigated their magnetic and
thermodynamic properties. The two iridates are isomorphic but exhibit
qualitatively different magnetic properties. ZnIrO$_3$ shows antiferromagnetic
ordering below 46.6 K, whereas MgIrO$_3$ displays weak ferromagnetic behavior
below 31.8 K owing to formation of a canted antiferromagnetic ordering. The
measurement of magnetic susceptibility with using an oriented powder sample
revealed the presence of an XY-like magnetic anisotropy and a tilting magnetic
structure which is possibly stabilized by the Kitaev interaction. Moreover,
magnetization curves of MgIrO3 and ZnIrO3 up to 60 T show different behaviors,
demonstrating that each magnetic ground state is different with each other. We
discuss the difference in the ground state between MgIrO$_3$ and ZnIrO$_3$ from
the viewpoint a magnetic model consisting of the Kitaev and
Dzyaloshinskii-Moriya interactions with the spin frustration effect on the
honeycomb lattice.",1807.06273v2
2019/8/7,Deformation of flexible ferromagnetic filaments under a rotating magnetic field,"Research on magnetic particles dispersed in a fluid medium, actuated by a
rotating magnetic field, is becoming increasingly active for both lab-on-chip
and bio-sensing applications. In this study, we experimentally investigate the
behaviour of ferromagnetic filaments in a rotating field. Filaments are
synthesized by linking micron-sized ferromagnetic particles with DNA strands.
The experiments were conducted under different magnetic field strengths,
frequencies and filament sizes, and deformation of the filaments was registered
via microscope and camera. The results obtained showed that the body
deformation is larger for longer filaments and higher frequencies and lower for
larger magnetic field. The angle between the filament tangent at the centre and
the magnetic field direction increases linearly with frequency at low-frequency
regime. A further increase in the frequency will result in filament movement
out of plane when the angle approaches 90 degrees. The experimental results
were used to estimate magnetic moment and the bending elasticity of the
filament.",1908.02604v2
2019/8/18,Anomalous magnetic behavior and complex magnetic structure of proximate LaCrO3 LaFeO3 system,"We investigated complex magnetic properties of multifunctional LaCrO3-LaFeO3
system. The magnetic measurements substantiate the presence of competing
complex magnetic ordering against temperature, showing paramagnetic to
ferrimagnetic transition at 300 K, followed by antiferromagnetic (AFM)
transition near 250 K superimposed on ferrimagnetic phase. The onset of weak
ferrimagnetic ordering is attributed to the competing complex interaction
between two AFM LaCrO3-LaFeO3 sublattices. The low-temperature AFM ordering is
also substantiated by temperature-dependent Raman measurements, where the
intensity ratio of 700 cm-1 Raman active mode showed the clear enhancement with
lowering the temperature. The non-saturating nature of magnetic moments in
LaCrO3-LaFeO6 suggests the predominating AFM ordering in conjunction with
ferrimagnetic ordering between 250 K to 300 K up to 5 T magnetic field. A
complex magnetic structure of LaCrO3-LaFeO3 is constructed, emphasizing the
metastable magnetic phase near room temperature and low temperature
antiferromagnetic state.",1908.06450v1
2012/10/16,Magnetic dichroism in angular resolved hard X-ray photoelectron spectroscopy from buried magnetic layers,"This work reports on the measurement of magnetic dichroism in
angular-resolved photoelectron spectroscopy from in-plane magnetized buried
thin films. The high bulk sensitivity of hard X-ray photoelectron spectroscopy
(HAXPES) in combination with circularly polarized radiation enables the
investigation of the magnetic properties of buried layers. Angular
distributions of high kinetic energy (7 to 8 keV) photoelectrons in a range of
about 60 deg were recorded in parallel to the energy distribution. Depending on
purpose, energy and angular resolutions of 150 to 250 meV and 0.17 to 2 deg can
be accomplished simultaneously in such experiments. Experiments were performed
on exchange-biased magnetic layers covered by thin oxide films. More
specifically, the angular distribution of photoelectrons from the ferromagnetic
layer Co2FeAl layer grown on MnIr exchange-biasing layer was investigated where
the magnetic structure is buried beneath a MgO layer. Pronounced magnetic
dichroism is found in the Co and Fe 2p states for all angles of emission. A
slightly increased magnetic dichroism was observed for normal emission in
agreement with theoretical considerations.",1210.4374v1
2017/9/9,Nature of the electromagnetic force between classical magnetic dipoles,"The Lorentz force law of classical electrodynamics states that the force F
exerted by the magnetic induction B on a particle of charge q moving with
velocity V is given by F=qVxB. Since this force is orthogonal to the direction
of motion, the magnetic field is said to be incapable of performing mechanical
work. Yet there is no denying that a permanent magnet can readily perform
mechanical work by pushing/pulling on another permanent magnet -- or by
attracting pieces of magnetizable material such as scrap iron or iron filings.
We explain this apparent contradiction by examining the magnetic Lorentz force
acting on an Amperian current loop, which is the model for a magnetic dipole.
We then extend the discussion by analyzing the Einstein-Laub model of magnetic
dipoles in the presence of external magnetic fields.",1709.02921v1
2018/8/28,Spatial dependence of the superexchange interactions for transition-metal trimers in graphene,"This study examines the magnetic interactions between spatially-variable
manganese and chromium trimers substituted into a graphene superlattice. Using
density functional theory, we calculate the electronic band structure and
magnetic populations for the determination of the electronic and magnetic
properties of the system. To explore the super-exchange coupling between the
transition-metal atoms, we establish the magnetic magnetic ground states
through a comparison of multiple magnetic and spatial configurations. Through
an analysis of the electronic and magnetic properties, we conclude that the
presence of transition-metal atoms can induce a distinct magnetic moment in the
surrounding carbon atoms as well as produce an RKKY-like super-exchange
coupling. It hoped that these simulations can lead to the realization of
spintronic applications in graphene through electronic control of the magnetic
clusters.",1808.09343v1
2012/9/11,Topological defects and misfit strain in magnetic stripe domains of lateral multilayers with perpendicular magnetic anisotropy,"Stripe domains are studied in perpendicular magnetic anisotropy films
nanostructured with a periodic thickness modulation that induces the lateral
modulation of both stripe periods and inplane magnetization. The resulting
system is the 2D equivalent of a strained superlattice with properties
controlled by interfacial misfit strain within the magnetic stripe structure
and shape anisotropy. This allows us to observe, experimentally for the first
time, the continuous structural transformation of a grain boundary in this 2D
magnetic crystal in the whole angular range. The magnetization reversal process
can be tailored through the effect of misfit strain due to the coupling between
disclinations in the magnetic stripe pattern and domain walls in the in-plane
magnetization configuration.",1209.2281v1
2016/8/16,Magnetic Yoking and Tunable Interactions in FePt-Based Hard/Soft Bilayers,"Assessing and controlling magnetic interactions in magnetic nanostructures
are critical to nanomagnetic and spintronic explorations, such as magnetic
recording media, permanent magnets, magnetic memory and logic devices, etc.
Here we demonstrate an extremely sensitive magnetic yoking effect and tunable
interactions in FePt based hard/soft bilayers mediated by the soft layer. Below
the exchange length, a thin soft layer strongly exchange couples to the
perpendicular moments of the hard layer; above the exchange length, just a few
nanometers thicker, the soft layer moments turn in-plane and act to yoke the
dipolar fields from the adjacent hard layer perpendicular domains. The
evolution from exchange to dipolar-dominated interactions is experimentally
captured by first-order reversal curves, the delta-M method, and polarized
neutron reflectometry, and confirmed by micromagnetic simulations. These
findings demonstrate an effective yoking approach to design and control
magnetic interactions in wide varieties of magnetic nanostructures and devices.",1608.04630v1
2010/4/2,Structure and magnetic properties of nanocrystalline PrCo3,"The structure and magnetic properties of nanocrystalline PrCo$_3$ prepared by
high-energy milling technique have been investigated by means of X-ray
diffraction using the Rietveld method coupled to Curie temperature and magnetic
measurements. The as-milled samples were subsequently annealed in temperature
range from 750 to 1050 {\deg}C for 30 min to optimize the extrinsic properties.
From x-ray studies of magnetic aligned samples, the magnetic anisotropy of this
compounds is found uniaxial. The Curie temperature is 349 {\deg}K and no
saturation reached at room temperature for applied field of 90 kOe. The
coercive field of 55 kOe and 12 kOe measured at 10 and 293 K respectively is
obtained after annealing at 750 {\deg}C for 30 min suggests that
nanocrystalline PrCo$_3$ are interesting candidates in the field of permanent
magnets. We have completed this experimental study by simulations in the
micromagnetic framework in order to get a qualitative picture of the
microstructure effect on the macroscopic magnetization curve. From this simple
model calculation, we can suggest that the after annealing the system behaves
as magnetically hard crystallites embedded in a weakly magnetized amorphous
matrix. PACS : 75.50.Bb, 75.50.Tt, 76.80.+y",1004.0307v2
2016/3/29,Revealing the nature of magnetic phases in the semi-Heusler alloy Cu0.85Ni0.15MnSb,"We report the magnetic, magnetocaloric, and magnetotransport properties of
the semi-Heusler alloy Cu0.85Ni0.15MnSb, which exhibits coexistence of
antiferromagnetic (AFM) and ferromagnetic (FM) phases. A broad magnetic phase
transition is evident from the temperature variations of magnetization, heat
capacity, and isothermal magnetic entropy change. This is due to the presence
of both AFM and FM phases at low temperatures. The variation of electrical
resistivity with temperature shows three distinct regions of magnetic phases.
The magnetoresistance (MR) results also show the presence of AFM and FM phases
at temperatures below 45 K, and a FM phase at temperature above 45K. Though
there is no signature of a spin-glass state at low temperatures, various
results point towards the presence of short-range magnetic correlations at low
temperatures.",1603.08618v1
2017/3/22,Magnetization process and magnetocaloric effect in geometrically frustrated Ising antiferromagnet and spin ice models on a `Star of David' nanocluster,"Magnetic and magnetocaloric properties of geometrically frustrated
antiferromagnetic Ising (IA) and ferromagnetic spin ice (SI) models on a
nanocluster with a `Star of David' topology, including next-nearest-neighbor
(NNN) interactions, are studied by an exact enumeration. In an external field
applied in characteristic directions of the respective models, depending on the
NNN interaction sign and magnitude, the ground state magnetization of the IA
model is found to display up to three intermediate plateaus at fractional
values of the saturation magnetization, while the SI model shows only one
zero-magnetization plateau and only for the antiferromagnetic NNN coupling. A
giant magnetocaloric effect is revealed in the the IA model with the NNN
interaction either absent or equal to the nearest-neighbor coupling. The latter
is characterized by abrupt isothermal entropy changes at low temperatures and
infinitely fast adiabatic temperature variations for specific entropy values in
the processes when the magnetic field either vanishes or tends to the critical
values related to the magnetization jumps.",1703.07756v1
2019/10/9,Observation of anomalous Ettingshausen effect and large transverse thermoelectric conductivity in permanent magnets,"This study focuses on the potential of permanent magnets as thermoelectric
converters. It is found that a SmCo$_5$-type magnet exhibits the large
anomalous Ettingshausen effect (AEE) at room temperature and that its
charge-to-heat current conversion coefficient is more than one order of
magnitude greater than that of typical ferromagnetic metals. The large AEE is
an exclusive feature of the SmCo$_5$-type magnet among various permanent
magnets in practical use, which is independent of the conventional performance
of magnets based on static magnetic properties. The experimental results show
that the large AEE originates from the intrinsic transverse thermoelectric
conductivity of SmCo$_5$. This finding makes a connection between permanent
magnets and thermal energy engineering, providing the basis for creating
""thermoelectric permanent magnets.""",1910.03748v2
2019/10/25,The influence of crosslinkers and magnetic particle distribution along the filament backbone on the magnetic properties of supracolloidal linear polymer-like chains,"Diverse polymer crosslinking techniques allow the synthesis of linear
polymer-like structures whose monomers are colloidal particles. In the case
where all or part of these colloidal particles are magnetic, one can control
the behaviour of these supracolloidal polymers, known as magnetic filaments
(MFs), by applied magnetic fields. However, the response of MFs strongly
depends on the crosslinking procedure. In the present study, we employ Langevin
dynamics simulations to investigate the influence of the type of crosslinking
and the distribution of magnetic particles within MFs on their response to an
external magnetic field. We found that if the rotation of the dipole moment of
particles is not coupled to the backbone of the filament, the impact of the
magnetic content is strongly decreased.",1910.11607v1
2019/10/27,Magnetic phase diagram of the triangular antiferromagnetic $Cs_2CuCl_{4-x}Br_x$ mixed system,"The novel magnetic phase diagram of the $Cs_2CuCl_{4-x}Br_x$ mixed system is
established by means of single crystal neutron diffraction in the lowest
temperature region and zero magnetic field. Two long-range ordered magnetic
phases exist in this mixed system depending on the Cl/Br concentration. In the
rich Cl concentration range, the ordered magnetic state occurs below the
ordering temperature $T_N = 0.51(1)K$ for $Cs_2CuCl_3Br_1$ and at
$Cs_2CuCl_{2.6}Br_{1.4}$ below $T_N = 0.24(2)K$. Magnetic order with a
temperature-independent position $(0, 0.573(1), 0)$ below the ordering
temperature $T_N = 0.63(1)K$ appears in the rich Br concentration for
$Cs_2CuCl_{0.6}Br_{3.4}$. Between the rich Cl and rich Br concentration ranges
(two magnetic phases), there is a range of x without magnetic order down to
$50mK$. A suggestion about the magnetic exchange paths in the $bc$-layer for
different regimes is presented, which can be controlled depending on the
preferred Br-occupation in the [CuX4] tetrahedra. The density functional theory
(DFT) calculations of the exchange coupling constants J, J^' for some ordered
compositions of the mixed system $Cs_2CuCl_{4-x}Br_x$ indicate that these are
not frustrated.",1910.12248v1
2020/3/28,Spin transport and dynamic properties of two-dimensional spin-momentum locked states,"Materials with spin-momentum locked surface or interface states provide an
interesting playground for studying physics and application of charge-spin
current conversion. To characterize their non-equilibrium magnetic and
transport properties in the presence of a time-dependent external magnetic
field and a spin injection from a contact, we introduce three macroscopic
variables: a vectorial helical magnetization, a scaler helical magnetization,
and the conventional magnetization. We derive a set of closed dynamic equations
for these variables by using the spinor Boltzmann approach with the collision
terms consistent with the symmetry of spin-momentum locked states. By solving
the dynamic equations, we predict several intriguing magnetic and transport
phenomena which are experimentally accessible, including magnetic resonant
response to an AC applied magnetic field, charge-spin conversion, and spin
current induced by the dynamics of helical magnetization.",2003.12700v1
2020/4/15,The magnetic field from a homogeneously magnetized cylindrical tile,"The magnetic field of a homogeneously magnetized cylindrical tile geometry,
i.e. an angular section of a finite hollow cylinder, is found. The field is
expressed as the product between a tensor field describing the geometrical part
of the problem and a column vector holding the magnetization of the tile.
Outside the tile, the tensor is identical to the demagnetization tensor. We
find that four components of the tensor, $N_{xy},N_{xz},N_{yz}$ and $N_{zy}$,
can be expressed fully analytically, while the five remaining components,
$N_{xx},N_{yx},N_{yy},N_{zx}$ and $N_{zz}$, contain integrals that have to be
evaluated numerically. When evaluated numerically the tensor is symmetric. A
comparison between the found solution, implemented in the open source magnetic
framework MagTense, and a finite element calculation of the magnetic flux
density of a cylindrical tile shows excellent agreement.",2004.11701v1
2020/8/3,Anisotropic skyrmion bubbles in ultra-thin epitaxial Au$_{0.67}$Pt$_{0.33}$/Co/W films,"We studied the symmetry of magnetic properties and the resulting magnetic
textures in ultra-thin epitaxial Au$_{0.67}$Pt$_{0.33}$/Co/W, a model system
exhibiting perpendicular magnetic anisotropy and interface
Dzyaloshinskii-Moriya interaction (DMI). As a peculiar feature, the
C$_\mathrm{2v}$ crystal symmetry induced by the Co/W interface results in an
additional uniaxial in-plane magnetic anisotropy in the cobalt layer.
Photoemission electron microscopy with magnetic sensitivity reveals the
formation of self-organized magnetic stripe domains oriented parallel to the
hard in-plane magnetization axis. We attribute this behavior to the lower
domain wall energy when oriented along this axis, where both the DMI and the
in-plane magnetic anisotropy favor a N\'{e}el domain wall configuration. The
anisotropic domain wall energy also leads to the formation of elliptical
skyrmion bubbles in a weak out-of-plane magnetic field.",2008.00717v1
2020/8/14,Cooperation and competition between magnetism and chemisorption,"Chemisorption on ferromagnetic and non-magnetic surfaces is discussed within
the Newns-Anderson-Grimley model along with the Stoner model of ferromagnetism.
In the case of ferromagnetic surfaces, the adsorption energy is formulated in
terms of the change in surface magnetic moments. Using such a formulation, we
address the issue of how an adsorbate's binding strength depends on the
magnetic moments of the surface and how the adsorption process reduces/enhances
the magnetic moments of the surface. Our results indicates a possible
adsorption energy scaling relationship in terms surface magnetic moments. In
the case of non-magnetic surfaces, we formulate a modified stoner criterion and
discuss the condition for the appearance of magnetism due to chemisorption on
an otherwise non-magnetic surface.",2008.06316v4
2009/7/15,The use of Lorentz microscopy for the determination of magnetic reversal mechanism of exchange-biased Co30Fe70/NiMn bilayer,"Lorentz transmission electron microscopy (LTEM) combined with in-situ
magnetizing experiments is a powerful tool for the investigation of the
magnetization of the reversal process at the micron scale. We have implemented
this tool on a conventional transmission electron microscope (TEM) to study the
exchange anisotropy of a polycrystalline Co35Fe65/NiMn bilayer.
Semi-quantitative maps of the magnetic induction were obtained at different
field values by the differential phase contrast (DPC) technique adapted for a
TEM (SIDPC). The hysteresis loop of the bilayer has been calculated from the
relative intensity of magnetic maps. The curve shows the appearance of an
exchange-bias field reveals with two distinct reversal modes of the
magnetization: the first path corresponds to a reversal by wall propagation
when the applied field is parallel to the anisotropy direction whereas the
second is a reversal by coherent rotation of magnetic moments when the field is
applied antiparallel to unidirectional anisotropy direction.",0907.2537v1
2016/6/6,Estimation of maximum possible trapped field in superconducting permanent magnets in 2D and 3D,"The ability of stacks of superconducting tapes to trap large magnetic fields
makes them ideal candidates for creating powerful permanent magnets of compact
size and mass. Experimentally, several techniques are used to trap the maximum
possible field in a given practical application. However, regardless of the
magnetization method used, there is a physical limit to the maximum magnetic
field that a given superconducting magnet can trap. This limit is given by the
geometric design, the particular superconducting material used and the
temperature of operation. Knowing the maximum possible trapped field is
important for device design as it provides an upper limit for applications such
as magnetic bearings or rotating machinery. In this work we present a
collection of finite element method (FEM) models in 2D and 3D capable of
estimating the maximum trapped field of stacked tape superconducting magnets.
The models are computationally fast and can be used to perform parametric
studies with ease. For the case of square stacks tape magnets, various sizes
are considered and their estimated maximum trapped field is compared with
experimental results.",1606.01817v1
2017/12/18,Complex magnetic behaviour and evidence of superspin glass state in a binary intermetallic compound Er5Pd2,"A binary intermetallic compound Er5Pd2 has been investigated using dc and ac
magnetic susceptibilities, magnetic memory effect, isothermal magnetization,
non-linear dc susceptibility, heat capacity and magnetocaloric effect studies.
Interestingly, even though the compound does not show geometrical frustration
it undergoes glassy magnetic phase transition below 17.2 K. Investigation of dc
magnetisation and heat capacity data divulged absence of long-ranged magnetic
ordering. Through magnetic memory effect, time dependent magnetization and ac
susceptibility studies it was revealed that the compound undergoes glass-like
freezing below 17.2 K. Analysis of frequency dependence of this transition
temperature through scaling and Arrhenius law; along with Mydosh parameter
indicate, that the dynamics in Er5Pd2 is due to the presence of strongly
interacting superspins rather than individual spins. This phase transition was
further investigated by non-linear dc susceptibility and was characterized by
static critical exponents {\gamma} and {\delta}. Our results indicate that this
compound show signature of superspin glass at low temperature. Additionally,
both conventional and inverse magnetocaloric effect was observed with large
value of magnetic entropy change and relative cooling power. Our results
suggest that Er5Pd2 can be classified as a superspin glass system with large
magnetocaloric effect.",1712.06388v1
2018/2/28,Structural Disorder and Elementary Magnetic Properties of Triangular Lattice ErMgGaO4 Single Crystals,"The single crystal growth, structure, and basic magnetic properties of
ErMgGaO4 are reported. The structure consists of triangular layers of magnetic
ErO6 octahedra separated by a double layer of randomly occupied non-magnetic
(Ga,Mg)O5 bipyramids. The Er atoms are positionally disordered. Magnetic
measurements parallel and perpendicular to the c axis of a single crystal
reveal dominantly antiferromagnetic interactions, with a small degree of
magnetic anisotropy. A weighted average of the directional data suggests an
antiferromagnetic Curie Weiss temperature of approximately -30 K. Below 10 K
the temperature dependences of the inverse susceptibilities in the in-plane and
perpendicular-to plane directions are parallel, indicative of an isotropic
magnetic moment at low temperatures. No sign of magnetic ordering is observed
above 1.8 K, suggesting that ErMgGaO4 is a geometrically frustrated magnet.",1802.10242v1
2018/11/1,First Empirical Constraints on the Low H$α$ Mass-Loss Rates of Magnetic O-Stars,"A small subset of Galactic O-stars possess surface magnetic fields that alter
the outflowing stellar wind by magnetically confining it. Key to the magnetic
confinement is that it induces rotational modulation of spectral lines over the
full EM domain; this allows us to infer basic quantities, e.g., mass-loss rate
and magnetic geometry. Here, we present an empirical study of the H$\alpha$
line in Galactic magnetic O-stars to constrain the mass fed from the stellar
base into the magnetosphere, using realistic multi-dimensional magnetized wind
models, and compare with theoretical predictions. Our results suggest that it
may be reasonable to use mass-feeding rates from non-magnetic wind theory if
the absolute mass-loss rate is scaled down according to the amount of wind
material falling back upon the stellar surface. This provides then some
empirical support to the proposal that such magnetic O-stars might evolve into
heavy stellar-mass black holes (Petit et al. 2017)",1811.00163v1
2018/11/13,X-ray magnetic linear dichroism as a probe for non-collinear magnetic state in ferrimagnetic single layer exchange bias systems,"Ferrimagnetic alloys are extensively studied for their unique magnetic
properties leading to possible applications in perpendicular magnetic
recording, due to their deterministic ultrafast switching and heat assisted
magnetic recording capabilities. On a prototype ferrimagnetic alloy we
demonstrate fascinating properties that occur close to a critical temperature
where the magnetization is vanishing, just as in an antiferromagnet. From the
X-ray magnetic circular dichroism measurements, an anomalous 'wing shape'
hysteresis loop is observed slightly above the compensation temperature. This
bears the characteristics of an intrinsic exchange bias effect, referred to as
atomic exchange bias. We further exploit the X-ray magnetic linear dichroism
(XMLD) contrast for probing non-collinear states which allows us to
discriminate between two main reversal mechanisms, namely perpendicular domain
wall formation versus spin-flop transition. Ultimately, we analyze the
elemental magnetic moments for the surface and the bulk parts, separately,
which allows to identify in the phase diagram the temperature window where this
effect takes place. Moreover, we suggests that this effect is a general
phenomenon in ferrimagnetic thin films which may also contribue to the
understanding of the mechanism behind the all optical switching effect.",1811.05362v1
2019/3/15,A complete description of the magnetic ground state in spinel vanadates,"Capturing the non-collinear magnetic ground state of the spinel vanadates
AV$_2$O$_4$ (A= Mn, Fe and Co) remains an outstanding challenge for
state-of-the-art ab-initio methods. We demonstrate that both the non-collinear
spin texture, as well as the magnitude of local moments, are captured by a
single value of the on-site Hubbard $U$ of 2.7~eV in conjunction with the local
spin density approximation (LSDA+$U$), provided the source term (i.e., magnetic
monopole term) is removed from the exchange-correlation magnetic field ${\bf
B}_{XC}$. We further demonstrate that the magnetic monopole structure in ${\bf
B}_{XC}$ is highly sensitive to the value of $U$, to the extent that the
interplay between on-site localization and local moment magnitude is
qualitatively different depending on whether the source term is removed or not.
This suggests that in treating strongly correlated magnetic materials within
the LSDA+$U$ formalism, subtraction of the unphysical magnetic monopole term
from the exchange-correlation magnetic field is essential to correctly treat
the magnetic ground state.",1903.06532v1
2019/5/13,Recycling of SmCo5 magnets by HD process,"Hydrogen decrepitation process has been applied for the first time for the
direct recycling of SmCo5 magnets. Industrially produced sintered SmCo5 magnets
were decrepitated by hydrogen gas at a pressure of 1 bar to 9.5 bar at room
temperature in a planetary rotating jar. After decrepitation, the starting
sintered magnets were reduced to a powder with a particle size of less than 200
microns. The produced powder was used for the preparation of recycled SmCo5
magnets. Scanning electron microscopy, energy-dispersive X-ray spectroscopy,
X-ray diffraction studies and magnetic measurements were used to follow the
decrepitation and the sintering processes. The measured remanence and maximum
energy product of the recycled magnet are 0.94 T and 171.1 kJ/m3, respectively,
in comparison with 0.91 T and 156.8 kJ/m3, respectively for the original magnet
before recycling. It was also observed that, there is refinement in the
microstructure after recycling in comparison to the original magnet.",1905.04829v1
2019/5/22,Magnetic ripple domain structure in FeGa/MgO thin films,"The magnetic domain structure is studied in epitaxial
Fe$_{100-x}$Ga$_x$/MgO(001) films with 0 $<$ x $<$ 30 and thicknesses below 60
nm by magnetic force microscopy. For low gallium content, domains with the
magnetization lying in the film plane and domain walls separating micrometric
areas are observed. Above x $\approx$ 20, the magnetic contrast shows a fine
corrugation, ranging from 300 to 900 nm, suggesting a ripple substructure with
a periodic oscillation of the magnetization. We discuss the presence of a
random magnetic anisotropy contribution, that superimposed to the cubic
coherent anisotropy, is able to break the uniform orientation of the
magnetization. The origin of that random anisotropy is attributed to several
factors: coexistence of crystal phases in the films, inhomogeneous distribution
of both internal strain and Ga-Ga next nearest neighbor pairs and interface
magnetic anisotropy due to the Fe-O bond.",1905.09180v2
2019/11/5,Foucault imaging and small-angle electron diffraction in controlled external magnetic fields,"We report a method for acquiring Foucault images and small-angle electron
diffraction patterns in external magnetic fields using a conventional
transmission electron microscope without any modification. In the electron
optical system that we have constructed, external magnetic fields parallel to
the optical axis can be controlled using the objective lens pole piece under
weak excitation conditions in the Foucault mode and the diffraction mode. We
observe two ferromagnetic perovskite-type manganese oxides,
La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ and Nd$_{0.5}$Sr$_{0.5}$MnO$_{3}$, in order to
visualize magnetic domains and their magnetic responses to external magnetic
fields. In rhombohedral-structured La$_{0.7}$Sr$_{0.3}$MnO$_{3}$, pinning of
magnetic domain walls at crystallographic twin boundaries was found to have a
strong influence on the generation of new magnetic domains in external applied
magnetic fields.",1911.01683v1
2019/12/9,Monte Carlo simulations study of the intermetallic compound NdCo$_2$Si$_2$ Magnetic properties,"Magnetic properties of the intermetallic compound NdCo$_2$Si$_2$ are
investigated by using the Monte Carlo simulation (MCs) under Metropolis
algorithm. The magnetism of the compound is caused by the existence of the rare
earth (Nd3+) ions with a magnetic moment taking the value 2.7 muB. Firstly, the
ground state phase diagrams are presented and discussed in different planes
corresponding to different physical parameters of the system. The stable phases
are explored for different configurations of the Hamiltonian of the system.
These stable phases are determined by the minimal energies. For non-null
temperature values, we compute the magnetizations and susceptibilities
behaviors as a function of temperature by using the Monte Carlo simulations
(MCS). Also, we present the magnetization behaviors as a function of the
exchange coupling interactions, the crystal field and the external magnetic
field. Finally, we present and discuss the magnetic hysteresis loops of the
intermetallic NdCo2Si2 compound as a function of the external magnetic field
for fixed values of temperature and the other physical parameters.",1912.04245v1
2019/12/13,An Investigation of Magnetic Hysteresis Error in Kibble Balances,"Yoke-based permanent magnetic circuits are widely used in Kibble balance
experiments. In these magnetic systems, the coil current, with positive and
negative signs in two steps of the weighing measurement, can cause an
additional magnetic flux in the circuit and hence a magnetic field change at
the coil position. The magnetic field change due to the coil current and
related systematic effects have been studied with the assumption that the yoke
material does not contain any magnetic hysteresis. In this paper, we present an
explanation of the magnetic hysteresis error in Kibble balance measurements. An
evaluation technique based on measuring yoke minor hysteresis loops is proposed
to estimate the effect. The dependence of the magnetic hysteresis effect and
some possible optimizations for suppressing this effect are discussed.",1912.06694v2
2020/1/17,Magnetic anisotropy in Cr$_2$GeC investigated by X-ray magnetic circular dichroism and \textit{ab initio} calculations,"The magnetism in the inherently nanolaminated ternary MAX-phase Cr$_{2}$GeC
is investigated by element-selective, polarization and temperature-dependent,
soft X-ray absorption spectroscopy and X-ray magnetic circular dichroism. The
measurements indicate an antiferro-magnetic Cr-Cr coupling along the $c$-axis
of the hexagonal structure modulated by a ferromagnetic ordering in the
nanolaminated $ab$-basal planes. The weak chromium magnetic moments are an
order of magnitude stronger in the nanolaminated planes than along the vertical
axis. Theoretically, a small but notable, non-spin-collinear component explains
the existence of a non-perfect spin compensation along the $c$-axis. As shown
in this work, this spin distortion generates an overall residual spin moment
inside the unit cell resembling that of a ferri-magnet. Due to the different
competing magnetic interactions, electron correlations and temperature effects
both need to be considered to achieve a correct theoretical description of the
Cr$_{2}$GeC magnetic properties.",2001.06396v1
2020/1/22,Macroscopic Manifestation of Domain-wall Magnetism and Magnetoelectric Effect in a Néel-type Skyrmion Host,"We report a magnetic state in GaV$_4$Se$_8$ which emerges exclusively in
samples with mesoscale polar domains and not in polar mono-domain crystals. Its
onset is accompanied with a sharp anomaly in the magnetic susceptibility and
the magnetic torque, distinct from other anomalies observed also in polar
mono-domain samples upon transitions between the cycloidal, the N\'eel-type
skyrmion lattice and the ferromagnetic states. We ascribe this additional
transition to the formation of magnetic textures localized at structural domain
walls, where the magnetic interactions change stepwise and spin textures with
different spiral planes, hosted by neighbouring domains, need to be matched. A
clear anomaly in the magneto-current indicates that the domain-wall-confined
magnetic states also have strong contributions to the magnetoelectric response.
We expect polar domain walls to commonly host such confined magnetic edge
states, especially in materials with long wavelength magnetic order.",2001.08076v1
2020/5/26,"Features of magnetic and magnetoelectric properties, H-T phase diagram of GdCr3(BO3)4","Comprehensive studies of magnetic properties of GdCr3(BO3)4 single crystal
have been carried out. The integrals of intrachain and interchain exchange
interactions in the chromium subsystem have been determined and the strength of
Cr-Gd exchange interaction has been estimated. The values of the exchange field
and the effective magnetic anisotropy field of GdCr3(BO3)4 have been estimated.
The electric polarization along the a axis in the longitudinal geometry of the
experiment has been detected. Correlations between the electric polarization
and the magnetization of the studied compound have been found. The
spin-reorientation phase transition in the magnetically ordered state has been
found. This transition exists for the external magnetic field applied along any
crystallographic direction and the transition field depends weakly on the
direction of the field. The nature of the spin-reorientation phase transition
has been discussed. Magnetic phase diagram has been constructed and spin
configurations for the low-field and high-field phases have been proposed.",2005.13045v1
2020/6/11,Embracing defects and disorder in magnetic nanoparticles,"Iron oxide nanoparticles have tremendous scientific and technological
potential in a broad range of technologies, from energy applications to
biomedicine. To improve their performance, single-crystalline and defect-free
nanoparticles have thus far been aspired. However, in several recent studies
defect-rich nanoparticles outperform their defect-free counterparts in magnetic
hyperthermia and magnetic particle imaging. Here, an overview on the
state-of-the-art of design and characterization of defects and resulting spin
disorder in magnetic nanoparticles is presented with a focus on iron oxide
nanoparticles. The beneficial impact of defects and disorder on intracellular
magnetic hyperthermia performance of magnetic nanoparticles for drug delivery
and cancer therapy is emphasized. Defect-engineering in iron oxide
nanoparticles emerges to become an alternative approach to tailor their
magnetic properties for biomedicine, as it is already common practice in
established systems such as semiconductors and emerging fields including
perovskite solar cells. Finally, perspectives and thoughts are given on how to
deliberately induce defects in iron oxide nanoparticles and their potential
implications for magnetic tracers to monitor cell therapy and immunotherapy by
magnetic particle imaging.",2006.06474v1
2020/10/12,Peculiarities of magnetic ordering in the S = 5/2 two-dimensional square-lattice antimonate NaMnSbO4,"An orthorhombic compound, NaMnSbO4, represents a square net of magnetic Mn2+
ions residing in vertex-shared oxygen octahedra. Its static and dynamic
magnetic properties were studied using magnetic susceptibility, specific heat,
magnetization, electron spin resonance (ESR), nuclear magnetic resonance (NMR)
and density functional calculations. Thermodynamic data indicate an
establishment of the long-range magnetic order with TN about 44 K, which is
preceded by a short-range one at about 55 K. In addition, a non-trivial
wasp-waisted hysteresis loop of the magnetization was observed, indicating that
the ground state is most probably canted antiferromagnetic. Temperature
dependence of the magnetic susceptibility is described reasonably well in the
framework of 2D square lattice model with the main exchange parameter J = -5.3
K, which is in good agreement with density functional analysis, NMR and ESR
data.",2010.05653v1
2020/10/14,Spin torque gate magnetic field sensor,"Spin-orbit torque provides an efficient pathway to manipulate the magnetic
state and magnetization dynamics of magnetic materials, which is crucial for
energy-efficient operation of a variety of spintronic devices such as magnetic
memory, logic, oscillator, and neuromorphic computing. Here, we describe and
experimentally demonstrate a strategy for the realization of a spin torque gate
magnetic field sensor with extremely simple structure by exploiting the
longitudinal field dependence of the spin torque driven magnetization
switching. Unlike most magnetoresistance sensors which require a delicate
magnetic bias to achieve a linear response to the external field, the spin
torque gate sensor can achieve the same without any magnetic bias, which
greatly simplifies the sensor structure. Furthermore, by driving the sensor
using an ac current, the dc offset is automatically suppressed, which
eliminates the need for a bridge or compensation circuit. We verify the concept
using the newly developed WTe2/Ti/CoFeB trilayer and demonstrate that the
sensor can work linearly in the range of 3-10 Oe with negligible dc offset.",2010.07158v1
2020/11/11,Quantization of edge currents along magnetic interfaces: A K-theory approach,"The purpose of this paper is to investigate the propagation of topological
currents along magnetic interfaces (also known as magnetic walls) of a
two-dimensional material. We consider tight-binding magnetic models associated
to generic magnetic multi-interfaces and describe the K-theoretical setting in
which a bulk-interface duality can be derived. Then, the (trivial) case of a
localized magnetic field and the (non trivial) case of the Iwatsuka magnetic
field are considered in full detail. This is a pedagogical preparatory work
that aims to anticipate the study of more complicated multi-interface magnetic
systems.",2011.05814v2
2020/11/27,Laser-induced torques in spin spirals,"We investigate laser-induced torques in magnetically non-collinear
ferromagnets with a spin-spiral magnetic structure using \textit{ab-initio}
calculations. Since spin-spirals may be used to approximate the magnetization
gradients locally in domain walls and skyrmions, our method may be used to
obtain the laser-induced torques in such objects from a multiscale approach.
Employing the generalized Bloch-theorem we obtain the electronic structure
computationally efficiently. We employ our method to assess the laser-induced
torques in bcc Fe, hcp Co, and L$_{1}0$ FePt when a spin-spiral magnetic
structure is imposed. We find that the laser-induced torques in these
magnetically noncollinear systems may be orders of magnitude larger than those
in the corresponding magnetically collinear systems and that they exist both
for linearly and circularly polarized light. This result suggests that
laser-induced torques driven by noncollinear magnetic order or by magnetic
fluctuations may contribute significantly to processes in ultrafast magnetism.",2011.13707v2
2020/12/15,Magnetism at the interface of non-magnetic Cu and C$_{60}$,"The signature of magnetism without a ferromagnet in a non-magnetic
heterostructure is novel as well as fascinating from fundamental research point
of view. It has been shown by Al'Mari et al: that magnetism can be induced at
the interface of Cu/C60 due to change in density of states. However, the
quantification of such interfacial magnetic moment has not been performed yet.
In order to quantify the induced magnetic moment in Cu, we have performed X-ray
magnetic circular dichroism (XMCD) measurements on Cu/C$_{60}$ multilayers. We
have observed room temperature ferromagnetism in Cu/C$_{60}$ stack. Further
XMCD measurements show that ~0.01 $\mu_B$/atom magnetic moment has been induced
in Cu at the Cu/C$_{60}$ interface.",2012.08670v1
2021/1/18,Single particle multipole expansions from Micromagnetic Tomography,"Micromagnetic tomography aims at reconstructing large numbers of individual
magnetizations of magnetic particles from combining high-resolution magnetic
scanning techniques with micro X-ray computed tomography (microCT). Previous
work demonstrated that dipole moments can be robustly inferred, and
mathematical analysis showed that the potential field of each particle is
uniquely determined. Here, we describe a mathematical procedure to recover
higher orders of the magnetic potential of the individual magnetic particles in
terms of their spherical harmonic expansions (SHE). We test this approach on
data from scanning superconducting quantum interference device microscopy and
microCT of a reference sample. For particles with high signal-to-noise ratio of
the magnetic scan we demonstrate that SHE up to order $n=3$ can be robustly
recovered. This additional level of detail restricts the possible internal
magnetization structures of the particles and provides valuable rock magnetic
information with respect to their stability and reliability as paleomagnetic
remanence carriers. Micromagnetic tomography therefore enables a new approach
for detailed rock magnetic studies on large ensembles of individual particles.",2101.07010v1
2021/2/4,Nanoscale magnetization and current imaging using scanning-probe magneto-thermal microscopy,"Magnetic microscopy that combines nanoscale spatial resolution with
picosecond scale temporal resolution uniquely enables direct observation of the
spatiotemporal magnetic phenomena that are relevant to future high-speed,
high-density magnetic storage and logic technologies. Magnetic microscopes that
combine these metrics has been limited to facility-level instruments. To
address this gap in lab-accessible spatiotemporal imaging, we develop a
time-resolved near-field magnetic microscope based on magneto-thermal
interactions. We demonstrate both magnetization and current density imaging
modalities, each with spatial resolution that far surpasses the optical
diffraction limit. In addition, we study the near-field and time-resolved
characteristics of our signal and find that our instrument possesses a spatial
resolution on the scale of 100 nm and a temporal resolution below 100 ps. Our
results demonstrate an accessible and comparatively low-cost approach to
nanoscale spatiotemporal magnetic microscopy in a table-top form to aid the
science and technology of dynamic magnetic devices with complex spin textures.",2102.02792v1
2021/2/23,Magnetic charge's relaxation propelled electricity in two-dimensional magnetic honeycomb lattice,"Emerging new concepts, such as magnetic charge dynamics in two-dimensional
magnetic material, can provide novel mechanism for spin based electrical
transport at macroscopic length. In artificial spin ice of single domain
elements, magnetic charge's relaxation can create an efficient electrical
pathway for conduction by generating fluctuations in local magnetic field that
couple with conduction electrons spins. In a first demonstration, we show that
the electrical conductivity is propelled by more than an order of magnitude at
room temperature due to magnetic charge defects sub-picosecond relaxation in
artificial magnetic honeycomb lattice. The direct evidence to the proposed
electrical conduction mechanism in two-dimensional frustrated magnet points to
the untapped potential for spintronic applications in this system.",2102.11949v1
2021/3/9,Carrier Tuning of Stoner Ferromagnetism in ThCr$_{\mathbf{2}}$Si$_{\mathbf{2}}$-Structure Cobalt Arsenides,"CaCo$_{2-y}$As$_2$ is an unusual itinerant magnet with signatures of extreme
magnetic frustration. The conditions for establishing magnetic order in such
itinerant frustrated magnets, either by reducing frustration or increasing
electronic correlations, is an open question. Here we use results from
inelastic neutron scattering and magnetic susceptibility measurements and
density functional theory calculations to show that hole doping in
Ca(Co$_{1-x}$Fe$_{x}$)$_{2-y}$As$_{2}$ suppresses magnetic order by quenching
the magnetic moment while maintaining the same level of magnetic frustration.
The suppression is due to tuning the Fermi energy away from a peak in the
electronic density of states originating from a flat conduction band. This
results in the complete elimination of the magnetic moment by $x\approx0.25$,
providing a clear example of a Stoner-type transition.",2103.05695v2
2021/9/8,Unusual Magnetic Properties in Layered Magnetic Topological Insulator EuSn2As2,"EuSn2As2 with layered rhombohedral crystal structure is proposed to be a
candidate of intrinsic antiferromagnetic (AFM) topological insulator. Here, we
have investigated systematic magnetoresistance (MR) and magnetization
measurements on the high quality EuSn2As2 single crystal with the magnetic
field both parallel and perpendicular to (00l) plane. Both the kink of magnetic
susceptibility and longitudinal resistivity reveal that EuSn2An2 undergoes an
AFM transition at TN = 21 K. At T = 2 K, the magnetization exhibits two
successive plateaus of ~ 5.6 {\mu}B/Eu and ~ 6.6 {\mu}B/Eu at the corresponding
critical magnetic fields. Combined with the negative longitudinal MR and
abnormal Hall resistance, we demonstrate that EuSn2An2 undergoes complicated
magnetic transitions from an AFM state to a canted ferromagnetic (FM) state at
Hc and then to a polarized FM state at Hs as the magnetic field increase.",2109.03414v1
2021/9/9,Adjustable 3D magnetic configuration in ferrimagnetic multilayers with competing interactions visualized by soft X-ray vector tomography,"Soft X-ray magnetic vector tomography has been used to visualize with
unprecedented detail and solely from experimental data the 3D magnetic
configuration of a ferrimagnetic Gd12Co88/Nd17Co83/Gd24Co76 multilayer with
competing anisotropy, exchange and magnetostatic interactions at different
depths. The trilayer displays magnetic stripe domains, arranged in a chevron
pattern, which are imprinted from the central Nd17Co83 into the bottom Gd12Co88
layer with a distorted closure domain structure across the thickness. Near the
top Gd24Co76 layer, local exchange springs with out-of-plane magnetization
reversal, modulated ripple patterns and magnetic vortices and antivortices
across the thickness are observed. The detailed analysis of the magnetic
tomogram shows that the effective strength of the exchange spring at the
NdCo/GdCo interface can be finely tuned by GdxCo1-x composition and anisotropy
(determined by sample fabrication) and in-plane stripe orientation
(adjustable), demonstrating the capability of 3D magnetic visualization
techniques in magnetic engineering research.",2109.04064v1
2021/10/10,Deterministic generation of skyrmions and antiskyrmions by electric current,"Magnetic skyrmions are nanoscale spin whirlpools that promise breakthroughs
in future spintronic applications. Controlled generation of magnetic skyrmions
by electric current is crucial for this purpose. While previous studies have
demonstrated this operation, the topological charge of the generated skyrmions
is determined by the direction of the external magnetic fields, thus is fixed.
Here, we report the current-induced skyrmions creation in a chiral magnet FeGe
nanostructure by using the \emph{in-situ} Lorentz transmission electron
microscopy. We show that magnetic skyrmions or antiskyrmions can be both
transferred from the magnetic helical ground state simply by controlling the
direction of the current flow at zero magnetic field. The force analysis and
symmetry consideration, backed up by micromagnetic simulations, well explain
the experimental results, where magnetic skyrmions or antiskyrmions are created
due to the edge instability of the helical state in the presence of spin
transfer torque. The on-demand generation of skyrmions and control of their
topology by electric current without the need of magnetic field will enable
novel purely electric-controlled skyrmion devices.",2110.04713v1
2021/11/9,Incommensurate-commensurate magnetic phase transition in the double tungstate Li2Co(WO4)2,"Magnetic susceptibility, specific heat, and neutron powder diffraction
measurements have been performed on polycrystalline Li2Co(WO4)2 samples. Under
zero magnetic field, two successive magnetic transitions at TN1 ~ 9.4 K and TN2
~ 7.4 K are observed. The magnetic ordering temperatures gradually decrease as
the magnetic field increases. Neutron diffraction reveals that Li2Co(WO4)2
enters an incommensurate magnetic state with a temperature dependent k between
TN1 and TN2. The magnetic propagation vector locks-in to a commensurate value k
= (1/2, 1/4, 1/4) below TN2. The antiferromagnetic structure is refined at 1.7
K with Co2+ magnetic moment 2.8(1) uB, consistent with our first-principles
calculations.",2111.04944v1
2021/12/7,Magnetization process of the S=1/2 Heisenberg antiferromagnet on the floret pentagonal lattice,"We study the S=1/2 Heisenberg antiferromagnet on the floret pentagonal
lattice by numerical diagonalization method. This system shows various
behaviours that are different from that of the Cairo-pentagonal-lattice
antiferromagnet. The ground-state energy without magnetic field and the
magnetization process of this system are reported. Magnetization plateaux
appear at one-ninth height of the saturation magnetization, at one-third
height, and at seven-ninth height. The magnetization plateaux at one-third and
seven-ninth heights come from interactions linking the sixfold-coordinated spin
sites. A magnetization jump appears from the plateau at one-ninth height to the
plateau at one-third height. Another magnetization jump is observed between the
heights corresponding to the one-third and seven-ninth plateaux; however the
jump is away from the two plateaux, namely, the jump is not accompanied with
any magnetization plateaux. The jump is a peculiar phenomenon that has not been
reported.",2112.03516v1
2021/12/13,Spontaneous anomalous Hall effect arising from an unconventional compensated magnetic phase in a semiconductor,"The anomalous Hall effect, commonly observed in metallic magnets, has been
established to originate from the time-reversal symmetry breaking by an
internal macroscopic magnetization in ferromagnets or by a non-collinear
magnetic order. Here we observe a spontaneous anomalous Hall signal in the
absence of an external magnetic field in an epitaxial film of MnTe, which is a
semiconductor with a collinear antiparallel magnetic ordering of Mn moments and
a vanishing net magnetization. The anomalous Hall effect arises from an
unconventional phase with strong time-reversal symmetry breaking and
alternating spin polarization in real-space crystal structure and
momentum-space electronic structure. The anisotropic crystal environment of
magnetic Mn atoms due to the non-magnetic Te atoms is essential for
establishing the unconventional phase and generating the anomalous Hall effect.",2112.06805v3
2022/1/27,Spin motive force by the momentum-space Berry phase in magnetic Weyl semimetals,"We show that the magnetic precession of ferromagnetic moments in a
noncentrosymmetric magnetic Weyl semimetal induces an electric current through
a mechanism analogous to the adiabatic charge pumping. The current is a
consequence of a Berry phase in the momentum space resulting from the circular
motion of Weyl nodes induced by the precession. This mechanism resembles the
Faraday effect, namely, induced magnetic field by circular electric current.
The circular motion of Weyl nodes induces magnetic charge current in the
momentum space, which results in a Berry phase that describes the adiabatic
pump. Experimentally, this phenomenon is similar to spin motive force, which is
an electric current induced by magnetic precision in the presence of the
spatial gradient of magnetization. However, unlike the conventional spin motive
force, this current occurs without a magnetization gradient. The result
demonstrates a nontrivial interplay between the topological electronic state
and magnetic dynamics.",2201.11568v2
2022/2/3,Magnetic domain wall dynamics under external electric field in bilayer CrI$_3$,"Motivated by manipulating the magnetic order of bilayer CrI$_3$, we carry out
microscopic calculations to find the magnetic order and various magnetic
domains of the system in the presence of an electric field. Making use of
density functional simulations, a spin model Hamiltonian is introduced
consisting of isotropic exchange couplings, Dzyaloshinskii-Moriya (DM)
interaction, and on-site magnetic anisotropy. The spin dynamics of two
well-known states of bilayer CrI$_3$, low temperature (LT) and high temperature
(HT) phases, are obtained by solving the Landau-Lifshitz-Gilbert equation. We
show that the magnetic texture is stacking-dependent in bilayer CrI$_3$ and
stable magnetic domains can appear in the HT stack which are tunable by
external electric and magnetic fields. Therefore, we suggest that the HT phase
represents a promising candidate for data storage in the modern generation of
spintronic devices working on magnetic domain engineering.",2202.01394v2
2022/4/19,Antiferromagnetic structure and magnetic properties of Dy2O2Te: An isostructural analog of the rare-earth superconductors R2O2Bi,"The rare-earth compounds R2O2Bi (R=Tb, Dy, Er, Lu, Y) are newly discovered
superconductors in the vicinity of a rare-earth magnetic long-range order. In
this work, we determine the magnetic order of the parent compound Dy2O2Te by
neutron scattering as the A-type antiferromagnetic structure below the N\'eel
temperature TN=9.7K. The large staggered magnetic moment 9.4(1) {\mu}B per Dy
at T=3.5K lies in the basal ab plane. In a magnetic field, anomalous magnetic
properties including the bifurcation between zero-field- and field-cooling
magnetization, a butterfly-shaped magnetic hysteresis, and slow magnetic
relaxation emerge, which are related to the field-induced metamagnetic
transitions in Dy2O2Te. Our experimental findings could stimulate further
research on the relation between antiferromagnetism and superconductivity in
these rare-earth compounds.",2204.09103v1
2022/6/1,Magnetic octupole tensor decomposition and second-order magnetoelectric effect,"We discuss the second-order magnetoelectric effect, in which a quadratic or
bilinear electric field induces a linear magnetization, in terms of the ferroic
ordering of magnetic octupoles. We present the decomposition of a general
rank-3 tensor into its irreducible spherical tensors, then reduce the
decomposition to the specific case of the magnetic octupole tensor,
$\mathcal{M}_{ijk} = \int \mu_i (\mathbf{r}) r_j r_k d^3 \mathbf{r}$. We use
first-principles density functional theory to compute the size of the local
magnetic multipoles on the chromium ions in the prototypical magnetoelectric
Cr$_2$O$_3$, and show that, in addition to the well established local magnetic
dipoles and magnetoelectric multipoles, the magnetic octupoles are non-zero.
The magnetic octupoles in Cr$_2$O$_3$ have an anti-ferroic arrangement, so
their net second-order magnetoelectric response is zero. Therefore they form a
kind of hidden order, which could be revealed as a linear magnetic
(antiferromagnetic) response to a non-zone-center (uniform) quadratic electric
field.",2206.00522v1
2022/6/1,LiYbSe2: Frustrated Magnetism in a New Pyrochlore Lattice,"Three-dimensionally (3D) frustrated magnets generally exist in the magnetic
diamond and pyrochlore lattices, in which quantum fluctuations suppress
magnetic orders and generate highly entangled ground states (GS). LiYbSe2 in a
previously unreported pyrochlore lattice was discovered from LiCl flux growth.
Distinct from the quantum spin liquid (QSL) candidate NaYbSe2 hosting a perfect
triangular lattice of Yb3+, LiYbSe2 crystallizes in the cubic pyrochlore
structure with space group Fd-3m (No. 227). The Yb3+ ions in LiYbSe2 are
arranged on a network of corner-sharing tetrahedra, which is particularly
susceptible to geometrical frustration. According to our temperature-dependent
magnetic susceptibility measurements, the dominant antiferromagnetic
interaction in LiYbSe2 is expected to appear around 8 K. However, no long-range
magnetic order is detected in thermomagnetic measurements above 70 mK. Specific
heat measurements also show magnetic correlations shifting with applied
magnetic field with a degree of missing entropy that may be related to the
slight mixture of Yb3+ on the Li site. Such magnetic frustration of Yb3+ is
rare in pyrochlore structures. Thus, LiYbSe2 shows promises in intrinsically
realizing disordered quantum states like QSL in pyrochlore structures.",2206.00565v1
2022/6/27,Field-Induced Magnetic States in the Metallic Rare-Earth Layered Triangular Antiferromagnet TbAuAl$_4$Ge$_2$,"Magnetic frustration in metallic rare earth lanthanides ($Ln$) with
$4f$-electrons is crucial for producing interesting magnetic phases with high
magnetic anisotropy where intertwined charge and spin degrees of freedom lead
to novel phenomena. Here we report on the magnetic, thermodynamic, and
electrical transport properties of TbAuAl$_4$Ge$_2$. Tb ions form 2-dimensional
triangular lattice layers which stack along the crystalline $c$-axis. The
magnetic phase diagram reveals multiple nearly degenerate ordered states upon
applying field along the magnetically easy $ab$-plane before saturation. The
magnetoresistance in this configuration exhibits intricate field dependence
that closely follows that of the magnetization while the specific heat reveals
a region of highly enhanced entropy, suggesting the possibility of a
non-trivial spin textured phase. For fields applied along the $c$-axis (hard
axis), we find linear magnetoresistance over a wide range of fields. We compare
the magnetic properties and magnetoresistance with an isostructral
GdAuAl$_4$Ge$_2$ single crystals. These results identify TbAuAl$_4$Ge$_2$ as an
environment for complex quantum spin states and pave the way for further
investigations of the broader $Ln$AuAl$_4$Ge$_2$ family of materials.",2206.13118v1
2022/8/14,Emergent orbital magnetization in Kitaev quantum magnets,"Unambiguous identification of the Kitaev quantum spin liquid (QSL) in
materials remains a huge challenge despite many encouraging signs from various
measurements. To facilitate the experimental detection of the Kitaev QSL, here
we propose to use remnant charge response in Mott insulators hosting QSL to
identify the key signatures of QSL. We predict an emergent orbital
magnetization in a Kitaev system in an external magnetic field. The direction
of the orbital magnetization can be flipped by rotating the external magnetic
field in the honeycomb plane. The orbital magnetization is demonstrated
explicitly through a detailed microscopic analysis of the multiorbital
Hubbard-Kanamori Hamiltonian and also supported by a phenomenological picture.
We first derive the localized electrical loop current operator in terms of the
spin degrees of freedom. Thereafter, utilizing the Majorana representation, we
estimate the loop currents in the ground state of the chiral Kitaev QSL state,
and obtain the consequent current textures, which are responsible for the
emergent orbital magnetization. Finally, we discuss the possible experimental
techniques to visualize the orbital magnetization which can be considered as
the signatures of the underlying excitations.",2208.06887v2
2022/8/15,Quantum Transport and Magnetism of Dirac Electrons in Solids,"The relativistic Dirac equation covers the fundamentals of electronic
phenomena in solids and as such it effectively describes the electronic states
of the topological insulators like Bi$_2$Se$_3$ and Bi$_2$Te$_3$. Topological
insulators feature gapless surface states and, moreover, magnetic doping and
resultant ferromagnetic ordering break time-reversal symmetry to realize
quantum anomalous Hall and Chern insulators. Here we focus on the bulk and
investigate the mutual coupling of electronic and magnetic properties of Dirac
electrons. Without carrier doping, spiral magnetic orders cause a ferroelectric
polarization through the spin-orbit coupling. In a doped metallic state, the
anisotropic magnetoresistance arises without uniform magnetization. We find
that electric current induces uniform magnetization and conversely an
oscillating magnetic order induces electric current. Our model provides a
coherent and unified description of all those phenomena. The mutual control of
electric and magnetic properties demonstrates implementations of
antiferromagnetic spintronics. We also discuss the stoichiometric magnetic
topological insulator MnBi$_2$Te$_4$.",2208.07255v2
2022/8/27,Magnon drag induced by magnon-magnon interactions characteristic of noncollinear magnets,"A noncollinear magnet consists of the magnetic moments forming a noncollinear
spin structure. Because of this structure, the Hamiltonian of magnons acquires
the cubic terms. Although the cubic terms are the magnon-magnon interactions
characteristic of noncollinear magnets, their effects on magnon transport have
not been clarified yet. Here we show that in a canted antiferromagnet the cubic
terms cause a magnon drag that magnons drag magnon spin current and heat
current, which can be used to enhance these currents by tuning a magnetic
field. For a strong magnetic field, we find that the cubic terms induce
low-temperature peaks of a spin-Seebeck coefficient, a magnon conductivity, and
a magnon thermal conductivity, and that each value is one order of magnitude
larger than the noninteracting value. This enhancement is mainly due to the
magnetic field dependence of the coupling constant of the cubic terms through
the magnetic-field dependent canting angle. Our magnon drag offers a way for
controlling the magnon currents of noncollinear magnets via the many-body
effect.",2208.12939v1
2022/9/4,Magnetic phase crossover in strongly correlated EuMn2P2,"Strong electron correlations underlie a plethora of electronic and magnetic
components and devices and are often used to identify and probe novel ground
states in quantum materials. Herein we report a magnetic phase crossover in
EuMn2P2, an insulator which shows Eu antiferromagnetism at TN=17K, but no phase
transition attributed to Mn magnetism. The absence of a Mn magnetic phase
transition contrasts with the formation of long-range Mn order at T=130K in
isoelectronic EuMn2Sb2 and EuMn2As2. Temperature-dependent specific heat and
31P NMR measurements provide evidence for the development of Mn magnetic
correlations from T=250-100 K. Density functional theory calculations
demonstrate an unusual sensitivity of the band structure to the details of the
imposed Mn and Eu magnetic order, with antiferromagnetic Mn order required to
recapitulate an insulating state. Our results imply a picture in which long
range Mn magnetic order is suppressed by chemical pressure, but that magnetic
correlations persist, narrowing bands and producing an insulating state.",2209.01707v1
2022/11/15,Nonlinear sub-switching regime of magnetization dynamics in photo-magnetic garnets,"We analyze, both experimentally and numerically, the nonlinear regime of the
photo-induced coherent magnetization dynamics in cobalt-doped yttrium iron
garnet films. Photo-magnetic excitation with femtosecond laser pulses reveals a
strongly nonlinear response of the spin subsystem with a significant increase
of the effective Gilbert damping. By varying both laser fluence and the
external magnetic field, we show that this nonlinearity originates in the
anharmonicity of the magnetic energy landscape. We numerically map the
parameter workspace for the nonlinear photo-induced spin dynamics below the
photo-magnetic switching threshold. Corroborated by numerical simulations of
the Landau-Lifshitz-Gilbert equation, our results highlight the key role of the
cubic symmetry of the magnetic subsystem in reaching the nonlinear spin
precession regime. These findings expand the fundamental understanding of
laser-induced nonlinear spin dynamics as well as facilitate the development of
applied photo-magnetism.",2211.08048v2
2023/1/22,Magnon bundle in a strongly dissipative magnet,"Hybrid quantum systems based on magnetic platforms have witnessed the birth
and fast development of quantum spintronics. Until now, most of the studies
rely on magnetic excitations in low-damping magnetic insulators, particularly
yttrium iron garnet, while a large class of magnetic systems is ruled out in
this interdisciplinary field. Here we propose the generation of a magnon bundle
in a hybrid magnet-qubit system, where two or more magnons are emitted
simultaneously. By tuning the driving frequency of qubit to match the detuning
between magnon and qubit mode, one can effectively generate a magnon bundle via
super-Rabi oscillations. In contrast with general wisdom, magnetic dissipation
plays an enabling role in generating the magnon bundle, where the relaxation
time of magnons determines the typical time delay between two successive
magnons. The maximal damping that allows an antibunched magnon bundle can reach
the order of 0.1, which may break the monopoly of low-dissipation magnetic
insulators in quantum spintronics and enables a large class of magnetic
materials for quantum manipulation. Further, our finding may provide a scalable
and generic platform to study multi-magnon physics and benefit the design of
magnonic networks for quantum information processing.",2301.09095v1
2023/2/14,Pressure-tunable magnetic topological phases in magnetic topological insulator MnSb4Te7,"Magnetic topological insulators, possessing both magnetic order and
topological electronic structure, provides an excellent platform to research
unusual physical properties. Here, we report a high-pressure study on the
anomalous Hall effect of magnetic TI MnSb4Te7 through transports measurements
combined with first-principle theoretical calculations. We discover that the
ground state of MnSb4Te7 experiences a magnetic phase transition from the
A-type antiferromagnetic state to ferromagnetic dominating state at 3.78 GPa,
although its crystal sustains a rhombohedral phase under high pressures up to 8
GPa. The anomalous Hall conductance {\sigma}xyA keeps around 10 {\Omega}-1
cm-1, dominated by the intrinsic mechanism even after the magnetic phase
transition. The results shed light on the intriguing magnetism in MnSb4Te7 and
pave the way for further studies of the relationship between topology and
magnetism in topological materials.",2302.07113v1
2023/3/16,Non-perturbative Many-Body Treatment of Molecular Magnets,"Molecular magnets have received significant attention because of their
potential applications in quantum information and quantum computing. A delicate
balance of electron correlation, spin-orbit coupling (SOC), ligand field
splitting, and other effects produces a persistent magnetic moment within each
molecular magnet unit. The discovery and design of molecular magnets with
improved functionalities would be greatly aided by accurate computations.
However, the competition among the different effects poses a challenge for
theoretical treatments. Electron correlation plays a central role, since d-, or
f-element ions, which provide the magnetic states in molecular magnets, often
require explicit many-body treatments. SOC, which expands the dimensionality of
the Hilbert space, can also lead to non-perturbative effects in the presence of
strong interaction. Furthermore, molecular magnets are large, with tens of
atoms in even the smallest systems. We show how an $\textit{ab initio}$
treatment of molecular magnets can be achieved with auxiliary-field quantum
Monte Carlo (AFQMC), in which electron correlation, SOC, and material
specificity are included accurately and on an equal footing. The approach is
demonstrated by an application to compute the zero-field splitting of a
locally-linear Co$^{2+}$ complex.",2303.09010v1
2023/3/27,Magnetic manipulation of superparamagnetic colloids in droplet-based optical devices,"Magnetically assembled superparamagnetic colloids have been exploited as
fluid mixers, swimmers and delivery systems in several microscale applications.
The encapsulation of such colloids in droplets may open new opportunities to
build magnetically controlled displays and optical components. Here, we study
the assembly of superparamagnetic colloids inside droplets under rotating
magnetic fields and exploit this phenomenon to create functional optical
devices. Colloids are encapsulated in monodisperse droplets produced by
microfluidics and magnetically assembled into dynamic two-dimensional clusters.
Using an optical microscope equipped with a magnetic control setup, we
investigate the effect of the magnetic field strength and rotational frequency
on the size, stability and dynamics of 2D colloidal clusters inside droplets.
Our results show that cluster size and stability depend on the magnetic forces
acting on the structure under the externally imposed field. By rotating the
cluster in specific orientations, we illustrate how magnetic fields can be used
to control the effective refractive index and the transmission of light through
the colloid-laden droplets, thus demonstrating the potential of the
encapsulated colloids in optical applications.",2303.15336v1
2023/4/30,Temperature-Dependent and Magnetism-Controlled Fermi Surface Changes in Magnetic Weyl Semimetals,"The coupling between band structure and magnetism can lead to intricate Fermi
surface modifications. Here we report on the comprehensive study of the
Shubnikov-de Haas (SdH) effect in two rare-earth-based magnetic Weyl
semimetals, NdAlSi and CeAlSi$_{0.8}$Ge$_{0.2}$. The results show that the
temperature evolution of topologically nontrivial Fermi surfaces strongly
depends on magnetic configurations. In NdAlSi, the SdH frequencies vary with
temperature in both the paramagnetic state and the magnetically ordered state
with a chiral spin texture, but become temperature independent in the
high-field fully polarized state. In CeAlSi$_{0.8}$Ge$_{0.2}$, SdH frequencies
are temperature-dependent only in the ferromagnetic state with magnetic fields
applied along the $c$ axis. First-principles calculations suggest that the
notable temperature and magnetic-configuration dependence of Fermi surface
morphology can be attributed to strong exchange coupling between the conduction
electrons and local magnetic moments.",2305.00437v1
2023/5/29,Interplay between optical emission and magnetism in the van der Waals magnetic semiconductor CrSBr in the two-dimensional limit,"The Van der Waals semiconductor metamagnet CrSBr offers an ideal platform for
studying the interplay between optical and magnetic properties in the
two-dimensional limit. Here, we carried out an exhaustive optical
characterization of this material by means of temperature and magnetic field
dependent photoluminescence (PL) on flakes of different thicknesses down to the
monolayer. We found a characteristic emission peak that is quenched upon
switching the ferromagnetic layers from an antiparallel to a parallel
configuration and exhibits a different temperature dependence from that of the
peaks commonly ascribed to excitons. The contribution of this peak to the PL is
boosted around 30-40 K, coinciding with the hidden order magnetic transition
temperature. Our findings reveal the connection between the optical and
magnetic properties via the ionization of magnetic donor vacancies. This
behavior enables a useful tool for the optical reading of the magnetic states
in atomically thin layers of CrSBr and shows the potential of the design of
two-dimensional heterostructures with magnetic and excitonic properties.",2305.18094v1
2023/6/22,Combination of Measurement Data and Domain Knowledge for Simulation of Halbach Arrays with Bayesian Inference,"Accelerator magnets made from blocks of permanent magnets in a zero-clearance
configuration are known as Halbach arrays. The objective of this work is the
fusion of knowledge from different measurement sources (material and field) and
domain knowledge (magnetostatics) to obtain an updated magnet model of a
Halbach array. From Helmholtz-coil measurements of the magnetized blocks, a
prior distribution of the magnetization is estimated. Measurements of the
magnetic flux density are used to derive, by means of Bayesian inference, a
posterior distribution. The method is validated on simulated data and applied
to measurements of a dipole of the FASER detector. The updated magnet model of
the FASER dipole describes the magnetic flux density one order of magnitude
better than the prior magnet model.",2306.12844v1
2023/7/6,NiCrAl piston-cylinder cell for magnetic susceptibility measurements under high pressures in pulsed high magnetic fields,"We developed a metallic pressure cell made of nickel-chromium-aluminum
(NiCrAl) for use with a non-destructive pulse magnet and a magnetic
susceptibility measurement apparatus with a proximity detector oscillator (PDO)
in pulsed magnetic fields of up to 51 T under pressures of up to 2.1 GPa. Both
the sample and sensor coil of the PDO were placed in the cell so that the
magnetic signal from NiCrAl would not overlay the intrinsic magnetic
susceptibility of the sample. A systematic investigation of the Joule heating
originating from metallic parts of the pressure cell revealed that the
temperature at the sample position remains at almost 1.4 K until approximately
80 $\%$ of the maximum applied magnetic field ($H_{\rm max}$) in the
field-ascending process (e.g., 40 T for $H_{\rm max}$ of 51 T). The
effectiveness of our apparatus was demonstrated, by investigating the pressure
dependence of the magnetization process of the triangular-lattice
antiferromagnet Ba$_3$CoSb$_2$O$_9$.",2307.02755v2
2023/7/6,Tuning the Magnetism in Ultrathin CrxTey Films by Lattice Dimensionality,"Two-dimensional (2D) magnetic transition metal compounds with atomic
thickness exhibit intriguing physics in fundamental research and great
potential for device applications. Understanding the correlations between their
macrosopic magnetic properties and the dimensionality of microscopic magnetic
exchange interactions are valuable for the designing and applications of 2D
magnetic crystals. Here, using spin-polarized scanning tunneling microscopy,
magnetization and magneto-transport measurements, we identify the
zigzag-antiferromagnetism in monolayer CrTe2, incipient ferromagnetism in
bilayer CrTe2, and robust ferromagnetism in bilayer Cr3Te4 films. Our density
functional theory calculations unravel that the magnetic ordering in ultrathin
CrTe2 is sensitive to the lattice parameters, while robust ferromagnetism with
large perpendicular magnetic anisotropy in Cr3Te4 is stabilized through its
anisotropic 3D magnetic exchange interactions.",2307.02857v1
2023/7/29,Unveiling Exotic Magnetic Phases in Fibonacci Quasicrystalline Stacking of Ferromagnetic Layers through Machine Learning,"In this study, we conduct a comprehensive theoretical analysis of a Fibonacci
quasicrystalline stacking of ferromagnetic layers, potentially realizable using
van der Waals magnetic materials. We construct a model of this magnetic
heterostructure, which includes up to second neighbor interlayer magnetic
interactions, that displays a complex relationship between geometric
frustration and magnetic order in this quasicrystalline system. To navigate the
parameter space and identify distinct magnetic phases, we employ a machine
learning approach, which proves to be a powerful tool in revealing the complex
magnetic behavior of this system. We offer a thorough description of the
magnetic phase diagram as a function of the model parameters. Notably, we
discover among other collinear and non-collinear phases, a unique ferromagnetic
alternating helical phase. In this non-collinear quasiperiodic ferromagnetic
configuration the magnetization decreases logarithmically with the stack
height.",2307.16052v1
2023/9/11,Magnetic anisotropy driven by ligand in 4d transition metal oxide SrRuO3,"The origin of magnetic anisotropy in magnetic compounds is a longstanding
issue in solid state physics and nonmagnetic ligand ions are considered to
contribute little to magnetic anisotropy. Here, we introduce the concept of
ligand driven magnetic anisotropy in a complex transition-metal oxide. We
conducted X ray absorption and X ray magnetic circular dichroism spectroscopies
at the Ru and O edges in the 4d ferromagnetic metal SrRuO3. Systematic
variation of the sample thickness in the range below 10 nm allowed us to
control the localization of Ru 4d t2g states, which affects the magnetic
coupling between the Ru and O ions. We found that the orbital magnetization of
the ligand induced via hybridization with the Ru 4d orbital determines the
magnetic anisotropy in SrRuO3.",2309.05228v2
2023/9/13,Non-collinear magnetism engendered by a hidden another order,"Standard microscopic approach to magnetic orders is based on assuming a
Heisenberg form for inter-atomic exchange interactions. These interactions are
considered as a driving force for the ordering transition with magnetic moments
serving as the primary order parameter. Any higher-rank multipoles appearing
simultaneously with such magnetic order are typically treated as auxiliary
order parameters rather than a principal cause of the transition. In this
study, we show that these traditional assumptions are violated in the case of
PrO$_2$. Evaluating the full set of Pr-Pr superexchange interactions from a
first-principles many-body technique we find that its unusual non-collinear 2k
magnetic structure stems from high-rank multipolar interactions, and that the
corresponding contribution of the Heisenberg interactions is negligible. The
observed magnetic order in PrO$_2$ is thus auxiliary to high-rank ""hidden""
multipoles. Within this picture we consistently account for previously
unexplained experimental observations like the magnitude of exchange splitting
and the evolution of magnetic structure in external field. Our findings
challenge the standard paradigm of observable magnetic moments being the
driving force for magnetic transitions.",2309.07071v1
2023/9/24,Greener processing of SrFe$_{12}$O$_{19}$ ceramic permanent magnets by two-step sintering,"With an annual production amounting to 800 kilotons, ferrite magnets
constitute the largest family of permanent magnets in volume, a demand that
will only increase as a consequence of the rare-earth crisis. With the global
goal of building a climate-resilient future, strategies towards a greener
manufacturing of ferrite magnets are of great interest. A new ceramic
processing route for obtaining dense Sr-ferrite sintered magnets is presented
here. Instead of the usual sintering process employed nowadays in ferrite
magnet manufacturing that demands long dwell times, a shorter two-step
sintering is designed to densify the ferrite ceramics. As a result of these
processes, dense SrFe$_{12}$O$_{19}$ ceramic magnets with properties comparable
to state-of-the-art ferrite magnets are obtained. In particular, the
SrFe$_{12}$O$_{19}$ magnet containing 0.2% PVA and 0.6% wt SiO$_2$ reaches a
coercivity of 164 kA/m along with a 93% relative density. A reduction of 31% in
energy consumption is achieved in the thermal treatment with respect to
conventional sintering, which could lead to energy savings for the industry of
the order of 7.109 kWh per year.",2309.15860v1
2023/10/16,Trompe L'oeil Ferromagnetism: magnetic point group analysis,"Ferromagnetism can be characterized by various unique phenomena such as
non-zero magnetization (inducing magnetic attraction/repulsion), diagonal
piezomagnetism, nonreciprocal circular dichroism (such as Faraday effect),
odd-order (including linear) anomalous Hall effect, and magneto-optical Kerr
effect. We identify all broken symmetries requiring each of the above
phenomena, and also the relevant magnetic point groups (MPGs) with those broken
symmetries. All of ferromagnetic point groups, relevant for ferromagnets,
ferri-magnets and weak ferromagnets, can certainly exhibit all of these
phenomena, including non-zero magnetization. Some of true antiferromagnets,
which are defined as magnets with MPGs that do not belong to ferromagnetic
point groups, can display these phenomena through magnetization induced by
external perturbations such as applied current, electric fields, light
illumination, and strain. Such MPGs are identified for each external
perturbation. Since high-density and ultrafast spintronic technologies can be
enabled by antiferromagnets, our findings will be an essential guidance for the
future magnetism-related science as well as technology.",2310.10562v1
2023/11/29,Observation of Hybrid Magnetic Skyrmion Bubbles in Fe3Sn2 Nanodisks,"It is well known that there are two types of magnetic bubbles in uniaxial
magnets. Here, using Lorentz-transimission electronic microscopy magnetic
imaging, we report the direct experimental observation of 3D type-III hybrid
bubbles, which comprise N\'eel-twisted skyrmion bubbles with topological charge
Q = -1 in near-surface layers and type-II bubbles with Q = 0 in interior
layers, in Fe3Sn2 nanodisks. Using the tilted magnetic field, we further show
the controlled topological magnetic transformations of three types of bubbles
in a confined ferromagnetic nanodisk. Our observations are well reproduced
using micromagnetic simulations based on measured magnetic parameters. Our
results advance fundamental classification and understanding of magnetic
bubbles, which could propel the applications of three-dimensional magnetism.",2311.17413v1
2023/12/5,Magnetic instability under ferroaxial moment,"Magnetic anisotropy is one of the important factors in determining magnetic
structures. A type of magnetic anisotropy is closely related to the symmetry of
crystals. We theoretically investigate magnetic anisotropy and its related
magnetic instability arising from an electric axial moment, which appears under
the breaking of the mirror symmetry parallel to the moment but does not require
the breakings of both spatial inversion and time-reversal symmetries. By
performing perturbation and mean-field calculations in a complementary way, we
show the appearance of the in-plane magnetic anisotropy when the electric axial
moment occurs, which tends to tilt in-plane spin moments from the crystal axes
in collaboration with relativistic spin--orbit coupling. We demonstrate such a
tendency for single-site and four-site cluster models, the latter of which
leads to the instability toward a spin vortex phase accompanying magnetic
monopole and magnetic toroidal dipole.",2312.02444v1
2024/2/6,A Mean-Field Study of Quantum Oscillations in Two-Dimensional Kondo Insulators,"Magnetic oscillations in strongly correlated insulating systems have garnered
interest due to oscillations seemingly originating from the bulk, despite an
anticipated gapped spectrum. We use the large-$N$ mean-field theory to study
the behavior of normal and topological Kondo insulators under a magnetic field.
In both cases spinons acquire a charge and hybridize with electrons, producing
magnetic oscillations that resemble two-band noninteracting systems. We show
that in such band insulators magnetic oscillations are exponentially suppressed
at weak magnetic fields. A self-consistent mean-field calculation for the Kondo
insulators reveals that the temperature dependence of the oscillations departs
from the noninteracting case due to the temperature and magnetic-field
dependence of the hybridization, even though mean-field parameters remain
homogeneous at low fields. Larger magnetic fields result in the Kondo
breakdown, where the magnetic oscillation is solely due to the decoupled
conduction electrons. These findings offer new insights into the magnetic
properties of Kondo insulators, with implications for interpreting experimental
results in heavy fermion materials like SmB$_6$.",2402.04125v1
2024/2/27,In-plane ordering and tunable magnetism in Cr-based MXenes,"MXene, the two-dimensional derivatives of MAX compounds, due to their
structural and compositional flexibility, is an ideal family of compounds to
study a number of structure-property relations. In this work, we have
investigated the tunability of magnetic properties in Cr-based MXenes that have
an in-plane ordering arising out of alloying Cr with another non-magnetic
transition metal atom. Using Density Functional Theory based calculations we
have explored the effects of composition and surface functionalisations on the
electronic and magnetic properties of these in-plane ordered MXenes known as
i-MXenes. We found that the electronic and magnetic ground states are quite
sensitive to the structure and composition. This provides enough tunability in
these compounds so that they can be used for practical applications. Our
calculated results of magnetic transition temperatures and magnetic anisotropy
energies are comparable to many a established two-dimensional magnets. These
put together widen the prospect of these i-MXenes for multiple usage as
magnetic devices making them attractive for further investigation.",2402.17577v1
2024/3/18,Magnetic properties of an individual Magnetospirillum gryphiswaldense cell,"Many bacteria share the fascinating ability to sense Earth's magnetic field
-- a process known as magnetotaxis. These bacteria synthesize magnetic
nanoparticles, called magnetosomes, within their own cell body and arrange them
to form a linear magnetic chain. The chain, which behaves like a compass
needle, aligns the microorganisms with the geomagnetic field. Here, we measure
the magnetic hysteresis of an individual bacterium of the species
Magnetospirillum gryphiswaldense via ultrasensitive torque magnetometry. These
measurements, in combination with transmission electron microscopy and
micromagnetic simulations, reveal the magnetic configurations of the
magnetosomes, their progression as a function of applied field, as well as the
total remanent magnetic moment and effective magnetic anisotropy of a chain
within a single bacterium. Knowledge of magnetic properties is crucial both for
understanding the mechanisms behind magnetotaxis and for the design of systems
exploiting magnetotactic bacteria in biomedical applications.",2403.11801v1
2019/4/19,Tunable Berry Curvature Through Magnetic Phase Competition in a Topological Kagome Magnet,"Magnetic topological phases of quantum matter are an emerging frontier in
physics and material science. Along these lines, several kagome magnets have
appeared as the most promising platforms. However, the magnetic nature of these
materials in the presence of topological state remains an unsolved issue. Here,
we explore magnetic correlations in the kagome magnet Co_3Sn_2S_2. Using muon
spin-rotation, we present evidence for competing magnetic orders in the kagome
lattice of this compound. Our results show that while the sample exhibits an
out-of-plane ferromagnetic ground state, an in-plane antiferromagnetic state
appears at temperatures above 90 K, eventually attaining a volume fraction of
80% around 170 K, before reaching a non-magnetic state. Strikingly, the
reduction of the anomalous Hall conductivity above 90 K linearly follows the
disappearance of the volume fraction of the ferromagnetic state. We further
show that the competition of these magnetic phases is tunable through applying
either an external magnetic field or hydrostatic pressure. Our results taken
together suggest the thermal and quantum tuning of Berry curvature field via
external tuning of magnetic order. Our study shows that Co_3Sn_2S_2 is a rare
example where the magnetic competition drives the thermodynamic evolution of
the Berry curvature field, thus tuning its topological state.",1904.09353v1
2019/7/22,Interactions of magnetized plasma flows in pulsed-power driven experiments,"A supersonic flow of magnetized plasma is produced by the application of a 1
MA-peak, 500 ns current pulse to a cylindrical arrangement of parallel wires,
known as an inverse wire array. The plasma flow is produced by the JxB
acceleration of the ablated wire material, and a magnetic field of several
Tesla is embedded at source by the driving current. This setup has been used
for a variety of experiments investigating the interactions of magnetized
plasma flows. In experiments designed to investigate magnetic reconnection, the
collision of counter-streaming flows, carrying oppositely directed magnetic
fields, leads to the formation of a reconnection layer in which we observe ions
reaching temperatures much greater than predicted by classical heating
mechanisms. The breakup of this layer under the plasmoid instability is
dependent on the properties of the inflowing plasma, which can be controlled by
the choice of the wire array material. In other experiments, magnetized shocks
were formed by placing obstacles in the path of the magnetized plasma flow. The
pile-up of magnetic flux in front of a conducting obstacle produces a magnetic
precursor acting on upstream electrons at the distance of the ion inertial
length. This precursor subsequently develops into a steep density transition
via ion-electron fluid decoupling. Obstacles which possess a strong private
magnetic field affect the upstream flow over a much greater distance, providing
an extended bow shock structure. In the region surrounding the obstacle the
magnetic pressure holds off the flow, forming a void of plasma material,
analogous to the magnetopause around planetary bodies with self-generated
magnetic fields.",1907.09447v1
2022/10/10,Breaking through the Mermin-Wagner limit in 2D van der Waals magnets,"The Mermin-Wagner theorem states that long-range magnetic order does not
exist in one- or two-dimensional (2D) isotropic magnets with short-ranged
interactions. The theorem has been a milestone in magnetism and has been
driving the research of recently discovered 2D van der Waals (vdW) magnetic
materials from fundamentals up to potential applications. In such systems, the
existence of magnetic ordering is typically attributed to the presence of a
significant magnetic anisotropy, which is known to introduce a spin-wave gap
and circumvent the core assumption of the theorem. Here we show that in
finite-size 2D vdW magnets typically found in lab setups (e.g., within
millimetres), short-range interactions can be large enough to allow the
stabilisation of magnetic order at finite temperatures without any magnetic
anisotropy for practical implementations. We demonstrate that magnetic ordering
can be created in flakes of 2D materials independent of the lattice symmetry
due to the intrinsic nature of the spin exchange interactions and finite-size
effects in two-dimensions. Surprisingly we find that the crossover temperature,
where the intrinsic magnetisation changes from superparamagnetic to a
completely disordered paramagnetic regime, is weakly dependent on the system
length, requiring giant sizes (e.g., of the order of the observable universe
~10$^{26}$ m) in order to observe the vanishing of the magnetic order at
cryogenic temperatures as expected from the Mermin-Wagner theorem. Our findings
indicate exchange interactions as the main driving force behind the
stabilisation of short-range order in 2D magnetism and broaden the horizons of
possibilities for exploration of compounds with low anisotropy at an atomically
thin level.",2210.04830v1
2002/8/2,Effect of transition layers on the electromagnetic properties of composites containing conducting fibres,"The approach to calculating the effective dielectric and magnetic response in
bounded composite materials is developed. The method is essentially based on
the renormalisation of the dielectric matrix parameters to account for the
surface polarisation and the displacement currents at the interfaces. This
makes it possible the use of the effective medium theory developed for
unbounded materials, where the spatially-dependent local dielectric constant
and magnetic permeability are introduced. A detailed mathematical analysis is
given for a dielectric layer having conducting fibres with in-plane positions.
The surface effects are most essential at microwave frequencies in
correspondence to the resonance excitation of fibres. In thin layers (having a
thickness of the transition layer), the effective dielectric constant has a
dispersion region at much higher frequencies compared to those for unbounded
materials, exhibiting a strong dependence on the layer thickness. For the
geometry considered, the effective magnetic permeability differs slightly from
unity and corresponds to the renormalised matrix parameter. The magnetic effect
is due entirely to the existence of the surface displacement currents.",0208035v1
2003/1/16,Magnetism and superconductivity in CeRh_{1-x}Ir_xIn_5 heavy fermion materials,"We report on zero-field muon spin relaxation studies of cerium based
heavy-fermion materials CeRh_{1-x}Ir_xIn_5. In the superconducting x=0.75 and 1
compositions muon spin relaxation functions were found to be temperature
independent across T_c; no evidence for the presence of electronic magnetic
moments was observed. The x=0.5 material is antiferromagnetic below T_N=3.75 K
and superconducting below T_c=0.8 K. Muon spin realxation spectra show the
gradual onset of damped coherent oscillations characteristic of magnetic order
below T_N. At 1.65 K the total oscillating amplitude accounts for at least 85%
of the sample volume. No change in muon precession frequency or amplitude is
detected on cooling below T_c, indicating the microscopic coexistence of
magnetism and superconductivity in this material.",0301309v2
2003/4/8,Elasticity-driven Nanoscale Texturing in Complex Electronic Materials,"Finescale probes of many complex electronic materials have revealed a
non-uniform nanoworld of sign-varying textures in strain, charge and
magnetization, forming meandering ribbons, stripe segments or droplets. We
introduce and simulate a Ginzburg-Landau model for a structural transition,
with strains coupling to charge and magnetization. Charge doping acts as a
local stress that deforms surrounding unit cells without generating defects.
This seemingly innocuous constraint of elastic `compatibility', in fact induces
crucial anisotropic long-range forces of unit-cell discrete symmetry, that
interweave opposite-sign competing strains to produce polaronic elasto-magnetic
textures in the composite variables. Simulations with random local doping below
the solid-solid transformation temperature reveal rich multiscale texturing
from induced elastic fields: nanoscale phase separation, mesoscale intrinsic
inhomogeneities, textural cross-coupling to external stress and magnetic field,
and temperature-dependent percolation. We describe how this composite textured
polaron concept can be valuable for doped manganites, cuprates and other
complex electronic materials.",0304198v1
2006/1/31,Multiferroics: different ways to combine magnetism and ferroelectricity,"Multiferroics - materials which are simultaneously (ferro)magnetic and
ferroelectric, and often also ferroelastic, attract now considerable attention,
both because of the interesting physics involved and as they promise important
practical applications. In this paper I give a survey of microscopic factors
determining the coexistence of these properties, and discuss different possible
routes to combine them in one material. In particular the role of the
occupation of d-states in transition metal perovskites is discussed, possible
role of spiral magnetic structures is stressed and the novel mechanism of
ferroelectricity in magnetic systems due to combination of site-centred and
bond-centred charge ordering is presented. Microscopic nature of multiferroic
behaviour in several particular materials, including magnetite Fe3O4, is
discussed.",0601696v1
2006/8/7,Non-collinear Magnetic states of Mn5Ge3 compound,"Mn5Ge3 thin films epitaxially grown on Ge(111) exhibit metallic conductivity
and strong ferromagnetism up to about 300 K. Recent experiments suggest a
non-collinear spin structure. In order to gain deep insights into the magnetic
structure of this compound, we have performed fully unconstrained ab-initio
pseudopotential calculations within density functional theory, investigating
the different magnetic states corresponding to Collinear (C) and Non-Collinear
(NC) spin configurations. We focus on their relative stability under pressure
and strain field. Under pressure, the C and NC configurations are degenerate,
suggesting the possible occurrence of accidental magnetic degeneracy also in
Mn5Ge3 real samples. We found a continuous transition from a ferromagnetic C
low-spin state at small volumes to a NC high-spin state at higher volumes.
Remarkably, the degeneracy is definitely removed under the effect of uniaxial
strain: in particular, NC spin configurations is favoured under tensile
uniaxial strain.",0608176v2
2007/11/6,"The Aharonov-Bohm-Effect, Non-commutative Geometry, Dislocation Theory, and Magnetism","The four items mentioned in the title are put into context in an informal
way.",0711.0855v2
2007/12/28,"Erratum: Landau Analysis of the Symmetry of the Magnetic Structure and Magnetoelectric Interaction in Multiferroics [Phys. Rev. B 76, 05447 (2007)]","An error in the spin wavefunction for the rare earth sublattices of TbMn_2O_5
is corrected.",0712.4307v1
2009/5/12,Large magnetic entropy change near room temperature in antipervoskite SnCMn3,"We report the observation of large magnetocaloric effect near room
temperature in antipervoskite SnCMn3. The maximal magnetic entropy change at
the first-order ferrimagnetic-paramagnetic transition temperature (TC 279 K) is
about 80.69mJ/cm3 K and 133mJ/cm3 K under the magnetic field of 20 kOe and 48
kOe, respectively. These values are close to those of typical magnetocaloric
materials. The large magnetocaloric effect is associated with the sharp change
of lattice, resistivity and magnetization in the vicinity of TC. Through the
measurements of Seebeck coefficient and normal Hall effect, the title system is
found to undergo a reconstruction of electronic structure at TC. Considering
its low-cost and innocuous raw materials, Mn-based antiperovskite compounds are
suggested to be appropriate for pursuing new materials with larger
magnetocaloric effect.",0905.1773v1
2013/6/24,Multi-field nanoindentation apparatus for measuring local mechanical properties of materials in external magnetic and electric fields,"Nano/micro-scale mechanical properties of multiferroic materials can be
controlled by the external magnetic or electric field due to the coupling
interaction. For the first time, a modularized multi-field nanoindentation
apparatus for carrying out testing on materials in external
magnetostatic/electrostatic field is constructed. Technical issues, such as the
application of magnetic/electric field and the processes to diminish the
interference between external fields and the other parts of the apparatus, are
addressed. Tests on calibration specimen indicate the feasibility of the
apparatus. The load-displacement curves of ferromagnetic, ferroelectric and
magnetoelectric materials in the presence/absence of external fields reveal the
small-scale magnetomechanical and electromechanical coupling, showing as the
Delta-E and Delta-H effects, i.e. the magnetic/electric field induced changes
in the apparent elastic modulus and indentation hardness.",1306.5666v1
2014/12/1,"Evolution of magnetic, transport, and thermal properties in Na$_{4-x}$Ir$_3$O$_8$","The hyper-kagome material Na$_4$Ir$_3$O$_8$ is a three-dimensional
spin-liquid candidate proximate to a quantum critical point (QCP). We present a
comprehensive study of the structure, magnetic susceptibility $\chi$, heat
capacity $C$, and electrical transport on polycrystalline samples of the doped
hyper-kagome material Na$_{4-x}$Ir$_3$O$_8$ ($x \approx 0, 0.1, 0.3, 0.7)$.
Materials with $x\leq 0.3$ are found to be Mott insulators with strong
antiferromagnetic interactions and no magnetic ordering down to $T = 2$ K\@.
All samples show irreversibility below $T \approx 6$ K between the
zero-field-cooled and field-cooled magnetization measured in low fields ($H =
0.050$ T) suggesting a frozen low temperature state although no corresponding
anomaly is seen in the heat capacity. The $x = 0.7$ sample shows $\rho(T)$
which weakly increases with decreasing temperature $T$, nearly $T$ independent
$\chi$, a linear in $T$ contribution to the low temperature $C$, and a Wilson
ratio $R_W \approx 7$ suggesting anomalous semi-metallic behavior.",1412.0455v2
2015/5/23,Long distance transport of magnon spin information in a magnetic insulator at room temperature,"The transport of spin information has been studied in various materials, such
as metals, semiconductors and graphene. In these materials, spin is transported
by diffusion of conduction electrons. Here we study the diffusion and
relaxation of spin in a magnetic insulator, where the large bandgap prohibits
the motion of electrons. Spin can still be transported, however, through the
diffusion of non-equilibrium magnons, the quanta of spin wave excitations in
magnetically ordered materials. Here we show experimentally that these magnons
can be excited and detected fully electrically in linear response, and can
transport spin angular momentum through the magnetic insulator yttrium iron
garnet (YIG) over distances as large as 40 micrometer. We identify two
transport regimes: the diffusion limited regime for distances shorter than the
magnon relaxation length, and the relaxation limited regime for larger
distances. With a model similar to the diffusion-relaxation model for electron
spin transport in (semi)conducting materials, we extract the magnon relaxation
length lambda = 9.4 micrometer in a 200 nm thin YIG film at room temperature.",1505.06325v1
2015/8/4,Energy based stochastic model for temperature dependent behavior of ferromagnetic materials,"An energy based stochastic model for temperature dependent anhysteretic
magnetization curves of ferromagnetic materials is proposed and bench marked
against experimental data. This is based on the calculation of macroscopic
magnetic properties by performing an energy weighted average over all possible
orientations of the magnetization vector. Most prior approaches that employ
this method are unable to independently account for the effect of both
inhomogeneity and temperature in performing the averaging necessary to model
experimental data. Here we propose a way to account for both effects
simultaneously and benchmark the model against experimental data from ~5K to
~300K for two different materials in both annealed (fewer inhomogeneities) and
deformed (more inhomogeneities) samples. This demonstrates that the independent
accounting for the effect of both inhomogeneity and temperature is necessary to
correctly model temperature dependent magnetization behavior.",1508.00853v1
2016/4/28,Mastering hysteresis in magnetocaloric materials,"Hysteresis is more than just an interesting oddity, which occurs in materials
with a first-order transition. It is a real obstacle on the path from existing
lab-scale prototypes of magnetic refrigerators towards commercialization of
this potentially disruptive cooling technology. Indeed, the reversibility of
the magnetocaloric effect, being essential for magnetic heat pumps, strongly
depends on the width of the thermal hysteresis and therefore it is necessary to
understand the mechanisms causing hysteresis and to find solutions how to
minimize losses associated with thermal hysteresis in order to maximize the
efficiency of magnetic cooling devices. In this work, we discuss fundamental
aspects, which can contribute to thermal hysteresis and we are developing
strategies for at least partially overcoming the hysteresis problem in some
selected classes of magnetocaloric materials with large application potential.
Doing so, we refer to the most relevant classes of magnetic refrigerants
La-Fe-Si-, Heusler- and Fe2P-type compounds.",1604.08487v2
2016/5/18,Interfacial magnetic anisotropy from a 3-dimensional Rashba substrate,"We study the magnetic anisotropy which arises at the interface between a thin
film ferromagnet and a 3-d Rashba material. The 3-d Rashba material is
characterized by the spin-orbit strength $\alpha$ and the direction of broken
bulk inversion symmetry $\hat n$. We find an in-plane uniaxial anisotropy in
the $\hat{z}\times\hat{n}$ direction, where $\hat z$ is the interface normal.
For realistic values of $\alpha$, the uniaxial anisotropy is of a similar order
of magnitude as the bulk magnetocrystalline anisotropy. Evaluating the uniaxial
anisotropy for a simplified model in 1-d shows that for small band filling, the
in-plane easy axis anisotropy scales as $\alpha^4$ and results from a twisted
exchange interaction between the spins in the 3-d Rashba material and the
ferromagnet. For a ferroelectric 3-d Rashba material, $\hat n$ can be
controlled with an electric field, and we propose that the interfacial magnetic
anisotropy could provide a mechanism for electrical control of the magnetic
orientation.",1605.05739v1
2019/6/5,Uncovering A Two-Dimensional Semiconductor with Intrinsic Ferromagnetism at Room Temperature,"Two-dimensional materials have been gaining great attention as they displayed
a broad series of electronic properties that ranging from superconductivity to
topology. Among them, those which possess magnetism are most desirable,
enabling us to manipulate charge and spin simultaneously. Here, based on
first-principles calculation, we demonstrate monolayer chromium iodide arsenide
(CrIAs), an undiscovered stable two-dimensional material, is an intrinsic
ferromagnetic semiconductor with out-of-plane spin magnetization. The indirect
bandgaps are predicted to be 0.32 eV for majority spin and 3.31 eV for minority
spin, large enough to preserve semiconducting features at room temperature. Its
Curie temperature, estimated by Heisenberg model with magnetic anisotropic
energy using Monte Carlo method, is as high as 655 K that well above the room
temperature, owing to strong direct exchange interaction between chromium d and
iodine p orbitals. This work offers the affirmative answer of whether there
exists two-dimensional ferromagnetic semiconductor at room temperature. And the
practical realization of quantum spintronic devices, which have been suppressed
because of lacking suitable room temperature magnetic materials, would embrace
a great opportunity.",1906.05444v1
2017/4/26,"Crystal and Magnetic Structures in Layered, Transition Metal Dihalides and Trihalides","Materials composed of two dimensional layers bonded to one another through
weak van der Waals interactions often exhibit strongly anisotropic behaviors
and can be cleaved into very thin specimens and sometimes into monolayer
crystals. Interest in such materials is driven by the study of low dimensional
physics and the design of functional heterostructures. Binary compounds with
the compositions MX2 and MX3 where M is a metal cation and X is a halogen anion
often form such structures. Magnetism can be incorporated by choosing a
transition metal with a partially filled d-shell for M, enabling ferroic
responses for enhanced functionality. Here a brief overview of binary
transition metal dihalides and trihalides is given, summarizing their
crystallographic properties and long-range-ordered magnetic structures,
focusing on those materials with layered crystal structures and partially
filled d-shells required for combining low dimensionality and cleavability with
magnetism.",1704.08225v1
2018/3/22,A Primary Exploration to Quasi-Two-Dimensional Rare-Earth Ferromagnetic Particles: Holmium-Doped MoS2 Sheet as Room-Temperature Magnetic Semiconductor,"Recently, two-dimensional materials and nanoparticles with robust
ferromagnetism are even of great interest to explore basic physics in nanoscale
spintronics. More importantly, room-temperature magnetic semiconducting
materials with high Curie temperature is essential for developing
next-generation spintronic and quantum computing devices. Here, we develop a
theoretical model on the basis of density functional theory calculations and
the Ruderman-Kittel-Kasuya-Yoshida theory to predict the thermal stability of
two-dimensional magnetic materials. Compared with other rare-earth (dysprosium
(Dy) and erbium (Er)) and 3d (copper (Cu)) impurities, holmium-doped (Ho-doped)
single-layer 1H-MoS2 is proposed as promising semiconductor with robust
magnetism. The calculations at the level of hybrid HSE06 functional predict a
Curie temperature much higher than room temperature. Ho-doped MoS2 sheet
possesses fully spin-polarized valence and conduction bands, which is a
prerequisite for flexible spintronic applications.",1803.08232v1
2008/11/28,Protodiscs around Hot Magnetic Rotator Stars,"We develop equations and obtain solutions for the structure and evolution of
a protodisc region that is initially formed with no radial motion and
super-Keplerian rotation speed when wind material from a hot rotating star is
channelled towards its equatorial plane by a dipole-type magnetic field. Its
temperature is around $10^7$K because of shock heating and the inflow of wind
material causes its equatorial density to increase with time. The centrifugal
force and thermal pressure increase relative to the magnetic force and material
escapes at its outer edge. The protodisc region of a uniformly rotating star
has almost uniform rotation and will shrink radially unless some instability
intervenes. In a star with angular velocity increasing along its surface
towards the equator, the angular velocity of the protodisc region decreases
radially outwards and magnetorotational instability (MRI) can occur within a
few hours or days. Viscosity resulting from MRI will readjust the angular
velocity distribution of the protodisc material and may assist in the formation
of a quasi-steady disc. Thus, the centrifugal breakout found in numerical
simulations for uniformly rotating stars does not imply that quasi-steady discs
with slow outflow cannot form around magnetic rotator stars with solar-type
differential rotation.",0811.4768v1
2017/3/6,A first-principles DFT+GW study of spin-filter and spin-gapless semiconducting Heusler compounds,"Among Heusler compounds, the ones being magnetic semiconductors (also known
as spin-filter materials) are widely studied as they offer novel
functionalities in spintronic/magnetoelectronic devices. The spin-gapless
semiconductors are a special case. They possess a zero or almost-zero energy
gap in one of the two spin channels. We employ the $GW$ approximation, which
allows an elaborate treatment of the electronic correlations, to simulate the
electronic band structure of these materials. Our results suggest that in most
cases the use of $GW$ self energy instead of the usual density functionals is
important to accurately determine the electronic properties of magnetic
semiconductors.",1703.02142v2
2019/10/17,A multi-scale approach for magnetisation dynamics: Unraveling exotic magnetic states of matter,"Crystallographic lattice defects strongly influence dynamical properties of
magnetic materials at both microscopic and macroscopic length scales. A
multi-scale approach to magnetisation dynamics, which is presented in this
paper, accurately captures such effects. The method is illustrated using
examples of systems with localized, non-trivial topological properties, e.g. in
the form of skyrmions and chiral domain walls that interact with lattice
dislocations. Technical aspects of the methodology involve multi-scale
magnetisation dynamics that connects atomistic and continuum descriptions. The
technique is capable of solving the Landau-Lifshitz-Gilbert equations
efficiently in two regions of a magnetic material --- the mesoscopic and the
atomistic regions, which are coupled in a seamless way. It is demonstrated that
this methodology allows simulating realistically-sized magnetic skyrmions
interacting with material defects and novel physical effects, uncovered using
this theoretical methodology, are described.",1910.07807v1
2020/8/19,Observation of plateau-like magnetoresistance in twisted Fe3GeTe2/Fe3GeTe2 junction,"Controlling the stacking of van der Waals (vdW) materials is found to produce
exciting new findings, since hetero- or homo- structures have added the diverse
possibility of assembly and manipulated functionalities. However, so far, the
homostructure with a twisted angle based on the magnetic vdW materials remains
unexplored. Here, we achieved a twisted magnetic vdW Fe3GeTe2/Fe3GeTe2 junction
with broken crystalline symmetry. A clean and metallic vdW junction is
evidenced by the temperature-dependent resistance and the linear I-V curve.
Unlike the pristine FGT, a plateau-like magnetoresistance (PMR) is observed in
the magnetotransport of our homojunction due to the antiparallel magnetic
configurations of the two FGT layers. The PMR ratio is found to be ~0.05% and
gets monotonically enhanced as temperature decreases like a metallic giant
magnetoresistance (GMR). Such a tiny PMR ratio is at least three orders of
magnitude smaller than the tunneling magnetoresistance (TMR) ratio, justifying
our clean metallic junction without a spacer. Our findings demonstrate the
feasibility of the controllable homostructure and shed light on future
spintronics using magnetic vdW materials.",2008.08313v1
2021/4/19,Colossal anomalous Nernst effect in a correlated noncentrosymmetric kagome ferromagnet,"Analogous to the Hall effect, the Nernst effect is the generation of a
transverse voltage due to a temperature gradient in the presence of a
perpendicular magnetic field. The Nernst effect has promise for thermoelectric
applications and as a probe of electronic structure. In magnetic materials, a
so-called anomalous Nernst effect (ANE) is possible in zero magnetic field.
Here we report a colossal ANE reaching 23 $\mu$V/K in the ferromagnetic metal
UCo$_{0.8}$Ru$_{0.2}$Al. Uranium's $5f$ electrons provide strong electronic
correlations that lead to narrow bands, which are a known route to producing a
large thermoelectric response. Additionally, the large nuclear charge of
uranium generates strong spin-orbit coupling, which produces an intrinsic
transverse response in this material due to the Berry curvature associated with
the relativistic electronic structure. Theoretical calculations show that at
least 148 Weyl nodes and two nodal lines exist within $\pm$ 60 meV of the Fermi
level in UCo$_{0.8}$Ru$_{0.2}$Al. This work demonstrates that magnetic actinide
materials can host strong Nernst and Hall responses due to their combined
correlated and topological nature.",2104.09060v1
2018/2/14,Engineering Dzyaloshinskii-Moriya interaction in B20 thin film chiral magnets,"Chiral magnetic Mn$_x$Fe$_{1-x}$Ge compounds have an antisymmetric exchange
interaction that is tunable with the manganese stoichiometric fraction, $x$.
Although millimeter-scale, polycrystalline bulk samples of this family of
compounds have been produced, thin-film versions of these materials will be
necessary for devices. In this study, we demonstrate the growth of epitaxial
Mn$_x$Fe$_{1-x}$Ge thin films on Si (111) substrates with a pure B20 crystal
structure in the stoichiometric fraction range x from 0 to 0.81. Following
systematic physical and magnetic characterization including microwave
absorption spectroscopy, we quantify the antisymmetric exchange interaction and
helical period as a function of $x$, which ranges from 200 nm to 8 nm. Our
results demonstrate an approach to engineering the size of magnetic skyrmions
in epitaxial films that are grown using scalable techniques.",1802.05107v1
2018/2/22,Magnetic-field enhanced high-thermoelectric performance in topological Dirac semimetal Cd$_3$As$_2$ crystal,"Thermoelectric materials can be used to convert heat to electric power
through the Seebeck effect. We study magneto-thermoelectric figure of merit
(ZT) in three-dimensional Dirac semimetal Cd$_3$As$_2$ crystal. It is found
that enhancement of power factor and reduction of thermal conductivity can be
realized at the same time through magnetic field although magnetoresistivity is
greatly increased. ZT can be highly enhanced from 0.17 to 1.1 by more than six
times around 350 K under a perpendicular magnetic field of 7 Tesla. The huge
enhancement of ZT by magnetic field arises from the linear Dirac band with
large Fermi velocity and the large electric thermal conductivity in
Cd$_3$As$_2$. Our work paves a new way to greatly enhance the thermoelectric
performance in the quantum topological materials.",1802.07868v1
2018/11/4,The trimer-based spin liquid candidate Ba4NbIr3O12,"Ba4NbIr3O12, a previously unreported material with a triangular planar
geometry of Ir3O12 trimers, is described. Magnetic susceptibility measurements
show no magnetic ordering down to 1.8 K despite the Curie-Weiss temperature of
-13 K. The material has a very low effective magnetic moment of 0.80
{\mu}B/f.u. To look at the lower temperature behavior, the specific heat (Cp)
was measured down to 0.35 K; it shows no indication of magnetic ordering and
fitting a power law to Cp vs. T below 2 K yields the power {\alpha} = 3/4.
Comparison to the previously unreported trimer compound made with the 4d
element Rh in place of the 5d element Ir, Ba4NbRh3O12, is presented. The
analysis suggests that Ba4NbIr3O12 is a candidate spin liquid material.",1811.01369v1
2019/3/6,Symmetry-protected topological magnons in three dimensional Kitaev materials,"Topological phases in magnetic materials offer novel tunability of
topological properties via varying the underlying magnetism. We show that three
dimensional Kitaev materials can provide a great opportunity for controlling
symmetry-protected topological nodal magnons. These materials are originally
considered as strong candidates for the Kitaev quantum spin liquid due to the
bond-dependent frustrating spin exchange interactions. As a concrete example,
we consider the symmetry and topology of the magnons in the canted zig-zag
ordered state in the hyperhoneycomb $\beta\text{-}\mathrm{Li_2IrO_3}$, which
can be obtained by applying a magnetic field in the counter-rotating spiral
state at zero field. It is shown that the magnetic glide symmetries and the
non-Hermitian nature of the bosonic magnons lead to unique topological
protection that is different from the case of the fermionic counterparts. We
investigate how such topological magnons can be controlled by changing the
symmetry of the underlying spin exchange interactions.",1903.02559v1
2019/3/29,Electrical Néel-order switching in magnetron-sputtered CuMnAs thin films,"Antiferromagnetic materials as active components in spintronic devices
promise insensitivity against external magnetic fields, the absence of own
magnetic stray fields, and ultrafast dynamics at the picosecond time scale.
Materials with certain crystal-symmetry show an intrinsic N\'eel-order
spin-orbit torque that can efficiently switch the magnetic order of an
antiferromagnet. The tetragonal variant of CuMnAs was shown to be electrically
switchable by this intrinsic spin-orbit effect and its use in memory cells with
memristive properties has been recently demonstrated for high-quality films
grown with molecular beam epitaxy. Here, we demonstrate that the magnetic order
of magnetron-sputtered CuMnAs films can also be manipulated by electrical
current pulses. The switching efficiency and relaxation as a function of
temperature, current density, and pulse width can be described by a
thermal-activation model. Our findings demonstrate that CuMnAs can be
fabricated with an industry-compatible deposition technique, which will
accelerate the development cycle of devices based on this remarkable material.",1903.12387v2
2019/11/26,Mapping Skyrmion Stability in Uniaxial Lacunar Spinel Magnets from First-Principles,"The identification of general principles for stabilizing magnetic skyrmion
phases in bulk materials over wide ranges of temperatures is a prerequisite to
the development of skyrmion-based spintronic devices. Lacunar spinels with the
formula GaM4X8 with M=V, Mo; X=S, Se are a convenient case study towards this
goal as they are some of the first bulk systems suggested to host equilibrium
chiral skyrmions far from the paramagnetic transition. We derive the magnetic
phase diagrams likely to be observed in these materials, accounting for all
possible magnetic interactions, and prove that skyrmion stability in the
lacunar spinels is a general consequence of their crystal symmetry rather than
the details of the material chemistry. Our results are consistent with all
experimental reports in this space and demonstrate that the differences in the
phase diagrams of particular spinel chemistries are determined by
magnetocrystalline anisotropy, up to a normalization factor. We conclude that
skyrmion formation over wide ranges of temperatures can be expected in all
lacunar spinels, as well as in a wide range of uniaxial systems with low
magnetocrystalline anisotropy.",1911.11297v2
2020/1/16,Evidence of standing spin-waves in a van der Waals magnetic material,"Spin-waves have been studied for data storage, communication and logic
circuits in the field of spintronics based on their potential to substitute
electrons. Recent discovery of magnetism in two-dimensional (2D) systems such
as monolayer CrI$_3$ and Cr$_2$Ge$_2$Te$_6$ has led to a renewed interest in
such applications of magnetism in the 2D limit. Here we present direct evidence
of standing spin-waves along with the uniform precessional resonance modes in
van der Waals magnetic material, CrCl$_3$. Our experiment is the first direct
observation of standing spin-wave modes, set up across a thickness of 20
$\mu$m, in a van der Waals material. We detect standing spin-waves in the
vicinity of both, optical and acoustic, branches of the antiferromagnetic
resonance. We also observe magnon-magnon coupling, softening of resonance modes
with temperature and extract the evolution of interlayer exchange field as a
function of temperature.",2001.05981v1
2020/1/23,Optical rotation in thin chiral/twisted materials and the gyrotropic magnetic effect,"The rotation of the plane of polarization of light passing through a
non-magnetic material is known as natural optical activity or optical
gyrotropy. The behavior of this effect in thin chiral conductors is of current
interest. For example, the low frequency limit of gyrotropy in chiral 3D
crystals, known as the gyrotropic magnetic effect (GME), is controlled by the
orbital magnetic moment of electrons, which has been proposed to be relevant to
current-induced switching in twisted bilayer graphene. We show that the GME is
not limited to bulk materials but also appears for quasi-2d systems with
minimal structure incorporated in the third direction. Starting from multi-band
Kubo formula, we derive a generic expression for GME current in quasi-2d
materials induced by low-frequency light, and provide a Feynman-diagrammatic
interpretation. The relations between the 2d finite layered formula and 3d bulk
formula are also discussed.",2001.08774v1
2020/6/27,A Comprehensible Review: Magnonic Magnetoelectric Coupling in Ferroelectric/ Ferromagnetic Composites,"Composite materials consisting of coupled magnetic and ferroelectric layers
hold the promise for new emergent properties such as controlling magnetism with
electric fields. Obviously, the interfacial coupling mechanism plays a crucial
role and its understanding is the key for exploiting this material class for
technological applications. This short review is focused on the magnonic-based
magnetoelectric coupling that forms at the interface of a metallic ferromagnet
with a ferroelectric insulator. After analyzing the physics behind this
coupling, the implication for the magnetic, transport, and optical properties
of these composite materials is discussed. Furthermore, examples for the
functionality of such interfaces are illustrated by the electric field
controlled transport through ferroelectric/ferromagnetic tunnel junctions, the
electrically and magnetically controlled optical properties, and the generation
of electromagnon solitons for the use as reliable information carriers.",2006.15290v2
2020/7/17,Quantum oscillation beyond the quantum limit in pseudospin Dirac materials,"Recently, many unexpected fine structures in electric, magnetic, and
thermoelectric responses at extremely magnetic fields in topological materials
have attracted tremendous interest. We propose a new mechanism of quantum
oscillation beyond the strong-field quantum limit for Dirac fermions. The
amplitude of the oscillation is far larger than the usual Shubnikov--de Haas
oscillation. The oscillation tends to be periodic in the magnetic field B,
instead of 1/B. The period of the oscillation does not depend on the Fermi
energy. These behaviors cannot be described by the famous Lifshitz-Kosevich
formula. The oscillation arises from a mechanism that we refer to as the
inversion of the lowest Landau level, resulted from the competition between the
pseudospin Dirac-type Landau levels and real-spin Zeeman spitting beyond the
quantum limit. This inversion gives rise to the oscillation of the Fermi energy
and conductivity at extremely large magnetic fields. This mechanism will be
useful for understanding the unexpected fine structures observed in the
strong-field quantum limit in Dirac materials.",2007.08720v1
2020/9/21,"Controllable Capillary Assembly of Magnetic Ellipsoidal Janus Particles into Tunable Rings, Chains and Hexagonal Lattices","Colloidal assembly at fluid interfaces has a great potential for the
bottom-up fabrication of novel structured materials. However, challenges remain
in realizing controllable and tunable assembly of particles into diverse
structures. Herein, we report the capillary assembly of magnetic ellipsoidal
Janus particles at a fluid-fluid interface. Depending on their tilt angle, i.e.
the angle the particle main axis forms with the fluid interface, these
particles deform the interface and generate capillary dipoles or hexapoles.
Driven by capillary interactions, multiple particles thus assemble into chain-,
hexagonal lattice- and ring-like structures, which can be actively controlled
by applying an external magnetic field. We predict a field-strength phase
diagram in which various structures are present as stable states. Owing to the
diversity, controllability, and tunability of assembled structures, magnetic
ellipsoidal Janus particles at fluid interfaces could therefore serve as
versatile building blocks for novel materials.",2009.09804v2
2020/11/25,Magnon-phonon hybridization in quasi-2D antiferromagnet MnPSe$_3$,"Magnetic excitations in van der Waals (vdW) materials, especially in the
two-dimensional (2D) limit, are an exciting research topic from both the
fundamental and applied perspectives. Using temperature-dependent,
magneto-Raman spectroscopy, we identify the hybridization of two-magnon
excitations with two separate E$_\mathrm{g}$ phonons in MnPSe$_3$, a magnetic
vdW material that could potentially host 2D antiferromagnetism. Results from
first principles calculations of the phonon and magnon spectra further support
our identification. The Raman spectra's rich temperature dependence through the
magnetic transition displays an avoided-crossing behavior in the phonons'
frequency and a concurrent decrease in their lifetimes. We construct a model
based on the interaction between a discrete level and a continuum that
reproduces these observations. The strong magnon-phonon hybridization reported
here highlights the need to understand its effects on spin transport
experiments in magnetic vdW materials.",2011.12557v2
2021/3/7,"Magnetic anisotropy and exchange interactions of two-dimensional FePS$_3$, NiPS$_3$ and MnPS$_3$ from first principles calculations","The van der Waals bonded transition metal phosphorous trichalcogenides
FePS$_3$, NiPS$_3$ and MnPS$_3$ have recently attracted renewed attention due
to the possibility of exfoliating them into their monolayers. Although the
three compounds have similar electronic structure, the magnetic structure
differs due to subtle differences in exchange and magnetic anisotropy and the
materials thus comprise a unique playground for studying different aspects of
magnetism in 2D. Here we calculate the exchange and anisotropy parameters of
the three materials from first principles paying special attention to the
choice of Hubbard parameter U. We find a strong dependence of the choice of U
and show that the calculated N\'eel temperature of FePS$_3$ varies by an order
of magnitude over commonly applied values of U for the Fe $d$-orbitals. The
results are compared with parameters fitted to experimental spin-wave spectra
of the bulk materials and we find excellent agreement between the exchange
constants when a proper value of U is chosen. However, the anisotropy
parameters are severely underestimated by DFT and we discuss possible origins
of this discrepancy.",2103.04474v1
2021/6/23,Theoretical design of all-carbon networks with intrinsic magnetism,"To induce intrinsic magnetism in the nominally nonmagnetic carbon materials
containing only $s$ and $p$ electrons is an intriguing yet challenging task.
Here, based on first-principles electronic structure calculations, we propose a
universal approach inspired by Ovchinnikov's rule to guide us the design of a
series of imaginative magnetic all-carbon structures. The idea is to combine
the differently stacked graphene layers via the acetylenic linkages
(-C$\equiv$C-) to obtain a class of two-dimensional (2D) and three-dimensional
(3D) carbon networks. With first-principles electronic structure calculations,
we confirm the effectiveness of this approach via concrete examples of
double-layer ALBG-C14, triple-layer ALTG-C22, and bulk IALG-C30. We show that
these materials are antiferromagnetic (AFM) semiconductors with intralayer
N\'eel and interlayer AFM couplings. According to the above idea, our work not
only provides a promising design scheme for magnetic all-carbon materials, but
also can apply to other $\pi$-bonding network systems.",2106.12158v1
2021/9/2,Magnetic Field Dependent Piezoelectricity in Atomically Thin Co$_2$Te$_3$,"Two dimensional (2D) materials have received a surge in research interest due
to their exciting range of properties. Here we show that 2D cobalt telluride
(Co2Te3), successfully synthesized via liquid-phase exfoliation in an organic
solvent, exhibits weak ferromagnetism and semiconducting behavior at room
temperature. The magnetic field-dependent piezoelectric properties of 2D Co2Te3
sample show magneto-electric response of the material and a linear relationship
between the output voltage and applied magnetic field. First-principles density
functional theory (DFT) and ab initio molecular dynamics are used to explain
these experimental results. Our work could pave the way for the development of
2D materials with coupled magnetism and piezoelectricity, leading to new
applications in electromagnetics.",2109.02781v1
2022/1/9,Intrinsic Nonlinear Spin Magnetoelectricity in Centrosymmetric Magnets,"We propose an intrinsic nonlinear spin magnetoelectric effect in magnetic
materials, offering the potential of all-electric control of spin degree of
freedom in centrosymmetric magnets, which reside outside of the current
paradigm based on linear spin response. We reveal the band geometric origin of
this effect in the momentum and magnetization space Berry connection
polarizabilities, and clarify its symmetry characters. As an intrinsic effect,
it is determined solely by the material's band structure and represents a
material characteristic. Combining our theory with first-principles
calculations, we predict sizable nonlinear spin magnetoelectricity in
single-layer MnBi$_{2}$Te$_{4}$, which can be detected in experiment. Our
theory paves the way for exploring rich nonlinear spintronic effects and novel
device concepts based on them.",2201.03060v1
2022/3/22,Intrinsic ferromagnetism and restrictive thermodynamic stability in MA$_2$N$_4$ and Janus VSiGeN$_4$ monolayers,"The seminal experimental discovery of the remarkably stable MoSi$_2$N$_4$
monolayer has led to a handful of predicted magnetic two-dimensional (2D)
materials in the MA$_2$Z$_4$ family (M = transition metals, A = Si, Ge, and Z =
N, P, As). These magnetic monolayers were predicted to be dynamically stable,
but none of them has been synthesized to date. In this Research Letter, from
first-principles thermodynamic stability analysis, we demonstrate that only the
nitrides are thermodynamically stable and this occurs under N-rich conditions.
Based on this finding, we propose two ferromagnetic, semiconducting Janus
monolayers in the family: VSiGeN$_4$ and VSiSnN$_4$. They are both dynamically
and thermally stable, but only the former is thermodynamically stable.
Intriguingly, Janus VSiGeN$_4$ and VSiSnN$_4$ monolayers show weak in-plane
anisotropy compared with the VSi$_2$N$_4$ monolayer. These two emerging Janus
magnetic semiconductors offer opportunities for studying 2D magnetism and spin
control for spintronics applications.",2203.11605v3
2022/4/14,Relativistic Tight-Binding Model for Hexagonal Lattice: Application to Graphene,"A non-perturbative relativistic tight-binding (TB) approximation method
applicable to crystalline material immersed in a magnetic field was developed
in 2015. To apply this method to any material in the magnetic field, the
electronic structure of the material in absence of a magnetic field must be
calculated. In this study, we present the relativistic TB approximation method
for graphene in a zero magnetic field. The Hamiltonian and overlap matrix is
constructed considering the nearest neighbouring atomic interactions between
the $s$ and $p$ valence orbitals, where the relativistic hopping and overlap
integrals are calculated using the relativistic version of the Slater-Koster
table. The method of constructing the Hamiltonian and overlap matrix and the
resulting energy-band structure of graphene in the first Brillouin zone is
presented in this paper. It is found that there is an appearance of a small
band-gap at the $\textbf{K}$ points (also known as the spin-orbit gap) due to
the relativistic effect, whose magnitude is $25$ $\mu$eV.",2204.06836v3
2022/5/9,Multiferroic materials based on transition-metal dichalcogenides: Potential platform for reversible control of Dzyaloshinskii-Moriya interaction and skyrmion via electric field,"Exploring novel two-dimensional multiferroic materials that can realize
electric-field control of two-dimensional magnetism has become an emerging
topic in spintronics. Using first-principles calculations, we demonstrate that
non-metallic bilayer transition metal dichalcogenides (TMDs) can be an ideal
platform for building multiferroics by intercalated magnetic atoms. Moreover,
we unveil that with Co intercalated bilayer MoS2, Co(MoS2)2, two energetic
degenerate states with opposite chirality of Dzyaloshinskii-Moriya interaction
(DMI) are the ground states, indicating electric-field control of the chirality
of topologic magnetism such as skyrmions can be realized in this type of
materials by reversing the electric polarization. These findings pave the way
for electric-field control of topological magnetism in two-dimensional
multiferroics with intrinsic magnetoelectric coupling.",2205.04118v1
2022/7/5,Strong bulk Dzyaloshinskii-Moriya interaction in composition-uniform centrosymmetric magnetic single layers,"Dzyaloshinskii-Moriya interaction (DMI) is the key ingredient of chiral
spintronic phenomena and the emerging technologies based on such phenomena. A
nonzero DMI usually occurs at magnetic interfaces or within non-centrosymmetric
single crystals. Here, we report the observation of a strong unexpected DMI
within a centrosymmetric polycrystalline ferromagnet that has neither a crystal
inversion symmetry breaking nor a composition gradient. This DMI is a bulk
effect, increases with the thickness of the magnetic layer, and is insensitive
to the symmetry of the interfaces or the neighboring materials. We observe a
total DMI strength that is a factor of >2 greater than the highest interfacial
DMI in the literature. This DMI most likely arises from the strong spin-orbit
coupling, strong orbital hybridization, and a ""hidden"" long-range asymmetry in
the material. Our discovery of the strong unconventional bulk DMI in
centrosymmetric, composition-uniform magnetic single layers provide fundamental
building blocks for the emerging field of spintronics and will stimulate the
exploitation of unconventional spin-orbit phenomena in a wide range of
materials.",2207.01766v1
2022/7/5,Experimental and micromagnetic investigation of texture influence on magnetic properties of anisotropic Co/Co3O4 exchange-bias composites,"The exchange interaction between nanostructured components is an effective
way to enhance the magnetic properties of materials. This effect is used in
exchange-coupled magnetic composites, which properties are governed by
synergetic impact of constituent phases. Texturing is one of the problems that
needs to be solved in order for such composites to be used in industry. In this
work, we performed experimental and micromagnetic investigation of the
exchange-bias properties in Co/Co3O4 nanocomposites based on nanorods array.
Specifically, we investigated how the resulting properties will change
depending on the nanorods texture. Our experiments proved previous theoretical
calculations of exchange-bias nanorods array-based composites that showed that
magnetic properties of such materials are dependent on the internal texture.
Tailoring the texture can lead to either increase of exchange-bias field, or to
enhancement of material coercivity.",2207.01881v2
2022/7/21,Magnetic imaging with spin defects in hexagonal boron nitride,"Optically-active spin defects hosted in hexagonal boron nitride (hBN) are
promising candidates for the development of a two-dimensional (2D) quantum
sensing unit. Here, we demonstrate quantitative magnetic imaging with hBN
flakes doped with negatively-charged boron-vacancy (V$_{\rm B}^-$) centers
through neutron irradiation. As a proof-of-concept, we image the magnetic field
produced by CrTe$_2$, a van der Waals ferromagnet with a Curie temperature
slightly above $300$ K. Compared to other quantum sensors embedded in 3D
materials, the advantages of the hBN-based magnetic sensor described in this
work are its ease of use, high flexibility and, more importantly, its ability
to be placed in close proximity to a target sample. Such a sensing unit will
likely find numerous applications in 2D materials research by offering a simple
way to probe the physics of van der Waals heterostructures.",2207.10477v1
2022/8/19,Intrinsic efficiency of injection photocurrents in magnetic materials,"The generation of shift and ballistic photocurrents in non-centrosymmetric
materials represents a promising alternative mechanism for light energy
harvesting. Many studies have focused on finding the best suited materials by
maximizing the photocurrent magnitude, but estimating the actual efficiency
requires knowledge of the light-induced DC photoconductivity and is rarely
considered. Using the recently proposed jerk current as photoconductivity, in
this work we show that only ballistic photocurrents have finite efficiency in
the limit of large relaxation times $\tau$. Moreover, at zero temperature the
only ballistic current which is finite for unpolarized light is the magnetic
injection current, only present in magnetic materials. We present a band
structure expression for the efficiency of such photocurrent, showing that it
scales as $(\hbar \Omega-E_g)^2$ near the band edge, and we present its
frequency dependence for a simple tight-binding model. Our work provides a new
tool to guide the search for efficient energy harvesting based on the magnetic
injection current.",2208.09464v1
2022/12/19,Multi-Meron Interactions and Statistics in Two-Dimensional Materials,"As a fundamental type of topological spin textures in two-dimensional (2D)
magnets, a magnetic meron carries half-integer topological charge and forms a
pair with its antithesis to keep the stability in materials. However, it is
challenging to quantitatively calculate merons and their dynamics by using the
widely used continuum model because of the characteristic highly inhomogeneous
spin textures. In this work, we develop a discrete method to address the
concentrated spin structures around the core of merons. We reveal a
logarithmic-scale interaction between merons when their distance is larger than
twice their core size and obtain subsequent statistics of meron gas. The model
also predicts how these properties of single and paired merons evolve with
magnetic exchange interactions, and the results are in excellent agreement with
the Monte Carlo simulations using the parameters of real 2D van der Waals
magnetic materials. This discrete approach not only shows equilibrium static
statistics of meron systems but also is useful to further explore the dynamic
properties of merons through the quantified pairing interactions.",2212.09698v1
2022/12/27,"Datasets on materials research of hard ferromagnet in TM-Fe-Si (TM=Ti, Zr, Hf, V, Nb, and Ta) ternary systems","The datasets presented in this article are related to materials research on
hard ferromagnet in TM-Fe-Si (TM=Ti, Zr, Hf, V, Nb, and Ta) ternary systems.
The motivation for data collection is based on the research paper entitled
""Novel hard magnetic phase with Zr$_{11.5}$Fe$_{53}$Si$_{35.5}$ composition"".
The datasets are composed of scanning electron microscope images, X-ray
diffraction (XRD) patterns, and magnetization data for
TM$_{7}$Fe$_{52}$Si$_{41}$ annealed at 1050 $^{\circ}$C. The chemical
compositions of constituent phases were determined by an energy dispersive
X-ray spectrometer (EDS). The phase analysis was performed using XRD and EDS
results. The Curie temperature of each sample was obtained using magnetization
data, and the coercive field was determined for hard ferromagnet samples
Zr$_{7}$Fe$_{52}$Si$_{41}$ and Hf$_{7}$Fe$_{52}$Si$_{41}$. The datasets would
be useful for developing an Fe-based rare-earth-free permanent magnet, which is
one of the central issues of materials science.",2212.13595v1
2023/1/6,Direct electrical probing of anomalous Nernst conductivity,"Despite the usefulness of the anomalous Nernst conductivity
($\alpha^{A}_{xy}$) for studying electronic band structures and exploring
magnetic materials with large transverse thermopower, there has not been a
straightforward way to obtain $\alpha^{A}_{xy}$ in the experiment. Here, we
propose a simple and versatile method enabling direct electrical probing of
$\alpha^{A}_{xy}$, which is realized by creating a closed circuit consisting of
a target magnetic material and a non-magnetic conductor. This method was
experimentally demonstrated on a thin film of magnetic Weyl semimetal
Co$_{2}$MnGa, where the closed circuit was formed simply by connecting both
ends of the Co$_{2}$MnGa film with a Au wire. A good approximation of
$\alpha^{A}_{xy}$ was obtained in a wide temperature range, validating the
proposed method and exhibiting its potential for aiding the further development
of topological materials science and transverse thermoelectrics.",2301.02465v3
2023/4/12,Janus monolayer TaNF: a new ferrovalley material with large valley splitting and tunable magnetic properties,"Materials with large intrinsic valley splitting and high Curie temperature
are a huge advantage for studying valleytronics and practical applications. In
this work, using first-principles calculations, a new Janus TaNF monolayer is
predicted to exhibit excellent piezoelectric properties and intrinsic valley
splitting, resulting from the spontaneous spin polarization, the spatial
inversion symmetry breaking and strong spin-orbit coupling (SOC). TaNF is also
a potential two-dimensional (2D) magnetic material due to its high Curie
temperature and huge magnetic anisotropy energy. The effective control of the
band gap of TaNF can be achieved by biaxial strain, which can transform TaNF
monolayer from semiconductor to semi-metal. The magnitude of valley splitting
at the CBM can be effectively tuned by biaxial strain due to the changes of
orbital composition at the valleys. The magnetic anisotropy energy (MAE) can be
manipulated by changing the energy and occupation (unoccupation) states of d
orbital compositions through biaxial strain. In addition, Curie temperature
reaches 373 K under only -3% biaxial strain, indicating that Janus TaNF
monolayer can be used at high temperatures for spintronic and valleytronic
devices.",2304.05670v1
2023/3/29,"Molecular Beam Epitaxy Growth of Transition Metal Dichalcogenide (Mo,Mn)Se$_2$ on 2D, 3D and polycrystalline substrates","Magnetic doping of 2D materials such as Transition Metal Dichalcogenides is
promising for the enhancement of magneto-optical properties, as it was
previously observed for 3D diluted magnetic semiconductors. To maximize the
effect of magnetic ions, they should be incorporated into the crystal lattice
of 2D material rather than form separated precipitates. This work shows a study
on incorporating magnetic manganese ions into the MoSe$_2$ monolayers using
molecular beam epitaxy. We test growth on various substrates with very
different properties: polycrystalline SiO$_2$ on Si, exfoliated 2D hexagonal
Boron Nitride flakes (placed on SiO$_2$ / Si), monocrystalline sapphire, and
exfoliated graphite (on tantalum foil). Although atomic force microscopy images
indicate the presence of MnSe precipitates, but at the same time, various
techniques reveal effects related to alloying MoSe$_2$ with Mn: Raman
scattering and photoluminescence measurements show energy shift related to the
presence of Mn, scanning transmission microscopy shows Mn induced partial
transformation of 1H to 1T^\prime phase. Above effects evidence partial
incorporation of Mn into the MoSe$_2$ layer.",2304.12428v2
2023/4/25,The anti-symmetric and anisotropic symmetric exchange interactions between electric dipoles in hafnia,"The anti-symmetric and anisotropic symmetric exchange interactions between
two magnetic dipole moments - responsible for intriguing magnetic textures
(e.g., magnetic skyrmions) - have been discovered since last century, while
their electric analogues were either hidden for a long time or still not known.
As a matter of fact, it is only recently that the anti-symmetric exchange
interactions between electric dipoles was proved to exist (with materials
hosting such an interaction being still rare) and the existence of anisotropic
symmetric exchange interaction between electric dipoles remains to be revealed.
Here, by symmetry analysis and first-principles calculations, we identify a
candidate material in which our aforementioned exchange interactions between
electric dipoles are perceptible. More precisely, we find that various phases
of hafnia showcase non-collinear alignment of electric dipoles, which is
interpreted by our phenomenological theories. This gives evidence that hafnia
simultaneously accommodates anti-symmetric and anisotropic symmetric exchange
interactions between electric dipoles. Our findings can hopefully deepen the
current knowledge of electromagnetism in ferroelectrics, magnets and
multiferroics, and have a potential to guide the discovery of novel states of
matter (e.g., electric skyrmions) in hafnia and related materials.",2304.12531v1
2023/6/7,MXene-based Ti2C/Ta2C lateral heterostructure: an intrinsic room temperature ferromagnetic material with large magnetic anisotropy,"(2D) lateral heterostructures (LH) combining Ti$_2$C and Ta$_2$C MXenes were
investigated by means of first-principles calculations. Our structural and
elastic properties calculations show that the lateral Ti$_2$C/Ta$_2$C
heterostructure results in a 2D material that is stronger than the original
isolated MXenes and other 2D monolayers such as germanene or MoS$_2$. The
analysis of the evolution of the charge distribution with the size of the LH
shows that, for small systems, it tends to distribute homogeneously between the
two monolayers, whereas for larger systems electrons tend to accumulate in a
region of $\sim$~6 {\AA} around the interface. The work function of the
heterostructure, one crucial parameter in the design of electronic nanodevices,
is found to be lower than that of some conventional 2D LH. Remarkably, all the
heterostructures studied show a very high Curie temperature (between 696 K and
1082 K), high magnetic moments %present in the ferromagnetic ground state, and
high magnetic anisotropy energies. These features make (Ti$_2$C)/(Ta$_2$C)
lateral heterostructures very suitable candidates for spintronic,
photocatalysis, and data storage applications based upon 2D magnetic materials.",2306.04257v1
2023/8/14,Density-functional description of materials for topological qubits and superconducting spintronics,"Interfacing superconductors with magnetic or topological materials offers a
playground where novel phenomena like topological superconductivity, Majorana
zero modes, or superconducting spintronics are emerging. In this work, we
discuss recent developments in the Kohn-Sham Bogoliubov-de Gennes method, which
allows to perform material-specific simulations of complex superconducting
heterostructures on the basis of density functional theory. As a model system
we study magnetically-doped Pb. In our analysis we focus on the interplay of
magnetism and superconductivity. This combination leads to Yu-Shiba-Rusinov
(YSR) in-gap bound states at magnetic defects and the breakdown of
superconductivity at larger impurity concentrations. Moreover, the influence of
spin-orbit coupling and on orbital splitting of YSR states as well as the
appearance of a triplet component in the order parameter is discussed. These
effects can be exploited in S/F/S-type devices (S=superconductor,
F=ferromagnet) in the field of superconducting spintronics.",2308.07383v1
2023/9/7,Nonreciprocal phonon dichroism induced by Fermi pocket anisotropy in two-dimensional Dirac materials,"Electrons in two-dimensional (2D) Dirac materials carry local band geometric
quantities, such as the Berry curvature and orbital magnetic moments, which,
combined with electron-phonon coupling, may affect the phonon dynamics in an
unusual way. Here, we propose intrinsic nonreciprocal linear and circular
phonon dichroism in magnetic 2D Dirac materials, which originate from nonlocal
band geometric quantities of electrons and reduce to pure Fermi-surface
properties for acoustic phonons. We find that to acquire the nonreciprocity,
the Fermi pocket anisotropy rather than the chirality of electrons is crucial.
Two possible mechanisms of Fermi pocket anisotropy are suggested: (i) trigonal
warping and out-of-plane magnetization or (ii) Rashba spin-orbit interaction
and in-plane magnetization. As a concrete example, we predict appreciable and
tunable nonreciprocal phonon dichroism in 2H-MoTe 2 on a EuO substrate. Our
finding points to a different route towards electrical control of phonon
nonreciprocity for acoustoelectronics applications based on 2D quantum
materials.",2309.03540v1
2023/11/26,Machine Learning-based estimation and explainable artificial intelligence-supported interpretation of the critical temperature from magnetic ab initio Heusler alloys data,"Machine Learning (ML) has impacted numerous areas of materials science, most
prominently improving molecular simulations, where force fields were trained on
previously relaxed structures. One natural next step is to predict material
properties beyond structure. In this work, we investigate the applicability and
explainability of ML methods in the use case of estimating the critical
temperature for magnetic Heusler alloys calculated using ab initio methods
determined materials-specific magnetic interactions and a subsequent Monte
Carlo (MC) approach. We compare the performance of regression and
classification models to predict the range of the critical temperature of given
compounds without performing the MC calculations. Since the MC calculation
requires computational resources in the same order of magnitude as the
density-functional theory (DFT) calculation, it would be advantageous to
replace either step with a less computationally intensive method such as ML. We
discuss the necessity to generate the magnetic ab initio results to make a
quantitative prediction of the critical temperature. We used state-of-the-art
explainable artificial intelligence (XAI) methods to extract physical relations
and deepen our understanding of patterns learned by our models from the
examined data.",2311.15423v1
2023/12/21,Magnetic Transparent Conductors for Spintronic Applications,"Transparent Conductors (TCs) exhibit optical transparency and electron
conductivity, and are essential for many opto-electronic and photo-voltaic
devices. The most common TCs are electron-doped oxides, which have few
limitations when transition metals are used as dopants. Non-oxides TCs have the
potential of extending the class of materials to the magnetic realm, bypass
technological bottlenecks, and bring TCs to the field of spintronics. Here we
propose new functional materials that combine transparency and conductivity
with magnetic spin polarization that can be used for spintronic applications,
such as spin filters. By using high-throughput first-principles techniques, we
identified a large number of potential TCs, including non-oxides materials. Our
results indicate that proper doping with transition metals introduces a finite
magnetization that can provide spin filtering up to 90% in the electrical
conductivity, still maintaining a transparency greater than 90%.",2312.13708v1
2003/5/13,Thermal Remagnetization in Polycrystalline Permanent Magnets,"The thermal remagnetization (TR), i.e. the reentrance of magnetization upon
heating in a steady-field demagnetized sample, is a common feature to the four
types of polycrystalline permanent magnets, mainly utilized for practical
purposes, i.e. barium ferrites, SmCo5, Sm2Co17 and NdFeB magnets. The effect is
small for pinning controlled and large for nucleation controlled magnets. The
effect is strongly dependent on the demagnetization factor and may reach nearly
100 per cent in SmCo5 samples measured in a closed circuit. The TR is very
sensitive to a small superimposed steady field. The maximum effect and the
position of the peak is dependent on the initial temperature. The direction of
the TR is correlated with the temperature coefficient of the coercivity,
resulting in a inverse TR in barium ferrite. The susceptibility of the
thermally remagnetized samples is increased. Repeated cycles of steady-field
demagnetization followed by heating result in the same TR. The phenomenology of
TR and ITR is explained by means of a model taking into account both the
internal field fluctuations due to grain interactions and the decay of single
domain grains into multi-domain state. By taking the measured temperature
dependencies of the coercivity and the saturation magnetization the theory is
able to reproduce the experiments very well, allowing to determine the width of
the field fluctuations, the width of the switching field distribution and an
internal demagnetization factor as characteristics of the materials by fitting.",0305292v1
2007/2/26,Electrical switching of vortex core in a magnetic disk,"A magnetic vortex is a curling magnetic structure realized in a ferromagnetic
disk, which is a promising candidate of a memory cell for future nonvolatile
data storage devices. Thus, understanding of the stability and dynamical
behaviour of the magnetic vortex is a major requirement for developing magnetic
data storage technology. Since the experimental proof of the existence of a
nanometre-scale core with out-of-plane magnetisation in the magnetic vortex,
the dynamics of a vortex has been investigated intensively. However, the way to
electrically control the core magnetisation, which is a key for constructing a
vortex core memory, has been lacking. Here, we demonstrate the electrical
switching of the core magnetisation by utilizing the current-driven resonant
dynamics of the vortex; the core switching is triggered by a strong dynamic
field which is produced locally by a rotational core motion at a high speed of
several hundred m/s. Efficient switching of the vortex core without magnetic
field application is achieved thanks to resonance. This opens up the
potentiality of a simple magnetic disk as a building block for spintronic
devices like a memory cell where the bit data is stored as the direction of the
nanometre-scale core magnetisation.",0702589v1
2010/5/27,First-principles prediction of spin-density-reflection symmetry driven magnetic transition of CsCl-type FeSe,"Based on results of density functional theory (DFT) calculations with the
local spin density approximation (LSDA) and the generalized gradient
approximation (GGA), we propose a new magnetic material, CsCl-type FeSe. The
calculations reveal the existence of ferromagnetic (FM) and antiferromagnetic
(AFM) states over a wide range of lattice constants. At 3.12\,{\AA} in the GGA,
the equilibrium state is found to be AFM with a local Fe magnetic moment of
$\pm 2.69\,\mu_\mathrm{B}$. A metastable FM state with Fe and Se local magnetic
moments of $2.00\,\mu_\mathrm{B}$ and $-0.032\,\mu_\mathrm{B}$, respectively,
lies 171.7\,{meV} above the AFM state. Its equilibrium lattice constant is
$\sim 2$\,{\%} smaller than that of the AFM state, implying that when the
system undergoes a phase transition from the AFM state to the FM one, the
transition is accompanied by volume contraction. Such an AFM-FM transition is
attributed to spin-density $z$-reflection symmetry; the symmetry driven AFM-FM
transition is not altered by spin-orbit coupling. The relative stability of
different magnetic phases is discussed in terms of the local density of states.
We find that CsCl-type FeSe is mechanically stable, but the magnetic states are
expected to be brittle.",1005.5112v2
2011/6/8,Electric-field control of magnetic ordering in the tetragonal BiFeO3,"We propose a way to use electric-field to control the magnetic ordering of
the tetragonal BiFeO3. Based on systematic first-principles studies of the
epitaxial strain effect on the ferroelectric and magnetic properties of the
tetragonal BiFeO3, we find that there exists a transition from C-type to G-type
antiferromagnetic (AFM) phase at in-plane constant a ~ 3.905 {\AA} when the
ferroelectric polarization is along [001] direction. Such magnetic phase
transition can be explained by the competition between the Heisenberg exchange
constant J1c and J2c under the influence of biaxial strain. Interestingly, when
the in-plane lattice constant enlarges, the preferred ferroelectric
polarization tends to be canted and eventually lies in the plane (along [110]
direction). It is found that the orientation change of ferroelectric
polarization, which can be realized by applying external electric-field, has
significant impact on the Heisenberg exchange parameters and therefore the
magnetic orderings of tetragonal BiFeO3. For example, at a ~ 3.79 {\AA}, an
electric field along [111] direction with magnitude of 2 MV/cm could change the
magnetic ordering from C-AFM to G-AFM. As the magnetic ordering affects many
physical properties of the magnetic material, e.g. magnetoresistance, we expect
such strategy would provide a new avenue to the application of multiferroic
materials.",1106.1502v1
2015/1/13,Strain-Induced Extrinsic High-Temperature Ferromagnetism in the Fe-Doped Hexagonal Barium Titanate,"Diluted magnetic semiconductors possessing intrinsic static magnetism at high
temperatures represent a promising class of multifunctional materials with high
application potential in spintronics and magneto-optics. In the hexagonal
Fe-doped diluted magnetic oxide, 6H-BaTiO$_{3-\delta}$, room-temperature
ferromagnetism has been previously reported. Ferromagnetism is broadly accepted
as an intrinsic property of this material, despite its unusual dependence on
doping concentration and processing conditions. However, the here reported
combination of bulk magnetization and complementary in-depth local-probe
electron spin resonance and muon spin relaxation measurements, challenges this
conjecture. While a ferromagnetic transition occurs around 700 K, it does so
only in additionally annealed samples and is accompanied by an extremely small
average value of the ordered magnetic moment. Furthermore, several additional
magnetic instabilities are detected at lower temperatures. These coincide with
electronic instabilities of the Fe-doped 3C-BaTiO$_{3-\delta}$ pseudocubic
polymorph. Moreover, the distribution of iron dopants with frozen magnetic
moments is found to be non-uniform. Our results demonstrate that the intricate
static magnetism of the hexagonal phase is not intrinsic, but rather stems from
sparse strain-induced pseudocubic regions. We point out the vital role of
internal strain in establishing defect ferromagnetism in systems with competing
structural phases.",1501.02938v1
2015/8/13,Magnetic and magnetocaloric properties of La$_{0.6}$Ca$_{0.4}$MnO$_{3}$ tunable by particle size and dimensionality,"Manganites have been attracted considerable attention due to some intriguing
magnetic properties, such as magnetoresistance, spin glass behavior and
superparamagnetism. In recent years, some studies point to the effect of
particle size and dimensionality of these compounds in their magnetic features.
Particularly, LaCaMnO material research is well explored concerning the bulk
material. To overcome the lack of the information we successfully produced
advanced nanostructures of La$_{0.6}$Ca$_{0.4}$MnO$_{3}$ manganites, namely
nanotubes and nanoparticles by using a sol-gel modified method, to determine
the size particle effect on the magnetism. The manganites crystal structure,
magnetic and magnetocaloric properties were studied in a broad temperature
range. Transmission electron microscopy revealed nanoparticles with sizes from
45 up to 223 nm, depending on the calcination temperature. It was found that
the magnetic and magnetocaloric properties can be optimized by tuning the
particle size; for instance, the magnetic transition broadening by decreasing
the particle size. We report the relative cooling power (RCP) of these samples;
it was found that the best RCP was observed for the 223 nm particle (508 J/Kg).
Finally, this work contributes to the research on the magnetic properties and
magnetocaloric potentials in nanostructured systems with distinct morphologies.",1508.03384v1
2016/9/22,Magnetization oscillations and waves driven by pure spin currents,"Recent advances in the studies of pure spin currents - flows of angular
momentum (spin) not accompanied by the electric currents - have opened new
horizons for the emerging technologies based on the electron's spin degree of
freedom, such as spintronics and magnonics. The main advantage of pure spin
current, as compared to the spin-polarized electric current, is the possibility
to exert spin transfer torque on the magnetization in thin magnetic films
without electrical current flow through the material. In addition to minimizing
Joule heating and electromigration effects, this characteristic enables the
implementation of spin torque devices based on the low-loss insulating magnetic
materials, and offers an unprecedented geometric flexibility. Here we review
the recent experimental achievements in investigations of magnetization
oscillations excited by pure spin currents in different magnetic nanosystems
based on metallic and insulating magnetic materials. We discuss the spectral
properties of spin-current nano-oscillators, and relate them to the spatial
characteristics of the excited dynamic magnetic modes determined by the
spatially-resolved measurements. We also show that these systems support
locking of the oscillations to external microwave signals, as well as their
mutual synchronization, and can be used as efficient nanoscale sources of
propagating spin waves.",1609.06899v1
2016/10/26,Skyrmion production on demand by homogeneous DC currents,"Topological magnetic textures - like skyrmions - have become a major player
in the design of next-generation magnetic storage technology due to their
stability and the control of their motion by ultra-low current densities. A
major challenge to develop this new skyrmion-based technology is to achieve the
controlled and deterministic creation of magnetic skyrmions without the need of
complex setups. We demonstrate a solution to this challenge by showing how to
create skyrmions and other magnetic textures in ferromagnetic thin films by
means of a homogeneous DC current and without requiring Dzyaloshinskii-Moriya
interactions. This is possible by exploiting a static loss of stability arising
from the interplay of current-induced spin-transfer torque and a spatially
inhomogeneous magnetization, which can be achieved, e.g., by locally
engineering the anisotropy, the magnetic field, or other magnetic interactions.
The magnetic textures are created controllably, efficiently, and periodically
with a period that can be tuned by the applied current strength. We propose
specific experimental setups realizable with simple materials, such as cobalt
based materials, to observe the periodic formation of skyrmions. We show that
adding chiral interactions will not influence the basics of the generations but
then influence the consequent dynamics with respect to the stabilization of
topological textures. Our findings allow for the production of skyrmions on
demand in simple ferromagnetic thin films by homogeneous DC currents.",1610.08313v2
2017/2/16,Plasma Brightenings in a Failed Solar Filament Eruption,"Failed filament eruptions are solar eruptions that are not associated with
coronal mass ejections. In a failed filament eruption, the filament materials
usually show some ascending and falling motions as well as generate bright EUV
emissions. Here we report a failed filament eruption that occurred in a
quiet-Sun region observed by the Atmospheric Imaging Assembly on board the
Solar Dynamics Observatory. In this event, the filament spreads out but gets
confined by the surrounding magnetic field. When interacting with the ambient
magnetic field, the filament material brightens up and flows along the magnetic
field lines through the corona to the chromosphere. We find that some materials
slide down along the lifting magnetic structure containing the filament and
impact the chromosphere to cause two ribbon-like brightenings in a wide
temperature range through kinetic energy dissipation. There is evidence
suggesting that magnetic reconnection occurs between the filament magnetic
structure and the surrounding magnetic fields where filament plasma is heated
to coronal temperatures. In addition, thread-like brightenings show up on top
of the erupting magnetic fields at low temperatures, which might be produced by
an energy imbalance from a fast drop of radiative cooling due to plasma
rarefaction. Thus, this single event of failed filament eruption shows
existence of a variety of plasma brightenings that may be caused by completely
different heating mechanisms.",1702.05136v1
2017/5/21,Non-Magnetic Half-Metals,"Half-metals are a class of materials that are metallic only for one spin
direction, and are essential for spintronics applications where one needs to
read, write, store and transfer spin-data. This spin sensitivity appears to
restrict them to be magnetic, and the known examples indeed are. The
fabrication of real spintronic devices from such materials is often hampered,
however, by stray magnetic fields, domain walls, short spin coherence times,
scattering on magnetic atoms or magnetically active interfaces, and other
characteristics that come along with the magnetism. The surfaces of topological
insulators, or Dirac or Weyl semimetals, could be an alternative, but
production of high-quality thin films without the presence of the bulk states
at the Fermi level remains very challenging. Here we introduce non-magnetic
half-metals and demonstrate that this state is realized in IrBiSe. Using
angle-resolved photoemission spectroscopy and band structure calculations we
find a record-high Dresselhaus spin-orbit splitting, fully spin-polarized
remnant Fermi surfaces and a chiral 3D spin-texture, all with no magnetism
present. Promising applications include using IrBiSe as a source of
spin-polarized electrons, and lightly doped IrBiSe is expected to generate
electric-field-controlled spin-polarized currents, free from back scattering,
and could host triplet superconductivity.",1705.07431v1
2017/8/5,Modification of the Magnetic Properties of Co2Y Hexaferrites by Divalent and Trivalent Metal Substitutions,"The present study is concerned with the fabrication and characterization of
Me2Y substituted hexaferrites, Ba2Me2Fe12-xTxO22 (Me = Co2+, Mg2+, and Cr2+,
and T = Fe3+, and Ga3+). The samples were prepared by the conventional ball
milling technique and sintering at 1200{\deg} C. The effect of the choices of
Me and T ions on the structural and magnetic properties of the hexaferrites
were investigated. XRD patterns, magnetic parameters, and M\""ossbauer spectra
of the Co2Y were consistent with a single phase Y-type hexaferrite. However,
the CoCr-Y sample was found to be dominated by the Y-type hexaferrite, and
M-type and BaCrO4 minority phases were observed in the XRD pattern of the
sample. The small increase in saturation magnetization from about 34 emu/g up
to 37.5 emu/g was therefore attributed to the development of the M-type phase.
On the other hand, XRD pattern of the Cr2Y sample indicated the dominance of
the M-type phase in this sample. The high coercivity (1445 Oe) of this sample
is evidence of the transformation of the material from a typically soft
magnetic material (Y-type) to a hard magnet (M-type). The Ga-substitution for
Fe in Co2Y did not affect the saturation magnetization significantly, but the
coercivity was reduced. However, the sample Ba2CoMgFe11GaO22 exhibited a
significant reduction of the saturation magnetization down to a value 26.6
emu/g, which could be due to the attenuation of the super-exchange interactions
induced by the Mg2+ substitution.",1708.01768v1
2018/7/12,First-Principles-Based Strain and Temperature Dependent Ferroic Phase Diagram of SrMnO$_3$,"Perovskite structure SrMnO$_3$ is a rare example of a multiferroic material
where strain-tuning and/or cation substitution could lead to coinciding
magnetic and ferroelectric ordering temperatures, which would then promise
strong magnetoelectric coupling effects. Here, we establish the temperature and
strain dependent ferroic phase diagram of SrMnO$_3$ using
first-principles-based effective Hamiltonians. All parameters of these
Hamiltonians are calculated using density functional theory, i.e., no fitting
to experimental data is required. Temperature dependent properties are then
obtained from Monte Carlo and molecular dynamics simulations. We observe a
sequence of several magnetic transitions under increasing tensile strain, with
a moderate variation of the corresponding critical temperatures. In contrast,
the ferroelectric Curie temperature increases strongly after its onset around
2.5\,\% strain, and indeed crosses the magnetic transition temperature just
above 3\,\% strain. Our results indicate pronounced magnetoelectric coupling,
manifested in dramatic changes of the magnetic ordering temperatures and
different magnetic ground states as function of the ferroelectric distortion.
In addition, coexisting ferroelectric and ferromagnetic order is obtained for
strains above 4\,\%. Our calculated phase diagram suggests the possibility to
control the magnetic properties of SrMnO$_3$ through an applied electric field,
significantly altering the magnetic transition temperatures, or even inducing
transitions between different magnetic states.",1807.04777v1
2018/10/9,"Magnetic behavior, Griffiths phase and magneto-transport study in 3$d$ based nano-crystalline double perovskite Pr$_2$CoMnO$_6$","Double perovskite (DP) oxide material receive extensive research interest due
to exciting physical properties with potential technological application. 3$d$
based DP oxides are promising for exciting physics like magnetodielectric,
ferroelectric, Griffith phase etc., specially Co/Mn DPs are gaining much
research interest. In this paper we present the study of magnetic phase and
transport properties in nano-crystalline Pr$_2$CoMnO$_6$ a 3$d$ based double
perovskite compound. This material shows a paramagnetic (PM) to ferromagnetic
(FM) phase transition below 173 K marked by a rapid increase in magnetic moment
due to spin ordering. We found divergence in inverse magnetic susceptibility
($\chi$$^{-1}$) from Curie weiss behavior around 206 K which indicates the
evolution of Griffiths phase before actual PM-FM transition. We found that the
Griffiths phase suppressed with increasing applied magnetic filed. For the
understanding of charge transport in this material we have measured temperature
dependent electrical resistivity. Pr$_2$CoMnO$_6$ is a strong insulator where
resistivity increase abruptly below magnetic phase transition. To understand
the effect of magnetic field on transport behavior we have also measured the
magnetoresistance (MR) at different temperatures. Sample shows the negative MR
with maximum value $\sim$22 $\%$ under applied magnetic field of 50 kOe at 125
K. MR follows quadratic field dependency above $T_c$ however below $T_c$ the MR
shows deviation from this field dependency at low field.",1810.03895v1
2020/4/4,Improved crystallographic compatibility and magnetocaloric reversibility in Pt substituted Ni2Mn1.4In0.6 magnetic shape memory Heusler alloy,"We present here the improved crystallographic/geometric compatibility and
magnetocaloric reversibility by measurement of magnetic entropy change using
different protocols in 10% Pt substituted Ni2Mn1.4In0.6 magnetic shape memory
alloy. The substitution of Pt reduces the thermal hysteresis about 50% to the
Ni2Mn1.4In0.6. The origin of the reduced thermal hysteresis is investigated by
the crystallographic compatibility of the austenite and martensite phases. The
calculated middle eigenvalue of the transformation matrix turned out to be
0.9982, which is very close to 1 (deviation is only 0.18%) suggests for the
crystallographic compatibility between the austenite and martensite phases in
Ni1.9Pt0.1Mn1.4In0.6. A very small thermal hysteresis and crystallographic
compatibility between two phases in this alloy system indicate a stress-free
transition layer (i.e. perfect habit plane) between the austenite and
martensite phase, which is expected to give reversible martensite phase
transition and therefore reversible magnetocaloric effect (MCE) as well. The
calculated value of the isothermal entropy change ({\Delta}Siso) using the
magnetization curve under three different measurement protocols (i.e.
isothermal, loop, and isofield measurement protocol) is found to be nearly same
indicating a reversible MCE in the present alloy system. Our work provides a
path to design new magnetic shape memory Heusler alloys for magnetic
refrigeration and also suggest that any of the above measurement protocol can
be used for the calculation of {\Delta}Siso for materials satisfying
geometrical compatibility condition.",2004.01854v1
2017/12/14,Real Time Visualization of Dynamic Magnetic Fields with a Nanomagnetic FerroLens,"Due to advancements in nanomagnetism and latest nanomagnetic materials and
devices, a new potential field has been opened up for research and applications
which was not possible before. We herein propose a new research field and
application for nanomagnetism for the visualization of dynamic magnetic fields
in real-time. In short, Nano Magnetic Vision. A new methodology, technique and
apparatus were invented and prototyped in order to demonstrate and test this
new application. As an application example the visualization of the dynamic
magnetic field on a transmitting antenna was chosen. Never seen before
high-resolution, photos and real-time color video revealing the actual dynamic
magnetic field inside a transmitting radio antenna rod has been captured for
the first time. The antenna rod is fed with six hundred volts, orthogonal
pulses. This unipolar signal is in the very low frequency (i.e. VLF) range. The
signal combined with an extremely short electrical length of the rod, ensures
the generation of a relatively strong fluctuating magnetic field, analogue to
the signal transmitted, along and inside the antenna. This field is induced
into a ferrolens and becomes visible in real-time within the normal human eyes
frequency spectrum. The name we have given to the new observation apparatus is,
SPIONs Superparamagnetic Ferrolens Microscope (SSFM), a powerful passive
scientific observation tool with many other potential applications in the near
future.",1712.05436v1
2017/12/17,"Low temperature ferromagnetic properties, magnetic field induced spin order and random spin freezing effect in Ni1.5Fe1.5O4 ferrite; prepared at different pH values and annealing temperatures","We present the low temperature magnetic properties in Ni1.5Fe1.5O4 ferrite as
the function of pH at which the material was prepared by chemical route and
post annealing temperature. The material is a ferri or ferromagnet, but showed
magnetic blocking and random spin freezing process on lowering the measurement
temperature down to 5 K. The sample prepared at pH =12 and annealed at 800 ^C
showed a sharp magnetization peak at 105 K, the superparamagnetic blocking
temperature of the particles. The magnetization peak remained incomplete within
measurement temperature up to 350 K for rest of the samples, although peak
temperature was brought down by increasing applied dc field. The fitting of
temperature dependence of coercivity data according to Kneller law suggested
random orientation of ferromagnetic particles. The fitting of saturation
magnetization according to Bloch law provided the exponent that largely
deviated from 1.5, a typical value for long ranged ferromagnet. An abrupt
increase of saturation magnetization below 50 K suggested the active role of
frozen surface spins in low temperature magnetic properties. AC susceptibility
data elucidated the low temperature spin freezing dynamics and exhibited the
characters of cluster spin glass in the samples depending on pH value and
annealing temperature.",1712.06114v1
2017/12/21,Emerging chiral edge states from the confinement of a magnetic Weyl semimetal in Co$_3$Sn$_2$S$_2$,"The quantum anomalous Hall effect (QAHE) and magnetic Weyl semimetals (WSMs)
are topological states induced by intrinsic magnetic moments and spin-orbit
coupling. Their similarity suggests the possibility of achieving the QAHE by
dimensional confinement of a magnetic WSM along one direction. In this study,
we investigate the emergence of the QAHE in the two-dimensional (2D) limit of
magnetic WSMs due to finite size effects in thin films and step-edges. We
demonstrate the feasibility of this approach with effective models and real
materials. To this end, we have chosen the layered magnetic WSM
Co$_3$Sn$_2$S$_2$, which features a large anomalous Hall conductivity and
anomalous Hall angle in its 3D bulk, as our material candidate. In the 2D limit
of Co$_3$Sn$_2$S$_2$ two QAHE states exist depending on the stoichiometry of
the 2D layer. One is a semimetal with a Chern number of 6, and the other is an
insulator with a Chern number of 3. The latter has a band gap of 0.05 eV, which
is much larger than that in magnetically doped topological insulators. Our
findings naturally explain the existence of chiral states in step edges of bulk
Co$_3$Sn$_2$S$_2$ which habe been reported in a recent experiment at $T = 4K$
and present a realistic avenue to realize QAH states in thin films of magnetic
WSMs.",1712.08115v3
2019/11/3,Optically Driven Magnetic Phase Transition of Monolayer RuCl3,"Strong light-matter interactions within nanoscale structures offer the
possibility of optically controlling material properties. Motivated by the
recent discovery of intrinsic long-range magnetic order in two-dimensional
materials, which allows for the creation of novel magnetic devices of
unprecedented small size, we predict that light can couple with magnetism and
efficiently tune magnetic orders of monolayer ruthenium trichloride (RuCl3).
First-principles calculations show that both free carriers and optically
excited electron-hole pairs can switch monolayer RuCl3 from the proximate
spin-liquid phase to a stable ferromagnetic phase. Specifically, a moderate
electron-hole pair density (on the order of 10^13 cm-2) can significantly
stabilize the ferromagnetic phase by 10 meV/f.u. in comparison to the zigzag
phase, so that the predicted ferromagnetism can be driven by optical pumping
experiments. Analysis shows that this magnetic phase transition is driven by a
combined effect of doping-induced lattice strain and itinerant ferromagnetism.
According to the Ising-model calculation, we find that the Curie temperature of
the ferromagnetic phase can be increased significantly by raising carrier or
electron-hole pair density. This enhanced opto-magnetic effect opens new
opportunities to manipulate two-dimensional magnetism through non-contact,
optical approaches.",1911.00979v1
2020/2/26,Effect of Magnetic-Field-Induced Restructuring on the Elastic Properties of Magnetoactive Elastomers,"Composite materials where magnetic micrometer-sized particles are embedded
into a compliant polymer matrix are known as magnetorheological or
magnetoactive elastomers (MAEs). They are distinguished by huge variations of
their physical properties in a magnetic field, which is commonly attributed to
the restructuring of the filler. The process of the magnetic-field-induced
restructuring in a magnetorheological elastomer is interpreted as progression
towards percolation. Such a physical model was previously used to explain the
dependence of the magnetic permeability and dielectric permittivity of MAEs on
the magnetic field strength. Based on this hypothesis, the magnetorheological
effect in MAEs is considered theoretically. The theoretical approach is built
upon a self-consistent effective-medium theory for the elastic properties,
extended to the variable (field dependent) percolation threshold. The proposed
model allows one to describe the large variations (over several orders of
magnitude) of the effective elastic moduli of these composite materials, known
as the giant magnetorheological (MR) and field-stiffening effects. An existence
of a giant magnetic Poisson effect is predicted. The relation of the proposed
model to the existing theories of the MR effect in MAEs is discussed. The
results can be useful for applications of MAEs in magnetic-field controlled
vibration dampers and isolators.",2002.11762v2
2020/5/13,Structural evolution and skyrmionic phase diagram of the lacunar spinel GaMo$_4$Se$_8$,"In the $AB_4Q_8$ lacunar spinels, the electronic structure is described on
the basis of inter- and intra-cluster interactions of tetrahedral $B_4$
clusters, and tuning these can lead to myriad fascinating electronic and
magnetic ground states. In this work, we employ magnetic measurements,
synchrotron X-ray and neutron scattering, and first-principles electronic
structure calculations to examine the coupling between structural and magnetic
phase evolution in GaMo$_4$Se$_8$, including the emergence of a skyrmionic
regime in the magnetic phase diagram. We show that the competition between two
distinct Jahn-Teller distortions of the room temperature cubic
$F\overline{4}3m$ structure leads to the coexistence of the ground state $R3m$
phase and a metastable $Imm2$ phase. The magnetic properties of these two
phases are computationally shown to be very different, with the $Imm2$ phase
exhibiting uniaxial ferromagnetism and the $R3m$ phase hosting a complex
magnetic phase diagram including equilibrium N\'eel--type skyrmions stable from
nearly $T$ = 28 K down to $T$ = 2 K, the lowest measured temperature. The large
change in magnetic behavior induced by a small structural distortion reveals
that GaMo$_4$Se$_8$ is an exciting candidate material for tuning unconventional
magnetic properties $via$ mechanical means.",2005.06662v1
2021/1/5,Symmetry-protected Nodal Points and Nodal Lines in Magnetic Materials,"Nodal-point and Nodal-line structures in the dispersion of electron energy
bands are characterized by their high degeneracy in certain corners or lines in
the Brillouin zone (BZ). These nodal structures can also exist in the
dispersion of itinerant electrons in magnetically ordered materials whose
symmetry groups are anti-unitary groups called the magnetic space groups. In
the present work, we provide a complete list of magnetic space groups which can
host symmetry-protected nodal-point/line band structures for spin-1/2 fermionic
particles, where the degeneracies at the nodal points/lines are guaranteed by
irreducible projective representations (IPReps) of the little co-groups. Our
discussion is restricted to the magnetic space groups whose magnetic point
group contains the space-time inversion operation $\tilde T=\mathcal IT$, the
combined operation of spacial inversion $\mathcal I$ and time reversal $T$,
such that the energy bands are at least doubly-degenerate at arbitrary points
in the BZ. For these magnetic point groups we provide the invariants to label
the classes of projective Reps, and for each class we calculate all the
inequivalent IPReps. From the results we select out all the groups and the
corresponding Rep classes which support high-dimensional ($d\geq$4) IPReps. We
then list the magnetic space groups and their high symmetry points/lines whose
little co-groups have high-dimensional ($d\geq$4) IPReps with the corresponding
factor systems. Examples of candidate materials are discussed.",2101.01733v2
2021/10/12,Anisotropically large anomalous and topological Hall effect in a kagome magnet,"Recently, kagome materials have become an engrossing platform to study the
interplay among symmetry, magnetism, topology, and electron correlation. The
latest works on RMn6Sn6 (R = rare earth metal) compounds have illustrated that
this family could be intriguing to investigate various physical phenomena due
to large spin-orbit coupling and strong magnetic ordering. However, combined
transport and spectroscopic studies in RMn6Sn6 materials are still limited.
Here, we report magnetic, magneto-transport, and angle-resolved photoemission
spectroscopy measurements of a kagome magnet ErMn6Sn6 that undergoes
antiferromagnetic (TN = 345 K) to ferrimagnetic (TC = 68 K) phase transitions
in the presence of field. We observe large anomalous and topological Hall
effects serving as transport signatures of the nontrivial Berry curvature. The
isothermal magnetization exhibits strong anisotropic nature and the topological
Hall effect of the compound depends on the critical field of metamagnetic
transition. Our spectroscopic results complemented by theoretical calculations
show the multi-orbital kagome fermiology. This work provides new insight into
the tunability and interplay of topology and magnetism in a kagome magnet.",2110.06012v1
2021/10/27,Unusual magnetic and transport properties in HoMn$_6$Sn$_6$ kagome magnet,"With intricate lattice structures, kagome materials are an excellent platform
to study various fascinating topological quantum states. In particular, kagome
materials, revealing large responses to external stimuli such as pressure or
magnetic field, are subject to special investigation. Here, we study the
kagome-net HoMn$_6$Sn$_6$ magnet that undergoes paramagnetic to ferrimagnetic
transition (below 376 K) and reveals spin-reorientation transition below 200 K.
In this compound, we observe the topological Hall effect and substantial
contribution of anomalous Hall effect above 100 K. We unveil the pressure
effects on magnetic ordering at a low magnetic field from the pressure tunable
magnetization measurement. By utilizing high-resolution angle-resolved
photoemission spectroscopy, Dirac-like dispersion at the high-symmetry point K
is revealed in the vicinity of the Fermi level, which is well supported by the
first-principles calculations, suggesting a possible Chern-gapped Dirac cone in
this compound. Our investigation will pave the way to understand the
magneto-transport and electronic properties of various rare-earth-based kagome
magnets.",2110.14155v1
2021/12/21,The intrinsic ferromagnetism of two-dimensional (2D) MnO$_2$ revisited: A many-body Quantum Monte Carlo and DFT+U study,"Monolayer MnO$_2$ is one of the few predicted two-dimensional (2D)
ferromagnets that has been experimentally synthesized and is commercially
available. The Mermin-Wagner theorem states that magnetic order in a 2D
material cannot persist unless magnetic anisotropy (MA) is present and
perpendicular to the plane, which permits a finite critical temperature.
Previous computational studies have predicted the magnetic ordering and Curie
temperature of 2D MnO$_2$ with DFT+U (Density Funtional Theory + Hubbard U
correction), with the results having a strong dependence on the Hubbard U
parameter. Diffusion Monte Carlo (DMC) is a correlated electronic structure
method that has had demonstrated success for the electronic and magnetic
properties of a variety of 2D and bulk systems since it has a weaker dependence
on the starting Hubbard parameter and density functional. In this study, we
used DMC and DFT+U to calculate the magnetic properties of monolayer MnO$_2$.
We found that the ferromagnetic ordering is more favorable than
antiferromagnetic and determined a statistical bound on the magnetic exchange
parameter ($J$). In addition, we performed spin-orbit MA energy calculations
using DFT+U and using our DMC and DFT+U parameters along with the analytical
model of Torelli and Olsen, we estimated an upper bound of 28.8 K for the
critical temperature of MnO$_2$. These QMC results intend to serve as an
accurate theoretical benchmark, necessary for the realization and development
of future 2D magnetic devices. These results also demonstrate the need for
accurate methodologies to predict magnetic properties of correlated 2D
materials.",2112.11579v2
2022/11/13,Coupling of Magnetic Phases at Nickelate Interfaces,"In this work we present a model system built out of artificially layered
materials, allowing us to understand the interrelation of magnetic phases with
that of the metallic-insulating phase at long length-scales, and enabling new
strategies for the design and control of materials in devices. The artificial
model system consists of superlattices made of SmNiO$_3$ and NdNiO$_3$ layers
-- two members of the fascinating rare earth nickelate family, having different
metal-to-insulator and magnetic transition temperatures. By combining two
complementary techniques -- resonant elastic x-ray scattering and muon spin
relaxation -- we show how the magnetic order evolves, in this complex
multicomponent system, as a function of temperature and superlattice
periodicity. We demonstrate that the length scale of the coupling between the
antiferromagnetic and paramagnetic phases is longer than that of the electronic
metal-insulator phase transition -- despite being subsidiary to it. This can be
explained via a Landau theory -- where the bulk magnetic energy plus a gradient
cost between magnetic and non magnetic phases are considered. These results
provide a clear understanding of the coupling of magnetic transitions in
systems sharing identical order parameters.",2211.06811v1
2023/2/23,The influence of crystalline electric field on the magnetic properties of CeCd3X3 (X = P and As),"CeCd$_3$P$_3$ and CeCd$_3$As$_3$ compounds adopt the hexagonal
ScAl$_3$C$_3$-type structure, where magnetic Ce ions on a triangular lattice
order antiferromagnetically below $T_\text{N} \sim$0.42~K. Their crystalline
electric field (CEF) level scheme has been determined by fitting magnetic
susceptibility curves, magnetization isotherms, and Schottky anomalies in
specific heat. The calculated results, incorporating the CEF excitation, Zeeman
splitting, and molecular field, are in good agreement with the experimental
data. The CEF model, with Ce$^{3+}$ ions in a trigonal symmetry, explains the
strong easy-plane magnetic anisotropy that has been observed in this family of
materials. A detailed examination of the CEF parameters suggests that the
fourth order CEF parameter $B_{4}^{3}$ is responsible for the strong CEF
induced magnetocrystalline anisotropy, with a large $ab$-plane moment and a
small $c$-axis moment. The reliability of our CEF analysis is assessed by
comparing the current study with earlier reports of CeCd$_{3}$As$_{3}$. For
both CeCd$_{3}X_{3}$ ($X$ = P and As) compounds, less than 40 \% of $R\ln(2)$
magnetic entropy is recovered by $T_\text{N}$ and full $R\ln(2)$ entropy is
achieved at the Weiss temperature $\theta_{p}$. Although the observed magnetic
entropy is reminiscent of delocalized 4$f$-electron magnetism with significant
Kondo screening, the electrical resistivity of these compounds follows a
typical metallic behavior. Measurements of thermoelectric power further
validate the absence of Kondo contribution in CeCd$_{3}X_{3}$.",2302.11714v1
2023/2/24,Antiferromagnetism of CeCd$_{0.67}$As$_{2}$ existing deep inside the narrow gap semiconducting state,"Single crystals of $R$Cd$_{0.67}$As$_2$ ($R$ = La and Ce) have been
synthesized by high temperature ternary melt and their physical properties have
been explored by means of magnetization, specific heat, electrical resistivity,
Hall coefficient, and thermoelectric power measurements. $R$Cd$_{0.67}$As$_2$
compounds indicate a (structural) phase transition at high temperatures,
accompanied by a remarkable increase of the electrical resistivity with an
extremely low carrier concentration. CeCd$_{0.67}$As$_2$ exhibits a large
magnetic anisotropy and an antiferromagnetic (AFM) order below $T_{N} = 4$~K.
Magnetic susceptibility curves, together with magnetization isotherms and
specific heat, are analyzed by the point charge model of crystalline electric
field (CEF). In the paramagnetic state, the observed magnetic properties can be
well explained by the CEF effects, implying that the 4$f$ moments remain
localized. Electrical resistivity measurements, together with Hall resistivity
and thermoelectric power, also suggest highly localized 4$f$ electrons, where
Kondo contributions are negligible. The low temperature physical properties
manifest strong magnetic field dependencies. For $H \perp c$, $T_{N}$ shifts to
lower temperature as magnetic field increases, and eventually disappears at
$H_{c} \sim 60$~ kOe. Inside the AFM state, three metamagnetic transitions are
clearly evidenced from the magnetization isotherms. The RKKY interaction may be
responsible for the AFM ordering in CeCd$_{0.67}$As$_2$, however it would have
to be mediated by extremely low charge carriers. Although the AFM ordering
temperature in CeCd$_{0.67}$As$_2$ can be continuously suppressed to zero, no
AFM quantum phase transition is expected due to the lack of conduction electron
clouds to screen the 4$f$ moments.",2302.12451v1
2023/3/24,Magnetohydrodynamic Model of Late Accretion onto a Protoplanetary Disk: Cloudlet Encounter Event,"Recent observations suggest late accretion, which is generally
nonaxisymmetric, onto protoplanetary disks. We investigated nonaxisymmetric
late accretion considering the effects of magnetic fields. Our model assumes a
cloudlet encounter event at a few hundred au scale, where a magnetized gas
clump (cloudlet) encounters a protoplanetary disk. We studied how the cloudlet
size and the magnetic field strength affect the rotational velocity profile in
the disk after the cloudlet encounter. The results show that a magnetic field
can either decelerate or accelerate the rotational motion of the cloudlet
material, primarily depending on the relative size of the cloudlet to the disk
thickness. When the cloudlet size is comparable to or smaller than the disk
thickness, magnetic fields only decelerate the rotation of the colliding
cloudlet material. However, if the cloudlet size is larger than the disk
thickness, the colliding cloudlet material can be super-Keplerian as a result
of magnetic acceleration. We found that the vertical velocity shear of the
cloudlet produces a magnetic tension force that increases the rotational
velocity. The acceleration mechanism operates when the initial plasma $\beta$
is $ \beta \lesssim 2\times 10^1 $. Our study shows that magnetic fields modify
the properties of spirals formed by tidal effects. These findings may be
important for interpreting observations of late accretion.",2303.14010v1
2023/6/12,Unraveling the connection between high-order magnetic interactions and local-to-global spin Hamiltonian in non-collinear magnetic dimers,"A spin Hamiltonian, which characterizes interatomic interactions between spin
moments, is highly valuable in predicting and comprehending the magnetic
properties of materials. A deeper understanding of the microscopic origin of
magnetic interactions can open new pathways toward realizing nanometer-scale
systems for future spintronic devices. Here, we explore a method for explicitly
calculating interatomic exchange interactions in non-collinear configurations
of magnetic materials considering only a bilinear spin Hamiltonian in a local
scenario. Based on density-functional theory (DFT) calculations of dimers
adsorbed on metallic surfaces, and with a focus on the Dzyaloshinskii-Moriya
interaction (DMI) which is essential for stabilizing chiral non-collinear
magnetic states, we discuss the interpretation of the DMI when decomposed into
microscopic electron and spin densities and currents. We clarify the distinct
origins of spin currents induced in the system and their connection to the DMI.
In addition, we reveal how non-collinearity affects the usual DMI, which is
solely induced by spin-orbit coupling, and DMI-like interactions brought about
by non-collinearity. We explain how the dependence of the DMI on the magnetic
configuration establishes a connection between high-order magnetic
interactions, enabling the transition from a local to a global spin
Hamiltonian.",2306.07222v2
2023/7/13,Manifestation of chiral magnetic current in Floquet-Weyl semimetals,"Materials that can host macroscopic persistent current are important because
they are useful for energy storage. However, there are very few examples of
such materials in nature. Superconductors are known as an example in which flow
of supercurrent can persist up to 100,000 years. The chiral magnetic current is
possibly the second example predicted by the chiral magnetic effect. It was
proposed to be realized in recently discovered Weyl semimetals. However, a
no-go theorem negates the chiral magnetic effect and shows that the chiral
magnetic current is generally absent in any equilibrium condensed-matter
system. Here we show how to break the no-go theorem by resorting to dynamical
transitions in time-frequency space. By driving an insulator using a
time-periodic potential and coupling it to a phonon heat bath that provides
suitable dissipation, we show that a Floquet-Weyl semi-metallic phase with
Fermi-Dirac-like distribution emerges. Furthermore, we show that even in the
presence of a static magnetic field, the resulting steady Floquet-Weyl
semimetal supports non-vanishing chiral magnetic current. Our dynamical model
provides a systematic way to fully realize the chiral magnetic effect in
condensed matter systems.",2307.06735v1
2023/8/17,Orbital Multiferroicity in Pentalayer Rhombohedral Graphene,"Ferroic orders describe spontaneous polarization of spin, charge, and lattice
degrees of freedom in materials. Materials featuring multiple ferroic orders,
known as multiferroics, play important roles in multi-functional electrical and
magnetic device applications. 2D materials with honeycomb lattices offer
exciting opportunities to engineer unconventional multiferroicity, where the
ferroic orders are driven purely by the orbital degrees of freedom but not
electron spin. These include ferro-valleytricity corresponding to the electron
valley and ferro-orbital-magnetism supported by quantum geometric effects. Such
orbital multiferroics could offer strong valley-magnetic couplings and large
responses to external fields-enabling device applications such as
multiple-state memory elements, and electric control of valley and magnetic
states. Here we report orbital multiferroicity in pentalayer rhombohedral
graphene using low temperature magneto-transport measurements. We observed
anomalous Hall signals Rxy with an exceptionally large Hall angle (tan{\Theta}H
> 0.6) and orbital magnetic hysteresis at hole doping. There are four such
states with different valley polarizations and orbital magnetizations, forming
a valley-magnetic quartet. By sweeping the gate electric field E we observed a
butterfly-shaped hysteresis of Rxy connecting the quartet. This hysteresis
indicates a ferro-valleytronic order that couples to the composite field E\cdot
B, but not the individual fields. Tuning E would switch each ferroic order
independently, and achieve non-volatile switching of them together. Our
observations demonstrate a new type of multiferroics and point to electrically
tunable ultra-low power valleytronic and magnetic devices.",2308.08837v2
2023/11/15,Infrared Imaging of Magnetic Octupole Domains in Non-collinear Antiferromagnets,"Magnetic structure plays a pivotal role in the functionality of
antiferromagnets (AFMs), which not only can be employed to encode digital data
but also yields novel phenomena. Despite its growing significance, visualizing
the antiferromagnetic domain structure remains a challenge, particularly for
non-collinear AFMs. Currently, the observation of magnetic domains in
non-collinear antiferromagnetic materials is feasible only in Mn$_{3}$Sn,
underscoring the limitations of existing techniques that necessitate distinct
methods for in-plane and out-of-plane magnetic domain imaging. In this study,
we present a versatile method for imaging the antiferromagnetic domain
structure in a series of non-collinear antiferromagnetic materials by utilizing
the anomalous Ettingshausen effect (AEE), which resolves both the magnetic
octupole moments parallel and perpendicular to the sample surface. Temperature
modulation due to the AEE originating from different magnetic domains is
measured by the lock-in thermography, revealing distinct behaviors of octupole
domains in different antiferromagnets. This work delivers an efficient
technique for the visualization of magnetic domains in non-collinear AFMs,
which enables comprehensive study of the magnetization process at the
microscopic level and paves the way for potential advancements in applications.",2311.08762v1
2023/12/5,Accurate Machine Learning Predictions of Coercivity in High-Performance Permanent Magnets,"Increased demand for high-performance permanent magnets in the electric
vehicle and wind turbine industries has prompted the search for cost-effective
alternatives. Nevertheless, the discovery of new magnetic materials with the
desired intrinsic and extrinsic permanent magnet properties presents a
significant challenge. Traditional density functional theory (DFT) accurately
predicts intrinsic permanent magnet properties such as magnetic moments,
magneto-crystalline anisotropy constants, and exchange interactions. However,
it cannot compute extrinsic macroscopic properties, such as coercivity ($H_c$),
which are influenced by factors like microscopic defects and internal grain
structures. Although micromagnetic simulation helps compute $H_c$, it
overestimates the values almost by an order of magnitude due to Brown's
paradox. To circumvent these limitations, we employ machine learning (ML)
methods in an extensive database obtained from experiments, DFT calculations,
and micromagnetic modeling. Our novel ML approach is computationally much
faster than the micromagnetic simulation program, the mumax$^3$. We
successfully utilize it to predict $H_c$ values for materials like cerium-doped
$\mathrm{Nd}_2\mathrm{Fe}_{14}\mathrm{B}$, and subsequently compare the
predicted values with experimental results. Remarkably, our ML model accurately
identifies uniaxial magnetic anisotropy as the primary contributor to $H_c$.
With DFT calculations, we predict the Nd-site dependent magnetic anisotropy
behavior in $\mathrm{Nd}_2\mathrm{Fe}_{14}\mathrm{B}$, confirming $4f$-site
planar and $4g$-site uniaxial to crystalline $c$-direction in good agreement
with experiment. The Green's function atomic sphere approximation calculated a
Curie temperature ($T_{\rm C}$) for $\mathrm{Nd}_2\mathrm{Fe}_{14}\mathrm{B}$
that also agrees well with experiment.",2312.02475v3
2023/12/25,Exploration of the two-dimensional Ising magnetic materials in the triangular prismatic crystal field,"Magnetic anisotropy is essential for stabilizing two-dimensional (2D)
magnetism, which has significant applications in spintronics and the
advancement of fundamental physics. In this work, we examine the electronic
structure and magnetic properties of triangular prismatic MSi$_2$N$_4$ (M = V,
Cr) monolayers, using crystal field theory, spin-orbital state analyses, and
density functional calculations. Our results reveal that the pristine
VSi$_2$N$_4$ monolayer exhibits magnetism with a V$^{4+}$ 3$d^1$ $S$ = 1/2
charge-spin state within the triangular prismatic crystal field. However, the
strong $d$ orbital hybridization between adjacent V$^{4+}$ ions disrupts the
$d$ orbital splitting in this crystal field, resulting in a relatively small
in-plane magnetic anisotropy of approximately 2 $\mu$eV per V atom.In contrast,
the pristine CrSi$_2$N$_4$ monolayer is nonmagnetic, characterized by the
Cr$^{4+}$ 3$d^2$ $S$ = 0 state. Upon substituting nonmagnetic Cr$^{4+}$ with
Si$^{4+}$, Cr$_\frac{1}{3}$Si$_\frac{8}{3}$N$_4$ transforms into an
antiferromagnetic insulator with Cr$^{4+}$ 3$d^2$ $S$ = 1 state, featuring a
large orbital moment of -1.06 $\mu_{\rm B}$ oriented along the $z$-axis and
huge perpendicular magnetic anisotropy of 18.63 meV per Cr atom. These findings
highlight the potential for further exploration of 2D Ising magnetic materials
within a unique triangular prismatic crystal field.",2312.15625v1
2024/2/24,Observation of the In-plane Anomalous Hall Effect induced by Octupole in Magnetization Space,"The Anomalous Hall Effect (AHE) manifests as a transverse voltage
proportional to magnetization in ferromagnetic materials under the application
of a charge current, being an indispensable tool for probing magnetism,
especially in nanoscale devices. However, the AHE primarily sensitizes to
out-of-plane magnetization, thereby hindering its capacity to discern the
in-plane magnetization, a characteristic prevalent in ferromagnetic films. Here
we challenge this conventional understanding by demonstrating the in-plane
magnetization-induced AHE in iron and nickel, two ubiquitous ferromagnets. This
observation of the in-plane AHE is remarkable as it contradicts existing
theories that forbid such phenomena in cubic crystal systems. We trace the
origin of this unanticipated phenomenon to a hitherto unconsidered octupole of
the anomalous Hall conductivity in the magnetization space, a mechanism we
propose could enable the detection of in-plane AHE in a wide range of
ferromagnetic materials. This work realizes the in-plane AHE in common
ferromagnets by exploiting the anomalous Hall conductivity octupole, revealing
a new physical origin of the AHE and promising to revolutionize the design of
magnetic devices and sensors.",2402.15741v1
2024/2/28,Multifunctional composite magnet for practical transverse thermoelectrics,"Permanent magnets are used in various products and essential for human
society. If omnipresent permanent magnets could directly convert heat into
electricity, they would lead to innovative energy harvesting and thermal
management technologies. However, achieving such ""multifunctionality"" has been
difficult because of the poor thermoelectric performance of conventional
magnets. Here, we develop a multifunctional composite magnet that enables giant
transverse thermoelectric conversion. The proposed composite material,
comprising alternately and obliquely stacked
SmCo$_5$/Bi$_{0.2}$Sb$_{1.8}$Te$_3$ multilayers, exhibits large remanent
magnetization and coercivity as well as an excellent figure of merit of 0.32
for transverse thermoelectric conversion around room temperature. While having
versatile transverse geometry and high mechanical durability, the thermopile
module based on these composite magnets generates 204 mW at a temperature
difference of 152 K owing to extremely low interfacial electrical and thermal
resistances. The corresponding power density per heat transfer area of 56.7
mW/cm$^2$ is not only record-high among all the transverse thermoelectric
modules but also comparable to those of commercial longitudinal thermoelectric
modules based on the Seebeck effect. The novel functional material enables the
integration of thermoelectric conversion capabilities wherever permanent
magnets are currently used.",2402.18019v1
2022/6/7,Evidence for surface spin structures from first order reversal curves in Co3Sn2S2 and Fe3GeTe2 magnetic topological semimetals,"We study magnetization reversal and first order reversal curves for two
different magnetic topological semimetals, Co3Sn2S2 and Fe3GeTe2, in a wide
temperature range. For the magnetization reversal, we observe strong
temperature dependence of the initial (low-temperature) step-like magnetization
switchings, so the inverted hysteresis appears at high temperatures. Usually,
the inverted hysteresis is a fingerprint of material with two independent
magnetic phases, the inversion reflects the phase interaction. First order
reversal curve analysis confirms the two-phase behavior even at the lowest
temperatures of the experiment. While the bulk ferromagnetic magnetization
shows strong temperature dependence, one of the observed phases demonstrates
perfect stability below the Curie temperature. The obtained hysteresis loops
are of the bow-tie type, which is usually ascribed to appearance of the
skyrmionic phase. The described two-phase behavior is mostly identical for
Co3Sn2S2 and Fe3GeTe2 magnetic topological semimetals, only the characteristic
temperatures differ for these materials. The specifics of our experiment is the
excellent temperature stability of the second phase, while the skyrmions are
usually observed near the Curie temperature. On the other hand, temperature
stability can be expected for surface-state induced spin textures due to the
topological protection of surface states in topological semimetals. This also
explains the universal behavior of the second phase for two different
topological semimetals Co3Sn2S2 and FGT. Both these materials have strongly
different bulk properties, the only similarity is the presence of the
topological surface states. Thus, we can ascribe the second, temperature-stable
magnetic phase to the surface states in topological semimetals.",2206.03357v2
2019/6/6,Novel Mechanocaloric Materials for Solid-State Cooling Applications,"Solid-state cooling is an environmentally friendly and highly scalable
technology that may solve most of the problems associated with current
refrigerant methods. Solid-state cooling consists of applying external fields
on caloric materials, which react thermally as a result of induced phase
transformations. From an energy efficiency point of view, mechanocaloric
compounds, in which the phase transitions of interest are driven by mechanical
stresses, probably represent the most encouraging type of caloric materials.
Conventional mechanocaloric materials like shape-memory alloys already display
good cooling performances however in most cases they also present critical
mechanical fatigue and hysteresis problems that limit their applicability.
Finding new mechanocaloric materials and mechanisms able to overcome those
problems while simultaneously rendering large temperature shifts, is necessary
to further advance the field of solid-state cooling. In this article, we review
novel families of mechanocaloric materials that in recent years have been shown
to be specially promising in the aspects that conventional mechanocaloric
materials are not, and which exhibit unconventional but significant caloric
effects. We put an emphasis on elastocaloric materials, in which the targeted
cooling spans are obtained through uniaxial stresses, since from an applied
perspective these appear to be the most accomplished. Two different types of
mechanocaloric materials emerge as particularly hopeful from our analysis,
compounds that exhibit field-induced order disorder phase transitions involving
either ions or molecules (fast-ion conductors and plastic crystals), and
multiferroics in which the structural parameters are strongly coupled with
polar and/or magnetic degrees of freedom (magnetic alloys and oxide
perovskites).",1906.02363v1
2018/10/24,High-throughput Discovery of Topologically Non-trivial Materials using Spin-orbit Spillage,"We present a novel methodology to identify topologically non-trivial
materials based on band inversion induced by spin-orbit coupling (SOC) effect.
Specifically, we compare the density functional theory (DFT) based
wavefunctions with and without spin-orbit coupling and compute the
spin-orbit-spillage as a measure of band-inversion. Due to its ease of
calculation, without any need for symmetry analysis or dense k-point
interpolation, the spillage is an excellent tool for identifying topologically
non-trivial materials. Out of 30000 materials available in the JARVIS-DFT
database, we applied this methodology to more than 4835 non-magnetic materials
consisting of heavy atoms and low bandgaps. We found 1868 candidate materials
with high-spillage (using 0.5 as a threshold). We validated our methodology by
carrying out conventional Wannier-interpolation calculations for 289 candidate
materials. We demonstrate that in addition to Z2 topological insulators, this
screening method successfully identified many semimetals and topological
crystalline insulators. Importantly, our approach is applicable to the
investigation of disordered or distorted as well as magnetic materials, because
it is not based on symmetry considerations. We discuss some individual example
materials, as well as trends throughout our dataset, which is available at the
websites: https://www.ctcms.nist.gov/~knc6/JVASP.html and
https://jarvis.nist.gov/.",1810.10640v2
2022/10/19,Self-supervised Representations and Node Embedding Graph Neural Networks for Accurate and Multi-scale Analysis of Materials,"Supervised machine learning algorithms, such as graph neural networks (GNN),
have successfully predicted material properties. However, the superior
performance of GNN usually relies on end-to-end learning on large material
datasets, which may lose the physical insight of multi-scale information about
materials. And the process of labeling data consumes many resources and
inevitably introduces errors, which constrains the accuracy of prediction. We
propose to train the GNN model by self-supervised learning on the node and edge
information of the crystal graph. Compared with the popular manually
constructed material descriptors, the self-supervised atomic representation can
reach better prediction performance on material properties. Furthermore, it may
provide physical insights by tuning the range information. Applying the
self-supervised atomic representation on the magnetic moment datasets, we show
how they can extract rules and information from the magnetic materials. To
incorporate rich physical information into the GNN model, we develop the node
embedding graph neural networks (NEGNN) framework and show significant
improvements in the prediction performance. The self-supervised material
representation and the NEGNN framework may investigate in-depth information
from materials and can be applied to small datasets with increased prediction
accuracy.",2211.03563v3
2024/3/5,Enhancing Magnetocaloric Material Discovery: A Machine Learning Approach Using an Autogenerated Database by Large Language Models,"Magnetic cooling based on the magnetocaloric effect is a promising
solid-state refrigeration technology for a wide range of applications in
different temperature ranges. Previous studies have mostly focused on near room
temperature (300 K) and cryogenic temperature (< 10 K) ranges, while important
applications such as hydrogen liquefaction call for efficient magnetic
refrigerants for the intermediate temperature 10K to 100 K. For efficient use
in this range, new magnetocaloric materials with matching Curie temperatures
need to be discovered, while conventional experimental approaches are typically
time-consuming and expensive. Here, we report a computational material
discovery pipeline based on a materials database containing more than 6000
entries auto-generated by extracting reported material properties from
literature using a large language model. We then use this database to train a
machine learning model that can efficiently predict magnetocaloric properties
of materials based on their chemical composition. We further verify the
magnetocaloric properties of predicted compounds using ab initio atomistic spin
dynamics simulations to close the loop for computational material discovery.
Using this approach, we identify 11 new promising magnetocaloric materials for
the target temperature range. Our work demonstrates the potential of combining
large language models, machine learning, and ab initio simulations to
efficiently discover new functional materials.",2403.02553v1
2022/2/23,Ultra-Hot plasma of magnetic monopoles as fifth phase of matter: Bonding dissociation conditions of N-S magnetic in a hot plasma medium and superlattices of solids,"A magnetic atom has two magnetic poles of N and S, and in normal conditions,
separation of magnetic poles cannot be happened, even in very small atomic
dimensions. Existence of magnetic dipoles is due to a fundamental property of
magnetic materials and belongs to intrinsic spin of electrons. For the
electron, N and S magnetic poles are considered, similar to a current loop. The
aim of this paper is theoretical calculate dissociation energy of N-S poles a
quantum magnetic particle with two approaches of classical and quantum
mechanics by providing a harmonic oscillator simple model to estimate
dissociation energy of the N-S poles and corresponding breakdown temperature
and internal pressure. The results showed that separation of magnetic poles
occurs in two states: (a) in an ultra-hot plasma medium with extremely high
temperatures, such as in the center of a hot star, and (b) at extremely high
pressures, such as between internal plates in complex superlattices of layered
solids. It will be shown that breakdown temperature is in order of {\theta}
=107 to 108 Kelvin. This temperature is very high and it only happens in an
ultra-hot plasma environment as fifth phase of matter. In addition, based on
this model, we calculated that the possibility of dissociation of bonds between
N and S magnetic poles for solid superlattices occurs at very high pressures
between crystal plates. According to these results, the presence of isolated
magnetic monopole in superlattices of solids under ultra-high-pressure
conditions is possible. Therefore, this model suggests that the conductivity of
magnetic monopole carries can be used in the manipulation of nanomaterials for
applications in the production of advanced devices such as new generation of
superconductors, new spin devices and magnetic-electronics advanced materials
with magnetic monopoles and super-dielectrics.",2202.11494v1
2018/8/13,Magnetic noise from ultra-thin abrasively deposited materials on diamond,"Sensing techniques based on the negatively charged nitrogen-vacancy (NV)
centre in diamond have emerged as promising candidates to characterise
ultra-thin and 2D materials. An outstanding challenge to this goal is isolating
the contribution of 2D materials from undesired contributions arising from
surface contamination, and changes to the diamond surface induced by the sample
or transfer process. Here we report on such a scenario, in which the abrasive
deposition of trace amounts of materials onto a diamond gives rise to a
previously unreported source of magnetic noise. By deliberately scratching the
diamond surface with macroscopic blocks of various metals (Fe, Cu, Cr, Au), we
are able to form ultra-thin structures (i.e. with thicknesses down to
$<1$\,nm), and find that these structures give rise to a broadband source of
noise. Explanation for these effects are discussed, including spin and charge
noise native to the sample and/or induced by sample-surface interactions, and
indirect effects, where the deposited material affects the charge stability and
magnetic environment of the sensing layer. This work illustrates the high
sensitivity of NV noise spectroscopy to ultra-thin materials down to sub-nm
regimes -- a key step towards the study of 2D electronic systems -- and
highlights the need to passivate the diamond surface for future sensing
applications in ultra-thin and 2D materials.",1808.04085v1
2022/6/24,Surface induced electronic Berry curvature in Berry curvature free bulk materials,"In recent years it has become clear that electronic Berry curvature (BC) is a
key concept to understand and predict physical properties of crystalline
materials. A wealth of interesting Hall-type responses in charge, spin and heat
transport are caused by the BC associated to electronic bands inside a solid:
anomalous Hall effects in magnetic materials, and various nonlinear Hall and
Nernst effects in non-magnetic systems that lack inversion symmetry. However,
for the largest class of known materials -- non-magnetic ones with inversion
symmetry -- electronic BC is strictly zero. Here we show that precisely for
these bulk BC-free materials, a finite BC can emerge at their surfaces and
interfaces. This immediately activates certain surfaces in producing Hall-type
transport responses. We demonstrate this by first principles calculations of
the BC at bismuth, mercury-telluride (HgTe) and rhodium surfaces of various
symmetries, revealing the presence of a surface Berry curvature dipole and
associated quantum nonlinear Hall effects at a number of these. This opens up a
plethora of materials to explore and harness the physical effects emerging from
the electronic Berry curvature associated exclusively to their boundaries.",2206.12219v1
2014/10/7,Decoding Spatial Complexity in Strongly Correlated Electronic Systems,"Inside the metals, semiconductors, and magnets of our everyday experience,
electrons are uniformly distributed throughout the material. By contrast,
electrons often form clumpy patterns inside of strongly correlated electronic
systems (SCES) such as colossal magnetoresistance materials and high
temperature superconductors. In copper-oxide based high temperature
superconductors, scanning tunneling microscopy (STM) has detected an electron
nematic on the surface of the material, in which the electrons form nanoscale
structures which break the rotational symmetry of the host crystal. These
structures may hold the key to unlocking the mystery of high temperature
superconductivity in these materials, but only if the nematic also exists
throughout the entire bulk of the material. Using newly developed methods for
decoding these surface structures, we find that the nematic indeed persists
throughout the bulk of the material. We furthermore find that the intricate
pattern formation is set by a delicate balance among disorder, interactions,
and material anisotropy, leading to a fractal nature of the cluster pattern.
The methods we have developed can be extended to many other surface probes and
materials, enabling surface probes to determine whether surface structures are
confined only to the surface, or whether they extend throughout the material.",1410.1787v1
2018/5/14,Automated computation of materials properties,"Materials informatics offers a promising pathway towards rational materials
design, replacing the current trial-and-error approach and accelerating the
development of new functional materials. Through the use of sophisticated data
analysis techniques, underlying property trends can be identified, facilitating
the formulation of new design rules. Such methods require large sets of
consistently generated, programmatically accessible materials data.
Computational materials design frameworks using standardized parameter sets are
the ideal tools for producing such data. This work reviews the state-of-the-art
in computational materials design, with a focus on these automated
$\textit{ab-initio}$ frameworks. Features such as structural prototyping and
automated error correction that enable rapid generation of large datasets are
discussed, and the way in which integrated workflows can simplify the
calculation of complex properties, such as thermal conductivity and mechanical
stability, is demonstrated. The organization of large datasets composed of
$\textit{ab-initio}$ calculations, and the tools that render them
programmatically accessible for use in statistical learning applications, are
also described. Finally, recent advances in leveraging existing data to predict
novel functional materials, such as entropy stabilized ceramics, bulk metallic
glasses, thermoelectrics, superalloys, and magnets, are surveyed.",1805.05309v2
2022/4/18,Influence of the presence of multiple resonances on material parameter determination using broadband ferromagnetic resonance spectroscopy,"The influence of the presence of multiple resonances in ferromagnetic
resonance spectra on extracted material parameters is investigated using
numerical simulations. Our results show that the systematic error of assuming
an incorrect number of resonances for a material can lead to the extraction of
material parameters that significantly deviate from any of the true material
parameters. When noise is present in experimental ferromagnetic resonance
spectra increasing the frequency range of the broadband characterization can
significantly reduce the error-margins when the data is analyzed assuming the
correct number of resonances present in the material. For the cases
investigated in this study it was found that analyzing the data using a single
resonance results in extracted gyromagnetic ratios and effective magnetization
parameters that are consistent with the weighted average of the true material
parameters. We further provide a cautionary example regarding the extraction of
the inhomogeneous linewidth broadening and damping parameters of materials that
contain an unknown number of resonances.",2204.08500v1
2022/7/19,Machine learning approach to genome of two-dimensional materials with flat electronic bands,"Many-body physics of electron-electron correlations plays a central role in
condensed mater physics, it governs a wide range of phenomena, stretching from
superconductivity to magnetism, and is behind numerous technological
applications. To explore this rich interaction-driven physics, two-dimensional
(2D) materials with flat electronic bands provide a natural playground thanks
to their highly localised electrons. Currently, thousands of 2D materials with
computed electronic bands are available in open science databases, awaiting
such exploration. Here we used a new machine learning algorithm combining both
supervised and unsupervised machine intelligence to automate the otherwise
daunting task of materials search and classification, to build a genome of 2D
materials hosting flat electronic bands. To this end, a feedforward artificial
neural network was employed to identify 2D flat band materials, which were then
classified by a bilayer unsupervised learning algorithm. Such a hybrid approach
of exploring materials databases allowed us to reveal completely new material
classes outside the known flat band paradigms, offering new systems for
in-depth study on their electronic interactions.",2207.09444v2
2002/3/4,Ring current effects on the dielectric function of cylindrical nano-organic materials,"We review recent results on the behaviour of the dielectric function of
cylindrical nano-organic materials at very low frequencies in a magnetic field.
For cylindrical structures - such as carbon nanotubes - the polarisability is
shown to be a discontinuous function of a longitudinal magnetic field where
plateau-like regions are separated by sudden jumps or peaks. A relation is
pointed out between each discontinuity in the polarisability and the cross-over
between ground and first excited states induced by the magnetic field. This one
to one correspondence suggests to use measurements of the dielectric function
in an applied magnetic field in order to obtain informations about the
electronic structures of cylindrical nanostructures. In addition, it is shown,
by studying finite graphene layers, that the measurement of the polarisability
in a magnetic field could be a powerful way for detecting possible edge-states
in amorphous carbon materials such as activated carbon fibres. Finally, the
importance of the electron-electron interaction is emphasised by discussing
examples of strongly interacting electrons on rings or cylinders, in the limit
of infinite interaction.",0203057v1
2005/1/17,"Spin structure and magnetic frustration in multiferroic RMn2O5 (R = Tb, Ho, Dy)","We have studied the crystal and magnetic structures of the magnetoelectric
materials RMn2O5 (R = Tb, Ho, Dy) using neutron diffraction as a function of
temperature. All three materials display incommensurate antiferromagnetic
ordering below 40 K, becoming commensurate on further cooling. For R = Tb, Ho,
a commensurate-incommensurate transition takes place at low temperatures. The
commensurate magnetic structures have been solved and are discussed in terms of
competing exchange interactions. The spin configuration within the ab plane is
essentially the same for each system, and the radius of R determines the sign
of the magnetic exchange between adjacent planes. The inherent magnetic
frustration in these materials is lifted by a small lattice distortion,
primarily involving shifts of the Mn3+ cations and giving rise to a canted
antiferroelectric phase.",0501382v1
2008/6/5,Theory of spin current in chiral helimagnet,"We give detailed description of the transport spin current in the chiral
helimagnet. Under the static magnetic field applied perpendicular to the
helical axis, the magnetic kink crystal (chiral soliton lattice) is formed.
Once the kink crystal begins to move under the Galilean boost, the spin-density
accumulation occurs inside each kink and there emerges periodic arrays of the
induced magnetic dipoles carrying the transport spin current. The coherent
motion of the kink crystal dynamically generates the spontaneous
demagnetization field. This mechanism is analogous to the
D\""{o}ring-Becker-Kittel mechanism of the domain wall motion in ferromagnets.
To describe the kink crystal motion, we took account of not only the tangential
$\phi$-fluctuations but the longitudinal $\theta$-fluctuations around the
helimagnetic configuration. Based on the collective coordinate method and the
Dirac's canonical formulation for the singular Lagrangian system, we derived
the closed formulae for the mass, spin current and induced magnetic dipole
moment accompanied with the kink crystal motion. To materialize the theoretical
model presented here, symmetry-adapted material synthesis would be required,
where the interplay of crystallographic and magnetic chirality plays a key role
there.",0806.0968v2
2008/7/9,"Molecular Beam Epitaxy grown (Ga,Mn)(As,P) with perpendicular to plane magnetic easy axis","We present an experimental investigation of the magnetic, electrical and
structural properties of Ga0.94Mn0.06As1-yPy layers grown by molecular beam
epitaxy on GaAs substrates for y less than or equal to 0.3. X-ray diffraction
measurements reveal that the layers are under tensile strain which gives rise
to a magnetic easy axis perpendicular to the plane of the layers. The strength
of the magnetic anisotropy and the coercive field increase as the phosphorous
concentration is increased. The resistivity of all samples shows metallic
behaviour with the resistivity increasing as y increases. These materials will
be useful for studies of micromagnetic phenomena requiring metallic
ferromagnetic material with perpendicular magnetic anisotropy.",0807.1469v1
2009/4/6,Anisotropic Reinforcement of Nanocomposites Tuned by Magnetic Orientation of the Filler Network,"We present a new material which displays anisotropic and mechanical
properties tuneable during synthesis under magnetic field. It is formulated by
mixing aqueous suspensions of polymer nanolatex and magnetic nanoparticles,
coated by a thin silica layer to improve their compatibility with the polymeric
matrix, followed by casting. The magnetic properties of these nanoparticles
enable their pre-orientation in the resulting nanocomposite when cast under
magnetic field. Detailed insight on dispersion by Small Angle Neutron
Scattering (SANS) shows chainlike nanoparticle aggregates aligned by the field
on the nanometer scale. Applying strain to the nanocomposite parallel to the
particle chains shows higher mechanical reinforcement, than when strain is
transverse to field. . SANS from strained samples shows that strain parallel to
the field induce an organization of the chains while strain perpendicular to
the field destroys the chain field-induced ordering. Thus improved mechanical
reinforcement is obtained from anisotropic interconnection of nanoparticle
aggregates.",0904.0857v1
2009/5/12,"Reversible room-temperature magnetocaloric effect with large temperature span in antiperovskite compounds Ga1-xCMn3+x (x=0, 0.06, 0.07, and 0.08)","The magnetic and magnetocaloric properties of Ga1-xCMn3+x have been
investigated. Reversible magnetocaloric effect (MCE) occurs near the Curie
temperature TC. The magnetic entropy change decreases with increasing x, though
TC and magnetization increases. Meanwhile, the temperature span of vs. T plot
becomes well broadened with x. Due to the competition between the broadening
temperature span and decreasing, the relative cooling power (RCP) increases
initially, and then decreases with increasing x. The largest RCP (2.1 J/cm3,
under 45 kOe) observed when x=0.07 (TC = 296.5 K) is comparable to the
contemporary magnetic refrigerant materials. Considering the reversible MCE,
inexpensive and innoxious raw materials, our result suggests that Ga1-xCMn3+x
can be promising candidate for magnetic refrigeration around room temperature.",0905.1777v2
2009/10/12,Room-temperature ferromagnetism in graphite driven by 2D networks of point defects,"Ferromagnetism in carbon-based materials is appealing for both applications
and fundamental science purposes because carbon is a light and bio-compatible
material that contains only s and p electrons in contrast to traditional
ferromagnets based on 3d or 4f electrons. Here we demonstrate direct evidence
for ferromagnetic order locally at defect structures in highly oriented
pyrolytic graphite (HOPG) with magnetic force microscopy and in bulk
magnetization measurements at room temperature. Magnetic impurities have been
excluded as the origin of the magnetic signal after careful analysis supporting
an intrinsic magnetic behavior of carbon. The observed ferromagnetism has been
attributed to originate from unpaired electron spins localized at grain
boundaries of HOPG. Grain boundaries form two-dimensional arrays of point
defects, where their spacing depends on the mutual orientation of two grains.
Depending on the distance between these point defects, scanning tunneling
spectroscopy of grain boundaries showed two intense split localized states for
small distances between defects (< 4 nm) and one localized state at the Fermi
level for large distances between defects (> 4 nm).",0910.2130v1
2010/1/14,Ab initio study of magnetism at the TiO2/LaAlO3 interface,"In this paper we study the possible relation between the electronic and
magnetic structure of the TiO2/LaAlO3 interface and the unexpected magnetism
found in undoped TiO2 films grown on LaAlO$_3$. We concentrate on the role
played by structural relaxation and interfacial oxygen vacancies.
  LaAlO3 has a layered structure along the (001) direction with alternating LaO
and AlO2 planes, with nominal charges of +1 and -1, respectively. As a
consequence of that, an oxygen deficient TiO2 film with anatase structure will
grow preferently on the AlO2 surface layer. We have therefore performed
ab-initio calculations for superlattices with TiO2/AlO2 interfaces with
interfacial oxygen vacancies. Our main results are that vacancies lead to a
change in the valence state of neighbour Ti atoms but not necessarily to a
magnetic solution and that the appearance of magnetism depends also on
structural details, such as second neighbor positions. These results are
obtained using both the LSDA and LSDA+U approximations.",1001.2531v1
2010/10/1,Understanding complex magnetic order in disordered cobalt hydroxides through analysis of the local structure,"In many ostensibly crystalline materials, unit-cell-based descriptions do not
always capture the complete physics of the system due to disruption in
long-range order. In the series of cobalt hydroxides studied here,
Co(OH)$_{2-x}$(Cl)$_x$(H$_2$O)$_{n}$, magnetic Bragg diffraction reveals a
fully compensated N\'eel state, yet the materials show significant and open
magnetization loops. A detailed analysis of the local structure defines the
aperiodic arrangement of cobalt coordination polyhedra. Representation of the
structure as a combination of distinct polyhedral motifs explains the existence
of locally uncompensated moments and provides a quantitative agreement with
bulk magnetic measurements and magnetic Bragg diffraction.",1010.0230v5
2010/12/15,Complex magnetic behavior and high spin polarization in Fe(3-x)Mn(x)Si alloys,"Fe3Si is a ferromagnetic material with possible applications in magnetic
tunnel junctions. When doped with Mn, the material shows a complex magnetic
behavior, as suggested by older experiments. We employed the
Korringa-Kohn-Rostoker (KKR) Green function method within density-functional
theory (DFT) in order to study the alloy Fe(3-x)Mn(x)Si, with 0 < x < 1.
Chemical disorder is described within the coherent potential approximation
(CPA). In agreement with experiment, we find that the Mn atoms align
ferromagnetically to the Fe atoms, and that the magnetization and Curie
temperature drop with increasing Mn-concentration $x$. The calculated spin
polarization P at the Fermi level varies strongly with x, from P=-0.3 at x=0
(ordered Fe3Si) through P=0 at x=0.28, to P=+1 for x>0.75; i.e., at high Mn
concentrations the system is half-metallic. We discuss the origin of the trends
of magnetic moments, exchange interactions, Curie temperature and the spin
polarization.",1012.3463v1
2012/7/12,Linear Magnetoelectric Effect by Orbital Magnetism,"We use symmetry analysis and first principles calculations to show that the
linear magnetoelectric effect can originate from the response of orbital
magnetic moments to the polar distortions induced by an applied electric field.
Using LiFePO4 as a model compound we show that spin-orbit coupling partially
lifts the quenching of the 3d orbitals and causes small orbital magnetic
moments ($\mu_{(L)}\approx 0.3 \mu_B$) parallel to the spins of the Fe$^{2+}$
ions. An applied electric field $\mathbf{E}$ modifies the size of these orbital
magnetic moments inducing a net magnetization linear in $\mathbf{E}$.",1207.2916v2
2012/12/12,Magnetic cryocooling with Gd3+ centers in a light and compact framework,"The magnetocaloric effect of gadolinium formate, Gd(OOCH)3, is experimentally
determined down to sub-Kelvin temperatures by direct and indirect methods. This
3D metal-organic framework material is characterized by a relatively compact
crystal lattice of weakly interacting Gd3+ spin centers interconnected via
light formate ligands, overall providing a remarkably large
magnetic:non-magnetic elemental weight ratio. The resulting volumetric magnetic
entropy change is decidedly superior in Gd(OOCH)3 than in the best known
magnetic refrigerant materials for liquid-helium temperatures and low-moderate
applied fields.",1212.2877v1
2013/6/26,Magnetic monopole polarons in spin ice with mixed coordination numbers,"Emergent quasiparticles that arise from the fractionalization of the
microscopic degrees of freedom have been one of the central themes in modern
condensed matter physics. The notion of magnetic monopoles, freely moving
quasiparticles fragmented from local dipole excitations, has enjoyed much
success in understanding the thermodynamic, static, and transport properties of
the so-called spin-ice materials. The artificial version of spin ice, where a
lattice of nanoscale magnetic dipoles is sculpted out of a ferromagnetic film,
provides a unique opportunity to study these unusual quasiparticles in a
material-by-design approach. Here we show that the elementary excitations in
the ice phase of a nano-magnetic array arranged in the pentagonal lattice are
composite objects comprised of the emergent monopole and a surrounding cloud of
opposite uncompensated magnetic charges.",1306.6154v1
2013/8/23,Tuning plasmonic cloaks with an external magnetic field,"We propose a mechanism to actively tune the operation of plasmonic cloaks
with an external magnetic field by investigating electromagnetic scattering by
a dielectric cylinder coated with a magneto-optical shell. In the long
wavelength limit we show that the presence of an external magnetic field may
drastically reduce the scattering cross-section at all observation angles. We
demonstrate that the application of external magnetic fields can modify the
operation wavelength without the need of changing material and/or geometrical
parameters. We also show that applied magnetic fields can reversibly switch on
and off the cloak operation. These results, which could be achieved for
existing magneto-optical materials, are shown to be robust to material losses,
so that they may pave the way for developing actively tunable, versatile
plasmonic cloaks.",1308.5022v2
2013/10/5,Engineered spin-valve type magnetoresistance in Fe$_3$O$_4$-CoFe$_2$O$_4$ core-shell nanoparticles,"Naturally occurring spin-valve-type magnetoresistance (SVMR), recently
observed in Sr2FeMoO6 samples, suggests the possibility of decoupling the
maximal resistance from the coercivity of the sample. Here we present the
evidence that SVMR can be engineered in specifically designed and fabricated
core-shell nanoparticle systems, realized here in terms of soft magnetic Fe3O4
as the core and hard magnetic insulator CoFe2O4 as the shell materials. We show
that this provides a magnetically switchable tunnel barrier that controls the
magnetoresistance of the system, instead of the magnetic properties of the
magnetic grain material, Fe3O4, and thus establishing the feasibility of
engineered SVMR structures.",1310.1469v1
2014/3/21,Colloidal Assemblies of Oriented Maghemite Nanocrystals and their NMR Relaxometric Properties,"Elevated-temperature polyol-based colloidal-chemistry approach allows for the
development of size-tunable (50 and 86 nm) assemblies of maghemite iso-oriented
nanocrystals, with enhanced magnetization. 1H-Nuclear Magnetic Resonance (NMR)
relaxometric experiments show that the ferrimagnetic cluster-like colloidal
entities exhibit a remarkable enhancement (4 to 5 times) in the transverse
relaxivity, if compared to that of the superparamagnetic contrast agent
Endorem, over an extended frequency range (1-60 MHz). The marked increase of
the transverse relaxivity r2 at a clinical magnetic field strength (1.41 T),
which is 405.1 and 508.3 mM-1 s-1 for small and large assemblies respectively,
allows to relate the observed response to the raised intra-aggregate magnetic
material volume fraction. Furthermore, cell tests with murine fibroblast
culture medium confirmed the cell viability in presence of the clusters. We
discuss the NMR dispersion profiles on the basis of relaxivity models to
highlight the magneto-structural characteristics of the materials for improved
T2-weighted magnetic resonance images.",1403.5450v1
2014/6/30,Quantum Kagome Ice,"Actively shought since the turn of the century, two-dimensional quantum spin
liquids (QSLs) are exotic phases of matter where magnetic moments remain
disordered even at extremely low temperatures. Despite ongoing searches, QSLs
remain elusive, due to a lack of concrete knowledge of the microscopic
mechanisms that inhibit magnetic order in real materials. Here, we study a
theoretical model for a broad class of frustrated magnetic rare-earth
pyrochlore materials called ""quantum spin ices"". When subject to an external
magnetic field along the [111] crystallographic direction, the resulting spin
interactions contain a mix of geometric frustration and quantum fluctuations in
decoupled two-dimensional kagome planes. Using large-scale quantum Monte Carlo
simulations, we identify a simple set of interactions sufficient to promote a
groundstate with no magnetic long-range order, and a gap to excitations,
consistent with a $Z_2$ spin liquid phase. This suggests a systematic
experimental procedure to search for two-dimensional QSLs within the broader
class of three-dimensional pyrochlore quantum spin ice materials.",1407.0037v1
2014/7/18,Magnetism and Superconductivity in Iron-based Superconductors Decided by Condensed Particle-hole Excitations away from the Fermi Level,"The origin of magnetism and superconductivity in iron-based superconductors
is still unclear. Here, by investigating the momentum-dependent particle-hole
excitations which quantify the tendency of itinerant electrons towards various
magnetic states or superconducting phases, we unravel a novel origin to account
for the variety of physical properties of iron-based compounds. We show that
condensation of particle-hole excitations away from the Fermi surface in
momentum space is the underlying mechanism in deciding the magnetic and
superconducting properties of iron-based materials. The applicability of this
scenario to the whole family of iron-based superconductors suggests that
inclusion of the orbital degrees of freedom, which may lead to competing
tendencies towards different magnetically ordered states, is more crucial than
taking into account the strong correlations. Our findings further indicate that
in order to properly model these materials, the electronic states away from the
Fermi level have to be considered.",1407.4888v1
2014/7/30,Synthetic magnetoelectric coupling in a nanocomposite multiferroic,"Given the paucity of single phase multiferroic materials (with large
ferromagnetic moment), composite systems seem an attractive solution in the
quest to realize magnetoelectric cou-pling between ferromagnetic and
ferroelectric order parameters. Despite having antiferro-magnetic order, BiFeO3
(BFO) has nevertheless been a key material in this quest due to excel-lent
ferroelectric properties at room temperature. We studied a superlattice
composed of 8 repetitions of 6 unit cells of La0.7Sr0.3MnO3 (LSMO) grown on 5
unit cells of BFO. Significant net uncompensated magnetization in BFO is
demonstrated using polarized neutron reflectometry in an insulating
superlattice. Remarkably, the magnetization enables magnetic field to change
the dielectric properties of the superlattice, which we cite as an example of
synthetic magnetoelectric coupling. Importantly, this controlled creation of
magnetic moment in BFO suggests a much needed path forward for the design and
implementation of integrated oxide devices for next generation magnetoelectric
data storage platforms.",1407.8157v2
2014/12/26,Observation of Devil's Staircase in the Novel Spin Valve System SrCo$_6$O$_{11}$,"Using resonant soft x-ray scattering as a function of both temperature and
magnetic field, we reveal a large number of almost degenerate magnetic orders
in SrCo6O11. The Ising-like spins in this frustrated material in fact exhibit a
so-called magnetic devil's staircase. It is demonstrated how a magnetic field
induces transitions between different microscopic spin configurations, which is
responsible for the magnetoresistance of SrCo6O11. This material therefore
constitutes a unique combination of a magnetic devil's staircase and spin valve
effects, yielding a novel type of magnetoresistance system.",1412.7945v1
2015/4/13,Evidence for In-Plane Tetragonal c-axis in Mn$_x$Ga$_{1-x}$ Thin Films using Transmission Electron Microscopy,"Tetragonal Mn$_x$Ga$_{1-x}$ (x=0.70, 0.75) thin films grown on SrTiO$_3$
substrates at different temperatures and thicknesses exhibit perpendicular
magnetic anisotropy with coercive fields between 1-2 T. Transmission electron
microscopy (TEM) and X-ray diffraction (XRD) reveal that 40nm samples grown at
300-350$^{o}$C lead to polycrystalline films with the tetragonal c-axis
oriented primarily perpendicular to the film plane but with some fraction of
the sample exhibiting the c-axis in the film plane. This structure results in a
secondary magnetic component in the out of plane magnetization. Growth at
300$^{o}$C with a reduced thickness or Mn concentration significantly decreases
the presence of the tetragonal c-axis in the film plane, thus improving the
magnetic properties. TEM is of critical importance in characterizing these
materials, since conventional XRD cannot always identify the presence of
additional crystallographic orientations although they can still affect the
magnetic properties. Our study points to ways that the microstructure of these
thin films can be controlled, which is critical for utilization of this
material in spintronic devices.",1504.03085v1
2015/8/12,Ferroelectricity driven magnetism at domain walls in LaAlO$_3$/PbTiO$_3$ superlattices,"Charge dipole moment and spin moment rarely coexist in single-phase bulk
materials except in some multiferroics. Despite the progress in the past
decade, for most multiferroics their magnetoelectric performance remains poor
due to the intrinsic exclusion between charge dipole and spin moment. As an
alternative approach, the oxide heterostructures may evade the intrinsic limits
in bulk materials and provide more attractive potential to realize the
magnetoelectric functions. Here we perform a first-principles study on
LaAlO$_3$/PbTiO$_3$ superlattices. Although neither of the components is
magnetic, magnetic moments emerge at the ferroelectric domain walls of
PbTiO$_3$ in these superlattices. Such a twist between ferroelectric domain and
local magnetic moment, not only manifests an interesting type of
multiferroicity, but also is possible useful to pursuit the electrical-control
of magnetism in nanoscale heterostructures.",1508.02889v1
2015/9/14,Optimization of vortex pinning by nanoparticles using simulations of time-dependent Ginzburg-Landau model,"Introducing nanoparticles into superconducting materials has emerged as an
efficient route to enhance their current-carrying capability. We address the
problem of optimizing vortex pinning landscape for randomly distributed
metallic spherical inclusions using large-scale numerical simulations of
time-dependent Ginzburg-Landau equations. We found the size and density of
particles for which the highest critical current is realized in a fixed
magnetic field. For each particle size and magnetic field, the critical current
reaches a maximum value at a certain particle density, which typically
corresponds to 15-23% of the total volume being replaced by nonsuperconducting
material. For fixed diameter, this optimal particle density increases with the
magnetic field. Moreover, we found that the optimal particle diameter slowly
decreases with the magnetic field from 4.5 to 2.5 coherence lengths at a given
temperature. This result shows that pinning landscapes have to be designed for
specific applications taking into account relevant magnetic field scales.",1509.04212v2
2016/4/21,Electronic and magnetic properties of single-layer MPX$_3$ metal phosphorous trichalcogenides,"We systematically investigate the electronic structure and magnetic
properties of two dimensional (2D) MPX$_3$ (M= V, Cr, Mn, Fe, Co, Ni, Cu, Zn,
and X = S, Se, Te) transition metal chacogenophosphates to examine their
potential role as single-layer van der Waals materials that exhibit magnetic
order. Our {\em ab initio} calculations predict that most of these single-layer
materials are antiferromagnetic semiconductors. The band gaps of the
antiferromagnetic states decrease as the atomic number of the chalcogen atom
increases (from S to Se, Te), leading in some cases to half-metallic
ferromagnetic states or to non-magnetic metallic states. We find that the phase
transition from antiferromagnetic semiconductor to ferromagnetic half-metal can
be controlled by gating or by strain engineering. The sensitive interdependence
we find between magnetic, structural, and electronic properties establishes the
potential of this 2D materials class for applications in spintronics.",1604.06445v2
2016/11/8,Effect of Mg-Al insertion on magnetotransport properties in epitaxial Fe/sputter-deposited $MgAl_{2}O_{4}$/Fe(001) magnetic tunnel junctions,"We investigated the effect of a Mg-Al layer insertion at the bottom interface
of epitaxial Fe/$MgAl_{2}O_{4}$/Fe(001) magnetic tunnel junctions (MTJs) on
their spin-dependent transport properties. The tunnel magnetoresistance (TMR)
ratio and differential conductance spectra for the parallel magnetic
configuration exhibited clear dependence on the inserted Mg-Al thickness. A
slight Mg-Al insertion (thickness < 0.1 nm) was effective for obtaining a large
TMR ratio above 200% at room temperature and observing a distinct local minimum
structure in conductance spectra. In contrast, thicker Mg-Al (> 0.2 nm) induced
a reduction of TMR ratios and featureless conductance spectra, indicating a
degradation of the bottom-Fe/$MgAl_{2}O_{4}$ interface. Therefore, a minimal
Mg-Al insertion was found to be effective to maximize the TMR ratio for a
sputtered $MgAl_{2}O_{4}$-based MTJ.",1611.02399v1
2016/11/24,Optically switched magnetism in photovoltaic perovskite CH$_3$NH$_3$(Mn:Pb)I$_3$,"The demand for ever-increasing density of information storage and speed of
manipulation boosts an intense search for new magnetic materials and novel ways
of controlling the magnetic bit. Here, we report the synthesis of a
ferromagnetic photovoltaic CH$_3$NH$_3$(Mn:Pb)I$_3$ material in which the
photo-excited electrons rapidly melt the local magnetic order through the
Ruderman-Kittel-Kasuya-Yosida interactions without heating up the spin system.
Our finding offers an alternative, very simple and efficient way of optical
spin control, and opens an avenue for applications in low power, light
controlling magnetic devices.",1611.08205v1
2017/5/25,Spin-wave spectroscopy on Dzyaloshinskii-Moriya interaction in room-temperature chiral magnets hosting skyrmions,"Propagation character of spin wave was investigated for chiral magnets FeGe
and Co-Zn-Mn alloys, which can host magnetic skyrmions near room temperature.
On the basis of the frequency shift between counter-propagating spin waves, the
magnitude and sign of Dzyaloshinskii-Moriya (DM) interaction were directly
evaluated. The obtained magnetic parameters quantitatively account for the size
and helicity of skyrmions as well as their materials variation, proving that
the DM interaction plays a decisive role in the skyrmion formation in this
class of room-temperature chiral magnets. The propagating spin-wave
spectroscopy can thus be an efficient tool to study DM interaction in bulk
single-phase compounds. Our results also demonstrate a function of spin-wave
diode based on chiral crystal structures at room temperature.",1705.09001v1
2017/8/2,Realistic finite temperature simulations of magnetic systems using quantum statistics,"We have performed realistic atomistic simulations at finite temperatures
using Monte Carlo and atomistic spin dynamics simulations incorporating quantum
(Bose-Einstein) statistics. The description is much improved at low
temperatures compared to classical (Boltzmann) statistics normally used in
these kind of simulations, while at higher temperatures the classical
statistics are recovered. This corrected low-temperature description is
reflected in both magnetization and the magnetic specific heat, the latter
allowing for improved modeling of the magnetic contribution to free energies. A
central property in the method is the magnon density of states at finite
temperatures and we have compared several different implementations for
obtaining it. The method has no restrictions regarding chemical and magnetic
order of the considered materials. This is demonstrated by applying the method
to elemental ferromagnetic systems, including Fe and Ni, as well as Fe-Co
random alloys and the ferrimagnetic system GdFe$_3$ .",1708.00709v1
2017/11/19,Ferroelectric Ferrimagnetic LiFe$_2$F$_6$: Charge Ordering Mediated Magnetoelectricity,"Trirutile-type LiFe$_2$F$_6$ is a charge-ordered material with
Fe$^{2+}$/Fe$^{3+}$ configuration. Here its physical properties, including
magnetism, electronic structure, phase transition, and charge ordering, are
studied theoretically. On one hand, the charge ordering leads to improper
ferroelectricity with a large polarization. On the other hand, its magnetic
ground state can be tuned from the antiferromagnetic to ferrimagnetic by
moderate compressive strain. Thus, LiFe$_2$F$_6$ can be a rare multiferroic
with both large magnetization and polarization. Most importantly, since the
charge ordering is the common ingredient for both ferroelectricity and
magnetization, the net magnetization may be fully switched by flipping the
polarization, rendering intrinsically strong magnetoelectric effect and
desirable function.",1711.06981v2
2017/11/21,Coupling magneto-elastic Lagrangians to spin transfer torque sources,"The consequences of coupling magnetic and elastic degrees of freedom, where
spins and deformations are carried by point-like objects subject to local
interactions, are studied, theoretically and by detailed numerical simulations.
From the constrained Lagrangians we derive consistent equations of motion for
the coupled dynamical variables. In order to probe the dynamics of such a
system, we consider external perturbations, such as spin transfer torques for
the magnetic part, and homogeneous stresses for the elastic part, associated to
their corresponding damping. This approach is applied to the study of ultrafast
switching processes in anti-ferromagnetic systems, which have recently
attracted attention as candidates for anti-ferromagnetic spintronic devices.
Our strategy is then checked in simple, but instructive, situations. We carried
out numerical experiments to study, in particular, how the magnetostrictive
coupling and external stresses affect the nature of the switching processes in
a prototype anti-ferromagnetic material.",1711.08062v2
2018/4/23,Probing condensed matter physics with magnetometry based on nitrogen-vacancy centres in diamond,"The magnetic fields generated by spins and currents provide a unique window
into the physics of correlated-electron materials and devices. Proposed only a
decade ago, magnetometry based on the electron spin of nitrogen-vacancy (NV)
defects in diamond is emerging as a platform that is excellently suited for
probing condensed matter systems: it can be operated from cryogenic
temperatures to above room temperature, has a dynamic range spanning from DC to
GHz, and allows sensor-sample distances as small as a few nanometres. As such,
NV magnetometry provides access to static and dynamic magnetic and electronic
phenomena with nanoscale spatial resolution. Pioneering work focused on
proof-of-principle demonstrations of its nanoscale imaging resolution and
magnetic field sensitivity. Now, experiments are starting to probe the
correlated-electron physics of magnets and superconductors and to explore the
current distributions in low-dimensional materials. In this Review, we discuss
the application of NV magnetometry to the exploration of condensed matter
physics, focusing on its use to study static and dynamic magnetic textures, and
static and dynamic current distributions.",1804.08742v1
2018/6/7,On the magnetic and electronic properties of NpPdSn,"We have studied NpPdSn by means of the heat capacity, electrical resistivity,
Seebeck and Hall effect, $^{237}$Np M\""{o}ssbauer spectroscopy, and neutron
diffraction measurements in the temperature range 2-300 K and under magnetic
fields up to 14 T. NpPdSn orders antiferromagnetically below the N\'eel
temperature $T_N$ = 19 K and shows localized magnetism of Np$^{3+}$ ion with a
a doubly degenerate ground state. In the magnetic state the electrical
resistivity and heat capacity are characterized by electron-magnon scattering
with spin-waves spectrum typical of anisotropic antiferromagnets. An enhanced
Sommerfeld coefficient and typical behavior of magnetorestistivity, Seebeck and
Hall coefficients are all characteristic of systems with strong electronic
correlations. The low temperature antiferromagnetic state of NpPdSn is verified
by neutron diffraction and $^{237}$Np M\""{o}ssbauer spectroscopy and possible
magnetic structures are discussed.",1806.02879v1
2018/7/10,Mass diffusion and liner material effect in a MagLIF fusion-like plasma,"In this paper, liner - fuel mass diffusion and the effect of the liner
material on mass ablation, energy and magnetic flux losses are studied in a
MagLIF fusion-like plasma. The analysis performed in [Garc\'ia-Rubio and Sanz,
Phys. Plasmas 24, 072710 (2017)] is extended to liner materials of an arbitrary
atomic number. The liner ablates and penetrates into the hot spot, compressing
and cooling down the fuel. The magnetic flux in the fuel is lost by Nernst
convection through the ablated liner - fuel interface, called ablated border.
Increasing the liner atomic number leads to a reduction of both energy and
magnetic flux losses in the fuel for a small and moderate magnetization values.
Mass diffusion is confined within a thin layer at the ablated border.
Concentration gradient and baro-diffusion are the predominant mechanisms
leading to liner - fuel mixing. The width of the diffusion layer may be
comparable to the turbulent mixing layer resulting from the Rayleigh-Taylor
instability at the ablated border. An asymptotic analysis performed for large
liner atomic number Z_{2} shows that mass ablation, energy and magnetic flux
losses and liner - fuel mass diffusion scale as 1/\sqrt{Z_{2}}.",1807.03560v1
2012/11/7,Magnetocapacitance without magnetism,"A substantial magnetodielectric effect is often an indication of coupled
magnetic and elastic order, such as is found in the multiferroics. However, it
has recently been shown that magnetism is not necessary to produce either a
magnetoresistance or a magnetocapacitance when the material is inhomogeneous
[M. M. Parish and P. B. Littlewood, Phys. Rev. Lett. 101, 166602 (2008)]. Here,
we will investigate the characteristic magnetic-field-dependent dielectric
response of such an inhomogeneous system using exact calculations and numerical
simulations of conductor-dielectric composites. In particular, we will show
that even simple conductor-dielectric layers exhibit a magnetocapacitance, and
thus random bulk inhomogeneities are not a requirement for this effect. Indeed,
this work essentially provides a natural generalisation of the Maxwell-Wagner
effect to finite magnetic field. We will also discuss how this phenomenon has
already been observed experimentally in some materials.",1211.1583v1
2019/1/3,Realization of Kondo chain in CeCo$_2$Ga$_8$,"We revisited the anisotropy of the heavy-fermion material CeCo$_2$Ga$_8$ by
measuring the electrical resistivity and magnetic susceptibility along all the
principal $\mathbf{a}$-, $\mathbf{b}$- and $\mathbf{c}$-axes. Resistivity along
$\mathbf{c}$-axis ($\rho_c$) shows clear Kondo coherence below about 17 K,
while both $\rho_{a}$ and $\rho_{b}$ remain incoherent down to 2 K. The
magnetic anisotropy is well understood within the theoretical frame of
crystalline electric field effect in combination with magnetic exchange
interactions. We found the anisotropy ratio of these magnetic exchange
interactions, $|J_{ex}^c/J_{ex}^{a,b}|$, reaches a large value of 4-5. We,
therefore, firmly demonstrate that CeCo$_2$Ga$_8$ is a quasi-one-dimensional
heavy-fermion compound both electrically and magnetically, and thus provide a
realistic example of \textit{Kondo chain}.",1901.00558v2
2019/1/31,Boundary conditions at the interface of finite thickness between ferromagnetic and antiferromagnetic materials,"Systematic approach has been applied to obtain the boundary conditions for
magnetization at an interface between ferromagnetic (FM) and antiferromagnetic
(AFM) materials in the continuous medium approximation. Three order parameters
are considered inside an interface of finite thickness magnetization
$\mathbf{\text{M}}$ of FM, magnetizations of both sublattices
$\mathbf{\text{M}}_{1}$ and $\mathbf{\text{M}}_{2}$ of AFM. The boundary
conditions are defined in terms of some average properties of the FM/AFM
interface. The interface has a finite thickness which is much less than spin
wave length. This approach allowed to take into account the interface
anisotropy, interface symmetric exchange coupling and interface coupling
resulting from inversion symmetry breaking in the vicinity of the interface.",1901.11470v1
2016/8/9,"NaSrMn2F7, NaCaFe2F7, and NaSrFe2F7: novel single crystal pyrochlore antiferromagnets","The crystal structures and magnetic properties of three previously unreported
A2B2F7 pyrochlore materials, NaSrMn2F7, NaCaFe2F7, and NaSrFe2F7 are presented.
In these compounds, either S=2 Fe2+ or S=5/2 Mn2+ is on the B site, while
nonmagnetic Na and Ca (Na and Sr) are disordered on the A site. The materials,
which were grown as crystals via the floating zone method, display high
effective magnetic moments and large Curie-Weiss thetas. Despite these
characteristics, freezing of the magnetic spins, characterized by peaks in the
susceptibility or specific heat, is not observed until low temperatures. The
empirical frustration index, f=- {\theta}cw/Tf, for the materials are 36
(NaSrMn2F7), 27 (NaSrFe2F7), and 19 (NaCaFe2F7). AC susceptibility, DC
susceptibility, and heat capacity measurements are used to characterize the
observed spin glass behavior. The results suggest that the compounds are
frustrated pyrochlore antiferromagnets with weak bond disorder. The magnetic
phenomena that these fluoride pyrochlores exhibit, in addition to their
availability as relatively large single crystals, make them promising
candidates for the study of geometric magnetic frustration.",1608.02907v1
2016/3/2,Blocking temperature of interacting magnetic nanoparticles with uniaxial and cubic anisotropies from Monte Carlo simulations,"The low temperature behavior of densely packed interacting spherical single
domain nanoparticles (MNP) is investigated by Monte Carlo simulations in the
framework of an effective one spin model. The particles are distributed through
a hard sphere like distribution with periodic boundary conditions and interact
through the dipole dipole interaction (DDI) with an anisotropy energy including
both cubic and uniaxial symmetry components. The cubic component is shown to
play a sizable role on the value of the blocking temperature $T_b$ only when
the MNP easy axes are parallel to the cubic easy direction ([111] direction for
a negative cubic anisotropy constant). The nature of the collective low
temperature state, either ferromagnetic or spin glass like, is found to depend
on the ratio of the anisotropy to the dipolar energies characterizing partly
the disorder in the system.",1603.00605v1
2016/3/2,"Magnetic transitions in the topological magnon insulator Cu(1,3-bdc)","Topological magnon insulators are a new class of magnetic materials that
possess topologically nontrivial magnon bands. As a result, magnons in these
materials display properties analogous to those of electrons in topological
insulators. Here, we present magnetization, specific heat, and neutron
scattering measurements of the ferromagnetic kagome magnet Cu(1,3-bdc). Our
measurements provide a detailed description of the magnetic structure and
interactions in this material, and confirm that it is an ideal prototype for
topological magnon physics in a system with a simple spin Hamiltonian.",1603.00901v2
2016/3/11,Atomic-scale control of magnetic anisotropy via novel spin-orbit coupling effect in La2/3Sr1/3MnO3/SrIrO3 superlattices,"Magnetic anisotropy (MA) is one of the most important material properties for
modern spintronic devices. Conventional manipulation of the intrinsic MA, i.e.
magnetocrystalline anisotropy (MCA), typically depends upon crystal symmetry.
Extrinsic control over the MA is usually achieved by introducing shape
anisotropy or exchange bias from another magnetically ordered material. Here we
demonstrate a pathway to manipulate MA of 3d transition metal oxides (TMOs) by
digitally inserting non-magnetic 5d TMOs with pronounced spin-orbit coupling
(SOC). High quality superlattices comprised of ferromagnetic La2/3Sr1/3MnO3
(LSMO) and paramagnetic SrIrO3 (SIO) are synthesized with the precise control
of thickness at atomic scale. Magnetic easy axis reorientation is observed by
controlling the dimensionality of SIO, mediated through the emergence of a
novel spin-orbit state within the nominally paramagnetic SIO.",1603.03794v2
2016/3/18,A Comparison between Abraham and Minkowski Momenta,"In this paper I compare the Abraham and the Minkowski forms for the momentum
pertaining to an electromagnetic wave inside a dielectric or a magnetic
material. The discussion is based on a careful treatment of the surface charges
and currents and of the forces acting on them. While in the dielectric case the
Abraham momentum is certainly more appealing from the physical point of view,
for a magnetic material it suggests an interpretation in terms of magnetic
charges and re- lated magnetic currents. The Minkowski momentum for magnetic
non conducting materials, on the contrary, has a natural interpretation in
terms of an amperian model, in which the dynamics is determined by the Lorentz
force acting on bulk and surface electric currents.",1603.05812v1
2017/3/9,Pseudomagnetic lens as a valley and chirality splitter in Dirac and Weyl materials,"It is proposed that strain-induced pseudomagnetic fields in Dirac and Weyl
materials could be used as valley and chirality sensitive lenses for beams of
Weyl quasiparticles. The study of the (pseudo-)magnetic lenses is performed by
using the eikonal approximation for describing the Weyl quasiparticles
propagation in magnetic and strain-induced pseudomagnetic fields. Analytical
expressions for the locations of the principal foci and the focal lengths are
obtained in the paraxial approximation in the models with uniform as well as
nonuniform effective magnetic fields inside the lens. The results show that the
left- and right-handed quasiparticles can be focused at different spatial
locations when both magnetic and pseudomagnetic fields are applied. It is
suggested that the use of magnetic and pseudomagnetic lenses could open new
ways of producing and manipulating beams of chiral Weyl quasiparticles.",1703.03415v2
2017/3/12,Quantum Hall effect in a bulk antiferromagnet EuMnBi$_2$ with magnetically confined two-dimensional Dirac fermions,"For the innovation of spintronic technologies, Dirac materials, in which the
low-energy excitation is described as relativistic Dirac fermions, are one of
the most promising systems, because of the fascinating magnetotransport
associated with the extremely high mobility. To incorporate Dirac fermions into
spintronic applications, their quantum transport phenomena are desired to be
manipulated to a large extent by magnetic order in a solid. We here report a
bulk half-integer quantum Hall effect in a layered antiferromagnet EuMnBi$_2$,
in which field-controllable Eu magnetic order significantly suppresses the
interlayer coupling between the Bi layers with Dirac fermions. In addition to
the high mobility more than 10,000 cm$^2$/Vs, Landau level splittings
presumably due to the lifting of spin and valley degeneracy are noticeable even
in a bulk magnet. These results will pave a route to the engineering of
magnetically functionalized Dirac materials.",1703.04127v1
2017/3/15,Model-Free Based Digital Control for Magnetic Measurements,"This paper presents a novel digital control strategy successfully implemented
for a soft magnetic material characterization bench (Epstein frame type). The
main objective is to control the magnetic induction waveform whatever the
applied excitation and the material under study. Given the nonlinear nature of
the magnetization curves of magnetic materials, an original model-free based
control technique is considered. Special mention should be made of the
interesting dynamic properties in closed-loop against the changes of the
operating point related basically to the hysteresis form. The operation and the
performances of the digital control method are illustrated in different working
conditions through both simulation and experimental measurements.",1703.05395v1
2018/9/11,On the saw-tooth torque in anisotropic $j_{\rm eff} = 1/2$ magnets: Application to $α$-RuCl$_3$,"The so-called ""Kitaev candidate"" materials based on $4d^5$ and $5d^5$ metals
have recently emerged as magnetic systems displaying strongly anisotropic
exchange interactions reminiscent of the Kitaev's honeycomb model. Recently,
these materials have been shown to commonly display a distinct saw-tooth
angular dependence of the magnetic torque over a wide range of magnetic fields.
While higher order chiral spin interactions have been considered as a source of
this observation, we show here that bilinear anisotropic interactions and/or
$g$-anisotropy are each sufficient to explain the observed torque response,
which may be distinguished on the basis of high-field measurements. These
findings unify the understanding of magnetic torque experiments in a variety of
Kitaev candidate materials.",1809.03943v3
2021/5/17,Eminuscent phase in frustrated magnets: a challenge to quantum spin liquids,"A geometrically frustrated (GF) magnet consists of localised magnetic
moments, spins, whose orientation cannot be arranged to simultaneously minimise
their interaction energies. Such materials may host novel fascinating phases of
matter, such as fluid-like states called quantum spin liquids. GF magnets have,
like all solid-state systems, randomly located impurities whose magnetic
moments may ``freeze'' at low temperatures, making the system enter a
spin-glass state. We analyse the available data for spin-glass transitions in
GF materials and find a surprising trend: the glass-transition temperature
grows with decreasing impurity concentration and reaches a finite value in the
impurity-free limit at a previously unidentified, ``hidden'', energy scale. We
propose a scenario in which the interplay of interactions and entropy leads to
a crossover in the permeability of the medium that assists glass freezing at
low temperatures. This low-temperature, ``eminuscent'', phase may obscure or
even destroy the widely-sought spin-liquid states in rather clean systems.",2105.08070v4
2013/11/6,Magnetization dynamics of cobalt grown on graphene,"Ferromagnetic resonance (FMR) spin pumping is a rapidly growing field which
has demonstrated promising results in a variety of material systems. This
technique utilizes the resonant precession of magnetization in a ferromagnet to
inject spin into an adjacent non-magnetic material. Spin pumping into graphene
is attractive on account of its exceptional spin transport properties. This
article reports on FMR characterization of cobalt grown on CVD graphene and
examines the validity of linewidth broadening as an indicator of spin pumping.
In comparison to cobalt samples without graphene, direct contact
cobalt-on-graphene exhibits increased FMR linewidth--an often used signature of
spin pumping. Similar results are obtained in Co/MgO/graphene structures, where
a 1nm MgO layer acts as a tunnel barrier. However, SQUID, MFM, and Kerr
microscopy measurements demonstrate increased magnetic disorder in cobalt grown
on graphene, perhaps due to changes in the growth process and an increase in
defects. This magnetic disorder may account for the observed linewidth
enhancement due to effects such as two-magnon scattering or mosaicity. As such,
it is not possible to conclude successful spin injection into graphene from FMR
linewidth measurements alone.",1311.1441v1
2014/1/10,The magnetic field generated by a charge in a uniaxial magnetoelectric material,"We revisit the description of the magnetic field around antiferromagnetic
magnetoelectrics in the context of recent developments regarding
magnetoelectric monopoles. Using Maxwell's equations, we calculate the magnetic
and electric fields associated with a free charge in a bulk uniaxial
magnetoelectric, as well as in a finite sphere of magnetoelectric material. We
show that a charge in the prototypical magnetoelectric Cr$_2$O$_3$, which is
uniaxial with a diagonal magnetoelectric response, induces an internal magnetic
field with both monopolar and quadrupolar components, but that only the
quadrupolar contribution extends beyond the sample surface. We discuss the
behavior of the external quadrupolar field and compare its magnitude to those
of magnetic fields from other sources.",1401.2388v1
2014/4/17,Large Noncollinearity and Spin Reorientation in the Novel Mn2RhSn Heusler Magnet,"Noncollinear magnets provide essential ingredients for the next generation
memory technology. It is a new prospect for the Heusler materials, already well
known due to the diverse range of other fundamental characteristics. Here, we
present a combined experimental and theoretical study of novel noncollinear
tetragonal Mn2RhSn Heusler material exhibiting unusually strong canting of its
magnetic sublattices. It undergoes a spin-reorientation transition, induced by
a temperature change and suppressed by an external magnetic field. Because of
the presence of Dzyaloshinskii-Moriya exchange and magnetic anisotropy, Mn2RhSn
is suggested to be a promising candidate for realizing the Skyrmion state in
the Heusler family.",1404.4581v2
2014/4/22,Constituents of magnetic anisotropy and a screening of spin-orbit coupling in solids,"Using quantum mechanical perturbation theory (PT) we analyze how the energy
of perturbation of different orders is renormalized in solids. We test the
validity of PT analysis by considering a specific case of spin-orbit coupling
as a perturbation. We further compare the relativistic energy and the magnetic
anisotropy from the PT approach with direct density functional calculations in
FePt, CoPt, FePd, MnAl, MnGa, FeNi, and tetragonally strained FeCo. In addition
using decomposition of anisotropy into contributions from individual sites and
different spin components we explain the microscopic origin of high anisotropy
in FePt and CoPt magnets.",1404.5546v2
2014/4/28,High-Curie-temperature ferrimagnetism and ferroelectricity in Bi2FeMoO6,"BiFeO3 is the most famous multiferroic material, but its G-type
antiferromagnetism is highly desirable to be replaced by strong macroscopic
magnetism beyond room temperature. Here we obtain double perovskite Bi2FeMoO6
with R3 (#146) space group by substituting Mo for 50% Fe in BiFeO3. Our
first-principles calculated results show that it is a semiconductor with gap
reaching to 0.725 eV, its net magnetic moment is 2\mu_B per formula unit, and
its ferroelectric polarization is 85\mu C/cm^2. This ferroelctricity is
comparable with that of BiFeO3, but here the magnetism is a strong
ferrimagnetism with Curie temperature of 650 K. Our first-principles phonon
spectra establishes that this R3 phase is stable. Electric polarization and
magnetic easy axis are shown to be in pseudo-cubic [111] axis. Our further
analysis shows that the multiferroic mechanism is similar to that in BiFeO3.
Therefore, this Bi2FeMoO6 can be used to achieve strong macroscopic magnetism
and ferroelectricity well above room temperature, being useful for designing
new multifunctional materials and devices.",1404.7058v2
2017/7/26,Counting Pseudo Landau Levels in Spatially Modulated Dirac Systems,"In a system with Dirac cones, spatial modulation in material parameters
induces a pseudo magnetic field, which acts like an external magnetic field.
Here, we derive a concise formula to count the pseudo Landau levels in the
simplest setup for having a pseudo magnetic field. The formula is so concise
that it is helpful in seeing the essence of the phenomenon, and in considering
the experimental design for the pseudo magnetic field. Furthermore, it is
revealed that anisotropic Dirac cones are advantageous in pseudo Landau level
formation in general. The proposed setup is relatively easy to be realized by
spatial modulation in the chemical composition, and we perform an estimation of
the pseudo magnetic field in an existing material (an antiperovskite material),
by following the composition dependence with the help of the ab-initio method.",1707.08601v1
2017/10/14,Magnetocaloric Effect and Magnetic refrigeration: analytic and numeric study,"This work aims to present an analytical and numerical study of the
magnetocaloric effects (MCE) providing realistic proposals about materials that
should be chosen in the design of new refrigerator appliances around the room
temperature. Starting from a spin Hamiltonian including the exchange
interaction, the single-ion anisotropy and the applied magnetic field terms, we
have calculated the partition function at a given temperature and derived a set
of relevant physical quantities as magnetization, magnetic entropy and specific
heat and analyzed their behavior with atomic parameters as spin, exchange and
anisotropy. Using numerical programs that we developed by ourselves, we were
able to better elucidate the role of each microscopic parameter in order to
reinforce the relative cooling power (RCP) and give rise to optimal
performances of the refrigerant compound. This approach could be extended to
composite materials underscoring a giant MCE at room temperature.
  Key-words Magnetic refrigeration, Magnetocaloric Effect, Energy efficiency,
Spin Hamiltonian",1712.01096v1
2017/12/12,Magnetization of topological line-node semimetals,"Using an approximate expression for the Landau levels of the electrons
located near a nodal line of a topological line-node semimetal, we obtain
formulas for the magnetization of this semimetal at an arbitrary shape of its
line. It is also shown that the dependence of the chemical potential on the
magnetic field can be strong in these materials, and this dependence can
essentially influence the de Haas - van Alphen oscillations. The obtained
results are applied to the rhombohedral graphite which is one of the line-node
semimetals. For this material, we find temperature and magnetic field
dependences of its magnetic susceptibility.",1712.04300v2
2019/2/7,Magnetic borophenes from evolutionary search,"A computation methodology based on ab initio evolutionary algorithms and the
spin-polarized density functional theory was developed to predict
two-dimensional (2D) magnetic materials. Its application to a model system
borophene reveals an unexpected rich magnetism and polymorphism. A stable
borophene with nonzero thickness was an antiferromagnetic (AFM) semiconductor
from first-principles calculations, which can be further turned into a half
metal by finite electron doping. In this borophene, the buckling and coupling
among three atomic layers are not only responsible for the magnetism, but also
result in an out-of-plane negative Poissons ratios under uniaxial tension,
making it the first elemental material possessing auxetic and magnetic
properties simultaneously.",1902.02617v1
2019/3/2,Near room temperature antiferromagnetic ordering with a potential low dimensional magnetism in AlMn$_2$B$_2$,"We present self flux growth and characterization of single crystalline
AlMn$_2$B$_2$. It is an orthorhombic (space group Cmmm), layered material with
a plate like morphology. The anisotropic bulk magnetization data, electrical
transport and $^{11}$B nuclear magnetic resonance(NMR) data revealed an
antiferromagnetic (AFM) transition at 313 $\pm$ 2 K. In the magnetization data,
there is also a broad local maximum significantly above the AFM transition that
could be a signature of low dimensional magnetic interactions in AlMn$_2$B$_2$.",1903.00630v1
2019/7/8,Optimizing configurations for determining the magnetic model based on ab-initio calculations,"In this paper, it is presented a novel strategy to optimize the determination
of magnetic couplings by using ab-initio calculations of the energy. This
approach allows determining efficiently, in terms of a proposed effective
magnetic spin model, an optimal set of magnetic configurations to be simulated
by DFT methods. Moreover, a procedure to estimate the values of the coupling
constants and their error bounds from the estimated energies is proposed. This
method, based on Monte Carlo sampling, takes into account the accuracy of the
ab - initio simulations. A strategy to refine models reusing previously
computed configuration energies is also presented. We apply the method to
determine a magnetic model for the recently synthesized material
Bi$_3$Mn$_4$O$_{12}$(NO$_3$). Finally, an open source software that implements
and automatizes the whole process is presented.",1907.03376v1
2019/11/17,Magnetic properties of a new cobalt hydrogen vanadate with a dumortierite-like structure: Co13.5(OH)6(H0.5VO3.5)2(VO4)6,"The magnetic properties of a novel cobalt-based hydrogen vanadate,
Co13.5(OH)6(H0.5VO3.5)2(VO4)6, are reported. This new magnetic material was
synthesized in single-crystal form using a conventional hydrothermal method.
Its crystal structure was determined from single-crystal X-ray diffraction data
and was also characterized by scanning electron microscopy. Its crystal
framework has a dumortierite-like structure consisting of large hexagonal and
trigonal channels; the large hexagonal channels contain one-dimensional chains
of face-sharing CoO6 octahedra linked to the framework by rings of VO4
tetrahedra, while the trigonal channels are occupied by chains of disordered
V2O4 pyramidal groups. The magnetic properties of this material were
investigated by DC magnetic measurements, which indicate the occurrence of
antiferromagnetic interactions.",1911.07178v1
2019/12/6,Increased Curie temperature and enhanced perpendicular magneto anisotropy of Cr2Ge2Te6/NiO heterostructure,"Magnetism in two-dimensional van der Waals materials has received significant
attention recently. The Curie temperature reported for those materials,
however, has been so far remained relatively low. Here, we measure
magneto-optical Kerr effects (MOKE) under perpendicular magnetic field for van
der Waals ferromagnet Cr2Ge2Te6 as well as its heterostructure with
antiferromagnetic insulator NiO. We observe a notable increase in both Curie
temperature and magnetic perpendicular anisotropy in Cr2Ge2Te6/NiO
heterostructures compared to those in Cr2Ge2Te6. Measurements on the same
exfoliated Cr2Ge2Te6 flake (on a SiO2/Si substrate) before and after depositing
NiO show that the hysteresis loop can change into a square shape with larger
coercive field for Cr2Ge2Te6/NiO. The maximum Curie temperature (TC) observed
for Cr2Ge2Te6/NiO reaches ~120 K, is nearly twice the maximum TC ~ 60 K
reported for Cr2Ge2Te6 alone. Both enhanced perpendicular anisotropy and
increased Curie temperature are observed for Cr2Ge2Te6 flakes with a variety of
thicknesses ranging from ~5 nm to ~200 nm. The results indicate that magnetic
properties of two-dimensional van der Waals magnets can be engineered and
controlled by using the heterostructure interface with other materials.",1912.03147v1
2019/12/22,Tuning Magnetism in Layered Magnet VI$_3$: A Theoretical Study,"When combined with transition metals with partially filled $d$-orbitals,
magnetism can be incorporated in two-dimensional materials, which greatly
expands the scope for fundamental researches and potential applications of
these materials. Here, a first-principles study of a new two-dimensional
ferromagnet VI$_3$ has been carried out. The structural symmetry, magnetic and
electronic properties of VI$_3$ in its bulk and single layer forms have been
confirmed and predicted, respectively. Its ferromagnetic Curie temperature is
predicted to be reduced by half in its monolayer form. In addition, the cation
substitution in its monolayer have also been studied, which can significantly
tune the magnetism.",1912.10418v1
2020/1/6,Giant anomalous Hall and Nernst effect in magnetic cubic Heusler compounds,"The interplay of magnetism and topology opens up the possibility for exotic
linear response effects, such as the anomalous Hall effect and the anomalous
Nernst effect, which can be strongly enhanced by designing a strong Berry
curvature in the electronic structure. It is even possible to utilize this to
create a quantum anomalous Hall state at high temperatures by reducing the
dimensionality. Magnetic Heusler compounds are a promising class of materials
for this purpose because they grow in thin films, have a high Curie
temperature, and their electronic structure hosts strong topological features.
Here, we provide a comprehensive study of the intrinsic anomalous transport for
magnetic cubic full Heusler compounds and we illustrate that several Heusler
compounds outperform the best so far reported materials. The results reveal the
importance of symmetries, especially mirror planes, in combination with
magnetism for giant anomalous Hall and Nernst effects, which should be valid in
general for linear responses (spin Hall effect, spin orbital torque, etc.)
dominated by intrinsic contributions.",2001.01698v3
2020/1/21,Huge linear magnetoresistance due to open orbits in $γ$-PtBi$_2$,"Some single-crystalline materials present an electrical resistivity which
decreases between room temperature and low temperatures at zero magnetic field
as in a good metal and switches to a nearly semiconductinglike behavior at low
temperatures with the application of a magnetic field. Often, this is
accompanied by a huge and nonsaturating linear magnetoresistance which remains
difficult to explain. Here we present a systematic study of the
magnetoresistance in single-crystal $\gamma$-PtBi$_2$. We observe that the
angle between the magnetic field and the crystalline $c$ axis fundamentally
changes the magnetoresistance, going from a saturating to a nonsaturating
magnetic field dependence. In between, there is one specific angle where the
magnetoresistance is perfectly linear with the magnetic field. We show that the
linear dependence of the nonsaturating magnetoresistance is due to the
formation of open orbits in the Fermi surface of $\gamma$-PtBi$_2$.",2001.07674v2
2020/5/7,Detecting quadrupole: a hidden source of magnetic anisotropy for Manganese alloys,"Mn-based alloys exhibit unique properties in the spintronics materials
possessing perpendicular magnetic anisotropy (PMA) beyond the Fe and Co-based
alloys. It is desired to figure out the quantum physics of PMA inherent to
Mn-based alloys, which have never been reported. Here, the origin of PMA in
ferrimagnetic Mn$_{3-{\delta}}$Ga ordered alloys is investigated to resolve
antiparallel-coupled Mn sites using x-ray magnetic circular and linear
dichroism (XMCD/XMLD) and a first-principles calculation. We found that the
contribution of orbital magnetic moments in PMA is small from XMCD and that the
finite quadrupole-like orbital distortion through spin-flipped electron hopping
is dominant from XMLD and theoretical calculations. These findings suggest that
the spin-flipped orbital quadrupole formations originate from the PMA in
Mn$_{3-{\delta}}$Ga and bring the paradigm shift in the researches of PMA
materials using x-ray magnetic spectroscopies.",2005.03249v1
2020/7/24,Remarkably enhanced Curie temperature in monolayer CrI3 by hydrogen and oxygen adsorption: A first-principles calculations,"wo-dimensional (2D) materials unique properties and their promising
applications in post-silicon microelectronics have attracted significant
attention in the past decade. Recently, ferromagnetic order with out-of-plane
easy axis in a monolayer of CrI3 has been observed and reported, with a Curie
temperature of 45 K. Here we study, using density functional theory (DFT)
calculations, how hydrogen and oxygen adsorption affects the structural,
electronic, and magnetic properties of a CrI3 monolayer. Our results show that
while the structure remains almost unchanged by the adsorption of hydrogen,
adsorption of oxygen completely distorts it. We have also found that both the
adsorption of hydrogen and oxygen atoms significantly influences the electronic
and magnetic properties of the monolayer. While hydrogen quenches the magnetic
moments of Cr atoms, oxygen introduces an impurity band in the gap.
Interestingly, we find a strong enhancement of the Curie temperature by full
hydrogenation, while the results are not conclusive for O. This result suggests
a simple and effective approach to manipulate the electronic and magnetic
properties of 2D magnets for spintronics applications.",2007.12739v1
2020/9/12,Magnetic ground state and electron doping tuning of Curie temperature in Fe$_3$GeTe$_2$: first-principles studies,"Intrinsic magnetic van der Waals (vdW) materials have attracted much
attention, especially Fe$_{3}$GeTe$_{2}$ (FGT), which exhibits highly tunable
properties. However, despite vast efforts, there are still several challenging
issues to be resolved. Here using a first-principles linear-response approach,
we carry out comprehensive investigation of both bulk and monolayer FGT. We
find that although the magnetic exchange interactions in FGT are frustrated,
our Monte Carlo simulations agree with the total energy calculations,
confirming that the ground state of bulk FGT is indeed ferromagnetic (FM). A
tiny electron doping reduces the magnetic frustration, resulting in significant
increasing of the Curie temperature. We also calculate the spin-wave
dispersion, and find a small spin gap as well as a nearly flat band in the
magnon spectra. These features can be used to compare with the future neutron
scattering measurement and finally clarify the microscopic magnetic mechanism
in this two-dimensional family materials.",2009.05701v1
2020/10/20,Tuning quantum transport by controlling spin reorientations in Dirac semimetal candidates Eu$_{1-x}$Sr$_{x}$MnSb$_{2}$,"Magnetic topological semimetals have attracted intense attention recently
since these materials carry a great promise for potential applications in novel
spintronic devices. Here, we report an intimate interplay between lattice, Eu
magnetic order and topological semimetallic behavior in
Eu$_{1-x}$Sr$_{x}$MnSb$_{2}$ driven by nonmagnetic Sr doping on magnetic Eu
site. Different types of Eu spin reorientations are controllable by the Sr
concentration, temperature or magnetic field, and coupled to the quantum
transport properties of Dirac fermions generated by the 2D Sb layers. Our study
opens a new pathway to achieving exotic magnetic order and topological
semimetallic state via controlling spin reorientation. The effective strategy
of substituting rare-earth site by nonmagnetic element demonstrated here may be
applicable to the AMnCh$_{2}$ (A=rare-earth elements; Ch=Bi/Sb) family and a
wide variation of other layered compounds involving spatially separated
rare-earth and transition metal layers.",2010.10405v1
2021/2/22,"Hund's physics and the magnetic ground state of CrOX (X = Cl, Br)","To understand the magnetic property of layered van der Waals materials CrOX
(X = Cl, Br), we performed the detailed first-principles calculations for both
bulk and monolayer. We found that the charge-only density functional theory
combined with the explicit on-site interaction terms (so-called cDFT$+U$) well
reproduces the experimental magnetic ground state of bulk CrOX, which is not
the case for the use of spin-dependent density functional (so-called sDFT$+U$).
Unlike some of the previous studies, our results show that CrOX monolayers are
antiferromagnetic as in the bulk. It is also consistent with our magnetic force
linear response calculation of exchange couplings $J_{\rm ex}$. The result of
orbital-decomposed $J_{\rm ex}$ calculations shows that the Cr
$t_\textrm{2g}$-$t_\textrm{2g}$ component mainly contributes to the
antiferromagnetic order in both bulk and monolayer. Our result and analysis
show that taking the correct Hund's physics into account is of key importance
to construct the magnetic phase diagram and to describe the electronic
structure.",2102.10729v1
2021/6/13,Floquet Engineering of Magnetism in Topological Insulator Thin Films,"Dynamic manipulation of magnetism in topological materials is demonstrated
here via a Floquet engineering approach using circularly polarized light.
Increasing the strength of the laser field, besides the expected topological
phase transition, the magnetically doped topological insulator thin film also
undergoes a magnetic phase transition from ferromagnetism to paramagnetism,
whose critical behavior strongly depends on the quantum quenching. In sharp
contrast to the equilibrium case, the non-equilibrium Curie temperatures vary
for different time scale and experimental setup, not all relying on change of
topology. Our discoveries deepen the understanding of the relationship between
topology and magnetism in the non-equilibrium regime and extend optoelectronic
device applications to topological materials.",2106.06977v1
2021/7/12,Instabilities of heavy magnons in an anisotropic magnet,"The search for new elementary particles is one of the most basic pursuits in
physics, spanning from subatomic physics to quantum materials. Magnons are the
ubiquitous elementary quasiparticle to describe the excitations of
fully-ordered magnetic systems. But other possibilities exist, including
fractional and multipolar excitations. Here, we demonstrate that strong quantum
interactions exist between three flavors of elementary quasiparticles in the
uniaxial spin-one magnet FeI2. Using neutron scattering in an applied magnetic
field, we observe spontaneous decay between conventional and heavy magnons and
the recombination of these quasiparticles into a super-heavy bound-state. Akin
to other contemporary problems in quantum materials, the microscopic origin for
new physics in FeI2 is the quasi-flat nature of excitation bands and the
presence of Kitaev anisotropic magnetic exchange interactions.",2107.05694v3
2021/8/2,Electrically tunable room-temperature ferromagnetism in CrBr$_3$,"The recent discovery of magnetic ordering in two-dimension has lead to
colossal efforts to find atomically thin materials that order at high
temperatures. However, due to fundamental spin fluctuation in reduced
dimension, the room-temperature ferromagnetism remains elusive. Here, we report
a dramatic manipulation of magnetic ordering up to room temperature in the
monolayer CrBr$_3$, within the first-principles Heisenberg XXZ model. The
exchange and anisotropic magnetic interactions are externally modulated by a
gate-induced charge carrier doping that triggers a nontrivial phase diagram.
High-temperature ferromagnetism is associated with a substantial increase in
both effective ferromagnetic exchange and overall magnetic anisotropy under
experimentally attainable hole doping. In contrast, electron doping quickly
switches the magnetic easy axis. The gate-tuneable room temperature
ferromagnetism in CrBr$_3$ presents new possibilities in electrically
controlled spintronic and magnetoelectric devices based on atomically thin
crystals.",2108.00684v1
2021/8/24,Magnetic Topological Semimetal Phase with Electronic Correlation Enhancement in SmSbTe,"The ZrSiS family of compounds hosts various exotic quantum phenomena due to
the presence of both topological nonsymmorphic Dirac fermions and nodal-line
fermions. In this material family, the LnSbTe (Ln= lanthanide) compounds are
particularly interesting owing to the intrinsic magnetism from magnetic Ln
which leads to new properties and quantum states. In this work, the authors
focus on the previously unexplored compound SmSbTe. The studies reveal a rare
combination of a few functional properties in this material, including
antiferromagnetism with possible magnetic frustration, electron correlation
enhancement, and Dirac nodal-line fermions. These properties enable SmSbTe as a
unique platform to explore exotic quantum phenomena and advanced
functionalities arising from the interplay between magnetism, topology, and
electronic correlations.",2108.10983v1
2021/9/10,Controlling magnetism through Ising superconductivity in magnetic van der Waals heterostructures,"Van der Waals heterostructures have risen as a tunable platform to combine
different electronic orders, due to the flexibility in stacking different
materials with competing symmetry broken states. Among them, van der Waals
ferromagnets such as CrI3 and superconductors as NbSe2 provide a natural
platform to engineer novel phenomena at ferromagnet-superconductor interfaces.
In particular, NbSe2 is well known for hosting strong spin-orbit coupling
effects that influence the properties of the superconducting state. Here we put
forward a ferromagnet/NbSe2/ferromagnet heterostructure where the interplay
between Ising superconductivity in NbSe2 and magnetism controls the magnetic
alignment of the heterostructure. In particular, we show that the interplay
between spin-orbit coupling and superconductivity allows controlling magnetic
states in van der Waals materials. Our results show how hybrid van der Waals
ferromagnet/superconductor heterostructure can be used as a tunable materials
platform for superconducting spin-orbitronics.",2109.04788v2
2021/10/7,Magnetic Frustration in a Zeolite,"Zeolites are so well known in real world applications and after decades of
scientific study that they hardly need any intro-duction: their importance in
chemistry cannot be overemphasized. Here we add to the remarkable properties
that they dis-play by reporting our discovery that the simplest zeolite,
sodalite, when doped with Cr3+ in the \b{eta}-cage, is a frustrated magnet.
Soft X-ray absorption spectroscopy and magnetic measurements reveal that the Cr
present is Cr(III). Cr(III), with its isotropic 3d3 valence electron
configuration, is well-known as the basis for many geometrically frustrated
magnets, but it is especially surprising that a material like the Ca8Al12Cr2O29
zeolite is a frustrated magnet. This finding illustrates the value of exploring
the properties of even well-known materials families.",2110.03539v1
2021/10/25,Engineering crystal structure and spin-phonon coupling in Ba1-xSrxMnO3,"The interplay between different degrees of freedom such as charge, spin,
orbital, and lattice has received a great deal of interest due to its potential
to engineer materials properties and their functionalities for device
applications. In this work, we have explored the crystallographic phase diagram
of Ba1-xSrxMnO3 and studied the correlation between two degrees of freedom,
namely phonons and spins using magnetization and inelastic light scattering
measurements. The system undergoes a series of crystallographic phase
transitions 2H -> 9R -> 4H as a function of doping (Sr) as observed by X-ray
diffraction measurements. Investigation of their temperature-dependent
magnetization reveals a para- to antiferro-magnetic transition for all the
compositions. An Eg phonon in the 9R phase and an E1g phonon in the 4H phase
involving Mn or O-vibrations, show anomalous temperature-dependence in the
antiferromagnetic phase arising due to spin-phonon coupling.",2110.12821v1
2021/11/2,Floquet engineering of Kitaev quantum magnets,"In recent years, there has been an intense search for materials realizing the
Kitaev quantum spin liquid model. A number of edge-shared compounds with strong
spin-orbit coupling, such as RuCl$_3$ and iridates, have been proposed to
realize this model. Nevertheless, an effective spin Hamiltonian derived from
the microscopic model relevant to these compounds generally contains terms that
are antagonistic toward the quantum spin liquid. This is consistent with the
fact the zero magnetic field ground state of these materials is generally
magnetically ordered. It is a pressing issue to identify protocols to drive the
system to the limit of the Kitaev quantum spin model. In this work, we propose
Floquet engineering of these Kitaev quantum magnets by coupling materials to a
circularly polarized laser. We demonstrate that all the magnetic interactions
can be tuned in situ by the amplitude and frequency of the laser, hence
providing a route to stabilize the Kitaev quantum spin liquid phase.",2111.01316v1
2021/12/23,Theory of Harmonic Hall Responses of Spin-Torque Driven Antiferromagnets,"Harmonic analysis is a powerful tool to characterize and quantify
current-induced torques acting on magnetic materials, but so far it remains an
open question in studying antiferromagnets. Here we formulate a general theory
of harmonic Hall responses of collinear antiferromagnets driven by
current-induced torques including both field-like and damping-like components.
By scanning a magnetic field of variable strength in three orthogonal planes,
we are able to distinguish the contributions from field-like torque,
damping-like torque, and concomitant thermal effects by analyzing the second
harmonic signals in the Hall voltage. The analytical expressions of the first
and second harmonics as functions of the magnetic field direction and strength
are confirmed by numerical simulations with good agreement. We demonstrate our
predictions in two prototype antiferromagnets, $\alpha-$Fe$_{2}$O$_{3}$ and
NiO, providing direct and general guidance to current and future experiments.",2112.12772v2
2022/2/13,Stable Ferromagnetism and High Curie Temperature in VGe$_2$N$_4$,"The discovery of monolayer MA$_2$Z$_4$ (M = transition metals; A = IVA
elements; Z = VA elements, Science 369, 2020, 670-674) family has led another
advance for facilitating and harnessing magnetism in low-dimensional materials.
However, only Cr and V based MA$_2$N$_4$ compounds exhibit intrinsic magnetism
yet with unsatisfied magnetic ordering temperature. Herein, we identify a
stable ferromagnetic number of this family, i.e., VGe$_2$Z$_4$ monolayer, by
means of first-principles calculations. It is found that the magnetic
configuration sustains under both compression and tensile uniaxial in-plane
strain, and the former can act as a positive modulator to enhance magnetic
ordering temperature (Tc). Electronic structure calculations reveal a large
band gap in the spin down channel while band-gapless in the spin up channel, an
impressive near-half-metallic character, which is a favorable candidate for
spintronic device.",2202.06424v2
2022/6/13,Anisotropic Dzyaloshinskii-Moriya interaction protected by D2d crystal symmetry in two-dimensional ternary compounds,"Magnetic skyrmions, topologically protected chiral spin swirling
quasiparticles, have attracted great attention in fundamental physics and
applications. Recently, the discovery of two-dimensional (2D) van der Waals
(vdW) magnets has aroused great interest due to their appealing physical
properties. Moreover, both experimental and theoretical works have revealed
that isotropic Dzyaloshinskii Moriya interaction (DMI) can be achieved in 2D
magnets or ferromagnet-based heterostructures. However, 2D magnets with
anisotropic DMI haven't been reported yet. Here, via using first-principles
calculations, we unveil that anisotropic DMI protected by D2d crystal symmetry
can exist in 2D ternary compounds MCuX2. Interestingly, by using micromagnetic
simulations, we demonstrate that ferromagnetic (FM) antiskyrmions, FM bimerons,
antiferromagnetic (AFM) antiskyrmions and AFM bimerons can be realized in MCuX2
family. Our discovery opens up an avenue to creating antiskyrmions and bimerons
with anisotropic DMI protected by D2d crystal symmetry in 2D magnets.",2206.06050v1
2022/7/4,Evidence against superconductivity in flux trapping experiments on hydrides under high pressure & On magnetic field screening and expulsion in hydride superconductors,"It has recently been reported that hydrogen-rich materials under high
pressure trap magnetic flux, a tell-tale signature of superconductivity
[arXiv:2206.14108v1]. Here we point out that under the protocol used in these
experiments the measured results indicate that the materials don't trap
magnetic flux. Instead, the measured results are either experimental artifacts
or originate in magnetic properties of the sample or its environment unrelated
to superconductivity, Together with other experimental evidence analyzed
earlier, this clearly indicates that these materials are not superconductors.
{\bf In a second part, we discuss magnetic field screening and expulsion.}",2207.01541v4
2022/7/21,Dzyaloshinskii-Moriya interaction in Nd$_{2}$Fe$_{14}$B as the origin of spin reorientation and rotating magnetocaloric effect,"The mechanism of spin reorientation in Nd$_{2}$Fe$_{14}$B, which is a host
crystal of a well-known neodymium permanent magnet, is studied by combining
first-principles calculations and Monte Carlo simulations. The spin
reorientation is thought to be derived from crystal field effects and gets less
attention because of the undesirable property for hard magnet application.
Dzyaloshinskii-Moriya interactions are usually less attractive or often ignored
in rare-earth bulk systems, including permanent magnets such as
Nd$_{2}$Fe$_{14}$B since people believe that the magnetic anisotropy is more
dominant than the Dzyaloshinskii-Moriya interactions. However, in this study,
we have found, for the first time, that the spin reorientation in
Nd$_{2}$Fe$_{14}$B is attributed to Dzyaloshinskii-Moriya interactions. We have
found, furthermore, the spin reorientation in Nd$_{2}$Fe$_{14}$B yields a great
stage of rotating magnetocaloric effect at practical application level. We have
found that the Dzyaloshinskii-Moriya interactions definitely contributes to the
physical properties as a non-negligible effect in magnetic materials.",2207.10408v2
2022/8/4,Electric-field induced magnetic-anisotropy transformation to achieve spontaneous valley polarization,"Valleytronics has been widely investigated for providing new degrees of
freedom to future information coding and processing. Here, it is proposed that
valley polarization can be achieved by electric field induced magnetic
anisotropy (MA) transformation. Through the first-principle calculations, our
idea is illustrated by a concrete example of $\mathrm{VSi_2P_4}$ monolayer. The
increasing electric field can induce a transition of MA from in-plane to
out-of-plane by changing magnetic anisotropy energy (MAE) from negative to
positive value, which is mainly due to increasing magnetocrystalline anisotropy
(MCA) energy. The out-of-plane magnetization is in favour of spontaneous valley
polarization in $\mathrm{VSi_2P_4}$. Within considered electric field range,
$\mathrm{VSi_2P_4}$ is always ferromagnetic (FM) ground state. In a certain
range of electric field, the coexistence of semiconductor and out-of-plane
magnetization makes $\mathrm{VSi_2P_4}$ become a true ferrovalley (FV)
material. The anomalous valley Hall effect (AVHE) can be observed under
in-plane and out-of-plane electrical field in $\mathrm{VSi_2P_4}$. Our works
pave the way to design the ferrovalley material by electric field.",2208.02425v1
2022/8/5,Interfacial phase frustration stabilizes unconventional skyrmion crystals,"Chiral magnetic phases with an unconventional topological twist in the
magnetization are of huge interest due to their potential in spintronics
applications. Here, we present a general method to induce such exotic magnetic
phases using interfacial phase frustration within artificially grown
superlattices. To demonstrate our method, we consider a multilayer with two
different chiral magnetic phases as the competing orders at the top and bottom
and show, using Monte Carlo calculations, that the interfacial phase
frustration is realized at the central layer. In particular, we obtain three
unconventional phases: a checkerboard skyrmion crystal, an incommensurate
skyrmion stripe, and a ferrimagnetic skyrmion crystal. In these
frustration-induced phases, the spin chirality driven topological Hall
conductivity can be largely enhanced. This method provides a playground to
realize unconventional magnetic phases in any family of materials that can be
grown in superlattices.",2208.03255v1
2022/9/1,Implications of electron and hole doping on the magnetic properties of spin-orbit entangled Ca$_\text{4}$IrO$_\text{6}$ from DFT calculations,"We investigate the electronic structure and magnetic properties of a
$J_\text{eff} = 1/2$ iridate Ca$_4$IrO$_6$ and the implications of doping
electrons and holes using ab initio density functional theory. Our calculations
considering spin-orbit interaction reveal that although the Mott-insulating
parent compound transforms into a conductor upon doping, antiferromagnetism
sustains in the doped system, albeit with a grossly noncollinear arrangement of
the spins. We find a strong spin-orbit interaction and magneto-crystalline
anisotropy, causing frustration in the system, possibly leading to the highly
noncollinear arrangement of spins upon non-magnetic doping. Our results may be
important from the viewpoint of spintronics using iridates or other $5d$
materials.",2209.00239v1
2022/9/30,Curing spurious magneto-mechanical coupling in soft non-magnetic materials,"The present work is concerned with the issue of spurious coupling effects
that are pervasive in fully coupled magneto-mechanical finite element
simulations involving very soft non-magnetic or air-like media. We first
address the characterization of the spurious magneto-mechanical effects and
their intuitive interpretation based on energy considerations. Then, as main
contribution, we propose two new ways to prune the undesired spurious
magneto-mechanical coupling in non-magnetic media. The proposed methods are
compared with established methods in the context of magnetic bodies embedded in
(i) air or vacuum and (ii) very soft elastic non-magnetic media. The comparison
shows that the proposed approaches are accurate and effective. They,
furthermore, allow for a consistent linearization of the coupled boundary value
problems, which is crucial for the simulation of compliant structures. For
reproducibility and accessibility of the proposed methods, we provide our
implementations with Netgen/NGSolve as well as all codes necessary for the
reproduction of our results as supplementary material.",2209.15349v1
2022/10/17,Ultrafast laser-driven topological spin textures on a 2D magnet,"Ultrafast laser excitations provide an efficient and low-power consumption
alternative since different magnetic properties and topological spin states can
be triggered and manipulated at the femtosecond (fs) regime. However, it is
largely unknown whether laser excitations already used in data information
platforms can manipulate the magnetic properties of recently discovered
two-dimensional (2D) van der Waals (vdW) materials. Here we show that
ultrashort laser pulses (30$-$85 fs) can not only manipulate magnetic domains
of 2D-XY CrCl$_3$ ferromagnets, but also induce the formation and control of
topological nontrivial meron and antimeron spin textures. We observed that
these spin quasiparticles are created within $\sim$100 ps after the excitation
displaying rich dynamics through motion, collision and annihilation with
emission of spin waves throughout the surface. Our findings highlight
substantial opportunities of using photonic driving forces for the exploration
of spin textures on 2D magnetic materials towards magneto-optical topological
applications.",2210.09210v1
2022/10/19,Generalised form of the magnetic anisotropy field in micromagnetic and atomistic spin models,"We present a general approach to the derivation of the effective anisotropy
field which determines the dynamical behaviour of magnetic spins according to
the Landau-Lifshitz-Gilbert equation. The approach is based on the gradient in
spherical polar coordinates with the final results being expressed in Cartesian
coordinates as usually applied in atomistic and micromagnetic model
calculations. The approach is generally valid for all orders of anisotropies
including higher order combinations of azimuthal and rotational anisotropies
often found in functional magnetic materials such as permanent magnets and an
emerging class of antiferromagnetic materials with applications in spintronics.
Anisotropies are represented in terms of spherical harmonics which have the
important property of rational temperature scaling. Effective field vectors are
given for anisotropies up to sixth order, presenting a unified framework for
implementing higher order magnetic anisotropies in numerical simulations.",2210.10916v4
2022/11/4,Picosecond x-ray magnetic circular dichroism spectroscopy at the Fe L-edges with a laser-driven plasma source,"Time-resolved x-ray magnetic circular dichroism (XMCD) enables a unique
spectroscopic view on complex spin and charge dynamics in multi-elemental
magnetic materials. So far, its application in the soft-x-ray range has been
limited to synchrotron-radiation sources and free-electron lasers. By combining
a laser-driven plasma source with a magnetic thin-film polarizer, we generate
circularly polarized photons in the soft x-ray regime, enabling the first XMCD
spectroscopy at the Fe L edges in a laser laboratory. Our approach can be
readily adapted to other transition metal L and rare earth M absorption edges
and with a temporal resolution of < 10 ps, a wide range of ultrafast
magnetization studies can be realized.",2211.02777v1
2022/11/9,CrRhAs: a member of a large family of metallic kagome antiferromagnets,"Kagome lattice materials are an important platform for highly frustrated
magnetism as well as for a plethora of phenomena resulting from flat bands,
Dirac cones and van Hove singularities in their electronic structures. We study
the little known metallic magnet CrRhAs, which belongs to a vast family of
materials that include $3d$, $4f$ and $5f$ magnetic elements, as well as
numerous nonmagnetic metals and insulators. Using noncollinear spin density
functional calculations (mostly spin spirals), we extract a model magnetic
Hamiltonian for CrRhAs. While it is dominated by an antiferromagnetic second
nearest neighbor coupling in the kagome plane, the metallic nature of the
compound leads to numerous nonzero longer range couplings and to important ring
exchange terms. We analyze this Hamiltonian and find unusual ground states
which are dominated by nearly isolated antiferromagnetic triangles that adopt
120$^\circ$ order either with positive or with negative vector chirality. We
discuss the connection to the few known experimental facts about CrRhAs.
Finally, we give a brief survey of other interesting magnetic members of this
family of kagome compounds.",2211.04646v1
2022/11/11,Tailoring the magnetic landscape in Al-doped LaMnO3: An experimental and computational perspective,"We have presented the synthesis, structural, and magnetic properties from the
experimental point of view. Then we verified our experimental observation by
studying the electronic and magnetic properties of Al-doped LaMnO3 from the
first principle density functional theory (DFT) and Monte-Carlo simulation. We
have synthesized the LaAlxMn1-xO3 (x= 0.05, 0.15, 0.25) and performed the
Rietveld refinement of XRD data to determine the lattice parameters. To see the
mixed valance of Mn-ion, we performed the XPS of 25% Al-doped material. The
magnetic study shows the ferromagnetic transition of these materials. Using XRD
refinement values, we have completed the DFT calculations. The Monte Carlo
simulation has been done through the anisotropic Ising model to analyze the
origin of magnetic transition. We have determined the anisotropy and the
interaction constants from the DFT calculations.",2211.06025v1
2022/12/5,Magnetic shielding for large photoelectron multipliers for the OSIRIS facility of the JUNO detector,"We present the technical design and characteristics of the magnetic shield
developed for 20"" PMTs of the low-background OSIRIS facility. A ribbon of
amorphous alloy with the extreme magnetic permeability was used in its design
providing the excellent efficiency in screening the Earth's magnetic field with
a relatively small amount of the material. The mass of materials is crucial for
the construction of low-background facilities from the point of view of
radioactive backgrounds. Using amorphous materials is cost-efficient compared
to other methods for screening the Earth's magnetic field.",2212.02562v3
2022/12/20,Mechanism of carrier doping induced magnetic phase transitions in two-dimensional materials,"Electrically tuning long-range magnetic orders has been realized in
two-dimensional (2D) semiconductors via electrostatic doping. On the other
hand, the observations are highly diverse: the transition can be realized by
either electrons or holes or both depending on specific materials. Moreover,
doped carriers seem to always favor the ferromagnetic (FM) ground state. The
mechanism behind those diverse observations remains uncovered. Combining
first-principles simulations, we analyze the spin superexchange paths of the
correlated d/f orbitals around band edges and assign 2D magnetic semiconductors
into three types by their projected density of states (PDOS). We find that each
type of PDOS corresponds to a specific carrier-driven magnetic phase transition
and the critical doping density and type of carriers can be quantitatively
obtained by calculating the superexchange coupling strength. The model results
are in good agreements with first-principles calculations and available
measurements. After understanding the mechanism, we can design heterostructures
to realize the FM to antiferromagnetic transition, which has not been realized
before. This model is helpful to understand diverse measurements and expand the
degrees of freedom to control long-range magnetic orders in 2D semiconductors.",2212.10386v1
2022/12/29,Field-free spin-orbit torque-induced switching of perpendicular magnetization at room temperature in WTe2/ferromagnet heterostructures,"Spin-orbit torque (SOT) provides an efficient way to achieve charge-to-spin
conversion and can switch perpendicular magnetization, which is essential for
designing novel energy-efficient spintronic devices. An out-of-plane SOT could
directly switch perpendicular magnetization. Encouragingly, field-free
perpendicular magnetization switching of a two-dimensional (2D) material
WTe2/ferromagnet (FM) bilayer has been reported recently, but the working
temperature (200 K) is below room temperature. Here, we report the field-free
perpendicular magnetization switching carried out at room temperature on a
WTe2/Pt/Co/Pt multilayer film. Controlled experiments confirm that the
field-free switching is caused by the in-plane antidamping SOT generated in the
Pt/Co/Pt multilayer and the out-of-plane generated in the a-axis WTe2 thin
film. This work offers a potential method for using spintronic devices made of
two-dimensional materials at room temperature.",2212.14281v1
2023/1/6,Lattice Distortions and Magnetic Interactions in Single-Layer VOCl,"Atomically thin layers exfoliated from magnetic van der Waals layered
materials are currently of high interest in solid state physics. VOCl is a
quasi-two-dimensional layered antiferromagnet which was recently synthesized in
monolayer form. Previous theoretical studies have assumed the high-temperature
orthorhombic lattice symmetry also in the low temperature range, where the bulk
system is known to be monoclinic due to a strong magnetoelastic coupling. We
demonstrate from \textit{ab-initio} calulations that this monoclinic distortion
is prevalent also in monolayers, which is in line with recent experimental
indications of monoclinic symmetry. Our calculations also show that competing
ferromagnetic and antiferromagnetic interactions give rise a frustrated
two-fold magnetic superstructure where higher-order magnetic interactions play
a key role to stabilize the observed magnetic ground state.",2301.02548v1
2023/2/8,Spin disorder in a stacking polytype of a layered magnet,"Strongly correlated ground states and exotic quasiparticle excitations in
low-dimensional systems are central research topics in the solid state research
community. The present work develops a new layered material and explores the
physical properties. Single crystals of 3R-Na2MnTeO6 were synthesized via a
flux method. Single crystal x-ray diffraction and transmission electron
microscopy reveal a crystal structure with ABC-type stacking and an R-3 space
group, which establishes this material as a stacking polytype to previously
reported 2H-Na2MnTeO6. Magnetic and heat capacity measurements demonstrate
dominant antiferromagnetic interactions, the absence of long-range magnetic
order down to 0.5 K, and field-dependent short range magnetic correlations. A
structural transition at ~ 23 K observed in dielectric measurements may be
related to displacements of the Na positions. Our results demonstrate that
3R-Na2MnTeO6 displays low-dimensional magnetism, disordered structure and
spins, and the system displays a rich structure variety.",2302.03870v1
2023/5/3,Kinetic Magnetism in Triangular Moiré Materials,"Magnetic properties of materials ranging from conventional ferromagnetic
metals to strongly correlated materials such as cuprates originate from Coulomb
exchange interactions. The existence of alternate mechanisms for magnetism that
could naturally facilitate electrical control have been discussed theoretically
but an experimental demonstration in an extended system has been missing. Here,
we investigate MoSe$_2$/WS$_2$ van der Waals heterostructures in the vicinity
of Mott insulator states of electrons forming a frustrated triangular lattice
and observe direct evidence for magnetic correlations originating from a
kinetic mechanism. By directly measuring electronic magnetization through the
strength of the polarization-selective attractive polaron resonance, we find
that when the Mott state is electron doped the system exhibits ferromagnetic
correlations in agreement with the Nagaoka mechanism.",2305.02150v2
2023/5/15,Band-filling-controlled magnetism from transition metal intercalation in $N_{1/3}$NbS$_2$ revealed with first-principles calculations,"We present a first-principles study of the effect of 3$d$ transition metal
intercalation on the magnetic properties of the 2H-NbS$_2$ system, using
spin-resolved density functional theory calculations to investigate the
electronic structure of $N_{1/3}$NbS$_2$ ($N$ = Ti, V, Cr, Mn, Fe, Co, Ni).
  We are able to accurately determine the magnetic moments and crystal field
splitting, and find that the magnetic properties of the materials are
determined by a mechanism based on filling rigid bands with electrons from the
intercalant.
  We predict the dominant magnetic interaction of these materials by
considering Fermi surface nesting, finding agreement with experiment where data
are available.",2305.08743v1
2023/6/23,Wireless magneto-ionics: voltage control of magnetism by bipolar electrochemistry,"Modulation of magnetic properties through voltage-driven ion motion and redox
processes, i.e., magneto-ionics, is a unique approach to control magnetism with
electric field for low-power memory and spintronic applications. So far,
magneto-ionics has been achieved through direct electrical connections to the
actuated material. Here we evidence that an alternative way to reach such
control exists in a wireless manner. Induced polarization in the conducting
material immersed in the electrolyte, without direct wire contact, promotes
wireless bipolar electrochemistry, an alternative pathway to achieve
voltage-driven control of magnetism based on the same electrochemical processes
involved in direct-contact magneto-ionics. A significant tunability of
magnetization is accomplished for cobalt nitride thin films, including
transitions between paramagnetic and ferromagnetic states. Such effects can be
either volatile or non-volatile depending on the electrochemical cell
configuration. These results represent a fundamental breakthrough that may
inspire future device designs for applications in bioelectronics, catalysis,
neuromorphic computing, or wireless communications.",2306.13417v1
2023/7/31,Nonvolatile Magneto-Thermal Switching in MgB2,"Ongoing research explores thermal switching materials to control heat flow.
Specifically, there has been interest in magneto-thermal switching (MTS)
materials based on superconductors, which only exhibited switching behavior
when a magnetic field was applied. However, a recent report highlighted
nonvolatile MTS in commercial Sn-Pb solders, attributed to magnetic flux
trapping. In this study, we focused on flux trapping in a type-II
superconductor MgB2. Magnetization and thermal conductivity measurements under
magnetic fields were conducted on polycrystalline MgB2. We confirmed that
magnetic flux was indeed trapped in MgB2 even after demagnetization.
Additionally, we observed nonvolatile MTS in MgB2 as well as Sn-Pb solders.
These results suggest that the nonvolatile MTS may be a widespread
characteristic of superconducting materials with flux trapping.",2307.16404v1
2023/8/27,Magnetostatic modes and criticality in uniaxial magnetic materials,"We analyze modes in a dipole-dipole coupled quantum magnetic material, taking
into consideration domain structure and other shape effects present in any real
magnet. We find that the soft mode governing quantum criticality in a
non-ellipsoidal sample is an inhomogeneous magnetostatic mode which negates
dynamic, demagnetization-field effects. The demagnetization field is analyzed
from a microscopic perspective. Furthermore, we find a magnetostatic mode
originating from variations in the magnetization of the sample, caused by
domain structure and quantum or thermal fluctuations, will be lower in energy
than the soft mode governing quantum criticality in the bulk of the magnet.
Experimental evidence for these theoretical results is provided by analysis of
electronuclear modes in LiHoF$_4$, an archetypal dipolar quantum Ising
material, in a microwave resonator.",2308.14169v1
2023/9/7,Surface sensitivity of magnetization in the mesoscopic regime,"We find that in the mesoscopic regime modification of the material's surface
can induce an extensive change of the material's magnetic moment. In other
words, perturbation of order $N^2$ atoms on the surface of a 3-dimensional
solid can change the magnetic moment proportionally to $N^3$. When the solid's
surface is perturbed, it triggers two changes in the magnetization. One arises
from variations of the electron wavefunction and energy, while the other arises
from a modification in the kinetic angular momentum operator. In the
macroscopic regime of our model, these two bulk effects cancel each other,
resulting in no impact of the surface perturbation on the magnetization --
consistent with prior work. In the mesoscopic regime, we find a departure from
this behavior, as the cancelation of two terms is not complete.",2309.03957v2
2023/9/10,Deterministic and non-volatile switching of all-van der Waals spin-orbit torque system above room temperature without external magnetic fields,"Two-dimensional van der Waals (vdW) magnetic materials hold promise for the
development of high-density, energy-efficient spintronic devices for memory and
computation. Recent breakthroughs in material discoveries and spin-orbit torque
(SOT) control of vdW ferromagnets have opened a path for integration of vdW
magnets in commercial spintronic devices. However, a solution for field-free
electric control of perpendicular magnetic anisotropy (PMA) vdW magnets at room
temperatures, essential for building compact and thermally stable spintronic
devices, is still missing. Here, we report the first demonstration of
field-free deterministic and non-volatile switching of a PMA vdW ferromagnet,
Fe$_3$GaTe$_2$ above room temperature (up to 320 K). We use the unconventional
out-of-plane anti-damping torque from an adjacent WTe$_2$ layer to enable such
switching with a low current density of $2.23 \times 10^6$ A/cm$^2$. This study
exemplifies the efficacy of low-symmetry vdW materials for spin-orbit torque
control of vdW ferromagnets and provides an all-vdW solution for the next
generation of scalable and energy-efficient spintronic devices.",2309.04930v1
2023/10/30,Plasma treatment as an unconventional molecular magnet engineering method,"Molecular magnetism aims to design materials with unique properties at the
molecular level, focusing on the systematic synthesis of new chemical
compounds. In this paper, we propose an alternative route to engineer molecular
magnetic materials through plasma irradiation. Our research indicates that the
long-range magnetic order temperature in the three-dimensional
$\mathrm{\{[Mn^{II}(H_2O)_2]_2[Nb^{IV}(CN)_8]\cdot 4H_2O\}_n}$ molecular
ferrimagnet increases by 20 K after plasma treatment. The core structure of the
compound does not reveal significant changes after plasma processing, as
confirmed by the X-ray powder diffraction analysis. The observed results are
attributed to the release of crystallized water molecules. The described
procedure can serve as a viable approach to altering the magnetic properties of
the molecular systems.",2310.19467v1
1998/6/4,Compensation Temperature of a Mixed Ising Ferrimagnetic Model in the Presence of External Magnetic Fields,"The behavior of the compensation temperature of a mixed Ising ferrimagnetic
system on a square lattice in which the two interpenetrating square sublattices
have spins $\sigma$ ($\pm 1/2$) and spins $S$ ($\pm 1,0$) has been studied with
Monte Carlo methods. Our model includes nearest and next-nearest neighbor
interactions, a crystal field and an external magnetic field. This model is
relevant for understanding bimetallic molecular ferrimagnetic materials. We
found that there is a narrow range of parameters of the Hamiltonian for which
the model has compensation temperatures and that the compensation point exists
only for small values of the external field.",9806063v1
2005/5/26,Inverse magnetocaloric effect in ferromagnetic Ni-Mn-Sn alloys,"The magnetocaloric effect (MCE) in paramagnetic materials has been widely
used for attaining very low temperatures by applying a magnetic field
isothermally and removing it adiabatically. The effect can be exploited also
for room temperature refrigeration by using recently discovered giant MCE
materials. In this letter, we report on an inverse situation in Ni-Mn-Sn
alloys, whereby applying a magnetic field adiabatically, rather than removing
it, causes the sample to cool. This has been known to occur in some
intermetallic compounds, for which a moderate entropy increase can be induced
when a field is applied, thus giving rise to an inverse magnetocaloric effect.
However, the entropy change found for some ferromagnetic Ni-Mn-Sn alloys is
just as large as that reported for giant MCE materials, but with opposite sign.
The giant inverse MCE has its origin in a martensitic phase transformation that
modifies the magnetic exchange interactions due to the change in the lattice
parameters.",0505652v1
2009/5/26,Compensated magnetism by design in double perovskite oxides,"Taking into account Goodenough's superexchange rules, including both full
structural relaxation and spin-orbit coupling, and checking strong correlation
effects, we look for compensated half metals within the class of oxide double
perovskites materials. Identifying likely half metallic (or half semimetallic)
antiferromagnets, the full complications including orbital magnetism are
included in order to arrive at realistic predictions of designed magnetic
compounds with (near) vanishing net moment. After sorting through several
candidates that have not been considered previously, two materials,
K$_2$MnRhO$_6$ and La$_2$CrWO$_6$, remain as viable candidates. An important
factor is obtaining compounds either with very small induced orbital moment
(helped by closed subshells) or with an orbital moment that compensates the
spin-orbit driven degradation of half metallic character. While thermodynamic
stability of these materials cannot be ensured, the development of
layer-by-layer oxide deposition techniques does not require that materials be
thermodynamically stable to be synthesized.",0905.4199v1
2009/8/17,Validity of effective material parameters for optical fishnet metamaterials,"Although optical metamaterials that show artificial magnetism are mesoscopic
systems, they are frequently described in terms of effective material
parameters. But due to intrinsic nonlocal (or spatially dispersive) effects it
may be anticipated that this approach is usually only a crude approximation and
is physically meaningless. In order to study the limitations regarding the
assignment of effective material parameters, we present a technique to retrieve
the frequency-dependent elements of the effective permittivity and permeability
tensors for arbitrary angles of incidence and apply the method exemplarily to
the fishnet metamaterial. It turns out that for the fishnet metamaterial,
genuine effective material parameters can only be introduced if quite stringent
constraints are imposed on the wavelength/unit cell size ratio. Unfortunately
they are only met far away from the resonances that induce a magnetic response
required for many envisioned applications of such a fishnet metamaterial. Our
work clearly indicates that the mesoscopic nature and the related spatial
dispersion of contemporary optical metamaterials that show artificial magnetism
prohibits the meaningful introduction of conventional effective material
parameters.",0908.2393v2
2010/6/4,Mueller matrices for anisotropic metamaterials generated using 4x4 matrix formalism,"Forward models for the Mueller Matrix (MM) components of materials with
relative magnetic permeability tensor {\mu} \neq 1 are studied. 4x4 matrix
formalism is employed to produce general solutions for the complex reflection
coefficients and MMs of dielectric-magnetic materials having arbitrary crystal
symmetry and arbitrary laboratory orientation. For certain orientations of
materials with simultaneously diagonalizable {\epsilon} and {\mu} tensors (with
coincident principal axes), analytic solutions to the Berreman equation are
available. For the single layer thin film configuration of these materials,
analytic formulas for the complex reflection and transmission coefficients are
derived for orthorhombic or higher crystal symmetry. The separation of the
magnetic and dielectric contributions to the optical properties of a material
are demonstrated using measurements of the MM at varying angles of incidence.",1006.0766v1
2011/2/2,Division of the Energy and of the Momentum of Electromagnetic Waves in Linear Media into Electromagnetic and Material Parts,"We defend a natural division of the energy density, energy flux and momentum
density of electromagnetic waves in linear media in electromagnetic and
material parts. In this division, the electromagnetic part of these quantities
have the same form as in vacuum when written in terms of the macroscopic
electric and magnetic fields, the material momentum is calculated directly from
the Lorentz force that acts on the charges of the medium, the material energy
is the sum of the kinetic and potential energies of the charges of the medium
and the material energy flux results from the interaction of the electric field
with the magnetized medium. We present reasonable models for linear dispersive
non-absorptive dielectric and magnetic media that agree with this division. We
also argue that the electromagnetic momentum of our division can be associated
with the electromagnetic relativistic momentum, inspired on the recent work of
Barnett [Phys. Rev. Lett. 104, 070401 (2010)] that showed that the Abraham
momentum is associated with the kinetic momentum and the Minkowski momentum is
associated with the canonical momentum.",1102.0491v1
2011/2/8,Dynamics of the Magnetic Susceptibility Deep in the Coulomb Phase of the Dipolar Spin Ice Material Ho2Ti2O7,"Low temperature measurements of the ac magnetic susceptibility along the
[110] direction of a single crystal of the dipolar spin ice material Ho2Ti2O7,
in zero static field, are presented. While behavior that is qualitatively
consistent with previous work on Ho2Ti2O7 and the related material Dy2Ti2O7 is
observed, this work extends measurements to appreciably lower temperatures and
frequencies. In the freezing regime, below 1 K, the dynamics are found to be
temperature activated, thus well described by an Arrhenius law with an
activation energy close to 6J_eff, a result that is not easily explained with
the current model of magnetic monopole excitations in dipolar spin ice. The
form and temperature dependence of the ac susceptibility spectra are found to
be nontrivial and distinct from standard glassy relaxation. Particular
attention has been paid to correcting for the demagnetization effect, which is
quite significant in these materials and has important, even qualitative,
effects on the susceptibility spectra.",1102.1703v2
2014/3/19,"Magnetic properties of materials for MR engineering, micro-MR and beyond","We present the results of a systematic measurement of the magnetic
susceptibility of small material samples in a 9.4 T MRI scanner. We measured
many of the most widely used materials in MR engineering and MR micro
technology, including various polymers, optical and substrate glasses, resins,
glues, photoresists, PCB substrates and some fluids. Based on our data, we
identify particularly suitable materials with susceptibilities close to water.
For polyurethane resins and elastomers, we also show the MR spectra, as they
may be a good substitute for silicone elastomers and good casting resins.",1403.4760v2
2015/7/31,Oscillating magnetocaloric effect of a 2D non-relativistic diamagnetic material,"Among the magnetic materials, those with ferromagnetic character are, by far,
the most studied in what concerns applications of the magnetocaloric effect.
However, recently, diamagnetic materials received due attention never received
before, and an oscillatory behavior, analogous to the de Haas-van Alphen
effect, has been found. The present effort describes in details the
magnetocaloric properties of a 2D non-relativistic material (a Gold thin film,
for instance), where oscillations, depending on the reciprocal magnetic field
$1/B$, are found. A comparison of the magnetic entropy change per electron for
some cases is presented and we found $\approx10^{-1}$ k$_{\text{B}}$ (@109.3 K)
for graphenes, $\approx10^{-5}$ k$_{\text{B}}$ (@0.7 K) for 2D Gold and
$\approx 10^{-7}$ k$_{\text{B}}$ (@0.7 K) for 3D Gold.",1507.08891v1
2016/10/25,Large Magnetocaloric effect and magnetic phase transitions in Nd$_2$NiMnO$_6$,"We present combined experimental and theoretical investigations on the
magnetic and magnetocaloric behavior of Nd$_2$NiMnO$_6$. The relative cooling
power (RCP) which quantifies the usefulness of a magnetocaloric (MC) material
is estimated to be $\approx 300$ J/Kg near the ferromagnetic transition at $T_C
\approx 195$ K. This RCP is comparable to the best known MC materials.
Additionally, the magnetic entropy change has a broad profile ($T_C - 50~{\rm
K} < T < T_C + 50~{\rm K}$) leading to an enhancement in the working-range of
temperatures for magnetocaloric based cooling. These features make
Nd$_2$NiMnO$_6$ a superior magnetocaloric material compared for example, to the
nonmagnetic counterpart Y$_2$NiMnO$_6$. We identify the mechanism for the
enhanced RCP which can guide search for future MC materials.",1610.07742v1
2016/11/6,Hidden Weyl Points in Centrosymmetric Paramagnetic Metals,"The transition metal dipnictides TaAs2 , TaSb2 , NbAs2 and NbSb2 have
recently sparked interest for exhibiting giant magnetoresistance. While the
exact nature of magnetoresistance in these materials is still under active
investigation, there are experimental results indicating anisotropic negative
magnetoresistance. We study the effect of magnetic field on the band structure
topology of these materials by applying a Zeeman splitting. In the absence of
magnetic field, we find that the materials are weak topological insulators,
which is in agreement with previous studies. When the magnetic field is
applied, we find that type-II Weyl points form. This result is found first from
a symmetry argument, and then numerically for a k.p model of TaAs2 and a
tight-binding model of NbSb2. This effect can be of help in search for an
explanation of the anomalous magnetoresistance in these materials.",1611.01858v4
2016/11/29,Optical Hall effect in strained graphene,"When passing an optical medium in the presence of a magnetic field, the
polarization of light can be rotated either when reflected at the surface (Kerr
effect) or when transmitted through the material (Faraday rotation). This
phenomenon is a direct consequence of the optical Hall effect arising from the
light-charge carrier interaction in solid state systems subjected to an
external magnetic field, in analogy with the conventional Hall effect. The
optical Hall effect has been explored in many thin films and also more recently
in 2D layered materials. Here, an alternative approach based on strain
engineering is proposed to achieve an optical Hall conductivity in graphene
without magnetic field. Indeed, strain induces lattice symmetry breaking and
hence can result in a finite optical Hall conductivity. First-principles
calculations also predict this strain-induced optical Hall effect in other 2D
materials. Combining with the possibility of tuning the light energy and
polarization, the strain amplitude and direction, and the nature of the optical
medium, large ranges of positive and negative optical Hall conductivities are
predicted, thus opening the way to use these atomistic thin materials in novel
specific opto-electro-mechanical devices.",1611.09529v1
2017/8/9,Three-Dimensional Anisotropic Magnetoresistance in the Dirac Node-Line Material ZrSiSe,"The family of materials defined as ZrSiX (X = S, Se, Te) has been established
as Dirac node-line semimetals, and subsequent study is urgent to exploit the
promising application of unusual magnetoresistance property. In this work, we
systematically investigated the anisotropic magnetoresistance in the
newly-discovered Dirac node-line material ZrSiSe. By applying a magnetic field
of 3 T by a vector field, the three-dimensional (3D) magnetoresistance (MR)
shows strong anisotropy. The MR ratio of maximum and minimum directions can
reach 7 at 3 T and keeps increasing at the higher magnetic field. The
anisotropic MR forms a butterfly-shaped curve, which indicates the quasi-2D
electronic structures. This is further confirmed by the angular-dependent
Shubnikov-de Haas (SdH) oscillations. The first-principles calculations
establish the quasi-2D tubular-shaped Fermi surface near the X point in the
Brillouin zone. Our findings shed light on the 3D mapping of MR and the
potential applications in magnetic sensors based on ZrSiSe Dirac materials.",1708.02779v2
2018/4/16,Calculation of impurity density and electron-spin relaxation times in p-type GaAs:Mn,"Magnetic semiconductors have aroused interest due to their various
functionalities related to spintronic devices. Manganese (Mn) as a
substitutional impurity in A3B5 semiconductors supplies not only holes, but
also localized spins. The ejection of Mn atoms with an uncompensated magnetic
moment leads to the appearance of ferromagnetic properties. The most suitable
material characterized by long-term spin dynamics is n-type GaAs. In p-type
GaAs, the spin relaxation time of electrons is generally much shorter. For
purposes of this research, electron-spin relaxation times in 3D and 2D p-type
GaAs were studied. Calculation of impurity densities and charge state of
magnetic acceptors demonstrate the essential composition of the material.
Comparison of theoretical and experimental data in optical-spin orientation of
electrons reveal the longest spin relaxation time of 77 ns in 2D GaAs:Mn, less
than twice the best time in the p-type 3D GaAs material.",1804.05581v2
2020/8/5,Anomalous Hall and Nernst effects in epitaxial films of topological kagome magnet Fe3Sn2,"The topological kagome magnet (TKM) Fe3Sn2 exhibits unusual topological
properties, flat electronic bands, and chiral spin textures, making it an
exquisite materials platform to explore the interplay between topological band
structure, strong electron correlations, and magnetism. Here we report the
first synthesis of high-quality epitaxial (0001) Fe3Sn2 films with large
intrinsic anomalous Hall effect close to that measured in bulk single crystals.
In addition, we measured a large, anisotropic anomalous Nernst coefficient Syx
of 1.26 {\mu}V/K, roughly 2-5x greater than that of common ferromagnets,
suggesting the presence of Berry curvature sources near the Fermi level in this
system. Crucially, the realization of high-quality Fe3Sn2 films opens the door
to explore emergent interfacial physics and create novel spintronic devices
based on TKMs by interfacing Fe3Sn2 with other quantum materials and by
nanostructure patterning.",2008.02202v1
2014/1/14,Simultaneously Magnetic- and Electric-dipole Active Spin Excitations Govern the Static Magnetoelectric Effect in Multiferroic Materials,"We derive a sum rule to demonstrate that the static magnetoelectric (ME)
effect is governed by optical transitions that are simultaneously excited via
the electric and magnetic components of light. By a systematic analysis of
magnetic point groups, we show that the ME sum rule is applicable to a broad
variety of non-centrosymmetric magnets including ME multiferroic compounds. Due
to the dynamical ME effect, the optical excitations in these materials can
exhibit directional dichroism, i.e. the absorption coefficient can be different
for counter-propagating light beams. According to the ME sum rule, the
magnitude of the linear ME effect of a material is mainly determined by the
directional dichroism of its low-energy optical excitations. Application of the
sum rule to the multiferroic Ba$_2$CoGe$_2$O$_7$, Sr$_2$CoSi$_2$O$_7$ and
Ca$_2$CoSi$_2$O$_7$ shows that in these compounds the static ME effect is
mostly governed by the directional dichroism of the spin-wave excitations in
the GHz-THz spectral range. On this basis, we argue that the studies of
directional dichroism and the application of ME sum rule can promote the
synthesis of new materials with large static ME effect.",1401.3306v1
2018/5/27,Prediction of new multiferroic and magnetoelectric material Fe3Se4,"Nowdays, multiferroic materials with magnetoelectric coupling have many
real-world applications in the fields of novel memory devices. It is
challenging is to create multiferroic materials with strongly coupled
ferroelectric and ferrimagnetic orderings at room temperature. The single
crystal of ferric selenide (Fe3Se4) shows type-II multiferroic due to the
coexistence of ferroelectric as well as magnetic ordering at room temperature.
We have investigated the lattice instability, electronic structure,
ferroelectric, ferrimagnetic ordering and transport properties of ferroelectric
metal Fe3Se4. The density of states shows considerable hybridization of Fe-3d
and Se-4p states near the Fermi level confirming its metallic behavior. The
magnetic moments of Fe cations follow a type-II ferrimagnetic and ferroelectric
ordering with a calculated total magnetic moment of 4.25 per unit cell
(Fe6Se8). The strong covalent bonding nature of Fe-Se leads to its
ferroelectric properties. In addition, the symmetry analysis suggests that
tilting of Fe sub-lattice with 3d-t2g orbital ordering is due to the
Jahn-Teller (JT) distortion. This study provides further insight in the
development of spintronics related technology using multiferroic materials.",1805.10607v1
2020/5/29,Exploiting femtosecond laser exposure for additive and subtractive fabrication of functional materials: A Route to designer 3D Magnetic Nanostructures,"Three-dimensional nanostructured functional materials are important systems,
allowing new means to intricately control electromagnetic properties. A key
problem is realising a 3D printing methodology upon the nanoscale that can
yield a range of functional materials. In this letter, it is shown that
two-photon lithography when combined with femtosecond machining of sacrificial
layers, can be used to realise such a vision and produce 3D functional
nanomaterials of complex geometry. This is demonstrated by fabricating 3D
magnetic nanowires that exhibit controlled domain wall injection and
propagation. Secondly, we fabricate large scale 3D artificial spin-ice
structures whose complex switching can be probed using optical magnetometry. We
show that by careful analysis of the magneto-optical Kerr effect signal and by
comparison with micro-magnetic simulations, depth dependent switching
information can be obtained from the 3DASI lattice. The work paves the way to
new materials, which exploit additional physics provided by non-trivial 3D
geometries.",2005.14479v2
2020/9/15,Widely Spaced Planes of Magnetic Dimers in the Ba6Y2Rh2Ti2O17-δ Hexagonal Perovskite,"We report the synthesis and initial characterization of
Ba6Y2Rh2Ti2O17-{\delta}, a previously unreported material with a hexagonal
symmetry structure. Face-sharing RhO6 octahedra form triangular planes of Rh2O9
dimers that are widely separated in the perpendicular direction. The material
displays a small effective magnetic moment, due to the Rh ions present, and a
negative Curie-Weiss temperature. The charge transport and optical band gaps
are very similar, near 0.16 eV. A large upturn in the heat capacity at
temperatures below 1 K, suppressed by applied magnetic fields larger than
{{\mu}0H = 2 Tesla, is observed. A large T-linear term in the specific heat
({\gamma}=166 mJ/mol f.u-K2) is seen, although the material is insulating at
low temperatures. These results suggest the possibility of a spin liquid ground
state in this material.",2009.07333v2
2021/2/19,Axion-matter coupling in multiferroics,"Multiferroics (MFs) are materials with two or more ferroic orders, like
spontaneous ferroelectric and ferromagnetic polarizations. Such materials can
exhibit a magnetoelectric effect whereby magnetic and ferroelectric
polarizations couple linearly, reminiscent of, but not identical to the
electromagnetic $\boldsymbol{E}\cdot \boldsymbol{B}$ axion coupling. Here we
point out a possible mechanism in which an external dark matter axion field
couples linearly to ferroic orders in these materials without external applied
fields. We find the magnetic response to be linear in the axion-electron
coupling. At temperatures close to the ferromagnetic transition fluctuations
can lead to an enhancement of the axion-induced magnetic response. Relevant
material candidates such as the Lu-Sc hexaferrite family are discussed.",2102.10171v2
2021/3/2,A mono-material Nernst thermopile with hermaphroditic legs,"A large transverse thermoelectric response, known as anomalous Nernst effect
(ANE) has been recently observed in several topological magnets. Building a
thermopile employing this effect has been the subject of several recent
propositions. Here, we design and build a thermopile with an array of tilted
adjacent crystals of Mn$_3$Sn. The design employs a single material and
replaces pairs of P and N thermocouples of the traditional design with
hermaphroditic legs. The design exploits the large lag angle between the
applied field and the magnetization, which we attribute to the interruption of
magnetic octupoles at the edge of $xy$-plane. Eliminating extrinsic contacts
between legs will boost the efficiency, simplify the process and pave the way
for a new generation of thermopiles.",2103.01467v1
2022/5/30,High-throughput study of the anomalous Hall effect,"Despite being known for a long time the anomalous Hall effect still attracts
attention because of its complex origins, its connection to topology and
because it serves as a useful probe of the magnetic order. Here we study the
anomalous Hall effect using automatic high-throughput calculation scheme. We
calculate the intrinsic anomalous Hall effect in 2871 ferromagnetic materials.
We use these results to study general properties of the anomalous Hall effect
such as its dependence on the strength of the spin-orbit coupling or
magnetization. We also examine the origin of the anomalous Hall effect in the
materials with the largest effect and show that the origin of the large
anomalous Hall effect is usually associated with symmetry protected band
degeneracies in the non-relativistic electronic structure, typically mirror
symmetry protected nodal lines. Additionally, we study the dependence of the
anomalous Hall effect on the magnetization direction, showing that in many
materials it differs significantly from the commonly assumed expression
$\mathbf{j}^\text{AHE} \sim \mathbf{M} \times \mathbf{E}$.",2205.14907v1
2022/8/25,Berry curvature induced anomalous Hall conductivity in magnetic topological oxide double perovskite Sr2FeMoO6,"Oxide materials exhibit several novel structural, magnetic, and electronic
properties. Their stability under ambient conditions, easy synthesis, and high
transition temperatures provide such systems with an ideal ground for realizing
topological properties and real-life technological applications. However,
experimental evidence of topological states in oxide materials is rare. In this
study, we have synthesized single crystals of oxide double perovskite Sr2FeMoO6
and revealed its topological nature by investigating its structural, magnetic,
and electronic properties. We observed that the system crystallized in the
cubic space group Fm-3m, which is a half-metallic ferromagnet. Transport
measurements show an anomalous Hall effect, and it is evident that the Hall
contribution originates from the Berry curvature. Assuming a shift of the Fermi
energy towards the conduction band, the contribution of the anomalous Hall
effect is enhanced owing to the presence of a gaped nodal line. This study can
be used to explore and realize the topological properties of bulk oxide
systems.",2208.11988v1
2023/2/22,Cavity Moiré Materials: Controlling Magnetic Frustration with Quantum Light-Matter Interaction,"Cavity quantum electrodynamics (QED) studies the interaction between light
and matter at the single quantum level and has played a central role in quantum
science and technology. Combining the idea of cavity QED with moir\'e
materials, we theoretically show that strong quantum light-matter interaction
provides a way to control frustrated magnetism. Specifically, we develop a
theory of moir\'e materials confined in a cavity consisting of thin polar van
der Waals crystals. We show that nontrivial quantum geometry of moir\'e flat
bands leads to electromagnetic vacuum dressing of electrons, which produces
appreciable changes in single-electron energies and manifests itself as
long-range electron hoppings. We apply our general formulation to a twisted
transition metal dichalcogenide heterobilayer encapsulated by ultrathin
hexagonal boron nitride layers and predict its phase diagram at different twist
angles and light-matter coupling strengths. Our results indicate that the
cavity confinement enables one to control magnetic frustration of moir\'e
materials and might allow for realizing various exotic phases such as a quantum
spin liquid.",2302.11582v1
2023/5/3,Large anomalous Hall effect and unusual domain switching in an orthorhombic antiferromagnetic material NbMnP,"Specific antiferromagnetic (AF) spin configurations generate large anomalous
Hall effects (AHEs) even at zero magnetic field through nonvanishing Berry
curvature in momentum space. In addition to restrictions on AF structures,
suitable control of AF domains is essential to observe this effect without
cancellations among its domains; therefore, compatible materials remain
limited. Here we show that an orthorhombic noncollinear AF material, NbMnP,
acquired AF structure-based AHE and controllability of the AF domains.
Theoretical calculations indicated that a large Hall conductivity of $\sim230$
$\Omega^{-1}$cm$^{-1}$ originated from the AF structure of NbMnP. Symmetry
considerations explained the production of a small net magnetization, whose
anisotropy enabled the generation and cancellation of the Hall responses using
magnetic fields in different directions. Finally, asymmetric hysteresis in
NbMnP shows potential for development of controllability of responses in AF
materials.",2305.02028v3
2023/7/11,The curvature-induced magnetization in CrI3 bilayer: flexomagnetic effect enhancement in van der Waals antiferromagnets,"The bilayer of CrI3 is a prototypical van der Waals 2D antiferromagnetic
material with magnetoelectric effect. It is not generally known, however, that
for symmetry reasons the flexomagnetic effect, i.e., the strain
gradient-induced magnetization, is also possible in this material. In the
present paper, based on the first principle calculations, we estimate the
flexomagnetic effect to be 200 {\mu}B{\AA} that is two orders of magnitude
higher than it was predicted for the referent antiperovskite flexomagnetic
material Mn3GaN. The two major factors of flexomagnetic effect enhancement
related to the peculiarities of antiferromagnetic structure of van der Waals
magnets is revealed: the strain-dependent ferromagnetic coupling in each layer
and large interlayer distance separating antiferromagnetically coupled ions.
Since 2D systems are naturally prone to mechanical deformation, the emerging
field of flexomagnetism is of special interest for application in spintronics
of van der Waals materials and straintronics in particular.",2307.05084v1
2018/12/6,Deciphering structural and magnetic disorder in the chiral skyrmion host materials Co$_x$Zn$_y$Mn$_z$ ($x+y+z=20$),"Co$_x$Zn$_y$Mn$_z$ ($x+y+z=20$) compounds crystallizing in the chiral
$\beta$-Mn crystal structure are known to host skyrmion spin textures even at
elevated temperatures. As in other chiral cubic skyrmion hosts, skyrmion
lattices in these materials are found at equilibrium in a small pocket just
below the magnetic Curie temperature. Remarkably, CoxZnyMnz compounds have also
been found to host metastable non-equilibrium skyrmion lattices in a broad
temperature and field range, including down to zero-field and low temperature.
This behavior is believed to be related to disorder present in the materials.
Here, we use neutron and synchrotron diffraction, density functional theory
calculations, and DC and AC magnetic measurements, to characterize the atomic
and magnetic disorder in these materials. We demonstrate that Co has a strong
site-preference for the diamondoid 8c site in the crystal structure, while Mn
tends to share the geometrically frustrated 12d site with Zn, due to its
ability to develop a large local moment on that site. This magnetism-driven
site specificity leads to distinct magnetic behavior for the Co-rich 8c
sublattice and the Mn on the 12d sublattice. The Co-rich sublattice orders at
high temperatures (compositionally tunable between 100K to 470K) with a moment
around 1 $\mu_B$/atom and maintains this order to low temperature. The Mn-rich
sublattice holds larger moments (about 3 $\mu_B$ which remain fluctuating below
the Co moment ordering temperature. At lower temperature, the fluctuating Mn
moments freeze into a reentrant disordered cluster-glass state with no net
moment, while the Co moments maintain order. This two-sublattice behavior
allows for the observed coexistence of strong magnetic disorder and ordered
magnetic states such as helimagnetism and skyrmion lattices.",1812.02767v2
2022/5/22,Electronic structure and magnetic properties of 3d-4f double perovskite material,"Double perovskite-based magnets wherein frustration and competition between
emergent degrees of freedom are at play can lead to novel electronic and
magnetic phenomena. Herein, we report the electronic structure and magnetic
properties of an ordered double perovskite material Ho2CoMnO6. In the double
perovskite with general class A2BB'O6, the octahedral B and B'-site has a
distinct crystallographic site. The Rietveld refinement of XRD data reveals
that Ho2CoMnO6 crystallizes in the monoclinic P21/n space group. The X-ray
photoelectron spectroscopy confirms the charge state of cations present in this
material. The temperature dependence of magnetization and specific heat exhibit
a long-range ferromagnetic ordering at Tc ~ 76 K owing to the presence of super
exchange interaction between Co2+ and Mn4+ moments. Furthermore, the
magnetization isotherm at 5 K shows a hysteresis curve that confirms
ferromagnetic behavior of this double perovskite. We observed a re-entrant
glassy state in the intermediate temperature regime, which is attributed to
inherent anti-site disorder and competing interactions. A large magnetocaloric
effect has been observed much below the ferromagnetic transition temperature.
The temperature-dependent Raman spectroscopy studies support the presence of
spin-phonon coupling and short-range order above Tc in this double perovskite.
The stabilization of magnetic ordering and charge states is further analyzed
through electronic structure calculations. The latter also infers the compound
to be a narrow band gap insulator with the gap arising between the lower and
upper Hubbard Co-d subbands. Our results demonstrate that anti-site disorder
and complex 3d-4f exchange interactions in the spin-lattice account for the
observed electronic and magnetic properties in this promising double perovskite
material.",2205.10877v2
2013/4/26,Signature of gate-tunable magnetism in graphene grafted with Pt-porphyrins,"Inducing magnetism in graphene holds great promises, such as controlling the
exchange interaction with a gate electrode and generating exotic magnetic
phases. Coating graphene with magnetic molecules or atoms has so far mostly
lead to decreased graphene mobility. In the present work, we show that
Pt-porphyrins adsorbed on graphene lead to an enhanced mobility and to
gate-dependent magnetism. We report that porphyrins can be donor or acceptor,
depending on graphene s initial doping. The porphyrins transfer charge and
ionize around the charged impurities on graphene, decreasing the graphene
doping and increasing its mobility. In addition, ionized porphyrins carry a
magnetic moment. Using the sensitivity of mesoscopic transport to magnetism, in
particular the superconducting proximity effect and conductance fluctuations,
we explore the magnetic order induced in graphene by the interacting magnetic
moments of the ionized porphyrins. Among the signatures of magnetism, we find
two-terminal-magnetoresistance fluctuations with an odd component, a tell-tale
sign of time reversal symmetry breaking at zero field, that does not exist in
uncoated graphene sample. When graphene is connected to superconducting
electrodes, the induced magnetism leads to a gate-voltage-dependent suppression
of the supercurrent, modified magnetic interference patterns, and
gate-voltage-dependent magnetic hysteresis. The magnetic signatures are
greatest for long superconductor graphene superconductor junctions and for
samples with the highest initial doping, compatible with a greater number of
ionized and thus magnetic porphyrins. Our findings suggest that long-range
magnetism is induced through graphene by the ionized porphyrins magnetic
moment. This magnetic interaction is controlled by the density of carriers in
graphene, a tunability that could be exploited in spintronic applications.",1304.7089v2
2023/9/19,Remanence Increase in SrFe$_{12}$O$_{19}$/Fe Exchange-Decoupled Hard-Soft Composite Magnets Owing to Dipolar Interactions,"In the search for improved permanent magnets, fueled by the geostrategic and
environmental issues associated with rare-earth-based magnets, magnetically
hard (high anisotropy)-soft (high magnetization) composite magnets hold promise
as alternative magnets that could replace modern permanent magnets, such as
rare-earth-based and ceramic magnets, in certain applications. However, so far,
the magnetic properties reported for hard-soft composites have been
underwhelming. Here, an attempt to further understand the correlation between
magnetic and microstructural properties in strontium ferrite-based composites,
hard SrFe$_{12}$O$_{19}$ (SFO) ceramics with different contents of Fe particles
as soft phase, both in powder and in dense injection molded magnets, is
presented. In addition, the influence of soft phase particle dimension, in the
nano- and micron-sized regimes, on these properties is studied. While Fe and
SFO are not exchange-coupled in our magnets, a remanence that is higher than
expected is measured. In fact, in composite injection molded anisotropic
(magnetically oriented) magnets, remanence is improved by 2.4% with respect to
a pure ferrite identical magnet. The analysis of the experimental results in
combination with micromagnetic simulations allows us to establish that the type
of interaction between hard and soft phases is of a dipolar nature, and is
responsible for the alignment of a fraction of the soft spins with the
magnetization of the hard. The mechanism unraveled in this work has
implications for the development of novel hard-soft permanent magnets.",2309.10676v1
2000/12/19,Mechanism of Magnetism in Stacked Nanographite: Theoretical Study,"Antiferromagnetism in stacked nanographite is investigated with using the
Hubbard-type model. The A-B stacking is favorable for the hexagonal
nanographite with zigzag edges, in order that magnetism appears. Next, we find
that the open shell electronic structures can be origins of the decreasing
magnetic moment with the decrease of the inter-graphene distance, as
experiments on adsorption of molecules suggest.",0012349v3
2001/1/15,Tunneling magnetoresistance in diluted magnetic semiconductor tunnel junctions,"Using the spin-polarized tunneling model and taking into account the basic
physics of ferromagnetic semiconductors, we study the temperature dependence of
the tunneling magnetoresistance (TMR) in the diluted magnetic semiconductor
(DMS) trilayer heterostructure system (Ga,Mn)As/AlAs/(Ga,Mn)As. The
experimentally observed TMR ratio is in reasonable agreement with our result
based on the typical material parameters. It is also shown that the TMR ratio
has a strong dependence on both the itinerant-carrier density and the magnetic
ion density in the DMS electrodes. This can provide a potential way to achieve
larger TMR ratio by optimally adjusting the material parameters.",0101206v1
2001/1/17,Negative Magnetoresistance Produced by Hall Fluctuations in a Ferromagnetic Domain Structure,"We present a model for a negative magnetoresistance (MR) that would develop
in a material with many ferromagnetic domains even if the individual domains
have no magnetoresistance and even if there is no boundary resistance. The
negative MR is due to a classical current-distortion effect arising from
spatial variations in the Hall conductivity, combined with a change in domain
structure due to an applied magnetic field. The negative MR can exceed 1000% if
the product of the carrier relaxation time and the internal magnetic field due
to spontaneous magnetization is sufficiently large.",0101268v2
2002/7/22,Thermodynamic properties of the exactly solvable transverse Ising model on decorated planar lattices,"The generalized mapping transformation technique is used to obtain the exact
solution for the transverse Ising model on decorated planar lattices. Within
this scheme, the basic thermodynamic quantities are calculated for different
planar lattices with arbitrary spins of decorating atoms. The particular
attention has been paid to the investigation of the transverse-field effects on
magnetic properties of the system under investigation. The most interesting
numerical results for the phase diagrams, compensation temperatures and several
thermodynamic quantities are discussed in detail for the ferrimagnetic version
of the model.",0207522v1
2002/10/30,Particle size effects in the antiferromagnetic spinel CoRh$_2$O$_4$,"We report the particle size dependent magnetic behaviour in the
antiferromagnetic spinel CoRh2O4. The nanoparticles were obtained by mechanical
milling of bulk material, prepared under sintering method. The XRD spectra show
that the samples are retaining the spinel structure. The particle size
decreases from 70 nm to 16 nm as the milling time increases from 12 hours to 60
hours. The magnetic measurements suggest that the antiferromagnetic ordering at
T$_N$ $\approx$ 27K exists in bulk as well as in nanoparticle samples. However,
the magnitude of the magnetization below T$_N$ increases with decreasing
particle size.",0210678v1
2003/2/11,Magnetic phase diagram of cubic perovskites SrMn_1-xFe_xO_3,"We combine the results of magnetic and transport measurements with Mossbauer
spectroscopy and room-temperature diffraction data to construct the magnetic
phase diagram of the new family of cubic perovskite manganites SrMn_1-xFe_xO_3.
We have found antiferromagnetic ordering for lightly and heavily Fe-substituted
material, while intermediate substitution leads to spin-glass behavior. Near
the SrMn_0.5Fe_0.5O_3 composition these two types of ordering are found to
coexist and affect one another. The spin glass behavior may be caused by
competing ferro- and antiferromagnetic interactions among Mn^4+ and observed
Fe^3+ and Fe^5+ ions.",0302214v1
2003/5/13,Sonochemical Modification of the Superconducting Properties of MgB2,"Ultrasonic irradiation of magnesium diboride slurries in decalin produces
material with significant inter-grain fusion. Sonication in the presence of
Fe(CO)5 produces magnetic Fe2O3 nanoparticles embedded in the MgB2 bulk. The
resulting superconductor-ferromagnet composite exhibits considerable
enhancement of the magnetic hysteresis, which implies an increase of vortex
pinning strength due to embedded magnetic nanoparticles.",0305303v1
2003/11/3,Disorder effects in diluted magnetic semiconductors,"In recent years, disorder has been shown to be crucial for the understanding
of diluted magnetic semiconductors. Effects of disorder in these materials are
reviewed with the emphasis on theoretical works. The types and spatial
distribution of defects are discussed. The effect of disorder on the intimately
related transport and magnetic properties are considered from the viewpoint of
both the band picture and the isolated-impurity approach. Finally, the
derivation and properties of spin-only models are reviewed.",0311029v2
2003/12/9,Structural and magnetic properties of transition metal substituted ZnO,"Structural and magnetic properties have been studied for polycrystalline
Zn_{1-x}TM_xO, where TM (transition metal ions) = Mn, Fe, and Co. No bulk
ferromagnetism was observed for single-phase materials, contrary to the
existing theories. Single-phase samples demonstrate paramagnetic Curie-Weiss
behavior with antiferromagnetic interactions, similar to other diluted magnetic
semiconductors. Non-optimal synthesis conditions lead to formation of second
phases that are responsible for spin-glass behavior (ZnMnO_3 impurity for
Zn_{1-x}Mn_xO (S. Kolesnik et al., J. Supercond.: Incorp. Novel Magn. 15, 251
(2002)) or high-temperature ferromagnetic ordering (Co metal for Zn_{1-x}Co_xO
with the Curie temperature T_C > 800 K or (Zn,Fe)_3O_4 for Zn_{1-x}Fe_xO with
T_C = 440 K).",0312233v1
2004/1/28,Superconducting Properties of Combustion Synthesized MgB2,"We have successfully prepared the MgB2 superconducting bulk and powdered
materials by the method of combustion synthesis. The starting materials used in
this study were powders of Mg and B. X-ray powder diffraction pattern was well
assigned to the P6/mmm MgB2 phase. The temperature dependence of magnetization
shows sharp superconducting transition around 38K. The critical current density
can be estimated from the hysteresis of the magnetization curvature using the
Bean's model. The powdered sample shows a high critical current density of
2x10^6 A/cm2 at 5K under the magnetic field of 1T.",0401572v1
2004/8/6,Electronic and magnetic properties of the (111) surfaces of NiMnSb,"Using an ab-initio electronic structure method, I study the (111) surfaces of
the half-metallic NiMnSb alloy. In all cases there is a very pronounced surface
state within the minority gap which destroys the half-metallicity This state
survives for several atomic layers below the surface contrary to the (001)
surfaces where surface states were located only at the surface layer. The lower
dimensionality of the surface leads in general to large enhancements of the
surface spin moments.",0408131v1
2004/11/16,Magnetic short range order above the Curie temperature in Fe and Ni,"We report the first results of time-dependent density functional simulations
of magnetic properties of Fe and Ni at finite temperatures. They reveal the
existence of local moments in Ni above the Curie temperature, coupled to strong
short range order. In Fe the short range order is also present to a lesser
extent but spin wave like excitations persist in both materials well above the
Curie temperature in the paramagnetic state. The prevailing view of magnetic
order should be reconsidered in light of these findings.",0411393v1
2005/5/5,The influence of electrostatic potentials on the apparent s-d exchange energy in III-V diluted magnetic semiconductors,"The muffin-tin model of an effective-mass electron interacting with magnetic
ions in semiconductors is extended to incorporate electrostatic potentials that
are present in the case of Mn-based III-V compounds (${Ga}_{1-x} {Mn}_x {N}$,
${Ga}_{1-x} {Mn}_x {As}$). Since the conduction band electron is repelled from
negatively charged magnetic ions and attracted by compensating donors, the
\emph{apparent} value of the s-d exchange coupling $N_0 \alpha$ is reduced. It
is shown that the magnitude of this effect increases when x diminishes. Our
model may explain an unusual behavior of electron spin splitting observed
recently in those two materials in the Mn concentration range x <= 0.2%.",0505126v1
2005/5/25,Sharp magnetization step across the ferromagnetic to antiferromagnetic transition in doped-CeFe$_2$ alloys,"Very sharp magnetization step is observed across the field induced
antiferromagnetic to ferromagnetic transition in various doped-CeFe$_2$ alloys,
when the measurement is performed below 5K. In the higher temperature regime
(T$>$5K) this transition is quite smooth in nature. Comparing with the recently
observed similar behaviour in manganites showing colossal magnetoresistance and
magnetocaloric material Gd$_5$Ge$_4$ we argue that such magnetization step is a
generalized feature of a disorder influenced first order phase transition.",0505609v1
2005/6/7,"Fast, Preisach-like characterization of hysteretic systems","Proposed is a substantially simplified, Preisach-like model for
characterization of hysteretic systems, in particular magnetic systems. The
main idea is to replace a two-dimensional Preisach density with just two real
functions, describing in a {\em unique way} the reversible and irreversible
processes. As a byproduct of our model we prove, that the major hysteresis loop
alone is insufficient to produce the unique Preisach map. Keywords: magnetic
hysteresis; magnetization processes; materials testing; modeling.",0506177v1
2005/6/23,Crystallography and Chemistry of Perovskites,"Despite the simplicity of the original perovskite crystal structure, this
family of compounds shows an enormous variety of structural modifications and
variants. In the following, we will describe several examples of perovskites,
their structural variants and discuss the implications of distortions and
non-stoichiometry on their electronic and magnetic properties.",0506606v1
2005/7/5,Magnetostatic field noise near metallic surfaces,"We develop an effective low-frequency theory of the electromagnetic field in
equilibrium with thermal objects. The aim is to compute thermal magnetic noise
spectra close to metallic microstructures. We focus on the limit where the
material response is characterized by the electric conductivity. At the
boundary between empty space and metallic microstructures, a large jump occurs
in the dielectric function which leads to a partial screening of low-frequency
magnetic fields generated by thermal current fluctuations. We resolve a
discrepancy between two approaches used in the past to compute magnetic field
noise spectra close to microstructured materials.",0507098v1
2005/10/8,Slater-Pauling Rule and Curie-Temperature of Co$_2$-based Heusler compounds,"A concept is presented serving to guide in the search for new materials with
high spin polarization. It is shown that the magnetic moment of half-metallic
ferromagnets can be calculated from the generalized Slater-Pauling rule.
Further, it was found empirically that the Curie temperature of Co$_2$ based
Heusler compounds can be estimated from a seemingly linear dependence on the
magnetic moment. As a successful application of these simple rules, it was
found that Co$_2$FeSi is, actually, the half-metallic ferromagnet exhibiting
the highest magnetic moment and the highest Curie temperature measured for a
Heusler compound.",0510210v1
2006/1/27,Fabrication of magnetic atom chips based on FePt,"We describe the design and fabrication of novel all-magnetic atom chips for
use in ultracold atom trapping. The considerations leading to the choice of
nanocrystalline exchange coupled FePt as best material are discussed. Using
stray field calculations, we designed patterns that function as magnetic atom
traps. These patterns were realized by spark erosion of FePt foil and e-beam
lithography of FePt film. A mirror magneto-optical trap (MMOT) was obtained
using the stray field of the foil chip.",0601633v1
2006/7/4,Effects of annealing time on structural and magnetic properties of L10-FePt nanoparticles synthesized by the SiO2-nanoreactor method,"We investigated effects of annealing time on structural and magnetic
properties of the L10-FePt nanoparticles synthesized by the SiO2-nanoreacter
method. The magnetization and powder X-ray diffraction studies revealed that
the annealing at 900 oC for 9 hr could convert all of the fcc-nanoparticles to
the well-crystallized L10 structure with a large coercivity while keeping their
particle size. Such monodisperse and highly crystalline L10-FePt nanoparticles
are a promising material for the realization of ultra-high density recording.",0607072v2
2006/7/7,Enhanced carrier scattering rates in dilute magnetic semiconductors with correlated impurities,"In III-V dilute magnetic semiconductors (DMSs) such as Ga$_{1-x}$Mn$_x$As,
the impurity positions tend to be correlated, which can drastically affect the
electronic transport properties of these materials. Within the memory function
formalism we have derived a general expression for the current relaxation
kernel in spin and charge disordered media and have calculated spin and charge
scattering rates in the weak-disorder limit. Using a simple model for magnetic
impurity clustering, we find a significant enhancement of the charge
scattering. The enhancement is sensitive to cluster parameters and may be
controllable through post-growth annealing.",0607177v1
2006/9/5,Relaxation of the Electron Spin in Quantum Dots Via One- and Two-Phonon Processes,"We have studied direct and Raman processes of the decay of electron spin
states in a quantum dot via radiation of phonons corresponding to elastic
twists. Universal dependence of the spin relaxation rate on the strength and
direction of the magnetic field has been obtained in terms of the electron
gyromagnetic tensor and macroscopic elastic constants of the solid.",0609108v1
1995/8/2,Search for Magnetic Monopoles Trapped in Matter,"There have been many searches for magnetic monopoles in flight, but few for
monopoles in matter. We have searched for magnetic monopoles in meteorites,
schists, ferromanganese nodules, iron ores and other materials. The detector
was a superconducting induction coil connected to a SQUID (Superconducting
Quantum Interference Device) with a room temperature bore 15 cm in diameter. We
tested a total of more than 331 kg of material including 112 kg of meteorites.
We found no monopole and conclude the overall monopole/nucleon ratio in the
samples is $<1.2 \times 10^{-29}$ with a 90\% confidence level.",9508003v1
2007/9/7,Theory of Electromotive Force Induced by Domain Wall Motion,"We formulate a theory on the dynamics of conduction electrons in the presence
of moving magnetic textures in ferromagnetic materials. We show that the
variation of local magnetization in both space and time gives rise to
topological fields, which induce electromotive forces on the electrons.
Universal results are obtained for the emf induced by both transverse and
vortex domain walls traveling in a magnetic film strip, and their measurement
may provide clear characterization on the motion of such walls.",0709.1117v3
2008/2/25,Electronic structure and ferromagnetic behavior in the $Mn_{1-x}A_xAs_{1-y}B_y$ alloys,"In this work, a systematic ab initio study of the influence of doping on
electronic structure and local magnetic moments of ferromagnetic MnAs has been
carried out. The majority of the considered substitution elements, potentially
suitable for modification of MnAs as working material of magnetic refrigerators
is shown to result in reduction of the ferromagnetic moment. But there are
variants of anionic substitution (for example, substitution of As for S and Se)
when the magnetic moment grows.",0802.3686v1
2008/4/25,"Structural, magnetic and electronic properties of quaternary oxybismuthides LaOMBi (where M = Sc, Ti ... Ni, Cu) - possible parent phases for new superconducting materials","The extensive ab initio total energy calculations using the VASP-PAW method
with the generalized gradient approximation (GGA) for the exchange-correlation
potential are applied to systematic investigation of structural, electronic and
magnetic properties in quaternary oxybismuthides LaOMBi (where M = Sc, Ti...Ni,
Cu). The energy spectrum features similar to lanthanum-iron oxyarsenide LaOFeAs
and non-magnetic ground state are indicative of superconductivity possible in
lanthanum-nickel oxybismuthide LaONiBi.",0804.4064v1
2009/4/27,Surface magnetization in non-doped ZnO nanostructures,"We have investigated the magnetic properties of non-doped ZnO nanostructures
by using {\it ab initio} total energy calculations. Contrary to many proposals
that ferromagnetism in non-doped semiconductors should be induced by intrinsic
point defects, we show that ferromagnetism in nanostructured materials should
be mediated by extended defects such as surfaces and grain boundaries. This
kind of defects create delocalized, spin polarized states that should be able
to warrant long-range magnetic interactions.",0904.4147v1
2009/8/26,Magnetic anisotropy in Li-phosphates and origin of magnetoelectricity in LiNiPO4,"Li-based phosphates are paradigmatic materials for magnetoelectricity. By
means of first-principles calculations, we elucidate the microscopic origin of
spin anisotropy and of magnetoelectric effects in LiNiPO4. The comparison with
LiCoPO4 reveals that Co-d7 and Ni-d8 electronic clouds show distinct orbital
shapes, which in turn result in an opposite trend of the local spin anisotropy
with respect to the surrounding O6 cages. Due to magnetic anisotropy, the
Ni-based phosphate shows a peculiar ""angled-cross"" spin ground-state, which is
responsible for magnetoelectricity. In this respect, we show that, under a
magnetic field Hx, an electronic polarization Pz arises, with an estimated
linear magneto-electric coefficient in good agreement with experiments.",0908.3802v1
2010/8/2,Tunneling spectroscopy probing magnetic and nonmagnetic electrodes in tunnel junctions,"Tunneling spectroscopy is applied to tunnel junctions with only one or no
ferromagnetic electrode to study the excitation of quasi particles in magnetic
tunnel junctions. The bias dependence is investigated with high accuracy by
inelastic electron tunneling spectroscopy. Both types of junctions show a zero
bias anomaly that is different in size and sign compared to magnetic tunnel
junctions, i.e. junctions with two ferromagnetic electrodes. A pronounced
difference is also found depending on the material that is probed by the
tunneling electrons, which might be attributed to the excitation of magnons.",1008.0326v1
2010/12/3,Spontaneous toroidic effects in Ba2CoGe2O7,"The unusual magnetoelectric effects observed in the multiferroic phase
arising below TN=6.7K in Ba2CoGe2O7 (BCG) are related to the spontaneous
toroidal moment existing in this compound. The transition to the multiferroic
state, which involves spontaneous magnetization, polarization and toroidal
moment gives rise to spontaneous toroidic effects. These effects produce
specific contributions to the spontaneous polarization and magnetization under
applied magnetic or electric fields which provide indirect indications of the
existence and role of the toroidal moment in multiferroic materials. The
toroidic contribution to the electric polarization in BCG is shown to result
from single-ion effects.",1012.0785v1
2011/9/28,Angular momentum transfer torques in spin valves with perpendicular magnetization,"Spin valves incorporating perpendicularly magnetized materials are promising
structures for memory elements and high-frequency generators. We report the
angular dependence of the spin-transfer torque in spin valves with
perpendicular equilibrium magnetization computed by first-principles circuit
theory and compare results with experiments by W.H. Rippard c.s. [Phys. Rev. B
81, 014426 (2010)] on the CoFe|Cu|CoNi system. Furthermore, we predict a
non-monotonous (""wavy"") spin-transfer torque when the Cu spacer is replaced by
a Ru layer.",1109.6074v1
2011/10/28,"Diffusion thermopower of (Ga,Mn)As/GaAs tunnel junctions","We report the observation of tunneling anisotropic magnetothermopower, a
voltage response to a temperature difference across an interface between a
normal and a magnetic semiconductor. The resulting voltage is related to the
energy derivative of the density of states in the magnetic material, and thus
has a strongly anisotropic response to the direction of magnetization in the
material. The effect will have relevance to the operation of semiconductor
spintronic devices, and may indeed already play a role in correctly
interpreting the details of some earlier spin injection studies.",1110.6339v1
2011/11/4,The RKKY coupling in diluted magnetic semiconductors,"This paper is an attempt to modify the classic Ruderman-Kittel-Kasuya-Yosida
(RKKY) model to allow the analysis of the magnetic resonance measurements. In
our calculations, we follow the treatment of the original authors of the RKKY
model but include the finite band splitting, {\Delta}, as a phenomenological
parameter. The RKKY exchange is not anymore of Heisenberg type and an
anisotropy induced by the direction of carrier magnetization occurs.",1111.1030v1
2011/11/27,Large Coercivity in Nanostructured Rare-earth-free MnxGa Films,"The magnetic hysteresis of MnxGa films exhibit remarkably large coercive
fields as high as 2.5 T when fabricated with nanoscale particles of a suitable
size and orientation. This coercivity is an order of magnitude larger than in
well-ordered epitaxial film counterparts and bulk materials. The enhanced
coercivity is attributed to the combination of large magnetocrystalline
anisotropy and ~ 50 nm size nanoparticles. The large coercivity is also
replicated in the electrical properties through the anomalous Hall effect. The
magnitude of the coercivity approaches that found in rare-earth magnets, making
them attractive for rare-earth-free magnet applications.",1111.6267v1
2011/12/7,Theory of the magnetoeletric effect in a lightly doped high-Tc cuprate,"In a recent study Viskadourakis et al. discovered that extremely underdoped
La_2CuO_(4+x) is a relaxor ferroelectric and a magnetoelectric material at low
temperatures. It is further observed that the magnetoelectric response is
anisotropic for different directions of electric polarization and applied
magnetic field. By constructing an appropriate Landau theory, we show that a
bi-quadratic magnetoelectric coupling can explain the experimentally observed
polarization dependence on magnetic field. This coupling leads to several novel
low-temperature effects including a feedback enhancement of the magnetization
below the ferroelectric transition, and a predicted magnetocapacitive effect.",1112.1524v1
2012/3/2,"From first-order magneto-elastic to magneto-structural transition in (Mn,Fe)1.95P0.50Si0.50 compounds","We report on structural, magnetic and magnetocaloric properties of
MnxFe1.95-xP0.50Si0.50 (x > 1.10) compounds. With increasing the Mn:Fe ratio, a
first-order magneto-elastic transition gradually changes into a first-order
magneto-structural transition via a second-order magnetic transition. The study
also shows that thermal hysteresis can be tuned by varying the Mn:Fe ratio.
Small thermal hysteresis (less than 1 K) can be obtained while maintaining a
giant magnetocaloric effect. This achievement paves the way for real
refrigeration applications using magnetic refrigerants.",1203.0555v2
2012/3/6,Switchable Hyperbolic Metamaterials With Magnetic Control,"A switchable hyperbolic material (SHM) is investigated, with which one can
turn on or off the hyperbolic dispersion of the material via magnetic control.
The SHM has simple structure, with a one-dimensional periodic stacking of
dielectric layer and gyromagnetic layer. The hyperbolic dispersion of SHM is
due to the negative effective permeability of gyromagnetic layers, and it can
be transformed into a regular circular dispersion when the d.c. magnetic field
is switched off. This switchable dispersion transition is reversible, which may
have great potential applications in many fields.",1203.1083v1
2012/5/15,Magnetic softness in iron-based superconductors,"We examine the relevance of several major material-dependent parameters to
the magnetic softness in iron-base superconductors by first-principles
electronic structure analysis of their parent compounds. The results are
explained in the spin-fermion model where localized spins and orbitally
degenerate itinerant electrons coexist and are coupled by Hund's rule coupling.
We found that the difference in the strength of the Hund's rule coupling term
is the major material-dependent microscopic parameter for determining the
ground-state spin pattern. The magnetic softness in iron-based superconductors
is essentially driven by the competition between the double-exchange
ferromagnetism and the superexchange antiferromagnetism.",1205.3509v1
2012/7/3,Evaluation of endohedral doping of hydrogenated Si fullerenes as a route to magnetic Si building blocks,"Density-functional theory based global geometry optimization is used to
scrutinize the possibility of endohedral doping of hydrogenated Si fullerenes
as a route to Si nanostructures with high magnetic moments. In contrast to
previous suggestions, our unbiased sampling finds the smallest Si16H16
endohedral cage generally too small to encapsulate 3d metal dopant atoms. For
the next larger fullerene-like cage though, we identify perfectly symmetric
MSi20H20 (M = Co, Ti, V, Cr) cage structures as ground states. These structures
conserve the high spin moment of the dopant atom and therewith underscore the
potential of this Si nanoform for novel cluster-based materials with unique
magnetic properties.",1207.0668v1
2013/5/3,Another dimension: investigations of molecular magnetism using muon-spin relaxation,"We review examples of muon-spin relaxation measurements on molecule-based
magnetic coordination polymers, classified by their magnetic dimensionality.
These include the one-dimensional s=1/2 spin chain Cu(pyz)(NO3)2 and the
two-dimensional s=1/2 layered material [Cu(HF2)(pyz)2]BF4. We also describe
some of the more exotic ground states that may become accessible in the future
given the ability to tune the interaction strengths of our materials through
crystal engineering.",1305.0654v1
2013/5/24,Strain engineering of magnetic states of vacancy-decorated hexagonal boron nitride,"Novel materials with tunable magnetic states play a significant role in the
development of next-generation spintronic devices. In this paper, we examine
the role of biaxial strain on the electronic properties of vacancy-decorated
hexagonal boron nitride (h-BN) monolayers using density functional theory
calculations. We found that the strain can lead to switching of the magnetic
state for h-BN monolayers with boron vacancy or divacancy. Our findings promise
a new route for the operation of low-dimensional spintronic devices.",1305.5861v1
2014/2/27,CPA for strongly correlated systems: Electronic structure and magnetic properties of NiO-ZnO solid solutions,"The method of electronic structure calculations for strongly correlated
disordered materials is developed employing the basic idea of coherent
potential approximation (CPA). Evolution of electronic structure and spin
magnetic moment value with concentration $x$ in strongly correlated
Ni$_{1-x}$Zn$_x$O solid solutions is investigated in the frame of this method.
The obtained values of energy gap and magnetic moment are in agreement with the
available experimental data.",1402.6789v1
2014/3/5,Non Linear Susceptibility from High DC Field Torque Magnetometry,"Torque magnetometry is a convenient technique to measure the magnetic
properties of anisotropic materials. Advances in micromachining and the
availability of robust materials with which such magnetometers can be
fabricated has made them reliable even in adverse conditions such as very high
magnetic fields and both high and very low temperatures. In most applications
with such magnetometers the measured torque signals are used to arrive at the
linear magnetic susceptibilities only. In this short note we extend torque
magnetometry to measure nonlinear susceptibilities and illustrate our methods
with representative data on the heavy fermion compound UPt3",1403.1287v1
2014/8/6,Electronic and magnetic properties of the Ti$_5$O$_9$ Magnéli phase,"Structural, electronic and magnetic properties of Ti$_5$O$_9$ have been
studied by \textit{ab initio} methods in low-, intermediate- and
high-temperature phases. We have found the charge and orbital order in all
three phases to be non-stable, and the formation of Ti$^{3+}$-Ti$^{3+}$
bipolaronic states less likely as compared to Ti$_4$O$_7$. Several
quasidegenerate magnetic configurations were calculated to have different width
of the band gap, suggesting that the reordering of the unpaired spins at
Ti$^{3+}$ ions might at least partially be responsible for the changes in
conductivity of this material.",1408.2542v1
2014/9/1,An Approach to Modeling and Scaling of Hysteresis in Soft Magnetic Materials. I Magnetization Curve,"A new mathematical model of hysteresis loop has been derived. Model consists
in an extansion of tanh($\cdot$) by extanding the base of exp function into an
arbitrary positive number. The presented model is self-similar and invariant
with respect to scaling. Scaling of magnetic hysteresis loop has been done
using the notion of homogenous function in general sense.",1409.0583v1
2014/9/19,Zitterbewegung in monolayer silicene in a magnetic field,"We study the Zitterbewegung in monolayer silicene under a perpendicular
magnetic field. Using an effective Hamiltonian, we have investigated the
autocorrelation function and the density currents in this material. Moreover,
we have analyzed other types of periodicities of the system (classical and
revival times). Finally, the above results are compared with their counterparts
in two other monolayer materials subject to a magnetic field: graphene and
MoS$_2$",1409.5566v1
2014/9/30,Spin-phonon and magnetostriction phenomena in CaMn7O12 helimagnet probed by Raman spectroscopy,"In this letter we investigated the temperature-dependent Raman spectra of
CaMn7O12 helimagnet from room temperature down to 10 K. The temperature
dependence of the Raman mode parameters show remarkable anomalies for both
antiferromagnetic and incommensurate transitions that this compound undergoes
at low temperatures. The anomalies observed at the magnetic ordering transition
indicate a spin-phonon coupling at higher-temperature magnetic transition in
this material, while a magnetostrinction effect at the lower-temperature
magnetic transition.",1410.0073v1
2015/3/29,Cooperative Multiscale Aging in a Ferromagnet/Antiferromagnet Bilayer,"We utilize anisotropic magnetoresistance to study temporal evolution of the
magnetization state in epitaxial Ni$_{80}$Fe$_{20}$/Fe$_{50}$Mn$_{50}$
ferromagnet/antiferromagnet bilayers. The resistance exhibits power-law
evolution over a wide range of temperatures and magnetic fields, indicating
that aging is characterized by a wide range of activation time scales. We show
that aging is a cooperative process, i.e. the magnetic system is not a
superposition of weakly interacting subsystems characterized by simple
Arrhenius activation. The observed effects are reminiscent of avalanches in
granular materials, providing a conceptual link to a broad class of critical
phenomena in other complex condensed matter systems.",1503.08380v1
2015/4/29,"L1$_0$ stacked binaries as candidates for hard magnets: FePt, MnAl and MnGa","A novel strategy of stacking binary magnets to enhance the magneto
crystalline anisotropy is explored. This strategy is used in the search for
hard magnets by studying FePt/MnGa and FePt/MnAl stacks. The choice of these
binaries is motivated by the fact that they already possess large magneto
crystalline anisotropy. Several possible alternative structures for these
materials are explored in order to reduce the amount of Pt owing to its high
cost.",1504.07827v1
2015/5/18,NMR in strongly correlated materials,"Electron-electron interactions are at the origin of many exotic electronic
properties of materials which have emerged from recent experimental
observations. The main important phenomena discovered are related with
electronic magnetic properties, which have been quite accessible to Nuclear
Magnetic Resonance techniques. Those specifically permit to distinguish the
orbitals or electronic bands responsible for the magnetism, the metallic
properties and superconductivity and to reveal the physical properties which
are distinct from expectations in an independent electron scheme. The
description of some selected experimental cases permits us to underline the
importance of the technique and to reveal altogether to the reader a wide range
of novel phenomena specific to correlated electron physics.",1505.04699v1
2015/7/31,Diamagnetic magnetocaloric effect due to a transversal oscillating magnetic field,"The present Letter describes the magnetocaloric effect of a diamagnetic
material with a magnetic field $B_\parallel$ along the $z$ axis and a
transversal and oscillating field $B_\perp (\ll B_\parallel)$ parallel to the
$x-y$ plane. We show that the magnetocaloric potentials due to a change in
$B_\parallel$ is the same as those due to a change in the frequency of
$B_\perp$. These results raise the possibility of building magnetocaloric
devices without moving parts, since changing frequency is a simple electronic
issue, while changing the field from permanent magnets depends on mechanical
aspects.",1507.08886v1
2015/11/23,Polarized neutron channeling as a tool for the investigations of weakly magnetic thin films,"We present and apply a new method to measure directly weak magnetization in
thin films. The polarization of a neutron beam channeling through a thin film
structure is measured after exiting the structure edge as a microbeam. We have
applied the method to a tri-layer thin film structure acting as a planar
waveguide for polarized neutrons. The middle guiding layer is a rare earth
based ferrimagnetic material TbCo5 with a low magnetization of about 20 mT. We
demonstrate that the channeling method is more sensitive than the specular
neutron reflection method.",1511.07286v2
2016/1/12,Understanding strongly coupling magnetism from holographic duality,"The unusual magnetic materials are significant in both science and
technology. However, because of the strongly correlated effects, it is
difficult to understand their novel properties from theoretical aspects.
Holographic duality offers a new approach to understanding such systems from
gravity side. This paper will give a brief review of our recent works on the
applications of holographic duality in understanding unusual magnetic
materials. Some quantitative compare between holographic results and
experimental data will be shown and some predictions from holographic duality
models will be discussed.",1601.02936v1
2016/11/16,Perpendicular magnetic anisotropy in Co$_2$MnGa,"We report perpendicular magnetic anisotropy in the ferromagnetic Heusler
alloy Co$_2$MnGa in a MgO/Co$_2$MnGa/Pd trilayer stack for Co$_2$MnGa
thicknesses up to 3.5 nm. There is a thickness- and temperature-dependent spin
reorientation transition from perpendicular to in-plane magnetic anisotropy
which we study through the anomalous Hall effect. From the temperature
dependence of the anomalous Hall effect, we observe the expected scaling of
$\rho_{xy}^{AHE}$ with $\rho_{xx}$, suggesting the intrinsic and side-jump
mechanisms are largely responsible for the anomalous Hall effect in this
material.",1611.05110v1
2017/8/21,Chiral response of twisted bilayer graphene,"We present an effective (minimal) theory for chiral two-dimensional
materials. These materials possess an electro-magnetic coupling without
exhibiting a topological gap. As an example, we study the response of doped
twisted bilayers, unveiling unusual phenomena in the zero frequency limit. An
in-plane magnetic field induces a huge paramagnetic response at the neutrality
point and, upon doping, also gives rise to a substantial longitudinal Hall
response. The system also accommodates nontrivial longitudinal plasmonic modes
which are associated with a longitudinal magnetic moment, thus endowing them
with a chiral character. Finally, we note that the optical activity can be
considerably enhanced upon doping.",1708.06116v2
2018/1/26,"Resonant-state expansion for open optical systems: Generalization to magnetic, chiral, and bi-anisotropic materials","The resonant-state expansion, a recently developed powerful method in
electrodynamics, is generalized here for open optical systems containing
magnetic, chiral, or bi-anisotropic materials. It is shown that the key matrix
eigenvalue equation of the method remains the same, but the matrix elements of
the perturbation now contain variations of the permittivity, permeability, and
bi-anisotropy tensors. A general normalization of resonant states in terms of
the electric and magnetic fields is presented.",1801.08883v1
2019/6/27,Density functional perturbation theory for lattice dynamics with fully relativistic ultrasoft pseudopotentials: the magnetic case,"We extend density functional perturbation theory for lattice dynamics with
fully relativistic ultrasoft pseudopotentials to magnetic materials. Our
approach is based on the application of the time-reversal operator to the
Sternheimer linear system and to its self-consistent solutions. Moreover, we
discuss how to include in the formalism the symmetry operations of the magnetic
point group which require the time-reversal operator. We validate our
implementation by comparison with the frozen phonon method in fcc Ni and in a
monatomic ferromagnetic Pt wire.",1906.11673v1
2019/8/22,Royal Society Inaugural Article Perspective: Multiferroics Beyond Electric-Field Control of Magnetism,"Multiferroic materials, with their combined and coupled magnetism and
ferroelectricity, providea playground for studying new physics and chemistry as
well as a platform for development ofnovel devices and technologies. Based on
my July 2017 Royal Society Inaugural Lecture, I review recent progress and
propose future directions in the fundamentals and applications of
multiferroics, with a focus on unanticipated developments outside of the core
activity of electric-field control of magnetism.",1908.08352v2
2018/8/28,Applicability of the strongly constrained and appropriately normed density functional to transition metal magnetism,"We find that the recently developed self consistent and appropriately normed
(SCAN) meta-generalized gradient approximation, which has been found to provide
highly accurate results for many materials, is, however, not able to describe
the stability and properties of phases of Fe important for steel. This is due
to an overestimated tendency towards magnetism and exaggeration of magnetic
energies, which we also find in other transition metals.",1808.09261v2
2019/1/29,Skyrmion meets magnetic tunnel junction: an efficient way for electrical skyrmion detection investigated by ab initio theory,"In our proof-of-principle study we examine the influence of skyrmions on
magnetoresistive transport. In particular, we show that magnetic tunnel
junctions are a technologically appealing and promising way for electrical
detection of non-collinear magnetic structures. The calculated effect is shown
to originate from scattering between different k-states and cannot be
identified through densities of states alone. Our results suggest that the
detection efficiency strongly depends on the utilized materials.",1901.10313v2
2012/9/10,Can doping graphite trigger room temperature superconductivity? Evidence for granular high-temperature superconductivity in water-treated graphite powder,"Trying to dope graphite flakes we found that the magnetization of pure,
several tens of micrometers grain size graphite powder and after a simple
treatment with pure water shows clear and reproducible granular superconducting
behavior with a critical temperature above 300K. The observed magnetic
characteristics as a function of temperature, magnetic field and time, provide
evidence for weakly coupled grains through Josephson interaction, revealing the
existence of superconducting vortices.",1209.1938v1
2015/12/17,Two-Dimensional Magnetic Boron,"We predict a two-dimensional (2D) antiferromagnetic (AFM) boron (designated
as M-boron) by using ab initio evolutionary methodology. M-boron is entirely
composed of B20 clusters in a hexagonal arrangement. Most strikingly, the
highest valence band of M-boron is isolated, strongly localized, and quite
flat, which induces spin polarization on each cap of the B20 cluster. This flat
band originates from the unpaired electrons of the capping atoms, and is
responsible for magnetism. M-boron is thermodynamically metastable and is the
first cluster-based 2D magnetic material in the elemental boron system.",1512.05790v1
2016/3/11,Regularization to orthogonal-polynomials fitting with application to magnetization data,"An obstacle encountered in applying orthogonal-polynomials fitting is how to
select out the proper fitting expression. By adding a Laplace term to the error
expression and introducing the concept of overfitting degree, a regularization
and corresponding cross validation scheme is proposed for two-variable
polynomials fitting. While the Fortran implementation of above scheme is
applied to magnetization data, a satisfactory fitting precision is reached, and
overfitting problem can be quantitatively assessed, which therefore offers the
quite reliable base for future comprehensive investigations of magnetocaloric
and phase-transition properties of magnetic functional materials.",1603.03532v1
2017/3/3,Spin-orbit effective fields in Pt/GdFeCo bilayers,"In the increasing interests on spin-orbit torque (SOT) with various magnetic
materials, we investigated SOT in rare earth-transition metal ferrimagnetic
alloys. The harmonic Hall measurements were performed in Pt/GdFeCo bilayers to
quantify the effective fields resulting from the SOT. It is found that the
damping-like torque rapidly increases near the magnetization compensation
temperature TM of the GdFeCo, which is attributed to the reduction of the net
magnetic moment.",1703.00995v1
2017/3/15,Generation of single skyrmions by picosecond magnetic field pulses,"We numerically demonstrate an ultrafast method to create $\textit{single}$
skyrmions in a $\textit{collinear}$ ferromagnetic sample by applying a
picosecond (effective) magnetic field pulse in the presence of
Dzyaloshinskii-Moriya interaction. For small samples the applied magnetic field
pulse could be either spatially uniform or nonuniform while for large samples a
nonuniform and localized field is more effective. We examine the phase diagram
of pulse width and amplitude for the nucleation. Our finding could ultimately
be used to design future skyrmion-based devices.",1703.05181v2
2019/10/17,Ordering of Fe and Zn ions and magnetic properties of FeZnMo3O8,"In the present paper electronic, magnetic, and structural properties of a
novel system FeZnMo$_3$O$_8$ with a polar crystal structure are investigated
using GGA+U calculations. It is shown that Fe ions preferably occupy octahedral
and Zn ions tetrahedral positions. This structural feature is caused by
different ionic radii of these ions and not by the exchange coupling. The
calculated exchange constants naturally explain magnetic structure observed in
this material.",1910.07736v1
2021/4/8,Ferromagnetism in a Semiconductor with Mobile Carriers via Low-Level Nonmagnetic Doping,"We show that doped cubic iron pyrite, which is a diamagnetic semiconductor,
becomes ferromagnetic when $p$-type doped. We furthermore find that this
material can exhibit high spin polarization both for tunneling and transport
devices. These results are based on first principles electronic structure and
transport calculations. This illustrates the use of $p$-type doping without
magnetic impurities as a strategy for obtaining ferromagnetic semiconducting
behavior, with implications for spintronic applications that require both
magnetic ordering and good mobility. This is a combination that has been
difficult to achieve by doping semiconductors with magnetic impurities. We show
that phosphorus and arsenic may be effective dopants for achieving this
behavior.",2104.03877v1
2021/5/10,Impurity-band optical transitions in two-dimensional Dirac materials under strain-induced synthetic magnetic field,"We develop a theory of optical transitions in Coulomb impurity-doped
two-dimensional transition metal dichalcogenide monolayers and study the
transitions from the spin-resolved valence band to the (Coulomb) donor and
acceptor impurities under the influence of a synthetic valley-selective
magnetic field produced by a mechanical strain. It is shown that the optical
properties of the system are determined by the strength of the synthetic
magnetic field, which uncovers an experimental tool, which can be used to
manipulate the properties of two-dimensional materials in valley
magneto-optoelectronics.",2105.04109v1
2012/2/23,Domain structure in CoFeB thin films with perpendicular magnetic anisotropy,"Domain structures in CoFeB-MgO thin films with a perpendicular easy
magnetization axis were observed by magneto-optic Kerr-effect microscopy at
various temperatures. The domain wall surface energy was obtained by analyzing
the spatial period of the stripe domains and fitting established domain models
to the period. In combination with SQUID measurements of magnetization and
anisotropy energy, this leads to an estimate of the exchange stiffness and
domain wall width in these films. These parameters are essential for
determining whether domain walls will form in patterned structures and devices
made of such materials.",1202.5128v1
2014/4/4,Electrical detection of microwave assisted magnetization reversal by spin pumping,"Microwave assisted magnetization reversal has been investigated in a bilayer
system of Pt/ferromagnet by detecting a change in the polarity of the spin
pumping signal. The reversal process is studied in two material systems,
Pt/CoFeB and Pt/NiFe, for different aspect ratios. The onset of the switching
behavior is indicated by a sharp transition in the spin pumping voltage. At a
threshold value of the external field, the switching process changes from
partial to full reversal with increasing microwave power. The proposed method
provides a simple way to detect microwave assisted magnetization reversal.",1404.1133v1
2015/2/12,Systematic Search and A New Family of Skyrmion Materials,"Magnetic skyrmions have recently attracted great attentions. However they are
harbored in very limited numbers of magnets up to now. The search of new
helimagnetic materials is thus an urgent topic in the field of skyrmion
physics. In this letter, we provide a guideline on this issue, and discuss the
possibility of realizing skyrmions in a new family of molybdenum nitrides
$A_2$Mo$_3$N ($A$=Fe, Co, and Rh). By means of the first-principles
calculations, the electronic and magnetic structures are calculated and the
existence of strong Dzyaloshinskii-Moriya interaction is demonstrated.",1502.03818v1
2016/12/27,Reinventing atomistic magnetic simulations with spin-orbit coupling,"We propose a powerful extension to combined molecular and spin dynamics that
fully captures the coupling between the atomic and spin subsystems via
spin-orbit interactions. Its foundation is the inclusion of the local magnetic
anisotropies that arise as a consequence of the lattice symmetry breaking due
to phonons or defects. We demonstrate that our extension enables the exchange
of angular momentum between the atomic and spin subsystems, which is critical
to the challenges arising in the study of fluctuations and non-equilibrium
processes in complex, natural, and engineered magnetic materials.",1612.08503v1
2018/2/6,Co/Ni multilayers for spintronics: high spin-polarization and tunable magnetic anisotropy,"In this paper we analyze in details the electronic properties of (Co/Ni)
multilayers, a model system for spintronics devices. We use magneto-optical
Kerr (MOKE), spin-polarized photoemission spectroscopy (SRPES), x-ray magnetic
circular dichroism (XMCD) and anomalous surface diffraction experiments to
investigate the electronic properties and perpendicular magnetic anisotropy
(PMA) in [Co(x)/Ni(y)] single-crystalline stacks grown by molecular beam
epitaxy.",1802.02020v1
2018/2/27,Magnetic and transport properties of Sb2Te3 doped with high concentration of Cr,"We report on molecular beam epitaxy and properties of a magnetic topological
insulator, Cr doped Sb2Te3. The composition analysis reveals that Cr replaces
Sb site, and x-ray diffraction confirms that single phase textured crystal
structure can be obtained for (CrxSb1-x)2Te3 with x up to 0.44. Further
increase in x results in phase separation or precipitates in the material. The
Curie temperature TC increases with x up to 0.44, and reaches to 250 K, which
is the highest TC observed till now in magnetically doped topological
insulators.",1802.09770v1
2018/11/5,Surface acoustic wave coupled to magnetic resonance on a multiferroic CuB$_2$O$_4$,"We observed surface acoustic wave (SAW) propagation on a multiferroic
material CuB$_2$O$_4$ with use of two interdigital transducers (IDTs). The
period of IDT fingers is as short as 1.6 $\mu$m so that the frequency of SAW is
3 GHz, which is comparable with that of magnetic resonance. In
antiferromagnetic phase, the SAW excitation intensity varied with the magnitude
and direction of the magnetic field, owing to the dynamical coupling between
SAWs and antiferromagnetic resonance of CuB$_2$O$_4$. The microscopic mechanism
is discussed based on the symmetrically allowed magentoelastic coupling.",1811.01527v1
2018/11/19,Controlling grain boundaries by magnetic fields,"The ability to use external magnetic fields to influence the microstructure
in polycrystalline materials has potential applications in microstructural
engineering. To explore this potential and to understand the complex
interactions between electromagnetic fields and solid-state matter transport we
consider a phase-field-crystal (PFC) model. Together with efficient and
scalable numerical algorithms this allows the examination of the role that
external magnetic fields play on the evolution of defect structures and grain
boundaries, on diffusive time scales. Examples for planar and circular grain
boundaries explain the essential atomistic processes and large scale
simulations in 2D are used to obtain statistical data on grain growth under the
influence of external fields.",1811.07710v1
2019/7/15,Exchange biased Anomalous Hall Effect driven by frustration in a magnetic Kagome lattice,"Co3Sn2S2 is a ferromagnetic Weyl semimetal that has been the subject of
intense scientific interest due to its large anomalous Hall effect. We show
that the coupling of this material's topological properties to its magnetic
texture leads to a strongly exchange biased anomalous Hall effect. We argue
that this is likely caused by the coexistence of ferromagnetism and spin glass
phases, the latter being driven by the geometric frustration intrinsic to the
Kagome network of magnetic ions.",1907.06651v1
2020/5/18,Tuning thermo-magnetic properties of dilute-ferromagnet multilayers using RKKY interaction,"We demonstrate a 20-fold enhancement in the strength of the RKKY interlayer
exchange in dilute-ferromagnet/normal-metal multilayers by incorporating
ultrathin Fe layers at the interfaces. Additionally, the resulting increase in
the interface magnetic polarization profoundly affects the finite-size effects,
sharpening the Curie transition of the multilayer, while allowing to separately
tune its Curie temperature via intralayer magnetic dilution. These results
should be useful for designing functional materials for applications in
magneto-caloric micro-refrigeration and thermally-assisted spin-electronics.",2005.08846v1
2020/5/19,Magnetic order and instability in newly synthesized CoSeAs marcasite,"Marcasite class of compounds provide facile platform to explore novel
phenomena of fundamental and technological importance, such as unconventional
superconductivity or high performance electrocatalyst. We report the synthesis
and experimental investigation of a new marcasite CoSeAs in this letter.
Experimental investigation of the new material using neutron scattering
measurements reveal weak magnetic correlation of cobalt ions below $T$ = 36.2
K. The modest isotropic exchange interaction between cobalt moments, inferred
from random phase approximation analysis, hints of magnetically unstable
environment. It is a desirable characteristic to induce unconventional
superconductivity via chemical pressure application",2005.09732v1
2020/5/30,A phenomenological model for the spontaneous exchange bias effect,"In this work we propose an alternative model to explain the spontaneous
exchange bias (SEB) effect observed in spin glass (SG)-like systems. As in a
previously proposed model (Ref. 1), it is based on the unconventional dynamics
of the SG-like moments at the magnetic hysteresis cycle. However, using a
reliable estimate of the amount of SG-spins that are relaxing during the cycle,
the new model can correctly describe the changes in the SEB observed for
measurements performed at different temperatures and different maximum applied
fields.",2006.00230v1
2020/9/7,Anomalous In-plane Magnetic Anisotropy in Strain-mediated Converse Magnetoelectric Coupling,"Magnetic axis rotation (MAR) in ferromagnetic (FM) layers is crucial for
strain-mediated converse magnetoelectric coupling. Employing the density
functional theory (DFT), we computationally study the magnetic anisotropy of
selected deformed FM materials such as body-centered iron. The results show
that the short axis is more energy-favorable at high in-plane strain difference
than previously predicted phenomenologically. This anomalous trend and the
complex energy behaviors at different strain conditions explain why
spin-lattice dynamics (SLD) simulation does not produce in-plane MAR and imply
couplings between different energy terms together with high order coefficient
contributions.",2009.03045v2
2020/11/11,Reduction of back switching by large damping ferromagnetic material,"Recent studies on magnetization dynamics induced by spin-orbit torque have
revealed a weak dependence of the critical current for magnetization switching
on the damping constant of a ferromagnetic free layer. This study, however,
reveals that the damping constant nevertheless plays a key role in
magnetization switching induced by spin-orbit torque. An undesirable switching,
returning to an initial state, named as back switching, occurs in a ferromagnet
with an easy axis parallel to the current direction. Numerical and theoretical
analyses reveal that back switching is strongly suppressed when the damping
constant of the ferromagnet is large.",2011.05566v1
2021/9/21,Ferromagnetic Double Perovskite Semiconductors with Tunable Properties,"We successfully dope the magnetically silent double perovskite semiconductor
Sr2GaSbO6 to induce ferromagnetism and tune its band gap, with Ga3+ partially
substituted by the magnetic trivalent cation Mn3+, in a rigid cation ordering
with Sb5+. Our new ferromagnetic semiconducting Sr2Ga1-xMnxSbO6 double
perovskite, which crystallizes in tetragonal symmetry (space group I4/m) and
has tunable ferromagnetic ordering temperature and band gap, suggests that
magnetic ion doping of double perovskites is a productive avenue towards
obtaining materials for application in next-generation oxide-based spintronic
devices.",2109.10405v1
2021/10/25,Signatures of Weak Spin-Phonon Coupling in 12R-BaTi0.4Mn0.6O3: A Raman Study,"Antiferromagnetic materials with strong spin-phonon coupling have the
potential for spintronic applications. Here, we report the structural,
magnetic, and vibrational properties of 12R-BaTi0.4Mn0.6O3.
Temperature-dependent magnetization data show the presence of weak
antiferromagnetic interactions. Correlation between magnetic and vibrational
properties are probed by using temperature-dependent Raman spectroscopic
measurements. Two of the Raman active phonons show deviation from anharmonic
behaviour at low temperatures which can be attributed to spin-phonon coupling.
The strength of coupling is estimated using mean-field approximation and is
found to be 1.1 and 1.2 cm-1 for phonons at 530 and 717 cm-1, respectively.",2110.13807v1
2022/5/30,Interaction of excitons with magnetic topological defects in 2D magnetic monolayers: localization and anomalous Hall effect,"Novel 2D material CrI3 reveals unique combination of 2D ferromagnetism and
robust excitonic response. We demonstrate that the possibility of the formation
of magnetic topological defects, such as Neel skyrmions, together with large
excitonic Zeeman splitting, leads to giant scattering asymmetry, which is the
necessary prerequisite for the excitonic anomalous Hall effect. In addition,
the diamagnetic effect breaks the inversion symmetry, and in certain cases can
result in exciton localization on the skyrmion. This enables the formation of
magnetoexcitonic quantum dots with tunable parameters.",2205.15221v1
2022/6/1,Dynamic Fingerprints of Synthetic Antiferromagnet Nanostructures with Interfacial Dzyaloshinskii-Moriya Interaction,"Synthetic antiferromagnet (SAF) nanostructures with interfacial
Dzyaloshinskii-Moriya interaction can host topologically distinct spin textures
such as skyrmions and thus are regarded as promising candidates for both
spintronics and magnonics applications. Here, we present comprehensive
micromagnetic simulations of such material systems and discuss the rich phase
diagrams that contain various types of magnetic configurations. Aside from the
static properties, we further discuss the resonant excitations of the
calculated magnetic states which include individual skyrmions and skyrmioniums.
Finally, the internal modes of SAF skyrmion clusters are studied and discussed
in the context of magnetic sensing applications based on the dynamic
fingerprint in broadband ferromagnetic resonance measurements.",2206.00554v2
2022/9/12,Pseudogap metal and magnetization plateau from doping moiré Mott insulator,"The problem of doping Mott insulators is of fundamental importance and
long-standing interest in the study of strongly correlated electron systems.
The advent of semiconductor based moir\'e materials opens a new ground for
simulating the Hubbard model on the triangular lattice and exploring the rich
phase diagram of doped Mott insulators as a function of doping and external
magnetic field. Based on our recent identification of spin polaron
quasiparticle in Mott insulator, in this work we predict a new metallic state
emerges at small doping and intermediate field range, a pseudogap metal that
exhibits a single-particle gap and a doping-dependent magnetization plateau.",2209.05430v1
2022/12/1,Density functional theory for homogeneous two dimensional materials with magnetic fields,"This paper studies DFT models for homogeneous 2D materials in 3D space, under
a constant perpendicular magnetic field. We show how to reduce the
three--dimensional energy functional to a one--dimensional one, similarly as in
our previous work. This is done by minimizing over states invariant under
magnetic translations and that commute with the Landau operator. In the reduced
model, the Pauli principle no longer appears. It is replaced by a penalization
term in the energy.",2212.00448v2
2023/1/6,Stacking-dependent topological magnons in bilayer CrI$_3$,"Motivated by the potential of atomically-thin magnets towards tunable
high-frequency magnonics, we detail the spin-wave dispersion of bilayer
CrI$_3$. We demonstrate that the magnonic behavior of the bilayer strongly
depends on its stacking configuration and the interlayer magnetic ordering,
where a topological bandgap opens in the dispersion caused by the
Dzyaloshinskii-Moriya and Kitaev interactions, classifying bilayer CrI$_3$ as a
topological magnon insulator. We further reveal that both size and topology of
the bandgap in a CrI$_3$ bilayer with an antiferromagnetic interlayer ordering
are tunable by an external magnetic field.",2301.02502v2
2023/1/20,Temperature-dependent magnetic particle imaging with multi-harmonic lock-in detection,"Advances in instrumentation and tracer materials are still required to enable
sensitive and accurate 3D temperature monitoring by magnetic particle imaging.
We have developed a magnetic particle imaging instrument to observe temperature
variations using MPI, and discuss resolution dependence on temperature and
harmonic number. Furthermore, we present a low noise approach using lock-in
detection for temperature measurement, and discuss implications for a new
detection modality of MPI.",2301.08539v1
2023/6/8,Tunable magnon topology in monolayer CrI$_\mathbf{3}$ under external stimuli,"Two-dimensional (2D) honeycomb ferromagnets, such as monolayer
chromium-trihalides, are predicted to behave as topological magnon insulators -
characterized by an insulating bulk and topologically protected edge states,
giving rise to a thermal magnon Hall effect. Here we report the behavior of the
topological magnons in monolayer CrI$_3$ under external stimuli, including
biaxial and uniaxial strain, electric gating, as well as in-plane and
out-of-plane magnetic field, revealing that one can thereby tailor the magnetic
states as well as the size and the topology of the magnonic bandgap. These
findings broaden the perspective of using 2D magnetic materials to design
topological magnonic devices.",2306.05104v1
2023/7/18,"Propagation of Coupled Acoustic, Electromagnetic and Spin Waves in Saturated Ferromagnetoelastic Solids","We study the propagation of plane waves in an unbounded body of a saturated
ferromagnetoelastic solid. The equations by Tiersten for small fields
superposed on finite initial fields in a saturated ferromagnetoelastic material
are employed, with their quasistatic magnetic field extended to dynamic
electric and magnetic fields for electromagnetic waves. Dispersion relations of
the plane waves are obtained. The cutoff frequencies and long wave
approximation of the dispersion curves are determined. Results show that
acoustic, electromagnetic and magnetic spin waves are coupled in such a
material. For YIG which is a cubic crystal without piezoelectric coupling, the
acoustic and electromagnetic waves are not directly coupled but they can still
interact indirectly through spin waves.",2307.09171v1
2023/7/31,Erbium-based multifuncional compounds as molecular microkelvin-tunable driving-sensing units,"We demonstrate the selective control of the magnetic response and
photoluminescence properties of Er3+ centers with light, by associating them
with a highly conjugated beta-diketonate (1,3-di(2-naphthyl)-1,3-propanedione)
ligand. We demonstrate this system to be an optically-pumped molecular compound
emittingin infra-red, which can be employed as a precise heat-driving and
detecting unit for low temperatures",2307.16476v1
2023/9/25,Zero-field finite-momentum and field-induced superconductivity in altermagnets,"We explore the possibilities for spin-singlet superconductivity in newly
discovered altermagnets. Investigating $d$-wave altermagnets, we show that
finite-momentum superconductivity can easily emerge in altermagnets even though
they have no net magnetization, when the superconducting order parameter also
has $d$-wave symmetry with nodes coinciding with the altermagnet nodes.
Additionally, we find a rich phase diagram when both altermagnetism and an
external magnetic field are considered, including superconductivity appearing
at high magnetic fields from a parent zero-field normal state.",2309.14427v2
2024/1/16,A tool to check whether a symmetry-compensated collinear magnetic material is antiferro- or altermagnetic,"Altermagnets (AM) is a recently discovered class of collinear magnets that
share some properties (anomalous transport, etc) with ferromagnets, some (zero
net magnetization) with antiferromagnets, while also exhibiting unique
properties (spin-splitting of electronic bands and resulting spin-splitter
current). Since the moment compensation in AM is driven by symmetry, it must be
possible to identify them by analyzing the crystal structure directly, without
computing the electronic structure. Given the significant potential of AM for
spintronics, it is very useful to have a tool for such an analysis. This work
presents an open-access code implementing such a direct check.",2401.08784v1
2017/11/11,Tunable dynamic moduli of magnetic elastomers: from X-$μ$CT characterization to mesoscopic modeling,"Ferrogels and magnetoelastomers are composite materials obtained by embedding
magnetic particles of mesoscopic size in a crosslinked polymeric matrix. They
combine the reversible elastic deformability of polymeric materials with the
high responsivity of ferrofluids to external magnetic fields. These materials
stand out, for example, for large magnetostriction as well as significant
increase of the elastic moduli in the presence of external magnetic fields. By
means of X-ray micro-computed tomography, position and size of each magnetic
particle can be measured with a high degree of accuracy. We here use data
extracted from real magnetoelastic samples as input for coarse-grained
dipole-spring modeling and calculations to investigate magnetostriction,
stiffening, and changes in the normal modes spectrum. More precisely, we assign
to each particle a dipole moment proportional to its volume and set a
randomized network of springs between them that mimics the behavior of the
polymeric elastic matrix. Extending our previously developed methods, we
compute the resulting structural changes in the systems, their overall
distortions, as well as the frequency-dependent elastic moduli when magnetic
interactions are turned on. Particularly, with increasing magnetization, we
observe the formation of chain-like aggregates, resulting in significant
overall deformations. Interestingly, the static elastic moduli can first show a
slight decrease with growing amplitude of the magnetic interactions, before a
pronounced increase appears upon the chain formation. The change of the dynamic
moduli with increasing magnetization depends on the frequency and can even show
nonmonotonic behavior. Overall, we demonstrate how theory and experiments can
complement each other to learn more about the dynamic behavior of this
interesting class of materials.",1711.04165v1
2003/3/21,Nonlinear properties of left-handed metamaterials,"We analyze nonlinear properties of microstructured materials with negative
refraction, the so-called left-handed metamaterials. We consider a
two-dimensional periodic structure created by arrays of wires and split-ring
resonators embedded into a nonlinear dielectric, and calculate the effective
nonlinear electric permittivity and magnetic permeability. We demonstrate that
the hysteresis-type dependence of the magnetic permeability on the field
intensity allows changing the material from left- to right-handed and back.
These effects can be treated as the second-order phase transitions in the
transmission properties induced by the variation of an external field.",0303443v1
2003/5/19,"Magnetism, Critical Fluctuations and Susceptibility Renormalization in Pd","Some of the most popular ways to treat quantum critical materials, that is,
materials close to a magnetic instability, are based on the Landau functional.
The central quantity of such approaches is the average magnitude of spin
fluctuations, which is very difficult to measure experimentally or compute
directly from the first principles. We calculate the parameters of the Landau
functional for Pd and use these to connect the critical fluctuations beyond the
local-density approximation and the band structure.",0305407v2
2005/7/30,"Multiferroic behavior in CdCr2X4 (X = S, Se)","The recently discovered multiferroic material CdCr2S4 shows a coexistence of
ferromagnetism and relaxor ferroelectricity together with a colossal
magnetocapacitive effect. The complex dielectric permittivity of this compound
and of the structurally related CdCr2Se4 was studied by means of broadband
dielectric spectroscopy using different electrode materials. The observed
magnetocapacitive coupling at the magnetic transition is driven by enormous
changes of the relaxation dynamics induced by the development of magnetic
order.",0508014v1
2005/8/22,A room-temperature polymeric spin-valve,"We report giant magnetoresistance up to 150 percent at low bias current and
low temperature as well as room temperature magnetoresistance in polymeric
spin-valves having the structure LSMO/conjugated polymer/Co. The conjugated
polymers, regiorandom and regioregular P3HT were used as the spacer materials.
We observed an asymmetric bias voltage dependence of different devices and
additional, hitherto unseen, peaks in MR vs. magnetic field plot with low bias
currents measurements that we attribute to local magnetic moments due to
spin-trapping in the defects in the spacer material. Also, various spacer
thicknesses led to variation of magnetoresistance within a certain temperature
range.",0508510v1
2002/2/20,Repulsive Casimir forces,"We discuss repulsive Casimir forces between dielectric materials with non
trivial magnetic susceptibility. It is shown that considerations based on naive
pair-wise summation of Van der Waals and Casimir Polder forces may not only
give an incorrect estimate of the magnitude of the total Casimir force, but
even the wrong sign of the force when materials with high dielectric and
magnetic response are involved. Indeed repulsive Casimir forces may be found in
a large range of parameters, and we suggest that the effect may be realized in
known materials. The phenomenon of repulsive Casimir forces may be of
importance both for experimental study and for nanomachinery applications.",0202114v1
2007/5/15,Exchange bias effect of ferro-/antiferromagnetic heterostructures,"The exchange bias (EB) effect was discovered 60 years ago by Meiklejohn and
Bean. Meanwhile the EB effect has become an integral part of modern magnetism
with implications for basic research and for numerous device applications. The
EB effect was the first of its kind which relates to an interface effect
between two different classes of materials, here between a ferromagnet and an
antiferromagnet. Here we review fundamental aspects of the exchange bias
effect.",0705.2055v1
2008/1/26,Polarization--universal rejection filtering by ambichiral structures made of indefinite dielectric--magnetic materials,"An ambichiral structure comprising sheets of an anisotropic dielectric
material rejects normally incident plane waves of one circular polarization
(CP) state but not of the other CP state, in its fundamental Bragg regime.
However, if the same structure is made of an dielectric--magnetic material with
indefinite permittivity and permeability dyadics, it may function as a
polarization--universal rejection filter because two of the four planewave
components of the electromagnetic field phasors in each sheet are of the
positive--phase--velocity type and two are of the negative--phase--velocity
type.",0801.4078v1
2009/9/18,A uni-directional optical pulse propagation equation for materials with both electric and magnetic responses,"I derive unidirectional wave equations for fields propagating in materials
with both electric and magnetic dispersion and nonlinearity. The derivation
imposes no conditions on the pulse profile except that the material modulates
the propagation slowly, that is, that loss, dispersion, and nonlinearity have
only a small effect over the scale of a wavelength. It also allows a direct
term-to-term comparison of the exact bidirectional theory with its approximate
unidirectional counterpart.",0909.3407v3
2010/2/19,Landau Theory of Domain Wall Magnetoelectricity,"We calculate the exact analytical solution to the domain wall properties in a
multiferroic system with two order parameters that are coupled
bi-quadratically. This is then adapted to the case of a magnetoelectric
multiferroic material such as BiFeO3, with a view to examine critically whether
the domain walls can account for the enhancement of magnetization reported for
thin films fo this material, in view of the correlation between increasing
magnetization and increasing volume fraction of domain walls as films become
thinner. The present analysis can be generalized to describe a class of
magnetoelectric devices based upon domain walls rather than bulk properties.",1002.3819v2
2011/3/20,Rational Design of Half-Metallic Heterostructures,"We present a rational approach to the design of half-metallic
heterostructures which allows the design of an infinite number of half-metallic
heterostructures. The wide range of materials that can be made half-metallic
using our approach makes it possible to engineer materials with tunable
characteristic properties, for example low intrinsic magnetic damping, small
magnetic moment or perpendicular anisotropy. We demonstrate the proposed design
scheme for a series of transition metal heterostructures based on the B2
crystal structure.",1103.3855v1
2012/6/28,Searching for magnetic monopoles trapped in accelerator material at the Large Hadron Collider,"If produced in high energy particle collisions at the LHC, magnetic monopoles
could stop in material surrounding the interaction points. Obsolete parts of
the beam pipe near the CMS interaction region, which were exposed to the
products of pp and heavy ion collisions, were analysed using a SQUID-based
magnetometer. The purpose of this work is to quantify the performance of the
magnetometer in the context of a monopole search using a small set of samples
of accelerator material ahead of the 2013 shutdown.",1206.6793v1
2012/12/20,Energy conserving Anisotropic Anhysteretic Magnetic Modelling for Finite Element Analysis,"To model ferromagnetic material in finite element analysis a correct
description of the constitutive relationship (BH-law) must be found from
measured data. This article proposes to use the energy density function as a
centrepiece. Using this function, which turns out to be a convex function of
the flux density, guarantees energy conservative modelling. The magnetic field
strength can be seen as a derivative with respect to the flux density.
Especially for anisotropic materials (from lamination and/or grain orientation)
this method has advantages. Strictly speaking this method is only valid for
anhysteretic and thermodynamically stable material.",1212.5163v1
2014/7/7,"Multiferroic hexagonal ferrites (h-RFeO$_3$, R=Y, Dy-Lu): an experimental review","Hexagonal ferrites (h-RFeO$_3$, R=Y, Dy-Lu) have recently been identified as
a new family of multiferroic complex oxides.
  The coexisting spontaneous electric and magnetic polarizations make
h-RFeO$_3$ rare-case ferroelectric ferromagnets at low temperature.
  Plus the room-temperature multiferroicity and predicted magnetoelectric
effect, h-RFeO$_3$ are promising materials for multiferroic applications.
  Here we review the structural, ferroelectric, magnetic, and magnetoelectric
properties of h-RFeO$_3$.
  The thin film growth is also discussed because it is critical in making high
quality single crystalline materials for studying intrinsic properties.",1407.1798v1
2014/8/13,Assembling Ellipsoidal Particles at Fluid Interfaces using Switchable Dipolar Capillary Interactions,"The fabrication of novel soft materials is an important scientific and
technological challenge. We investigate the response of magnetic ellipsoidal
particles adsorbed at fluid-fluid interfaces to external magnetic fields. By
exploiting previously discovered first-order orientation phase transitions we
show how to switch on and off dipolar capillary interactions between particles,
leading to the formation of distinctive self-assembled structures and allowing
dynamic control of the bottom-up fabrication of reconfigurable novel-structured
materials",1408.3140v1
2015/3/23,The method of exchange perturbation theory as applied to magnetic ordering in high-Tc materials,"We unify the method of exchange perturbation theory for multicenter systems.
For the case of exchange degeneracy in the total spin of the system we give a
secular equation that is more compact and convenient for calculations than
those obtained earlier. On the basis of this formalism we develop an algorithm
for calculating the Heisenberg parameter for magnetic materials. Finally, we
calculate the characteristics of antiferromagnetic transitions for the high-Tc
materials La2-xMeCuO4 and YBa2Cu3O6.",1503.06790v1
2018/6/20,Asymmetric Cherenkov Emission in a Topological Plasmonic Waveguide,"Here, we investigate the Cherenkov emission by an array of moving electric
charges in the vicinity of a topologically nontrivial gyrotropic material. It
is shown that the nonreciprocal material response may result in a robustly
asymmetric Cherenkov emission, such that the spectrum of the emitted radiation
and the stopping power depend strongly on the sign of the particle velocity. It
is demonstrated that the main emission channels are determined by the
unidirectional edge states supported by the topological material. We consider
as examples both magnetized plasmas and Weyl semi-metals. The latter may
exhibit a spontaneous nonreciprocal response without a biasing magnetic field.",1806.07695v1
2018/10/1,Spins in Semiconductor Nanocrystals,"Semiconductor nanocrystals are being used as hosts to trap and manipulate
single spins. Spins in nanocrystals can have different properties than their
bulk counterparts, owing both to quantum confinement and surface effects. We
will show that spins can be generated in nanocrystals by the insertion of
impurities, either magnetic or not, or by magnetic polarons present at dangling
bonds at their surfaces. This chapter reports theoretical contributions to this
field, where the Density Functional Theory is used to simulate these
functionalized nanocrystals.",1810.00726v1
2018/10/6,Identifying materials with charge-spin physics using charge-spin susceptibility computed from first principles,"The authors present a quantity termed charge-spin susceptibility, which
measures the charge response to spin degrees of freedom in strongly correlated
materials. This quantity is simple to evaluate using both standard density
functional theory and many-body electronic structure techniques, enabling
comparison between different levels of theory. A benchmark on 28 layered
magnetic materials shows that large values of charge-spin susceptibility
correlate with unconventional ground states such as disordered magnets and
unconventional superconductivity.",1810.03014v3
2007/7/17,Weak localization in GaMnAs: evidence of impurity band transport,"We report the observation of negative magnetoresistance in the ferromagnetic
semiconductor GaMnAs at low temperatures ($T<3$ K) and low magnetic fields ($0<
B <20$ mT). We attribute this effect to weak localization. Observation of weak
localization provides a strong evidence of impurity band transport in these
materials, since for valence band transport one expects either weak
anti-localization due to strong spin-orbit interactions or total suppression of
interference by intrinsic magnetization. In addition to the weak localization,
we observe Altshuler-Aronov electron-electron interactions effect in this
material.",0707.2416v1
2012/2/22,Transverse Field Ising Ferromagnetism in Mn$_{12}$-acetate-MeOH,"We report measurements of the magnetic susceptibility of single crystals of
Mn$_{12}$-acetate-MeOH, a new high-symmetry variant of the original single
molecule magnet Mn$_{12}$-acetate. A comparison of these data to theory and to
data for the Mn$_{12}$ acetate material shows that Mn$_{12}$-acetate-MeOH is a
realization of a transverse-field Ising ferromagnet in contrast to the original
Mn$_{12}$ acetate material, in which solvent disorder leads to effects
attributed to random field Ising ferromagnetism.",1202.4963v1
2017/12/11,"Dimensionality, nematicity and Superconductivity in Fe-based systems","Study of Fe based compounds have drawn much attention due to the discovery of
superconductivity as well as many other exotic electronic properties. Here, we
review some of our works in these materials carried out employing density
functional theory and angle resolved photoemission spectroscopy. The results
presented here indicate that the dimensionality of the underlying electronic
structure plays important role in deriving their interesting electronic
properties. The nematicity found in most of these materials appears to be
related to the magnetic long range order. We argue that the exoticity in the
electronic properties are related to the subtlety in competing structural and
magnetic instabilities present in these materials.",1712.03710v1
2021/1/25,A solution to the permalloy problem,"We propose a solution to the longstanding permalloy problem$-$why the
particular composition of permalloy, Fe$_{21.5}$Ni$_{78.5}$, achieves a
dramatic drop in hysteresis, while its material constants show no obvious
signal of this behavior. We use our recently developed coercivity tool to show
that a delicate balance between local instabilities and magnetic material
constants are necessary to explain the dramatic drop of hysteresis at 78.5% Ni.
Our findings are in agreement with the permalloy experiments and, more broadly,
provide theoretical guidance for the discovery of novel low hysteresis magnetic
alloys.",2101.09857v1
2021/2/22,A review of modelling in ferrimagnetic spintronics,"In this review we introduce computer modelling and simulation techniques
which are used for ferrimagnetic materials. We focus on models where thermal
effects are accounted for, atomistic spin dynamics and finite temperature
macrospin approaches. We survey the literature of two of the most commonly
modelled ferrimagnets in the field of spintronics--the amorphous alloy GdFeCo
and the magnetic insulator yttrium iron garnet. We look at how generic models
and material specific models have been applied to predict and understand
spintronic experiments, focusing on the fields of ultrafast magnetisation
dynamics, spincaloritronics and magnetic textures dynamics and give an outlook
for modelling in ferrimagnetic spintronics.",2102.11004v1
2021/7/7,Origin of nonlinear magnetoelectric response in rare-earth orthoferrite perovskite oxides,"We report a theoretical study of the non-linear magnetoelectric response of
GdFeO$_3$ through an analytical approach combined with a Heisenberg model which
is fitted against first-principles calculations. Our theory reproduces the
non-linear change of polarization under applied magnetic field reported
experimentally such that it allows to analyze the origin of the large responses
in the different directions. We show that the non-linear character of the
response in these materials originates from the fact that the antiferromagnetic
order of Gd atoms changes non-linearly with respect to the applied magnetic
field. Our model can be generalized to other materials in which the
antiferromagnetic ordering breaks inversion symmetry.",2107.03228v1
2022/6/28,Magnetic Resonance Imaging study of sheared granular matter,"We introduce a Magnetic Resonance Imaging technique to study the geometry of
shear zones of soft, low-frictional and hard, frictional granular materials and
their mixtures. Hydrogel spheres serve as the soft, low-frictional material
component, while mustard seeds represent rigid, frictional grains. Some of the
hydrogel spheres are doped with CuSO4 salt to serve as tracers. A split-bottom
shear cell is sheared stepwise and the shear profiles are determined from the
differences of tomograms after successive shear steps, using Particle Imaging
Velocimetry.We find that the shear zone geometry differs considerably between
soft grains submersed in water and the same material without the embedding
fluid.",2206.14111v1
2023/10/10,Emerging Spin-Orbit Torques in Low Dimensional Dirac Materials,"We report a theoretical description of novel spin-orbit torque components
emerging in two-dimensional Dirac materials with broken inversion symmetry. In
contrast to usual metallic interfaces where field-like and damping-like torque
components are competing, we find that an intrinsic damping-like torque which
derives from all Fermi-sea electrons can be simultaneously enhanced along with
the field-like component. Additionally, hitherto overlooked torque components
unique to Dirac materials, emerge from the coupling between spin and pseudospin
degrees of freedom. These torques are found to be resilient to disorder and
could enhance the magnetic switching performance of nearby magnets.",2310.06447v1
2003/7/7,The magnetic stress tensor in magnetized matter,"We derive the form of the magnetic stress tensor in a completely general,
stationary magnetic medium, with an arbitrary magnetization field $\vec M(\vec
r)$ and free current density $\vec j(\vec r)$. We start with the magnetic force
density $\vec f$ acting on a matter element, modelled as a collection of
microscopic magnetic dipoles in addition to the free currents. We show that
there is a unique tensor ${\bf T}$ quadratic in the magnetic flux density $\vec
B(\vec r)$ and the magnetic field $\vec H(\vec r)=\vec B-4\pi\vec M$ whose
divergence is $\nabla\cdot{\bf T}=\vec f$. In the limit $\vec M=0$, the
well-known vacuum magnetic stress tensor is recovered. However, the general
form of the tensor is asymmetric, leading to a divergent angular acceleration
for matter elements of vanishing size. We argue that this is not inconsistent,
because it occurs only if $\vec M$ and $\vec B$ are not parallel, in which case
the macroscopic field does indeed exert a torque on each of the microscopic
dipoles, so this state is only possible if there are material stresses which
keep the dipoles aligned with each other and misaligned with the macroscopic
field. We briefly discuss the consequences for the stability of strongly
magnetized stars.",0307134v1
2007/6/19,Synthesis and magnetic properties of NiFe_{2-x}Al_{x}O_{4} nanoparticles,"Nanocrystalline Al-doped nickel ferrite powders have been synthesized by
sol-gel auto-ignition method and the effect of non-magnetic aluminum content on
the structural and magnetic properties has been studied. The X-ray diffraction
(XRD) revealed that the powders obtained are single phase with inverse spinel
structure. The calculated grain sizes from XRD data have been verified using
transmission electron microscopy (TEM). TEM photographs show that the powders
consist of nanometer-sized grains. It was observed that the characteristic
grain size decreases from 29 to 6 nm as the non-magnetic Al content increases,
which was attributed to the influence of non-magnetic Al concentration on the
grain size. Magnetic hysteresis loops were measured at room temperature with a
maximum applied magnetic field of 1T. As aluminum content increases, the
measured magnetic hysteresis curves become more and more narrow and the
saturation magnetization and remanent magnetization both decreased. The
reduction of agnetization compared to bulk is a consequence of spin
non-collinearity. Further reduction of magnetization with increase of aluminum
content is caused by non-magnetic Al^{3+} ions and weakened interaction between
sublattices. This, as well as the decrease in hysteresis was understood in
terms of the decrease in particle size.",0706.2794v1
2008/4/29,Anisotropic magnetization and sign change of dynamic susceptibility in Na0.85CoO2 single crystal,"The DC and AC magnetic susceptibilities of Na0.85CoO2 single crystals were
measured for the different crystal orientations of H//(ab)- and H//(c)-axis.
The DC-magnetic susceptibility for H//(c)-direction exhibited the
antiferromagnetic transition at TN= 22 K. The thermal hysteresis between the
zero-field-cooled (ZFC) and the field-cooled (FC) magnetization below TN and
the large frustration parameter indicated the spin frustration along the
(c)-axis. For an applied magnetic field in H//(ab)-plane, the DC magnetic
susceptibility exhibited the logarithmic divergent behavior at low temperatures
(T < 6.8 K). This could be understood by the impurity spin effect, dressed by
the spin fluctuation. From the AC magnetic susceptibility measurements, the
real part of the AC-susceptibility for H//(ab) exhibited the spin glass-like
behavior at low temperatures (T < 4 K). Remarkably, for an applied AC magnetic
field with H//(c)-axis, the sign of the AC magnetic susceptibility changed from
a positive to a negative value with increasing AC magnetic field frequency (f >
3 kHz) at low temperatures (T > 7 K). We interpret the sign change of AC
magnetic susceptibility along the (c)-axis in terms of the sudden sign reversal
of the phase difference from in-phase to out-of-phase response with an applied
AC magnetic field in the AC-susceptibility phase space.",0804.4532v1
2008/10/2,Voltage controlled inversion of magnetic anisotropy in a ferromagnetic thin film at room temperature,"The control of magnetic properties by means of an electric field is an
important aspect in magnetism and magnetoelectronics. We here utilize
magnetoelastic coupling in ferromagnetic/piezoelectric hybrids to realize a
voltage control of magnetization orientation at room temperature. The samples
consist of polycrystalline nickel thin films evaporated onto piezoelectric
actuators. The magnetic properties of these multifunctional hybrids are
investigated at room temperature as a function of the voltage controlled stress
exerted by the actuator on the Ni film. Ferromagnetic resonance spectroscopy
shows that the magnetic easy axis in the Ni film plane is rotated by 90 degree
upon changing the polarity of the voltage Vp applied to the actuator. In other
words, the in-plane uniaxial magnetic anisotropy of the Ni film can be inverted
via the application of an appropriate voltage Vp. Using SQUID magnetometry, the
evolution of the magnetization vector is recorded as a function of Vp and of
the external magnetic field. Changing Vp allows to reversibly adjust the
magnetization orientation in the Ni film plane within a range of approximately
70 degree. All magnetometry data can be quantitatively understood in terms of
the magnetic free energy determined from the ferromagnetic resonance
experiments. These results demonstrate that magnetoelastic coupling in hybrid
structures indeed is a viable option to control magnetization orientation in
technologically relevant ferromagnetic thin films at room temperature.",0810.0389v1
2008/12/17,Theory of Spin-Transfer Torque in the Current-in-Plane Geometries,"Two alternative current-induced switching geometries, in which the current
flows parallel to the magnet/nonmagnet interface, are investigated
theoretically using the nonequilibrium Keldysh theory. In the first geometry,
the current is perpendicular to the polarizing magnet/nonmagnet interface but
parallel to the nonmagnet/switching magnet interface (CPIP). In the second
geometry, the current is parallel to both the polarizing magnet/nonmagnet and
nonmagnet/switching magnet interfaces (CIP). Calculations for a single-orbital
tight binding model indicate that the spin current flowing parallel to the
switching magnet/nonmagnet interface can be absorbed by a lateral switching
magnet as efficiently as in the traditional current-perpendicular-to-plane
(CPP) geometry. The results of the model calculations are shown to be valid
also for experimentally relevant Co/Cu CPIP system described by fully realistic
tight binding bands fitted to an ab initio band structure. It is shown that
almost complete absorption of the incident spin current by a lateral switching
magnet occurs when the lateral dimensions of the switching magnet are of the
order of 50-100 interatomic distances, i.e., about 20nm and its height as small
as a few atomic planes. It is also demonstratedthat strong spin current
absorption in the CPIP/CIP geometry is not spoilt by the presence of a rough
interface between the switching magnet and nonmagnetic spacer. Polarization
achieved using a lateral magnet in the CIP geometry is found to be about 25% of
that in the traditional CPP geometry. The present CPIP calculations of the spin
transfer torque are also relevant to the so called pure-spin-current-induced
magnetization switching that had been recently observed.",0812.3346v1
2009/10/27,Asymmetric Two-dimensional Magnetic Lattices for Ultracold Atoms Trapping and Confinement,"A new method to implement an asymmetrical two-dimensional magnetic lattice is
proposed. The asymmetrical two-dimensional magnetic lattice can be created by
periodically distributing magnetic minima across the surface of magnetic thin
film where the periodicity can be achieved by milling $n\times n$ square holes
on the surface of the film. The quantum device is proposed for trapping and
confining ultracold atoms and quantum degenerate gases prepared in the low
magnetic field seeking-state at low temperature, such as the Bose-Einstein
Condensate (BEC) and ultracold fermions. We present detailed analysis of the
analytical expressions and the numerical simulation procedure used to calculate
the external magnetic field. We also, describe the magnetic band gap structure
exhibited by the asymmetric effect of the magnetic minima and show some of the
possible application. We analyze the effect of changing the characteristic
parameters of the magnetic lattice, such as the separating periodicity length
and the hole size along with the applications of the external magnetic bias
fields to maintain and allocate a suitable non-zero magnetic local minima at
effective $z$-distance above the thin film surface. Suitable values are shown
which keep the trapped ultracold atoms away from the thermal Majorana spin-flip
and the surface Casimir-Polder effect.",0910.5032v1
2009/12/14,Anisotropic magnetic field responses of ferroelectric polarization in a trigonal multiferroic CuFe1-xAlxO2 (x=0.015),"We have investigated magnetic field dependences of a ferroelectric
incommensurate-helimagnetic order in a trigonal magneto-electric (ME)
multiferroic CuFe1-xAlxO2 with x=0.015, which exhibits the ferroelectric phase
as a ground state, by means of neutron diffraction, magnetization and
dielectric polarization measurements under magnetic fields applied along
various directions. From the present results, we have established the H-T
magnetic phase diagrams for the three principal directions of magnetic fields;
(i) parallel to the c axis, (ii) parallel to the helical axis, and (iii)
perpendicular to the c and the helical axes. While the previous dielectric
polarization (P) measurements on CuFe1-xGaxO2 with x=0.035 have demonstrated
that the magnetic field dependence of the `magnetic domain structure' results
in distinct magnetic field responses of P [S. Seki et al., Phys. Rev. Lett.,
103 237601 (2009)], the present study have revealed that the anisotropic
magnetic field dependence of the ferroelectric helimagnetic order `in each
magnetic domain' can be also a source of a variety of magnetic field responses
of P in CuFe1-xAxO2 systems (A=Al, Ga).",0912.2584v1
2011/10/7,Evolution of magnetic properties in the normal spinel solid solution Mg(1-x)Cu(x)Cr2O4,"We examine the evolution of magnetic properties in the normal spinel oxides
Mg(1-x)Cu(x)Cr2O4 using magnetization and heat capacity measurements. The
end-member compounds of the solid solution series have been studied in some
detail because of their very interesting magnetic behavior. MgCr2O4 is a highly
frustrated system that undergoes a first order structural transition at its
antiferromagnetic ordering temperature. CuCr2O4 is tetragonal at room
temperature as a result of Jahn-Teller active tetrahedral Cu^2+ and undergoes a
magnetic transition at 135 K. Substitution of magnetic cations for diamagnetic
Mg^2+ on the tetrahedral A site in the compositional series Mg(1-x)Cu(x)Cr2O4
dramatically affects magnetic behavior. In the composition range 0 < x < 0.3,
the compounds are antiferromagnetic. A sharp peak observed at 12.5K in the heat
capacity of MgCr2O4 corresponding to a magnetically driven first order
structural transition is suppressed even for small x suggesting glassy
disorder. Uncompensated magnetism - with open magnetization loops - develops
for samples in the x range 0.43 < x < 1. Multiple magnetic ordering
temperatures and large coercive fields emerge in the intermediate composition
range 0.43 < x < 0.47. The Neel temperature increases with increasing x across
the series while the value of the Curie-Weiss Theta decreases. A magnetic
temperature-composition phase diagram of the solid solution series is
presented.",1110.1662v1
2013/10/12,The mechanics of a chain or ring of spherical magnets,"Strong magnets, such as neodymium-iron-boron magnets, are increasingly being
manufactured as spheres. Because of their dipolar characters, these spheres can
easily be arranged into long chains that exhibit mechanical properties
reminiscent of elastic strings or rods. While simple formulations exist for the
energy of a deformed elastic rod, it is not clear whether or not they are also
appropriate for a chain of spherical magnets. In this paper, we use
discrete-to-continuum asymptotic analysis to derive a continuum model for the
energy of a deformed chain of magnets based on the magnetostatic interactions
between individual spheres. We find that the mechanical properties of a chain
of magnets differ significantly from those of an elastic rod: while both
magnetic chains and elastic rods support bending by change of local curvature,
nonlocal interaction terms also appear in the energy formulation for a magnetic
chain. This continuum model for the energy of a chain of magnets is used to
analyse small deformations of a circular ring of magnets and hence obtain
theoretical predictions for the vibrational modes of a circular ring of
magnets. Surprisingly, despite the contribution of nonlocal energy terms, we
find that the vibrations of a circular ring of magnets are governed by the same
equation that governs the vibrations of a circular elastic ring.",1310.3436v1
2013/10/21,"Controlled nucleation of topological defects in the stripe domain patterns of Lateral multilayers with Perpendicular Magnetic Anisotropy: competition between magnetostatic, exchange and misfit interactions","Magnetic lateral multilayers have been fabricated on weak perpendicular
magnetic anisotropy amorphous Nd-Co films in order to perform a systematic
study on the conditions for controlled nucleation of topological defects within
their magnetic stripe domain pattern. A lateral thickness modulation of period
$w$ is defined on the nanostructured samples that, in turn, induces a lateral
modulation of both magnetic stripe domain periods $\lambda$ and average
in-plane magnetization component $M_{inplane}$. Depending on lateral multilayer
period and in-plane applied field, thin and thick regions switch independently
during in-plane magnetization reversal and domain walls are created within the
in-plane magnetization configuration coupled to variable angle grain boundaries
and disclinations within the magnetic stripe domain patterns. This process is
mainly driven by the competition between rotatable anisotropy (that couples the
magnetic stripe pattern to in-plane magnetization) and in-plane shape
anisotropy induced by the periodic thickness modulation. However, as the
structural period $w$ becomes comparable to magnetic stripe period $\lambda$,
the nucleation of topological defects at the interfaces between thin and thick
regions is hindered by a size effect and stripe domains in the different
thickness regions become strongly coupled.",1310.5566v1
2014/10/28,Current driven asymmetric magnetization switching in perpendicularly magnetized CoFeB/MgO heterostructures,"The flow of in-plane current through ultrathin magnetic heterostructures can
cause magnetization switching or domain wall nucleation owing to bulk and
interfacial effects. Within the magnetic layer, the current can create magnetic
instabilities via spin transfer torques (STT). At interface(s), spin current
generated from the spin Hall effect in a neighboring layer can exert torques,
referred to as the spin Hall torques, on the magnetic moments. Here, we study
current induced magnetization switching in perpendicularly magnetized CoFeB/MgO
heterostructures with a heavy metal (HM) underlayer. Depending on the thickness
of the HM underlayer, we find distinct differences in the inplane field
dependence of the threshold switching current. The STT is likely responsible
for the magnetization reversal for the thinner underlayer films whereas the
spin Hall torques cause the switching for thicker underlayer films. For the
latter, we find differences in the switching current for positive and negative
currents and initial magnetization directions. We find that the growth process
during the film deposition introduces an anisotropy that breaks the symmetry of
the system and causes the asymmetric switching. The presence of such symmetry
breaking anisotropy enables deterministic magnetization switching at zero
external fields.",1410.7473v2
2017/1/2,Ferromagnetic films with three to twenty spin layers as described using second order perturbed Heisenberg Hamiltonian,"Modified second order perturbed Heisenberg Hamiltonian was employed to
describe the magnetic properties of ferromagnetic films with three to twenty
spin layers for the first time. Previously, the solution of second order
perturbed Heisenberg Hamiltonian was found for ferromagnetic films with two to
five layers under some assumptions by us. In this report, the exact solution is
presented without any assumptions by calculating the pseudo inverse of matrix
C. All eight magnetic parameters such as spin exchange interaction, second
order magnetic anisotropy, fourth order magnetic anisotropy, stress induced
magnetic anisotropy, demagnetization factor, in plane magnetic field, out of
plane magnetic field and magnetic dipole interaction were taken into account.
The easy and hard directions were found using 3-D and 2-D plots of total
magnetic energy versus these magnetic parameters. Angle between easy and hard
directions was nearly 107 degrees in many cases. The magnetic easy axis
gradually rotates from out of plane to in plane direction by indicating a
preferred in plane orientation of magnetic easy axis for films with higher
number of spin layers. These theoretical results agree with some experimental
research data of ferromagnetic thin films.",1701.07780v1
2018/4/12,Magnetic Force Microscopy Imaging Using Geometrically Constrained Nano-Domain Walls,"Domain wall probes (DW-probes) were custom-made by modifying standard
commercial magnetic force microscopy (MFM) probes using focused ion beam
lithography. Excess of magnetic coating from the probes was milled out, leaving
a V-shaped nanostructure on one face of the probe apex. Owing to the
nanostructure's shape anisotropy, such probe has four possible magnetic states
depending on the direction of the magnetization along each arm of the V-shape.
Two states of opposite polarity are characterised by the presence of a
geometrically constrained DW, pinned at the corner of the V-shape
nanostructure. In the other two states, the magnetization curls around the
corner with opposite chirality. Electron holography studies, supported by
numerical simulations, demonstrate that a strong stray field emanates from the
pinned DW, whilst a much weaker stray field is generated by the curling
configurations. Using in situ MFM, we show that the magnetization states of the
DW-probe can be easily controlled by applying an external magnetic field,
thereby demonstrating that this type of probe can be used as a switchable tool
with a low or high stray field intensity. We demonstrate that DW-probes enable
acquiring magnetic images with a negligible interference with the sample
magnetization, similar to that of commercial low moment probes, but with a
higher magnetic contrast. In addition, the DW-probe in the curl state provides
complementary information about the in-plane component of the sample's
magnetization, which is not achievable by standard methods and provides
additional information about the stray fields, e.g. as when imaging DWs.",1804.04400v1
2020/3/14,Field induced single molecule magnet behavior in Dy-based coordination polymer,"A new mononuclear Dysprosium based Coordination Polymer {Dy-CP} was
investigated magnetically using dc and ac magnetic susceptibility. The dc
magnetic susceptibility does not exhibit any long-range ordering down to 1.8 K
and the negative value of Curie Constant (~ - 4 K) indicate the dominance of
antiferromagnetic interactions between the Dy (III) spins. Ac susceptibility
exhibits absence of single molecular magnet behavior at zero dc magnetic field
and shows signal of quantum tunneling magnetization (QTM) below 8 K. However,
on the superimposition of dc magnetic field (3 kOe), frequency dependent
relaxation peak emerged at T_f = 5 K and QTM signal suppress at higher fields.
The intermediate value of Mydosh parameter calculated from the shift in peak
position (T_f) in ac susceptibility reflects the formation of superparamagnetic
state. Further, the temperature dependence of Tf is analyzed with Arrhenius and
Cole-Cole plot. The magnetic susceptibility analysis yields characteristics
pre-relaxation factor 1.40x10^(-12) sec and energy barrier {\Delta}E/k_B = 93.4
K, indicating the slow spin relaxation. The Cole-Cole fit to the ac
susceptibility data shows further evidence for the single ion spin relaxation.
Thus, the magnetic measurements support the single-molecule magnet behavior in
Dy-CP under the application of dc magnetic field.",2003.06609v1
2007/7/16,Magnetodipolar interlayer interaction effect on the magnetization dynamics of a trilayer square element with the Landau domain structure,"We present a detailed numerical simulation study of the effects caused by the
magnetodipolar interaction between ferromagnetic (FM) layers of a trilayer
magnetic nanoelement on its magnetization dynamics. As an example we use a
Co/Cu/Ni80Fe20 element with a square lateral shape where the magnetization of
FM layers forms a closed Landau-like domain pattern. First we show that when
the thickness of the non-magnetic (NM) spacer is in the technology relevant
region h ~ 10 nm, magnetodipolar interaction between 90o Neel domain walls in
FM layers qualitatively changes the equilibrium magnetization state of these
layers. In the main of the paper we compare the magnetization dynamics induced
by a sub-nsec field pulse in a single-layer Ni80Fe20 (Py) element and in the
Co/Cu/Py trilayer element. Here we show that (i) due to the spontaneous
symmetry breaking of the Landau state in the FM/NM/FM trilayer its domains and
domain walls oscillate with different frequencies and have different spatial
oscillation patterns; (ii) magnetization oscillations of the trilayer domains
are strongly suppressed due to different oscillation frequencies of domains in
Co and Py; (iii) magnetization dynamics qualitatively depends on the relative
rotation sense of magnetization states in Co and Py layers and on the
magnetocrystalline anisotropy kind of Co crystallites. Finally we discuss the
relation of our findings with experimental observations of magnetization
dynamics in magnetic trilayers, performed using the element-specific
time-resolved X-ray microscopy.",0707.2344v1
2017/12/13,Magnetically gated accretion in an accreting 'non-magnetic' white dwarf,"White dwarfs are often found in binary systems with orbital periods ranging
from tens of minutes to hours in which they can accrete gas from their
companion stars. In about 15% of these binaries, the magnetic field of the
white dwarf is strong enough ($\geq 10^6$ Gauss) to channel the accreted matter
along field lines onto the magnetic poles. The remaining systems are referred
to as ""non-magnetic"", since to date there has been no evidence that they have a
dynamically significant magnetic field. Here we report an analysis of archival
optical observations of the ""non-magnetic"" accreting white dwarf in the binary
system MV Lyrae (hereafter MV Lyr), whose lightcurve displayed quasi-periodic
bursts of $\approx 30$ minutes duration every $\approx 2$ hours. The
observations indicate the presence of an unstable magnetically-regulated
accretion mode, revealing the existence of magnetically gated accretion, where
disk material builds up around the magnetospheric boundary (at the co-rotation
radius) and then accretes onto the white dwarf, producing bursts powered by the
release of gravitational potential energy. We infer a surface magnetic field
strength for the white dwarf in MV Lyr between $2 \times 10^4 \leq B \leq 10^5$
Gauss, too low to be detectable by other current methods. Our discovery
provides a new way of studying the strength and evolution of magnetic fields in
accreting white dwarfs and extends the connections between accretion onto white
dwarfs, young stellar objects and neutron stars, for which similar magnetically
gated accretion cysles have been identified.",1712.04949v1
2018/2/23,Revisiting the Magnetic Structure and Charge Ordering in La$_{1/3}$Sr$_{2/3}$FeO$_3$ by Neutron Powder Diffraction and Mössbauer Spectroscopy,"The magnetic ordering of La$_{1/3}$Sr$_{2/3}$FeO$_3$ perovskite has been
studied by neutron powder diffraction and $^{57}$Fe M\""ossbauer spectroscopy
down to 2 K. From symmetry analysis, a chiral helical model and a collinear
model are proposed to describe the magnetic structure. Both are commensurate,
with propagation vector k = (0,0,1) in R-3c space group. In the former model,
the magnetic moments of Fe adopt the magnetic space group P3$_{2}$21 and have
helical and antiferromagnetic ordering propagating along the c axis. The model
allows only one Fe site, with a magnetic moment of 3.46(2) $\mu_{\rm{B}}$ at 2
K. In the latter model, the magnetic moments of iron ions adopt the magnetic
space group C2/c or C2'/c' and are aligned collinearly. The model allows the
presence of two inequivalent Fe sites with magnetic moments of amplitude
3.26(3) $\mu_{\rm{B}}$ and 3.67(2) $\mu_{\rm{B}}$, respectively. The neutron
diffraction pattern is equally well fitted by either model. The M\""ossbauer
spectroscopy study suggests a single charge state Fe$^{3.66+}$ above the
magnetic transition and a charge disproportionation into Fe$^{(3.66-\zeta)+}$
and Fe$^{(3.66+2\zeta)+}$ below the magnetic transition. The compatibility of
the magnetic structure models with the M\""ossbauer spectroscopy results is
discussed.",1802.08610v2
2019/7/26,Magnetic stray fields in nanoscale magnetic tunnel junctions,"The magnetic stray field is an unavoidable consequence of ferromagnetic
devices and sensors leading to a natural asymmetry in magnetic properties. Such
asymmetry is particularly undesirable for magnetic random access memory
applications where the free layer can exhibit bias. Using atomistic
dipole-dipole calculations we numerically simulate the stray magnetic field
emanating from the magnetic layers of a magnetic memory device with different
geometries. We find that edge effects dominate the overall stray magnetic field
in patterned devices and that a conventional synthetic antiferromagnet
structure is only partially able to compensate the field at the free layer
position. A granular reference layer is seen to provide near-field flux closure
while additional patterning defects add significant complexity to the stray
field in nanoscale devices. Finally we find that the stray field from a
nanoscale antiferromagnet is surprisingly non-zero arising from the imperfect
cancellation of magnetic sublattices due to edge defects. Our findings provide
an outline of the role of different layer structures and defects in the
effective stray magnetic field in nanoscale magnetic random access memory
devices and atomistic calculations provide a useful tools to study the stray
field effects arising from a wide range of defects.",1907.11798v2
2020/2/5,Direct control of magnetic chirality in NdMn2O5 by external electric field,"Detailed investigation of the incommensurate magnetic ordering in a single
crystal of multiferroic NdMn2O5 has been performed using both non-polarized and
polarized neutron diffraction techniques. Below TN = 30.5 K magnetic Bragg
reflections corresponding to the non-chiral type magnetic structure with
propagation vector k1 = (0.5 0 kz1) occurs. Below about 27 K a new distorted
magnetic modulation with a similar vector kz2 occurs, which is attributed to
the magnetization of the Nd3+ ions by the Mn-sub-lattice. Strong temperature
hysteresis in the occurrence of the incommensurate magnetic phases in NdMn2O5
was observed depending on the cooling or heating history of the sample. Below
about 20 K the magnetic structure became of a chiral type. From spherical
neutron polarimetry measurements, the resulting low-temperature magnetic
structure kz3 was approximated by the general elliptic helix. The parameters of
the magnetic helix-like ellipticity and helical plane orientation in regard to
the crystal structure were determined. A reorientation of the helix occurs at
an intermediate temperature between 4 K and 18 K. A difference between the
population of right- and left-handed chiral domains of about 0.2 was observed
in the as-grown crystal when cooling without an external electric field. The
magnetic chiral ratio can be changed by the application of an external electric
field of a few kV/cm, revealing strong magnetoelectric coupling. A linear
dependence of the magnetic chirality on the applied electric field in NdMn2O5
was found. The results are discussed within the frame of the antisymmetric
super-exchange model for Dzyaloshinsky-Moria interaction.",2002.01683v1
2021/3/17,Emergence of a noncollinear magnetic state in twisted bilayer CrI3,"The emergence of two-dimensional (2D) magnetic crystals and moir\'e
engineering has opened the door for devising new magnetic ground states via
competing interactions in moir\'e superlattices. Although a suite of
interesting phenomena, including multi-flavor magnetic states, noncollinear
magnetic states, moir\'e magnon bands and magnon networks, has been predicted,
nontrivial magnetic ground states in twisted bilayer magnetic crystals have yet
to be realized. Here, by utilizing the stacking-dependent interlayer exchange
interactions in CrI3, we demonstrate in small-twist-angle bilayer CrI3 a
noncollinear magnetic ground state. It consists of both antiferromagnetic (AF)
and ferromagnetic (FM) domains and is a result of the competing interlayer AF
coupling in the monoclinic stacking regions of the moir\'e superlattice and the
energy cost for forming AF-FM domain walls. Above the critical twist angle of ~
3{\deg}, the noncollinear state transitions abruptly to a collinear FM ground
state. We further show that the noncollinear magnetic state can be controlled
by gating through the doping-dependent interlayer AF interaction. Our results
demonstrate the possibility of engineering moir\'e magnetism in twisted bilayer
magnetic crystals, as well as gate-voltage-controllable high-density magnetic
memory storage.",2103.09850v1
2021/3/25,Influence of the distribution of the properties of permanent magnets on the field homogeneity of magnet assemblies for mobile NMR,"We optimised the magnetic field homogeneity of two canonical designs for
mobile microfluidic NMR applications: two parallel magnets with an air gap and
a modified Halbach array. Along with the influence of the sample length,
general design guidelines will be presented. For a fair comparison the
sensitive length of the sample has been chosen to be the same as the gap size
between the magnets to ensure enough space for the transmitting and receiving
unit, as well as basic electric shimming components. Keeping the compactness of
the final device in mind, a box with an edge length 5 times the gap size has
been defined, in which the complete magnet configuration should fit. With the
chosen boundary conditions, the simple parallel cuboid configuration reaches
the best homogeneity without active shimming (0.5$\mathrm{B_{s}}$, 41 ppm),
while the Pseudo-Halbach configuration has the highest field strength
(0.9$\mathrm{B_{s}}$, 994 ppm), assuming perfect magnets. However, permanent
magnet configurations suffer from imperfections, such as magnetisation,
fabrication and positioning errors, which results in worse magnetic field
homogeneities than expected from simulations using a fixed optimised parameter
set. We present a sensitivity analysis for a magnetic cube and the results of
studies of the variations in the magnetisation and angle of magnetisation of
magnets purchased from different suppliers, composed of different materials and
coatings, and of different sizes. We performed a detailed Monte Carlo
simulation on the effect of the measured distribution of magnetic properties on
the mentioned configurations. The cuboid design shows a mean homogeneity of 430
ppm (std dev. 350 ppm), the Pseudo-Halbach has a mean homogeneity of 1086 ppm
(std dev. 8 ppm).",2103.13691v1
2021/11/24,Valence fluctuation in Ce$_2$Re$_3$Si$_5$ and Ising-type magnetic ordering in Pr$_2$Re$_3$Si$_5$ single crystals,"Single crystals of ${\rm Ce_2Re_3Si_5}$ and ${\rm Pr_2Re_3Si_5}$ have been
grown by Czochralski method in a tetra-arc furnace. Powder x-ray diffraction
confirmed that these compounds crystallize in the ${\rm U_2Mn_3Si_5}$-type
tetragonal crystal structure with space group $P4/mnc$ (No. 128). The
anisotropic physical properties have been studied comprehensively by measuring
the magnetic susceptibility, isothermal magnetization, electrical transport and
specific heat. The low value of magnetic susceptibility together with no
magnetic transition down to $2$~K gives evidence that the Ce-ions are in the
intermediate valence state in ${\rm Ce_2Re_3Si_5}$. On the other hand ${\rm
Pr_2Re_3Si_5}$ revealed a magnetic ordering at $9$~K. The sharp drop in the
magnetic susceptibility and a spin flip like metamagnetic transition, for
$H~\parallel~[001]$ in the magnetization plot of ${\rm Pr_2Re_3Si_5}$ suggest
an Ising-type antiferromagnetic ordering. Based on magnetic susceptibility and
isothermal magnetization data, a detailed crystal electric field (CEF) analysis
shows that degenerate ${J} = 4$ Hund's rule derived ground state of ${\rm
Pr^{3+}}$ ion splits into nine singlets with an overall splitting of $1179$~K.
The magnetic ordering in ${\rm Pr_2Re_3Si_5}$ is due to the exchange-generated
admixture of the lowest lying CEF energy levels. Heat capacity data reveal a
sharp peak at $9$~K, that confirms the bulk nature of the magnetic ordering in
${\rm Pr_2Re_3Si_5}$.",2111.12597v2
2022/7/12,Crystal and magnetic structures of $R_2$Ni$_2$In compounds ($R$ = Tb and Ho),"Crystal and magnetic structures of $R_2$Ni$_2$In ($R$ = Tb and Ho) have been
studied by powder neutron diffraction at low temperatures. The compounds
crystallize in an orthorhombic crystal structure of the Mn$_2$AlB$_2$-type. At
low temperatures, the magnetic moments localized solely on the rare earth atoms
form antiferromagnetic structures. The Tb magnetic moments, equal to 8.65(6)
$\mu_B$ and parallel to the $c$-axis, form a collinear magnetic structure
described by the propagation vector $\boldsymbol{k} = [\frac{1}{2},
\frac{1}{2}, \frac{1}{2}]$. This magnetic structure is stable up to the N\'eel
temperature equal to 40 K. For Ho$_2$Ni$_2$In a complex, temperature-dependent
magnetic structure is detected. In the temperature range 3.5-8.6 K, an
incommensurate magnetic structure, described by the propagation vector
$\boldsymbol{k}_1 = [0.76, 0, 0.52]$ is observed, while in the temperature
interval 2.2-3.1 K the magnetic order is described by two propagation vectors,
namely, $\boldsymbol{k}_2 = [\frac{5}{6}, 0.16, \frac{1}{2}]$ and its third
harmonics $3\boldsymbol{k}_2 = [\frac{5}{2}, 0.48, \frac{3}{2}]$. Below 2 K, a
coexistence of all magnetic structures detected at higher temperatures is
observed. For all magnetic phases, the Ho magnetic moments are parallel to the
$c$-axis. The low temperature heat capacity data confirm a first order
transition near 3 K.",2207.05651v2
2022/8/4,Reversible Tuning of Collinear versus Chiral Magnetic Order by Chemical Stimulus,"The Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction mediates collinear
magnetic interactions via the conduction electrons of a non-magnetic spacer,
resulting in a ferro- or antiferromagnetic magnetization in magnetic
multilayers. The resulting spin-polarized charge transport effects have found
numerous applications. Recently it has been discovered that heavy non-magnetic
spacers are able to mediate an indirect magnetic coupling that is non-collinear
and chiral. This Dzyaloshinskii-Moriya-enhanced RKKY (DME-RKKY) interaction
causes the emergence of a variety of interesting magnetic structures, such as
skyrmions and spin spirals. Applications using these magnetic quasi-particles
require a thorough understanding and fine-tuning of the balance between the
Dzyaloshinskii-Moriya interaction and other magnetic interactions, e.g., the
exchange interaction and magnetic anisotropy contributions. Here, we show by
spin-polarized scanning tunneling microscopy that the spin structure of
manganese oxide chains on Ir(001) can reproducibly be switched from chiral to
collinear antiferromagnetic interchain interactions by increasing the oxidation
state of MnO$_2$ while the reverse process can be induced by thermal reduction.
The underlying structural change is revealed by low-energy electron diffraction
intensity data (LEED-IV) analysis. Density functional theory calculations
suggest that the magnetic transition may be caused by a significant increase of
the Heisenberg exchange upon oxidation.",2208.02570v1
2023/2/24,Dielectric tunability of magnetic properties in orthorhombic ferromagnetic monolayer CrSBr,"Monolayer CrSBr is a recently discovered semiconducting spin-3/2 ferromagnet
with a Curie temperature around 146 K. Unlike many other known two-dimensional
(2D) magnets, CrSBr has an orthorhombic lattice, giving rise, for instance, to
spatial anisotropy of the magnetic excitations within the 2D plane. Theoretical
description of CrSBr within a spin Hamiltonian approach turns out to be
nontrivial due to the triaxial magnetic anisotropy as well as due to magnetic
dipolar interactions, comparable to spin-orbit effects in CrSBr. Here, we
employ a Green's function formalism combined with first-principles calculations
to systematically study the magnetic properties of monolayer CrSBr in different
regimes of surrounding dielectric screening. We find that the magnetic
anisotropy and thermodynamical properties of CrSBr depend significantly on the
Coulomb interaction and its external screening. In the free-standing limit, the
system turns out to be close to an easy-plane magnet, whose long-range ordering
is partially suppressed. On the contrary, in the regime of large external
screening, monolayer CrSBr behaves like an easy-axis ferromagnet with more
stable magnetic ordering. Despite being relatively large, the magnetic dipolar
interactions have only little effect on the magnetic properties. Our findings
suggests that 2D CrSBr is suitable platform for studying the effects of
substrate screening on magnetic ordering in low dimensions.",2302.12672v1
2023/5/1,Making Atomic-Level Magnetism Tunable with Light at Room Temperature,"The capacity to manipulate magnetization in two-dimensional dilute magnetic
semiconductors (2D-DMSs) using light, specifically in magnetically doped
transition metal dichalcogenide (TMD) monolayers (M-doped TX2, where M = V, Fe,
Cr; T = W, Mo; X = S, Se, Te), may lead to innovative applications in
spintronics, spin-caloritronics, valleytronics, and quantum computation. This
Perspective paper explores the mediation of magnetization by light under
ambient conditions in 2D-TMD DMSs and heterostructures. By combining magneto-LC
resonance (MLCR) experiments with density functional theory (DFT) calculations,
we show that the magnetization can be enhanced using light in V-doped TMD
monolayers (e.g., V-WS2, V-WSe2, V-MoS2). This phenomenon is attributed to
excess holes in the conduction and valence bands, as well as carriers trapped
in magnetic doping states, which together mediate the magnetization of the
semiconducting layer. In 2D-TMD heterostructures such as VSe2/WS2 and
VSe2/MoS2, we demonstrate the significance of proximity, charge-transfer, and
confinement effects in amplifying light-mediated magnetism. This effect is
attributed to photon absorption at the TMD layer (e.g., WS2, MoS2) that
generates electron-hole pairs mediating the magnetization of the
heterostructure. These findings will encourage further research in the field of
2D magnetism and establish a novel direction for designing 2D-TMDs and
heterostructures with optically tunable magnetic functionalities, paving the
way for next-generation magneto-optic nanodevices.",2305.01026v1
2023/5/4,Magnetic properties of Nd6Fe13Cu single crystals,"The understanding of coercivity mechanism in high performance Nd-Fe-B
permanent magnets relies on the analysis of the magnetic properties of all
phases present in the magnets. By adding Cu in such compounds, a new Nd6Fe13Cu
grain boundary phase is formed, however, the magnetic properties of this phase
and its role in the magnetic decoupling of the matrix Nd2Fe14B grains are still
insufficiently studied. In this work, we have grown Nd6Fe13Cu single crystals
by the reactive flux method and studied their magnetic properties in detail. It
is observed that below the N\'eel temperature (TN = 410 K), the Nd6Fe13Cu is
antiferromagnetic in zero magnetic field; whereas when a magnetic field is
applied along the a-axis, a spin-flop transition occurs at approx. 6 T,
indicating a strong competition between antiferromagnetic and ferromagnetic
interactions in two Nd layers below and above the Cu layers. Our atomistic spin
dynamics simulation confirms that an increase in temperature and/or magnetic
field can significantly change the antiferromagnetic coupling between the two
Nd layers below and above the Cu layers, which, in turn, is the reason for the
observed spin-flop transition. These results suggest that the role of
antiferromagnetic Nd6Fe13Cu grain boundary phase in the coercivity enhancement
of Nd-Fe-B-Cu magnets is more complex than previously thought, mainly due to
the competition between its antiferro- and ferro-magnetic exchange
interactions.",2305.02889v1
2023/8/22,Controlling the 2D magnetism of CrBr$_3$ by van der Waals stacking engineering,"The manipulation of two-dimensional (2D) magnetic order is of significant
importance to facilitate future 2D magnets for low-power and high-speed
spintronic devices. Van der Waals stacking engineering makes promises for
controllable magnetism via interlayer magnetic coupling. However, directly
examining the stacking order changes accompanying magnetic order transitions at
the atomic scale and preparing device-ready 2D magnets with controllable
magnetic orders remain elusive. Here, we demonstrate effective control of
interlayer stacking in exfoliated CrBr$_3$ via thermally assisted strain
engineering. The stable interlayer ferromagnetic (FM), antiferromagnetic (AFM),
and FM-AFM coexistent ground states confirmed by the magnetic circular
dichroism measurements are realized. Combined with the first-principles
calculations, the atomically-resolved imaging technique reveals the correlation
between magnetic order and interlay stacking order in the CrBr$_3$ flakes
unambiguously. A tunable exchange bias effect is obtained in the mixed phase of
FM and AFM states. This work will introduce new magnetic properties by
controlling the stacking order, and sequence of 2D magnets, providing ample
opportunities for their application in spintronic devices.",2308.11219v1
2023/9/24,Dense strontium hexaferrite-based permanent magnet composites assisted by cold sintering process,"The use of rare-earth-based permanent magnets is one of the critical points
for the development of the current technology. On the one hand, industry of the
rare-earths is highly polluting due to the negative environmental impact of
their extraction and, on the other hand, the sector is potentially dependent on
China. Therefore, investigation is required both in the development of
rare-earth-free permanent magnets and in sintering processes that enable their
greener fabrication with attractive magnetic properties at a more competitive
price. This work presents the use of a cold sintering process (CSP) followed by
a post-annealing at 1100 {\deg}C as a new way to sinter composite permanent
magnets based on strontium ferrite (SFO). Composites that incorporate a
percentage < 10% of an additional magnetic phase have been prepared and the
morphological, structural and magnetic properties have been evaluated after
each stage of the process. CSP induces a phase transformation of SFO in the
composites, which is partially recovered by the post-thermal treatment
improving the relative density to 92% and the magnetic response of the final
magnets with a coercivity of up to 3.0 kOe. Control of the magnetic properties
is possible through the composition and the grain size in the sintered magnets.
These attractive results show the potential of the sintering approach as an
alternative to develop modern rare-earth-free composite permanent magnets.",2309.16038v1
2023/10/30,Strong in-plane magnetic anisotropy (Co0.15Fe0.85)5GeTe2/graphene van der Waals heterostructure spin-valve at room temperature,"Van der Waals (vdW) magnets are promising owing to their tunable magnetic
properties with doping or alloy composition, where the strength of magnetic
interactions, their symmetry, and magnetic anisotropy can be tuned according to
the desired application. However, most of the vdW magnet based spintronic
devices are so far limited to cryogenic temperatures with magnetic anisotropies
favouring out-of-plane or canted orientation of the magnetization. Here, we
report room-temperature lateral spin-valve devices with strong in-plane
magnetic anisotropy of the vdW ferromagnet (Co0.15Fe0.85)5GeTe2 (CFGT) in
heterostructures with graphene. Magnetization measurements reveal above
room-temperature ferromagnetism in CFGT with a strong in-plane magnetic
anisotropy. Density functional theory calculations show that the magnitude of
the anisotropy depends on the Co concentration and is caused by the
substitution of Co in the outermost Fe layer. Heterostructures consisting of
CFGT nanolayers and graphene were used to experimentally realize basic building
blocks for spin valve devices such as efficient spin injection and detection.
The spin transport and Hanle spin precession measurements prove a strong
in-plane and negative spin polarization at the interface with graphene, which
is supported by the calculated spin-polarized density of states of CFGT. The
in-plane magnetization of CFGT at room temperature proves its usefulness in
graphene lateral spin-valve devices, thus opening further opportunities for
spintronic technologies.",2310.19618v1
2024/1/29,Canted antiferromagnetism in a spin-orbit coupled $S_{\text{eff}} = 3/2$ triangular-lattice magnet DyAuGe,"Exploration of nontrivial magnetic states induced by strong spin-orbit
interaction is a central topic of frustrated magnetism. Extensive studies are
concentrated on rare-earth-based magnets and 4d/5d transition metal compounds,
which are mostly described by an effective spin $S_{\text{eff}} = 1/2$ for the
Kramers doublet of the lowest crystal-electric-field levels. Variety of
magnetic orderings may be greatly enhanced when magnetic dipolar moments
intertwined with multipolar degrees of freedom which are described by
higher-rank tensors and often require the magnetic ions with $S_{\text{eff}} >
1/2$. Here, our synchrotron x-ray diffraction near the Dy $L_3$ edge has
unveiled a canted antiferromagnetic ground state arising from a quasi-quartet
($S_{\text{eff}} = 3/2$) of 4f electrons in a triangular-lattice (TL)
rare-earth intermetallics DyAuGe. Magnetic moment and electric-quadrupole
moment are closely interlocked and noncollinear magnetic-dipole alignment is
induced by antiferroic electric-quadrupole (AFQ) ordering in the TL layers. The
correlation between the AFQ and canted magnetic structures is further confirmed
by phase transitions in an in-plane magnetic field. These findings offer
insights into the emergence of nontrivial magnetic states in frustrated TL
systems described beyond the $S_{\text{eff}} = 1/2$.",2401.16622v1
2016/9/23,Influence of heavy metal materials on magnetic properties of Pt/Co/heavy metal tri-layered structures,"Pt/Co/heavy metal (HM) tri-layered structures with interfacial perpendicular
magnetic anisotropy (PMA) are currently under intensive research for several
emerging spintronic effects, such as spinorbit torque, domain wall motion, and
room temperature skyrmions. HM materials are used as capping layers to generate
the structural asymmetry and enhance the interfacial effects. For instance, the
Pt/Co/Ta structure attracts a lot of attention as it may exhibit large
Dzyaloshinskii-Moriya interaction. However, the dependence of magnetic
properties on different capping materials has not been systematically
investigated. In this paper, we experimentally show the interfacial PMA and
damping constant for Pt/Co/HM tri-layered structures through time-resolved
magneto-optical Kerr effect measurements as well as magnetometry measurements,
where the capping HM materials are W, Ta, and Pd. We found that the Co/HM
interface plays an important role on the magnetic properties. In particular,
the magnetic multilayers with a W capping layer features the lowest effective
damping value, which may be attributed to the different spin-orbit coupling and
interfacial hybridization between Co and HM materials. Our findings allow a
deep understanding of the Pt/Co/HM tri-layered structures. Such structures
could lead to a better era of data storage and processing devices.",1609.07320v2
2017/2/13,"Recent progress in voltage control of magnetism: Materials, mechanisms, and performance","Voltage control of magnetism (VCM) is attracting increasing interest and
exciting significant research activity driven by its profound physics and
enormous potential for application. This review article aims to provide a
comprehensive review of recent progress in VCM in different thin films. We
first present a brief summary of the modulation of magnetism by electric fields
and describe its discovery, development, classification, mechanism, and
potential applications. In the second part, we focus on the classification of
VCM from the viewpoint of materials, where both the magnetic medium and
dielectric gating materials, and their influences on magnetic modulation
efficiency are systematically described. In the third part, the nature of VCM
is discussed in detail, including the conventional mechanisms of charge,
strain, and exchange coupling at the interfaces of heterostructures, as well as
the emergent models of orbital reconstruction and electrochemical effect. The
fourth part mainly illustrates the typical performance characteristics of VCM,
and discusses, in particular, its promising application for reducing power
consumption and realizing high-density memory in several device configurations.
The present review concludes with a discussion of the challenges and future
prospects of VCM, which will inspire more in-depth research and advance the
practical applications of this field.",1702.03730v1
2018/1/15,Photoinduced Topological Phase Transitions in Topological Magnon Insulators,"Topological magnon insulators are the bosonic analogs of electronic
topological insulators. They are manifested in magnetic materials with
topologically nontrivial magnon bands as realized experimentally in a
quasi-two-dimensional (quasi-2D) kagome ferromagnet Cu(1-3, bdc), and they also
possess protected magnon edge modes. These topological magnetic materials can
transport heat as well as spin currents, hence they can be useful for
spintronic applications. Moreover, as magnons are charge-neutral spin-${\bf 1}$
bosonic quasiparticles with a magnetic dipole moment, topological magnon
materials can also interact with electromagnetic fields through the
Aharonov-Casher effect. In this report, we study photoinduced topological phase
transitions in intrinsic topological magnon insulators in the kagom\'e
ferromagnets. Using magnonic Floquet-Bloch theory, we show that by varying the
light intensity, periodically driven intrinsic topological magnetic materials
can be manipulated into different topological phases with different sign of the
Berry curvatures and the thermal Hall conductivity. We further show that, under
certain conditions, periodically driven gapped topological magnon insulators
can also be tuned to synthetic gapless topological magnon semimetals with
Dirac-Weyl magnon cones. We envision that this work will pave the way for
interesting new potential practical applications in topological magnetic
materials",1801.04932v3
2016/3/1,Time-Reversal-Breaking Weyl Fermions in Magnetic Heusler Alloys,"Weyl fermions have recently been observed in several time-reversal-invariant
semimetals and photonics materials with broken inversion symmetry. These
systems are expected to have exotic transport properties such as the chiral
anomaly. However, most discovered Weyl materials possess a substantial number
of Weyl nodes close to the Fermi level that give rise to complicated transport
properties. Here we predict, for the first time, a new family of Weyl systems
defined by broken time-reversal symmetry, namely, Co-based magnetic Heusler
materials XCo2Z (X = IVB or VB; Z = IVA or IIIA). To search for Weyl fermions
in the centrosymmetric magnetic systems, we recall an easy and practical
inversion invariant, which has been calculated to be -1, guaranteeing the
existence of an odd number of pairs of Weyl fermions. These materials exhibit,
when alloyed, only two Weyl nodes at the Fermi level - the minimum number
possible in a condensed matter system. The Weyl nodes are protected by the
rotational symmetry along the magnetic axis and separated by a large distance
(of order 2$\pi$) in the Brillouin zone. The corresponding Fermi arcs have been
calculated as well. This discovery provides a realistic and promising platform
for manipulating and studying the magnetic Weyl physics in experiments.",1603.00479v2
2018/9/4,Enhanced perpendicular magnetocrystalline anisotropy energy in an artificial magnetic material with bulk spin-momentum coupling,"We systematically investigate the perpendicular magnetocrystalline anisotropy
(MCA) in Co$-$Pt/Pd-based multilayers. Our magnetic measurement data shows that
the asymmetric Co/Pd/Pt multilayer has a significantly larger perpendicular
magnetic anisotropy (PMA) energy compared to the symmetric Co/Pt and Co/Pd
multilayer samples. We further support this experiment by first principles
calculations on the CoPt$_2$, CoPd$_2$, and CoPtPd, which are composite bulk
materials that consist of three atomic layers in a unit cell, Pt/Co/Pt,
Pd/Co/Pd, Pt/Co/Pd, respectively. By estimating the contribution of bulk
spin-momentum coupling to the MCA energy, we show that the CoPtPd multilayer
with the symmetry breaking has a significantly larger perpendicular magnetic
anisotropy (PMA) energy than the other multilayers that are otherwise similar
but lack the symmetry breaking. This observation thus provides an evidence of
the PMA enhancement due to the structural inversion symmetry breaking and
highlights the asymmetric CoPtPd as the first artificial magnetic material with
bulk spin-momentum coupling, which opens a new pathway toward the design of
materials with strong PMA.",1809.00801v3
2020/4/29,Magnetically induced elastic deformations of magnetic gels and elastomers containing particles of mixed size,"Soft elastic composite materials can serve as actuators when they transform
changes in external fields into mechanical deformation. Here, we address the
corresponding deformational behavior of magnetic gels and elastomers,
consisting of magnetizable colloidal particles in a soft polymeric matrix and
exposed to external magnetic fields. Since many practical realizations of such
materials involve particulate inclusions of polydisperse size distributions, we
concentrate on the effect that mixed particle sizes have on the overall
deformational response. To perform a systematic study, our focus is on binary
size distributions. We systematically vary the fraction of larger particles
relative to smaller ones and characterize the resulting magnetostrictive
behavior. The consequences for systems of various different spatial particle
arrangements and different degrees of compressibility of the elastic matrix are
evaluated. In parts, we observe a qualitative change in the overall response
for selected systems of mixed particle sizes. Specifically, overall changes in
volume and relative elongations or contractions in response to an induced
magnetization can be reversed into the opposite types of behavior. Our results
should apply to the characteristics of other soft elastic composite materials
like electrorheological gels and elastomers when exposed to external electric
fields as well. Overall, we hope to stimulate the further investigation on the
purposeful use of mixed particle sizes as a means to design tailored requested
material behavior.",2004.14225v1
2020/5/26,Caloric effects around phase transitions in magnetic materials described by ab initio theory: The electronic glue and fluctuating local moments,"We describe magneto-, baro- and elastocaloric effects (MCEs, BCEs and eCEs)
in materials which possess both discontinuous (first-order) and continuous
(second-order) magnetic phase transitions. Our ab initio theory of the
interacting electrons of materials in terms of disordered local moments (DLMs)
has produced explicit mechanisms for the drivers of these transitions and here
we study associated caloric effects in three case studies where both types of
transition are evident. Our earlier work had described FeRh's magnetic phase
diagram and large MCE. Here we present calculations of its substantial BCE and
eCE. We describe the MCE of dysprosium and find very good agreement with
experimental values for isothermal entropy ($\Delta S_{iso}$) and adiabatic
temperature ($\Delta T_{ad}$) changes over a large temperature span and
different applied magnetic field values. We examine the conditions for optimal
values of both $\Delta S_{iso}$ and $\Delta T_{ad}$ that comply with a
Clausius-Clapeyron analysis, which we use to propose a promising elastocaloric
cooling cycle arising from the unusual dependence of the entropy on temperature
and biaxial strain found in our third case study - the Mn$_3$GaN
antiperovskite. We explain how both $\Delta S_{iso}$ and $\Delta T_{ad}$ can be
kept large by exploiting the complex tensile strain-temperature magnetic phase
diagram which we had earlier predicted for this material and also propose that
hysteresis effects will be absent from half the caloric cycle. This rich and
complex behavior stems from the frustrated nature of the interactions among the
Mn local moments.",2005.12670v1
2020/12/15,Induced anomalous Hall effect of massive Dirac fermions in ZrTe5 and HfTe5 thin flakes,"Researches on anomalous Hall effect (AHE) have been lasting for a century to
make clear the underlying physical mechanism. Generally, the AHE appears in
magnetic materials, in which extrinsic process related to scattering effects
and intrinsic contribution connected with Berry curvature are crucial.
Recently, AHE has been counterintuitively observed in non-magnetic topological
materials and attributed to the existence of Weyl points. However, the Weyl
point scenario would lead to unsaturated AHE even in large magnetic fields and
contradicts the saturation of AHE in several tesla (T) in experiments. In this
work, we investigate the Hall effect of ZrTe5 and HfTe5 thin flakes in static
ultrahigh magnetic fields up to 33 T. We find the AHE saturates to 55 (70)
Ohm^-1*cm^-1 for ZrTe5 (HfTe5) thin flakes above ~ 10 T. Combining detailed
magnetotransport experiments and Berry curvature calculations, we clarify that
the splitting of massive Dirac bands without Weyl points can be responsible for
AHE in non-magnetic topological materials ZrTe5 and HfTe5 thin flakes. This
model can identify our thin flake samples to be weak topological insulators and
serve as a new tool to probe the band structure topology in topological
materials.",2012.08188v1
2020/12/22,Quantum Anomalous Hall Effect in Magnetic Doped Topological Insulators and Ferromagnetic Spin-Gapless Semiconductors -- A Perspective Review,"Quantum anomalous Hall effect, with a trademark of dissipationless chiral
edge states for electronics/spintronics transport applications, can be realized
in materials with large spin-orbit coupling and strong intrinsic magnetization.
After Haldane seminal proposal, several models have been presented to
control/enhance the spin-orbit coupling and intrinsic magnetic exchange
interaction. After brief introduction of Haldane model for spineless fermions,
following three fundamental quantum anomalous Hall models are discussed in this
perspective review: (i) low-energy effective four band model for magnetic-doped
topological insulator (Bi,Sb)2Te3 thin films, (ii) four band tight-binding
model for graphene with magnetic adatoms, and (iii) two (three) band spinfull
tight-binding model for ferromagnetic spin-gapless semiconductors with
honeycomb (kagome) lattice where ground state is intrinsically ferromagnetic.
These models cover two-dimensional Dirac materials hosting spinless, spinful
and spin-degenerate Dirac points where various mass terms open a band gap and
lead to quantum anomalous Hall effect. With emphasize on the topological phase
transition driven by ferromagnetic exchange interaction and its interplay with
spin-orbit-coupling, we discuss various symmetry constraints on the nature of
mass term and the materialization of these models. We hope this study will shed
light on the fundamental theoretical perspectives of quantum anomalous Hall
materials.",2101.01074v1
2022/7/4,"Moiré-driven multiferroic order in twisted CrCl$_3$, CrBr$_3$ and CrI$_3$ bilayers","Layered van der Waals materials have risen as a powerful platform to engineer
artificial competing states of matter. Here we show the emergence of
multiferroic order in twisted chromium trihalide bilayers, an order fully
driven by the moir\'e pattern and absent in aligned multilayers. Using a
combination of spin models and ab initio calculations, we show that a spin
texture is generated in the moir\'e supercell of the twisted system as a
consequence of the competition between stacking-dependent interlayer magnetic
exchange and magnetic anisotropy. An electric polarization arises associated
with such a non-collinear magnetic state due to the spin-orbit coupling,
leading to the emergence of a local ferroelectric order following the moir\'e.
Among the stochiometric trihalides, our results show that twisted CrBr$_3$
bilayers give rise to the strongest multiferroic order. We further show the
emergence of a strong magnetoelectric coupling, which allows the electric
generation and control of magnetic skyrmions. Our results put forward twisted
chromium trihalide bilayers, and in particular CrBr$_3$ bilayers, as a powerful
platform to engineer artificial multiferroic materials and electrically tunable
topological magnetic textures.",2207.01416v2
2022/9/9,Understanding magnetocrystalline anisotropy based on orbital and quadrupole moments,"Understanding magnetocrystalline anisotropy (MCA) is fundamentally important
for developing novel magnetic materials. Therefore, clarifying the relationship
between MCA and local physical quantities observed by spectroscopic
measurements, such as the orbital and quadrupole moments, is necessary. In this
review, we discuss MCA and the distortion effects in magnetic materials with
transition metals (TMs) based on the orbital and quadrupole moments, which are
related to the spin-conserving and spin-flip terms in the second-order
perturbation calculations, respectively. We revealed that orbital moment
stabilized the spin moment in the direction of the larger orbital moment, while
the quadrupole moment stabilized the spin moment along the longitudinal
direction of the spin-density distribution. The MCA of the magnetic materials
with TMs and their interfaces can be determined from the competition between
these two contributions. We showed that the perpendicular MCA of the
face-centered cubic (fcc) Ni with tensile tetragonal distortion arose from the
orbital moment anisotropy, whereas that of Mn-Ga alloys originated from the
quadrupole moment of spin density. In contrast, in the Co/Pd(111) multilayer
and Fe/MgO(001), both the orbital moment anisotropy and quadrupole moment of
spin density at the interfaces contributed to the perpendicular MCA.
Understanding the MCA of magnetic materials and interfaces based on orbital and
quadrupole moments is essential to design MCA of novel magnetic applications.",2209.04070v1
2022/10/4,High-field Studies on Layered Magnetic and Polar Dirac Metals,"Recently, the interplay between the Dirac/Weyl fermion and various bulk
properties, such as magnetism, has attracted considerable attention, since
unconventional transport and optical phenomena were discovered. However, the
design principles for such materials have not been established well. Here, we
propose that the layered material $A$Mn$X_2$ ($A$: alkaline and rare-earth
ions, $X$: Sb, Bi) is a promising platform for systematically exploring
strongly correlated Dirac metals, which consists of the alternative stack of
the $X^-$ square net layer hosting a 2D Dirac fermion and the
$A^{2+}$-Mn$^{2+}$-$X^{3-}$ magnetic block layer. In this article, we shall
review recent high-field studies on this series of materials to demonstrate
that various types of Dirac fermions are realized by designing the block layer.
First, we give an overview of the Dirac fermion coupled with the magnetic order
in EuMnBi$_2$ ($A$=Eu). This material exhibits large magnetoresistance by the
field-induced change in the magnetic order of Eu layers, which is associated
with the strong exchange interaction between the Dirac fermion and the local Eu
moment. Second, we review the Dirac fermion coupled with the lattice
polarization in BaMn$X_2$ ($A$=Ba). There, spin-valley coupling manifests
itself owing to the Zeeman-type spin-orbit interaction, which is experimentally
evidenced by the bulk quantum Hall effect observed at high fields.",2210.01717v1
2022/11/2,2D-Double transition metal MXenes for spintronics applications: surface functionalization induced ferromagnetic half-metallic complexes,"MXenes are rapidly emerging two-dimensional (2D) materials with thickness,
composition, and functionalization-dependent outstanding properties having
applications in diverse fields. To disclose nano-spintronic applications of
2D-double transition metal (DTM) carbide and nitride-based pristine and
surface-functionalized MXenes (M'2M""X2Tx, M' and M"" = Cr, Mo, W; X = C/N; T =
-F/-OH/=O), a systematic investigation has been performed on structural
stability, magnetic properties and electronic structure using spin-polarized
first-principles calculations. 36 stables functionalized MXenes were screened
from 144 explored DTM based MXenes. The explored materials exhibit striking
properties, having wide range of magnetic ground states, from non-magnetic to
ferromagnetic, and then to antiferromagnetic, accompanied by metallic to
half-metallic or gapless half-metallic properties, depending on transition
metal(s) and terminating group. Mo and W-based MXenes are found to be
nonmagnetic and metallic, whereas Cr-Mo and Cr-W-based MXenes are magnetic with
varying metallic behavior. W2CrN2O2 and Mo2CrN2O2 systems are found to be
ferromagnetic half-metallic 2D materials with a direct band gap of 1.35 eV and
0.77 eV respectively, in the minority spin channel. The comprehensive study on
DTM MXenes, provide intrinsic half-metallic properties along with robust
ferromagnetism, opens up a class of promising new 2D materials with tunable
magnetic and electronic properties for potential device applications in
nano-spintronics and electronics.",2211.00846v1
2022/12/13,High-throughput screening assisted discovery of a stable layered anti-ferromagnetic semiconductor: CdFeP2Se6,"Recent advances in two-dimensional (2D) magnetism have heightened interest in
layered magnetic materials due to their potential for spintronics. In
particular, layered semiconducting antiferromagnets exhibit intriguing
low-dimensional semiconducting behavior with both charge and spin as carrier
controls. However, synthesis of these compounds is challenging and remains
rare. Here, we conducted firstprinciples based high-throughput search to screen
potentially stable mixed metal phosphorous trichalcogenides (MM'P2X6, where M
and M' are transition metals and X is a chalcogenide) that have a wide range of
tunable bandgaps and interesting magnetic properties. Among the potential
candidates, we successfully synthesized a stable semiconducting layered
magnetic material, CdFeP2Se6, that exhibits a short-range antiferromagnetic
order at TN = 21 K with an indirect band gap of 2.23 eV. Our work suggests that
highthroughput screening assisted synthesis be an effective method for layered
magnetic materials discovery.",2212.06289v2
2022/12/21,"Large anomalous Hall, Nernst effect and topological phases in the 3d-4d/5d based oxide double perovskites","Magnetic topological quantum materials are attracting considerable attention
owing to their potential technological applications. However, only a small
number of these materials have been experimentally realized, thereby giving
rise to the need for new stable magnetic topological quantum materials.
Magnetism and spin-orbit coupling, two essential ingredients of the oxide
materials, lead to various topological transport phenomena such as the
anomalous Hall and anomalous Nernst effects, which can be significantly
enhanced by designing an electronic structure with a large Berry curvature. In
that respect, double perovskites with the general formula A$_2$BB'O$_6$ with an
alternating ordered arrangement of two transition metal sites, B(3d) and
B'(4d/5d), present attractive possibilities as they are robustly stable against
oxidation under ambient conditions and versatile. These double perovskites also
offer a high energy scale for magnetism as well as strong spin-orbit coupling
with a high magnetic ordering temperature. Here, using first-principles density
functional theory calculations, we present a comprehensive study of the
intrinsic anomalous transport for 3d-4d/5d based cubic and tetragonal stable
double perovskite (DP) compounds. A few of the DPs exhibit a very large
anomalous Hall effect with a distinct topological band crossing in the vicinity
of the Fermi energy. Our results show the importance of symmetries,
particularly the mirror planes, as well as the clean topological band crossing
near the Fermi energy, which is primarily contributed by the 5d-t$_{2g}$ for
large anomalous Hall and Nernst effects.",2212.11324v1
2023/11/7,Magnetic functionalization and Catalytic behavior of magnetic nanoparticles during laser photochemical graphitization of polyimide,"We report laser-assisted photochemical graphitization of polyimides (PI) into
functional magnetic nanocomposites using laser irradiation of PI in the
presence of magnetite nanoparticles (MNP). PI Kapton sheets covered with MNP
were photochemically treated under ambient conditions using a picosecond pulsed
laser (1064nm) to obtain an electrically conductive material. Scanning electron
microscopy of the treated material revealed layered magnetic
nanoparticles/graphite nanocomposite structure (MNP/graphite). Four probe
conductivity measurements indicated that nanocomposite has an electrical
conductivity of 1550 S/m. Superconducting quantum interference device (SQUID)
magnetometer-based magnetic characterization of the treated material revealed
an anisotropic ferromagnetic response in the MNP/graphite nanocomposite
compared to the isotropic response of MNP. Raman spectroscopy of MNP/graphite
nanocomposite revealed a four-fold improvement in graphitization, suppression
in disorder, and decreased nitrogenous impurities compared to the graphitic
material obtained from laser treatment of just PI sheets. X-ray photoelectron
spectroscopy, x-ray diffraction, and energy-dispersive x-ray spectroscopy were
used to delineate the phase transformations of MNP during the formation of
MNP/graphite nanocomposite. Post-mortem characterization indicates a possible
photocatalytic effect of MNP during MNP/graphite nanocomposite formation. Under
laser irradiation, MNP transformed from the initial Fe3O4 phase to
{\gamma}-Fe2O3 and Fe5C2 phases and acted as nucleation spots to catalyze the
graphitization process of PI.",2311.04264v1
2022/10/3,"Polymer-bonded magnets produced by laser powder bed fusion: Influence of powder morphology, filler fraction and energy input on the magnetic and mechanical properties","Bonded permanent magnets are key components in many energy conversion, sensor
and actuator devices. These applications require high magnetic performance and
freedom of shape. With additive manufacturing processes, for example laser
powder bed fusion (LPBF), it is possible to produce bonded magnets with
customized stray field distribution. Up to now, most studies use spherical
powders as magnetic fillers due to their good flowability. Here, the behavior
of large SmFeN platelets with a high aspect ratio as filler material and its
influence on the arrangement and the resulting magnetic properties are examined
in comparison to a spherical magnetic filler. The 3D distribution and
orientation of the magnetic filler was studied by computed tomography and
digital image analysis. The platelet-shaped particles align themselves
perpendicular to the buildup direction during the process, which offers a new
and cost-effective way of producing composites by LPBF with anisotropic
structural and functional properties. The influence of LPBF parameters on the
properties of the composites is investigated. Highest filling fractions are
required for high magnetic remanence, however the powder itself limits this
maximum due to particle shape and required minimal polymer fraction to form
mechanically stable magnets. The coercivity decreases for higher filling
fractions, which is attributed to increased rotation of insufficiently embedded
magnetic particles in the matrix. It is discussed how filler morphology
influences the observed change in coercivity since the rotation of spherical
particles in comparison to platelet-shaped particles requires less energy. Our
work shows the challenges and opportunities of large platelet shaped fillers
used in LPBF for the production of anisotropic functional and structural
composites.",2210.00696v1
2023/1/24,Spin Dynamics in van der Waals Magnetic Systems,"The discovery of atomic monolayer magnetic materials has stimulated intense
research activities in the two-dimensional (2D) van der Waals (vdW) materials
community. The field is growing rapidly and there has been a large class of 2D
vdW magnetic compounds with unique properties, which provides an ideal platform
to study magnetism in the atomically thin limit. In parallel, based on
tunneling magnetoresistance and magneto-optical effect in 2D vdW magnets and
their heterostructures, emerging concepts of spintronic and optoelectronic
applications such as spin tunnel field-effect transistors and spin-filtering
devices are explored. While the magnetic ground state has been extensively
investigated, reliable characterization and control of spin dynamics play a
crucial role in designing ultrafast spintronic devices. Ferromagnetic resonance
(FMR) allows direct measurements of magnetic excitations, which provides
insight into the key parameters of magnetic properties such as exchange
interaction, magnetic anisotropy, gyromagnetic ratio, spin-orbit coupling,
damping rate, and domain structure. In this review article, we present an
overview of the essential progress in probing spin dynamics of 2D vdW magnets
using FMR techniques. Given the dynamic nature of this field, we focus mainly
on broadband FMR, optical FMR, and spin-torque FMR, and their applications in
studying prototypical 2D vdW magnets. We conclude with the recent advances in
laboratory- and synchrotron-based FMR techniques and their opportunities to
broaden the horizon of research pathways into atomically thin magnets.",2301.09822v2
2023/7/16,Magnetic-domain-dependent pseudogap induced by Fermi surface nesting in a centrosymmetric skyrmion magnet,"Skyrmions in non-centrosymmetric materials are believed to occur due to the
Dzyaloshinskii-Moriya interaction. In contrast, the skyrmion formation
mechanism in centrosymmetric materials remains elusive. Among those, Gd-based
compounds are the prototype compounds; however, their electronic structure is
not uncovered, even though it should be the foundation for elucidating the
skyrmion mechanism. Here, we reveal the intrinsic electronic structure of
GdRu2Si2 for the first time by magnetic domain selective measurements of
angle-resolved photoemission spectroscopy (ARPES). In particular, we find the
robust Fermi surface (FS) nesting, consistent with the q-vector detected by the
previous resonant X-ray scattering (RXS) measurements. Most importantly, we
find that the pseudogap is opened at the nested portions of FS at low
temperatures. The momentum locations of the pseudogap vary for different
magnetic domains, most likely having a direct relationship with the screw-type
spin modulation that changes direction for each domain. Intriguingly, the
anomalous pseudogap disconnects the FS to generate Fermi arcs with 2-fold
symmetry. These results indicate the significance of
Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, in which itinerant electrons
mediate to stabilize the local magnetic moment, as the mechanism for the
magnetism in the Gd-based skyrmion magnets. Our data also predict that the
momentum space where the pseudogap opens is doubled (or Fermi arcs shrink) and
thereby stabilizes the skyrmion phase under a magnetic field. Furthermore, we
demonstrate the flexible nature of magnetism in GdRu2Si2 by manipulating
magnetic domains with a magnetic field and temperature cyclings, providing a
possibility of future application for data storage and processing device with
centrosymmetric skyrmion magnets.",2307.08000v1
2010/5/18,Micromagnetic simulations of spinel ferrite particles,"This paper presents the results of simulations of the magnetization field
{\it ac} response (at $2$ to $12$ GHz) of various submicron ferrite particles
(cylindrical dots). The ferrites in the present simulations have the spinel
structure, expressed here by M$_{1-n}$Zn$_{n}$Fe$_2$O$_4$ (where M stands for a
divalent metal), and the parameters chosen were the following: (a) for $n=0$: M
= \{ Fe, Mn, Co, Ni, Mg, Cu \}; (b) for $n=0.1$: M = \{ Fe, Mg \} (mixed
ferrites). These runs represent full 3D micromagnetic (one-particle) ferrite
simulations. We find evidences of confined spin waves in all simulations, as
well as a complex behavior nearby the main resonance peak in the case of the M
= \{ Mg, Cu \} ferrites. A comparison of the $n=0$ and $n=0.1$ cases for fixed
M reveals a significant change in the spectra in M = Mg ferrites, but only a
minor change in the M = Fe case. An additional larger scale simulation of a $3$
by $3$ particle array was performed using similar conditions of the Fe$_3$O$_4$
(magnetite; $n=0$, M = Fe) one-particle simulation. We find that the main
resonance peak of the Fe$_3$O$_4$ one-particle simulation is disfigured in the
corresponding 3 by 3 particle simulation, indicating the extent to which
dipolar interactions are able to affect the main resonance peak in that
magnetic compound.",1005.3169v1
2010/11/25,Calculation of the Expected Zero Field Muon Relaxation Rate in the Geometrically Frustrated Rare Earth Pyrochlore Gd2Sn2O7 Antiferromagnet,"The magnetic insulator Gd2Sn2O7 is one of many geometrically frustrated
magnetic materials known to exhibit a nonzero muon spin polarization relaxation
rate, $\lambda(T)$, down to the lowest temperature (T) studied. Such behaviour
is typically interpreted as a significant level of persisting spin dynamics
(PSD) of the host material. In the case of Gd2Sn2O7, such PSD comes as a
surprise since magnetic specific heat measurements suggest conventional gapped
magnons, which would naively lead to an exponentially vanishing $\lambda(T)$ as
$T \rightarrow 0$. In contrast to most materials that display PSD, the ordered
phase of Gd2Sn2O7 is well characterized and both the nature and the magnitude
of the interactions have been inferred from the magnetic structure and the
temperature dependence of the magnetic specific heat. Based on this
understanding, the temperature dependence of the muon spin polarization
relaxation through the scattering of spin waves (magnons) is calculated. The
result explicitly shows that, despite the unusual extensive number of weakly
dispersive (gapped)excitations characterizing Gd2Sn2O7, a remnant of the zero
modes of the parent frustrated pyrochlore Heisenberg antiferromagnet, the
temperature dependence of the calculated $\lambda(T)$ differs dramatically from
the experimental one. Indeed, the calculation conforms to the naive expectation
of an exponential collapse of $\lambda(T)$ at temperatures below ~ 0.7K. This
result, for the first time, illustrates crisply and quantitatively the paradox
that presents itself with the pervasive occurrence of PSD in highly frustrated
magnetic systems as evinced by muon spin relaxation measurements.",1011.5689v1
2012/6/1,"Dirac point spectral weight suppression and surface ""gaps"" in nonmagnetic and magnetic topological insulators","It is predicted that electrons on the surface of a topological insulator can
acquire a mass (massive Dirac fermion) by opening up a gap at the Dirac point
when time-reversal symmetry is broken via the out-of-plane magnetization. We
report photoemission studies on a series of topological insulator materials
focusing on the spectral behavior in the vicinity of the Dirac node. Our
results show that the spectral intensity is suppressed resulting in a
""gap""-like feature in materials with or without any magnetic impurity or
doping. The Zeeman gap in magnetically doped samples, expected to be rather
small, is likely masked by the non-magnetic strong spectral weight suppression
involving a large energy scale we report. The photoemission spectral weight
suppression observed around the Dirac node thus cannot be taken as the sole
evidence for a time-reversal symmetry breaking magnetic gap. We discuss a few
possible extrinsic and kinematic origins of the Dirac point spectral weight
suppression (""gap"") observed in many commonly studied topological materials.",1206.0278v3
2015/3/27,Magnetic Correlations in the Quasi-2D Semiconducting Ferromagnet CrSiTe$_3$,"Intrinsic, two-dimensional ferromagnetic semiconductors are an important
class of materials for overcoming the limitations of dilute magnetic
semiconductors for spintronics applications. CrSiTe$_3$ is a particularly
interesting member of this class, since it can likely be exfoliated down to
single layers, where T$_C$ is predicted to increase dramatically. Establishing
the nature of the magnetism in the bulk is a necessary precursor to
understanding the magnetic behavior in thin film samples and the possible
applications of this material. In this work, we use elastic and inelastic
neutron scattering to measure the magnetic properties of single crystalline
CrSiTe$_3$. We find that there is a very small single ion anisotropy favoring
magnetic ordering along the $c$-axis and that the measured spin waves fit well
to a model where the moments are only weakly coupled along that direction.
Finally, we find that both static and dynamic correlations persist within the
$ab$-plane up to at least 300 K, strong evidence of this material's
two-dimensional characteristics that are relevant for future studies on thin
film and monolayer samples.",1503.08199v2
2018/4/12,Insight into the origin of Lithium/Nickel ions exchange in layered Li(NixMnyCoz)O2 cathode materials,"In layered LiNixMnyCozO2 cathode material for lithium-ion batteries, the
spins of transition metal (TM) ions construct a two-dimensional triangular
networks, which can be considered as a simple case of geometrical frustration.
By performing neutron powder diffraction experiments and magnetization
measurements, we find that long-range magnetic order cannot be established in
LiNixMnyCozO2 even at low temperature of 3 K. Remarkably, the frustration
parameters of these compounds are estimated to be larger than 30, indicating
the existence of strongly frustrated magnetic interactions between spins of TM
ions. As frustration will inevitably give rise to lattice instability, the
formation of Li/Ni exchange in LiNixMnyCozO2 will help to partially relieve the
degeneracy of the frustrated magnetic lattice by forming a stable
antiferromagnetic state in hexagonal sublattice with nonmagnetic ions located
in centers of the hexagons. Moreover, Li/Ni exchange will introduce 180{\deg}
superexchange interaction, which further relieves the magnetic frustration
through bringing in new exchange paths. Thus, the variation of Li/Ni exchange
ratio vs. TM mole fraction in LiNixMnyCozO2 with different compositions can be
well understood and predicted in terms of magnetic frustration and
superexchange interactions. This provides a unique viewpoint to study the Li/Ni
ions exchange in layered Li(NixMnyCoz)O2 cathode materials.",1804.04598v1
2018/6/1,"Magnetic phases of skyrmion-hosting GaV$_4$S$_{8-y}$Se$_{y}$ ($y = 0, 2, 4, 8$) probed with muon spectroscopy","We present the results of a muon-spin spectroscopy investigation of
GaV$_4$S$_{8-y}$Se$_{y}$ with $y=0, 2, 4$ and 8. Zero-field measurements
suggest that GaV$_{4}$Se$_{8}$ and GaV$_{4}$S$_{8}$ have distinct magnetic
ground states, with the latter material showing an anomalous
temperature-dependence of the local magnetic field. It is not possible to
evolve the magnetic state continuously between these two systems, with the
intermediate $y=2$ and $4$ materials showing glassy magnetic behaviour at low
temperature. The skyrmion lattice (SkL) phase is evident in the $y=0$ and 8
materials through an enhanced response of the muon-spin relaxation to the
emergent dynamics that accompany the SkL. For our polycrystalline samples of
GaV$_4$Se$_{8}$, this enhanced dynamic response is confined to a smaller region
of the magnetic field-temperature phase diagram than the previous reports of
the SkL in single crystals.",1806.00412v3
2018/6/18,Anomalous Nernst effect beyond the magnetization scaling relation in the ferromagnetic Heusler compound Co$_2$MnGa,"Applying a temperature gradient in a magnetic material generates a voltage
that is perpendicular to both the heat flow and the magnetization. This is the
anomalous Nernst effect (ANE) which was thought to be proportional to the value
of the magnetization for a long time. However, more generally, the ANE has been
predicted to originate from a net Berry curvature of all bands near the Fermi
level. Subsequently, a large anomalous Nernst thermopower has recently been
observed in topological materials with no net magnetization but large net Berry
curvature around E$_F$. These experiments clearly fall outside the scope of the
conventional magnetization-model of the ANE, but a significant question
remains: Can the value of the ANE in topological ferromagnets exceed the
highest values observed in conventional ferromagnets? Here, we report a
remarkably high anomalous Nernst thermopower value of ~6.0 \mu V/K at 1 T in
the ferromagnetic topological Heusler compound Co$_2$MnGa at room temperature,
which is around 7-times larger than any anomalous Nernst thermopower value ever
reported for a conventional ferromagnet. Combined electrical, thermoelectric
and first-principles calculations reveal that this high value of the ANE arises
from a large net Berry curvature near the Fermi level associated with nodal
lines and Weyl points.",1806.06753v1
2019/6/11,Van der Waals epitaxy of Mn-doped MoSe$_2$ on mica,"The magnetic order associated with the degree of freedom of spin in
two-dimensional (2D) materials is subjected to intense investigation because of
its potential application in 2D spintronics and valley-related magnetic
phenomena. We report here a bottom-up strategy using molecular beam epitaxy to
grow and dope large-area (cm$^2$) few-layer MoSe$_2$ with Mn as a magnetic
dopant. High-quality Mn-doped MoSe$_2$ layers are obtained for Mn content of
less than 5 % (atomic). When increasing the Mn content above 5 % we observe a
clear transition from layer-by-layer to cluster growth. Magnetic measurements
involving a transfer process of the cm$^2$-large doped layers on
100-micron-thick silicon substrate, show plausible proof of high-temperature
ferromagnetism of 1 % and 10 % Mn-doped MoSe$_2$. Although we could not point
to a correlation between magnetic and electrical properties, we demonstrate
that the transfer process described in this report permits to achieve
conventional electrical and magnetic measurements on the doped layers
transferred on any substrate. Therefore, this study provides a promising route
to characterize stable ferromagnetic 2D layers, which is broadening the current
start-of-the-art of 2D materials-based applications.",1906.04801v1
2019/8/1,Quasi-Two-Dimensional Magnon Identification in Antiferromagnetic FePS3 via Magneto-Raman Spectroscopy,"Recently it was discovered that van der Waals-bonded magnetic materials
retain long range magnetic ordering down to a single layer, opening many
avenues in fundamental physics and potential applications of these fascinating
materials. One such material is FePS3, a large spin (S=2) Mott insulator where
the Fe atoms form a honeycomb lattice. In the bulk, FePS3 has been shown to be
a quasi-two-dimensional-Ising antiferromagnet, with additional features in the
Raman spectra emerging below the Neel temperature of approximately 120 K. Using
magneto-Raman spectroscopy as an optical probe of magnetic structure, we show
that one of these Raman-active modes in the magnetically ordered state is
actually a magnon with a frequency of of approximately 3.7 THz (122 cm-1).
Contrary to previous work, which interpreted this feature as a phonon, our
Raman data shows the expected frequency shifting and splitting of the magnon as
a function of temperature and magnetic field, respectively, where we determine
the g-factor to be approximately 2. In addition, the symmetry behavior of the
magnon is studied by polarization-dependent Raman spectroscopy and explained
using the magnetic point group of FePS3.",1908.00608v1
2018/10/4,Chiral Magnetic Photocurrent in Dirac and Weyl Materials,"Circularly polarized light (CPL) can induce an asymmetry between the number
of left- and right-handed chiral quasiparticles in Dirac and Weyl semimetals.
We show that if the photoresponse of the material is dominated by chiral
quasiparticles, the total chiral charge induced in the material by CPL can be
evaluated in a model-independent way through the chiral anomaly. In the
presence of an external magnetic field perpendicular to the incident CPL, this
allows to predict the linear density of the induced photocurrent resulting from
the chiral magnetic effect. The predicted effect should exist in any kind of
Dirac or Weyl materials, with both symmetric and asymmetric band structure. An
estimate of the resulting chiral magnetic photocurrent in a typical Dirac
semimetal irradiated by an infrared laser of intensity $\simeq 5 \times 10^6\,
\mathrm{W/m^2}$ and a wavelength of $\lambda \simeq 10\, \mu\mathrm{m}$ in an
external magnetic field $B \simeq 2\, \mathrm{T}$ yields a current $J \simeq
50\,\mathrm{nA}$ in the laser spot of size $\simeq 50\,\mu\mathrm{m}$. This
current scales linearly with the magnetic field and wavelength, opening up
possibilities for applications in photonics, optoelectronics, and THz sensing.",1810.02399v2
2019/1/23,Revisiting the Kitaev material candidacy of Ir4+ double perovskite iridates,"Quantum magnets with significant bond-directional Ising interactions,
so-called Kitaev materials, have attracted tremendous attention recently in the
search for exotic spin liquid states. Here we present a comprehensive set of
measurements that enables us to investigate the crystal structures, Ir$^{4+}$
single ion properties, and magnetic ground states of the double perovskite
iridates La$_2B$IrO$_6$ ($B$ $=$ Mg, Zn) and $A_2$CeIrO$_6$ ($A$ $=$ Ba, Sr)
with a large nearest neighbor distance $>$ 5 Angstroms between Ir$^{4+}$ ions.
Our neutron powder diffraction data on Ba$_2$CeIrO$_6$ can be refined in the
cubic space group Fm$\bar{3}$m, while the other three systems are characterized
by weak monoclinic structural distortions. Despite the variance in the
non-cubic crystal field experienced by the Ir$^{4+}$ ions in these materials,
X-ray absorption spectroscopy and resonant inelastic x-ray scattering are
consistent with $J_{\rm eff}$ $=$ 1/2 moments in all cases. Furthermore,
neutron scattering and resonant magnetic x-ray scattering show that these
systems host A-type antiferromagnetic order. These electronic and magnetic
ground states are consistent with expectations for face-centered-cubic magnets
with significant antiferromagnetic Kitaev exchange, which indicates that
spacing magnetic ions far apart may be a promising design principle for
uncovering additional Kitaev materials.",1901.08146v2
2019/1/28,Suppression of magnetic ordering in XXZ-type antiferromagnetic monolayer NiPS3,"How a certain ground state of complex physical systems emerges, especially in
two-dimensional materials, is a fundamental question in condensed-matter
physics. A particularly interesting case is systems belonging to the class of
XY Hamiltonian where the magnetic order parameter of conventional nature is
unstable in two-dimensional materials leading to a
Berezinskii-Kosterlitz-Thouless transition. Here, we report how the XXZ-type
antiferromagnetic order of a magnetic van der Waals material, NiPS3, behaves
upon reducing the thickness and ultimately becomes unstable in the monolayer
limit. Our experimental data are consistent with the findings based on
renormalization group theory that at low temperatures a two-dimensional XXZ
system behaves like a two-dimensional XY one, which cannot have a long-range
order at finite temperatures. This work provides experimental examination of
the XY magnetism in the atomically thin limit and opens new opportunities of
exploiting these fundamental theorems of magnetism using magnetic van der Waals
materials.",1901.10890v1
2018/12/12,First-principles prediction of half-Heusler half-metals above room temperature,"Half-metallicity (HM) offers great potential for engineering spintronic
applications, yet only few magnetic materials present metallicity in just one
spin channel. In addition, most HM systems become magnetically disordered at
temperatures well below ambient conditions, which further hinders the
development of spin-based electronic devices. Here, we use first-principles
methods based on density functional theory (DFT) to investigate the electronic,
magnetic, structural, mixing, and vibrational properties of $90$ $XYZ$
half-Heusler (HH) alloys ($X =$ Li, Na, K, Rb, Cs; $Y =$ V,Nb, Ta; $Z =$ Si,
Ge, Sn, S, Se, Te). We disclose a total of $28$ new HH compounds that are
ferromagnetic, vibrationally stable, and HM, with semiconductor band gaps in
the range of $1$-$4$ eV and HM band gaps of $0.2$-$0.8$ eV. By performing Monte
Carlo simulations of a spin Heisenberg model fitted to DFT energies, we
estimate the Curie temperature, $T_{\rm C}$, of each HM compound. We find that
$17$ HH HM remain magnetically ordered at and above room temperature, namely,
$300 \le T_{\rm C} \le 450$ K, with total magnetic moments of $2$ and $4$
$\mu_{\rm B}$. A further materials sieve based on zero-temperature mixing
energies let us to conclude $5$ overall promising ferromagnetic HH HM at and
above room temperature: NaVSi, RbVTe, CsVS, CsVSe, and RbNbTe. We also predict
$2$ ferromagnetic materials that are semiconductor and magnetically ordered at
ambient conditions: LiVSi and LiVGe.",1812.04813v1
2008/11/6,Tunable magnetic exchange interactions in manganese-doped inverted core/shell ZnSe/CdSe nanocrystals,"Magnetic doping of semiconductor nanostructures is actively pursued for
applications in magnetic memory and spin-based electronics. Central to these
efforts is a drive to control the interaction strength between carriers
(electrons and holes) and the embedded magnetic atoms. In this respect,
colloidal nanocrystal heterostructures provide great flexibility via
growth-controlled `engineering' of electron and hole wavefunctions within
individual nanocrystals. Here we demonstrate a widely tunable magnetic sp-d
exchange interaction between electron-hole excitations (excitons) and
paramagnetic manganese ions using `inverted' core-shell nanocrystals composed
of Mn-doped ZnSe cores overcoated with undoped shells of narrower-gap CdSe.
Magnetic circular dichroism studies reveal giant Zeeman spin splittings of the
band-edge exciton that, surprisingly, are tunable in both magnitude and sign.
Effective exciton g-factors are controllably tuned from -200 to +30 solely by
increasing the CdSe shell thickness, demonstrating that strong quantum
confinement and wavefunction engineering in heterostructured nanocrystal
materials can be utilized to manipulate carrier-Mn wavefunction overlap and the
sp-d exchange parameters themselves.",0811.1036v1
2018/9/7,In situ compensation method for high-precision and high-sensitivity integral magnetometry,"An ongoing process of miniaturization of spintronics and magnetic-films-based
devices, as well as a growing necessity for basic material research place
stringent requirements for sensitive and accurate magnetometric measurements of
minute magnetic constituencies deposited on large magnetically responsive
carriers. However, the most popular multipurpose commercial superconducting
quantum interference device (SQUID) magnetometers are not object-selective
probes, so the sought signal is usually buried in the magnetic response of the
carrier, contaminated by signals from the sample support, system instabilities
and additionally degraded by an inadequate data reduction. In this report a
comprehensive method based on the in situ magnetic compensation for mitigating
all these weak elements of SQUID-based magnetometry is presented. Practical
solutions and proper expressions to evaluate the final outcome of the
investigations are given. Their universal form allows to employ the suggested
design in investigations of a broad range of specimens of different sizes,
shapes and compositions. The method does not require any extensive numerical
modelling, it relies only on the data taken from the standard magnetometer
output. The solution can be straightforwardly implemented in every field where
magnetic investigations are of a prime importance, including in particular
emerging new fields of topological insulators, 3D-Dirac semimetals and
2D-materials.",1809.02346v3
2019/3/9,A New Magnetic Topological Quantum Material Candidate by Design,"Magnetism, when combined with an unconventional electronic band structure,
can give rise to forefront electronic properties such as the quantum anomalous
Hall effect, axion electrodynamics, and Majorana fermions. Here we report the
characterization of high-quality crystals of EuSn$_2$P$_2$, a new quantum
material specifically designed to engender unconventional electronic states
plus magnetism. EuSn$_2$P$_2$ has a layered, Bi$_2$Te$_3$-type structure.
Ferromagnetic interactions dominate the Curie-Weiss susceptibility, but a
transition to antiferromagnetic ordering occurs near 30 K. Neutron diffraction
reveals that this is due to two-dimensional ferromagnetic spin alignment within
individual Eu layers and antiferromagnetic alignment between layers - this
magnetic state surrounds the Sn-P layers at low temperatures. The bulk
electrical resistivity is sensitive to the magnetism. Electronic structure
calculations reveal that EuSn$_2$P$_2$ might be a strong topological insulator,
which can be a new magnetic topological quantum material (MTQM) candidate. The
calculations show that surface states should be present, and they are indeed
observed by ARPES measurements.",1903.03888v1
2019/4/15,Crystal field coefficients for yttrium analogues of rare-earth/transition-metal magnets using density-functional theory in the projector-augmented wave formalism,"We present a method of calculating crystal field coefficients of
rare-earth/transition-metal (RE-TM) magnets within density-functional theory
(DFT). The principal idea of the method is to calculate the crystal field
potential of the yttrium analogue (""Y-analogue"") of the RE-TM magnet, i.e. the
material where the lanthanide elements have been substituted with yttrium. The
advantage of dealing with Y-analogues is that the methodological and conceptual
difficulties associated with treating the highly-localized 4f electrons in DFT
are avoided, whilst the nominal valence electronic structure principally
responsible for the crystal field is preserved. In order to correctly describe
the crystal field potential in the core region of the atoms we use the
projector-augmented wave formalism of DFT, which allows the reconstruction of
the full charge density and electrostatic potential. The Y-analogue crystal
field potentials are combined with radial 4f charge densities obtained in
self-interaction-corrected calculations on the lanthanides to obtain crystal
field coefficients. We demonstrate our method on a test set of 10 materials
comprising 9 RE-TM magnets and elemental Tb. We show that the calculated easy
directions of magnetization agree with experimental observations, including a
correct description of the anisotropy within the basal plane of Tb and
NdCo$_5$. We further show that the Y-analogue calculations generally agree
quantitatively with previous calculations using the open-core approximation to
treat the 4f electrons, and argue that our simple approach may be useful for
large-scale computational screening of new magnetic materials.",1904.06896v1
2019/7/3,Dirac magnons in a honeycomb lattice quantum XY magnet CoTiO3,"The discovery of massless Dirac electrons in graphene and topological
Dirac-Weyl materials has prompted a broad search for bosonic analogues of such
Dirac particles. Recent experiments have found evidence for Dirac magnons above
an Ising-like ferromagnetic ground state in a two-dimensional (2D) kagome
lattice magnet and in the van der Waals layered honeycomb crystal CrI$_3$, and
in a 3D Heisenberg magnet Cu$_3$TeO$_6$. Here we report on our inelastic
neutron scattering investigation on large single crystals of a stacked
honeycomb lattice magnet CoTiO$_3$, which is part of a broad family of ilmenite
materials. The magnetically ordered ground state of CoTiO$_3$ features
ferromagnetic layers of Co$^{2+}$, stacked antiferromagnetically along the
$c$-axis. We discover that the magnon dispersion relation exhibits strong
easy-plane exchange anisotropy and hosts a clear gapless Dirac cone along the
edge of the 3D Brillouin zone. Our results establish CoTiO$_3$ as a model
pseudospin-$1/2$ material to study interacting Dirac bosons in a 3D quantum XY
magnet.",1907.02061v1
2020/1/17,Single-layer graphene on epitaxial FeRh thin films,"Graphene is a 2D material that displays excellent electronic transport
properties with prospective applications in many fields. Inducing and
controlling magnetism in the graphene layer, for instance by proximity of
magnetic materials, may enable its utilization in spintronic devices. This
paper presents fabrication and detailed characterization of single-layer
graphene formed on the surface of epitaxial FeRh thin films. The magnetic state
of the FeRh surface can be controlled by temperature, magnetic field or strain
due to interconnected order parameters. Characterization of graphene layers by
X-ray Photoemission and X-ray Absorption Spectroscopy, Low-Energy Ion
Scattering, Scanning Tunneling Microscopy, and Low-Energy Electron Microscopy
shows that graphene is single-layer, polycrystalline and covers more than 97%
of the substrate. Graphene displays several preferential orientations on the
FeRh(001) surface with unit vectors of graphene rotated by 30{\deg}, 15{\deg},
11{\deg}, and 19{\deg} with respect to FeRh substrate unit vectors. In
addition, the graphene layer is capable to protect the films from oxidation
when exposed to air for several months. Therefore, it can be also used as a
protective layer during fabrication of magnetic elements or as an atomically
thin spacer, which enables incorporation of switchable magnetic layers within
stacks of 2D materials in advanced devices.",2001.06559v1
2020/10/7,Orbital isotropy of magnetic fluctuations in correlated electron materials induced by Hund's exchange coupling,"Characterizing non-local magnetic fluctuations in materials with strong
electronic Coulomb interactions remains one of the major outstanding challenges
of modern condensed matter theory. In this work we address the spatial symmetry
and orbital structure of magnetic fluctuations in perovskite materials. To this
aim, we develop a consistent multi-orbital diagrammatic extension of dynamical
mean field theory, which we apply to an anisotropic three-orbital model of
cubic $t_{2g}$ symmetry. We find that the form of spatial spin fluctuations is
governed by the local Hund's coupling. For small values of the coupling,
magnetic fluctuations are anisotropic in orbital space, which reflects the
symmetry of the considered $t_{2g}$ model. Large Hund's coupling enhances
collective spin excitations, which mixes orbital and spatial degrees of
freedom, and magnetic fluctuations become orbitally isotropic. Remarkably, this
effect can be seen only in two-particle quantities; single-particle observables
remain anisotropic for any value of the Hund's coupling. Importantly, we find
that the orbital isotropy can be induced both, at half-filling and for the case
of $4$ electrons per lattice site, where the magnetic instability is associated
with different, antiferromagnetic and ferromagnetic modes, respectively.",2010.03433v4
2020/12/10,Evidence of non-trivial Berry phase and Kondo physics in SmBi,"Realization of semimetals with non-trivial topologies such as Dirac and Weyl
semimetals, have provided a boost in the study of these quantum materials.
Presence of electron correlation makes the system even more exotic due to
enhanced scattering of charge carriers, Kondo screening etc. Here, we studied
the electronic properties of single crystalline, SmBi employing varied state of
the art bulk measurements. Magnetization data reveals two magnetic transitions;
an antiferromagnetic order with a Neel temperature of ~ 9 K and a second
magnetic transition at a lower temperature (= 7 K). The electrical resistivity
data shows an upturn typical of a Kondo system and the estimated Kondo
temperature is found to be close to the Neel temperature. High quality of the
crystal enabled us to discover signature of quantum oscillation in the
magnetization data even at low magnetic field. Using a Landau level fan diagram
analysis, a non-trivial Berry phase is identified for a Fermi pocket revealing
the topological character in this material. These results demonstrate an unique
example of the Fermiology in the antiferromagnetic state and opens up a new
paradigm to explore the Dirac fermion physics in correlated topological metal
via interplay of Kondo interaction, topological order and magnetism.",2012.05459v1
2021/8/30,Highly efficient nonvolatile magnetization switching and multi-level states by current in single van der Waals topological ferromagnet Fe3GeTe2,"Robust multi-level spin memory with the ability to write information
electrically is a long-sought capability in spintronics, with great promise for
applications. Here we achieve nonvolatile and highly energy-efficient
magnetization switching in a single-material device formed of van-der-Waals
topological ferromagnet Fe3GeTe2, whose magnetic information can be readily
controlled by a tiny current. Furthermore, the switching current density and
power dissipation are about 400 and 4000 times smaller than those of the
existing spin-orbit-torque magnetic random access memory based on conventional
magnet/heavy-metal systems. Most importantly, we also demonstrate multi-level
states, switched by electrical current, which can dramatically enhance the
information capacity density and reduce computing costs. Thus, our observations
combine both high energy efficiency and large information capacity density in
one device, showcasing the potential applications of the emerging field of
van-der-Waals magnets in the field of spin memory and spintronics.",2108.13022v1
2021/9/8,Coherent spin rotation-induced zero thermal expansion in MnCoSi-based spiral magnets,"Materials exhibiting zero thermal expansion (ZTE), namely, volume invariance
during temperature change, can resist thermal shock and are highly desired in
modern industries as high-precision components. However, pure ZTE materials are
rare, especially those that are metallic. Here, we report the discovery of a
pure metallic ZTE material: an orthorhombic Mn1-xNixCoSi spiral magnet. The
introduction of Ni can efficiently enhance the ferromagnetic exchange
interaction and construct the transition from a spiral magnetic state to a
ferromagnetic-like state in MnCoSi-based alloys. Systematic in situ neutron
powder diffraction revealed a new cycloidal spiral magnetic structure in bc
plane at ground state which would transform to the helical spiral in the ab
plane with increasing temperature. Combined with Lorentz transmission electron
microscopy techniques, the cycloidal and helical spin order coherently rotated
at varying periods along the c axis during the magnetic transition. This spin
rotation drove the continuous movement of the coupled crystalline lattice and
induced a large negative thermal expansion along the a axis, eventually leading
to a wide-temperature ZTE effect. Our work not only introduces a new ZTE alloy
but also presents a new mechanism by which to discover or design ZTE magnets.",2109.03557v1
2021/12/5,Variation between Antiferromagnetism and Ferrimagnetism in NiPS3 by Electron Doping,"How to electrically control magnetic properties of a magnetic material is
promising towards spintronic applications, where the investigation of carrier
doping effects on antiferromagnetic (AFM) materials remains challenging due to
their zero net magnetization. In this work, we found electron doping dependent
variation of magnetic orders of a two-dimensional (2D) AFM insulator NiPS3,
where doping concentration is tuned by intercalating various organic cations
into the van der Waals gaps of NiPS3 without introduction of defects and
impurity phases. The doped NiPS3 shows an AFM-ferrimagnetic (FIM) transition at
doping level of 0.2-0.5 electrons/cell and a FIM-AFM transition at doping level
of >= 0.6 electrons/cell. We propose that the found phenomenon is due to
competition between Stoner exchange dominated inter-chain ferromagnetic order
and super-exchange dominated inter-chain AFM order at different doping level.
Our studies provide a viable way to exploit correlation between electronic
structures and magnetic properties of 2D magnetic materials for realization of
magnetoelectric effect.",2112.02544v2
2021/12/6,Complex magnetic structure and spin waves of the noncollinear antiferromagnet Mn5Si3,"The investigations of the interconnection between micro- and macroscopic
properties of materials hosting noncollinear antiferromagnetic ground states
are challenging. These forefront studies are crucial for unraveling the
underlying mechanisms at play, which may prove beneficial in designing cutting
edge multifunctional materials for future applications. In this context, Mn5Si3
has regained scientific interest since it displays an unusual and complex
ground state, which is considered to be the origin of the anomalous transport
and thermodynamic properties that it exhibits. Here, we report the magnetic
exchange couplings of the noncollinear antiferromagnetic phase of Mn5Si3 using
inelastic neutron scattering measurements and density functional theory
calculations. We determine the ground-state spin configuration and compute its
magnon dispersion relations which are in good agreement with the ones obtained
experimentally. Furthermore, we investigate the evolution of the spin texture
under the application of an external magnetic field to demonstrate
theoretically the multiple field-induced phase transitions that Mn5Si3
undergoes. Finally, we model the stability of some of the material's magnetic
moments under a magnetic field and we find that very susceptible magnetic
moments in a frustrated arrangement can be tuned by the field.",2112.03368v1
2022/4/14,Piezoelectric ferromagnetism in Janus monolayer YBrI: a first-principle prediction,"Coexistence of intrinsic ferromagnetism and piezoelectricity, namely
piezoelectric ferromagnetism (PFM), is crucial to advance multifunctional
spintronic technologies. In this work, we demonstrate that Janus monolayer YBrI
is a PFM, which is dynamically, mechanically and thermally stable. Electronic
correlation effects on physical properties of YBrI are investigated by using
generalized gradient approximation plus $U$ (GGA+$U$) approach. For
out-of-plane magnetic anisotropy, YBrI is a ferrovalley (FV) material, and the
valley splitting is larger than 82 meV in considered $U$ range. The anomalous
valley Hall effect (AVHE) can be achieved under an in-plane electric field.
However, for in-plane magnetic anisotropy, YBrI is a common ferromagnetic (FM)
semiconductor. When considering intrinsic magnetic anisotropy, the easy axis of
YBrI is always in-plane with magnetic anisotropy energy (MAE) from 0.309 meV to
0.237 meV ($U$=0.0 eV to 3.0 eV). However, the magnetization can be adjusted
from the in-plane to off-plane direction by external magnetic field, and then
lead to the occurrence of valley polarization. Moreover, missing centrosymmetry
along with mirror symmetry breaking results in both in-plane and out-of-plane
piezoelectricity in YBrI monolayer. At a typical $U$=2.0 eV, the $d_{11}$ is
predicted to be -5.61 pm/V, which is higher than or compared with ones of other
two-dimensional (2D) known materials. The electronic and piezoelectric
properties of YBrI can be effectively tuned by applying a biaxial strain. For
example, tensile strain can enhance valley splitting and $d_{11}$ (absolute
value). The predicted Curie temperature of YBrI is higher than those of
experimentally synthesized 2D ferromagnetic materials $\mathrm{CrI_3}$ and
$\mathrm{Cr_2Ge_2Te_6}$.",2204.06713v1
2022/6/17,Multiscale Modelling of the Antiferromagnet Mn2Au: From ab-initio to Micromagnetics,"Antiferromagnets (AFMs) are strong candidates for the future spintronic and
memory applications largely because of their inherently fast dynamics and lack
of stray fields, with Mn2Au being one of the most promising. For the numerical
modelling of magnetic material properties, it is common to use ab-initio
methods, atomistic models and micromagnetics. However, each method alone
describes the physics within certain limits. Multiscale methods bridging the
gap between these three approaches have been already proposed for ferromagnetic
materials. Here, we present a complete multiscale model of the AFM Mn2Au as an
exemplar material, starting with results from ab-initio methods going via
atomistic spin dynamics (ASD) to an AFM Landau-Lifshitz-Bloch (AFM-LLB) model.
Firstly, bulk is modelled using a classical spin Hamiltonian constructed based
on earlier first-principles calculations. Secondly, this spin model is used in
the stochastic Landau-Lifshitz-Gilbert (LLG) to calculate temperature-dependent
equilibrium properties, such as magnetization and magnetic susceptibilities.
Thirdly, the temperature dependent micromagnetic parameters are used in the
AFM-LLB. We validate our approach by comparing the ASD and AFM-LLB models for
three paradigmatic cases; (i) Damped magnetic oscillations, (ii) magnetization
dynamics following a heat pulse resembling pump-probe experiments, (iii)
magnetic domain wall motion under thermal gradients.",2206.08625v1
2022/9/21,"Systematic DFT+U and Quantum Monte Carlo benchmark of magnetic two-dimensional (2D) CrX$_3$ (X = I, Br, Cl, F)","The search for two-dimensional (2D) magnetic materials has attracted a great
deal of attention because of the experimental synthesis of 2D CrI$_3$, which
has a measured Curie temperature of 45 K. Often times, these monolayers have a
higher degree of electron correlation and require more sophisticated methods
beyond density functional theory (DFT). Diffusion Monte Carlo (DMC) is a
correlated electronic structure method that has been demonstrated successful
for calculating the electronic and magnetic properties of a wide variety of 2D
and bulk systems, since it has a weaker dependence on the Hubbard parameter (U)
and density functional. In this study we designed a workflow that combines
DFT+U and DMC in order to treat 2D correlated magnetic systems. We chose
monolayer CrX$_3$ (X = I, Br, Cl, F), with a stronger focus on CrI$_3$ and
CrBr$_3$, as a case study due to the fact that they have been experimentally
realized and have a finite critical temperature. With this DFT+U and DMC
workflow and the analytical method of Torelli and Olsen, we estimated an upper
bound of 43.56 K for the T$_c$ of CrI$_3$ and 20.78 K for the T$_c$ of
CrBr$_3$, in addition to analyzing the spin densities and magnetic properties
with DMC and DFT+U. We expect that running this workflow for a well-known
material class will aid in the future discovery and characterization of lesser
known and more complex correlated 2D magnetic materials.",2209.10379v2
2022/11/5,Designing magnetic properties in CrSBr through hydrostatic pressure and ligand substitution,"The ability to control magnetic properties of materials is crucial for
fundamental research and underpins many information technologies. In this
context, two-dimensional materials are a particularly exciting platform due to
their high degree of tunability and ease of implementation into nanoscale
devices. Here we report two approaches for manipulating the A-type
antiferromagnetic properties of the layered semiconductor CrSBr through
hydrostatic pressure and ligand substitution. Hydrostatic pressure compresses
the unit cell, increasing the interlayer exchange energy while lowering the
N\'eel temperature. Ligand substitution, realized synthetically through Cl
alloying, anisotropically compresses the unit cell and suppresses the
Cr-halogen covalency, reducing the magnetocrystalline anisotropy energy and
decreasing the N\'eel temperature. A detailed structural analysis combined with
first-principles calculations reveal that alterations in the magnetic
properties are intricately related to changes in direct Cr-Cr exchange
interactions and the Cr-anion superexchange pathways. Further, we demonstrate
that Cl alloying enables chemical tuning of the interlayer coupling from
antiferromagnetic to ferromagnetic, which is unique amongst known
two-dimensional magnets. The magnetic tunability, combined with a high ordering
temperature, chemical stability, and functional semiconducting properties, make
CrSBr an ideal candidate for pre- and post-synthetic design of magnetism in
two-dimensional materials.",2211.02788v1
2023/2/7,Pressure-induced magnetic properties of quasi-2D Cr2Si2Te6 and Mn3Si2Te6,"Recently, the pressure has been used as external stimuli to induce structural
and magnetic phase transitions in many layered quantum materials whose layers
are linked by van der Waals forces. Such materials with weakly held layers
allow relatively easy manipulation of the superexchange mechanism and lead to
novel magnetic behavior. Using the hydrostatic pressure as a disorderless means
to manipulate the interlayer coupling, we applied pressure on two quasi-2D
sister compounds, namely, Cr2Si2Te6 (CST) and Mn3Si2Te6 (MST), up to ~1 GPa.
Magnetic property measurements with the application of pressure revealed that
the ferromagnetic transition temperature decreases in CST while the opposite
trend occurs for the ferrimagnet MST. In MST, the magnetization decreases with
the increase in the pressure, and such trend is not clearly noticed in CST,
within the pressure range studied. Theoretical calculations showed the overall
pressure effect on layer separation, bond angle, and exchange coupling,
strongly influencing the change in subsequent magnetic characteristics.
Exchange coupling in Mn3Si2Te6 is strongly frustrated and the first nearest
neighbor interaction is the most dominant of the components with the strongest
pressure dependence. Whereas, in Cr2Si2Te6, the exchange coupling parameters
exhibit very little dependence on the pressure. This combined experimental and
theoretical work has the potential to expand to other relevant quantum
materials.",2302.03170v1
2023/3/6,Phononic-magnetic dichotomy of the thermal Hall effect in the Kitaev-Heisenberg candidate material Na$_2$Co$_2$TeO$_6$,"Majorana fermions as emergent excitations of the Kitaev quantum spin liquid
ground state constitute a promising concept in fault tolerant quantum
computation. Experimentally, the recently reported topological half-quantized
thermal Hall effect in the Kitaev material $\alpha$-RuCl$_3$ seems to confirm
the Majorana nature of the material's magnetic excitations. It has been argued,
however, that the thermal Hall signal in $\alpha$-RuCl$_3$ rather stems from
phonons or topological magnons than from Majorana fermions. Here we investigate
the thermal Hall effect of the closely related Kitaev quantum material
Na$_2$Co$_2$TeO$_6$, and we show that the thermal Hall signal emerges from at
least two components, phonons and magnetic excitations. This dichotomy results
from our discovery that the transversal heat conductivity $\kappa_{xy}$ carries
clear signatures of the phononic $\kappa_{xx}$, but changes sign upon entering
the low-temperature, magnetically ordered phase. We systematically resolve the
two components by considering the detailed temperature and field dependence of
both $\kappa_{xy}$ and $\kappa_{xx}$. Our results demonstrate that uncovering a
genuinely quantized magnetic thermal Hall effect in a Kitaev topological
quantum spin liquid requires to disentangle phonon vs. magnetic contributions
where the latter include potentially fractionalized excitations such as the
expected Majorana fermions.",2303.03067v1
2023/6/25,Antiferromagnetic $α$-MnTe: Molten-Salt-Assisted Chemical Vapor Deposition Growth and Magneto-Transport Properties,"Antiferromagnetic (AF) materials are attracting increasing interest of
research in magnetic physics and spintronics. Here, we report controllable
synthesis of room-temperature AF $\alpha$-MnTe nanocrystals (N\'eel temperature
~ 307 K) via molten-salt-assisted chemical vapor deposition method. The growth
kinetics are investigated regarding the dependence of flake dimension and
macroscopic shape on growth time and temperature. The high crystalline quality
and atomic structure are confirmed by various crystallographic characterization
means. Cryogenic magneto-transport measurements reveal anisotropic
magnetoresistance (MR) response and a complicated dependence of MR on
temperature, owing to the subtle competition among multiple scattering
mechanisms of thermally excited magnetic disorders (magnon drag), magnetic
transition and thermally populated lattice phonons. Overall positive MR
behavior with twice transitions in magnitude is observed when out-of-plane
external magnetic field ($B$) is applied, while a transition from negative to
positive MR response is recorded when in-plane $B$ is applied. The rich
magnetic transport properties render $\alpha$-MnTe a promising material for
exploiting functional components in magnetic devices.",2307.13615v1
2023/8/22,Magnetic ordering in the $J_{\rm eff}$ = 0 Nickelate NiRh$_2$O$_4$ prepared via a solid-state metathesis,"In spinel-type nickelate NiRh$_2$O$_4$, magnetic ordering is observed upon
the sample synthesized via kinetically controlled low-temperature solid-state
metathesis, as opposed to previously-reported samples obtained through
conventional solid-state reaction. Our findings are based on a combination of
bulk susceptibility and specific heat measurements that disclose a N$\'e$el
transition temperature of $T_N$ = 45 K in this material, which might feature
spin-orbit entanglement in the tetragonally-coordinated $d^8$ Mott insulators.
The emergence of magnetic ordering upon alteration of the synthesis route
indicates that the suppression of magnetic ordering in the previous sample was
rooted in the cation-mixing assisted by the entropy gain that results from
high-temperature reactions. Furthermore, the $J_{\rm eff}$ = 0 physics, instead
of solely the spin-only $S = 1$, describes the observed enhancement of
effective magnetic moment well. Overseeing all observations and speculations,
we propose that the possible mechanism responsible for the emergent magnetic
orderings in NiRh$_2$O$_4$ is the condensation of $J_{\rm eff}$ = 0 exciton,
driven by the interplay of the tetragonal crystal field and superexchange
interactions.",2308.11172v1
2023/9/27,Disclosing the nature of asymmetric interface magnetism in Co/Pt multilayers,"Nowadays a wide number of applications based on magnetic materials relies on
the properties arising at the interface between different layers in complex
heterostructures engineered at the nanoscale. In ferromagnetic/heavy metal
multilayers, such as the [Co/Pt]$_N$ and [Co/Pd]$_N$ systems, the magnetic
proximity effect was demonstrated to be asymmetric, thus inducing a magnetic
moment on the Pt(Pd) layer that is typically higher at the top Co/Pt(Pd)
interface. In this work, advanced spectroscopic and imaging techniques were
combined with theoretical approaches to clarify the origin of this asymmetry
both in Co/Pt trilayers and, for the first time, in multilayer systems that are
more relevant for practical applications. The different magnetic moment induced
at the Co/Pt interfaces was correlated to the microstructural features, which
are in turn affected by the growth processes that induce a different
intermixing during the film deposition, thus influencing the interface magnetic
profile.",2309.15663v1
2023/11/2,Investigation of the Impact of Magnetic Fields on Scattering Muography Images,"Muography is a non-invasive imaging technique that exploits cosmic-ray muons
to probe various targets by analyzing the absorption or scattering of muons.
The method is particularly useful for applications ranging from geophysical
exploration to security screening, including the identification of nuclear
materials. This study leverages both Monte Carlo simulations and the Point of
Closest Approach (PoCA) algorithm for image reconstruction to specifically
explore the distortions caused by magnetic fields in scattering muography
images. In the PoCA algorithm, it is assumed that all scattering of a muon
during its travel in material occurs at a single point, known as the PoCA
point. Each PoCA point is characterized by a scattering angle, whose
distribution provides insights into the density and elemental composition of
the target material. However, magnetic fields can influence muon trajectories
according to Lorentz law, affecting the estimated positions of the PoCA points
and the calculated scattering angles. This introduces challenges in
applications such as border security control systems. Moreover, the presence of
magnetic fields can lead to what we term ""magnetic jamming"", where the
resulting muography image is distorted or misleading. This effect further
complicates the accurate identification and interpretation of target materials.
Our findings underline the necessity to account for magnetic field distortions
when utilizing scattering muography in practical scenarios.",2311.00972v1
2015/8/28,Magnetically-Functionalized Self-Aligning Graphene Fillers for High-Efficiency Thermal Management Applications,"We report on heat conduction properties of thermal interface materials with
self-aligning ""magnetic grapheme"" fillers. Graphene enhanced nano-composites
were synthesized by an inexpensive and scalable technique based on liquid-phase
exfoliation. Functionalization of graphene and few-layer-graphene flakes with
Fe3O4 nanoparticles allowed us to align the fillers in an external magnetic
field during dispersion of the thermal paste to the connecting surfaces. The
filler alignment results in a strong increase of the apparent thermal
conductivity and thermal diffusivity through the layer of nano-composite
inserted between two metallic surfaces. The self-aligning ""magnetic grapheme""
fillers improve heat conduction in composites with both curing and non-curing
matrix materials. The thermal conductivity enhancement with the oriented
fillers is a factor of two larger than that with the random fillers even at the
low ~1 wt. % of graphene loading. The real-life testing with computer chips
demonstrated the temperature rise decrease by as much as 10oC with use of the
non-curing thermal interface material with ~1 wt. % of the oriented fillers.
Our proof-of-concept experiments suggest that the thermal interface materials
with functionalized graphene and few-layer-graphene fillers, which can be
oriented during the composite application to the surfaces, can lead to a new
method of thermal management of advanced electronics.",1508.07061v1
2020/10/7,Topological electronic structure in the antiferromagnet HoSbTe,"Magnetic topological materials, in which the time-reversal symmetry is
broken, host various exotic quantum phenomena, including the quantum anomalous
Hall effect, axion insulator states, and Majorana fermions. The study of
magnetic topological materials is at the forefront of condensed matter physics.
Recently, a variety of magnetic topological materials have been reported, such
as Mn$_3$Sn, Co$_3$Sn$_2$S$_2$, Fe$_3$Sn$_2$, and MnBi$_2$Te$_4$. Here, we
report the observation of a topological electronic structure in an
antiferromagnet, HoSbTe, a member of the ZrSiS family of materials, by
angle-resolved photoemission spectroscopy measurements and first-principles
calculations. We demonstrate that HoSbTe is a Dirac nodal line semimetal when
spin-orbit coupling (SOC) is neglected. However, our theoretical calculations
show that the strong SOC in HoSbTe fully gaps out the nodal lines and drives
the system to a weak topological insulator state, with each layer being a
two-dimensional topological insulator. Because of the strong SOC in HoSbTe, the
gap is as large as hundreds of meV along specific directions, which is directly
observed by our ARPES measurements. The existence of magnetic order and
topological properties in HoSbTe makes it a promising material for realization
of exotic quantum devices.",2010.03528v1
2022/10/6,All hourglass bosonic excitations in the 1651 magnetic space groups and 528 magnetic layer groups,"The band connectivity as imposed by the compatibility relations between the
irreducible representations of little groups can give rise to the exotic
hourglass-like shape composed of four branches of bands and five band crossings
(BCs). Such an hourglass band connectivity could enforce the emergence of
nontrivial excitations like Weyl fermion, Dirac fermion or even beyond them. On
the other hand, the bosons, like phonons, magnons, and photons, were also shown
to possess nontrivial topology and a comprehensive symmetry classification of
the hourglass bosonic excitations would be of great significance to both
materials design and device applications. Here we firstly list all concrete
positions and representations of little groups in the Brillouin zone (BZ)
related with the hourglass bosonic excitations in all the 1651 magnetic space
groups and 528 magnetic layer groups, applicable to three dimensional (3D) and
two dimensional (2D) systems, respectively. 255 (42) MSGs (MLGs) are found to
essentially host such hourglass BCs: Here ``essentially'' means that the
bosonic hourglass BC exists definitely as long as the studied system is
crystallized in the corresponding MSG/MLG. We also perform first-principles
calculations on hundreds of 3D nonmagnetic materials essentially hosting
hourglass phonons and propose that the 2D material AlI can host hourglass
phonons. We choose AuX (X=Br and I) as illustrative examples to demonstrate
that two essential hourglass band structures can coexist in the phonon spectra
for both materials while for AuBr, an accidental band crossing sticking two
hourglasses is found interestingly. Our results of symmetry conditions for
hourglass bosonic excitations can provide a useful guide of designing
artificial structures with hourglass bosonic excitations.",2210.02954v1
2023/2/28,Combinatorial exploration of quantum spin liquid candidates in the herbertsmithite material family,"Geometric frustration of magnetic ions can lead to a quantum spin liquid
ground state where long range magnetic order is avoided despite strong exchange
interactions. The physical realization of quantum spin liquids comprises a
major unresolved area of contemporary materials science. One prominent
magnetically-frustrated structure is the kagome lattice. The naturally
occurring minerals herbertsmithite [ZnCu$_3$(OH)$_6$Cl$_2$] and Zn-substituted
barlowite [ZnCu$_3$(OH)$_6$BrF] both feature perfect kagome layers of
spin-$1/2$ copper ions and display experimental signatures consistent with a
quantum spin liquid state at low temperatures. To investigate other possible
candidates within this material family, we perform a systematic
first-principles combinatorial exploration of structurally related compounds
[$A$Cu$_3$(OH)$_6B_2$ and $A$Cu$_3$(OH)$_6BC$] by substituting non-magnetic
divalent cations ($A$) and halide anions ($B$, $C$). After optimizing such
structures using density functional theory, we compare various structural and
thermodynamic parameters to determine which compounds are most likely to favor
a quantum spin liquid state. Convex hull calculations using binary compounds
are performed to determine feasibility of synthesis. We also estimate the
likelihood of interlayer substitutional disorder and spontaneous distortions of
the kagome layers. After considering all of these factors as a whole, we select
several promising candidate materials that we believe deserve further
attention.",2303.00082v1
2023/4/26,Direct observation of Néel-type skyrmions and domain walls in a ferrimagnetic DyCo$_3$ thin film,"Isolated magnetic skyrmions are stable, topologically protected spin textures
that are at the forefront of research interests today due to their potential
applications in information technology. A distinct class of skyrmion hosts are
rare earth - transition metal (RE-TM) ferrimagnetic materials. To date, the
nature and the control of basic traits of skyrmions in these materials are not
fully understood. We show that for an archetypal ferrimagnetic material
DyCo$_3$ that exhibits a strong perpendicular anisotropy, the ferrimagnetic
skyrmion size can be tuned by an external magnetic field. Moreover, by taking
advantage of the high spatial resolution of scanning transmission X-ray
microscopy (STXM) and utilizing a large x-ray magnetic linear dichroism (XMLD)
contrast that occurs naturally at the RE resonant edges, we resolve the nature
of the magnetic domain walls of ferrimagnetic skyrmions. We demonstrate that
through this method one can easily discriminate between Bloch and N\'eel type
domain walls for each individual skyrmion. For all isolated ferrimagnetic
skyrmions, we observe that the domain walls are of N\'eel-type. This key
information is corroborated with results of micromagnetic simulations and
allows us to conclude on the nature of the Dzyaloshinskii-Moriya interaction
(DMI) which concurs to the stabilisation of skyrmions in this ferrimagnetic
system. Establishing that an intrinsic DMI occurs in RE-TM materials will also
be beneficial towards a deeper understanding of chiral spin texture control in
ferrimagnetic materials.",2304.13698v2
2023/9/26,Designing superhard magnetic material in clathrate \b{eta}-C3N2 through atom embeddedness,"Designing new compounds with the coexistence of diverse physical properties
is of great significance for broad applications in multifunctional electronic
devices. In this work, based on density functional theory, we predict the
coexistence of mechanical superhardness and the controllable magnetism in the
clathrate material \b{eta}-C3N2 through the implant of the external atom into
the intrinsic cage structure. Taking hydrogen-doping (H@\b{eta}-C3N2) and
fluorine-doping (F@\b{eta}-C3N2) as examples, our calculations indicate these
two doped configurations are stable and discovered that they belong to
antiferromagnetic semiconductor and ferromagnetic semi-metal, respectively.
These intriguing magnetic phase transitions originate from their distinctive
band structure around the Fermi level and can be well understood by the 3D
Hubbard model with half-filling occupation and the Stoner model. Moreover, the
high Vickers hardness of 49.0 GPa for H@\b{eta}-C3N2 and 48.2 GPa for
F@\b{eta}-C3N2 are obtained, suggesting they are clathrate superhard materials
as its host. Therefore, the incorporation of H and F in \b{eta}-C3N2 gives rise
to a new type of superhard antiferromagnetic semiconductor and superhard
ferromagnetic semimetal, respectively, which could have potential applications
in harsh conditions. Our work provides an effective strategy to design a new
class of highly desirable multifunctional materials with excellent mechanical
properties and magnetic properties, which may arouse spintronic applications in
superhard materials in the future.",2309.14739v1
2023/10/25,Magnetic elastomers as specific soft actuators -- predicting particular modes of deformation from selected configurations of magnetizable inclusions,"Amongst the various fascinating types of material behavior featured by
magnetic gels and elastomers are magnetostrictive effects. That is,
deformations in shape or changes in volume are induced from outside by external
magnetic fields. Application of the materials as soft actuators is therefore
conceivable. Mostly, straight contraction or extension of the materials along a
certain direction is discussed and investigated in this context. Here, we
demonstrate that various further, different, higher modes of deformation can be
excited. To this end, different spatial arrangements of the magnetizable
particles enclosed by the soft elastic matrix, which constitute the materials,
need to be controlled and realized. We address various different types of
spatial configurations of the particles and evaluate resulting types of
deformation using theoretical tools developed for this purpose. Examples are
sheet-like arrangements of particles, circular or star-shaped arrangements of
chain-like aggregates, or actual three-dimensional star-like particle
configurations. We hope to stimulate with our work the development of
experimental design and engineering methods so that selected spatial particle
arrangements in magnetic gels and elastomers can be put to reality. Overall, we
in this way wish to promote the transfer of these promising class of materials
to real-world applications.",2310.16833v2
2011/12/22,Decorated Shastry-Sutherland lattice in the spin-1/2 magnet CdCu2(BO3)2,"We report the microscopic magnetic model for the spin-1/2 Heisenberg system
CdCu2(BO3)2, one of the few quantum magnets showing the 1/2-magnetization
plateau. Recent neutron diffraction experiments on this compound [M. Hase et
al., Phys. Rev. B 80, 104405 (2009)] evidenced long-range magnetic order,
inconsistent with the previously suggested phenomenological magnetic model of
isolated dimers and spin chains. Based on extensive density-functional theory
band structure calculations, exact diagonalizations, quantum Monte Carlo
simulations, third-order perturbation theory, as well as high-field
magnetization measurements, we find that the magnetic properties of CdCu2(BO3)2
are accounted for by a frustrated quasi-2D magnetic model featuring four
inequivalent exchange couplings: the leading antiferromagnetic coupling J_d
within the structural Cu2O6 dimers, two interdimer couplings J_t1 and J_t2,
forming magnetic tetramers, and a ferromagnetic coupling J_it between the
tetramers. Based on comparison to the experimental data, we evaluate the ratios
of the leading couplings J_d : J_t1 : J_t2 : J_it = 1 : 0.20 : 0.45 : -0.30,
with J_d of about 178 K. The inequivalence of J_t1 and J_t2 largely lifts the
frustration and triggers long-range antiferromagnetic ordering. The proposed
model accounts correctly for the different magnetic moments localized on
structurally inequivalent Cu atoms in the ground-state magnetic configuration.
We extensively analyze the magnetic properties of this model, including a
detailed description of the magnetically ordered ground state and its evolution
in magnetic field with particular emphasis on the 1/2-magnetization plateau.
Our results establish remarkable analogies to the Shastry-Sutherland model of
SrCu2(BO3)2, and characterize the closely related CdCu2(BO3)2 as a material
realization for the spin-1/2 decorated anisotropic Shastry-Sutherland lattice.",1112.5323v2
2020/10/9,Thermal disorder driven magnetic phases in van der Waals magnet CrI3,"Magnetic phase transitions often occur spontaneously at specific critical
temperatures. The presence of more than one critical temperature (Tc) has been
observed in several compounds where the coexistence of competing magnetic
orders highlights the importance of phase separation driven by different
factors such as pressure, temperature and chemical composition. However, it is
unknown whether recently discovered two-dimensional (2D) van der Walls (vdW)
magnetic materials show such intriguing phenomena that can result in rich phase
diagrams with novel magnetic features to be explored. Here we show the
existence of three magnetic phase transitions at different Tc's in 2D vdW
magnet CrI3 revealed by a complementary suite of muon spin relaxation-rotation,
superconducting quantum interference device magnetometry, and large-scale
atomistic simulations including higher-order exchange interactions. We find
that the traditionally identified Curie temperature of bulk CrI3 at 61 K does
not correspond to the long-range order in the full volume (VM) of the crystal
but rather a partial transition with less than 25% of VM being magnetically
spin-ordered. This transition is composed of highly disordered domains with the
easy-axis component of the magnetization Sz not being fully spin-polarized but
disordered by in-plane components (Sx, Sy) over the entire layer. As the system
cools down, two additional phase transitions at 50 K and 25 K drive the system
to 80% and nearly 100% of the magnetically ordered volume, respectively, where
the ferromagnetic ground state has a marked Sz character yet also displaying
finite contributions of Sx and Sy to the total magnetization. Our results
indicate that volume-wise competing electronic phases play an important role in
the magnetic properties of CrI3 which set a much lower threshold temperature
for exploitation in magnetic device-platforms than initially considered.",2010.04544v1
2001/2/9,Magnetic Screening in Accreting Neutron Stars,"We investigate whether the magnetic field of an accreting neutron star may be
diamagnetically screened by the accreted matter. We assume the freshly
accumulated material is unmagnetized, and calculate the rate at which the
intrinsic stellar magnetic flux is transported into it by Ohmic diffusion. We
calculate the one-dimensional steady-state magnetic field profiles, and show
that the magnetic field strength decreases as one moves up through the outer
crust and ocean by roughly (Mdot/0.02 Mdot_Edd) orders of magnitude, where Mdot
is the accretion rate and Mdot_Edd the Eddington accretion rate. We show that
buoyancy instabilities set a limit to the strength of any buried field of
roughly 10^10-10^11 G.
  Our results show that magnetic screening is ineffective for Mdot<0.01
Mdot_Edd, so that, no matter how the accreted material joins onto the star, the
underlying stellar field should always be evident. In this respect, we point
out the only known persistently-pulsing accreting X-ray millisecond pulsar, SAX
J1808.4-3658, has an accretion rate of 10^-3 Mdot_Edd, far below the regime
where magnetic screening can play a role.
  Most steadily accreting neutron stars in low-mass X-ray binaries in our
Galaxy accrete at rates where screening would be effective if the simplified
magnetic and accretion geometry we adopt were correct. If screened, then the
underlying field will emerge after accretion halts, on a timescale of only
100--1000 years, set by the Ohmic diffusion time across the outer crust. It
thus seems unlikely that screening alone can explain the low magnetic fields of
the millisecond radio pulsars.",0102178v1
2003/5/15,Thermal structure and cooling of superfluid neutron stars with accreted magnetized envelopes,"We study the thermal structure of neutron stars with magnetized envelopes
composed of accreted material, using updated thermal conductivities of plasmas
in quantizing magnetic fields, as well as equation of state and radiative
opacities for partially ionized hydrogen in strong magnetic fields. The
relation between the internal and local surface temperatures is calculated and
fitted by an analytic function of the internal temperature, magnetic field
strength, angle between the field lines and the normal to the surface, surface
gravity, and the mass of the accreted material. The luminosity of a neutron
star with a dipole magnetic field is calculated for various values of the
accreted mass, internal temperature, and magnetic field strength. Using these
results, we simulate cooling of superfluid neutron stars with magnetized
accreted envelopes. We consider slow and fast cooling regimes, paying special
attention to very slow cooling of low-mass superfluid neutron stars. In the
latter case, the cooling is strongly affected by the combined effect of
magnetized accreted envelopes and neutron superfluidity in the stellar crust.
Our results are important for interpretation of observations of isolated
neutron stars hottest for their age, such as RX J0822-43 and PSR B1055-52.",0305256v2
2002/9/19,"Magnetic Interactions and Transport in (Ga,Cr)As","The magnetic, transport, and structural properties of (Ga,Cr)As are reported.
Zincblende Ga$_{1-x}$Cr$_{x}$As was grown by low-temperature molecular beam
epitaxy (MBE). At low concentrations, x$\sim$0.1, the materials exhibit unusual
magnetic properties associated with the random magnetism of the alloy. At low
temperatures the magnetization M(B) increases rapidly with increasing field due
to the alignment of ferromagnetic units (polarons or clusters) having large
dipole moments of order 10-10$^2$$\mu_B$. A standard model of
superparamagnetism is inadequate for describing both the field and temperature
dependence of the magnetization M(B,T). In order to explain M(B) at low
temperatures we employ a distributed magnetic moment (DMM) model in which
polarons or clusters of ions have a distribution of moments. It is also found
that the magnetic susceptibility increases for decreasing temperature but
saturates below T=4 K. The inverse susceptibility follows a linear-T
Curie-Weiss law and extrapolates to a magnetic transition temperature
$\theta$=10 K. In magnetotransport measurements, a room temperature resistivity
of $\rho$=0.1 $\Omega$cm and a hole concentration of $\sim10^{20}$ cm$^{-3}$
are found, indicating that Cr can also act as a acceptor similar to Mn. The
resistivity increases rapidly for decreasing temperature below room
temperature, and becomes strongly insulating at low temperatures. The
conductivity follows exp[-(T$_1$/T)$^{1/2}$] over a large range of
conductivity, possible evidence of tunneling between polarons or clusters.",0209477v2
2005/1/26,Quantum Theory of Molecular Magnetism,"The synthesis of molecular magnets has undergone rapid progress in recent
years. Each of the identical molecular units can contain as few as two and up
to several dozens of paramagnetic ions (spins). Although these materials appear
as macroscopic samples, i.e. crystals or powders, the intermolecular magnetic
interactions are utterly negligible as compared to the intramolecular
interactions. Therefore, measurements of their magnetic properties reflect
mainly ensemble properties of single molecules.
  Their magnetic features promise a variety of applications in physics,
magneto-chemistry, biology, biomedicine and material sciences as well as in
quantum computing.
  It appears that in the majority of these molecules the localized
single-particle magnetic moments couple antiferromagnetically and the spectrum
is rather well described by the Heisenberg model with isotropic nearest
neighbor interaction sometimes augmented by anisotropy terms. Thus, the
interest in the Heisenberg model, which is known already for a long time, but
used mostly for infinite one-, two-, and three-dimensional systems, was renewed
by the successful synthesis of magnetic molecules. Studying such spin arrays
focuses on qualitatively new physics caused by the finite size of the system.
  Theoretical inorganic chemistry itself provides several methods to understand
and describe molecular magnetism. In this contribution we would like to focus
on those subjects which are of general interest in the context of quantum
magnetism.",0501625v1
2005/5/12,"Perpendicular magnetization reversal, magnetic anisotropy, multi-step spin switching, and domain nucleation and expansion in Ga1-xMnxAs films","We present a comprehensive study of the reversal process of perpendicular
magnetization in thin layers of the ferromagnetic semiconductor Ga1-xMnxAs. For
this investigation we have purposely chosen Ga1-xMnxAs with a low Mn
concentration (x ~ 0.02), since in such specimens contributions of cubic and
uniaxial anisotropy parameters are comparable, allowing us to identify the role
of both types of anisotropy in the magnetic reversal process. As a first step
we have systematically mapped out the angular dependence of ferromagnetic
resonance in thin Ga1-xMnxAs layers, which is a highly effective tool for
obtaining the magnetic anisotropy parameters of the material. The process of
perpendicular magnetization reversal was then studied by magneto-transport
(i.e., Hall effect and planar Hall effect measurements). These measurements
enable us to observe coherent spin rotation and non-coherent spin switching
between the (100) and (010) planes. A model is proposed to explain the observed
multi-step spin switching. The agreement of the model with experiment indicates
that it can be reliably used for determining magnetic anisotropy parameters
from magneto-transport data. An interesting characteristic of perpendicular
magnetization reversal in Ga1-xMnxAs with low x is the appearance of a double
hysteresis loops in the magnetization data. This double-loop behavior can be
understood by generalizing the proposed model to include the processes of
domain nucleation and expansion.",0505322v1
2005/9/2,Chemically Induced Nanoscale Josephson Effects in Non-Stoichiometric High-Temperature Superconductors,"This paper reviews some of the recently suggested (by the author) novel
effects expected to occur in intrinsically granular non-stoichiometric material
modeled by 2D Josephson junction arrays which are created by a regular 2D
network of twin-boundary dislocations with strain fields acting as an
insulating barrier between hole-rich domains in underdoped crystals. In Section
2 we consider phase-related magnetization effects, including Josephson
chemomagnetism (chemically induced magnetic moment in zero applied magnetic
field) and its influence on a low-field magnetization (chemically induced PME),
and magnetoconcentration effect (creation of extra oxygen vacancies in applied
magnetic field) and its influence on a high-field magnetization (chemically
induced analog of ""fishtail"" anomaly). Section 3 addresses charge-related
phenomena which are actually dual to the chemomagnetic effects described in
Section 2. More specifically, we discuss a possible existence of a non-zero
electric polarization (chemomagnetoelectic effect) and the related change of
the charge balance in intrinsically granular non-stoichiometric material under
the influence of an applied magnetic field. In particular, we predict an
anomalous low-field magnetic behavior of the effective junction charge and
concomitant magnetocapacitance in paramagnetic Meissner phase and a charge
analog of ""fishtail"" anomaly at high magnetic fields as well as field-dependent
weakening of the chemically-induced Coulomb blockade.",0509057v1
2005/11/4,Magnetic Inhomogeneity and Magnetotransport in Electron-Doped Ca(1-x)La(x)MnO(3) (0<=x<=0.10),"The dc magnetization (M) and electrical resistivity (\rho) as functions of
magnetic field and temperature are reported for a series of lightly electron
dopedCa(1-x)La(x)MnO(3) (0<=x<=0.10) specimens for which magnetization [Phys.
Rev. B {\bf 61}, 14319 (2000)] and scattering studies [Phys. Rev. B {\bf 68},
134440 (2003)] indicate an inhomogeneous magnetic ground state composed of
ferromagnetic (FM) droplets embedded in a G-type antiferromagnetic matrix. A
change in the magnetic behavior near x=0.02 has been suggested to be the
signature of a crossover to a long-ranged spin-canted phase. The data reported
here provide further detail about this crossover in the magnetization, and
additional insight into the origin of this phenomenon through its manifestation
in the magnetotransport. In the paramagnetic phase (T>=125 K) we find a
magnetoresistance =-C(M/M_S)^2 (M_S is the low-T saturation magnetization), as
observed in many manganites in the ferromagnetic (FM), colossal
magnetoresistance (CMR) region of the phase diagram, but with a value of C that
is two orders of magnitude smaller than observed for CMR materials. The doping
behavior C(x) follows that of M_S(x), indicating that electronic inhomogeneity
associated with FM fluctuations occurs well above the magnetic ordering
transition.",0511117v1
2008/5/1,Spin Ordering in LaOFeAs and Its Suppression in Superconductor LaO0.89F0.11FeAs Probed by Mössbauer Spectroscopy,"The 57Fe M\""ossbauer spectroscopy was applied to an iron-based layered
superconductor LaO0.89F0.11FeAs with a transition temperature of 26 K and its
parent material LaOFeAs. Throughout the temperature range from 4.2 to 298 K, a
singlet spectrum with no magnetic splitting was observed as a main component of
each M\""ossbauer spectrum of the F-doped superconductor. No additional internal
magnetic field was observed for the spectrum measured at 4.2 K under a magnetic
field of 7 T. On the other hand, the parent LaOFeAs shows a magnetic transition
at around 140 K, and this temperature is slightly lower than that of a
structural phase transition from tetragonal to orthorhombic phase, which
accompanies the resistivity anomaly at around 150 K. The magnetic moment is
estimated to be ~0.35 $\mu$B/Fe at 4.2 K in the orthorhombic phase, and the
spin disorder remains in the magnetic ordered state even at 4.2 K. The fact
that no magnetic transition in LaO0.89F0.11FeAs was observed even at 4.2 K
under 7 T implies a strong spin fluctuation above Tc or small magnetic moment
in this system. Therefore, the present results show that the F-doping
effectively suppresses the magnetic and structural transitions in the parent
material and the suppression leads to emergence of superconductivity in this
system.",0805.0041v1
2009/9/24,Polar properties of Eu0.6Y0.4MnO3 ceramics and their magnetic field dependence,"Eu1-xYxMnO3 exhibits, unlike other magnetoelectric systems, very distinctive
features. Its magnetoelectric properties is driven by the magnetic spin of the
Mn3+ ion, but they can be drastically changed by varying the content of Y3+,
which it does not carry any magnetic moment. Though the x = 0.40 composition
has been studied extensively, some basic questions still remain to be
thoroughly understood. Thus, this work is aimed at studying some of its polar
properties and their magnetic field dependence as well. The experimental
results here reported have shown that this material is very easily polarisable
under external electric fields, and so, whenever the polarization is obtained
from time integration of the displacement currents, an induced polarization is
superposed to the spontaneous one, eventually masking the occurrence of
ferroelectricity. We have found clear evidence for the influence of a magnetic
field in the polar properties of Eu0.6Y0.4MnO3. The study of electric
polarization of Eu0.6Y0.4MnO3 under an external magnetic field yields a value
with the same order of magnitude of the remanent polarization determined from
polarization reversal experiments. The comparison of the magnetic induced
changes on the polarization obtained in polycrystalline samples and single
crystals confirms the threshold magnetic field value for the polarization
rotation from the a- to the c-direction, and evidencing the importance of the
granular nature of the samples in the polar response to magnetic field.",0909.4521v1
2012/3/28,"Multifunctional L10-Mn1.5Ga films with ultrahigh coercivity, giant perpendicular magnetocrystalline anisotropy and large magnetic energy product","We present the fascinating magnetic properties in homogenous noble-metal-free
and rare-earth-free L10-Mn1.5Ga epitaxial films on GaAs (001), including
ultrahigh perpendicular coercivity remarkably tunable from 8.1 to 42.8 kOe,
giant perpendicular magnetocrystalline anisotropy with a maximum of 22.9
Merg/cc, easily controllable magnetization from 27.3 to 270.5 emu/cc, excellent
squareness exceeding 0.94 and large magnetic energy product up to 2.6 MGOe.
These magnificent room-temperature magnetic characteristics make our
L10-Mn1.5Ga films multifunctional as outstanding and cost-effective alternative
for not only perpendicular magnetic recording bits with areal density over 30
Tb inch-2 and thermal stability over 60 years, but variety of novel devices
with high magnetic-noise immunity and thermal stability like spin-torque MRAMs
and oscillators pillars below 5 nm in dimension, and giant magnetoresistance
sensors able to measure high fileds up to 42 kOe . Moreover, this kind of
materials can also be expected as permanent magnets for replacing the expensive
rare-earth magnets widely used today.",1203.6176v5
2012/6/13,Magnetic anomalies in single crystalline Tb5Si3,"The polycrystalline form of the compound, Tb5Si3, crystallizing in
Mn5Si3-type hexagonal structure, which was earlier believe to order
antiferromagnetically below 69 K, has been recently reported by us to exhibit
interesting magnetoresistance (MR) anomalies. In order to understand the
magnetic anomalies of this compound better, we synthesized single crystals of
this compound and subjected them to intense magnetization and MR studies. The
results reveal that the magnetic behavior is strongly anisotropic as the easy
axis is along a basal plane. There appear to be multiple magnetic features in
the close vicinity of 70 K. In addition, there are multiple steps in isothermal
magnetization (which could not be resolved in the data for polycrystalline
data) for magnetic-field (H) along a basal plane. The sign of MR is positive in
the magnetically ordered state, and, interestingly, the magnitude dramatically
increases at the initial step for H parallel to basal plane, but decreases at
subsequent steps as though the origin of these steps are different. However,
for the perpendicular orientation (H || [0 0 0 1]), there is no evidence for
any step either in M(H) or in MR(H). These results establish this compound is
an interesting magnetic material.",1206.2738v1
2013/4/16,"Magnetoelectric coupling in Haldane spin chain system, Dy2BaNiO5","We report the results of various measurements, namely magnetization, complex
dielectric permittivity and electric polarization (P) on Dy2BaNiO5 as a
function of temperature (T) and magnetic-field (H), apart from heat-capacity
(C), with the primary motivation of exploring the existence of magnetoelectric
(ME) coupling among Haldane spin-chain systems. The M(T) and C(T) data
establish long range magnetic ordering at 58K. The most noteworthy observations
are: (i) Distinct anomalies are observed in dielectric constant ({\epsilon}')
vs T and loss (tan{\delta}) vs T at different temperatures, i.e. 12.5, 30, 50
and 58K; at low temperatures, three magnetic-field-induced transitions are
observed in {\epsilon}' vs H at 6, 40 and 60 kOe. These transition temperatures
and critical magnetic fields track those obtained from magnetization data. This
establishes the existence of strong magnetoelectric coupling in this compound.
(ii) Correspondingly, electric polarization could be observed as a function of
T and H in the magnetically ordered state, thereby indicating magnetism-induced
ferroelectricity in this compound; this result suggests that this compound is a
possible new multiferroic material among spin = 1 (nickel containing) compounds
with successive magnetic transitions and strong magnetoelectric coupling.",1304.4550v2
2014/7/8,Cascade of field-induced magnetic transitions in a frustrated antiferromagnetic metal,"Frustrated magnets can exhibit many novel forms of order when exposed to high
magnetic fields, however, much less is known about materials where frustration
occurs in the presence of itinerant electrons. Here we report thermodynamic and
transport measurements on micron-sized single crystals of the
triangular-lattice metallic antiferromagnet 2H-AgNiO2, in magnetic fields of up
to 90 T and temperatures down to 0.35 K. We observe a cascade of magnetic phase
transitions at 13.5 20, 28 and 39T in fields applied along the easy axis, and
we combine magnetic torque, specific heat and transport data to construct the
field-temperature phase diagram. The results are discussed in the context of a
frustrated easy-axis Heisenberg model for the localized moments where
intermediate applied magnetic fields are predicted to stabilize a magnetic
supersolid phase. Deviations in the measured phase diagram from this model
predictions are attributed to the role played by the itinerant electrons.",1407.2175v1
2016/4/23,Stretching magnetism with an electric field in a nitride semiconductor,"By direct magnetization measurements, performed employing a new detection
scheme, we demonstrate an electrical control of magnetization in wurtzite
(Ga,Mn)N. In this dilute magnetic insulator the Fermi energy is pinned by Mn
ions in the mid-gap region, and the Mn3+ ions show strong single-ion
anisotropy. We establish that (Ga,Mn)N sustains an electric field up to at
least 5 MV/cm, indicating that Mn doping turns GaN into a worthwhile
semi-insulating material. Under these conditions, the magnetoelectric coupling
may be driven by the inverse piezoelectric effect that stretches the elementary
cell along the c axis and, thus, affects the magnitude of magnetic anisotropy.
We develop a corresponding theory and show that it describes the experimentally
determined dependence of magnetization on the electric field quantitatively
with no adjustable parameters as a function of the magnetic field and
temperature. In this way, our work bridges two research domains developed so
far independently: piezoelectricity of wurtzite semiconductors and electrical
control of magnetization in hybrid and composite magnetic structures containing
piezoelectric components.",1604.06937v2
2016/9/21,"Magnetic Susceptibility of Dirac Fermions, Bi-Sb Alloys, Interacting Bloch Fermions, Dilute Nonmagnetic Alloys, and Kondo Alloys","Wide ranging interest in Dirac Hamiltomian is due to the emergence of novel
materials, namely, graphene, topological insulators and superconductors, the
newly-discovered Weyl semimetals, and still actively-sought after Majorana
fermions in real materials. We give a brief review of the relativistic Dirac
quantum mechanics and its impact in the developments of modern physics. The
quantum band dynamics of Dirac Hamiltonian is crucial in resolving the giant
diamagnetism of bismuth and Bi-Sb alloys. Quantitative agreement of the theory
with the experiments on Bi-Sb alloys has been achieved, and physically
meaningful contributions to the diamagnetism has been identified. We also treat
relativistic Dirac fermion as an interband dynamics in uniform magnetic fields.
For the interacting Bloch electrons, the role of translation symmetry for
calculating the magnetic susceptibility avoids any approximation to second
order in the field. The magnetic susceptibility of Hubbard model and those of
Fermi liquids are readily obtained as limiting cases. The expressions for
magnetic susceptibility of dilute nonmagnetic alloys give a firm theoretical
foundation of the empirical formulas used in fitting experimental results. For
completeness, the magnetic susceptibility of dilute magnetic or Kondo alloys is
also given for high and low temperature regimes.",1609.06419v1
2017/8/1,"Rare-earth/transition-metal magnetic interactions in pristine and (Ni,Fe)-doped YCo5 and GdCo5","We present an investigation into the intrinsic magnetic properties of the
compounds YCo5 and GdCo5, members of the RETM5 class of permanent magnets (RE =
rare earth, TM = transition metal). Focusing on Y and Gd provides direct
insight into both the TM magnetization and RE-TM interactions without the
complication of strong crystal field effects. We synthesize single crystals of
YCo5 and GdCo5 using the optical floating zone technique and measure the
magnetization from liquid helium temperatures up to 800 K. These measurements
are interpreted through calculations based on a Green's function formulation of
density-functional theory, treating the thermal disorder of the local magnetic
moments within the coherent potential approximation. The rise in the
magnetization of GdCo5 with temperature is shown to arise from a faster
disordering of the Gd magnetic moments compared to the antiferromagnetically
aligned Co sublattice. We use the calculations to analyze the different Curie
temperatures of the compounds and also compare the molecular (Weiss) fields at
the RE site with previously published neutron scattering experiments. To gain
further insight into the RE-TM interactions, we perform substitutional doping
on the TM site, studying the compounds RECo4.5Ni0.5, RECo4Ni, and RECo4.5Fe0.5.
Both our calculations and experiments on powdered samples find an
increased/decreased magnetization with Fe/Ni doping, respectively. The
calculations further reveal a pronounced dependence on the location of the
dopant atoms of both the Curie temperatures and the Weiss field at the RE site.",1708.00288v1
2018/4/26,Realizing Majorana zero mode with a stripe of \emph{ionized} and \emph{isolated} magnetic atoms on a \emph{layered} superconductor,"It has been proposed that a line junction between spiral magnet and
superconductor or between ferromagnet and superconductor with Rashba
spin-orbital coupling can produce Majorana zero mode (MZM) at the ends of the
line. However, a strong magnetic exchange coupling between the magnetic atoms
and the superconductor (about half of the bandwidth of the superconductor) is
needed to obtain MZM. Here, we design devices to reduce the needed magnetic
exchange coupling. In the first proposal, we cover a very narrow $s$-wave
superconducting wire formed by a monolayer film or a layered material (such as
FeSe or FeSe monolayer on SrTiO$_3$) with \emph{isolated} magnetic atoms. In
our second proposal, we place a line of \emph{isolated} magnetic \emph{ions} on
a monolayer superconductor or a \emph{layered} superconductor (such as FeSe).
We show that, in the above devices, a spiral magnetic order will develop
spontaneously to produce a 1D $p$-wave topological superconductor with a
sizable gap (above 1/2 of the parent superconducting gap), even for a weak
magnetic exchange coupling (less than 1/10 of the bandwidth). The topological
superconductor has MZM at ends of the wire.",1804.10198v3
2018/6/28,Quantum Magnetism in Minerals,"The discovery of magnetism by the ancient Greeks was enabled by the natural
occurrence of lodestone -- a magnetized version of the mineral magnetite.
Nowadays, natural minerals continue to inspire the search for novel magnetic
materials with quantum-critical behavior or exotic ground states such as spin
liquids. The recent surge of interest in magnetic frustration and quantum
magnetism was largely encouraged by crystalline structures of natural minerals
realizing pyrochlore, kagome, or triangular arrangements of magnetic ions. As a
result, names like azurite, jarosite, volborthite, and others, which were
barely known beyond the mineralogical community a few decades ago, found their
way into cutting-edge research in solid-state physics. In some cases, the
structures of natural minerals are too complex to be synthesized artificially
in a chemistry lab, especially in single-crystalline form, and there is a
growing number of examples demonstrating the potential of natural specimens for
experimental investigations in the field of quantum magnetism. On many other
occasions, minerals may guide chemists in the synthesis of novel compounds with
unusual magnetic properties. The present review attempts to embrace this
quickly emerging interdisciplinary field that bridges mineralogy with
low-temperature condensed-matter physics and quantum chemistry.",1806.10967v3
2019/8/1,Giant magnetoelectric coupling in multiferroic PbTi$_{1-x}$V$_x$O$_{3}$ from density functional calculations,"The giant magnetoelectric coupling is a very rare phenomenon which has gained
a lot of attention for the past few decades because of fundamental interest as
well as practical applications. Here, we have successfully achieved the giant
magnetoelectric coupling in PbTi1-xVxO3 (x= 0-1) with the help of a series of
generalized-gradient-corrected (GGA), GGA including on-site coulomb repulsion
(U) corrected spin polarized calculations based on accurate density functional
theory. Our total energy calculations show that PbTi1-xVxO3 stabilizes in
C-type antiferromagnetic ground state for x>0.123. With the substitution of V
into PbTiO3, the tetragonal distortion is highly enhanced accompanied by a
linear increase in polarization. In addition, our band structure analysis shows
that for lower x values, the tendency to form 2Dmagnetism of PbTi1-xVxO3
decreases. A non-magnetic metallic ground state is observed for the
paraelectric phase for V concentration (x) = 1 competing with a volume change
of 10% showing a large magnetovolume effect. Our orbital projected DOS as well
as orbital ordering analysis suggest that the orbital ordering plays a major
role in the magnetic to non-magnetic transition when going from ferroelectric
to paraelectric phase. The calculated magnetic anisotropic energy shows that
the direction [110] is the easy axis of magnetization for x= 1 composition. The
present study adds a new series of compounds to the magnetoelectric family with
rarely existing giant coupling between electric and magnetic order parameters.
These results show that such kind of materials can be used for novel practical
applications where one can change the magnetic properties drastically (magnetic
to non-magnetic as shown here) with external electric fieldand vice-versa.",1908.00238v1
2019/1/18,Impurity-potential-induced gap at the Dirac point of topological insulators with in-plane magnetization,"The quantum anomalous Hall effect (QAHE), characterized by dissipationless
quantized edge transport, relies crucially on a non-trivial topology of the
electronic bulk bandstructure and a robust ferromagnetic order that breaks
time-reversal symmetry. Magnetically-doped topological insulators (TIs) satisfy
both these criteria, and are the most promising quantum materials for realizing
the QAHE. Because the spin of the surface electrons aligns along the direction
of magnetic-impurity exchange field, only magnetic TIs with an out-of-plane
magnetization are thought to open a gap at the Dirac point (DP) of the surface
states, resulting in the QAHE. Using a continuum model supported by atomistic
tight-binding and first-principles calculations of transition-metal doped
Bi$_2$Se$_3$, we show that a surface-impurity potential generates an additional
effective magnetic field which spin-polarizes the surface electrons along the
direction perpendicular to the surface. The predicted gap-opening mechanism
results from the interplay of this additional field and the in-plane
magnetization that shifts the position of the DP away from the $\Gamma$ point.
This effect is similar to the one originating from the hexagonal warping
correction of the bandstructure but is one order of magnitude stronger. Our
calculations show that in a doped TI with in-plane magnetization the
impurity-potential-induced gap at the DP is comparable to the one opened by an
out-of-plane magnetization.",1901.06395v2
2016/8/31,Superelastic stress-strain behavior in ferrogels of different types of magneto-elastic coupling,"Colloidal magnetic particles embedded in an elastic polymer matrix constitute
a smart material called ferrogel. It responds to an applied external magnetic
field by changes in elastic properties, which can be exploited for various
applications like dampers, vibration absorbers, or actuators. Under appropriate
conditions, the stress-strain behavior of a ferrogel can display a fascinating
feature: superelasticity, the capability to reversibly deform by a huge amount
while barely altering the applied load. In a previous work, using numerical
simulations, we investigated this behavior assuming that the magnetic moments
carried by the embedded particles can freely reorient to minimize their
magnetic interaction energy. Here, we extend the analysis to ferrogels where
restoring torques by the surrounding matrix hinder rotations towards a
magnetically favored configuration. For example, the particles can be
chemically cross-linked into the polymer matrix and the magnetic moments can be
fixed to the particle axes. We demonstrate that these systems still feature a
superelastic regime. As before, the nonlinear stress-strain behavior can be
reversibly tailored during operation by external magnetic fields. Yet, the
different coupling of the magnetic moments causes different types of response
to external stimuli. For instance, an external magnetic field applied parallel
to the stretching axis hardly affects the superelastic regime but stiffens the
system beyond it. Other smart materials featuring superelasticity, e.g.
metallic shape-memory alloys, have already found widespread applications. Our
soft polymer systems offer many additional advantages like a typically higher
deformability and enhanced biocompatibility combined with high tunability.",1608.08826v1
2017/3/16,"3D magnetization currents, magnetization loop, and saturation field in superconducting rectangular prisms","Bulk superconductors are used in both many applications and material
characterization experiments, being the bulk shape of rectangular prism very
frequent. However the magnetization currents are still mostly unknown for this
kind of three dimensional (3D) shape, specially below the saturation magnetic
field. Knowledge of the magnetization currents in this kind of samples is
needed to interpret the measurements and the development of bulk materials for
applications. This article presents a systematic analysis of the magnetization
currents in prisms of square base and several thicknesses. We make this study
by numerical modeling using a variational principle that enables high number of
degrees of freedom. We also compute the magnetization loops and the saturation
magnetic field, using a definition that is more relevant for thin prisms than
previous ones. The article presents a practical analytical fit for any aspect
ratio. For applied fields below the saturation field, the current paths are not
rectangular, presenting 3D bending. The thickness-average results are
consistent with previous modeling and measurements for thin films. The 3D
bending of the current lines indicates that there could be flux cutting effects
in rectangular prisms. The component of the critical current density in the
applied field direction may play a role, being the magnetization currents in a
bulk and a stack of tapes not identical.",1703.05529v3
2017/3/24,Electronic structure and direct observation of ferrimagnetism in multiferroic hexagonal YbFeO3,"The magnetic interaction between rare-earth and Fe ions in hexagonal
rare-earth ferrites (h-REFeO3), may amplify the weak ferromagnetic moment on
Fe, making these materials more appealing as multiferroics. To elucidate the
interaction strength between the rare-earth and Fe ions as well as the magnetic
moment of the rare-earth ions, element specific magnetic characterization is
needed. Using X-ray magnetic circular dichroism, we have studied the
ferrimagnetism in h-YbFeO3 by measuring the magnetization of Fe and Yb
separately. The results directly show anti-alignment of magnetization of Yb and
Fe ions in h-YbFeO3 at low temperature, with an exchange field on Yb of about
17 kOe. The magnetic moment of Yb is about 1.6 \muB at low-temperature,
significantly reduced compared with the 4.5 \muB moment of a free Yb3+. In
addition, the saturation magnetization of Fe in h-YbFeO3 has a sizable
enhancement compared with that in h-LuFeO3. These findings directly demonstrate
that ferrimagnetic order exists in h-YbFeO3; they also account for the
enhancement of magnetization and the reduction of coercivity in h-YbFeO3
compared with those in h-LuFeO3 at low temperature, suggesting an important
role for the rare-earth ions in tuning the multiferroic properties of h-REFeO3.",1703.08482v2
2019/10/1,Magnetostriction in magnetic gels and elastomers as a function of the internal structure and particle distribution,"Magnetic gels and elastomers are promising candidates to construct reversibly
excitable soft actuators, triggered from outside by magnetic fields. These
magnetic fields induce or alter the magnetic interactions between discrete
rigid particles embedded in a soft elastic polymeric matrix, leading to overall
deformations. It is a major challenge in theory to correctly predict from the
discrete particle configuration the type of deformation resulting for a
finite-sized system. Considering an elastic sphere, we here present such an
approach. The method is in principle exact, at least within the framework of
linear elasticity theory and for large enough interparticle distances.
Different particle arrangements are considered. We find, for instance, that
regular simple cubic configurations show elongation of the sphere along the
magnetization if oriented along a face or space diagonal of the cubic unit
cell. Contrariwise, with the magnetization along the edge of the cubic unit
cell, they contract. The opposite is true in this geometry for body- and
face-centered configurations. Remarkably, for the latter configurations but the
magnetization along a face or space diagonal of the unit cell, contraction was
observed to revert to expansion with decreasing Poisson ratio of the elastic
material. Randomized configurations were considered as well. They show a
tendency of elongating the sphere along the magnetization, which is more
pronounced for compressible systems. Our results can be tested against actual
experiments for spherical samples. Moreover, our approach shall support the
search of optimal particle distributions for a maximized effect of actuation.",1910.00236v1
2020/4/17,Reversible and magnetically unassisted voltage-driven switching of magnetization in FeRh/PMN-PT,"Reversible control of magnetization by electric fields without assistance
from a subsidiary magnetic field or electric current could help reduce the
power consumption in spintronic devices. When increasing temperature above room
temperature, FeRh displays an uncommon antiferromagnetic to ferromagnetic phase
transition linked to a unit cell volume expansion. Thus, using the strain
exerted by an adjacent piezoelectric layer, the relative amount of
antiferromagnetic and ferromagnetic regions can be tuned by an electric field
applied to the piezoelectric material. Indeed, large variations in the
saturation magnetization have been observed when straining FeRh films grown on
suitable piezoelectric substrates. In view of its applications, the variations
in the remanent magnetization rather than those of the saturation magnetization
are the most relevant. Here, we show that in the absence of any bias external
magnetic field, permanent and reversible magnetization changes as high as 34%
can be induced by an electric field, which remain after this has been zeroed.
Bulk and local magnetoelectric characterization reveals that the fundamental
reason for the large magnetoelectric response observed at remanence is the
expansion (rather than the nucleation) of ferromagnetic nanoregions.",2004.08087v1
2020/8/2,Tailoring Magnetism in Self-intercalated Cr1+δTe2 Epitaxial Films,"Magnetic transition metal dichalcogenide (TMD) films have recently emerged as
promising candidates to host novel magnetic phases relevant to next-generation
spintronic devices. However, systematic control of the magnetization
orientation, or anisotropy, and its thermal stability, characterized by Curie
temperature (Tc) remains to be achieved in such films. Here we present
self-intercalated epitaxial Cr1+{\delta}Te2 films as a platform for achieving
systematic/smooth magnetic tailoring in TMD films. Using a molecular beam
epitaxy (MBE) based technique, we have realized epitaxial Cr1+{\delta}Te2 films
with smoothly tunable over a wide range (0.33-0.82), while maintaining
NiAs-type crystal structure. With increasing {\delta}, we found monotonic
enhancement of Tc from 160 to 350 K, and the rotation of magnetic anisotropy
from out-of-plane to in-plane easy axis configuration for fixed film thickness.
Contributions from conventional dipolar and orbital moment terms are
insufficient to explain the observed evolution of magnetic behavior with
{\delta}. Instead, ab initio calculations suggest that the emergence of
antiferromagnetic interactions with {\delta}, and its interplay with
conventional ferromagnetism, may play a key role in the observed trends. To our
knowledge, this constitutes the first demonstration of tunable Tc and magnetic
anisotropy across room temperature in TMD films, and paves the way for
engineering novel magnetic phases for spintronic applications.",2008.00381v1
2020/8/20,Magnetic Two-Dimensional Chromium Trihalides: A Theoretical Perspective,"The discovery of ferromagnetic order in monolayer 2D crystals has opened a
new venue in the field of two dimensional (2D) materials. 2D magnets are not
only interesting on their own, but their integration in van der Waals
heterostructures allows for the observation of new and exotic effects in the
ultrathin limit. The family of Chromium trihalides, CrI$_3$, CrBr$_3$ and
CrCl$_3$, is, so far, the most studied among magnetic 2D crystals. In this
mini-review, we provide a perspective of the state of the art of the
theoretical understanding of magnetic 2D trihalides, most of which will also be
relevant for other 2D magnets, such as vanadium trihalides. We discuss both the
well-established facts, such as the origin of the magnetic moment and magnetic
anisotropy and address as well open issues such as the nature of the
anisotropic spin couplings and the magnitude of the magnon gap. Recent
theoretical predictions on Moir\' e magnets and magnetic skyrmions are also
discussed. Finally, we give some prospects about the future interest of these
materials and possible device applications.",2008.08855v2
2021/5/13,Prediction of unconventional magnetism in doped FeSb2,"It is commonly believed that in typical collinear antiferromagnets, with no
net magnetization, the energy bands are spin-(Kramers-degenerate. The opposite
case is usually associated with a global time-reversal symmetry breaking (e.g.,
via ferro(i)magnetism), or with the spin-orbit interaction is combined with the
broken spatial inversion symmetry. Recently, another type of spin splitting was
demonstrated to emerge in some fully compensated by symmetry, nonrelativistic,
collinear magnets, and not even necessarily non-centrosymmetric. These
materials feature non-zero spin density staggered not only in real, but also in
momentum space. This duality results in a combination of characteristics
typical of ferro- and antiferromagnets. Here we discuss this novel concept in
application to a well-known semiconductor, FeSb2, and predict that upon certain
alloying it becomes magnetic, and features such magnetic duality. The
calculated energy bands split antisymmetrically with respect to spin degenerate
nodal surfaces (and not nodal points, as in the case of spin-orbit splitting.
This combination of a large (0.2 eV) spin splitting, compensated net
magnetization and metallic ground-state, and a particular magnetic easy axis
generate a large anomalous Hall conductivity (~150 S/cm) and a sizable
magneto-optical Kerr effect, all deemed to be hallmarks of nonzero net
magnetization. We identify a large contribution to the anomalous response
originating from the spin-orbit interaction gapped anti-Kramers nodal surfaces,
a mechanism distinct from the nodal lines and Weyl {\it points} in
ferromagnets.",2105.06356v2
2014/1/24,"Manipulation of electronic and magnetic properties of M$_2$C (M=Hf, Nb, Sc, Ta, Ti, V, Zr) monolayer by applying mechanical strains","Tuning the electronic and magnetic properties of a material through strain
engineering is an effective strategy to enhance the performance of electronic
and spintronic devices. Recently synthesized two-dimensional transition metal
carbides M$_2$C (M=Hf, Nb, Sc, Ta, Ti, V, Zr), known as MXenes, has aroused
increasingly attentions in nanoelectronic technology due to their unusual
properties. In this paper, first-principles calculations based on density
functional theory are carried out to investigate the electronic and magnetic
properties of M$_2$C subjected to biaxial symmetric mechanical strains. At the
strain-free state, all these MXenes exhibit no spontaneous magnetism except for
Ti$_2$C and Zr$_2$C which show a magnetic moment of 1.92 and 1.25 $\mu_B$/unit,
respectively. As the tensile strain increases, the magnetic moments of MXenes
are greatly enhanced and a transition from nonmagnetism to ferromagnetism is
observed for those nonmagnetic MXenes at zero strains. The most distinct
transition is found in Hf$_2$C, in which the magnetic moment is elevated to 1.5
$\mu_B$/unit at a strain of 15%. We further show that the magnetic properties
of Hf$_2$C are attributed to the band shift mainly composed of Hf(5$d$) states.
This strain-tunable magnetism can be utilized to design future spintronics
based on MXenes.",1401.6259v2
2016/6/16,The iridium double perovskite Sr2YIrO6 revisited: A combined structural and specific heat study,"Recently, the iridate double perovskite Sr$_2$YIrO$_6$ has attracted
considerable attention due to the report of unexpected magnetism in this
Ir$^{5+}$ (5d$^4$) material, in which according to the J$_{eff}$ model, a
non-magnetic ground state is expected. However, in recent works on
polycrystalline samples of the series Ba$_{2-x}$Sr$_x$YIrO$_6$ no indication of
magnetic transitions have been found. We present a structural, magnetic and
thermodynamic characterization of Sr$_2$YIrO$_6$ single crystals, with emphasis
on the temperature and magnetic field dependence of the specific heat. Here, we
demonstrate the clue role of single crystal X-ray diffraction on the structural
characterization of the Sr$_2$YIrO$_6$ double perovskite crystals by reporting
the detection of a $\sqrt{2}a \times \sqrt{2}a \times 1c$ supercell, where $a$,
$b$ and $c$ are the unit cell dimensions of the reported monoclinic subcell. In
agreement with the expected non-magnetic ground state of Ir$^{5+}$ (5d$^4$) in
Sr$_2$YIrO$_6$, no magnetic transition is observed down to 430~mK. Moreover,
our results suggest that the low temperature anomaly observed in the specific
heat is not related to the onset of long-range magnetic order. Instead, it is
identified as a Schottky anomaly caused by paramagnetic impurities present in
the sample, of the order of $n \sim 0.5(2)$ \%. These impurities lead to
non-negligible spin correlations, which nonetheless, are not associated with
long-range magnetic ordering.",1606.05104v1
2016/6/24,Robust metastable skyrmions and their triangular-square lattice-structural transition in a high-temperature chiral magnet,"Skyrmions, topologically-protected nanometric spin vortices, are being
investigated extensively in various magnets. Among them, many of
structurally-chiral cubic magnets host the triangular-lattice skyrmion crystal
(SkX) as the thermodynamic equilibrium state. However, this state exists only
in a narrow temperature and magnetic-field region just below the magnetic
transition temperature $T_\mathrm{c}$, while a helical or conical magnetic
state prevails at lower temperatures. Here we describe that for a
room-temperature skyrmion material, $\beta$-Mn-type Co$_8$Zn$_8$Mn$_4$, a
field-cooling via the equilibrium SkX state can suppress the transition to the
helical or conical state, instead realizing robust metastable SkX states that
survive over a very wide temperature and magnetic-field region, including down
to zero temperature and up to the critical magnetic field of the ferromagnetic
transition. Furthermore, the lattice form of the metastable SkX is found to
undergo reversible transitions between a conventional triangular lattice and a
novel square lattice upon varying the temperature and magnetic field. These
findings exemplify the topological robustness of the once-created skyrmions,
and establish metastable skyrmion phases as a fertile ground for technological
applications.",1606.07543v1
2019/2/5,The Dynamics of Magnetism in Fe-Cr Alloys with Cr Clustering,"The dynamics of magnetic moments in iron-chromium alloys with different
levels of Cr clustering show unusual features resulting from the fact that even
in a perfect body-centred cubic structure, magnetic moments experience
geometric magnetic frustration resembling that of a spin glass. Due to the long
range exchange coupling and configuration randomness, magnetic moments of Cr
solutes remain non-collinear at all temperatures. To characterise magnetic
properties of Fe-Cr alloys, we explore the temperature dependence of
magnetisation, susceptibility, Curie temperature and spin-spin correlations
with spatial resolution. The static and dynamic magnetic properties are
correlated with the microstructure of Fe-Cr, where magnetisation and
susceptibility are determined by the size of Cr precipitates at nominal Cr
concentrations. The Curie temperature is always maximised when the solute
concentration of Cr in the $\alpha$ phase is close to 5 to 6 at.\%, and the
susceptibility of Fe atoms is always enhanced at the boundary between a
precipitate and solid solution. Interaction between Cr and Fe stimulates
magnetic disorder, lowering the effective Curie temperature. Dynamic simulation
of evolution of magnetic correlations shows that the spin-spin relaxation time
in Fe-Cr alloys is in the 20 to 40 ps range.",1902.01645v1
2019/2/28,Giant enhancement of interlayer exchange in an ultrathin 2D magnet,"Following the recent isolation of monolayer CrI3, there has been a surge of
new two-dimensional van der Waals magnetic materials, whose incorporation in
van der Waals heterostructures offers a new platform for spintronics, proximity
magnetism, and quantum spin liquids. A primary question in this burgeoning
field is how exfoliating crystals to the few-layer limit influences their
magnetism. Studies on CrI3 have shown a different magnetic ground state for
ultrathin exfoliated films but the origin is not yet understood. Here, we use
electron tunneling through few-layer crystals of the layered antiferromagnetic
insulator CrCl3 to probe its magnetic order, finding a ten-fold enhancement in
the interlayer exchange compared to bulk crystals. Moreover, temperature- and
polarization-dependent Raman spectroscopy reveal that the crystallographic
phase transition of bulk crystals does not occur in exfoliated films. This
results in a different low temperature stacking order and, we hypothesize,
increased interlayer exchange. Our study provides new insight into the
connection between stacking order and interlayer interactions in novel
two-dimensional magnets, which may be relevant for correlating stacking faults
and mechanical deformations with the magnetic ground states of other more
exotic layered magnets, such as RuCl3.",1903.00002v1
2019/11/5,Zero-field spin-orbit-torque switching driven by magnetic spin Hall effect,"Spin Hall effect plays an essential role in generating spin current from the
injected charge current, following the Dyakonov-Perel rule that the directions
of charge flow, spin flow and spin polarization are mutually perpendicular to
each other. Recently, its generalization from an antiferromagnet, so-called
magnetic spin Hall effect, has been studied and verified by measuring anomalous
spin accumulations. Here, we investigate the magnetic spin Hall effect in
bilayer materials made of a heavy metal and an antiferromagnet. The spin
current generated by the magnetic spin Hall effect accomplishes
spin-orbit-torque switching for ferromagnetic magnetization and exchange bias
concurrently without any external magnetic field. The switching mechanism
crucially relies on the non-collinear spin texture in the antiferromagnet,
capable of generating symmetry-breaking components in the spin-current tensor
so that the external magnetic field is no longer necessary. The zero-field
concurrent switching of magnetization and exchange bias is a significant
technological breakthrough. Furthermore, our findings pave the way to explore
the magnetic spin Hall effects in various spin textures through
spin-orbit-torque switching.",1911.01785v1
2019/11/27,Coexistence of Magnetic Orders in Two-Dimensional Magnet CrI$_3$,"The magnetic properties in two-dimensional van der Waals materials depend
sensitively on structure. CrI3, as an example, has been recently demonstrated
to exhibit distinct magnetic properties depending on the layer thickness and
stacking order. Bulk CrI3 is ferromagnetic (FM) with a Curie temperature of 61
K and a rhombohedral layer stacking, while few-layer CrI3 has a layered
antiferromagnetic (AFM) phase with a lower ordering temperature of 45 K and a
monoclinic stacking. In this work, we use cryogenic magnetic force microscopy
to investigate CrI3 flakes in the intermediate thickness range (25 - 200 nm)
and find that the two types of magnetic orders hence the stacking orders can
coexist in the same flake, with a layer of ~13 nm at each surface being in the
layered AFM phase similar to few-layer CrI3 and the rest in the bulk FM phase.
The switching of the bulk moment proceeds through a remnant state with nearly
compensated magnetic moment along the c-axis, indicating formation of c-axis
domains allowed by a weak interlayer coupling strength in the rhombohedral
phase. Our results provide a comprehensive picture on the magnetism in CrI3 and
point to the possibility of engineering magnetic heterostructures within the
same material.",1911.12428v1
2019/12/19,Long range magnetic order in hydroxide layer doped (Li$_{1-x-y}$Fe$_{x}$Mn$_{y}$OD)FeSe,"The (Li$_{1-x}$Fe$_{x}$OH)FeSe superconductor has been suspected to exhibit
long-range magnetic ordering due to Fe substitution in the LiOH layer. However,
no direct observation such as magnetic reflection from neutron diffraction has
be reported. Here, we use a chemical design strategy to manipulate the doping
level of transition metals in the LiOH layer to tune the magnetic properties of
the (Li$_{1-x-y}$Fe$_{x}$Mn$_{y}$OD)FeSe system. We find Mn doping exclusively
replaces Li in the hydroxide layer resulting in enhanced magnetization in the
(Li$_{0.876}$Fe$_{0.062}$Mn$_{0.062}$OD)FeSe superconductor without
significantly altering the superconducting behavior as resolved by magnetic
susceptibility and electrical/thermal transport measurements. As a result,
long-range magnetic ordering was observed below 12 K with neutron diffraction
measurements. This work has implications for the design of magnetic
superconductors for the fundamental understanding of superconductivity and
magnetism in the iron chalcogenide system as well as exploitation as functional
materials for next generation devices.",1912.09329v1
2020/5/1,Tunable Ferromagnetism and Thermally Induced Spin Flip in Vanadium-doped Tungsten Diselenide Monolayers at Room Temperature,"The outstanding optoelectronic and valleytronic properties of transition
metal dichalcogenides (TMDs) have triggered intense research efforts by the
scientific community. An alternative to induce long-range ferromagnetism (FM)
in TMDs is by introducing magnetic dopants to form a dilute magnetic
semiconductor. Enhancing ferromagnetism in these semiconductors not only
represents a key step towards modern TMD-based spintronics, but also enables
exploration of new and exciting dimensionality-driven magnetic phenomena. To
this end, we show tunable ferromagnetism at room temperature and a thermally
induced spin flip (TISF) in monolayers of V-doped WSe2. As vanadium
concentrations increase within the WSe2 monolayers the saturation magnetization
increases, and it is optimal at ~4at.% vanadium; the highest doping/alloying
level ever achieved for V-doped WSe2 monolayers. The TISF occurs at ~175 K and
becomes more pronounced upon increasing the temperature towards room
temperature. We demonstrate that TISF can be manipulated by changing the
vanadium concentration within the WSe2 monolayers. We attribute TISF to the
magnetic field and temperature dependent flipping of the nearest W-site
magnetic moments that are antiferromagnetically coupled to the V magnetic
moments in the ground state. This is fully supported by a recent spin-polarized
density functional theory calculation. Our findings pave the way for the
development of novel spintronic and valleytronic nanodevices based on
atomically thin magnetic semiconductors and stimulate further studies in this
rapidly expanding research field of 2D magnetism.",2005.00493v1
2020/5/8,Sublattice magnetizations of ultrathin ferrimagnetic lamellar nanostructures between cobalt leads,"In this work we model the salient magnetic properties of the alloy lamellar
ferrimagnetic nanostructures
$[Co_{1-c}Gd_c]_{\ell^{\prime}}[Co]_\ell[Co_{1-c}Gd_c]_{\ell^{\prime}}$ between
$Co$ semi-infinite leads. We have employed the Ising spin effective field
theory (EFT) to compute the reliable magnetic exchange constants for the pure
cobalt $J_{Co-Co}$ and gadolinium $J_{Gd-Gd}$ materials, in complete agreement
with their experimental data. The sublattice magnetizations of the $Co$ and
$Gd$ sites on the individual hcp atomic (0001) planes of the $Co-Gd$ layered
nanostructures are computed for each plane and corresponding sites, by using
the combined EFT and mean field theory (MFT) spin methods. The sublattice
magnetizations, effective site magnetic moments, and ferrimagnetic compensation
characteristics for the individual hcp atomic planes of the embedded
nanostructures, are computed as a function of temperature, and for various
stable eutectic concentrations in the range $c\leq$ 0.5. The theoretical
results for the sublattice magnetizations and the local magnetic variables of
these ultrathin ferrimagnetic lamellar nanostructured systems, between cobalt
leads, are necessary for the study of their magnonic transport properties, and
eventually their spintronic dynamic computations. The method developed in this
work is general and can be applied to comparable magnetic systems
nanostructured with other materials.",2005.03965v3
2020/6/5,Competing Antiferromagnetic-Ferromagnetic States in $\it{d^7}$ Kitaev Honeycomb Magnet,"The Kitaev model is a rare example of an analytically solvable and physically
instantiable Hamiltonian yielding a topological quantum spin liquid ground
state. Here we report signatures of Kitaev spin liquid physics in the honeycomb
magnet $Li_3Co_2SbO_6$, built of high-spin $\it{d^7}$ ($Co^{2+}$) ions, in
contrast to the more typical low-spin $\it{d^5}$ electron configurations in the
presence of large spin-orbit coupling. Neutron powder diffraction measurements,
heat capacity, and magnetization studies support the development of a
long-range antiferromagnetic order space group of $\it{C_C}2/\it{m}$, below
$\it{T_N}$ = 11 K at $\it{\mu_0H}$ = 0 T. The magnetic entropy recovered
between $\it{T}$ = 2 K and 50 K is estimated to be 0.6Rln2, in good agreement
with the value expected for systems close to a Kitaev quantum spin liquid
state. The temperature-dependent magnetic order parameter demonstrates a
$\beta$ value of 0.19(3), consistent with XY anisotropy and in-plane ordering,
with Ising-like interactions between layers. Further, we observe a spin-flop
driven crossover to ferromagnetic order with space group of $\it{C}2/\it{m}$
under an applied magnetic field of $\it{\mu_0H}$ $\approx$ 0.7 T at $\it{T}$ =
2 K. Magnetic structure analysis demonstrates these magnetic states are
competing at finite applied magnetic fields even below the spin-flop
transition. Both the $\it{d^7}$ compass model, a quantitative comparison of the
specific heat of $Li_3Co_2SbO_6$, and related honeycomb cobaltates to the
anisotropic Kitaev model further support proximity to a Kitaev spin liquid
state. This material demonstrates the rich playground of high-spin $\it{d^7}$
systems for spin liquid candidates, and complements known $\it{d^5}$ Ir- and
Ru-based materials.",2006.03724v1
2020/6/8,Higher-order exchange interactions in two-dimensional magnets,"Magnetism in recently discovered van der Waals materials has opened new
avenues in the study of fundamental spin interactions in truly two-dimensions.
A paramount question is what effect higher-order interactions beyond bilinear
Heisenberg exchange have on the magnetic properties of few-atom thick
compounds. Here we demonstrate that biquadratic exchange interactions, which is
the simplest and most natural form of non-Heisenberg coupling, assume a key
role in the magnetic properties of layered magnets. Using a combination of
nonperturbative analytical techniques, non-collinear first-principles methods
and classical Monte Carlo calculations that incorporate higher-order exchange,
we show that several quantities including magnetic anisotropies, spin-wave gaps
and topological spin-excitations are intrinsically renormalized leading to
further thermal stability of the layers. We develop a spin Hamiltonian that
also contains antisymmetric exchanges (e.g. Dzyaloshinskii-Moriya interactions)
to successfully rationalize numerous observations currently under debate, such
as the non-Ising character of several compounds despite a strong magnetic
anisotropy, peculiarities of the magnon spectrum of 2D magnets, and the
discrepancy between measured and calculated Curie temperatures. Our results lay
the foundation of a universal higher-order exchange theory for novel 2D
magnetic design strategies.",2006.04891v1
2020/7/13,The magnetic obliquity of accreting T Tauri stars,"Classical T Tauri stars (CTTS) accrete material from their discs through
their magnetospheres. The geometry of the accretion flow strongly depends on
the magnetic obliquity, i.e., the angle between the rotational and magnetic
axes. We aim at deriving the distribution of magnetic obliquities in a sample
of 10 CTTSs. For this, we monitored the radial velocity variations of the
HeI$\lambda$5876 line in these stars' spectra along their rotational cycle. HeI
is produced in the accretion shock, close to the magnetic pole. When the
magnetic and rotational axes are not aligned, the radial velocity of this line
is modulated by stellar rotation. The amplitude of modulation is related to the
star's projected rotational velocity, $v\sin i$, and the latitude of the
hotspot. By deriving $v\sin i$ and HeI$\lambda$5876 radial velocity curves from
our spectra we thus obtain an estimate of the magnetic obliquities. We find an
average obliquity in our sample of 11.4$^{\circ}$ with an rms dispersion of
5.4$^{\circ}$. The magnetic axis thus seems nearly, but not exactly aligned
with the rotational axis in these accreting T Tauri stars, somewhat in
disagreement with studies of spectropolarimetry, which have found a significant
misalignment ($\gtrsim 20^{\circ}$) for several CTTSs. This could simply be an
effect of low number statistics, or it may be due to a selection bias of our
sample. We discuss possible biases that our sample may be subject to. We also
find tentative evidence that the magnetic obliquity may vary according to the
stellar interior and that there may be a significant difference between fully
convective and partly radiative stars.",2007.06642v1
2020/7/27,Role of magnetic exchange interactions in chiral-type Hall effects of epitaxial Mn$_{x}$PtSn films,"Tetragonal Mn-based Heusler compounds feature rich exchange interactions and
exotic topological magnetic textures, such as antiskyrmions, complimented by
the chiral-type Hall effects. This makes the material class interesting for
device applications. We report the relation of the magnetic exchange
interactions to the thickness and Mn concentration of Mn$_{x}$PtSn films, grown
by magnetron sputtering. The competition of the magnetic exchange interactions
determines the finite temperature magnetic texture and thereby the chiral-type
Hall effects in external magnetic fields. We investigate the magnetic and
transport properties as a function of magnetic field and temperature. We focus
on the anomalous and chiral-type Hall effects and the behavior of the
dc-magnetization, in relation to chiral spin textures. We further determine the
stable crystal phase for a relative Mn concentration between 1.5 and 1.85 in
the $I\overline{4}2d$ structure. We observe a spin-reorientation transition in
all compounds studied, which is due to the competition of exchange interactions
on different Mn sublattices. We discuss our results in terms of exchange
interactions and compare them with theoretical atomistic spin calculations.",2007.13412v1
2020/9/30,Magnetic coupling in colloidal clusters for hierarchical self-assembly,"Manipulating the way in which colloidal particles self-organise is a central
challenge in the design of functional soft materials. Meeting this challenge
requires the use of building blocks that interact with one another in a highly
specific manner. Their fabrication, however, is limited by the complexity of
the available synthesis procedures. Here, we demonstrate that, starting from
experimentally available magnetic colloids, we can create a variety of complex
building blocks suitable for hierarchical self-organisation using a simple
scalable process. Using computer simulations, we compress spherical and cubic
magnetic colloids in spherical confinement, and investigate their suitability
to form small clusters with reproducible structural and magnetic properties. We
find that, while the structure of these clusters is highly reproducible, their
magnetic character depends on the particle shape. Only spherical particles have
the rotational degrees of freedom to produce consistent magnetic
configurations, whereas cubic particles frustrate the minimisation of the
cluster energy, resulting in various magnetic configurations. To highlight
their potential for self-assembly, we demonstrate that already clusters of
three magnetic particles form highly nontrivial Archimedean lattices, namely
staggered kagome, bounce and honeycomb, when viewing different aspects of the
same monolayer structure. The work presented here offers a conceptually
different way to design materials by utilizing pre-assembled magnetic building
blocks that can readily self-organise into complex structures.",2009.14669v2
2020/12/30,Ferrofluidic Manipulator: Automatic Manipulation of Non-magnetic Microparticles at Air-Ferrofluid Interface,"Manipulation of small-scale matter is a fundamental topic in micro- and
nanorobotics. Numerous magnetic robotic systems have been developed for the
manipulation of microparticles in an ambient environment, liquid as well as on
the air-liquid interface. These systems move intrinsically magnetic or
magnetically tagged objects by inducing a magnetic torque or force. However,
most of the materials found in nature are non-magnetic. Here, we report a
ferrofluidic manipulator for automatic two-dimensional manipulation of
non-magnetic objects floating on top of a ferrofluid. The manipulation system
employs eight centimeter-scale solenoids, which can move non-magnetic particles
by deforming the air-ferrofluid interface. Using linear programming, we can
control the motion of the non-magnetic particles with a predefined trajectory
of a line, square, and circle with a precision of 25.1+/-19.5 um, 34.4+/-28.4
um and 33.4+/-26.6 um, respectively. The ferrofluidic manipulator is versatile
with the materials and the shapes of the objects under manipulation. We have
successfully manipulated particles made of polyethylene, polystyrene, a silicon
chip, and poppy and sesame seeds. This work shows a promising venue for the
manipulation of living and non-living matter at the air-liquid interface.",2101.02782v2
2021/6/8,On numerical aspects of parameter identification for the Landau-Lifshitz-Gilbert equation in Magnetic Particle Imaging,"The Landau-Lifshitz-Gilbert equation yields a mathematical model to describe
the evolution of the magnetization of a magnetic material, particularly in
response to an external applied magnetic field. It allows one to take into
account various physical effects, such as the exchange within the magnetic
material itself. In particular, the Landau-Lifshitz-Gilbert equation encodes
relaxation effects, i.e., it describes the time-delayed alignment of the
magnetization field with an external magnetic field. These relaxation effects
are an important aspect in magnetic particle imaging, particularly in the
calibration process. In this article, we address the data-driven modeling of
the system function in magnetic particle imaging, where the
Landau-Lifshitz-Gilbert equation serves as the basic tool to include relaxation
effects in the model. We formulate the respective parameter identification
problem both in the all-at-once and the reduced setting, present reconstruction
algorithms that yield a regularized solution and discuss numerical experiments.
Apart from that, we propose a practical numerical solver to the nonlinear
Landau-Lifshitz-Gilbert equation, not via the classical finite element method,
but through solving only linear PDEs in an inverse problem framework.",2106.07625v1
2021/12/23,Stress-tailoring magnetic anisotropy of V$_2$O$_3$/Ni bilayers,"We report on a temperature-driven reversible change of the in-plane magnetic
anisotropy of V$_2$O$_3$/Ni bilayers. This is caused by the rhombohedral to
monoclinic structural phase transition of V$_2$O$_3$ at $T_C$ = 160 K. The
in-plane magnetic anisotropy is uniaxial above $T_C$, but as the bilayer is
cooled through the structural phase transition, a secondary magnetic easy axis
emerges. Ferromagnetic resonance measurements show that this change in magnetic
anisotropy is reversible with temperature. We identify two structural
properties of the V$_2$O$_3$/Ni bilayers affecting the in-plane magnetic
anisotropy: (1) a growth-induced uniaxial magnetic anisotropy associated with
step-like terraces in the bilayer microstructure and (2) a low-temperature
strain-induced biaxial anisotropy associated with the V$_2$O$_3$ structural
phase transition. Magnetoresistance measurements corroborate the change in
magnetic anisotropy across the structural transition and suggest that the
negative magnetostriction of Ni leads to the emergence of a strain-induced
easy-axis. This shows that a temperature-dependent structural transition in
V$_2$O$_3$ may be used to tune the magnetic anisotropy in an adjacent
ferromagnetic thin film.",2112.12826v1
2021/12/27,Magnetically driven in-plane modulation of the 3D orientation of vertical ferromagnetic flakes,"External magnetic fields are known to attract and orient magnetically
responsive colloidal particles. In the case of 2D microplatelets, rotating
magnetic fields are typically used to orient them parallel to each other in a
brick-and-mortar fashion. Thanks to this microstructure, the resulting
composites achieve enhanced mechanical and functional properties. However,
parts with complex geometry require their microstructure to be specifically
tuned and controlled locally in 3D. Although the tunability of the
microstructure along the vertical direction has already been demonstrated using
magnetic orientation combined with sequential or continuous casting,
controlling the particle orientation in the horizontal plane in a fast and
effective fashion remains challenging. Here, we propose to use rotating
magnetic arrays to control the in-plane orientation of ferromagnetic Nickel
flakes distributed in uncured polymeric matrices. We experimentally studied the
orientation of the flakes in response to magnets rotating at various
frequencies and precessing angles. Then, we used COMSOL to model the magnetic
field from rotating magnetic arrays and predicted the resulting in-plane
orientations. To validate the approach, we created composites with locally
oriented flakes. This work could initiate reverse-engineering methods to design
the microstructure in composite materials with intricate geometrical shapes for
structural or functional applications.",2201.05097v1
2022/1/13,Real-space visualization of short-range antiferromagnetic correlations in a magnetically enhanced thermoelectric,"Short-range magnetic correlations can significantly increase the thermopower
of magnetic semiconductors, representing a noteworthy development in the
decades-long effort to develop high-performance thermoelectric materials. Here,
we reveal the nature of the thermopower-enhancing magnetic correlations in the
antiferromagnetic semiconductor MnTe. Using magnetic pair distribution function
analysis of neutron scattering data, we obtain a detailed, real-space view of
robust, nanometer-scale, antiferromagnetic correlations that persist into the
paramagnetic phase above the N\'eel temperature $T_{\mathrm{N}}$ = 307 K. The
magnetic correlation length in the paramagnetic state is significantly longer
along the crystallographic $c$ axis than within the $ab$ plane, pointing to
anisotropic magnetic interactions. Ab initio calculations of the spin-spin
correlations using density functional theory in the disordered local moment
approach reproduce this result with quantitative accuracy. These findings
constitute the first real-space picture of short-range spin correlations in a
magnetically enhanced thermoelectric and inform future efforts to optimize
thermoelectric performance by magnetic means.",2201.05241v1
2022/2/10,"Magnetic excitations in double perovskite iridates La$_{2}$$\mathit{M}$IrO$_{6}$ ($\mathit{M}$ = Co, Ni, and Zn) mediated by 3$\mathit{d}$-5$\mathit{d}$ hybridization","By performing resonant inelastic x-ray scattering (RIXS) measurements at the
Ir $\mathit{L_{\mathrm{3}}}$ edge, we have investigated the low-energy
elementary excitations in a series of double perovskite iridate single
crystals, La$_{2}$$\mathit{M}$IrO$_{6}$ ($\mathit{M}$ = Co, Ni, and Zn). Almost
dispersionless magnetic excitations at $\sim$ 42(6) meV and $\sim$ 35(5) meV
have been observed in crystals containing magnetic 3$\mathit{d}$ ions,
La$_{2}$CoIrO$_{6}$ and La$_{2}$NiIrO$_{6}$, respectively. In contrast, this
low-energy magnetic excitation is absent in La$_{2}$ZnIrO$_{6}$ in which the
3$\mathit{d}$ ions are non-magnetic, suggesting the importance of
3$\mathit{d}$-5$\mathit{d}$ hybridization in the magnetic properties of these
double perovskite iridates. The magnetic excitation is suppressed completely
above the magnetic ordering temperature, suggesting the inadequacy of using a
simple spin Hamiltonian to describe magnetism of these materials.",2202.04803v1
2022/2/17,Consecutive topological phase transitions and colossal magnetoresistance in a magnetic topological semimetal,"The combination of magnetic symmetries and electronic band topology provides
a promising route for realizing topologically nontrivial quasiparticles, and
the manipulation of magnetic structures may enable the switching between
topological phases, with the potential for achieving functional physical
properties. Here, we report measurements of the electrical resistivity of
EuCd$_2$As$_2$ under pressure, which show an intriguing insulating dome at
pressures between $p_{\rm c1}\sim1.0$~GPa and $p_{\rm c2}\sim2.0$~GPa, situated
between two regimes with metallic transport. The insulating state can be fully
suppressed by a small magnetic field, leading to a colossal negative
magnetoresistance on the order of $10^5$\%, accessible via a modest field of
$\sim0.2$~T. First-principles calculations reveal that the dramatic evolution
of the resistivity under pressure is due to consecutive transitions of
EuCd$_2$As$_2$ from a magnetic topological insulator to a trivial insulator,
and then to a Weyl semimetal, with the latter resulting from a pressure-induced
change in the magnetic ground state. Similarly, the colossal magnetoresistance
results from a field-induced polarization of the magnetic moments, transforming
EuCd$_2$As$_2$ from a trivial insulator to a Weyl semimetal. These findings
underscore weak magnetic exchange couplings and spin anisotropy as ingredients
for discovering tunable magnetic topological materials with desirable
functionalities.",2202.08454v1
2022/4/11,Magnetic order and spin liquid behavior in [Mo3+]^{11+} triangular magnets,"Molecular magnets based on [Mo$_3$]$^{11+}$ units with one unpaired electron
per trimer have attracted recent interest due to the identification of quantum
spin liquid candidacy in some family members. Here, we present comprehensive
measurements on polycrystalline samples of ZnScMo$_3$O$_8$, MgScMo$_3$O$_8$,
and Na$_3$Sc$_2$Mo$_5$O$_{16}$ with the same Mo$_3$O$_{13}$ magnetic building
blocks. The crystal structures are characterized with x-ray or neutron powder
diffraction and the magnetic ground states are determined by performing ac and
dc susceptibility, specific heat, neutron powder diffraction, and $\mu$SR
measurements. Our work indicates that ZnScMo$_3$O$_8$ and MgScMo$_3$O$_8$ have
ferromagnetic Curie-Weiss temperatures of 18.5 K and 11.9 K, ordered ground
states with net moments (low-moment ferromagnetism or canted
antiferromagnetism), and zero field ordering temperatures of $T_c =$ 6 K and
$<$ 2 K respectively. On the other hand, Na$_3$Sc$_2$Mo$_5$O$_{16}$ hosts a
dynamical magnetic ground state with no evidence for magnetic ordering or spin
freezing down to 20 mK despite an antiferromagnetic Curie-Weiss temperature of
-36.2 K, and therefore is a candidate for quantum spin liquid behavior. By
comparing the present results to past work on the same family of materials, we
construct a phase diagram which illustrates that the magnetic ground states of
these Mo-based molecular magnets are very sensitive to small changes in the
nearest neighbor Mo-Mo distance.",2204.05377v1
2022/4/25,Antiferromagnetic Spin Orientation and Magnetic Domain Structure in Epitaxially Grown MnN Studied using Optical Second Harmonic Generation,"MnN is a centrosymmetric collinear antiferromagnet belonging to the
transition metal nitride family with a high Neel temperature, a low anisotropy
field, and a large magnetic moment per Mn atom. Despite several recent
experimental and theoretical studies, the spin symmetry (magnetic point group)
and magnetic domain structure of the material remain unknown. In this work, we
use optical second harmonic generation (SHG) to study the magnetic structure of
thin epitaxially-grown single-crystal (001) MnN films. Our work shows that spin
moments in MnN are tilted away from the [001] direction and the components of
the spin moments in the (001) plane are aligned along one of the two possible
in-plane symmetry axes ([100] or [110]) resulting in a magnetic point group
symmetry of 2/m1'. Our work rules out magnetic point group symmetries 4/mmm1'
and mmm1' that have been previously discussed in the literature. Four different
spin domains consistent with the 2/m1' magnetic point group symmetry are
possible in MnN. A statistical model based on the observed variations in the
polarization-dependent intensity of the second harmonic signal collected over
large sample areas puts an upper bound of 0.65 microns on the mean domain size.
Our results show that SHG can be used to probe the magnetic order in metallic
antiferromagnets. This work is expected to contribute to the recent efforts in
using antiferromagnets for spintronic applications.",2204.11741v2
2022/5/28,Magnetic collapse in Fe$_3$Se$_4$ under high pressure,"Electronic structure and magnetic properties of Fe$_3$Se$_4$ are calculated
using the density functional approach. Due to the metallic properties, magnetic
moments of the iron atoms in two nonequivalent positions in the unit cell are
different from ionic values for Fe$^{3+}$ and Fe$^{2+}$ and are equal to
$M_1=2.071 \mu_B$ and $M_2=-2.042 \mu_B$, making the system ferrimagnetic. The
total magnetic moment for the unit cell is $2.135 \mu_B$. Under isotropic
compression, the total magnetic moment decreases non-monotonically and
correlates with the non-monotonic dependence of the density of states at the
Fermi level $N(E_F)$. For 7% compression, the magnetic order changes from the
ferrimagnetic to the ferromagnetic. At 14% compression, the magnetic order
disappears and the total magnetic moment becomes zero, leaving the system in a
paramagnetic state. This compression corresponds to the pressure of 114 GPa.
The magnetic ordering changes faster upon application of an isotropic external
pressure due to the sizeable anisotropy of the chemical bondings in
Fe$_3$Se$_4$. The ferrimagnetic and paramagnetic states occur under pressures
of 5.0 and 8.0 GPa, respectively. The system remains in the metallic state for
all values of compression.",2205.14346v2
2022/6/27,Gate-tunable anomalous Hall effect in stacked van der Waals ferromagnetic insulator - topological insulator heterostructures,"The search of novel topological phases, such as the quantum anomalous Hall
insulator (QAHI) or the axion insulator, has motivated different schemes to
introduce magnetism into topological insulators. One scheme is to introduce
ferromagnetic dopants in topological insulators. However, it is generally
challenging and requires carefully engineered growth/heterostructures or
relatively low temperatures to observe the QAHI due to issues such as the added
disorder with ferromagnetic dopants. Another promising scheme is using the
magnetic proximity effect with a magnetic insulator to magnetize the
topological insulator. Most of these heterostructures are synthesized so far by
growth techniques such as molecular beam epitaxy and metallic organic chemical
vapor deposition. These are not readily applicable to allow mixing and matching
many of the available ferromagnetic and topological insulators due to
difference in growth conditions and lattice mismatch. Here, we demonstrate that
the magnetic proximity effect can still be obtained in stacked heterostructures
assembled via the dry transfer of exfoliated micrometer-sized thin flakes of
van der Waals topological insulator and magnetic insulator materials
(BiSbTeSe2/Cr2Ge2Te6), as evidenced in the observation of an anomalous Hall
effect (AHE). Furthermore, devices made from these heterostructures can allow
modulation of the AHE when controlling the carrier density via electrostatic
gating. These results show that simple mechanical transfer of magnetic van der
Waals materials provides another possible avenue to magnetize topological
insulators by magnetic proximity effect, a key step towards further realization
of novel topological phases such as QAHI and axion insulators.",2206.13045v1
2022/7/14,Attosecond magnetization dynamics in non-magnetic materials driven by intense femtosecond lasers,"Irradiating solids with ultrashort laser pulses is known to initiate
femtosecond timescale magnetization dynamics. However, sub-femtosecond spin
dynamics have not yet been observed or predicted. Here, we explore ultrafast
light-driven spin dynamics in a highly non-resonant strong-field regime.
Through state-of-the-art ab-initio calculations, we predict that a non-magnetic
material can be transiently transformed into a magnetic one via dynamical
extremely nonlinear spin-flipping processes, which occur on attosecond
timescales and are mediated by a combination of multi-photon and spin-orbit
interactions. These are non-perturbative non-resonant analogues to the inverse
Faraday effect that build up from cycle-to-cycle as electrons gain angular
momentum. Remarkably, we show that even for linearly polarized driving, where
one does not intuitively expect any magnetic response, the magnetization
transiently oscillates as the system interacts with light. This oscillating
response is enabled by transverse anomalous light-driven currents in the solid,
and typically occurs on timescales of ~500 attoseconds. We further demonstrate
that the speed of magnetization can be controlled by tuning the laser
wavelength and intensity. An experimental set-up capable of measuring these
dynamics through pump-probe transient absorption spectroscopy is outlined and
simulated. Our results pave the way for new regimes of ultrafast manipulation
of magnetism.",2207.06711v1
2022/7/25,"Creating and controlling Dirac fermions, Weyl fermions, and nodal lines in the magnetic antiperovskite Eu$_3$PbO","The band topology of magnetic semimetals is of interest both from the
fundamental science point of view and with respect to potential spintronics and
memory applications. Unfortunately, only a handful of suitable topological
semimetals with magnetic order have been discovered so far. One such family
that hosts these characteristics is the antiperovskites, A$_3$BO, a family of
3D Dirac semimetals. The A=Eu$^{2+}$ compounds magnetically order with multiple
phases as a function of applied magnetic field. Here, by combining band
structure calculations with neutron diffraction and magnetic measurements, we
establish the antiperovskite Eu$_3$PbO as a new topological magnetic semimetal.
This topological material exhibits a multitude of different topological phases
with ordered Eu moments which can be easily controlled by an external magnetic
field. The topological phase diagram of Eu$_3$PbO includes an antiferromagnetic
Dirac phase, as well as ferro- and ferrimagnetic phases with both Weyl points
and nodal lines. For each of these phases, we determine the bulk band
dispersions, the surface states, and the topological invariants by means of
$\textit{ab-initio}$ and tight-binding calculations. Our discovery of these
topological phases introduces Eu$_3$PbO as a new platform to study and
manipulate the interplay of band topology, magnetism, and transport.",2207.12434v1
2022/7/27,Distinct magnetic gaps between antiferromagnetic and ferromagnetic orders driven by surface defects in the topological magnet MnBi2Te4,"The magnetic topological insulator, MnBi$_2$Te$_4$, shows metallic behavior
at zero magnetic fields (antiferromagnetic phase, AFM) in thin film transport,
which coincides with gapless surface states observed by angle-resolved
photoemission spectroscopy, while it can become a Chern insulator at field
larger than 6 T (ferromagnetic phase, FM). Thus, the zero-field surface
magnetism was once speculated to be different from the bulk AFM phase. However,
recent magnetic force microscopy refutes this assumption by detecting
persistent AFM order on the surface. In this work, we propose a mechanism
related to surface defects that can rationalize these contradicting
observations in different experiments. We find that co-antisites (exchanging Mn
and Bi atoms in the surface van der Waals layer) can strongly suppress the
magnetic gap down to several meV in the AFM phase without violating the
magnetic order but preserve the magnetic gap in the FM phase. The different gap
sizes between AFM and FM phases are caused by the defect-induced surface charge
redistribution among top two van der Waals layers. This theory can be validated
by the position- and field-dependent gap in future surface spectroscopy
measurements. Our work suggests suppressing related defects in samples to
realize the quantum anomalous Hall insulator or axion insulator at zero fields.",2207.13511v1
2022/7/28,Antiferromagnetic order in Co-doped Fe$_5$GeTe$_2$ probed by resonant magnetic x-ray scattering,"The quasi-two-dimensional van der Waals magnet Fe$_{5-\delta}$GeTe$_2$ has
emerged as a promising platform for electronic and spintronic functionalities
at room temperature, owing to its large ferromagnetic ordering temperature
$T_{\text{C}}$ $\sim$ 315 K. Interestingly, by cobalt (Co) substitution of iron
in F5GT, $i.e.$ $({\text{Fe}}_{1-x}{\text{Co}}_x)_{5-\delta}{\text{GeTe}}_2$
(Co-F5GT), not only can its magnetic transition temperature be further
enhanced, but the magnetic and structural ground states can also be tuned.
Specifically, an antiferromagnetic (AFM) order is induced beyond the Co doping
level $x \ge 0.4$. Here, we investigate the magnetic properties of a Co-F5GT
single crystal at $x = 0.45(1)$, by utilizing the element specific, resonant
magnetic x-ray scattering technique. Our study reveals an A-type, Ising-like
AFM ground state, with a transition temperature $T_{\text{N}}$ $\sim$ 340 K. In
addition, our work unveils an important contribution from Co magnetic moments
to the magnetic order. The application of the in-plane magnetic fields
gradually polarize the spin moments along the field direction, but without
inducing incommensurate spin texture(s).",2207.14412v1
2022/8/2,Direct visualization of magnetic correlations in frustrated spinel ZnFe$_2$O$_4$,"Magnetic materials with the spinel structure (A$^{2+}$B$^{3+}_2$O$^4$) form
the core of numerous magnetic devices, but ZnFe$_2$O$_4$ constitutes a peculiar
example where the nature of the magnetism is still unresolved. Susceptibility
measurements revealed a cusp around $T_c=13\;\mathrm{K}$ resembling an
antiferromagnetic transition, despite the positive Curie-Weiss temperature
determined to be $\Theta_{CW}=102.8(1)\;\mathrm{K}$. Bifurcation of
field-cooled and zero-field-cooled data below $T_c$ in conjunction with a
frequency dependence of the peak position and a non-zero imaginary component
below $T_c$ shows it is in fact associated with a spin-glass transition. Highly
structured magnetic diffuse neutron scattering from single crystals develops
between $50\;\mathrm{K}$ and $25\;\mathrm{K}$ revealing the presence of
magnetic disorder which is correlated in nature. Here, the 3D-m$\Delta$PDF
method is used to visualize the local magnetic ordering preferences, and
ferromagnetic nearest-neighbor and antiferromagnetic third nearest-neighbor
correlations are shown to be dominant. Their temperature dependence is
extraordinary with some flipping in sign, and a strongly varying correlation
length. The correlations can be explained by orbital interaction mechanisms for
the magnetic pathways, and a preferred spin cluster. Our study demonstrates the
power of the 3D-m$\Delta$PDF method in visualizing complex quantum phenomena
thereby providing a way to obtain an atomic scale understanding of magnetic
frustration.",2208.01431v1
2022/9/22,Enhancement of charge-neutral fermionic excitation near spin-flop transition\\ in magnetic Kondo material YbIr$_3$Si$_7$,"The new Kondo material YbIr$_3$Si$_7$, similar to other Kondo insulators, has
been reported to exhibit charge-neutral fermionic excitations through
measurements of specific heat and thermal conductivity at low temperatures. We
performed $^{29}$Si-NMR on YbIr$_3$Si$_7$ to investigate the magnetic response
of charge-neutral fermions from a microscopic perspective. In low magnetic
fields parallel to the $c$ axis, a single NMR peak in the paramagnetic state
splits into three peaks below $T_{\rm N}$. In contrast, only a slight shift of
the single NMR peak was observed in high magnetic fields. This spectral change
as a function of the $c$-axis magnetic field is interpreted as spin-flop
transition, at which the magnetic moments oriented along the $c$ axis (AF-I
phase) are rotated to the $ab$ plane with ferromagnetic component along the
$c$-axis (AF-II phase). In the vicinity of the spin-flop magnetic field $H_{\rm
M}$, nuclear spin-lattice relaxation rate $1/T_1$ was found to be proportional
to temperature at low temperatures, indicating the existence of charge-neutral
fermions. Furthermore, a peak of $1/T_1$ vs. the $c$-axis magnetic field
suggests that the charge-neutral fermions in YbIr$_3$Si$_7$ are closely related
to its magnetic properties. Our findings shed light on the origin of
charge-neutral fermions in insulators.",2209.10844v1
2022/11/1,Fermi level dependence of magnetism and magnetotransport in the magnetic topological insulators Bi$_{2}$Te$_{3}$ and BiSbTe$_{3}$ containing self-organized MnBi$_{2}$Te$_{4}$ septuple layers,"The magnetic coupling mechanisms underlying ferromagnetism and
magnetotransport phenomena in magnetically doped topological insulators have
been a central issue to gain controlled access to the magneto-topological
phenomena such as quantum anomalous Hall effect and topological axion
insulating state. Here, we focus on the role of bulk carriers in magnetism of
the family of magnetic topological insulators, in which the host material is
either Bi$_{2}$Te$_{3}$ or BiSbTe$_{3}$, containing Mn self-organized in
MnBi$_{2}$Te$_{4}$ septuple layers. We tune the Fermi level using the electron
irradiation technique and study how magnetic properties vary through the change
in carrier density, the role of the irradiation defects is also discussed.
Ferromagnetic resonance spectroscopy and magnetotransport measurements show no
effect of the Fermi level position on the magnetic anisotropy field and the
Curie temperature, respectively, excluding bulk magnetism based on a
carrier-mediated process. Furthermore, the magnetotransport measurements show
that the anomalous Hall effect is dominated by the intrinsic and
dissipationless Berry-phase driven mechanism, with the Hall resistivity
enhanced near the bottom/top of the conduction/valence band, due to the Berry
curvature which is concentrated near the avoided band crossings. These results
demonstrate that the anomalous Hall effect can be effectively managed,
maximized, or turned off, by adjusting the Fermi level.",2211.00546v5
2022/11/15,Dynamical criticality of spin-shear coupling in van der Waals antiferromagnets,"The interplay between a multitude of electronic, spin, and lattice degrees of
freedom underlies the complex phase diagrams of quantum materials. Layer
stacking in van der Waals (vdW) heterostructures is responsible for exotic
electronic and magnetic properties, which inspires stacking control of
two-dimensional magnetism. Beyond the interplay between stacking order and
interlayer magnetism, we discover a spin-shear coupling mechanism in which a
subtle shear of the atomic layers can have a profound effect on the intralayer
magnetic order in a family of vdW antiferromagnets. Using time-resolved x-ray
diffraction and optical linear dichroism measurements, interlayer shear is
identified as the primary structural degree of freedom that couples with
magnetic order. The recovery times of both shear and magnetic order upon
optical excitation diverge at the magnetic ordering temperature with the same
critical exponent. The time-dependent Ginzburg-Landau theory shows that this
concurrent critical slowing down arises from a linear coupling of the
interlayer shear to the magnetic order, which is dictated by the broken mirror
symmetry intrinsic to the monoclinic stacking. Our results highlight the
importance of interlayer shear in ultrafast control of magnetic order via
spin-mechanical coupling.",2211.08189v1
2023/2/23,First-principles based Monte Carlo modeling of oxygen deficient Fe-substituted SrTiO$_3$ experimental magnetization,"Ferroics based on transition-metal (TM) substituted SrTiO$_{3}$ have called
much attention as magnetism and/or ferroelectricity can be tuned by using
cations substitution and defects, strain and/or oxygen deficiency. C. A. Ross
et al. [Phys. Rev. Applied 7, 024006 (2017)] demonstrated the
SrTi$_{1-x}$Fe$_{x}$O$_{3-\delta}$ (STF) magnetization behavior for different
deposition oxygen-pressures, substrates and magnetic fields. The relation
between oxygen deficiency and ferroic orders is yet to be well understood, for
which the full potential of oxygen-stoichiometry engineered materials remain an
open question. Here, we use hybrid-DFT to calculate different oxygen vacancy
($v_{o}$) states in STF with a variety of TM distributions. The resulting
cations' magnetic states and alignments associated to the $v_{o}$ ground-states
for $x=\{0.125,0.25\}$ are used within a Monte Carlo scope for collinear
magnetism to simulate the spontaneous magnetization. Our model captures several
experimental STF features i.e., display a maximum of the magnetization at
intermediate number of vacancies, a monotonous quenching from
$\sim{0.35}\mu{_{B}}$ for small ${\delta}$, and a slower decreasing of such
saturation for larger number of vacancies. Moreover, our approach gives a
further insight into the relations between defects stabilization and
magnetization, vacancy density and the oxygen pressure required to maximize
such ferroic order, and sets guidelines for future Machine Learning based
computational synthesis of multiferroic oxides.",2302.12174v1
2023/3/20,Magnetic order in 2D antiferromagnets revealed by spontaneous anisotropic magnetostriction,"The temperature dependent order parameter provides important information on
the nature of magnetism. Using traditional methods to study this parameter in
two-dimensional (2D) magnets remains difficult, however, particularly for
insulating antiferromagnetic (AF) compounds. Here, we show that its temperature
dependence in AF MPS$_{3}$ (M(II) = Fe, Co, Ni) can be probed via the
anisotropy in the resonance frequency of rectangular membranes, mediated by a
combination of anisotropic magnetostriction and spontaneous staggered
magnetization. Density functional calculations followed by a derived
orbital-resolved magnetic exchange analysis confirm and unravel the microscopic
origin of this magnetization inducing anistropic strain. We further show that
the temperature and thickness dependent order parameter allows to deduce the
material's critical exponents characterising magnetic order. Nanomechanical
sensing of magnetic order thus provides a future platform to investigate 2D
magnetism down to the single-layer limit.",2303.11234v2
2023/3/28,L1$_0$ FePt thin films with tilted and in-plane magnetic anisotropy: first-principles study,"Ultrathin L1$_0$ films with different $c$-axis orientations relative to the
film plane are promising candidates for data storage materials. In this work,
within the framework of density functional theory, we calculated the magnetic
properties of ultrathin L1$_0$ (111) and (010) films with thicknesses ranging
from 4 to 16 atomic monolayers (from about 0.8 to 3.5~nm). The highest average
magnetic moments are observed for the thinnest films considered, and with
increasing film thickness, the values converge towards the magnetic moment for
bulk. The observed increase comes mainly from enhanced moments in the two
atomic monolayers closest to the surface of the films. The easy axis of
magnetization of (111) films prefers an alignment close to the tetragonal axis,
an example of tilted magnetic anisotropy. The 6-monolayer (111) film (about
1.3~nm thick) inclines the easy axis of magnetization of about 45{\deg} to the
film plane, which can find use in applications. The (010) films show an
in-plane easy magnetization axis in a unique L1$_0$ tetragonal direction. This
is an unusual type of in-plane anisotropy, as the particular direction
preference is very strong. The computational results encourage further
experimental studies of L1$_0$ systems with tilted and in-plane fixed magnetic
anisotropy.",2303.15877v2
2023/5/20,Ba9RE2(SiO4)6 (RE=Ho-Yb): A New Family of Rare-earth based Honeycomb Lattice Magnets,"Rare-earth (RE) based honeycomb-lattice materials with strong spin-orbit
coupled Jeff=1/2 moments have attracted great interest as a platform to realize
Kitaev quantum spin liquid (QSL) state. Herein, we report the discovery of a
new family of RE based honeycomb-lattice magnets Ba9RE2(SiO4)6(RE=Ho-Yb), which
crystallize into the rhombohedral structure with space group R-3. In these
serial compounds, magnetic RE3+ ions are arranged on a perfect honeycomb
lattice within the ab-plane and stacked in the ABCABC-type fashion along the
c-axis. All Ba9RE2(SiO4)6(RE=Ho-Yb) polycrystals exhibit the dominant
antiferromagnetic interactions and absence of magnetic order down to 2 K. In
combination with the magnetization and electron spin resonance (ESR) results,
distinct anisotropic magnetic behaviors are proposed for compounds with
different RE ions. Moreover, the synthesized Ba9Yb2Si6O24 single crystals show
large magnetic frustration and no long-range magnetic ordering down to 0.15 K,
being a possible QSL candidate state. These serial compounds are attractive for
exploring the exotic magnetic phases of Kitaev materials with 4f electrons.",2305.12214v1
2023/7/3,Efficient current-induced spin torques and field-free magnetization switching in a room-temperature van der Waals magnet,"The discovery of magnetism in van der Waals (vdW) materials has established
unique building blocks for the research of emergent spintronic phenomena. In
particular, owing to their intrinsically clean surface without dangling bonds,
the vdW magnets hold the potential to construct a superior interface that
allows for efficient electrical manipulation of magnetism. Despite several
attempts in this direction, it usually requires a cryogenic condition and the
assistance of external magnetic fields, which is detrimental to the real
application. Here, we fabricate heterostructures based on Fe3GaTe2 flakes that
possess room-temperature ferromagnetism with excellent perpendicular magnetic
anisotropy. The current-driven non-reciprocal modulation of coercive fields
reveals a high spin-torque efficiency in the Fe3GaTe2/Pt heterostructures,
which further leads to a full magnetization switching by current. Moreover, we
demonstrate the field-free magnetization switching resulting from out-of-plane
polarized spin currents by asymmetric geometry design. Our work could expedite
the development of efficient vdW spintronic logic, memory and neuromorphic
computing devices.",2307.01329v1
2023/9/20,Magnetic imaging and domain nucleation in CrSBr down to the 2D limit,"Recent advancements in 2D materials have revealed the potential of van der
Waals magnets, and specifically of their magnetic anisotropy that allows
applications down to the 2D limit. Among these materials, CrSBr has emerged as
a promising candidate, because its intriguing magnetic and electronic
properties have appeal for both fundamental and applied research in spintronics
or magnonics. Here, nano SQUID-on-tip (SOT) microscopy is used to obtain direct
magnetic imaging of CrSBr flakes with thicknesses ranging from monolayer (N=1)
to few-layer (N=5). The ferromagnetic order is preserved down to the monolayer,
while the antiferromagnetic coupling of the layers starts from the bilayer
case. For odd layers, at zero applied magnetic field, the stray field resulting
from the uncompensated layer is directly imaged. The progressive spin
reorientation along the out-of-plane direction (hard axis) is also measured
with a finite applied magnetic field, allowing to evaluate the anisotropy
constant, which remains stable down to the monolayer and is close to the bulk
value. Finally, by selecting the applied magnetic field protocol, the formation
of N\'eel magnetic domain walls is observed down to the single layer limit.",2309.11550v1
2023/11/22,Effects of magnetic fields and orbital angular momentum on excitonic condensation in two-orbital Hubbard model,"We investigate the magnetic-field effects on a two-orbital Hubbard model that
describes multiple spin states. Cobalt oxides have been investigated as
materials possessing spin-state degrees of freedom due to the interplay between
the Hund coupling interaction and crystalline field effect. In the competing
region, quantum hybridizations between distinct spin states are expected to
emerge, corresponding to excitonic condensation. Applied magnetic fields could
also induce such a competition. To understand magnetic-field effects on
excitonic condensation in multi-orbital systems, it is crucial to account for
contributions from both spin and orbital degrees of freedom to magnetic
properties. Here, we study field-induced phenomena in the two-orbital Hubbard
model by focusing on the role of the orbital angular momentum. We
comprehensively analyze this model on a square lattice employing the
Hartree-Fock approximation. Omitting contributions from the orbital moment, we
find that an applied magnetic field gives rise to two excitonic phases, besides
the spin-state ordered phase, between the nonmagnetic low-spin and
spin-polarized high-spin phases. One of these excitonic phases manifests a
staggered-type spin-state order, interpreted as an excitonic supersolid state.
Conversely, the other phase is not accompanied by it and exhibits only a spin
polarization due to the applied magnetic field. When spin-orbit coupling is
present, this phase displays a ferrimagnetic spin alignment attributed to spin
anisotropy. Our analysis also reveals that incorporating the contribution of
the orbital magnetic moment to the Zeeman term significantly alters the overall
structure of the phase diagram. Notably, the orbital magnetization destabilizes
the excitonic phase in contrast to scenarios without this contribution. We also
discuss the relevance of our findings to real materials, such as cobalt oxides.",2311.13191v1
2023/11/27,Charge-density wave transition in magnetic topological semimetal EuAl$_4$,"The interplay among topology, charge-density wave (CDW), and magnetism can
give rise to a plethora of exotic quantum phenomena. Recently, a group of
magnetic topological semimetals with tetragonal lattices and CDW order were
found to exhibit anomalous magnetic instability, helical spin ordering, and the
presence of skyrmions. However, the underlying mechanism responsible for these
observations remains unclear. Here, we conducted a comprehensive investigation
into the impact of CDW on the topological and magnetic properties of EuAl$_4$
using optical spectroscopy and the first-principles calculations. Through
optical spectroscopy, we observed a partial gap (60~meV) on the Fermi surface
and an enhanced mid-infrared absorption around 0.4~eV after the CDW transition.
Magneto-optical spectroscopy and the first-principles calculations proved that,
by affecting the band structure, the CDW order frustrates the antiferromagnetic
interactions but strengthened the ferromagnetic ones, which can destabilize the
magnetism. With lower symmetry in the CDW ordered state, carriers from the Weyl
bands will mediate the anisotropic magnetic interactions promoting the
formation of chiral spin textures. Conversely, without the CDW order, the
counterpart EuGa$_4$ shows robust collinear antiferromagnetic order. Our
findings uncover the pivotal role played by CDW order in arousing intricate
magnetism in topological materials and provide valuable insights into
controlling topological and magnetic properties through the manipulation of CDW
orders.",2311.15834v1
2024/2/9,Magnetic field-temperature phase diagram of spin-1/2 triangular lattice antiferromagnet KYbSe$_2$,"A quantum spin liquid (QSL) is a state of matter characterized by
fractionalized quasiparticle excitations, quantum entanglement, and a lack of
long-range magnetic order. However, QSLs have evaded definitive experimental
observation. Several Yb$^{3+}$-based triangular lattice antiferromagnets with
effective $S$ = $\frac{1}{2}$ have been suggested to stabilize the QSL state as
the ground state. Here, we build a comprehensive magnetic temperature phase
diagram of a high-quality single crystalline KYbSe$_2$ via heat capacity and
magnetocaloric effect down to 30 mK with magnetic field applied along the
$a$-axis. At zero magnetic field, we observe the magnetic long-range order at
$T_N$ = 0.29 K entering 120 degrees ordered state in heat capacity, consistent
with neutron scattering studies. Analysis of the low-temperature ($T$) specific
heat ($C$) at zero magnetic field indicates linear $T$-dependence of $C/T$ and
a broad hump of $C/T$ in the proximate QSL region above $T_N$. By applying
magnetic field, we observe the up-up-down phase with 1/3 magnetization plateau
and oblique phases, in addition to two new phases. These observations strongly
indicate that while KYbSe$_2$ closely exhibits characteristics resembling an
ideal triangular lattice, deviations may exist, such as the effect of the
next-nearest-neighbor exchange interaction, calling for careful consideration
for spin Hamiltonian modeling. Further investigations into tuning parameters,
such as chemical pressure, could potentially induce an intriguing QSL phase in
the material.",2402.06788v1
2024/2/21,Multi-step topological transitions among meron and skyrmion crystals in a centrosymmetric magnet,"Topological swirling spin textures, such as skyrmions and merons, have
recently attracted much attention as a unique building block for high-density
magnetic information devices. The controlled transformation among different
types of such quasi-particles is an important challenge, while it was
previously achieved only in a few non-centrosymmetric systems characterized by
Dzyaloshinskii-Moriya interaction. Here, we report an experimental discovery of
multi-step topological transitions among a variety of meron and skyrmion
crystal states in a centrosymmetric magnet GdRu$_2$Ge$_2$. By performing the
detailed magnetic structure analysis based on resonant X-ray and neutron
scattering experiments as well as electron transport measurements, we have
found that this compound hosts periodic lattice of elliptic skyrmions,
meron/anti-meron pairs, and circular skyrmions as a function of external
magnetic field. The diameter of these objects is as small as 2.7 nm, which is
almost two orders of magnitude smaller than typical non-centrosymmetric
magnets. Such an intricate manner of topological magnetic transitions are well
reproduced by a theoretical model considering the competition between RKKY
interactions at inequivalent wave vectors. The present findings demonstrate
that even a simple centrosymmetric magnet with competing interactions can be a
promising material platform to realize a richer variety of nanometric magnetic
quasi-particles with distinctive symmetry and topology, whose stability may be
tunable by various external stimuli.",2402.13751v1
2024/2/22,On the origin of the above-room-temperature magnetism in the 2D van der Waals ferromagnet Fe$_3$GaTe$_2$,"Recent advancements in 2D magnetic materials have attracted a growing
interest driven by their unique properties and potential applications in
spintronic devices. However, the scarcity of systems that exhibit magnetism at
room-temperature has limited their practical implementation into functional
devices. In this work we focus on the recently synthetised van der Waals (vdW)
ferromagnet Fe$_3$GaTe$_2$, which exhibits above-room-temperature magnetism
(T$_{\mathrm{c}}$ = 350-380 K) and strong perpendicular magnetic anisotropy.
Through first-principles calculations, we examine the magnetic properties of
Fe$_3$GaTe$_2$ and compare them with the widely known Fe$_3$GeTe$_2$
ferromagnet. Our calculations unveil the complex microscopic mechanisms
governing their magnetic behaviour, emphasizing the pivotal role of the
ferromagnetic in-plane exchange interactions in the stabilization of the
elevated T$_{\mathrm{c}}$ in Fe$_3$GaTe$_2$. Additionally, we predict the
stability, strong perpendicular anisotropy and high T$_{\mathrm{c}}$ of
single-layer Fe$_3$GaTe$_2$. We also demonstrate the potential of strain
engineering and electrostatic doping to modulate its magnetic exchange
interactions and anisotropy. Our results incentivise the isolation of the
monolayer and pave the way for the future optimization of Fe$_3$GaTe$_2$ in
magnetic and spintronic nanodevices.",2402.14618v1
1998/10/6,Magnetoresistance of Granular Ferromagnets - Observation of a Magnetic Proximity Effect?,"We have observed a superparamagnetic to ferromagnetic transition in films of
isolated Ni grains covered by non-magnetic overlayers. The magnetoresistance
(MR) of the films was measured as a function of the overlayer thickness.
Initially, the granular Ni films exhibited negative MR curves peaked at H=0. As
different materials were deposited onto the grains hysteresis developed in the
MR. This behavior is ascribed to an increase of the typical domain size due to
magnetic coupling between grains. The strength of the inter-grain coupling is
found to correlate with the magnetic susceptibility of the overlayer material.
We discuss possible mechanisms for this coupling and suggest that the data may
reflect the existence of a magnetic proximity effect (analogous to the
well-known effect in superconductivity) in which a ferromagnetic moment is
induced in the metallic non-magnetic medium.",9810061v1
2001/3/29,"Magnetic properties of hexagonal YMnO$_3$, LuMnO$_3$ and ScMnO$_3$ Magnetic susceptibility, specific heat and dielectric constant of hexagonal YMnO_3, LuMnO_3 and ScMnO_3","We report the magnetic susceptibility, specific heat and dielectric constant
on high purity polycrystalline samples of three hexagonal manganites: YMnO_3,
LuMnO_3 and ScMnO_3. These materials can exhibit a ferroelectric transition at
very high temperatures (T_{FE} > 700K). At lower temperatures there is magnetic
ordering of the frustrated Mn^{3+} spins (S=2) on a triangular Mn lattice
(YMnO_3:T_N=71K; LuMnO$_3:T_N=90K and ScMnO_3:T_N=130K). The transition is
characterized by a sharp kink in the magnetic susceptibility at T_N below which
it continues to increase due to the frustration on the triangular lattice. The
specific heat shows one clear continuous phase transition at T_N, which is
independent of external magnetic field up to 9T with an entropy content as
expected for Mn^{3+} ions. The temperature dependent dielectric constant
displays a distinct anomaly at T_N.",0103609v2
2001/11/26,Bound Magnetic Polaron Interactions in Insulating Doped Diluted Magnetic Semiconductors,"The magnetic behavior of insulating doped diluted magnetic semiconductors
(DMS) is characterized by the interaction of large collective spins known as
bound magnetic polarons. Experimental measurements of the susceptibility of
these materials have suggested that the polaron-polaron interaction is
ferromagnetic, in contrast to the antiferromagnetic carrier-carrier
interactions that are characteristic of nonmagnetic semiconductors. To explain
this behavior, a model has been developed in which polarons interact via both
the standard direct carrier-carrier exchange interaction (due to virtual
carrier hopping) and an indirect carrier-ion-carrier exchange interaction (due
to the interactions of polarons with magnetic ions in an interstitial region).
Using a variational procedure, the optimal values of the model parameters were
determined as a function of temperature. At temperatures of interest, the
parameters describing polaron-polaron interactions were found to be nearly
temperature-independent. For reasonable values of these constant parameters, we
find that indirect ferromagnetic interactions can dominate the direct
antiferromagnetic interactions and cause the polarons to align. This result
supports the experimental evidence for ferromagnetism in insulating doped DMS.",0111497v1
2003/9/11,Theory of Current-Induced Magnetization Precession,"We solve appropriate drift-diffusion and Landau-Lifshitz-Gilbert equations to
demonstrate that unpolarized current flow from a non-magnet into a ferromagnet
can produce a precession-type instability of the magnetization. The fundamental
origin of the instability is the difference in conductivity between majority
spins and minority spins in the ferromagnet. This leads to spin accumulation
and spin currents that carry angular momentum across the interface. The
component of this angular momentum perpendicular to the magnetization drives
precessional motion that is opposed by Gilbert damping. Neglecting magnetic
anisotropy and magnetostatics, our approximate analytic and exact numerical
solutions using realistic values for the material parameters show (for both
semi-infinite and thin film geometries) that a linear instability occurs when
both the current density and the excitation wave vector parallel to the
interface are neither too small nor too large. For many aspects of the problem,
the variation of the magnetization in the direction of the current flows makes
an important contribution.",0309289v1
2003/10/16,AC magnetic behavior of large grain magneto-resistive La0.78Ca0.22Mn0.90Ox materials,"We report a detailed set of AC magnetic measurements carried out on bulk
large grain La-Ca-Mn-O samples extracted from a floating zone method-grown rod.
Three samples with $La_{0.78}Ca_{0.22}Mn_{0.90}O_{x}$ stoichiometry but
differing in their microstructure were investigated by electrical resistivity
and AC susceptibility measurements: (i) a single grain sample, (ii) a sample
containing two grains and (iii) a polycrystalline sample. We show that the
superimposition of DC magnetic fields during AC magnetic susceptibility
measurements is an efficient way for characterizing the magnetic transition of
samples with different microstructures. Whereas both single grain and
polycrystalline samples display a single susceptibility peak, an additional
kink structure is observed in the case of the double grain sample. The
temperature dependence of the AC susceptibility measured with superimposed DC
magnetic fields is analyzed in the framework of second-order phase transition
ideas. The relations between the critical exponents ($\beta + \gamma$ ~ 1.5,
$\delta$ ~ 2.5) are found to be close to those of the mean-field model for all
samples. This is attributed to the disordering caused by unoccupied Mn sites.",0310376v1
2004/5/31,Orbital order and ferrimagnetic properties of the new compound $Sr_8 Ca Re_3 Cu_4 O_{24}$,"By means of the LSDA+U method and the Green function method, we investigate
the electronic and magnetic properties of the new material of
Sr$_8$CaRe$_3$Cu$_4$O$_{24}$. Our LSDA+U calculation shows that this system is
an insulator with a net magnetic moment of 1.01 $\mu_{\rm B}$/f.u., which is in
good agreement with the experiment. Magnetic moments are mainly located at Cu
atoms, and the magnetic moments of neighboring Cu sites align anti-parallel. It
is the non-magnetic Re atoms that induce an orbital order of $d$ electrons of
Cu atoms, which is responsible for the strong exchange interaction and the high
magnetic transition temperature. Based on the LSDA+U results, we introduce an
effective model for the spin degrees of freedom, and investigate the
finite-temperature properties by the Green function method. The obtained
results are consistent with the experimental results, indicating that the
spin-alternating Heisenberg model is suitable for this compound.",0405684v1
2004/6/18,Magnetic Superconducting Heterostructures,"Heterogeneous magnetic superconducting systems (HMSS) represent a new class
of nanostructures. They are made of ferromagnetic (FM) and superconducting (SC)
pieces separated by thin layers of insulating oxides. In contrast to the case
of a homogeneous ferromagnetic superconductor studied during the last two
decades, the two order parameters, the magnetization and the SC electron
density do not suppress each other. In HMSS, the interaction between the two
order parameters is due to the magnetic field created by the magnetic and SC
textures. Strong interaction of the FM and SC systems not only gives rise to a
new class of novel phenomena and physical effects, but also shows the important
technological promise of devices whose transport properties can be easily tuned
by comparatively weak magnetic fields.",0406443v1
2004/9/3,Films of Mn12-acetate deposited by low-energy laser ablation,"Thin films of the molecular magnet Mn12-acetate, [Mn12 O12(CH3COO)16 (H2O)4]
2CH3COOH 4H2O, have been prepared using a laser ablation technique with a
nitrogen laser at low laser energies of 0.8 and 2 mJ. Chemical and magnetic
characterizations show that the Mn12-acetate cores remain intact and the films
show similar magnetic properties to those of the parent molecular starting
material. In addition, the magnetic data exhibit a peak in the magnetization at
27 K indicating the creation of an additional magnetic phase not noted in
previous studies of crystalline phases.",0409086v1
2004/12/21,GaN:Gd: A superdilute ferromagnetic semiconductor with a Curie temperature above 300 K,"We investigate the magnetic and magneto-optic properties of epitaxial GaN:Gd
layers as a function of the external magnetic field and temperature. An
unprecedented magnetic moment is observed in this diluted magnetic
semiconductor. The average value of the moment per Gd atom is found to be as
high as 4000 \mub as compared to its atomic moment of 8 \mub. The long-range
spin-polarization of the GaN matrix by Gd is also reflected in the circular
polarization of magneto-photoluminescence measurements. Moreover, the materials
system is found to be ferromagnetic above room temperature in the entire
concentration range under investigation (7$\times10^{15}$ to 2$\times10^{19}$
cm$^{-3}$). We propose a phenomenological model to understand the macroscopic
magnetic behavior of the system. Our study reveals a close connection between
the observed ferromagnetism and the colossal magnetic moment of Gd.",0412564v2
2005/1/28,Finite-temperature Simulations for Magnetic Nanostructures,"We examine different models and methods for studying finite-temperature
magnetic hysteresis in nanoparticles and ultrathin films. This includes
micromagnetic results for the hysteresis of a single magnetic nanoparticle
which is misaligned with respect to the magnetic field. We present results from
both a representation of the particle as a one-dimensional array of magnetic
rotors, and from full micromagnetic simulations. The results are compared with
the Stoner-Wohlfarth model. Results of kinetic Monte Carlo simulations of
ultrathin films are also presented. In addition, we discuss other topics of
current interest in the modeling of magnetic hysteresis in nanostructures,
including kinetic Monte Carlo simulations of dynamic phase transitions and
First-Order Reversal Curves.",0501692v2
2005/7/5,Suppressed magnetization in La$_{0.7}$Ca$_{0.3}$MnO$_3$/YBa$_2$Cu$_3$O$_{7-δ}$ superlattices,"We studied the magnetic properties of La$_{0.7}$Ca$_{0.3}$MnO$_3$ /
YBa$_2$Cu$_3$O$_{7-\delta}$ superlattices. Magnetometry showed that with
increasing YBa$_2$Cu$_3$O$_{7-\delta}$ layer thickness the saturation
magnetization per La$_{0.7}$Ca$_{0.3}$MnO$_3$ layer decreases. From polarized
neutron reflectometry we determined that this magnetization reduction is due to
an inhomogenous magnetization depth profile arising from the suppression of
magnetization near the La$_{0.7}$Ca$_{0.3}$MnO$_3$ /
YBa$_2$Cu$_3$O$_{7-\delta}$ interface. Electron energy loss spectroscopy
indicates an increased 3d band occupation of the Mn atoms in the
La$_{0.7}$Ca$_{0.3}$MnO$_3$ layers at the interface. Thus, the suppression of
ferromagnetic order at the La$_{0.7}$Ca$_{0.3}$MnO$_3$ /
YBa$_2$Cu$_3$O$_{7-\delta}$ interface is most likely due to charge transfer
between the two materials.",0507123v2
2005/9/8,Frustration effects in magnetic molecules,"Besides being a fascinating class of new materials, magnetic molecules
provide the opportunity to study concepts of condensed matter physics in zero
dimensions. This contribution will exemplify the impact of molecular magnetism
on concepts of frustrated spin systems. We will discuss spin rings and the
unexpected rules that govern their low-energy behavior. Rotational bands, which
are experimentally observed in various molecular magnets, provide a useful,
simplified framework for characterizing the energy spectrum, but there are also
deviations thereof with far-reaching consequences. It will be shown that
localized independent magnons on certain frustrated spin systems lead to giant
magnetization jumps, a new macroscopic quantum effect. In addition a
frustration-induced metamagnetic phase transitions will be discussed, which
demonstrates that hysteresis can exist without anisotropy. Finally, it is
demonstrated that frustrated magnetic molecules could give rise to an enhanced
magnetocaloric effect.",0509204v1
2006/4/28,High and low-temperature crystal and magnetic structures of epsilon-Fe2O3 and their correlation to its magnetic properties,"The crystal and magnetic structures of the orthorhombic e-Fe2O3 have been
studied by simultaneous Rietveld refinement of X-ray and neutron powder
diffraction data in combination with Mossbauer spectroscopy, as well as
magnetisation and heat capacity measurements. It has been found that above 150
K the e-Fe2O3 polymorph is a collinear ferrimagnet with the magnetic moments
directed along the a axis, while the magnetic ordering below 80 K is
characterised by a square-wave incommensurate structure. The transformation
between these two states is a second order phase transition and involves subtle
structural changes mostly affecting the coordination of the tetrahedral and one
of the octahedral Fe sites. The temperature dependence of the e-Fe2O3 magnetic
properties is discussed in the light of these results.",0604677v1
2006/7/8,Magnetic Magnetoelectric and Magnetoelastic Properties of new multiferroic material NdFe3(BO3)4,"Complex experimental and theoretical study of the magnetic, magnetoelectric,
and magnetoelastic properties of neodymium iron borate NdFe3(BO3)4 along
various crystallographic directions have been carried out in strong pulsed
magnetic fields up to 230 kOe in a temperature range of 4.2-50 K. It has been
found that neodymium iron borate, as well as gadolinium iron borate, is a
multiferroic. It has much larger (above 3 10^(-4) C/m^2) electric polarization
controlled by the magnetic field and giant quadratic magnetoelectric effect.
The exchange field between the rare-earth and iron subsystems (~50 kOe) has
been determined for the first time from experimental data. The theoretical
analysis based on the magnetic symmetry and quantum properties of the Nd ion in
the crystal provides an explanation of an unusual behavior of the
magnetoelectric and magnetoelastic properties of neodymium iron borate in
strong magnetic fields and correlation observed between them.",0607217v1
2006/7/18,Magnetic properties of Fe/Dy multilayers: a Monte Carlo investigation,"We investigate the magnetic properties of a Heisenberg ferrimagnetic
multilayer by using Monte Carlo simulations. The aim of this work is to study
the local structural anisotropy model which is a possible origin of the
perpendicular magnetic anisotropy in transition metal/rare earth amorphous
multilayers. We have considered a face centered cubic lattice where each site
is occupied by a classical Heisenberg spin. We have introduced in our model of
amorphous multilayers a small fraction of crystallized Fe-Dy nanoclusters with
a mean anisotropy axis along the deposition direction. We show that a
competition in the energy terms takes place between the mean uniaxial
anisotropy of the Dy atoms in the nanoclusters and the random anisotropy of the
Dy atoms in the matrix.",0607437v1
2006/7/19,Magnetic-field dependence of valley splitting for Si quantum wells grown on tilted SiGe substrates,"The valley splitting of the first few Landau levels is calculated as a
function of the magnetic field for electrons confined in a strained silicon
quantum well grown on a tilted SiGe substrate, using a parameterized
tight-binding method. For a zero substrate tilt angle, the valley splitting
slightly decreases with increasing magnetic field. In contrast, the valley
splitting for a finite substrate tilt angle exhibits a strong and
non-monotonous dependence on the magnetic field strength. The valley splitting
of the first Landau level shows an exponential increase followed by a slow
saturation as the magnetic field strength increases. The valley splitting of
the second and third Landau levels shows an oscillatory behavior. The
non-monotonous dependence is explained by the phase variation of the Landau
level wave function along the washboard-like interface between the tilted
quantum well and the buffer material. The phase variation is the direct
consequence of the misorientation between the crystal axis and the confinement
direction of the quantum well. This result suggests that the magnitude of the
valley splitting can be tuned by controlling the Landau-level filling factor
through the magnetic field and the doping concentration.",0607462v1
2006/11/17,Electronic structure of half-metallic magnets,"We have analyzed the electronic structure of half-metallic magnets based on
first principles electronic structure calculations of a series of semi-Heusler
alloys. The characteristic feature of the electronic structure of semi-Heusler
systems is a d-d gap in the density of states lying at/close to the Fermi level
depending on the number of valence electrons. We have employed various
indicators of chemical bonding to understand the origin of the gap in these
systems, which is crucial for their half-metallic property. The density of
states of other half-metallic magnets also supports a gap and it is a generic
feature of these systems. We have discussed in some details the origin of
magnetism, in particular, how the presence of the gap is crucial to stabilize
half-metallic ferro and ferri magnetism in these systems. Finally, we have
studied the role of magnetic impurities in semiconducting semi-Heusler systems.
We show with the aid of model supercell calculations that these systems are not
only ferromagnetic but also half-metallic with possibly high Curie temperature.",0611476v1
2007/9/26,Influence of Zeeman splitting and thermally excited polaron states on magneto-electrical and magneto-thermal properties of magnetoresistive polycrystalline manganite La_{0.8}Sr_{0.2}MnO_3,"Some possible connection between spin and charge degrees of freedom in
magneto-resistive manganites is investigated through a thorough experimental
study of the magnetic (AC susceptibility and DC magnetization) and transport
(resistivity and thermal conductivity) properties. Measurements are reported in
the case of well characterized polycrystalline La_{0.8}Sr_{0.2}MnO_3 samples.
The experimental results suggest rather strong field-induced polarization
effects in our material, clearly indicating the presence of ordered FM regions
inside the semiconducting phase. Using an analytical expression which fits the
spontaneous DC magnetization, the temperature and magnetic field dependences of
both electrical resistivity and thermal conductivity data are found to be well
reproduced through a universal scenario based on two mechanisms: (i) a
magnetization dependent spin polaron hopping influenced by a Zeeman splitting
effect, and (ii) properly defined thermally excited polaron states which have
to be taken into account in order to correctly describe the behavior of the
less conducting region. Using the experimentally found values of the magnetic
and electron localization temperatures, we obtain L=0.5nm and m_p=3.2m_e for
estimates of the localization length (size of the spin polaron) and effective
polaron mass, respectively.",0709.4210v1
2008/2/12,Localized Magnetic States in Graphene,"We examine the conditions necessary for the presence of localized magnetic
moments on adatoms with inner shell electrons in graphene. We show that the low
density of states at the Dirac point, and the anomalous broadening of the
adatom electronic level,lead to the formation of magnetic moments for
arbitrarily small local charging energy. As a result, we obtain an anomalous
scaling of the boundary separating magnetic and non-magnetic states. We show
that, unlike any other material, the formation of magnetic moments can be
controlled by an electric field effect.",0802.1711v3
2008/2/20,Small angle neutron scattering study of the step-like magnetic transformation in Pr0.70Ca0.30MnO3,"Small angle neutron scattering (SANS) magnetic and electrical transport
measurements were performed to study a single crystal of Pr0.7Ca0.3MnO3, a
colossal magnetoresistive (CMR) material. While the magnetic field induced
transformation of this phase separated compound consisting of an
antiferromagnetic insulating phase (AFI) and a ferromagnetic insulating phase
(FI), is continuous at high temperature (above 5K), at lower temperature a step
like transformation is observed (around 5T at 2K). Macroscopic magnetization
measurements and SANS indicate that this transformation occurs by the formation
of mesoscopic ferromagnetic metallic (FM) domains in the AFI phase, and,
eventually, in the FI phase. Although above 5K this transformation is
continuous, below 5K a magnetization step marks the abrupt transition from a
large scale FI/AFI phase separation to a large scale phase separation between
AFI, FI and FM phases. Our results suggest that relaxation of elastic strains
inherent to the coexistence of these different phases plays a crucial role in
the mechanism of these transformations. The occurrence of magnetization steps
could result from an intrinsic behavior of the AFI phase at low temperature.",0802.2883v1
2008/6/3,Electric-field switchable magnetization via the Dzyaloshinskii-Moriya interaction: FeTiO_3 versus BiFeO_3,"In this article we review and discuss a mechanism for coupling between
electric polarization and magnetization that can ultimately lead to
electric-field switchable magnetization. The basic idea is that a ferroelectric
distortion in an antiferromagnetic material can ""switch on"" the
Dzyaloshinskii-Moriya interaction which leads to a canting of the
antiferromagnetic sublattice magnetizations, and thus to a net magnetization.
This magnetization M is coupled to the polarization P via a trilinear free
energy contribution of the form P(M x L), where L is the antiferromagnetic
order parameter. In particular, we discuss why such an invariant is present in
R3c FeTiO_3 but not in the isostructural multiferroic BiFeO_3. Finally, we
construct symmetry groups that in general allow for this kind of
ferroelectrically-induced weak ferromagnetism.",0806.0589v1
2009/3/13,Half-metallic ferrimagnetism in the [Sc$_{1-x}$V$_x$]C and [Sc$_{1-x} $V$_x$]Si alloys adopting the zinc-blende and wurtzite structures from first-principles,"Employing first-principles calculations we study the structural, electronic
and magnetic properties of the [Sc$_{1-x}$V$_x$]C and [Sc$_{1-x}$V$_x$]Si
alloys. In their equilibrium rocksalt structure all alloys are non-magnetic.
The zincblende and wurtzite structures are degenerated with respect to the
total energy. For all concentrations the alloys in these lattice structures are
half-metallic with the gap located in the spin-down band. The total spin moment
follows the Slater-Pauling behavior varying linearly between the -1 $\mu_B$ of
the perfect ScC and ScSi alloys and the +1 $\mu_B$ of the perfect VC and VSi
alloys. For the intermediate concentrations V and Sc atoms have antiparallel
spin magnetic moments and the compounds are half-metallic ferrimagnets. At the
critical concentration, both [Sc$_{0.5}$V$_{0.5}$]C and [Sc$_{0.5}$V$_{0.5}$]Si
alloys present zero total spin-magnetic moment but the C-based alloy shows a
semiconducting behavior contrary to the Si-based alloys which is a
half-metallic antiferromagnet.",0903.2331v1
2009/3/31,Giant Antiferromagnetically Coupled Moments in a Molecule-Based Magnet with Interpenetrating Lattices,"The molecule-based magnet [Ru$_2$(O$_2$CMe)$_4$]$_3$[Cr(CN)$_6$] contains two
weakly-coupled, interpenetrating sublattices in a body-centered cubic
structure. Although the field-dependent magnetization indicates a metamagnetic
transition from an antiferromagnet to a paramagnet, the hysteresis loop also
exhibits a substantial magnetic remanance and coercive field uncharacteristic
of a typical metamagnet. We demonstrate that this material behaves like two
giant moments with a weak antiferromagnetic coupling and a large energy barrier
between the orientations of each moment. Because the sublattice moments only
weakly depend on field in the transition region, the magnetic correlation
length can be directly estimated from the magnetization.",0904.0015v2
2009/4/10,Prediction of electrically-induced magnetic reconstruction at the manganite/ferroelectric interface,"The control of magnetization via the application of an electric field, known
as magnetoelectric coupling, is among the most fascinating and active research
areas today. In addition to fundamental scientific interest, magnetoelectric
effects may lead to new device concepts for data storage and processing. There
are several known mechanisms for magnetoelectric coupling that include
intrinsic effects in single-phase materials, strain induced coupling in
two-phase composites, and electronically-driven effects at interfaces. Here we
explore a different type of magnetoelectric effect at a
ferromagnetic-ferroelectric interface: magnetic reconstruction induced by
switching of electric polarization. We demonstrate this effect using
first-principles calculations of a La1-xAxMnO3/BaTiO3 (001) interface, where A
is a divalent cation. By choosing the doping level x to be near a transition
between magnetic phases we show that the reversal of the ferroelectric
polarization of BaTiO3 leads to a change in the magnetic order at the interface
from ferromagnetic to antiferromagnetic. This predicted electrically-induced
magnetic reconstruction at the interface represents a substantial interfacial
magnetoelectric effect.",0904.1726v4
2009/5/20,Distorted magnetic orders and electronic structures of tetragonal FeSe from first-principles,"We use the state-of-the-arts density-functional-theory method to study
various magnetic orders and their effects on the electronic structures of the
FeSe. Our calculated results show that, for the spins of the single Fe layer,
the striped antiferromagnetic orders with distortion are more favorable in
total energy than the checkerboard antiferromagnetic orders with tetragonal
symmetry, which is consistent with known experimental data, and the inter-layer
magnetic interaction is very weak. We investigate the electronic structures and
magnetic property of the distorted phases. We also present our calculated spin
coupling constants and discuss the reduction of the Fe magnetic moment by
quantum many-body effects. These results are useful to understand the
structural, magnetic, and electronic properties of FeSe, and may have some
helpful implications to other FeAs-based materials.",0905.3300v1
2009/6/8,Tunable magnetic properties of arrays of Fe(110) nanowires grown on kinetically-grooved W(110) self-organized templates,"We report a detailed magnetic study of a new type of self-organized nanowires
disclosed briefly previously [B. Borca et al., Appl. Phys. Lett. 90, 142507
(2007)]. The templates, prepared on sapphire wafers in a kinetically-limited
regime, consist of uniaxially-grooved W(110) surfaces, with a lateral period
here tuned to 15nm. Fe deposition leads to the formation of (110) 7 nm-wide
wires located at the bottom of the grooves. The effect of capping layers (Mo,
Pd, Au, Al) and underlayers (Mo, W) on the magnetic anisotropy of the wires was
studied. Significant discrepancies with figures known for thin flat films are
evidenced and discussed in terms of step anisotropy and strain-dependent
surface anisotropy. Demagnetizing coeffcients of cylinders with a triangular
isosceles cross-section have also been calculated, to estimate the contribution
of dipolar anisotropy. Finally, the dependence of magnetic anisotropy with the
interface element was used to tune the blocking temperature of the wires, here
from 50K to 200 K.",0906.1510v1
2009/6/18,Intrinsic exchange bias in Zn$_x$Mn$_{3-x}$O$_4$ ($x \leq 1$) solid solutions,"Bulk specimens of the hetaerolite solid solution Zn$_x$Mn$_{3-x}$O$_4$, with
$x$ = 0, 0.25, 0.5, 0.75, and 1 have been prepared as homogeneous, phase-pure
polycrystalline samples as ascertained by neutron diffraction measurements.
Samples with $x$ = 0.25, 0.5, and 0.75 exhibit shifted magnetic hysteresis
loops at low temperature, characteristic of exchange bias typically seen in
magnetic composites. We propose that the unusual magnetic behavior arises as a
result of a nanoscale mixture of ferrimagnetic and antiferromagnetic regions
that are distinct but lack long-range order. While some glassy behavior is seen
in AC magnetic measurements, its magnitude is not sufficient to account for the
observed dramatic exchange bias. Furthermore, isothermal and thermoremanent
magnetization measurements distinguish this material from a pure spin glass.
The title system offers insights into the alloying of a ferrimagnet Mn$_3$O$_4$
with an antiferromagnet ZnMn$_2$O$_4$ wherein distinct magnetic clusters grow
and percolate to produce a smooth transition between competing orders.",0906.3534v2
2009/8/27,"A low field technique for measuring magnetic and magneto-resistance anisotropy coefficients applied to (Ga,Mn)As","We demonstrate a simple, low cost, magneto-transport method for rapidly
characterizing the magnetic anisotropy and anisotropic magneto-resistance (AMR)
of ferromagnetic devices with uniaxial magnetic anisotropy. This transport
technique is the analogue of magnetic susceptibility measurements of bulk
material but is applicable to very small samples with low total moment. The
technique is used to characterize devices fabricated from the dilute magnetic
semiconductor (Ga,Mn)As. The technique allows us to probe the behavior of the
parameters close to the Curie temperature, in the limit of the applied magnetic
field tending to zero. This avoids the complications arising from the presence
of paramagnetism.",0908.3960v1
2009/11/30,Kondo-like behaviors in magnetic and thermal properties of single crystal Tm5Si2Ge2,"We grew the single crystal of stoichiometric Tm5Si2.0Ge2.0 using a Bridgeman
method and performed XRD, EDS, magnetization, ac and dc magnetic
susceptibilities, specific heat, electrical resistivity and XPS experiments. It
crystallizes in orthorhombic Sm5Ge4-type structure. The mean valence of Tm ions
in Tm5Si2.0Ge2.0 is almost trivalent. The 4f states is split by the crystalline
electric field. The ground state exhibits the long range antiferromagnetic
order with the ferromagnetically coupled magnetic moments in the ac plane below
8.01 K, while the exited states exhibit the reduction of magnetic moment and
magnetic entropy and -log T-behaviors observed in Kondo materials.",0911.5640v1
2010/6/4,Magnetization dynamics of a CrO$_2$ grain studied by micro-Hall magnetometry,"Micro-Hall magnetometry is employed to study the magnetization dynamics of a
single, micron-size CrO$_2$ grain. With this technique we track the motion of a
single domain wall, which allows us to probe the distribution of imperfections
throughout the material. An external magnetic field along the grain's easy
magnetization direction induces magnetization reversal, giving rise to a series
of sharp jumps in magnetization. Supported by micromagnetic simulations, we
identify the transition to a state with a single cross-tie domain wall, where
pinning/depinning of the wall results in stochastic Barkhausen jumps.",1006.0889v1
2010/8/31,Intrinsic magnetism at silicon surfaces,"It has been a long-standing goal to create magnetism in a nonmagnetic
material by manipulating its structure at the nanometer scale. This idea may be
realized in graphitic carbon: evidence suggests magnetic states at the edges of
graphene ribbons and at grain boundaries in graphite. Such phenomena have long
been regarded as unlikely in silicon because there is no graphitic bulk phase.
Here we show theoretically that intrinsic magnetism indeed exists in a class of
silicon surfaces whose step edges have a nanoscale graphitic structure. This
magnetism is intimately connected to recent observations, including the
coexistence of double- and triple-period distortions and the absence of edge
states in photoemission. Magnetism in silicon may ultimately provide a path
toward spin-based logic and storage at the atomic level.",1008.5358v1
2010/10/20,Unconventional magnetization processes and thermal runaway in spin-ice Dy$_2$Ti$_2$O$_7$,"We investigate the non-equilibrium behavior of the spin-ice material
Dy$_2$Ti$_2$O$_7$ by studying its magnetization as a function of the rate at
which an external field is swept. At temperatures below the enigmatic
""freezing"" temperature $T_{\rm equil}\approx600$ mK, we find that even the
slowest sweeps fail to yield the equilibrium magnetization curve and instead
give a smooth, initially much flatter curve. For higher sweep rates, the
magnetization develops sharp steps accompanied by similarly sharp peaks in the
temperature of the sample. We ascribe the former behavior to the energy
barriers encountered in the magnetization process, which proceeds via flipping
of spins on filaments traced out by the field-driven motion of the gapped,
long-range interacting magnetic monopole excitations. In contrast, the peaks in
temperature result from the released Zeeman energy not being carried away
efficiently into the bath, with the resulting heating triggering a chain
reaction.",1010.4143v1
2010/12/6,Multi-step approach to microscopic models for frustrated quantum magnets - the case of the natural mineral azurite,"The natural mineral azurite Cu$_3$(CO$_3$)$_2$(OH)$_2$ is a frustrated magnet
displaying unusual and controversially discussed magnetic behavior. Motivated
by the lack of a unified description for this system, we perform a theoretical
study based on density functional theory as well as state-of-the-art numerical
many-body calculations. We propose an effective generalized spin-1/2 diamond
chain model which provides a consistent description of experiments:
low-temperature magnetization, inelastic neutron scattering, nuclear magnetic
resonance measurements, magnetic susceptibility as well as new specific heat
measurements. With this study we demonstrate that the balanced combination of
first principles with powerful many-body methods successfully describes the
behavior of this frustrated material.",1012.1090v2
2011/3/23,Numerical Simulation of Magnetic Interactions in Polycrystalline YFeO3,"The magnetic behavior of polycrystalline yttrium orthoferrite was studied
from the experimental and theoretical points of view. Magnetization
measurements up to 170 kOe were carried out on a single-phase YFeO3 sample
synthesized from heterobimetallic alkoxides. The complex interplay between
weak-ferromagnetic and antiferromagnetic interactions, observed in the
experimental M(H) curves, was successfully simulated by locally minimizing the
magnetic energy of two interacting Fe sublattices. The resulting values of
exchange field (H_E = 5590 kOe), anisotropy field (H_A = 0.5 kOe) and
Dzyaloshinsky-Moriya antisymmetric field (H_D = 149 kOe) are in good agreement
with previous reports on this system.",1103.4462v1
2011/7/2,A General Relation Between Real and Imaginary Parts of the Magnetic Susceptibility,"This paper is devoted to the study and the obtaining of the general relation
between the real part and the imaginary part of the magnetic susceptibility
function in the Laplace domain.
  This new theoretical technique is general, and can be applied to any magnetic
material, that can be considered like causal and Linear time invariant (LTI).
  A discussion of the causality which is extensively used in Physics has been
done. To obtain the relations, some important concepts like Titchmarsh's
theorem and Cauchy's Theorem have been reviewed, which results in the integral
of a analytic function, that is formed with the magnetic susceptibility used in
the Laplace domain.
  The Cauchy Integral expression in the Laplace domain under certain conditions
leads to a general relations between real and imaginary part of the magnetic
susceptibility in the complex \textit{s}-plane. These new relationships allow
the validation of the magnetic susceptibilility functions developed by
different researchers, in the Laplace domain, not just the frequency response
like the well known Kramers-Kronig relations. Under certain conditions in these
new general relations, the well known K-K relations can be obtained as a
particular case.",1107.0419v1
2011/7/5,Hidden spin liquid in an antiferromagnet: Applications to FeCrAs,"The recently studied material FeCrAs exhibits a surprising combination of
experimental signatures, with metallic, Fermi liquid like specific heat but
resistivity showing strong non-metallic character. The Cr sublattice posseses
local magnetic moments, in the form of stacked (distorted) Kagome lattices.
Despite the high degree of magnetic frustration, anti-ferromagnetic order
develops below ~125K suggesting the non-magnetic Fe sublattice may play a role
in stabilizing the ordering. From the material properties we propose a
microscopic Hamiltonian for the low energy degrees of freedom, including the
non-magnetic Fe sublattice, and study its properties using slave-rotor mean
field theory. Using this approach we find a spin liquid phase on the Fe
sublattice, which survives even in the presence of the magnetic Cr sublattice.
Finally, we suggest that the features of FeCrAs can be qualitatively explained
by critical fluctuations in the non-magnetic sublattice Fe due to proximity to
a metal-insulator transition.",1107.1002v1
2011/9/11,Mössbauer study of the field induced uniaxial anisotropy in electro-deposited FeCo alloy films,"Thin ferromagnetic films with in-plane magnetic anisotropy are promising
materials for obtaining high microwave permeability. The paper reports on the
M\""ossbauer study of the field induced in-plane uniaxial anisotropy in
electro-deposited $FeCo$ alloy films. The $FeCo$ alloy films have been prepared
by electro-deposition method with and without external magnetic field applied
parallel to the film plane during deposition. The vibrating sample magnetometry
and M\""ossbauer spectroscopy measurements at room temperature indicate that the
film deposited in external field shows an in-plane uniaxial anisotropy with an
easy direction coincides with the external field direction and a hard direction
perpendicular to the field direction, whereas the film deposited without
external field doesn't show any in-plane anisotropy. M\""ossbauer spectra taken
in three geometric arrangements show that the magnetic moments are almost
constrained in the film plane for the film deposited with applied magnetic
field. And the magnetic moments are tend to align in the direction of the
applied external magnetic field during deposition, indicating that the observed
anisotropy should be attributed to directional ordering of atomic pairs.",1109.2286v1
2011/12/8,Wannier-based calculation of the orbital magnetization in crystals,"We present a first-principles scheme that allows the orbital magnetization of
a magnetic crystal to be evaluated accurately and efficiently even in the
presence of complex Fermi surfaces. Starting from an initial
electronic-structure calculation with a coarse ab initio k-point mesh,
maximally localized Wannier functions are constructed and used to interpolate
the necessary k-space quantities on a fine mesh, in parallel to a
previously-developed formalism for the anomalous Hall conductivity [X.Wang, J.
Yates, I. Souza, and D. Vanderbilt, Phys. Rev. B 74, 195118 (2006)]. We
formulate our new approach in a manifestly gauge-invariant manner, expressing
the orbital magnetization in terms of traces over matrices in Wannier space.
Since only a few (e.g., of the order of 20) Wannier functions are typically
needed to describe the occupied and partially occupied bands, these Wannier
matrices are small, which makes the interpolation itself very efficient. The
method has been used to calculate the orbital magnetization of bcc Fe, hcp Co,
and fcc Ni. Unlike an approximate calculation based on integrating orbital
currents inside atomic spheres, our results nicely reproduce the experimentally
measured ordering of the orbital magnetization in these three materials.",1112.1938v1
2011/12/14,Magnetic moment of an electron near a surface with dispersion,"Boundary-dependent radiative corrections that modify the magnetic moment of
an electron near a dielectric or conducting surface are investigated.
Normal-mode quantization of the electromagnetic field and perturbation theory
applied to the Dirac equation for a charged particle in a weak magnetic field
yields a general formula for the magnetic moment correction in terms of any
choice of electromagnetic mode functions. For two particular models, a
non-dispersive dielectric and an undamped plasma, it is shown that, by using
contour integration techniques over a complex wave vector, this can be
simplified to a formula featuring just integrals over TE and TM reflection
coefficients of the surface. Analysing the magnetic moment correction for
several models of surfaces, we obtain markedly different results from the
previously considered simplistic `perfect reflector' model, which is due to the
inclusion of physically important features of the surface like evanescent field
modes and dispersion in the material. Remarkably, for a general dispersive
dielectric surface, the magnetic moment correction of an electron nearby has a
peak whose position and height can be tuned by choice of material parameters.",1112.3224v2
2012/3/5,A dynamical magnetosphere model for periodic Halpha emission from the slowly rotating magnetic O star HD191612,"The magnetic O-star HD191612 exhibits strongly variable, cyclic Balmer line
emission on a 538-day period. We show here that its variable Halpha emission
can be well reproduced by the rotational phase variation of synthetic spectra
computed directly from full radiation magneto-hydrodynamical simulations of a
magnetically confined wind. In slow rotators such as HD191612, wind material on
closed magnetic field loops falls back to the star, but the transient
suspension of material within the loops leads to a statistically overdense, low
velocity region around the magnetic equator, causing the spectral variations.
We contrast such ""dynamical magnetospheres"" (DMs) with the more steady-state
""centrifugal magnetospheres"" of stars with rapid rotation, and discuss the
prospects of using this DM paradigm to explain periodic line emission from also
other non-rapidly rotating magnetic massive stars.",1203.1050v1
2012/3/21,High-field magnetization and magnetoresistance of the $A$-site ordered perovskite oxide CaCu$_{3}$Ti$_{4-x}$Ru$_{x}$O$_{12}$~($0 \le x \le 4$),"We have measured high-field magnetization and magnetoresistance of
polycrystalline samples of the A-site ordered perovskite CaCu3Ti4-xRuxO12 (x=0
- 4) utilizing a non-destructive pulsed magnet. We find that the magnetization
for x=0.5, 1.0 and 1.5 is nonlinear, and tends to saturate in high fields. This
is highly nontrivial because the magnetization for x=0 and 4 is linear in
external field up to the highest one. We have analyzed this field dependence
based on the thermodynamics of magnetic materials, and propose that the
external fields delocalize the holes on the Cu2+ ions in order to maximize the
entropy. This scenario is qualitatively consistent with a large
magnetoresistance of -70% observed at 4.2 K at 52 T for x=1.5.",1203.4660v1
2012/6/7,Observation of different spin behavior with temperature variation and Cr substitution in a multiferroic compound YMn$_2$O$_5$,"In this article, the collective response of the spins is explored through low
field bulk magnetic measurement for the series YMn$_{2-x}$Cr$_x$O$_5$ (x= 0.0,
0.05). Low field ac susceptibility and dc magnetization of YMn$_2$O$_5$ shows
multiple transition in analogy to those observed in electrical measurement of
the compound. Using various time dependent magnetization protocols it has been
observed that the behavior of spins in commensurate and incommensurate phase
are drastically different. YMn$_{1.95}$Cr$_{0.05}$O$_5$ undergoes a
ferrimagnetic ordering with an enhanced magnetic ordering temperature as
compared to the parent, which undergoes an antiferromagnetic ordering.
Appearance of spontaneous magnetization without any major change in the atomic
structure is rather significant since the parent compound is an important
multiferroic material. In addition, magnetic memory effect is observed in the
Cr substituted compound whereas it is absent in the parent compound.",1206.1446v1
2012/6/12,A cascade of magnetic field induced spin transitions in LaCoO3,"We present magnetization and magnetostriction studies of the insulating
perovskite LaCoO3 in magnetic fields approaching 100 T. In marked contrast with
expectations from single-ion models, the data reveal two distinct first-order
spin transitions and well-defined magnetization plateaux. The magnetization at
the higher plateau is only about half the saturation value expected for spin-1
Co3+ ions. These findings strongly suggest collective behavior induced by
strong interactions between different electronic -- and therefore spin --
configurations of Co3+ ions. We propose a model of these interactions that
predicts crystalline spin textures and a cascade of four magnetic phase
transitions at high fields, of which the first two account for the experimental
data.",1206.2603v1
2012/6/22,Ultrasonic triggering of giant magnetocaloric effect in MnAs thin films,"Mechanical control of magnetic properties in magnetostrictive thin films
offers the unexplored opportunity to employ surface wave acoustics in such a
way that acoustic triggers dynamic magnetic effects. The strain-induced
modulation of the magnetic anisotropy can play the role of a high frequency
varying effective magnetic field leading to ultrasonic tuning of electronic and
magnetic properties of nanostructured materials, eventually integrated in
semiconductor technology. Here, we report about the opportunity to employ
surface acoustic waves to trigger magnetocaloric effect in
MnAs(100nm)/GaAs(001) thin films. During the MnAs magnetostructural phase
transition, in an interval range around room temperature (0{\deg}C -
60{\deg}C), ultrasonic waves (170 MHz) are strongly attenuated by the phase
coexistence (up to 150 dB/cm). We show that the giant magnetocaloric effect of
MnAs is responsible of the observed phenomenon. By a simple anelastic model we
describe the temperature and the external magnetic field dependence of such a
huge ultrasound attenuation. Strain-manipulation of the magnetocaloric effect
could be a further interesting route for dynamic and static caloritronics and
spintronics applications in semiconductor technology.",1206.5217v1
2012/12/19,Spontaneous atomic ordering and magnetism in epitaxially stabilized double perovskites,"We have studied the atomic ordering of B-site transition metals and magnetic
properties in the pulsed-laser deposited films of La2CrFeO6 (LCFO) and La2VMnO6
(LVMO), whose bulk materials are known to be single perovskites with random
distribution of the B-site cations. Despite similar ionic characters of
constituent transition metals in each compound, the maximum B-site order
attained was surprisingly high, ~90% for LCFO and ~80% for LVMO, suggesting a
significant role of epitaxial stabilization in the spontaneous ordering
process. Magnetization and valence state characterizations revealed that the
magnetic ground state of both compounds was coincidently ferrimagnetic with
saturation magnetization of ~2myuB per formula unit, unlike those predicted
theoretically. In addition, they were found to be insulating with optical band
gaps of 1.6 eV and 0.9 eV for LCFO and LVMO, respectively. Our results present
a wide opportunity to explore novel magnetic properties of binary
transition-metal perovskites upon epitaxial stabilization of the ordered phase.",1212.4622v1
2013/3/21,Tuning magnetic anisotropy in (001) oriented L10 (Fe1-xCux)55Pt45 films,"We have achieved (001) oriented L10 (Fe1-xCux)55Pt45 thin films, with
magnetic anisotropy up to 3.6x10^7 erg/cm^3, using atomic-scale multilayer
sputtering and post annealing at 400 {\deg}C for 10 seconds. By fixing the Pt
concentration, structure and magnetic properties are systematically tuned by
the Cu addition. Increasing Cu content results in an increase in the tetragonal
distortion of the L10 phase, significant changes to the film microstructure,
and lowering of the saturation magnetization and anisotropy. The relatively
convenient synthesis conditions, along with the tunable magnetic properties,
make such materials highly desirable for future magnetic recording
technologies.",1303.5208v1
2013/4/4,Anomalous magnetic moment of an electron near a dispersive surface,"Changes in the magnetic moment of an electron near a dielectric or conducting
surface due to boundary-dependent radiative corrections are investigated. The
electromagnetic field is quantized by normal mode expansion for a
non-dispersive dielectric and an undamped plasma, but the electron is described
by the Dirac equation without matter-field quantization. Perturbation theory in
the Dirac equation leads to a general formula for the magnetic moment shift in
terms of integrals over products of electromagnetic mode functions. In each of
the models investigated contour integration techniques over a complex wave
vector can be used to derive a general formula featuring just integrals over
transverse electric and transverse magnetic reflection coefficients of the
surface. Analysis of the magnetic moment shift for several classes of materials
yields markedly different results from the previously considered simplistic
'perfect reflector' model, due to the inclusion of physically important
features of the electromagnetic response of the surface such as evanescent
field modes and dispersion in the material. For a general dispersive dielectric
surface, the magnetic moment shift of a nearby electron can exceed the previous
prediction of the perfect-reflector model by several orders of magnitude.",1304.1480v3
2013/5/22,Magnetoelectric coupling in the paramagnetic state of a metal-organic framework,"Although the magnetoelectric effects - the mutual control of electric
polarization by magnetic fields and magnetism by electric fields, have been
intensively studied in a large number of inorganic compounds and
heterostructures, they have been rarely observed in organic materials. Here we
demonstrate magnetoelectric coupling in a metal-organic framework
[(CH3)2NH2]Mn(HCOO)3 which exhibits an order-disorder type of ferroelectricity
below 185 K. The magnetic susceptibility starts to deviate from the Curie-Weiss
law at the paraelectric-ferroelectric transition temperature, suggesting an
enhancement of short-range magnetic correlation in the ferroelectric state.
Electron spin resonance study further confirms that the magnetic state indeed
changes following the ferroelectric phase transition. Inversely, the
ferroelectric polarization can be improved by applying high magnetic fields. We
interpret the magnetoelectric coupling in the paramagnetic state in the
metal-organic framework as a consequence of the magnetoelastic effect that
modifies both the superexchange interaction and the hydrogen bonding.",1305.5126v1
2013/8/1,Thermodynamic properties of the new multiferroic material (NH$_4$)$_2$[FeCl$_5$(H$_2$O)],"(NH$_4$)$_2$[FeCl$_5$(H$_2$O)], a member of the family of antiferromagnetic
$A_2$[Fe$X_5$(H$_2$O)] compounds ($X$ = halide ion, $A$ = alkali metal or
ammonium ion) is classified as a new multiferroic material. We report the onset
of ferroelectricity below ~6.9 K within an antiferromagnetically ordered state
($T_N \sim 7.25 K$). The corresponding electric polarization can drastically be
influenced by applying magnetic fields. Based on measurements of pyroelectric
currents, dielectric constants and magnetization we characterize the
magnetoelectric, dielectric and magnetic properties of
(NH$_4$)$_2$[FeCl$_5$(H$_2$O)]. Combining these data with measurements of
thermal expansion, magnetostriction and specific heat, we derive detailed
magnetic field versus temperature phase diagrams. Depending on the direction of
the magnetic field up to three different multiferroic phases are identified,
which are separated by a magnetically ordered, but non-ferroelectric phase from
the paramagnetic phase. Besides these low-temperature transitions, we observe
an additional phase transition at ~79 K, which we suspect to be of structural
origin.",1308.0285v1
2013/9/26,Magnetic frustration in BaCuSi2O6 released,"Han Purple (BaCuSi2O6) is not only an ancient pigment, but also a valuable
model material for studying Bose-Einstein condensation (BEC) of magnons in high
magnetic fields. Using precise low-temperature structural data and extensive
density-functional calculations, we elucidate magnetic couplings in this
compound. The resulting magnetic model comprises two types of nonequivalent
spin dimers, in excellent agreement with the (63,65)Cu nuclear magnetic
resonance data. We further argue that leading interdimer couplings connect the
upper site of one dimer to the bottom site of the contiguous dimer, and not the
upper-to-upper and bottom-to-bottom sites, as assumed previously. This finding
is verified by inelastic neutron scattering data and implies the lack of
magnetic frustration in BaCuSi2O6, thus challenging existing theories of the
magnon BEC in this compound.",1309.6762v1
2013/9/27,Beating the superparamagnetic size limit of nanoparticles on a ferroelectric substrate,"When decreasing the size of nanoscale magnetic particles their magnetization
becomes vulnerable to thermal fluctuations as approaching the superparamgnetic
limit, hindering thus applications relying on a stable magnetization. Here, we
show theoretically that a magnetoelectric coupling to a ferroelectric substrate
renders possible the realization of substantially smaller nano clusters with
thermally stable magnetization. For an estimate of cluster size we perform
calculations with realistic material parameters for iron nano particles on
ferroelectric BaTiO3 substrate. We find, steering the polarization of BaTiO3
with electric fields affects the magnetism of the deposited magnetic clusters.
These findings point to a qualitatively new class of superparamagnetic
composites.",1309.7136v1
2014/2/13,Unusual spin fluctuations and magnetic frustration in olivine and non-olivine LiCoPO$_4$ detected by $^{31}$P and $^7$Li nuclear magnetic resonance,"We report $^{31}$P and $^{7}$Li nuclear magnetic resonance (NMR) studies in
new non-olivine LiZnPO$_4$-type LiCoPO$_4^\text{tetra}$ microcrystals, where
the Co$^{2+}$ ions are tetrahedrally coordinated. Olivine LiCoPO$_4$, which was
directly transformed from LiCoPO$_4^\text{tetra}$ by an annealing process, was
also studied and compared. The uniform bulk magnetic susceptibility and the
$^{31}$P Knight shift obey the Curie-Weiss law for both materials with a high
spin Co$^{2+}$ ($3d^7$, $S=3/2$), but the Weiss temperature $\Theta$ and the
effective magnetic moment $\mu_\text{eff}$ are considerably smaller in
LiCoPO$_4^\text{tetra}$. The spin-lattice relaxation rate $T_1^{-1}$ reveals a
quite different nature of the spin dynamics in the paramagnetic state of both
materials. Our NMR results imply that strong geometrical spin frustration
occurs in tetrahedrally coordinated LiCoPO$_4$, which may lead to the
incommensurate magnetic ordering.",1402.3082v2
2014/2/17,Magnetic dipole radiation tailored by substrates: numerical investigation,"Nanoparticles of high refractive index materials can possess strong magnetic
polarizabilities and give rise to artificial magnetism in the optical spectral
range. While the response of individual dielectric or metal spherical particles
can be described analytically via multipole decomposition in the Mie series,
the influence of substrates, in many cases present in experimental
observations, requires different approaches. Here, the comprehensive numerical
studies of the influence of a substrate on the spectral response of high- index
dielectric nanoparticles were performed. In particular, glass, perfect electric
conductor, gold, and hyperbolic metamaterial substrates were investigated.
Optical properties of nanoparticles were characterized via scattering
cross-section spectra, electric field profiles, and induced electric and
magnetic moments. The presence of substrates was shown to introduce significant
impact on particle's magnetic resonances and resonant scattering
cross-sections. Variation of substrate material provides an additional degree
of freedom in tailoring properties of emission of magnetic multipoles,
important in many applications.",1402.3911v1
2014/2/24,Low-temperature heat transport of the geometrically frustrated antiferromagnets R_2Ti_2O_7 (R = Gd and Er),"We report a systematic study on the low-temperature thermal conductivity
(\kappa) of R_2Ti_2O_7 (R = Gd and Er) single crystals with different
directions of magnetic field and heat current. It is found that the magnetic
excitations mainly act as phonon scatterers rather than heat carriers, although
these two materials have long-range magnetic orders at low temperatures. The
low-T \kappa(H) isotherms of both compounds show rather complicated behaviors
and have good correspondences with the magnetic transitions, where the
\kappa(H) curves show drastic dip- or step-like changes. In comparison, the
field dependencies of \kappa are more complicated in Gd_2Ti_2O_7, due to the
complexity of its low-T phase diagram and field-induced magnetic transitions.
These results demonstrate the significant coupling between spins and phonons in
these materials and the ability of heat-transport properties probing the
magnetic transitions.",1402.5846v1
2014/3/6,Optical Magnetic Mirrors without Metals,"The reflection of an optical wave from a metal, arising from strong
interactions between the optical electric field and the free carriers of the
metal, is accompanied by a phase reversal of the reflected electric field. A
far less common route to achieve high reflectivity exploits strong interactions
between the material and the optical magnetic field to produce a magnetic
mirror which does not reverse the phase of the reflected electric field. At
optical frequencies, the magnetic properties required for strong interaction
can only be achieved through the use of artificially tailored materials. Here
we experimentally demonstrate, for the first time, the magnetic mirror behavior
of a low-loss, all-dielectric metasurface at infrared optical frequencies
through direct measurements of the phase and amplitude of the reflected optical
wave. The enhanced absorption and emission of transverse electric dipoles
placed very close to magnetic mirrors can lead to exciting new advances in
sensors, photodetectors, and light sources.",1403.1308v1
2014/5/5,A single crystal high-temperature pyrochlore antiferromagnet,"We report the magnetic characterization of the frustrated transition metal
pyrochlore NaCaCo$_2$F$_7$. This material has high spin Co$^{2+}$ in CoF$_6$
octahedra in a pyrochlore lattice, and disordered non-magnetic Na and Ca on the
large-atom sites in the structure. Large crystals grown by the floating zone
method were studied. The magnetic susceptibility is isotropic, the Co moment is
larger than the spin-only value, and in spite of the large Curie Weiss theta
(-140 K), freezing of the spin system, as characterized by peaks in the ac and
dc susceptibility and specific heat, does not occur until around 2.4 K. This
yields a frustration index of f = $-\theta_{CW}$/$T_f$ $\approx$ 56, an
indication that the system is highly frustrated. The observed entropy loss at
the freezing transition is low, indicating that magnetic entropy remains
present in the system at 0.6 K. The compound may be the realization of a
frustrated pyrochlore antiferromagnet with weak bond disorder. The high
magnetic interaction strength, strong frustration, and the availability of
large single crystals makes NaCaCo$_2$F$_7$ an interesting alternative to rare
earth oxide pyrochlores for the study of geometric magnetic frustration in
pyrochlore lattices.",1405.0956v1
2014/6/1,Effect of carrier concentration on magnetism and magnetic order in the pyrochlore iridates,"We present resistivity, magnetization, and zero field muon spin relaxation
($\mu$SR) data for the pyrochlore iridate materials
Nd$_{2-x}$Ca$_{x}$Ir$_{2}$O$_{7}$ ($x = 0, 0.06$, and $0.10$) and
Sm$_2$Ir$_2$O$_7$. While Nd$_{2}$Ir$_{2}$O$_{7}$ (Nd227) is weakly conducting,
Sm$_{2}$Ir$_{2}$O$_{7}$ (Sm227) has slowly diverging resistivity at low
temperature. Nd227 and Sm227 exhibit magnetic anomalies at $T_{M} = 105 K$ and
$137 K$, respectively. However, zero-field $\mu$SR measurements show that
long-range magnetic order of the Ir$^{4+}$ sublattice sets in at much lower
temperatures ($T_{LRO} \sim 8 K$ for Nd227 and $70 K$ for Sm227); both
materials show heavily damped muon precession with a characteristic frequency
near 9 MHz. The magnetic anomaly at $T_{M}$ in Nd227 is not significantly
affected by the introduction of hole carriers by Ca-substitution in the
conducting Nd$_{2-x}$Ca$_{x}$Ir$_{2}$O$_{7}$ samples, but the muon precession
is fully suppressed for both.",1406.0194v1
2014/6/4,Hyperfine magnetic field in ferromagnetic graphite,"Information on atomic-scale features is required for a better understanding
of the mechanisms leading to magnetism in non-metallic, carbon-based materials.
This work reports a direct evaluation of the hyperfine magnetic field produced
at 13C nuclei in ferromagnetic graphite by nuclear magnetic resonance (NMR).
The experimental investigation was made possible by the results of
first-principles calculations carried out in model systems, including graphene
sheets with atomic vacancies and graphite nanoribbons with edge sites partially
passivated by oxygen. A similar range of maximum hyperfine magnetic field
values (18-21T) was found for all systems, setting the frequency span to be
investigated in the NMR experiments; accordingly, a significant 13C NMR signal
was detected close to this range without any external applied magnetic field in
ferromagnetic graphite.",1406.1119v1
2014/7/25,Interface induced states at the boundary between a 3D topological insulator Bi$_2$Se$_3$ and a ferromagnetic insulator EuS,"By means of relativistic density functional theory (DFT) calculations we
study electron band structure of the topological insulator (TI) Bi$_2$Se$_3$
thin films deposited on the ferromagnetic insulator (FMI) EuS substrate. In the
Bi$_2$Se$_3$/EuS heterostructure, the gap opened in the spectrum of the
topological state has a hybridization character and is shown to be controlled
by the Bi$_2$Se$_3$ film thickness, while magnetic contribution to the gap is
negligibly small. We also analyzed the effect of Eu doping on the magnetization
of the Bi$_2$Se$_3$ film and demonstrated that the Eu impurity induces magnetic
moments on neighboring Se and Bi atoms an order of magnitude larger than the
substrate-induced moments. Recent magnetic and magneto-transport measurements
in EuS/Bi$_2$Se$_3$ heterostructure are discussed.",1407.6880v1
2014/7/31,Metamagnetic behavior and effect of field cooling on sharp magnetization jumps in multiferroic Y2CoMnO6,"We present sharp magnetization jumps and field induced irreversibility in
magnetization in multiferroic Y2CoMnO6. Appearance of magnetic relaxation and
field sweep rate dependence of magnetization jumps resemble the martensite like
scenario and suggests the coexistence of E*-type antiferromagnetic and
ferromagnetic phases at low temperatures. In Y2CoMnO6, the critical field
required for the sharp jump can be increased or decreased depening on the
magnitude and direction of the cooling field; this is remarkably different from
manganites or other metamagnetic materials where the critical field increases
irrespective of the direction of the field cooling. The cooling field
dependence on the sharp magnetization jumps has been described by considering
exchange pinning mechanism at the interface, like in exchange bias model.",1407.8276v2
2014/9/2,Anisotropic magnetodielectric coupling behavior of Ca3Co1.4Rh0.6O6 due to geometrically frustrated magnetism,"We have investigated the magnetic, dielectric and magnetodielectric (MDE)
behavior of a geometrically frustrated spin-chain system, Ca3Co1.4Rh0.6O6, in
the single crystalline form for different orientations. The results bring out
that the magnetic behavior of this compound is by itself interesting in the
sense that this compound exhibits an anisotropic glassy-like magnetic behavior
with a huge frequency dependence of ac susceptibility peak for an orientation
along the spin-chain in the range 30-60 K; this behavior is robust to
applications of large external magnetic fields (H) unlike in canonical
spin-glasses. The temperature dependence of dielectric constant also shows
strong frequency dependence with similar robustness to H. The isothermal
H-dependent dielectric results at low temperatures establishes anisotropic MDE
coupling. It is intriguing to note that there is a 'step' roughly at one-third
of saturation values as in the case of isothermal magnetization curves for same
temperatures (for orientation along spin-chain), a correlation hitherto
unrealized for geometrically frustrated systems.",1409.0783v1
2014/9/18,Symmetry of re-entrant tetragonal phase in Ba1-xNaxFe2As2: Magnetic versus orbital ordering mechanism,"Magneto-structural phase transitions in Ba1-xAxFe2As2 (A = K, Na) materials
are discussed for both magnetically and orbitally driven mechanisms, using a
symmetry analysis formulated within the Landau theory of phase transitions.
Both mechanisms predict identical orthorhombic space-group symmetries for the
nematic and magnetic phases observed over much of the phase diagram, but they
predict different tetragonal space-group symmetries for the newly discovered
re-entrant tetragonal phase in Ba1-xNaxFe2As2 (x ~ 0.24-0.28). In a magnetic
scenario, magnetic order with moments along the c-axis, as found
experimentally, does not allow any type of orbital order, but in an orbital
scenario, we have determined two possible orbital patterns, specified by
P4/mnc1' and I4221' space groups, which do not require atomic displacements
relative to the parent I4/mmm1' symmetry and, in consequence, are
indistinguishable in conventional diffraction experiments. We demonstrate that
the three possible space groups are however, distinct in resonant X-ray Bragg
diffraction patterns created by Templeton & Templeton scattering. This provides
an experimental method of distinguishing between magnetic and orbital models.",1409.5324v1
2014/11/4,Magnetoimpedance effect at the high frequency range for the thin film geometry: Numerical calculation and experiment,"The magnetoimpedance effect is a versatile tool to investigate ferromagnetic
materials, revealing aspects on the fundamental physics associated to
magnetization dynamics, broadband magnetic properties, important issues for
current and emerging technological applications for magnetic sensors, as well
as insights on ferromagnetic resonance effect at non-saturated magnetic states.
Here, we perform a theoretical and experimental investigation of the
magnetoimpedance effect for the thin film geometry in a wide frequency range.
We calculate the longitudinal magnetoimpedance for single layered, multilayered
or exchange biased systems from an approach that considers a magnetic
permeability model for planar geometry and the appropriate magnetic free energy
density for each structure. From numerical calculations and experimental
results found in literature, we analyze the magnetoimpedance behavior, and
discuss the main features and advantages of each structure. To test the
robustness of the approach, we directly compare theoretical results with
experimental magnetoimpedance measurements obtained in a wide range of
frequencies for an exchange biased multilayered film. Thus, we provide
experimental evidence to confirm the validity of the theoretical approach
employed to describe the magnetoimpedance in ferromagnetic films, revealed by
the good agreement between numerical calculations and experimental results.",1411.0971v1
2014/12/7,Pressure-Induced Enhancement of the Magnetic Anisotropy in Mn(N(CN)$_{2}$)$_{2}$,"Using dc and ac magnetometry, the pressure dependence of the magnetization of
the three-dimensional antiferromagnetic coordination polymer
Mn(N(CN)$_{2}$)$_{2}$ was studied up to 12 kbar and down to 8K. The magnetic
transition temperature, $T_c$, increases dramatically with applied pressure
$(P)$, where a change from $T_c(P=\text{ambient}) = 16.0$ K to
$T_c(P=12.1$~kbar$) = 23.5$ K was observed. In addition, a marked difference in
the magnetic behavior is observed above and below 7.1 kbar. Specifically, for
$P<7.1$ kbar, the differences between the field-cooled and zero-field-cooled
(fc-zfc) magnetizations, the coercive field, and the remanent magnetization
decrease with increasing pressure. However, for $P>7.1$ kbar, the behavior is
inverted. Additionally, for $P>8.6$ kbar, minor hysteresis loops are observed.
All of these effects are evidence of the increase of the superexchange
interaction and the appearance of an enhanced exchange anisotropy with applied
pressure.",1412.2318v1
2014/12/11,Local electrical control of magnetic order and orientation by ferroelastic domain arrangements just above room temperature,"Ferroic materials (ferromagnetic, ferroelectric, ferroelastic) usually divide
into domains with different orientations of their order parameter. Coupling
different ferroic systems creates new functionalities, for instance the
electrical control of macroscopic magnetic properties including magnetization
and coercive field. Here we show that ferroelastic domains can be used to
control both magnetic order and magnetization direction at the nanoscale with a
voltage. We use element-specific x-ray imaging to map the magnetic domains as a
function of temperature and voltage in epitaxial FeRh on ferroelastic BaTiO3.
Exploiting the nanoscale phase-separation of FeRh, we locally interconvert
between ferromagnetism and antiferromagnetism with a small electric field just
above room temperature. Our results emphasize the importance of nanoscale
ferroic domain structure to achieve enhanced coupling in artificial
multiferroics.",1412.3675v1
2014/12/18,Scaling of Coercivity in a 3d Random Anisotropy Model,"The random-anisotropy Heisenberg model is numerically studied on lattices
containing over ten million spins. The study is focused on hysteresis and
metastability due to topological defects, and is relevant to magnetic
properties of amorphous and sintered magnets. We are interested in the limit
when ferromagnetic correlations extend beyond the size of the grain inside
which the magnetic anisotropy axes are correlated. In that limit the coercive
field computed numerically roughly scales as the fourth power of the random
anisotropy strength and as the sixth power of the grain size. Theoretical
arguments are presented that provide an explanation of numerical results. Our
findings should be helpful for designing amorphous and nanosintered materials
with desired magnetic properties.",1412.6182v1
2015/3/25,Spin Hall torque driven chiral domain walls in magnetic heterostructures,"The motion of magnetic domain walls in ultrathin magnetic heterostructures
driven by current via the spin Hall torque is described. We show results from
perpendicularly magnetized CoFeB|MgO heterostructures with various heavy metal
underlayers. The domain wall moves along or against the current flow depending
on the underlayer material. The direction to which the domain wall moves is
associated with the chirality of the domain wall spiral formed in these
heterostructures. The one-dimensional model is used to describe the
experimental results and extract parameters such as the Dzyaloshinskii-Moriya
exchange constant which is responsible for the formation of the domain wall
spiral. Fascinating effects arising from the control of interfaces in magnetic
heterostructures are described.",1503.07250v1
2015/4/2,Micro and nano patternable magnetic carbon,"Carbon is conventionally not associated with magnetism, and much of the
discussion of its nanotechnology perspectives appears to be centered on its
electron transport properties. Among the few existing examples of magnetic
carbon production, none has found a direct applicability in scalable micro and
nano fabrication, Here we introduce a paramagnetic form of carbon whose
precursor polymers can be lithographically patterned into micro and nano
structures prior to pyrolysis. This unreactive and thermally robust material
features strong room-temperature paramagnetism owing to a large number of
unpaired electrons with restricted mobility, which is achieved by controlling
the progression of bond dissociation and formation during pyrolysis. The
manufacture of this magnetic carbon, having (3.97 x 0.8) 10^17 spins/ mg, can
immediately benefit a number of spintronic and magnetic MEMS applications, and
also shed light on the controversial theories concerning the existence and
mechanisms of magnetism in carbon.",1504.00516v1
2015/7/3,Magnetization switching by spin-orbit torque in an antiferromagnet/ferromagnet bilayer system,"Spin-orbit torque (SOT)-induced magnetization switching shows promise for
realizing ultrafast and reliable spintronics devices. Bipolar switching of
perpendicular magnetization via SOT is achieved under an in-plane magnetic
field collinear with an applied current. Typical structures studied so far
comprise a nonmagnet/ferromagnet (NM/FM) bilayer, where the spin Hall effect in
the NM is responsible for the switching. Here we show that an
antiferromagnet/ferromagnet (AFM/FM) bilayer system also exhibits a SOT large
enough to switch the magnetization of FM. In this material system, thanks to
the exchange-bias effect of the AFM, we observe the switching under no applied
field by using an antiferromagnetic PtMn and ferromagnetic Co/Ni multilayer
with a perpendicular easy axis. Furthermore, tailoring the stack achieves a
memristor-like behaviour where a portion of the reversed magnetization can by
controlled in an analogue manner. The AFM/FM system is thus a promising
building block for SOT devices as well as providing an attractive pathway
towards neuromorphic computing.",1507.00888v1
2015/8/17,Large adiabatic temperature and magnetic entropy changes in EuTiO3,"We have investigated the magnetocaloric effect in single and polycrystalline
samples of quantum paraelectric EuTiO3 by magnetization and heat capacity
measurements. Single crystalline EuTiO3 shows antiferromagnetic ordering due to
Eu2+ magnetic moments below TN = 5.6 K. This compound shows a giant
magnetocaloric effect around its Neel temperature. The isothermal magnetic
entropy change is 49 Jkg-1K-1, the adiabatic temperature change is 21 K and the
refrigeration capacity is 500 JKg-1 for a field change of 7 T at TN. The single
crystal and polycrystalline samples show similar values of the magnetic entropy
change and adiabatic temperature changes. The large magnetocaloric effect is
due to suppression of the spin entropy associated with localized 4f moment of
Eu2+ ions. The giant magnetocaloric effect together with negligible hysteresis,
suggest that EuTiO3 could be a potential material for magnetic refrigeration
below 20 K.",1508.03963v1
2015/10/28,Intrinsic diamagnetism in the Weyl semimetal TaAs,"We investigate the magnetic properties of TaAs, a prototype Weyl semimetal.
TaAs crystals show weak diamagnetism with magnetic susceptibility of about -7 *
10^{-7} emu/(g*Oe) at 5 K. A general feature is the appearance of a minimum at
around 185 K in magnetization measurements as a function of temperature. No
phase transition is observed in the temperature range between 5 K and 400 K.
The magnetic properties indicate that the intrinsic Fermi level in TaAs is not
located at the Weyl nodes, in agreement with the theory prediction.",1510.08497v3
2016/2/3,Topological magnetic dipolar interaction and non-local electric magnetization control in topological insulator heterostructures,"The magnetoelectric effect predicted in topological insulators makes
heterostructures that combine magnetic materials and such insulators promising
candidates for spintronics applications. Here, we theoretically consider a
setup that exhibits two well-separated interfaces between a topological
insulator and a ferromagnetic insulator. We show that there is a topological
magnetic dipole-dipole interaction stemming from long-range Coulomb
interactions. We analytically derive the magnetization dynamics at the two
interfaces and discuss how the long-range coupling can be applied to
non-locally induce the formation of a magnetic texture at one interface by
suitably gating the other interface.",1602.01469v4
2016/2/29,Strong reduction of the coercivity by a surface acoustic wave in an out-of-plane magnetized epilayer,"Inverse magnetostriction is the effect by which magnetization can be changed
upon application of stress/strain. A strain modulation may be created
electrically by exciting interdigitated transducers to generate surface
acoustic waves (SAWs). Hence SAWs appear as a possible route towards
induction-free undulatory magnetic data manipulation. Here we demonstrate
experimentally on an out-of-plane magnetostrictive layer a reduction of the
coercive field of up to 60$\%$ by a SAW, over millimetric distances. A simple
model shows that this spectacular effect can be partly explained by the
periodic lowering of the strain-dependent domain nucleation energy by the SAW.
This proof of concept was done on (Ga,Mn)(As,P), a magnetic semiconductor in
which the out-of-plane magnetic anisotropy can be made very weak by epitaxial
growth; it should guide material engineering for all-acoustic magnetization
switching.",1602.09064v1
2016/4/21,Magnetic properties and Curie temperatures of disordered Heusler compounds: Co(1+x)Fe(2-x)Si,"The local atomic environments and magnetic properties were investigated for a
series of Co(1+x)Fe(2-x)Si (0<x<1) Heusler compounds. While the total magnetic
moment in these compounds increases with the number of valance electrons, the
highest Curie temperature (Tc) in this series was found for Co1.5Fe1.5Si, with
a Tc of 1069 K (24 K higher than the well known Co2FeSi). 57Fe M\""ossbauer
spectroscopy was used to characterize the local atomic order and to estimate
the Co and Fe magnetic moments. Consideration of the local magnetic moments and
the exchange integrals is necessary to understand the trend in Tc.",1604.06235v1
2016/5/31,Spin-Orbit Torques in ferrimagnetic GdFeCo Alloys,"The spin-orbit torque switching of ferrimagnetic
Gd$_x$(Fe$_{90}$Co$_{10}$)$_{100-x}$ films was studied for both transition
metal (TM)-rich and rare earth (RE)-rich configurations. The spin-orbit torque
driven magnetization switching follows the same handedness in TM-rich and
RE-rich samples with respect to the total magnetization, but the handedness of
the switching is reversed with respect to the TM magnetization. This indicates
that the sign of the spin-orbit-torque-driven magnetic switching follows the
total magnetization, although transport based techniques such as anomalous Hall
effect are only sensitive to the transition metal magnetization. These results
provide important insight into the physics of spin angular momentum transfer in
materials with antiferromagnetically coupled sublattices.",1605.09498v1
2016/7/11,Powerful and Tunable THz Emitters Based on the Fe/Pt Magnetic Heterostructure,"In this work, we report our study on the THz emission in Fe/Pt magnetic
heterostructures. We have carried out a comprehensive investigation of THz
emission from Fe/Pt magnetic heterostructures, employing time-domain THz
spectroscopy. We reveal that by properly tuning the thickness of Fe or Pt
layer, THz emission can be greatly improved in this type of heterostructure. We
further demonstrate that the THz field strength emitted from a newly designed
multilayer (Pt/Fe/MgO)$_n$ with n=3 can reach a value of ~1.6 kV/cm, which is
comparable to the values from the conventional GaAs antenna with a bias of 4
kV/cm, and the nonlinear crystals, e.g., 100 micrometer GaP and 2 mm ZnTe. For
the first time, the intensity and spectrum of THz wave is demonstrated to be
tunable by the magnetic field applied on the patterned magnetic Fe/Pt
heterostructures. These findings thus promise novel approaches to fabricate
powerful and tunable THz emitters based on magnetic heterostructure.",1607.02814v1
2016/7/19,Electrical detection of spiral spin structures in Pt|Cu_2OSeO_3 heterostructures,"The interaction between the itinerant spins in metals and localized spins in
magnetic insulators thus far has only been explored in collinear spin systems,
such as garnets. Here, we report the spin-Hall magnetoresistance (SMR)
sensitive to the surface magnetization of the spin-spiral material, Cu_2OSeO_3.
We experimentally demonstrate that the angular dependence of the SMR changes
drastically at the transition between the helical spiral and the conical spiral
phases. Furthermore, the sign and magnitude of the SMR in the conical spiral
state are controlled by the cone angle. We show that this complex behaviour can
be qualitatively explained within the SMR theory initially developed for
collinear magnets. In addition, we studied the spin Seebeck effect (SSE), which
is sensitive to the bulk magnetization. It originates from the conversion of
thermally excited low-energy spin waves in the magnet, known as magnons, into
the spin current in the adjacent metal contact (Pt). The SSE displays
unconventional behavior where not only the magnitude but also the phase of the
SSE vary with the applied magnetic field.",1607.05630v1
2016/7/29,Weak de-localization in graphene on a ferromagnetic insulating film,"Graphene has been predicted to develop a magnetic moment by proximity effect
when placed on a ferromagnetic film, a promise that could open exciting
possibilities in the fields of spintronics and magnetic data recording. In this
work, we study in detail the interplay between the magnetoresistance of
graphene and the magnetization of an underlying ferromagnetic insulating film.
A clear correlation between both magnitudes is observed but we find, through a
careful modelling of the magnetization and the weak localization measurements,
that such correspondence can be explained by the effects of the magnetic stray
fields arising from the ferromagnetic insulator. Our results emphasize the
complexity arising at the interface between magnetic and two-dimensional
materials.",1607.08772v1
2016/9/13,Spin-flop transition accompanied with changing the type of magnetic ordering,"We discuss theoretically rather rear example of spin-flop transition which is
accompanied with changing the type of magnetic ordering and which seemingly has
not been addressed yet. We demonstrate that changing the type of magnetic
ordering can manifest itself in antiferromagnetic (AF) resonance experiments as
an apparent peculiar switching of the anisotropy at the transition from the
easy-axis type to the easy-plane one. We argue that this kind of spin-flop
transition is observed recently by K.Yu. Povarov et al., Phys. Rev. B 87,
214402 (2013) in Cu(pz)$_2$(ClO$_4$)$_2$ (where pz denotes pyrazine), one of
the best realizations of spin-1/2 Heisenberg AFs on square lattice having a
very small anisotropy. We show that the magnetic ordering changes at the
spin-flop transition in this material in the direction perpendicular to AF
square planes. We examine the microscopic mechanism of such behavior in
Cu(pz)$_2$(ClO$_4$)$_2$ and find that dipolar forces and extremely small
exchange coupling between spins from neighboring planes are responsible for it.",1609.03702v2
2016/10/24,"Field-free, spin-current control of magnetization in non-collinear chiral antiferromagnets","Non-collinear chiral antiferromagnets like Mn3Sn and Mn3Ge are known to show
gigantic anomalous Hall response depending on the orientation of their inverse
chiral magnetic order of Mn atoms in Kagome layers. Here we study the stability
of such magnetic order in the absence of external magnetic fields on the basis
of stochastic Landau-Lifshitz-Gilbert equation for a simplified two-dimensional
model of these materials. We find that even without external magnetic fields,
the ordered state is, once formed, highly stable against thermal fluctuations.
Moreover, we show that if Mn spins are well confined inside each Kagome layers,
by injecting spin-current using spin-filtering effect of ferromagnetic metals,
we can control the in-plane magnetic structure in a field free way.",1610.07615v2
2016/10/29,Tailoring magnetic insulator proximity effects in graphene: First-principles calculations,"We report a systematic first-principles investigation of the influence of
different magnetic insulators on the magnetic proximity effect induced in
graphene. Four different magnetic insulators are considered: two ferromagnetic
europium chalcogenides namely EuO and EuS and two ferrimagnetic insulators
yttrium iron garnet (YIG) and cobalt ferrite (CFO). The obtained
exchange-splitting varies from tens to hundreds of meV. We also find an
electron doping induced by YIG and europium chalcogenides substrates, that
shift the Fermi level up to 0.78 eV and 1.3 eV respectively, whereas hole
doping up to 0.5 eV is generated by CFO. Furthermore, we study the variation of
the extracted exchange and tight binding parameters as a function of the EuO
and EuS thicknesses. We show that those parameters are robust to thickness
variation such that a single monolayer of magnetic insulator can induce a large
magnetic proximity effect on graphene. Those findings pave the way towards
possible engineering of graphene spin-gating by proximity effect especially in
view of recent experiments advancement.",1610.09554v1
2017/1/27,Mixed Weyl semimetals and dissipationless magnetization control in insulators by spin-orbit torques,"Reliable and energy efficient magnetization switching by electrically-induced
spin-orbit torques is of crucial technological relevance for spintronic devices
implementing memory and logic functionality. Here we predict that the strength
of spin-orbit torques and the related Dzyaloshinskii-Moriya interaction in
topologically non-trivial magnetic insulators can exceed by far that of
conventional metallic magnets. In analogy to the quantum anomalous Hall effect,
we explain this extraordinary response in absence of longitudinal currents as a
hallmark of magnetic monopoles in the electronic structure of systems that are
interpreted most naturally within the framework of mixed Weyl semimetals. We
thereby launch the effect of spin-orbit torque into the field of topology and
reveal its crucial role in mediating the topological phase transitions arising
due to the complex interplay between magnetization direction and momentum-space
topology. The concepts presented here may be exploited to understand and
utilize magneto-electric coupling phenomena in insulating ferromagnets and
antiferromagnets.",1701.08050v2
2017/2/13,Atomic-Scale Magnetometry of Dynamic Magnetization,"The spatial resolution of imaging magnetometers has benefited from scanning
probe techniques. The requirement that the sample perturbs the scanning probe
through a magnetic field external to its volume limits magnetometry to samples
with pre-existing magnetization. We propose a magnetometer in which the
perturbation is reversed: the probe's magnetic field generates a response of
the sample, which acts back on the probe and changes its energy. For an NV$^-$
spin center in diamond this perturbation changes the fine-structure splitting
of the spin ground state. Sensitive measurement techniques using coherent
detection schemes then permit detection of the magnetic response of
paramagnetic and diamagnetic materials. This technique can measure the
thickness of magnetically dead layers with better than $0.1$ \AA$~$accuracy.",1702.03863v1
2017/5/20,The Spin-Orbit Torque from a Magnetic Heterostructure with High-Entropy Alloy,"High-entropy alloy (HEA) is a family of metallic materials with nearly equal
partitions of five or more metals, which might possess mechanical and transport
properties that are different from conventional binary or tertiary alloys. In
this work, we demonstrate current-induced spin-orbit torque (SOT) magnetization
switching in a Ta-Nb-Hf-Zr-Ti HEA-based magnetic heterostructure with
perpendicular magnetic anisotropy (PMA). The maximum damping-like SOT
efficiency from this particular HEA-based magnetic heterostructure is further
determined to be $|\zeta^{\operatorname{HEA}}_{DL}|\approx0.033$ by hysteresis
loop shift measurements, while that for the Ta control sample is
$|\zeta^{\operatorname{Ta}}_{DL}|\approx0.04$. Our results indicate that
HEA-based magnetic heterostructures can serve as a new group of potential
candidates for SOT device applications.",1705.07248v1
2017/5/30,"Enhanced magnetocaloric effect from Cr substitution in Ising lanthanide gallium garnets $Ln_3\text{CrGa}_4\text{O}_{12}$ ($Ln$ = Tb, Dy, Ho)","A detailed study on the crystal structure and bulk magnetic properties of Cr
substituted Ising type lanthanide gallium garnets
$Ln_3\text{CrGa}_4\text{O}_{12}$ ($Ln$ = Tb, Dy, Ho) has been carried out using
room temperature powder X-Ray and neutron diffraction, magnetic susceptibility,
isothermal magnetisation and heat capacity measurements. The magnetocaloric
effect (MCE) in $Ln_3\text{CrGa}_4\text{O}_{12}$ is compared to that of
$Ln_3\text{Ga}_5\text{O}_{12}$. In lower magnetic fields attainable by a
permanent magnet ($\leq$ 2 T), Cr substitution greatly enhances the MCE by 20%
for $Ln$ = Dy and 120% for $Ln$ = Ho compared to the unsubstituted
$Ln_3\text{Ga}_5\text{O}_{12}$. This is likely due to changes in the magnetic
ground state as Cr substitution also significantly reduces the frustration in
the magnetic lattice for the Ising type $Ln_3\text{Ga}_5\text{O}_{12}$.",1705.10547v1
2017/5/31,Skyrmion knots in frustrated magnets,"A magnetic Skyrmion is a stable two-dimensional nanoparticle describing a
localized winding of the magnetization in certain magnetic materials. Skyrmions
are the subject of intense experimental and theoretical investigation and have
potential technological spintronic applications. Here we show that numerical
computations of frustrated magnets predict that Skyrmions can be tied into
knots to form new stable three-dimensional nanoparticles. These stable
equilibria of twisted loops of Skyrmion strings have an integer-valued
topological charge, known as the Hopf charge, that counts the number of
particles. Rings are formed for low values of this charge, but for higher
values it is energetically favourable to form links and then knots. This
computational study provides a novel impetus for future experimental work on
these nanoknots and an exploration of the potential technological applications
of three-dimensional nanoparticles encoding knotted magnetization.",1705.10966v1
2017/8/16,Effective magnetic susceptibility of suspensions,"We characterize how suspensions of magnetic particles in a liquid respond to
a magnetic field in terms of the effective magnetic susceptibility $\chi_{eff}$
using inductance measurements. We test a model that predicts how $\chi_{eff}$
varies due to demagnetization, as a function of sample aspect ratio, particle
packing fraction, and particle aspect ratio. For spherical particles or
cylindrical particles aligned with external magnetic field, the model can be
fitted to the measured data with agreement within 17\%. However, we find that
the random alignment of particles relative to the magnetic field plays a role,
reducing $\chi_{eff}$ by a factor of 3 in some cases, which is not accounted
for in models yet. While suspensions are predicted to have $\chi_{eff}$ that
approach the particle material susceptibility in the limit of large particle
aspect ratio, instead we find a much smaller particle aspect ratio where
$\chi_{eff}$ is maximized. A prediction that $\chi_{eff}$ approaches the bulk
material susceptibility in the limit of the packing fraction of the
liquid-solid transition also fails. We find $\chi_{eff}$ no larger than about 4
for suspensions of iron particles.",1708.05051v1
2017/8/25,Spin torque control of antiferromagnetic moments in NiO,"For a long time, there have been no efficient ways of controlling
antiferromagnets. Quite a strong magnetic field was required to manipulate the
magnetic moments because of a high molecular field and a small magnetic
susceptibility. It was also difficult to detect the orientation of the magnetic
moments since the net magnetic moment is effectively zero. For these reasons,
research on antiferromagnets has not been progressed as drastically as that on
ferromagnets which are the main materials in modern spintronic devices. Here we
show that the magnetic moments in NiO, a typical natural antiferromagnet, can
indeed be controlled by the spin torque with a relatively small electric
current density (~5 x 10^7 A/cm^2) and their orientation is detected by the
transverse resistance resulting from the spin Hall magnetoresistance . The
demonstrated techniques of controlling and detecting antiferromagnets would
outstandingly promote the methodologies in the recently emerged
""antiferromagnetic spintronics"". Furthermore, our results essentially lead to a
spin torque antiferromagnetic memory.",1708.07682v1
2017/10/11,Néel-type skyrmion lattice in tetragonal polar magnet VOSe$_2$O$_5$,"Formation of the triangular skyrmion-lattice is found in a tetragonal polar
magnet VOSe$_2$O$_5$. By magnetization and small-angle neutron scattering
measurements on the single crystals, we identify a cycloidal spin state at zero
field and a N\'eel-type skyrmion-lattice phase under a magnetic field along the
polar axis. Adjacent to this phase, another magnetic phase of an incommensurate
spin texture is identified at lower temperatures, tentatively assigned to a
square skyrmion-lattice phase. These findings exemplify the versatile features
of N\'eel-type skyrmions in bulk materials, and provide a unique occasion to
explore the physics of topological spin textures in polar magnets.",1710.04000v1
2017/10/23,Chiral orbital magnetism of $p$-orbital bosons in optical lattices,"Chiral magnetism is a fascinating quantum phenomena that has been found in
low-dimensional magnetic materials. It is not only interesting for
understanding the concept of chirality, but also important for potential
applications in spintronics. Past studies show that chiral magnets require both
lack of the inversion symmetry and spin-orbit coupling to induce the
Dzyaloshinskii-Moriya (DM) interaction. Here we report that the combination of
inversion symmetry breaking and quantum degeneracy of orbital degrees of
freedom will provide a new paradigm to achieve the chiral orbital magnetism. By
means of the density matrix renormalization group (DMRG) calculation, we
demonstrate that the chiral orbital magnetism can be found when considering
bosonic atoms loaded in the $p$-band of an optical lattice in the Mott regime.
The high tunability of our scheme is also illustrated through simply
manipulating the inversion symmetry of the system for the cold atom
experimental conditions.",1710.08145v1
2018/1/4,Crystal growth and magnetic anisotropy in the spin-chain ruthenate Na$_2$RuO$_4$,"We report single crystal growth, electrical resistivity $\rho$, anisotropic
magnetic susceptibiltiy $\chi$, and heat capacity $C_p$ measurements on the
one-dimensional spin-chain ruthenate Na$_2$RuO$_4$. We observe variable range
hopping (VRH) behaviour in $\rho(T)$. The magnetic susceptibility with magnetic
field perpendicular ($\chi_\perp$) and parallel ($\chi_\parallel$) to the
spin-chains is reported. The magnetic properties are anisotropic with
$\chi_\perp > \chi_\parallel$ in the temperature range of measurements T
$\approx 2$ to $305$ K with $\chi_\perp / \chi_\parallel$ $\approx 1.4$ at
$305$ K. Analysis of the $\chi(T)$ data reveals an anisotropy in the $g$-factor
and Van-Vleck paramagnetic contribution. An anomaly in $\chi(T)$ and a
corresponding lambda-like anomaly in $C_p$ at $T_N = 37$ K confirms long-range
antiferromagnetic ordering. This temperature is an order of magnitude smaller
than the Weiss temperature $\theta \sim -250$ K and points to suppression of
long range magnetic order due to low dimensionality. However, we were unable to
get a satisfactory fit of the experimental $\chi(T)$ by an isolated
one-dimensional spin-chain model, suggesting the importance of inter-chain
interactions in Na$_2$RuO$_4$.",1801.01524v1
2018/4/22,Spin torque oscillator for microwave assisted magnetization reversal,"A theoretical study is given for the self-oscillation excited in a spin
torque oscillator (STO) consisting of an in-plane magnetized free layer and a
perpendicularly magnetized pinned layer in the presence of a perpendicular
magnetic field. This type of STO is a potential candidate for a microwave
source of microwave assisted magnetization reversal (MAMR). It is, however,
found that the self-oscillation applicable to MAMR disappears when the
perpendicular field is larger than a critical value, which is much smaller than
a demagnetization field. This result provides a condition that the reversal
field of a magnetic recording bit by MAMR in nanopillar structure should be
smaller than the critical value. The analytical formulas of currents
determining the critical field are obtained, which indicate that a material
with a small damping is not preferable to acheive a wide range of the
self-oscillation applicable to MAMR, although such a material is preferable
from the view point of the reduction of the power consumption.",1804.08076v1
2018/6/1,Static Hopf Solitons and Knotted Emergent Fields in Solid-State Noncentrosymmetric Magnetic Nanostructures,"Two-dimensional topological solitons, commonly called Skyrmions, are
extensively studied in solid-state magnetic nanostructures and promise many
spintronics applications. However, three-dimensional topological solitons
dubbed hopfions have not been demonstrated as stable spatially localized
structures in solid-state magnetic materials. Here we model the existence of
such static solitons with different Hopf index values in noncentrosymmetric
solid magnetic nanostructures with a perpendicular interfacial magnetic
anisotropy. We show how this surface anisotropy, along with the
Dzyaloshinskii-Moriya interactions and the geometry of nanostructures,
stabilize hopfions. We demonstrate knots in emergent field lines and computer
simulate Lorentz transmission electron microscopy images of such solitonic
configurations to guide their experimental discovery in magnetic solids.",1806.00453v3
2019/6/1,"Theory of skyrmion, meron, anti-skyrmion and anti-meron in chiral magnets","We find closed-form solution of the Euler equation for a chiral magnet in
terms of a skyrmion or a meron depending on the relative strengths of magnetic
anisotropy and magnetic field. We show that the relevant length scales for
these solutions primarily depend on the strengths of Dzyaloshinskii-Moriya
interaction through its ratios, respectively, with magnetic field and magnetic
anisotropy. We thus unambiguously determine the parameter dependencies on the
radius of the topological structures particularly of the skyrmions, showing an
excellent agreement with experiments and first-principle studies. An
anisotropic Dzyaloshinskii-Moriya interaction suitable for thin films made with
$C_{nv}$ symmetric materials is found to stabilize anti-skyrmion and
anti-meron, which are prototypical for $D_{2d}$ symmetric systems, depending on
the degree of anisotropy. Based on these solutions, we obtain phase diagram by
comparing the energies of various collinear and non-collinear competing phases.",1906.00210v2
2019/8/27,Thickness-dependent magnetic order in CrI$_3$ single crystals,"Two-dimensional (2D) materials with intrinsic ferromagnetism provide unique
opportunity to engineer new functionalities in nano-spintronics. One such
material is CrI$_3$, showing long-range magnetic order in monolayer with the
Curie temperature ($T_c$) of 45 K. Here we study detailed evolution of magnetic
transition and magnetic critical properties in response to systematic reduction
in crystal thickness down to 50 nm. Bulk $T_c$ of 61 K is gradually suppressed
to 57 K, however, the satellite transition at $T^*$ = 45 K is observed
layer-independent at fixed magnetic field of 1 kOe. The origin of $T^*$ is
proposed to be a crossover from pinning to depinning of magnetic domain walls.
The reduction of thickness facilitates a field-driven metamagnetic transition
around 20 kOe with out-of-plane field, in contrast to the continuous changes
with in-plane field. The critical analysis around $T_c$ elucidates the
mean-field type interactions in microscale-thick CrI$_3$.",1908.09969v1
2017/4/11,Role of polar compensation in interfacial ferromagnetism of LaNiO$_3$/CaMnO$_3$ superlattices,"Polar compensation can play an important role in the determination of
interfacial electronic and magnetic properties in oxide heterostructures. Using
x-ray absorption spectroscopy, x-ray magnetic circular dichroism, bulk
magnetometry, and transport measurements, we find that interfacial charge
redistribution via polar compensation is essential for explaining the evolution
of interfacial ferromagnetism in LaNiO$_3$/CaMnO$_3$ superlattices as a
function of LaNiO$_3$ layer thickness. In insulating superlattices (4 unit
cells or less of LaNiO$_3$), magnetism is dominated by Ni-Mn superexchange,
while itinerant electron-based Mn-Mn double-exchange plays a role in thicker
metallic superlattices. X-ray magnetic circular dichroism and resonant x-ray
scattering show that Ni-Mn superexchange contributes to the magnetization even
in metallic superlattices. This Ni-Mn superexchange interaction can be
explained in terms of polar compensation at the LaNiO$_3$-CaMnO$_3$ interface.
These results highlight the different mechanisms responsible for interfacial
ferromagnetism and the importance of understanding compensation due to polar
mismatch at oxide-based interfaces when engineering magnetic properties.",1704.03163v1
2017/4/12,On the origin of magnetic anisotropy in two dimensional CrI$_3$,"The observation of ferromagnetic order in a monolayer of CrI$_3$ has been
recently reported, with a Curie temperature of 45 Kelvin and off-plane easy
axis. Here we study the origin of magnetic anisotropy, a necessary ingredient
to have magnetic order in two dimensions, combining two levels of modeling,
density functional calculations and spin model Hamiltonians. We find two
different contributions to the magnetic anisotropy of the material, both
favoring off-plane magnetization and contributing to open a gap in the spin
wave spectrum. First, ferromagnetic super-exchange across the $\simeq $ 90
degree Cr-I-Cr bonds, are anisotropic, due to the spin orbit interaction of the
ligand I atoms. Second, a much smaller contribution that comes from the single
ion anisotropy of the $S=3/2$ Cr atom. Our results permit to establish the XXZ
Hamiltonian, with a very small single ion anisotropy, as the adequate spin
model for this system. Using spin wave theory we estimate the Curie temperature
and we highlight the essential role played by the gap that magnetic anisotropy
induces on the magnon spectrum.",1704.03849v4
2017/4/26,Magnetic Proximity Effects in Transition-Metal Dichalcogenides: Converting Excitons,"The two-dimensional character and reduced screening in monolayer
transition-metal dichalcogenides (TMDs) lead to the ubiquitous formation of
robust excitons with binding energies orders of magnitude larger than in bulk
semiconductors. Focusing on neutral excitons, bound electron-hole pairs, that
dominate the optical response in TMDs, it is shown that they can provide
fingerprints for magnetic proximity effects in magnetic heterostructures. These
proximity effects cannot be described by the widely used single-particle
description, but instead reveal the possibility of a conversion between
optically inactive and active excitons by rotating the magnetization of the
magnetic substrate. With recent breakthroughs in fabricating Mo- and W-based
magnetic TMD-heterostructures, this emergent optical response can be directly
tested experimentally.",1704.07984v2
2017/6/2,Power Loss for a Periodically Driven Ferromagnetic Nanoparticle in a Viscous Fluid: the Finite Anisotropy Aspects,"The joint magnetic and mechanical motion of a ferromagnetic nanoparticle in a
viscous fluid is considered within the dynamical approach. The equation based
on the total momentum conservation law is used for the description of the
mechanical rotation, while the modified Landau-Lifshitz-Gilbert equation is
utilized for the description of the internal magnetic dynamics. The exact
expressions for the particles trajectories and the power loss are obtained in
the linear approximation. The comparison with the results of other widespread
approaches, such as the model of fixed particle and the model of frozen
magnetic moment, is performed. It is established that in the small oscillations
mode the damping precession of the nanopartile magnetic moment is the main
channel of energy dissipation, but the motion of the nanoparticle easy axis can
significantly influence the value of the resulting power loss.",1706.00777v2
2017/9/18,Skyrmion morphology in ultrathin magnetic films,"Nitrogen-vacancy magnetic microscopy is employed in quenching mode as a
non-invasive, high resolution tool to investigate the morphology of isolated
skyrmions in ultrathin magnetic films. The skyrmion size and shape are found to
be strongly affected by local pinning effects and magnetic field history.
Micromagnetic simulations including static disorder, based on a physical model
of grain-to-grain thickness variations, reproduce all experimental observations
and reveal the key role of disorder and magnetic history in the stabilization
of skyrmions in ultrathin magnetic films. This work opens the way to an
in-depth understanding of skyrmion dynamics in real, disordered media.",1709.06027v2
2018/3/4,Optimization of Time-Resolved Magneto-optical Kerr Effect Signals for Magnetization Dynamics Measurements,"Recently magnetic storage and magnetic memory have shifted towards the use of
magnetic thin films with perpendicular magnetic anisotropy (PMA). Understanding
the magnetic damping in these materials is crucial, but normal Ferromagnetic
Resonance (FMR) measurements face some limitations. The desire to quantify the
damping in materials with PMA has resulted in the adoption of Time-Resolved
Magneto-optical Kerr Effect (TR-MOKE) measurements. In this paper, we discuss
the angle and field dependent signals in TR-MOKE, and utilize a numerical
algorithm based on the Landau-Lifshitz-Gilbert (LLG) equation to provide
information on the optimal conditions to run TR-MOKE measurements.",1803.01280v2
2018/3/15,Synthetic antiferromagnetic coupling between ultra-thin insulating garnets,"The use of magnetic insulators is attracting a lot of interest due to a rich
variety of spin-dependent phenomena with potential applications to spintronic
devices. Here we report ultra-thin yttrium iron garnet (YIG) / gadolinium iron
garnet (GdIG) insulating bilayers on gadolinium iron garnet (GGG). From spin
Hall magnetoresistance (SMR) and X-ray magnetic circular dichroism
measurements, we show that the YIG and GdIG magnetically couple antiparallel
even in moderate in-plane magnetic fields. The results demonstrate an
all-insulating equivalent of a synthetic antiferromagnet in a garnet-based thin
film heterostructure and could open new venues for insulators in magnetic
devices. As an example, we demonstrate a memory element with orthogonal
magnetization switching that can be read by SMR.",1803.05545v1
2018/3/19,Vegas: Software package for the atomistic simulation of magnetic materials,"We present an open-source software package, Vegas, for the atomistic
simulation of magnetic materials. Using the classical Heisenberg model and the
Monte Carlo Metropolis algorithm, Vegas provides the required tools to simulate
and analyze magnetic phenomena of a great variety of systems. Vegas stores the
history of the simulation, i.e. the magnetization and energy of the system at
every time step, allowing to analyze static and dynamic magnetic phenomena from
results obtained in a single simulation. Also, standardized input and output
file formats are employed to facilitate the simulation process and the exchange
and archiving of data. We include results from simulations performed using
Vegas, showing its applicability to study different magnetic phenomena.",1803.07030v1
2018/8/30,The effect of pressure on La$_{1.5}$Ca$_{0.5}$CoIrO$_{6}$ re-entrant spin-glass,"La$_{1.5}$Ca$_{0.5}$CoIrO$_{6}$ is a re-entrant spin-glass (SG) that exhibits
antiferromagnetic and ferromagnetic couplings at $T\sim95$ and $\sim86$ K,
respectively, and at $T\sim25$ K a SG phase emerges. In this work we
investigated the effect of hydrostatic pressure ($P$) on
La$_{1.5}$Ca$_{0.5}$CoIrO$_{6}$ magnetic properties. By means of magnetization
as a function of temperature measurements, carried under different applied
pressures and/or magnetic fields, we have found that the freezing temperature
of the SG phase exhibits an initial increase followed by a decrease with
increasing $P$, and that the maximum $P$ = 7.9 kbar was not sufficient to
prevent the formation of the frozen state. Since the ordering temperatures of
the antiferromagnetic and ferromagnetic phases are also affected by $P$, we
discuss the results here found in terms of changes on the balance between the
magnetic phases.",1808.10403v1
2018/10/11,Intertwined dipolar and multipolar order in the triangular-lattice magnet TmMgGaO$_4$,"A phase transition is often accompanied by the appearance of an order
parameter and symmetry breaking. Certain magnetic materials exhibit exotic
hidden-order phases, in which the order parameters are not directly accessible
to conventional magnetic measurements. Thus, experimental identification and
theoretical understanding of a hidden order are difficult. Here we combine
neutron scattering and thermodynamic probes to study the newly discovered
rare-earth triangular-lattice magnet TmMgGaO$_4$. Clear magnetic Bragg peaks at
K points are observed in the elastic neutron diffraction measurements. More
interesting, however, is the observation of sharp and highly dispersive spin
excitations that cannot be explained by a magnetic dipolar order, but instead
is the direct consequence of the underlying multipolar order that is ""hidden""
in the neutron diffraction experiments. We demonstrate that the observed
unusual spin correlations and thermodynamics can be accurately described by a
transverse field Ising model on the triangular lattice with an intertwined
dipolar and ferro-multipolar order.",1810.05054v2
2018/10/24,Electronic and optical properties of spinel zinc ferrite: $Ab$ $initio$ hybrid functional calculations,"Spinel ferrites in general show a rich interplay of structural, electronic,
and magnetic properties. Here, we particularly focus on zinc ferrite (ZFO),
which has been observed experimentally to crystallise in the cubic $normal$
spinel structure. However, its magnetic ground state is still under dispute. In
addition, some unusual magnetic properties in ZFO thin films or nanostructures
have been explained by a possible partial cation inversion and a different
magnetic interaction between the two cation sublattices of the spinel structure
compared to the crystalline bulk material. Here, density functional theory has
been applied to investigate the influence of different inversion degrees and
magnetic couplings among the cation sublattices on the structural, electronic,
magnetic, and optical properties. Effects of exchange and correlation have been
modelled using the generalised gradient approximation (GGA) together with the
Hubbard `+$U$' parameter, and the more elaborate hybrid functional PBE0. While
the GGA+$U$ calculations yield an antiferromagnetically coupled $normal$ spinel
structure as the ground state, in the PBE0 calculations the ferromagnetically
coupled $normal$ spinel is energetically slightly favoured, and the hybrid
functional calculations perform much better with respect to structural,
electronic and optical properties.",1810.10555v1
2019/1/10,The demagnetization factor for randomly packed spheroidal particles,"We investigate if the demagnetization factor for a randomly packed powder of
magnetic spheroidal particles depend on the shape of the spheroidal particles
and what the internal variation in magnetization is within such a powder. A
spheroid is an ellipsoid of revolution, i.e. an ellipsoid with two semi-major
axis being equal. The demagnetization factor is calculated as function of
particle aspect ratio using two independent numerical models for several
different packings, and assuming a relative permeability of 2. The calculated
demagnetization factor is shown to depend on particle aspect ratio, not because
of direct magnetic interaction but because the particle packing depend on the
aspect ratio of the particles. The relative standard deviation of the
magnetization across the powder was 3\%-8\%, increasing as the particle shape
deviates from spherical, while the relative standard deviation within each
particle was relatively constant around 5\%.",1901.03111v1
2019/1/15,Uncompensated-spins Induced Weak Ferromagnetism in Ca3Mn2O7: Magneto-conductive and dual Magneto-capacitive Effects,"Temperature dependent magnetization study on single phase orthorhombic
Ruddlesden-Popper manganite Ca3Mn2O7 evidences antiferromagnetic (AFM) ordering
below 123K. Field-dependent magnetization M(H) depicts off-centered hysteretic
loops below ~110K-- confirming the existence of both weak ferromagnetism (WFM)
and exchange bias, whose development upon cooling is examined in detail. WFM is
attributed to the formation of uncompensated-spin-clusters within the
AFM-matrix, stabilized by the high-anisotropy in the manganite, favoring
Dzyaloshinskii-Moriya (D-M) interaction. Temperature dependence of an evaluated
average canting angle from the M(H) loops provides a quantitative measure of
the WFM-evolution. Dielectric measurements exhibit magneto-conductive effects
concurrent to the WFM-onset. Temperature dependence of the
low-frequency/dc-limit of Jonscher-fits to the conductivity isotherms confirms
the presence of relatively more-conductive clusters, embedded in the
insulating-bulk. Nyquist impedance-analysis of complex impedance reveals two
relaxations, yielding dual magnetic-field effects; the lumped circuit
parameters feature anomalies across the magnetic phase changes.",1901.04778v2
2015/12/2,Investigation of Arrott plot and magnetocaloric effect in the complex CaMn7O12 perovskite,"Detailed magnetic studies including magneto-caloric measurements on magnetic
multiferroic quadruple perovskite CaMn7O12 are presented. Based on the
collective response of Arrott plots and {\Delta}SM (T), a magnetic phase
diagram of CaMn7O12 is suggested. A new magnetic transition at TN3 ~20 K where
the system changes from noncollinear AFM to collinear AFM is reported. An
anomaly observed in both {\Delta}SM (T) and Arrott plots around 64 K has been
attributed to high external field induced spin canting leading to change in
magnetic order inducing phase transition. Magneto-caloric effect in this
material is presented for the first time. The peak value of change in
isothermal magnetic entropy is 1.3 J/K-Kg and the value of refrigeration
capacity is reported to be 34.5 J/Kg for the field of 7 T.",1512.00618v1
2015/12/8,Anomalous coercivity enhancement with temperature and tunable exchange bias in Gd and Ti co-doped BiFeO$_3$ multiferroics,"We have investigated the effect of temperature on magnetic properties of
Bi$_{0.9}$Gd$_{0.1}$Fe$_{1-x}$Ti$_x$O$_3$ (x = 0.00-0.20) multiferroic system.
Unexpectedly, the coercive fields ($H_{c}$) of this multiferroic system
increased with increasing temperature. The coercive fields and remanent
magnetization were higher over a wide range of temperatures in sample x = 0.10
i.e. in sample having composition Bi$_{0.9}$Gd$_{0.1}$Fe$_{0.9}$Ti$_{0.1}$O$_3$
than those of x = 0.00 and 0.20 compositions. Therefore, we have carried out
temperature dependent magnetization experiments extensively for sample x =
0.10. The magnetic hysteresis loops at different temperatures exhibit an
asymmetric shift towards the magnetic field axes which indicate the presence of
exchange bias effect in this material system. The hysteresis loops were also
carried out at temperatures 150 K and 250 K by cooling down the sample from 300
K in various cooling magnetic fields ($H_{cool}$). The exchange bias field
($H_{EB}$) values increased with $H_{cool}$ and decreased with temperature. The
$H_{EB}$ values were tunable by field cooling at temperatures up to 250 K.",1512.02444v1
2015/12/24,Review of magnetic properties and magnetocaloric effect in the intermetallic compounds of rare earth with low boiling point metal(s),"The magnetocaloric effect (MCE) in many rare earth (RE) based intermetallic
compounds has been extensively investigated during last two decades, not only
due to their potential applications for magnetic refrigeration but also for
better understanding of the fundamental problems of the materials. This paper
reviews our recent progress of magnetic properties and MCE in some binary or
ternary intermetallic compounds of RE with low boiling point metal(s) (Zn, Mg,
and Cd). Some of them are exhibiting promising MCE properties which make them
also attractive for low temperature magnetic refrigeration. Characteristics of
the magnetic transition, origin of large MCE as well as the potential
application of these compounds were thoroughly discussed. Additionally, a brief
review of the magnetic and magnetocaloric properties in the quaternary rare
earth nickel boroncarbides RENi2B2C superconductors is also presented.",1512.07692v1
2018/12/21,Structural and Magnetic Characterization of Spin Canted Mixed Ferrite-Cobaltites: LnFe0.5Co0.5O3 (Ln = Eu and Dy),"The mixed ferrite-cobaltites LnFe0.5Co0.5O3, with Ln = Eu & Dy have been
prepared by a sol-gel method and the samples have been characterized using
X-ray diffraction and electron microscopy. The magnetic investigations reveal
that both samples ordered in canted antiferromagnetic structures near room
temperature. The Dzyaloshinskii-Moriya or antisymmetric exchange interaction
induces weak ferromagnetism due to canting of the antiferromagnetically ordered
spins. In the case of Ln-Fe-Co orthoferrites, two magnetic sublattices (Ln3+-4f
and Fe3+/Co3+-3d) generally align in opposite directions and interesting
temperature dependent phenomena: e.g. uncompensated antiferromagnetic
sublattices and spin-reorientations, are observed in the system. The existence
of hysteresis at low temperature region has been explained in terms of the
strength of magnetic interactions between Fe3+ and Co3+ ions with different
A-site rare earth cations.",1812.09031v2
2016/3/1,Ferromagnetic resonance and magnetic damping in C-doped Mn5Ge3,"Ferromagnetic resonance (FMR) was used to investigate the static and dynamic
magnetic properties of carbon-doped Mn5Ge3 (C$_{0.1}$ and C$_{0.2}$) thin films
grown on Ge(111). The temperature dependence of magnetic anisotropy shows an
increased perpendicular magneto-crystalline contribution at 80K with an
in-plane easy axis due to the large shape contribution. We find that our
samples show a small FMR linewidth (corresponding to an intrinsic magnetic
damping parameter $\alpha$=0.005), which is a measure of the spin relaxation
and directly related with the magnetic and structural quality of the material.
In the perpendicular-to-plane geometry, the FMR linewidth shows a minimum at
around 200K for all the samples, which seems to be not correlated to the
C-doping. The magnetic relaxation parameters have been determined and indicate
the two-magnon scattering as the main extrinsic contribution. We observe a
change in the main contribution from scattering centres in Mn5Ge3C0.2 at low
temperatures, which could be related to the minimum in linewidth.",1603.00190v1
2017/3/3,Magnetic and Hyperfine interactions in HoFe1-xCrxO3 compounds,"We report on the magnetic and Mossbauer properties of polycrystalline
HoFe1-xCrxO3 compounds. Magnetization data reveals the continuous tailoring of
magnetic transition due to weakening of Ho3+ Fe3+ and Fe3+ Fe3+ interactions in
the entire temperature range by replacing the Fe3+ ions with Cr3+ ions. The
observed decrease in Neel temperature (TN) and increase in spin re-orientation
transition temperature (TSR) with the replacement of Fe3+ with Cr3+ is ascribed
to the weakening of Fe(Cr) O Fe(Cr) antiferromagnetic exchange interaction. In
addition, we also attribute such a change in TN to the enhancement of
ferromagnetic interaction of adjacent Cr3+ moments through t e hybridization as
a result of the structural distortion. The decrease in isomer shift (IS)
suggests enhancement of the interaction between nuclear charge with the 3s
electrons as a result of decrease in radial part of 3d wave function with Cr
addition. In this paper we also discuss about the variation of quadrupole
splitting (QS) and hyperfine fields (Hhf) with Cr addition in HoFe1-xCrxO3
compounds.",1703.02094v1
2017/3/27,Spin transfer due to quantum fluctuations of magnetization,"Spin transfer - the transfer of angular momentum from spin-polarized
electrical current to magnetic materials - has been extensively researched as
an efficient mechanism for the electronic manipulation of the static and
dynamic states in nanomagnetic systems, advancing our understanding of
nanomagnetism and electronic transport, and enabling the development of
energy-efficient magnetic nanodevices. Our present understanding of spin
transfer is based on the classical approximation for the magnetization, even
though the spin-polarized electrons mediating spin transfer are treated
quantum-mechanically. Here, we utilize a nanoscale magnetic spin-valve
structure to demonstrate that quantum zero-point fluctuations of magnetization,
neglected in the existing theories of spin transfer, provide the dominant
contribution to this effect at cryogenic temperatures, and remain
non-negligible even at room temperature. The demonstrated quantum spin transfer
(QST) is distinguished by a non-smooth piecewise-linear dependence of the
fluctuation intensity on current, and can be driven not only by the directional
flows of electrons, but also by their thermal motion. This effect can enhance
current-induced phenomena, overcoming the efficiency limitations that are
presently perceived as fundamental to the spin transfer mechanism.",1703.09335v2
2018/9/5,Microscopic understanding of magnetic interactions in bilayer CrI$_3$,"We performed the detailed microscopic analysis of the inter-layer magnetic
couplings for bilayer CrI$_3$. As the first step toward understanding the
recent experimental observations and utilizing them for device applications, we
estimated magnetic force response as well as total energy. Various van der
Waals functionals equivocally point to the ferromagnetic ground state for the
low-temperature structured bilayer CrI$_3$ which is further confirmed
independently by magnetic force response calculations. The calculated
orbital-dependent magnetic forces clearly show that $e_g$-$t_{2g}$ interaction
is the key to stabilize this ferromagnetic order. By suppressing this
ferromagnetic interaction and enhancing antiferromagnetic orbital channels of
$e_g$-$e_g$ and $t_{2g}$-$t_{2g}$, one can realize the desirable
antiferromagnetic order. We showed that high-temperature monoclinic stacking
can be the case. Our results provide unique information and insight to
understand the magnetism of multi-layer CrI$_3$ paving the way to utilize it
for applications.",1809.01388v3
2018/9/13,Incipient spin-dipole coupling in a 1D helical-chain metal-organic hybrid,"Low dimensional magnetic systems (such as spin-chain) are extensively studied
due to their exotic magnetic properties. Here, we would like to address that
such systems should also be interesting in the field of dielectric,
ferroelectricity and magnetodielectric coupling. As a prototype example, we
have investigated a one-dimensional (1D) helical-chain metal-organic hybrid
system with a chiral structure which shows a broad hump in magnetic
susceptibility around 55 K (Tmax). The complex dielectric constant exactly
traces this feature, which suggests intrinsic magnetodielectric coupling in
this chiral system. The dipolar ordering at Tmax occurs due to
lattice-distortion which helps to minimize the magnetic energy accompanied by
1D-magnetic ordering or vice-versa. This experimental demonstration initiates a
step to design and investigate hybrid organic-inorganic magnetic systems
consisting of chiral structure towards ferroelectricity and magnetodielectric
coupling.",1809.04809v1
2019/9/20,Dimer Physics in the Frustrated Cairo Pentagonal Antiferromagnet Bi2Fe4O9,"The research field of magnetic frustration is dominated by triangle-based
lattices but exotic phenomena can also be observed in pentagonal networks. A
peculiar noncollinear magnetic order is indeed known to be stabilized in
Bi2Fe4O9 materializing a Cairo pentagonal lattice. We present the spin wave
excitations in the magnetically ordered state, obtained by inelastic neutron
scattering. They reveal an unconventional excited state related to local
precession of pairs of spins. The magnetic excitations are then modeled to
determine the superexchange interactions for which the frustration is indeed at
the origin of the spin arrangement. This analysis unveils a hierarchy in the
interactions, leading to a paramagnetic state (close to the N\'eel temperature)
constituted of strongly coupled dimers separated by much less correlated spins.
This produces two types of response to an applied magnetic field associated
with the two nonequivalent Fe sites, as observed in the magnetization
distributions obtained using polarized neutrons.",1909.09573v2
2019/10/1,Selected graphenelike zigzag nanoribbons with chemically functionalized edges: Implications for electronic and magnetic properties,"It is known that there is a wide class of quasi-two-dimensional graphenelike
nanomaterials which in many respects can outperform graphene. So, here in
addition to graphene, the attention is directed to stanene (buckled honeycomb
structure) and phosphorene (puckered honeycomb structure). It is shown that,
depending on the doping, these materials can have magnetically ordered edges.
Computed diagrams of magnetic phases illustrate that, on the one hand, n-type
doped narrow zigzag nanoribbons of graphene and stanene have
antiferromagnetically aligned magnetic moments between the edges. On the other
hand, however, in the case of phosphorene nanoribbons the zigzag edges can have
ferromagnetically aligned magnetic moments for the p-type doping. The edge
magnetism critically influences transport properties of the nanoribbons, and if
adequately controlled can make them attractive for spintronics.",1910.00301v1
2019/10/3,Finite size effects on the ultrafast remagnetization dynamics of FePt,"We investigate the ultrafast magnetization dynamics of FePt in the L10 phase
after an optical heating pulse, as used in heat assisted magnetic recording. We
compare continuous and nanogranular thin films and emphasize the impact of the
finite size on the remagnetization dynamics. The remagnetization speeds up
significantly with increasing external magnetic field only for the continuous
film, where domain wall motion governs the dynamics. The ultrafast
remagnetization dynamics in the continuous film are only dominated by heat
transport in the regime of high magnetic fields, whereas the timescale required
for cooling is prevalent in the granular film for all magnetic field strengths.
These findings highlight the necessary conditions for studying the intrinsic
heat transport properties in magnetic materials.",1910.01413v1
2019/10/16,"Temperature-dependent magnetocrystalline anisotropy of rare earth/transition metal permanent magnets from first principles: The light RCo$_5$ (R=Y, La-Gd) intermetallics","Computational design of more efficient rare earth/transition metal (RE-TM)
permanent magnets requires accurately calculating the magnetocrystalline
anisotropy (MCA) at finite temperature, since this property places an upper
bound on the coercivity. Here, we present a first-principles methodology to
calculate the MCA of RE-TM magnets which fully accounts for the effects of
temperature on the underlying electrons. The itinerant electron TM magnetism is
described within the disordered local moment picture, and the localized RE-4f
magnetism is described within crystal field theory. We use our model, which is
free of adjustable parameters, to calculate the MCA of the RCo$_5$ (R=Y, La-Gd)
magnet family for temperatures 0--600 K. We correctly find a huge uniaxial
anisotropy for SmCo$_5$ (21.3 MJm$^{-3}$ at 300 K) and two finite temperature
spin reorientation transitions for NdCo$_5$. The calculations also demonstrate
dramatic valency effects in CeCo$_5$ and PrCo$_5$. Our calculations provide
quantitative, first-principles insight into several decades of RE-TM
experimental studies.",1910.07436v1
2020/3/4,"Two-dimensional CoSe structures: Intrinsic magnetism, strain-tunable anisotropic valleys, magnetic Weyl point, and antiferromagnetic metal state","The interplay between magnetism, band topology, and electronic correlation in
low dimensions has been a fascinating subject of research. Here, we propose
two-dimensional (2D) material systems which demonstrate such an interesting
interplay. Based on first-principles calculations and structural search
algorithms, we identify three lowest energy 2D CoSe structures, termed as the
$\alpha$-, $\beta$-, and $\gamma$-CoSe. {We show that $\alpha$- and
$\beta$-CoSe are two rare examples of 2D antiferromagnetic metals, which are
related to their Fermi surfaces nesting features, and meanwhile, $\gamma$-CoSe
is a ferromagnetic metal. They possess a range of interesting physical
properties, including anisotropic valleys connected by crystalline symmetries,
strain-tunable valley polarization, strain-induced metal-semiconductor and/or
magnetic phase transitions, as well as topological band features such as the
magnetic Weyl point and the magnetic Weyl loop. Remarkably, all the topological
features here are robust against spin-orbit coupling.} Some experimental
aspects of our predictions have been discussed.",2003.01963v2
2020/3/9,Interplay between chemical order and magnetic properties in L1$_0$ FeNi (tetrataenite): A First-Principles Study,"We use first-principles-based calculations to investigate the interplay
between chemical order and the magnetic properties of $L1_0$ FeNi. In
particular, we investigate how deviations from perfect chemical order affect
the energy difference between the paramagnetic and ferromagnetic states as well
as the important magneto-crystalline anisotropy energy. Our calculations
demonstrate a strong effect of the magnetic order on the chemical
order-disorder transition temperature, and conversely, a strong enhancement of
the magnetic transition temperature by the chemical order. Most interestingly,
our results indicate that the magnetic anisotropy does not decrease
significantly as long as the deviations from perfect order are not too large.
Moreover, we find that in certain cases a slight disorder can result in a
higher anisotropy than for the fully ordered structure. We further analyze the
correlation between the magneto-crystalline anisotropy and the orbital magnetic
moment anisotropy, which allows to study the effect of the local chemical
environment on both quantities, potentially enabling further optimization of
the magneto-crystalline anisotropy with respect to chemical order and
stoichiometric composition.",2003.04181v2
2020/3/16,Protected helical transport in magnetically doped quantum wires: Beyond the one-dimensional paradigm,"One-dimensional (1D) quantum wires, which are functionalized by magnetic
ad-atoms, can host ballistic helical transport. Helicity protects transport
from an undesirable influence of material imperfections, and it makes the
magnetically doped wire a very promising element for nanoelectronics and
spintronics. However, fabricating purely 1D conductors is experimentally very
challenging and not always feasible. In this paper, we show that the protected
helical transport can exist even in quasi-1D wires. We model the quasi-1D
magnetically doped wire as two coupled dense 1D Kondo chains. Each chain
consists of itinerant electrons interacting with localized quantum magnetic
moments -- Kondo impurities. We have analyzed the regimes of weak-,
intermediate-, and strong inter-chain coupling, and we found conditions
necessary for the origin of the aforementioned protected transport. Our results
may pave the way for experimental realizations of helical states in
magnetically doped wires.",2003.07261v3
2020/4/1,Suppression of magnetic phase transition at high magnetic field and non-Debye's nature of nano-crystalline Gd$_2$CoMnO$_6$: a detail study of physical properties,"Structural, magnetization, phonon behavior, and dielectric response of
nano-crystalline Gd$_2$CoMnO$_6$ have been presented in this paper. The study
shows that the material crystallizes in $\textit{P2$_1$/n}$ phase group of the
monoclinic crystal structure. XPS measurement shows Co$^{2+}$ and Mn$^{4+}$
oxidation states are present in the sample. Magnetization study reveals that
the sample undergoes a ferromagnetic ordering of Co$^{2+}$ and Mn$^{4+}$
magnetic ions around $T_c$ $\sim$132 K. However we have seen that with the
application of external magnetic field the phase transition is largely
suppressed. Raman study reveals the presence spin-phonon coupling in
Gd$_2$CoMnO$_6$. Dielectric study reveals that the sample shows large
dielectric constant and strong dispersion in mid frequency range. The
dielectric loss shows there are two relaxation processes present in the
material with different relaxation time and which are driven by thermally
activated relaxation mechanics. Further, the Nyquist plot and AC conductivity
study show that this sample is non-Debye's in nature.",2004.00737v1
2020/4/16,Magnetic resonance imaging of spin-wave transport and interference in a magnetic insulator,"Spin waves - the elementary excitations of magnetic materials - are prime
candidate signal carriers for low dissipation information processing. Being
able to image coherent spin-wave transport is crucial for developing
interference-based spin-wave devices. We introduce a platform for probing
coherent spin waves based on magnetic resonance imaging with electron spins in
diamond. Focusing on a thin-film magnetic insulator, we quantify spin-wave
amplitudes, visualize the dispersion, and demonstrate time-domain measurements
of spin-wave packets. We use our platform to study spin-wave interference,
revealing uni-directional, autofocused spin-wave patterns with
frequency-controlled numerical apertures. A theoretical analysis explains the
patterns in terms of chiral spin-wave excitation and stray-field coupling to
the sensor spins. These results pave the way for probing spin waves in
atomically thin magnets, even when embedded between opaque materials.",2004.07746v1
2020/8/3,Observation of compact ferrimagnetic skyrmions in DyCo$_3$ film,"Owing to the experimental discovery of magnetic skyrmions stabilized by the
Dzyaloshinskii-Moriya and/or dipolar interactions in thin films, there is a
recent upsurge of interest in magnetic skyrmions with antiferromagnetic spins
in order to overcome the fundamental limitations inherent with skyrmions in
ferromagnetic materials. Here, we report on the observation of compact
ferrimagnetic skyrmions for the class of amorphous alloys consisting of 4f
rare-earth and 3d transition-metal elements with perpendicular magnetic
anisotropy, using a DyCo$_3$ film, that are identified by combining x-ray
magnetic scattering, scanning transmission x-ray microscopy, and Hall transport
technique. These skyrmions, with antiparallel aligned Dy and Co magnetic
moments and a characteristic core radius of about 40~nm, are formed during the
nucleation and annihilation of the magnetic maze-like domain pattern exhibiting
a topological Hall effect contribution. Our findings provide a promising route
for fundamental research in the field of ferrimagnetic/antiferromagnetic
spintronics towards practical applications.",2008.00725v1
2020/8/11,Effect of doping on SGS and weak half-metallic properties of inverse Heusler Alloys,"Heusler alloys with Mn and Co have been found to exhibit interesting
electronic and magnetic properties. Mn$_2$CoAl is well known SGS compound while
Mn$_2$CoGa has weak half metallic character. By using plane wave
pseudo-potential method, we studied the effect of Fe and Cr doping on
half-metalicity and magnetism of these compounds. The doping destroys the SGS
nature of Mn$_2$CoAl while the small-scale doping enhance the half-metallicity
of Mn$_2$CoGa making it perfect half-metal. In case of Mn$_2$CoAl, the doping
decrease the band gap while increase in band width is noticed for Mn$_2$CoGa.
The half-metallicity is destroyed in both cases when the doping level is beyond
certain degree. Moreover, we have also computed magnetic behavior of Mn$_2$CoZ
alloys and we found that total magnetic moments of dopped samples have higher
values than that of pristine compounds.",2008.04536v1
2020/8/12,Measurements of the magnetic properties of conduction electrons,"We consider various methods and techniques for measuring electron
magnetization and susceptibility, which are used in experimental condensed
matter physics. The list of considered methods for macroscopic measurements
includes magnetomechanic, electromagnetic, modulation-type, and also
thermodynamic methods based on the chemical potential variation. We also
consider local methods of magnetic measurements based on the spin Hall effects
and NV-centers. Several scanning probe magnetometers-microscopes are
considered, such as magnetic resonance force microscope, SQUID-microscope, and
Hall microscope. The review focuses on the spin magnetization measurements of
electrons in non-magnetic materials and artificial systems, particularly, in
low-dimensional electron systems in semiconductors and in nanosystems, which
came to the forefront in recent years.",2008.05451v1
2020/8/24,Unconventional magnetic ferroelectricity in the quadruple perovskite NaMn$_7$O$_{12}$,"By means of magnetic, specific heat and pyroelectric measurements, we report
on magnetic ferroelectricity in the quadruple perovskite \namno, characterized
by a canted antiferromagnetic (AFM) CE structure. Surprisingly,
ferroelectricity is concomitant to a dramatic broadening of the magnetic
hysteresis loop, well below the AFM ordering temperature. This unconventional
behavior shows that the formation of ferroelectric domains is induced by the
symmetric exchange interaction in the local scale, e.g. at magnetic domain
boundaries or defects. The value of electric polarization, $P = 0.027 \mu$C
cm$^{-2}$, measured in polycrystalline samples is comparatively large as
compared to other magnetic multiferroics, suggesting that the above scenario is
promising indeed for the rational design of practical multiferroic materials.",2008.10405v2
2021/4/15,Super strong paramagnetism induced by polar functional groups and water,"We experimentally demonstrate that some commonly used materials such as
cellulose acetate and chitin which are traditionally considered to be
non-magnetic show super strong paramagnetism in aqueous solutions under ambient
conditions when they are agglomerated by nanoparticles. Theoretical
computations show that strongly polar functional groups can reduce the
potential barrier for a singlet-triplet interconversion with the help of
surrounding water, inducing the magnetic moments. These magnetic moments
distributed on the surfaces of the nanoparticles, which make a large number of
magnetic moments gather in a very small space, greatly enhance the alignment of
the moments along and amplify the effect of the external magnetic field,
resulting in the super strong paramagnetism. Our findings suggest that the
polar functional group may always induce paramagnetism and the magnetic effect
may be universal as the electric effects since the polarization is very common
in materials.",2104.07287v1
2021/4/20,Multiferroics and beyond: electric properties of different magnetic textures,"This article presents a survey of many nontrivial effects connected with the
coupling of electric and magnetic degrees of freedom in solids -- the field
initiated by I.~E.~Dzyaloshinskii in 1959. I briefly consider the main physics
of ultiferroic materials, and concentrate on different effects ""beyond
multiferroics"", based on the same physical mechanisms which operate in
multiferroics. In particular they lead to nontrivial electric properties of
different magnetic textures -- such as the appearance of dipoles on magnetic
monopoles in spin ice, dipoles on some domain walls in the usual ferromagnets,
on skyrmions etc. The inverse effect, the appearance of magnetic monopoles on
electric charges in magnetoelectrics, is also discussed. This nontrivial
electric activity of different magnetic textures has manifestations in many
experimental properties of these materials, and it can potentially lead to
novel applications.",2104.10216v1
2021/5/3,Dislocation-driven relaxation processes at the conical to helical phase transition in FeGe,"The formation of topological spin textures at the nanoscale has a significant
impact on the long-range order and dynamical response of magnetic materials. We
study the relaxation mechanisms at the conical-to-helical phase transition in
the chiral magnet FeGe. By combining ac susceptibility, magnetic force
microscopy measurements and micromagnetic simulations, we demonstrate how the
motion of magnetic topological defects, here edge dislocations, impacts the
local formation of a stable helimagnetic spin structure. Although the
simulations show that the edge dislocations move with a velocity of about 100
m/s through the helimagnetic background, their dynamics are observed to disturb
the magnetic order on the timescale of minutes due to pinning by randomly
distributed structural defects. The results corroborate the substantial impact
of dislocation motions on the nanoscale spin structure in chiral magnets,
revealing previously hidden effects on the formation of helimagnetic domains
and domain walls.",2105.00658v1
2007/7/20,Ordering effects in diluted magnetic semiconductors,"We review recently developed two-step approach for description of electronic
and magnetic properties of a new class of materials, the diluted magnetic
semiconductors. In the first step we construct, on the basis of the
state-of-the-art first-principles electronic structure calculations, the
effective Ising and Heisenberg Hamiltonians which describe, respectively, the
alloy phase stability and the magnetic excitations in the system. In the second
step, we analyze properties of these effective Hamiltonians by various methods
of statistical physics. As a case study, the prototypical diluted magnetic
semiconductor Ga_{1-x}Mn_{x}As is studied in detail. We determine, among
others, a possibility for clustering in this system, formation energies of
various compensating defects, and estimate short-range order parameters
describing ordering tendencies in a system. On the other hand, by using
recently developed local random-phase approximation approach, we evaluate the
system Curie temperature and demonstrate its strong dependence on the sample
preparation. We also emphasize the relevance of proper inclusion of the
randomness in positions of magnetic impurities for a reliable estimate of the
system critical temperature. Finally, we compare calculated Curie temperatures
with available experimental data and briefly mention relation to other
theoretical approaches.",0707.3079v1
2012/2/28,Avian magnetoreception model realized by coupling magnetite-based mechanism with radical-pair-based mechanism,"Many animal species were verified to use geomagnetic field for their
navigation, but the biophysical mechanism of magnetoreception has remained
enigmatic. This paper presents a special biophysical model that consists of
magnetite-based and radical-pair-based mechanisms for avian magnetoreception.
The amplitude of the resultant magnetic field around the magnetic particles
corresponds to the geomagnetic field direction and affects the yield of
singlet/triplet state products in the radical-pair reactions. Therefore, in the
proposed model, the singlet/triplet state product yields are related to the
geomagnetic field information for orientational detection. The resultant
magnetic fields corresponding to two materials with different magnetic
properties were analyzed under different geomagnetic field directions. The
results showed that ferromagnetic particles in organisms can provide more
significant changes in singlet state products than superparamagnetic particles,
and the period of variation for the singlet state products with an included
angle in the geomagnetic field is approximately 180{\deg} when the magnetic
particles are ferromagnetic materials, consistent with the experimental results
obtained from avian magnetic compass. Further, the calculated results of the
singlet state products in a reception plane showed that the proposed model can
explain the avian magnetoreception mechanism with an inclination compass.",1202.6108v2
2013/10/31,Dilute Magnetism and Spin-Orbital Percolation Effects in Rh-doped Sr2IrO4,"We have used a combination of resonant magnetic x-ray scattering (RMXS) and
x-ray absorption spectroscopy (XAS) to investigate the properties of the doped
spin-orbital Mott insulator Sr2Ir(1-x)Rh(x)O4 (0.07 < x < 0.70). We show that
Sr2Ir(1-x)Rh(x)O4 represents a unique model system for the study of dilute
magnetism in the presence of strong spin-orbit coupling, and provide evidence
of a doping-induced change in magnetic structure and a suppression of magnetic
order at x_c ~ 0.17. We demonstrate that Rh-doping introduces Rh3+/Ir5+ ions
which effectively hole-dope this material. We propose that the magnetic phase
diagram for this material can be understood in terms of a novel spin-orbital
percolation picture.",1311.0039v2
2014/1/20,Magnetic Properties and Large Coercivity of MnxGa Nanostructures,"To investigate structure-property correlations, high-coercivity MnxGa
nanoparticles were synthesized by the method of sequential deposition of Ga and
Mn fluxes using molecular beam epitaxy. Spontaneous nanostructuring was
assisted by the use of an Au precursor and thermal annealing, and the growth
properties, structure and magnetic properties were characterized. Atomic force
microscopy revealed average particle dimensions of 100 nm and X-ray diffraction
revealed a dominant tetragonal D022 crystal structures. Magnetic
characterization at room temperature identified the presence of two magnetic
phases, dominated by a high-coercivity (2.3 T) component in addition to a
low-coercivity component.",1401.4914v1
2014/4/6,Preparation and Characterization of Nano-particle Substituted Barium Hexaferrite,"High density magnetic recording requires high coercivity magnetic media and
small particle size. Barium hexaferrite has been considered as a leading
candidate material because of its chemical stability, fairly large crystal
anisotropy and suitable magnetic characteristics. In this work, we present the
preparation of the hexagonal ferrite BaFe12O19 and one of its derivative; the
Zn-Sn substituted hexaferrite by the chemical co-precipitation method. The main
advantage of this method on the conventional glass-ceramic one, resides in
providing a small enough particle size for magnetic recording. We demonstrate
using the X-ray diffraction patterns that the particle size decreases when
substituting the hexaferrite by the Zn-Sn combination. This may improve the
magnetic properties of the hexaferrite as a medium for HD magnetic recording",1404.1573v1
2016/6/13,"Structural, electronic and magnetic properties of Fe doped CoCr$_{2}$O$_{4}$: insights from ab initio calculations","CoCr$_2$O$_4$ has attracted significant attention recently due to several
interesting properties such as magnetostriction, magnetoelectricity etc.. More
recent experiments on Fe substituted CoCr$_2$O$_4$ observed a variety of novel
phenomena such as the magnetic compensation accompanied by the occurrence of
exchange bias, which reverses its sign. Understanding of such phenomena may
lead to control the properties of these material in an efficient way to enhance
its potential for multifunctional applications. In this paper, we study the
microscopic understanding of Fe doping in modifying the structural and magnetic
properties of CoCr$_{2}$O$_{4}$ with varying composition and substitution of Fe
at different sublattices by first-principles density functional calculations.
We have analysed in detail the effect of Fe substitution on crystal field and
exchange splittings, magnetic moments and interatomic exchange parameters. It
is also observed that with increasing concentration of Fe impurity, the system
has a tendency towards forming an ""Inverse Spinel"" structure as observed in
experiments. Such tendencies are crucial to understand this system as it would
lead to modifications in the magnetic exchange interactions associated with
sites with different symmetry finally affecting the magnetic structure and the
multiferrocity in turn.",1606.03849v1
2016/6/15,Driving Skyrmions in a Composite Bilayer,"Magnetic Skyrmions and multiferroics are the most interesting objects in
nanostructure science that have great potential in future spin-electronic
technology. The study of multiferroic Skyrmions has attracted much interest in
recent years. This article reports magnetic Bloch Skyrmions induced by an
electric driving field in a composite bilayer (chiral-magnetic/ferroelectric
bilayer) lattice. By using the spin dynamics method, we use a classical
magnetic spin model and an electric pseudospin model, which are coupled by a
strong magnetoelectric coupling in the dynamical simulations. Interestingly, we
observe some skyrmion-like objects in the electric component either during the
switching process or by applying a magnetic field, which is due to the
connection between the electric and the magnetic structures.",1606.04595v3
2016/6/23,Inversion of ferrimagnetic magnetization by ferroelectric switching via a novel magnetoelectric coupling,"Although several multiferroic materials/heterostructures have been
extensively studied, finding strong magnetoelectric couplings for the electric
field control of the magnetization remains challenging. Here, a novel
interfacial magnetoelectric coupling based on three components (ferroelectric
dipole, magnetic moment, and antiferromagnetic order) is analytically
formulated. As an extension of carrier-mediated magnetoelectricity, the new
coupling is shown to induce an electric-magnetic hysteresis loop. Realizations
employing BiFeO$_3$ bilayers grown along the [$111$] axis are proposed. Without
involving magnetic phase transitions, the magnetization orientation can be
switched by the carrier modulation driven by the field effect, as confirmed
using first-principles calculations.",1606.07203v1
2017/7/3,Heavy-mass magnetic modes in pyrochlore iridates due to dominant Dzyaloshinskii-Moriya interaction,"Materials with strong spin-orbit interactions are presently a main target in
the search for systems with novel magnetic properties. Magnetic anisotropies
can be very large in such compounds, ranging from strongly frustrated Kitaev
exchange in honeycomb iridates and the associated spin-liquid states to robust
antisymmetric couplings in square-lattice Sr_2IrO_4 . Here we predict from ab
initio quantum chemistry calculations that another highly unusual regime is
realized in pyrochlore iridium oxides: the nearest-neighbor Heisenberg
interaction can vanish whilst the antisymmetric Dzyaloshinskii- Moriya exchange
reaches values as large as 5 meV, a result which challenges common notions and
existing phenomenological models of magnetic superexchange. The resulting spin
excitation spectra reveal a very flat magnon dispersion in the Nd- and Tb-based
pyrochlore iridates, suggesting the possibility of using these modes to store
magnetic information. Indeed the magnetization dynamics indicates that these
modes are unable to propagate out of the excitation region.",1707.00500v1
2017/7/25,Thermodynamics of a model solid with magnetoelastic coupling,"In the paper a study of a model magnetoelastic solid system is presented. The
system of interest is a mean-field magnet with nearest-neighbour ferromagnetic
interactions and the underlying s.c. crystalline lattice with the long-range
Morse interatomic potential and the anharmonic Debye model for the lattice
vibrations. The influence of the external magnetic field on the thermodynamics
is investigated, with special emphasis put on the consequences of the
magnetoelastic coupling, introduced by the power-law distance dependence of the
magnetic exchange integral. Within the fully self-consistent, Gibbs
energy-based formalism such thermodynamic quantities as the entropy, the
specific heat as well as the lattice and magnetic response functions are
calculated and discussed. To complete the picture, the magnetocaloric effect is
characterized by analysis of the isothermal entropy change and the adiabatic
temperature change in the presence of the external pressure.",1707.07937v3
2017/7/26,Evidence of Spontaneous Vortex Ground State in An Iron-Based Ferromagnetic Superconductor,"Spontaneous vortex phase (SVP) is an exotic quantum matter in which quantized
superconducting vortices form in the absence of external magnetic field.
Although being predicted theoretically nearly 40 years ago, its rigorous
experimental verification still appears to be lacking. Here we present
low-field magnetic measurements on single crystals of the iron-based
ferromagnetic superconductor Eu(Fe$_{0.91}$Rh$_{0.09}$)$_{2}$As$_{2}$ which
undergoes a superconducting transition at $T_\mathrm{sc}$ = 19.6 K followed by
a magnetic transition at $T_\mathrm{m}$ = 16.8 K. We observe a characteristic
first-order transition from a Meissner state within
$T_\mathrm{m}<T<T_\mathrm{sc}$ to an SVP below $T_\mathrm{m}$, under a magnetic
field approaching zero. Additional isothermal magnetization and ac
magnetization measurements at $T\ll T_\mathrm{sc}$ confirm that the system is
intrinsically in a spontaneous-vortex ground state. The unambiguous
demonstration of SVP in the title material lays a solid foundation for future
imaging and spectroscopic studies on this intriguing quantum matter.",1707.08420v1
2018/2/16,Manipulating surface magnetic order in iron telluride,"Control of emergent magnetic orders in correlated electron materials promises
new opportunities for applications in spintronics. For their technological
exploitation, it is important to understand the role of surfaces and interfaces
to other materials and their impact on the emergent magnetic orders. Here, we
demonstrate for iron telluride, the nonsuperconducting parent compound of the
iron chalcogenide superconductors, determination and manipulation of the
surface magnetic structure by low-temperature spin-polarized scanning tunneling
microscopy. Iron telluride exhibits a complex structural and magnetic phase
diagram as a function of interstitial iron concentration. Several theories have
been put forward to explain the different magnetic orders observed in the phase
diagram, which ascribe a dominant role either to interactions mediated by
itinerant electrons or to local moment interactions. Through the controlled
removal of surface excess iron, we can separate the influence of the excess
iron from that of the change in the lattice structure.",1802.05978v2
2018/5/7,Optical control of magnetism in NiFe/VO2 heterostructures,"Optical methods for magnetism manipulation have been considered as a
promising strategy for ultralow-power and ultrahigh-speed spin switches, which
becomes a hot spot in the field of spintronics. However, a widely applicable
and efficient method to combine optical operation with magnetic modulation is
still highly desired. Here, the strongly correlated electron material VO2 is
introduced to realize phase-transition based optical control of the magnetism
in NiFe. The NiFe/VO2 bilayer heterostructure features appreciable modulations
in electrical conductivity (55%), coercivity (60%), and magnetic anisotropy
(33.5%). Further analyses indicate that interfacial strain coupling plays a
crucial role in this modulation. Utilizing this optically controlled magnetism
modulation feature, programmable Boolean logic gates (AND, OR, NAND, NOR, XOR,
NXOR and NOT) for high-speed and low-power data processing are demonstrated
based on this engineered heterostructure. As a demonstration of
phase-transition spintronics, this work may pave the way for next-generation
electronics in the post-Moore era.",1805.02453v3
2018/11/8,Calculated magnetic exchange interactions in Dirac magnon material Cu3TeO6,"Recently topological aspects of magnon band structure have attracted much
interest, and especially, the Dirac magnons in Cu3TeO6 have been observed
experimentally. In this work, we calculate the magnetic exchange interactions
J's using the first-principles linear-response approach and find that these J's
are short-range and negligible for the Cu-Cu atomic pair apart by longer than 7
Angstrom. Moreover there are only 5 sizable magnetic exchange interactions, and
according to their signs and strengths, modest magnetic frustration is
expected. Based on the obtained magnetic exchange couplings, we successfully
reproduce the experimental spin-wave dispersions. The calculated neutron
scattering cross section also agrees very well with the experiments. We also
calculate Dzyaloshinskii-Moriya interactions (DMIs) and estimate the canting
angle (about 1.3{\deg}) of the magnetic non-collinearity based on the
competition between DMIs and J's, which is consistent with the experiment. The
small canting angle agrees with that the current experiments cannot distinguish
the DMI induced nodal line from a Dirac point in the spin-wave spectrum.
Finally we analytically prove that the ""sum rule"" conjectured in [Nat. Phys.
14, 1011 (2018)] holds but only up to the 11th nearest neighbour.",1811.03603v1
2019/2/22,A highly sensitive magnetic sensor using a 2D van der Waals ferromagnetic material,"Two-dimensional (2D) van der Waals ferromagnetic materials are emerging as
promising candidates for applications in ultra-compact spintronic nanodevices,
nanosensors, and information storage. Our recent discovery of the strong room
temperature ferromagnetism in single layers of VSe2 grown on graphite or MoS2
substrate has opened new opportunities to explore these ultrathin magnets for
such applications. In this paper, we present a new type of magnetic sensor that
utilizes the single layer VSe2 film as a highly sensitive magnetic core. The
sensor relies in changes in resonance frequency of the LC circuit composed of a
soft ferromagnetic microwire coil that contains the ferromagnetic VSe2 film
subject to applied DC magnetic fields. The sensitivity of the sensor reaches an
extremely high value of 16x10^6 Hz/Oe, making it an excellent candidate for a
wide range of magnetic sensing applications.",1902.08365v1
2019/2/27,Nuclear magnetic resonance spectroscopy as a dynamical structural probe of high pressure hydrogen,"An unambiguous crystallographic structure solution for the observed phases
II-VI of high pressure hydrogen does not exist due to the failure of standard
structural probes at extreme pressure. In this work we propose that nuclear
magnetic resonance spectroscopy provides a complementary structural probe for
high pressure hydrogen. We show that the best structural models available for
phases II, III, and IV of high pressure hydrogen exhibit markedly distinct
nuclear magnetic resonance spectra which could therefore be used to
discriminate amongst them. As an example, we demonstrate how nuclear magnetic
resonance spectroscopy could be used to establish whether phase III exhibits
polymorphism. Our calculations also reveal a strong renormalisation of the
nuclear magnetic resonance response in hydrogen arising from quantum
fluctuations, as well as a strong isotope effect. As the experimental
techniques develop, nuclear magnetic resonance spectroscopy can be expected to
become a useful complementary structural probe in high pressure experiments.",1902.10721v2
2019/3/7,Quantum-mechanical treatment of atomic resolution differential phase contrast imaging of magnetic materials,"Utilizing the Pauli equation based multislice method, introduced in Phys.
Rev. Lett. 116, 127203 (2016), we study the atomic resolution differential
phase contrast (DPC) imaging on an example of a hard magnet FePt with in-plane
magnetization. Simulated center of mass pattern in a scanning transmission
electron microscopy (STEM) experiment carries information about both electric
and magnetic fields. The momentum transfer remains curl-free, which has
consequences for interpretation of the integrated DPC technique. The extracted
magnetic component of the pattern is compared to the expected projected
microscopic magnetic field as obtained by density functional theory
calculation. Qualitative agreement is obtained for low sample thicknesses and a
suitable range of collection angles.",1903.03083v1
2019/5/16,Transition between canted antiferromagnetic and spin-polarized ferromagnetic quantum Hall states in graphene on a ferrimagnetic insulator,"In the quantum Hall regime of graphene, antiferromagnetic and spin-polarized
ferromagnetic states at the zeroth Landau level compete, leading to a canted
antiferromagnetic state depending on the direction and magnitude of an applied
magnetic field. Here, we investigate this transition at 2.7 K in graphene Hall
bars that are proximity coupled to the ferrimagnetic insulator
Y$_{3}$Fe$_{5}$O$_{12}$. From nonlocal transport measurements, we demonstrate
an induced magnetic exchange field in graphene, which lowers the magnetic field
required to modulate the magnetic state in graphene. These results show that a
magnetic proximity effect in graphene is an important ingredient for the
development of two-dimensional materials in which it is desirable for ordered
states of matter to be tunable with relatively small applied magnetic fields (>
6 T).",1905.06866v2
2019/7/4,Resonant Acoustic Wave Assisted Spin-Transfer-Torque Switching of Nanomagnets,"We report the possibility of achieving an order of magnitude reduction in the
energy dissipation needed to write bits in perpendicular magnetic tunnel
junctions (p-MTJs) by simulating the magnetization dynamics under a combination
of resonant surface acoustic waves (r-SAW) and spin-transfer-torque (STT). The
magnetization dynamics were simulated using the Landau-Lifshitz-Gilbert
equation under macrospin assumption with the inclusion of thermal noise. The
resonant magnetization dynamics in the magnetostrictive nanomagnet build over
few 10s of cycles of SAW application that drives the magnetization to precess
in a cone with a deflection of ~45 degrees from the perpendicular direction.
This reduces the STT current density required to switch the magnetization
direction without increasing the STT application time or degrading the
switching probability in the presence of room temperature thermal noise. This
could lead to a pathway to achieve energy efficient switching of spin transfer
torque random access memory (STTRAM) whose lateral dimensions can be scaled
aggressively despite using materials with low magnetostriction by employing
resonant excitation.",1907.02255v1
2019/7/4,Strain-tunable magnetic order and electronic structure in 2D CrAsS$_4$,"The effect of strain on the magnetic order and band structure of single-layer
CrAsS$_4$ has been investigated by first-principles calculations based on
density functional theory. We found that single-layer CrAsS$_4$ was an
antiferromagnetic (AFM) semiconductor, and would have a phase transition from
AFM state to ferromagnetic (FM) state by applying a uniaxial tensile strain of
2.99\% along the y-direction or compressive strain of 1.76\% along the
x-direction. The underlying physical mechanism of strain-dependent magnetic
stability was further elucidated as the result of the competition between the
direct exchange and indirect superexchange interactions. Moreover, band gap
exhibit a abrupt change along with phase transition of magnetic order. Our
study provides an intuitional approach to design strain-modulated spintronic
devices.",1907.02439v1
2019/11/3,Magnetic damping modulation in $IrMn_{3}/Ni_{80}Fe_{20}$ via the magnetic spin Hall effect,"Non-collinear antiferromagnets can have additional spin Hall effects due to
the net chirality of their magnetic spin structure, which provides for more
complex spin-transport phenomena compared to ordinary non-magnetic materials.
Here we investigated how ferromagnetic resonance of permalloy
($Ni_{80}Fe_{20}$) is modulated by spin Hall effects in adjacent epitaxial
$IrMn_{3}$ films. We observe a large dc modulation of the ferromagnetic
resonance linewidth for currents applied along the [001] $IrMn_{3}$ direction.
This very strong angular dependence of spin-orbit torques from dc currents
through the bilayers can be explained by the magnetic spin Hall effect where
$IrMn_{3}$ provides novel pathways for modulating magnetization dynamics
electrically.",1911.00943v1
2019/11/5,Numerical methods for antiferromagnetics,"Compared with ferromagnetic counterparts, antiferromagnetic materials are
considered as the future of spintronic applications since these materials are
robust against the magnetic perturbation, produce no stray field, and display
ultrafast dynamics. There are (at least) two sets of magnetic moments in
antiferromagnets (with magnetization of the same magnitude but antiparallel
directions) and ferrimagnets (with magnetization of the different magnitude).
The coupled dynamics for the bipartite collinear antiferromagnets is modeled by
a coupled system of Landau-Lifshitz-Gilbert equations with an additional term
originated from the antiferromagnetic exchange, which leads to femtosecond
magnetization dynamics. In this paper, we develop three Gauss-Seidel projection
methods for micromagnetics simulation in antiferromagnets and ferrimagnets.
They are first-order accurate in time and second-order in space, and only solve
linear systems of equations with constant coefficients at each step.
Femtosecond dynamics, N\'{e}el wall structure, and phase transition in presence
of an external magnetic field for antiferromagnets are provided with the
femtosecond stepsize.",1911.01717v1
2019/11/20,Optical magnetic dipole levitation using a plasmonic surface,"Optically-induced magnetic resonances in non-magnetic media have unlocked
magnetic light-matter interactions and led to new technologies in many research
fields. Previous proposals for the levitation of nanoscale particles without
structured illumination have worked on the basis of epsilon-near-zero surfaces
or anisotropic materials but these carry with them significant fabrication
difficulties. We report the optical levitation of a magnetic dipole over a wide
range of realistic materials, including bulk metals, thereby relieving these
difficulties. The repulsion is independent of surface losses and we propose an
experiment to detect this force which consists of a core-shell nanoparticle,
exhibiting a magnetic resonance, in close proximity to a gold substrate under
plane wave illumination. We anticipate the use of this phenomenon in new
nanomechanical devices.",1911.08825v1
2019/11/27,Block-spiral magnetism: An exotic type of frustrated order,"Competing interactions in Quantum Materials induce novel states of matter
such as frustrated magnets, an extensive field of research both from the
theoretical and experimental perspectives. Here, we show that competing energy
scales present in the low-dimensional orbital-selective Mott phase (OSMP)
induce an exotic magnetic order, never reported before. Earlier neutron
scattering experiments on iron-based 123 ladder materials, where OSMP is
relevant, already confirmed our previous theoretical prediction of
block-magnetism (magnetic order of the form
$\uparrow\uparrow\downarrow\downarrow$). Now we argue that another novel phase
can be stabilized in multi-orbital Hubbard models, the {\it block-spiral
state}. In this state, the magnetic islands form a spiral propagating through
the chain but with the blocks maintaining their identity, namely rigidly
rotating. This new spiral state is stabilized without any apparent frustration,
the common avenue to generate spiral arrangements in multiferroics. By
examining the behaviour of the electronic degrees of freedom, parity breaking
quasiparticles are revealed. Finally, a simple phenomenological model that
accurately captures the macroscopic spin spiral arrangement is also introduced,
and fingerprints for the neutron scattering experimental detection of our new
state are provided.",1911.12248v2
2020/5/9,"Structural, electronic and magnetic properties of point defects in polyaniline (C3N) and graphene monolayers: A comparative study","The newly synthesized two-dimensional polyaniline (C3N) is structurally
similar to graphene, and has interesting electronic, magnetic, optical, and
thermal properties. Motivated by the fact that point defects in graphene give
rise to interesting features, like magnetization in an all carbon material, we
perform density functional theory calculations to investigate vacancy and
Stone-Wales type point defects in monolayer C3N. We compare and contrast the
structural, electronic and magnetic properties of these defects with those in
graphene. While monovacancies and Stone-Wales defects of C3N result in
reconstructions similar to those in graphene, divacancies display dissimilar
geometrical features. Different from graphene, all vacancies in C3N have
metallic character because of altered stoichiometry, those which have
low-coordinated atoms have finite magnetic moments. We further investigate the
robustness of the reconstructed structures and the changes in the magnetic
moments by applying tensile and compressive biaxial strain. We find that, with
the advantage of finite band gap, point defects in C3N are qualified as good
candidates for future spintronics applications.",2005.04419v1
2020/5/28,Magnetic properties of quasi-one-dimensional lanthanide calcium oxyborates Ca$_4$LnO(BO$_3$)$_3$,"This study examines the lanthanide calcium oxyborates Ca$_4$LnO(BO$_3$)$_3$
(Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, Yb). The reported monoclinic
structure (space group $Cm$) was confirmed using powder X-ray diffraction. The
magnetic Ln$^{3+}$ ions are situated in well-separated chains parallel to the c
axis in a quasi-one-dimensional array. Here we report the first bulk magnetic
characterisation of Ca$_4$LnO(BO$_3$)$_3$ using magnetic susceptibility
$\chi$(T) and isothermal magnetisation M(H) measurements at T $\geq$ 2 K. With
the sole exception of Ca$_4$TbO(BO$_3$)$_3$, which displays a transition at T =
3.6 K, no magnetic transitions occur above 2 K, and Curie-Weiss analysis
indicates antiferromagnetic nearest-neighbour interactions for all samples.
Calculation of the magnetic entropy change $\Delta S_m$ indicates that
Ca$_4$GdO(BO$_3$)$_3$ and Ca$_4$HoO(BO$_3$)$_3$ are viable magnetocaloric
materials at liquid helium temperatures in the high-field and low-field regimes
respectively.",2005.14183v1
2020/6/4,Prediction of the Curie temperature considering the dependence of the phonon free energy on magnetic states,"Prediction of the Curie temperature is of significant importance for the
design of ferromagnetic materials. Even though the Curie temperature has been
estimated using the Heisenberg model, magnetic exchange coupling parameters
widely used is thus far based on first-principles calculations at zero
temperature. In the explicit consideration of temperature effects, it is
important to minimise the total free energy, because the magnetic and phonon
free energies correlate with each other. Here, we propose a first-principles
thermodynamic approach to minimise the total free energy considering both the
influences of magnetism on phonons and the feedback effect from phonons to
magnetism. By applying our scheme to bcc Fe, we find a significant reduction of
the Curie temperature due to the feedback effect. This result inevitably
enforces us to change our convention as follows: we should use exchange
coupling constants for the disordered local moment state, not for the
ferromagnetic state, in the prediction of the Curie temperature. Our results
not only change the fundamental understanding of finite-temperature magnetism
but also provide a general framework to predict the Curie temperature more
accurately.",2006.02604v1
2020/6/19,Topological transport of deconfined hedgehogs in magnets,"We theoretically investigate the dynamics of magnetic hedgehogs, which are
three-dimensional topological spin textures that exist in common magnets,
focusing on their transport properties and connections to spintronics. We show
that fictitious magnetic monopoles carried by hedgehog textures obey a
topological conservation law, based on which a hydrodynamic theory is
developed. We propose a nonlocal transport measurement in the disordered phase,
where the conservation of the hedgehog flow results in a nonlocal signal
decaying inversely proportional to the distance. The bulk-edge correspondence
between hedgehog number and skyrmion number, the fictitious electric charges
arising from magnetic dynamics, and the analogy between bound states of
hedgehogs in ordered phase and the quark confinement in quantum chromodynamics
are also discussed. Our study points to a practical potential in utilizing
hedgehog flows for long-range neutral signal propagation or manipulation of
skyrmion textures in three-dimensional magnetic materials.",2006.10910v3
2020/7/3,From Weak Antilocalization to Kondo Scattering in a Magnetic Complex Oxide Interface,"Quantum corrections to electrical resistance can serve as sensitive probes of
the magnetic landscape of a material. For example, interference between
time-reversed electron paths gives rise to weak localization effects, which can
provide information about the coupling between spins and orbital motion, while
the Kondo effect is sensitive to the presence of spin impurities. Here we use
low-temperature magnetotransport measurements to reveal a transition from weak
antilocalization (WAL) to Kondo scattering in the quasi-two-dimensional
electron gas formed at the interface between SrTiO$_3$ and the Mott insulator
NdTiO$_3$. This transition occurs as the thickness of the NdTiO$_3$ layer is
increased. Analysis of the Kondo scattering and WAL points to the presence of
atomic-scale magnetic impurities coexisting with extended magnetic regions that
affect transport via a strong magnetic exchange interaction. This leads to
distinct magnetoresistance behaviors that can serve as a sensitive probe of
magnetic properties in two dimensions.",2007.01853v1
2020/7/5,Novel magnetic states and nematic spin chirality in the kagome lattice metal YMn$_{6}$Sn$_{6}$,"Identification, understanding, and manipulation of novel magnetic textures is
essential for the discovery of new quantum materials for future spin-based
electronic devices. In particular, materials that manifest a large response to
external stimuli such as a magnetic field are subject to intense investigation.
Here, we study the kagome-net magnet YMn$_{6}$Sn$_{6}$ by magnetometry,
transport, and neutron diffraction measurements combined with first principles
calculations. We identify a number of nontrivial magnetic phases, explain their
microscopic nature, and demonstrate that one of them hosts a large topological
Hall effect (THE). We propose a new nematic chirality mechanism, reminiscent of
the nematicity in Fe-based superconductors, which leads to the THE at elevated
temperatures. This interesting physics comes from parametrically frustrated
interplanar exchange interactions that trigger strong magnetic fluctuations.
Our results pave a path to new chiral spin textures, promising for novel
spintronics.",2007.02399v1
2020/7/15,Janus Monolayers of Magnetic Transition Metal Dichalcogenides as an All-in-One Platform for Spin-Orbit Torque,"We theoretically predict that vanadium-based Janus dichalcogenide monolayers
constitute an ideal platform for spin-orbit-torque memories. Using first
principles calculations, we demonstrate that magnetic exchange and magnetic
anisotropy energies are higher for heavier chalcogen atoms, while the broken
inversion symmetry in the Janus form leads to the emergence of Rashba-like
spin-orbit coupling. The spin-orbit torque efficiency is evaluated using
optimized quantum transport methodology and found to be comparable to heavy
nonmagnetic metals. The coexistence of magnetism and spin-orbit coupling in
such materials with tunable Fermi-level opens new possibilities for monitoring
magnetization dynamics in the perspective of non-volatile magnetic random
access memories.",2007.07579v1
2020/10/16,Nonlinear electric transport in odd-parity magnetic multipole systems: Application to Mn-based compounds,"Violation of parity symmetry gives rise to various physical phenomena such as
nonlinear transport and cross-correlated responses. In particular, the
nonlinear conductivity has been attracting a lot of attentions in spin-orbit
coupled semiconductors, superconductors, topological materials, and so on. In
this paper we present theoretical study of the nonlinear conductivity in
odd-parity magnetic multipole ordered systems whose $\mathcal{PT}$-symmetry is
essentially distinct from the previously studied acentric systems. Combining
microscopic formulation and symmetry analysis, we classify the nonlinear
responses in the $\mathcal{PT}$-symmetric systems as well as
$\mathcal{T}$-symmetric (non-magnetic) systems, and uncover nonlinear
conductivity unique to the odd-parity magnetic multipole systems. A giant
nonlinear Hall effect, nematicity-assisted dichroism and magnetically-induced
Berry curvature dipole effect are proposed and demonstrated in a model for
Mn-based magnets.",2010.08480v1
2020/10/21,Strong tuning of magnetism and electronic structure by spin orientation,"To efficiently manipulate magnetism is a key physical issue for modern
condensed matter physics, which is also crucial for magnetic functional
applications. Most previous relevant studies rely on the tuning of spin
texture, while the spin orientation is often negligible. As an exception,
spin-orbit coupled $J_{\rm eff}$ states of $4d$/$5d$ electrons provide an ideal
platform for emergent quantum effects. However, many expectations have not been
realized due to the complexities of real materials. Thus the pursuit for more
ideal $J_{\rm eff}$ states remains ongoing. Here a near-ideal $J_{\rm
eff}$=$3/2$ Mott insulating phase is predicted in the family of hexachloro
niobates, which avoid some common drawbacks of perovskite oxides. The local
magnetic moment is nearly compensated between spin and orbital components,
rendering exotic recessive magnetism. More interestingly, the electronic
structure and magnetism can be strongly tuned by rotating spin axis, which is
rare but crucial for spintronic applications.",2010.10741v1
2020/11/23,Neutron study of magnetic correlations in rare-earth-free Mn-Bi magnets,"We report the results of an unpolarized small-angle neutron scattering (SANS)
study on Mn-Bi-based rare-earth-free permanent magnets. The magnetic SANS cross
section is dominated by long-wavelength transversal magnetization fluctuations
and has been analyzed in terms of the Guinier-Porod model and the distance
distribution function. This provides the radius of gyration which, in the
remanent state, ranges between about $220-240 \, \mathrm{nm}$ for the three
different alloy compositions investigated. Moreover, computation of the
distance distribution function in conjunction with results for the so-called
$s$-parameter obtained from the Guinier-Porod model indicate that the magnetic
scattering of a Mn$_{45}$Bi$_{55}$ sample has its origin in slightly
shape-anisotropic structures.",2011.11446v2
2020/11/27,Entropic signatures of the skyrmion lattice phase in MnSi1-xAlx and Fe1-yCoySi,"The entropic signatures of magnetic phase transitions in the skyrmion lattice
host compounds MnSi0.962Al0.038 and Fe0.7Co0.3Si were investigated through low
field magnetization and ac susceptibility measurements. These data indicate
that the conical to skyrmion transition that occurs with the application of
magnetic field in MnSi0.962Al0.038 is characterized by clear discontinuity in
the magnetic entropy as expected for first order topological phase transition.
These same magnetoentropic features are negligibly small in isostructural
Fe0.7Co0.3Si due to the level of chemical substitution related disorder and
differences in the spin dynamics (range and timescales). Despite the obvious
similarities in the magnetic structures of these two compounds, the transitions
between these phases is substantially different indicating a surprising
non-universality to the magnetic phase transitions in this class of materials.",2011.14025v1
2020/12/8,Mean field theory and Monte Carlo simulation of Phase transitions and Magnetic Properties of a tridimensional Fe7S8 Compound,"The structural, electronic and magnetic properties of Fe7S8 material have
been studied within the framework of the ab-initio calculations, the mean field
approximation (MFA) and Monte Carlo simulation (MCS). Our study shows that two
forms of the iron atoms, Fe2+ with spin S=2, and Fe3+ with spin {\sigma}=5/2
are the most probable configurations. A mixed Ising model with ferromagnetic
spin coupling between Fe2+ and Fe3+ ions and between Fe3+ and Fe3+ ions, and
with antiferromagnetic spin coupling between Fe2+ ions of adjacent layers has
been used to study the magnetic properties of this compound. We demonstrated
that the magnetic phase transition can be either of the first or of the second
order, depending on the value of the exchange interaction and crystal field.
The presence of vacancies in every second iron layer leads to incomplete
cancellation of magnetic moments, hence to the emergence of the ferrimagnetism.
Anomalies in the magnetization behavior have been found and compared with the
experimental results.",2012.04306v1
2021/2/15,On the magnetic nanostructure of a Co-Cu alloy processed by high-pressure torsion,"In this study, a preparation route of Co-Cu alloys with soft magnetic
properties by high-pressure torsion deformation is introduced. Nanocrystalline,
supersaturated single-phase microstructures are obtained after deformation of
Co-Cu alloys, which are prepared from an initial powder mixture with
Co-contents above 70 wt.%. Isochronal annealing treatments up to 400{\deg}C
further reveal a remarkable microstructural stability. Only at 600{\deg}C, the
supersaturated phase decomposes into two fcc-phases. The coercivity, measured
by SQUID as a function of annealing temperature, remains significantly below
the value for bulk-Co in all states investigated. In order to understand the
measured magnetic properties in detail, a quantitative analysis of the magnetic
microstructure is carried out by magnetic force microscopy and correlated to
the observed changes in coercivity. Our results show that the rising coercivity
can be explained by a magnetic hardening effect occurring in context with
spinodal decomposition.",2102.07630v1
2021/3/9,Phonon Magnetic Moment from Electronic Topological Magnetization,"The traditional theory of magnetic moments for chiral phonons is based on the
picture of the circular motion of the Born effective charge, typically yielding
a small fractional value of the nuclear magneton. Here we investigate the
adiabatic evolution of electronic states induced by lattice vibration of a
chiral phonon and obtain an electronic orbital magnetization in the form of a
topological second Chern form. We find that the traditional theory needs to be
refined by introducing a $\bm{k}$ resolved Born effective charge, and identify
another contribution from the phonon-modified electronic energy together with
the momentum-space Berry curvature. The second Chern form can diverge when
there is a Yang's monopole near the parameter space of interest as illustrated
by considering a phonon at the Brillouin zone corner in a gaped graphene model.
We also find large magnetic moments for the optical phonon in bulk topological
materials where non-topological contribution is also important. The magnetic
moment experiences a sign change when the band inversion happens.",2103.05786v2
2021/3/12,Dynamically induced magnetism in KTaO$_3$,"Dynamical multiferroicity features entangled dynamic orders: fluctuating
electric dipoles induce magnetization. Hence, the material with paraelectric
fluctuations can develop magnetic signatures if dynamically driven. We identify
the paraelectric KTaO$_3$ (KTO) as a prime candidate for the observation of the
dynamical multiferroicity. We show that when a KTO sample is exposed to a
circularly polarized laser pulse, the dynamically induced ionic magnetic
moments are of the order of 5\% of the nuclear magneton per unit cell. We
determine the phonon spectrum using ab initio methods and identify T$_{1u}$ as
relevant soft phonon modes that couple to the external field and induce
magnetic polarization. We also predict a corresponding electron effect for the
dynamically induced magnetic moment which is enhanced by several orders of
magnitude due to the significant mass difference between electron and ionic
nucleus.",2103.07244v1
2021/3/15,"Magnetic phase diagram of $A_{2}$[FeCl$_{5}$(H$_{2}$O)] ($A$ = K, Rb, NH$_{4}$)","Erythrosiderites with the formula A2FeX5H2O, where A = Rb, K, and (NH4) and X
= Cl and Br are intriguing systems that possess various magnetic and electric
phases, as well as multiferroic phases in which magnetism and ferroelectricity
are coupled. In this report, we study the magnetic phase diagram of
erythrosiderites as a function of superexchange interactions. To this end, we
perform classical Monte Carlo simulations on magnetic Hamiltonians that contain
five different superexchange interactions with single-ion anisotropies. Our
phase diagram contains all magnetic ground states that have been experimentally
observed in these materials. We argue that the ground states can be explained
by varying the ratio of J4/J2. For J4/J2 > 0.95 a cycloidal spins structure is
stabilized as observed in (NH4)2FeCl5H2O and otherwise, a collinear spin
structure is stabilized as observed in (K,Rb)2FeCl5H2O. We also show that the
difference in the single-ion anisotropy along a- and c- axes is essential to
stabilize the intermediate state observed in (NH)2FeCl5H2O.",2103.08500v2
2021/6/1,A DMI guide to magnets micro-world,"Dzyaloshinskii-Moriya interaction, DMI in short, represents an antisymmetric
type of magnetic interactions that favour orthogonal orientation of spins and
competes with Heisenberg exchange. Being introduced to explain weak
ferromagnetism in antiferromagnets without an inversion center between magnetic
atoms such an anisotropic interaction can be used to analyze other non-trivial
magnetic structures of technological importance including spin spirals and
skyrmions. Despite the fact that the corresponding DMI contribution to the
magnetic energy of the system has a very compact form of the vector product of
spins, the determination of DMI from first-principles electronic structure is a
very challenging methodological and technical problem whose solution opens a
door into the fascinating microscopic world of complex magnetic materials. In
this paper we review a few such methods developed by us for calculating DMI and
their applications to study the properties of real materials.",2106.00398v1
2021/9/1,Magnetic field driven dielectric relaxation in non-magnetic composite medium: a low temperature study,"The frequency dependence of dielectric constant for composites of polyaniline
(PANI) and multi-walled carbon nanotube (MWCNT) with different degree of
functionalization is studied at low temperature (down to 4.2 K) and magnetic
field (up to 3 Tesla) applied both in parallel and perpendicular direction of
ac electric field. A relaxation phenomenon is observed in all the MWCNT/PANI
composites by applying magnetic field in both the directions, below 10$^3$ Hz.
However, PANI does not show any relaxation peak with applied magnetic field in
either direction. The relaxation peak frequency does not depend on the strength
of magnetic field but it varies with temperature and degree of
functionalization of MWCNT in composites. This relaxation phenomenon occurs due
to the inhomogeneity of the medium of two highly mismatched conductive
materials at low temperatures. We have tried to explain our results in the
light of Parish and Littlewood theory about magnetocapacitance in nonmagnetic
composite.",2109.00325v1
2021/9/23,The free energy of twisting spins in Mn$_3$Sn,"The magnetic free energy is usually quadratic in magnetic field and depends
on the mutual orientation of the magnetic field and the crystalline axes. Tiny
in magnitude, this magnetocrystalline anisotropy energy (MAE) is nevertheless
indispensable for the existence of permanent magnets. Here, we show that in
Mn$_3$Sn, a non-collinear antiferromagnet attracting much attention following
the discovery of its large anomalous Hall effect, the free energy of spins has
superquadratic components, which drive the MAE. We experimentally demonstrate
that the thermodynamic free energy includes terms odd in magnetic field
($\mathcal{O}(H^3)+\mathcal{O}(H^5)$) and generating sixfold and twelve-fold
angular oscillations in the torque response. We show that they are
quantitatively explained by theory, which can be used to quantify relevant
energy scales (Heisenberg, Dzyaloshinskii-Moriya, Zeeman and single-ion
anisotropy) of the system. Based on the theory, we conclude that, in contrast
with common magnets, what drives the MAE in Mn$_3$Sn is the field-induced
deformation of the spin texture.",2109.11122v1
2021/11/17,Large photogalvanic spin current by magnetic resonance in bilayer Cr trihalides,"Magnetic materials show rich optical responses related to the magnetic order.
These phenomena reflect the nature of their excitations, providing a powerful
probe for the magnetic states and a way to control them. In recent years, such
studies were extended to the optical control of spin current using nonlinear
optical response similar to the photogalvanic effect. However, neither a
candidate material nor a general formula for calculating the photogalvanic spin
current is known so far. In this work, we develop a general theory for the
photogalvanic spin current through a magnetic resonance process. Using the
nonlinear response formalism, we find the nonlinear conductivity consists of
two contributions that involve one and two magnon bands; the latter is a
contribution unknown to date. We argue that the two-band process produces a
large photogalvanic spin current in the antiferromagnetic phase of bilayer
CrI$_3$ and CrBr$_3$, whose resonance frequency can be tuned between GHz-THz
range by an external magnetic field. Our findings open a route to the studies
on the photogalvanic effect of spin angular momentum in realistic setups.",2111.09007v1
2021/11/29,Element selective ultrafast magnetization dynamics of hybrid Stoner-Heisenberg magnets,"Stoner and Heisenberg excitations in magnetic materials are inherently
different. The former involves an effective reduction of the exchange
splitting, whereas the latter comprises excitation of spin-waves. In this work,
we test the impact of these two excitations in the hybrid Stoner-Heisenberg
system FePd. We present a microscopic picture of ultrafast demagnetization
dynamics in this alloy, which represents both components of strong local
exchange splitting in Fe, and induced polarization in Pd. We identify
spin-orbit coupling and optical inter-site spin transfer as the two dominant
factors for demagnetization at ultrashort timescales. By tuning the external
laser pulse, the extrinsic inter-site spin transfer can be manipulated for site
selective demagnetization on femtosecond time scales providing the fastest way
for optical and selective control of the magnetization dynamics in alloys.
Remarkably, the drastic difference in origin of the magnetic moment of the Fe
and Pd species is not deciding the initial magnetization dynamics in this
alloy.",2111.14607v1
2021/12/9,Exchange-bias dependent diffusion rate of hydrogen discovered from evolution of hydrogen-induced noncollinear magnetic anisotropy in FePd thin films,"Hydrogenation-induced noncollinear magnetic anisotropy is observed from the
evolution of the magnetic domains in FePd alloy thin films using magneto-optic
Kerr effect (MOKE) microscopy. MOKE images reveal complicated competitions
between different magnetic anisotropies during hydrogen diffusion into the
film. An intriguing enhancement of the hydrogen diffusion rate due to the
presence of an initial exchange bias induced by a high magnet field is thereby
discovered, pointing to an additional scope of controllability of magnetic
metal hydrides as potential future hydrogen sensing and storage materials.",2112.05079v1
2021/12/23,Control of site occupancy by variation of the Zn and Al content in NiZnAl ferrite epitaxial films with low magnetic damping,"The structural and magnetic properties of Zn/Al doped nickel ferrite thin
films can be adjusted by changing the Zn and Al content. The films are
epitaxially grown by reactive magnetron sputtering using a triple cluster
system to sputter simultaneously from three different targets. Upon the
variation of the Zn content the films remain fully strained with similar
structural properties, while the magnetic properties are strongly affected. The
saturation magnetization and coercivity as well as resonance position and
linewidth from ferromagnetic resonance (FMR) measurements are altered depending
on the Zn content in the material. The reason for these changes can be
elucidated by investigation of the x-ray magnetic circular dichroism spectra to
gain site and valence specific information with elemental specificity.
Additionally, from a detailed investigation by broadband FMR a minimum in
g-factor and linewidth could be found as a function of film thickness.
Furthermore, the results from a variation of the Al content using the same set
of measurement techniques is given. Other than for Zn, the variation of Al
affects the strain and even more pronounced changes to the magnetic properties
are apparent.",2112.12456v1
2022/4/1,Magnetic hot-spots generation at optical frequencies in all-dielectric mesoscale Janus particles,"At optical frequencies due to the small value of the magnetic permeability of
natural materials, the magnetic effects are week. To this end, the natural
dielectric materials are unemployable for practical magnetic applications in
optics. We have shown that it is possible to induce the intense magnetic hot
spots in a Janus dielectric mesoscale particle. The basic idea of the Janus
particle based on a combination of the effects of a photonic jet, whispering
gallery waves and the concept of solid immersion. Simulations show that H^2/E^2
contrast maybe more 10 and maximal magnetic field intensity enhancement is more
than 1000 for a wavelength-scaled particle with refractive index less than 2.",2204.01534v1
2022/4/7,Polycrystalline exchange-biased bilayers: magnetically effective vs. structural antiferromagnetic grain volume distribution,"The magnetic characteristics of polycrystalline exchange-biased
antiferromagnet/ferromagnet-bilayers are determined by a complex interplay of
parameters, describing structural and magnetic properties of the material
system, including in particular the grain volume distribution of the
antiferromagnet. An ideal characterization of such systems would be a
non-destructive determination of the relevant parameters for each individual
grain. This is in most cases not feasible, since typical characterization
methods do average over larger areas. Here, we show that it is however possible
to determine averaged microscopic parameters from averaged macroscopic magnetic
quantities measured by vectorial Kerr magnetometry in comparison to an
elaborate model. In particular, we estimate the magnetically effective
antiferromagnetic grain size distribution, being essential for the interface
exchange coupling to the ferromagnetic layer. We found that the distribution of
magnetically active grain sizes differs from the structural one, indicating
that the antiferromagnetic order, relevant for the exchange bias, extends only
over a part of the grains' structural volumes.",2204.03336v1
2022/5/2,Magnetic characterization of oblique angle deposited Co/CoO on gold nanoparticles,"The influence of a patterned substrate on obliquely deposited, exchange
biased Co/CoO films was studied. It was found that substrates decorated with
nanoparticle patterns provide the option to manipulate the orientation of the
magnetic easy axis in obliquely deposited thin films. The complementary methods
of SQUID magnetometry and polarized neutron reflectometry were used to
disentangle the different contributions to the magnetic hysteresis of such
complex magnetic systems.",2205.00004v1
2022/5/14,Highly anisotropic geometrical Hall effect via f-d exchange fields in doped pyrochlore molybdates,"When a conduction electron couples with a non-coplanar localized magnetic
moment, the realspace Berry curvature is exerted to cause the geometrical Hall
effect, which is not simply proportional to the magnetization. So far, it has
been identified in the case mostly where the non-coplanar magnetic order is
present on the sublattice of conduction electrons. Here, we demonstrate that
the geometrical Hall effect shows up even without long-range magnetic order of
conduction electrons, as induced by non-coplanar exchange fields from the
localized magnetic moments, in hole-doped phyrochlore molybdates. We find that
the geometrical Hall effect is markedly anisotropic with respect to the applied
magnetic field direction, which is in good accordance with the field-dependent
magnitude and sign change of the real-space scalar spin chirality of local Tb
moments. These results may facilitate the understanding of emergent
electromagnetic responses induced by the Kondo-like coupling between conduction
electrons and local spins in a broad material class.",2205.07020v3
2022/5/15,Momentum-inversion symmetry breaking on the Fermi surface of magnetic topological insulators,"Magnetic topological insulators (MnBi$_2$Te$_4$)(Bi$_2$Te$_3$)$_n$ were
anticipated to exhibit magnetic energy gaps while recent spectroscopic studies
did not observe them. Thus, magnetism on the surface is under debate. In this
work, we propose another symmetry criterion to probe the surface magnetism.
Because of both time-reversal symmetry-breaking and inversion
symmetry-breaking, we demonstrate that the surface band structure violates
momentum-inversion symmetry and leads to a three-fold rather than six-fold
rotational symmetry on the Fermi surface if corresponding surface states couple
strongly to the surface magnetism. Such a momentum-inversion symmetry violation
is significant along the $\Gamma-K$ direction for surface bands on the (0001)
plane.",2205.07343v1
2022/5/18,Visualizing the interplay of Dirac mass gap and magnetism at nanoscale in intrinsic magnetic topological insulators,"In intrinsic magnetic topological insulators, Dirac surface state gaps are
prerequisites for quantum anomalous Hall and axion insulating states.
Unambiguous experimental identification of these gaps has proved to be a
challenge, however. Here we use molecular beam epitaxy to grow intrinsic
MnBi2Te4 thin films. Using scanning tunneling microscopy/spectroscopy, we
directly visualize the Dirac mass gap and its disappearance below and above the
magnetic order temperature. We further reveal the interplay of Dirac mass gaps
and local magnetic defects. We find that in high defect regions, the Dirac mass
gap collapses. Ab initio and coupled Dirac cone model calculations provide
insight into the microscopic origin of the correlation between defect density
and spatial gap variations. This work provides unambiguous identification of
the Dirac mass gap in MnBi2Te4, and by revealing the microscopic origin of its
gap variation, establishes a material design principle for realizing exotic
states in intrinsic magnetic topological insulators.",2205.09195v2
2022/5/30,Spin-orbit-derived giant magnetoresistance in a layered magnetic semiconductor AgCrSe2,"Two-dimensional magnetic materials have recently attracted great interest due
to their unique functions as the electric field control of a magnetic phase and
the anomalous spin Hall effect. For such remarkable functions, a spin-orbit
coupling (SOC) serves as an essential ingredient. Here we report a giant
positive magnetoresistance in a layered magnetic semiconductor AgCrSe2, which
is a manifestation of the subtle combination of the SOC and Zeeman-type spin
splitting. When the carrier concentration approaches the critical value of
2.5\times10^18 cm^-3, a sizable positive magnetoresistance of ~400 % emerges
upon the application of magnetic fields normal to the conducting layers. Based
on the magneto-Seebeck effect and the first-principles calculations, the
unconventional magnetoresistance is ascribable to the enhancement of effective
carrier mass in the SOC induced J = 3/2 state, which is tuned to the Fermi
level through the Zeeman splitting enhanced by the p-d coupling. This study
demonstrates a new aspect of the SOC-derived magnetotransport in
two-dimensional magnetic semiconductors, paving the way to novel spintronic
functions.",2205.14795v1
2022/5/31,Highly anisotropic magnetism in the vanadium-based kagome metal TbV6Sn6,"RV6Sn6 (R=rare earth) compounds are appealing materials platforms for
exploring the interplay between R-site magnetism and nontrivial band topology
associated with the nonmagnetic vanadium-based kagome network. Here we present
the synthesis and characterization of the kagome metal TbV6Sn6 via
single-crystal x-ray diffraction, magnetization, transport, and heat capacity
measurements. Magnetization measurements reveal strong, uniaxial magnetic
anisotropy rooted in the alignment of Tb3{\AA} moments in the interplane
direction below 4.3(2) K. TbV6Sn6 exhibits multiband transport behavior with
high mobilities of charge carriers, and our measurements suggest TbV6Sn6 is a
promising candidate for hosting Chern gaps driven via the interplay between
Tb-site magnetic order and the band topology of the V-site kagome network.",2205.15559v3
2022/6/24,Detection and characterisation of conductive objects using electromagnetic induction and a fluxgate magnetometer,"Eddy currents induced in electrically conductive objects can be used to
locate metallic objects as well as to assess the properties of materials
non-destructively without physical contact. This technique is useful for
material identification, such as measuring conductivity and for discriminating
whether a sample is magnetic or non-magnetic. In this study, we carried out
experiments and numerical simulations for the evaluation of conductive objects.
We investigated the frequency dependence of the secondary magnetic field
generated by induced eddy currents when a conductive object is placed in a
primary oscillating magnetic field. According to the electromagnetic theory,
conductive objects have different responses at different frequencies. Using a
table-top setup consisting of a fluxgate magnetometer and a primary coil
generating a magnetic field with frequency up to 1 kHz, we are able to detect
aluminium and steel cylinders using the principle of electromagnetic induction.
The experimental results are compared with numerical simulations and we find
overall a good agreement. This technique enables identification and
characterisation of objects using their electrical conductivity and magnetic
permeability.",2206.12187v1
2022/7/5,Noncollinear magnetism in two-dimensional CrTe$_2$,"The discovery of two-dimensional (2D) van der Waals magnets opened
unprecedented opportunities for the fundamental exploration of magnetism in
quantum materials and the realization of next generation spintronic devices.
Here, based on a multiscale modelling approach that combines first-principles
calculations and a Heisenberg model supplied with ab-initio parameters, we
report a strong magnetoelastic coupling in a free-standing monolayer of
CrTe$_2$. We demonstrate that different crystal structures of a single CrTe$_2$
give rise to non-collinear magnetism through magnetic frustration and emergence
of the Dzyaloshinskii-Moriya interaction (DMI). Utilizing atomistic spin
dynamics, we perform a detailed investigation of the complex magnetic
properties pertaining to this 2D material impacted by the presence of various
types of structural distortions akin to charge density waves.",2207.01926v2
2022/8/19,The $S=1$ dimer system K$_2$Ni(MoO$_4$)$_2$: a candidate for magnon Bose-Einstein condensation,"Dimerized quantum magnets provide a unique possibility to investigate
Bose-Einstein condensation of magnetic excitations in crystalline systems at
low temperature. Here, we model the low-temperature magnetic properties of the
recently synthesized spin $S=1$ dimer system K${}_2$Ni(MoO${}_4$)$_2$ and
propose it as a new candidate material for triplon and quintuplon condensation.
Based on a first principles analysis of its electronic structure, we derive an
effective spin-dimer model that we first solve within a mean-field
approximation to refine its parameters in comparison to experiment. Finally,
the model is solved by employing a numerically exact quantum Monte Carlo
technique which leads to magnetic properties in good agreement with
experimental magnetization and thermodynamic results. We discuss the emergent
spin model of K${}_2$Ni(MoO${}_4$)$_2$ in view of condensation of magnetic
excitations in a broad parameter regime. Finally, we comment on a geometrical
peculiarity of the proposed model and discuss how it could host a supersolid
phase upon structural distortions.",2208.09246v1
2022/10/20,Structural distortion induced Dzyaloshinskii-Moriya interaction in monolayer CrI3 at van der Waals heterostructures,"The van der Waals (vdW) magnetic heterostructures provide flexible ways to
realize particular magnetic properties that possess both scientific and
practical significance. Here, by firstprinciples calculation, we predict strong
Dzyaloshinskii-Moriya interactions (DMIs) by constructing CrI3/Metal vdW
heterostructures. The underlaying mechanisms are ascribed the large
spin-orbital coupling (SOC) of the I atom and the structural distortion in CrI3
layer caused by interlayer interaction. This is different from the traditional
way that deposit magnetic films on substrate to generate DMI, wherein DMI is
dominated by interlayer hybridization and large SOC of substrates. In addition,
both Heisenberg exchange and magnetic anisotropy are modulated dramatically,
such as Heisenberg exchange is nearly doubled on Au(111), and the out-of-plane
magnetism is enhanced by 88% on Ir(111). Our work may provide a experimentally
accessible strategy to induce DMI in vdW magnetic materials, which will be
helpful to the design of spintronics devices.",2210.10949v1
2022/11/21,Magnetocaloric effect at the reorientation of the magnetization in ferromagnetic multilayers with perpendicular anisotropy,"We investigate the magnetocaloric effect obtained by the rotation of a
magnetic field applied to an exchange-coupled multilayer system composed of two
different ferromagnetic (FM) materials. We specifically consider a system in
which the two FMs have perpendicular uniaxial anisotropy axes and utilise
conditions which yield a reorientation of the total magnetization when
compensation between the anisotropies of the two layers occurs. We calculate
the consequent entropy change associated with the ""artificial"" reorientation.
By using known parameters from MnBi and Co we predict an entropy change of
$\Delta s = 0.34$ Jkg$^{-1}$K$^{-1}$ for perfect coupling. Lastly, we study the
behavior of the multilayer under a rotating magnetic field via a micromagnetic
model. When the layer thicknesses are of the order of the local domain wall
width, the magnetic field-induced entropy change can be obtained with magnetic
fields one order of magnitude lower than in the uncoupled case.",2211.11146v3
2022/12/6,Magnetic domain structure and domain wall bound states of topological semimetal EuB6,"Electrically manipulating domain wall (DW) is at central in the field of
spintronics. Magnetic Weyl semimetal (WSM) offers an additional knob for
electric manipulation of DW by utilizing the topological DW bound states. Using
magnetic WSM material EuB6 as a prototype system, we investigate its DW bound
states combining first principles calculations and domain imaging via magnetic
force microscopy (MFM). The MFM measurements reveal that domains with
magnetization aligned along three [100] directions dominate over others under a
small magnetic field along [001] direction. Accordingly, first principles
calculations are performed based on experimentally determined DW type, which
show a robust DW bound state featuring a spectral distribution over a large
portion of the DW Brillouin zone. Such DW bound states should result in
significant amount of localized charges which can be used to drive DW motion
via the electrostatic forces exerted on the localized DW charges.",2212.03170v1
2022/12/16,"One-dimensional magnetism in synthetic Pauflerite, $β$-VOSO$_4$","We have synthesized single-crystal samples of $\beta$-VOSO$_4$ and fully
characterized their magnetic properties. Our magnetic susceptibility, high
field magnetization and powder inelastic neutron scattering results are in
excellent agreement with theoretical expressions for a one-dimensional spin-1/2
Heisenberg chain with an exchange parameter of $3.83(2)$ meV. Ab initio
calculations identify the superexchange pathway, revealing that the spin-chain
does not run along the expected crystallographic chain $a$ direction but
instead between V$^{4+}$O$_{6}$ octahedra that are linked via SO$_{4}$
tetrahedra along the $b$ axis. We do not detect any phase transition to a
long-range magnetic order within our experimental conditions, indicating
$\beta$-VOSO$_4$ is very close to an ideal one-dimensional magnetic system.",2212.08473v4
2022/12/28,Frustrated magnetic interactions and quenched spin fluctuations in CrAs,"The discovery of pressure-induced superconductivity in helimagnets (CrAs,
MnP) has attracted considerable interest in understanding the relationship
between complex magnetism and unconventional superconductivity. However, the
nature of the magnetism and magnetic interactions that drive the unusual
double-helical magnetic order in these materials remains unclear. Here, we
report neutron scattering measurements of magnetic excitations in CrAs single
crystals at ambient pressure. Our experiments reveal well defined spin wave
excitations up to about 150 meV with a pseudogap below 7 meV, which can be
effectively described by the Heisenberg model with nearest neighbor exchange
interactions. Most surprisingly, the spin excitations are largely quenched
above the Neel temperature, in contrast to cuprates and iron pnictides where
the spectral weight is mostly preserved in the paramagnetic state. Our results
suggest that the helimagnetic order is driven by strongly frustrated exchange
interactions, and that CrAs is at the verge of itinerant and
correlation-induced localized states, which is therefore highly
pressure-tunable and favorable for superconductivity.",2212.13865v1
2022/12/28,First-principles study of spin orbit coupling contribution to anisotropic magnetic interaction,"Anisotropic magnetic exchange interactions lead to a surprisingly rich
variety of the magnetic properties. Considering the spin orbit coupling (SOC)
as perturbation, we extract the general expression of a bilinear spin
Hamiltonian, including isotropic exchange interaction, antisymmetric
Dzyaloshinskii-Moriya (DM) interaction and symmetric $\Gamma $ term. Though it
is commonly believed that the magnitude of the DM and $\Gamma $ interaction
correspond to the first and second order of SOC strength $% \lambda $
respectively, we clarify that the term proportional to $\lambda ^{2}$ also has
contribution to DM interaction. Based on combining magnetic force theorem and
linear-response approach, we have presented the method of calculating
anisotropic magnetic interactions, which now has been implemented in the open
source software WienJ. Furthermore, we introduce another method which could
calculate the first and second order SOC contribution to the DM interaction
separately, and overcome some shortcomings of previous methods. Our methods are
successfully applied to several typical weak ferromagnets for $3d$, $4d$ and
$5d$ transition metal oxides. We also predict the conditions where the DM
interactions proportional to $\lambda $ are symmetrically forbidden while the
DM interactions proportional to $\lambda ^{2}$ are nonzero, and believe that it
is widespread in certain magnetic materials.",2212.13963v1
2023/2/11,Room Temperature d$^0$ Ferromagnetism in Carbon Doped LaH$_3$: Insights From Density Functional Theory Simulations,"Employing the state-of-the-art Density Functional Theory with both GGA and
hybrid HSE06 functional along with the incorporation of spin-orbit coupling, we
have engineered stable room temperature ferromagnetism in non-magnetic LaH$_3$
through C substitution at octahedral and tetrahedral H sites where the induced
magnetic moment is mostly contributed by 2p orbital of C atom. It is
interesting that the magnetic signature is switched on with an impurity
concentration as low as 1.04 at% with a magnetic moment of $\approx$ 1.0
$\mu_B$ per impurity, where the localized behavior of the 2p states of C along
with significant exchange splitting energy can be attributed as the origin of
the induced magnetic moment. The verification of the Stoner criterion in the
material further confirmed the onset of ferromagnetism in the system, and the
computed Curie temperature is found to be well above room temperature. Reduced
formation energy and requirement of lower impurity concentration ensure
practical feasibility towards a spintronic device where room temperature
ferromagnetism is established from the non-magnetic host and the dopant.",2302.05625v1
2023/2/13,Magnetic and electronic properties of Eu$_5$In$_2$Sb$_6$,"The intermetallic compound Eu$_5$In$_2$Sb$_6$, an antiferromagnetic material
with nonsymmorphic crystalline structure, is investigated by magnetic,
electronic transport and specific heat measurements. Being a Zintl phase,
insulating behavior is expected. Our thermodynamic and magnetotransport
measurements along different crystallographic directions strongly indicate
polaron formation well above the magnetic ordering temperatures. Pronounced
anisotropies of the magnetic and transport properties even above the magnetic
ordering temperature are observed despite the Eu$^{2+}$ configuration which
testify to complex and competing magnetic interactions between these ions and
give rise to intricate phase diagrams discussed in detail. Our results provide
a comprehensive framework for further detailed study of this multifaceted
compound with possible nontrivial topology.",2302.06324v1
2023/3/3,Magneto-optical sensing of the pressure driven magnetic ground states in bulk CrSBr,"Competition between exchange interactions and magnetocrystalline anisotropy
may bring new magnetic states that are of great current interest. An applied
hydrostatic pressure can further be used to tune their balance. In this work we
investigate the magnetization process of a biaxial antiferromagnet in an
external magnetic field applied along the easy axis. We find that the single
metamagnetic transition of the Ising type observed in this material under
ambient pressure transforms under hydrostatic pressure into two transitions, a
first-order spin flop transition followed by a second order transition towards
a polarized ferromagnetic state near saturation. This reversible tuning into a
new magnetic phase is obtained in layered bulk CrSBr at low temperature by
varying the interlayer distance using high hydrostatic pressure, which
efficiently acts on the interlayer magnetic exchange, and is probed by
magneto-optical spectroscopy.",2303.01823v2
2023/3/16,Magnetic-field-induced corner states in quantum spin Hall insulators,"We address the general problem of magnetic-field-induced corner states in
quantum spin Hall insulators (QSHIs). Our analytical findings reveal that when
applied to the QSHIs in zinc-blende semiconductor quantum wells (QWs), the
presence of corner states extends beyond the anticipated range of meeting
edges, surpassing the limitations imposed by crystal symmetry. We clearly
demonstrate that, in the most general scenario, magnetic field-induced corner
states in QSHIs are not topological. However, we find that the presence of
crystal symmetry can stabilize these states only under specific orientations of
the in-plane magnetic field and meeting edges. Therefore, contrary to previous
assumptions, our research unveils that QSHIs in the presence of a magnetic
field cannot be accurately considered as higher-order topological insulators.
Furthermore, the lack of an inversion center in zinc-blende semiconductor QWs
enables the emergence of corner states through the influence of a perpendicular
magnetic field.",2303.09260v2
2023/4/28,Competing signatures of intersite and interlayer spin transfer in the ultrafast magnetization dynamics,"Optically driven intersite and interlayer spin transfer are individually
known as the fastest processes for manipulating the spin order of magnetic
materials on the sub 100 fs time scale. However, their competing influence on
the ultrafast magnetization dynamics remains unexplored. In our work, we show
that optically induced intersite spin transfer (also known as OISTR) dominates
the ultrafast magnetization dynamics of ferromagnetic alloys such as Permalloy
(Ni80Fe20) only in the absence of interlayer spin transfer into a substrate.
Once interlayer spin transfer is possible, the influence of OISTR is
significantly reduced and interlayer spin transfer dominates the ultrafast
magnetization dynamics. This provides a new approach to control the
magnetization dynamics of alloys on extremely short time scales by fine-tuning
the interlayer spin transfer.",2304.14957v1
2023/7/12,Electronic ground-state hysteresis under magnetic field in GdMn$_2$O$_5$,"In this paper, we investigate the physical properties of the type II
multiferroic GdMn$_2$O$_5$ material by means of neutrons scattering, electric
polarization and magnetization measurements. A complex $(T,H)$ phase diagram
shows up, with especially a field induced magnetic transition around 12 T at
low temperature. The high field phase is accompanied by an additional electric
polarization along both the $a$ and $$b directions, as authorized by symmetry,
but never observed experimentally up to now. While the magnetic properties
recover their initial states after driving the field back to zero, the
polarization along $a$ shows a significant increase. This behavior is observed
for all directions of the magnetic field. It constitutes a novel and striking
manifestation of the magneto-electric coupling, resulting in the establishment
of a new ground state at zero magnetic field.",2307.06247v1
2023/7/18,Optical Tellegen metamaterial with spontaneous magnetization,"The nonreciprocal magnetoelectric effect, also known as the Tellegen effect,
promises a number of groundbreaking phenomena connected to fundamental (e.g.,
electrodynamics of axion and relativistic matter) and applied physics (e.g.,
magnetless isolators). We propose a three-dimensional metamaterial with an
isotropic and resonant Tellegen response in the visible frequency range. The
metamaterial is formed by randomly oriented bi-material nanocylinders in a host
medium. Each nanocylinder consists of a ferromagnet in a single-domain magnetic
state and a high-permittivity dielectric operating near the magnetic Mie-type
resonance. The proposed metamaterial requires no external magnetic bias and
operates on the spontaneous magnetization of the nanocylinders. By leveraging
the emerging magnetic Weyl semimetals, we further show how a giant bulk
effective magnetoelectric effect can be achieved in a proposed metamaterial,
exceeding that of natural materials by almost four orders of magnitude.",2307.09275v1
2023/7/23,Spin Space Group Theory and Unconventional Magnons in Collinear Magnets,"Topological magnons have received substantial interest for their potential in
both fundamental research and device applications due to their exotic uncharged
yet topologically protected boundary modes. However, their understanding has
been impeded by the lack of fundamental symmetry descriptions of magnetic
materials, of which the spin Hamiltonians are essentially determined by the
isotropic Heisenberg interaction. The corresponding magnon band structures
allows for more symmetry operations with separated spin and spatial operations,
forming spin space groups (SSGs), than the conventional magnetic space groups.
Here we developed spin space group (SSG) theory to describe collinear magnetic
configurations, identifying all the 1421 collinear SSGs and categorizing them
into four types, constructing band representations for these SSGs, and
providing a full tabulation of SSGs with exotic nodal topology. Our
representation theory perfectly explains the band degeneracies of previous
experiments and identifies new magnons beyond magnetic space groups with
topological charges, including duodecuple point, octuple nodal line and
charge-4 octuple point. With an efficient algorithm that diagnoses topological
magnons in collinear magnets, our work offers new pathways to exploring exotic
phenomena of magnonic systems, with the potential to advance the
next-generation spintronic devices.",2307.12366v1
2023/7/26,Symmetry of the emergent inductance tensor exhibited by magnetic textures,"Metals hosting gradually varying spatial magnetic textures are attracting
attention as a new class of inductor. Under the application of an alternating
current, the spin-transfer-torque effect induces oscillating dynamics of the
magnetic texture, which subsequently yields the spin-motive force as a back
action, resulting in an inductive voltage response. In general, a second-order
tensor representing a material's response can have an off-diagonal component.
However, it is unclear what symmetries the emergent inductance tensor has and
also which magnetic textures can exhibit a transverse inductance response. Here
we reveal both analytically and numerically that the emergent inductance tensor
should be a symmetric tensor in the so-called adiabatic limit. By considering
this symmetric tensor in terms of symmetry operations that a magnetic texture
has, we further characterize the magnetic textures in which the transverse
inductance response can appear. This finding provides a basis for exploring the
transverse response of emergent inductors, which has yet to be discovered.",2307.14542v2
2023/8/7,Metallization and Spin Fluctuations in Cu-doped Lead Apatite,"An electronic structure and magnetic properties analysis of the recently
proposed Cu-doped lead apatite is performed. We show that electronic structures
of differently Cu-substituted structures are characterized by localized
molecular Cu-O bands at or near the Fermi level. The Cu substitutions can
happen at both Pb1 and Pb2 sites, leading to metallic and semiconducting states
differently. The electronic states in these bands are highly unstable
magnetically and form clusters of rigidly ferromagnetically coupled magnetic
moments on Cu and neighboring oxygen atoms with a total moment of about 1
$\mu_B$. The ground state of uniformly Cu-doped lead apatite appears to be
magnetic and semiconducting. The non-uniform distribution of two Cu atoms at
the nearest Pb2 sites leads to an antiferromagnetic semiconducting state with
formation energy close to uniformly distributed Cu configurations. The
inclusion of quantum spin fluctuations confirms the stability of magnetic Cu-O
clusters. Our calculations revealed the absence of the long-range magnetic
order between uniformly distributed Cu-O clusters, creating the spin glass type
of system.",2308.03454v2
2023/8/11,Chiral magnetism in lithium-decorated monolayer CrTe$_{2}$: Interplay between Dzyaloshinskii-Moriya interaction and higher-order interactions,"Chiral magnetic states in two-dimensional (2D) layered noncentrosymmetric
magnets, which are promising advanced spintronic materials, are usually
attributed to Dzyaloshinskii-Moriya interactions (DMI). However, the role of
underlying higher-order spin couplings in determining the properties of chiral
spin textures has much less reported. In this work, taking the
lithium-decorated monolayer CrTe$_{2}$ (monolayer LiCrTe$_{2}$) as an example,
we develop a first-principles-based comprehensive spin model constructed by
using the symmetry-adapted cluster expansion method. Based on this spin model,
we identify the ground state of monolayer LiCrTe$_{2}$ as a chiral spin spiral
state, which can further assemble macroscopic chiral labyrinth domains (LD)
under zero-field conditions as well as evolve into skyrmions under a finite
magnetic field. Moreover, higher-order biquadratic and three-site interactions
are identified to be responsible for modulating both the size and the field
stability of the spin spiral state. Our study sheds light on complex magnetic
couplings in 2D magnets.",2308.06030v2
2023/8/15,"Reflective, polarizing, and magnetically soft amorphous Fe/Si multilayer neutron optics with isotope-enriched 11B4C inducing atomically flat interfaces","The utilization of polarized neutrons is of great importance in scientific
disciplines spanning materials science, physics, biology, and chemistry.
Polarization analysis offers insights into otherwise unattainable sample
information such as magnetic domains and structures, protein crystallography,
composition, orientation, ion-diffusion mechanisms, and relative location of
molecules in multicomponent biological systems. State-of-the-art multilayer
polarizing neutron optics have limitations, particularly low specular
reflectivity and polarization at higher scattering vectors/angles, and the
requirement of high external magnetic fields to saturate the polarizer
magnetization. Here, we show that by incorporating 11B4C into Fe/Si
multilayers, amorphization and smooth interfaces can be achieved, yielding
higher neutron reflectivity, less diffuse scattering and higher polarization.
Magnetic coercivity is eliminated, and magnetic saturation can be reached at
low external fields (>2 mT). This approach offers prospects for significant
improvement in polarizing neutron optics, enabling; nonintrusive positioning of
the polarizer, enhanced flux, increased data accuracy, and further
polarizing/analyzing methods at neutron scattering facilities.",2308.07630v1
2023/8/17,Magnetic Order in A Quenched-High-Temperature-Phase of Cu-Doped MnBi,"Permanent magnets are of great importance due to their vast applications.
MnBi has been proposed to be a potential permanent magnet that can be widely
used while past efforts have been focused on optimizing the ferromagnetic
low-temperature phase of MnBi. Herein, we report a series of new materials,
CuxMn1-xBi, crystallizing in a quenched high-temperature-phase (QHTP)
MnBi-related structure. We synthesized single crystals of CuxMn1-xBi and found
that they crystallize in an unreported trigonal structure (P -31c). Magnetic
properties measurements imply high-temperature antiferromagnetic (AFM) ordering
and low-temperature ferromagnetic or ferrimagnetic (FM/FiM) ordering. By
analyzing the doping effect on crystal structure and magnetic properties, we
established a magnetic phase diagram for Cu-doped MnBi and attributed the AFM
and FM/FiM to two different atomic sites of Mn.",2308.08952v2
2023/9/16,Anisotropy of Antiferromagnetic Domains in a Spin-orbit Mott Insulator,"The temperature-dependent behavior of magnetic domains plays an essential
role in the magnetic properties of materials, leading to widespread
applications. However, experimental methods to access the three-dimensional
(3D) magnetic domain structures are very limited, especially for
antiferromagnets. Over the past decades, the spin-orbit Mott insulator iridate
$Sr_2IrO_4$ has attracted particular attention because of its interesting
magnetic structure and analogy to superconducting cuprates. Here, we apply
resonant x-ray magnetic Bragg coherent diffraction imaging to track the
real-space 3D evolution of antiferromagnetic ordering inside a $Sr_2IrO_4$
single crystal as a function of temperature, finding that the antiferromagnetic
domain shows anisotropic changes. The anisotropy of the domain shape reveals
the underlying anisotropy of the antiferromagnetic coupling strength within
$Sr_2IrO_4$. These results demonstrate the high potential significance of 3D
domain imaging in magnetism research.",2309.09091v1
2023/9/18,Coherent x-ray magnetic imaging with 5 nm resolution,"Soft x-ray microscopy plays an important role in modern spintronics. However,
the achievable resolution of most x-ray magnetic imaging experiments is above
10 nm, limiting access to fundamental and technologically relevant length
scales. Here, we demonstrate x-ray magnetic microscopy with 5 nm resolution by
combining holography-assisted coherent diffractive imaging with heterodyne
amplification of the weak magnetic signal. The gain in resolution and contrast
allows direct access to key magnetic properties, including domain wall profiles
and the position of pinning sites. The ability to detect and map such
properties with photons opens new horizons for element-specific, time-resolved,
and in-operando research on magnetic materials and beyond.",2309.09964v1
2023/11/2,Electrical engineering of topological magnetism in two-dimensional heterobilayers,"The emergence of topological magnetism in two-dimensional (2D) van der Waals
(vdW) magnetic materials promoted 2D heterostructures as key building-blocks of
devices for information technology based on topological concepts. Here, we
demonstrate the all-electric switching of the topological nature of individual
magnetic objects emerging in 2D vdW heterobillayers. We show from the first
principles that an external electric field modifies the vdW gap between CrTe
$_2$ and (Rh, Ti)Te$_2$ layers and alters the underlying magnetic interactions.
This enables switching between ferromagnetic skyrmions and meron pairs in the
CrTe$_2$/RhTe$_2$ heterobilayer while it enhances the stability of frustrated
antiferromagnetic merons in the CrTe$_2$/TiTe$_2$ heterobilayer. We envision
that the electrical engineering of distinct topological magnetic solitons in a
single device could pave the way for novel energy-efficient mechanisms to store
and transmit information with applications in spintronics.",2311.01294v1
2023/12/5,Electrical tuning of the magnetic properties of 2D magnets: the case of ${\rm Cr}_2{\rm Ge}_2{\rm Te}_6$,"Motivated by growing interest in atomically-thin van der Waals magnetic
materials, we present an {\it ab initio} theoretical study of the dependence of
their magnetic properties on the electron/hole density $\rho$ induced via the
electrical field effect. By focusing on the case of monolayer ${\rm Cr}_2{\rm
Ge}_2{\rm Te}_6$ (a prototypical 2D Ising ferromagnet) and employing a hybrid
functional, we first study the dependence of the gap and effective mass on the
carrier concentration $\rho$. We then investigate the robustness of magnetism
by studying the dependencies of the exchange couplings and magneto-crystalline
anisotropy energy (MAE) on $\rho$. In agreement with experimental results, we
find that magnetism displays a bipolar electrically-tunable character, which
is, however, much more robust for hole ($\rho>0$) rather than electron
($\rho<0$) doping. Indeed, the MAE vanishes for an electron density
$\rho\approx - 7.5 \times 10^{13}~{\rm e} \times {\rm cm}^{-2}$, signalling the
failure of a localized description based on a Heisenberg-type anisotropic spin
Hamiltonian. This is in agreement with the rapid increase of the coupling
between fourth-neighbor atoms with increasing electron density.",2312.02887v1
2023/12/31,Spinterface Mediated Magnetic Properties of Co20Fe60B20/Alq3 Heterostructures,"Organic semiconductors (OSCs) are suitable materials for spintronics
applications as they form a spinterface when placed next to a ferromagnet,
which in turn leads to novel functionalities. The evolution of spinterface can
tune the global magnetic anisotropy, magnetization reversal, magnetization
dynamics, etc. Planar tris-(8-hydroxyquinoline)aluminum (Alq3) OSC has shown
tremendous potential for spintronics applications, thanks to its efficient
spin-polarized current transport ability. Here, we establish the spinterface
when the Alq3 molecules are deposited on amorphous ferromagnet
Co20Fe60B20(CFB). The $\pi$-d hybridization in CFB/Alq3 enhances the coercive
field and significantly modifies the shape and size of the magnetic domains. A
$\sim$100% increase in uniaxial anisotropic energies and a reduction in
magnetic damping are also evident owing to the strong interfacial
hybridization.",2401.00487v1
2024/1/5,Polarisation of radio-frequency magnetic fields in magnetic induction measurements with an atomic magnetometer,"We explore properties of the radio-frequency atomic magnetometer,
specifically its sensitivity to the polarisation of an oscillating magnetic
field. This aspect can be particularly relevant to configurations where the
sensor monitors fields created by more than one source. The discussion,
illustrated by theoretical and experimental studies, is done in the context of
the signals produced by electrically conductive and magnetically permeable
plates in magnetic induction tomography measurements. We show that different
components of the secondary magnetic fields create the object response
depending on the properties of the material, with the polarisation of the rf
field varying across the object's surface. We argue that the ability of the
sensor to simultaneously detect different field components enables the
optimisation of measurement strategies for different object compositions.",2401.02891v1
2024/1/23,Pitfalls of Exchange-Correlation Functionals in Descriptions of Magnetism: Cautionary Tale of the FeRh Alloy,"The magnetic ground state of FeRh is highly sensitive towards the lattice
constant. This, in addition to partially filled d-shells of Fe and Rh, posed a
significant challenge for Density Functional Theory (DFT) calculations in the
past. Here, we have investigated the performance of various
exchange-correlation (XC) functionals within the DFT formalism for this
challenging binary alloy. We have employed Local Spin Density Approximation
(LSDA), various Generalized Gradient Approximations (GGAs), and newly developed
Strongly Constrained and Appropriately Normed (SCAN) meta-GGA functional. Our
results show the limitations of any single functional in capturing the
intricate interplay of structural, electronic, and magnetic properties in FeRh.
While SCAN can accurately describe some magnetic features and phonon
dispersion, it significantly overestimates the Fe-Fe magnetic interactions,
leading to an unreasonable magnetic ordering temperature. Conversely, the
Perdew-Burke-Ernzerhof (PBE) GGA exhibits the opposite behavior. These findings
highlight the challenges in simulating materials with partially filled
$d$-shells using DFT, underscoring the crucial need for developing a versatile
XC functional that can effectively account for the multifaceted nature of such
systems.",2401.12563v1
2024/2/6,Evidence of temperature-dependent interplay between spin and orbital moment in van der Waals ferromagnet VI3,"Van der Waals materials provide a versatile toolbox for the emergence of new
quantum phenomena and the fabrication of functional heterostructures. Among
them, the trihalide VI3 stands out for its unique magnetic and structural
landscape. Here we investigate the spin and orbital magnetic degrees of freedom
in the layered ferromagnet VI3 by means of temperature-dependent x-ray
absorption spectroscopy and x-ray magnetic circular and linear dichroism. We
detect localized electronic states and reduced magnetic dimensionality, due to
electronic correlations. We furthermore provide experimental evidence of (a) an
unquenched orbital magnetic moment (up to 0.66(7)) in the ferromagnetic state,
and (b) an instability of the orbital moment in proximity of the spin
reorientation transition. Our results support a coherent picture where
electronic correlations give rise to a strong magnetic anisotropy and a large
orbital moment, and establish VI3 as a prime candidate for the study of orbital
quantum effects.",2402.04063v1
2024/2/6,"Coupling between magnetic and thermodynamic properties in $R$Rh$_2$Si$_2$ ($R$ = Dy, Ho)","Single crystals of DyRh$_2$Si$_2$ and HoRh$_2$Si$_2$ were investigated by
thermal expansion and magnetostriction. The different types of magnetic order
can clearly be seen in these measurements, particularly the canting of the
moments away from the crystallographic $c$ direction below about 12~K and the
spin-flip for magnetic field applied along the $c$ direction. For
HoRh$_2$Si$_2$, an additional transition just below $T_{\rm N}$ is analyzed by
means of the Gr\""{u}neisen ratio and is likely caused by a change of the
magnetic structure. Our results nicely corroborate findings from other magnetic
and thermodynamic measurements on these materials and provide further evidence
suggesting the formation of magnetic domains.",2402.04072v1
2024/2/14,Manipulation of magnetic anisotropy of 2D magnetized graphene by ferroelectric In$_2$Se$_3$,"The capacity to externally manipulate magnetic properties is highly desired
from both fundamental and technological perspectives, particularly in the
development of magnetoelectronics and spintronics devices. Here, using
first-principles calculations, we have demonstrated the ability of controlling
the magnetism of magnetized graphene monolayers by interfacing them with a
two-dimensional ferroelectric material. When the 3$d$ transition metal (TM) is
adsorbed on the graphene monolayer, its magnetization easy axis can be flipped
from in-plane to out-of-plane by the ferroelectric polarization reversal of
In$_2$Se$_3$, and the magnetocrystalline anisotropy energy (MAE) can be high to
-0.692 meV/atom when adopting the Fe atom at bridge site with downward
polarization. This may be a universal method since the 3$d$ TM-adsorbed
graphene has a very small MAE, which can be easily manipulated by the
ferroelectric polarization. As a result, the inherent mechanism is analyzed by
second variation method.",2402.09153v1
2024/2/16,Tuning properties of phase-separated magnetic fluid with temperature,"Phase-separated magnetic fluids provide a very strong magnetic response
($\mu>25$) in a liquid state material. Even small fields can cause a notable
material response, but this depends on its properties, which are often
difficult to control. Here, we investigate how temperature affects the
properties of the system, where phase separation is induced by an increase in
ionic strength. Following the deformations of individual microscopic droplets,
we can extract surface tension, magnetic permeability, and viscosity. We find
that the temperature increase does not affect the surface tension, while the
magnetic permeability and viscosity increase. Applying this knowledge to induce
a shape instability for a drop only using temperature shows the potential of
applicability of our findings.",2402.11117v1
2024/3/12,Plasmon-driven creation of magnetic topological structures,"In the present research, we demonstrate the usage of plasmonic effects in
thin film structures to control magnetic topological textures, specifically
skyrmions and skyrmioniums. We investigate numerically the generation and
alteration of these topological structures caused by hemisphere gold
nanoparticle placed over a magnetic layer coated with a dielectric material.
The electromagnetic and photothermal models are used to clarify the processes
of producing heat and absorption, and the results were implemented in
micromagnetic formalism to reveal the dynamics of magnetization under various
conditions. Our findings demonstrate the significance of the laser pulse
duration and the contact area between nanoparticles and the underlying magnetic
layer in forming topological textures. In particular, we show how to generate a
single skyrmion, multiple skyrmions, and skyrmioniums, and how to dynamically
transition between these states. These results highlight the possibility of
manipulating magnetic textures by using plasmonic effects, which presents
significant opportunities for spintronics and non-conventional computer
applications.",2403.07382v1
2018/6/6,Numerical general relativistic MHD with magnetically polarized matter,"The magnetically polarized matter in astrophysical systems may be relevant in
some magnetically dominated regions. For instance, the funnel that is generated
in some highly magnetized disks configurations whereby relativistic jets are
thought to spread, or in pulsars where the fluids are subject to very intense
magnetic fields. With the aim of dealing with magnetic media in the
astrophysical context, we present for the first time the conservative form of
the GRMHD equations with a non-zero magnetic polarization vector $m^{\mu}$.
Then, we follow the Anile method to compute the eigenvalue structure in the
case where the magnetic polarization is parallel to the magnetic field, and it
is parametrized by the magnetic susceptibility $\chi_m$. This approximation
allows us to describe diamagnetic fluids, for which $\chi_m<0$, and
paramagnetic fluids where $\chi_m>0$. The theoretical results were implemented
in the CAFE code to study the role of the magnetic polarization in some 1D
Riemann problems. We found that independently of the initial condition, the
first waves that appear in the numerical solutions are faster in diamagnetic
materials than in paramagnetic ones. Moreover, the constant states between the
waves change notably for different magnetic susceptibilities. All these effects
are more appreciable if the magnetic pressure is much bigger than the fluid
pressure. Additionally, with the aim of analysing a magnetic media in a strong
gravitational field, we carry out for the first time the magnetized Michel
accretion of a magnetically polarized fluid. With this test, we found that the
numerical solution is effectively maintained over time ($t>4000$), and that the
global convergence of the code is $\gtrsim$ 2 for $\chi_{m}\lesssim 0.005$, for
all the magnetic field strength $\beta$ we considered.",1806.02266v1
2023/3/6,Sawtooth lattice multiferroic BeCr$_2$O$_4$: Non-collinear magnetic structure and multiple magnetic transitions,"Noncollinear magnetic structures and multiple magnetic phase transitions in a
sawtooth lattice antiferromagnet consisting of Cr$^{3+}$ are experimentally
identified in this work, thereby proposing the scenario of magnetism-driven
ferroelectricity in a sawtooth lattice. The title compound, BeCr$_2$O$_4$,
displays three magnetic phase transitions at low temperatures, at
$T_{N1}\approx$ 7.5 K, at $T_{N2}\approx$ 25 K and at $T_{N3}\approx$ 26 K,
revealed through magnetic susceptibility, specific heat and neutron diffraction
in this work. These magnetic phase transitions are found to be influenced by
externally applied magnetic fields. Isothermal magnetization curves at low
temperatures below the magnetic transitions indicate the antiferromagnetic
nature of \bco\ with two spin-flop-like transitions occurring at
$H_{c1}\approx$ 29 kOe and $H_{c2} \approx$ 47 kOe. Our high-resolution X-ray
and neutron diffraction studies, performed on single crystal and powder samples
unambiguously determined the crystal structure as orthorhombic $Pbnm$. By
performing the magnetic superspace group analysis of the neutron diffraction
data at low temperatures, the magnetic structure in the temperature range
$T_{N3,N2} < T < T_{N1}$ is determined to be the polar magnetic space group,
$P21nm.1^{\prime}(00g)0s0s$ with a cycloidal magnetic propagation vector
$\textbf{k}_1$ = (0, 0, 0.090(1)). The magnetic structure in the newly
identified phase below $T_{N1}$, is determined as $P21/b.1^{\prime}[b](00g)00s$
with the magnetic propagation vector $\textbf{k}_2$ = (0, 0, 0.908(1)). The
cycloidal spin structure determined in our work is usually associated with
electric polarization, thereby making \bco\ a promising multiferroic belonging
to the sparsely populated family of sawtooth lattice antiferromagnets.",2303.02806v2
2023/4/24,Magnetic levitation by rotation,"A permanent magnet can be levitated simply by placing it in the vicinity of
another permanent magnet that rotates in the order of 200 Hz. This surprising
effect can be easily reproduced in the lab with off-the-shelf components. Here
we investigate this novel type of magnetic levitation experimentally and
clarify the underlying physics. Using a 19 mm diameter spherical NdFeB magnet
as rotor magnet, we capture the detailed motion of levitating, spherical NdFeB
magnets, denoted floater magnets. We find that as levitation occurs, the
floater magnet frequency-locks with the rotor magnet, and, noticeably, that the
magnetization of the floater is oriented close to the axis of rotation and
towards the like pole of the rotor magnet. This is in contrast to what might be
expected by the laws of magnetostatics as the floater is observed to align its
magnetization essentially perpendicular to the magnetic field of the rotor.
Moreover, we find that the size of the floater has a clear influence on the
levitation: the smaller the floater, the higher the rotor speed necessary to
achieve levitation, and the further away the levitation point shifts. We verify
that magnetostatic interactions between the rotating magnets are responsible
for creating the equilibrium position of the floater. Hence, this type of
magnetic levitation does not rely on gravity as a balancing force to achieve an
equilibrium position. Based on theoretical arguments and a numerical model, we
show that a constant, vertical field and eddy-current enhanced damping is
sufficient to produce levitation from rest. This enables a gyroscopically
stabilised counter-intuitive steady-state moment orientation, and the resulting
magnetostatically stable, mid-air equilibrium point. The numerical model
display the same trends with respect to rotation speed and the floater magnet
size as seen in the experiments.",2305.00812v3
2012/7/4,IrSr_2Sm_{1.15}Ce_{0.85}Cu_{2.175}O_{10}: A Novel Reentrant Spin-Glass Material,"A new iridium containing layered cuprate material,
IrSr_2Sm_{1.15}Ce_{0.85}Cu_{2.175}O_{10, has been synthesized by conventional
ambient-pressure solid-state techniques. The material's structure has been
fully characterized by Rietveld refinement of high resolution synchrotron X-ray
diffraction data; tilts and rotations of the IrO_6 octahedra are observed as a
result of a bond mismatch between in-plane Ir-O and Cu-O bond lengths.
DC-susceptibility measurements evidence a complex set of magnetic transitions
upon cooling that are characteristic of a reentrant spin-glass ground-state.
The glassy character of the lowest temperature, Tg=10 K, transition is further
confirmed by AC-susceptibility measurements, showing a characteristic frequency
dependence that can be well fitted by the Vogel-Fulcher law and yields a value
of \Delta_(T_f)/[T_f \Delta log({\omega})] =0.015(1), typical of dilute
magnetic systems. Electronic transport measurements show the material to be
semiconducting at all temperatures with no transition to a superconducting
state. Negative magnetoresistance is observed when the material is cooled below
25 K, and the magnitude of this magnetoresistance is seen to increase upon
cooling to a value of MR = -9 % at 8 K.",1207.0962v1
2014/6/20,Linear magnetoelectricity at room temperature in perovskite superlattices by design,"Discovering materials that display a linear magnetoelectric effect at room
temperature is challenge. Such materials could facilitate novel devices based
on the electric-field control of magnetism. Here we present simple, chemically
intuitive design rules to identify a new class of bulk magnetoelectric
materials based on the 'bicolor' layering of $Pnma$ ferrite perovskites, e.g.,
LaFeO$_3$/ LnFeO$_3$ superlattices for which Ln = lanthanide cation. We use
first-principles density-functional theory calculations to confirm these ideas.
Additionally, we elucidate the origin of this effect and show it is a general
consequence of the layering of any bicolor, $Pnma$ perovskite superlattice in
which the number of constituent layers are odd (leading to a form of hybrid
improper ferroelectricity) and Goodenough- Kanamori rules. Here, the polar
distortions induce both weak ferromagnetism and a linear magnetoelectric
effect. Our calculations suggest that the effect is 2-3 times greater in
magnitude than that observed for the prototypical magnetoelectric material,
Cr$_2$O$_3$. We use a simple mean field model to show that the considered
materials order magnetically above room temperature.",1406.5488v1
2017/5/2,Machine learning reveals orbital interaction in crystalline materials,"We propose a novel representation of crystalline materials named
orbital-field matrix (OFM) based on the distribution of valence shell
electrons. We demonstrate that this new representation can be highly useful in
mining material data. Our experiment shows that the formation energies of
crystalline materials, the atomization energies of molecular materials, and the
local magnetic moments of the constituent atoms in transition metal--rare-earth
metal bimetal alloys can be predicted with high accuracy using the OFM.
Knowledge regarding the role of coordination numbers of transition-metal and
rare-earth metal elements in determining the local magnetic moment of
transition metal sites can be acquired directly from decision tree regression
analyses using the OFM.",1705.01043v2
2019/6/27,Perspectives of Electrically generated spin currents in ferromagnetic materials,"Spin-orbit coupling enables charge currents to give rise to spin currents and
vice versa, which has applications in non-volatile magnetic memories, miniature
microwave oscillators, thermoelectric converters and Terahertz devices. In the
past two decades, a considerable amount of research has focused on electrical
spin current generation in different types of nonmagnetic materials. However,
electrical spin current generation in ferromagnetic materials has only recently
been actively investigated. Due to the additional symmetry breaking by the
magnetization, ferromagnetic materials generate spin currents with different
orientations of spin direction from those observed in nonmagnetic materials.
Studies centered on ferromagnets where spin-orbit coupling plays an important
role in transport open new possibilities to generate and detect spin currents.
We summarize recent developments on this subject and discuss unanswered
questions in this emerging field.",1906.11772v1
2017/9/25,Exfoliation and van der Waals heterostructure assembly of intercalated ferromagnet Cr1/3TaS2,"Ferromagnetic van der Waals (vdW) materials are in demand for spintronic
devices with all-two-dimensional-materials heterostructures. Here, we
demonstrate mechanical exfoliation of magnetic-atom-intercalated transition
metal dichalcogenide Cr1/3TaS2 from its bulk crystal; previously such
intercalated materials were thought difficult to exfoliate. Magnetotransport in
exfoliated tens-of-nanometres-thick flakes revealed ferromagnetic ordering
below its Curie temperature TC ~ 110 K as well as strong in-plane magnetic
anisotropy; these are identical to its bulk properties. Further, van der Waals
heterostructure assembly of Cr1/3TaS2 with another intercalated ferromagnet
Fe1/4TaS2 is demonstrated using a dry-transfer method. The fabricated
heterojunction composed of Cr1/3TaS2 and Fe1/4TaS2 with a native Ta2O5 oxide
tunnel barrier in between exhibits tunnel magnetoresistance (TMR), revealing
possible spin injection and detection with these exfoliatable ferromagnetic
materials through the vdW junction.",1709.08313v1
2019/1/5,Discovery of Weyl nodal lines in a single-layer ferromagnet,"Two-dimensional (2D) materials have attracted great attention and spurred
rapid development in both fundamental research and device applications. The
search for exotic physical properties, such as magnetic and topological order,
in 2D materials could enable the realization of novel quantum devices and is
therefore at the forefront of materials science. Here, we report the discovery
of two-fold degenerate Weyl nodal lines in a 2D ferromagnetic material, a
single-layer gadolinium-silver compound, based on combined angle-resolved
photoemission spectroscopy measurements and theoretical calculations. These
Weyl nodal lines are symmetry protected and thus robust against external
perturbations. The coexistence of magnetic and topological order in a 2D
material is likely to inform ongoing efforts to devise and realize novel
nanospintronic devices.",1901.01429v1
2016/3/22,Contributions to the Monte Carlo study of the magnetic properties of nanomaterials such as graphyne and graphone,"Attracted by the importance of new materials in nanotechnology area, this
thesis develops this research field while deepening results. We started by
introducing the more sophisticated simulation and calculation methods, such as
the Monte Carlo method, the mean field theory, the effectif field theory and
the transfer matrix. Subsequently, we studied the magnetic and hysteretic
properties of the materials. Then we have detailed some of our contributions
related to the materials based on graphene and ferrimagnetic nanomaterials with
different morphologies. We discussed the effect of defects on the thermodynamic
properties of these novel materials. Particular attention was paid to the
physical parameters that influence the compensation behavior that is of crucial
importance for technological applications such as thermo-optical recording.
With all these elements, we are opened ourselves up to the latest developments
in physics of new materials. Finally, we finished with the conclusion and
perspectives.",1603.06766v1
2017/3/8,Aperiodic topological order in the domain configurations of functional materials,"In numerous functional materials, such as steels, ferroelectrics and magnets,
new functionalities can be achieved through the engineering of the domain
structures, which are associated with the ordering of certain parameters within
the material. The recent progress in imaging techniques with atomic-scale
spatial resolution transformed our understanding of domain topology revealing
that, along with simple stripe-like or irregularly shaped domains, intriguing
vortex-type topological domain configurations also exist. In this Review, we
present a new classification scheme of ""ZmxZn domains with Zl vortices"" for
two-dimensional macroscopic domain structures with m directional variants and n
translational antiphases. This classification, together with the concept of
topological protection and topological charge conservation, can be applied to a
wide range of materials, such as multiferroics, improper ferroelectrics,
layered transition-metal dichalcogenides and magnetic superconductors, as we
discuss through selected examples. The resulting topological considerations
provide a new basis for the understanding of the formation, kinetics,
manipulation and property optimization of domains and domain boundaries in
functional materials.",1703.03037v1
2020/8/12,Stabilization of a honeycomb lattice of IrO$_6$ octahedra in superlattices with ilmenite-type MnTiO$_3$,"In the quest for quantum spin liquids, thin films are expected to open the
way for the control of intricate magnetic interactions in actual materials by
exploiting epitaxial strain and two-dimensionality. However, materials
compatible with conventional thin-film growth methods have largely remained
undeveloped. As a promising candidate towards the materialization of quantum
spin liquids in thin films, we here present a robust ilmenite-type oxide with a
honeycomb lattice of edge-sharing IrO$_6$ octahedra artificially stabilized by
superlattice formation with an ilmenite-type antiferromagnetic oxide MnTiO$_3$.
The stabilized sub-unit-cell-thick Mn-Ir-O layer is isostructural to MnTiO$_3$,
having the atomic arrangement corresponding to ilmenite-type MnTiO$_3$ not
discovered yet. By spin Hall magnetoresistance measurements, we found that
antiferromagnetic ordering in the ilmenite Mn sublattice is suppressed by
modified magnetic interactions in the MnO$_6$ planes via the IrO$_6$ planes.
These findings lay the foundation for the creation of two-dimensional Kitaev
candidate materials, accelerating the discovery of exotic physics and
applications specific to quantum spin liquids.",2008.05236v2
2021/9/3,Multiferroic properties of oxygen functionalized magnetic i-MXene,"Two dimensional multiferroics inherit prominent physical properties from both
low dimensional materials and magnetoelectric materials, and can go beyond
their three dimensional counterparts for their unique structures. Here, based
on density functional theory calculations, a MXene derivative, i.e., i-MXene
(Ta$_{2/3}$Fe$_{1/3}$)$_2$CO$_2$, is predicted to be a type-I multiferroic
material. Originated from the reliable $5d^0$ rule, its ferroelectricity is
robust, with a moderate polarization up to $\sim12.33$ $\mu$C/cm$^2$ along the
a-axis, which can be easily switched and may persist above room temperature.
Its magnetic ground state is layered antiferromagnetism. Although it is a
type-I multiferroic material, its N\'eel temperature can be significantly tuned
by the paraelectric-ferroelectric transition, manifesting a kind of intrinsic
magnetoelectric coupling. Such magnetoelectric effect is originated from the
conventional magnetostriction, but unexpectedly magnified by the exchange
frustration. Our work not only reveals a nontrivial magnetoelectric mechanism,
but also provides a strategy to search for more multiferroics in the two
dimensional limit.",2109.01454v1
2021/9/21,Exploiting Localized Transition Waves to Tune Sound Propagation in Soft Materials,"Programmable materials hold great potential for many applications such as
deployable structures, soft robotics, and wave control, however, the presence
of instability and disorder might hinder their utilization. Through a
combination of analytical, numerical, and experimental analyses, we harness the
interplay between instabilities, geometric frustration, and mechanical
deformations to control the propagation of sound waves within self-assembled
soft materials. We consider levitated magnetic disks confined by a magnetic
boundary in-plane. The assemblies can be either ordered or disordered depending
on the intrinsic disk symmetry. By applying an external load to the assembly,
we observe the nucleation and propagation of different topological defects
within the lattices. In the presence of instabilities, the defect propagation
gives rise to time-independent localized transition waves. Surprisingly, in the
presence of frustration, the applied load briefly introduces
deformation-induced order to the material. By further deforming the lattices,
new patterns emerge across all disk symmetries. We utilize these patterns to
tune sound propagation through the material. Our findings could open new
possibilities for designing exotic materials with potential applications
ranging from sound control to soft robotics.",2109.10178v1
2021/12/10,High-throughput computational screening for bipolar magnetic semiconductors,"Searching ferromagnetic semiconductor materials with electrically
controllable spin polarization is a long-term challenge for spintronics.
Bipolar magnetic semiconductors (BMS), with valence and conduction band edges
fully spin-polarized in different spin directions, show great promise in this
aspect because the carrier's spin polarization direction can be easily tuned by
voltage gate. Here, we propose a standard high-throughput computational
screening scheme for searching BMS materials. The application of this scheme to
the Materials Project database gives 11 intrinsic BMS materials (1 experimental
and 10 theoretical) from nearly 40000 structures. Among them, a room
temperature BMS Li2V3TeO8 (mp-771246) is discovered with a Curie temperature of
478K. Moreover, the BMS feature can be maintained well when cutting the bulk
Li2V3TeO8 into (001) nanofilms for realistic applications. This work provides a
feasible solution for discovering novel intrinsic BMS materials from various
crystal structure databases, paving the way for realizing electric-field
controlled spintronic devices.",2112.05421v1
2022/5/30,Progress and prospects in the quantum anomalous Hall effect,"The quantum anomalous Hall effect refers to the quantization of Hall effect
in the absence of applied magnetic field. The quantum anomalous Hall effect is
of topological nature and well suited for field-free resistance metrology and
low-power information processing utilizing dissipationless chiral edge
transport. In this Perspective, we provide an overview of the recent
achievements as well as the materials challenges and opportunities, pertaining
to engineering intrinsic/interfacial magnetic coupling, that are expected to
propel future development of the field.",2205.15226v3
2022/8/25,Magnetoresistive behaviour of ternary Cu-based materials processed by high-pressure torsion,"Severe plastic deformation using high-pressure torsion of ternary Cu-based
materials (CuFeCo and CuFeNi) was used to fabricate bulk samples with a
nanocrystalline microstructure. The goal was to produce materials featuring the
granular giant magnetoresistance effect, requiring interfaces between ferro-
and nonmagnetic materials. This magnetic effect was found for both ternary
systems; adequate subsequent annealing had a positive influence. The
as-deformed states, as well as microstructural changes upon thermal treatments,
were studied using scanning electron microscopy and X-ray diffraction
measurements. Deducing from electron microscopy, a single-phase structure was
observed for all as-deformed samples, indicating the formation of a
supersaturated solid solution. However, judging from the presence of the
granular giant-magnetoresistive effect, small ferromagnetic particles have to
be present. The highest drop in room temperature resistivity (2.45% at 1790
kA/m) was found in Cu62Fe19Ni19 after annealing for 1 h at 400 {\deg}C.
Combining the results of classical microstructural studies and magnetic
measurements, insights into the evolution of ferromagnetic particles are
accessible.",2208.11895v1
2022/10/30,Controllable chirality and band gap of quantum anomalous Hall insulators,"Finding guiding principles to optimize properties of quantum anomalous Hall
(QAH) insulators is of pivotal importance to fundamental science and
applications. Here, we build a first-principles QAH material database of
chirality and band gap, explore microscopic mechanisms determining the QAH
material properties, and obtain a general physical picture that can
comprehensively understand the QAH data. Our results reveal that the usually
neglected Coulomb exchange is unexpectedly strong in a large class of QAH
materials, which is the key to resolve experimental puzzles. Moreover, we
identify simple indicators for property evaluation and suggest material design
strategies to control QAH chirality and gap by tuning cooperative or competing
contributions via magnetic co-doping, heterostructuring, spin-orbit proximity,
etc. The work is valuable to future research of magnetic topological physics
and materials.",2210.16873v1
2023/6/19,Pseudo-spin model of argentophilicity in honeycomb bilayered materials,"We introduce a pseudo-spin model for the argentophilic bond expected in
silver-based bilayered materials arising from a spontaneous pseudo-magnetic
field interacting with pseudo-spins of two unconventional Ag ions, namely $\rm
Ag^{2+}$ and $\rm Ag^{1-}$ electronically distinct from (albeit energetically
degenerate to) the conventional $\rm Ag^{1+}$ cation typically observed in
monolayered materials. This model suggests the possibility of tuning the
dimensionality and hence the conductor-semiconductor-insulator properties of
honeycomb bilayered materials by application of external fields, analogous to
driving a superconducting or Coulomb blockade system to the normal regime by
critical magnetic or electric fields respectively.",2307.13651v3
2018/7/23,Catalogue of Topological Electronic Materials,"Topological electronic materials are new quantum states of matter hosting
novel linear responses in the bulk and anomalous gapless states at the
boundary, and are for scientific and applied reasons under intensive research
in physics and in materials sciences. The detection for such materials has so
far been hindered by the level of complication involved in the calculation of
the so-called topological invariants, and is hence considered a specialized
task that requires both experience with materials and expertise with advanced
theoretical tools. Here we introduce an effective, efficient and fully
automated algorithm in obtaining the topological invariants for all
non-magnetic materials that are known to human, based on recently developed
principles that allow for exhaustive mappings between the symmetry
representation of occupied bands and the topological invariants. Our algorithm
requires as input only the occupied-band information (energy and wavefunction)
at a handful (up to eight) of high-symmetry points in the Brillouin zone, which
is readily calculable with any first-principles software. In return, it is
capable of providing a detailed topological classification of all non-magnetic
materials. Equipped with this method we have scanned through a total of 39519
materials available in structural databases, and found that as many as 8056 of
them are actually topological (8889 if spin-orbital coupling is neglected).
These are further catalogued into classes of 5005 topological semimetals,1814
topological insulators and 1237 topological crystalline insulators, most of
which are new to human knowledge. All the results are available and searchable
at http://materiae.iphy.ac.cn/ .",1807.08756v1
2022/9/28,Two-dimensional ferroelectrics from high throughput computational screening,"We report a high throughput computational search for two-dimensional
ferroelectric materials. The starting point is 252 pyroelectric materials from
the computational 2D materials database (C2DB) and from these we identify 64
ferroelectric materials by explicitly constructing adiabatic paths connecting
states of reversed polarization. In particular we find 49 materials with
in-plane polarization, 8 materials with out-of-plane polarization and 6
materials with coupled in-plane and out-of-plane polarization. Most of the
known 2D ferroelectrics are recovered by the screening and the far majority of
the new predicted ferroelectrics are known as bulk van der Waals bonded
compounds, which implies that these could be experimentally accessible by
direct exfoliation. For roughly 25{\%} of the materials we find a metastable
state in the non-polar structure, which could have important consequences for
the thermodynamical properties and may imply a first order transition to the
polar phase. Finally, we list the magnetic pyroelectrics extracted from the
C2DB and focus on the case of VAgP$_2$Se$_6$, which exhibits a three-state
switchable polarization vector that is strongly coupled to the magnetic
excitation spectrum.",2209.13911v1
2023/5/19,Recent progress in the JARVIS infrastructure for next-generation data-driven materials design,"The Joint Automated Repository for Various Integrated Simulations (JARVIS)
infrastructure at the National Institute of Standards and Technology (NIST) is
a large-scale collection of curated datasets and tools with more than 80000
materials and millions of properties. JARVIS uses a combination of electronic
structure, artificial intelligence (AI), advanced computation and experimental
methods to accelerate materials design. Here we report some of the new features
that were recently included in the infrastructure such as: 1) doubling the
number of materials in the database since its first release, 2) including more
accurate electronic structure methods such as Quantum Monte Carlo, 3) including
graph neural network-based materials design, 4) development of unified
force-field, 5) development of a universal tight-binding model, 6) addition of
computer-vision tools for advanced microscopy applications, 7) development of a
natural language processing tool for text-generation and analysis, 8) debuting
a large-scale benchmarking endeavor, 9) including quantum computing algorithms
for solids, 10) integrating several experimental datasets and 11) staging
several community engagement and outreach events. New classes of materials,
properties, and workflows added to the database include superconductors,
two-dimensional (2D) magnets, magnetic topological materials, metal-organic
frameworks, defects, and interface systems. The rich and reliable datasets,
tools, documentation, and tutorials make JARVIS a unique platform for modern
materials design. JARVIS ensures openness of data and tools to enhance
reproducibility and transparency and to promote a healthy and collaborative
scientific environment.",2305.11842v2
1992/9/8,A Simple Model for Coupled Magnetic and Quadrupolar Instabilities in Uranium Heavy-Fermion Materials,"We present a mean-field calculation of the phase diagram of a simple model of
localized moments, in the hexagonal uranium heavy-fermion compounds. The model
considers a non-Kramers quadrupolar doublet ground state magnetically coupled
with a singlet excited-state, favoring in-plane van-Vleck magnetism, as has
been conjectured for UPt$_3$. The Hamiltonian which defines the model is
Heisenberg like in both, magnetic and quadrupolar moments. Among our main
results are: (i) for zero intersite quadrupolar coupling, the magnetic order is
achieved by a first order transition above a critical intersite magnetic
coupling value which becomes second order at higher coupling strengths. (ii)
for finite intersite quadrupolar coupling, at temperatures below a second order
quadrupolar ordering transition, the minimal magnetic coupling value is
increased but (a) the magnetic ordering temperature is enhanced above this
value, and (b) the ordering of first and second order transitions in the phase
diagram is reversed.",9209008v1
1998/11/14,Magnetic irreversibility and relaxation in assembly of ferromagnetic nanoparticles,"Measurements of the magnetic irreversibility line and time-logarithmic decay
of the magnetization are described for three $Fe_{2}O_{3}$ samples composed of
regular amorphous, acicular amorphous and crystalline nanoparticles. The
relaxation rate is the largest and the irreversibility temperature is the
lowest for the regular amorphous nanoparticles. The crystalline material
exhibits the lowest relaxation rate and the largest irreversibility
temperature. We develop a phenomenological model to explain the details of the
experimental results. The main new aspect of the model is the dependence of the
barrier for magnetic relaxation on the instantaneous magnetization and
therefore on time. The time dependent barrier yields a natural explanation to
the time-logarithmic decay of the magnetization. Interactions between particles
as well as shape and crystalline magnetic anisotropies define a new energy
scale that controls the magnetic irreversibility. Introducing this energy scale
yields a self-consistent explanation of the experimental data.",9811206v2
2000/9/8,"Magnetization reversal in a ""quasi"" single domain magnetic grain: a new numerical micromagnetic technique","Magnetization reversal in a fine ferromagnetic grain is simulated for the
case of an instantaneously applied reversal magnetic field. The Hamiltonian of
the system contains the exchange interaction, the uniaxial anisotropy, the
Zeeman energy and the dipole-dipole interactions. A cubic grain is discretized
into 64 cubic subgrains and the coupled gyromagnetic equations of motion are
solved without phenomenological damping. A new scheme to solve these equations
is developed that utilizes only two variables per sub-cube magnetization and
strictly conserves the absolute magnitude. The initial stage of reversal is
uniform rotation followed by a nonlinear excitation of nonuniform magnetic
oscillations driven by this uniform mode. An excess of the initial Zeeman
energy is transformed into nonlinear spin waves, allowing the average
magnetization to substantially reverse. The process of magnetization reversal
in fine quasi-single-domain grain exhibits general features of Hamiltonian wave
systems with nonlinear diffusion. This nonlinear diffusion is forbidden for
either a strong reversal field and/or a small grain size.",0009136v1
2001/4/30,Growth-related profiles of remanent flux in bulk melt-textured YBaCuO crystal magnetized by pulsed fields,"We have studied the remanent magnetic flux distribution in bulk melt-textured
YBa2Cu3O7 (YBCO) crystals after their magnetization in quasi-static and pulsed
magnetic fields up to 6T. It has been shown that, provided that the magnetic
pulse is sharp enough and its amplitude much exceeds the twice penetration
magnetic field, the pulse magnetization technique becomes extremely sensitive
to the sample inhomogeneities. Using this method with appropriate parameters of
the magnetic pulse, we have particularly demonstrated that the growth of YBCO
crystals in the growth sectors (GSs) responds for a macroscopic arrangement of
weaks links -- they mostly appear inside of GSs, but not along the GS
boundaries.",0104578v3
2001/11/12,On the ground states of an array of magnetic dots in the vortex state and subject to a normal magnetic field,"Dipole-dipole interactions in a square planar array of sub-micron magnetic
disks (magnetic dots) have been studied theoretically. Under a normal magnetic
field the ground-state of the array undergoes many structural transitions
between the limiting chessboard antiferromagnetic state at zero field and the
ferromagnet at a threshold field. At intermediate fields, numerous
ferrimagnetic states having mean magnetic moments between zero and that of the
ferromagnetic state are favorable energetically. The structures and energies of
a selection of states are calculated and plotted, as are the fields required to
optimally reverse the magnetic moment of a single dot within them. Approximate
formulae for the dipolar energy and anhysteretic magnetization curve are
presented.",0111225v1
2002/4/22,"Magnetic ordering, electronic structure and magnetic anisotropy energy in the high-spin Mn$_{10}$ single molecule magnet","We report the electronic structure and magnetic ordering of the single
molecule magnet [Mn$_{10}$O$_{4}$(2,2'-biphenoxide)$_{4}$Br$_{12}$]$^{4-}$
based on first-principles all-electron density-functional calculations. We find
that two of the ten core Mn atoms are coupled antiferromagnetically to the
remaining eight, resulting in a ferrimagnetic ground state with total spin
S=13. The calculated magnetic anisotropy barrier is found to be 9 K in good
agreement with experiment. The presence of the Br anions impact the electronic
structure and therefore the magnetic properties of the 10 Mn atoms. However,
the electric field due to the negative charges has no significant effect on the
magnetic anisotropy.",0204479v1
2002/11/14,Magnetic relaxation and dipole-coupling-induced magnetization in nanostructured thin films during growth: A cluster Monte Carlo study,"For growing inhomogeneous thin films with an island nanostructure similar as
observed in experiment, we determine the nonequilibrium and equilibrium
remanent magnetization. The single-island magnetic anisotropy, the dipole
coupling, and the exchange interaction between magnetic islands are taken into
account within a micromagnetic model. A cluster Monte Carlo method is developed
which includes coherent magnetization changes of connected islands. This causes
a fast relaxation towards equilibrium for irregularly connected systems. We
analyse the transition from dipole coupled islands at low coverages to a
strongly connected ferromagnetic film at high coverages during film growth. For
coverages below the percolation threshold, the dipole interaction induces a
collective magnetic order with ordering temperatures of 1 - 10 K for the
assumed model parameters. Anisotropy causes blocking temperatures of 10 - 100 K
and thus pronounced nonequilibrium effects. The dipole coupling leads to a
somewhat slower magnetic relaxation.",0211290v2
2002/12/18,Coexistence of ferro- and antiferromagnetic order in Mn-doped Ni$_2$MnGa,"Ni-Mn-Ga is interesting as a prototype of a magnetic shape-memory alloy
showing large magnetic field induced strains. We present here results for the
magnetic ordering of Mn-rich Ni-Mn-Ga alloys based on both experiments and
theory. Experimental trends for the composition dependence of the magnetization
are measured by a vibrating sample magnetometer (VSM) in magnetic fields of up
to several tesla and at low temperatures. The saturation magnetization has a
maximum near the stoichiometric composition and it decreases with increasing Mn
content. This unexpected behaviour is interpreted via first-principles
calculations within the density-functional theory. We show that extra Mn atoms
are antiferromagnetically aligned to the other moments, which explains the
dependence of the magnetization on composition. In addition, the effect of Mn
doping on the stabilization of the structural phases and on the magnetic
anisotropy energy is demonstrated.",0212442v1
2003/3/11,The magnetic field influence on magnetostructural phase transition in Ni2.19Mn0.81Ga,"Magnetic properties of a polycrystalline alloy Ni$_{2.19}$Mn$_{0.81}$Ga,
which undergoes a first-order magnetostructural phase transition from cubic
paramagnetic to tetragonal ferromagnetic phase, are studied. Hysteretic
behavior of isothermal magnetization $M(H)$ has been observed in a temperature
interval of the magnetostructural transition in magnetic fields from 20 to 100
kOe. Temperature dependencies of magnetization $M$, measured in magnetic fields
$H = 400$ and 60 kOe, indicate that the temperature of the magnetostructural
transition increases with increasing magnetic field.",0303187v1
2003/3/15,Carrier States and Ferromagnetism in Diluted Magnetic Semiconductors,"Applying the dynamical coherent potential approximation to a simple model, we
have systematically studied the carrier states in $A_{1-x}$Mn$_xB$-type diluted
magnetic semiconductors (DMS's). The model calculation was performed for three
typical cases of DMS's: The cases with strong and moderate exchange
interactions in the absence of nonmagnetic potentials, and the case with strong
attractive nonmagnetic potentials in addition to moderate exchange interaction.
When the exchange interaction is sufficiently strong, magnetic impurity bands
split from the host band. Carriers in the magnetic impurity band mainly stay at
magnetic sites, and coupling between the carrier spin and the localized spin is
very strong. The hopping of the carriers among the magnetic sites causes
ferromagnetism through a {\it double-exchange (DE)-like} mechanism. We have
investigated the condition for the DE-like mechanism to operate in DMS's. The
result reveals that the nonmagnetic attractive potential at the magnetic site
assists the formation of the magnetic impurity band and makes the DE-like
mechanism operative by substantially enhancing the effect of the exchange
interaction. Using conventional parameters we have studied the carrier states
in Ga$_{1-x}$Mn$_x$As. The result shows that the ferromagnetism is caused
through the DE-like mechanism by the carriers in the bandtail originating from
the impurity states.",0303285v1
2003/4/9,Field-induced magnetic anisotropy in La0.7Sr0.3CoO3,"Magnetic anisotropy has been measured for the ferromagnetic La0.7Sr0.3CoO3
perovskite from an analysis of the high-field part of the magnetization vs.
field curves, i.e., the magnetic saturation regime. These measurements give a
magnetic anistropy one order of magnitude higher than that of reference
manganites. Surprisingly, the values of the magnetic anisotropy calculated in
this way do not coincide with those estimated from measurements of coercive
fields which are one order of magnitude smaller. It is proposed that the reason
of this anomalous behaviour is a transition of the trivalent Co ions under the
external magnetic field from a low-spin to an intermediate-spin state. Such a
transition converts the Co3+ ions into Jahn-Teller ions having an only
partially quenched orbital angular momentum, which enhances the intra-atomic
spin-orbit coupling and magnetic anisotropy.",0304211v1
2003/7/7,"Electronic, magnetic, and vibrational properties of the molecular magnet Mn4 monomer and dimer","A new type of the single-molecule magnet [Mn_4 O_3 Cl_4 (O_2 CEt)_3(py)_3]
forms dimers. Recent magnetic hysteresis measurements on this single-molecular
magnet revealed interesting phenomena: an absence of quantum tunneling at zero
magnetic field and tunneling before magnetic field reversal. This is attributed
to a significant antiferromagnetic exchange interaction between different
monomers. To investigate this system, we calculate the electronic structure,
magnetic properties, intramolecular and intermolecular exchange interactions
using density-functional theory within the generalized-gradient approximation.
Our calculations agree with experiment. We also calculate vibrational infrared
absorption and Raman scattering intensities for the monomer which can be tested
experimentally.",0307145v1
2003/7/29,Observation of a Distribution of Internal Transverse Magnetic Fields in a Mn12-Based Single Molecule Magnet,"A distribution of internal transverse magnetic fields has been observed in
single molecule magnet (SMM) Mn12-BrAc in the pure magnetic quantum tunneling
(MQT) regime. Magnetic relaxation experiments at 0.4 K are used to produce a
hole in the distribution of transverse fields whose angle and depth depend on
the orientation and amplitude of an applied transverse ``digging field.'' The
presence of such transverse magnetic fields can explain the main features of
resonant MQT in this material, including the tunneling rates, the form of the
relaxation and the absence of tunneling selection rules. We propose a model in
which the transverse fields originate from a distribution of tilts of the
molecular magnetic easy axes.",0307706v1
2003/9/29,Extraction of domain-specific magnetization reversal for nanofabricated periodic arrays using soft x-ray resonant magnetic scattering,"A simple scheme to extract the magnetization reversals of characteristic
magnetic domains on nanofabricated periodic arrays from soft x-ray resonant
magnetic scattering (SXRMS) data is presented. The SXRMS peak intensities from
a permalloy square ring array were measured with field cycling using circularly
polarized soft x-rays at the Ni L$_3$ absorption edge. Various SXRMS hysteresis
loops observed at different diffraction orders enabled the determination of the
magnetization reversal of each magnetic domain using a simple linear algebra.
The extracted domain-specific hysteresis loops reveal that the magnetization of
the domain parallel to the field is strongly pinned, while that of the
perpendicular domain rotates continuously.",0309672v1
2004/5/25,Magnetic induction and domain walls in magnetic thin films at remanence,"Magnetic domain walls in thin films can be well analyzed using polarized
neutron reflectometry. Well defined streaks in the off-specular spin-flip
scattering maps are explained by neutron refraction at perpendicular N\'{e}el
walls. The position of the streaks depends only on the magnetic induction
within the domains, whereas the intensity of the off-specular magnetic
scattering depends on the spin-flip probability at the domain walls and on the
average size of the magnetic domains. This effect is fundamentally different
and has to be clearly distinguished from diffuse scattering originating from
the size distribution of magnetic domains. Polarized neutron reflectivity
experiments were carried out using a $^3$He gas spin-filter with a analyzing
power as high as 96% and a neutron transmission of approx 35%. Furthermore, the
off-specular magnetic scattering was enhanced by using neutron resonance and
neutron standing wave techniques.",0405586v2
2004/7/30,Correlation between tunneling magnetoresistance and magnetization in dipolar coupled nanoparticle arrays,"The tunneling magnetoresistance (TMR) of a hexagonal array of dipolar coupled
anisotropic magnetic nanoparticles is studied using a resistor network model
and a realistic micromagnetic configuration obtained by Monte Carlo
simulations. Analysis of the field-dependent TMR and the corresponding
magnetization curve shows that dipolar interactions suppress the maximum TMR
effect, increase or decrease the field-sensitivity depending on the direction
of applied field and introduce strong dependence of the TMR on the direction of
the applied magnetic field. For off-plane magnetic fields, maximum values in
the TMR signal are associated with the critical field for irreversible rotation
of the magnetization. This behavior is more pronounced in strongly interacting
systems (magnetically soft), while for weakly interacting systems (magnetically
hard) the maximum of TMR (Hmax) occurs below the coercive field (Hc), in
contrast to the situation for non-interacting nanoparticles or in-plane fields
(Hmax=Hc). The relation of our simulations to recent TMR measurements in
self-assembled Co nanoparticle arrays is discussed.",0407814v1
2004/9/6,Ferromagnet-Superconductor Hybrids,"A new class of phenomena discussed in this review is based on interaction
between spatially separated, but closely located ferromagnets and
superconductors. They are called Ferromagnet-Superconductor Hybrids (FSH).
These systems include coupled smooth and textured Ferromagnetic and
Superconducting films, magnetic dots, wires etc.The interaction may be provided
by the magnetic flux from magnetic textures and supercurrents. The magnetic
flux from magnetic textures or topological defects can pin vortices or create
them, changing drastically the properties of the superconductor. On the other
hand, the magnetic field from supercurrents (vortices) strongly interacts with
the magnetic subsystem leading to formation of coupled magnetic-superconducting
topological defects. We discuss possible experimental realization of the FSH.
The presence of ferromagnetic layer can change dramatically the properties of
the superconducting film due to proximity effect. We discuss experimental and
theoretical studies of the proximity effect in the FSH including transition
temperature and order parameter oscillations and triplet superconductivity.",0409137v1
2005/2/28,Magnetization of nanomagnet assemblies: Effects of anisotropy and dipolar interactions,"We investigate the effect of anisotropy and weak dipolar interactions on the
magnetization of an assembly of nanoparticles with distributed magnetic
moments, i.e., assembly of magnetic nanoparticles in the one-spin
approximation, with textured or random anisotropy.
  The magnetization of a free particle is obtained either by a numerical
calculation of the partition function or analytically in the low and high field
regimes, using perturbation theory and the steepest-descent approximation,
respectively. The magnetization of an interacting assembly is computed
analytically in the range of low and high field, and numerically using the
Monte Carlo technique.
  Approximate analytical expressions for the assembly magnetization are
provided which take account of the dipolar interactions, temperature, magnetic
field, and anisotropy. The effect of anisotropy and dipolar interactions are
discussed and the deviations from the Langevin law they entail are
investigated, and illustrated for realistic assemblies with the lognormal
moment distribution.",0502660v2
2005/7/5,Three-dimensional magnetic flux-closure patterns in mesoscopic Fe islands,"We have investigated three-dimensional magnetization structures in numerous
mesoscopic Fe/Mo(110) islands by means of x-ray magnetic circular dichroism
combined with photoemission electron microscopy (XMCD-PEEM). The particles are
epitaxial islands with an elongated hexagonal shape with length of up to 2.5
micrometer and thickness of up to 250 nm. The XMCD-PEEM studies reveal
asymmetric magnetization distributions at the surface of these particles.
Micromagnetic simulations are in excellent agreement with the observed magnetic
structures and provide information on the internal structure of the
magnetization which is not accessible in the experiment. It is shown that the
magnetization is influenced mostly by the particle size and thickness rather
than by the details of its shape. Hence, these hexagonal samples can be
regarded as model systems for the study of the magnetization in thick,
mesoscopic ferromagnets.",0507119v2
2005/9/5,Magnetic behavior of EuCu2As2: Delicate balance between antiferromagnetic and ferromagnetic order,"The Eu-based compound, EuCu2As2, crystallizing in the ThCr2Si2-type
tetragonal structure, has been synthesized and its magnetic behavior has been
investigated by magnetization (M), heat-capacity (C) and electrical resistivity
(rho) measurements as a function of temperature (T) and magnetic field (H) as
well as by 151Eu Moessbauer measurements. The results reveal that Eu is
divalent ordering antiferromagnetically below 15 K in the absence of magnetic
field, apparently with the formation of magnetic Brillouin-zone boundary gaps.
A fascinating observation is made in a narrow temperature range before
antiferromagnetism sets in: That is, there is a remarkable upturn just below 20
K in the plot of magnetic susceptibility versus T even at low fields, as though
the compound actually tends to order ferromagnetically. There are corresponding
anomalies in the magnetocaloric effect data as well. In addition, a small
application of magnetic field (around 1 kOe at 1.8 K) in the antiferromagnetic
state causes spin-reorientation effect. These results suggest that there is a
close balance between antiferromagnetism and ferromagnetism in this compound",0509108v1
2005/9/19,Observation of field-dependent magnetic parameters in the magnetic molecule {Ni4Mo12},"We investigate the bulk magnetic, electron paramagnetic resonance, and
magneto-optical properties of {Ni4Mo12}, a magnetic molecule with
antiferromagnetically coupled tetrahedral {Ni4Mo12} in a diamagnetic molybdenum
matrix. The low-temperature magnetization exhibits steps at irregular field
intervals, a result that cannot be explained using a Heisenberg model even if
it is augmented by magnetic anisotropy and biquadratic terms. Allowing the
exchange and anisotropy parameters to depend on the magnetic field provides the
best fit to our data, suggesting that the molecular structure (and thus the
interactions between spins) may be changing with applied magnetic field.",0509476v2
2005/9/26,Collective Magnetic Excitations in SrCu_2(BO_3)_2,"We study low temperature Raman data on phononic and magnetic excitations in
SrCu_2(BO_3)_2. Regarding the former, in the 0 to 350 cm-1 range we find
several pairs of quasi-degenerate modes which have different symmetries. Group
theoretical analysis suggests that the existence of these modes is related to
quite different atomic vibrational pattern, i.e. in-plane and c-axis.
Collective magnetic excitations are studied in terms of symmetry, resonance and
coupling mechanisms in zero and applied magnetic fields. The analysis of a
4-spin cluster allows us to understand the group symmetries of the zero field
Brillouin zone center spin gap branches around 24 cm-1 confirming the picture
of local elementary one-triplet modes. By considering an additional intra-dimer
DM interaction we are also able to understand the observed selection rules and
intensity variations of the spin gap branches in external magnetic fields
applied parallel or perpendicular to the dimer planes. We identified two
effective magnetic light scattering Hamiltonians responsible for the coupling
to the magnetic modes which allowed us to explain their resonance behavior.",0509630v1
2006/2/5,Magnetic properties of vanadium-oxide nanotubes probed by static magnetization and {51}V NMR,"Measurements of the static magnetic susceptibility and of the nuclear
magnetic resonance of multiwalled vanadium-oxide nanotubes are reported. In
this nanoscale magnet the structural low-dimensionality and mixed valency of
vanadium ions yield a complex temperature dependence of the static
magnetization and the nuclear relaxation rates. Analysis of the different
contributions to the magnetism allows to identify individual interlayer
magnetic sites as well as strongly antiferromagnetically coupled vanadium spins
(S = 1/2) in the double layers of the nanotube's wall. In particular, the data
give strong indications that in the structurally well-defined vanadium-spin
chains in the walls, owing to an inhomogeneous charge distribution,
antiferromagnetic dimers and trimers occur. Altogether, about 30% of the
vanadium ions are coupled in dimers, exhibiting a spin gap of the order of 700
K, the other ~ 30% comprise individual spins and trimers, whereas the remaining
\~ 40% are nonmagnetic.",0602114v2
2006/3/9,Signatures of Molecular Magnetism in Single-Molecule Transport Spectroscopy,"Single-molecule transistors provide a unique experimental tool to investigate
the coupling between charge transport and the molecular degrees of freedom in
individual molecules. One interesting class of molecules for such experiments
are the single-molecule magnets, since the intramolecular exchange forces
present in these molecules should couple strongly to the spin of transport
electrons, thereby providing both new mechanisms for modulating electron flow
and also new means for probing nanoscale magnetic excitations. Here we report
single-molecule transistor measurements on devices incorporating Mn12
molecules. By studying the electron-tunneling spectrum as a function of
magnetic field, we are able to identify clear signatures of magnetic states and
their associated magnetic anisotropy. A comparison of the data to simulations
also suggests that electron flow can strongly enhance magnetic relaxation of
the magnetic molecule.",0603276v1
2006/3/10,Dielectric anomalies and spiral magnetic order in CoCr2O4,"We have investigated the structural, magnetic, thermodynamic, and dielectric
properties of polycrystalline CoCr$_2$O$_4$, an insulating spinel exhibiting
both ferrimagnetic and spiral magnetic structures. Below $T_c$ = 94 K the
sample develops long-range ferrimagnetic order, and we attribute a sharp phase
transition at $T_N$ $\approx$ 25 K with the onset of long-range spiral magnetic
order. Neutron measurements confirm that while the structure remains cubic at
80 K and at 11 K; there is complex magnetic ordering by 11 K. Density
functional theory supports the view of a ferrimagnetic semiconductor with
magnetic interactions consistent with non-collinear ordering. Capacitance
measurements on CoCr$_2$O$_4$, show a sharp decrease in the dielectric constant
at $T_N$, but also an anomaly showing thermal hysteresis falling between
approximately $T$ = 50 K and $T$ = 57 K. We tentatively attribute the
appearance of this higher temperature dielectric anomaly to the development of
\textit{short-range} spiral magnetic order, and discuss these results in the
context of utilizing dielectric spectroscopy to investigate non-collinear
short-range magnetic structures.",0603307v1
2006/3/14,Spin dynamics and magnetic order in magnetically frustrated Tb2Sn2O7,"We report a study of the geometrically frustrated magnetic material Tb2Sn2O7
by the positive muon spin relaxation technique. No signature of a static
magnetically ordered state is detected while neutron magnetic reflections are
observed in agreement with a published report. This is explained by the
dynamical nature of the ground state of Tb2Sn2O7: the Tb3+ magnetic moment
characteristic fluctuation time is ~ 10^{-10} s. The strong effect of the
magnetic field on the muon spin-lattice relaxation rate at low fields indicates
a large field-induced increase of the magnetic density of states of the
collective excitations at low energy.",0603379v1
2006/3/22,"Out-of-plane magnetization reversal processes of (Ga,Mn)As with two different hole concentrations","We study magnetization reversal processes of in-plane magnetized (Ga,Mn)As
epilayers with different hole concentrations in out-of-plane magnetic fields
using magnetotransport measurements. A clear difference in the magnetization
process is found in two separate samples with hole concentrations of 10^20
cm^-3 and 10^21 cm^-3 as the magnetization rotates from the out-of-plane
saturation to the in-plane remanence. Magnetization switching process from the
in-plane remanence to the out-of-plane direction, on the other hand, shows no
hole concentration dependence, where the switching process occurs via domain
wall propagation. We show that the balance of <100> cubic magnetocrystalline
anisotropy and uniaxial [110] anisotropy gives an understanding of the
difference in the out-of-plane magnetization processes of (Ga,Mn)As epilayers.",0603568v1
2006/3/24,Theory of domain structure in ferromagnetic phase of diluted magnetic semiconductors near the phase transition temperature,"We discuss the influence of disorder on domain structure formation in
ferromagnetic phase of diluted magnetic semiconductors (DMS) of p-type. Using
analytical arguments we show the existence of critical ratio $\nu_{\rm {cr}}$
of concentration of charge carriers and magnetic ions such that sample critical
thickness $L_{\rm{cr}}$ (such that at $L<L_{\rm{cr}}$ a sample is monodomain)
diverges as $\nu \to \nu_{\rm {cr}}$. At $\nu > \nu_{\rm {cr}}$ the sample is
monodomain. This feature makes DMS different from conventional ordered magnets
as it gives a possibility to control the sample critical thickness and emerging
domain structure period by variation of $\nu $. As concentration of magnetic
impurities grows, $\nu_{\rm {cr}}\to \infty$ restoring conventional behavior of
ordered magnets. Above facts have been revealed by examination of the
temperature of transition to inhomogeneous magnetic state (stripe domain
structure) in a slab of finite thickness $L$ of p-type DMS. Our analysis is
carried out on the base of homogeneous exchange part of magnetic free energy of
DMS calculated by us earlier [\prb, {\bf 67}, 195203 (2003)].",0603676v1
2006/5/22,Palladium: A localised paramagnetism,"We report on the origin of ferromagnetic like behaviour observed for 2.4 nm
size Pd nanoparticles. Localised magnetic moments on metallic surfaces have
been recently shown to induce orbital motion of the itinerant electrons via
spin-orbit coupling. As a result of this coupling the magnetic anisotropy is
enhanced and the surface magnetic moments can be blocked up to above room
temperature. Since Pd has been customary treated as a paradigmatic itinerant
system, localisation of magnetic moments at its surfaces was not initially
expected. However, it is shown, through the experimental thermal dependence of
both magnetic susceptibility and Hall resistance, that magnetism of bulk Pd, is
a localised paramagnetism and, consequently, can give rise to permanent
magnetism at its surface. Such surface permanent magnetism is experimentally
observed only when the percentage of surface moments is outstanding as is the
case for nanoparticles.",0605496v1
2006/5/22,Magnetic interactions in transition metal doped ZnO : An abinitio study,"We calculate the nature of magnetic interactions in transition-metal doped
ZnO using the local spin density approximation and LSDA+\textit{U} method of
density functional theory. We investigate the following four cases: (i) single
transition metal ion types (Cr, Mn, Fe, Co, Ni and Cu) substituted at Zn sites,
(ii) substitutional magnetic transition metal ions combined with additional Cu
and Li dopants, (iii) substitutional magnetic transition metal ions combined
with oxygen vacancies and (iv) pairs of magnetic ion types (Co and Fe, Co and
Mn, etc.). Extensive convergence tests indicate that the calculated magnetic
ground state is unusually sensitive to the k-point mesh and energy cut-off, the
details of the geometry optimizations and the choice of the
exchange-correlation functional. We find that ferromagnetic coupling is
sometimes favorable for single type substitutional transition metal ions within
the local spin density approximation. However, the nature of magnetic
interactions changes when correlations on the transition-metal ion are treated
within the more realistic LSDA + \textit{U} method, often disfavoring the
ferromagnetic state. The magnetic configuration is sensitive to the detailed
arrangement of the ions and the amount of lattice relaxation, except in the
case of oxygen vacancies when an antiferromagnetic state is always favored.",0605543v1
2006/7/31,Dynamical and thermal effects in nanoparticle systems driven by a rotating magnetic field,"We study dynamical and thermal effects that are induced in nanoparticle
systems by a rotating magnetic field. Using the deterministic Landau-Lifshitz
equation and appropriate rotating coordinate systems, we derive the equations
that characterize the steady-state precession of the nanoparticle magnetic
moments and study a stability criterion for this type of motion. On this basis,
we describe (i) the influence of the rotating field on the stability of the
small-angle precession, (ii) the dynamical magnetization of nanoparticle
systems, and (iii) the switching of the magnetic moments under the action of
the rotating field. Using the backward Fokker-Planck equation, which
corresponds to the stochastic Landau-Lifshitz equation, we develop a method for
calculating the mean residence times that the driven magnetic moments dwell in
the up and down states. Within this framework, the features of the induced
magnetization and magnetic relaxation are elucidated.",0607820v1
2006/10/20,Magnetic Switching of a Single Molecular Magnet due to Spin-Polarized Current,"Magnetic switching of a single molecular magnet (SMM) due to spin-polarized
current flowing between ferromagnetic metallic electrodes is investigated
theoretically. Magnetic moments of the electrodes are assumed to be collinear
and parallel to the magnetic easy axis of the molecule. Electrons tunneling
through a barrier between magnetic leads are coupled to the SMM via exchange
interaction. The current flowing through the system as well as the spin
relaxation times of the SMM are calculated from the Fermi golden rule. It is
shown that spin of the SMM can be reversed by applying a voltage between the
two magnetic electrodes. Moreover, the switching is reflected in the
corresponding current-voltage characteristics.",0610556v2
2006/12/4,Penetration of an external magnetic field into a multistrip superconductor/soft-magnet heterostructure,"The magnetization of a planar heterostructure of periodically alternating
type-II superconductor and soft-magnet strips exposed to a transverse external
magnetic field is studied. An integral equation governing the sheet current
distribution in the Meissner state of the superconductor constituents is
derived. The field of complete penetration of magnetic flux in the critical
state of the superconductor constituents is calculated for different widths of
the superconductor and the soft-magnet constituents and a range of values of
the relative permeability of the soft-magnet constituents.",0612082v1
2006/12/15,Domain Nucleation and Annihilation in Uniformly Magnetized State under Current Pulses in Narrow Ferromagnetic Wires,"We investigate the current-driven magnetization dynamics in narrow Permalloy
wires by means of Lorentz microscopy and electron holography. Current pulses
are found to transform the magnetic structure in the uniformly magnetized state
below the Curie temperature. A variety of magnetic states including reversed
magnetic domains are randomly obtained in low probability. The dynamics of
vortices found in most of observed magnetic states seems to play a key role in
triggering the magnetization reversal.",0612383v2
2007/1/15,"Magnetic anomalies in a spin-chain compound, Sr3CuRhO6: Griffiths-phase-like behavior of magnetic susceptibility","We report the results of ac and dc magnetic susceptibility (chi),
heat-capacity (C), isothermal magnetization and isothermal remanent
magnetization measurements on the compound, Sr3CuRhO6, crystallizing in a
K4CdCl6-derived monoclinic structure. The magnetization data reveal distinct
magnetic anomalies near 6 and 12 K with decreasing temperature (T). While the
transition below (To=) 6K appears to be of a spin-glass-type as inferred from
all the data, the one at 12 K is not typical of bulk ferromagnetism in contrast
to an earlier proposal. In the range 6 to 12 K, the dc chi obeys the
theoretically expected form for very low dc fields and the values of chi
decrease gradually with the application of higher magnetic fields, mimicking
the behavior Griffiths-phases.",0701336v1
2007/3/12,Spin moment over 10-300 K and delocalization of magnetic electrons above the Verwey transition in magnetite,"In order to probe the magnetic ground state, we have carried out temperature
dependent magnetic Compton scattering experiments on an oriented single crystal
of magnetite (Fe$_3$O$_4$), together with the corresponding first-principles
band theory computations to gain insight into the measurements. An accurate
value of the magnetic moment $\mu_S$ associated with unpaired spins is obtained
directly over the temperature range of 10-300K. $\mu_S$ is found to be
non-integral and to display an anomalous behavior with the direction of the
external magnetic field near the Verwey transition. These results reveal how
the magnetic properties enter the Verwey energy scale via spin-orbit coupling
and the geometrical frustration of the spinel structure, even though the Curie
temperature of magnetite is in excess of 800 K. The anisotropy of the magnetic
Compton profiles increases through the Verwey temperature $T_v$ and indicates
that magnetic electrons in the ground state of magnetite become delocalized on
Fe B-sites above $T_v$.",0703305v1
2007/3/14,Ab initio Studies of the Possible Magnetism in BN Sheet by Non-magnetic Impurities and Vacancies,"We performed first-principles calculations to investigate the possible
magnetism induced by the different concentrations of non-magnetic impurities
and vacancies in BN sheet. The atoms of Be, B, C, N, O, Al and Si are used to
replace either B or N in the systems as impurities. We discussed the changes in
density of states as well as the extent of the spatial distributions of the
defect states, the possible formation of magnetic moments, the magnitude of the
magnetization energies and finally the exchange energies due to the presence of
these defects. It is shown that the magnetization energies tend to increase as
the concentrations of the defects decreases in most of the defect systems which
implies a definite preference of finite magnetic moments. The calculated
exchange energies are in general tiny but not completely insignificant for two
of the studied defect systems, i.e. one with O impurities for N and the other
with B vacancies.",0703356v1
2007/4/24,Scanning magnetoresistance microscopy of atom chips,"Surface based geometries of microfabricated wires or patterned magnetic films
can be used to magnetically trap and manipulate ultracold neutral atoms or
Bose-Einstein condensates. We investigate the magnetic properties of such atom
chips using a scanning magnetoresistive (MR) microscope with high spatial
resolution and high field sensitivity. We show that MR sensors are ideally
suited to observe small variations of the magnetic field caused by
imperfections in the wires or magnetic materials which ultimately lead to
fragmentation of ultracold atom clouds. Measurements are also provided for the
magnetic field produced by a thin current-carrying wire with small geometric
modulations along the edge. Comparisons of our measurements with a full numeric
calculation of the current flow in the wire and the subsequent magnetic field
show excellent agreement. Our results highlight the use of scanning MR
microscopy as a convenient and powerful technique for precisely characterizing
the magnetic fields produced near the surface of atom chips.",0704.3137v1
2007/6/9,Geometrically frustrated magnetic behavior of Sr3NiRhO6 and Sr3NiPtO6,"The results of ac and dc magnetic susceptibility isothermal magnetization and
heat-capacity measurements as a function of temperature (T) are reported for
Sr3NiRhO6 and Sr3NiPtO6 containing magnetic chains arranged in a triangular
fashion in the basal plane and crystallizing in K4CdCl6-derived rhombohedral
structure. The results establish that both the compounds are magnetically
frustrated, however in different ways. In the case of the Rh compound, the
susceptibility data reveal that there are two magnetic transitions, one in the
range 10 -15 K and the other appearing as a smooth crossover near 45 K, with a
large frequency dependence of ac susceptibility in the range 10 to 40 K; in
addition, the features in C(T) are smeared out at these temperatures. The
magnetic properties are comparable to those of previously known few compounds
with partially disordered antiferromagnetic structure. On the other hand, for
Sr3NiPtO6, there is no evidence for long-range magnetic ordering down to 1.8 K
despite large value of paramagnetic Curie temperature.",0706.1308v2
2007/9/20,"Symmetry and magnetically driven ferroelectricity in rare-earth manganites RMnO3 (R=Gd, Tb, Dy)","This work investigates the magnetically driven ferroelectricity in
orthorhombic manganites RMnO3 (R=Gd, Dy or Tb) from the point of view of the
symmetry. The method adopted generalizes the one used to characterize the polar
properties of displacive modulated structures to the case of an irreducible
magnetic order parameter. The symmetry conditions for magnetically induced
ferroelectricity are established and the Landau-Devonshire free energy
functionals derived from general symmetry considerations. The ferroelectric
polarisation observed in DyMnO3 and TbMnO3 at zero magnetic field is explained
in terms of the symmetry of a reducible magnetic order parameter. The
polarisation rotation induced in these compounds by external magnetic fields
and the stabilization of a ferroelectric phase in GdMnO3 are accounted for by a
mechanism in which magnetization and polarization are secondary order
parameters that are not directly coupled but compete with each other through
their coupling to competing primary modulated order parameters.",0709.3234v1
2008/3/8,Magnetism of Ru and Rh thin films on Ag(001) substrate,"In a very recent x-ray magnetic circular dichroism experiment concerning with
Ru and Rh impurities and metal films on Ag(001) substrate, no local magnetic
momen ts were displayed in direct contradiction with previous theoretical
works. It is thought that there can be three main reasons for this
inconsistency: relaxation, alloying and many-body effects. Some of the
above-mentioned systems are studie d by using a first-principles method in
which relaxation and alloying are taken into account, even so magnetism is
still obtained. For low-coverage systems, hig h magnetic moments in both Ru
($\sim$ 2.49 $\mu_{B}$) and Rh ($\sim$ 2.00 $\mu_{B}$) are obtained. Naturally,
as the coverage is increased the magnetic moments are approached to zero. Also,
it is noticed that the relaxation distances are in creased by magnetism, which
in turn is decreased by alloying. The behavior of th e magnetic properties is
explained in terms of Stoner model.",0803.1257v1
2008/4/21,"Magnetic phenomena, spin-orbit effects, and Landauer conductance in Pt nanowire contacts","Platinum monatomic nanowires were predicted to spontaneously develop
magnetism, involving a sizable orbital moment via spin orbit coupling, and a
colossal magnetic anisotropy. We present here a fully-relativistic (spin-orbit
coupling included) pseudo-potential density functional calculation of
electronic and magnetic properties, and of Landauer ballistic conductance of Pt
model nanocontacts consisting of short nanowire segments suspended between Pt
leads or tips, reprented by bulk planes. Even if short, and despite the
nonmagnetic Pt leads, the nanocontact is found to be locally magnetic with
magnetization strictly parallel to its axis. Especially under strain, the
energy barrier to flip the overall spin direction is predicted to be tens of
meV high, and thus the corresponding blocking temperatures large, suggesting
the use of static Landauer ballistic electrical conductance calculations. We
carry out such calculations, to find that inclusion of spin-orbit coupling and
of magnetism lowers the ballistic conductance by about $15\div20$% relative to
the nonmagnetic case, yielding $ G\sim 2 G_0$ ($G_0=2e^2/h$), in good agreement
with break junction results. The spin filtering properties of this highly
unusual spontaneously magnetic nanocontact are also analysed.",0804.3340v1
2008/5/13,"Electronic structure and magnetism in BeO nanotubes induced by boron, carbon and nitrogen impurities","We have performed ab initio calculations to systematically investigate
electronic properties and magnetism of insulating non-magnetic beryllium
monoxide nanotubes induced by non-magnetic sp impurities: boron, carbon and
nitrogen. We found that in the presence of these sp impurities, which replace
oxygen atoms, the non-magnetic BeO NTs transform into magnetic semiconductors,
which acquire magnetization caused by spin splitting of (B,C,N) 2p states
located in the forbidden gap of a BeO tube. The magnetic moments of the
impurities vary from 0.65 to 1.60. On the contrary, when (B,C,N) dopants
substitute for Be atoms or in the presence of an oxygen vacancy, the
nonmagnetic state of the BeO tubes is retained.",0805.1774v1
2008/7/29,Dose dependence of ferromagnetism in Co-implanted ZnO,"We have studied the structural, magnetic and electronic properties of
Co-implanted ZnO (0001) films grown on Al2O3 (1120) substrates for different
implantation doses and over a wide temperature range. Strong room temperature
ferromagnetism is observed with magnetic parameters depending on the cobalt
implantation dose. A detailed analysis of the structural and magnetic
properties indicates that there are two magnetic phases in Co-implanted ZnO
films. One is a ferromagnetic phase due to the formation of long range
ferromagnetic ordering between implanted magnetic cobalt ions in the ZnO layer,
the second one is a superparamagnetic phase, which occurs due to the formation
of metallic cobalt clusters in the Al2O3 substrate. Using x-ray resonant
magnetic scattering, the element specific magnetization of cobalt, oxygen and
Zn was investigated. Magnetic dichroism was observed at the Co L2,3 edges as
well as at the O K edge. In addition, the anomalous Hall effect is also
observed, supporting the intrinsic nature of ferromagnetism in Co-implanted ZnO
films.",0807.4711v1
2008/8/15,Alignment Dynamics of Single-Walled Carbon Nanotubes in Pulsed Ultrahigh Magnetic Fields,"We have measured the dynamic alignment properties of single-walled carbon
nanotube (SWNT) suspensions in pulsed high magnetic fields through linear
dichroism spectroscopy. Millisecond-duration pulsed high magnetic fields up to
56 T as well as microsecond-duration pulsed ultrahigh magnetic fields up to 166
T were used. Due to their anisotropic magnetic properties, SWNTs align in an
applied magnetic field, and because of their anisotropic optical properties,
aligned SWNTs show linear dichroism. The characteristics of their overall
alignment depend on several factors, including the viscosity and temperature of
the suspending solvent, the degree of anisotropy of nanotube magnetic
susceptibilities, the nanotube length distribution, the degree of nanotube
bundling, and the strength and duration of the applied magnetic field. In order
to explain our data, we have developed a theoretical model based on the
Smoluchowski equation for rigid rods that accurately reproduces the salient
features of the experimental data.",0808.2205v1
2008/9/22,Elementary transitions and magnetic correlations in two-dimensional disordered nanoparticle ensembles,"The magnetic relaxation processes in disordered two-dimensional ensembles of
dipole-coupled magnetic nanoparticles are theoretically investigated by
performing numerical simulations. The energy landscape of the system is
explored by determining saddle points, adjacent local minima, energy barriers,
and the associated minimum energy paths (MEPs) as functions of the structural
disorder and particle density. The changes in the magnetic order of the
nanostructure along the MEPs connecting adjacent minima are analyzed from a
local perspective. In particular, we determine the extension of the correlated
region where the directions of the particle magnetic moments vary
significantly. It is shown that with increasing degree of disorder the magnetic
correlation range decreases, i.e., the elementary relaxation processes become
more localized. The distribution of the energy barriers, and their relation to
the changes in the magnetic configurations are quantified. Finally, some
implications for the long-time magnetic relaxation dynamics of nanostructures
are discussed.",0809.3640v1
2008/12/19,Magnetic structure of actinide metals,"In comparison to 3d or 4f metals, magnetism in actinides remains poorly
understood due to experimental complications and the exotic behavior of the 5f
states. In particular, plutonium metal is most especially vexing. Over the last
five decades theories proposed the presence of either ordered or disordered
local moments at low temperatures. However, experiments such as magnetic
susceptibility, electrical resistivity, nuclear magnetic resonance, specific
heat, and elastic and inelastic neutron scattering show no evidence for ordered
or disordered magnetic moments in any of the six phases of plutonium. Beyond
plutonium, the magnetic structure of other actinides is an active area of
research given that temperature, pressure, and chemistry can quickly alter the
magnetic structure of the 5f states. For instance, curium metal has an
exceedingly large spin polarization that results in a total moment of about 8
Bohr magneton/atom, which influences the phase stability of the metal. Insight
in the actinide ground state can be obtained from core-level x-ray absorption
spectroscopy (XAS) and electron energy-loss spectroscopy (EELS). A sum rule
relates the branching ratio of the core-level spectra measured by XAS or EELS
to the expectation value of the angular part of the spin-orbit interaction.",0812.3868v1
2008/12/29,Temperature dependent dynamic and static magnetic response in magnetic tunnel junctions with Permalloy layers,"Ferromagnetic resonance and static magnetic properties of CoFe/Al2O3/CoFe/Py
and CoFe/Al2O3/CoFeB/Py magnetic tunnel junctions and of 25nm thick
single-layer Permalloy(Py) films have been studied as a function of temperature
down to 2K. The temperature dependence of the ferromagnetic resonance excited
in the Py layers in magnetic tunnel junctions shows knee-like enhancement of
the resonance frequency accompanied by an anomaly in the magnetization near
60K. We attribute the anomalous static and dynamic magnetic response at low
temperatures to interface stress induced magnetic reorientation transition at
the Py interface which could be influenced by dipolar soft-hard layer coupling
through the Al2O3 barrier.",0812.4953v1
2009/1/14,In search of antiferromagnetic interlayer coupling in diluted magnetic thin films with RKKY interaction,"We study a model thin film containing diluted bilayer structure with the RKKY
long-range interaction. The magnetic subsystem is composed of two magnetically
doped layers, separated by an undoped nonmagnetic spacer and placed inside a
wider film modelled by a quantum well of infinite depth. We focus our study on
the range of parameters for which the antiferromagnetic coupling between the
magnetic layers can be expected. The critical temperatures for such system are
found and their dependence on magnetic layer thickness and charge carriers
concentration is discussed. The magnetization distribution within each magnetic
layer is calculated as a function of layer thickness. The external field
required to switch the mutual orientation of layer magnetizations from
antiferromagnetic to ferromagnetic state is also discussed.",0901.2088v1
2009/3/16,Magnetic Structure and Susceptibility of CoSe$_2$O$_5$: A Low Dimensional Antiferromagnet,"CoSe$_2$O$_5$ has a crystal structure consisting of zig-zag chains of edge
shared CoO$_6$ octahedra running along the c axis, with the chains separated by
Se$_2$O$_5^{2-}$ units. Magnetic susceptibility measurements indicate a
transition at 8.5 K to an ordered state. We investigate here the nature of this
magnetic ordering using magnetization and specific heat measurements in
addition to powder neuttron diffraction. A transition to long-range
antiferromagnetic order is found below $T_N$ = 8.5 K as identified by magnetic
susceptibility measurements and magnetic Bragg reflections, with a propagation
vector $\mathbf{k}$ = 0. The magnetic structure shows that the moments align
perpendicular to the c-axis, but with the spins canting with respect to the a
axis by, alternately, $+8^\circ$ and $-8^\circ$. Interestingly, the low-field
magnetic susceptibility does not show the anticipated cusp-like behavior
expected for a well-ordered antiferromagnet. When the susceptibility is
acquired under field-cooling conditions under a 10 kOe field, the the usual
downturn expected for antiferromagnetic ordering is obtained. Heat capacity
measurements at low temperatures indicate the presence of gapped behavior with
a gap of 6.5 K.",0903.2513v1
2009/3/19,Magnetic Anisotropy and Magnetization Dynamics of Individual Atoms and Clusters of Fe and Co on Pt(111),"The recently discovered giant magnetic anisotropy of single magnetic Co atoms
raises the hope of magnetic storage in small clusters. We present a joint
experimental and theoretical study of the magnetic anisotropy and the spin
dynamics of Fe and Co atoms, dimers, and trimers on Pt(111). Giant anisotropies
of individual atoms and clusters as well as lifetimes of the excited states
were determined with inelastic scanning tunneling spectroscopy. The short
lifetimes due to hybridization-induced electron-electron scattering oppose the
magnetic stability provided by the magnetic anisotropies.",0903.3337v1
2009/3/20,On-chip manipulation of magnetic nanoparticles through domain walls conduits,"The manipulation of geometrically constrained magnetic domain walls (DWs) in
nanoscale magnetic strips has attracted much interest recently, with proposals
for prospective memory and logic devices. Here we propose to use the high
controllability of the motion of geometrically constrained DWs for the
manipulation of individual nanoparticles on a chip with an active control of
position at the nanometer scale. The proposed method exploits the fact that
magnetic nanoparticles in solution can be captured by a DW, whose position can
be manipulated with nanometric accuracy in a specifically designed magnetic
nanowire structure. We show that the high control over DW nucleation,
displacement, and annihilation processes in such structures can be used to
capture, transport and release magnetic nanoparticles. As magnetic particles
with functionalized surfaces are commonly used as molecule carriers or labels,
the accurate control over the handling of the single magnetic nanoparticle is
crucial for several applications including single molecule manipulation,
separation, cells manipulation and biomagnetic sensing.",0903.3516v1
2009/3/26,Exact solution of the mixed spin-1/2 and spin-S Ising-Heisenberg diamond chain,"The geometric frustration in a class of the mixed spin-1/2 and spin-S
Ising-Heisenberg diamond chains is investigated by combining three exact
analytical techniques: Kambe projection method, decoration-iteration
transformation and transfer-matrix method. The ground state, the magnetization
process and the specific heat as a function of the external magnetic field are
particularly examined for different strengths of the geometric frustration. It
is shown that the increase of the Heisenberg spin value S raises the number of
intermediate magnetization plateaux, which emerge in magnetization curves
provided that the ground state is highly degenerate on behalf of a sufficiently
strong geometric frustration. On the other hand, all intermediate magnetization
plateaux merge into a linear magnetization versus magnetic field dependence in
the limit of classical Heisenberg spin S -> infinity. The enhanced
magnetocaloric effect with cooling rate exceeding the one of paramagnetic salts
is also detected when the disordered frustrated phase constitutes the ground
state and the external magnetic field is small enough.",0903.4566v1
2009/5/28,Hydrodynamic theory of coupled current and magnetization dynamics in spin-textured ferromagnets,"We develop the hydrodynamical theory of collinear spin currents coupled to
magnetization dynamics in metallic ferromagnets. The collective spin density
couples to the spin current through a U(1) Berry-phase gauge field determined
by the local texture and dynamics of the magnetization. We determine
phenomenologically the dissipative corrections to the equation of motion for
the electronic current, which consist of a dissipative spin-motive force
generated by magnetization dynamics and a magnetic texture-dependent
resistivity tensor. The reciprocal dissipative, adiabatic spin torque on the
magnetic texture follows from the Onsager principle. We investigate the effects
of thermal fluctuations and find that electronic dynamics contribute to a
nonlocal Gilbert damping tensor in the Landau-Lifshitz-Gilbert equation for the
magnetization. Several simple examples, including magnetic vortices, helices,
and spirals, are analyzed in detail to demonstrate general principles.",0905.4544v2
2009/6/18,Zig-zag ladders with staggered magnetic chirality in S = 3/2 compound beta-CaCr2O4,"The crystal and magnetic structures of the S = 3/2 chain antiferromagnet
beta-CaCr2O4 have been investigated by means of specific heat, magnetization,
muon relaxation and neutron powder diffraction between 300K and 1.5K. Owing to
the original topology of the Cr3+ magnetic lattice, which can be described as a
network of triangular ladders, equivalent to chains with nearest and
next-nearest neighbors interactions, evolution of the magnetic scattering
intensity in this compound evidences two magnetic regimes : for 21K < T < 270K,
a low-dimensionality magnetic ordering of the Cr3+ spins is observed,
simultaneously with a strong contraction of the ladder legs, parallel to c.
Below TN = 21K, a complex antiferromagnetic ordering is evidenced, with an
incommensurate propagation vector k = (0, 0, q) (q ~ 0.477 at 1.5K), as
exchange interactions between ladders become significant. This complex magnetic
ordering can be described as a honeycomb-like arrangement of cycloids, running
along c, with staggered chiralities. The experimental observation of this
staggered chirality can be understood by taking into account antisymmetric
Dzyaloshinskii-Moriya exchange terms.",0906.3378v1
2009/6/24,Detection of sub-lattice magnetism in sigma-phase Fe-V compounds by zero-field NMR,"The first successful measurements of a sub-lattice magnetism with 51V NMR
techniques in the sigma-phase Fe(100-x)Vx alloys with x = 34.4, 39.9 and 47.9
are reported. Vanadium atoms present on all five crystallographic sites are
magnetic. Their magnetic properties are characteristic of a given site, which
strongly depend on the composition. The strongest magnetism exhibit sites A and
the weakest one sites D. The estimated average magnetic moment per V atom
decreases from 0.36 muB for x = 34.4 to 0.20 muB for x = 47.9. The magnetism
revealed at V atoms is linearly correlated with the magnetic moment of Fe
atoms, which implies that the former is induced by the latter.",0906.4458v2
2009/9/1,Magnetism in Re-based ferrimagnetic double perovskites,"We have investigated spin and orbital magnetic moments of the Re 5d ion in
the double perovskites A2FeReO6 (A = Ba, Sr, Ca) by X-ray magnetic circular
dichroism (XMCD) at the Re L(2,3) edges. In these ferrimagnetic compounds an
unusually large negative spin and positive orbital magnetic moment at the Re
atoms was detected. The presence of a finite spin magnetic moment in a
'non-magnetic' double perovskite as observed in the double perovskite Sr2ScReO6
proves that Re has also a small, but finite intrinsic magnetic moment. We
further show for the examples of Ba and Ca that the usually neglected alkaline
earth ions undoubtedly also contribute to the magnetism in the ferrimagnetic
double perovskites.",0909.0209v1
2009/9/16,Chalcogen-height dependent magnetic interactions and magnetic order switching in FeSe$_x$Te$_{1-x}$,"Magnetic properties of iron chalcogenide superconducting materials are
investigated using density functional calculations. We find the stability of
magnetic phases is very sensitive to the height of chalcogen species from the
Fe plane: while FeTe with optimized Te height has the double-stripe-type
$(\pi,0)$ magnetic ordering, the single-stripe-type $(\pi,\pi)$ ordering
becomes the ground state phase when Te height is lowered below a critical value
by, e.g., Se doping. This behavior is understood by opposite Te-height
dependences of the superexchange interaction and a longer-range magnetic
interaction mediated by itinerant electrons. We also demonstrate a linear
temperature dependence of the macroscopic magnetic susceptibility in the
single-stripe phase in contrast to a constant behavior in the double-stripe
phase. Our findings provide a comprehensive and unified view to understand the
magnetism in FeSe$_x$Te$_{1-x}$ and iron pnictide superconductors.",0909.2916v1
2009/12/11,"Magnetic and electrical transport anomalies in RMAs2 (R= Pr and Sm, M= Ag and Au)","The results of magnetization, heat-capacity, and electrical resistivity (rho)
studies of the compounds, RMAs2 (R= Pr and Sm; M= Ag, Au), crystallizing in
HfCuSi2-derived structure are reported. PrAgAs2 orders antiferromagnetically at
T_N= 5 K. The Au analogue, however, does not exhibit long range magnetic order
down to 1.8 K. We infer that this is due to subtle differences in their
crystallographic features, particularly noting that both the Sm compounds with
identical crystal structure as that of former order magnetically nearly at the
same temperature (about 17 K). It appears that, in PrAgAs2, SmAgAs2, and
SmAuAs2, there is an additional magnetic transition at a lower temperature, as
though the similarity in the crystal structure results in similarities in
magnetism as well. The rho for PrAgAs2 and PrAuAs2 exhibits negative
temperature coefficient in some temperature range in the paramagnetic state.
SmAuAs2 exhibits magnetic Brillouin-zone gap effect in rho at T_N, while
SmAgAs2 shows a well-defined broad minimum well above T_N around 45 K. Thus,
these compounds reveal interesting magnetic and transport properties.",0912.2277v1
2009/12/17,How Gold nanoparticle acquires magnetism? - Formation of large orbital moment at the interface,"In this paper, we have tried to find out the origin of magnetism in Gold
nanoparticles (Au- NPs). We observe that upon incorporating Gold nanoparticles
(Au-NPs) in Fe3O4 nanoparticle medium the net magnetisation increases compared
to the pure Fe3O4 nanoparticle medium. This increase of magnetization can be
attributed to the large orbital magnetic moment formation at the Au/magnetic
particle interface indicating that magnetism observed in Au-NPs is an
interfacial effect. This interfacial effect has been supported by the
observation of sudden transition from positive saturated magnetisation to a
negative diamagnetic contribution as a function of magnetic field on citrate
coated gold Au-NPs.",0912.3319v2
2010/6/29,Helical magnetic state in the distorted triangular lattice of alpha-CaCr2O4,"The magnetic properties of the high temperature alpha form of the CaCr2O4
compound have been investigated for the first time by magnetic susceptibility,
specific heat and powder neutron diffraction. The system undergoes a unique
magnetic phase transition at 43K to a long range order incommensurate helical
phase with magnetic propagation vector k=(0,0.3317(2),0). The magnetic model
proposed from neutron diffraction data shows that the plane of rotation of the
spins is perpendicular to the wave-vector, and that the magnetic modulation is
consistent with two modes belonging to distinct irreducible representations of
the group. The magnetic point group 2221' is not compatible with
ferroelectricity unlike the CuCrO2 delafossite [Kimura et al., Phys. Rev. B, 78
140401 (2008)] but predicts the existence of quadratic magnetoelectric effects,
discussed based on a Landau analysis.",1006.5678v1
2010/11/30,Neutron diffraction studies and the magnetism of an ordered perovskite: Ba2CoTeO6,"The complex perovskite Ba2CoTeO6 (BCTO) has been synthesised, and the crystal
structure and magnetic properties have been investigated using a combination of
X-ray and neutron powder diffraction, electron microscopy and dielectric,
calorimetric and magnetic measurements. It was shown that at room temperature
this compound adopts the 6L-trigonal perovskite structure, space group P-3m (N
164) (a= 5.7996(1){\AA}, c=14.2658(3){\AA}). The structure comprises dimers of
face-sharing octahedra as well as octahedra which share only vertices with
their neighbours. A long-range antiferromagnetically ordered state has been
identified from neutron diffraction and magnetic studies. The magnetic
diffraction peaks were registered below the magnetic transition at about 15 K
and a possible model for the magnetic structure is proposed. The structural and
magnetic features of this compound are discussed and compared with those of
other Co-based quaternary oxides adopting the perovskite structure.",1011.6637v1
2011/1/11,Enhanced electrical resistance at the field-induced magnetic transitions in some stoichiometric and nonstoichiometric Tb-based ternary germanides,"We present the magnetic and transport behavior of some Tb compounds, viz.,
TbIrGe2, TbFe(0.4)Ge2, and TbCo(0.4)Ge2. The stoichoometric germanide TbIrGe2
exhibits at least two distinct magnetic transitions in a close temperature
interval around 10 K. The non-stoichiometric compounds, TbFe(0.4)Ge2 and
TbCo(0.4)Ge2, undergo magnetic ordering around 17 and 19 K respectively. The
magnetic state of these compouds appears to be antiferromagnetic-like.
Qualitatively, there is a correlation between the field response of the
magnetization (M), the magnetoresistance (MR) and the entropy change curve in
all these compouds. That is, these Tb compounds exhibit a ""positive"" MR and
entropy change beyond a magnetic field where M also shows a field-induced
transition. On the basis of this correlaion, we conclude that magnetic
disorder/fluctuations beyond a critical field - ""a phenomenon called inverse
metamagnetism"" - rather than metamagnetism,is induced in these compounds.",1101.2013v2
2011/2/1,One-dimentional magnonic crystal as a medium with magnetically tunable disorder on a periodical lattice,"We show that periodic magnetic nanostructures (magnonic crystals) represent
an ideal system for studying excitations on disordered periodical lattices
because of the possibility of controlled variation of the degree of disorder by
varying the applied magnetic field. Ferromagnetic resonance (FMR) data
collected inside minor hysteresis loops for a periodic array of Permalloy
nanowires of alternating width and magnetic force microscopy images of the
array taken after running each of these loops were used to establish convincing
evidence that there is a strong correlation between the type of FMR response
and the degree of disorder of the magnetic ground state. We found two types of
dynamic responses: anti-ferromagnetic (AFM) and ferromagnetic (FM), which
represent collective spin wave modes or collective magnonic states. Depending
on the history of sample magnetization either AFM or FM state is either the
fundamental FMR mode or represents a state of a magnetic defect on the
artificial crystal. A fundamental state can be transformed into a defect one
and vice versa by controlled magnetization of the sample.",1102.0069v1
2011/2/14,Chiral skyrmions in thin magnetic films: new objects for magnetic storage technologies?,"Axisymmetric magnetic lines of nanometer sizes (chiral vortices or skyrmions)
have been predicted to exist in a large group of noncentrosymmetric crystals
more than two decades ago. Recently these magnetic textures have been directly
observed in nanolayers of cubic helimagnets and monolayers of magnetic metals.
We develop a micromagnetic theory of chiral skyrmions in thin magnetic layers
for magnetic materials with intrinsic and induced chirality. Such particle-like
and stable micromagnetic objects can exist in broad ranges of applied magnetic
fields including zero field. Chiral skyrmions can be used as a new type of
highly mobile nanoscale data carriers.",1102.2726v1
2011/3/1,Magnetic behavior of curium dioxide with non-magnetic ground state,"In order to understand magnetic behavior observed in CmO$_2$ with
non-magnetic ground state, we numerically evaluate magnetic susceptibility on
the basis of a seven-orbital Anderson model with spin-orbit coupling. Naively
we do not expect magnetic behavior in CmO$_2$, since Cm is considered to be
tetravalent ion with six $5f$ electrons and the ground state is characterized
by $J$=0, where $J$ is total angular momentum. However, there exists magnetic
excited state and the excitation energy is smaller than the value of the
Land\'e interval rule due to the effect of crystalline electric field
potential. Then, we open a way to explain magnetic behavior in CmO$_2$.",1103.0076v1
2011/5/26,Theory of Orbital Magnetization in Solids,"In this review article, we survey the relatively new theory of orbital
magnetization in solids-often referred to as the ""modern theory of orbital
magnetization""-and its applications. Surprisingly, while the calculation of the
orbital magnetization in finite systems such as atoms and molecules is straight
forward, in extended systems or solids it has long eluded calculations owing to
the fact that the position operator is ill-defined in such a context.
Approaches that overcome this problem were first developed in 2005 and in the
first part of this review we present the main ideas reaching from a Wannier
function approach to semi-classical and finite-temperature formalisms. In the
second part, we describe practical aspects of calculating the orbital
magnetization, such as taking k-space derivatives, a formalism for
pseudopotentials, a single k-point derivation, a Wannier interpolation scheme,
and DFT specific aspects. We then show results of recent calculations on Fe,
Co, and Ni. In the last part of this review, we focus on direct applications of
the orbital magnetization. In particular, we will review how properties such as
the nuclear magnetic resonance shielding tensor and the electron paramagnetic
resonance g-tensor can elegantly be calculated in terms of a derivative of the
orbital magnetization.",1105.5251v1
2011/7/1,"Magnetic model for A2CuP2O7 (A = Na, Li) revisited: 1D versus 2D behavior","We report magnetization measurements, full-potential band structure
calculations, and microscopic modeling for the spin-1/2 Heisenberg magnets
A2CuP2O7 (A = Na, Li). Based on a quantitative evaluation of the leading
exchange integrals and the subsequent quantum Monte-Carlo simulations, we
propose a quasi-one-dimensional magnetic model for both compounds, in contrast
to earlier studies that conjectured on the two-dimensional scenario. The
one-dimensional nature of A2CuP2O7 is unambiguously verified by magnetization
isotherms measured in fields up to 50 T. The saturation fields of about 40 T
for both Li and Na compounds are in excellent agreement with the intrachain
exchange J1 ~ 27 K extracted from the magnetic susceptibility data. The
proposed magnetic structure entails spin chains with the dominating
antiferromagnetic nearest-neighbor interaction J1 and two inequivalent,
nonfrustrated antiferromagnetic interchain couplings of about 0.01*J1 each. A
possible long-range magnetic ordering is discussed in comparison with the
available experimental information.",1107.0250v3
2011/7/13,"Technique for high axial shielding factor performance of large-scale, thin, open-ended, cylindrical Metglas magnetic shields","Metglas 2705M is a low-cost commercially-available, high-permeability
Cobalt-based magnetic alloy, provided as a 5.08-cm wide and 20.3-$\mu$m thick
ribbon foil. We present an optimized construction technique for single-shell,
large-scale (human-size), thin, open-ended cylindrical Metglas magnetic
shields. The measured DC axial and transverse magnetic shielding factors of our
0.61-m diameter and 1.83-m long shields in the Earth's magnetic field were 267
and 1500, for material thicknesses of only 122 $\mu$m (i.e., 6 foil layers).
The axial shielding performance of our single-shell Metglas magnetic shields,
obtained without the use of magnetic shaking techniques, is comparable to the
performance of significantly thicker, multiple-shell, open-ended Metglas
magnetic shields in comparable-magnitude, low-frequency applied external fields
reported previously in the literature.",1107.2625v1
2011/9/14,"The Effect of dopants on magnetic properties of the ordered Fe_{65-x}Al_{35-y}M_{x,y} (M=Ga,B,V; x,y=5,10) alloys","The results of X-ray diffraction, complex in-field (up to 9 T) and
temperature (5-300 K) Moessbauer and magnetometric studies of the ordered
Fe_{65}Al_{35-x}M_x (M=Ga, B; x=0,5,10) and Fe_{65-x}V_xAl_{35} (x=5,10) alloys
are presented. Analysis of the magnetometry studies shows that the systems
Fe_{65}Al_{35} and Fe_{65}Al_{35-x}Ga_x (x=5, 10) are characterized by two
different magnetic states with essentially distinguishing hysteresis loops and
AC susceptibility values. The temperature and external magnetic field values
inducing the transition from one magnetic state to another are higher in the
Ga-doped alloys than in the reference Fe_{65}Al_{35} alloy. The boron addition
transforms the magnetic state of the initial alloy Fe_{65}Al_{35} into a
ferromagnetic one exhibiting high magnetic characteristics. Substitution of V
for Fe in the ternary alloys Fe_{65-x}V_xAl_{35} results in reduction of
magnetic characteristics and collapsing of 57Fe hyperfine magnetic filed.",1109.3064v1
2011/10/4,Trans-Alfvenic Motions in the Taurus Molecular Cloud,"Magnetically aligned velocity anisotropy over varying physical conditions and
environments within the Taurus Molecular Cloud is evaluated from analysis of
wide field spectroscopic imaging of 12CO and 13CO J=1-0 emission. Such
anisotropy is a result of MHD turbulence in the strong magnetic field regime
and provides an indirect measure of the role of magnetic fields upon the gas.
Velocity anisotropy aligned with the local, projected mean magnetic field
direction is limited to fields with low surface brightness 12CO emission
corresponding to regions of low visual extinction and presumably, low gas
volume density. The more optically thin 13CO J=1-0 emission shows little
evidence for velocity anisotropy. We compare our results with computational
simulations with varying degrees of magnetic field strength and Alfvenic Mach
numbers. In the diffuse, molecular envelope of the cloud, a strong magnetic
field and sub-Alfvenic turbulent motions are inferred. Super-Alfvenic motions
are present within the high column density filaments of the Taurus cloud. From
this trans-Alfvenic flow, we constrain the scaling exponent, kappa, of the
magnetic field density relation (B ~ n^kappa) to be near zero as expected for
ambipolar diffusion or material loading of magnetic flux tubes.",1110.0808v1
2011/10/5,Molecule Induced Strong Exchange Coupling between Ferromagnetic Electrodes of a Magnetic Tunnel Junction,"Multilayer edge molecular spintronics device (MEMSD) approach can produce
novel logic and memory units for the computers. MEMSD are produced by bridging
the molecular channels across the insulator, in the exposed edge region(s) of a
magnetic tunnel junction (MTJ). The bridged molecular channels start serving as
the dominant exchange coupling medium between the two ferromagnetic electrodes
of a MTJ. Present study focus on the effect of molecule enhanced exchange
coupling on the magnetic properties of the MTJ. This paper shows that
organometallic molecular clusters (OMCs) strongly increased the magnetic
coupling between the two ferromagnetic electrodes. SQUID magnetometer showed
that OMCs transformed the typical hysteresis magnetization curve of a
Co/NiFe/AlOx/NiFe MTJ into linear one. Ferromagnetic resonance studies showed
that OMC bridges affected the two fundamental resonance peaks of the
Co/NiFe/AlOx/NiFe MTJ. According to magnetic force microscopy, OMCs caused the
disappearance of magnetic contrast from the Co/NiFe/AlOx/NiFe tunnel junction
area. These three independent and complimentary experiments, suggested the
development of extremely strong interlayer exchange coupling. This work
delineated a practical route to control the exchange coupling between
ferromagnetic electrodes. Ability to tailor magnetic coupling can lead to the
development of molecule based quantum computation device architecture.",1110.0885v1
2011/10/5,Self-organizing magnetic beads for biomedical applications,"In the field of biomedicine magnetic beads are used for drug delivery and to
treat hyperthermia. Here we propose to use self-organized bead structures to
isolate circulating tumor cells using lab-on-chip technologies. Typically blood
flows past microposts functionalized with antibodies for circulating tumor
cells. Creating these microposts with interacting magnetic beads makes it
possible to tune the geometry in size, position and shape. We developed a
simulation tool that combines micromagnetics and discrete particle dynamics, in
order to design micropost arrays made of interacting beads. The simulation
takes into account the viscous drag of the blood flow, magnetostatic
interactions between the magnetic beads and gradient forces from external
aligned magnets. We developed a particle-particle particle-mesh method for
effective computation of the magnetic force and torque acting on the particles.",1110.0983v1
2011/10/27,Magnetically Controlling the Explosion of Dirac Fermions during the Oxidation of Graphene,"The different physical properties of multilayered graphene or graphite
relative to single layer graphene result from the Dirac spins symmetry in
graphene and the Pauli spin symmetry in graphite. The Dirac symmetry in
multilayers of graphene (graphite) is hindered by interlayer interactions.
Different magnetizations, electronics and chemistry of graphite and graphene
follow from absence of interlayer interactions in graphene. The distinct
kinetics and dynamics of graphite and graphene by oxidation by the Hummer's
method in weak external magnetic field are observed in this work. Graphite
manifest enhanced non-explosive oxidation of Pauli spins in weak magnetic field
with background paramagnetic oxygen slowing the magnetic acceleration. Graphene
and graphite oxide manifest explosive oxidation and magnetically decelerated
explosive oxidation of Dirac spins in weak magnetic field for temperatures
below 20 oCelsius. The explosive oxidation of graphene and its deceleration in
weak external magnetic field are interpreted resulting from the giant
nonlocality and spin Hall Effect in the chemically reacting graphene. This is
the first identification, analysis and interpretation of the chemistry of the
Dirac spins and the magnetochemistry of relativistic electrons.",1110.6060v1
2012/5/9,Magnetically ordered state at correlated oxide interfaces: the role of random oxygen defects,"Using an effective one-band Hubbard model with disorder, we consider magnetic
states of the correlated oxide interfaces, where effective hole self-doping and
a magnetially ordered state emerge due to electronic and ionic reconstructions.
By employing the coherent potential approximation, we analyze the effect of
random oxygen vacancies on the two-dimensional magnetism. We find that the
random vacancies enhance the ferromagnetically ordered state and stabilize a
robust magnetization above a critical vacancy concentration of about c=0.1. In
the strong-correlated regime, we also obtain a nonmonotonic increase of the
magnetization upon an increase of vacancy concentration and a substantial
increase of the magnetic moments, which can be realized at oxygen reduced
high-Tc cuprate interfaces.",1205.1981v1
2012/5/30,The Submm and mm Excess of the SMC: Magnetic Dipole Emission from Magnetic Nanoparticles?,"The Small Magellanic Cloud (SMC) has surprisingly strong submm and
mm-wavelength emission that is inconsistent with standard dust models,
including those with emission from spinning dust. Here we show that the
emission from the SMC may be understood if the interstellar dust mixture
includes magnetic nanoparticles, emitting magnetic dipole radiation resulting
from thermal fluctuations in the magnetization. The magnetic grains can be
metallic iron, magnetite Fe3O4, or maghemite gamma-Fe2O3. The required mass of
iron is consistent with elemental abundance constraints. The magnetic dipole
emission is predicted to be polarized orthogonally to the normal electric
dipole radiation if the nanoparticles are inclusions in larger grains. We
speculate that other low-metallicity galaxies may also have a large fraction of
the interstellar Fe in magnetic materials.",1205.6810v1
2012/6/25,Modification of structural and magnetic properties of Zn0.96 Mn0.04O samples by Li3+ ion irradiation,"Zn0.96Mn0.04O samples were synthesized by solid state reaction technique to
explore their magnetic behavior. Structural, morphological and magnetic
properties of the samples have been found to be modified by 50 MeV Li+3 ion
beam irradiation. The samples exhibit impurity phase and upon irradiation it
disappears. Rietveld refinement analysis indicates that substitutional
incorporation of Mn in the host lattice increases with irradiation. Grain size
decreases with irradiation. Field dependent magnetization (M-H) measurement
explicitly indicates ferromagnetic (FM) nature. It has been established from
temperature dependent magnetization (M-T) measurement (500 Oe) and ac
susceptibility (\chi-T) measurement that ferromagnetism in the system seems to
be mainly intrinsic; though superparamagnetic Mn nanoparticles also has a minor
role. The analysis of M-T data at comparatively high field (5000-Oe) provides
an estimation of antiferromagnetic (AFM) exchange, which acts as a reducing
agent for observed magnetic moment. The value of saturation magnetization has
been increased upon irradiation and is highly correlated with dissolution of
impurity phase. Actually structural property has been modified with ion
irradiation and this modification may cause some definite positive change in
magnetic property.",1206.5619v1
2012/7/30,"Magnetic frustration, phase competition and the magneto-electric effect in NdFe3(BO3)4","We present an element selective resonant magnetic x-ray scattering study of
NdFe3(BO3)4 as a function of temperature and applied magnetic field. Our
measurements show that the magnetic order of the Nd sublattice is induced by
the Fe spin order. When a magnetic field is applied parallel to the hexagonal
basal plane, the helicoidal spin order is suppressed and a collinear ordering,
where the moments are forced to align in a direction perpendicular to the
applied magnetic field, is stabilized. This result excludes a non-collinear
spin order as the origin of the magnetically induced electric polarization in
this compound. Instead our data imply that magnetic frustration results in a
phase competition, which is the origin of the magneto-electric response.",1207.6913v1
2012/8/7,Mutual induction of magnetic 3d and 4f order in multiferroic hexagonal ErMnO3,"The complex interplay between the 3d and 4f moments in hexagonal ErMnO3 is
investigated by magnetization, optical second harmonic generation, and
neutron-diffraction measurements. We revise the phase diagram and provide a
microscopic model for the emergent spin structures with a special focus on the
intermediary phase transitions. Our measurements reveal that the 3d exchange
between Mn^{3+} ions dominates the magnetic symmetry at 10 K < T < T_N with
Mn^3+ order according to the Gamma_4 representation triggering 4f ordering
according to the same representation on the Er^{3+}(4b) site. Below 10 K the
magnetic order is governed by 4f exchange interactions of Er^{3+} ions on the
2a site. The magnetic Er^{3+}(2a) order according to the representation Gamma_2
induces a magnetic reorientation (Gamma_4 --> Gamma_2) at the Er^{3+}(4b) and
the Mn^{3+} sites. Our findings highlight the fundamentally different roles the
Mn^{3+}, R^{3+}(2a), and R^{3+}(4b) magnetism play in establishing the magnetic
phase diagram of the hexagonal RMnO3 system.",1208.1316v1
2012/8/17,Non-volatile voltage control of magnetization and magnetic domain walls in magnetostrictive epitaxial thin films,"We demonstrate reproducible voltage induced non-volatile switching of the
magnetization in an epitaxial thin Fe81Ga19 film. Switching is induced at room
temperature and without the aid of an external magnetic field. This is achieved
by the modification of the magnetic anisotropy by mechanical strain induced by
a piezoelectric transducer attached to the layer. Epitaxial Fe81Ga19 is shown
to possess the favourable combination of cubic magnetic anisotropy and large
magnetostriction necessary to achieve this functionality with experimentally
accessible levels of strain. The switching of the magnetization proceeds by the
motion of magnetic domain walls, also controlled by the voltage induced strain.",1208.3567v1
2012/8/19,A Deformable Model for Magnetic Vortex Pinning,"A two-parameter analytical model of the magnetic vortex in a thin disk of
soft magnetic material is constructed. The model is capable of describing the
change in evolution of net vortex state magnetization and of core position when
the vortex core interacts with a magnetic pinning site. The model employs a
piecewise, physically continuous, magnetization distribution obtained by the
merger of two extensively used one-parameter analytical models of the vortex
state in a disk. Through comparison to numerical simulations of ideal disks
with and without pinning sites, the model is found to accurately predict the
magnetization, vortex position, hysteretic transitions, and 2-D displacement of
the vortex in the presence of pinning sites. The model will be applicable to
the quantitative determination of vortex pinning energies from measurements of
magnetization.",1208.3797v2
2012/8/28,Magnetic field sensor with voltage-tunable sensing properties,"We report on a magnetic field sensor based on CoFeB/MgO/CoFeB magnetic tunnel
junctions. By taking advantage of the perpendicular magnetic anisotropy of the
CoFeB/MgO interface, the magnetization of the sensing layer is tilted
out-of-plane which results in a linear response to in-plane magnetic fields.
The application of a bias voltage across the MgO tunnel barrier of the field
sensor affects the magnetic anisotropy and thereby its sensing properties. An
increase of the maximum sensitivity and simultaneous decrease of the magnetic
field operating range by a factor of two is measured. Based on these results,
we propose a voltage-tunable sensor design that allows for active control of
the sensitivity and the operating filed range with the strength and polarity of
the applied bias voltage.",1208.5588v1
2012/12/6,A Superparamagnetic State Induced by a Spin Reorientation Transition in Ultrathin Magnetic Films,"We investigate a spin reorientation transition (SRT) in ultrathin magnetic
films by Monte-Carlo simulations. We assume that the lateral size of the film
is relatively small and it has a single-domain structure. To gain insights into
the SRT, we measure a free-energy as a function of perpendicular and in-plane
magnetizations. As a result, we find that the system is in a superparamagnetic
state at the SRT temperature. The disappearance of magnetization around the SRT
temperature, which is observed in experiments, emerges due to dynamical
fluctuations in magnetization which are inherent in the superparamagnetic
state. This observation is in contrast to that in large ultrathin magnetic
films that the disappearance of magnetization is caused by a static magnetic
structure with many complex domains.",1212.1228v2
2012/12/8,Square-lattice magnetism of diaboleite Pb2Cu(OH)4Cl2,"We report on the quasi-two-dimensional magnetism of the natural mineral
diaboleite Pb2Cu(OH)4Cl2 with a tetragonal crystal structure, which is closely
related to that of the frustrated spin-1/2 magnet PbVO3. Magnetic
susceptibility of diaboleite is well described by a Heisenberg spin model on a
diluted square lattice with the nearest-neighbor exchange of J~35 K and about
5% of non-magnetic impurities. The dilution of the spin lattice reflects the
formation of Cu vacancies that are tolerated by the crystal structure of
diaboleite. The weak coupling between the magnetic planes triggers the
long-range antiferromagnetic order below TN~11 K. No evidence of magnetic
frustration is found. We also analyze the signatures of the long-range order in
heat-capacity data, and discuss the capability of identifying magnetic
transitions with heat-capacity measurements.",1212.1837v2
2012/12/31,Magnetization-based assessment of correlation energy in canted Single-Chain Magnets,"We demonstrate numerically that for the strongly anisotropic homometallic S=2
canted single-chain magnet described by the quantum antiferromagnetic
Heisenberg model the correlation energy and exchange coupling constant can be
directly estimated from the in-field-magnetization profile found along the
properly selected crystallographic direction. In the parameter space defined by
the spherical angles (\phi, \theta) determining the axes orientation, four
regions are identified with different sequences of the characteristic
field-dependent magnetization profiles representing the antiferromagnetic,
metamagnetic and weak ferromagnetic type behavior. These sequences provide a
criterion for the applicability of the anisotropic quantum Heisenberg model to
a given experimental system. Our analysis shows that the correlation energy
decreases linearly with field and vanishes for a given value H_{cr} which
defines a special coordinates in the metamagnetic profile relevant for the
zero-field correlation energy and magnetic coupling. For the single-chain
magnet formed by the strongly anisotropic manganese(III) acetate
meso-tetraphenylporphyrin complexes coupled to the phenylphosphinate ligands,
the experimental metamagnetic-type magnetization curve in the c direction
yields an accurate estimate of the values of correlation energy
\Delta_{\xi}/k_B = 7.93 K and exchange coupling J/k_B=1.20 K.",1212.6914v1
2013/1/10,Magnetic impurities on the surface of topological superconductor,"We consider the effects of magnetic impurities on the surface of
superconducting Cu doped $Bi_{2}Se_{3}$ in the odd parity pairing phase which
support topologically protected Majorana fermions surface states with linear
spectrum. We show that a single magnetic impurity on the surface may induce a
pair of in-gap localized bound states. The energy of the in-gap state is
extremely sensitive to the orientation of the magnetic impurity due to the
so-called Ising properties of Majorana fermions. The magnetic impurity induced
spin-texture, which can be measured using spin sensitive STM, is calculated. We
also show that the RKKY interactions between magnetic impurities mediated via
the Majorana fermions are always ferromagnetic and dense enough magnetic
impurities will develop long-range magnetic order and break the time-reversal
symmetry on the material surface eventually.",1301.2068v1
2013/5/26,Giant magnetic anisotropy of transition-metal dimers on defected graphene,"Continuous miniaturization of magnetic units in spintronics and quantum
computing devices inspires efforts to search for magnetic nanostructures with
large magnetic anisotropy energy (MAE). Typical nanostructures including
molecular magnets, magnetic nanoclusters and magnetic nanowires have MAEs of a
few meV so their blocking temperature is mostly lower than 50 K. In this work,
we demonstrated the feasibility of achieving giant MAE in systems with
transition metal dimers on defected and decorated graphene, based on density
functional theory calculations. In particular, either a Pt-Ir dimer on a single
vacancy or an Os-Ru dimer on a nitrogen-decorated divacancy possesses an MAE
larger than 60 meV and high structural stability. Interestingly, their magnetic
anisotropy can be conveniently manipulated by using external electric field.
These features make them good candidates for the use in room temperature
spintronics and quantum computing devices.",1305.5978v4
2013/7/11,Magnetism of sodium superoxide,"By combining first-principles electronic-structure calculations with the
model Hamiltonian approach, we systematically study the magnetic properties of
sodium superoxide (NaO2), originating from interacting superoxide molecules. We
show that NaO2 exhibits a rich variety of magnetic properties, which are
controlled by relative alignment of the superoxide molecules as well as the
state of partially filled antibonding molecular \pi_g-orbitals. The orbital
degeneracy and disorder in the high-temperature pyrite phase gives rise to weak
isotropic antiferromagnetic (AFM) interactions between the molecules. The
transition to the low-temperature marcasite phase lifts the degeneracy, leading
to the orbital order and formation of the quasi-one-dimensional AFM spin
chains. Both tendencies are consistent with the behavior of experimental
magnetic susceptibility data. Furthermore, we evaluate the magnetic transition
temperature and type of the long-range magnetic order in the marcasite phase.
We argue that this magnetic order depends on the behavior of weak isotropic as
well as anisotropic and Dzyaloshinskii-Moriya exchange interactions between the
molecules. Finally, we predict the existence of a multiferroic phase, where the
inversion symmetry is broken by the long-range magnetic order, giving rise to
substantial ferroelectric polarization.",1307.3028v1
2013/7/14,In-plane and out of plane magnetic properties in Ni46Co4Mn38Sb12 Heusler alloys ribbons,"Magnetic, magnetocaloric and exchange bias properties have been
systematically investigated in Ni46Co4Mn38Sb12 ribbon by applying magnetic
field along (IP) and perpendicular (OP) to the ribbon plane. From the
thermo-magnetization curves, the sharpness of the martensitic transition is
observed to be nearly the same for both IP and OP ribbons. The thermomagnetic
irreversibility region is found to be larger in the OP ribbon at 500 Oe,
indicating that the magnetic anisotropy is larger in this case. The OP ribbon
shows the Hopkinson maximum at 500 Oe, both for the FCC and ZFC modes. The
magnetization curve for IP ribbon shows a faster approach to saturation,
compared to the OP ribbon. Isothermal magnetic entropy change at 50 kOe has
been found to be nearly same for both the ribbons. At 5 K the coercivity and
exchange bias values are larger for the OP ribbon. Crystallographic texturing
of the ribbons and its effect in the easy magnetization direction are found to
be the reason behind the differences between the two ribbons.",1307.3778v1
2013/8/15,Shape-induced anisotropy in antiferromagnetic nanoparticles,"High fraction of the surface atoms considerably enhances the influence of
size and shape on the magnetic and electronic properties of nanoparticles.
Shape effects in ferromagnetic nanoparticles are well understood and allow to
set and control the parameters of a sample that affect its magnetic anisotropy
during production. In the present paper we study the shape effects in the other
widely used magnetic materials -- antiferromagnets, -- which possess
vanishingly small or zero macroscopic magnetization. We take into account the
difference between the surface and bulk magnetic anisotropy of a nanoparticle
and show that the effective magnetic anisotropy depends on the particle shape
and crystallographic orientation of its faces. Corresponding shape-induced
contribution to the magnetic anisotropy energy is proportional to the particle
volume, depends on magnetostriction, and can cause formation of equilibrium
domain structure. Crystallographic orientation of the nanoparticle surface
determines the type of domain structure. The proposed model allows to predict
the magnetic properties of antiferromagnetic nanoparticles depending on their
shape and treatment.",1308.3327v1
2013/10/18,"Tunneling, Remanence, and Frustration in Dysprosium based Endohedral Single Molecule Magnets","A single molecule magnet (SMM) can maintain its magnetization direction over
a long period of time [1,2]. It consists in a low number of atoms that
facilitates the understanding and control of the ground state, which is
essential in future applications such as high-density information storage or
quantum computers [3,4]. Endohedral fullerenes realize robust, nanometer sized,
and chemically protected magnetic clusters that are not found as free species
in nature. Here we demonstrate how adding one, two, or three dysprosium atoms
to the carbon cage results in three distinct magnetic ground states. The
significantly different hysteresis curves demonstrate the decisive influence of
the number of magnetic moments and their interactions. At zero field the
comparison relates tunneling of the magnetization, with remanence, and
frustration. The ground state of the tridysprosium species turns out to be one
of the simplest realizations of a frustrated, ferromagnetically coupled
magnetic system.",1310.5040v1
2014/2/10,Orbital magnetization in dilute ferromagnetic semiconductors,"The relationship between the modern and classical Landau's approach to
carrier orbital magnetization is studied theoretically within the envelope
function approximation, taking ferromagnetic (Ga,Mn)As as an example. It is
shown that while the evaluation of hole magnetization within the modern theory
does not require information on the band structure in a magnetic field, the
number of basis wave functions must be much larger than in the Landau approach
to achieve the same quantitative accuracy. A numerically efficient method is
proposed, which takes advantages of these two theoretical schemes. The computed
magnitude of orbital magnetization is in accord with experimental values
obtained by x-ray magnetic circular dichroism in (III,Mn)V compounds. The
direct effect of the magnetic field on the hole spectrum is studied too, and
employed to interpret a dependence of the Coulomb blockade maxima on the
magnetic field in a single electron transistor with a (Ga,Mn)As gate.",1402.2179v3
2014/5/8,A nonlinearity in permanent-magnet systems used in watt balances,"Watt balances are used to measure the Planck constant and will be used in the
future to realize mass at the kilogram level. They increasingly rely on
permanent magnet systems to generate the magnetic flux. It has been known that
the weighing current might effect the magnetization state of the permanent
magnetic system used in these systems causing a systematic bias that can lead
to an error in the result if not accounted for. In this article a simple model
explaining the effect of the weighing current on the yoke of the magnet is
developed. This model leads to a nonlinear dependence of the magnetic flux
density in the gap that is proportional to the squared value of the coil
current. The effect arises from changing the reluctance of the yoke by the
additional field produced by the coil. Our analysis shows that the effect
depends on the width of the air gap, the magnetic flux density in the air gap,
and the $BH$ curve of the yoke material. Suggestions to reduce the nonlinear
effect are discussed.",1405.1904v1
2014/6/8,Perpendicular magnetic anisotropy and magnetization process in CoFeB/Pd multilayer films,"Perpendicular magnetic anisotropy (PMA) and dynamic magnetization reversal
process in [CoFeB $t$ nm/Pd 1.0 nm]$_n$ ($t$ = 0.4, 0.6, 0.8, 1.0, and 1.2 nm;
$n$ = 2 - 20) multilayer films have been studied by means of magnetic
hysteresis and Kerr effect measurements. Strong and controllable PMA with an
effective uniaxial anisotropy up to 7.7$\times$ 10$^6$ J.m$^{-3}$ and a
saturation magnetization as low as 200 emu/cc are achieved. Surface/interfacial
anisotropy of CoFeB/Pd interfaces, the main contribution to the PMA, is
separated from the effective uniaxial anisotropy of the films, and appears to
increase with the number of the CoFeB/Pd bilayers. Observation of the magnetic
domains during a magnetization reversal process using polar magneto-optical
Kerr microscopy shows the detailed behavior of nucleation and displacement of
the domain walls.",1406.2028v1
2014/6/30,Near-field aperture-probe as a magnetic dipole source and optical magnetic field detector,"Scanning near-field field optical microscopy (SNOM) is a technique, which
allows sub-wavelength optical imaging of photonic structures. While the
electric field components of light can be routinely obtained, imaging of the
magnetic components has only recently become of interest. This is so due to the
development of artificial materials, which enhance and exploit the typically
weak magnetic light-matter interactions to offer extraordinary optical
properties. Consequently, both sources and detectors of the magnetic field of
light are now required.
  In this paper, assisted by finite-difference time-domain simulations, we
suggest that the circular aperture at the apex of a metal coated hollow-pyramid
SNOM probe can be approximated by a lateral magnetic dipole source. This
validates its use as a detector for the lateral magnetic near-field, as
illustrated here for a plasmonic nanobar sample. Verification for a dielectric
sample is currently in progress. We experimentally demonstrate the equivalence
of the reciprocal configurations when the probe is used as a source
(illumination mode) and as a detector (collection mode). The simplification of
the probe to a simple magnetic dipole facilitates the simulations and the
understanding of the near-field images.",1406.7827v1
2014/7/8,Extension of the Anderson impurity model for finite systems: Band gap control of magnetic moments,"We study the spin magnetic moment of a single impurity embedded in a
finite-size non-magnetic host exhibiting a band gap. The calculations were
performed using a tight-binding model Hamiltonian. The simple criterion for the
magnetic to non-magnetic transition as given in the Anderson impurity model
breaks down in these cases. We show how the spin magnetic moment of the
impurity that normally would be quenched can be restored upon introducing a gap
at the Fermi level in the host density of states. The magnitude of the impurity
spin magnetic moment scales monotonically with the size of the band gap. This
observation even holds for a host material featuring a strongly discretized
density of states. Thus, it should be possible to tune the magnetic moment of
doped nano-particles by varying their size and thereby their band gap.",1407.2018v1
2014/7/20,Multiferroicity and magneto-electric effect in Gd$_2$BaNiO$_5$,"We report the observation of electric polarization in the magnetically
ordered state of the Haldane chain compound, Gd$_2$BaNiO$_5$, with strongly
correlated magnetic and dielectric properties. The results of dc magnetic
susceptibility and heat capacity measurements indicate two magnetic
transitions,one corresponding to the anti-ferromagnetic order at T$_N$ around
55 K and the other to spin-reorientation transition at T$_{SR}$ around 24 K.
The dielectric permittivity ($\epsilon'$) and loss (tan$\delta$) also exhibit
anomalies in the vicinity of T$_{SR}$ and T$_N$ respectively. Below the
spin-reorientation transition, concurrently magnetic-field-induced spin-flop
and the meta-electric transitions are observed at a critical magnetic field in
isothermal magnetization and magneto-dielectric results respectively. Another
interesting finding is that the change in dielectric constant changes its sign
at the critical magnetic field. The origin of the observed magneto-electric
effect is discussed on the basis of spin-phonon coupling.",1407.5307v1
2014/11/25,Reversible Electric-Field Driven Magnetic Domain Wall Motion,"Control of magnetic domain wall motion by electric fields has recently
attracted scientific attention because of its potential for magnetic logic and
memory devices. Here, we report on a new driving mechanism that allows for
magnetic domain wall motion in an applied electric field without the concurrent
use of a magnetic field or spin-polarized electric current. The mechanism is
based on elastic coupling between magnetic and ferroelectric domain walls in
multiferroic heterostructures. Pure electric-field driven magnetic domain wall
motion is demonstrated for epitaxial Fe films on BaTiO$_3$ with in-plane and
out-of-plane polarized domains. In this system, magnetic domain wall motion is
fully reversible and the velocity of the walls varies exponentially as a
function of out-of-plane electric field strength.",1411.6798v1
2015/3/11,Influence of elastically pinned magnetic domain walls on magnetization reversal in multiferroic heterostructures,"In elastically coupled multiferroic heterostructures that exhibit full domain
correlations between ferroelectric and ferromagnetic sub-systems, magnetic
domain walls are firmly pinned on top of ferroelectric domain boundaries. In
this work we investigate the influence of pinned magnetic domain walls on the
magnetization reversal process in a Co40Fe40B20 wedge film that is coupled to a
ferroelectric BaTiO3 substrate via interface strain transfer. We show that the
magnetic field direction can be used to select between two distinct
magnetization reversal mechanisms, namely (1) double switching events involving
alternate stripe domains at a time or (2) synchronized switching of all
domains. Furthermore, scaling of the switching fields with domain width and
film thickness is also found to depend on field orientation. These results are
explained by considering the dissimilar energies of the two types of pinned
magnetic domain walls that are formed in the system.",1503.03222v1
2015/3/24,On the magnetism of sigma-Fe54Cr46 alloy: AC and DC susceptibility studies,"Sigma-phase intermetallic compound of Fe54Cr46 was investigated using DC and
AC magnetic susceptibility techniques. A clear-cut evidence was found that the
sample orders magnetically at Tc=23.5 K and its ground magnetic state is
constituted by a spin glass. The temperature at which the zero-field cooled
magnetization has its maximum decreases with an external magnetic field in line
with the Gabay-Toulouse prediction. The temperature at which the AC magnetic
susceptibility has its maximum does not depend on frequency which, in the light
of the mean-field theory, testifies to very long magnetic interactions.",1503.06991v1
2015/5/28,Large ground state magnetic moment and magnetocaloric effect in Ni2Mn1.4In0.6,"A large conventional magnetocaloric effect at the second order magnetic
transition in cubic Ni2Mn1.4In0.6 Heusler alloy is reported. The isothermal
magnetization at 2K shows a huge ground state magnetic moment of about 6.17
{\mu}B/f.u. The theoretical calculations show that the origin of the large
magnetic moment in cubic Ni2Mn1.4In0.6 results from the strong ferromagnetic
interaction between Mn- Ni and Mn-Mn sublattices. The experimental magnetic
moment is in excellent agreement with the moment calculated from the theory.
The large magnetic moment gives rise to considerably high adiabatic temperature
and entropy changes at the magnetic transition. The present study opens up the
possibility to explore cubic Heusler alloys for magnetocaloric applications.",1505.07677v2
2015/6/29,Magnetization and magneto-transport studies on Fe$_2$VAl$_{1-x}$Si$_x$,"We report on magnetoresistance, Hall and magnetization measurements of
Fe2VAl1-xSix Heusler compounds for x= 0.005, 0.015, 0.02. There is a systematic
change in the temperature coefficient of resistance (TCR) from negative to
positive as the Si composition is increased. The Hall co-efficient shows that
the carriers are electron like and the carrier density increases with Si
concentration. Resistance measurements under magnetic field indicate a
decreasing behavior under the application of magnetic field at low temperature
region (T< 60 K), suggesting the suppression of scattering by magnetic field.
Temperature and field dependent magnetization measurements did not show any
significant change apart from the fact that the presence of super paramagnetic
(SPM) cluster and its ordering at low temperatures. Arrott plot analysis of
magnetization versus field also indicates the magnetic ordering with applied
field below 60 K.",1506.08516v1
2015/7/24,Unveiling hidden ferrimagnetism and giant magnetoelectricity in polar magnet Fe2Mo3O8,"Magnetoelectric (ME) effect is recognized for its utility for low-power
electronic devices.Largest ME coefficients are often associated with phase
transitions in which ferroelectricity is induced by magnetic order.
Unfortunately, in these systems, large ME response is revealed only upon
elaborate poling procedures. These procedures may become unnecessary in
single-polar-domain crystals of polar magnets. Here we report giant ME effects
in a polar magnet Fe2Mo3O8 at temperatures as high as 60 K.Polarization jumps
of 0.3 {\mu}C/cm2, and repeated mutual control of ferroelectric and magnetic
moments with differential ME coefficients on the order of 10$^4$ ps/m are
achieved.Importantly, no electric or magnetic poling is needed, as necessary
for applications.The sign of the ME coefficients can be switched by changing
the applied ""bias"" magnetic field. The observed effects are associated with a
hidden ferrimagnetic order unveiled by application of a magnetic field.",1507.06847v1
2015/7/26,Fragile magnetic order in the honeycomb lattice Iridate Na$_{2}$IrO$_3$ revealed by magnetic impurity doping,"We report the structure, magnetic, and thermal property measurements on
single crystalline and polycrystalline samples of Ru substituted honeycomb
lattice iridate Na$_2$Ir$_x$Ru$_{1-x}$O$_3$ (x = 0, 0.05, 0.1, 0.15, 0.2, 0.3,
0.5). The evolution of magnetism in Na$_2$Ir$_x$Ru$_{1-x}$O$_3$ has been
studied using dc and ac magnetic susceptibility, and heat capacity
measurements. The parent compound Na$_2$IrO$_3$ is a spin-orbit driven Mott
insulator with magnetic order of reduced moments below $T_N = 15$~K\@. In the
Ru substituted samples the antiferromagnetic long range state is replaced by a
spin glass like state even for the smallest substitution suggesting that the
magnetic order in Na$_2$IrO$_3$ is extremely fragile. We argue that these
behaviors indicate the importance of nearest-neighbor magnetic exchange in the
parent Na$_2$IrO$_3$. Additionally, all samples show insulating electrical
transport.",1507.07222v1
2015/7/30,"First-order ferromagnetic transition in single-crystalline (Mn,Fe)2(P,Si)","(Mn,Fe)2(P,Si) single crystals have been successfully grown by flux method.
Single crystal diffraction demonstrates that Mn0.83Fe1.17P0.72Si0.28
crystallizes in a hexagonal crystal structure (space group P-62m) at both 100
and 280 K, in the ferromagnetic and paramagnetic states, respectively. The
magnetization measurements show that the crystals display a first-order
ferromagnetic phase transition at their Curie temperature (TC). The preferred
magnetization direction in is along the c axis. A weak magnetic anisotropy of
K1 = 0.25x106 J/m3 and K2 = 0.19x106 J/m3 is found at 5 K. These values
indicate a soft magnetic behaviour favourable for magnetic refrigeration. A
series of discontinuous magnetization jumps is observed far below TC by
increasing the field at a constant temperature. These magnetization jumps are
irreversible, occur spontaneously at constant temperature and magnetic field,
but can be restored by cycling across the first-order phase transition.",1507.08655v1
2015/8/17,Engineering the magnetic anisotropy of atomic-scale nanostructure under electric field,"Atomic-scale magnetic nanostructures are promising candidates for future
information processing devices. Utilizing external electric field to manipulate
their magnetic properties is an especially thrilling project. Here, by careful
identifying different contributions of each atomic orbital to the magnetic
anisotropy energy (MAE) of the ferromagnetic metal films, we argue that it is
possible to engineer both the MAE and the magnetic response to the electric
field of atomic-scale magnetic nanostructures. Taking the iron monolayer as a
matrix, we propose several interesting iron nanostructures with dramatically
different magnetic properties. Such nanostructures could exhibit strong
magnetoelectric effect. Our work may open a new avenue to the artificial design
of electrically controlled magnetic devices.",1508.03917v1
2015/8/17,Increased magnetic damping of a single domain wall and adjacent magnetic domains detected by spin torque diode in a nanostripe,"We use spin-torque resonance to probe simultaneously and separately the
dynamics of a magnetic domain wall and of magnetic domains in a nanostripe
magnetic tunnel junction. Thanks to the large associated resistance variations
we are able to analyze quantitatively the resonant properties of these single
nanoscale magnetic objects. In particular, we find that the magnetic damping of
both domains and domain walls is doubled compared to the damping value of their
host magnetic layer. We estimate the contributions to damping arising from
dipolar couplings between the different layers in the junction and from the
intralayer spin pumping effect. We find that they cannot explain the large
damping enhancement that we observe. We conclude that the measured increased
damping is intrinsic to large amplitudes excitations of spatially localized
modes or solitons such as vibrating or propagating domain walls",1508.04043v1
2015/9/1,Magnetic-Field-Induced Polar Phase in Chiral Magnet CsCuCl$_3$,"Magnetoelectric effects in the chiral magnet CsCuCl$_3$ have been
investigated through the magnetization and electric polarization measurements
in pulsed high magnetic fields. If the magnetic field is applied normal to the
spin chiral c-axis, a plateau and a jump in magnetization are observed. Between
the plateau and the jump in magnetization, a small but significant electric
polarization of about 0.25 {\mu}C/m$^2$ along the a-axis is observed with the
field applied almost perpendicular to the ac-plane. In addition, the
paramagnetoelectric effect expected from the point group symmetry is confirmed.
The emergence of the electric polarization is explained by the cooperation of
the local electric polarization on the chiral solitonic spin arrangement and
the paramagnetoelectric effect. Hence, we interpret this novel multiferroic
phase in CsCuCl$_3$ as a polar solitonic phase.",1509.00280v1
2015/11/5,Oxygen-enabled control of Dzyaloshinskii-Moriya Interaction in ultra-thin magnetic films,"The search for chiral magnetic textures in systems lacking spatial inversion
symmetry has attracted a massive amount of interest in the recent years with
the real space observation of novel exotic magnetic phases such as skyrmions
lattices, but also domain walls and spin spirals with a defined chirality. The
electrical control of these textures offers thrilling perspectives in terms of
fast and robust ultrahigh density data manipulation. A powerful ingredient
commonly used to stabilize chiral magnetic states is the so-called
Dzyaloshinskii-Moriya interaction (DMI) arising from spin-orbit coupling in
inversion asymmetric magnets. Such a large antisymmetric exchange has been
obtained at interfaces between heavy metals and transition metal ferromagnets,
resulting in spin spirals and nanoskyrmion lattices. Here, using relativistic
first-principles calculations, we demonstrate that the magnitude and sign of
DMI can be entirely controlled by tuning the oxygen coverage of the magnetic
film, therefore enabling the smart design of chiral magnetism in ultra-thin
films. We anticipate that these results extend to other electronegative ions
and suggest the possibility of electrical tuning of exotic magnetic phases.",1511.01614v1
2016/2/17,"Magnetism, superconductivity, and spontaneous orbital order in iron-based superconductors: who comes first and why?","Magnetism and nematic order are the two non-superconducting orders observed
in iron-based superconductors. To elucidate the interplay between them and
ultimately unveil the pairing mechanism, several models have been investigated.
In models with quenched orbital degrees of freedom, magnetic fluctuations
promote stripe magnetism which induces orbital order. In models with quenched
spin degrees of freedom, charge fluctuations promote spontaneous orbital order
which induces stripe magnetism. Here we develop an unbiased approach, in which
we treat magnetic and orbital fluctuations on equal footing. Key to our
approach is the inclusion of the orbital character of the low-energy electronic
states into renormalization group analysis. Our results show that in systems
with large Fermi energies, such as BaFe2As2, LaFeAsO, and NaFeAs, orbital order
is induced by stripe magnetism. However, in systems with small Fermi energies,
such as FeSe, the system develops a spontaneous orbital order, while magnetic
order does not develop. Our results provide a unifying description of different
iron-based materials.",1602.05503v1
2016/4/19,Electric field control of deterministic current-induced magnetization switching in a hybrid ferromagnetic/ferroelectric structure,"All-electrical and programmable manipulations of ferromagnetic bits are
highly pursued for the aim of high integration and low energy consumption in
modern information technology. Methods based on the spin-orbit torque switching
in heavy metal/ferromagnet structures have been proposed with magnetic field,
and recently are heading toward deterministic switching without external
magnetic field. Here we demonstrate that an in-plane effective magnetic field
can be induced by an electric field without breaking the symmetry of the
structure of the thin film, and realize the deterministic magnetization
switching in a hybrid ferromagnetic/ferroelectric structure with Pt/Co/Ni/Co/Pt
layers on PMN-PT substrate. The effective magnetic field can be reversed by
changing the direction of the applied electric field on the PMN-PT substrate,
which fully replaces the controllability function of the external magnetic
field. The electric field is found to generate an additional spin-orbit torque
on the CoNiCo magnets, which is confirmed by macrospin calculations.",1604.05561v1
2016/5/13,Magnetic edge states and magnetotransport in graphene antidot barriers,"Magnetic fields are often used for characterizing transport in nanoscale
materials. Recent magnetotransport experiments have demonstrated that ballistic
transport is possible in graphene antidot lattices (GALs). These experiments
have inspired the present theoretical study of GALs in a perpendicular magnetic
field. We calculate magnetotransport through graphene antidot barriers (GABs),
which are finite rows of antidots arranged periodically in a pristine graphene
sheet, using a tight-binding model and the Landauer-B\""uttiker formula. We show
that GABs behave as ideal Dirac mass barriers for antidots smaller than the
magnetic length, and demonstrate the presence of magnetic edge states, which
are localized states on the periphery of the antidots due to successive
reflections on the antidot edge in the presence of a magnetic field. We show
that these states are robust against variations in lattice configuration and
antidot edge chirality. Moreover, we calculate the transmittance of disordered
GABs and find that magnetic edge states survive a moderate degree of disorder.
Due to the long phase-coherence length in graphene and the robustness of these
states, we expect magnetic edge states to be observable in experiments as well.",1605.04114v1
2016/9/16,Switching of a large anomalous Hall effect between metamagnetic phases of a non-collinear antiferromagnet,"The anomalous Hall effect (AHE), which in long-range ordered ferromagnets
appears as a voltage transverse to the current and usually is proportional to
the magnetization, often is believed to be of negligible size in
antiferromagnets due to their low uniform magnetization. However, recent
experiments and theory have demonstrated that certain antiferromagnets with a
non-collinear arrangement of magnetic moments exhibit a sizeable spontaneous
AHE at zero field due to a non-vanishing Berry curvature arising from the
quantum mechanical phase of the electron's wave functions. Here we show that
antiferromagnetic Mn5Si3 single crystals exibit a large AHE which is strongly
anisotropic and shows multiple transitions with sign changes at different
magnetic fields due to field-induced rearrangements of the magnetic structure
despite only tiny variations of the total magnetization. The presence of
multiple non-collinear magnetic phases offers the unique possiblity to explore
the details of the AHE and the sensitivity of the Hall effect on the details of
the magnetic texture.",1609.05047v1
2017/1/7,Dynamics of exciton magnetic polarons in CdMnSe/CdMgSe quantum wells: the effect of self-localization,"We study the exciton magnetic polaron (EMP) formation in (Cd,Mn)Se/(Cd,Mg)Se
diluted-magnetic-semiconductor quantum wells using time-resolved
photoluminescence (PL). The magnetic field and temperature dependencies of this
dynamics allow us to separate the non-magnetic and magnetic contributions to
the exciton localization. We deduce the EMP energy of 14 meV, which is in
agreement with time-integrated measurements based on selective excitation and
the magnetic field dependence of the PL circular polarization degree. The
polaron formation time of 500 ps is significantly longer than the corresponding
values reported earlier. We propose that this behavior is related to strong
self-localization of the EMP, accompanied with a squeezing of the heavy-hole
envelope wavefunction. This conclusion is also supported by the decrease of the
exciton lifetime from 600 ps to 200 - 400 ps with increasing magnetic field and
temperature.",1701.01824v1
2017/2/27,New Insights into the Puzzling P-Cygni Profiles of Magnetic Massive Stars,"Magnetic massive stars comprise approximately 10% of the total OB star
population. Modern spectropolarimetry shows these stars host strong, stable,
large-scale, often nearly dipolar surface magnetic fields of 1 kG or more.
These global magnetic fields trap and deflect outflowing stellar wind material,
forming an anisotropic magnetosphere that can be probed with wind-sensitive UV
resonance lines. Recent HST UV spectra of NGC 1624-2, the most magnetic O star
observed to date, show atypically unsaturated P-Cygni profiles in the Civ
resonant doublet, as well as a distinct variation with rotational phase. We
examine the effect of non-radial, magnetically-channeled wind outflow on
P-Cygni line formation, using a Sobolev Exact Integration (SEI) approach for
direct comparison with HST UV spectra of NGC 1624-2. We demonstrate that the
addition of a magnetic field desaturates the absorption trough of the P-Cygni
profiles, but further efforts are needed to fully account for the observed line
profile variation. Our study thus provides a first step toward a broader
understanding of how strong magnetic fields affect mass loss diagnostics from
UV lines.",1702.08535v1
2017/8/31,Phase separated magnetic ground state in Mn$_3$Ga$_{0.45}$Sn$_{0.55}$C,"Existence of non-ergodic ground states is considered as a precursor to a
first order long range magnetostructural transformation.
Mn$_3$Ga$_{0.45}$Sn$_{0.55}$C lies compositionally between two compounds,
Mn$_3$GaC and Mn$_3$SnC, undergoing first order magnetic transformation.
Mn$_3$Ga$_{0.45}$Sn$_{0.55}$C though crystallizes in single phase cubic
structure, exhibits more than one long range magnetic transitions. Using a
combination of magnetization, ac susceptibility, neutron diffraction and XAFS
techniques it is shown that, though Mn$_3$Ga$_{0.45}$Sn$_{0.55}$C exhibits long
range magnetic order, it presents a cluster glassy ground state due to
formation of magnetically ordered Ga rich and Sn rich clusters. The clusters
are big enough to present signatures of long range magnetic order but are
distributed in such way that it limits interactions between two clusters of the
same type leading to a frozen magnetic state at low temperatures. The main
reason for such a cluster glass state is the difference in local structure of
Mn atoms that find themselves in Ga rich and Sn rich clusters.",1708.09553v1
2017/10/20,Out-of-plane Enhanced Magnetic Anisotropy Energy in Ni$_{3}$Bz$_{3}$ molecule,"Organometallic complexes formed by transition metals clusters and benzene
molecules have already been synthesized, and in selected cases display magnetic
properties controlled by external magnetic fields. We have studied Ni$_n$Bz$_n$
complexes made of nickel atoms surrounded by benzene molecules and here we
focus specifically on the magnetic molecule Ni$_{3}$Bz$_{3}$. By means of
calculations including relativistic spin-orbit terms, we show that this
molecule reveals a large magnetic anisotropy energy of approximately 8 meV,
found with the easy axis perpendicular to the metal atoms plane. Note that the
matching bare Ni$_{3}$ cluster have similar magnetic anisotropy, however the
easy axis is in-plane. Covering with benzene molecules is thus switching the
easy axis from in-plane for Ni$_3$ to out-of-plane for Ni$_{3}$Bz$_{3}$. The
large out-of-plane magnetic anisotropy of Ni$_{3}$Bz$_{3}$ suggests that this
molecule could indeed be used as part in the design of molecular magnetic
memories.",1710.07519v2
2018/1/29,Hall effect driven by non-collinear magnetic polarons in diluted magnetic semiconductors,"In this letter we develop the theory of Hall effect driven by non-collinear
magnetic textures (topological Hall effect - THE) in diluted magnetic
semiconductors (DMS). We show that a carrier spin-orbit interaction induces a
chiral magnetic ordering inside a bound magnetic polaron (BMP). The inner
structure of non-collinear BMP is controlled by the type of spin-orbit
coupling, allowing to create skyrmion- (Rashba) or antiskyrmion-like
(Dresselhaus) configurations. The asymmetric scattering of itinerant carriers
on polarons leads to the Hall signal which exists in weak external magnetic
fields and low temperatures. We point out that DMS-based systems allow one to
investigate experimentally the dependence of THE both on a carrier spin
polarization and on a non-collinear magnetic texture shape.",1801.09459v1
2018/4/4,Emergence of topological Hall effect in half-metallic manganite thin films by tuning perpendicular magnetic anisotropy,"Magnetic materials hosting topological spin textures like magnetic skyrmion
exhibit nontrivial Hall effect, namely, topological Hall effect (THE). In this
study, we demonstrate the emergence of THE in thin films of half-metallic
perovskite manganites. To stabilize magnetic skyrmions, we control the
perpendicular magnetic anisotropy by imposing a compressive epitaxial strain as
well as by introducing a small Ru doping. When the perpendicular magnetic
anisotropy is tuned so that it is balanced with the magnetic dipolar
interaction, the film exhibits a sizable THE in a magnetization reversal
process. Real-space observations indicate the formation of skyrmions and some
of them have high topological charge number. The present result opens up the
possibility for novel functionalities that emerge under keen competition
between the skyrmion phase and other rich phases of perovskite manganites with
various orders in spin, charge, and orbital degrees of freedom.",1804.01425v2
2018/4/11,Continuous Nucleation Dynamics of Magnetic Skyrmions in T-shaped Helimagnetic Nanojunction,"Magnetic skyrmions are topologically-protected spin textures existing in
helimagentic materials, which can be utilized as information carriers for
non-volatile memories and logic circuits in spintronics. Searching simple and
controllable way to create isolated magnetic skyrmions is desirable for further
technology developments and industrial designs. Based on micromagnetic
simulations, we show that the temporal dissipative structure can be developed
in the T-shaped helimagnetic nanojunction when it is driven to the
far-from-equilibrium regime by a constant spin-polarized current. Then the
magnetic skyrmions can be continuously nucleated during the periodic
magnetization dynamics of the nanojunction. We have systematically investigated
the effects of current density, Dzyaloshinskii-Moriya interaction, external
magnetic field, and thermal fluctuation on the nucleation dynamics of the
magnetic skyrmions. Our results here suggest a novel and promising mechanism to
continuously create magnetic skyrmions for the development of skyrmion-based
spintronics devices.",1804.04022v1
2018/4/17,Magnetoelectric multipoles in metals,"We demonstrate computationally the existence of magnetoelectric multipoles,
arising from the second order term in the multipole expansion of a
magnetization density in a magnetic field, in noncentrosymmetric magnetic
metals. While magnetoelectric multipoles have long been discussed in the
context of the magnetoelectric effect in noncentrosymmetric magnetic
insulators, they have not previosuly been identified in metallic systems, in
which the mobile carriers screen any electrical polarization. Using
first-principles density functional calculations we explore three specific
systems: First, a conventional centrosymmetric magnetic metal, Fe, in which we
break inversion symmetry by introducing a surface, which both generates
magnetoelectric monopoles and allows a perpendicular magnetoelectric response.
Next, the hypothetical cation-ordered perovskite, SrCaRu$_2$O$_6$, in which we
study the interplay between the magnitude of the polar symmetry breaking and
that of the magnetic dipoles and multipoles, finding that both scale
proportionally to the structural distortion. Finally, we identify a hidden
antiferromultipolar order in the noncentrosymmetric, antiferromagnetic metal
Ca$_3$Ru$_2$O$_7$, and show that, while its competing magnetic phases have
similar magnetic dipolar structures, their magnetoelectric multipolar
structures are distinctly different, reflecting the strong differences in
transport properties.",1804.06314v1
2018/6/7,Terahertz Emission from Compensated Magnetic Heterostructures,"Terahertz emission spectroscopy (TES) has recently played an important role
in unveiling the spin dynamics at a terahertz (THz) frequency range. So far,
ferromagnetic (FM)/nonmagnetic (NM) heterostructures have been intensively
studied as THz sources. Compensated magnets such as a ferrimagnet (FIM) and
antiferromagnet (AFM) are other types of magnetic materials with interesting
spin dynamics. In this work, we study TES from compensated magnetic
heterostructures including CoGd FIM alloy or IrMn AFM layers. Systematic
measurements on composition and temperature dependences of THz emission from
CoGd/Pt bilayer structures are conducted. It is found that the emitted THz
field is determined by the net spin polarization of the laser induced spin
current rather than the net magnetization. The temperature robustness of the
FIM based THz emitter is also demonstrated. On the other hand, an AFM plays a
different role in THz emission. The IrMn/Pt bilayer shows negligible THz
signals, whereas Co/IrMn induces sizable THz outputs, indicating that IrMn is
not a good spin current generator, but a good detector. Our results not only
suggest that a compensated magnet can be utilized for robust THz emission, but
also provide a new approach to study the magnetization dynamics especially near
the magnetization compensation point.",1806.02517v1
2018/6/20,Magnetic field dependence of antiferromagnetic resonance in NiO,"We report on measurements of magnetic field and temperature dependence of
antiferromagnetic resonances in the prototypical antiferromagnet NiO. The
frequencies of the magnetic resonances in the vicinity of 1 THz have been
determined in the time-domain via time-resolved Faraday measurements after
selective excitation by narrow-band superradiant terahertz (THz) pulses at
temperatures down to 3K and in magnetic fields up to 10 T. The measurements
reveal two antiferromagnetic resonance modes, which can be distinguished by
their characteristic magnetic field dependencies. The nature of the two modes
is discussed by comparison to an eight-sublattice antiferromagnetic model,
which includes superexchange between the next-nearest-neighbor Ni spins,
magnetic dipolar interactions, cubic magneto-crystalline anisotropy, and Zeeman
interaction with the external magnetic field. Our study indicates that a
two-sublattice model is insufficient for the description of spin dynamics in
NiO, while the magnetic-dipolar interactions and magneto-crystalline anisotropy
play important roles.",1806.07968v1
2018/6/26,Ultrahigh Magnetic Fields Produced by Shearing Carbon Nanotubes,"In laboratories, ultrahigh magnetic fields are usually produced with very
large currents through superconducting, resistive or hybrid magnets, which
require extreme conditions, such as low temperature, huge cooling water or tens
of megawatts of power. In this work we report that when single walled carbon
nanotubes (SWNTs) are cut, there are magnetic moments at the shearing end of
SWNTs. The average magnetic moment is found to be 41.5+-9.8uB per carbon atom
in the end states with a width of 1 nm at temperature of 300.0K, suggesting
ultrahigh magnetic fields can be produced. The dangling sigma and pi bonds of
the carbon atoms at the shearing ends play important roles for this
unexpectedly high magnetic moments because the oxidation temperature of cut
SWNTs is found to be as low as 312 in dry air. Producing ultrahigh magnetic
field with SWNTs has the advantage of working at higher working temperature and
with low energy consumption, suggesting great potentials of applications.",1806.09891v1
2018/7/10,The dual nature of magnetism in a uranium heavy fermion system,"The duality between localized and itinerant nature of magnetism in
$5\textit{f}$ electron systems has been a longstanding puzzle. Here, we report
inelastic neutron scattering measurements, which reveal both local and
itinerant aspects of magnetism in a single crystalline system of
UPt$_{2}$Si$_{2}$. In the antiferromagnetic state, we observe broad continuum
of diffuse magnetic scattering with a resonance-like gap of $\approx$ 7 meV,
and surprising absence of coherent spin-waves, suggestive of itinerant
magnetism. While the gap closes above the Neel temperature, strong dynamic spin
correlations persist to high temperature. Nevertheless, the size and
temperature dependence of the total magnetic spectral weight can be well
described by local moment with $J=4$. Furthermore, polarized neutron
measurements reveal that the magnetic fluctuations are mostly transverse, with
little or none of the longitudinal component expected for itinerant moments.
These results suggest that a dual description of local and itinerant magnetism
is required to understand UPt$_{2}$Si$_{2}$, and by extension, other 5$f$
systems in general.",1807.03686v1
2012/10/1,"Field tuned critical fluctuations in YFe2Al10: Evidence from magnetization, 27Al (NMR, NQR) investigations","We report magnetization, specific heat, and NMR investigations on YFe2Al10
over a wide range in temperature and magnetic field and zero field (NQR)
measurements. Magnetic susceptibility, specific heat and spin-lattice
relaxation rate divided by T (1/T1T) follow a weak power law (T^-0.4)
temperature dependence, which is a signature of critical fluctuations of Fe
moments. The value of the Sommerfeld-Wilson ratio and linear relation between
1/T1T and chi(T) suggest the existence of ferromagnetic correlations in this
system. No magnetic ordering down to 50 mK in Cp(T) and the unusual temperature
and field scaling of the bulk and NMR data are associated with a magnetic
instability which drives the system to quantum criticality. The magnetic
properties of the system are tuned by field wherein ferromagnetic fluctuations
are suppressed and a crossover from quantum critical to FL behavior is observed
with increasing magnetic field.",1210.0326v1
2012/10/1,Magnetic impurities in graphane with dehydrogenated channels,"We have investigated the electronic and magnetic response of a single Fe atom
and a pair of interacting Fe atoms placed in patterned dehydrogenated channels
in graphane within the framework of density functional theory. We have
considered two channels: ""armchair"" and ""zigzag"" channels. Fully relaxed
calculations have been carried out for three different channel widths. Our
calculations reveal that the response to the magnetic impurities is very
different for these two channels. We have also shown that one can stabilize
magnetic impurities (Fe in the present case) along the channels of bare carbon
atoms, giving rise to a magnetic insulator or a spin gapless semiconductor. Our
calculations with spin-orbit coupling shows a large in-plane magnetic
anisotropy energy for the case of the armchair channel. The magnetic exchange
coupling between two Fe atoms placed in the semiconducting channel with an
armchair edge is very weakly ferromagnetic whereas a fairly strong
ferromagnetic coupling is observed for reasonable separations between Fe atoms
in the zigzag-edged metallic channel with the coupling mediated by the bare
carbon atoms. The possibility of realizing an ultrathin device with interesting
magnetic properties is discussed.",1210.0465v2
2012/10/20,Stabilizing intrinsic defects in SnO$_{2}$,"TThe magnetism and electronic structure of Li-doped SnO$_{2}$ are
investigated using first-principles LDA/LDA$+U$ calculations. We find that Li
induces magnetism in SnO$_{2}$ when doped at the Sn site but becomes
non-magnetic when doped at the O and interstitial sites. The calculated
formation energies show that Li prefers the Sn site as compared with the O
site, in agreement with previous experimental works. The interaction of Li with
native defects (Sn V$_\mathrm{Sn}$ and O V$_\mathrm{O}$ vacancies) is also
studied, and we find that Li not only behaves as a spin polarizer, but also a
vacancy stabilizer, i.e. Li significantly reduces the defect formation energies
of the native defects and helps the stabilization of magnetic oxygen vacancies.
The electronic densities of states reveals that these systems, where the Fermi
level touches the conduction (valence) band, are non-magnetic
(magnetic).cancies. The electronic densities of states reveal that those
systems, where the Fermi levels touch the conduction (valence) band, are
non-magnetic (magnetic).",1210.5602v3
2017/6/26,Perpendicular magnetic anisotropy in insulating ferrimagnetic gadolinium iron garnet thin films,"We present experimental control of the magnetic anisotropy in a gadolinium
iron garnet (GdIG) thin film from in-plane to perpendicular anisotropy by
simply changing the sample temperature. The magnetic hysteresis loops obtained
by SQUID magnetometry measurements unambiguously reveal a change of the
magnetically easy axis from out-of-plane to in-plane depending on the sample
temperature. Additionally, we confirm these findings by the use of temperature
dependent broadband ferromagnetic resonance spectroscopy (FMR). In order to
determine the effective magnetization, we utilize the intrinsic advantage of
FMR spectroscopy which allows to determine the magnetic anisotropy independent
of the paramagnetic substrate, while magnetometry determines the combined
magnetic moment from film and substrate. This enables us to quantitatively
evaluate the anisotropy and the smooth transition from in-plane to
perpendicular magnetic anisotropy. Furthermore, we derive the temperature
dependent $g$-factor and the Gilbert damping of the GdIG thin film.",1706.08488v1
2017/9/25,Chirality in magnetic multilayers probed by the symmetry and the amplitude of dichroism in X-ray resonant magnetic scattering,"Chirality in condensed matter is now a topic of the utmost importance because
of its significant role in the understanding and mastering of a large variety
of new fundamental physicals mechanisms. Versatile experimental approaches,
capable to reveal easily the exact winding of order parameters are therefore
essential. Here we report X-ray resonant magnetic scattering (XRMS) as a
straightforward tool to identify directly the properties of chiral magnetic
systems. We show that it can straight-forwardly and unambiguously determine the
main characteristics of chiral magnetic distributions: i.e. its chiral nature,
the quantitative winding sense (clockwise or counter-clockwise) and its type
(N\'eel/cycloidal or Bloch/helical). This method is model-independent, does not
require a-priori knowledge of magnetic parameters and can be applied to any
system with magnetic domains ranging from few nanometers (wavelength limited)
to several microns. By using prototypical multilayers with tailored magnetic
chiralities based on the Co|Pt interface we illustrate the strength of this
method.",1709.08352v1
2018/2/28,Roles of chiral renormalization on magnetization dynamics in chiral magnets,"In metallic ferromagnets, the interaction between local magnetic moments and
conduction electrons renormalizes parameters of the Landau-Lifshitz-Gilbert
equation such as the gyromagnetic ratio and the Gilbert damping, and makes them
dependent on the magnetic configurations. Although the effects of the
renormalization for nonchiral ferromagnets are usually minor and hardly
detectable, we show that the renormalization does play a crucial role for
chiral magnets. Here the renormalization is chiral and as such we predict
experimentally identifiable effects on the phenomenology of magnetization
dynamics. In particular, our theory for the self-consistent magnetization
dynamics of chiral magnets allows for a concise interpretation of domain wall
creep motion. We also argue that the conventional creep theory of the domain
wall motion, which assumes Markovian dynamics, needs critical reexamination
since the gyromagnetic ratio makes the motion non-Markovian. The non-Markovian
nature of the domain wall dynamics is experimentally checkable by the chirality
of the renormalization.",1803.00017v2
2018/3/2,Switching of the Chiral Magnetic Domains in the Hybrid Multiferroic (ND4)2[FeCl5(D2O)],"Neutron spherical polarimetry, which is directly sensitive to the absolute
magnetic configuration and domain population, has been used in this work to
unambiguously prove the multiferroicity of (ND4)2[FeCl5(D2O)]. We demonstrate
that the application of an electric field upon cooling results in the
stabilization of a single-cycloidal magnetic domain below 6.9 K, while poling
in the opposite electric field direction produces the full population of the
domain with opposite magnetic chirality. We prove the complete switchability of
the magnetic domains at low temperature by the applied electric field, which
constitutes a direct proof of the strong magnetoelectric coupling.
Additionally, we refine the magnetic structure of the ordered ground state,
determining the underlying magnetic space group consistent with the direction
of the ferroelectric polarization, and we provide evidence of a collinear
amplitude-modulated state with magnetic moments along the a-axis in the
temperature region between 6.9 and 7.2 K.",1803.00826v1
2018/3/5,Generation and stability of dynamical skyrmions and droplet solitons,"A spin-polarized current in a nanocontact to a magnetic film can create
collective magnetic oscillations by compensating the magnetic damping. In
particular, in materials with uniaxial magnetic anisotropy, droplet solitons
have been observed a self-localized excitation consisting of partially reversed
magnetization that precesses coherently in the nanocontact region. It is also
possible to generate topological droplet solitons, known as \emph{dynamical
skyrmions}. Here we study the conditions that promote either droplet or
dynamical skyrmion formation and describe their stability in magnetic films
without Dzyaloshinskii-Moriya interactions. We show that Oersted fields from
the applied current as well as the initial magnetization state can determine
whether a droplet or dynamical skyrmion forms. Dynamical skyrmions are found to
be more stable than droplets. We also discuss electrical characteristics that
can be used distinguish these magnetic objects.",1803.01750v1
2018/3/14,Thermal Behavior of a Single Magnetic Vortex Studied with Magnetotransport,"Spin textures such as skyrmions and magnetic vortices are good candidates for
a variety of applications, such as magnetic memories, oscillators and
neuromorphic computing. Understanding the magnetic process of these systems is
important, as it determines the system's response in field and frequency. In
this work, we investigated the magnetization process of single microdisks by
measuring their magnetotransport properties as a function of temperature. The
strong dependence of resistance on the disks magnetic state helped us
understand the magnetization configurations of a single microdisk for different
temperatures and fields. We determined the thermal barriers for the nucleation
and annihilation processes by fitting the nucleation and annihilation fields to
an exponential model. Moreover, we observed and characterized the domain wall
depinning effect for temperatures below 100 K. This effect prevents the
formation of a magnetic vortex during the nucleation process.",1803.05511v1
2018/8/3,"Structural, Ferroelectric, Magnetic and Magnetoelectric Response in Multiferroic (1-x)Bi(Ni1/2Ti1/2)O3-PbTiO3/xNi0.6Zn0.4Fe2O4 Particulate Composites","Multiferroic particulate composites have been fabricated by taking the
morphotropic phase boundary composition of ferroelectric phase
Bi(Ni1/2Ti1/2)O3-PbTiO3 and magnetic phase (Ni,Zn)Fe2O4. The ferroelectric
phase has coexisting monoclinic and tetragonal perovskite structures with space
group Pm and P4mm, respectively whereas the magnetic phase has spinel cubic
structure with space group Fd3m. Rietveld structural analysis for the each
components of composite reveals that the tetragonality (c/a) of the
ferroelectric phase continuously increases with increasing the concentration of
magnetic phase suggesting partial ionic diffusion between ferroelectric and
magnetic phases, after composite formation. Composition dependent M\""ossbauer
spectra of (1-x)Bi(Ni1/2Ti1/2)O3-PbTiO3/x(Ni,Zn)Fe2O4 reveals the
superparamagnetic like behavior for the ferroelectric rich composition with
x=0.2. The magnetic ordering increases for the composition with x=0.4 and 0.6
which completely transform into ferrimagnetic for the composition with x=0.9
for the magnetic phase rich compositions. Unlike the ferroelectric or magnetic
components which do not exhibit the magnetoelectric response separately, large
value of magnetoelectric coefficient (30 mV/Oe-cm) in
(1-x)Bi(Ni1/2Ti1/2)O3-PbTiO3/xNi0.6Zn0.4Fe2O4 composite makes it promise for
multifunctional applications.",1808.01148v1
2018/8/17,Magnetic and structural studies of G-phase compound Mn$_6$Ni$_{16}$Si$_7$,"Transition metal compounds with complex crystal structures tend to
demonstrate interesting magnetic coupling resulting in unusual magnetic
properties. In this work, the structural and magnetic characterization of a
single crystal of the Ni-Mn-Si based G-phase compound, Mn$_6$Ni$_{16}$Si$_7$,
grown by the Czochralski method, is reported. In this structure isolated
octahedral Mn$_6$ clusters form a f.c.c. lattice. As each octahedron consists
of eight edge-sharing equilateral triangles, the possibility for geometric
frustration exists. Magnetization and specific heat measurements showed two
magnetic phase transitions at 197 K and 50 K, respectively. At 100 K neutron
diffraction on powder samples shows a magnetic structure with k = (001) in
which only four of the six Mn spins per cluster order along $<100>$ directions
giving a two dimensional magnetic structure consistent with intra-cluster
frustration. Below the 50 K phase transition the Mn spins cant away from
$<100>$ directions and a weak moment develops on the two remaining Mn
octahedral sites.",1808.05741v2
2018/10/9,Edge-Insensitive Magnetism and Half Metallicity in Graphene Nanoribbons,"Realizing magnetism in graphene/carbon nanostructures is a decade-long
challenge. The magnetic edge state and half metallicity in zigzag graphene
nanoribbons are particularly promising [Y.-W. Son, et al., Nature 444, 347
(2006)]. However, its experimental realization has been hindered by the
stringent requirement of the mono-hydrogenated zigzag edge. Using
first-principle calculations, we predict that free-carrier doping can overcome
this challenge and realize ferromagnetism and half-metallicity in narrow
graphene nanoribbons of general types of edge structures. This magnetism exists
within the density range of gate-doping experiments (~1013 cm-2) and has large
spin polarization energy up to 17 meV per carrier, which induces a Zeeman
splitting equivalent to an external magnetic field of a few hundred Tesla.
Finally, we trace the formation mechanics of this edge-insensitive magnetism to
the quantum confinement of the electronic state near the band edge and reveal
the scaling law of magnetism versus the ribbon width. Our findings suggest that
combining doping with quantum confinement could be a general tool to realize
transition-metal-free magnetism in light-element nanostructures.",1810.04266v1
2012/9/6,Field-driven femtosecond magnetization dynamics induced by ultrastrong coupling to THz transients,"Controlling ultrafast magnetization dynamics by a femtosecond laser is
attracting interest both in fundamental science and industry because of the
potential to achieve magnetic domain switching at ever advanced speed. Here we
report experiments illustrating the ultrastrong and fully coherent light-matter
coupling of a high-field single-cycle THz transient to the magnetization vector
in a ferromagnetic thin film. We could visualize magnetization dynamics which
occur on a timescale of the THz laser cycle and two orders of magnitude faster
than the natural precession response of electrons to an external magnetic
field, given by the Larmor frequency. We show that for one particular
scattering geometry the strong coherent optical coupling can be described
within the framework of a renormalized Landau Lifshitz equation. In addition to
fundamentally new insights to ultrafast magnetization dynamics the coherent
interaction allows for retrieving the complex time-frequency magnetic
properties and points out new opportunities in data storage technology towards
significantly higher storage speed.",1209.1280v1
2012/9/27,Magnetocaloric effect and nature of magnetic transition in nanoscale Pr0.5Ca0.5MnO3,"Systematic measurements pertinent to the magnetocaloric effect and nature of
magnetic transition around the transition temperature are performed in the 10
nm Pr0.5Ca0.5MnO3 nanoparticles (PCMO10) . Maxwell relation is employed to
estimate the change in magnetic entropy. At Curie temperature TC, 83.5 K, the
change in magnetic entropy discloses a typical variation with a value 0.57 J/kg
K, and is found to be magnetic field dependent. From the area under the curve
Delta S vs T, the refrigeration capacity is calculated at TC, 83.5 K and it is
found to be 7.01 J/kg. Arrott plots infer that due to the competition between
the ferromagnetic and anti ferromagnetic interactions, the magnetic phase
transition in PCMO10 is broadly spread over both in temperature as well as in
magnetic field coordinates. Upon tuning the particle size, size distribution,
morphology, and relative fraction of magnetic phases, it may be possible to
enhance the magnetocalorific effect further in PCMO10.",1209.6175v1
2015/12/4,Magnetic proximity effect at interface between a cuprate superconductor and an oxide spin valve,"Heterostructures consisting of a cuprate superconductor YBa2Cu3O7x and a
ruthenate/manganite (SrRuO3/La0.7Sr0.3MnO3) spin valve have been studied by
SQUID magnetometry, ferromagnetic resonances and neutron reflectometry. It was
shown that due to the influence of magnetic proximity effect a magnetic moment
is induced in the superconducting part of heterostructure and at the same time
the magnetic moment is suppressed in the ferromagnetic spin valve. The
experimental value of magnetization induced in the superconductor has the same
order of magnitude with the calculations based on the induced magnetic moment
of Cu atoms due to orbital reconstruction at the superconductor-ferromagnetic
interface. It corresponds also to the model that takes into account the change
in the density of states at a distance of order of the coherence length in the
superconductor. The experimentally obtained characteristic length of
penetration of the magnetic moment into superconductor exceeds the coherence
length for cuprate superconductor. This fact points on the dominance of the
mechanism of the induced magnetic moment of Cu atoms due to orbital
reconstruction.",1512.01336v1
2018/12/14,Anisotropic magnetic properties and giant rotating magnetocaloric effect in double-perovskite Tb2CoMnO6,"We investigated the anisotropy of the magnetic and magnetocaloric properties
of singlecrystalline double perovskite Tb2CoMnO6, which crystallizes in a
monoclinic P21/n structure. Due to dissimilar magnetic anisotropy, the
ferromagnetic order of the Co2+ and Mn4+ moments emerges along the c-axis at TC
= 100 K, and the larger Tb3+ moments align perpendicular to the c-axis, below
TTb = 15 K. The intricate temperature development of the metamagnetism along
the c-axis results in a large negative change in the magnetic entropy at low
temperature. On the other hand, the larger but almost reversible magnetization,
perpendicular to the c-axis, results in a small and positive entropy change.
This highly anisotropic magnetocaloric effect (MCE) leads to a giant rotational
MCE, estimated to be 20.8 J/kg K. Our findings, based on the magnetic
anisotropy in Tb2CoMnO6, enrich fundamental and applied research on magnetic
materials, considering the distinct magnetic characteristics of double
perovskites.",1812.05798v1
2018/12/24,Scaling behaviour of magnetic entropy change in bilayered manganites by two-variable polynomials fitting to magnetization,"Based on the two-variable polynomial model of magnetization, magnetic entropy
change of bilayered manganites with $327$-structure and its scaling behaviour
with respect to applied magnetic fields are investigated. It's found that the
Curie temperature, which is defined as the point at which the partial
derivative of magnetization with respect to temperature reaches its maximum, is
different from the temperature of peak magnetic entropy change. Thus a
mean-field model can not apply to this kind of manganites. In contrast to what
has been found in manganites with the $113$-structure, the scaling behaviour at
the Curie temperature in manganites with $327$-structure is much different from
that at the temperature of peak magnetic entropy. It's also found that the
temperature dependence of the scaling exponent under weak fields is distinct
from that under strong fields.This difference is attributed to an crossover
from one-step transition under weak fields to two-step transition under strong
fields.",1812.09827v1
2008/11/13,Selection rules for Single-Chain-Magnet behavior in non-collinear Ising systems,"The magnetic behavior of molecular Single-Chain Magnets is investigated in
the framework of a one-dimensional Ising model with single spin-flip Glauber
dynamics. Opportune modifications to the original theory are required in order
to account for reciprocal non-collinearity of local anisotropy axes and the
crystallographic (laboratory) frame. The extension of Glauber's theory to the
case of a collinear Ising ferrimagnetic chain is also discussed. Within this
formalism, both the dynamics of magnetization reversal in zero field and the
response of the system to a weak magnetic field, oscillating in time, are
studied. Depending on the geometry, selection rules are found for the
occurrence of slow relaxation of the magnetization at low temperatures, as well
as for resonant behavior of the a.c. susceptibility as a function of
temperature at low frequencies. The present theory applies successfully to some
real systems, namely Mn-, Dy-, and Co-based molecular magnetic chains, showing
that Single-Chain-Magnet behavior is not only a feature of collinear ferro- and
ferrimagnetic, but also of canted antiferromagnetic chains.",0811.2118v1
2016/3/17,Electrical Writing of Magnetic and Resistive Multistates in CoFe Films Deposited onto Pb[Zr$_x$Ti$_{1-x}$]O$_3$,"Electric control of magnetic properties is an important challenge for modern
magnetism and spintronic development. In particular, an ability to write
magnetic state electrically would be highly beneficial. Among other methods,
the use of electric field induced deformation of piezoelectric elements is a
promising low-energy approach for magnetization control. We investigate the
system of piezoelectric substrate Pb[Zr$_x$Ti$_{1-x}$]O$_3$ with CoFe
overlayers, extending the known reversible bistable electro-magnetic coupling
to surface and multistate operations, adding the initial state reset
possibility. Increasing the CoFe thickness improves the magnetoresistive
sensitivity, but at the expenses of decreasing the strain-mediated coupling,
with optimum magnetic thin film thickness of the order of 100 nm. The simplest
resistance strain gauge structure is realized and discussed as a multistate
memory cell demonstrating both resistive memory (RRAM) and magnetoresistive
memory (MRAM) functionalities in a single structure.",1603.05476v1
2017/3/7,Possible devil's staircase in the Kondo lattice CeSbSe,"The temperature ($T$) - magnetic field ($H$) phase diagram for the tetragonal
layered compound CeSbSe, is determined from magnetization, specific heat, and
electrical resistivity measurements. This system exhibits complex magnetic
ordering at $T_{\rm{M}}$ $=$ 3 K and the application of a magnetic field
results in a cascade of magnetically ordered states for $H$ $\lesssim$ 1.8 T
which are characterized by fractional integer size steps: i.e., a possible
Devil's staircase is observed. Electrical transport measurements show a weak
temperature dependence and large residual resistivity which suggest a small
charge carrier density and strong scattering from the $f$-moments. These
features reveal Kondo lattice behavior where the $f$-moments are incompletely
screened, resulting in a fine balanced magnetic interaction between different
Ce neighbors that is mediated by the RKKY interaction. This produces the nearly
degenerate magnetically ordered states that are accessed under an applied
magnetic field.",1703.02204v3
2017/3/17,Sensing Noncollinear Magnetism at the Atomic Scale Combining Magnetic Exchange and Spin-Polarized Imaging,"Storing and accessing information in atomic-scale magnets requires magnetic
imaging techniques with single-atom resolution. Here, we show simultaneous
detection of the spin-polarization and exchange force, with or without the flow
of current, with a new method, which combines scanning tunneling microscopy and
non-contact atomic force microscopy. To demonstrate the application of this new
method, we characterize the prototypical nano-skyrmion lattice formed on a
monolayer of Fe/Ir(111). We resolve the square magnetic lattice by employing
magnetic exchange force microscopy, demonstrating its applicability to
non-collinear magnetic structures, for the first time. Utilizing
distance-dependent force and current spectroscopy, we quantify the exchange
forces in comparison to the spin-polarization. For strongly spin-polarized
tips, we distinguish different signs of the exchange force which we suggest
arises from a change in exchange mechanisms between the probe and a skyrmion.
This new approach may enable both non-perturbative readout combined with
writing by current-driven reversal of atomic-scale magnets.",1703.06059v2
2017/3/24,Enhancement of magnetic ordering temperature and magnetodielectric coupling by hole doping in a multiferroic DyFe0.5Cr0.5O3,"We report the results of our investigation of magnetic, thermodynamic and
dielectric properties of Ca substituted half-doped orthochromite,
Dy0.6Ca0.4Fe0.5Cr0.5O3. Magnetic susceptibility and heat capacity data bring
out that this compound undergoes two antiferromagnetic transitions, one at ~132
and the other at ~22 K. These values are higher than those of DyFe0.5Cr0.5O3.
This finding highlights that non-magnetic hole doping in form of Ca+2 in the
place of magnetic Dy+3 tends to enhance magnetic transition temperatures in
this half-doped orthochromite. We attribute it to possible change in the
valence state of Cr/ Fe-ion ions due to hole doping. Dielectric anomalies are
also seen near the magnetic ordering temperatures indicating magnetodielectric
coupling, which is confirmed by magnetic field dependent dielectric studies.
The most notable observation is that magnetodielectric coupling strength gets
significantly enhanced as compared to DyFe0.5Cr0.5O3. The results reveal that
it is possible to tune magnetodielectric coupling by hole doping in this
system.",1703.08318v1
2019/9/30,Visualization of local magnetic moments emerging from impurities in the Hund's metal states of FeSe,"Understanding the origin of the magnetism of high temperature superconductors
is crucial for establishing their unconventional pairing mechanism. Recently,
theory predicts that FeSe is close to a magnetic quantum critical point, and
thus weak perturbations such as impurities could induce local magnetic moments.
To elucidate such quantum instability, we have employed scanning tunneling
microscopy and spectroscopy. In particular, we have grown FeSe film on
superconducting Pb(111) using molecular beam epitaxy and investigated magnetic
excitation caused by impurities in the proximity-induced superconducting gap of
FeSe. Our study provides a deep insight into the origin of the magnetic
ordering of FeSe by showing the way local magnetic moments develop in response
to impurities near the magnetic quantum critical point.",1909.13515v2
2019/10/3,Magnetization process of the breathing pyrochlore magnet CuInCr$_4$S$_8$ in ultra-high magnetic fields up to 150 T,"The magnetization process of the breathing pyrochlore magnet CuInCr4S8 has
been investigated in ultra-high magnetic fields up to 150 T. Successive phase
transitions characterized with a substantially wide 1/2-plateau from 55 T to
110 T are observed in this system, resembling those reported in chromium spinel
oxides. In addition to the 1/2-plateau phase, the magnetization is found to
exhibit two inherent behaviors: a slight change in the slope of the M-H curve
at ~ 85 T and a shoulder-like shape at ~ 130 T prior to the saturation. Both of
them are accompanied by a hysteresis, suggesting first-order transitions. The
theoretical calculation applicable to CuInCr4S8 is also shown, based on the
microscopic model with the spin-lattice coupling. The calculation fairly well
reproduces the main features of the experimentally observed magnetization
process, including a relatively wide cant 2:1:1 phase clearly observed in the
previous work [Y. Okamoto et al., J. Phys. Soc. Jpn. 87, 034709 (2018)]. The
robust 1/2-plateau on CuInCr4S8 seems to be originated from the dominant
antiferromagnetic interactions and the strong spin-lattice coupling.",1910.01315v1
2019/10/22,Magnetic properties of clusters of supracolloidal magnetic polymers with central attraction,"Supracolloidal magnetic polymers (SMPs) are structures made by crosslinking
magnetic particles. In this work, using Langevin dynamics simulations, we study
the zero-field magnetic properties of clusters formed in suspensions of SMPs
with different topologies -- chains, rings, X and Y -- that interact via
Stockmayer potential. We find that the presence of central attraction,
resulting in the formation of large compact clusters, leads to a dramatic
decrease of the suspension initial susceptibility, independently from SMP
topology. However, the largest decrease corresponds to chain-like SMPs with
strongly interacting particles. This is due to the higher rotational degrees of
freedom of SMPs with such topology, which allows the particles to reorganise
themselves inside the clusters in such a way that their magnetic moments form
energetically advantageous vortex structures with negligible net magnetic
moments.",1910.10040v1
2020/3/26,Quasiclassical theory of $C_4$-symmetric magnetic order in disordered multiband metals,"Recent experimental studies performed in the normal state of iron-based
superconductors have discovered the existence of the $C_4$-symmetric
(tetragonal) itinerant magnetic state. This state can be described as a spin
density wave with two distinct magnetic vectors ${\vec Q}_1$ and ${\vec Q}_2$.
Given an itinerant nature of magnetism in iron-pnictides, we develop a
quasiclassical theory of tetragonal magnetic order in disordered three-band
metal with anisotropic band structure. Within our model we find that the
$C_4$-symmetric magnetism competes with the $C_2$-symmetric state with a single
${\vec Q}$ magnetic structure vector. Our main results is that disorder
promotes tetragonal magnetic state which is in agreement with earlier
theoretical studies.",2003.12124v1
2020/3/31,Chiral magnetic effect of hot electrons,"We propose a way to observe the chiral magnetic effect in non-centrosymmetric
Weyl semimetals under the action of strong electric field, via the non-linear
part of their I-V characteristic that is odd in the external magnetic field, or
odd-in-magnetic field voltages in electrically open circuits. This effect
relies on valley-selective heating in such materials, which in general leads to
nonequilibrium valley population imbalances. In the presence of an external
magnetic field, such a valley-imbalanced Weyl semimetal will in general develop
an electric current along the direction of the magnetic field -- the chiral
magnetic effect. We also discuss a specific experimental setup to observe the
chiral magnetic effect of hot electrons.",2004.00165v1
2020/4/29,Featureless quantum paramagnet with frustrated criticality and competing spiral magnetism on spin-1 honeycomb lattice magnet,"We study the spin-1 honeycomb lattice magnets with frustrated exchange
interactions. The proposed microscopic spin model contains first and second
neighbor Heisenberg interactions as well as the single-ion anisotropy. We
establish a rich phase diagram that includes a featureless quantum paramagnet
and various spin spiral states induced by the mechanism of order by quantum
disorder. Although the quantum paramagnet is dubbed featureless, it is shown
that, the magnetic excitations develop a contour degeneracy in the reciprocal
space at the band minima. These contour degenerate excitations are responsible
for the frustrated criticality from the quantum paramagnet to the ordered
phases. This work illustrates the effects of magnetic frustration on both
magnetic orderings and the magnetic excitations. We discuss the experimental
relevance to various Ni-based honeycomb lattice magnets.",2004.14313v1
2021/4/8,Large Magnetic-Field-Induced Strain at the Magnetic Order Transition in Triangular Antiferromagnet AgCrS2,"Strain induced by a magnetic field is a common phenomenon for ferromagnets,
but few antiferromagnets show large strain induced by a magnetic field. On the
basis of linear strain measurements of sintered samples of triangular
antiferromagnet ACrS2 (A = Cu, Ag, and Au) in magnetic fields up to 9 T, the
AgCrS2 sample was found to show a large strain, yielding a large volume change
over 700 ppm, which is one of the largest volume changes measured to date for
an antiferromagnet. This large strain appeared only at the N\'eel temperature
of 42 K and was not restored to its initial state when the applied magnetic
field was decreased to zero; however, it was initialized by cooling the sample
to far below the N\'eel temperature. These results suggest that the coexistence
of magnetically ordered and paramagnetic phases at the first-order phase
transition plays an important role. AuCrS2 showed a magnetic-field-induced
strain with similar features, although it was smaller than that in AgCrS2.",2104.03471v1
2021/4/30,Control of stripe domain wall magnetization in perpendicular anisotropy multilayers,"We report on the controlled switching of domain wall (DW) magnetization in
aligned stripe domain structures, stabilized in [Co (0.44 nm)/Pt (0.7 nm)]$_X$
($X = 48$, 100, 150) multilayers with perpendicular magnetic anisotropy. The
switching process, induced by an external magnetic field, is monitored by
measuring the evolution of the in-plane magnetization. % We show that the
remanent in-plane magnetization originates from the polarization of the
Bloch-type DWs. With micromagnetic simulations, we reveal that the reversal of
the DW polarization is the result of the emergence and collapse of horizontal
Bloch lines within the DWs at particular strengths of the external magnetic
field, applied opposite to the DW polarization. Our findings are relevant for
DW-based magnonics and bubble skyrmion applications in magnetic multilayers.",2104.14934v1
2013/11/21,Magnetization Enhancement in Magnetite Nanoparticles Capped with Alginic Acid,"We report on the effect of organic acid capping on the behavior of magnetite
nanoparticles. The nanoparticles of magnetite were obtained using microwave
activated process, and the magnetic properties as well as the electron magnetic
resonance behavior were studied for the Fe3O4 nanoparticles capped with alginic
acid. The capped nanoparticles exhibit improved crystalline structure of the
surface which leads to an enhanced magnetization. The saturation magnetization
Ms increases to ~75% of the bulk magnetization. The improved structure also
facilitates quantization of spin-wave spectrum in the finite size nanoparticles
and this in turn is responsible for unconventional behavior at low
temperatures. In magnetic resonance these anomalies are manifested as an
unusual increase in the resonant field Hr(T) and also as a maximum of the
spectroscopic splitting geff parameter at low temperatures. The unconventional
behavior of the nanoparticles also leads to pronounced upturn of magnetization
at low temperatures and a deviation from the Bloch law M(T) T^3/2.",1311.5379v1
2013/11/25,Target-skyrmions and skyrmion clusters in nanowires of chiral magnets,"In bulk non-centrosymmetric magnets the chiral Dzyaloshinskii-Moriya exchange
stabilizes tubular skyrmions with a reversed magnetization in their centers.
While the double-twist is favorable in the center of a skyrmion, it gives rise
to an excess of the energy density at the outskirt. Therefore, magnetic
anisotropies are required to make skyrmions more favorable than the conical
spiral state in bulk materials. Using Monte Carlo simulations, we show that in
magnetic nanowires unusual skyrmions with a doubly twisted core and a number of
concentric helicoidal undulations (target-skyrmions) are thermodynamically
stable even in absence of single-ion anisotropies. Such skyrmions are free of
magnetic charges and, since the angle describing the direction of magnetization
at the surface depends on the radius of the nanowire and an applied magnetic
field, they carry a non-integer skyrmion charge s > 1. This state competes with
clusters of spatially separated s=1 skyrmions. For very small radii, the
target-skyrmion transforms into a skyrmion with s < 1, that resembles the
vortex-like state stabilized by surface-induced anisotropies.",1311.6283v1
2014/1/24,Partial spin reversal in magnetic deflagration,"The reversal of spins in a magnetic material as they relax toward equilibrium
is accompanied by the release of Zeeman energy which can lead to accelerated
spin relaxation and the formation of a well-defined self-sustained propagating
spin-reversal front known as magnetic deflagration. To date, studies of
Mn$_{12}$-acetate single crystals have focused mainly on deflagration in large
longitudinal magnetic fields and found a fully spin-reversed final state. We
report a systematic study of the effect of transverse magnetic field on
magnetic deflagration and demonstrate that in small longitudinal fields the
final state consists of only partially reversed spins. Further, we measured the
front speed as a function of applied magnetic field. The theory of magnetic
deflagration, together with a modification that takes into account the partial
spin reversal, fits the transverse field dependence of the front speed but not
its dependence on longitudinal field. The most significant result of this study
is the finding of a partially spin-reversed final state, which is evidence that
the spins at the deflagration front are also only partially reversed.",1401.6431v1
2015/2/12,Spin Freezing in the Spin Liquid Compound FeAl2O4,"Spin freezing in the $A$-site spinel FeAl$_2$O$_4$ which is a spin liquid
candidate is studied using remnant magnetization and nonlinear magnetic
susceptibility and isofield cooling and heating protocols. The remnant
magnetization behavior of FeAl$_2$O$_4$ differs significantly from that of a
canonical spin glass which is also supported by analysis of the nonlinear
magnetic susceptibility term $\chi_3 (T)$. Through the power-law analysis of
$\chi_3 (T)$, a spin-freezing temperature, $T_g$ = 11.4$\pm$0.9~K and critical
exponent, $\gamma$ = 1.48$\pm$0.59 are obtained. Cole-Cole analysis of magnetic
susceptibility shows the presence of broad spin relaxation times in
FeAl$_2$O$_4$, however, the irreversible dc susceptibility plot discourages an
interpretation based on conventional spin glass features. The magnetization
measured using the cooling-and-heating-in-unequal-fields protocol brings more
insight to the magnetic nature of this frustrated magnet and reveals
unconventional glassy behaviour. Combining our results, we arrive at the
conclusion that the present sample of FeAl$_2$O$_4$ consists of a majority spin
liquid phase with ""glassy"" regions embedded.",1502.03565v1
2015/2/23,Anisotropic Friedel oscillations inside the domain wall,"The influence of the non-collinear magnetic configuration on Friedel is
investigated theoretically. Specifically the influence of the magnetic
configuration on the induced electric charge in a N\'{e}el type domain wall
(DW) has been obtained. The well-known Levy and Zhang eigenstates for a linear
DW have been employed. Then the dielectric function of this magnetic system has
been obtained within the random phase approximation. Results of the current
work demonstrated that magnetic configuration of the system manifests itself in
the electric properties such as induced charge distribution. Meanwhile the
anisotropy of the induced charge distribution in the real space provides a
measurable way for the determination of the DW orientation. In addition
anisotropy of the dielectric function in k-space arises as a result of the
anisotropy of the magnetic configuration. Therefore the orientation of the
magnetic DW could also be captured by full optical measurements.",1502.06421v1
2016/12/20,Nanosecond magnetization dynamics during spin Hall switching of in-plane magnetic tunnel junctions,"We present a study of the magnetic dynamics associated with nanosecond scale
magnetic switching driven by the spin Hall effect in 3-terminal nanoscale
magnetic tunnel junctions (3T-MTJs) with in-plane magnetization. Utilizing fast
pulse measurements in a variety of material stacks and detailed micromagnetic
simulations, we demonstrate that this unexpectedly fast and reliable magnetic
reversal is facilitated by the self-generated Oersted field, and the
short-pulse energy efficiency can be substantially enhanced by micromagnetic
curvature in the magnetic free layer. The sign of the Oersted field is
essential for this enhancement --- in simulations in which we artificially
impose a field-like torque with a sign opposite to the effect of the Oersted
field, the result is a much slower and stochastic switching process that is
reminiscent of the so-called incubation delay in conventional 2-terminal
spin-torque-switched MTJs.",1612.06463v3
2017/7/28,Quantized chiral edge conduction on reconfigurable domain walls of a magnetic topological insulator,"The electronic orders in magnetic and dielectric materials form the domains
with different signs of order parameters. The control of configuration and
motion of the domain walls (DWs) enables gigantic, nonvolatile responses
against minute external fields, forming the bases of contemporary electronics.
As an extension of the DW function concept, we realize the one-dimensional
quantized conduction on the magnetic DWs of a topological insulator (TI). The
DW of a magnetic TI is predicted to host the chiral edge state (CES) of
dissipation-less nature when each magnetic domain is in the quantum anomalous
Hall state. We design and fabricate the magnetic domains in a magnetic TI film
with the tip of the magnetic force microscope, and clearly prove the existence
of the chiral one-dimensional edge conduction along the prescribed DWs. The
proof-of-concept devices based on the reconfigurable CES and Landauer-Buttiker
formalism are exemplified for multiple-domain configurations with the
well-defined DW channels.",1707.09105v1
2017/12/5,Third order perturbed modified Heisenberg Hamiltonian of fcc structured ferromagnetic films with seventy spin layers,"Magnetic properties of fcc structured ferromagnetic films with the number of
spin layers up to seventy was described using third order perturbed Heisenberg
Hamiltonian. The variation of magnetic easy direction, magnetic energies in
easy and hard directions, magnetic anisotropy energy and the angle between easy
and hard directions was investigated by varying the number of spin layers. Spin
exchange interaction, magnetic dipole interaction, second and fourth order
magnetic anisotropies, in and out of plane applied magnetic fields,
demagnetization factor and stress induced anisotropy were considered in the
model. Because magnetic dipole interaction and demagnetization factor represent
microscopic and macroscopic properties of the sample, respectively, both these
terms were incorporated in our theoretical model. Although our model is a
semi-classical model, some discrete variations of angle of easy axis were
observed. Our theoretical data qualitatively agree with experimental data of Fe
and Ni ferromagnetic films.",1712.02636v1
2017/12/17,Magnetostatics of Magnetic Skyrmion Crystals,"Magnetic skyrmion crystals are topological magnetic textures arising in the
chiral ferromagnetic materials with Dzyaloshinskii-Moriya interaction. The
magnetostatic fields generated by magnetic skyrmion crystals are first studied
by micromagnetic simulations. For N\'eel-type skyrmion crystals, the fields
will vanish on one side of the crystal plane, which depend on the helicity;
while for Bloch-type skyrmion crystals, the fields will distribute over both
sides, and are identical for the two helicities. These features and the
symmetry relations of the magetostatic fields are understood from the magnetic
scalar potential and magnetic vector potential of the hybridized triple-Q
state. The possibility to construct magnetostatic field at nanoscale by
stacking chiral ferromagnetic layers with magnetic skyrmion crystals is also
discussed, which may have potential applications to trap and manipulate neutral
atoms with magnetic moments.",1712.06111v1
2017/12/23,Shape anisotropy revisited in single-digit nanometer magnetic tunnel junctions,"Nanoscale magnetic tunnel junction plays a pivotal role in magnetoresistive
random access memories. Successful implementation depends on a simultaneous
achievement of low switching current for the magnetization switching by
spin-transfer torque and high thermal stability, along with a continuous
reduction of junction size. Perpendicular-easy-axis CoFeB/MgO stacks possessing
interfacial anisotropy have paved the way down to 20-nm scale, below which a
new approach needs to be explored. Here we show magnetic tunnel junctions that
satisfy the requirements at ultrafine scale by revisiting shape anisotropy,
which is a classical part of magnetic anisotropy but has not been fully
utilized in the current perpendicular systems. Magnetization switching solely
driven by current is achieved for junctions smaller than 10 nm where sufficient
thermal stability is provided by shape anisotropy without adopting new material
systems. This work is expected to push forward the development of magnetic
tunnel junctions towards single-digit-nm-scale nano-magnetics/spintronics.",1712.08774v1
2018/2/19,Hill plot focusing on Ce compounds with high magnetic-ordering-temperatures and consequent study of Ce2AuP3,"Hill plot is a well-known criterion of the f-electron element interatomic
threshold-distance separating the nonmagnetic state from the magnetic one in
actinides or lanthanides. We have reinvestigated the Hill plot of Ce compounds
using a commercial crystallographic database CRYSTMET, focusing on a
relationship between the Ce-Ce distance and the magnetic ordering temperature,
because a Ce compound with no other magnetic elements scarcely has a magnetic
ordering temperature higher than 20 K. The Hill plot of approximately 730
compounds has revealed that a Ce compound, especially for ferromagnet, showing
the high magnetic-ordering-temperature would require a short Ce-Ce distance
with a suppression of valence instability of Ce ion. Through the study, we had
interest in Ce2AuP3 with the Curie temperature of 31 K. The ferromagnetic
nature has been examined by a doping effect, which suggests a possible increase
of magnetic anisotropy energy.",1802.06899v1
2018/5/28,Technical design and commissioning of the sensor net for fine meshed measuring of magnetic field at KATRIN Spectrometer,"The KArlsruhe TRItium Neutrino experiment (KATRIN) aims to measure the
absolute neutrino mass scale with an unprecedented sensitivity of 0.2 eV/c2
(90% C.L.), using beta decay electrons from tritium decay. The kinetic energy
of the decay electrons is measured using an electrostatic integrating main
spectrometer (MS) with magnetic adiabatic collimation and requires a certain
magnetic field profile. For the control of the magnetic field in the MS area
two networks of mobile magnetic field sensor units are developed and
commissioned. The radial system is operated close to the outer surface of the
MS whereas the vertical one is mounted along vertical planes left and right of
the MS. The sensor setup can take several thousands magnetic field samples at a
fine meshed grid, thus allowing to study the magnetic field inside the MS and
the influence of magnetic materials in the vicinity of the main spectrometer.",1805.10819v2
2018/5/30,Interplay of Magnetism and Transport in HoBi,"We report the observation of an extreme magnetoresistance (XMR) in HoBi with
a large magnetic moment from Ho f-electrons. Neutron scattering is used to
determine the magnetic wave vectors across several metamagnetic (MM)
transitions on the phase diagram of HoBi. Unlike other magnetic rare-earth
monopnictides, the field dependence of resistivity in HoBi is non-monotonic and
reveals clear signatures of every metamagnetic transition in the
low-temperature and low-field regime, at T < 2 K and H < 2.3 T. The XMR appears
at H > 2.3 T after all the metamagnetic transitions are complete and the system
is spin-polarized by the external magnetic field. The existence of an onset
field for XMR and the intimate connection between magnetism and transport in
HoBi are unprecedented among the magnetic rare-earth monopnictides. Therefore,
HoBi provides a unique opportunity to understand the electrical transport in
magnetic XMR semimetals.",1805.12260v1
2019/2/6,Measuring magnetic fields with magnetic field insensitive transitions,"Magnetometry is an important tool prevalent in many applications such as
fundamental research, material characterization and biological imaging. Atomic
magnetometry conventionally makes use of two quantum states, the energy
difference of which depends linearly on the magnetic field due to the Zeeman
effect. The magnetic field is evaluated from repeated measurements of the
accumulated dynamic phase between the two Zeeman states in a superposition.
Here we propose a magnetometry method that employs a superposition of clock
states with energies that do not depend, to first-order, on the magnetic field
magnitude. Our method makes use of the geometrical dependence of the
clock-states wavefunctions on the magnetic field orientation. We propose
detailed schemes for measuring both static and time-varying magnetic fields,
and analyze the sensitivity of these methods. We show that, similarly to
Zeeman-based methods, the smallest measurable signal scales inversely with the
system coherence-time, which for clock transitions is typically significantly
longer than for magnetically sensitive transitions. Finally, we experimentally
demonstrate our method on an ensemble of optically trapped 87Rb atoms.",1902.02370v1
2019/2/12,Threshold Interface Magnetization Required to Induce Magnetic Proximity Effect,"Proximity-induced magnetization (PIM) has broad implications across
interface-driven spintronics applications employing spin-currents. We directly
determine the scaling between PIM in Pt and the temperature-dependent interface
magnetization in an adjacent ferromagnet (FM) using depth-resolved
magnetometry. The magnetization due to PIM does not follow the generally
expected linear scaling with the FM interface magnetization, as a function of
temperature. Instead, it vanishes whilst the FM interface magnetization
remains. The effective magnetic susceptibilities of heavy metal (HM) layers are
shown to give rise to the previously unexplained asymmetric PIM found in
HM/FM/HM trilayers.",1902.04308v2
2019/2/24,Evidence of a cluster spin-glass state in the B-site disordered perovskite SrTi0.5Mn0.5O3,"SrTi0.5Mn0.5O3 (STMO) is a chemically disordered perovskite having random
distribution of Ti and Mn over 1b site. Striking discrepancies about the
structural and magnetic properties of STMO demands detailed analysis which is
addressed. To explore the magnetic ground state of STMO, static and dynamic
magnetic properties were studied over a broad temperature range (2-300 K). The
dc, ac magnetization show a cusp like peak at Tf ~ 14 K, which exhibits field
and frequency dependence. The thermoremanent magnetization is characterized by
using stretched exponential function and characteristic time suggests the
existence of spin clusters. Also the other features observed in magnetic memory
effect, muon spin resonance/rotation and neutron powder diffraction confirm the
existence of cluster spin glass state in STMO, rather than the long range
ordered ground state. Intriguingly, the observed spin relaxation can be
attributed to the dilute magnetism due to non-magnetic doping at Mn-site and
competing antiferromagnetic and ferromagnetic interactions resulting from the
site disorder.",1902.08961v1
2019/3/18,A series of magnon crystals appearing under ultrahigh magnetic fields in a kagomé antiferromagnet,"Search for a new quantum state of matter emerging in a crystal is one of
recent trends in condensed matter physics. For magnetic materials, geometrical
frustration and high magnetic field are two key ingredients to realize it: a
conventional magnetic order is possibly destroyed by competing interactions
(frustration) and is replaced by an exotic state that is characterized in terms
of quasiparticles, that are magnons, and the magnetic field can control the
density and chemical potential of the magnons. Here we show that a synthetic
copper mineral, Cd-kapellasite, comprising a kagome lattice made of
corner-sharing triangles of Cu2+ ions carrying spin-1/2 exhibits an
unprecedented series of fractional magnetization plateaux in ultrahigh magnetic
fields up to 160 T, which may be interpreted as crystallizations of emergent
magnons localized on the hexagon of the kagome lattice. Our observation reveals
a novel type of particle physics realized in a highly frustrated magnet.",1903.07283v1
2019/3/30,Disentangling spin-orbit coupling and local magnetism in a quasi-two-dimensional electron system,"Quantum interference between time-reversed electron paths in two dimensions
leads to the well-known weak localization correction to resistance. If
spin-orbit coupling is present, the resistance correction is negative, termed
weak anti-localization (WAL). Here we report the observation of WAL coexisting
with exchange coupling between itinerant electrons and localized magnetic
moments. We use low-temperature magneto-transport measurements to investigate
the quasi-two-dimensional, high-electron-density interface formed between
SrTiO$_3$ (STO) and the anti-ferromagnetic Mott insulator NdTiO$_3$ (NTO). As
the magnetic field angle is gradually tilted away from the sample normal, the
data reveals the interplay between strong $k$-cubic Rashba-type spin-orbit
coupling and a substantial magnetic exchange interaction from local magnetic
regions. The resulting quantum corrections to the conduction are in excellent
agreement with existing models and allow sensitive determination of the small
magnetic moments (22 $\mu_B$ on average), their magnetic anisotropy and mutual
coupling strength. This effect is expected to arise in other 2D magnetic
materials systems.",1904.00295v2
2019/5/17,Chiral p-wave superconductors have complex coherence and magnetic field penetration lengths,"We show that in superconductors that break time reversal symmetry and have
anisotropy, such as p+ip materials, all order parameters and magnetic modes are
mixed. Excitation of the gap fields produces an excitation of the magnetic
field and vice versa. Correspondingly the long-range decay of the magnetic
field and order parameter are in general given by the same exponent. Thus one
cannot characterize p+ip superconductors by the usual coherence and magnetic
field penetration lengths. Instead the system has normal modes that are
associated with linear combinations of magnetic fields, moduli of and phases of
the order parameter components. Each such normal mode has its own decay length
that plays the role of a hybridized coherence/magnetic field penetration
length. On a large part of the parameter space these exponents are complex.
Therefore the system in general has damped oscillatory decay of the magnetic
field accompanied by damped oscillatory variation of the order parameter
fields.",1905.07296v2
2019/5/27,Magnetic Field Induced Competing Phases in Spin-Orbital Entangled Kitaev Magnets,"There has been a great interest in magnetic field induced quantum spin
liquids in Kitaev magnets after the discovery of neutron scattering continuum
and half quantized thermal Hall conductivity in the material $\alpha$-RuCl$_3$.
In this work, we provide a semiclassical analysis of the relevant theoretical
models on large system sizes, and compare the results to previous studies on
quantum models with small system sizes. We find a series of competing magnetic
orders with fairly large unit cells at intermediate magnetic fields, which are
most likely missed by previous approaches. We show that quantum fluctuations
are typically strong in these large unit cell orders, while their magnetic
excitations may resemble a scattering continuum and give rise to a large
thermal Hall conductivity. Our work provides an important basis for a thorough
investigation of emergent spin liquids and competing phases in Kitaev magnets.",1905.11408v2
2019/7/2,Revealing 3D Magnetization of Thin Films with Soft X-ray Tomography: Closure Domains and Magnetic Singularities,"The knowledge of how the magnetization looks inside a ferromagnet is often
hindered by the limitations of the available experimental methods that are
sensitive only to the surface regions or limited in spatial resolution. We
report the 3D tomographic reconstruction of the magnetization within a
ferromagnetic film of 240 nm in thickness using soft X ray microscopy and
magnetic dichroism. The film has periodic magnetic domains forming stripes and
closure domains found to be shifted from the stripe array by 1/4 of the period.
In addition, the bifurcations of the stripes, which act as inversion nuclei of
the magnetization, evidence in 3D meron singularities and Bloch points at the
interior of the film. This novel method can be easily extended to magnetic
stacks in spintronics applications and other singularities in films.",1907.01261v2
2019/12/29,Synchronized excitation of magnetization dynamics via spin waves in Bi-YIG thin film by slot line waveguide,"We have studied magnetization dynamics of a single Bi-YIG thin film by means
of the high frequency power response induced by a slot line waveguide. Multiple
absorption peaks that correspond to excitement states in magnetization dynamics
appeared without the ferromagnetic resonance (FMR) condition. The peaks were
strongly influenced by a waveguide line width and a distance between the lines.
Micromagnetics simulation reveals that each line induces a local magnetization
dynamics oscillation and generates spin waves. The spin wave that propagates
from one of the lines interferences with the other side of local magnetization
dynamics oscillation around the other line, resulting in an amplification of
the oscillation when they are in synchronization with each other. This
amplification occurs at both sides of the lines by the interference. Thus, the
possible mechanism of the excitation in the magnetization dynamics oscillation
is the synchronization of mutual magnetization dynamics oscillation via spin
waves. This technique resonantly excites the local magnetization dynamics
without the FMR condition, which is applicable as a highly coherent spin waves
source.",1912.12663v1
2020/1/12,Imaging of Strain Driven Magnetic Domains and Strong Spin-Phonon Coupling in Epitaxial Thin Films of SrRuO3,"Epitaxial thin films of SrRuO3 with large strain disorder were grown using
pulsed laser deposition method which showed two distinct transition
temperatures in Magnetic measurements. For the first time, we present visual
evolution of magnetic domains across the two transitions using Magnetic force
microscopy on these films. The study clearly showed that the magnetic
anisotropy corresponding to the two transitions is different. It is observed
that the perpendicular magnetic anisotropy is dominating in films which results
in domain spin orientation preferably in out of plane direction. The Raman
studies showed that the lattice is highly influenced by the magnetic order. The
analysis of the phonon spectra around magnetic transition reveals the existence
of strong spin-phonon coupling and the calculations resulted in spin-phonon
coupling strength ({\lambda}) values of {\lambda} ~ 5 cm-1 and {\lambda} ~ 8.5
cm-1, for SrRuO3 films grown on LSAT and SrTiO3 single crystal substrates,
respectively.",2001.03901v1
2020/1/22,Imaging three-dimensional nanoscale magnetization dynamics,"The ability to experimentally map the three-dimensional structure and
dynamics in bulk and patterned three-dimensional ferromagnets is essential both
for understanding fundamental micromagnetic processes, as well as for
investigating technologically-relevant micromagnets whose functions are
connected to the presence and dynamics of fundamental micromagnetic structures,
such as domain walls and vortices. Here, we demonstrate time-resolved magnetic
laminography, a technique which offers access to the temporal evolution of a
complex three-dimensional magnetic structure with nanoscale resolution. We
image the dynamics of the complex three-dimensional magnetization state in a
two-phase bulk magnet with a lateral spatial resolution of 50 nm, mapping the
transition between domain wall precession and the dynamics of a uniform
magnetic domain that is attributed to variations in the magnetization state
across the phase boundary. The capability to probe three-dimensional magnetic
structures with temporal resolution paves the way for the experimental
investigation of novel functionalities arising from dynamic phenomena in bulk
and three-dimensional patterned nanomagnets.",2001.07940v1
2020/2/13,High-Field Magnetization and Magnetic Phase Diagram of Metamagnetic Shape Memory Alloys Ni50-xCoxMn31.5Ga18.5 (x = 9 and 9.7),"Magnetic phase diagrams of the metamagnetic shape memory alloys
Ni50-xCoxMn31.5Ga18.5 (x = 9 and 9.7) were produced from high-field
magnetization measurements up to 56 T. For both compounds, magnetic field
induced martensitic transformations are observed at various temperatures below
300 K. Hysteresis of the field-induced transformation shows unconventional
temperature dependence: it decreases with decreasing temperature after showing
a peak. Magnetic susceptibility measurement, microscopy, and X-ray diffraction
data suggest a model incorporating the magnetic anisotropy and Zeeman energy in
two variants, which qualitatively explains the thermal and the magnetic field
history dependence of the hysteresis in these alloys.",2002.05303v1
2020/2/26,Skyrmion formation in nanodiscs using magnetic force microscopy tip,"In this manuscript we demonstrate the skyrmion formation in ultrathin
nanodots using magnetic force microscopy tip. Submicron-size dots based on
Pt/Co/Au multilayers hosting interfacial Dzyaloshiskii-Morya interaction were
used in the experiments. We have found that the tip field generated by the
magnetic tip significantly affects the magnetization state of the nanodots and
leads to the formation of skyrmions. Micromagnetic simulations explain the
evolution of the magnetic state during magnetic force microscopy scans and
confirm the possibility of the skyrmion formation. The key transition in this
process is the formation of the horseshoe magnetic domain. We have found that
formation of skyrmion by the magnetic probe is a reliable and repetitive
procedure. Our findings provide a simple solution for skyrmions formation in
nanodots.",2002.11685v1
2020/5/7,Ultrafast All Optical Magnetization Control for Broadband Terahertz Spin Wave Generation,"Terahertz spin waves could be generated on-demand via all-optical
manipulation of magnetization by femtosecond laser pulse. Here, we present an
energy balance model, which explains the energy transfer rates from laser pulse
to electron bath coupled with phonon, spin, and magnetization of five different
magnetic metallic thin films: Iron, Cobalt, Nickel, Gadolinium and Ni$_{2}$MnSn
Heusler alloy. Two types of transient magnetization dynamics emerge in metallic
magnetic thin films based on their Curie temperatures (T$_{C}$): type I (Fe,
Co, and Ni with T$_{C}$ > room temperature, RT) and type II films (Gd and
Ni$_{2}$MnSn with T$_{C}$ $\approx$ RT). We study the effect of laser fluence
and pulse width for single Gaussian laser pulses and the effect of metal film
thickness on magnetization dynamics. Spectral dynamics show that broadband spin
waves up to 24 THz could be generated by all-optical manipulation of
magnetization in these nanofilms.",2005.03493v1
2020/5/12,Topology optimization of permanent magnets for stellarators,"We introduce a topology optimization method to design permanent magnets for
advanced stellarators. Recent researches show that permanent magnets have great
potentials to simplify stellarator coils. We adopt state-of-the-art numerical
techniques to determine the presence of magnets in the entire designing space.
The FAMUS code is developed and it can design engineering-feasible permanent
magnets for general stellarators satisfying the constraints of the maximum
material magnetization and explicitly forbidden regions. FAMUS has been
successfully verified against the previously proposed linear method. Three
different permanent magnet designs together with planar TF coils for a
half-Tesla NCSX configuration have been obtained for demonstrations. The
designs have good accuracy in generating the desired equilibrium and offer
considerably large plasma access on the outboard side. The results show that
FAMUS is a flexible, advanced numerical tool for future permanent magnet
stellarator designs.",2005.05504v1
2020/5/13,Magneto-optics of excitons interacting with magnetic ions in CdSe/CdMnS colloidal nanoplatelets,"Excitons in diluted magnetic semiconductors represent excellent probes for
studying the magnetic properties of these materials. Various magneto-optical
effects, which depend sensitively on the exchange interaction of the excitons
with the localized spins of the magnetic ions can be used for probing. Here, we
study core/shell CdSe/(Cd,Mn)S colloidal nanoplatelets hosting diluted magnetic
semiconductor layers. The inclusion of the magnetic Mn$^{2+}$ ions is evidenced
by three magneto-optical techniques using high magnetic fields up to 15 T:
polarized photoluminescence, optically detected magnetic resonance, and
spin-flip Raman scattering. In particular, information on the Mn$^{2+}$
concentration in the CdS shell layers can be obtained from the spin-lattice
relaxation dynamics of the Mn$^{2+}$ spin system.",2005.06548v1
2020/6/4,Substitutional Doping of Symmetrical Small Fullerene Dimers,"Magnetic carbon nano-structures have potential applications in the field of
spintronics as they exhibit valuable magnetic properties. Symmetrically sized
small fullerene dimers are substitutional doped with nitrogen (electron rich)
and boron (electron deficient) atoms to visualize the effect on their magnetic
properties. Interaction energies suggests that the resultant dimer structures
are energetically favourable and hence can be formed experimentally. There is
significant change in the total magnetic moment of dimers of the order of 0.5
uB after the substitution of C atoms with N and B, which can also be seen in
the change of density of states. The HOMO-LUMO gaps of spin up and spin down
electronic states have finite energy difference which confirm their magnetic
behaviour, whereas for non-magnetic doped dimers, the HOMO-LUMO gaps for spin
up and down states are degenerate. The optical properties show that the dimers
behave as optical semiconductors and are useful in optoelectronic devices. The
induced magnetism in these dimers makes them fascinating nanocarbon magnetic
materials.",2006.02728v1
2020/6/18,Large Surface Magnetization in Noncentrosymmetric Antiferromagnets,"Thin-film antiferromagnets (AFs) with Rashba spin-orbit coupling are
theoretically investigated. We demonstrate that the relativistic
Dzyaloshinskii-Moriya interaction (DMI) produces a large surface magnetization
and a boundary-driven twist state in the antiferromagnetic N\' eel vector. We
predict a magnetization on the order of $2.3\cdot 10^4$~A/m, which is
comparable to the magnetization of ferromagnetic semiconductors. Importantly,
the magnetization is characterized by ultra-fast terahertz dynamics and
provides new approaches for efficiently probing and controlling the spin
dynamics of AFs as well as detecting the antiferromagnetic DMI. Notably, the
magnetization does not lead to any stray magnetic fields except at corners
where weak magnetic monopole fields appear.",2006.10435v2
2020/9/3,Nature of Partial Magnetic Order in the Frustrated Antiferromagnet Gd2Ti2O7,"Partially-ordered magnets are distinct from both spin liquids and
conventional ordered magnets because order and disorder coexist in the same
magnetic phase. Here, we determine the nature of partial order in the canonical
frustrated pyrochlore antiferromagnet Gd$_2$Ti$_{2}$O$_{7}$. Using
single-crystal neutron-diffraction measurements in applied magnetic field,
magnetic symmetry analysis, inelastic neutron-scattering measurements, and
spin-wave modeling, we show that its low-temperature magnetic structure
involves two propagation vectors (2-$\mathbf{k}$ structure) with suppressed
ordered magnetic moments and enhanced spin-wave fluctuations. Our experimental
results support theoretical predictions of thermal fluctuation-driven order in
Gd$_{2}$Ti$_{2}$O$_{7}$.",2009.01670v1
2020/9/26,Magnetization Plateau Observed by Ultra-High Field Faraday Rotation in a Kagomé Antiferromagnet Herbertsmithite,"To capture the high-field magnetization process of herbertsmithite
(ZnCu3(OH)6Cl2), Faraday rotation (FR) measurements were carried out on a
single crystal in magnetic fields of up to 190 T. The magnetization data
evaluated from the FR angle exhibited a saturation behavior above 150 T at low
temperatures, which was attributed to the 1/3 magnetization plateau. The
overall behavior of the magnetization process was reproduced by theoretical
models based on the nearest-neighbor Heisenberg model. This suggests that
herbertsmithite is a proximate kagome antiferromagnet hosting an ideal quantum
spin liquid in the ground state. A distinguishing feature is the superlinear
magnetization increase, which is in contrast to the Brillouin function-type
increase observed by conventional magnetization measurements and indicates a
reduced contribution from free spins located at the Zn sites to the FR signal.",2009.12476v1
2020/10/1,Frequency-dependent magnetic susceptibility of magnetic nanoparticles in a polymer solution: a simulation study,"Magnetic composite materials i.e. elastomers, polymer gels, or polymer
solutions with embedded magnetic nanoparticles are useful for many technical
and bio-medical applications. However, the microscopic details of the coupling
mechanisms between the magnetic properties of the particles and the mechanical
properties of the (visco)elastic polymer matrix remain unresolved. Here we
study the response of a single-domain spherical magnetic nanoparticle that is
suspended in a polymer solution to alternating magnetic fields. As interactions
we consider only excluded volume interactions with the polymers and
hydrodynamic interactions mediated through the solvent. The AC susceptibility
spectra are calculated using a linear response Green-Kubo approach, and the
influences of changing polymer concentration and polymer length are
investigated. Our data is compared to recent measurements of the AC
susceptibility for a typical magnetic composite system [Roeben et al., Colloid
and Polymer Science, 2014, 2013--2023], and demonstrates the importance of
hydrodynamic coupling in such systems.",2010.00299v2
2020/10/12,Nonmagnetic-magnetic transition and magnetically ordered structure in SmS,"SmS, a prototypical intermediate valence compound, has been studied by
performing high-pressure nuclear magnetic resonance measurements on a
$^{33}$S-enriched sample. The observation of an additional signal below 15-20 K
above a nonmagnetic-magnetic transition pressure $P_{\rm c2} \approx 2$ GPa
gives evidence of a magnetic transition. The absence of a Curie-term in the
Knight shift near $P_{\rm c2}$ indicates that the localized character of $4f$
electrons is entirely screened and the mechanism of the magnetic ordering is
not described within a simple localized model. Simultaneously, the line shape
in the magnetically ordered state is incompatible with a spin density wave
order. These suggest that the magnetic order in SmS may require an
understanding beyond the conventional framework for heavy fermions. The fact
that hyperfine fields from the ordered moments cancel out at the S site leads
us to a conclusion that the ordered phase has a type II antiferromagnetic
structure.",2010.05539v2
2020/10/14,"Magnetization relaxation and search for the magnetic gap in bulk-insulating V-doped (Bi, Sb)$_2$Te$_3$","V-doped (Bi,Sb)$_2$Te$_3$ has a ten times higher magnetic coercivity than its
Cr-doped counterpart and therefore is believed to be a superior system for the
quantum anomalous Hall effect (QAHE). The QAHE requires the opening of a
magnetic band gap at the Dirac point. We do not find this gap by angle-resolved
photoelectron spectroscopy down to 1 K. By x-ray magnetic circular dichroism
(XMCD) we directly probe the magnetism at the V site and in zerofield.
Hysteresis curves of the XMCD signal show a strong dependence of the coercivity
on the ramping velocity of the magnetic field. The XMCD signal decays on a time
scale of minutes which we conclude contributes to the absence of a detectable
magnetic gap at the Dirac point.",2010.07083v1
2020/10/23,Magnetic and structural properties of Ni-substituted magnetoelectric Co$_4$Nb$_2$O$_9$,"The magnetic and structural properties of polycrystalline Co$_{4-x}$ Ni$_x$
Nb$_2$ O$_9$ (x=1,2) have been investigated by neutron powder diffraction,
magnetization and heat capacity measurements, and density functional theory
(DFT) calculations. For x=1, the compound crystallizes in the trigonal
P$\bar{3}$c1 space group. Below T$_N$ = 31 K it develops a weakly non-collinear
antiferromagnetig structure with magnetic moments in the ab-plane. The compound
with x=2 has crystal structure of the orthorhombic Pbcn space group and shows a
hard ferrimagnetic behavior below T$_C$ =47 K. For this compound a weakly
non-collinear ferrimagnetic structure with two possible configurations in ab
plane was derived from ND study. By calculating magnetic anisotropy energy via
DFT, the ground-state magnetic configuration was determined for this compound.
The heat capacity study in magnetic fields up to 140 kOe provide further
information on the magnetic structure of the compounds.",2010.12285v1
2020/10/27,Metastable and localized Ising magnetism in $α$-CoV$_{2}$O$_{6}$ magnetization plateaus,"$\alpha$-CoV$_{2}$O$_{6}$ consists of $j_{\mathrm{eff}}={1 \over 2}$ Ising
spins located on an anisotropic triangular motif with magnetization plateaus in
an applied field. We combine neutron diffraction with low temperature
magnetization to investigate the magnetic periodicity in the vicinity of these
plateaus. We find these steps to be characterized by metastable and spatially
short-range ($\xi\sim$ 10 $\r{A}$) magnetic correlations with antiphase
boundaries defining a local periodicity of $\langle \hat{T}^{2} \rangle =\
\uparrow \downarrow$ to $\langle \hat{T}^{3} \rangle =\ \uparrow \uparrow
\downarrow$, and $\langle \hat{T}^{4} \rangle=\ \uparrow \uparrow \downarrow
\downarrow$ or $\uparrow \uparrow \uparrow \downarrow$ spin arrangements. This
shows the presence of spatially short range and metastable/hysteretic,
commensurate magnetism in Ising magnetization steps.",2010.14097v1
2020/11/17,Ultra-efficient magnetism modulation in a Weyl ferromagnet by current-assisted domain wall motion,"Flexible and efficient manipulation of magnetic configurations can be
challenging. In the design of practical devices, achieving a high effective
magnetic field with a low working current is under tight demand. Here, we
report a unique method for efficient magnetism modulation by direct current
injection in magnetic Weyl semimetal Co3Sn2S2. We demonstrate that the
modulation process stems from current-assisted domain wall motion. Through two
independent methods, we reveal that the spin-transfer torque efficiency of
Co3Sn2S2 reaches as high as 2.4-5.6 kOe MA^(-1) cm^2, and the threshold current
density for driving the magnetic domain walls is as low as <5.1*10^5 A/cm^2
without an external field, and <1.5*10^5 A/cm^2 with a moderate external field.
Our findings manifest a new and powerful approach for sub-micron magnetism
manipulation, and also open the door towards a new paradigm of spintronics that
combines magnetism, topology, and metallicity for low-energy consumption memory
and computing.",2011.08391v2
2021/1/18,Magnetization switching induced by spin-orbit torque from Co2MnGa magnetic Weyl semimetal thin films,"This study reports the magnetization switching induced by spin-orbit torque
(SOT) from the spin current generated in Co2MnGa magnetic Weyl semimetal (WSM)
thin films. We deposited epitaxial Co2MnGa thin films with highly B2-ordered
structure on MgO(001) substrates. The SOT was characterized by harmonic Hall
measurements in a Co2MnGa/Ti/CoFeB heterostructure and a relatively large spin
Hall efficiency of -7.8% was obtained.The SOT-induced magnetization switching
of the perpendicularly magnetized CoFeB layer was further demonstrated using
the structure. The symmetry of second harmonic signals, thickness dependence of
spin Hall efficiency, and shift of anomalous Hall loops under applied currents
were also investigated. This study not only contributes to the understanding of
the mechanisms of spin-current generation from magnetic-WSM-based
heterostructures, but also paves a way for the applications of magnetic WSMs in
spintronic devices.",2101.06881v1
2021/3/24,Proximity Effect of Epitaxial Iron Phthalocyanine Molecules on High-Quality Graphene Devices,"Depositing magnetic insulators on graphene has been a promising route to
introduce magnetism via exchange proximity interaction in graphene for future
spintronics applications. Molecule-based magnets may offer unique opportunities
because of their synthesis versatility. Here, we investigated the magnetic
proximity effect of epitaxial iron phthalocyanine (FePc) molecules on
high-quality monolayer and bilayer graphene devices on hexagonal boron nitride
substrate by probing the local and non-local transport. Although the FePc
molecules introduce large hole doping effects combined with mobility
degradation, the magnetic proximity gives rise to a canted antiferromagnetic
state under a magnetic field in the monolayer graphene. On bilayer graphene and
FePc heterostructure devices, the non-local transport reveals a pronounced
Zeeman spin-Hall effect. Further analysis of the scattering mechanism in the
bilayer shows a dominated long-range scattering. Our findings in
graphene/organic magnetic insulator heterostructure provide a new insight for
the use of molecule-based magnets in two-dimensional spintronic devices.",2103.12974v1
2021/6/21,Large exchange bias and low temperature glassy state in frustrated triangular-lattice antiferromagnet Ba$_3$NiIr$_2$O$_9$,"Here, we report both ac and dc magnetization, thermodynamic and electric
properties of hexagonal Ba$_3$NiIr$_2$O$_9$. The Ni$^{2+}$ (spin-1) forms
layered triangular-lattice and interacts antiferromagnetically while Ir$^{5+}$
is believed to act as magnetic link between the layers. This complex magnetic
interaction results in magnetic frustration leading to a spin-glass transition
at $T_f$ $\sim$ 8.5 K. The observed magnetic relaxation and aging effect also
confirms the nonequilibrium ground state. The system further shows large
exchange bias which is tunable with cooling field. Below the Curie-Weiss
temperature $\theta_{CW}$ ($\sim$ -29 K), the magnetic specific heat $C_m$
displays a broad hump and at low temperature follows $C_m = \gamma T^\alpha$
dependence where both $\gamma$ and $\alpha$ show dependence on temperature and
magnetic field. A sign change in magnetoresistace is observed which is due to
an interplay among magnetic moment, field and spin-orbit coupling.",2106.11402v1
2021/6/30,"Untangling the structural, magnetic dipole, and charge multipolar orders in Ba$_2$MgReO$_6$","We present a density functional theory study of the low-temperature
structural, magnetic, and proposed charge-quadrupolar ordering in the double
perovskite, Ba$_2$MgReO$_6$. Ba$_2$MgReO$_6$ is a spin-orbit-driven Mott
insulator with a symmetry-lowering structural phase transition at 33\,K and a
canted antiferromagnetic ordering of $5d^1$ Re magnetic moments at 18\,K. Our
calculations confirm the existence of the proposed charge quadrupolar order and
discover an additional, previously hidden, ordered charge quadrupolar
component. By separately isolating the structural distortions and the
orientations of the magnetic dipoles, we determine the relationship between the
charge quadrupolar, structural and magnetic orders, finding that either a local
structural distortion or a specific magnetic dipole orientation is required to
lower the symmetry and enable the existence of charge quadrupoles. Our work
establishes the crystal structure -- magnetic dipole -- charge multipole
relationship in Ba$_2$MgReO$_6$ and related 5$d^1$ double perovskites, and
illustrates a method for separating and analyzing the contributions and
interactions of structural, magnetic, and charge orders beyond the usual dipole
level.",2106.15976v1
2021/7/14,Spacer-layer-tunable magnetism and high-field topological Hall effect in topological insulator heterostructures,"Controlling magnetic order in magnetic topological insulators (MTIs) is a key
to developing spintronic applications with MTIs, and is commonly achieved by
changing the magnetic doping concentration, which inevitably affects
spin-orbit-coupling strength and the very topological properties. Here, we
demonstrate tunable magnetic properties in topological heterostructures over a
wide range, from a ferromagnetic phase with Curie temperature of around 100 K
all the way to a paramagnetic phase, while keeping the overall chemical
composition the same, by controlling the thickness of non-magnetic spacer
layers between two atomically-thin magnetic layers. This work showcases that
spacer-layer control is a powerful tool to manipulate magneto-topological
functionalities in MTI heterostructures. Furthermore, the interaction between
the MTI and the Cr2O3 buffer layers also led to robust topological Hall effect
surviving up to a record-high 6 T of magnetic field, shedding light on the
critical role of interfacial layers in thin film topological materials.",2107.06805v1
2021/9/24,Magnetostriction and magnetostructural domains in CoTiO$_3$,"We report the magnetostrictive length changes of CoTiO$_3$ studied by means
of high-resolution dilatometry in magnetic fields ($B$) up to 15~T. In the
long-range antiferromagnetically ordered phase below $T_N$ = 38~K, the
easy-plane type spin structure undergoes a spin-reorientation transition in the
$ab$ plane in magnetic fields $B || ab \approx 2$~T. We observe pronounced
length changes driven by external magnetic field in this field region
indicating significant magnetoelastic coupling in CoTiO$_3$. Specifically, we
observe anisotropic deformation of the lattice for fields applied in the $ab$
plane. While, for $B \lesssim 2$~T, in-plane magnetostriction shows that the
lattice expands (contracts) parallel (perpendicular) to the field direction,
the opposite behaviour appear at higher fields. Furthermore, there are
remarkable effects of slight changes in the applied uniaxial pressure on the
magnetostrictive response of CoTiO$_3$ persisting to temperatures well above
$T_N$. The data evidence the presence of magnetic domains below $T_N$ as well
as of structural ones in CoTiO$_3$. The presence of magnetic domains in the
spin ordered phase is further evidenced by an additional 3-fold magnetic
anisotropy appearing below $T_N$. We discuss the effects of rotational magnetic
domains on isothermal magnetization and magnetostriction and interpret our
results on the basis of a multi-domain phenomenological model.",2109.11923v1
2021/9/29,Magnetic interlayer coupling between ferromagnetic SrRuO$_3$ layers through a SrIrO$_3$ spacer,"A key element to tailor the properties of magnetic multilayers is the
coupling between the individual magnetic layers. In case of skyrmion hosting
multilayers, coupling of skyrmions across the magnetic layers is highly
desirable. Here the magnetic interlayer coupling was studied in epitaxial
all-oxide heterostructures of ferromagnetic perovskite SrRuO$_3$ layers
separated by spacers of the strong spin-orbit coupling oxide SrIrO$_3$. This
combination of oxide layers is being discussed as a potential candidate system
to host N\'{e}el skyrmions. First order reversal curve (FORC) measurements were
performed in order to distinguish between magnetic switching processes of the
individual layers and to disentangle the signal of soft magnetic impurities
from the samples$'$ signal. Additionally, FORC investigations enabled to
determine whether the coupling between the magnetic layers is ferromagnetic or
antiferromagnetic. The observed interlayer coupling strength was weak for all
the heterostructures, with SrIrO$_3$ spacers between 2 monolayers and 12
monolayers thick.",2109.14292v2
2021/10/19,Superconductivity-driven ferromagnetism and spin manipulation using vortices in the magnetic superconductor EuRbFe4As4,"Magnetic superconductors are specific materials exhibiting two antagonistic
phenomena, superconductivity and magnetism, whose mutual interaction induces
various emergent phenomena, such as the reentrant superconducting transition
associated with the suppression of superconductivity around the magnetic
transition temperature (Tm), highlighting the impact of magnetism on
superconductivity. In this study, we report the experimental observation of the
ferromagnetic order induced by superconducting vortices in the
high-critical-temperature (high-Tc) magnetic superconductor EuRbFe4As4.
Although the ground state of the Eu2+ moments in EuRbFe4As4 is helimagnetism
below Tm, neutron diffraction and magnetization experiments show a
ferromagnetic hysteresis of the Eu2+ spin alignment. We demonstrate that the
direction of the Eu2+ moments is dominated by the distribution of pinned
vortices based on the critical state model. Moreover, we demonstrate the
manipulation of spin texture by controlling the direction of superconducting
vortices, which can help realize spin manipulation devices using magnetic
superconductors.",2110.09675v1
2021/10/22,Magnetization dynamics fingerprints of an excitonic condensate $t_{2g}^{4}$ magnet,"The competition between spin-orbit coupling $\lambda$ and electron-electron
interaction $U$ leads to a plethora of novel states of matter, extensively
studied in the context of $t_{2g}^4$ and $t_{2g}^5$ materials, such as
ruthenates and iridates. Excitonic magnets -- the antiferromagnetic state of
bounded electron-hole pairs -- is a prominent example of phenomena driven by
those competing energy scales. Interestingly, recent theoretical studies
predicted that excitonic magnets can be found in the ground-state of
spin-orbit-coupled $t_{2g}^4$ Hubbard models. Here, we present a detailed
computational study of the magnetic excitations in that excitonic magnet,
employing one-dimensional chains (via density matrix renormalization group) and
small two-dimensional clusters (via Lanczos). Specifically, first we show that
the low-energy spectrum is dominated by a dispersive (acoustic) magnonic mode,
with extra features arising from the $\lambda=0$ state in the phase diagram.
Second, and more importantly, we found a novel magnetic excitation forming a
high-energy optical mode with the highest intensity at wavevector $q\to 0$. In
the excitonic condensation regime at large $U$, we also have found a novel
high-energy $\pi$-mode composed solely of orbital excitations. These unique
fingerprints of the $t_{2g}^4$ excitonic magnet are important in the analysis
of neutron and RIXS experiments.",2110.11828v1
2021/11/5,Emergent magnetic states due to stacking and strain in the van der Waals magnetic trilayer CrI3,"Recently, three different magnetic states were observed experimentally in
trilayer CrI3 under pressure,including ferromagnetic (FM)-upupup, FM-downupdown
and FM-upupdown. To reveal the nature of the observed three magnetic states, we
studied the magnetic properties of four possible stacking structures in
trilayer CrI3: I (rhombohedral), II (monoclinic), III (hexagonal) and IV
(triclinic). We find that all four stacking structures possess the FM-upupup
ground state. After applying a few strains, the FM-downupdown becomes the
ground state in II and III structures, and the FM-upupdown is preferred in IV
structure, while the FM-upupup persists in I structure. Our results unveil that
the three magnetic states observed in trilayer CrI3 may correspond to different
stacking structures with small tensile strains, which can well interpret the
experimentally obtained pressure dependent interlayer coupling and Curie
temperature. Our present study paves a way to design the magnetic multilayers
with required magnetic states by tuning stacking and strain.",2111.03287v1
2021/11/9,Oxygen Defect Engineered Magnetism of La2NiMnO6 Thin Films,"The double perovskite La2NiMnO6 (LNMO) exhibits complex magnetism due to the
competition of magnetic interactions that are strongly affected by structural
and magnetic inhomogeneities. In this work, we study the effect of oxygen
annealing on the structure and magnetism of epitaxial thin films grown by
pulsed laser deposition. The key observations are that a longer annealing time
leads to a reduction of saturation magnetization and an enhancement in the
ferromagnetic transition temperature. We explain these results based upon
epitaxial strain and oxygen defect engineering. The oxygen enrichment by
annealing caused a decrease in the volume of the perovskite lattice. This
increased the epitaxial strain of the films that are in-plane locked to the
SrTiO3 substrate. The enhanced strain caused a reduction in the saturation
magnetization due to randomly distributed anti-site defects. The reduced oxygen
defects concentration in the films due to the annealing in oxygen improved the
ferromagnetic long-range interaction and caused an increase in the magnetic
transition temperature.",2111.05037v1
2022/2/8,Electronic chiralization as an indicator of the anomalous Hall effect in unconventional magnetic systems,"The anomalous Hall effect (AHE) can appear in certain antiferromagnetic
metals when it is allowed by symmetry. Since the net magnetization is usually
small in such anomalous Hall antiferromagnets, it is useful to have other
physical indicators of the AHE that have the same symmetry properties as the
latter and can be conveniently measured and calculated. Here we propose such
indicators named as electronic chiralization (EC), which are constructed using
spatial gradients of spin and charge densities in general periodic crystals,
and can potentially be measured directly by scattering experiments. Such
constructions particularly reveal the important role of magnetic charge in the
AHE in unconventional magnetic systems with vanishing net magnetization. Guided
by the EC we give two examples of the AHE when magnetic charge is explicitly
present: A minimum honeycomb model inspired by the magnetic-charge-ordered
phase of kagome spin ice, and skew scattering of two-dimensional Dirac
electrons by magnetic charge.",2202.03581v2
2022/3/16,Advancing Superconducting Magnet Diagnostics for Future Colliders,"Future colliders will operate at increasingly high magnetic fields pushing
limits of electromagnetic and mechanical stress on the conductor [1].
Understanding factors affecting superconducting (SC) magnet performance in
challenging conditions of high mechanical stress and cryogenic temperatures is
only possible with the use of advanced magnet diagnostics. Diagnostics provide
a unique observation window into mechanical and electromagnetic processes
associated with magnet operation, and give essential feedback to magnet design,
simulations and material research activities. Development of novel diagnostic
capabilities is therefore an integral part of next-generation magnet
development. In this paper, we summarize diagnostics development needs from a
prospective of the US Magnet Development Program (MDP), and define main
research directions that could shape this field in the near future.",2203.08869v1
2022/3/26,Theoretical analysis of magnetic properties and the magnetocaloric effect using the Blume-Capel model,"This work investigates the magnetic properties and the magnetocaloric effect
in the spin-1 Blume-Capel model. The study was carried out using the mean-field
theory from the Bogoliubov inequality to obtain the expressions of free energy,
magnetization and entropy. The magnetocaloric effect was calculated from the
variation of the entropy obtained by the mean-field theory. Due to the
dependence on the external magnetic field and the anisotropy included in the
model, the results for the magnetocaloric effect provided the system with
first-order and continuous phase transitions. To ensure the results, the
Maxwell relations were used in the intervals where the model presents
continuous variations in magnetization and the Clausius-Clapeyron equation in
the intervals where the model presents discontinuity in the magnetization. The
methods and models for the analysis of a magnetic entropy change and
first-order and continuous magnetic phase transitions, such as mean-field
theory and the Blume-Capel model, are useful tools in understanding the nature
of the magnetocaloric effect and its physical relevance.",2203.14136v1
2022/3/30,Atomistic modeling of spin and electron dynamics in two-dimensional magnets switched by two-dimensional topological insulators,"To design fast memory devices, we need material combinations which can
facilitate fast read and write operation. We present a heterostructure
comprising a two-dimensional (2D) magnet and a 2D topological insulator (TI) as
a viable option for designing fast memory devices. We theoretically model
spin-charge dynamics between the 2D magnets and 2D TIs. Using the adiabatic
approximation, we combine the non-equilibrium Green's function method for
spin-dependent electron transport, and time-quantified Monte-Carlo for
simulating magnetization dynamics. We show that it is possible to switch the
magnetic domain of a ferromagnet using spin-torque from spin-polarized edge
states of 2D TI. We further show that the switching between TIs and 2D magnets
is strongly dependent on the interface exchange ($J_{\mathrm{int}}$), and an
optimal interface exchange depending on the exchange interaction within the
magnet is required for efficient switching. Finally, we compare the
experimentally grown Cr-compounds and show that Cr-compounds with higher
anisotropy (such as $\rm CrI_3$) results in lower switching speed but more
stable magnetic order.",2203.16008v1
2022/3/30,Exploring the hysteresis properties of nanocrystalline permanent magnets using deep learning,"We demonstrate the use of model order reduction and neural networks for
estimating the hysteresis properties of nanocrystalline permanent magnets from
microstructure. With a data-driven approach, we learn the demagnetization curve
from data-sets created by grain growth and micromagnetic simulations. We show
that the granular structure of a magnet can be encoded within a low-dimensional
latent space. Latent codes are constructed using a variational autoencoder. The
mapping of structure code to hysteresis properties is a multi-target regression
problem. We apply deep neural network and use parameter sharing, in order to
predict anchor points along the demagnetization curves from the magnet's
structure code. The method is applied to study the magnetic properties of
nanocrystalline permanent magnets. We show how new grain structures can be
generated by interpolation between two points in the latent space and how the
magnetic properties of the resulting magnets can be predicted.",2203.16676v1
2022/4/12,Solar Flares and Magnetic Helicity,"Solar flares and coronal mass ejections are the largest energy release
phenomena in the current solar system. They cause drastic enhancements of
electromagnetic waves of various wavelengths and sometimes eject coronal
material into the interplanetary space, disturbing the magnetic surroundings of
orbiting planets including the Earth. It is generally accepted that solar
flares are a phenomenon in which magnetic energy stored in the solar atmosphere
above an active region is suddenly released through magnetic reconnection.
Therefore, to elucidate the nature of solar flares, it is critical to estimate
the complexity of the magnetic field and track its evolution. Magnetic
helicity, a measure of the twist of coronal magnetic structures, is thus used
to quantify and characterize the complexity of flare-productive active regions.
This chapter provides an overview of solar flares and discusses how the
different concepts of magnetic helicity are used to understand and predict
solar flares.",2204.06010v1
2022/5/13,Precession dynamics of a small magnet with non-Markovian damping: Theoretical proposal for an experiment to determine the correlation time,"Recent advances in experimental techniques have made it possible to
manipulate and measure the magnetization dynamics on the femtosecond time scale
which is the same order as the correlation time of the bath degrees of freedom.
In the equations of motion of magnetization, the correlation of the bath is
represented by the non-Markovian damping. For development of the science and
technologies based on the ultrafast magnetization dynamics it is important to
understand how the magnetization dynamics depend on the correlation time. It is
also important to determine the correlation time experimentally. Here we study
the precession dynamics of a small magnet with the non-Markovian damping.
Extending the theoretical analysis of Miyazaki and Seki [J. Chem. Phys. 108,
7052 (1998)] we obtain analytical expressions of the precession angular
velocity and the effective damping constant for any values of the correlation
time under assumption of small Gilbert damping constant. We also propose a
possible experiment for determination of the correlation time.",2205.06399v1
2022/6/9,Nanomechanical Characterization of an Antiferromagnetic Topological Insulator,"The antiferromagnetic topological insulator MnBi2Te4 (MBT) exhibits an ideal
platform to study exotic topological phenomena and magnetic properties. The
transport signatures of magnetic phase transitions in the MBT family materials
have been well-studied. However, their mechanical properties and
magneto-mechanical coupling have not been well-explored. We use
nanoelectromechanical systems to study the intrinsic magnetism in MBT thin
flakes via their magnetostrictive coupling. We investigate mechanical resonance
signatures of magnetic phase transitions from antiferromagnetic (AFM) to canted
antiferromagnetic (cAFM) to ferromagnetic (FM) phases versus magnetic field at
different temperatures. The spin-flop transitions in MBT are revealed by
frequency shifts of mechanical resonance. With temperatures going above TN, the
transitions disappear in the resonance frequency map, consistent with transport
measurements. We use a magnetostrictive model to correlate the frequency shifts
with the spin-canting states. Our work demonstrates a technique to study
magnetic phase transitions, magnetization and magnetoelastic properties of the
magnetic topological insulator.",2206.04786v1
2022/8/25,Incommensurate Magnetic Order in Hole-Doped Infinite-layer Nickelate Superconductors,"Magnetism and superconductivity are closely entangled, elucidating the
magnetic interactions in nickelate superconductors is at the heart of
understanding the pairing mechanism. Our first-principles and spin-wave theory
calculations highlight that NdNiO$_2$ is in the vicinity of a transition
between a quasi-two-dimensional (2D) antiferromagnetic (AFM) state and a
three-dimensional (3D) C-AFM state. Both states could accurately reproduce the
experimentally measured magnetic excitation spectra, which was previously
explained in terms of a 2D model. We further reveal that hole doping stabilizes
an incommensurate (IC) spin state and the IC wave vector increases
continuously. Direct links between hole doping, magnetization, exchange
constants, and magnetic order are established, revealing that the competition
between first-neighbor and third-neighbor in-plane magnetic interactions is the
key for the IC magnetic order.",2208.12200v3
2022/9/5,Widely-sweeping magnetic field-temperature phase diagrams for skyrmion-hosting centrosymmetric tetragonal magnets,"We numerically investigate the stabilization mechanisms of skyrmion crystals
under thermal fluctuations and external magnetic field in itinerant
centrosymmetric tetragonal magnets. By adopting an efficient steepest descent
method with a small computational cost, we systematically construct the
magnetic field-temperature phase diagrams of the effective spin model derived
from the itinerant electron model on a two-dimensional square lattice. As a
result, we find that a square-type skyrmion crystal is stabilized by either or
both of the high-harmonic wave-vector interaction and the biquadratic
interaction under an external magnetic field. Especially, we discover that the
former high-harmonic wave-vector interaction can stabilize the skyrmion crystal
only at finite temperatures when its magnitude is small. In addition to the
skyrmion crystal, we also find other stable multiple-$Q$ states in the phase
diagram. Lastly, we discuss the correspondence of the phase diagrams between
the effective spin model and the skyrmion-hosting material GdRu$_2$Si$_2$. The
present results suggest a variety of multiple-$Q$ states could be driven by
thermal fluctuations and external magnetic fields in centrosymmetric itinerant
magnets.",2209.01810v1
2022/9/7,Intrinsic chiral field as vector potential of the magnetic current in the zig-zag lattice of magnetic dipoles,"Chiral magnetic insulators manifest novel phases of matter where the sense of
rotation of the magnetization is associated with exotic transport phenomena.
Effective control of such phases and their dynamical evolution points to the
search and study of chiral fields like the Dzyaloshinskii-Moriya interaction.
Here we combine experiments, numerics, and theory to study a zig-zag dipolar
lattice as a model of an interface between magnetic in-plane layers with
perpendicular magnetization. The zig-zag lattice comprises two parallel
sublattices of dipoles with perpendicular easy plane of rotation. The dipolar
energy of the system is exactly separable into a sum of symmetric and
antisymmetric long-range exchange interactions between dipoles, where the
antisymmetric coupling generates a nonlocal Dzyaloshinskii-Moriya field which
stabilizes winding textures with the form of chiral solitons. The
Dzyaloshinskii-Moriya interaction acts as a vector potential or gauge field of
the magnetic current and gives rise to emergent magnetic and electric fields
that allow the manifestation of the magnetoelectric effect in the system.",2209.03052v2
2022/10/19,Magnetic wallpaper Dirac fermions and topological magnetic Dirac insulators,"Topological crystalline insulators (TCIs) can host anomalous surface states
which inherits the characteristics of crystalline symmetry that protects the
bulk topology. Especially, the diversity of magnetic crystalline symmetries
indicates the potential for novel magnetic TCIs with distinct surface
characteristics. Here, we propose a topological magnetic Dirac insulator
(TMDI), whose two-dimensional surface hosts fourfold-degenerate Dirac fermions
protected by either the $p'_c4mm$ or $p4'g'm$ magnetic wallpaper group. The
bulk topology of TMDIs is protected by diagonal mirror symmetries, which give
chiral dispersion of surface Dirac fermions and mirror-protected hinge modes.
We propose candidate materials for TMDIs including Nd$_4$Te$_8$Cl$_4$O$_{20}$
and DyB$_4$ based on first-principles calculations, and construct a general
scheme for searching TMDIs using the space group of paramagnetic parent states.
Our theoretical discovery of TMDIs will facilitate future research on magnetic
TCIs and illustrate a distinct way to achieve anomalous surface states in
magnetic crystals.",2210.10740v2
2022/10/20,Encyclopedia of emergent particles in 528 magnetic layer groups and 394 magnetic rod groups,"We present a systematic classification of emergent particles in all 528
magnetic layer groups and 394 magnetic rod groups, which describe
two-dimensional and one-dimensional crystals respectively. Our approach is via
constructing a correspondence between a given magnetic layer/rod group and one
of the magnetic space group, such that all irreducible representations of the
layer/rod group can be derived from those of the corresponding space group.
Based on these group representations, we explicitly construct the effective
models for possible band degeneracies and identify all emergent particles,
including both spinless and spinful cases. We find that there are six kinds of
particles protected by magnetic layer groups and three kinds by magnetic rod
groups. Our work provides a useful reference for the search and design of
emergent particles in lower dimensional crystals.",2210.11080v2
2022/10/21,Anisotropy and crystallite misalignment in textured superconductors,"A misalignment of anisotropic crystallites causes small values of anisotropy
and decreases the critical current density of textured polycrystalline
superconductors. To relate the crystallite misalignment and out-plane
anisotropy, the magnetic properties of the textured Bi2223 polycrystalline
superconductor were investigated. A distribution of orientation angles of
crystallites was determined using different data: scanning electron microscopy
images and hysteresis magnetization loops when an external magnetic field was
applied at different angles with respect to the texturing plane of the sample.
It was demonstrated that the standard deviation of the distribution and the
magnetic disorder angle of crystallites in textured samples can be determined
from the magnetization data in perpendicular directions. These data may be
either the irreversible magnetization measured for two different orientations
of the sample or the simultaneously measured magnetization projections parallel
and perpendicular to the magnetic field.",2210.11712v1
2022/11/10,Tracing magnetic atom diffusion with annealing at the interface between CoMn alloy and MnGa layer by X-ray magnetic circular dichroism,"The magnetic atom diffusion at the interface between CoMn alloy and MnGa
layer with annealing is studied using x-ray magnetic circular dichroism (XMCD)
analysis. We found that the spins in bcc CoMn are coupled parallel to those in
perpendicularly magnetized MnGa layer under the as-grown conditions, while the
post-annealing modulates the interfacial magnetic coupling to antiferromagnetic
in Co. The element-specific hysteresis curves at each absorption edge revealed
the large coercive fields in Mn and Co through the exchange coupling with MnGa.
After the annealing process, the changes of XMCD spectral line shapes are
related to the interfacial reactions promoting the formation of Mn and Co2MnGa
layers, which is deduced from the analysis of transmission electron microscopy.
The interfacial diffusion of Mn atoms modulates the magnetic exchange coupling
between Mn and Co sites and reverses the direction of perpendicular
magnetization.",2211.05315v1
2023/2/3,Defect-induced magnetism in TiO$_2$: An example of quasi 2D magnetic order with perpendicular anisotropy,"Magnetic order at room temperature induced by atomic lattice defects, like
vacancies, interstitials or pairs of them, has been observed in a large number
of different nonmagnetic hosts, such as pure graphite, oxides and silicon-based
materials. High Curie temperatures and time independent magnetic response at
room temperature indicate the extraordinary robustness of this new phenomenon
in solid state magnetism. In this work, we review experimental and theoretical
results in pure TiO$_2$ (anatase), which magnetic order can be triggered by
low-energy ion irradiation. In particular, we discuss the systematic
observation of an ultrathin magnetic layer with perpendicular magnetic
anisotropy at the surface of this oxide.",2302.01803v1
2023/2/27,Rotating hematite cube chains,"Recently a two-dimensional chiral fluid was experimentally demonstrated. It
was obtained from cubic-shaped hematite colloidal particles placed in a
rotating magnetic field. Here we look at building blocks of that fluid, by
analyzing short hematite chain behavior in a rotating magnetic field. We find
equilibrium structures of chains in static magnetic fields and observe chain
dynamics in rotating magnetic fields. We find and experimentally verify that
there are three planar motion regimes and one where the cube chain goes out of
the plane of the rotating magnetic field. In this regime we observe interesting
dynamics -- the chain rotates slower than the rotating magnetic field. In order
to catch up with the magnetic field, it rolls on an edge and through rotation
in the third dimension catches up with the magnetic field. The same dynamics is
also observable for a single cube when gravitational effects are explicitly
taken into account.",2302.13978v3
2023/5/15,Magnetic bubble crystal in tetragonal magnets,"A magnetic bubble crystal is a two-dimensional soliton lattice consisting of
multiple spin density waves similar to a magnetic skyrmion crystal.
Nevertheless, the emergence of the bubble crystal with a collinear spin texture
is rare compared to that of the skyrmion crystal with a noncoplanar spin
texture. Here we theoretically report the stabilization mechanisms of the
bubble crystal in tetragonal magnets. By performing numerical calculations
based on an efficient steepest descent method for an effective spin model with
magnetic anisotropy and multiple spin interactions in momentum space on a
two-dimensional square lattice, we construct magnetic field-temperature phase
diagrams for various sets of model parameters. We find that the bubble crystal
is stabilized at finite temperatures near the skyrmion crystal by an easy-axis
anisotropic two-spin interaction. Through a detailed analysis, we also show
that the high-harmonic wave-vector interaction and the biquadratic interaction
play important roles in the stability of the bubble crystal. Our results
indicate a close relationship between the bubble crystal and the skyrmion
crystal in terms of the stabilization mechanisms, which suggests the
possibility of the bubble crystal in the skyrmion-hosting materials by
controlling the easy-axis magnetic anisotropy through external and/or chemical
pressure.",2305.08333v1
2023/5/23,Roughness-induced magnetic decoupling at organic-inorganic interface,"We have investigated structural, electronic and magnetic properties of
H$_2$Pc on Fe$_2$N/Fe using low-energy electron diffraction and soft x-ray
absorption spectroscopy/x-ray magnetic circular dichroism. Element specific
magnetization curves reveal that the magnetic coupling with H$_2$Pc enhances
the perpendicular magnetic anisotropy of Fe$_2$N/Fe at the H$_2$Pc coverage of
1 molecular layer. However, adding two and three molecular layers of H$_2$Pc
reverts the shape of magnetization curve back to the initial state before
H$_2$Pc deposition. We successfully link appearance and disappearance of the
magnetic coupling at the H$_2$Pc-Fe$_2$N/Fe interface with the change of
hybridization strength at N sites accompanied by the increase in the H$_2$Pc
coverage.",2305.13727v1
2023/5/25,Crystallization dynamics of magnetic skyrmions in a frustrated itinerant magnet,"We investigate the phase ordering kinetics of skyrmion lattice (SkL) in a
metallic magnet. The SkL can be viewed as a superposition of magnetic stripes
whose periods are determined by the quasi-nesting wave vectors of the
underlying Fermi surface. An effective magnetic Hamiltonian that describes the
electron-mediated spin-spin interaction is obtained for a two-dimensional s-d
model with the Rashba spin-orbit coupling. Large-scale Landau-Lifshitz-Gilbert
dynamics simulations based on the effective spin Hamiltonian reveal a two-stage
phase ordering of the SkL phase after a thermal quench. The initial fast
crystallization of skyrmions is followed by a slow relaxation dominated by the
annihilation dynamics of dislocations, which are topological defects of the
constituent magnetic stripe orders. The late-stage phase ordering also exhibits
a dynamical scaling symmetry. We further show that the annihilation of
dislocations follows a power-law time dependence with a logarithmic correction
that depends on magnetic fields. Implications of our results for SkL phases in
magnetic materials are also discussed.",2305.16182v1
2023/6/6,Time-reversal switching responses in antiferromagnets,"We propose emergent time-reversal switching responses in antiferromagnets,
which is triggered by an accompanying magnetic toroidal monopole, i.e.,
time-reversal odd scalar distinct from electric and magnetic monopoles. We show
that simple collinear antiferromagnets exhibit unconventional responses to
external electric and/or magnetic fields once magnetic symmetry accommodates
the magnetic toroidal monopole. We specifically demonstrate that the emergence
of the magnetic toroidal monopole in antiferromagnets enables us to control
rotational distortion by an external magnetic field, switch vortex-type
antiferromagnetic structure by an external electric field, and convert
right/left-handedness in chirality by a composite electromagnetic field. We
also present the symmetry conditions to induce the magnetic toroidal monopole
and exhibit candidate materials including noncollinear antiferromagnets in
order to stimulate experimental observations.",2306.04017v2
2023/6/21,A magnetic structure of ruthenium dioxide (RuO2) and altermagnetism,"The magnetic structure of RuO2 and the Ru atomic configuration are unknown. A
magnetic structure is inferred by confronting measured and calculated Bragg
diffraction patterns and adjusting the latter to achieve satisfactory
agreement. An accepted pattern, a magnetic symmetry, includes symmetry of sites
occupied by the magnetic ions. As a realistic starting point, we provide
diffraction patterns for a magnetic symmetry of RuO2, a descendent of the
tetragonal parent structure, which accommodates a departure of Ru axial dipoles
from the crystal c axis. A chiral signal and piezomagnetic effect are
permitted, and a linear magnetoelectric effect forbidden. Features of the
neutron diffraction pattern test the non-relativistic requirement of
altermagnetism, and we scrutinize published room-temperature data.
Specifically, one Bragg point is consistent with Ru orbital angular momentum
and magnetic quadrupole both zero, and the latter result is not expected from
non-relativistic altermagnetism. Azimuthal angle scans in resonant x-ray
diffraction are sensitive to the Ru site symmetry and the atomic configuration.
Acid tests of the studied magnetic symmetry include a chiral signature and null
intensity for unrotated photon polarization.",2306.12130v1
2023/8/2,Universal conductance fluctuations in a MnBi$_2$Te$_4$ thin film,"Quantum coherence of electrons can produce striking behaviors in mesoscopic
conductors, including weak localization and the Aharonov-Bohm effect. Although
magnetic order can also strongly affect transport, the combination of coherence
and magnetic order has been largely unexplored. Here, we examine quantum
coherence-driven universal conductance fluctuations in the antiferromagnetic,
canted antiferromagnetic, and ferromagnetic phases of a thin film of the
topological material MnBi$_2$Te$_4$. In each magnetic phase we extract a charge
carrier phase coherence length of about 100 nm. The conductance
magnetofingerprint is repeatable when sweeping applied magnetic field within
one magnetic phase, but changes when the applied magnetic field crosses the
antiferromagnetic/canted antiferromagnetic magnetic phase boundary.
Surprisingly, in the antiferromagnetic and canted antiferromagnetic phase, but
not in the ferromagnetic phase, the magnetofingerprint depends on the direction
of the field sweep. To explain these observations, we suggest that conductance
fluctuation measurements are sensitive to the motion and nucleation of magnetic
domain walls in MnBi$_2$Te$_4$.",2308.01183v1
2023/10/3,The influence of the magnetic field on the nucleation and properties of 0-degree domain boundaries in uniaxial films with inhomogeneous magnetoelectric interaction,"The paper investigates the behavior of 0 degree domain boundaries arising in
uniaxial magnetic films with flexomagnetoelectric effect in a magnetic field.
It is shown that at certain orientations of the magnetic field, it is possible
to significantly enhance (or weaken) the degree of manifestation of the
flexomagnetoelectric effect in the studied films. In addition, by varying the
magnitude and directions of the magnetic field, it is possible to significantly
lower (up to zero) the value of the critical electric field of the origin of
this inhomogeneity. It is also established that a 0 degree domain boundary of
non-Anelian type, in which induced bound charges do not create a resultant
field (field shielding), when a magnetic field directed perpendicular to the
plane of rotation of magnetic moments is applied, a flexomagnetoelectric effect
occurs, which increases with increasing magnitude of the magnetic field.",2310.01836v1
2023/10/7,Manipulation of magnetic topological textures via perpendicular strain and polarization in van der Waals magnetoelectric heterostructure,"Multi-functional manipulation of magnetic topological textures such as
skyrmions and bimerons in energy-efficient ways is of great importance for
spintronic applications, but still being a big challenge. Here, by
first-principles calculations and atomistic simulations, the creation and
annihilation of skyrmions/bimerons, as key operations for the reading and
writing of information in spintronic devices, are achieved in van der Waals
magnetoelectric CrISe/In2Se3 heterostructure via perpendicular strain or
electric field without external magnetic field. Besides, the bimeron-skyrmion
conversion, size modulation and the reversible magnetization switching from
in-plane to out-of-plane could also be realized in magnetic-field-free ways.
Moreover, the topological charge and morphology can be precisely controlled by
a small magnetic field. The strong Dzyaloshinskii-Moriya interaction and
tunable magnetic anisotropy energy in a wide window are found to play vital
roles in such energy efficient multi-functional manipulation, and the
underlying physical mechanisms are elucidated. Our work predicts the
CrISe/In2Se3 heterostructure being an ideal platform to address this challenge
in spintronic applications, and theoretically guides the low-dissipation
multi-functional manipulation of magnetic topological textures.",2310.04810v1
2023/10/25,Mapping the magnetic field using a magnetometer array with noisy input Gaussian process regression,"Ferromagnetic materials in indoor environments give rise to disturbances in
the ambient magnetic field. Maps of these magnetic disturbances can be used for
indoor localisation. A Gaussian process can be used to learn the spatially
varying magnitude of the magnetic field using magnetometer measurements and
information about the position of the magnetometer. The position of the
magnetometer, however, is frequently only approximately known. This negatively
affects the quality of the magnetic field map. In this paper, we investigate
how an array of magnetometers can be used to improve the quality of the
magnetic field map. The position of the array is approximately known, but the
relative locations of the magnetometers on the array are known. We include this
information in a novel method to make a map of the ambient magnetic field. We
study the properties of our method in simulation and show that our method
improves the map quality. We also demonstrate the efficacy of our method with
experimental data for the mapping of the magnetic field using an array of 30
magnetometers.",2310.16577v1
2023/11/17,First-principles investigation of the magnetoelectric properties of Ba$_7$Mn$_4$O$_{15}$,"Type-II multiferroics, in which the magnetic order breaks inversion symmetry,
are appealing for both fundamental and applied research due their intrinsic
coupling between magnetic and electrical orders. Using first-principles
calculations we study the ground state magnetic behaviour of
Ba$_7$Mn$_4$O$_{15}$ which has been classified as a type-II multiferroic in
recent experiments. Our constrained moment calculations with the proposed
experimental magnetic structure shows the spontaneous emergence of a polar mode
giving rise to an electrical polarisation comparable to other known type-II
multiferroics. When the constraints on the magnetic moments are removed, the
spins self-consistently relax into a canted antiferromagnetic ground state
configuration where two magnetic modes transforming as distinct irreducible
representations coexist. While the dominant magnetic mode matches well with the
previous experimental observations, the second mode is found to possess a
different character resulting in a non-polar ground state. Interestingly, the
non-polar magnetic ground state exhibits a significantly strong linear
magnetoelectric coupling comparable to the well-known multiferroic BiFeO$_3$,
suggesting strategies to design new linear magnetoelectrics.",2311.10555v1
2024/1/5,"Interlayer magnetic interactions and ferroelectricity in $π$/3-twisted CrX$_2$ (X = Se, Te) bilayers","Recently, two-dimensional (2D) bilayer magnetic systems have been widely
studied. Their interlayer magnetic interactions play a vital role in the
magnetic properties. In this paper, we theoretically studied the interlayer
magnetic interactions, magnetic states and ferroelectricity of $\pi$/3-twisted
CrX$_2$ (X = Se, Te) bilayers ($\pi$/3-CrX$_2$). Our study reveals that the
lateral shift could switch the magnetic state of the $\pi$/3-CrSe$_2$ between
interlayer ferromagnetic and antiferromagnetic, while just tuning the strength
of the interlayer antiferromagnetic interactions in $\pi$/3-CrTe$_2$.
Furthermore, the lateral shift can alter the off-plane electric polarization in
both $\pi$/3-CrSe$_2$ and $\pi$/3-CrTe$_2$. These results show that stacking is
an effective way to tune both the magnetic and ferroelectric properties of
1T-CrX$_2$ bilayers, making the 1T-CrX$_2$ bilayers hold promise for 2D
spintronic devices.",2401.02693v1
1997/11/22,Formation of the Ring-like Structure in the SN 1987A Nebula due to the Magnetic Pressure of the Toroidal Field,"Several weeks after the explosion of supernova (SN) 1987A, the UV flash of
the SN illuminated a ring-like structure in the circumstellar material at about
0.65 ly from the SN. The interaction between the stellar winds from the SN
progenitor is considered to be the candidate for the formation of the
circumstellar structure. In the case that the stellar winds are spherically
symmetric, the interaction should result in a shell-like structure. However, in
this paper we show that the magnetic field in the winds causes an anisotropy
which leads to the formation of a ring-like structure. When the fast wind of
the blue supergiant phase of the progenitor sweeps up the surrounding slow wind
of the red-supergiant phase, the magnetic field as well as the wind material
are piled up in the interaction region. Since the magnetic energy increases in
proportion to the square of the amplitude, the magnetic field exhibits its
effect prominently at the interaction region; due to the magnetic pressure
force the material at lower latitudes is compressed into a ring-like structure.
It is suggested that this magnetic process can also explain the newly observed
pair of rings of the SN 1987A nebula.",9711271v1
2005/6/28,"Geometric, electronic, and magnetic structure of Co$_2$FeSi: Curie temperature and magnetic moment measurements and calculations","In this work a simple concept was used for a systematic search for new
materials with high spin polarization. It is based on two semi-empirical
models. Firstly, the Slater-Pauling rule was used for estimation of the
magnetic moment. This model is well supported by electronic structure
calculations. The second model was found particularly for Co$_2$ based Heusler
compounds when comparing their magnetic properties. It turned out that these
compounds exhibit seemingly a linear dependence of the Curie temperature as
function of the magnetic moment. Stimulated by these models, Co$_2$FeSi was
revisited. The compound was investigated in detail concerning its geometrical
and magnetic structure by means of X-ray diffraction, X-ray absorption and
M\""o\ss bauer spectroscopies as well as high and low temperature magnetometry.
The measurements revealed that it is, currently, the material with the highest
magnetic moment ($6\mu_B$) and Curie-temperature (1100K) in the classes of
Heusler compounds as well as half-metallic ferromagnets. The experimental
findings are supported by detailed electronic structure calculations.",0506729v4
2008/9/20,Proposal for a [111] Magnetization Plateau in the Spin Liquid State of Tb2Ti2O7,"Despite a Curie-Weiss temperature $\theta_{\rm CW} \sim -14$ K, the Tb2Ti2O7
pyrochlore magnetic material lacks long range magnetic order down to at least
$T^*\approx 50$ mK. It has recently been proposed that the low temperature
collective paramagnetic or spin liquid regime of this material may be akin to a
spin ice state subject to both thermal and quantum fluctuations $-$ a {\it
quantum spin ice} (QSI) of sorts. Here we explore the effect of a magnetic
field ${\bm B}$ along the $[111]$ direction on the QSI state. To do so, we
investigate the magnetic properties of a microscopic model of Tb2Ti2O7 in an
independent tetrahedron approximation in a finite ${\bm B}$ along $[111]$. Such
a model describes semi-quantitatively the collective paramagnetic regime where
nontrivial spin correlations start to develop at the shortest lengthscale, that
is over a single tetrahedron, but where no long range order is yet present. Our
results show that a magnetization plateau develops at low temperatures as the
system develops ${\bm B}=0$ ferromagnetic spin-ice-like ""two-in/two-out""
correlations at the shortest lengthscale. From these results, we are led to
propose that the observation of such a [111] magnetization plateau in Tb2Ti2O7
would provide compelling evidence for a QSI at ${\bm B}=0$ in this material and
help guide the development of a theory for the origin of its spin liquid state.",0809.3477v2
2011/4/18,Magnetic order in quasi-two-dimensional molecular magnets investigated with muon-spin relaxation,"We present the results of a muon-spin relaxation (muSR) investigation into
magnetic ordering in several families of layered quasi-two-dimensional
molecular antiferromagnets based on transition metal ions such as S=1/2 Cu2+
bridged with organic ligands such as pyrazine. In many of these materials
magnetic ordering is difficult to detect with conventional magnetic probes. In
contrast, muSR allows us to identify ordering temperatures and study the
critical behavior close to T_N . Combining this with measurements of in-plane
magnetic exchange J and predictions from quantum Monte Carlo simulations we may
assess the degree of isolation of the 2D layers through estimates of the
effective inter-layer exchange coupling and in-layer correlation lengths at T_N
. We also identify the likely metal-ion moment sizes and muon stopping sites in
these materials, based on probabilistic analysis of the magnetic structures and
of muon-fluorine dipole-dipole coupling in fluorinated materials.",1104.3505v2
2013/7/18,Numerical response of the magnetic permeability as a funcion of the frecuency of NiZn ferrites using Genetic Algorithm,"The magnetic permeability of a ferrite is an important factor in designing
devices such as inductors, transformers, and microwave absorbing materials
among others. Due to this, it is advisable to study the magnetic permeability
of a ferrite as a function of frequency.
  When an excitation that corresponds to a harmonic magnetic field \textbf{H}
is applied to the system, this system responds with a magnetic flux density
\textbf{B}; the relation between these two vectors can be expressed as
\textbf{B}=$\mu(\omega)$ \textbf{H} . Where $\mu$ is the magnetic permeability.
  In this paper, ferrites were considered linear, homogeneous, and isotropic
materials. A magnetic permeability model was applied to NiZn ferrites doped
with Yttrium.
  The parameters of the model were adjusted using the Genetic Algorithm. In the
computer science field of artificial intelligence, Genetic Algorithms and
Machine Learning does rely upon nature's bounty for both inspiration nature's
and mechanisms. Genetic Algorithms are probabilistic search procedures which
generate solutions to optimization problems using techniques inspired by
natural evolution, such as inheritance, mutation, selection, and crossover.
  For the numerical fitting usually is used a nonlinear least square method,
this algorithm is based on calculus by starting from an initial set of variable
values. This approach is mathematically elegant compared to the exhaustive or
random searches but tends easily to get stuck in local minima. On the other
hand, random methods use some probabilistic calculations to find variable sets.
They tend to be slower but have greater success at finding the global minimum
regardless of the initial values of the variables",1307.5007v1
2014/7/28,Microscopic electronic configurations after ultrafast magnetization dynamics,"We provide a model for the prediction of the electronic and magnetic
configurations of ferromagnetic Fe after an ultrafast decrease or increase of
magnetization. The model is based on the well-grounded assumption that, after
the ultrafast magnetization change, the system achieves a partial thermal
equilibrium. With statistical arguments it is possible to show that the
magnetic configurations are qualitatively different in the case of reduced or
increased magnetization. The predicted magnetic configurations are then used to
compute the dielectric response at the 3p (M) absorption edge, which can be
related to the changes observed in the experimental T-MOKE data. The good
qualitative agreement between theory and experiment offers a substantial
support to the existence of an ultrafast increase of magnetisation, which has
been fiercely debated in the last years.",1407.7411v2
2014/8/28,A pathway to optimize the properties of magnetocaloric MnxFe2-x(P1-yGey) for magnetic refrigeration,"Magnetocaloric materials can be useful in magnetic refrigeration
applications, but to be practical the magneto-refrigerant needs to have a very
large magnetocaloric effect (MCE) near room temperature for modest applied
fields (<2 Tesla) with small hysteresis and magnetostriction, and should have a
complete magnetic transition, be inexpensive, and environmentally friendly. One
system that may fulfill these requirements is MnxFe2-xP1-yGey, where a combined
first-order structural and magnetic transition occurs between the high
temperature paramagnetic and low temperature ferromagnetic phase. We have used
neutron diffraction, differential scanning calorimetry, and magnetization
measurements to study the effects of Mn and Ge location in the structure on the
ordered magnetic moment, MCE, and hysteresis for a series of compositions of
the system near optimal doping. The diffraction results indicate that the Mn
ions located on the 3f site enhance the desirable properties, while those
located on the 3g sites are detrimental. The entropy changes measured directly
by calorimetry can exceed 40 J/kg-K. The phase fraction that transforms,
hysteresis of the transition, and entropy change can be controlled by both the
compositional homogeneity and the particle size, and an annealing procedure has
been developed that substantially improves the performance of all three
properties of the material. On the basis of these results we have identified a
pathway to optimize the MCE properties of this system for magnetic
refrigeration applications.",1408.6791v1
2014/11/18,Spin transfer torques generated by the anomalous Hall effect and anisotropic magnetoresistance,"Spin-orbit coupling in ferromagnets gives rise to the anomalous Hall effect
and the anisotropic magnetoresistance, both of which can be used to create
spin-transfer torques in a similar manner as the spin Hall effect. In this
paper we show how these effects can be used to reliably switch perpendicularly
magnetized layers and to move domain walls. A drift-diffusion treatment of the
anomalous Hall effect and the anisotropic magnetoresistance describes the spin
currents that flow in directions perpendicular to the electric field. In
systems with two ferromagnetic layers separated by a spacer layer, an in-plane
electric field cause spin currents to be injected from one layer into the
other, creating spin transfer torques. Unlike the related spin Hall effect in
non-magnetic materials, the anomalous Hall effect and the anisotropic
magnetoresistance allow control of the orientation of the injected spins, and
hence torques, by changing the direction of the magnetization in the injecting
layer. The torques on one layer show a rich angular dependence as a function of
the orientation of the magnetization in the other layer. The control of the
torques afforded by changing the orientation of the magnetization in a fixed
layer makes it possible to reliably switch a perpendicularly magnetized free
layer. Our calculated critical current densities for a representative
CoFe/Cu/FePt structure show that the switching can be efficient for appropriate
material choices. Similarly, control of the magnetization direction can drive
domain wall motion, as shown for NiFe/Cu/NiFe structures.",1411.4863v1
2016/2/26,Two types of all-optical magnetization switching mechanisms using femtosecond laser pulses,"Magnetization manipulation in the absence of an external magnetic field is a
topic of great interest, since many novel physical phenomena need to be
understood and promising new applications can be imagined. Cutting-edge
experiments have shown the capability to switch the magnetization of magnetic
thin films using ultrashort polarized laser pulses. In 2007, it was first
observed that the magnetization switching for GdFeCo alloy thin films was
helicity-dependent and later helicity-independent switching was also
demonstrated on the same material. Recently, all-optical switching has also
been discovered for a much larger variety of magnetic materials (ferrimagnetic,
ferromagnetic films and granular nanostructures), where the theoretical models
explaining the switching in GdFeCo films do not appear to apply, thus
questioning the uniqueness of the microscopic origin of all-optical switching.
Here, we show that two different all-optical switching mechanisms can be
distinguished; a ""single pulse"" switching and a ""cumulative"" switching process
whose rich microscopic origin is discussed. We demonstrate that the latter is a
two-step mechanism; a heat-driven demagnetization followed by a
helicity-dependent remagnetization. This is achieved by an all-electrical and
time-dependent investigation of the all-optical switching in ferrimagnetic and
ferromagnetic Hall crosses via the anomalous Hall effect, enabling to probe the
all-optical switching on different timescales.",1602.08525v2
2017/6/11,First principles study of the structural phase stability and magnetic order in various structural phases of Mn$_2$FeGa,"We investigate the structural and magnetic properties of Mn$_{2}$FeGa for
different phases(cubic, hexagonal and tetragonal) reported experimentally using
density functional theory. The relative structural stabilities, and the
possible phase transformation mechanisms are discussed using results for total
energy, electronic structure and elastic constants. We find that the phase
transformation form hexagonal to ground state tetragonal structure would take
place through a Heusler-like phase which has a pronounced electronic
instability. The electronic structures, the elastic constants and the
supplementary phonon dispersions indicate that the transition from the
Heusler-like to the tetragonal phase is of pure Jahn-Teller origin. We also
describe the ground state magentic structures in each phase by computations of
the exchange interactions. For Heusler-like and tetragonal phases, the
ferromagnetic exchange interactions associated with the Fe atoms balance the
dominating antiferromagnetic interactions between the Mn atoms leading to
collinear magnetic structures. In the hexagonal phase, the direction of atomic
moment are completely in the planes with a collinear like structure, in stark
contrast to the well known non-collinear magnetic structure in the hexagonal
phase of Mn$_{3}$Ga, another material with similar structural properties. The
overwhelmingly large exchange interactions of Fe with other magnetic atoms
destroy the possibility of magnetic frustration in the hexagonal phase of
Mn$_{2}$FeGa. This comprehensive study provides significant insights into the
microscopic physics associated with the structural and magnetic orders in this
compound.",1706.03425v1
2018/3/7,Highly thermally stable sub-20nm magnetic random-access memory based on perpendicular shape anisotropy,"A new approach to increase the downsize scalability of perpendicular STT-MRAM
is presented. It consists in significantly increasing the thickness of the
storage layer in out-of-plane magnetized tunnel junctions (pMTJ) as compared to
conventional pMTJ in order to induce a perpendicular shape anisotropy (PSA) in
this layer. This PSA is obtained by depositing a thick ferromagnetic (FM) layer
on top of an MgO/FeCoB based magnetic tunnel junction (MTJ) so that the
thickness of the storage layer becomes of the order or larger than the diameter
of the MTJ pillar. In contrast to conventional spin transfer torque magnetic
random access memory (STT-MRAM) wherein the demagnetizing energy opposes the
interfacial perpendicular magnetic anisotropy (iPMA), in these novel memory
cells, both PSA and iPMA contributions favor out-of-plane orientation of the
storage layer magnetization. Using thicker storage layers in these PSA-STT-MRAM
has several advantages. Thanks to the PSA, very high and easily tunable thermal
stability factors can be achieved, even down to sub-10 nm diameters. Moreover,
low damping material can be used for the thick FM material thus leading to a
reduction of the write current. The paper describes this new PSA-STT-MRAM
concept, practical realization of such memory arrays, magnetic characterization
demonstrating thermal stability factor above 200 for MTJs as small as 8nm in
diameter and possibility to maintain thermal stability factor above 60 down to
4nm diameter.",1803.02663v1
2018/7/13,Absence of induced magnetic monopoles in Maxwellian magnetoelectrics,"The electromagnetic response of topological insulators is governed by axion
electrodynamics, which features a topological magnetoelectric term in the
Maxwell equations. As a consequence magnetic fields become the source of
electric fields and vice-versa, a phenomenon that is general for any material
exhibiting a linear magnetoelectric effect. Axion electrodynamics has been
associated with the possibility to create magnetic monopoles, in particular by
an electrical charge that is screened above the surface of a magnetoelectric
material. Here we explicitly solve for the electromagnetic fields in this
geometry and show that while vortex-like magnetic screening fields are
generated by the electrical charge their divergence is identically zero at
every point in space which implies an absence of induced magnetic monopoles.
Nevertheless magnetic image charges can be made explicit in the problem and
even if no bound state with electric charges yielding a dyon arises, a
dyon-like angular momentum follows from our analysis. Because of its dependence
on the dielectric constant this angular momentum is not quantized, which is
consistent with a general argument that precludes magnetic monopoles to be
generated in Maxwell magnetoelectrics. We also solve for topologically
protected zero modes in the Dirac equation induced by the point charge. Since
the induced topological defect on the TI surface carries an electric charge as
a result of the axion term, these zero modes are not self-conjugated.",1808.08825v4
2018/12/13,"Noncentrosymmetric compensated half-metal hosting pure spin Weyl nodes, triple nodal points, nodal loops, and nexus fermions","Materials containing multiple topological characteristics become more exotic
when combined with noncentrosymmetric crystal structures and unusual magnetic
phases such as the compensated half-metal state, which is gapped in one spin
direction and conducting in the other. First principles calculations reveal
these multiple topological features in the compensated half-metal Cr$_2$CoAl
having neither time-reversal nor inversion symmetries. In the absence of
(minor) spin-orbit coupling (SOC), there are (1) a total of twelve pairs of
magnetic Weyl points, (2) three distinct sets of triple nodal points near the
Fermi level that are (3) interconnected with six symmetry related nodal lines.
This combination gives rise to fully spin polarized nexus fermions, in a system
with broken time-reversal symmetry but negligible macroscopic magnetic field.
The observed high Curie temperature of 750 K and calculated SOC hybridization
mixing of several meV should make these nexus fermions readily measurable.
Unlike topological features discussed for other Heuslers which emphasize their
strong ferromagnetism, this compensated half-metal is impervious to typical
magnetic fields, thus providing a complementary set of experimental phenomena.
Making use of the soft calculated magnetic state, large magnetic fields can be
used to rotate the direction of magnetism, during which certain topological
features will evolve. Our results suggest that these features may be common in
inverse-Heusler systems, particularly the isostructural and isovalent Ga and In
analogs.",1812.05273v2
2018/9/27,Design of magnetic spirals in layered perovskites: extending the stability range far beyond room temperature,"In insulating materials with ordered magnetic spiral phases, ferroelectricity
can emerge due to the breaking of inversion symmetry. This property is of both
fundamental and practical interest, in particular with a view to exploiting it
in low-power electronic devices. Advances towards technological applications
have been hindered, however, by the relatively low ordering temperatures
$T_\mathrm{spiral}$ of most magnetic spiral phases, which rarely exceed 100 K.
We have recently established that the ordering temperature of a magnetic spiral
can be increased up to 310 K by the introduction of chemical disorder. Here we
explore the design space opened up by this novel mechanism by combining it with
a targeted lattice control of some magnetic interactions. In Cu-Fe layered
perovskites we obtain $T_\mathrm{spiral}$ values close to 400 K, comfortably
far from room temperature and almost 100 K higher than using chemical disorder
alone. Moreover, we reveal a linear, universal relationship between the
spiral's wave vector and the onset temperature of the spiral phase. This linear
law ends at a paramagnetic-collinear-spiral triple point, which defines the
highest spiral ordering temperature that can be achieved in this class of
materials. Based on these findings, we propose a general set of rules for
designing magnetic spirals in layered perovskites using external pressure,
chemical substitutions and/or epitaxial strain, which should guide future
efforts to engineer magnetic spiral phases with ordering temperatures suitable
for technological applications.",1809.10395v1
2019/9/10,"Twisting and tweezing the spin wave: on vortices, skyrmions, helical waves, and the magnonic spiral phase plate","Spin waves are the low-energy excitations of magnetically ordered materials.
They are key elements in the stability analysis of the ordered phase and have a
wealth of technological applications. Recently, we showed that spin waves of a
magnetic nanowire may carry a definite amount of orbital angular momentum
components along the propagation direction. This helical, in addition to the
chiral, character of the spin waves is related to the spatial modulations of
the spin wave phase across the wire. It, however, remains a challenge to
generate and control such modes with conventional magnetic fields. Here, we
make the first proposal for a \textit{magnetic} spiral phase plate by
appropriately synthesizing two magnetic materials that have different speeds of
spin waves. It is demonstrated with full-numerical micromagnetic simulations
that despite the complicated structure of demagnetization fields, a homogeneous
spin wave passing through the spiral phase plate attains the required twist and
propagates further with the desired orbital angular momentum. While excitations
from the ordered phase may have a twist, the magnetization itself can be
twisted due to internal fields and forms what is known as a magnetic vortex. We
point out the differences between both types of magnetic phenomena and discuss
their possible interaction.",1909.04457v2
2020/2/28,Traps for pinning and scattering of antiferromagnetic skyrmions via magnetic properties engineering,"Micromagnetic simulations have been performed to investigate the
controllability of the skyrmion position in antiferromagnetic nanotracks with
their magnetic properties modified spatially. In this study we have modeled
magnetic defects as local variations on the material parameters, such as the
exchange stiffness, saturation magnetization, perpendicular magnetocrystalline
anisotropy and Dzyaloshinskii-Moriya constant. Thus, we have observed not only
pinning (potential well) but also scattering (potential barrier) of
antiferromagnetic skyrmions, when adjusting either a local increase or a local
reduction for each material parameter. In order to control of the skyrmion
motion it is very important to impose certain positions along the nanotrack
where the skyrmion can stop. Magnetic defects incorporated intentionally in
antiferromagnetic racetracks can be useful for such purpose. In order to
provide guidelines for experimental studies, we vary both material parameters
and size of the modified region. The found results show that the efficiency of
skyrmion trap depends on a suitable combination of magnetic defect parameters.
Furthermore, we discuss the reason why skyrmions are either attracted or
repelled by a region magnetically modified.",2003.00907v2
2020/3/6,"Strengthening the magnetic interactions in pseudobinary first-row transition metal thiocyanates, $\it{M}$(NCS)$_{2}$","Understanding the effect of chemical composition on the strength of magnetic
interactions is key to the design of magnets with stronger exchange
interactions. The magnetic divalent first-row transition metal (TM)
thiocyanates are a class of chemically simple layered molecular frameworks.
Here, we report two new members of the family, manganese (II) thiocyanate,
Mn(NCS)$_{2}$, and iron (II) thiocyanate, Fe(NCS)$_{2}$. Using magnetic
susceptibility measurements on these materials and on cobalt (II) thiocyanate
and nickel (II) thiocyanate, Co(NCS)$_{2}$ and Ni(NCS)$_{2}$, respectively, we
identify significantly stronger net antiferromagnetic interactions between the
earlier TM ions-a decrease in the Weiss constant, \theta, from 29 K for
Ni(NCS)$_{2}$ to -115 K for Mn(NCS)$_{2}$-a consequence of more diffuse 3d
orbitals, increased orbital overlap and increasing numbers of unpaired
$\it{t}$$_{2g}$ electrons. We elucidate the magnetic structures of these
materials: Mn(NCS)$_{2}$, Fe(NCS)$_{2}$ and Co(NCS)$_{2}$ order into the same
antiferromagnetic commensurate ground state, whilst Ni(NCS)$_{2}$ adopts a
ground state structure consisting of ferromagnetically ordered layers stacked
antiferromagnetically. We show that magnetic molecular frameworks with
significantly stronger net exchange interactions can be constructed by using
earlier TMs.",2003.03448v5
2020/4/6,Spin Hall magnetoresistance in antiferromagnetic insulators,"Antiferromagnetic materials promise improved performance for spintronic
applications, as they are robust against external magnetic field perturbations
and allow for faster magnetization dynamics compared to ferromagnets. The
direct observation of the antiferromagnetic state, however, is challenging due
to the absence of a macroscopic magnetization. Here, we show that the spin Hall
magnetoresistance (SMR) is a versatile tool to probe the antiferromagnetic spin
structure via simple electrical transport experiments by investigating the
easy-plane antiferromagnetic insulators $\alpha$-Fe2O3 (hematite) and NiO in
bilayer heterostructures with a Pt heavy metal top electrode. While rotating an
external magnetic field in three orthogonal planes, we record the longitudinal
and the transverse resistivities of Pt and observe characteristic resistivity
modulations consistent with the SMR effect. We analyze both their amplitude and
phase and compare the data to the results from a prototypical collinear
ferrimagnetic Y3Fe5O12/Pt bilayer. The observed magnetic field dependence is
explained in a comprehensive model, based on two magnetic sublattices and
taking into account magnetic field-induced modifications of the domain
structure. Our results show that the SMR allows us to understand the spin
configuration and to investigate magnetoelastic effects in antiferromagnetic
multi-domain materials. Furthermore, in $\alpha$-Fe2O3/Pt bilayers, we find an
unexpectedly large SMR amplitude of $2.5 \times 10^{-3}$, twice as high as for
prototype Y3Fe5O12/Pt bilayers, making the system particularly interesting for
room-temperature antiferromagnetic spintronic applications.",2004.02639v2
2021/4/16,Interlayer magnetophononic coupling in MnBi2Te4,"The emergence of magnetism in quantum materials creates a platform to realize
spin-based applications in spintronics, magnetic memory, and quantum
information science. A key to unlocking new functionalities in these materials
is the discovery of tunable coupling between spins and other microscopic
degrees of freedom. We present evidence for interlayer magnetophononic coupling
in the layered magnetic topological insulator MnBi2Te4. Employing magneto-Raman
spectroscopy, we observe anomalies in phonon scattering intensities across
magnetic field-driven phase transitions, despite the absence of discernible
static structural changes. This behavior is a consequence of a magnetophononic
wave-mixing process that allows for the excitation of zone-boundary phonons
that are otherwise 'forbidden' by momentum conservation. Our microscopic model
based on density functional theory calculations reveals that this phenomenon
can be attributed to phonons modulating the interlayer exchange coupling.
Moreover, signatures of magnetophononic coupling are also observed in the time
domain through the ultrafast excitation and detection of coherent phonons
across magnetic transitions. In light of the intimate connection between
magnetism and topology in MnBi2Te4, the magnetophononic coupling represents an
important step towards coherent on-demand manipulation of magnetic topological
phases.",2104.08356v2
2014/4/2,Twisted magnetic patterns: Exploring the Dzyaloshinskii--Moriya vector,"Magnetism - the spontaneous alignment of atomic moments in a material - is
driven by quantum-mechanical `exchange' interactions which operate over atomic
distances as a result of the fundamental symmetry of electrons. Currently, one
of the most active fields of condensed matter physics involves the study of
magnetic interactions that cause, or are caused by a twisting of nearby atoms.
This can lead to the magnetoelectric effect that couples electric and magnetic
properties, and is predicted to play a prominent role in future technology.
Here, we discuss the complex relativistic interplay between magnetism and
atomic crystal structure in a class of materials called `weak ferromagnets'.
The sign of the underpinning Dzyaloshinskii--Moriya interaction has been
determined for the first time, by using synchrotron radiation to study iron
borate (FeBO3). We present a novel experimental technique based on interference
between two x-ray scattering processes (one acts as a reference wave) which we
combine with a second unusual approach of turning the atomic antiferromagnetic
motif with a small magnetic field. We show that the experimental results
provide a clear validation of state-of-the-art theoretical calculations. These
experimental and theoretical approaches open up new possibilities for
exploring, modelling and exploiting novel magnetic and magnetoelectric
materials.",1404.0501v1
2019/2/15,Interlayer RKKY Coupling in Bulk Rashba Semiconductors under Topological Phase Transition,"The bulk Rashba semiconductors BiTeX (X=I, Cl and Br) with intrinsically
enhanced Rashba spin-orbit coupling provide a new platform for investigation of
spintronic and magnetic phenomena in materials. We theoretically investigate
the interlayer exchange interaction between two ferromagnets deposited on
opposite surfaces of a bulk Rashba semiconductor BiTeI in its trivial and
topological insulator phases. In the trivial phase BiTeI, we find that for
ferromagnets with a magnetization orthogonal to the interface, the exchange
coupling is reminiscent of that of a conventional three-dimensional metal.
Remarkably, ferromagnets with a magnetization parallel to the interface display
a magnetic exchange qualitatively different from that of conventional
three-dimensional metal due to the spin-orbit coupling. In this case, the
interlayer exchange interaction acquires two periods of oscillations and decays
as the inverse of the thickness of the BiTeI layer. For topological BiTeI, the
magnetic exchange interaction becomes mediated only by the helical surface
states and acts between the one-dimensional spin chains at the edges of the
sample. The surface state-mediated interlayer exchange interaction allows for
the coupling of ferromagnets with non-collinear magnetization and displays a
decay power different from that of trivial BiTeI, allowing the detection of the
topological phase transition in this material. Our work provides insights into
the magnetic properties of these newly discovered materials and their possible
functionalization.",1902.06001v2
2019/4/2,Electric field assisted amplification of magnetic fields in tilted Dirac cone systems,"We show that the continuum limit of the tilted Dirac cone in materials such
as $8Pmmn$-borophene and layered organic conductor $\alpha$-(BEDT-TTF)$_2$I$_3$
deformation of the Minkowski spacetime of Dirac materials. From its Killing
vectors we construct an emergent tilted-Lorentz (t-Lorentz) symmetry group for
such systems. With t-Lorentz transformations we are able to obtain the exact
solution of the Landau bands for a crossed configuration of electric and
magnetic fields. For any given tilt parameter $0\le\zeta<1$ if the ratio
$\chi=v_FB_z/cE_y$ of the crossed magnetic and electric fields that satisfies
$\chi\ge 1+\zeta$ one can always find appropriate t-boosts in both valleys
labeled by $\pm$ in such a way the electric field can be t-boosted away,
whereby the resulting pure effective magnetic field $B^\pm_z$ governs the
Landau level spectrum around each valley. The effective magnetic field in one
of the valleys is always larger than the applied perpendicular magnetic field.
This amplification comes at the expense of of diminishing the effective field
in the opposite valleyand can be detected in various quantum oscillation
phenomena in tilted Dirac cone systems. Tuning the ratio of electric and
magnetic fields to $\chi_{\rm min}=1+\zeta$ leads to valley selective collapse
of Landau levels. Our geometric description of the tilt in Dirac systems
reveals an important connection between the tilt and an incipient ""rotating
source"" when the tilt parameter can be made to depend on spacetime in certain
way.",1904.01328v2
2019/5/22,Ultra-low magnetic damping in Co 2 Mn-based Heusler compounds: promising materials for spintronic,"The prediction of ultra-low magnetic damping in Co 2 MnZ Heusler half-metal
thin-film magnets is explored in this study and the damping response is shown
to be linked to the underlying electronic properties. By substituting the Z
elements in high crystalline quality films (Co 2 MnZ with Z=Si, Ge, Sn, Al, Ga,
Sb), electronic properties such as the minority spin band gap, Fermi energy
position in the gap and spin polarization can be tuned and the consequence on
magnetization dynamics analyzed. The experimental results allow us to directly
explore the interplay of spin polarization, spin gap, Fermi energy position and
the magnetic damping obtained in these films, together with ab initio
calculation predictions. The ultra-low magnetic damping coefficients measured
in the range 4.1 10-4-9 10-4 for Co 2 MnSi, Ge, Sn, Sb are the lowest values
obtained on a conductive layer and offers a clear experimental demonstration of
theoretical predictions on Half-Metal Magnetic Heusler compounds and a pathway
for future materials design.",1905.08987v1
2019/5/31,Fingerprints of Kitaev physics in the magnetic excitations of honeycomb iridates,"In the quest for realizations of quantum spin liquids, the exploration of
Kitaev materials - spin-orbit entangled Mott insulators with strong
bond-directional exchanges - has taken center stage. However, in these
materials the local spin-orbital j=1/2 moments typically show long-range
magnetic order at low temperature, thus defying the formation of a spin-liquid
ground state. Using resonant inelastic x-ray scattering (RIXS), we here report
on a proximate spin liquid regime with clear fingerprints of Kitaev physics in
the magnetic excitations of the honeycomb iridates alpha-Li2IrO3 and Na2IrO3.
We observe a broad continuum of magnetic excitations that persists up to at
least 300K, more than an order of magnitude larger than the magnetic ordering
temperatures. We prove the magnetic character of this continuum by an analysis
of the resonance behavior. RIXS measurements of the dynamical structure factor
for energies within the continuum show that dynamical spin-spin correlations
are restricted to nearest neighbors. Notably, these spectroscopic observations
are also present in the magnetically ordered state for excitation energies
above the conventional magnon excitations. Phenomenologically, our data agree
with inelastic neutron scattering results on the related honeycomb compound
RuCl3, establishing a common ground for a proximate Kitaev spin-liquid regime
in these materials.",1905.13590v1
2019/12/2,Direct demonstration of topological stability of magnetic skyrmions via topology manipulation,"Topological protection precludes a continuous deformation between
topologically inequivalent configurations in a continuum. Motivated by this
concept, magnetic skyrmions, topologically nontrivial spin textures, are
expected to exhibit the topological stability, thereby offering a prospect as a
nanometer-scale non-volatile information carrier. In real materials, however,
atomic spins are configured as not continuous but discrete distribution, which
raises a fundamental question if the topological stability is indeed preserved
for real magnetic skyrmions. Answering this question necessitates a direct
comparison between topologically nontrivial and trivial spin textures, but the
direct comparison in one sample under the same magnetic fields has been
challenging. Here we report how to selectively achieve either a skyrmion state
or a topologically trivial bubble state in a single specimen and thereby show
how robust the skyrmion structure is in comparison with the bubbles for the
first time. We demonstrate that topologically nontrivial magnetic skyrmions
show longer lifetimes than trivial bubble structures, evidencing the
topological stability in a real discrete system. Our work corroborates the
physical importance of the topology in the magnetic materials, which has
hitherto been suggested by mathematical arguments, providing an important step
towards ever-dense and more-stable magnetic devices.",1912.00630v2
2020/6/25,Observation of Weyl fermions in a magnetic non-centrosymmetric crystal,"Characterized by the absence of inversion symmetry, non-centrosymmetric
materials are of great interest because they exhibit ferroelectricity, second
harmonic generation, emergent Weyl fermions, and other fascinating phenomena.
It is expected that if time-reversal symmetry is also broken, additional
magneto-electric effects can emerge from the interplay between magnetism and
electronic order. Here we report topological conducting properties in the
non-centrosymmetric magnet PrAlGe. By photoemission spectroscopy, we observe an
arc parametrizing surface-localized states---a topological arc. Using the
bulk-boundary correspondence, we conclude that these arcs correspond to
projected topological charges of $\pm{1}$ in the surface Brillouin zone,
demonstrating the presence of magnetic Weyl quasiparticles in bulk. We further
observe a large anomalous Hall response, arising from diverging bulk Berry
curvature fields associated with the magnetic Weyl band structure. Our results
demonstrate a topological phase with robust electronic surface states and
anomalous transport in a non-centrosymmetric magnet for the first time,
providing a novel material platform to study the interplay between magnetic
order, band topology and transport.",2006.14713v1
2020/7/28,"Critical behavior of ferromagnets CrI3, CrBr3, CrGeTe3, and anti-ferromagnet FeCl2: a detailed first-principles study","We calculate the Curie temperature of layered ferromagnets, chromium
tri-iodide (CrI3), chromium tri-bromide (CrBr3), chromium germanium
tri-telluride (CrGeTe3), and the Neel temperature of a layered anti-ferromagnet
iron di-chloride (FeCl2), using first-principles density functional theory
calculations and Monte-Carlo simulations. We develop a computational method to
model the magnetic interactions in layered magnetic materials and calculate
their critical temperature. We provide a unified method to obtain the magnetic
exchange parameters (J) for an effective Heisenberg Hamiltonian from
first-principles, taking into account both the magnetic ansiotropy as well as
the out-of-plane interactions. We obtain the magnetic phase change behavior, in
particular the critical temperature, from the susceptibility and the
specific-heat, calculated using the three-dimensional Monte-Carlo (Metropolis)
algorithm. The calculated Curie temperatures for ferromagnetic materials (CrI3,
CrBr3 and CrGeTe3), match very well with experimental values. We show that the
interlayer interaction in bulk CrI3 with R3 stacking is significantly stronger
than the C2/m stacking, in line with experimental observations. We show that
the strong interlayer interaction in R3 CrI results in a competition between
the in-plane and the out-of-plane magnetic easy axis. Finally, we calculate the
Neel temperature of FeCl2 to be 47 +- 8 K, and show that the magnetic phase
transition in FeCl2 occurs in two steps with a high-temperature intralayer
ferromagnetic phase transition, and a low-temperature interlayer
anti-ferromagnetic phase transition.",2007.14379v3
2020/9/9,Half-Magnetic Topological Insulator,"Topological magnets are a new family of quantum materials providing great
potential to realize emergent phenomena, such as quantum anomalous Hall effect
and axion-insulator state. Here we present our discovery that stoichiometric
ferromagnet MnBi8Te13 with natural heterostructure MnBi2Te4-(Bi2Te3)3 is an
unprecedented half-magnetic topological insulator, with the magnetization
existing at the MnBi2Te4 surface but not at the opposite surface terminated by
triple Bi2Te3 layers. Our angle-resolved photoemission spectroscopy
measurements unveil a massive Dirac gap at the MnBi2Te4 surface, and gapless
Dirac cone on the other side. Remarkably, the Dirac gap (~28 meV) at MnBi2Te4
surface decreases monotonically with increasing temperature and closes right at
the Curie temperature, thereby representing the first smoking-gun spectroscopic
evidence of magnetization-induced topological surface gap among all known
magnetic topological materials. We further demonstrate theoretically that the
half-magnetic topological insulator is desirable to realize the half-quantized
surface anomalous Hall effect, which serves as a direct proof of the general
concept of axion electrodynamics in condensed matter systems.",2009.04140v1
2020/10/26,Structure and magnetism of the skyrmion hosting family GaV$_4$S$_{8-y}$Se$_y$ with low levels of substitutions between $0 \leq y \leq 0.5$ and $7.5 \leq y\leq 8$,"Polycrystalline members of the GaV$_4$S$_{8-y}$Se$_y$ family of materials
with small levels of substitution between $0 \leq y \leq 0.5$ and $7.5 \leq
y\leq 8$ have been synthesized in order to investigate their magnetic and
structural properties. Substitutions to the skyrmion hosting parent compounds
GaV$_4$S$_8$ and GaV$_4$Se$_8$, are found to suppress the temperature of the
cubic to rhombohedral structural phase transition that occurs in both end
compounds and to create a temperature region around the transition where there
is a coexistence of these two phases. Similarly, the magnitude of the
magnetization and temperature of the magnetic transition are both suppressed in
all substituted compounds until a glassy-like magnetic state is realized. There
is evidence from the $ac$ susceptibility data that skyrmion lattices with
similar dynamics to those in GaV$_4$S$_8$ and GaV$_4$Se$_8$ are present in
compounds with very low levels of substitution, $0 < y< 0.2$ and $7.8 < y < 8$,
however, these states vanish at higher levels of substitution. The magnetic
properties of these substituted materials are affected by the substitution
altering exchange pathways and resulting in the creation of increasingly
disordered magnetic states.",2010.13450v1
2020/12/2,Engineered magnetization and exchange stiffness in direct-write Co-Fe nanoelements,"Media with engineered magnetization are essential building blocks in
superconductivity, magnetism and magnon spintronics. However, the established
thin-film and lithographic techniques insufficiently suit the realization of
planar components with on-demand-tailored magnetization in the lateral
dimension. Here, we demonstrate the engineering of the magnetic properties of
CoFe-based nanodisks fabricated by the mask-less technique of focused electron
beam induced deposition (FEBID). The material composition in the nanodisks is
tuned \emph{in-situ} via the e-beam waiting time in the FEBID process and their
post-growth irradiation with Ga ions. The magnetization $M_s$ and exchange
stiffness $A$ of the disks are deduced from perpendicular ferromagnetic
resonance measurements. The achieved $M_s$ variation in the broad range from
$720$ emu/cm$^3$ to $1430$ emu/cm$^3$ continuously bridges the gap between the
$M_s$ values of such widely used magnonic materials as permalloy and CoFeB. The
presented approach paves a way towards nanoscale 2D and 3D systems with
controllable and space-varied magnetic properties.",2012.01481v1
2020/12/18,Rare-earth-free ferrimagnetic Mn4N sub-20 nm thin films as high-temperature spintronic material,"Ferrimagnetic alloy thin films that exhibit perpendicular (out-of-plane)
magnetic anisotropy (PMA) with low saturation magnetization, such as GdCo and
Mn4N, were predicted to be favorable for hosting small Neel skyrmions for room
temperature applications. Due to the exponential decay of interfacial
Dzyaloshinskii-Moriya interaction (DMI) and the limited range of
spin-orbit-torques, which can be used to drive skyrmion motion, the thickness
of the ferrimagnetic layer has to be small, preferably under 20 nm. While there
are examples of sub-20 nm, rare earth-transition metal (RE-TM), ferrimagnetic
thin films fabricated by sputter deposition, to date rare-earth-free sub-20 nm
Mn4N films with PMA have only been reported to be achieved by molecular beam
epitaxy, which is not suitable for massive production. Here we report the
successful thermal growth of sub-20 nm Mn4N films with PMA at 400-450 {\deg}C
substrate temperatures on MgO substrates by reactive sputtering. The Mn4N films
were achieved by reducing the surface roughness of MgO substrate through a
high-temperature vacuum annealing process. The optimal films showed low
saturation magnetization (Ms = 43 emu/cc), low magnetic anisotropy energy (0.7
Merg/cc), and a remanent magnetization to saturation magnetization ratio
(Mr/Ms) near 1 at room temperature. Preliminary ab-initio density functional
theory (DFT) calculations have confirmed the ferrimagnetic ground state of Mn4N
grown on MgO. The magnetic properties, along with the high thermal stability of
Mn4N thin films in comparison with RE-TM thin films, provide the platform for
future studies of practical skyrmion-based spintronic materials.",2012.10493v1
2021/3/10,Evidences for the random singlet phase in a new honeycomb iridate SrIr$_2$O$_{6-δ}$,"Strong spin-orbital-coupling magnetic systems with the honeycomb structure
can provide bond-directional interactions which may result in Kitaev quantum
spin liquids and exotic anyonic excitations. However, one of the key
ingredients in real materials$-$disorders$-$has been much less studied in
Kitaev systems. Here we synthesized a trigonal SrIr$_2$O$_{6-\delta}$ with
$\delta \approx 0.25$, which consists of two-dimensional honeycomb Ir planes
with edge-sharing IrO$_6$ octahedra. First-principles computation and
experimental measurements suggest that the electronic system is gapped, and
there should be no magnetic moment as the Ir$^{5+}$ ion has no unpaired
electrons. However, significant magnetism has been observed in the material,
and it can be attributed to disorders that are most likely from oxygen
vacancies. No magnetic order is found down to 0.05 K, and the low-temperature
magnetic properties exhibit power-law behaviors in magnetic susceptibility and
zero-field specific heat, and a single-parameter scaling of the specific heat
under magnetic fields. These results provide strong evidence for the existence
of the random singlet phase in SrIr$_2$O$_{6-\delta}$, which offers a different
member to the family of spin-orbital entangled iridates and Kitaev materials.",2103.05820v2
2021/3/20,Magnetic properties of the Shastry-Sutherland lattice material BaNd$_2$ZnO$_5$,"We investigate the physical properties of the Shastry-Sutherland lattice
material BaNd$_2$ZnO$_5$. Neutron diffraction, magnetic susceptibility, and
specific heat measurements reveal antiferromagnetic order below 1.65 K. The
magnetic order is found to be a 2-$\boldsymbol{Q}$ magnetic structure with the
magnetic moments lying in the Shastry-Sutherland lattice planes comprising the
tetragonal crystal structure of BaNd$_2$ZnO$_5$. The ordered moment for this
structure is 1.9(1) $\mu_B$ per Nd ion. Inelastic neutron scattering
measurements reveal that the crystal field ground state doublet is well
separated from the first excited state at 8 meV. The crystal field Hamiltonian
is determined through simultaneous refinement of models with both the LS
coupling and intermediate coupling approximations to the inelastic neutron
scattering and magnetic susceptibility data. The ground state doublet indicates
that the magnetic moments lie primarily in the basal plane with magnitude
consistent with the size of the determined ordered moment.",2103.11255v1
2021/3/24,Magnetic ordering of the distorted kagome antiferromagnet Y$_3$Cu$_9$(OH)$_{18}$[Cl$_8$(OH)] prepared via optimal synthesis,"Experimental studies of high-purity kagome-lattice antiferromagnets (KAFM)
are of great importance in attempting to better understand the predicted
enigmatic quantum spin-liquid ground state of the KAFM model. However,
realizations of this model can rarely evade magnetic ordering at low
temperatures due to various perturbations to its dominant isotropic exchange
interactions. Such a situation is for example encountered due to sizable
Dzyaloshinskii-Moriya magnetic anisotropy in YCu$_3$(OH)$_6$Cl$_3$, which
stands out from other KAFM materials by its perfect crystal structure. We find
evidence of magnetic ordering also in the distorted sibling compound
Y$_3$Cu$_9$(OH)$_{18}$[Cl$_8$(OH)], which has recently been proposed to feature
a spin-liquid ground state arising from a spatially anisotropic kagome lattice.
Our findings are based on a combination of bulk susceptibility, specific heat,
and magnetic torque measurements that disclose a N\'eel transition temperature
of $T_N=11$~K in this material, which might feature a coexistence of magnetic
order and persistent spin dynamics as previously found in
YCu$_3$(OH)$_6$Cl$_3$. Contrary to previous studies of single crystals and
powders containing impurity inclusions, we use high-purity single crystals of
Y$_3$Cu$_9$(OH)$_{18}$[Cl$_8$(OH)] grown via an optimized hydrothermal
synthesis route that minimizes such inclusions. This study thus demonstrates
that the lack of magnetic ordering in less pure samples of the investigated
compound does not originate from the reduced symmetry of spin lattice but is
instead of extrinsic origin.",2103.13254v2
2021/6/25,A magnetic continuum observed by terahertz spectroscopy in a quantum spin liquid candidate BaCo$_2$(AsO$_4$)$_2$,"Quantum spin liquids (QSLs) are topologically ordered exotic states of matter
that host fractionalized excitations. Kitaev proposed a particular route
towards a QSL via strongly bond-dependent interactions on the hexagonal
lattice. A number of candidate Kitaev QSL materials have been pursued, but all
have appreciable non-Kitaev interactions, which put these systems far from the
QSL regime. Using time-domain terahertz spectroscopy (TDTS) we observed a broad
magnetic continuum over a wide range of temperature and field in the honeycomb
cobalt-based magnet, BaCo$_2$(AsO$_4$)$_2$, which has been proposed to be more
ideal versions of a Kitaev QSL. Applying a small in-plane magnetic field of
$\sim$ 0.5 T suppresses the magnetic order and at at even higher fields gives
rise to a spin-polarized state. With 4T magnetic field oriented principally
out-of-plane, a broad magnetic continuum was observed that could be consistent
with a field induced QSL. Our results indicate BaCo$_2$(AsO$_4$)$_2$ to be a
promising QSL candidate.",2106.13418v3
2021/7/13,Investigation of spin-phonon coupling and local magnetic properties in magnetoelectric Fe2TeO6,"Spin-phonon coupling originated from spin-lattice correlation depends upon
different exchange interactions in transition metal oxides containing 3d
magnetic ions. Spin-lattice coupling can influence the coupling mechanism in
magnetoelectric material. To understand the spin-lattice correlation in inverse
trirutile Fe2TeO6 (FTO), magnetic properties and phonon spectra are studied.
Signature of short-range magnetic correlation induced by 5/2-5/2 dimeric
interaction and magnetic anomaly at 150 K is perceived apart from the familiar
sharp transition (TN~210K) corresponding to long-range order by magnetization
and heat capacity measurement. The magnetic transitions and the spin dynamics
are further locally probed by muon spin resonance ({\mu}SR) measurement in both
zero fields (ZF) and longitudinal field (LF) mode. Three dynamically distinct
temperature regimes; (i) T >TN, (ii) TN>T>150 K, and (iii) T<150 K, are
observed. A swift change in spin dynamics is realized at 150K by {\mu}SR,
though previous studies suggest long-range antiferromagnetic order. The
observation of renormalization of different Raman modes below 210K suggests the
existence of spin-phonon coupling in the material. The coupling strength is
quantified as in the range 0.1-1.2 cm-1 following the two-spin cluster
approximation. We propose that the spin-phonon coupling is mediated by the
Fe-O2-Fe interbilayer exchange play a significant role in ME coupling observed
in the material.",2107.06269v2
2021/11/1,Interface-enhanced ferromagnetism with long-distance effect in van der Waals semiconductor,"Ferromagnetic semiconductors discovered in two-dimensional (2D) materials
open an avenue for highly integrated and multifunctional spintronics. The Curie
temperature (TC) of existed 2D ferromagnetic semiconductors is extremely low
and the modulation effect of their magnetism is limited compared with their 2D
metallic counterparts. The interfacial effect was found to effectively
manipulate the three-dimensional magnetism, providing a unique opportunity for
tailoring the 2D magnetism. Here we demonstrate that the TC of 2D ferromagnetic
semiconductor Cr2Ge2Te6 can be enhanced by 130% (from ~65 K to above 150 K)
when adjacent to a tungsten layer. The interfacial W-Te bonding contributes to
the TC enhancement with a strong perpendicular magnetic anisotropy (PMA),
guaranteeing an efficient magnetization switching by the spin-orbit torque with
a low current density at 150 K. Distinct from the rapid attenuation in
conventional magnets, the interfacial effect exhibits a weak dependence on
Cr2Ge2Te6 thickness and a long-distance effect (more than 10 nanometers) due to
the weak interlayer coupling inherent to 2D magnets. Our work not only reveals
a unique interfacial behavior in 2D materials, but also advances the process
towards practical 2D spintronics.",2111.00645v1
2021/12/28,"Phonon, Electron, and Magnon Excitations in Antiferromagnetic L1$_{0}$-type MnPt","Antiferromagnetic L1$_{0}$-type MnPt is a material with relatively simple
crystal and magnetic structure, recently attracting interest due to its high
N{\'{e}}el temperature and wide usage as a pinning layer in magnetic devices.
While it is experimentally well characterized, the theoretical understanding is
much less developed, in part due to the challenging accuracy requirements
dictated by the small underlying energy scales that govern magnetic ordering in
antiferromagnetic metals. In this work, we use density functional theory, the
Korringa-Kohn-Rostoker formalism, and a Heisenberg model to establish a
comprehensive theoretical description of antiferromagnetic L1$_{0}$-type MnPt,
along with accuracy limits, by thoroughly comparing to available literature
data. Our simulations show that the contribution of the magnetic dipole
interaction to the magnetocrystalline anisotropy energy of $K_{1}$=1.07$\times
10^{6}$\,J/m$^3$ is comparable in magnitude to the spin-orbit contribution.
Using our result for the magnetic susceptibility of $5.25\times10^{-4}$, a
lowest magnon frequency of about 2.02\,THz is predicted, confirming THz spin
dynamics in this material. From our data for electron, phonon, and magnon
dispersion we compute the individual contributions to the total heat capacity
and show that the dominant term at or above 2\,K arises from phonons. From the
Landau-Lifshitz-Gilbert equation, we compute a N\'{e}el temperature of
990--1070 K. Finally, we quantify the magnitude of the magneto-optical Kerr
effect generated by applying an external magnetic field. Our results provide
insight into the underlying physics, which is critical for a deep understanding
of fundamental limits of the time scale of spin dynamics, stability of the
magnetic ordering, and the possibility of magneto-optical detection of
collective spin motion.",2112.13954v1
2022/4/11,DFT calculation of intrinsic properties of magnetically hard phase L1$\mathrm{_0}$ FePt,"Due to its strong magnetocrystalline anisotropy, FePt L1$\mathrm{_0}$ phase
is considered as a promising magnetic recording media material. Although the
magnetic properties of this phase have already been analyzed many times using
density functional theory (DFT), we decided to study it again, emphasizing on
full potential methods, including spin-polarized relativistic
Korringa-Kohn-Rostoker (SPR-KKR) and full-potential local-orbital (FPLO)
scheme. In addition to the determination of exact values of the
magnetocrystalline anisotropy constants K$\mathrm{_1}$ and K$\mathrm{_2}$, the
magnetic moments (m), the Curie temperature, and the magnetostriction
coefficient, we focused on the investigation of the magnetocrystalline
anisotropy energy (MAE) dependence on the magnetic moment values using the
fully relativistic fixed spin moment (FSM) method with various
exchange-correlation potentials. We present nearly identical MAE(m) curves near
the equilibrium point, along with different equilibrium values of MAE and
magnetic moments. For a magnetic moment reduced by about 10%, we determined a
theoretical MAE maximum in the ground state (0 K) equal to about 20.3 MJ
m$\mathrm{^{-3}}$ and independent of the choice of the exchange-correlation
potential form. These calculations allow us to understand the discrepancies
between the previous MAE results for different exchange-correlation potentials.",2204.05073v1
2022/5/18,Gadolinium halide monolayers: a fertile family of two-dimensional 4f magnets,"Two-dimensional (2D) magnets have great potentials for applications in
next-generation information devices. Since the recent experimental discovery of
intrinsic 2D magnetism in monolayer CrI$_3$ and few-layer Cr$_2$Ge$_2$Te$_6$,
intensive studies have been stimulated in pursuing more 2D magnets and
revealing their intriguing physical properties. In comparison to the magnetism
based on $3d$ electrons, $4f$ electrons can provide larger magnetic moments and
stronger spin-orbit coupling, but have been much less studied in the 2D forms.
Only in very recent years, some exciting results have been obtained in this
area. In this mini-review, we will introduce some recent progress in 2D Gd
halides from a theoretical aspect. It is noteworthy that $4f$ and $5d$ orbitals
of Gd both play key roles in these materials. For Gd$X_2$ ($X$=I, Br, Cl and F)
monolayers and related Janus monolayers, robust ferromagnetism with large
exchanges comes from the $4f^7$+$5d^1$ hybridization of Gd$^{2+}$. The
spatially expanded $5d$ electrons act as a bridge to couple localized $4f$
spins. For Gd$X_3$ monolayers, the intercalation of metal atoms can dope
electrons into Gd's $5d$ orbitals, which leads to numerous intriguing physical
properties, such as ferroelasticity, ferromagnetism, and anisotropic
conductance. In brief, Gd halides establish an effective strategy to take
advantage of $f$-electron magnetism in 2D materials.",2205.08666v1
2022/5/11,Layer-dependent interlayer antiferromagnetic spin reorientation in air-stable semiconductor CrSBr,"Magnetic van der Waals (vdW) materials offer a fantastic platform to
investigate and exploit rich spin configurations stabilized in reduced
dimensions. One tantalizing magnetic order is the interlayer antiferromagnetism
in A-type vdW antiferromagnet, which may be effectively modified by the
magnetic field, stacking order and thickness scaling. However, atomically
revealing the interlayer spin orientation in the vdW antiferromagnet is highly
challenging, because most of the material candidates exhibit an insulating
ground state or instability in ambient conditions. Here, we report the
layer-dependent interlayer antiferromagnetic reorientation in air-stable
semiconductor CrSBr using magnetotransport characterization and
first-principles calculations. We reveal a pronounced odd-even layer effect of
interlayer reorientation, which originates from the competitions among
interlayer exchange, magnetic anisotropy energy and extra Zeeman energy of
uncompensated magnetization. Furthermore, we quantitatively constructed the
layer-dependent magnetic phase diagram with the help of a linear-chain model.
Our work uncovers the layer-dependent interlayer antiferromagnetic
reorientation engineered by magnetic field in the air-stable semiconductor,
which could contribute to future vdW spintronic devices.",2205.09077v2
2022/8/30,Towards 20 T Hybrid Accelerator Dipole Magnets,"The most effective way to achieve very high collision energies in a circular
particle accelerator is to maximize the field strength of the main bending
dipoles. In dipole magnets using Nb-Ti superconductor the practical field limit
is considered to be 8-9 T. When Nb3Sn superconductor material is utilized, a
field level of 15-16 T can be achieved. To further push the magnetic field
beyond the Nb3Sn limits, High Temperature Superconductors (HTS) need to be
considered in the magnet design. The most promising HTS materials for particle
accelerator magnets are Bi2212 and REBCO. However, their outstanding
performance comes with a significantly higher cost. Therefore, an economically
viable option towards 20 T dipole magnets could consist in an hybrid solution,
where both HTS and Nb3Sn materials are used. We discuss in this paper
preliminary conceptual designs of various 20 T hybrid magnet concepts. After
the definition of the overall design criteria, the coil dimensions and
parameters are investigated with finite element models based on simple sector
coils. Preliminary 2D cross-section computation results are then presented and
three main layouts compared: cos-theta, block, and common-coil. Both
traditional designs and more advanced stress-management options are considered.",2208.14323v1
2022/9/30,Single-crystal study of the honeycomb XXZ magnet BaCo$_2$(PO$_4$)$_2$ in magnetic fields,"We present a study of high-quality BaCo$_2$(PO$_4$)$_2$ single crystals via
magnetization, heat-capacity, thermal-expansion and magnetostriction
measurements. Sharp anomalies in the thermodynamic properties at $T_N=3.4\,$K
reveal a long-range antiferromagnetic order in these single-crystalline
samples, which is absent in polycrystalline BaCo$_2$(PO$_4$)$_2$. The
temperature dependent magnetic susceptibilities for in-plane and out-of-plane
magnetic fields are strongly anisotropic and reveal a pronounced easy-plane
anisotropy. A Curie-Weiss analysis implies strong orbital magnetism, as it is
known from the sister compound BaCo$_2$(AsO$_4$)$_2$ that is discussed as a
potential Kitaev spin-liquid material. When applying in-plane magnetic fields
at low temperature, BaCo$_2$(PO$_4$)$_2$ is driven to another ordered phase at
a critical field $H_{C1}\approx 0.11\,$T and then undergoes a further
field-induced transition to a highly polarized paramagnetic phase at
$H_{C2}\approx 0.3\,$T, which is again similar to the case of
BaCo$_2$(AsO$_4$)$_2$. In addition, our lowest-temperature data reveal that the
field-induced transitions in BaCo$_2$(PO$_4$)$_2$ become dominated by thermally
assisted domain-wall motion.",2209.15510v2
2022/11/19,MSGCorep: A package for corepresentations of magnetic space groups,"Motivated by easy access to complete corepresentation (corep) data of all the
1651 magnetic space groups (MSGs) in three-dimensional space, we have developed
a Mathematica package MSGCorep to provide an offline database of coreps and
various functions to manipulate them, based on our previous package
SpaceGroupIrep. One can use the package MSGCorep to obtain the elements of any
MSG and magnetic little group, to calculate the multiplication of group
elements, to obtain the small coreps at any k-point and full coreps of any
magnetic k-star for any MSG and show them in a user-friendly table form, to
calculate and show the decomposition of direct products of full coreps between
any two specified magnetic k-stars, and to determine the small coreps of energy
bands. Both single-valued and double-valued coreps are supported. In addition,
the 122 magnetic point groups (MPGs) and their coreps are also supported by
this package. To the best of our knowledge, MSGCorep is the first package that
is able to calculate the direct product of full coreps for any MSG and able to
determine small coreps of energy bands for general purpose. In a word, the
MSGCorep package is an offline database and tool set for MSGs, MPGs, and their
coreps, and it is very useful to study the symmetries in magnetic and
nonmagnetic materials.",2211.10740v1
2023/1/2,"Ferroelectrically switchable magnetic multistates in MnBi$_2$Te$_4$(Bi$_2$Te$_3$)$_n$ and MnSb$_2$Te$_4$(Sb$_2$Te$_3$)$_n$ (n = 0, 1) thin films","Ferroelectric control of two-dimensional magnetism is promising in
fabricating electronic devices with high speed and low energy consumption. The
newly discovered layered MnBi$_2$Te$_4$(Bi$_2$Te$_3$)$_n$ and their Sb
counterparts exhibit A-type antiferromagnetism with intriguing topological
properties. Here, we propose to obtain tunable magnetic multistates in their
thin films by ferroelectrically manipulating the interlayer magnetic couplings
(IMCs) based on the Heisenberg model and first-principles calculations. Our
strategy relies on that interfacing the thin films with appropriate
ferroelectric materials can switch on/off an interlayer hopping channel between
Mn-$e_g$ orbitals as the polarizations reversed, thus resulting in a switchable
interlayer antiferromagnetism-to-ferromagnetism transition. On the other hand,
the interface effect leads to asymmetric energy barrier heights for the two
polarization states. These properties allow us to build ferroelectrically
switchable triple and quadruple magnetic states with multiple Chern numbers in
thin films. Our study reveals that ferroelectrically switchable magnetic and
topological multistates in MnBi$_2$Te$_4$ family can be obtained by rational
design for multifunctional electronic devices, which can also be applied to
other two-dimensional magnetic materials.",2301.00515v3
2023/3/27,Strain effects on magnetic compensation and spin reorientation transition of Co/Gd synthetic ferrimagnets,"Synthetic ferrimagnets are an attractive materials class for spintronics as
they provide access to all-optical switching of magnetization and, at the same
time, allow for ultrafast domain wall motion at angular momentum compensation.
In this work, we systematically study the effects of strain on the
perpendicular magnetic anisotropy and magnetization compensation of Co/Gd and
Co/Gd/Co/Gd synthetic ferrimagnets. Firstly, the spin reorientation transition
of a bilayer system is investigated in wedge type samples, where we report an
increase in the perpendicular magnetic anisotropy in the presence of in-plane
strain. Using a model for magnetostatics and spin reorientation transition in
this type of system, we confirm that the observed changes in anisotropy field
are mainly due to the Co magnetoelastic anisotropy. Secondly, the magnetization
compensation of a quadlayer is studied. We find that magnetization compensation
of this synthetic ferrimagnetic system is not altered by external strain. This
confirms the resilience of this material system against strain that may be
induced during the integration process, making Co/Gd ferrimagnets suitable
candidates for spintronics applications.",2303.15191v4
2023/4/29,"Structural, electronic, and magnetic properties of CrTe2","Two-dimensional chromium ditelluride (CrTe2) is a promising ferromagnetic
layered material that exhibits long-range ferromagnetic ordering in the
monolayer limit. The formation energies of the different possible structural
phases (1T, 1H, 2H) calculated from density functional theory (DFT) show that
the 1T phase is the ground state, and the energetic transition barriers between
the phases, calculated by the nudged elastic band method, are large, on the
order of 0.5 eV. The self-consistent Hubbard $U$ correction parameters are
calculated for all the phases of CrTe$_2$. The calculated magnetic moment of
1T-CrTe$_2$ with $\geq 2$ layers lies in the plane, whereas the magnetic moment
of a monolayer is out-of-plane. Band filling and tensile bi-axial strain cause
the magnetic moment of a monolayer to switch from out-of-plane to in-plane, and
compressive bi-axial strain in a bilayer causes the magnetic moment to switch
from in-plane to out-of-plane. The magnetic anisotropy is shown to originate
from the large spin orbit coupling (SOC) of the Te atoms and the anisotropy of
the exchange coupling constants $J_{xy}$ and $J_z$ in an XXZ type Hamiltonian.
Renormalized spin wave theory using experimental values for the magnetic
anisotropy energy and Curie temperatures provides a range of values for the
nearest neighbor exchange coupling.",2305.00168v1
2023/7/20,Layer thickness crossover of type-II multiferroic magnetism in NiI2,"The discovery of atomically thin van der Waals ferroelectric and magnetic
materials encourages the exploration of 2D multiferroics, which holds the
promise to understand fascinating magnetoelectric interactions and fabricate
advanced spintronic devices. In addition to building a heterostructure
consisting of ferroelectric and magnetic ingredients, thinning down layered
multiferroics of spin origin such as NiI2 becomes a natural route to realize 2D
multiferroicity. However, the layer-dependent behavior, widely known in the
community of 2D materials, necessitates a rigorous scrutiny of the multiferroic
order in the few-layer limit. Here, we interrogate the layer thickness
crossover of helimagnetism in NiI2 that drives the ferroelectricity and thereby
type-II multiferroicity. By using wavelength-dependent polarization-resolved
optical second harmonic generation (SHG) to probe the ferroic symmetry, we find
that the SHG arises from the inversion-symmetry-breaking magnetic order, not
previously assumed ferroelectricity. This magnetism-induced SHG is only
observed in bilayer or thicker layers, and vanishes in monolayer, suggesting
the critical role of interlayer exchange interaction in breaking the degeneracy
of geometrically frustrated spin structures in triangular lattice and
stabilizing the type-II multiferroic magnetism in few-layers. While the
helimagnetic transition temperature is layer dependent, the few-layer NiI2
exhibits another thickness evolution and reaches the bulk-like behavior in
trilayer, indicated by the intermediate centrosymmetric antiferromagnetic state
as revealed in Raman spectroscopy. Our work therefore highlights the magnetic
contribution to SHG and Raman spectroscopy in reduced dimension and guides the
optical study of 2D multiferroics.",2307.10686v1
2023/9/25,"Magnetic States and Electronic Properties of Manganese-Based Intermetallic Compounds Mn$_2$YAl and Mn$_3$Z (Y = V, Cr, Fe, Co, Ni; Z = Al, Ge, Sn, Si, Pt)","We present a brief review of experimental and theoretical papers on studies
of electron transport and magnetic properties in manganese-based compounds
Mn$_2$YZ and Mn$_3$Z (Y = V, Cr, Fe, Co, Ni, etc.; Z = Al, Ge, Sn, Si, Pt,
etc.). It has been shown that in the electronic subsystem of Mn$_2$YZ
compounds, the states of a half-metallic ferromagnet and a spin gapless
semiconductor can arise with the realization of various magnetic states, such
as a ferromagnet, a compensated ferrimagnet, and a frustrated antiferromagnet.
Binary compounds Mn$_3$Z have the properties of a half-metallic ferromagnet and
a topological semimetal with a large anomalous Hall effect, spin Hall effect,
spin Nernst effect, and thermal Hall effect. Their magnetic states are also
very diverse: from a ferrimagnet and an antiferromagnet to a compensated
ferrimagnet and a frustrated antiferromagnet, as well as an antiferromagnet
with a kagome-type lattice. It has been demonstrated that the electronic and
magnetic properties of such materials are very sensitive to external influences
(temperature, magnetic field, external pressure), as well as the processing
method (cast, rapidly quenched, nanostructured, etc.). Knowledge of the
regularities in the behavior of the electronic and magnetic characteristics of
Mn$_2$YAl and Mn$_3$Z compounds can be used for applications in micro- and
nanoelectronics and spintronics.",2309.14140v1
2023/10/12,3D Heisenberg universality in the Van der Waals antiferromagnet NiPS$_3$,"Van der Waals (vdW) magnetic materials are comprised of layers of atomically
thin sheets, making them ideal platforms for studying magnetism at the
two-dimensional (2D) limit. These materials are at the center of a host of
novel types of experiments, however, there are notably few pathways to directly
probe their magnetic structure. We report the magnetic order within a single
crystal of NiPS$_3$ and show it can be accessed with resonant elastic X-ray
diffraction along the edge of the vdW planes in a carefully grown crystal by
detecting structurally forbidden resonant magnetic X-ray scattering. We find
the magnetic order parameter has a critical exponent of $\beta\sim0.36$,
indicating that the magnetism of these vdW crystals is more adequately
characterized by the three-dimensional (3D) Heisenberg universality class. We
verify these findings with first-principle density functional theory,
Monte-Carlo simulations, and density matrix renormalization group calculations.",2310.07948v2
2024/2/15,Emergent topological quasiparticle kinetics in constricted nanomagnets,"The ubiquitous domain wall kinetics under magnetic field or current
application describes the dynamic properties in nanostructured magnets.
However, when the geometrical size of a nanomagnetic system is constricted to
the limiting domain wall length scale, the competing energetics between
anisotropy, exchange and dipolar interactions can cause emergent kinetics due
to quasiparticle relaxation, similar to bulk magnets of atomic origin. Here, we
present a joint experimental and theoretical study to support this argument --
constricted nanomagnets, made of antiferromagnetic and paramagnetic neodymium
thin film with honeycomb motif, reveal fast kinetic events at ps time scales
due to the relaxation of chiral vortex loop-shaped topological quasiparticles
that persist to low temperature in the absence of any external stimuli. Such
phenomena are typically found in macroscopic magnetic materials. Our discovery
is especially important considering the fact that paramagnets or
antiferromagnets have no net magnetization. Yet, the kinetics in neodymium
nanostructures is quantitatively similar to that found in ferromagnetic
counterparts and only varies with the thickness of the specimen. This suggests
that a universal, topological quasiparticle mediated dynamical behavior can be
prevalent in nanoscopic magnets, irrespective of the nature of underlying
magnetic material.",2402.10143v2
2024/3/4,Magnetic Weyl-Kondo semimetals induced by quantum fluctuation,"Kondo effect exemplifies the type of quantum fluctuations driven by strong
correlations, and its cooperation with space group symmetries underlies the
Weyl-Kondo semimetals. Because the Kondo effect of the $f$-electrons is
believed to be suppressed in a magnetic environment, Weyl-Kondo semimetals have
so far been confined to paramagnetic settings. Here we develop the theory of
magnetic Weyl-Kondo semimetal. The key of the proposed mechanism is that the
magnetic order is originated from the conduction $d$ electrons, such that the
local moments can still fluctuate. We illustrate the extreme case where the
magnetic space group symmetries prevent any magnetization on the sites with the
$f$-orbitals. In this case, hourglass Weyl-Kondo nodal lines appear when the
space group symmetry acts on the Kondo-driven low-energy excitations. We
suggest a third-order nonlinear spontaneous Hall response as a means to
diagnose this type of topological crossings. Based on the theoretical
mechanism, we explore the interplay between correlations and symmetries in
magnetic square-net materials, leading to several candidate materials with a
variety of nonlinear Hall responses. Our findings pave the way for future
experimental exploration and theoretical investigations in this new and
promising materials class as a part of an overarching effort to understand and
harness the interplay between strong correlations and topology.",2403.02295v1
2024/3/12,Noncentrosymmetric Triangular Magnet CaMnTeO$_6$: Strong Quantum Fluctuations and Role of s0 vs. s2 Electronic States in Competing Exchange Interactions,"Noncentrosymmetric triangular magnets offer a unique platform for realizing
strong quantum fluctuations. However, designing these quantum materials remains
an open challenge attributable to a knowledge gap in the tunability of
competing exchange interactions at the atomic level. Here, we create a new
noncentrosymmetric triangular S = 3/2 magnet CaMnTeO$_6$ based on careful
chemical and physical considerations. The model material displays competing
magnetic interactions and features nonlinear optical responses with the
capability of generating coherent photons. The incommensurate magnetic ground
state of CaMnTeO$_6$ with an unusually large spin rotation angle of 127 deg.(1)
indicates that the anisotropic interlayer exchange is strong and competing with
the isotropic interlayer Heisenberg interaction. The moment of 1.39(1) $\mu$B,
extracted from low-temperature heat capacity and neutron diffraction
measurements, is only 46% of the expected value of the static moment 3 $\mu$B.
This reduction indicates the presence of strong quantum fluctuations in the
half-integer spin S = 3/2 CaMnTeO$_6$ magnet, which is rare. By comparing the
spin-polarized band structure, chemical bonding, and physical properties of
AMnTeO$_6$ (A = Ca, Sr, Pb), we demonstrate how quantum-chemical interpretation
can illuminate insights into the fundamentals of magnetic exchange
interactions, providing a powerful tool for modulating spin dynamics with
atomically precise control.",2403.08069v1
2018/8/26,Intrinsic magnetic topological insulators in van der Waals layered MnBi$_2$Te$_4$-family materials,"The interplay of magnetism and topology is a key research subject in
condensed matter physics and material science, which offers great opportunities
to explore emerging new physics, like the quantum anomalous Hall (QAH) effect,
axion electrodynamics and Majorana fermions. However, these exotic physical
effects have rarely been realized in experiment, due to the lacking of suitable
working materials. Here we predict that van der Waals layered
MnBi$_2$Te$_4$-family materials show two-dimensional (2D) ferromagnetism in the
single layer and three-dimensional (3D) $A$-type antiferromagnetism in the
bulk, which could serve as a next-generation material platform for the
state-of-art research. Remarkably, we predict extremely rich topological
quantum effects with outstanding features in an experimentally available
material MnBi$_2$Te$_4$, including a 3D antiferromagnetic topological insulator
with the long-sought topological axion states, the type-II magnetic Weyl
semimetal (WSM) with simply one pair of Weyl points, and the high-temperature
intrinsic QAH effect. These striking predictions, if proved experimentally,
could profoundly transform future research and technology of topological
quantum physics.",1808.08608v1
2022/3/21,Sm-Co-based amorphous alloy films for zero-field operation of transverse thermoelectric generation,"Transverse thermoelectric generation using magnetic materials is essential to
develop active thermal engineering technologies, for which the improvements of
not only the thermoelectric output but also applicability and versatility are
required. In this study, using combinatorial material science and lock-in
thermography technique, we have systematically investigated the transverse
thermoelectric performance of Sm-Co-based alloy films. The high-throughput
material investigation revealed the best Sm-Co-based alloys with the large
anomalous Nernst effect (ANE) as well as the anomalous Ettingshausen effect
(AEE). In addition to ANE/AEE, we discovered unique and superior material
properties in these alloys: the amorphous structure, low thermal conductivity,
and large in-plane coercivity and remanent magnetization. These properties make
it advantageous over conventional materials to realize heat flux sensing
applications based on ANE, as our Sm-Co-based films can generate thermoelectric
output without an external magnetic field. Importantly, the amorphous nature
enables the fabrication of these films on various substrates including flexible
sheets, making the large-scale and low-cost manufacturing easier. Our
demonstration will provide a pathway to develop flexible transverse
thermoelectric devices for smart thermal management.",2203.10737v2
2022/9/6,Skyrmions in van der Waals centrosymmetric materials with Dzyaloshinskii-Moriya interactions,"Skyrmions can appear in non-centrosymmetric material because of the
non-vanishing Dzyaloshinskii-Moriya interactions (DMI). In this paper, we study
the magnetic properties of the rhombohedral MX$_{3}$ (M: V, Cr, Mn, and Fe. X:
Cl, Br, and I) van der Waals materials with centrosymmetric lattice by
combining first-principles calculations and Monte Carlo simulations. We found
that the Dzyaloshinskii-Moriya vector acting between the second nearest
neighbor sites of the intra-layer is non-zero and quite large even in MX$_{3}$
due to the breaking of the local inversion symmetry. We have found that the
large DMI causes nano-scale magnetic vortexes, so-called skyrmions in MX$_{3}$.
The diameter of skyrmions, e.g., in CrCl$_{3}$, is small, i.e., 2 nm, which is
promising for the application of high-density magnetic memory devices. We have
also found that not only conventional skyrmions in CrCl$_{3}$ and VCl$_{3}$ but
also antiferromagnetic skyrmions in FeCl$_{3}$ and meron in MnCl$_{3}$ appear.
Furthermore, we have found that the skyrmions in ClCl$_{3}$ and VCl$_{3}$ have
a different helicity, which shows the possibility of controlling the helicity
by electron/hole doping in MX$_{3}$ materials. Van der Waals materials, which
have a great advantage of high degrees of freedom in structures such as
heterostructures and twisted structures, exhibit high potential as skyrmion
materials.",2209.02333v1
2014/9/7,Magnetic properties of the RbMnPO4 zeolite-ABW type material: a frustrated zigzag spin chain,"The crystal structure and magnetic properties of the RbMnPO4 zeolite-ABW type
material have been studied by temperature-dependent neutron powder diffraction,
low temperature magnetometry and heat capacity measurements. RbMnPO4 represents
a rare example of a weak ferromagnetic polar material, containing Mn2+ ions
with TN = 4.7 K. The neutron powder diffraction pattern recorded at T = 10 K
shows that the compound crystallizes in the chiral and polar monoclinic space
group P21 (No. 4) with the unit-cell parameters: a = 8.94635(9) {\AA}, b =
5.43415(5) {\AA}, c = 9.10250(8) {\AA} and beta = 90.4209(6){\deg}. A close
inspection of the crystal structure of RbMnPO4 shows that this material
presents two different types of zigzag chains running along the b axis. This is
a unique feature among the zeolite-ABW type materials exhibiting the P21
symmetry. At low temperature, RbMnPO4 exhibits a canted antiferromagnetic
structure characterized by the propagation vector k1 = 0 resulting in the
magnetic symmetry P21. The magnetic moments lie mostly along the b axis with
the ferromagnetic component being in the ac plane. Due to the geometrical
frustration present in this system, an intermediate phase appears within the
temperature range 4.7 - 5.1 K characterized by the propagation vector k2 = (kx,
0, kz) with kx/kz = 2. This ratio is reminiscent of the multiferroic phase of
the orthorhombic RMnO3 phases (R = rare earth). This suggests that RbMnPO4
could present some multiferroic properties at low temperature. Our density
functional calculations confirm the presence of magnetic frustration, which
explains this intermediate incommensurate phase. Taking into account the
strongest magnetic interactions, we are able to reproduce the magnetic
structure observed experimentally at low temperature.",1410.0344v1
2016/12/15,Magnons and Magnetodielectric Effects in CoCr$_2$O$_4$: Raman Scattering Studies,"Magnetoelectric materials have generated wide technological and scientific
interest because of the rich phenomena these materials exhibit, including the
coexistence of magnetic and ferroelectric orders, magnetodielectric behavior,
and exotic hybrid excitations such as electromagnons. The multiferroic spinel
material, CoCr$_2$O$_4$, is a particularly interesting example of a
multiferroic material, because evidence for magnetoelectric behavior in the
ferrimagnetic phase seems to conflict with traditional noncollinear-spin-driven
mechanisms for inducing a macroscopic polarization. This paper reports an
inelastic light scattering study of the magnon and phonon spectrum of
CoCr$_2$O$_4$ as simultaneous functions of temperature, pressure, and magnetic
field. Below the Curie temperature ($T_C \sim 94$ K) of CoCr$_2$O$_4$ we
observe a $\omega \sim 16 \,\text{cm}^{-1}$ $\boldsymbol q=0$ magnon having
T$_{1g}$-symmetry, which has the transformation properties of an axial vector.
The anomalously large Raman intensity of the T$_{1g}$-symmetry magnon is
characteristic of materials with a large magneto-optical response and likely
arises from large magnetic fluctuations that strongly modulate the dielectric
response in CoCr$_2$O$_4$. The Raman susceptibility of the T$_{1g}$-symmetry
magnon exhibits a strong magnetic-field dependence that is consistent with the
magnetodielectric response observed in CoCr$_2$O$_4$, suggesting that
magnetodielectric behavior in CoCr$_2$O$_4$ primarily arises from the
field-dependent suppression of magnetic fluctuations that are strongly coupled
to long-wavelength phonons. Increasing the magnetic anisotropy in CoCr$_2$O$_4$
with applied pressure decreases the magnetic field-dependence of the
T$_{1g}$-symmetry magnon Raman susceptibility in CoCr$_2$O$_4$, suggesting that
strain can be used to control the magnetodielectric response in CoCr$_2$O$_4$.",1612.05283v1
2021/6/8,Polarized phonons carry the missing angular momentum in femtosecond demagnetization,"Magnetic phenomena are ubiquitous in our surroundings and indispensable for
modern science and technology, but it is notoriously difficult to change the
magnetic order of a material in a rapid way. However, if a thin nickel film is
subjected to ultrashort laser pulses, it can lose its magnetic order almost
completely within merely femtosecond times. This phenomenon, in the meantime
also observed in many other materials, has connected magnetism with femtosecond
optics in an efficient, ultrafast and complex way, offering opportunities for
rapid information processing or ultrafast spintronics at frequencies
approaching those of light. Consequently, the physics of ultrafast
demagnetization is central to modern material research, but a crucial question
has remained elusive: If a material loses its magnetization within only
femtoseconds, where is the missing angular momentum in such short time? Here we
use ultrafast electron diffraction to reveal in nickel an almost instantaneous,
long-lasting, non-equilibrium population of anisotropic high-frequency phonons
that appear as quickly as the magnetic order is lost. The anisotropy plane is
perpendicular to the direction of the initial magnetization and the atomic
oscillation amplitude is 2 pm. We explain these observations by means of
circularly polarized phonons that quickly absorb the missing angular momentum
of the spin system before the slower onset of a macroscopic sample rotation.
The time that is needed for demagnetization is related to the time it takes to
accelerate the atoms. These results provide an atomistic picture of ultrafast
demagnetization under adherence to all conservation laws but also demonstrate
the general importance of polarized phonons for non-equilibrium dynamics and
provide innovative ways for controlling materials on atomic dimensions.",2106.04189v1
2023/10/13,High temperature ferrimagnetic semiconductors by spin-dependent doping in high temperature antiferromagnets,"To realize room temperature ferromagnetic (FM) semiconductors is still a
challenge in spintronics. Many antiferromagnetic (AFM) insulators and
semiconductors with high Neel temperature $T_N$ are obtained in experiments,
such as LaFeO$_3$, BiFeO$_3$, etc. High concentrations of magnetic impurities
can be doped into these AFM materials, but AFM state with very tiny net
magnetic moments was obtained in experiments, because the magnetic impurities
were equally doped into the spin up and down sublattices of the AFM materials.
Here, we propose that the effective magnetic field provided by a FM substrate
could guarantee the spin-dependent doping in AFM materials, where the doped
magnetic impurities prefer one sublattice of spins, and the ferrimagnetic (FIM)
materials are obtained. To demonstrate this proposal, we study the Mn-doped AFM
insulator LaFeO$_3$ with FM substrate of Fe metal by the density functional
theory (DFT) calculations. It is shown that the doped magnetic Mn impurities
prefer to occupy one sublattice of AFM insulator, and introduce large magnetic
moments in La(Fe,Mn)O$_3$. For the AFM insulator LaFeO$_3$ with high $T_N$ =
740 K, several FIM semiconductors with high Curie temperature $T_C >$ 300 K and
the band gap less than 2 eV are obtained by DFT calculations, when 1/8 or 1/4
Fe atoms in LaFeO$_3$ are replaced by the other 3d, 4d transition metal
elements. The large magneto-optical Kerr effect (MOKE) is obtained in these
LaFeO$_3$-based FIM semiconductors. In addition, the FIM semiconductors with
high $T_C$ are also obtained by spin-dependent doping in some other AFM
materials with high $T_N$, including BiFeO$_3$, SrTcO$_3$, CaTcO$_3$, etc. Our
theoretical results propose a way to obtain high $T_C$ FIM semiconductors by
spin-dependent doping in high $T_N$ AFM insulators and semiconductors.",2310.09061v1
2006/5/25,High-Pressure Synthesized Materials: a Chest of Treasure and Hints,"The present review covers the production of new materials under high
pressures. A primary limitation on the use of pressures higher than 1 GPa is a
small volume and mass of a produced material. Therefore, despite an extremely
wide range of new high-pressure synthesized substances with unique properties,
synthesis on an commercial scale is applied up to now only to obtain superhard
materials, this real treasure of today's industry. At the same time,
high-pressure experiments often give material scientists a hint at what new
intriguing substances can exist in principle. This is true for new superhard,
semiconducting, magnetic, superconducting and optical materials already
synthesized under pressure, and as well as for a large number of hypothetic new
polymers from low-Z elements. Many of new materials, including the above
polymers, may exist in the metastable form at normal pressure at sufficiently
high temperatures.",0605626v1
2013/3/15,Advanced materials for solid-state refrigeration,"Recent progress on caloric effects are reviewed. The application of external
stimuli such as magnetic field, hydrostatic pressure, uniaxial stress and
electric field give rise respectively to magnetocaloric, barocaloric,
elastocaloric and electrocaloric effects. The values of the relevant quantities
such as isothermal entropy and adiabatic temperature-changes are compiled for
selected materials. Large values for these quantities are found when the
material is in the vicinity of a phase transition. Quite often there is
coupling between different degrees of freedom, and the material can exhibit
cross-response to different external fields. In this case, the material can
exhibit either conventional or inverse caloric effects when a field is applied.
The values reported for the many caloric effects at moderate fields are large
enough to envisage future application of these materials in efficient and
environmental friendly refrigeration.",1303.3811v1
2014/11/5,Homogenization of Composite Ferromagnetic Materials,"Nowadays, nonhomogeneous and periodic ferromagnetic materials are the subject
of a growing interest. Actually such periodic configurations often combine the
attributes of the constituent materials, while sometimes, their properties can
be strikingly different from the properties of the different constituents.
These periodic configurations can be therefore used to achieve physical and
chemical properties difficult to achieve with homogeneous materials. To predict
the magnetic behavior of such composite materials is of prime importance for
applications. The main objective of this paper is to perform, by means of
Gamma-convergence and two-scale convergence, a rigorous derivation of the
homogenized Gibbs-Landau free energy functional associated to a composite
periodic ferromagnetic material, i.e. a ferromagnetic material in which the
heterogeneities are periodically distributed inside the ferromagnetic media. We
thus describe the Gamma-limit of the Gibbs-Landau free energy functional, as
the period over which the heterogeneities are distributed inside the
ferromagnetic body shrinks to zero.",1411.1231v1
2016/11/10,Spectroscopic investigation of defects in two dimensional materials,"Two-dimensional (2D) materials have been extensively studied in recent years
due to their unique properties and great potential for applications. Different
types of structural defects could present in 2D materials and have strong
influence on their properties. Optical spectroscopic techniques, e.g. Raman and
photoluminescence (PL) spectroscopy, have been widely used for defect
characterization in 2D materials. In this review, we briefly introduce
different types of defects and discuss their effects on the mechanical,
electrical, optical, thermal, and magnetic properties of 2D materials. Then, we
review the recent progress on Raman and PL spectroscopic investigation of
defects in 2D materials, i.e. identifying of the nature of defects and also
quantifying the numbers of defects. Finally, we highlight perspectives on
defect characterization and engineering in 2D materials.",1611.03149v1
2017/1/24,Kitaev Materials,"In transition-metal compounds with partially filled $4d$ and $5d$ shells
spin-orbit entanglement, electronic correlations, and crystal-field effects
conspire to give rise to a variety of novel forms of topological quantum
matter. This includes Kitaev materials -- a family of spin-orbit assisted Mott
insulators, in which local, spin-orbit entangled $j=1/2$ moments form that are
subject to strong bond-directional interactions. On a conceptual level, Kitaev
materials attract much interest for their unconventional forms of magnetism,
such as spin liquid physics in two- and three-dimensional lattice geometries or
the formation of non-trivial spin textures. Experimentally, a number of Kitaev
materials have been synthesized, which includes the honeycomb materials
Na$_2$IrO$_3$, $\alpha$-Li$_2$IrO$_3$, and RuCl$_3$, the triangular materials
Ba$_3$Ir$_x$Ti$_{3-x}$O$_9$, as well as the three-dimensional hyper-honeycomb
and stripy-honeycomb materials $\beta$-Li$_2$IrO$_3$ and
$\gamma$-Li$_2$IrO$_3$. These lecture notes provide a short review of the
current status of the theoretical and experimental exploration of these Kitaev
materials.",1701.07056v1
2020/5/9,Quest for New Quantum States via Field-Editing Technology,"We report new quantum states in spin-orbit-coupled single crystals that are
synthesized using a game-changing technology that ""field-edits"" crystal
structures (borrowing from the phrase ""genome editing"") via application of
magnetic field during crystal growth. This study is intended to fundamentally
address a major challenge facing the research community today: A great deal of
theoretical work predicting exotic states for strongly spin-orbit-coupled,
correlated materials has thus far met very limited experimental confirmation.
These conspicuous discrepancies are due chiefly to the extreme sensitivity of
these materials to structural distortions. The results presented here
demonstrate that the ""field-edited"" materials not only are much less distorted
but also exhibit novel phenomena absent in their ""non-edited"" counterparts. The
field-edited materials include an array of 4d and 5d transition metal oxides,
and three representative materials presented here are Ba4Ir3O10, Ca2RuO4, and
Sr2IrO4. This study provides an entirely new paradigm for discovery of new
quantum states and materials otherwise unavailable.",2005.04327v3
2020/10/16,A universal method for depositing patterned materials in-situ,"Current techniques of patterned material deposition require separate steps
for patterning and material deposition. The complexity and harsh working
conditions post serious limitations for fabrication. Here, we introduce a novel
single-step and easy-to-adapt method that can deposit materials in-situ. Its
unique methodology is based on the semiconductor nanoparticle assisted
photon-induced chemical reduction and optical trapping. This universal
mechanism can be used for depositing a large selection of materials including
metals, insulators and magnets, with quality on par with current technologies.
Patterning with several materials together with optical-diffraction-limited
resolution accuracy can be achieved from macroscopic to microscopic scale.
Furthermore, the setup is naturally compatible with optical microscopy based
measurements, thus sample characterisation and material deposition can be
realised in-situ. Various devices fabricated with this method in 2D or 3D show
it is ready for deployment in practical applications. This revolutionary method
will provide a distinct tool in material technology.",2010.08305v1
2023/11/18,Enhancing metallicity and basal plane reactivity of 2D materials via self-intercalation,"Intercalation (ic) of metal atoms into the van der Waals (vdW) gap of layered
materials constitutes a facile strategy to create new materials whose
properties can be tuned via the concentration of the intercalated atoms. Here
we perform systematic density functional theory calculations to explore various
properties of an emergent class of crystalline 2D materials (ic-2D materials)
comprising vdW homobilayers with native metal atoms on a sublattice of
intercalation sites. From an initial set of 1348 ic-2D materials, generated
from 77 vdW homobilayers, we find 95 structures with good thermodynamic
stability (formation energy within 200 meV/atom of the convex hull). A
significant fraction of the semiconducting host materials are found to undergo
an insulator to metal transition upon self-intercalation with only PdS$_2$,
PdSe$_2$, and GeS$_2$ maintaining a finite electronic gap. In five cases,
self-intercalation introduces magnetism. In general, self-intercalation is
found to promote metallicity and enhance the chemical reactivity on the basal
plane. Based on the calculated H binding energy we find that self-intercalated
SnS$_2$ and Hf$_3$Te$_2$ are promising candidates for hydrogen evolution
catalysis. All the stable ic-2D structures and their calculated properties can
be explored in the open C2DB database.",2311.11131v1
2021/5/13,Near-Room-Temperature Ferromagnetic Behavior of Single-Atom-Thick 2D Iron in Nanolaminated Ternary MAX Phases,"Two dimensional (2D) ferromagnetic materials have attracted much attention in
the fields of condensed matter physics and materials science, but their
synthesis is still a challenge given their limitations on structural stability
and susceptibility to oxidization. MAX phases nanolaminated ternary carbides or
nitrides possess a unique crystal structure in which single-atom-thick A
sublayers are interleaved by two dimensional MX slabs, providing nanostructured
templates for designing 2D ferromagnetic materials if the non-magnetic A
sublayers can be substituted replaced by magnetic elements. Here, we report
three new ternary magnetic MAX phases (Ta2FeC, Ti2FeN and Nb2FeC) with A
sublayers of single-atom-thick 2D iron through an isomorphous replacement
reaction of MAX precursors (Ta2AlC, Ti2AlN and Nb2AlC) with a Lewis acid salts
(FeCl2). All these MAX phases exhibit ferromagnetic (FM) behavior. The Curie
temperature (Tc) of Ta2FeC and Nb2FeC MAX phase are 281 K and 291 K,
respectively, i.e. close to room temperature. The saturation magnetization of
these ternary magnetic MAX phases is almost two orders of magnitude higher than
that of V2(Sn,Fe)C MAX phase whose A-site is partial substituted by Fe.
Theoretical calculations on magnetic orderings of spin moments of Fe atoms in
these nanolaminated magnetic MAX phases reveal that the magnetism can be mainly
ascribed to intralayer exchange interaction of the 2D Fe atomic layers. Owning
to the richness in composition of MAX phases, there is a large compositional
space for constructing functional single-atom-thick 2D layers in materials
using these nanolaminated templates.",2105.06139v1
2014/10/23,The 2014 Magnetism Roadmap,"Magnetism is a very fascinating and dynamic field. Especially in the last 30
years it has experienced many major advances in the full range from novel
fundamental phenomena to new products. Applications such as hard disk drives
and magnetic sensors are part of our daily life, and new applications, such as
in non-volatile computer random access memory, are expected to surface shortly.
Thus it is timely for describing the current status, and current and future
challenges in the form of a Roadmap article. This 2014 Magnetism Roadmap
provides a view on several selected, currently very active innovative
developments. It consists of 12 sections, each written by an expert in the
field and addressing a specific subject, with strong emphasize on future
potential. This Roadmap cannot cover the entire field. We have selected several
highly relevant areas without attempting to provide a full review - a future
update will have room for more topics. The scope covers mostly nano-magnetic
phenomena and applications, where surfaces and interfaces provide additional
functionality. New developments in fundamental topics such as interacting
nano-elements, novel magnon-based spintronics concepts, spin-orbit torques and
spin-caloric phenomena are addressed. New materials, such as organic magnetic
materials and permanent magnets are covered. New applications are presented
such as nano-magnetic logic, non-local and domain-wall based devices,
heat-assisted magnetic recording, magnetic random access memory, and
applications in biotechnology. May the Roadmap serve as a guideline for future
emerging research directions in modern magnetism.",1410.6404v1
2016/4/8,Ultrafast energy and momentum resolved dynamics of magnetic correlations in photo-doped Mott insulator Sr$_2$IrO$_4$,"Measuring how the magnetic correlations throughout the Brillouin zone evolve
in a Mott insulator as charges are introduced dramatically improved our
understanding of the pseudogap, non-Fermi liquids and high $T_C$
superconductivity. Recently, photoexcitation has been used to induce similarly
exotic states transiently. However, understanding how these states emerge has
been limited because of a lack of available probes of magnetic correlations in
the time domain, which hinders further investigation of how light can be used
to control the properties of solids. Here we implement magnetic resonant
inelastic X-ray scattering at a free electron laser, and directly determine the
magnetization dynamics after photo-doping the Mott insulator Sr$_2$IrO$_4$. We
find that the non-equilibrium state 2~ps after the excitation has strongly
suppressed long-range magnetic order, but hosts photo-carriers that induce
strong, non-thermal magnetic correlations. The magnetism recovers its
two-dimensional (2D) in-plane N\'eel correlations on a timescale of a few ps,
while the three-dimensional (3D) long-range magnetic order restores over a far
longer, fluence-dependent timescale of a few hundred ps. The dramatic
difference in these two timescales, implies that characterizing the
dimensionality of magnetic correlations will be vital in our efforts to
understand ultrafast magnetic dynamics.",1604.02439v2
2016/5/13,Superconducting Pb stripline resonators in parallel magnetic field and their application for microwave spectroscopy,"Planar superconducting microwave resonators are key elements in a variety of
technical applications and also act as sensitive probes for microwave
spectroscopy of various materials of interest. Here superconducting Pb is a
suitable material as a basis for microwave stripline resonators.
  To utilize Pb stripline resonators in a variable magnetic field (e.g. in
ESR), the electrodynamics of such resonators in finite magnetic field has to be
well understood. Therefore we performed microwave transmission measurements on
superconducting Pb stripline resonators in a variable, parallel magnetic field.
We determined surface resistance, penetration depth as well as real and
imaginary parts, \sigma$_1$ and \sigma$_2$, of the complex conductivity of
superconducting Pb as a function of magnetic field. Here we find features
reminiscent of those in temperature-dependent measurements, such as a maximum
in \sigma$_1$ (coherence peak). At magnetic fields above the critical field of
this type-I superconductor we still find low-loss microwave response, which we
assign to remaining superconductivity in the form of filaments within the Pb.
Hysteresis effects are found in the quality factor of resonances once the swept
magnetic field has exceeded the critical magnetic field. This is due to normal
conducting areas that are pinned and can therefore persist in the
superconducting phase. Besides zero-field-cooling we show an alternative way to
eliminate these even at T<T$_c$. Based on our microwave data, we determine the
critical magnetic field and the critical temperature of Pb in a temperature
range between 1.6K and 6.5K and magnetic fields up to 140mT, showing good
agreement with BCS predictions. We study a Sn sample in a Pb resonator to
demonstrate the applicability of superconducting Pb stripline resonators in the
experimental study of other (super-)conducting materials in a variable magnetic
field.",1605.04273v2
2023/11/20,Electrical control of magnetism by electric field and current-induced torques,"While early magnetic memory designs relied on magnetization switching by
locally generated magnetic fields, key insights in condensed matter physics
later suggested the possibility to do it electrically. In the 1990s,
Slonczewzki and Berger formulated the concept of current-induced spin torques
in magnetic multilayers through which a spin-polarized current may switch the
magnetization of a ferromagnet. This discovery drove the development of
spin-transfer-torque magnetic random-access memories (STT-MRAMs). More recent
research unveiled spin-orbit-torques (SOTs) and will lead to a new generation
of devices including SOT-MRAMs. Parallel to these advances, multiferroics and
their magnetoelectric coupling experienced a renaissance, leading to novel
device concepts for information and communication technology such as the MESO
transistor. The story of the electrical control of magnetization is that of a
dance between fundamental research (in spintronics, condensed matter physics,
and materials science) and technology (MRAMs, MESO, microwave emitters,
spin-diodes, skyrmion-based devices, components for neuromorphics, etc). This
pas de deux led to major breakthroughs over the last decades (pure spin
currents, magnetic skyrmions, spin-charge interconversion, etc). As a result,
this field has propelled MRAMs into consumer electronics products but also
fueled discoveries in adjacent research areas such as ferroelectrics or
magnonics. Here, we cover recent advances in the control of magnetism by
electric fields and by current-induced torques. We first review fundamental
concepts in these two directions, then discuss their combination, and finally
present various families of devices harnessing the electrical control of
magnetic properties for various application fields. We conclude by giving
perspectives in terms of both emerging fundamental physics concepts and new
directions in materials science.",2311.11724v1
2006/7/20,Dipolar interaction effects in the magnetic and magnetotransport properties of ordered nanoparticle arrays,"Assemblies of magnetic nanoparticles exhibit interesting physical properties
arising from the competition of intraparticle dynamics and interparticle
interactions. In ordered arrays of magnetic nanoparticles magnetostatic
interparticle interactions introduce collective dynamics acting competitively
to random anisotropy. Basic understanding, characterization and control of
dipolar interaction effects in arrays of magnetic nanoparticles is an issue of
central importance. To this end, numerical simulation techniques offer an
indispensable tool. We report on Monte Carlo studies of the magnetic hysteresis
and spin-dependent transport in thin films formed by ordered arrays of magnetic
nanoparticles. Emphasis is given to the modifications of the single-particle
behavior due to interparticle dipolar interactions as these arise in quantities
of experimental interest, such as, the magnetization, the susceptibility and
the magnetoresistance. We investigate the role of the structural parameters of
an array (interparticle separation, number of stacked monolayers) and the role
of the internal structure of the nanoparticles (single phase, core-shell).
Dipolar interactions are responsible for anisotropic magnetic behavior between
the in-plane and out-of-plane directions of the sample, which is reflected on
the investigated magnetic properties (magnetization, transverse susceptibility
and magnetoresistance) and the parameters of the array (remanent magnetization,
coercive field, and blocking temperature). Our numerical results are compared
to existing measurements on self-assembled arrays of Fe-based and Co
nanoparticles is made.",0607520v3
2007/3/14,Remagnetization of bulk high-temperature superconductors subjected to crossed and rotating magnetic fields,"Bulk melt-processed Y-Ba-Cu-O (YBCO) has significant potential for a variety
of high field permanent magnet-like applications, such as the rotor of a
brushless motor. When used in rotating devices of this kind, however, the YBCO
can be subjected to both transient and alternating magnetic fields that are not
parallel to the direction of magnetization and which have a detrimental effect
on the trapped field. These effects may lead to a long-term decay of the
magnetization of the bulk sample. In the present work, we analyze both
experimentally and numerically the remagnetization process of a melt-processed
YBCO single domain that has been partially demagnetized by a magnetic field
applied orthogonal to the initial direction of trapped flux. Magnetic torque
measurements are used as a tool to probe changes in the remanent magnetization
during various sequences of applied field. The application of a small magnetic
field between the transverse cycles parallel to the direction of original
magnetization results in partial remagnetization of the sample. Rotating the
applied field, however, is found to be much more efficient at remagnetizing the
bulk material than applying a magnetizing field pulse of the same amplitude.
The principal features of the experimental data can be reproduced qualitatively
using a two-dimensional finite-element numerical model based on an E-J power
law. Finally, the remagnetization process is shown to result from the complex
modification of current distribution within the cross-section of the bulk
sample.",0703362v1
2008/4/8,Piezo-control of magnetic anisotropy in GaMnAs: Reversible manipulation of magnetization orientation and irreversible magnetization switching,"We have investigated the magnetic properties of a piezoelectric
actuator/ferromagnetic semiconductor hybrid structure. Using a GaMnAs epilayer
as the ferromagnetic semiconductor and applying the piezo-stress along its
[110] direction, we quantify the magnetic anisotropy as a function of the
voltage V_p applied to the piezoelectric actuator using anisotropic
magnetoresistance techniques. We find that the easy axis of the strain-induced
uniaxial magnetic anisotropy contribution can be inverted from the [110] to the
[1-10] direction via the application of appropriate voltages V_p. At T=5K the
magnetoelastic term is a minor contribution to the magnetic anisotropy.
Nevertheless, we show that the switching fields of rho(H) loops are shifted as
a function of V_p at this temperature. At 50K - where the magnetoelastic term
dominates the magnetic anisotropy - we are able to tune the magnetization
orientation by about 70 degree solely by means of the electrical voltage V_p
applied. Furthermore, we derive the magnetostrictive constant lambda_111 as a
function of temperature and find values consistent with earlier results. We
argue that the piezo-voltage control of magnetization orientation is directly
transferable to other ferromagnetic/piezoelectric hybrid structures, paving the
way to innovative multifunctional device concepts. As an example, we
demonstrate piezo-voltage induced irreversible magnetization switching at
T=40K, which constitutes the basic principle of a nonvolatile memory element.",0804.1336v1
2008/10/31,The magnetic state of 1212-type ruthenocuprate in magnetocaloric and magnetoresistivity measurements of polycrystalline samples of RuSr2Gd1-xCexCu2O8 and Ru1-xSr2GdCu2O8,"The magnetic properties of superconducting Ru1-xSr2GdCu2O8 (x=0, 0.02) and
non-superconducting RuSr2Gd1-xCexCu2O8 (x=0.07, 0.1) were investigated by means
of magnetocaloric experiments with complementary magnetoresistivity and ac
susceptibility measurements. The isothermal magnetocaloric coefficient M_{T}(B)
assumes positive values in a broad range of temperatures (20K<T<231 K) and
magnetic fields (0<B<13 T), i.e. also in the magnetically ordered state
(T_{m}=132 K for RuSr2GdCu2O8 and T_{m}=150 K for RuSr2Gd0.93Ce0.07Cu2O8),
which indicates no gain in the system's magnetic entropy with increasing
magnetic field. The maximum in the M_{T}(B) dependence was observed for
RuSr2GdCu2O8 in a temperature vicinity of T_{m}, which indicates a
ferromagnetic character of the accessed magnetic correlations. No spontaneous
ferromagnetic order was revealed as the M_{T} assumes limiting zero values at
zero magnetic field for the whole range of investigated temperatures.
Temperature dependencies of the specific heat reveal the magnetic-field-induced
positive temperature shift of the anomaly associated with the magnetic
transition in the Ru spin system. The M_{T}(B) dependencies and the
magnetoresistivity data suggest that the magnetic system may be inhomogeneous.",0810.5588v3
2009/5/20,Measuring magnetic profiles at manganite surfaces with monolayer resolution,"The performance of manganite-based magnetic tunnel junctions (MTJs) has
suffered from reduced magnetization present at the junction interfaces that is
ultimately responsible for the spin polarization of injected currents; this
behavior has been attributed to a magnetic ""dead layer"" that typically extends
a few unit cells into the manganite. X-ray magnetic scattering in resonant
conditions (XRMS) is one of the most innovative and effective techniques to
extract surface or interfacial magnetization profiles with subnanometer
resolution, and has only recently been applied to oxide heterostructures. Here
we present our approach to characterizing the surface and interfacial
magnetization of such heterostructures using the XRMS technique, conducted at
the BEAR beamline (Elettra synchrotron, Trieste). Measurements were carried out
in specular reflectivity geometry, switching the left/right elliptical
polarization of light as well the magnetization direction in the scattering
plane. Spectra were collected across the Mn L2,3 edge for at least four
different grazing angles in order to better analyse the interference phenomena.
The resulting reflectivity spectra have been carefully fit to obtain the
magnetization profiles, minimizing the number of free parameters as much as
possible. Optical constants of the samples (real and imaginary part of the
refractive index) in the interested frequency range are obtained through
absorption measurements in two magnetization states and subsequent
Kramers-Kronig transformation, allowing quantitative fits of the magnetization
profile at different temperatures. We apply this method to the study of
air-exposed surfaces of epitaxial La2/3Sr1/3MnO3 (001) films grown on SrTiO3
(001) substrates.",0905.3204v1
2010/2/10,Magnetic field regulated infall on the disc around the massive protostar Cepheus A HW2,"We present polarization observations of the 6.7-GHz methanol masers around
the massive protostar Cepheus A HW2 and its associated disc. The data were
taken with the Multi-Element Radio Linked Interferometer Network. The maser
polarization is used to determine the full three-dimensional magnetic field
structure around Cepheus A HW2. The observations suggest that the masers probe
the large scale magnetic field and not isolated pockets of a compressed field.
We find that the magnetic field is predominantly aligned along the protostellar
outflow and perpendicular to the molecular and dust disc. From the
three-dimensional magnetic field orientation and measurements of the magnetic
field strength along the line of sight, we are able to determine that the high
density material, in which the masers occurs, is threaded by a large scale
magnetic field of ~23 mG. This indicates that the protostellar environment at
~1000 AU from Cepheus A HW2 is slightly supercritical (lambda approximately
1.7) and the relation between density and magnetic field is consistent with
collapse along the magnetic field lines. Thus, the observations indicate that
the magnetic field likely regulates accretion onto the disc. The magnetic field
dominates the turbulent energies by approximately a factor of three and is
sufficiently strong to be the crucial component stabilizing the massive
accretion disc and sustaining the high accretion rates needed during massive
star-formation.",1002.2214v1
2010/5/6,The magnetic interactions in spin-glasslike Ge/1-x-y/Sn/x/Mn/y/Te diluted magnetic semiconductor,"We investigated the nature of the magnetic phase transition in the
Ge/1-x-y/Sn/x/Mn/y/Te mixed crystals with chemical composition changing in the
range of 0.083 < x < 0.142 and 0.012 < y < 0.119. The DC magnetization
measurements performed in the magnetic field up to 90 kOe and temperature range
2-200 K showed that the magnetic ordering at temperatures below T = 50 K
exhibits features characteristic for both spin-glass and ferromagnetic phases.
The modified Sherrington - Southern model was applied to explain the observed
transition temperatures. The calculations showed that the spin-glass state is
preferred in the range of the experimental carrier concentrations and Mn
content. The value of the Mn hole exchange integral was estimated to be J/pd/ =
0.45+/-0.05 eV. The experimental magnetization vs temperature curves were
reproduced satisfactory using the non-interacting spin-wave theory with the
exchange constant J/pd/ values consistent with those calculated using modified
Sherrington - Southern model. The magnetization vs magnetic field curves showed
nonsaturating behavior at magnetic fields B < 90 kOe indicating the presence of
strong magnetic frustration in the system. The experimental results were
reproduced theoretically with good accuracy using the molecular field
approximation-based model of a disordered ferromagnet with long-range RKKY
interaction.",1005.0922v2
2013/7/19,Quantitative magnetic imaging at the nanometer scale by ballistic electron magnetic microscopy,"We demonstrate quantitative ballistic electron magnetic microscopy (BEMM)
imaging of simple model Fe(001) nanostructures. We use in situ nanostencil
shadow mask resistless patterning combined with molecular beam epitaxy
deposition to prepare under ultra-high vacuum conditions nanostructured
epitaxial Fe/Au/Fe/GaAs(001) spin-valves. In this epitaxial system, the
magnetization of the bottom Fe/GaAs(001) electrode is parallel to the [110]
direction, defining accurately the analysis direction for the BEMM experiments.
The large hot-electron magnetoresistance of the Fe/Au/Fe/GaAs(001) epitaxial
spin-valve allows us to image various stable magnetic configurations on the
as-grown Fe(001) microstructures with a high sensitivity, even for small
misalignments of both magnetic electrodes. The angular dependence of the
hot-electron magnetocurrent is used to convert magnetization maps calculated by
micromagnetic simulations into simulated BEMM images. The calculated BEMM
images and magnetization rotation profiles show quantitative agreement with
experiments and allow us to investigate the magnetic phase diagram of these
model Fe(001) microstructures. Finally, magnetic domain reversals are observed
under high current density pulses. This opens the way for further BEMM
investigations of current-induced magnetization dynamics.",1307.5150v1
2014/5/19,Approaching the Ground State of Frustrated A-site Spinels: A Combined Magnetization and Polarized Neutron Scattering Study,"We re-investigate the magnetically frustrated, {\it
diamond-lattice-antiferromagnet} spinels FeAl$_2$O$_4$ and MnAl$_2$O$_4$ using
magnetization measurements and diffuse scattering of polarized neutrons. In
FeAl$_2$O$_4$, macroscopic measurements evidence a ""cusp"" in zero field-cooled
susceptibility around 13~K. Dynamic magnetic susceptibility and {\it memory
effect} experiments provide results that do not conform with a canonical
spin-glass scenario in this material. Through polarized neutron scattering
studies, absence of long-range magnetic order down to 4~K is confirmed in
FeAl$_2$O$_4$. By modeling the powder averaged differential magnetic neutron
scattering cross-section, we estimate that the spin-spin correlations in this
compound extend up to the third nearest-neighbour shell. The estimated value of
the Land\'{e} $g$ factor points towards orbital contributions from Fe$^{2+}$.
This is also supported by a Curie-Weiss analysis of the magnetic
susceptibility. MnAl$_2$O$_4$, on the contrary, undergoes a magnetic phase
transition into a long-range ordered state below $\approx$ 40~K, which is
confirmed by macroscopic measurements and polarized neutron diffraction.
However, the polarized neutron studies reveal the existence of prominent
spin-fluctuations co-existing with long-range antiferromagnetic order. The
magnetic diffuse intensity suggests a similar short range order as in
FeAl$_2$O$_4$. Results of the present work supports the importance of spin-spin
correlations in understanding magnetic response of frustrated magnets like
$A$-site spinels which have predominant short-range spin correlations
reminiscent of the ""spin liquid"" state.",1405.4694v1
2014/10/23,The influence of the magnetic field on the performance of an active magnetic regenerator (AMR),"The influence of the time variation of the magnetic field, termed the
magnetic field profile, on the performance of a magnetocaloric refrigeration
device using the active magnetic regeneration (AMR) cycle is studied for a
number of process parameters for both a parallel plate and packed bed
regenerator using a numerical model. The cooling curve of the AMR is shown to
be almost linear far from the Curie temperature of the magnetocaloric material.
It is shown that a magnetic field profile that is 10% of the cycle time out of
sync with the flow profile leads to a drop in both the maximum temperature span
and the maximum cooling capacity of 20-40\% for both parallel plate and packed
bed regenerators. The maximum cooling capacity is shown to depend very weakly
on the ramp rate of the magnetic field. Reducing the temporal width of the high
field portion of the magnetic field profile by 10% leads to a drop in maximum
temperature span and maximum cooling capacity of 5-20%. An increase of the
magnetic field from 1 T to 1.5 T increases the maximum cooling capacity by
30-50% but the maximum temperature span by only 20-30%. Finally, it was seen
that the influence of changing the magnetic field was more or less the same for
the different regenerator geometries and operating parameters studied here.
This means that the design of the magnet can be done independently of the
regenerator geometry.",1410.6246v1
2015/5/21,Magnetic coupling at ferromagnetic rare earth / transition-metal interfaces: A comprehensive study,"Thin film magnetic heterostructures with competing interfacial coupling and
Zeeman energy pro- vide a fertile ground to study phase transition between
different equilibrium states as a function of external magnetic field and
temperature. A rare-earth (RE) / transition metal (TM) ferro- magnetic
multilayer is a classic example where the magnetic state is determined by a
competition between the Zeeman energy and antiferromagnetic interfacial
exchange coupling energy. Techno- logically, such structures offer the
possibility to engineer the macroscopic magnetic response by tuning the
microscopic interactions between the layers. We have performed an exhaustive
study of a nickel/gadolinium system by using the element-specific measurement
technique x-ray magnetic circular dichroism, and determined the full magnetic
state diagrams as a function of temperature and magnetic layer thickness. We
explain our result based on a modified Stoner-Wohlfarth formal- ism and provide
evidence of a thickness-dependent phase transition to a magnetic fan state
which is critical in understanding magnetoresistance effects in RE/TM systems.
The results provide im- portant insight for spintronics and superconducting
spintronics where engineering tunable magnetic inhomogeneity is key for certain
applications.",1505.05864v2
2015/5/26,Nano Superconducting Quantum Interference device: a powerful tool for nanoscale investigations,"The magnetic sensing at nanoscale level is a promising and interesting
research topic of nanoscience. Indeed, magnetic imaging is a powerful tool for
probing biological, chemical and physical systems. The study of small spin
cluster, like magnetic molecules and nanoparticles, single electron, cold atom
clouds, is one of the most stimulating challenges of applied and basic research
of the next years. In particular, the magnetic nanoparticle investigation plays
a fundamental role for the modern material science and its relative
technological applications like ferrofluids, magnetic refrigeration and
biomedical applications, including drug delivery, hyper-thermia cancer
treatment and magnetic resonance imaging contrast-agent. In this framework,
several efforts have been devoted to the development of a high sensitivity
magnetic nanosensor pushing sensing capability to the individual spin level.
Among the different magnetic sensors, Superconducting QUantum Interference
Devices (SQUIDs) exhibit an ultra high sensitivity and are widely employed in
numerous applications. In the recent years, it has been proved that the
magnetic response of nano-objects can be effectively measured by using a SQUID
with a very small sensitive area (nanoSQUID). In fact, the sensor noise,
expressed in terms of the elementary magnetic moment (spin or Bohr magneton),
is linearly dependent on the SQUID loop side length. For this reason, SQUIDs
have been progressively miniaturized in order to improve the sensitivity up to
few spin per unit of bandwidth. With respect to other techniques, nanoSQUIDs
offer the advantage of direct measurement of magnetization changes in small
spin systems. In this review, we focus on nanoSQUIDs and its applications. In
particular, we will discuss the motivations, the theoretical aspects, the
fabrication techniques, the different nanoSQUIDs and the relative nanoscale
applications.",1505.06887v1
2015/8/10,Magneto-optical imaging of thin magnetic films using spins in diamond,"Imaging the fields of magnetic materials provides crucial insight into the
physical and chemical processes surrounding magnetism, and has been a key
ingredient in the spectacular development of magnetic data storage. Existing
approaches using the magneto-optic Kerr effect (MOKE), x-ray and electron
microscopy have limitations that constrain further development, and there is
increasing demand for imaging and characterisation of magnetic phenomena in
real time with high spatial resolution. In this work, we show how the
magneto-optical response of an array of negatively-charged nitrogen-vacancy
spins in diamond can be used to image and map the sub-micron stray magnetic
field patterns from thin ferromagnetic films. Using optically detected magnetic
resonance, we demonstrate wide-field magnetic imaging over 100x100 {\mu}m^2
with a diffraction-limited spatial resolution of 440 nm at video frame rates,
under ambient conditions. We demonstrate a novel all-optical spin relaxation
contrast imaging approach which can image magnetic structures in the absence of
an applied microwave field. Straightforward extensions promise imaging with
sub-{\mu}T sensitivity and sub-optical spatial and millisecond temporal
resolution. This work establishes practical diamond-based wide-field microscopy
for rapid high-sensitivity characterisation and imaging of magnetic samples,
with the capability for investigating magnetic phenomena such as domain wall
and skyrmion dynamics and the spin Hall effect in metals.",1508.02135v1
2015/11/14,Magnetic field induced augmented thermal conduction phenomenon in magneto nanocolloids,"Magnetic field induced drastically augmented thermal conductivity of magneto
nanocolloids involving magnetic oxide nanoparticles, viz. Fe2O3, Fe3O4, Nickel
oxide (NiO), Cobalt oxide (Co3O4), dispersed in different base fluids (heat
transfer oil, kerosene, and ethylene glycol) have been reported. Experiments
reveal the augmented thermal transport under the external applied magnetic
field, with kerosene based MNCs showing at relatively low magnetic field
intensities as compared to the heat transfer oil and EG based MNCs. A maximum
thermal conductivity enhancement of 114 % is attained at 7.0 vol. %
concentration and 0.1 T field intensity for Fe3O4/EG magneto nanocolloid.
However, a maximum of 82% thermal conductivity enhancement is observed for
Fe3O4/Kerosene magneto nanocolloid for the same concentration but relatively at
low magnetic field (600 G). Thereby, a strong effect of fluid as well as
particle physical properties on the chain formation propensity, leading to
enhanced conduction, in such systems is observed. Co3O4 nanoparticles show
insignificant effect on the thermal conductivity enhancement of MNCs due to
their minimal magnetic moment. An analytical approach has been proposed to
understand the mechanism and physics behind the thermal conductivity
enhancement under external applied magnetic field, in tune with near field
magnetostatic interactions as well as Neel relaxivity of the magnetic
nanoparticles. Furthermore, the analytical model is able to predict the
phenomenon of enhanced thermal conductivity as a function of physical
parameters such as chain length, size and types of nanoparticles, fluid
characteristics, magnetic field intensity, saturation magnetic moment,
nanoparticle concentration etc. and good agreement with the experimental
results has been observed.",1511.04560v1
2016/5/11,"Magnetic behavior of Gd3Ru4Al12, a layered compound with a distorted Kagome net","The magnetic behavior of the compound, Gd3Ru4Al12, which has been reported to
crystallize in a hexagonal structure about two decades ago, had not been
investigated in the past literature despite interesting structural features
(that is, magnetic layers and triangles as well as Kagome-lattice features
favouring frustrated magnetism) characterizing this compound. We report here
the results of magnetization, heat-capacity, and magnetoresistance studies in
the temperature (T) range 1.8-300 K. The results establish that there is a
long-range magnetic order of an antiferromagnetic type below (TN= ) 18.5 K,
despite a much large value (about 80 K) of paramagnetic Curie temperature with
a positive sign characteristic of ferromagnetic interaction. We attribute this
to geometric frustration. The most interesting finding is that there is an
additional magnetic anomaly below about 55 K before the onset of long range
order in the magnetic susceptibility data. Concurrent with this observation,
the sign of isothermal entropy change remains positive above TN with a broad
peak above TN. This observation indicates the presence of ferromagnetic
clusters before the onset of long range magnetic order. Thus, this compound may
serve as an example for a situation in which magnetic frustration due to
geometrical reasons is faced by competition with such precursor effects. There
is also a reversal of the sign of entropy-change in the curves for lower final
fields (for H less than 30 kOe) on entering into magnetically ordered state
consistent with the entrance into antiferromagnetic state. The
magnetoresistance behavior is consistent with above conclusions.",1605.03528v1
2016/9/20,NanoSQUIDs: Basics & recent advances,"Superconducting Quantum Interference Devices (SQUIDs) are one of the most
popular devices in superconducting electronics. They combine the Josephson
effect with the quantization of magnetic flux in superconductors. This gives
rise to one of the most beautiful manifestations of macroscopic quantum
coherence in the solid state. In addition, SQUIDs are extremely sensitive
sensors allowing to transduce magnetic flux into measurable electric signals.
As a consequence, any physical observable that can be converted into magnetic
flux, e.g., current, magnetization, magnetic field or position, becomes easily
accessible to SQUID sensors. In the late 1980's it became clear that downsizing
the dimensions of SQUIDs to the nanometric scale would encompass an enormous
increase of their sensitivity to localized tiny magnetic signals. Indeed,
nanoSQUIDs opened the way to the investigation of, e.g., individual magnetic
nanoparticles or surface magnetic states with unprecedented sensitivities. The
purpose of this review is to present a detailed survey of microscopic and
nanoscopic SQUID sensors. We will start by discussing the principle of
operation of SQUIDs, placing the emphasis on their application as
ultrasensitive detectors for small localized magnetic signals. We will continue
by reviewing a number of existing devices based on different kinds of Josephson
junctions and materials, focusing on their advantages and drawbacks. The last
sections are left for applications of nanoSQUIDs in the fields of scanning
SQUID microscopy and magnetic particle characterization, putting special stress
on the investigation of individual magnetic nanoparticles.",1609.06182v4
2016/10/3,Hidden momentum and the Abraham-Minkowski debate,"We use an extended version of electrodynamics, which admits the existence of
magnetic charges and currents, to discuss how different models for electric and
magnetic dipoles do or do not carry hidden momentum under the influence of
external electromagnetic fields. Based on that, we discuss how the models
adopted for the electric and magnetic dipoles from the particles that compose a
material medium influence the expression for the electromagnetic part of the
light momentum in the medium. We show that Abraham expression is compatible
with electric dipoles formed by electric charges and magnetic dipoles formed by
magnetic charges, while Minkowski expression is compatible with electric
dipoles formed by magnetic currents and magnetic dipoles formed by electric
currents. The expression $\varepsilon_0\mathbf{E}\times\mathbf{B}$, on the
other hand, is shown to be compatible with electric dipoles formed by electric
charges and magnetic dipoles formed by electric currents, which are much more
natural models. So this expression has an interesting interpretation in the
Abraham-Minkowski debate about the momentum of light in a medium: It is the
expression compatible with the nonexistence of magnetic charges. We also
provide a simple justification of why Abraham and Minkowski momenta can be
associated with the kinetic and canonical momentum of light, respectively.",1610.05785v3
2016/11/9,Simultaneous imaging of strain waves and induced magnetization dynamics at the nanometer scale,"Changes in strain can be used to modify electronic and magnetic properties in
crystal structures, to manipulate nanoparticles and cells, or to control
chemical reactions. The magneto-elastic (ME) effect--the change of magnetic
properties caused by the elastic deformation (strain) of a magnetic
material--has been proposed as an alternative approach to magnetic fields for
the low power control of magnetization states of nanoelements since it avoids
charge currents, which entail ohmic losses. Multiferroic heterostructures
\cite{Zheng2004} and nanocomposites have exploited this effect in search of
electric control of magnetic states, mostly in the static regime. Quantitative
studies combining strain and magnetization dynamics are needed for practical
applications and so far, a high resolution technique for this has been lacking.
Here, we have studied the effect of the dynamic strain accompanying a surface
acoustic wave on magnetic nanostructures. We have simultaneously imaged the
temporal evolution of both strain waves and magnetization dynamics of
nanostructures at the picosecond timescale. The newly developed experimental
technique, based on X-ray microscopy, is versatile and provides a pathway to
the study of strain-induced effects at the nanoscale. Our results provide
fundamental insight in the coupling between strain and magnetization in
nanostructures at the picosecond timescale, having implications in the design
of strain-controlled magnetostrictive nano-devices.",1611.02847v1
2017/1/26,3D Printing of Polymer Bonded Rare-Earth Magnets With a Variable Magnetic Compound Density for a Predefined Stray Field,"Additive manufacturing of polymer bonded magnets is a recently developed
technique, for single-unit production, and for structures that have been
impossible to manufacture previously. Also new possibilities to create a
specific stray field around the magnet are triggered. The current work presents
a method to 3D print polymer bonded magnets with a variable magnetic compound
density distribution. A low-cost, end-user 3D printer with a mixing extruder is
used to mix permanent magnetic filaments with pure PA12 filaments. The magnetic
filaments are compounded, extruded, and characterized for the printing process.
To deduce the quality of the manufactured magnets with a variable compound
density, an inverse stray field framework is used. The effectiveness of the
printing process and the simulation method is shown. It can also be used to
manufacture magnets that produce a predefined stray field in a given region.
Examples for sensor applications are presented. This setup and simulation
framework allows the design and manufacturing of polymer bonded permanent
magnets which are impossible to create with conventional methods.",1701.07703v1
2017/5/3,Surface-plasmon opto-magnetic field enhancement for all-optical magnetization switching,"The demand for faster magnetization switching speeds and lower energy
consumption has driven the field of spintronics in recent years. The magnetic
tunnel junction is the most developed spintronic memory device in which the
magnetization of the storage layer is switched by spin-transfer-torque or
spin-orbit torque interactions. Whereas these novel spin-torque interactions
exemplify the potential of electron-spin-based devices and memory, the
switching speed is limited to the ns regime by the precessional motion of the
magnetization. All-optical magnetization switching, based on the inverse
Faraday effect, has been shown to be an attractive method for achieving
magnetization switching at ps speeds. Successful magnetization reversal in thin
films has been demonstrated by using circularly polarized light. However, a
method for all-optical switching of on-chip nanomagnets in high density memory
modules has not been described. In this work we propose to use plasmonics, with
CMOS compatible plasmonic materials, to achieve on-chip magnetization reversal
in nanomagnets. Plasmonics allows light to be confined in dimensions much
smaller than the diffraction limit of light. This in turn, yields higher
localized electromagnetic field intensities. In this work, through simulations,
we show that using localized surface plasmon resonances, it is possible to
couple light to nanomagnets and achieve significantly higher opto-magnetic
field values in comparison to free space light excitation.",1705.01311v1
2017/11/26,Magnetization reversal in bent nanofibers of different cross-sections,"Artificial ferromagnetic nanofiber networks with new electronic, magnetic,
mechanical and other physical properties can be prepared by electrospinning and
may be regarded as the base of bio-inspired cognitive computing units. For this
purpose, it is necessary to examine all relevant physical parameters of such
nanofiber networks. Due to the more or less random arrangement of the
nanofibers and the possibility of gaining bent nanofibers in this production
process, elementary single nanofibers with varying bending radii, from straight
fibers to those bent along half-circles, were investigated by micromagnetic
simulations, using different angles with respect to the external magnetic
field. As expected from the high aspect ratios and the resulting strong shape
anisotropy, all magnetization reversal processes took place via domain wall
processes. Changing the cross-section from circular to a circle-segment or a
rectangle significantly altered the coercive fields and its dependence on the
bending radius, especially for the magnetic field oriented perpendicular (90
deg) to the fiber axes. In all three cross-sections, an angle of 45{\deg}
between the fiber orientation and the external magnetic field resulted in the
smallest influence of the bending radius. The shapes of the longitudinal and
transverse hysteresis curves showed strong differences, depending on
cross-section, bending radius and orientation to the magnetic field, often
depicting distinct transverse magnetization peaks perpendicular to the fibers
for fibers which were not completely oriented parallel to the magnetic field.
Varying these parameters thus provides a broad spectrum of magnetization
reversal processes in magnetic nanofibers and correspondingly scenarios for a
variety of fiber-based information processing.",1711.09370v2
2018/4/19,Probing Magnetic Sublattices in Multiferroic Ho$_{0.5}$Nd$_{0.5}$Fe$_{3}$(BO$_{3}$)$_{4}$ Single Crystal using X-ray Magnetic Circular Dichroism,"Using element-specific X-ray magnetic circular dichroism (XMCD) technique we
have studied different magnetic sublattices in a multiferroic
Ho$_{0.5}$Nd$_{0.5}$Fe$_{3}$(BO$_{3}$)$_{4}$ single crystal. The XMCD
measurements at the \emph{L}$_{2,3}$-edges of Ho and Nd, and at the Fe
\emph{K}-edge have been performed at \emph{T}=2~K under a magnetic field up to
17~T applied along the trigonal \emph{c}-axis as well as in the basal
\emph{ab}-plane. All three magnetic sublattices are shown to undergo a
spin-reorientation transition under magnetic field applied along the
\emph{c}-axis. On the contrary, when magnetic field is applied in the
\emph{ab}-plane only the holmium atoms exhibit a magnetization jump. Thus, the
element-specific magnetization curves revealed the Ho sublattice to be much
stronger coupled to the Fe one than the Nd sublattice. The results demonstrate
that the Ho$^{3+}$ subsystem plays even more dominant role in magnetic behavior
of Ho$_{0.5}$Nd$_{0.5}$Fe$_{3}$(BO$_{3}$)$_{4}$ crystal than in pure
HoFe$_{3}$(BO$_{3}$)$_{4}$ crystal.",1804.07057v1
2018/4/21,Effects of external magnetic field and hydrostatic pressure on magnetic and structural phase transitions in Pr0.6Sr0.4MnO3,"We investigate the effect of hydrostatic pressure on temperature dependence
of magnetization and also the influence of magnetic field on linear thermal
expansion in polycrystalline Pr0.6Sr0.4MnO3, which is ferromagnetic at room
temperature (TC = 305 K) but its magnetization undergoes an abrupt decrease at
TS = 89 K within the ferromagnetic state. Normal and inverse magnetocaloric
effects around TC and TS, respectively, were reported earlier in this single
phase compound [D. V. M. Repaka et al., J. Appl. Phys. 112, 123915 (2012)]. The
thermal expansion shows an abrupt decrease at TS in zero magnetic field but it
transforms into an abrupt increase at the same temperature under 7 T, which we
interpret as the consequence of magnetic field-induced structural transition
from a low-volume monoclinic (I2/a symmetry) to a high volume orthorhombic
(Pnma symmetry) phase in corroboration with a published neutron diffraction
study in zero magnetic field. While the external magnetic field does not change
TS, application of a hydrostatic pressure of P = 1.16 GPa shifts the magnetic
anomaly at TS towards high temperature. The pressure induced shift of the
low-temperature anomaly (deltaTS = 27 K) is nine-times more than that of the
ferromagnetic Curie temperature (deltaTC = 3K). Our results suggest that while
hydrostatic pressure stabilizes the low temperature monoclinic phase at the
expense of orthorhombic phase, magnetic field has an opposite effect.",1804.07903v1
2019/6/26,Intrinsic skyrmions in monolayer Janus magnets,"Skyrmions are localized solitonic spin textures with protected topology,
which are promising as information carriers in ultra-dense and energy-efficient
logic and memory devices. Recently, magnetic skyrmions have been observed in
magnetic thin films, and are stabilized by the extrinsic interfacial
Dzyaloshinskii-Moriya interaction (DMI) and/or external magnetic fields. The
specific effects in magnetic monolayer materials have not been thoroughly
studied. Here, we investigate the intrinsic magnetic skyrmions in a family of
monolayer Janus van der Waals magnets, MnSTe, MnSeTe, VSeTe, and MnSSe, by the
first-principles calculations combined with the micromagnetic simulations. The
monolayer Janus MnSTe, MnSeTe, and VSeTe with out-of-plane geometric asymmetry
and strong spin-orbit coupling (SOC) have a large intrinsic DMI, which could
stabilize a sub-50 nm intrinsic skyrmions in monolayer MnSTe and MnSeTe at zero
magnetic field. While monolayer VSeTe with in-plane easy axis forms magnetic
domain rather than skyrmions. Moreover, the size and shape of skyrmions can be
tuned by an external magnetic field. Therefore, our work motivates a new vista
for seeking intrinsic skyrmions in atomic-scale magnets.",1906.10836v2
2019/8/30,Giant Orbital Magneto-electric effect and Current-driven Magnetization Switching in Twisted Bilayer Graphene,"Recently, signatures of quantum anomalous Hall states with spontaneous
ferromagnetism were observed in twisted bilayer graphenes (TBGs) near 3/4
filling [1, 2]. Importantly, it was demon-strated that an extremely small
current can switch the direction of the magnetization. This offers the prospect
of realizing low energy dissipation magnetic memories. However, the mechanism
of the current-driven magnetization switching is poorly understood as the
charge currents in graphene layers are generally believed to be non-magnetic.
In this work, we demonstrate that, in TBGs, the twist-induced reduction of
lattice symmetry allows a charge current to generate net orbital magnetization
at a general filling factor through magnetoelectric effects. Substrate-induced
strain and sublattice symmetry breaking further reduce the symmetry such that
an out-of-plane orbital magnetization can be generated. Due to the large
non-trivial Berry phase of the flat bands, the orbital magnetization of a Bloch
state can be as large as tens of Bohr magnetons and therefore a small current
would be sufficient to generate a large orbital magnetization. We further
demonstrate how the charge current with orbital magnetization can switch the
magnetization of the quantum anomalous Hall state near 3/4 filling as observed
in the experiments [1, 2].",1908.11718v4
2012/9/10,"Glassy magnetic phase driven by short range charge and magnetic ordering in nanocrystalline La$_{1/3}$Sr$_{2/3}$FeO$_{3-δ}$: Magnetization, Mossbauer, and polarised neutron studies","The charge ordered La$_{1/3}$Sr$_{2/3}$FeO$_{3-\delta}$ (LSFO) in bulk and
nanocrystalline forms are investigated using ac and dc magnetization,
M\""{o}ssbauer, and polarised neutron studies. A complex scenario of short range
charge and magnetic ordering is realized from the polarised neutron studies in
nanocrystalline specimen. This short range ordering does not involve any change
in spin state and modification in the charge disproportion between Fe$^{3+}$
and Fe$^{5+}$ compared to bulk counterpart as evident in the M\""{o}ssbauer
results. The refinement of magnetic diffraction peaks provides magnetic moments
of Fe$^{3+}$ and Fe$^{5+}$ are about 3.15$\mu_B$ and 1.57$\mu_B$ for bulk, and
2.7$\mu_B$ and 0.53$\mu_B$ for nanocrystalline specimen, respectively. The
destabilization of charge ordering leads to magnetic phase separation, giving
rise to the robust exchange bias (EB) effect. Strikingly, EB field at 5 K
attains a value as high as 4.4 kOe for average size $\sim$ 70 nm, which is zero
for the bulk counterpart. A strong frequency dependence of ac susceptibility
reveals cluster-glass like transition around $\sim$ 65 K, below which EB
appears. Overall results propose that finite size effect directs the complex
glassy magnetic behavior driven by unconventional short range charge and
magnetic ordering, and magnetic phase separation appears in nanocrystalline
LSFO.",1209.1923v1
2015/12/23,Magnetic Ordering and Crystal Field Effects in Quasi Caged Structure Compound PrFe$_2$Al$_8$,"The compound PrFe$_2$Al$_8$ possesses a three-dimensional network structure
resulting from the packing of Al polyhedra centered at the transition metal
element Fe and the rare earth Pr. Along the $c$-axis, Fe and Pr form {\em
chains} which are separated from each other by the Al-network. In this paper,
the magnetism and crystalline electric field effects in PrFe$_2$Al$_8$ are
investigated through the analysis of magnetization and specific heat data. A
magnetic phase transition in the Pr lattice is identified at
$T^{Pr}_{N}\approx$ 4~K in dc magnetization and ac susceptibility data. At 2~K,
the magnetization isotherm presents a ferromagnetic saturation, however,
failing to reach full spin-only ferromagnetic moment of Pr$^{3+}$. Metamagnetic
step-like low-field features are present in the magnetization curve at 2~K
which is shown to shift upon field-cooling the material. Arrott plots centered
around $T^{Pr}_{N}$ display ""S""-like features suggestive of an inhomogeneous
magnetic state. The magnetic entropy, $S_m$, estimated from specific heat
outputs a value of $R$ ln(2) at $T_{N2}$ suggesting a doublet state for
Pr$^{3+}$. The magnetic specific heat is modeled by using a 9-level Schottky
equation pertinent to the Pr$^{3+}$ ion with $J$ = 4. Given the crystalline
electric field situation of Pr$^{3+}$, the inference of a doublet state from
specific heat and consequent long-range magnetic order is an unexpected result.",1512.07488v1
2010/4/29,Magnetization Vorticity and Exchange Bias Phenomena in Arrays of Small Asymmetric Magnetic Rings,"Arrays of nanoscopic magnetic asymmetric rings, 150 nm in outer diameter, are
fabricated using the techniques of electron-beam lithography, angular
deposition and ion-beam etching. Magnetic measurements for cobalt asymmetric
rings at room temperature verifies previous reports of vortex magnetic state
formation of a desired circulation direction for the application of external
magnetic field along the asymmetry axis of the rings. However, the main theme
of this article is the observation of exchange bias phenomena when the ring
samples are cooled down to low temperature in the presence of a positive
magnetic field. Very interestingly, the observed exchange bias effect is
negative for along and perpendicular orientations of ring's asymmetry axis with
respect to the in-plane external magnetic field. This is in good quantitative
agreement with the random interface model proposed by Malozemoff et al. For the
application of inplane external magnetic field at 45 degree with respect to the
asymmetry axis, the exchange bias effect is positive. Unlike the exchange bias
effects in thin films, this is a very unusual observation indicating that
exchange bias phenomena of opposite natures can be manipulated by appropriate
combination of geometrical constraint and external magnetic field direction, in
addition to the interfacial interactions between ferromagnetic (FM) and
antiferromagnetic (AFM) layer.",1004.5177v1
2018/9/26,Rare earth permanent magnets prepared by hot deformation process,"Hot deformation process is one of the primary methods to produce anisotropic
rare earth permanent magnets. Firstly, rapidly quenched powder flakes with
nanocrystal structure are condensed into the full dense isotropic precursors by
hot pressing process. And then, the prepared isotropic precursors are hot
deformed to produce high-anisotropy uniaxial bulk rare earth permanent magnets,
in which the highly textured structure is obtained in the hot plastic
deformation process. The obtained hot-deformed magnets possess many advantages,
such as near net-shape, outstanding corrosion resistance and ultrafine-grain
structure. The noteworthy effects of preparation parameters employed in
hot-pressing and deformation processes on the magnetic properties and
microstructures characterizations are systemically summarized in this academic
monograph. As a near net-shape technique, hot deformation process has
noteworthy advantages in producing irregular shape magnets, especially for
radially oriented ring-shape magnets with high length-diameter ratio or thin
wall. The difficulties in producing crack-free, homogeneous and non-decentered
ring-shaped magnets are basically resolved through mold design, adjustment of
deformation parameters and application of theoretical simulation. Considering
the characteristics of hot-deformed magnets, such as the grain shapes and
sizes, anisotropic distribution of intergranular phases, etc., there is
practical significance to study and improve the mechanical, electric properties
and thermal stability to enlarge the applicable area of hot-deformed magnets or
ring-shaped magnets.",1809.09838v1
2019/9/27,Magnetic Guinier law,"Small-angle scattering of x-rays and neutrons is a routine method for the
determination of nanoparticle sizes. The so-called Guinier law represents the
low-q approximation for the small-angle scattering curve from an assembly of
particles. The Guinier law has originally been derived for nonmagnetic
particle-matrix-type systems, and it is successfully employed for the
estimation of particle sizes in various scientific domains (e.g., soft matter
physics, biology, colloidal chemistry, materials science). An important
prerequisite for it to apply is the presence of a discontinuous interface
separating particles and matrix. Here, we introduce the Guinier law for the
case of magnetic small-angle neutron scattering (SANS) and experimentally
demonstrate its applicability for the example of nanocrystalline cobalt. It is
well-known that the magnetic microstructure of nanocrystalline ferromagnets is
highly nonuniform on the nanometer length scale and characterized by a spectrum
of continuously varying long-wavelength magnetization fluctuations, i.e., these
systems do not manifest sharp interfaces in their magnetization profile. The
magnetic Guinier radius depends on the applied magnetic field, on the magnetic
interactions (exchange, magnetostatics), and on the magnetic anisotropy-field
radius, which characterizes the size over which the magnetic anisotropy field
is coherently aligned into the same direction. In contrast to the nonmagnetic
conventional Guinier law, the magnetic version can be applied to fully dense
random-anisotropy-type ferromagnets.",1909.12687v2
2020/3/5,Tunable magnetic properties in van der Waals crystals (Fe$_{1-x}$Co$_x$)$_5$GeTe$_2$,"We report the doping effects of cobalt on van der Waals (vdW) magnet
Fe$_5$GeTe$_2$. A series of (Fe$_{1-x}$Co$_x$)$_5$GeTe$_2$ (0$\leq$x$\leq$0.44)
single crystals have been successfully grown, their structural, magnetic and
transport properties are investigated. For x=0.20, The Curie temperature $T_C$
increases from 276~K to 337~K. Moreover, the magnetic easy-axis is reoriented
to the $ab$-plane from the $c$-axis in undoped Fe$_5$GeTe$_2$ with largely
enhanced magnetic anisotropy. These magnetic properties would make
(Fe$_{0.8}$Co$_{0.2}$)$_5$GeTe$_2$ more effective in stabilizing magnetic order
in the two-dimensional limit. A complex magnetic phase diagram is identified on
the higher doping side. The x=0.44 crystal first orders ferromagnetically at
$T_C$=363~K then undergoes an antiferromagnetic transition at $T_N$=335~K.
Furthermore magnetic-field-induced spin-flop transitions are observed for the
AFM ground state. Our work reveals (Fe$_{1-x}$Co$_x$)$_5$GeTe$_2$ as promising
candidates for developing new spin-related applications and proposes a method
to engineer the magnetic properties of vdW magnet.",2003.02728v1
2021/5/12,Altermagnetism: spin-momentum locked phase protected by non-relativistic symmetries,"The search for novel magnetic quantum phases, phenomena and functional
materials has been guided by relativistic magnetic-symmetry groups in coupled
spin and real space from the dawn of the field in 1950s to the modern era of
topological matter. However, the magnetic groups cannot disentangle
non-relativistic phases and effects, such as the recently reported
unconventional spin physics in collinear antiferromagnets from the typically
weak relativistic spin-orbit coupling phenomena. Here we discover that more
general spin symmetries in decoupled spin and crystal space categorize
non-relativistic collinear magnetism in three phases: conventional ferromagnets
and antiferromagnets, and a third distinct phase combining zero net
magnetization with an alternating spin-momentum locking in energy bands, which
we dub ""altermagnetic"". For this third basic magnetic phase, which is omitted
by the relativistic magnetic groups, we develop a spin-group theory describing
six characteristic types of the altermagnetic spin-momentum locking. We
demonstrate an extraordinary spin-splitting mechanism in altermagnetic bands
originating from a local electric crystal field, which contrasts with the
conventional magnetic or relativistic splitting by global magnetization or
inversion asymmetry. Based on first-principles calculations, we identify
altermagnetic candidates ranging from insulators and metals to a parent crystal
of cuprate superconductor. Our results underpin emerging research of quantum
phases and spintronics in high-temperature magnets with light elements,
vanishing net magnetization, and strong spin-coherence.",2105.05820v2
2009/7/16,Particle size effect on magnetic properties of interacting La0.67Sr0.33MnO3 nanoparticles,"Magnetic nanoparticles of La0.67Sr0.33MnO3 (LSMO) manganite with mean
particle sizes of 13, 16, 18 and 21 nm were prepared by the sol-gel method. The
crystal structure and mean particle size of the synthesized powders were
estimated by X-ray diffraction (XRD) analysis using rietveld refinement and
transmission electron microscopy (TEM). Fourier transform infrared (FTIR)
transmission spectroscopy revealed that stretching and bending modes are
influenced by calcinations temperature. Dc magnetization versus magnetic field
of the samples was carried out at room temperature. Magnetic dynamics of the
samples was studied by the measurement of ac magnetic susceptibility versus
temperature at different frequencies and ac magnetic fields. A
frequency-dependent peak was observed in ac magnetic susceptibility versus
temperature which is well described by Vogel-Fulcher and critical slowing down
laws, and empirical and parameters. By fitting the experimental data with
Vogel-Fulcher and critical slowing down laws, the relaxation time,
characteristic temperature, magnetic anisotropy energy, effective magnetic
anisotropy constant and critical exponent zv have been estimated. The obtained
values of c1, c2, T0 and t0 from the Vogel-Fulcher law support of the presence
of strong interaction between magnetic nanoparticles. The values of zv and t0
obtained from critical slowing down fit suggest the presence of superspin glass
behavior in LSMO nanoparticles of different sizes.",0907.2815v1
2015/2/23,Table-top Measurement of Local Magnetization Dynamics Using Picosecond Thermal Gradients: Toward Nanoscale Magnetic Imaging,"Recent advances in nanoscale magnetism have demonstrated the potential for
spin-based technology including magnetic random access memory, nanoscale
microwave sources, and ultra-low power signal transfer. Future engineering
advances and new scientific discoveries will be enabled by research tools
capable of examining local magnetization dynamics at length and time scales
fundamental to spatiotemporal variations in magnetic systems - typically 10 -
200 nm and 5 - 50 ps. A key problem is that current table-top magnetic
microscopy cannot access both of these scales simultaneously. In this letter,
we introduce a spatiotemporal magnetic microscopy that uses
magneto-thermoelectric interactions to measure local magnetization via the
time-resolved anomalous Nernst effect (TRANE). By generating a short-lived,
local thermal gradient, the magnetic moment is transduced into an electrical
signal. Experimentally, we show that TRANE microscopy has time resolution below
30 ps and spatial resolution limited by the thermal excitation area.
Furthermore, we present numerical simulations to show that the thermal spot
size sets the limits of the spatial resolution, even at 50 nm. The thermal
effects used for TRANE microscopy have no fundamental limit on their spatial
resolution, therefore a future TRANE microscope employing a scanning plasmon
antenna could enable measurements of nanoscale magnetic dynamics.",1502.06505v1
2019/5/26,Switching 2D Magnetic States via Pressure Tuning of Layer Stacking,"The physical properties of two-dimensional van der Waals (2D vdW) crystals
depend sensitively on the interlayer coupling, which is intimately connected to
the stacking arrangement and the interlayer spacing. For example, simply
changing the twist angle between graphene layers can induce a variety of
correlated electronic phases, which can be controlled further in a continuous
manner by applying hydrostatic pressure to decrease the interlayer spacing. In
the recently discovered 2D magnets, theory suggests that the interlayer
exchange coupling strongly depends on layer separation, while the stacking
arrangement can even change the sign of the magnetic exchange, thus drastically
modifying the ground state. Here, we demonstrate pressure tuning of magnetic
order in the 2D magnet CrI3. We probe the magnetic states using tunneling and
scanning magnetic circular dichroism microscopy measurements. We find that the
interlayer magnetic coupling can be more than doubled by hydrostatic pressure.
In bilayer CrI3, pressure induces a transition from layered antiferromagnetic
to ferromagnetic phases. In trilayer CrI3, pressure can create coexisting
domains of three phases, one ferromagnetic and two distinct antiferromagnetic.
The observed changes in magnetic order can be explained by changes in the
stacking arrangement. Such coupling between stacking order and magnetism
provides ample opportunities for designer magnetic phases and functionalities.",1905.10860v1
2019/5/31,Magnetic Anisotropy and Low Field Magnetic Phase Diagram of Quasi Two-Dimensional Ferromagnet Cr$_2$Ge$_2$Te$_6$,"In this work we present a comprehensive investigation on magnetic and
thermodynamic properties of the two-dimensional layered honeycomb system
Cr$_2$Ge$_2$Te$_6$. Using magnetization and specific heat measurements under
magnetic field applied along two crystallographic directions we obtain the
magnetic phase diagram for both directions. Cr$_2$Ge$_2$Te$_6$ is a ferromagnet
with a Curie temperature $T_C=65$ K and exhibits an easy magnetization axis
perpendicular to the structural layers in the $ab$-plane. Under magnetic fields
applied parallel to the hard plane $ab$ below the magnetic saturation, a
downturn with an onset temperature $T\textrm{*}$ is observed in the temperature
dependent magnetization curve. $T\textrm{*}$ shows a monotonous shift towards
lower temperatures with increasing field. The nature of this anisotropic and
specific behavior for fields in the hard plane is discussed as an interplay
among field, temperature and effective magnetic anisotropy. Similarities to
structurally related compounds such as CrX$_3$ (X = Br, I) hint towards a
universality of this behavior in ferromagnetic quasi two-dimensional honeycomb
materials.",1905.13609v2
2019/7/4,Micromagnetic modelling of magnetic domain walls and domains in cylindrical nanowires,"Magnetic cylindrical nanowires are very fascinating objects where the curved
geometry allows many novel magnetic effects and a variety of non-trivial
magnetic structures. Micromagnetic modelling plays an important role in
revealing the magnetization distribution in magnetic nanowires, often not
accessible by imaging methods with sufficient details. Here we review the
magnetic properties of the shape anisotropy-dominated nanowires and the
nanowires with competing shape and magnetocrystalline anisotropies, as revealed
by micromagnetic modelling. We discuss the variety of magnetic walls and
magnetic domains reported by micromagnetic simulations in cylindrical
nanowires. The most known domain walls types are the transverse and vortex
(Bloch point) domain walls and the transition between them is materials and
nanowire diameter dependent. Importantly, the field or current-driven domain
walls in cylindrical nanowires can achieve very high velocities. In recent
simulations of nanowires with larger diameter the skyrmion tubes are also
reported. In nanowires with large saturation magnetization the core of these
tubes may form a helicoidal ('corkscrew') structure. The topology of the
skyrmion tubes play an important role in the pinning mechanism, discussed here
on the example of FeCo modulated nanowires. Other discussed examples include
the influence of antinotches ('bamboo' nanowires) on the remanent magnetization
configurations for hcp Co and FeCo nanowires and Co-Ni multisegmented
nanowires.",1907.02318v1
2019/11/22,"Spin, atomic and inter-atomic orbital magnetism induced by 3d nanostructures deposited on transition metal surfaces","We present a first-principles study of the surface magnetism induced by Cr,
Mn, Fe and Co adatoms on the (111) surfaces of Rh, Pd, Ag, Ir, Pt and Au. We
first describe how the different contributions to the surface magnetism enter
the magnetic stray field, with special attention paid to the induced orbital
moments. Then we present results for the spin and orbital magnetic moments of
the adatoms, and for the induced surface spin and orbital magnetic moments, the
latter being further divided into atomic and inter-atomic contributions. We
investigate how the surface magnetism is determined by the chemical nature of
the elements involved, such as the filling of the magnetic d-orbitals of the
adatoms and the properties of the itinerant electrons at the surface (whether
they are sp- or d-like, and whether the spin-orbit interaction is relevant),
and how it is modified if the magnetic adatoms are brought together to form a
cluster, with Cr, Mn, Fe, and Co trimers on Pt(111) as an example. We also
explore the impact of computational approximations, such as the distance
between the adatom and the Pt(111) surface, or confinement effects due to the
finite thickness of the slab used to model it. Our discussion of the magnetic
stray field generated by a single adatom and its environment suggests a
possible way of disentangling the induced surface magnetism from the adatom
one, which could be feasible with scanning NV-center microscopy.",1911.10053v1
2019/12/5,Deterministic magnetization switching using lateral spin-orbit torque,"Current-induced magnetization switching by spin-orbit torque (SOT) holds
considerable promise for next generation ultralow-power memory and logic
applications. In most cases, generation of spin-orbit torques has relied on an
external injection of out-of-plane spin currents into the magnetic layer, while
an external magnetic field along the electric current direction is generally
required for realizing deterministic switching by SOT. Here, we report
deterministic current-induced SOT full magnetization switching by lateral
spin-orbit torque in zero external magnetic field. The Pt/Co/Pt magnetic
structure was locally annealed by a laser track along the in-plane current
direction, resulting in a lateral Pt gradient within the ferromagnetic layer,
as confirmed by microstructure and chemical composition analysis. In zero
magnetic field, the direction of the deterministic current-induced
magnetization switching depends on the location of the laser track, but shows
no dependence on the net polarization of external out-of-plane spin currents.
From the behavior under external magnetic fields, we identify two independent
mechanisms giving rise to SOT, i.e. the lateral Pt-Co asymmetry as well as
out-of-plane injected spin currents, where the polarization and the magnitude
of the SOT in the former case depends on the relative location and the laser
power of the annealing track. Our results demonstrate an efficient field-free
deterministic full magnetization switching scheme, without requiring
out-of-plane spin current injection or complex external stack structures.",1912.02388v1
2020/5/28,Unconventional critical behaviors at the magnetic phase transition of Co3Sn2S2 kagome ferromagnet,"Co3Sn2S2 has generated a growing interest as a rare example of the highly
uniaxial anisotropic kagome ferromagnet showing a combination of
frustrated-lattice magnetism and topology. Recently, via precise measurements
of the magnetization and AC susceptibility we have found a low-field anomalous
magnetic phase (A-phase) with very slow spin dynamics that appears just below
the Curie temperature (T_C). The A-phase hosts high-density domain bubbles
after cooling through T_C as revealed in a previous in-situ Lorentz-TEM study.
Here, we present further signatures of the anomalous magnetic transition (MT)
at T_C revealed by a study of the critical behaviors of the magnetization and
magnetocaloric effect using a high-quality single crystal. Analyses of numerous
magnetization isotherms around T_C (177 K) using different approaches (the
modified Arrot plot, Kouvel-Fisher method and magnetocaloric effect) result in
consistent critical exponents that do not satisfy the theoretical predictions
of standard second-order-MT models. Scaling analyses for the magnetization,
magnetic entropy change and field-exponent of the magnetic entropy change, all
consistently show low-field deviations below TC from the universal curves. Our
results reveal that the MT of Co3Sn2S2 can not be explained as a conventional
second-order type and suggest an anomalous magnetic state below T_C.",2005.13920v2
2020/5/28,Suppression of superconducting parameters by correlated quasi-two-dimensional magnetic fluctuations,"We consider a clean layered magnetic superconductor in which a continuous
magnetic transition takes place inside superconducting state and the exchange
interaction between superconducting and magnetic subsystems is weak so that
superconductivity is not destroyed at the magnetic transition. An example of
such material is RbEuFe$_{4}$As$_{4}$. We investigate the suppression of the
superconducting gap and superfluid density by correlated magnetic fluctuations
in the vicinity of the magnetic transition. The influence of nonuniform
exchange field on superconducting parameters is sensitive to the relation
between the magnetic correlation length, $\xi_{h}$, and superconducting
coherence length $\xi_{s}$ defining the 'scattering' ($\xi_{h}<\xi_{s}$) and
'smooth' ($\xi_{h}>\xi_{s}$) regimes. As a small uniform exchange field does
not affect the superconducting gap and superfluid density at zero temperature,
smoothening of the spatial variations of the exchange field reduces its effects
on these parameters. We develop a quantitative description of this
'scattering-to-smooth' crossover for the case of quasi-two-dimensional magnetic
fluctuations. Since the magnetic-scattering probability varies at the energy
scale comparable with the gap, the quasiclassical approximation is not
applicable in the crossover region and microscopic treatment is required. We
find that the corrections to both the gap and superfluid density grow
proportionally to $\xi_{h}$ until it remains much smaller than $\xi_{s}$. When
$\xi_{h}$ exceeds $\xi_{s}$, both parameters have much weaker dependence on
$\xi_{h}$. Moreover, the gap correction may decrease with increasing of
$\xi_{h}$ in the vicinity of the magnetic transition. We also find that the
crossover is unexpectedly broad: the standard scattering approximation becomes
sufficient only when $\xi_{h}$ is substantially smaller than $\xi_{s}$.",2005.14145v3
2020/6/10,Study of magnetic interface and its effect in Fe/NiFe bilayers of alternating order,"We present a comprehensive study on the magnetization reversal in Fe/NiFe
bilayer system by alternating the order of the magnetic layers. All the samples
show growth-induced uniaxial magnetic anisotropy due to oblique angle
deposition technique. Strong interfacial exchange coupling between the Fe and
NiFe layers leads to the single-phase hysteresis loops in the bilayer system.
The strength of coupling being dependent on the interface changes upon
alternating the order of magnetic layers. The magnetic parameters such as
coercivity HC, and anisotropy field HK become almost doubled when NiFe layer is
grown over the Fe layers. This enhancement in the magnetic parameters is
primarily dependent on the increase of the thickness and magnetic moment of
Fe-NiFe interfacial layer as revealed from the polarized neutron reectivity
(PNR) data of the bilayer samples. The difference in the thickness and
magnetization of the Fe-NiFe interfacial layer indicates the modification of
the microstructure by alternating the order of the magnetic layers of the
bilayers. The interfacial magnetic moment increased by almost 18 % when NiFe
layer is grown over the Fe layer. In spite of the different values of
anisotropy fields and modified interfacial exchange coupling, the Gilbert
damping constant values of the ferromagnetic bilayers remain similar to single
NiFe layer.",2006.05756v1
2021/6/16,Magnetic and geometrical control of spin textures in the itinerant kagome magnet Fe$_3$Sn$_2$,"Magnetic materials with competing magnetocrystalline anisotropy and dipolar
energies can develop a wide range of domain patterns, including classical
stripe domains, domain branching, as well as topologically trivial and
non-trivial (skyrmionic) bubbles. We image the magnetic domain pattern of
Fe$_3$Sn$_2$ by magnetic force microscopy (MFM) and study its evolution due to
geometric confinement, magnetic fields, and their combination. In Fe$_3$Sn$_2$
lamellae thinner than 3 $\mu$m, we observe stripe domains whose size scales
with the square root of the lamella thickness, exhibiting classical Kittel
scaling. Magnetic fields turn these stripes into a highly disordered bubble
lattice, where the bubble size also obeys Kittel scaling. Complementary
micromagnetic simulations quantitatively capture the magnetic field and
geometry dependence of the magnetic patterns, reveal strong reconstructions of
the patterns between the surface and the core of the lamellae, and identify the
observed bubbles as skyrmionic bubbles. Our results imply that geometrical
confinement together with competing magnetic interactions can provide a path to
fine-tune and stabilize different types of topologically trivial and
non-trivial spin structures in centrosymmetric magnets.",2106.08791v1
2021/7/1,"Short range magnetic correlation, metamagnetism and coincident dielectric anomaly in Na$_5$Co$_{15.5}$Te$_6$O$_{36}$","Here we explore the structural, magnetic and dielectric properties of Co
based compound Na$_5$Co$_{15.5}$Te$_6$O$_{36}$ as a candidate of short-range
magnetic correlations driven development of dielectric anomaly above
N$\acute{e}$el temperature of ($T_N$=) 50 K. Low temperature neutron powder
diffraction (NPD) in zero applied magnetic field clearly indicates that the
canted spin structure is responsible for the antiferromagnetic transition and
partially occupied Co form short range magnetic correlation with other Co,
which further facilitates the structural distortion and consequent development
of dielectric anomaly above antiferromagnetic transition. Additionally, the
temperature dependent magnetic heat capacity and electron spin resonance
measurements reveal the presence of short-range magnetic correlations which
coincides with an anomaly in the dielectric constant vs temperature curve.
Moreover, significant changes in the lattice parameters are also observed
around the same temperature, indicating presence of noticeable spin-lattice
coupling. Further, sharp jump in the magnetic field dependent magnetization
clearly indicates the presence of metamagnetic transition and magnetic field
dependent NPD confirms that rotations of Co spins with applied magnetic field
are responsible for this metamagnetic phase transition. As a result, this
transition causes the magnetocaloric effect to be developed in the system,
which is suitable for the application in low temperature refrigeration.",2107.00262v1
2021/8/5,Magnetic and magnetocaloric effect in the stuffed honeycomb antiferromagnet GdInO3 polycrystalline,"The magnetic and magnetocaloric (MCE) properties were studied in a stuffed
honeycomb antiferromagnet GdInO3 polycrystalline. No long-range magnetic
ordering was observed with only a sharp upturn in the temperature dependent
magnetization curves at TN ~ 2.1 K. The large value of frustration index value
~ 5.0 suggests short-range antiferromagnetic interactions existing between the
Gd3+ moments in this frustrated magnetic system. Negligible thermal and
magnetic hysteresis suggest a second-order feature of phase transition and a
reversible magnetocaloric effect (MCE) in GdInO3 compound. In the magnetic
field changes of 0-50 kOe and 0-70 kOe, the maximum magnetic entropy change
values are 9.31 J/kg K and 17.53 J/kg K near the liquid helium temperature,
with the corresponding RCP values of 106.61 and 196.38 J/kg, respectively. The
relative lower MCE performance of GdInO3 polycrystalline than the other
Gd-based magnetocaloric effect is understood by the high magnetic frustration
in this system. Our investigation results reveal GdInO3 polycrystalline has a
large reversible MCE, which not only provides another possibility of exploiting
magnetocaloric refrigerants in the frustrated magnetic systems near the
cryogenic temperature region, but also serves to excavate more exotic
properties in the frustrated stuffed honeycomb magnetic systems.",2108.02675v3
2021/8/9,Structure dependent and strain tunable magnetic ordering in ultrathin chromium telluride,"Two-dimensional (2D) chromium tellurides have attracted considerable research
interest for their high Curie temperatures. Their magnetic properties have been
found diverse in various experiments, the understanding of which however
remains limited. In this work, we report that the magnetic ordering of
ultrathin chromium tellurides is structure dependent and can be tuned by
external strain. Based on first-principles calculations and Monte Carlo
simulations, we show long-range stable magnetism with high and low Curie
temperature, and short-range magnetism in 2D Cr5Te8, CrTe2, and Cr2Te3 layers,
respectively. We further find that ferromagnetic-to-antiferromagnetic
transition can be realized by 2% compressive strain for CrTe2 and 2% tensile
strain for Cr2Te3, and their magnetic easy axis is tuned from out-of-plane to
in-plane by the medium tensile and compressive strain. This strain dependent
magnetic coupling is found to be related to Cr-Cr direct exchange and the
change of magnetic anisotropy is understood by the atom and orbital resolved
magnetic anisotropy energy and second order perturbation theory. Our results
reveal the important roles of the structure and strain in determining the
magnetic ordering in 2D chromium telluride, shedding light on understanding of
the diverse magnetic properties observed in experiments.",2108.03822v1
2021/9/7,Intermediate anomalous Hall states induced by noncollinear spin structure in magnetic topological insulator MnBi2Te4,"The combination of topology and magnetism is attractive to produce exotic
quantum matters, such as the quantum anomalous Hall state, axion insulators and
the magnetic Weyl semimetals. MnBi2Te4, as an intrinsic magnetic topological
insulator, provides a platform for the realization of various topological
phases. Here we report the intermediate Hall steps in the magnetic hysteresis
of MnBi2Te4, where four distinguishable magnetic memory states at zero magnetic
field are revealed. The gate and temperature dependence of the magnetic
intermediate states indicates the noncollinear spin structure in MnBi2Te4,
which can be attributed to the Dzyaloshinskii-Moriya interaction as the
coexistence of strong spin-orbit coupling and local inversion symmetry breaking
on the surface. Moreover, these multiple magnetic memory states can be
programmatically switched among each other through applying designed pulses of
magnetic field. Our results provide new insights of the influence of bulk
topology on the magnetic states, and the multiple memory states should be
promising for spintronic devices.",2109.02982v1
2021/9/26,Disorder-Induced Complex Magnetization Dynamics in Planar Ensembles of Nanoparticles,"The magnetic relaxation characteristics are investigated in the
two-dimensional ($l^{}_x\times l^{}_y$) assembly of nanoparticles as a function
of out-of-plane positional disorder strength $\Delta(\%)$ using numerical
simulations. Such defects are redundantly observed in experimentally fabricated
nanostructures, resulting in unusual magnetization dynamics. The magnetization
decays exponentially for small and negligible dipolar interaction strength
$h^{}_d\leq0.2$. In such a case, the magnetization relaxation does not depend
on $\Delta$ and aspect ratio $A^{}_r=l^{}_y/l^{}_x$, as expected. In
square-like MNPs ensembles and perfectly ordered system ($\Delta(\%)=0$), the
magnetization relaxes rapidly with an increase in $h^{}_d$. Consequently, the
effective N\'eel relaxation time $\tau^{}_N$ decreases with $h^{}_d$. The
dipolar interaction of sufficient strength promotes antiferromagnetic coupling
in such a system, resulting in rapid magnetization decay. Remarkably, the
out-of-plane disorder instigates the magnetic moment to interact
ferromagnetically in the presence of large $h^{}_d$, even in the square-like
assembly of MNPs. As a result, magnetization relaxation slows down, resulting
in a monotonous increase of $\tau^{}_N$ with an increase in $\Delta$ and
$h^{}_d$ in such cases. Notably, there is a prolonged magnetization decay in
the highly anisotropic system with large $h^{}_d$. The dipolar interaction
induces ferromagnetic coupling along the long axis of the system in such cases.
Therefore, the magnetization ceases to relax as a function of time for large
$h^{}_d$, irrespective of disorder strength $\Delta(\%)$. The present work
could provide a concrete theoretical basis to explain the unexpected relaxation
behaviour observed in experiments. These results are also beneficial in digital
data storage and spintronics based applications where such nanostructures are
extensively used.",2109.12596v1
2021/10/5,Thermal transport of the frustrated spin-chain mineral linarite: Magnetic heat transport and strong spin-phonon scattering,"The mineral linarite (PbCuSO$_4$(OH)$_2$) forms a monoclinic structure where
a sequence of Cu(OH)$_2$ units forms a spin-$\frac{1}{2}$ chain. Competing
ferromagnetic nearest-neighbor ($J_1$) and antiferromagnetic
next-nearest-neighbor interactions ($J_2$) in this quasi-one-dimensional spin
structure imply magnetic frustration and lead to magnetic ordering below $T_N
=$2.8 K in a mutliferroic elliptical spin-spiral ground state. Upon the
application of a magnetic field along the spin-chain direction, distinct
magnetically ordered phases can be induced. We studied the thermal conductivity
$\kappa$ in this material across the magnetic phase diagram as well as in the
paramagnetic regime in the temperature ranges 0.07-1 K and 9-300 K. We found
that in linarite the heat is carried mainly by phonons but shows a peculiar
non-monotonic behavior in field. In particular, $\kappa$ is highly suppressed
at the magnetic phase boundaries, indicative of strong scattering of the
phonons off critical magnetic fluctuations. Even at temperatures far above the
magnetically ordered phases, the phononic thermal conductivity is reduced due
to scattering off magnetic fluctuations. The mean free path due to spin-phonon
scattering ($l_{\text{spin-phonon}}$) was determined as function of
temperature. A power law behavior was observed mainly above 0.5 K indicating
the thermal activation of spin fluctuations. In the critical regime close to
the saturation field, $l_{\text{spin-phonon}}$ shows a $1/T$ dependence.
Furthermore, a magnon thermal transport channel was verified in the helical
magnetic phase. We estimate a magnon mean free path which corresponds to about
1000 lattice spacings.",2110.01865v1
2021/12/1,Vector DC magnetic-field sensing with reference microwave field using perfectly aligned nitrogen-vacancy centers in diamond,"The measurement of vector magnetic fields with high sensitivity and spatial
resolution is important for both fundamental science and engineering
applications. In particular, magnetic-field sensing with nitrogen-vacancy (NV)
centers in diamond is a promising approach that can outperform existing
methods. Recent studies have demonstrated vector DC magnetic-field sensing with
perfectly aligned NV centers, which showed a higher readout contrast than NV
centers having four equally distributed orientations. However, to estimate the
azimuthal angle of the target magnetic field with respect to the NV axis in
these previous approaches, it is necessary to apply a strong reference DC
magnetic field, which can perturb the system to be measured. This is a crucial
problem, especially when attempting to measure vector magnetic fields from
materials that are sensitive to applied DC magnetic fields. Here, we propose a
method to measure vector DC magnetic fields using perfectly aligned NV centers
without reference DC magnetic fields. More specifically, we used the direction
of linearly polarized microwave fields to induce Rabi oscillation as a
reference and estimated the azimuthal angle of the target fields from the Rabi
frequency. We further demonstrate the potential of our method to improve
sensitivity by using entangled states to overcome the standard quantum limit.
Our method of using a reference microwave field is a novel technique for
sensitive vector DC magnetic-field sensing.",2112.00506v2
2022/6/12,The magnetic properties of a stack of elliptical nanomagnets for the initiation of apoptosis in cancer cells,"The use of drugs or radiation to attack cancerous cells often leaves the
treatment material within the body where it could affect healthy cells or
damages healthy tissue; as is the case with traditional invasive surgery. An
alternative approach is the creation of a nano machine that is directed to its
target (the cancerous tissue), then activated to engage cancerous cells and
""surgically"" induce controlled apoptosis. A magneto-mechanical device composed
of nanomagnets that potentially meets this objective is thus predicated. The
magnetic particles must be bio-functionalised for ""in-body"" use where their
uniqueness allows precise tracking and manipulation. In order to
bio-functionalize magnetic particles they have to be embedded in a
biocompatible coating or shell. Even enclosed within a biological entity the
application of magnetic field gradients result in significant forces acting
upon the magnetic particles. As such, single domain, ferromagnetic particles
can be used inside the body for a number of applications. The lack of naturally
occurring ferromagnetic particles inside the human body allows the
bio-functionalized particles to be detectable, without the interference of
noise from the host environment. Therefore, it is of paramount importance, for
medical applications, to understand exactly how the magnetic particles will
respond to a magnetic field gradient. Accordingly, the magnetic response of a
system of four interacting magnetic particles is examined and it is shown that
such a system can be optimised for targeting cancer cells and performing
nano-surgical operations. The range of magnetic field required for such
nano-medical applications is specified and the connection of these applications
to different phase transitions arising in the magnetic field is described.",2206.05738v1
2022/7/13,Magnetic-field induced melting of long-range magnetic order akin to Kitaev insulators in the metallic compound Tb5Si3,"There have been constant efforts to find exotic quantum spin-liquid (QSL)
materials. Some of the transition metal insulators dominated by the direction
dependent anisotropic exchange interaction (Kitaev model for honeycomb network
of magnetic ions) are considered to be promising cases for the same. In such
Kitaev insulators, QSL is achieved from the zero-field antiferromagnetic state
by the application of magnetic field, suppressing other exchange interactions
responsible for magnetic order. Here, we show that the features attributable to
long-range magnetic ordering of the intermetallic compound, Tb5Si3 (T_N= 69 K),
containing honey-comb network of Tb ions, are completely suppressed by a
critical applied field, H_cr, in heat-capacity and magnetization data,
mimicking the behavior of Kitaev physics candidates. The neutron diffraction
patterns as a function of H reveal that it is an incommensurate magnetic
structure that gets suppressed, showing peaks arising from multiple wave
vectors beyond Hcr. Increasing magnetic entropy as a function of H with a peak
in the magnetically ordered state is in support of some kind of magnetic
disorder in a narrow field range after H_cr. Such a high-field behavior for a
metallic heavy rare-earth system to our knowledge has not been reported in the
past and therefore is intriguing.",2207.06138v2
2022/7/15,Controlling polarization of spintronic THz emitter by remanent magnetization texture,"Terahertz (THz) sciences and technologies have contributed to a rapid
development of a wide range of applications and expanded the frontiers in
fundamental science. Spintronic terahertz emitters offer conceptual advantages
since the spin orientation in the magnetic layer can be easily controlled
either by the externally applied magnetic field or by the internal magnetic
field distribution determined by the specific shape of the magnetic elements.
Here, we report a switchable terahertz source based on micropatterned magnetic
heterostructures driven by femtosecond laser pulses. We show that the precise
tunability of the polarization state is facilitated by the underlying
magnetization texture of the magnetic layer that is dictated by the shape of
the microstructure. These results also reveal the underlying physical
mechanisms of a nonuniform magnetization state on the generation of ultrafast
spin currents in the magnetic heterostructures. Our findings indicate that the
emission of the linearly polarized THz waves can be switched on and off by
saturating the sample using a biasing magnetic field, opening fascinating
perspectives for integrated on-chip THz devices with wide-ranging potential
applications.",2207.07707v1
2022/7/27,Importance of magnetic shape anisotropy in determining magnetic and electronic properties of monolayer $\mathrm{VSi_2P_4}$,"Two-dimensional (2D) ferromagnets have been a fascinating subject of
research, and magnetic anisotropy (MA) is indispensable for stabilizing the 2D
magnetic order. Here, we investigate magnetic anisotropy energy (MAE), magnetic
and electronic properties of $\mathrm{VSi_2P_4}$ by using the generalized
gradient approximation plus $U$ (GGA+$U$) approach. For large $U$, the magnetic
shape anisotropy (MSA) energy has a more pronounced contribution to the MAE,
which can overcome the magnetocrystalline anisotropy (MCA) energy to evince an
easy-plane. For fixed out-of-plane MA, monolayer $\mathrm{VSi_2P_4}$ undergoes
ferrovalley (FV), half-valley-metal (HVM), valley-polarized quantum anomalous
Hall insulator (VQAHI), HVM and FV states with increasing $U$. However, for
assumptive in-plane MA, there is no special quantum anomalous Hall (QAH) state
and spontaneous valley polarization within considered $U$ range. According to
the MAE and electronic structure with fixed out-of-plane or in-plane MA, the
intrinsic phase diagram shows common magnetic semiconductor (CMS), FV and VQAHI
in monolayer $\mathrm{VSi_2P_4}$. At representative $U$$=$3 eV widely used in
references, $\mathrm{VSi_2P_4}$ can be regarded as a 2D-$XY$ magnet, not
Ising-like 2D long-range order magnets predicted in previous works with only
considering MCA energy. Our findings shed light on importance of MSA in
determining magnetic and electronic properties of monolayer
$\mathrm{VSi_2P_4}$.",2207.13420v1
2022/8/22,Topological melting of the metastable skyrmion lattice in the chiral magnet Co$_9$Zn$_9$Mn$_2$,"In a $\beta$-Mn-type chiral magnet Co$_9$Zn$_9$Mn$_2$, we demonstrate that
the magnetic field-driven collapse of a room temperature metastable topological
skyrmion lattice passes through a regime described by a partial topological
charge inversion. Using Lorentz transmission electron microscopy, the
magnetization distribution was observed directly as the magnetic field was
swept antiparallel to the original skyrmion core magnetization, i.e. negative
magnetic fields. Due to the topological stability of skyrmions, a direct
transition of the metastable skyrmion lattice to the equilibrium helical state
is avoided for increasingly negative fields. Instead, the metastable skyrmion
lattice gradually transforms into giant magnetic bubbles separated by $2\pi$
domain walls. Eventually these large structures give way to form a
near-homogeneously magnetized medium that unexpectedly hosts a low density of
isolated skyrmions with inverted core magnetization, and thus a total
topological charge of reduced size and opposite sign compared with the initial
state. A similar phenomenon has been observed previously in systems hosting
ordered lattices of magnetic bubbles stabilized by the dipolar interaction and
called ""topological melting"". With support from numerical calculations, we
argue that the observed regime of partial topological charge inversion has its
origin in the topological protection of the starting metastable skyrmion state.",2208.10185v1
2022/9/6,Temperature- and field angular-dependent helical spin period characterized by magnetic dynamics in a chiral helimagnet $MnNb_3S_6$,"The chiral magnets with topological spin textures provide a rare platform to
explore topology and magnetism for potential application implementation. Here,
we study the magnetic dynamics of several spin configurations on the monoaxial
chiral magnetic crystal $MnNb_3S_6$ via broadband ferromagnetic resonance (FMR)
technique at cryogenic temperature. In the high-field forced ferromagnetic
state (FFM) regime, the obtained frequency f vs. resonance field Hres
dispersion curve follows the well-known Kittel formula for a single FFM, while
in the low-field chiral magnetic soliton lattice (CSL) regime, the dependence
of Hres on magnetic field angle can be well-described by our modified Kittel
formula including the mixture of a helical spin segment and the FFM phase.
Furthermore, compared to the sophisticated Lorentz micrograph technique, the
observed magnetic dynamics corresponding to different spin configurations allow
us to obtain temperature- and field-dependent proportion of helical spin
texture and helical spin period ratio L(H)/L(0) via our modified Kittel
formula. Our results demonstrated that field- and temperature-dependent
nontrivial magnetic structures and corresponding distinct spin dynamics in
chiral magnets can be an alternative and efficient approach to uncovering and
controlling nontrivial topological magnetic dynamics.",2209.02266v1
2022/11/14,"First principles investigations of the electronic and magnetic properties of RVO3 (R = Er, Ho, Y, Lu) vanadates","In this paper, we investigate the influence of the rare earth element (R) on
the physical properties of RVO3 (R = Er, Ho, Y, Lu). For this purpose, a
theoretical work is reported in this study using ab initio method with the
intent of enhancing our knowledge of the electronic, and magnetic properties of
RVO3 (R = Er, Ho, Y, Lu) compounds. The electronic properties of these
materials show the presence of Jahn-Teller effect, with a band gap of
approximately 0.58eV, 1.57eV, 1.12eV, 1.28eV, for ErVO3, HoVO3, YVO3, LuVO3,
respectively. The magnetic contribution of Ho, Er, and V atoms in HoVO3, and
ErVO3 compounds was disentangled using X-ray magnetic circular dichroism
(XMCD). The magnetic anisotropies of RVO3 with (R = Er, Ho, Y, Lu) are studied
and analyzed using spin orbit coupling. We noticed an easy axis of
magnetization along the c-direction with strong magneto-crystalline anisotropy
energies for the non-magnetic rare earth elements (R = Lu, Y)VO3. For the
magnetic rare earth elements, the easy and hard magnetization direction were
found to be along b-axis and c-axis, and a- axis and c-axis for HoVO3, and
ErVO3, respectively. This means that instead of the standard magnetization
demagnetization process, large thermal effects can be obtained by spinning
their single crystals in constant magnetic fields. The exchange coupling
between (Ho-V) is also found to be greater than the other exchange interactions
in HoVO3. Accordingly, a large conventional magnetocaloric effect could be
created in HoVO3, since the Ho Ising moments experience a metamagnetic
transition. However, the magnetocaloric effect (MCE) is expected to be lower in
ErVO3 due to the weak (Er-V) exchange coupling.",2211.07554v1
2023/2/11,Multi-k magnetic structure and large anomalous Hall effect in candidate magnetic Weyl semimetal NdAlGe,"The magnetic structure, magnetoresistance, and Hall effect of
non-centrosymmetric magnetic semimetal NdAlGe are investigated revealing an
unusual magnetic state and anomalous transport properties that are associated
with the electronic structure of this non-centrosymmetric compound. The
magnetization and magnetoresistance measurements are both highly anisotropic
and indicate an Ising-like magnetic system. The magnetic structure is complex
in that it involves three magnetic ordering vectors including an incommensurate
spin density wave and commensurate ferrimagnetic state in zero field. We have
discovered a large anomalous Hall conductivity that reaches = 430
{\Omega}-1cm-1 implying that it originates from an intrinsic Berry curvature
effect stemming from Weyl nodes found in the electronic structure. These
electronic structure calculations indicate the presence of nested Fermi surface
pockets with nesting wave vectors similar to the measured magnetic ordering
wavevector and the presence of Weyl nodes in proximity to the Fermi surface. We
associate the incommensurate magnetic structure with the large anomalous Hall
response to be the result of the combination of Fermi surface nesting and the
Berry curvature associated with Weyl nodes.",2302.05596v2
2023/4/28,"Noncollinear magnetic order, in-plane anisotropy, and magnetoelectric coupling in a pyroelectric honeycomb antiferromagnet Ni$_{2}$Mo$_{3}$O$_{8}$","Ni$_{2}$Mo$_{3}$O$_{8}$ is a pyroelectric honeycomb antiferromagnet
exhibiting peculiar changes of its electric polarization at magnetic
transitions. Ni$_{2}$Mo$_{3}$O$_{8}$ stands out from the isostructural magnetic
compounds, showing an anomalously low magnetic transition temperature and
unique magnetic anisotropy. We determine the magnetic structure of
Ni$_{2}$Mo$_{3}$O$_{8}$ utilizing high-resolution powder and single-crystal
neutron diffraction. A noncollinear stripy antiferromagnetic order is found in
the honeycomb planes. The magnetic space group is \textit{P$_C$na}2$_1$. The
in-plane magnetic connection is of the stripy type both for the $ab$-plane and
the $c$-axis spin components. This is a simpler connection than the one
proposed previously. The ferromagnetic interlayer order of the $c$-axis spin
components in our model is also distinct. The magnetic anisotropy of
Ni$_{2}$Mo$_{3}$O$_{8}$ is characterized by orientation-dependent magnetic
susceptibility measurements on a single crystal, consistent with neutron
diffraction analysis. The local magnetoelectric tensor analysis using our
magnetic models provides new insights into its magnetoelectric coupling and
polarization. Thus, our results deliver essential information for understanding
both the unusual magnetoelectric properties of Ni$_{2}$Mo$_{3}$O$_{8}$ and the
prospects for observation of exotic nonreciprocal, Hall, and magnonic effects
characteristic to this compound family.",2304.14641v2
2023/4/28,Towards engineering the perfect defect in high-performing permanent magnets,"Permanent magnets draw their properties from a complex interplay, across
multiple length scales, of the composition and distribution of their
constituting phases, that act as building blocks, each with their associated
intrinsic properties. Gaining a fundamental understanding of these interactions
is hence key to decipher the origins of their magnetic performance and
facilitate the engineering of better-performing magnets, through unlocking the
design of the ""perfect defects"" for ultimate pinning of magnetic domains. Here,
we deployed advanced multiscale microscopy and microanalysis on a bulk
Sm2(CoFeCuZr)17 pinning-type high-performance magnet with outstanding thermal
and chemical stability. Making use of regions with different chemical
compositions, we showcase how both a change in the composition and distribution
of copper, along with the atomic arrangements enforce the pinning of magnetic
domains, as imaged by nanoscale magnetic induction mapping. Micromagnetic
simulations bridge the scales to provide an understanding of how these
peculiarities of micro- and nanostructure change the hard magnetic behaviour of
Sm2(CoFeCuZr)17 magnets. Unveiling the origins of the reduced coercivity allows
us to propose an atomic-scale defect and chemistry manipulation strategy to
define ways toward future hard magnets.",2304.14958v2
2023/10/9,Super-resolution diamond magnetic microscopy of superparamagnetic nanoparticles,"Scanning-probe and wide-field magnetic microscopes based on Nitrogen-Vacancy
(NV) centers in diamond have enabled remarkable advances in the study of
biology and materials, but each method has drawbacks. Here, we implement an
alternative method for nanoscale magnetic microscopy based on optical control
of the charge state of NV centers in a dense layer near the diamond surface. By
combining a donut-beam super-resolution technique with optically detected
magnetic resonance spectroscopy, we imaged the magnetic fields produced by
single 30-nm iron-oxide nanoparticles. The magnetic microscope has a lateral
spatial resolution of ~100 nm, and it resolves the individual magnetic dipole
features from clusters of nanoparticles with interparticle spacings down to
~190 nm. The magnetic feature amplitudes are more than an order of magnitude
larger than those obtained by confocal magnetic microscopy due to the smaller
characteristic NV-nanoparticle distance within nearby sensing voxels. We
analyze the magnetic point-spread function and sensitivity as a function of the
microscope's spatial resolution and identify sources of background fluorescence
that limit the present performance, including diamond second-order Raman
emission and imperfect NV charge-state control. Our method, which uses less
than 10 mW laser power and can be parallelized by patterned illumination,
introduces a new format for nanoscale magnetic imaging.",2310.05436v1
2024/1/24,Magnetism and spin dynamics of an S=3/2 frustrated trillium lattice antiferromagnet K2CrTi(PO4)3,"Competing magnetic interactions, frustration driven quantum fluctuations, and
spin correlations offer an ideal route for the experimental realization of
emergent quantum phenomena and exotic quasi particle excitations in 3D
frustrated magnets. In this context, trillium lattice, wherein magnetic ions
decorate a three-dimensional chiral network of corner-shared equilateral
triangular motifs, provides a viable ground. Herein, we present the crystal
structure, magnetic susceptibility, specific heat, electron spin-resonance,
muSR results on the polycrystalline samples of K2CrTi(PO4)3 wherein the Cr3+
ions form a perfect trillium lattice without any detectable anti-site disorder.
The Curie-Weiss fit of the magnetic susceptibility data above 100 K yields a
Curie-Weiss temperature of -23 K, which indicates the presence of dominant
antiferromagnetic interactions between Cr3+ (S=3/2) moments. The specific heat
measurements reveal the occurrence of two consecutive phase transitions, at
temperatures TL = 4.3 K and TH = 8 K, corresponding to two different magnetic
phases and it unveils the existence of short-range spin correlations above the
ordering temperature TH. The power-law behavior of ESR linewidth suggests the
persistence of short-range spin correlations over a relatively wide critical
region in agreement with the specific heat results. The muSR resultsprovide
concrete evidence of two different phases corresponding to two transitions,
coupled with thecritical slowing down of spin fluctuations above TL and
persistent spin dynamics below TL, consistent with the thermodynamic results.
Moreover, the muSR results reveal the coexistence of static and dynamic local
magnetic fields below TL, signifying the presence of complex magnetic phases
owing to the entwining of spin correlations and competing magnetic interactions
in this three-dimensional frustrated magnet.",2401.13445v1
2024/2/20,Exploring magnetic anisotropy in bcc-structured ferromagnetic thin films with three spin layers using the fourth order perturbed Heisenberg Hamiltonian,"This study investigates into the analysis of ferromagnetic thin films with a
body centered cubic lattice and three spin layers, utilizing the solution of
the fourth-order perturbed Heisenberg Hamiltonian equation with seven magnetic
energy parameters. Spin-exchange interaction, magnetic dipole interaction,
second-order magnetic anisotropy,fourth-order magnetic anisotropy, applied
magnetic field, demagnetization energy, and stress-induced anisotropy were all
taken into account. According to 3D plots, the minimum order of energy was
observed when the second order magnetic anisotropy constant in the middle spin
layer is less than those of the bottom and top spin layers. In all cases, the
values of stress-induced anisotropy at the maxima of 3D plots are exactly the
same when the values of the second-order magnetic anisotropy constants of the
bottom, middle, and top spin layers are interchanged with each other. In 2D
plots, the angle between consecutive magnetic easy and hard directions is
approximately 90 degrees in all cases. Additionally, the magnetic easy and hard
directions were observed to have exactly the same values when the second-order
magnetic anisotropy constant of the spin layers changes. These results were
compared with the results obtained using the second and third order perturbed
Heisenberg Hamiltonian.",2403.13817v1
2020/3/18,"Magnetic structures, spin-flop transition and coupling of Eu and Mn magnetism in the Dirac semimetal EuMnBi$_2$","We report here a comprehensive study of the AFM structures of the Eu and Mn
magnetic sublattices as well as the interplay between Eu and Mn magnetism in
this compound by using both polarized and non-polarized single-crystal neutron
diffraction. Magnetic susceptibility, specific heat capacity measurements and
the temperature dependence of magnetic diffractions suggest that the AFM
ordering temperature of the Eu and Mn moments is at 22 and 337 K, respectively.
The magnetic moments of both Eu and Mn ions are oriented along the
crystallographic $c$ axis, and the respective magnetic propagation vector is
$\textbf{k}_{Eu} = (0,0,1)$ and $\textbf{k}_{Mn}=(0,0,0)$. With proper neutron
absorption correction, the ordered moments are refined at 3 K as 7.7(1) $\mu_B$
and 4.1(1) $\mu_B$ for the Eu and Mn ions, respectively. In addition, a
spin-flop (SF) phase transition of the Eu moments in an applied magnetic field
along the $c$ axis was confirmed to take place at a critical field of B$_c$
$\sim$ 5.3 T. The evolution of the Eu magnetic moment direction as a function
of the applied magnetic field in the SF phase was also determined. Clear kinks
in both field and temperature dependence of the magnetic reflections ($\pm1$,
0, 1) of Mn were observed at the onset of the SF phase transition and the AFM
order of the Eu moments, respectively. This unambiguously indicates the
existence of a strong coupling between Eu and Mn magnetism. The interplay
between two magnetic sublattices could bring new possibilities to tune Dirac
fermions via changing magnetic structures by applied fields in this class of
magnetic topological semimetals.",2003.08346v2
2021/9/24,Real time display with the ferrolens of homogeneous magnetic fields,"In our previous published research we have studied the applications of the
ferrolens for the observation and qualitative analysis of non-homogeneous
magnetic fields. Latest developments over the last few years of the ferrolens
increased multifold the sensitivity of this device allowing it to display
magnetic fields as low as 10mT in strength and therefore it is possible now to
observe also the homogeneous (i.e. straight parallel magnetic flux lines of
uniform density in space) magnetic field existing inside air solenoids and
between N-S poles of two attracting separated permanent magnets. We present and
analyze herein these novel observations of homogeneous magnetic fields with the
ferrolens and as a potential new application of this device. The ferrolens can
now display the projected magnetic field on air from a distance without needing
to be in physical contact with the field source. Experiments were carried out
to demonstrate these new capabilities of the ferrolens as a nanomagnetic flux
viewer, real-time physical device and scientific qualitative tool. We compare
the geometry of magnetic fields of condensed matter ferromagnets with that of
magnetic fields inside electrical air solenoids. Specifically, the homogeneous
field between two N-S attracting magnets at a distance as well as inside air
solenoids and Helmholtz coils and also the non-homogeneous total field of
single dipole permanent magnets were observed using a latest generation very
sensitive ferrolens. The unique feature of this magneto optic fluid thin film
physical device is that it can display discrete magnetic flux lines of the
macroscopic field. Also we show how the ferrolens can be used to detect
qualitatively the symmetry center of a non ideal homogeneous magnetic field.",2109.12044v1
2021/11/23,Controlling magnetic configuration in soft-hard bilayers probed by polarized neutron reflectometry,"Hard/soft magnetic bilayer thin films have been widely used in data storage
technologies and permanent magnet applications. The magnetic configuration and
response to temperatures and magnetic fields in these heterostructures are
considered to be highly dependent on the interfacial coupling. However, the
intrinsic properties of each of the layers, such as the saturation
magnetization and layer thickness, also strongly influence the magnetic
configuration. Changing these parameters provides an effective method to tailor
magnetic properties in composite magnets. Here, we use polarized neutron
reflectometry (PNR) to experimentally probe the interfacial magnetic
configurations in hard/soft bilayer thin films: L10-FePt/A1-FePt, [Co/Pd]
/CoPd, [Co/Pt] /FeNi and L10-FePt/Fe, which all have a perpendicular magnetic
anisotropy in the hard layer. These films were designed with different soft and
hard layer thicknesses (t_soft and t_hard) and saturation magnetization
(M_s^soft and M_s^hard), respectively. The influences of an in-plane magnetic
field (H_ip) and temperature (T) are also studied using a L10 FePt/A1-FePt
bilayer sample. Comparing the PNR results to micromagnetic simulations reveals
that the interfacial magnetic configuration is highly dependent on t_soft,
M_s^soft and the external factors (H_ip and T), and has a relatively weak
dependence on t_hard and M_s^hard. Key among these results, for thin t_soft,
the hard and soft layers are rigidly coupled in the out-of-plane direction,
then undergo a transition to relax in-plane. This transition can be delayed to
larger t_soft by decreasing M_s^soft. Understanding the influence of these
parameters on the magnetic configuration is critical to designing functional
composite magnets for applications.",2111.12191v1
2022/11/13,Field Tunable Magnetic Transitions of CsCo2(MoO4)2(OH): A Triangular Chain Structure with a Frustrated Geometry,"Identifying and characterizing new magnetic systems with Co2+ ions can
enhance our understanding of quantum behavior since Co2+ can host a
pseudospin-1/2 magnetic ground state. Understanding the magnetic ground state
and the phase diagrams of such systems are central to the development of new
theoretical models to described emergent quantum properties of complex magnetic
systems. The sawtooth chain compound, CsCo2MoO4_2OH, is one such complex
magnetic system and here, we present a comprehensive series of magnetic and
neutron scattering measurements to determine its magnetic phase diagram. The
magnetic properties of CsCo2MoO4_2OH exhibit a strong coupling to the crystal
lattice and its magnetic ground state can be easily manipulated by applied
magnetic fields. There are two unique Co2+ ions, base and vertex, with Jbb and
Jbv magnetic exchange. The magnetism is highly anisotropic with the b-axis
(chain) along the easy axis and the material orders antiferromagnetically at TN
= 5 K. The zero field antiferromagnetic phase contains vertex magnetic vectors
Co1 aligned parallel to the b-axis, while the base vectors Co2 are canted by 34
and aligned in an opposite direction to the vertex vectors. The spins in
parallel adjacent chains align in opposite directions, creating an overall
antiferromagnetic structure. At a 3 kOe applied magnetic field, adjacent chains
flip by 180{\deg} to generate a ferrimagnetic phase. An increase in field
gradually induces the Co(1) moment to rotate along the b-axis and align in the
same direction with Co2 generating a ferromagnetic structure. Our results
demonstrate that the CsCo2MoO4_2OH is a promising candidate to study new
physics associated with sawtooth chain magnetism.",2211.07030v1
2023/3/6,Magnetic field induced valence change in Eu(Co$_{1-x}$Ni$_{x}$)$_{2}$P$_{2}$ up to 60 T,"The solid solution 122 compounds, Eu(Co$_{1-x}$Ni$_{x}$)$_{2}$P$_{2}$, show
valence transition between divalent state and intermediate valence states at
Eu, which is firmly correlated to multiple degrees of freedom in the solid such
as the isostructural transition between the collapsed tetragonal (cT) and
uncollapsed tetragonal (ucT) structures, $3d$ magnetism, and the formation of
P-P dimers. To gain insights into the correlated behavior, we investigate the
effect of high magnetic fields on the samples of $x = 0.4$ and $0.5$ using
magnetostriction and magnetization measurements up to 60 T. The samples are in
the Eu valence fluctuating regime, where the possible structural transition
from cT to ucT may be induced by the Eu valence change under the magnetic
fields. For both samples, magnetostriction smoothly increases with increasing
magnetic fields. The behavior is in good agreement with the calculated results
using the interconfigurational fluctuation (ICF) model that describes the
valence change. This indicates that $\Delta L$ represents the change of the Eu
valence state in these compounds. Magnetization curves for both compounds show
good agreement with the ICF model at high magnetic fields. In contrast, in the
low magnetic field region, magnetization curves do not agree with the ICF
model. These results indicate that the Eu valence changes manifest themselves
in the magnetization curves at high magnetic fields and that the magnetism of
the $3d$ electrons manifests itself in the magnetization at low magnetic
fields. Hence, we conclude that the valence change occurs within the Eu valence
fluctuation regime coupled with the cT structure. Thereby, we believe that the
transition to ucT structure which is firmly coupled with the divalent Eu state
does not occur within the magnetic field range of the present study.
(Continued)",2303.02910v3
1995/9/27,Oscillatory Thickness Dependence of Magnetic Moments and interface-induced Changes of the Exchange Coupling in Co/Cu and Co-Ni/Cu Multilayers,"We perform first-principles calculations for the three multilayer systems
(100)-Co_1/Cu_n, -NiCo_2Ni/Cu_n and -Co_4/Cu_n, and find from a comparison x of
the results for system 2 and 3 that amplitude and phase of the exchange
coupling are sensitive to the magnetic-slab/nonmagnetic-spacer interface.
Moreover, we observe that for the system 1 and 2 the averaged magnetic moment
of the magnetic slab oscillates with the spacer thickness similarly as the
exchange coupling.",9509164v1
1997/5/30,Exchange coupling between magnetic layers across non-magnetic superlattices,"The oscillation periods of the interlayer exchange coupling are investigated
when two magnetic layers are separated by a metallic superlattice of two
distinct non-magnetic materials. In spite of the conventional behaviour of the
coupling as a function of the spacer thickness, new periods arise when the
coupling is looked upon as a function of the number of cells of the
superlattice. The new periodicity results from the deformation of the
corresponding Fermi surface, which is explicitly related to a few controllable
parameters, allowing the oscillation periods to be tuned.",9705310v2
1998/10/6,Lattice Models for Magnetic Fluids: Correlations Between Order Parameters,"Magnetic fluids are colloidal suspensions of ferromagnetic particles covered
with a surfactant layer, dispersed in a host liquid. The existence of
cooperative phenomena in such magnetic colloidal systems, makes the determining
of their physical properties a difficult task. In the framework of statistical
mechanics, taking into consideration interparticle interactions, the study of
equilibrium properties and phase transitions of magnetic fluids can be best
done. In this paper we analyze some basic aspects about the real possibility of
describing the critical properties of these systems in the language of spin-1
lattice-gas model and we also propose the use of a higher spin (3/2) model.",9810052v1
1999/9/10,Magnetic Properties of disordered CoCu alloys:A first principles approach,"Crystalline Co$_{x}$Cu$_{1-x}$ alloys show interesting magnetic behavior over
the entire concentration regime. We here present a fully self- consistent first
principles electronic structure studies of the electronic structure and
magnetic properties of the system.We present results for the variation of
density of states, magnetic moment,spin susceptibility and Curie temperature.",9909145v1
1999/10/13,Low Energy Excitations of Yb4As3 in a Magnetic Field,"We discuss the effects of an applied magnetic field on the low energy
excitations in the low temperature phase of Yb4As3. We show also why the
magnetic interaction of the Yb{3+} ions is nearly of an isotropic Heisenberg
spin-1/2 type. A small anisotropy due to an intrachain dipolar interaction
leads to the opening of a gap when a magnetic field is applied. The model
agrees with available experimental data. Simple experiments are suggested in
order to further test the present theory.",9910196v1
1999/11/9,Dipolar interactions induced order in assemblies of magnetic particles,"We discuss the appareance of ordered structures in assemblies of magnetic
particles. The phenomenon occurs when dipolar interactions and the thermal
motion of the particles compete, and is mediated by screening and excluded
volume effects. It is observed irrespective of the dimensionality of the system
and the resulting structures, which may be regular or fractal, indicate that
new ordered phases may emerge in these system when dipolar interactions play a
significant role.",9911126v2
1999/12/14,From spatially indirect to momentum-space indirect exciton by in-plane magnetic field,"In-plane magnetic field is found to change drastically the photoluminescence
spectra and kinetics of interwell excitons in GaAs/AlGaAs coupled quantum
wells. The effect is due to the in-plane magnetic field induced displacement of
the interwell exciton dispersion in a momentum space, which results in the
transition from the momentum-space direct exciton ground state to the
momentum-space indirect exciton ground state. In-plane magnetic field is,
therefore, an effective tool for the exciton dispersion engineering.",9912242v1
2000/1/13,Quantum Dynamics in Nanoscale Magnets in Dissipative Environments,"In discrete energy structure of nanoscale magnets, nonadiabatic transitions
at avoided level crossings lead to fundamental processes of dynamics of
magnetizations. The thermal environment causes dissipative effects on these
processes. In this paper we review the features of the nonadiabatic transition
and the influence of the thermal environment. In particular we discuss the
temperature independent stepwise structure of magnetization at very low
temperatures (deceptive nonadiabatic transition), the alternate enhancement of
relaxation in the sequence of resonant tunneling points (parity effects), and
processes caused by combinations of nonadiabatic transitions and disturbance
due to external noises.",0001179v1
2000/1/25,Magnetic excitations in coupled Haldane spin chains near the quantum critical point,"Two quasi-1-dimensional S=1 quantum antiferromagnetic materials, PbNi2V2O8
and SrNi2V2O8, are studied by inelastic neutron scattering on powder samples.
While magnetic interactions in the two systems are found to be very similar,
subtle differences in inter-chain interaction strengths and magnetic anisotropy
are detected. The latter are shown to be responsible for qualitatively
different ground state properties: magnetic long-range order in SrNi2V2O8 and
disordered ``spin liquid'' Haldane-gap state in PbNi2V2O8.",0001374v2
2000/3/25,Thermokinetic approach of the generalized Landau-Lifshitz-Gilbert equation with spin polarized current,"In order to describe the recently observed effect of current induced
magnetization reversal in magnetic nanostructures, the thermokinetic theory is
applied to a metallic ferromagnet in contact with a reservoir of spin polarized
conduction electrons. The spin flip relaxation of the conduction electrons is
described thermodynamically as a chemical reaction. The diffusion equation of
the chemical potential (or the giant magnetoresistance) and the usual
Landau-Lifshitz-Gilbert (LLG) equation are derived from the entropy variation.
The expression of the conservation laws of the magnetic moments, including spin
dependent scattering processes, leads then to the generalized LLG equation with
spin polarized current. The equation is applied to the measurements obtained on
single magnetic Ni nanowires.",0003409v1
2000/7/25,Electronic structure and magnetism in disordered bcc Fe alloys,"We here study electronic structure and magnetic properties of bcc
Co$_{x}$Fe$_{1-x}$, Cr$_{x}$Fe$_{1-x}$ and Mn$_{x}$Fe$_{1-x}$ in their
ferromagnetic phases using Augmented Space Recursion technique coupled with
tight-binding linearized muffin tin orbital (TB-LMTO) method. We make a
systematic study of magnetic properties like magnetic moment and Curie
temperature and try to draw some conclusions on their variation across the row
of 3-{\it d} transition metal series in periodic table using arguments based on
effects like charge transfer, exchange splitting and hybridization.",0007384v1
2000/12/8,Phase Separation and the Low-Field Bulk Magnetic Properties of Pr0.7Ca0.3MnO3,"We present a detailed magnetic study of the perovskite manganite
Pr0.7Ca0.3MnO3 at low temperatures including magnetization and a.c.
susceptibility measurements. The data appear to exclude a conventional spin
glass phase at low fields, suggesting instead the presence of correlated
ferromagnetic clusters embedded in a charge-ordered matrix. We examine the
growth of the ferromagnetic clusters with increasing magnetic field as they
expand to occupy almost the entire sample at H ~ 0.5 T. Since this is well
below the field required to induce a metallic state, our results point to the
existence of a field-induced ferromagnetic insulating state in this material.",0012143v1
2001/3/19,Spontaneous magnetization of aluminum nanowires deposited on the NaCl(100) surface,"We investigate electronic structures of Al quantum wires, both unsupported
and supported on the (100) NaCl surface, using the density-functional theory.
We confirm that unsupported nanowires, constrained to be linear, show
magnetization when elongated beyond the equilibrium length. Allowing ions to
relax, the wires deform to zig-zag structures with lower magnetization but no
dimerization occurs. When an Al wire is deposited on the NaCl surface, a
zig-zag geometry emerges again. The magnetization changes moderately from that
for the corresponding unsupported wire. We analyse the findings using electron
band structures and simple model wires.",0103384v1
2001/6/20,"Comment on ""Magnetoviscosity and relaxation in ferrofluids""","It is shown and discussed how the conventional system of hydrodynamic
equations for ferrofluids was derived. The set consists of the equation of
fluid motion, the Maxwell equations, and the magnetization equation. The latter
was recently revised by Felderhof [Phys. Rev. E, v.62, p.3848 (2000)]. His
phenomenological magnetization equation looks rather like corresponding
Shliomis' equation, but leads to wrong consequences for the dependence of
ferrofluid viscosity and magnetization relaxation time on magnetic field.",0106414v1
2001/6/26,Magnetic Susceptibility Study of the Heavy Rare Earth Stannate Pyrochlores,"The series of magnetic rare earth pyrochlore stannates R2Sn2O7 (R = rare
earth, except Ce and Pm) have been investigated by powder susceptibility
measurements down to T =1.8 K. The results are compared to results for the
analogous titanate series, which are well-known frustrated magnets. Unlike the
titanates, the whole series can be formed in the cubic pyrochlore structure.
Possible experimental advantages of studying the stannates are discussed.",0106527v1
2001/6/26,Resonant peak splitting for ballistic conductance in magnetic superlattices,"We investigate theoretically the resonant splitting of ballistic conductance
peaks in magnetic superlattices. It is found that, for magnetic superlattices
with periodically arranged $n$ identical magnetic-barriers, there exists a
general $(n-1)$-fold resonant peak splitting rule for ballistic conductance,
which is the analogy of the $(n-1)$-fold resonant splitting for transmission in
$n$-barrier electric superlattices (R. Tsu and L. Esaki, Appl. Phys. Lett. {\bf
22}, 562 (1973)).",0106537v1
2001/7/3,Importance of Correlation Effects on Magnetic Anisotropy in Fe and Ni,"We calculate magnetic anisotropy energy of Fe and Ni by taking into account
the effects of strong electronic correlations, spin-orbit coupling, and
non-collinearity of intra--atomic magnetization. The LDA+U method is used and
its equivalence to dynamical mean--field theory in the static limit is
emphasized. Both experimental magnitude of MAE and direction of magnetization
are predicted correctly near U=1.9 eV, J=1.2 eV for Ni and U=1.2 eV, J=0.8 eV
for Fe. Correlations modify the one--electron spectra which are now in better
agreement with experiments.",0107063v1
2001/7/27,Large magnetoresistance using hybrid spin filter devices,"A magnetic ""spin filter"" tunnel barrier, sandwiched between a non-magnetic
metal and a magnetic metal, is used to create a new magnetoresistive tunnel
device, somewhat analogous to an optical polarizer-analyzer configuration. The
resistance of these trilayer structures depends on the relative magnetization
orientation of the spin filter and the ferromagnetic electrode. The spin
filtering in this configuration yields a previously unobserved
magnetoresistance effect, exceeding 100%.",0107571v1
2001/8/9,Surface barrier and bulk pinning in MgB$_2$ superconductor,"We present a modified method of preparation of the new superconductor
MgB$_2$. The polycrystalline samples were characterized using x-ray and
magnetic measurements. The surface barriers control the isothermal
magnetization loops in powder samples. In bulk as prepared samples we always
observed symmetric magnetization loops indicative of the presence of a bulk
pinning mechanism. Magnetic relaxation measurements in the bulk sample reveal a
crossover of surface barrier to bulk pinning.",0108153v1
2001/10/19,Magnetic properties of 3d-impurities substituted in GaAs,"We have calculated the magnetic properties of substituted 3d-impurities
(Cr-Ni) in a GaAs host by means of first principles electronic structure
calculations. We provide a novel model explaining the ferromagnetic long rang
order of III-V dilute magnetic semiconductors. The origin of the ferromagnetism
is shown to be due to delocalized spin-uncompensated As dangling bond
electrons. Besides the quantitative prediction of the magnetic moments, our
model provides an understanding of the halfmetallicity, and the raise of the
critical temperature with the impurity concentration.",0110405v1
2001/11/5,Non-uniform thermal magnetization noise in thin films: application to GMR heads,"A general scheme is developed to analyze the effect of non-uniform thermal
magnetization fluctuations in a thin film. The normal mode formalism is
utilized to calculate random magnetization fluctuations. The magnetization
noise is proportional to the temperature and inversely proportional to the film
volume. The total noise power is the sum of normal mode spectral noises and
mainly determined by spin-wave standing modes with an odd number of
oscillations. The effect rapidly decreases with increasing mode number. An
exact analytical calcutaion is presented for a two-cell model.",0111072v1
2002/1/22,Enhancement of the Thermal Conductivity in gapped Quantum Spin Chains,"We study mechanism of magnetic energy transport, motivated by recent
measurements of the thermal conductivity in low dimensional quantum magnets. We
point out a possible mechanism of enhancement of the thermal conductivity in
gapped magnetic system, where the magnetic energy transport plays a crucial
role. This mechanism gives an interpretation for the recent experiment of
CuGeO_3, where the thermal conductivity depends on the crystal direction.",0201392v2
2002/2/12,Magnetic and Transport Properties of NiFe/SiO_{2}/NiFe Trilayers,"Magnetic coupling between Ni_{81}Fe_{19} double thin films separated by an
insulating SiO_{2} spacer layer is investigated with structural measurements,
cross sectional imaging, magnetization measurements (BH loop) and transport
under the conditions of variable spacer thickness ranging from 0 to 5000
Angstroms. We investigate several models to explain the coercivity variation
with spacer thickness as well as the transport measurements.",0202204v2
2002/3/5,Ferromagnetism in Diluted Magnetic Semiconductor Heterojunction Systems,"Diluted magnetic semiconductors (DMSs), in which magnetic elements are
substituted for a small fraction of host elements in a semiconductor lattice,
can become ferromagnetic when doped. In this article we discuss the physics of
DMS ferromagnetism in systems with semiconductor heterojunctions. We focus on
the mechanism that cause magnetic and magnetoresistive properties to depend on
doping profiles, defect distributions, gate voltage, and other system
parameters that can in principle be engineered to yield desired results.",0203080v1
2002/3/29,Inhomogeneous magnetism in single crystalline Sr$_3$CuIrO$_{6+δ}$: Implications to phase-separation concepts,"The single crystalline form of an insulator, Sr$_3$CuIrO$_{6+\delta}$, is
shown to exhibit unexpectedly more than one magnetic transition (at 5 and 19 K)
with spin-glass-like magnetic susceptibility behaviour. On the basis of this
finding, viz., inhomogeneous magnetism in a chemically homogeneous material, we
propose that the idea of ""phase- separation"" described for manganites [1] is
more widespread in different ways. The observed experimental features enable us
to make a comparison with the predictions of a recent toy model [2] on {\it
magnetic} phase separation in an insulating environment.",0203606v1
2002/7/9,Superconductivity in Magnetically Ordered CeTe$_{1.82}$,"We report the discovery of pressure-induced superconductivity in a
semimetallic magnetic material CeTe$_{1.82}$. The superconducting transition
temperature $T_{SC}$ = 2.7 K (well below the magnetic ordering temperatures)
under pressure ($>$ 2 kbar) is remarkably high, considering the relatively low
carrier density due to a charge-density-wave transition associated with lattice
modulation. The coexisting magnetic structure of a mixed ferromagnetism and
antiferromagnetism can provide a clue for this high $T_{SC}$. We discuss a
theoretical model for its possible pairing symmetry and pairing mechanism.",0207239v1
2002/8/1,Magneto-optical study of ZnO based diluted magnetic semiconductors,"Magneto-optical properties of ZnO:Co and ZnO:Ni films were measured.
Magnetization measurements show that some of the films are paramagnetic and
others are ferromagnetic. Magnetic circular dichroism clarified that Zn1-xCoxO
and Zn1-xNixO included in samples are paramagnetic diluted magnetic
semiconductors. Ferromagnetic precipitations seem to be responsible for the
observed ferromagnetic behaviors. Criteria to judge the ferromagnetic DMS are
also discussed.",0208010v1
2002/8/14,Plasticity of Ferromagnets near the Curie Point,"We propose an explanation of the anomalous growth of plasticity in
ferromagnets near the Curie point. We demonstrate that this effect is caused by
spin-dependent detachment of dislocations from obstacles under an influence of
the internal magnetic field. Magnetization fluctuations grow in the vicinity of
the Curie point, yield an increase of the detachment probability and, hence, an
increase of the plasticity. We apply this model for a description of the
temperature behaviour of the critical stress in nickel and of the microhardness
of gadolinium. An external magnetic field suppresses the magnetization
fluctuations and, hence may suppress the above singularities.",0208271v1
2002/9/10,Canted ferromagnetism in RuSr$_2$GdCu$_2$O$_8$,"First principles calculations using the full-potential linearized augmented
plane wave (FLAPW) method including intra-atomic noncollinear magnetism have
been performed to determine the magnetic structures of
RuSr$_{2}$GdCu$_{2}$O$_{8}$. The magnetism clearly arises from the RuO$_{6}$
octahedra where the moments on neighboring Ru sites order antiferromagnetically
but cant perpendicular to the AFM axis - and so induce a weak ferromagnetism.
The projected Ru moments along the AFM and FM axes result in magnetic moments
of 1.16 and 0.99 $\mu_{B}$ respectively. The results are consistent with the
possible coexistence of canted ferromagnetism and superconductivity in the
RuSr$_{2}$GdCu$_{2}$O$_{8}$ - inferred from experiments.",0209224v1
2002/9/24,Dilatometric study of Ni2+xMn1-xGa under magnetic field,"A study of polycrystalline and single crystalline Ni$_{2+x}$Mn$_{1-x}$Ga
alloys by means of dilatometric and strain gage techniques shows that large
strain can be induced in the temperature range of the martensitic
transformation by application of an external magnetic field. The biggest strain
induced by magnetic field was observed in the samples of chemical compositions
where the structural and magnetic transitions couple, i.e. occur at the same
temperature.",0209545v1
2002/9/25,Crossed-anisotropy films for magnetic tunnel junctions and magnetic memory applications,"A prototype of magnetoresistive random access memory (MRAM) based on magnetic
tunnel junctions (MTJ) was fabricated with crossed-anisotropy of magnetic
layers on either side of the tunnelling barrier layer. It is demonstrated that
the introduction of crossed-anisotropy results in smaller switching fields and
better switching times compared to the conventional case of aligned
anisotropies. The magnetoresistive properties of fabricated devices are in good
agreement with the micromagnetic model.",0209578v1
2002/9/26,Ordering intermetallic alloys by ion irradiation: a way to tailor magnetic media,"Combining He ion irradiation and thermal mobility below 600K, we both trigger
and control the transformation from chemical disorder to order in thin films of
an intermetallic ferromagnet (FePd). Kinetic Monte Carlo simulations show how
the initial directional short range order determines order propagation.
Magnetic ordering perpendicular to the film plane was achieved, promoting the
initially weak magnetic anisotropy to the highest values known for FePd films.
This post-growth treatment should find applications in ultrahigh density
magnetic recording.",0209612v1
2002/10/4,Surface contribution to the anisotropy of magnetic nanoparticles,"We calculate the contribution of the Neel surface anisotropy to the effective
anisotropy of magnetic nanoparticles of spherical shape cut out of a simple
cubic lattice. The effective anisotropy arises because deviations of atomic
magnetizations from collinearity and thus the energy depends on the orientation
of the global magnetization. The result is second order in the Neel surface
anisotropy, scales with the particle volume and has cubic symmetry with
preferred directions [+-1,+-1,+-1].",0210098v1
2002/10/21,Competing SDW Phases and Quantum Oscillations in (TMTSF)2ClO4 in Magnetic Field,"We propose a new approach for studying spin density waves (SDW) in the
Bechgaard salt (TMTSF)2ClO4 where lattice is dimerized in transverse direction
due to anion ordering. The SDW response is calculated in the matrix formulation
that rigorously treats the hybridization of inter-band and intra-band SDW
correlations. Since the dimerization gap is large, of the order of transverse
bandwidth, we also develop an exact treatment of magnetic breakdown in the
external magnetic field. The obtained results agree with the experimental data
on the fast magneto-resistance oscillations. Experimentally found 260T rapid
oscillations and the characteristic Tc dependance on magnetic field of relaxed
material are fitted with our results for anion potential of the order of
interchain hopping.",0210452v1
2002/11/22,Nonlinear microscopic relaxation of uniform magnetization precession,"Dynamic relaxation for nonlinear magnetization excitation is analyzed. For
direct processes, such as magnon-electron scattering and two-magnon scattering,
the relaxation rate is determined from the linear case simply by utilizing the
magnetization oscillation frequency for nonlinear excitation. For an indirect
process, such as slow-relaxing impurities, the analysis gives an additional
relaxation term proportional to the excitation level. In all cases the
effective magnetization damping is increased compared to
Landau-Lifshitz-Gilbert damping.",0211499v1
2002/12/5,Spatially resolved ultrafast precessional magnetization reversal,"Spatially resolved measurements of quasi-ballistic precessional magnetic
switching in a microstructure are presented. Crossing current wires allow
detailed study of the precessional switching induced by coincident longitudinal
and transverse magnetic field pulses. Though the response is initially
spatially uniform, dephasing occurs leading to nonuniformity and transient
demagnetization. This nonuniformity comes in spite of a novel method for
suppression of end domains in remanence. The results have implications for the
reliability of ballistic precessional switching in magnetic devices.",0212089v1
2002/12/5,Non-exponential relaxation and quantum tunnel splitting in molecular magnet Fe8,"Magnetic relaxation in molecular magnets under a sweeping field is studied by
taking into account local stray fields. It is found that the randomness of
local stray field leads to a distribution of the relaxation rate which
subsequently makes the relaxation deviate from the exponential law as predicted
by the Landau-Zener model such that the Landau-Zener method needs to be revised
to deduce an exact tunneling splitting. The tunneling splitting and
distribution width of local stray fields are derived from the experimental data
for molecular magnets Fe8.",0212109v1
2002/12/17,Magnetic nanographite,"Hydrogenated nanographite can display spontaneous magnetism. Recently we
proposed that hydrogenation of nanographite is able to induce finite
magnetization. We have performed theoretical investigation of a graphene ribbon
in which each carbon is bonded to two hydrogen atoms at one edge and to a
single hydrogen atom at another edge. Application of the local-spin-density
approximation to the calculation of the electronic band-structure of the ribbon
shows appearance of a spin-polarized flat band at the Fermi energy. Producing
different numbers of mono-hydrogenated carbons and di-hydrogenated carbons can
create magnetic moments in nanographite.",0212391v1
2003/2/4,Specific heat at the transition in a superconductor with fluctuating magnetic moments,"In the heavy-fermion materials CeCoIn$_5$ and UBe$_{13}$, the superconducting
order parameter is coupled to flucutating magnetization of the uncompensated
part of the localized $f$-moments. We find that this coupling decreases the
superconducting transition temperature and increases the jump of the
specific-heat coefficient, which indicates entropy transfer from the magnetic
to the superconducting degree of freedom at the transition temperature. Below
the transition, we find that the magnetic fluctuations are suppressed. We
discuss the relation of our results to experiments on CeCoIn$_5$ under
pressure.",0302089v1
2003/4/24,Reversal-field memory in magnetic hysteresis,"We report results demonstrating a singularity in the hysteresis of magnetic
materials, the reversal-field memory effect. This effect creates a
nonanalyticity in the magnetization curves at a particular point related to the
history of the sample. The microscopic origin of the effect is associated with
a local spin-reversal symmetry of the underlying Hamiltonian. We show that the
presence or absence of reversal-field memory distinguishes two widely studied
models of spin glasses (random magnets).",0304541v1
2003/4/24,Domain wall propagation in magnetic nanowires by spin polarized current injection,"We demonstrate movement of a head-to-head domain wall through a magnetic
nanowire simply by passing an electrical current through the domain wall and
without any external magnetic field applied. The effect depends on the sense
and magnitude of the electrical current and allows direct propagation of domain
walls through complex nanowire shapes, contrary to the case of magnetic field
induced propagation. The efficiency of this mechanism has been evaluated and
the effective force acting on the wall has been found equal to 0.88x10-9 N.A-1.",0304549v1
2003/4/29,Magnetically-ordered quasicrystals: Enumeration of spin groups and calculation of magnetic selection rules,"We provide the details of the theory of magnetic symmetry in quasicrystals,
which has previously only been outlined. We develop a practical formalism for
the enumeration of spin point groups and spin space groups, and for the
calculation of selection rules for neutron scattering experiments. We
demonstrate the formalism using the simple, yet non-trivial, example of
magnetically-ordered octagonal quasicrystals in two dimensions. In a companion
paper we shall provide complete results for octagonal quasicrystals in three
dimensions.",0304669v2
2003/5/13,Dipolar interaction effects in the thermally activated magnetic relaxation of two-dimensional nanoparticle ensembles,"The thermally activated magnetic relaxation in two-dimensional ensembles of
dipolar interacting nanoparticles with large uniaxial perpendicular anisotropy
is studied by a numerical method and within the mean-field approximation. The
role that the correlation effects in the presence of a bias magnetic field and
taking into account the lattice structure play in magnetic relaxation is
revealed",0305291v1
2003/5/14,Temperature dependence of magnetism near defects in SrB_6,"The T-dependence of magnetic moments in SrB_6 is studied through
spin-polarized band calculations for a supercell of Sr_{27}B_{156} containing a
B_6 vacancy. The magnetic moment decays rather quickly with T despite the fact
that only electronic Fermi-Dirac effects are included. This result and the
T-dependence of moments near a La impurity can hardly explain the reports of a
very high Curie temperature in hexaborides, but suggest that the magnetism is
caused by some other type of impurity.",0305327v1
2003/5/22,Coherent Spin Oscillations in a Disordered Magnet,"Most materials freeze when cooled to sufficiently low temperature. We find
that magnetic dipoles randomly distributed in a solid matrix condense into a
spin liquid with spectral properties on cooling that are the diametric opposite
of those for conventional glasses. Measurements of the non-linear magnetic
dynamics in the low temperature liquid reveal the presence of coherent spin
oscillations composed of hundreds of spins with lifetimes up to ten seconds.
These excitations can be labeled by frequency, manipulated by the magnetic
fields from a loop of wire, and permit the encoding of information at multiple
frequencies simultaneously.",0305541v1
2003/5/27,Double Magnetic Transition in Pr0.5Sr0.5CoO3,"We report studies of polycrystalline samples of the metallic ferromagnet
Pr0.5Sr0.5CoO3 through measurements of the magnetization, a.c. magnetic
susceptibility, resistivity, and specific heat. We find an unusual anomaly
around TA = 120 K, much below the ferromagnetic transition (TC = 226 K). The
anomaly is manifested in field cooled magnetization as a downward step in low
fields (H less than or equal to 0.01 T) but is transformed into an upward step
for H greater than or equal to 0.05 T. The anomaly cannot be easily attributed
to antiferromagnetic ordering, but may correspond to a second ferromagnetic
transition or an alteration of the ferromagnetic state associated with orbital
ordering.",0305621v1
2003/6/2,Ferromagnetism in Fe-doped Ba6Ge25 Chiral Clathrate,"We have successfully synthesized a Ba6Ge25 clathrate, substituting 3 Fe per
formula unit by Ge. This chiral clathrate has Ge sites forming a framework of
closed cages and helical tunnel networks. Fe atoms randomly occupy these sites,
and exhibit high-spin magnetic moments. A ferromagnetic transition is observed
with Tc = 170 K, the highest observed Tc for a magnetic clathrate. However, the
magnetic phase is significantly disordered, and exhibits a transformation to a
re-entrant spin glass phase. This system has a number of features in common
with other dilute magnetic semiconductors.",0306044v1
2003/6/6,Projective Dynamics Analysis of Magnetization Reversal,"The computational Projective Dynamics method is used to analyze simulations
of magnetization reversal in nanoscale magnetic pillars. It is shown that this
method can be used to determine the magnetizations corresponding to the
metastable minimum and saddle point in the free energy, and the free-energy
barrier associated with those points. For the nanopillars studied here, entropy
is found to provide a significant contribution to the free-energy barrier which
determines the reversal time scale.",0306168v1
2003/6/11,Magnetic energy-level diagrams of high-spin (Mn$_{12}$-acetate) and low-spin (V$_{15}$) molecules,"The magnetic energy-level diagrams for models of the Mn12 and V15 molecule
are calculated using the Lanczos method with full orthogonalization and a
Chebyshev-polynomial-based projector method. The effect of the
Dzyaloshinskii-Moriya interaction on the appearance of energy-level repulsions
and its relevance to the observation of steps in the time-dependent
magnetization data is studied. We assess the usefulness of simplified models
for the description of the zero-temperature magnetization dynamics.",0306275v1
2003/6/21,The Effect of Disorder on a Quantum Phase Transition,"The conductivity and magnetization of Fe1-xCoxS2 were measured to investigate
quantum critical behavior in disordered itinerant magnets. Small x (<0.001) is
required to convert insulating iron pyrite into a metal, followed by a
paramagnetic-to-ferromagnetic metal transition at x = 0.032+/-0.004. Singular
contributions are discovered that are distinct from those at either
metal-insulator or magnetic transitions. Our data reveal that disorder and low
carrier density associated with proximity to a metal-insulator transition
fundamentally modifies the critical behavior of the magnetic transition.",0306541v1
2003/6/26,Quantum tunneling in a three dimensional network of exchange coupled single-molecule magnets,"A Mn4 single-molecule magnet (SMM) is used to show that quantum tunneling of
magnetization (QTM) is not suppressed by moderate three dimensional exchange
coupling between molecules. Instead, it leads to an exchange bias of the
quantum resonances which allows precise measurements of the effective exchange
coupling that is mainly due to weak intermolecular hydrogen bounds. The
magnetization versus applied field was recorded on single crystals of [Mn4]2
using an array of micro-SQUIDs. The step fine structure was studied via minor
hysteresis loops.",0306669v1
2003/7/1,Magnetic Properties of Fe75Cu4Ni4Mo2B15 Alloy,"The structural and magnetic properties of ball-milled Fe75Cu4Ni4Mo2B15 alloy
have been investigated through powder X-ray diffraction studies, magnetization
and magnetoimpedance measurements. The particle size decreased rapidly with
ball-milling up to 165 hours and then remained as a constant with further hours
of milling while, the lattice expanded with milling time up to 165 hours and
contracted back with further milling. Saturation magnetization is found to
decrease rapidly up to 165 hours of milling and then started decreasing slowly
with further milling time. Magnetoimpedance studies were carried out in pellets
and thin films of Fe75Cu4Ni4Mo2B15. Magnetoimpedance in pellet is observed to
be ~2.5% at 5Hz whereas, in thin films, it is observed to be ~1.5% at 3 MHz.",0307019v1
2003/7/9,Remarks on quantum critical behavior in heavy fermions,"Generalized scaling relations and renormalization group results are used to
discuss the phase diagrams of heavy fermion systems. We consider the cases
where these materials are driven to a magnetic quantum critical point either by
applying external pressure or a magnetic field. The Ehrenfest equation relating
the pressure derivative of the critical temperature to the ratio of thermal
expansion and specific heat close to a magnetic quantum critical point (QCP) is
analyzed from the scaling point of view. We consider different phase diagrams
of antiferromagnetic heavy fermions in an external uniform magnetic field and
the implication of renormalization group results for predicting their behavior.",0307218v1
2003/7/17,"Specific heat and magnetization study on single crystals of a frustrated, quasi one-dimensional oxide: Ca3Co2O6","Specific heat and magnetization measurements have been carried out under a
range of magnetic fields on single crystals of Ca3Co2O6. This compound is
composed of Ising magnetic chains that are arranged on a triangular lattice.
The intrachain and interchain couplings are ferromagnetic and
antiferromagnetic, respectively. This situation gives rise to geometrical
frustration, that bears some similarity to the classical problem of a
two-dimensional Ising triangular antiferromagnet. This paper reports on the
ordering process at low-T and the possibility of one-dimensional features at
high-T.",0307429v1
2003/7/18,Dynamics of a nanoparticle as a one-spin system and beyond,"We review some recent results beyond the now established theory of
magnetization switching of a nanoparticle within the single-spin approximation.
The first extension is that of the Stoner-Wohlfarth model for magnetization
static switching under applied magnetic field including the effect of
temperature at long-time scales. The second concerns a generalization of the
N\'eel-Brown model for thermoactivated dynamic magnetization switching to
include the effect of exchange interaction in the framework of Langer's theory
in the intermediate-to-high damping limit. We finally argue why the single-spin
approximation is not appropriate for very small nanoparticles.",0307457v1
2003/9/16,Field-Induced Magnetization Steps in Intermetallic Compounds and Manganese Oxides: The Martensitic Scenario,"Field-induced magnetization jumps with similar characteristics are observed
at low temperature for the intermetallic germanide Gd5Ge4and the mixed-valent
manganite Pr0.6Ca0.4Mn0.96Ga0.04O3. We report that the field location -and even
the existence- of these jumps depends critically on the magnetic field sweep
rate used to record the data. It is proposed that, for both compounds, the
martensitic character of their antiferromagnetic-to-ferromagnetic transitions
is at the origin of the magnetization steps.",0309389v1
2003/9/19,Anisotropic flux creep in Bi2212:Pb single crystal in crossed magnetic fields,"An experimental study of magnetic flux penetration under crossed magnetic
fields in Bi2212:Pb single crystals is performed by the magneto-optic
technique. The anisotropy of the flux creep rate induced by the in-plane
magnetic field is observed at $T<54\pm 2$ K. This observation confirms the
existence of the three-dimensional flux line structure in Bi2212:Pb at low
temperatures. An asymmetry of the flux relaxation with respect to the direction
of the in-plane field is found. This effect can be attributed to the influence
of the laminar structure on the pinning in Bi2212:Pb single crystals.",0309451v1
2003/10/27,Spin Fluctuations and the Magnetic Phase Diagram of ZrZn2,"The magnetic properties of the weak itinerant ferromagnet ZrZn_2 are analyzed
using Landau theory based on a comparison of density functional calculations
and experimental data as a function of field and pressure. We find that the
magnetic properties are strongly affected by the nearby quantum critical point,
even at zero pressure; LDA calculations neglecting quantum critical spin
fluctuations overestimate the magnetization by a factor of approximately three.
Using renormalized Landau theory, we extract pressure dependence of the
fluctuation amplitude. It appears that a simple scaling based on the
fluctuation-dissipation theorem provides a good description of this pressure
dependence.",0310630v1
2003/10/30,Magnetization reversal by injection and transfer of spin: experiments and theory,"Reversing the magnetization of a ferromagnet by spin transfer from a current,
rather than by applying a magnetic field, is the central idea of an extensive
current research. After a review of our experiments of current-induced
magnetization reversal in Co/Cu/Co trilayered pillars, we present the model we
have worked out for the calculation of the current-induced torque and the
interpretation of the experiments.",0310737v1
2003/11/18,Domain-specific magnetization reversals on a permalloy square ring array,"We present domain-specific magnetization reversals extracted from soft x-ray
resonant magnetic scattering measurement on a permalloy square ring array. The
extracted domain-specific hysteresis loops reveal that the magnetization of the
domain parallel to the field is strongly pinned, while those of other domains
rotate continuously. In comparison with the micromagnetic simulation, the
hysteresis loop on the pinned domain indicates a possibility of the coexistence
of the square rings with the vortex and onion states.",0311417v1
2003/12/18,Spin momentum transfer in current perpendicular to the plane spin valves,"We present experimental and numerical micromagnetic data on the effect of
spin momentum transfer in current perpendicular to the plane spin valves.
Starting from a configuration with orthogonal free and pinned layer
magnetizations, the free layer magnetization exhibits abrupt current induced
switching that is qualitatively consistent with the spin torque model. When
operating the spin valve as a field sensor, spin transfer can produce a change
in resistance that mimics an effective magnetic field and induce magnetic
instability that requires a larger bias field in order to stabilize the device.",0312505v1
2004/2/10,Effect of uniaxial and biaxial crystal-field potential on magnetic properties of a mixed spin-1/2 and spin-1 Ising model on honeycomb lattice,"Magnetic properties of a mixed spin-1/2 and spin-1 Ising model on honeycomb
lattice are exactly investigated within the framework of generalized
star-triangle mapping transformation. The particular attention is focused on
the effect of uniaxial and biaxial crystal-field anisotropies that basically
influence the magnetic behaviour of the spin-1 atoms. Our results for the basic
thermodynamic quantities, as well as the dynamical time-dependent
autocorrelation function indicate the spin tunneling between the $| +1>$ and $|
- 1>$ states in the magnetically ordered phase.",0402280v2
2004/3/16,Rashba Effect at Magnetic Metal Surfaces,"We give experimental and theoretical evidence of the Rashba effect at the
magnetic rare-earth metal surface Gd(0001). The Rashba effect is substantially
enhanced and the Rashba parameter changes its sign when a metal-oxide surface
layer is formed. The experimental observations are quantitatively described by
ab initio calculations that give a detailed account of the near-surface charge
density gradients causing the Rashba effect. Since the sign of the Rashba
splitting depends on the magnetization direction, the findings open up new
opportunities for the study of surface and interface magnetism.",0403405v2
2004/3/17,Giant Magnetoresistance in Multilayers with Noncollinear Magnetizations,"We study the dependence of perpendicular-current magnetoresistance in
magnetic multilayers on the angle between the magnetizations of the layers.
This dependence varies with the thickness of one of the layers, and is
different for multilayers with two and three magnetic layers. We derive a
system of equations representing an extension of the two-current series
resistor model, and show that the angular dependence of magnetoresistance gives
information about the noncollinear spin-transport in ferromagnets.",0403441v1
2004/3/19,"Current-driven Magnetization Reversal in a Ferromagnetic Semiconductor (Ga,Mn)As/GaAs/(Ga,Mn)As Tunnel Junction","Current-driven magnetization reversal in a ferromagnetic semiconductor based
(Ga,Mn)As/GaAs/(Ga,Mn)As magnetic tunnel junction is demonstrated at 30 K.
Magnetoresistance measurements combined with current pulse application on a
rectangular 1.5 x 0.3 um^2 device revealed that magnetization switching occurs
at low critical current densities of 1.1 - 2.2 x 10^5 A/cm^2 despite the
presence of spin-orbit interaction in the p-type semiconductor system. Possible
mechanisms responsible for the effect are discussed.",0403500v3
2004/4/14,Investigation of the field-treated magnetic state in Gd5Ge4,"At low temperatures, the intermetallic compound Gd$_5$Ge$_4$ shows a sharp
field-induced transition into a ferromagnetic state around 25 kOe of applied
field. The material remains in the field treated ferromagnetic state even when
the magnetic field is removed. We have investigated the character of this
field-treated state by magnetization and heat capacity measurements. The nature
of the magnetization and the heat capacity are found to be different above and
below a charactersitic temperature Tirr = 25 K.",0404302v1
2004/5/18,Thermal ratchet effects in ferrofluids,"Rotational Brownian motion of colloidal magnetic particles in ferrofluids
under the influence of an oscillating external magnetic field is investigated.
It is shown that for a suitable time dependence of the magnetic field, a noise
induced rotation of the ferromagnetic particles due to rectification of thermal
fluctuations takes place. Via viscous coupling, the associated angular momentum
is transferred from the magnetic nano-particles to the carrier liquid and can
then be measured as macroscopic torque on the fluid sample. A thorough
theoretical analysis of the effect in terms of symmetry considerations,
analytical approximations, and numerical solutions is given which is in
accordance with recent experimental findings.",0405393v1
2004/5/19,Ballistic conductance of magnetic Co and Ni nanowires with ultrasoft pseudo-potentials,"The scattering-based approach for calculating the ballistic conductance of
open quantum systems is generalized to deal with magnetic transition metals as
described by ultrasoft pseudo-potentials. As an application we present
quantum-mechanical conductance calculations for monatomic Co and Ni nanowires
with a magnetization reversal. We find that in both Co and Ni nanowires, at the
Fermi energy, the conductance of $d$ electrons is blocked by a magnetization
reversal, while the $s$ states (one per spin) are perfectly transmitted. $d$
electrons have a non-vanishing transmission in a small energy window below the
Fermi level. Here, transmission is larger in Ni than in Co.",0405433v1
2004/5/24,Determination of the magnetic anisotropy axes of single-molecule magnets,"Simple methods are presented allowing the determination of the magnetic
anisotropy axes of a crystal of a single-molecule magnet (SMM). These methods
are used to determine an upper bound of the easy axis tilts in a standard
Mn12-Ac crystal. The values obtained in the present study are significately
smaller than those reported in recent high frequency electron paramagnetic
resonance (HF-EPR) studies which suggest distributions of hard-axes tilts.",0405565v1
2004/5/26,Different steady states for spin currents in noncollinear multilayers,"We find there are at least two different steady states for transport across
noncollinear magnetic multilayers. In the conventional one there is a
discontinuity in the spin current across the interfaces which has been
identified as the source of current induced magnetic reversal; in the one
advocated herein the spin torque arises from the spin accumulation transverse
to the magnetization of a magnetic layer. These two states have quite different
attributes which should be discerned by current experiments.",0405613v1
2004/7/7,Influence of surface anisotropy on the magnetization reversal of nanoparticles,"The influence of surface anisotropy on the magnetization processes of
maghemite nanoparticles with ellipsoidal shape is studied by means of Monte
Carlo simulations. Radial surface anisotropy is found to favor the formation of
hedgehog-like spin structures that become more stable as the surface anisotropy
constant at the surface $k_S$ is increased form the value at the core. We have
studied the change in the low temperature hysteresis loops with the particle
aspect ratio and with $k_S$, finding a change in the magnetization reversal
mode as $k_S$ or the particle elongation is increased.",0407176v1
2004/7/8,Polydispersity-linked Memory Effects in a Magnetic Nanoparticle System,"We have performed a series of measurements on the low temperature behavior of
a magnetic nano-particle system. Our results show striking memory effects in
the dc magnetization. Dipolar interactions among the nano-particles {\em
suppress} the memory effect. We explain this phenomenon by the superposition of
different super paramagnetic relaxation times of single domain magnetic nano-
particles. Moreover, we observe a crossover in the temperature dependence of
coercivity. We show that a dilute dispersion of particles with a flat size
distribution yields the best memory.",0407202v1
2004/8/2,Carrier Concentration Dependencies of Magnetization & Transport in Ga1-xMnxAs1-yTey,"We have investigated the transport and magnetization characteristics of
Ga1-xMnxAs intentionally compensated with shallow Te donors. Using ion
implantation followed by pulsed-laser melting, we vary the Te compensation and
drive the system through a metal-insulator transition (MIT). This MIT is
associated with enhanced low-temperature magnetization and an evolution from
concave to convex temperature-dependent magnetization.",0408021v1
2004/8/6,Proposal for a spintronic femto-Tesla magnetic field sensor,"We propose a spintronic magnetic field sensor, fashioned out of quantum
wires, which may be capable of detecting very weak magnetic fields with a
sensitivity of ~ 1 femto-Tesla per root Hertz at a temperature of 4.2 K and ~
80 femto-Tesla per root Hertz at room temperature. Such sensors have
applications in magnetometry, quantum computing, solid state nuclear magnetic
resonance, magneto-encephalography, mine detection, ground incursion detection
and anti-submarine warfare.",0408137v2
2004/8/28,"Current-Induced Magnetization Switching in Permalloy-based Nanopillars with Cu, Ag, and Au","We compare magnetoresistances (MR) and switching currents (I_s) at room
temperature (295K) and 4.2K for Permalloy/N/Permalloy nanopillars undergoing
current-induced magnetization switching (CIMS), with non-magnetic metals N =
Cu, Ag, and Au. The N-metal thickness is held fixed at 10 nm. Any systematic
differences in MR and I_s for the different N-metals are modest, suggesting
that Ag and Au represent potentially viable alternatives for CIMS studies and
devices to the more widely used Cu.",0408632v1
2004/8/30,Magnetically-controlled impurities in quantum wires with strong Rashba coupling,"We investigate the effect of strong spin-orbit interaction on the electronic
transport through non-magnetic impurities in one-dimensional systems. When a
perpendicular magnetic field is applied, the electron spin polarization becomes
momentum-dependent and spin-flip scattering appears, to first order in the
applied field, in addition to the usual potential scattering. We analyze a
situation in which, by tuning the Fermi level and the Rashba coupling, the
magnetic field can suppress the potential scattering. This mechanism should
give rise to a significant negative magnetoresistance in the limit of large
barriers.",0408656v2
2004/9/5,Bias voltage controlled magnetization switch in ferromagnetic semiconductor resonant tunneling diodes,"We predict that the Curie temperature of a ferromagnetic resonant tunneling
diode will decrease abruptly, by approximately a factor of two, when the
downstream chemical potential falls below the quantum well resonance energy.
This property follows from elementary quantum transport theory notions combined
with a mean field description of diluted magnetic semiconductor ferromagnetism.
We illustrate this effect by solving coupled non-equilibrium Green's function,
magnetic mean-field, and electrostatic Poisson equations self-consistently to
predict the bias voltage and temperature dependence of the magnetization of a
model system.",0409106v2
2004/9/17,Searching for a magnetic proximity effect in magnetite-carbon structures,"In order to study a possible magnetic proximity effect in magnetite-carbon
structures, we have performed magnetization measurements of graphite-magnetite
composites with different mass ratios as well as the measurement of the
magnetoresistance of one of them and of the magnetization of a magnetite-carbon
bilayer. The overall results do not indicate the induction of bulk
ferromagnetism in graphite and disordered carbon structures through their
contact with magnetite.",0409447v1
2004/10/1,"Effect of Ga$^{+}$ irradiation on magnetic and magnetotransport properties in (Ga,Mn)As epilayers","We report on the magnetic and magnetotransport properties of ferromagnetic
semiconductor (Ga,Mn)As modified by Ga$^{+}$ ion irradiation using focused ion
beam. A marked reduction in the conductivity and the Curie temperature is
induced after the irradiation. Furthermore, an enhanced negative
magnetoresistance (MR) and a change in the magnetization reversal process are
also demonstrated at 4 K. Raman scattering spectra indicate a decrease in the
concentration of hole carriers after the irradiation, and a possible origin of
the change in the magnetic properties is discussed.",0410024v1
2004/12/9,Modified Spin-Wave Theory for Nanomagnets : Application to the Keplerate Molecule Mo(72)Fe(30),"We adapt Takahashi's modified spin-wave theory to the context of
nano-magnets, and apply it to the molecular compound based on the giant
magnetic molecule Mo(72)Fe(30). This involves solving numerically the
mean-field equations and then forcing the sublattice magnetizations to zero by
means of local chemical potentials for the magnons. We have thus constructed a
quantum state with no local magnetization at all temperatures, appropriate to a
finite-size system, but with strong correlations. We compare theoretical
results to specific heat and ESR measurements.",0412244v1
2005/2/7,Electron paramagnetic resonance detected via magnetization measurements,"Presented are magnetization measurements on a crystal of Fe8 single-molecule
magnets using a Hall probe magnetometer. Irradiation with microwaves at
frequencies of 92 and 110-120 GHz leads to the observation of electron
paramagnetic resonance (EPR) detected via magnetization measurements. A
quantitative analysis of the results are introduced by means of the spin
temperature. It is shown that pulsed microwave experiments allow a better
control over the spin excitation.",0502175v1
2005/3/7,Manipulating nonequilibrium magnetism through superconductors,"Electrostatic control of the magnetization of a normal mesoscopic conductor
is analyzed in a hybrid superconductor-normal-superconductor system. This
effect stems from the interplay between the non-equilibrium condition in the
normal region and the Zeeman splitting of the quasiparticle density of states
of the superconductor subjected to a static in-plane magnetic field. Unexpected
spin-dependent effects such as magnetization suppression, diamagnetic-like
response of the susceptibility as well as spin-polarized current generation are
the most remarkable features presented. The impact of scattering events is
evaluated and let us show that this effect is compatible with realistic
material properties and fabrication techniques.",0503126v1
2005/4/4,Band structure model of magnetic coupling in semiconductors,"We present a unified band structure model to explain magnetic ordering in
Mn-doped semiconductors. This model is based on the $p$-$d$ and $d$-$d$ level
repulsions between the Mn ions and host elements and can successfully explain
magnetic ordering observed in all Mn doped II-VI and III-V semiconductors such
as CdTe, GaAs, ZnO, and GaN. This model, therefore, provides a simple guideline
for future band structure engineering of magnetic semiconductors.",0504084v1
2005/4/7,Evolution of ferromagnetic circular dichroism coincident with magnetization and anomalous Hall effect in Co-doped rutile TiO2,"Magnetic circular dichroism (MCD) of rutile Ti1-xCoxO2-d is systematically
examined with various x and d to reveal a phase diagram for the appearance of
ferromagnetism at higher carrier concentration and Co content. The phase
diagram exactly matches with that determined from anomalous Hall effect (AHE).
The magnetic field dependence of MCD also shows good coincidence with those of
the magnetization and AHE. The coincidence of these independent measurements
strongly suggests single and intrinsic ferromagnetic origin.",0504167v1
2005/4/7,Magnetic oxide semiconductors,"Magnetic oxide semiconductors, oxide semiconductors doped with transition
metal elements, are one of the candidates for a high Curie temperature
ferromagnetic semiconductor that is important to realize semiconductor
spintronics at room temperature. We review in this paper recent progress of
researches on various magnetic oxide semiconductors. The magnetization,
magneto-optical effect, and magneto-transport such as anomalous Hall effect are
examined from viewpoint of feasibility to evaluate the ferromagnetism. The
ferromagnetism of Co-doped TiO2 and transition metal-doped ZnO is discussed.",0504168v1
2005/6/3,Magnetic and Transport Properties of Fe-Ag granular multilayers,"Results of magnetization, magnetotransport and Mossbauer spectroscopy
measurements of sequentially evaporated Fe-Ag granular composites are
presented. The strong magnetic scattering of the conduction electrons is
reflected in the sublinear temperature dependence of the resistance and in the
large negative magnetoresistance. The simultaneous analysis of the magnetic
properties and the transport behavior suggests a bimodal grain size
distribution. A detailed quantitative description of the unusual features
observed in the transport properties is given.",0506072v2
2005/6/10,"Symmetry analysis of k = (1/3,1/3,0) three-sublattice ordering in A14B51 compounds","Bulk magnetic, X-ray and neutron diffraction measurements were performed on
polycrystalline Tb14Ag51 in the temperature range from 1.5 K to room
temperature. Its chemical Gd14Ag51 type structure corresponds to space group
P6/m. Combined with group theoretical symmetry analysis, we show that the
magnetic structure of this intermetallic compound is of a new k = (1/3,1/3,0)
type with three magnetic Tb sublattices ordering simultaneously below TN =
27.5(5) K according to the combined irreducible representations tau4 and tau6.
Here we present a general analysis of possible magnetic A ordering for k =
(1/3,1/3,0) in A14B51 compounds.",0506249v1
2005/6/22,"Quantum tunneling of magnetization in lanthanide single-molecule magnets, bis(phthalocyaninato)terbium and bis(phthalocyaninato)-dysprosium anions","Magnetization versus field measurements were performed on single crystals of
[(Pc)2TbIII0.02YIII0.98]^TBA+ and [(Pc)2DyIII0.02YIII0.98]^TBA+ (Pc:
phthalocyaninato, TBA: tetrabutylammonium) at 0.04 K. The [(Pc)2TbIII] complex,
the first lanthanide single-molecule magnet, exhibited clear staircase-like
structures, which are assigned to resonant quantum tunneling between entangled
states of the electron and nuclear spin systems.",0506583v1
2005/6/23,Fluctuating magnetic moments in liquid metals,"We re-analyze literature data on neutron scattering by liquid metals to show
that non-magnetic liquid metals possess a magnetic moment that fluctuates on a
picosecond time scale. This time scale follows the motion of the cage-diffusion
process in which an ion rattles around in the cage formed by its neighbors. We
find that these fluctuating magnetic moments are present in liquid Hg, Al, Ga
and Pb, and possibly also in the alkali metals.",0506612v1
2005/7/28,Magnetic relaxation of superconducting YBCO samples in weak magnetic fields,"For the first time, magnetization of high-Tc samples with different
crystalline structure and its isothermal relaxation is studied at very weak
constant fields (H <= 0.1 Oe) for temperatures close to the critical ones.
Essential influence of twin boundaries in YBCO single crystals on magnetic
relaxation rate is shown. An estimation of effective pinning potential is made
in the framework of the collective pinning model.",0507671v1
2005/8/1,The Ruthenocuprates - Natural Superconductor-Ferromagnet Multilayers,"The recently discovered ruthenocuprates have attracted great interest because
of the microscopic coexistence of superconducting and ferromagnetic order.
Typically, these materials become magnetically ordered at temperatures around
125-145 K and superconductivity sets in between 15 and 50 K. While
superconductivity arises in the CuO2 layers the RuO2 layers in between order
magnetically. In this paper we summarize some of the crystallographic, magnetic
and superconducting properties of the ruthenocuprates, as obtained from
investigations on polycrystalline samples as well as single crystals.",0508044v1
2005/8/30,Effects of spin current on ferromagnets,"When a spin-polarized current flows through a ferromagnet, the local
magnetization receives a spin torque. Two consequences of this spin torque are
studied. First, the uniformly magnetized ferromagnet becomes unstable if a
sufficiently large current is applied. The characteristics of the instability
include spin wave generation and magnetization chaos. Second, the spin torque
has profound effects on the structure and dynamics of the magnetic domain wall.
A detail analysis on the domain wall mass, kinetic energy and wall depinning
threshold is given.",0508735v1
2005/9/5,"Large magnetoresistance and magnetocaloric effect above 70 K in Gd2Co2Al, Gd2Co2Ga and Gd7Rh3","The electrical resistivity, magnetization and heat-capacity behavior of the
Gd-based compounds, Gd2Co2Al, Gd2Co2Ga and Gd7Rh3, ordering magnetically at TC=
78 K, TC= 76 K and TN= 140 K have been investigated as a function of
temperature and magnetic field. All these compounds are found to show large
magnetoresistance (with a negative sign) in the paramagnetic state at rather
high temperatures with the magnitude peaking at respective magnetic ordering
temperatures. There is a corresponding behavior in the magnetocaloric effect as
inferred from the entropy derived from these data.",0509107v1
2005/10/5,Orbital Polarization in Itinerant Magnets,"We propose a parameter-free scheme of calculation of the orbital polarization
(OP) in metals, which starts with the strong-coupling limit for the screened
Coulomb interactions in the random-phase approximation (RPA). For itinerant
magnets, RPA can be further improved by restoring the spin polarization of the
local-spin-density approximation (LSDA) through the local-field corrections.
The OP is then computed in the static GW approach, which systematically
improves the orbital magnetization and the magnetic anisotropy energies in
transition-metal and actinide compounds.",0510100v1
2005/10/27,Monte Carlo simulation study of exchange biased hysteresis loops in nanoparticles,"We present the results of Monte Carlo simulations of the magnetic properties
of a model for a single nanoparticle consisting in a ferromagnetic core
surrounded by an antiferromagnetic shell. The simulations of hysteresis loops
after cooling in a magnetic field display exchange bias effects. In order to
understand the origin of the loop shifts, we have studied the thermal
dependence of the shell and interface magnetizations under field cooling. These
results, together with inspection of the snapshots of the configurations
attained at low temperature, show the existence of a net magnetization at the
interface which is responsible for the bias of the hysteresis loops.",0510730v1
2005/11/1,Magnetic properties of carbon phases synthesized using high pressure-high temperature treatment,"Two sets of samples were synthesized at 3.5 GPa near the point of C60 cage
collapse at different annealing times. A clear structural transformation from
mixture of C60 polymeric phases to graphite-like hard carbon phase was
confirmed by X-ray diffraction and Raman spectroscopy. Magnetic force
microscopy and superconducting quantum interference device were used to
characterize the magnetic properties of the synthesized samples. We found that
the sample preparation conditions used in this study are not suitable to
produce bulk magnetic carbon.",0511022v1
2005/11/7,Effect of the intrinsic Josephson coupling on the pancake lattice in layered superconductors,"We study the pancake lattice system induced by application of transverse
magnetic filed to the layered superconductor. A simple statistical field theory
for the pancake lattice is derived. It incorporates effects of the magnetic
interaction between pancakes as well as those of the interlayer Josephson
coupling. The proposed description enables us to estimate the pancake crystal
melting temperature from above. Also, it allows us to compare directly the
effects of the magnetic and Josephson energies on the statistical properties of
the pancake lattice. We demonstrate that even for such an anisotropic material
as BSCCO the pancake interaction induced by the Josephson coupling is of the
same order as the magnetic interaction.",0511155v1
2005/12/2,Magnetic properties of Sr_2Fe_1+xMo_1-xO_6 with -1 <= x <= 0.25,"We have synthesized the solid solution, Sr_2Fe_1+xMo_1-xO_6 with -1 <= x <=
0.25, the composition x = 0 corresponding to the well-known double perovskite
system Sr2FeMoO6. We report structural and magnetic properties of the above
system, exhibiting systematic variations across the series. These results
restrict the range of models that can explain magnetism in this family of
compounds, providing an understanding of the magnetic structure.",0512059v1
2006/1/9,Phase equilibrium in two orbital model under magnetic field,"The phase equilibrium in manganites under magnetic field is studied using a
two orbital model, based on the equivalent chemical potential principle for the
competitive phases. We focus on the magnetic field induced melting process of
CE phase in half-doped manganites. It is predicted that the homogenous CE phase
begins to decompose into coexisting ferromagnetic phase and CE phase once the
magnetic field exceeds the threshold field. In a more quantitative way, the
volume fractions of the two competitive phases in the phase separation regime
are evaluated.",0601166v1
2006/1/11,Relaxing-Precessional Magnetization Switching,"A new way of magnetization switching employing both the spin-transfer torque
and the torque by a magnetic field is proposed. The solution of the
Landau-Lifshitz-Gilbert equation shows that the dynamics of the magnetization
in the initial stage of the switching is similar to that in the precessional
switching, while that in the final stage is rather similar to the relaxing
switching. We call the present method the relaxing-precessional switching. It
offers a faster and lower-power-consuming way of switching than the relaxing
switching and a more controllable way than the precessional switching.",0601227v1
2006/1/30,Magnetic Moment Softening and Domain Wall Resistance in Ni Nanowires,"Magnetic moments in atomic scale domain walls formed in nanoconstrictions and
nanowires are softened which affects dramatically the domain wall resistance.
We perform ab initio calculations of the electronic structure and conductance
of atomic-size Ni nanowires with domain walls only a few atomic lattice
constants wide. We show that the hybridization between noncollinear spin states
leads to a reduction of the magnetic moments in the domain wall. This magnetic
moment softening strongly enhances the domain wall resistance due to scattering
produced by the local perturbation of the electronic potential.",0601662v1
2006/2/16,BaNiF4: an electric field-switchable weak antiferromagnet,"We show that in the antiferromagnetic ferroelectric BaNiF4 the
Dzyaloshinskii-Moriya interaction leads to a small canting of the magnetic
moments, away from the easy axis, resulting in a noncollinear magnetic
structure. The canting corresponds to an additional ""weak"" antiferromagnetic
order parameter whose orientation is determined by the polar structural
distortion and can be reversed by switching the ferroelectric polarization with
an electric field. Our results point the way to a more general coupling
mechanism between structural distortions and magnetic order parameters in
magnetoelectric multiferroics which can be exploited in the design of electric
field-switchable magnets.",0602400v2
2006/3/6,Influence of surface tension on the conical miniscus of a magnetic fluid in the field of a current-carrying wire,"We study the influence of surface tension on the shape of the conical
miniscus built up by a magnetic fluid surrounding a current-carrying wire.
Minimization of the total energy of the system leads to a singular second order
boundary value problem for the function $\zeta(r)$ describing the axially
symmetric shape of the free surface. An appropriate transformation regularizes
the problem and allows a straightforward numerical solution. We also study the
effects a superimposed second liquid, a nonlinear magnetization law of the
magnetic fluid, and the influence of the diameter of the wire on the free
surface profile.",0603136v1
2006/3/20,Role of magnetic and orbital ordering at the metal-insulator transition in NdNiO3,"Soft x-ray resonant scattering at the Ni L2,3 edges is used to test models of
magnetic and orbital-ordering below the metal-insulator transition in NdNiO3.
The large branching ratio of the L3 to L2 intensities of the (1/2,0,1/2)
reflection and the observed azimuthal angle and polarization dependence
originates from a non collinear magnetic structure. The absence of an orbital
signal and the non collinear magnetic structure show that the nickelates are
materials for which orbital ordering is absent at the metal-insulator
transition.",0603496v1
2006/5/18,Magnetically Mediated Transparent Conductors: In$_2$O$_3$ doped with Mo,"First-principles band structure investigations of the electronic, optical and
magnetic properties of Mo-doped In$_2$O$_3$ reveal the vital role of magnetic
interactions in determining both the electrical conductivity and the
Burstein-Moss shift which governs optical absorption. We demonstrate the
advantages of the transition metal doping which results in smaller effective
mass, larger fundamental band gap and better overall optical transmission in
the visible -- as compared to commercial Sn-doped In$_2$O$_3$. Similar behavior
is expected upon doping with other transition metals opening up an avenue for
the family of efficient transparent conductors mediated by magnetic
interactions.",0605443v2
2006/7/5,Electronic structure of spheroidal fullerenes in a weak uniform magnetic field: a continuum field-theory model,"The effect of a weak uniform magnetic field on the electronic structure of
slightly deformed fullerene molecules is studied within the continuum
field-theory model. It is shown how the existing due to spheroidal deformation
fine structure of the electronic energy spectrum modifies in the presence of
the magnetic field. Hyperfine splitting of the energy-levels dictated by the
topological defects is also influenced by the weak external magnetic field.
Exact analytical solutions for zero-energy modes are found.",0607114v2
2006/8/1,"Structural and magnetic properties of ZnO:TM (TM: Co,Mn) nanopowders","We report on the structural and magnetic characterization of Co0.1Zn0.9O and
Mn0.1Zn0.9O nanopowders obtained by a soft chemistry route. We show that those
samples fired at low temperatures display a ferromagnetic interaction that can
not be attributed to the presence of impurities. A magnetic aging mechanism is
observed, reflecting the key role played by defects in the stabilization of
ferromagnetism in this kind of diluted magnetic semiconductors.",0608014v1
2006/8/23,A New Multiferroic Material: MnWO4,"We report the multiferroic behaviour of MnWO$_4$, a magnetic oxide with
monoclinic crystal structure and spiral long-range magnetic order. Based upon
recent theoretical predictions MnWO$_4$ should exhibit ferroelectric
polarization coexisting with the proper magnetic structure. We have confirmed
the multiferroic state below 13 K by observing a finite electrical polarization
in the magnetically ordered state via pyroelectric current measurements.",0608498v1
2006/8/25,Critical current under an optimal time-dependent polarization direction for Stoner particles in spin-transfer torque induced fast magnetization reversal,"Fast magnetization reversal of uniaxial Stoner particles by spin-transfer
torque due to the spin-polarized electric current is investigated. It is found
that a current with a properly designed time-dependent polarization direction
can dramatically reduce the critical current density required to reverse a
magnetization. Under the condition that the magnitude and the polarization
degree of the current do not vary with time, the shape of the optimal
time-dependent polarization direction is obtained such that the magnetization
reversal is the fastest.",0608563v1
2006/9/6,"Magnitude and crystalline anisotropy of hole magnetization in (Ga,Mn)As","Theory of hole magnetization Mc in zinc-blende diluted ferromagnetic
semiconductors is developed relaxing the spherical approximation of earlier
approaches. The theory is employed to determine Mc for (Ga,Mn)As over a wide
range of hole concentrations and a number of crystallographic orientations of
Mn magnetization. It is found that anisotropy of Mc is practically negligible
but the obtained magnitude of Mc is significantly greater than that determined
in the spherical approximation. Its sign and value compares favorably with the
results of available magnetization measurements and ferromagnetic resonance
studies.",0609128v1
2006/9/8,Magneto-optical characterization of MnxGe1-x alloys obtained by ion implantation,"Magneto-optical Kerr effect hysteresis loops at various wavelengths in the
visible/near-infrared range have been used to characterize the magnetic
properties of alloys obtained by implanting Mn ions at fixed energy in a Ge
matrix. The details of the hysteresis loops reveal the presence of multiple
magnetic contributions. They may be attributed to the inhomogeneous
distribution of the magnetic atoms and, in particular, to the known coexistence
of diluted Mn in the Ge matrix and metallic Mn-rich nanoparticles embedded in
it [Phys. Rev. B 73, 195207(2006)].",0609194v1
2006/9/8,Magnetically controlled current flow in coupled-dot arrays,"Quantum transport through an open periodic array of up to five dots is
investigated in the presence of a magnetic field. The device spectrum exhibits
clear features of the band structure of the corresponding one-dimensional
artificial crystal which evolves with varying field. A significant magnetically
controlled current flow is induced with changes up to many orders of magnitude
depending on temperature and material parameters. Our results put forward a
simple design for measuring with current technology the magnetic subband
formation of quasi one-dimensional Bloch electrons.",0609207v3
2006/9/12,RKKY interaction of magnetic moments in nanosized systems,"Nanosized spherical system of magnetic moments interacting indirectly via the
RKKY mechanism is studied. The interaction energy that determines the
temperature of the ferromagnetic ordering, depends strongly on the system size.
Obtained in the mean-field approximation, dimensional and concentration
dependencies of the Curie temperature testify to the necessity of taking into
account the finite size of such systems to calculate their features. Results
may concern both artificially constructed nanosystems and naturally arising
formations (such as clusters of magnetic ions in diluted magnetic
semiconductors, etc.).",0609266v2
2006/9/13,Spin density distribution in a partially magnetized organic quantum magnet,"Polarized neutron diffraction experiments on an organic magnetic material
reveal a highly skewed distribution of spin density within the magnetic
molecular unit. The very large magnitude of the observed effect is due to
quantum spin fluctuations. The data are in quantitative agreement with direct
diagonalization results for a model spin Hamiltonian, and provide insight on
the actual microscopic origin of the relevant exchange interactions.",0609299v2
2006/9/28,Derivation of effective parameters of magnetic metamaterials composed of passive resonant LC inclusions,"We determine rigorously the effective permeability of magnetic metamaterials
composed of passive particles exhibiting magnetic resonances. The effective
permeability is expressed in terms of circuit parameters characteristic to
these particles (L, C, and R) and particle geometry. The derivation takes into
account the magnetic coupling between particles. We show that a bigger
concentration of particles leads to an improvement in the metamaterial
performances (such as bandwidth or loss tangent), but this effect saturates as
the particles are packed more tightly. The theory is validated through
numerical simulations of physically realizable metamaterials.",0609745v1
2006/10/5,Magnetic excitations in the Kagome staircase compounds,"Inelastic neutron scattering measurements have been performed on single
crystal samples of Co3V2O8 and Ni3V2O8. The magnetic system in these compounds
is believed to be frustrated, as the magnetic ions Co2+ with S=3/2 and Ni2+
with S=1 adopt a buckled version of the Kagome lattice. Magnetic excitations
have been observed in both samples using a time-of-flight neutron spectrometer.
The excitation spectrum is dispersive for both samples and has a considerable
gap in the low temperature phases, while the intermediate temperature phases
are marked by a significant softening of the excitations energy.",0610143v1
2006/10/19,Gap-mediated magnetization of a pseudo-one-dimensional system with a spin-orbit interaction,"We argue that a pseudo-one-dimensional electron gas is magnetized when a
voltage bias is applied with the Fermi level tuned to be in the energy gap
generated by a spin-orbit interaction. The magnetization is an indication of
spin-carrying currents due to the spin-orbit interaction. The origin of the
magnetization, however, is essentially different from the ""spin accumulation""
in two-dimensional systems with spin-orbit interactions.",0610531v1
2006/11/27,Microscopic Calculation of Spin Torques and Forces,"Spin torques, that is, effects of conduction electrons on magnetization
dynamics, are calculated microscopically in the first order in spatial gradient
and time derivative of magnetization. Special attention is paid to the
so-called \beta-term and the Gilbert damping, \alpha, in the presence of
electrons' spin-relaxation processes, which are modeled by quenched magnetic
impurities. Two types of forces that the electric/spin current exerts on
magnetization are identified based on a general formula relating the force to
the torque.",0611669v1
2006/12/4,Analytical and Monte Carlo study of two antidots in magnetic nanodisks with vortex-like magnetization,"How stable vortex-like magnetization in magnetic nanodisks with small aspect
ratio ($L/R<<1$) is affected by two antidots is investigated analytically and
by Monte Carlo simulations. For suitable ranges of the physical parameters this
vortex presents bistable states when pinned around the antidots. The hysteresis
loop obtained shows a central loop associated to the pinning mechanism of the
vortex at the antidots. Our results agree qualitatively well with those
provided by experiments and micromagnetic simulations.",0612070v1
2006/12/5,Dynamics of Spontaneous Magnetization Reversal in Exchange Biased Heterostructures,"The dependence of thermally induced spontaneous magnetization reversal on
time-dependent cooling protocols was studied. Slower cooling and longer waiting
close to the N\`{e}el temperature of the antiferromagnet ($T_N$) enhances the
magnetization reversal. Cycling the temperature around $T_N$ leads to a thermal
training effect under which the reversal magnitude increases with each cycle.
These results suggest that spontaneous magnetization reversal is energetically
favored, contrary to our present understanding of positive exchange bias.",0612113v1
2007/1/18,Cooperative Effect of Electron Correlation and Spin-Orbit Coupling on the Electronic and Magnetic Properties of Ba2NaOsO6,"The electronic and magnetic properties of the cubic double perovskite
Ba2NaOsO6 were examined by performing first-principles density functional
theory calculations and analyzing spin-orbit coupled states of an Os7+ (d1) ion
at an octahedral crystal field. The insulating behavior of Ba2NaOsO6 was shown
to originate from a cooperative effect of electron correlation and spin-orbit
coupling. This cooperative effect is responsible not only for the absence of
orbital ordering in Ba2 NaOsO6 but also for a small magnetic moment and a weak
magnetic anisotropy in Ba2NaOsO6.",0701460v1
2007/1/20,Structure and Magnetism of the mono-layer hydrate Na0.3NiO2 0.7H2O,"The mono-layer hydrate (Ni-MLH) Na0.3NiO2 0.7H2O was synthesized with an
average Ni valence close to one in the bi-layer hydrate (Ni-BLH) Na0.3NiO2
1.3H2O. A weak unsaturated ferromagnetism and divergence of the magnetic
susceptibilities of field and zero-field cooled samples of both Ni-MLH and
Ni-BLH are observed. However, as a result of the increased 3-dimensional
electronic and magnetic character present in Ni-MLH a frequency dependence of
the AC magnetic susceptibility indicative of the spin glass-like behavior as
seen in Ni-BLH was no longer observed in Ni-MLH.",0701498v1
2007/3/9,Symmetry of Multiferroicity in a Frustrated Magnet TbMn$_2$O$_5$,"Based on measurements of soft x-ray magnetic scattering and symmetry
considerations, we demonstrate that the magnetoelectric effect in TbMn$_2$O$_5$
arises from an internal field determined by $\vec{S}_{\vec{q}} \times
{\vec{S}_{-\vec{q}}}$ with $\vec{S}_{\vec{q}}$ being the magnetization at
modulation vector $\vec{q}$, whereas the magneto-elastic effect in the exchange
energy governs the response to external electric fields. Our results set
fundamental symmetry constraints on the microscopic mechanism of
multiferroicity in frustrated magnets.",0703234v1
2007/3/15,rf SQUID metamaterials,"An rf superconducting quantum interference device (SQUID) array in an
alternating magnetic field is investigated with respect to its effective
magnetic permeability, within the effective medium approximation. This system
acts as an inherently nonlinear magnetic metamaterial, leading to negative
magnetic response, and thus negative permeability, above the resonance
frequency of the individual SQUIDs. Moreover, the permeability exhibits
oscillatory behavior at low field intensities, allowing its tuning by a slight
change of the intensity of the applied field.",0703400v1
2001/11/23,Shape transformations in rotating ferrofluid drops,"Floating drops of magnetic fluid can be brought into rotation by applying a
rotating magnetic field. We report theoretical and experimental results on the
transition from a spheroid equilibrium shape to non-axissymmetrical three-axes
ellipsoids at certain values of the external field strength. The transitions
are continuous for small values of the magnetic susceptibility and show
hysteresis for larger ones. In the non-axissymmetric shape the rotational
motion of the drop consists of a vortical flow inside the drop combined with a
slow rotation of the shape. Nonlinear magnetization laws are crucial to obtain
quantitative agreement between theory and experiment.",0111054v1
2000/3/31,"Hierarchic Theory of Condensed Matter: Long relaxation, macroscopic oscillations and the effects of magnetic field","1. Theoretical background for macroscopic oscillations in condensed matter;
2. The hypothesis of [entropy - mass - time] interrelation; 3. The entropy -
information content of matter as a hierarchic system; 4. Experimentally
revealed macroscopic oscillations; 5. Phenomena in water and aqueous systems,
induced by magnetic field: Coherent radio-frequency oscillations in water,
revealed by C. Smith; 6. Influence of weak magnetic field on the properties of
solid bodies; 7. Possible mechanism of perturbations of nonmagnetic materials
under magnetic treatment.",0003107v1
2000/4/28,"Fluctuation, Dissipation, and Entanglement: the Classical and Quantum Theory of Thermal Magnetic Noise","A general theory of thermal magnetic fluctuations near conductive materials
is developed; such fluctuations are the magnetic analog of Johnson noise. For
realistic experiments in quantum computing and magnetic resonance force
microscopy, the predicted relaxation can be rapid enough that substantial
experimental care should be taken to minimize it. The same Hamiltonian matrix
elements that govern fluctuation and dissipation are shown to also govern
entanglement and renormalization, and a specific example of a
fluctuation-dissipation-entanglement theorem is constructed.",0004106v2
2007/4/2,Comparison of exact-exchange calculations for solids in current-spin-density- and spin-density-functional theory,"The relative merits of current-spin-density- and spin-density-functional
theory are investigated for solids treated within the exact-exchange-only
approximation. Spin-orbit splittings and orbital magnetic moments are
determined at zero external magnetic field. We find that for magnetic (Fe, Co
and Ni) and non-magnetic (Si and Ge) solids, the exact-exchange
current-spin-density functional approach does not significantly improve the
accuracy of the corresponding spin-density functional results.",0704.0244v2
2007/4/22,Sm2Al: Another ferromagnet with spin-orbital compensation?,"We report the observation of a compensation point in the temperature
dependence of magnetization data of polycrystalline Sm2Al. Magnetization
measurements show that this compound magnetically orders at about 150 K. Below
this temperature, the magnetization data shows a compensation point, which
shifts with field. Hysteresis loops obtained below the compensation temperature
show that the compound possesses exchange anisotropy. Both the exchange
anisotropy field and the coercive field are found to be quite large and
comparable to those of the classical spin-orbit compensated ferromagnet
(Sm,Gd)Al2. The heat capacity data also suggest that there are similarities
between (Sm,Gd)Al2 and Sm2Al.",0704.2864v1
2007/5/4,Guiding superconducting vortices by magnetic domain walls,"We demonstrate a unique prospect for inducing anisotropic vortex pinning and
manipulating the directional motion of vortices using the stripe domain
patterns of a uniaxial magnetic film in a the superconducting/ferromagnetic
hybrid. Our observations can be described by a model, which considers
interactions between magnetic charges of vortices and surface magnetic charges
of domains resulting in the enhanced pinning of vortices on domain walls.",0705.0555v3
2007/5/22,"The Influence of Magnetic Domain Walls on Longitudinal and Transverse Magnetoresistance in Tensile Strained (Ga,Mn)As Epilayers","We present a theoretical analysis of recent experimental measurements of
magnetoresistance in (Ga,Mn)As epilayers with perpendicular magnetic
anisotropy. The model reproduces the field-antisymmetric anomalies observed in
the longitudinal magnetoresistance in the planar geometry (magnetic field in
the epilayer plane and parallel to the current density), as well as the unusual
shape of the accompanying transverse magnetoresistance. The magnetoresistance
characteristics are attributed to circulating currents created by the presence
of magnetic domain walls.",0705.3213v1
2007/5/29,Solution of the Dirac equation in presence of an uniform magnetic field,"In this work we discuss the properties of the solutions of the Dirac equation
in presence of an uniform background magnetic field. In particular we focus on
the nature of the solutions, their ortho-normality properties and how these
solutions depend on the choice of the vector potential giving rise to the
magnetic field. We explicitly calculate the spin-sum of the solutions and using
it we calculate the propagator of the electron in presence of an uniform
background magnetic field.",0705.4275v2
2007/5/30,Thermodynamics of carrier-mediated magnetism in semiconductors,"We propose a model of carrier-mediated ferromagnetism in semiconductors that
accounts for the temperature dependence of the carriers. The model permits
analysis of the thermodynamic stability of competing magnetic states, opening
the door to the construction of magnetic phase diagrams. As an example we
analyze the stability of a possible reentrant ferromagnetic semiconductor, in
which increasing temperature leads to an increased carrier density, such that
the enhanced exchange coupling between magnetic impurities results in the onset
of ferromagnetism as temperature is raised.",0705.4464v1
2007/6/4,Exchange bias with Fe substitution in LaMnO_3,"The exchange bias (EB) in LaMn_{0.7}Fe_{0.3}O_3 is observed by the negative
shift and training effect of the hysteresis loops, while the sample was cooled
in external magnetic field. The analysis of cooling field dependence of EB
gives the size of the ferromagnetic (FM) cluster ~ 25 Angstrom, where the
magnetic anisotropy of FM cluster is found two order of magnitude higher than
the FM bulk manganites. We propose that the nanoscale FM clusters are embedded
in the glassy magnetic host with EB at the FM/glassy magnetic interface.",0706.0376v1
2007/7/27,"Photo-induced precession of magnetization in ferromagnetic (Ga,Mn)As","Precession of magnetization induced by pulsed optical excitation is observed
in a ferromagnetic semiconductor (Ga,Mn)As by time-resolved magneto-optical
measurements. It appears as complicated oscillations of polarization plane of
linearly-polarized probe pulses, but is reproduced by gyromagnetic theory
incorporating an impulsive change in an effective magnetic field due to changes
in magnetic anisotropy. It is inferred from the shape of the impulse that the
changes in anisotropy result from non-equilibrium carrier population: cooling
of hot photo-carriers and subsequent annihilation of photo-carriers.",0707.4055v2
2007/8/20,Eigen electric moments of magnetic-dipolar modes in quasi-2D ferrite disk particles,"A property associated with a vortex structure becomes evident from an
analysis of confinement phenomena of magnetic oscillations in a quasi-2D
ferrite disk with a dominating role of magnetic-dipolar
(non-exchange-interaction) spectra. The vortices are guaranteed by the chiral
edge states of magnetic-dipolar modes which result in appearance of eigen
electric moments oriented normally to the disk plane. Due to the
eigen-electric-moment properties, a ferrite disk placed in a microwave cavity
is strongly affected by the cavity RF electric field with a clear evidence for
multi-resonance oscillations. For different cavity parameters, one may observe
the ""resonance absorption"" and ""resonance repulsion"" behaviors.",0708.2678v1
2007/9/21,On the magnetically driven ferroelectric phase in GdMnO3,"At room temperature, GdMnO3 is a paraelectric and paramagnetic with a
distorted perovskite structure of orthorhombic symmetry (space group Pnma). On
cooling, it undergoes a phase transition sequence to a magnetic incommensurate
phase (k=delta a*; Tc1=42K) and a A-type antiferromagnetic phase (Tc2=27K). At
low temperatures (T<12K), a magnetic field applied along the a-axis
destabilizes the antiferromagnetic phase and induces a first order transition
to a magnetic commensurate modulated phase (delta=1/4) that is also
ferroelectric (P//c). This work analyses this field induced phase transition
from the point of view of the symmetry and Landau theory.",0709.3369v1
2007/9/24,Magnetoresistance in an all-manganite heterostructure,"We study the magnetic and transport properties of all-manganite
heterostructures consisting of ferromagnetic metallic electrodes separated by
an antiferromagnetic barrier. We find that the magnetic ordering in the barrier
is influenced by the relative orientation of the electrodes magnetization
producing a large difference in resistance between the parallel and
antiparallel orientations of the ferromagnetic layers. The external application
of a magnetic field in a parallel configuration also leads to large
magnetoresistance.",0709.3720v1
2007/10/30,Discovery of Griffiths phase in itinerant magnetic semiconductor Fe_{1-x}Co_xS_2,"Critical points that can be suppressed to zero temperature are interesting
because quantum fluctuations have been shown to dramatically alter electron gas
properties. Here, the metal formed by Co doping the paramagnetic insulator
FeS$_2$, Fe$_{1-x}$Co$_x$S$_2$, is demonstrated to order ferromagnetically at
$x>x_c=0.01\pm0.005$ where we observe unusual transport, magnetic, and
thermodynamic properties. We show that this magnetic semiconductor undergoes a
percolative magnetic transition with distinct similarities to the Griffiths
phase, including singular behavior at $x_c$ and zero temperature.",0710.5760v1
2007/11/10,Structural and magnetic properties in the ruthenate Bi2.67Pr0.33Ru3O11,"An unreported praseodymium substituted phase of the Bi-Ru-O system with
formula Bi2.67Pr0.33Ru3O11was prepared. Its crystal structure and magnetic
properties were investigated. Pr substituted occurs only on one of the two Bi
sites. The magnetism of the compound is essentially dominated by a Pr3+
contribution. A non linear variation of the reciprocal magnetic susceptibility
is observed that appears to account for crystal electric field interactions on
the Pr3+ ions.",0711.1577v1
2007/11/15,Self-organization and magnetic domain microstructure of Fe nanowire arrays,"Starting from essentially flat nanometer-thick Fe films, epitaxially grown at
room temperature on W(110) surfaces, we used carefully tuned annealing
schedules to produce periodic arrays of nanoscale ferromagnetic wires. The
structural transition from continuous films to nanowire arrays is accompanied
with an in-plane 90 degree rotation of the spontaneous magnetization. Using
spin-polarized low-energy electron microscopy to map the local magnetization
directions while annealing, we studied the role of the dewetting mechanism on
the self-organization and magnetization reorientation processes.",0711.2487v1
2007/12/10,The influence of structural short-range order on the phase diagrams of diluted FCC magnet with arbitrary spin and modified RKKY interaction,"A diluted FCC magnet with modified long-range RKKY interaction and arbitrary
Ising spin S is considered within two-sublattice model. In the molecular field
approximation the Gibbs free-energy is derived, from which all magnetic
thermodynamic properties can be self-consistently obtained. In particular, the
phase diagrams are studied for different magnetic ion and free-charge
concentration, the atomic short-range-order (Warren-Cowley) parameter being
taken into account.",0712.1561v1
2007/12/12,Magnetic phase transition and magnetocaloric effect in PrCo9Si4 and NdCo9Si4,"The compounds, PrCo9Si4 and NdCo9Si4, have been recently reported to exhibit
first-order ferromagnetic transitions near 24 K. We have subjected this
compound for further characterization by magnetization, heat-capacity and
electrical resistivity measurements at low temperatures in the presence of
magnetic fields, particularly to probe magnetocaloric effect and
magnetoresistance. The compounds are found to exhibit rather modest
magnetocaloric effect at low temperatures peaking at Curie temperature,
tracking the behavior of magnetoresistance. The magnetic transition does not
appear to be first order in its character.",0712.1989v1
2008/1/11,Thermal Dynamics in Symmetric Magnetic Nanopillars Driven by Spin Transfer,"We study the effects of spin transfer on thermally activated dynamics of
magnetic nanopillars with identical thicknesses of the magnetic layers. The
symmetric nanopillars exhibit anomalous dependencies of switching statistics on
magnetic field and current. We interpret our data in terms of simultaneous
current-induced excitation of both layers. We also find evidence for coupling
between the fluctuations of the layers due to the spin transfer.",0801.1807v1
2008/1/25,"Optimization of parameters of nanostructure for study inverse proximity effects on ""superconductor-ferromagnetic"" interface using Polarized Neutron Reflectometry in enhanced standing wave regime","This work is devoted to experimental study of influence of superconductivity
(S) on ferromagnetism (FM) (inverse proximity effects) with the help of
Polarized Neutron Reflectivity. Combining meausurements of specular and diffuse
intensities it is possible to obtain full picture of magnetization change in
S/FM layered systems like magnetization rotation, domain state formation,
inducing of magnetization in S layer, etc. To increase weak magnetic signal we
propose to use enhanced neutron standing wave regime (e.g. waveguides). Choose
of materials, optimization of thicknesses of layers, estimation of roughnesses
influence is presented in this work.",0801.3967v1
2008/2/5,Order Parameters and Phase Diagram of Multiferroic RMn$_2$O$_5$,"The generic magnetic phase diagram of multiferroic RMn$_2$O$_5$ (with R=Y,
Ho, Tb, Er, Tm), which allows different sequences of ordered magnetic
structures for different R's and different control parameters, is described
using order parameters which explicitly incorporate the magnetic symmetry. A
phenomenological magneto-electric coupling is used to explain why some of these
magnetic phases are also ferroelectric. Several new experiments, which can test
this theory, are proposed.",0802.0604v2
2008/3/27,Current-induced persistent magnetization in a relaxorlike manganite,"A single crystal of 7% Fe-doped
(La$_{0.7}$Pr$_{0.3}$)$_{0.65}$Ca$_{0.35}$MnO$_3$ shows up as a typical relaxor
ferromagnet, where ferromagnetic metallic and charge-orbital-ordered insulating
clusters coexist with controllable volume fraction by external stimuli. There,
the persistent ferromagnetic metallic state can be produced by an
electric-current excitation as the filamentary region, the magnetization in
which is increased by ~0.4$\mu_{\rm B}$ per Mn. A clear distinction from the
current heating effect in a magnetic field, which conversely leads to a
decrease in ferromagnetic fraction, enables us to bi-directionally switch both
the magnetization and resistance by applying the voltages with different
magnitudes.",0803.3922v1
2008/4/21,Studies of Effects of Current on Exchange-Bias: A Brief Review,"MacDonald and co-workers recently predicted that high current densities could
affect the magnetic order of antiferromagnetic (AFM) multilayers, in ways
similar to those that occur in ferromagnetic (F) multilayers, and that changes
in AFM magnetic order can produce an antiferromagnetic Giant Magnetoresistance
(AGMR). Four groups have now studied current-driven effects on exchange bias at
F/AFM interfaces. In this paper, we first briefly review the main predictions
by MacDonald and co-workers, and then the results of experiments on exchange
bias that these predictions stimulated.",0804.3358v1
2008/4/29,Muon spin relaxation study of LaTiO3 and YTiO3,"We report muon spin relaxation measurements on two Ti3+ containing
perovskites, LaTiO3 and YTiO3, which display long range magnetic order at low
temperature. For both materials, oscillations in the time-dependence of the
muon polarization are observed which are consistent with three-dimensional
magnetic order. From our data we identify two magnetically inequivalent muon
stopping sites. The muon spin relaxation results are compared with the magnetic
structures of these compounds previously derived from neutron diffraction and
muon spin relaxation studies on structurally similar compounds.",0804.4591v1
2008/7/15,Magnetic properties of the insulating ferromagnetic phase in strained Pr_0.6Ca_0.4MnO_3 thin films,"Bulk magnetization in Pr_{0.6}Ca_{0.4}MnO_3 thin films with tensile (SrTiO_3)
and compressive (LaAlO_3) substrate-induced strain is compared to the
magnetooptical Kerr effect (MOKE) measurements. In the absence of an external
magnetic field, in both films, a stable ferromagnetic insulating majority phase
coexists with an antiferromagnetic insulating phase below ~120K. MOKE
measurements indicate that at 5K a metastable ferromagnetic metallic (FM) phase
is formed at the surface of the stretched film in a magnetic field below 1.1T
already, while in the bulk the FM phase starts to form in the field above ~4T
in both films.",0807.2312v1
2008/7/28,Static and dynamic properties of vortices in anisotropic magnetic disks,"We investigate the effect of the magnetic anisotropy ($K_z$) on the static
and dynamic properties of magnetic vortices in small disks. Our micromagnetic
calculations reveal that for a range of $K_z$ there is an enlargement of the
vortex core. We analyze the influence of $K_z$ on the dynamics of the vortex
core magnetization reversal under the excitation of a pulsed field. The
presence of $K_z$, which leads to better resolved vortex structures, allows us
to discuss in more details the role played by the in-plane and perpendicular
components of the gyrotropic field during the vortex-antivortex nucleation and
annihilation.",0807.4546v1
2008/8/26,Dynamical pinning of domain wall in magnetic nanowire induced by Walker breakdown,"Transmission probability of a domain wall through a magnetic nanowire is
investigated as a function of the external magnetic field. Very intriguing
phenomenon is found that the transmission probability shows a significant drop
after exceeding the threshold driving field, which contradicts our intuition
that a domain wall is more mobile in the higher magnetic field. The
micromagnetics simulation reveals that the domain wall motion in the wire with
finite roughness causes the dynamical pinning due to the Walker breakdown,
which semi-quantitatively explains our experimental results.",0808.3446v1
2008/8/27,"Coherent control of magnetization precession in ferromagnetic semiconductor (Ga,Mn)As","We report single-color, time resolved magneto-optical measurements in
ferromagnetic semiconductor (Ga,Mn)As. We demonstrate coherent optical control
of the magnetization precession by applying two successive ultrashort laser
pulses. The magnetic field and temperature dependent experiments reveal the
collective Mn-moment nature of the oscillatory part of the time-dependent Kerr
rotation, as well as contributions to the magneto-optical signal that are not
connected with the magnetization dynamics.",0808.3738v2
2008/9/3,Detection of coherent magnons via ultrafast pump-probe reflectance spectroscopy in multiferroic Ba0.6Sr1.4Zn2Fe12O22,"We report the detection of a magnetic resonance mode in multiferroic
Ba0.6Sr1.4Zn2Fe12O22 using time domain pump-probe reflectance spectroscopy.
Magnetic sublattice precession is coherently excited via picosecond thermal
modification of the exchange energy. Importantly, this precession is recorded
as a change in reflectance caused by the dynamic magnetoelectric effect. Thus,
transient reflectance provides a sensitive probe of magnetization dynamics in
materials with strong magnetoelectric coupling, such as multiferroics,
revealing new possibilities for application in spintronics and ultrafast
manipulation of magnetic moments.",0809.0672v1
2008/10/23,Composition dependence of magnetocaloric effect in Sm1-xSrxMnO3 (x = 0.3-0.5),"We investigated magnetic and magnetocaloric properties in Sm1-xSrxMnO3 (x =
0.30-0.5). We report a magnetic field driven first-order metamagnetic
transition in the paramagnetic state in x = 0.4 and 0.5 and a second-order
transition in x = 0.3. The highest magnetic entropy (-Sm = 6.2 J/kgK for H = 5
T at T = 125 K) that occurs in x = 0.4 is associated with the metamagnetic
transition resulting from the field-induced growth and coalescence of
ferromagnetic nano clusters preexisting in the paramagnetic state. Our results
suggest that manganites with intrinsic nanoscale phase separation can be
exploited for magnetic refrigeration.",0810.4212v1
2008/10/27,Macroscopic signature of protected spins in a dense frustrated magnet,"The inability of systems of interacting objects to satisfy all constraints
simultaneously leads to frustration. A particularly important consequence of
frustration is the ability to access certain protected parts of a system
without disturbing the others. For magnets such ""protectorates"" have been
inferred from theory and from neutron scattering, but their practical
consequences have been unclear. We show that a magnetic analogue of optical
hole-burning can address these protected spin clusters in a well-known,
geometrically frustrated Heisenberg system, gadolinium gallium garnet. Our
measurements additionally provide a resolution of a famous discrepancy between
the bulk magnetometry and neutron diffraction results for this magnetic
compound.",0810.4744v1
2008/11/13,Magnetoelastic coupling in BaTiO3-based multiferroic structures,"Analytical expressions for the magnetoelastic anisotropy constants of cubic
magnetic systems are derived for rectangular and oblique distortions
originating from epitaxial growth on substrates with lower crystal symmetry. In
particular, the temperature variation of the magnetic properties of magnetic
films grown on barium titanate (BaTiO3) substrates are explained in terms of
strain-induced magnetic anisotropies caused by the temperature dependent phase
transitions of BaTiO3. Our results quantify the experimental observations in
ferromagnet/\bto-based structures, which have been proposed as templates for
magnetoelectric composite heterostructures.",0811.2146v1
2008/11/27,Anomaly in Nonlinear Magnetoelectric Response of YbMnO3,"We observe a seemingly complex magnetic field dependence of dielectric
constant of hexagonal YbMnO3 near the spin ordering temperature. After
rescaling, the data taken at different temperatures and magnetic fields
collapse on a single curve describing the sharp anomaly in nonlinear
magnetoelectric response at the magnetic transition. We show that this anomaly
is a result of the competition between two magnetic phases. The scaling and the
shape of the anomaly are explained using the phenomenological Landau
description of the competing phases in hexagonal manganites.",0811.4547v1
2008/12/3,Relationship between the magnetic hyperfine field and the magnetic moment,"Based on experimental data it is shown, for some chosen alloys and compounds
of iron, that there is no one unique relationship between the 57Fe-site
magnetic hyperfine field, Bhf, and the magnetic moment per Fe atom, m. Instead,
the Bhf-m plot consists of several branches, each of them being characteristic
of a given alloy or compound. Consequently, the effective proportionality
constant (hyperfine coupling constant) depends on the alloy system or compound,
and for a given alloy system or compound it depends on the composition or even
on the lattice site. Consequently, the scaling of Bhf into the underlying m
cannot be done a priopri.",0812.0671v1
2008/12/10,Effect of oxygen concentration on the structural and magnetic properties of LaRh1/2Mn1/2O3 thin films,"Epitaxial LaRh1/2Mn1/2O3 thin films have been grown on (001)-oriented LaAlO3
and SrTiO3 substrates using pulsed laser deposition. The optimized thin film
samples are semiconducting and ferromagnetic with a Curie temperature close to
100 K, a coercive field of 1200 Oe, and a saturation magnetization of 1.7muB
per formula unit. The surface texture, structural, electrical, and magnetic
properties of the LaRh1/2Mn1/2O3 films was examined as a function of the oxygen
concentration during deposition. While an elevated oxygen concentration yields
thin films with optimal magnetic properties, slightly lower oxygen
concentrations result in films with improved texture and crystallinity.",0812.1852v1
2008/12/13,A Novel Temperature-Induced Magnetization Transition in Pt/Co/Pt Sandwiches,"It is found in the Pt/Co/Pt(111) sandwiches that perpendicular magnetic
anisotropy weakens associated with the dramatic magnetization enhancement as
the temperature decreases below a critical temperature, T_cri, which increases
with the Pt overlayer thickness t_Pt. For the sandwich with enough thick Pt
overlayer, it trends to an unusual state with weak perpendicular magnetic
anisotropy in the absence of obvious easy direction behavior at low
temperature. It suggests that Pt is more significantly polarized in the film
with thicker Pt overlayer. The results reveal the strong influence of both
thick nonmagnetic coverage and temperature on the electronic structure of the
Pt/Co/Pt(111) sandwich.",0812.2512v1
2008/12/17,Jahn-Teller like origin of the tetragonal distortion in disordered Fe-Pd magnetic shape memory alloys,"The electronic structure and magnetic properties of disordered
Fe$_{x}$Pd$_{100-x}$ alloys $(50 < x < 85)$ are investigated in the framework
of density functional theory using the full potential local orbital method
(FPLO). Disorder is treated in the coherent potential approximation (CPA). Our
calculations explain the experimental magnetization data. The origin of the
tetragonal distortion in the Fe-Pd magnetic shape memory alloys is found to be
a Jahn-Teller like effect which allows the system to reduce its band energy in
a narrow composition range. Prospects for an optimization of the alloys'
properties by adding third elements are discussed.",0812.3332v1
2009/1/14,Interface coupling properties and reflection of bulk spin waves from biaxial multilayer ferromagnetic media,"The reflection coefficient of bulk spin waves from multilayer ferromagnetic
structure with periodically modulated parameters of exchange interaction,
uniaxial and rhombic magnetic anisotropy and saturation magnetization is
calculated with a non-ideal coupling between layers. The strong dependence of
spin-wave reflection coefficient on frequency, magnetic field and parameter of
interfacial coupling is revealed. It allows changing the reflection intensity
from 0 to 1 by changing either only external magnetic field value or frequency.
The proposed model of boundary conditions gives the opportunity to take into
account the quality of interfaces when studying the reflection processes of
spin waves in multilayer structures.",0901.2012v1
2009/1/15,Vortex stabilization in magnetic trilayer dots,"The magnetization reversal and spin structure in circular
Co/insulator/Ni80Fe20 trilayer dots has been investigated numerically. The
effect of dipolar coupling between a soft ferromagnetic Permalloy (Py=Ni80Fe20)
layer and a hard ferromagnetic Cobalt layer inside one stack is studied. We
find either a stabilization or even a triggering of the vortex state in the Py
layer due to the magnetic stray field of the Co layer, while the Co
magnetization remains in a single-domain state. Furthermore, for thin Py layers
a 360 deg-domain wall is observed. We construct a phase diagram, where regions
of vortex stabilization, triggering, and occurrence of a 360 deg domain wall
are marked.",0901.2209v1
2009/2/3,Dependence of critical current of spin transfer torque-driven magnetization dynamics on free layer thickness,"The dependence of the critical current of spin transfer torque-driven
magnetization dynamics on the free-layer thickness was studied by taking into
account both the finite penetration depth of the transverse spin current and
spin pumping. We showed that the critical current remains finite in the
zero-thickness limit of the free layer for both parallel and anti-parallel
alignments. We also showed that the remaining value of the critical current of
parallel to anti-parallel switching is larger than that of anti-parallel to
parallel switching.",0902.0420v1
2009/2/16,Magnetic-Field-Dependent Raman Scattering in Multiferroic Bilayer Films: Evidence for Stress-Mediated Magnetoelectric Coupling,"We report the first magnetic-field-dependent Raman scattering studies on
Pb(Zr,Ti)O3-CoFe2O4 bilayer multiferroic system. The phonon frequencies of the
nano-bilayers obviously change with magnetic field, which is absent in the
single Pb(Zr,Ti)O3 films. The magnetostriction of the CoFe2O4 layer generates
stress mechanically transferred to the Pb(Zr,Ti)O3 layer, resulting in the mode
changes. The observed magnetic-field-induced softening of the soft mode in the
Pb(Zr,Ti)O3 layer bears a striking resemblance to direct magnetoelectric output
in the bilayers, providing evidence for stress-mediated magnetoelectric
coupling mechanism in the multiferroic bi-layers.",0902.2592v1
2009/2/19,Spin-orbit induced non-collinear spin structure in deposited transition metal clusters,"The influence of the spin-orbit coupling on the magnetic structure of
deposited transition metal nanostructure systems has been studied by fully
relativistic electronic structure calculations. The interplay of exchange
coupling and magnetic anisotropy was monitored by studying the corresponding
magnetic torque calculated within ab-initio and model approaches. It is found
that a spin-orbit induced Dzyaloshinski-Moriya interaction can stabilise a
non-collinear spin structure even if there is a pronounced isotropic
ferromagnetic exchange interaction between the magnetic atoms.",0902.3336v1
2009/2/22,Fermi-surface pockets in magnetic underdoped cuprates from first principles,"Using an innovative first-principles band theory enabling the exploration of
Mott-insulating magnetic cuprates, we study the Fermi surface of underdoped
Y$_{1-x}$Ca$_x$Ba$_2$Cu$_3$O$_6$ in a selection of magnetically ordered and
polaronic states. All phases exhibit qualitatively similar, hole-like
nodal-point small pockets. Their properties (area, masses, mass sign) only
partially match those extracted from recent quantum-oscillation experiments. Ab
initio calculations, therefore, do not straightforwardly support a magnetic
origin of quantum oscillations.",0902.3809v1
2009/3/27,Creation of Dirac monopoles in spinor Bose-Einstein condensates,"We demonstrate theoretically that using standard external magnetic fields,
one can imprint point-like topological defects to the spin texture of a dilute
Bose-Einstein condensate. Symmetries of the condensate order parameter render
this topological defect to be accompanied with a vortex filament corresponding
to the Dirac string of a magnetic monopole. The vorticity in the condensate
coincides with the magnetic field of a magnetic monopole, providing an ideal
analogue to the monopole studied by Dirac.",0903.4732v1
2009/4/3,Indication of a non-magnetic surface layer on a magnetic single crystal,"The structural and electronic properties of the surfaces of Sm(0001) and
Eu/Gd(0001) were studied by scanning tunneling microscopy and spectroscopy at
temperatures between 10 and 110 K. In both systems, an unoccupied surface state
is observed that exhibits a temperature-dependent splitting into two states for
Eu/Gd(0001), while it is unsplit on Sm(0001). This strongly indicates that the
divalent outermost surface layer of Sm(0001) is non-magnetic despite the
antiferromagnetic trivalent Sm substrate. These findings open new opportunities
for magnetic studies of ultra-thin Sm films.",0904.0653v1
2009/5/12,Magnetic vortex as a ground state for sub-micron antiferromagnetic particles,"For submicron particles shaped as any axisymmetric body and made with
standard canted antiferromagnet like hematite or iron borate, the ground state
may comprise of a magnetic vortex with topologically non-trivial distribution
of the sublattice magnetization $\vec{l}$ and planar coreless vortex-like
structure for the net magnetization $\vec{M}$. For antiferromagnetic particles
in the vortex state, in addition to low-frequency modes, there are high
frequency modes with frequencies over the range of hundreds gigahertz,
including a mode localized in the region of the radius 30-40 nm near a vortex
core.",0905.1966v2
2009/5/13,Magnetic and transport properties of n-type Fe-doped In2O3 ferromagnetic thin films,"Room temperature ferromagnetism was observed in n-type Fe-doped In2O3 thin
films deposited on c-cut sapphire substrates by pulsed laser deposition.
Structure, magnetism, composition, and transport studies indicated that Fe
occupied the In sites of the In2O3 lattice rather than formed any metallic Fe
or other magnetic impurity phases. Magnetic moments of films were proved to be
intrinsic and showed to have a strong dependence on the carrier densities which
depended on the Fe concentration and its valance state as well as oxygen
pressure.",0905.2083v1
2009/5/22,Correlation effects in p-electron magnets: the case of RbO_2,"We present results of GGA+U calculations for the ""d^0 magnet"" RbO_2, where
magnetic properties are due to partially filled oxygen p orbitals. We show that
on-site interactions on the oxygen sites lead to a strong tendency towards the
formation of an orbitally polarized insulating state, in contrast to the
half-metallic behavior predicted for this class of compounds within pure
LDA/GGA. The obtained energy differences between different orbitally ordered
configurations are sizeable, indicating an orbital ordering temperature higher
than the antiferromagnetic Neel temperature of ~15 K. Our results demonstrate
the importance of correlation effects in p electron magnets such as RbO_2.",0905.3721v1
2009/5/24,Magnetic impurities in the two-band $s_\pm$-wave superconductors,"We investigate the effects of magnetic impurities in a superconducting state
with $s_\pm$ pairing symmetry. Within a two-band model, we find that the
intra-band magnetic scattering serves as a pair breaker while the inter-band
magnetic scattering preserves pairing and hardly affects transition temperature
in the Born limit. We also show that the same physics can persist beyond the
weak scattering region. Our results coincide with recent experimental
measurements in iron-based superconductors and thus provides an indirect
evidence of the possible $s_\pm$ pairing symmetry in these materials.",0905.3883v2
2009/5/25,Rare earth magnetism and ferroelectricity in RMnO3,"Magnetic rare earths R have been proven to have a significant effect on the
multiferroic properties of the orthorhombic manganites RMnO3. A re-examination
of previous results from synchrotron based x-ray scattering experiments
suggests that symmetric exchange striction between neighboring R and Mn ions
may account for the enhancement of the ferroelectric polarization in DyMnO3 as
well as the magnetic-field induced ferroelectricity in GdMnO3. In general,
adding a second magnetic species to a multiferroic material may be a route to
enhance its ferroelectric properties.",0905.4019v1
2009/6/2,Effect of annealing on the magnetic and superconducting properties of single-crystalline UCoGe,"Single-crystals of the new ferromagnetic superconductor UCoGe have been
grown. The quality of as-grown samples can be significantly improved by a
heat-treatment procedure, which increases the residual resistance ratio (RRR)
from ~5 to ~30. Magnetization and resistivity measurements show the annealed
samples have a sharp ferromagnetic transition with a Curie temperature T_C is
2.8 K. The ordered moment of 0.06 mu_B is directed along the orthorhombic
c-axis. Superconductivity is found below a resistive transition temperature T_s
= 0.65 K.",0906.0497v1
2009/7/10,"""Topological"" Hall effect in the ferromagnetic microparticles with noncoplanar magnetization distribution","The phenomenological theory for ""topological"" Hall effect (THE) is proposed.
The theory can be used for qualitative analysis of THE in the medium with
arbitrary magnetization distribution. In the paper the cylindrical particle
with ""vortex"" magnetization is considered. The hysteresis loop of THE is
qualitatively different comparing to abnormal Hall effect. The estimation of
THE magnitude in the ""vortex"" particle is made. For Co particle with 100 nm
diameter the THE exceeds normal and abnormal Hall effects until an external
magnetic field less than 200 Oe.",0907.1808v1
2009/7/11,Resonant Magnetic X-ray Diffraction Study on the Triangular Lattice Antiferromagnet GdPd2Al3,"Resonant magnetic x-ray diffraction experiments were carried out on the
stacked triangular lattice antiferromagnet GdPd2Al3. The experiments revealed
an expected initial collinear c-axis order at TN1 followed by an additional
in-plane order at TN2, while at the same time we found that the ground state is
a helically ordered state of a very long incommensurate period of approximately
700A. The distribution of K-domains was highly anisotropic, and the domain with
the modulation vector normal to the surface of the crystal was ascendant.
Low-field magnetization is discussed on the basis of the observed
incommensurate magnetic structure.",0907.1941v1
2009/8/2,Nonlinear response of a thin metamaterial film containing Josephson junctions,"An interaction of electromagnetic field with metamaterial thin film
containing split-ring resonators with Josephson junctions is considered. It is
shown that dynamical self-inductance in a split rings results in reduction of
magnetic flux through a ring and this reduction is proportional to a time
derivative of split ring magnetization. Evolution of thin film magnetization
taking into account dynamical self-inductance is studied. New mechanism for
excitation of waves in one dimensional array of split-ring resonators with
Josephson junctions is proposed. Nonlinear magnetic susceptibility of such thin
films is obtained in the weak amplitude approximation.",0908.0103v1
2009/8/21,Nonzero macroscopic magnetization in half-metallic antiferromagnets at finite temperatures,"Combining density-functional theory calculations with many-body
Green's-function technique, we reveal that the macroscopic magnetization in
half-metallic antiferromagnets does not vanish at finite temperature as for the
T=0 limit. This anomalous behavior stems from the inequivalent magnetic
sublattices which lead to different intrasublattice exchange interactions. As a
consequence, the spin fluctuations suppress the magnetic order of the
sublattices in a different way leading to a ferrimagnetic state at finite
temperatures. Computational results are presented for the half-metallic
antiferromagnetic CrMnZ (Z=P,As,Sb) semi-Heusler compounds.",0908.3044v1
2009/9/7,Anomalous magnetotransport and cyclotron resonance of high mobility magnetic 2DHGs in the quantum Hall regime,"Low temperature magnetotransport measurements and far infrared transmission
spectroscopy are reported in molecular beam epitaxial grown two-dimensional
hole systems confined in strained InAs quantum wells with magnetic impurities
in the channel. The interactions of the free holes spin with the magnetic
moment of 5/2 provided by manganese features intriguing localization phenomena
and anomalies in the Hall and the quantum Hall resistance. In magnetic field
dependent far infrared spectroscopy measurements well pronounced cyclotron
resonance and an additional resonance are found that indicates an anticrossing
with the cyclotron resonance.",0909.1124v1
2009/9/7,Direct measurements of the penetration depth in a superconducting film using magnetic force microscopy,"We report the local measurements of the magnetic penetration depth $\lambda$
in a superconducting Nb film using magnetic force microscopy (MFM). We
developed a method for quantitative extraction of the penetration depth from
single-parameter simultaneous fits to the lateral and height profiles of the
MFM signal, and demonstrate that the obtained value is in excellent agreement
with that obtained from the bulk magnetization measurements.",0909.1360v1
2009/9/9,Flexomagnetic effect in Mn-based antiperovskites,"We report appearance of the net magnetization in Mn-based antiperovskite
compounds as a result of the external strain gradient (flexomagnetic effect).
In particular, we describe the mechanism of the magnetization induction in the
Mn_{3}GaN at the atomic level in terms of the behavior of the local magnetic
moments (LMM) of the Mn atoms. We show that the flexomagnetic effect is linear
and results from the non-uniformity of the strain, i.e. it is absent not only
in the ground state but also when the applied external strain is uniform. We
estimate the flexomagnetic coefficient to be 1.95 mu_{B}*angstrom. We show that
at the moderate values of the strain gradient (~ 0.1%) the flexomagnetic
contribution is the only non-vanishing input to the induced magnetization.",0909.1813v1
2009/9/24,Induced magnetic moment in graphene with a nonmagnetic impurity,"We consider a two-dimensional crystalline monolayer of carbon atoms with a
single non-magnetic impurity. Using the Weyl Hamiltonian to describe electronic
energy spectrum near the Dirac points, we calculate the wave function and
energy of impurity states, as well as the induced magnetic moment associated
with polarization of the electron system. We present a phase diagram of the
localized magnetic state as a function of the chemical potential $\mu $ and
coupling constant $g_c$.",0909.4405v1
2009/9/24,Discovery of localized states of Fe 3d electrons in Fe16N2 and Fe8N films: an evidence of the existence of giant saturation magnetization,"The mystery of giant saturation magnetization of Fe16N2 has remained for 37
years. In this letter, X-ray absorption spectroscopy (XAS) and magnetic
circular dichroism (XMCD) are used to study the electron states of Fe atoms in
Fe16N2 and Fe8N films. Localized Fe 3d electron states, which are not expected
from current theories (models), are observed. The XMCD spectra and elemental
hysteresis loops reveal the polarization of N atoms and the hybridization of N
and Fe atoms. This discovery points to the origin of giant saturation
magnetization in Fe16N2.",0909.4478v1
2009/10/22,Spin density wave dislocation in chromium probed by coherent x-ray diffraction,"We report on the study of a magnetic dislocation in pure chromium. Coherent
x-ray diffraction profiles obtained on the incommensurate Spin Density Wave
(SDW) reflection are consistent with the presence of a dislocation of the
magnetic order, embedded at a few micrometers from the surface of the sample.
Beyond the specific case of magnetic dislocations in chromium, this work may
open up a new method for the study of magnetic defects embedded in the bulk.",0910.4252v1
2009/11/19,Magnetically hindered chain formation in transition-metal break junctions,"Based on first-principles calculations, we demonstrate that magnetism impedes
the formation of long chains in break junctions. We find a distinct softening
of the binding energy of atomic chains due to the creation of magnetic moments
that crucially reduces the probability of successful chain formation. Thereby,
we are able to explain the long standing puzzle why most of the
transition-metals do not assemble as long chains in break junctions and provide
thus an indirect evidence that in general suspended atomic chains in
transition-metal break junctions are magnetic.",0911.3768v1
2009/11/30,The Spontaneous Generation of Magnetic Moment of Beryllium Dimer on Graphene,"Graphene has various potential applications in electronics and scientists are
seeking to introduce magnetic properties on graphene. Here we report our
theoretical findings that a local magnetic moment as large as 1 $\mu_B$ can be
generated from the adsorption of the diamagnetic beryllium dimer on perfect
diamagnetic graphene. Unexpectedly the adsorption system is remarkably stable
as evidenced by the binding energy of 1.04 eV, indicating that the formation of
beryllium dimer is energetically much favorable. Analyses reveal that the
magnetic moment and stability is originated from the spontaneous transfer of
one electron from the anti-bonding orbital of the dimer to graphene.",0911.5562v1
2009/12/1,Vertically Graded Anisotropy in Co/Pd Multilayers,"Depth-grading of magnetic anisotropy in perpendicular magnetic media has been
predicted to reduce the field required to write data without sacrificing
thermal stability. To study this prediction, we have produced Co/Pd multilayers
with depth-dependent Co layer thickness. Polarized neutron reflectometry shows
that the thickness grading results in a corresponding magnetic anisotropy
gradient. Magnetometry reveals that the anisotropy gradient promotes domain
nucleation upon magnetization reversal - a clear experimental demonstration of
the effectiveness of graded anisotropy for reducing write-field.",0912.0256v1
2009/12/2,Phase Diagram of Magnetization Reversal Processes in Nanorings,"We investigate magnetization reversal processes of magnetic nanorings. Using
a recently developed efficient cartesian coordinates fast multipole method,
magnetization switching phase diagrams are constructed for such structures. We
find that the dominant switching mechanisms strongly depend on the relative
spatial dimensions of the rings, i.e. height, width and radius. Furthermore,
they are found to depend on a characteristic exchange length scale, which is
determined by the competing short-range ferromagnetic and long-range dipolar
interactions in these systems. Detailed simulations allow us to identify three
novel switching mechanisms, which should be useful for building high density
storage systems.",0912.0319v1
2010/1/3,Electrically stabilized magnetic vortex and antivortex states in magnetic dielectrics,"The micromagnetic distribution in a dielectric nanoparticle is theoretically
considered. It is shown that the existence of inhomogeneous magnetoelectric
interaction in magnetic dielectrics provides the possibility to stabilize the
vortex and antivortex state. The estimation of the critical voltage necessary
for vortex/antivortex nucleation in bismuth ferrite and iron garnet
nanoparticles yields a value of +/-150 V. This system can be considered as
electrically switchable two state-logic magnetic element.",1001.0391v4
2010/3/16,Field-driven magnetisation steps in Ca3Co2O6: A single-crystal neutron-diffraction study,"We present single-crystal neutron-diffraction data for the spin-chain
compound Ca3Co2O6. The intensity and line shapes of the two families of Bragg
peaks characterising both the antiferromagnetic and the ferromagnetic
components of the magnetic order present in this material have been measured as
a function of temperature and applied magnetic fields of up to 5 T. We have
studied the microscopic nature of the magnetic order at each step seen in the
bulk magnetisation and investigated the evolution of the long and short-range
components of the magnetic order in Ca3Co2O6.",1003.3200v1
2010/4/5,Magnetic vortex as a ground state for micron-scale antiferromagnetic samples,"Here we consider micron-sized samples with any axisymmetric body shape and
made with a canted antiferromagnet, like hematite or iron borate. We find that
its ground state can be a magnetic vortex with a topologically non-trivial
distribution of the sublattice magnetization $\vec{l}$ and planar coreless
vortex-like structure for the net magnetization $\vec{M}$. For
antiferromagnetic samples in the vortex state, in addition to low-frequency
modes, we find high-frequency modes with frequencies over the range of hundreds
of gigahertz, including a mode localized in a region of radius $\sim$ 30--40 nm
near the vortex core.",1004.0606v1
2010/6/21,Roles of Bond Alternation in Magnetic Phase Diagram of RMnO3,"In order to investigate nature of the antiferromagnetic structures in
perovskite RMnO3, we study a Heisenberg J1-J2 model with bond alternation using
analytical and numerical approaches. The magnetic phase diagram which includes
incommensurate spiral states and commensurate collinear states is reproduced.
We discuss that the magnetic structure with up-up-down-down spin configuration
(E-type structure) and the ferroelectricity emerge cooperatively to stabilize
this phase. Magnetoelastic couplings are crucial to understand the magnetic and
electric phase diagram of RMnO3.",1006.3996v1
2010/6/28,A theory for magnetic-field effects of nonmagnetic organic semiconducting materials (Revised),"A universal mechanism for strong magnetic-field effects of nonmagnetic
organic semiconductors is presented. A weak magnetic field (less than hundreds
mT) can substantially change the charge carrier hopping coefficient between two
neighboring organic molecules when the two hopping states are not too
symmetric. Under the illumination of lights or under a high electric field, the
change of hopping coefficients leads also to the change of polaron density so
that photocurrent, photoluminescence, electroluminescence, magnetoresistance
and electrical-injection current become sensitive to a weak magnetic field. The
present theory can not only explain all observed features, but also provide a
solid theoretical basis for the widely used empirical fitting formulas.",1006.5292v1
2010/8/8,3D magnetization profile and multi-axes exchange bias in Co antidot arrays,"Cu/Co/Cu trilayers have been deposited on nanoporous alumina membranes.
Magnetic properties of the resulting Co antidot arrays are investigated using
SQUID magnetometry. Hysteresis loops of these arrays show two-step
magnetization reversal. In addition, exchange bias is observed, whether the
cooling field is applied within or perpendicular to the surface plane. In the
former case, the exchange bias changes sign close to the blocking temperature,
and becomes positive. We attribute these effects to the local, crescent shape
of the Co films, induced by the surface morphology of the alumina membranes.
This morphology leads to a three-dimensional magnetization distribution at the
nanoscale.",1008.1407v1
2010/8/12,"Spin polarization of the magnetic spiral in NaCu_2O_2, as seen by NMR","The incommensurate (IC) spin ordering in quasi-1D edge-shared cuprate
NaCu_2O_2 has been studied by ^{23}Na nuclear magnetic resonance spectroscopy
in an external magnetic field near 6 Tesla applied along the main
crystallographic axes. The NMR lineshape evolution above and below T_N\approx12
K yields a clear signature of an IC static modulation of the local magnetic
field consistent with a Cu^{2+} spin spiral polarized in the bc-plane rather
than in the ab-plane as reported from earlier neutron diffraction data.",1008.2118v1
2010/9/8,The temperature-dependent magnetization profile across an epitaxial bilayer of ferromagnetic La2/3Ca1/3MnO3 and superconducting YBa2Cu3O7-d,"Epitaxial bilayers of ferromagnetic La2/3Ca1/3MnO3 (LCMO) and superconducting
YBa2Cu3O7-d (YBCO) have been grown on single-crystalline SrTiO3 (STO)
substrates by pulsed laser deposition. The Manganese magnetization profile
across the FM layer has been determined with high spatial resolution at low
temperatures by X-ray resonant magnetic reflectivity (XRMR). It is found that
not only the adjacent superconductor but also the substrate underneath
influences the magnetization of the LCMO film at the interfaces at low
temperatures. Both effects can be investigated individually by XRMR.",1009.1553v1
2010/10/12,Cooperative ordering of superparamagnetic ZnO nanograins,"In this paper we have tried to understand the precise nature of magnetism in
ZnO nanoparticles. Cooling field dependence of magnetic hysteresis and coercive
field was observed for high temperature annealed sample indicating cooperative
magnetic correlation and ordering within the agglomerated nanograins. The
increasing induced internal magnetic field along the direction of external
field for the high temperature annealed sample has been fitted with the
modified Weiss-Brillouin model indicating emergence of long range intergrain
interaction among the superparamagnetic grains. We propose a simple idea that
explains the reduction of magnetisation due to vortex state like flux closure
situation.",1010.2381v1
2010/10/20,Electrically controllable surface magnetism on the surface of topological insulator,"We study theoretically the RKKY interaction between magnetic impurities on
the surface of three-dimensional topological insulators, mediated by the
helical Dirac electrons. Exact analytical expression shows that the RKKY
interaction consists of the Heisenberg-like, Ising-like and DM-like terms. It
provides us a new way to control surface magnetism electrically. The gap opened
by doped magnetic ions can lead to a short-range Bloembergen-Rowland
interaction. The competition among the Heisenberg, Ising and DM terms leads to
rich spin configurations and anomalous Hall effect on different lattices.",1010.4134v1
2010/10/26,Giant directional dichroism of terahertz light in resonance with magnetic excitations of the multiferroic oxide BaCo$_2$Ge$_2$O$_7$,"We propose that concurrently magnetic and ferroelectric, i.e. multiferroic,
compounds endowed with electrically-active magnetic excitations
(electromagnons) provide a key to produce large directional dichroism for long
wavelengths of light. By exploiting the control of ferroelectric polarization
and magnetization in a multiferroic oxide Ba$_2$CoGe$_2$O$_7$, we demonstrate
the realization of such a directional light-switch function at terahertz
frequecies in resonance with the electromagnon absorption. Our results imply
that this hidden potential is present in a broad variety of multiferroics.",1010.5420v1
2010/10/29,The Structural and Magnetic ordering in $La{}_{0.5-x}Nd_{x}Ca_{0.5}MnO_{3}$ (0.1 \ensuremath{\le} x \ensuremath{\le} 0.5) Manganites,"The crystal and magnetic structure of polycrystalline
$La{}_{0.5-x}Nd{}_{x}Ca_{0.5}MnO{}_{3}$ (0.0 \ensuremath{\le} x
\ensuremath{\le} 0.5) samples have been investigated using magnetization,
resistivity, transmission electron microscope, and neutron diffraction
techniques. The samples are isostructural and possess orthorhombic structure in
\textit{Pnma} space group. On lowering of temperature, the samples exhibit CE -
type antiferromagnetic structure coexisting with a weak ferromagnetic ordering.
The charge and orbitally ordered antiferromagnetic phase is weakened by the
growth of ferromagnetic phase. The evolution of structural distortions and
magnetic structure at low temperature as a function of Nd doping exhibit a
strong correlation with A - site disorder ($\sigma{}^{2}$).",1010.6124v1
2010/11/10,Repair of magnetism in oxidized graphene nanoribbons,"Novel route for the establishing of magnetism in realistic oxidized graphene
nanoribbons is proposed. Modelling of the migration of hydroxyl groups from
central part to the zig-zag edges of graphene nanoribbons passivated by oxygen
are performed with using density functional theory. The presence of hydroxyl
groups near the edges leads formation of dangling bonds there instead saturated
due to oxidation and repairs of magnetism diminished by edges oxidation. The
route of manufacturing and stability of new type of magnetic graphene
nanoribbons are also discussed.",1011.2342v1
2010/12/3,Energy-efficient mixed mode switching of a multiferroic nanomagnet for logic and memory,"In magnetic memory and logic devices, a magnet's magnetization is usually
flipped with a spin polarized current delivering a spin transfer torque (STT).
This mode of switching consumes too much energy and considerable energy saving
can accrue from using a multiferroic nanomagnet switched with a combination of
STT and mechanical stress generated with a voltage (VGS). The VGS mode consumes
less energy than STT, but cannot rotate magnetization by more than 90?, so that
a combination of the two modes is needed for energy-efficient switching.",1012.0819v1
2010/12/9,Ferroelectromagnets. Fifty years after discovery,"Ferroelectromagnets - compounds with ferroelectric and magnetic orderings -
were discovered about fifty years ago. They are of great interest due to the
possibility of mutual control of electric (magnetic) properties by magnetic
(electric) field. At present such possibility of magnetoelectric control has
become reality which stimulated revival of scientific and practical interest in
ferroelectromagnets. The progress in experimental and theoretical
investigations of magnetoelectric phenomena in ferroelectromagnets for the last
years, especially the colossal magnetoelectric effects observed recently, are
considered. The problems and future prospects of enhancing magnetoelectric
effects in ferroelectromagnets are being discussed. The book is intended for
researchers in ferroelectricity and magnetism and for students of physical
specialities.",1012.2024v1
2011/1/25,Large exchange bias after zero-field cooling from an unmagnetized state,"Exchange bias (EB) is usually observed in systems with interface between
different magnetic phases after field cooling. Here we report an unusual
phenomenon in which a large EB can be observed in Ni-Mn-In bulk alloys after
zero-field cooling from an unmagnetized state. We propose this is related to
the newly formed interface between different magnetic phases during the initial
magnetization process. The magnetic unidirectional anisotropy, which is the
origin of EB effect, can be created isothermally below the blocking
temperature.",1101.4737v1
2011/1/25,Sensitive SQUID magnetometry for studying nano-magnetism,"The superconducting quantum interference device (SQUID) magnetometer is one
of the most sensitive experimental techniques to magnetically characterize
samples with high sensitivity. Here we present a detailed discussion of
possible artifacts and pitfalls characteristic for commercial SQUID
magnetometers. This includes intrinsic artifacts which stem from the inherent
design of the magnetometer as well as potential issues due to the user. We
provide some guidelines how to avoid and correct these, which is of particular
importance when the proper magnetization of nano-scale objects shall be
established in cases where its response is dwarfed by that of the substrate it
comes with, a situation frequently found in the field of nano-magnetism.",1101.4764v1
2011/2/7,Anomalous magnetic anisotropy of the topmost surface layer of Ni(110),"The orientation of the magnetization of a Ni(110) surface was investigated
using techniques with different probing depths. By making use of electron
capture into excited states of fast He atoms, we found that the magnetization
of the topmost surface layer is not aligned along the easy axes of Ni. However,
for a 50 ML film Fe on Ni(110) we observed the magnetization of the topmost Fe
surface layer is along the easy axes of Fe.",1102.1392v1
2011/2/26,Angular dependent magnetization reversal in exchange biased bilayers under a modified 'effective field model',"A modified effective field model was developed to quantitatively interpret
the angular dependent magnetization reversal processes in exchange biased
Fe/IrMn bilayers. Several kinds of multi-step loops with distinct magnetization
reversal routes were observed for the samples measured at various field
orientations. Two types of angular dependent switching fields are observed and
their transitions are investigated, which are found to be driven by both Fe and
IrMn layer thicknesses. Our modified effective field model can nicely describe
all the switching field behaviors including the critical effects of the
exchange bias induced uniaxial anisotropy on the magnetization reversal
processes.",1102.5387v1
2011/4/14,Spin-orbit Hanle effect in high-mobility quantum wells,"We study the depolarization of optically oriented electrons in quantum wells
subjected to an in-plane magnetic field and show that the Hanle curve
drastically depends on the carrier mobility. In low-mobility structures, the
Hanle curve is described by a Lorentzian with the width determined by the
effective g-factor and the spin lifetime. In contrast, the magnetic field
dependence of spin polarization in high-mobility quantum wells is nonmonotonic:
The spin polarization rises with the magnetic field induction at small fields,
reaches maximum and then decreases. We show that the position of the Hanle
curve maximum can be used to directly measure the spin-orbit Rashba/Dresselhaus
magnetic field.",1104.2701v1
2011/5/19,Magnetic order near 270 K in mineral and synthetic Mn$_2$FeSbO$_6$ ilmenite,"The structural and magnetic properties of Mn$_2$FeSbO$_6$ single-crystalline
mineral and ceramic samples synthesized under thermobaric treatment have been
investigated, and compared to theoretical predictions based on first-principles
electronic structure calculations. This ilmenite system displays a sharp
magnetic transition just below the room temperature related to a ferrimagnetic
ordering of the Mn$^{2+}$ and Fe$^{3+}$ cations, which makes Mn$_2$FeSbO$_6$ a
promising candidate for designing functional magnetic materials.",1105.3973v1
2011/6/7,Stability of magnetic nanoparticles inside ferromagnetic nanotubes,"During the last years great attention has been given to the encapsulation of
magnetic nanoparticles. In this work we investigated the stability of small
magnetic particles inside magnetic nanotubes. Multisegmented nanotubes were
tested in order to optimize the stability of the particle inside the nanotubes.
Our results evidenced that multisegmented nanotubes are more efficient to
entrap the particles at temperatures up to hundreds of kelvins.",1106.1410v1
2011/6/15,Magnetic behavior of nanoparticles in patterned thin films,"The magnetic behavior of truncated conical nanoparticles in patterned thin
films is investigated as a function of their size and shape. Using a scaling
technique, phase diagrams giving the relative stability of characteristic
internal magnetic structures of the particles are obtained. The role of the
uniaxial anisotropy in determining the magnetic properties of such systems is
discussed, and a simple method for stablishing its strength is proposed.",1106.2868v1
2011/7/6,Hysteretic magnetic pinning and reversible resistance switching in High-Tc superconductor/ferromagnet multilayers,"We study a high-TC superconducting (YBa2Cu3O7-d) / ferromagnetic (Co/Pt
multilayer) hybrid which exhibits resistance switching driven by the magnetic
history: depending on the direction of the external field, a pronounced
decrease or increase of the mixed-state resistance is observed as magnetization
reversal occurs within the Co/Pt multilayer. We demonstrate that stray magnetic
fields cause these effects via i) creation of vortices/antivortices and ii)
magnetostatic pinning of vortices that are induced by the external field.",1107.1122v1
2011/7/11,Exchange bias effect in alloys and compounds,"The phenomenology of exchange bias effects observed in structurally
single-phase alloys and compounds but composed of a variety of coexisting
magnetic phases such as ferromagnetic, antiferromagnetic, ferrimagnetic,
spin-glass, cluster-glass and disordered magnetic states are reviewed. The
investigations on exchange bias effects are discussed in diverse types of
alloys and compounds where qualitative and quantitative aspects of magnetism
are focused based on macroscopic experimental tools such as magnetization and
magnetoresistance measurements. Here, we focus on improvement of fundamental
issues of the exchange bias effects rather than on their technological
importance.",1107.1978v1
2011/7/18,Molecular-spin dynamics study of electromagnons in multiferroic RMn$_2$O$_5$,"We investigate the electromagnon in magnetoferroelectrics RMn$_2$O$_5$ using
combined molecular-spin dynamics simulations. We identify the origin of the
electromagnon modes observed in the optical spectra and reproduce the most
salient features of the electromagnon in these compounds. We find that the
electromagnon frequencies are very sensitive to the magnetic wave vector along
the $a$ direction. We further investigate the electromagnon in magnetic field.
Although the modes frequencies change significant under magnetic field, the
static dielectric constant electromagnon does not change much in the magnetic
field.",1107.3349v1
2011/8/8,Density-operator theory of orbital magnetic susceptibility in periodic insulators,"The theoretical treatment of homogeneous static magnetic fields in periodic
systems is challenging, as the corresponding vector potential breaks the
translational invariance of the Hamiltonian. Based on density operators and
perturbation theory, we propose, for insulators, a periodic framework for the
treatment of magnetic fields up to arbitrary order of perturbation, similar to
widely used schemes for electric fields. The second-order term delivers a new,
remarkably simple, formulation of the macroscopic orbital magnetic
susceptibility for periodic insulators. We validate the latter expression using
a tight-binding model, analytically from the present theory and numerically
from the large-size limit of a finite cluster, with excellent numerical
agreement.",1108.1732v1
2011/10/3,Spin transfer torque oscillator based on asymmetric magnetic tunnel junctions,"We present a study of the spin transfer torque oscillator based on
CoFeB/MgO/CoFeB asymmetric magnetic tunnel junctions. We observe microwave
precession in junctions with different thickness of the free magnetization
layer. Taking advantage of the ferromagnetic interlayer exchange coupling
between the free and reference layer in the MTJ and perpendicular interface
anisotropy in thin CoFeB electrode we demonstrate the nanometer scale device
that can generate high frequency signal without external magnetic field
applied. The amplitude of the oscillation exceeds 10 nV/Hz^0.5 at 1.5 GHz.",1110.0295v1
2011/10/21,Giant optical nonlinearity of graphene in a strong magnetic field,"We present quantum-mechanical density-matrix formalism for calculating the
nonlinear optical response of magnetized graphene, valid for arbitrarily strong
magnetic and optical fields. We show that magnetized graphene possesses by far
the highest third-order optical nonlinearity among all known materials. The
giant nonlinearity originates from unique electronic properties and selection
rules near the Dirac point. As a result, even one monolayer of graphene gives
rise to appreciable nonlinear frequency conversion efficiency for incident
infrared radiation.",1110.4869v3
2011/10/24,Angular momentum transport through magnetic accretion curtains inside disrupted discs,"The structure of accretion curtain flows arising from magnetically disrupted
discs is considered. It is shown that a sub-Alfvenic, magnetically channelled
flow is consistent with matching the magnetic field across the curtain base. It
is shown that some angular momentum is necessarily fed back into the disc, and
this reduces the accretion torque acting on the star.
  The sonic point coordinates are found and a critical rotation rate results
below which the sonic point merges with the curtain flow base so, for such
stellar rotation rates, little or no thermal assistance is required for
material to make the transition to a supersonic flow.",1110.5215v1
2011/12/3,Microwave-induced DC Signal in a Permalloy Thin Strip at Low Applied Magnetic Field,"We investigated the ferromagnetic resonance signals in a polycrystalline
permalloy thin strip under in-plane low static magnetic field. A series of DC
voltages, which contain ferromagnetic resonance or spin wave resonance signals,
were measured by inducing microwave frequencies greater than 10 gigahertz. The
resonant signals measured in low magnetic field show different properties from
those detected in high field condition. Based on the theory of DC effects in
ferromagnetic resonance and the experimental data of anisotropic
magnetoresistance, a quantitative model was proposed. We found that the shape
anisotropy significantly affects magnetization, and distorts the resonant
signals in low field condition.",1112.0610v1
2011/12/16,"Comment on ""Unconventional Magnetism in a Nitrogen-Containing Analog of Cupric Oxide""","In a recent Letter [PRL, 107, 047208 (2011)], Zorko et al. report on an
""unexpected inhomogeneous magnetism"" related to ""a peculiar fragility"" of the
resonating-valence-bond (RVB) electronic state in the spin-1/2 quantum magnet
CuNCN. Here, we show that: i) the spin model of the anisotropic triangular
lattice (ATL), as proposed by Zorko et al., does not apply to CuNCN; ii) this
model does not support the proclaimed RVB ground state in the relevant
parameter range; iii) the magnetic state of CuNCN is not necessarily
inhomogeneous.",1112.3894v1
2012/1/11,Frequency domain studies of current-induced magnetization dynamics in single magnetic-layer nanopillars,"Spin transfer torque-induced high-frequency dynamics of single thin
cobalt-layer nanopillars of circular and elliptical shape have been observed
directly. Two types of precessional modes can be identified as a function of
magnetic field perpendicular to the layer plane, excited for negative current
polarity only. They are assigned to vortex-core and transverse spin-wave
excitations, which corroborate recent model predictions. The observed narrow
linewidth of 4 MHz at room temperature indicates the high coherence of the
magnetic excitations.",1201.2268v1
2012/1/23,Local lattice distortions around $\rm{Mn^{2+}}$ cause in-plane uniaxial magnetic anisotropy in Ga(Mn)As,"We theoretically investigate the interplay between local lattice distortions
around $\rm{Mn^{2+}}$ ion impurity and the ion's magnetic polarization,
mediated through spin-orbit coupling of hole. We show that the tetrahedral
symmetry around $\rm{Mn^{2+}}$ ion impurity is spontaneously broken even in the
paramagnetic regime. Modest local lattice distortions around the impurity
$\rm{Mn^{2+}}$ ion, along with the growth strain, stabilize magnetization along
$< 110 >$ directions, in the ferromagnetic regime. We explain the
experimentally observed in-plane uniaxial magnetic anisotropy seen in this
system using this symmetry-breaking mechanism.",1201.4879v2
2012/3/5,Thermo-mechanical sensitivity calibration of nanotorsional magnetometers,"We report on the fabrication of sensitive nanotorsional resonators, which can
be utilized as magnetometers for investigating the magnetization dynamics in
small magnetic elements. The thermo-mechanical noise is calibrated with the
resonator displacement in order to determine the ultimate mechanical torque
sensitivity of the magnetometer.",1203.0998v1
2012/3/7,Temperature Induced Spin Density Wave in Magnetic Doped Topological Insulators,"We study the magnetic properties of topological insulators doped with
isoelectronic magnetic impurities. We obtain that at zero temperature the
impurities order ferromagnetically, but when raising the temperature the
topological insulator undergoes a first order phase transition to a spin
density wave phase before the system reaches the paramagnetic phase. The origin
of this phase is the non-trivial dependence of the topological insulator spin
susceptibility on the momentum. We analyze the coupling of the non-uniform
magnetic phase with the Dirac electronic system that occurs at the surfaces of
the topological insulators.",1203.1436v2
2012/4/11,On the large magnetic anisotropy of Fe_{2}P,"We present an investigation on the large magnetic anisotropy of Fe_{2}P,
based on {\it Ab Initio} density-functional theory calculations, with a full
potential linear muffin-tin orbital (FP-LMTO) basis. We obtain an uniaxial
magnetic anisotropy energy (MAE) of 664 \mu eV/f.u., which is in decent
agreement with experimental observations. Based on a band structure analysis
the microscopical origin of the large magnetic anisotropy is explained. We also
show that by straining the crystal structure, the MAE can be enhanced further.",1204.2419v2
2012/4/19,"Electronic structure and magnetism in M(=IA, IIA)C compounds with the rocksalt structure","Electronic structures of MC where M is the alkali and alkaline earth metals
with the rocksalt structure are calculated by full potential density functional
codes. We find that the spin magnetic moment in the compounds is mainly
contributed by the spin polarized p-orbitals of carbon. The large distance
between the carbon makes the p-orbitals localized, which induces magnetic
instability according to the Stoner criterion. The electronic structure can be
mapped to the rigid band model. SrC, BaC and RaC are half-metals, while KC, RbC
and CsC are magnetic semiconductors",1204.4233v2
2012/4/26,Magnetism: the Driving Force of Order in CoPt. A First-Principles Study,"CoPt or FePt equiatomic alloys order according to the tetragonal L10
structure which favors their strong magnetic anisotropy. Conversely magnetism
can influence chemical ordering. We present here {\it ab initio} calculations
of the stability of the L10 and L12 structures of Co-Pt alloys in their
paramagnetic and ferromagnetic states. They show that magnetism strongly
reinforces the ordering tendencies in this system. A simple tight-binding
analysis allows us to account for this behavior in terms of some pertinent
parameters.",1204.5845v1
2012/5/2,Piezoelectric control of the magnetic anisotropy via interface strain coupling in a composite multiferroic structure,"We investigate theoretically the magnetic dynamics in a
ferroelectric/ferromagnetic heterostructure coupled via strain-mediated
magnetoelectric interaction. We predict an electric field-induced magnetic
switching in the plane perpendicular to the magneto-crystalline easy axis, and
trace this effect back to the piezoelectric control of the magnetoelastic
coupling. We also investigate the magnetic remanence and the electric
coercivity.",1205.0391v1
2012/5/2,Strain and structure driven complex magnetic ordering of a CoO overlayer on Ir(100),"We have investigated the magnetic ordering in the ultrathin c(10$\times$2)
CoO(111) film supported on Ir(100) on the basis of ab-initio calculations. We
find a close relationship between the local structural properties of the oxide
film and the induced magnetic order, leading to alternating ferromagnetically
and anti-ferromagnetically ordered segments. While the local magnetic order is
directly related to the geometric position of the Co atoms, the mismatch
between the CoO film and the Ir substrate leads to a complex long-range order
of the oxide.",1205.0493v1
2012/5/15,Highly anisotropic magnetic states of Co dimers bound to graphene-vacancies,"The adsorption behavior and the magnetic states of cobalt atoms and dimers on
single vacancies in a graphene sheet are investigated by means of relativistic
density functional calculations. It is found that local magnetic moments are
formed in both cases, despite strong chemical binding. Of particular interest
are kinetically stable isomers with two cobalt atoms attached to the same side
of the graphene sheet. Magnetic bi-stability with an anisotropy barrier of
about 50 meV is possible in this geometry. The feasibility of its preparation
is discussed.",1205.3469v1
2012/5/16,Magnetic properties of BiFeO3 micro-cubes synthesized by microwave agitation,"In this report we present results of magnetization measurements and
investigation of aging and memory effect in bismuth ferrite multiferroic
micro-cubes obtained by means of simple microwave synthesis procedure. It is
found that difference between FC and ZFC magnetizations appears at the
temperature of freezing of ferromagnetic domain walls. The decay of the
magnetic moment vs. time described by power-law relation and the absence of
memory effect indicate domain growth mechanism rather than the spin-glass
phase.",1205.3653v1
2012/5/31,Imprinting magnetic information in manganites with X-rays,"The effect of x-rays on an orbital and charge ordered epitaxial film of a
Pr$_{0.5}$Ca$_{0.5}$MnO$_{3}$ is presented. As the film is exposed to x-rays,
the antiferromagnetic response increases and concomitantly the conductivity of
the film improve. These results are discussed in terms of a persistent x-ray
induced doping, leading to a modification of the magnetic structure. This
effect allows writing electronic and magnetic domains in the film and
represents a novel way of manipulating magnetism.",1205.6922v1
2012/7/17,Magnetic properties of Mn-doped Ge46 and Ba8Ge46 clathrates,"We present a detailed study of the magnetic properties of unique cluster
assembled solids namely Mn doped Ge46 and Ba8Ge46 clathrates using density
functional theory. We find that ferromagnetic (FM) ground states may be
realized in both the compounds when doped with Mn. In Mn2Ge44, ferromagnetism
is driven by hybridization induced negative exchange splitting, a generic
mechanism operating in many diluted magnetic semiconductors. However, for
Mn-doped Ba8Ge46 clathrates incorporation of conduction electrons via Ba
encapsulation results in RKKY-like magnetic interactions between the Mn ions.
We show that our results are consistent with the major experimental
observations for this system.",1207.3996v1
2012/8/29,CoFeB Thickness Dependence of Thermal Stability Factor in CoFeB/MgO Perpendicular Magnetic Tunnel Junctions,"Thermal stability factor (delta) of recording layer was studied in
perpendicular anisotropy CoFeB/MgO magnetic tunnel junctions (p-MTJs) with
various CoFeB recording layer thicknesses and junction sizes. In all series of
p-MTJs with different thicknesses, delta is virtually independent of the
junction sizes of 48-81 nm in diameter. The values of delta increase linearly
with increasing the recording layer thickness. The slope of the linear fit is
explained well by a model based on nucleation type magnetization reversal.",1208.5828v1
2012/8/29,The Hall effect in accretion flows,"Magnetic diffusion in accretion flows changes the structure and angular
momentum of the accreting material. We present two power law similarity
solutions for flattened accretion flows in the presence of magnetic diffusion:
a secularly-evolving Keplerian disc and a magnetically-diluted free fall onto
the central object. The influence of Hall diffusion on the solutions is evident
even when this is small compared to ambipolar and Ohmic diffusion, as the
surface density, accretion rate and angular momentum in the flow all depend
upon the product \eta_H(B.\Omega), and the inclusion of Hall diffusion may be
the solution to the magnetic braking catastrophe of star formation simulations.",1208.5887v1
2012/9/9,Temperature-dependent proximity magnetism in Pt,"We experimentally demonstrate the existence of magnetic coupling between two
ferromagnets separated by a thin Pt layer. The coupling remains ferromagnetic
regardless of the Pt thickness, and exhibits a significant dependence on
temperature. Therefore, it cannot be explained by the established mechanisms of
magnetic coupling across nonmagnetic spacers. We show that the experimental
results are consistent with the presence of magnetism induced in Pt in
proximity to ferromagnets, in direct analogy to the well-known proximity
effects in superconductivity.",1209.1802v1
2012/9/19,Asymmetry of modal profiles of dipole-exchange spin waves in thin high-magnetic moment metallic ferromagnetic films,"The asymmetry of the modal profiles for dipole-exchange spin waves
propagating in in-plane magnetized ferromagnetic films at a right angle to the
applied magnetic field has been investigated theoretically. It was found that
in the large-magnetic moment ferromagnetic metallic films with typical
thicknesses 10-60 nm the fundamental mode of the spectrum is localized at the
surface opposite to the surface of localization of the exchange-free
Damon-Eshbach surface wave. This anomalous localization of the wave does not
affect the non-reciprocity of spin wave excitation by microstrip and coplanar
transducers but may be detected in other types of experiments.",1209.4153v1
2012/9/25,Modulated structure in the martensite phase of Ni1.8Pt0.2MnGa: a neutron diffraction study,"7M orthorhombic modulated structure in the martensite phase of Ni1.8Pt0.2MnGa
is reported by powder neutron diffraction study, which indicates that it is
likely to exhibit magnetic field induced strain. The change in the unit cell
volume is less than 0.5% between the austenite and martensite phases, as
expected for a volume conserving martensite transformation. The magnetic
structure analysis shows that the magnetic moment in the martensite phase is
higher compared to Ni2MnGa, which is in good agreement with magnetization
measurement.",1209.5508v1
2012/9/27,Interaction effects and transport properties of Pt capped Co nanoparticles,"We studied the magnetic and transport properties of Co nanoparticles (NPs)
being capped with varying amounts of Pt. Beside field and temperature dependent
magnetization measurements we performed delta-M measurements to study the
magnetic interactions between the Co NPs. We observe a transition from
demagnetizing towards magnetizing interactions between the particles for an
increasing amount of Pt capping. Resistivity measurements show a crossover from
giant magnetoresistance towards anisotropic magnetoresistance.",1209.6255v1
2012/10/9,Spin convertance at magnetic interfaces,"The exchange interaction between the conduction electrons and magnetic
moments at magnetic interface leads to mutual conversion between electron spin
current and magnon current. We introduce a concept of spin convertance which
quantitatively measures the magnon current induced by electron spin
accumulation and the spin current created by magnon accumulation at the
interface. We predict the phenomena on charge and spin drag across a magnetic
insulator spacer for several layered structures.",1210.2735v3
2012/10/11,Spin liquid behaviour in Jeff=1/2 triangular lattice Ba3IrTi2O9,"Ba3IrTi2O9 crystallizes in a hexagonal structure consisting of a layered
triangular arrangement of Ir4+ (Jeff=1/2). Magnetic susceptibility and heat
capacity data show no magnetic ordering down to 0.35K inspite of a strong
magnetic coupling as evidenced by a large Curie-Weiss temperature=-130K. The
magnetic heat capacity follows a power law at low temperature. Our measurements
suggest that Ba3IrTi2O9 is a 5d, Ir-based (Jeff=1/2), quantum spin liquid on a
2D triangular lattice.",1210.3137v1
2012/12/19,Magnetism and electronic properties of BiFeO3 under lower pressure,"Ab initio calculations show an antiferromagnetic-ferromagnetic phase
transition around 9-10 GPa and a magnetic anomaly at 12 GPa in BiFeO3. The
magnetic phase transition also involves a structural and insulator-metal
transition. The G-type AFM configuration under pressure leads to an increase of
the y component and decrease of the z component of the magnetization, which is
caused by the splitting of the dz2 orbital from doubly degenerate eg states.
Our results agree with recent experimental results.",1212.4591v1
2013/1/26,Electric field induced magnetic domain wall tilting,"The inclination of the magnetic domain wall plane in electric field is
observed. The simple theoretical model of this phenomenon that takes into
account the spin flexoelectricity is proposed. The value of electric
polarization of the magnetic domain wall is estimated as 0.3{\mu}C/m^2 that
agrees well with the results of electric field driven magnetic domain wall
motion measurements.",1301.6279v1
2013/2/25,Gravity and magnetic field dependent study of diffraction patterns in ferrofluids,"In this paper, we report the experimental observation of diffraction patterns
in a ferrofluid comprising of Fe3O4 nanoparticles in hexane by a 10 mW He-Ne
laser beam. An external dc magnetic field (0-2 kG) was applied perpendicular to
the beam. The diffraction pattern showed variation at different depths of the
sample in both zero and applied magnetic field. The patterns also exhibit a
change in shape and size as the external field is varied. This effect is
presumably arising due to thermally induced self-diffraction under the
influence of gravity and external magnetic field.",1302.6177v1
2013/3/28,Observation of giant magnetocaloric effect in HoCoSi,"We report the magnetic and magnetocaloric properties of HoCoSi, which shows
second order ferro-para magnetic transition at 14 K. It is found to exhibit a
large magnetic entropy change of 13 J/kg K for a field change of 20 kOe, which
increases to 20.5 J/kg K at 50 kOe. The refrigerant capacity is found to be 135
and 410 J/kg for 20 and 50 kOe, respectively. The large, low-field adiabatic
temperature change (~ 3 K) and a large refrigerant capacity make this compound
a suitable candidate for magnetic refrigeration applications at around 15 K.",1303.7188v2
2013/4/24,Casimir Momentum of a Chiral Molecule in a Magnetic Field,"In a classical description, a neutral, polarizable object acquires a kinetic
momentum when exposed to crossed electric and magnetic fields. In the presence
of only a magnetic field no such momentum exists classically, although it is
symmetry-allowed for an object lacking mirror symmetry. We perform a full QED
calculation to show that the quantum vacuum coupled to a chiral molecule
provides a kinetic ""Casimir"" momentum directed along the magnetic field,
proportional to its rotatory power and the fine structure constant.",1304.6767v2
2013/5/11,Magnetic Properties of the Spin-1/2 Deformed Kagome Antiferromagnet Edwardsite,"We prepared a powder sample of edwardsite Cd2Cu3(SO4)2(OH)6 4H2O, which is a
new candidate compound for the spin-1/2 kagome antiferromagnet, and studied its
magnetic properties by magnetic susceptibility and heat capacity measurements.
Edwardsite has a deformed kagome lattice with an average antiferromagnetic
interaction of 51 K between nearby spins and shows an antiferromagnetic order
accompanied by a small ferromagnetic moment below 4.3 K. The weak
ferromagnetism is likely due to spin canting caused by sizable
Dzyaloshinsky-Moriya interactions, which may stabilize the long-range magnetic
order instead of a spin-liquid state expected for the kagome antiferromagnet.",1305.2477v1
2013/6/21,Exchange interactions and frustrated magnetism in single-side hydrogenated and fluorinated graphene,"Magnetism in single-side hydrogenated (C$_2$H) and fluorinated (C$_2$F)
graphene is analyzed in terms of the Heisenberg model with parameters
determined from first principles. We predict a frustrated ground state for both
systems, which means the instability of collinear spin structures and sheds
light on the absence of a conventional magnetic ordering in defective graphene
demonstrated in recent experiments. Moreover, our findings suggest a highly
correlated magnetic behavior at low temperatures offering the possibility of a
spin-liquid state.",1306.5190v1
2013/7/2,Phase Field Crystal Model for Magneto-Elasticity in Isotropic Ferromagnetic Solids,"A new isotropic magneto-elastic phase field crystal (PFC) model to study the
relation between morphological structure and magnetic properties of pure
ferromagnetic solids is introduced. Analytic calculations were used to
determine the phase diagram and obtain the relationship between elastic strains
and magnetization. Time dependent numerical simulations were used to
demonstrate the effect of grain boundaries on the formation of magnetic
domains. It was shown that the grain boundaries act as nucleating sites for
domains of reverse magnetization. Finally, we derive a relation for coercivity
versus grain mis-orientation in the isotropic limit.",1307.0758v1
2013/7/10,Magnetocrystalline Anisotropy and the Magnetocaloric Effect in Fe2P,"Magnetic and magnetocaloric properties of high-purity, giant magnetocaloric
polycrystalline and single-crystalline Fe2P are investigated. Fe2P displays a
moderate magnetic entropy change which spans over 70 K and the presence of
strong magnetization anisotropy proves this system is not fully itinerant but
displays a mix of itinerant and localized magnetism. The properties of pure
Fe2P are compared to those of giant magnetocaloric (Fe,Mn)2(P,A) compounds
helping understand the exceptional characteristics shown by the latter which
are so promising for heat pump and energy conversion applications.",1307.2784v1
2013/7/24,Measurement of magnetization using domain compressibility in CoFeB films with perpendicular anisotropy,"We present a method to map the saturation magnetization of soft ultrathin
films with perpendicular anisotropy, and we illustrate it to assess the
compositional dependence of the magnetization of CoFeB(1 nm)/MgO films. The
method relies on the measurement of the dipolar repulsion of parallel domain
walls that define a linear domain. The film magnetization is linked to the
field compressibility of the domain. The method also yields the minimal
distance between two walls before their merging, which sets a practical limit
to the storage density in spintronic devices using domain walls as storage
entities.",1307.6479v1
2013/9/4,Low temperature magnetic transitions of single crystal HoBi,"We present resistivity, specific heat and magnetization measurements in high
quality single crystals of HoBi, with a residual resistivity ratio of 126. We
find, from the temperature and field dependence of the magnetization, an
antiferromagnetic transition at 5.7 K, which evolves, under magnetic fields,
into a series of up to five metamagnetic phases.",1309.1113v1
2013/9/25,Spontaneous electric polarization and Magneto-dielectric coupling in ceramic multiferroic Co3TeO6,"We report observation of magneto-electric and magneto-dielectric couplings in
ceramic Co3TeO6. Temperature dependent DC magnetization and dielectric constant
measurements together indicate coupling between magnetic order and electronic
polarization. Strong anomaly in dielectric constant at ~ 18K in zero magnetic
field indicates presence of spontaneous polarization. Observations like weak
ferromagnetic order at lower temperature, field and temperature dependences of
the ferroelectric transition provide experimental verification of the recent
theoretical proposal by P. Toledano et al., Phys. Rev. B 85, 214439 (2012). We
provide direct evidence of spin-phonon coupling as possible origin of magnetic
order.",1309.6417v1
2013/11/17,Giant magnetothermopower in charge ordered Nd0.75Na0.25MnO3,"We report magnetization, resistivity and thermopower in the charge-orbital
ordered antiferromagnet Nd0.75Na0.25MnO3. Magnetic-field induced collapse of
antiferromagnetism is found to be accompanied by a giant negative
magnetothermopower (= 80-100% for a field change of 5T) over a wide temperature
(T = 60-225K) and giant magnetoresistance. While the field-induced metamagnetic
transition in magnetization is reversible upon field-cycling at T > 40 K, it is
irreversible at lower temperatures and this has impact on magnetoresistance,
magnetothermopower as well as change in the temperature of the sample. Our
results indicate high sensitivity of thermopower to changes in the magnetic
state of the sample.",1311.4165v1
2013/12/3,Magnetic systems at criticality: different signatures of scaling,"Different aspects of critical behaviour of magnetic materials are presented
and discussed. The scaling ideas are shown to arise in the context of purely
magnetic properties as well as in that of thermal properties as demonstrated by
magnetocaloric effect or combined scaling of excess entropy and order
parameter. Two non-standard approaches to scaling phenomena are described. The
presented concepts are exemplified by experimental data gathered on four
representatives of molecular magnets.",1312.0756v1
2013/12/6,First Principles Study of the Magnetic Properties of LaOMnAs,"Recent experiments reported giant magnetoresistance at room temperature in
LaOMnAs. Here a density functional theory calculation is performed to
investigate magnetic properties of LaOMnAs. The ground state is found to be the
G-type antiferromagnetic order within the $ab$ plane but coupled
ferromagnetically between planes, in agreement with recent neutron
investigations. The electronic band structures suggest an insulating state
which is driven by the particular G-type magnetic order, while a metallic state
accompanies the ferromagnetic order. This relation between magnetism and
conductance may be helpful to qualitatively understand the giant
magnetoresistance effects.",1312.1775v1
2013/12/26,An effective-field theory study of hexagonal Ising nanowire: Thermal and magnetic properties,"By means of the effective-field theory (EFT) with correlations, the
thermodynamic and magnetic quantities such as magnetization, susceptibility,
internal energy, free energy, hysteresis curves and compensation behaviors of
the spin-1/2 hexagonal Ising nanowire (HIN) system with core/shell structure
have been presented. The hysteresis curves are obtained for different values of
the system parameters on both ferromagnetic and antiferromagnetic case. It has
been shown that the system only undergoes a second-order phase transition.
Moreover, from the thermal variations of the total magnetization, the five
compensation types can be found under certain conditions, namely the Q-, R-,
S-, P-, and N-types.",1312.7106v1
2014/1/14,Defects induced ferromagnetism in plasma-enabled graphene nanopetals,"Ferromagnetism in graphene is fascinating, but it is still a big challenge
for practical applications due to the weak magnetization. In order to enhance
the magnetization, here, we design plasma-enabled graphene nanopetals with
ultra-long defective edges of up to 105 m/g, ultra-dense lattice vacancies and
hydrogen chemisorptions. The designed graphene nanopetals display robust
ferromagnetism with large saturation magnetization of up to 2 emu/g at 5 K and
1.2 emu/g at room temperatures. This work identifies the plasma-enabled
graphene nanopetals as a promising candidate for graphene-based magnetic
devices.",1401.3060v1
2014/2/12,Hydrostatic pressure to trigger and assist magnetic transitions: baromagnetic refrigeration,"The possible application of the barocaloric effect to produce solid state
refrigerators is a topic of interest in the field of applied physics. In this
work, we present experimental data about the influence of external pressure on
the magnetic properties of a manganite with phase separation. Using the Jahn
Teller effect associated with the presence of the charge ordering we were able
to follow the transition to the ferromagnetic state induced by pressure. We
also demonstrated that external pressure can assist the ferromagnetic state,
decreasing the magnetic field necessary to generate the magnetic transition.",1402.2824v1
2014/3/15,Magnetostructural and magnetocaloric properties of bulk LaCrO3 system,"We studied the magnetic properties of bulk LaCrO3; a GdFeO3-type distorted
perovskite, with a predominant antiferromagnetic phase transition at ~ 290 K.
The bulk LaCrO3 exhibits intrinsic weak ferromagnetism at room temperature,
which may arise due to the tilting of CrO6 octahedra, resulting in a non-zero
net magnetic moment, as confirmed from the magnetization measurements. A broad
magnetically-induced entropy change (-{\Delta}S) is observed with the maximum
at 290 K, close to room temperature in LaCrO3 system.",1403.3784v1
2014/3/19,Ab-inito study of low temperature magnetic properties of double perovskite Sr2FeOsO6,"Using density-functional theory calculations, we investigated the electronic
structure and magnetic exchange interactions of the ordered 3d-5d double
perovskite Sr2FeOsO6, which has recently drawn attention for interesting
antiferromagnetic transitions. Our study reveals the vital role played by
long-range magnetic exchange interactions in this compound. The competition
between the ferromagnetic nearest neighbor Os-O-Fe interaction and
antiferromagnetic next nearest neighbor Os-O-Fe-O-Os interaction induces strong
frustration in this system, which explains the lattice distortion and magnetic
phase transitions observed in experiments.",1403.4894v1
2014/4/3,Magnetic and Thermodynamic properties of face-centered cubic Fe-Ni alloys,"A model lattice ab initio parameterised Hamiltonian spanning a broad range of
alloy compositions and a large variety of chemical and magnetic configurations
has been developed for face-centered cubic Fe-Ni alloys. Thermodynamic and
magnetic properties of the alloys are explored using configuration and magnetic
Monte Carlo simulations in a temperature range extending well over 1000 K.",1404.0888v1
2014/5/11,Tuning perpendicular magnetic anisotropy in the MgO/CoFeB/Ta thin films,"Understanding the magnetic anisotropy at ferromagnetic metal/oxide interface
is a fundamental and intriguing subject. Here we propose an approach to
manipulate the strength of perpendicular magnetic anisotropy (PMA) by varying
MgO thickness in the MgO/CoFeB/Ta thin films. We identify that the PMA at the
MgO/CoFeB interface is tuned by the crystalline structure of bulk MgO layer and
decreases dramatically due to the onset of crystalline MgO forming with the
increase of MgO thickness. Our work opens an avenue to manipulate the magnetic
anisotropy by the modification of the ferromagnetic metal/oxide interface.",1405.2551v2
2014/5/28,Breathing modes of confined skyrmions in ultrathin magnetic dots,"The dynamics of individual magnetic skyrmions confined in ultrathin film dots
is studied theoretically. The systems considered are transition metal
ferromagnets possessing perpendicular magnetic anisotropy and particular
attention is given to the dynamic response of the skyrmions to perpendicular
driving fields. By using micromagnetics simulations, it is shown that breathing
modes can hybridize with geometrically-quantized spin wave eigenmodes of the
circular dots considered, leading to distinct features in the power spectrum
that differ to the behavior expected for uniformly magnetized systems. The
field dependence of the breathing modes offers a direct means of detecting and
characterizing such skyrmion states in experiment.",1405.7414v1
2014/7/9,Spontaneous gap generation on the surface of weakly interacting topological insulators using nonmagnetic impurities,"Strong nonmagnetic impurities on the surface of three-dimensional topological
insulators (TIs) generate localized resonance peaks close to the Dirac point.
We show that this results in a strongly reduced critical Coulomb interaction
strength to reach a magnetic surface state, following a Stoner-like criterion.
Thus even weakly interacting TIs host a finite (local) magnetization around
strong nonmagnetic impurities. The local magnetization gives rise to a global
energy gap, linearly dependent on the maximum value of the magnetization but
decreasing with reduced impurity concentration.",1407.2484v1
2014/7/25,Ferromagnetism in UGe2 : A microscopic model,"Anderson lattice model is used to rationalize the principal features of the
heavy fermion compound UGe2 by means of the generalized Gutzwiller approach
(the SGA method). This microscopic approach successfully reproduces magnetic
and electronic properties of this material, in a qualitative agreement with
experimental findings from the magnetization measurements, the neutron
scattering, and the de Haas-van Alphen oscillations. Most importantly, it
explains the appearance, sequence, character, and evolution in an applied
magnetic field of the observed in UGe2 ferro- and, para-magnetic phases as an
effect of a competition between the f-f electrons Coulomb interaction energy
and f-conduction electrons kinetic energy (hybridization)",1407.6911v1
2014/9/24,Direct magnetocaloric effect measurement technique in alternating magnetic fields,"A method for direct measurement of the magnetocaloric effect (MCE) in
alternating magnetic fields is offered. Main advantages of the method compared
to a classical direct one are the high temperature sensitivity (better than
10-3 K); the ability of measuring of MCE in weak magnetic fields (by several
tens oersteds and higher); the ability of measuring of MCE on small-sized
samples (1x1x 0.01 mm3 and larger); the ability of measuring of MCE in
alternating magnetic fields up to 50 Hz of frequency. The results on
measurement of MCE on Gd and Ni-Mn-In Heusler alloy are reported.",1409.6898v1
2014/10/5,Planar Hall effect in Y3Fe5O12(YIG)/IrMn films,"The planar Hall effect of IrMn on an yttrium iron garnet (YIG = Y3Fe5O12) was
measured in the magnetic field rotating in the film plane. The magnetic field
angle dependence of planar Hall resistance (PHR) has been observed in YIG/IrMn
bilayer at different temperatures, while the GGG/IrMn (GGG= Gd3Ga5O12) shows
constant PHR for different magnetic field angles at both 10 K and 300 K. This
provides evidence that IrMn has interfacial spins which can be led by FM in
YIG/IrMn structure. A hysteresis can be observed in PHR-magnetic field angle
loop of YIG/IrMn films at 10 K, indicating the irreversible switching of IrMn
interfacial spins at low temperature.",1410.1112v1
2014/10/18,Structural and magnetic characterisation of iron oxyselenides Ce2O2Fe2OSe2 and Nd2O2Fe2OSe2,"We present here an investigation of the magnetic ordering in the Mott
insulating oxyselenide materials Ln2O2Fe2OSe2 (Ln = Ce, Nd). Neutron powder
diffraction data are consistent with a non-collinear multi-k ordering on the
iron sublattice structure and analysis indicates a reduced magnetic correlation
length perpendicular to the [Fe2O]2+ layers. The magnetic role of the Ln3+
cations is investigated and Ce3+ moments are found to order for T < 16 K.",1410.4990v1
2014/11/3,Optimum reduction of the dynamo threshold by a ferromagnetic layer located in the flow,"We consider a fluid dynamo model generated by the flow on both sides of a
moving layer. The magnetic permeability of the layer is larger than that of the
flow. We show that there exists an optimum value of magnetic permeability for
which the critical magnetic Reynolds number for dynamo onset is smaller than
for a nonmagnetic material and also smaller than for a layer of infinite
magnetic permeability. We present a mechanism that provides an explanation for
recent experimental results. A similar effect occurs when the electrical
conductivity of the layer is large.",1411.0449v1
2014/11/7,Preparation of magnetic tips for spin-polarized STM on Fe_{1+y}Te,"The interplay of electronic nematic modulations, magnetic order,
superconductivity and structural distortions in strongly correlated electron
materials calls for methods which allow characterizing them simultaneously - to
allow establishing directly the relationship between these different phenomena.
Spin-polarized STM enables studying both, electronic excitations as well as
magnetic structure in the same measurement at the atomic scale. Here we
demonstrate preparation of magnetic tips, both ferromagnetic and
antiferromagnetic, on single crystals of FeTe. This opens up preparation of
spin-polarized tips without the need for sophisticated ultra-high vacuum
preparation.",1411.1976v1
2014/11/8,"Correlations among magnetic, magnetocaloric and magneto-transport properties in HoNiSi","Magnetic, magnetocaloric and magneto-transport properties of polycrystalline
HoNiSi have been studied. The compound crystallizes in orthorhombic crystal
structure and orders antiferromagnetically at TN=4.6 K. Magnetization isotherms
show curvature at small fields, revealing a field induced metamagnetic
transition. Magnetocalroic effect (MCE) has been estimated using magnetization
data and is found to be 12.8 J/kg K for a field of 50 kOe. Application of field
reduces the resistivity near TN, which results in a large negative MR. The
maximum value of MR has been found to be -24% at 4 K for 50 kOe. Below 4 K, the
compound shows positive MR with shape changing with field.",1411.2135v1
2014/12/25,Cu codoping control over magnetic precipitate formation in ZnCoO nanowires,"Using electrodeposition, we have grown nanowires of ZnCoO with Cu codoping
concentrations varying from 4-10 at.%, controlled only by the deposition
potential. We demonstrate control over magnetic Co oxide nano-precipitate
formation in the nanowires via the Cu concentration. The different magnetic
behavior of the Co oxide nano-precipitates indicates the potential of ZnCoO for
magnetic sensor applications.",1412.7792v1
2015/2/24,Spin rectification for collinear and non-collinear magnetization and external magnetic field configurations,"Spin rectification in a single crystal Fe/Au/Fe sandwich is electrically
detected for collinear and non-collinear magnetization and external magnetic
field configurations. The line shape, line width and signal polarity are
analysed. The spin rectication theory has been much extended by taking the
magneto-crystalline anisotropy and shape anisotropy into account, which
explained non-collinear resonances and agrees very well with experimental data.
Thus, a comprehensive understanding of spin rectification in ferromagnetic
metal was demonstrated in this work.",1502.06859v1
2015/3/12,Chirp spectroscopy applied to the characterization of Ferromagnetic Resonance in Magnetic Tunnel Junctions,"Magnetic Tunnel Junction devices find use in several applications based on
the exploitation of the Spin-Transfer Torque phenomenon. The Ferromagnetic
Resonance curve is a key characteristic of any Magnetic Tunnel Junctions. It is
usually characterized both experimentally and numerically by performing a lot
of measurements of the magnetic response to a sinusoidal field or current. Here
we propose the use of a chirp signal as excitation signal to reconstruct the
Ferromagnetic resonance curve with a single measurement/simulation. A
micromagnetic comparison of the proposed method with the traditional one is
shown.",1503.03719v1
2015/3/12,Micromagnetic study of electrical-field-assisted magnetization switching in MTJ devices,"Perpendicular MgO-based Magnetic Tunnel Junctions are optimal candidates as
building block of Spin Transfer Torque (STT) magnetoresistive memories.
However, up to now, the only STT is not enough to achieve switching current
density below 106 A/cm2. A recent work [Wang et al., Nature Mater., vol. 11, pp
64-68, Jan. 2012] has experimentally demonstrated the possibility to perform
magnetization switching assisted by an electric-field at ultra-low current
density. Theoretically, this switching has been studied by using a macrospin
approach only. Here, we show a full micromagnetic study. We found that the
switching occurs via a complex nucleation process including the nucleation of
magnetic vortexes.",1503.03721v1
2015/5/19,Magnetization Process of the Spin-S Kagome-Lattice Heisenberg Antiferromagnet,"The magnetization process of the spin-S Heisenberg antiferromagnet on the
kagome lattice is studied by the numerical-diagonalization method. Our
numerical-diagonalization data for small finite-size clusters with S=1, 3/2, 2,
and 5/2 suggest that a magnetization plateau appears at one-third of the height
of the saturation in the magnetization process irrespective of S. We discuss
the S dependences of the edge fields and the width of the plateau in comparison
with recent results obtained by real-space perturbation theory.",1505.04853v1
2015/6/30,Rapid magnetic oscillations and magnetic breakdown in quasi-1D conductors,"We review the physics of magnetic quantum oscillations in quasi-one
dimensional conductors with an open Fermi surface, in the presence of modulated
order. We emphasize the difference between situations where a modulation
couples states on the same side of the Fermi surface and a modulation couples
states on opposite sides of the Fermi surface. We also consider cases where
several modulations coexist, which may lead to a complex reorganization of the
Fermi surface. The interplay between nesting effects and magnetic breakdown is
discussed. The experimental situation is reviewed.",1507.00037v2
2015/7/2,Magnetic circular polarization of luminescence in Bismuth-doped silica glass,"The magnetic field induced circular polarization of near infrared
photoluminescence in Bi-doped pure silica glass was studied in the spectral
range of 660 - 1600 nm covering three excited state levels. The highest degree
of magnetic circular polarization of luminescence was observed in the lasing,
first excited state (peak emission at 1440 nm). The results of variable
temperature and variable magnetic field measurements allows to conclude that
the near infrared luminescence originates from an isolated non-Kramers doublet
of the even-electron system.",1507.00523v1
2015/7/18,Step-like features on caloric effects of graphenes,"We considered a graphene nano-ribbon with a longitudinal electric field
(along $x$ direction) and a transversal magnetic field (along $z$ direction),
and then observe (i) the electrocaloric effect ruled by an applied magnetic
field and (ii) the magnetocaloric effect ruled by an applied electric field. We
focused our attention to the limit of low temperatures, and then observed
interesting step-like features. For each filled Landau level $n$, created by
the applied magnetic field, both caloric effects increase proportionally to
$n+1/2$; and this step measures either important graphene properties (like
Fermi velocity) or quantum fundamental quantities (like Planck constant and
magnetic flux quantum).",1507.05186v1
2015/8/24,Spin Dynamics Simulation of the Magneto-Electric Effect in a Composite Multiferroic Chain,"A composite multiferroic chain with an interfacial linear magneto-electric
coupling is used to study the magnetic and electric responses to an external
magnetic or electric field. The simulation uses continuous spin dynamics
through the Landau-Lifshitz-Gilbert equations of the magnetic spin and the
electric pseudo-spin. The results demonstrate an accurate description of the
distribution of the magnetisation and polarisation are induced by applied
electric and magnetic field, respectively.",1508.05693v1
2015/8/26,Magneto-oscillations on specific heat of graphene monolayer,"Measurement of magnetic oscillations on thermodynamic quantities (like
magnetization and specific heat), is one of the experimental methods to access
the density of states of electronic systems. In the present paper we therefore
theoretically explore the oscillatory phenomena on the specific heat of
graphenes considering gapped and gapless cases in a quantized magnetic field.
Further situations is also considered, as the influence of impurities, Coulomb
interaction and phonons. We could then map the magnetic oscillations on the
specific heat of graphenes under these constraints and the obtained results are
a good starting point and guide for further experimental works.",1508.06648v1
2015/10/18,Two-Fluid Theory for Spin Superfluidity in Magnetic Insulators,"We investigate coupled spin and heat transport in easy-plane magnetic
insulators. These materials display a continuous phase transition between
normal and condensate states that is controlled by an external magnetic field.
Using hydrodynamic equations supplemented by Gross-Pitaevski phenomenology and
magnetoelectric circuit theory, we derive a two-fluid model to describe the
dynamics of thermal and condensed magnons, and the appropriate boundary
conditions in a hybrid normal-metal|magnetic-insulator|normal-metal
heterostructure. We discuss how the emergent spin superfluidity can be
experimentally probed via a spin Seebeck effect measurement.",1510.05316v2
2015/11/26,Spin textures and spin-wave excitations in doped Dirac-Weyl semimetals,"We study correlations and magnetic textures of localized spins, doped in
three-dimensional Dirac semimetals. An effective field theory for magnetic
moments is constructed by integrating out the fermionic degrees of freedom. The
spin correlation shows a strong anisotropy, originating from spin-momentum
locking of Dirac electrons, in addition to the conventional Heisenberg-like
ferromagnetic correlation. The anisotropic spin correlation allows
topologically nontrivial magnetic excitation textures such as a transient
hedgehog state, as well as the ferromagnetic ground state. The spin-wave
dispersion in ferromagnetic Weyl semimetal also becomes anisotropic, being less
dispersed perpendicular to the magnetization.",1511.08381v1
2016/2/6,Lieb-Mattis ferrimagnetism in diluted magnetic semiconductors,"We show the possibility of long-range ferrimagnetic ordering with a
saturation magnetisation of the order of 1 Bohr magneton per spin for
arbitrarily low concentration of magnetic impurities in semiconductors,
provided that the impurities form a superstructure satisfying the conditions of
the Lieb-Mattis theorem. Explicit examples of such superstructures are given
for the wurtzite lattice, and the temperature of ferrimagnetic transition is
estimated from a high-temperature expansion. Exact diagonalization studies show
that small fragments of the structure exhibit enhanced magnetic response and
isotropic superparamagnetism at low temperatures. A quantum transition in a
high magnetic field is considered and similar superstructures in cubic
semiconductors are discussed as well.",1602.02239v1
2016/4/12,Magnetization distribution and domain wall dynamics in nanotube with surface anisotropy,"The period of magnetization oscillations that occur near the surface of a
nanotube or nanowire under the influence of surface magnetic anisotropy is
determined by means of numerical simulation as a function of nanowire geometry
and material parameters. The hopping mode is observed for stationary movement
of a head-to-head domain wall along nanowire axis in applied magnetic field.
The average speed of the domain wall in the hopping mode is found to be several
times less than the stationary velocity of the wall in the absence of surface
anisotropy.",1604.03523v1
2016/5/17,Effects of spin fluctuation on the magnetic anisotropy constant of itinerant electron magnets,"In the disordered local moment picture, we calculated the magnetization (M)
and magnetic anisotropy energy (MAE) of FePt, CoPt, and MnAl ordered alloys and
body-centered tegragonal FeCo (bct-FeCo) disordered alloy, assuming spatially
fluctuated spin configurations at finite temperatures. All alloys exhibit the
relation K1(T)/K1(0)=(M(T)/M(0))^n with the exponent (n) around 2. This is
consistent with the two-ion anisotropy model, in contrast to the usual
single-ion anisotropy model exhibiting n=3. Because these systems have
different mechanisms of MAE, we suggest that this relation is a general rule
for itinerant electron systems.",1605.05058v1
2016/5/24,Microwave Magneto-Chiral Effect in a Noncentro-symmetric Magnet CuB2O4,"We have investigated microwave nonreciprocity in a noncentro-symmetric magnet
CuB2O4. We simultaneously observed differently originated nonreciprocities; the
classical magnetic dipolar effect and the magneto-chiral (MCh) effect. By
rotating magnetic field in a tetragonal plane, we clearly unveil qualitative
difference between them. The MCh effect signal reveals chiral transitions from
one enantiomer to the other via intermediate achiral state. We show
magnetoelectric effect plays an essential role for the emergence of microwave
MCh effect.",1605.07414v1
2016/7/4,Transversal-rotational and zero group velocity modes in tunable magneto-granular phononic crystals,"We report on the design and operation of a 1D magneto-granular phononic
crystal composed of a chain of steel spherical beads on top of permanent
magnets. The magnetic field of the permanent magnets induces forces in the
granular structure. By changing its strength, we can tune the dynamic response
of the granular structure. We present experimental results with evidence of
coupled transversal-rotational modes, and zero group velocities modes. These
observations are well supported by a proposed model taking into account the
mechanical coupling between the beads and the magnets by linear stiffnesses and
including all degrees of freedom in translations and rotations.",1607.00831v2
2016/9/7,Magnetic decoupling of ferromagnetic metals through a graphene spacer,"We study the magnetic coupling between different ferromagnetic metals (FMs)
across a graphene (G) layer, and the role of graphene as a thin covalent
spacer. Starting with G grown on a FM substrate (Ni or Co), we deposit on top
at room temperature different FM metals (Fe, Ni, Co). By measuring the dichroic
effect of 3p photoemission lines we detect the magnetization of the substrate
and the sign of the exchange coupling in FM overlayer at room temperature. We
show that the G layer magnetically decouples the FM metals.",1609.01861v1
2016/9/18,Detecting Chiral Magnetic Effect by Lattice Dynamics,"In the present paper, we propose that the chiral magnetic effect, the direct
consequence of the presence of Weyl points in the band structure, can be
detected by its coupling to certain phonon modes, which behave like pseudo
scalars under point group transformations. Such coupling can generate resonance
between intrinsic plasmon oscillation and the corresponding phonon modes,
leading to dramatic modification of the optical response by the external
magnetic field, which provides a new way to study chiral magnetic effect by
optical measurements.",1609.05442v1
2016/10/14,Local environment effects in the magnetic properties and electronic structure of disordered FePt,"Local aspects of magnetism of disordered FePt are investigated by ab initio
fully relativistic full potential calculations, employing the supercell
approach and the coherent potential approximation (CPA). The focus is on trends
of the spin and orbital magnetic moments with chemical composition and with
bond lengths around the Fe and Pt atoms. A small but distinct difference
between average magnetic moments obtained when using the supercells and when
relying on the CPA is identified and linked to the neglect of the Madelung
potential in the CPA.",1610.04474v1
2016/10/19,Resonant Magnetization Switching Conditions of an Exchange-coupled Bilayer under Spin Wave Excitation,"We systematically investigated the spin wave-assisted magnetization switching
(SWAS) of a L10-FePt / Ni81Fe19 (Permalloy; Py) exchange-coupled bilayer using
a pulse-like rf field (hrf) and mapped the switching events in the magnetic
field (H) - hrf frequency (f) plane to reveal the switching conditions. The
switching occurred only in a limited region following the dispersion
relationship of the perpendicular standing spin wave (PSSW) modes in Py. The
results indicate that SWAS is a resonant magnetization switching process, which
is different from the conventional microwave assisted switching, and has the
potential to be applied to selective switching for multilevel recording media.",1610.05864v1
2016/11/7,A magnetostatic energy formula arising from the $L^2$-orthogonal decomposition of the stray field,"A formula for the magnetostatic energy of a finite magnet is proven. In
contrast to common approaches, the new energy identity does not rely on
evaluation of a nonlocal boundary integral inside the magnet or the solution of
an equivalent Dirichlet problem. The formula is therefore computationally
efficient, which is also shown numerically. Algorithms for the simulation of
magnetic materials could benefit from incorporating the presented
representation of the energy. In addition, a natural analogue for the energy
via the magnetic induction is given. Proofs are carried out within a setting
which is suitable for common discretizations in computational micromagnetics.",1611.02088v2
2016/11/16,Dynamic chiral magnetic effect and Faraday rotation in macroscopically disordered helical metals,"We develop an effective medium theory for electromagnetic wave propagation
through gapless non-uniform systems with dynamic chiral magnetic effect. The
theory allows to calculate macroscopic-disorder-induced corrections to the
values of optical, as well as chiral magnetic conductivities. In particular, we
show that spatial fluctuations of optical conductivity induce corrections to
the effective value of the chiral magnetic conductivity. Experimentally, these
corrections can be observed as sharp features in the Faraday rotation angle
near frequencies that correspond to the bulk plasmon resonances of a material.
Such features are not expected to be present in single crystal samples.",1611.05491v1
2016/12/6,Exceptional magneto-electric coupling and spontaneous electric polarization in anti-ferromagnet Co4Nb2O9,"Synthesis and extensive structural, pyroelectric, magnetic, dielectric and
magneto-electric characterizations are reported for polycrystalline Co4Nb2O9
towards unraveling the multiferroic state especially in reference to the
magnetic spin flop transition. Magnetic measurements confirm the Co4Nb2O9
becomes antiferromagnetic (AFM) at around 28 K but no clear evidence for
spin-flop effect was found. Associated with the magnetic phase transition, a
sharp peak in pyroelectric current indicates the appearance of the strong
magneto-electric coupling below Neel temperature (TN) with a large coupling
constant upto 17.8 uC/m^2T. Using temperature oscillation technique, we
establish Co4Nb2O9 to be a genuine multiferroic with spontaneous electric
polarization in the anti-ferromagnetic state.",1612.01970v1
2016/12/21,Grain boundary relaxation and reconstruction: effect on local magnetic moment,"We present a detailed numerical study on structure and local magnetic
properties of $\langle 100 \rangle$ symmetric tilt grain boundaries in
bcc-iron. Particular attention is paid to connection between type of grain
boundary relaxation and local magnetic properties. Results from first
principles calculation showed that grain boundary reconstruction leads to
non-uniform distribution of local magnetic moments in grain boundary plane.
This is in contrast with the result obtained in grain boundary plane, where
simple relaxation is observed. Well optimized atomic configurations in the
vicinity of the interface were achieved by simulated annealing optimization
technique improved by combination with genetic algorithm.",1612.07181v1
2017/1/20,Probing of the interfacial Heisenberg and Dzyaloshinskii--Moriya exchange interaction by magnon spectroscopy,"This Topical Review presents an overview of the recent experimental results
on the quantitative determination of the magnetic exchange parameters in
ultrathin magnetic films and multilayers, grown on different substrates. The
experimental approaches to probe both the symmetric Heisenberg as well as the
antisymmetric Dzyaloshinskii--Moriya exchange interaction in ultrathin magnetic
films and at interfaces are discussed in detail. It is explained how the
experimental spectrum of magnetic excitations can be used to quantify the
strength of these interactions.",1701.05850v1
2017/2/1,A new magnetic phase in the nickelate perovskite TlNiO$_3$,"The RNiO$_3$ perovskites are known to order antiferromagnetically below a
material-dependent N\'eel temperature $T_\text{N}$. We report experimental
evidence indicating the existence of a second magnetically-ordered phase in
TlNiO$_3$ above $T_\text{N} = 104$ K, obtained using nuclear magnetic resonance
and muon spin rotation spectroscopy. The new phase, which persists up to a
temperature $T_\text{N}^* = 202$ K, is suppressed by the application of an
external magnetic field of approximately 1 T. It is not yet known if such a
phase also exists in other perovskite nickelates.",1702.00273v1
2017/3/30,Interplay of dilution and magnetic field in the nearest-neighbor spin-ice model on the pyrochlore lattice,"We study the magnetic field effects on the diluted spin-ice materials using
the replica-exchange Monte Carlo simulation. We observe five plateaus in the
magnetization curve of the diluted nearest-neighbor spin-ice model on the
pyrochlore lattice when a magnetic field is applied in the [111] direction.
This is in contrast to the case of the pure model with two plateaus. The origin
of five plateaus is investigated from the spin configuration of two
corner-sharing tetrahedra in the case of the diluted model.",1703.10309v1
2017/6/20,Raman scattering of graphene based systems in high magnetic fields,"We review the different results obtained in the last decade in the field of
Raman scattering of graphene based systems, with an applied magnetic field.
Electronic properties of graphene based systems with an applied magnetic field
will first be described. The phonon response in magnetic field, the
magneto-phono resonance, will then be introduced and described in different
systems, including graphene, multilayer graphene and bulk graphite. Electronic
Raman scattering is then be discussed in the context of Landau level
spectroscopy, of electron phonon interaction and of electron-electron
interaction.",1706.06303v2
2017/6/23,On magnetic structure of CuFe2Ge2: constrains from the 57Fe Mossbauer spectroscopy,"57Fe Mossbauer spectroscopy measurements were performed on a powdered
CuFe2Ge2 sample that orders antiferromagnetically at ~ 175 K. Whereas a
paramagnetic doublet was observed above the Neel temperature, a superposition
of paramagnetic doublet and magnetic sextet (in approximately 0.5 : 0.5 ratio)
was observed in the magnetically ordered state, suggesting a magnetic structure
similar to a double-Q spin density wave with half of the Fe paramagnetic and
another half bearing static moment of ~ 0.5 - 1 mu_B. These results call for a
re-evaluation of the recent neutron scattering data and band structure
calculations.",1706.07874v1
2017/6/29,"Off-axis electron holography of magnetic nanostructures: magnetic behavior of Mn rich nanoprecipitates in (Mn,Ga)As system","The Lorentz off-axis electron holography technique is applied to study the
magnetic nature of Mn rich nanoprecipitates in (Mn,Ga)As system. The
effectiveness of this technique is demonstrated in detection of the magnetic
field even for small nanocrystals having an average size down to 20 nm.",1706.09794v1
2017/7/5,Multiband Electronic Structure of Magnetic Quantum Dots: Numerical Studies,"Semiconductor quantum dots (QDs) doped with magnetic impurities have been a
focus of continuous research for a couple of decades. A significant effort has
been devoted to studies of magnetic polarons (MP) in these nanostructures.
These collective states arise through exchange interaction between a carrier
confined in a QD and localized spins of the magnetic impurities (typically:
Mn). We discuss our theoretical description of various MP properties in
self-assembled QDs. We present a self-consistent, temperature-dependent
approach to MPs formed by a valence band hole. We use the Luttinger-Kohn k.p
Hamiltonian to account for the important effects of spin-orbit interaction.",1707.01565v1
2017/7/11,Nature of Magnetoelectric coupling in corundum antiferromagnet Co4Ta2O9,"We study the magnetocapacitance (MC) effect and magnetoelectric (ME) coupling
in spin-flop driven antiferromagnet Co4Ta2O9. The magnetocapacitance data at
high magnetic fields are analyzed by phenomenological Ginzburg-landau theory of
ferroelectromagnets and it is found that change in dielectric constant is
proportional to the square of magnetization. The saturation polarization and
magnetoelectric coupling are estimated to be 52microC/m2 and $\gamma$ = 1.4
x10-3 (emu/g)-2 respectively at 6 Tesla. Electric polarization is achieved
below Neel temperature only when the sample is cooled in the presence of
magnetic field and it is established that the ground state is non-ferroelectric
implying that magnetic lattice does not lead to spontaneous symmetry breaking
in Co4Ta2O9.",1707.03127v1
2017/7/23,Tuning the Magnetic Properties of M-type Hexaferrites,"In this article, common experimental techniques and preparation conditions
adopted for the synthesis of M-type hexaferrites and their influence on the
magnetic properties are briefly reviewed. The effects of various strategies of
cationic substitutions on the properties of the hexaferrites are addressed.
Further, our synthesis and findings on Co-Ti substituted hexaferrites are
presented. It was found that Co-Ti substitution results in improving the
saturation magnetization, and reducing the coercivity down to values favorable
for high density magnetic recording. Also, evidence of inter-particle
interactions in the particulate samples was observed.",1707.07243v1
2017/9/17,Magnetic shape-memory effect in SrRuO$_3$,"Like most perovskites, SrRuO$_3$ exhibits structural phase transitions
associated with rotations of the RuO$_6$ octahedra. The application of moderate
magnetic fields in the ferromagnetically ordered state allows one to fully
control these structural distortions, although the ferromagnetic order occurs
at six times lower temperature than the structural distortion. Our neutron
diffraction and macroscopic measurements unambiguously show that magnetic
fields rearrange structural domains, and that for the field along a cubic
[110]$_c$ direction a fully detwinned crystal is obtained. Subsequent heating
above the Curie temperature causes a magnetic shape-memory effect, where the
initial structural domains recover.",1709.05688v1
2017/11/23,Angle-dependent Weiss oscillations in a nanocorrugated two-dimensional electron gas,"We investigate the diffusive magnetotransport properties of a two-dimensional
electron gas residing in a wrinkled nanostructure. The curved geometry of the
nanostructure renders an effective inhomogeneous magnetic field which, in
turns, yields Weiss oscillations. Since the relative strength of the effective
inhomogeneous magnetic field can be tailored by changing the direction of the
externally applied magnetic field, these Weiss oscillations exhibit a strong
directional dependence. For large external magnetic fields we also find an
anisotropic positive magnetoresistance.",1711.08697v1
2017/12/30,"Electronic, magnetic and ferroelectric properties of rhombohedral AgFeO2: an ab initio study","Using first principle calculations under the framework of density functional
theory we have investigated the electronic structure, magnetism and
ferroelectric polarization in the triangular lattice antiferromagnet AgFeO2,
and its comparison to the isostructural system CuFeO2. Our calculations reveal
that spin orbit interaction plays an important role in determining the magnetic
property of AgFeO2 and is possibly responsible for its different magnetic
ground state in comparison to CuFeO2. Calculations of ferroelectric
polarization of AgFeO2 suggest that the spontaneous polarization arises from
noncollinear spin arrangement via spin-orbit coupling. Our calculations also
indicate that in addition to electronic contribution, the lattice mediated
contribution to the polarization are also important for AgFeO2.",1801.00093v1
2018/1/11,Fullerene Faraday Cage Keeps Magnetic Properties of Inner Cluster Pristine,"Any single molecular magnets (SMM) perspective for application is as good as
its magnetization stability in ambient conditions. Endohedral metallofullerenes
(EMFs) provide a solid basis for promising SMMs. In this study, we investigated
the behavior of functionalized EMFs on a gold surface (EMF-L-Au). Having
followed the systems molecular dynamics paths, we observed that the chemically
locked inner cluster inside fullerene cage will remain locked even at room
temperature due to the ligand-effect. We have located multiple possible minima
with different charge arrangements between EMF-L-Au fragments. Remarkably, the
charge state of the EMF inner cluster remained virtually constant and so
magnetic properties are expected to be untouched.",1801.03808v2
2018/2/2,The Lieb-Schultz-Mattis-type filling constraints in the 1651 magnetic space groups,"We present the first systematic study of the filling constraints to realize a
`trivial' insulator symmetric under magnetic space group $\mathcal{M}$. The
filling $\nu$ must be an integer multiple of $m^{\mathcal{M}}$ to avoid
spontaneous symmetry breaking or fractionalization in gapped phases. We improve
the value of $m^{\mathcal{M}}$ in the literature and prove the tightness of the
constraint for the majority of magnetic space groups. The result may shed light
on the material search of exotic magnets with fractionalization.",1802.00587v2
2018/4/25,New magnetic phases on chiral magenet CsCuCl$_3$ under high pressures,"We study a magnetic phase diagram of CsCuCl3 by a spin wave theory. We
clarify an existence of new magnetic phases, i.e. up-up-down (uud) phase and Y
coplanar phase under a high pressure. We also discuss a magnetic
field(H)-temperature(T) phase diagram under ambient and high pressures.",1804.09481v2
2018/4/26,Rotational magnetocaloric effect of anisotropic giant spin systems,"The magnetocaloric effect, that consists of adiabatic temperature changes in
a varying external magnetic field, appears not only when the amplitude is
changed, but in cases of anisotropic magnetic materials also when the direction
is varied. In this article we investigate the magnetocaloric effect
theoretically for the archetypical single molecule magnets Fe8 and Mn12 that
are rotated with respect to a magnetic field. We complement our calculations
for equilibrium situations with investigations of the influence of
non-equilibrium thermodynamic cycles.",1804.09957v1
2018/8/23,"Bond relaxation, electronic and magnetic behavior of 2D metals structures Y on Li(110) surface","We investigated the bond, electronic and magnetic behavior of adsorption
Yttrium atoms on Lithium (110) surface using a combination of
Bond-order-length-strength(BOLS) correlation and density-functional
theory(DFT). We found that adsorption Y atoms on Li(110) surfaces form
two-dimensional (2D) geometric structures of hexagon, nonagon, solid hexagonal,
quadrangle and triangle. The consistent with the magnetic moment are
6.66{\mu}B, 5.54{\mu}B, 0.28{\mu}B, 1.04{\mu}B, 2.81{\mu}B, respectively. In
addition, this work could pave the way for design new 2D metals electronic and
magnetic properties.",1809.03407v1
2018/10/13,Proposal for measuring magnetism with patterned apertures,"We propose a magnetic measurement method utilizing a patterned post-sample
aperture in a transmission electron microscope. While utilizing electron
magnetic circular dichroism, the method circumvents previous needs to shape the
electron probe to an electron vortex beam or astigmatic beam. The method can be
implemented in standard scanning transmission electron microscopes by replacing
the spectrometer entrance aperture with a specially shaped aperture, hereafter
called ventilator aperture. The proposed setup is expected to work across the
whole range of beam sizes -- from wide parallel beams down to atomic resolution
magnetic spectrum imaging.",1810.05838v1
2018/10/16,Polarized neutron channeling in weakly magnetic films,"We describe a new sensitive method for the investigation of weakly magnetic
films placed inside a tri-layer planar waveguide. Polarized neutrons tunnel
into the waveguide through the surface, channel along the layers and are
emitted from the end face as a narrow and slightly divergent microbeam.
Polarization analysis permits to detect very small magnetization in the order
of a few 10 Gauss. The magnetic film containing the rare-earth element Tb was
investigated using both fixed wavelength and time-of-flight polarized neutron
reflectometers. The experimental results are presented and discussed.",1810.06845v1
2018/11/7,Inhomogeneous Magnetic Field Influence on Magnetic Properties of NiFe/IrMn Thin Film Structures,"We demonstrate how the configuration and magnitude of a magnetic field,
applied during magnetron sputtering of a NiFe/IrMn bilayer, influence the
magnetic properties of the structure, such as hysteresis loop shape,
coercivity, and exchange bias. Furthermore, we illustrate that it is possible
to create a stepwise hysteresis loop in the sample's region with the highest
field gradient. The found features can be used for future sensor applications.",1811.02941v1
2018/11/8,Magnetic-field controlled anomalous refraction in doped semiconductors,"We predict here that a slab made of a doped semiconductor can exhibit
anomalous refraction under the application of a static magnetic field. This
anomalous refraction takes place in the far-infrared range and it occurs for
any angle of incidence. We show that this effect is due to the fact that a
doped semiconductor under a magnetic field can behave, to some extent, as a
hyperbolic metamaterial. We also show that the occurrence of this anomalous
refraction enables a semiconductor slab under a magnetic field to partially
focus the electromagnetic radiation. The remarkable thing in our case is that
we deal with naturally occurring materials and the anomalous refraction can be
tuned at will with an external field.",1811.03574v1
2018/11/12,Choking non-local magnetic damping in exchange biased ferromagnets,"We investigated the temperature dependence of the magnetic damping in the
exchange biased Pt/ Fe50Mn50 /Fe20Ni80 /SiOx multilayers. In samples having a
strong exchange bias, we observed a drastic decrease of the magnetic damping of
the FeNi with increasing temperature up to the blocking temperature. The
results essentially indicate that the non-local enhancement of the magnetic
damping can be choked by the adjacent antiferromagnet and its temperature
dependent exchange bias. We also pointed out that such a strong temperature
dependent damping may be very beneficial for spintronic applications.",1811.04821v1
2018/12/18,Magnetic hard nanobubble: a possible magnetization structure behind the bi-skyrmion,"Transport of intensity equation (TIE) has been applied to process the
simulated and experimental images of the magnetic hard nanobubbles, which were
acquired in the Lorentz transmission electron microscope (LTEM). Systematic
studies demonstrated that the processing parameter in TIE can modulate the
features of the retrieved magnetization and induce the bi-spiral structures
which may be identified as the bi-skyrmions.",1812.07332v2
2019/1/15,On soliton solutions of the time-discrete generalized lattice Heisenberg magnet model,"Generalized lattice Heisenberg magnet model is an integrable model exhibiting
soliton solutions. The model is physically important for describing the magnon
bound states (or soliton excitations) with arbitrary spin, in magnetic
materials. In this paper, a time-discrete generalized lattice Heisenberg magnet
(GLHM) model is investigated. By writing down the Lax pair representation of
the time-discrete GLHM model, we present explicitly the underlying integrable
structure like, the Darboux transformation and soliton solutions.",1901.04671v1
2019/1/28,Manipulation of magnetization in Pd(100) ultrathin films with quantum well structure using modification of Schottky barrier potentials,"The magnetization of Pd(100) ultrathin films that show ferromagnetism due to
quantum well states was manipulated by changing the quantum well state with an
applied bias voltage. The voltage dependence of the magnetic moment of
Pd/SrTiO$_{3-x}$/Ti/Au intrinsically depends on the Pd film thickness. The
induced change in the magnetic moment is due to the modulation of the phase
shift at the interface between the Pd thin film and the semiconductor
SrTiO$_{3-x}$ substrate.",1901.09481v1
2019/2/24,Theory of Magnetism-Driven Negative Thermal Expansion in Inverse Perovskite Antiferromagnets,"Magnetism-induced negative thermal expansion (NTE) observed in inverse
perovskite antiferromagnets Mn3AN (A=Zn, Ga, etc.) is theoretically studied by
a classical spin model with competing bond-length-dependent exchange
interactions. We numerically reproduce the crystal-volume expansion upon
cooling triggered by a non-coplanar antiferromagnetic order and show that the
expansion occurs so as to maximize an energy gain of the nearest-neighbor
antiferromagnetic interactions. This mechanism is not specific to inverse
perovskite magnets and might also be expected in magnets with other crystal
structures. We propose other candidate crystal structures that might exhibit
NTE through this mechanism.",1902.08904v1
2019/4/17,Planar Sensor for RF Characterization of magnetic samples,"A magnetic measurement of the bar shaped test specimen placed inside the
planar sensor is presented. A magnetic material characterization approach using
planar cavity is proposed in this work. The proposed planar sensor relaxes the
main limitations of conventional approach by using the proper feeding section.
The proposed sensor is numerically verified using the full wave EM simulator
for the magnetic property estimation. It is found that the developed sensor is
able to characterize the test specimen with improved accuracy than that of
conventional approach.",1904.08072v3
2019/7/6,Angle-resolved broadband ferromagnetic resonance apparatus enabled through a spring-loaded sample mounting manipulator,"Broadband ferromagnetic resonance is a useful technique to determine the
magnetic anisotropy and study the magnetization dynamics of magnetic thin
films. We report a spring-loaded sample loading manipulator for reliable sample
mounting and rotation. The manipulator enables maximum signal, enhances system
stability and is particularly useful for fully automated in-plane-field
angle-resolved measurements. This angle-resolved broadband ferromagnetic
resonance apparatus provides a viable method to study anisotropic damping and
weak magnetic anisotropies, both vital for fundamental research and
applications.",1907.03097v1
2019/9/10,Optimizing magnetoresistive sensor signal-to-noise via pinning field tuning,"The presence of magnetic noise in magnetoresistive-based magnetic sensors
degrades their detection limit at low frequencies. In this paper, different
ways of stabilizing the magnetic sensing layer to suppress magnetic noise are
investigated by applying a pinning field, either by an external field,
internally in the stack or by shape anisotropy. We show that these three
methods are equivalent, could be combined and that there is a competition
between noise suppression and sensitivity reduction, which results in an
optimum total pinning field, for which the detection limit of the sensor is
improved up to a factor of ten.",1909.04531v1
2019/12/16,Topological magnetotorsional effect in Weyl semimetals,"In this work we introduce a thermal magnetotorsional effect (TME) as a novel
topological response in magnetic Weyl semimetals. We predict that magnetization
gradients perpendicular to the Weyl node separation give rise to temperature
gradients depending only on the local positions of the Weyl nodes. The TME is a
consequence of magnetization-induced effective torsional spacetime geometry and
the finite temperature Nieh-Yan anomaly. Similarly to anomalous Hall effect and
chiral anomaly, the TME has a universal material-independent form. We predict
that the TME can be observed in magnetic Weyl semimetal EuCd$_2$As$_2$.",1912.07732v2
2020/1/18,Synthesis of Fe$_3$O$_4$ nanoparticles and their magnetic properties,"Fe$_3$O$_4$ magnetic nanoparticles (MNPs) were synthesized by a
co-precipitation method using sodium citrate and oleic acid as modifiers. Phase
composition and microstructure analysis indicate that the sodium citrate and
oleic acid have been successfully grafted onto the surface of Fe$_3$O$_4$ MNPs.
The magnetic behaviors reveal that the modification can decrease the saturation
magnetization of Fe$_3$O$_4$ MNPs due to the surface effect. Fe$_3$O$_4$ MNPs
modified by sodiumcitrate and oleic acid show excellent dispersion capability,
which should be ascribed to the great reduction of high surface energy and
dipolar attraction of the nanoparticles.",2001.06583v1
2020/2/19,Pressure effect on the order-disorder transformation in L1$_0$ FeNi,"The ordered phase of the FeNi system is known to have promising magnetic
properties as a rare-earth-free permanent magnet. Understanding the parameter
space that controls the order-disorder transformation is important to find
growth conditions that stabilize the $L1_0$ phase. Magnetic properties and
chemical order-disorder transformation of FeNi are investigated as a function
of lattice expansion using first-principles theory. Thermodynamic and magnetic
calculations are performed using long-range order parameters, which is used to
find the ordering temperature. Negative pressure promotes ordering and thus
synthetic routes involving an increase in volume is expected to expand the
stability field of the $L1_0$ phase.",2002.08076v1
2020/3/28,Magnon binding in BaCdVO(PO$_4$)$_2$,"The bond-nematic state has both long-range ordering of magnetic quadrupoles
and the high entanglement typical of spin liquids, and as such can be thought
of as a spin liquid crystal. One of the most promising materials in which to
find such a state is BaCdVO(PO$_4$)$_2$, in which a magnetically silent phase
has been found between a magnetically ordered low-field phase and the
high-field polarised phase. Here I study the magnetic Hamiltonian of
BaCdVO(PO$_4$)$_2$, and, for the Hamiltonian-parameters determined by fits to
inelastic neutron scattering experiments, show that magnons condense out of the
polarised state as bound pairs. This is direct theoretical support for the
existence of a bond-nematic state just below the saturation field.",2003.12747v1
2020/5/25,Multiple Spin-Phonon Relaxation Pathways in a Kramer Single-Ion Magnet,"We present a first-principles investigation of spin-phonon relaxation in a
molecular crystal of Co(II) single-ion magnets. Our study combines electronic
structure calculations with machine-learning force fields and unravels the
nature of both the Orbach and the Raman relaxation channels in terms of
atomistic processes. We find that although both mechanisms are mediated by the
excited spin states, the low temperature spin dynamics is dominated by phonons
in the THz energy range, which partially suppress the benefit of having a large
magnetic anisotropy. This study also determines the importance of
intra-molecular motions for both the relaxation mechanisms and paves the way to
the rational design of a new generation of single-ion magnets with tailored
spin-phonon coupling.",2005.12429v1
2020/7/25,Controlling the helicity of magnetic skyrmions by electrical field in frustrated magnets,"The skyrmions generated by frustration in centrosymmetric structures host
extra internal degrees of freedom: vorticity and helicity, resulting in
distinctive properties and potential functionality, which are not shared by the
skyrmions stemming from the Dzyaloshinskii-Moriya interaction in
noncentrosymmetric structures. The present work indicates that the
magnetism-driven electric polarization carried by skyrmions provides a direct
handle for tuning helicity. Especially for the in-plane magnetized skyrmions,
the helicity can be continuously rotated and exactly picked by applying an
external electric field for both skyrmions and antiskyrmions. The in-plane
uniaxial anisotropy is beneficial to this manipulation.",2007.12822v1
2020/8/3,Physical foundations and basic properties of magnetic skyrmions,"Magnetic skyrmions (or vortices) are spatially inhomogeneous spin textures
localized in nanoscale cylindrical regions. Topological protection and small
size make skyrmions especially attractive for the study of spin topology and
technologies wherein information is carried by the electron spin further to, or
instead of the electron charge. Despite achievements in the synthesis of
materials where axisymmetric magnetic skyrmions can be stabilized and
characterized, there is disproportionate progress in elucidating the basic
properties. The Perspective aims to bridge this gap and deliver an intelligible
guide on the physical principles governing these magnetic whirls.",2008.00641v1
2020/8/1,Magnetic ratchet effect in phosphorene,"The magnetic ratchet effect has been studied in phosphorene by the use of the
Boltzmann kinetic equation that is a semi-classical approach. The Hamiltonian
of phosphorene in a steady parallel magnetic field is derived using the
tight-binding model. We consider the effect of the magnetic field on
non--linear dynamics in the presence of an ac laser field and spatial inversion
asymmetry. We have shown that for anisotropic 2D materials and phosphorene, the
ratchet current has the response to three different light polarizations:
linearly polarized light, circularly polarized light, and unpolarized light.",2008.01561v3
2020/8/7,Anisotropic Ultrafast Spin Dynamics in Epitaxial Cobalt,"We investigate the ultrafast spin dynamics in an epitaxial hcp(1100) cobalt
thin film. By performing pump-probe magneto-optical measurements with the
magnetization along either the easy or hard magnetic axis, we determine the
demagnetization and recovery times for the two axes. We observe a 35% slower
dynamics along the easy magnetization axis, which we attribute to
magneto-crystalline anisotropy of the electron-phonon coupling, supported by
our ab initio calculations. This points towards an unambiguous and previously
undisclosed role of anisotropic electron-lattice coupling in ultrafast
magnetism.",2008.03119v1
2020/11/9,Proposal for a scalable charging-energy-protected topological qubit in a quantum spin Hall system,"The quantum spin Hall edge is predicted to reliably produce Majorana zero
modes on the border between magnetic insulator- and superconductor-proximitized
regions of the edge. The direction of magnetization determines the size of the
induced magnetic gap and can control the resulting tunnel barrier. Here we
propose a way to avoid magnetic manipulations of the material and use
electric-only local control of the barrier. We follow with a design of a
charging-energy-protected qubit and a layout of a quantum computer based on the
quantum spin Hall effect. We estimate relevant scales and show that they allow
for testing of these ideas in the near future.",2011.04691v1
2020/11/12,Antiferromagnetically ordered state in the half-filled Hubbard model on the Socolar dodecagonal tiling,"We investigate the antiferromagnetically ordered state in the half-filled
Hubbard model on the Socolar dodecagonal tiling. When the interaction is
introduced, the staggered magnetizations suddenly appear, which results from
the existence of the macroscopically degenerate states in the tightbinding
model. The increase of the interaction strength monotonically increases the
magnetizations although its magnitude depends on the local environments.
Magnetization profile is discussed in the perpendicular space. The similarity
and difference are also addressed in magnetic properties in the Hubbard model
on the Penrose, Ammann-Beenker, and Socolar dodecagonal tilings.",2011.06160v1
2020/11/28,Quantum body in uniform magnetic fields,"In this article it will be presented the first attempt made in order to
perform gauge invariant calculations of eigenstates of a quantum body in its
condensed phase, the latter reacting to an external uniform magnetic field. The
target is achieved introducing a new unitary translation operator transforming
eigenstates into a new set of eigenstates having different total linear
momentum. This new quantum representation solves the problem of calculating the
magnetic response of quantum eigenstates of finite or either infinite periodic
systems to uniform magnetic fields, where equivalence between the customarily
used representation and the new representation has been made.",2011.14082v1
2020/12/15,Dynamically stabilized spin superfluidity in frustrated magnets,"We study the onset of spin superfluidity, namely coherent spin transport
mediated by a topological spin texture, in frustrated exchange-dominated
magnetic systems, engendered by an external magnetic field. We show that for
typical device geometries used in nonlocal magnetotransport experiments, the
magnetic field stabilizes a spin superflow against fluctuations, up to a
critical current. For a given current, the critical field depends on the
precessional frequency of the texture, which can be separately controlled. We
contrast such dynamic stabilization of a spin superfluid to the conventional
approaches based on topological stabilization.",2012.08340v1
2021/1/15,"Frustration, strain and phase co-existence in the mixed valent hexagonal iridate Ba$_{3}$NaIr$_{2}$O$_{9}$","Using detailed synchrotron diffraction, magnetization, thermodynamic and
transport measurements, we investigate the relationship between the mixed
valence of Ir, lattice strain and the resultant structural and magnetic ground
states in the geometrically frustrated triple perovskite iridate
Ba$_{3}$NaIr$_{2}$O$_{9}$. We observe a complex interplay between lattice
strain and structural phase co-existence, which is in sharp contrast to what is
typically observed in this family of compounds. The low temperature magnetic
ground state is characterized by the absence of long range order, and points
towards the condensation of a cluster glass state from an extended regime of
short range magnetic correlations.",2101.06075v1
2021/1/25,Magnetized Reissner-Nordstrom-Taub-NUT spacetime and microscopic entropy,"We present a novel solution describing magnetized spacetime outside a massive
object with electric charge equipped with NUT parameter. To get the solution,
we employ the Ernst magnetization to the Reissner-Nordstrom-Taub-NUT spacetime
as the seed. After discussing some physical aspects of the spacetime, we show
that the extremal entropy of a magnetized Reissner-Nordstrom-Taub-NUT black
hole can be reproduced by using the Cardy formula.",2101.10302v3
2021/1/27,Magnetic Particles for Multidimensional In-vitro Bioanalysis,"Multidimensional or multiplex bioanalysis represents a crucial approach to
improve diagnostic precision, increase assay throughput and advance fundamental
discoveries in analytical industry, life science and nanomedicine. Along this
line, bio-interfacing magnetic particles have been playing an important role.
Fully exploiting the properties of magnetic particles is the key to tailoring
recent technology development for better translational outcomes. In this
mini-review, typical magnetophysical dimensions of magnetic particles are
introduced. Recent progress of implementing these dimensions with advanced
sensor and actuator technologies in multiplex bioanalysis is discussed.
Outlooks on potential biomedical applications and challenges are provided.",2101.11195v1
2021/1/30,Nearly ideal memristive functionality based on viscous magnetization dynamics,"We experimentally demonstrate a proof-of-principle implementation of an
almost ideal memristor - a two-terminal circuit element whose resistance is
approximately proportional to the integral of the input signal over time. The
demonstrated device is based on a thin-film ferromagnet/antiferromagnet
bilayer, where magnetic frustration results in viscous magnetization dynamics
enabling memristive functionality, while the external magnetic field plays the
role of the driving input. The demonstrated memristor concept is amenable to
downscaling and can be adapted for electronic driving, making it attractive for
applications in neuromorphic circuits.",2102.00123v1
2021/3/25,Compact susceptometer for studies under transverse field geometries at very low temperatures,"We present the design of a compact AC susceptometer for studies under
arbitrarily oriented static magnetic fields, in particular magnetic fields
oriented transverse to the AC excitation field. The small size of the
susceptometer permits versatile use in conventional cryostats with
superconducting magnet systems. The design of the susceptometer minimizes
parasitic signal contributions while providing excellent thermal anchoring
suitable for measurements in a wide range down to very low temperatures. The
performance is illustrated by means of measurements of the transverse
susceptibility at the magnetic field tuned quantum phase transition of the
dipolar-coupled Ising ferromagnet LiHoF$_4$.",2103.13637v1
2021/4/25,High Pressure RTSC-Hydrides are Extreme Hard Type-II Superconductors,"It is argued that most of the RTSC hydrides are intrinsic hard type-II
superconductors with strong pinning effects. The pinning centers are long
columnar-like defects, with the radius of the order of the superconducting
coherence length. The core and electromagnetic pinning are both equally
operative, thus giving maximal pinning potential when vortices are oriented
along the columnar axis. The theory predicts: (i) large critical currents, (ii)
huge decrease of the temperature broadening of the resistance in magnetic field
compared with standard superconductors, (iii) large magnetization hysteresis,
(iv) the magnetic irreversible line is pushed toward the second critical field
and magnetization relaxation is much slower. That the RTSC-hydrides are hard
type-II SC can give rise to new physics in these materials.",2104.12214v1
2021/4/27,Field-driven dynamics of magnetic Hopfions,"We present micromagnetic simulations on resonant spin wave modes of magnetic
Hopfions up to 15 GHz driven by external magnetic fields. A sharp transition is
found around 32 mT coinciding with a transition from Hopfions to magnetic
torons. The modes exhibit characteristic amplitudes in frequency space
accompanied by unique localization patterns in real space, and are found to be
robust to damping around topological features, particularly vortex lines in
Hopfions and Bloch points in torons. The marked differences in spin wave
spectra between Hopfions, torons and target skyrmions can serve as fingerprints
in future experimental validation studies of these novel 3d topological spin
textures.",2104.13349v1
2021/5/23,Ab initio investigation of impurity ferromagnetism in the Pd1-xFex alloys: concentration and position dependence,"We present the ab initio results of the structural and magnetic properties of
the Pd host matrix implanted with Fe solute atoms at various concentrations. By
means of density functional theory we confirm that iron impurities are able to
initialize significant magnetization of the Pd atoms, when the impurity
consentation exceeds 3 at.%. Besides, we demonstrate that the imposed
magnetization depends on impurity positions in the host matrix, in particular,
there is a maximum of magnetization for a uniform distribution of the iron
impurity.",2105.10918v1
2021/11/10,Observation of spontaneous x-ray magnetic circular dichroism in a chiral antiferromagnet,"X-ray magnetic circular dichroism (XMCD) signals are usually absent in
antiferromagnets. In this letter, we report the observation of spontaneous XMCD
spectra originating from the inverse triangular spin structure, or the
polarization of the cluster magnetic octupole, in the chiral antiferromagnet
Mn$_{3}$Sn thin film. The result is consistent with the recent theoretical
predictions that the inverse triangular spin structure can give rise to finite
XMCD signals in the absence of net magnetization [J. Phys. Soc. Jpn. 89, 083703
(2020) and Phys. Rev. Lett. 126, 157402 (2021)].",2111.05465v1
2022/3/27,Quantized and half-quantized Anomalous Hall effect induced by in-plane magnetic field,"In this paper we propose that, quantized and nearly half-quantized intrinsic
anomalous Hall effect can be induced by in-plane external magnetic field
through the Zeeman coupling in non-magnetic 2D systems with sizeable
spin-orbital coupling but without two-fold rotational symmetry. An analytical
result is derived for 2D electron gas model with $C_{3v}$ symmetry. Based on
the $\boldsymbol{k\cdot p}$ Hamiltonian derived from first principle
calculations, we find that quantized and nearly half-quantized conductance can
be observed in $\mathrm{Sb_2Te_3}$ thin film in the clean limit with strong
in-plane magnetic field $B>20\ \mathrm{T}$ and low temperature $T<100\
\mathrm{mK}$.",2203.14301v1
2022/6/13,Configurational entropy of skyrmions and half-skyrmions in planar magnetic elements,"This works deals with the presence of localized planar structures in magnetic
materials that admit integer or half-integer topological charge. We study
models in which the internal disposition of magnetization is driven by a single
parameter, that controls the topological charge density of the magnetic
structure. In particular, we focus mainly on the configurational entropy of
these skyrmions and half-skyrmions and show how to increase or diminish their
informational capabilities.",2206.06351v1
2022/7/6,Magnetic Skyrmions: Theory and Applications,"Using the field theory method and coherent spin state approach, we
investigate properties of magnetic solitons in spacetime while focussing on 1D
kinks, 2D and 3D skyrmions. We also study the case of a rigid skyrmion
dissolved in a magnetic background induced by the electronic spins; and derive
the effective rigid skyrmion equation of motion. We investigate as well the
interaction between an electron and a 3D skyrmion.",2207.02892v1
2022/8/3,Electrical transport and magnetic properties of the triangular-lattice compound Zr$_2$NiP$_2$,"We report the first investigation of the electrical and magnetic properties
of the triangular-lattice compound Zr$_2$NiP$_2$ (space group $P$6$_3$/$mmc$).
The temperature evolution of electrical resistivity follows the
Bloch-Gr\""uneisen-Mott law, and exhibits a typically metallic behavior. No
transition is visible by both electrical and magnetic property measurements,
and nearly no magnetization is detected ($M_0$ $<$ 0.002$\mu_\mathrm{B}$/Ni)
down to 1.8 K up to 7 T. The metallic and nonmagnetic characters are well
understood by the first-principles calculations for Zr$_2$NiP$_2$.",2208.01799v1
2022/11/12,Spin Nematic Liquid of the $S=1/2$ Distorted Diamond Spin Chain in Magnetic Field,"The magnetization process of the $S=1/2$ distorted diamond spin chain with
the anisotropic ferromagnetic interaction is investigated using the numerical
diagonalization of finite-size clusters. It is found that the spin nematic and
SDW Tomonaga-Luttinger liquids can appear for sufficiently large easy axis
anisotropy.",2211.06618v1
2023/2/3,Spectral Theorems for Generalized Weyl Nodes with Impurities in a Magnetic Field,"We prove a few spectral theorems for the density of states of a Weyl node
with arbitrary topology. We show that the density of extended states of a Weyl
node with random impurity potentials remains gapless in the presence of a
magnetic field. Therefore, a magnetic field precludes Anderson localization in
Weyl semi-metals, when inter-node transitions are suppressed for smooth enough
potentials. We also provide a rigorous quantum mechanical proof of the chiral
magnetic effect for arbitrary topology of a Weyl node.",2302.02955v2
2023/2/16,First-principles calculations of magnetic states in pyrochlores using a source-corrected exchange and correlation functional,"We present a first-principles investigation of the spin-ice state in
Dy$_2$Ti$_2$O$_7$ using a magnetic source-free exchange and correlation
functional, implemented in the Castep electronic-structure code. By comparing
results from the conventional local spin-density approximation, we show that a
spin-ice state in Dy$_2$Ti$_2$O$_7$ can be reliably obtained by removing the
magnetic sources from the exchange and correlation contributions to the
potential, and we contrast this against the computed ground states of other
frustrated pyrochlore magnets.",2302.08564v1
2023/3/5,The Fractional Orbital Chern Hall Effect,"The fractional quantum hall effect (FQHE) is a milestone of modern day
physics, its disovery paved the way for the study of fractional charges which
do not obey abelian physics. However, all FQHE require an external magnetic
field in order for there to be fractionally charged electrons. This work shows
a theoretical study of strongly interaction electrons in the Kagome lattice
with magnetism. Under optimal conditions, a band gap opens on the surface of
the material which hosts fractional Fermions. These fractional Fermions form
composite quasi-electrons without the need for external magnetic field. These
states are predicted to host the FQHE without the need for an external magnetic
field.",2303.02734v1
2023/3/20,"Anapole, chiral and orbital states in Mn3Si2Te6","The ferrimagnet Mn3Si2Te6 attracts attention because of a recently discovered
colossal magnetoresistance (CMR) with unique magnetic field properties. An
improved magnetic structure for the material has emerged from a neutron
diffraction study linked to understanding the CMR. A deeper theoretical
investigation of the magnetic structure has now revealed anapole, chiral and
orbital states of manganese ions not previously mentioned. Moreover, it is
shown that existence of these states in the low temperature form of Mn3Si2Te6,
with a magnetic field applied, can be tested by neutron and resonant x-ray
diffraction.",2303.10979v2
2023/3/28,Role of intersublattice exchange interaction on ultrafast longitudinal and transverse magnetization dynamics in Permalloy,"We report about element specific measurements of ultrafast demagnetization
and magnetization precession damping in Permalloy (Py) thin films.
Magnetization dynamics induced by optical pump at $1.5$eV is probed
simultaneously at the $M_{2,3}$ edges of Ni and Fe with High order Harmonics
for moderate demagnetization rates (less than $50$%). The role of the
intersublattice exchange interaction on both longitudinal and transverse
dynamics is analyzed with a Landau Lifshitz Bloch description of
ferromagnetically coupled Fe and Ni sublattices. It is shown that the
intersublattice exchange interaction governs the dissipation during
demagnetization as well as precession damping of the magnetization vector.",2303.15837v1
2023/4/1,All-optical magnetization control in CrI$_3$ monolayers: a microscopic theory,"Bright excitons in ferromagnetic monolayers CrI$_3$ efficiently interact with
lattice magnetization, which makes possible all-optical resonant magnetization
control in this material. Using the combination of ab-initio simulations within
Bethe-Salpeter approach, semiconductor Bloch equations and Landau-Lifshitz
equations, we construct a microscopic theory of this effect. Solving
numerically the resulting system of the coupled equations describing the
dynamics of atomic spins and spins of the excitons, we demonstrate the
possibility of a tunable control of macroscopic magnetization of a sample.",2304.00331v2
2023/7/3,A Study of Electronic and Magnetic Properties of Transition Metal Trihalides,"We present the electronic and magnetic structure calculations of VCl3, VBr3,
CrCl3 and CrBr3. The results are obtained by density functional theory with
plane wave basis sets. The trihalides generally optimize either in trigonal or
monoclinic structures. We have focused on the effect of symmetry on the
electronic and magnetic properties of the systems. We have found that magnetic
moments change considerably depending on the symmetry. Both CrX3 have shown a
bandgap around 2eV while the V-based systems have shown half-metallic
properties.",2307.00693v1
2023/6/20,Magneto-optical-electric joint-measurement scanning imaging system for identification of two-dimensional vdW multiferroic,"As an advanced imaging system, the magneto-optical-electric joint-measurement
scanning imaging system (MOEJSI) brings spectroscopic techniques with unmatched
spatial resolution to very low temperature, high magnetic field and high
electric field measurements. It was developed for investigating the magnetic
and ferroelectric properties and their mutual control through
magneto-optical-electric joint-measurements, besides Raman and
photoluminescence features. In particular, the reflective magnetic circular
dichroism (RMCD) loops and imaging, linear dichroism (LD) imaging and
polarization-electric field hysteresis loop can be achieved when simultaneously
applied high magnetic field (7 T) and electric field (100 V) at low temperature
of 10 K.",2307.05363v1
2023/7/19,Electrons in helical magnetic field: a new class of topological metals,"Two theorems on electron states in helimagnets are proved. They reveal a
Kramers-like degeneracy in helical magnetic field. Since a commensurate helical
magnetic system is transitionally invariant with two multiple periods (ordinary
translations and generalized ones with rotations), the band structure turns out
to be topologically nontrivial. Together with the degeneracy, this gives an
unusual spin structure of electron bands. A 2D model of nearly free electrons
is proposed to describe conductive hexagonal palladium layers under an
effective field of magnetically ordered CrO$_2$ spacers in PdCrO$_2$. The spin
texture of the Fermi surface leads to abnormal conductivity.",2307.09884v1
2023/9/8,Emergence of Chaos in Magnetic-Field-Driven Skyrmions,"We explore magnetic-field-driven chaos in magnetic skyrmions. Oscillating
magnetic fields induce nonlinear dynamics in skyrmions, arising from the
coupling of the secondary gyrotropic mode with a non-uniform, breathing-like
mode. Through micromagnetic simulations, we observe complex patterns of
hypotrochoidal motion in the orbital trajectories of the skyrmions, which are
interpreted using bifurcation diagrams and local Lyapunov exponents. Our
findings demonstrate that different nonlinear behaviors of skyrmions emerge at
distinct temporal stages, depending on the nonlinear dynamic parameters.
Investigating the abundant dynamic patterns of skyrmions during the emergence
of chaos not only enhances device reliability but also provides useful
guidelines for establishing chaos computing based on skyrmion dynamics.",2309.04243v1
2023/9/26,On the interpretation of flux trapping experiments in hydrides,"In Ref. [1], Minkov et al. reported measurements of the magnetic moment that
remains after a magnetic field is turned on and then turned off for hydride
materials under high pressure in a diamond anvil cell. In Refs. [2,3], Minkov
et al. reported magnetization measurements on the same samples as a function of
applied magnetic field. Here we argue that the latter indicate that the signal
measured in the former does not provide evidence for superconductivity in these
samples. Instead, the measured signal likely originates in ferromagnetism of
either the sample or the background.",2309.14952v1
2023/11/12,Absence of strong magnetic fluctuations or interactions in the normal state of LaNiGa$_2$,"We present nuclear magnetic (NMR) and qudrupole (NQR) resonance and
magnetization data in the normal state of the topological crystalline
superconductor LaNiGa$_2$. We find no evidence of magnetic fluctuations or
enhanced paramagnetism. These results suggest that the time-reversal symmetry
breaking previously reported in the superconducting state of this material is
not driven by strong electron correlations.",2311.06988v1
2023/11/14,Revisit of magnetic orders in 1/1 approximant crystals of Tsai-type quasicrystal from theoretical points of view,"The various magnetic orders observed in approximant crystals of Tsai-type
quasicrystal are important for deepening our understanding of mysterious
magnetism in quasicrystals. Using an icosahedral cluster model with
inter-cluster interactions, we give an intuitive explanation of the mechanism
of magnetic orders previously reported by classical Monte-Carlo simulations for
an approximant-crystal model describing a Gd-based Tsai-type 1/1 approximant
crystal.",2311.08055v1
2023/12/18,Peculiarities of spin-orbit interaction systematically measured in FeCoB nanomagnets,"This study introduces a method to measure strength of spin-orbit interaction
(SO) in a nanomagnet, investigating fundamental phenomena governing magnetic
anisotropy. The method explores the fundamental property of SO in its linear
proportionality to the external magnetic field, a relationship validated
through experimental observation. Systematic study of SO in FeCoB nanomagnets
reveals distinct SO behaviors in bulk and at an interface, its substantial
disparities in single- and multi-layer nanomagnets, intriguing periodic
oscillations in SO strength, and the systematic relationship between SO
strength, demagnetization field, and magnetic anisotropy based on surface
imperfections. These findings provide crucial insights into diverse spin-orbit
interaction behaviors, crucial for understanding and optimizing magnetic
anisotropy and nanomagnet properties.",2312.11056v1
2023/12/22,Magnetic droplet solitons,"Magnetic droplets are nanoscale, non-topological, dynamical solitons that can
be nucleated in different spintronic devices, such as spin torque
nano-oscillators (STNOs) and spin Hall nano-oscillators (SHNOs). This chapter
first briefly discusses the theory of spin current driven dissipative magnetic
droplets in ferromagnetic thin films with uniaxial anisotropy. We then
thoroughly review the research literature on magnetic droplets and their
salient features, as measured using electrical, microwave, and synchrotron
techniques, and as envisaged by micromagnetic simulations. We also touch upon a
closely related soliton, the dynamical skyrmion. Finally, we present an outlook
of new routes in droplet science.",2312.14621v1
2024/1/19,Raman scattering signatures of spinons and triplons in frustrated antiferromagnets,"Magnetically frustrated spin systems compose a significant proportion of
topological quantum spin liquid candidates. Evidence for spin liquids in these
materials comes largely from the detection of fractionalised spin-1/2
quasiparticles, known as spinons. However, the one-dimensional Heisenberg
chain, which is topologically trivial, also hosts spinons. Thus, observing
spinons does not necessarily signify long-range entanglement. Here, we show
that spinons arising from one-dimensional physics leave a clear fingerprint in
magnetic Raman scattering. We achieve this by calculating the magnetic Raman
intensity of coupled Heisenberg chains. Our findings are in excellent agreement
with the magnetic Raman scattering measurements on the anisotropic triangular
antiferromagnet Ca$_3$ReO$_5$Cl$_2$.",2401.10452v1
2024/1/21,Structure-property relationships for weak-ferromagnetic perovskites,"Despite several decades of active experimental and theoretical studies of
rare-earth orthoferrites, the mechanism of the formation of specific magnetic,
magnetoelastic, optical, and magneto-optical properties remains a subject of
discussion. This paper provides an overview of simple theoretical model
approaches to quantitatively describing the structure-property relationships,
in particular, interplay between FeO$_6$ octahedral deformations/rotations and
main magnetic and optic characteristics such as N\'{e}el temperature, overt and
hidden canting of magnetic sublattices, magnetic and magnetoelastic anisotropy,
optic and photoelastic anisotropy.",2401.11424v1
2024/3/7,Re-investigation of Moment Direction in a Kitaev Material $α$-RuCl$_{3}$,"We report X-ray diffraction and resonant elastic X-ray scattering (REXS)
studies on two $\alpha$-RuCl$_{3}$ crystals with distinct magnetic transition
temperatures: T$_{N}$=7.3K and 6.5K. We find that the sample with T$_{N}$=6.5K
exhibits a high degree of structural twinning at low temperature, whereas the
T$_{N}$=7.3K sample primarily comprises a single domain of R$\bar{3}$.
Notwithstanding, both samples exhibit an identical zigzag magnetic structure,
with magnetic moments pointing away from the honeycomb plane by
$\alpha=31(2)^{\circ}$. We argue that the identical ordered moment directions
in these samples suggest that the intralayer magnetic Hamiltonian remains
mostly unchanged regardless of T$_{N}$.",2403.04176v1
2024/3/19,Magnetoelectric coupling at the domain level in polycrystalline ErMnO3,"We explore the impact of a magnetic field on the ferroelectric domain pattern
in polycrystalline hexagonal ErMnO3 at cryogenic temperatures. Utilizing
piezoelectric force microscopy measurements at 1.65 K, we observe modifications
of the topologically protected ferroelectric domain structure induced by the
magnetic field. These alterations likely result from strain induced by the
magnetic field, facilitated by intergranular coupling in polycrystalline
multiferroics. Our findings give insights into the interplay between electric
and magnetic properties at the local scale and represent a so far unexplored
pathway for manipulating topologically protected ferroelectric vortex patterns
in hexagonal manganites.",2403.13168v1
2024/3/31,Chiral Spin Textures Driven by Emergent Spin-Orbit Interaction: A Numerical Study,"We explore numerically the intricate interplay between Berry phases in both
real and momentum spaces within itinerant magnets. This interplay manifests as
an emergent spin-orbit coupling, where charge carriers occupying a Berry-curved
band generate an orbital magnetization, inducing a pseudo-magnetic field
originating in chiral spin textures. Using density-matrix-renormalization-group
techniques, we demonstrate that switching on a band Berry curvature in a
metallic ferromagnetic phase results in chiral magnetic textures. Furthermore,
employing a two-leg strip geometry, we establish a connection between charge
and spin chirality, further supporting this emergent spin-orbit interaction.",2404.00706v2
2018/6/8,The Computational 2D Materials Database: High-Throughput Modeling and Discovery of Atomically Thin Crystals,"We introduce the Computational 2D Materials Database (C2DB), which organises
a variety of structural, thermodynamic, elastic, electronic, magnetic, and
optical properties of around 1500 two-dimensional materials distributed over
more than 30 different crystal structures. Material properties are
systematically calculated by state-of-the art density functional theory and
many-body perturbation theory (G$_0\!$W$\!_0$ and the Bethe-Salpeter Equation
for $\sim$200 materials) following a semi-automated workflow for maximal
consistency and transparency. The C2DB is fully open and can be browsed online
or downloaded in its entirety. In this paper, we describe the workflow behind
the database, present an overview of the properties and materials currently
available, and explore trends and correlations in the data. Moreover, we
identify a large number of new potentially synthesisable 2D materials with
interesting properties targeting applications within spintronics,
(opto-)electronics, and plasmonics. The C2DB offers a comprehensive and easily
accessible overview of the rapidly expanding family of 2D materials and forms
an ideal platform for computational modeling and design of new 2D materials and
van der Waals heterostructures.",1806.03173v2
2018/6/25,A materials informatics approach to the identification of one-band correlated materials analogous to the cuprates,"One important yet exceedingly rare property of the cuprate high-temperature
superconductors is the presence of a single correlated $d$ band in the
low-energy spectrum, leading to the one-band Hubbard model as the minimal
description. In order to search for materials with interesting strong
correlation physics as well as possible benchmark systems for the one-band
Hubbard model, here we present a new approach to find one-band correlated
materials analogous to the cuprates by leveraging the emerging area of
materials informatics. Using the composition, structure, and formation energy
of more than half a million real and hypothetical inorganic crystalline
materials in the Open Quantum Materials Database, we search for synthesizable
materials whose nominal transition metal $d$ electron count and crystal field
are compatible with achieving an isolated half-filled $d$ band. Five Cu
compounds, including bromide, oxide, selenate, and pyrophosphate chemistries,
are shown to successfully achieve the one-band electronic structure based on
density functional theory band structure calculations. Further calculations
including magnetism and explicit on-site Coulomb interaction reveal significant
evidence for strong correlation physics in the five candidates, including Mott
insulating behavior and antiferromagnetism. The success of our data-driven
approach to discovering new correlated materials opens up new avenues to design
and discover materials with rare electronic properties.",1806.09662v1
2021/6/1,Topological Materials Discovery from Crystal Symmetry,"Topological materials discovery has evolved at a rapid pace over the past 15
years following the identification of the first nonmagnetic topological
insulators (TIs), topological crystalline insulators (TCIs), and 3D topological
semimetals (TSMs). Most recently, through complete analyses of symmetry-allowed
band structures - including the theory of Topological Quantum Chemistry (TQC) -
researchers have determined crystal-symmetry-enhanced Wilson-loop and complete
symmetry-based indicators for nonmagnetic topological phases, leading to the
discovery of higher-order TCIs and TSMs. The recent application of TQC and
related methods to high-throughput materials discovery has revealed that over
half of all of the known stoichiometric, solid-state, nonmagnetic materials are
topological at the Fermi level, over 85% of the known stoichiometric materials
host energetically isolated topological bands, and that just under $2/3$ of the
energetically isolated bands in known materials carry the stable topology of a
TI or TCI. In this Review, we survey topological electronic materials discovery
in nonmagnetic crystalline solids from the prediction of the first 2D and 3D
TIs to the recently introduced methods that have facilitated large-scale
searches for topological materials. We also discuss future venues for the
identification and manipulation of solid-state topological phases, including
charge-density-wave compounds, magnetic materials, and 2D few-layer devices.",2106.00709v2
2017/1/5,Magnetic switching in granular FePt layers promoted by near-field laser enhancement,"Light-matter interaction at the nanoscale in magnetic materials is a topic of
intense research in view of potential applications in next-generation
high-density magnetic recording. Laser-assisted switching provides a pathway
for overcoming the material constraints of high-anisotropy and high-packing
density media, though much about the dynamics of the switching process remains
unexplored. We use ultrafast small-angle x-ray scattering at an x-ray
free-electron laser to probe the magnetic switching dynamics of FePt
nanoparticles embedded in a carbon matrix following excitation by an optical
femtosecond laser pulse. We observe that the combination of laser excitation
and applied static magnetic field, one order of magnitude smaller than the
coercive field, can overcome the magnetic anisotropy barrier between ""up"" and
""down"" magnetization, enabling magnetization switching. This magnetic switching
is found to be inhomogeneous throughout the material, with some individual FePt
nanoparticles neither switching nor demagnetizing. The origin of this behavior
is identified as the near-field modification of the incident laser radiation
around FePt nanoparticles. The fraction of not-switching nanoparticles is
influenced by the heat flow between FePt and a heat-sink layer.",1701.01237v1
2017/8/17,"Effect of Fe and Co substitution on martensitic stability, elastic, electronic and magnetic properties of Mn$_2$NiGa: insights from \textit{ab initio} calculations","We investigate the effects of Fe and Co substitutions on the phase stability
of the martensitic phase, mechanical, electronic and magnetic properties of
magnetic shape memory system Mn$_{2}$NiGa by first-principles Density
functional theory(DFT) calculations. The evolution of these aspects upon
substitution of Fe and Co at different crystallographic sites are investigated
by computing the electronic structure, mechanical properties and magnetic
exchange parameters. We find that the martensitic phase of Mn$_{2}$NiGa
gradually de-stabilises with increase in concentration of Fe/Co due to the
weakening of the minority spin hybridisation of Ni and Mn atoms occupying
crystallographically equivalent sites. The interplay between relative
structural stability and the compositional changes are understood from the
variations in the elastic modulii and electronic structures. We find that the
elastic shear modulus C$^{\prime}$ can be considered as a predictor of
composition dependence of martensitic transformation temperature in substituted
Mn$_{2}$NiGa. The magnetic properties of Mn$_{2}$NiGa are found to be greatly
improved by the substitutions due to stronger ferromagnetic interactions in the
compounds. The gradually weaker(stronger) Jahn-Teller distortion (covalent
bonding) in the minority spin densities of states due to substitutions lead to
a half-metallic like gap in these compounds resulting in materials with high
spin-polarisation when the substitutions are complete. The substitutions at the
Ga site result in two new compounds Mn$_{2}$NiFe and Mn$_{2}$NiCo with very
high magnetic moments and Curie temperatures. Thus, our work indicates that
although the substitutions de-stabilise the martensitic phase in Mn$_{2}$NiGa,
new magnetic materials with very good magnetic parameters and potentially
useful for novel magnetic applications can be obtained.",1708.05146v1
2021/4/21,Atomic Layer Deposition of Yttrium Iron Garnet Thin Films for 3D Magnetic Structures,"A wide variety of new phenomena such as novel magnetization configurations
have been predicted to occur in three dimensional magnetic nanostructures.
However, the fabrication of such structures is often challenging due to the
specific shapes required, such as magnetic tubes and spirals. Furthermore, the
materials currently used to assemble these structures are predominantly
magnetic metals that do not allow to study the magnetic response of the system
separately from the electronic one. In the field of spintronics, the
prototypical material used for such experiments is the ferrimagnetic insulator
yttrium iron garnet (Y$_3$Fe$_5$O$_{12}$, YIG). YIG is one of the best
materials especially for magnonic studies due to its low Gilbert damping. Here,
we report the first successful fabrication of YIG thin films via atomic layer
deposition. To that end we utilize a supercycle approach based on the
combination of sub-nanometer thin layers of the binary systems Fe$_2$O$_3$ and
Y$_2$O$_3$ in the correct atomic ratio on Y$_3$Al$_5$O$_{12}$ substrates with a
subsequent annealing step. Our process is robust against typical growth-related
deviations, ensuring a good reproducibility. The ALD-YIG thin films exhibit a
good crystalline quality as well as magnetic properties comparable to other
deposition techniques. One of the outstanding characteristics of atomic layer
deposition is its ability to conformally coat arbitrarily-shaped substrates.
ALD hence is the ideal deposition technique to grant an extensive freedom in
choosing the shape of the magnetic system. The atomic layer deposition of YIG
enables the fabrication of novel three dimensional magnetic nanostructures,
which in turn can be utilized for experimentally investigating the phenomena
predicted in those structures.",2104.10293v2
2022/11/21,Room Temperature Optically and Magnetically Active Edges in Phosphorene Nanoribbons,"Nanoribbons - nanometer wide strips of a two-dimensional material - are a
unique system in condensed matter physics. They combine the exotic electronic
structures of low-dimensional materials with an enhanced number of exposed
edges, where phenomena including ultralong spin coherence times, quantum
confinement and topologically protected states can emerge. An exciting prospect
for this new material concept is the potential for both a tunable
semiconducting electronic structure and magnetism along the nanoribbon edge.
This combination of magnetism and semiconducting properties is the first step
in unlocking spin-based electronics such as non-volatile transistors, a route
to low-energy computing, and has thus far typically only been observed in doped
semiconductor systems and/or at low temperatures. Here, we report the magnetic
and semiconducting properties of phosphorene nanoribbons (PNRs). Static (SQUID)
and dynamic (EPR) magnetization probes demonstrate that at room temperature,
films of PNRs exhibit macroscopic magnetic properties, arising from their edge,
with internal fields of ~ 250 to 800 mT. In solution, a giant magnetic
anisotropy enables the alignment of PNRs at modest sub-1T fields. By leveraging
this alignment effect, we discover that upon photoexcitation, energy is rapidly
funneled to a dark-exciton state that is localized to the magnetic edge and
coupled to a symmetry-forbidden edge phonon mode. Our results establish PNRs as
a unique candidate system for studying the interplay of magnetism and
semiconducting ground states at room temperature and provide a stepping-stone
towards using low-dimensional nanomaterials in quantum electronics.",2211.11374v1
2023/3/12,Emergence of a Non-van der Waals Magnetic Phase in a van der Waals Ferromagnet,"Manipulation of long-range order in two-dimensional (2D) van der Waals (vdW)
magnetic materials (e.g., CrI$_3$, CrSiTe$_3$ etc.), exfoliated in few-atomic
layer, can be achieved via application of electric field,
mechanical-constraint, interface engineering, or even by chemical
substitution/doping. Usually, active surface oxidation due to the exposure in
the ambient condition and hydrolysis in the presence of water/moisture causes
degradation in magnetic nanosheets which, in turn, affects the
nanoelectronic/spintronic device performance. Counterintuitively, our current
study reveals that exposure to the air at ambient atmosphere results in advent
of a stable nonlayered secondary ferromagnetic phase in the form of
Cr$_2$Te$_3$ (T$_{C2}$ ~ 160 K) in the parent vdW magnetic semiconductor
Cr$_2$Ge$_2$Te$_6$ (T$_{C1}$ ~ 69 K). In addition, the magnetic anisotropy
energy (MAE) enhances in the hybrid by an order from the weakly anisotropic
pristine Cr$_2$Ge$_2$Te$_6$ crystal, increasing the stability of the FM ground
state with time. Comparing with the freshly prepared Cr$_2$Ge$_2$Te$_6$, the
coexistence of the two ferromagnetic phases in the time elapsed bulk crystal is
confirmed through systematic investigation of crystal structure along with
detailed dc/ac magnetic susceptibility, specific heat, and magnetotransport
measurement. To capture the concurrence of the two ferromagnetic phases in a
single material, Ginzburg-Landau theory with two independent order parameters
(as magnetization) with a coupling term can be introduced. In contrast to
rather common poor environmental stability of the vdW magnets, our results open
possibilities of finding air-stable novel materials having multiple magnetic
phases.",2303.06732v1
2023/7/19,Enumeration of spin-space groups: Towards a complete description of symmetries of magnetic orders,"Symmetries of three-dimensional periodic scalar fields are described by 230
space groups (SGs). Symmetries of three-dimensional periodic (pseudo-) vector
fields, however, are described by the spin-space groups (SSGs), which were
initially used to describe the symmetries of magnetic orders. In SSGs, the
real-space and spin degrees of freedom are unlocked in the sense that an
operation could have different spacial and spin rotations. SSGs gives a
complete symmetry description of magnetic structures, and have natural
applications in the band theory of itinerary electrons in magnetically ordered
systems with weak spin-orbit coupling.\textit{Altermagnetism}, a concept raised
recently that belongs to the symmetry-compensated collinear magnetic orders but
has non-relativistic spin splitting, is well described by SSGs. Due to the vast
number and complicated group structures, SSGs have not yet been systematically
enumerated. In this work, we exhaust SSGs based on the invariant subgroups of
SGs, with spin operations constructed from three-dimensional (3D) real
representations of the quotient groups for the invariant subgroups. For
collinear and coplanar magnetic orders, the spin operations can be reduced into
lower dimensional real representations. As the number of SSGs is infinite, we
only consider SSGs that describe magnetic unit cells up to 12 times crystal
unit cells. We obtain 157,289 non-coplanar, 24,788 coplanar-non-collinear, and
1,421 collinear SSGs. The enumerated SSGs are stored in an online database at
\url{https://cmpdc.iphy.ac.cn/ssg} with a user-friendly interface. We also
develop an algorithm to identify SSG for realistic materials and find SSGs for
1,626 magnetic materials. Our results serve as a solid starting point for
further studies of symmetry and topology in magnetically ordered materials.",2307.10371v1
2003/8/14,Resistivity Ratio of Niobium Superconducting Cavities,"Resistivity measurements have been made on Nb cavities, as well as on Pb and
Cu, at 296, 77, and 4.2 K by means of a contactless induced-current method. For
superconductors, a constant magnetic field drives the material normal below the
transition temperature. These measurements provide a simple means for initial
material evaluation as well as a direct means of monitoring the effects of
material parameters (purity, heat treatment, gas incorporation, etc.) on the
electron mean free path. Approximate determinations of Hc, Hc1, and Hc2 can
also be derived from these measurements. Normal-state thermal conductivity and
the Ginzburg-Landau parameter kappa are calculated from the resistivity
measurements.",0308266v1
2007/3/2,The slow dynamics of glassy materials: Insights from computer simulations,"The physics of glasses can be studied from many viewpoints, from material
scientists interested in the development of new materials to statistical
physicists inventing new theoretical tools to deal with disordered systems. In
these lectures I described a variety of physical phenomena observed in actual
glassy materials, from disordered magnetic systems to soft gels. Despite the
very large gap between experimental and numerical time windows, I showed that
computer simulations represent an efficient theoretical tool which can shed
light on the microscopic origins of glassy dynamics.",0703058v1
2002/5/9,Microfabrication of Three-Dimensional Structures in Polymer and Glass by Femtosecond Pulses,"We report three-dimensional laser microfabrication, which enables
microstructuring of materials on the scale of 0.2-1 micrometers. The two
different types of microfabrication demonstrated and discussed in this work are
based on holographic recording, and light-induced damage in transparent
dielectric materials. Both techniques use nonlinear optical excitation of
materials by ultrashort laser pulses (duration < 1 ps).",0205025v1
2007/7/18,"Encapsulation, compensation, and substitution of catalyst particles during continuous growth of carbon nanotubes","By sequential feeding of catalyst materials, it is revealed that the active
growth sites are at the bottom of the carbon nanotubes (CNTs), and that
catalyst particles are constantly encapsulated into nanotubes from the bottom.
This gives a better insight into the mechanism of CNT formation and on ways to
control the growth process. CNTs encapsulated with different materials should
enable the study of their electronic or magnetic properties, with potential
applications as building blocks for nanoelectronics and as fillers in
composites for electromagenetic shielding.",0707.2759v1
2007/10/23,Parametrically Shielding Electromagnetic Fields by Nonlinear Metamaterials,"An analytical theory is developed for parametric interactions in metamaterial
multilayer structures with simultaneous nonlinear electronic and magnetic
responses and with near-zero refractive-index. We demonstrate theoretically
that electromagnetic fields of certain frequencies can be parametrically
shielded by a nonlinear left-handed material slab, where the permittivity and
permeability are both negative. The skin depth is tunable, and even in the
absence of material absorption, can be much less than the wavelength of the
electromagnetic field being shielded. This exotic behavior is a consequence of
the intricate nonlinear response in the left-handed materials and vanishing
optical refractive-index at the pump frequency.",0710.4337v1
2007/10/30,On metallic gratings coated conformally with isotropic negative-phase-velocity materials,"Application of the differential method (also called the C method) to
plane-wave diffraction by a perfectly conducting, sinusoidally corrugated
metallic grating coated with a linear, homogeneous, isotropic, lossless
dielectric-magnetic material shows that coating materials with negative index
of refraction may deliver enhanced maximum nonspecular reflection efficiencies
in comparison to coating materials with positive index of refraction.",0710.5777v1
2008/3/24,Repulsive and restoring Casimir forces with left-handed materials,"We investigate repulsive Casimir force between slabs containing left-handed
materials with controllable electromagnetic properties. The sign of Casimir
force is determined by the electric and magnetic properties of the materials,
and it is shown that the formation of the repulsive force is related to the
wave impedances of two slabs. The sign change of the Casimir force as a
function of the distance is studied. Special emphasis is put on the restoring
Casimir force which may be found to exist between perfectly conducting material
and metamaterial slabs. This restoring force is a natural power for the system
oscillation in vacuum and also can be used for system stabilization.",0803.3382v1
2009/5/2,Implications and consequences of ferromagnetism universally exhibited by inorganic nanoparticles,"Occurrence of surface ferromagnetism in inorganic nanoprticles as a universal
property not only explains many of the unusual magnetic features of oxidic thin
films, but also suggests its possible use in creating new materials, as
exemplified by multiferroic BaTiO3 nanoparticles. While the use of Mn-doped ZnO
and such materials in spintronics appears doubtful, it is possible to have
materials exhibiting coexistence of (bulk) superconductivity with (surface)
ferromagnetism.",0905.0183v1
2009/7/1,"Supplementary material for ""Impurity-induced magnetic order in low dimensional spin gapped materials""","In this supplementary material, we investigate further the impurity-induced
freezing mechanism in a doped system of 3D weakly coupled ladders resembling
Bi(Cu$_{1-x}$Zn$_x$)$_2$ZnPO$_6$ using large scale Quantum Monte Carlo
simulations.",0907.0211v2
2015/1/28,Material Properties at Low Temperature,"From ambient down to cryogenic temperatures, the behaviour of materials
changes greatly. Mechanisms leading to variations in electrical, thermal,
mechanical, and magnetic properties in pure metals, alloys, and insulators are
briefly introduced from a general engineering standpoint. Data sets are
provided for materials commonly used in cryogenic systems for design purposes.",1501.07100v1
2016/7/12,Thermal spin dynamics of yttrium iron garnet,"Yttrium Iron Garnet is the prototypical material used to study pure spin
currents. It is a complex material with 20 magnetic atoms in the unit cell.
Almost all theories and experimental analysis approximates this complicated
material to a simple ferromagnet with a single spin wave mode. We use the
method of atomistic spin dynamics to study the temperature evolution of the
full 20 mode exchange spin wave spectrum. Our results show a strong frequency
dependence of the modes in quantitative agreement with neutron scattering
experiments. We find this causes in a reduction in the net spin pumping due to
the thermal occupation of optical modes with the opposite chirality to the FMR
mode.",1607.03263v1
2016/11/22,Electron spin dynamics of two-dimensional layered materials,"The growing library of two-dimensional layered materials is providing
researchers with a wealth of opportunity to explore and tune physical phenomena
at the nanoscale. Here, we review the experimental and theoretical state-of-art
concerning the electron spin dynamics in graphene, silicene, phosphorene,
transition metal dichalcogenides, covalent heterostructures of organic
molecules and topological materials. The spin transport, chemical and defect
induced magnetic moments, and the effect of spin-orbit coupling and spin
relaxation, are also discussed in relation to the field of spintronics.",1611.07208v1
2018/5/2,"Accurate Cathode Properties of LiNiO2, LiCoO2, and LiMnO2 Using the SCAN Meta-GGA Density Functional","Layered lithium intercalating transition metal (TM) oxides are promising
cathode materials for Li-ion batteries. Here we scrutinize the recently
developed strongly constrained and appropriately normed (SCAN) density
functional method to study structural, magnetic and electrochemical properties
of prototype cathode materials LiNiO2, LiCoO2, and LiMnO2 at different
Li-intercalation limits. We show that SCAN outperforms earlier popular
functional combinations, providing results in considerably better agreement
with experiment without use of Hubbard parameters, and dispersion corrections
are found to have a small effect. In particular, SCAN provides a good
description of the electronic structures, electron densities, band gaps,
predicted cell parameters, and voltage profiles.",1805.00642v1
2020/2/27,Role of non-locality in exchange-correlation for magnetic 2D van der Waals materials,"To obtain accurate independent-particle descriptions for ferromagnetic
two-dimensional van der Waals materials, we apply the quasiparticle
self-consistent $GW$ (QSGW) method to VI$_3$, CrI$_3$, CrGeTe$_3$, and
Fe$_3$GeTe$_2$. QSGW provides a description of the nonlocal
exchange-correlation term in the one-particle Hamiltonian. The nonlocal term is
important not only as the $U$ of density functional theory (DFT)+$U$ but also
for differentiating occupied and unoccupied states in semiconductors. We show
the limitations of DFT+$U$ in mimicking QSGW.",2002.12417v2
2022/6/10,Characteristic Mode Decomposition Using the Scattering Dyadic in Arbitrary Full-Wave Solvers,"Characteristic modes are formulated using the scattering dyadic, which maps
incident plane waves to scattered far fields generated by an object of
arbitrary material composition. Numerical construction of the scattering dyadic
using arbitrary full-wave electromagnetic solvers is demonstrated in examples
involving a variety of dielectric and magnetic materials. Wrapper functions for
computing characteristic modes in method-of-moments, finite-difference time
domain, and finite element solvers are provided as supplementary material.",2206.06783v2
2001/8/14,Diamagnetic Screening of the Magnetic Field in Accreting Neutron Stars,"A possible mechanism for screening of the surface magnetic field of an
accreting neutron star, by the accreted material, is investigated. We model the
material flow in the surface layers of the star by an assumed 2-D velocity
field satisfying all the physical requirements. Using this model velocity we
find that, in the absence of magnetic buoyancy, the surface field is screened
(submergence of the field by advection) within the time scale of material flow
of the top layers. On the other hand, if magnetic buoyancy is present, the
screening happens over a time scale which is characteristic of the slower flow
of the deeper (hence, denser) layers. For accreting neutron stars, this longer
time scale turns out to be about $10^5$ years, which is of the similar order as
the accretion time scale of most massive X-ray binaries.",0108229v2
2002/1/23,Spin Ice State in Frustrated Magnetic Pyrochlore Materials,"A frustrated system is one whose symmetry precludes the possibility that
every pairwise interaction (``bond'') in the system can be satisfied at the
same time. Such systems are common in all areas of physical and biological
science. In the most extreme cases they can have a disordered ground state with
``macroscopic'' degeneracy, that is, one that comprises a huge number of
equivalent states of the same energy. Pauling's description of the low
temperature proton disorder in water ice was perhaps the first recognition of
this phenomenon, and remains the paradigm. In recent years a new class of
magnetic substance has been characterised, in which the disorder of the
magnetic moments at low temperatures is precisely analogous to the proton
disorder in water ice. These substances, known as spin ice materials, are
perhaps the ``cleanest'' examples of such highly frustrated systems yet
discovered. They offer an unparalleled opportunity for the study of frustration
in magnetic systems at both an experimental and a theoretical level. This
article describes the essential physics of spin ice, as it is currently
understood, and identifies new avenues for future research on related materials
and models.",0201427v1
2004/10/22,Magnetic Small World Nanomaterials: Physical Small World Networks,"The question addressed is whether magnetic materials based on physical small
world networks are possible. Physical constraints, such as uniform bond length
and embedding in three dimensions, are the new features added to make small
world networks physical. Results are presented to further determine if physical
small world networks can exist, and the effect of the small world connections
on the critical phenomena of Ising models on such networks. Spectra of the
Laplacian on randomly-collapsed bead-chain networks are studied. The scaling
function for the order parameter of an Ising model with physical small world
connections is presented.",0410589v1
2005/2/23,Enhanced magnetic moment and conductive behavior in NiFe2O4 spinel ultrathin films,"Bulk NiFe2O4 is an insulating ferrimagnet. Here, we report on the epitaxial
growth of spinel NiFe2O4 ultrathin films onto SrTiO3 single-crystals. We will
show that - under appropriate growth conditions - epitaxial stabilization leads
to the formation of a spinel phase with magnetic and electrical properties that
radically differ from those of the bulk material : an enhanced magnetic moment
(Ms) - about 250% larger - and a metallic character. A systematic study of the
thickness dependence of Ms allows to conclude that its enhanced value is due to
an anomalous distribution of the Fe and Ni cations among the A and B sites of
the spinel structure resulting from the off-equilibrium growth conditions and
to interface effects. The relevance of these findings for spinel- and, more
generally, oxide-based heterostructures is discussed. We will argue that this
novel material could be an alternative ferromagetic-metallic electrode in
magnetic tunnel junctions.",0502558v1
2006/3/5,Supplementary Information for: 'Spontaneous Skyrmion Ground States in Magnetic Metals',"Supplementary information for our manuscript, entitled 'Spontaneous Skyrmion
Ground States of Magnetic Metals', cond-mat/0603103, is presented. The physical
nature of the gradient terms of our generalized micromagnetic model for
ferromagnets with softened longitudinal fluctuations is explained. The
relationship of our micromagnetic model with the spin fluctuation theory of
itinerant-electron magnets is discussed. Experimental estimates of the
parameter eta, which accounts for an effective reduced longitudinal stiffness,
are presented for real materials from published polarized neutron scattering
experiments on EuS, Ni and MnSi. The available experimental data clearly show
that eta is significantly reduced for the latter two systems. It is suggested
that particle-hole excitations are at the root of this longitudinal softness in
itinerant-electron ferromagnets. The current status of the experimental
evidence supporting spontaneous, amorphous skyrmion textures in MnSi and other
materials is reviewed. Finally, we also address the general potential of
skyrmion textures in chiral magnets for other fields of physics.",0603104v1
2006/12/12,Magnetic heat conductivity in $\rm\bf CaCu_2O_3$: linear temperature dependence,"We present experimental results for the thermal conductivity $\kappa$ of the
pseudo 2-leg ladder material $\rm CaCu_2O_3$. The strong buckling of the ladder
rungs renders this material a good approximation to a $S=1/2$ Heisenberg-chain.
Despite a strong suppression of the thermal conductivity of this material in
all crystal directions due to inherent disorder, we find a dominant magnetic
contribution $\kappa_\mathrm{mag}$ along the chain direction.
  $\kappa_\mathrm{mag}$ is \textit{linear} in temperature, resembling the
low-temperature limit of the thermal Drude weight $D_\mathrm{th}$ of the
$S=1/2$ Heisenberg chain. The comparison of $\kappa_\mathrm{mag}$ and
$D_\mathrm{th}$ yields a magnetic mean free path of $l_\mathrm{mag}\approx 22
\pm 5$ \AA, in good agreement with magnetic measurements.",0612298v1
2004/1/19,Laser Generated Magnetic Pulses: Hot Electron Propagation in Conducting and Dielectric Material,"We report experimental evidence of electrostatic inhibition of fast
electrons, generated in a highly resistive material upon irradiation with an
intense ultra-short ($10^{16} W/cm^{2}$, $100 fmsec$) laser pulse. The
experiment involves measurement of temporal evolution of self-generated
magnetic pulses using pump-probe polarimetry. A comparison is made between the
temporal behaviour of magnetic pulses generated with Aluminum and Glass
targets. It is found that in contrast to Aluminium, self-generated magnetic
pulse decays much faster in glass. This is attributed to the absence of return
shielding currents in glass, which results in build up of electrostatic field,
which in turn inhibits the movement of fast electrons. Fitting of experimental
measurements using a one dimensional model, yields estimate of conductivity of
Aluminium and glass, and penetration depth of hot electrons in these materials.",0401084v1
2007/6/20,Oxide spintronics,"Concomitant with the development of metal-based spintronics in the late
1980's and 1990's, important advances were made on the growth of high-quality
oxide thin films and heterostructures. While this was at first motivated by the
discovery of high-temperature superconductivity in perovskite Cu oxides, this
technological breakthrough was soon applied to other transition metal oxides,
and notably mixed-valence manganites. The discovery of colossal
magnetoresistance in manganite films triggered an intense research activity on
these materials, but the first notable impact of magnetic oxides in the field
of spintronics was the use of such manganites as electrodes in magnetic tunnel
junctions, yielding tunnel magnetoresistance ratios one order of magnitude
larger than what had been obtained with transition metal electrodes. Since
then, the research on oxide spintronics has been intense with the latest
developments focused on diluted magnetic oxides and more recently on
multiferroics. In this paper, we will review the most important results on
oxide spintronics, emphasizing materials physics as well as spin-dependent
transport phenomena, and finally give some perspectives on how the flurry of
new magnetic oxides could be useful for next-generation spintronics devices.",0706.3015v1
2008/3/2,Structural anisotropy of silica hydrogels prepared under magnetic field,"Birefringence measurements have been carried out on the Pb-doped silica
hydrogels prepared under various magnetic fields up to 5T. The silica gels
prepared at 5T were used as a medium of crystal growth of PbBr2, whose result
implied the structural anisotropy; an aligned array of crystallites was
obtained by transmission electron microscopy. While the samples prepared at 0,
1, and 3T have no birefringence, we found that the samples have negative
birefringence on the order of magnitude 10^-6 as if the direction of the
magnetic field is the optic axis of a uniaxal crystal. To the authors'
knowledge, the birefringent silica hydrogels were obtained by gelation under
magnetic field for the first time. Also, scanning microscopic light scattering
experiments have been performed. The results indicate that the characteristic
length distribution for birefringent samples is narrower than that for
non-birefringent ones.",0803.0114v2
2008/11/27,Two-dimensional magnetism in the pnictide superconductor parent material SrFeAsF probed by muon-spin relaxation,"We report muon-spin relaxation measurements on SrFeAsF, which is the parent
compound of a newly discovered iron-arsenic-fluoride based series of
superconducting materials. We find that this material has very similar magnetic
properties to LaFeAsO, such as separated magnetic and structural transitions
(TN = 120 K, Ts = 175 K), contrasting with SrFe2As2 where they are coincident.
The muon oscillation frequencies fall away very sharply at TN, which suggests
that the magnetic exchange between the layers is weaker than in comparable
oxypnictide compounds. This is consistent with our specific heat measurements,
which find that the entropy change S = 0.05 J/mol/K largely occurs at the
structural transition and there is no anomaly at TN.",0811.4598v1
2009/4/1,The impact of magnetic properties on atom-wall interaction,"The Lifshitz-type formulas for the free energy and Casimir-Polder force
acting between an atom possessing a permanent magnetic moment and a wall made
of different materials are derived. Simple model allowing analytic results is
considered where the atomic magnetic susceptibility is frequency-independent
and wall is made of ideal metal. Numerical computations of the Casimir-Polder
force are performed for H atom interacting with walls made of ideal metal,
nonmagnetic (Au) and ferromagnetic (Fe) metals and of ferromagnetic dielectric.
It is shown that for the first three wall materials the inclusion of the
magnetic moment of an atom decreases and for the fourth material increases the
magnitude of the Casimir-Polder force.",0904.0234v1
2009/4/3,A radical approach to promote multiferroic coupling in double perovskites,"Double perovskites provide a unique opportunity to induce and control
multiferroic behaviors in oxide systems. The appealing possibility to design
materials with a strong coupling between the magnetization and the polarization
fields may be achieved in this family since these magnetic insulators can
present structural self-ordering in the appropriate growth conditions. We have
studied the functional properties of La2CoMnO6 and Bi2CoMnO6 epitaxial thin
films grown by pulsed laser deposition. Cation-ordered La2CoMnO6 films display
a magnetic Curie temperature of 250 K while cation-disordered Bi2CoMnO6 films
present ferromagnetism up to ~ 800 K. Such high transition temperature for
magnetic ordering can be further tuned by varying the strain in the films
indicating an important contribution from the structural characteristics of the
materials. Our approach might be generalized for other oxide systems. At this
end, our results are compared with other multiferroic systems. The roles of
various cations, their arrangements and structural effects are further
discussed.",0904.0615v1
2009/4/13,First-principles theory of the orbital magnetization,"We compute the orbital magnetization in real materials by evaluating a
recently discovered formula for periodic systems, within density functional
theory. We obtain improved values of the orbital magnetization in the
ferromagnetic metals Fe, Co, and Ni, by taking into account the contribution of
the interstitial regions neglected so far in literature. We also use the
orbital magnetization to compute the EPR $g$-tensor in molecules and solids.
The present approach reproduces the $g$-tensor obtained by linear response
(LR), when the spin-orbit can be treated as a perturbation. However, it can
also be applied to radicals and defects with an orbital-degenerate ground-state
or containing heavy atoms, that can not be properly described by LR.",0904.1988v3
2010/1/27,"An anomalous butterfly-shaped magnetoresistance loop in an alloy, Tb4LuSi3","Magnetic-field (H) induced first-order magnetic transition and the assiciated
electronic phase-separation phenomena are active topics of research in
magnetism. Magnetoresistance (MR) is a key property to probe these phenomena
and, in literature, a butterfly-shaped MR loop has been noted while cycling the
field, with the envelope curve lying below the virgin curve in MR versus H
plots of such materials. Here, we report an opposite behavior of MR loop for an
alloy, Tb4LuSi3, at low temperatures (<<20 K) in the magnetically ordered
state. Such an anomalous curve reveals unexpected domination of higher
resistive high-field phase in electronic conduction, unlike in other materials
where conducion is naturally by low-resistive high-field phase that follows
first-order transition. The observed features reveal an unusual electronic
phase separation, namely involving high-resistive high-field phase and
low-resistive virgin phase.",1001.4942v1
2010/3/13,Ferromagnetic Clusters in the Brownmillerite Bilayered Compounds Ca2.5-xLaxSr0.5GaMn2O8: An Approach to Achieve Layered Spintronics Materials,"We report the effect of La-substitution on the magnetic and magnetotransport
properties of Brownmillerite-like bilayered compounds Ca2.5-xLaxSr0.5GaMn2O8 (x
= 0, 0.05, 0.075, and 0.1) by using dc-magnetization, resistivity and
magnetoresistance techniques. The Rietveld analysis of the room temperature
x-ray diffraction patterns confirms no observable change of average crystal
structure with the La-substitution. Both magnetic and magnetotransport
properties are found to be very sensitive to the La-substitution.
Interestingly, the La-substituted compounds show ferromagnetic-like behavior
(due to the occurrence of a double exchange mechanism) whereas, the parent
compound is an antiferromagnet (TN 150 K). All compounds show an insulating
behavior, in the measured temperature range of 100 - 300 K, with an overall
decrease in the resistivity with the substitution. A higher value of
magnetoresistance has been successfully achieved by the La-substitution. We
have proposed an electronic phase separation model, considering the formation
of ferromagnetic clusters in the antiferromagnetic matrix, to interpret the
observed magnetization and magnetotransport results for the La-substituted
samples. The present study demonstrates an approach to achieve new functional
materials, based on naturally occurring layered system like
Ca2.5-xLaxSr0.5GaMn2O8, for possible spintronics applications.",1003.2685v1
2010/10/5,Magnetic Monopole Dynamics in Spin Ice,"One of the most remarkable examples of emergent quasi-particles, is that of
the ""fractionalization"" of magnetic dipoles in the low energy configurations of
materials known as ""spin ice"", into free and unconfined magnetic monopoles
interacting via Coulomb's 1/r law [Castelnovo et. al., Nature, 451, 42-45
(2008)]. Recent experiments have shown that a Coulomb gas of magnetic charges
really does exist at low temperature in these materials and this discovery
provides a new perspective on otherwise largely inaccessible phenomenology. In
this paper, after a review of the different spin ice models, we present
detailed results describing the diffusive dynamics of monopole particles
starting both from the dipolar spin ice model and directly from a Coulomb gas
within the grand canonical ensemble. The diffusive quasi-particle dynamics of
real spin ice materials within ""quantum tunneling"" regime is modeled with
Metropolis dynamics, with the particles constrained to move along an underlying
network of oriented paths, which are classical analogues of the Dirac strings
connecting pairs of Dirac monopoles.",1010.0970v1
2011/1/30,Spin transport in magnetically ordered systems: effect of the lattice relaxation time,"Spin resistivity $R$ has been shown to result mainly from the scattering of
itinerant spins with magnetic impurities and lattice spins. $R$ is proportional
to the spin-spin correlation so that its behavior is very complicated near and
at the magnetic phase transition of the lattice spins. For the time being there
are many new experimental data on the spin resistivity going from
semiconductors to superconductors. Depending on materials, various behaviors
have been observed. There is however no theory so far which gives a unified
mechanism for spin resistivity in magnetic materials. Recently, we have showed
Monte Carlo results for different systems. We found that the spin resistivity
is very different from one material to another. In this paper, we show for the
first time how the dynamic relaxation time of the lattice spins affects the
resistivity of itinerant spins observed in Monte Carlo simulation.",1101.5789v1
2011/4/14,Long-Range Magnetic Interactions in the Multiferroic Antiferromagnet $\rm MnWO_4$,"The spin-wave excitations of the multiferroic $\rm MnWO_4$ have been measured
in its low-temperature collinear commensurate phase using high-resolution
inelastic neutron scattering. These excitations can be well described by a
Heisenberg model with competing long-range exchange interactions and a
single-ion anisotropy term. The magnetic interactions are strongly frustrated
within the zigzag spin chain along c axis and between chains along the a axis,
while the coupling between spin along the b axis is much weaker. The balance of
these interactions results in the noncollinear incommensurate spin structure
associated with the magnetoelectric effect, and the perturbation of the
magnetic interactions leads to the observed rich phase diagrams of the
chemically-doped materials. This delicate balance can also be tuned by the
application of external electric or magnetic fields to achieve magnetoelectric
control of this type of materials.",1104.2867v1
2011/4/30,Magnetic hydrogels derived from polysaccharides with improved specific power absorption: potential devices for remotely triggered drug delivery,"We report on novel ferrogels derived from polysaccharides (sodium alginate
and chitosan) with embedded iron oxide nanoparticles synthesized in situ and
their combination with thermally responsive poly (N-isopropylacrylamide) for
externally-driven drug release using AC magnetic fields. Samples were
characterized by Raman spectroscopy, transmission electron microscopy (TEM) and
magnetic measurements. The obtained nanoparticles were found to be of ca. 10 nm
average size, showing magnetic properties very close to those of the bulk
material. The thermal response was measured by power absorption experiments,
finding specific power absorption (SPA) values between 100-300 W/g, which was
enough for attaining the lower critical solution temperature (LCST) of the
polymeric matrix within few minutes. This fast response makes these materials
good candidates for externally controlled drug release.",1105.0075v1
2011/8/30,Reducing Disorder in Artificial Kagome Ice,"Artificial spin ice has become a valuable tool for understanding magnetic
interactions on a microscopic level. The strength in the approach lies in the
ability of a synthetic array of nanoscale magnets to mimic crystalline
materials, composed of atomic magnetic moments. Unfortunately, these nanoscale
magnets, patterned from metal alloys, can show substantial variation in
relevant quantities such as coercive field, with deviations up to 6%. By
carefully studying the reversal process of artificial kagome ice, we can
directly measure the distribution of coercivities, and by switching from
disconnected islands to a connected structure, we find that the coercivity
distribution can achieve a deviation of only 3.3%. These narrow deviations
should allow the observation of behavior that mimics canonical spin-ice
materials more closely.",1108.6071v1
2012/3/10,Room temperature ferromagnetism and giant permittivity in chemical routed Co1.5Fe1.5O4 ferrite particles and their composite with NaNO3,"We report structural, magnetic and dielectric properties of Co1.5Fe1.5O4
nanoparticles and their composites with non-magnetic NaNO3. The samples were
derived from metal nitrates solution at different pH values. The chemical
routed sample was air heated at 200 0C and 500 0C. Heating of the material
showed unusual decrease of crystallite size, but cubic spinel structure is seen
in all samples. The samples of Co1.5Fe1.5O4 showed substantially large room
temperature ferromagnetic moment, electrical conductivity, dielectric constant,
and low dielectric loss. The samples are soft ferromagnet and electrically
highly polarized. The interfaces of grains and grain boundaries are actively
participating to determine the magnetic and dielectric properties of the
ferrite grains. The effects of interfacial contribution are better realized
using the ferrite and NaNO3 composite samples. We have examined different
scopes of modifying the magnetic and dielectric parameters using same material
in pure and composite form.",1203.2944v1
2012/5/6,A new look at spherical accretion in High Mass X-ray Binaries,"Currently used model of spherical accretion onto a magnetized rotating
neutron star encounters major difficulties in explaining the entry rate of
accreting material into the stellar field and spin evolution of long-period
X-ray pulsars. These difficulties can be, however, avoided if the magnetic
field of the material captured by the neutron star is incorporated into the
model. The magnetic field of the flow itself under certain conditions controls
the accretion process and significantly affects the parameters of the accreting
material. The mode by which the accretion flow enters the stellar magnetosphere
in that case can be associated with Bohm (or turbulent) diffusion and the
torque applied to the neutron star appears to be substantially higher than that
evaluated in the non-magnetized accretion scenario.",1205.1220v1
2012/7/11,Photoinduced Perturbations of the Magnetic Superexchange in Core-Shell Prussian Blue Analogues,"Cubic heterostructured (BA) particles of Prussian blue analogues, composed of
a shell of ferromagnetic K_{0.3}Ni[Cr(CN)_6]_{0.8} \cdot 1.3H_2O (A), Tc ~ 70
K, surrounding a bulk core of photoactive ferrimagnetic
Rb_{0.4}Co[Fe(CN)_6]_{0.8} \cdot 1.2H_2O (B), Tc ~20 K, have been studied.
Below Tc ~ 70 K, these samples exhibit a persistent photoinduced decrease in
low-field magnetization, and these results resemble data from other core-shell
particles and analogous ABA heterostructured films. This net decrease suggests
that the photoinduced lattice expansion in the B layer generates a
strain-induced decrease in the magnetization of the A layer, similar to a
pressure-induced decrease observed by others in a pure A-like material and by
us in our BA cubes. Upon further examination, the data also reveal a
significant portion of the A material whose superexchange, J, is perturbed by
the photoinduced strain from the B constituent.",1207.2623v1
2012/11/2,Symmetry Conditions for Non-reciprocal Light Propagation in Magnetic Crystals,"Recent studies demonstrated the violation of reciprocity in optical processes
in low-symmetry magnetic crystals. In these crystals the speed of light can be
different for counter-propagating beams. Correspondingly, they can show strong
directional anisotropies such as direction dependent absorption also called
directional dichroism[S. Bord\'acs et al., Nat. Phys. 8, 734 (2012); M. Saito
et al., J. Phys. Soc. Jpn. 77, 013705 (2008)]. Based on symmetry
considerations, we identify the magnetic point groups of materials which can
host such directional anisotropies and also provide a list of possible
candidate materials to observe these phenomena. In most of these cases, the
symmetry of the crystal allows directional anisotropy not only for optical
processes but also for the propagation of beams of particles and scalar waves.
We also predict new types of directional optical anisotropies -- besides the
optical magnetoelectric effect and the magnetochiral dichroism investigated so
far -- and specify the magnetic point groups of crystals where they can emerge.",1211.0530v2
2012/11/26,Low temperature dynamic freezing and the fragility of ordering in Tb2Sn2O7,"We have probed the low temperature magnetic behavior of the ordered spin ice
material Tb2Sn2O7 through ac magnetic susceptibility measurements of both the
pure material and samples with small percentages of Ti substituted on the Sn
sublattice. We observe a clear signature for the previously reported ordering
transition at TC = 850 mK, as well as evidence for dynamic freezing at
temperatures well below TC, confirming the persistence of significant magnetic
fluctuations deep in the spin-ordered regime. The long range ordering
transition was completely suppressed with as little as 5% Ti for Sn
substitution, and 10% Ti substitution resulted in a spin-glass-like spin
freezing transition near 250 mK. The results demonstrate that the long range
magnetic ordering is surprisingly fragile in this system.",1211.6047v1
2013/2/21,Large zero-field cooled exchange-bias in bulk Mn2PtGa,"We report a large exchange-bias (EB) effect after zero-field cooling the new
tetragonal Heusler compound Mn2PtGa from the paramagnetic state. The
first-principle calculation and the magnetic measurements reveal that Mn2PtGa
orders ferrimagnetically with some ferromagnetic (FM) inclusions. We show that
ferrimagnetic (FI) ordering is essential to isothermally induce the exchange
anisotropy needed for the zero-field cooled (ZFC) EB during the virgin
magnetization process. The complex magnetic behavior at low temperatures is
characterized by the coexistence of a field induced irreversible magnetic
behavior and a spin-glass-like phase. The field induced irreversibility
originates from an unusual first-order FI to antiferromagnetic transition,
whereas, the spin-glass like state forms due to the existence of anti-site
disorder intrinsic to the material.",1302.5229v1
2013/3/26,A unified model for the dynamics of driven ribbon with strain and magnetic order parameters,"We develop a unified model to explain the dynamics of driven one dimensional
ribbon for materials with strain and magnetic order parameters. We show that
the model equations in their most general form explain several results on
driven magnetostrictive metallic glass ribbons such as the period doubling
route to chaos as a function of a dc magnetic field in the presence of a
sinusoidal field, the quasiperiodic route to chaos as a function of the
sinusoidal field for a fixed dc field, and induced and suppressed chaos in the
presence of an additional low amplitude near resonant sinusoidal field. We also
investigate the influence of a low amplitude near resonant field on the period
doubling route. The model equations also exhibit symmetry restoring crisis with
an exponent close to unity. The model can be adopted to explain certain results
on magnetoelastic beam and martensitic ribbon under sinusoidal driving
conditions. In the latter case, we find interesting dynamics of a periodic one
orbit switching between two equivalent wells as a function of an ac magnetic
field that eventually makes a direct transition to chaos under resonant driving
condition. The model is also applicable to magnetomartensites and materials
with two order parameters.",1303.6621v1
2014/1/5,Phase-coexistence and glass-like behavior in magnetic and dielectric solids with long range order,"Phase-coexistence in the manganese-oxide compounds or manganites with
colossal magneto-resistance (CMR) has been generally considered to be an
inhomogeneous ground state. An alternative explanation of phase-coexistence as
the manifestation of a disorder-broadened first order magnetic phase transition
being interrupted by the glasslike arrest of kinetics is now gradually gaining
ground. This kinetic arrest of a first order phase transitions, between two
states with long-range magnetic order, has actually been observed in various
other classes of magnetic materials in addition to the CMR manganites. The
underlying common features of this kinetic arrest of a first order phase
transition are discussed in terms of the phenomenology of glasses. The possible
manifestations of such glass-like arrested states across disorder-influenced
first order phase transitions in dielectric solids and in multiferroic
materials, are also discussed.",1401.0891v2
2014/6/3,Propagation of defects in doped magnetic materials of different dimensionality,"Defects intentionally introduced into magnetic materials often have a
profound effect on the physical properties. Specifically tailored neutron
spectroscopic experiments can provide detailed information on both the local
exchange interactions and the local distances between the magnetic atoms around
the defects. This is demonstrated for manganese dimer excitations observed for
the magnetically diluted three- and two-dimensional compounds KMn(x)Zn(1-x)F(3)
and K(2)Mn(x)Zn(1-x)F(4), respectively. The resulting local exchange
interactions deviate up to 10% from the average, and the local Mn-Mn distances
are found to vary stepwise with increasing internal pressure due to the Mn/Zn
substitution. Our analysis qualitatively supports the theoretically predicted
decay of atomic displacements according to 1/r**2, 1/r, and constant (for
three-, two-, and one-dimensional compounds, respectively) where r denotes the
distance of the displaced atoms from the defect.",1406.0602v1
2014/10/28,Magnetism and electronic structure of ($001$)- and ($111$)-oriented LaTiO$_3$ bilayers sandwiched in LaScO$_3$ barriers,"In this study, the magnetism and electronic structure of LaTiO$_3$ bilayers
along both the ($001$) and ($111$) orientations are calculated using the
density functional theory. The band insulator LaScO$_3$ is chosen as the
barrier layer and substrate to obtain the isolating LaTiO$_3$ bilayer. For both
the ($001$)- and ($111$)-oriented cases, LaTiO$_3$ demonstrates the G-type
antiferromagnetism as the ground state, similar to the bulk material. However,
the electronic structure is significantly changed. The occupied bands of Ti are
much narrower in the ($111$) case, giving a nearly flat band. As a result, the
exchange coupling between nearest-neighbor Ti ions are reformed in these
superlattices, which will affect the N\'{e}el temperature significantly.",1410.7492v1
2015/1/5,Exchange striction induced giant ferroelectric polarization in copper based multiferroic material $α$-Cu$_2$V$_2$O$_7$,"We report $\alpha$-Cu$_2$V$_2$O$_7$ to be an improper multiferroic with the
simultaneous development of electric polarization and magnetization below $T_C$
= 35 K. The observed spontaneous polarization of magnitude 0.55 $\mu$Ccm$^{-2}$
is highest among the copper based improper multiferroic materials. Our study
demonstrates sizable amount of magneto-electric coupling below $T_C$ even with
a low magnetic field. The theoretical calculations based on density functional
theory (DFT) indicate magnetism in $\alpha$-Cu$_2$V$_2$O$_7$ is a consequence
of {\em ferro-orbital} ordering driven by polar lattice distortion due to the
unique pyramidal (CuO$_{5}$) environment of Cu. The spin orbit coupling (SOC)
further stabilize orbital ordering and is crucial for magnetism. The
calculations indicate that the origin of the giant ferroelectric polarization
is primarily due to the symmetric exchange-striction mechanism and is
corroborated by temperature dependent X-ray studies.",1501.00809v2
2015/2/26,Coils and the Electromagnet Used in the Joule Balance at the NIM,"In the joule balance developed at National Institute of Metrology (NIM), the
dynamic phase of a watt balance is replaced by the mutual inductance
measurement in an attempt to provide an alternative method for the kg
redefinition. But for this method a rather large current in the exciting coil,
is needed to offer the necessary magnetic field in the force weighing phase,
and the coil heating becomes an important uncertainty source. To reduce coil
heating, a new coil system, in which a ferromagnetic material is used to
increase the magnetic field was designed recently. But adopting the
ferromagnetic material brings the difficulty from the nonlinear characteristic
of material. This problem can be removed by measuring the magnetic flux linkage
difference of the suspended coil at two vertical positions directly to replace
the mutual inductance parameter. Some systematic effects of this magnet are
discussed.",1502.07456v1
2015/6/28,Calorimetric and magnetic study for Ni$_{50}$Mn$_{36}$In$_{14}$ and relative cooling power in paramagnetic inverse magnetocaloric systems,"The non-stoichiometric Heusler alloy Ni$_{50}$Mn$_{36}$In$_{14}$ undergoes a
martensitic phase transformation in the vicinity of 345 K, with the high
temperature austenite phase exhibiting paramagnetic rather than ferromagnetic
behavior, as shown in similar alloys with lower-temperature transformations.
Suitably prepared samples are shown to exhibit a sharp transformation, a
relatively small thermal hysteresis, and a large field-induced entropy change.
We analyzed the magnetocaloric behavior both through magnetization and direct
field-dependent calorimetry measurements. For measurements passing through the
first-order transformation, an improved method for heat-pulse relaxation
calorimetry was designed. The results provide a firm basis for the analytic
evaluation of field-induced entropy changes in related materials. An analysis
of the relative cooling power (RCP), based on the integrated field-induced
entropy change and magnetizing behavior of the Mn spin system with
ferromagnetic correlations, shows that a significant RCP may be obtained in
these materials by tuning the magnetic and structural transformation
temperatures through minor compositional changes or local order changes.",1506.08351v1
2015/7/28,Dzyaloshinskii-Moriya interactions and magnetic texture in the Fe films deposited on transition-metal dichalcogenides,"The magnetic properties of materials based on two-dimensional
transition-metal dichalcogenides (TMDC) have been investigated by means of
first-principles DFT calculations, namely Fe-intercalated bulk
Fe$_{1/4}$TaS$_2$ compounds as well as TMDC monolayers with deposited Fe films.
Changing the structure and the composition of systems consisting of Fe
overlayers on top of a TMDC monolayers resulted in considerable variations of
their physical properties. For the considered systems the Dzyaloshinskii-Moriya
(DM) interaction has been determined and used for the subsequent investigation
of their magnetic structure using Monte Carlo simulations. Rather strong DM
interactions as well as large $D/J$ ratios have been obtained in some of these
materials, which can lead to the formation of skyrmionic structures varying
with the strength of the applied external magnetic field.",1507.07712v2
2015/8/21,Homogeneous solutions for elliptically polarized light in a cavity containing materials with electric and magnetic nonlinearities,"We study evolution equations and stationary homogeneous solutions for
electric and magnetic field amplitudes in a ring cavity with flat mirrors. The
cavity is filled with a positive or negative refraction index material with
third order Kerr-like electric nonlinearities and also magnetic nonlinearities,
which can be relevant in metamaterials. We consider the degree of freedom of
polarization in the incident beam. It is found that considering a magnetic
nonlinearity increases the variety of possible qualitatively different
solutions. A classification of solutions is proposed in terms of the number of
bifurcations. The analysis can be useful for the implementation of optical
switching or memory storage using ring cavities with non linear materials.",1508.05155v1
2015/8/26,Electronic topological transition and non-collinear magnetism in compressed hcp Co,"Recent experiments showed that Co undergoes a phase transition from
ferromagnetic hcp phase to non-magnetic fcc one around 100 GPa. Since the
transition is of first order, a certain region of co-existence of the two
phases is present. By means of \textit{ab initio} calculations, we found that
the hcp phase itself undergoes a series of electronic topological transitions
(ETTs), which affects both elastic and magnetic properties of the material.
Most importantly, we propose that the sequence of ETTs lead to the
stabilisation of a non-collinear spin arrangement in highly compressed hcp Co.
Details of this non-collinear magnetic state and the interatomic exchange
parameters that are connected to it, are presented here.",1508.06602v1
2015/10/2,Local structures and local exchange interactions in doped magnetic materials of different dimensionality,"Defects intentionally introduced into magnetic materials often have a
profound effect on the physical properties. Specifically tailored neutron
spectroscopic experiments can provide detailed information on both the local
exchange interactions and the local distances between the magnetic atoms around
the defects. This is demonstrated for manganese dimer excitations observed for
the magnetically diluted three-, two- and one-dimensional compounds
KMnxZn1-xF3, K2MnxZn1-xF4 and CsMnxMg1-xBr3, respectively, with x=0.10. The
resulting local exchange interactions deviate up to 10% from the average, and
the local Mn-Mn distances are found to vary stepwise with increasing internal
chemical pressure due to the Mn/Zn or Mn/Mg substitution. Our analysis
qualitatively supports the theoretically predicted decay of atomic
displacements according to 1/r**2, 1/r and constant (for three-, two- and
one-dimensional compounds, respectively) where r denotes the distance of the
displaced atoms from the defect.",1510.00570v1
2015/10/15,Filament Shape Versus Coronal Potential Magnetic Field Structure,"Solar filament shape in projection on disc depends on the structure of the
coronal magnetic field. We calculate the position of polarity inversion lines
(PILs) of coronal potential magnetic field at different heights above the
photosphere, which compose the magnetic neutral surface, and compare with them
the distribution of the filament material in H$\alpha$ chromospheric images. We
found that the most of the filament material is enclosed between two polarity
inversion lines (PILs), one at a lower height close to the chromosphere and one
at a higher level, which can be considered as a height of the filament spine.
Observations of the same filament on the limb by the {\it STEREO} spacecraft
confirm that the height of the spine is really very close to the value obtained
from the PIL and filament border matching. Such matching can be used for
filament height estimations in on-disk observations. Filament barbs are housed
within protruding sections of the low-level PIL. On the base of simple model,
we show that the similarity of the neutral surfaces in potential and
non-potential fields with the same sub-photospheric sources is the reason for
the found tendency for the filament material to gather near the potential-field
neutral surface.",1510.04546v1
2015/11/7,Mn3TeO6 - A New Multiferroic Material with Two Magnetic Substructures,"From magnetic susceptibility, dielectric permittivity, electric polarization
and specific heat measurements, we discover spin-induced ferroelectricity and
magnetoelectric coupling in Mn3TeO6 and observe two successive magnetic
transitions at low temperatures. A non-ferroelectric intermediate magnetic
state occurs below 23 K and a multiferroic ground state emerges below 21 K.
Moreover, Mn3TeO6 is a candidate for a multiferroic material where two types of
incommensurate spin structures, cycloidal and helical, coexist. Theoretically,
both spin substructures may contribute to the macro electric polarization via
different mechanisms.",1511.02370v3
2016/2/17,Fermionic response from fractionalization in an insulating two-dimensional magnet,"Conventionally ordered magnets possess bosonic elementary excitations, called
magnons. By contrast, no magnetic insulators in more than one dimension are
known whose excitations are not bosons but fermions. Theoretically, some
quantum spin liquids (QSLs) -- new topological phases which can occur when
quantum fluctuations preclude an ordered state -- are known to exhibit Majorana
fermions as quasiparticles arising from fractionalization of spins. Alas,
despite much searching, their experimental observation remains elusive. Here,
we show that fermionic excitations are remarkably directly evident in
experimental Raman scattering data across a broad energy and temperature range
in the two-dimensional material $\alpha$-RuCl$_3$. This shows the importance of
magnetic materials as hosts of Majorana fermions. In turn, this first
systematic evaluation of the dynamics of a QSL at finite temperature emphasizes
the role of excited states for detecting such exotic properties associated with
otherwise hard-to-identify topological QSLs.",1602.05277v1
2016/3/30,Magnetic Interactions and Electronic Structure of Pt$_{2}$Mn$_{1-x}$Y$_{x}$Ga (Y = Cr and Fe) system : An ab-initio calculation,"First principles density functional theory based calculations have been
carried out to predict the effects of Mn replacement by Fe and Cr on electronic
as well as magnetic properties of Pt$_{2}$MnGa as well as Ni$_{2}$MnGa. All the
materials studied here are predicted to have conventional Heusler alloy
structure in their ground state and they are found to be electronically stable
on the basis of their respective formation energy. The replacement of Mn by Fe
leads to a ferromagnetic ground state whereas in case of Mn replacement by Cr
an {\it intra-sublattice} anti-ferromagnetic configuration has been observed to
have lower energy. We study the magnetic exchange interaction between the atoms
for the materials with ferromagnetic and anti-ferromagnetic configurations to
show the effects of Fe and Cr substitution at Mn site on the magnetic
interactions of these systems. Detailed analysis of electronic structure in
terms of density of states has been carried out to study the effect of
substitution.",1603.09139v1
2016/5/7,Persistence of slow dynamics in Tb(OETAP)$_2$ single molecule magnets embedded in conducting polymers,"The spin dynamics of Tb(OETAP)$_2$ single ion magnets was investigated by
means of muon spin resonance ($\mu$SR) both in the bulk material as well as
when the system is embedded into PEDOT:PSS polymer conductor. The
characteristic spin fluctuation time is characterized by a high temperature
activated trend, with an energy barrier around 320 K, and by a low temperature
tunneling regime. When the single ion magnet is embedded into the polymer the
energy barrier only slightly decreases and the fluctuation time remains of the
same order of magnitude even at low temperature. This finding shows that these
single molecule magnets preserve their characteristics which, if combined with
those of the conducting polymer, result in a hybrid material of potential
interest for organic spintronics.",1605.02148v1
2016/6/17,Electronic ground state of MnB$_{4}$,"Recent studies have dealt with the electronic and magnetic ground state
properties of the tetraboride material MnB$_4$. So far, however, the ground
state properties could not be established unambiguously. Therefore, here we
present an experimental study on single-crystalline MnB$_4$ by means of
resistivity and magnetization measurements. For this, we have developed a
sample holder that allows four-point ac resistivity measurements on these very
small ($\sim$\,100\,$\mu$m) samples. With our data we establish that the
electronic ground state of MnB$_4$ is intrinsically that of a pseudo-gap
system, in agreement with recent band structure calculations. Furthermore, we
demonstrate that the material does neither show magnetic order nor a behavior
arising from the vicinity to a magnetically ordered state, this way disproving
previous claims.",1606.05484v3
2016/7/1,Generation of Spin Currents by Magnetic Field in $\mathcal{T}$- and $\mathcal{P}$-Broken Materials,"Pure spin currents carry information in quantum spintronics and could play an
essential role in the next generation low-energy-consumption electronics. Here
we theoretically predict that the magnetic field can induce a quantum spin
current without a concomitant charge current in metals without time reversal
symmetry $\mathcal{T}$ and inversion symmetry $\mathcal{P}$ but respect the
combined $\mathcal{PT}$ symmetry. It is governed by the magnetic moment of the
Bloch states on the Fermi surface, and can be regarded as a spinful
generalization of the gyrotropic magnetic effect in $\mathcal{P}$-broken
metals. The effect is explicitly studied for a minimal model of an
antiferromagnetic Dirac semimetal, where the experimental signature is
proposed. We further propose candidate materials, including topological
antiferromagnetic Dirac semimetals, Weyl semimetals, and tenary Heusler
compounds.",1607.00116v1
2016/11/8,"Single crystal growth, structure and magnetic properties of Pr2Hf2O7 pyrochlore","Large single crystals of the pyrochlore Pr2Hf2O7 have been successfully grown
by the floating zone technique using an optical furnace equipped with high
power Xenon arc lamps. Structural investigations have been carried out by both
synchrotron X-ray and neutron powder diffraction to establish the
crystallographic structure of the materials produced. The magnetic properties
of the single crystals have been determined for magnetic fields applied along
different crystallographic axes. The results reveal that Pr2Hf2O7 is an
interesting material for further investigations as a frustrated magnet. The
high quality of the crystals produced make them ideal for detailed
investigations, especially those using neutron scattering techniques.",1611.02536v1
2017/3/18,A thermodynamically consistent model of magneto-elastic materials under diffusion at large strains and its analysis,"The theory of elastic magnets is formulated under possible diffusion and heat
flow governed by Fick's and Fourier's laws in the deformed (Eulerian)
configuration, respectively. The concepts of nonlocal nonsimple materials and
viscous Cahn-Hilliard equations are used. The formulation of the problem uses
Lagrangian (reference) configuration while the transport processes are pulled
back. Except the static problem, the demagnetizing energy is ignored and only
local non-selfpenetration is considered. The analysis as far as existence of
weak solutions of the (thermo)dynamical problem is performed by a careful
regularization and approximation by a Galerkin method, suggesting also a
numerical strategy. Either ignoring or combining particular aspects, the model
has numerous applications as ferro-to-paramagnetic transformation in elastic
ferromagnets, diffusion of solvents in polymers possibly accompanied by
magnetic effects (magnetic gels), or metal-hydride phase transformation in some
intermetalics under diffusion of hydrogen accompanied possibly by magnetic
effects (and in particular ferro-to-antiferromagnetic phase transformation),
all in the full thermodynamical context under large strains.",1703.06267v2
2017/6/6,Antiferromagnetic Domain Wall as Spin Wave Polarizer and Retarder,"As a collective quasiparticle excitation of the magnetic order in magnetic
materials, spin wave, or magnon when quantized, can propagate in both
conducting and insulating materials. Like the manipulation of its optical
counterpart, the ability to manipulate spin wave polarization is not only
important but also fundamental for magnonics. With only one type of magnetic
lattice, ferromagnets can only accommodate the right-handed circularly
polarized spin wave modes, which leaves no freedom for polarization
manipulation. In contrast, antiferromagnets, with two opposite magnetic
sublattices, have both left and right circular polarizations, and all linear
and elliptical polarizations. Here we demonstrate theoretically and confirm by
micromagnetic simulations that, in the presence of Dzyaloshinskii-Moriya
interaction, an antiferromagnetic domain wall acts naturally as a spin wave
polarizer or a spin wave retarder (waveplate). Our findings provide extremely
simple yet flexible routes toward magnonic information processing by harnessing
the polarization degree of freedom of spin wave.",1706.01617v1
2017/10/13,Mode-Dependent Damping in Metallic Antiferromagnets Due to Inter-Sublattice Spin Pumping,"Damping in magnetization dynamics characterizes the dissipation of magnetic
energy and is essential for improving the performance of spintronics-based
devices. While the damping of ferromagnets has been well studied and can be
artificially controlled in practice, the damping parameters of
antiferromagnetic materials are nevertheless little known for their physical
mechanisms or numerical values. Here we calculate the damping parameters in
antiferromagnetic dynamics using the generalized scattering theory of
magnetization dissipation combined with the first-principles transport
computation. For the PtMn, IrMn, PdMn and FeMn metallic antiferromagnets, the
damping coefficient associated with the motion of magnetization ($\alpha_m$) is
one to three orders of magnitude larger than the other damping coefficient
associated with the variation of the N\'eel order ($\alpha_n$), in sharp
contrast to the assumptions made in the literature.",1710.04766v1
2017/10/27,The Quantum Hall Effect with Wilczek's charged magnetic flux tubes instead of electrons,"Composites formed from charged particles and magnetic flux tubes, proposed by
Wilczek, are one model for anyons - particles obeying fractional statistics.
Here we propose a scheme for realizing charged flux tubes, in which a charged
object with an intrinsic magnetic dipole moment is placed between two
semi-infinite blocks of a high permeability ($\mu_r$) material, and the images
of the magnetic moment create an effective flux tube. We show that the scheme
can lead to a realization of Wilczek's anyons, when a two-dimensional electron
system, which exhibits the integer quantum Hall effect (IQHE), is sandwiched
between two blocks of the high-$\mu_r$ material with a temporally fast response
(in the cyclotron and Larmor frequency range). The signature of Wilczek's
anyons is a slight shift of the resistivity at the plateau of the IQHE. Thus,
the quest for high-$\mu_r$ materials at high frequencies, which is underway in
the field of metamaterials, and the quest for anyons, are here found to be on
the same avenue.",1710.10108v2
2017/11/16,Homogenization in magnetic-shape-memory polymer composites,"Magnetic-shape-memory materials (e.g. specific NiMnGa alloys) react with a
large change of shape to the presence of an external magnetic field. As an
alternative for the difficult to manifacture single crystal of these alloys we
study composite materials in which small magnetic-shape-memory particles are
embedded in a polymer matrix. The macroscopic properties of the composite
depend strongly on the geometry of the microstructure and on the
characteristics of the particles and the polymer.
  We present a variational model based on micromagnetism and elasticity, and
derive via homogenization an effective macroscopic model under the assumption
that the microstructure is periodic. We then study numerically the resulting
cell problem, and discuss the effect of the microstructure on the macroscopic
material behavior. Our results may be used to optimize the shape of the
particles and the microstructure.",1711.06098v1
2017/12/13,Co$_{2}$PtGa: A promising magnetic shape memory alloy with high martensite transition temperature,"In the present work, a combined theoretical and experimental study on
Co$_{2}$PtGa Heusler alloy shows that it exhibits a martensite transition
around 1320 K with a small thermal hysteresis (10 K). Dynamical stability of
Co$_2$PtGa in the tetragonal phase has been established by the theoretically
calculated phonon dispersion curves. Magnetization measurements suggest that
this alloy is a ferromagnetic material with a saturation magnetic moment of
2.83 $\mu_B$/f.u. at 2 K, which is in excellent agreement with the value
obtained from \textit{ab-initio} calculations (2.87 $\mu_B$/f.u.). Our present
study demonstrates that Co$_{2}$PtGa is a promising material for high
temperature magnetic shape memory application.",1712.04765v4
2017/12/20,Planar Hall torque,"Spin-orbit torques in bilayers of ferromagnetic and nonmagnetic materials
hold promise for energy efficient switching of magnetization in nonvolatile
magnetic memories. Previously studied spin Hall and Rashba torques originate
from spin-orbit interactions within the nonmagnetic material and at the bilayer
interface, respectively. Here we report a spin-orbit torque that arises from
planar Hall current in the ferromagnetic material of the bilayer and acts as
either positive or negative magnetic damping. This planar Hall torque exhibits
unusual biaxial symmetry in the plane defined by the applied electric field and
the bilayer normal. The magnitude of the planar Hall torque is similar to that
of the giant spin Hall torque and is large enough to excite auto-oscillations
of the ferromagnetic layer magnetization.",1712.07335v1
2018/3/16,Multiple structure and symmetry types in narrow temperature and magnetic field ranges in two-dimensional Cr2Ge2Te6 crystal,"Multiple structure and symmetry types and their transformations are
discovered in quasi-two-dimensional (quasi-2D) Cr2Ge2Te6 crystal in
surprisingly very narrow temperature range of 2 K and magnetic field range of
0.07 T using a homebuilt magnetic force microscope (MFM). A series of basic
domain patterns are extracted from the MFM images. Some of them seem unique to
2-D materials as they are not observed in 3-D materials, such as self-fitting
disks, and fine ladder structure within Y-connected walls. Based on these
findings, a phase map is drawn for the magnetic phase structures. The symmetry
of the patterns are discussed. The results are not only important in developing
new theories but also highly desirable in applications.",1803.06113v3
2018/4/13,Revisiting the elastic solution for an inner-pressured functionally graded thick-walled tube within a uniform magnetic field,"In this paper, the mechanical responses of a thick-walled functionally graded
hollow cylinder subjected to uniform magnetic field and inner-pressurized loads
are studied. Rather than directly assuming the material constants into some
certain function forms as displayed in previous researches, we firstly give the
volume fractions of different constituents of the FGM cylinder and then
determine the expressions of material constants. By the use of the Voigt method
the corresponding analytical solutions of displacements in radical direction,
the strain and stress components and the perturbation magnetic field vector are
derived by the following. In numerical part, the influences of volume fraction
on displacement, stain and stress components and the magnetic perturbation
filed vector are investigated; indicated by the results, we can conclude that
the Poisson's ratio has a significant effect on the FGM cylinder's mechanical
behaviors. Moreover, by some appropriate choices of the material constants it
can be found that the obtained results in this paper can reduce to some special
cases given in previous literatures.",1805.01403v1
2018/7/12,Many-body correlations brought to light in absorption spectra of diluted magnetic semiconductors,"Diluted magnetic semiconductors are materials well known to exhibit strong
correlations which typically manifest in carrier-mediated magnetic ordering. In
this Rapid Communication, we show that the interaction between excitons and
magnetic impurities in these materials is even strong enough to cause a
significant deviation from the bare exciton picture in linear absorption
spectra of quantum well nanostructures. It is found that exciton-impurity
correlations induce a characteristic fingerprint in the form of an additional
feature close to the exciton resonance in combination with a shift of the main
exciton line of up to a few meV. We trace back these features to the form of
the self-energy and demonstrate that reliable values of the average correlation
energy per exciton can be extracted directly from the spectra. Since the only
requirement for our findings is sufficiently strong correlations, the results
can be generalized to other strongly correlated systems.",1807.04490v2
2018/7/27,Effect of Coulomb Interactions on the Electronic and Magnetic Properties of Two-Dimensional CrSiTe$_3$ and CrGeTe$_3$ Materials,"We investigate the electronic and magnetic structures of two-dimensional
transition metal tri-chalcogenide CrSiTe$_{3}$ and CrGeTe$_{3}$ materials by
carrying out first-principles calculations. The single-layer CrSiTe$_3$ and
CrGeTe$_3$ are found to be a ferromagnetic insulator, where the presence of the
strong $dp\sigma$-hybridization of Cr $e_{\mathrm{g}}$-Te $p$ plays a crucial
role for the ferromagnetic coupling between Cr ions. We observe that the
bandgaps and the interlayer magnetic order vary notably depending on the
magnitude of on-site Coulomb interaction $U$ for Cr $d$ electrons. The bandgaps
are formed between the Cr $e_{\mathrm{g}}$ conduction bands and the Te $p$
valence bands for both CrSiTe$_3$ and CrGeTe$_3$ in the majority-spin channel.
The dominant Te $p$ antibonding character in the valence bands just below the
Fermi level is related to the decrease of the bandgap for the increase of $U$.
We elucidate the energy band diagram, which may serve to understand the
electronic and magnetic properties of the $ABX_3$-type transition metal
tri-chalcogenides in general.",1807.10686v1
2018/8/10,Origin of $sp$-electron magnetism in Graphitic Carbon Nitride,"Based on first principles calculations, this study reveals that magnetism in
otherwise non-magnetic materials can originate from the partial occupation of
antibonding states. Since the antibonding wavefunctions are spatially
antisymmetric, the spin wavefunctions should be symmteric according to the
exchange antisymmetric principle of quantum mechanics. We demonstrate that this
phenomenon can be observed in a graphitic carbon nitride material,
$g$-C$_4$N$_3$, which can be experimentally synthesized and seen as a honeycomb
structure with a vacancy. Three dangling bonds of N atoms pointing to the
vacancy site interact with each other to form one bonding and two antibonding
states. As the two antibonding states are near the Fermi level, and electrons
should partially occupy the antibonding states in spin polarization, this leads
to 1~$\mu_B$ magnetic moment.",1808.03505v1
2018/8/31,Strain engineering a multiferroic monodomain in thin-film BiFeO$_3$,"The presence of domains in ferroic materials can negatively affect their
macroscopic properties and hence their usefulness in device applications. From
an experimental perspective, measuring materials comprising multiple domains
can complicate the interpretation of material properties and their underlying
mechanisms. In general, BiFeO$_3$ films tend to grow with multiple magnetic
domains and often contain multiple ferroelectric and ferroelastic domain
variants. By growing (111)-oriented BiFeO$_3$ films on an orthorhombic
TbScO$_3$ substrate, we are able to overcome this, and, by exploiting the
magnetoelastic coupling between the magnetic and crystal structures, bias the
growth of a given magnetic-, ferroelectric-, and structural-domain film. We
further demonstrate the coupling of the magnetic structure to the ferroelectric
polarisation by showing the magnetic polarity in this domain is inverted upon
180$^\circ$ ferroelectric switching",1808.10666v1
2018/11/13,Spin-orbit torques acting upon a perpendicularly-magnetized Py layer,"We show that Py, a commonly-used soft ferromagnetic material with weak
anisotropy, can become perpendicularly-magnetized while depositing on Ta buffer
layer with Hf or Zr insertion layers (ILs) and MgO capping layer. By using two
different approaches, namely harmonic voltage measurement and hysteresis loop
shift measurement, the dampinglike spin-orbit torque (DL-SOT) efficiencies from
Ta/IL/Py/IL/MgO magnetic heterostructures with perpendicular magnetic
anisotropy are characterized. We find that though Ta has a significant spin
Hall effect, the DL-SOT efficiencies are small in systems with the Ta/Py
interface compared to that obtained from the control sample with the
traditional Ta/CoFeB interface. Our results indicate that the spin transparency
for the Ta/Py interface is much less than that for the Ta/CoFeB interface,
which might be related to the variation of spin mixing conductance for
different interfaces.",1811.05164v1
2019/3/30,Magnetic hopfions in solids,"Hopfions are an intriguing class of string-like solitons, named according to
a classical topological concept classifying three-dimensional direction fields.
The search of hopfions in real physical systems is going on for nearly half a
century, starting with the seminal work of Faddeev. But so far realizations in
solids are missing. Here, we present a theory that identifies magnetic
materials featuring hopfions as stable states without the assistance of
confinement or external fields. Our results are based on an advanced
micromagnetic energy functional derived from a spin-lattice Hamiltonian.
Hopfions appear as emergent particles of the classical Heisenberg model.
Magnetic hopfions represent three-dimensional particle-like objects of
nanometre-size dimensions opening the gate to a new generation of spintronic
devices in the framework of a truly three-dimensional architecture. Our
approach goes beyond the conventional phenomenological models. We derive
material-realistic parameters that serve as concrete guidance in the search of
magnetic hopfions bridging computational physics with materials science.",1904.00250v1
2019/4/10,Intrinsic Ferromagnetism in Electrenes,"We report intrinsic ferromagnetism in monolayer electrides or electrenes, in
which excess electrons act as anions. Our first-principles calculations
demonstrate that magnetism in such electron-rich two-dimensional (2D) materials
originates from the anionic electrons rather than partially filled d orbitals,
which is fundamentally different from ferromagnetism found in other 2D
intrinsic magnetic materials. Taking the honeycomb LaBr$_2$
(La$^{3+}$Br$^{-}_{2}\cdot e^{-}$) as an example, our calculations reveal that
the excess electron is localized at the center of the hexagon, which leads to
strong Stoner-instability of the associated states at the Fermi energy,
resulting in spontaneous magnetization and formation of a local moment. The
overlap of extended tails of the wave functions of these electrons mediates a
long-range ferromagnetic interaction, contributing to a Curie temperature
($T_\textrm{c}$) of 235 K and a coercive field ($H_\textrm{c}$) of 0.53 T,
which can be further enhanced by hole doping. The dual nature, localization and
extension, of the electronic states suggests a unique mechanism in such
magnetic-element-free electrenes as intrinsic 2D ferromagnets.",1904.04952v1
2019/7/10,The superior role of the Gilbert damping on the signal-to-noise ratio in heat-assisted magnetic recording,"In magnetic recording the signal-to-noise ratio (SNR) is a good indicator for
the quality of written bits. However, a priori it is not clear which parameters
have the strongest influence on the SNR. In this work, we investigate the role
of the Gilbert damping on the SNR. Grains consisting of FePt like hard magnetic
material with two different grain sizes $d_1=5\,$nm and $d_2=7\,$nm are
considered and simulations of heat-assisted magnetic recording (HAMR) are
performed with the atomistic simulation program VAMPIRE. The simulations
display that the SNR saturates for damping constants larger or equal than 0.1.
Additionally, we can show that the Gilbert damping together with the bit length
have a major effect on the SNR whereas other write head and material parameters
only have a minor relevance on the SNR.",1907.04577v2
2019/7/11,Hole compensation effect in III-Mn-V dilute ferromagnetic semiconductors,"A systematic study of hole compensation effect on magnetic properties, which
is controlled by defect compensation through ion irradiation, in (Ga,Mn)As,
(In,Mn)As and (Ga,Mn)P is presented in this work. In all materials, both Curie
temperature and magnetization decrease upon increasing the hole compensation,
confirming the description of hole mediated ferromagnetism according to the p-d
Zener model. The material dependence of Curie temperature and magnetization
versus hole compensation reveals that the manipulation of magnetic properties
in III-Mn-V dilute ferromagnetic semiconductors by ion irradiation is strongly
influenced by the energy level location of the produced defect relative to the
band edges in semiconductors.",1907.05160v1
2019/7/16,Current-driven Rashba Field in a Magnetic Quantum Well,"In materials lacking inversion symmetry, the spin-orbit coupling enables the
direct connection between the electron's spin and its linear momentum, a
phenomenon called inverse spin galvanic effect. In magnetic materials, this
effect promotes current-driven torques that can be used to control the
magnetization direction electrically. In this work, we investigate the
current-driven inverse spin galvanic effect in a quantum well consisting in a
magnetic material embedded between dissimilar insulators. Assuming the presence
of Rashba spin-orbit coupling at the interfaces, we investigate the nature of
the non-equilibrium spin density and the influence of the quantum well
parameters. We find that the torque is governed by the interplay between the
number of states participating to the transport and their spin chirality, the
penetration of the wave function into the tunnel barriers, and the strength of
the Rashba term.",1907.07116v1
2019/7/25,Phase-Change Control of Interlayer Exchange Coupling,"Changing the interlayer exchange coupling between magnetic layers in-situ is
a key issue of spintronics, as it allows for the optimization of properties
that are desirable for applications, including magnetic sensing and memory. In
this paper, we utilize the phase change material VO2 as a spacer layer to
regulate the interlayer exchange coupling between ferromagnetic layers with
perpendicular magnetic anisotropy. The successful growth of ultra-thin (several
nanometres) VO2 films is realized by sputtering at room temperature, which
further enables the fabrication of [Pt/Co]2/VO2/[Co/Pt]2 multilayers with
distinct interfaces. Such a magnetic multilayer exhibits an evolution from
antiferromagnetic coupling to ferromagnetic coupling as the VO2 undergoes a
phase change. The underlying mechanism originates from the change in the
electronic structure of the spacer layer from an insulating to a metallic
state. As a demonstration of phase change spintronics, this work may reveal the
great potential of material innovations for next-generation spintronics.",1907.10784v2
2019/8/15,Magnetic proximity in a van der Waals heterostructure of magnetic insulator and graphene,"Engineering two-dimensional material heterostructures by combining the best
of different materials in one ultimate unit can offer a plethora of
opportunities in condensed matter physics. Here, in the van der Waals
heterostructures of the ferromagnetic insulator Cr2Ge2Te6 and graphene, our
observations indicate an out-of-plane proximity-induced ferromagnetic exchange
interaction in graphene. The perpendicular magnetic anisotropy of Cr2Ge2Te6
results in significant modification of the spin transport and precession in
graphene, which is ascribed to the proximity-induced exchange interaction.
Furthermore, the observation of a larger lifetime for perpendicular spins in
comparison to the in-plane counterpart suggests the creation of a
proximity-induced anisotropic spin texture in graphene. Our experimental
results and density functional theory calculations open up opportunities for
the realization of proximity-induced magnetic interactions and spin filters in
2D material heterostructures and can form the basic building blocks for future
spintronic and topological quantum devices.",1908.05524v2
2019/9/12,Perspectives on spin hydrodynamics in ferromagnetic materials,"The field of spin hydrodynamics aims to describe magnetization dynamics from
a fluid perspective. For ferromagnetic materials, there is an exact mapping
between the Landau-Lifshitz equation and a set of dispersive hydrodynamic
equations. This analogy provides ample opportunities to explore novel
magnetization dynamics and magnetization states that can lead to applications
relying entirely upon magnetic materials, for example, long-distance transport
of information. This article provides an overview of the theoretical
foundations of spin hydrodynamics and their physical interpretation in the
context of spin transport. We discuss other proposed applications for spin
hydrodynamics as well as our view on challenges and future research directions.",1909.05756v1
2019/11/25,Current-Induced Helicity Reversal of a Single Skyrmionic Bubble Chain in a Nanostructured Frustrated Magnet,"Helicity indicates the in-plane magnetic-moment swirling direction of a
skyrmionic configuration. The ability to reverse the helicity of a skyrmionic
bubble via purely electrical means has been predicted in frustrated magnetic
systems, however its experimental observation has remained challenging. Here,
we experimentally demonstrate the current-driven helicity reversal of the
skyrmionic bubble in a nanostructured frustrated Fe3Sn2 magnet. The critical
current density required to trigger the helicity reversal is 109 - 1010 A/m2,
with a corresponding pulse-width varying from 1 {\mu}s to 100 ns. Computational
simulations reveal that both the pinning effect and dipole-dipole interaction
play a crucial role in the helicity-reversal process.",1911.10697v1
2019/12/5,Anomalous Transition Magnetic Moments in two-dimensional Dirac Materials,"We show that the magnetic response of atomically thin materials with Dirac
spectrum and spin-orbit interactions can exhibit strong dependence on
electron-electron interactions. While graphene itself has a very small
spin-orbit coupling, various two-dimensional (2D) compounds ""beyond graphene""
are good candidates to exhibit the strong interplay between spin-orbit and
Coulomb interactions. Materials in this class include dichalcogenides (such as
MoS$_2$ and WSe$_2$), silicene, germanene, as well as 2D topological insulators
described by the Kane-Mele model. We present a unified theory for their
in-plane magnetic field response leading to ""anomalous"", i.e. electron
interaction dependent transition moments. Our predictions can be potentially
used to construct unique magnetic probes with high sensitivity to electron
correlations.",1912.02749v3
2020/1/17,Intrinsic topological phases in Mn$_2$Bi$_2$Te$_5$ tuned by the layer magnetization,"The interplay between band topology and magnetic order could generate a
variety of time-reversal-breaking gapped topological phases with exotic
topological quantization phenomena, such as quantum anomalous Hall (QAH)
insulators and axion insulators (AxI). Here by combining analytic models and
first-principles calculations, we predict QAH and AxI phases can be realized in
thin film of an intrinsic antiferromagnetic van der Waal material
Mn$_2$Bi$_2$Te$_5$. The phase transition between QAH and AxI is tuned by the
layer magnetization, which would provide a promising platform for chiral
superconducting phases. We further present a simple and unified continuum model
that captures the magnetic topological features, and is generic for
Mn$_2$Bi$_2$Te$_5$ and MnBi$_2$Te$_4$ family materials.",2001.06133v2
2020/1/20,Ab initio design of quaternary Heusler compounds for reconfigurable magnetic tunnel diodes and transistors,"Reconfigurable magnetic tunnel diodes and transistors are a new concept in
spintronics. The realization of such a device requires the use of materials
with unique spin-dependent electronic properties such as half-metallic magnets
(HMMs) and spin-gapless semiconductors (SGSs). Quaternary Heusler compounds
offer a unique platform to design within the same family of compounds HMMs and
SGSs with similar lattice constants to make coherent growth of the consecutive
spacers of the device possible. Employing state-of-the-art first-principles
calculations, we scan the quaternary Heusler compounds and identify suitable
candidates for these spintronic devices combining the desirable properties: (i)
HMMs with sizable energy gap or SGSs with spin gaps both below and above the
Fermi level, (ii) high Curie temperature, (iii) convex hull energy distance
less than 0.20 eV, and (iv) negative formation energies. Our results pave the
way for the experimental realization of the proposed magnetic tunnel diodes and
transistors.",2001.07029v1
2020/2/14,Two-channel anomalous Hall effect in SrRuO3,"The Hall effect in SrRuO$_3$ thin-films near the thickness limit for
ferromagnetism shows an extra peak in addition to the ordinary and anomalous
Hall effects. This extra peak has been attributed to a topological Hall effect
due to two-dimensional skyrmions in the film around the coercive field;
however, the sign of the anomalous Hall effect in SrRuO$_3$ can change as a
function of saturation magnetization. Here we report Hall peaks in SrRuO$_3$ in
which volumetric magnetometry measurements and magnetic force microscopy
indicate that the peaks result from the superposition of two anomalous Hall
channels with opposite sign. These channels likely form due to thickness
variations in SrRuO$_3$, creating two spatially separated magnetic regions with
different saturation magnetizations and coercive fields. The results are
central to the development of strongly correlated materials for spintronics.",2002.06062v2
2020/3/13,Nonreciprocal Second-Harmonic Generation in Few-Layer Chromium Triiodide,"It is of fundamental importance but challenging to simultaneously identify
atomic and magnetic configurations of two-dimensional van der Waals materials.
In this work, we show that the nonreciprocal second-harmonic generation (SHG)
can be a powerful tool to answer this challenge. Despite the preserved lattice
inversion symmetry, the interlayer antiferromagnetic order and spin-orbit
coupling generate enhanced SHG in PT-symmetric bilayer chromium triiodide
(CrI3). Importantly, the in-plane polarization-resolved SHG is sensitive to
subtly different interlayer structures that cannot be told by linear optical
spectra. Beyond bilayer, we further predict that the intensity and
angle-resolved SHG can be employed to identify both interlayer atomic and
magnetic configurations of trilayer CrI3. Our first-principles results agree
with available measurements and show the potential of SHG as a non-contacting
approach to explore correlations between interlayer structures and magnetic
orders of emerging ultra-thin magnetic materials.",2003.06385v1
2020/3/17,Strong antiferromagnetic interaction owing to a large trigonal distortion in the spin-orbit-coupled honeycomb lattice iridate CdIrO$_3$,"We investigated the magnetic properties of the ilmenite-type iridate
CdIrO$_3$ with a honeycomb lattice formed by Ir$^{4+}$ ions prepared via a
solid-state metathesis. The magnetization measurements with using the powder
sample reveal a large effective magnetic moment and a fairly strong
antiferromagnetic interaction, indicating a deviation from the Kitaev model.
Considering the relationship between magnetism and crystal structure in
CdIrO$_3$ with comparing with the other ilmenite-type iridates ZnIrO$_3$ and
MgIrO$_3$, we conclude that insulating CdIrO$_3$ cannot be describe as a
$J_{\rm eff} = 1/2$ Mott state owing to a metathetically-stabilized large
trigonal distortion of IrO$_6$ octahedra.",2003.07531v1
2020/3/25,Zero-field Nernst effect in a ferromagnetic kagome-lattice Weyl-semimetal Co3Sn2S2,"The discovery of magnetic topological semimetals recently attracted
significant attention in the field of topology and thermoelectrics. In a
thermoelectric device based on the Nernst geometry, an external magnet is
required as an integral part. We report a zero-field Nernst effect in a newly
discovered hard-ferromagnetic kagome-lattice Weyl-semimetal Co3Sn2S2. A maximum
Nernst thermopower of 3 microvolt/K at 80 K in zero field is achieved in this
magnetic Weyl-semimetal. Our results demonstrate the possibility of application
of topological hard magnetic semimetals for low-power thermoelectric devices
based on the Nernst effect and are thus valuable for the comprehensive
understanding of transport properties in this class of materials.",2003.11327v1
2020/4/15,Antisite disorder in the battery material LiFePO$_4$,"We report detailed magnetometry and high-frequency electron spin resonance
(HF-ESR) measurements which allow detailed investigation on Li-Fe antisite
disorder in single-crystalline LiFePO$_4$, i.e., exchange of Fe$^{2+}$- and
Li$^+$-ions. The data imply that magnetic moments of Fe$^{2+}$-ions at
Li-positions do not participate in long-range antiferromagnetic order in
LiFePO$_4$ but form quasi-free moments. Anisotropy axes of the magnetic moments
at antisite defects are attached to the main crystallographic directions. The
local character of these moments is confirmed by associated linear resonance
branches detected by HF-ESR studies. Magnetic anisotropy shows up in
significant zero-field splittings of $\Delta = 220(3)$~GHz, $\Delta'\sim50$~GHz
and a highly anisotropic $g$-factor, i.e., $g_\mathrm{a} = 1.4$, $g_\mathrm{b}
= 2.0$, and $g_\mathrm{c} = 6.3$. We demonstrate a general method to precisely
determine Fe-antisite disorder in LiFePO$_4$ from magnetic studies which
implies a density of paramagnetic Fe$^{2+}$-ions at Li-positions of 0.53\%.",2004.07091v1
2020/5/10,Determination of the magnetocaloric effect from thermophysical parameters and their relationships near magnetic phase transition in doped manganites,"We present the results of a comparative analysis of the magnetocaloric effect
(MCE) in Pr0.7Sr0.2Ca0.1MnO3, through direct and indirect measurements, using
experimentally measured magnetization, specific heat, magnetostriction,
resistivity, thermal diffusivity and thermal conductivity parameters. We have
demonstrated that the change in each parameter in response to a magnetic field
near the ferromagnetic-paramagnetic phase transition temperature of the
material correlates with the change in magnetic entropy. These findings allow
us to interrelate these parameters and provide an alternative, effective
approach for accessing the usefulness of magnetocaloric materials.",2005.04569v1
2020/6/1,Interlayer magnetism in Fe3-xGeTe2,"Fe$_{3-x}$GeTe$_2$ is a layered van der Waals magnetic material with a
relatively high ordering temperature and large anisotropy. While most studies
have concluded the interlayer ordering to be ferromagnetic, there have also
been reports of interlayer antiferromagnetism in Fe$_{3-x}$GeTe$_2$. Here, we
investigate the interlayer magnetic ordering by neutron diffraction
experiments, scanning tunneling microscopy (STM) and spin-polarized STM
measurements, density functional theory plus U calculations and STM
simulations. We conclude that the layers of Fe$_{3-x}$GeTe$_2$ are coupled
ferromagnetically and that in order to capture the magnetic and electronic
properties of Fe$_{3-x}$GeTe$_2$ within density functional theory, Hubbard U
corrections need to be taken into account.",2006.01094v2
2020/6/9,Electronic and Magnetic Properties of Topological Semimetal Candidate NdSbTe,"ZrSiS-type materials represent a large material family with unusual
coexistence of topological nonsymmorphic Dirac fermions and nodal-line
fermions. As a special group of ZrSiS-family, LnSbTe (Ln = Lanthanide rare
earth) compounds provide a unique opportunity to explore new quantum phases due
to the intrinsic magnetism induced by Ln. Here we report the single crystal
growth and characterization of NdSbTe, a previously unexplored LnSbTe compound.
NdSbTe has an antiferromagnetic ground state with field-driven metamagnetic
transitions similar to other known LnSbTe, but exhibits distinct enhanced
electronic correlations characterized by large a Sommerfeld coefficient of 115
mJ/mol $K^2$, which is the highest among the known LnSbTe compounds.
Furthermore, our transport studies have revealed the coupling with magnetism
and signatures of Kondo localization. All these findings establish NdSbTe as a
new platform for observing novel phenomena arising from the interplay between
magnetism, topology, and electron correlations.",2006.05536v1
2020/6/16,Hybrid Magneto Photonic Material Structure for Plasmon Assisted Magnetic Switching,"We have proposed the use of surface plasmon resonances at the interface of
hybrid magneto-photonic heterostructures [Opt. Mat. Exp., 7, 4316 (2017)] for
all-optical control of the macroscopic spin orientation in nanostructures in fs
time scales. This requires strong spin-photon coupling for the resonant
enhancement of opto-magnetic fields, generated through the inverse Faraday
effect, in magnetic nanostructures with perpendicular anisotropy. Here we
report on the development of nm thick interlayers to control the growth
orientation of hcp-Co alloys grown on refractory plasmonic materials to align
the magnetic axis out-of-plane, thereby meeting key requirements for the
realization of ultrafast magneto-photonic devices.",2006.09524v2
2020/6/30,Spin-orbit torque magnetization switching in MoTe2/permalloy heterostructures,"The ability to switch magnetic elements by spin-orbit-induced torques has
recently attracted much attention for a path towards high-performance,
non-volatile memories with low power consumption. Realizing efficient
spin-orbit-based switching requires harnessing both new materials and novel
physics to obtain high charge-to-spin conversion efficiencies, thus making the
choice of spin source crucial. Here we report the observation of spin-orbit
torque switching in bilayers consisting of a semimetallic film of 1T'-MoTe2
adjacent to permalloy. Deterministic switching is achieved without external
magnetic fields at room temperature, and the switching occurs with currents one
order of magnitude smaller than those typical in devices using the
best-performing heavy metals. The thickness dependence can be understood if the
interfacial spin-orbit contribution is considered in addition to the bulk spin
Hall effect. Further threefold reduction in the switching current is
demonstrated with resort to dumbbell-shaped magnetic elements. These findings
foretell exciting prospects of using MoTe2 for low-power semimetal material
based spin devices.",2006.16618v1
2020/7/23,Pressure induced collapse of magnetic order in jarosite,"We report a pressure-induced phase transition in the frustrated kagom\'e
material jarosite at ~45 GPa, which leads to the disappearance of magnetic
order. Using a suite of experimental techniques, we characterize the
structural, electronic, and magnetic changes in jarosite through this phase
transition. Synchrotron powder X-ray diffraction and Fourier transform infrared
spectroscopy experiments, analyzed in aggregate with the results from density
functional theory calculations, indicate that the material changes from a R-3m
structure to a structure with a R-3c space group. The resulting phase features
a rare twisted kagom\'e lattice in which the integrity of the equilateral Fe3+
triangles persists. Based on symmetry arguments we hypothesize that the
resulting structural changes alter the magnetic interactions to favor a
possible quantum paramagnetic phase at high pressure.",2007.12024v1
2020/9/16,Topological Kagome magnet Co3Sn2S2 thin flakes with high electron mobility and large anomalous Hall effect,"Magnetic Weyl semimetals attract considerable interest not only for their
topological quantum phenomena but also as an emerging materials class for
realizing quantum anomalous Hall effect in the two-dimensional limit. A
shandite compound Co3Sn2S2 with layered Kagome-lattices is one such material,
where vigorous efforts have been devoted to synthesize the two-dimensional
crystal. Here we report a synthesis of Co3Sn2S2 thin flakes with a thickness of
250 nm by chemical vapor transport method. We find that this facile bottom-up
approach allows the formation of large-sized Co3Sn2S2 thin flakes of
high-quality, where we identify the largest electron mobility (~2,600
cm2V-1s-1) among magnetic topological semimetals, as well as the large
anomalous Hall conductivity (~1,400 {\Omega}-1cm-1) and anomalous Hall angle
(~32 %) arising from the Berry curvature. Our study provides a viable platform
for studying high-quality thin flakes of magnetic Weyl semimetal and stimulate
further research on unexplored topological phenomena in the two-dimensional
limit.",2009.07431v1
2020/10/6,Emergent spin dynamics enabled by lattice interactions in a bicomponent artificial spin ice,"Artificial spin ice (ASI) are arrays on nanoscaled magnets that can serve
both as models for frustration in atomic spin ice as well as for exploring new
spin-wave-based strategies to transmit, process, and store information. Here,
we exploit the intricate interplay of the magnetization dynamics of two
dissimilar ferromagnetic metals arranged on complimentary lattice sites in a
square ASI to effectively modulate the spin-wave properties. We show that the
interaction between the two sublattices results in unique spectra attributed to
each sublattice and we observe inter- and intra-lattice dynamics facilitated by
the distinct magnetization properties of the two materials. The dynamic
properties are systematically studied by angular-dependent broadband
ferromagnetic resonance and confirmed by micromagnetic simulations. We show
that the combination of materials with dissimilar magnetic properties enables
the realization of a wide range of two-dimensional structures potentially
opening the door to new concepts in nanomagnonics.",2010.03008v1
2020/11/24,Learning Effective Spin Hamiltonian of Quantum Magnet,"Interacting spins in quantum magnet can cooperate and exhibit exotic states
like the quantum spin liquid. To explore the materialization of such intriguing
states, the determination of effective spin Hamiltonian of the quantum magnet
is thus an important, while at the same time, very challenging inverse
many-body problem. To efficiently learn the microscopic spin Hamiltonian from
the macroscopic experimental measurements, here we propose an unbiased
Hamiltonian searching approach that combines various optimization strategies,
including the automatic differentiation and Bayesian optimization, etc, with
the exact diagonalization and many-body thermal tensor network calculations. We
showcase the accuracy and powerfulness by applying it to training thermal data
generated from a given spin Hamiltonian, and then to realistic experimental
data measured in the spin-chain compound Copper Nitrate and triangular-lattice
materials TmMgGaO4. This automatic Hamiltonian searching constitutes a very
promising approach in the studies of the intriguing spin liquid candidate
magnets and correlated electron materials in general.",2011.12282v2
2020/11/30,Domain wall patterning and giant response functions in ferrimagnetic spinels,"The manipulation of mesoscale domain wall phenomena has emerged as a powerful
strategy for designing ferroelectric responses in functional devices, but its
full potential has not yet been realized in the field of magnetism. We show
that mechanically strained samples of Mn$_3$O$_4$ and MnV$_2$O$_4$ exhibit a
stripe-like patterning of the bulk magnetization below known magnetostructural
transitions, similar to the structural domains reported in ferroelectric
materials. Building off our previous magnetic force microscopy data, we use
small angle neutron scattering to show that these patterns extend to the bulk,
and demonstrate an ability to manipulate the domain walls via applied magnetic
field and mechanical stress. We then connect these domains back to the
anomalously large magnetoelastic and magnetodielectric response functions
reported in these materials, directly correlating local and macroscopic
measurements on the same crystals.",2011.14970v1
2020/12/8,Decoupled Strain Response of Ferroic Properties in Multiferroic VOCl2 Monolayer,"Two-dimensional (2D) magnetoelectric multiferroics are promising
multifunctional materials for miniaturized logic and memory devices. Herein, we
explore the effectiveness of strain-engineering for tuning the properties of a
recently predicted 2D antiferromagnetic-ferroelectric, VOCl2 monolayer.
Interestingly, we find that magnetic-ordering and electric polarization can be
tuned independently using uniaxial tensile strain along different in-plane
lattice vectors. A 4% tensile strain along lattice vector b induces a
transition from an antiferromagnetic (AFM) ground state with an out-of-plane
magnetization to a ferromagnetic (FM) ground state with in-plane magnetization.
On the other hand, tensile strain along lattice vector a enhances spontaneous
electric polarization, without affecting the magnetic ordering. The monolayers
remain dynamically stable under tensile strain, which further helps to raise
the Curie temperature of ferromagnetism, as well as ferroelectricity. Such a
strain-tunable multiferroic material holds great promises for future generation
nanoelectronic devices.",2012.04592v2
2021/1/9,Quarter-filled Kane-Mele Hubbard model: Dirac half-metals,"Recent experimental success in the realization of two-dimensional (2D)
magnetism has stimulated the search for new magnetic 2D materials with strong
magnetic anisotropy and high Curie temperature. One promising subgroup of 2D
magnetic systems are Dirac half-metals (DHM) which have gained a lot of
interest recently, as they host a high-temperature quantum anomalous Hall
effect (QAHE). This article discusses predictions for intrinsic DHMs and
identifies them as realizations of the Kane-Mele Hubbard model at quarter
filling. This proposed unification contributes to a firmer understanding of
these materials and suggests pathways for the discovery of new DHM systems.",2101.03352v1
2021/2/17,Modified Curie-Weiss Law for $j_{\rm eff}$ Magnets,"In spin-orbit-coupled magnetic materials, the usually applied Curie-Weiss law
can break down. This is due to potentially sharp temperature-dependence of the
local magnetic moments. We therefore propose a modified Curie-Weiss formula
suitable for analysis of experimental susceptibility. We show for octahedrally
coordinated materials of $d^5$ filling that the Weiss constant obtained from
the improved formula is in excellent agreement with the calculated Weiss
constant from microscopic exchange interactions. Reanalyzing the measured
susceptibility of several Kitaev candidate materials with the modified formula
resolves apparent discrepancies between various experiments regarding the
magnitude and anisotropies of the underlying magnetic couplings.",2102.08964v1
2021/2/22,"Sub-nanoscale Temperature, Magnetic Field and Pressure sensing with Spin Centers in 2D hexagonal Boron Nitride","Spin defects in solid-state materials are strong candidate systems for
quantum information technology and sensing applications. Here we explore in
details the recently discovered negatively charged boron vacancies ($V_B^-$) in
hexagonal boron nitride (hBN) and demonstrate their use as atomic scale sensors
for temperature, magnetic fields and externally applied pressure. These
applications are possible due to the high-spin triplet ground state and bright
spin-dependent photoluminescence (PL) of the $V_B^-$. Specifically, we find
that the frequency shift in optically detected magnetic resonance (ODMR)
measurements is not only sensitive to static magnetic fields, but also to
temperature and pressure changes which we relate to crystal lattice parameters.
Our work is important for the future use of spin-rich hBN layers as intrinsic
sensors in heterostructures of functionalized 2D materials.",2102.10890v1
2021/4/6,Sampling the Cu-Fe-Co phase diagram by severe plastic deformation for enhanced soft magnetic properties,"Initial powder mixtures of Cu, Fe and Co are exposed to severe plastic
deformation by high-pressure torsion to prepare solid solutions. A broad range
of compositions is investigated, whereas this study aims at the synthesis of
soft magnetic materials and therefore at the formation of a homogeneous and
nanocrystalline microstructure. For intermediate ferromagnetic contents,
high-pressure torsion at room temperature yields single-phase supersaturated
solid solutions. For higher ferromagnetic contents, two consecutive steps of
high-pressure torsion deformation at different temperatures yield the desired
nanocrystalline microstructure. Depending on the Co-to-Fe-ratio, either a
single-phase supersaturated solid solution or a nanocomposite forms. The
composite exhibits an enhanced magnetic moment, indicating the formation of a
(Fe,Co)-alloy upon severe plastic deformation. Soft magnetic properties are
verified for large Co-to-Fe-ratios and this microstructure is found to remain
stable up to 400 {\deg}C.",2104.02343v1
2021/5/13,Bicircular light tuning of magnetic symmetry and topology in Dirac semimetal Cd$_3$As$_2$,"We show that Floquet engineering using bicircular light (BCL) is a versatile
way to control magnetic symmetries and topology in materials. The electric
field of BCL, which is a superposition of two circularly polarized light waves
with frequencies that are integer multiples of each other, traces out a rose
pattern in the polarization plane that can be chosen to break selective
symmetries, including spatial inversion. Using a realistic low-energy model, we
theoretically demonstrate that the three-dimensional Dirac semimetal
Cd$_3$As$_2$ is a promising platform for BCL Floquet engineering. Without
strain, BCL irradiation induces a transition to a non-centrosymmetric magnetic
Weyl semimetal phase with tunable energy separation between the Weyl nodes. In
the presence of strain, we predict the emergence of a magnetic topological
crystalline insulator with exotic unpinned surface Dirac states that are
protected by a combination of twofold rotation and time-reversal $(2')$ and can
be controlled by light.",2105.06439v1
2021/5/30,Routes to realize the axion-insulator phase in MnBi$_{2}$Te$_{4}$(Bi$_{2}$Te$_{3}$)$_{n}$ family: a perspective,"Axion, first postulated as a hypothetical particle in high-energy physics, is
now extended to describe a novel topological magnetoelectric effect derived
from the Chern-Simons theory in condensed matter systems. The recent discovered
intrinsic magnetic topological insulators MnBi2Te4 and its derivatives have
attracted great attention because of their potential as a material platform to
realize such a quantized axion field. Since the magnetic exchange gap can bring
the half-quantized anomalous Hall effect at the surface, an axion insulator
manifests as quantum anomalous Hall and zero Hall plateau effects in the thin
films. However, many puzzles about this material family remain elusive yet,
such as the gapless surface state and the direct experimental evidence of the
axion insulator. In this Perspective, we discuss the preconditions,
manifestations and signatures of the axion-insulator phase, in the context of
the development of the natural magnetic topological heterostructure
MnBi2Te4(Bi2Te3)n family with various intriguing quantum phenomena. Recent
theoretical and experimental efforts regarding the intrinsic magnetic
topological insulators are summarized here to pave the way for this
phenomenally developing field.",2105.14575v1
2021/7/29,Light-driven topological and magnetic phase transitions in thin-layer antiferromagnets,"We theoretically study the effect of low-frequency light pulses in resonance
with phonons in the topological and magnetically ordered two septuple-layer
(2-SL) MnBi2Te4 (MBT) and MnSb2Te4 (MST). These materials share symmetry
properties and an antiferromagnetic ground state in pristine form but present
different magnetic exchange interactions. In both materials, shear and
breathing Raman phonons can be excited via non-linear interactions with
photo-excited infrared phonons using intense laser pulses attainable in current
experimental setups. The light-induced transient lattice distortions lead to a
change in the sign of the effective interlayer exchange interaction and
magnetic order accompanied by a topological band transition. Furthermore, we
show that moderate anti-site disorder, typically present in MBT and MST
samples, can facilitate such an effect. Therefore, our work establishes 2-SL
MBT and MST as candidate platforms to achieve non-equilibrium
magneto-topological phase transitions.",2107.14361v3
2021/9/24,B20-MnSi films grown on Si(100) substrates with magnetic skyrmion signature,"Magnetic skyrmions have been suggested as information carriers for future
spintronic devices. As the first material with experimentally confirmed
skyrmions, B20-type MnSi was the research focus for decades. Although B20-MnSi
films have been successfully grown on Si(111) substrates, there is no report
about B20-MnSi films on Si(100) substrates, which would be more preferred for
practical applications. In this letter, we present the first preparation of
B20-MnSi on Si(100) substrates. It is realized by sub-second solid-state
reaction between Mn and Si via flash-lamp annealing at ambient pressure. The
regrown layer shows an enhanced Curie temperature of 43 K compared with bulk
B20-MnSi. The magnetic skyrmion signature is proved in our films by magnetic
and transport measurements. The millisecond-range flash annealing provides a
promising avenue for the fabrication of Si-based skyrmionic devices.",2109.11836v1
2021/12/29,Harnessing re-programmable phase transitions to control the propagation of sound waves,"Metamaterials can enable peculiar static and dynamic behavior (such as
negative effective mass density, dynamical stiffness, and Poisson's ratio) due
to their geometry rather than their chemical composition. The geometry of these
metamaterials can be thought of as the phase of the material, which is usually
fixed once the material is fabricated. While there exist many theoretical and
numerical studies of metamaterials that can change phase, or re-program,
experimental realizations remain limited due to challenges in
manufacturability, the destructive nature of the re-programming and inherent
non-linearities. Through a combination of analytical, numerical and
experimental analyses, we utilize tunable, self-assembled, nonlinear magnetic
lattices to realize metamaterials with reversible phase transitions. Our
metamaterials are composed of free-floating disks, with embedded permanent
magnets, confined within magnetic boundaries. We exploit the non-destructive
nature of the adjustable magnetic boundaries to create a set of re-programmable
metamaterials to control the propagation of sound waves. Furthermore, we
demonstrate a robust, real-time tunable wave filter at ultra-low frequencies.
Our findings can expand the metamaterials horizon into functional and tunable
devices.",2112.14787v1
2022/1/18,In-plane magnetic structure and exchange interactions in the high-temperature antiferromagnet Cr2Al,"The ordered tetragonal intermetallic Cr$_2$Al forms the same structure type
as Mn$_2$Au, and the latter has been heavily investigated for its potential in
antiferromagnetic spintronics due to its degenerate in-plane N\'{e}el vector.
We present the single crystal flux growth of Cr$_2$Al and orientation-dependent
magnetic properties. Powder neutron diffraction of Cr$_2$Al and
first-principles simulations reveal that the magnetic ordering is likely
in-plane and therefore identical to Mn$_2$Au, providing a second material
candidate in the MoSi$_2$ structure type to evaluate the fundamental
interactions that govern spintronic effects. The single ordering transition
seen in thermal analysis and resistivity indicates that no canting of the
moments along the $c$ axis is likely. Magnetometry, resistivity, and
differential scanning calorimetry measurements confirm the N\'{e}el temperature
to be $634 \pm 2$ K. First-principles simulations indicate that the system has
a small density of states at the Fermi energy and confirm the lowest-energy
magnetic ground state ordering, while Monte Carlo simulations match the
experimental N\'{e}el temperature.",2201.07356v1
2022/2/14,Magnetic APFC modeling and the influence of magneto-structural interactions on grain shrinkage,"We derive the amplitude expansion for a phase-field-crystal (APFC) model that
captures the basic physics of magneto-structural interactions. The symmetry
breaking due to magnetization is demonstrated, and the characterization of the
magnetic anisotropy for a BCC crystal is provided. This model enables a
convenient coarse-grained description of crystalline structures, in particular
when considering the features of the APFC model combined with numerical methods
featuring inhomogeneous spatial resolution. This is shown by addressing the
shrinkage of a spherical grain within a matrix, chosen as a prototypical system
to demonstrate the influence of different magnetizations. These simulations
serve as a proof of concept for the modeling of manipulation of dislocation
networks and microstructures in ferromagnetic materials within the APFC model.",2202.06654v2
2022/3/2,Polaronic Conductivity in Cr$_2$Ge$_2$Te$_6$ Single Crystals,"Intrinsic, two-dimensional (2D) ferromagnetic semiconductors are an important
class of materials for spin-charge conversion applications. Cr$_2$Ge$_2$Te$_6$
retains long-range magnetic order in bilayer at cryogenic temperatures and
shows complex magnetic interactions with considerable magnetic anisotropy.
Here, we performed a series of structural, magnetic, X-ray scattering,
electronic, thermal transport and first-principles calculation studies which
reveal that localized electronic charge carriers in Cr$_2$Ge$_2$Te$_6$ are
dressed by surrounding lattice and are involved in polaronic transport via
hopping that is sensitive on details of magnetocrystalline anisotropy. This
opens possibility for manipulation of charge transport in Cr$_2$Ge$_2$Te$_6$ -
based devices by electron-phonon- and spin-orbit coupling-based tailoring of
polaron properties.",2203.00817v1
2022/3/2,Enhanced colloidal transport in twisted magnetic patterns,"Bilayers of two-dimensional materials twisted at specific angles can exhibit
exceptional properties such as the occurrence of unconventional
superconductivity in twisted graphene. We demonstrate here that novel phenomena
in twisted materials emerges also in particle-based classical systems. We study
the transport of magnetic colloidal particles driven by a drift force and
located between two twisted periodic magnetic patterns with either hexagonal or
square symmetry. The magnetic potential generated by patterns twisted at
specific magic angles develops flat channels, which increase the mobility of
the colloidal particles compared to that in single patterns. We characterize
the effect of the temperature and that of the magnitude of the drift force on
the colloidal mobility. The transport is more enhanced in square than in
hexagonal twisted patterns. Our work extends twistronics to classical soft
matter systems with potential applications to lab-on-a-chip devices.",2203.01034v1
2022/3/8,Field-tunable toroidal moment and anomalous Hall effect in noncollinear antiferromagnetic Weyl semimetal Co1/3TaS2,"Combining magnetism with band topology provides various novel phases that are
otherwise impossible. Among several cases, noncollinear metallic
antiferromagnets can reveal particularly rich topological physics due to their
diverse magnetic ground states. However, there are only a few experimental
studies due to the lack of suitable materials, especially with triangular
lattice antiferromagnets. Here, we report that metallic triangular
antiferromagnet Co1/3TaS2 exhibits a substantial anomalous Hall effect (AHE)
related to its noncollinear magnetic order. Our first-principles calculations
found that hourglass Weyl fermions from the non-symmorphic symmetry trigger
AHE. We further show that AHE in Co1/3TaS2 can be characterized by the toroidal
moment, a vortex-like multipole component that arises from a combination of
chiral lattice and geometrical frustration. Finally, the unusual
field-tunability of the toroidal moment puts Co1/3TaS2 as a rare example of a
noncollinear metallic antiferromagnet filled with interesting magnetic and
topological properties.",2203.03826v1
2022/3/11,Engineering magnetic topological insulators in Eu$_5M_2X_6$ Zintls,"Magnetic topological insulator provide a prominent material platform for
quantum anomalous Hall physics and axion electrodynamics. However, the lack of
material realizations with cleanly gapped surfaces hinders technological
utilization of these exotic quantum phenomena. Here, using the Zintl concept
and the properties of non-symmorphic space groups, we computationally engineer
magnetic topological insulators. Specifically, we explore Eu$_5M_2X_6$
($M$=metal, $X$=pnictide) Zintl compounds and find that Eu$_5$Ga$_2$Sb$_6$,
Eu$_5$Tl$_2$Sb$_6$ and Eu$_5$In$_2$Bi$_6$ form stable structures with
non-trivial $\mathbb{Z}_2$ indices. We also show that epitaxial and uniaxial
strain can be used to control the $\mathbb{Z}_2$ index and the bulk energy gap.
Finally, we discuss experimental progress towards the synthesis of the proposed
candidates and provide insights that can be used in the search for robust
magnetic topological insulators in Zintl compounds.",2203.06212v2
2022/6/6,Anomalous Transport Properties of Re$_3$Ge$_7$,"Single crystals of intermetallic Re$_3$Ge$_7$ were grown and characterized by
measuring magnetization, electrical resistivity, Hall coefficient, and specific
heat. Magnetization measurements show the material is weakly diamagnetic. A
phase transition is indicated by a kink in magnetic susceptibility at $T_{c} =
58.5$K and is confirmed by a $\lambda$-like anomaly in specific heat. In
zero-field, the temperature dependence of electrical resistivity $\rho(T)$
follows a typical metallic behavior above $T_c$ and sharply increases below
$T_c$, showing a metal-to-insulator-like transition. When a magnetic field is
applied, strong effects on the transport properties are observed. The
temperature dependence of magnetoresistivity $\Delta\rho$ = $\rho (T, H)$ -
$\rho (T, H=0)$ develops a maximum around 30 K, deviating from ordinary
metallic behavior. Analysis of the Hall coefficient measurements indicates that
the carrier density is 0.04 per formula unit at 300 K and drops by two orders
of magnitude below $T_c$. The effective mass of charge carriers is inferred
from the analysis of the Shubnikov-de Haas quantum oscillations to be close to
the bare electron mass.",2206.02943v1
2022/7/28,Magnetic properties of CrSnS3: A new Van der Waals ferromagnet,"We report an experimental discovery of CrSnS3, a new Van der Waals
ferromagnetic (FM) with Curie temperature TC ~119K. The Curie temperature is in
qualitative agreement of Chittari et. al. DFT prediction (TC =112.3K) for an
Ising model with the addition of Coulomb potential. The FM ordering temperature
in CrSnS3 is the highest among Cr-based Van der Waals materials: CrI3, CrSiTe3
and CrGeTe3. The dc-susceptibility revealed a sharp increase at Tc (~119K)
indicative of a first order transition; then raises to a wide maximum at AFM
Neel temperature TN~90K.The ac-susceptibility reveals the presence of two sharp
peaks; one close to Tc (119K) and the other at TN~90K. Ac-susceptibility
measurements in an applied dc-magnetic field indicates that CrSnS3 undergoes
two successive phase transitions: a sharp increase in the susceptibility
indicates a first order PM to FM at 119K, followed by more gradual decrease at
the onset of AFM transition at TN~90K. The magnetization isotherms below 30K
indicates that the materials orders in an AFM state; while the magnetic
isotherms at T >30K rises sharply to its saturated values confirming the
ferromagnetic state.",2207.14129v1
2022/8/4,"Ab-initio study of stable 3d, 4d and 5d transition metal based Quaternary Heusler compounds","The realization of the stable structure of Heusler compounds and the study of
different properties is an important step for their potential application in
spintronics and magnetoelectronic devices. In this paper, using the plane-wave
pseudopotential method within the framework of density functional theory (DFT),
we investigate 25 Quaternary Heusler compounds for their electronic, magnetic,
and mechanical properties. The Open Quantum Materials Database (OQMD) is used
to screen a large number of compounds to narrow down the possible synthesizable
materials. The convex-hull distance and elastic constants are exploited to
confirm the thermodynamic and mechanical stability of the compounds. The
careful study of the different structures suggests that 5 of the compounds
crystallize in type-1 structure whereas 20 compounds adopt type-3 structure.
The possible explanation for the observed behavior is made by invoking
electronegativity arguments and through the study of individual spin magnetic
moments in different structures. The compounds with diverse electronic and
magnetic properties such as half-metallicity, spin gapless semiconducting
behavior, and non-magnetic semi-conducting property have been identified.",2208.02401v2
2022/8/19,Strain-Driven Zero-Field Near-10 nm Skyrmions in Two-Dimensional van der Waals Heterostructures,"Magnetic skyrmions $-$ localized chiral spin structures $-$ show great
promise for spintronic applications. The recent discovery of two-dimensional
(2D) magnetic materials opened new opportunities for exploring such topological
spin structures in atomically thin van der Waals (vdW) materials. Despite
recent progress in stabilizing metastable skyrmions in 2D magnets, their
diameters are still beyond 100~nm and their lifetime, which is essential for
applications, has not been explored yet. Here, using first-principles
calculations and atomistic spin simulations, we predict that compressive
mechanical strain leads to stabilizing zero-field skyrmions with diameters
close to 10 nm in a Fe$_3$GeTe$_2$/germanene vdW heterostructure. The origin of
these unique skyrmions is attributed to the high tunability of
Dzyaloshinskii-Moriya interaction and magnetocrystalline anisotropy energy by
strain, an effect which is shown to be general for Fe$_3$GeTe$_2$
heterostructures with buckled substrates. Based on our first-principles
parameters for the magnetic interactions, we calculate the energy barriers
protecting skyrmions against annihilation and their lifetimes using
transition-state theory. We show that nanoscale skyrmions in strained
Fe$_3$GeTe$_2$/germanene can be stable for hours at temperatures up to 20 K.",2208.09210v1
2022/9/18,Out-of-plane polarization and topological magnetic vortices in multiferroic CrPSe$_3$,"Two-dimensional (2D) multiferroic materials are ideal systems for exploring
new coupling mechanisms between different ferroic orders and producing novel
quantum phenomena with potential applications. We employed first-principles
density functional theory calculations to discover intrinsic ferroelectric and
anti-ferroelectric phases of CrPSe$_3$, which show ferromagnetic order and
compete with the centrosymmetric phase with an antiferromagnetic order. Our
analysis show that the electrical dipoles of such type-I multiferroic phases
come from the out-of-plane displacements of phosphorus ions due to the
stereochemically active lone pairs. The coupling between polar and magnetic
orders creates the opportunity for tunning the magnetic ground state by
switching from the centrosymmetric to the ferroelectric phase using an
out-of-plane electric field. In ferroelectric and antiferroelectric phases, the
combination of easy-plane anisotropy and Dzyaloshinskii-Moriya interactions
(DMI) indicate they can host topological magnetic vortices like meron pairs.",2209.08442v1
2022/9/28,Unconventional thermoelectric transport in tilted Weyl semimetals,"We analyze the effect of the tilt on the transverse thermoelectric
coefficient of Weyl semimetals in the \emph{conformal} limit, i.e., zero
temperature and zero chemical potential. Using the Kubo formalism, we find a
nonmonotonic behavior of the thermoelectric conductivity as a function of the
tilt perpendicular to the magnetic field, and a linear behavior when the tilt
is aligned to the magnetic field. An ``axial Nernst"" current (chiral currents
counter propagating perpendicularly to the magnetic field and the temperature
gradient) is generated in inversion symmetric Weyl materials when the tilt
vector has a projection in the direction of the magnetic field. This analysis
will help in the design and interpretation of thermoelectric transport
experiments in recently discovered topological quantum materials.",2209.14331v2
2022/10/13,Cryogenic Magneto-Terahertz Scanning Near-field Optical Microscope (cm-SNOM),"We have developed a versatile near-field microscopy platform that can operate
at high magnetic fields and below liquid-helium temperatures. We use this
platform to demonstrate an extreme terahertz (THz) nanoscope operation and to
obtain the first cryogenic magneto-THz time-domain nano-spectroscopy/imaging at
temperatures as low as 1.8 K and magnetic fields of up to 5 T simultaneously.
Our cryogenic magneto-THz scanning near-field optical microscopy, or cm-SNOM,
instrument comprises three main equipment: i) a 5 T split pair magnetic
cryostat with a custom made insert for mounting SNOM inside; ii) an atomic
force microscope (AFM) unit that accepts ultrafast THz excitation and iii) a
MHz repetition rate, femtosecond laser amplifier for high-field THz pulse
generation and sensitive detection. We apply the cm-SNOM to obtain proof of
principle measurements of superconducting and topological materials. The new
capabilities demonstrated break grounds for studying quantum materials that
requires extreme environment of cryogenic operation and applied magnetic fields
simultaneously in nanometer space, femtosecond time, and terahertz energy
scales.",2210.07319v1
2022/10/27,Quantum-state engineering in cavity magnomechanics formed by two-dimensional magnetic materials,"Cavity magnomechanics has become an ideal platform to explore macroscopic
quantum effects. Bringing together magnons, phonons, and photons in a system,
it opens many opportunities for quantum technologies. It was conventionally
realized by an yttrium iron garnet, which exhibits a parametric magnon-phonon
coupling $\hat{m}^\dag\hat{m}(\hat{b}^\dag+\hat{b})$, with $\hat{m}$ and
$\hat{b}$ being the magnon and phonon modes. Inspired by the recent realization
of two-dimensional (2D) magnets, we propose a cavity magnomechanical system
using a 2D magnetic material with both optical and magnetic drivings. It
features the coexisting photon-phonon radiation-pressure coupling and quadratic
magnon-phonon coupling $\hat{m}^\dag\hat{m}(\hat{b}^\dag+\hat{b})^2$ induced by
the magnetostrictive interaction. A stable squeezing of the phonon and bi- and
tri-partite entanglements among the three modes are generated in the regimes
with a suppressed phonon number. Compared with previous schemes, ours does not
require any extra nonlinear interaction and reservoir engineering and is robust
against the thermal fluctuation. Enriching the realization of cavity
magnomechanics, our system exhibits its superiority in quantum-state
engineering due to the versatile interactions enabled by its 2D feature.",2210.15519v2
2022/11/10,Tailoring Bulk Photovoltaic Effects in Magnetic Sliding Ferroelectric Materials,"The bulk photovoltaic effect that is intimately associated with crystalline
symmetry has been extensively studied in various nonmagnetic materials,
especially ferroelectrics with a switchable electric polarization. In order to
further engineer the symmetry, one could resort to spin-polarized systems
possessing an extra magnetic degree of freedom. Here, we investigate the bulk
photovoltaic effect in two-dimensional magnetic sliding ferroelectric (MSFE)
systems, illustrated in VSe2, FeCl2, and CrI3 bilayers. The transition metal
elements in these systems exhibit intrinsic spin polarization, and the stacking
mismatch between the two layers produce a finite out-of-plane electric dipole.
Through symmetry analyses and first-principles calculations, we show that
photoinduced in-plane bulk photovoltaic current can be effectively tuned by
their magnetic order and the out-of-plane dipole moment. The underlying
mechanism is elucidated from the quantum metric dipole distribution in the
reciprocal space. The ease of the fabrication and manipulation of MSFEs
guarantee practical optoelectronic applications.",2211.05353v1
2022/11/14,Controlling the magnetic state of the proximate quantum spin liquid $α$-RuCl$_3$ with an optical cavity,"Harnessing the enhanced light-matter coupling and quantum vacuum fluctuations
resulting from mode volume compression in optical cavities is a promising route
towards functionalizing quantum materials and realizing exotic states of
matter. Here, we extend cavity quantum electrodynamical materials engineering
to correlated magnetic systems, by demonstrating that a Fabry-P\'erot cavity
can be used to control the magnetic state of the proximate quantum spin liquid
$\alpha$-RuCl$_3$. Depending on specific cavity properties such as the mode
frequency, photon occupation, and strength of the light-matter coupling, any of
the magnetic phases supported by the extended Kitaev model can be stabilized.
In particular, in the THz regime, we show that the cavity vacuum fluctuations
alone are sufficient to bring $\alpha$-RuCl$_3$ from a zigzag antiferromagnetic
to a ferromagnetic state. By external pumping of the cavity in the few photon
limit, it is further possible to push the system into the antiferromagnetic
Kitaev quantum spin liquid state.",2211.07247v1
2022/12/3,Magnetoplasmonics: current challenges and future opportunities,"Plasmonics represents a unique approach to confine and enhance
electromagnetic radiation well below the diffraction limit, bringing a huge
potential for novel applications, for instance in energy harvesting,
optoelectronics, and nanoscale biochemistry. To achieve novel functionalities,
the combination of plasmonic properties with other material functions has
become increasingly attractive. In this Perspective, we review the current
state of the art, challenges, and future opportunities in nanoscale
magnetoplasmonics, an emerging area aiming to merge magnetism and plasmonics in
confined geometries to control either plasmons, electromagnetic-induced
collective electronic excitations, using magnetic properties, or magnetic
phenomena with plasmons. We begin by highlighting the cornerstones of the
history and principles of this research field. We then provide our vision of
its future development by showcasing raising research directions in
mid-infrared light-driven spintronics and novel materials for
magnetoplasmonics, such as transparent conductive oxides and hyperbolic
metamaterials. As well, we provide an overview of recent developments in
plasmon-driven magnetization dynamics, nanoscale optomagnetism and
acousto-magnetoplasmonics. We conclude by giving our personal vision of the
future of this thriving research field.",2212.01684v1
2023/2/20,Magnetic properties of ferromagnetic Gd$_5$Si$_4$-Fe$_3$O$_4$ bilayer thin film heterostructure,"Magnetic properties of thin films differs from that of the corresponding bulk
materials and show novel physics as a result of their reduced size and
dimensionality. Profound changes in magnetic properties can also result with
exchange bias between the interface of the thin films of different materials.
Here we present Fe$_3$O$_4$, Gd$_5$Si$_4$ and Fe$_3$O$_4$-Gd$_5$Si$_4$ bilayer
thin films of varying thicknesses were prepared by RF Magnetron sputtering of
Fe$_3$O$_4$ and Gd$_5$Si$_4$ targets on silicon substrates in high vacuum.
Their magnetization was measured at room temperature in fields of 3T and
between 50 K to 400 K temperatures. Gd5Si4 films resulted in oxidation due to
the exposure to the air. Deposited film thickness of all the specimens are
larger than 50nm and show ferromagnetic behavior.",2302.09774v1
2023/2/27,Strain-induced interlayer magnetic coupling spike of two-dimensional van der Waals material Fe$_5$GeTe$_2$,"A stronger interlayer magnetic coupling (ILMC) can open up new opportunities
in spintronics devices for Fe$_5$GeTe$_2$ (F5GT), a demonstrated
two-dimensional (2D) van der Waals (vdW) material with high Currie temperature.
Here we observe an extraordinary ILMC spike in F5GT, jumping from 1.15 to 12.79
meV/f.u, by applying a 3% in-plane strain. This spike is mainly ascribed to a
significant increase in the magnetic moment of the Fe5 ion. Moreover, the
applied in-plane strain can also significantly enhance the magnetic anisotropy
energy (MAE) of the system, triggering the transition between the in/off-plane
configurations in multi-layer F5GT.",2302.13664v1
2023/3/21,"Structure, physical properties, and magnetically tunable topological phases in topological semimetal EuCuBi","A single material achieving multiple topological phases can provide potential
application for topological spintronics, whereas the candidate materials are
very limited. Here, we report the structure, physical properties, and possible
emergence of multiple topological phases in the newly discovered, air-stable
EuCuBi single crystal. EuCuBi crystallizes in a hexagonal space group P63/mmc
(No. 194) in ZrBeSi-type structure with an antiferromagnetic (AFM) ground state
below TN = 11.2 K. There is a competition between AFM and ferromagnetic (FM)
interactions below TN revealed by electrical resistivity and magnetic
susceptibility measurements. With the increasing magnetic field, EuCuBi evolves
from the AFM ground state with a small amount of FM component, going through
two possible metamagnetic phases, finally reaches the field-induced FM phase.
Based on the first-principles calculations, we demonstrate that the Dirac,
Weyl, and possible mirror Chern insulator can be achieved in EuCuBi by tuning
the temperature and applying magnetic field, making EuCuBi a promising
candidate for exploring multiple topological phases.",2303.11894v1
2023/4/11,Adsorption tuning of polarity and magnetism in AgCr2S4 monolayer,"As a recent successfully exfoliated non van der Waals layered material,
AgCrS2 has received a lot of attentions. Motivated by its structure related
magnetic and ferroelectric behavior, a theoretical study on its exfoliated
monolayer AgCr2S4 has been carried out in the present work. Based on density
functional theory, the ground state and magnetic order of monolayer AgCr2S4
have been determined. The centrosymmetry emerges upon two-dimensional
confinement and thus eliminates the bulk polarity. Moreover, two-dimensional
ferromagnetism appears in the CrS2 layer of AgCr2S4 and can persist up to room
temperature. The surface adsorption has also been taken into consideration,
which shows a nonmonotonic effect on the ionic conductivity through ion
displacement of the interlayer Ag, but has little impact on the layered
magnetic structure.",2304.05307v2
2023/6/8,Stochastic homogenization of micromagnetic energies and emergence of magnetic skyrmions,"We perform a stochastic-homogenization analysis for composite materials
exhibiting a random microstructure. Under the assumptions of stationarity and
ergodicity, we characterize the Gamma-limit of a micromagnetic energy
functional defined on magnetizations taking value in the unit sphere, and
including both symmetric and antisymmetric exchange contributions. This
Gamma-limit corresponds to a micromagnetic energy functional with homogeneous
coefficients. We provide explicit formulas for the effective magnetic
properties of the composite material in terms of homogenization correctors.
Additionally, the variational analysis of the two exchange energy terms is
performed in the more general setting of functionals defined on manifold-valued
maps with Sobolev regularity, in the case in which the target manifold is a
bounded, orientable smooth surface with tubular neighborhood of uniform
thickness. Eventually, we present an explicit characterization of minimizers of
the effective exchange in the case of magnetic multilayers, providing
quantitative evidence of Dzyaloshinskii's predictions on the emergence of
helical structures in composite ferromagnetic materials with stochastic
microstructure.",2306.05151v1
2023/7/7,Magnetically and electrically controllable valley splittings in MXene monolayers,"The modulation of the valley structure in two-dimensional valley materials is
vital in the field of valleytronics. The multiferroicity provides possibility
for multiple modulations of the valley, including the magnetic and electric
means. Based on the first-principle calculations, we study the valley
properties and associated manipulations of multiferroic Co$_2$CF$_2$ monolayers
with different stacking patterns. Our calculations show that the Co$_2$CF$_2$
monolayer in the H$^{\prime}$ phase is a ferrovalley material, with sizable
valley splittings. By rotating the magnetization direction, the valley
splittings can be tuned for both the magnitude and sign. The electric field,
driving the reversal of the electric polarization, can also change the
magnitude of the valley splittings. Besides, a metastable T$^{\prime}$ phase
exhibits valley splittings as well, of which the magnitude and sign can be
simultaneously controlled by applied magnetic and electric fields. These
findings offer a practical way for realizing highly tunable valleys by
multiferroic couplings.",2307.03414v1
2023/8/31,Electronic band reconstruction across the insulator-metal transition in colossal magnetoresistive EuCd2P2,"While colossal magnetoresistance (CMR) in Eu-based compounds is often
associated with strong spin-carrier interactions, the underlying reconstruction
of the electronic bands is much less understood from spectroscopic experiments.
Here using angle-resolved photoemission, we directly observe an electronic band
reconstruction across the insulator-metal (and magnetic) transition in the
recently discovered CMR compound EuCd2P2. This transition is manifested by a
large magnetic band splitting associated with the magnetic order, as well as
unusual energy shifts of the valence bands: both the large ordered moment of Eu
and carrier localization in the paramagnetic phase are crucial. Our results
provide spectroscopic evidence for an electronic structure reconstruction
underlying the enormous CMR observed in EuCd2P2, which could be important for
understanding Eu-based CMR materials, as well as designing CMR materials based
on large-moment rare-earth magnets.",2308.16844v1
2023/9/27,Goodenough-Kanamori-Anderson high-temperature ferromagnetism in tetragonal transition-metal xenes,"Seminal Goodenough-Kanamori-Anderson (GKA) rules provide the inceptive
understanding of the superexchange interaction of two magnetic metal ions
bridged with an anion, and suggest fostered ferromagnetic interaction for
orthogonal bridging bonds. However, there are no examples of two-dimensional
(2D) materials with structure that optimizes the GKA arguments towards enhanced
ferromagnetism and its critical temperature. Here we reveal that an ideally
planar GKA ferromagnetism is indeed stable in selected tetragonal
transition-metal xenes (tTMXs), with Curie temperature above 300~K found in CrC
and MnC. We provide the general orbitally-resolved analysis of magnetic
interactions that supports the claims and sheds light at the mechanisms
dominating the magnetic exchange process in these structures. With recent
advent of epitaxially-grown tetragonal 2D materials, our findings earmark tTMXs
for facilitated spintronic and magnonic applications, or as a desirable
magnetic constituent of functional 2D heterostructures.",2309.15445v1
2023/10/18,Magnetic eight-fold nodal-point and nodal-network fermions in MnB2,"Realizing topological semimetal states with novel emergent fermions in
magnetic materials is a focus of current research. Based on first-principle
calculations and symmetry analysis, we reveal interesting magnetic emergent
fermions in an existing material MnB2. In the temperature range from 157 K to
760 K, MnB2 is a collinear antiferromagnet. We find the coexistence of
eightfold nodal points and nodal net close to the Fermi level, which are
protected by the spin group in the absence of spin-orbit coupling. Depending on
the Neel vector orientation, consideration of spin-orbit coupling will either
open small gaps at these nodal features, or transform them into magnetic linear
and quadratic Dirac points and nodal rings. Below 157 K, MnB2 acquires weak
ferromagnetism due to spin tilting. We predict that this transition is
accompanied by a drastic change in anomalous Hall response, from zero above 157
K to 200 $\Omega\cdot \text{cm}^{-1}$ below 157 K.",2310.11669v1
2023/10/24,Strain-driven switching between antiferromagnetic states in frustrated antiferromagnet UO2 probed by exchange bias effect,"Frustrated antiferromagnets offer a captivating platform to study the
intricate relationship of magnetic interactions, geometric constraints, and
emergent phenomena. By controlling spin orientations, these materials can be
tailored for applications in spintronics and quantum information processing.
The research focuses on the interplay of magnetic and exchange anisotropy
effects in artificial heterostructures based on a canonical frustrated
antiferromagnet, UO2. The potential to manipulate the spin directions in this
material and switch between distinct antiferromagnetic states is investigated
using substrate-induced strain. The phenomenon is probed using exchange bias
(EB) effects in stoichiometric UO2/Fe3O4 bilayers. By employing many-body
first-principles calculations magnetic configurations in the UO2 layers are
identified. Even a minor tetragonal distortion triggers a transition between
antiferromagnetic states of different symmetries, driven by a robust alteration
of single-ion anisotropy due to the distortion. Consequently, this change
influences the arrangement of magnetic moments at the UO2/Fe3O4 interface,
affecting the magnitude of exchange bias. The findings showcase how epitaxial
strain can effectively manipulate the antiferromagnetic states in frustrated
antiferromagnets by controlling single-site anisotropy.",2310.15696v1
2023/11/24,Light--absorbed orbital angular momentum in the linear response regime,"In exploring the light-induced dynamics within the linear response regime,
this study investigates the induced orbital angular momentum on a wide variety
of electronic structures. We derive a general expression for the torque induced
by light on different electronic systems based on their characteristic
dielectric tensor. We demonstrate that this phenomenon diverges from the
inverse Faraday effect as it produces an orbital magnetization persistent
post-illumination. Indeed, our results reveal that, while isotropic
non-dissipative materials do not absorb orbital angular momentum from
circularly polarized light, any symmetry-breaking arrangement of matter, be it
spatial or temporal, introduces novel channels for the absorption of orbital
angular momentum, or magnetization. Most notably, in dissipative materials,
circularly polarized light imparts a torque corresponding to a change in
orbital angular momentum of $\hbar$ per absorbed photon. The potential of these
mechanisms to drive helicity-dependent magnetic phenomena paves the way for a
deeper understanding of light-matter interactions. Notably, the application of
pump-probe techniques in tandem with our findings allows experimentalists to
quantitatively assess the amount of orbital angular momentum transferred to
electrons in matter, thus hopefully enhancing our ability to steer ultrafast
light-induced magnetization dynamics.",2311.14774v1
2023/12/12,Bulk Photovoltaic Effects in Helimagnets,"The bulk photovoltaic (BPV) effect that converts light into electric current
is highly sensitive to the system symmetry and its electronic Bloch
wavefunction. To create a sizable net electric current, it is necessary to
break the centrosymmetry P in its host material. Here, we investigate how
helical spin polarization breaks P that is otherwise kept in its crystalline
geometry. The magnetic helix widely exists in multiferroics and magnon
excitation in collinear magnets. We apply symmetry analysis and a tight-binding
model to show how the symmetry is reduced in helimagnetic platforms under
various degrees of freedom, namely, different types of spin spiral
configurations, spin winding angles, magnetic propagation vectors, and spin
chirality. They offer effective and versatile manipulation of BPV generation in
helimagnets. Our concept is further illustrated in the monolayer NiI2, a
typical helimagnetic material. It could host observable direction-dependent BPV
current, which serves as an opto-electric probe to track the subtle magnetic
configurations and potential ferroic nature. Our work reveals the fundamental
mechanism of the multiferroic order and the nonlinear optics process.",2312.06977v1
2023/12/14,Tuning the spontaneous exchange bias effect in La1.5Sr0.5CoMnO6 with sintering temperature,"Here, we present a study of the influence of microstructure on the magnetic
properties of polycrystalline samples of the La1.5Sr0.5CoMnO6 double
perovskite, with primary attention to the spontaneous exchange bias effect, a
fascinating recently discovered phenomena for which some materials exhibit
unidirectional magnetic anisotropy after being cooled in zero magnetic field.
By sintering La1.5Sr0.5CoMnO6 at different temperatures, we obtained samples
with distinct average grain sizes, ranging from 0.76(21) to 4.95(1.73) mu_m. A
detailed investigation of the material's structural, morphologic, electronic,
and magnetic properties using X-ray powder diffraction, powder neutron
diffraction, X-ray absorption near edge structure spectroscopy, scanning
electron microscopy, and AC and DC magnetometry has revealed a systematic
enhancement of the exchange bias effect with increasing the grain size and the
intergrain coalescence. Our results regarding the strengthening of the exchange
coupling at the grain interfaces and its influence on the dynamics of the spin
glass-like moments present in the samples are discussed.",2312.09149v1
2024/1/19,Nature of the unconventional heavy fermion Kondo state in monolayer CeSiI,"CeSiI has been recently isolated in the ultrathin limit, establishing CeSiI
as the first intrinsic two-dimensional van der Waals heavy-fermion material up
to 85 K. We show that, due to the strong Ce spin-orbit coupling, the local
moments develop a multipolar real-space magnetic texture, leading to local
pseudospins with a nearly vanishing net moment. To elucidate its Kondo-screened
regime, we extract from first principles the parameters of the Kondo lattice
model describing this material. We develop a fractional pseudofermion
methodology in combination with ab initio calculations to reveal the nature of
the Kondo-screened heavy fermion state in CeSiI. Using this formalism, we
analyze the competing magnetic interactions leading to a heavy-fermion order as
a function of the magnetic exchange between the localized f-electrons and the
strength of the Kondo coupling. Our results show that the magnetic exchange
interactions promote an unconventional momentum-dependent heavy-fermion Kondo
screened phase, establishing the nature of the heavy-fermion behavior of
ultrathin CeSiI observed experimentally.",2401.10855v1
2024/1/25,Magnon dispersion and spin transport in CrCl$_3$ bilayers under different strain-induced magnetic states,"Atomically-thin van der Waals magnetic materials offer exceptional
opportunities to mechanically and electrically manipulate magnetic states and
spin textures. The possibility of efficient spin transport in these materials
makes them promising for the development of novel nanospintronics technology.
Using atomistic spin dynamics simulations, we investigate magnetic ground
state, magnon dispersion, critical temperature, and magnon spin transport in
CrCl$_3$ bilayers in the absence and presence of compressive and tensile
strains. We show that in the presence of mechanical strain, the magnon band gap
at the $\Gamma$ point and the critical temperature of the bilayer are
increased. Furthermore, our simulations show that the magnon diffusion length
is reduced in the presence of strain. Moreover, by exciting magnons through the
spin Seebeck effect and spin Hall-induced torque, we illustrate distinctions
between magnon spin transport in the antiferromagnetic state, under compressive
strains, and ferromagnetic states, under tensile strains or in the unstrained
case.",2401.13984v1
2024/2/2,Magnetic interactions in doped silicene for spintronics,"Silicon is a material whose technological application is well established,
and obtaining this material in nanostructured form increases its possibility of
integration in current technology. Silicene is a natural compatibility with
current silicon-based electronics industry. Furthermore, doping is a technique
that can be often used to adjust the band gap of silicene and at the same time
introduce new functions. Here we investigate Several aspects of silicene doping
with chromium, such as dopant solubility limits, site preference for adsorption
and doping, and formation of magnetic domains. In this work we carried out
investigation on diffusion and doping of chromium atoms on silicene. We use
density-functional theory to identify the electronic and magnetic properties of
tchromium atoms on monolayer and bilayer silicene. We find that magnetization
depends on key parameters such as buckling, interlayer distance and adsorption
site.",2402.01880v1
2024/3/4,Realization of a Spin Glass in a two-dimensional van der Waals material,"Recent advances in van der Waals (vdW) materials have sparked renewed
interest in the impact of dimensionality on magnetic phase transitions. While
ordered magnetic phases have been demonstrated to survive in the
two-dimensional (2D) limit, the quest for a spin-glass with quenched magnetic
disorder in lower dimensions has proven elusive. Here we show evidence of a
spin-glass emerging from randomly distributed Fe atoms in Fe3GeTe2, the first
time such a state has been reported in a vdW material. AC magnetic
susceptibility displays a strong frequency dependence indicative of slow spin
dynamics. Additional distinctive phenomena, including ageing, chaos, and memory
effects, further substantiate the existence of a glassy state. Remarkably, we
find that this state persists even in single-unit-cell thick Fe3GeTe2, thereby
confirming the existence of a 2D spin-glass. The formation of spin-glass states
via intercalation in vdW systems allows for highly tunable spin-glass states
that are otherwise difficult to realize.",2403.02088v1
1998/10/28,An ordered stack of spin valves in a layered magnetoresistive perovskite,"The layered compound La2-2xSr1+2xMn2O7 (x=0.3) consists of bilayers of
metallic MnO2 sheets separated by insulating material. The compound exhibits
markedly anisotropic magnetoresistance at temperatures well below the
three-dimensional magnetic ordering temperature TC=90 K in addition to colossal
magnetoresistance around TC. We present neutron diffraction data which show
that the magnetic structure of this material switches from antiferromagnetic
stacking of the (ferromagnetically ordered) sheets in zero field to
ferromagnetic stacking in a field of 1.5 Tesla. The data are the first to be
collected on any manganite as a function of applied field, exactly as the
magnetoresistance data themselves are collected. They provide a natural
explanation of the low-field magnetoresistance in the ordered phase in terms of
spin-polarised tunnelling between the magnetic layers and suggest that the
material is a bulk stack of spin-valve devices.",9810382v1
2001/11/16,Density functional calculations for III-V diluted ferromagnetic semiconductors: A Review,"In this paper we review the latest achievements of density functional theory
in understanding the physics of diluted magnetic semiconductors. We focus on
transition metal doped III-V semiconductors, which show spontaneous
ferromagnetic order at relatively high temperature and good structural
compatibility with existing III-V devices. We show that density functional
theory is a very powerful tool for i) studying the effects of local doping
defects and disorder on the magnetic properties of these materials, ii)
predicting properties of new materials and iii) providing parameters, often not
accessible from experiments, for use in model Hamiltonian calculations. Such
studies are facilitated by recent advances in numerical implementations of
density functional theory, which make the study of systems with a very large
number of atoms possible.",0111300v1
2002/2/27,Anisotropic Magnetoresistance in Ga$_{1-x}$Mn$_x$As,"We have measured the magnetoresistance in a series of Ga$_{1-x}$Mn$_x$As
samples with 0.033$\le x \le$ 0.053 for three mutually orthogonal orientations
of the applied magnetic field. The spontaneous resistivity anisotropy (SRA) in
these materials is negative (i.e. the sample resistance is higher when its
magnetization is perpendicular to the measuring current than when the two are
parallel) and has a magnitude on the order of 5% at temperatures near 10K and
below. This stands in contrast to the results for most conventional magnetic
materials where the SRA is considerably smaller in magnitude for those few
cases in which a negative sign is observed. The magnitude of the SRA drops from
its maximum at low temperatures to zero at T$_C$ in a manner that is consistent
with mean field theory. These results should provide a significant test for
emerging theories of transport in this new class of materials.",0202508v1
2002/5/25,A possible path to a new class of ferromagnetic and half metallic ferromagnetic materials,"We introduce a path to a possibly new class of magnetic materials whose
properties are determined entirely by the presence of a low concentration of
specific point defects in their crystal structure. Using model Hamiltonian and
ab-initio band structure methods we demonstrate that even large band gap
nonmagnetic materials as simple as CaO can exhibit extraordinary properties
like half metallic ferromagnetism upon introducing a small concentration of Ca
vacancies. We show that such defects will initially bind the introduced charge
carriers at neighboring sites and depending on the internal symmetry of the
clusters formed by neighboring sites form ""local"" magnetic moments which for
concentrations as low as 3% transform this non-magnetic insulator into a half
metallic ferromagnet.",0205530v1
2004/7/5,Absence of ferromagnetism in Mn- and Co-doped ZnO,"Following the theoretical predictions of ferromagnetism in Mn- and Co-doped
ZnO, several workers reported ferromagnetism in thin films as well as in bulk
samples of these materials. While some observe room-temperature ferromagnetism,
others find magnetization at low temperatures. Some of the reports, however,
cast considerable doubt on the magnetism of Mn- and Co-doped ZnO. In order to
conclusively establish the properties of Mn- and Co-doped ZnO, samples with 6
percent and 2 percent dopant concentrations, have been prepared by the
low-temperature decomposition of acetate solid solutions. The samples have been
characterized by x-ray diffraction, EDAX and spectroscopic methods to ensure
that the dopants are substitutional. All the Mn- and Co-doped ZnO samples
(prepared at 400 deg C and 500 deg C) fail to show ferromagnetism. Instead,
their magnetic properties are best described by a Curie-Weiss type behavior. It
appears unlikely that these materials would be useful for spintronics, unless
additional carriers are introduced by some means.",0407108v2
2005/5/17,Robust Half-Metallic Character and Large Oxygen Magnetism in a Perovskite Cuprate,"The new perovskite cuprate material Sr$_{8}$CaRe$_{3}$Cu$_{4}$O$_{24}$, which
behaves ferrimagnetically and shows an unusually high Curie temperature ($T_c
\sim$ 440 K), is found from density-functional theory calculation to display
several surprising properties after hole doping or chemical substitution: (1)
Half metal (HM) is realized by replacing Re with W or Mo while $T_c$ remains
high; (2) hole-doped Sr$_{8}$CaRe$_{3}$Cu$_{4}$O$_{24}$ is also HM with high
$T_c$. Moreover, we find that the O atoms will carry a large magnetic moment
after hole doping, which is in sharp contrast with the generally accepted
concept that magnetism in solid requires partially filled shells of $d$ or $f$
electrons in cations. The material Sr$_8$CaRe$_3$Cu$_4$O$_{24}$ is therefore
expected to provide a very useful platform for material design and development.",0505408v1
2006/12/22,Clear Experimental Signature of Charge-Orbital density wave in Nd$_{1-x}$Ca$_{1+x}$MnO$_{4}$:Heat Capacity and Magnetization study,"Single Crystals of Nd$_{1-x}$Ca$_{1+x}$MnO$_{4}$ have been prepared by the
traveling floating-zone method, and possible evidence of a charge -orbital
density wave in this material presented earlier [PRB68,092405 (2003)] using
High Resolution Electron Microscopy [HRTEM] and Electron Diffraction [ED]. In
the current note we present direct evidence of charge-orbital ordering in this
material using heat capacity measurements. Our heat capacity measurements
indicate a clear transition consistent with prior observation. We find two main
transitions, one at temperature $T_{_H}^{HC}=310-314$ K, and other in the
vicinity of $T_{_A}^{HC}=143$ K. In addition, we may also conclude that there
is a strong electron-phonon coupling in this material. In order to further
study and confirm theseanomalies we have performed dc magnetization
measurements. The dc magnetic measurements confirm these two transitions.
Again,we find two main transitions, one at temperature $T_{_H}^{M}=318-323$ K,
and other at around $T_{_A}^{M}=164$ K.",0612587v1
2007/1/9,Pressure Study of Superconductivity and Magnetism in Pure and Rh-Doped RuSr2GdCu2O8 Materials,"A hydrostatic pressure study was made on pure and Rh-doped specimens of the
superconducting ferromagnetic compounds Ru1-xRhxSr2GdCu2O8 (x = 0-0.15) by
means of measurement of electrical resistivity vs temperature, in pressures up
to 2 GPa. Partial substitution of Rh for Ru decreases the magnetization of the
material, lowers both the magnetic ordering temperature Tm, and the
superconducting transition temperature Tc, and promotes granularity. The effect
of pressure for all compositions is an increase in both the intra- and
intergranular superconductivity transition temperatures, Tc and Tp
respectively, as well as Tm. The rate of change of each transition temperature
with pressure first drops for Rh concentrations near 5%, increasing latter for
higher concentrations. While the rate of increase of Tc with pressure for all
compositions is 2-3 times lower than in YBCO materials, the simultaneous
increase of Tc and Tm with pressure could support the notion of competition
between superconductivity and ferromagnetism in these materials. The effect of
pressure on the weak-links was a significant improvement of inter-granular
connectivity.",0701183v1
2004/10/24,Nonlinear left-handed metamaterials,"We analyze nonlinear properties of microstructured materials with negative
refraction, the so-called left-handed metamaterials. We demonstrate that the
hysteresis-type dependence of the magnetic permeability on the field intensity
allows changing the material properties from left- to right-handed and back.
Using the finite-difference time-domain simulations, we study wave transmission
through the slab of nonlinear left-handed material, and predict existence of
temporal solitons in such materials. We demonstrate also that nonlinear
left-handed metamaterials can support both TE- and TM-polarized self-trapped
localized beams, spatial electromagnetic solitons. Such solitons appear as
single- and multi-hump beams, being either symmetric or antisymmetric, and they
can exist due to the hysteresis-type magnetic nonlinearity and the effective
domains of negative magnetic permeability.",0410243v2
2005/4/11,Patch antennas with new artificial magnetic layers,"A new type of high-impedance surfaces (HIS) has been introduced by C.R.
Simovski et al. recently. In this paper, we propose to use such layers as
artificial magnetic materials in the design of patch antennas. The new HIS is
simulated and patch antennas partially filled by these composite layers are
measured in order to test how much the antenna dimensions can be reduced. In
order to experimentally investigate the frequency behavior of the material,
different sizes of the patches are designed and tested with the same material
layer. Also the height of the patch is changed in order to find the best
possible position for minimizing the antenna size. This composite layer of an
artificial magnetic material has made the antenna smaller while keeping the
bandwidth characteristics of the antenna about the same. About 40% of size
reduction has been achieved.",0504075v1
2006/2/27,Generalized Permeability Function and Field Energy Density in Artificial Magnetics Using the Equivalent Circuit Method,"The equivalent circuit model for artificial magnetic materials based on
various arrangements of split rings is generalized by taking into account
losses in the substrate or matrix material. It is shown that a modification is
needed to the known macroscopic permeability function in order to correctly
describe these materials. Depending on the dominating loss mechanism
(conductive losses in metal parts or dielectric losses in the substrate) the
permeability function has different forms. The proposed circuit model and
permeability function are experimentally validated. Furthermore, starting from
the generalized circuit model we derive an explicit expression for the
electromagnetic field energy density in artificial magnetic media. This
expression is valid at low frequencies and in the vicinity of the resonance
also when dispersion and losses in the material are strong. The presently
obtained results for the energy density are compared with the results obtained
using different methods.",0602182v2
2008/6/17,"Magnetic order in BaFe2As2, the parent compound of the FeAs based superconductors in a new structural family","In addition to higher Tc compared with the ubiquitous cuprates for a material
composed of a single electronically active layer, the newly discovered LnFeAsO
superconductors offer additional compositional variation. In a similar fashion
to the CuO2 layers in cuprates, the FeAs layers now dominate the electronic
states that produce superconductivity. Cuprate superconductors distinguish
themselves structurally by adopting different stacking of the Cu-O and
electronically inactive ""spacer"" layers. Using the same structural philosophy,
materials with the formula (A,K)Fe2As2,A=Ba or Sr have been reported and
possess a Tc~38 K. Here, we report the neutron diffraction studies of BaFe2As2
that shows, in contrast to previous studies on the LnFeAsO materials, an
antiferromagnetic transition which concurs with first-order structural
transition. Although the magnetic and structural transitions occur differently
in the AFe2As2 and LnFeAsO-type materials, this work clearly demonstrates that
the complete evolution to a low symmetry structure is a pre-requirement for the
magnetic order.",0806.2776v2
2010/2/1,Orbital magnetoelectric coupling in band insulators,"Magnetoelectric responses are a fundamental characteristic of materials that
break time-reversal and inversion symmetries (notably multiferroics) and,
remarkably, of ""topological insulators"" in which those symmetries are unbroken.
Previous work has shown how to compute spin and lattice contributions to the
magnetoelectric tensor. Here we solve the problem of orbital contributions by
computing the frozen-lattice electronic polarization induced by a magnetic
field. One part of this response (the ""Chern-Simons term"") can appear even in
time-reversal-symmetric materials and has been previously shown to be quantized
in topological insulators. In general materials there are additional orbital
contributions to all parts of the magnetoelectric tensor; these vanish in
topological insulators by symmetry and also vanish in several simplified models
without time-reversal and inversion those magnetoelectric couplings were
studied before. We give two derivations of the response formula, one based on a
uniform magnetic field and one based on extrapolation of a long-wavelength
magnetic field, and discuss some of the consequences of this formula.",1002.0290v2
2011/5/30,Dependence of microwave absorption properties on ferrite volume fraction in MnZn ferrite/rubber radar absorbing materials,"We report the analysis of measurements of the complex magnetic permeability
($\mu_r$) and dielectric permittivity ($\epsilon_r$) spectra of a rubber radar
absorbing material (RAM) with various MnZn ferrite volume fractions. The
transmission/reflection measurements were carried out in a vector network
analyzer. Optimum conditions for the maximum microwave absorption were
determined by substituting the complex permeability and permittivity in the
impedance matching equation. Both the MnZn ferrite content and the RAM
thickness effects on the microwave absorption properties, in the frequency
range of 2 to 18 GHz, were evaluated. The results show that the complex
permeability and permittivity spectra of the RAM increase directly with the
ferrite volume fraction. Reflection loss calculations by the impedance matching
degree (reflection coefficient) show the dependence of this parameter on both
thickness and composition of RAM.",1105.5969v1
2012/1/15,Magnetocaloric materials: the search for new systems,"The prospect of efficient solid state refrigeration at room temperature is
driving research into magnetic cooling engine design and magnetic phase
transition-based refrigerants. In this Viewpoint an Ashby-style map of magnetic
refrigerant properties is constructed, comparing popular materials with limits
derived from an idealised first order transition model. This comparison
demonstrates the potential for new magnetocaloric material systems to be
established through structural control and optimisation at the atomic-, nano-
and micro-scale.",1201.3113v5
2012/7/4,Colossal Magnetoresistance in the Mn2+ Oxypnictides NdMnAsO1-xFx,"Colossal magnetoresistance (CMR) is a rare phenomenon in which the electronic
resistivity of a material can be decreased by orders of magnitude upon
application of a magnetic field. Such an effect could be the basis of the next
generation of magnetic memory devices. Here we report CMR in the
antiferromagnetic oxypnictide NdMnAsO1-xFx as a result of competition between
an antiferromagnetic insulating phase with strong electron correlations and a
paramagnetic semiconductor upon application of a magnetic field. The discovery
of CMR in antiferromagnetic Mn2+ oxypnictide materials could open up an array
of materials for further investigation and optimisation for technological
applications.",1207.0958v1
2013/2/5,Breaking the thermally induced write error in heat assisted recording by using low and high Tc materials,"Heat assisted recording is believed as a key technology in order to further
increase the areal density of magnetic recording. In the work of Richter et al.
[Richter et al. J. Appl. Phys. 111, 033909 (2012)] it is stated that storage
densities will be limited to 15 to 20 Tbit/in2 due to thermally induced write
errors. In this letter we propose a composite structure consisting of two
materials with different Curie temperatures. A hard magnetic layer is on top of
a high Tc soft magnetic layer. In this composite material the thermal write
error is negligible up to areal densities of 50 to 100 Tbit/in2. It is shown
that the effective thermal field gradient, which is reduced in this composite
structure, is not relevant for a possible increase of the transition jitter.
The transition jitter is dominated by a small distribution of the Curie
temperature. The smallest jitter is obtained for the composite structure.",1302.1092v1
2013/2/26,$M$Si$_{20}$H$_{20}$ Aggregates: From Simple Building Blocks to Highly Magnetic Functionalized Materials,"Density-functional theory based global geometry optimization is used to
scrutinize the possibility of using endohedrally-doped hydrogenated Si clusters
as building blocks for constructing highly magnetic materials. In contrast to
the known clathrate-type facet-sharing, the clusters exhibit a predisposition
to aggregation through double Si-Si bridge bonds. For the prototypical
CrSi$_{20}$H$_{20}$ cluster we show that reducing the degree of hydrogenation
may be used to control the number of reactive sites to which other cages can be
attached, while still preserving the structural integrity of the building block
itself. This leads to a toolbox of CrSi$_{20}$H$_{20-2n}$ monomers with
different number of double ""docking sites"", that allows building network
architectures of any morphology. For (CrSi$_{20}$H$_{18}$)$_{2}$ dimer and
[CrSi$_{20}$H$_{16}$](CrSi$_{20}$H$_{18}$)$_{2}$ trimer structures we
illustrate that such aggregates conserve the high spin moments of the dopant
atoms and are therefore most attractive candidates for cluster-assembled
materials with unique magnetic properties. The study suggests that the
structural completion of the individual endohedral cages within the
doubly-bridge bonded structures and the high thermodynamic stability of the
obtained aggregates are crucial for potential synthetic polymerization routes
$via$ controlled dehydrogenation.",1302.6410v1
2013/10/5,Unified Model of Temperature Dependence of Core Losses in Soft Magnetic Materials Exposed to Nonsinusoidal Flux Waveforms and DC Bias Condition,"Assuming that Soft Magnetic Material is a Complex System and expressing this
feature by scaling invariance of the power loss characteristic, the unified
model of the temperature dependence of Core Losses in Soft Magnetic Materials
Exposed to Nonsinusoidal Flux Waveforms and DC Bias Condition has been
constructed.
  In order to verify this achievement the appropriate measurement data
concerning power losses and the all independent variables have been collected.
The model parameters have been estimated and the power losses modeling has been
performed. Comparison of the experimental values of power losses with their
calculated values has showed good agreement.",1310.1522v1
2014/1/7,Dynamical magnetic charges and linear magnetoelectricity,"Magnetoelectric (ME) materials are of fundamental interest and have been
investigated for their broad potential for technological applications. The
search for, and eventually the theoretical design of, materials with large ME
couplings present challenging issues. First-principles methods have only
recently been developed to calculate the full ME response tensor $\alpha$
including both electronic and ionic (i.e., lattice-mediated) contributions. The
latter is proportional to both the Born dynamical electric charge $Z^{\rm e}$
and its analogue, the dynamical magnetic charge $Z^{\rm m}$. Here we present a
theoretical study of the magnetic charge $Z^{\rm m}$ and the mechanisms that
could enhance it. Using first-principles density-functional methods, we
calculate the atomic $Z^{\rm m}$ tensors in $\rm{Cr_2O_3}$, a prototypical
magnetoelectric, and in KITPite, a fictitious material that has previously been
reported to show a strong ME response arising from exchange striction effects.
Our results confirm that in $\rm{Cr_2O_3}$, the $Z^{\rm m}$ values and
resulting ME responses arise only from spin-orbit coupling (SOC) and are
therefore rather weak. In KITPite, by contrast, the exchange striction acting
on the non-collinear spin structure induces much $Z^{\rm m}$ values that
persist even when SOC is completely absent.",1401.1538v1
2014/1/27,Functional Approach to Electrodynamics of Media,"In this article, we put forward a new approach to electrodynamics of
materials. Based on the identification of induced electromagnetic fields as the
microscopic counterparts of polarization and magnetization, we systematically
employ the mutual functional dependencies of induced, external and total field
quantities. This allows for a unified, relativistic description of the
electromagnetic response without assuming the material to be composed of
electric or magnetic dipoles. Using this approach, we derive universal
(material-independent) relations between electromagnetic response functions
such as the dielectric tensor, the magnetic susceptibility and the microscopic
conductivity tensor. Our formulae can be reduced to well-known identities in
special cases, but more generally include the effects of inhomogeneity,
anisotropy, magnetoelectric coupling and relativistic retardation. If combined
with the Kubo formalism, they would also lend themselves to the ab initio
calculation of all linear electromagnetic response functions.",1401.6800v7
2015/5/11,"Influence of short time milling in R5(Si,Ge)4, R =Gd and Tb, magnetocaloric materials","The effect of the short milling times on R5(Si,Ge)4 R =Gd, Tb magnetocaloric
material properties was investigated. In particular, the effect of milling on
atomic structure, particles size and morphology, magnetic, and magnetocaloric
effect was studied. With short milling times (< 2.5h), a reduction of the
Gd5Si1.3Ge2.7 and Tb5Si2Ge2 particles size was achieved down to approximately
3.5 DSm. For both compositions the main differences are a consequence of the
milling effect on the coupling of the structural and magnetic transitions. In
the Gd5Si1.3Ge2.7 case, a second-order phase transition emerges at high
temperatures as a result of ball milling. Consequently, there is a decrease in
the magnetocaloric effect of 35% after 150 minutes of milling. Interestingly,
an opposite effect is observed in Tb5Si2Ge2 where a 23% increase of the
magnetocaloric effect was achieved, driven by the enhancement of the coupling
between magnetic and structural transitions arising from internal strain
promoted by the milling process.",1505.02573v1
2016/3/10,Carboxylate based molecular magnet: one path toward achieving stable quantum correlations at room temperature,"The control of quantum correlations in solid state systems by means of
material engineering is a broad avenue to be explored, since it makes possible
steps toward the limits of quantum mechanics and the design of novel materials
with applications on emerging quantum technologies. In this context, this
Letter explores the potential of molecular magnets to be prototypes of
materials for quantum information technology. More precisely, we engineered a
material and from its geometric quantum discord we found significant quantum
correlations up to 9540 K (even without entanglement); and, in addition, a pure
singlet state occupied up to around 80 K (above liquid nitrogen temperature).
These results could only be achieved due to the carboxylate group promoting a
metal-to-metal huge magnetic interaction.",1603.03226v1
2016/3/28,"Ab initio Studies on Electronic and Magnetic Properties of X$_{2}$PtGa (X = Cr, Mn, Fe, Co) Heusler Alloys","Using first-principles calculations based on density functional theory, we
probe the electronic and magnetic properties of X$_{2}$PtGa (X being Cr, Mn,
Fe, Co) Heusler alloys. Our calculations predict that all these systems possess
inverse Heusler alloy structure in their respective ground states. Application
of tetragonal distortion leads to lowering of energy with respect to the cubic
phase for all the materials. The equilibrium volumes of both the phases are
nearly the same. These results of our calculations indicate that all these
materials are prone to undergo martensite transition, as has been recently
shown theoretically for Mn$_{2}$PtGa in the literature. Ground state with a
tetragonal symmetry of these materials is supported by the observation of soft
tetragonal shear constants in their cubic phase. By comparing the energies of
various types of magnetic configurations of these alloys we predict that
Cr$_{2}$PtGa and Mn$_{2}$PtGa possess ferrimagnetic configuration whereas
Fe$_{2}$PtGa and Co$_{2}$PtGa possess ferromagneic configuration in their
respective ground states.",1603.08350v2
2017/2/17,Molecular Beam Epitaxy Growth of [CrGe/MnGe/FeGe] Superlattices: Toward Artificial B20 Skyrmion Materials with Tunable Interactions,"Skyrmions are localized magnetic spin textures whose stability has been shown
theoretically to depend on material parameters including bulk Dresselhaus spin
orbit coupling (SOC), interfacial Rashba SOC, and magnetic anisotropy. Here, we
establish the growth of a new class of artificial skyrmion materials, namely
B20 superlattices, where these parameters could be systematically tuned.
Specifically, we report the successful growth of B20 superlattices comprised of
single crystal thin films of FeGe, MnGe, and CrGe on Si(111) substrates. Thin
films and superlattices are grown by molecular beam epitaxy and are
characterized through a combination of reflection high energy electron
diffraction, x-ray diffraction, and cross-sectional scanning transmission
electron microscopy (STEM). X-ray energy dispersive spectroscopy (XEDS)
distinguishes layers by elemental mapping and indicates good interface quality
with relatively low levels of intermixing in the [CrGe/MnGe/FeGe] superlattice.
This demonstration of epitaxial, single-crystalline B20 superlattices is a
significant advance toward tunable skyrmion systems for fundamental scientific
studies and applications in magnetic storage and logic.",1702.05191v1
2017/4/27,Full phase diagram of isolated skyrmions in a ferromagnet,"Magnetic skyrmions are topological quasi particles of great interest for data
storage applications because of their small size, high stability, and ease of
manipulation via electric current. Theoretically, however, skyrmions are poorly
understood since existing theories are not applicable to small skyrmion sizes
and finite material thicknesses. Here, we present a complete theoretical
framework to determine the energy of any skyrmion in any material, assuming
only a circular symmetric 360$^\circ$ domain wall profile and a homogeneous
magnetization profile in the out-of-plane direction. Our model precisely agrees
with existing experimental data and micromagnetic simulations. Surprisingly, we
can prove that there is no topological protection of skyrmions. We discover and
confirm new phases, such as bi-stability, a phenomenon unknown in magnetism so
far. The outstanding computational performance and precision of our model allow
us to obtain the complete phase diagram of static skyrmions and to tackle the
inverse problem of finding materials corresponding to given skyrmion
properties, a milestone of skyrmion engineering.",1704.08489v1
2017/5/25,Nontrivial Berry phase in magnetic BaMnSb2 semimetal,"The subject of topological materials has attracted immense attention in
condensed-matter physics, because they host new quantum states of matter
containing Dirac, Majorana, or Weyl fermions. Although Majorana fermions can
only exist on the surface of topological superconductors, Dirac and Weyl
fermions can be realized in both 2D and 3D materials. The latter are semimetals
with Dirac/Weyl cones either not tilted (type I) or tilted (type II). Although
both Dirac and Weyl fermions have massless nature with the nontrivial Berry
phase, the formation of Weyl fermions in 3D semimetals require either
time-reversal or inversion symmetry breaking to lift degeneracy at Dirac
points. Here, we demonstrate experimentally that canted antiferromagnetic
BaMnSb2 is a 3D Weyl semimetal with a 2D electronic structure. The Shubnikov-de
Hass oscillations of the magnetoresistance give nearly zero effective mass with
high mobility and the nontrivial Berry phase. The ordered magnetic arrangement
(ferromagnetic ordering in the ab plane and antiferromagnetic ordering along
the c axis below 286 K) breaks the time-reversal symmetry, thus offering us an
ideal platform to study magnetic Weyl fermions in a centrosymmetric material.",1705.09009v1
2017/6/7,PbTi1-xPdxO3: A New Room-temperature Magnetoelectric Multiferroic Device Material,"There have been a large number of papers on bismuth ferrite (BiFeO3) over the
past few years, trying to exploit its room-temperature magnetoelectric
multiferroic properties. Although these are attractive, BiFeO3 is not the ideal
multiferroic, due to weak magnetization and the difficulty in limiting leakage
currents. Thus there is an ongoing search for alternatives, including such
materials as gallium ferrite (GaFeO3). In the present work we report a
comprehensive study of the perovskite PbTi1-xPdxO3 with 0 < x < 0.3. Our study
includes dielectric, impedance and magnetization measurements, conductivity
analysis and study of crystallographic phases present in the samples with
special attention paid to minor phases, identified as PdO, PbPdO2, and Pd3Pb.
The work is remarkable in two ways: Pd is difficult to substitute into ABO3
perovskite oxides (where it might be useful for catalysis), and Pd is magnetic
under only unusual conditions (under strain or internal electric fields). The
new material, as a PZT derivative, is expected to have much stronger
piezoelectric properties than BiFeO3.",1706.02194v1
2017/6/20,Magneto-optical conductivity of anisotropic two-dimensional Dirac-Weyl materials,"In the presence of an external magnetic field, the optical response of
two-dimensional materials, whose charge carriers behave as massless Dirac
fermions with arbitrary anisotropic Fermi velocity, is investigated. Using Kubo
formalism, we obtain the magneto-optical conductivity tensor for these
materials, which allows to address the magneto-optical response of anisotropic
Dirac fermions from the well known magneto-optical conductivity of isotropic
Dirac fermions. As an application, we analyse the combined effects of
strain-induced anisotropy and magnetic field on the transmittance, as well as
on the Faraday rotation, of linearly polarized light after passing strained
graphene. The reported analytical expressions can be a useful tool to predict
the absorption and the Faraday angle of strained graphene under magnetic field.
Finally, our study is extended to anisotropic two-dimensional materials with
Dirac fermions of arbitrary pseudospin.",1706.06567v2
2018/4/13,Significant enhancement of magneto-optical effect in one-dimensional photonic crystals with magnetized epsilon-near-zero defect,"Nonreciprocal (NOR) transmission with magneto-optical materials plays a
critical role in a broad range of applications, such as optical isolation,
all-optical signal processing, and integrated photonic circuits. The underlying
mechanism is that a static magnetic field can break the time-reversal symmetry
in the presence of magneto-optical materials. However, the typical NOR devices
usually need a large size because the weak magneto-optical activity of
materials. Here, our theoretical investigations show that the NOR transmission
can be obtained in the one-dimensional photonic crystal with a magnetized
epsilon-near-zero (ENZ) defect due to strong field localization in the ENZ
medium. The inherent weak magneto-optical activity is significantly enhanced in
ENZ medium. In our configuration, the wavelength shift of transmission peaks
along two opposite incident directions can be up to 100 times higher than that
in the case that the defect layer is a normal bismuth iron garnet. Such results
will provide a new degree to design novel magneto-optical devices with small
size, and may open novel routes to exploit advanced materials for steering the
electromagnetic waves in nano-scale structures.",1804.04805v1
2018/6/29,Intra-cell dynamics and cyclotron motion without magnetic field,"Intra-cell motion endows rich non-trivial phenomena to a wide variety of
quantum materials. The most prominent example is a transverse current in the
absence of a magnetic field (i.e. the anomalous Hall effect). Here we show
that, in addition to a dc Hall effect, anomalous Hall materials possess
circulating currents and cyclotron motion without magnetic field. These are
generated from the intricate wavefunction dynamics within the unit cell, and
correspond to interband transitions (coherences) in much the same way that
cyclotron resonances arise from inter-Landau level transitions in
magneto-optics. Curiously, anomalous cyclotron motion exhibits an intrinsic
decay in time (even in pristine materials) displaying a characteristic power
law decay. This reveals an intrinsic dephasing similar to that of inhomogeneous
broadening of spinors. Circulating currents can manifest as the emission of
circularly polarized light pulses in response to incident linearly polarized
(pulsed) electric field, and provide a direct means of interrogating the
intra-unit-cell dynamics of quantum materials.",1807.00014v1
2018/11/7,Linear magnetoresistance in the low-field limit in density-wave materials,"The magnetoresistance (MR) of a material is typically insensitive to
reversing the applied field direction and varies quadratically with magnetic
field in the low-field limit. Quantum effects [1], unusual topological band
structures [2], and inhomogeneities that lead to wandering current paths [3, 4]
can induce a crossover from quadratic to linear magnetoresistance with
increasing magnetic field. Here we explore a series of metallic charge- and
spin-density-wave systems that exhibit extremely large positive linear
magnetoresistance. By contrast to other linear MR mechanisms, this effect
remains robust down to miniscule magnetic fields of tens of Oersted at low
temperature. We frame an explanation of this phenomenon in a semi-classical
narrative for a broad category of materials with partially-gapped Fermi
surfaces due to density waves.",1811.02758v1
2018/11/17,Thermal control of spin excitations in the coupled Ising-chain material RbCoCl3,"We have used neutron spectroscopy to investigate the spin dynamics of the
quantum (S = 1/2) antiferromagnetic Ising chains in RbCoCl3. The structure and
magnetic interactions in this material conspire to produce two magnetic phase
transitions at low temperatures, presenting an ideal opportunity for thermal
control of the chain environment. The high-resolution spectra we measure of
two-domain-wall excitations therefore characterize precisely both the continuum
response of isolated chains and the ""Zeeman-ladder"" bound states of chains in
three different effective staggered fields in one and the same material. We
apply an extended Matsubara formalism to obtain a quantitative description of
the entire dataset, Monte Carlo simulations to interpret the magnetic order,
and finite-temperature DMRG calculations to fit the spectral features of all
three phases.",1811.07178v2
2018/11/29,Efficient spin transport in a paramagnetic insulator,"The discovery of new materials that efficiently transmit spin currents has
been important for spintronics and material science. The electric insulator
$\mathrm{Gd}_3\mathrm{Ga}_5\mathrm{O}_{12}$ (GGG) is a superior substrate for
growing magnetic films, but has never been considered as a conduit for spin
currents. Here we report spin current propagation in paramagnetic GGG over
several microns. Surprisingly, the spin transport persists up to temperatures
of 100 K $\gg$ $T_{\mathrm{g}} = 180$ mK, GGG's magnetic glass-like transition
temperature. At 5 K we find a spin diffusion length ${\lambda_{\mathrm{GGG}}} =
1.8 \pm 0.2 {\mu}$m and a spin conductivity ${\sigma}_{\mathrm{GGG}} = (7.3 \pm
0.3) \times10^4$ $\mathrm{Sm}^{-1}$ that is larger than that of the record
quality magnet $\mathrm{Y}_3\mathrm{Fe}_5\mathrm{O}_{12}$ (YIG). We conclude
that exchange coupling is not required for efficient spin transport, which
challenges conventional models and provides new material-design strategies for
spintronic devices.",1811.11972v1
2018/12/22,Design and experimental study of Tesla's thermomagnetic engine,"The scientists have shown great interest in the search for alternative means
to generate energy, which are not contaminants and generate significant damage
to the environment. One of the quite viable possibilities for this is to
consider the construction of thermomagnetic motors, using mainly ferromagnetic
materials. These materials are those that for a given temperature value; these
lose the magnetic properties they have, that is, to be paramagnetic they become
completely diamagnetic during a certain period of exposure to heat.
  With the objective of demonstrate the Curie's law applied to this type of
materials, we designed the model of an engine that works based on this law, to
achieve this the tests of the running system were taken, which were filmed and
then analyzed using the program Tracker Video Analysis and Modeling Tool for
Physics Education.
  In this paper, we present the results related to the magnetic and
thermodynamic study of the efficiency of a motor designed by us, with the aim
of showing the validation of Curie's law for iron and also being able to obtain
the representative characteristics of this material such as magnetization and
the Curie's constant using an experimental method.",1812.09440v1
2019/1/8,Zeeman-type spin splitting in non-magnetic three-dimensional compounds: Materials prediction and electrical control,"Despite its potential for device application, the non-magnetic Zeeman effect
has only been predicted and observed in two-dimensional compounds. We
demonstrate that non-centrosymmetric three-dimensional compounds can also
exhibit a Zeeman-type spin splitting, allowing the splitting control by
changing the growth direction of slabs formed by these compounds. We determine
the required conditions for this effect: $i$) non-centrosymmetric including
polar and non-polar point groups, $ii$) valence band maximum or conduction band
minimum in a generic $k$-point, i.e., non-time-reversal-invariant momentum, and
$iii$) zero magnetic moment. Using these conditions as filters, we perform a
material screening to systematically search for these systems in the aflow-ICSD
database. We find 20 material candidates featuring the Zeeman-type effect. We
also found that the spin-splitting in confined systems can be controlled by an
external electric field, which in turns can induce a metal-insulator
transition. We believe that the Zeeman-type effect in three-dimensional
compounds can potentially be used for spin-filtering devices.",1901.02276v1
2019/2/13,Cu-substituted Fe2P: An emerging candidates for magnetic RAM application,"We propose that Cu-substituted Fe$_2$P, (Fe$_{1-x}$Cu$_x$)$_2$P ($x\sim
0.16$), to be an outstanding contender for the STT-MRAM application. Using
first principles based calculations in the framework of density functional
theory and through Monte Carlo simulations, we demonstrate that this material
can be used as ferromagnetic electrode in the magnetic tunnel junction (MTJ) of
STT-MRAM due to its moderate perpendicular magnetic anisotropy (PMA), large
tunnel magneto-resistance (TMR), good thermal stability and high ferromagnetic
transition temperature. We point out that the simplicity in the synthesis, huge
abundance, and non-toxicity make this material a very good candidate to replace
the current MTJ materials for STT-MRAM such as FePt,~FeCo or FeCoB.",1902.04876v1
2019/6/10,Quantum oscillation of thermal conductivity and violation of Weidemann-Franz law in TaAs$_2$ and NbAs$_2$,"We report a study of thermal conductivity and resistivity at ultra-low
temperatures and in high magnetic fields for semi-metal materials TaAs$_2$ and
NbAs$_2$ by using single crystal samples. The thermal conductivity is strongly
suppressed in magnetic fields, having good correspondence with the large
positive magnetoresistance, which indicates a dominant electronic contribution
to thermal conductivity. In addition, not only the resistivity but also the
thermal conductivity display clear quantum oscillations behavior at subKelvin
temperatures and in magnetic fields up to 14 T. The most striking phenomenon is
that the thermal conductivity show a $T^4$ behavior at very low temperatures,
while the resistivity show a $T$-independent behavior. This indicates a strong
violation of the Weidemann-Franz law and points to a non-Feimi liquid state of
these materials.",1906.03961v3
2019/7/17,Mechanical and liquid phase exfoliation of cylindrite: a natural van der Waals superlattice with intrinsic magnetic interactions,"We report the isolation of thin flakes of cylindrite, a naturally occurring
van der Waals superlattice, by means of mechanical and liquid phase
exfoliation. We find that this material is a heavily doped p-type semiconductor
with a narrow gap (<0.85 eV) with intrinsic magnetic interactions that are
preserved even in the exfoliated nanosheets. Due to its environmental stability
and high electrical conductivity, cylindrite can be an interesting alternative
to the existing two-dimensional magnetic materials.",1907.07362v1
2019/8/22,Quantum Spin Liquid in a depleted triangular lattice Iridate K$_x$Ir$_y$O$_2$,"We report discovery of a new iridate family K$_x$Ir$_y$O$_2$ with depleted
triangular lattice planes made up of edge sharing IrO$_6$ octahedra separated
by K planes. Such a material interpolates between the triangular and honeycomb
lattices and is a new playground for Kitaev physics. The materials are Mott
insulators with $y = 1 - x/4$. Physical property measurements for the $x
\approx 0.85$ material are reported. Using magnetic susceptibility $\chi$
versus temperature $T$ measurements we find $S_{eff} = 1/2$ moments interacting
strongly with a Weiss temperature $\theta \approx - 180$~K and no magnetic
order or spin freezing down to $T = 1.8$~K\@. Heat capacity shows a broad
maximum around $30$~K which is insensitive to magnetic fields and a $T$-linear
low temperature behaviour with $\gamma \sim 10$~mJ/mol~K$^2$. These results are
consistent with a gapless QSL state in K$_{0.85}$Ir$_{0.79}$O$_2$.",1908.08475v1
2019/9/1,A flexible rheometer design to measure the visco-elastic response of soft solids over a wide range of frequency,"We present a flexible set-up for determining the rheology of visco-elastic
materials which is based on the mechanical response of a magnet deposited at
the surface of a slab of material and excited electromagnetically. An
interferometric measurement of the magnet displacement allows one to reach an
excellent accuracy over a wide range of frequency. Except for the magnet, there
is no contact between the material under investigation and the apparatus. At
low frequency, inertial effects are negligible so that the mechanical response,
obtained through a lock-in amplifier, directly gives the material complex
modulus. At high frequency, damped waves are emitted and the rheology must be
extracted numerically from a theoretical model. To validate the design, the
instrument was used to measure the rheology of a test PDMS gel which presents
an almost perfect scale free response at high frequency.",1909.00461v1
2019/12/18,Observation of multiple Dirac states in a magnetic topological material EuMg2Bi2,"Initiated by the discovery of topological insulators, topologically
non-trivial materials, more specifically topological semimetals and metals have
emerged as new frontiers in the field of quantum materials. In this work, we
perform a systematic measurement of EuMg2Bi2, a compound with antiferromagnetic
transition temperature at 6.7 K, observed via electrical resistivity,
magnetization and specific heat capacity measurements. By utilizing
angle-resolved photoemission spectroscopy in concurrence with first-principles
calculations, we observe Dirac cones at the corner and the zone center of the
Brillouin zone. From our experimental data, multiple Dirac states at G and K
points are observed, where the Dirac nodes are located at different energy
positions from the Fermi level. Our experimental investigations of detailed
electronic structure as well as transport measurements of EuMg2Bi2 suggest that
it could potentially provide a platform to study the interplay between topology
and magnetism.",1912.08645v1
2020/8/4,Self-hybridization and tunable magnon-magnon coupling in van der Waals synthetic magnets,"Van der Waals magnets are uniquely positioned at the intersection between
two-dimensional materials, antiferromagnetic spintronics, and magnonics. The
interlayer exchange interaction in these materials enables antiferromagnetic
resonances to be accessed at GHz frequencies. Consequently, these layered
antiferromagnets are intriguing materials out of which quantum hybrid magnonic
devices can be fashioned. Here, we use both a modified macrospin model and
micromagnetic simulations to demonstrate a comprehensive antiferromagnetic
resonance spectra in van der Waals magnets near the ultrathin (monolayer)
limit. The number of optical and acoustic magnon modes, as well as the mode
frequencies, are found to be exquisitely sensitive to the number of layers. We
discover a self-hybridization effect where pairs of either optical or acoustic
magnons are found to interact and self-hybridize through the dynamic exchange
interaction. This leads to characteristic avoided energy level crossings in the
energy spectra. Through simulations, we show that by electrically controlling
the damping of surface layers within heterostructures both the strength and
number of avoided energy level crossings in the magnon spectra can be
controlled.",2008.01298v1
2020/9/28,Electronic and magnetic characterization of epitaxial CrBr$_3$ monolayers,"The ability to imprint a given material property to another through proximity
effect in layered two-dimensional materials has opened the way to the creation
of designer materials. Here, we use molecular-beam epitaxy (MBE) for a direct
synthesis of a superconductor-magnet hybrid heterostructure by combining
superconducting niobium diselenide (NbSe$_2$) with the monolayer ferromagnetic
chromium tribromide (CrBr$_3$). Using different characterization techniques and
density-functional theory (DFT) calculations, we have confirmed that the
CrBr$_3$ monolayer retains its ferromagnetic ordering with a magnetocrystalline
anisotropy favoring an out-of-plane spin orientation. Low-temperature scanning
tunneling microscopy (STM) measurements show a slight reduction of the
superconducting gap of NbSe$_2$ and the formation of a vortex lattice on the
CrBr$_3$ layer in experiments under an external magnetic field. Our results
contribute to the broader framework of exploiting proximity effects to realize
novel phenomena in 2D heterostructures.",2009.13465v1
2021/1/6,Two-dimensional honeycomb-kagome V2O3: a robust room-temperature magnetic Chern insulator interfaced with graphene,"The possibility of dissipationless chiral edge states without the need of an
external magnetic field in the quantum anomalous Hall effect (QAHE) offers a
great potential in electronic/spintronic applications. The biggest hurdle for
the realization of a room-temperature magnetic Chern insulator is to find a
structurally stable material with a sufficiently large energy gap and Curie
temperature that can be easily implemented in electronic devices. This work
based on first-principle methods shows that a single atomic layer of V2O3 with
honeycomb-kagome (HK) lattice is structurally stable with a spin-polarized
Dirac cone which gives rise to a room-temperature QAHE by the existence of an
atomic on-site spin-orbit coupling (SOC). Moreover, by a strain and substrate
study, it was found that the quantum anomalous Hall system is robust against
small deformations and can be supported by a graphene substrate.",2101.02162v2
2021/3/9,Characteristic singular behaviors of nodal line materials emerging in orbital magnetic susceptibility and Hall conductivity,"The bulk properties of nodal line materials have been an important research
topic in recent years. In this paper, we study the orbital magnetic
susceptibility and the Hall conductivity of nodal line materials using the
formalism with thermal Green's functions and find characteristic singular
behaviors of them. It is shown that, in the vicinity of the gapless nodal line,
the orbital magnetic susceptibility shows a $\delta$-function singularity and
the Hall conductivity shows a step function behavior in their chemical
potential dependences. Furthermore, these singular behaviors are found to show
strong field angle dependences corresponding to the orientation of the nodal
line in the momentum space. These singular behaviors and strong angle
dependences will give clear evidence for the presence of the nodal line and its
orientation and can be used to experimentally detect nodal line materials.",2103.05591v1
2021/4/9,High-throughput imaging measurements of thermoelectric figure of merit,"We demonstrate a method for the simultaneous determination of the
thermoelectric figure of merit of multiple martials by means of the lock-in
thermography (LIT) technique. This method is based on the thermal analyses of
the transient temperature distribution induced by the Peltier effect and Joule
heating, which enables high-throughput estimation of the thermal diffusivity,
thermal conductivity, volumetric heat capacity, Seebeck or Peltier coefficient
of the materials. The LIT-based approach has high reproducibility and
reliability because it offers sensitive noncontact temperature measurements and
does not require the installation of an external heater. By performing the same
measurements and analyses with applying an external magnetic field, the
magnetic field and/or magnetization dependences of the Seebeck or Peltier
coefficient and thermal conductivity can be determined simultaneously. We
demonstrate the validity of this method by using several ferromagnetic metals
(Ni, Ni$_{95}$Pt$_{5}$, and Fe) and a nonmagnetic metal (Ti). The proposed
method will be useful for materials research in thermoelectrics and spin
caloritronics and for investigation of magneto-thermal and
magneto-thermoelectric transport properties.",2104.04173v2
2021/6/3,Quaternary-digital data storage based on magnetic bubbles in anisotropic materials,"The topologically non-trivial nano-whirls, called magnetic skyrmions, are
often considered attractive for spintronic applications like the racetrack data
storage device. However, skyrmions do not move parallel to applied currents and
typically do not coexist with other nano-objects, making the realization of
such storage concepts difficult. Herein we consider materials with an
anisotropic DMI, like tetragonal Heusler materials, and show that four distinct
types of topologically trivial bubbles can coexist. We show that each of them
can be written by spin torques and that they can be distinguished using a
single magnetic tunneling junction. Due to their trivial topology, the four
types of bubbles move parallel to applied electrical currents and remain
equidistant under motion. Still, the bubbles have a small size and high
stability comparable to topologically non-trivial spin textures. This allows to
construct a quaternary-digit-based racetrack storage device that overcomes the
two mentioned drawbacks of skyrmion-based racetracks.",2106.01747v2
2021/7/17,Valley-Filling Instability and Critical Magnetic Field for Interaction-Enhanced Zeeman Response in Doped WSe$_2$ Monolayers,"Carrier-doped transition metal dichalcogenide (TMD) monolayers are of great
interest in valleytronics due to the large Zeeman response (g-factors) in these
spin-valley-locked materials, arising from many-body interactions. We develop
an \textit{ab initio} approach based on many-body perturbation theory to
compute the interaction-enhanced g-factors in carrier-doped materials. We show
that the g-factors of doped WSe$_2$ monolayers are enhanced by screened
exchange interactions resulting from magnetic-field-induced changes in band
occupancies. Our interaction-enhanced g-factors $g^*$ agree well with
experiment. Unlike traditional valleytronic materials such as silicon, the
enhancement in g-factor vanishes beyond a critical magnetic field $B_c$
achievable in standard laboratories. We identify ranges of $g^*$ for which this
change in g-factor at $B_c$ leads to a valley-filling instability and Landau
level alignment, which is important for the study of quantum phase transitions
in doped TMDs. We further demonstrate how to tune the g-factors and optimize
the valley-polarization for the valley Hall effect.",2107.08197v1
2021/8/19,"IrCrMnZ (Z=Al, Ga, Si, Ge) Heusler alloys as electrode materials for MgO-based magnetic tunneling junctions: A first-principles study","We study IrCrMnZ (Z=Al, Ga, Si, Ge) systems using first-principles
calculations from the perspective of their application as the electrode
materials of MgO-based MTJs. These materials have highly spin-polarized
conduction electrons with partially occupied $\Delta_1$ band, which is
important for coherent tunneling in parallel magnetization configuration. The
Curie temperatures of IrCrMnAl and IrCrMnGa are very high (above 1300 K) as
predicted from mean-field-approximation. The stability of ordered phase against
various antisite disorders has been investigated. We discuss here the effect of
""spin-orbit-coupling"" on the electronic structure around Fermi level. Further,
we investigate the electronic structure of IrCrMnZ/MgO heterojunction along
(001) direction. IrCrMnAl/MgO and IrCrMnGa/MgO maintain half-metallicity even
at the MgO interface, with no interfacial states at/around Fermi level in the
minority-spin channel. Large majority-spin conductance of IrCrMnAl/MgO/IrCrMnAl
and IrCrMnGa/MgO/IrCrMnGa is reported from the calculation of ballistic
spin-transport property for parallel magnetization configuration. We propose
IrCrMnAl/MgO/IrCrMnAl and IrCrMnGa/MgO/IrCrMnGa as promising MTJs with a weaker
temperature dependence of tunneling magnetoresistance ratio, owing to their
very high Curie temperatures.",2108.08501v1
2021/10/9,Field induced spin freezing and low temperature heat capacity of disordered pyrochlore oxide Ho$_{2}$Zr$_{2}$O$_{7}$,"Spin ice materials are the model systems that have a zero-point entropy as
\textit{T} $\rightarrow$ 0 K, owing to the frozen disordered states. Here, we
chemically alter the well-known spin ice Ho$_{2}$Ti$_{2}$O$_{7}$ by replacing
Ti sites with isovalent but larger Zr ion. Unlike the Ho$_{2}$Ti$_{2}$O$_{7}$
which is a pyrochlore material, Ho$_{2}$Zr$_{2}$O$_{7}$ crystallizes in
disordered pyrochlore structure. We have performed detailed structural, ac
magnetic susceptibility and heat capacity studies on Ho$_{2}$Zr$_{2}$O$_{7}$ to
investigate the interplay of structural disorder and frustrated interactions.
The zero-field ground state exhibits large magnetic susceptibility and remains
dynamic down to 30 mK without showing Pauling's residual entropy. The dynamic
state is suppressed continuously with the magnetic field and freezing
transition evolves ($\sim$ 10 K) at a field of $\sim$ 10 kOe. These results
suggest that the alteration of chemical order and local strain in
Ho$_{2}$Ti$_{2}$O$_{7}$ prevents the development of spin ice state and provides
a new material to study the geometrical frustration based on the structure.",2110.04555v1
2021/10/19,Van der Waals heterostructures for spintronics and opto-spintronics,"The large variety of 2D materials and their co-integration in van der Waals
(vdW) heterostructures enable innovative device engineering. In addition, their
atomically-thin nature promotes the design of artificial materials by proximity
effects that originate from short-range interactions. Such a designer approach
is particularly compelling for spintronics, which typically harnesses
functionalities from thin layers of magnetic and non-magnetic materials and the
interfaces between them. Here, we overview recent progress on 2D spintronics
and opto-spintronics using vdW heterostructures. After an introduction to the
forefront of spin transport research, we highlight the unique spin-related
phenomena arising from spin-orbit and magnetic proximity effects. We further
describe the ability to create multi-functional hybrid heterostructures based
on vdW materials, combining spin, valley and excitonic degrees of freedom. We
end with an outlook on perspectives and challenges for the design and
production of ultra-compact all-2D spin devices and their potential
applications in conventional and quantum technologies.",2110.09944v1
2021/11/19,Confirming the trilinear form of the optical magnetoelectric effect in the polar honeycomb antiferromagnet Co$_{2}$Mo$_3$O$_8$,"Magnetoelectric phenomena are intimately linked to relativistic effects and
also require the material to break spatial inversion symmetry and time reversal
invariance. Magnetoelectric coupling can substantially affect light-matter
interaction and lead to non-reciprocal light propagation. Here, we confirm on a
fully experimental basis, without invoking either symmetry-based or
material-specific assumptions, that the optical magnetoelectric effect in
materials with non-parallel magnetization ($\boldsymbol{M}$) and electric
polarization ($\boldsymbol{P}$) generates a trilinear term in the refractive
index, $\delta
n\propto\boldsymbol{k}\cdot(\boldsymbol{P}\times\boldsymbol{M})$, where
$\boldsymbol{k}$ is the propagation vector of light. Its sharp magnetoelectric
resonances, that are simultaneously electric and magnetic dipole active
excitations, make Co$_{2}$Mo$_3$O$_8$ an ideal compound to demonstrate this
fundamental relation via independent variation of $\boldsymbol{M}$,
$\boldsymbol{P}$ and $\boldsymbol{k}$. Remarkably, the material shows almost
perfect one-way transparency in moderate magnetic fields at some of the
magnetoelectric resonances.",2111.10217v1
2021/12/9,Pivotal role of magnetic ordering and strain in lattice thermal conductivity of chromium-trihalide monolayers,"Understanding the coupling between spin and phonons is critical for
controlling the lattice thermal conductivity ($\kappa_l$) in magnetic
materials, as we demonstrate here for CrX$_3$ (X = Br and I) monolayers. We
show that these compounds exhibit large spin-phonon coupling (SPC), dominated
by out-of-plane vibrations of Cr atoms, resulting in significantly different
phonon dispersions in ferromagnetic (FM) and paramagnetic (PM) phases. Lattice
thermal conductivity calculations provide additional evidence for strong SPC,
where particularly large $\kappa_l$ is found for the FM phase. Most strikingly,
PM and FM phases exhibit radically different behavior with tensile strain,
where $\kappa_l$ increases with strain for the PM phase, and strongly decreases
for the FM phase -- as we explain through analysis of phonon lifetimes and
scattering rates. Taken all together, we uncover the very high significance of
SPC on the phonon transport in CrX$_3$ monolayers, a result extendable to other
2D magnetic materials, that will be useful in further design of thermal spin
devices.",2112.04813v1
2022/1/16,Metastable Kitaev Magnets,"Nearly two decades ago, Alexei Kitaev proposed a model for spin-$1/2$
particles with bond-directional interactions on a two-dimensional honeycomb
lattice which had the potential to host a quantum spin-liquid ground state.
This work initiated numerous investigations to design and synthesize materials
that would physically realize the Kitaev Hamiltonian. The first-generation of
such materials, such as Na$_{2}$IrO$_{3}$, $\alpha$-Li$_{2}$IrO$_{3}$, and
$\alpha$-RuCl$_{3}$, revealed the presence of non-Kitaev interactions such as
the Heisenberg and off-diagonal exchange. Both physical pressure and chemical
doping were used to tune the relative strength of the Kitaev and competing
interactions; however, little progress was made towards achieving a purely
Kitaev system. Here, we review the recent breakthrough in modifying Kitaev
magnets via topochemical methods that has led to the second-generation of
Kitaev materials. We show how structural modifications due to the topotactic
exchange reactions can alter the magnetic interactions in favor of a quantum
spin-liquid phase.",2201.06085v1
2022/4/6,Observation of giant surface second harmonic generation coupled to nematic orders in the van der Waals antiferromagnet FePS$_3$,"Second harmonic generation has been applied to study lattice, electronic and
magnetic proprieties in atomically thin materials. However, inversion symmetry
breaking is usually required for the materials to generate a large signal. In
this work, we report a giant second-harmonic generation that arises below the
N\'eel temperature in few-layer centrosymmetric FePS$_3$. Layer-dependent study
indicates the detected signal is from the second-order nonlinearity of the
surface. The magnetism-induced surface second-harmonic response is two orders
of magnitude larger than those reported in other magnetic systems, with the
surface nonlinear susceptibility reaching 0.08--0.13 nm$^2$/V in 2 L--5 L
samples. By combing linear dichroism and second harmonic generation
experiments, we further confirm the giant second-harmonic generation is coupled
to nematic orders formed by the three possible Zigzag antiferromagnetic
domains. Our study shows that the surface second-harmonic generation is also a
sensitive tool to study antiferromagnetic states in centrosymmetric atomically
thin materials.",2204.02931v1
2022/4/11,Anisotropic magnetotransport in the layered antiferromagnet TaFe$_{1.25}$Te$_3$,"The discovery of fascinating ways to control and manipulate antiferromagnetic
materials have garnered considerable attention as an attractive platform to
explore novel spintronic phenomena and functionalities. Layered
antiferromagnets (AFMs) exhibiting interesting magnetic structures, can serve
as an attractive starting point to establish novel functionalities down to the
two-dimensional limit. In this work, we explore the magnetoresistive properties
of the spin-ladder AFM TaFe$_{1.25}$Te$_3$. Magnetization studies reveal an
anisotropic magnetic behavior resulting in the stabilization of a spin-flop
configuration for H $\perp$ (10-1) plane (i.e., out-of-plane direction).
Angle-dependent longitudinal and transverse magnetoresistances show an unusual
anharmonic behavior. A significant anisotropic enhancement of magnetoresistance
when H $\perp$ (10-1) plane compared to H $\parallel$ (10-1) directions has
been observed. The present results deepen our understanding of the
magnetoresistive properties of low-dimensional layered AFMs, and point towards
the possibility of utilizing these novel material systems for antiferromagnetic
spintronics.",2204.05213v1
2022/4/27,Hidden interplay of current-induced spin and orbital torques in bulk Fe$_3$GeTe$_2$,"Low crystal symmetry of magnetic van der Waals materials naturally promotes
spin-orbital complexity unachievable in common magnetic materials used for
spin-orbit torque switching. Here, using first-principles methods, we
demonstrate that an interplay of spin and orbital degrees of freedom has a
profound impact on spin-orbit torques in a prototype van der Waals ferromagnet:
Fe$_3$GeTe$_2$ (FGT). While we show that bulk FGT hosts strong ""hidden""
current-induced torques harvested by each of its layers, we uncover that their
origin alternates between the conventional spin flux torque and the so-called
orbital torque as the magnetization direction is varied. A drastic difference
in the behavior of the two types of torques results in a non-trivial evolution
of switching properties with doping. Our findings promote the design of
non-equilibrium orbital properties as the guiding mechanism for crafting the
properties of spin-orbit torques in layered van der Waals materials.",2204.13052v3
2022/8/30,In-plane anomalous Hall effect in PT-symmetric antiferromagnetic materials,"Anomalous Hall effect (AHE), a protocol of various low-power dissipation
quantum phenomena and a fundamental precursor of intriguing topological phases
of matter, is usually observed in ferromagnetic materials with orthogonal
configuration between the electric field, magnetization and the Hall current.
Here, based on the symmetry analysis, we find an unconventional AHE induced by
the in-plane magnetic field (IPAHE) via spin-canting effect in $\mathcal{PT}$
symmetric antiferromagnetic (AFM) systems, featuring a linear dependence of
magnetic field and 2$\pi$ angle periodicity with a comparable magnitude as
conventional AHE. We demonstrate the key findings in the known AFM Dirac
semimetal CuMnAs and a new kind of AFM heterodimensional VS$_2$-VS superlattice
with a nodal-line Fermi surface and also briefly discuss the experimental
detection. Our work provides an efficient pathway to search and/or design
realistic materials for novel IPAHE that could greatly facilitate their
application in AFM spintronic devices.",2208.14251v1
2022/9/9,2D Weyl Materials in the Presence of Constant Magnetic Fields,"In this work we investigate the effect of a constant external, or artificial,
magnetic field on the nonlinear response of 2D Weyl materials. We calculate the
Landau Levels for tilted cones in 2D Weyl materials by treating the tilting in
a perturbative manner, and employ perturbation theory to calculate the
tilting-induced correction to the magnetic field induced Landau spectrum. We
then calculate the induced current as a function of the tilting coefficients
and extract the correspondent nonlinear signal. Then, we analyze how changing
tilting parameter affects nonlinear signal. Our findings show the possibility
of achieving a significant tunability of the nonlinear response, by suitably
engineering the orientation and degree of tilt of Dirac cones in 2D Weyl
materials.",2209.04295v2
2022/9/30,Perspectives on Antiferromagnetic Spintronics,"Although the development of spintronic devices has advanced significantly
over the past decade with the use of ferromagnetic materials, the extensive
implementation of such devices has been limited by the notable drawbacks of
these materials. Antiferromagnets claim to resolve many of these shortcomings
leading to faster, smaller, more energy-efficient, and more robust electronics.
Antiferromagnets exhibit many desirable properties including zero net
magnetization, imperviousness to external magnetic fields, intrinsic
high-frequency dynamics with a characteristic precession frequency on the order
of terahertz (THz), and the ability to serve as passive exchange-bias materials
in multiple magnetoresistance (MR)- based devices. In this Perspective article,
we will discuss the fundamental physics of magnetic structures in
antiferromagnets and their interactions with external stimuli such as spin
current, voltage, and magnons. A discussion on the challenges lying ahead is
also provided along with an outlook of future research directions of these
systems.",2209.15187v2
2023/1/26,"Magnetic, Optoelectronic, and Rietveld refined structural properties of Al3+ substituted nanocrystalline Ni-Cu spinel ferrites: An experimental and DFT based study","The nanocrystalline Ni0.7Cu0.3AlxFe2-xO4 (x=0.00: 0.02: 0.10) is prepared
through the sol-gel autocombustion route.Both XRD and Rietveld confirm the
single-phase cubic spinel structure of the investigated materials.Other
structural parameters refined by the Rietveld refinement analysis are
corroborated to single-phase cubic spinel formation of the NPs.Leveraging a
vibrating sample magnetometer (VSM) the consequence of Al3+ substitution on the
magnetic parameters is studied.The saturation magnetization (MS) and Bohr
magneton are found to decrease with Al3+ substitution.The Remanence ratio and
coercivity (HC) are observed to be very low suggesting the materials are soft
ferromagnetic.First-principle calculations were carried out using the density
functional theory (DFT) to demonstrate the optoelectronic behavior of the
materials.The electronic bandgap is found low as Eg=2.99eV for the explored
materials with observing defect states at 0.62eV.The optoelectronic properties
of Al3+ substituted Ni-Cu ferrite NPs have been characterized through the DFT
simulation for the first time, demonstrating their potentiality for
optoelectronic device applications.The materials' optical anisotropy is
observed along the x-axis, which manifests their tunability through
light-matter interaction.",2301.11373v1
2023/3/6,Quantum states and intertwining phases in kagome materials,"In solid materials, nontrivial topological states, electron correlations, and
magnetism are central ingredients for realizing quantum properties, including
unconventional superconductivity, charge and spin density waves, and quantum
spin liquids. The Kagome lattice, made up of connected triangles and hexagons,
can host these three ingredients simultaneously and has proven to be a fertile
platform for studying diverse quantum phenomena including those stemming from
the interplay of these ingredients. In this review, we introduce the
fundamental properties of the Kagome lattice as well as discuss the complex
observed phenomena seen in several emergent material systems such as the
intertwining of charge order and superconductivity in some Kagome metals,
modulation of magnetism and topology in some Kagome magnets, and symmetry
breaking with Mott physics in the breathing Kagome insulators. We also
highlight many open questions in the field as well as future research
directions of Kagome systems.",2303.03359v1
2023/6/7,Intrinsic antiferromagnetic multimeronic Néel spin-textures in ultrathin films,"The realization of topological antiferromagnetic (AFM) solitons in real
materials is a major goal towards their use in information technology. While
they bear various advantages with respect to their ferromagnetic cousins, their
observation is scarce. Utilizing first-principles simulations, here we predict
new chiral particles in the realm of AFM topological magnetism, frustrated
multimeronic spin-textures hosted by a N\'eel magnetic state, arising in single
Mn layers directly grown on Ir(111) surface or interfaced with Pd-based films.
These topological structures are intrinsic, i.e. they form in a single AFM
material, can carry distinct topological charges and can combine in various
multimeronic sequences with enhanced stability against external magnetic
fields. We envision the frustrated N\'eel AFM multimerons as exciting
highly-sought after AFM solitons having the potential to be utilized in novel
spintronic devices hinging on non-synthetic AFM quantum materials.",2306.04720v1
2023/7/11,Spin-splitting in electric-potential-difference antiferromagnetism,"The antiferromagnetic (AFM) materials are robust to external magnetic
perturbation due to missing any net magnetic moment. In general, the spin
splitting in the band structures disappears in these antiferromagnets. However,
the altermagnetism can achieve spin-split bands in collinear
symmetry-compensated antiferromagnet with special magnetic space group. Here,
we propose a new mechanism that can achieve spin splitting in two-dimensional
(2D) Janus A-type AFM materials. Since the built-in electric field caused by
Janus structure creates a layer-dependent electrostatic potential, the
electronic bands in different layers will stagger, producing the spin
splitting, which can be called electric-potential-difference antiferromagnetism
(EPD-AFM). We demonstrate that Janus monolayer $\mathrm{Mn_2ClF}$ is a possible
candidate to achieve the EPD-AFM by the first-principles calculations. It is
proposed that the spin splitting can be tuned in EPD-AFM by piezoelectric
effect. Our works provide a new design principle for generating spin
polarization in 2D AFM materials.",2307.05010v1
2023/12/7,Cryogenic platform to investigate strong microwave cavity-spin coupling in correlated magnetic materials,"We present a comprehensive exploration of loop-gap resonators (LGRs) for
electron spin resonance (ESR) studies, enabling investigations into the
hybridization of solid-state magnetic materials with microwave polariton modes.
The experimental setup, implemented in a Physical Property Measurement System
by Quantum Design, allows for ESR spectra at temperatures as low as 2 Kelvin.
The versatility of continuous wave ESR spectroscopy is demonstrated through
experiments on CuSO4.5H2O and MgCr2O4, showcasing the g-tensor and magnetic
susceptibilities of these materials. The study delves into the challenges of
fitting spectra under strong hybridization conditions and underscores the
significance of proper calibration and stabilization. The detailed guide
provided serves as a valuable resource for laboratories interested in exploring
hybrid quantum systems through microwave resonators.",2312.04750v2
2023/12/29,Electron-doped magnetic Weyl semimetal LixCo3Sn2S2 by bulk-gating,"Manipulating carrier density through gate effects, both in electrostatic
charge storage and electrochemical intercalation mode, offers powerful control
over material properties, although commonly restricted to ultra-thin films or
van der Waals materials. Here we demonstrate the application of gate-driven
carrier modulation in the microdevice of magnetic Weyl semimetal Co3Sn2S2,
fabricated from a bulk single crystal via focused ion beam (FIB). We discovered
a Li-intercalated phase LixCo3Sn2S2 featuring electron doping exceeding 5*1021
cm-3, resulting in the Fermi energy shift of 200 meV. The carrier density
dependent anomalous Hall conductivity shows fair agreement with density
functional theory (DFT) calculation, which also predicts intercalated Li+ ion
stabilization within the anion layer while maintaining the kagome-lattice
intact. This likely explains the observed rigid band behavior and constant
Curie temperature, contrasting with magnetic site substitution experiments. Our
findings suggest ionic gating on FIB devices broadens the scope of gate-tuning
in quantum materials.",2312.17547v1
2024/2/7,Breaking surface plasmon excitation constraint via surface spin waves,"Surface plasmons in two-dimensional (2D) electron systems have attracted
great attention for their promising light-matter applications. However, the
excitation of a surface plasmon, in particular, transverse-electric (TE)
surface plasmon, remains an outstanding challenge due to the difficulty to
conserve energy and momentum simultaneously in the normal 2D materials. Here we
show that the TE surface plasmons ranging from gigahertz to terahertz regime
can be effectively excited and manipulated in a hybrid dielectric, 2D material
and magnet structure. The essential physics is that the surface spin wave
supplements an additional freedom of surface plasmon excitation and thus
greatly enhances the electric field in the 2D medium. Based on widely-used
magnetic materials like yttrium iron garnet (YIG) and manganese difluoride
($\mathrm{MnF}_2$), we further show that the plasmon excitation manifests
itself as a measurable dip in the reflection spectrum of the hybrid system
while the dip position and the dip depth can be well controlled by the electric
gating on the 2D layer and an external magnetic field. Our findings should
bridge the fields of low-dimensional physics, plasmonics and spintronics and
open a novel route to integrate plasmonic and spintronic devices.",2402.04626v1
1999/10/25,Finite-size versus Surface effects in nanoparticles,"We study the finite-size and surface effects on the thermal and spatial
behaviors of the magnetisation of a small magnetic particle. We consider two
systems: 1) A box-shaped isotropic particle of simple cubic structure with
either periodic or free boundary conditions. This case is treated analytically
using the isotropic model of D-component spin vectors in the limit $D\to
\infty$, including the magnetic field. 2) A more realistic particle ($\gamma
$-Fe$_{2}$O$_{3}$) of ellipsoidal (or spherical) shape with open boundaries.
The magnetic state in this particle is described by the anisotropic classical
Dirac-Heisenberg model including exchange and dipolar interactions, and bulk
and surface anisotropy. This case is dealt with by the classical Monte Carlo
technique. It is shown that in both systems finite-size effects yield a
positive contribution to the magnetisation while surface effects render a
larger and negative contribution, leading to a net decrease of the
magnetisation of the small particle with respect to the bulk system. In the
system 2) the difference between the two contributions is enhanced by surface
anisotropy. The latter also leads to non saturation of the magnetisation at low
temperatures, showing that the magnetic order in the core of the particle is
perturbed by the magnetic disorder on the surface. This is confirmed by the
profile of the magnetisation.",9910393v1
2006/9/26,"Spin-flop transition in uniaxial antiferromagnets: magnetic phases, reorientation effects, multidomain states","The classical spin-flop is the field-driven first-order reorientation
transition in easy-axis antiferromagnets. A comprehensive phenomenological
theory of easy-axis antiferromagnets displaying spin-flops is developed. It is
shown how the hierarchy of magnetic coupling strengths in these
antiferromagnets causes a strongly pronounced two-scale character in their
magnetic phase structure. In contrast to the major part of the magnetic phase
diagram, these antiferromagnets near the spin-flop region are described by an
effective model akin to uniaxial ferromagnets. For a consistent theoretical
description both higher-order anisotropy contributions and dipolar stray-fields
have to be taken into account near the spin-flop. In particular,
thermodynamically stable multidomain states exist in the spin-flop region,
owing to the phase coexistence at this first-order transition. For this region,
equilibrium spin-configurations and parameters of the multidomain states are
derived as functions of the external magnetic field. The components of the
magnetic susceptibility tensor are calculated for homogeneous and multidomain
states in the vicinity of the spin-flop. The remarkable anomalies in these
measurable quantities provide an efficient method to investigate magnetic
states and to determine materials parameters in bulk and confined
antiferromagnets, as well as in nanoscale synthetic antiferromagnets. The
method is demonstrated for experimental data on the magnetic properties near
the spin-flop region in the orthorhombic layered antiferromagnet
(C_2H_5NH_3)_2CuCl_4.",0609648v2
2007/8/21,Theory of induced quadrupolar order in tetragonal YbRu_{2}Ge_{2},"The tetragonal compound YbRu$_{2}$Ge$_{2}$ exhibits a non-magnetic transition
at $T_0$=10.2K and a magnetic transition at $T_1$=6.5K in zero magnetic field.
We present a model for this material based on a quasi-quartet of Yb$^{3+}$
crystalline electric field (CEF) states and discuss its mean field solution.
Taking into account the broadening of the specific heat jump at $T_0$ for
magnetic field perpendicular to [001] and the decrease of $T_0$ with magnetic
field parallel to [001], it is shown that ferro-quadrupole order of either
O$_{2}^{2}$ or O$_{\rm xy}$ - type are prime candidates for the non-magnetic
transition. Considering the matrix element of these quadrupole moments, we show
that the lower CEF states of the level scheme consist of a $\Gamma_{6}$ and a
$\Gamma_{7}$ doublet. This leads to induced type of O$_{2}^{2}$ and O$_{\rm
xy}$ quadrupolar order parameters. The quadrupolar order introduces exchange
anisotropy for planar magnetic moments. This causes a spin flop transition at
low fields perpendicular [001] which explains the observed metamagnetism. We
also obtain a good explanation for the temperature dependence of magnetic
susceptibility and specific heat for fields both parallel and perpendicular to
the [001] direction.",0708.2872v2
2009/1/27,X-ray Magnetic Circular Dichroism of Valence Fluctuating State in Eu at High Magnetic Fields,"X-ray magnetic circular dichroism (XMCD) at the Eu L-edge (2p->5d) in two
compounds exhibiting valence fluctuation, namely EuNi2(Si0.18Ge0.82)2 and
EuNi2P2, has been investigated at pulsed high magnetic fields of up to 40 T. A
distinct XMCD peak corresponding to the trivalent state (Eu3+; f6), whose
ground state is nonmagnetic (J=0), was observed in addition to the main XMCD
peak corresponding to the magnetic (J=7/2) divalent state (Eu2+; f7). This
result indicates that the 5d electrons belonging to both valence states are
magnetically polarized. It was also found that the ratio P5d(3+)/P5d(2+)
between the polarization of 5d electrons (P5d) in the Eu3+ state and that of
Eu2+ is ~ 0.1 in EuNi2(Si0.18Ge0.82)2 and ~ 0.3 in EuNi2P2 at magnetic fields
where their macroscopic magnetization values are the same. The possible origin
of the XMCD of the Eu3+ state and an explanation of the dependence of
P5d(3+)/P5d(2+) on the material are discussed in terms of hybridization between
the conduction electrons and the f electrons.",0901.4259v3
2009/3/17,In search for the superconducting spin-switch: Magnetization induced resistance switching effects in La$_{0.67}$Sr$_{0.33}$MnO$_3$/YBa$_2$Cu$_3$O$_{7-δ}$ bi- and trilayers,"We have studied the influence of the magnetization on the superconducting
transition temperature ($T_c$) in bi- and trilayers consisting of the
half-metallic ferromagnet La$_{0.67}$Sr$_{0.33}$MnO$_3$ (LSMO) and the
high-temperature superconductor YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO). We have
made use of tilted epitaxial growth in order to achieve contacts between the
two materials that are partly in the crystallographic $ab$-plane of the YBCO.
As a result of uniaxial magnetic anisotropy in the tilted structures, we
observe sharp magnetization switching behavior. At temperatures close to $T_c$,
the magnetization switching induces resistance jumps in trilayers, resulting in
a magnetization dependence of $T_c$. In bilayers, this switching effect can be
observed as well, provided that the interface to the ferromagnetic layer is
considerably rough. Our results indicate that the switching behavior arises
from magnetic stray fields from the ferromagnetic layers that penetrate into
the superconductor. A simple model describes the observed behavior well. We
find no evidence that the switching behavior is caused by a so-called
superconducting spin-switch, nor by accumulation of spin-polarized electrons.
Observation of magnetic coupling of the ferromagnetic layers, through the
superconductor, supports the idea of field induced resistance switching.",0903.2993v1
2009/4/15,Magnetic excitations and optical transitions in the multiferroic spin-1/2 system LiCu$_2$O$_2$,"Magnetic excitations in cycloidal magnet LiCu$_2$O$_2$ are explored using THz
absorption spectroscopy in magnetic fields up to 12 T. Below the spin ordering
temperature we observe eight optically active transitions in the spin system of
LiCu$_2$O$_2$ in the energy range from 4 to 30 cm$^{-1}$. In magnetic field the
number of modes increases and the electric polarization flop is seen as a
change in magnetic field dependence of mode energies. The polarization
dependence of two of the modes in zero magnetic field fits the selection rules
for the cycloid tilted by $\theta=41\pm1^{\circ}$ from the bc plane. For the
remaining six modes electric and magnetic dipole approximations cannot explain
the observed polarization dependence. We do not see the electromagnon in the
explored energy range although there is evidence that it could exist below 4
cm$^{-1}$.",0904.2329v2
2010/6/2,Antiferromagnetic Mott insulating state in single crystals of the hexagonal lattice material Na2IrO3,"We have synthesized single crystals of Na_2IrO_3 and studied their structure,
transport, magnetic, and thermal properties using powder x-ray diffraction
(PXRD), electrical resistivity, isothermal magnetization M versus magnetic
field H, magnetic susceptibility \chi versus temperature T, and heat capacity C
versus T measurements. Na_2IrO_3 crystallizes in the monoclinic \emph{C2/c}
(No. 15) type structure which is made up of Na and NaIr_2O_6 layers alternately
stacked along the c axis. The \chi(T) data show Curie-Weiss behavior at high T
> 200K with an effective moment \mu_eff = 1.82(1) \mu_B indicating an effective
spin S_eff = 1/2 on the Ir^4+ moments. A large Weiss temperature \theta = -
116(3)K indicates substantial antiferromagnetic interactions between these
S_eff = 1/2, Ir^4+ moments. Sharp anomalies in \chi(T) and C(T) data indicate
that Na_2IrO_3 undergoes a transition into a long-range antiferromagnetically
ordered state below T_N = 15 K. The magnetic entropy at T_N is only about 20%
of what is expected for S_eff = 1/2 moment ordering. The reduced entropy and
the small ratio T_N/\theta \approx 0.13 suggest geometrical magnetic
frustration and/or low-dimensional magnetic interactions in Na_2IrO_3. In plane
resistivity measurements show insulating behavior. This together with the local
moment magnetism indicates that bulk Na_2IrO_3 is a Mott insulator.",1006.0437v1
2010/7/10,Magnetic Lattice Dynamics of the Oxygen-Free FeAs Pnictides: How Sensitive are Phonons to Magnetic Ordering?,"To shed light on the role of magnetism on the superconducting mechanism of
the oxygen-free FeAs pnictides, we investigate the effect of magnetic ordering
on phonon dynamics in the low-temperature orthorhombic parent compounds, which
present a spin-density wave. The study covers both the 122 (AFe2As2; A=Ca, Sr,
Ba) and 1111 (AFeAsF; A=Ca, Sr) phases. We extend our recent work on the Ca
(122 and 1111) and Ba (122) cases by treating computationally and
experimentally the 122 and 1111 Sr compounds. The effect of magnetic ordering
is investigated through detailed non-magnetic and magnetic lattice dynamical
calculations. The comparison of the experimental and calculated phonon spectra
shows that the magnetic interactions/ordering have to be included in order to
reproduce well the measured density of states. This highlights a
spin-correlated phonon behavior which is more pronounced than the apparently
weak electron-phonon coupling estimated in these materials. Furthermore, there
is no noticeable difference between phonon spectra of the 122 Ba and Sr,
whereas there are substantial differences when comparing these to CaFe2As2
originating from different aspects of structure and bonding.",1007.1711v1
2011/3/7,Quantum Simulation of Antiferromagnetic Spin Chains in an Optical Lattice,"Understanding exotic forms of magnetism in quantum mechanical systems is a
central goal of modern condensed matter physics, with implications from high
temperature superconductors to spintronic devices. Simulating magnetic
materials in the vicinity of a quantum phase transition is computationally
intractable on classical computers due to the extreme complexity arising from
quantum entanglement between the constituent magnetic spins. Here we employ a
degenerate Bose gas confined in an optical lattice to simulate a chain of
interacting quantum Ising spins as they undergo a phase transition. Strong spin
interactions are achieved through a site-occupation to pseudo-spin mapping. As
we vary an applied field, quantum fluctuations drive a phase transition from a
paramagnetic phase into an antiferromagnetic phase. In the paramagnetic phase
the interaction between the spins is overwhelmed by the applied field which
aligns the spins. In the antiferromagnetic phase the interaction dominates and
produces staggered magnetic ordering. Magnetic domain formation is observed
through both in-situ site-resolved imaging and noise correlation measurements.
By demonstrating a route to quantum magnetism in an optical lattice, this work
should facilitate further investigations of magnetic models using ultracold
atoms, improving our understanding of real magnetic materials.",1103.1372v2
2011/6/24,Magnetic dichroism in angular-resolved hard X-ray photoelectron spectroscopy from buried layers,"This work reports the measurement of magnetic dichroism in angular-resolved
photoemission from in-plane magnetized buried thin films. The high bulk
sensitivity of hard X-ray photoelectron spectroscopy (HAXPES) in combination
with circularly polarized radiation enables the investigation of the magnetic
properties of buried layers. HAXPES experiments with an excitation energy of 8
keV were performed on exchange-biased magnetic layers covered by thin oxide
films. Two types of structures were investigated with the IrMn exchange-biasing
layer either above or below the ferromagnetic layer: one with a CoFe layer on
top and another with a Co$_2$FeAl layer buried beneath the IrMn layer. A
pronounced magnetic dichroism is found in the Co and Fe $2p$ states of both
materials. The localization of the magnetic moments at the Fe site conditioning
the peculiar characteristics of the Co$_2$FeAl Heusler compound, predicted to
be a half-metallic ferromagnet, is revealed from the magnetic dichroism
detected in the Fe $2p$ states.",1106.4976v1
2012/2/24,Evolution of the nuclear and magnetic structures of TlFe1.6Se2 with temperature,"The evolution of the nuclear and magnetic structures of TlFe$_{1.6}$Se$_2$
was determined in the temperature range of 5-450\,K using single crystal
neutron diffraction. The Fe layers in these materials develop a corrugation in
the magnetically ordered state. A canting away from the block checkerboard
magnetic structure is observed in the narrow temperature range between
approximately 100 and 150\,K. In this same temperature range, an increase in
the corrugation of the Fe layers is observed. At lower temperatures, the block
checkerboard magnetic structure is recovered with a suppressed magnetic moment
and abrupt changes in the lattice parameters. Microstructure analysis at 300\,K
using atomic-resolution Z-contrast scanning transmission electron microscopy
reveals regions with ordered and disordered Fe vacancies, and the iron content
is found to be uniform across the crystal. These findings highlight the
differences between the alkali-metal and thallium materials, and indicate
competition between magnetic ground states and a strong coupling of magnetism
to the lattice in TlFe$_{1.6}$Se$_2$.",1202.5564v1
2013/2/9,Field-induced long-range magnetic order in the spin-singlet ground state system YbAl3C3: Neutron diffraction study,"The $4f$-electron system YbAl$_3$C$_3$ with a non-magnetic spin-dimer ground
state has been studied by neutron diffraction in an applied magnetic field. A
long-range magnetic order involving both ferromagnetic and antiferromagnetic
components has been revealed above the critical field H$_C\sim $ 6T at
temperature T=0.05K. The magnetic structure indicates that the geometrical
frustration of the prototype hexagonal lattice is not fully relieved in the
low-temperature orthorhombic phase. The suppression of magnetic ordering by the
remanent frustration is the key factor stabilizing the non-magnetic singlet
ground state in zero field. Temperature dependent measurements in the applied
field H=12T revealed that the long-range ordering persists up to temperatures
significantly higher than the spin gap indicating that this phase is not
directly related to the singlet-triplet excitation. Combining our neutron
diffraction results with the previously published phase diagram, we support the
existence of an intermediate disordered phase as the first excitation from the
non-magnetic singlet ground state. Based on our results, we propose
YbAl$_3$C$_3$ as a new material for studying the quantum phase transitions of
heavy-fermion metals under the influence of geometrical frustration.",1302.2245v1
2013/11/8,"Magnetic Properties of RFe2Si2 and R(Fe1-xMx)2Si2 Systems (R=La, Y and Lu, M= Ni, Mn and Cu)","Due to the similarity to BaFe2As2 and SrFe2As2 the RFe2Si2 (R=La, Y and Lu)
system has been proposed as a potential candidate for a new superconducting
family containing Fe-Si layers as a structural unit. Various R(Fe1-xMx)2Si2
M=Ni, Mn and Cu) materials were synthesized and measured for their magnetic
properties. None of these materials is superconducting down to 5 K. Fe in
RFe2Si2 is paramagnetic. A pronounced peak at 232 K was observed in the
magnetization curve of YFe2Si2. 57Fe M\""ossbauer studies confirm the absence of
any magnetic ordering at low temperatures. Similar peaks at various
temperatures also appear in R(Fe1-xMx)2Si2 samples. Four independent factors
affect the peak position and shift it to lower temperatures: (i) the lattice
parameters, (ii) the concentration of x, (iii) the applied magnetic field, and
(iv) the magnetic nature of M. The peak position is dramatically affected by
the magnetic Mn dopants. It is propose that the magnetic peaks observed in
RFe2Si2 and in R(Fe1-xMx)2Si2 represent a new nearly ferromagnetic Fermi liquid
(NFFL) system and their nature is yet to be determined.",1311.1984v1
2013/12/10,Magnetic structure of an activated filament in a flaring active region,"While the magnetic field in quiescent prominences has been widely
investigated, less is known about the field in activated prominences. We
introduce observational results on the magnetic field structure of an activated
filament in a flaring active region. We study, in particular, its magnetic
structure and line-of-sight flows during its early activated phase, shortly
before it displays signs of rotation. We invert the Stokes profiles of the
chromospheric He I 10830 A triplet and the photospheric Si I 10827 A line
observed in this filament by the VTT on Tenerife. Using these inversion results
we present and interpret the first maps of velocity and magnetic field obtained
in an activated filament, both in the photosphere and the chromosphere. Up to 5
different magnetic components are found in the chromospheric layers of the
filament, while outside the filament a single component is sufficient to
reproduce the observations. Magnetic components displaying an upflow are
preferentially located towards the centre of the filament, while the downflows
are concentrated along its periphery. Also, the upflowing gas is associated
with an opposite-polarity magnetic configuration with respect to the
photosphere, while the downflowing gas is associated with a same-polarity
configuration. The activated filament has a rather complex structure.
Nonetheless, it is compatible with a flux rope, although with a distorted one,
in the normal configuration. The observations are best explained by a rising
flux rope in which a part of the filament material is still stably stored
(upflowing material, rising with the field), while a part is no longer stably
stored and flows down along the field lines.",1312.2781v1
2014/4/15,Realization of magnetic monopoles current in an artificial spin ice device: A step towards magnetronics,"Magnetricity- the magnetic equivalent of electricity- was recently verified
experimentally for the first time. Indeed, just as the stream of electric
charges produces electric current, emergent magnetic monopoles have been
observed to roam freely (generating magnetic current) in geometrically
frustrated magnets known as spin ice. However, this is realized only by
considering extreme physical conditions as a single crystal of spin ice has to
be cooled to a temperature of $0.36 K$. Candidates to overcome this difficulty
are artificial analogues of spin ice crystals, the so-called artificial spin
ices. Here we show that, by tuning geometrical frustration down, a peculiar
type of these artificial systems is an excellent candidate. We produce this
material and experimentally observe the emergent monopoles; then, we calculate
the effects of external magnetic fields, illustrating how to generate
controlled magnetic currents. This potential nano-device for use in
magnetronics can be practical even at room temperature and the relevant
parameters (such as magnetic charge strength etc) for developing this
technology can be tuned at will.",1404.4082v1
2014/9/3,Nanoscale confinement of all-optical switching in TbFeCo using plasmonic antennas,"All-optical switching (AOS) of magnetic domains by femtosecond laser pulses
was first observed in the transition metal-rare earth (TM-RE) alloy GdFeCo1-5;
this phenomenon demonstrated the potential for optical control of magnetism for
the development of ever faster future magnetic recording technologies. The
technological potential of AOS has recently increased due to the discovery of
the same effect in other materials, including RE-free magnetic multilayers6,7.
However, to be technologically meaningful, AOS must compete with the bit
densities of conventional storage devices, restricting optically-switched
magnetic areas to sizes well below the diffraction limit. Here, we demonstrate
reproducible and robust all-optical switching of magnetic domains of 53 nm size
in a ferrimagnetic TbFeCo alloy using gold plasmonic antenna structures. The
confined nanoscale magnetic reversal is imaged around and beneath plasmonic
antennas using x-ray resonant holographic imaging. Our results demonstrate the
potential of future AOS-based magnetic recording technologies.",1409.1280v1
2014/10/1,"Tuning the Structural, Electronic, and Magnetic Properties of Germanene by the Adsorption of 3$d$ Transition Metal Atoms","The structural, electronic, and magnetic properties of 3$d$ transition metal
(TM) atoms (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) adsorbed germanene are
addressed using density functional theory. Based on the adsorption energy, TM
atoms prefer to occupy at the hollow site for all the cases. The obtained
values of the total magnetic moment vary from 0.97 $\mu_B$ to 4.95 $\mu_B$ in
case of Sc to Mn-adsorption, respectively. A gap of 74 meV with a strongly
enhanced splitting of 67 meV is obtained in case of Sc-adsorption, whereas
metallic states are obtained in case of Ti, Cr, Mn, Fe, and Co. Non-magnetic
states are realized for Ni, Cu, and Zn-adsorption. Moreover, semiconducting
nature is obtained for non-magnetic cases with a gap of 26 to 28 meV.
Importantly, it is found that V-adsorbed germanene can host the quantum
anomalous Hall effect. The obtained results demonstrate that TM atoms and
nearest neighbour Ge atoms are ferro-magnetically ordered in the cases of V,
Mn, Fe, Co, Ni, Cu, and Zn, while anti-ferromagnetic ordering is obtained for
Sc, Ti, and Cr. In addition, the effects of the coverage of all TM atoms on the
electronic structure and the ferro-magnetic and anti-ferro-magnetic coupling in
case of Mn are examined. The results could help to understand the effect of TM
atoms in a new class of two-dimensional materials beyond graphene and silicene.",1410.0395v1
2014/11/6,Electromagnetic coupling of spins and pseudospins in bilayer graphene,"We present a detailed theoretical study of bilayer-graphene's electronic
properties in the presence of electric and magnetic fields. Using
group-theoretical methods, we derive an invariant expansion of the Hamiltonian
for electron states near the K point of the Brillouin zone. In contrast to
known materials, including single-layer graphene, any possible coupling of
physical quantities to components of the external electric (magnetic) field has
a counterpart where the analogous component of the magnetic (electric) field
couples to exactly the same combination of quantities. For example, a purely
electric spin splitting appears as the magneto-electric analogue of the
familiar magnetic Zeeman spin splitting. The measurable thermodynamic response
induced by magnetic and electric fields is thus completely symmetric. The Pauli
magnetization induced by a magnetic field takes exactly the same functional
form as the polarization induced by an electric field. Our findings thus reveal
unconventional behavior of spin and pseudospin degrees of freedom in their
coupling to external fields. We explain how these counterintuitive couplings
are consistent with fundamental principles such as time reversal symmetry. For
example, only a magnetic field can give rise to a macroscopic spin
polarization, whereas only a perpendicular electric field can induce a
macroscopic polarization of the sublattice-related pseudospin degree of freedom
characterizing the intravalley orbital motion in bilayer graphene. These rules
enforced by symmetry for the matter-field interactions clarify the nature of
spins versus pseudospins. We also provide numerical values of prefactors for
relevant coupling terms. While our theoretical arguments use bilayer graphene
as an example, they are generally valid for any material with similar
symmetries.",1411.1720v2
2016/4/11,Unified Theory of Magnetoelastic Effects in B20 chiral magnets,"A magnetic skyrmion is a spin whirl with topological protection and high
mobility to electric current. Intrinsic magnetoelastic coupling in chiral
magnets permits manipulation of magnetic skyrmions and their lattice using
mechanical loads, which is essential for developing future spintronics devices.
It is found in experiments that the stability and deformation of skyrmions are
sensitive to stresses, while the appearance of magnetic skyrmions in turn has a
significant effect on the mechanical properties of the underlying material.
However, a theory which explains these related phenomena within a unified
framework is not seen. Here we construct a thermodynamic model for B20
helimagnets incorporating a magnetoelastic functional with necessary higher
order interactions derived by group theory. Within the model, we establish the
methodology to calculate the phase diagram and equilibrium properties of
helimagnets under coupled temperature-magneto-elastic field. Applying the model
to bulk MnSi, we calculate the temperature-magnetic field phase diagram under
stress-free condition and its variation when uniaxial compression is applied.
We also calculate the variation of all the elastic constants with magnetic
field. The results obtained agree quantitatively with corresponding
experiments. Our model provides a reliable basis for further theoretical
studies concerning any magnetoelastic related phenomena in chiral magnets.",1604.02766v3
2016/12/20,Current-nonlinear Hall effect and spin-orbit torque magnetization switching in a magnetic topological insulator,"Precise estimation of spin Hall angle as well as successful maximization of
spin-orbit torque (SOT) form a basis of electronic control of magnetic
properties with spintronic functionality. Until now, current-nonlinear Hall
effect, or second harmonic Hall voltage has been utilized as one of the methods
for estimating spin Hall angle, which is attributed to the magnetization
oscillation by SOT. Here, we argue the second harmonic Hall voltage in
magnetic/nonmagnetic topological insulator (TI) heterostructures,
Cr$_x$(Bi$_{1-y}$Sb$_y$)$_{2-x}$Te$_3$/(Bi$_{1-y}$Sb$_y$)$_2$Te$_3$. From the
angular, temperature and magnetic field dependence, it is unambiguously shown
that the large second harmonic Hall voltage in TI heterostructures is governed
not by SOT but mainly by asymmetric magnon scattering mechanism without
magnetization oscillation. Thus, this method does not allow an accurate
estimation of spin Hall angle when magnons largely contribute to electron
scattering. Instead, the SOT contribution in a TI heterostructure is
exemplified by current pulse induced non-volatile magnetization switching,
which is realized with a current density of $\sim 2.5 \times 10^{10}
\mathrm{A/m}^2$, showing its potential as spintronic materials.",1612.06862v2
2017/6/16,Long-distance spin transport in a disordered magnetic insulator,"Spin transport through magnetic insulators via magnons has recently been
explored for a growing variety of magnetic systems with long-range order and
well-understood spin excitation spectra. Here we show dramatic effects of spin
transport through an amorphous magnetic insulator, which is both magnetically
and structurally disordered. We generate and detect spin flow though amorphous
yttrium-iron-garnet ($a$-YIG) thin films in a non-local geometry by use of the
spin Hall and inverse spin Hall effects in platinum strips separated by 10 or
more microns. By comparing non-local spin transport in $a$-YIG on suspended
micromachined thermal isolation platforms to the same experiment performed on a
bulk substrate, we show strong effects of in-plane thermal gradients on spin
transport in the disordered magnetic insulator. The resulting non-local voltage
signals are orders of magnitude larger than those seen in crystalline magnetic
insulators, with easily measurable spin signals seen even at distances in
excess of $100$ microns. In analogy to heat transport, where disordered
materials support a range of vibrational excitations that can allow large
thermal conductivities, we suggest that efficient spin transport in disordered
magnetic systems can occur via a similar spectrum of excitations that relies on
strong local exchange interactions and does not require long-range order. This
work not only opens a new area for fundamental experimental and theoretical
studies of spin transport, but also sets a new direction in materials science
for magnonic and spintronic devices.",1706.05196v1
2017/7/3,Emerging Magnetic Order In Copper Induced By Proximity To Cobalt: A Detailed Soft X-Ray Spectroscopy Study,"We present an x-ray magnetic dichroism (XMCD) and soft x-ray absorption
spectroscopy (XAS) study to address the nature of emerging magnetic order in
metallic Copper as Cobalt is added to the matrix. For this purpose line shape
and energy position of XAS and XMCD spectra will be analyzed for a series of
Co/Cu alloys as well as a multilayer reference. We observe an increased
hybridization between Cu and Co sites as well as increased localization of the
Cu d-electrons and an induced magnetic moment in Cu. The emergence of long
range magnetic order in non-magnetic materials that are in proximity to a
ferromagnet is significant for a comprehensive interpretation of transport
phenomena at ferromagnetic/non-magnetic interfaces, like e.g. the giant
magnetoresistance effect. The presented results will further enable us to
interpret Cu XMCD and XAS spectra acquired from unknown Co/Cu samples to
identify the environment of Cu atoms exhibiting proximity induced magnetism.",1707.00774v2
2017/7/26,Stabilizing isolated skyrmions at low magnetic fields exploiting vanishing magnetic anisotropy,"Skyrmions are topologically protected non-collinear magnetic structures.
Their stability and dynamics, arising from their topological character, have
made them ideal information carriers e.g. in racetrack memories. The success of
such a memory critically depends on the ability to stabilize and manipulate
skyrmions at low magnetic fields. The driving force for skyrmion formation is
the non-collinear Dzyaloshinskii-Moriya exchange interaction (DMI) originating
from spin-orbit coupling (SOC). It competes with both the nearest neighbour
Heisenberg exchange interaction and the magnetic anisotropy, which favour
collinear states. While skyrmion lattices might evolve at vanishing magnetic
fields, the formation of isolated skyrmions in ultra-thin films so far required
the application of an external field which can be as high as several T. Here,
we show that isolated skyrmions in a monolayer (ML) of Co epitaxially grown on
a Ru(0001) substrate can be stabilized at magnetic fields as low as 100 mT.
Even though SOC is weak in the 4d element Ru, a homochiral spin spiral ground
state and isolated skyrmions could be detected and laterally resolved using a
combination of tunneling and anisotropic tunneling magnetoresistance effect in
spin-sensitive scanning tunneling microscopy (STM). Density functional theory
(DFT) calculations confirm these chiral magnetic textures, even though the
stabilizing DMI interaction is weak. We find that the key factor is the absence
of magnetocristalline anisotropy in this system which enables non-collinear
states to evolve in spite of weak SOC, opening up a wide choice of materials
beyond 5d elements.",1707.08519v1
2018/1/21,Ce$_{3-x}$Mg$_x$Co$_{9}$: transformation of a Pauli paramagnet into a strong permanent magnet,"We report on the synthesis of single crystalline and polycrystalline samples
of Ce$_{3-x}$Mg$_x$Co$_9$ solid solution ($0\leq x \lesssim 1.4$) and
characterization of their structural and magnetic properties. The crystal
structure remains rhombohedral in the whole composition range and Mg partially
replaces Ce in the 6\textit{c} site of the CeCo$_3$ structure. Ferromagnetism
is induced by Mg substitutions starting as low as $x=0.18$ and reaching a Curie
temperature as high as $450$\,K for $x=1.35$. Measurements on single crystals
with $x=1.34$ and $T_\textrm{C}=440$\,K indicate an axial magnetic anisotropy
with the anisotropy field of $6$\,T and a magnetization of $6$\,$\mu_B/$f.u. at
$300$\,K. Coercicity is observed in the polycrystalline samples consistent with
the observed axial magnetic anisotropy. Our discovery of ferromagnetism with
large axial magnetic anisotropy induced by substituting a rare-earth element by
Mg is a very promising result in the search of inexpensive permanent-magnet
materials and suggests other non-magnetic phases, similar to CeCo$_3$, may also
conceal nearby ferromagnetic phases.",1801.06743v2
2018/2/3,Possible gapless spin liquid in a rare-earth kagomé lattice magnet Tm$_{3}$Sb$_{3}$Zn$_{2}$O$_{14}$,"We report the thermodynamic and muon spin relaxation ($\mu$SR) evidences for
a possible gapless spin liquid in Tm$_{3}$Sb$_{3}$Zn$_{2}$O$_{14}$, with the
rare-earth ions Tm$^{3+}$ forming a two-dimensional kagom\'{e} lattice. We
extract the magnetic specific heat of Tm$_{3}$Sb$_{3}$Zn$_{2}$O$_{14}$ by
subtracting the phonon contribution of the non-magnetic isostructural material
La$_{3}$Sb$_{3}$Zn$_{2}$O$_{14}$. We obtain a clear linear-$T$ temperature
dependence of magnetic specific heat at low temperatures, with the
heat-capacity coefficient $\gamma$ = 26.6(1) mJ mol-Tm$^{-1}$ K$^{-2}$ in the
zero temperature limit. No long-range magnetic order was observed down to 0.35
K in the heat capacity measurement. A broad hump around 9 K was observed in the
zero field magnetic specific heat and is gradually suppressed in the magnetic
fields that also create a spin gap in the specific heat. The absence of
magnetic order is further confirmed by the $\mu$SR measurement down to 20 mK.
We find that the spin-lattice relaxation time remains constant down to the
lowest temperatures. We point out that the physics in
Tm$_{3}$Sb$_{3}$Zn$_{2}$O$_{14}$ is fundamentally different from the Cu-based
herbertsmithite and propose spin liquid ground states with non-Kramers doublets
on the kagom\'{e} lattice to account for the experimental results.",1802.00968v2
2018/4/26,Ultrasensitive Detection Enabled by Nonlinear Magnetization of Nanomagnetic Labels,"Geometrically confined magnetic particles due to their unique response to
external magnetic fields find a variety of applications, including magnetic
guidance, heat and drug delivery, magneto-mechanical actuation, and contrast
enhancement. Highly sensitive detection and imaging techniques based on
nonlinear properties of nanomagnets were recently proposed as innovative
strong-translational potential methods applicable in complex, often opaque,
biological systems. Here we report on significant enhancement of the detection
capability using optical-lithography-defined, ferromagnetic iron-nickel alloy
disk-shaped particles. We show that an irreversible transition between a
strongly non-collinear (vortex) and single domain states, driven by an
alternating magnetic field translates into a nonlinear magnetic response that
enables ultrasensitive detection of these particles. The record sensitivity of
~ 3.5x10-9 emu, which is equivalent to ~39 pg of magnetic material is
demonstrated at room temperature for arrays of patterned disks. We also show
that unbound disks re-suspended in aqueous buffer can be successfully detected
and quantified in real-time when administrated into a live animal allowing for
tracing their biodistribution. Use of nanoscale ferromagnetic particles with
engineered nonlinear properties opens prospects for further enhancing
sensitivity, scalability and tunability of noise-free magnetic tag detection in
high-background environments for various applications spanning from biosensing
and medical imaging to anti-counterfeiting technologies.",1804.09908v1
2018/6/6,High performance magnetic material with Ce and La: an alternative to Nd-Fe-B magnet,"A systematic study of magnetocrystalline anisotropy is performed for
R(La/Ce/Nd)2Fe14B tetragonal compound with the site substitution mechanism.
Theoretical calculation suggests the 50% doping with Ce at 4f-site can lead to
competitive magnetic anisotropy to that of the champion magnet Nd2Fe14B.
Electronic structure calculations are performed using the full-potential
linearized augmented plane wave method by inclusion of the spin-orbit coupling
and Hubbard (U) interaction in the calculation for the rare-earth elements to
get the correct influence of the localized 4f orbitals. Detailed analysis of
the magnetic moment and magnetic anisotropy change has been studied by
individually inserting the La and Ce atoms at the two inequivalent sites (4g
and 4f sites) of the 2-14-B tetragonal structure. Accurate prediction of the
total magnetic moment with the orbital contribution in the 2-14-B structure
shows the maximum moment for Ce2Fe14B (3.86 {\mu}B/f.u less) compared to
Nd2Fe14B. Theoretical analysis confirms that regardless of the anti-parallel
spin moment emerging in the Ce atom the complex structure of the Ce substituted
compound at 4f-site gives the maximum anisotropy of 2.27 meV/cell with lowering
the magnetic moment by 1.26 {\mu}B/f.u. compared to the Nd2Fe14B compound.",1806.01990v1
2018/8/19,Spin-dependent scattering and magnetic proximity effect in Ni-doped Co/Cu multilayers as a probe of atomic magnetism,"We investigate the spin transport and ferromagnetic resonance properties of
giant magnetoresistive (GMR) Co/Cu-Ni multilayers with variable levels of Ni
doping in the Cu spacer. We present an experimental evidence for a
magnetic-to-diamagnetic transition in the atomic magnetic moment of Ni in the
Cu matrix for concentrations below 15 at. % Ni. As its concentration is
increased, Ni atoms turn into spin scattering centers, which is manifested
experimentally as a step-like change in the GMR of the multilayers. This
behavior is observed in multilayers with gradient-doped Cu spacers, where only
the inner region was doped with Ni. In the uniformly doped spacers the GMR
decreases monotonously with increasing Ni content, indicating that Ni atoms are
magnetic and act as spin relaxation centers in the entire dopant-concentration
range studied. We explain the difference in the observed GMR behavior as due to
a strong magnetic proximity effect in the uniform spacers, which is efficiently
suppressed in the gradient spacers. The observed magnetic phase transition is
fully supported by our detailed ab-initio calculations, taking into
consideration structural relaxation in the system as well as potential Ni
clustering. Controlling the loss or gain of the atomic magnetism for a specific
dopant can be a tool in probing and controlling spin relaxation in materials
and devices for spin-valve and spin-torque based applications.",1808.06198v1
2018/9/4,Chiral magnetic interlayer coupling in synthetic antiferromagnets,"The exchange coupling underlies ferroic magnetic coupling and is thus the key
element that governs statics and dynamics of magnetic systems. This fundamental
interaction comes in two flavors - symmetric and antisymmetric coupling. While
symmetric coupling leads to ferro- and antiferromagnetism, antisymmetric
coupling has attracted significant interest owing to its major role in
promoting topologically non-trivial spin textures that promise high-speed and
energy-efficient devices. So far, the antisymmetric exchange coupling rather
short-ranged and limited to a single magnetic layer has been demonstrated,
while the symmetric coupling also leads to long-range interlayer exchange
coupling. Here, we report the missing component of the long-range antisymmetric
interlayer exchange coupling in perpendicularly magnetized synthetic
antiferromagnets with parallel and antiparallel magnetization alignments.
Asymmetric hysteresis loops under an in-plane field unambiguously reveal a
unidirectional and chiral nature of this novel interaction, which cannot be
accounted for by existing coupling mechanisms, resulting in canted
magnetization alignments. This can be explained by spin-orbit coupling combined
with reduced symmetry in multilayers. This new class of chiral interaction
provides an additional degree of freedom for engineering magnetic structures
and promises to enable a new class of three-dimensional topological structures.",1809.01080v2
2018/9/10,"Nature of glassy magnetic state in magnetocaloric materials Dy5Pd2-xNix (x = 0 and 1) and universal scaling analysis of R5Pd2 (R = Tb, Dy and Er)","We report a systematic investigation of the magnetic and magnetocaloric
properties of Dy5Pd2 and Dy5PdNi. Our study on these compounds gave evidence
that they exhibit complex magnetic behaviour along with the presence of
glass-like magnetic phase. Furthermore, in these compounds both second order
and first order phase transitions were present, which were validated through
Arrott plots and Landau parameter analysis. AC susceptibility along with time
dependent magnetisation study has confirmed the presence of double cluster
glass-like freezing in both Dy5Pd2 and Dy5PdNi. These compounds show
significant value of isothermal entropy change and relative cooling power and
these values increased with Ni substitution. Beside conventional magnetocaloric
effect, inverse magnetocaloric effect was noted in these compounds, which might
arise due to the presence of complex non-equilibrium magnetic state. Along with
these compounds a universal characteristic curve involving two other members of
R5Pd2 family i.e. Er5Pd2 and Tb5Pd2 was constructed. The master curve
reaffirmed the presence of both second and first order magnetic phase
transition in such compounds which were in analogy to our results of Arrott
plots and Landau parameter analysis. Additionally, magnetic entropy change
followed the power law and the obtained exponent values indicated the presence
of mixed magnetic interactions in these compounds.",1809.03249v1
2019/2/4,Probing magnetism in 2D materials at the nanoscale with single spin microscopy,"The recent discovery of ferromagnetism in 2D van der Waals (vdw) crystals has
generated widespread interest, owing to their potential for fundamental and
applied research. Advancing the understanding and applications of vdw magnets
requires methods to quantitatively probe their magnetic properties on the
nanoscale. Here, we report the study of atomically thin crystals of the vdw
magnet CrI$_3$ down to individual monolayers using scanning single-spin
magnetometry, and demonstrate quantitative, nanoscale imaging of magnetisation,
localised defects and magnetic domains. We determine the magnetisation of
CrI$_3$ monolayers to be $\approx16~\mu_B/$nm$^2$ and find comparable values in
samples with odd numbers of layers, whereas the magnetisation vanishes when the
number of layers is even. We also establish that this inscrutable even-odd
effect is intimately connected to the material structure, and that structural
modifications can induce switching between ferro- and anti-ferromagnetic
interlayer ordering. Besides revealing new aspects of magnetism in atomically
thin CrI$_3$ crystals, these results demonstrate the power of single-spin
scanning magnetometry for the study of magnetism in 2D vdw magnets.",1902.01406v1
2019/2/15,Current-driven magnetization switching in a van der Waals ferromagnet Fe3GeTe2,"The recent discovery of ferromagnetism in two-dimensional (2D) van der Waals
(vdW) materials holds promises for novel spintronic devices with exceptional
performances. However, in order to utilize 2D vdW magnets for building
spintronic nanodevices such as magnetic memories, key challenges remain in
terms of effectively switching the magnetization from one state to the other
electrically. Here, we devise a bilayer structure of Fe3GeTe2/Pt, in which the
magnetization of few-layered Fe3GeTe2 can be effectively switched by the
spin-orbit torques (SOTs) originated from the current flowing in the Pt layer.
The effective magnetic fields corresponding to the SOTs are further
quantitatively characterized using harmonic measurements. Our demonstration of
the SOT-driven magnetization switching in a 2D vdW magnet could pave the way
for implementing low-dimensional materials in the next-generation spintronic
applications.",1902.05794v1
2019/10/14,Crystal and magnetic structures of magnetic topological insulators MnBi$_2$Te$_4$ and MnBi$_4$Te$_7$,"Using single crystal neutron diffraction, we present a systematic
investigation of the crystal structure and magnetism of van der Waals
topological insulators MnBi$_2$Te$_4$ and MnBi$_4$Te$_7$, where rich
topological quantum states have been recently predicted and observed.
Structural refinements reveal that considerable Bi atoms occupied on the Mn
sites in both materials, distinct from the previously reported antisite
disorder. We show unambiguously that MnBi$_{2}$Te$_{4}$ orders
antiferromagnetically below 24 K featured by a magnetic symmetry $R_I$-${3c}$
while MnBi$_{4}$Te$_{7}$ is antiferromagnetic below 13 K with a magnetic space
group $P_c$-${3c1}$. They both present antiferromagnetically coupled
ferromagnetic layers with spins along the $c$-axis. We put forward a stacking
rule for the crystal structure of an infinitely adaptive series
MnBi$_{2n}$Te$_{3n+1}$ (n$\geq$1) with the building unit of [Bi$_2$Te$_3$]. A
comparison of magnetic properties between MnBi$_{2}$Te$_{4}$ and
MnBi$_{4}$Te$_{7}$, together with the recent density-functional theory
calculations, enables us to draw that a two-dimensional magnetism limit might
be realized in the derivatives. Our work may promote the theoretical studies of
topological magnetic states in the series of MnBi$_{2n}$Te$_{3n+1}$.",1910.06248v3
2019/11/14,"Minimal model for the magnetic phase diagram of CeTi$_{1-x}$Sc$_{x}$Ge, GdFe$_{1-x}$Co$_{x}$Si, and related materials","We present a theoretical analysis of the magnetic phase diagram of
CeTi$_{1-x}$Sc$_{x}$Ge and GdFe$_{1-x}$Co$_{x}$Si as a function of the
temperature and the Sc and Co concentration $x$, respectively. CeScGe and
GdCoSi, as many other RTX (R=rare earth, T=transition metal, X=p-block element)
compounds, present a tetragonal crystal structure where bilayers of R are
separated by layers of T and X. While GdFeSi and CeTi$_{0.75}$Sc$_{0.25}$Ge are
ferromagnetic, CeScGe and GdCoSi order antiferromagnetically with the R 4f
magnetic moments on the same bilayer aligned ferromagnetically and magnetic
moments in nearest neighbouring bilayers aligned antiferromagnetically. The
antiferromagnetic transition temperature $T_N$ decreases with decreasing
concentration $x$ in both compounds and for low enough values of $x$ the
compounds show a ferromagnetic behavior. Based on these observations we
construct a simplified model Hamiltonian that we solve numerically for the
specific heat and the magnetization. We find a good qualitative agreement
between the model and the experimental data. Our results show that the main
magnetic effect of the Sc $\to$ Ti and Co $\to$ Fe substitution in these
compounds is consistent with a change in the sign of the exchange coupling
between magnetic moments in neighbouring bilayers. We expect a similar
phenomenology for other magnetic RTX compounds with the same type of crystal
structure.",1911.06235v1
2020/3/31,Skyrmions in antiferromagnets: thermal stability and the effect of external field and impurities,"Calculations of skyrmions in antiferromagnets (AFMs) are presented, and their
properties compared with skyrmions in corresponding ferromagnets (FMs). The
rates of skyrmion collapse and escape through the boundary of a track, as well
as the binding to and collapse at a non-magnetic impurity, are calculated as a
function of applied magnetic field. The activation energy for skyrmion
annihilation is the same in AFMs and corresponding FMs in the absence of an
applied magnetic field. The pre-exponential factor in the Arrhenius rate law
is, however, different because skyrmion dynamics is different in the two
systems. An applied magnetic field has opposite effects on skyrmions in the two
types of materials. In AFMs the rate of collapse of skyrmions as well as the
rate of escape through the edge of a magnetic strip decreases slightly with
increasing field, while these rates increase strongly for a skyrmion in the
corresponding FMs when the field is directed antiparallel to the magnetization
in the center of the skyrmion. A non-magnetic impurity is less likely to trap a
skyrmion in AFMs especially in the presence of a magnetic field. This, together
with the established fact that a spin polarized current moves skyrmions in AFMs
in the direction of the current, while in FMs skyrmions move at an angle to the
current, demonstrates that skyrmions in AFMs have several advantageous
properties over skyrmions in FMs for memory and spintronic devices.",2004.00095v2
2020/5/5,Coupled spin states in armchair graphene nanoribbons with asymmetric zigzag edge extensions,"Carbon-based magnetic structures promise significantly longer coherence times
than traditional magnetic materials, which is of fundamental importance for
spintronic applications. An elegant way of achieving carbon-based magnetic
moments is the design of graphene nanostructures with an imbalanced occupation
of the two sublattices forming the carbon honeycomb lattice. According to
Lieb's theorem, this induces local magnetic moments that are proportional to
the sublattice imbalance. Exact positioning of sublattice imbalanced
nanostructures in graphene nanomaterials hence offers a route to control
interactions between induced local magnetic moments and to obtain graphene
nanomaterials with magnetically non-trivial ground states. Here, we show that
such sublattice imbalanced nanostructures can be incorporated along a large
band gap armchair graphene nanoribbon on the basis of asymmetric zigzag edge
extensions, which is achieved by incorporating specifically designed precursor
monomers during the bottom-up fabrication of the graphene nanoribbons. Scanning
tunneling spectroscopy of an isolated and electronically decoupled zigzag edge
extension reveals Hubbard-split states in accordance with theoretical
predictions. Investigation of pairs of such zigzag edge extensions reveals
ferromagnetic, antiferromagnetic or quenching of the magnetic interactions
depending on the relative alignment of the asymmetric edge extensions.
Moreover, a ferromagnetic spin chain is demonstrated for a periodic pattern of
zigzag edge extensions along the nanoribbon axis. This work opens a route
towards the design and fabrication of graphene nanoribbon-based spin chains
with complex magnetic ground states.",2005.02147v2
2020/5/7,Spin caloritronics in a CrBr$_3$-based magnetic van der Waals heterostructure,"The recently reported magnetic ordering in insulating two-dimensional (2D)
materials, such as chromium triiodide (CrI$_3$) and chromium tribromide
(CrBr$_3$), opens new possibilities for the fabrication of magneto-electronic
devices based on 2D systems. Inevitably, the magnetization and spin dynamics in
2D magnets are strongly linked to Joule heating. Therefore, understanding the
coupling between spin, charge and heat, i.e. spin caloritronic effects, is
crucial. However, spin caloritronics in 2D ferromagnets remains mostly
unexplored, due to their instability in air. Here we develop a fabrication
method that integrates spin-active contacts with 2D magnets through hBN
encapsulation, allowing us to explore the spin caloritronic effects in these
materials. The angular dependence of the thermal spin signal of the CrBr$_3$/Pt
system is studied, for different conditions of magnetic field and heating
current. We highlight the presence of a significant magnetic proximity effect
from CrBr$_3$ on Pt revealed by an anomalous Nernst effect in Pt, and suggest
the contribution of the spin Seebeck effect from CrBr$_3$. These results pave
the way for future magnonic devices using air-sensitive 2D magnetic insulators.",2005.03561v1
2020/6/21,Chemical Bonding Governs Complex Magnetism in MnPt5P,"Subtle changes in chemical bonds may result in dramatic revolutions in
magnetic properties in solid state materials. MnPt5P, a new derivative of the
rare-earth-free ferromagnetic MnPt5As, was discovered and is presented in this
work. MnPt5P was synthesized and its crystal structure and chemical composition
were characterized by X-ray diffraction as well as energy-dispersive X-ray
spectroscopy. Accordingly, MnPt5P crystallizes in the layered tetragonal
structure with the space group P4/mmm (No. 123), in which the face-shared
Mn@Pt12 polyhedral layers are separated by P layers. In contrast to the
ferromagnetism observed in MnPt5As, the magnetic properties measurements on
MnPt5P show antiferromagnetic ordering occurs at ~188 K with a strong magnetic
anisotropy in and out of the ab-plane. Moreover, a spin-flop transition appears
when a high magnetic field is applied. An A-type antiferromagnetic structure
was obtained from the analysis of powder neutron diffraction (PND) patterns
collected at 150 K and 9 K. Calculated electronic structures imply that
hybridization of Mn-3d and Pt-5d orbitals are critical for both the structural
stability and observed magnetic properties. Semi-empirical molecular orbitals
calculations on both MnPt5P and MnPt5As indicate that the lack of 4p character
on the P atoms at the highest occupied molecular orbital (HOMO) in MnPt5P may
cause the different magnetic behavior in MnPt5P compared to MnPt5As. The
discovery of MnPt5P, along with our previously reported MnPt5As, parametrizes
the end points of a tunable system to study the chemical bonding which tunes
the magnetic ordering from ferromagnetism to antiferromagnetism with strong
spin-orbit coupling (SOC) effect.",2006.11903v1
2020/6/23,"Crystal field model simulations of magnetic response of pairs, triplets and quartets of Mn$^{3+}$ ions in GaN","A ferromagnetic coupling between localized Mn spins was predicted in a series
of \textit{ab initio} and tight binding calculations and experimentally
verified for the dilute magnetic semiconductor Ga$_{1-x}$Mn$_x$N. In the limit
of small Mn concentrations, $x \lesssim 0.01$, the paramagnetic properties of
this material were successfully described using a single ion crystal field
model approach. In order to obtain the description of magnetization in (Ga,Mn)N
in the presence of interacting magnetic centers, we extend the previous model
of a single substitutional Mn$^{3+}$ ion in GaN by considering pairs, triplets
and quartets of Mn$^{3+}$ ions coupled by a ferromagnetic superexchange
interaction. Using this approach we investigate how the magnetic properties,
particularly the magnitude of the uniaxial anisotropy field, change as the
number of magnetic Mn$^{3+}$ ions in a given cluster increases from 1 to 4. Our
simulations are then exploited in explaining experimental magnetic properties
of Ga$_{1-x}$Mn$_x$N with $x \cong 0.03$, where the presence of small magnetic
clusters gains in significance. As a result the approximate lower and upper
limits for the values of exchange couplings between Mn$^{3+}$ ions in GaN,
being in nearest neighbors $J_{\mathrm{nn}}$ and next nearest neighbors
$J_{\mathrm{nnn}}$ positions, respectively, are established.",2006.12945v2
2020/7/3,Light-controlled room temperature ferromagnetism in vanadium-doped tungsten diselenide semiconducting monolayers,"Atomically thin transition metal dichalcogenide (TMD) semiconductors hold
enormous potential for modern optoelectronic devices and quantum computing
applications. By inducing long-range ferromagnetism (FM) in these
semiconductors through the introduction of small amounts of a magnetic dopant,
it is possible to extend their potential in emerging spintronic applications.
Here, we demonstrate light-mediated, room temperature (RT) FM, in V-doped WS2
(V-WS2) monolayers. We probe this effect using the principle of magnetic LC
resonance, which employs a soft ferromagnetic Co-based microwire coil driven
near its resonance in the radio frequency (RF) regime. The combination of LC
resonance with an extraordinary giant magneto-impedance effect, renders the
coil highly sensitive to changes in the magnetic flux through its core. We then
place the V-WS2 monolayer at the core of the coil where it is excited with a
laser while its change in magnetic permeability is measured. Notably, the
magnetic permeability of the monolayer is found to depend on the laser
intensity, thus confirming light control of RT magnetism in this
two-dimensional (2D) material. Guided by density functional calculations, we
attribute this phenomenon to the presence of excess holes in the conduction and
valence bands, as well as carriers trapped in the magnetic doping states, which
in turn mediates the magnetization of the V-WS2 monolayer. These findings
provide a unique route to exploit light-controlled ferromagnetism in low
powered 2D spintronic devices capable of operating at RT.",2007.01505v1
2020/9/25,Alternation of Magnetic Anisotropy Accompanied by Metal-Insulator Transition in Strained Ultrathin Manganite Heterostructures,"Fundamental understanding of interfacial magnetic properties in ferromagnetic
heterostructures is essential to utilize ferromagnetic materials for spintronic
device applications. In this paper, we investigate the interfacial magnetic and
electronic structures of epitaxial single-crystalline LaAlO$_3$
(LAO)/La$_{0.6}$Sr$_{0.4}$MnO$_3$ (LSMO)/Nb:SrTiO$_3$ (Nb:STO) heterostructures
with varying LSMO-layer thickness, in which the magnetic anisotropy strongly
changes depending on the LSMO thickness due to the delicate balance between the
strains originating from both the Nb:STO and LAO layers, using x-ray magnetic
circular dichroism (XMCD) and photoemission spectroscopy (PES). We successfully
detect the clear change of the magnetic behavior of the Mn ions concomitant
with the thickness-dependent metal-insulator transition (MIT). Our results
suggest that double-exchange interaction induces the ferromagnetism in the
metallic LSMO film under tensile strain caused by the SrTiO$_3$ substrate,
while superexchange interaction determines the magnetic behavior in the
insulating LSMO film under compressive strain originating from the top LAO
layer. Based on those findings, the formation of a magnetic dead layer near the
LAO/LSMO interface is attributed to competition between the superexchange
interaction via Mn 3$d_{3z^2-r^2}$ orbitals under compressive strain and the
double-exchange interaction via the 3$d_{x^2-y^2}$ orbitals.",2009.12327v2
2020/10/10,Coherent Helicity-Dependent Spin-Phonon Oscillations in the Ferromagnetic van der Waals Crystal CrI3,"The discovery of two-dimensional (2D) systems hosting intrinsic long-range
magnetic order represents a seminal addition to the rich physical landscape of
van der Waals (vdW) materials. CrI3 has emerged as perhaps the most salient
example, as the interdependence of crystalline structure and magnetic order,
along with strong light-matter interactions provides a promising platform to
explore the optical control of magnetic, vibrational, and charge degrees of
freedom at the 2D limit. However, the fundamental question of how this
relationship between structure and magnetism manifests on their intrinsic
timescales has rarely been explored. Here, we use ultrafast optical
spectroscopy to probe magnetic and vibrational dynamics in CrI3, revealing
demagnetization dynamics governed by spin-flip scattering and remarkably, a
strong transient exchange-mediated interaction between lattice vibrations and
spin oscillations. The latter yields a coherent spin-coupled phonon mode that
is highly sensitive to the helicity of the driving pulse in the magnetically
ordered phase. Our results shed light on the nature of spin-lattice coupling in
vdW magnets on ultrafast timescales and highlight their potential for
applications requiring non-thermal, high-speed control of magnetism at the
nanoscale.",2010.04915v1
2020/10/19,Chirality-Induced Electrical Generation of Magnetism in Nonmagnetic Elemental Tellurium,"Chiral matter has a structure that lacks inversion, mirror, and
rotoreflection symmetry; thus, a given chiral material has either a right- or
left-handed structure. In chiral matter, electricity and magnetism can be
coupled in an exotic manner beyond the classical electromagnetism (e.g.,
magneto chiral effect in chiral magnets). In this paper, we give a firm
experimental proof of the linear electric-current-induced magnetization effect
in bulk nonmagnetic chiral matter elemental trigonal tellurium. We measured a
$^{125} $Te nuclear magnetic resonance (NMR) spectral shift under a pulsed
electric current for trigonal tellurium single crystals. We provide general
symmetry considerations to discuss the electrically (electric-field- and
electric-current-) induced magnetization and clarify that the NMR shift
observed in trigonal tellurium is caused by the linear current-induced
magnetization effect, not by a higher-order magnetoelectric effect. We also
show that the current-induced NMR shift is reversed by a chirality reversal of
the tellurium crystal structure. This result is the first direct evidence of
crystal-chirality-induced spin polarization, which is an inorganic-bulk-crystal
analogue of the chirality-induced spin selectivity in chiral organic molecules.
The present findings also show that nonmagnetic chiral crystals may be applied
to spintronics and coil-free devices to generate magnetization beyond the
classical electromagnetism.",2010.09210v1
2020/11/25,Evolution from sinusoidal to collinear A-type antiferromagnetic spin-ordered magnetic phase transition in Tb0.6Pr0.4MnO3,"The present study reports on the structural and magnetic phase transitions in
Pr-doped polycrystalline Tb0.6Pr0.4MnO3, using high-resolution neutron powder
diffraction (NPD) collected at SINQ spallation source (PSI), to emphasize the
suppression of the sinusoidal magnetic structure of pure TbMnO3 and the
evolution to a collinear A-type antiferromagnetic ordering. The phase purity,
Jahn-Teller distortion, and one-electron bandwidth for eg orbital of Mn3+
cation have been calculated for polycrystalline Tb0.6Pr0.4MnO3, in comparison
to the parent materials TbMnO3 and PrMnO3, through the Rietveld refinement
study from X-ray diffraction data at room temperature. The
temperature-dependent zero field-cooled and field-cooled dc magnetization study
at low temperature down to 5 K reveals a variation in the magnetic phase
transition due to the effect of Pr3+ substitution at the Tb3+ site, which gives
the signature of the antiferromagnetic nature of the sample, with a weak
ferromagnetic component at low temperature induced by an external magnetic
field. The field-dependent magnetization study at low temperatures gives the
weak coercivity having the order of 2 kOe, which is expected due to canted-spin
arrangement or ferromagnetic nature of Terbium ordering. The NPD data for
Tb0.6Pr0.4MnO3 confirms that the nuclear structure of the synthesized sample
maintains its orthorhombic symmetry down to 1.5 K. Also, the magnetic
structures have been solved at 50 K, 25 K, and 1.5 K through the NPD study,
which shows A-type antiferromagnetic spin arrangement.",2011.12553v2
2020/12/8,"Effect of O-doping or N-vacancy on the structural, electronic and magnetic properties of MoSi2N4 monolayer","In this letter, the effect of four types of defects (ONout, ONin, VNout and
VNin) on the structural, electronic and magnetic properties of MoSi2N4
monolayer were investigated using first-principles calculations. The calculated
results reveal that all the four types of defects lead to structural
distortions around the O-dopant or N-vacancy, and thereby change the lattice
parameter and monolayer height h. Specifically, ONout or ONin increases the
lattice parameter, but VNout or VNin is on the contrary. ONout or VNout
increases the monolayer height, whereas the height decreases for ONin or VNin.
Each of the four types of defects has a fundamental effect on the electronic
properties of MoSi2N4 monolayer, which can induce a transition from
semiconductor to metal. ONin or VNin plays a vital role in the occurrence of a
transition from non-magnetism to ferrimagnetism in MoSi2N4 monolayer. The
effect of biaxial strain on the magnetic properties of the two systems with
ONin and VNin was subsequently investigated. It is found that the total
magnetic moments are less sensitive to biaxial strain whereas the local
magnetic moments residing on the Mo atoms are increased for the two systems
with ONin and VNin, as strain increases from -3% to 10% and from -9% to 10%,
respectively. Furthermore, the magnetic phase transitions between ferrimagnetic
and paramagnetic states were found to occur around -4% strain and within the
range from -10% to -9% for the two systems with ONin and VNin, respectively.
This study may provide a guidance for the application of MoSi2N4 monolayer in
the spintronic and magnetic materials.",2012.04162v1
2021/3/18,Size limit of superparamagnetic inclusions in dust grains and difficulty of magnetic grain alignment in protoplanetary disks,"Alignment of non-spherical grains with magnetic fields is an important
problem as it lays the foundation of probing magnetic fields with polarized
dust thermal emissions. In this paper, we investigate the feasibility of
magnetic alignment in protoplanetary disks (PPDs). We use an alignment
condition that Larmor precession should be fast compared with the damping
timescale. We first show that the Larmor precession timescale is some three
orders of magnitude longer than the damping time for millimeter-sized grains
under conditions typical of PPDs, making the magnetic alignment unlikely. The
precession time can be shortened by superparamagnetic inclusions (SPIs), but
the reduction factor strongly depends on the size of the SPI clusters, which we
find is limited by the so-called ""N\'{e}el's relaxation process."" In
particular, the size limit of SPIs is set by the so-called ""anisotropic energy
constant"" of the SPI material, which describes the energy barrier needed to
change the direction of the magnetic moment of an SPI. For the most common
iron-bearing materials, we find maximum SPI sizes corresponding to a reduction
factor of the Larmor precession timescale of order $10^3$. We also find that
reaching this maximum reduction factor requires fine-tuning on the SPI sizes.
Lastly, we illustrate the effects of the SPI size limits on magnetic alignment
of dust grains with a simple disk model, and we conclude that it is unlikely
for relatively large grains of order 100 $\mu$m or more to be aligned with
magnetic fields even with SPIs.",2103.10243v1
2021/4/19,Magnetic coupling in Y$_3$Fe$_5$O$_{12}$/Gd$_3$Fe$_5$O$_{12}$ heterostructures,"Ferrimagnetic Y$_3$Fe$_5$O$_{12}$ (YIG) is the prototypical material for
studying magnonic properties due to its exceptionally low damping. By
substituting the yttrium with other rare earth elements that have a net
magnetic moment, we can introduce an additional spin degree of freedom. Here,
we study the magnetic coupling in epitaxial
Y$_3$Fe$_5$O$_{12}$/Gd$_3$Fe$_5$O$_{12}$ (YIG/GIG) heterostructures grown by
pulsed laser deposition. From bulk sensitive magnetometry and surface sensitive
spin Seebeck effect (SSE) and spin Hall magnetoresistance (SMR) measurements,
we determine the alignment of the heterostructure magnetization through
temperature and external magnetic field. The ferromagnetic coupling between the
Fe sublattices of YIG and GIG dominates the overall behavior of the
heterostructures. Due to the temperature dependent gadolinium moment, a
magnetic compensation point of the total bilayer system can be identified. This
compensation point shifts to lower temperatures with increasing thickness of
YIG due the parallel alignment of the iron moments. We show that we can control
the magnetic properties of the heterostructures by tuning the thickness of the
individual layers, opening up a large playground for magnonic devices based on
coupled magnetic insulators. These devices could potentially control the magnon
transport analogously to electron transport in giant magnetoresistive devices.",2104.09592v1
2021/5/11,Spin-dependent magnetism and superparamagnetic contribution to the magnetocaloric effect of non-stoichiometric manganite nanoparticles,"Despite extensive researches on manganites owing to widespread use in modern
electronics, this class of metal oxides does not cease to surprise with its
unique properties and new phenomena. Here we have studied structural and
magnetic properties of non-Heisenberg manganite nanoparticles with a strong
spin-electron coupling. During transition from low temperature ferromagnetic to
high temperature paramagnetic state, the change in charge, valence and spin
(magnetic moment) with the localization of eg-electrons on the manganese ions
have been detected. With decrease in a temperature, the overstated effective
magnetic moment of Mn ions in paramagnetic phase is reduced dramatically
testifying to spin-dependent magnetism. The critical behavior of magnetization
with determination of critical parameters near second-order phase transition
has been studied comprehensively. Based on unusual behavior of temperature and
field dependences of magnetic entropy change under different magnetic field, an
additional influence of superparamagnetism of nanoparticles on the
magnetocaloric effect has been found.",2105.04831v1
2021/7/23,Intermixing Induced Anisotropy Variations in CoB-based Chiral Multilayer Films,"We examine the atomic intermixing phenomenon in three distinct amorphous
CoB-based multilayer thin film platforms - Pt/CoB/Ir, Ir/CoB/Pt and Pt/CoB/MgO
- which are shown to stabilise room-temperature chiral magnetic textures.
Intermixing occurs predominantly between adjacent metallic layers. Notably, it
is stack-order dependent, and particularly extensive when Ir sits atop CoB.
Intermixing induced variations in magnetic properties are ascribed to the
formation of magnetic dead layer arising from CoIr alloying in the metallic
stacks. It also produces systematic variations in saturation magnetization, by
as much as 30%, across stacks. Crucially, the resulting crossover CoB thickness
for the transition from perpendicular to in-plane magnetic anisotropy differs
by more than 2x across the stacks. Finally, with thermal annealing treatment
over moderate temperatures of 150-300 degree Celsius, the magnetic anisotropy
increases monotonically across all stacks, coupled with discernibly larger Hc
for the metallic stacks. These are attributed to thermally induced CoPt
alloying and MgO crystallization in the metallic and oxide stacks,
respectively. Remarkably, the CoB in the Pt/CoB/MgO stacks retains its
amorphous nature after annealing. Our results set the stage for harnessing the
collective attributes of amorphous CoB-based material platforms and associated
annealing processes for modulating magnetic interactions, enabling the tuning
of chiral magnetic texture properties in ambient conditions.",2107.11034v1
2021/12/16,Plastic vortex creep and dimensional crossovers in the highly anisotropic superconductor HgBa$_2$CuO$_{4+x}$,"In type-II superconductors exposed to magnetic fields between upper and lower
critical values, $H_{c1}$ and $H_{c2}$, penetrating magnetic flux forms a
lattice of vortices whose motion can induce dissipation. Consequently, the
magnetization $M$ of superconductors is typically progressively weakened with
increasing magnetic field $B \propto n_v$ (for vortex density $n_v$). However,
some materials exhibit a non-monotonic $M(B)$, presenting a maximum in $M$ at
what is known as the second magnetization peak. This phenomenon appears in most
classes of superconductors, including low $T_c$ materials, iron-based, and
cuprates, complicating pinpointing its origin and garnering intense interest.
Here, we report on vortex dynamics in optimally doped and overdoped
HgBa$_2$CuO$_{4+x}$ crystals, with a focus on a regime in which plastic
deformations of the vortex lattice govern magnetic properties. Specifically, we
find that both crystals exhibit conspicuous second magnetization peaks and,
from measurements of the field- and temperature- dependent vortex creep rates,
identify and characterize phase boundaries between elastic and plastic vortex
dynamics, as well as multiple previously unreported transitions within the
plastic flow regime. We find that the second magnetization peak coincides with
the elastic-to-plastic crossover for a very small range of high fields, and a
sharp crossover within the plastic flow regime for a wider range of lower
fields. We find evidence that this transition in the plastic flow regime is due
to a dimensional crossover, specifically a transition from 3D to 2D plastic
dynamics.",2112.08667v1
2022/3/18,Structural and Magnetic Properties of Pt/Co/Mn-Based Multilayers,"Magnetic multilayers are a rich class of materials systems with numerous
highly tunable physical parameters that determine both their magnetic and
electronic properties. Here we present a comprehensive experimental study of a
novel system, Pt/Co/Mn, which extends the group of Pt/Co/X ($\mathrm{X}=$
metal) multilayers that have been investigated thus far. We demonstrate that an
increasing Co layer thickness changes the magnetic anisotropy from out-of-plane
to in-plane, whereas the deposition of thicker Mn layers leads to a decrease in
the saturation magnetization. Temperature-dependent magnetometry measurements
reinforce the hypothesis of antiferromagnetic coupling at the Co/Mn interfaces
being responsible for the observed Mn thickness dependence of the magnetization
reversal. Moreover, magneto-optical imaging experiments indicate systematic
changes in magnetic domain patterns as a function of the Co and Mn layer
thickness, suggesting the existence of bubble-like domains -- potentially even
magnetic skyrmions -- in the case of sufficiently thick Mn layers, which are
expected to contribute to a sizeable Dzyaloshinskii-Moriya interaction in the
multilayer stacks. We identify Pt/Co/Mn as a highly complex multilayer system
with strong potential for further fundamental studies and possible
applications.",2203.10059v2
2022/4/22,Gas-atomized particles of giant magnetocaloric compound HoB2 for magnetic hydrogen liquefiers,"The processing of promising magnetocaloric materials into spheres is one of
the important issues on developing high-performance magnetic refrigeration
systems. In the present study, we achieved in producing spherical particles of
a giant magnetocaloric compound HoB2 by a crucible-free gas atomization
process, despite its high melting point of 2350 C. The particle size
distribution ranges from 100 to 710 micrometers centered at 212-355 micrometers
with the highest yield of 14-20wt% of total melted electrode, which is suitable
for magnetic refrigeration systems. The majority of the resulting particles are
mostly spherical with no contamination during the processing, while unique
microstructures are observed on the surface and inside. These spherical
particles exhibit sharp magnetic transitions and huge magnetic entropy change
of 0.34 J cm^{-3} K^{-1} for a magnetic field change of 5 T at 15.5 K. The high
sphericality and the high magnetocaloric performance suggest that the HoB2
gas-atomized particles have good potential as magnetic refrigerants for use in
magnetic refrigerators for hydrogen liquefaction.",2204.10711v1
2022/6/2,A mechanically strong and ductile soft magnet with extremely low coercivity,"Soft magnetic materials (SMMs) serve in electrical applications and
sustainable energy supply, allowing magnetic flux variation in response to
changes in applied magnetic field, at low energy loss1. The electrification of
transport, households and manufacturing leads to an increase in energy
consumption due to hysteresis losses2. Therefore, minimizing coercivity, which
scales these losses, is crucial3. Yet, meeting this target alone is not enough:
SMMs in electrical engines must withstand severe mechanical loads, i.e., the
alloys need high strength and ductility4. This is a fundamental design
challenge, as most methods that enhance strength introduce stress fields that
can pin magnetic domains, thus increasing coercivity and hysteretic losses5.
Here, we introduce an approach to overcome this dilemma. We have designed a
Fe-Co-Ni-Ta-Al multicomponent alloy with ferromagnetic matrix and paramagnetic
coherent nanoparticles (~91 nm size, ~55% volume fraction). They impede
dislocation motion, enhancing strength and ductility. Their small size, low
coherency and small magnetostatic energy create an interaction volume below the
magnetic domain wall width, leading to minimal domain wall pinning, thus
maintaining the soft magnetic properties. The alloy has a tensile strength of
1336 MPa at 54% tensile elongation, extremely low coercivity of 78 A/m (<1 Oe),
moderate saturation magnetization of 100 Am2/kg, and high electrical
resistivity of 103 {\mu}{\Omega} u Ohm cm.",2207.05686v1
2022/9/21,Role of Magnetic Defects and Defect-engineering of Magnetic Topological Insulators,"Magnetic defects play an important, but poorly understood, role in magnetic
topological insulators (TIs). For example, topological surface transport and
bulk magnetic properties are controlled by magnetic defects in
Bi$_2$Se$_3$-based dilute ferromagnetic (FM) TIs and MnBi$_2$Te$_4$ (MBT)-based
antiferromagnetic (AFM) TIs. Despite its nascent ferromagnetism, our inelastic
neutron scattering data show that a fraction of the Mn defects in Sb$_2$Te$_3$
form strong AFM dimer singlets within a quintuple block. The AFM superexchange
coupling occurs via Mn-Te-Mn linear bonds and is identical to the AFM coupling
between antisite defects and the FM Mn layer in MBT, establishing common
interactions in the two materials classes. We also find that the FM
correlations in (Sb$_{1-x}$Mn$_x$)$_2$Te$_3$ are likely driven by magnetic
defects in adjacent quintuple blocks across the van der Waals gap. In addition
to providing answers to long-standing questions about the evolution of FM order
in dilute TI, these results also show that the evolution of global magnetic
order from AFM to FM in Sb-substituted MBT is controlled by defect engineering
of the intrablock and interblock coupling.",2209.10694v1
2022/10/17,Towards a theory of surface orbital magnetization,"The theory of bulk orbital magnetization has been formulated both in
reciprocal space based on Berry curvature and related quantities, and in real
space in terms of the spatial average of a quantum mechanical local marker.
Here we consider a three-dimensional antiferromagnetic material having a
vanishing bulk but a nonzero surface orbital magnetization. We ask whether the
surface-normal component of the surface magnetization is well defined, and if
so, how to compute it. As the physical observable corresponding to this
quantity, we identify the macroscopic current running along a hinge shared by
two facets. However, the hinge current only constrains the difference of the
surface magnetizations on the adjoined facets, leaving a potential ambiguity.
By performing a symmetry analysis, we find that only crystals exhibiting a
pseudoscalar symmetry admit well-defined magnetizations at their surfaces at
the classical level. We then explore the possibility of computing surface
magnetization via a coarse-graining procedure applied to a quantum local
marker. We show that multiple expressions for the local marker exist, and apply
constraints to filter out potentially meaningful candidates. Using several
tight-binding models as our theoretical test bed and several potential markers,
we compute surface magnetizations for slab geometries and compare their
predictions with explicit calculations of the macroscopic hinge currents of rod
geometries. We find that only a particular form of the marker consistently
predicts the correct hinge currents.",2210.08736v3
2022/11/8,Spin polarization induced by magnetic field and the relativistic Barnett effect,"First, I study the analogy between the magnetization of a material and the
spin polarization of particles in a fluid. Using the relativistic version of
the Barnett effect, i.e. the magnetization of a material induced by mechanical
rotation, the spin polarization induced by thermal vorticity is obtained within
a purely classical model, where spin is treated as an intrinsic magnetic moment
and rotation is included as a non-inertial effect. I argue that since spin
polarization induced by thermal vorticity can be obtained in a classical
theory, it can not be dominated by quantum anomalies.
  Second, the spin polarization induced by magnetic field is obtained for a
fluid at local thermal equilibrium using statistical quantum field theory. The
obtained formula is valid beyond the weak field approximation and when
contributions from the non-homogeneity of the magnetic field are small. The
exact form of spin polarization is studied for a free Dirac field at global
equilibrium, and, like magnetic susceptibility, it oscillates according to the
de Haas - van Alphen effect.
  Finally, I briefly review how magnetic field contributes to the difference
between the spin polarization of $\Lambda$ and $\bar{\Lambda}$ observed in
heavy-ion collisions.",2211.04549v2
2022/11/11,"Accretion process, magnetic fields, and apsidal motion in the pre-main sequence binary DQ Tau","Classical T Tauri stars (CTTSs) are young stellar objects that accrete
materials from their accretion disc influenced by their strong magnetic field.
The magnetic pressure truncates the disc at a few stellar radii and forces the
material to leave the disc plane and fall onto the stellar surface by following
the magnetic field lines. However, this global scheme may be disturbed by the
presence of a companion interacting gravitationally with the accreting
component. This work is aiming to study the accretion and the magnetic field of
the tight eccentric binary DQ Tau, composed of two equal-mass ($\sim$ 0.6 \msun
) CTTSs interacting at different orbital phases. We investigated the
variability of the system using a high-resolution spectroscopic and
spectropolarimetric monitoring performed with ESPaDOnS at the CFHT. We provide
the first ever magnetic field analysis of this system, the Zeeman-Doppler
imaging revealed a stronger magnetic field for the secondary than the primary
(1.2 kG and 0.5 kG, respectively), but the small-scale fields analysed through
Zeeman intensification yielded similar strengths (about 2.5 kG). The magnetic
field topology and strengths are compatible with the accretion processes on
CTTSs. Both components of this system are accreting, with a change of the main
accretor during the orbital motion. In addition, the system displays a strong
enhancement of the mass accretion rate at periastron and apastron. We also
discovered, for the first time in this system, the apsidal motion of the
orbital ellipse.",2211.06191v1
2023/1/31,Signature of weakly coupled $f$ electrons and conduction electrons in magnetic Weyl semimetal candidates PrAlSi and SmAlSi,"Magnetic topological materials are a class of compounds with the underlying
interplay of nontrivial band topology and magnetic spin configuration.
Extensive interests have been aroused due to their application potential
involved with an array of exotic quantum states. With angle-resolved
photoemission spectroscopy and first-principles calculations, here we study the
electronic properties of two magnetic Weyl semimetal candidates PrAlSi and
SmAlSi. Though the two compounds harbor distinct magnetic ground states
(ferromagnetic and antiferromagnetic for PrAlSi and SmAlSi, respectively) and
4$f$ shell fillings, we find that they share quite analogous low-energy band
structure. By the measurements across the magnetic transitions, we further
reveal that there is no evident evolution of the band structure in both
compounds and the experimental spectra can be well reproduced by the
nonmagnetic calculations, together suggesting a negligible effect of the
magnetism on their electronic structures and a possibly weak coupling between
the localized 4$f$ electrons and the itinerant conduction electrons. Our
results offer essential insights into the interactions between magnetism,
electron correlations, and topological orders in the $R$Al$X$ ($R$ = light rare
earth and $X$ = Si or Ge) family.",2301.13768v1
2023/2/8,Quantum sensing of magnetic fields with molecular color centers,"Molecular color centers, such as $S=1$ Cr($o$-tolyl)$_{4}$, show promise as
an adaptable platform for magnetic quantum sensing. Their intrinsically small
size, i.e., 1-2 nm, enables them to sense fields at short distances and in
various geometries. This feature, in conjunction with tunable optical read-out
of spin information, offers the potential for molecular color centers to be a
paradigm shifting materials class beyond diamond-NV centers by accessing a
distance scale opaque to NVs. This capability could, for example, address
ambiguity in the reported magnetic fields arising from two-dimensional magnets
by allowing for a single sensing technique to be used over a wider range of
distances. Yet, so far, these abilities have only been hypothesized with
theoretical validation absent. We show through simulation that
Cr($o$-tolyl)$_{4}$ can spatially resolve proximity-exchange versus direct
magnetic field effects from monolayer CrI$_{3}$ by quantifying how these
interactions impact the excited states of the molecule. At short distances,
proximity exchange dominates through molecule-substrate interactions, but at
further distances the molecule behaves as a typical magnetic sensor, with
magnetostatic effects dominating changes to the energy of the excited state.
Our models effectively demonstrate how a molecular color center could be used
to measure the magnetic field of a 2D magnet and the role different
distance-dependent interactions contribute to the measured field.",2302.04248v1
2023/2/15,Magnetically-dressed CrSBr exciton-polaritons in ultrastrong coupling regime,"The strong coupling between photons and matter excitations such as excitons,
phonons, and magnons is of central importance in the study of light-matter
interactions. Bridging the flying and stationary quantum states, the strong
light-matter coupling enables the coherent transmission, storage, and
processing of quantum information, which is essential for building photonic
quantum networks. Over the past few decades, exciton-polaritons have attracted
substantial research interest due to their half-light-half-matter bosonic
nature. Coupling exciton-polaritons with magnetic orders grants access to rich
many-body phenomena, but has been limited by the availability of material
systems that exhibit simultaneous exciton resonances and magnetic ordering.
Here we report magnetically-dressed microcavity exciton-polaritons in the van
der Waals antiferromagnetic (AFM) semiconductor CrSBr coupled to a Tamm plasmon
microcavity. Angle-resolved spectroscopy reveals an exceptionally high
exciton-polariton coupling strength attaining 169 meV, demonstrating
ultrastrong coupling that persists up to room temperature.
Temperature-dependent exciton-polariton spectroscopy senses the magnetic order
change from AFM to paramagnetism in CrSBr, confirming its magnetic nature. By
applying an out-of-plane magnetic field, an effective tuning of the polariton
energy is further achieved while maintaining the ultrastrong exciton-photon
coupling strength, which is attributed to the spin canting process that
modulates the interlayer exciton interaction. Our work proposes a hybrid
quantum platform enabled by robust opto-electronic-magnetic coupling, promising
for quantum interconnects and transducers.",2302.07616v1
2023/5/8,Thermal Hall effects in quantum magnets,"In the recent years, the thermal Hall transport has risen as an important
diagnosis of the physical properties of the elementary excitations in various
quantum materials, especially among the Mott insulating systems where the
electronic transports are often featureless. Here we review the recent
development of thermal Hall effects in quantum magnets where all the relevant
excitations are charge-neutral. In addition to summarizing the existing
experiments, we pay a special attention to the underlying mechanisms of the
thermal Hall effects in various magnetic systems, and clarify the connection
between the microscopic physical variables and the emergent degrees of freedom
in different quantum phases. The external magnetic field is shown to modify the
intrinsic Berry curvature properties of various emergent and/or exotic
quasiparticle excitations in distinct fashions for different quantum systems
and quantum phases, contributing to the thermal Hall transports. These include,
for example, the conventional ones like the magnons in ordered magnets, the
triplons in dimerized magnets, the exotic and fractionalized quasparticles such
as the spinons and the magnetic monopoles in quantum spin liquids. We review
their contribution and discuss their presence in the thermal Hall conductivity
in different physical contexts. We expect this review to provide a useful
guidance for the physical mechanism of the thermal Hall transports in quantum
magnets.",2305.04830v1
2023/5/25,Observation of c-axis Magnetization at Low Temperatures in Weak Ferromagnet FeBO$_3$ Reveals a Spin-Reorientation Transition,"The weak ferromagnet FeBO$_3$ is well known for being a unique system for
modelling and testing magnetic dynamics primarily due to relatively simple and
localized magnetic structure and its interesting spin wave dynamics. At room
temperature, it has slightly canted iron moments lying in the a-b plane that
result in a strong antiferromagnetic moment and a weak ferromagnetic moment,
which results in pronounced ferromagnetic and antiferromagnetic spin modes.
However, some previous studies have shown unusual low-temperature behavior that
suggests a phase transition. By performing low-temperature magnetization
measurements, both in bulk and on the mesoscale, we have observed a low
temperature magnetic texture in this material in which a large c-axis
magnetization occurs. Magnetic fields along the c-axis as high as 1300 Oe were
observed close to the sample surface. This presents evidence for the onset of a
Morin transition or another type of spin-reorientation phase transition wherein
the Fe3+ moments would acquire a c-axis component to their canting below a
critical temperature. The observation of this c-axis magnetization suggests
that there is a different ground state in this material than has been
previously expected and could be due to as yet unexplored intricacies of the
Dzyaloshinskii-Moriya interaction.",2305.16082v1
2023/6/8,Non-coplanar helimagnetism in the layered van-der-Waals metal DyTe$_3$,"Magnetic materials with highly anisotropic chemical bonding can be exfoliated
to realize ultrathin sheets or interfaces with highly controllable optical or
spintronics responses, while also promising novel cross-correlation phenomena
between electric polarization and the magnetic texture. The vast majority of
these van-der-Waals magnets are collinear ferro-, ferri-, or antiferromagnets,
with a particular scarcity of lattice-incommensurate helimagnets of defined
left- or right-handed rotation sense, or helicity. Here we use polarized
neutron scattering to reveal cycloidal, or conical, magnetic structures in
DyTe$_3$, with coupled commensurate and incommensurate order parameters, where
covalently bonded double-slabs of dysprosium square nets are separated by
highly metallic tellurium layers. Based on this ground state and its evolution
in a magnetic field as probed by small-angle neutron scattering (SANS), we
establish a one-dimensional spin model with off-diagonal on-site terms,
spatially modulated by the unconventional charge order in DyTe$_3$. The
CDW-driven term couples to antiferromagnetism, or to the net magnetization in
applied magnetic field, and creates a complex magnetic phase diagram indicative
of competing interactions in an easily cleavable helimagnet. Our work paves the
way for twistronics research, where helimagnetic layers can be combined to form
complex spin textures on-demand, using the vast family of rare earth
chalcogenides and beyond.",2306.04854v2
2023/8/28,Anisotropic magnetism and band evolution induced by ferromagnetic phase transition in titanium-based kagome ferromagnet SmTi3Bi4,"Kagome magnets with diverse topological quantum responses are crucial for
next-generation topological engineering. The anisotropic magnetism and band
evolution induced by ferromagnetic phase transition (FMPT) is reported in a
newly discovered titanium-based kagome ferromagnet S mTi3 Bi4, which features a
distorted Ti kagome lattice and S m atomic zig-zag chains.
Temperature-dependent resistivity, heat capacity, and magnetic susceptibility
reveal a ferromagnetic ordering temperature Tc of 23.2 K. A large magnetic
anisotropy, observed by applying the magnetic field along three
crystallographic axes, identifies the b axis as the easy axis. Angle-resolved
photoemission spectroscopy with first-principles calculations unveils the
characteristic kagome motif, including the Dirac point at the Fermi level and
multiple van Hove singularities. Notably, a band splitting and gap closing
attributed to FMPT is observed, originating from the exchange coupling between
S m 4 f local moments and itinerant electrons of the kagome Ti atoms, as well
as the time-reversal symmetry breaking induced by the long-range ferromagnetic
order. Considering the large in-plane magnetization and the evolution of
electronic structure under the influence of ferromagnetic ordering, such
materials promise to be a new platform for exploring the intricate electronic
properties and magnetic phases based on the kagome lattice.",2308.14349v2
2023/10/20,X-Type Antiferromagnets,"Magnetically ordered materials reveal various types of magnetic moment
alignment that affects their functional properties. This makes the exploration
of unconventional magnetic orderings promising for the discovery of new
physical phenomena and spintronic applications. Here, we introduce cross-chain
antiferromagnets, dubbed X-type antiferromagnets, as an uncharted class of
magnetically ordered crystals, where the stacking of two magnetic sublattices
form an orthogonal pattern of intersecting atomic chains. These largely
unexplored X-type antiferromagnets reveal unique spin-dependent transport
properties that are not present in conventional magnets. Using $\beta$-Fe2PO5
as a representative example of such X-type antiferromagnets, we predict the
emergence of sublattice-selective spin-polarized transport, where one magnetic
sublattice is conducting, while the other is not. As a result, spin torque can
be exerted solely on a single sublattice, leading to unconventional ultrafast
dynamics of the N\`eel vector capable of deterministic switching of the
antiferromagnetic domains. Our work uncovers a previously overlooked type of
magnetic moment alignment in antiferromagnets and reveals sublattice-selective
physical properties promising for high-performance spintronic applications.",2310.13271v1
2023/10/24,Linear magneto-conductivity as a DC probe of time-reversal symmetry breaking,"Several optical experiments have shown that in magnetic materials the
principal axes of response tensors can rotate in a magnetic field. Here we
offer a microscopic explanation of this effect, and propose a closely related
DC transport phenomenon -- an off-diagonal \emph{symmetric} conductivity linear
in a magnetic field, which we refer to as linear magneto-conductivity (LMC).
Although LMC has the same functional dependence on magnetic field as the Hall
effect, its origin is fundamentally different: LMC requires time-reversal
symmetry to be broken even before a magnetic field is applied, and is therefore
a sensitive probe of magnetism. We demonstrate LMC in three different ways: via
a tight-binding toy model, density functional theory calculations on MnPSe$_3$,
and a semiclassical calculation. The third approach additionally identifies two
distinct mechanisms yielding LMC: momentum-dependent band magnetization and
Berry curvature. Finally, we propose an experimental geometry suitable for
detecting LMC, and demonstrate its applicability using Landauer-B\""{u}ttiker
simulations. Our results emphasize the importance of measuring the full
conductivity tensor in magnetic materials, and introduce LMC as a new transport
probe of symmetry.",2310.15631v1
2023/11/1,Generation of Strong Fields to Study the Phase Transitions of Magnetized Warm Dense Matter,"Warm dense matter is a regime where Fermi degenerate electrons take an
important role in the macroscopic properties of a material. While recent
experiments hinged us closer to better understanding the unmagnetized processes
in such dense materials, their magnetized counterpart has been more difficult
to study since kilo-Tesla order magnetic fields are required. Although there
are examples of field compression generating such fields by compressing
pre-magnetized targets, this approach uses a closed configuration, where a
converging liner compresses the magnetic flux dynamically. The plasma produced
to compress the field is so dense that the fast-heating laser beam required to
form warm dense matter cannot penetrate where the field is the highest. In this
paper, numerical simulations are used to show that magnetic field compression
is also possible by shining the laser beams onto the inner surface of the
target, rather than on the outer surface. This approach relies on field
compression done by a low-density high-temperature plasma, rather than a
high-density low-temperature plasma, used in the more conventional approach.
With this novel configuration, the region of the large magnetic field is now
mostly free of plasma so the heating beam can reach the sample, located where
the magnetic field is the strongest.",2311.00879v2
2023/11/6,Controlling effective field contributions to laser-induced magnetization precession by heterostructure design,"Nanoscale heterostructure design can control laser-induced heat dissipation
and strain propagation as well as their efficiency for driving magnetization
precession. We use insulating MgO layers incorporated into metallic Pt-Cu-Ni
heterostructures to block the propagation of hot electrons. Ultrafast x-ray
diffraction (UXRD) experiments quantify how this enables controlling the
spatio-temporal shape of the transient heat and strain, which drive the
magnetization dynamics in the Ni layer. The frequency of the magnetization
precession observed by the time-resolved magneto-optical Kerr effect (MOKE) in
polar geometry is systematically tuned by the magnetic field orientation. The
combined experimental analysis (UXRD and MOKE) and modeling of transient
strain, heat and magnetization uniquely highlights the importance of
quasi-static strain as a driver of precession, when the magnetic material is
rapidly heated via electrons. The concomitant effective field change
originating from demagnetization partially compensates the change induced by
quasi-static strain. Tailored strain pulses shaped via the nanoscale
heterostructure design provide an equally efficient, phase-matched driver of
precession, paving the way for opto-magneto-acoustic devices with low heat
energy deposited in the magnetic layer.",2311.03158v2
2023/12/15,Topological magnon gap engineering in van der Waals CrI$_3$ ferromagnets,"The microscopic origin of the topological magnon band gap in CrI$_3$
ferromagnets has been a subject of controversy for years since two main models
with distinct characteristics, i.e., Dzyaloshinskii-Moriya (DM) and Kitaev,
provided possible explanations with different outcome implications. Here we
investigate the angular magnetic field dependence of the magnon gap of CrI$_3$
by elucidating what main contributions play a major role in its generation. We
implement stochastic atomistic spin dynamics simulations to compare the impact
of these two spin interactions on the magnon spectra. We observe three distinct
magnetic field dependencies between these two gap opening mechanisms. First, we
demonstrate that the Kitaev-induced magnon gap is influenced by both the
direction and amplitude of the applied magnetic field, while the DM-induced gap
is solely affected by the magnetic field direction. Second, the position of the
Dirac cones within the Kitaev-induced magnon gap shifts in response to changes
in the magnetic field direction, whereas they remain unaffected by the magnetic
field direction in the DM-induced gap scenario. Third, we find a
direct-indirect magnon band-gap transition in the Kitaev model by varying the
applied magnetic field direction. These differences may distinguish the origin
of topological magnon gaps in CrI$_3$ and other van der Waals magnetic layers.
Our findings pave the way for exploration and engineering topological gaps in
van der Waals materials.",2312.09903v1
2023/12/29,Spin-glass states generated in van der Waals magnet Cr$_2$Ge$_2$Te$_6$ by alkali-ion intercalation,"Tuning magnetic properties in layered van der Waals (vdW) materials has
captured a significant attention due to the efficient control of ground-states
by heterostructuring and external stimuli. Electron doping by electrostatic
gating, interfacial charge transfer and intercalation is particularly effective
in manipulating the exchange and spin-orbit properties, resulting in a control
of Curie temperature ($T_{\text{C}}$) and magnetic anisotropy. Here, we
discover an uncharted role of intercalation to generate magnetic frustration.
As a model study, we intercalate Na atoms into the vdW gaps of pristine
Cr$_2$Ge$_2$Te$_6$ (CGT) where generated magnetic frustration leads to emerging
spin-glass states coexisting with a ferromagnetic order. A series of dynamic
magnetic susceptibility measurements/analysis confirms the formation of
magnetic clusters representing slow dynamics with a distribution of relaxation
times. The intercalation also modifies other macroscopic physical parameters
including the significant enhancement of $T_{\text{C}}$ from 66K\, to 240\,K
and the switching of magnetic easy-hard axis direction. Our study identifies
intercalation as a unique route to generate emerging frustrated spin states in
simple vdW crystals.",2312.17554v2
2024/3/13,Impact of spin-entropy on the thermoelectric properties of a 2D magnet,"Heat-to-charge conversion efficiency of thermoelectric materials is closely
linked to the entropy per charge carrier. Thus, magnetic materials are
promising building blocks for highly efficient energy harvesters, as their
carrier entropy is boosted by a spin degree of freedom. In this work, we
investigate how this spin entropy impacts heat-to-charge conversion in A-type
antiferromagnet CrSBr. We perform simultaneous measurements of electrical
conductance and thermocurrent while changing magnetic order using temperature
and magnetic field as tuning parameters. We find a strong enhancement of the
thermoelectric power factor around the N\'eel temperature. We further reveal
that the power factor at low temperature can be increased by up to 600% upon
applying a magnetic field. Our results demonstrate that the thermoelectric
properties of 2D magnets can be optimized by exploiting the sizeable impact of
spin entropy and confirm thermoelectric measurements as a sensitive tool to
investigate subtle magnetic phase transitions in low-dimensional magnets.",2403.08581v2
2024/4/3,Even-Odd Layer-Dependent Exchange Bias Effect in MnBi2Te4 Chern Insulator Devices,"Magnetic topological materials with coexisting magnetism and non-trivial band
structures exhibit many novel quantum phenomena, including the quantum
anomalous Hall effect, the axion insulator state, and the Weyl semimetal phase.
As a stoichiometric layered antiferromagnetic topological insulator, thin films
of MnBi2Te4 show fascinating even-odd layer-dependent physics. In this work, we
fabricate a series of thin-flake MnBi2Te4 devices using stencil masks and
observe the Chern insulator state at high magnetic fields and a square
hysteresis loop near zero magnetic field in all these devices. Upon magnetic
field training, a large exchange bias effect is observed in odd but not in even
septuple layer (SL) devices. Our theoretical calculations interpret this
even-odd layer-dependent exchange bias effect as a consequence of contrasting
surface and bulk magnetic properties of MnBi2Te4 devices. Our findings reveal
the microscopic magnetic configuration of MnBi2Te4 thin flakes and highlight
the challenges in replicating the zero magnetic field quantum anomalous Hall
effect in odd SL MnBi2Te4 devices.",2404.03032v1
2014/12/12,Magnetoresistance from broken spin helicity,"The propensity of some materials and multilayers to have a magnetic field
dependent resistance, called magnetoresistance, has found commercial
applications such as giant magnetoresistance harddisk read heads. But
magnetoresistance can also be a powerful probe of electronic and magnetic
interactions in matter. For example, magnetoresistance can be used to analyze
multiband conductivity, conduction inhomogeneity, localized magnetic moments,
and (fractional) Landau level structure. For materials with strong spin-orbit
interaction, magnetoresistance can be used as a probe for weak antilocalization
or a nontrivial Berry phase, such as in topological insulator surface states.
For the three dimensional topological insulators a large and linear
magnetoresistance is often used as indication for underlying non-trivial
topology, although the origin of this effect has not yet been established.
Here, we observe a large magnetoresistance in the conducting bulk state of
Bi$_2$Te$_3$. We show that this type of large magnetoresistance is due to the
competition between helical spin-momentum locking (i.e. spin rotates with
momentum direction) and the unidirectional spin alignment by an applied
magnetic field. Warping effects are found to provide the (quasi) linear
dependence on magnetic field. We provide a quantitative model for the helicity
breaking induced magnetoresistance that can be applied to a vast range of
materials, surfaces or interfaces with weak to strong spin-orbit interactions,
such as the contemporary oxide interfaces, bulk Rashba systems, and topological
insulator surface states.",1412.4065v1
2015/6/23,Design of compensated ferrimagnetic Heusler alloys for giant tunable exchange bias,"The discovery of materials with improved functionality can be accelerated by
rational material design. Heusler compounds with tunable magnetic sublattices
allow to implement this concept to achieve novel magnetic properties. Here, we
have designed a family of Heusler alloys with a compensated ferrimagnetic
state. In the vicinity of the compensation composition in Mn-Pt-Ga, a giant
exchange bias (EB) of more than 3 T and a similarly large coercivity are
established. The large exchange anisotropy originates from the exchange
interaction between the compensated host and ferrimagnetic clusters that arise
from intrinsic anti-site disorder. We demonstrate the applicability of our
design concept on a second material, Mn-Fe-Ga, with a magnetic transition above
room temperature, exemplifying the universality of the concept and the
feasibility of room-temperature applications. Our study points to a new
direction for novel magneto-electronic devices. At the same time it suggests a
new route for realizing rare-earth free exchange-biased hard magnets, where the
second quadrant magnetization can be stabilized by the exchange bias.",1506.07028v1
2016/5/7,Giant interfacial perpendicular magnetic anisotropy in MgO/CoFe/capping layer structures,"Magnetic tunnel junction (MTJ) based on CoFeB/MgO/CoFeB structures is of
great interest due to its application in the spin-transfer-torque magnetic
random access memory (STT-MRAM). Large interfacial perpendicular magnetic
anisotropy (PMA) is required to achieve high thermal stability. Here we use
first-principles calculations to investigate the magnetic anisotropy energy
(MAE) of MgO/CoFe/capping layer structures, where the capping materials include
5d metals Hf, Ta, Re, Os, Ir, Pt, Au and 6p metals Tl, Pb, Bi. We demonstrate
that it is feasible to enhance PMA by using proper capping materials.
Relatively large PMA is found in the structures with capping materials of Hf,
Ta, Os, Ir and Pb. More importantly, the MgO/CoFe/Bi structure gives rise to
giant PMA (6.09 mJ/m2), which is about three times larger than that of the
MgO/CoFe/Ta structure. The origin of the MAE is elucidated by examining the
contributions to MAE from each atomic layer and orbital. These findings provide
a comprehensive understanding of the PMA and point towards the possibility to
achieve advanced-node STT-MRAM with high thermal stability.",1605.02247v5
2016/5/23,Reinforced magnetic properties of Ni-doped BiFeO3 ceramic,"Multiferroic materials attract considerable interest because of the wide
range of potential applications such as spintronic devices, data storage and
sensors. As a strong candidate for the applications among the limited list of
single-phase multiferroic materials, BiFeO3 (BFO) is a quite attractive
material due to its multiferroic properties at room temperature (RT). However,
BFO is widely known to have large leakage current and small spontaneous
polarization due to the existence of crystalline defects such as oxygen
vacancies. Furthermore, the magnetic moment of pure BFO is very weak owing to
its antiferromagnetic nature. In this paper, the effects of Ni2+ substitution
on the magnetic properties of bulk BFO have been investigated. BFO, and
BiFe0.99Ni0.01O3, BiFe0.98Ni0.02O3 and BiFe0.97Ni0.03O3 (BFNO: Ni-doped BFO)
ceramics were prepared by solid-state reaction and rapid sintering, and
analyzed by structural and magnetic-property measurements. The leakage current
density was measured at RT by using a standard ferroelectric tester. All the
Ni-doped BFO exhibit the similar rhombohedral perovskite structure (R3c) to
that of BFO. The magnetic properties of Ni-doped BFO are much enhanced with
respect to BFO prepared at the same conditions, since the enhanced
ferromagnetic interaction is caused by the Fe/Ni coupling.",1605.07558v1
2016/12/22,Bismuth iron garnet Bi3Fe5O12: a room temperature magnetoelectric material,"The possibility to control the magnetic properties of a material with an
electric field at room temperature is highly desirable for modern applications.
Moreover, a coupling between magnetic and electric orders within a single
material presenting a wide range of exceptional physical properties, such as
bismuth iron garnet (BIG), may lead to great advances in the field of
spintronic applications. In particular, the combination of the magnetoelectric
(ME) coupling with the low damping of spin waves in BIG can allow the control
and manipulation of spin waves by an electric field in magnonic devices. Here
we report the unambiguous observation of linear magnetoelectric coupling above
300 K in BIG using ferromagnetic resonance technique with electric field
modulation. The measured coupling value is comparable with that observed for
prototypal magnetoelectric Cr2O3. On the basis of our experimental results, the
strength of this linear ME coupling is directly linked to the presence of
bismuth ions inducing strong spin orbit coupling and to the appearance of local
magnetic inhomogeneities related to the magnetic domain structure. The
unprecedented combination of magnetic, optical and magnetoelectrical properties
in BIG is expected to trigger significant interest for technological
applications as well as for theoretical studies.",1612.07531v3
2017/6/30,Layer- and doping-tunable long range ferromagnetic order-ing in two-dimensional CrS2,"Interlayer coupling is of vital importance for manipulating physical
properties, e.g. electronic bandgap, in two-dimensional materials. However,
tuning magnetic proper-ties in these materials is yet to be addressed. Here, we
found a striped antiferromag-netic (sAFM) to ferromagnetic (FM) transition
undergoing from monolayer to bilayer and thicker CrS2. This transition is
attributed to charge sharing of interlayer S atoms and its resulting charge
transfer from Cr d eg to t2g orbitals. The transferred charge reduces a portion
of Cr4+ to Cr3+, which enhances the double-exchange mechanism favoring FM
rather than sAFM ordering. Doping of electrons shares the same effect with
stacking induced charge sharing. Therefore, charge doping could either
manip-ulate the magnetic ordering between sAFM and FM or tune CrS2 between p-
and n-doped magnetic semiconductors. We also proposed several prototype devices
ena-bling to use external electric field for manipulating magnetic orderings of
CrS2 layers. These results manifest the role of interlayer coupling in
modifying magnetic proper-ties of layered materials",1706.10213v5
2017/7/11,Tunable Weyl and Dirac states in the nonsymmorphic compound $\rm\mathbf{CeSbTe}$,"Recent interest in topological semimetals has lead to the proposal of many
new topological phases that can be realized in real materials. Next to Dirac
and Weyl systems, these include more exotic phases based on manifold band
degeneracies in the bulk electronic structure. The exotic states in topological
semimetals are usually protected by some sort of crystal symmetry and the
introduction of magnetic order can influence these states by breaking time
reversal symmetry. Here we show that we can realize a rich variety of different
topological semimetal states in a single material, $\rm CeSbTe$. This compound
can exhibit different types of magnetic order that can be accessed easily by
applying a small field. It allows, therefore, for tuning the electronic
structure and can drive it through a manifold of topologically distinct phases,
such as the first nonsymmorphic magnetic topological material with an
eight-fold band crossing at a high symmetry point. Our experimental results are
backed by a full magnetic group theory analysis and ab initio calculations.
This discovery introduces a realistic and promising platform for studying the
interplay of magnetism and topology.",1707.03408v1
2017/10/24,Recent advances in iron-based superconductors toward applications,"Iron with a large magnetic moment was widely believed to be harmful to the
emergence of superconductivity because of the competition between the static
ordering of electron spins and the dynamic formation of electron pairs (Cooper
pairs). Thus, the discovery of a high critical temperature (Tc) iron-based
superconductor (IBSC) in 2008 was accepted with surprise in the condensed
matter community and rekindled extensive study globally. IBSCs have since grown
to become a new class of high-Tc superconductors next to the high-Tc cuprates
discovered in 1986. The rapid research progress in the science and technology
of IBSCs over the past decade has resulted in the accumulation of a vast amount
of knowledge on IBSC materials, mechanisms, properties, and applications with
the publication of more than several tens of thousands of papers. This article
reviews recent progress in the technical applications (bulk magnets, thin
films, and wires) of IBSCs in addition to their fundamental material
characteristics. Highlights of their applications include high-field bulk
magnets workable at 15-25 K, thin films with high critical current density (Jc)
> 1 MA/cm2 at ~10 T and 4 K, and an average Jc of 1.3*104 A/cm2 at 10 T and 4 K
achieved for a 100-m-class-length wire. These achievements are based on the
intrinsically advantageous properties of IBSCs such as the higher
crystallographic symmetry of the superconducting phase, higher critical
magnetic field, and larger critical grain boundary angle to maintain high Jc.
These properties also make IBSCs promising for applications using high magnetic
fields.",1710.08574v1
2018/6/25,"Boundary twists, instabilities, and creation of skyrmions and antiskyrmions","We formulate and study the general boundary conditions dictating the
magnetization profile in the vicinity of an interface between magnets with
dissimilar properties. Boundary twists in the vicinity of an edge due to
Dzyaloshinskii-Moriya interactions have been first discussed in [Wilson et al.,
Phys. Rev. B 88, 214420 (2013)] and in [Rohart and Thiaville, Phys. Rev. B 88,
184422 (2013)]. We show that in general case the boundary conditions lead to
the magnetization profile corresponding to the N\'eel, Bloch, or intermediate
twist. We explore how such twists can be utilized for creation of skyrmions and
antiskyrmions, e.g., in a view of magnetic memory applications. To this end, we
study various scenarios how skyrmions and antiskyrmions can be created from
interface magnetization twists due to local instabilities. We also show that a
judicious choice of Dzyaloshinskii-Moriya tensor (hence a carefully designed
material) can lead to local instabilities generating certain types of skyrmions
or antiskyrmions. The local instabilities are shown to appear in solutions of
the Bogoliubov-de-Gennes equations describing ellipticity of magnon modes bound
to interfaces. In one considered scenario, a skyrmion-antiskyrmion pair can be
created due to instabilities at an interface between materials with properly
engineered Dzyaloshinskii-Moriya interactions. We use micromagnetics
simulations to confirm our analytical predictions.",1806.09546v3
2018/7/16,"The effect of magnetism and temperature on the stability of Cr, V, Al carbide MAX phases","The stability of Cr, V, Al carbide MAX phases, materials of interest for a
variety of magnetic as well as high temperature applications, has been studied
using density-functional-theory first-principles calculations. The enthalpy of
mixing predicts these alloys to be unstable towards unmixing at 0 K. The
calculations also predict, however, that these phases would be thermally
stabilised by configurational entropy at temperatures well below the values
used for synthesis. The temperature Ts below which they become unstable is
found to be quite sensitive to the presence of magnetic moments on Cr ions, as
well as to the material's magnetic order, in addition to chemical order and
composition. Allowing for magnetism, the value of Ts for helf V and half Cr
with chemically disordered Cr and V atoms, is estimated to be between 516 K and
645 K depending on the level of theory, while, if constrained to spin-paired,
Ts drops to 142 K. Antiferromagnetic spin arrangements are found to be favoured
at low temperatures, but they are most likely lost at synthesis temperatures,
and probably at room temperature as well. However, the combination of
antiferromagnetic frustration and configurational disorder should give rise to
interesting spin textures at low temperatures.",1807.05809v1
2018/7/27,Magnetic Structural Unit with Convex Geometry: a Building Block Hosting an Exchange-striction-driven Magnetoelectric Coupling,"We perform a combined experimental and theoretical study of a magnetic-field
($B$) induced evolution of magnetic and ferroelectric properties in an
antiferromagnetic material Pb(TiO)Cu$_4$(PO$_4$)$_4$, whose structure is
characterized by a staggered array of Cu$_4$O$_{12}$ magnetic units with convex
geometry known as square cupola. Our experiments show a $B$-induced phase
transition from a previously reported low-$B$ linear magnetoelectric phase to a
new high-$B$ magnetoelectric phase, which accompanies a 90$^\circ$ flop of
electric polarization and gigantic magnetodielectric effect. Moreover, we
observe a $B$-induced sign reversal of ferroelectric polarization in the
high-$B$ phase. Our model and first-principles calculations reveal that the
observed complex magnetoelectric behavior is well explained in terms of a
$B$-dependent electric polarization generated in each Cu$_4$O$_{12}$ unit by
the so-called exchange striction mechanism. The present study demonstrates that
the materials design based on the magnetic structural unit with convex geometry
deserves to be explored for developing strong magnetoelectric couplings.",1807.10457v1
2019/7/13,Topological magnetic-spin textures in two-dimensional van der Waals Cr2Ge2Te6,"Two-dimensional (2D) van der Waals (vdW) materials show a range of profound
physical properties that can be tailored through their incorporation in
heterostructures and manipulated with external forces. The recent discovery of
long-range ferromagnetic order down to atomic layers provides an additional
degree of freedom in engineering 2D materials and their heterostructure devices
for spintronics, valleytronics and magnetic tunnel junction switches. Here,
using direct imaging by cryo-Lorentz transmission electron microscopy we show
that topologically nontrivial magnetic-spin states, skyrmionic bubbles, can be
realized in exfoliated insulating 2D vdW Cr2Ge2Te6. Due to the competition
between dipolar interactions and uniaxial magnetic anisotropy,
hexagonally-packed nanoscale bubble lattices emerge by field cooling with
magnetic field applied along the out-of-plane direction. Despite a range of
topological spin textures in stripe domains arising due to pair formation and
annihilation of Bloch lines, bubble lattices with single chirality are
prevalent. Our observation of topologically-nontrivial homochiral skyrmionic
bubbles in exfoliated vdW materials provides a new avenue for novel quantum
states in atomically-thin insulators for magneto-electronic and quantum
devices.",1907.05983v2
2019/10/8,Semiconductor - Ferromagnetic Insulator - Superconductor Nanowires: Stray Field and Exchange Field,"Nanowires can serve as flexible substrates for hybrid epitaxial growth on
selected facets, allowing for design of heterostructures with complex material
combinations and geometries. In this work we report on hybrid epitaxy of
semiconductor - ferromagnetic insulator - superconductor (InAs/EuS/Al) nanowire
heterostructures. We study the crystal growth and complex epitaxial matching of
wurtzite InAs / rock-salt EuS interfaces as well as rock-salt EuS /
face-centered cubic Al interfaces. Because of the magnetic anisotropy
originating from the nanowire shape, the magnetic structure of the EuS phase
are easily tuned into single magnetic domains. This effect efficiently ejects
the stray field lines along the nanowires. With tunnel spectroscopy
measurements of the density of states, we show the material has a hard induced
superconducting gap, and magnetic hysteretic evolution which indicates that the
magnetic exchange fields are not negligible. These hybrid nanowires fulfil key
material requirements for serving as a platform for spin-based quantum
applications, such as scalable topological quantum computing.",1910.03364v1
2020/3/10,Room-temperature ferrimagnetism of anti-site-disordered Ca2MnOsO6,"Room-temperature ferrimagnetism was discovered for the anti-site-disordered
perovskite Ca2MnOsO6 with Tc = 305 K. Ca2MnOsO6 crystallizes into an
orthorhombic structure with a space group of Pnma, in which Mn and Os share the
oxygen-coordinated-octahedral site at an equal ratio without a noticeable
ordered arrangement. The material is electrically semiconducting with
variable-range-hopping behavior. X-ray absorption spectroscopy confirmed the
trivalent state of the Mn and the pentavalent state of the Os. X-ray magnetic
circular dichroism spectroscopy reveals that the Mn and Os magnetic moments are
aligned antiferromagnetically, thereby classifying the material as a
ferrimagnet which is in accordance with band structure calculations. It is
intriguing that the magnetic signal of the Os is very weak, and that the
observed total magnetic moment is primarily due to the Mn. The Tc = 305 K is
the second highest in the material category of so-called disordered
ferromagnets such as CaRu1-xMnxO3, SrRu1-xCrxO3, and CaIr1-xMnxO3, and hence,
may support the development of spintronic oxides with relaxed requirements
concerning the anti-site disorder of the magnetic ions.",2003.04608v1
2020/3/11,A two-dimensional electron gas at the (001) surface of ferromagnetic EuTiO$_{3}$(001),"Studies on oxide quasi-two dimensional electron gas (q2DEG) have been a
playground for the discovery of novel and sometimes unexpected phenomena, like
the reported magnetism at the surface and at the interface between LaAlO$_{3}$
and SrTiO$_{3}$ non-magnetic materials. However, magnetism in this system is
weak and there are evidences of a not intrinsic origin. Here, by using in-situ
high-resolution angle resolved photoemission we demonstrate that ferromagnetic
EuTiO$_{3}$, the magnetic counterpart of SrTiO$_{3}$ in the bulk, hosts a q2DEG
at its (001) surface. This is confirmed by density functional theory
calculations with Hubbard U terms in the presence of oxygen divacancies in
various configurations, all of them leading to a spin-polarized q2DEG related
to the ferromagnetic order of Eu-4f magnetic moments. The results suggest
EuTiO$_{3}$(001) as a new material platform for oxide q2DEGs, characterized by
broken inversion and time reversal symmetries.",2003.05494v2
2020/3/17,"Anomalous critical point behavior in dilute magnetic semiconductor (Ca,Na)(Zn,Mn)2Sb2","In this paper we report successful synthesis and magnetic properties of
(Ca,Na)(Zn,Mn)2Sb2 as a new ferromagnetic dilute magnetic semiconductor (DMS).
In this DMS material the concentration of magnetic moments can be controlled
independently from the concentration of electric charge carriers that are
required for mediating magnetic interactions between these moments. This
feature allows us to separately investigate the effect of carriers and of spins
on the ferromagnetic properties of this new DMS alloy, and particularly of the
critical ferromagnetic behavior. We use modified Arrott plot technique to
establish critical exponents b, g, and d of this alloy. We find that at low Mn
concentrations (< 10 at.%), it is governed by short-range 3D-Ising behavior,
with experimental values of b, g, and d very close to theoretical 3D-Ising
values of 0.325, 1.24, and 4.815. However, as the Mn concentration increases,
this DMS material exhibits a mixed-phase behavior, with g retaining its
3D-Ising characteristics, but b crossing over to longer-range mean-field
behavior.",2003.07617v3
2020/4/27,Tailoring high-TN interlayer antiferromagnetism in a van der Waals itinerant magnet,"Antiferromagnetic (AFM) van der Waals (vdW) materials provide a novel
platform for synthetic AFM spintronics, in which the spin-related
functionalities are derived from manipulating spin configurations between the
layers. Metallic vdW antiferromagnets are expected to have several advantages
over the widely-studied insulating counterparts in switching and detecting the
spin states through electrical currents but have been much less explored due to
the lack of suitable materials. Here, utilizing the extreme sensitivity of the
vdW interlayer magnetism to material composition, we report the itinerant
antiferromagnetism in Co-doped Fe4GeTe2 with TN ~ 210 K, an order of magnitude
increased as compared to other known AFM vdW metals. The resulting spin
configurations and orientations are sensitively controlled by doping, magnetic
field, temperature, and thickness, which are effectively read out by electrical
conduction. These findings manifest strong merits of metallic vdW magnets with
tunable interlayer exchange interaction and magnetic anisotropy, suitable for
AFM spintronic applications.",2004.12650v1
2020/5/13,Layered Antiferromagnetism Induces Large Negative Magnetoresistance in the van der Waals Semiconductor CrSBr,"The recent discovery of magnetism within the family of exfoliatable van der
Waals (vdW) compounds has attracted considerable interest in these materials
for both fundamental research and technological applications. However current
vdW magnets are limited by their extreme sensitivity to air, low ordering
temperatures, and poor charge transport properties. Here we report the magnetic
and electronic properties of CrSBr, an air-stable vdW antiferromagnetic
semiconductor that readily cleaves perpendicular to the stacking axis. Below
its N\'{e}el temperature, $T_N = 132 \pm 1$ K, CrSBr adopts an A-type
antiferromagnetic structure with each individual layer ferromagnetically
ordered internally and the layers coupled antiferromagnetically along the
stacking direction. Scanning tunneling spectroscopy and photoluminescence (PL)
reveal that the electronic gap is $\Delta_E = 1.5 \pm 0.2$ eV with a
corresponding PL peak centered at $1.25 \pm 0.07$ eV. Using magnetotransport
measurements, we demonstrate strong coupling between magnetic order and
transport properties in CrSBr, leading to a large negative magnetoresistance
response that is unique amongst vdW materials. These findings establish CrSBr
as a promising material platform for increasing the applicability of vdW
magnets to the field of spin-based electronics.",2005.06110v2
2020/7/12,Energy-efficient generation of skyrmion phases in Co/Ni/Pt-based multilayers using Joule heating,"We have studied the effects of electrical current pulses on skyrmion
formation in a series of Co/Ni/Pt-based multilayers. Transmission X-ray
microscopy reveals that by applying electrical current pulses of duration and
current density on the order of $\tau$=50 $\mu$s and j=1.7x10$^1$$^0$ A/m$^2$,
respectively, in an applied magnetic field of $\mu$$_0$Hz=50 mT,
stripe-to-skyrmion transformations are attained. The skyrmions remain stable
across a wide range of magnetic fields, including zero field. The skyrmions
then remain stable across a wide range of magnetic fields, including zero
field. We primarily attribute the transformation to current-induced Joule
heating on the order of ~125 K. Reducing the magnetic moment and perpendicular
anisotropy using thin rare-earth spacers dramatically reduces the pulse
duration, current density, and magnetic field necessary to 25 $\mu$s,
2.4x10$^9$ A/m$^2$, and 27 mT, respectively. These findings show that energetic
inputs allow for the formation of skyrmion phases in a broad class of materials
and that material properties can be tuned to yield more energy-efficient access
to skyrmion phases.",2007.06008v2
2020/10/13,Dipolar-stabilized first and second-order antiskyrmions in ferrimagnetic multilayers,"Skyrmions and antiskyrmions are topologically protected spin structures with
opposite topological charge. Particularly in coexisting phases, these two types
of magnetic quasi-particles may show fascinating physics and potential for
spintronic devices. While skyrmions are observed in a wide range of materials,
until now antiskyrmions were exclusive to materials with D2d symmetry. In this
work, we show first and second-order antiskyrmions stabilized by magnetic
dipole-dipole interaction in Fe/Gd-based multilayers. We modify the magnetic
properties of the multilayers by Ir insertion layers. Using Lorentz
transmission electron microscopy imaging, we observe coexisting antiskyrmions,
Bloch skyrmions, and type-2 bubbles and determine the range of material
properties and magnetic fields where the different spin objects form and
dissipate. We perform micromagnetic simulations to obtain more insight into the
studied system and conclude that the reduction of saturation magnetization and
uniaxial anisotropy leads to the existence of this zoo of different spin
objects and that they are primarily stabilized by dipolar interaction.",2010.06555v3
2020/10/19,Inhomogeneous ferromagnetism mimics signatures of the topological Hall effect in SrRuO$_3$ films,"Topological transport phenomena in magnetic materials are a major topic of
current condensed matter research. One of the most widely studied phenomena is
the ``topological Hall effect'' (THE), which is generated via spin-orbit
interactions between conduction electrons and topological spin textures such as
skyrmions. We report a comprehensive set of Hall effect and magnetization
measurements on epitaxial films of the prototypical ferromagnetic metal
SrRuO$_3$ the magnetic and transport properties of which were systematically
modulated by varying the concentration of Ru vacancies. We observe Hall effect
anomalies that closely resemble signatures of the THE, but a quantitative
analysis demonstrates that they result from inhomogeneities in the
ferromagnetic magnetization caused by a non-random distribution of Ru
vacancies. As such inhomogeneities are difficult to avoid and are rarely
characterized independently, our results call into question the identification
of topological spin textures in numerous prior transport studies of quantum
materials, heterostructures, and devices. Firm conclusions regarding the
presence of such textures must meet stringent conditions such as probes that
couple directly to the non-collinear magnetization on the atomic scale.",2010.09349v1
2021/4/2,Observation of two independent skyrmion phases in a chiral magnetic material,"Magnetic materials can host skyrmions, which are topologically non-trivial
spin textures. In chiral magnets with cubic lattice symmetry, all
previously-observed skyrmion phases require thermal fluctuations to become
thermodynamically stable in bulk materials, and therefore exist only at
relatively high temperature, close to the helimagnetic transition temperature.
Other stabilization mechanisms require a lowering of the cubic crystal
symmetry. Here, we report the identification of a second skyrmion phase in
Cu$_{2}$OSeO$_{3}$ at low temperature and in the presence of an applied
magnetic field. The new skyrmion phase is thermodynamically disconnected from
the well-known, nearly-isotropic, high-temperature phase, and exists, in
contrast, when the external magnetic field is oriented along the
$\langle100\rangle$ crystal axis only. Theoretical modelling provides evidence
that the stabilization mechanism is given by well-known cubic anisotropy terms,
and accounts for an additional observation of metastable helices tilted away
from the applied field. The identification of two distinct skyrmion phases in
the same material and the generic character of the underlying mechanism suggest
a new avenue for the discovery, design, and manipulation of topological spin
textures.",2104.01234v1
2021/4/29,"Competing magnetic interactions and magnetoresistance anomalies in cubic intermetallic compounds, Gd4RhAl and Tb4RhAl, and enhanced magnetocaloric effect for the Tb case","We report complex magnetic, magnetoresistance (MR) and magnetocaloric
properties of Gd4RhAl and Tb4RhAl forming in the Gd4RhIn type cubic structure.
Though the synthesis of the compounds was reported long ago, to our knowledge,
no attempt was made to investigate the properties of these compounds. The
present results of ac and dc magnetization, electrical resistivity and
heat-capacity measurements down to 1.8 K establish that these compounds undergo
antiferromagnetic order initially, followed by complex spin-glass features with
decreasing temperature. These characteristic temperatures are: For Gd case, TN
is about 46K and TG is about 21 K, and for Tb, about 32 and 28 K respectively.
Additionally, there are field induced magnetic effects, interestingly leading
to non-monotonic variations in MR. There is a significant MR over a wide
temperature range above TN, similar to the behavior of magnetocaloric effect
(MCE) as measured by isothermal entropy change (DeltaS). An intriguing finding
we made is that DeltaS at the onset of magnetic order is significantly larger
for the Tb compound than that observed for the Gd analogue near its TN. On the
basis of this observation in a cubic material, we raise a question whether
aspherical nature of the 4f orbital can play a role to enhance MCE under
favorable circumstances, a clue that could be useful to find materials for
magnetocaloric applications.",2104.14521v1
2021/7/8,"Magnetism, symmetry and spin transport in van der Waals layered systems","The discovery of an ever increasing family of atomic layered magnetic
materials, together with the already established vast catalogue of strong
spin-orbit coupling (SOC) and topological systems, calls for some guiding
principles to tailor and optimize novel spin transport and optical properties
at their interfaces. Here we focus on the latest developments in both fields
that have brought them closer together and make them ripe for future fruitful
synergy. After outlining fundamentals on van der Waals (vdW) magnetism and SOC
effects, we discuss how their coexistence, manipulation and competition could
ultimately establish new ways to engineer robust spin textures and drive the
generation and dynamics of spin current and magnetization switching in 2D
materials-based vdW heterostructures. Grounding our analysis on existing
experimental results and theoretical considerations, we draw a prospective
analysis about how intertwined magnetism and spin-orbit torque (SOT) phenomena
combine at interfaces with well-defined symmetries, and how this dictates the
nature and figures-of-merit of SOT and angular momentum transfer. This will
serve as a guiding role in designing future non-volatile memory devices that
utilize the unique properties of 2D materials with the spin degree of freedom.",2107.03763v2
2022/2/3,Field-induced Topological Hall effect in antiferromagnetic axion insulator candidate EuIn$_2$As$_2$,"The magnetic topological materials have attracted significant attention due
to their potential realization of variety of novel quantum phenomena.
EuIn$_2$As$_2$ has recently been theoretically recognized as a long awaited
intrinsic antiferromagnetic bulk axion insulator. However, the experimental
study on transport properties arising from the topological states in this
material is scarce. In this paper, we perform the detailed magnetoresistance
(MR) and Hall measurements to study the magnetotransport properties of this
material. We find that the transport is strongly influenced by the spin
configuration of the Eu moments from the concomitant change in the field
dependence of the MR and that of the magnetization below the N\'eel
temperature. Most importantly, an anomalous Hall effect (AHE) and a large
topological Hall effect (THE) are observed. We suggest that the AHE is
originated from a nonvanishing net Berry curvature due to the helical spin
structure and that the THE is attributed to the formation of a noncoplanar spin
texture with a finite scalar spin chirality induced by the external magnetic
field in EuIn$_2$As$_2$. Our studies provide a platform to understand the
influence of the interplay between the topology of electronic bands and the
field-induced magnetic structure on magnetoelectric transport properties. In
addition, our observations give a hint to realize axion insulator states and
high-order topological insulator states through manipulating the magnetic state
of EuIn$_2$As$_2$.",2202.01370v1
2022/2/28,Modeling of ultrafast X-ray induced magnetization dynamics in magnetic multilayer systems,"In this work, we report on modelling results obtained with our recently
developed simulation tool enabling nanoscopic description of electronic
processes in X-ray irradiated ferromagnetic materials. With this tool, we have
studied the response of Co/Pt multilayer system irradiated by an ultrafast
extreme ultraviolet pulse at the M-edge of Co (photon energy $\sim$ 60 eV). It
was previously investigated experimentally at the FERMI free-electron-laser
facility, using the magnetic small-angle X-ray scattering technique. Our
simulations show that the magnetic scattering signal from cobalt decreases on
femtosecond timescales due to electronic excitation, relaxation and transport
processes both in the cobalt and in the platinum layers, following the trend
observed in the experimental data. The confirmation of the predominant role of
electronic processes for X-ray induced demagnetization in the regime below the
structural damage threshold is a step towards quantitative control and
manipulation of X-ray induced magnetic processes on femtosecond timescales.",2202.13845v2
2022/3/22,Quantum sensing and imaging of spin-orbit-torque-driven spin dynamics in noncollinear antiferromagnet Mn3Sn,"Novel noncollinear antiferromagnets with spontaneous time-reversal symmetry
breaking, nontrivial band topology, and unconventional transport properties
have received immense research interest over the past decade due to their rich
physics and enormous promise in technological applications. One of the central
focuses in this emerging field is exploring the relationship between the
microscopic magnetic structure and exotic material properties. Here, the
nanoscale imaging of both spin-orbit-torque-induced deterministic magnetic
switching and chiral spin rotation in noncollinear antiferromagnet Mn3Sn films
using nitrogen-vacancy (NV) centers is reported. Direct evidence of the
off-resonance dipole-dipole coupling between the spin dynamics in Mn3Sn and
proximate NV centers is also demonstrated with NV relaxometry measurements.
These results demonstrate the unique capabilities of NV centers in accessing
the local information of the magnetic order and dynamics in these emergent
quantum materials and suggest new opportunities for investigating the interplay
between topology and magnetism in a broad range of topological magnets.",2203.11465v1
2022/4/18,Frustrated magnetic interactions in a Wigner-Mott insulator,"Two-dimensional semiconductor moir\'e materials have emerged as a highly
controllable platform to simulate and explore quantum condensed matter.
Compared to real solids, electrons in semiconductor moir\'e materials are less
strongly attracted to the moir\'e lattice sites, making the nonlocal
contributions to the magnetic interactions as important as the Anderson
super-exchange. It provides a unique platform to study the effects of competing
magnetic interactions. Here, we report the observation of strongly frustrated
magnetic interactions in a Wigner-Mott insulating state at 2/3 filling of the
moir\'e lattice in angle-aligned WSe2/WS2 heterobilayers. Magneto-optical
measurements show that the net exchange interaction is antiferromagnetic for
filling factors below 1 with a strong suppression at 2/3 filling. The
suppression is lifted upon screening of the long-range Coulomb interactions and
melting of the Wigner-Mott insulator by a nearby metallic gate. The results can
be qualitatively captured by a honeycomb-lattice spin model with an
antiferromagnetic nearest-neighbor coupling and a ferromagnetic second-neighbor
coupling. Our study establishes semiconductor moir\'e materials as a model
system for the lattice-spin physics and frustrated magnetism.",2204.08148v1
2022/5/23,Direct Determination of Spin-Splitting Energy in Magnetic Graphene by Landau Fan Shifts,"Spin-polarized two-dimensional materials with large and tunable
spin-splitting energy promise the field of 2D spintronics. While graphene has
been a canonical 2D material, its spin properties and tunability are limited.
Here, we demonstrate the emergence of robust spin-polarization in graphene with
large and tunable spin-splitting energy of up to 132 meV at zero applied
magnetic fields. The spin polarization is induced through a magnetic exchange
interaction between graphene and the underlying ferrimagnetic oxide insulating
layer, Tm3Fe5O12, as confirmed by its X-ray magnetic circular dichroism. The
spin-splitting energies are directly measured and visualized by the shift in
their landau fan diagram mapped by analyzing the measured subnikov-de-Haas
oscillations as a function of applied electric fields, showing consistent fit
with our first-principles and machine learning calculations. Further, the
observed spin-splitting energies can be tuned over a broad range between 98 and
166 meV by cooling fields. Our methods and results are applicable to other
two-dimensional (magnetic) materials and heterostructures, and offer great
potential for developing next-generation spin logic and memory devices.",2205.11042v2
2022/6/6,Quantitative theory of magnetic interactions in solids,"In this report we review the method of explicit calculations of interatomic
exchange interactions of magnetic materials. This involves exchange mechanisms
normally referred to as Heisenberg exchange, Dzyaloshinskii-Moriya interaction
and anisotropic symmetric exchange. The connection between microscopic theories
of the electronic structure, such as density functional theory or dynamical
mean field theory, and interatomic exchange, is given in detail. The different
aspects of extracting information for an effective spin Hamiltonian that
involves thousands of atoms, from electronic structure calculations considering
significantly fewer atoms (1-50) is highlighted. Examples of exchange
interactions of a large group of materials is presented, which involves heavy
elements of the 3d period, alloys between transition metals, Heusler compounds,
multilayer systems as well as overlayers and adatoms on a substrate, transition
metal oxides, 4f elements, magnetic materials in two dimensions and molecular
magnets. Where possible, a comparison to experimental data is made, that
naturally becomes focused on the magnon dispersion. The influence of relativity
is reviewed for a few cases, as is the importance of dynamical correlations.
Development to theories that handle out of equilibrium conditions is also
described here. The review ends with a short description of extensions of the
theories behind explicit calculations of interatomic exchange, to non-magnetic
situations, e.g. that describe chemical (charge) order and superconductivity.",2206.02415v2
2022/6/23,High pressure tuning of magnon-polarons in the layered antiferromagnet FePS$_3$,"Magnetic layered materials have emerged recently as promising systems to
introduce magnetism in structures based on two-dimensional (2D) materials and
to investigate exotic magnetic ground states in the 2D limit. In this work, we
apply high hydrostatic pressures up to P = 8.7 GPa to the bulk layered
antiferromagnet FePS$_3$ to tune the collective lattice excitations (phonons)
in resonance with magnetic excitations (magnons). Close to P = 4 GPa, the
magnon-phonon resonance is achieved and the strong coupling between these
collective modes leads to the formation of new quasi-particles, the
magnon-polarons, evidenced in our low temperature Raman scattering experiments
by a particular avoided crossing behavior between the phonon and the doubly
degenerate antiferromagnetic magnon. At the pressure-induced magnon-phonon
resonance, three distinct coupled modes emerge. As it is mainly defined by
intralayer properties, we show that the energy of the magnon is nearly pressure
independent. We additionally apply high magnetic fields up to B = 30 T to fully
identify and characterize the magnon excitations, and to explore the different
magnon-polaron regimes for which the phonon has an energy lower-, equal to-, or
higher- than the magnon energy. The description of our experimental data
requires introducing a phonon-phonon coupling not taken into account in actual
calculations.",2206.11963v1
2022/6/24,Intertwining of magnetism and charge ordering in kagome FeGe,"Recent experiments report a charge density wave (CDW) in the antiferromagnet
FeGe, but the nature of the charge ordering and the associated structural
distortion remains elusive. We discuss the structural and electronic properties
of FeGe. Our proposed ground state phase accurately captures atomic
topographies acquired by scanning tunneling microscopy. We show that the
2$\times$2$\times$1 CDW likely results from the Fermi surface nesting of
hexagonal-prism-shaped kagome states. FeGe is found to exhibit distortions in
the positions of the Ge atoms instead of the Fe atoms in the kagome layers.
Using in-depth first-principles calculations and analytical modeling, we
demonstrate that this unconventional distortion is driven by the intertwining
of magnetic exchange coupling and CDW interactions in this kagome material.
Movement of Ge atoms from their pristine positions also enhances the magnetic
moment of the Fe kagome layers. Our study indicates that magnetic kagome
lattices provide a material candidate for exploring the effects of strong
electronic correlations on the ground state and their implications for
transport, magnetic, and optical responses in materials.",2206.12033v2
2022/9/20,Modeling of 3D Printable Electrical Machineries Ferromagnetic Parts,"The electrical machinery core is formed with a ferromagnetic material that
offers high magnetic properties. As ferromagnetic materials have high relative
magnetic permeability, they are important in the formation of electromagnetic
device cores. Conventional subtractive and powder metallurgy methods for
fabrication electrical machineries offer significant core losses and reduce
magnetic flux density and magnetic permeability. With the advancement of
technology, the limitation of the traditional process can be overcome by using
the additive manufacturing process. Hence, this paper proposes a 3D printable
model of two types of single-phase transformers, referred to as E-I shape and
U-I shape transformers respectively. Possibilities of designing the electrical
machinery part which has a ferromagnetic core are investigated. The efficiency
of the transformers is evaluated in terms of magnetic flux density distribution
and volumetric loss density based on the results of a large number of Finite
element simulation methods under various operating situations on COMSOL. The
performance of various ferromagnetic materials such as Soft Iron (Fe) and
Ferrite (Fe2O3) on the transformer core is evaluated. This analysis reveals
that if U-I shaped transformer can be made from 3D printing, it will be the
best feasible structure for higher operating frequency.",2209.09894v1
2022/10/3,Interwoven atypical quantum states in CeLiBi$_2$,"We report the discovery of CeLiBi$_2$, the first example of a material in the
tetragonal Ce$TX_2$ ($T$ = transition metal; $X$ = pnictogen) family wherein an
alkali cation replaces the typical transition metal. Magnetic susceptibility
and neutron powder diffraction measurements are consistent with a crystal-field
$\Gamma_6$ ground state Kramers doublet that orders antiferromagnetically below
$T_N = 3.4$ K with an incommensurate propagation wave vector ${\bf{k}} = (0,
0.0724(4), 0.5)$ that generates a nanometric modulation of the magnetic
structure. The best model of the ordered state is an elliptical cycloid with Ce
moments primarily residing in the $ab$ plane. This is highly unusual, as all
other $\Gamma_6$ Ce$TX_2$ members order ferromagnetically. Further, we observe
an atypical hard-axis metamagnetic transition at $2$ T in magnetostriction,
magnetization, and resistivity measurements. CeLiBi$_2$ is a rare example of a
highly conductive material with dominant skew scattering leading to a large
anomalous Hall effect. Quantum oscillations with five frequencies arise in
magnetostriction and magnetic susceptibility data to $T = 30$ K and $\mu_0H =
55$ T, which indicate small Fermi pockets of light carriers with effective
masses as low as 0.07$m_e$. Density functional theory calculations indicate
that square-net Dirac-like Bi$-p$ bands are responsible for these ultralight
carriers. Together, our results show that CeLiBi$_2$ enables multiple atypical
magnetic and electronic properties in a single clean material.",2210.01031v2
2023/2/17,A Dirac-material-inspired non-linear electrodynamic model,"We propose and study the properties of a non-linear electrodynamics that
emerges inspired on the physics of Dirac materials. This new electrodynamic
model is an extension of the one-loop corrected non-linear effective Lagrangian
computed in the work of ref. [3]. In the particular regime of a strong magnetic
and a weak electric field, it reduces to the photonic non-linear model worked
out by the authors of ref. [3]. We pursue our investigation of the proposed
model by analyzing properties of the permittivity and permeability tensors, the
energy-momentum tensor and wave propagation effects in presence of a uniform
magnetic background. It is shown that the electrodynamics here presented
exhibits the vacuum birefringence phenomenon. Subsequently, we calculate the
lowest-order modifications to the interaction energy, considering still the
presence of a uniform external magnetic field. Our analysis is carried out
within the framework of the gauge-invariant but path-dependent variables
formalism. The calculation reveals a screened Coulomb-like potential with an
effective electric charge that runs with the external magnetic field but, as
expected for Dirac-type materials, the screening disappears whenever the
external magnetic field is switched off.",2303.03098v2
2023/3/18,Tunneling magnetoresistance in Mn$_2$Au-based pure antiferromagnetic tunnel junction,"Antiferromagnetic (AF) spintronics is merit on ultra-high operator speed and
stability in the presence of magnetic field. To fully use the merit, the device
should be pure rather than hybrid with ferromagnet or ferrimagnet. For the
magnetism in the antiferromagnet is canceled by that of different sublattices,
breaking the symmetry in the material can revive the native magnetism, which
can be detected by the magnetoresistance (MR) effect. Achieving noticeable MR
effect in the pure AF device is diffcult but essential for the AF spintronic
applications. Here, we study the tunnel magnetoresistance(TMR) effect in the
Nb/Mn$_2$Au/CdO/Mn$_2$Au/Nb pure AF magnetic tunnel junctions (AF-MTJs) based
on a first-principle scattering theory. Giant TMRs with order of 1000% are
predicted in some symmetric junctions, which is originated from the interfacial
resonance tunneling effect related with the k dependent complex band structures
of CdO and Mn$_2$Au in companion with the enhanced spin polarization of the
interfacial magnetic atoms. The effect of voltage bias and interfacial disorder
such as Oxygen vacancy, Manganese vacancy, and Manganese-Cadmium exchanges at
Mn2Au/CdO interfaces are studied also. Our studies suggest
Nb/Mn$_2$Au/CdO/Mn$_2$Au/Nb AFMTJs promising material for AF spintronic
application, and rocksalt CdO a potential symmetry filtering material for
spintronic applications.",2303.10448v1
2023/7/7,Observation of the anomalous Hall effect in a layered polar semiconductor,"Progress in magnetoelectric materials is hindered by apparently contradictory
requirements for time-reversal symmetry broken and polar ferroelectric
electronic structure in common ferromagnets and antiferromagnets. Alternative
routes could be provided by recent discoveries of a time-reversal symmetry
breaking anomalous Hall effect in noncollinear magnets and altermagnets, but
hitherto reported bulk materials are not polar. Here, we report the observation
of a spontaneous anomalous Hall effect in doped AgCrSe$_2$, a layered polar
semiconductor with an antiferromagnetic coupling between Cr spins in adjacent
layers. The anomalous Hall resistivity 3 $\mu\Omega$ cm is comparable to the
largest observed in compensated magnetic systems to date, and is rapidly
switched off when the angle of an applied magnetic field is rotated to $\sim
80^{\circ}$ from the crystalline $c$-axis. Our ionic gating experiments show
that the anomalous Hall conductivity magnitude can be enhanced by modulating
the $p$-type carrier density. We also present theoretical results that suggest
the anomalous Hall effect is driven by Berry curvature due to noncollinear
antiferromagnetic correlations among Cr spins, which are consistent with the
previously suggested magnetic ordering in AgCrSe$_2$. Our results open the
possibility to study the interplay of magnetic and ferroelectric-like responses
in this fascinating class of materials.",2307.03541v1
2024/1/2,"Origin of zigzag antiferromagnetic orders in XPS3 (X= Fe, Ni) monolayers","Recently, two monolayer magnetic materials, i.e., FePS3 and NiPS3, have been
successfully fabricated. Despite that they have the same atomic structure, the
two monolayers exhibit distinct magnetic properties. FePS3 holds an
out-of-plane zigzag antiferromagnetic (AFM-ZZ) structure, while NiPS3 exhibits
an in-plane AFM-ZZ structure. However, there is no theoretical model which can
properly describe its magnetic ground state due to the lack of a full
understanding of its magnetic interactions. Here, by combining the
first-principles calculations and the newly developed machine learning method,
we construct an exact spin Hamiltonian of the two magnetic materials. Different
from the previous studies which failed to fully consider the spin-orbit
coupling effect, we find that the AFM-ZZ ground state in FePS3 is stabilized by
competing ferromagnetic nearest-neighbor and antiferromagnetic third
nearest-neighbor exchange interactions, and combining single-ion anisotropy.
Whereas, the often ignored nearest-neighbor biquadratic exchange is responsible
for the in-plane AFM-ZZ ground state in NiPS3. We additionally calculate
spin-wave spectrum of AFM-ZZ structure in the two monolayers based on the exact
spin Hamiltonian, which can be directly verified by the experimental
investigation. Our work provides a theoretical framework for the origin of
AFM-ZZ ground state in two-dimensional materials.",2401.01203v1
2024/1/13,Electrodynamics of the quantum anomalous Hall state in a magnetically doped topological insulator,"Magnetically doped topological insulators have been extensively studied over
the past decade as a material platform to exhibit quantum anomalous Hall
effect. Most material realizations are magnetically doped and despite material
advances suffer from large disorder effects. In such systems, it is believed
that magnetic disorder leads to a spatially varying Dirac mass gap and chemical
potential fluctuations, and hence quantized conductance is only observed at
very low temperatures. Here, we use a recently developed high-precision
time-domain terahertz (THz) polarimeter to study the low-energy electrodynamic
response of Cr-doped (Bi,Sb)$_2$Te$_3$ thin films. These films have been
recently shown to exhibit a dc quantized anomalous Hall response up to T = 2 K
at zero gate voltage. We show that the real part of the THz range Hall
conductance $\sigma_{xy}(\omega)$ is slightly smaller than $e^2/h$ down to T =
2 K with an unconventional decreasing dependence on frequency. The imaginary
(dissipative) part of $\sigma_{xy}(\omega)$ is small, but increasing as a
function of omega. We connect both aspects of our data to a simple model for
effective magnetic gap disorder. Our work highlights the different effect that
disorder can have on the dc vs. ac quantum anomalous Hall effect.",2401.06985v1
2024/2/2,Probing of magnetic dimensional crossover in CrSiTe$_{3}$ through picosecond strain pulses,"Elucidating the emergence of long-range magnetic ordering from its precursor
short-range magnetic ordering (SRMO) in two-dimensional van der Waals materials
holds profound implications for fundamental research and technological
advancements. However, directly observing the intricate stages of this magnetic
dimensional crossover (MDC) remains a significant experimental challenge. While
magneto-elastic coupling offers a promising avenue, detecting the minute
lattice response to SRMO proves challenging. Recent investigations utilizing
second harmonic generation have unveiled a two-step MDC in a van der Waals
ferromagnetic insulator. However, an unambiguous detection of MDC through the
time-resolved techniques remains elusive. To meet this goal, we have executed
an alternative approach by employing picosecond acoustic strain pulses
generated by femtosecond lasers to probe the various stages of MDC through the
magneto-elastic coupling for the first time. By analyzing the shape of the
strain pulse in both the time and frequency domains as a function of
temperature, we clearly demonstrate the detection of the subtle influence of
spin fluctuations on the lattice. Additionally, the ultrafast carrier dynamics
also show signatures of MDC. Our measurements pave the way towards
characterizing magnetic materials in time-resolved experiments that are crucial
in designing a new generation of spin-based optoelectronic devices.",2402.01256v1
2008/6/15,Magnetic interactions of cold atoms with anisotropic conductors,"We analyze atom-surface magnetic interactions on atom chips where the
magnetic trapping potentials are produced by current carrying wires made of
electrically anisotropic materials. We discuss a theory for time dependent
fluctuations of the magnetic potential, arising from thermal noise originating
from the surface. It is shown that using materials with a large electrical
anisotropy results in a considerable reduction of heating and decoherence rates
of ultra-cold atoms trapped near the surface, of up to several orders of
magnitude. The trap loss rate due to spin flips is expected to be significantly
reduced upon cooling the surface to low temperatures. In addition, the
electrical anisotropy significantly suppresses the amplitude of static spatial
potential corrugations due to current scattering within imperfect wires. Also
the shape of the corrugation pattern depends on the electrical anisotropy: the
preferred angle of the scattered current wave fronts can be varied over a wide
range. Materials, fabrication, and experimental issues are discussed, and
specific candidate materials are suggested.",0806.2427v2
2009/6/16,Microwave Technologies-- Determination of Magnetic and Dielectric Materials Microwave Properties,"In this study, four different techniques are presented. 1 Rectangular
waveguide measurement technique for normal microwave materials microwave
properties such as permeability and permittivity. This technique removed guess
parameter and dispersive effect issues of the old waveguide measurement
techniques. It projects a new route for determination of any microwave
materials magnetic and dielectric properties without using any guesses. 2
Coaxial probe measurement technique for the liquid and biological tissues
dielectric permittivity. This coaxial probe technique has an advantage which is
to attain the highest reflected signal from the coaxial probe tip, so that it
is a fast and very sensitive technique to differentiate lossy materials
dielectric permittivity. This technique could be useful non destructive
detections for tumors in hospital and non destructive detections for chemical
liquids as well. 3 A microstripline measurement technique for oxides microwave
measurement at low frequency spectra where the waveguide technique becomes
robot and cumbersome. 4 A new methodology is presented for the rectangular
waveguide technique to determine microwave metamaterials refractive index,
permeability and permittivity using the rectangular waveguide. In summary, the
presented techniques are capable enough to determine magnetic and non magnetic
solid state materials, liquids, powders and biological tissues microwave
properties from the broad microwave frequencies spectra between 1 GHz to 50
GHz. Lastly, a special ferrites microwave properties are also presented since
the negative refractive index from the insulator ferrite could be an
interesting subject.",0906.2928v1
2012/7/2,"Establishing micromagnetic parameters of ferromagnetic semiconductor (Ga,Mn)As","(Ga,Mn)As is at the forefront of research exploring the synergy of magnetism
with the physics and technology of semiconductors, and has led to discoveries
of new spin-dependent phenomena and functionalities applicable to a wide range
of material systems. Its recognition and utility as an ideal model material for
spintronics research has been undermined by the large scatter in reported
semiconducting doping trends and micromagnetic parameters. In this paper we
establish these basic material characteristics by individually optimizing the
highly non-equilibrium synthesis for each Mn-doping level and by simultaneously
determining all micromagnetic parameters from one set of magneto-optical
pump-and-probe measurements. Our (Ga,Mn)As thin-film epilayers, spannig the
wide range of accessible dopings, have sharp thermodynamic Curie point
singularities typical of uniform magnetic systems. The materials show
systematic trends of increasing magnetization, carrier density, and Curie
temperature (reaching 188 K) with increasing doping, and monotonous doping
dependence of the Gilbert damping constant of ~0.1-0.01 and the spin stiffness
of ~2-3 meVnm^2. These results render (Ga,Mn)As well controlled degenerate
semiconductor with basic magnetic characteristics comparable to common band
ferromagnets.",1207.0310v1
2017/6/20,Coulomb drag in topological materials,"Dirac fermions are at the forefront of modern condensed matter physics
research. They are known to occur in materials as diverse as graphene,
topological insulators, and transition metal dichalcogenides, while closely
related Weyl fermions have been discovered in other materials. They have been
predicted to lend themselves to a variety of technological applications, while
the recent prediction and discovery of the quantized anomalous Hall effect of
massive Dirac fermions is regarded as a potential gateway towards low-energy
electronics. Some materials hosting Dirac fermions are natural platforms for
interlayer coherence effects such as Coulomb drag and exciton condensation. The
top and bottom surfaces of a thin topological insulator film provide such a
prototype system. Here we describe recent insights into Coulomb drag between
two layers of Dirac fermions relying primarily on topological insulator films
as a minimal model. We consider both non-magnetic topological insulators,
hosting massless Dirac fermions, and magnetic topological insulators, in which
the fermions are massive. We discuss in general terms the dynamics of the
thin-film spin density matrix, outlining numerical results and approximate
analytical expressions where appropriate for the drag resistivity \r{ho}D at
low temperatures and low electron densities. In magnetic topological insulators
with out-of-plane magnetizations in both the active and passive layers we
analyze the role of the anomalous Hall effect in Coulomb drag.",1706.07291v2
2018/2/5,Electrical-current-induced magnetic hysteresis in self-assembled vertically aligned La_{2/3}Sr_{1/3}MnO_3:ZnO-nanopillar composites,"Magnetoresistive random-access memory (MRAM) is poised to become a
next-generation information storage device. Yet, many materials challenges
remain unsolved before it can become a widely used memory storage solution.
Among them, an urgent need is to identify a material system that is suitable
for downscaling and is compatible with low-power logic applications.
Self-assembled, vertically-aligned La_{2/3}Sr_{1/3}MnO_3:ZnO nanocomposites, in
which La_{2/3}Sr_{1/3}MnO_3 (LSMO) matrix and ZnO nanopillars form an
intertwined structure with coincident-site-matched growth occurring between the
LSMO and ZnO vertical interfaces, may offer new MRAM applications by combining
their superior electric, magnetic (B), and optical properties. In this paper,
we show the results of electrical current induced magnetic hysteresis in
magneto-resistance measurements in these nano-pillar composites. We observe
that when the current level is low, for example, 1 uA, the magneto-resistance
displays a linear, negative, non-hysteretic B field dependence. Surprisingly,
when a large current is used, I > 10 uA, a hysteretic behavior is observed when
the B field is swept in the up and down directions. This hysteresis weakens as
the sample temperature is increased. A possible spin-valve mechanism related to
this electrical current induced magnetic hysteresis is proposed and discussed.",1802.01632v1
2019/3/19,Kitaev quantum spin liquid - concept and materialization,"A decade ago, Alexei Kitaev proposed an exactly solvable $S$ = 1/2 model on a
two-dimensional honeycomb lattice, where the spins fractionalize into Majorana
fermions and form a topological quantum spin liquid (QSL) in the ground state.
It was soon recognized that a family of complex iridium oxides, as well as
ruthenium chloride, with honeycomb structure are magnetic insulators and
accommodate essential ingredients of the Kitaev model, due to the interplay of
electron correlation and spin-orbit coupling. This initiated a race to
materialize the Kitaev QSL and to capture the signature of Majorana fermions.
In this review, we provide a wide perspective of this rapidly growing field,
including theory, materials and experiment. We first summarize the theoretical
background of the Kitaev QSL ground state and its materialization using
spin-orbital-entangled $J_{\rm eff}$ = 1/2 moments. This is followed by an
overview of candidate materials and their magnetic properties, including
Na$_2$IrO$_3$, $\alpha$, $\beta$, $\gamma$-Li$_2$IrO$_3$,$\alpha$-RuCl$_3$ and
H$_3$LiIr$_2$O$_6$. Finally, we review the latest exciting progress in the
search for the Kitaev QSL. In particular, H$_3$LiIr$_2$O$_6$ and
$\alpha$-RuCl$_3$ in applied magnetic field show signatures of the QSL state,
and $\alpha$-RuCl$_3$ has unusual magnetic excitations and thermal transport
properties that are consistent with spin fractionalization.",1903.08081v1
2020/2/24,Flexible Amorphous Superconducting Materials and Quantum Devices with Unexpected Tunability,"In superconductivity, electrons exhibit unique macroscopic collective quantum
behavior that is the key for many modern quantum technologies. This electron
behavior stems vastly from coupling to a correlated motion of atoms in the
material, as well as from synchronized directional movement that screens
external magnetic fields perfectly. Hence, the inter-atomic distance and
material geometry are expected to affect fundamental superconductive
characteristics. These parameters are tunable with strain, but strain
application is hindered by the rigidity of superconductors, which in turn
increases at device-relevant temperatures. Here, we present flexible, foldable
and transferable superconducting materials, and functional quantum
nanostructures by depositing superconductive amorphous-alloy films on a
flexible adhesive tape. Specifically, flexible superconducting films, nanowires
and quantum interference devices (SQUIDs) were fabricated and characterized
under variable magnetic-field, current, temperature and flexure conditions. The
SQUID interference periodicity, which represents a single flux quantum,
exhibits unexpected tunability with folding curvature. This tunability raises a
need for a relook at the fundamentals of superconductivity, mainly with respect
to effects of geometry, magnetic-field inhomogeneity and strain. Our work paves
the way for novel magnetic devices and quantum-technology platforms with local
tunability.",2002.10297v2
2020/3/24,"First-principles study on the bulk and two-dimensional structures of AMnBi(A =K, Rb, Cs)-family materials","Magnetic materials with high mobilities are intriguing subject of research
from both fundamental and application perspectives. Based on first-principle
calculations, we investigate the physical properties of the already synthesized
AMnBi(A =K, Rb, Cs)-family materials. We show that these materials are
antiferromagnetic (AFM), with Neel temperatures above 300 K. They contain AFM
ordered Mn layers, while the interlayer coupling changes from ferromagnetic
(FM) for KMnBi to AFM for RbMnBi and CsMnBi. We find that these materials are
narrow gap semiconductors. Owing to the small effective mass, the electron
carrier mobility can be very high, reaching up to 100,000 cm2/(Vs) for KMnBi.
In contrast, the hole mobility is much suppressed, typically lower by two
orders of magnitude. We further study their two-dimensional (2D) single layer
structures, which are found be AFM with fairly high mobility (1000 cm2/(Vs)).
Their Neel temperatures can still reach room temperature. Interesting, we find
that the magnetic phase transition is also accompanied by a metal-insulator
phase transition, with the paramagnetic metal phase possessing a pair of
nonsymmorphic-symmetry-protected 2D spin-orbit Dirac points. Furthermore, the
magnetism can be effectively controlled by the applied strain. When the
magnetic ordering is turned into FM, the system can become a quantum anomalous
Hall insulator with gapless chiral edge states.",2003.10671v1
2020/4/14,Materials Requirements of High-Speed and Low-Power Spin-Orbit-Torque Magnetic Random-Access Memory,"As spin-orbit-torque magnetic random-access memory (SOT-MRAM) is gathering
great interest as the next-generation low-power and high-speed on-chip cache
memory applications, it is critical to analyze the magnetic tunnel junction
(MTJ) properties needed to achieve sub-ns, and ~fJ write operation when
integrated with CMOS access transistors. In this paper, a 2T-1MTJ cell-level
modeling framework for in-plane type Y SOT-MRAM suggests that high spin Hall
conductivity and moderate SOT material sheet resistance are preferred. We
benchmark write energy and speed performances of type Y SOT cells based on
various SOT materials experimentally reported in the literature, including
heavy metals, topological insulators and semimetals. We then carry out detailed
benchmarking of SOT material Pt, beta-W, and BixSe(1-x) with different
thickness and resistivity. We further discuss how our 2T-1MTJ model can be
expanded to analyze other variations of SOT-MRAM, including perpendicular (type
Z) and type X SOT-MRAM, two-terminal SOT-MRAM, as well as spin-transfer-torque
(STT) and voltage-controlled magnetic anisotropy (VCMA)-assisted SOT-MRAM. This
work will provide essential guidelines for SOT-MRAM materials, devices, and
circuits research in the future.",2004.06268v2
2020/4/29,Revealing the Phase Diagram of Kitaev Materials by Machine Learning: Cooperation and Competition between Spin Liquids,"Kitaev materials are promising materials for hosting quantum spin liquids and
investigating the interplay of topological and symmetry-breaking phases. We use
an unsupervised and interpretable machine-learning method, the tensorial-kernel
support vector machine, to study the honeycomb Kitaev-$\Gamma$ model in a
magnetic field. Our machine learns the global classical phase diagram and the
associated analytical order parameters, including several distinct spin
liquids, two exotic $S_3$ magnets, and two modulated $S_3 \times Z_3$ magnets.
We find that the extension of Kitaev spin liquids and a field-induced
suppression of magnetic order already occur in the large-$S$ limit, implying
that critical parts of the physics of Kitaev materials can be understood at the
classical level. Moreover, the two $S_3 \times Z_3$ orders are induced by
competition between Kitaev and $\Gamma$ spin liquids and feature a different
type of spin-lattice entangled modulation, which requires a matrix description
instead of scalar phase factors. Our work provides a direct instance of a
machine detecting new phases and paves the way towards the development of
automated tools to explore unsolved problems in many-body physics.",2004.14415v4
2020/6/5,2D ferromagnetism at finite temperatures under quantum scrutiny,"Recent years have seen a tremendous rise of two-dimensional (2D) magnetic
materials, several of which verified experimentally. However, most of the
theoretical predictions to date rely on ab-initio methods, at zero temperature
and fluctuations-free, while one certainly expects detrimental quantum
fluctuations at finite temperatures. Here we present the solution of the
quantum Heisenberg model for honeycomb/hexagonal lattices with anisotropic
exchange interaction up to third nearest neighbors and in an applied field in
arbitrary direction, that answers the question whether long-range magnetization
can indeed survive in the ultrathin limit of materials, up to which
temperature, and what the characteristic excitation (magnon) frequencies are,
all essential to envisaged applications of magnetic 2D materials. We find that
long-range magnetic order persists at finite temperature for materials with
overall easy-axis anisotropy. We validate the calculations on the examples of
monolayer CrI3, CrBr3 and MnSe2. Moreover, we provide an easy-to-use tool to
calculate Curie temperatures of new 2D computational materials.",2006.03287v2
2020/9/15,Correlated electron metal properties of the honeycomb ruthenate Na$_2$RuO$_3$,"We report the synthesis and characterisation of polycrystalline
Na$_2$RuO$_3$, a layered material in which the Ru$^{4+}$ ($4d^4$ configuration)
form a honeycomb lattice. The optimal synthesis condition was found to produce
a nearly ordered Na$_2$RuO$_3$ ($C2/c$ phase), as assessed from the refinement
of the time-of-flight neutron powder diffraction. Magnetic susceptibility
measurements reveal a large temperature-independent Pauli paramagnetism
($\chi_0 \sim 1.42(2)\times10^{-3}$ emu/mol Oe) with no evidence of magnetic
ordering down to 1.5 K, and with an absence of dynamic magnetic correlations,
as evidenced by neutron scattering spectroscopy. The intrinsic susceptibility
($\chi_0$) together with the Sommerfeld coeficient of $\gamma=11.7(2)$ mJ/Ru
mol K$^2$ estimated from heat capacity measurements, gives an enhanced Wilson
ratio of $R_W\approx8.9(1)$, suggesting that magnetic correlations may be
present in this material. While transport measurements on pressed pellets show
nonmetallic behaviour, photoemission spectrocopy indicate a small but finite
density of states at the Fermi energy, suggesting that the bulk material is
metallic. Except for resistivity measurements, which may have been compromised
by near surface and interface effects, all other probes indicate that
Na$_2$RuO$_3$ is a moderately correlated electron metal. Our results thus stand
in contrast to earlier reports that Na$_2$RuO$_3$ is an antiferromagnetic
insulator at low temperatures.",2009.07105v1
2020/11/19,Multipolar exchange interaction and complex order in insulating lanthanides,"In insulating lanthanides, unquenched orbital momentum and weak crystal-field
(CF) splitting of the atomic $J$ multiplet at lanthanide ions result in a
highly ranked (multipolar) exchange interaction between them and a complex
low-temperature magnetic order not fully uncovered by experiment. Explicitly
correlated {\it ab initio } methods proved to be highly efficient for an
accurate description of CF multiplets and magnetism of individual lanthanide
ions in such materials. Here we extend this {\it ab initio } methodology and
develop a first-principles microscopic theory of multipolar exchange
interaction between $J$-multiplets in $f$ metal compounds. The key point of the
approach is a complete account of Goodenough's exchange mechanism along with
traditional Anderson's superexchange and other contributions, the former being
dominant in many lanthanide materials. Application of this methodology to the
description of the ground-state order in the neodymium nitride with rocksalt
structure reveals the multipolar nature of its ferromagnetic order. We found
that the primary and secondary order parameters (of $T_{1u}$ and $E_g$
symmetry, respectively) contain non-negligible $J$-tensorial contributions up
to the ninth order. The calculated spin-wave dispersion and magnetic and
thermodynamic properties show that they cannot be simulated quantitatively by
confining to the ground CF multiplet on the Nd sites. Our results demonstrate
that the {\it ab initio } approach to the low-energy Hamiltonian represents a
powerful tool for the study of materials with complex magnetic order.",2011.09626v4
2021/1/21,Phenomenological analysis of transverse thermoelectric generation and cooling performance in magnetic/thermoelectric hybrid systems,"We phenomenologically calculate the performance of the recently-observed
Seebeck-driven transverse thermoelectric generation (STTG) for various systems
in terms of the thermopower, power factor, and figure of merit to demonstrate
the usefulness of STTG. The STTG system consists of a closed circuit comprising
thermoelectric and magnetic materials which exhibit the Seebeck and anomalous
Hall effects, respectively. When a temperature gradient is applied to the
hybrid system, the Seebeck effect in the thermoelectric material layer
generates a longitudinal charge current in the closed circuit and the charge
current subsequently drives the anomalous Hall effect in the magnetic material
layer. The anomalous Hall voltage driven by the Seebeck effect has a similar
symmetry to the transverse thermoelectric conversion based on the anomalous
Nernst effect. We find that the thermoelectric properties of STTG can be much
better than those of the anomalous Nernst effect by increasing the Seebeck
coefficient and anomalous Hall angle of the thermoelectric and magnetic
materials, respectively, as well as by optimizing their dimensions. We also
formulate the electronic cooling performance in the STTG system, confirming the
reciprocal relation for the hybrid transverse thermoelectric conversion.",2101.08443v3
2021/7/23,Quasi-nodal lines in rhombohedral magnetic materials,"A well-established result in condensed matter physics states that materials
crystallizing in symmetry groups containing glide reflection symmetries possess
nodal lines on the energy bands. These nodal lines are topologically protected
and appear on the fixed planes of the reflection in reciprocal space. In the
presence of inversion symmetry, the energy bands are degenerate and the nodal
lines on the fixed plane may hybridize or may cross. In the former case, the
crossing is avoided, thus producing lines on reciprocal space where the energy
gap is small, and in the latter, the nodal lines will endure, thus producing
Dirac or double nodal lines. In addition, if the material crystallizes in a
ferromagnetic phase where the glide reflection symmetry is broken, the nodal
lines hybridize, thus defining lines in reciprocal space where the energy gap
is small. In this work we concentrate our efforts on the study of nodal lines
that hybridize due to magnetization; we have coined the term of quasi-nodal
lines for those lines in reciprocal space where the energy gap is small (less
than what can be detected experimentally). We study magnetic trifluorides and
trioxides which crystallize in magnetic space groups 167.107 and 161.71 and we
show the existence of quasi-nodal lines on these materials. We furthermore show
that whenever the quasi-nodal lines are located around the Fermi level then
interesting charge and spin transport effects are induced and can be used to
detect experimentally these lines. Of particular interest are the half-metallic
ferromagnetic phases of PdF3 and LiCuF3 where the large signal of the anomalous
Hall conductance is due to the presence of the quasi-nodal lines on the Fermi
level.",2107.11103v1
2022/1/13,Magnetoelectricity in two-dimensional materials,"Since the initial isolation of few-layer graphene, a plethora of
two-dimensional atomic crystals has become available, covering almost all known
materials types including metals, semiconductors, superconductors, ferro- and
antiferromagnets. These advances have augmented the already existing variety of
two-dimensional materials that are routinely realized by quantum confinement in
bulk-semiconductor heterostructures. This review focuses on the type of
material for which two-dimensional realizations are still being actively
sought: magnetoelectrics. We present an overview of current theoretical
expectation and experimental progress towards fabricating low-dimensional
versions of such materials that can be magnetized by electric charges and
polarized electrically by an applied magnetic field - unusual electromagnetic
properties that could be the basis for various useful applications. The
interplay between spatial confinement and magnetoelectricity is illustrated
using the paradigmatic example of magnetic-monopole fields generated by
electric charges in or near magnetoelectric media. For the purpose of this
discussion, the image-charge method familiar from electrostatics is extended to
solve the boundary-value problem for a magnetoelectric medium in the
finite-width slab geometry using image dyons, i.e., point objects having both
electric and magnetic charges. We discuss salient features of the
magnetoelectrically induced fields arising in the thin-width limit.",2201.04801v3
2022/3/23,A Class of Magnetic Topological Material Candidates with Hypervalent Bi Chains,"The link between crystal and electronic structure is crucial for
understanding structure-property relations in solid-state chemistry. In
particular, it has been instrumental in understanding topological materials,
where electrons behave differently than they would in conventional solids.
Herein, we identify 1D Bi chains as a structural motif of interest for
topological materials. We focus on Sm$_3$ZrBi$_5$, a new quasi-one-dimensional
(1D) compound in the Ln$_3$MPn$_5$ (Ln = lanthanide; M = metal; Pn = pnictide)
family that crystallizes in the P$6_{3}$/mcm space group. Density functional
theory calculations indicate a complex, topologically non-trivial electronic
structure that changes significantly in the presence of spin-orbit coupling.
Magnetic measurements show a quasi-1D antiferromagnetic structure with two
magnetic transitions at 11.7 and 10.7 K that are invariant to applied field up
to 9 T, indicating magnetically frustrated spins. Heat capacity, electrical,
and thermal transport measurements support this claim and suggest complex
scattering behavior in Sm$_3$ZrBi$_5$. This work highlights 1D chains as an
unexplored structural motif for identifying topological materials, as well as
the potential for rich physical phenomena in the Ln$_3$MPn$_5$ family.",2203.12690v3
2023/3/9,Magnetic field filtering of the hinge supercurrent in unconventional metal NiTe$_2$-based Josephson junctions,"Topological materials with boundary (surface/edge/hinge) states have
attracted tremendous research interest. Besides, unconventional (obstructed
atomic) materials have recently drawn lots of attention owing to their
obstructed boundary states. Experimentally, Josephson junctions (JJs)
constructed on materials with boundary states produce the peculiar boundary
supercurrent, which was utilized as a powerful diagnostic approach. Here, we
report the observations of conspicuous hinge supercurrent in NiTe$_2$-based
JJs. Particularly, applying an in-plane magnetic field along the Josephson
current could rapidly suppress the bulk supercurrent and retain the nearly pure
hinge supercurrent, namely the magnetic field filtering of supercurrent.
Further systematic comparative analysis and theoretical calculations
demonstrate the existence of unconventional nature and obstructed hinge states
in NiTe$_2$. Our results revealed the unique hinge states in unconventional
metal NiTe$_2$, and demonstrated in-plane magnetic field as an efficient method
to filter out the futile bulk contributions and thereby to highlight the hinge
states hidden in topological/unconventional materials.",2303.05041v1
2024/3/19,Observation of the anomalous Nernst effect in altermagnetic candidate Mn5Si3,"The anomalous Nernst effect generates transverse voltage to the applied
thermal gradient in magnetically ordered systems. The effect was previously
considered excluded in compensated magnetic materials with collinear ordering.
However, in the recently identified class of compensated magnetic materials,
dubbed altermagnets, time-reversal symmetry breaking in the electronic band
structure makes the presence of the anomalous Nernst effect possible despite
the collinear spin arrangement. In this work, we investigate epitaxial Mn5Si3
thin films known to be an altermagnetic candidate. We show that the material
manifests a sizable anomalous Nernst coefficient despite the small net
magnetization of the films. The measured magnitudes of the anomalous Nernst
coefficient reach a scale of microVolts per Kelvin. We support our
magneto-thermoelectric measurements by density-functional theory calculations
of the material's spin-split electronic structure, which allows for the finite
Berry curvature in the reciprocal space. Furthermore, we present our
calculations of the intrinsic Berry-curvature Nernst conductivity, which agree
with our experimental observations.",2403.12929v1
2022/8/30,"Prediction of Magnetoelectric Multiferroic Janus Monolayers VOXY(X/Y = F, Cl, Br, or I, and X$\not=$Y) with in-plane ferroelectricity and out-of-plane piezoelectricity","Multifunctional two-dimensional (2D) multiferroics are promising materials
for designing low-dimensional multipurpose devices. The key to
multifunctionality in these materials is breaking the space-inversion and the
time-reversal symmetry, which results in spontaneous electric polarization and
magnetization in the same phase. A new class of 2D materials, Janus 2D
materials, has emerged, which works on a similar principle of breaking
out-of-plane symmetry to invoke new exciting functionalities in the 2D
materials, such as an out-of-plane piezoelectric polarization. In this work, a
new group of 2D multiferroic Janus monolayers VOXY (X/Y = F, Cl, Br, or I, and
X$\not=$Y) is derived by breaking the out-of-plane symmetry in the parent
multiferroics VOX$_2$ (X = F, Cl, Br, or I). The structural, magnetic, and
ferroelectric properties of multiferroics VOX$_2$ are compared with their Janus
derivatives. We calculated in-plane and out-of-plane piezoelectric polarization
for VOX$_2$ and VOXY series, where VOFCl, VOFBr, VOFI, and VOClI are found to
have significant out-of-plane piezoelectric polarization. Our theoretical work
predicts a new series of 2D multiferroic materials and encourages their further
investigation for high-performance nanoelectronic devices.",2208.14203v1
2010/3/29,Ferromagnetism in defect-ridden oxides and related materials,"The existence of high-temperature ferromagnetism in thin films and
nanoparticles of oxides containing small quantities of magnetic dopants remains
controversial. Some regard these materials as dilute magnetic semiconductors,
while others think they are ferromagnetic only because the magnetic dopants
form secondary ferromagnetic impurity phases such as cobalt metal or magnetite.
There are also reports in d0 systems and other defective oxides that contain no
magnetic ions. Here, we investigate TiO2 (rutile) containing 1 - 5% of iron
cations and find that the room-temperature ferromagnetism of films prepared by
pulsed-laser deposition is not due to magnetic ordering of the iron. The films
are neither dilute magnetic semiconductors nor hosts to an iron-based
ferromagnetic impurity phase. A new model is developed for defect-related
ferromagnetism which involves a spin-split defect band populated by charge
transfer from a proximate charge reservoir in the present case a mixture Fe2+
and Fe3+ ions in the oxide lattice. The phase diagram for the model shows how
inhomogeneous Stoner ferromagnetism depends on the total number of electrons
Ntot, the Stoner exchange integral I and the defect bandwidth W; the band
occupancy is governed by the d-d Coulomb interaction U. There are regions of
ferromagnetic metal, half-metal and insulator as well as nonmagnetic metal and
insulator. A characteristic feature of the high-temperature Stoner magnetism is
an an anhysteretic magnetization curve which is practically temperature
independent below room temperature. This is related to a wandering
ferromagnetic axis which is determined by local dipole fields. The
magnetization is limited by the defect concentration, not by the 3d doping.
Only 1-2 % of the volume of the films is magnetically ordered.",1003.5558v1
2010/7/16,Magnetism and Charge Dynamics in Iron Pnictides,"In a wide variety of materials, such as copper oxides, heavy fermions,
organic salts, and the recently discovered iron pnictides, superconductivity is
found in close proximity to a magnetically ordered state. The character of the
proximate magnetic phase is thus believed to be crucial for understanding the
differences between the various families of unconventional superconductors and
the mechanism of superconductivity. Unlike the AFM order in cuprates, the
nature of the magnetism and of the underlying electronic state in the iron
pnictide superconductors is not well understood. Neither density functional
theory nor models based on atomic physics and superexchange, account for the
small size of the magnetic moment. Many low energy probes such as transport,
STM and ARPES measured strong anisotropy of the electronic states akin to the
nematic order in a liquid crystal, but there is no consensus on its physical
origin, and a three dimensional picture of electronic states and its relations
to the optical conductivity in the magnetic state is lacking. Using a first
principles approach, we obtained the experimentally observed magnetic moment,
optical conductivity, and the anisotropy of the electronic states. The theory
connects ARPES, which measures one particle electronic states, optical
spectroscopy, probing the particle hole excitations of the solid and neutron
scattering which measures the magnetic moment. We predict a manifestation of
the anisotropy in the optical conductivity, and we show that the magnetic phase
arises from the paramagnetic phase by a large gain of the Hund's rule coupling
energy and a smaller loss of kinetic energy, indicating that iron pnictides
represent a new class of compounds where the nature of magnetism is
intermediate between the spin density wave of almost independent particles, and
the antiferromagnetic state of local moments.",1007.2867v1
2017/11/15,Magnetism in Semiconducting Molybdenum Dichalcogenides,"Transition metal dichalcogenides (TMDs) are interesting for understanding
fundamental physics of two-dimensional materials (2D) as well as for many
emerging technologies, including spin electronics. Here, we report the
discovery of long-range magnetic order below TM = 40 K and 100 K in bulk
semiconducting TMDs 2H-MoTe2 and 2H-MoSe2, respectively, by means of muon
spin-rotation (muSR), scanning tunneling microscopy (STM), as well as density
functional theory (DFT) calculations. The muon spin rotation measurements show
the presence of a large and homogeneous internal magnetic fields at low
temperatures in both compounds indicative of long-range magnetic order. DFT
calculations show that this magnetism is promoted by the presence of defects in
the crystal. The STM measurements show that the vast majority of defects in
these materials are metal vacancies and chalcogen-metal antisites which are
randomly distributed in the lattice at the sub-percent level. DFT indicates
that the antisite defects are magnetic with a magnetic moment in the range of
0.9-2.8 mu_B. Further, we find that the magnetic order stabilized in 2H-MoTe2
and 2H-MoSe2 is highly sensitive to hydrostatic pressure. These observations
establish 2H-MoTe2 and 2H-MoSe2 as a new class of magnetic semiconductors and
opens a path to studying the interplay of 2D physics and magnetism in these
interesting semiconductors.",1711.05392v2
2020/9/2,New highly-anisotropic Rh-based Heusler compound for magnetic recording,"The development of high-density magnetic recording media is limited by the
superparamagnetism in very small ferromagnetic crystals. Hard magnetic
materials with strong perpendicular anisotropy offer stability and high
recording density. To overcome the difficulty of writing media with a large
coercivity, heat assisted magnetic recording (HAMR) has been developed, rapidly
heating the media to the Curie temperature Tc before writing, followed by rapid
cooling. Requirements are a suitable Tc, coupled with anisotropic thermal
conductivity and hard magnetic properties. Here we introduce Rh2CoSb as a new
hard magnet with potential for thin film magnetic recording. A
magnetocrystalline anisotropy of 3.6 MJm-3 is combined with a saturation
magnetization of {\mu}0Ms = 0.52 T at 2 K (2.2 MJm-3 and 0.44 T at
room-temperature). The magnetic hardness parameter of 3.7 at room temperature
is the highest observed for any rare-earth free hard magnet. The anisotropy is
related to an unquenched orbital moment of 0.42 {\mu}B on Co, which is
hybridized with neighbouring Rh atoms with a large spin-orbit interaction.
Moreover, the pronounced temperature-dependence of the anisotropy that follows
from its Tc of 450 K, together with a high thermal conductivity of 20 Wm-1K-1,
makes Rh2CoSb a candidate for development for heat assisted writing with a
recording density in excess of 10 Tb/in2.",2009.01034v1
2020/9/28,"Magnetic-field dependence of low-energy magnons, anisotropic heat conduction, and spontaneous relaxation of magnetic domains in the cubic helimagnet ZnCr2Se4","Anisotropic low-temperature properties of the cubic spinel helimagnet
ZnCr2Se4 in the single-domain spin-spiral state are investigated by a
combination of neutron scattering, thermal conductivity, ultrasound velocity,
and dilatometry measurements. In an applied magnetic field, neutron
spectroscopy shows a complex and nonmonotonic evolution of the spin-wave
spectrum across the quantum-critical point that separates the spin-spiral phase
from the field-polarized ferromagnetic phase at high fields. A tiny spin gap of
the pseudo-Goldstone magnon mode, observed at wave vectors that are
structurally equivalent but orthogonal to the propagation vector of the spin
helix, vanishes at this quantum critical point, restoring the cubic symmetry in
the magnetic subsystem. The anisotropy imposed by the spin helix has only a
minor influence on the lattice structure and sound velocity but has a much
stronger effect on the heat conductivities measured parallel and perpendicular
to the magnetic propagation vector. The thermal transport is anisotropic at T <
2 K, highly sensitive to an external magnetic field, and likely results
directly from magnonic heat conduction. We also report long-time thermal
relaxation phenomena, revealed by capacitive dilatometry, which are due to
magnetic domain motion related to the destruction of the single-domain magnetic
state, initially stabilized in the sample by the application and removal of
magnetic field. Our results can be generalized to a broad class of helimagnetic
materials in which a discrete lattice symmetry is spontaneously broken by the
magnetic order.",2009.13424v1
2022/2/17,"Doping control of magnetic anisotropy for stable antiskyrmion formation in schreibersite (Fe,Ni)$_3$P with $S_4$ symmetry","Magnetic skyrmions, vortex-like topological spin textures, have attracted
much interest in a wide range of research fields from fundamental physics to
spintronics applications. Recently, growing attention has also been paid to
antiskyrmions emerging in opposite topological charge in non-centrosymmetric
magnets with $D_{2\mathrm{d}}$ or $S_4$ symmetry. In these magnets, complex
interplay among anisotropic Dzyaloshinskii-Moriya interaction, uniaxial
magnetic anisotropy, and magnetic dipolar interactions generates a variety of
magnetic structures. However, the relation between the stability of
antiskyrmions and these magnetic interactions remains to be elucidated. In this
work, we control the uniaxial magnetic anisotropy of schreibersite (Fe,Ni)$_3$P
with $S_4$ symmetry by doping and investigate its impact on the stability of
antiskyrmions. Our magnetometry study, supported by ferromagnetic resonance
spectroscopy, shows that the variation of the Ni content and slight doping with
4$d$ transition metals considerably change the magnetic anisotropy. In
particular, doping with Pd induces easy-axis anisotropy, giving rise to
formation of antiskyrmions, while a temperature-induced spin reorientation is
observed in a Rh-doped compound. In combination with Lorentz transmission
electron microscopy and micromagnetic simulations, we quantitatively analyze
the stability of antiskyrmion as functions of uniaxial anisotropy and
demagnetization energy, and demonstrate that subtle balance between them is
necessary to stabilize the antiskyrmions.",2202.08483v1
2017/7/10,Complex nature of magnetic field-induced ferroelectricity in GdCrTiO5,"This work shows an unconventional route for spin-driven ferroelectricity
originating from a metastable magnetic field-induced canting of chromium
sublattice in the presence of gadolinium moments in GdCrTiO5 at low
temperatures. Compared to the isostructural neodymium compound, significant
differences of magnetism and magnetoelectric effects are seen. We present the
results of thorough investigations of temperature and magnetic field dependent
magnetization as well as ac and dc magnetic susceptibility. These bulk
measurements are complemented by local-probe spectroscopy utilizing
electron-spin resonance and muon-spin rotation/relaxation for probing the
chromium moments. Ferroelectric order is inferred from pyro- and magnetocurrent
measurements. GdCrTiO5 shows a pyrocurrent signal around 10 K, only if the
system is cooled in an applied magnetic field exceeding 10 kOe. A distinct
spin-driven ferroelectric order is revealed in this state for temperatures
below 10 K, which can be switched by changing magnetic-field direction and the
polarity of the electric field. But, the magnetic measurements reveal no clear
signature of long-range magnetic ordering. The presence of such
meta-magnetoelectric-type behaviour in the absence of any meta-magnetic
behavior is rare in the literature. Our microscopic spectroscopy results
indicate significant changes of the magnetic properties around 10 K. Probably
there is an exchange frustration between Gd and Cr moments, which prevents
long-range magnetic ordering at further high temperature. Below 10 K, weak
magnetic ordering occurs by minimizing frustration due to lattice distortion,
which helps in magnetodielectric coupling. However, the non-polar distortion
attains appreciable values after application of magnetic fields above 10 kOe to
break the spatial inversion symmetry, which creates ferroelectricity.",1707.02756v4
2018/7/23,The Quantum Field Of A Magnet Shown By A Nanomagnetic Ferrolens,"It has been more than two hundred years since the first iron filings
experiment, showing us the 2D macroscopic magnetic imprint of the field of a
permanent magnet. However, latest developments in modern nanomagnetic passive
direct observation devices reveal in real-time and color a more intriguing 3D
dynamic and detailed image of the field of a magnet, with surprising new
findings, that can change our perspective for dipole magnetism forever and lead
to new research. This research is a continuation of our previous work (DOI:
10.1016/j.jmmm.2017.12.023). The magnetostatic fields were under our scope and
examined with the aid of the ferrolens. We are presenting experimental and
photographical evidence, demonstrating the true complex 3D Euclidian geometry
of the quantum field of permanent magnets that have never been seen before and
the classic iron filings experiment, apart of its 2D limitations, fails to
depict. An analysis of why and what these iron filings inherent limitations
are, giving us an incomplete and also in some degree misguiding image of the
magnetic field of a magnet is carried out, whereas, as we prove the ferrolens
is free of these limitations and its far more advanced visualization
capabilities is allowing it to show the quantum image with depth of field
information, of the dipole field of a permanent magnet. For the first time the
domain wall (i.e. Bloch or Neel wall) region of the field of a magnet is
clearly made visible by the ferrolens along with what phenomenon is actually
taking place there, leading to the inescapable conclusion, novel observation
and experimental evidence that the field of any dipole magnet actually consists
of two distinct and separate toroidal shaped 3D magnetic bubbles, each located
at either side of the dipole around the exact spatial regions where the two
poles of the magnet reside.",1807.08751v1
2022/2/9,Magnetic field-temperature phase diagrams for multiple-$Q$ magnetic orderings: Exact steepest descent approach to long-range interacting spin systems,"Multiple-$Q$ magnetic orderings represent magnetic textures composed of
superpositions of multiple spin density waves or spin spirals, as represented
by skyrmion crystals and hedgehog lattices. Such magnetic orderings have been
observed in various magnetic materials in recent years, and attracted enormous
attention, especially from the viewpoint of topology and emergent
electromagnetic fields originating from noncoplanar magnetic structures.
Although they often exhibit successive phase transitions among different
multiple-$Q$ states while changing temperature and an external magnetic field,
it is not straightforward to elucidate the phase diagrams, mainly due to the
lack of concise theoretical tools as well as appropriate microscopic models.
Here, we provide a theoretical framework for a class of effective spin models
with long-range magnetic interactions mediated by conduction electrons in
magnetic metals. Our framework is based on the steepest descent method with a
set of self-consistent equations that leads to exact solutions in the
thermodynamic limit, and has many advantages over existing methods such as
biased variational calculations and numerical Monte Carlo simulations. Applying
the framework to the models with instabilities toward triple- and hextuple-$Q$
magnetic orderings, we find that interesting reentrant phase transitions where
the multiple-$Q$ phases appear only at finite temperature and/or nonzero
magnetic field. Furthermore, we show that the multiple-$Q$ states can be
topologically-nontrivial stacked skyrmion crystals or hedgehog lattices, which
exhibit large net spin scalar chirality associated with nonzero skyrmion
number. The results demonstrate that our framework could be a versatile tool
for studying magnetic and topological phase transitions and related quantum
phenomena in actual magnetic metals hosting multiple-$Q$ magnetic orderings.",2202.04407v2
2024/1/31,Exploring the impact of the inverse Faraday effect on all-optical helicity-dependent magnetization switching,"All-optical helicity-dependent magnetization switching (AO-HDS) is the
quickest deterministic technique for data storage by solely using ultrashort
laser pulses. Granular high data density magnetic storage media developed for
heat-assisted magnetic recording (HAMR) provide an ideal playground to
investigate the interplay of effects leading to magnetization switching. In the
latest perception, we identify two effects, the magnetic circular dichroism
(MCD) and the inverse Faraday effect (IFE), as the forces driving the switching
process. During photon absorption, which leads to a rapid temperature rise and
thus to magnetization quenching, the MCD ensures two distinct electron
temperatures due to helicity-dependent absorption. This effect already holds a
nonvanishing probability for magnetization switching. At the same time, the IFE
induces a magnetic moment within the material, enhancing the switching
probability. We present AO-HDS experiments using ultrashort laser pulses
($\lesssim 200\,\mathrm{fs}$) in the near-infrared range from
$800\,\mathrm{nm}$ to $1500\,\mathrm{nm}$. The experiments demonstrate a strong
dependence of the switching efficiency on the absorbed energy density,
elevating the electron temperature in the vicinity of the Curie point, allowing
for the IFE to take full effect, inducing a magnetic moment for deterministic
switching in the quenched magnetization state. While we do not observe an
enhanced switching due to an increased MCD, a higher induced magnetization
usually improves the switching rate if the electron temperature reaches the
transition temperature vicinity. Therefore, we conclude that the magnetic
moment generated by the IFE is crucial for the switching efficiency and the
distinct deterministic character of the switching process. Laser pulses with a
higher absorption induce a higher magnetic moment and switch magnetization at
lower fluences.",2401.18010v1
2020/8/29,Exploring a quantum-information-relevant magnonic material: Ultralow damping at low temperature in the organic ferrimagnet V[TCNE]x,"Quantum information science and engineering requires novel low-loss magnetic
materials for magnon-based quantum-coherent operations. The search for low-loss
magnetic materials, traditionally driven by applications in microwave
electronics near room-temperature, has gained additional constraints from the
need to operate at cryogenic temperatures for many applications in quantum
information science and technology. Whereas yttrium iron garnet (YIG) has been
the material of choice for decades, the emergence of molecule-based materials
with robust magnetism and ultra-low damping has opened new avenues for
exploration. Specifically, thin-films of vanadium tetracyanoethylene (V[TCNE]x)
can be patterned into the multiple, connected structures needed for hybrid
quantum elements and have shown room-temperature Gilbert damping ({\alpha} = 4
\times 10^-5) that rivals the intrinsic (bulk) damping otherwise seen only in
highly-polished YIG spheres (far more challenging to integrate into arrays).
Here, we present a comprehensive and systematic study of the low-temperature
magnetization dynamics for V[TCNE]x thin films, with implications for their
application in quantum systems. These studies reveal a temperature-driven,
strain-dependent magnetic anisotropy that compensates the thin-film shape
anisotropy, and the recovery of a magnetic resonance linewidth at 5 K that is
comparable to room-temperature values (roughly 2 G at 9.4 GHz). We can account
for these variations of the V[TCNE]x linewidth within the context of scattering
from very dilute paramagnetic impurities, and anticipate additional linewidth
narrowing as the temperature is further reduced.",2008.13061v3
2022/3/17,Magnetically tunable Dirac and Weyl fermions in the Zintl materials family,"Recent classification efforts encompassing crystalline symmetries have
revealed rich possibilities for solid-state systems to support a tapestry of
exotic topological states. However, finding materials that realize such states
remains a daunting challenge. Here we show how the interplay of topology,
symmetry, and magnetism combined with doping and external electric and magnetic
field controls can be used to drive the previously unreported SrIn$_2$As$_2$
materials family into a variety of topological phases. Our first-principles
calculations and symmetry analysis reveal that SrIn$_2$As$_2$ is a dual
topological insulator with $Z_2=(1;000)$ and mirror Chern number $C_M= -1$. Its
isostructural and isovalent antiferromagnetic cousin EuIn$_2$As$_2$ is found to
be an axion insulator with $Z_4= 2$. The broken time-reversal symmetry via Eu
doping in Sr$_{1-x}$Eu$_x$In$_2$As$_2$ results in a higher-order or topological
crystalline insulator state depending on the orientation of the magnetic easy
axis. We also find that antiferromagnetic EuIn$_2$P$_2$ is a trivial insulator
with $Z_4= 0$, and that it undergoes a magnetic field-driven transition to an
ideal Weyl fermion or nodal fermion state with $Z_4= 1$ with applied magnetic
field. Our study identifies Sr$_{1-x}$Eu$_x$In$_2$(As, P)$_2$ as a new tunable
materials platform for investigating the physics and applications of Weyl and
nodal fermions in the scaffolding of crystalline and axion insulator states.",2203.09084v1
2022/5/16,Ferrimagnetism in stable non-metal covalent organic framework,"We synthesized a pure organic non-metal crystalline covalent organic
framework TAPA-BTD-COF by bottom-up Schiff base chemical reaction. And this
imine-based COF is stable in aerobic condition and room-temperature. We
discovered that this TAPA-BTD-COF exhibited strong magneticity in 300 K
generating magnetic hysteresis loop in M-H characterization and giant chimol up
to 0.028. And we further conducted zero-field cooling and field-cooling
measurement of M-T curves. The as-synthesized materials showed a large chi/mol
up to 0.028 in 300 K and increasing to 0.037 in 4.0 K with 200 Oe measurement
field. The TAPA-BTD-COF 1/chimol~T curve supported its ferrimagnetism, with an
intrinsic delta temperature as -33.03 K by extrapolating the 1/chimol~T curve.
From the continuously increasing slope of 1/chimol~T, we consider that this
TAPA-BTD-COF belongs to ferrimagnetic other than antiferromagnetic materials.
And the large chimol value 0.028 at 300 K and 0.037 at 4.0 K also supported
this, since common antiferromagnetic materials possess chimol in the range of
10-5 to 10-3 as weak magnetics other than strong magnetic materials such as
ferrimagnetics and ferromagnetics. Since this material is purely non-metal
organic polymer, the possibility of d-block and f-block metal with
unpaired-electron induced magnetism can be excluded. Besides, since the COF
does not involve free-radical monomer in the processes of synthesis, we can
also exclude the origin of free-radical induced magnetism. According to recent
emerging flat-band strong correlated exotic electron property, this
unconventional phenomenon may relate to n-type doping on the flat-band locating
in the CBM, thus generating highly-localized electron with infinite effective
mass and exhibiting strong correlation, which accounts for this non-trivial
strong and stable ferrimagneticity at room-temperature and aerobic atmospheric
conditions.",2205.07541v1
2024/2/16,Multiple localized-itinerant dualities in magnetism of 5f electron systems. The case of UPt$_2$Si$_2$,"The paper deals with the U based compound UPt$_2$Si$_2$ (UPS). The material
was first treated as a localized 5f-electron system. Later, an opposite opinion
of a predominantly itinerant nature of the system was put forward. The most
recent publications treat UPS as a dual material. We suggest a material
specific theoretical model based on the density functional theory plus Hubbard
$U$ (DFT+$U$) calculations that describes the set of fundamental ground-state
properties and high magnetic field experiment. The ground state properties
include antiferromagnetic magnetic structure, magnetic easy axis, and the value
of the U atomic moment. The in-field experiment shows the presence of a strong
metamagnetic transition for the field parallel to the easy axis in contrast to
the hard field direction where such a feature is absent. On the other hand,
comparable induced magnetization values are obtained for both easy and hard
field directions. Within the framework of the suggested model we show that the
compound possesses well-formed atomic moments built by electrons treated as
delocalized. To understand the experimental high-field properties we estimate
exchange energy, magnetic anisotropy energy, and Zeeman energy. All three
energies are shown to have comparable values what is crucial for the
interpretation of the experiment. At all steps of the study we devote special
attention to revealing and emphasizing the dual itinerant-localized properties
of the material. The obtained forms of the duality are different: well defined
atomic moments formed by the itinerant electrons, interplay of the single-site
and two-site anisotropies, strong localization of two of the 5f electrons in
contrast to the itinerant nature of the 5f electrons contributing to the states
around the Fermi level.",2402.10507v1
2012/6/21,Magnetic Order and Fluctuations in the Presence of Quenched Disorder in the Kagome Staircase System (Co(1-x)Mg(x))3V2O8,"Co3V2O8 is an orthorhombic magnet in which S=3/2 magnetic moments reside on
two crystallographically inequivalent Co2+ sites, which decorate a stacked,
buckled version of the two dimensional kagome lattice, the stacked kagome
staircase. The magnetic interactions between the Co2+ moments in this structure
lead to a complex magnetic phase diagram at low temperature, wherein it
exhibits a series of five transitions below 11 K that ultimately culminate in a
simple ferromagnetic ground state below T~6.2 K. Here we report magnetization
measurements on single and polycrystalline samples of (Co(1-x)Mg(x))3V2O8 for
x<0.23, as well as elastic and inelastic neutron scattering measurements on
single crystals of magnetically dilute (Co(1-x)Mg(x))3V2O8 for x=0.029 and
x=0.194, in which non-magnetic Mg2+ ions substitute for magnetic Co2+. We find
that a dilution of 2.9% leads to a suppression of the ferromagnetic transition
temperature by ~15% while a dilution level of 19.4% is sufficient to destroy
ferromagnetic long-range order in this material down to a temperature of at
least 1.5 K. The magnetic excitation spectrum is characterized by two spin-wave
branches in the ordered phase for (Co(1-x)Mg(x))3V2O8 (x=0.029), similar to
that of the pure x=0 material, and by broad diffuse scattering at temperatures
below 10 K in (Co(1-x)Mg(x))3V2O8 (x=0.194). Such a strong dependence of the
transition temperatures to long range order in the presence of quenched
non-magnetic impurities is consistent with two-dimensional physics driving the
transitions. We further provide a simple percolation model that
semi-quantitatively explains the inability of this system to establish
long-range magnetic order at the unusually-low dilution levels which we observe
in our experiments.",1206.4913v1
2020/7/23,Site Mixing for Engineering Magnetic Topological Insulators,"The van der Waals compound, MnBi$_2$Te$_4$, is the first intrinsic magnetic
topological insulator, providing a materials platform for exploring exotic
quantum phenomena such as the axion insulator state and the quantum anomalous
Hall effect. However, intrinsic structural imperfections lead to bulk
conductivity, and the roles of magnetic defects are still unknown. With higher
concentrations of same types of magnetic defects, the isostructural compound
MnSb$_2$Te$_4$ is a better model system for a systematic investigation of the
connections among magnetic, topology and lattice defects. In this work, the
impact of antisite defects on the magnetism and electronic structure is studied
in MnSb$_2$Te$_4$. Mn-Sb site mixing leads to complex magnetic structures and
tunes the interlayer magnetic coupling between antiferromagnetic and
ferromagnetic. The detailed nonstoichiometry and site-mixing of MnSb$_2$Te$_4$
crystals depend on the growth parameters, which can lead to $\approx$40\% of Mn
sites occupied by Sb and $\approx$15\% of Sb sites by Mn in as-grown crystals.
Single crystal neutron diffraction and electron microscopy studies show nearly
random distribution of the antisite defects. Band structure calculations
suggest that the Mn-Sb site-mixing favors a FM interlayer coupling, consistent
with experimental observation, but is detrimental to the band inversion
required for a nontrivial topology. Our results suggest a long range magnetic
order of Mn ions sitting on Bi sites in MnBi$_2$Te$_4$. The effects of site
mixing should be considered in all layered heterostructures that consist of
alternating magnetic and topological layers, including the entire family of
MnTe(Bi$_2$Te$_3$)$_n$, its Sb analogs and their solid solution.",2007.12217v2
2022/3/23,Large anomalous Hall effect in layered antiferromagnet Co$_{0.29}$TaS$_2$,"We present a study on the magnetization, anomalous Hall effect (AHE) and
novel longitudinal resistivity in layered antiferromagnet Co$_{0.29}$TaS$_{2}$.
Of particular interests in Co$_{0.29}$TaS$_{2}$ are abundant magnetic
transitions, which show that the magnetic structures are tuned by temperature
or magnetic field. With decreasing temperature, Co$_{0.29}$TaS$_{2}$ undergoes
two transitions at T$_{t1}\sim$ 38.3 K and T$_{t2}\sim$ 24.3 K. Once the
magnetic field is applied, another transition T$_{t3}\sim$ 34.3 K appears
between 0.3 T and 5 T. At 2 K, an obvious ferromagnetic hysteresis loop within
H$_{t1}\sim\pm$ 6.9 T is observed, which decreases with increasing temperature
and eventually disappears at T$_{t2}$. Besides, Co$_{0.29}$TaS$_{2}$ displays
step-like behavior as another magnetic transition around H$_{t2}\sim\pm$ 4 T,
which exists until $\sim$ T$_{t1}$. These characteristic temperatures and
magnetic fields mark complex magnetic phase transitions in
Co$_{0.29}$TaS$_{2}$, which are also evidenced in transport results. Large AHE
dominates in the Hall resistivity with the conspicuous value of
R$_{s}$/R$_{0}\sim 10^{5}$, considering that the tiny net magnetization
(0.0094$\mu_{B}$/Co) alone would not lead to this value, thus the contribution
of Berry curvature is necessary. The longitudinal resistivity illustrates a
prominent irreversible behavior within H$_{t1}$. The abrupt change at H$_{t2}$
below T$_{t1}$, corresponding to the step-like magnetic transitions, is also
observed. Synergy between the magnetism and topological properties, both
playing a crucial role, may be the key factor of large AHE in antiferromagnet,
which also offers a new perspective in magnetic topological materials with the
platform of Co$_{0.29}$TaS$_{2}$.",2203.12771v1
2023/10/2,Control of the magnetic anisotropy in multi-repeat Pt/Co/Al heterostructures using magneto-ionic gating,"Controlling magnetic properties through the application of an electric field
is a significant challenge in modern nanomagnetism. In this study, we
investigate the magneto-ionic control of magnetic anisotropy in the topmost Co
layer in Ta/Pt/[Co/Al/Pt]$_n$/Co/Al/AlO$_\text{x}$ multilayer stacks comprising
$n +1$ Co layers and its impact on the magnetic properties of the multilayers.
We demonstrate that the perpendicular magnetic anisotropy can be reversibly
quenched through gate-driven oxidation of the intermediary Al layer between Co
and AlO$_\text{x}$, enabling dynamic control of the magnetic layers
contributing to the out-of-plane remanence - varying between $n$ and $n +1$.
For multilayer configurations with $n = 2$ and $n = 4$, we observe reversible
and non-volatile additions of 1/3 and 1/5, respectively, to the anomalous Hall
effect amplitude based on the applied gate voltage. Magnetic imaging reveals
that the gate-induced spin-reorientation transition occurs through the
propagation of a single 90$^{\circ}$ magnetic domain wall separating the
perpendicular and in-plane anisotropy states. In the 5-repetition multilayer,
the modification leads to a doubling of the period of the magnetic domains at
remanence. These results demonstrate that the magneto-ionic control of the
anisotropy of a single magnetic layer can be used to control the magnetic
properties of coupled multilayer systems, extending beyond the gating effects
on a single magnetic layer.",2310.01623v1
2023/10/3,The effect of surface oxidation and crystal thickness on magnetic properties and magnetic domain structures of Cr2Ge2Te6,"Van der Waals (vdW) magnetic materials such as Cr2Ge2Te6 (CGT) show promise
for novel memory and logic applications. This is due to their broadly tunable
magnetic properties and the presence of topological magnetic features such as
skyrmionic bubbles. A systematic study of thickness and oxidation effects on
magnetic domain structures is important for designing devices and vdW
heterostructures for practical applications. Here, we investigate thickness
effects on magnetic properties, magnetic domains, and bubbles in
oxidation-controlled CGT crystals. We find that CGT exposed to ambient
conditions for 5 days forms an oxide layer approximately 5 nm thick. This
oxidation leads to a significant increase in the oxidation state of the Cr
ions, indicating a change in local magnetic properties. This is supported by
real space magnetic texture imaging through Lorentz transmission electron
microscopy. By comparing the thickness dependent saturation field of oxidized
and pristine crystals, we find that oxidation leads to a non-magnetic surface
layer which is thicker than the oxide layer alone. We also find that the stripe
domain width and skyrmionic bubble size are strongly affected by the crystal
thickness in pristine crystals. These findings underscore the impact of
thickness and surface oxidation on the properties of CGT such as saturation
field and domain/skyrmionic bubble size and suggest a pathway for manipulating
magnetic properties through a controlled oxidation process.",2310.02319v2
2023/12/4,Three-Dimensional Quantum Anomalous Hall Effect in Magnetic Topological Insulator Trilayers of Hundred-Nanometer Thickness,"Magnetic topological states refer to a class of exotic phases in magnetic
materials with their non-trivial topological property determined by magnetic
spin configurations. An example of such states is the quantum anomalous Hall
(QAH) state, which is a zero magnetic field manifestation of the quantum Hall
effect. Current research in this direction focuses on QAH insulators with a
thickness of less than 10nm. The thick QAH insulators in the
three-dimensional(3D) regime are limited, largely due to inevitable bulk
carriers being introduced in thick magnetic TI samples. Here, we employ
molecular beam epitaxy (MBE) to synthesize magnetic TI trilayers with a
thickness of up to ~106 nm. We find these samples exhibit well-quantized Hall
resistance and vanishing longitudinal resistance at zero magnetic field. By
varying magnetic dopants, gate voltages, temperature, and external magnetic
fields, we examine the properties of these thick QAH insulators and demonstrate
the robustness of the 3D QAH effect. The realization of the well-quantized 3D
QAH effect indicates that the nonchiral side surface states of our thick
magnetic TI trilayers are gapped and thus do not affect the QAH quantization.
The 3D QAH insulators of hundred-nanometer thickness provide a promising
platform for the exploration of fundamental physics, including axion physics
and image magnetic monopole, and the advancement of electronic and spintronic
devices to circumvent Moore's law.",2312.01614v2
2024/2/9,Ubiquitous order-disorder transition in the Mn antisite sublattice of the (MnBi$_2$Te$_4$)(Bi$_2$Te$_3$)$_n$ magnetic topological insulators,"Magnetic topological insulators (TIs) herald a wealth of applications in
spin-based technologies, relying on the novel quantum phenomena provided by
their topological properties. Particularly promising is the
(MnBi$_2$Te$_4$)(Bi$_2$Te$_3$)$_n$ layered family of established intrinsic
magnetic TIs that can flexibly realize various magnetic orders and topological
states. High tunability of this material platform is enabled by
manganese-pnictogen intermixing, whose amounts and distribution patterns are
controlled by synthetic conditions. Positive implication of the strong
intermixing in MnSb$_2$Te$_4$ is the interlayer exchange coupling switching
from antiferromagnetic to ferromagnetic, and the increasing magnetic critical
temperature. On the other side, intermixing also implies atomic disorder which
may be detrimental for applications. Here, we employ nuclear magnetic resonance
and muon spin spectroscopy, sensitive local probe techniques, to scrutinize the
impact of the intermixing on the magnetic properties of
(MnBi$_2$Te$_4$)(Bi$_2$Te$_3$)$_n$ and MnSb$_2$Te$_4$. Our measurements not
only confirm the opposite alignment between the Mn magnetic moments on native
sites and antisites in the ground state of MnSb$_2$Te$_4$, but for the first
time directly show the same alignment in (MnBi$_2$Te$_4$)(Bi$_2$Te$_3$)$_n$
with n = 0, 1 and 2. Moreover, for all compounds, we find the static magnetic
moment of the Mn antisite sublattice to disappear well below the intrinsic
magnetic transition temperature, leaving a homogeneous magnetic structure
undisturbed by the intermixing. Our findings provide a microscopic
understanding of the crucial role played by Mn-Bi intermixing in
(MnBi$_2$Te$_4$)(Bi$_2$Te$_3$)$_n$ and offer pathways to optimizing the
magnetic gap in its surface states.",2402.06340v1
1999/1/3,Disk-Anchored Magnetic Propellers - A Cure for the SW Sex Syndrome,"In AE Aqr, magnetic fields transfer energy and angular momentum from a
rapidly spinning white dwarf to material in the gas stream from the companion
star, with the effect of spinning down the white dwarf while flinging the gas
stream material out of the binary system. This magnetic propeller produces a
host of observable signatures, chief among which are broad single-peaked
flaring emission lines with phase-shifted orbital kinematics. SW Sex stars have
accretion disks, but also broad single-peaked phase-shifted emission lines
similar to those seen in AE Aqr. We propose that a magnetic propeller similar
to that which operates in AE Aqr is also at work in SW Sex stars -- and to some
extent in all nova-like systems. The propeller is anchored in the inner
accretion disk, rather than or in addition to the white dwarf. Energy and
angular momentum are thereby extracted from the inner disk and transferred to
gas stream material flowing above the disk, which is consequently pitched out
of the system. This provides a non-local dissipationless angular momentum
extraction mechanism, which should result in cool inner disks with temperature
profiles flatter than $T\propto R^{-3/4}$, as observed in eclipse mapping
studies of nova-like variables. The disk-anchored magnetic propeller model
appears to explain qualitatively most if not all of the peculiar features of
the SW Sex syndrome.",9901007v1
2008/1/29,Flux pinning and phase separation in oxygen rich La2-xSrxCuO4+y system,"We have studied the magnetic characteristics of a series of super-oxygenated
La2-xSrxCuO4+y samples. As shown in previous work, these samples spontaneously
phase separate into an oxygen rich superconducting phase with a TC near 40 K
and an oxygen poor magnetic phase that also orders near 40 K. All samples
studied are highly magnetically reversible even to low temperatures. Although
the internal magnetic regions of these samples might be expected to act as
pinning sites, our present study shows that they do not favor flux pinning.
Flux pinning requires a matching condition between the defect and the
superconducting coherence length. Thus, our results imply that the magnetic
regions are too large to act as pinning centers. This also implies that the
much greater flux pinning in typical La2-xSrxCuO4 materials is the result of
nanoscale inhomogeneities that grow to become the large magnetic regions in the
super-oxygenated materials. The superconducting regions of the phase separated
materials are in that sense cleaner and more homogenous than in the typical
cuprate superconductor.",0801.4580v1
2008/7/27,Do the Tellegen particles really exist in electromagnetics?,"In 1948 Tellegen suggested that an assembly of the lined up electric-magnetic
dipole twins can construct a new type of an electromagnetic material. Till now,
however, the problem of creation of the Tellegen medium is a subject of strong
discussions. An elementary symmetry analysis makes questionable an idea of a
simple combination of two (electric and magnetic) dipoles to realize local
materials with the Tellegen particles as structural elements. In this paper we
show that in his search of sources with local junctions of the electrical and
magnetic properties one cannot rely on the induced parameters of small
electromagnetic scatterers. No near-field electromagnetic structures and
classical motion equations for point charges give a physical basis to realize
sources with the local junction of the electrical and magnetic properties. We
advance a hypothesis that local magnetoelectric (ME) particles should be the
physical objects with eigenmode oscillation spectra and non-classical symmetry
breaking effects. Our studies convincingly prove this assumption. We show that
a quasi-2D ferrite disk with magnetic-dipolar-mode oscillations is
characterized by unique symmetry features with topological phases resulting in
appearance of the ME properties. The entire ferrite disk can be characterized
as a combined system with eigen electric and magnetic moments. The fields near
such a particle are distinguished by special symmetry properties.",0807.4280v1
2008/7/30,Coexistence of static magnetism and superconductivity in SmFeAsO1-xFx as revealed by muon spin rotation,"The recent observation of superconductivity with critical temperatures up to
55 K in the FeAs based pnictide compounds marks the first discovery of a non
copper-oxide based layered high-Tc superconductor (HTSC) [1-3]. It has raised
the suspicion that these new materials share a similar pairing mechanism to the
cuprates, since both exhibit superconductivity following charge doping of a
magnetic parent material. Here we present a muon spin rotation study on
SmFeAsO1-xFx (x=0-0.30), which shows that static magnetism persists well into
the superconducting regime. The analogy with the cuprates is quite surprising
since the parent compounds appear to have different magnetic ground states:
itinerant spin density wave for the pnictides contrasted with the Mott-Hubbard
insulator in the cuprates. Our findings suggest that proximity to magnetic
order and associated soft magnetic fluctuations, rather than the strong
electronic correlations in the vicinity of a Mott-Hubbard-metal-to-insulator
transition, may be the key ingredients of HTSC.",0807.4876v2
2009/6/29,A novel wear-resistant magnetic thin film material based on a $Ti_{1-x}Fe_xC_{1-y}$ nanocomposite alloy,"In this study we report on the film growth and characterization of thin
(approximately 50 nm thick) Ti-Fe-C films deposited on amorphous quartz. The
experimental studies have been complemented by first principles density
functional theory (DFT) calculations. Upon annealing of as-prepared films, the
composition of the metastable Ti-Fe-C film changes. An iron-rich phase is first
formed close to the film surface, but with increasing annealing time this phase
is gradually displaced toward the film-substrate interface where its position
stabilizes. Both the magnetic ordering temperature and the saturation
magnetization changes significantly upon annealing. The DFT calculations show
that the critical temperature and the magnetic moment both increase with
increasing Fe and C-vacancy concentration. The formation of the metastable
iron-rich Ti-Fe-C compound is reflected in the strong increase of the magnetic
ordering temperature. Eventually, after enough annealing time ($\geq 10$
minutes), nano-crystalline $\alpha$-Fe starts to precipitate and the amount and
size of these precipitates can be controlled by the annealing procedure; after
20 minutes of annealing, the experimental results indicate a nano-crystalline
iron-film embedded in a wear resistant TiC compound. This conclusion is further
supported by transmission electron microscopy studies on epitaxial Ti-Fe-C
films deposited on single crystalline MgO substrates where, upon annealing, an
iron film embedded in TiC is formed. Our results suggest that annealing of
metastable Ti-Fe-C films can be used as an efficient way of creating a
wear-resistant magnetic thin film material.",0906.5386v1
2009/7/21,Ferromagnetic transition metal implanted ZnO: a diluted magnetic semiconductor?,"Recently theoretical works predict that some semiconductors (e.g. ZnO) doped
with magnetic ions are diluted magnetic semiconductors (DMS). In DMS magnetic
ions substitute cation sites of the host semiconductor and are coupled by free
carriers resulting in ferromagnetism. One of the main obstacles in creating DMS
materials is the formation of secondary phases because of the solid-solubility
limit of magnetic ions in semiconductor host. In our study transition metal
ions were implanted into ZnO single crystals with the peak concentrations of
0.5-10 at.%. We established a correlation between structural and magnetic
properties. By synchrotron radiation X-ray diffraction (XRD) secondary phases
(Fe, Ni, Co and ferrite nanocrystals) were observed and have been identified as
the source for ferromagnetism. Due to their different crystallographic
orientation with respect to the host crystal these nanocrystals in some cases
are very difficult to be detected by a simple Bragg-Brentano scan. This results
in the pitfall of using XRD to exclude secondary phase formation in DMS
materials. For comparison, the solubility of Co diluted in ZnO films ranges
between 10 and 40 at.% using different growth conditions pulsed laser
deposition. Such diluted, Co-doped ZnO films show paramagnetic behaviour.
However, only the magnetoresistance of Co-doped ZnO films reveals possible s-d
exchange interaction as compared to Co-implanted ZnO single crystals.",0907.3536v1
2010/2/12,Magnetic materials and the problem of thermal Casimir force,"We investigate the thermal Casimir interaction between two magnetodielectric
plates made of real materials. On the basis of the Lifshitz theory, it is shown
that for diamagnets and for paramagnets in the broad sense (with exception of
ferromagnets) the magnetic properties do not influence the magnitude of the
Casimir force. For ferromagnets, taking into account the realistic dependence
of magnetic permeability on frequency, we conclude that the impact of magnetic
properties on the Casimir interaction arises entirely from the contribution of
the zero-frequency term in the Lifshitz formula. The computations of the
Casimir free energy and pressure are performed for the configurations of two
plates made of ferromagnetic metals (Co and Fe), for one plate made of
ferromagnetic metal and the other of nonmagnetic metal (Au), for two
ferromagnetic dielectric plates (on the basis of polystyrene), and for a
ferromagnetic dielectric plate near a nonmagnetic metal plate. The dielectric
permittivity of metals is described using both the Drude and the plasma model
approaches. It is shown that the Casimir repulsion through the vacuum gap can
be realized in the configuration of a ferromagnetic dielectric plate near a
nonmagnetic metal plate described by the plasma model. In all cases considered,
the respective analytical results in the asymptotic limit of large separations
between the plates are obtained. The impact of the magnetic phase transition
through the Curie temperature on the Casimir interaction is considered. In
conclusion, we propose several experiments allowing to determine whether the
magnetic properties really influence the Casimir interaction and to
independently verify the Drude and plasma model approaches to the thermal
Casimir force.",1002.2484v1
2010/11/20,Depairing critical current achieved in superconducting thin films with through-thickness arrays of artificial pinning centers,"Large area arrays of through-thickness nanoscale pores have been milled into
superconducting Nb thin films via a process utilizing anodized aluminum oxide
thin film templates. These pores act as artificial flux pinning centers,
increasing the superconducting critical current, Jc, of the Nb films. By
optimizing the process conditions including anodization time, pore size and
milling time, Jc values approaching and in some cases matching the
Ginzburg-Landau depairing current of 30 MA/cm^2 at 5 K have been achieved - a
Jc enhancement over as-deposited films of more than 50 times. In the field
dependence of Jc, a matching field corresponding to the areal pore density has
also been clearly observed. The effect of back-filling the pores with magnetic
material has then been investigated. While back-filling with Co has been
successfully achieved, the effect of the magnetic material on Jc has been found
to be largely detrimental compared to voids, although a distinct influence of
the magnetic material in producing a hysteretic Jc versus applied field
behavior has been observed. This behavior has been tested for compatibility
with currently proposed models of magnetic pinning and found to be most closely
explained by a model describing the magnetic attraction between the flux
vortices and the magnetic inclusions.",1011.4599v2
2012/11/2,Direct Observation of Giant Saturation Magnetization in Fe16N2,"Magnetic materials with giant saturation magnetization have been a holy grail
for magnetic researchers and condensed matter physicists for decades because of
its great scientific and technological impacts. As described by the famous
Slater-Pauling curve the material with highest Ms is the Fe65Co35 alloy. This
was challenged in 1972 by a report on the compound Fe16N2 with Ms much higher
than that of Fe65Co35. Following this claim, there have been enormous efforts
to reproduce this result and to understand the magnetism of this compound.
However, the reported Ms by different groups cover a broad range, mainly due to
the unavailability of directly assessing Ms in Fe16N2. In this article, we
report a direct observation of the giant saturation magnetization up to 2500
emu/cm3 using polarized neutron reflectometry (PNR) in epitaxial constrained
Fe16N2 thin films prepared using a low-energy and surface-plasma-free
sputtering process. The observed giant Ms is corroborated by a previously
proposed Cluster + Atom model, the characteristic feature of which, namely, the
directional charge transfer is evidenced by polarization-dependent x-ray
absorption near edge spectroscopy (XANES).",1211.0553v1
2013/7/23,Study of the flux effect on nuclear pressure vessel steel by measurement of magnetic properties,"Since Reactor Pressure Vessel steels are ferromagnetic, they provide a
convenient means to monitor changes in the mechanical properties of the
material upon irradiation with high energy particles, by measuring their
magnetic properties. Here, we discuss the correlation between these two
properties (i.e. mechanical and magnetic properties) and microstructure, by
studying the flux effect on the nuclear pressure vessel steel used in reactors
currently under construction in Argentina. Charpy-V notched specimens of this
steel were irradiated in the RA1 experimental reactor at 275{\deg}C with two
lead factors (LFs), 93 and 183. The magnetic properties were studied by means
of DC magnetometry and ferromagnetic resonance. The results show that the
coercive field and magnetic anisotropy spatial distribution are sensitive to
the LF and can be explained by taking into account the evolution of the
microstructure with this parameter. The saturation magnetization shows a
dominant dependence on the accumulated damage. Consequently, the mentioned
techniques are suitable to estimate the degradation of the reactor vessel
steel.",1307.6124v2
2013/9/16,Anomalous Hall effect arising from noncollinear antiferromagnetism,"In most conductors current flow perpendicular to electric field direction
(Hall current) can be explained in terms of the Lorentz forces present when
charged particles flow in an external magnetic field. However, as established
in the very early work of Edwin Hall, ferromagnetic conductors such as Fe, Co,
and Ni have an anomalous Hall conductivity contribution that cannot be
attributed to Lorentz forces and therefore survives in the absence of a
magnetic field. Although the anomalous Hall effect is experimentally strong, it
has stood alone among metallic transport effects for much of the last century
because it lacked a usefully predictive, generally accepted theory. Progress
over the past decade has explained why. It is now clear that the anomalous Hall
effect in ferromagnets has contributions from both extrinsic scattering
mechanisms similar to those that determine most transport coefficients, and
from an intrinsic mechanism that is independent of scattering. The anomalous
Hall effect is also observed in paramagnets, which have nonzero magnetization
induced by an external magnetic field. Although no explicit relationship has
been established, the anomalous Hall effect in a particular material is usually
assumed to be proportional to its magnetization. In this work we point out that
it is possible to have an anomalous Hall effect in a noncollinear
antiferromagnet with zero net magnetization provided that certain common
symmetries are absent, and predict that Mn3Ir, a technologically important
antiferromagnetic material with noncollinear order that survives to very high
temperatures, has a surprisingly large anomalous Hall effect comparable in size
to those of the elemental transition metal ferromagnets.",1309.4041v1
2014/6/28,Disorder in a Quantum Critical Superconductor,"In four classes of materials, the layered copper-oxides, organics,
iron-pnictides and heavy-fermion compounds, an unconventional superconducting
state emerges as a magnetic transition is tuned toward absolute zero
temperature, that is, toward a magnetic quantum-critical point (QCP). In most
materials, the QCP is accessed by chemical substitutions or applied pressure.
CeCoIn5 is one of the few materials that are born as a quantum-critical
superconductor and, therefore, offers the opportunity to explore the
consequences of chemical disorder. Cadmium-doped crystals of CeCoIn5 are a
particularly interesting case where Cd substitution induces long-range magnetic
order, as in Zn-doped copper-oxides. Applied pressure globally supresses the
Cd-induced magnetic order and restores bulk superconductivity. Here we show,
however, that local magnetic correlations, whose spatial extent decreases with
applied pressure, persist at the extrapolated QCP. The residual droplets of
impurity-induced magnetic moments prevent the reappearance of conventional
signatures of quantum criticality, but induce a heterogeneous electronic state.
These discoveries show that spin droplets can be a source of electronic
heterogeneity in classes of strongly correlated electron systems and emphasize
the need for caution when interpreting the effects of tuning a correlated
system by chemical substitution.",1406.7370v1
2015/12/7,Insulating phase in Sr$_2$IrO$_4$: An investigation using critical analysis and magnetocaloric effect,"The nature of insulating phase in 5$d$ based Sr$_2$IrO$_4$ is quite debated
as the theoretical as well as experimental investigations have put forward
evidences in favor of both magnetically driven Slater-type and interaction
driven Mott-type insulator. To understand this insulating behavior, we have
investigated the nature of magnetic state in Sr$_2$IrO$_4$ through studying
critical exponents, low temperature thermal demagnetization and magnetocaloric
effect. The estimated critical exponents do not exactly match with any
universality class, however, the values obey the scaling behavior. The exponent
values suggest that spin interaction in present material is close to mean-field
model. The analysis of low temperature thermal demagnetization data, however,
shows dual presence of localized- and itinerant-type of magnetic interaction.
Moreover, field dependent change in magnetic entropy indicates magnetic
interaction is close to mean-field type. While this material shows an
insulating behavior across the magnetic transition, yet a distinct change in
slope in resistivity is observed around $T_c$. We infer that though the
insulating phase in Sr$_2$IrO$_4$ more close to be Slater-type but the
simultaneous presence of both Slater- and Mott-type is the likely scenario for
this material.",1512.02041v1
2016/1/25,"Synthesis, crystal structure, and magnetic properties of RE3Sb3Mg2O14 (RE=La, Pr, Sm, Eu, Tb, Ho): new 2D Kagome materials","We present the crystal structures and magnetic properties of RE3Sb3Mg2O14
(La3Sb3Mg2O14, Pr3Sb3Mg2O14, Sm3Sb3Mg2O14, Eu3Sb3Mg2O14, Tb3Sb3Mg2O14, and
Ho3Sb3Mg2O14), a family of novel materials based on a perfect geometry 2D rare
earth Kagome lattice. Structure refinements were performed by the Rietveld
method using X-ray diffraction data, indicating that the layered compounds are
fully structurally ordered. The compounds crystallize in a rhombohedral
supercell of the cubic pyrochlore structure, in the space group R-3m. As
indicated by magnetic susceptibility measurements, they exhibit predominantly
antiferromagnetic interactions between rare earth moments. Except for possibly
Pr3Sb3Mg2O14 and Eu3Sb3Mg2O14, none of the compounds show any signs of magnetic
ordering above 2 K. This RE3Sb3Mg2O14 family of compounds is similar to that of
RE3Sb3Zn2O14, except the series reported here features a fully ordered
distribution of cations in both the nonmagnetic antimony and magnesium sites
and the magnetic rare earth kagome sites. The compounds appear to be relatively
defect-free and are therefore model systems for investigating magnetic
frustration on an ideal 2D rare earth Kagome lattice.",1601.06639v2
2016/7/29,"A rock-salt type Li-based oxide, Li3Ni2RuO6, exhibiting a chaotic ferrimagnetism with cluster spin-glass dynamics and thermally frozen charge carriers","The area of research to discover new Li containing materials and to
understand their physical properties has been of constant interest due to
applications potential for rechargeable batteries. Here, we present the results
of magnetic investigations on a Li compound, Li3Ni2RuO6, which was believed to
be a ferrimagnet below 80K. While our neutron diffraction (ND) and isothermal
magnetization (M) data support ferrimagnetism, more detailed magnetic studies
establish that this ferrimagnetic phase exhibits some features similar to
spin-glasses. In addition, we find another broad magnetic anomaly around 40-55
K in magnetic susceptibility, attributable to cluster spin-glass phenomenon.
Gradual dominance of cluster spin-glass dynamics with a decrease of temperature
(T) and the apparent spread in freezing temperature suggest that the
ferrimagnetism of this compound is a chaotic one. The absence of a unique
freezing temperature for a crystalline material is interesting. In addition,
pyroelectric current data reveals a feature in the range 40-50 K, attributable
to thermally stimulated depolarization current. We hope this finding motivates
future work to explore whether there is any intriguing correlation of such a
feature with spin-glass dynamics. We attribute these magnetic and electric
dipole anomalies to the crystallographic disorder intrinsic to this compound.",1607.08689v1
2016/8/3,Tailoring magnetic energies to form dipole skyrmions and skyrmion lattices,"The interesting physics and potential memory technologies resulting from
topologically protected spin textures such as skyrmions, has prompted efforts
to discover new material systems that can host these kind of magnetic
structures. Here we use the highly tunable magnetic properties of amorphous
Fe/Gd multilayer films to explore the magnetic properties that lead to
dipole-stabilized skyrmions and skyrmion lattices that form from the
competition of dipolar field and exchange energy. Using both real space imaging
and reciprocal space scattering techniques we determined the range of material
properties and magnetic fields where skyrmions form. Micromagnetic modeling
closely matches our observation of small skyrmion features (~50 to 70nm) and
suggests these class of skyrmions have a rich domain structure that is Bloch
like in the center of the film and more N\'eel like towards each surface. Our
results provide a pathway to engineer the formation and controllability of
dipole skyrmion phases in a thin film geometry at different temperatures and
magnetic fields.",1608.01368v2
2016/10/3,Multiferroic magnetic spirals induced by random magnetic exchanges,"Multiferroism can originate from the breaking of inversion symmetry caused by
magnetic-spiral order. The usual mechanism for stabilizing a magnetic spiral is
competition between magnetic exchange interactions differing by their range and
sign, such as nearest-neighbor and next-nearest- neighbor interactions. Since
the latter are usually weak the onset temperatures for multiferroism via this
mechanism are typically low. By considering a realistic model for YBaCuFeO$_5$
we propose an alternative mechanism for magnetic-spiral order, and hence for
multiferroism, that occurs at much higher temperatures. We show using
Monte-Carlo simulations and electronic structure calculations based on density
functional theory that the Heisenberg model on a geometrically non-frustrated
lattice with only nearest-neighbor interactions can have a spiral phase up to
high temperature when frustrating bonds are introduced randomly along a single
crystallographic direction as caused, e.g., by a particular type of chemical
disorder. This long-range correlated pattern of frustration avoids
ferroelectrically inactive spin glass order. Finally, we provide an intuitive
explanation for this mechanism and discuss its generalization to other
materials.",1610.00783v3
2016/10/25,Strong modulation of spin currents in bilayer graphene by static and fluctuating proximity exchange fields,"Two dimensional (2D) materials provide a unique platform to explore the full
potential of magnetic proximity driven phenomena, which can be further used for
applications in next generation spintronic devices. Of particular interest is
to understand and control spin currents in graphene by the magnetic exchange
field of a nearby ferromagnetic material in graphene/ferromagnetic-insulator
(FMI) heterostructures. Here, we present the experimental study showing the
strong modulation of spin currents in graphene layers by controlling the
direction of the exchange field due to FMI magnetization. Owing to clean
interfaces, a strong magnetic exchange coupling leads to the experimental
observation of complete spin modulation at low externally applied magnetic
fields in short graphene channels. Additionally, we discover that the graphene
spin current can be fully dephased by randomly fluctuating exchange fields.
This is manifested as an unusually strong temperature dependence of the
non-local spin signals in graphene, which is due to spin relaxation by
thermally-induced transverse fluctuations of the FMI magnetization.",1610.08017v3
2016/10/28,"Electronic structure, magnetism, and optical properties of orthorhombic GdFeO3 from first principles","Orthorhombic GdFeO$_3$ has attracted considerable attention in recent years
because its magnetic structure is similar to that in the well-known BiFeO$_3$
material. We investigate electronic structure, magnetism, and optical
properties of the orthorhombic GdFeO$_3$ in terms of density-functional-theory
calculations. The modified Becke-Johnson (mBJ) exchange potential is adopted to
improve on the description of the electronic structure. Our calculation show
that the G-type antiferromagnetic (G-AFM ordering of Fe spins) phase of
orthorhombic GdFeO$_3$ is stable compared to other magnetic phases. The
semiconductor gap calculated with mBJ, substantially larger than that with GGA,
is in good agreement with recent experimental values. Besides, we also
investigate effect of the spin-orbit coupling on the electronic structure, and
calculate with mBJ the complex dielectric functions and other optical functions
of photon energy. The magnetic exchange interactions are also investigated,
which gives a Neel temperature close to experimental observation. For
comparison towards supporting our results, we study the electronic structure of
rhombohedral (R3c) BiFeO$_3$ with mBJ. These lead to a satisfactory theoretical
understanding of the electronic structure, magnetism, and optical properties of
orthorhombic GdFeO$_3$ and can help elucidate electronic structures and optical
properties of other similar materials.",1610.09172v1
2017/7/22,Electronic and magnetic properties of the monolayer RuCl$_3$: A first-principles and Monte Carlo study,"Recent experiments revealed that monolayer $\alpha$-RuCl$_3$ can be obtain by
chemical exfoliation method and exfoliation or restacking of nanosheets can
manipulate the magnetic properties of the materials. In this present paper, the
electronic and magnetic properties of $\alpha$-RuCl$_3$ monolayer are
investigated by combining first-principles calculations and Monte Carlo
simulations. From first-principles calculations, we found that the spin
configuration FM corresponds to the ground state for $\alpha$-RuCl$_3$,
however, the other excited zigzag oriented spin configuration has energy of 5
meV/atom higher than the ground state. Energy band gap has been obtained as $3$
meV using PBE functionals. When spin-orbit coupling effect is taken into
account, corresponding energy gap is determined to be as $57$ meV. We also
investigate the effect of Hubbard U energy terms on the electronic band
structure of $\alpha$-RuCl$_3$ monolayer and revealed band gap increases
approximately linear with increasing U value. Moreover, spin-spin coupling
terms ($J_1$, $J_2$, $J_3$) have been obtained using first principles
calculations. By benefiting from these terms, Monte Carlo simulations with
single site update Metropolis algorithm have been implemented to elucidate
magnetic properties of the considered system. Thermal variations of
magnetization, susceptibility and also specific heat curves indicate that
monolayer $\alpha$-RuCl$_3$ exhibits a phase transition between ordered and
disordered phases at the Curie temperature $14.21$ K. We believe that this
study can be utilized to improve two-dimensional magnet materials.",1707.07198v2
2017/8/17,Tailoring tricolor structure of magnetic topological insulator for robust axion insulator,"Exploration of novel electromagnetic phenomena is a subject of great interest
in topological quantum materials. One of the unprecedented effects to be
experimentally verified is topological magnetoelectric (TME) effect originating
from an unusual coupling of electric and magnetic fields in materials. A
magnetic heterostructure of topological insulator (TI) hosts such an exotic
magnetoelectric coupling and can be expected to realize the TME effect as an
axion insulator. Here we designed a magnetic TI with tricolor structure where a
non-magnetic layer of (Bi, Sb)2Te3 is sandwiched by a soft ferromagnetic
Cr-doped (Bi, Sb)2Te3 and a hard ferromagnetic V-doped (Bi, Sb)2Te3.
Accompanied by the quantum anomalous Hall (QAH) effect, we observe zero Hall
conductivity plateaus, which are a hallmark of the axion insulator state, in a
wide range of magnetic field between the coercive fields of Cr- and V-doped
layers. The resistance of the axion insulator state reaches as high as 10^9
ohm, leading to a gigantic magnetoresistance ratio exceeding 10,000,000% upon
the transition from the QAH state. The tricolor structure of TI may not only be
an ideal arena for the topologically distinct phenomena, but also provide
magnetoresistive applications for advancing dissipationless topological
electronics.",1708.05387v1
2017/12/19,Revealing the nature of the ultrafast magnetic phase transition in Ni by correlating extreme ultraviolet magneto-optic and photoemission spectroscopies,"By correlating time- and angle-resolved photoemission and time-resolved
transverse- magneto- optical Kerr effect measurements, both at extreme
ultraviolet wavelengths, we uncover the universal nature of the ultrafast
photoinduced magnetic phase transition in Ni. This allows us to explain the
ultrafast magnetic response of Ni at all laser fluences - from a small
reduction of the magnetization at low laser fluences, to complete quenching at
high laser fluences. Both probe methods exhibit the same demagnetization and
recovery timescales. We further show that the ultrafast demagnetization in Ni
is indeed a magnetic phase transition that is launched within 20 fs, followed
by demagnetization of the material within ~200 fs, and subsequent recovery of
the magnetization on timescales ranging from 500 fs to >70 ps. We also provide
evidence of two competing channels with two distinct timescales in the recovery
process, that suggest the presence of coexisting phases in the material.",1712.07085v2
2018/2/3,First-principles theory of magnetic multipoles in condensed matter systems,"The multipole concept, which characterizes the spacial distribution of scalar
and vector objects by their angular dependence, has already become widely used
in various areas of physics. In recent years it has become employed to
systematically classify the anisotropic distribution of electrons and
magnetization around atoms in solid state materials. This has been fuelled by
the discovery of several physical phenomena that exhibit unusual higher rank
multipole moments, beyond that of the conventional degrees of freedom as charge
and magnetic dipole moment. Moreover, the higher rank electric/magnetic
multipole moments have been suggested as promising order parameters in exotic
hidden order phases. While the experimental investigations of such anomalous
phases have provided encouraging observations of multipolar order, theoretical
approaches have developed at a slower pace. In particular, a materials'
specific theory has been missing. The multipole concept has furthermore been
recognized as the key quantity which characterizes the resultant configuration
of magnetic moments in a cluster of atomic moments. This cluster multipole
moment has then been introduced as macroscopic order parameter for a
noncollinear antiferromagnetic structure in crystals that can explain unusual
physical phenomena whose appearance is determined by the magnetic point group
symmetry. It is the purpose of this review to discuss the recent developments
in the first-principles theory investigating multipolar degrees of freedom in
condensed matter systems. These recent developments exemplify that ab initio
electronic structure calculations can unveil detailed insight in the mechanism
of physical phenomena caused by the unconventional, multipole degree of
freedom.",1802.00925v1
2018/6/14,Tunneling spin valves based on Fe$_3$GeTe$_2$/hBN/Fe$_3$GeTe$_2$ van der Waals heterostructures,"Thin van der Waals (vdW) layered magnetic materials disclose the possibility
to realize vdW heterostructures with new functionalities. Here we report on the
realization and investigation of tunneling spin valves based on van der Waals
heterostructures consisting of an atomically thin hBN layer acting as tunnel
barrier and two exfoliated Fe3GeTe2 crystals acting as ferromagnetic
electrodes. Low-temperature anomalous Hall effect measurements show that thin
Fe3GeTe2 crystals are metallic ferromagnets with an easy axis perpendicular to
the layers, and a very sharp magnetization switching at magnetic field values
that depend slightly on their geometry. In Fe3GeTe2/hBN/Fe3GeTe2
heterostructures, we observe a textbook behavior of the tunneling resistance,
which is minimum (maximum) when the magnetization in the two electrodes is
parallel (antiparallel) to each other. The magnetoresistance is 160% at low
temperature, from which we determine the spin polarization of Fe3GeTe2 to be
0.66, corresponding to 83% and 17% of majority and minority carriers,
respectively. The measurements also show that, with increasing temperature, the
evolution of the spin polarization extracted from the tunneling
magnetoresistance is proportional to the temperature dependence of the
magnetization extracted from the analysis of the anomalous Hall conductivity.
This suggests that the magnetic properties of the surface are representative of
those of the bulk, as it may be expected for vdW materials.",1806.05411v1
2018/8/7,On the possibility of magnetic Weyl fermions in non-symmorphic compound PtFeSb,"Weyl fermions are expected to exhibit exotic physical properties such as the
chiral anomaly, large negative magnetoresistance or Fermi arcs. Recently a new
platform to realize these fermions has been introduced based on the appearance
of a three-fold band crossing at high symmetry points of certain space groups.
These band crossings are composed of two linearly dispersed bands that are
topologically protected by a Chern number, and a at band with no topological
charge. In this paper we present a new way of inducing two kinds of Weyl
fermions, based on two- and three-fold band crossings, in the non-symmorphic
magnetic material PtFeSb. By means of density functional theory calculations
and group theory analysis we show that magnetic order can split a six-fold
degeneracy enforced by non-symmoprhic symmetry to create three-fold or two-fold
degenerate Weyl nodes. We also report on the synthesis of a related phase
potentially containing two-fold degenerate magnetic Weyl points and extend our
group theory analysis to that phase. This is the first study showing that
magnetic ordering has the potential to generate new threefold degenerate Weyl
nodes, advancing the understanding of magnetic interactions in topological
materials.",1808.02460v1
2018/10/17,Precipitating Ordered Skyrmion Lattices from Helical Spaghetti,"Magnetic skyrmions have been the focus of intense research due to their
potential applications in ultra-high density data and logic technologies, as
well as for the unique physics arising from their antisymmetric exchange term
and topological protections. In this work we prepare a chiral jammed state in
chemically disordered (Fe, Co)Si consisting of a combination of
randomly-oriented magnetic helices, labyrinth domains, rotationally disordered
skyrmion lattices and/or isolated skyrmions. Using small angle neutron
scattering, (SANS) we demonstrate a symmetry-breaking magnetic field sequence
which disentangles the jammed state, resulting in an ordered, oriented skyrmion
lattice. The same field sequence was performed on a sample of powdered Cu2OSeO3
and again yields an ordered, oriented skyrmion lattice, despite relatively
non-interacting nature of the grains. Micromagnetic simulations confirm the
promotion of a preferred skyrmion lattice orientation after field treatment,
independent of the initial configuration, suggesting this effect may be
universally applicable. Energetics extracted from the simulations suggest that
approaching a magnetic hard axis causes the moments to diverge away from the
magnetic field, increasing the Dzyaloshinskii-Moriya energy, followed
subsequently by a lattice re-orientation. The ability to facilitate an emergent
ordered magnetic lattice with long-range orientation in a variety of materials
despite overwhelming internal disorder enables the study of skyrmions even in
imperfect powdered or polycrystalline systems and greatly improves the ability
to rapidly screen candidate skyrmion materials.",1810.07631v1
2018/12/1,Rectification in Spin-Orbit Materials Using Low Energy Barrier Magnets,"The coupling of spin-orbit materials to high energy barrier ($\sim$40-60
$k_BT$) nano-magnets has attracted growing interest for exciting new physics
and various spintronic applications. We predict that a coupling between the
spin-momentum locking (SML) observed in spin-orbit materials and low-energy
barrier magnets (LBM) should exhibit a unique multi-terminal rectification for
arbitrarily small amplitude channel currents. The basic idea is to measure the
charge current induced spin accumulation in the SML channel in the form of a
magnetization dependent voltage using an LBM, either with an in-plane or
perpendicular anisotropy (IMA or PMA). The LBM feels an instantaneous
spin-orbit torque due to the accumulated spins in the channel which causes the
average magnetization to follow the current, leading to the non-linear
rectification. We discuss the frequency band of this multi-terminal
rectification which can be understood in terms of the angular momentum
conservation in the LBM. For a fixed spin-current from the SML channel, the
frequency band is same for LBMs with IMA and PMA, as long as they have the same
total magnetic moment in a given volume. The proposed all-metallic structure
could find application as highly sensitive passive rf detectors and as energy
harvesters from weak ambient sources where standard technologies may not
operate.",1812.00286v2
2018/12/24,Strain Controlled Magnetic and Optical Properties of Monolayer 2H-TaSe$_2$,"First-principles calculations are used to probe the effects of mechanical
strain on the magnetic and optical properties of monolayer (ML) 2H-TaSe$_2$. A
complex dependence of these physical properties on strain results in unexpected
behavior, such as ferromagnetism under uniaxial, in-plane, tensile strain and a
lifting of the Raman-active E' phonon degeneracy. While ferromagnetism is
observed under compression along x-axis and expansion along y-axis, no magnetic
order occurs when interchanging the strain direction. The calculations show
that the magnetic behavior of the system depends on the exchange within the 5d
orbitals of the Ta atoms. The magnetic moment per Ta atom persists even when an
additional compressive strain along the z-axis is added to a biaxially-strained
ML, which suggests stability of the magnetic order. Exploring the effects of
this mechanical strain on the Raman-active phonon modes, we find that the E$^""$
and E' modes are red-shifted due to Ta-Se bond elongation, and that strain
lifts the E' mode degeneracy, except for the symmetrical biaxial tensile case.
Our results demonstrate the possibility of tuning the properties of
2D-materials for nanoelectronic applications through strain.",1812.09829v1
2019/8/7,A nano-carbon route to rare earth free permanent magnetism,"High coercivity magnets are an important resource for renewable energy,
electric vehicles and memory technologies. Most hard magnetic materials
incorporate rare-earths such as neodymium and samarium, but the concerns about
the environmental impact and supply stability of these materials is prompting
research into alternatives. Here, we present a hybrid bilayer of cobalt and the
nano-carbon molecule C60 which exhibits significantly enhanced coercivity with
minimal reduction in magnetisation. We demonstrate how this anisotropy
enhancing effect cannot be described by existing models of molecule-metal
magnetic interfaces. We outline a new form of magnetic anisotropy, arising from
asymmetric magneto-electric coupling in the metal-molecule interface. Because
this phenomenon arises from pi-d hybrid orbitals, we propose calling this
effect pi-anisotropy. While the critical temperature of this effect is
currently limited by the rotational degree of freedom of the chosen molecule,
C60, we describe how surface functionalisation would allow for the design of
room-temperature, carbon based hard magnetic films.",1908.02544v3
2019/9/26,Electrical manipulation of magnetic anisotropy in a Fe$_{81}$Ga$_{19}$/PMN-PZT magnetoelectric multiferroic composite,"Magnetoelectric composites are an important class of multiferroic materials
that pave the way towards a new generation of multifunctional devices directly
integrable in data storage technology and spintronics. This study focuses on
strain-mediated electrical manipulation of magnetization in an extrinsic
multiferroic. The composite includes 5 nm or 60 nm Fe$_{81}$Ga$_{19}$ thin
films coupled to a piezoelectric (011)-PMN-PZT. The magnetization reversal
study reveals a converse magnetoelectric coefficient $\alpha_\mathrm{CME,max}
\approx 2.7 \times {10^{-6}}$ s.m$^{-1}$ at room temperature. This reported
value of $\alpha_\mathrm{CME}$ is among the highest so far compared to previous
reports of single-phase multiferroics as well as composites. An angular
dependency of $\alpha_\mathrm{CME}$ is also shown for the first time, arising
from the intrinsic magnetic anisotropy of FeGa. The highly efficient
magnetoelectric composite FeGa/PMN-PZT demonstrates drastic modifications of
the in-plane magnetic anisotropy, with an almost 90$^{\circ}$ rotation of the
preferential anisotropy axis in the thinner films under an electric field E =
10.8 kV.cm$^{-1}$. Also, the influence of thermal strain on the bilayer's
magnetic coercivity is compared to that of a reference bilayer FeGa/Glass at
cryogenic temperatures. A different evolution is observed as a function of
temperature, revealing a substrate thermo-mechanical influence which has not
yet been reported in FeGa thin films coupled to a piezoelectric material.",1909.12431v1
2019/11/27,Spin flop and crystalline anisotropic magnetoresistance in CuMnAs,"Recent research works have shown that the magnetic order in some
antiferromagnetic materials can be manipulated and detected electrically, due
to two physical mechanisms: Neel-order spin-orbit torques and anisotropic
magnetoresistance. While these observations open up opportunities to use
antiferromagnets for magnetic memory devices, different physical
characterization methods are required for a better understanding of those
mechanisms. Here we report a magnetic field induced rotation of the
antiferromagnetic Neel vector in epitaxial tetragonal CuMnAs thin films. Using
soft x-ray magnetic linear dichroism spectroscopy, x-ray photoemission electron
microscopy, integral magnetometry and magneto-transport methods, we demonstrate
spin-flop switching and continuous spin reorientation in antiferromagnetic
films with uniaxial and biaxial magnetic anisotropies, respectively. From
field-dependent measurements of the magnetization and magnetoresistance, we
obtain key material parameters including the anisotropic magnetoresistance
coefficients, magnetocrystalline anisotropy, spin-flop and exchange fields.",1911.12381v2
2019/12/24,Observation of Magnetic Skyrmion Bubbles in a van der Waals ferromagnet Fe3GeTe2,"Two-dimensional (2D) van der Waals (vdW) magnetic materials have recently
been introduced as a new horizon in materials science and enable the potential
applications for next-generation spintronic devices. Here, in this
communication, the observations of stable Bloch-type magnetic skyrmions in
single crystals of 2D vdW Fe3GeTe2 (FGT) are reported by using in-situ Lorentz
transmission electron microscopy (TEM). We find the ground-state magnetic
stripe domains in FGT transform into skyrmion bubbles when an external magnetic
field is applied perpendicularly to the (001) thin plate with temperatures
below the Curie-temperature TC. Most interestingly, a hexagonal lattice of
skyrmion bubbles is obtained via field cooling manipulation with magnetic field
applied along the [001] direction. Owing to their topological stability, the
skyrmion bubble lattices are stable to large field-cooling tilted angles and
further reproduced by utilizing the micromagnetic simulations. These
observations directly demonstrate that the 2D vdW FGT possesses a rich variety
of topological spin textures, being of a great promise candidate for future
applications in the field of spintronics.",1912.11228v1
2020/1/9,Antiferromagnetic and Electric Polarized States in Two-Dimensional Janus Semiconductor Fe2Cl3I3,"Two-dimensional (2D) Janus semiconductors with mirror asymmetry can introduce
novel properties, such as large spin-orbit coupling (SOC) and normal
piezoelectric polarization, which have attracted a great interest for their
potential applications. Inspired by the recently fabricated 2D ferromagnetic
(FM) semiconductor CrI3, a stable 2D (in x-y plane) antiferromagnetic (AFM)
Janus semiconductor Fe2Cl3I3 with normal sublattice magnetization (m//z) is
obtained by density functional theory calculations. By applying a tensile
strain, the four magnetic states sequentially occur: AFM with m//z of
sublattice, AFM with m//xy of sublattice, FM with m//xy, and FM with m//z. Such
novel magnetic phase diagram driven by strain can be well understood by the
spin-spin interactions including the third nearest-neighbor hoppings with the
single-ion anisotropy, in which the SOC of I atoms is found to play an
essential role. In addition, the electric polarization of Fe2Cl3I3 preserves
with strain due to the broken inversion symmetry. Our results predict the rare
Janus material Fe2Cl3I3 as an example of 2D semiconductors with both spin and
charge polarizations, and reveal the highly sensitive strain-controlled
magnetic states and magnetization direction, which highlights the 2D magnetic
Janus semiconductor as a new platform to design spintronic materials.",2001.02842v2
2020/1/28,Tailoring Magnetic Anisotropy in Cr$_2$Ge$_2$Te$_6$ by Electrostatic Gating,"Electrical control of magnetism of a ferromagnetic semiconductor offers
exciting prospects for future spintronic devices for processing and storing
information. Here, we report observation of electrically modulated magnetic
phase transition and magnetic anisotropy in thin crystal of Cr$_2$Ge$_2$Te$_6$
(CGT), a layered ferromagnetic semiconductor. We show that heavily
electron-doped ($\sim$ $10^{14}$ cm$^{-2}$) CGT in an electric double-layer
transistor device is found to exhibit hysteresis in magnetoresistance (MR), a
clear signature of ferromagnetism, at temperatures up to above 200 K, which is
significantly higher than the known Curie temperature of 61 K for an undoped
material. Additionally, angle-dependent MR measurements reveal that the
magnetic easy axis of this new ground state lies within the layer plane in
stark contrast to the case of undoped CGT, whose easy axis points in the
out-of-plane direction. We propose that significant doping promotes
double-exchange mechanism mediated by free carriers, prevailing over the
superexchange mechanism in the insulating state. Our findings highlight that
electrostatic gating of this class of materials allows not only charge flow
switching but also magnetic phase switching, evidencing their potential for
spintronics applications.",2001.10217v1
2020/3/24,Quasiparticle Energies and Excitonic Effects of Chromium Trichloride: from Two Dimensions to Bulk,"Layered van der Waals (vdW) magnetic materials have attracted significant
research interest to date. In this work, we employ the first-principles
many-body perturbation theory to calculate excited-state properties of a
prototype vdW magnet, chromium trichloride (CrCl3), covering monolayer,
bilayer, and bulk structures. Unlike usual non-magnetic vdW semiconductors, in
which many-electron interactions and excited states are sensitive to
dimensionality, many-electron interactions are always enhanced and dominate
quasiparticle energies and optical responses of both two-dimensional and bulk
CrCl3. The electron-hole (e-h) binding energy can reach 3 eV in monolayer and
remains as high as 2 eV in bulk. Because of the cancellation effect between
self-energy corrections and e-h binding energies, the lowest-energy exciton
(optical gap) is almost not affected by the change of dimensionality. Besides,
for the excitons with similar e-h binding energies, their dipole oscillator
strength can differ by a few orders of magnitude.Our analysis shows that such a
big difference is from a unique interference effect between complex exciton
wavefunctions and interband transitions. Finally, we find that the interlayer
stacking sequence and magnetic coupling barely change quasiparticle band gaps
and optical absorption spectra of CrCl3. Our calculated low-energy exciton peak
positions agree with available measurements. These findings give insight into
the understanding of many-electron interactions and the interplay between
magnetic orders and optical excitations in vdW magnetic materials.",2003.11083v2
2020/8/13,Half-metallic ferromagnetism in layered CdOHCl induced by hole doping,"Next-generation spintronic devices will benefit from low-dimensionality,
ferromagnetism, and half-metallicity, possibly controlled by electric fields.
We find these technologically-appealing features to be combined with an exotic
microscopic origin of magnetism in doped CdOHCl, a van der Waals material from
which 2D layers may be exfoliated. By means of first principles simulations, we
predict homogeneous hole-doping to give rise to $p$-band magnetism in both the
bulk and monolayer phases and interpret our findings in terms of Stoner
instability: as the Fermi level is tuned via hole-doping through singularities
in the 2D-like density of states, ferromagnetism develops with large saturation
magnetization of 1 $\mu_B$ per hole, leading to a half-metallic behaviour for
layer carrier densities of the order of 10$^{14}$ cm$^{-2}$. Furthermore, we
put forward electrostatic doping as an additional handle to induce magnetism in
monolayers and bilayers of CdOHCl. Upon application of critical electric fields
perpendicular to atomically-thin-films (as low as 0.2 V/$A{\deg}$ and 0.5
V/$A{\deg}$ in the bilayer and monolayer case, respectively), we envisage the
emergence of a magnetic half-metallic state. The different behaviour of
monolayer vs bilayer systems, as well as an observed asymmetric response to
positive and negative electric fields in bilayers, are interpreted in terms of
intrinsic polarity of CdOHCl atomic stacks, a distinctive feature of the
material. In perspective, given the experimentally accessible magnitude of
critical fields in bilayer of CdOHCl, one can envisage $p$ band magnetism to be
exploited in miniaturized spintronic devices.",2008.05766v1
2020/10/22,"Structural and Magnetic Characterization of CuxMn1-xFe2O4 (x= 0.0, 0.25) Ferrites Using Neutron Diffraction and Other Techniques","Manganese ferrite (MnFe2O4) and copper doped manganese ferrite
(Mn0.75Cu0.25Fe2O4) soft materials were synthesized through solid-state
sintering method. The phase purity and quality were confirmed from x-ray
diffraction patterns. Then the samples were subjected to neutron diffraction
experiment and the diffraction data were analyzed using FullProf software
package. The surface morphology of the soft material samples was studied using
a scanning electron microscope (SEM). Crystal parameters, crystallite
parameters, occupancy at A and B sites of the spinel structure, magnetic
moments of the atoms at various locations, symmetries, oxygen position
parameters, bond lengths etc. were measured and compared with the reference
data. In MnFe2O4, both octahedral (A) and tetrahedral (B) positions are shared
by Mn2+ and Fe2+/3+ cations, here A site is predominantly occupied by Fe2+ and
B site is occupied by Mn at 0.825 occupancy. The Cu2+ ions in Cu0.25Mn0.75Fe2O4
mostly occupy the B site. Copper mostly occupy the Octahedral (16d) sites. The
length of the cubic lattice decreases with the increasing Copper content. The
magnetic properties, i.e. A or B site magnetic moments, net magnetic moment
etc. were measured using neutron diffraction analysis and compared with the
bulk magnetic properties measured with VSM studies.",2010.11739v1
2021/1/7,Polymorphous density-functional description of paramagnetic phases of quantum magnets,"The kernel of the study of magnetic quantum materials focuses on the magnetic
phase transitions, among which the most common phenomenon is the transition
between low-temperature magnetic-ordered phase to high-temperature paramagnetic
phase. A paramount question is if such paramagnetic phase of the correlated
solids can be well described by single-particle band theory to facilitate the
experimental observations. In this work, we investigate the properties of
temperature-driven paramagnetic phase via two different approaches within the
framework of density functional theory, monomorphous and polymorphous
description. From a comprehensive comparison of total energies, symmetries and
band structures, we demonstrate the necessity for a proper treatment of
paramagnetic phases with several prototypical examples. For Pauli paramagnetism
phase, the vanishing of spin moments permits us to apply a nonmagnetic
monomorphous description, while for paramagnetism with disordered local
moments, such description imposes unrealistic high symmetry, leading to a
metallic state in certain cases, inconsistent with the experimental
observation. In contrast, the polymorphous description based on a large-enough
supercell with disordered local moments is able to count in the effects of
distinct local environments, such as symmetry lowing, providing a more reliable
paramagnetic electronic structure and total energy compared with experiments.
Our work shed new insights on discovering the temperature-dependent magnetic
phase transition in the field of magnetic quantum materials.",2101.02539v1
2021/1/12,Interdependent scaling of long-range oxygen and magnetic ordering in non-stoichiometric Nd${}_2$NiO${}_{4.10}$,"Hole doping in Nd${}_{2}$NiO${}_{4.00}$ can be either achieved by
substituting the trivalent Nd atoms by bivalent alkaline earth metals or by
oxygen doping, yielding Nd${}_{2}$NiO${}_{4+\delta}$. In this study, we
investigated the interplay between oxygen and spin ordering for a low oxygen
doping concentration i.e. Nd${}_{2}$NiO${}_{4.10}$. Although the extra oxygen
doping level remains rather modest with only one out of 20 possible
interstitial tetrahedral lattice sites occupied, we observed by single crystal
neutron diffraction the presence of a complex 3D modulated structure related to
oxygen ordering already at ambient, the modulation vectors being
$\pm$2/13\textit{\textbf{a*}}$\pm$3/13\textit{\textbf{b*}},
$\pm$3/13\textit{\textbf{b*}}$\pm$2/13\textit{\textbf{b*}} and
$\pm$1/5\textit{\textbf{a*}}$\pm$1/2\textit{\textbf{c*}} and satellite
reflections up to fourth order. Temperature dependent neutron diffraction
studies indicate the coexistence of oxygen and magnetic ordering below
T${}_{N}$ $\simeq$ 48 K, the wave vector of the Ni sublattice being
\textbf{\textit{k}}=(100). In addition, magnetic satellite reflections adapt
exactly the same modulation vectors as found for the oxygen ordering,
evidencing a unique coexistence of 3D modulated ordering for spin and oxygen
ordering in Nd${}_{2}$NiO${}_{4.10}$. Temperature dependent measurements of
magnetic intensities suggest two magnetic phase transitions below 48 K and 20
K, indicating two distinct onsets of magnetic ordering for the Ni and Nd
sublattice, respectively.",2101.04641v1
2021/2/4,Topological magnetic materials of the (MnSb$_2$Te$_4$)$\cdot$(Sb$_2$Te$_3$)$_n$ van der Waals compounds family,"Combining robust magnetism, strong spin-orbit coupling and unique
thickness-dependent properties of van der Waals crystals could enable new
spintronics applications. Here, using density functional theory, we propose the
(MnSb$_2$Te$_4$)$\cdot$(Sb$_2$Te$_3$)$_n$ family of stoichiometric van der
Waals compounds that harbour multiple topologically-nontrivial magnetic phases.
In the groundstate, the first three members of the family, i.e. MnSb$_2$Te$_4$,
($n=0$), MnSb$_4$Te$_7$, ($n=1$), and MnSb$_6$Te$_{10}$, ($n=2$), are 3D
antiferromagnetic topological insulators (AFMTIs), while for $n \geq 3$ a
special phase is formed, in which a nontrivial topological order coexists with
a partial magnetic disorder in the system of the decoupled 2D ferromagnets,
whose magnetizations point randomly along the third direction. Furthermore, due
to a weak interlayer exchange coupling, these materials can be field-driven
into the FM Weyl semimetal ($n=0$) or FM axion insulator states ($n \geq 1$).
Finally, in two dimensions we reveal these systems to show intrinsic quantum
anomalous Hall and AFM axion insulator states, as well as quantum Hall state,
achieved under external magnetic field, but without Landau levels. Our results
provide a solid computational proof that MnSb$_2$Te$_4$, is not topologically
trivial as was previously believed that opens possibilities of realization of a
wealth of topologically-nontrivial states in the
(MnSb$_2$Te$_4$)$\cdot$(Sb$_2$Te$_3$)$_n$ family.",2102.02532v1
2021/3/1,Absence of magnetic evidence for superconductivity in hydrides under high pressure,"It is generally believed that magnetization measurements on sulfur hydride
under high pressure performed in 2015 [1] provided ""final convincing evidence
of superconductivity"" [2] in that material, in agreement with theoretical
predictions [3,4]. Supported by this precedent, drops in resistance that were
later observed in several other hydrides under high pressure [2,5] have been
generally accepted as evidence of superconductivity without corroborating
evidence from magnetic measurements. In this paper we challenge the original
interpretation that the magnetic measurements on sulfur hydride performed in
2015 were evidence of superconductivity. We point out that a large paramagnetic
contribution to the magnetic susceptibility was detected below Tc and argue
that its temperature dependence rules out the possibility that it would be a
background signal; instead the temperature dependence indicates that the
paramagnetic behavior originated in the sample. We discuss possible
explanations for this remarkable behavior and conclude that standard
superconductors would not show such behavior. We also survey all the other
published data from magnetic measurements on this class of materials and
conclude that they do not provide strong evidence for superconductivity.
Consequently, we call into question the generally accepted view that
conventional superconductivity in hydrogen-rich materials at high temperature
and pressure is a reality, and discuss the implications if it is not.",2103.00701v3
2021/3/25,Magnetic generation and switching of topological quantum phases in a trivial semimetal $α{\mathrm{-EuP}}_3$,"Topological materials have drawn increasing attention owing to their rich
quantum properties, as highlighted by a large intrinsic anomalous Hall effect
(AHE) in Weyl and nodal-line semimetals. However, the practical applications
for topological electronics have been hampered by the difficulty in the
external control of the band topology. Here we demonstrate a
magnetic-field-induced switching of band topology in $\alpha{\mathrm{-EuP}}_3$,
a magnetic semimetal with a layered crystal structure derived from black
phosphorus. When the magnetic field is applied perpendicular to the single
mirror plane of the monoclinic structure, a giant AHE signal abruptly emerges
at a certain threshold magnetization value, giving rise to a prominently large
anomalous Hall angle of $\left|\Theta_{\mathrm{AHE}}\right| \sim 20^{\circ}$.
When the magnetic field is applied along the inter-layer direction, which
breaks the mirror symmetry, the system shows a pronounced negative longitudinal
magnetoresistance. On the basis of electronic structure calculations and
symmetry considerations, these anomalous magneto-transport properties can be
considered as manifestations of two distinct topological phases: topological
nodal-line and Weyl semimetals, respectively. Notably, the nodal-line structure
is composed of bands with the same spin character and spans a wide energy range
around the Fermi level. These topological phases are stabilized via the
exchange coupling between localized Eu-4$f$ moments and mobile carriers
conducting through the phosphorus layers. Our findings provide a realistic
solution for external manipulation of band topology, enriching the functional
aspects of topological materials.",2103.13966v2
2021/3/26,Single-crystal investigations on the multiferroic material LiFe(WO$_4$)$_2$,"The crystal and magnetic structure of multiferroic LiFe(WO$_4$)$_2$ were
investigated by temperature and magnetic-field dependent specific heat,
susceptibility and neutron diffraction experiments on single crystals.
Considering only the two nearest-neighbour magnetic interactions, the system
forms a $J_1$, $J_2$ magnetic chain but more extended interactions are
sizeable. Two different magnetic phases exhibiting long-range incommensurate
order evolve at $T_{\text{N}1}\approx 22.2 \text{ K}$ and $T_{\text{N}2}\approx
19 \text{ K}$. First, a spin-density wave develops with moments lying in the
$ac$ plane. In its multiferroic phase below $T_{\text{N}2}$, LiFe(WO$_4$)$_2$
exhibits a spiral arrangement with an additional spin-component along $b$.
Therefore, the inverse Dzyaloshinskii-Moriya mechanism fully explains the
multiferroic behavior in this material. A partially unbalanced multiferroic
domain distribution was observed even in the absence of an applied electric
field. For both phases only a slight temperature dependence of the
incommensurability was observed and there is no commensurate phase emerging at
low temperature or at finite magnetic fields up to $6\text{ T}$.
LiFe(WO$_4$)$_2$ thus exhibits a simple phase diagram with the typical sequence
of transitions for a type-II multiferroic material.",2103.14523v1
2021/5/4,Phase Diagram of YbZnGaO4 in Applied Magnetic Field,"Recently, Yb-based triangular lattice antiferromagnets have garnered
significant interest as possible quantum spin liquid candidates. One example is
YbMgGaO4, which showed many promising spin liquid features, but also possesses
a high degree of disorder owing to site-mixing between the non-magnetic
cations. To further elucidate the role of chemical disorder and to explore the
phase diagram of these materials in applied field, we present neutron
scattering and sensitive magnetometry measurements of the closely related
compound, YbZnGaO4. Our results suggest a difference in magnetic anisotropy
between the two compounds, and we use key observations of the magnetic phase
crossover to motivate an exploration of the field- and exchange
parameter-dependent phase diagram, providing an expanded view of the available
magnetic states in applied field. This enriched map of the phase space serves
as a basis to restrict the values of parameters describing the magnetic
Hamiltonian with broad application to recently discovered related materials.",2105.01790v1
2021/6/29,Spanning Fermi arcs in a two-dimensional magnet,"The discovery of topological states of matter has led to a revolution in
materials research. When external or intrinsic parameters break certain
symmetries, global properties of topological materials change drastically. A
paramount example is the emergence of Weyl nodes under broken inversion
symmetry, acting like magnetic monopoles in momentum space. However, while a
rich variety of non-trivial quantum phases could in principle also originate
from broken time-reversal symmetry, realizing systems that combine magnetism
with complex topological properties is remarkably elusive due to both
considerable experimental and theoretical challenges. Here, we demonstrate that
giant open Fermi arcs are created at the surface of ultrathin hybrid magnets.
The Fermi-surface topology of an atomically thin ferromagnet is substantially
modified by the hybridization with a heavy-metal substrate, giving rise to
Fermi-surface discontinuities that are bridged by the Fermi arcs. Due to the
interplay between magnetism and topology, we can control both the shape and the
location of the Fermi arcs by tuning the magnetization direction. The
hybridization points in the Fermi surface can be attributed to a non-trivial
""mixed"" topology and induce hot spots in the Berry curvature, dominating spin
and charge transport as well as magneto-electric coupling effects.",2106.15670v1
2021/7/7,Anomalous Hall antiferromagnets,"The Hall effect, in which current flows perpendicular to an applied
electrical bias, has played a prominent role in modern condensed matter physics
over much of the subject's history. Appearing variously in classical,
relativistic and quantum guises, it has among other roles contributed to
establishing the band theory of solids, to research on new phases of strongly
interacting electrons, and to the phenomenology of topological condensed
matter. The dissipationless Hall current requires time-reversal symmetry
breaking. For over a century it has either been ascribed to externally applied
magnetic field and referred to as the ordinary Hall effect, or ascribed to
spontaneous non-zero total internal magnetization (ferromagnetism) and referred
to as the anomalous Hall effect. It has not commonly been associated with
antiferromagnetic order. More recently, however, theoretical predictions and
experimental observations have identified large Hall effects in some
compensated magnetic crystals, governed by neither of the global
magnetic-dipole symmetry breaking mechanisms mentioned above. The goals of this
article are to systematically organize the present understanding of anomalous
antiferromagnetic materials that generate a non-zero Hall effect, which we will
call anomalous Hall antiferromagnets, and to discuss this class of materials in
a broader fundamental and applied research context. Our motivation in drawing
attention to anomalous Hall antiferromagnets is two-fold. First, since Hall
effects that are not governed by magnetic dipole symmetry breaking are at odds
with the traditional understanding of the phenomenon, the topic deserves
attention on its own. Second, this new reincarnation has again placed the Hall
effect in the middle of an emerging field of physics at the intersection of
multipole magnetism, topological condensed matter, and spintronics.",2107.03321v1
2021/9/2,A unified numerical approach for soft to hard magneto-viscoelastically coupled polymers,"The last decade has witnessed the emergence of magneto-active polymers (MAPs)
as one of the most advanced multi-functional soft composites. Depending on the
magnetisation mechanisms and responsive behaviour, MAPs are mainly classified
into two groups: i) hard magnetic MAPs in which a large residual magnetic flux
density sustains even after the removal of the external magnetic field, and ii)
soft magnetic MAPs where the magnetisation of the filler particles disappear
upon the removal of the external magnetic field. Polymeric materials are widely
treated as fully incompressible solids that require special numerical treatment
to solve the associated boundary value problem. Furthermore, both soft and hard
magnetic particles-filled soft polymers are inherently viscoelastic. Therefore,
the aim of this paper is to devise a unified finite element method-based
numerical framework for magneto-mechanically coupled systems that can work for
compressible and fully incompressible materials and from hard to soft MAPs,
including the effects of the time-dependent viscoelastic behaviour of the
underlying matrix. First, variational formulations for the uncoupled problem
for hard MAPs and the coupled problem for soft MAPs are derived. The weak forms
are then discretised with higher-order B\'ezier elements while the evolution
equation for internal variables in viscoelastic models is solved using the
generalised-alpha time integration scheme, which is implicit and second-order
accurate. Finally, a series of experimentally-driven boundary value problems
consisting of the beam and robotic gripper models are solved in
magneto-mechanically coupled settings, demonstrating the versatility of the
proposed numerical framework. The effect of viscoelastic material parameters on
the response characteristics of MAPs under coupled magneto-mechanical loading
is also studied.",2109.00844v1
2021/10/16,Giant magnetoresistance and topological Hall effect in the EuGa4 antiferromagnet,"We report on systematic temperature- and magnetic field-dependent studies of
the EuGa$_4$ binary compound, which crystallizes in a centrosymmetric
tetragonal BaAl$_4$-type structure with space group $I4/mmm$. The electronic
properties of EuGa$_4$ single crystals, with an antiferromagnetic (AFM)
transition at $T_\mathrm{N} \sim 16.4$ K, were characterized via electrical
resistivity and magnetization measurements. A giant nonsaturating
magnetoresistance was observed at low temperatures, reaching $\sim 7 \times
10^4$ % at 2 K in a magnetic field of 9 T. In the AFM state, EuGa$_4$ undergoes
a series of metamagnetic transitions in an applied magnetic field, clearly
manifested in its field-dependent electrical resistivity. Below $T_\mathrm{N}$,
in the $\sim$4-7 T field range, we observe also a clear hump-like anomaly in
the Hall resistivity which is part of the anomalous Hall resistivity. We
attribute such a hump-like feature to the topological Hall effect, usually
occurring in noncentrosymmetric materials known to host topological spin
textures (as e.g., magnetic skyrmions). Therefore, the family of materials with
a tetragonal BaAl$_4$-type structure, to which EuGa$_4$ and EuAl$_4$ belong,
seems to comprise suitable candidates on which one can study the interplay
among correlated-electron phenomena (such as charge-density wave or exotic
magnetism) with topological spin textures and topologically nontrivial bands.",2110.08522v1
2021/11/2,Scaling of the thermally induced sign inversion of longitudinal spin Seebeck effect in a compensated ferrimagnet: Role of magnetic anisotropy,"We report on a systematic investigation of the longitudinal spin Seebeck
effect (LSSE) in a GGG(Gd3Ga5O12)/GdIG(Gd3Fe5O12)/Pt film series exhibiting an
in-plane magnetic easy axis with a compensation temperature (T_Comp) that
decreases from 270 to 220 K when decreasing GdIG film thickness from 272 to 31
nm, respectively. For all the films, the LSSE signal flips its sign below
T_Comp. We demonstrate a universal scaling behavior of the temperature
dependence of LSSE signal for our GdIG films around their respective T_Comp.
Additionally, we demonstrate LSSE in a 31 nm GdIG film grown on a
lattice-mismatched GSGG (Gd3Sc2Ga3O12) substrate that exhibits an out-of-plane
magnetic easy axis at room temperature. However, this sample reveals a spin
reorientation transition where the magnetic easy axis changes its orientation
to in-plane at low temperatures. We observed a clear distinction in the LSSE
signal for the GSGG/GdIG(31 nm)/Pt heterostructure, relative to
GGG/GdIG(31nm)/Pt showing an in-plane magnetic easy axis. Our findings
underscore a strong correlation between the LSSE signal and the orientation of
magnetic easy axis in compensated ferrimagnets and opens the possibility to
tune LSSE through effective anisotropy.",2111.01379v1
2021/11/11,Tuning the Room Temperature Ferromagnetism in Fe5GeTe2 by Arsenic Substitution,"In order to tune the magnetic properties of the cleavable high-Curie
temperature ferromagnet Fe$_{5-x}$GeTe$_2$, the effect of increasing the
electron count through arsenic substitution has been investigated. Small
additions of arsenic (2.5 and 5%) seemingly enhance ferromagnetic order in
polycrystalline samples by quenching fluctuations on one of the three magnetic
sublattices, whereas larger As concentrations decrease the ferromagnetic Curie
temperature ($T_{\rm C}$) and saturation magnetization. This work also
describes the growth and characterization of Fe$_{4.8}$AsTe$_2$ single crystals
that are structurally analogous to Fe$_{5-x}$GeTe$_2$ but with some phase
stability complications. Magnetization measurements reveal dominant
antiferromagnetic behavior in Fe$_{4.8}$AsTe$_2$ with a N\'{e}el temperature of
$T_{\rm N}$ $\approx$42K. A field-induced spin-flop below $T_{\rm N}$ results
in a switch from negative to positive magnetoresistance, with significant
hysteresis causing butterfly-shaped resistance loops. In addition to reporting
the properties of Fe$_{4.8}$AsTe$_2$, this work shows the importance of
manipulating the individual magnetic sublattices in Fe$_{5-x}$GeTe$_2$ and
motivates further efforts to control the magnetic properties in related
materials by fine tuning of the Fermi energy or crystal chemistry.",2111.06439v1
2021/12/1,Pressure dependent magnetic properties on bulk CrBr3 single crystals,"The van der Waals class of materials offer an approach to two-dimensional
magnetism as their spin fluctuations can be tuned upon exfoliation of layers.
Moreover, it has recently been shown that spin-lattice coupling and long-range
magnetic ordering can be modified with pressure in van der Waals materials. In
this work, the magnetic properties of quasi two-dimensional CrBr3 are reported
applying hydrostatic pressure. The application of pressure (0 - 0.8 GPa) shows
a 72 % decrease in saturation magnetization with small decrease in the Curie
temperature from 33 to 29 K. Density functional theory calculations with
pressure up to 1 GPa show a reduction in volume and interplanar distance as
pressure increases. To further understand magnetic properties with applied
pressure, the magnetocrystalline anisotropy energy (MAE) and exchange coupling
parameter (J) are calculated. There is minimal decrease in MAE and the first
nearest neighbor interaction (J1) (U = 2.7 eV and J = 0.7 eV), shows an
increase in J1 with respect to pressure. Overall, CrBr3 displays ferromagnetic
interlayer coupling and the calculated exchange coupling and MAE parameters
match well with the observations from the experimental work.",2112.00233v1
2021/12/6,A material view on extrinsic magnetic domain wall pinning in cylindrical CoNi nanowires,"Speed and reliability of magnetic domain wall (DW) motion are key parameters
that must be controlled to realize the full potential of DW-based magnetic
devices for logic and memory applications. A major hindrance to this is
extrinsic DW pinning at specific sites related to shape and material defects,
which may be present even if the sample synthesis is well controlled.
Understanding the origin of DW pinning and reducing it is especially desirable
in electrochemically-deposited cylindrical magnetic nanowires (NWs), for which
measurements of the fascinating physics predicted by theoretical computation
have been inhibited by significant pinning. We experimentally investigate DW
pinning in Co$_x$Ni$_{100-x}$ NWs, by applying quasistatic magnetic fields.
Wire compositions were varied with $x=20,30,40$, while the microstructure was
changed by annealing or varying the pH of the electrolyte for deposition. We
conclude that pinning due to grain boundaries is the dominant mechanism,
decreasing inversely with both the spontaneous magnetization and grain size.
Second-order effects include inhomogeneities in lattice strain and the residual
magnetocrystalline anisotropy. Surface roughness, dislocations and impurities
are not expected to play a significant role in DW pinning in these wire
samples.",2112.03132v1
2022/2/11,Spin Hall magnetoresistance effect from a disordered interface,"The Spin Hall magnetoresistance (SMR) emerged as a reference tool to
investigate the magnetic properties of materials with an all-electrical set-up.
Its sensitivity to the magnetization of thin films and surfaces may turn it
into a valuable technique to characterize Van der Waals magnetic materials,
which support long range magnetic order in atomically thin layers. However,
realistic surfaces can be affected by defects and disorder, which may result in
unexpected artifacts in the SMR, rather than the sole appearance of electrical
noise. Here, we study the SMR response of heterostructures combining a platinum
(Pt) thin film with the Van der Waals antiferromagnet MnPSe3 and observe a
robust SMR-like signal, which turns out to originate from the presence of
strong interfacial disorder in the system. We use transmission electron
microscopy (TEM) to characterize the interface between MnPSe3 and Pt, revealing
the formation of a few-nanometer-thick platinum-chalcogen amorphous layer. The
analysis of the transport and TEM measurements suggests that the signal arises
from a disordered magnetic system formed at the Pt/MnPSe3 interface, washing
out the interaction between the spins of the Pt electrons and the MnPSe3
magnetic lattice. Our results show that damaged interfaces can yield an
important contribution to SMR, questioning a widespread assumption on the role
of disorder in such measurements.",2202.05534v1
2022/4/5,Widely Tunable Berry curvature in the Magnetic Semimetal Cr1+dTe2,"Magnetic semimetals have increasingly emerged as lucrative platforms hosting
spin-based topological phenomena in real and momentum spaces. Of particular
interest is the emergence of Berry curvature, whose geometric origin,
accessibility from Hall transport experiments, and material tunability, bodes
well for new physics and practical devices. Cr1+dTe2, a self-intercalated
magnetic transition metal dichalcogenide, TMD, exhibits attractive natural
attributes relevant to such applications, including topological magnetism,
tunable electron filling, magnetic frustration etc. While recent studies have
explored real-space Berry curvature effects in this material, similar
considerations of momentum-space Berry curvature are lacking. Here, we
systematically investigate the electronic structure and transport properties of
epitaxial Cr1+dTe2 thin films over a wide range of doping, d between 0.33 and
0.71. Spectroscopic experiments reveal the presence of a characteristic
semi-metallic band region near the Brillouin Zone edge, which shows a rigid
band like energy shift as a function of d. Transport experiments show that the
intrinsic component of the anomalous Hall effect, AHE, is sizable, and
undergoes a sign flip across d. Finally, density functional theory calculations
establish a causal link between the observed doping evolution of the band
structure and AHE: the AHE sign flip is shown to emerge from the sign change of
the Berry curvature, as the semi-metallic band region crosses the Fermi energy.
Our findings underscore the increasing relevance of momentum-space Berry
curvature in magnetic TMDs and provide a unique platform for intertwining
topological physics in real and momentum spaces.",2204.02518v2
2022/4/17,Topological Electronic Structure Evolution with Symmetry Breaking Spin Reorientation in (Fe$_{1-x}$Co$_{x}$)Sn,"Topological materials hosting kagome lattices have drawn considerable
attention due to the interplay between topology, magnetism, and electronic
correlations. The (Fe$_{1-x}$Co$_x$)Sn system not only hosts a kagome lattice
but has a tunable symmetry breaking magnetic moment with temperature and
doping. In this study, angle resolved photoemission spectroscopy and first
principles calculations are used to investigate the interplay between the
topological electronic structure and varying magnetic moment from the planar to
axial antiferromagnetic phases. A theoretically predicted gap at the Dirac
point is revealed in the low temperature axial phase but no gap opening is
observed across a temperature dependent magnetic phase transition. However,
topological surface bands are observed to shift in energy as the surface
magnetic moment is reduced or becomes disordered over time during experimental
measurements. The shifting surface bands may preclude the determination of a
temperature dependent bulk gap but highlights the intricate connections between
magnetism and topology with a surface/bulk dichotomy that can affect material
properties and their interrogation.",2204.08066v1
2022/5/14,Strain effects on topological and valley properties of Janus monolayer $\mathrm{VSiGeN_4}$,"Strain is an effective method to tune the electronic properties of
two-dimension (2D) materials, and can induce novel phase transition. Recently,
2D $\mathrm{MA_2Z_4}$ family materials are of interest because of their
emerging topological, magnetic and superconducting properties. Here, we
investigate the impact of strain effects ($a/a_0$:0.96$\sim$1.04) on the
physical properties of Janus monolayer $\mathrm{VSiGeN_4}$ as a derivative of
$\mathrm{VSi_2N_4}$ or $\mathrm{VGe_2N_4}$, which possesses dynamical,
mechanical and thermal stabilities. For out-of-plane magnetic anisotropy, with
increasing strain, $\mathrm{VSiGeN_4}$ undergoes transition between ferrovalley
semiconductor (FVS), half-valley-metal (HVM), valley-polarized quantum
anomalous Hall insulator (VQAHI), HVM and FVS. These imply twice topological
phase transitions, which are related with sign-reversible Berry curvature and
band inversion between $d_{xy}$+$d_{x^2-y^2}$ and $d_{z^2}$ orbitals for K or
-K valley. The band inversion also leads to transformation of valley splitting
strength between valence and conduction bands. However, for in-plane magnetic
anisotropy, no special quantum anomalous Hall (QAH) states and valley
polarization exist within the considered strain range. The actual magnetic
anisotropy energy (MAE) shows no special QAH and HVM states in monolayer
$\mathrm{VSiGeN_4}$. Fortunately, these can be easily achieved by external
magnetic field, which adjusts the easy magnetization axis of
$\mathrm{VSiGeN_4}$ from in-plane one to out-of-plane one. Our findings shed
light on how strain can be employed to engineer the electronic states of
$\mathrm{VSiGeN_4}$, which may open new perspectives for multifunctional
quantum devices in valleytronics and spintronics.",2205.07012v2
2022/6/12,Kagome lattice promotes chiral spin fluctuations,"Magnetic materials with tilted electron spins often exhibit conducting
behavior that cannot be explained from semiclassical theories without invoking
fictitious (emergent) electromagnetic fields. Quantum-mechanical models
explaining such phenomena are rooted in the concept of a moving quasiparticle's
Berry phase, driven by a chiral (left- or right-handed) spin-habit. Dynamical
and nearly random spin fluctuations, with a slight bent towards left- or
right-handed chirality, represent a promising route to realizing Berry-phase
phenomena at elevated temperatures, but little is known about the effect of
crystal lattice geometry on the resulting macroscopic observables. Here, we
report thermoelectric and electric transport experiments on two metals with
large magnetic moments on a triangular and on a slightly distorted kagom\'e
lattice, respectively. We show that the impact of chiral spin fluctuations is
strongly enhanced for the kagom\'e lattice. Both these spiral magnets have
similar magnetic phase diagrams including a periodic array of magnetic
skyrmions. However, our modelling shows that the geometry of the kagom\'e
lattice, with corner-sharing spin-trimers, helps to avoid cancellation of
Berry-phase contributions; spin fluctuations are endowed with a net chiral
habit already in the thermally disordered (paramagnetic) state. Hence, our
observations for the kagom\,e material contrast with theoretical models
treating magnetization as a continuous field, and emphasize the role of lattice
geometry on emergent electrodynamic phenomena.",2206.05756v2
2022/6/20,Asymmetric magnetic proximity interactions in MoSe$_{2}$/CrBr$_{3}$ van der Waals heterostructures,"Magnetic proximity interactions (MPIs) between atomically-thin semiconductors
and two-dimensional magnets provide a means to manipulate spin and valley
degrees of freedom in nonmagnetic monolayers, without the use of applied
magnetic fields. In such van der Waals (vdW) heterostructures, MPIs originate
in the nanometer-scale coupling between the spin-dependent electronic
wavefunctions in the two materials, and typically their overall effect is
regarded as an effective magnetic field acting on the semiconductor monolayer.
Here we demonstrate that this picture, while appealing, is incomplete: The
effects of MPIs in vdW heterostructures can be markedly asymmetric, in contrast
to that from an applied magnetic field. Valley-resolved optical reflection
spectroscopy of MoSe$_{2}$/CrBr$_{3}$ vdW structures reveals strikingly
different energy shifts in the $K$ and $K'$ valleys of the MoSe$_2$, due to
ferromagnetism in the CrBr$_3$ layer. Strong asymmetry is observed at both the
A- and B-exciton resonances. Density-functional calculations indicate that
valley-asymmetric MPIs depend sensitively on the spin-dependent hybridization
of overlapping bands, and as such are likely a general feature of such hybrid
vdW structures. These studies suggest routes to selectively control
\textit{specific} spin and valley states in monolayer semiconductors.",2206.09958v1
2022/7/11,Emergence of bond-dependent highly anisotropic magnetic interactions in Sr$_4$RhO$_6$: a theoretical study,"The quantum spin liquid states as a natural ground state of the Kitaev model
has led to a quest for new materials candidates hosting Kitaev physics. Yet,
there are very few material candidates in this category. Using a combination of
$ab$ $initio$ and model Hamiltonian methods, we propose that Ruddlesden-Popper
compound Sr$_4$RhO$_6$ belongs to this category. With a tight-binding model and
exact diagonalization approach, we show that despite substantial trigonal-like
distortion, the electronic and magnetic properties of Sr$_4$RhO$_6$ can be well
described in terms of pseudo-spin = 1/2 states. Magnetic interactions among
pseudo-spins, estimated using the second-order perturbation method are highly
bond-dependent anisotropic in nature with two particularly noticeable features,
antiferromagnetic Kitaev and Dzyaloshinskii-Moriya interactions. The gaped
spin-wave spectra of Sr$_4$RhO$_6$ obtained with linear spin-wave theory is
consistent with the underlying magnetic frustration. Additional analysis of the
role of individual or a particular combination of magnetic interactions reveals
that the spin-wave spectra of Sr$_4$RhO$_6$ is a combined effect of the highly
anisotropic interactions and a relatively simpler minimal model may not be
plausible in the current case. The crucial insights about coupling between the
local structural features and magnetic properties of Sr$_4$RhO$_6$ obtained in
this study may be helpful for future studies belonging to this class.",2207.05045v3
2022/7/31,Interface Engineering Enabled Low Temperature Growth of Magnetic Insulator on Topological Insulator,"Combining topological insulators (TIs) and magnetic materials in
heterostructures is crucial for advancing spin-based electronics. Magnetic
insulators (MIs) can be deposited on TIs using the spin-spray process, which is
a unique non-vacuum, low-temperature growth process. TIs have highly reactive
surfaces that oxidize upon exposure to atmosphere, making it challenging to
grow spin-spray ferrites on TIs. In this work, it is demonstrated that a thin
titanium capping layer on TI, followed by oxidation in atmosphere to produce a
thin TiOx interfacial layer, protects the TI surface, without significantly
compromising spin transport from the magnetic material across the TiOx to the
TI surface states. First, it was demonstrated that in Bi2Te3/TiOx/Ni80Fe20
heterostructures that TiOx provided an excellent barrier against diffusion of
magnetic species, yet maintained a large spin-pumping effect. Second, the TiOx
was also used as a protective capping layer on Bi2Te3, followed by the
spin-spray growth of the MI, NixZnyFe2O4 (NZFO). For the thinnest TiOx
barriers, Bi2Te3/TiOx/NZFO samples had AFM disordered interfacial layer because
of diffusion. With increasing TiOx barrier thickness, the diffusion was
reduced, but still maintained strong interfacial spin-pumping interaction.
These experimental results demonstrate a novel method of low-temperature growth
of magnetic insulators on TIs enabled by interface engineering.",2208.00499v1
2022/8/25,Challenges and opportunities to assure future manufacturing of magnet conductors for the accelerator sector,"We take a comprehensive look at conductors used in superconducting magnets
for the accelerator sector and explore the ramifications of the present
marketplace for supply of conductor to future accelerator facilities. While
there are thousands of superconductors, many of which have promising properties
for applications, we outline the journey a promising material must take to
become a magnet conductor that is manufactured at the scale needed for an
accelerator facility. Among the few materials that actually reach this scale,
Nb$_{3}$Sn is arguably the workhorse conductor for the next generation of
accelerators. Yet, a marketplace pull equivalent to the medical imaging magnet
industry, which consumes close to 1000 tons of commodity-scale Nb-Ti conductor
per year, has not emerged. This aspect greatly complicates the steps that must
be taken to assure readiness of manufacturing for the next accelerator
facility. Meanwhile, high-temperature superconductors (HTS), which are capable
of extremely high fields at low temperature, are advancing rapidly as magnet
conductors, and the long horizons of large physics projects could provide time
for them to emerge and displace Nb-based materials. We close by examining in
more detail the ecosystem that connects accelerator magnet conductors with
broader industry applications, in particular areas that are presently in rapid
development such as fusion and wind turbines and which would potentially
require hundreds of tons of conductor.",2208.12379v1
2022/8/29,Room temperature spin-orbit torque efficiency and magnetization switching in SrRuO3-based heterostructures,"Spin-orbit torques (SOTs) from transition metal oxides (TMOs) in conjunction
with magnetic materials have recently attracted tremendous attention for
realizing high-efficient spintronic devices. SrRuO3 is a promising candidate
among TMOs due to its large and tunable SOT-efficiency as well as high
conductivity and chemical stability. However, a further study for benchmarking
the SOT-efficiency and realizing SOT-driven magnetization switching in SrRuO3
is still highly desired so far. Here, we systematically study the SOT
properties of high-quality SrRuO3 thin film heterostructuring with different
magnetic alloys of both IMA and PMA configuration by the harmonic Hall voltage
technique. Our results indicate that SrRuO3 possesses pronounced SOT-efficiency
of about 0.2 at room temperature regardless of the magnetic alloys, which is
comparable to typical heavy metals (HMs). Furthermore, we achieve SOT-driven
magnetization switching with a low threshold current density of 3.8x10^10
A/m^2, demonstrating the promising potential of SrRuO3 for practical devices.
By making a comprehensive comparison with HMs, our work unambiguously
benchmarks the SOT properties and concludes the advantages of SrRuO3, which may
bring more diverse choices for SOT applications by utilizing hybrid-oxide/metal
and all-oxide systems.",2208.13574v1
2022/9/13,Design of Core-Shell Structured Magnetic Microwires with Desirable Properties for Multifunctional Applications,"Amorphous Co-rich microwires with excellent soft magnetic and mechanical
properties produced by melt-extraction technique are emerging as a
multifunctional material for a variety of applications ranging from
ultrasensitive magnetic field sensors to structural health self-monitoring
composites. There is a pressing need for enhancing these properties to make the
microwires practical for integration into new technologies. Conventional heat
treatments at temperature below crystallization may improve the magnetic
softness of an as-quenched amorphous wire, but usually deteriorate the good
mechanical characteristic of the wire due to crystallization. To overcome this,
we propose a new approach that utilizes the advantages of a multi-step Joule
current annealing method to design novel (nanocrystal, amorphous)/amorphous
core/shell structures directly from as-quenched amorphous microwires. These
results show that the density and size of nanocrystals in the core can be
optimized by controlling the Joule current intensity, resulting in the large
enhancement of soft magnetic and giant magneto-impedance properties, while the
amorphous shell preserves the excellent mechanical strength of the microwire.
This study also provides a new pathway for the design of novel core/shell
structures directly from rapidly quenched amorphous magnetic materials that are
currently exploited in high frequency transformers, sensing and cooling
devices.",2209.06238v1
2022/10/28,Field-free-switching state diagram of perpendicular magnetization subjected to conventional and unconventional spin-orbit torques,"The lack of certain crystalline symmetries in strong spin-orbit-coupled
non-magnetic materials allows for the existence of uncoventional spin Hall
responses, with electrically generated transverse spin currents possessing
collinear flow and spin directions. The injection of such spin currents into an
adjacent ferromagnetic layer can excite magnetization dynamics via
unconventional spin-orbit torques, leading to deterministic switching in
ferromagnets with perpendicular magnetic anisotropy. We study the interplay
between conventional and unconventional spin-orbit torques on the magnetization
dynamics of a perpendicular ferromagnet in the small intrinsic damping limit,
and identify a rich set of dynamical regimes that includes deterministic and
probabilistic switching, precessional and pinning states. Contrary to common
belief, we found that there exists a critical conventional spin Hall angle,
beyond which deterministic magnetization switching transitions to a
precessional or pinned state. Conversely, we showed that larger unconventional
spin Hall angle is generally beneficial for deterministic switching. We derive
an approximate expression that qualitatively describes the state diagram
boundary between the full deterministic switching and precessional states and
discuss a criterion for searching symmetry-broken spin Hall materials in order
to maximize switching efficiency. Our work offers a roadmap towards energy
efficient spintronic devices, which might opens doors for applications in
advanced in-memory computing technologies.",2210.16344v1
2022/11/30,Asymptotic Homogenization in the Determination of Effective Intrinsic Magnetic Properties of Composites,"We present a computational framework for two-scale asymptotic homogenization
to determine the intrinsic magnetic permeability of composites. To this end,
considering linear magnetostatics, both vector and scalar potential
formulations are used. Our homogenization algorithm for solving the cell
problem is based on the displacement method presented in Lukkassen et al. 1995,
Composites Engineering, 5(5), 519-531. We propose the use of the meridional
eccentricity of the permeability tensor ellipsoid as an anisotropy index
quantifying the degree of directionality in the linear magnetic response. As
application problems, 2D regular and random microstructures with overlapping
and nonoverlapping monodisperse disks, all of which are periodic, are
considered. We show that, for the vanishing corrector function, the derived
effective magnetic permeability tensor gives the (lower) Reuss and (upper)
Voigt bounds with the vector and scalar potential formulations, respectively.
Our results with periodic boundary conditions show an excellent agreement with
analytical solutions for regular composites, whereas, for random heterogeneous
materials, their convergence with volume element size is fast. Predictions for
material systems with monodisperse overlapping disks for a given inclusion
volume fraction provide the highest magnetic permeability with the most
increased inclusion interaction. In contrast, the disk arrangements in regular
square lattices result in the lowest magnetic permeability and inadequate
inclusion interaction. Such differences are beyond the reach of the isotropic
effective medium theories, which use only the phase volume fraction and shape
as mere statistical microstructural descriptors.",2212.00150v1
2023/2/3,The role of electron correlations in the electronic structure of putative Chern magnet TbMn$_6$Sn$_6$,"A member of the RMn$_6$Sn$_6$ rare-earth family materials, TbMn$_6$Sn$_6$,
recently showed experimental signatures of the realization of a quantum-limit
Chern magnet. In this work, we use quantum Monte Carlo (QMC) and density
functional theory with Hubbard $U$ (DFT$+U$) calculations to examine the
electronic structure of TbMn$_6$Sn$_6$. To do so, we optimize accurate,
correlation-consistent pseudopotentials for Tb and Sn using coupled-cluster and
configuration-interaction (CI) methods. We find that DFT$+U$ and
single-reference QMC calculations suffer from the same overestimation of the
magnetic moments as meta-GGA and hybrid density functional approximations. Our
findings point to the need for improved orbitals/wavefunctions for this class
of materials, such as natural orbitals from CI, or for the inclusion of
multi-reference effects that capture the static correlations for an accurate
prediction of magnetic properties. DFT$+U$ with Mn magnetic moments adjusted to
experiment predict the Dirac crossing in bulk to be close to the Fermi level,
within $\sim 120$ meV, in agreement with the experiments. Our
non-stoichiometric slab calculations show that the Dirac crossing approaches
even closer to the Fermi level, suggesting the possible realization of Chern
magnetism in this limit.",2302.01903v2
2023/4/13,Hidden magnetism uncovered in charge ordered bilayer kagome material ScV_6Sn_6,"Charge ordered kagome lattices have been demonstrated to be intriguing
platforms for studying the intertwining of topology, correlation, and
magnetism. The recently discovered charge ordered kagome material ScV_6Sn_6
does not feature a magnetic groundstate or excitations, thus it is often
regarded as a conventional paramagnet. Here, using advanced muon-spin rotation
spectroscopy, we uncover an unexpected hidden magnetism of the charge order. We
observe a striking enhancement of the internal field width sensed by the muon
ensemble, which takes place within the charge ordered state. More remarkably,
the muon spin relaxation rate below the charge ordering temperature is
substantially enhanced by applying an external magnetic field. Taken together
with the hidden magnetism found in AV_3Sb_5 (A = K, Rb, Cs) and FeGe kagome
systems, our results suggest ubiqitous time-reversal symmetry-breaking in
charge ordered kagome lattices.",2304.06436v1
2023/4/29,Weyl metallic state induced by helical magnetic order,"In the rapidly expanding field of topological materials there is growing
interest in systems whose topological electronic band features can be induced
or controlled by magnetism. Magnetic Weyl semimetals, which contain linear band
crossings near the Fermi level, are of particular interest owing to their
exotic charge and spin transport properties. Up to now, the majority of
magnetic Weyl semimetals have been realized in ferro- or ferrimagnetically
ordered compounds, but a disadvantage of these materials for practical use is
their stray magnetic field which limits the minimum size of devices. Here we
show that Weyl nodes can be induced by a helical spin configuration, in which
the magnetization is fully compensated. Using a combination of neutron
diffraction and resonant elastic x-ray scattering, we find that EuCuAs develops
a planar helical structure below $T_\textrm{N}$ = 14.5 K which induces Weyl
nodes along the $\Gamma$--A high symmetry line in the Brillouin zone.",2305.00295v1
2023/5/15,Large magneto-thermal-switching ratio in superconducting Pb wires,"Thermal switching by magnetic fields is one of the important functionalities
in thermal management technologies. In low-temperature devices, superconducting
states can be used as a magneto-thermal-switching (MTS) component, because
carrier thermal conductivity (\k{appa}) is strongly suppressed in
superconducting states. Recently, we demonstrated that the MTS ratio (MTSR) of
pure Nb reached 650% at a temperature (T) of 2.5 K under a magnetic field (H)
of 4.0 kOe [M. Yoshida et al., Appl. Phys. Express 16, 033002 (2023)]. In this
study, to enrich knowledge on MTS of superconductors, the MTSRs of pure Pb
wires with 5N and 3N purities were investigated by measuring the temperature or
magnetic field dependences of \k{appa}. For 5N-Pb, a large MTSR exceeding 1000%
was observed below 3.6 K under H > 600 Oe. Although higher MTSRs were expected
at lower temperatures under H > 600 Oe, the obtained data under those
conditions were accompanied by large errors due to magnetic-field-induced huge
\k{appa} at low temperatures. In contrast, the \k{appa} for 3N-Pb were observed
to be clearly lower than that for 5N-Pb. Although the magnetic-field-induced
change in \k{appa} was small, the MTSR at T = 2.5 K was 300%. These results
suggest that Pb is a promising material for low-temperature magneto-thermal
switching because of wide-range \k{appa} tunable by magnetic field and the
purity.",2305.08332v1
2023/8/23,Room-Temperature Highly-Tunable Coercivity and Highly-Efficient Nonvolatile Multi-States Magnetization Switching by Small Current in Single 2D Ferromagnet Fe$_3$GaTe$_2$,"Room-temperature electrically-tuned coercivity and nonvolatile multi-states
magnetization switching is crucial for next-generation low-power 2D
spintronics. However, most methods have limited ability to adjust the
coercivity of ferromagnetic systems, and room-temperature electrically-driven
magnetization switching shows high critical current density and high power
dissipation. Here, highly-tunable coercivity and highly-efficient nonvolatile
multi-states magnetization switching are achieved at room temperature in
single-material based devices by 2D van der Waals itinerant ferromagnet
Fe$_3$GaTe$_2$. The coercivity can be readily tuned up to ~98.06% at 300 K by a
tiny in-plane electric field that is 2-5 orders of magnitude smaller than that
of other ferromagnetic systems. Moreover, the critical current density and
power dissipation for room-temperature magnetization switching in 2D
Fe$_3$GaTe$_2$ are down to ~1.7E5 A cm$^{-2}$ and ~4E12 W m$^{-3}$,
respectively. Such switching power dissipation is 2-6 orders of magnitude lower
than that of other 2D ferromagnetic systems. Meanwhile, multi-states
magnetization switching are presented by continuously controlling the current,
which can dramatically enhance the information storage capacity and develop new
computing methodology. This work opens the avenue for room-temperature
electrical control of ferromagnetism and potential applications for
vdW-integrated 2D spintronics.",2308.12007v1
2023/9/29,Self-intercalation as origin of high-temperature ferromagnetism in epitaxially grown Fe5GeTe2 thin films,"The role of self-intercalation in 2D van der Waals materials is key to the
understanding of many of their properties. Here we show that the magnetic
ordering temperature of thin films of the 2D ferromagnet Fe5GeTe2 is
substantially increased by self-intercalated Fe that resides in the van der
Waals gaps. The epitaxial films were prepared by molecular beam epitaxy and
their magnetic properties explored by element-specific x-ray magnetic circular
dichroism that showed ferromagnetic ordering up to 375 K. Both surface and bulk
sensitive x-ray absorption modes were used to confirm that the magnetic signal
is of an intrinsic nature. Fe occupation within the van der Waals gaps was
determined by high-precision x-ray diffraction analysis which showed a notably
higher Fe occupation than in bulk crystals. We thus infer that the higher
magnetic ordering temperature results from an increased exchange interaction
among the Fe5GeTe2 layers mediated by iron within the gaps between these
layers. Our findings establish self-intercalation during epitaxial growth as an
efficient mechanism to achieve high-temperature magnetism in a broad class of
van der Waals materials.",2309.17439v3
2023/10/19,Dispersion and absorption effects in the linearized Born-Infeld electrodynamics under an external magnetic field,"The effects of the Ohmic and magnetic density currents are investigated in
the linearized Born-Infeld electrodynamics. The linearization is introduced
through an external magnetic field, in which the vector potential of the
Born-Infeld electrodynamics is expanded around of a magnetic background field,
that we consider uniform and constant in this paper. From the Born-Infeld
linearized equations, we obtain the solutions for the refractive index
associated with the electromagnetic wave superposition, when the current
density is ruled by the Ohm law, and in the second case, when the current
density is set by a isotropic magnetic conductivity. These solutions are
functions of the magnetic background $({\bf B})$, of the wave propagation
direction $({\bf k})$, and also it depends on the material conductivity, and on
the wave frequency. As consequence, the dispersion and the absorption of waves
change when ${\bf B}$ is parallel to ${\bf k}$ in relation to the case of ${\bf
B}$ perpendicular to ${\bf k}$ in the material medium. These characteristics of
the refraction index related to directions of ${\bf B}$ and ${\bf k}$ open a
discussion of the birefringence in the material medium.",2311.02080v1
2024/1/17,Grayscale control of local magnetic properties with direct-write laser annealing,"Across the fields of magnetism, microelectronics, optics, and others,
engineered local variations in physical properties can yield groundbreaking
functionalities that play a crucial role in enabling future technologies.
Beyond binary modifications, 1D lateral gradients in material properties
(achieved by gradients in thickness, stoichiometry, temperature, or strain)
give rise to a plethora of new effects in thin film magnetic systems. However,
extending such gradient-induced behaviors to 2D is challenging to realize with
existing methods, which are plagued by slow processing speeds, dose
instabilities, or limitation to variation along one dimension. Here, we show
for the first time how commonplace direct-write laser exposure techniques,
initially developed for grayscale patterning of photoresist surfaces, can be
repurposed to perform grayscale direct-write laser annealing. With this
technique, we demonstrate the ease with which two-dimensional, continuous
variations in magnetic properties can be created at the mesoscopic scale in
numerous application-relevant materials, including ferromagnetic,
ferrimagnetic, and synthetic antiferromagnetic thin-film systems. The speed,
versatility, and new possibilities to create complex magnetic energy landscapes
offered by direct-write laser annealing opens the door to the lateral
modification of the magnetic, electronic, and structural properties of a
variety of thin films with an abundance of applications.",2401.09314v1
2024/2/3,Magnetochiral Tunneling in Paramagnetic Co$_{1/3}$NbS$_2$,"Electric currents have the intriguing ability to induce magnetization in
nonmagnetic crystals with sufficiently low crystallographic symmetry. Some
associated phenomena include the non-linear anomalous Hall effect in polar
crystals and the nonreciprocal directional dichroism in chiral crystals when
magnetic fields are applied. In this work, we demonstrate that the same
underlying physics is also manifested in the electronic tunneling process
between the surface of a nonmagnetic chiral material and a magnetized scanning
probe. In the paramagnetic but chiral metallic compound Co$_{1/3}$NbS$_2$, the
magnetization induced by the tunneling current is shown to become detectable by
its coupling to the magnetization of the tip itself. This results in a contrast
across different chiral domains, achieving atomic-scale spatial resolution of
structural chirality. To support the proposed mechanism, we used
first-principles theory to compute the chirality-dependent current-induced
magnetization and Berry curvature in the bulk of the material. Our
demonstration of this magnetochiral tunneling effect opens up a new avenue for
investigating atomic-scale variations in the local crystallographic symmetry
and electronic structure across the structural domain boundaries of
low-symmetry nonmagnetic crystals.",2402.02248v1
2024/3/14,"Magnetotransport properties in van-der-Waals \textit{\textbf{R}}Te$_{3}$ (\textit{\textbf{R}} = La, Ce, Tb)","Rare-earth tritellurides are van-der-Waals antiferromagnets which have been
attracting attention as materials not only with high mobility, but also with
various states such as superconductivity under high pressure, incommensurate
charge-density-wave (CDW) phase, and multiple antiferromagnetic phases. In this
work, we performed longitudinal resistivity and Hall resistivity measurements
simultaneously in exfoliated $R$Te$_{3}$ ($R$ =La, Ce, Tb) thin film devices,
in order to investigate the influence of magnetic ordering on transport
properties in van-der-Waals magnetic materials. We have obtained carrier
mobility and concentration using a two-band model, and have observed an
increase in carrier mobility in the antiferromagnets CeTe$_{3}$ and TbTe$_{3}$
due to the magnetic transition. Especially in CeTe$_{3}$, the carrier
concentration has changed drastically below the magnetic transition
temperature, suggesting the interaction between the CDW and antiferromagnetic
phases. In addition, the analysis of the Shubnikov-de Haas oscillations in
CeTe$_{3}$ supports the possibility of Fermi surface modulation by magnetic
ordering. This research will pave the way not only for spintronic devices that
take advantage of high mobility, but also for the study of the correlation
between CDW and magnetism states in low-dimensional materials.",2403.09250v2
2024/4/3,Discovery of universal phonon thermal Hall effect in crystals,"Thermal Hall effect (THE) in insulator is a remarkable phenomenon that arises
from the motion of chargeless quasi-particles under a magnetic field. While
magnons or exotic spin excitations were considered as the origin of THE in some
magnetic materials, there are more and more evidences suggest that phonons play
a significant role. However, the mechanism behind phonon THE is still unknown.
Here we report the observation of THE, including planar THE, in a broad range
of non-magnetic insulators and semiconductor: SrTiO$_3$, SiO$_2$ (quartz), MgO
and Si. While the presence of antiferrodistortive domains in SrTiO$_3$ and
chiral phonons in SiO$_2$ may complicate the interpretation of THE, the
striking observations of THE in the trivial insulator MgO and high-purity
intrinsic semiconductor Si demonstrate that phonon THE is a universal property
of crystals. Without other effects on phonons such as from magnons, this
universal phonon THE is characterized by a scaling law of |$\kappa_{xy}$|
$\sim$ $\kappa_{xx}^2$. Our results experimentally discover a fundamental
physics of phonons in magnetic field, which must come from the direct coupling
between atom vibrations and the field. Starting from this universal phonon THE
in crystals, all previous interpretations of THE in magnetic or non-magnetic
materials need to be reconsidered.",2404.02863v1
2020/6/5,Imitation of spin density wave order in Cu$_3$Nb$_2$O$_8$,"Spin density waves, based on modulated local moments, are usually associated
with metallic materials, but have recently been reported in insulators which
display coupled magnetic and structural order parameters. We discuss one such
example, the multiferroic Cu$_3$Nb$_2$O$_8$, which is reported to undergo two
magnetic phase transitions, first to a spin density wave phase at $T_N \approx
26.5K$, and then to a helicoidal structure coupled to an electric polarization
below $T_2 \approx 24K$ [R. D. Johnson, et al., Phys. Rev. Lett., 107, 137205
(2011)] which breaks the crystallographic inversion symmetry. We apply
spherical polarimetry to confirm the low-temperature magnetic structure, yet
only observe a single magnetic phase transition to helicoidal order. We argue
that the reported spin density wave originates from a decoupling of the
components of the magnetic order parameter, as allowed by symmetry and driven
by thermal fluctuations. This provides a mechanism for the magnetic, but not
nuclear, structure to break inversion symmetry thereby creating an intermediate
phase where the structure imitates a spin density wave. As the temperature is
reduced, this intermediate structure destabilizes the crystal such that a
structural chirality is induced, as reflected by the emergence of the electric
polarization, and the imitation spin density wave relaxes into a generic
helicoid. This provides a situation where the magnetic structure breaks
inversion symmetry while the crystal structure remains centrosymmetric.",2006.03425v1
2021/1/18,"Magnetic properties of wurtzite (Ga,Mn)As","Here we report on detailed studies of the magnetic properties of the wurtzite
(Ga,Mn)As cylindrical shells. Ga$_{0.94}$Mn$_{0.06}$As shells have been grown
by molecular beam epitaxy at low temperature as a part of multishell cylinders
overgrown on wurtzite (Ga,In)As nanowires cores, synthesized on GaAs (111)B
substrates. Our studies clearly indicate the presence of a low temperature
ferromagnetic coupling, which despite a reasonably high Mn contents of 6\% is
limited only to below 30~K. A set of dedicated measurements shows that despite
a high structural quality of the material the magnetic order has a granular
form, which gives rise to the dynamical slow-down characteristic to blocked
superparamagnets. The lack of the long range order has been assigned to a very
low hole density, caused primarily by numerous compensation donors, arsenic
antisites, formed in the material due to a specific geometry of the growth of
the shells on the nanowire template. The associated electrostatic disorder has
formed a patchwork of spontaneously magnetized (macrospin) and nonmagnetic
(paramagnetic) volumes in the material. Using high field results it has been
evaluated that the total volume taken by the macrospins constitute about 2/3 of
the volume of the (Ga,Mn)As whereas in the remaining 1/3 only paramagnetic Mn
ions reside. By establishing the number of the uncoupled ions the two
contributions were separated. The Arrott plot method applied to the
superparamagnetic part yielded the first experimental assessment of the
magnitude of the spin-spin coupling temperature within the macrospins in
(Ga,Mn)As, $T_{\mathrm{C}}=28$~K. In a broader view our results constitute an
important contribution to the still ongoing dispute on the true and the
dominant form(s) of the magnetism in this model dilute ferromagnetic
semiconductor.",2101.07194v1
2022/8/28,Giant and Reversible Electronic Structure Evolution in a Magnetic Topological Material EuCd2As2,"The electronic structure and the physical properties of quantum materials can
be significantly altered by charge carrier doping and magnetic state
transition. Here we report a discovery of a giant and reversible electronic
structure evolution with doping in a magnetic topological material. By
performing high-resolution angle-resolved photoemission measurements on
EuCd2As2,we found that a huge amount of hole doping can be introduced into the
sample surface due to surface absorption. The electronic structure exhibits a
dramatic change with the hole doping which can not be described by a rigid band
shift. Prominent band splitting is observed at high doping which corresponds to
a doping-induced magnetic transition at low temperature (below -15 K) from an
antiferromagnetic state to a ferromagnetic state. These results have
established a detailed electronic phase diagram of EuCd2As2 where the
electronic structure and the magnetic structure change systematically and
dramatically with the doping level. They further suggest that the transport,
magnetic and topological properties of EuCd2As2 can be greatly modified by
doping. These work will stimulate further investigations to explore for new
phenomena and properties in doping this magnetic topological material.",2208.13203v1
2023/12/1,Magneto-transport in the monolayer MoS2 material system for high-performance field-effect transistor applications,"Electronic transport in monolayer MoS2 is significantly constrained by
several extrinsic factors despite showing good prospects as a transistor
channel material. Our paper aims to unveil the underlying mechanisms of the
electrical and magneto-transport in monolayer MoS2. In order to quantitatively
interpret the magneto-transport behavior of monolayer MoS2 on different
substrate materials, identify the underlying bottlenecks, and provide
guidelines for subsequent improvements, we present a deep analysis of the
magneto-transport properties in the diffusive limit. Our calculations are
performed on suspended monolayer MoS2 and MoS2 on different substrate materials
taking into account remote impurity and the intrinsic and extrinsic phonon
scattering mechanisms. We calculate the crucial transport parameters such as
the Hall mobility, the conductivity tensor elements, the Hall factor, and the
magnetoresistance over a wide range of temperatures, carrier concentrations,
and magnetic fields. The Hall factor being a key quantity for calculating the
carrier concentration and drift mobility, we show that for suspended monolayer
MoS2 at room temperature, the Hall factor value is around 1.43 for magnetic
fields ranging from 0.001 to 1 Tesla, which deviates significantly from the
usual value of unity. In contrast, the Hall factor for various substrates
approaches the ideal value of unity and remains stable in response to the
magnetic field and temperature. We also show that the MoS2 over an Al2O3
substrate is a good choice for the Hall effect detector. Moreover, the
magnetoresistance increases with an increase in magnetic field strength for
smaller magnetic fields before reaching saturation at higher magnetic fields.
The presented theoretical model quantitatively captures the scaling of mobility
and various magnetoresistance coefficients with temperature, carrier densities
and magnetic fields.",2312.00378v1
2007/2/25,Magnetic flux emergence in granular convection: Radiative MHD simulations and observational signatures,"We study the emergence of magnetic flux from the near-surface layers of the
solar convection zone into the photosphere. To model magnetic flux emergence,
we carried out a set of numerical radiative magnetohydrodynamics simulations.
Our simulations take into account the effects of compressibility, energy
exchange via radiative transfer, and partial ionization in the equation of
state. All these physical ingredients are essential for a proper treatment of
the problem. Furthermore, the inclusion of radiative transfer allows us to
directly compare the simulation results with actual observations of emerging
flux. We find that the interaction between the magnetic flux tube and the
external flow field has an important influence on the emergent morphology of
the magnetic field. Depending on the initial properties of the flux tube (e.g.
field strength, twist, entropy etc.), the emergence process can also modify the
local granulation pattern. The emergence of magnetic flux tubes with a flux of
$10^{19}$ Mx disturbs the granulation and leads to the transient appearance of
a dark lane, which is coincident with upflowing material. These results are
consistent with observed properties of emerging magnetic flux.",0702666v1
1998/10/16,Evidence of a first order like jump in equilibrium magnetization across the peak effect region in superconducting 2H-NbSe$_2$,"We report magnetization hysteresis measurements in the peak effect region of
a very clean single crystal of superconducting 2H-NbSe$_2$ at temperatures very
close to T$_c$(0). Through measurement of minor magnetization curves, we infer
the equilibrium magnetization curve across the PE region. We observe a small
first order like change in equilibrium magnetization across the peak effect. We
relate this observation to the entropy change associated with the
order-disorder transformation. We further note that the first order like change
in the equilibrium magnetization observed in 2H-NbSe$_2$ is comparable to the
change(s)observed in the equilibrium magnetization at the FLL melting
transition in various high temperature superconductors.",9810204v1
1999/5/6,Measuring the interaction force between a high temperature superconductor and a permanent magnet,"Repulsive and attractive forces are both possible between a superconducting
sample and a permanent magnet, and they can give place to magnetic levitation
or free-suspension phenomena, respectively. We show experiments to quantify
this magnetic interaction which represents a promising field regarding to
short-term technological applications of high temperature superconductors. The
measuring technique employs an electronic balance and a rare-earth magnet that
induces a magnetic moment in a melt-textured YBa2Cu3O7 superconductor immersed
in liquid nitrogen. The simple design of the experiments allows a fast and easy
implementation in the advanced physics laboratory with a minimum cost. Actual
levitation and suspension demonstrations can be done simultaneously as a help
to interpret magnetic force measurements.",9905084v1
1999/12/22,Incommensurate Geometry of the Elastic Magnetic Peaks in Superconducting La1.88Sr0.12CuO4,"We report magnetic neutron scattering measurements of incommensurate magnetic
order in a superconducting single crystal of La1.88Sr0.12CuO4. We find that the
incommensurate wavevectors which describe the static magnetism do not lie along
high-symmetry directions of the underlying CuO2 lattice. The positions of the
elastic magnetic peaks are consistent with those found in excess-oxygen doped
La2CuO4+y. This behavior differs from the precise magnetic order found in the
low temperature tetragonal La1.6-xNd0.4SrxCuO4 material for which stripes of
spin and charge have been observed. These observations have clear implications
for any stripe model proposed to describe the static magnetism in orthorhombic
La2CuO4-based superconductors.",9912401v1
2000/1/26,"""Quasi two-dimensional"" spin distributions in II-VI magnetic semiconductor heterostructures: Clustering and dimensionality","Spin clustering in diluted magnetic semiconductors (DMS) arises from
antiferromagnetic exchange between neighboring magnetic cations and is a strong
function of reduced dimensionality. Epitaxially-grown single monolayers and
abrupt interfaces of DMS are, however, never perfectly two-dimensional (2D) due
to the unavoidable inter-monolayer mixing of atoms during growth. Thus the
magnetization of DMS heterostructures, which is strongly modified by spin
clustering, is intermediate between that of 2D and 3D spin distributions. We
present an exact calculation of spin clustering applicable to arbitrary
distributions of magnetic spins in the growth direction. The results reveal a
surprising insensitivity of the magnetization to the form of the intermixing
profile, and identify important limits on the maximum possible magnetization.
High-field optical studies of heterostructures containing ""quasi-2D"" spin
distributions are compared with calculation.",0001378v1
2000/6/7,Theory of Magnetic Anisotropy in III_{1-x}Mn_{x}V Ferromagnets,"We present a theory of magnetic anisotropy in ${\rm III}_{1-x}{\rm
Mn}_{x}{\rm V}$ diluted magnetic semiconductors with carrier-induced
ferromagnetism. The theory is based on four and six band envelope functions
models for the valence band holes and a mean-field treatment of their exchange
interactions with ${\rm Mn}^{++}$ ions. We find that easy-axis reorientations
can occur as a function of temperature, carrier density $p$, and strain. The
magnetic anisotropy in strain-free samples is predicted to have a $p^{5/3}$
hole-density dependence at small $p$, a $p^{-1}$ dependence at large $p$, and
remarkably large values at intermediate densities. An explicit expression,
valid at small $p$, is given for the uniaxial contribution to the magnetic
anisotropy due to unrelaxed epitaxial growth lattice-matching strains. Results
of our numerical simulations are in agreement with magnetic anisotropy
measurements on samples with both compressive and tensile strains. We predict
that decreasing the hole density in current samples will lower the
ferromagnetic transition temperature, but will increase the magnetic anisotropy
energy and the coercivity.",0006093v1
2001/4/26,Structure and magnetic order in Fe2+xV1-xAl,"We present a detailed structural investigation via neutron diffraction of
differently heat treated samples Fe2VAl and Fe2+xV1-xAl. Moreover, the magnetic
behaviour of these materials is studied by means of mSR and
Mossbauer-experiments. Our structural investigation indicates that quenched
Fe2VAl, exhibiting the previously reported ""Kondo insulating like"" behaviour,
is off-stoichiometric (6%) in its Al content. Slowly cooled Fe2VAl is
structurally better ordered and stoichiometric, and the microscopic magnetic
probes establish long range ferromagnetic order below TC = 13K, consistent with
results from bulk experiments. The magnetic state can be modelled as being
generated by diluted magnetic ions in a non-magnetic matrix. Quantitatively,
the required number of magnetic ions is too large as to be explained by a model
of Fe/V site exchange. We discuss the implications of our findings for the
ground state properties of Fe2VAl, in particular with respect to the role of
crystallographic disorder.",0104512v2
2001/5/11,Magnetization Process of Nanoscale Iron Cluster,"Low-temperature magnetization process of the nanoscale iron cluster in
linearly sweeped fields is investigated by a numerical analysis of
time-dependent Schr$\ddot{\rm o}$dinger equation and the quantum master
equation. We introduce an effective basis method extracting important states,
by which we can obtain the magnetization process effectively. We investigate
the structure of the field derivative of the magnetization. We find out that
the antisymmetric interaction determined from the lattice structure reproduces
well the experimental results of the iron magnets and that this interaction
plays an important role in the iron cluster. Deviations from the adiabatic
process are also studied. In the fast sweeping case, our calculations indicate
that the nonadiabatic transition dominantly occurs at the level crossing for
the lowest field. In slow sweeping case, due to the influence of the thermal
environment to the spin system, the field derivative of the magnetization shows
an asymmetric behavior, the magnetic F$\ddot{\rm o}$hn effect, which explains
the substructure of the experimental results in the pulsed field.",0105227v1
2001/7/26,Magnetic-field-induced superconductivity in layered organic molecular crystals with localized magnetic moments,"The synthetic organic compound lambda-(BETS)2FeCl4 undergoes successive
transitions from an antiferromagnetic insulator to a metal and then to a
superconductor as a magnetic field is increased. We use a Hubbard-Kondo model
to clarify the role of the Fe(3+) magnetic ions in these phase transitions. In
the high-field regime, the magnetic field acting on the electron spins is
compensated by the exchange field He due to the magnetic ions. This suggests
that the field-induced superconducting state is the same as the zero-field
superconducting state which occurs under pressure or when the Fe(3+) ions are
replaced by non-magnetic Ga(3+) ions. We show how He can be extracted from the
observed splitting of the Shubnikov-de Haas frequencies. Furthermore, we use
this method of extracting He to predict the field range for field-induced
superconductivity in other materials.",0107535v1
2001/10/18,Magnetic and transport properties of the new antiferromagnetic Kondo-lattice CeNiBi2,"We report results of the first studies on the magnetic and transport
properties of a new material CeNiBi_2. The magnetic susceptibility exhibits a
sharp peak at T_N = 6K, indicating an antiferromagnetic phase transition. This
antiferromagnetic order below T_N is confirmed by magnetization measurement,
which displays a metamagnetic-like transition at H_m = 5 T. Both
low-temperature susceptibility and high-field magnetization are suggestive of
strong crystalline-electric-field effect in CeNiBi_2. The electrical
resistivity shows the presence of Kondo and crystal-field effects with a sharp
drop below TN due to the antiferromagnetic ordering. This sharp drop below T_N
in the electrical resistivity is suppressed slightly to higher temperatures by
an applied magnetic field to 18 T. With increasing magnetic field, the slope of
magnetoresistance changes from positive to negative, being indicative of the
transition to a ferromagnetic state.",0110380v1
2001/11/9,Diluted Magnetic Semiconductors in the Low Carrier Density Regime,"This paper, based on a presentation at the Spintronics 2001 conference,
provides a review of our studies on II-VI and III-V Mn-doped Diluted Magnetic
Semiconductors. We use simple models appropriate for the low carrier density
(insulating) regime, although we believe that some of the unusual features of
the magnetization curves should qualitatively be present at larger dopings
(metallic regime) as well. Positional disorder of the magnetic impurities
inside the host semiconductor is shown to have observable consequences for the
shape of the magnetization curve. Below the critical temperature the
magnetization is spatially inhomogeneous, leading to very unusual temperature
dependence of the average magnetization as well as specific heat. Disorder is
also found to enhance the ferromagnetic transition temperature. Unusual spin
and charge transport is implied.",0111184v1
2002/4/16,Evidence for Magnetic Field Induced Changes of the Phase of Tunneling States: Spontaneous Echoes in (KBr)$_{1-x}$(KCN)$_x$ in Magnetic Fields,"Recently, it has been discovered that in contrast to expectations the
low-temperature dielectric properties of some multi-component glasses depend
strongly on magnetic fields. In particular, the low-frequency dielectric
susceptibility and the amplitude of coherent polarization echoes show striking
non-monotonic magnetic field dependencies. The low-temperature dielectric
response of these materials is governed by atomic tunneling systems. We now
have investigated the coherent properties of tunneling states in a crystalline
host in magnetic fields up to 230$ $mT. Two-pulse echo experiments have been
performed on a KBr crystal containing about 7.5% CN$^-$. Like in glasses, but
perhaps even more surprising in the case of a crystalline system, we observe a
very strong magnetic field dependence of the echo amplitude. Moreover, for the
first time we have direct evidence that magnetic fields change the phase of
coherent tunneling systems in a well-defined way. We present the data and
discuss the possible origin of this intriguing effect.",0204348v1
2002/5/28,"Ferromagnetism in (In,Mn)As Diluted Magnetic Semiconductor Thin Films Grown by Metalorganic Vapor Phase Epitaxy","In1-xMnxAs diluted magnetic semiconductor (DMS) thin films have been grown
using metalorganic vapor phase epitaxy (MOVPE).
Tricarbonyl(methylcyclopentadienyl)manganese was used as the Mn source.
Nominally single-phase, epitaxial films were achieved with Mn content as high
as x=0.14 using growth temperatures Tg>475 C. For lower growth temperatures and
higher Mn concentrations, nanometer scale MnAs precipitates were detected
within the In1-xMnxAs matrix. Magnetic properties of the films were
investigated using a superconducting quantum interference device (SQUID)
magnetometer. Room-temperature ferromagnetic order was observed in a sample
with x=0.1. Magnetization measurements indicated a Curie temperature of 333 K
and a room-temperature saturation magnetization of 49 emu/cm^3. The remnant
magnetization and the coercive field were small, with values of 10 emu/cm^3 and
400 Oe, respectively. A mechanism for this high-temperature ferromagnetism is
discussed in light of the recent theory based on the formation of small
clusters of a few magnetic atoms.",0205602v1
2002/9/17,Anisotropic magnetic behavior of GdBa_2Cu_3O_{6+y} single crystals,"Magnetic properties of high-quality Al-free nonsuperconducting
GdBa_2Cu_3O_{6+y} single crystals grown by flux method have been studied. The
magnetic anisotropy below the N\'eel temperature T_N~2.3K corresponds to the
direction of Gd^{3+} magnetic moments along the tetragonal c-axis. At T < T_N
clear indications of spin-flop transitions for H||c have been observed on
magnetization curves at H_{sf}~10kOe. Magnetic phase diagrams have been
obtained for H||c as well as for H||ab. A pronounced anisotropy in the magnetic
susceptibility (unexpected for Gd-based compounds) has been found above T_N.",0209404v1
2003/1/20,Unusual Behavior of Antiferromagnetic Superconductors in Low Magnetic Fields,"In this article, we examine the superconducting properties of low- and
high-$T_c$ magnetic superconductors in magnetic fields close to the first
penetration field. Attention is paid to the properties that relate to the
interactions between antiferromagnetism and superconductivity. It is suggested
that several features characterizing the interplay between magnetic and
superconducting subsystems in low-$T_c$ superconductors can also be present in
high-$T_c$ materials, however, they have not been observed for any
non-substituted antiferromagnetic superconductors of the Y123 type. For the
Gd$_{1+x}$Ba$_{2-x}$Cu$_3$O$_{7-\delta}$ compound, a peak in the temperature
dependence of the ac susceptibility has been found for $x = 0.2$ near the
N\'{e}el temperature of the Gd sublattice. This peak is attributed to the
suppression of superconducting persistent currents due to the pair breaking
effect that results from the enhanced magnetic fluctuations in the vicinity of
the phase transition temperature. This observation indicates that the
interaction between magnetic and conducting electrons is present for the
composition with $x = 0.2$, where magnetism is enhanced and superconductivity
diminished.",0301358v1
2003/5/9,X-ray resonant magnetic scattering from structurally and magnetically rough interfaces in multilayered systems I. Specular reflectivity,"The theoretical formulation of x-ray resonant magnetic scattering from rough
surfaces and interfaces is given for specular reflectivity. A general
expression is derived for both structurally and magnetically rough interfaces
in the distorted-wave Born approximation (DWBA) as the framework of the theory.
For this purpose, we have defined a ``structural'' and a ``magnetic'' interface
to represent the actual interfaces. A generalization of the well-known
Nevot-Croce formula for specular reflectivity is obtained for the case of a
single rough magnetic interface using the self-consistent method. Finally, the
results are generalized to the case of multiple interfaces, as in the case of
thin films or multilayers. Theoretical calculations for each of the cases are
illustrated with numerical examples and compared with experimental results of
magnetic reflectivity from a Gd/Fe multilayer.",0305220v1
2003/5/15,Magnetic relaxation in finite two-dimensional nanoparticle ensembles,"We study the slow phase of thermally activated magnetic relaxation in finite
two-dimensional ensembles of dipolar interacting ferromagnetic nanoparticles
whose easy axes of magnetization are perpendicular to the distribution plane.
We develop a method to numerically simulate the magnetic relaxation for the
case that the smallest heights of the potential barriers between the
equilibrium directions of the nanoparticle magnetic moments are much larger
than the thermal energy. Within this framework, we analyze in detail the role
that the correlations of the nanoparticle magnetic moments and the finite size
of the nanoparticle ensemble play in magnetic relaxation.",0305343v1
2003/7/12,Nanoscale Zeeman localization of charge carriers in diluted magnetic semiconductor-permalloy hybrids,"We investigate the possibility of charge carrier localization in magnetic
semiconductors due to the presence of a highly inhomogeneous external magnetic
field. As an example, we study in detail the properties of a magnetic
semiconductor-permalloy disk hybrid system. We find that the giant Zeeman
respose of the magnetic semiconductor in conjuction with the highly non-uniform
magnetic field created by the vortex state of a permalloy disk can lead to
Zeeman localized states at the interface of the two materials. These trapped
state are chiral, with chirality controlled by the orientation of the core
magnetization of the permalloy disk. We calculate the energy spectrum and the
eigenstates of these Zeeman localized states, and discuss their experimental
signatures in spectroscopic probes.",0307305v1
2003/8/3,Interaction between soft magnetic and superconducting films,"We study theoretically the interaction between soft magnetic and
superconducting films. It is shown that the vortex induces a magnetization
distribution in the magnetic film, thus modifying the magnetic field as well as
the interactions with e.g. Bloch walls. In particular, the field from the
vortex may change sign close to the core as a result of the vortex-induced
magnetization, thus resulting in a crossover from attraction to repulsion
between vortices and Bloch walls. Moreover, we show that by tuning the
anisotropy field of the magnetic film, one may enhance the interaction between
Bloch walls and vortices. Finally, we discuss how the structure of a Bloch wall
in presence of the thin film superconductor can be revealed by magneto-optic
imaging using an additional magneto-optic indicator.",0308039v1
2003/8/5,Magnetization reversal and current hysteresis due to spin injection in magnetic junction,"Magnetic junction is considered which consists of two ferromagnetic metal
layers, a thin nonmagnetic spacer in between, and nonmagnetic lead. Theory is
developed of a magnetization reversal due to spin injection in the junction.
Spin-polarized current is perpendicular to the interfaces. One of the
ferromagnetic layers has pinned spins and the other has free spins. The current
breaks spin equilibrium in the free spin layer due to spin injection or
extraction. The nonequilibrium spins interact with the lattice magnetic moment
via the effective s-d exchange field, which is current dependent. Above a
certain current density threshold, the interaction leads to a magnetization
reversal. Two threshold currents are found, which are reached as the current
increases or decreases, respectively, so that a current hysteresis takes place.
The theoretical results are in accordance with the experiments on magnetization
reversal by current in three-layer junctions Co/Cu/Co prepared in a pillar
form.",0308076v2
2003/11/3,Nonuniform switching ferromagnetic layers by spin polarized current,"The magnetic reversal by spin-polarized current of a magnetic junction
consisting of two ferromagnetic layers and a nonmagnetic spacer in between is
considered. Initially, the free layer is magnetized antiparallel to the pinned
layer by an external magnetic field. Under current flowing, a nonequilibrium
spin polarization appears in the free layer. The interaction between the
injected spins and the lattice leads to instability of the antiparallel
orientation at the high enough current density and to switching the free layer
to a state with magnetization parallel to one in the pinned layer. If the free
layer thickness and the external magnetic field strength are large enough, then
a nonuniform switching is favorable, so that only a part of the free layer near
the injector switches. Such a switching is accompanied with appearance of a
domain wall between the switched and non-switched regions. The domain wall can
oscillate around the equilibrium position with some natural frequency depending
on the external magnetic field.",0311028v2
2003/11/20,Trapped field and related properties in a superconducting disk magnetized by pulse field,"The distributions of the magnetic field and temperature in a
superconducting-disk magnetized by pulse field, and the levitation force
between this disk and a permanent magnet are calculated from first principles.
The calculation is based upon the current motion and the heat diffusion
equations in the disk. The critical current density as a function of magnetic
field and temperature is taken into account. The dissipation power in the
superconducting or the normal state region is distinguished. The trapped field
may reach 17 T at 29 K by pulsed field magnetization. The effects of the
amplitude of the current pulse on the distributions of magnetic field in the
disk and on the levitation force are discussed.",0311490v1
2004/2/16,Measuring electron orbital magnetic moments in carbon nanotubes,"The remarkable transport properties of carbon nanotubes (NTs) are determined
by their unique electronic structure (1). The electronic states of a NT form
one-dimensional electron and hole subbands which, in general, are separated by
an energy gap (2,3). States near the energy gap are predicted to have a large
orbital magnetic moment much larger than the Bohr magneton (4,5). The moment is
due to electron motion around the NT circumference. This orbital magnetic
moment is thought to play a role in the magnetic susceptibility of NTs (6-9)
and the magneto-resistance observed in large multi-walled NTs (10-12). However,
the coupling between magnetic field and the electronic states of an individual
NT has not been experimentally quantified. We have made electrical measurements
of relatively small diameter (2 - 5 nm) individual NTs in the presence of an
axial magnetic field. We observe energy shifts of electronic states and the
associated changes in subband structure. Our results quantitatively confirm
predicted values for orbital magnetic moments in NTs.",0402425v2
2004/4/5,Distribution of the sheet current in a magnetically shielded superconducting filament,"The distribution of the transport current in a superconducting filament
aligned parallel to the flat surface of a semi-infinite bulk magnet is studied
theoretically. An integral equation governing the current distribution in the
Meissner state of the filament is derived and solved numerically for various
filament-magnet distances and different relative permeabilities. This reveals
that the current is depressed on the side of the filament adjacent to the
surface of the magnet and enhanced on the averted side. Substantial current
redistributions in the filament can already occur for low values of the
relative permeability of the magnet, when the distance between the filament and
the magnet is short, with evidence of saturation at moderately high values of
this quantity, similar to the findings for magnetically shielded strips.",0404094v1
2004/4/14,"Exchange interactions and magnetic anisotropy in the ""Ni_4"" magnetic molecule","Magnetic properties of a tetrahedral ""Ni_4"" molecule are discussed in terms
of the Heisenberg model, with magnetic anisotropy terms included, and on the
basis of first-principle calculations within the density functional theory. It
is shown that the isotropic Heisenberg model does not provide an adequate
description of magnetization at low temperatures; an inclusion of single-site
anisotropy terms does not help to improve the situation either. We suppose that
the magnetostriction of the molecule and hence the dependence of interatomic
coupling parameters on the magnetization might be important for an adequate
description of magnetic properties. The first-principle calculations confirm
the system's general preference for antiferromagnetic coupling, as well as the
failure of the isotropic Heisenberg model. A conjugated-gradient search for the
relaxed structure of the ""Ni_4"" molecule in ferromagnetic and antiferromagnetic
configurations did not show any clear tendency to diversification of
interatomic distances. These calculations however have not yet included the
spin-orbit coupling, which can be essential for analyzing the effects of
magnetostriction.",0404343v1
2004/5/7,Magnetic properties and magnetostructural phase transitions in Ni2+xMn1-xGa shape memory alloys,"A systematic study of magnetic properties of Ni2+xMn1-xGa (0 \le x \le 0.19)
Heusler alloys undergoing structural martensite-austenite transformations while
in ferromagnetic state has been performed. From measurements of spontaneous
magnetization, Ms(T), jumps \Delta M at structural phase transitions were
determined. Virtual Curie temperatures of the martensite were estimated from
the comparison of magnetization in martensitic and austenitic phases. Both
saturation magnetic moments in ferromagnetic state and effective magnetic
moments in paramagnetic state of Mn and Ni atoms were estimated and the
influence of delocalization effects on magnetism in these alloys was discussed.
The experimental results obtained show that the shift of martensitic transition
temperature depends weakly on composition. The values of this shift are in good
correspondence with Clapeyron-Clausius formalism taking into account the
experimental data on latent heat at martensite-austenite transformations.",0405134v1
2004/7/1,A universal relationship between magnetization and local structure changes below the ferromagnetic transition in La_{1-x}Ca_xMnO_3; evidence for magnetic dimers,"We present extensive X-ray Absorption Fine Structure (XAFS) measurements on
La_{1-x}Ca_xMnO_3 as a function of B-field (to 11T) and Ca concentration, x
(21-45%). These results reveal local structure changes (associated with polaron
formation) that depend only on the magnetization for a given sample,
irrespective of whether the magnetization is achieved through a decrease in
temperature or an applied magnetic field. Furthermore, the relationship between
local structure and magnetization depends on the hole doping. A model is
proposed in which a filamentary magnetization initially develops via the
aggregation of pairs of Mn atoms involving a hole and an electron site. These
pairs have little distortion and it is likely that they pre-form at
temperatures above T_c.",0407044v2
2004/7/8,"Heat-capacity anomalies in the presence of high magnetic fields in the spin-chain compound, Ca3Co2O6","Heat-capacity behavior in the presence of externally applied magnetic field
(H) up to 140 kOe is investigated (2-35 K) for the quasi-1-dimensional
compound, Ca3Co2O6, believed to order magnetically with the so-called partially
disordered anti-ferromagnetic structure. The results reveal that there is a
shift of the magnetic transition occurring around 24 K to a marginally higher
temperature (by 0.5 K) as H is increased from 10 to 30 kOe, uncharacteristic of
anti-ferromagnets. No peak attributable to magnetic ordering could be observed
in the entire field range of investigation in the vicinity of the second
magnetic transition, occurring around 10 K. However, hysteresis studies of
H-dependence of C indicate a subtle change in the magnetic structure as the T
is lowered across 10 K.",0407189v1
2004/8/18,Theory of Magnetic Polaron,"The concept of magnetic polaron is analysed and developed to elucidate the
nature of itinerant charge carrier states in magnetic semiconductors and
similar complex magnetic materials. By contrasting the scattering and bound
states of carriers within the $s-d$ exchange model, the nature of bound states
at finite temperatures is clarified. The free magnetic polaron at certain
conditions is realized as a bound state of the carrier (electron or hole) with
the spin wave. Quite generally, a self-consistent theory of a magnetic polaron
is formulated within a nonperturbative many-body approach, the Irreducible
Green Functions (IGF) method which is used to describe the quasiparticle
many-body dynamics at finite temperatures. Within the above many-body approach
we elaborate a self-consistent picture of dynamic behavior of two interacting
subsystems, the localized spins and the itinerant charge carriers. In
particular, we show that the relevant generalized mean fields emerges naturally
within our formalism. At the same time, the correct separation of elastic
scattering corrections permits one to consider the damping effects (inelastic
scattering corrections) in the unified and coherent fashion. The damping of
magnetic polaron state, which is quite different from the damping of the
scattering states, finds a natural interpretation within the present
self-consistent scheme.",0408404v2
2004/9/8,Electronic structure and magnetic anisotropy for nickel-based molecular magnets,"Recent magnetic measurements on tetra-nickel molecular magnets
[Ni(hmp)(ROH)Cl]$_4$, where R=CH$_3$, CH$_2$CH$_3$, or
(CH$_2$)$_2$C(CH$_3$)$_3$ and hmp$^-$ is the monoanion of
2-hydroxymethylpyridine, revealed a strong exchange bias prior to the external
magnetic field reversal as well as anomalies in electron paramagnetic resonance
peaks at low temperatures. To understand the exchange bias and observed
anomalies, we calculate the electronic structure and magnetic properties for
the Ni$_4$ molecules with the three different ligands, employing
density-functional theory. Considering the optimized structure with possible
collinear spin configurations, we determine a total spin of the lowest-energy
state to be S=0, which does not agree with experiment. We also calculate
magnetic anisotropy barriers for all three types of Ni$_4$ molecules to be in
the range of 4-6 K.",0409207v1
2004/9/8,Low Temperature Magnetic Domain Patterns in MnAs Films Grown on GaAs(001),"Magnetic properties of MnAs were studied as a function of temperature with a
superconducting interference device (5 K to 350 K), and atomic force
microscopy/magnetic force microscopy (20 K to 360 K). Structural and magnetic
properties of MnAs depend on film thickness both near and far below the Curie
temperature. In samples with coexisting ferromagnetic alpha-MnAs and
paramagnetic beta-MnAs, the domain structures are affected by the distribution
of two phases. The magnetic domain structures below the temperature range of
this mixed phase resemble that of a single domain structure with uniform
magnetization along the easy axis, except there are regions elongated along the
easy axis embedded where the magnetization is along the second easy axis, i.e.,
normal to the films. The shape of those regions and their temperature
dependence are also related to the MnAs layer thickness.",0409214v1
2004/11/28,Quasistatic x-ray speckle metrology of microscopic magnetic return point memory,"We have used coherent, resonant, x-ray magnetic speckle patterns to measure
the statistical evolution of the microscopic magnetic domains in perpendicular
magnetic films as a function of the applied magnetic field. Our work
constitutes the first direct, ensemble-averaged study of microscopic magnetic
return point memory, and demonstrates the profound impact of interfacial
roughness on this phenomenon. At low fields, the microscopic magnetic domains
forget their past history with an exponential field dependence.",0411695v1
2004/12/1,Magnetoresistive Effects in Ferromagnet-Superconductor Multilayers,"We consider a nanoscale system consisting of Manganite-ferromagnet and
Cuprate-superconductor multilayers in a spin valve configuration. The
magnetization of the bottom Manganite-ferromagnet is pinned by a
Manganite-antiferromagnet. The magnetization of the top Manganite-ferromagnet
is coupled to the bottom one via indirect exchange through the superconducting
layers. We study the behavior of the critical temperature and the
magnetoresistance as a function of an externally applied parallel magnetic
field, when the number of Cuprate-superconductor layers are changed. There are
two typical behaviors in the case of a few monolayers of the Cuprates: a) For
small magnetic fields, the critical temperature and the magnetoresistance
change abruptly when the flipping field of the top Manganite-ferromagnet is
reached. b) For large magnetic fields, the multilayered system re-enters the
zero-resistance (superconducting) state after having become resistive (normal).",0412005v1
2005/1/31,Unusual magnetic properties of the low-dimensional quantum magnet Na2V3O7,"We report the results of low-temperature measurements of the specific heat
Cp(T), ac susceptibility chi(T) and 23Na nuclear magnetic resonance NMR of
Na2V3O7. At liquid He temperatures Cp(T)/T exhibits broad field-dependent
maxima, which shift to higher temperatures upon increasing the applied magnetic
field H. Below 1.5 K the ac magnetic susceptibility chi(T) follows a
Curie-Weiss law and exhibits a cusp at 0.086 mK which indicates a phase
transition at very low temperatures. These results support the previous
conjecture that Na2V3O7 is close to a quantum critical point (QCP) at mu_{0}H =
0 T. The entire data set, including results of measurements of the NMR
spin-lattice relaxation 1/T1(T), reveals a complex magnetic behavior at low
temperatures. We argue that it is due to a distribution of singlet-triplet
energy gaps of dimerized V moments. The dimerization process evolves over a
rather broad temperature range around and below 100 K. At the lowest
temperatures the magnetic properties are dominated by the response of only a
minor fraction of the V moments.",0501756v1
2005/3/2,Graphitic-BN Based Metal-free Molecular Magnets From A First Principle Study,"We perform a first principle calculation on the electronic properties of
carbon doped graphitic boron nitride graphitic BN. It was found that carbon
substitution for either boron or nitrogen atom in graphitic BN can induce
spontaneous magnetization. Calculations based on density functional theory with
the local spin density approximation on the electronic band structure revealed
a spin polarized, dispersionless band near the Fermi energy. Spin density
contours showed that the magnetization density originates from the carbon atom.
The magnetization can be attributed to the carbon 2p electron. Charge density
distribution shows that the carbon atom forms covalent bonds with its three
nearest neighbourhood. The spontaneous magnetization survives the curvature
effect in BN nanotubes, suggesting the possibility of molecular magnets made
from BN. Compared to other theoretical models of light-element or metal-free
magnetic materials, the carbon-doped BN are more experimentally accessible and
can be potentially useful.",0503045v1
2005/5/12,Dynamics of magnetization coupled to a thermal bath of elastic modes,"We study the dynamics of magnetization coupled to a thermal bath of elastic
modes using a system plus reservoir approach with realistic magnetoelastic
coupling. After integrating out the elastic modes we obtain a self-contained
equation for the dynamics of the magnetization.
  We find explicit expressions for the memory friction kernel and hence, {\em
via} the Fluctuation-Dissipation
  Theorem, for the spectral density of the magnetization thermal fluctuations.
  For magnetic samples in which the single domain approximation is valid, we
derive an equation for the dynamics of the uniform mode.
  Finally we apply this equation to study the dynamics of the uniform
magnetization mode in insulating ferromagnetic thin films.
  As experimental consequences we find that the fluctuation correlation time is
of the order of the ratio between the film thickness, $h$, and the speed of
sound in the magnet and that the line-width of the ferromagnetic resonance peak
should scale as $B_1^2h$ where $B_1$ is the magnetoelastic coupling constant.",0505331v3
2005/5/29,Dynamical Aspects of Photoinduced Magnetism and Spin-Crossover phenomena in Prussian Blue Analogs,"We present dynamical properties of spin crossover compounds with
photomagnetization, proposing a new model in which the spin-crossover phenomena
and magnetic ordering are incorporated in a unified way. By using this model,
the novel characteristics observed in Prussian blue analogs are qualitatively
well reproduced. We investigate the time evolution of the magnetization and
high spin fraction taking into account multi-time scales in a master equation
approach for the magnetic relaxation, the lattice (electronic) relaxation, and
the photoexcitation process. In particular, processes with different
temperature cycles starting from the photoinduced saturated magnetic state are
studied including the effect of photoirradiation. In the temperature cycle in
the low temperature region where the high spin state has a strong
metastability, the magnetization almost exactly follows the quasi-static
process. On the other hand, when the temperature is raised above the region,
the dynamics of the spin state and the magnetization couple and exhibit various
types of dynamical cooperative phenomena under time-dependent control of
temperature and photoirradiation.",0505702v1
2005/6/2,Magnetic moments of W 5d in Ca2CrWO6 and Sr2CrWO6 double perovskites,"We have investigated the magnetic moment of the W ion in the ferrimagnetic
double perovskites Sr2CrWO6 and Ca2CrWO6 by X-ray magnetic circular dichroism
(XMCD) at the W L(2,3) edges. In both compounds a finite negative spin and
positive orbital magnetic moment was detected. The experimental results are in
good agreement with band-structure calculations for (Sr/Ca)2CrWO6 using the
full-potential linear muffin-tin orbital method. It is remarkable, that the
magnetic ordering temperature, TC, is correlated with the magnetic moment at
the 'non-magnetic' W atom.",0506048v2
2005/6/16,Electronic structure and X-ray magnetic circular dichroism of CrO$_2$,"A detailed theoretical study on the electronic structure and magnetic
properties of half-metallic ferromagnet CrO$_2$ was carried out by means of
relativistic full-potential linear muffin-tin orbital method within the
generalized gradient approximation (GGA) to the exchange correlation potential.
Our calculation favours the [001] magnetization axis to be the easy axis of
magnetization when compared to the [100] axis which is in agreement with the
experiments. The calculated spin and orbital magnetic moments of Cr agrees well
with the experimental and other theoretical works. The Cr L$_{2,3}$ x-ray
absorption and x-ray magnetic circular dichroism (XMCD) spectra were calculated
for both the quantization axis and compared with the experiment. In addition
the oxygen K edge and XMCD spectra were also calculated which compares well
with the experiments. The XMCD sum rules were used to compute the spin and
orbital magnetic moments and results agree quite well with the direct
calculation.",0506410v1
2005/7/12,Magnetic reordering in the vicinity of a ferromagnetic/antiferromagnetic interface,"The magnetic arrangement in the vicinity of the interface between a
ferromagnet and an antiferromagnet is investigated, in particular its
dependence on the exchange couplings and the temperature. Applying a Heisenberg
model, both sc(001) and fcc(001) lattices are considered and solved by a mean
field approximation. Depending on the parameter values a variety of different
magnetic configurations emerge. Usually the subsystem with the larger ordering
temperature induces a magnetic order into the other one (magnetic proximity
effect). With increasing temperature a reorientation of the magnetic
sublattices is obtained. For coupled sc(001) systems both FM and AFM films are
disturbed from their collinear magnetic order, hence exhibit a similar
behavior. This symmetry is absent for fcc(001) films which, under certain
circumstances, may exhibit two different critical temperatures. Analytical
results are derived for simple bilayer systems.",0507265v1
2005/11/14,Magnetic contribution to the specific heat of Pb_{1-x}Eu_{x}Te,"The temperature dependence of the magnetic specific heat has been studied
experimentally and theoretically in the semimagnetic semiconductor
Pb_{1-x}Eu_{x}Te for x=0.027 and x=0.073, over the temperature range from 0.5 K
to 10 K, in magnetic fields up to 2 T. There was a maximum in the magnetic
specific heat between 1 and 3 K even in zero and low magnetic fields; this
maximum shifted toward higher temperatures with increasing magnetic field. The
experimental data have been analyzed in the framework of a model in which we
assume that the ground states of europium ions are split even without an
external magnetic field. We present arguments which support this assumption and
we show that it is possible to find a physical mechanism leading to the
splitting which can explain the experimental results.",0511338v1
2005/11/22,Magnetic interactions of supported magnetic clusters,"It is demonstrated that the magnetic interactions can be drastically
different for nano-sized systems compared to those of bulk or surfaces. Using a
real-space formalism we have developed a method to calculate non-collinear
magnetization structures and hence exchange interactions. Our results for
magnetic clusters supported on a Cu(111) surface show that the magnetic
ordering as a rule is non-collinear and can not always be described using a
simple Heisenberg Hamiltonian. We suggest that ab initio calculations allowing
for non-collinear coupling between atomic spins is the best tool for analyzing
nano-sized magnets.",0511542v1
2006/1/18,Magnetic domain structure and dynamics in interacting ferromagnetic stacks with perpendicular anisotropy,"The time and field dependence of the magnetic domain structure at
magnetization reversal were investigated by Kerr microscopy in interacting
ferromagnetic Co/Pt multilayers with perpendicular anisotropy. Large local
inhomogeneous magnetostatic fields favor mirroring domain structures and domain
decoration by rings of opposite magnetization. The long range nature of these
magnetostatic interactions gives rise to ultra-slow dynamics even in zero
applied field, i.e. it affects the long time domain stability. Due to this
additionnal interaction field, the magnetization reversal under short magnetic
field pulses differs markedly from the well-known slow dynamic behavior.
Namely, in high field, the magnetization of the coupled harder layer has been
observed to reverse more rapidly by domain wall motion than the softer layer
alone.",0601401v1
2006/3/1,Possible Magnetic Chirality in Optically Chiral Magnet [Cr(CN)$_6$][Mn($S$)-pnH(H$_2$O)](H$_2$O) Probed by Muon Spin Rotation and Relaxation,"Local magnetic fields in a molecule-based optically chiral magnet
[Cr(CN)$_6$][Mn($S$)-pnH(H$_2$O)](H$_2$O) (GN-S) and its enantiomer (GN-R) are
studied by means of muon spin rotation and relaxation (muSR). Detailed analysis
of muon precession signals under zero field observed below T_c supports the
average magnetic structure suggested by neutron powder diffraction. Moreover,
comparison of muSR spectra between GN-S and GN-R suggests that they are a pair
of complete optical isomers in terms of both crystallographic and magnetic
structure. Possibility of magnetic chirality in such a pair is discussed.",0603012v1
2006/5/2,Remnant magnetization above room temperature in semiconducting Y_0.5Ca_0.5BaCo_4O_7,"The Y_0.5Ca_0.5BaCo_4O_7 compound exhibits four magnetic anomalies at the
temperatures 387, 281, 52, and 14 K; all anomalies show characteristics typical
for spin freezing into disordered states: frequency dependent transition
temperature in the AC magnetic susceptibility together with relaxation of
thermoremnant magnetization. Y_0.5Ca_0.5BaCo_4O_7 is a semiconductor with a
small band-gap of 0.17 eV concluded from four-point conductivity measurements
and the conductivity is proportional to T^(-3/4), suggesting an electron
hopping mechanism involving Co^(2+) and Co^(3+) ions; at higher temperatures,
double-exchange is the proposed reason for the strong magnetic interaction. At
lower temperatures, super-exchange interactions start to compete with the
double-exchange for domination and this competition together with geometrical
frustrations in the structure are responsible for magnetic disorder down to 2
K. Covalence between Co and O is also discussed as additional reason for the
strong magnetic interactions.",0605063v1
2006/6/23,Dynamical spin chirality and spin anisotropy in gapped S=1/2 quantum systems,"We have studied the spin anisotropy in spin-singlet ground state compounds
and the magnetic chirality, as measured by inelastic polarized neutron
scattering techniques, in the chain-sublattice of Sr14Cu24O41. In-plane and out
of plane magnetic fluctuations are measured to be anisotropic and further
discussed in the light of the current hypothesis of spin-orbit coupling. We
show that under appropriate conditions of magnetic field and neutron
polarization, the \textit{trivial} magnetic chirality selects only one of the
Zeeman splitted triplet states for scattering and erases the other one that
posses opposite helicity. Our analysis pertains to previous studies on
dynamical magnetic chirality and chiral critical exponents, where the ground
state is chiral itself, the so-called \textit{non-trivial} dynamical magnetic
chirality. As it turns out, both \textit{trivial} and \textit{non-trivial}
dynamical magnetic chirality have identical selection rules for inelastic
polarized neutron scattering experiments and it is not at all evident that they
can be distinguished in a paramagnetic compound.",0606598v1
2006/6/26,Epitaxial film growth and magnetic properties of Co_2FeSi,"We have grown thin films of the Heusler compound Co_2FeSi by RF magnetron
sputtering. On (100)-oriented MgO substrates we find fully epitaxial
(100)-oriented and L2_1 ordered growth. On Al_2O_3 (11-20) substrates, the film
growth is (110)-oriented, and several in-plane epitaxial domains are observed.
The temperature dependence of the electrical resistivity shows a power law with
an exponent of 7/2 at low temperatures. Investigation of the bulk magnetic
properties reveals an extrapolated saturation magnetization of 5.0 mu_B/fu at 0
K. The films on Al_2O_3 show an in-plane uniaxial anisotropy, while the
epitaxial films are magnetically isotropic in the plane. Measurements of the
X-ray magnetic circular dichroism of the films allowed us to determine element
specific magnetic moments. Finally we have measured the spin polarization at
the surface region by spin-resolved near-threshold photoemission and found it
strongly reduced in contrast to the expected bulk value of 100%. Possible
reasons for the reduced magnetization are discussed.",0606666v2
2006/7/28,Influence of magnetic field on paramagnetic-ferromagnetic transition in La$_{1-x}$Ca$_{x}$MnO$_{3}$ ($x\approx 0.25$) crystal: ultrasonic and transport studies,"The ultrasonic properties of La$_{1-x}$Ca$_{x}$MnO$_{3}$ ($x\approx 0.25$)
with the Curie temperature $T_C$ about 200 K are studied. Temperature
dependences of longitudinal and transverse sound velocities were measured in
zero magnetic field and for different constant magnetic fields as well. The
ultrasonic study is supported by magnetic, resistive, magnetoresistive,
structural and other measurements of the sample that facilitate interpretation
of the results obtained. The magnetic field influence on sound properties found
in this study presents some new features of the interplay between the elastic
and magnetic properties of these compounds. It is shown that the
paramagnetic-ferromagnetic transition in the sample studied is first order, but
can become second order under the influence of applied magnetic field.",0607761v1
2006/9/26,Localized Wavefunctions and Magnetic Band Structure for Lateral Semiconductor Superlattices,"In this paper we present calculations on the electronic band structure of a
two-dimensional lateral superlattice subject to a perpendicular magnetic field
by employing a projection operator technique based on the ray-group of
magnetotranslation operators. We construct a new basis of appropriately
symmetrized Bloch-like wavefunctions as linear combination of well-localized
magnetic-Wannier functions. The magnetic field was consistently included in the
Wannier functions defined in terms of free-electron eigenfunctions in the
presence of external magnetic field in the symmetric gauge. Using the above
basis, we calculate the magnetic energy spectrum of electrons in a lateral
superlattice with bi-directional weak electrostatic modulation. Both a square
lattice and a triangular one are considered as special cases. Our approach
based on group theory handles the cases of integer and rational magnetic fluxes
in a uniform way and the provided basis could be convenient for further both
analytic and numerical calculations.",0609662v1
2006/10/4,Magnetic phases in the Kagome staircase compound Co3V2O8,"The low temperature properties of the Kagome-type system Co3V2O8 have been
studied by powder neutron diffraction both in zero field and in applied
magnetic field of up to 8 T. Below 6 K, the zero-field ground state is
ferromagnetic with the magnetic moments aligned along the a-axis. The size of
the moment on one of the two Co sites, the so called cross-tie site, is
considerably reduced compared to the fully polarized state. The application of
a magnetic field in this phase is found to rapidly enhance the cross-tie site
magnetic moment, which reaches the expected value of ~3muB by the maximum
applied field of 8 T. Different reorientation behaviors are found for the Co
cross-tie and spine sites, suggesting a more pronounced easy-axis anisotropy
for moments on the spine sites. Rietveld refinements reveal that a simple
model, where the spins on both cross-tie and spine sites rotate in the ac-plane
in a magnetic field, reproduces the experimental diffraction patterns well. In
addition, it is found that at higher temperatures and moderate magnetic fields,
the incommensurate antiferromagnetic order, corresponding to a transverse
sinusoidal modulation above 8 K, is suppressed to be replaced by ferromagnetic
order.",0610098v1
2006/10/19,Bose-Einstein condensation of magnons in magnets with predominant ferromagnetic interaction,"We discuss Bose-Einstein condensation of magnons (BEC) in magnets with
predominant ferromagnetic (FM) interaction in magnetic field $H$ near
saturation ($H_c$). Because $H_c$ is independent of FM couplings, magnetic
materials of this type can have small $H_c$ that makes them promising
candidates for experimental investigation of BEC. Ferromagnets with easy-plane
anisotropy and antiferromagnets (AFs) containing weakly coupled FM planes or
chains are discussed in detail. We observe small effective interaction between
magnons near the QCP in such magnets, in contrast to AFs with strong AF
coupling previously discussed. In particular, this smallness allows us to find
crossovers in the critical temperature $T_c(H)\propto (H_c-H)^{1/\phi}$ from
$\phi=3/2$ to $\phi=1$ in quasi-1D magnets, and from $\phi=3/2$ to
$\phi\approx1$ ($T_c\ln T_c\propto H_c-H$) in quasi-2D ones.",0610536v4
2006/10/23,Influence of external magnetic fields on growth of alloy nanoclusters,"Kinetic Monte Carlo simulations are performed to study the influence of
external magnetic fields on the growth of magnetic fcc binary alloy
nanoclusters with perpendicular magnetic anisotropy. The underlying kinetic
model is designed to describe essential structural and magnetic properties of
CoPt_3-type clusters grown on a weakly interacting substrate through molecular
beam epitaxy. The results suggest that perpendicular magnetic anisotropy can be
enhanced when the field is applied during growth. For equilibrium bulk systems
a significant shift of the onset temperature for L1_2 ordering is found, in
agreement with predictions from Landau theory. Stronger field induced effects
can be expected for magnetic fcc-alloys undergoing L1_0 ordering.",0610589v1
2006/10/23,Magnetism in Graphene Induced by Single-Atom Defects,"We study from first principles the magnetism in graphene induced by single
carbon atom defects. For two types of defects considered in our study, the
hydrogen chemisorption defect and the vacancy defect, the itinerant magnetism
due to the defect-induced extended states has been observed. Calculated
magnetic moments are equal to 1 $\mu_B$ per hydrogen chemisorption defect and
1.12$-$1.53 $\mu_B$ per vacancy defect depending on the defect concentration.
The coupling between the magnetic moments is either ferromagnetic or
antiferromagnetic, depending on whether the defects correspond to the same or
to different hexagonal sublattices of the graphene lattice, respectively. The
relevance of itinerant magnetism in graphene to the high-$T_C$ magnetic
ordering is discussed.",0610638v3
2006/11/8,Magnetostriction in the Bose-Einstein Condensate quantum magnet NiCl2-4SC(NH2)2,"The quantum magnet NiCl$_2$-4SC(NH$_2$)$_2$ is a candidate for observing
Bose-Einstein Condensation of spin degrees of freedom in applied magnetic
fields. An XY antiferromagnetic ordered state occurs in a dome-shaped region of
the temperature-field phase diagram between H$_{c1}$ = 2.1 T and H$_{c2}$ =
12.6 T and below 1.2 K. BEC corresponds to the field-induced quantum phase
transition into the ordered state. We investigate magnetostriction in single
crystals of this compound at dilution refrigerator temperatures in magnetic
fields up to 18 T, and as a function of magnetic field angle. We show that
significant changes in the lattice parameters are induced by magnetic fields,
and argue that these result from antiferromagnetic couplings between the Ni
spins along the tetragonal c-axis. The magnetic phase diagram as a function of
temperature, field, and field angle can be extracted from these data. We
discuss the implications of these results to Bose-Einstein Condensation in this
system.",0611229v1
2006/11/19,Magnetic coupling in CoCr_2O_4 and MnCr_2O_4: an LSDA+U study,"We present a first principles LSDA+U study of the magnetic coupling constants
in the spinel magnets CoCr_2O_4 and MnCr_2O_4. Our calculated coupling
constants highlight the possible importance of AA interactions in spinel
systems with magnetic ions on both A and B sites. Furthermore, we show that a
careful analysis of the dependence of the magnetic coupling constants on the
LSDA+U parameters provides valuable insights in the underlying coupling
mechanisms, and allows to obtain a quantitative estimate of the magnetic
coupling constants. We discuss in detail the capabilities and possible pitfalls
of the LSDA+U method in determining magnetic coupling constants in complex
transition metal oxides.",0611502v3
2006/11/23,Quantum dissipation theory of slow magnetic relaxation mediated by domain-wall motion in one-dimensional chain compound [Mn(hfac)_{2}BNO_{H}}],"Based on a quantum dissipation theory of open systems, we present a
theoretical study of slow dynamics of magnetization for the ordered state of
the new molecule-based magnetic complex [Mn(hfac)_{2}BNO_{H}] composed from
antiferromagnetically coupled ferrimagnetic (5/2,1) spin chains. Experimental
investigations of the magnetization process in pulsed fields have shown that
this compound exhibits a metamagnetic AF-FI transition at a critical field in
the order of the interchain coupling. A strong frequency dependence for the
ac-susceptibility has been revealed in the vicinity of the AF-FI transition and
was associated with an AF-FI interface kink motion. We model these processes by
a field-driven domain-wall motion along the field-unfavorable chains correlated
with a dissipation effect due to a magnetic system-bath coupling. The
calculated longitudinal magnetization has a two-step relaxation after the field
is switched off and are found in good agreement with the experiment. The
relaxation time determined from the imaginary part of the model
ac-susceptibility agrees qualitatively with that found from the remanent
magnetization data.",0611610v1
2006/12/7,Magnetism of 3d transition metal atoms on W(001): submonolayer films,"We have investigated random submonolayer films of 3d transition metals on
W(001). The tight-binding linear muffin-tin orbital method combined with the
coherent potential approximation was employed to calculate the electronic
structure of the films. We have estimated local magnetic moments and the
stability of different magnetic structures, namely the ferromagnetic order, the
disordered local moments and the non-magnetic state, by comparing the total
energies of the corresponding systems. It has been found that the magnetic
moments of V and Cr decrease and eventually disappear with decreasing coverage.
On the other hand, Fe retains approximately the same magnetic moment throughout
the whole concentration range from a single impurity to the monolayer coverage.
Mn is an intermediate case between Cr and Fe since it is non-magnetic at very
low coverages and ferromagnetic otherwise.",0612190v1
2006/12/12,Magnetic and Resonance Properties of the Compound (NH3)2(CH2)3CoCl4 - an Antiferromagnet with the Dzyaloshinskii Interaction,"The static magnetic and dynamic properties of the compound (NH3)2(CH2)3CoCl4
are investigated in the temperature interval 0.5-50 K. It is shown that at TN
=2.05 K this compound undergoes a transition to a magnetically ordered
antiferromagnet state. A distinctive feature of this compound is the presence
of temperature hysteresis at the transition to the ordered state (corresponding
to a first order magnetic phase transition) and of a spontaneous magnetic
moment along the x axis. The paramagnetic Curie temperatures are determined.
The frequency-field curves of the AFMR spectrum in the xy plane are
investigated at a temperature below TN. The main magnetic parameters of the
biaxial AFM - the value of the low-frequency gap and the effective magnetic
anisotropy field - are determined.",0612285v1
2006/12/13,Coupled Negative magnetocapacitance and magnetic susceptibility in a Kagome staircase-like compound Co3V2O8,"The dielectric constant of the Kagome staircase-like Co3V2O8 polycrystalline
compound has been measured as function of temperature and magnetic field up to
14T. It is found that the application of an external magnetic field suppresses
the anomaly for the dielectric constant beyond 6.1K. Furthermore, its magnetic
field dependence reveals a negative magnetocapacitance which is proportional to
the magnetic susceptibility, suggesting a common magnetostrictive origin for
the magnetic field dependence of the two quantities. This result is very
different from that obtained from the isostructural compound Ni3V2O8 that
presents a peak in the dielectric constant at the incommensurate magnetic phase
transition coupled to a sign change of the magnetocapacitance.",0612335v1
2006/12/19,Tailoring Magnetism in Quantum Dots,"We study magnetism in magnetically doped quantum dots as a function of
confining potential, particle numbers, temperature, and strength of Coulomb
interactions. We explore possibility of tailoring magnetism by controlling the
electron-electron Coulomb interaction, without changing the number of
particles. The interplay of strong Coulomb interactions and quantum confinement
leads to enhanced inhomogeneous magnetization which persist at higher
temperatures than in the non-interacting case. The temperature of the onset of
magnetization can be controlled by changing the number of particles as well as
by modifying the quantum confinement and the strength of Coulomb interactions.
We predict a series of electronic spin transitions which arise from the
competition between the many-body gap and magnetic thermal fluctuations.",0612489v1
2007/2/22,"Magnetization reversal in the orthovanadate RVO3 compounds (R = La, Nd, Sm, Gd, Er and Y): Inhomogeneities caused by defects in the orbital sector of quasi-one-dimensional orbital systems","We report on a study of various RVO3 single-crystal samples (R = La, Nd, Sm,
Gd, Er and Y) which show temperature-induced magnetization reversal. For
compounds with lighter rare-earths (R = La, Nd and Sm), magnetization reversal
can be observed for magnetic field applied in the ab plane and along the c
axis, whereas for the heavy rare-earths (R = Gd, Er) magnetization reversal is
only observed when the field is applied along the a axis. YVO3 has a
magnetization reversal along all the main crystallographic axes in a modest
applied field. We have found that some compounds are very sensitive to small
trapped fields present in the superconducting solenoid of the magnetometer
during the cooling. Based on the observed results, we argue that inhomogeniety
caused by defects in the orbital sector in the quasi one-dimensional orbital
systems could account for the unusual magnetization reversal.",0702527v1
2007/3/12,Magnetic irreversibility and Verwey transition in nano-crystalline bacterial magnetite,"The magnetic properties of biologically-produced magnetite nanocrystals
biomineralized by four different magnetotactic bacteria were compared to those
of synthetic magnetite nanocrystals and large, high quality single crystals.
The magnetic feature at the Verwey temperature, $T_{V}$, was clearly seen in
all nanocrystals, although its sharpness depended on the shape of individual
nanoparticles and whether or not the particles were arranged in magnetosome
chains. The transition was broader in the individual superparamagnetic
nanoparticles for which $T_{B}<T_{V}$, where $T_{B}$ is the superparamagnetic
blocking temperature. For the nanocrystals organized in chains, the effective
blocking temperature $T_{B}>T_{V}$ and the Verwey transition is sharply
defined. No correlation between the particle size and $T_{V}$ was found.
Furthermore, measurements of $M(H,T,time)$ suggest that magnetosome chains
behave as long magnetic dipoles where the local magnetic field is directed
along the chain and this result confirms that time-logarithmic magnetic
relaxation is due to the collective (dipolar) nature of the barrier for
magnetic moment reorientation.",0703306v2
2001/10/31,Results from a Prototype Permanent Magnet Dipole-Quadrupole Hybrid for the PEP-II B-Factory,"We describe the construction of a prototype hybrid permanent magnet dipole
and quadruple. The magnet consists of two concentric rings of SmCo magnetic
material 5 cm in length. The outer ring is made of 16 uniformly magnetized
blocks assembled as a Halbach dipole and the inner ring has 32 blocks oriented
in a similar fashion so as to generate a quadruple field. The resultant
superimposed field is an offset quadruple field which allows us to center the
field on the high-energy beam in the interaction region of the PEPII B factory.
The dipole blocks are glued to the inside surface of an outer support collar
and the quadruple blocks are held in a fixture that allows radial adjustment of
the blocks prior to potting the entire assembly with epoxy. An extensive
computer model of the magnet has been made and from this model we developed a
tuning algorithm that allowed us to greatly reduce the n=3-17 harmonics of the
magnet.",0110089v1
2006/7/12,The Stoner-Wohlfarth model of Ferromagnetism: Dynamic and Statistical properties,"The physics of magnetic state change or reversal in single domain magnetic
grains (called Stoner particles) is interesting from the fundamental as well as
the applied points of view. A change in magnetization can be finely tuned with
a specific time variation o f an externally applied magnetic field. It may also
occur naturally (without application of a field) at very low tempe rature with
quantum tunneling and at higher temperature with thermal excitation. The
optimal (usually shortest) time altering the magn etisation along with the
smallest applied magnetic field are sought in technological applications s uch
as high-density reading or writing of information, spintronics, quantum inform
ation and quantum communication systems. This work reviews the magnetization
change with a time dependent field and tem perature and discusses the time it
takes to alter the magnetization as a function of the control parameter chosen,
temperature and material parameters.",0607118v4
2006/12/21,Analysis of Particle Transport in a Magnetophoretic Microsystem,"An analytical analysis is presented of the transport and capture of magnetic
micro/nano-particles in a magnetophoretic microsystem that consists of an array
of integrated soft-magnetic elements embedded beneath a microfluidic channel.
The elements, which are polarized by a bias field, produce a nonuniform field
distribution that gives rise to a force on magnetic particles within the
microchannel. The equations governing particle motion are derived using
analytical expressions for the dominant magnetic and fluidic forces. The
magnetic force is obtained using an analytical expression for the field
distribution in the microchannel combined with a linear magnetization model for
the magnetic response of particles. The theory takes into account particle size
and material properties, the bias field, the dimensions of the microchannel,
the fluid properties, and the flow velocity. The equations of motion are solved
to study particle transport and capture. The analysis indicates that the
particles exhibit an oscillatory motion as they traverse the microsystem, and
that a high capture efficiency can be obtained in practice.",0612211v1
2007/3/11,A low-noise ferrite magnetic shield,"Ferrite materials provide magnetic shielding performance similar to commonly
used high permeability metals but have lower intrinsic magnetic noise generated
by thermal Johnson currents due to their high electrical resistivity.
Measurements inside a ferrite shield with a spin-exchange relaxation-free
atomic magnetometer reveal a noise level of 0.75 fT Hz^(-1/2), 25 times lower
than what would be expected in a comparable mu-metal shield. The authors
identify a 1/f component of the magnetic noise due to magnetization
fluctuations and derive general relationships for the Johnson current noise and
magnetization noise in cylindrical ferromagnetic shields in terms of their
conductivity and complex magnetic permeability.",0703115v2
2007/4/2,Huge magneto-crystalline anisotropy of x-ray linear dichroism observed on Co/FeMn bilayers,"We present an x-ray spectromicroscopic investigation of single-crystalline
magnetic FeMn/Co bilayers on Cu(001), using X-ray magnetic circular (XMCD) and
linear (XMLD) dichroism at the Co and Fe L3 absorption edges in combination
with photoelectron emission microscopy (PEEM). Using the magnetic coupling
between the ferromagnetic Co layer and the antiferromagnetic FeMn layer we are
able to produce magnetic domains with two different crystallographic
orientations of the magnetic easy axis within the same sample at the same time.
We find a huge difference in the XMLD contrast between the two types of
magnetic domains, which we discuss in terms of intrinsic magneto-crystalline
anisotropy of XMLD of the Co layer. We also demonstrate that due to the high
sensitivity of the method, the small number of induced ferromagnetic Fe moments
at the FeMn-Co interface is sufficient to obtain magnetic contrast from XMLD in
a metallic system.",0704.0182v1
2007/4/10,Magnetic superelasticity and inverse magnetocaloric effect in Ni-Mn-In,"Applying a magnetic field to a ferromagnetic Ni$_{50}$Mn$_{34}$In$_{16}$
alloy in the martensitic state induces a structural phase transition to the
austenitic state. This is accompanied by a strain which recovers on removing
the magnetic field giving the system a magnetically superelastic character. A
further property of this alloy is that it also shows the inverse magnetocaloric
effect. The magnetic superelasticity and the inverse magnetocaloric effect in
Ni-Mn-In and their association with the first order structural transition is
studied by magnetization, strain, and neutron diffraction studies under
magnetic field.",0704.1243v1
2007/4/27,Theory of magnetic deflagration,"Theory of magnetic deflagration (avalanches) in crystals of molecular magnets
has been developed. The phenomenon resembles the burning of a chemical
substance, with the Zeeman energy playing the role of the chemical energy.
Non-destructive reversible character of magnetic deflagration, as well as the
possibility to continuously tune the flammability of the crystal by changing
the magnetic field, makes molecular magnets an attractive toy system for a
detailed study of the burning process. Besides simplicity, new features, as
compared to the chemical burning, include possibility of quantum decay of
metastable spin states and strong temperature dependence of the heat capacity
and thermal conductivity. We obtain analytical and numerical solutions for
criteria of the ignition of magnetic deflagration, and compute the ignition
rate and the speed of the developed deflagration front.",0704.3751v1
2007/5/3,Planar spin-transfer device with a dynamic polarizer,"In planar nano-magnetic devices magnetization direction is kept close to a
given plane by the large easy-plane magnetic anisotropy, for example by the
shape anisotropy in a thin film. In this case magnetization shows effectively
in-plane dynamics with only one angle required for its description. Moreover,
the motion can become overdamped even for small values of Gilbert damping. We
derive the equations of effective in-plane dynamics in the presence of
spin-transfer torques. The simplifications achieved in the overdamped regime
allow to study systems with several dynamic magnetic pieces (``free layers'').
A transition from a spin-transfer device with a static polarizer to a device
with two equivalent magnets is observed. When the size difference between the
magnets is less than critical, the device does not exhibit switching, but goes
directly into the ``windmill'' precession state.",0705.0406v1
2007/7/7,Magnetization and heat capacity studies of double perovskite compounds Ba2SmRuO6 and Ba2DyRuO6,"Here we report the magnetic and heat capacity studies of the double
perovskite com-pounds Ba2SmRuO6 and Ba2DyRuO6. Antiferromagnetic transitions
are inferred at 54 K and 47 K in Ba2SmRuO6 and Ba2DyRuO6, respectively in the
magnetization measure-ments. Heat capacity measurements show large jumps at the
corresponding temperatures and confirm the bulk magnetic ordering. Both the
measurements provide clear indication of the ordering of the rare earth moments
also along with the Ruthenium moments. How-ever, the heat capacity results
suggest that the ordering of rare earth magnetic moments is spread over a large
temperature range and is affected by a large crystal field effect on Ru and
rare earth ions. The anomaly observed in the magnetization measurements at 42 K
(below the magnetic ordering) in Ba2SmRuO6 is discerned as a reorientation of
Sm3+ moments",0707.1090v1
2007/7/9,"Effective chiral magnetic currents, topological magnetic charges, and microwave vortices in a cavity with an enclosed ferrite disk","In microwaves, a TE-polarized rectangular-waveguide resonator with an
inserted thin ferrite disk gives an example of a nonintegrable system. The
interplay of reflection and transmission at the disk interfaces together with
the material gyrotropy effect gives rise to whirlpool-like electromagnetic
vortices in the proximity of the ferromagnetic resonance. Based on numerical
simulation, we show that a character of microwave vortices in a cavity can be
analyzed by means of consideration of equivalent magnetic currents. Maxwell
equations allows introduction of a magnetic current as a source of the
electromagnetic field. Specifically, we found that in such nonintegrable
structures, magnetic gyrotropy and geometrical factors leads to the effect of
symmetry breaking resulting in effective chiral magnetic currents and
topological magnetic charges. As an intriguing fact, one can observe precessing
behavior of the electric-dipole polarization inside a ferrite disk.",0707.1216v1
2007/7/23,"Magnetocrystalline anisotropy controlled local magnetic configurations in (Ga,Mn)As spin-transfer-torque microdevices","The large saturation magnetization in conventional dense moment ferromagnets
offers flexible means of manipulating the ordered state through demagnetizing
shape anisotropy fields but these dipolar fields, in turn, limit the
integrability of magnetic elements in information storage devices. We show that
in a (Ga,Mn)As dilute moment ferromagnet, with comparatively weaker magnetic
dipole interactions, locally tunable magnetocrystalline anisotropy can take the
role of the internal field which determines the magnetic configuration.
Experiments and theoretical modeling are presented for lithographically
patterned microchannels and the phenomenon is attributed to lattice relaxations
across the channels. The utility of locally controlled magnetic anisotropies is
demonstrated in current induced switching experiments. We report structure
sensitive, current induced in-plane magnetization switchings well below the
Curie temperature at critical current densities 10^5 Acm^-2. The observed
phenomenology shows signatures of a contribution from domain-wall
spin-transfer-torque effects.",0707.3329v1
2007/7/25,Electronic structure of unidirectional superlattices in crossed electric and magnetic fields and related terahertz oscillations,"We have studied Bloch electrons in a perfect unidirectional superlattice
subject to crossed electric and magnetic fields, where the magnetic field is
oriented ``in-plane'', i.e. in parallel to the sample plane. Two orientation of
the electric field are considered. It is shown that the magnetic field
suppresses the intersubband tunneling of the Zener type, but does not change
the frequency of Bloch oscillations, if the electric field is oriented
perpendicularly to both the sample plane and the magnetic field. The electric
field applied in-plane (but perpendicularly to the magnetic field) yields the
step-like electron energy spectrum, corresponding to the magnetic-field-tunable
oscillations alternative to the Bloch ones.",0707.3675v1
2007/10/4,Mapping giant magnetic fields around dense solid plasmas by high resolution magneto-optical microscopy,"We investigate distribution of magnetic fields around dense solid plasmas
generated by intense p-polarized laser (~10^{16} W.cm^{-2}, 100 fs) irradiation
of magnetic tapes, using high sensitivity magneto optical microscopy. We
present evidence for giant axial magnetic fields and map out for the first time
the spatial distribution of these fields. By using the axial magnetic field
distribution as a diagnostic tool we uncover evidence for angular momentum
associated with the plasma. We believe this study holds significance for
investigating the process under which a magnetic material magnetizes or
demagnetizes under the influence of ultrashort intense laser pulses.",0710.0932v1
2007/10/10,"Commensurate magnetic structures ofRMn2O5 (R=Y, Ho, Bi) determined by Single-crystal Neutron Diffraction","Precise magnetic structures of RMn2O5, with R= Y, Ho, Bi in the
commensurate/ferroelectric regime, have been determined by single-crystal
neutron diffraction. For each system, the integrated intensities of a large
number of independent magnetic Bragg reflections have been measured, allowing
unconstrained least-squares refinement of the structures. The analysis confirms
the previously reported magnetic configuration in the ab-plane, in particular
the existence of zig-zag antiferromagnetic chains. For the Y and Ho compounds
additional weak magnetic components parallel to the c-axis were detected which
are modulated in phase quadrature with the a-b components. This component is
extremely small in the BiMn2O5 sample, therefore supporting symmetric exchange
as the principal mechanism inducing ferroelectricity. For HoMn2O5, a magnetic
ordering of the Ho moments was observed, which is consistent with a
super-exchange interaction through the oxygens. For all three compounds, the
point symmetry in the magnetically ordered state is m2m, allowing the polar
b-axis found experimentally.",0710.2065v1
2007/11/1,Magnetic Correlations at Graphene Edges,"Magnetic zigzag edges of graphene are considered as a basis for novel
spintronics devices despite the fact that no true long-range magnetic order is
possible in one dimension. We study the transverse and longitudinal
fluctuations of magnetic moments at zigzag edges of graphene from first
principles. We find a high value for the spin wave stiffness $D$ = 2100 meV
\AA$^2$ and a spin-collinear domain wall creation energy $E_dw$ = 114 meV
accompanied by low magnetic anisotropy. Above the crossover temperature $T_x
\approx$10 K the spin correlation length $\xi \propto T^{-1}$ limits the
long-range magnetic order to ~1 nm at 300 K while below $T_x$ it grows
exponentially with decreasing temperature. We discuss possible ways of
increasing the range of magnetic order and effects of edge roughness on it.",0711.0207v1
2007/12/8,Induced magnetism by single carbon vacancies in a three-dimensional graphitic network: a supercell study,"We present an ab initio DFT study of the magnetic moments that arise in
graphite by creating single carbon vacancies in a 3-D graphite network, using a
full potential, all electron, spin polarized electronic structure calculations.
In previous reports the appearance of magnetic moments was explained in a 2-D
graphene sheet just through the existence of the vacancies itself [1-5]. The
dependence of the arising magnetic moment on the nature and geometry of the
vacancies for different supercells is reported. We found that the highest value
of magnetic moment is obtained for a 3x3x1 supercell and that the highly
diluted 5x5x1 supercell shows no magnetic ordering. The results obtained in
this manuscript are indicative of the importance of interlayer interactions
present in a 3-D stacking. We conclude that this should not be underestimated
when vacancies-based studies on magnetism in graphitic systems are carried out.",0712.1268v1
2007/12/13,Breakdown of an intermediate plateau in the magnetization process of anisotropic spin-1 Heisenberg dimer: theory vs. experiment,"The magnetization process of the spin-1 Heisenberg dimer model with axial and
rhombic single-ion anisotropy terms is particularly investigated in connection
with recent experimental high-field measurements performed on the
single-crystal sample of the homodinuclear nickel(II) compound
[Ni2(Medpt)2(ox)(H2O)2](ClO4)2.2H2O (Medpt=methyl-bis(3-aminopropyl)amine). The
results obtained from the exact numerical diagonalization reveal a striking
magnetization process with a marked spatial dependence on the applied magnetic
field for arbitrary but non-zero single-ion anisotropy. It is demonstrated that
the field range, which corresponds to an intermediate magnetization plateau
emerging at a half of the saturation magnetization, basically depends on
single-ion anisotropy terms as well as a spatial orientation of the applied
field. The breakdown of the intermediate magnetization plateau is discussed at
length in relation to the single-ion anisotropy strength.",0712.2109v2
2008/1/24,EPR and magnetization studies on single crystals of a heterometallic (Cu^{II}} and Cr^{III}) complex: zero-field splitting determination,"Magnetic properties of single crystals of the heterometallic complex
[Cu(bpy)$_3$]$_2$[Cr(C$_2$O$_4$)$_3$]NO$_3\cdot $9H$_2$O (bpy =
2,2'-bipyridine) have been investigated. From the recorded EPR spectra, the
spin-Hamiltonian parameters have been determined. The magnetization
measurements have shown magnetic anisotropy at low temperatures, which has been
analysed as a result of the zero-field splitting of the Cr$^{\mathrm{III}}$
ion. By fitting the exactly derived magnetization expression to the measured
magnetization data, the axial zero-field splitting parameter, D, has been
calculated. Comparing to the EPR measurements, it has been confirmed that $D$
can be determined from the measurements of the macroscopic magnetization on the
single crystals.",0801.3763v1
2008/2/12,Temperature dependent magnetization dynamics of magnetic nanoparticles,"Recent experimental and theoretical studies show that the switching behavior
of magnetic nanoparticles can be well controlled by external time-dependent
magnetic fields. In this work, we inspect theoretically the influence of the
temperature and the magnetic anisotropy on the spin-dynamics and the switching
properties of single domain magnetic nanoparticles (Stoner-particles). Our
theoretical tools are the Landau-Lifshitz-Gilbert equation extended as to deal
with finite temperatures within a Langevine framework. Physical quantities of
interest are the minimum field amplitudes required for switching and the
corresponding reversal times of the nanoparticle's magnetic moment. In
particular, we contrast the cases of static and time-dependent external fields
and analyze the influence of damping for a uniaxial and a cubic anisotropy.",0802.1740v1
2008/2/28,Magnetic studies of multi-walled carbon nanotube mats: Evidence for the paramagnetic Meissner effect,"We report magnetic measurements up to 1200 K on multi-walled carbon nanotube
mats using Quantum Design vibrating sample magnetometer. Extensive magnetic
data consistently show two ferrromagnetic-like transitions at about 1000 K and
1275 K, respectively. The lower transition at about 1000 K is associated with
an Fe impurity phase and its saturation magnetization is in quantitative
agreement with the Fe concentration measured by an inductively coupled plasma
mass spectrometer. On the other hand, the saturation magnetization for the
higher transition phase ($\geq$1.0 emu/g) is about four orders of magnitude
larger than that expected from the measured concentration of Co or CoFe, which
has a high enough Curie temperature to explain this high transition. We show
that this transition at about 1275 K is not consistent with a magnetic
proximity effect of Fe-carbon systems and ferromagnetism of any carbon-based
materials or magnetic impurities but with the paramagnetic Meissner effect due
to the existence of $\pi$ Josephson junctions in a granular superconductor.",0802.4108v2
2008/3/5,"The behavior of magnetic ordering and the KOndo effect in the alloys, Ce2Rh(1-x)Co(x)Si3: Evidence from bulk studies for Fermi-surface change during magnetic ordering - QCP transformation and applicability of SDW pictur","The results of magnetic susceptibility, electrical resistivity (rho), and
heat capacity measurements as a function of temperature are reported for the
alloys, Ce2Rh(1-x)Co(x)Si3, crystallizing in an AlB2-derived hexagonal
strcture. Ce2RhSi3 exhibits antiferromagnetic ordering at 7 K. The Neel
temperature decreases gradually with the increase in Co concentration. For x
greater than 0.6, no magnetic ordering is observed down to 0.5 K.
Interestingly, the x= 0.6 alloy exhibits signatutes of non-Fermi liquid
behavior, while the Co end member is a Fermi liquid. Thus, a transformation of
magnetic ordering state to non-magnetism via non-Fermiliquid state by
isoelectronic chemical doping is evident in this solid solution. The electrical
resistivity data for x= 0.2 and 0.3 alloys show an upturn at respective Neel
temperatures, establishing the formation of a magnetism-induced pseudo-gap for
these intermediate compositions alone as though there is a gradual Fermi
surface transformation as the quantum critical point is approached.",0803.0652v1
2008/3/14,Magnetoresistance and spin-transfer torque in magnetic tunnel junctions,"We comment on both recent progress and lingering puzzles related to research
on magnetic tunnel junctions (MTJs). MTJs are already being used in
applications such as magnetic-field sensors in the read heads of disk drives,
and they may also be the first device geometry in which spin-torque effects are
applied to manipulate magnetic dynamics, in order to make nonvolatile magnetic
random access memory. However, there remain many unanswered questions about
such basic properties as the magnetoresistance of MTJs, how their properties
change as a function of tunnel-barrier thickness and applied bias, and what are
the magnitude and direction of the spin-transfer-torque vector induced by a
tunnel current.",0803.2254v1
2008/4/11,The S1 Shell and Interstellar Magnetic Field and Gas near the Heliosphere,"Many studies of the Loop I magnetic superbubble place the Sun at the edges of
the bubble. One recent study models the polarized radio continuum of Loop I as
two magnetic shells with the Sun embedded in the rim of the 'S1' shell. If the
Sun is in such a shell, it should be apparent in both the local interstellar
magnetic field and the distribution of nearby interstellar material. The
properties of these subshells are compared to optical polarization data that
trace the nearby interstellar magnetic field (ISMF), and the distribution of
interstellar FeII and CaII within about 55 pc of the Sun. The result is that a
model of Loop I as composed of two magnetic subshells is a viable description
of the distribution of nearby low density ISM. Column densities of the
recombinant ion CaII are found to increase with the strength of the
interstellar radiation field, rather than with star distance or total
pathlength through the two magnetic subshells. As found earlier, the symmetry
of the dipole moment of the cosmic microwave background corresponds to the
symmetries of the heliosphere and local ISMF (to within 10 degrees).",0804.1901v2
2008/4/24,Oersted fields and current density profiles in spin-torque driven magnetization dynamics -- Finite element modelling of realistic geometries,"The classical impact of electrical currents on magnetic nanostructures is
analyzed with numerical calculations of current-density distributions and
Oersted fields in typical contact geometries. For the Oersted field
calculation, a hybrid finite element / boundary element method (FEM/BEM)
technique is presented which can be applied to samples of arbitrary shape.
Based on the FEM/BEM analysis, it is argued that reliable micromagnetic
simulations on spin-tranfer-torque driven magnetization processes should
include precise calculations of the Oersted field, particularly in the case of
pillar contact geometries. Similarly, finite-element simulations demonstrate
that numerical calculations of current-density distributions are required,
e.g., in the case of magnetic strips with an indentation. Such strips are
frequently used for the design of devices based on current-driven domain-wall
motion. A dramatic increase of the current density is found at the apex of the
notch, which is expected to strongly affect the magnetization processes in such
strips.",0804.4010v1
2008/4/30,Biased quasi ballistic spin torque magnetization reversal,"We explore the fundamental time limit of ultra fast spin torque induced
magnetization reversal of a magnetic memory cell. Spin torque precession during
a spin torque current pulse and free precessional magnetization ringing after
spin torque pulse excitation is detected by time resolved magneto transport.
Adapting the duration of the spin torque excitation pulse to the spin torque
precession period allows suppression of the magnetization ringing and thus
coherent control of the final orientation of the magnetization. In the presence
of a hard axis bias field such coherent control enables an optimum ultra fast,
quasi ballistic spin torque magnetization reversal by a single precessional
turn directly from the initial to the reversed equilibrium state.",0804.4840v1
2008/5/22,Repeated magnetic compensation behaviour in Nd0.75Gd0.25Rh3B2 alloy having hexagonal structure and planar anisotropy,"The results of dc and ac magnetization, electrical resistance and heat
capacity studies in an admixed rare earth alloy Nd0.75Gd0.25Rh3B2, which is
close to the zero magnetization limit, are reported. Novel observations include
the two antiferromagnetic like transitions, concomitant repeated/multiple
magnetic compensation behaviour and a characteristic oscillatory magnetic
response, with temperature dependence of magnetization at low fields crossing
the M = 0 axis thrice. The effective coercive field relating to the residual
remanence also has an oscillatory response, with two minima located close to
two zero-crossover temperatures. The unusual behavior in Nd0.75Gd0.25Rh3B2 is
conjectured to arise from its anisotropic hexagonal structure, with planar
anisotropy, resulting in a quasi one dimensional electronic structure and the
accentuated role of conduction electron polarization near the zero
magnetization limit.",0805.3412v2
2008/6/28,Theory of spin magnetohydrodynamics,"We develop a phenomenological hydrodynamic theory of coherent magnetic
precession coupled to electric currents. Exchange interaction between electron
spin and collective magnetic texture produces two reciprocal effects:
spin-transfer torque on the magnetic order parameter and the Berry-phase gauge
field experienced by the itinerant electrons. The dissipative processes are
governed by three coefficients: the ohmic resistance, Gilbert damping of the
magnetization, and the ""beta coefficient"" describing viscous coupling between
magnetic dynamics and electric current, which stems from spin mistracking of
the magnetic order. We develop general magnetohydrodynamic equations and
discuss the net dissipation produced by the coupled dynamics. The latter in
particular allows us to determine a lower bound on the magnetic-texture
resistivity.",0806.4656v2
2008/7/11,Magnetic interactions and high-field properties of Ag(2)VOP(2)O(7): frustrated alternating chain close to the dimer limit,"We report on high-field magnetic properties of the silver vanadium phosphate
Ag(2)VOP(2)O(7). This compound has a layered crystal structure, but the
specific topology of the V-P-O framework gives rise to a one-dimensional spin
system, a frustrated alternating chain. Low-field magnetization measurements
and band structure calculations show that Ag(2)VOP(2)O(7) is close to the dimer
limit with the largest nearest-neighbor interaction of about 30 K. High-field
magnetization data reveal the critical fields \mu_0H_{c1} of about 23 T
(closing of the spin gap) and \mu_0H_{c2} of about 30 T (saturation by full
alignment of the magnetic moments). From H_{c1} to H_{c2} the magnetization
increases sharply similar to the system of isolated dimers. Thus, the magnetic
frustration in Ag(2)VOP(2)O(7) bears little influence on the high-field
properties of this compound.",0807.1849v1
2008/8/9,Transport and Magnetic properties of Fe1/3VSe2,"Electrical conductivity, thermopower and magnetic properties of
Fe-intercalated Fe0.33VSe2 has been reported between 4.2K - 300K. We observe a
first order transition in the resistivity of the sintered pellets around 160K
on cooling. The electronic properties including the transitional hysteresis in
the resistance anomaly (from 80K-160K) are found to be very sensitive to the
structural details of the samples, which were prepared in different annealing
conditions. The thermopower results on the sintered pellets are reported
between 10K - 300K. The magnetic measurements between 2K - 300K and up to 14
Tesla field show the absence of any magnetic ordering in Fe0.33VSe2. The
magnetic moment per Fe -atom at room temperature (between 1.4 to 1.7 Bohr
Magneton) is much lower than in previously reported anti-ferromagnetic FeV2Se4.
Furthermore, the Curie constant shows a rapid and continuous reduction and
combined with the high field magnetization result at 2K suggests a rapid
decrease in the paramagnetic moments on cooling to low temperatures and the
absence of any magnetic order in Fe0.33VSe2 at low temperatures.",0808.1334v1
2008/8/20,Low-temperature magnetic ordering in SrEr$_2$O$_4$,"SrEr$_2$O$_4$ has been characterised by low-temperature powder neutron
diffraction, as well as single crystal specific heat and magnetisation
measurements. Magnetisation measurements show that the magnetic system is
highly anisotropic at temperature above ordering. A magnetic field of 280 kOe
applied at $T=1.6$ K does not overcome the anisotropic magnetisation and fails
to fully saturate the system. Long range antiferromagnetic ordering develops
below $T_N=0.75$ K, identified by magnetic Bragg reflections with propagation
vector ${\bf k}=0$ and a lambda anomaly in the specific heat. The magnetic
structure consists of ferromagnetic chains running along the \textit{c} axis,
two adjacent chains being stacked antiferromagnetically. The moments point
along the \textit{c} direction, but only one of the two crystallographically
in-equivalent Er sites has a sizeable ordered magnetic moment, 4.5 $\rm \mu_B$
at 0.55 K. The magnetic properties of SrEr$_2$O$_4$ are discussed in terms of
the interplay between the low-dimensionality, competing exchange interactions,
dipolar interactions and low lying crystal field levels.",0808.2675v1
2008/10/12,Electronic and Magnetic Structure of the (LaMnO$_3$)$_{2n}$/(SrMnO$_3$)$_n$ Superlattices,"We study the magnetic structure of the (LaMnO$_3$)$_{2n}$/(SrMnO$_3$)$_n$
superlattices from density-functional calculations. In agreement with the
experiments, we find that the magnetism changes with the layer thickness `n'.
The reason for the different magnetic structures is shown to be the varying
potential barrier across the interface, which controls the leakage of the
Mn-e$_g$ electrons from the LMO side to the SMO side. This in turn affects the
interfacial magnetism via the carrier-mediated Zener double exchange. For n=1
superlattice, the Mn-e$_g$ electrons are more or less spread over the entire
lattice, so that the magnetic behavior is similar to the equivalent alloy
compound La$_{2/3}$Sr$_{1/3}$MnO$_3$. For larger n, the e$_g$ electron transfer
occurs mostly between the two layers adjacent to the interface, thus leaving
the magnetism unchanged and bulk-like away from the interface region.",0810.2126v1
2008/10/15,Vacancy-induced magnetism in SnO$_{2}$: A density functional study,"We study the magnetic and electronic properties of defects in SnO$_{2}$ using
pseudopotential and all electron methods. Our calculations show that bulk
SnO$_{2}$ is non-magnetic, but it shows magnetism with a magnetic moment around
4.00 $\mu_{B}$ due to Sn vacancy (V$_\mathrm{Sn}$). The magnetic moment comes
mainly from O atoms surrounding V$_\mathrm{Sn}$ and Sn atoms, which couple
antiferromagnetically with the O atoms in the presence of V$_\mathrm{Sn}$. The
coupling between different Sn vacancies is also studied and we find that these
defects not only couple ferromagnetically but also antiferromagnetically and
ferrimagnetically. Our calculations demonstrate that the experimentally
observed giant magnetic moment of transition metal doped SnO$_{2}$ can be
attributed to V$_\mathrm{Sn}$.",0810.2720v1
2008/11/14,Magnetic remanent states in antiferromagnetically coupled multilayers,"In antiferromagnetically coupled multilayers with perpendicular anisotropy
unusual multidomain textures can be stabilized due to a close competition
between long-range demagnetization fields and short-range interlayer exchange
coupling.
  In particular, the formation and evolution of specific topologically stable
planar defects within the antiferromagnetic ground state, i.e. wall-like
structures with a ferromagnetic configuration extended over a finite width,
explain configurational hysteresis phenomena recently observed in
[Co/Pt(Pd)]/Ru and [Co/Pt]/NiO multilayers.
  Within a phenomenological theory, we have analytically derived the
equilibrium sizes of these ""ferroband"" defects as functions of the
antiferromagnetic exchange, a bias magnetic field, and geometrical parameters
of the multilayers. In the magnetic phase diagram, the existence region of the
ferrobands mediates between the regions of patterns with sharp
antiferromagnetic domain walls and regular arrays of ferromagnetic stripes.
  The theoretical results are supported by magnetic force microscopy images of
the remanent states observed in [Co/Pt]/Ru.",0811.2378v1
2008/11/21,Magnetic Domains and Surface Effects in Hollow Maghemite Nanoparticles,"In the present work, we investigate the magnetic properties of ferrimagnetic
and noninteracting maghemite (g-Fe2O3) hollow nanoparticles obtained by the
Kirkendall effect. From the experimental characterization of their magnetic
behavior, we find that polycrystalline hollow maghemite nanoparticles are
characterized by low superparamagnetic-to-ferromagnetic transition
temperatures, small magnetic moments, significant coercivities and
irreversibility fields, and no magnetic saturation on external magnetic fields
up to 5 T. These results are interpreted in terms of the microstructural
parameters characterizing the maghemite shells by means of an atomistic Monte
Carlo simulation of an individual spherical shell model. The model comprises
strongly interacting crystallographic domains arranged in a spherical shell
with random orientations and anisotropy axis. The Monte Carlo simulation allows
discernment between the influence of the structure polycrystalline and its
hollow geometry, while revealing the magnetic domain arrangement in the
different temperature regimes.",0811.3592v2
2008/12/15,Structural and magnetic properties of the (Bi2-xPrx)Ru2O7 pyrochlore solid solution (0 <= x <= 2),"We report a detailed study of structural and magnetic properties of the
pyrochlore-type (Bi2-xPrx)Ru2O7 series. Eleven compositions with 0 <= x <= 2
were prepared by solid state reaction at 1050 degrees C and found to form a
solid solution in the whole range of compositions. Structural refinements from
X-ray powder diffraction data by the Rietveld method show that the main
variation concerns the ruthenium site. Ru-O distances increase and the Ru-O-Ru
angle (bridging corner-sharing Ru-O octahedra) decreases with increasing
praseodymium content, in agreement with the metal-semiconductor transition
observed previously in this system. Magnetic measurements show that the
metallic Pauli paramagnetism of Ru in Bi2Ru2O7 evolves to a magnetism of
localized low spin moments coexisting with the magnetism of Pr3+ cations
moments. Strong magnetic correlations are present at high Pr content, as
illustrated by a N\'eel temperature of -224 K for Pr2Ru2O7. However no evidence
of a magnetic ordering was found, suggesting that the end compound Pr2Ru2O7 of
the series might stabilize a spin liquid phase.",0812.2759v1
2008/12/23,Multiferroicity and spiral magnetism in FeVO$_4$ with quenched Fe orbital moments,"FeVO$_4$ has been studied by heat capacity, magnetic susceptibility, electric
polarization and single crystal neutron diffraction experiments. The triclinic
crystal structure is made of \emph{S}-shaped clusters of six Fe$^{3+}$ ions,
linked by VO$_4^{3-}$ groups. Two long-range magnetic ordering transitions
occur at T$_{N1}$=22K and T$_{N2}$=15K. Both magnetic structures are
incommensurate. That stable below T$_{N1}$ is collinear with amplitude
modulated moments whereas below T$_{N2}$ the arrangement is non-collinear with
a helicoidal modulation. Below T$_{N2}$, \fevo becomes weakly ferroelectric
coincidentally with the loss of the collinearity of the magnetic structure. We
conclude that \fevo provides another example of frustrated spiral magnet
similar to the classical TbMnO$_3$ compound. However, \fevo has quenched
orbital moments and a particular structure clarifying the respective role of
anisotropy and magnetic frustration in this type of multiferroic materials.",0812.4429v1
2009/2/25,Anomalous Lattice Parameter of Magnetic Semiconductor Alloys,"The addition of transition metals (TM) to III-V semiconductors radically
changes their electronic, magnetic and structural properties. In contrast to
the conventional semiconductor alloys, the lattice parameter in magnetic
semiconductor alloys, including the ones with diluted concentration (the
diluted magnetic semiconductors - DMS), cannot be determined uniquely from the
composition. By using first-principles calculations, we find a direct
correlation between the magnetic moment and the anion-TM bond lengths. We
derive a simple formula that determines the lattice parameter of a particular
magnetic semiconductor by considering both the composition and magnetic moment.
The formula makes accurate predictions of the lattice parameter behavior of
AlMnN, AlCrN, GaMnN, GaCrN, GaCrAs and GaMnAs alloys. This new dependence can
explain some of the hitherto puzzling experimentally observed anomalies, as
well as, stimulate other kind of theoretical and experimental investigations.",0902.4368v1
2009/3/15,Direct Observation of Magnetic Gradient in Co/Pd Pressure-Graded Media,"Magnetometry and neutron scattering have been used to study the magnetic
properties of pressure graded Co/Pd multilayers. The grading of the multilayer
structure was done by varying the deposition pressure during sputtering of the
samples. Magnetic depth profiling by polarized neutron reflectometry directly
shows that for pressure-graded samples, the magnetization changes significantly
from one pressure region to the next, while control samples sputtered at
uniform pressure exhibit essentially uniform magnetic depth profiles.
Complementary magnetometry results suggest that the observed graded magnetic
profiles are due in part to a decrease in saturation magnetization for regions
deposited at progressively higher pressure. Increased deposition pressure is
shown to increase coercivity, and for graded samples, the absence of discrete
steps in the hysteresis loops implies exchange coupling among regions deposited
at different pressures.",0903.2650v1
2009/5/29,Magnetic doping of a thiolated-gold superatom,"The Au25(SR)18- cluster is a new member in the superatom family which
features a centered icosahedral shell (Au13) protected by six RS(AuSR)2 motifs
(RS- being a alkylthiolate group). Here we show that this superatom can be
magnetically doped by replacing the center Au atom with Cr, Mn, or Fe. We find
that Cr and Mn-doped clusters have an optimized magnetic moment of 5 Bohr
magnetons while the Fe-doped cluster has an optimized magnetic moment of 3 Bohr
magnetons. Although the dopant atom's local magnetic moment makes a major
contribution to the total moment, the icosahedral Au12 shell is also found to
be significantly magnetized. Our work here provides a new scenario of magnetic
doping of a metal-cluster superatom which is protected by ligands and made by
wet chemistry.",0906.0030v3
2009/6/26,"Magnetic anomalies in nanocrystalline Ca3CoRhO6, a geometrically frustrated spin-chain compound,","We have investigated the magnetic behavior of the nano crystals, synthesized
by high-energy ball-milling, for a well-known geometrically frustrated
spin-chain system, Ca3CoRhO6, and compared its magnetic characteristics with
those of the bulk form by measuring ac and dc magnetization. The features
attributable to the onset of 'partially disordered antiferromagnetism'
(characterizing the bulk form) are not seen in the magnetization data of the
nano particles; the magnetic moment at high fields in the very low temperature
range in the magnetically ordered state gets relatively enhanced in the nano
particles. It appears that the ferromagnetic intrachain interaction, judged by
the sign of the paramagnetic Curie temperature, is preserved in the nano
particles. These trends are opposite to those seen in Ca3Co2O6. However, the
complex spin-dynamics as evidenced by large frequency dependence of ac
susceptibility is retained in the nano particles as well. Thus, there are some
similarities and dissimilarities between the properties of the nano particles
and those of the bulk. We believe that these findings would be useful to
understand correlation lengths deciding various properties of geometrical
frustration and/or spin-chain phenomena.",0906.4886v1
2009/6/26,Magnetic ordering in the fine particles of some bulk Pauli-paramgnets,"Fine particles of some of the extensively studied 'enhanced' Pauli
paramagnets - LuCo2, ScCo2, ZrCo2 and CeRu2Si2, have been prepared by
high-energy ball-milling and investigated for their magnetic behavior. In the
case of Co systems, these particles show ferromagnetic features even at room
temperature. In the case of CeRu2Si2, a well-known Kondo lattice which is
non-magnetic in the bulk form, features attributable to the onset of magnetic
order below about 8 K could be seen in the fine particles. The magnitudes of
the magnetic moment of these small particles at high fields are sufficiently
large to conclude that the observed magnetic ordering is not just a surface
effect. This transformation to magnetic ordering in small particles could be
widespread among enhanced Pauli paramagnets.",0906.4887v1
2009/7/24,Induced magnetism of carbon atoms at the graphene/Ni(111) interface,"We report an element-specific investigation of electronic and magnetic
properties of the graphene/Ni(111) system. Using magnetic circular dichroism,
the occurrence of an induced magnetic moment of the carbon atoms in the
graphene layer aligned parallel to the Ni 3d magnetization is observed. We
attribute this magnetic moment to the strong hybridization between C $\pi$ and
Ni 3d valence band states. The net magnetic moment of carbon in the graphene
layer is estimated to be in the range of $0.05-0.1 \mu_B$ per atom.",0907.4344v2
2009/8/13,Pulsed-field magnetization of drilled bulk high-temperature superconductors: flux front propagation in the volume and on the surface,"We present a method for characterizing the propagation of the magnetic flux
in an artificially drilled bulk high-temperature superconductor (HTS) during a
pulsed-field magnetization. As the magnetic pulse penetrates the cylindrical
sample, the magnetic flux density is measured simultaneously in 16 holes by
means of microcoils that are placed across the median plane, i.e. at an equal
distance from the top and bottom surfaces, and close to the surface of the
sample. We discuss the time evolution of the magnetic flux density in the holes
during a pulse and measure the time taken by the external magnetic flux to
reach each hole. Our data show that the flux front moves faster in the median
plane than on the surface when penetrating the sample edge; it then proceeds
faster along the surface than in the bulk as it penetrates the sample further.
Once the pulse is over, the trapped flux density inside the central hole is
found to be about twice as large in the median plane than on the surface. This
ratio is confirmed by modelling.",0908.1907v1
2009/8/15,Thermal-magnetic noise measurement of spin-torque effects on ferromagnetic resonance in MgO-based magnetic tunnel junctions,"Thermal-magnetic noise at ferromagnetic resonance (T-FMR) can be used to
measure magnetic perpendicular anisotropy of nanoscale magnetic tunnel
junctions (MTJs). For this purpose, T-FMR measurements were conducted with an
external magnetic field up to 14 kOe applied perpendicular to the film surface
of MgO-based MTJs under a dc bias. The observed frequency-field relationship
suggests that a 20 A CoFeB free layer has an effective demagnetization field
much smaller than the intrinsic bulk value of CoFeB, with 4PiMeff = (6.1 +/-
0.3) kOe. This value is consistent with the saturation field obtained from
magnetometry measurements on extended films of the same CoFeB thickness.
In-plane T-FMR on the other hand shows less consistent results for the
effective demagnetization field, presumably due to excitations of more complex
modes. These experiments suggest that the perpendicular T-FMR is preferred for
quantitative magnetic characterization of nanoscale MTJs.",0908.2164v1
2009/8/31,Lorentz microscopy mapping for domain walls structure study in L1$_0$ FePd thin films,"Thin film alloys with perpendicular anisotropy were studied using Lorentz
Transmission Electron Microscopy (LTEM). This work focuses on the configuration
of domain walls and demonstrates the suitability and accuracy of LTEM for the
magnetic characterisation of perpendicular magnetic anisotropy materials. Thin
films of chemically ordered ($\unit{L1_0}$) FePd alloys were investigated by
micro-magnetic modelling and LTEM phase retrieval approach. The different
components of magnetization described by the modeling were studied on
experimental images and confirmed by LTEM contrast simulation. Furthermore,
quantitative measurements of magnetic induction inside the domain walls were
made by using an original method to separate the electrical and magnetical
contributions to the phase information. Irregularities were also observed along
the domain walls which could play a major role during the magnetization
processes.",0908.4463v1
2009/11/3,"Symmetry, incommensurate magnetism and ferroelectricity: the case of the rare-earth manganites RMnO3","The complete irreducible co-representations of the paramagnetic space group
provide a simple and direct path to explore the symmetry restrictions of
magnetically driven ferroelectricity. The method consists of a straightforward
generalization of the method commonly used in the case of displacive modulated
systems and allows us to determine, in a simple manner, the full magnetic
symmetry of a given phase originated from a given magnetic order parameter. The
potential ferroic and magneto-electric properties of that phase can then be
established and the exact Landau free energy expansions can be derived from
general symmetry considerations. In this work, this method is applied to the
case of the orthorhombic rare-earth manganites RMnO3. This example will allow
us to stress some specific points, such as the differences between commensurate
or incommensurate magnetic phases regarding the ferroic and magnetoelectric
properties, the possible stabilization of ferroelectricity by a single
irreducible order parameter or the possible onset of a polarization oriented
parallel to the magnetic modulation. The specific example of TbMnO3 will be
considered in more detail, in order to characterize the role played by the
magneto-electric effect in the mechanism for the polarization rotation induced
by an external magnetic field.",0911.0551v1
2009/11/23,Magnetic properties of the quasi-two-dimensional S = 1/2 Heisenberg antiferromagnet [Cu(pyz)2(HF2)]PF6,"We report on high-field magnetization, specific-heat and electron spin
resonance (ESR) studies of the quasi-two-dimensional spin-1/2 Heisenberg
antiferromagnet [Cu(pyz)2(HF2)]PF6. The frequency-field diagram of ESR modes
below TN = 4.38 K is described in the frame of the meanfield theory, confirming
a collinear magnetic structure with an easy-plane anisotropy. The obtained
results allowed us to determine the anisotropy/exchange interaction ratio, A/J
= 0.003, and the upper limit for the inter/intra-plane exchange-interaction
ratio, J'/J = 1/16. It is argued that despite the onset of 3D long-range
magnetic ordering the magnetic properties of this material (including
high-magnetic-field magnetization and non-monotonic field dependence of the
Neel temperature) are strongly affected by two-dimensional spin correlations.",0911.4402v1
2009/12/11,Influence of pressure on the magnetic behavior and the anomalous magnetoresistance in Tb5Si3,"The compound, Tb5Si3, crystallizing in Mn5Si3-type hexagonal structure, was
recently reported by us to exhibit a sudden and huge enhancement in electrical
resistivity (rho) at a critical magnetic field (H_cr) in the magnetically
ordered state (<70 K) tracking isothermal magnetization (M) behavior. We have
investigated the influence of external pressure (<15 kbar) and negative
chemical pressure induced by Ge substitution for Si on M and rho as a function
of temperature (5-300 K) and magnetic field (<120 kOe), with the primary aim of
understanding the field-induced anomalies. Focussing on isothermal M and
magnetoresistance (MR) at two temperatures, 5 and 20K, we find that this rho
anomaly persists under external as well as negative chemical pressures, however
with a large change in the H_cr. The pressure-derivative of H_cr is negative
and this trend and the MR behavior at the H_cr are comparable to that observed
in some Laves phase itinerant magnetic systems. On the basis of this
observation, we speculate that the magnetic fluctuations induced at this
critical field could be responsible for the MR anomal.ies",0912.2275v1
2010/1/2,Surface magnetic states of Ni nanochains modified by using different organic surfactants,"Three powder samples of Ni nanochains formed of polycrystalline Ni
nanoparticles with an estimated diameter of about 30 nm have been synthesized
by a wet chemical method using different organic surfactants. These samples,
having magnetically/structurally core-shell structures, all with a
ferromagnetic Ni core, are Ni@Ni3C nanochains, Ni@NiSG nanochains with a spin
glass (SG) surface layer, and Ni@NiNM nanochains with a nonmagnetic (NM)
surface layer. The average thickness of the shell for these three samples is
determined as about 2 nm. Magnetic properties tailored by the different surface
magnetism are studied. In particular, suppression in saturation magnetization
usually observed with magnetic nanoparticles is revealed to arise from the
surface magnetic states with the present samples.",1001.0298v1
2010/1/14,Performance engineering of semiconductor spin qubit systems,"The performance of a quantum computation system is investigated, with qubits
represented by magnetic impurities in coupled quantum dots filled with two
electrons. Magnetic impurities are electrically manipulated by electrons. The
dominant noise source is the electron mediated indirect coupling between
magnetic impurities and host spin bath. As a result of the electron mediated
coupling, both noise properties and the time needed for elementary gate
operations, depend on controllable system parameters, such as size and geometry
of the quantum dot, and external electric and magnetic fields. We find that the
maximum number of quantum operations per coherence time for magnetic impurities
increases as electron spin singlet triplet energy gap decreases. The advantage
of magnetic impurities over electrons for weak coupling and large magnetic
fields will be illustrated.",1001.2313v2
2010/1/14,Surface-induced magnetism in C-doped SnO$_{2}$,"The magnetism of C-doped SnO$_{2}$ (001) surfaces is studied using
first-principles calculations. It is found that carbon does not induce
magnetism in bulk SnO$_{2}$ when located at the oxygen site, but shows a large
magnetic moment at the SnO$_{2}$ (001) surface. The magnetic moment is mainly
contributed by the carbon atoms due to empty minority spins of $p$ orbitals and
is localized at the surface and subsurface atoms. No magnetism is observed when
the carbon atom is located at the subsurface oxygen sites. The origin of
magnetism is discussed in the context of surface bonding.",1001.2443v2
2010/1/18,Magnetic Avalanches in Molecular Nanomagnets,"The magnetization of the prototypical molecular magnet Mn12-acetate exhibits
a series of sharp steps at low temperatures due to quantum tunneling at
specific resonant values of magnetic field applied along the easy c-axis. An
abrupt reversal of the magnetic moment of such a crystal can also occur as an
avalanche, where the spin reversal proceeds along a ""deflagration"" front that
travels through the sample at subsonic speed. In this article we review
experimental results that have been obtained for the ignition temperature and
the speed of propagation of magnetic avalanches in molecular nanomagnets. Fits
of the data with the theory of magnetic deflagration yield overall qualitative
agreement. However, numerical discrepancies indicate that our understanding of
these avalanches is incomplete.",1001.3112v2
2010/1/25,"Interplay between Symmetric Exchange Anisotropy, Uniform Dzyaloshinskii-Moriya Interaction and Magnetic Fields in the Phase Diagram of Quantum Magnets and Superconductors","We theoretically study the joint influence of uniform Dzyaloshinskii-Moriya
(DM) interactions, symmetric exchange anisotropy (with its axis parallel to the
DM vector) and arbitrarily oriented magnetic fields on one-dimensional spin 1/2
antiferromagnets. We show that the zero-temperature phase diagram contains
three competing phases: (i) an antiferromagnet with Neel vector in the plane
spanned by the DM vector and the magnetic field, (ii) a {\em dimerized}
antiferromagnet with Neel vector perpendicular to both the DM vector and the
magnetic field, and (iii) a gapless Luttinger liquid. Phase (i) is destroyed by
a small magnetic field component along the DM vector and is furthermore
unstable beyond a critical value of easy-plane anisotropy, which we estimate
using Abelian and non-Abelian bosonization along with perturbative
renormalization group. We propose a mathematical equivalent of the spin model
in a one-dimensional Josephson junction (JJ) array located in proximity to a
bulk superconductor.
  We discuss the analogues of the magnetic phases in the superconducting
context and comment on their experimental viability.",1001.4290v1
2010/3/12,Magnetic interaction of Co ions near the {10\bar{1}0} ZnO surface,"Co-doped ZnO is the prototypical dilute magnetic oxide showing many of the
characteristics of ferromagnetism. The microscopic origin of the long range
order however remains elusive, since the conventional mechanisms for the
magnetic interaction, such as super-exchange and double exchange, fail either
at the fundamental or at a quantitative level. Intriguingly, there is a growing
evidence that defects both in point-like or extended form play a fundamental
role in driving the magnetic order. Here we explore one of such possibilities
by performing {\it ab initio} density functional theory calculations for the
magnetic interaction of Co ions at or near a ZnO \{10$\bar{1}$0\} surface. We
find that extended surface states can hybridize with the $e$-levels of Co and
efficiently mediate the magnetic order, although such a mechanism is effective
only for ions placed in the first few atomic planes near the surface. We also
find that the magnetic anisotropy changes at the surface from an hard-axis
easy-plane to an easy axis, with an associated increase of its magnitude. We
then conclude that clusters with high densities of surfacial Co ions may
display blocking temperatures much higher than in the bulk.",1003.2576v1
2010/6/30,Micromagnetic analysis of magnetic noise in ferromagnetic nanowires,"We investigate the magnetic thermal noise in magnetic nanowires with and
without a domain wall by employing micromagnetic simulations. The magnetic
thermal noise due to random thermal fluctuation fields gives important physical
quantities related with the magnetic susceptibility. We find that the resonance
frequency of a domain wall is distinguishable from one of a magnetic domain
itself. For the single domain without a domain wall, the resonance frequency is
well described by the Kittel's formula considering a ferromagnetic specimen as
a simple ellipsoid with demagnetizing factors for various wire widths and
thicknesses. However, additional resonance frequencies from the magnetic domain
wall show the different dependences of the wire width and thickness. It implies
that the spins inside the domain wall have different effective fields and the
spin dynamics.",1006.5763v1
2010/7/21,Magnetic structures of $δ$-O$_2$ resulting from competition of interplane exchange interactions,"Solid oxygen is a unique molecular crystal whose phase diagram is mostly
imposed by magnetic ordering, i.e., each crystal phase has a specific magnetic
structure. However, recent experiments showed that high-pressure $\delta$-phase
is implemented in different magnetic structures. In the present paper we study
the role of interplane exchange interactions in formation of the magnetic
structures with different stacking sequences of the close-packed planes. We
show that temperature-induced variation of intermolecular distances can give
rise to compensation of the exchange coupling between the nearest close-packed
planes and result in the phase transition between different magnetic structures
within $\delta$-O$_2$. Variation of the magnetic ordering is, in turn,
accompanied by the step-wise variation of interplane distance governed by space
and angular dependence of interplane exchange constants.",1007.3600v1
2010/9/1,Metal-insulator transition induced by fluctuations of the magnetic potential in semiconductors with magnetic impurities,"We investigate the metal-insulator transition occurring in semiconductors
with magnetic impurities when lowering temperature. In contrast to the usually
considered percolation transition in the non-uniform medium induced by the
localization of charge carriers in the fluctuating \emph{electric} potential,
the studied transition is connected with their localization in the fluctuating
\emph{magnetic} potential produced by magnetized impurities (more accurately -
in the combined fluctuating potential). When decreasing temperature, the
magnetization of magnetic impurities in the semiconductor becomes higher and
even at the invariable (temperature independent) amplitude of the electric
potential, the magnetic component of the total potential increases. With
increasing fluctuation amplitude, the Fermi level of charge carriers sinks
deeper and deeper into the growing tail of density of states until it falls
under the percolation level. For that, fluctuations of the total potential have
to run up to some critical value. On reaching that value, the transition occurs
from the metal conductivity to the activation one (the metal-insulator
transition).",1009.0164v1
2010/10/22,Thermally activated magnetization reversal in monoatomic magnetic chains on surfaces studied by classical atomistic spin-dynamics simulations,"We analyze the spontaneous magnetization reversal of supported monoatomic
chains of finite length due to thermal fluctuations via atomistic spin-dynamics
simulations. Our approach is based on the integration of the Landau-Lifshitz
equation of motion of a classical spin Hamiltonian at the presence of
stochastic forces. The associated magnetization lifetime is found to obey an
Arrhenius law with an activation barrier equal to the domain wall energy in the
chain. For chains longer than one domain-wall width, the reversal is initiated
by nucleation of a reversed magnetization domain primarily at the chain edge
followed by a subsequent propagation of the domain wall to the other edge in a
random-walk fashion. This results in a linear dependence of the lifetime on the
chain length, if the magnetization correlation length is not exceeded. We
studied chains of uniaxial and tri-axial anisotropy and found that a tri-axial
anisotropy leads to a reduction of the magnetization lifetime due to a higher
reversal attempt rate, even though the activation barrier is not changed.",1010.4730v2
2010/11/4,Probing the magnetic ground state of the molecular Dysprosium triangle,"We present zero field muon spin lattice relaxation measurements of a
Dysprosium triangle molecular magnet. The local magnetic fields sensed by the
implanted muons indicate the coexistence of static and dynamic internal
magnetic fields below $T^* ~35$ K. Bulk magnetization and heat capacity
measurements show no indication of magnetic ordering below this temperature. We
attribute the static fields to the slow relaxation of the magnetization in the
ground state of Dy3. The fluctuation time of the dynamic part of the field is
estimated to be ~0.55 $\mu$s at low temperatures",1011.1164v1
2010/12/22,Magnetic Structure in Fe/Sm-Co Exchange Spring Bilayers with Intermixed Interfaces,"The depth profile of the intrinsic magnetic properties in an Fe/Sm-Co bilayer
fabricated under nearly optimal spring-magnet conditions was determined by
complementary studies of polarized neutron reflectometry and micromagnetic
simulations. We found that at the Fe/Sm-Co interface the magnetic properties
change gradually at the length scale of 8 nm. In this intermixed interfacial
region, the saturation magnetization and magnetic anisotropy are lower and the
exchange stiffness is higher than values estimated from the model based on a
mixture of Fe and Sm-Co phases. Therefore, the intermixed interface yields
superior exchange coupling between the Fe and Sm-Co layers, but at the cost of
average magnetization.",1012.5086v1
2011/1/4,High-sensing properties of magnetic plasmon resonances in double- and triple-rod structures,"We numerically investigated the magnetic plasmon resonances in double-rod and
triple-rod structures (DRSs and TRSs, respectively) for sensing applications.
According to the equivalent circuit model, one magnetic plasmon mode was
induced in the DRS. Due to the hybridization effect, two magnetic plasmon modes
were obtained in the TRS. Compared with the electric plasmon resonance in a
single-rod structure (SRS), the electromagnetic fields near the DRS and TRS
were much more localized in the dielectric surrounding the structures at the
resonance wavelengths. This caused the magnetic plasmon resonance wavelengths
to become very sensitive to refractive index changes in the environment medium.
As a result, a large figure of merit that is much larger than the electric
plasmon modes of SRS could be obtained in the magnetic plasmon modes of DRS and
TRS. These magnetic plasmon mode properties enable the use of DRSs and TRSs as
sensing elements with remarkable performance.",1101.0735v1
2011/1/31,"Electronic structure, magnetism and spin fluctuations in the superconducting weak ferromagnet Y4Co3","Results of the first principles study on the electronic structure and
magnetism of the superconducting weak ferromagnet Y$_4$Co$_3$, are presented.
Using the full potential Korringa-Kohn-Rostoker (FP-KKR) method, densities of
states, dispersion curves and magnetic moments were calculated for
quasi-ordered structural model of the compound in the framework of the local
density approximation. Spin-polarized KKR calculations confirm that weak
ferromagnetic properties of Y$_4$Co$_3$ can be attributed to only one cobalt
atom located on (2b) site in the unit cell, while other twenty Co and Y atoms
acts as a diamagnetic environment. Moreover, the magnetic Co atoms form a
quasi-one-dimensional chains along $z$ direction. The magnitude of Co(2b)
magnetic moment ($0.55~\mu_B$) markedly overestimates the experimental value
(0.23~$\mu_B$), which suggests the importance of spin fluctuations in this
system. Calculated distribution of spin magnetization in the unit cell provides
a background for discussion of the coexistence of ferromagnetism and
superconductivity in Y$_4$Co$_3$. Finally, the effect of pressure on magnetism
is discussed and compared with experimental data, also supporting weak
ferromagnetic behaviors in the system.",1101.5932v1
2011/3/15,Spiral ground state against ferroelectricity in the frustrated magnet BiMnFe2O6,"The spiral magnetic structure and underlying spin lattice of BiMnFe2O6 are
investigated by low-temperature neutron powder diffraction and density
functional theory band structure calculations. In spite of the random
distribution of the Mn3+ and Fe3+ cations, this compound undergoes a transition
into an incommensurate antiferromagnetically ordered state below TN ~ 220 K.
The magnetic structure is characterized by the propagation vector k=[0,beta,0]
with beta ~ 0.14 and the P22_12_11'(0 \beta 0)0s0s magnetic superspace
symmetry. It comprises antiferromagnetic helixes propagating along the b-axis.
The magnetic moments lie in the ac plane and rotate about pi*(1+beta) ~ 204.8
deg angle between the adjacent magnetic atoms along b. The spiral magnetic
structure arises from the peculiar frustrated arrangement of exchange couplings
in the ab plane. The antiferromagnetic coupling along the c-axis leads to the
cancellation of electric polarization, and results in the lack of
ferroelectricity in BiMnFe2O6.",1103.2972v2
2011/3/25,Excitons and Optical Absorption on the Surface of a Strong Topological Insulator with a Magnetic Energy Gap,"We present a theoretical study of interacting electron-hole pairs located on
a magnetized surface of a strong topological insulator (TI). The excitonic
energy levels and the optical absorption on such surface display unique and
potentially measurable features such as (i) an enhanced binding energy for
excitons whose total angular momentum is aligned with the magnetic exchange
field, (ii) a stark dependence of the optical absorption on the direction of
the magnetic exchange field as well as on the chirality of the incident light,
and (iii) a tunable center-of-mass motion of spinful excitons induced by
particle-hole asymmetry in the exchange field. Our predictions are relevant to
surfaces of magnetically doped TIs or surfaces coated with magnetic films, in
addition to TI nanowires placed under longitudinal magnetic fields.",1103.5059v2
2011/4/4,qPlus Magnetic Force Microscopy in Frequency-Modulation Mode with milli-Hertz Resolution,"Magnetic force microscopy (MFM) allows one to image the domain structure of
ferromagnetic samples by probing the dipole forces between a magnetic probe tip
and a magnetic sample. The magnetic domain structure of the sample depends on
the atomic arrangement of individual electron spins. It is desirable to be able
to image both individual atoms and domain structures with a single probe.
However, the force gradients of the interactions responsible for atomic
contrast and those causing domain contrast are orders of magnitude apart -
ranging from up to 100N/m for atomic interactions down to 0.0001N/m for
magnetic dipole interactions. Here, we show that this gap can be bridged with a
qPlus sensor, with a stiffness of 1800N/m (optimized for atomic interaction),
that is sensitive enough to measure milli-Hertz frequency contrast caused by
magnetic dipole-dipole interactions. Thus we have succeeded to establish a
sensing technique that performs Scanning Tunneling Microscopy, Atomic Force
Microscopy and MFM with a single probe.",1104.0528v1
2011/4/11,Asymmetric magnetization splitting in diamond domain structure: Dependence on exchange interaction and anisotropy,"The distributions of magnetization orientation for both Landau and diamond
domain structures in nano-rectangles have been investigated by micromagnetic
simulation with various exchange coefficient and anisotropy constant. Both
symmetric and asymmetric magnetization splitting are found in diamond domain
structure, as well as only symmetric magnetization splitting in Landau
structure. In the Landau structure, the splitting angle increases with the
exchange coefficient but decreases slightly with the anisotropy constant,
suggesting that the exchange interaction mainly contributes to the
magnetization splitting in Landau structure. However in the diamond structure,
the splitting angle increases with the anisotropy constant but derceases with
the exchange coefficient, indicating that the magnetization splitting in
diamond structure is resulted from magnetic anisotropy.",1104.1819v1
2011/4/25,Critical Crossover Between Yosida-Kondo Dominant Regime and Magnetic Frustration Dominant Regime in the System of a Magnetic Trimer on a Metal Surface,"Quantum Monte Carlo simulations were carried out for the system of a magnetic
trimer on a metal surface. The magnetic trimer is arranged in two geometric
configurations, viz., isosceles and equilateral triangles. The calculated
spectral density and magnetic susceptibility show the existence of two phases:
Yosida-Kondo dominant phase and magnetic frustration dominant phase.
Furthermore, a critical transition between these two phases can be induced by
changing the configuration of the magnetic trimers from isosceles to
equilateral triangle.",1104.4699v4
2011/4/29,New type of incommensurate magnetic ordering in Mn3TeO6,"The complex metal oxide Mn3TeO6 exhibits a corundum related structure and has
been prepared both in forms of single crystals by chemical transport reactions
and of polycrystalline powders by a solid state reaction route. The crystal
structure and magnetic properties have been investigated using a combination of
X-ray and neutron powder diffraction, electron microscopy, calorimetric and
magnetic measurements. At room temperature this compound adopts a trigonal
structure, space group R3 with a = 8.8679(1) {\AA}, c = 10.6727(2) {\AA}. A
long-range magnetically ordered state is identified below 23 K. An unexpected
feature of this magnetic structure is several types of Mn-chains. Under the
action of the incommensurate magnetic propagation vector k = [0, 0, 0.4302(1)]
the unique Mn site is split into two magnetically different orbits. One orbit
forms a perfect helix with the spiral axis along the c-axis while the other
orbit has a sine wave character along the c-axis.",1104.5560v1
2011/5/2,Coexistence of Magnetic Order and Two-dimensional Superconductivity at LaAlO$_3$/SrTiO$_3$ Interfaces,"A two dimensional electronic system with novel electronic properties forms at
the interface between the insulators LaAlO$_3$ and SrTiO$_3$. Samples
fabricated until now have been found to be either magnetic or superconducting,
depending on growth conditions. We combine transport measurements with
high-resolution magnetic torque magnetometry and report here evidence of
magnetic ordering of the two-dimensional electron liquid at the interface. The
magnetic ordering exists from well below the superconducting transition to up
to 200 K, and is characterized by an in-plane magnetic moment. Our results
suggest that there is either phase separation or coexistence between magnetic
and superconducting states. The coexistence scenario would point to an
unconventional superconducting phase in the ground state.",1105.0235v1
2011/5/18,Interplay of Sm4f and Co3d spins in SmCoAsO,"We present detailed magnetization and magneto-transport studies on the title
compound SmCoAsO. In a recent paper we reported [1] the complex magnetism of
this compound. SmCoAsO undergoes successive paramagnetic (PM) - ferro-magnetic
(FM) - anti-ferro-magnetic (AFM) transitions with decrease in temperature. This
is mainly driven via the c-direction interaction of Sm4f (SmO layer) spins with
adjacent (CoAs layer) ordered Co3d spins. In this article we present an
evidence of kinetic arrest for FM-AFM transition. The isothermal magnetization
(MH) loops for SmCoAsO exhibited the meta-magnetic transitions at 6, 8 and 10K
at around 80, 60 and 50kOe fields respectively with characteristic hysteresis
shoulders along with the non-zero moment at origin, thus suggesting the
possibility of kinetic arrest. Suggested kinetic arrest is further evident in
zero field-cooled (ZFC) and field-cooled (FC) hysteresis under high fields of
up to 140kOe magnetization (MT) and the magneto-transport measurements R(T)H
during FM-AFM transition. The time dependent moment experiments exhibited very
small (~2-3%) increase of the same below 20kO and decrease for 30kOe at 15K.",1105.3546v1
2011/7/22,Magnetic configurations in cubic Bi2MnFeO6 alloys from first-principles,"We expand our study on cubic BiFeO$_3$ alloys presented in [K. Koumpouras and
I. Galanakis, \textit{J. Magn. Magn. Mater} 323, 2328 (2011)] to include also
the BiMnO$_3$ and Bi$_2$MnFeO$_6$ alloys. For the latter we considered three
different cases of distribution of the Fe-Mn atoms in the lattice and six
possible magnetic configurations. We show that Fe and Mn atoms in all cases
under study retain a large spin magnetic moment, the magnitude of which exceeds
the 3 $\mu_B$. Their electronic and magnetic properties are similar to the ones
in the parent BiMnO$_3$ and BiFeO$_3$ compounds. Thus oxygen atoms which are
the nearest-neighbors of Fe(Mn) atoms play a crucial role since they mediate
the magnetic interactions between the transition metal atoms and screen any
change in their environment. Finally, we study the effect of lattice
contraction on the magnetic properties of Bi$_2$MnFeO$_6$.",1107.4448v1
2011/8/21,Quantum Tunneling of the Magnetic Moment in a Free Particle,"We study tunneling of the magnetic moment in a particle that has full
rotational freedom. Exact energy levels are obtained and the ground-state
magnetic moment is computed for a symmetric rotor. The effect of the mechanical
freedom on spin tunneling manifests itself in a strong dependence of the
magnetic moment on the moments of inertia of the rotor. Energy of the particle
exhibits quantum phase transitions between states with different values of the
magnetic moment. Particles of various shapes are investigated and quantum phase
diagram is obtained.",1108.4189v2
2011/8/31,Magnetization profile for impurities in graphene nanoribbons,"The magnetic properties of graphene-related materials and in particular the
spin-polarised edge states predicted for pristine graphene nanoribbons (GNRs)
with certain edge geometries have received much attention recently due to a
range of possible technological applications. However, the magnetic properties
of pristine GNRs are not predicted to be particularly robust in the presence of
edge disorder. In this work, we examine the magnetic properties of GNRs doped
with transition-metal atoms using a combination of mean-field Hubbard and
Density Functional Theory techniques. The effect of impurity location on the
magnetic moment of such dopants in GNRs is investigated for the two principal
GNR edge geometries - armchair and zigzag. Moment profiles are calculated
across the width of the ribbon for both substitutional and adsorbed impurities
and regular features are observed for zigzag-edged GNRs in particular. Unlike
the case of edge-state induced magnetisation, the moments of magnetic
impurities embedded in GNRs are found to be particularly stable in the presence
of edge disorder. Our results suggest that the magnetic properties of
transition-metal doped GNRs are far more robust than those with moments arising
intrinsically due to edge geometry.",1108.6199v1
2011/9/26,Electric-field control of magnetic domain wall motion and local magnetization reversal,"Spintronic devices currently rely on magnetic switching or controlled motion
of domain walls by an external magnetic field or spin-polarized current.
Achieving the same degree of magnetic controllability using an electric field
has potential advantages including enhanced functionality and low power
consumption. Here, we report on an approach to electrically control local
magnetic properties, including the writing and erasure of regular ferromagnetic
domain patterns and the motion of magnetic domain walls, in multiferroic
CoFe-BaTiO3 heterostructures. Our method is based on recurrent strain transfer
from ferroelastic domains in ferroelectric media to continuous magnetostrictive
films with negligible magnetocrystalline anisotropy. Optical polarization
microscopy of both ferromagnetic and ferroelectric domain structures reveals
that domain correlations and strong inter-ferroic domain wall pinning persist
in an applied electric field. This leads to an unprecedented electric
controllability over the ferromagnetic microstructure, an accomplishment that
produces giant magnetoelectric coupling effects and opens the way to
multiferroic spintronic devices.",1109.5514v1
2011/11/16,Magnetic hyperfine field at \textit{s-p} impurities on Laves phase compounds,"Recent experimental results for the magnetic hyperfine field B_{\rm hf} at
the nuclei of \textit{s-p} impurities such as ${}^{119}$Sn in intermetallic
Laves phases RM_2 (R = Gd, Tb, Dy, Ho, Er; M = Fe, Co) and ${}^{111}$Cd in
RCo_{2}, the impurity occupying a $R$ site indicate that the ratio B_{\rm
hf}/\mu_{3d} exhibits different behavior when one goes from RFe_2 to RCo_2. In
this work, we calculate these local moments and the magnetic hyperfine fields.
In our model, B_{\rm hf} has two contributions: one arising from the $R$ ions,
and the other arising from magnetic 3d-elements; these separate contributions
allow the identification of the origin of different behavior of the ratio
mentioned above. For {}^{111}Cd in RCo_2 we present also the contributions for
B_{\rm hf} in the light rare earth Pr, Nd, Pm, Sm compounds. For the sake of
comparison we apply also the model to {}^{111}Cd diluted in RNi_2. Our
self-consistent magnetic hyperfine field results are in good agreement with
those recent experimental data.",1111.3790v1
2011/11/21,Electronic phase transitions in Pr$_{0.5}$Ca$_{0.5}$MnO$_3$ epitaxial thin films revealed by resonant soft x-ray scattering,"We report the study of magnetic and orbital order in
Pr$_{0.5}$Ca$_{0.5}$MnO$_3$ epitaxial thin films grown on
(LaAlO$_3$)$_{0.3}$-(SrAl$_{0.5}$Ta$_{0.5}$O$_3$)$_{0.7}$ (LSAT) (011)$_c$. In
a new experimental approach, the polarization and energy dependence of resonant
soft x-ray scattering are used to reveal significant modifications of the
magnetic order in the film as compared to the bulk, namely (i) a different
magnetic ordering wave vector, (ii) a different magnetic easy axis and (iii) an
additional magnetic reordering transition at low temperatures. These
observations indicate a strong impact of the epitaxial strain on the spin
order, which is mediated by the orbital degrees of freedom and which provides a
promising route to tune the magnetic properties of manganite films. Our results
further demonstrate that resonant soft x-ray scattering is a very suitable
technique to study the magnetism in thin films, to which neutron scattering
cannot easily be applied due to the small sample volume.",1111.4725v1
2011/12/11,Spin-polarized current effect on antiferromagnet magnetization in a ferromagnet - antiferromagnet nanojunction: Theory and simulation,"Spin-polarized current effect is studied on the static and dynamic
magnetization of the antiferromagnet in a ferromagnet - antiferromagnet
nanojunction. The macrospin approximation is generalized to antiferromagnets.
Canted antiferromagnetic configuration and resulting magnetic moment are
induced by an external magnetic field. The resonance frequency and damping are
calculated, as well as the threshold current density corresponding to
instability appearance. A possibility is shown of generating low-damping
magnetization oscillations in terahertz range. The fluctuation effect is
discussed on the canted antiferromagnetic configuration. Numerical simulation
is carried out of the magnetization dynamics of the antiferromagnetic layer in
the nanojunction with spin-polarized current. Outside the instability range,
the simulation results coincide completely with analytical calculations using
linear approximation. In the instability range, undamped oscillations occur of
the longitudinal and transverse magnetization components.",1112.2362v1
2011/12/14,"Structural and magnetic properties of Mn3-xCdxTeO6 (x = 0, 1, 1.5 and 2)","Mn3TeO6 exhibits a corundum-related A3TeO6 structure and a complex magnetic
structure involving two magnetic orbits for the Mn atoms [*]. Mn3-xCdxTeO6
(x=0, 1, 1.5 and 2) ceramics were synthesized by solid state reaction and
investigated using X-ray powder diffraction, electron microscopy, calorimetric
and magnetic measurements. Cd2+ replaces Mn2+ cations without greatly affecting
the structure of the compound. The Mn and Cd cations were found to be randomly
distributed over the A-site. Magnetization measurements indicated that the
samples order antiferromagnetically at low temperature with a transition
temperature that decreases with increasing Cd doping. The nuclear and magnetic
structure of one specially prepared 114Cd containing sample:
Mn1.5(114Cd)1.5TeO6, was studied using neutron powder diffraction over the
temperature range 2 to 295 K. Mn1.5(114Cd)1.5TeO6 was found to order in an
incommensurate helical magnetic structure, very similar to that of Mn3TeO6 [*].
However, with a lower transition temperature and the extension of the ordered
structure confined to order 240(10) {\AA}. [*] S. A. Ivanov et al. Mater. Res.
Bull. 46 (2011) 1870.",1112.3225v1
2012/1/12,Influence of a transverse static magnetic field on the magnetic hyperthermia properties and high-frequency hysteresis loops of ferromagnetic FeCo nanoparticles,"The influence of a transverse static magnetic field on the magnetic
hyperthermia properties is studied on a system of large-losses ferromagnetic
FeCo nanoparticles. The simultaneous measurement of the high-frequency
hysteresis loops and of the temperature rise provides an interesting insight
into the losses and heating mechanisms. A static magnetic field of only 40 mT
is enough to cancel the heating properties of the nanoparticles, a result
reproduced using numerical simulations of hysteresis loops. These results cast
doubt on the possibility to perform someday magnetic hyperthermia inside a
magnetic resonance imaging setup.",1201.2536v1
2012/1/25,Universal Magnetic Properties of sp$^3$-type Defects in Covalently Functionalized Graphene,"Using density-functional calculations, we study the effect of sp$^3$-type
defects created by different covalent functionalizations on the electronic and
magnetic properties of graphene. We find that the induced magnetic properties
are {\it universal}, in the sense that they are largely independent on the
particular adsorbates considered. When a weakly-polar single covalent bond is
established with the layer, a local spin-moment of 1.0 $\mu_B$ always appears
in graphene. This effect is similar to that of H adsorption, which saturates
one $p_z$ orbital in the carbon layer. The magnetic couplings between the
adsorbates show a strong dependence on the graphene sublattice of
chemisorption. Molecules adsorbed at the same sublattice couple
ferromagnetically, with an exchange interaction that decays very slowly with
distance, while no magnetism is found for adsorbates at opposite sublattices.
Similar magnetic properties are obtained if several $p_z$ orbitals are
saturated simultaneously by the adsorption of a large molecule. These results
might open new routes to engineer the magnetic properties of graphene
derivatives by chemical means.",1201.5326v1
2012/2/23,Tuning magnetism in FeAs-based materials via tetrahedral structure,"Resistivity, magnetic susceptibility, neutron scattering and x-ray
crystallography measurements were used to study the evolution of magnetic order
and crystallographic structure in single-crystal samples of the Ba1-xSrxFe2As2
and Sr1-yCayFe2As2 series. A non-monotonic dependence of the magnetic ordering
temperature T0 on chemical pressure is compared to the progression of the
antiferromagnetic staggered moment, characteristics of the ordering transition
and structural parameters to reveal a distinct relationship between the
magnetic energy scale and the tetrahedral bond angle, even far above T0. In
Sr1-yCayFe2As2, an abrupt drop in T0 precisely at the Ca concentration where
the tetrahedral structure approaches the ideal geometry indicates a strong
coupling between the orbital bonding structure and the stabilization of
magnetic order, providing strong constraints on the nature of magnetism in the
iron-arsenide superconducting parent compounds.",1202.5324v2
2012/2/24,Block magnetism coupled with local distortion in the iron-based spin-ladder compound BaFe2Se3,"Magnetism in the insulating BaFe$_2$Se$_3$ was examined through
susceptibility, specific heat, resistivity and neutron diffraction
measurements. After formation of a short-range magnetic correlation, a
long-range ordering was observed below $T_{\rm N}\sim 255$ K. The transition is
obscured by bulk properties. Magnetic moments ($\parallel a$) are arranged to
form a Fe$_4$ ferromagnetic unit, and each Fe$_4$ stacks antiferromagnetically.
This block magnetism is of the third type among magnetic structures of ferrous
materials. The magnetic ordering drives unusually large distortion via
magnetoelastic coupling.",1202.5371v1
2012/6/12,Magnetic Moment Formation in Graphene Detected by Scattering of Pure Spin Currents,"Hydrogen adatoms are shown to generate magnetic moments inside single layer
graphene. Spin transport measurements on graphene spin valves exhibit a dip in
the non-local spin signal as a function of applied magnetic field, which is due
to scattering (relaxation) of pure spin currents by exchange coupling to the
magnetic moments. Furthermore, Hanle spin precession measurements indicate the
presence of an exchange field generated by the magnetic moments. The entire
experiment including spin transport is performed in an ultrahigh vacuum
chamber, and the characteristic signatures of magnetic moment formation appear
only after hydrogen adatoms are introduced. Lattice vacancies also demonstrate
similar behavior indicating that the magnetic moment formation originates from
pz-orbital defects.",1206.2628v3
2012/6/14,Fowler-Nordheim Electron Cold Emission Formalism in Presence of Strong Magnetic Field,"Formalisms for both non-relativistic as well as relativistic versions of
field emission of electrons in presence of strong quantizing magnetic field,
relevant for strongly magnetized neutron stars or magnetars are developed. In
the non-relativistic scenario, where electrons obey Schr{$\ddot{\rm{o}}$}dinger
equation, we have noticed that when Landau levels are populated for electrons
in presence of strong quantizing magnetic field the transmission probability
exactly vanishes unless the electrons are spin polarized in the opposite
direction to the external magnetic field. On the other hand, the cold electron
emission under the influence of strong electrostatic field at the poles is
totally forbidden from the surface of those compact objects for which the
surface magnetic field strength is $\gg 10^{15}$G (in the eventuality that they
may exist). Whereas in the relativistic case, where the electrons obey Dirac
equation, the presence of strong quantizing magnetic field completely forbids
the emission of electrons from the surface of compact objects if $B >10^{13}$G.",1206.3024v1
2012/6/22,Effects of the randomly distributed magnetic field on the phase diagrams of the Ising Nanowire II: continuous distributions,"The effect of the random magnetic field distribution on the phase diagrams
and ground state magnetizations of the Ising nanowire has been investigated
with effective field theory with correlations. Gaussian distribution has been
chosen as a random magnetic field distribution. The variation of the phase
diagrams with that distribution parameters has been obtained and some
interesting results have been found such as disappearance of the reentrant
behavior and first order transitions which appear in the case of discrete
distributions. Also for single and double Gaussian distributions, ground state
magnetizations for different distribution parameters have been determined which
can be regarded as separate partially ordered phases of the system.",1206.5156v1
2012/6/22,Investigation of bond dilution effects on the magnetic properties of a cylindrical Ising nanowire,"A cylindrical magnetic nanowire system composed of ferromagnetic core and
shell layers has been investigated by using effective field theory with
correlations. Both ferromagnetic and antiferromagnetic exchange couplings at
the core-shell interface have been considered. Main attention has been focused
on the effects of the quenched disordered shell bonds, as well as interface
bonds on the magnetic properties of the system. A complete picture of the phase
diagrams and magnetization profiles has been represented. It has been shown
that for the antiferromagnetic nanowire system, the magnetization curves can be
classified according to N\'{e}el theory of ferrimagnetism and it has been found
that under certain conditions, the magnetization profiles may exhibit Q-type,
P-type, N-type and L-type behaviors. The observed L-type behavior has not been
reported in the literature before for the equilibrium properties of nanoscaled
magnets. As another interesting feature of the system, it has been found that a
compensation point can be induced by a bond dilution process in the surface.
Furthermore, we have not found any evidence of neither the first order phase
transition characteristics, nor the reentrance phenomena.",1206.5326v1
2012/6/29,Light-induced magnetization reversal of high-anisotropy TbCo alloy films,"Magnetization reversal using circularly polarized light provides a new way to
control magnetization without any external magnetic field and has the potential
to revolutionize magnetic data storage. However, in order to reach ultra-high
density data storage, high anisotropy media providing thermal stability are
needed. Here, we evidence all-optical magnetization switching for different
TbxCo1-x ferrimagnetic alloy composition and demonstrate all-optical switching
for films with anisotropy fields reaching 6 T corresponding to anisotropy
constants of 3x106 ergs/cm3. Optical magnetization switching is observed only
for alloys which compensation temperature can be reached through sample
heating.",1206.6978v1
2012/7/6,Spin-interactions in Mineral Libethenite Series: Evolution of Low-dimensional Magnetism,"Interesting magnetic properties and spin-exchange interactions along various
possible pathways in half-integral spin quantum magnetic tetramer system:
A$_{2}$PO$_{4}$OH (A = Co, Cu) are investigated. Interplay of structural
distortion and the magnetic properties with the evolution of localized band
structure explain the gradual transition from a three-dimensional
antiferromagnet to a low-dimensional frustrated magnetic system along the
series. Detailed study of exchange mechanism in this system explores various
possibilities of complex magnetic interaction. Electronic structure of this
series, studied with the help of different appropriate density-functional
approaches like N-th order Muffin-Tin orbital(NMTO) and Planewave
Pseudopotential calculations incorporating onsite Coulomb repulsion(U),
identifies the underlying magnetic exchange mechanism of this series.
Thereafter a generalized minimal model spin-Hamiltonian is constructed for the
low-dimensional system. Solution of this model Hamiltonian within first order
perturbation theory results into the evaluation of spin-gap in the
spin-tetramer system. In addition, the effects of size-confinement and volume
reduction on the relevant exchange integrals and spin-gap of the
low-dimensional system are also discussed.",1207.1529v1
2012/8/10,Ferroelectric control of magnetization in La_{1-x}Sr_xMnO3 manganites: A first-principle study,"We present a first-principles study on the interface between perovskite
ferroelectrics (PbTiO3) and conducting magnetic manganites La_{1-x}Sr_xMnO3. We
show that by switching the ferroelectric polarization, additional carriers are
accumulated or depleted at the interfacial region of the manganite and that
this change in carrier density can modify the magnetic spin configuration of
the interfacial Mn, which is consistent with the experimentally observed
anomalously large change in the magnetization. We also describe an unexpected
purely interfacial phenomenon whereby the ferroelectric polarization of the
interfacial region changes the magnetic energetics --- a degree of freedom not
present in bulk manganites. Theoretically, we show the the ground-state
magnetic structure depends sensitively on the precise choice of Hubbard $U$
parameter within the widely-used DFT+U class of exchange correlation
functionals. We provide a simple Ising-like model that explains the evolution
of the magnetic structure with U in tandem with a discussion of various
different ways in which one might try to choose an appropriate U parameter.",1208.2219v1
2012/9/5,Gate voltage modulation of spin-Hall-torque-driven magnetic switching,"Two promising strategies for achieving efficient control of magnetization in
future magnetic memory and non-volatile spin logic devices are spin transfer
torque from spin polarized currents and voltage-controlled magnetic anisotropy
(VCMA). Spin transfer torque is in widespread development as the write
mechanism for next-generation magnetic memory, while VCMA offers the potential
of even better energy performance due to smaller Ohmic losses. Here we
introduce a 3-terminal magnetic tunnel junction (MTJ) device that combines both
of these mechanisms to achieve new functionality: gate-voltage-modulated spin
torque switching. This gating makes possible both more energy-efficient
switching and also improved architectures for memory and logic applications,
including a simple approach for making magnetic memories with a maximum-density
cross-point geometry that does not require a control transistor for every MTJ.",1209.0962v1
2012/10/22,Accelerating the switching of logical units by anisotropy driven magnetization dynamics,"In this work the magnetization dynamics of clusters supported on non-magnetic
substrates is shown to exhibit an unprecedented complex response when subjected
to external magnetic fields. The field-driven magnetization reversal of small
Co clusters deposited on a Cu(111) surface has been studied by means of
first-principles calculations and atomistic spin dynamics simulations. For
applied fields ranging from 1 Tesla to 10 Tesla, we observe a coherent
magnetization reversal with switching times in the range of several tenths of
picoseconds to several nanoseconds, depending on the field strength. We find a
non-monotonous dependence of the switching times with respect to the strength
of the applied field, which we prove to have its origin in the complex magnetic
anisotropy landscape of these low dimensional systems. This effect is shown to
be stable for temperatures around 10 K, and is possible to realize over a range
of exchange interactions and anisotropy landscapes. Possible experimental
routes to achieve this unique switching behaviour are discussed.",1210.5836v1
2013/1/12,Magnetic Behaviour of the $Bi_{2-y} Sr_y Ir_2 O_7$ Pyrochlore Solid Solution,"The temperature dependence of magnetic susceptibility of the
Bi$_{2-y}$Sr$_{y}$Ir$_{2}$O$_{7}$ system was studied from 2 to 300 K. According
to these measurements, the solid solution $(0\leq y\leq 0.9)$ does not show any
magnetic transition; however, a noticeable deviation from the Curie-Weiss law
occurs and the magnetic behavior of this system can be ascribed to short-range
magnetic order that is also present in several geometrically frustrated
systems. The Pauli magnetic susceptibility decreases as the Sr content
increases, this can be associated with a shift towards Ir$^{5+}$ in samples;
also the Ir effective magnetic moment decreases. The estimated Wilson-ratio
indicates the presence of strong electron-electron correlations.",1301.2720v1
2013/1/21,In-plane Magnetization Induced Quantum Anomalous Hall Effect,"In a two-dimensional electron gas, the quantized Hall conductance can be
induced by a strong magnetic field, known as the quantum Hall effect, and it
can also result from the strong exchange coupling of magnetic ions, dubbed as
the ""quantum anomalous Hall effect"". The quantum Hall effect requires the
out-of-plane magnetic field, and similarly, it is commonly believed that the
magnetization should be out-of-plane for the quantum anomalous Hall effect. In
the present work, we find this condition is not necessary and predict that the
quantum anomalous Hall effect can also be induced by the purely in-plane
magnetization in two realistic systems, including Bi$_2$Te$_3$ thin film with
magnetic doping and HgMnTe quantum wells with shear strains, when all the
reflection symmetries are broken. An experimental setup is proposed to confirm
this effect, the observation of which will pave the way to search for the
quantum anomalous Hall effect in a wider range of materials.",1301.4772v1
2013/2/9,The effect of uniaxial pressure on the magnetic anisotropy of the Mn_{12}-Ac single-molecule magnet,"We study the effect of uniaxial pressure on the magnetic hysteresis loops of
the single-molecule magnet Mn_{12}-Ac. We find that the application of pressure
along the easy axis increases the fields at which quantum tunneling of
magnetization occurs. The observations are attributed to an increase in the
molecule's magnetic anisotropy constant D of 0.142(1)%/kbar. The increase in D
produces a small, but measurable increase in the effective energy barrier for
magnetization reversal. Density-functional theory calculations also predict an
increase in the barrier with applied pressure.",1302.2276v2
2013/2/22,Unconventional magnetostructural transition in CoCr2O4 at high magnetic fields,"The magnetic-field and temperature dependencies of ultrasound propagation and
magnetization of single-crystalline CoCr2O4 have been studied in static and
pulsed magnetic fields up to 14 T and 62 T, respectively. Distinct anomalies
with significant changes in the sound velocity and attenuation are found in
this spinel compound at the onset of long-range incommensurate spiral-spin
order at T_s = 27 K and at the transition from the incommensurate to the
commensurate state at T_l = 14 K, evidencing strong spin-lattice coupling.
While the magnetization evolves gradually with field, steplike increments in
the ultrasound clearly signal a transition into a new magneto-structural state
between 6.2 and 16.5 K and at high magnetic fields. We argue that this is a
high-symmetry phase with only the longitudinal component of the magnetization
being ordered, while the transverse helical component remains disordered. This
phase is metastable in an extended H-T phase space.",1302.5605v1
2013/3/8,"Anisotropic Current-Controlled Magnetization Reversal in the Ferromagnetic Semiconductor (Ga,Mn)As","Electrical current manipulation of magnetization switching through
spin-orbital coupling in ferromagnetic semiconductor (Ga,Mn)As Hall bar devices
has been investigated. The efficiency of the current-controlled magnetization
switching is found to be sensitive to the orientation of the current with
respect to the crystalline axes. The dependence of the spin-orbit effective
magnetic field on the direction and magnitude of the current is determined from
the shifts in the magnetization switching angle. We find that the strain
induced effective magnetic field is about three times as large as the Rashba
induced magnetic field in our GaMnAs devices.",1303.1907v1
2013/3/15,Single-Chain Magnets,"Single-chain magnets are molecular spin chains displaying slow relaxation of
the magnetisation on a macroscopic time scale. To this similarity with
single-molecule magnets they own their name. In this chapter the distinctive
features of single-chain magnets as opposed to their precursors will be
pinpointed. In particular, we will show how their behaviour is dictated by the
physics of thermally-excited domain walls. The basic concepts needed to
understand and model single-chain magnets will also be reviewed.",1303.3731v1
2013/3/28,Non-magnetic impurities to induce magnetism in $α$-PbO crystal structure,"A new route to $d^0$ magnetism is established with help of the first
principles methods. Non-magnetic interstitial impurities from group 14 in the
periodic table are found to induce $p$-orbital magnetism in polycrystalline
PbO-type structures. The half-filled $p$-orbitals occupied by two electrons is
generated on the impurity site for which the ferromagnetic state of high
stability is guaranteed by the first Hund's rule. Since the impurity is
embedded between layers of the host, its atomic radius is a key to tune not
only its solubility but also the magnetic behavior: the on-site stability of
the spin polarized state grows with reduction of the atomic radius while losing
in the long-rang order interactions. However, for impurities of smaller radius
the weaker inter-site magnetic coupling can be compensated by their
concentration as the impurity solubility limit is shifted to higher magnitudes.",1303.7250v2
2013/4/12,Noncollinear magnetism and half-metallicity in biased bilayer zigzag graphene nanoribbons,"We study in this paper the edge polarizations and their consequences for a
biased Bernal stacked bilayer graphene nanoribbon with zigzag termination. The
magnetic states are classified according to the interlayer and intralayer
couplings between the edge polarizations, and the magnetic phase diagram of
doping versus bias voltage is given. Coplanar magnetic phase is found and the
variation of its magnetic structure with the bias voltage is investigated. For
all the magnetic states, we also discuss the possibility of the
half-metallicity, and for a ribbon with perfect zigzag edges we predict seven
kinds of the half-metallic states, which are characterized by their distinct
magnetic structures and quantized electrical conductances along the ribbon.",1304.3534v1
2013/5/7,Nonmagnetic Impurity Effect of the S=1/2 Spin Ladder System (pipdH)_2Cu_{1-x}Zn_xBr_4,"We report the synthesis and the magnetic susceptibility of
(pipdH)2Cu1-xZnxBr4, which is a nonmagnetic impurity-doped S=1/2 spin ladder
system. The samples were synthesized from a solution by using a slow
evaporation method. Samples were confirmed to be in a single phase and to have
the same crystal structure as the pure system (pipdH)2CuBr4 by using X-ray
diffraction measurements. To check the magnetic properties, we performed
magnetic susceptibility and magnetization measurements with a SQUID
magnetometer. A plot of the inverse magnetic susceptibility indicates the
presence of dominant antiferromagnetic coupling. The magnetic susceptibility
shows a broad maximum due to low dimensionality and a spin gap behavior related
to the two-leg spin ladder at low temperature. The spin gap and the Curie
constants of Zn-doped samples, as estimated from an analysis of the magnetic
susceptibility, monotonically decrease as the Zn concentration decreases. A
nonmagnetic impurity of S=1/2 spin ladder system affects the spin gap.",1305.1499v2
2013/5/9,Low-temperature muon spin rotation studies of the monopole charges and currents in Y doped Ho2Ti2O7,"In the ground state of Ho2Ti2O7 spin ice, the disorder of the magnetic
moments follows the same rules as the proton disorder in water ice. Excitations
take the form of magnetic monopoles that interact via a magnetic Coulomb
interaction. Muon spin rotation has been used to probe the low-temperature
magnetic behaviour in single crystal Ho2-xYxTi2O7 (x=0, 0.1, 1, 1.6 and 2). At
very low temperatures, a linear field dependence for the relaxation rate of the
muon precession lambda(B), that in some previous experiments on Dy2Ti2O7 spin
ice has been associated with monopole currents, is observed in samples with
x=0, and 0.1. A signal from the magnetic fields penetrating into the silver
sample plate due to the magnetization of the crystals is observed for all the
samples containing Ho allowing us to study the unusual magnetic dynamics of Y
doped spin ice.",1305.2048v1
2013/5/9,Transport current and magnetization problems for thin type-II superconducting films,"Thin film magnetization problems in type-II superconductivity are usually
formulated in terms of the magnetization function alone, which allows one to
compute the sheet current density and the magnetic field but often inhibits
computing the electric field in the film. Accounting for the current leads
presents an additional difficulty encountered in thin film transport current
problems.
  We generalize, to the presence of a transport current, the two-variable
variational formulation proposed recently for thin film magnetization problems.
The formulation, written in terms of the magnetization function and the
electric field, is used as a basis for a new numerical approximation enabling
us to solve the magnetization and transport current problems for flat films of
arbitrary shapes, including multiply connected films. The advantage of this
approach is in its ability to compute accurately all variables of interest,
including the electric field, for any value of the power in the power law
current-voltage relation characterizing the superconducting material. In the
high power limit the critical state model solution is obtained.",1305.2101v1
2013/5/13,Backhopping effect in magnetic tunnel junctions: comparison between theory and experiment,"We report on the magnetic switching and backhopping effects due to
spin-transfer-torque in magnetic tunnel junctions. Experimental data on the
current-induced switching in junctions with MgO tunnel barrier reveal a random
back-and-forth switching between the magnetization states, which appears when
the current direction favors the parallel magnetic configuration. The effect
depends on the barrier thickness $t_b$, and is not observed in tunnel junctions
with very thin MgO tunnel barriers, $t_b$ $<$ 0.95 nm. Switching dependence on
the bias voltage and barrier thickness is explained in terms of the macrospin
model, with the magnetization dynamics described by the modified
Landau-Lifshitz-Gilbert equation. Numerical simulations indicate that the
competition between in-plane and out-of-plane torque components can result at
high bias voltages in a non-deterministic switching behavior, in agreement with
experimental observations. When the barrier thickness is reduced, the overall
coupling between the magnetic layers across the barrier becomes ferromagnetic,
which suppresses the backhopping effect.",1305.2711v1
2013/5/29,Enhanced interface perpendicular magnetic anisotropy in Ta|CoFeB|MgO using nitrogen doped Ta underlayers,"We show that the magnetic characteristics of Ta|CoFeB|MgO magnetic
heterostructures are strongly influenced by doping the Ta underlayer with
nitrogen. In particular, the saturation magnetization drops upon doping the Ta
underlayer, suggesting that the doped underlayer acts as a boron diffusion
barrier. In addition, the thickness of the magnetic dead layer decreases with
increasing nitrogen doping. Surprisingly, the interface magnetic anisotropy
increases to ~1.8 erg/cm2 when an optimum amount of nitrogen is introduced into
the Ta underlayer. These results show that nitrogen doped Ta serves as a good
underlayer for Spintronics applications including magnetic tunnel junctions and
domain wall devices.",1305.6660v1
2013/7/17,Spectrum of Coupled Waves in Orthorhombic Multiferroics With Cycloidal Antiferromagnetic Structure in External Electric and Magnetic Fields,"Spectrum of coupled spin, acoustic, electro-dipole and electromagnetic waves
in orthorhombic perovskite multiferroics placed in external electric and
magnetic field has been calculated. Frequency and field dependencies of
electric, magnetic, and magnetoelectric susceptibilities of multiferroics with
cycloidal antiferromagnetic structure in external electric and magnetic fields
have been investigated as well. The spectrum of coupled waves has a band
structure. Width and frequency ranges of bands depend on external fields. The
possibility of control of electrodynamic properties of orthorhombic perovskite
multiferroics with cycloidal antiferromagnetic structure by external electric
and magnetic fields has been shown.",1307.4664v1
2013/7/21,Room-Temperature Electronically-Controlled Ferromagnetism at the LaAlO3/SrTiO3 Interface,"Reports of emergent conductivity, superconductivity, and magnetism at oxide
interfaces have helped to fuel intense interest in their rich physics and
technological potential. Here we employ magnetic force microscopy to search for
room-temperature magnetism in the well-studied LaAlO3/SrTiO3 system. Using
electrical top gating to deplete electrons from the oxide interface, we
directly observe an in-plane ferromagnetic phase with sharply defined domain
walls. Itinerant electrons, introduced by a top gate, align
antiferromagnetically with the magnetization, at first screening and then
destabilizing it as the conductive state is reached. Subsequent depletion of
electrons results in a new, uncorrelated magnetic pattern. This newfound
control over emergent magnetism at the interface between two non-magnetic
oxides portends a number of important technological applications.",1307.5557v2
2013/8/30,Magnetocapacitance as a sensitive probe of magnetostructural changes in NiCr$_2$O$_4$,"The spinel NiCr$_2$O$_4$ is characterized using dielectric and high magnetic
field measurements. The trends in the magnetodielectric response fall into
three clear temperature regimes corresponding to known magnetic and structural
transitions. Above 65\,K, weak magnetic field dependence of the dielectric
constant is observed with no hysteresis. When 30\,K\,$\leq\,T\,\leq$\,65\,K, a
strong dependence of the dielectric constant on the magnetic field is observed
and hysteresis develops resulting in so called butterfly loops. Below 30\,K,
magnetodielectric hysteresis is enhanced. Magnetodielectric hysteresis mirrors
magnetic hysteresis suggesting that spin-spin interactions are the mechanism
for the magnetoelectric effect in NiCr$_2$O$_4$. At high fields however, the
magnetization continues to increase while the dielectric constant saturates.
Magnetodielectric measurements of NiCr$_2$O$_4$ suggest an additional,
previously unobserved transition at 20\,K. Subtle changes in magnetism and
structure suggest that this 20\,K anomaly corresponds to the completion of
ferrimagnetic ordering and the spin driven structural distortion. We
demonstrate that magnetocapacitance is a sensitive probe of magnetostructural
distortion.",1309.0016v1
2013/10/29,Switching probability investigation of electric field-induced precessional magnetization switching,"We report theoretical investigation of the switching probability of electric
field-induced precessional magnetization switching by solving the Fokker-Planck
equation numerically with finite difference method. The switching probability
is determined by the net magnetic field induced by the deviation of precession
angle from its equilibrium position after precession process. The error rate
has the lowest value under an appropriate applied external field for the
voltage pulse duration ${\tau}_{pulse}$ a little longer than the half
precession period. The calculated results show that ultra-low error rate down
to the order of $10^{-12}$ can be achieved for thermal stability factor
{\Delta} = 50 and low damping factor material should be used for free layer to
improve the switching probability. For parallel (anti-parallel) magnetization
to anti-parallel (parallel) magnetization switching process, the spin transfer
torque tends to decrease (increase) the error rate when the ${\tau}_{pulse}$ is
shorter than the half precession period, and increase (decrease) the error rate
when ${\tau}_{pulse}$ is longer than the half-period. These results exhibit
potential of electric field-induced precessional magnetization switching for
ultra-low power, high speed magnetic random access memory (MRAM) application.",1310.7685v3
2013/10/30,Spin-orbit-torque magnetization switching of a three terminal perpendicular magnetic tunnel junction,"We report on the current-induced magnetization switching of a three-terminal
perpendicular magnetic tunnel junction by spin-orbit torque and the read-out
using the tunnelling magnetoresistance (TMR) effect. The device is composed of
a perpendicular Ta/FeCoB/MgO/FeCoB stack on top of a Ta current line. The
magnetization of the bottom FeCoB layer can be switched reproducibly by the
injection of current pulses with density $5\times10^{11}$ A/m$^2$ in the Ta
layer in the presence of an in-plane bias magnetic field, leading to the
full-scale change of the TMR signal. Our work demonstrates the proof of concept
of a perpendicular spin-orbit torque magnetic memory cell.",1310.8235v2
2013/11/26,Superconductivity and Magnetism in YFe$_2$Ge$_2$,"We report calculations of the electronic structure and magnetic properties of
YFe$_2$Ge$_2$ and discuss the results in terms of the observed
superconductivity near magnetism. We find that YFe$_2$Ge$_2$ is a material near
a magnetic quantum critical point based on comparison of standard density
functional results that predict magnetism with experiment. The band structure
and Fermi surfaces are very three dimensional and higher conductivity is
predicted in the $c$-axis direction. The magnetism is of Stoner type and is
predominately from an in-plane ferromagnetic tendency. The inter-layer coupling
is weak giving a perhaps 2D character to the magnetism, which is in contrast to
the conductivity and may be important for suppressing the ordering tendency.
This is compatible with a triplet superconducting state mediated by spin
fluctuations.",1311.6630v1
2013/12/22,Magnetic phase diagram and first principles study of Pb3TeCo3V2O14,"An antiferromagnetic ordering in Pb3TeCo3V2O14 takes place through formation
of short range correlation regime with T* ~ 10.5 K and succession of second
order phase transition at TN1 = 8.9 K and first order phase transition at TN2 =
6.3 K. An external magnetic field rapidly destroys magnetic structure at T <
TN2 and influences the magnetic order at TN2 < T < TN1 resulting in complex
magnetic phase diagram of Pb3TeCo3V2O14 as derived from magnetization and
specific heat measurements. The first principles calculations indicate that in
variance with layered crystal structure the magnetic subsystem of Pb3TeCo3V2O14
is quasi-one-dimensional and highly unusual consisting of weakly coupled
triangular tubes.",1312.6392v2
2014/1/13,Dispersive magnetic resonance mode in the Kondo semiconductor CeFe2Al10,"The CeT2Al10 family of orthorhombic compounds exhibits a very peculiar
evolution from a Kondo-insulator (T: Fe) to an unconventional long-range
magnetic order (T: Ru, Os). Inelastic neutron scattering experiments performed
on single-crystal CeFe2Al10 reveal that this material develops a spin-gap in
its magnetic spectral response below ~ 50 K, with a magnetic excitation
dispersing from $E = 10.2 \pm 0.5$ meV at the Y zone-boundary point [q =
(0,1,0)] to $\approx 12$ meV at the top of the branch. The excitation shows a
pronounced polarization of the magnetic fluctuations along a, the easy
anisotropy axis. Its behavior is contrasted with that of the (magnonlike) modes
previously reported for CeRu2Al10, which have transverse character and exist
only in the antiferromagnetic state. The present observation is ascribed to a
""magnetic exciton"" mechanism invoked to explain a similar magnetic response
previously discovered in YbB12.",1401.2892v1
2014/2/27,Sensitive Magnetic Force Detection with a Carbon Nanotube Resonator,"We propose a technique for sensitive magnetic point force detection using a
suspended carbon nanotube (CNT) mechanical resonator combined with a magnetic
field gradient generated by a ferromagnetic gate electrode. Numerical
calculations of the mechanical resonance frequency show that single Bohr
magneton changes in the magnetic state of an individual magnetic molecule
grafted to the CNT can translate to detectable frequency shifts, on the order
of a few kHz. The dependences of the resonator response to device parameters
such as length, tension, CNT diameter, and gate voltage are explored and
optimal operating conditions are identified. A signal-to-noise analysis shows
that in principle, magnetic switching at the level of a single Bohr magneton
can be read out in a single shot on timescales as short as 10 microseconds.
This force sensor should enable new studies of spin dynamics in isolated single
molecule magnets, free from the crystalline or ensemble settings typically
studied.",1402.6780v1
2014/3/17,A reentrant phenomenon in magnetic and dielectric properties of Dy2BaNiO5 and an intriguing influence of external magnetic field,"We report that the spin-chain compound Dy2BaNiO5 recently proven to exhibit
magnetoelectric coupling below its Neel temperature (T_N) of 58 K, exhibits
strong frequency-dependent behavior in ac magnetic susceptibility and complex
dielectric properties at low temperatures (<10K), mimicking 'reentrant'
multiglass phenomenon. Such a behavior is not known among undoped compounds. A
new finding in the field of multiferroics is that the characteristic magnetic
feature at such low temperatures moves towards higher temperatures in the
presence of a magnetic-field (H), whereas the corresponding dielectric feature
shifts towards lower temperatures with H, unlike the situation near T_N. This
observation indicates that the alignment of spins by external magnetic fields
tends to inhibit glassy-like slow electric-dipole dynamics, at least in this
system, possibly arising from peculiarities in the magnetic structure.",1403.4166v1
2014/3/19,Magnetic order in the frustrated Ising-like chain compound Sr$_3$NiIrO$_6$,"We have studied the field and temperature dependence of the magnetization of
single crystals of Sr3NiIrO6. These measurements evidence the presence of an
easy axis of anisotropy and two anomalies in the magnetic susceptibility.
Neutron powder diffraction realized on a polycrystalline sample reveals the
emergence of magnetic reflections below 75 K with magnetic propagation vector k
~ (0, 0, 1), undetected in previous neutron studies [T.N. Nguyen and H.-C zur
Loye, J. Solid State Chem., 117, 300 (1995)]. The nature of the magnetic ground
state, and the presence of two anomalies common to this family of material, are
discussed on the basis of the results obtained by neutron diffraction,
magnetization measurements, and symmetry arguments.",1403.4815v2
2014/3/20,Magnetization of densely packed interacting magnetic nanoparticles with cubic and uniaxial anisotropies: A Monte Carlo study,"The magnetization curves of densely packed single domain magnetic
nanoparticles (MNP) are investigated by Monte Carlo simulations in the
framework of an effective one spin model. The particles whose size
polydispersity is taken into account are arranged in spherical clusters and
both dipole dipole interactions (DDI) and magnetic anisotropy energy (MAE) are
included in the total energy. Having in mind the special case of spinel
ferrites of intrinsic cubic symmetry, combined cubic and uniaxial
magnetocrystalline anisotropies are considered with different configurations
for the orientations of the cubic and uniaxial axes. It is found that the DDI,
together with a marked reduction of the linear susceptibility are responsible
for a damping of the peculiarities due to the MAE cubic component on the
magnetization. As an application, we show that the simulated magnetization
curves compare well to experimental results for $\gamma$--Fe$_2$O$_3$ MNP for
small to moderate values of the field.",1403.5157v1
2014/3/24,Magnetic structure and dynamics of a strongly one-dimensional cobalt$^{II}$ metal-organic framework,"We investigate the magnetism of the
Co$^{II}_4$(OH)$_2$(C$_1$$_0$H$_1$$_6$O$_4$)$_3$ metal-organic framework which
displays complex inorganic chains separated from each other by distances of 1
to 2 nm, and which orders at ~5.4 K. The zero-field magnetic structure is
determined using neutron powder diffraction: it is mainly antiferromagnetic but
posseses a ferromagnetic component along the $\textbf{c}$-axis. This magnetic
structure persists in presence of a magnetic field. Ac susceptibility
measurements confirm the existence of a single thermally activated regime over
7 decades in frequency ($E/k_B\approx64 K$) whereas time-dependent relaxation
of the magnetization after saturation in an external field leads to a two times
smaller energy barrier. These experiments probe the slow dynamics of domain
walls within the chains: we propose that the ac measurements are sensitive to
the motion of existing domain walls within the chains, while the magnetization
measurements are governed by the creation of domain walls.",1403.5931v1
2014/4/4,Deposition Order Dependent Magnetization Reversal in Pressure Graded Co/Pd films,"Magnetization reversal mechanisms and depth-dependent magnetic profile have
been investigated in Co/Pd thin films magnetron-sputtered under continuously
varying pressure with opposite deposition orders. For samples grown under
increasing pressure, magnetization reversal is dominated by domain nucleation,
propagation and annihilation; an anisotropy gradient is effectively
established, along with a pronounced depth-dependent magnetization profile.
However, in films grown under decreasing pressure, disorders propagate
vertically from the bottom high-pressure region into the top low-pressure
region, impeding domain wall motion and forcing magnetization reversal via
rotation; depth-dependent magnetization varies in an inverted order, but the
spread is much suppressed.",1404.1350v1
2014/5/12,Electromagnetic Waves Reflectance of Graphene -- Magnetic Semiconductor Superlattice in Magnetic Field,"Electrodynamic properties of the graphene - magnetic semiconductor - graphene
superlattice placed in magnetic field have been investigated theoretically in
Faraday geometry with taking into account dissipation processes. Frequency and
field dependences of the reflectance, transmittance and absorbtance of
electromagnetic waves by such superlattice have been calculated for different
numbers of periods of the structure and different sizes of the periods with
using a transfer matrix method. The possibility of efficient control of
electrodynamic properties of graphene - magnetic semiconductor - graphene
superlattice has been shown.",1405.3585v1
2014/6/12,Temperature evolution of structural and magnetic properties of stoichiometric LiCu2O2: correlation of thermal expansion coefficient and magnetic order,"Temperature-dependent crystallographic and magnetic studies on stoichiometric
single crystals of LiCu2O2 are reported. The magnetic properties are similar to
earlier findings demonstrating antiferromagnetic ordering below 25 K. Evidence
of magnetoelastic coupling is observed in the thermal expansion along the
c-direction; not only at the low temperature antiferromagnetic transitions, but
an anomalous behavior of the thermal expansion indicate magnetoelastic coupling
also to the magnetic ordering related to a weak spontaneous magnetic moment
appearing at 150 K. Ac-susceptibility measurements at different frequencies and
superposed dc- fields are employed to further characterize this magnetic
anomaly.",1406.3115v1
2014/6/27,Magnetic properties of Co/Cu/Py antidot films,"The magnetic properties of ordered nanoscale Co/Cu/Py multilayer antidot
films with different pore sizes prepared on top of nanoporous alumina membranes
are presented. By using Co and Py films separated by a Cu thin layer, and
tuning the pore diameters of the NAMs we were able to play with the coercivity
of the films and observe stepped magnetization curves, as a consequence of the
different coercivities of the Co and Py films. The magnetic properties of the
multilayer antidots have been measured and compared with results obtained for
antidots of Cu/Py. The magnetization reversal process that occurs in each
individual layer and in the multilayer was studied by means of micromagnetic
simulations.",1406.7322v1
2014/7/2,Element-Specific Depth Profile of Magnetism and Stoichiometry at the La0.67Sr0.33MnO3/BiFeO3 Interface,"Depth-sensitive magnetic, structural and chemical characterization is
important in the understanding and optimization of novel physical phenomena
emerging at interfaces of transition metal oxide heterostructures. In a
simultaneous approach we have used polarized neutron and resonant X-ray
reflectometry to determine the magnetic profile across atomically sharp
interfaces of ferromagnetic La0.67Sr0.33MnO3 / multiferroic BiFeO3 bi-layers
with sub-nanometer resolution. In particular, the X-ray resonant magnetic
reflectivity measurements at the Fe and Mn resonance edges allowed us to
determine the element specific depth profile of the ferromagnetic moments in
both the La0.67Sr0.33MnO3 and BiFeO3 layers. Our measurements indicate a
magnetically diluted interface layer within the La0.67Sr0.33MnO3 layer, in
contrast to previous observations on inversely deposited layers. Additional
resonant X-ray reflection measurements indicate a region of an altered Mn- and
O-content at the interface, with a thickness matching that of the magnetic
diluted layer, as origin of the reduction of the magnetic moment.",1407.0737v1
2014/7/5,Spin reorientation in Na-doped BaFe$_2$As$_2$ studied by neutron diffraction,"We have studied the magnetic ordering in Na doped BaFe$_2$As$_2$ by
unpolarized and polarized neutron diffraction using single crystals. Unlike
previously studied FeAs-based compounds that magnetically order,
Ba$_{1-x}$Na$_x$Fe$_2$As$_2$ exhibits two successive magnetic transitions: For
x=0.35 upon cooling magnetic order occurs at $\sim$70\ K with in-plane magnetic
moments being arranged as in pure or Ni, Co and K-doped BaFe$_2$As$_2$ samples.
At a temperature of $\sim$46\ K a second phase transition occurs, which the
single-crystal neutron diffraction experiments can unambiguously identify as a
spin reorientation. At low temperatures, the ordered magnetic moments in
Ba$_{0.65}$Na$_{0.35}$Fe$_2$As$_2$ point along the $c$ direction. Magnetic
correlations in these materials cannot be considered as Ising like, and
spin-orbit coupling must be included in a quantitative theory.",1407.1417v1
2014/7/8,Highly reliable low-energy writing of bits in non-volatile multiferroic memory based on 180-degree magnetization switching with voltage-generated stress,"Rotating the magnetization of a magnetostrictive nanomagnet with electrically
generated mechanical strain dissipates miniscule amount of energy compared to
any other rotation method and would have been the ideal method to write bits in
nonvolatile magnetic memory, except strain cannot ordinarily rotate the
magnetization of magnet by more than 90 degrees and ""flip"" it. Here, we
describe a scheme to achieve complete 180 degree rotation of the magnetization
of a nanomagnet with strain that will enable writing of binary bits in
non-volatile magnetic memory implemented with magneto-tunneling junctions whose
soft layers are two-phase magnetostrictive/piezoelectric multiferroics. At room
temperature, this writing method results in: (1) energy dissipation < 6200 kT
per bit, (2) write error probability < 10^-6, (3) write time of ~ 1 ns, and (4)
low read error. This could potentially lead to a new genre of non-volatile
memory that is extremely reliable, fast and, at the same time,
ultra-energy-efficient.",1407.2140v1
2014/7/24,Successive magnetic transitions of Ca$_2$CoSi$_2$O$_7$ in high magnetic fields,"Magnetic and dielectric properties of \aa kermanite Ca$_2$CoSi$_2$O$_7$
single crystals were investigated in pulsed high magnetic fields. In magnetic
fields along the $c$ axis, this material shows a magnetization plateau in a
wide range of field below the saturation. Magnetization processes for fields
along the $a$ and $b$ axes show multiple anomalies but different traces to each
other, indicating the breaking of four-fold symmetry. Measurements of the
magnetoelectric effects exhibit the changes in electric polarization according
to the changes in the spin system. The experimentally determined quadratic
magnetoelectric tensor is consistent with that expected in the crystal symmetry
of orthorhombic $P2_12_12$.",1407.6450v1
2014/7/29,Prediction of magnetic moment collapse in ZrFe$_2$ under hydrostatic pressure,"Electronic structure and magnetic properties of ZrFe$_2$ with a cubic Laves
phase are investigated by calculations based on the density functional theory.
The total magnetic moment (m) of 3.14 $\mu_B$ per formula unit (\emph{f.u.}) is
obtained at the experimental lattice constant (7.06 \AA), which is larger than
3.06 $\mu_B$/\emph{f.u.} obtained at the theoretical equilibrium lattice
constant (6.85 \AA). The localized $3d$ magnetic moment is in negative
diffusive sp background moment. We predict a two-step magnetic collapse under
pressure: one is from 3.06 $\mu_B$/\emph{f.u.} to 1.26 $\mu_B$/\emph{f.u.} at
about 3.6 GPa, and the other is from 0.5 $\mu_B$/\emph{f.u.} to nonmagnetic
state at about 15 GPa. We understand this process by the changes of density of
states. The magnetic moment decreases under the pressure in the vicinity of the
experimental lattice constant with $d\ln m/dp=-0.038$ GPa$^{-1}$. The
spontaneous volume magnetostriction is 0.015. We suggest that the Invar effect
of this alloy may be understood when considering the magnetic moment variation
according to the Weiss $2\gamma$-model.",1407.7880v1
2014/8/6,Orbital Nematic Order and Interplay with Magnetism in the Two-Orbital Hubbard Model,"Motivated by the recent angle-resolved photoemission spectroscopy (ARPES) on
FeSe and iron pnictide families of iron-based superconductors, we have studied
the orbital nematic order and its interplay with antiferromagnetism within the
two-orbital Hubbard model. We used random phase approximation (RPA) to
calculate the dependence of the orbital and magnetic susceptibilities on the
strength of interactions and electron density (doping). To account for strong
electron correlations not captured by RPA, we further employed non-perturbative
variational cluster approximation (VCA) capable of capturing symmetry broken
magnetic and orbitally ordered phases. Both approaches show that the electron
and hole doping affect the two orders differently. While hole doping tends to
suppress both magnetism and orbital ordering, the electron doping suppresses
magnetism faster. Crucially, we find a realistic parameter regime for moderate
electron doping that stabilizes orbital nematicity in the absence of long-range
antiferromagnetic order. This is reminiscent of the non-magnetic orbital
nematic phase observed recently in FeSe and a number of iron pnictide materials
and raises the possibility that at least in some cases, the observed electronic
nematicity may be primarily due to orbital rather than magnetic fluctuations.",1408.1408v2
2014/8/14,Particle Capture Efficiency in a Multi-Wire Model for High Gradient Magnetic Separation,"High gradient magnetic separation (HGMS) is an efficient way to remove
magnetic and paramagnetic particles, such as heavy metals, from waste water. As
the suspension flows through a magnetized filter mesh, high magnetic gradients
around the wires attract and capture the particles, removing them from the
fluid. We model such a system by considering the motion of a paramagnetic
tracer particle through a periodic array of magnetized cylinders. We show that
there is a critical Mason number (ratio of viscous to magnetic forces) below
which the particle is captured irrespective of its initial position in the
array. Above this threshold, particle capture is only partially successful and
depends on the particle's entry position. We determine the relationship between
the critical Mason number and the system geometry using numerical and
asymptotic calculations. If a capture efficiency below 100% is sufficient, our
results demonstrate how operating the HGMS system above the critical Mason
number but with multiple separation cycles may increase efficiency.",1408.3313v1
2014/9/3,Improper Ferroelectricity in Helicoidal Antiferromagnet Cu3Nb2O8,"Cu3Nb2O8 is an unusual multiferroic compound that undergoes a series of
magnetic ordering at low temperatures. Concurrent development of electric
polarization has been reported at TN1 ~25 K corresponding to a non-collinear
helicoidal ordering (Phys. Rev. Lett. 107, 137205 (2011)). But questions remain
on the microscopic origin of such phenomena. In this communication, we report a
detailed study of induced polar ordering in Cu3Nb2O8 by performing
polarization, magnetization, dielectric constant and heat capacity measurements
over a broad range of temperature and magnetic field. The dielectric constant
shows suppression in the magnetic field but it does not shift to lower
temperature with the application of external field. The appearance of
magneto-dielectric effect signifies the contribution of q-dependent magnetic
correlation function with enhanced weightage in the presence of magnetic field.
This magnetic correlation function is associated with the ferro-axial vector
and our overall results support this mechanism for the observation of
muliferroicity in Cu3Nb2O8.",1409.1070v1
2014/9/10,Magnetization Effects in Proton Micro-Irradiated Diamond,"We report the magnetic response of high purity type IIa single crystal CVD
diamond following high energy irradiation by 2.2 MeV proton micro-beams,
produced using Nuclear Microprobe techniques. Post-irradiation microanalysis is
achieved using Atomic Force, Magnetic Force and Electrostatic Force Microscopy
(AFM, MFM & EFM) as well as Raman spectroscopy. Comparison between MFM and EFM
measurements at zero electrical bias is used to preclude artefacts of
electrostatic origin suggesting the presence of magnetic states in the
microscale regions induced by proton micro-irradiation. Analysis of the
irradiated regions using probe polarization dependent magnetization
measurements shows an irradiation induced magnetic response consistent with
ferromagnetic ordering at room temperature. Structural characterization of the
micro-irradiated regions using micro-Raman spectroscopy indicates a correlation
between formation of the sp2 carbon phase in the diamond matrix with the scale
of the observed magnetization, in the investigated experimental regime.",1409.2997v1
2014/9/13,Experimental Evidences of Quantum Phase Transition in a Spin Cluster Compound,"Experimental realization of magnetic field induced quantum phase transition
(QPT) is reported for NH4CuPO4.H2O, a two spin cluster material with isotropic
Heisenberg interaction. Experimental magnetization and specific heat data have
been collected as a function of temperature and magnetic field. Experimental
data have been analyzed in terms of Heisenberg dimer model. Two quantum
complementary observables representing local and non-local properties of the
spins are constructed using the experimental data and a clear evidence of QPT
is observed through partial quantum information sharing when the magnetic field
is swept through a particular value. Signature of QPT is also observed when
specific heat is measured as a function of magnetic field at low temperature.
Furthermore, using the experimental specific heat data, magnetic energy values
are calculated and their variations are captured as a function of magnetic
field and temperature.",1409.3919v1
2014/9/15,Tunable Magnetic Semiconductor Behavior Driven by Half-Filled One Dimensional Band in Zigzag Phosphorene Nanoribbons,"An antiferromagnetic insulating state has been found in the zigzag
phosphorene nanoribbons (ZPNRs) from a comprehensive density functional theory
calculations. Comparing with other one-dimensional systems, the magnetism in
ZPNRs display several surprising characteristics: (i) the magnetic moments are
antiparallel arranged at each zigzag edge; (ii) the magnetism is quite stable
in energy (about 29 meV/magnetic-ion) and the band gap is big (about 0.7 eV);
(iii) a moderate compressive strain will induce a magnetic to nonmagnetic as
well as semiconductor to metal transition. All of these phenomena arise
naturally due to one unique mechanism, namely the electronic instability
induced by the half-filled one dimensional bands which cross the Fermi level at
around {\pi}/2a. The unusual electronic and magnetic properties in ZPNRs endow
them great potential for the applications in nanoelectronic devices.",1409.4134v1
2014/9/25,Quantitative simulation of temperature dependent magnetization dynamics and equilibrium properties of elemental ferromagnets,"Atomistic spin model simulations are immensely useful in determining
temperature dependent magnetic prop- erties, but are known to give the
incorrect dependence of the magnetization on temperature compared to exper-
iment owing to their classical origin. We find a single parameter rescaling of
thermal fluctuations which gives quantitative agreement of the temperature
dependent magnetization between atomistic simulations and experi- ment for the
elemental ferromagnets Ni, Fe, Co and Gd. Simulating the sub-picosecond
magnetization dynam- ics of Ni under the action of a laser pulse we also find
quantitative agreement with experiment in the ultrafast regime. This enables
the quantitative determination of temperature dependent magnetic properties
allowing for accurate simulations of magnetic materials at all temperatures.",1409.7397v2
2014/10/8,Phase diagram of CeRuPO under pressure investigated by $^{31}$P-NMR - Comparison between CeRuPO under pressure and the Ce(Ru$_{1-x}$Fe$_{x}$)PO system -,"We have performed $^{31}$P-NMR measurements on single-crystalline CeRuPO
under pressure in order to understand the variation in magnetic character
against pressure. The NMR spectra for $H \perp c$ and $H \parallel c$ at
2.15GPa split below the ordered temperature, which is a microscopic evidence of
the change in the magnetic ground state from the ferromagnetic (FM) state at
ambient pressure to the antiferromagnetic (AFM) state under pressure. The
analysis of NMR spectra suggests that the magnetic structure in AFM state is
the stripe-type AFM state with the AFM moment $m_{\rm AFM} \perp c$-axis and
changes by magnetic field perpendicular to $c$-axis. In addition, the
dimensionality of magnetic correlations in the spin and the $k$ space is
estimated. We reveal that three-dimensional magnetic correlations in CeRuPO are
robust against pressure, which is quite different from the suppression of the
magnetic correlations along the $c$-axis by Fe substitution in
Ce(Ru$_{1-x}$Fe$_{x}$)PO.",1410.1982v1
2014/11/14,Photo-induced magnetization enhancement in two-dimensional weakly anisotropic Heisenberg magnets,"By comparing the photo-induced magnetization dynamics in simple layered
systems we show how light-induced modifications of the magnetic anisotropy
directly enhance the magnetization. It is observed that the spin precession in
(CH3NH3)2CuCl4, initiated by a light pulse, increases in amplitude at the
critical temperature TC. The phenomenon is related to the dependence of the
critical temperature on the axial magnetic anisotropy. The present results
underline the possibility and the importance of the optical modifications of
the anisotropy, opening new paths toward the control of the magnetization state
for ultrafast memories.",1411.3918v1
2015/1/13,Magnetic properties of the helimagnet Cr1/3NbS2 observed by muSR,"We have performed muon spin rotation/relaxation (muSR) measurements on single
crystals of the chiral helimagnet Cr1/3NbS2 at zero to low magnetic field. The
transition from the paramagnetic to helical magnetically ordered phase at zero
field is marked by the onset of a coherent oscillation of the zero-field muon
spin polarization below a critical temperature Tc. An enhancement of the muon
spin precession frequency is observed below T ~ 50K, where anomalous behavior
has been observed in bulk transport measurements. The enhanced precession
frequency indicates a low-temperature modification of the helical magnetic
structure. A Landau free energy analysis suggests that the low-temperature
change in the magnetic structure is caused by a structural change, whereas the
magnetic order above Tc is the result of an attractive interaction between the
ferromagnetic moment induced by the applied field and the magnetic moments of
the helical structure. We also suggest a longer periodicity of helicity below T
~ 50K, which can be verified by neutron scattering.",1501.03094v2
2015/1/14,Spectro-polarimetric Imaging Reveals Helical Magnetic Fields in Solar Prominence Feet,"Solar prominences are clouds of cool plasma levitating above the solar
surface and insulated from the million-degree corona by magnetic fields. They
form in regions of complex magnetic topology, characterized by non-potential
fields, which can evolve abruptly, disintegrating the prominence and ejecting
magnetized material into the heliosphere. However, their physics is not yet
fully understood because mapping such complex magnetic configurations and their
evolution is extremely challenging, and must often be guessed by proxy from
photometric observations.Using state-of-the-art spectro-polarimetric data, we
reconstruct the structure of the magnetic field in a prominence. We find that
prominence feet harbor helical magnetic fields connecting the prominence to the
solar surface below.",1501.03295v1
2015/2/5,Domain structure and perpendicular magnetic anisotropy in CoFe/Pd multilayers using off-axis electron holography,"Multilayers of Co90Fe10/Pd with different bilayer thicknesses, have been
deposited by dc-magnetron sputtering on thermally oxidized Si wafers.
Transmission electron microscopy showed that the highly textured crystalline
films had columnar structure, while scanning transmission electron microscopy
and atomic force microscopy respectively indicated some layer waviness and
surface roughness. The magnetic domain structure and perpendicular magnetic
anisotropy (PMA) of the Co90Fe10/Pd multilayers were investigated by off-axis
electron holography and magnetic force microscopy. The Co90Fe10 layer thickness
was the primary factor determining the magnetic domain size and the
perpendicular magnetization: both decreased as the thickness increased. The
strongest PMA was observed in the sample with the thinnest magnetic layer of
0.45 nm.",1502.01422v1
2015/2/19,Plentiful magnetic moments in oxygen deficient SrTiO3,"Correlated band theory is employed to investigate the magnetic and electronic
properties of different arrangements of oxygen di- and tri-vacancy clusters in
SrTiO$_3$. Hole and electron doping of oxygen deficient SrTiO$_3$ yields
various degrees of magnetization as a result of the interaction between
localized magnetic moments at the defected sites. Different kinds of Ti atomic
orbital hybridization are described as a function of the doping level and
defect geometry. We find that magnetism in SrTiO$_{3-\delta}$ is sensitive to
the arrangement of neighbouring vacancy sites, charge carrier density, and
vacancy-vacancy interaction. Permanent magnetic moments in the absence of
vacancy doping electrons are observed. Our description of the charged clusters
of oxygen vacancies widens the previous descriptions of mono and
multi-vacancies and points out the importance of the controled formation at the
atomic level of defects for the realization of transition metal oxide based
devices with a desirable magnetic performance.",1502.05749v1
2015/1/18,Theoretical Exploration on the Magnetic Properties of Ferromagnetic Metallic Glass: An Ising Model on Random Recursive Lattice,"The ferromagnetic Ising spins are modeled on a recursive lattice constructed
from random-angled rhombus units with stochastic configurations, to study the
magnetic properties of the bulk Fe-based metallic glass. The integration of
spins on the structural glass model well represents the magnetic moments in the
glassy metal. The model is exactly solved by the recursive calculation
technique. The magnetization of the amorphous Ising spins, i.e. the glassy
metallic magnet is investigated by our modeling and calculation on a
theoretical base. The results show that the glassy metallic magnets has a lower
Curie temperature, weaker magnetization, and higher entropy comparing to the
regular ferromagnet in crystal form. These findings can be understood with the
randomness of the amorphous system, and agrees well with others' experimental
observations.",1502.06561v2
2015/3/9,"Alternating magnetic anisotropy of Li$_2$(Li$_{1-x}T_x$)N with $T$ = Mn, Fe, Co, and Ni","Substantial amounts of the transition metals Mn, Fe, Co, and Ni can be
substituted for Li in single crystalline Li$_2$(Li$_{1-x}T_x$)N. Isothermal and
temperature-dependent magnetization measurements reveal local magnetic moments
with magnitudes significantly exceeding the spin-only value. The additional
contributions stem from unquenched orbital moments that lead to rare-earth-like
behavior of the magnetic properties. Accordingly, extremely large magnetic
anisotropies have been found. Most notably, the magnetic anisotropy alternates
as easy-plane $\rightarrow$ easy-axis $\rightarrow$ easy-plane $\rightarrow$
easy-axis when progressing from $T$ = Mn $\rightarrow$ Fe $\rightarrow$ Co
$\rightarrow$ Ni. This behavior can be understood based on a perturbation
approach in an analytical, single-ion model. The calculated magnetic
anisotropies show a surprisingly good agreement with the experiment and capture
the basic features observed for the different transition metals.",1503.02501v2
2015/4/10,Computational Study of the Magnetic Structure of Na$_2$IrO$_3$,"The magnetic structure of honeycomb iridate Na$_2$IrO$_3$ is of paramount
importance to its exotic properties. The magnetic order is established
experimentally to be zigzag antiferromagnetic. However, the previous assignment
of ordered moment to the $\bm{a}$-axis is tentative. We examine the magnetic
structure of Na$_{2}$IrO$_{3}$ using first-principles methods. Our calculations
reveal that total energy is minimized when the zigzag antiferromagnetic order
is magnetized along $\bm{g}\approx\bm{a}+\bm{c}$. Such a magnetic configuration
is explained by adding anisotropic interactions to the nearest-neighbor
Kitaev-Heisenberg model. Spin-wave spectrum is also calculated, where the
calculated spin gap of $10.4$ meV can in principle be measured by future
inelastic neutron scattering experiments. Finally we emphasize that our
proposal is consistent with all known experimental evidence, including the most
relevant resonant x-ray magnetic scattering measurements [X. Liu \emph{et al.}
{Phys. Rev. B} \textbf{83}, 220403(R) (2011)].",1504.02699v1
2015/4/16,Ferrogels cross-linked by magnetic particles: Field-driven deformation and elasticity studied using computer simulations,"Ferrogels, i.e. swollen polymer networks into which magnetic particles are
immersed, can be considered as ""smart materials"" since their shape and
elasticity can be controlled by an external magnetic field. Using molecular
dynamics simulations on the coarse-grained level we study a ferrogel in which
the magnetic particles act as the cross-linkers of the polymer network. In a
homogeneous external magnetic field the direct coupling between the orientation
of the magnetic moments and the polymers by means of covalent bonds gives rise
to a deformation of the gel, independent of the interparticle dipole-dipole
interaction. In this paper we report quantitative measurements of this
deformation, the gel's elastic moduli and its magnetic response. Our results
demonstrate that these properties depend significantly on the topology of the
polymer network.",1504.04280v2
2015/4/28,Surface-termination dependent magnetism and strong perpendicular magnetocrystalline anisotropy of a FeRh (001) thin film: A density-functional study,"Magnetism of FeRh (001) films strongly depends on film thickness and surface
terminations. While magnetic ground state of bulk FeRh is G-type
antiferromagnetism, the Rh-terminated films exhibit ferromagnetism with strong
perpendicular MCA whose energy +2.1 meV/$\Box$ is two orders of magnitude
greater than 3$d$ magnetic metals, where $\Box$ is area of two-dimensional unit
cell. While Goodenough-Kanamori-Anderson rule on the superexchange interaction
is crucial in determining the magnetic ground phases of FeRh bulk and thin
films, the magnetic phases are results of interplay and competition between
three mechanisms - the superexchange interaction, the Zener direct-interaction,
and magnetic energy gain.",1504.07349v3
2015/6/16,Visualization of superparamagnetic dynamics in magnetic topological insulators,"Quantized Hall conductance is a generic feature of two dimensional electronic
systems with broken time reversal symmetry. In the quantum anomalous Hall state
recently discovered in magnetic topological insulators, time reversal symmetry
is believed to be broken by long-range ferromagnetic order, with quantized
resistance observed even at zero external magnetic field. Here, we use scanning
nanoSQUID magnetic imaging to provide a direct visualization of the dynamics of
the quantum phase transition between the two anomalous Hall plateaus in a
Cr-doped (Bi,Sb)$_2$Te$_3$ thin film. Contrary to naive expectations based upon
macroscopic magnetometry, our measurements reveal a superparamagnetic state
formed by weakly interacting magnetic domains with a characteristic size of few
tens of nanometers. The magnetic phase transition occurs through random
reversals of these local moments, which drive the electronic Hall plateau
transition. Surprisingly, we find that the electronic system can in turn drive
the dynamics of the magnetic system, revealing a subtle interplay between the
two coupled quantum phase transitions.",1506.05114v1
2015/6/17,Electronic magnetization of a quantum point contact measured by nuclear magnetic resonance,"We report an electronic magnetization measurement of a quantum point contact
(QPC) based on nuclear magnetic resonance (NMR) spectroscopy. We find that NMR
signals can be detected by measuring the QPC conductance under in-plane
magnetic fields. This makes it possible to measure, from Knight shifts of the
NMR spectra, the electronic magnetization of a QPC containing only a few
electron spins. The magnetization changes smoothly with the QPC potential
barrier height and peaks at the conductance plateau of 0.5 $\times$ $2e^2/h$.
The observed features are well captured by a model calculation assuming a
smooth potential barrier, supporting a no bound state origin of the 0.7
structure.",1506.05477v1
2015/7/2,Magnetic anisotropy energy in disordered Ge_{1-x}Mn_{x}Te,"We theoretically analyze the influence of chemical disorder on magnetic
anisotropy in Ge_{1-x}Mn_{x}Te semiconductor layers known to exhibit
carrier-induced ferromagnetism and ferroelectric distortion of rhombohedral
crystal lattice. Using DFT method we determine the local changes in the crystal
structure due to Mn ions substitution for Ge and due to the presence in
Ge_{1-x}Mn_{x}Te of very high concentration of cation vacancies. We calculate
the effect of this structural and chemical disorder on single ion magnetic
anisotropy mechanism and show that its contribution is order of magnitude
smaller as compared to magnetic anisotropy mechanism originating from the spin
polarization induced by Mn ions into neighboring Te and Ge ions. We also
discuss magnetic anisotropy effects due to pairs of Mn ions differently
allocated in the lattice. The spatial averaging over chemical disorder strongly
reduces the strength of this magnetic anisotropy mechanism and restores the
global rhombohedral symmetry of magnetic system.",1507.00762v1
2015/7/17,"Possibility of Emergence of Chiral Magnetic Soliton in Hexagonal Metal Formate [NH4][M(HCOO)3] with M2+ = Mn, Fe, Co, and Ni and KCo(HCOO)3","Search of chiral magnetic solitons on the basis of the data on the crystal
structure is important from both fundamental and technological points of view.
Potential chiral magnetic solitons - hexagonal metal formates [NH4][M(HCOO)3]
with M2+ = Mn, Fe, Co, and Ni and KCo(HCOO)3 containing dominating left-handed
chiral antiferromagnetic helices that compete with interhelix interactions have
been identified. The sign and strength of magnetic interactions not only
between nearest neighbors, but also for longer-range neighbors in the metal
formates have been calculated on the basis of structural data. Magnetic
structures of these compounds are similar to that of the chiral magnetic
soliton Cr1/3NbS2. The interrelation between chiral polarization of crystalline
and magnetic structures in the metastable polymorph KCo(HCOO)3 has been
demonstrated.",1507.04852v4
2015/8/18,Quasistatic and Pulsed Current-Induced Switching with Spin-Orbit Torques in Ultrathin Films with Perpendicular Magnetic Anisotropy,"Spin-orbit interaction derived spin torques provide a means of reversing the
magnetization of perpendicularly magnetized ultrathin films with currents that
flow in the plane of the layers. A basic and critical question for applications
is the speed and efficiency of switching with nanosecond current pulses. Here
we investigate and contrast the quasistatic (slowly swept current) and pulsed
current-induced switching characteristics of micron scale Hall crosses
consisting of very thin ($<1$ nm) perpendicularly magnetized CoFeB layers on
$\beta$-Ta. While complete magnetization reversal is found at a threshold
current density in the quasistatic case, short duration ($\leq 10$ ns) larger
amplitude pulses ($\simeq 10 \times$ the quasistatic threshold current) lead to
only partial magnetization reversal and domain formation. We associate the
partial reversal with the limited time for reversed domain expansion during the
pulse.",1508.04336v1
2015/9/9,Orbital Magnetization of Quantum Spin Hall Insulator Nanoparticles,"Both spin and orbital degrees of freedom contribute to the magnetic moment of
isolated atoms. However, when inserted in crystals, atomic orbital moments are
quenched because of the lack of rotational symmetry that protects them when
isolated. Thus, the dominant contribution to the magnetization of magnetic
materials comes from electronic spin. Here we show that nanoislands of quantum
spin Hall insulators can host robust orbital edge magnetism whenever their
highest occupied Kramers doublet is singly occupied, upgrading the spin edge
current into a charge current. The resulting orbital magnetization scales
linearly with size, outweighing the spin contribution for islands of a few nm
in size. This linear scaling is specific of the Dirac edge states and very
different from Schrodinger electrons in quantum rings. Modelling Bi(111)
flakes, whose edge states have been recently observed, we show that orbital
magnetization is robust with respect to disorder, thermal agitation, shape of
the island and crystallographic direction of the edges, reflecting its
topological protection.",1509.02661v1
2015/9/14,Thickness-Dependent Magnetoelasticity and its Effects on Perpendicular Magnetic Anisotropy in Ta|CoFeB|MgO Thin Films,"We report measurements of the in-plane magnetoelastic coupling in ultra-thin
Ta|CoFeB|MgO layers as a function of uniaxial strain, conducted using a
four-point bending apparatus. For annealed samples, we observe a strong
dependence on the thickness of the CoFeB layer in the range 1.3-2.0 nm, which
can be modeled as arising from a combination of effective surface and volume
contributions to the magnetoelastic coupling. We point out that if similar
thickness dependence exists for magnetoelastic coupling in response to biaxial
strain, then the standard N\'eel model for the magnetic anisotropy energy
acquires a term inversely proportional to the magnetic layer thickness. This
contribution can significantly change the overall magnetic anisotropy, and
provides a natural explanation for the strongly nonlinear dependence of
magnetic anisotropy energy on magnetic layer thickness that is commonly
observed for ultrathin annealed CoFeB|MgO films with perpendicular magnetic
anisotropy.",1509.04134v1
2015/9/17,Dynamics of magnetic single domain particles embedded in a viscous liquid,"Kinetic equations for magnetic nano particles dispersed in a viscous liquid
are developed and analyzed numerically. Depending on the amplitude of an
applied oscillatory magnetic field the particles orient their time averaged
anisotropy axis perpendicular to the applied field for low magnetic field
amplitudes and nearly parallel to the direction of the field for high
amplitudes. The transition between these regions takes place in a narrow field
interval. In the low field region the magnetic moment is locked to some crystal
axis and the energy absorption in an oscillatory driving field is dominated by
viscous losses associated with particle rotation in the liquid. In the opposite
limit the magnetic moment rotates within the particle while its easy axis being
nearly parallel to the external field direction oscillates. The kinetic
equations are generalized to include thermal fluctuations. This leads to a
significant increase of the power absorption in the low and intermediate field
region with a pronounced absorption peak as function of particle size. In the
high field region, on the other hand, the inclusion of thermal fluctuations
reduces the power absorption. The illustrative numerical calculations presented
are performed for magnetic parameters typical for iron oxide.",1509.05233v1
2015/10/7,Spontaneous Liquid Crystal and Ferromagnetic Ordering of Colloidal Magnetic Nanoplates,"Ferrofluids are familiar as colloidal suspensions of ferromagnetic
nanoparticles in aqueous or organic solvents. The dispersed particles are
randomly oriented but their moments become aligned if a magnetic field is
applied, producing a variety of exotic and useful magneto-mechanical effects. A
longstanding interest and challenge has been to make such suspensions
macroscopically ferromagnetic, that is having uniform magnetic alignment in
absence of a field. Here we report a fluid suspension of magnetic nanoplates
which spontaneously aligns into an equilibrium nematic liquid crystal phase
that is also macroscopically ferromagnetic. Its zero-field magnetization
produces distinctive magnetic self-interaction effects, including liquid
crystal textures of fluid block domains arranged in closed flux loops, and
makes this phase highly sensitive, with it dramatically changing shape even in
the Earth's magnetic field.",1510.02161v2
2015/10/19,Effect of magnetism on lattice dynamics in SrFe$_2$As$_2$ as seen via high resolution inelastic x-ray scattering,"Phonon spectra of detwinned {SrFe$_2$As$_2$} crystals, as measured by
inelastic x-ray scattering, show clear anisotropy accompanying the
magneto-structural transition at 200 K. We model the mode splitting using
magnetic DFT calculations, including a phenomenological reduction in
force-constant anisotropy that can be attributed to magnetic fluctuations. This
serves as a starting point for a general model of phonons in this material
applicable to both magnetic and non-magnetic phase. Using this model, the
measured splitting in the magnetic phase below $\it T_{N}$, and the measured
phonon linewidth, we set a lower bound on the mean magnetic fluctuation
frequency above $\it T_{N}$ at 210 K.",1510.05487v2
2015/10/30,Some aspects of Magnetic Force Microscopy of hard magnetic films,"A number of aspects of magnetic force microscopy (MFM) specific to the
imaging of hard magnetic films have been studied. Firstly, we show that
topographic images made in tapping mode with probes characterized by the
moderate cantilever stiffness usual for MFM (1--4 N/m), contain artifacts due
to strong probe-sample interactions which lead to probe retraction. As a
result, stiffer cantilevers (e.g. 40 N/m) are better adapted to characterizing
such hard magnetic films. Secondly, imaging with probes coated by a hard
magnetic film leads to phase maps which show a twofold symmetry, with paired
dark/light contrast on opposite domain edges along the direction of the
cantilever. This is due to the tilt of the direction of tip magnetizaiton and
direction of oscillation, with respect to the sample normal. Thirdly, due to
the long-range nature of the stray field produced by hard magnetic films
containing micron-sized domains, MFM phase contrast reflects the stray field
itself, as opposed to that of its spatial derivatives, as is generally the case
in MFM.",1510.09004v1
2015/11/1,Observation of long range magnetic ordering in pyrohafnate Nd2Hf2O7: A neutron diffraction study,"We have investigated the physical properties of a pyrochlore hafnate Nd2Hf2O7
using ac magnetic susceptibility \chi_ac(T), dc magnetic susceptibility
\chi(T), isothermal magnetization M(H) and heat capacity C_p(T) measurements,
and determined the magnetic ground state by neutron powder diffraction study.
An upturn is observed below 6 K in C_p(T)/T, however both C_p(T) and \chi(T) do
not show any clear anomaly down to 2 K. The \chi_ac(T) shows a well pronounced
anomaly indicating an antiferromagnetic transition at T_N = 0.55 K. The long
range antiferromagnetic ordering is confirmed by neutron diffraction. The
refinement of neutron diffraction pattern reveals an all-in/all-out
antiferromagnetic structure, where for successive tetrahedra, the four Nd3+
magnetic moments point alternatively all-into or all-out-of the tetrahedron,
with an ordering wavevector k = (0, 0, 0) and an ordered state magnetic moment
of m = 0.62(1) \mu_B/Nd at 0.1 K. The ordered moment is strongly reduced
reflecting strong quantum fluctuations in ordered state.",1511.00256v1
2015/11/25,Theory of Magnetic-Field-Induced Polarization Flop in Spin-Spiral Multiferroics,"The magnetic-field-induced 90-degree flop of ferroelectric polarization P in
a spin-spiral multiferroic material TbMnO3 is theoretically studied based on a
microscopic spin model. We find that the direction of the P-flop or the choice
of +Pa or -Pa after the flop is governed by magnetic torques produced by the
applied magnetic field H acting on the Mn spins and thus is selected in a
deterministic way, in contradistinction to the naively anticipated
probabilistic flop. This mechanism resolves a puzzle of the previously reported
memory effect in the P direction depending on the history of the magnetic-field
sweep, and enables controlled switching of multiferroic domains by externally
applied magnetic fields. Our Monte-Carlo analysis also uncovers that the
magnetic structure in the P||a phase under H||b is not a so-far anticipated
simple ab-plane spin cycloid but a conical spin structure.",1511.07960v1
2015/12/1,Epitaxial patterning of nanometer-thick Y3Fe5O12 films with low magnetic damping,"Magnetic insulators such as yttrium iron garnet, Y3Fe5O12, with extremely low
magnetic damping have opened the door for low power spin-orbitronics due to
their low energy dissipation and efficient spin current generation and
transmission. We demonstrate reliable and efficient epitaxial growth and
nanopatterning of Y3Fe5O12 thin-film based nanostructures on insulating
Gd3Ga5O12 substrates. In particular, our fabrication process is compatible with
conventional sputtering and liftoff, and does not require aggressive ion
milling which may be detrimental to the oxide thin films. Structural and
magnetic properties indicate good qualities, in particular low magnetic damping
of both films and patterned structures. The dynamic magnetic properties of the
nanostructures are systematically investigated as a function of the lateral
dimension. By comparing to ferromagnetic nanowire structures, a distinct edge
mode in addition to the main mode is identified by both experiments and
simulations, which also exhbits cross-over with the main mode upon varying the
width of the wires. The non-linear evolution of dynamic modes over
nanostructural dimensions highlights the important role of size confinement to
their material properties in magnetic devices where Y3Fe5O12 nanostructures
serve as the key functional component.",1512.00286v1
2015/12/24,Spin frustration and magnetic ordering in triangular lattice antiferromagnet Ca$_3$CoNb$_2$O$_9$,"We synthesized a quasi-two-dimensional distorted triangular lattice
antiferromagnet Ca$_3$CoNb$_2$O$_9$, in which the effective spin of Co$^{2+}$
is 1/2 at low temperatures, whose magnetic properties were studied by dc
susceptibility and magnetization techniques. The x-ray diffraction confirms the
quality of our powder samples. The large Weiss constant $\theta_{CW}\sim$ $-55$
K and the low Neel temperature($T_N\sim$ 1.45 K) give a frustration factor $f$
($=\mid\theta_{CW}/T_N \mid$) $\approx$ 38, suggesting that Ca$_3$CoNb$_2$O$_9$
resides in strong frustration regime. Slightly below $T_N$, deviation between
the susceptibility data under zero-field cooling (ZFC) and field cooling (FC)
is observed. A new magnetic state with 1/3 of the saturate magnetization $M_s$
is suggested in the magnetization curve at 0.46 K. Our study indicates that
Ca$_3$CoNb$_2$O$_9$ is an interesting material to investigate magnetism in
triangular lattice antiferromagnets with weak anisotropy.",1512.07792v1
2016/1/8,Magnetic structure of the magnetocaloric compound AlFe2B2,"The crystal and magnetic structures of AlFe2B2 have been studied with a
combination of X-ray and neutron diffraction and electronic structure
calculations. The magnetic and magnetocaloric properties have been investigated
by magnetisation measurements. The samples have been produced using high
temperature synthesis and subsequent heat treatments. The compound crystallises
in the orthorhombic crystal system Cmmm and it orders ferromagnetically at 285
K through a second order phase transition. At temperatures below the magnetic
transition the magnetic moments align along the crystallographic $a$-axis. The
magnetic entropy change from 0 to 800 kA/m was found to be -1.3 J/K kg at the
magnetic transition temperature.",1601.01953v1
2016/2/8,Dual nature of magnetic dopants and competing trends in topological insulators,"Topological insulators interacting with magnetic impurities have been
reported to host several unconventional effects. These phenomena are described
within the framework of gapping Dirac quasiparticles due to broken
time-reversal symmetry. However, the overwhelming majority of studies
demonstrate the presence of a finite density of states near the Dirac point
even once Topological insulators become magnetic. Here, we map the response of
topological states to magnetic impurities at the atomic scale. We demonstrate
that magnetic order and gapless states can coexist. We show how this is the
result of the delicate balance between two opposite trends, i.e. gap opening
and emergence of a Dirac node impurity band, both induced by the magnetic
dopants. Our results evidence a more intricate and rich scenario with respect
to the once generally assumed, showing how different electronic and magnetic
states may be generated and controlled in this fascinating class of materials.",1602.02516v2
2016/2/26,Theory of light-induced effective magnetic field in Rashba ferromagnets,"Motivated by recent experiments on all-optical magnetization reversal in
conductive ferromagnetic thin films we use nonequilibrium formalism to
calculate the effective magnetic field induced in a Rashba ferromagnet by a
short laser pulse. The main contribution to the effect originates in the direct
optical transitions between spin-split subbands. The resulting effective
magnetic field is inversely proportional to the impurity scattering rate and
can reach the amplitude of a few Tesla in the systems like Co/Pt bilayers. We
showthat the total light-induced effective magnetic field in ferromagnetic
systems is the sum of two contributions: a helicity dependent term, which is an
even function of magnetization, and a helicity independent term, which is an
odd function of magnetization. The primary role of the spin-orbit interaction
is to widen the frequency range for direct optical transitions.",1602.08305v2
2016/3/17,Spin-Wave Fiber,"Spin waves are collective excitations propagating in the magnetic medium with
ordered magnetizations. Magnonics, utilizing the spin wave (magnon) as
information carrier, is a promising candidate for low-dissipation computation
and communication technologies. We discover that, due to the
Dzyaloshinskii-Moriya interaction, the scattering behavior of spin wave at a
magnetic domain wall follows a generalized Snell's law, where two magnetic
domains work as two different mediums. Similar to optical total reflection that
occurs at the water-air interfaces, spin waves may experience total reflection
at magnetic domain walls when their incident angle larger than a critical
value. We design a spin wave fiber using a magnetic domain structure with two
domain walls, and demonstrate that such a spin wave fiber can transmit spin
waves over long distance by total internal reflections, in analogy to an
optical fiber. Our design of spin wave fiber opens up new possibilities in pure
magnetic information processing.",1603.05325v1
2016/4/13,Tuning emergent magnetism in a Hund's impurity,"The recently proposed theoretical concept of a Hund's metal is regarded as a
key to explain the exotic magnetic and electronic behavior occuring in the
strongly correlated electron systems of multiorbital metallic materials.
However, a tuning of the abundance of parameters, that determine these systems,
is experimentally challenging. Here, we investigate the smallest possible
realization of a Hund's metal, a Hund's impurity, realized by a single magnetic
impurity strongly hybridized to a metallic substrate. We experimentally control
all relevant parameters including magnetic anisotropy and hybridization by
hydrogenation with the tip of a scanning tunneling microscope and thereby tune
it through a regime from emergent magnetic moments into a multi-orbital Kondo
state. Our comparison of the measured temperature and magnetic field dependent
spectral functions to advanced many-body theories will give relevant input for
their application to non-Fermi liquid transport, complex magnetic order, or
unconventional superconductivity.",1604.03854v1
2016/5/11,Exploring metamagnetism of single crystalline \eun\ by neutron scattering,"We present here a neutron diffraction study, both in zero field and as a
function of magnetic field, of the magnetic structure of the tetragonal
intermetallic \eun\ on a single crystalline sample. This material is known to
undergo a cascade of transitions, first at 13.2\,K towards an incommensurate
modulated magnetic structure, then at 10.5\,K to an equal moment, yet
undetermined, antiferromagnetic structure. We show here that the low
temperature phase presents a spiral moment arrangement with wave-vector {\bf k}
= ($\frac{1}{4},\delta,0)$. For a magnetic field applied along the tetragonal
{\bf c}-axis, the square root of the scattering intensity of a chosen
reflection matches very well the complex metamagnetic behavior of the
magnetization along {\bf c} measured previously. For the magnetic field applied
along the {\bf b}-axis, two magnetic transitions are observed below the
transition to a fully polarized state.",1605.03497v1
2016/5/13,Fragmentation of magnetism in artificial kagome dipolar spin ice,"Geometrical frustration in magnetic materials often gives rise to exotic,
low-temperature states of matter, like the ones observed in spin ices. Here we
report the imaging of the magnetic states of a thermally-active artificial
magnetic ice that reveal the fingerprints of a spin fragmentation process. This
fragmentation corresponds to a splitting of the magnetic degree of freedom into
two channels and is evidenced in both real and reciprocal space. Furthermore,
the internal organization of both channels is interpreted within the framework
of a hybrid spin-charge model that directly emerges from the parent spin model
of the kagome dipolar spin ice. Our experimental and theoretical results
provide insights into the physics of frustrated magnets and deepen our
understanding of emergent fields through the use of tailor-made magnetism.",1605.04133v1
2016/5/16,Defect energetics and magnetic properties of 3d-transition-metal-doped topological crystalline insulator SnTe,"The introduction of magnetism in SnTe-class topological crystalline
insulators is a challenging subject with great importance in the quantum device
applications. Based on the first-principles calculations, we have studied the
defect energetics and magnetic properties of 3d transition-metal (TM)-doped
SnTe. We find that the doped TM atoms prefer to stay in the neutral states and
have comparatively high formation energies, suggesting that the uniform TM
doping in SnTe with a higher concentration will be difficult unless clustering.
In the dilute doping regime, all the magnetic TM atoms are in the high-spin
states, indicating that the spin splitting energy of 3d TM is stronger than the
crystal splitting energy of the SnTe ligand. Importantly, Mn-doped SnTe has
relatively low defect formation energy, largest local magnetic moment, and no
defect levels in the bulk gap, suggesting that Mn is a promising magnetic
dopant to realize the magnetic order for the theoretically-proposed
large-Chern-number quantum anomalous Hall effect (QAHE) in SnTe.",1605.04781v1
2016/5/21,Magnetic shielding and exotic spin-dependent interactions,"Experiments searching for exotic spin-dependent interactions typically employ
magnetic shielding between the source of the exotic field and the interrogated
spins. We explore the question of what effect magnetic shielding has on
detectable signals induced by exotic fields. Our general conclusion is that for
common experimental geometries and conditions, magnetic shields should not
significantly reduce sensitivity to exotic spin-dependent interactions,
especially when the technique of comagnetometry is used. However, exotic fields
that couple to electron spin can induce magnetic fields in the interior of
shields made of a soft ferro- or ferrimagnetic material. This induced magnetic
field must be taken into account in the interpretation of experiments searching
for new spin-dependent interactions and raises the possibility of using a flux
concentrator inside magnetic shields to amplify exotic spin-dependent signals.",1606.00696v1
2016/7/26,Two-phase flow of ferrofluids,"Ferrofluids currently are the only type of magnetic liquid materials with
wide practical use. The theory on ferrofluids is an example of success to apply
statistics to science. Ferrofluids are two-phase liquids consisting of
dispersed nanoscale ferromagnetic particles suspended in a carrier fluid. Due
to their tiny size, individual ferromagnetic particles clearly exhibit Brownian
motions. Only when a large number of randomly-moving particles are subject to
an external magnetic field, can they collectively exhibit magnetization at a
macroscale. Using statistical theory, the magnetization of a ferrofluid can be
characterized by the celebrated Langevin equation. The monograph combines
statistical theory and the method of Dirac function to establish equations for
ferrofluids under several conditions, including magnetization relaxation,
magnetization equilibrium, and magnetization freezing. It thus provides a quite
complete account of the theory of ferrofluid dynamics.",1607.07838v1
2016/8/8,Magnetic-Field-Induced Change of Magneto-Electric Coupling in the in Molecular Multiferroic (ND4)2[FeCl5(D2O)],"Our results describe an unprecedented example of change in the mechanism of
magnetically-induced electric polarization from spin current to spin-dependent
p-d hybridization model. We have followed the evolution of the magnetic
structures of (ND4)2[FeCl5 D2O] compound using single crystal neutron
diffraction under external magnetic field. The spin arrangements change from
incommensurate cycloidal to commensurate distorted-cycloidal and finally to
quasi-collinear. The determination of the magnetic structures allows us to
explain the observed electric polarization in the different ferroelectric
phases. Two different magneto-electric coupling mechanisms are at play: the
spin-current mechanism for external magnetic field below 5 T, and the spin
dependent p-d hybridization mechanism for magnetic field above this value,
being this compound the first example reported presenting this sequence of
magneto-electric coupling mechanisms.",1608.02369v1
2016/9/26,Topology optimized permanent magnet systems,"Topology optimization of permanent magnet systems consisting of permanent
magnets, high permeability iron and air is presented. An implementation of
topology optimization for magnetostatics is discussed and three examples are
considered. First, the Halbach cylinder is topology optimized with iron and an
increase of 15% in magnetic efficiency is shown, albeit with an increase of 3.8
pp. in field inhomogeneity - a value compared to the inhomogeneity in a 16
segmented Halbach cylinder. Following this a topology optimized structure to
concentrate a homogeneous field is shown to increase the magnitude of the field
by 111% for the chosen dimensions. Finally, a permanent magnet with alternating
high and low field regions is considered. Here a $\Lambda_\mathrm{cool}$ figure
of merit of 0.472 is reached, which is an increase of 100% compared to a
previous optimized design.",1609.08113v2
2016/10/13,Nanoscale distribution of magnetic anisotropies in bimagnetic soft core-hard shell MnFe$_2$O$_4$@CoFe$_2$O$_4$ nanoparticles,"The nanoscale distribution of magnetic anisotropies was measured in
core@shell MnFe$_2$O$_4$@CoFe$_2$O$_4$ 7.0 nm particles using a combination of
element selective magnetic spectroscopies with different probing depths. As
this picture is not accessible by any other technique, emergent magnetic
properties were revealed. The coercive field is not constant in a whole
nanospinel. The very thin (0.5 nm) CoFe$_2$O$_4$ hard shell imposes a strong
magnetic anisotropy to the otherwise very soft MnFe$_2$O$_4$ core: a large
gradient in coercivity was measured inside the MnFe$_2$O$_4$ core with lower
values close to the interface region, while the inner core presents a
substantial coercive field (0.54 T) and a very high remnant magnetization (90%
of the magnetization at saturation).",1610.04263v2
2016/12/11,Magnetic-proximity-induced magnetoresistance on topological insulators,"We theoretically study the magnetoresistance (MR) of two-dimensional massless
Dirac electrons as found on the surface of three-dimensional topological
insulators (3D TIs) that is capped by a ferromagnetic insulator (FI). We
calculate charge and spin transport by Kubo and Boltzmann theories, taking into
account the ladder-vertex correction and the in-scattering due to normal and
magnetic disorder. The induced exchange splitting is found to generate an
electric conductivity that depends on the magnetization orientation, but its
form is very different from both the anisotropic and spin Hall MR. The in-plane
MR vanishes identically for non-magnetic disorder, while out-of-plane
magnetizations cause a large MR ratio. On the other hand, we do find an
in-plane MR and planar Hall effect in the presence of magnetic disorder aligned
with the FI magnetization. Our results may help understand recent transport
measurements on TI|FI systems.",1612.03395v2
2016/12/21,Volume dependence of magnetic properties in Co2Cr1-xYxGa (Y=Ti-Ni) Heusler alloys: a first-principles study,"The magnetic properties tuning and volume dependence in the series of
quaternary full Heusler alloys with formula Co2Cr1-xYGa (Y = Ti, V, Mn, Fe, Co,
Ni) were studied with a detailed first-principles exploration. We employ the
density functional KKR method with the coherent potential approximation,
estimating effective Heisenberg exchange constants via the magnetic force
theorem together with mean-field Curie temperature (TC) and magnetic moment for
compositions in the whole concentration range. The volumetric dependency of
these magnetic properties is studied, particularly the pressure derivatives of
TC at equilibrium. Our ternary alloy calculations show good agreement with
local-density and generalized gradient approximations in the literature. The
quaternary alloys show a wide range of tunable magnetic properties, where
magnetic moments range from 0.8 to 4.9 mu_B, TC from 130 K to 1250 K, and
dTC/dV values range from -7 to +6.3 K A-3.",1612.07071v1
2016/12/22,Tunable Finite-Sized Chains to Control Magnetic Relaxation,"The magnetic dynamics of low-dimensional iron ion chains have been studied
with regards to the tunable finite-sized chain length using iron phthalocyanine
thin films. The deposition temperature varies the diffusion length during thin
film growth by limiting the average crystal size in the range from 40 to 110
nm. Using a method common for single chain magnets, the magnetic relaxation
time for each chain length is determined from temporal remanence data and fit
to a stretched exponential form in the temperature range below 5 K, the onset
for magnetic hysteresis. A temperature-independent master curve is generated by
scaling the remanence by its relaxation time to fit the energy barrier for spin
reversal, and the single spin relaxation time. The energy barrier of 95 K is
found to be independent of the chain length. In contrast, the single spin
relaxation time increases with longer chains from under 1 ps to 800 ps. We show
that thin films provide the nano-architecture to control magnetic relaxation
and a testbed to study finite-size effects in low-dimensional magnetic systems.",1612.07397v1
2017/1/7,Magnetization and the Concurrence of the Spin-1/2 Ising-Heisenberg Pyrochlore Ladder,"We have established a quantum antiferromagnetic Heisenberg-Ising model on a
spin-1/2 pyrochlore edge-shared ladder with Heisenberg intra-rung and Ising
inter-rung interactions as a perspicuous candidate to exhibit magnetization mid
and zero plateaus, characteristic peaks of magnetic susceptibility, and thermal
entanglement mid plateau. The model is exactly solvable and thus, all the
essential properties such as the thermal entanglement and the magnetic
properties of the system can be exactly calculated. The calculations are done
both through the transfer matrix technique and through the reduced density
matrix. The magnetization plateaus are observed at zero and half the saturation
value and the magnetic susceptibility exhibits a clear demonstration of the
associated characteristic peaks. The model also displays the mid plateau of the
thermal entanglement as a function of the external magnetic field at low
temperatures.",1701.01880v1
2017/1/9,"Magnetic properties of ultra-thin 3d transition-metal binary alloys I: spin and orbital moments, anisotropy, and confirmation of Slater-Pauling behavior","The structure and static magnetic properties - saturation magnetization,
perpendicular anisotropy, spectroscopic g-factor, and orbital magnetization -
of thin-film 3d transition metal alloys are determined over the full range of
alloy compositions via X-ray diffraction, magnetometry, and ferromagnetic
resonance measurements. We determine the interfacial perpendicular magnetic
anisotropy by use of samples sets with varying thickness for specific alloy
concentrations. The results agree with prior published data and theoretical
predictions. They provide a comprehensive compilation of the magnetic
properties of thin-film Ni-Co, Ni-Fe and Co-Fe alloys that goes well beyond the
often-cited Slater-Pauling dependence of magnetic moment on alloy
concentration.",1701.02177v1
2017/2/11,Structure and Magnetization of Co4N Thin Film,"In this work, we studied the local structure and the magnetization of Co4N
thin films deposited by a reactive dc magnetron sputtering process. The
interstitial incorporation of N atoms in a fcc Co lattice is expected to expand
the structure and such expansion yields interesting magnetic properties
characterized by a larger than Co magnetic moment and a very high value of spin
polarization ratio in Co4N. By optimizing the growth conditions, we prepared
Co4N film having lattice parameter close to its theoretically predicted value.
The N concentration was measured using secondary ion mass spectroscopy.
Detailed magnetization measurements using bulk magnetization method and
polarized neutron reflectivity confirm that the magnetic moment of Co in Co4N
is higher than that of Co.",1702.03392v1
2017/2/12,Electric-field-driven domain wall dynamics in perpendicularly magnetized multilayers,"We report on reversible electric-field-driven magnetic domain wall motion in
a Cu/Ni multilayer on a ferroelectric BaTiO$_3$ substrate. In our
heterostructure, strain-coupling to ferroelastic domains with in-plane and
perpendicular polarization in the BaTiO$_3$ substrate causes the formation of
domains with perpendicular and in-plane magnetic anisotropy, respectively, in
the Cu/Ni multilayer. Walls that separate magnetic domains are elastically
pinned onto ferroelectric domain walls. Using magneto-optical Kerr effect
microscopy, we demonstrate that out-of-plane electric field pulses across the
BaTiO$_3$ substrate move the magnetic and ferroelectric domain walls in unison.
Our experiments indicate an exponential increase of domain wall velocity with
electric field strength and opposite domain wall motion for positive and
negative field pulses. Magnetic fields do not affect the velocity of magnetic
domain walls, but independently tailor their internal spin structure, causing a
change in domain wall dynamics at high velocities.",1702.03553v1
2017/2/18,Low-field anomalous magnetic phase in the kagome-lattice shandite Co3Sn2S2,"The magnetization process of single crystals of the metallic kagom\'e
ferromagnet Co3Sn2S2 was carefully measured via magnetization and AC
susceptibility. Field-dependent anomalous transitions in the magnetization
indicate a low-field unconventionally ordered phase stabilized just below TC.
The magnetic phase diagrams in applied fields along different crystallographic
directions were determined. The magnetic relaxation process studied in
frequencies covering five orders of magnitude from 0.01 to 1000 Hz indicates
characteristic relaxation times of several seconds at the boarders of the
anomalous phase. Our results arise a lot of questions about the nature of
Co3Sn2S2 magnetic states.",1702.05627v2
2017/1/10,Current-driven skyrmion expulsion from magnetic nanostrips,"We study the current-driven skyrmion expulsion from magnetic nanostrips using
micromagnetic simulations and analytic calculations. We explore the threshold
current density for the skyrmion expulsion, and show that this threshold is
determined by the critical boundary force as well as the spin-torque
parameters. We also find the dependence of the critical boundary force on the
magnetic parameters; the critical boundary force decreases with increasing the
exchange stiffness and perpendicular anisotropy constants, while it increases
with increasing Dzyaloshinskii-Moriya interaction and saturation magnetization
constants. Using a simple model describing the skyrmion and locally-tilted edge
magnetization, we reveal the underlying physics of the dependence of the
critical boundary force on the magnetic parameters based on the relation
between the scaled Dzyaloshinskii-Moriya-interaction parameter and the critical
boundary force. This work provides a fundamental understanding of the skyrmion
expulsion and the interaction between the skymion and boundaries of devices and
shows that the stability of the skyrmion in devices can be related to the
scaled Dzyaloshinskii-Moriya-interaction parameter of magnetic materials.",1702.05672v2
2017/2/20,Evolution of magnetism in cerium doped LaCo2P2 crystals: a magnetic phase diagram,"ThCr2Si2-type phosphide ACo2P2 (A=Rare earth elements) has the same structure
as iron arsenides, but their magnetic behaviors are quite distinct. In this
paper, we for the first time grew a series of La1-xCexCo2P2 single crystals
(x=0.0 to1.0), and made structural and magnetic characterizations. This allows
us to carry out a careful investigation on the evolution of magnetism with
cerium content and build a magnetic phase diagram. We found that the
introduction of cerium induces a rapid decrease of c-axis and a change from
ferromagnetic (FM) to antiferromagnetic (AFM) states. By employing
first-principles band-structure calculations, we identify the formation of P-P
bonding with the shortening of c-axis, which effectively drives an increase of
AFM interaction and eventually leads to AFM ordering in the high doping region.
The present study may shed light on the interplay between the structural
collapsing and electronic/magnetic properties in 122 iron pnictides.",1702.05965v1
2017/2/21,Topological staggered field-electric effect with bipartite magnets,"We study the interface physics of bipartite magnetic materials deposited on a
topological insulator. This comprises antiferromagnets as well as ferrimagnets
and ferromagnets with multiple magnetic moments per unit cell. If an energy gap
is induced in the Dirac states on the topological surface, a topological
magnetoelectric effect has been predicted. Here, we show that this effect can
act in opposite directions on the two components of the magnet in certain
parameter regions. Consequently, an electric field will mainly generate a
staggered field rather than a net magnetization in the plane. This is relevant
for the current attempts to detect the magnetoelectric effect experimentally,
as well as for possible applications. We take a field-theoretic approach that
includes the quantum fluctuations of both the Dirac fermions on the topological
surface as well as the fermions in the surface layer of the magnet in an
analytically solvable model. The effective Lagrangian and the Landau-Lifshitz
equation describing the interfacial magnetization dynamics are derived.",1702.06483v2
2017/2/21,"Long period helical structures and twist-grain boundary phases induced by non magnetic ion doping in Mn$_{1-x}$(Co,Rh)$_{x}$Ge chiral magnet","We study the evolution of helical magnetism in MnGe chiral magnet upon
partial substitution of Mn for non magnetic 3d-Co and 4d-Rh ions. At high
doping levels, we observe spin helices with very long periods -more than ten
times larger than in the pure compound- and sizable ordered moments. This
behavior calls for a change in the energy balance of interactions leading to
the stabilization of the observed magnetic structures. Strikingly, neutron
scattering unambiguously shows a double periodicity in the observed spectra at
$x \gtrsim 0.45$ and $\gtrsim 0.25$ for Co- and Rh-doping, respectively. In
analogy with observations made in cholesteric liquid crystals, we suggest that
it reveals the presence of magnetic twist-grain-boundary phases, involving a
dense short-range correlated network of screw dislocations. The dislocation
cores are described as smooth textures made of non-radial double-core
skyrmions.",1702.06511v1
2017/2/25,Unveiling the role of Co-O-Mg bond in magnetic anisotropy of Pt/Co/MgO using atomically controlled deposition and in-situ electrical measurement,"Despite the crucial role of interfacial perpendicular magnetic anisotropy in
Co(Fe)/MgO based magnetic tunnel junction, the underlying mechanism is still
being debated. Here, we report an anatomical study of oxygen and Mg effect on
Pt/Co bilayers through repeated in-situ anomalous Hall effect measurements,
controlled oxygen exposure and Mg deposition in an ultrahigh vacuum system. We
found that chemisorbed oxygen not only quenches the effective magnetic moment
of the Co surface layer, but also softens its magnetic anisotropy. However, a
subsequent Mg dusting on the oxygen pre-exposed Pt/Co surface can recover the
magnetic anisotropy. The ab initio calculations on the exchange splitting and
orbital hybridization near the Fermi level give a clear physical explanation of
the experimental observations. Our results suggest that Co(Fe)-O-M bond plays a
more important role than the widely perceived Co(Fe)-O bond does in realizing
interfacial perpendicular magnetic anisotropy in Co(Fe)/MgO heterostructures.",1702.07852v1
2017/2/28,Magnetic ground state of SrRuO$_3$ thin film and applicability of standard first-principles approximations to metallic magnetism,"A systematic first-principles study has been performed to understand the
magnetism of thin film SrRuO$_3$ which lots of research efforts have been
devoted to but no clear consensus has been reached about its ground state
properties. The relative t$_{2g}$ level difference, lattice distortion as well
as the layer thickness play together in determining the spin order. In
particular, it is important to understand the difference between two standard
approximations, namely LDA and GGA, in describing this metallic magnetism.
Landau free energy analysis and the magnetization-energy-ratio plot clearly
show the different tendency of favoring the magnetic moment formation, and it
is magnified when applied to the thin film limit where the experimental
information is severely limited. As a result, LDA gives a qualitatively
different prediction from GGA in the experimentally relevant region of strain
whereas both approximations give reasonable results for the bulk phase. We
discuss the origin of this difference and the applicability of standard methods
to the correlated oxide and the metallic magnetic systems.",1702.08647v2
2017/3/1,Ultrasensitive Inertial and Force Sensors with Diamagnetically Levitated Magnets,"We theoretically show that a magnet can be stably levitated on top of a
punctured superconductor sheet in the Meissner state without applying any
external field. The trapping potential created by such induced-only
superconducting currents is characterized for magnetic spheres ranging from
tens of nanometers to tens of millimeters. Such a diamagnetically levitated
magnet is predicted to be extremely well isolated from the environment. We
therefore propose to use it as an ultrasensitive force and inertial sensor. A
magnetomechanical read-out of its displacement can be performed by using
superconducting quantum interference devices. An analysis using current
technology shows that force and acceleration sensitivities on the order of
$10^{-23}\text{N}/\sqrt{\text{Hz}}$ (for a 100 nm magnet) and
$10^{-14}g/\sqrt{\text{Hz}}$ (for a 10 mm magnet) might be within reach in a
cryogenic environment. Such unprecedented sensitivities can be used for a
variety of purposes, from designing ultra-sensitive inertial sensors for
technological applications (i.e. gravimetry, avionics, and space industry), to
scientific investigations on measuring Casimir forces of magnetic origin and
gravitational physics.",1703.00221v1
2017/3/6,Magnetically induced Ferroelectricity in Bi$_2$CuO$_4$,"The tetragonal copper oxide Bi$_2$CuO$_4$ has an unusual crystal structure
with a three-dimensional network of well separated CuO$_4$ plaquettes. This
material was recently predicted to host electronic excitations with an
unconventional spectrum and the spin structure of its magnetically ordered
state appearing at T$_N$ $\sim$43 K remains controversial. Here we present the
results of detailed studies of specific heat, magnetic and dielectric
properties of Bi$_2$CuO$_4$ single crystals grown by the floating zone
technique, combined with the polarized neutron scattering and high-resolution
X-ray measurements. Our polarized neutron scattering data show Cu spins are
parallel to the $ab$ plane. Below the onset of the long range antiferromagnetic
ordering we observe an electric polarization induced by an applied magnetic
field, which indicates inversion symmetry breaking by the ordered state of Cu
spins. For the magnetic field applied perpendicular to the tetragonal axis, the
spin-induced ferroelectricity is explained in terms of the linear
magnetoelectric effect that occurs in a metastable magnetic state. A relatively
small electric polarization induced by the field parallel to the tetragonal
axis may indicate a more complex magnetic ordering in Bi$_2$CuO$_4$.",1703.02069v1
2017/3/21,Influence of magnetic field and ferromagnetic film thickness on domain pattern transfer in multiferroic heterostructures,"Domains in BaTiO$_3$ induces a regular modulation of uniaxial magnetic
anisotropy in CoFeB via an inverse magnetostriction effect. As a result, the
domain structures of the CoFeB wedge film and BaTiO$_3$ substrate correlate
fully and straight ferroelectric domain boundaries in BaTiO$_3$ pin magnetic
domain walls in CoFeB. We use x-ray photoemission electron microscopy and
magneto-optical Kerr effect microscopy to characterize the spin structure of
the pinned domain walls. In a rotating magnetic field, abrupt and reversible
transitions between two domain wall types occur, namely, narrow walls where the
magnetization vectors align head-to-tail and much broader walls with
alternating head-to-head and tail-to-tail magnetization configurations. We
characterize variations of the domain wall spin structure as a function of
magnetic field strength and CoFeB film thickness and compare the experimental
results with micromagnetic simulations.",1703.07227v1
2017/4/24,Interface magnetism and electronic structure: ZnO(0001)/Co3O4(111),"We have studied the structural, electronic and magnetic properties of spinel
$\rm Co_3O_4$(111) surfaces and their interfaces with ZnO (0001) using density
functional theory (DFT) within the Generalized Gradient Approximation with
on-site Coulomb repulsion term (GGA+U). Two possible forms of spinel surface,
containing $\rm Co^{2+} $ and $\rm Co^{3+} $ ions and terminated with either
cobalt or oxygen ions were considered, as well as their interface with zinc
oxide. Our calculations demonstrate that $\rm Co^{3+} $ ions attain non-zero
magnetic moments at the surface and interface, in contrast to the bulk, where
they are not magnetic, leading to the ferromagnetic ordering. Since heavily
Co-doped ZnO samples can contain $\rm Co_3O_4 $ secondary phase, such a
magnetic ordering at the interface might explain the origin of the magnetism in
these diluted magnetic semiconductors (DMS).",1704.07148v4
2017/4/26,Magnetic Force Microscopy for Nanoparticle Characterization,"Since the invention of the atomic force microscope (AFM) in 1986, there has
been a drive to apply this scanning probe technique or a form of this technique
to various disciplines in nanoscale science. Magnetic force microscopy (MFM) is
a member of a growing family of scanning probe methods and has been widely used
for the study of magnetic materials. In MFM a magnetic probe is used to
raster-scan the surface of the sample, of which its magnetic field interacts
with the magnetic tip to offer insight into its magnetic properties. This
review will focus on the use of MFM in relation to nanoparticle
characterization, including superparamagnetic iron oxide nanoparticles,
covering MFM imaging in air and in liquid environments.",1704.08289v1
2017/5/2,Magnetic Field-Free Giant Magnetoresistance in a Proximity- and Gate-Induced Graphene Spin Valve,"Due to its two dimensional nature, ferromagnetism and charge doping can be
induced by proximity and electric field effects in graphene. Taking advantage
of these features, we propose an electrically engineered spin valve by
combining two magnetic insulators (using EuO, EuS, or YIG) and three coating
gates. Two top gates are used to cancel the heavy electron doping's in these
magnets and one back gate is used to utilize the normal or half-metallic
ferromagnetisms. We demonstrate that, when the second top gate is tuned to
utilize the insulating or spin insulating states, huge giant magnetoresistance
(GMR) at high temperature (several times of $10^5\%$ at 68K and 100K) can be
achieved for EuO and YIG. These results imply a distinguished GMR that is
magnetism tunable, vertical configured (ferromagnetism versus insulating), and
magnetic field-free. Our work may offer a viable path to a tantalizing magnetic
field-free spintronics.",1705.00773v1
2017/5/8,Disentangling magnetic order on nanostructured surfaces,"We present a synchrotron-based X-ray scattering technique which allows
disentangling magnetic properties of heterogeneous systems with nanopatterned
surfaces. This technique combines the nmrange spatial resolution of surface
morphology features provided by Grazing Incidence Small Angle X-ray Scattering
and the high sensitivity of Nuclear Resonant Scattering to magnetic order. A
single experiment thus allows attributing magnetic properties to structural
features of the sample; chemical and structural properties may be correlated
analogously. We demonstrate how this technique shows the correlation between
structural growth and evolution of magnetic properties for the case of a
remarkable magnetization reversal in a structurally and magnetically
nanopatterned sample system.",1705.02825v2
2017/5/23,"Magnetic behavior of new compounds, Gd3RuSn6 and Tb3RuSn6","We report temperature (T) dependence of dc magnetization, electrical
resistivity (rho(T)), and heat-capacity of rare-earth (R) compounds, Gd3RuSn6
and Tb3RuSn6, which are found to crystallize in the Yb3CoSn6-type orthorhombic
structure (space group: Cmcm). The results establish that there is an onset of
antiferromagnetic order near (T_N) 19 and 25 K respectively. In addition, we
find that there is another magnetic transition for both the cases around 14 and
17 K respectively. In the case of the Gd compound, the spin-scattering
contribution to rho is found to increase below 75 K as the material is cooled
towards T_N, thereby resulting in a minimum in the plot of rho(T) unexpected
for Gd based systems. Isothermal magnetization at 1.8 K reveals an upward
curvature around 50 kOe. Isothermal magnetoresistance plots show interesting
anomalies in the magnetically ordered state. There are sign reversals in the
plot of isothermal entropy change versus T in the magnetically ordered state,
indicating subtle changes in the spin reorientation with T. The results reveal
that these compounds exhibit interesting magnetic properties.",1705.08436v2
2017/5/30,Low-temperature heat transport of CuFe$_{1-x}$Ga$_x$O$_2$ ($x =$ 0--0.12) single crystals,"We report a study on the thermal conductivity of CuFe$_{1-x}$Ga$_x$O$_2$ ($x
=$ 0--0.12) single crystals at temperatures down to 0.3 K and in magnetic
fields up to 14 T. CuFeO$_2$ is a well-known geometrically frustrated
triangular lattice antiferromagnet and can be made to display multiferroicity
either by applying magnetic field along the $c$ axis or by doping nonmagnetic
impurities, accompanied with rich behaviors of magnetic phase transitions. The
main experimental findings of this work are: (i) the thermal conductivities
($\kappa_a$ and $\kappa_c$) show drastic anomalies at temperature- or
field-induced magnetic transitions; (ii) the low-$T$ $\kappa(H)$ isotherms
exhibit irreversibility in a broad region of magnetic fields; (iii) there are
phonon scattering effect caused by magnetic fluctuations at very low
temperatures. These results demonstrate strong spin-phonon coupling in this
material and reveal the non-negligible magnetic fluctuations in the ""ground
state"" of pure and Ga-doped samples.",1705.10666v1
2017/6/10,Mapping the magnonic landscape in patterned magnetic structures,"We report the development of a hybrid numerical / analytical model capable of
mapping the spatially-varying distributions of the local ferromagnetic
resonance (FMR) frequency and dynamic magnetic susceptibility in a wide class
of patterned and compositionally modulated magnetic structures. Starting from
the numerically simulated static micromagnetic state, the magnetization is
deliberately deflected orthogonally to its equilibrium orientation, and the
magnetic fields generated in response to this deflection are evaluated using
micromagnetic software. This allows us to calculate the elements of the
effective demagnetizing tensor, which are then used within a linear analytical
formalism to map the local FMR frequency and dynamic magnetic susceptibility.
To illustrate the typical results that one can obtain using this model, we
analyze three micromagnetic systems boasting non-uniformity in either one or
two dimensions, and successfully explain the spin-wave emission observed in
each case, demonstrating the ubiquitous nature of the Schl\""omann excitation
mechanism underpinning the observations. Finally, the developed model of local
FMR frequency could be used to explain how spin waves could be confined and
steered using magnetic non-uniformities of various origins, rendering it a
powerful tool for the mapping of the graded magnonic index in magnonics.",1706.03212v1
2017/6/19,Magnetic Excitations and Continuum of a Field-Induced Quantum Spin Liquid in $α$-RuCl$_3$,"We report on terahertz spectroscopy of quantum spin dynamics in
$\alpha$-RuCl$_3$, a system proximate to the Kitaev honeycomb model, as a
function of temperature and magnetic field. An extended magnetic continuum
develops below the structural phase transition at $T_{s2}=62$K. With the onset
of a long-range magnetic order at $T_N=6.5$K, spectral weight is transferred to
a well-defined magnetic excitation at $\hbar \omega_1 = 2.48$meV, which is
accompanied by a higher-energy band at $\hbar \omega_2 = 6.48$meV. Both
excitations soften in magnetic field, signaling a quantum phase transition at
$B_c=7$T where we find a broad continuum dominating the dynamical response.
Above $B_c$, the long-range order is suppressed, and on top of the continuum,
various emergent magnetic excitations evolve. These excitations follow clear
selection rules and exhibit distinct field dependencies, characterizing the
dynamical properties of the field-induced quantum spin liquid.",1706.06157v1
2017/6/24,The magnetic properties and structure of the quasi-two-dimensional antiferromagnet CoPS$_3$,"The magnetic properties and magnetic structure are presented for CoPS$_3$, a
quasi-two-dimensional antiferromagnet on a honeycomb lattice with a N\'eel
temperature of $T_N \sim 120$ K. The compound is shown to have XY-like
anisotropy in its susceptibility, and the anisotropy is analysed to extract
crystal field parameters. For temperatures between 2 K and 300 K, no phase
transitions were observed in the field-dependent magnetization up to 10 Tesla.
Single-crystal neutron diffraction shows that the magnetic propagation vector
is {\bf{k}}= $\left[010\right]$ with the moments mostly along the $\mathbf{a}$
axis and with a small component along the $\mathbf{c}$ axis, which largely
verifies the previously-published magnetic structure for this compound. The
magnetic Bragg peak intensity decreases with increasing temperature as a power
law with exponent $2\beta = 0.60 \pm 0.01$ for $T > 0.9~T_N$.",1706.07989v1
2017/8/11,Dimensional reduction by pressure in the magnetic framework material CuF$_{2}$(D$_{2}$O)$_{2}$pyz: from spin-wave to spinon excitations,"Metal organic magnets have enormous potential to host a variety of electronic
and magnetic phases that originate from a strong interplay between the spin,
orbital and lattice degrees of freedom. We control this interplay in the
quantum magnet CuF$_2$(D$_2$O)$_2$pyz by using high pressure to drive the
system through a structural and magnetic phase transition. Using neutron
scattering, we show that the low pressure state, which hosts a two-dimensional
square lattice with spin-wave excitations and a dominant exchange coupling of
0.89 meV, transforms at high pressure into a one-dimensional spin-chain
hallmarked by a spinon continuum and a reduced exchange interaction of 0.43
meV. This direct microscopic observation of a magnetic dimensional crossover as
a function of pressure opens up new possibilities for studying the evolution of
fractionalised excitations in low dimensional quantum magnets and eventually
pressure-controlled metal--insulator transitions.",1708.03586v1
2017/8/28,Electric-field-induced changes of magnetic moments and magnetocrystalline anisotropy in ultrathin cobalt films,"In this study, the microscopic origins of the voltage-controlled magnetic
anisotropy (VCMA) in 3d-ferromagnetic metals are revealed. Using in-situ X-ray
fluorescence spectroscopy that provides a high quantum efficiency,
electric-field-induced changes in orbital magnetic moment and magnetic dipole
Tz terms in ultrathin Co films are demonstrated. An orbital magnetic moment
difference of 0.013{\mu}B. was generated in the presence of electric fields of
+(-)0.2 V/nm. The VCMA of Co was properly estimated by the induced change in
orbital magnetic moment, according to the perturbation theory model. The
induced change in magnetic dipole Tz term only slightly contributed to the VCMA
in 3d-ferromagnetic metals.",1708.08549v2
2017/9/25,"The structural, magnetic and optical properties of TMn@(ZnO)42 (TM = Fe, Co and Ni) hetero-nanostructure","The magnetic transition-metal (TM) @ oxide nanoparticles have been of great
interest due to their wide range of applications, from medical sensors in
magnetic resonance imaging to photo-catalysis. Although several studies on
small clusters of TM@oxide have been reported, the understanding of the
physical electronic properties of TMn@(ZnO)42 is far from sufficient. In this
work, the electronic, magnetic and optical properties of TMn@(ZnO)42 (TM = Fe,
Co and Ni) hetero-nanostructure are investigated using the density functional
theory (DFT). It has been found that the core-shell nanostructure Fe13@(ZnO)42,
Co15@(ZnO)42 and Ni15@(ZnO)42 are the most stable structures. Moreover, it is
also predicted that the variation of the magnetic moment and magnetism of Fe,
Co and Ni in TMn@ZnO42 hetero-nanostructure mainly stems from effective
hybridization between core TM-3d orbitals and shell O-2p orbitals, and a
magnetic moment inversion for Fe15@(ZnO)42 is investigated. Finally, optical
properties studied by calculations show a red shift phenomenon in the
absorption spectrum compared with the case of (ZnO)48.",1709.08502v1
2017/10/5,Magnetic Skyrmionic Polarons,"We study a two-dimensional electron gas exchanged-coupled to a system of
classical magnetic ions. For large Rashba spin-orbit coupling a single electron
can become self-trapped in a skyrmion spin texture self-induced in the magnetic
ions system. This new quasiparticle carries electrical and topological charge
as well as a large spin, and we named it as magnetic skyrmionic polaron. We
study the range of parameters; temperature, exchange coupling, Rashba coupling
and magnetic field, for which the magnetic skyrmionic polaron is the
fundamental state in the system. The dynamics of this quasiparticle is studied
using the collective coordinate approximation, and we obtain that in presence
of an electric field the new quasiparticle shows, because the chirality of the
skyrmion, a Hall effect. Finally we argue that the magnetic skyrmionic polarons
can be found in large Rashba spin-orbit coupling semiconductors as GeMnTe.",1710.02182v1
2017/10/27,Evidence for the Confinement of Magnetic Monopoles in Quantum Spin Ice,"Magnetic monopoles are hypothesised elementary particles connected by Dirac
strings that behave like infinitely thin solenoids. Despite decades of
searches, free magnetic monopoles and their Dirac strings have eluded
experimental detection, although there is substantial evidence for deconfined
magnetic monopole quasiparticles in spin ice materials. Here we report the
detection of a hierarchy of unequally-spaced magnetic excitations \emph{via}
high resolution inelastic neutron spectroscopic measurements on the quantum
spin ice candidate Pr$_{2}$Sn$_{2}$O$_{7}$. These excitations are
well-described by a simple model of monopole pairs bound by a linear potential
with an effective tension of 0.642(8) K~$\cdot$\AA$^{-1}$ at 1.65~K. The
success of the linear potential model suggests that these low energy magnetic
excitations are direct spectroscopic evidence for the confinement of magnetic
monopole quasiparticles in the quantum spin ice candidate
Pr$_{2}$Sn$_{2}$O$_{7}$.",1710.10337v1
2017/12/12,Substitution- and Strain-induced Magnetic Phase Transition in Iron Carbide,"Cementite-type carbides are of interest for magnetocaloric applications owing
to their temperature- or pressure-induced magnetic phase transition. Here,
using first-principles calculations, we investigate the magnetism and the
magnetic phase transition in iron carbide (Fe3C) with the substitution of Cr
atoms at Fe sites with the strain effect. The presence of Cr atoms is found to
give rise to a second-order magnetic phase transition from a ferromagnetic
phase for Fe3C to a nonmagnetic phase in chromium carbide (Cr3C).While the
ternary Fe2CrC and Cr2FeC compounds prefer the ferrimagnetic ground state, the
magnitudes of both the Fe and Cr spin moments, which are antiparallel in
orientation, decrease as x increases in Fe3-xCrxC (x = 0, 1, 2, and 3).
Furthermore, the fixed spin-moment calculations indicate that the magnetization
of Fe3-xCrxC compounds can be delicately altered via the strain effect and that
the magnetic-nonmagnetic phase transition occurs at an early stage of Cr
substitution, x = 2.",1712.04128v1
2018/1/23,Magnetic and Structural Properties of A-Site Ordered Chromium Spinel Sulfides: Alternating Antiferromagnetic and Ferromagnetic Interactions in the Breathing Pyrochlore Lattice,"We report a comprehensive study on the magnetic and structural properties of
the spinel sulfides LiInCr4S8, LiGaCr4S8, and CuInCr4S8, where Li+/Cu+ and
Ga3+/In3+ ions form a zinc-blende-type order. On the basis of synchrotron X-ray
diffraction and magnetization data obtained using polycrystalline samples,
these three sulfides are suggested to be breathing pyrochlore magnets with
alternating antiferromagnetic and ferromagnetic interactions on the small and
large tetrahedra, respectively. The measured magnetization processes of the
three sulfides up to 72 T are significantly different. The magnetization curves
of LiInCr4S8 and CuInCr4S8 have large hysteresis loops with different shapes,
while there is no hysteresis in that of LiGaCr4S8. Geometrical frustration of
the small tetrahedron is likely to give rise to a wide variety of ground
states, indicating the rich physics in these antiferromagnetic-ferromagnetic
breathing pyrochlore magnets.",1801.07354v1
2018/1/23,Charge/Spin Supercurrent and the Fulde-Ferrell State Induced by Crystal Deformation in Weyl/Dirac Superconductors,"It has been predicted that emergent chiral magnetic fields can be generated
by crystal deformation in Weyl/Dirac metals and superconductors. The emergent
fields give rise to chiral anomaly phenomena as in the case of Weyl semimetals
with usual electromagnetic fields. Here, we clarify effects of the chiral
magnetic field on Cooper pairs in Weyl/Dirac superconductors on the basis of
the Ginzburg-Landau equation microscopically derived from the quasiclassical
Eilenberger formalism. It is found that Cooper pairs are affected by the
emergent chiral magnetic field in a dramatic way, and the pseudo-Lorentz force
due to the chiral magnetic field stabilizes the Fulde-Ferrell state and causes
a charge/spin supercurrent which flows parallel to the chiral magnetic field in
the case of Weyl/Dirac superconductors. This effect is in analogy with the
chiral magnetic effect (CME) of Weyl semimetals. In addition, we elucidate that
neither Meissner effect nor vortex state due to chiral magnetic fields occurs.",1801.07401v2
2018/1/26,Probing magnetism in 2D van der Waals crystalline insulators via electron tunneling,"Magnetic insulators are a key resource for next-generation spintronic and
topological devices. The family of layered metal halides promises ultrathin
insulating multiferroics, spin liquids, and ferromagnets, but new
characterization methods are required to unlock their potential. Here, we
report tunneling through the layered magnetic insulator CrI3 as a function of
temperature and applied magnetic field. We electrically detect the magnetic
ground state and inter-layer coupling and observe a field-induced metamagnetic
transition. The metamagnetic transition results in magnetoresistances of 95%,
300%, and 550% for bilayer, trilayer, and tetralayer CrI3 barriers,
respectively. We further measure inelastic tunneling spectra for our junctions,
unveiling a rich spectrum of collective magnetic excitations (magnons) in CrI3.
Our results establish vertical tunneling as a versatile probe of magnetism in
atomically thin insulators.",1801.10075v1
2018/3/12,Focused ion beam direct writing of magnetic patterns with controlled structural and magnetic properties,"Focused ion beam irradiation of metastable Fe$_{78}$Ni$_{22}$ thin films
grown on Cu(100) substrates is used to create ferromagnetic,
body-centered-cubic patterns embedded into paramagnetic, face-centered-cubic
surrounding. The structural and magnetic phase transformation can be controlled
by varying parameters of the transforming gallium ion beam. The focused ion
beam parameters as ion dose, number of scans, and scanning direction can be
used not only to control a degree of transformation, but also to change the
otherwise four-fold in-plane magnetic anisotropy into the uniaxial anisotropy
along specific crystallographic direction. This change is associated with a
preferred growth of specific crystallographic domains. The possibility to
create magnetic patterns with continuous magnetization transitions and at the
same time to create patterns with periodical changes in magnetic anisotropy
makes this system an ideal candidate for rapid prototyping of a large variety
of nanostructured samples. Namely spin-wave waveguides and magnonic crystals
can be easily combined into complex devices in a single fabrication step.",1803.04348v1
2018/4/29,Diluted magnetic Dirac-Weyl materials: Susceptibility and ferromagnetism in three-dimensional chiral gapless semimetals,"We theoretically investigate the temperature-dependent static susceptibility
and long-range magnetic coupling of three-dimensional (3D) chiral gapless
electron-hole systems (semimetals) with arbitrary band dispersion [i.e.,
$\varepsilon(k) \sim k^N$, where $k$ is the wave vector and $N$ is a positive
integer]. We study the magnetic properties of these systems in the presence of
dilute random magnetic impurities. Assuming carrier-mediated
Ruderman-Kittel-Kasuya-Yosida indirect exchange interaction, we find that the
magnetic ordering of intrinsic 3D chiral semimetals in the presence of dilute
magnetic impurities is ferromagnetic for all values of $N$. Using
finite-temperature self-consistent field approximation, we calculate the
ferromagnetic transition temperature ($T_{\rm c}$). We find that $T_{\rm c}$
increases with increasing $N$ due to the enhanced density of states, and the
calculated $T_{\rm c}$ is experimentally accessible assuming reasonable
coupling between the magnetic impurities and itinerant carriers.",1804.10867v2
2018/5/7,Anatomy of interfacial spin-orbit coupling in Co/Pd multilayers using X-ray magnetic circular dichroism and first-principles calculations,"Element-specific orbital magnetic moments and their anisotropies in
perpendicularly magnetised Co/Pd multilayers are investigated using Co L-edge
and Pd M-edge angle-dependent x-ray magnetic circular dichroism. We show that
the orbital magnetic moments in Co are anisotropic, whereas those in Pd are
isotropic. The first-principles density-functional-theory calculations also
suggest that the Co/Pd interfacial orbital magnetic moments in Co are
anisotropic and contribute to the perpendicular magnetic anisotropy (PMA), and
that the isotropic ones in Pd manipulates the Co orbitals at the interface
through proximity effects. Orbital-resolved anatomy of Co/Pd interfaces reveals
that the orbital moment anisotropy in Co and spin-flipped transition related to
the magnetic dipoles in Pd are essential for the appearance of PMA.",1805.02416v1
2018/5/8,Topological Contributions to the Anomalous Nernst and Hall Effect in the Chiral Double-Helimagnetic System,"MnP and FeP are show complex magnetic spiral states with geometric phase
contributions to the anomalous Hall effect and the topological Hall effect,
where both have thermoelectric Nernst counterparts. We use state of the art
first principle calculations to show that both Hall and Nernst effects are
enhanced in MnP and FeP due to the temperature dependent magnetic texture. At
ambient pressure the inversion breaking crystals shows a transition from a
double-spiral helimagnetic phase to a topologically trivial magnetic phase.
This helimagnetic structure is determined by exchange frustration and the
Dzyaloshinskii-Moriya interaction. In the presence of an external magnetic
field the magnetic structure transforms into a fan-like phase with a finite
spin chirality that gives rise to an effective magnetic field on the order
$\sim$1 T. The topological Hall and Nernst effect from this field are
comparable or larger to tightly-wound skyrmion systems. Lastly, we show that
the topological effects are strongly dependent on the Fermi surface topology,
which has strong variations and even sign changes for similar magnetic
textures.",1805.02976v1
2018/5/28,The effect of boundary-induced chirality on magnetic textures in thin films,"In the quest for miniaturizing magnetic devices, the effects of boundaries
and surfaces become increasingly important. Here we show how the recently
predicted boundary-induced Dzyaloshinskii-Moriya interaction (DMI) affects the
magnetization of ferromagnetic films with a $C_{\infty v}$ symmetry and a
perpendicular magnetic anisotropy. For an otherwise uniformly magnetized film,
we find a surface twist when the magnetization in the bulk is canted by an
in-plane external field. This twist at the surfaces caused by the
boundary-induced DMI differs from the common canting caused by internal DMI
observed at the edges of a chiral magnet. Further, we find that the surface
twist due to the boundary-induced DMI strongly affects the width of the domain
wall at the surfaces. We also find that the skyrmion radius increases in the
depth of the film, with the average size of the skyrmion increasing with
boundary-induced DMI. This increase suggests that the boundary-induced DMI
contributes to the stability of the skyrmion.",1805.11110v1
2018/6/5,Electromagnetic effects induced by time-dependent axion field,"We studied the dynamics of the so-called $\theta$-term, which exists in
topological materials and is related to a hypothetical field predicted by
Peccei-Quinn in particle physics, in a magnetic superlattice constructed using
a topological insulator and two ferromagnetic insulators, where the
ferromagnetic insulators had perpendicular magnetic anisotropies and different
magnetic coercive fields. We examined a way to drive the dynamics of the
$\theta$-term in the magnetic superlattice through changing the inversion
symmetry (from an anti-parallel to a parallel magnetic configuration) using an
external magnetic field. As a result, we found that unconventional
electromagnetic fields, which are magnetic field-induced charge currents and
vice versa, are generated by the nonzero dynamics of the $\theta$-term.",1806.01548v1
2018/6/6,The Anomalous Hall Effect in Magnetic Topological Insulators,"The anomalous Hall effect (AHE) is studied on the surface of a 3D magnetic
topological insulator. By applying a modified semi-classical framework, all
three contributions to the AHE, the intrinsic Berry phase curvature effect, the
side-jump effect and the skew scattering effects are systematically treated,
and analytical expressions for the conductivities are obtained in terms of the
Fermi level, the spatial orientation of the surface magnetization and the
concentration of magnetic and non-magnetic impurities.
  We demonstrate that the AHE can change sign by altering the orientation of
the surface magnetization, the concentration of the impurities and also the
position of the chemical potential, in agreement with recent experimental
observations. Hence, each contribution to the AHE, or even the whole AHE, can
be turned off by properly adjusting the given parameters. For example, one can
turn off the anomalous hall conductivity in a system with in-plane
magnetization by pushing the system into the fully metallic regime.",1806.02245v1
2018/6/20,Magnetic Imaging and Microscopy,"The magnetic domain configuration of a system reveals a wealth of information
about the fundamental magnetic properties of that system and can be a critical
factor in the operation of magnetic devices. Not only are the details of the
domain structure strongly governed by materials parameters, but in thin-films
and mesoscopic elements the geometry has an often pivotal effect, providing a
convenient handle to tailor desired domain states. Furthermore a full
understanding of a system requires, in addition, investigation of the dynamic
evolution of the spin-state, which is of particular importance for applications
relying on e.g. the switching of magnetic elements. Here we review some of the
main modern techniques for magnetic imaging, highlighting their respective
advantages and limitations. The methods for imaging domain configurations and
spin structures cover various spatial and temporal resolution scales and
encompass those based on electron and x-ray microscopy as well as scanning
probe techniques. Furthermore, away from the discipline of condensed-matter
physics, magnetic effects are instrumental in a number of techniques for
medical imaging, some key examples of which we also present.",1806.07767v2
2018/7/11,Dynamical coupling of dilute magnetic impurities with quantum spin liquid state in the S = 3/2 dimer compound Ba3ZnRu2O9,"We have investigated the dilute magnetic impurity effect on the magnetic
properties of a quantum spin liquid candidate Ba3ZnRu2O9 and a spin gapped
compound Ba3CaRu2O9. The magnetic ground state of each compound stands against
2% substitution of magnetic impurities for Zn or Ca. We have found that the
magnetic response of these impurities, which behave as paramagnetic spins,
depends on the host materials and the difference of the two manifests itself in
the Weiss temperature, which can hardly be explained by the dilute magnetic
impurities alone in the case of Ba3ZnRu2O9. We consider a contribution from the
Ru5+ ions which would appear only in the substituted Ba3ZnRu2O9 and discuss a
possible physical meaning of the observed Weiss temperature.",1807.04076v1
2018/7/13,Engineering Chiral and Topological Orbital Magnetism of Domain Walls and Skyrmions,"Electrons which are slowly moving through chiral magnetic textures can
effectively be described as if they where influenced by electromagnetic fields
emerging from the real-space topology. This adiabatic viewpoint has been very
successful in predicting physical properties of chiral magnets. Here, based on
a rigorous quantum-mechanical approach, we unravel the emergence of chiral and
topological orbital magnetism in one- and two-dimensional spin systems. We
uncover that the quantized orbital magnetism in the adiabatic limit can be
understood as a Landau-Peierls response to the emergent magnetic field. Our
central result is that the spin-orbit interaction in interfacial skyrmions and
domain walls can be used to tune the orbital magnetism over orders of magnitude
by merging the real-space topology with the topology in reciprocal space. Our
findings point out the route to experimental engineering of orbital properties
of chiral spin systems, thereby paving the way to the field of chiral
orbitronics.",1807.05040v1
2018/7/16,Magnetic freezing transition in a CoO/Permalloy bilayer revealed by transverse ac susceptibility,"We utilize variable-temperature, variable-frequency magneto-optical
transverse magnetic susceptibility technique to study the static and dynamical
magnetic properties of a thin-film CoO/Permalloy bilayer. Our measurements
demonstrate that in the studied system, the directional asymmetry of the
hysteresis loop is associated mainly with the difference in the reversal
mechanisms between the two reversed states of magnetization stabilized by the
exchange-induced uniaxial anisotropy. The latter is found to be much larger
than the exchange-induced unidirectional anisotropy of the ferromagnet. We also
observe an abrupt variation of the frequency-dependent imaginary part of ac
susceptibility near the exchange bias blocking temperature, consistent with the
magnetic freezing transition inferred from the previous time-domain studies of
magnetic aging in similar systems. The developed measurement approach enables
precise characterization of the dynamical and static characteristics of
thin-film magnetic heterostructures that can find applications in
reconfigurable magnonic and neuromorphic circuits.",1807.05990v2
2018/7/30,Dynamics of topological defects in a two-dimensional magnetic domain stripe pattern,"Two dimensional magnetic films with perpendicular magnetization spontaneously
form magnetic domain patterns that evolve or undergo symmetry transformations
as a function of temperature. When the system is driven from equilibrium by a
rapid change in temperature, topological pattern defects are the elementary
pattern excitations that affect this evolution. An elastic continuum model is
adapted to describe how a metastable population of topological defects alters
the domain density and the magnetic susceptibility of the ""stripe"" magnetic
domain pattern. Temporal changes in the susceptibility are interpreted using a
dynamical equation describing the defect population. Recent experiments provide
a quantitative verification of the model, and illustrate the use of the
magnetic susceptibility to follow the population dynamics of topological
defects in this system, and its potential role in investigating a pattern
melting phase transition.",1807.11424v1
2018/8/28,Tuning magnetic charge population and mobility in unidirectional array of nanomagnets as a function of lattice parameters,"Sets of nanomagnets are often utilized to mimic cellular automata in design
of nanomagnetic logic devices or frustration and emergence of magnetic charges
in artificial spin ice systems. in previous work we showed that unidirectional
arrangement of nanomagnets can behave as artificial spin ice, with frustration
arising from second neighbor dipolar interaction, and present good magnetic
charge mobility due to the low string tension among charges. Here, we present
an experimental investigation of magnetic charge population and mobility in
function of lateral and longitudinal distance among nanomagnets. Our results
corroborate partially the theoretical predictions, performed elsewhere by
emergent interaction model, could be useful in nanomagnet logic devices design
and brings new insights about the best design for magnetic charge ballistic
transport under low external magnetic field with magnetic charge mobility
tunning for application in magnetricity.",1808.09466v2
2018/9/20,Multiple-$Q$ magnetic orders in Rashba-Dresselhaus metals,"We study magnetic textures realized in noncentrosymmetric Kondo lattice
models, in which localized magnetic moments weakly interact with itinerant
electrons subject to Rashba and Dresselhaus spin-orbit couplings. By virtue of
state-of-the-art numerical simulations as well as variational calculations, we
uncover versatile multiple-$Q$ orderings under zero magnetic field, which are
found to originate in the instabilities of the Fermi surface whose spin
degeneracy is lifted by the spin-orbit couplings. In the case with
equally-strong Rashba and Dresselhaus spin-orbit couplings, which is known to
realize a persistent spin helix in semiconductor quantum wells, we discover a
sextuple-$Q$ magnetic ordering with a checkerboard-like spatial pattern of the
spin scalar chirality. In the presence of either Rashba or Dresselhaus
spin-orbit coupling, we find out another multiple-$Q$ ordering, which is
distinct from Skyrmion crystals discussed under the same symmetry. Our results
indicate that the cooperation of the spin-charge and spin-orbit couplings
brings about richer magnetic textures than those studied within effective spin
models. The situations would be experimentally realized, e.g., in
noncentrosymmetric heavy-fermion compounds and heterostructures of spin-orbit
coupled metals and magnetic insulators.",1809.07582v1
2018/10/1,Investigation of magneto-optical properties of ferrofluids by laser light scattering techniques,"Investigation of magnetooptical characteristics of ferrofluids is an
important task aimed at the development of novel optoelectronic systems. This
article reports on the results obtained in the experimental studies of the
factors that affect the intensity and spatial distribution of the laser
radiation scattered by magnetic particles and their agglomerates in a magnetic
field. Laser correlation spectroscopy and direct measurements of laser
radiation scattering for studies of the interactions and magnetooptical
properties of magnetic particles in solutions were employed. The objects were
samples of nanodispersed magnetite (Fe3O4) suspended in kerosene and in water.
Our studies revealed some new behavior of magnetic particles in external
magnetic and light fields, which make ferrofluids promising candidates for
optical devices.",1810.00690v1
2018/10/3,Possible origin of the absence of magnetic order in LiOsO$_3$: Spin-orbit coupling controlled ground state,"LiOsO$_3$ is the first experimentally confirmed polar metal with
ferroelectric-like distortion. One puzzling experimental fact is its
paramagnetic state down to very low temperature with negligible magnetic
moment, which is anomalous considering its $5d^3$ electron configuration since
other osmium oxides (e.g. NaOsO$_3$) with $5d^3$ Os ions are magnetic. Here the
magnetic and electronic properties of LiOsO$_3$ are re-investigated carefully
using the first-principles density functional theory. Our calculations reveal
that the magnetic state of LiOsO$_3$ can be completely suppressed by the
spin-orbit coupling. The subtle balance between significant spin-orbit coupling
and weak Hubbard $U$ of $5d$ electrons can explain both the nonmagnetic
LiOsO$_3$ and magnetic NaOsO$_3$. Our work provides a reasonable understanding
of the long-standing puzzle of magnetism in some osmium oxides.",1810.01639v1
2018/10/12,Room temperature biaxial magnetic anisotropy in La0.67Sr0.33MnO3 thin films on SrTiO3 buffered MgO (001) substrates for spintronic applications,"Spintronics exploits the magnetoresistance effects to store or sense the
magnetic information. Since the magnetoresistance strictly depends on the
magnetic anisotropy of the system, it is fundamental to set a defined
anisotropy to the system. Here, we investigate by means of vectorial
Magneto-Optical Kerr Magnetometry (v-MOKE), half-metallic La0.67Sr0.33MnO3
(LSMO) thin films that exhibit at room temperature pure biaxial magnetic
anisotropy if grown onto MgO (001) substrate with a thin SrTiO3 (STO) buffer.
In this way, we can avoid unwanted uniaxial magnetic anisotropy contributions
that may be detrimental for specific applications. The detailed study of the
angular evolution of the magnetization reversal pathways, critical fields
(coercivity and switching) allows for disclosing the origin of the magnetic
anisotropy, which is magnetocrystalline in nature and shows four-fold symmetry
at any temperature.",1810.05435v1
2018/10/18,Profile approach for recognition of three-dimensional magnetic structures,"We propose an approach for low-dimensional visualisation and classification
of complex topological magnetic structures formed in magnetic materials. Within
the approach one converts a three-dimensional magnetic configuration to a
vector containing the only components of the spins that are parallel to the z
axis. The next crucial step is to sort the vector elements in ascending or
descending order. Having visualized profiles of the sorted spin vectors one can
distinguish configurations belonging to different phases even with the same
total magnetization. For instance, spin spiral and paramagnetic states with
zero total magnetic moment can be easily identified. Being combined with a
simplest neural network our profile approach provides a very accurate phase
classification for three-dimensional magnets characterized by complex
multispiral states even in the critical areas close to phases transitions. By
the example of the skyrmionic configurations we show that profile approach can
be used to separate the states belonging to the same phase.",1810.07915v1
2018/11/4,Magnetic Nanoparticles in Nanomedicine,"Nanomaterials, in addition to their small size, possess unique
physicochemical properties that differ from the bulk materials, making them
ideal for a host of novel applications. Magnetic nanoparticle (MNP) is one
important class of nanomaterials that have been widely studied for their
potential applications in nanomedicine. Due to the fact that MNPs can be
detected and manipulated by remote magnetic fields, it opens a wide opportunity
for them to be used in vivo. Nowadays, MNPs have been used for diverse
applications including magnetic biosensing (diagnostics), magnetic imaging,
magnetic separation, drug and gene delivery, and hyperthermia therapy, etc.
This review aims to provide a comprehensive assessment of the state-of-the-art
biological and biomedical applications of MNPs. In addition, the development of
high magnetic moment MNPs with proper surface functionalization has progressed
exponentially over the past decade. Herein, we also reviewed the recent
advances in the synthesis and surface coating strategies of MNPs. This review
is not only to provide in-depth insights into the different synthesis,
biofunctionalization, biosensing, imaging, and therapy methods but also to give
an overview of limitations and possibilities of each technology.",1811.01418v1
2018/11/28,Magnetization and ac susceptibility study of the cubic chiral magnet Mn$_{1-x}$Fe$_x$Si,"We present a comprehensive and systematic magnetization and ac susceptibility
study of Mn$_{1-x}$Fe$_{x}$Si over an extensive range of ten Fe concentrations
between $x$ = 0 - 0.32. With increasing Fe substitution, the critical
temperature decreases but the magnetic phase diagrams remain qualitatively
unaltered for $x$ $\leq$ $x^*$ $\approx$ 0.11 with clear boundaries between the
helical, conical, and skyrmion lattice phase as well as an enhanced precursor
phase. A notably different behavior sets in for $x$ $=$ 0.11, 0.13 and 0.14,
where certain characteristics of helimagnetic correlations persist, but without
clear phase boundaries. Although a qualitative change already sets in at $x^*$,
the transition temperature and spontaneous magnetization vanish only at $x_C$ =
0.17 where also the average magnetic interactions change sign. Although the
Curie-Weiss temperature reaches -12~K for $x$ = 0.32, no signature of
long-range magnetic order is found down to the lowest temperature, indicating a
possible significant role for quantum fluctuations in these systems.",1811.11650v1
2018/12/3,Magnetic excitations in the quasi-2D ferromagnet Fe3-xGeTe2 measured with inelastic neutron scattering,"Fe3-xGeTe2 is an itinerant ferromagnet composed of two-dimensional layers
weakly connected by van der Waals bonding that shows a variety of intriguing
phenomena. Inelastic neutron scattering measurements on bulk single crystals of
Fe2.75GeTe2 were performed to quantify the magnetic exchange interaction
energies and anisotropy. The observed inelastic excitations are indicative of
dominant in-plane correlations with negligible magnetic interactions between
the layers. A spin-gap of 3.9 meV is observed allowing a measure of the
magnetic anisotropy. As the excitations disperse to their maximum energy (~65
meV) they become highly damped, reflective of both the magnetic site occupancy
reduction of 25{\%} on one Fe sublattice and the itinerant interactions. A
minimal model is employed to describe the excitation spectra and extract
nearest neighbor magnetic exchange interaction values. The temperature
evolution of the excitations are probed and correlations shown to persist above
Tc, indicative of low dimensional magnetism.",1812.00519v1
2018/12/4,Substrate-Controlled Magnetism: Fe nanowires on vicinal Cu surfaces,"Here we present a novel approach to control magnetic interactions in
atomic-scale nanowires. Our ab initio calculations demonstrate the possibility
to tune magnetic properties of Fe nanowires formed on vicinal Cu surfaces. Both
intrawire and interwire magnetic exchange parameters are extracted from DFT
calculations. This study suggests that the effective interwire magnetic
exchange parameters exhibit Ruderman--Kittel--Kasuya--Yosida-like (RKKY)
oscillations as a function of Fe interwire separation. The choice of vicinal Cu
surface offers possibilities for controlling the magnetic coupling.
Furthermore, an anisotropic Heisenberg model was used in Monte Carlo
simulations to examine the stability of these magnetic configurations at finite
temperature. The predicted critical temperatures of the Fe nanowires on Cu(422)
and Cu(533) surfaces are well-above room temperature.",1812.01683v3
2018/12/18,The Wu-Yang potential of Magnetic Skyrmion from SU(2) Flat Connection,"The theoretical research of the origin of magnetic skyrmion is very
interesting. By using decomposition theory of gauge potential and the gauge
parallel condition of local bases of $su(2)$ Lie algebra, its $SU(2)$ gauge
potential is expressed as flat connection. As an example of application, we
obtain the inner topological structure of second Chern number by $SU(2)$ flat
connection method. It's well known that if magnetic monopole exists in
electrodynamics, its Wu-Yang potential is indispensable in $U(1)$ invariant
electromagnetic field. In $2$-dim magnetic materials, we prove that if magnetic
skyrmion exists, its integral kernel must be $U(1)$ Wu-Yang curvature, where
its $U(1)$ Wu-Yang potential is the projection of $SU(2)$ flat connection on
$su(2)$ local Cartan subalgebra. The magnetic skyrmion can be created by
performing concrete $SU(2)$ local gauge transformation to $su(2)$ Cartan
subalgebra $\sigma_3$. The components of the $U(1)$ Wu-Yang curvature
correspond to the emergent electromagnetic field of magnetic skyrmion",1812.07974v2
2019/2/5,Long-range magnetic ordering in rocksalt-type high-entropy oxides,"We report the magnetic properties of
Mg$_{0.2}$Co$_{0.2}$Ni$_{0.2}$Cu$_{0.2}$Zn$_{0.2}$O, a high-entropy oxide with
rocksalt structure, and the influence of substitutions on these properties.
From the magnetic susceptibility and neutron diffraction measurements, we found
that this compound exhibits long-range magnetic order below 120 K despite the
substantial structuraldisorder. The other rocksalt-type high-entropy oxides
with various chemical substitutions were found to host either an
antiferromagnetic order or spin-glass state depending on the amount of magnetic
ions. The presence of magnetic order for such a disordered material potentially
provide a route to explore novel magnetic properties and functions.",1902.01825v2
2019/2/19,Magnetic interaction and anisotropy axes arrangement in nanoparticle aggregates can enhance or reduce the effective magnetic anisotropy,"The magnetic response of nanostructures plays an important role on biomedical
applications being strongly influenced by the magnetic anisotropy. In this work
we investigate the role of temperature, particle concentration and nanoparticle
arrangement forming aggregates in the effective magnetic anisotropy of Mn-Zn
ferrite-based nanoparticles. Electron magnetic resonance and coercivity
temperature dependence analyses, were critically compared for the estimation of
the anisotropy. We found that the temperature dependence of the anisotropy
follows the Callen-Callen model, while the symmetry depends on the particle
concentration. At low concentration one observes only an uniaxial term, while
increasing a cubic contribution has to be added. The effective anisotropy was
found to increase the higher the particle concentration on magnetic colloids,
as long as the easy axis was at the same direction of the nanoparticle chain.
Increasing even further the concentration up to a highly packed condition
(powder sample) one observes a decrease of the anisotropy, that was attributed
to the random anisotropy axes configuration.",1902.07188v1
2019/2/23,"The spin-1/2 coupled tetramer system Ba(TiO)Cu$_4$(PO$_4$)$ _4$ probed by magnetization, specific heat, and $^{31}$P-NMR","We present the synthesis and a detailed investigation of structural and
magnetic properties of polycrystalline Ba(TiO)Cu$_{4}$(PO$_{4}$)$_{4}$ (BTCPO)
via x-ray diffraction, magnetic susceptibility, heat capacity, and $^{31}$P
Nuclear Magnetic Resonance (NMR) measurements. BTCPO has a 2D layered structure
with interlinked Cu$_{4}$O$_{12}$ tetramer units. A broad maximum is observed
around 16.5 K in our magnetization data accompanied by a sharp anomaly around
$T$ = 9.5 K in the heat capacity. An anomaly at $T$ = 9.5 K is also found in
the temperature dependence of the $^{31}$P NMR spin-lattice relaxation rate
$1/T_1$. A power law behavior for the heat capacity as well as for the $^{31}$P
$1/T_1$ below the ordering temperature could be obtained. The $^{31}$P NMR
lineshape is asymmetric and the NMR shift tracks the bulk spin-susceptibility.
We estimated the isotropic and axial components of the hyperfine coupling
tensor to be as the $A^{iso}_{hf} \backsimeq 6794$ $\rm{Oe/\mu_{B}}$ and
$A^{ax}_{hf} \backsimeq 818$ $\rm{Oe/\mu_{B}}$, respectively.",1902.08782v2
2019/3/11,High Field Anomalies of Equilibrium and Ultrafast Magnetism in Rare-Earth-Transition Metal Ferrimagnets,"Magneto-optical spectroscopy in fields up to 30 Tesla reveals anomalies in
the equilibrium and ultrafast magnetic properties of the ferrimagnetic
rare-earth-transition metal alloy TbFeCo. In particular, in the vicinity of the
magnetization compensation temperature, each of the magnetizations of the
antiferromagnetically coupled Tb and FeCo sublattices show triple hysteresis
loops. Contrary to state-of-the-art theory, which explains such loops by sample
inhomogeneities, here we show that they are an intrinsic property of the
rare-earth ferrimagnets. Assuming that the rare-earth ions are paramagnetic and
have a non-zero orbital momentum in the ground state and, therefore, a large
magnetic anisotropy, we are able to reproduce the experimentally observed
behavior in equilibrium. The same theory is also able to describe the
experimentally observed critical slowdown of the spin dynamics in the vicinity
of the magnetization compensation temperature, emphasizing the role played by
the orbital momentum in static and ultrafast magnetism of ferrimagnets.",1903.04293v1
2019/3/19,H-T Phase Diagram of Rare-Earth -- Transition Metal Alloy in the Vicinity of the Compensation Point,"Anomalous hysteresis loops of ferrimagnetic amorphous alloys in high magnetic
field and in the vicinity of the compensation temperature have so far been
explained by sample inhomogeneities. We obtain H-T magnetic phase diagram for
ferrimagnetic GdFeCo alloy using a two-sublattice model in the paramagnetic
rare-earth ion approximation and taking into account rare-earth (Gd) magnetic
anisotropy. It is shown that if the magnetic anisotropy of the $f$-sublattice
is larger than that of the $d$-sublattice, the tricritical point can be at
higher temperature than the compensation point. The obtained phase diagram
explains the observed anomalous hysteresis loops as a result of high-field
magnetic phase transition, the order of which changes with temperature. It also
implies that in the vicinity of the magnetic compensation point the shape of
magnetic hysteresis loop is strongly temperature dependent.",1903.07941v1
2019/4/4,Superconductivity-driven magnetization modulation in YBa2Cu3O7-δ /SrTiO3/La0.67Sr0.33MnO3 heterostructures,"Using spin polarized neutron reflectivity experiments, we demonstrate an
unusual proximity behaviour when the superconductor (SC) and the ferromagnet
(FM) are coupled through an insulator (I) in YBa2Cu3O7-{\delta} (SC)/SrTiO3
(I)/La0.67Sr0.33MnO3 (FM) heterostructures. We have observed an unexpected
magnetic modulation at the interface region of the FM below the superconducting
transition temperature. The magnetization of the FM layer at the I/FM interface
was drastically reduced as compared to the magnetization in the rest of the FM
layer. This result indicates that the Cooper pairs tunnel across the insulator
and interact with the local magnetization at the interface region (extending ~
30 {\AA}) of the FM causing modification of the magnetization at the interface.
This unexpected magnetic behavior cannot be explained on the basis of the
existing theoretical models. However, the length scale associated here clearly
suggests the long range proximity effect as a result of tunneling of Cooper
pairs.",1904.02511v1
2019/5/7,Modulation of magnetism via electric field in MgO nanoribbons,"We report on a theoretical study of electromagnetic properties of zigzag
magnesium oxides nanoribbons (Z-MgONRs). We propose that the polar charges and
the spin polarization are the two key factors for edge magnetism. Based on
first-principle calculations, we demonstrate that both O- and Mg-edges are
magnetic and their magnetic moments all can be efficiently modulated via
external electric field.And the edge magnetism is further studied in the
framework of effective tight-binding model, which provides a starting point for
the calculation of one particle Green's function and the determination of
exchange interactions. Utilizing the linear response model, we find that
Z-MgONRs exhibit two kinds of exchange interaction with extremely different
natures. The magnetism in O-edge is strongly localized with ferromagnetic order
while the magnetism in Mg-edge is itinerant with Ruderman-Kittel-Kasuya-Yosida
(RKKY) like interactions. And these two couplings can also be modulated by
electric field, giving rise to the electrical modulations of spin-density-wave
(SDW) and the modulation of Curie temperature in O-edge. All these suggest that
Z-MgONRs are ideal platforms for ME coupling and appealing candidates for
manifold applications.",1905.02328v1
2019/5/17,Extended Magnetic Dome Induced by Low Pressures in Superconducting FeSe$_\mathrm{1\text{-}x}$S$_\mathrm{x}$,"We report muon spin rotation ($\mu$SR) and magnetization measurements under
pressure on Fe$_{1+\delta}$Se$_\mathrm{1\text{-}x}$S$_\mathrm{x}$ with x
$\approx 0.11$.Above $p\approx0.6$ GPa we find microscopic coexistence of
superconductivity with an extended dome of long range magnetic order that spans
a pressure range between previously reported separated magnetic phases. The
magnetism initially competes on an atomic scale with the coexisting
superconductivity leading to a local maximum and minimum of the superconducting
$T_\mathrm{c}(p)$. The maximum of $T_\mathrm{c}$ corresponds to the onset of
magnetism while the minimum coincides with the pressure of strongest
competition. A shift of the maximum of $T_\mathrm{c}(p)$ for a series of single
crystals with x up to 0.14 roughly extrapolates to a putative magnetic and
superconducting state at ambient pressure for x $\geq0.2$.",1905.07164v2
2019/5/29,Extracting the Dynamic Magnetic Contrast in Time-Resolved X-ray Transmission Microscopy,"Using a time-resolved detection scheme in scanning transmission X-ray
microscopy (STXM) we measured element resolved ferromagnetic resonance (FMR) at
microwave frequencies up to 10\,GHz and a spatial resolution down to 20\,nm at
two different synchrotrons. We present different methods to separate the
contribution of the background from the dynamic magnetic contrast based on the
X-ray magnetic circular dichroism (XMCD) effect. The relative phase between the
GHz microwave excitation and the X-ray pulses generated by the synchrotron, as
well as the opening angle of the precession at FMR can be quantified. A
detailed analysis for homogeneous and inhomogeneous magnetic excitations
demonstrates that the dynamic contrast indeed behaves as the usual XMCD effect.
The dynamic magnetic contrast in time-resolved STXM has the potential be a
powerful tool to study the linear and non-linear magnetic excitations in
magnetic micro- and nano-structures with unique spatial-temporal resolution in
combination with element selectivity.",1905.12497v2
2019/6/11,"Skyrmion-electronics: Writing, deleting, reading and processing magnetic skyrmions toward spintronic applications","The field of magnetic skyrmions has been actively investigated across a wide
range of topics during the last decades. In this topical review, we mainly
review and discuss key results and findings in skyrmion research since the
first experimental observation of magnetic skyrmions in 2009. We particularly
focus on the theoretical, computational and experimental findings and advances
that are directly relevant to the spintronic applications based on magnetic
skyrmions, i.e. their writing, deleting, reading and processing driven by
magnetic field, electric current and thermal energy. We then review several
potential applications including information storage, logic computing gates and
non-conventional devices such as neuromorphic computing devices. Finally, we
discuss possible future research directions on magnetic skyrmions, which also
cover rich topics on other topological textures such as antiskyrmions and
bimerons in antiferromagnets and frustrated magnets.",1906.04718v3
2019/6/23,Probing magnetism via spin dynamics in graphene/2D-ferromagnet heterostructures,"The recent discovery of two-dimensional magnetic insulators has generated a
great deal of excitement over their potential for nanoscale manipulation of
spin or magnetism. One intriguing use for these materials is to put them in
contact with graphene, with the goal of making graphene magnetic while
maintaining its unique electronic properties. Such a system could prove useful
in applications such as magnetic memories, or could serve as a host for exotic
states of matter. Proximity to a magnetic insulator will alter the spin
transport properties of graphene, and the strength of this interaction can be
probed with Hanle spin precession experiments. To aid in the analysis of such
experiments, in this work we derive an explicit expression for Hanle spin
precession in graphene interfaced with a ferromagnetic insulator whose
magnetization points perpendicular to the graphene plane. We find that this
interface results in a shifted and asymmetric Hanle response, and we discuss
how this behavior can be used to interpret measurements of spin transport in
these systems.",1906.09568v2
2019/7/12,Extending generalized Debye analysis to long timescale magnetic relaxation,"As the ability to generate magnetic anisotropy in molecular materials
continues to hit new milestones, concerted effort has shifted towards
understanding, and potentially controlling, the mechanisms of magnetic
relaxation across a large time and temperature space. Slow magnetic relaxation
in molecules is highly temperature-, field-, and environment-dependent with the
relevant timescale easily traversing ten orders of magnitude for current
single-molecule magnets (SMM). The prospect of synthetic control over the
nature of (and transition probabilities between) magnetic states make
unraveling the underlying mechanisms an important yet daunting challenge.
Currently, instrumental considerations dictate that the characteristic
relaxation time, $\tau$, is determined by separate methods depending on the
timescale of interest. Static and dynamic probe fields are used for long and
short timescales, respectively. Each method captures a distinct,
non-overlapping time range, and experimental differences lead to the
possibility of fundamentally different meanings for $\tau$ being plotted and
fitted globally as a function of temperature. Herein, we present a method to
generate long-timescale waveforms with standard vibrating sample magnetometry
(VSM) instrumentation, allowing extension of alternating current (AC) magnetic
impedance measurements to SMMs and other superparamagnets with arbitrarily long
relaxation time.",1907.05962v1
2019/7/16,Enhanced Magnetization from Proton Irradiated Bulk van der Waals Magnet CrSiTe3,"Van der Waals (vdWs) crystals have attracted a great deal of scientific
attention due to their interesting physical properties and widespread practical
applications. Among all, CrSiTe3 (CST) is a ferromagnetic semiconductor with
the Curie temperature (TC) of ~32 K. In this letter, we study the magnetic
properties of bulk CST single-crystal upon proton irradiation with the fluence
of 1x1018 protons/cm2. Most significantly, we observed an enhancement (23%) in
the saturation magnetization from 3.9 {\mu}B to 4.8 {\mu}B and is accompanied
by an increase in the coercive field (465-542 Oe) upon proton irradiation.
Temperature-dependent X-band electron paramagnetic resonance measurements show
no additional magnetically active defects/vacancies that are generated upon
proton irradiation. The findings from X-ray photoelectron spectroscopy and
Raman measurements lead us to believe that modification in the spin-lattice
coupling and introduction of disorder could cause enhancement in saturation
magnetization. This work demonstrates that proton irradiation is a feasible
method in modifying the magnetic properties of vdWs crystals, which represents
a significant step forward in designing future spintronic and
magneto-electronic applications.",1907.07222v2
2019/8/1,Chiral Magnetic Josephson junction: a base for low-noise superconducting qubits?,"Superconducting materials with non-centrosymmetric lattices lacking the space
inversion symmetry are known to exhibit a variety of interesting
parity-breaking phenomena, including the anomalous Josephson effect. Here we
consider a Josephson junction consisting of two non-centrosymmetric
superconductors (NCSs) connected by a uniaxial ferromagnet, and demonstrate
that it exhibits a direct analog of the Chiral Magnetic Effect observed in
Dirac and Weyl semimetals. We propose to use this ""Chiral Magnetic Josephson
junction"" (CMJ junction) as an element of a qubit with a Hamiltonian tunable by
the ferromagnet's magnetization. The CMJ junction allows to avoid the use of an
offset magnetic flux in inductively shunted qubits, thus enabling a simpler and
more robust architecture. The resulting""`chiral magnetic qubit"" is protected
from the noise caused by fluctuations in magnetization when the easy axis of
the uniaxial ferromagnet is directed across the junction.",1908.00392v1
2019/8/12,Exchange Bias and Quantum Anomalous Hall Effect in the MnBi2Te4-CrI3 Heterostructure,"The layered antiferromagnetic MnBi2Te4 films have been proposed to be an
intrinsic quantum anomalous Hall (QAH) insulator with a large gap. To realize
this proposal, it is crucial to open a magnetic gap of surface states. However,
recent experiments have observed gapless surface states, indicating the absence
of out-of-plane surface magnetism, and thus the quantized Hall resistance can
only be achieved at the magnetic field above 6 T. In this work, we propose to
induce out-of-plane surface magnetism of MnBi2Te4 films via the magnetic
proximity with magnetic insulator CrI3. Our calculations have revealed a strong
exchange bias ~ 40 meV, originating from the long Cr-eg orbital tails that
hybridize strongly with Te p-orbitals. By stabilizing surface magnetism, the
QAH effect can be realized in the MnBi2Te4/CrI3 heterostructure. Our
calculations also demonstrate the high Chern number QAH state can be achieved
by controlling external electric gates. Thus, the MnBi2Te4/CrI3 heterostructure
provides a promising platform to realize the electrically tunable zero-field
QAH effect.",1908.04322v2
2019/7/31,On the Magnetism of C14 Nb(Fe89.4Al10.6)2 Laves Phase Intermetallic Compound,"C14 Nb(Fe89.4Al10.6)2 Laves phase intermetallic compound was investigated by
DC magnetization (M) measurements performed in the temperature (T) interval of
20 to 175 K,under an applied magnetic field (H) ranging between 50 and 1250 Oe.
Magnetization curves were recorded in the field-cooled (FC) and in the
zero-field-cooled (ZFC) modes. They clearly showed an irreversible character
that vanished at H=1250 Oe. Both magnetization curves exhibited well-defined
peaks around T_N =72.3 K whose positions were H-independent, so they were
identified as the compound's N\'eel temperature. The existence of
irreversibility which decreases with H testify to a re-entrant character of
magnetism in the studied compound. An increase of both MFC and MZFC observed
below TN likely indicates a mixed i.e. ferromagnetic and antiferromagnetic
ground magnetic state of the studied system.",1908.07995v1
2019/8/28,Raman scattering study of lattice and magnetic excitations in CrAs,"We report on the lattice and spin dynamics in the monopnictide CrAs using
polarized Raman scattering. This system exhibits a first-order
magneto-structural phase transition at T_N~ 265 K, below which the magnetic
moments of Cr form an incommensurate double helical magnetic structure while
the unit cell volume abruptly expands. Across the transition, the frequencies
of the fully symmetric Ag phonons strongly renormalize, which along with the
results of first-principle calculations suggest the presence of a sizeable
coupling of the phonons to the magnetic degrees of freedom in this compound. In
addition, we observe two broad modes around 350 and 1700 cm-1 in the magnetic
phase, which we associate with two-magnon Raman scattering. This work provides
one of the few examples of magnetic Raman scattering from a non-collinear
magnet.",1908.10908v2
2019/8/30,"Magnetization reversal, damping properties and magnetic anisotropy of L10-ordered FeNi thin films","L10 ordered magnetic alloys such as FePt, FePd, CoPt and FeNi are well known
for their large magnetocrystalline anisotropy. Among these, L10-FeNi alloy is
economically viable material for magnetic recording media because it does not
contain rare earth and noble elements. In this work, L10-FeNi films with three
different strengths of anisotropy were fabricated by varying the deposition
process in molecular beam epitaxy system. We have investigated the
magnetization reversal along with domain imaging via magneto optic Kerr effect
based microscope. It is found that in all three samples, the magnetization
reversal is happening via domain wall motion. Further ferromagnetic resonance
(FMR) spectroscopy was performed to evaluate the damping constant and magnetic
anisotropy. It was observed that the FeNi sample with moderate strength of
anisotropy exhibits low value of damping constant ~ 4.9X10^-3. In addition to
this, it was found that the films possess a mixture of cubic and uniaxial
anisotropies.",1908.11761v1
2019/9/8,Morphology and magnetic properties of nanocomposite magnetic multilayers {[(Co$_{40}$Fe$_{40}$B$_{20}$)$_{34}$(SiO$_2$)$_{66}$]/[C]}$_{47}$,"We report on the investigation of morphology, magnetic and conductive
properties of the mutilayered nanostructures
[(Co$_{40}$Fe$_{40}$B$_{20}$)$_{34}$(SiO$_2$)$_{66}$]/[C]$_{47}$ consisting of
the contacting magnetic (Co$_{40}$Fe$_{40}$B$_{20}$)$_{34}$(SiO$_2$)$_{66}$
nanocomposite and amorphous semiconductor carbon C layers. It is shown by
Grazing-Incidence Small-Angle X-ray Scattering method that the ordering and the
size of nanoparticles in the magnetic layers do not change profoundly with
increasing of carbon layer thickness. Meanwhile, the electrical conductance and
the magnetic properties are significantly varied: resistance of the samples
changes by four orders of magnitude and superparamagnetic blocking temperature
changes from 15 K to 7 K with the increment of carbon layer thickness $h_c$
from 0.4 nm to 1.8 nm. We assume that the formation of the homogeneous
semiconductor interlayer leads to modification of the metal-insulator growth
process that drives the changes in the magnetic and conductive properties.",1909.03420v1
2019/9/27,Magnetoresistance effects in the metallic antiferromagnet Mn$_2$Au,"In antiferromagnetic spintronics, it is essential to separate the resistance
modifications of purely magnetic origin from other effects generated by current
pulses intended to switch the N\'eel vector. We investigate the
magnetoresistance effects resulting from magnetic field induced reorientations
of the staggered magnetization of epitaxial antiferromagnetic Mn2Au(001) thin
films. The samples were exposed to 60 T magnetic field pulses along different
crystallographic in-plane directions of Mn2Au(001), while their resistance was
measured. For the staggered magnetization aligned via a spin-flop transition
parallel to the easy [110]-direction, an ansiotropic magnetoresistance of -0.15
% was measured. In the case of a forced alignment of the staggered
magnetization parallel to the hard [100]-direction, evidence for a larger
anisotropic magnetoresistance effect was found. Furthermore, transient
resistance reductions of about 1 % were observed, which we associate with the
annihilation of antiferromagnetic domain walls by the magnetic field pulses.",1909.12606v3
2019/9/29,Effect of Ge-substitution on Magnetic Properties in the Itinerant Chiral Magnet MnSi,"We have investigated the effect of Ge-substitution to the magnetic ordering
in the B20 itinerant chiral magnet MnSi prepared by melting and annealing under
ambient pressure. From metallurgical survey, the solubility limit of Ge was
found to be $x=0.144(5)$ with annealing temperature $T_\mathrm{an} = 1073$ K.
Magnetization measurements on MnSi$_{1-x}$Ge$_x$ samples show that the helical
ordering temperature $T_{\mathrm{c}}$ increases rapidly in the low-$x$ range,
whereas it becomes saturated at higher concentration $x>~0.1$. The Ge
substitution also increases both the saturation magnetization $M_\mathrm{s}$
and the critical field to the fully polarized state $H_\mathrm{c2}$. In
contrast to the saturation behavior of $T_\mathrm{c}$, those parameters
increase linearly up to the highest Ge concentration investigated. In the
temperature-magnetic field phase diagram, we found enlargement of the skyrmion
phase region for large $x$ samples. We, furthermore, observed the non-linear
behavior of helical modulation vector $k$ as a function of Ge concentration,
which can be described qualitatively using the mean field approximation.",1909.13246v1
2019/10/3,Homogenization of an elastodynamics system with a strong magnetic field and soft inclusions inducing a viscoelastic effective behavior,"In this paper we study the homogenization of a linear elastodynamics system
in an elastic body with soft inclusions, which is embedded in a highly
oscillating magnetic field. We show two limit behaviors according to the
magnetic field. On the one hand, if the magnetic field has two different
directions on the interface between the hard phase and the soft phase, then the
limit of the displacement in the hard phase is independent of time, so that the
magnetic field induces an effective infinite mass. On the other hand, if the
magnetic field has a constant direction $\xi$ on the interface, then the limit
of the displacement in the hard phase and in the direction $\xi$ is solution to
an elastodynamics equation with a memory mass, a memory stress tensor and
memory external forces depending on the initial conditions, which read as time
convolutions with some kernel. When the magnetic has the same direction $\xi$
in the soft phase with smooth inclusions, we prove that the space-average of
the kernel is regular and that the limit of the overall displacement in the
direction $\xi$ is solution to a viscoelasticity equation.",1910.01328v1
2019/10/11,Magnetic tubules,"Dispersion of tubules made of diacetylenic phospholipids (DC 8,9 PC), in
aqueous colloidal dispersions of magnetic nanoparticles is studied as a
function of the sign of particles surface charges. In every case the
tubule-vesicle transition temperature is decreased by the presence of the
magnetic nanoparticles. Electrophoresis experiments on the tubules in pure
water permits to conclude on a negative apparent surface charge. We study the
magnetic response of the system to a static or stationary rotating field and to
a magnetic field gradient. These experiments reveal an excess or a lack of
magnetic permeability between tubules and the surrounding medium. Electron
microscopy confirms these results showing an electrostatic interaction between
the phospholipidic bilayer and the magnetic particles.",1910.05165v1
2019/10/14,Ultrafast enhancement of ferromagnetic spin exchange induced by ligand-to-metal charge transfer,"Directly modifying spin exchange energies in a magnetic material with light
can enable ultrafast control of its magnetic states. Current approaches rely on
tuning charge hopping amplitudes that mediate exchange by optically exciting
either virtual or real charge-transfer transitions (CT) between magnetic sites.
Here we show that when exchange is mediated by a non-magnetic ligand, it can be
substantially enhanced by optically exciting a real CT transition from the
ligand to magnetic site, introducing lower order virtual hopping contributions.
We demonstrate sub-picosecond enhancement in a superexchange dominated
ferromagnet CrSiTe3 through this mechanism using phase-resolved coherent phonon
spectroscopy. This technique can also be applied in the paramagnetic phase to
disentangle light induced exchange modification from other ultrafast effects
that alter the magnetization. This protocol can potentially be broadly applied
to engineer thermally inaccessible spin Hamiltonians in superexchange dominated
magnets.",1910.06376v1
2019/10/15,Magnetic imaging of antiferromagnetic domain walls,"The control of domain walls or spin textures is crucial for spintronic
applications of antiferromagnets. Despite many efforts, it has been challenging
to directly visualize antiferromagnetic domains or domain walls with nanoscale
resolution, especially in magnetic field. Here, we report magnetic imaging of
domain walls in several uniaxial antiferromagnets, the topological insulator
MnBi$_2$Te$_4$ family and the Dirac semimetal EuMnBi$_2$, using cryogenic
magnetic force microscopy (MFM). Our MFM results reveal higher magnetic
susceptibility or net moments inside the domain walls than in domains. Domain
walls in these antiferromagnets form randomly with strong thermal and magnetic
field dependences. The direct visualization of domain walls and domain
structure in magnetic field will not only facilitate the exploration of
intrinsic phenomena in topological antiferromagnets, but also open a new path
toward control and manipulation of domain walls or spin textures in functional
antiferromagnets.",1910.06488v1
2019/10/20,"Magnetic and transport properties in magnetic topological insulators MnBi2Te4(Bi2Te3)n (n=1,2)","The observation of quantized anomalous Hall conductance in the forced
ferromagnetic state of MnBi2Te4 thin flakes has attracted much attentions.
However, strong magnetic field is needed to fully polarize the magnetic moments
due to the large antiferromagnetic interlayer exchange coupling. Here, we
reported the magnetic and electrical transport properties of the magnetic van
der Waals MnBi2Te4(Bi2Te3)n (n=1,2) single crystals, in which the interlayer
antiferromagnetic exchange coupling is greatly suppressed with the increase of
the separation layers Bi2Te3. MnBi4Te7 and MnBi6Te10 show weak
antiferromagnetic transition at 12.3 and 10.5 K, respectively. The
ferromagnetic hysteresis was observed at low temperature for both of the
crystals, which is quite crucial for realizing the quantum anomalous Hall
effect without external magnetic field. Our work indicates that
MnBi2Te4(Bi2Te3)n (n=1,2) provide ideal platforms to investigate the rich
topological phases with going to their 2D limits.",1910.08912v1
2019/10/23,Magnetic Proximity Effect in 2D Ferromagnetic CrBr3/Graphene van der Waals Heterostructures,"Two-dimensional (2D) van der Waals heterostructures serve as a promising
platform to exploit various physical phenomena in a diverse range of novel
spintronic device applications. The efficient spin injection is the
prerequisite for these devices. The recent discovery of magnetic 2D materials
leads to the possibility of fully 2D van der Waals spintronics devices by
implementing spin injection through magnetic proximity effect (MPE). Here, we
report the investigation of magnetic proximity effect in 2D CrBr3/graphene van
der Waals heterostructures, which is probed by Zeeman spin Hall effect through
non-local measurements. Zeeman splitting field estimation demonstrates a
significant magnetic proximity exchange field even in a low magnetic field.
Furthermore, the observed anomalous longitudinal resistance changes at the
Dirac point R_(XX,D)with increasing magnetic field at {\nu} = 0 may attribute
to the MPE induced new ground state phases. This MPE revealed in our
CrBr3/graphene van der Waals heterostructures therefore provides a solid
physics basis and key functionality for next generation 2D spin logic and
memory devices.",1910.10411v1
2019/10/23,Computational screening of Fe-Ta hard magnetic phases,"In this work we perform a systematic calculation of the Fe-Ta phase diagram
to discover novel hard magnetic phases. By using structure prediction methods
based on evolutionary algorithms, we identify two new energetically stable
magnetic structures: a tetragonal Fe$_3$Ta (space group 122) and cubic Fe$_5$Ta
(space group 216) binary phases. The tetragonal structure is estimated to have
both high saturation magnetization ($\mu_0$M$_s$=1.14 T) and magnetocrystalline
anisotropy (K$_1$=2.17 MJ/m$^3$) suitable for permanent magnet applications.
The high-throughput screening of magneto-crystalline anisotropy also reveals
two low energy metastable hard magnetic phases: Fe$_5$Ta$_2$ (space group 156)
and Fe$_{6}$Ta (space group 194), that may exhibit intrinsic magnetic
properties comparable to SmCo$_5$ and Nd$_2$Fe$_{14}$B, respectively.",1910.10531v1
2019/11/8,Skyrmions at Vanishingly Small Dzyaloshinskii-Moriya Interaction or Zero Magnetic Field,"By introducing biquadratic together with usual bilinear ferromagnetic nearest
neighbor exchange interaction in a square lattice, we find that the energy of
the spin-wave mode is minimized at a finite wavevector for a vanishingly small
Dzyaloshinskii-Moriya interaction (DMI), supporting a ground state with
spin-spiral structure whose pitch length is unusually short as found in some of
the experiments. Apart from reproducing the magnetic structures that can be
obtained in a canonical model with nearest neighbor exchange interaction only,
a numerical simulation of this model with further introduction of magnetic
anisotropy and magnetic field predicts many other magnetic structures some of
which are already observed in the experiments. Amongst many observed
structures, nanoscale skyrmion even at vanishingly small DMI is found for the
first time in a model. The model provides the nanoscale skyrmions of unit
topological charge at zero magnetic field as well. We obtain phase diagrams for
all the magnetic structures predicted in the model.",1911.03171v3
2019/11/15,Hybrid Magnetoacoustic Metamaterials for Ultrasound Control,"We propose a class of metamaterials in which propagation of acoustic waves is
controlled magnetically through magnetoelastic coupling. The metamaterials are
formed by a periodic array of thin magnetic layers ('resonators') embedded in a
non-magnetic matrix. Acoustic waves carrying energy through the structure
hybridize with the magnetic modes of the resonators ('Fano resonance'). This
leads to a rich set of effects, enhanced by Bragg scattering and being most
pronounced when the magnetic resonance frequency is close to or lies within
acoustic band gaps. The acoustic reflection from the structure exhibits
magnetically induced transparency and Borrmann effect. Our analysis shows that
the combined effect of the Bragg scattering and Fano resonance may overcome the
magnetic damping ubiquitous in realistic systems. This paves a route towards
application of such structures in wave computing and signal processing",1911.06774v1
2019/11/18,Theoretical condition for switching the magnetization in a perpendicularly magnetized ferromagnet via the spin Hall effect,"A theoretical formula is derived for the threshold current to switch a
perpendicular magnetization in a ferromagnet by the spin Hall effect. The
numerical simulation of the Landau-Lifshitz-Gilbert equation indicates that
magnetization switching is achieved when the steady-state solution of the
magnetization in the presence of the current is outside an energetically
unstable region. Based on the numerical result, an analytical theory deriving
the threshold current is developed by focusing on the first-order perturbation
to the unstable state. The analytical formula clarifies that the magnitude of
the magnetic field applied to the current direction should be larger than 15\%
of the perpendicular magnetic anisotropy field, and the current is less than
the derived threshold value.",1911.07961v1
2019/11/21,Coupled spin-charge dynamics in magnetic van der Waals heterostructures,"We present a phenomenological theory for coupled spin-charge dynamics in
magnetic van der Waals heterostructures. The system studied consists of a
layered antiferromagnet inserted into a capacitive vdW heterostructure. It has
been recently demonstrated that charge doping in such layered antiferromagnets
can modulate the strength, and even the sign, of exchange coupling between the
layer magnetizations. This provides a mechanism for electrically generating
magnetization dynamics. The central result we predict here is that the
magnetization dynamics reciprocally results in inducing charge dynamics. Such
dynamics makes magnetic van der Waals heterostructures interesting candidates
for spintronics applications. To this end, we also show that these systems can
be used to convert sub-THz radiation induced magnetization dynamics into
electrical signals.",1911.09688v2
2019/11/26,Magnetic domain wall motion in SrRuO$_3$ thin films,"Influence of substrate miscut on magnetization dynamics in SrRuO$_3$ (SRO)
thin films was studied. Two films were grown on SrTiO$_3$ substrates with high
($\sim1^{\circ}$) and low ($\sim0.1^{\circ}$) miscut angles, respectively. As
expected, high miscut angle leads to suppression of multi-variant growth. By
means of SQUID magnetometry, comparable relaxation effects were observed in
both the multi-variant and the nearly single-variant sample. Differences in the
magnetization reversal process were revealed by magnetic force microscopy. It
showed that the multi-variant growth leads to higher density of defects acting
as pinning or nucleation sites for magnetic domains, which consequently results
in deterioration of magnetic properties. It was demonstrated that the use of
high miscut substrate is important for fabrication of high quality SRO thin
films with low density of crystallographic defects and excellent magnetic
properties.",1911.11655v1
2019/12/5,Metamagnetic transitions and magnetoelectric responses in a chiral polar helimagnet Ni$_2$InSbO$_6$,"Magnetic-field effect on the magnetic and electric properties in a chiral
polar ordered corundum Ni$_2$InSbO$_6$ has been investigated. Single-crystal
soft x-ray and neutron diffraction measurements confirm long-wavelength
magnetic modulation. The modulation direction tends to align along the magnetic
field applied perpendicular to the polar axis, suggesting that the nearly
proper-screw type helicoid should be formed below 77\,K. The application of a
high magnetic field causes a metamagnetic transition. In a magnetic field
applied perpendicular to the polar axis, a helix-to-canted antiferromagnetic
transition takes place through the intermediate soliton lattice type state. On
the other hand, a magnetic field applied along the polar axis induces a
first-order metamagnetic transition. These metamagnetic transitions accompany a
change in the electric polarization along the polar axis.",1912.02363v1
2019/12/24,First-Principles study of an S = 1 quasi-1D quantum molecular magnetic material,"We use density functional theory to study the structural, magnetic and
electronic structure of the organo-metallic quantum magnet
$\mathrm{NiCl_2-4SC(NH_2)_2}$ (DTN). Recent work has demonstrated the quasi-1D
nature of the molecular crystal and its quantum phase transitions at low
temperatures. This includes a magneto-electric coupling and, when doped with
Br, the presence of an exotic Bose-glass state. We systematically show that, by
using the generalized gradient approximation (GGA) with inclusion of a van der
Waals term to account for weak inter-molecular forces and by introducing a
Hubbard $U$ term to the total energy, our calculations reproduce the magnetic
anisotropy, the inter-molecular exchange coupling strength and the
magneto-electric effect in DTN, which were observed in previous experiments.
Further analysis into the electronic structure gives insight into the
underlying magnetic interactions, including what mechanisms may be causing the
ME effect. Using this computationally efficient model, we predict what effect
applying an electric field might have on the magnetic properties of this
quantum magnet.",1912.11457v2
2020/1/7,Growth-sequence-dependent interface magnetism of SrIrO$_3$ - La$_{0.7}$Sr$_{0.3}$MnO$_3$ bilayers,"Bilayers of the oxide 3d ferromagnet La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ (LSMO) and
the 5d paramagnet SrIrO$_{3}$ (SIO) with large spin-orbit coupling (SOC) have
been investigated regarding the impact of interfacial SOC on magnetic order.
For the growth sequence of LSMO on SIO, ferromagnetism is strongly altered and
large out-of-plane-canted anisotropy associated with lacking magnetic
saturation up to 4 T has been observed. Thin bilayer films have been grown
coherently in both growth sequences on SrTiO$_3$ (001) by pulsed laser
deposition and structurally characterized by scanning transmission electron
microscopy (STEM) and x-ray diffraction (XRD). Measurements of magnetization
and field-dependent Mn L$_{2,3}$ edge x-ray magnetic circular dichroism (XMCD)
reveal changes of LSMO magnetic order which are strong in LSMO on SIO and weak
in LSMO underneath of SIO. We attribute the impact of the growth sequence to
the interfacial lattice structure/symmetry which is known to influence the
interfacial magnetic coupling.",2001.02083v1
2020/1/25,Strain engineered domain structure and their relaxation in perpendicularly magnetized Co/Pt deposited on flexible polyimide,"The demand of fast and power efficient spintronics devices with flexibility
requires additional energy for magnetization manipulation. Stress/and strain
have shown their potentials for tuning magnetic properties to the desired
level. Here, we report a systematic study for the effect of both tensile and
compressive stresses on the magnetic anisotropy (MA). Further the effect of
stress on the domain structure and magnetization relaxation mechanism in a
perpendicularly magnetized Co/Pt film has been studied. It is observed that a
minimal in-plane tensile strain has increased the coercivity of the film by
38$\%$ of its initial value, while a very small change of coercivity has been
found under compressive strain. The size of ferromagnetic domains decreases
under tensile strain, while no change is observed under the compressive strain.
Magnetization relxation measured at sub-coercive fields yields longer
relaxation time in the strained state.",2001.09290v1
2020/1/14,Low power switching of magnetization using enhanced magnetic anisotropy with short-voltage-pulse application,"A low power magnetization switching scheme based on the voltage control of
magnetic anisotropy (VCMA) is proposed. In contrast to the conventional
switching scheme using VCMA, where the magnetic anisotropy is eliminated during
the voltage pulse, the magnetic anisotropy is enhanced to induce precession
around the axis close to the easy axis. After turning off the voltage
proximately at a half of precession period, the magnetization relaxes to the
opposite equilibrium direction. We perform numerical simulations and show that
the pulse duration of the proposed switching scheme is as short as a few tens
of pico seconds. Such a short pulse duration is beneficial for low power
consumption because of the reduction of energy loss by Joule heating.",2001.11088v1
2020/2/8,Higher-order exceptional points in all-magnetic structures,"Magnetometers with exceptional sensitivity are highly demanded in solving a
variety of physical and engineering problems, such as measuring Earth's weak
magnetic fields and prospecting mineral deposits and geological structures. It
has been shown that the non-Hermitian degeneracy at exceptional points (EPs)
can provide a new route for that purpose, because of the nonlinear response to
external perturbations. One recent work [H. Yang et al., Phys. Rev. Lett. 121,
197201 (2018)] has made the first step to realize the second-order magnonic EP
in ferromangetic bilayers respecting the parity-time symmetry. In this paper,
we generalize the idea to higher-order cases by considering ferromagnetic
trilayers consisting of a gain, a neutral, and a (balanced-)loss layer. We
observe both second- and third-order magnonic EPs by tuning the interlayer
coupling strength, the external magnetic field, and the gain-loss parameter. We
show that the magnetic sensitivity can be enhanced by $3$ orders of magnitude
comparing to the conventional magnetic tunneling junction based sensors. Our
results pave the way for studying high-order EPs in purely magnetic system and
for designing magnetic sensors with ultrahigh sensitivity.",2002.03085v1
2020/2/18,Magnetic phase diagram and magneto-elastic coupling of NiTiO3,"We report high-resolution dilatometry on high-quality single crystals of
NiTiO3 grown by means of the optical floating-zone technique. The anisotropic
magnetic phase diagram is constructed from thermal expansion and
magnetostriction studies up to B=15T and magnetization studies in static (15T)
and pulsed (60T) magnetic fields. Our data allow to quantitatively study
magneto-elastic coupling and to determine uniaxial pressure dependencies. While
the entropy changes are found to be of magnetic nature, Gr\""{u}neisen analysis
implies only one relevant energy scale in the whole low-temperature regime.
Thereby, our data suggest that the observed structural changes due to
magneto-elastic coupling and previously reported magnetodielectric coupling[1]
are driven by the same $magnetic$ degrees of freedom that lead to long-range
magnetic order in NiTiO3, which in turn, establishes a linear magnetodielectric
coupling in this compound.",2002.07447v1
2020/2/20,Effects of biaxial strain on the impurity-induced magnetism in P-doped graphene and N-doped silicene: A first principles study,"The effects of biaxial strain on the impurity-induced magnetism in P-doped
graphene (P-graphene) and N-doped silicene (N-silicene) are studied by means of
spin-polarized density functional calculations, using the supercell approach.
The calculations were performed for three different supercell sizes $4\times
4$, $5\times 5$, and $6\times 6$, in order to simulate three different dopant
concentrations 3.1, 2.0 and 1.4 %, respectively. For both systems, the
calculated magnetic moment is 1.0 $\mu_B$ per impurity atom for the three
studied concentrations. From the analysis of the electronic structure and the
total energy as a function of the magnetization, we show that a Stoner-type
model describing the electronic instability of the narrow impurity band
accounts for the origin of $sp$-magnetism in P-graphene and N-silicene. Under
biaxial strain the impurity band dispersion increases and the magnetic moment
gradually decreases, with the consequent collapse of the magnetization at
moderate strain values. Thus, we found that biaxial strain induces a magnetic
quantum phase transition in P-graphene and N-silicene.",2002.08998v1
2020/2/24,Miniature capacitive Faraday force magnetometer for magnetization measurements at low temperatures and high magnetic fields,"A Faraday force magnetometer is presented for measurements of magnetization
at temperatures down to 100~mK and in magnetic fields up to 14~T. The specimen
is mounted on a flexible cantilever forming a force-sensing capacitor in
combination with a fixed back plate. Two different cantilever designs are
presented. A torsion resistant cantilever allows to measure magnetization of
highly anisotropic single crystal samples. Measurements of the metal organic
quantum magnets (C$_5$H$_{12}$N)$_2$CuBr$_4$ (BPCB) and NiCl$_2$$\cdot$4
SC(NH$_2$)$_2$ (DTN) demonstrate the device's capabilities. Routinely, a
specimen's magnetic moment is measured with a resolution better than $10^{-7}$
A$\,$m$^2$ ($10^{-4}$ emu). The device in miniaturized to fit is almost any
cryostat.",2002.10168v1
2020/3/2,Tailored flux pinning in superconductor/ferromagnet multilayers with engineered magnetic domain morphology from stripes to skyrmions,"Superconductor/Ferromagnet (S/F) hybrid systems show interesting
magneto-transport behaviors that result from the transfer of properties between
both constituents. For instance, magnetic memory can be transferred from the F
into the S through the pinning of superconducting vortices by the ferromagnetic
textures. The ability to tailor this type of induced behavior is important to
broaden its range of applications. Here we show that engineering the F
magnetization reversal allows tuning the strength of the vortex pinning (and
memory) effects, as well as the field range in which they appear. This is done
by using magnetic multilayers in which Co thin films are combined with
different heavy metals (Ru, Ir, Pt). By choosing the materials, thicknesses,
and stacking order of the layers, we can design the characteristic domain size
and morphology, from out-of-plane magnetized stripe domains to much smaller
magnetic skyrmions. These changes strongly affect the magneto-transport
properties. The underlying mechanisms are identified by comparing the
experimental results to a magnetic pinning model.",2003.01065v1
2020/3/7,Field-selective classical spin liquid and magnetization plateaus on kagome lattice,"We obtain a classical spin liquid (CSL) phase by applying a magnetic field in
$J_1$-$J_2$-$J_3$ Ising model on a kagome lattice. As we proved in the previous
study [Phys. Rev. Lett. {\bf 119}, 077207 (2017)], this model realizes one
species of CSL, the hexamer CSL, at zero magnetic field, which consists of
macroscopically degenerate spin configurations with mixed total magnetization,
$M$. The magnetic field selects its subset, which can be mapped to a trimer
covering of the dual lattice, and forms a magnetization plateau of $M=1/9$. In
addition to this CSL, we find two other magnetization plateaus at $M=5/9$ and
$17/27$, which are ascribed to the ""multimer"" superstructures on a dual
lattice.",2003.03594v5
2020/4/24,Formation mechanisms of magnetic bubbles in an M-type hexaferrite: the role of chirality reversals at domain walls,"We examined the formation mechanisms of magnetic bubbles in an M-type
hexaferrite via Lorentz microscopy. When magnetic fields were perpendicularly
applied to a thin sample of BaFe$_{12-x-0.05}$Sc$_x$Mg$_{0.05}$O$_{19}$ ($x =
1.6$), Bloch lines, which were identified as reversals of domain-wall
chirality, appeared, and magnetic bubbles were formed when the magnetic stripes
were pinched off at these Bloch lines. The number of Bloch lines increased with
the amount of Sc in BaFe$_{12-x-0.05}$Sc$_x$Mg$_{0.05}$O$_{19}$ probably
because of the reduction in magnetic anisotropy. A Lorentz microscopic
observation revealed that Bloch lines with high magnetostatic energy may play
an important role in the formation of magnetic bubbles.",2004.11593v1
2020/4/24,Electronic structure and magnetic exchange interactions of Cr-based van der Waals ferromagnets. A comparative study between CrBr3 and Cr2Ge2Te6,"Low dimensional magnetism has been powerfully boosted as a promising
candidate for numerous applications. The stability of the long-range magnetic
order is directly dependent on the electronic structure and the relative
strength of the competing magnetic exchange constants. Here, we report a
comparative pressure-dependent theoretical and experimental study of the
electronic structure and exchange interactions of two-dimensional ferromagnets
CrBr3 and Cr2Ge2Te6 . While CrBr3 is found to be a Mott-Hubbard-like insulator,
Cr2Ge2Te6 shows a charge-transfer character due to the broader character of the
Te 5p bands at the Fermi level. This different electronic behaviour is
responsible of the robust insulating state of CrBr3 , in which the magnetic
exchange constants evolve monotonically with pressure, and the proximity to a
metal-insulator transition predicted for Cr2Ge2Te6 , which causes a
non-monotonic evolution of its magnetic ordering temperature. We provide a
microscopic understanding for the pressure evolution of the magnetic properties
of the two systems.",2004.11789v1
2020/4/28,"Current-Induced Dynamics of Chiral Magnetic Structures: Creation, Motion, and Applications","Magnetic textures can be manipulated by electric currents via the mechanisms
of spin-transfer and spin-orbit-torques. We review how these torques can be
exploited to create chiral magnetic textures in magnets with broken inversion
symmetries, including domain walls and skyrmions. These chiral textures can
also be moved by (electric) currents and obey very rich dynamics. For example,
magnetic domain walls feature the famous Walker breakdown, and magnetic whirls
are subject to the skyrmion Hall effect, which is rooted in their real-space
topology. These properties led to a variety of potential novel applications
which we briefly overview.",2004.13535v2
2020/4/28,Chiral symmetry breaking for deterministic switching of perpendicular magnetization by spin-orbit torque,"Symmetry breaking is a characteristic to determine which branch of a
bifurcation system follows upon crossing a critical point. Specifically, in
spin-orbit torque (SOT) devices, a fundamental question arises: how to break
the symmetry of the perpendicular magnetic moment by the in-plane spin
polarization? Here, we show that the chiral symmetry breaking by the DMI can
induce the deterministic SOT switching of the perpendicular magnetization. By
introducing a gradient of saturation magnetization or magnetic anisotropy,
non-collinear spin textures are formed by the gradient of effective SOT
strength, and thus the chiral symmetry of the SOT-induced spin textures is
broken by the DMI, resulting in the deterministic magnetization switching. We
introduce a strategy to induce an out-of-plane (z) gradient of magnetic
properties, as a practical solution for the wafer-scale manufacture of SOT
devices.",2004.13872v1
2020/5/5,"Magnetic hexamers interacting in layers in the (Na,K)$_2$Cu$_3$O(SO$_4)_3$ minerals","Magnetic properties and underlying magnetic models of the synthetic
A$_2$Cu$_3$O(SO$_4)_3$ fedotovite (A = K) and puninite (A = Na) minerals, as
well as the mixed euchlorine-type NaKCu$_3$O(SO$_4)_3$ are reported. We show
that all these compounds contain magnetic Cu$_6$ hexamer units, which at
temperatures below about 100 K act as single spin-1 entities. Weak interactions
between these magnetic molecules lead to long-range order below $T_N$ = 3.4 K
(A = Na), 4.7 K (A = NaK), and about 3.0 K (A = K). The formation of the
magnetic order is elucidated by ab initio calculations that reveal
two-dimensional inter-hexamer interactions within crystallographic $bc$ planes.
This model indicates the presence of a weakly distorted square lattice of $S=1$
magnetic ions and challenges the earlier description of the
A$_2$Cu$_3$O(SO$_4)_3$ minerals in terms of Haldane spin chains.",2005.02028v2
2020/5/7,Structural and magnetic behavior of Cr$_2$Co$_{(1-x)}$Cr$_x$Al inverse Heusler alloys,"We report the structural and magnetic behavior of single phase inverse
Heusler alloys Cr$_2$Co$_{(1-x)}$Cr$_x$Al ($x = $ 0, 0.2, 0.4) using x-ray
diffraction (XRD), Raman spectroscopy, isothermal magnetization, and magnetic
susceptibility measurements. Interestingly, the Rietveld refinement of XRD data
with the space group I$\bar{4}m2$ reveal a tetragonal distortion with c/a ratio
around 1.38 in these inverse Heusler structures. The bulk compositions have
been confirmed by energy dispersive x-ray spectroscopy measurements. The active
Raman mode F$_{2g}$ is observed at 320~cm$^{-1}$, which confirms the X-type
Heusler structure as the A2 and B2 type structures are known to be not Raman
active. The area of F$_{2g}$ mode decreases with Cr concentration, which
indicate the origin of this mode due to Co vibrations. The isothermal
magnetization data confirm the magnetic moment close to zero ($\le$0.02
$\mu_B/f.u.$) at $\approx$70~kOe and negligible coercive field suggest the
fully compensated ferrimagnetic nature of these samples. The susceptibility
behavior indicates irreversibility between zero-field and field-cooled curves
and complex magnetic interactions at low temperatures.",2005.03528v1
2020/6/6,Proximate Kitaev system for an intermediate magnetic phase in in-plane magnetic fields,"Motivated by the magnetic phase transition of a proximate Kitaev system
$\alpha$-RuCl$_3$ in the presence of a magnetic field, we study the simplest
but essential quantum spin model with the ferromagnetic nearest neighboring
(NN) Kitaev interaction and additional antiferromagnetic third NN Heisenberg
interaction. Employing both exact diagonalization and density matrix
renormalization group methods, we demonstrate that the model shows the magnetic
phase transition from the zigzag order phase to the spin polarized phase
through an intermediate phase in both cases when an in-plane magnetic field is
applied perpendicular to the NN bond direction and when an out-of-plane field
is applied, in good agreement with experimental observations. Furthermore, we
verify that additional symmetric off-diagonal $\Gamma$ interaction and
ferromagnetic Heisenberg interaction between NN spins can both suppress the
intermediate phase with the in-plane field. Our result gives important clues on
determining relevant interactions in the field-induced magnetic phase
transition of proximate Kiteav systems.",2006.03778v2
2020/6/7,Changes of Magnetism in a Magnetic Insulator due to Proximity to a Topological Insulator,"This letter reports the modification of magnetism in a magnetic insulator
Y3Fe5O12 thin film by topological surface states (TSS) in an adjacent
topological insulator Bi2Se3 thin film. Ferromagnetic resonance measurements
show that the TSS in Bi2Se3 produces a perpendicular magnetic anisotropy,
results in a decrease in the gyromagnetic ratio, and enhances the damping in
Y3Fe5O12. Such TSS-induced changes become more pronounced as the temperature
decreases from 300 K to 50 K. These results suggest a completely new approach
for control of magnetism in magnetic thin films.",2006.04035v1
2020/6/29,Domain switching and exchange bias control by electric field in multiferroic conical magnet Mn$_2$GeO$_4$,"The electric field effect on magnetism was examined in the multiferroic
conical magnet Mn$_2$GeO$_4$, which shows a strong coupling between
ferromagnetic and ferroelectric order parameters. The systematic evaluation of
the electric polarization in the multiferroic phase below 5.5 K under various
field cooling conditions reveals that small magnetic fields of 0.1 T
significantly reduce the required electric fields needed to reach saturation.
By applying electric fields during magnetic field dependent hysteresis
measurements of magnetization M and polarization P an electrically controllable
exchange bias was observed, a phenomenon exceedingly rare in single phase
multiferroics. Furthermore, non-reversible electric switching of P and M
domains was achieved under specific magnetic field conditions.",2006.16080v1
2020/7/4,Putative quantum critical point in the itinerant magnet ZrFe$_4$Si$_2$ with a frustrated quasi-one-dimensional structure,"The Fe sublattice in the compound ZrFe$_4$Si$_2$ features geometrical
frustration and quasi-one-dimensionality. We therefore investigated the
magnetic behavior in ZrFe$_4$Si$_2$ and its evolution upon substituting Ge for
Si and under the application of hydrostatic pressure using structural,
magnetic, thermodynamic, and electrical-transport probes. Magnetic measurements
reveal that ZrFe$_4$Si$_2$ holds paramagnetic Fe moments with an effective
moment $\mu_{\rm eff}= 2.18~\mu_{B}$. At low temperatures the compound shows a
weak short-range magnetic order below 6 K. Our studies demonstrate that
substituting Ge for Si increases the unit-cell volume and stabilizes the
short-range order into a long-range spin-density wave type magnetic order. On
the other hand, hydrostatic pressure studies using electrical-resistivity
measurements on ZrFe$_4$(Si$_{0.88}$Ge$_{0.12}$)$_2$ indicate a continuous
suppression of the magnetic ordering upon increasing pressure. Therefore, our
combined chemical substitution and hydrostatic pressure studies suggest the
existence of a lattice-volume-controlled quantum critical point in
ZrFe$_4$Si$_2$.",2007.02129v2
2020/8/4,Multiple magnetic ordering phenomena in multiferroic o-HoMnO3,"Orthorhombic HoMnO3 is a multiferroic in which Mn antiferromagnetic order
induces ferroelectricity. A second transition occurs within the multiferroic
phase, in which a strong enhancement of the ferroelectric polarization occurs
concomitantly to antiferromagnetic ordering of Ho 4f magnetic moments. Using
the element selectivity of resonant X-ray diffraction, we study the magnetic
order of the Mn 3d and Ho 4f moments. We explicitly show that the Mn magnetic
order is affected by the Ho 4f magnetic ordering transition. Based on the
azimuthal dependence of the (0 q 0) and (0 1-q 0) magnetic reflections, we
suggest that the Ho 4f order is similar to that previously observed for Tb 4f
in TbMnO3, which resembles an ac-cycloid. This is unlike the Mn order, which
has already been shown to be different for the two materials. Using
non-resonant diffraction, we show that the magnetically-induced ferroelectric
lattice distortion is unaffected by the Ho ordering, suggesting a mechanism
through which the Ho order affects polarization without affecting the lattice
in the same manner as the Mn order.",2008.01383v1
2020/8/12,Prediction on Properties of Rare-earth 2-17-X Magnets Ce2Fe17-xCoxCN : A Combined Machine-learning and Ab-initio Study,"We employ a combination of machine learning and first-principles calculations
to predict magnetic properties of rare-earth lean magnets. For this purpose,
based on training set constructed out of experimental data, the machine is
trained to make predictions on magnetic transition temperature (Tc), largeness
of saturation magnetization ({\mu}0Ms), and nature of the magnetocrystalline
anisotropy (Ku). Subsequently, the quantitative values of {\mu}0Ms and Ku of
the yet-to-be synthesized compounds, screened by machine learning, are
calculated by first-principles density functional theory. The applicability of
the proposed technique of combined machine learning and first-principles
calculations is demonstrated on 2-17-X magnets, Ce2Fe17-xCoxCN. Further to this
study, we explore stability of the proposed compounds by calculating vacancy
formation energy of small atom interstitials (N/C). Our study indicates a
number of compounds in the proposed family, offers the possibility to become
solution of cheap, and efficient permanent magnet.",2008.05125v1
2020/9/1,Great enhancement of Curie temperature and magnetic anisotropy in two-dimensional van der Waals magnetic semiconductor heterostructures,"In two-dimensional (2D) magnetic systems, large magnetic anisotropy is needed
to stabilize the magnetic order according to Mermin-Wagner theorem. Based on
density functional theory (DFT) calculations, we propose that the magnetic
anisotropic energy (MAE) of 2D ferromagnetic (FM) semiconductors can be
strongly enhanced in van der Waals heterostructures by attaching a nonmagnetic
semiconductor monolayer with large spin-orbit coupling. We studied
Cr2Ge2Te6/PtSe2 bilayer heterostructures, where each layer has been realized in
recent experiments. The DFT calculations show that the MAE of Cr2Ge2Te6/PtSe2
is enhanced by 70%, and the Curie temperature TC is increased far beyond room
temperature. A model Hamiltonian is suggested to analyze the DFT results,
showing that both the Dzyaloshinskii-Moriya interaction and the single-ion
anisotropy contribute to the enhancement of the MAE. Based on the superexchange
picture, we find that the decreased energy difference between 3d orbitals of Cr
and 5p orbitals of Te contributes partially to the increase of TC. Our present
work indicates a promising way to enhance the MAE and TC by constructing van
der Waals semiconductor heterostructures, which will inspire further studies on
the 2D magnetic semiconductor systems.",2009.00317v1
2020/9/24,Phase diagram of multi-layer ferromagnet system with dipole-dipole interaction,"We investigate various magnetic configurations caused by the dipole-dipole
interaction (DDI) in the thin-film magnet with the perpendicular anisotropy
under the open boundary conditions. Two different approaches are simulated: one
starts from a random magnetic configuration and decreases temperatures
step-wisely; the other starts from the saturated out-of-plane ferromagnetic
state to evaluate its metastability. As typical patterns of magnetic
configuration, five typical configurations are found: an out-of-plane
ferromagnetic, in-plane ferromagnetic, vortex, multi-domain, and canted
multi-domain states. Notably, the canted multi-domain forms a concentric
magnetic-domain-pattern with an in-plane vortex structure, resulting from the
open boundary conditions. Concerning to the coercivity, a comparison of the
magnetic configurations in both processes reveals that the out-of-plane
ferromagnetic state exhibits metastability in the multi-domain state, while not
in the vortex state. We also confirm that the so-called Neel-cap
magnetic-domain-wall structure, which is originally discussed in the in-plane
anisotropy system, appears at the multi-domain state.",2009.11574v1
2020/9/24,Magnetic anisotropy and exchange paths for octa- and tetrahedrally coordinated Mn$^{2+}$ ions in the honeycomb multiferroic Mn$_2$Mo$_3$O$_8$,"We investigated the static and dynamic magnetic properties of the polar
ferrimagnet Mn$_2$Mo$_3$O$_8$ in three magnetically ordered phases via
magnetization, magnetic torque, and THz absorption spectroscopy measurements.
The observed magnetic field dependence of the spin-wave resonances, including
Brillouin zone-center and zone-boundary excitations, magnetization, and torque,
are well described by an extended two-sublattice antiferromagnetic classical
mean-field model. In this orbitally quenched system, the competing weak
easy-plane and easy-axis single-ion anisotropies of the two crystallographic
sites are determined from the model and assigned to the tetra- and octahedral
sites, respectively, by ab initio calculations.",2009.11683v1
2020/9/25,Gadolinium as a single atom catalyst in a single molecule magnet,"Endohedral fullerenes are perfect nanolaboratories for the study of
magnetism. The substitution of a diamagnetic scandium atom in Dy2ScN@C80 with
gadolinium decreases the stability of a given magnetization and demonstrates Gd
to act as a single atom catalyst that accelerates the reaching of thermal
equilibrium. X-ray magnetic circular dichroism at the M4,5 edges of Gd and Dy
shows that the Gd magnetic moment follows the sum of the external and the
dipolar magnetic field of the two Dy ions and compared to Dy2ScN@C80 a lower
exchange barrier is found between the ferromagnetic and the antiferromagnetic
Dy configuration. The Arrhenius equilibration barrier as obtained from
superconducting quantum interference device magnetometry is more than one order
of magnitude larger, though a much smaller prefactor imposes faster
equilibration in Dy2GdN@C80. This sheds light on the importance of the angular
momentum balance in magnetic relaxation.",2009.12259v1
2020/10/1,"Anisotropic spin distribution and perpendicular magnetic anisotropy in the layered ferromagnetic semiconductor (Ba,K)(Zn,Mn)$_{2}$As$_{2}$","Perpendicular magnetic anisotropy of the new ferromagnetic semiconductor
(Ba,K)(Zn,Mn)$_{2}$As$_{2}$ is studied by angle-dependent x-ray magnetic
circular dichroism measurements. The large magnetic anisotropy with the
anisotropy field of 0.85 T is deduced by fitting the Stoner-Wohlfarth model to
the magnetic-field-angle dependence of the projected magnetic moment.
Transverse XMCD spectra highlights the anisotropic distribution of Mn 3$d$
electrons, where the $d_{xz}$ and $d_{yz}$ orbitals are less populated than the
$d_{xy}$ state because of the $D_{2d}$ splitting arising from the elongated
MnAs$_{4}$ tetrahedra. It is suggested that the magnetic anisotropy originates
from the degeneracy lifting of $p$-$d_{xz}$, $d_{yz}$ hybridized states at the
Fermi level and resulting energy gain due to spin-orbit coupling when spins are
aligned along the $z$ direction.",2010.00158v1
2020/10/2,Synthetic chiral magnets promoted by the Dzyaloshinskii-Moriya interaction,"The ability to engineer the interactions in assemblies of nanoscale magnets
is central to the development of artificial spin systems and spintronic
technologies. Following the emergence of the Dzyaloshinskii-Moriya interaction
(DMI) in thin film magnetism, new routes have been opened to couple the
nanomagnets via strong chiral interactions, which is complementary to the
established dipolar and exchange coupling mechanisms. In this Perspective, we
review recent progress in the engineering of synthetic magnets coupled by the
interlayer and intralayer DMI. We show how multilayer chiral magnetic
structures and two-dimensional synthetic antiferromagnets, skyrmions, and
artificial spin systems can be realized by simultaneous control of the DMI and
magnetic anisotropy. In addition, we show that, with the combination of DMI and
current-induced spin-orbit torques, field-free switching of synthetic magnetic
elements is obtained as well as all-electric domain wall logic circuits.",2010.01077v1
2020/10/14,Interface-driven magnetic anisotropy in relaxed La$_{0.7}$Sr$_{0.3}$CrO$_3$/La$_{0.7}$Sr$_{0.3}$MnO$_3$ heterostructures on MgO,"We investigate the structural and magnetic properties of
La$_{0.7}$Sr$_{0.3}$CrO$_3$ (LSCO)/La$_{0.7}$Sr$_{0.3}$MnO$_3$(LSMO)
heterostructures grown on (001)-oriented MgO by molecular beam epitaxy. Due to
the large film-substrate lattice mismatch, strain relaxation is found to occur
within the first 2-3 unit cells (uc) of the film as evidenced by reflection
high energy electron diffraction and high-resolution synchrotron X-ray
reciprocal space mapping. We find that the presence of the LSCO spacer and
capping layers leads to ferromagnetism in ultra-thin LSMO layers with
thicknesses on the order of 2 uc with the magnetic easy axis oriented in the
film plane. Net magnetic moments of 1.4 and 2.4 $\mu_B$/Mn are measured for [2
uc LSCO/ 2 uc LSMO] and [2 uc LSCO/ 4 uc LSMO] superlattices, respectively by
SQUID magnetometry. The effective magnetic anisotropy of the relaxed [2 uc
LSCO/ 4 uc LSMO] heterostructure is found to be an order of magnitude higher
than bulk LSMO highlighting the critical role of interfacial magnetic exchange
interactions in tuning magnetic anisotropy at complex oxide interfaces.",2010.07180v1
2020/10/16,Insights on magnon topology and valley-polarization in 2D bilayer quantum magnets,"The rich and unconventional physics in layered 2D magnets can open new
avenues for topological magnonics and magnon valleytronics. In particular,
two-dimensional (2D) bilayer quantum magnets are gaining increasing attention
due to their intriguing stacking-dependent magnetism, controllable ground
states, and topological excitations induced by magnetic spin-orbit couplings
(SOCs). Despite the substantial research on these materials, their topological
features remain widely unexplored to date. The present study comprehensively
investigates the magnon topology and magnon valley-polarization in honeycomb
bilayers with collinear magnetic order. We elucidate the separate and combined
effects of the SOC, magnetic ground-states, stacking order, and inversion
symmetry breaking on the topological phases, magnon valley transport, and the
Hall and Nernst effects. The comprehensive analysis suggests clues to determine
the SOC's nature and predicts unconventional Hall and Nernst conductivities in
topologically trivial phases. We further report on novel bandgap closures in
layered antiferromagnets and detail their topological implications. We believe
the present study provides important insights into the fundamental physics and
technological potentials of topological 2D magnons.",2010.08621v4
2020/10/22,Spin-current version of solar cells in non-centrosymmetric magnetic insulators,"Photovoltaic effect, e.g., solar cells, converts light into DC electric
current. This phenomenon takes place in various setups such as in
noncentrosymmetric crystals and semiconductor pn junctions. Recently, we
proposed a theory for producing DC spin current in magnets using
electromagnetic waves, i.e., the spin-current counterpart of the solar cells.
Our calculation shows that the nonlinear conductivity for the spin current is
nonzero in a variety of noncentrosymmetric magnets, implying that the
phenomenon is ubiquitous in inversion-asymmetric materials with magnetic
excitations. Intuitively, this phenomenon is a bulk photovoltaic effect of
magnetic excitations, where electrons and holes, visible light, and
inversion-asymmetric semiconductors are replaced with magnons or spinons, THz
or GHz waves, and asymmetric magnetic insulators, respectively. We also show
that the photon-driven spin current is shift current type, and as a result, the
current is stable against impurity scattering. This bulk photovoltaic spin
current is in sharp contrast to that of well-known spin pumping that takes
place at the interface between a magnet and a metal.",2010.11795v1
2020/10/26,Ultrafast phononic switching of magnetization,"Identifying an efficient pathway to change the order parameter via a subtle
excitation of the coupled high-frequency mode is the ultimate goal of the field
of ultrafast phase transitions. This is an especially interesting research
direction in magnetism, where the coupling between spin and lattice excitations
is required for magnetization reversal. Despite several attempts however, the
switching between magnetic states via resonant pumping of phonon modes has not
yet been demonstrated. Here we show how an ultrafast resonant excitation of the
longitudinal optical phonon modes in magnetic garnet films switches
magnetization into a peculiar quadrupolar magnetic domain pattern,
unambiguously revealing the magneto-elastic mechanism of the switching. In
contrast, the excitation of strongly absorbing transverse phonon modes results
in thermal demagnetization effect only.",2010.13671v1
2020/10/27,Square skyrmion crystal in centrosymmetric itinerant magnets,"We theoretically investigate the origin of the square-type skyrmion crystal
in centrosymmetric itinerant magnets, motivated from the recent experimental
finding in GdRu$_2$Si$_2$ [N. D. Khanh $\mathit{et}$ $\mathit{al.}$, Nat.
Nanotech. $\mathbf{15}$, 444 (2020)]. By simulated annealing for an effective
spin model derived from the Kondo lattice model on a square lattice, we find
that a square skyrmion crystal composed of a superposition of two spin helices
is stabilized in a magnetic field by synergy between the positive biquadratic,
bond-dependent anisotropic, and easy-axis anisotropic interactions. This is in
stark contrast to triangular skyrmion crystals which are stabilized by only one
of the three, suggesting that the square skyrmion crystal is characteristic of
itinerant magnets with magnetic anisotropy. We also show that a variety of
noncollinear and noncoplanar spin textures appear depending on the model
parameters as well as the applied magnetic field. The present systematic study
will be useful not only for identifying the key ingredients in GdRu$_2$Si$_2$
but also for exploring further skyrmion-hosting materials in centrosymmetric
itinerant magnets.",2010.14671v1
2020/11/12,Picoscale Magnetoelasticity Governs Heterogeneous Magnetic Domains in a Noncentrosymmetric Ferromagnetic Weyl Semimetal,"Magnetic Weyl semimetals are predicted to host emergent electromagnetic
fields at heterogeneous strained phases or at the magnetic domain walls.
Tunability and control of the topological and magnetic properties is crucial
for revealing these phenomena, which are not well understood or fully realized
yet. Here, we use a scanning SQUID microscope to image spontaneous
magnetization and magnetic susceptibility of CeAlSi, a noncentrosymmetric
ferromagnetic Weyl semimetal candidate. We observe large metastable domains
alongside stable ferromagnetic domains. The metastable domains most likely
embody a type of frustrated or glassy magnetic phase, with excitations that may
be of an emergent and exotic nature. We find evidence that the heterogeneity of
the two types of domains arises from magnetoelastic or magnetostriction
effects. We show how these domains form, how they interact, and how they can be
manipulated or stabilized with estimated lattice strains on picometer levels.
CeAlSi is a frontier material for straintronics in correlated topological
systems.",2011.06168v1
2020/11/14,Voltage-controlled magnetic anisotropy under the electronic structure modulation in quantum wells,"Voltage-controlled magnetic anisotropy (VCMA) offers an emerging approach to
realize energy-efficient magnetization switching in spintronic devices such as
magnetic random access memories (MRAMs). Here, we show that manipulating the
condensed states, i.e., introducing quantum well (QW) can significantly
influence the VCMA in a Cr/Fe-QW/MgAl2O4 based magnetic tunnel junction (MTJ).
Only for the MTJ with an even number of Fe atomic layers, we observed a novel
A-shaped VCMA curve for a particular QW state, where magnetic anisotropy energy
(MAE) reaches a local maximum at zero bias and reduces when applying both
positive and negative bias, i.e., a novel bi-polar VCMA effect. Our ab initio
calculations demonstrate that the QW states give an additional contribution to
perpendicular magnetic anisotropy (PMA), which can explain not only the
A-shaped VCMA but also the Fe-layer-number parity dependence of VCMA. The
present study suggests that the QW-modulated VCMA should open a new pathway to
design VCMA-assisted MRAM.",2011.07217v1
2020/12/9,Magnetocaloric and electrocaloric properties of the Hubbard pair cluster,"The paper contains the discussion of the magnetocaloric and electrocaloric
effect in a model dimer (pair cluster). The system of interest is modelled with
a Hubbard Hamiltonian including the external electric and magnetic field. The
thermodynamics of such pair is described exactly, on the grounds of the grand
canonical ensemble, focusing on the half-filling of energy states. The
quantities of interest, such as magnetic entropy, magnetic specific heat as
well as isothermal entropy change resulting from the variation of either
electric or magnetic field and appropriate Gr\""uneisen ratios are calculated
and discussed in a wide range of external fields. The importance of singlet to
triplet transition for the observed behaviour is emphasized. The ranges of
direct and inverse caloric effects are found and the manifestations of the
magnetoelectric phenomena are described. In particular, the tunability of the
magnetocaloric effect with electric field as well as tunability of the
electrocaloric effect with magnetic field are demonstrated.",2012.04913v2
2020/12/7,Explaining high-braking indice of magnetars SGR 0501+4516 and 1E 2259+586 using the double magnetic-dipole model,"In this paper, we attribute high braking indices $n>3$ of two magnetars SGR
0501$+$4516 and 1E 2259$+$586 to the decrease in their inclination angles using
the double magnetic-dipole model proposed by Hamil et al.(2016). In this model,
there are two magnetic moments inside a neutron star, one is generated by the
rotation effect of a charged sphere, $M_{1}$, and the other is generated by the
magnetization of ferromagnetically ordered material, $M_{2}$. Our calculations
indicate that the magnetic moment $M_{2}$ would evolve towards alignment with
the spin axis of the two magnetars, and cause their magnetic inclination angles
to decrease. We also define a ratio $\eta=M_{2}/M_{1}$, which reflects the
magnetization degree, and find that the values of $\eta$ of the two magnetars
are about two-orders of magnitude higher than that of rotationally powered
pulsar PSR J1640-4631 with $n=3.15(3)$, assuming that they have the same rate
of decrease in their inclination angles.",2012.06307v1
2020/12/17,Geometric magnonics with chiral magnetic domain walls,"Spin wave, the collective excitation of magnetic order, is one of the
fundamental angular momentum carriers in magnetic systems. Understanding the
spin wave propagation in magnetic textures lies in the heart of developing pure
magnetic information processing schemes. Here we show that the spin wave
propagation across a chiral domain wall follows simple geometric trajectories,
similar to the geometric optics. And the geometric behaviors are qualitatively
different in normally magnetized film and tangentially magnetized film. We
identify the lateral shift, refraction, and total reflection of spin wave
across a ferromagnetic domain wall. Moreover, these geometric scattering
phenomena become polarization-dependent in antiferromagnets, indicating the
emergence of spin wave birefringence inside antiferromagnetic domain wall.",2012.09420v1
2021/1/20,Spin-current mediated exchange coupling in MgO-based magnetic tunnel junctions,"Heterostructures composed of ferromagnetic layers that are mutually
interacting through a nonmagnetic spacer are at the core of magnetic sensor and
memory devices. In the present study, layer-resolved ferromagnetic resonance
was used to investigate the coupling between the magnetic layers of a
Co/MgO/Permalloy magnetic tunnel junction. Two magnetic resonance peaks were
observed for both magnetic layers, as probed at the Co and Ni L3 x-ray
absorption edges, showing a strong interlayer interaction through the
insulating MgO barrier. A theoretical model based on the
Landau-Lifshitz-Gilbert-Slonczewski equation was developed, including exchange
coupling and spin pumping between the magnetic layers. Fits to the experimental
data were carried out, both with and without a spin pumping term, and the
goodness of the fit was compared using a likelihood ratio test. This rigorous
statistical approach provides an unambiguous proof of the existence of
interlayer coupling mediated by spin pumping.",2101.08157v1
2021/2/5,Time-resolved imaging of Œrsted field induced magnetization dynamics in cylindrical magnetic nanowires,"Recent studies in three dimensional spintronics propose that the \OE rsted
field plays a significant role in cylindrical nanowires. However, there is no
direct report of its impact on magnetic textures. Here, we use time-resolved
scanning transmission X-ray microscopy to image the dynamic response of
magnetization in cylindrical Co$_{30}$Ni$_{70}$ nanowires subjected to
nanosecond \OE rsted field pulses. We observe the tilting of longitudinally
magnetized domains towards the azimuthal \OE rsted field direction and create a
robust model to reproduce the differential magnetic contrasts and extract the
angle of tilt. Further, we report the compression and expansion, or breathing,
of a Bloch-point domain wall that occurs when weak pulses with opposite sign
are applied. We expect that this work lays the foundation for and provides an
incentive to further studying complex and fascinating magnetization dynamics in
nanowires, especially the predicted ultra-fast domain wall motion and
associated spin wave emissions.",2102.03067v3
2021/3/18,Magnetic structure and low temperature properties of geometrically frustrated SrNd$_2$O$_4$,"We report the low-temperature properties of SrNd$_2$O$_4$, a geometrically
frustrated magnet. Magnetisation and heat capacity measurements performed on
polycrystalline samples indicate the appearance of a magnetically ordered state
at $T_{\rm N}=2.28(4)$~K. Powder neutron diffraction measurements reveal that
an \afm\ state with the propagation vector \QV\ is stabilised below this
temperature. The magnetic order is incomplete, as only one of the two Nd$^{3+}$
sites carries a significant magnetic moment while the other site remains
largely disordered. The presence of a disordered magnetic component below
$T_{\rm N}$ is confirmed with polarised neutron diffraction measurements. In an
applied magnetic field, the bulk properties measurements indicate a phase
transition at about 30~kOe. We construct a tentative $H$-$T$ phase diagram of
\sno\ from these measurements.",2103.10539v1
2021/4/27,Topological quantum phase transitions of anisotropic AFM Kitaev model driven by magnetic field,"We investigate the quantum spin liquid (QSL) ground state of anisotropic
Kitaev model with antiferromagnetic (AFM) coupling under the $[001]$ magnetic
field with the finite-temperature Lanczos method (FTLM). In this anisotropic
AFM Kitaev model with $K_{X}=K_{Y}$, $K_{X}+K_{Y}+K_{Z}=-3K$, and $K_{Z}<-K$,
with magnetic field increasing, the gapped QSL experiences a transition to a
gapless QSL at $h_{c1}=g\mu_{B}H_{z1}/K$, to another gapless QSL with $C_{6}$
rotational symmetry at $h_{c2}$, and to a new $U(1)$ gapless QSL between
$h_{c3}$ and $h_{c4}$, respectively. These indicate that magnetic field could
first turn the anisotropic gapped or gapless QSL back into the isotropic
$C_{6}$ gapless one and then make it to undergo the similar evolution as the
isotropic case. Moreover, the critical magnetic fields $h_{c1}$, $h_{c2}$,
$h_{c3}$, and $h_{c4}$ come up monotonically with the increasing Kitaev
coupling; this suggests that the magnetic field can be applied to the
modulation of the anisotropic Kitaev materials.",2104.12935v2
2021/4/27,Twisted magnetic topological insulators,"Motivated by the discovery of the quantum anomalous Hall effect in Cr-doped
\ce{(Bi,Sb)2Te3} thin films, we study the generic states for magnetic
topological insulators and explore the physical properties for both magnetism
and itinerant electrons. First-principles calculations are exploited to
investigate the magnetic interactions between magnetic Co atoms adsorbed on the
\ce{Bi2Se3} (111) surface. Due to the absence of inversion symmetry on the
surface, there are Dzyaloshinskii-Moriya-like twisted spin interactions between
the local moments of Co ions. These nonferromagnetic interactions twist the
collinear spin configuration of the ferromagnet and generate various magnetic
orders beyond a simple ferromagnet. Among them, the spin spiral state generates
alternating counterpropagating modes across each period of spin states, and the
skyrmion lattice even supports a chiral mode around the core of each skyrmion.
The skyrmion lattice opens a gap at the surface Dirac point, resulting in the
anomalous Hall effect. These results may inspire further experimental
investigation of magnetic topological insulators.",2104.13235v2
2021/6/4,Giant Biquadratic Exchange in 2D Magnets and its Role in Stabilizing Ferromagnetism of NiCl2 Monolayer,"Two-dimensional (2D) van der Waals (vdW) magnets provide an ideal platform
for exploring, on the fundamental side, new microscopic mechanisms and for
developing, on the technological side, ultra-compact spintronic applications.
So far, bilinear spin Hamiltonians have been commonly adopted to investigate
the magnetic properties of 2D magnets, neglecting higher order magnetic
interactions. However, we here provide quantitative evidence of giant
biquadratic exchange interactions in monolayer NiX2 (X=Cl, Br and I), by
combining first-principles calculations and the newly developed machine
learning method for constructing Hamiltonian. Interestingly, we show that the
ferromagnetic ground state within NiCl2 single layers cannot be explained by
means of bilinear Heisenberg Hamiltonian; rather, the nearest-neighbor
biquadratic interaction is found to be crucial. Furthermore, using a
three-orbitals Hubbard model, we propose that the giant biquadratic exchange
interaction originates from large hopping between unoccupied and occupied
orbitals on neighboring magnetic ions. On a general framework, our work
suggests biquadratic exchange interactions to be important in 2D magnets with
edge-shared octahedra.",2106.02211v1
2021/6/16,Topological Magnetic Hysteresis in Single Crystals of CeAgSb2 Ferromagnet,"Closed-topology magnetic domains are usually observed in thin films and in an
applied magnetic field. Here we report the observation of rectangular
cross-section tubular ferromagnetic domains in thick single crystals of CeAgSb2
in zero applied field. Relatively low exchange energy, small net magnetic
moment, and anisotropic in-plane crystal electric fields lower the domain wall
energy and allow for the formation of the closed-topology patterns. Upon
cycling the magnetic field, the domain structure irreversibly transforms into a
dendritic open-topology pattern. This transition between closed and open
topologies results in a ""topological magnetic hysteresis"" - the actual
hysteresis in magnetization, not due to the imperfections and pinning, but due
to the difference in the pattern morphology. Similar physics was suggested
before in pure type-I superconductors and is believed to be a generic feature
of other nonlinear multi-phase systems in the clean limit.",2106.09154v1
2021/6/17,Quantum error as an emergent magnetic field,"We investigate the effect of quantum errors on a monitored Brownian
Sachdev-Ye-Kitaev (SYK) model featuring a measurement-induced phase transition
that can be understood as a symmetry-breaking transition of an effective $Z_4$
magnet in the replica space. The errors describe the loss of information about
the measurement outcomes and are applied during the non-unitary evolution or at
the end of the evolution. In the former case, we find that this error can be
mapped to an emergent magnetic field in the $Z_4$ magnet, and as a consequence,
the symmetry is explicitly broken independent of the measurement rate. R\'enyi
entropies computed by twisting boundary conditions now generate domain walls
even in the would-be symmetric phase at a high measurement rate. The entropy is
therefore volume-law irrespective of the measurement rate. In the latter case,
the error-induced magnetic field only exists near the boundary of the magnet.
Varying the magnetic field leads to a pinning transition of domain walls,
corresponding to error threshold of the quantum code prepared by the
non-unitary SYK dynamics.",2106.09635v1
2021/6/22,Magnetic particles and strings in iron langasite,"Particle-like topological magnetic defects that can propagate in all spatial
directions open a new dimension for design of magnetic memory and data
processing devices. We show that three-dimensional magnetic skyrmions can be
stabilized in non-collinear antiferromagnets, such as the Fe-langasite,
Ba$_3$TaFe$_3$Si$_2$O$_{14}$. Spins in the crystallographic unit cell of this
material form a 120-degree ordering transformed by competing exchange
interactions into a short-period spiral, which in turn forms a basis for
complex large-scale magnetic superstructures stabilized by
Dzyaloshinskii-Moriya interactions and applied magnetic fields. We derive an
effective continuum model describing modulated states of Fe-langasite at the
100 nm scale and explore its magnetic phases and topological defects. The order
parameter space of this model is similar to that of superfluid $^{3}$He-A and
the three-dimensional topological defect is closely related to the Shankar
monopole and hedgehog soliton in the Skyrme model of baryons.",2106.11910v1
2021/7/12,Origin of Perpendicular Magnetic Anisotropy in Yttrium Iron Garnet Thin Films Grown on Si (100),"We report the magnetic properties of yttrium iron garnet (YIG) thin films
grown by pulsed laser deposition technique. The films were deposited on Si
(100) substrates in the range of 15-50 nm thickness. Magnetic characterizations
were investigated by ferromagnetic resonance spectra. Perpendicular magnetic
easy axis was achieved up to 50 nm thickness. We observed that the
perpendicular anisotropy values decreased by increasing the film thickness. The
origin of the perpendicular magnetic anisotropy (PMA) was attributed to the
texture and the lattice distortion in the YIG thin films. We anticipate that
perpendicularly magnetized YIG thin films on Si substrates pave the way for a
cheaper and compatible fabrication process.",2107.05591v1
2021/7/14,Magnetic order and its interplay with structure phase transition in van der Waals ferromagnet VI$_3$,"Van der Waals magnet VI$_3$ demonstrates intriguing magnetic properties that
render it great for use in various applications. However, its microscopic
magnetic structure has not been determined yet. Here, we report neutron
diffraction and susceptibility measurements in VI$_3$ that revealed a
ferromagnetic order with the moment direction tilted from the $c$-axis by
~36{\deg} at 4 K. A spin reorientation accompanied by a structure distortion
within the honeycomb plane is observed at a temperature of ~27 K, before the
magnetic order completely disappears at $T_C$ = 50 K. The refined magnetic
moment of ~1.3 $\mu_B$ at 4 K is considerably lower than the fully ordered spin
moment of 2 $\mu_B$/ V$^{3+}$, suggesting the presence of a considerable
orbital moment antiparallel to the spin moment and strong spin-orbit coupling
in VI$_3$. This results in strong magnetoelastic interactions that make the
magnetic properties of VI$_3$ easily tunable via strain and pressure.",2107.06443v1
2021/7/14,Magnetic correlations in triangular antiferromagnet FeGa$_2$S$_4$,"The crystal structure and magnetic correlations in triangular antiferromagnet
FeGa$_2$S$_4$ are studied by x-ray diffraction, magnetic susceptibility,
neutron diffraction and neutron inelastic scattering. We report significant
mixing at the cation sites and disentangle magnetic properties dominated by
major and minor magnetic sites. The magnetic short-range correlations at 0.77
\AA$^{-1}$ correspond to the major sites and being static at base temperature
they evolve into dynamic correlations around 30 - 50 K. The minor sites
contribute to the magnetic peak at 0.6 \AA$^{-1}$, which vanishes at 5.5 K. Our
analytical studies of triangular lattice models with bilinear and biquadratic
terms provide the ratios between exchanges for the proposed ordering vectors.
The modelling of the inelastic neutron spectrum within linear spin wave theory
results in the set of exchange couplings $J_1=1.7$\,meV, $J_2=0.9$\,meV,
$J_3=0.8$\,meV for the bilinear Heisenberg Hamiltonian. However, not all
features of the excitation spectrum are explained with this model.",2107.06904v1
2021/8/2,Quadratic Optical Responses in a Chiral Magnet,"Chiral magnets, which break both spatial inversion and time reversal
symmetries, carry a potential for quadratic optical responses. Despite the
possibility of enhanced and controlled responses through the magnetic degree of
freedom, the systematic understanding remains yet to be developed. We here
study nonlinear optical responses in a prototypical chiral magnetic state with
a one-dimensional conical order by using the second-order response theory. We
show that the photovoltaic effect and the second harmonic generation are
induced by asymmetric modulation of the electronic band structure under the
conical magnetic order, and the coefficients, including the sign, change
drastically depending on the frequency of incident lights, the external
magnetic field, and the strength of spin-charge coupling. We find that both
effects can be enormously large compared to those in the conventional
nonmagnetic materials. Our results would pave the way for next-generation
optical electronic devices, such as unconventional solar cells and optical
sensors, based on chiral magnets.",2108.00674v1
2021/8/9,Interplay of the orbital magnetic moment and the chiral magnetic effect in Shubnikov-de Haas quantum oscillations,"Emergent Lorentz symmetry and chiral anomaly are well known to play an
essential role in anomalous transport phenomena of Weyl metals. In particular,
the former causes a Berry-curvature induced orbital magnetic moment to modify
the group velocity of Weyl electrons, and the latter results in the chiral
magnetic effect to be responsible for a ""dissipationless"" longitudinal current
channel of the bulk. In this study, we verify that intertwined these two
effects can be measured in Shubnikov-de Haas (SdH) quantum oscillations, where
a double-peak structure of the SdH oscillation appears to cause a kink in the
Landau fan diagram. We examine three different cases which cover all possible
experimental situations of external electric/magnetic fields and identify the
experimental condition for the existence of the double-peak structure. We claim
that interplay of the orbital magnetic moment and the chiral magnetic effect in
SdH quantum oscillations is an interesting feature of the Weyl metal state.",2108.03934v1
2021/8/11,Critical Magnetic Behavior of the Half Heusler Alloy RhCrSi: Monte Carlo Study,"In this paper, we study the critical magnetic properties of the Half Heusler
alloy RhCrSi, using Monte Carlo simulations (MCS) under the Metropolis
algorithm. In fact, to study this alloy, we apply an Ising model using the MCS
simulations, we concentrate only on the magnetic atoms: Rh and Cr. For this
purpose, these magnetic atoms are modeled by the spin moments S=5/2 for Rh
atoms and sigma=2 for Cr atoms, respectively. In addition, we discuss the
ground state phase diagrams in different planes corresponding to different
physical parameters. On the other hand, for non-null temperature values, we
perform the Monte Carlo simulations (MCS) to study the critical behavior of the
compound RhCrSi, in the Ising approximation. Indeed, we present a detailed
discussion of the obtained results for the magnetizations as a function of the
temperature, the crystal field and the exchange coupling interactions.
Additionally, we give the reliance of the basic temperature as an element of
precious crystal field when fixing the exchange coupling interactions. To
finish this work, we built up and examined the magnetic hysteresis cycles and
the relating coercive fields as a part of the external magnetic field.",2108.05162v1
2021/9/16,Oxygen vacancy-induced anomalous Hall effect in a nominally non-magnetic oxide,"The anomalous Hall effect, a hallmark of broken time-reversal symmetry and
spin-orbit coupling, is frequently observed in magnetically polarized systems.
Its realization in non-magnetic systems, however, remains elusive. Here, we
report on the observation of anomalous Hall effect in nominally non-magnetic
KTaO3. Anomalous Hall effect emerges in reduced KTaO3 and shows an extrinsic to
intrinsic crossover. A paramagnetic behavior is observed in reduced samples
using first principles calculations and quantitative magnetometry. The observed
anomalous Hall effect follows the oxygen vacancy-induced magnetization
response, suggesting that the localized magnetic moments of the oxygen
vacancies scatter conduction electrons asymmetrically and give rise to
anomalous Hall effect. The anomalous Hall conductivity becomes insensitive to
scattering rate in the low temperature limit (T<5 K), implying that the Berry
curvature of the electrons on the Fermi surface controls the anomalous Hall
effect. Our observations describe a detailed picture of many-body interactions,
triggering anomalous Hall effect in a non-magnetic system.",2109.08073v2
2021/9/30,Signatures of quartic asymmetric exchange in a class of two dimensional magnets,"Indirect quartic interaction of spins is suggested to play an important role
in two dimensional magnets with trigonal prismatic symmetry such as
Fe$_3$GeTe$_2$ monolayer. The proposed interaction is described by terms in
micromagnetic energy that are linear in magnetization gradients. Such terms
enable the stability of non-collinear magnetic textures. We investigate
signatures of the quartic interaction in magnon spectra in the presence of
anisotropy and external magnetic field. We also show how magnetic spirals,
which are induced by the proposed interaction, can be manipulated by external
field. Our analysis is based on symmetry considerations and can be used to
quantify the quartic interaction strength in experiments with magnetic
monolayers.",2109.15297v1
2021/10/22,Angle dependent field-driven reorientation transitions in uniaxial antiferromagnet MnBi$_2$Te$_4$ single crystal,"MnBi$_2$Te$_4$, a two-dimensional magnetic topological insulator with a
uniaxial antiferromagnetic structure, is an ideal platform to realize quantum
anomalous Hall effect. However, the strength of magnetic interactions is not
clear yet. We performed systematic studies on the magnetization and angle
dependent magnetotransport of MnBi$_2$Te$_4$ single crystal. The results show
that the direction of the magnetic field has significant effects on the
critical field values and magnetic structure of this compound, which leads to
different magnetotransport behaviors. The field-driven reorientation
transitions can be utilized to estimate the AFM interlayer exchange interaction
coupling and uniaxial magnetic anisotropy D. The obtained Hamiltonian can well
explain the experimental data by Monte Carlo simulations. Our comprehensive
studies on the field-driven magnetic transitions phenomenon in MnBi$_2$Te$_4$
provide a general approach for other topological systems with
antiferromagnetism.",2110.11686v1
2021/11/6,GdV6Sn6: a Multi-carrier Metal with Non-magnetic 3d-electron Kagome Bands and 4f-electron Magnetism,"Electronic properties of the single crystal of GdV6Sn6, where non-magnetic
V-kagome layers are separated by magnetic Gd-triangular lattice, are
investigated. GdV6Sn6 exhibits unique magnetotransport properties at
low-temperature such as non-linear Hall resistivity and increase of resistance
R in magnetic field H as R ~ H^0.75 up to 56 T with Shubnikov-De Haas
oscillations. Investigation of the non-magnetic analogue YV6Sn6 and the first
principles calculations reveal these properties are relevant to the bands
arising from the V-kagome layer. A magnetic transition at 5 K in GdV6Sn6
modifies the transport properties, pointing to a coupling between Gd-spins on
the triangular lattice and carriers in the V-kagome layer.",2111.03806v1
2021/12/16,Magnetic properties of pressurized CsV$_{3}$Sb$_{5}$ calculated by using a hybrid functional,"Based on the hybrid functional, we find that at 0 GPa, the pristine
CsV$_{3}$Sb$_{5}$ has local magnetic moment of 0.85 $\mu_B$ /unit cell, which
is suppressed at pressure of 2.5 GPa resulting in a spin-crossover. Since the
ground sate of CsV$_{3}$Sb$_{5}$ with charge density wave (CDW) distortion is
non-magnetic state, the local magnetic moment of pristine CsV$_{3}$Sb$_{5}$
will be suppressed by temperature-induced CDW transition at 94 K. The schematic
evolution of magnetic moments as functions of pressure and temperature are
presented. At low temperature, CsV$_{3}$Sb$_{5}$ is a rare example of materials
hosting pressureinduced local magnetic moment, and we suggeste that the effects
of local magnetic moments should be considered for understanding its
properties.",2112.08559v1
2022/1/31,Disorder-mediated quenching of magnetization in NbVTiAl: Theory and Experiment,"In this paper, we present the structural, electronic, magnetic and transport
properties of a equiatomic quaternary alloy NbVTiAl. The absence of (111) and
(200) peaks in X-ray diffraction (XRD) data confirms the A2-type structure.
Magnetization measurements indicate a high Curie temperature and a negligibly
small magnetic moment ($\sim 10^{-3} \mu_B/f.u.$) These observations are
indicative of fully compensated ferrimagnetism in the alloy.
Temperature-dependent resistivity indicates metallic nature. Ab-initio
calculation of fully ordered NbVTiAl structure confirms a nearly half metallic
behavior with a high spin polarization ($\sim$ 90 \%) and a net magnetic moment
of 0.8 $\mu_B/f.u.$ (in complete contrast to the experimental observation). One
of the main objective of the present paper is to resolve and explain the
long-standing discrepancy between theoretical prediction and experimental
observation of magnetization for V-based quaternary Heusler alloys, in general.
To gain an in-depth understanding, we modelled various disordered states and
its subsequent effect on the magnetic and electronic properties. The
discrepancy is attributed to the A2 disorder present in the system, as
confirmed by our XRD data. The presence of disorder also causes the emergence
of finite states at the Fermi level, which impacts the spin polarization of the
system.",2201.13037v1
2022/2/4,Influence of the triangular Mn-O breathing mode on the magnetic ordering in multiferroic hexagonal manganites,"We use a combination of symmetry analysis, phenomenological modelling and
first-principles density functional theory to explore the interplay between the
magnetic ground state and the detailed atomic structure in the hexagonal
rare-earth manganites. We find that the magnetic ordering is sensitive to a
breathing mode distortion of the Mn and O ions in the $ab$ plane, which is
described by the K\textsubscript{1} mode of the high-symmetry structure. Our
density functional calculations of the magnetic interactions indicate that this
mode particularly affects the single-ion anisotropy and the inter-planar
symmetric exchanges. By extracting the parameters of a magnetic model
Hamiltonian from our first-principles results, we develop a phase diagram to
describe the magnetic structure as a function of the anisotropy and exchange
interactions. This in turn allows us to explain the dependence of the magnetic
ground state on the identity of the rare-earth ion and on the
K\textsubscript{1} mode.",2202.02304v1
2022/2/7,Chern Number Tunable Quantum Anomalous Hall Effect in Monolayer Transitional Metal Oxides via Manipulating Magnetization Orientation,"Although much effort has been made to explore quantum anomalous Hall effect
(QAHE) in both theory and experiment, the QAHE systems with tunable Chern
numbers are yet limited. Here, we theoretically propose that NiAsO$_3$ and
PdSbO$_3$, monolayer transitional metal oxides, can realize QAHE with tunable
Chern numbers via manipulating their magnetization orientations. When the
magnetization lies in the \textit{x-y} plane and all mirror symmetries are
broken, the low-Chern-number (i.e., $\mathcal{C}=\pm1$) phase emerges. When the
magnetization exhibits non-zero \textit{z}-direction component, the system
enters the high-Chern-number (i.e., $\mathcal{C}=\pm3$) phase, even in the
presence of canted magnetization. The global band gap can approach the
room-temperature energy scale in monolayer PdSbO$_3$ (23.4 meV), when the
magnetization is aligned to \textit{z}-direction. By using Wannier-based
tight-binding model, we establish the phase diagram of magnetization induced
topological phase transition. Our work provides a high-temperature QAHE system
with tunable Chern number for the practical electronic application.",2202.02945v2
2022/2/10,Field-driven skyrmion motion through velocity equipartition between skyrmions and a domain wall,"Magnetic skyrmions, as a whirling spin texture with axisymmetry, cannot be
propelled by a uniform magnetic field. Therefore, reported skyrmion motions
have been induced using other sorts of stimuli; typically, electric currents in
magnetic metals as well as spin waves, thermal gradient, and field gradient
have manifested their ability to drive skyrmion motion. Here, we demonstrate,
through micromagnetic simulations and analytically, that magnetic skyrmions can
be displaced by a uniform perpendicular magnetic field via a domain-wall (DW)
mediator. For a fixed field strength, the velocity of a skyrmion train evolves
in terms of 1 / (1 + Ns) with Ns denoting the number of skyrmions. Based on
Thiele's model, we reproduce the velocity-Ns relation first identified from
numerical results and reveal that the skyrmion-DW and inter-skyrmion repulsions
offer the direct driving force for skyrmion motion. This study underlines the
role of spin textures' interaction in skyrmion dynamics, and opens an
alternative route for skyrmion manipulation especially relevant to insulating
magnets. Given the correspondence between magnetism and electricity, we
anticipate that the scheme should also work for polar skyrmions in
ferroelectrics.",2202.05149v1
2022/2/22,Electronic and magnetic properties of silicene monolayer under bi-axial mechanical strain: a first-principles study,"Mechanical control of electronic and magnetic properties of 2D Van-der-Waals
heterostructures gives new possibilities for further development of spintronics
and information-related technologies. Using the density functional theory, we
investigate the structural, electronic, and magnetic properties of silicene
monolayer with substituted Chromium atoms and under a small biaxial strain
($-6\%< \epsilon < 8\%$). Our results indicate that the Cr-doped silicene
nanosheets without strain have magnetic metallic, half-metallic or
semiconducting properties depending on the type of substitution. We also show
that the magnetic moments associated with the monomer and vertical dimer
substitutions change very weakly with strain. However, the magnetic moment
associated with the horizontal dimer substitution decreases when either
compressive or tensile strain is applied to the system. Additionally, we show
that the largest semiconductor band-gap is approximately 0.13 eV under zero
strain for the vertical Cr-doped silicene. Finally, biaxial compressive strain
leads to irregular changes in the magnetic moment for Cr vertical dimer
substitution.",2202.10929v1
2022/2/23,"Spontaneous magnetic skyrmions in single-layer CrInX3(X=Te, Se)","The realization of magnetic skyrmions in nanostructures holds great promise
for both fundamental research and device applications. Despite recent progress,
intrinsic magnetic skyrmions in two-dimensional lattice are still rarely
explored. Here, using first-principles calculations and Monte-Carlo
simulations, we report the identification of spontaneous magnetic skyrmions in
single-layer CrInX3 (X = Te, Se). Due to the joint effect of broken inversion
symmetry and strong spin-orbit coupling, inherent large Dzyaloshinskii-Moriya
interaction occurs in both systems, endowing the intriguing Neel-type skyrmions
in the absence of magnetic field. By further imposing moderate magnetic field,
the skyrmion phase can be obtained and is stable within a wide temperature
range. Particularly for single-layer CrInTe3, the size of skyrmions is sub-10
nm and the skyrmion phase can be maintained at an elevated temperature of 180
K. In addition, the phase diagrams of their topological spin textures under the
variation of magnetic parameters of D, J, and K are mapped out. Our results
greatly enrich the research of 2D skyrmionics physics.",2202.11270v1
2022/2/24,In-plane epitaxy strain tuning intralayer and interlayer magnetic couplings in CrSe2 and CrTe2 mono- and bi-layers,"Mismatched lattice-constants at a van-der-Waals epitaxy interface often
introduce in-plane strains to the lattice of the epitaxial layer, termed
epitaxy-strain, where the strains do not follow the intra-layer Poisson's
relation. Here, we presented the magnetic phase diagrams of the CrSe2 and CrTe2
mono- and bi-layers under epitaxy-strain up to 8 %, as predicted using
density-functional-theory calculations. They show that the in-plane
epitaxy-strain manipulates either the intra- or inter-layer magnetism of them.
The in-plane strain varies the interlayer distance, defined using an
inter-layer Poisson's ratio, which governs the inter-layer magnetism in two
opposite ways depending on the in-plane magnetism. The tunability of the
intra-layer magnetism is a result of competing intra-layer Cr-Cr super-exchange
interactions. A graphene substrate was introduced to examine the validity of
our diagrams in practice. Our work also gives a tentative explanation on the
controversially reported magnetizations in CrSe2 and CrTe2 epitaxial mono- or
bi-layers under epitaxy-strains.",2202.11956v1
2022/3/9,Magnetochemical effects on phase stability and vacancy formation in fcc Fe-Ni alloys,"We investigate phase stability and vacancy formation in fcc Fe-Ni alloys over
a broad composition-temperature range, via a density functional theory
parametrized effective interaction model, which includes explicitly spin and
chemical variables. On-lattice Monte Carlo simulations based on this model are
used to predict the temperature evolution of the magnetochemical phase. The
experimental composition-dependent Curie and chemical order-disorder transition
temperatures are successfully predicted. We point out a significant effect of
chemical and magnetic orders on the magnetic and chemical transitions,
respectively. The resulting phase diagram shows a magnetically driven phase
separation around 10-40% Ni and 570-700 K, between ferromagnetic and
paramagnetic solid solutions, in agreement with experimental observations. We
compute vacancy formation magnetic free energy as a function of temperature and
alloy composition. We identify opposite magnetic and chemical disordering
effects on vacancy formation in the alloys with 50% and 75% Ni. We find that
thermal magnetic effects on vacancy formation are much larger in concentrated
Fe-Ni alloys than in fcc Fe and Ni due to a stronger magnetic interaction.",2203.04688v1
2022/3/20,White Paper on High Temperature Superconducting Bi-2212 Magnets for Energy Frontier Circular Colliders,"As the only high-temperature superconducting (HTS) material available as an
isotropic, twisted, multifilamentary round wire, Bi-2212 is very promising for
expanding the high-field superconducting accelerator magnet toolbox beyond the
round-wire, isotropic Nb-Ti and Nb3Sn conductors used by HEP so far. In this
paper, we describe the important roles that Bi-2212 might play for future high
energy circular colliders including both high energy proton and muon colliders.
We describe its present technology status (conductor development, magnet design
concepts, prototype magnet status) and then provide a ten-year plan for >15 T
accelerator magnets and >25 T solenoid magnets within an integrated strategy to
engage industry and the entire US and international scientific enterprise
interested in HTS magnet applications.",2203.10564v2
2022/3/22,Unconventional pressure-driven metamagnetic transitions in topological van der Waals magnets,"Activating metamagnetic transitions between ordered states in van der Waals
magnets and devices bring great opportunities in spintronics. We show that
external pressure, which enhances the interlayer hopping without introducing
chemical disorders, triggers multiple metamagnetic transitions upon cooling in
the topological van der Waals magnets Mn(Bi$_{1-x}$Sb$_x$)$_4$Te$_7$, where the
antiferromagnetic interlayer superexchange coupling competes with the
ferromagnetic interlayer coupling mediated by the antisite Mn spins. The
temperature-pressure phase diagrams reveal that while the ordering temperature
from the paramagnetic to ordered states is almost pressure-independent, the
metamagnetic transitions show non-trivial pressure and temperature dependence,
even re-entrance. For these highly anisotropic magnets, we attribute the former
to the ordering temperature being only weakly dependent on the intralayer
parameters, the latter to the parametrically different pressure and temperature
dependence of the two interlayer couplings. Our independent probing of these
disparate magnetic interactions paves an avenue for efficient magnetic
manipulations in van der Waals magnets.",2203.11925v1
2022/3/29,CP$^2$ Skyrmions and Skyrmion Crystals in Realistic Quantum Magnets,"Magnetic skyrmions are nanoscale topological textures that have been recently
observed in different families of quantum magnets. These textures are known as
CP$^1$ skyrmions because the target manifold of the magnetization field is the
2D sphere $S^2 \cong$ CP$^{1}$. Here we report the emergence of magnetic CP$^2$
skyrmions in realistic spin-$1$ models. Unlike CP$^1$ skyrmions, CP$^2$
skyrmions can also arise as metastable textures of quantum paramagnets, opening
a new road to discover emergent topological solitons in non-magnetic materials.
The quantum phase diagram of the spin-$1$ models also includes magnetic
field-induced CP$^2$ skyrmion crystals that can be detected with regular
momentum- (diffraction) and real-space (Lorentz transmission electron
microscopy) experimental techniques.",2203.15248v1
2022/4/27,Refining magnetic interactions from the magnetic field dependence of spin-wave excitations in magnetoelectric LiFePO$_4$,"We investigated the spin excitations of magnetoelectric $\text{LiFePO}_4$ by
THz absorption spectroscopy in magnetic fields up to 33$\,$T. By studying their
selection rules, we found not only magnetic-dipole, but also electric-dipole
active (electromagnons) and magnetoelectric resonances. The magnetic field
dependence of four strong low-energy modes is reproduced well by our
four-sublattice spin model for fields applied along the three orthorhombic
axes. From the fit, we refined the exchange couplings, single-ion anisotropies,
and the Dzyaloshinskii-Moriya interaction parameters. Additional spin
excitations not described by the mean-field model are observed at higher
frequencies. Some of them shows a strong shift with magnetic field, up to
4$\,\text{cm}^{-1}/\text{T}$, when the field is applied along the easy axis.
Based on this field dependence, we attribute these high frequency resonances to
excitation of higher spin multipoles and of two magnons, which become
THz-active due to the low symmetry of the magnetically ordered state.",2204.12967v1
2022/5/10,A Machine-Learned Spin-Lattice Potential for Dynamic Simulations of Defective Magnetic Iron,"A machine-learned spin-lattice interatomic potential (MSLP) for magnetic iron
is developed and applied to mesoscopic scale defects. It is achieved by
augmenting a spin-lattice Hamiltonian with a neural network term trained to
descriptors representing a mix of local atomic configuration and magnetic
environments. It reproduces the cohesive energy of BCC and FCC phases with
various magnetic states. It predicts the formation energy and complex magnetic
structure of point defects in quantitative agreement with density functional
theory (DFT) including the reversal and quenching of magnetic moments near the
core of defects. The Curie temperature is calculated through spin-lattice
dynamics showing good computational stability at high temperature. The
potential is applied to study magnetic fluctuations near sizable dislocation
loops. The MSLP transcends current treatments using DFT and molecular dynamics,
and surpasses other spin-lattice potentials that only treat near-perfect
crystal cases.",2205.04732v1
2022/5/13,Anomalous depinning of magnetic domain walls within the ferromagnetic phase of the Weyl semimetal Co3Sn2S2,"We report bulk magnetization measurements and spatially resolved measurements
of magnetic domains in Co3Sn2S2 single crystals. The results indicate that a
previously reported magnetic anomaly around 130 K is due to an anomalous domain
wall depinning upon cooling. Our measurements also reveal a hysteresis between
field-cooled-cooling (FCC) and field-cooled-warming (FCW) magnetization curves
acquired under a constant magnetic field below 300 Oe. This observation rules
out the possibility that the anomaly stems from a second-order phase
transition. Our results further suggest that changes in the shape of hysteresis
loops from 5 K to 170 K are caused by an unusual temperature-dependent domain
nucleation field that changes sign around 130 K. The Kerr rotation images of
the magnetic domains confirm that the domain walls depin between 120 K and 140
K.",2205.06420v3
2022/5/18,Superconducting magnet designs and MRI accessibility: a review,"Presently, Magnetic Resonance Imaging (MRI) magnets must deliver excellent
magnetic field (B0) uniformity to achieve optimum image quality. Long magnets
can satisfy the homogeneity requirements but require considerable
superconducting material. These designs result in large, heavy, costly, and
unstable systems that aggravate as field strength increases. This issue is a
crucial factor in the disparity of MR density and field strength use across the
globe. Low-income settings show reduced access to MRI, especially to high field
strengths. This article summarizes the proposed modifications to MRI
superconducting magnet design and their impact on accessibility, including
compact, reduced liquid Helium and specialty systems. Reducing the amount of
superconductor inevitably entails shrinking the magnet size, resulting in
higher field inhomogeneity. This work also reviews the state-of-the-art imaging
and reconstruction methods to overcome this issue. Finally, we summarize the
current and future challenges and opportunities in the design of accessible
MRI.",2205.08918v1
2022/6/6,Magnetic Transition in Monolayer VSe2 via Interface Hybridization,"Magnetism in monolayer (ML) VSe2 has attracted broad interest in spintronics
while existing reports have not reached consensus. Using element-specific X-ray
magnetic circular dichroism, a magnetic transition in ML VSe2 has been
demonstrated at the contamination-free interface between Co and VSe2. Via
interfacial hybridization with Co atomic overlayer, a magnetic moment of about
0.4 uB per V atom in ML VSe2 is revealed, approaching values predicted by
previous theoretical calculations. Promotion of the ferromagnetism in ML VSe2
is accompanied by its antiferromagnetic coupling to Co and a reduction in the
spin moment of Co. In comparison to the absence of this interface-induced
ferromagnetism at the Fe/MLMoSe2 interface, these findings at the Co/ML-VSe2
interface provide clear proof that the ML VSe2, initially with magnetic
disorder, is on the verge of magnetic transition.",2206.02429v1
2022/6/9,Direct visualization of surface spin-flip transition in MnBi4Te7,"We report direct visualization of spin-flip transition of the surface layer
in antiferromagnet MnBi4Te7, a natural superlattice of alternating MnBi2Te4 and
Bi2Te3 layers, using cryogenic magnetic force microscopy (MFM). The observation
of magnetic contrast across domain walls and step edges confirms that the
antiferromagnetic order persists to the surface layers. The magnetic field
dependence of the MFM images reveals that the surface magnetic layer undergoes
a first-order spin-flip transition at a magnetic field that is lower than the
bulk transition, in excellent agreement with a revised Mills' model. Our
analysis indicates an enhancement of the order parameter in the surface
magnetic layer, implying robust ferromagnetism in the single-layer limit. The
direct visualization of surface spin-flip transition not only opens up
exploration of surface metamagnetic transitions in layered antiferromagnets,
but also provides experimental support for realizing quantized transport in
ultra-thin films of MnBi4Te7 and other natural superlattice topological
magnets.",2206.04582v1
2022/6/12,Novel Sample Stages for Detecting Magnetic Feedback Due to Superconducting Transition Based on the Mirror Image Method,"In traditional detection of the magnetic signal in the experiment,
complicated electronic devices are usually set up to explore the feedback from
the superconducting transition due to the external magnetic field. This kind of
direct detection will be more time-consuming, especially in experiments with
strict requirements like low temperature and high vacuum. To make the signal
detection more convenient to realize, we design a novel sample stage with
functions of both placement and acceptance of the magnetic field based on the
mirror image method. This device consists of two parts, drive coils and
receiver coils. The drive coils apply the initial magnetic field to the
superconducting material while the receiver coils are used to collect the
magnetic signal feedback. With only the power supply and a signal amplifier
needed to be connected to the coils, our device makes it more convenient to
finish magnetic signal detection. Another highlight of our design is using
first-principles numerical simulation to help accurately determine the size and
parameters of the device. With these calculated parameters, we build a 3D model
of the device using the software SOLIDWORKS.",2206.05686v2
2022/8/2,Temperature-induced changes in the magnetism of Laves phase rare-earth--iron intermetallics by ab~initio calculations,"Laves RFe2 compounds, where R is a rare earth, exhibit technologically
relevant properties associated with the interplay between their lattice
geometry and magnetism. We apply ab~initio calculations to explore how magnetic
properties of Fe in RFe2 systems vary with temperature. We found that the ratio
between the orbital magnetic moment m_orb and the spin magnetic moment m_spin
increases with increasing temperature for YFe2, GdFe2, TbFe2, DyFe2, and HoFe2.
This increase is significant and it should be experimentally observable by
means of x-ray magnetic circular dichroism. We conjecture that the predicted
increase of the m_orb/m_spin ratio with temperature is linked to the reduction
of hybridization between same-spin-channel states of atoms with fluctuating
magnetic moments and to the associated increase of their atomic-like character.",2208.01477v2
2022/8/7,Transition state theory characterizes thin film macrospin dynamics driven by an oscillatory magnetic field: Inertial effects,"Understanding the magnetization switching process in ferromagnetic thin films
is essential for many technological applications. We investigate the effects of
periodic driving via magnetic fields on a macrospin system under explicit
consideration of inertial dynamics. This is usually achieved by extending the
Landau-Lifshitz-Gilbert equation with a term including the second time
derivative of the magnetization. The dynamics of the magnetization switching
can then be characterized by its switching rate. We apply methods from
transition state theory for driven systems to resolve the rate of magnetization
switching in this general case. In doing so, we find that magnetization
exhibits resonance-like behavior under certain driving conditions, and it can
be affected strongly by the system's relaxation rate.",2208.03613v1
2022/8/8,Effect of intense x-ray free-electron laser transient gratings on the magnetic domain structure of Tm:YIG,"Magnetic patterns can be controlled globally using fields or spin polarized
currents. In contrast, the local control of the magnetization on the nanometer
length scale remains challenging. Here, we demonstrate how magnetic domain
patterns in a Tm-doped yttrium iron garnet (Tm:YIG) thin film with
perpendicular magnetic anisotropy can be permanently and locally imprinted by
high intensity photon pulses of a hard x-ray transient grating (XTG).
Micromagnetic simulations provide a qualitative understanding of the observed
changes in the orientation of magnetic domains in Tm:YIG and XTG-induced
changes. The presented results offer a route for the local manipulation of the
magnetic state using hard XTG.",2208.04200v2
2022/8/22,"Current-induced magnetization reversal in (Ga,Mn)(Bi,As) epitaxial layer with perpendicular magnetic anisotropy","Pulsed current-induced magnetization reversal is investigated in the layer of
(Ga,Mn)(Bi,As) dilute ferromagnetic semiconductor (DFS) epitaxially grown under
tensile misfit strain causing perpendicular magnetic anisotropy in the layer.
The magnetization reversal, recorded through measurements of the anomalous Hall
effect, appearing under assistance of a static magnetic field parallel to the
current, is interpreted in terms of the spin-orbit torque mechanism. Our
results demonstrate that an addition of a small fraction of heavy Bi atoms,
substituting As atoms in the prototype DFS (Ga,Mn)As and increasing the
strength of spin-orbit coupling in the DFS valence band, significantly enhances
the efficiency of current-induced magnetization reversal thus reducing
considerably the threshold current density necessary for the reversal. Our
findings are of technological importance for applications to spin-orbit
torque-driven nonvolatile memory and logic elements.",2208.10318v1
2022/9/5,Generation and routing of nanoscale droplet solitons without compensation of magnetic damping,"Magnetic droplet soliton is a localized dynamic spin state which can serve as
a nanoscale information carrier and nonlinear oscillator. The present opinion
is that the formation of droplet solitons requires the compensation of magnetic
damping by a torque created by a spin-polarized electric current or pure spin
current. Here we demonstrate theoretically that nanoscale droplet solitons can
be generated and routed in ferromagnetic nanostructures with voltage-controlled
magnetic anisotropy in the presence of uncompensated magnetic damping.
Performing micromagnetic simulations for the MgO/Fe/MgO trilayer with almost
perpendicular-to-plane magnetization, we reveal the formation of the droplet
soliton under a nanoscale gate electrode subjected to a sub-nanosecond voltage
pulse. The soliton lives up to 50 ns at room temperature and can propagate over
micrometer distances in a ferromagnetic waveguide due to nonzero gradient of
the demagnetizing field. Furthermore, we show that an electrical routing of the
soliton to different outputs of a spintronic device can be realized with the
aid of an additional semiconducting nanostripe electrode creating controllable
gradient of the perpendicular magnetic anisotropy.",2209.01893v1
2022/9/21,Effect of Co Substitution on Ferrimagnetic Heusler compound Mn3Ga,"Effect of Co substitution on Mn$_3$Ga is investigated using first-principles
study for structural and magnetic properties. Without Co, ferrimagnetic Heusler
compound Mn3Ga is in tetragonal phase. With Co substitution, depending on Co
concentration (x) Mn$_3$Ga prefers tetragonal (cubic) phase when x \leq 0.5 (x
\geq 0.5). Ferrimagnetism is robust regardless of x in both phases. While
magnetic moments of two Mn do not vary significantly with x, Co magnetic moment
in two phases exhibit different behaviors, leading to distinct features in
total magnetic moment (M_{tot}). When x \leq 0.5, in tetragonal phase, Co
magnetic moment is vanishingly small, resulting in a decrease of M_{tot} with
x. In contrast, when x \geq 0.5, in cubic phase, Co magnetic moment is roughly
1$\mu_B$, which is responsible for an increase of Mtot. Electronic structure is
analyzed with partial density of states for various x. To elucidate the
counterintuitively small Co moment, the magnetic exchange interaction is
investigated where exchange coefficient between Co and Mn is much smaller in x
\leq 0.5 case than x \geq 0.5 one.",2209.10216v1
2022/11/14,Magnetization Dynamics in Synthetic Antiferromagnets with Perpendicular Magnetic Anisotropy,"Understanding the rich physics of magnetization dynamics in perpendicular
synthetic antiferromagnets (p-SAFs) is crucial for developing next-generation
spintronic devices. In this work, we systematically investigate the
magnetization dynamics in p-SAFs combining time-resolved magneto-optical Kerr
effect (TR-MOKE) measurements with theoretical modeling. These model analyses,
based on a Landau-Lifshitz-Gilbert approach incorporating exchange coupling,
provide details about the magnetization dynamic characteristics including the
amplitudes, directions, and phases of the precession of p-SAFs under varying
magnetic fields. These model-predicted characteristics are in excellent
quantitative agreement with TR-MOKE measurements on an asymmetric p-SAF. We
further reveal the damping mechanisms of two procession modes co-existing in
the p-SAF and successfully identify individual contributions from different
sources, including Gilbert damping of each ferromagnetic layer, spin pumping,
and inhomogeneous broadening. Such a comprehensive understanding of
magnetization dynamics in p-SAFs, obtained by integrating high-fidelity TR-MOKE
measurements and theoretical modeling, can guide the design of p-SAF-based
architectures for spintronic applications.",2211.07744v2
2022/11/24,Large Magnetic-Field-Induced Strains in Sintered Chromium Tellurides,"Sintered samples of Cr3Te4 and Cr2Te3 are found to show large strains
accompanied by large volume changes under a magnetic field. In Cr3Te4, volume
increases of deltaV/V = 500-1170 ppm by applying a magnetic field of 9 T are
observed over the entire temperature range below 350 K. At room temperature,
the deltaV/V value exceeds 1000 ppm, which is considerably larger than the
maximum values reported for Cr-based magnets thus far and is comparable to the
room-temperature value of forced-volume magnetostriction in invar alloys.
Cr2Te3 show a large deltaV/V of 680 ppm when applying a magnetic field of 9 T
at 200 K. Both samples display particularly large volume increases around the
Curie temperature, where they also show negative thermal expansion due to
microstructural effects, suggesting that the cooperation between anisotropic
lattice deformation associated with the magnetic ordering and microstructural
effects is essential for the manifestation of the large magnetic-field-induced
volume changes.",2211.13388v1
2022/11/28,Moiré Magnetic Exchange Interactions in Twisted Magnets,"Besides moir\'e superlattice, twisting can also generate moir\'e magnetic
exchange interactions (MMEIs) in van der Waals magnets. However, due to the
extreme complexity and twist-angle-dependent sensitivity, all existing models
fail to capture the MMEIs, preventing the understanding of MMEIs-induced new
physics. Here, we develop a microscopic moir\'e spin Hamiltonian that enables
the effective description of MMEIs via a sliding-mapping approach in twisted
magnets, as demonstrated in twisted bilayer CrI3. Unexpectedly, we discover
that the emergence of MMEIs can create an unprecedented magnetic skyrmion
bubble (SkB) with non-conversed helicity, named as moir\'e-type SkB,
representing a unique spin texture solely generated by MMEIs and ready to be
detected under the current experimental conditions. Importantly, the size and
population of SkBs can be finely controlled by twist angle, a key step for
skyrmion-based quantum computing and information storage. Furthermore, we
reveal that the MMEIs can be effectively manipulated by the substrate-induced
interfacial Dzyaloshinskii-Moriya interaction, modulating the
twist-angle-dependent magnetic phase diagram, which solves the outstanding
disagreements between prior theories and experiments and verifies our theory.",2211.15186v2
2022/12/7,Magnetic octupoles as the order parameter for unconventional antiferromagnetism,"We show that time-reversal symmetry broken, centrosymmetric antiferromagnets
with nonrelativistic spin-splitting are conveniently described in terms of the
ferroic ordering of magnetic octupoles. The magnetic octupoles are the
lowest-order ferroically ordered magnetic quantity in this case, and so are the
natural order parameter for the transition into the magnetically ordered state.
They provide a unified description of the broken time-reversal symmetry and the
non-relativistic spin splitting as well as a platform for manipulating the
latter, and account for other phenomena, such as piezomagnetism, characteristic
of this class of antiferromagnets. Unusually for antiferromagnets, we show that
the magnetic octupoles cause a non-zero magnetic Compton scattering, providing
a route for their direct experimental detection. We illustrate these concepts
using density-functional and model calculations for the prototypical
non-relativistic spin-split antiferromagnet, rutile-structure manganese
difuoride, MnF2.",2212.03756v1
2022/12/15,Electric field tuning of magnetic states in single magnetic molecules,"Single magnetic molecules may be the smallest functional magnets. An
electric-field controllable spin state of magnetic molecules is of fundamental
importance for applications while its realization remains challenging. To date
the observed spin-electric interaction based on spin-orbit coupling or spin
dipole coupling is useful to tune fine spin structures but too weak to flip the
spin state. In this work, we propose a new mechanism to realize enhanced
spin-electric coupling and flip the spin states by tuning the spin
superexchange between local spins. Using first-principles calculations and
Heisenberg Hamiltonian, we demonstrate this effect in a family of magnetic
molecules, transition metallic Porphyrins. We show that their d-{\pi} and
{\pi}-{\pi} spin superexchange couplings are determined by the relative
energies of d and {\pi} electronic states, which are sensitive to the applied
electric field. Therefore, applying electric field can tune a wide range of
magnetic ground states, including ferromagnetic, ferrimagnetic, and
antiferromagnetic configurations. This spin-electric coupling may provide a new
approach for designing and controlling molecular spintronics.",2212.08010v1
2022/12/17,Densely packed skyrmions stabilized at zero magnetic field by indirect exchange coupling in multilayers,"Room-temperature stabilization of skyrmions in magnetic multilayered systems
is the result of a fine balance between different magnetic interactions namely
symmetric and antisymmetric exchange, dipolar, perpendicular magnetic
anisotropy as well as, in most cases, Zeeman through an applied external field.
Such field-driven stabilization approach is not compatible with most of the
anticipated skyrmion based applications, e.g. skyrmion memories, logic or
neuromorphic computing which motivates a reduction or a cancellation of field
requirements. Here we present a method to stabilize at room-temperature and
zero-field, a densely packed skyrmion phase in ferromagnetic multilayers with
moderate number of repetitions. To this aim, we finely tune the multilayer
parameters to stabilize a dense skyrmion phase. Then, relying on the interlayer
electronic coupling to an adjacent bias magnetic layer with strong
perpendicular magnetic anisotropy and uniform magnetization, we demonstrate the
stabilization of sub-60 nm diameter skyrmion at zero-field with adjustable
skyrmion density.",2212.08920v1
2023/1/4,Magnetization dynamics with time-dependent spin-density functional theory: significance of exchange-correlation torques,"In spin-density-functional theory (SDFT) for noncollinear magnetic materials,
the Kohn-Sham system features exchange-correlation (xc) scalar potentials and
magnetic fields. The significance of the xc magnetic fields is not very well
explored; in particular, they can give rise to local torques on the
magnetization, which are absent in standard local and semilocal approximations.
Exact benchmark solutions for a five-site extended Hubbard lattice at half
filling and in the presence of spin-orbit coupling are compared with SDFT
results obtained using orbital-dependent exchange-only approximations. The
magnetization dynamics following short-pulse excitations is found to be
reasonably well described in the exchange-only approximation for weak to
moderate interactions. For stronger interactions and near transitions between
magnetically ordered and frustrated phases, exchange and correlation torques
tend to compensate each other and must both be accounted for.",2301.01509v1
2023/1/24,Parameter free treatment of a layered correlated van der Waals magnet: CrPS$_{4}$,"The electronic and magnetic structure of CrPS$_{4}$, a 2D magnetic
semiconductor is examined by employing the SCAN meta-GGA density functional. We
find the resulting magnetic moment and band gap are in excellent agreement with
experiment. From the bulk magnetic configurations, we confirm the
experimentally observed A-type antiferromagnetic (A-AFM) ordered ground state
with a magnetic moment of 2.78 $\mu_B$ per chromium atom and band gap of 1.34
eV. To gain insight into the evolution of the ground state with layers, the
total energy of each magnetic configuration is calculated for a variety of
thicknesses. Monolayer CrPS$_{4}$ is predicted to be a ferromagnetic insulator
with a band gap of 1.37 eV, and A-AFM for bilayer and trilayer, with band gaps
of 1.35 eV and 1.30 eV, respectively. The electronic structure is reported for
the single, two, three layer and bulk CrPS$_{4}$. Finally, we explore the
optical properties of the 2D structure and report the dielectric tensor
components and Kerr parameters for the monolayer.",2301.10291v2
2023/2/13,Orbital Gravito-Magnetoelectric response and Orbital magnetic quadrupole moment correction,"The magnetoelectric effect has been actively studied in multiferroics since
the first observation in an antiferromagnetic, $\mathrm{Cr_2O_3}$. This effect
appears in systems without spatial inversion symmetry and time-reversal
symmetry and is sensitive to detecting magnetic quadrupole moments. It is often
discussed as inducing spin magnetizations; however, the orbital magnetoelectric
effect in metals has recently attracted much attention since its observation in
$\mathrm{MoS_2}$ and twisted bilayer graphene. In this work, we propose the
full quantum formalism for the temperature gradient induced-orbital
magnetoelectric effect (orbital gravito-ME effect). The effect consists of two
parts, i.e., an extrinsic part and an intrinsic part. We demonstrate that the
intrinsic part needs a correction from the orbital magnetic quadrupole moment
besides the usual Kubo formula to avoid an unphysical divergence at zero
temperature and to satisfy the Mott relation. Furthermore, we show the
classification table with the magnetic point group for the intrinsic and
extrinsic effects. Finally, we analyze the intrinsic part in a
$\mathcal{PT}$-symmetric model exhibiting an orbital magnetization order, i.e.,
a loop current order, and demonstrate the enhancement near Dirac points. We
believe that these results will contribute to the detection and usage of
orbital magnetic moments beyond spin moments.",2302.06047v1
2023/2/16,Magnetization reversal in FePt thin films: Experiments and simulations,"The competition between shape and perpendicular magnetic anisotropies (PMA)
in magnetic thin films gives rise to unusual magnetic behaviors. In
ferromagnetic films with moderate PMA the magnetic domain configuration
transitions from planar to stripe-like domains above a critical thickness,
$t_c$. In this article, we present a detailed study of the magnetization
switching mechanism in FePt thin films, where this phenomenon is observed.
Using micromagnetic simulations and experiments, we found that below $t_c$ the
reversal mechanism is well described by the two-phase model while above this
thickness the magnetization within each stripe reverses by coherent rotation.
We also analyzed the PMA and its temperature dependence, probing that
substrate-induced strains are responsible for the abnormal coercive field
behavior observed for FePt films with $t>t_c$.",2302.08538v1
2023/1/21,Investigation the effect of pH and reducing agent concentration on the structural properties of zinc-substitution magnetite nanoparticles,"Today, spinel ferrite nanoparticles are widely used in the medical field for
cancer treatment, drug delivery, and magnetic resonance imaging contrast agent
due to their superior magnetic properties and biocompatibility. Due to the
strong dependence of magnetic properties on morphology and other structural
aspects, the magnetic properties of these nanoparticles depend on their
manufacturing process. One of the goals of the researchers is to improve the
magnetic properties of these nanoparticles by substituting elements such as
manganese, cobalt, zinc, nickel, magnesium and iron. In this research, first,
magnetic Zn0.3Fe0.6O4 nanoparticles were synthesized by hydrothermal method in
the presence of citric acid as a reducing agent. In order to reduce the amount
of impurity and obtain the pure spinel phase and reduce the size of magnetic
nanoparticles, the hydrothermal process was carried out in the presence of
different concentrations of the reducing agent and pH level of the medium. The
structural investigations of the resulting nanoparticles were carried out by
X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results
showed that in order to obtain pure and single-phase spinel nanoparticles with
appropriate particle size and size distribution, it is necessary to control the
concentration of reducing agent and pH.",2302.10168v1
2023/2/23,Interfacial and Surface Magnetism in Epitaxial NiCo2O4(001)/MgAl2O4 Films,"NiCo2O4 (NCO) films grown on MgAl2O4 (001) substrates have been studied using
magnetometry, x-ray magnetic circular dichroism (XMCD) based on x-ray
absorption spectroscopy, and spin-polarized inverse photoemission spectroscopy
(SPIPES) with various thickness down to 1.6 nm. The magnetic behavior can be
understood in terms of a layer of optimal NCO and an interfacial layer (1.2+/-
0.1 nm), with a small canting of magnetization at the surface. The thickness
dependence of the optimal layer can be described by the finite-scaling theory
with a critical exponent consistent with the high perpendicular magnetic
anisotropy. The interfacial layer couples antiferromagnetically to the optimal
layer, generating exchange-spring styled magnetic hysteresis in the thinnest
films. The non-optimal and measurement-speed-dependent magnetic properties of
the interfacial layer suggest substantial interfacial diffusion.",2302.11744v1
2023/2/24,Type-II magnetic domain contrasts caused by internal-magnetisation induced electron scattering anisotropy,"Previous studies have shown that type-II magnetic domain contrasts are caused
by differences in the backscattering yields of magnetic domains of opposite
magnetisation. Imaging the magnetic domains when the magnetisation vectors in
the opposite-magnetisation domains are perpendicular to the tilt axis of the
specimen has been considered impossible, because of the lack of change in the
backscattering yields between the domains. However, we found that it is
possible to observe the type-II magnetic domain contrast even in cases where
the backscattering coefficients of the domains are the same. The contrast
arises from the electron-scattering anisotropy created because of the
deflection of the electron trajectories by the Lorentz force. We verify this by
distinguishing all four possible in-plane magnetisation vectors on a Fe-Si(100)
surface, using an electron backscatter diffraction detector as an arrya of
electron detectors. The change in contrast between the magnetic domains, with
respect to the location of a virtual electron detector, can provide information
on the directions of the magnetisation vectors. A method to suppress the
topographic contrast superimposed on the magnetic domain contrast is also
demonstrated.",2302.12374v1
2023/3/6,"Annealing time, temperature, and field dependence of pinned magnetic moments in the collinear antiferromagnet PdMn","Magnetic annealing of the collinear antiferromagnet PdMn with excess Pd
produces strongly pinned magnetic moments in the annealing field direction.
This behaviour can be understood with the help of the magnetic-field-biased
diffusion model. Here, the magnetic field creates an energy difference between
the two possible occupations of the antiferromagnetic Mn-sublattices by the
Pd-excess atoms. This, mediated by diffusion, leads to an imbalance in the
amount of the Pd-excess atoms in these sublattices and, subsequently, to an
imbalance in the total magnetization of the sublattices. We investigate this
effect's dependence on the annealing field, time, and temperature. The results
are then compared to the results of the magnetic-field-biased diffusion model,
which gives good agreement.",2303.03114v1
2023/3/21,Unveiling the magnetic structure and phase transition of Cr$_2$CoAl using neutron diffraction,"We report the detailed analysis of temperature dependent neutron diffraction
pattern of the Cr$_2$CoAl inverse Heusler alloy and unveil the magnetic
structure up to the phase transition as well as its fully compensated
ferrimagnetic nature. The Rietveld refinement of the diffraction pattern using
the space group I$\bar4${\it m}2 confirm the inverse tetragonal structure over
the large temperature range from 100~K to 900~K. The refinement of the magnetic
phase considering the wave vector $k=$ (0, 0, 0) reveals the ferrimagnetic
nature of the sample below 730$\pm$5~K. This transition temperature is obtained
from empirical power law fitting of the variation in the ordered net magnetic
moment and intensity of (110) peak as a function of temperature. The spin
configuration of the microscopic magnetic structure suggests the nearly fully
compensated ferrimagnetic behavior where the magnetic moments of Cr2 are
antiparallel with respect to the Cr1, and Co moments. Moreover, the observed
anomaly in the thermal expansion and lattice parameters at 730$\pm$5~K suggest
that the distortion in crystal structure may play an important role in the
magnetic phase transition.",2303.11869v1
2023/3/29,Magnetic Anisotropy and Its Structural Origins in Ru-Substituted Manganite Films,"Controlling magnetic anisotropy (MA) is important in a variety of
applications including magnetic memories, spintronic sensors, and
skyrmion-based data distribution. The perovskite manganite family provides a
fertile playground for complex, intricate, and potentially useful
structure-magnetism relations. Here we report on the MA that emerges in 10% Ru
substituted $La_{0.7}Sr_{0.3}MnO_{3}$ (Ru-LSMO) films for which strong
perpendicular magnetization and anisotropic in-plane magnetization are found.
These moderately compressively strained films possess a rich microstructure,
consisting of coherently strained phase which evolves into a one dimensional
(1D) periodically-modulated structure above a critical thickness. We illustrate
how 10% Ru substitution plays a crucial role behind the observed MA, and how
the structural distortion and 1D periodic structural modulation produce the
anisotropic in-plane magnetization. We highlight the practical significance of
the observed MA, which could pave the way towards the realization of
cutting-edge oxide-based room temperature spintronic memory devices.",2303.17008v2
2023/5/11,Consequences and control of multi-scale (dis)order in chiral magnetic textures,"Transition metal-intercalated transition metal dichalcogenides (TMDs) are
promising platforms for next-generation spintronic devices based on their wide
range of electronic and magnetic phases, which can be tuned by varying the host
lattice or the identity of the intercalant, along with its stoichiometry and
spatial order. Some of these compounds host a chiral magnetic phase in which
the helical winding of magnetic moments propagates along a high-symmetry
crystalline axis. Previous studies have demonstrated that variation in
intercalant concentrations can have a dramatic impact on the formation of
chiral domains and ensemble magnetic properties. However, a systematic and
comprehensive study of how atomic-scale order and disorder impacts collective
magnetic behavior are so far lacking. Here, we leverage a combination of
imaging modes in the (scanning) transmission electron microscope (S/TEM) to
directly probe (dis)order across multiple length scales and show how subtle
changes in the atomic lattice can be leveraged to tune the mesoscale spin
textures and bulk magnetic response, with direct implications for the
fundamental understanding and technological implementation of such compounds.",2305.06656v1
2023/6/16,Magnetic structure and Kondo lattice behavior in CeVGe$_3$: an NMR and neutron scattering study,"We present nuclear magnetic resonance (NMR), neutron diffraction,
magnetization, and transport measurements on a single crystal and powder of
CeVGe$_3$. This material exhibits heavy fermion behavior at low temperature,
accompanied by antiferromagnetic (AFM) order below 5.8 K. We find that the
magnetic structure is incommensurate with AFM helical structure, characterized
by a magnetic modulated propagation vector of $(0, 0, 0.49)$ with in-plane
moments rotating around the $c$-axis. The NMR Knight shift and spin-lattice
relaxation rate reveal a coherence temperature $T^*\sim 15$ K, and the presence
of significant antiferromagnetic fluctuations reminiscent of the archetypical
heavy fermion compound CeRhIn$_5$. We further identify a metamagnetic
transition above $H_m\sim 2.5$ T for magnetic fields perpendicular to $c$. We
speculate that the magnetic structure in this field-induced phase consists of a
superposition with both ferromagnetic and antiferromagnetic components, which
is consistent with the NMR spectrum in this region of the phase diagram. Our
results thus indicate that CeVGe$_3$ is a hexagonal structure analog to
tetragonal CeRhIn$_5$.",2306.10166v1
2023/6/22,Strain-induced frustrated helimagnetism and topological spin textures in LiCrTe$_{2}$,"By performing first-principles calculations in conjunction with Monte Carlo
simulations, we systematically investigated the frustrated magnetic states
induced by in-plane compressive strain in LiCrTe$_{2}$. Our calculations
support that the magnetic ground state of LiCrTe$_{2}$ crystal is A-type
antiferromagnetic (AFM), with an in-plane ferromagnetic (FM) state and
interlayer AFM coupling. Furthermore, it is found that compressive strain can
significantly alter the magnetic interactions, giving rise to a transition from
an in-plane FM to an AFM state, undergoing a helimagnetic phase. Remarkably, a
highly frustrated helimagnetic state with disordered spin spirals under
moderate strain arises from the competition between spiral propagation modes
along distinct directions. In addition, various topological spin defects emerge
in this frustrated helimagnetic phase, which are assembled from various domain
wall units. These topological defects can be further tuned with external
magnetic fields. Our calculations not only uncover the origin of exotic
frustrated magnetism in triangular lattice magnetic systems, but also offer a
promising route to engineer the frustrated and topological magnetic state,
which is of significance in both fundamental research and technological
applications.",2306.13035v1
2023/6/26,Distorted triangular skyrmion lattice in a noncentrosymmetric tetragonal magnet,"Magnetic skyrmions are particle-like spin-swirling objects ubiquitously
realized in magnets. They are topologically stable chiral kinks composed of
multiple modulation waves of spiral spin structures, where the helicity of each
spiral is usually selected by antisymmetric exchange interactions in
noncentrosymmetric crystals. We report an experimental observation of a
distorted triangular lattice of skyrmions in the polar tetragonal magnet
EuNiGe$_3$, reflecting a strong coupling with the lattice. Moreover, through
resonant x-ray diffraction, we find that the magnetic helicity of the original
spiral at zero field is reversed when the skyrmion lattice is formed in a
magnetic field. This means that the energy gain provided by the skyrmion
lattice formation is larger than the antisymmetric exchange interaction. Our
findings will lead us to a further understanding of emergent magnetic states.",2306.14767v1
2023/7/5,Multi-level recording in dual-layer FePt-C granular film for heat-assisted magnetic recording,"Multi-level magnetic recording is a new concept for increasing the data
storage capacity of hard disk drives. However, its implementation has been
limited by a lack of suitable media capable of storing information at multiple
levels. Herein, we overcome this problem by developing dual FePt-C nanogranular
films separated by a Ru-C breaking layer with a cubic crystal structure. The
FePt grains in the bottom and top layers of the developed media exhibited
different effective magnetocrystalline anisotropies and Curie temperatures. The
former is realized by different degrees of ordering in the L10-FePt grains,
whereas the latter was attributed to the diffusion of Ru, thereby enabling
separate magnetic recordings at each layer under different magnetic fields and
temperatures. Furthermore, the magnetic measurements and heat-assisted magnetic
recording simulations showed that these media enabled 3-level recording and
could potentially be extended to 4-level recording, as the up-down and down-up
states exhibited non-zero magnetization.",2307.02213v1
2023/7/19,Magnetization amplification in the interlayer pairing superconductor 4Hb-TaS$_2$,"A recent experiment on the bulk compound 4Hb-TaS$_2$ reveals an unusual
time-reversal symmetry-breaking superconducting state that possesses a magnetic
memory not manifest in the normal state. Here we provide one mechanism for this
observation by studying the magnetic and electronic properties of 4Hb-TaS$_2$.
We discuss the criterion for a small magnetization in the normal state in terms
of spin and orbital magnetization. Based on an analysis of lattice symmetry and
Fermi surface structure, we propose that 4Hb-TaS$_2$ realizes superconductivity
in the interlayer, equal-spin channel with a gap function whose phase winds
along the Fermi surface by an integer multiple of $6\pi$. The enhancement of
the magnetization in the superconducting state compared to the normal state can
be explained if the state with a gap winding of $6\pi$ is realized, accounting
for the observed magnetic memory. We discuss how this superconducting state can
be probed experimentally by spin-polarized scanning tunneling microscopy.",2307.10389v1
2023/7/21,Magnetism and topological property in icosahedral quasicrystal,"Quasicrystal (QC) has no periodicity but has a unique rotational symmetry
forbidden in periodic crystals. Lack of microscopic theory of the crystalline
electric field (CEF) in the QC and approximant crystal (AC) has prevented us
from understanding the electric property, especially the magnetism. By
developing the general formulation of the CEF in the rare-earth based QC and
AC, we have analyzed the CEF in the QC Au-SM-Tb and AC (SM=Si, Ge, and Ga). The
magnetic anisotropy arising from the CEF plays an important role in realizing
unique magnetic states on the icosahedron (IC). By constructing the minimal
model with the magnetic anisotropy, we have analyzed the ground-state
properties of the IC, 1/1 AC, and QC. The hedgehog state is characterized by
the topological charge of one and the whirling-moment state is characterized by
the topological charge of three. The uniform arrangement of the ferrimagnetic
state is stabilized in the QC with the ferromagnetic (FM) interaction, which is
a candidate for the magnetic structure recently observed FM long-range order in
the QC Au-Ga-Tb. The uniform arrangement of the hedgehog state is stabilized in
the QC with the antiferromagnetic interaction, which suggests the possibility
of the topological magnetic long-range order.",2307.11898v1
2023/9/6,In-plane dominant anisotropy stochastic magnetic tunnel junction for probabilistic computing: A Fokker-Planck study,"Recently there is considerable interest to realize efficient and low-cost
true random number generators (RNGs) for practical applications. One important
way is through the use of bistable magnetic tunnel junctions (MTJs). Here we
study the magnetization dynamics of an MTJ, with a focus to realize efficient
random bit generation under the assumption that the orientation dependence of
the energy of the nanomagnet is described by two perpendicular in-plane
anisotropies. We find that a high rate of random bit generation is achievable
away from the pure easy-axis situation by tuning a single parameter $H_z$ so
that it is either (a) toward a barrierless-like single easy plane situation
when $H_z$ reduces to zero, or (b) toward a stronger easy plane situation when
$H_z$ becomes increasingly negative where transitions between low energy states
are confined in the stronger easy plane that contains the saddle points. We
find that the MTJs maintain their fast magnetization dynamical characteristics
even in the presence of a magnetic field. Our findings provide a valuable guide
to achieving efficient generation of probabilistic bits for applications in
probabilistic computing.",2309.03056v1
2023/9/12,Probing spatial variation of magnetic order in strained SrMnO$_3$ thin films using Spin Hall Magnetoresistance,"SrMnO$_{3}$ (SMO) is a magnetic insulator and predicted to exhibit a
multiferroic phase upon straining. Strained films of SMO display a wide range
of magnetic orders, ranging from G-type to C-and A-type, indicative of
competing magnetic interactions. The potential of spin Hall magnetoresistance
(SMR) is exploited as an electrical probe for detecting surface magnetic order,
to read surface magnetic moments in SMO and its spatial variation, by designing
and positioning electrodes of different sizes on the film. The findings
demonstrate antiferromagnetic domains with different magnetocrystalline
anisotropies along with a ferromagnetic order, where the magnetization arises
from double exchange mediated ferromagnetic order and canted antiferromagnetic
moments. Further, from a complete analysis of the SMR, a predominance of
antiferromagnetic domain sizes of 3.5 $\mu$m$^2$ is extracted. This work
enhances the applicability of SMR in unraveling the richness of correlation
effects in complex oxides, as manifested by the detection of coexisting and
competing ground states and lays the foundation for the study of magnon
transport for different magnetoelectric based computing applications.",2309.06279v1
2023/9/16,Antiferromagnetic to Ferrimagnetic Phase Transition and Possible Phase Coexistence in Polar Magnets (Fe$_{1-x}$Mn$_x$)$_2$Mo$_3$O$_8$,"In the present work, magnetic properties of single crystal
(Fe$_{1-x}$Mn$_x$)$_2$Mo$_3$O$_8$ ($0<x<1$) have been studied by performing
extensive measurements. A detailed magnetic phase diagram is built up, in which
antiferromagnetic state dominates for $x<0.25$ and ferrimagnetic phase arises
for $x>0.3$. Meanwhile, sizeable electric polarization of spin origin is
commonly observed in all samples, no matter what the magnetic state is. For the
samples hosting a ferrimagnetic state, square-like magnetic hysteresis loops
are revealed, while the remnant magnetization and coercive field can be tuned
drastically by simply varying the Mn-content or temperature. Possible
coexistence of the antiferromagnetic and ferrimagnetic phases is proposed to be
responsible for the remarkable modulation of magnetic properties in the
samples.",2309.08990v1
2023/10/10,Dynamic Terahertz Beamforming Based on Magnetically Switchable Hyperbolic Materials,"In this work, we introduce a concept to enable dynamic beamforming of
terahertz (THz) wavefronts using applied magnetic fields (B). The proposed
system exploits the magnetically switchable hyperbolic dispersion of the InSb
semiconductor. This phenomenology, combined with diffractive surfaces and
magnetic tilting of scattered fields, allows the design of a metasurface that
works with either circularly or linearly polarized wavefronts. In particular,
we demonstrate numerically that the transmitted beam tilting can be manipulated
with the direction and magnitude of B. Numerical results, obtained through the
finite element method (FEM), are qualitatively supported by semi-analytical
results from the generalized dipole theory. Motivated by potential applications
in future Tera-WiFi active links, a proof of concept is conducted for the
working frequency f = 300 GHz. The results indicate that the transmitted field
can be actively tuned to point in five different directions with beamforming of
45{\deg}, depending on the magnitude and direction of B. In addition to
magnetic beamforming, we also demonstrate that our proposal exhibits magnetic
circular dichroism (MCD), which can also find applications in magnetically
tunable THz isolators for one-way transmission/reflection.",2310.06529v1
2023/10/19,Micromagnetic Simulation of Three-dimensional Nanoarchitectures,"The thesis discusses micromagnetic simulation studies on high-frequency
magnetic dynamics in three-dimensional ferromagnetic nanoarchitectures made of
interconnected magnetic nanowire networks. Such artificial magnetic materials
with nanoscale features have recently emerged as a vivid topic of research, as
their geometry has a decisive impact on their magnetic properties. By studying
their static magnetization structure, we find that these systems display a
behavior analogous to that of 3D artificial spin ice lattices, with frustrated
interactions and the emergence of monopole-like defect structures at the wires'
intersection points. Our simulations reveal a high activity of these defect
sites in the magnonic high-frequency spectrum. We study various 3D
nanoarchitectures and show that their geometry and magnetization state results
in characteristic high-frequency signatures. Controlling these features could
open new pathways for magnonics research and reprogrammable magnetic
metamaterials.",2310.12839v1
2023/10/27,Understanding the effect of curvature on the magnetization reversal of three-dimensional nanohelices,"Comprehending the interaction between geometry and magnetism in
three-dimensional (3D) nanostructures is of importance to understand the
fundamental physics of domain wall (DW) formation and pinning. Here, we use
focused electron beam-induced deposition to fabricate magnetic nanohelices with
increasing helical curvature with height. Using electron tomography and Lorentz
transmission electron microscopy, we reconstruct the 3D structure and
magnetization of the nanohelices. The surface curvature, helical curvature and
torsion of the nanohelices are then quantified from the tomographic
reconstructions. Furthermore, by using the experimental 3D reconstructions as
inputs for micromagnetic simulations we can reveal the influence of surface and
helical curvature on the magnetic reversal mechanism. Hence, we can directly
correlate the magnetic behavior of a 3D nanohelix to its experimental
structure. These results demonstrate how control of geometry in nanohelices can
be utilized in the stabilization of DWs and control of the response of the
nanostructure to applied magnetic fields.",2310.18456v1
2023/11/7,"Magnetism in AV3Sb5 (A = Cs, Rb, K): Complex Landscape of the Dynamical Magnetic Textures","We have investigated the dynamical magnetic properties of the V-based kagome
stibnite compounds by combining the ab-initio calculated magnetic parameters of
a spin Hamiltonian like inter-site exchange parameters, magnetocrystalline
anisotropy and site projected magnetic moments, with full-fledged simulations
of atomistic spin-dynamics. Our calculations reveal that in addition to a
ferromagnetic order along the [001] direction, the system hosts a complex
landscape of magnetic configurations comprised of commensurate and
incommensurate spin-spirals along the [010] direction. The presence of such
chiral magnetic textures may be the key to solve the mystery about the origin
of the experimentally observed inherent breaking of the C6 rotational symmetry-
and the time-reversal symmetry.",2311.04099v1
2023/11/27,Coherent control of photomagnetic back-switching by double-pump laser pulses,"The control of nonthermal, all-optical magnetization switching under the
regime with an independent state of laser polarization opens up new
opportunities for ultrafast magnetic recording. Here, we investigate the
photo-magnetic back-switching capabilities of the write and erase magnetic
domain pattern using double-pump pulse excitations in an iron garnet film with
pure cubic magnetocrystalline symmetry. It is essential to note that forward
and backward magnetization switching is achievable in two distinctive
scenarios: using identical linearly polarized laser pulses and with pulses
having orthogonal polarization planes. By observing the switch of magnetization
at domains independent of the initial state, one can nonthermally toggle the
magnetization, equivalent to XOR logical operation, at frequencies reaching up
to 50 GHz.",2311.16336v2
2023/12/5,Iron and gold thin films: first-principles study,"Using density functional theory, we carried out systematic calculations for a
series of ultrathin iron layers with thicknesses ranging from one atomic
monolayer to eleven monolayers (up to about 1.5 nm). We considered three cases:
(1) iron layers both on a gold substrate and coated with gold, (2) iron layers
on a gold substrate but without coverage, and (3) freestanding iron layers
adjacent to a vacuum. For our models, we chose initial bcc Fe(001) surfaces and
fcc Au(001) substrates. Based on the calculations, we determined the details of
the geometry and magnetic properties of the systems. We calculate lattice
parameters, magnetic moments, Curie temperatures and magnetocrystalline
anisotropy energies. From the thickness dependence, we determined the volume
and surface contributions to the magnetic anisotropy constant. The further
analysis allowed us to determine the thickness ranges of the occurrence of
perpendicular magnetic anisotropy, as well as the effect of thickness and the
presence of a substrate and cap layer on the direction of the magnetization
easy axis.",2312.02701v1
2023/12/7,Frustration-Mediated Crossover from Long-Range to Short-Range Magnetic Ordering in $\mathbf{Y_{1-x}Lu_xBaCo_4O_7} $,"We present a comprehensive magnetic and structural phase diagram for
$\mathrm{Y_{1-x}Lu_xBaCo_4O_7}$, established through neutron diffraction and
magnetization measurements. Our results outline the evolution of various
nuclear structures, encompassing both orthorhombic and monoclinic symmetries,
in response to changes in composition and temperature. The phase transition
temperature of the orthorhombic phase, $T_{s1}$, decreases with increasing Lu
content from 310 K for x = 0.0 to 110 K for x = 1.0. In Lu-rich compositions
(0.7 \le x \le 1.0), first-order structural transitions are observed with
coexisting and competing orthorhombic Pbn$2_1$ and metastable monoclinic Cc
phases. Composition- and temperature-dependent refinements of the magnetic
structure reveal an antiferromagnetic arrangement of Co spin pairs, below the
magnetic transition temperatures of the Y-rich compositions, in the ab plane
within both the triangular and Kagom\'e layers. A gradual suppression of
long-range magnetic order is observed with increasing the Lu content,
accompanied by the development of short-range magnetic correlations present in
all the samples.",2312.04042v1
2023/12/7,Dissipationless gyrotropic magnetic Hall effect,"A dissipationless longitudinal current can be generated by a pure magnetic
field through the chiral magnetic effect. Herein, we propose that a pure
oscillating magnetic field through Zeeman coupling can further drive an AC
magnetic Hall current in two-dimensional systems without inversion symmetry. We
dub this effect the ""gyrotropic magnetic Hall effect"" (GMHE), in analogy with
the gyrotropic current achieved by rectifying the optical fields. Importantly,
we find that the GMHE conductivity is a reactive or dissipationless transport
coefficient, which is even under time-reversal symmetry. We reveal the ""Zeeman
Berry curvature"" as the quantum origin of the GMHE, whose integral over all
states below the Fermi energy gives the GMHE conductivity. Furthermore, by
symmetry analysis, we show that the GMHE can appear in a wide range of
two-dimensional materials. To demonstrate our proposal, we evaluate the GMHE
current in two-dimensional Rashba system and in the surface of topological
insulator, where a low-frequency magnetic field with a small amplitude can be
converted into a detectable Hall voltage.",2312.04093v1
2023/12/17,Magnetic Fluctuations in Niobium Pentoxide,"Using a spin-polarized muon beam we were able to capture magnetic dynamics in
an amorphous niobium pentoxide thin film. Muons are used to probe internal
magnetic fields produced by defects. Magnetic fluctuations could be described
by the dynamical Kubo-Toyabe model considering a time-dependent local magnetic
field. We state that observed fluctuations result from the correlated motion of
electron spins. We expect that oxygen vacancies play a significant role in
these films and lead to a complex magnetic field distribution which is
non-stationary. The characteristic average rate of magnetic field change is on
the order of 100~MHz. The observed dynamics may provide insight into potential
noise sources in Nb-based superconducting devices, while also highlighting the
limitations imposed by amorphous oxides.",2312.10697v1
2024/1/12,Magnetic properties of van der Waals layered single crystals DyOBr and SmOCl,"Two-dimensional van der Waals single crystals DyOBr and SmOCl have been grown
by flux method and their anisotropic magnetic properties are reported. DyOBr
orders antiferromagnetically at T$_{N}$=9.5~K with magnetic moments lying along
$a$-axis, similar as DyOCl. Its magnetic susceptibility shows anisotropic
anomalies at T$^{*}$=30~K possibly due to the crystal field effect. Furthermore
a fractional magnetization plateau is clearly observed under H$\parallel$a and
H$\parallel$[110], which suggests the existence of a possible field-induced
quantum magnetic state. On the other hand, isostructural SmOCl undergoes
antiferromagnetic transition at T$_{N}$=7.3~K and exhibits an Ising-like
perpendicular $c$-axis magnetic anisotropy, which could be well explained by
our crystal field calculations. Both DyOBr and SmOCl are insulators with band
gap of $\sim$5~eV, our results suggest they are promising in building van der
Waals heterostructures and applications in multifunctional devices.",2401.06741v1
2024/1/19,Experimental determination of the spin Hamiltonian of the cubic chiral magnet MnSi,"A thorough description of the physics of a magnetic compound requires the
validation of its microscopic spin Hamiltonian. Here, from the analysis of
muon-spin rotation spectra recorded in the magnetically ordered state at low
temperature in zero and finite magnetic fields, we determine the minimal
Hamiltonian for the chiral binary intermetallic magnet MnSi, consistent with
its high-temperature nonsymmorphic cubic space group P$2_1$3. The model
provides constraints for the orientation of the Moriya vector characterizing
the microscopic Dzyaloshinskii-Moriya interaction, with respect to the Mn
nearest-neighbor bonds. Small twist and canting of the magnetic structure are
revealed. Our result indicates that, within experimental uncertainties, the
magnetoelastic coupling is not strong enough to lower the paramagnetic crystal
symmetry in the magnetically ordered state. Additional implications from our
work are discussed and complementary studies are suggested.",2401.10687v1
2024/1/31,Tailoring magnetic and hyperthermia properties of biphase iron oxide nanocubes through post-annealing,"Tailoring the magnetic properties of iron oxide nanosystems is essential to
expand their biomedical applications. In this study, the 34 nm iron oxide
nanocubes with two phases consisting of Fe3O4 and alpha-Fe2O3 were annealed for
2 hours in the presence of O2, N2, He, and Ar to tune the respective phase
volume fractions and control the magnetic properties. X-ray diffraction and
magnetic measurements were carried out post-treatment to evaluate the changes
of the treated samples compared to the as-prepared, which showed an enhancement
of the alpha-Fe2O3 phase in the samples annealed with O2, while the others
indicated Fe3O4 enhancement. Furthermore, the latter samples indicated
enhancements in the crystallinity and saturation magnetization while coercivity
enhancement was most significant in the samples annealed with O2, resulting in
the highest specific absorption rates (up to 1000 W/g) in all the applied
fields of 800, 600, and 400 Oe in agar during magnetic hyperthermia
measurements. The general enhancement in the specific absorption rate
post-annealing underscores the importance of the annealing atmosphere in the
enhancement of the magnetic and structural properties of nanostructures.",2401.18009v1
2024/2/5,Nematic heavy fermions and coexisting magnetic order in CeSiI,"Motivated by the recent discovery of magnetism and heavy quasiparticles in
van der Waals material CeSiI, we develop an effective model that incorporates
the conduction electrons residing at the silicene layer interacting with the
local moments of the Ce ions. Ce sites are arranged on two layers of triangular
lattices, above and below the silicene layer, and they are located at the
center of the honeycomb lattice. This arrangement results in an effective
extended Kondo interaction along with a predominant ferromagnetic RKKY
interaction. Via mean-field theory of Abrikosov fermions, our analysis
indicates that the ground state of the monolayer can exhibit a non-magnetic
nematic heavy fermion phase that breaks $C_6$ rotational symmetry for small
Heisenberg exchange and a magnetically ordered phase for large Heisenberg
exchange. For intermediate values, a coexistence of magnetic order and a
uniform heavy Fermi liquid is stabilized where they reside on separate Ce
layers. We show that this phase can further be enhanced by an external electric
field. Our results provide a natural mechanism for the coexistence of magnetic
order and heavy fermions in CeSiI and highlight the possibility of
unconventional non-magnetic heavy fermions with broken rotational symmetry.",2402.03442v1
2024/2/19,"Unusual Multiple Magnetic Transitions and Anomalous Hall Effect Observed in Antiferromagnetic Weyl Semimetal, Mn$_{2.94}$Ge (Ge-rich)","We report on the magnetic and Hall effect measurements of the magnetic Weyl
semimetal, Mn$_{2.94}$Ge (Ge-rich) single crystal. From the magnetic properties
study, we identify unusual multiple magnetic transitions below the
N$\acute{e}$el temperature of 353 K, such as the spin-reorientation ($T_{SR}$)
and ferromagnetic-like transitions. Consistent with the magnetic properties,
the Hall effect study shows unusual behavior around the spin-reorientation
transition. Specifically, the anomalous Hall conductivity (AHC) increases with
increasing temperature, reaching a maximum at $T_{SR}$, which then gradually
decreases with increasing temperature. This observation is quite in contrast to
the Mn$_{3+\delta}$Ge (Mn-rich) system, though both compositions share the same
hexagonal crystal symmetry. This study unravels the sensitivity of magnetic and
topological properties on the Mn concentration.",2402.11923v1
2024/3/1,Cooperatively Modulating Magnetic Anisotropy and Colossal Magnetoresistance via Atomic-Scale Buffer Layers in Highly Strained La0.7Sr0.3MnO3 Films,"Simultaneous control of magnetic anisotropy and magnetoresistance, especially
with atomic scale precision, remains a pivotal challenge for realizing advanced
spintronic functionalities. Here we demonstrate cooperative continuous control
over both magnetoresistance and magnetic anisotropy in highly strained
La0.7Sr0.3MnO3 (LSMO) thin films. By inserting varying perovskite buffer
layers, compressively strained LSMO films transition from a ferromagnetic
insulator with out-of-plane magnetic anisotropy to a metallic state with
in-plane anisotropy. Atomic-scale buffer layer insertion enables remarkably
acute, precise control to sharply modulate this magnetic phase transformation.
A gigantic 10,000% modulation of the colossal magnetoresistance (CMR) and an
exceptionally sharp transition from out-of-plane to in-plane magnetic
anisotropy are attained in just a few contiguous layers. These atomic-scale
correlations among electronic, magnetic, and structural order parameters yield
flexible multifunctional control promising for next-generation oxide
spintronics.",2403.00361v1
2024/3/9,Intrinsic magnetism in KTaO$_3$ heterostructures,"There has been intense recent interest in the two-dimensional electron gases
(2DEGs) that form at the surfaces and interfaces of KTaO$_3$ (KTO), with the
discovery of superconductivity at temperatures significantly higher than those
of similar 2DEGs based on SrTiO$_3$ (STO). Like STO heterostructures, these KTO
2DEGs are formed by depositing an overlayer on top of appropriately prepared
KTO surfaces. Some of these overlayers are magnetic, and the resulting 2DEGs
show signatures of this magnetism, including hysteresis in the
magnetoresistance (MR). Here we show that KTO 2DEGs fabricated by depositing
AlO$_x$ on top of KTO also show hysteretic MR, indicative of long range
magnetic order, even though the samples nominally contain no intrinsic magnetic
elements. The hysteresis appears in both the transverse and longitudinal
resistance in magnetic fields both perpendicular to and in the plane of the
2DEG. The hysteretic MR has different characteristic fields and shapes for
surfaces of different crystal orientations, and vanishes above a few Kelvin.
Density functional theory (DFT) calculations indicate that the magnetism likely
arises from Ta$^{4+}$ local moments created in the presence of oxygen
vacancies.",2403.06022v1
2024/3/11,$^{27}$Al NMR study of the magnetic Weyl semimetal CeAlGe,"Motivated by the recent observations of electronic correlation effect [M.
Corasaniti \textit{et al}., Phys. Rev. B \textbf{104}, L121112 (2021)] and
topology-stabilized magnetic fluctuations [N. Drucker \textit{et al}., Nat.
Commun. \textbf{14}, 5182 (2023)] in the noncentrosymmetric magnetic Weyl
semimetal candidate CeAlGe, we performed systematic studies on the local static
and dynamic spin susceptibilities by $^{27}$Al nuclear magnetic resonance. Due
to the large spin susceptibility from Ce-$4f$ electrons, the theoretically
predicted responses from Weyl fermions are overwhelmed. A Knight-shift anomaly
is observed below $T^*\sim50$ K, a signature of the onset of coherent Kondo
coupling. In addition, an anomalous peak is found in $1/T_1T$ near 15 K, well
above the magnetic ordering temperature $T_N \approx 5$ K, which probably is a
consequence of topology-stabilized magnetic fluctuations. These results
highlight the interplay among electronic correlation, magnetism and band
topology in this family of Kondo Weyl semimetals.",2403.06476v1
2024/3/25,Embedded skyrmion bags in thin films of chiral magnets,"Magnetic skyrmions are topologically nontrivial spin configurations that
possess particle-like properties. Earlier research was mainly focused on a
specific type of skyrmion with topological charge Q = -1. However, theoretical
analyses of two-dimensional chiral magnets have predicted the existence of
skyrmion bags -- solitons with arbitrary positive or negative topological
charge. Although such spin textures are metastable states, recent experimental
observations have confirmed the stability of isolated skyrmion bags in a
limited range of applied magnetic fields. Here, by utilizing Lorentz
transmission electron microscopy, we show the extraordinary stability of
skyrmion bags in thin plates of B20-type FeGe. In particular, we show that
skyrmion bags embedded within a skyrmion lattice remain stable even in zero or
inverted external magnetic fields. A robust protocol for nucleating such
embedded skyrmion bags is provided. Our results agree perfectly with
micromagnetic simulations and establish thin plates of cubic chiral magnets as
a powerful platform for exploring a broad spectrum of topological magnetic
solitons.",2403.16931v1
2006/9/1,Magnetar-Driven Magnetic Tower as a Model for Gamma-Ray Bursts and Asymmetric Supernovae,"We consider a newly-born millisecond magnetar, focusing on its interaction
with the dense stellar plasma in which it is initially embedded. We argue that
the confining pressure and inertia of the surrounding plasma acts to collimate
the magnetar's Poynting-flux-dominated outflow into tightly beamed jets and
increases its magnetic luminosity. We propose this process as an essential
ingredient in the magnetar model for gamma-ray burst and asymmetric supernova
central engines. We introduce the ``pulsar-in-a-cavity'' as an important model
problem representing a magnetized rotating neutron star inside a collapsing
star. We describe its essential properties and derive simple estimates for the
evolution of the magnetic field and the resulting spin-down power. We find that
the infalling stellar mantle confines the magnetosphere, enabling a gradual
build-up of the toroidal magnetic field due to continuous twisting. The growing
magnetic pressure eventually becomes dominant, resulting in a
magnetically-driven explosion. The initial phase of the explosion is
quasi-isotropic, potentially exposing a sufficient amount of material to
$^{56}$Ni-producing temperatures to result in a bright supernova. However, if
significant expansion of the star occurs prior to the explosion, then very
little $^{56}$Ni is produced and no supernova is expected. In either case, hoop
stress subsequently collimates the magnetically-dominated outflow, leading to
the formation of a magnetic tower. After the star explodes, the decrease in
bounding pressure causes the magnetic outflow to become less beamed. However,
episodes of late fallback can reform the beamed outflow, which may be
responsible for late X-ray flares.",0609047v2
2002/9/6,The Transition State in Magnetization Reversal,"We consider a magnet with uniaxial anisotropy in an external magnetic field
along the anisotropy direction, but with a field magnitude smaller than the
coercive field. There are three representative magnetization configurations
corresponding to three extrema of the free energy. The equilibrium and
metastable configurations, which are magnetized approximately parallel and
antiparallel to the applied field, respectively, both correspond to local
free-energy minima. The third extremum configuration is the saddle point
separating these minima. It is also called the transition state for
magnetization reversal. The free-energy difference between the metastable and
transition-state configurations determines the thermal stability of the magnet.
However, it is difficult to determine the location of the transition state in
both experiments and numerical simulations. Here it is shown that the
computational Projective Dynamics method, applied to the time dependence of the
total magnetization, can be used to determine the transition state. From
large-scale micromagnetic simulations of a simple model of magnetic nanowires
with no crystalline anisotropy, the magnetization associated with the
transition state is found to be linearly dependent on temperature, and the
free-energy barrier is found to be dominated by the entropic contribution at
reasonable temperatures and external fields. The effect of including
crystalline anisotropy is also discussed. Finally, the influence of the spin
precession on the transition state is determined by comparison of the
micromagnetic simulations to kinetic Monte Carlo simulations of precession-free
(overdamped) dynamics.",0209166v1
2004/8/24,Novel Field-Induced Phases in HoMnO3 at Low Temperatures,"The novel field-induced re-entrant phase in multiferroic hexagonal HoMnO3 is
investigated to lower temperatures by dc magnetization, ac susceptibility, and
specific heat measurements at various magnetic fields. Two new phases have been
unambiguously identified below the Neel transition temperature, TN=76 K, for
magnetic fields up to 50 kOe. The existence of an intermediate phase between
the P[6]_3[c]m and P[6]_3c[m] magnetic structures (previously predicted from
dielectric measurements) was confirmed and the magnetic properties of this
phase have been investigated. At low temperatures (T<5 K) a dome shaped phase
boundary characterized by a magnetization jump and a narrow heat capacity peak
was detected between the magnetic fields of 5 kOe and 18 kOe. The transition
across this phase boundary is of first order and the magnetization and entropy
jumps obey the magnetic analogue of the Clausius-Clapeyron relation. Four of
the five low-temperature phases coexist at a tetracritical point at 2 K and 18
kOe. The complex magnetic phase diagram so derived provides an informative
basis for unraveling the underlying driving forces for the occurrence of the
various phases and the coupling between the different orders.",0408499v1
2006/10/18,Magnetic Properties and Metastable States in Spin-Crossover Transition of Co-Fe Prussian Blue Analogues,"The combination of spin transitions and magnetic ordering provides an
interesting structure of phase transitions in Prussian blue analogues (PBAs).
To understand the structure of stable and metastable states of Co-Fe PBA, it is
necessary to clarify free energy as a function of magnetization and the
fraction of the high-temperature component. Including the magnetic interaction
between high-temperature states, we study the magnetic phase transition of
Co-Fe PBA in addition to spin transitions. Here, we take into account the
degeneracy changes due to charge transfer between Co and Fe atoms accompanying
the spin transition. In this study, the charge transfer between Co and Fe atoms
is explicitly taken into account and also the ferrimagnetic structure of Co-Fe
PBAs is expressed in the proper way. First, we found systematic changes in the
structures of stable and metastable states as functions of system parameters
using mean field theory. In particular, the existence of a metastable
magnetic-ordered high-temperature state is confirmed at temperatures lower than
that of the hysteresis region of spin transitions. Second, we found that the
magnetic interaction causes complex ordering processes of a spin transition and
a magnetic phase transition. The effect of a magnetic field on the phase
structure is also investigated and we found metamagnetic magnetization
processes. Finally, the dynamical properties of this metastable state are
studied by Monte Carlo method.",0610500v2
2007/1/4,Spin-modulated quasi-1D antiferromagnet LiCuVO_4,"We report on magnetic resonance studies within the magnetically ordered phase
of the quasi-1D antiferromagnet LiCuVO_4. Our studies reveal a spin
reorientational transition at a magnetic field H_c1 ~ 25 kOe applied within the
crystallographical (ab)-plane in addition to the recently observed one at H_c2
\~75 kOe [ M.G. Banks et al., cond-mat/0608554 (2006)]. Spectra of the
antiferromagnetic resonance (AFMR) along low-frequency branches can be
described in the frame of a macroscopic theory of exchange-rigid planar
magnetic structures. These data allow to obtain the anisotropy of the exchange
interaction together with a constant of the uniaxial anisotropy. Spectra of 7Li
nuclear magnetic resonance (NMR) show that, within the magnetically ordered
phase of LiCuVO_4 in the low-field range H < H_c1, a planar spiral spin
structure is realized with the spins lying in the (ab)-plane in agreement with
neutron scattering studies of B.J. Gibson et al. [Physica B Vol. 350, 253
(2004)]. Based on NMR spectra simulations, the transition at H_c1 can well be
described as a spin-flop transition, where the spin plane of the magnetically
ordered structure rotates to be perpendicular to the direction of the applied
magnetic field. For H > H_c2 ~ 75 kOe, our NMR spectra simulations show that
the magnetically ordered structure exhibits a modulation of the spin
projections along the direction of the applied magnetic field H.",0701083v1
2007/3/29,Magnetic-field cycling induced anomalous irreversibility in resistivity of charge-ordered manganites,"The rare-earth ions (RE = Eu, Dy Ho, Tm, Y) substituted charge-ordered
antiferromagnetic manganites, Pr0.45RE0.05Ca0.5MnO3, were studied for the
magnetic and the transport properties in the presence of external
magnetic-fields of up to 14 Tesla. Regardless of the intrinsic magnetic
property of RE ions, all the compounds exhibit successive step-like
metamagnetic transitions at low temperatures, which are strongly correlated to
their electronic transitions. At any fixed temperature in two different
temperature-regimes, we observed contrary effects of the magnetic-field cycling
on the resistivity of these manganites, namely, i) in the low temperature
regime (<70 K), the resistivity was irreversible showing lower values than
initial after a magnetic-field cycle was over, which is consistent with the
irreversible magnetization, and ii) in a temperature regime above 70 K, the
resistivity is irreversible with noticeably higher values than initial, whereas
the magnetization was found to be reversible. For the latter case, we further
show that this irreversibility of resistivity systematically depends on the
temperature and the magnitude of applied magnetic-field. These results suggest
that the observed resistivity behavior originated from the magnetic-field
induced metamagnetic transitions and training effect.",0703771v1
2007/12/12,Magnetic anomalies in single crystalline ErPd2Si2,"Considering certain interesting features in the previously reported 166Er
Moessbauer effect and neutron diffraction data on the polycrystalline form of
ErPd2Si2 crystallizing in ThCr2Si2-type tetragonal structure, we have carried
out magnetic measurements (1.8 to 300 K) on the single crystalline form of this
compound. We observe significant anisotropy in the absolute values of
magnetization (indicating that the easy axis is c-axis) as well as in the
features due to magnetic ordering in the plot of magnetic susceptibility (chi)
versus temperature (T) at low temperatures. The chi(T) data reveal that there
is a pseudo-low dimensional magnetic order setting in at 4.8 K, with a
three-dimensional antiferromagnetic ordering setting in at a lower temperature
(3.8 K). A new finding in the chi(T) data is that, for H//<110>, but not for
H//<001>, there is a broad shoulder in the range 8-20 K, indicative of the
existence of magnetic correlations above 5 K as well, which could be related to
the previously reported slow-relaxation-dominated Moessbauer spectra.
Interestingly, the temperature coefficient of electrical resistivity is found
to be isotropic; no feature due to magnetic ordering could be detected in the
electrical resistivity data at low temperatures, which is attributed to
magnetic Brillioun-zone boundary gap effects. The results reveal complex nature
of the magnetism of this compound.",0712.2002v1
2008/12/11,Magnetic properties of undoped Cu2O fine powders with magnetic impurities and/or cation vacancies,"Fine powders of micron- and submicron-sized particles of undoped Cu2O
semiconductor, with three different sizes and morphologies have been
synthesized by different chemical processes. These samples include nanospheres
200 nm in diameter, octahedra of size 1 micron, and polyhedra of size 800 nm.
They exhibit a wide spectrum of magnetic properties. At low temperature, T = 5
K, the octahedron sample is diamagnetic. The nanosphere is paramagnetic. The
other two polyhedron samples synthesized in different runs by the same process
are found to show different magnetic properties. One of them exhibits weak
ferromagnetism with T_C = 455 K and saturation magnetization, M_S = 0.19 emu/g
at T = 5 K, while the other is paramagnetic. The total magnetic moment
estimated from the detected impurity concentration of Fe, Co, and Ni, is too
small to account for the observed magnetism by one to two orders of magnitude.
Calculations by the density functional theory (DFT) reveal that cation
vacancies in the Cu2O lattice are one of the possible causes of induced
magnetic moments. The results further predict that the defect-induced magnetic
moments favour a ferromagnetically coupled ground state if the local
concentration of cation vacancies, n_C, exceeds 12.5%. This offers a possible
scenario to explain the observed magnetic properties. The limitations of the
investigations in the present work, in particular in the theoretical
calculations, are discussed and possible areas for further study are suggested.",0812.2079v1
2009/9/28,Magnetic order and dynamics of the charge-ordered antiferromagnet La1.5Sr0.5CoO4,"We describe neutron scattering experiments performed to investigate the
magnetic order and dynamics of half-doped La1.5Sr0.5CoO4. This layered
perovskite exhibits a near-ideal checkerboard pattern of Co2+/Co3+ charge order
at temperatures below ~ 800 K. Magnetic correlations are observed at
temperatures below ~ 60 K but static magnetic order only becomes established at
31 K, a temperature at which a kink is observed in the susceptibility. On
warming above 31 K we observed a change in the magnetic correlations which we
attribute either to a spin canting or to a change in the proportion of
inequivalent magnetic domains. The magnetic excitation spectrum is dominated by
an intense band extending above a gap of approximately 3 meV up to a maximum
energy of 16 meV. A weaker band exists in the energy range 20-30 meV. We show
that the excitation spectrum is in excellent quantitative agreement with the
predictions of a spin-wave theory generalized to include the full magnetic
degrees of freedom of high-spin Co2+ ions in an axially distorted crystal
field, coupled by Heisenberg exchange interactions. The magnetic order is found
to be stabilized by dominant antiferromagnetic Co2+ -- Co2+ interactions acting
in a straight line through Co3+. No evidence is found for magnetic scattering
from the Co3+ ions, supporting the view that Co3+ is in the S = 0 state in this
material.",0909.4964v1
2010/1/8,"The superconducting and magnetic states in RuSr2GdCu2O8, based on the magnetic, transport and magneto-caloric characteristics","The article discusses selected properties of the non- and superconducting
polycrystalline samples of RuSr2GdCu2O8 and comments the consequences of
introducing insignificant sub-stoichiometry of Ru into the nominal formula. The
magneto-resistive and the magnetic characteristics are interpreted in favour of
the formation of the intrinsically inhomogeneous superconducting phase, which
seems to be stabilized along with the structural modifications likely enhanced
with the modification of starting stoichiometry. The specific heat data reveals
the shift of temperature of the magnetic ordering T_{m}, suggesting the
dilution in magnetic sublattice of the Ru moments. The measurements of the
magnetic field dependences of the isothermal magnetocaloric coefficient M_{T}
show that there is no gain in magnetic entropy in a broad range of the accessed
fields and temperatures. Whereas the multi-component character of the probed
magnetic system precludes from concluding on the ground state for the Ru
ordering, the maximum in M_{T}(H) which occurs at weak magnetic fields for
temperature vicinity of T_{m} may reflect dominance of the ferromagnetic type
interactions with a constrained correlation range. The literature explored
models for the Ru magnetic ordering and possible phase separation in the
RuSr2GdCu2O8 are brought into the discussion.",1001.1239v2
2010/3/29,"From (pi, 0) magnetic order to superconductivity with (pi, pi) magnetic resonance in Fe1.02(Te1-xSex)","The iron chalcogenide Fe1+y(Te1-xSex) is structurally the simplest of the
Fe-based superconductors. Although the Fermi surface is similar to iron
pnictides, the parent compound Fe1+yTe exhibits antiferromagnetic order with
in-plane magnetic wave-vector (pi, 0). This contrasts the pnictide parent
compounds where the magnetic order has an in-plane magnetic wave-vector (pi,
pi) that connects hole and electron parts of the Fermi surface. Despite these
differences, both the pnictide and chalcogenide Fe-superconductors exhibit
superconducting spin resonances around (pi, pi), suggesting a common symmetry
for their superconducting order parameter. A central question in this
burgeoning field is therefore how (pi, pi) superconductivity can emerge from a
(pi, 0) magnetic instability. Here, we report that the magnetic soft mode
evolving from the (pi, 0)-type magnetic long-range order is associated with
weak charge carrier localization. Bulk superconductivity occurs only as the
magnetic mode at (pi, pi) becomes dominant upon doping. Our results suggest a
common magnetic origin for superconductivity in iron chalcogenide and pnictide
superconductors.",1003.5647v1
2012/1/30,High--field NMR of the quasi--1D antiferromagnet LiCuVO$_4$,"We report on NMR studies of the quasi one--dimensional (1D) antiferromagnetic
$S=1/2$ chain cuprate LiCuVO$_4$ in magnetic fields $H$ up to $\mu_0H$ = 30 T
($\approx 70$% of the saturation field $H_{\rm sat}$). NMR spectra in fields
higher than $H_{\rm c2}$ ($\mu_0H_{\rm c2} \approx 7.5$ T) and temperatures
$T<T_{\rm N}$ can be described within the model of a spin-modulated phase in
which the magnetic moments are aligned parallel to the applied field $H$ and
their values alternate sinusoidally along the magnetic chains. Based on
theoretical concepts about magnetically frustrated 1D chains, the field
dependence of the modulation strength of the magnetic structure is deduced from
our experiments. Relaxation time $T_2$ measurements of the $^{51}$V nuclei show
that $T_2$ depends on the particular position of the probing $^{51}$V nucleus
with respect to the magnetic copper moments within the 1D chains: the largest
$T_2$ value is observed for the vanadium nuclei which are very next to the
magnetic Cu$^{2+}$ ion with largest ordered magnetic moment. This observation
is in agreement with the expectation for the spin-modulated magnetic structure.
The $(H,T)$ magnetic phase diagram of LiCuVO$_4$ is discussed.",1201.6182v1
2012/6/10,Magnetic glass in Shape Memory Alloy : Ni45Co5Mn38Sn12,"The first order martensitic transition in the ferromagnetic shape memory
alloy Ni45Co5Mn38Sn12 is also a magnetic transition and has a large field
induced effect. While cooling in the presence of field this first order
magnetic martensite transition is kinetically arrested. Depending on the
cooling field, a fraction of the arrested ferromagnetic austenite phase
persists down to the lowest temperature as a magnetic glassy state, similar to
the one observed in various intermetallic alloys and in half doped manganites.
A detailed investigation of this first order ferromagnetic austenite (FM-A) to
low magnetization martensite (LM-M) state transition as a function of
temperature and field has been carried out by magnetization measurements.
Extensive cooling and heating in unequal field (CHUF) measurements and a novel
field cooled protocol for isothermal MH measurements (FC-MH) are utilized to
investigate the glass like arrested states and show a reverse martensite
transition. Finally, we determine a field -temperature (HT) phase diagram of
Ni45Co5Mn38Sn12 from various magnetization measurements which brings out the
regions where thermodynamic and metastable states co-exist in the HT space
clearly depicting this system as a 'Magnetic Glass'.",1206.2024v2
2013/5/2,Magnetic and electric properties of CaMn7O12 based multiferroic compounds: effect of electron doping,"The mixed-valent multiferroic compound CaMn7O12 is studied for its magnetic
and electric properties. The compound undergoes magnetic ordering below 90 K
with a helimagnetic structure followed by a low temperature magnetic anomaly
observed around 43 K. The present study shows that the magnetic anomaly at 43 K
is associated with thermal hysteresis indicating first order nature of the
transition. The compound also shows field-cooled magnetic memory and relaxation
below 43 K, although no zero-field-cooled memory is present. Clear magnetic
hysteresis loop is present in the magnetization versus field measurements
signifying the presence of some ferromagnetic clusters in the system. We doped
trivalent La at the cite of divalent Ca expecting to enhance the fraction of
Mn$^{3+}$ ions. The La doped samples show reduced magnetization, although the
temperatures associated with the magnetic anomalies remain almost unaltered.
Interestingly, the spontaneous electrical polarization below 90 K increases
drastically on La substitution. We propose that the ground state of the pure as
well as the La doped compositions contain isolated superparamagnetic like
clusters, which can give rise to metastability in the form of field-cooled
memory and relaxation. The ground state is not certainly spin glass type as it
is evident from the absence of zero-field-cooled memory and frequency shift in
the ac suceptibility measurements.",1305.0351v1
2013/5/31,"Relation between exciton splittings, magnetic circular dichroism, and magnetization in wurtzite (Ga,Fe)N","The question of the correlation between magnetization, band splittings, and
magnetic circular dichroism (MCD) in the fundamental gap region of dilute
magnetic semiconductors is examined experimentally and theoretically taking the
case of wurtzite Ga(1-x)FexN as an example. Magnetization and
polarization-resolved reflectivity measurements have been performed down to 2K
and up to 7T for x = 0.2%. Optical transitions originating from all three free
excitons A, B and C, specific to the wurtzite structure, have been observed and
their evolution with the magnetic field determined. It is demonstrated that the
magnitude of the exciton splittings evaluated from reflectivity-MCD data can be
overestimated by more than a factor of 2, as compared to the values obtained by
describing the polarization-resolved reflectivity spectra with appropriate
dielectric functions. A series of model calculations shows that the
quantitative inaccuracy of MCD originates from a substantial influence of the
magnetization-dependent exchange interactions not only on the spin splittings
of excitons but also upon their linewidth and oscillator strength. At the same
time, a method is proposed that allows to evaluate the field and temperature
dependencies of the magnetization from MCD spectra. The accurate values of the
excitonic splittings and of the magnetization reported here substantiate the
magnitudes of the apparent $sp-d$ exchange integrals in (Ga,Fe)N previously
determined.",1305.7496v2
2013/9/27,Phonons correlation with magnetic excitations in weak ferromagnet YCrO3,"We report on the temperature dependent Raman spectroscopic studies of
orthorombic distorted perovskite YCrO3 in the temperature range of 20-300K.
Temperature dependence of DC-magnetization measurement under field cooled and
zero field cooled modes confirmed the transition temperature (TN ~142K) and
anomalous characteristic temperature (T* ~60K), above which magnetization tends
to saturate. Magnetization isotherm recorded below TN at 125K shows clear loop
opening without magnetization saturation up to 20kOe, indicating the
coexistence of antiferromagnetic (AFM) interaction with weak ferromagnetic
(WFM) phase. Mean field calculation for exchange constants further confirms the
complex magnetic phase below TN. Temperature evolution of lineshape parameters
of selected modes (associated with the octahedral rotation and A-shift in the
unit cell) revealed anomalous phonon shift near Cr3+ magnetic ordering
temperature (TN ~142K). Additional phonon anomaly was identified at T* ~60K in
agreement with the magnetization results and reflects the change in spin
dynamics, plausibly due to the change in Cr-spin configuration. Moreover, the
positive and negative shift in Raman frequency below TN revel the existence of
competing WFM and AFM exchanges. The phonon shift of B3g (3)-octahedral
rotation mode fairly scaled with the square of sublattice magnetization from TN
to T*, below which it start to depart from theconventional behaviour and need
further attention. This correlation between magnetic and Raman data elucidate
the spin-phonon coupling owing to the multiferroic phenomenon in YCrO3.",1309.7254v1
2013/11/5,Cluster glass magnetism in the phase-separated Nd2/3Ca1/3MnO3 perovskite,"A detailed study of the low-temperature magnetic state and the relaxation in
the phase-separated colossal magnetoresistance Nd2/3Ca1/3MnO3 perovskite has
been carried out. Clear experimental evidence of the cluster-glass magnetic
behavior of this compound has been revealed. Well defined maxima in the
in-phase linear ac susceptibility $\chi ^{/}(T)$ were observed, indicative of
the magnetic glass transition at $T_{g}$ = 60 K. Strongly divergent
zero-field-cooled and field-cooled static magnetizations and frequency
dependent ac susceptibility are evident of the glassy-like magnetic state of
the compound at low temperatures. The frequency dependence of the cusp
temperature Tmax of the $\chi ^{/}(T)$ susceptibility was found to follow the
critical slowing down mechanism. The Cole-Cole analysis of the dynamic
susceptibility at low temperature has shown extremely broad distribution of
relaxation times, indicating that spins are frozen at ""macroscopic"" time scale.
Slow relaxation in the zero-field-cooled magnetization has been experimentally
revealed. The obtained results do not agree with a canonical spin-glass state
and indicate a cluster glass magnetic state of the compound below $T_{g}$,
associated with its antiferromagnetic-ferromagnetic nano-phase segregated
state. It was found that the relaxation mechanisms below the cluster glass
freezing temperature $T_{g}$ and above it are strongly different. Magnetic
field up to about $\mu_{0}$H = 0.4 T suppresses the glassy magnetic state of
the compound.",1311.1123v2
2014/9/2,Switching of Perpendicularly Polarized Nanomagnets with Spin Orbit Torque without an External Magnetic Field by Engineering a Tilted Anisotropy,"Spin orbit torque (SOT) provides an efficient way of generating spin current
that promises to significantly reduce the current required for switching
nanomagnets. However, an in-plane current generated SOT cannot
deterministically switch a perpendicularly polarized magnet due to symmetry
reasons. On the other hand, perpendicularly polarized magnets are preferred
over in-plane magnets for high-density data storage applications due to their
significantly larger thermal stability in ultra-scaled dimensions. Here we show
that it is possible switch a perpendicularly polarized magnet by SOT without
needing an external magnetic field. This is accomplished by engineering an
anisotropy in the magnets such that the magnetic easy axis slightly tilts away
from the film-normal. Such a tilted anisotropy breaks the symmetry of the
problem and makes it possible to switch the magnet deterministically. Using a
simple Ta/CoFeB/MgO/Ta heterostructure, we demonstrate reversible switching of
the magnetization by reversing the polarity of the applied current. This
demonstration presents a new approach for controlling nanomagnets with spin
orbit torque.",1409.0620v3
2014/9/23,Structural and Magnetic Phase Diagram of CrAs and its Relationship with Pressure-induced Superconductivity,"Most unconventional superconductors, including cuprates and iron-based
superconductors, are derived from chemical doping or application of pressure on
their collinearly magnetic-ordered parent compounds[1-5]. The recently
discovered pressure-induced superconductor CrAs, as a rare example of a
non-collinear helimagnetic superconductor, has therefore generated great
interest in understanding microscopic magnetic properties and their interplay
with superconductivity [6-8]. Unlike cuprates and iron based superconductors
where the magnetic moment direction barely changes upon doping, here we show
that CrAs exhibits a spin reorientation from the ab plane to the ac plane,
along with an abrupt drop of the magnetic propagation vector at a critical
pressure (Pc~0.6 GPa). This magnetic phase transition coincides with the
emergence of bulk superconductivity, indicating a direct connection between
magnetism and superconductivity. With further increasing pressure, the magnetic
order completely disappears near the optimal Tc regime (P~0.94 GPa). Moreover,
the Cr magnetic moments between nearest neighbors tend to be aligned
antiparallel with increasing pressure toward the optimal superconductivity
regime. Our findings suggest that the non-collinear helimagnetic order is
strongly coupled to structural and electronic degrees of freedom, and that
antiferromagnetic correlations associated with the low magnetic vector phase
are crucial for superconductivity.",1409.6615v3
2014/12/2,Effect of phase separation induced supercooling on magnetotransport properties of epitaxial La5/8-yPryCa3/8MnO3 (y~0.4) thin film,"Thin films of La5/8-yPryCa3/8MnO3 (y~0.4) have been grown on single crystal
SrTiO3 (001) by RF sputtering. The structural and surface characterizations
confirm the epitaxial nature of these film. However, the difference between the
rocking curve of the (002) and (110) peaks and the presence of pits/holes in
the step-terrace type surface morphology suggests high density of defect in
these films. Pronounced hysteresis between the field cool cooled (FCC) and
field cooled warming (FCW) magnetization measurements suggest towards the
non-ergodic magnetic state. The origin of this nonergodicity could be traced to
the magnetic liquid like state arising from the delicacy of the coexisting
magnetic phases, viz., ferromagnetic and antiferromagnetic-charge ordered
(FM/AFM-CO). The large difference between the insulator metal transitions
during cooling and warming cycles (TIMC~64 K and TIMW~123 K) could be regarded
as a manifestation of the nonergodicity leading to supercooling of the magnetic
liquid while cooling. The nonergodicity and supercooling are weakened by the
AFM-FM phase transition induced by an external magnetic field. TIM and small
polaron activation energy corresponding the magnetic liquid state (cooling
cycle) vary nonlinearly with the applied magnetic field but become linear in
the crystalline solid state (warming cycle). The analysis of the low
temperature resistivity data shows that electron-phonon interaction is
drastically reduced by the applied magnetic field. The resistivity minimum in
the lower temperature region of the self-field warming curve has been explained
in terms of the Kondo like scattering in the magnetically inhomogeneous regime.",1412.0862v1
2015/1/8,"Incommensurate magnetic structure, Fe/Cu chemical disorder and magnetic interactions in the high-temperature multiferroic YBaCuFeO5","Motivated by the recent observations of incommensurate magnetic order and
electric polarization in YBaCuFeO5 up to temperatures TN2 as high as 230K [1,2]
we report here for the first time a model for the incommensurate magnetic
structure of this material that we complement with ab-initio calculations of
the magnetic exchange parameters. Using neutron powder diffraction we show that
the appearance of polarization below TN2 is accompanied by the replacement of
the high temperature collinear magnetic order by a circular inclined spiral
with propagation vector ki=(1/2, 1/2, 1/2+-q). Moreover, we find that the
polarization approximately scales with the modulus of the magnetic modulation
vector q down to the lowest temperature investigated (T=3K). Further, we
observe occupational Fe/Cu disorder in the FeO5-CuO5 bipyramids, although a
preferential occupation of such units by Fe-Cu pairs is supported by the
observed magnetic order and by density functional calculations. We calculate
exchange coupling constants for different Fe/Cu distributions and show that,
for those containing Fe-Cu dimers, the resulting magnetic order is compatible
with the experimentally observed collinear magnetic structure (kc=(1/2, 1/2,
1/2), TN2 > T > TN1 = 440K). Based on these results we discuss possible origins
for the incommensurate modulation and its coupling with ferroelectricity.",1501.01935v1
2015/2/18,"Magnetocrystalline anisotropic effect in GdCo$_{1-x}$Fe$_x$AsO ($x = 0, 0.05$)","From a systematic study of the electrical resistivity $\rho(T,H)$, magnetic
susceptibility $\chi(T,H)$, isothermal magnetization $M(H)$ and the specific
heat $C(T,H)$, a temperature-magnetic field ($T$-$H$) phase diagram has been
established for GdCo$_{1-x}$Fe$_x$AsO ($x = 0$ and $0.05$) polycrystalline
compounds. GdCoAsO undergoes two long-range magnetic transitions: ferromagnetic
(FM) transition of Co $3d$ electrons ($T_\textup{C}^\textup{Co}$) and
antiferromagnetic (AFM) transition of Gd $4f$ electrons
($T_\textup{N}^\textup{Gd}$). For the Fe-doped sample ($x=0.05$), an extra
magnetic reorientation transition takes place below $T_\textup{N}^\textup{Gd}$,
which is likely associated with Co moments. The two magnetic species of Gd and
Co are coupled antiferromagnetically to give rise to ferrimagnetic (FIM)
behavior in the magnetic susceptibility. Upon decreasing the temperature ($T <
T_\textup{C}^\textup{Co}$), the magnetocrystalline anisotropy breaks up the FM
order of Co by aligning the moments with the local easy axes of the various
grains, leading to a spin reorientation transition at
$T_\textup{R}^\textup{Co}$. By applying a magnetic field,
$T_\textup{R}^\textup{Co}$ monotonically decreases to lower temperatures, while
the $T_\textup{N}^\textup{Gd}$ is relatively robust against the external field.
On the other hand, the applied magnetic field pulls the magnetization of grains
from the local easy direction to the field direction via a first-order
reorientation transition, with the transition field ($H_\textup{M}$) increasing
upon cooling the temperature.",1502.05139v1
2015/5/12,"Structural and Magnetic Investigations of Single-Crystals of the Neodymium Zirconate Pyrochlore, Nd2Zr2O7","We report structural and magnetic properties studies of large high quality
single-crystals of the frustrated magnet, Nd$_2$Zr$_2$O$_7$. Powder x-ray
diffraction analysis confirms that Nd$_2$Zr$_2$O$_7$ adopts the pyrochlore
structure. Room-temperature x-ray diffraction and time-of-flight neutron
scattering experiments show that the crystals are stoichiometric in composition
with no measurable site disorder. The temperature dependence of the magnetic
susceptibility shows no magnetic ordering at temperatures down to 0.5 K. Fits
to the magnetic susceptibility data using a Curie-Weiss law reveal a
ferromagnetic coupling between the Nd moments. Magnetization versus field
measurements show a local Ising anisotropy along the <111> axes of the
Nd$^{3+}$ ions in the ground state. Specific heat versus temperature
measurements in zero applied magnetic field indicate the presence of a thermal
anomaly below $T\sim7$ K, but no evidence of magnetic ordering is observed down
to 0.5 K. The experimental temperature dependence of the single-crystal bulk dc
susceptibility and isothermal magnetization are analyzed using crystal field
theory and the crystal field parameters and exchange coupling constants
determined.",1505.02931v1
2015/5/21,Thickness-dependent magnetic properties and strain-induced orbital magnetic moment in SrRuO3 thin films,"Thin films of the ferromagnetic metal SrRuO3 (SRO) show a varying easy
magnetization axis depending on the epitaxial strain and undergo a
metal-to-insulator transition with decreasing film thickness. We have
investigated the magnetic properties of SRO thin films with varying thicknesses
fabricated on SrTiO3(001) substrates by soft x-ray magnetic circular dichroism
(XMCD) at the Ru M2,3 edge. Results have shown that, with decreasing film
thickness, the film changes from ferromagnetic to non-magnetic around
3monolayer thickness, consistent with previous magnetization and
magneto-optical Kerr effect measurements. The orbital magnetic moment
perpendicular to the film was found to be ~ 0.1{\mu}B/Ru atom, and remained
nearly unchanged with decreasing film thickness while the spin magnetic moment
decreases. Mechanism for the formation of the orbital magnetic moment is
discussed based on the electronic structure of the compressively strained SRO
film.",1505.05692v2
2015/10/17,Ferrimagnetic nanostructures for magnetic memory bits,"Increasing the magnetic data recording density requires reducing the size of
the individual memory elements of a recording layer as well as employing
magnetic materials with temperature-dependent functionalities. Therefore, it is
predicted that the near future of magnetic data storage technology involves a
combination of energy-assisted recording on nanometer-scale magnetic media. We
present the potential of heat-assisted magnetic recording on a patterned
sample; a ferrimagnetic alloy composed of a rare earth and a transition metal,
DyCo$_5$, which is grown on a hexagonal-ordered nanohole array membrane. The
magnetization of the antidot array sample is out-of-plane oriented at room
temperature and rotates towards in-plane upon heating above its
spin-reorientation temperature (T$_R$) of ~350 K, just above room temperature.
Upon cooling back to room temperature (below T$_R$), we observe a well-defined
and unexpected in-plane magnetic domain configuration modulating with ~45 nm.
We discuss the underlying mechanisms giving rise to this behavior by comparing
the magnetic properties of the patterned sample with the ones of its extended
thin film counterpart. Our results pave the way for novel applications of
ferrimagnetic antidot arrays of superior functionality in magnetic nano-devices
near room temperature.",1510.05087v1
2016/3/8,Magnetic fields in early protostellar disk formation,"We consider formation of accretion disks from a realistically turbulent
molecular gas using 3D MHD simulations. In particular, we analyze the effect of
the fast turbulent reconnection described by the Lazarian & Vishniac (1999)
model for the removal of magnetic flux from a disk. With our numerical
simulations we demonstrate how the fast reconnection enables protostellar disk
formation resolving the so-called ""magnetic braking catastrophe"". In
particular, we provide a detailed study of the dynamics of a 0.5 M$_\odot$
protostar and the formation of its disk for up to several thousands years. We
measure the evolution of the mass, angular momentum, magnetic field, and
turbulence around the star. We consider effects of two processes that strongly
affect the magnetic transfer of angular momentum, both of which are based on
turbulent reconnection: the first, ""reconnection diffusion"", removes the
magnetic flux from the disk, the other involves the change of the magnetic
field's topology, but does not change the absolute value of the magnetic flux
through the disk. We demonstrate that for the first mechanism, turbulence
causes a magnetic flux transport outward from the inner disk to the ambient
medium, thus decreasing the coupling of the disk to the ambient material. A
similar effect is achieved through the change of the magnetic field's topology
from a split monopole configuration to a dipole configuration. We explore how
both mechanisms prevent the catastrophic loss of disk angular momentum and
compare both above turbulent reconnection mechanisms with alternative
mechanisms from the literature.",1603.02691v1
2016/5/2,"Active role of the nonmagnetic cations in magnetic interactions for the double-perovskite Sr2BOsO6 (B=Y, In, Sc)","Using first-principles density functional theory, we have investigated the
electronic and magnetic properties of recently synthesized and characterized 5d
double-perovskites Sr2BOsO6 (B=Y, In, Sc). The electronic structure
calculations show that in all compounds, the Os5+ (5d3) site is the only
magnetically active one, while Y3+, In3+ and Sc3+ remain in nonmagnetic states,
with Sc/Y and In featuring d0 and d10 electronic configurations, respectively.
Our studies reveal the important role of closed-shell (d10) versus open-shell
(d0) electronic configurations of the nonmagnetic sites in determining the
overall magnetic exchange interactions. Although the magnetic Os5+ (5d3) site
is the same in all compounds, the magnetic super-exchange interactions mediated
by non-magnetic Y/In/Sc species are strongest for Sr2ScOsO6, weakest for
Sr2InOsO6, and intermediate in case of the Y (d0), due to different energy
overlaps between Os-5d and Y/In/Sc-d states. This explains the experimentally
observed substantial differences in the magnetic transition temperatures of
these materials, despite of an identical magnetic site and underlying magnetic
ground state. Furthermore, short range Os-Os exchange-interactions are more
prominent than long range Os-Os interactions in these compounds, which
contrasts with the behavior of other 3d-5d double-perovskites.",1605.00540v1
2016/7/17,Second order perturbed Heisenberg Hamiltonian of Fe3O4 ultra-thin films,"Due to the wide range of applications, theoretical models of Fe3O4 films are
found to be important. Ultra thin Fe3O4 films with ferrite structure have been
theoretically investigated using second order perturbed modified Heisenberg
Hamiltonian. Matrices for ultra thin films with two and three spin layers are
presented in this manuscript. Total magnetic energy was expressed in terms of
spin exchange interaction, magnetic dipole interaction, second order magnetic
anisotropy and stress induced magnetic anisotropy. Magnetic properties were
observed for films with two spin layers and variant second order magnetic
anisotropy. For the film with three spin layers, second order anisotropy
constant was fixed to avoid tedious derivations. Magnetic easy axis rotates
toward the in plane direction as the number of spin layers is increased from
two to three because the stress induced anisotropy energy dominates at higher
number of spin layers. According to some other experimental data, the magnetic
easy axis of thin films rotates toward the in plane direction as the thickness
is increased. For ferrite film with two spin layers, magnetic easy and hard
directions can be observed at 0.75 and 1.2 radians, respectively, when the
ratio of stress induced anisotropy to the long range dipole interaction
strength is 3.9. For ferrite film with three spin layers, magnetic easy and
hard directions can be observed at 2.4 and 2.3 radians, respectively, when the
ratio of stress induced anisotropy to the long range dipole interaction
strength is 4.2.",1611.02225v2
2016/11/17,Low-temperature heat transport of spin-gapped quantum magnets,"This article reviews low-temperature heat transport studies of spin-gapped
quantum magnets in the last few decades. Quantum magnets with small spins and
low dimensionality exhibit a variety of novel phenomena. Among them, some
systems are char-acteristic of having quantum-mechanism spin gap in their
magnetic excitation spectra, including spin-Peierls systems, S = 1 Haldane
chains, S = 1/2 spin ladders, and spin dimmers. In some particular spin-gapped
systems, the XY-type antiferromagnetic state induced by magnetic field that
closes the spin gap can be described as a magnon Bose-Einstein condensation
(BEC). Heat transport is effective in probing the magnetic excitations and
magnetic phase transitions, and has been extensively studied for the
spin-gapped systems. A large and ballistic spin thermal conductivity was
observed in the two-leg Heisenberg S = 1/2 ladder compounds. The characteristic
of magnetic thermal transport of the Haldane chain systems is quite
controversial on both the theoretical and experimental results. For the
spin-Peierls system, the spin excitations can also act as heat carriers. In
spin-dimer compounds, the magnetic excitations mainly play a role of scattering
phonons. The magnetic excitations in the magnon BEC systems displayed dual
roles, carrying heat or scattering phonons, in different materials.",1611.05578v1
2016/12/22,Unravelling incommensurate magnetism and its emergence in iron-based superconductors,"We focus on a broad class of tetragonal itinerant systems sharing a tendency
towards the spontaneous formation of incommensurate magnetism with ordering
wavevectors $\mathbf{Q}_{1,2}=(\pi-\delta,0)/(0,\pi-\delta)$ or
$\mathbf{Q}_{1,2}=(\pi,\delta)/(-\delta,\pi)$. Employing a Landau approach, we
obtain the generic magnetic phase diagram and identify the leading
instabilities near the paramagnetic-magnetic transition. Nine distinct magnetic
phases exist that either preserve or violate the assumed $C_4$-symmetry of the
paramagnetic phase. These are single- and double-$\mathbf{Q}$ phases consisting
of magnetic stripes, helices and whirls, either in an individual or coexisting
manner. These nine phases can be experimentally distinguished by polarized
neutron scattering, or, for example, by combining measurements of the induced
charge order and magnetoelectric coupling. Within two representative
five-orbital models, suitable for BaFe$_2$As$_2$ and LaFeAsO, we find that the
incommensurate magnetic phases discussed here are accessible in iron-based
superconductors. Our investigation unveils a set of potential candidates for
the unidentified $C_2$-symmetric magnetic phase that was recently observed in
Ba$_{1-x}$Na$_x$Fe$_{2}$As$_{2}$. Among the phases stabilized we find a
spin-whirl crystal, which is a textured magnetic $C_4$-symmetric phase. The
possible experimental observation of textured magnetic orders in iron-based
superconductor, opens new directions for realizing intrinsic topological
superconductors.",1612.07633v3
2017/5/14,"Magnetic behavior of metallic kagome lattices, Tb3Ru4Al12 and Er3Ru4Al12","We report magnetic behavior of two intermetallics-based kagome lattices,
Tb3Ru4Al12 and Er3Ru4Al12, crystallizing in the Gd3Ru4Al12-type hexagonal
crystal structure, by measurements in the range 1.8-300 K with bulk
experimental techniques (ac and dc magnetization, heat-capacity and
magnetoresistance). The main finding is that the Tb compound, known to order
antiferromagnetically below (T_N=) 22 K, shows glassy characteristics at lower
temperatures (<15K), thus characterizing this compound as a re-entrant
spin-glass. The data reveal that glassy phase is quite complex and is of a
cluster type. Since the glassy behavior was not seen for the Gd analogue in the
past literature, this finding for the Tb compound emphasizes that this kagome
family could provide an opportunity to explore the role of higher order (such
as quadrupole) in bringing out magnetic frustration. Additional findings
reported here for this compound are: (i) The temperature dependence of magnetic
susceptibility and electrical resistivity in the range 12 - 20 K are found to
be hysteretic leading to a magnetic phase in this temperature range, mimicking
disorder-induced first-order magnetic phase-transition. (ii) Features
attributable to an interesting magnetic phase co-existence phenomenon in the
magnetoresistance in zero field, after cycling across metamagnetic transition
fields, are observed. With respect to the Er compound, we do not find any
evidence for long-range magnetic ordering down to 2 K, but this appears to be
on the verge of magnetic order at 2 K.",1705.04921v2
2017/5/31,Lattice and spin dynamics in a low-symmetry antiferromagnet NiWO$_4$,"Lattice and magnetic dynamics of NiWO$_4$ single crystals were studied with
the use of polarized Raman spectroscopy in a wide temperature range of 10-300 K
including the antiferromagnetic ordering temperature $T_N$=62 K. Static
magnetic measurements were used for characterizing the single crystals. All
Raman-active phonons predicted by the group theory were observed and
characterized. Magnetic symmetry analysis was used to determine possible
magnetic space groups for NiWO$_4$ which can be also applied to any other
isostructural crystal with the same magnetic propagation vector k=(1/2,0,0).
Though the magnetic structure of NiWO$_4$ is relatively simple, a rich set of
narrow and broad magnetic excitations with different polarization properties
and temperature behavior in the very broad frequency range of 10-200 cm$^{-1}$
was observed, with some modes surviving at temperatures much higher than $T_N$
up to 220 K. Part of the magnetic excitations was identified as acoustic and
optical spin-wave branches which allow us to construct exchange structure and
estimate exchange and anisotropy constants with the use of linear spin-wave
theory. Since the magnetic structure can be described as exchange-coupled AFM
chains of $S=1$ ions, previously unobserved magnetic excitation at 24 cm$^{-1}$
is tentatively assigned to a Haldane gap mode.",1705.11137v1
2017/6/2,Dirac-Electrons-Mediated Magnetic Proximity Effect in Topological Insulator / Magnetic Insulator Heterostructures,"The possible realization of dissipationless chiral edge current in a
topological insulator / magnetic insulator heterostructure is based on the
condition that the magnetic proximity exchange coupling at the interface is
dominated by the Dirac surface states of the topological insulator. Here we
report a polarized neutron reflectometry observation of Dirac electrons
mediated magnetic proximity effect in a bulk-insulating topological insulator
(Bi$_{0.2}$Sb$_{0.8}$)$_{2}$Te$_{3}$ / magnetic insulator EuS heterostructure.
We are able to maximize the proximity induced magnetism by applying an
electrical back gate to tune the Fermi level of topological insulator to be
close to the charge neutral point. A phenomenological model based on
diamagnetic screening is developed to explain the suppressed proximity induced
magnetism at high carrier density. Our work paves the way to utilize the
magnetic proximity effect at the topological insulator/magnetic insulator
hetero-interface for low-power spintronic applications.",1706.00847v1
2017/8/29,Novel magnetoelectric effects via penta-linear interactions,"Magnetoelectric multiferroic materials, particularly with the perovskite
structure, are receiving a lot of attention because of their inherent coupling
between electrical polarization and magnetic ordering. However, very few types
of direct coupling between polarization and magnetization are known, and it is
unclear whether they can be useful to the design of novel spintronic devices
exploiting the control of magnetization by electric fields. For instance, the
typical bi-quadratic coupling only allows to change the magnitude of the
magnetization by an electric field, but it does not permit an
electric-field-induced switching of the magnetization. Similarly, the so-called
Lifshitz invariants allow an electric-field control of complicated magnetic
orderings, but not of the magnetization. Here, we report the discovery of novel
direct couplings between polarization and magnetization in epitaxial perovskite
films, via the use of first-principles methods and the development of an
original Landau-type phenomenological theory. Our results feature penta-linear
interactions involving the ferromagnetic and anti-ferromagnetic vectors as well
as the polar distortions and oxygen octahedral tilting, and permit a number of
striking effects. Examples include a continuous electric-field control of the
magnetization magnitude and sign, and the discrete switching of the
magnetization magnitude. Thus, the high-order, penta-linear couplings
demonstrated in this work may open new paths towards novel magneto-electric
effects, as well as, spintronic and magnonic devices.",1709.01789v1
2018/2/3,Temperature-dependent magnetic properties of a magnetoactive elastomer: immobilization of the soft-magnetic filler,"Magnetic properties of a magnetoactive elastomer (MAE) filled with
{\mu}m-sized soft-magnetic iron particles have been experimentally studied in
the temperature range between 150 K and 310 K. By changing the temperature, the
elastic modulus of the elastomer matrix was modified and it was possible to
obtain magnetization curves for an invariable arrangement of particles in the
sample as well as in the case when the particles were able to change their
position within the MAE under the influence of magnetic forces. At low (less
than 220 K) temperatures, when the matrix becomes rigid, the magnetization of
the MAE does not show a hysteresis behavior and it is characterized by a
negative value of the Rayleigh constant. At room temperature, when the polymer
matrix is compliant, a magnetic hysteresis exists and exhibits local maxima of
the field dependence of the differential magnetic susceptibility. The
appearance of these maxima is explained by the elastic resistance of the matrix
to the displacement of particles under the action of magnetic forces.",1802.00950v1
2018/7/2,Defects-driven magnetism in bulk $α$-Li$ _{3}$N,"\textit{Ab-initio} calculations based on density functional theory with local
spin density approximation are used to study defects-driven magnetism in bulk
$\alpha$-Li$ _{3}$N. Our calculations show that bulk Li$ _{3} $N is a
non-magnetic semiconductor. Two types of Li vacancies (Li-I and Li-II) are
considered, and Li-vacancies (either Li-I or Li-II type) can induce magnetism
in Li$ _{3}$N with a total magnetic moment of 1.0 $\mu_{\rm B}$ which arises
mainly due to partially occupied N-$p$-orbitals around the Li vacancies. The
defect formation energies dictate that Li-II vacancy, which is in the Li$
_{2}$N plane, is thermodynamically more stable as compared with Li-I vacancy.
The electronic structures of Li-vacancies show half-metallic behavior. On the
other hand N-vacancy does not induce magnetism and has a larger formation
energy than Li-vacancies. N vacancy derived bands at the Fermi energy are
mainly contributed by the Li atoms. Carbon is also doped at Li-I and Li-II
sites, and it is expected that doping C at Li-I site is thermodynamically more
stable as compared with Li-II site. Carbon can induce metallicity with zero
magnetic moment when doped at Li-I site, whereas magnetism is observed when
Li-II site is occupied by the C impurity atom and C-driven magnetism is spread
over the N atoms as well. Carbon can also induce half-metallic magnetism when
doped at N site in Li$ _{3}$N, and has a smaller defect formation energy as
compared with Li-II site doping. The ferromagnetic (FM) and antiferromagnetic
(AFM) coupling between the C atoms is also investigated, and we conclude that
FM state is more stable than the AFM state.",1807.00857v1
2018/7/21,Uniform and Nonuniform Precession of a Nanoparticle with Finite Anisotropy in a Liquid: Opportunities and Limitations for Magnetic Fluid Hyperthermia,"We focus on an in-depth study of the forced dynamics of a ferromagnetic
single-domain uniaxial nanoparticle placed in a viscous fluid and driven by an
external rotating magnetic field. The process of conversion of magnetic and
mechanical energies into heat is a physical basis for magnetic fluid
hyperthermia that is very promising for cancer treatment. The dynamical
approximation allows us to establish the limits of the heating rate and
understand the logic of selection of the system parameters to optimize the
therapy. Based on the developed analytical and numerical tools, we analyze from
a single viewpoint the synchronous and asynchronous rotation of the
nanoparticle or/and its magnetization in the following three cases. For the
beginning, we actualize the features of the internal magnetic dynamics, when
the nanoparticle body is supposed to be fixed. Then, we study the rotation of
the whole nanoparticle, when its magnetization is supposed to be locked to the
crystal lattice. And, finally, we realize the analysis of the coupled motion,
when the internal magnetic dynamics is performed in the rotated nanoparticle
body. In all these cases, we describe analytically the uniform mode, or
synchronous rotation along with an external field, while the nonuniform mode,
or asynchronous rotation, is investigated numerically.",1807.08120v1
2018/9/27,Low-temperature Atomistic Spin Relaxation and Non-equilibrium Intensive Properties Using Steepest-Entropy-Ascent Quantum-Inspired Thermodynamics Modeling,"The magnetization of body-centered cubic iron at low temperatures is
calculated with the steepest-entropy-ascent quantum thermodynamics (SEAQT)
framework. This framework assumes that a thermodynamic property in an isolated
system traces the path through state space with the greatest entropy
production. Magnetization is calculated from the expected value of a
thermodynamic ensemble of quantized spin waves based on the Heisenberg spin
model applied to an ensemble of coupled harmonic oscillators. A realistic
energy landscape is obtained from a magnon dispersion relation calculated using
spin-density-functional-theory. The equilibrium magnetization as well as the
evolution of magnetization from a non-equilibrium state to equilibrium are
calculated from the path of steepest entropy ascent determined from the SEAQT
equation of motion in state space. The framework makes it possible to model the
temperature- and time-dependence of magnetization without a detailed
description of magnetic damping. The approach is also used to define intensive
properties (temperature and magnetic field strength) that are fundamentally,
i.e., canonically or grand canonically, valid for any non-equilibrium state.
Given the assumed magnon dispersion relation, the SEAQT framework is used to
calculate the equilibrium magnetization at different temperatures and external
magnetic fields and the results are shown to closely agree with experiment for
temperatures less than 500 K. The time-dependent evolution of magnetization
from different initial states and interactions with a reservoir is also
predicted.",1809.10619v2
2018/10/2,Building traps for skyrmions by the incorporation of magnetic defects into nanomagnets: pinning and scattering traps by magnetic properties engineering,"In this work we have used micromagnetic simulations to report four ways to
build traps for magnetic skyrmions. Magnetic defects have been modeled as local
variations in the material parameters, such as the exchange stiffness,
saturation magnetization, magnetocrystalline anisotropy and
Dzyaloshinskii-Moriya constant. We observe both pinning (potential well) and
scattering (potential barrier) traps when tuning either a local increase or a
local reduction for each one of these magnetic properties. It is found that the
skyrmion-defect aspect ratio is a crucial parameter to build traps for
skyrmions. In particular, the efficiency of the trap is compromised if the
defect size is smaller than the skyrmion size, because they interact weakly. On
the other hand, if the defect size is larger than the skyrmion diameter, the
skyrmion-defect interaction becomes evident. Thus, the strength of the
skyrmion-defect interaction can be tuned by the modification of the magnetic
properties within a region with suitable size. Furthermore, the basic physics
behind the mechanisms for pinning and for scattering is discussed. In
particular, we discover that skyrmions move towards the magnetic region which
tends to maximize its diameter; it enables the magnetic system to minimize its
energy. Thus, we are able to explain why skyrmions are either attracted or
repelled by a region with modified magnetic properties. Results here presented
are of utmost significance for the development and realization of future
spintronic devices, in which skyrmions will work as information carriers.",1810.03754v2
2018/11/2,Spinning superconductors and ferromagnets,"When a magnetic field is applied to a ferromagnetic body it starts to spin
(Einstein-de Haas effect). This demonstrates the intimate connection between
the electron's magnetic moment $\mu_B=e\hbar/2m_ec$, associated with its spin
angular momentum $S=\hbar/2$, and ferromagnetism. When a magnetic field is
applied to a superconducting body it also starts to spin (gyromagnetic effect),
and when a normal metal in a magnetic field becomes superconducting and expels
the magnetic field (Meissner effect) the body also starts to spin. Yet
according to the conventional theory of superconductivity the electron's spin
only role is to label states, and the electron's magnetic moment plays no role
in superconductivity. Instead, within the unconventional theory of hole
superconductivity, the electron's spin and associated magnetic moment play a
fundamental role in superconductivity. Just like in ferromagnets the
magnetization of superconductors is predicted to result from an aggregation of
magnetic moments with angular momenta $\hbar/2$. This gives rise to a ""Spin
Meissner effect"", the existence of a spin current in the ground state of
superconductors. The theory explains how a superconducting body starts spinning
when it expels magnetic fields, it provides a dynamical explanation for the
Meissner effect, and it explains how supercurrents stop without dissipation,
all of which we argue the conventional theory fails to explain. Essential
elements of the theory of hole superconductivity are that superconductivity is
driven by lowering of kinetic energy, which we have also proposed is true for
ferromagnets], that the normal state charge carriers in superconducting
materials are holes, and that the spin-orbit interaction plays a key role in
superconductivity. The theory is proposed to apply to all superconductors.",1811.03938v1
2018/12/14,Upper branch magnetism in quantum magnets: Collapses of excited levels and emergent selection rules,"In many quantum magnets especially the rare-earth ones, the low-lying crystal
field states are not well separated from the excited ones and thus are
insufficient to describe the low-temperature magnetic properties. Inspired by
this simple observation, we develop a microscopic theory to describe the
magnetic physics due to the collapses of the weak crystal field states. We find
two cases where the excited crystal field states should be seriously included
into the theory. One case is when the bandwidth of the excited crystal field
states is comparable to the crystal field gap. The other case is when the
exchange energy gain between the low-lying and excited crystal field states
overcomes the crystal field gap. Both cases could drive a phase transition and
result in magnetic orders by involving the excited crystal field states. We dub
the above physics as upper branch magnetism and phase transition. We discuss
the multitude of magnetic phases and the emergent selection rules for the
detection of the underlying excitations. We expect our results to help improve
the understanding of many rare-earth magnets with weak crystal field gaps such
as Tb$_2$Ti$_2$O$_7$ and Tb$_2$Sn$_2$O$_7$, and also provide a complementary
perspective to the prevailing local ""$J$"" physics in $4d$/$5d$ magnets.",1812.06036v1
2019/1/16,"Magnetic properties of double perovskite $Ln_2$CoIrO$_6$ ($Ln$ = Eu, Tb, Ho): hetero-tri-spin $3d$-$5d$-$4f$ systems","The field of double perovskites is now advancing to three magnetic elements
on the A, B and B$'$ sites. A series of iridium-based double perovskite
compounds, $Ln_2$CoIrO$_6$ ($Ln$ = Eu, Tb, Ho) with three magnetic elements
were synthesized as polycrystalline samples. The compounds crystalize in
monoclinic structures with the space group $P2_1/n$. Magnetic properties of
these hetero-tri-spin $3d$-$5d$-$4f$ systems were studied by magnetic
susceptibility and field dependent magnetization in both DC and pulsed magnetic
fields. All these compounds show ferrimagnetic transitions at temperatures
$T_C$ above 100 K, which are attributable to antiferromagnetic coupling between
Co$^{2+}$ and Ir$^{4+}$ spins. For Eu$_2$CoIrO$_6$, the magnetic properties are
similar to those of La$_2$CoIrO$_6$. The Eu$^{3+}$ spins show Van Vleck
paramagnetism that don't significantly interact with transition-metal cations.
By contrast, Tb$_2$CoIrO$_6$ and Ho$_2$CoIrO$_6$ reveal a second transition to
antiferromagnetic order below a lower temperature $T_N$. The
temperature-induced ferrimagnetic-to-antiferromagnetic phase transition might
be explained by a spin-reorientation transition. Moreover, a
magnetic-field-induced spin-flop transition with a small hysteresis was
observed below $T_N$ in these two compounds. The magnetic moment of all three
compounds do not saturate up to 60 T at low temperatures. Moderate
magnetocaloric effect was also observed in all three compounds. Our results
should motivate further investigation of the spin configuration on single
crystals of these iridium-based double perovskites.",1901.05412v1
2019/8/11,Temperature-induced band shift in ferromagnetic Weyl semimetal Co3Sn2S2,"The discovery of nonmagnetic Weyl semimetals (WSMs) in TaAs compounds has
triggered lots of efforts in finding its magnetic counterpart. While the direct
observation of the Weyl nodes and Fermi arcs in a magnetic candidate through
angle-resolved photoemission spectroscopy is hindered by the complex magnetic
domains. The transport features of magnetic WSMs, including negative
magnetoresistivity and anomalous Hall conductivity, are not conclusive since
these are sensitive to extrinsic factors like defects and disorders in lattice
or magnetic ordering. Here, we systematically study the temperature-dependent
optical spectra of ferromagnetic Co$_3$Sn$_2$S$_2$ experimentally and simulated
by first-principles calculations. The many-body correlation effect due to Co
$3d$ electrons leads to the renormalization of bands by a factor about 1.33,
which is moderate and the description within density functional theory is
suitable. As the temperature drops down, the magnetic phase transition happens
and the magnetization drives the band shift through exchange splitting. The
optical spectra can well detect these changes, including the transitions
sensitive and insensitive to the magnetization, and those from the bands around
the Weyl nodes. The results strongly support that Co$_3$Sn$_2$S$_2$ is a
magnetic WSM and the Weyl nodes can be tuned by magnetization with temperature
change.",1908.03895v2
2019/9/4,"Application of a two dipole model to PSR J1640-4631, a pulsar with an anomalous braking index","Recent timing observation provides an intriguing result for the braking index
of the X-ray pulsar PSR J1640-4631, which has a measured braking index
$n=3.15\pm0.03$. The decrease of the inclination angle between between the spin
axis and the magnetic axis can be responsible for such a high braking index.
However, the physical mechanisms causing the change of the magnetic inclination
angle have not been fully understood. In this Letter, we apply a two-dipole
model given by Hamil et al (2016) to explain the decrease of the magnetic
inclination angle of PSR J1640-4631. The rotation effect of a charged sphere
and the magnetization of ferromagnetically ordered material produce magnetic
moments $M_{1}$ and $M_{2}$, respectively. There exist a minimum of the
potential energy for the magnetic moment $M_{2}$ in the magnetic field of
$M_{1}$, hence the $M_{2}$ will freely rotate around the minimum energy
position (i. e equilibrium position), similar to a simple pendulum. Our
calculation indicate the magnetic moment $M_{2}$ would evolve towards alignment
with the spin axis for PSR J1640-4631, and cause the magnetic inclination angle
to decrease. The single peak in the pulse profile favors a relatively low
change rate of the magnetic inclination angle.",1909.01699v1
2019/11/18,Magnetic structure in square cupola compound Ba(TiO)Cu$_4$(PO$_4$)$_4$: a $^{31}$P NMR Study,"The magnetic structure of the antiferromagnetic square cupola compound
Ba(TiO)Cu$_4$(PO$_4$)$_4$ with the tetragonal structure is studied with 31P
nuclear magnetic resonance techniques. The magnetic hyperfine shift K shows a
clear splitting at the N\'eel temperature T$_N$ = 9.5 K, where the resonance
splits into two lines when an external magnetic field is oriented along the c
axis and into four lines when the field is along the a axis. In the
paramagnetic region K(T) follows temperature dependence of the magnetic
susceptibility $\chi(T)$. From K vs $\chi$ plot we determined nearly isotropic
hyperfine field values Ha_hf = 765 mT/$\mu_B$ and Hc_hf = 740 mT/$\mu_B$ for
the magnetic field oriented along a and c, respectively. From the rotation of
the single crystal in the external magnetic field we determined eight different
orientations of K-tensor in the paramagnetic region. In the antiferromagnetic
state at T = 6 K we found that the local field at phosphorus is mainly due to
dipolar field of coppers. Here the rotation of the single crystal shows eight
different orientations of the local field Bint = 35.6 mT. The orientations
correspond to the calculation of dipolar fields at phosphorus assuming magnetic
quadrupolar configuration of magnetic moments $\varGamma_3(1)$ described
previously [Nat. Commun. 7, 13039 (2016); Phys. Rev. B 96, 214436 (2017)].",1911.07684v1
2020/8/6,Paramagnetic spin Hall magnetoresistance,"Spin Hall magnetoresistance (SMR) refers to a resistance change in a metallic
film reflecting the magnetization direction of a magnet attached to the film.
The mechanism of this phenomenon is spin exchange between conduction-electron
spins and magnetization at the interface. SMR has been used to read out
information written in a small magnet and to detect magnetization dynamics, but
it has been limited to magnets; magnetic ordered phases or instability of
magnetic phase transition has been believed to be indispensable. Here, we
report the observation of SMR in a paramagnetic insulator
Gd$_{3}$Ga$_{5}$O$_{12}$ (GGG) without spontaneous magnetization combined with
a Pt film. The paramagnetic SMR can be attributed to spin-transfer torque
acting on localized spins in GGG. We determine the efficiencies of spin torque
and spin-flip scattering at the Pt/GGG interface, and demonstrate these
quantities can be tuned with external magnetic fields. The results clarify the
mechanism of spin-transport at a metal/paramagnetic insulator interface, which
gives new insight into the spintronic manipulation of spin states in
paramagnetic systems.",2008.02446v2
2020/8/31,Robust topological Hall effect driven by tunable noncoplanar magnetic state in Mn-Pt-In inverse tetragonal Heusler alloys,"Manipulation of magnetic ground states by effective control of competing
magnetic interactions has led to the finding of many exotic magnetic states. In
this direction, the tetragonal Heusler compounds consisting of multiple
magnetic sublattices and crystal symmetry favoring chiral Dzyaloshinskii-Moriya
interaction (DMI) provide an ideal base to realize non-trivial magnetic
structures. Here, we present the observation of a large robust topological Hall
effect (THE) in the multi-sublattice Mn$_{2-x}$PtIn Heusler magnets. The
topological Hall resistivity, which originates from the non-vanishing real
space Berry curvature in the presence of non-zero scalar spin chirality,
systematically decreases with decreasing the magnitude of the canting angle of
the magnetic moments at different sublattices. With help of first principle
calculations, magnetic and neutron diffraction measurements, we establish that
the presence of a tunable non-coplanar magnetic structure arising from the
competing Heisenberg exchanges and chiral DMI from the D$_{2d}$ symmetry
structure is responsible for the observed THE. The robustness of the THE with
respect to the degree of non-collinearity adds up a new degree of freedom for
designing THE based spintronic devices.",2008.13505v1
2021/1/18,Specific heat of CeRhIn$_5$ in high magnetic fields: Magnetic phase diagram revisited,"CeRhIn$_5$ is a prototypical antiferromagnetic heavy-fermion compound, whose
behavior in a magnetic field is unique. A magnetic field applied in the basal
plane of the tetragonal crystal structure induces two additional phase
transitions. When the magnetic field is applied along, or close to, the $c$
axis, a new phase characterized by a pronounced in-plane electronic anisotropy
emerges at $B^* \approx$ 30 T, well below the critical field, $B_c \simeq$ 50
T, to suppress the antiferromagnetic order. The exact origin of this new phase,
originally suggested to be an electronic-nematic state, remains elusive. Here
we report low-temperature specific-heat measurements in CeRhIn$_5$ in high
static magnetic fields up to 36 T applied along both the $a$ and $c$ axes. For
fields applied along the $a$ axis, we confirmed the previously suggested phase
diagram, and extended it to higher fields. This allowed us to observe a triple
point at $\sim$ 30 T, where the first-order transition from an incommensurate
to commensurate magnetic structure merges into the onset of the second-order
antiferromagnetic transition. For fields applied along the $c$ axis, we
observed a small but distinct anomaly at $B^*$, which we discuss in terms of a
possible field-induced transition, probably weakly first-order. We further
suggest that the transition corresponds to a change of magnetic structure. We
revise magnetic phase diagrams of CeRhIn$_5$ for both principal orientations of
the magnetic field based entirely on thermodynamic anomalies.",2101.07013v1
2021/3/24,Structural and Magnetic Transitions in the Planar Antiferromagnet Ba$_4$Ir$_3$O$_{10}$,"We report the structural and magnetic ground state properties of the
monoclinic compound barium iridium oxide Ba$_4$Ir$_3$O$_{10}$ using a
combination of resonant x-ray scattering, magnetometry, and thermodynamic
techniques. Magnetic susceptibility exhibits a pronounced antiferromagnetic
transition at $T_{\text{N}}$ $\approx$ 25K, a weaker anomaly at $T_{\text{S}}$
$\approx$ 142K, and strong magnetic anisotropy at all temperatures. Resonant
elastic x-ray scattering experiments reveal a second order structural phase
transition at $T_{\text{S}}$ and a magnetic transition at $T_{\text{N}}$. Both
structural and magnetic superlattice peaks are observed at $L$ = half integer
values. The magnetization anomaly at $T_{\text{S}}$ implies the presence of
magneto-elastic coupling, which conceivably facilitates the symmetry lowering.
Mean field critical scattering is observed above $T_{\text{S}}$. The magnetic
structure of the antiferromagnetic ground state is discussed based on the
measured magnetic superlattice peak intensity. Our study not only presents
essential information for understanding the intertwined structural and magnetic
properties in Ba$_4$Ir$_3$O$_{10}$, but also highlights the necessary
ingredients for exploring novel ground states with octahedra trimers.",2103.12979v1
2021/5/18,Asteroid Magnetization from the Early Solar Wind,"Magnetic fields provide an important probe of the thermal, material, and
structural history of planetary and sub-planetary bodies. Core dynamos are a
potential source of magnetic fields for differentiated bodies, but evidence of
magnetization in undifferentiated bodies requires a different mechanism. Here
we study the amplified field provided by the stellar wind to an initially
unmagnetized body using analytic theory and numerical simulations, employing
the resistive MHD AstroBEAR adaptive mesh refinement (AMR) multiphysics code.
We obtain a broadly applicable scaling relation for the peak magnetization
achieved once a wind advects, piles-up, and drapes a body with magnetic field,
reaching a quasi-steady state. We find that the dayside magnetic field for a
sufficiently conductive body saturates when it balances the sum of incoming
solar wind ram, magnetic, and thermal pressures. Stronger amplification results
from pileup by denser and faster winds. Careful quantification of numerical
diffusivity is required for accurately interpreting the peak magnetic field
strength from simulations, and corroborating with theory. As specifically
applied to the Solar System, we find that early solar wind-induced field
amplification is a viable source of magnetization for observed paleointensities
in meteorites from some undifferentiated bodies. This mechanism may also be
applicable to other Solar System bodies, including metal-rich bodies to be
visited in future space missions such as the asteroid (16) Psyche.",2105.08852v3
2021/11/4,Computational thresholds for the fixed-magnetization Ising model,"The ferromagnetic Ising model is a model of a magnetic material and a central
topic in statistical physics. It also plays a starring role in the algorithmic
study of approximate counting: approximating the partition function of the
ferromagnetic Ising model with uniform external field is tractable at all
temperatures and on all graphs, due to the randomized algorithm of Jerrum and
Sinclair. Here we show that hidden inside the model are hard computational
problems. For the class of bounded-degree graphs we find computational
thresholds for the approximate counting and sampling problems for the
ferromagnetic Ising model at fixed magnetization (that is, fixing the number of
$+1$ and $-1$ spins). In particular, letting $\beta_c(\Delta)$ denote the
critical inverse temperature of the zero-field Ising model on the infinite
$\Delta$-regular tree, and $\eta_{\Delta,\beta,1}^+$ denote the mean
magnetization of the zero-field $+$ measure on the infinite $\Delta$-regular
tree at inverse temperature $\beta$, we prove, for the class of graphs of
maximum degree $\Delta$:
  1. For $\beta < \beta_c(\Delta)$ there is an FPRAS and efficient sampling
scheme for the fixed-magnetization Ising model for all magnetizations $\eta$.
  2. For $\beta > \beta_c(\Delta)$, there is an FPRAS and efficient sampling
scheme for the fixed-magnetization Ising model for magnetizations $\eta$ such
that $|\eta| >\eta_{\Delta,\beta,1}^+ $.
  3. For $\beta > \beta_c(\Delta)$, there is no FPRAS for the
fixed-magnetization Ising model for magnetizations $\eta$ such that $|\eta|
<\eta_{\Delta,\beta,1}^+ $ unless NP=RP\@.",2111.03033v1
2021/12/15,Effect of magnetocrystalline anisotropy on magnetocaloric properties of AlFe$_{2}$B$_{2}$ compound,"It is well known that the temperature dependence of the effective
magnetocrystalline anisotropy energy obeys the $l(l+1)/2$ power law of
magnetization in the Callen-Callen theory. Therefore, according to the
Callen-Callen theory, the magnetocrystalline anisotropy energy is assumed to be
zero at the critical temperature where the magnetization is approximately zero.
This study estimates the temperature dependence of the magnetocrystalline
anisotropy energy by integrating the magnetization versus magnetic field
($M$--$H$) curves, and found that the magnetocrystalline anisotropy is still
finite even above the Curie temperature in the uniaxial anisotropy, whereas
this does not appear in the cubic anisotropy case. The origin is the fast
reduction of the anisotropy field, which is the magnetic field required to
saturate the magnetization along the hard axis, in the case of cubic
anisotropy. Therefore, the magnetization anisotropy and anisotropic magnetic
susceptibility, those are the key factors of magnetic anisotropy, could not be
established in the case of cubic anisotropy. In addition, the effect of
magnetocrystalline anisotropy on magnetocaloric properties, as the difference
between the entropy change curves of AlFe$_{2}$B$_{2}$ appears above the Curie
temperature, which is in good agreement with a previous experimental study.
This is proof of magnetic anisotropy at slightly above Curie temperature.",2112.08154v1
2022/3/4,Reservoir Computing with Spin Waves in Skyrmion Crystal,"Magnetic skyrmions are nanometric spin textures characterized by a quantized
topological invariant in magnets and often emerge in a crystallized form called
skyrmion crystal in an external magnetic field. We propose that magnets hosting
a skyrmion crystal possess high potential for application to reservoir
computing, which is one of the most successful information processing
techniques inspired by functions of human brains. Our skyrmion-based reservoir
exploits precession dynamics of magnetizations, i.e., spin waves, propagating
in the skyrmion crystal. Because of complex interferences and slow relaxations
of the spin-wave dynamics, the skyrmion spin-wave reservoir attains several
important characteristics required for reservoir computing, e.g., the
generalization ability, the nonlinearity, and the short-term memory. We
investigate these properties by imposing three standard tasks to test the
performances of reservoir, i.e., the duration-estimation task, the short-term
memory task, and the parity-check task. Through these investigations, we
demonstrate that magnetic skyrmion crystals are promising materials for
spintronics reservoir devices. Because magnetic skyrmions emerge spontaneously
in magnets via self-organization process under application of a static magnetic
field, the proposed skyrmion reservoir requires neither advanced
nanofabrication nor complicated manufacturing for production in contrast to
other previously proposed magnetic reservoirs constructed with fabricated
spintronics devices. Our proposal is expected to realize a breakthrough in the
research of spintronics reservoirs of high performance.",2203.02160v1
2022/4/4,Nano-scale collinear multi-Q states driven by higher-order interactions,"Complex magnetic order arises due to the competition of different
interactions between the magnetic moments. Recently, there has been an
increased interest in such states not only to unravel the fundamental physics
involved, but also with regards to applications exploiting their unique
interplay with moving electrons. Whereas it is the Dzyaloshinskii-Moriya
interaction (DMI) that has attracted much attention because of its nature to
induce non-collinear magnetic order including magnetic-field stabilized
skyrmions, it is the frustration of exchange interactions that can drive
magnetic order down to the nano-scale. On top of that, interactions between
multiple spins can stabilize two-dimensional magnetic textures as zero-field
ground states, known as multi-Q states. Here, we introduce a two-dimensional
itinerant magnet with various competing atomic-scale magnetic phases. Using
spin-polarized scanning tunneling microscopy we observe several zero-field
uniaxial or hexagonal nano-scale magnetic states. First-principles calculations
together with an atomistic spin model reveal that these states are stabilized
by the interplay of frustrated exchange and higher-order interactions while the
DMI is weak. Unexpectedly, it is found that not only non-collinear magnetic
states arise, but that higher-order interactions can also lead to collinear
nano-scale multi-Q states.",2204.01358v1
2022/4/4,Evidence of Noncollinear Spin Texture in Magnetic Moiré Superlattices,"Moir\'e magnetism, parallel with moir\'e electronics that has led to novel
correlated and topological electronic states, emerges as a new venue to design
and control exotic magnetic phases in twisted magnetic two-dimensional(2D)
crystals. Here, we report direct evidence of noncollinear spin texture in 2D
twisted double bilayer (tDB) magnet chromium triiodide (CrI$_3$). Using
magneto-optical spectroscopy in tDB CrI$_3$, we revealed the presence of a net
magnetization, unexpected from the composing antiferromagnetic bilayers with
compensated magnetizations, and the emergence of noncollinear spins, originated
from the moir\'e exchange coupling-induced spin frustrations. Exploring the
twist angle dependence, we demonstrated that both features are present in tDB
CrI$_3$ with twist angles from 0.5$^o$ to 5$^o$, but are most prominent in the
1.1$^o$ tDB CrI$_3$. Focusing on the temperature dependence of the 1.1$^o$ tDB
CrI$_3$, we resolved the dramatic suppression in the net magnetization onset
temperature and the significant softening of noncollinear spins, as a result of
the moir\'e induced frustration. Our results demonstrate the power of moir\'e
superlattices in introducing novel magnetic phenomena that are absent in
natural 2D magnets.",2204.01636v1
2022/5/5,Intrinsic spin Hall torque in a moire Chern magnet,"In spin torque magnetic memories, electrically actuated spin currents are
used to switch a magnetic bit. Typically, these require a multilayer geometry
including both a free ferromagnetic layer and a second layer providing spin
injection. For example, spin may be injected by a nonmagnetic layer exhibiting
a large spin Hall effect, a phenomenon known as spin-orbit torque. Here, we
demonstrate a spin-orbit torque magnetic bit in a single two-dimensional system
with intrinsic magnetism and strong Berry curvature. We study AB-stacked
MoTe2/WSe2, which hosts a magnetic Chern insulator at a carrier density of one
hole per moire superlattice site. We observe hysteretic switching of the
resistivity as a function of applied current. Magnetic imaging using a
superconducting quantum interference device reveals that current switches
correspond to reversals of individual magnetic domains. The real space pattern
of domain reversals aligns precisely with spin accumulation measured near the
high-Berry curvature Hubbard band edges. This suggests that intrinsic spin- or
valley-Hall torques drive the observed current-driven magnetic switching in
both MoTe2/WSe2 and other moire materials. The switching current density of
10^3 Amps per square centimeter is significantly less than reported in other
platforms paving the way for efficient control of magnetic order.",2205.02823v1
2022/5/20,"A reduced-order, rotation-based model for thin hard-magnetic plates","We develop a reduced-order model for thin plates made of hard
magnetorheological elastomers (hard-MREs), which are materials composed of
hard-magnetic particles embedded in a polymeric matrix. First, we propose a new
magnetic potential, as an alternative to an existing torque-based 3D continuum
theory of hard-MREs, obtained by reformulating the remnant magnetization of a
deformed hard-MRE body. Specifically, the magnetizations in the initial and
current configurations are related by the rotation tensor decomposed from the
deformation gradient, independently of stretching deformation. This description
is motivated by recently reported observations in microscopic homogenization
simulations. Then, we derive a 2D plate model through the dimensional reduction
of our proposed rotation-based 3D theory. For comparison, we also provide a
second plate model derived from the existing 3D theory. Finally, we perform
precision experiments to thoroughly evaluate the proposed 3D and 2D models on
hard-magnetic plates under various magnetic and mechanical loading conditions.
We demonstrate that our rotation-based modification of the magnetic potential
is crucial in correctly capturing the behavior of plates subjected to an
applied field aligned with the magnetization, and undergoing in-plane
stretching. In all the tested cases, our rotation-based 3D and 2D models yield
predictions in excellent quantitative agreement with the experiments and can
thus serve as predictive tools for the rational design of hard-magnetic plate
structures.",2205.10208v1
2022/6/14,Gate-tunable proximity effects in graphene on layered magnetic insulators,"The extreme versatility of two-dimensional van der Waals (vdW) materials
derives from their ability to exhibit new electronic properties when assembled
in proximity with dissimilar crystals. For example, although graphene is
inherently non-magnetic, recent work has reported a magnetic proximity effect
in graphene interfaced with magnetic substrates, potentially enabling a pathway
towards achieving a high-temperature quantum anomalous Hall effect. Here, we
investigate heterostructures of graphene and chromium trihalide magnetic
insulators (CrI$_3$, CrBr$_3$, and CrCl$_3$). Surprisingly, we are unable to
detect a magnetic exchange field in the graphene, but instead discover
proximity effects featuring unprecedented gate-tunability. The graphene becomes
highly hole-doped due to charge transfer from the neighboring magnetic
insulator, and further exhibits a variety of atypical transport features. These
include highly extended quantum Hall plateaus, abrupt reversals in the Landau
level filling sequence, and hysteresis over at least days-long time scales. In
the case of CrI$_3$, we are able to completely suppress the charge transfer and
all attendant atypical transport effects by gating. The charge transfer can
additionally be altered in a first-order phase transition upon switching the
magnetic states of the nearest CrI$_3$ layers. Our results provide a roadmap
for exploiting the magnetic proximity effect in graphene, and motivate further
experiments with other magnetic insulators.",2206.06949v1
2022/7/28,Evolution of short-range magnetic correlations in ferromagnetic Ni-V alloys,"We experimentally study how the magnetic correlations develop in a binary
alloy close to the ferromagnetic quantum critical point with small-angle
neutron scattering (SANS). Upon alloying the itinerant ferromagnet nickel with
vanadium, the ferromagnetic order is continuously suppressed. The critical
temperature Tc vanishes when vanadium concentrations reach the critical value
of xc=0.116 indicating a quantum critical point separating the ferromagnetic
and paramagnetic phases. Earlier magnetization and $\mu$SR data have indicated
the presence of magnetic inhomogeneities in Ni(1-x)V(x) and, in particular,
recognize the magnetic clusters close to xc, on the paramagnetic and on the
ferromagnetic sides with nontrivial dynamical properties [R. Wang et al., Phys.
Rev. Lett. 118, 267202 (2017)]. We present the results of SANS study with full
polarization analysis of polycrystalline Ni(1-x)V(x) samples with x=0.10 and
x=0.11 with low critical temperatures Tc below 50 K. For both Ni-V samples
close to xc we find isotropic magnetic short-range correlations in the
nanometer-scale persisting at low temperatures. They are suppressed gradually
in higher magnetic fields. In addition, signatures of long-range ordered
magnetic domains are present below Tc. The fraction of these magnetic clusters
embedded in the ferromagnetic ordered phase grows towards xc and agrees well
with the cluster fraction estimate from the magnetization and $\mu$SR data. Our
SANS studies provide new insights into the nature of the inhomogeneities in a
ferromagnetic alloy close to a quantum critical point.",2207.14196v2
2022/11/9,Magnetization reversal through an antiferromagnetic state,"Magnetization reversal in ferro- and ferrimagnets is a well-known archetype
of non-equilibrium processes, where the volume fractions of the oppositely
magnetized domains vary and perfectly compensate each other at the coercive
magnetic field. Here, we report on a fundamentally new pathway for
magnetization reversal that is mediated by an antiferromagnetic state.
Consequently, an atomic-scale compensation of the magnetization is realized at
the coercive field, instead of the mesoscopic or macroscopic domain
cancellation in canonical reversal processes. We demonstrate this unusual
magnetization reversal on the Zn-doped polar magnet Fe$_2$Mo$_3$O$_8$. Hidden
behind the conventional ferrimagnetic hysteresis loop, the surprising emergence
of the antiferromagnetic phase at the coercive fields is disclosed by a sharp
peak in the field-dependence of the electric polarization. In addition, at the
magnetization reversal our THz spectroscopy studies reveal the reappearance of
the magnon mode that is only present in the pristine antiferromagnetic state.
According to our microscopic calculations, this unusual process is governed by
the dominant intralayer coupling, strong easy-axis anisotropy and spin
fluctuations, which result in a complex interplay between the ferrimagnetic and
antiferromagnetic phases. Such antiferro-state-mediated reversal processes
offer novel concepts for magnetization control, and may also emerge for other
ferroic orders.",2211.05028v1
2023/1/8,Structural tuning magnetism and topology in a magnetic topological insulator,"To date, the most widely-studied quantum anomalous Hall insulator (QAHI)
platform is achieved by dilute doping of magnetic ions into thin films of the
alloyed tetradymite topological insulator (TI) (Bi$_{1-x}$Sb$_x$)$_2$Te$_3$
(BST). In these films, long-range magnetic ordering of the transition metal
substituants opens an exchange gap $\Delta$ in the topological surface states,
stabilizing spin-polarized, dissipationless edge channels with a nonzero Chern
number $\mathcal{C}$. The long-range ordering of the spatially separated
magnetic ions is itself mediated by electronic states in the host TI, leading
to a sophisticated feedback between magnetic and electronic properties. Here we
present a study of the electronic and magnetic response of a BST-based QAHI
system to structural tuning via hydrostatic pressure. We identify a systematic
closure of the topological gap under compressive strain accompanied by a
simultaneous enhancement in the magnetic ordering strength. Combining these
experimental results with first-principle calculations we identify structural
deformation as a strong tuning parameter to traverse a rich topological phase
space and modify magnetism in the magnetically doped BST system.",2301.03078v1
2023/1/17,Magnetic frustration driven by conduction carrier blocking in Nd$_2$Co$_{0.85}$Si$_{2.88}$,"The intermetallic compound Nd$_2$Co$_{0.85}$Si$_{2.88}$ having a triangular
lattice could be synthesized in single-phase only with defect crystal
structure. Investigation through different experimental techniques indicate the
presence of two magnetic transitions in the system. As verified experimentally
and theoretically, the high-temperature transition T$_H$ ~ 140 K is associated
with the development of ferromagnetic interaction between itinerant Co moments,
whereas the low-temperature transition at T$_L$ ~ 6.5 K is due to the coupling
among Nd-4f and Co-3d moments, which is antiferromagnetic in nature. Detailed
studies of temperature-dependent dc magnetic susceptibility, field dependence
of isothermal magnetization, non-equilibrium dynamical behavior, viz. magnetic
relaxation, aging effect, magnetic-memory effect, and temperature dependence of
heat capacity, along with density functional theory (DFT) calculations, suggest
that the ground state is magnetically frustrated spin-glass in nature, having
competing magnetic interactions of equivalent energies. DFT results further
reveal that the 3d/5d-conduction carriers are blocked in the system and act as
a barrier for the 4f-4f RKKY interactions, resulting in spin-frustration.
Presence of vacancy defects in the crystal are also conducive to the
spin-frustration. This is an unique mechanism of magnetic frustration, not
emphasized so far in any of the ternary R$_2$TX$_3$ (R=rare-earth, T=transition
elements and X=Si, Ge, In) type compounds. Due to the competing character of
the itinerant 3d and localized 4f moments, the compound exhibits anomalous
field dependence of magnetic coercivity.",2301.07140v1
2023/2/7,Masterthesis: Ab Initio Magnetic Properties of Rare-Earth Lean Nd-based Hard Magnets,"Due to the resource criticality of rare-earths (RE), an alternative to the
well-known Nd$_2$Fe$_{14}$B magnets with a lower amount of critical elements is
required. In this work, density functional theory (DFT) calculations to
investigate the influence of partial Nd substitution with more abundant
elements (X: Y and Ce) in ThMn$_{12}$-type (Nd,X)Fe$_{11}$Ti compounds were
performed. In order to have a systematic understanding, the intrinsic magnetic
properties such as the saturation magnetization $M_S$, Curie temperature $T_C$
and magnetocrystalline anisotropy energy, are screened starting from binaries
RFe$_{12}$ (R: Y, Ce and Nd), and only considering the spin magnetic
contribution in case of the $f$ electrons. Ti is considered for the
thermodynamic stabilization and different concentrations of Ti are taken into
account for ternaries RFe$_{12-y}$Ti$_y$ and quaternaries
(Nd,X)Fe$_{12-y}$Ti$_y$ (0.5$\le$ $y$ $\le$1). In addition, the effect of
nitrogenation is examined for each considered compound. In case of
(Nd,Y)Fe$_{11}$Ti, $|BH|$$_{max}$ is found to be 384 kJ/m$^3$ and $T_C$ is
calculated to be 595 K. Similarly, $|BH|$$_{max}$ and $T_C$ are calculated to
be 365 kJ/m$^3$ and 593 K for (Nd,Ce)Fe$_{11}$Ti magnet, respectively. Both 50
% Nd-lean magnets exhibit higher $|BH|$$_{max}$ compared to Sm$_2$Co$_{17}$ and
$T_C$ than Nd$_2$Fe$_{14}$B. For both cases, the theoretical magnetic hardness
factor $\kappa$ is calculated to be 1.20, which qualifies them as good
candidates for RE-lean permanent magnets.",2302.03417v1
2023/4/19,Thickness-dependent magnetic properties in Pt[CoNi]n multilayers with perpendicular magnetic anisotropy,"We systematically investigated the Ni and Co thickness-dependent
perpendicular magnetic anisotropy (PMA) coefficient, magnetic domain
structures, and magnetization dynamics of Pt(5 nm)/[Co(t_Co nm)/Ni(t_Ni
nm)]5/Pt(1 nm) multilayers by combining the four standard magnetic
characterization techniques. The magnetic-related hysteresis loops obtained
from the field-dependent magnetization M and anomalous Hall resistivity (AHR)
\r{ho}_xy found that the two serial multilayers with t_Co = 0.2 and 0.3 nm have
the optimum PMA coefficient K_U well as the highest coercivity H_C at the Ni
thickness t_Ni = 0.6 nm. Additionally, the magnetic domain structures obtained
by Magneto-optic Kerr effect (MOKE) microscopy also significantly depend on the
thickness and K_U of the films. Furthermore, the thickness-dependent linewidth
of ferromagnetic resonance is inversely proportional to K_U and H_C, indicating
that inhomogeneous magnetic properties dominate the linewidth. However, the
intrinsic Gilbert damping constant determined by a linear fitting of
frequency-dependent linewidth does not depend on Ni thickness and K_U. Our
results could help promote the PMA [Co/Ni] multilayer applications in various
spintronic and spin-orbitronic devices.",2304.09366v1
2023/4/19,Real-time observation of magnetization and magnon dynamics in a two-dimensional topological antiferromagnet MnBi2Te4,"Atomically thin van der Waals magnetic materials have not only provided a
fertile playground to explore basic physics in the two-dimensional (2D) limit
but also created vast opportunities for novel ultrafast functional devices.
Here we systematically investigate ultrafast magnetization dynamics and spin
wave dynamics in few-layer topological antiferromagnetic MnBi2Te4 crystals as a
function of layer number, temperature, and magnetic field. We find
laser-induced (de)magnetization processes can be used to accurately track the
distinct magnetic states in different magnetic field regimes, including showing
clear odd-even layer number effects. In addition, strongly field-dependent
antiferromagnetic magnon modes with tens of gigahertz frequencies are optically
generated and directly observed in the time domain. Remarkably, we find that
magnetization and magnon dynamics can be observed in not only the time-resolved
magneto-optical Kerr effect but also the time resolved reflectivity, indicating
strong correlation between the magnetic state and electronic structure. These
measurements present the first comprehensive overview of ultrafast spin
dynamics in this novel 2D antiferromagnet, paving the way for potential
applications in 2D antiferromagnetic spintronics and magnonics as well as
further studies of ultrafast control of both magnetization and topological
quantum states.",2304.09390v2
2023/4/21,Magnetic properties of a spin-orbit entangled Jeff = 1/2 honeycomb lattice,"The interplay between spin-orbit coupling, anisotropic magnetic interaction,
frustration-induced quantum fluctuations and spin correlations can lead to
novel quantum states with exotic excitations in rare-earth-based quantum
magnets. Herein, we present the crystal structure, magnetization, electron spin
resonance (ESR), specific heat, and nuclear magnetic resonance (NMR)
experiments on the polycrystalline samples of Ba9Yb2Si6O24, in which Yb3+ ions
form a perfect honeycomb lattice without detectable anti-site disorder. The
magnetization data reveal antiferromagnetically coupled spin-orbit entangled
Jeff = 1/2 degrees of freedom of Yb3+ ions in the Kramers doublet state. The
ESR measurements reveal that the first excited Kramers doublet is 32.3(7) meV
above the ground state. The specific heat results suggest the absence of any
long-range magnetic order in the measured temperature range. Furthermore, the
29Si NMR results do not indicate any signature of magnetic ordering down to 1.6
K, and the spin-lattice relaxation rate reveals the presence of a field-induced
gap that is attributed to the Zeeman splitting of Kramers doublet state in this
quantum material. Our experiments detect neither spin freezing nor long-range
magnetic ordering down to 1.6 K. The current results suggest the presence of
short-range spin correlations in this spin-orbit entangled Jeff =1/2 rare-earth
magnet on a honeycomb lattice.",2304.10890v2
2023/5/29,"Structural, Optical and Single-domain Magnetic Features of the Noncollinear Ferrimagnetic Nano-spinel Chromites ACr$_2$O$_4$ (A = Ni, Co, and Mn)","Spinel chromites ACr$_2$O$_4$ with inherent magnetic geometrical frustration
usually exhibit a noncollinear ferrimagnetic ground state when A are magnetic
ions, with possibly crystallite-size dependent intriguing magnetic features.
Here, we report single-domain magnetic properties of ACr$_2$O$_4$ (A = Ni, Co,
and Mn) nanocrystals, with an average crystallite size of 18, 15 and 10 nm,
exhibiting an optical energy gap of 2.87, 3.05 and 2.9 eV, respectively. The
temperature dependence of magnetization indicates the main bulk magnetic
transitions with a commonly coexisting spin-glass-like state and finite-size
effects on the noncolinear ferrimagnetic transitions. An anomaly observed at Ts
= 15, 24 and 10 K is attributed to the bulk magnetic transition to a canted
antiferromagnetic state in NiCr$_2$O$_4$ and incommensurate spiral orders in
CoCr$_2$O$_4$ and MnCr$_2$O$_4$ NCs, respectively. A further bulk magnetic
transition to a commensurate spiral order is observed for CoCr$_2$O$_4$ NCs at
a lock-in temperature Tl = 5 K much lower than that reported using bulk
samples, while it is completely suppressed in the MnCr$_2$O$_4$ NCs.
Finite-size effects and single-domain magnetic behaviors indicated by anomalous
temperature-dependences of the coercive field and the hysteresis-loop
squareness, mainly driven by a magnetocrystalline anisotropy, are discussed in
comparison to results reported using bulk counterparts.",2305.17856v1
2023/8/1,Electrical detection and nucleation of a magnetic skyrmion in a magnetic tunnel junction observed via operando magnetic microscopy,"Magnetic skyrmions are topological spin textures which are envisioned as
nanometre scale information carriers in magnetic memory and logic devices. The
recent demonstration of room temperature stabilization of skyrmions and their
current induced manipulation in industry compatible ultrathin films were first
steps towards the realisation of such devices. However, important challenges
remain regarding the electrical detection and the low-power nucleation of
skyrmions, which are required for the read and write operations. Here, we
demonstrate, using operando magnetic microscopy experiments, the electrical
detection of a single magnetic skyrmion in a magnetic tunnel junction (MTJ) and
its nucleation and annihilation by gate voltage via voltage control of magnetic
anisotropy. The nucleated skyrmion can be further manipulated by both gate
voltage and external magnetic field, leading to tunable intermediate resistance
states. Our results unambiguously demonstrate the readout and voltage
controlled write operations in a single MTJ device, which is a major milestone
for low power skyrmion based technologies.",2308.00445v1
2023/9/24,Hexaferrite-based permanent magnets with upper magnetic properties by cold sintering process via a non-aqueous solvent,"The incessant technological pursuit towards a more sustainable and green
future depends strongly on permanent magnets. At present, their use is
widespread, making it imperative to develop new processing methods that
generate highly competitive magnetic properties reducing the fabrication
temperatures and costs. Herein, a novel strategy for developing dense sintered
magnets based on Sr-hexaferrites with upper functional characteristics is
presented. An innovative cold sintering approach using glacial acetic acid as
novelty, followed by a post-annealing at 1100 {\deg}C, achieves a densification
of the ceramic magnets of 92% with respect to the theoretical density and
allows controlling the particle growth. After the cold sintering process, a
fraction of amorphous SrO is identified, in addition to a partial
transformation to {\alpha}-Fe2O3 as secondary crystalline phase. 46 wt% of
SrFe12O19 remains, which is mostly recuperated after the post-thermal
treatment. These findings do not significantly modify the final structure of
ferrite magnets, neither at short- nor long-range order. The innovative process
has a positive impact on the magnetic properties, yielding competitive ferrite
magnets at lower sintering temperatures with an energy efficiency of at least
25%, which opens up a new horizon in the field of rare-earth free permanent
magnets and new possibilities in other applications.",2309.13719v1
2023/10/9,Controlling Topology through Targeted Symmetry Manipulation in Magnetic Systems,"The possibility of selecting magnetic space groups by orienting the
magnetization direction or tuning magnetic orders offers a vast playground for
engineering symmetry protected topological phases in magnetic materials. In
this work, we study how selective tuning of symmetry and magnetism can
influence and control the resulting topology in a 2D magnetic system, and
illustrate such procedure in the ferromagnetic monolayer MnPSe$_3$. Density
functional theory calculations reveals a symmetry-protected accidental
semimetalic (SM) phase for out-of-plane magnetization which becomes an
insulator when the magnetization is tilted in-plane, reaching band gap values
close to $100$ meV. We identify an order-two composite antiunitary symmetry and
threefold rotational symmetry that induce the band crossing and classify the
possible topological phases using symmetry analysis, which we support with
tight-binding and $\mathbf{k}\cdot\mathbf{p}$ models. Breaking of inversion
symmetry opens a gap in the SM phase, giving rise to a Chern insulator. We
demonstrate this explicitly in the isostructural Janus compound
Mn$_2$P$_2$S$_3$Se$_3$, which naturally exhibits Rashba spin-orbit coupling
that breaks inversion symmetry. Our results map out the phase space of
topological properties of ferromagnetic transition metal phosphorus
trichalcogenides and demonstrate the potential of the magnetization-dependent
metal-to-insulator transition as a spin switch in integrated two-dimensional
electronics.",2310.05896v1
2024/1/2,Visualizing Magnetic Order in Self-Assembly of Superparamagnetic Nanoparticles,"We use soft x-ray vector-ptychographic tomography to determine the
three-dimensional magnetization field in superparamagnetic nanoparticles
self-assembled at the liquid-liquid interface and reveal the magnetic order
induced by layered structure. The spins in individual nanoparticles become more
aligned with increasing number of layers, resulting in a larger net
magnetization. Our experimental results show a magnetic short-range order in
the monolayer due to the proliferation of thermally induced magnetic vortices
and a magnetic long-range order in the bilayer and trilayer, stemming from the
strengthened dipolar interactions that effectively suppress thermal
fluctuations. We also observe a screening effect of magnetic vortices and the
attractive interaction between the magnetic vortices with opposite topological
charges. Our work demonstrates the crucial role of layered structure in shaping
the magnetization of nanoparticle assemblies, providing new opportunities to
modulate these properties through strategic layer engineering.",2401.01284v1
2024/1/5,Machine learning inspired models for Hall effects in non-collinear magnets,"The anomalous Hall effect has been front and center in solid state research
and material science for over a century now, and the complex transport
phenomena in nontrivial magnetic textures have gained an increasing amount of
attention, both in theoretical and experimental studies. However, a clear path
forward to capturing the influence of magnetization dynamics on anomalous Hall
effect even in smallest frustrated magnets or spatially extended magnetic
textures is still intensively sought after. In this work, we present an
expansion of the anomalous Hall tensor into symmetrically invariant objects,
encoding the magnetic configuration up to arbitrary power of spin. We show that
these symmetric invariants can be utilized in conjunction with advanced
regularization techniques in order to build models for the electric transport
in magnetic textures which are, on one hand, complete with respect to the point
group symmetry of the underlying lattice, and on the other hand, depend on a
minimal number of order parameters only. Here, using a four-band tight-binding
model on a honeycomb lattice, we demonstrate that the developed method can be
used to address the importance and properties of higher-order contributions to
transverse transport. The efficiency and breadth enabled by this method
provides an ideal systematic approach to tackle the inherent complexity of
response properties of noncollinear magnets, paving the way to the exploration
of electric transport in intrinsically frustrated magnets as well as
large-scale magnetic textures.",2401.03044v1
2024/3/1,Spin current control of magnetism,"Exploring novel strategies to manipulate the order parameter of magnetic
materials by electrical means is of great importance, not only for advancing
our understanding of fundamental magnetism, but also for unlocking potential
practical applications. A well-established concept to date uses gate voltages
to control magnetic properties, such as saturation magnetization, magnetic
anisotropies, coercive field, Curie temperature and Gilbert damping, by
modulating the charge carrier population within a capacitor structure. Note
that the induced carriers are non-spin-polarized, so the control via the
electric-field is independent of the direction of the magnetization. Here, we
show that the magnetocrystalline anisotropy (MCA) of ultrathin Fe films can be
reversibly modified by a spin current generated in Pt by the spin Hall effect.
The effect decreases with increasing Fe thickness, indicating that the origin
of the modification can be traced back to the interface. Uniquely, the change
in MCA due to the spin current depends not only on the polarity of the charge
current but also on the direction of magnetization, i.e. the change in MCA has
opposite sign when the direction of magnetization is reversed. The control of
magnetism by the spin current results from the modified exchange splitting of
majority- and minority-spin bands, and differs significantly from the
manipulation by gate voltages via a capacitor structure, providing a
functionality that was previously unavailable and could be useful in advanced
spintronic devices.",2403.00709v1
2024/3/5,Stretch-independent magnetization in incompressible magnetorheological elastomers,"In this study, we perform a critical examination of the phenomenon where the
magnetization is stretch-independent in incompressible hard-magnetic
magnetorheological elastomers (h-MREs), as observed in several recent
experimental and numerical investigations. We demonstrate that the fully
dissipative model proposed by Mukherjee et al. (2021) may be reduced, under
physically consistent assumptions, to that of Yan et al. (2023), but not that
of Zhao et al. (2019). In cases where the h-MRE solid undergoes non-negligible
stretching, the model of Zhao et al. (2019) provides predictions that are in
disagreement with experimental observations, given that, by construction, that
model produces a magnetization response that is not stretch-independent. By
contrast, the other two models are able to describe this important feature
present in h-MREs, as well as in incompressible magnetically soft s-MRES. Note
that in cases where stretching is negligible, such as for inextensible slender
structures under bending deformation, the Zhao et al. (2019) model provides
accurate predictions despite its underlying assumptions. Additionally, our
analysis reveals two key points about the magnetization vector in the context
of the more general, fully dissipative model. First, the magnetization can be
related to an internal variable in that theory. However, it cannot be formally
used as an internal variable except in the special case of an ideal magnet,
and, as such, it is subject to constitutive assumptions. Furthermore, we
clarify that the magnetization vector alone is insufficient to describe
entirely the magnetic response of an MRE solid; instead, the introduction of
one of the original Maxwell fields is always necessary for a complete
representation.",2403.03096v1
2012/3/9,Material Laws and Numerical Methods in Applied Superconductivity,"Contents Preface I Electromagnetism of type II superconductors 1 General
Statements Of The Critical State 1.1 The CS In The Maxwell Equations Formalism
1.2 The CS Regime And The MQS Limit 2 Variational Theory for CS Problems 2.1
General Principles Of The Variational Method 2.2 The Material Law: SCs with
magnetic anisotropy 2.2.1 Onto the 1D Critical States 2.2.2 Towards The 3D
Critical States 3 Computational Method Conclusions I References I II Critical
State Problems:Effects & Applications 4 Type-II SCs With Intrinsic Magnetic
Anisotropy 4.1 3D variational statement in slab geometry 4.2 Isotropic
predictions in -3D- configurations 4.3 T-states in -3D- configurations 4.4
CT-states in -3D- configurations 4.5 Smooth critical states in -3D-
configurations Appendix I Critical angle gradient in -3D- configurations 5 The
Longitudinal Transport Problem 5.1 Simplified analytical models and beyond
5.1.1 The simplest analytical model 5.1.2 The SDCST statement and the BM's
approach 5.2 Magnetic anisotropy and the uncommon effects 5.2.1 Extremal case:
The T-states model 5.2.2 Material laws with magnetic anisotropy: CT\chi -
models 6 Electromagnetism For Superconducting Wires 6.1 Theoretical framework
and general considerations 6.2 SC wires subjected to isolated external sources
6.2.1 Wires with an injected AC transport current 6.2.2 Wires under an external
AC magnetic flux 6.2.3 Ultimate considerations on the AC losses 6.3 SC wires
under simultaneous AC excitations (B_{0},I_{tr}) 6.3.1 Synchronous excitations
6.3.2 Asynchronous excitations Conclusions II References II Supplementary
Material II III Microscopical aspects also analyzed 7 E-Ph Theory And The Nodal
Kink Effect In HTSC 8 Is it necessary to go beyond the E-Ph mode? Conclusions
III References III Supplementary Material III IV Addenda",1203.2159v1
2004/9/29,A Magnetic Rotator Wind Disk Model for Be Stars,"A Magnetic Rotator Wind-Disk(MRWD) model is considered for the formation of
Keplerian disks around Be stars. Material from low latitudes of the stellar
surface flows along magnetic flux tubes and passes through a shock surface to
form a pre-Keplerian disk region. Initially, the density in this region is
small. After a fill-up time, the density of the disk is significantly larger
and the magnetic force becomes negligible compared with the centrifugal force.
The material then expands to form a Keplerian disk. During disk fill-up, the
meridional component B-star of the magnetic field at the stellar surface must
be larger than a minimum value B-star-min. The radial extent of the Keplerian
region will be larger when B-star is larger or when viscosity plays a role. In
B-type stars, B-star-min must be of order 1 G to 10 G. In faster rotating
stars, the wind speed must be correspondingly larger for the formation of
shock-compressed disk regions.",0409738v1
1997/7/28,Magnetic sublayers effect on the exchange coupling oscillations vs. cap-layer thickness,"We have found that some periods of interlayer exchange coupling (IEC)
oscillations as a function of cap-layer (CL) thickness may be suppressed if the
in-plane extremal spanning vectors of the cap- and ferromagnet-materials Fermi
surfaces do not coincide. The suppression of the IEC oscillations vs. the CL
thickness holds also if the magnetic slab thickness tends to infinity. On the
one hand, we have shown by means of very simple arguments that apart from the
well-known selection rules concerning the spacer- and cap-layers, another one
related with the magnetic sublayers has to be fulfilled in order that the
interlayer coupling oscillations $vs.$ CL thickness could survive. On the other
hand, the distribution of induced magnetic moments across the non-magnetic cap-
and spacer-sublayers have been computed and shown to reveal the underlying
periodicity of the materials they are made of (i.e. related to their bulk Fermi
surfaces) independently of whether or not the selection rules are fulfilled.
This means that the IEC oscillations are of global nature and depend on all the
sublayers the system consists of.",9707278v2
1999/2/19,Heat Capacity Measurements in Pulsed Magnetic Fields,"The new NHMFL 60T quasi-continuous magnet produces a flat-top field for a
period of 100 ms at 60 Tesla, and for longer time at lower fields, e.g. 0.5 sec
at 35 Tesla. We have developed for the first time the capability to measure
heat capacity at very high magnetic fields in the NHMFL 60 T quasi-continuous
magnet at LANL, using a probe built out of various plastic materials. The field
plateau allows us to utilize a heat-pulse method to obtain heat capacity data.
Proof-of-principle heat capacity experiments were performed on a variety of
correlated electron systems. Both magnet performance characteristics and
physical properties of various materials studied hold out a promise of wide
application of this new tool.",9902263v1
2000/5/24,Frustrated trimer chain model and Cu3Cl6(H2O)2 2H8C4SO2 in a magnetic field,"Recent magnetization and susceptibility measurements on Cu3Cl6(H2O)2 2H8C4SO2
by Ishii et.al. [J. Phys. Soc. Jpn. 69, 340 (2000)] have demonstrated the
existence of a spin gap. In order to explain the opening of a spin gap in this
copper-trimer system, Ishii et.al. have proposed a frustrated trimer chain
model. Since the exchange constants for this model have not yet been
determined, we develop a twelfth-order high-temperature series for the magnetic
susceptibility and fit it to the experimentally measured one. We find that some
of the coupling constants are likely to be ferromagnetic. The combination of
several arguments does not provide any evidence for a spin gap in the parameter
region with ferromagnetic coupling constants, but further results e.g. for the
magnetization process are in qualitative agreement with the experimental
observations.",0005398v2
2001/5/2,Ferromagnetic Domain Distribution in Thin Films During Magnetization Reversal,"We have shown that polarized neutron reflectometry can determine in a
model-free way not only the mean magnetization of a ferromagnetic thin film at
any point of a hysteresis cycle, but also the mean square dispersion of the
magnetization vectors of its lateral domains. This technique is applied to
elucidate the mechanism of the magnetization reversal of an exchange-biased
Co/CoO bilayer. The reversal process above the blocking temperature is governed
by uniaxial domain switching, while below the blocking temperature the reversal
of magnetization for the trained sample takes place with substantial domain
rotation.",0105040v2
2002/1/2,Kinetic exchange vs. room temperature ferromagnetism in diluted magnetic semiconductors,"Guided by the internal-reference rule and the known band offsets in III-V and
II-VI diluted magnetic semiconductors, we discuss the feasibility of obtaining
p-type conductivity, required for the carrier-induced ferromagnetism, as well
as the cases for which the doping by shallow impurities may lead to the
ferromagnetism driven by the double exchange. We consider the dependence of
kinetic exchange on the p-d hybridization, on the electronic configurations of
the magnetic ions, and on the energies of the charge transfer between the
valence band of host materials and the magnetic ions. In the case of Mn-based
II-VI compounds, the doping by acceptors is necessary for the hole-induced
ferromagnetism. The latter is, however, possible without any doping for some of
Mn-, Fe- or Co-based III-V magnetic semiconductors. In nitrides with Fe or Co
carrier-induced ferromagnetism with T_C>300K is expected in the presence of
acceptor doping.",0201012v1
2002/1/16,Ferromagnetic semiconductors,"The current status and prospects of research on ferromagnetism in
semiconductors are reviewed. The question of the origin of ferromagnetism in
europium chalcogenides, chromium spinels and, particularly, in diluted magnetic
semiconductors is addressed. The nature of electronic states derived from 3d of
magnetic impurities is discussed in some details. Results of a quantitative
comparison between experimental and theoretical results, notably for Mn-based
III-V and II-VI compounds, are presented. This comparison demonstrates that the
current theory of the exchange interactions mediated by holes in the valence
band describes correctly the values of Curie temperatures T_C magnetic
anisotropy, domain structure, and magnetic circular dichroism. On this basis,
chemical trends are examined and show to lead to the prediction of
semiconductor systems with T_C that may exceed room temperature, an expectation
that are being confirmed by recent findings. Results for materials containing
magnetic ions other than Mn are also presented emphasizing that the double
exchange involving hoping through d states may operate in those systems.",0201282v1
2002/3/12,Magnetoresistances observed by decomposition of the magnetic moment in La1-xCaxMnO3 films,"A ferromagnetic phase, characterized by electron carriers and a high
temperature colossal magnetoresistance (HTCMR) dependent on the magnetic
moment, and a semiconducting phase, characterized by hole carriers and a low
temperature CMR (LTCMR), are observed in La$_{1-x}$Ca$_{x}$MnO$_3$ thin films
by the van der Pauw method. The LTCMR is much more sensitive to the magnetic
field than the HTCMR. In the ferromagnetic phase for films with anisotropic
moments in two dimensions, a remnant resistivity of the order of 10$^{-8}
\~{\Omega}m$ is observed up to 100 K and increases exponentially with both a
temperature up to $T_c$ and a magnetic field above one Tesla (a positive
magnetoresistivity). We found that the ferromagnetic phase below $T_c$ is in a
polaronic state with a polaronic mobile conduction, and the carrier density
dips near $T_c$. For resistances measured by the four-probe method with line
electrodes, low temperature information of the HTCMR is not revealed. The van
der Pauw method is more effective for the resistance measurement of a magnetic
material than the four-probe method.",0203245v2
2002/4/25,Interpretation of large room-temperature diamagnetism at low magnetic fields in films of oxidised atactic polypropylene in terms of superconducting current loops,"A simple model is used to analyse published results on large room-temperature
diamagnetism for two films of oxidised atactic polypropylene (OAPP) at low
magnetic fields. The model involves induced currents expected in circular
closed loops of superconductors in fields below the lower critical field H_{c1}
at which flux penetration would first occur if a metamagnetic transition did
not intervene as in OAPP, and the assumption that resistance would be restored
at H_{c1} (negligible pinning). Fits to the data for the more strongly magnetic
sample with the model, allowing two different types of loops with different
loop radii b_1 and b_2, but with the same cross section a of loop material
yield H_{c1} is approximately equal to 5260 Oe, and fits to the data for the
less strongly magnetic sample with two loop sizes and with the same value of
H_{c1}, combined with the knowledge that the minimum number of closed loops of
any type is one, requires that the radius a of the cross section of the
material should be less than about 0.8 micrometres, in fair agreement with a
maximum radius of 1 micrometre obtained previously from other data.",0204556v1
2002/5/20,Phase diagram of the La$_{1-x}$Ca$_{x}$MnO$_{3}$ compound for $0.5\leq x\leq 0.9$,"We have studied the phase diagram of La$_{1-x}$Ca$_{x}$MnO$_{3}$ for $0.5\leq
x\leq 0.9$ using neutron powder diffraction and magnetization measurements. At
300 K all samples are paramagnetic and single phase with crystallographic
symmetry $Pnma$. As the temperature is reduced a structural transition is
observed which is to a charge-ordered state only for certain x. On further
cooling the material passes to an antiferromagnetic ground state with Neel
temperature $T_N$ that depends on x. For $0.8\leq x\leq 0.9$ the structural
transformation occurs at the same temperature as the magnetic transition.
Overall, the neutron diffraction patterns were explained by considering four
phase boundaries for which La$_{1-x}$Ca$_x$MnO$_3$ forms a distinct phase: the
CE phase at $x=0.5-0.55$, the charge-ordered phase at x=2/3, the monoclinic and
C-type magnetic structure at $x=0.80-0.85$ and the G-type magnetic structure at
x=1. Between these phase boundaries the magnetic reflections suggest the
existence of mixed compounds containing both phases of the adjacent phase
boundaries in a ratio determined by the lever rule.",0205410v1
2002/6/6,High magnetic field transport measurement of charge-ordered Pr$_{0.5}$Ca$_{0.5}$MnO$_3$ strained thin films,"We have investigated the magnetic-field-induced phase transition of
charge-ordered (CO) Pr$_{0.5}$Ca$_{0.5}$MnO$_3$ thin films, deposited onto
(100)-oriented LaAlO$_3$ and (100)-oriented SrTiO$_3$ substrates using the
pulsed laser deposition technique, by measuring the transport properties with
magnetic fields up to 22T. The transition to a metallic state is observed on
both substrates by application of a critical magnetic field ($H_C>10T$ at 60K).
The value of the field required to destroy the charge-ordered insulating state,
lower than the bulk compound, depends on both the substrate and the thickness
of the film. The difference of the critical magnetic field between the films
and the bulk material is explained by the difference of in-plane parameters at
low temperature (below the CO transition). Finally, these results confirm that
the robustness of the CO state, depends mainly on the stress induced by the
difference in the thermal dilatations between the film and the substrate.",0206072v1
2002/8/2,Superconducting Properties of Highly Dense MgB2 Bulk Materials,"Highly dense MgB2 policrystalline bulk materials, obtained by reactive liquid
infiltration, have been characterized in their superconducting transport and
magnetic properties in magnetic field and in a temperature range of interest
for the MgB2 compound. The products have a granular morphology of composite
nature and their overall density affects their properties. The irreversibility
line, Bc1(T) values, magnetically measured current densities and the trapped
magnetic field are evaluated by susceptibility curves and hysteresis curves,
both obtained by SQUID magnetometry for samples of different density, up to 35K
and up to 5T applied magnetic field. The experimental results have been
compared with the best values reported in the literature for other bulk
sintering techniques.",0208043v1
2002/8/3,Relativity and Magnetism in Ni-Pd and Ni-Pt Alloys,"We show that the differences in the magnetic properties of Ni-Pd and Ni-Pt
alloys arise mainly due to relativity. In particular, we find that the local
magnetic moment of Ni increases with the addition of Pd in Ni-Pd while it
decreases with the addition of Pt in Ni-Pt, as found experimentally, only if
relativity is present. Our analysis is based on the effects of relativity on
(i) the spin-polarized densities of states of Ni, (ii) the splitting of
majority and minority spin d-band centers of Ni, and (iii) the separation
between s-d band centers of Pd and Pt in Ni-Pd and Ni-Pt alloys.",0208062v2
2002/11/19,NMR and Mossbauer study of spin dynamics and electronic structure of Fe{2+x}V{1-x}Al and Fe2VGa,"In order to assess the magnetic ordering process in Fe2VAl and the related
material Fe2VGa, we have carried out nuclear magnetic resonance (NMR) and
Mossbauer studies. 27Al NMR relaxation measurements covered the temperature
range 4 -- 500 K in Fe(2+x)V(1-x)Al samples. We found a peak in the NMR
spin-lattice relaxation rate, 27T1^-1, corresponding to the magnetic
transitions in each of these samples. These peaks appear at 125 K, 17 K, and
165 K for x = 0.10, 0, and - 0.05 respectively, and we connect these features
with critical slowing down of the localized antisite defects. Mossbauer
measurements for Fe2VAl and Fe2VGa showed lines with no hyperfine splitting,
and isomer shifts nearly identical to those of the corresponding sites in Fe3Al
and Fe3Ga, respectively. We show that a model in which local band filling leads
to magnetic regions in the samples, in addition to the localized antisite
defects, can account for the observed magnetic ordering behavior.",0211416v2
2002/12/20,"Chemomagnetism, magnetoconcentration effect and ""fishtail"" anomaly in chemically-induced granular superconductors","Within a 2D model of Josephson junction arrays (created by 2D network of twin
boundary dislocations with strain fields acting as insulating barrier between
hole-rich domains in underdoped crystals), a few novel effects expected to
occur in intrinsically granular material are predicted including: (i) Josephson
chemomagnetism (chemically induced magnetic moment in zero applied magnetic
field) and its influence on a low-field magnetization (chemically induced
paramagnetic Meissner effect), and (ii) magnetoconcentration effect (creation
of oxygen vacancies in applied magnetic field) and its influence on a
high-field magnetization (chemically induced analog of ""fishtail"" anomaly). The
conditions under which these effects can be experimentally measured in
non-stoichiometric high-T_c superconductors are discussed.",0212507v1
2003/3/18,Calculation of magnetic anisotropy energy in SmCo5,"SmCo5 is an important hard magnetic material, due to its large magnetic
anisotropy energy (MAE). We have studied the magnetic properties of SmCo5 using
density functional theory (DFT) calculations where the Sm f-bands, which are
difficult to include in DFT calculations, have been treated within the LDA+U
formalism. The large MAE comes mostly from the Sm f-shell anisotropy, stemming
from an interplay between the crystal field and the spin-orbit coupling. We
found that both are of similar strengths, unlike some other Sm compounds,
leading to a partial quenching of the orbital moment (f-states cannot be
described as either pure lattice harmonics or pure complex harmonics), an
optimal situation for enhanced MAE. A smaller portion of the MAE can be
associated with the Co-d band anisotropy, related to the peak in the density of
states at the Fermi energy. Our result for the MAE of SmCo5, 21.6 meV/f.u.,
agrees reasonably with the experimental value of 13-16 meV/f.u., and the
calculated magnetic moment (including the orbital component) of 9.4 mu_B agrees
with the experimental value of 8.9 mu_B.",0303368v1
2003/4/9,How to make semiconductors ferromagnetic: A first course on spintronics,"The rapidly developing field of ferromagnetism in diluted magnetic
semiconductors, where a semiconductor host is magnetically doped by transition
metal impurities to produce a ferromagnetic semiconductor (e.g. Ga_{1-x}Mn_xAs
with x ~ 1-10 %), is discussed with the emphasis on elucidating the physical
mechanisms underlying the magnetic properties. Recent key developments are
summarized with critical discussions of the roles of disorder, localization,
band structure, defects, and the choice of materials in producing good magnetic
quality and high Curie temperature. The correlation between magnetic and
transport properties is argued to be a crucial ingredient in developing a full
understanding of the properties of ferromagnetic semiconductors.",0304219v1
2004/1/31,Magnetic properties of amorphous Co$_x$Nb$_{100-x}$ alloys produced by mechanical alloying,"Three amorphous Co$_x$Nb$_{100-x}$ alloys, Co$_{25}$Nb$_{75}$,
Co$_{57}$Nb$_{43}$ and Co$_{80}$Nb$_{20}$, were produced by Mechanical Alloying
starting from the elemental powders. Their magnetic properties were determined
using an alternating gradient force magnetometer (AGFM), and the remanent
magnetizations, saturation fields and coercive fields were obtained from the
hysteresis loop. The alloys have a relatively high saturation field, which
decreases as the composition becomes richer in Co. The coercivity and remanent
magnetization reach an optimal value around 57% at.Co, making {\em
a}-Co$_{57}$Nb$_{43}$ the hardest magnetic material among the three alloys.
Further addition of Co produces a soft alloy.",0402014v1
2004/2/18,Entangled Quantum States of Magnetic Dipoles,"Free magnetic moments usually manifest themselves in Curie Laws, where weak
external magnetic fields produce magnetizations diverging as the reciprocal 1/T
of the temperature. for a variety of materials that do not disply static
magnetism, including doped semiconductors and certain rare earth
intermetallics, the 1/T law is changed to a power law T^-a with a<1. We report
here that a considerably simpler material, namely an insulating magneticsalt
can also display such a power law, and show via comparison to specific heat
data and numerical simulations that quantum mechanics is crucial for its
formation. Two quantum mechanical phenomena are needed, namely level splitting
- which affects the spectrum of excited states - and entanglement - where the
wavefunction of a system with several degrees of freedom cannot be written as a
product of wavefunctions for each degree of freedom. Entanglement effects
become visible for remarkably small tunnelling terms, and are turned on well
before tunnelling has visible effects on the spectrum. Our work is significant
because it illustrates that entanglement is at the very heart of a very simple
experimental observation for an insulating quantum spin system.",0402456v1
2004/6/17,Reorientation in Antiferromagnetic Multilayers: Spin-Flop Transition and Surface Effects,"Nanoscale superlattices with uniaxial ferromagnetic layers
antiferromagnetically coupled through non-magnetic spacers are recently used as
components of magnetoresistive and recording devices. In the last years
intensive experimental investigations of these artificial antiferromagnets have
revealed a large variety of surface induced reorientational effects and other
remarkable phenomena unknown in other magnetic materials. In this paper we
review and generalize theoretical results, which enable a consistent
description of the complex magnetization processes in antiferromagnetic
multilayers, and we explain the responsible physical mechanism. The general
structure of phase diagrams for magnetic states in these systems is discussed.
In particular, our results resolve the long standing problem of a ``surface
spin-flop'' in antiferromagnetic layers. This explains the different appearance
of field-driven reorientation transitions in systems like Fe/Cr (001) and (211)
superlattices, and in [CoPt]/Ru multilayers with strong perpendicular
anisotropy.",0406412v1
2004/10/21,Temperature dependent orbital degree of freedom in a bilayer manganite by magnetic Compton scattering,"We have measured temperature-dependent magnetic Compton profiles (MCPs) from
a single crystal of La$_{1.2}$Sr$_{1.8}$Mn$_2$O$_7$. The MCPs, which involved
the scattering of circularly polarized x-rays, are in general related to the
momentum density of all the unpaired spins in the system. Nevertheless, we show
that when the x-ray scattering vector lies along the [110] direction, the
number of magnetic electrons of a specific symmetry, i.e. $d$-electrons of
$x^2-y^2$ symmetry, yield a distinct signature in the MCP, allowing us to
monitor substantial changes in the occupancy of the $d_{x^2-y^2}$ states over
the investigated temperature range of 5-200K. This study indicates that
magnetic Compton scattering can provide a powerful window on the properties of
specific magnetic electrons in complex materials.",0410553v1
2004/12/22,Role of Point Defects on the Properties of Manganites,"La1-xCaxMnO3+delta and La1-xNaxMnO3+delta samples with well defined cation
molecularity and oxygen contents are analyzed with XRPD, electrical
conductivity, electron paramagnetic resonance and static magnetization
measurements. Point defects are introduced in the structure by: i) aliovalent
cation doping (substitutional defects), ii) oxygen over-stoichiometry (cation
vacancies) and iii) oxygen under-stoichiometry (oxygen vacancies). The cation
doping mainly influences the material by affecting the tolerance factor and the
oxidation of the Mn ions; the cation vacancies affect the magnetic properties
by interrupting the interaction paths between Mn4+-Mn3+ ions whereas the oxygen
vacancies have a stronger influence on the structural and electrical properties
and act on the magnetic properties by the overall decrease on the Mn4+ amount
and by the creation of sample regions with different magnetic features. We can
state that the basic magnetic and electrical behaviors of the Ca- and Na-doped
lanthanum manganite compounds are driven from the Mn4+-Mn3+ ratio and all the
peculiar behaviors are indeed caused by defects, concentration gradient and,
more generally, by lattice disorder.",0412606v1
2005/2/3,Current distribution and giant magnetoimpedance in composite wires with helical magnetic anisotropy,"The giant magnetoimpedance effect in composite wires consising of a
non-magnetic inner core and soft magnetic shell is studied theoretically. It is
assumed that the magnetic shell has a helical anisotropy. The current and field
distributions in the composite wire are found by means of a simultaneous
solution of Maxwell equations and the Landau-Lifshitz equation. The expressions
for the diagonal and off-diagonal impedance are obtained for low and high
frequencies. The dependences of the impedance on the anisotropy axis angle and
the shell thickness are analyzed. Maximum field sensitivity is shown to
correspond to the case of the circular anisotropy in the magnetic shell. It is
demonstrated that the optimum shell thickness to obtain maximum impedance ratio
is equal to the effective skin depth in the mahnetic material.",0502086v2
2005/6/10,Low Field Magnetotransport in Manganites,"The perovskite manganites of general formula RE_1-xAe_xMnO_3 (RE= rare
earth,AE=Ca, Sr, Ba and Pb)have drawn considerable attention, especially
following the discovery of colossal magnetoresistance (CMR). They exhibit
extraordinary large magnetoresistance pronounced as CMR in the vicinity of
insulator-metal/paramagnetic-ferromagnetic transition at a relatively large
applied magnetic fields. However, for applied aspectes, occurence of
significant CMR at low applied magnetic fields would be required. This review
consists of of two sections: In the first section we have extensively reviewed
the salient features e.g. structure, phase diagram, double exchange mechansim,
Jahn Teller effect, different types of ordering and phase separation of CMR
mangnaites. The second is devoted to an overview of experimental results on CMR
and related magnetotransport characteristics at low magnetic fields for doped
manganites such as polycrystalline La_0.67Ca_0.33MnO_3 films, Ag admixed
La_0.67Ca_0.33MnO_3 films, polycrystalline (La_0.7Ca_0.2Ba_0.1MnO_3)and
epitaxial (La_0.67Ca_0.33MnO_3) films on different substrates, nanophasic
La_0.7Ca_0.3MnO_3, mangnaite-polymer composites (La_0.7Ba_0.2Sr_0.1MnO_3-PMMA
and La_0.67Ca_0.33MnO_3-PMMA)and double layered polycrystalline
(La_1.4Ca_1.6-xBa_xMn_2O_7) and films (La_1.4Ca_1.6Mn_2O_7). Some other
potential magnetoresistive materials e.g. pyrochlores, chalcogenides,
ruthenates, diluted magnetic semiconductors, magnetic tunnel junctions,
nanocontacts etc have aslo been briefly dealt with. The review concludes with
the summary of results for low field magnetotransport behaviour and prospectes
for applications.",0506239v1
2006/1/19,Enhancement of giant magnetoresistance effect in the Ruddlesden-Popper phase Sr3Fe2-xCoxO7-d: Predominant role of oxygen nonstoichiometry and magnetic phase separation,"The magnetic and magnetotransport properties of the Sr3Fe2-xCoxO7-d system
(0.2 <= x <= 1.0) were systematically investigated. This oxide system exhibits
a giant magnetoresistance (GMR) effect at low temperatures, reaching up to 80%
in 7 T at 5 K. Ac-susceptibility measurements show that there exists a strong
competition between ferromagnetic (F) and spin glass states, and the balance
between these two magnetic states can be controlled by varying cobalt (x)
and/or oxygen contents (d). Importantly, the MR effect is closely related to
the magnetic property: the development of magnetic disordering leads to
enhancement in the negative MR effect. It is suggested that the compound
segregates into F clusters embedded in a non-F matrix, being a naturally
occurring analog of the artificial granular-GMR materials, as in the doped
perovskite cobaltites, La1-xSrxCoO3 (x < 0.18).",0601428v1
2006/2/7,Possible evidence for electromagnons in multiferroic manganites,"Magnetodielectric materials are characterized by a strong coupling of
magnetic and dielectric properties and in rare cases simultaneously exhibit
both, magnetic and polar order. Among other multiferroics, TbMnO3 and GdMnO3
reveal a strong magneto-dielectric (ME) coupling and as a consequence
fundamentally new spin excitations exist: Electro-active magnons, or
electromagnons, i. e. spin waves which can be excited by ac electric fields.
Here we show that these excitations appear in the phase with an incommensurate
(IC) magnetic structure of the manganese spins. In external magnetic fields
this IC structure can be suppressed and the electromagnons are wiped out,
thereby inducing considerable changes in the index of refraction from dc up to
THz frequencies. Hence, besides adding a new creature to the zoo of fundamental
excitations, the refraction index can be tuned by moderate magnetic fields,
which allows the design of a new generation of optical switches and
optoelectronic devices.",0602173v1
2006/2/9,Field-induced ferroelectric and commensurate spin state in mutiferroic HoMn$_{2}$O$_{5}$,"Neutron diffraction measurements under high magnetic fields have been
performed for the multiferroic compound HoMn$_{2}$O$_{5}$. At zero field,
high-temperature incommensurate magnetic (HT-ICM) -- commensurate magnetic (CM)
-- low-temperature incommensurate magnetic (LT-ICM) orders occur with
decreasing temperature, where ferroelectric polarization arises only in the CM
phase. Upon applying a magnetic field, the LT-ICM phase completely disappears
and the CM phase is induced at the lowest temperature. This field-induced CM
state is completely associated with the field-induced electric polarization in
this material [Higashiyama {\it et al}., Phys. Rev. B {\bf 72}, 064421
(2005).], strongly indicating that the commensurate spin state is essential to
the ferroelectricity in the multiferroic $R$Mn$_{2}$O$_{5}$ system.",0602226v1
2006/4/15,Magnetic Field and Displacement sensor based on Giant Magneto-impedance effect,"A two-core transducer assembly using a Fe73.5Nb3Cu1Si13.5B9 ribbon to detect
a change of magnetic field is proposed and tested for displacement (linear and
angular) and current sensor. Two identical inductors, with the ribbon as core,
are a part of two series resonance network, and are in high impedance state
when excited by a small a.c field of 1MHz in absence of d.c biasing field
(Hdc). When the magnetic state of one inductor is altered by biasing field,
produced by a bar magnet or current carrying coil, an ac signal proportional to
Hdc is generated by transducer. The results for the sensitivity and linearity
with displacement (linear and angular) of a magnet and with field from the
current carrying coil are presented for two particular configurations of the
transducer. High sensitivities of voltage response as much as
12micro-volt/micro-meter and 3mV/degree have been obtained for the transducer
as a linear and angular displacement sensor respectively in the transverse
configuration of exciting a.c and biasing d.c fields.",0604381v2
2006/5/15,Domain wall formation and spin reorientation in finite-size magnetic systems,"We investigate the formation of stable one-dimensional N\'eel walls in a
ferromagnetic slab with finite thickness and finite width. Taking into account
the dipolar, the exchange and the uniaxial anisotropic crystalline field
interactions, we derive an approximative analytical self-consistent expression
that gives the wall width in terms of ratios between the three different energy
scales of the problem. We also show that, even when the crystalline anisotropy
does not favour the formation of domain walls, they can yet be formed due to
the dipolar interaction and the finiteness of the system. Moreover, using a
Stoner-Wohlfarth approach, we study the magnetization reorientation inside the
domains under the action of an external magnetic field and obtain the
respective hysteresis loops, showing that their shapes change from squared to
inclined as the width of the slab varies. Finally, we discuss possible
applications of this model to describe qualitatively some recent experimental
data on thin films of MnAs grown over GaAs substrates.",0605357v2
2006/10/5,Finite dipolar hexagonal columns on piled layers of triangular lattice,"We have investigated, by the Monte Carlo simulation, spin systems which
represent moments of arrayed magnetic nanoparticles interacting with each other
only by the dipole-dipole interaction. In the present paper we aim the
understanding of finite size effects on the magnetic nanoparticles arrayed in
hexagonal columns cut out from the close-packing structures or from those with
uniaxial compression. In columns with the genuine close-packing structures, we
observe a single vortex state which is also observed previously in finite
2-dimensional systems. On the other hand in the system with the inter-layer
distance set $1/\sqrt{2}$ times of the close-packing one, we found ground
states which depend on the number of layers. The dependence is induced by a
finite size effect and is related to a orientation transition in the
corresponding bulk system.",0610137v1
2006/10/8,Multiferroicity induced by dislocated spin-density waves,"We uncover a new pathway towards multiferroicity, showing how magnetism can
drive ferroelectricity without relying on inversion symmetry breaking of the
magnetic ordering. Our free-energy analysis demonstrates that any commensurate
spin-density-wave ordering with a phase dislocation, even if it is collinear,
gives rise to an electric polarization. Due to the dislocation the electronic
and magnetic and inversion centers do not coincide, which turns out to be a
sufficient condition for multiferroic coupling. The novel mechanism explains
the formation of multiferroic phases at the magnetic commensurability
transitions, such as the ones observed in YMn$_{2}$O$_{5}$ and related
compounds. We predict that in these multiferroics an oscillating electrical
polarization is concomitant with the uniform polarization. On the basis of our
theory we put forward new types of magnetic materials that are potentially
ferroelectric.",0610214v2
2007/2/23,"Evolution of the magnetic anisotropy with carrier density in hydrogenated (Ga,Mn)As","The magnetic properties of (Ga,Mn)As thin films depend on both the Mn doping
level and the carrier concentration. Using a post growth hydrogenation process
we show that it is possible to decrease the hole density from 1.1021 cm-3 to
<1017 cm-3 while maintaining the manganese concentration constant. For such a
series of films we have investigated the variation of the magnetization, the
easy and hard axes of magnetization, the critical temperatures, the coercive
fields and the magnetocrystalline anisotropy constants as a function of
temperature using magnetometry, ferromagnetic resonance and magneto-transport
measurements. In particular, we evidenced that magnetic easy axes flipped from
out-of-plane [001] to in-plane [100] axis, followed by the <110> axes, with
increasing hole density and temperature. Our study concluded on a general
agreement with mean-field theory predictions of the expected easy axis
reversals, and of the weight of uniaxial and cubic anisotropies in this
material.",0702548v1
2007/3/23,Transition-metal dimers and physical limits on magnetic anisotropy,"Recent advances in nanoscience have raised interest in the minimum bit size
required for classical information storage, i.e. for bistability with
suppressed quantum tunnelling and energy barriers that exceed ambient
temperatures. In the case of magnetic information storage much attention has
centred on molecular magnets[1] with bits consisting of ~ 100 atoms, magnetic
uniaxial anisotropy energy barriers ~ 50 K, and very slow relaxation at low
temperatures. In this article we draw attention to the remarkable magnetic
properties of some transition metal dimers which have energy barriers
approaching ~ 500 K with only two atoms. The spin dynamics of these ultra small
nanomagnets is strongly affected by a Berry phase which arises from
quasi-degeneracies at the electronic Highest Occupied Molecular Orbital (HOMO)
energy. In a giant spin-approximation, this Berry phase makes the effective
reversal barrier thicker. [1] Gatteschi, D., Sessoli, R. & Villain, J.
Molecular Nanomagnets. (Oxford, New York 2006).",0703607v2
2005/1/20,Creating Ioffe-Pritchard micro-traps from permanent magnetic film with in-plane magnetization,"We present designs for Ioffe-Pritchard type magnetic traps using planar
patterns of hard magnetic material. Two samples with different pattern designs
were produced by spark erosion of 40 $\mu$m thick FePt foil. The pattern on the
first sample yields calculated axial and radial trap frequencies of 51 Hz and
6.8 kHz, respectively. For the second sample the calculated frequencies are 34
Hz and 11 kHz. The structures were used successfully as a magneto-optical trap
for $^{87}$Rb and loaded as a magnetic trap. A third design, based on
lithographically patterned 250 nm thick FePt film on a Si substrate, yields an
array of 19 traps with calculated axial and radial trap frequencies of 1.5 kHz
and 110 kHz, respectively.",0501109v2
2005/4/5,Reduction of Magnetic Noise in Atom Chips by Material Optimization,"We discuss the contribution of the material type in metal wires to the
electromagnetic fluctuations in magnetic microtraps close to the surface of an
atom chip. We show that significant reduction of the magnetic noise can be
achieved by replacing the pure noble metal wires with their dilute alloys. The
alloy composition provides an additional degree of freedom which enables a
controlled reduction of both magnetic noise and resistivity if the atom chip is
cooled. In addition, we provide a careful re-analysis of the magnetically
induced trap loss observed by Yu-Ju Lin et al. [Phys. Rev. Lett. 92, 050404
(2004)] and find good agreement with an improved theory.",0504027v2
2008/5/16,Tunneling Spectra of Individual Magnetic Endofullerene Molecules,"The manipulation of single magnetic molecules may enable new strategies for
high-density information storage and quantum-state control. However, progress
in these areas depends on developing techniques for addressing individual
molecules and controlling their spin. Here we report success in making
electrical contact to individual magnetic N@C60 molecules and measuring spin
excitations in their electron tunneling spectra. We verify that the molecules
remain magnetic by observing a transition as a function of magnetic field which
changes the spin quantum number and also the existence of nonequilibrium
tunneling originating from low-energy excited states. From the tunneling
spectra, we identify the charge and spin states of the molecule. The measured
spectra can be reproduced theoretically by accounting for the exchange
interaction between the nitrogen spin and electron(s) on the C60 cage.",0805.2585v2
2008/5/23,Angular momentum transport and element mixing in the stellar interior I. Application to the rotating Sun,"The purpose of this work was to obtain diffusion coefficient for the magnetic
angular momentum transport and material transport in a rotating solar model. We
assumed that the transport of both angular momentum and chemical elements
caused by magnetic fields could be treated as a diffusion process. The
diffusion coefficient depends on the stellar radius, angular velocity, and the
configuration of magnetic fields. By using of this coefficient, it is found
that our model becomes more consistent with the helioseismic results of total
angular momentum, angular momentum density, and the rotation rate in a
radiative region than the one without magnetic fields. Not only can the
magnetic fields redistribute angular momentum efficiently, but they can also
strengthen the coupling between the radiative and convective zones. As a
result, the sharp gradient of the rotation rate is reduced at the bottom of the
convective zone. The thickness of the layer of sharp radial change in the
rotation rate is about 0.036 $R_{\odot}$ in our model. Furthermore, the
difference of the sound-speed square between the seismic Sun and the model is
improved by mixing the material that is associated with angular momentum
transport.",0805.3647v1
2008/8/29,Spin-lozenge thermodynamics and magnetic excitations in Na$_3$RuO$_4$,"We report inelastic and elastic neutron scattering, magnetic susceptibility,
and heat capacity measurements of polycrystalline sodium ruthenate
(Na$_3$RuO$_4$). Previous work suggests this material consists of isolated
tetramers of $S=3/2$ Ru$^{5+}$ ions in a so-called ""lozenge"" configuration.
Using a Heisenberg antiferromagnet Hamiltonian, we analytically determine the
energy eigenstates for general spin $S$. From this model, the neutron
scattering cross-sections for excitations associated with spin-3/2
spin-tetramer configurations is determined. Comparison of magnetic
susceptibility and inelastic neutron scattering results shows that the proposed
""lozenge"" model is not distinctly supported, but provides evidence that the
system may be better described as a pair of non-interacting inequivalent
dimers, \textit{i.e} double dimers. However, the existence of long-range
magnetic order below $T_c \approx 28$ K immediately questions such a
description. Although no evidence of the lozenge model is observed, future
studies on single crystals may further clarify the appropriate magnetic
Hamiltonian.",0808.4150v1
2008/8/30,From diluted magnetic semiconductors to self-organized nanocolumns of GeMn in Germanium,"While achieving high Curie temperatures (above room temperature) in diluted
magnetic semiconductors remains a challenge in the case of well controlled
homogeneous alloys, several systems characterized by a strongly inhomogeneous
incorporation of the magnetic component appear as promising. Incorporation of
manganese into germanium drastically alters the growth conditions, and in
certain conditions of low temperature Molecular Beam Epitaxy it leads to the
formation of well organized nanocolumns of a Mn-rich material, with a
crystalline structure in epitaxial relationship with the Mn-poor germanium
matrix. A strong interaction between the Mn atoms in these nanocolums is
demonstrated by x-ray absorption spectroscopy, giving rise to a ferromagnetic
character as observed through magnetometry and x-ray magnetic circular
dichroism. Most interesting, intense magneto-transport features are observed on
the whole structure, which strongly depend on the magnetic configuration of the
nanocolumns.",0809.0065v1
2008/9/12,Two insulating phases in compressed Pr1-xCaxMnO3 thin films,"The temperature dependent resistivity of two Pr1-xCaxMnO3 (x=0.5 and 0.4)
thin films grown on LaAlO3 has been studied as a function of hydrostatic
pressure (up to 2.5 GPa) and magnetic field (up to 9T). Both samples show a
monotonic decrease in the resistivity with an increase in pressure,
corresponding to a change of -35% at 2.5 GPa. No pressure induced
metal-to-insulator transition was observed in the temperature-dependent
resistivity. The non-trivial interaction between high pressure and magnetic
field reveals that the effect of pressure cannot be simply rescaled to that of
a specific field, as has been reported for the corresponding bulk material. We
propose an interpretation of the data based on phase separation, where two
different insulating phases coexist: the charge ordered phase, which is
sensitive to both magnetic field and pressure, and a second insulating phase
that can be tuned by magnetic field. Such a result demonstrates that phase
separation can be manipulated in thin films by independent application of
magnetic field and/or external pressure.",0809.2184v1
2008/10/20,Optical Properties of III-Mn-V Ferromagnetic Semiconductors,"We review the first decade of extensive optical studies of ferromagnetic,
III-Mn-V diluted magnetic semiconductors. Mn introduces holes and local moments
to the III-V host, which can result in carrier mediated ferromagnetism in these
disordered semiconductors. Spectroscopic experiments provide direct access to
the strength and nature of the exchange between holes and local moments; the
degree of itineracy of the carriers; and the evolution of the states at the
Fermi energy with doping. Taken together, diversity of optical methods reveal
that Mn is an unconventional dopant, in that the metal to insulator transition
is governed by the strength of the hybridization between Mn and its p-nictogen
neighbor. The interplay between the optical, electronic and magnetic properties
of III-Mn-V magnetic semiconductors is of fundamental interest and may enable
future spin-optoelectronic devices.",0810.3669v1
2009/1/7,Evidence for large electric polarization from collinear magnetism in TmMnO3,"There has been tremendous research activity in the field of magneto-electric
(ME) multiferroics after Kimura et al. [1] showed that antiferromagnetic and
ferroelectric order coexist in orthorhom- bically distorted perovskite TbMnO3
and are strongly coupled. It is now generally accepted that ferroelectricity in
TbMnO3 is induced by magnetic long range order that breaks the symmetry of the
crystal and creates a polar axis [2]. One remaining key question is whether
magnetic order can induce ferroelectric polarization that is as large as that
of technologically useful materials. We show that ferroelectricity in
orthorhombic (o) TmMnO3 is induced by collinear magnetic order, and that the
lower limit for its electric polarization is larger than in previously
investigated orthorhombic heavy rare-earth manganites. The temperature
dependence of the lattice constants provides fur- ther evidence of large
spin-lattice coupling effects. Our experiments suggest that the ferroelectric
polarization in the orthorhombic perovskites with commensurate magnetic ground
states could pass the 1 microC/cm2 threshold, as suggested by theory [3, 4].",0901.0787v1
2009/1/28,Epitaxial growth and magnetic properties of Sr2CrReO6 thin films,"The double perovskite Sr2CrReO6 is an interesting material for spintronics,
showing ferrimagnetism up to 635 K with a predicted high spin polarization of
about 86%. We fabricated Sr2CrReO6 epitaxial films by pulsed laser deposition
on (001)-oriented SrTiO3 substrates. Phase-pure films with optimum
crystallographic and magnetic properties were obtained by growing at a
substrate temperature of 700 degree C in pure O2 of 6.6x10-4 mbar. The films
are c-axis oriented, coherently strained, and show less than 20% anti-site
defects. The magnetization curves reveal high saturation magnetization of 0.8
muB per formula unit and high coercivity of 1.1 T, as well as a strong magnetic
anisotropy.",0901.4499v1
2009/4/23,Magnetic avalanches of minor fast-relaxing species of Mn12-acetate,"Using micron-sized thermometers and Hall bars, we report time-resolved
studies of the local temperature and local magnetization for two types of
magnetic avalanches (abrupt spin reversals) in the molecular magneti
Mn12-acetate, corresponding to avalanches of the main slow-relaxing crystalline
form and avalanches of the fast-relaxing minor species that exists in all
as-grown crystals of this material. An experimental protocol is used that
allows the study of each type of avalanche without triggering avalanches in the
other, and of both types of avalanches simultaneously. In samples prepared
magnetically to enable both types of avalanches, minor species avalanches are
found to act as a catalyst for the major species avalanches. magnetically to
enable both types of avalanches, minor species avalanches are found to act as a
catalyst for the major species avalanches.",0904.3755v1
2009/4/24,Microscopic origin of magnetism and magnetic interactions in ferropnictides,"One year after their initial discovery, two schools of thought have
crystallized regarding the electronic structure and magnetic properties of
ferropnictide systems. One postulates that these are itinerant weakly
correlated metallic systems that become magnetic by virtue of spin-Peierls type
transition due to near-nesting between the hole and the electron Fermi surface
pockets. The other argues these materials are strongly or at least moderately
correlated, the electrons are considerably localized and close to a
Mott-Hubbard transition, with the local magnetic moments interacting via
short-range superexchange. In this paper we argue that neither picture is fully
correct. The systems are moderately correlated, but with correlations driven by
Hund's rule coupling rather than by the on-site Hubbard repulsion. The iron
moments are largely local, driven by Hund's intra-atomic exchange.
Superexchange is not operative and the interactions between the Fe moments are
considerably long-range and driven mostly by one-electron energies of all
occupied states.",0904.3857v1
2009/6/4,Spin-induced optical second harmonic generation in the centrosymmetric magnetic semiconductors EuTe and EuSe,"Spectroscopy of the centrosymmetric magnetic semiconductors EuTe and EuSe
reveals spin-induced optical second harmonic generation (SHG) in the band gap
vicinity at 2.1-2.4eV. The magnetic field and temperature dependence
demonstrates that the SHG arises from the bulk of the materials due to a novel
type of nonlinear optical susceptibility caused by the magnetic dipole
contribution combined with spontaneous or induced magnetization. This
spin-induced susceptibility opens access to a wide class of centrosymmetric
systems by harmonics generation spectroscopy.",0906.0907v1
2009/6/25,Field dependent competing magnetic ordering in multiferroic Ni3V2O8,"The geometrically frustrated magnet Ni3V2O8 undergoes a series of competing
magnetic ordering at low temperatures. Most importantly, one of the
incommensurate phases has been reported to develop a ferroelectric correlation
caused by spin frustration. Here we report an extensive thermodynamic,
dielectric and magnetic study on clean polycrystalline samples of this novel
multiferroic compound. Our low temperature specific heat data at high fields up
to 14 Tesla clearly identify the development of a new magnetic field induced
phase transition below 2 K that shows signatures of simultaneous electric
ordering. We also report temperature and field dependent dielectric constant
that enables us to quantitatively estimate the strength of magneto-electric
coupling in this improper ferroelectric material.",0906.4635v1
2009/7/23,Electrostatic co-assembly of magnetic nanoparticles and fluorescent nanospheres: a versatile approach toward bimodal nanorods,"The elaboration of multimodal nanoparticles stimulates tremendous interest
owing to their numerous potentialities in many applicative fields like
optoelectronics, photonics and especially bioimaging. The concomitant
association of various properties (optical, electrochemical, magnetic) allows
for the use of complementary stimuli in order to probe the interactions between
the nanoparticles and their surroundings.Nanoparticles (NPs) have thus become
highly praised tools to image cells and tissues with a large contrast
compatible with the dimensions of biological materials and the existence of
quantum confinement effects induced by the reduced dimensions. In this context,
the combination of magnetism and emissive properties such as fluorescence
appears particularly attractive for non-invasive investigations, cell sorting
or drug vectorization. Therefore, combining both fluorescence and magnetism
requires the delicate construction of hybrid assemblies. Most of the magnetic
nanoparticles are made of metallic oxides or alloys, e.g. gamma-Fe2O3, Fe3O4,
FePt, while the target fluorescent entities are often organic dyes or quantum
dots (QDs).",0907.3979v1
2009/11/25,Synthesis and characterization of FePt/Au core-shell nanoparticles,"In this work, the structural and magnetic properties of the gold-coated FePt
nanoparticles synthesized from high-temperature solution phase are presented.
The amount of gold was optimized to obtain most of the FePt particles coated.
The particle diameter increases from 4 to 10 nm as observed by TEM. The
magnetic properties are largely affected by the coating. At low temperature,
the coercive field Hc of the coated nanoparticles decreases about three times
respect to the uncoated and the blocking temperature reduces to the half. The
changes of the magnetic behavior are discussed in terms of the effect of the
gold atoms at the FePt core surface.",0911.4785v1
2009/12/18,Room temperature magnetism in LaVO3/SrVO3 superlattices by geometrically confined doping,"Based on the Hubbard model of strongly correlated systems, a reduction in the
bandwidth of the electrons can yield a substantial change in the properties of
the material. One method to modify the bandwidth is geometrically confined
doping, i.e. the introduction of a (thin) dopant layer in a material. In this
paper, the magnetic properties of LaVO$_3$/SrVO$_3$ superlattices, in which the
geometrically confined doping is produced by a one monolayer thick SrVO$_3$
film, are presented. In contrast to the solid solution La$_{1-x}$Sr$_x$VO$_3$,
such superlattices have a finite magnetization up to room temperature.
Furthermore, the total magnetization of the superlattice depends on the
thickness of the LaVO$_3$ layer, indicating an indirect coupling of the
magnetization that emerges at adjacent dopant layers. Our results show that
geometrically confined doping, like it can be achieved in superlattices,
reveals a way to induce otherwise unaccessible phases, possibly even with a
large temperature scale.",0912.3663v1
2010/1/12,A theory for magnetic-field effects of nonmagnetic organic semiconducting materials,"A universal mechanism for strong magnetic-field effects of nonmagnetic
organic semiconductors is presented. A weak magnetic field (less than hundreds
mT) can substantially change the charge carrier hopping coefficient between two
neighboring organic molecules when the magnetic length is not too much longer
than the molecule-molecule separation and localization length of electronic
states involved. Under the illumination of lights or under a high electric
field, the change of hopping coefficients leads also to the change of polaron
density so that photocurrent, photoluminescence, electroluminescence,
magnetoresistance and electrical-injection current become sensitive to a weak
magnetic field. The present theory can not only explain all observed features,
but also provide a solid theoretical basis for the widely used empirical
fitting formulas.",1001.1796v1
2010/1/20,Robust charge and magnetic order under electric field and current in the multiferroic LuFe(2)O(4),"We performed elastic neutron scattering measurements on the charge- and
magnetically-ordered multiferroic material LuFe(2)O(4). An external electric
field along the [001] direction with strength up to 20 kV/cm applied at low
temperature (~100 K) does not affect either the charge or magnetic structure.
At higher temperatures (~360 K), before the transition to three-dimensional
charge-ordered state, the resistivity of the sample is low, and an electric
current was applied instead. A reduction of the charge and magnetic peak
intensities occurs when the sample is cooled under a constant electric current.
However, after calibrating the real sample temperature using its own
resistance-temperature curve, we show that the actual sample temperature is
higher than the thermometer readings, and the ""intensity reduction"" is entirely
due to internal sample heating by the applied current. Our results suggest that
the charge and magnetic orders in LuFe(2)O(4) are unaffected by the application
of external electric field/current, and previously observed electric
field/current effects can be naturally explained by internal sample heating.",1001.3611v2
2010/5/22,Dominance of magnetoelastic coupling in multiferroic hexagonal YMnO_3,"Hexagonal YMnO_3 with space group P63cm is one of the rare examples of
multiferroic materials that exhibit co-dependence of a robust ferroelectric
phase along with antiferromagnetic ordering. This is primarily ascribed to
tilting of the MnO_5 polyhedra driven by magnetoelectric coupling. We report on
the effect of magnetic field at the atomic level in YMnO_3 by utilizing
magnetic field and temperature dependent neutron diffraction measurements. We
show that near the N\'eel temperature the lattice parameters, effective
magnetic moment per site, Mn-O bond lengths and O-Mn-O bond angles show large
variations and these are further modified in the presence of magnetic field. We
observe distinct changes with the application of magnetic field in the
paramagnetic state both in atomic positions and in the bulk dielectric
constant. Our results provide unambiguous confirmation of the role played by
exchange-striction over and above the much studied magnetoelectric coupling in
this frustrated antiferromagnet.",1005.4106v1
2010/7/8,Absence of Meissner State and Robust Ferromagnetism in the Superconducting State of UCoGe: Possible Evidence of Spontaneous Vortex State,"We report ac magnetic susceptibility and dc magnetization measurements on the
superconducting ferromagnet UCoGe (with superconducting and Curie temperatures
of $T_{{\rm SC}} \sim 0.5$~K and $T_{{\rm Curie}} \sim 2.5$~K, respectively).
In the normal, ferromagnetic state ($T_{{\rm SC}} < T < T_{{\rm Curie}}$), the
magnetization curve exhibits a hysteresis loop similar to that of a regular
itinerant ferromagnet. Upon lowering the temperature below $T_{{\rm SC}}$, the
spontaneous magnetization is unchanged, but the hysteresis is markedly
enhanced. Even deeply inside the superconducting state, ferromagnetism is not
completely shielded, and there is no Meissner region, a magnetic field region
of $H < H_{\rm c1}$ (a lower critical field). From these results, we suggest
that UCoGe is the first material in which ferromagnetism robustly survives in
the superconducting state and a spontaneous vortex state without the Meissner
state is realized.",1007.1344v1
2010/7/20,Symmetry Theory of the Flexomagnetoelectric Effect in the Magnetic Domain Walls,"A local flexomagnetoelectric (A.P. Pyatakov, A.K. Zvezdin, 2009) effect in
the magnetic domain walls (DWs) of the cubic hexoctahedral crystal has been
investigated on the basis of a symmetry analysis. The strong connection between
magnetic symmetry of the DW and the type of the distribution of the electric
polarization was shown. Results were systemized in the scope of the DW
chirality. It was shown, that new type of the local flexomagnetoelectric
coupling can be experimentally detected using the external homogeneous electric
field.",1007.3524v4
2010/8/4,Spin relaxation due to electron-electron magnetic interaction in high Lande g-factor semiconductors,"We investigate spin transport in InSb/InAlSb heterostructure using the Monte
Carlo approach, generalized by including density matrix description of spin for
taking spin dynamics into account. In addition to the dominant Dyakonov-Perel
(DP) mechanism for spin control and relaxation, we consider magnetic
interaction between electrons which assumes importance due to high electronic
Lande g-factor in the material. It is found that while the effect of magnetic
interaction is not important at low densities, it reduces the spin relaxation
length by as much as 50% at higher densities. We also present a calculation
which elucidates the suppression of decoherence attributed to wave vector
dependent magnetic field in the DP relaxation mechanism. We note that magnetic
interaction is a general relaxation mechanism which may assume importance in
materials with high electronic Lande g-factor.",1008.0739v1
2010/10/8,Time-resolved detection of spin-transfer-driven ferromagnetic resonance and spin torque measurement in magnetic tunnel junctions,"Several experimental techniques have been introduced in recent years in
attempts to measure spin transfer torque in magnetic tunnel junctions (MTJs).
The dependence of spin torque on bias is important for understanding
fundamental spin physics in magnetic devices and for applications. However,
previous techniques have provided only indirect measures of the torque and
their results to date for the bias dependence are qualitatively and
quantitatively inconsistent. Here we demonstrate that spin torque in MTJs can
be measured directly by using time-domain techniques to detect resonant
magnetic precession in response to an oscillating spin torque. The technique is
accurate in the high-bias regime relevant for applications, and because it
detects directly small-angle linear-response magnetic dynamics caused by spin
torque it is relatively immune to artifacts affecting competing techniques. At
high bias we find that the spin torque vector differs markedly from the simple
lowest-order Taylor series approximations commonly assumed.",1010.1777v1
2010/12/17,Model for screening of resonant magnetic perturbations by plasma in a realistic tokamak geometry and its impact on divertor strike points,"This work addresses the question of the relation between strike-point
splitting and magnetic stochasticity at the edge of a poloidally diverted
tokamak in the presence of externally imposed magnetic perturbations. More
specifically, ad-hoc helical current sheets are introduced in order to mimic a
hypothetical screening of the external resonant magnetic perturbations by the
plasma. These current sheets, which suppress magnetic islands, are found to
reduce the amount of splitting expected at the target, which suggests that
screening effects should be observable experimentally. Multiple screening
current sheets reinforce each other, i.e. less current relative to the case of
only one current sheet is required to screen the perturbation.",1012.4015v2
2011/1/12,Multiferroic Properties of CaMn$_7$O$_{12}$,"We report that CaMn$_7$O$_{12}$ is a new magnetic multiferroic material. The
appearance of a ferroelectric polarization coinciding with the magnetic phase
transition ($\sim90$ K) suggests the presence of ferroelectricity induced by
magnetism, further confirmed by its strong magnetoelectric response. With
respect to other known magnetic multiferroics, CaMn$_7$O$_{12}$ displays
attractive multiferroic properties, such as a high ferroelectric critical
temperature and large polarization. More importantly, these results open a new
avenue to search for magnetic multiferroics in the catalogue of doped oxides.",1101.2276v4
2011/1/13,Optical identification of hybrid magnetic and electric excitations in Dy3Fe5O12 garnet,"Far-infrared spectra of magneto-dielectric Dy3Fe5O12 garnet were studied
between 13 and 100 cm-1 and at low temperatures between 5 and 80 K. A
combination of transmission, reflectivity, and rotating analyzer ellipsometry
was used to unambiguously identify the type of the dipole activity of the
infrared modes. In addition to purely dielectric and magnetic modes, we
observed several hybrid modes with a mixed magnetic and electric dipole
activity. These modes originate from the superexchange between magnetic moments
of Fe and Dy ions. Using 4x4 matrix formalism for materials with Mu=/=1, we
modeled the experimental optical spectra and determined the far-infrared
dielectric and magnetic permeability functions. The matching condition
Mu(Wh)*Se=Eps(Wh)*Sm for the oscillator strengths Se(m) explains the observed
vanishing of certain hybrid modes at Wh in reflectivity.",1101.2675v1
2011/1/18,Statistical Mechanics and the Physics of the Many-Particle Model Systems,"The development of methods of quantum statistical mechanics is considered in
light of their applications to quantum solid-state theory. We discuss
fundamental problems of the physics of magnetic materials and the methods of
the quantum theory of magnetism, including the method of two-time temperature
Green's functions, which is widely used in various physical problems of
many-particle systems with interaction. Quantum cooperative effects and
quasiparticle dynamics in the basic microscopic models of quantum theory of
magnetism: the Heisenberg model, the Hubbard model, the Anderson Model, and the
spin-fermion model are considered in the framework of novel
self-consistent-field approximation. We present a comparative analysis of these
models; in particular, we compare their applicability for description of
complex magnetic materials. The concepts of broken symmetry, quantum
protectorate, and quasiaverages are analyzed in the context of quantum theory
of magnetism and theory of superconductivity. The notion of broken symmetry is
presented within the nonequilibrium statistical operator approach developed by
D.N. Zubarev. In the framework of the latter approach we discuss the derivation
of kinetic equations for a system in a thermal bath. Finally, the results of
investigation of the dynamic behavior of a particle in an environment, taking
into account dissipative effects, are presented.",1101.3423v1
2011/2/24,The role of magnetic anisotropy in spin filter junctions,"We have fabricated oxide based spin filter junctions in which we demonstrate
that magnetic anisotropy can be used to tune the transport behavior of spin
filter junctions. Until recently, spin filters have been largely comprised of
polycrystalline materials where the spin filter barrier layer and one of the
electrodes are ferromagnetic. These spin filter junctions have relied on the
weak magnetic coupling between one ferromagnetic electrode and a barrier layer
or the insertion of a nonmagnetic insulating layer in between the spin filter
barrier and electrode. We have demonstrated spin filtering behavior in
La0.7Sr0.3MnO3/chromite/Fe3O4 junctions without nonmagnetic spacer layers where
the interface anisotropy plays a significant role in determining transport
behavior. Detailed studies of chemical and magnetic structure at the interfaces
indicate that abrupt changes in magnetic anisotropy across the
non-isostructural interface is the cause of the significant suppression of
junction magnetoresistance in junctions with MnCr2O4 barrier layers.",1102.4978v1
2011/3/11,Hysteresis and nucleation in condensed matter,"The physical origin of hysteresis in condensed matter had not been previously
identified. The current ""science of hysteresis"" is useful, but limited by
phenomenological modeling. This article fills the void by revealing the
exclusive cause of the hysteresis in structural, ferromagnetic and
ferroelectric phase transitions, as well as upon magnetization in magnetic
fields and polarization in electric fields. This exclusive cause is nucleation
lags. The lags are inevitable due to the nucleation specifics, far from the
classical ""random fluctuation"" model. A major assumption that spin orientation
is determined by the orientation of its carrier explains why ferromagnetic
transitions and magnetization in magnetic fields materialize by structural
rearrangements at interfaces, as well as why magnetization by ""rotation"" is
impossible. Formation of the structural and ferromagnetic hysteresis loops is
considered in detail.",1103.2194v1
2011/4/28,Magnetic and structural properties of nanocrystalline PrCo$_3$,"The structure and magnetic properties of nanocrystalline PrCo$_3$ obtained
from high energy milling technique are investigated by X-ray diffraction, Curie
temperature determination and magnetic properties measurements are reported.
The as-milled samples have been annealed in a temperature range of 1023 K to
1273 K for 30 mn to optimize the extrinsic properties. The Curie temperature is
349\,K and coercive fields of 55\,kOe at 10\,K and 12\,kOe at 293\,K are
obtained on the samples annealed at 1023\,K. A simulation of the magnetic
properties in the framework of micromagnetism has been performed in order to
investigate the influence of the nanoscale structure. A composite model with
hard crystallites embedded in an amorphous matrix, corresponding to the
as-milled material, leads to satisfying agreement with the experimental
magnetization curve. [ K. Younsi, V. Russier and L. Bessais, J. Appl. Phys.
{\bf 107}, 083916 (2010)]. The microscopic scale will also be considered from
DFT based calculations of the electronic structure of $R$Co$_x$ compounds,
where $R$ = (Y, Pr) and $x$ = 2,3 and 5.",1104.5433v1
2011/5/10,The crystal and magnetic structure of the magnetocaloric compound FeMnP0.5Si0.5,"The crystal and magnetic structure of the magnetocaloric compound
FeMnP0.5Si0.5 have been studied by means of neutron and X-ray powder
diffraction. Single phase samples of nominal composition FeMnP0.5Si0.5 have
been prepared by the drop synthesis method. The compound crystallizes in the
Fe2P-type structure (P-62m) with the magnetic moments aligned along the aaxis.
It is found that the Fe atoms are mainly situated in the tetrahedral 3g site
while the Mn atoms prefer the pyramidal 3f position. The material is
ferromagnetic (TC = 382 K) and at 296 K the total magnetic moment is 4.4 \mu
B/f.u. It is shown that the magnetic moment in the 3f site is larger (2.5 \mu
B) than in the 3g site (1.9 \mu B).",1105.1942v1
2011/5/10,Multiferroic behavior in the new double-perovskite Lu$_2$MnCoO$_6$,"We present a new member of the multiferroic oxides, Lu$_2$MnCoO$_6$, which we
have investigated using X-ray diffraction, neutron diffraction, specific heat,
magnetization, electric polarization, and dielectric constant measurements.
This material possesses an electric polarization strongly coupled to a net
magnetization below 35 K, despite the antiferromagnetic ordering of the $S =
3/2$ Mn$^{4+}$ and Co$^{2+}$ spins in an $\uparrow \uparrow \downarrow
\downarrow$ configuration along the c-direction. We discuss the magnetic order
in terms of a condensation of domain boundaries between $\uparrow \uparrow$ and
$\downarrow \downarrow$ ferromagnetic domains, with each domain boundary
producing a net electric polarization due to spatial inversion symmetry
breaking. In an applied magnetic field the domain boundaries slide, controlling
the size of the net magnetization, electric polarization, and magnetoelectric
coupling.",1105.2058v1
2011/8/1,Spin Pumping and Spin Transfer,"Spin pumping is the emission of a spin current by a magnetization dynamics
while spin transfer stands for the excitation of magnetization by spin
currents. Using Onsager's reciprocity relations we prove that spin pumping and
spin-transfer torques are two fundamentally equivalent dynamic processes in
magnetic structures with itinerant electrons. We review the theory of the
coupled motion of the magnetization order parameter and electron for textured
bulk ferromagnets (e.g. containing domain walls) and heterostructures (such as
spin valves). We present first-principles calculations for the
material-dependent damping parameters of magnetic alloys. Theoretical and
experimental results agree in general well.",1108.0385v3
2011/8/2,"Superconducting wires under simultaneous oscillating sources: involved magnetic response, dissipation of energy and low pass filtering","Numerical simulations of filamentary type II superconducting wires under
simultaneous AC transport current and oscillating transverse magnetic fields
are performed within the critical state approximation. The time dependences of
the current density profiles, magnetic flux lines, local power dissipation and
magnetic moment are featured. Noticeable non-homogeneous dissipation and field
distortions are displayed. Also, significant differences between the obtained
AC-losses and those predicted by regular approximation formulas are reported.
Finally, an outstanding low pass filtering effect intrinsic to the magnetic
response of the system is described.",1108.0659v1
2011/8/31,Multicore magnetite nanoparticles prepared by glass crystallisation and their magnetic properties,"A potassium alumina borosilicate glass with the composition
13K2O*13Al2O3*16B2O3*43SiO2*15Fe2O3-x was melted using Fe2O3 as raw material.
The melt was dumped from a Pt-crucible with a downpipe in water which resulted
in the formation of phase separated droplets with a size of around 100 - 150
nm. In this droplets, magnetite crystals with a size of around 10-20 nm were
observed. These magnetite nanoparticles with superparamagnetic behaviour are
arranged to larger aggregates. This leads to a higher effective magnetic
radius. According to magnetisation measurements the particles show hysteresis.
The ratio of remanent vs. saturation magnetisation is not as high as it is
necessary for uniaxial anisotropy. It is possible to elude the phase
separations by cooking the pulverized glass in concentrated sodium hydroxide.
Additional temperature dependent magnetorelaxometry (TMRX) measurements show in
the distribution of the relaxation of magnetic moments over the course of
temperature two peaks at 13 and 39 K. According to an interparticle distance
smaller than 5 dC (the core diameter) could that be a result of strong magnetic
interactions. Other magnetic relaxation processes also explain this measured
effect.",1108.6201v1
2011/9/4,"""Color-tripole ice"" as a conceptual generalization of ""spin ice""","""Spin Ice"" is an exotic type of frustrated magnet realized in ""pyrochlore""
materials Ho_{2}Ti_{2}O_{7}, Dy_{2}Ti_{2}O_{7}, Ho_{2}Sn_{2}O_{7}, etc., in
which magnetic atoms (spins) reside on a sublattice made of the vertices of
corner-sharing tetrahedra. Each spin is Ising-like with respect to a local axis
which connects the centers of two tetrahedra sharing the vertex occupied by the
spin. The macroscopically degenerate ground states of these magnets obey the
""two-in two-out"" ""ice rule"" within each tetrahedron. Magnetic monopoles and
anti-monopoles emerge as elementary excitations, ""fractionalizing"" the
constituent magnetic dipoles. This system is also a novel type of statistical
mechanical system. Here we introduce a conceptual generalization of ""spin ice""
to what we shall call ""color-tripole ice"", in which three types of ""color
charges"" can emerge as elementary excitations, which are Abelian approximations
of the color charges introduced in high energy physics. Two two-dimensional
(2D) models are introduced first, where the color charges are found to be 1D
and constrained 2D, respectively. Generalizations of these two models to 3D are
then briefly discussed, In the second one the color charges are likely 3D.
Pauling-type estimates of the ""residual (or zero-point) entropy"" are also made
for these models.",1109.0678v1
2011/9/19,Magnetic nanocomposites: new methodology for micromagnetic modeling and SANS experiments,"A new methodology for micromagnetic simulations of magnetic nanocomposites is
presented. The methodology is especially suitable for simulations of two-phase
composites consisting of magnetically hard inclusions in a soft magnetic matrix
phase. The proposed technique allows to avoid the unnecessary discretization of
the 'hard' inclusions (these are normally in a single-domain state), but
enables an arbitrary fine discretization of the 'soft' phase. The method is
applied to the determination of the equilibrium magnetization state of an
iron-based nanocomposite from the Nanoperm (FeZrBCu) family of alloys and to
the calculation of the corresponding small-angle neutron scattering (SANS)
cross-section. For this highly interesting material, the results of our
simulations exhibit a remarkable agreement with the nontrivial 'clover-leaf'
SANS cross-sections observed experimentally (A. Michels et al., Phys. Rev. B,
v. 74, 134407 (2006)).",1109.4075v1
2011/10/22,Hopping magneto-transport via nonzero orbital momentum states and organic magnetoresistance,"In hopping magnetoresistance of doped insulators, an applied magnetic field
shrinks the electron (hole) s-wave function of a donor or an acceptor and this
reduces the overlap between hopping sites resulting in the positive
magnetoresistance quadratic in a weak magnetic field, B. We extend the theory
of hopping magnetoresistance to states with nonzero orbital momenta. Different
from s-states, a weak magnetic field expands the electron (hole) wave functions
with positive magnetic quantum numbers, m > 0, and shrinks the states with
negative m in a wide region outside the point defect. This together with a
magnetic-field dependence of injection/ionization rates results in a negative
weak-field magnetoresistance, which is linear in B when the orbital degeneracy
is lifted. The theory provides a possible explanation of a large low-field
magnetoresistance in disordered pi-conjugated organic materials (OMAR).",1110.4979v1
2011/11/21,Electron-phonon scattering dynamics in ferromagnets on ultrafast timescales: Influence of the phonon temperature,"The magnetization response of bulk ferromagnets after excitation by an
ultrashort optical pulse is calculated using a dynamical model of the
Elliott-Yafet type that includes the effects of the spin-orbit interaction in
the ab-initio ferromagnetic band structure, the electron-phonon interaction at
the level of Boltzmann scattering integrals, and dynamical changes in the
temperature of the phonon bath. Using realistic parameters for the ultrashort
optical pulse, the computed maximum magnetization quenching achievable with
electron-phonon scattering in a fixed band structure is much smaller than the
quenching observed in experiments. Heating of the phonon bath is found to not
appreciably change the magnetization dynamics on ultrashort timescales.",1111.4783v1
2011/12/5,Magnetic anisotropy of elongated thin ferromagnetic nano-islands for artifical spin ice arrays,"The energetics of thin elongated ferromagnetic nano-islands is considered for
some different shapes, aspect ratios, and applied magnetic field directions.
These nano-island particles are important for artificial spin-ice materials.
For low temperature, the magnetic internal energy of an individual particle is
evaluated numerically as a function of the direction of a particle's net
magnetization. This leads to estimations of effective anisotropy constants for
(1) the easy axis along the particle's long direction, and (2) the hard axis
along the particle's thin direction. A spin relaxation algorithm together with
fast Fourier transform for the demagnetization field is used to solve the
micromagnetics problem for a thin system. The magnetic hysteresis is also
found. The results indicate some possibilities for controlling the equilibrium
and dynamics in spin-ice materials by using different island geometries.",1112.0913v2
2012/1/3,CHUF and `unfreezing' (or de-arrest) of kinetic arrest in magnetic shape memory alloys,"CHUF (cooling and heating in unequal field) protocol allows establishing
phase coexistence through macroscopic measurements and enables distinguishing
the metastable and stable phases (amongst the coexisting phase fractions across
a first order magnetic transition) of a glass-like arrested state (GLAS). The
observation of kinetic arrest in magnetic shape memory alloys has become a very
active area of research. We highlight recent CHUF measurements on these
materials that show behaviour similar to that reported earlier in manganites
and other intermetallic alloys, emphasizing the generality. The martensitic
transition provides an opportunity to study various properties as the CHUF
protocol enables tuning of phase fractions, and controlled devitrification, of
GLAS.",1201.0575v1
2012/1/9,Majorana fermions in spin-singlet nodal superconductors with coexisting non-collinear magnetic order,"Realizations of Majorana fermions in solid state materials have attracted
great interests recently in connection to topological order and quantum
information processing. We propose a novel way to create Majorana fermions in
superconductors. We show that an incipient non-collinear magnetic order turns a
spin-singlet superconductor with nodes into a topological superconductor with a
stable Majorana bound state in the vortex core; at a topologically-stable
magnetic point defect; and on the edge. We argue that such an exotic
non-Abelian phase can be realized in extended t-J models on the triangular and
square lattices. It is promising to search for Majorana fermions in correlated
electron materials where nodal superconductivity and magnetism are two common
caricatures.",1201.1908v3
2012/1/27,Dimensionality selection in a molecule-based magnet,"Gaining control of the building blocks of magnetic materials and thereby
achieving particular characteristics will make possible the design and growth
of bespoke magnetic devices. While progress in the synthesis of molecular
materials, and especially coordination polymers, represents a significant step
towards this goal, the ability to tune the magnetic interactions within a
particular framework remains in its infancy. Here we demonstrate a chemical
method which achieves dimensionality selection via preferential inhibition of
the magnetic exchange in an $S=1/2$ antiferromagnet along one crystal
direction, switching the system from being quasi-two- to quasi-one-dimensional
while effectively maintaining the nearest-neighbour coupling strength.",1201.5864v1
2012/4/10,Large magnetothermopower effect in Dirac materials (Sr/Ca)MnBi2,"We report temperature and magnetic field dependence of the thermal transport
properties in single crystals of (Sr/Ca)MnBi$_2$ with linear energy dispersion.
In SrMnBi$_2$ thermopower is positive, indicating hole-type carriers and the
magnetic field enhances the thermopower significantly. The maximum change of
thermopower is about 1600% in 9 T field and at 10 K. A negative thermopower is
observed in CaMnBi$_2$ with dominant electron-type carriers and, in contrast,
the magnetic field suppresses the absolute value of thermopower.
First-principle band structure shows that the chemical potential is close to
the Dirac-cone-like points in linear bands. The magnetic field suppresses the
apparent Hall carrier density of CaMnBi$_2$ below 50 K. The large
magnetothermopower effect in (Sr/Ca)MnBi$_2$ is attributed to the magnetic
field shift of chemical potential",1204.2256v1
2012/5/2,Enhanced magnetic anisotropy of Nickel nanosheet prepared in Na-4 mica,"Nanosheets of nickel with thickness equal to 0.6 nm have been grown within
the interlayer spaces of Na-4 mica. The sheets are made up of percolative
clusters of nanodisks. Magnetization characteristics indicate a
superparamagnetic behavior with a blocking temperature of 428 K.The magnetic
anisotropy constant as extracted from the coercivity data has been found to be
higher than that of bulk nickel by two orders of magnitude. This is ascribed to
a large aspect ratio of the nickel nanophase. The Bloch exponent is also found
to be considerably different from that of bulk nickel because of a size effect.
The Bloch Equation is still found to be valid for the two dimensional
structures.",1205.0405v1
2012/5/11,First-principles computed electronic and magnetic properties of zincblende alkaline-earth pnictides,"Employing first-principle electronic structure calculations, we study the
magnetic and electronic properties of the XY (X= Mg, Ca, Sr and Y= N, P, As,
Sb) compounds crystallizing in the zincblende structure. The Ca and Sr
alkaline-earth metal monopnictides are found to be half-metallic with a total
spin magnetic moment per formula unit of 1.0 $\mu_B$. In the case of the Mg
alloys the p-d hybridization effect is much weaker and only MgN is a
half-metal. Electron counting of the bands explains the Slater-Pauling behavior
exhibited by the total spin magnetic moment. We also study for these alloys the
effect of deformation taking into account both the cases of hydrostatic
pressure and tetragonalization keeping constant either the in-plane lattice
parameters or the unit cell volume. Even large degrees of deformation only
marginally affect the electronic and magnetic properties of these alloys.
Finally, we show that this stands also for the rocksalt structure. Our results
suggest that alkaline-earth metal monopnictides are promising materials for
magnetoelectronic applications.",1205.2722v1
2012/5/22,The Magnetic Structure of DyMn2O5 Determined by Resonant X-ray Scattering,"Resonant magnetic x-ray scattering has been used to investigate the magnetic
structure of the magnetoelectric multiferroic DyMn2O5. We have studied the
magnetic structure in the ferroelectric phase of this material, which displays
the strongest ferroelectric polarisation and magnetodielectric effect of the
RMn2O5 (where R is a rare earth ion, Y or Bi) family. The magnetic structure
observed is similar to that of the other members of the series, but differs in
the direction of the ordered moments. In DyMn2O5 both the Dy and Mn moments lie
close to the b-axis, whereas in other RMn2O5 they lie close to the a-axis.",1205.4920v1
2012/6/7,Magnetic structure determination of Ca$_3$LiOsO$_6$ using neutron and x-ray scattering,"We present a neutron and x-ray scattering investigation of Ca$_3$LiOsO$_6$, a
material predicted to host magnetic ordering solely through an extended
superexchange pathway involving two anions, an interaction mechanism that has
undergone relatively little investigation. This contrasts with the ubiquitous
superexchange interaction mechanism involving a single anion that has well
defined and long standing rules. Despite the apparent 1D nature and triangular
units of magnetic osmium ions the onset of magnetic correlations has been
observed at a high temperature of 117 K in bulk measurements. We experimentally
determine the magnetically ordered structure and show it to be long range and
three dimensional. Our results support the model of extended superexchange
interaction.",1206.1608v1
2012/6/17,Spin Transfer Torque in Fully Insulating Magnetic Tunnel Junctions,"Voltage-driven spin transfer torque in a magnetic tunnel junction comprising
magnetic insulating electrodes is studied theoretically. In contrast with the
conventional magnetic tunnel junctions comprising transition metal
ferromagnets, the spin transfer torque presents unconventional bias
dependencies, related to the presence of spin-dependent Fowler-Nordheim
tunneling processes. In particular, we find that (i) the out-of-plane torque
generally dominates the in-plane torque, (ii) out-of-plane torque and in-plane
torque are symmetric and asymmetric at low bias voltage, respectively, and
(iii) both of torques show a dramatic enhancement at large bias voltage.
Materials consideration are discussed and we show that due to the low damping
parameter expected in magnetic insulators a spin transfer torque can be
experimentally observed in such systems.",1206.3743v1
2012/7/17,Bipolar-Driven Large Magnetoresistance in Silicon,"Large linear magnetoresistance (MR) in electron-injected p-type silicon at
very low magnetic field is observed experimentally at room temperature. The
large linear MR is induced in electron-dominated space-charge transport regime,
where the magnetic field modulation of electron-to-hole density ratio controls
the MR, as indicated by the magnetic field dependence of Hall coefficient in
the silicon device. Contrary to the space-charge-induced MR effect in unipolar
silicon device, where the large linear MR is inhomogeneity-induced, our results
provide a different insight into the mechanism of large linear MR in
non-magnetic semiconductors that is not based on the inhomogeneity model. This
approach enables homogeneous semiconductors to exhibit large linear MR at low
magnetic fields that until now has only been appearing in semiconductors with
strong inhomogeneities.",1207.3886v2
2012/7/20,Current induced domain wall dynamics in the presence of a transverse magnetic field in out-of-plane magnetized materials,"An analytical model was developped to describe the current induced DW
dynamics of a Bloch DW in the presence of an external transverse magnetic
field. The model takes into account the DW deformation and the magnetization
tilting in the domain. The model is compared to the results of micromagnetic
simulation and an excellent agreement is obtained. In the steady state regime,
the model shows that the domain tilting does not change the DW mobility. An
external or current induced transverse magnetic field such as the Oersted or
Rashba field can prevent the Walker breakdown leading to a higher domain wall
velocity.",1207.4970v1
2012/8/22,Massive Dirac surface states in topological insulator/magnetic insulator heterostructures,"Topological insulators are new states of matter with a bulk gap and robust
gapless surface states protected by time-reversal symmetry. When time-reversal
symmetry is broken, the surface states are gapped, which induces a topological
response of the system to electromagnetic field--the topological
magnetoelectric effect. In this paper we study the behavior of topological
surface states in heterostructures formed by a topological insulator and a
magnetic insulator. Several magnetic insulators with compatible magnetic
structure and relatively good lattice matching with topological insulators
${\rm Bi_2Se_3}, {\rm Bi_2Se_3}, {\rm Sb_2Te_3}$ are identified, and the best
candidate material is found to be MnSe, an anti-ferromagnetic insulator. We
perform first-principles calculation in ${\rm Bi_2Se_3/MnSe}$ superlattices and
obtain the surface state bandstructure. The magnetic exchange coupling with
MnSe induces a gap of $\sim$54 meV at the surface states. In addition we tune
the distance between Mn ions and TI surface to study the distance dependence of
the exchange coupling.",1208.4638v1
2012/12/19,Large magnetic heat transport in a Haldane chain material Ni(C$_3H_{10}N_2)_2NO_2ClO_4,"We report a study on the heat transport of an S = 1 Haldane chain compound
Ni(C_3H_{10}N_2)_2NO_2ClO_4 at low temperatures and in magnetic fields. The
zero-field thermal conductivities show a remarkable anisotropy for the heat
current along the spin-chain direction (\kappa_b) and the vertical direction
(\kappa_c), implying a magnetic contribution to the heat transport along the
spin-chain direction. The magnetic-field-induced change of the spin spectrum
has obviously opposite impacts on \kappa_b and \kappa_c. In particular,
\kappa_b(H) and \kappa_c(H) curves show peak-like increases and dip-like
decreases, respectively, at \sim 9 T, which is the critical field that
minimizes the spin gap. These results indicate a large magnetic thermal
transport in this material.",1212.4725v1
2013/1/1,Using x-ray diffraction to identify precipitates in transition metal doped semiconductors,"In the past decade, room temperature ferromagnetism was often observed in
transition metal doped semiconductors, which were claimed as diluted magnetic
semiconductors (DMS). Nowadays intensive activities are devoted to clarify
wether the observed ferromagnetism stems from carrier mediated magnetic
impurities, ferromagnetic precipitates, or spinodal decomposition. In this
paper, we have correlated the structural and magnetic properties of transition
metal doped ZnO, TiO2, and Si, prepared by ion implantation. Crystalline
precipitates, i.e., transition metal (Co, Ni) and Mn-silicide nanocrystals, are
responsible for the magnetism. Additionally due to their orientation nature
with respect to the host, these nanocrystals in some cases are not detectable
by conventional x-ray diffraction (XRD). This nature results in the pitfall of
using XRD to exclude magnetic precipitates in DMS materials.",1301.0100v1
2013/2/5,Bulk magnetoelectricity in the hexagonal manganites and ferrites,"Improper ferroelectricity (trimerization) in the hexagonal manganites
RMnO$_3$ leads to a network of coupled structural and magnetic vortices that
induce domain wall magnetoelectricity and magnetization neither of which,
however, occurs in the bulk. Here we combined first-principles calculations,
group-theoretic techniques, and microscopic spin models to show how the
trimerization not only induces a polarization but also a bulk magnetization and
bulk magnetoelectric (ME) effect. This results in the existence of a bulk
linear ME vortex structure or a bulk ME coupling such that if direction of
polarization reverses so does magnetization. To measure the predicted ME
vortex, we suggest RMnO$_3$ under large magnetic field. We suggest a family of
materials, the hexagonal RFeO$_3$ ferrites, also display the predicted
phenomena in their ground state.",1302.1099v2
2013/4/9,Paramagnetic Fe_xTa_{1-x} alloys for engineering of perpendicularly magnetized tunnel junctions,"Exchange coupling between two magnetic layers through an interlayer is of
broad interest for numerous recent applications of nano-magnetic systems. In
this Letter we study ferromagnetic exchange coupling through amorphous
paramagnetic Fe-Ta alloys. We show that the exchange coupling depends
exponentially on spacer thickness and scales with the Fe-Ta susceptibility,
which can be tuned via the alloy composition and/or temperature. Such materials
are of high interest for the engineering of perpendicularly magnetized
CoFeB-MgO based tunnel junctions as it enables ferromagnetic coupling of
magnetic layers with differing crystalline lattices, suppresses dead layers and
can act as an inter-diffusion barrier during annealing.",1304.2763v1
2013/4/23,Long-Distance Transfer and Routing of Static Magnetic Fields,"We show how the static magnetic field of a finite source can be transferred
and routed to arbitrary long distances. This is achieved by using
transformation optics, which results in a device made of a material with a
highly anisotropic magnetic permeability. We show that a simplified version of
the device, made by a superconducting-ferromagnet hybrid, also leads to an
excellent transfer of the magnetic field. The latter is demonstrated with a
proof-of-principle experiment where a ferromagnet tube coated with a
superconductor improves the transfer of static magnetic fields with respect to
conventional methods by a 400\% factor over distances of 14cm.",1304.6300v4
2013/6/18,Glassy magnetic behavior in the metamagnetic DyAlO3 doped with Cr,"Magnetic properties of DyAl$_{0.926}$Cr$_{0.074}$O$_3$ and DyAlO$_3$ were
studied. We found that both compounds are antiferromagnetic with a low N\'eel
transition temperature. At higher temperatures the magnetic characteristics
show a Curie-Weiss dependence. The N\'eel temperature disappears when a field
of about 2 T is applied, the system changes from an antiferromagnetic to a weak
ferromagnetic behavior due to a metamagnetic transition. Furthermore, AC
magnetic measurements in the Cr doped compound, at different frequencies, show
a spin glass-like behavior. These transitions were studied and corroborated by
specific heat measurements. We found the presence of metamagnetism and spin
glass in the compound doped with chromium, determining that the small addition
of chromium atoms modifies the magnetic properties of the compound DyAlO$_3$,
resulting in new features such as the spin glass-like behavior.",1306.4378v1
2013/6/21,Magnetic properties of a family of quinternary oxalates,"We report on the magnetic properties of four isomorphous compounds of a
family of quinternary oxalates down to 60 mK. In all these materials, the
magnetic FeII ions with a strong magneto-crystalline anisotropy form a
distorted kagome lattice, topologically equivalent to a perfect kagome one if
nearest-neighbor interactions only are considered. All the compounds order at
low temperature in an antiferromagnetic arrangement with magnetic moments at
120{\deg}. A remarkable magnetic behavior emerges below the N\'eel temperature
in three compounds (with inter-kagome-layer Zr, Sn, Fe but not with Al): the
spin anisotropy combined with a low exchange path network connectivity lead to
domain walls intersecting the kagome planes through strings of free spins.
These produce an unfamiliar slow spin dynamics in the ordered phase observed by
AC susceptibility, evolving from exchange-released spin-flips towards a
cooperative behavior on decreasing the temperature.",1306.5188v1
2013/12/25,Structural and electronic origin of the magnetic structures in hexagonal LuFeO$_3$,"Using combined theoretical and experimental approaches, we studied the
structural and electronic origin of the magnetic structure in hexagonal
LuFeO$_3$. Besides showing the strong exchange coupling that is consistent with
the high magnetic ordering temperature, the previously observed spin
reorientation transition is explained by the theoretically calculated magnetic
phase diagram. The structural origin of this spin reorientation that is
responsible for the appearance of spontaneous magnetization, is identified by
theory and verified by x-ray diffraction and absorption experiments.",1312.6984v3
2014/1/5,Spin torque building blocks,"The discovery of the spin torque effect has made magnetic nanodevices
realistic candidates for active elements of memory devices and applications.
Magnetoresistive effects allow the read-out of increasingly small magnetic
bits, and the spin torque provides an efficient tool to manipulate - precisely,
rapidly and at low energy cost - the magnetic state, which is in turn the
central information medium of spintronic devices. By keeping the same magnetic
stack, but by tuning a device's shape and bias conditions, the spin torque can
be engineered to build a variety of advanced magnetic nanodevices. Here we show
that by assembling these nanodevices as building blocks with different
functionalities, novel types of computing architectures can be envisisaged. We
focus in particular on recent concepts such as magnonics and spintronic neural
networks.",1401.0874v1
2014/1/8,"Enhancement of the magnetocaloric effect driven by changes in the crystal structure of Al doped GGG, Gd3Ga5-xAlxO12 (0 < x < 5)","The Gd3Ga5-xAlxO12 (0 < x < 5) solid solution has been prepared using ceramic
synthesis routes and the structural and magnetic properties investigated using
X-ray diffraction, magnetic susceptibility, chi, and isothermal magnetisation,
M(H), measurements. Our results indicate a contraction of the unit cell and
more significant antiferromagnetic interactions as x increases. Despite the
decrease in the magnetic polarisation on application of a field and the
corresponding decrease in the change in the magnetic entropy we find that
Gd3Al5O12 has a significantly higher observed (17%) and theoretical (14%) DS
per unit mass than Gd3Ga5O12. Per unit volume the theoretical increase in DS
(7%) is offset by the increased antiferromagnetic interactions in Gd3Al5O12.
The differences in DS are driven by a decrease in both the mass and density as
Al ions replace Ga ions. These results highlight the importance of changes to
the crystal structure when considering materials for solid state magnetic
cooling.",1401.1744v1
2014/3/8,Ab initio study of CrNF: the first half-metallic ferromagnet nitride fluoride mimicking CrO2,"Based on the different covalent versus ionic chemical bonding and
isoelectronic rutile CrO2, CrNF is proposed starting from ordered rutile
derivative structures subjected to full geometry optimizations. The ground
state structure defined from cohesive energies is of MgUO4-type, characterized
by short covalent Cr-N and long ionic Cr-F distances. Like CrO2 it is a
half-metallic ferromagnet with M = 2 Bohr Magnetons integer magnetization per
formula unit with reduced band gap at minority spins. Major differences of
magnetic response to pressure characterize CrNF as a soft ferromagnet versus
hard magnetic CrO2. The chemical bonding properties point to prevailing
covalent Cr-N versus ionic Cr-F bonding. Synthesis routes with two different
protocols are proposed and analyzed.",1403.1961v1
2014/4/1,Modification of the Bloch law in ferromagnetic nanostructures,"The temperature dependence of magnetization in ferromagnetic nanostructures
(e.g., nanoparticles or nanoclusters) is usually analyzed by means of an
empirical extension of the Bloch law sufficiently flexible for a good fitting
to the observed data and indicates a strong softening of magnetic coupling
compared to the bulk material. We analytically derive a microscopic
generalization of the Bloch law for the Heisenberg spin model which takes into
account the effects of size, shape and various surface boundary conditions. The
result establishes explicit connection to the microscopic parameters and
differs significantly from the existing description. In particular, we show
with a specific example that the latter may be misleading and grossly
overestimates magnetic softening in nanoparticles. It becomes clear why the
usual $T^{3/2}$ dependence appears to be valid in some nanostructures, while
large deviations are a general rule. We demonstrate that combination of
geometrical characteristics and coupling to environment can be used to
efficiently control magnetization and, in particular, to reach a magnetization
higher than in the bulk material.",1404.0233v1
2014/4/8,Modulation of pure spin currents with a ferromagnetic insulator,"We propose and demonstrate spin manipulation by magnetically controlled
modulation of pure spin currents in cobalt/copper lateral spin valves,
fabricated on top of the magnetic insulator Y$_3$Fe$_5$O$_{12}$ (YIG). The
direction of the YIG magnetization can be controlled by a small magnetic field.
We observe a clear modulation of the non-local resistance as a function of the
orientation of the YIG magnetization with respect to the polarization of the
spin current. Such a modulation can only be explained by assuming a finite
spin-mixing conductance at the Cu/YIG interface, as it follows from the
solution of the spin-diffusion equation. These results open a new path towards
the development of spin logics.",1404.2311v2
2014/4/12,"The Lorentz force law and its connections to hidden momentum, the Einstein-Laub force, and the Aharonov-Casher effect","The Lorentz force of classical electrodynamics, when applied to magnetic
materials, gives rise to hidden energy and hidden momentum. Removing the
contributions of hidden entities from the Poynting vector, from the
electromagnetic momentum density, and from the Lorentz force and torque
densities simplifies the equations of the classical theory. In particular, the
reduced expression of the electromagnetic force-density becomes very similar
(but not identical) to the Einstein-Laub expression for the force exerted by
electric and magnetic fields on a distribution of charge, current, polarization
and magnetization. Examples reveal the similarities and differences among
various equations that describe the force and torque exerted by electromagnetic
fields on material media. An important example of the simplifications afforded
by the Einstein-Laub formula is provided by a magnetic dipole moving in a
static electric field and exhibiting the Aharonov-Casher effect.",1404.3261v1
2014/5/5,Planar array of self-assembled Ga$_{x}$Fe$_{4-x}$N nanocrystals in GaN: Magnetic anisotropy determined via ferromagnetic resonance,"The magnetic anisotropy of a planar array of Ga$_{x}$Fe$_{4-x}$N nanocrystals
(NCs) embedded in a GaN host is studied by ferromagnetic resonance. X-ray
diffraction and transmission electron microscopy are employed to determine the
phase and distribution of the nanocrystals. The magnetic anisotropy is found to
be primarily uniaxial with the hard axis normal to the NCs plane and to have a
comparably weak in-plane hexagonal symmetry. The origin of the magnetic
anisotropy is discussed taking into consideration the morphology of the
nanocrystals, the epitaxial relations, strain effects and magnetic coupling
between the NCs.",1405.0906v2
2014/5/12,Theory of Mn-doped I-II-V Semiconductors,"A recently discovered magnetic semiconductor
Ba$_{1-x}$K$_{x}$(Zn$_{1-y}$Mn$_{y}$)$_2$As$_{2}$, with its decoupled spin and
charge doping, provides a unique opportunity to elucidate the microscopic
origin of the magnetic interaction and ordering in dilute magnetic
semiconductors (DMS). We show that (i) the conventional density functional
theory accurately describes this material, and (ii) the magnetic interaction
emerges from the competition of the short-range superexchange and the
longer-range spin-spin interaction mediated by the itinerant As holes. The
latter can be viewed as a high-doping extrapolation of with the
Schrieffer-Wolff $p-d$ interaction representing an effective Hund's rule
coupling, $J_{H}^{\text{eff}}$. The key difference between the classical double
exchange and the actual interaction in DMS is that an effective
$J_{H}^{\text{eff}}$, as opposed to the standard Hund's coupling $J_{H}$,
depends on the Mn $d-$band position with respect to the Fermi level, and thus
allows tuning of the magnetic interactions. The physical picture revealed for
this transparent system may also be applicable to more complicated DMS systems.",1405.2854v1
2014/6/4,Magnetic-Field Induced Semimetal in Topological Crystalline Insulator Thin Films,"We investigate electromagnetic properties of a topological crystalline
insulator (TCI) thin film under external electromagnetic fields. The TCI thin
film is a topological insulator indexed by the mirror-Chern number. It is
demonstrated that the gap closes together with the emergence of a pair of
gapless cones carrying opposite chirarities by applying in-plane magnetic
field. A pair of gapless points have opposite vortex numbers. This is a
reminiscence of a pair of Weyl cones in 3D Weyl semimetal. We thus present an a
magnetic-field induced semimetal-semiconductor transition in 2D material. This
is a giant-magnetoresistance, where resistivity is controlled by magnetic
field. Perpendicular electric field is found to shift the gapless points and
also renormalize the Fermi velocity in the direction of the in-plane magnetic
field.",1406.1009v2
2014/9/5,Magneto-ionic Control of Interfacial Magnetism,"In metal/oxide heterostructures, rich chemical, electronic, magnetic and
mechanical properties can emerge from interfacial chemistry and structure. The
possibility to dynamically control interface characteristics with an electric
field paves the way towards voltage control of these properties in solid-state
devices. Here we show that electrical switching of the interfacial oxidation
state allows for voltage control of magnetic properties to an extent never
before achieved through conventional magnetoelectric coupling mechanisms. We
directly observe, for the first time, in situ voltage driven O$^{2-}$ migration
in a Co/metal-oxide bilayer, which we use to toggle the interfacial magnetic
anisotropy energy by >0.6 erg/cm$^2$. We exploit the thermally-activated nature
of ion migration to dramatically increase the switching efficiency and to
demonstrate reversible patterning of magnetic properties through local
activation of ionic migration. These results suggest a path towards
voltage-programmable materials based on solid-state switching of interface
oxygen chemistry.",1409.1843v1
2014/9/19,"Magnetic anisotropy of Fe_1-yX_yPt-L10 [X=Cr,Mn,Co,Ni,Cu] bulk alloys","We demonstrate by means of fully relativistic first principles calculations
that, by substitution of Fe by Cr, Mn, Co, Ni or Cu in FePt-L10 bulk alloys,
with fixed Pt content, it is possible to tune the magnetocrystalline anisotropy
energy by adjusting the content of the non-magnetic species in the material.
The changes in the geometry due to the inclusion of each element induces
different values of the tetragonality and hence changes in the magnetic
anisotropy and in the net magnetic moment. The site resolved magnetic moments
of Fe increase with the X content whilst those of Pt and X are simultaneously
reduced. The calculations are in good quantitative agreement with experimental
data and demonstrate that models with fixed band structure but varying numbers
of electrons per unit cell are insufficient to describe the experimental data
for doped FePt-L10 alloys.",1409.5806v1
2014/11/7,Temperature evolution of magnetic and transport behavior in 5\textit{d} Mott insulator Sr$_2$IrO$_4$: Significance of magneto-structural coupling,"We have investigated the temperature evolution of magnetism and its
interrelation with structural parameters in perovskite-based layered compound
Sr$_2$IrO$_4$, which is believed to be a $J_{eff}$ = 1/2 Mott insulator. The
structural distortion plays an important role in this material which induces a
weak ferromagnetism in otherwise antiferromagnetically ordered magnetic state
with transition temperature around 240 K. Interestingly, at low temperature
below around 100 K, a change in magnetic moment has been observed. Temperature
dependent x-ray diffraction measurements show sudden changes in structural
parameters around 100 K are responsible for this. Resistivity measurements show
insulating behavior throughout the temperature range across the magnetic phase
transition. The electronic transport can be described with Mott's
two-dimensional variable range hopping (VRH) mechanism, however, three
different temperature ranges are found for VRH, which is a result of varying
localization length with temperature. A negative magnetoresistance (MR) has
been observed at all temperatures in contrast to positive behavior generally
observed in strongly spin-orbit coupled materials. The quadratic field
dependence of MR implies a relevance of a quantum interference effect.",1411.1946v1
2014/12/11,Biquadratic and ring exchange interactions in orthorhombic perovskite manganites,"We use ab initio electronic structure calculations within the generalized
gradient approximation (GGA+U) to density functional theory (DFT) to determine
the microscopic exchange interactions in the series of orthorhombic rare-earth
manganites, o-$R$MnO$_3$. Our motivation is to construct a model Hamiltonian
(excluding effects due to spin-orbit coupling), which can provide an accurate
description of the magnetism in these materials. First, we consider TbMnO$_3$,
which exhibits a spiral magnetic order at low temperatures. We map the exchange
couplings in this compound onto a Heisenberg Hamiltonian and observe a clear
deviation from the Heisenberg-like behavior. We consider first the coupling
between magnetic and orbital degrees of freedom as a potential source of
non-Heisenberg behavior in TbMnO$_3$, but conclude that it does not explain the
observed deviation. We find that higher order magnetic interactions
(biquadratic and four-spin ring couplings) should be taken into account for a
proper treatment of the magnetism in TbMnO$_3$ as well as in the other
representatives of the o-$R$MnO$_3$ series with small radii of the $R$ cation.",1412.3702v1
2014/12/17,Collinear order in a frustrated three-dimensional spin-$\frac12$ antiferromagnet Li$_2$CuW$_2$O$_8$,"Magnetic frustration in three dimensions (3D) manifests itself in the
spin-$\frac12$ insulator Li$_2$CuW$_2$O$_8$. Density-functional band-structure
calculations reveal a peculiar spin lattice built of triangular planes with
frustrated interplane couplings. The saturation field of 29 T contrasts with
the susceptibility maximum at 8.5 K and a relatively low N\'eel temperature
$T_N\simeq 3.9$ K. Magnetic order below $T_N$ is collinear with the propagation
vector $(0,\frac12,0)$ and an ordered moment of 0.65(4) $\mu_B$ according to
neutron diffraction data. This reduced ordered moment together with the low
maximum of the magnetic specific heat ($C^{\max}/R\simeq 0.35$) pinpoint strong
magnetic frustration in 3D. Collinear magnetic order suggests that quantum
fluctuations play crucial role in this system, where a non-collinear spiral
state would be stabilized classically.",1412.5578v2
2014/12/22,"Interplay between tetragonal magnetic order, stripe magnetism, and superconductivity in iron-based materials","Motivated by recent experiments in Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$ {[}A. E.
B\""ohmer \textit{et al}, to be published{]}, we analyze the type of
spin-density wave (SDW) order in doped iron-pnictides and the discontinuities
of the superconducting transition temperature $T_{c}$ in the coexistence phase
with SDW magnetism. By tracking the magnetic transition line $T_{N}(x)$ towards
optimal doping within an itinerant fermionic model, we find a sequence of
transitions from the stripe-orthorhombic ($C_{2}$) SDW order to the tetragonal
($C_{4}$) order and then back to the $C_{2}$ order. We argue that the
superconducting $T_{c}$ has two discontinuities -- it jumps to a smaller value
upon entering the coexistence region with the $C_{4}$ magnetic phase, and then
jumps to a larger value inside the SDW state when it crosses the boundary
between the $C_{4}$ and $C_{2}$ SDW orders. The full agreement with the
experimental phase diagram provides a strong indication that the itinerant
approach is adequate to describe the physics of weakly/moderately doped
iron-pnictides.",1412.7079v2
2015/1/28,Large Superconducting Magnet Systems,"The increase of energy in accelerators over the past decades has led to the
design of superconducting magnets for both accelerators and the associated
detectors. The use of Nb-Ti superconducting materials allows an increase in the
dipole field by up to 10 T compared with the maximum field of 2 T in a
conventional magnet. The field bending of the particles in the detectors and
generated by the magnets can also be increased. New materials, such as Nb3Sn
and high temperature superconductor (HTS) conductors, can open the way to
higher fields, in the range 13-20 T. The latest generations of fusion machines
producing hot plasma also use large superconducting magnet systems.",1501.07169v1
2015/2/19,"Ferrimagnetism in 2D networks of porphyrin-X and -XO (X=Sc,...,Zn) with acetylene bridges","Magnetism in 2D networks of the acetylene-bridged transition metal porphyrins
M(P)-2(C-C)-2 (denoted P-TM), and oxo-TM-porphyrins OM(P)-2(C-C)-2 (denoted
P-TMO), is studied with the density functional theory (DFT) and the
self-interaction corrected pseudopotential scheme (pSIC). Addition of oxygen
lowers magnetism of P-TMO with respect to the corresponding P-TM for most of
the first-half $3d$-row TMs. In contrast, binding O with the second-half
$3d$-row TMs or Sc increases the magnetic moments. Ferrimagnetism is found for
the porphyrin networks with the TMs from V to Co and also for these cases with
oxygen. This is a long-range effect of the delocalized spin-polarization,
extended even to the acetylene bridges.",1502.05738v3
2015/2/25,Atomically thin dilute magnetism in Co-doped phosphorene,"Two-dimensional dilute magnetic semiconductors can provide fundamental
insights in the very nature of magnetic orders and their manipulation through
electron and hole doping. Despite the fundamental physics, due to the large
charge density control capability in these materials, they can be extremely
important in spintronics applications such as spin valve and spin-based
transistors. In this article, we studied a two-dimensional dilute magnetic
semiconductors consisting of phosphorene monolayer doped with cobalt atoms in
substitutional and interstitial defects. We show that these defects can be
stabilized and are electrically active. Furthermore, by including holes or
electrons by a potential gate, the exchange interaction and magnetic order can
be engineered, and may even induce a ferromagnetic-to-antiferromagnetic phase
transition in p-doped phosphorene.",1502.07351v1
2015/2/25,Observation of room temperature magnetic skyrmions and their current-driven dynamics in ultrathin Co films,"Magnetic skyrmions are topologically-protected spin textures that exhibit
fascinating physical behaviors and large potential in highly energy efficient
spintronic device applications. The main obstacles so far are that skyrmions
have been observed in only a few exotic materials and at low temperatures, and
manipulation of individual skyrmions has not yet been achieved. Here, we report
the observation of stable magnetic skyrmions at room temperature in ultrathin
transition metal ferromagnets with magnetic transmission soft x-ray microscopy.
We demonstrate the ability to generate stable skyrmion lattices and drive
trains of individual skyrmions by short current pulses along a magnetic
racetrack. Our findings provide experimental evidence of recent predictions and
open the door to room-temperature skyrmion spintronics in robust thin-film
heterostructures.",1502.07376v1
2015/3/11,Dynamical influence of vortex-antivortex pairs in magnetic vortex oscillators,"We study the magnetization dynamics in a nanocontact magnetic vortex
oscillators as function of temperature. Low temperature experiments reveal that
the dynamics at low and high currents differ qualitatively. At low currents, we
excite a temperature independent standard oscillation mode, consisting in the
gyrotropic motion of a free layer vortex about the nanocontact. Above a
critical current, a sudden jump of the frequency is observed, concomitant with
a substantial increase of the frequency versus current slope factor. Using
micromagnetic simulation and analytical modeling, we associate this new regime
to the creation of a vortex-antivortex pair in the pinned layer of the spin
valve. The vortex-antivortex distance depends on the Oersted field which favors
a separation, and on the exchange bias field, which favors pair merging. The
pair in the pinned layer provides an additional spin torque altering the
dynamics of the free layer vortex, which can be quantitatively accounted for by
an analytical model.",1503.03365v2
2015/3/12,A single crystal Co2+ fluoride pyrochlore antiferromagnet,"We report the crystal growth, crystal structure and basic magnetic properties
of a new cobalt-based pyrochlore, NaSrCo$_2$F$_7$. Na and Sr are completely
disordered on the non-magnetic large atom A sites, while magnetic S=3/2
Co$^{2+}$ fully occupies the pyrochlore lattice B sites. This system exhibits
an isotropic magnetic susceptibility with strong antiferromagnetic interactions
(${\theta}_{CW}$ = -127(1)), a large effective moment (${\rho_{eff}}$ = 5.9(1)
${\mu_B}$/Co) and no spin freezing until 3 K. Thus NaSrCo$_2$F$_7$ is a
geometrically frustrated antiferromagnet with a frustration index f =
-${\theta_{CW}}$/T$_f$ = 42. AC susceptibility, DC susceptibility, and heat
capacity are utilized to characterize the spin freezing at low temperatures. We
propose that NaSrCo$_2$F$_7$, compared here to the related material
NaCaCo$_2$F$_7$, may be the realization of a frustrated pyrochlore
antiferromagnet with weak bond disorder. The strong magnetic frustration at an
easily accessible temperature and the availability of large single crystals
make this one of the potentially interesting alternatives to the more commonly
studied rare earth oxide pyrochlores.",1503.03751v1
2015/3/23,Electron-Irradiation Induced Nanocrystallization of Pb(II) in Silica Gels Prepared in High Magnetic Field,"In a previous study, structure of silica gels prepared in a high magnetic
field was investigated. While a direct application of such anisotropic silica
gels is for an optical anisotropic medium possessing chemical resistance, we
show here their possibility of medium in materials processing. In this
direction, for example, silica hydrogels have so far been used as media of
crystal growth. In this paper, as opposed to the soft-wet state, dried silica
gels have been investigated. We have found that lead (II) nanocrystallites were
formed induced by electron irradiation to lead (II)-doped dried silica gels
prepared in a high magnetic field such as B = 10 T. Hydrogels made from a
sodium metasilicate solution doped with lead (II) acetate were prepared. The
dried specimens were irradiated by electrons in a transmission electron
microscope environment. Electron diffraction patterns indicated the
crystallinity of lead (II) nanocrystallites depending on B. An advantage of
this processing technique is that the crystallinity can be controlled through
the strength of magnetic field B applied during gel preparation. Specific
skills are not required to control the strength of magnetic field.",1503.06863v1
2015/4/13,Evidence for Localized Moment Picture in Mn-based Heusler Compounds,"X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism
(XMCD) were used to probe the oxidation state and element specific magnetic
moments of Mn in Heusler compounds with different crystallographic structure.
The results were compared with theoretical calculations, and it was found that
in full Heusler alloys, Mn is metallic (oxidation state near 0) on both
sublattices. The magnetic moment is large and localized when octahedrally
coordinated by the main group element, consistent with previous theoretical
work, and reduced when the main group coordination is tetrahedral. By contrast,
in the half Heusler compounds the magnetic moment of the Mn atoms is large and
the oxidation state is +1 or +2. The magnetic and electronic properties of Mn
in full and half Heusler compounds are strongly dependent on the structure and
sublattice, a fact that can be exploited to design new materials.",1504.03088v1
2015/4/14,Magnetic charges and magnetoelectricity in hexagonal rare-earth manganites and ferrites,"Magnetoelectric (ME) materials are of fundamental interest and show broad
potential for technological applications. Commonly the dominant contribution to
the ME response is the lattice-mediated one, which is proportional to both the
Born electric charge $Z^{\rm e}$ and its analogue, the dynamical magnetic
charge $Z^{\rm m}$. Our previous study has shown that exchange striction acting
on noncollinear spins induces much larger magnetic charges than those that
depend on spin-orbit coupling. The hexagonal manganites $R$MnO$_3$ and ferrites
$R$FeO$_3$ ($R$ = Sc, Y, In, Ho-Lu) exhibit strong couplings between electric,
magnetic and structural degrees of freedom, with the transition-metal ions in
the basal plane antiferromagnetically coupled through super-exchange so as to
form a 120$^\circ$ noncollinear spin arrangement. Here we present a theoretical
study of the magnetic charges, and of the spin-lattice and spin-electronic ME
constants, in these hexagonal manganites and ferrites, clarifying the
conditions under which exchange striction leads to an enhanced $Z^{\rm m}$
values and anomalously large in-plane spin-lattice ME effects.",1504.03405v1
2015/4/27,Magnetic fluctuations driven insulator-to-metal transition in Ca(Ir$_{1-x}$Ru$_{x}$)O$_{3}$,"Magnetic fluctuations in transition metal oxides are a subject of intensive
research because of the key role they are expected to play in the transition
from the Mott insulator to the unconventional metallic phase of these
materials, and also as drivers of superconductivity. Despite much effort, a
clear link between magnetic fluctuations and the insulator-to-metal transition
has not yet been established. Here we report the discovery of a compelling link
between magnetic fluctuations and the insulator-to-metal transition in
Ca(Ir$_{1-x}$Ru$_{x}$)O$_{3}$ perovskites as a function of the doping
coefficient x. We show that when the material turns from insulator to metal, at
a critical value of x$\sim$ 0.3, magnetic fluctuations change their character
from antiferromagnetic, a Mott insulator phase, to ferromagnetic, an itinerant
electron state with Hund's orbital coupling. These results are expected to have
wide-ranging implications for our understanding of the unconventional
properties of strongly correlated electrons systems",1504.06901v1
2015/6/1,Magnetism in Na-filled Fe-based skutterudites,"The interplay of superconductivity and magnetism is a subject of ongoing
interest, stimulated most recently by the discovery of Fe-based
superconductivity and the recognition that spin-fluctuations near a magnetic
quantum critical point may provide an explanation for the superconductivity and
the order parameter. Here we investigate magnetism in the Na filled Fe-based
skutterudites using first principles calculations. NaFe4Sb12 is a known
ferromagnet near a quantum critical point. We find a ferromagnetic metallic
state for this compound driven by a Stoner type instability, consistent with
prior work. In accord with prior work, the magnetization is overestimated, as
expected for a material near an itinerant ferromagnetic quantum critical point.
NaFe4P12 also shows a ferromagnetic instability at the density functional
level, but this instability is much weaker than that of NaFe4Sb12, possibly
placing it on the paramagnetic side of the quantum critical point. NaFe4As12
shows intermediate behavior. We also present results for skutterudite FeSb3,
which is a metastable phase that has been reported in thin film form.",1506.00514v1
2015/6/4,Low-moment ferrimagnetic phase of the Heusler compound Cr2CoAl,"Synthesizing half-metallic fully-compensated ferrimagnets that form in the
inverse Heusler phase could lead to superior spintronic devices. These
materials would have high spin polarization at room temperature with very
little fringing magnetic fields. Previous theoretical studies indicated that
Cr2CoAl should form in a stable inverse Heusler lattice due to its low
activation energy. Here, stoichiometric Cr2CoAl samples were arc-melted and
annealed at varying temperatures, followed by studies of their structural and
magnetic properties. High-resolution synchrotron X-ray diffraction revealed a
chemically ordered Heusler phase in addition to CoAl and Cr phases. Soft X-ray
magnetic circular dichroism revealed that the Cr and Co magnetic moments are
antiferromagnetically oriented leading to the observed low magnetic moment in
Cr2CoAl.",1506.01738v1
2015/7/23,"Electronic, magnetic and transport properties of Fe intercalated 2H-TaS$_2$ studied by means of the KKR-CPA method","The electronic, magnetic and transport properties of Fe intercalated
2H-TaS$_2$ have been investigated by means of the Korringa-Kohn-Rostoker (KKR)
method. The non-stoichiometry and disorder in the system has been accounted for
using the Coherent Potential Approximation (CPA) alloy theory. A pronounced
influence of disorder on the spin magnetic moment has been found for the
ferro-magnetically ordered material. The same applies for the spin-orbit
induced orbital magnetic moment and magneto-crystalline anisotropy energy. The
temperature-dependence of the resistivity of disordered 2H-Fe$_{0.28}$TaS$_2$
investigated on the basis of the Kubo-St\v{r}eda formalism in combination with
the alloy analogy model has been found in very satisfying agreement with
experimental data. This also holds for the temperature dependent anomalous Hall
resistivity $ \rho_{\rm xy}(T) $. The role of thermally induced lattice
vibrations and spin fluctuations for the transport properties is discussed in
detail.",1507.06544v1
2015/9/24,Magnetic behavior of volborthite Cu3V2O7(OH)2(H2O)2 determined by coupled trimers rather than frustrated chains,"Motivated by recent experiments on volborthite single crystals showing a wide
1/3-magnetization plateau, we perform microscopic modeling by means of density
functional theory (DFT) with the single-crystal structural data as a starting
point. Using DFT+U, we find four leading magnetic exchanges: antiferromagnetic
J and J2, as well as ferromagnetic J' and J1. Simulations of the derived spin
Hamiltonian show good agreement with the experimental low-field magnetic
susceptibility and high-field magnetization data. The 1/3-plateau phase
pertains to polarized magnetic trimers formed by strong J bonds. An effective
J$\rightarrow\infty$ model shows a tendency towards condensation of magnon
bound states preceding the plateau phase.",1509.07333v2
2015/10/5,Resonant Spin and Charge Hall Effects in 2D Electron Gas with Unequal Rashba and Dresselhaus Spin-Orbit Couplings under a Perpendicular Magnetic Field,"We have investigated the complex two-dimensional electron system with unequal
Rashba and Dresselhaus spin-orbit interactions in the presence of a
perpendicular magnetic field. The spin polarizations are obtained in a wide
range of magnetic fields. It is shown that such a system is hard to be
magnetized. We also find that the resonant charge and spin Hall conductances
occurs simultaneously at a certain magnetic field, at which two (nearly)
degenerate Landau levels are filled partly. The resonant Hall effects are
universal in this type of semiconductor materials, and could have potential
application for semiconductor spintronics.",1510.01012v1
2015/11/13,Structure stability and magnetism in graphene impurity complexes with embedded V and Nb atoms,"First-principles density functional theory (DFT) study of embedding V and Nb
atom in monovacant and divacant graphene is reported. Complete/almost complete
spin polarization is verified for V/Nb embedding in MV/DV graphene. The origin
of magnetism has been identified via interaction of 3d-states of embedded
trnasition metal atom with p-states of inequivalent C atoms present in the
vicinity of embedding site. Band structure analysis has been performed to
address the semiconducting behavior of graphene in minority spin channel on
embedding V/Nb atom. The isosurface plots also confirm the magnetic nature of
present nanosystems. Our results reveal that these nanosystems have potential
for futuristic applications such as spintronics, energy resources and high
frequency transistors.",1511.04313v2
2015/12/3,Electronic and magnetic properties of dopant atoms in SnSe monolayer: a first-principles study,"SnSe monolayer with orthorhombic Pnma GeS structure is an important
two-dimensional (2D) indirect band gap material at room temperature. Based on
first-principles density functional theory calculations, we present systematic
studies on the electronic and magnetic properties of X (X = Ga, In, As, Sb)
atoms doped SnSe monolayer. The calculated electronic structures show that
Ga-doped system maintains semiconducting property while In-doped SnSe monolayer
is half-metal. The As- and Sb- doped SnSe systems present the characteristics
of n-type semiconductor. Moreover, all considered substitutional doping cases
induce magnetic ground states with the magnetic moment of 1{\mu}B. In addition,
the calculated formation energies also show that four types of doped systems
are thermodynamic stable. These results provide a new route for the potential
applications of doped SnSe monolayer in 2D photoelectronic and magnetic
semiconductor devices.",1512.01228v1
2015/12/10,Piezomagnetic effect as a counterpart of negative thermal expansion in magnetically frustrated Mn-based antiperovskite nitrides,"Electric-field control of magnetization promises to substantially enhance the
energy efficiency of device applications ranging from data storage to
solid-state cooling. However, the intrinsic linear magnetoelectric effect is
typically small in bulk materials. In thin films electric-field tuning of
spin-orbit interaction phenomena (e.g., magnetocrystalline anisotropy) has been
reported to achieve a partial control of the magnetic state. Here we explore
the piezomagnetic effect (PME), driven by frustrated exchange interactions,
which can induce a net magnetization in an antiferromagnet and reverse its
direction via elastic strain generated piezoelectrically. Our $ab~initio$ study
of PME in Mn-antiperovskite nitrides identified an extraordinarily large PME in
Mn$_3$SnN available at room temperature. We explain the magnitude of PME based
on features of the electronic structure and show an inverse-proportionality
between the simulated zero-temperature PME and the negative thermal expansion
at the magnetic (N\'eel) transition measured by Takenaka et al. in 9
antiferromagnetic Mn$_3$AN systems.",1512.03470v2
2015/12/24,Modeling of Magnetostriction of Soft Elastomer,"Small magnetic particles placed in a relatively soft polymer (with elastic
modulus E ~ 10-100 kPa) are magnetically soft elastomers. The external magnetic
field acts on each particle which leads to microscopic deformation of the
material and consequently to changing of its shape - magnetostriction. For
purposes of studying of magnetostriction the model of movable cellular automata
(MCA), in which a real heterogeneous material is an ensemble of interacting
elements of finite size - automata, is used. It is supposed to be that the
motion of each automata can be described by Newton's Second law. The force
acting on the i-th automata consists of the following components:
volume-dependent force acting on the automata i which is caused by pressure
from the surrounding automata; force of an external magnetic field acting on
the i-th automata with some magnetic moment; and normal and tangential
interaction force between a pair of i and j automata. This approach was used
for modeling of magnetostriction elastomer.",1512.07718v1
2016/1/22,Determination of the Spin-Hall-Effect-Induced and the Wedged-Structure-Induced Spin Torque Efficiencies in Heterostructures with Perpendicular Magnetic Anisotropy,"We report that by measuring current-induced hysteresis loop shift versus
in-plane bias magnetic field, the spin Hall effect (SHE) contribution of the
current-induced effective field per current density, $\chi_{SHE}$, can be
estimated for Pt and Ta-based magnetic heterostructures with perpendicular
magnetic anisotropy (PMA). We apply this technique to a Pt-based sample with
its ferromagnetic (FM) layer being wedged-deposited and discover an extra
effective field contribution, $\chi_{Wedged}$, due to the asymmetric nature of
the deposited FM layer. We confirm the correlation between $\chi_{Wedged}$ and
the asymmetric depinning process in FM layer during magnetization switching by
magneto-optical Kerr (MOKE) microscopy. These results indicate the possibility
of engineering deterministic spin-orbit torque (SOT) switching by controlling
the symmetry of domain expansion through the materials growth process.",1601.05854v1
2016/2/5,Skyrmions in thin films with easy-plane magnetocrystalline anisotropy,"We demonstrate that chiral skyrmionic magnetization configurations can be
found as the minimum energy state in B20 thin film materials with easy-plane
magnetocrystalline anisotropy with an applied magnetic field perpendicular to
the film plane. Our observations contradict results from prior analytical work,
but are compatible with recent experimental investigations. The size of the
observed skyrmions increases with the easy-plane magnetocrystalline anisotropy.
We use a full micromagnetic model including demagnetization and a
three-dimensional geometry to find local energy minimum (metastable)
magnetization configurations using numerical damped time integration. We
explore the phase space of the system and start simulations from a variety of
initial magnetization configurations to present a systematic overview of
anisotropy and magnetic field parameters for which skyrmions are metastable and
global energy minimum (stable) states.",1602.02064v2
2016/2/27,Observation of magnetoelectric effects in a S=1/2 frustrated spin chain magnet SrCuTe2O6,"The magnetoelectric (ME) effects are investigated in a cubic compound
SrCuTe2O6, in which uniform Cu2+ (S=1/2) spin chains with considerable spin
frustration exhibit a concomitant antiferromagnetic transition and dielectric
constant peak at TN=5.5 K. Pyroelectric Jp(T) and magnetoelectric current
JME(H) measurements in the presence of a bias electric field are used to reveal
that SrCuTe2O6 shows clear variations of Jp(T) across TN at constant magnetic
fields. Furthermore, isothermal measurements of JME(H) also develop clear peaks
at finite magnetic fields, of which traces are consistent with the spin-flop
transitions observed in the magnetization studies. As a result, the anomalies
observed in Jp(T) and JME(H) curves well match with the field-temperature phase
diagram constructed from magnetization and dielectric constant measurements,
demonstrating that SrCuTe2O6 is a new magnetoelectric compound with S=1/2 spin
chains.",1602.08560v1
2016/3/9,Topological strength of magnetic skyrmions,"We deal with magnetic structures that attain integer and half-integer
skyrmion numbers. We model and solve the problem analytically, and show how the
solutions appear in materials that engender distinct, very specific physical
properties, and use them to describe their topological features. In particular,
we found a way to model skyrmion with a large transition region correlated with
the presence of a two-peak skyrmion number density. Moreover, we run into the
issue concerning the topological strength of a vortex-like structure and
suggest an experimental realization, important to decide how to modify and
measure the topological strength of the magnetic structure.",1603.02749v2
2016/3/11,Mechanocaloric effects in Shape Memory Alloys,"Shape memory alloys are a class of ferroic materials which undergo a
structural (martensitic) transition where the associated ferroic property is a
lattice distortion (strain). The sensitiveness of the transition to the
conjugated external field (stress), together with the latent heat of the
transition gives rise to giant mechanocaloric effects. In non-magnetic shape
memory alloys, the lattice distortion is mostly described by a pure shear and
the martensitic transition in this family of alloys is strongly affected by
uniaxial stress whereas it is basically insensitive to hydrostatic pressure. As
a result, non-magnetic alloys exhibit giant elastocaloric effects but
negligible barocaloric effects. By contrast, in a number of magnetic shape
memory alloys, the lattice distortion at the martensitic transition involves a
volume change in addition to the shear strain. Those alloys are affected by
both uniaxial stress and hydrostatic pressure and they exhibit giant
elastocaloric and barocaloric effects. The paper aims at providing a critical
survey of available experimental data on elastocaloric and barocaloric effects
in magnetic and non-magnetic shape memory alloys.",1603.03658v1
2016/3/15,Ordering in rolled-up single-walled ferromagnetic nanomembranes,"Magnetization of soft-ferromagnetic nano- and microtubes of nanometer-thin
walls (a single-widening rolled-up nanomembranes) is theoretically studied
using analytical and numerical approaches including different stress-induced
anisotropies. Within the analytical study, we consider magnetostatic effects
qualitatively, with an effective anisotropy, while they are fully treated in
the micromagnetic simulations (limited to the tubes of submicrometer diameters
however). Basic types of the periodic ordering have been established and their
presence in nanotubes of polycrystalline Permalloy and cobalt has been verified
within the simulations. The domain structure is basically determined by a
material-deposition-induced helical stress or a cooling-induced axial stress
via the volume magnetostriction while it is influenced by the distribution of
magnetic charges as well. Also, it is dependent on the initial state of the
magnetization process.",1603.04883v2
2016/4/22,Robust Zero-Field Skyrmion Formation in FeGe Epitaxial Thin Films,"B20 phase magnetic materials, such as FeGe, have been of significant
interests in recent years because they enable magnetic skyrmions, which can
potentially lead to low energy cost spintronic applications. One major effort
in this emerging field is the stabilization of skyrmions at room temperature
and zero external magnetic field. We report the growth of phase-pure FeGe
epitaxial thin films on Si(111) substrates by ultrahigh vacuum off-axis
sputtering. The high crystalline quality of the FeGe films was confirmed by
x-ray diffraction and scanning transmission electron microscopy. Hall effect
measurements reveal strong topological Hall effect after subtracting out the
ordinary and anomalous Hall effects, demonstrating the formation of high
density skyrmions in FeGe films between 5 and 275 K. In particular, substantial
topological Hall effect was observed at zero magnetic field, showing a robust
skyrmion phase without the need of an external magnetic field.",1604.06684v1
2016/5/11,Magnetic properties of single nanomagnets: EMCD on FePt nanoparticles,"Energy-loss magnetic chiral dichroism (EMCD) allows for the quantification of
magnetic properties of materials at the nanometer scale. It is shown that with
the support of simulations that help to identify the optimal conditions for a
successful experiment and upon implementing measurement routines that
effectively reduce the noise floor, EMCD measurements can be pushed towards
quantitative magnetic measurements even on individual nanoparticles. With this
approach, the ratio of orbital to spin magnetic moments for the Fe atoms in a
single L$1_0$ ordered FePt nanoparticle is determined to be ${m_l}/{m_s} = 0.08
\pm 0.02$. This finding is in good quantitative agreement with the results of
XMCD ensemble measurements.",1605.03545v1
2016/5/16,Tailoring Exchange Couplings in Magnetic Topological Insulator/Antiferromagnet Heterostructures,"Magnetic topological insulators such as Cr-doped (Bi,Sb)2Te3 provide a
platform for the realization of versatile time-reversal symmetry-breaking
physics. By constructing heterostructures with N\'eel order in an
antiferromagnetic CrSb and magnetic topological order in Cr-doped (Bi,Sb)2Te3,
we realize emergent interfacial magnetic phenomena which can be tailored
through artificial structural engineering. Through deliberate geometrical
design of heterostructures and superlattices, we demonstrate the use of
antiferromagnetic exchange coupling in manipulating the magnetic properties of
the topological surface massive Dirac fermions. This work provides a new
framework on integrating topological insulators with antiferromagnetic
materials and unveils new avenues towards dissipationless topological
antiferromagnetic spintronics.",1605.04854v1
2016/5/18,Heat-Treatment-Induced Switching of Magnetic States in the Doped Polar Semiconductor Ge$_{1-x}$Mn$_x$Te,"Cross-control of a material property - manipulation of a physical quantity
(e.g., magnetisation) by a nonconjugate field (e.g., electrical field) - is a
challenge in fundamental science and also important for technological device
applications. It has been demonstrated that magnetic properties can be
controlled by electrical and optical stimuli in various magnets. Here we find
that heat-treatment allows the control over two competing magnetic phases in
the Mn-doped polar semiconductor GeTe. The onset temperatures $T_{\rm c}$ of
ferromagnetism vary at low Mn concentrations by a factor of five to six with a
maximum $T_{\rm c} \approx 180$ K, depending on the selected phase. Analyses in
terms of synchrotron x-ray diffraction and energy dispersive x-ray spectroscopy
indicate a possible segregation of the Mn ions, which is responsible for the
high-$T_{\rm c}$ phase. More importantly, we demonstrate that the two states
can be switched back and forth repeatedly from either phase by changing the
heat-treatment of a sample, thereby confirming magnetic phase-change- memory
functionality.",1605.05461v1
2016/5/20,Rewritable Artificial Magnetic Charge Ice,"Artificial ices enable the study of geometrical frustration by design and
through direct observation. However, it has proven difficult to achieve
tailored long-range ordering of their diverse configurations, limiting both
fundamental and applied research directions. We designed an artificial spin
structure that produces a magnetic charge ice with tunable long-range ordering
of eight different configurations. We also developed a technique to precisely
manipulate the local magnetic charge states and demonstrate write-read-erase
multifunctionality at room temperature. This globally reconfigurable and
locally writable magnetic charge ice could provide a setting for designing
magnetic monopole defects, tailoring magnonics, and controlling the properties
of other two-dimensional materials.",1605.06209v1
2016/5/22,Colossal magnetic phase transition asymmetry in mesoscale FeRh stripes,"Coupled order parameters in phase-transition materials can be controlled
using various driving forces such as temperature, magnetic and electric field,
strain, spin-polarized currents and optical pulses. Tuning the material
properties to achieve efficient transitions would enable fast and low-power
electronic devices. Here we show that the first-order metamagnetic phase
transition in FeRh films becomes strongly asymmetric in mesoscale structures.
In patterned FeRh stripes we observed pronounced supercooling and an
avalanche-like abrupt transition from the ferromagnetic to the
antiferromagnetic phase while the reverse transition remains nearly continuous
over a broad temperature range. Although modest asymmetry signatures have been
found in FeRh films, the effect is dramatically enhanced at the mesoscale. The
asymmetry in the transitions is independent of applied magnetic fields and the
activation volume of the antiferromagnetic phase is more than two orders of
magnitude larger than typical magnetic heterogeneities observed in films. The
collective behavior upon cooling results from the role of long-range
ferromagnetic exchange correlations that become important at the mesoscale and
should be a general property of first-order magnetic phase transitions.",1605.06823v1
2016/6/3,Multidomain Skyrmion Lattice State in Cu$_2$OSeO$_3$,"Magnetic skyrmions in chiral magnets are nanoscale, topologically-protected
magnetization swirls that are promising candidates for spintronics memory
carriers. Therefore, observing and manipulating the skyrmion state on the
surface level of the materials are of great importance for future applications.
Here, we report a controlled way of creating a multidomain skyrmion state near
the surface of a Cu$_{2}$OSeO$_{3}$ single crystal, observed by soft resonant
elastic x-ray scattering. This technique is an ideal tool to probe the magnetic
order at the $L_{3}$ edge of $3d$ metal compounds giving a depth sensitivity of
${\sim}50$ nm. The single-domain sixfold-symmetric skyrmion lattice can be
broken up into domains overcoming the propagation directions imposed by the
cubic anisotropy by applying the magnetic field in directions deviating from
the major cubic axes. Our findings open the door to a new way to manipulate and
engineer the skyrmion state locally on the surface, or on the level of
individual skyrmions, which will enable applications in the future.",1606.01187v1
2016/6/6,Enhanced spin reorientation temperature and origin of magnetocapacitance in HoFeO3,"We report on the increase in the spin reorientation temperature in
HoFe0.5Cr0.5O3 compound by isovalent substitution Cr3+ at the Fe-site and the
magnetocapacitance in the HoFeO3 compound. Spin reorientation transition is
evident around 50 K and 150 K for the x = 0 and x = 0.5 compounds respectively.
The increase in the spin reorientation transition temperature in case of x =
0.5 compound can be attributed to the domination of the Ho3+ to Fe3+
interaction over the Fe3+ to Fe3+ interaction. Decrease in Neel temperature
from 643 K (x = 0) to 273 K (x = 0.5) can be ascribed to the decrease in the
interaction between antiferromagnetically aligned Fe3+ moments as a result of
the dilution of the Fe3+ moments with the Cr3+ addition. From the magnetization
M vs magnetic field H variation it is evident that the coercivity, HC decreases
for x = 0.5 compound, hinting the magnetic softening of the HoFeO3 compound.
Observed magnetocapacitance could be due to lossy dielectric mechanism in the
present compound. Indeed, present results would be helpful in understanding the
physics behind rare- earth orthoferrites.",1606.01703v1
2016/6/14,Origin of the large positive magnetoresistance in Ge1-xMnx granular thin films,"GeMn granular thin films are a unique and promising material for spintronics
applications due to large positive magnetoresistance (MR). Previous studies on
GeMn have suggested that the large MR is related to nanospinodal decomposition
of GeMn into Mn-rich ferromagnetic nanoparticles and Mn-poor paramagnetic
matrix. However, its microscopic origin of the MR has not been clarified yet.
Here, using X-ray magnetic circular dichroism (XMCD), which is extremely
sensitive to the local magnetic state of each atom, we investigate the magnetic
properties of the nanoparticles and the matrix in GeMn separately. We find that
the MR ratio is proportional to the product of the magnetizations originating
from the nanoparticles and the matrix. This result indicates that
spin-polarized holes in the nanoparticles penetrate into the matrix and that
these holes undergo spin-disorder magnetic scattering by the paramagnetic Mn
atoms in the matrix, which induces the large MR.",1606.04263v1
2016/6/14,Chiral Ordering Spin Associated Glass like State in SrRuO3SrIrO3 Superlattice,"Heterostructure interface provides a powerful platform to observe rich
emergent phenomena, such as interfacial superconductivity, nontrivial
topological surface state. Here SrRuO3/SrIrO3 superlattices were epitaxially
synthesized. The magnetic and electrical properties of these superlattices were
characterized. Broad cusps in the zero field cooling magnetization curves and
near stable residual magnetization below the broad cusps, as well as two steps
magnetization hysteresis loops are observed. The magnetization relaxes
following a modified Stretched function model indicating coexistence of spin
glass and ferromagnetic ordering in the superlattices. Topological Hall effect
was demonstrated at low temperature and weakened with the increase of SrIrO3
layer thickness. These results suggest that chiral ordering spin texture were
generated at the interfaces due to the interfacial Dzyaloshinskii-Moriya (DM)
interaction, which generates the spin glass behaviors. The present work
demonstrates that SrIrO3 can effectively induce interface DM interactions in
heterostructures, it would pave light on the new research directions of strong
spin orbit interaction oxides, from the viewpoints of both basic science and
prospective spintronics devices applications.",1606.04313v2
2016/7/18,Study of spin-phonon coupling and magnetic field induced spin reorientation in polycrystalline multiferroic $GdFeO_3$,"The present work reports the preparation of polycrystalline multiferroic
$GdFeO_3$ (GdFO) and characterization with x-ray diffraction (XRD),
magnetization, temperature dependent Raman spectroscopy, temperature and
magnetic field dependent $^{57}Fe$ M$\ddot{o}$ssbauer spectroscopy
measurements. The sample is found to be phase pure from Rietveld refinement of
XRD pattern. The M$\ddot{o}$ssbauer spectra measured in the presence of
external magnetic field show the signatures of field induced spin reorientation
transition, which are corroborated by magnetization measurements. From the
temperature dependent variation of internal hyperfine field, N$\grave{e}$el
transition temperature ($T_{N,Fe}$) of 672.5$\pm$0.2 K and critical exponent
($\beta$) of 0.333$\pm$0.003 is obtained. Temperature dependent (300 - 760 K)
Raman spectroscopy measurements show the signatures of spin-phonon coupling and
local structural re-arrangement across $T_{N,Fe}$.",1607.04996v1
2016/8/22,Emptying Dirac valleys in bismuth using high magnetic fields,"The Fermi surface of elemental bismuth consists of three small rotationally
equivalent electron pockets, offering a valley degree of freedom to charge
carriers. A relatively small magnetic field can confine electrons to their
lowest Landau level. This is the quantum limit attained in other dilute metals
upon application of sufficiently strong magnetic field. Here, we report on the
observation of another threshold magnetic field never encountered before in any
other solid. Above this field, $B_{\rm{empty}}$, one or two valleys become
totally empty. Drying up a Fermi sea by magnetic field in the Brillouin zone
leads to a manyfold enhancement in electric conductance. We trace the origin of
the large drop in magnetoresistance across $B_{\rm{empty}}$ to transfer of
carriers between valleys with highly anisotropic mobilities. The
non-interacting picture of electrons with field-dependent mobility explains
most results. Coulomb interaction may play a role in shaping the fine details.",1608.06199v2
2016/10/11,Large magnetic anisotropy predicted for rare-earth free Fe16-xCoxN2 alloys,"Structures and magnetic properties of Fe16-xCoxN2 are studied using adaptive
genetic algorithm and first-principles calculations. We show that substituting
Fe by Co in Fe16N2 with Co/Fe ratio smaller than 1 can greatly improve the
magnetic anisotropy of the material. The magnetocrystalline anisotropy energy
from first-principles calculations reaches 3.18 MJ/m3 (245.6 {\mu}eV per metal
atom) for Fe12Co4N2, much larger than that of Fe16N2 and is one of the largest
among the reported rare-earth free magnets. From our systematic crystal
structure searches, we show that there is a structure transition from
tetragonal Fe16N2 to cubic Co16N2 in Fe16-xCoxN2 as the Co concentration
increases, which can be well explained by electron counting analysis. Different
magnetic properties between the Fe-rich (x < 8) and Co-rich (x > 8) Fe16-xCoxN2
is closely related to the structural transition.",1610.03544v1
2016/10/22,Giant nonreciprocal emission of spin waves in Ta/Py bilayers,"Spin waves are propagating disturbances in the magnetization of magnetic
materials. One of their interesting properties is the nonreciprocity,
exhibiting that their amplitude depends on the magnetization direction.
Nonreciprocity in spin waves is of great interest in both fundamental science
and applications, as it offers an extra knob to control the flow of waves for
the technological fields of logics and switch applications. We show a high
nonreciprocity in spin waves from Ta/Py bilayer systems with out-of-plane
magnetic fields. The nonreciprocity depends on the thickness of Ta underlayer
which is found to induce an interfacial anisotropy. The origin of observed high
nonreciprocity is twofold; different polarities of the in-plane magnetization
due to different angles of canted out-of-plane anisotropy and the spin pumping
effect at the Ta/Py interface. Our findings provide an opportunity to engineer
highly efficient nonreciprocal spin wave based applications such as
nonreciprocal microwave devices, magnonic logic gates, and information
transports.",1610.07023v1
2016/12/2,First-principles design of the spinel iridate Ir2O4 for high-temperature quantum spin ice,"Insulating magnetic rare-earth pyrochlores related to spin ice host emergent
bosonic monopolar spinons, which obey a magnetic analogue of quantum
electrodynamics and may open a route to a magnetic analogue of electronics.
However, the energy scales of the interactions among rare-earth moments are so
low as 1 K that the possible quantum coherence can only be achieved at a
sub-Kelvin. Here, we desgin high-temperature quantum spin ice materials from
first principles. It is shown that the A-site deintercalated spinel iridate
Ir2O4, which has been experimentally grown as epitaxial thin films, is a
promising candidate for quantum spin ice with a spin-ice-rule interaction of a
few tens of meV. Controlling electronic structures of Ir2O4 through substrates,
it is possible to tune magnetic interactions so that a magnetic Coulomb liquid
persists at high temperatures.",1612.00553v1
2017/1/13,Collinear order and chirality-reorientation transition in the Cairo pentagonal magnet Bi$_4$Fe$_5$O$_{13}$F,"We show that interlayer spins play a dual role in the Cairo pentagonal magnet
Bi$_4$Fe$_5$O$_{13}$F, on one hand mediating the three-dimensional (3D)
magnetic order and on the other driving spin-reorientation transitions both
within and between the planes. The corresponding sequence of magnetic orders
unraveled by neutron diffraction and M\""ossbauer spectroscopy features two
orthogonal magnetic structures described by opposite local vector chiralities,
and an intermediate, partly disordered phase with nearly collinear spins. A
similar collinear phase has been predicted theoretically to be stabilized by
quantum fluctuations, but Bi$_4$Fe$_5$O$_{13}$F is very far from the relevant
parameter regime. While the observed in-plane reorientation cannot be explained
by any standard frustration mechanism, our ab initio band-structure
calculations reveal strong single-ion anisotropy of the interlayer Fe$^{3+}$
spins that turns out to be instrumental in controlling the local vector
chirality and the associated interlayer order.",1701.03739v2
2017/1/14,Paving Spin-Wave Fibers in Magnonic Nanocircuits Using Spin-Orbit Torque,"Recent studies have revealed that domain walls in magnetic nanostructures can
serve as compact, energy-efficient spin-wave waveguides for building magnonic
devices that are considered promising candidates for overcoming the challenges
and bottlenecks of today's CMOS technologies. However, imprinting long
strip-domain walls into magnetic nanowires remains a challenge, especially in
curved geometries. Here, through micromagnetic simulations, we present a method
for writing strip-domain walls into curved magnetic nanowires using spin-orbit
torque. We employ Y-shaped magnetic nanostructures as well as an S-shaped
magnetic nanowire to demonstrate the injection process. In addition, we verify
that the Y-shaped nanostructures that incorporate strip-domain walls can
function as superior spin-wave multiplexers, and that spin-wave propagation
along each conduit can be controllably manipulated. This spin-wave multiplexer
based on strip-domain walls is expected to become a key signal-processing
component in magnon spintronics.",1701.03886v1
2017/1/14,Systematic comprehension the metal phase of Pr0.7(CaxSr1-x)0.3MnO3 via temperature and magnetic induction,"Temperature, magnetic induction and substitution dependent resistivity are a
crucial factor in determining the physical properties of magneto-resistive
materials. The first objective of this work was to find out an applicable
method of using temperature to predict the resistivity of
Pr0.7(CaxSr1-x)0.3MnO3 in the metal phase within the transition area. Based on
non-linear curve fitting, a typical numerical method is used to quantitatively
analyze the temperature-dependent resistivity within temperatures lower than
the metal-insulator transition temperature (Tp). The simulations agree very
well with the observed curves (resistivity versus temperature). The second
objective of this work is to search for the applicable method to link
magneto-resistivity to magnetic induction, calculation on the principle of
non-linear curve fitting, four typical numerical methods are highlighted
because the magnetic induction-dependent magneto-resistivity are quantitatively
analyzed by these methods. The observed effects of magnetic induction on the
shift of temperature-resistive curve should be more essential in physics and
are quantitatively discussed in magneto-resistive materials. Lastly, the
influences of Ca substitution on magneto-resistivity are detected.",1701.04688v1
2017/2/2,In-vivo biomagnetic characterisation of the American cockroach,"We present a quantitative method, utilising a highly sensitive quantum
sensor, that extends applicability of magnetorelaxometry to biological samples
at physiological temperature. The observed magnetic fields allow for
non-invasive determination of physical properties of magnetic materials and
their surrounding environment inside the specimen. The method is applied to
American cockroaches and reveals magnetic deposits with strikingly different
behaviour in alive and dead insects. We discuss consequences of this finding to
cockroach magneto-reception. To our knowledge, this work represents the first
characterisation of the magnetisation dynamics in live insects and helps to
connect results from behavioural experiments on insects in magnetic fields with
characterisation of magnetic materials in their corpses.",1702.00538v2
2017/2/15,"Unusual magnetic structure of high-pressure synthesized perovskites ACrO3(A=Sc, In, Tl)","Magnetic structures of metastable perovskites ScCrO3, InCrO3 and TlCrO3,
stabilized under high-pressure and high-temperature conditions, have been
studied by neutron powder diffraction. Similar to the other orthochromites
LnCrO3 (Ln=lanthanide or Y), these materials crystallize into the orthorhombic
structure with Pnma10 symmetry. The spin configuration of the metastable
perovskites has been found to be C-type, contrasting with the G-type structure
usually observed in LnCrO3. First-principles calculations demonstrate that the
Ctype structure found in ScCrO3 and InCrO3 is attributed to a ferromagnetic
(FM) nearest-neighbor interaction, while in TlCrO3, this type of magnetic
ordering is stabilized by a strong next-nearest-neighbor antiferromagnetic
(AFM) exchange. The spins in the C-type magnetic structure line up along the
orthorhombic b-axis, yielding the Pnma magnetic symmetry. The dominant
mechanism controlling this spin direction has been concluded to be the single
ion anisotropy imposed by a uniaxial distortion of CrO6 octahedra.",1702.04523v1
2017/2/16,Extended spin model in atomistic simulations of alloys,"An extended atomistic spin model allowing for studies of the finite
temperature magnetic properties of alloys is proposed. The model is obtained by
extending the Heisenberg Hamiltonian via a parameterization from a first
principles basis, interpolating from both the low temperature ferromagnetic and
the high temperature paramagnetic reference states. This allows us to treat
magnetic systems with varying degree of itinerant character within the model.
Satisfactory agreement with both previous theoretical studies and experiments
are obtained in terms of Curie temperatures and paramagnetic properties. The
proposed model is not restricted to elements but is also applied to binary
alloys, such as the technologically important material Permalloy, where
significant differences in the finite magnetic properties of Fe and Ni magnetic
moments are found. The proposed model strives to find the right compromise
between accuracy and computational feasibility for accurate modeling, even for
complex magnetic alloys and compounds.",1702.05011v1
2017/2/24,Antiskyrmions stabilized at interfaces by anisotropic Dzyaloshinskii-Moriya interaction,"Chiral magnets are an emerging class of topological matter harbouring
localized and topologically protected vortex-like magnetic textures called
skyrmions, which are currently under intense scrutiny as a new entity for
information storage and processing. Here, on the level of micromagnetics we
rigorously show that chiral magnets cannot only host skyrmions but also
antiskyrmions as least-energy configurations over all non-trivial homotopy
classes. We derive practical criteria for their occurrence and coexistence with
skyrmions that can be fulfilled by (110)-oriented interfaces in dependence on
the electronic structure. Relating the electronic structure to an atomistic
spin-lattice model by means of density-functional calculations and minimizing
the energy on a mesoscopic scale applying spin-relaxation methods, we propose a
double layer of Fe grown on a W(110) substrate as a practical example. We
conjecture that ultrathin magnetic films grown on semiconductor or heavy metal
substrates with $C_{2v}$ symmetry are prototype classes of materials hosting
magnetic antiskyrmions.",1702.07573v2
2017/2/27,Breakdown of Magnons in a Strongly Spin-Orbital Coupled Magnet,"The description of quantized collective excitations stands as a landmark in
the quantum theory of condensed matter. A prominent example occurs in
conventional magnets, which support bosonic magnons - quantized harmonic
fluctuations of the ordered spins. In striking contrast is the recent discovery
that strongly spin-orbital coupled magnets, such as $\alpha$-RuCl$_3$, may
display a broad excitation continuum inconsistent with conventional magnons.
Due to incomplete knowledge of the underlying interactions unraveling the
nature of this continuum remains challenging. The most discussed explanation
refers to a coherent continuum of fractional excitations analogous to the
celebrated Kitaev spin liquid. Here we present a more general scenario. We
propose that the observed continuum represents incoherent excitations
originating from strong magnetic anharmoniticity that naturally occurs in such
materials. This scenario fully explains the observed inelastic magnetic
response of $\alpha$-RuCl$_3$ and reveals the presence of nontrivial
excitations in such materials extending well beyond the Kitaev state.",1702.08466v3
2017/3/31,High-speed 100 MHz strain monitor using fiber Bragg grating and optical filter for magnetostriction measurements under ultrahigh magnetic fields,"A high-speed 100 MHz strain monitor using a fiber Bragg grating, an optical
filter, and a mode-locked optical fiber laser has been devised, which has a
resolution of $\Delta L/L\sim10^{-4}$. The strain monitor is sufficiently fast
and robust for the magnetostriction measurements of magnetic materials under
ultrahigh magnetic fields generated with destructive pulse magnets, where the
sweep rate is in the range of 10-100 T/$\mu$s. As a working example, the
magnetostriction of LaCoO$_{3}$ was measured at room temperature, 115 K, and
7$\sim$4.2 K up to a maximum magnetic field of 150 T. The smooth $B^{2}$
dependence and the first-order transition were observed at 115 K and 7$\sim$4.2
K, respectively, reflecting the field-induced spin-state evolution.",1703.10971v2
2017/4/1,Thermally nucleated magnetic reversal in CoFeB/MgO nanodots,"Power consumption is the main limitation in the development of new high
performance random access memory for portable electronic devices. Magnetic RAM
(MRAM) with CoFeB/MgO based magnetic tunnel junctions (MTJs) is a promising
candidate for reducing the power consumption given its non-volatile nature
while achieveing high performance. The dynamic properties and switching
mechanisms of MTJs are critical to understanding device operation and to enable
scaling of devices below 30 nm in diameter. Here we show that the magnetic
reversal mechanism is incoherent and that the switching is thermally nucleated
at device operating temperatures. Moreover, we find an intrinsic thermal
switching field distribution arising on the sub-nanosecond timescale even in
the absence of size and anisotropy distributions or material defects. These
features represent the characteristic signature of the dynamic properties in
MTJs and give an intrinsic limit to reversal reliability in small magnetic
nanodevices.",1704.00106v1
2017/4/14,"Structures, phase transitions, and magnetic properties of Co3Si from first-principles calculations","Co3Si was recently reported to exhibit remarkable magnetic properties in the
nanoparticle form [Appl. Phys. Lett. 108, 152406 (2016)], yet better
understanding of this material is to be promoted. Here we report a study on the
crystal structures of Co3Si using adaptive genetic algorithm, and discuss its
electronic and magnetic properties from first-principles calculations. Several
competing phases of Co3Si have been revealed from our calculations. We show
that the hexagonal Co3Si structure reported in experiments has lower energy in
non-magnetic state than ferromagnetic state at zero temperature. The
ferromagnetic state of the hexagonal structure is dynamically unstable with
imaginary phonon modes and transforms to a new orthorhombic structure, which is
confirmed by our structure searches to have the lowest energy for both Co3Si
and Co3Ge. Magnetic properties of the experimental hexagonal structure and the
lowest-energy structures obtained from our structure searches are investigated
in detail.",1704.04514v2
2017/5/9,Topological spin dynamics in cubic FeGe near room temperature,"Understanding spin-wave dynamics in chiral magnets is a key step for the
development of high-speed, spin-wave based spintronic devices that take
advantage of chiral and topological spin textures for their operation. Here we
present an experimental and theoretical study of spin-wave dynamics in a cubic
B20 FeGe single crystal. Using the combination of waveguide microwave
absorption spectroscopy (MAS), micromagnetic simulations, and analytical
theory, we identify the resonance dynamics in all magnetic phases (field
polarized, conical, helical, and skyrmion phases). Because the resonance
frequencies of specific chiral spin textures are unique, quantitative agreement
between our theoretical predictions and experimental findings for all resonance
frequencies and spin wave modes enables us to unambiguously identify chiral
magnetic phases and to demonstrate that MAS is a powerful tool to efficiently
extract a magnetic phase diagram. These results provide a new tool to
accelerate the integration of chiral magnetic materials into spintronic
devices.",1705.03397v1
2017/5/24,Modal phenomena of surface and bulk polaritons in magnetic-semiconductor superlattices,"We discuss peculiarities of bulk and surface polaritons propagating in a
composite magnetic-semiconductor superlattice influenced by an external static
magnetic field. Three particular configurations of magnetization, namely the
Voigt, polar and Faraday geometries are considered. In the long-wavelength
limit, involving the effective medium theory, the proposed superlattice is
described as an anisotropic uniform medium defined by the tensors of effective
permittivity and effective permeability. The study is carried out in the
frequency band where the characteristic resonant frequencies of the underlying
constitutive magnetic and semiconductor materials of the superlattice are
different but closely spaced. The effects of mode crossing and anti-crossing in
dispersion characteristics of both bulk and surface polaritons are revealed and
explained with an assistance of the concept of Morse critical points from the
catastrophe theory.",1705.08597v1
2017/6/11,Magnetization spin dynamics in a (LuBi)3Fe5O12 (BLIG) epitaxial film,"Bismuth substituted lutetium iron garnet (BLIG) films exhibit larger Faraday
rotation, and have a higher Curie temperature than yttrium iron garnet. We have
observed magnetic stripe domains and measured domain widths of 1.4 {\mu}{\mu}m
using Fourier domain polarization microscopy, Faraday rotation experiments
yield a coercive field of 5 Oe. These characterizations form the basis of
micromagnetic simulations that allow us to estimate and compare spin wave
excitations in BLIG films. We observed that these films support thermal magnons
with a precessional frequency of 7 GHz with a line width of 400 MHz. Further,
we studied the dependence of precessional frequency on the externally applied
magnetic field. Brillouin light scattering experiments and precession
frequencies predicted by simulations show similar trend with increasing field.",1706.03340v1
2017/7/15,Structural and magnetic properties of lightly doped M-type hexaferrites,"Vanadium substituted SrM hexaferrites (SrFe12-xVxO19 with x = 0.2, 0.4) and
Eu-substituted BaM hexaferrite (Ba0.8Eu0.2Fe12O19) were prepared by high energy
ball milling and sintering at 1200{\deg} C. X-ray diffraction measurements
revealed that the V-substituted SrM samples exhibited phase separation
resulting in the coexistence of the pure SrM magnetic phase with nonmagnetic
Sr3(VO4)2 vanadate and {\alpha}-Fe2O3 iron oxide phase. Also, the
Eu-substituted BaM hexaferrite revealed the formation of the pure BaM phase
coexisting with {\alpha}-Fe2O3 secondary phase, and Eu-garnet minor phase.
Although the magnetic properties of the samples deteriorated with respect to
pure hexaferrite properties, the magnetic parameters of the substituted samples
were found to be of potential importance for practical applications. Further,
the results of the study suggest methods for the preparation of high quality
SrM hexaferrites, and hexaferrite/garnet composites.",1707.04709v1
2017/7/11,Two-photon Lithography for 3D Magnetic Nanostructure Fabrication,"Ferromagnetic materials have been utilised as recording media within data
storage devices for many decades. Confinement of the material to a two
dimensional plane is a significant bottleneck in achieving ultra-high recording
densities and this has led to the proposition of three dimensional (3D)
racetrack memories that utilise domain wall propagation along nanowires.
However, the fabrication of 3D magnetic nanostructures of complex geometry is
highly challenging and not easily achievable with standard lithography
techniques. Here, by using a combination of two-photon lithography and
electrochemical deposition, we show a new approach to construct 3D magnetic
nanostructures of complex geometry. The magnetic properties are found to be
intimately related to the 3D geometry of the structure and magnetic imaging
experiments provide evidence of domain wall pinning at a 3D nanostructured
junction.",1707.07009v1
2017/7/25,Probing $α$-RuCl$_3$ Beyond Magnetic Order: Effects of Temperature and Magnetic Field,"Recent studies have brought $\alpha$-RuCl$_3$ to the forefront of
experimental searches for materials realizing Kitaev spin-liquid physics. This
material exhibits strongly anisotropic exchange interactions afforded by the
spin-orbit coupling of the 4d Ru centers. We investigate the dynamical response
at finite temperature and magnetic field for a realistic model of the magnetic
interactions in $\alpha$-RuCl$_3$. These regimes are thought to host
unconventional paramagnetic states that emerge from the suppression of magnetic
order. Using exact diagonalization calculations of the quantum model
complemented by semi-classical analysis, we find a very rich evolution of the
spin dynamics as the applied field suppresses the zigzag order and stabilizes a
quantum paramagnetic state that is adiabatically connected to the fully
polarized state at high fields. At finite temperature, we observe large
redistributions of spectral weight that can be attributed to the anisotropic
frustration of the model. These results are compared to recent experiments, and
provide a roadmap for further studies of these regimes.",1707.08144v2
2017/7/26,Reorientable Spin Direction for Spin Current Produced by the Anomalous Hall Effect,"We show experimentally that the spin direction of the spin current generated
by spin-orbit interactions within a ferromagnetic layer can be reoriented by
turning the magnetization direction of this layer. We do this by measuring the
field-like component of spin-orbit torque generated by an exchange-biased FeGd
thin film and acting on a nearby CoFeB layer. The relative angle of the CoFeB
and FeGd magnetic moments is varied by applying an external magnetic field. We
find that the resulting torque is in good agreement with predictions that the
spin current generated by the anomalous Hall effect from the FeGd layer depends
on the FeGd magnetization direction $\hat{m}_{FeGd}$ according to
$\vec{\sigma}\propto\left ( \hat{y}\cdot \hat{m}_{FeGd} \right
)\hat{m}_{FeGd}$, where $\hat{y}$ is the in-plane direction perpendicular to
the applied charge current. Because of this angular dependence, the spin-orbit
torque arising from the anomalous Hall effect can be non-zero in a sample
geometry for which the spin Hall torque generated by non-magnetic materials is
identically zero.",1707.08631v1
2017/8/24,MgO thickness-induced spin reorientation transition in Co0.9Fe0.1/MgO/Co0.9Fe0.1 structure,"The magnetic anisotropy (MA) of Mo/Au/Co0.9Fe0.1/Au/MgO(0.7 - 3
nm)/Au/Co0.9Fe0.1/Au heterostructure has been investigated at room temperature
as a function of MgO layer thickness (tMgO). Our studies show that while the MA
of the top layer does not change its character upon variation of tMgO, the
uniaxial out-of-plane MA of the bottom one undergoes a spin reorientation
transition at tMgO of about 0.8 nm, switching to the regime where the
coexistence of in- and out-of-plane magnetization alignments is observed. The
magnitudes of the magnetic anisotropy constants have been determined from
ferromagnetic resonance and dc-magnetometry measurements. The origin of MA
evolution has been attributed to a presence of an interlayer exchange coupling
(IEC) between Co0.9Fe0.1 layers through the thin MgO film.",1708.07382v1
2017/9/21,Current-induced magnetization switching using electrically-insulating spin-torque generator,"Current-induced magnetization switching through spin-orbit torques (SOTs) is
the fundamental building block of spin-orbitronics. The SOTs generally arise
from the spin-orbit coupling of heavy metals. However, even in a
heterostructure where a metallic magnet is sandwiched by two different
insulators, a nonzero current-induced SOT is expected because of the broken
inversion symmetry; an electrical insulator can be a spin-torque generator.
Here, we demonstrate current-induced magnetization switching using an
insulator. We show that oxygen incorporation into the most widely used
spintronic material, Pt, turns the heavy metal into an electrically-insulating
generator of the SOTs, enabling the electrical switching of perpendicular
magnetization in a ferrimagnet sandwiched by electrically-insulating oxides. We
further found that the SOTs generated from the Pt oxide can be controlled
electrically through voltage-driven oxygen migration. These findings open a
route towards energy-efficient, voltage-programmable spin-orbit devices based
on solid-state switching of heavy metal oxidation.",1709.07127v1
2017/10/3,d-zero Magnetism in Nanoporous Amorphous Alumina Membranes,"Nanoporous alumina membranes produced by mild or hard anodisation in oxalic
acid at potentials ranging from 5 - 140 V have a controllable pore surface area
of up to 200 times the membrane area. They exhibit a saturating magnetic
response that is temperature-independent and almost anhysteretic below room
temperature. The magnetism cannot be explained by the ~1 ppm of
transition-metal impurities present in the membranes. The magnetic moment
increases with the area of the open nanopores, reaching values of 0.6 Bohr
magnetons per square nanometer for mild anodisation and 8 muB/nm2 for hard
anodisation where the growth rate is faster. Crystallization of the membrane or
chemical treatment with salicylic acid reduces the effect by up to 90 %. The
magnetism is therefore associated with the open pore surfaces of the amorphous
Al2O3, and it is independent of the orientation of the applied field with
respect to the membrane surface. Possible explanations in terms of electrons
associated with oxygen vacancies (F or F+ centres) are discussed and it is
concluded that the effect is due to giant orbital paramagnetism rather than
collective ferromagnetic spin order.",1710.01232v2
2017/11/1,Tunable magnetization relaxation of Fe_{2}Cr_{1-x}Co_{x}Si half-metallic Heusler alloys by band structure engineering,"We report a systematic investigation on the magnetization relaxation
properties of iron-based half-metallic Heusler alloy
Fe$_{2}$Cr$_{1-x}$Co_${x}$Si (FCCS) thin films using broadband angular-resolved
ferromagnetic resonance. Band structure engineering through Co doping (x)
demonstrated by first-principles calculations is shown to tune the intrinsic
magnetic damping over an order of magnitude, namely 0.01-0.0008. Notably, the
intrinsic damping constants for samples with high Co concentration are among
the lowest reported for Heusler alloys and even comparable to magnetic
insulator yttrium iron garnet. Furthermore, a significant reduction of both
isotropic and anisotropic contributions of extrinsic damping of the FCCS alloys
was found in the FCCS films with x=0.5-0.75, which is of particular importance
for applications. These results demonstrate a practical recipe to tailor
functional magnetization for Heusler alloy-based spintronics at room
temperature",1711.00406v1
2017/11/26,Magnetization and Thermal Entanglement of the Spin-1 Ising-Heisenberg Polymer Chain,"We establish a solvable Heisenberg-Ising model on a spin-1 Ni-containing
polymer chain, $[Ni (NN'-dmen) (\mu-N_3)_2]$, with $NN'-dmen$ being
$NN'-dimethylethylenediamine$, that fully covers the interaction
characteristics of the material and by which, we can characterize all the
peculiar magnetic features of the polymer, which has been partly studied in
experiment. By purely analytical calculations, we can see that the
magnetization exhibits three plateaus at zero, mid, and 3/4 of the saturation
value at low temperatures below 2 K. The corresponding featuring peaks of
magnetic susceptibility are clearly shown. The model also displays plateaus in
thermal entanglement that captures the one-to-one correspondence between
thermal entanglement plateaus and those of the magnetization. The calculations
are done by the transfer matrix technique.",1711.09350v1
2017/12/4,Magnetic fields: a tool for the study of organic solar cells,"Charge transfer in polymer devices represents a crucial, though highly
inaccessible stage of photocurrent generation. In this article we propose
studying the properties and behaviour of organic solar cells through the
modification of photocurrent generation when an external magnetic field is
applied. By allowing the parameters of our theoretical model not to be
constrained to any specific material, we are able to show that not only a
modest external magnetic field leads to a significant increase in photocurrent
intensity, but also how such magnetic field can be used to study in detail the
energy levels and transition rates within the polymer compound. Systematic
exploration of key properties in organic composites thus can lead to highly
optimised devices in which a magnetic field produces an enhancement in the
efficiency of polymer solar cells.",1712.01165v2
2017/12/8,Generation of a localized microwave magnetic field by coherent phonons in a ferromagnetic nanograting,"A high-amplitude microwave magnetic field localized at the nanoscale is a
desirable tool for various applications within the rapidly developing field of
nanomagnetism. Here, we drive magnetization precession by coherent phonons in a
metal ferromagnetic nanograting and generate ac-magnetic induction with
extremely high amplitude (up to $10$ mT) and nanometer scale localization in
the grating grooves. We trigger the magnetization by a laser pulse which
excites localized surface acoustic waves. The developed technique has
prospective uses in several areas of research and technology, including
spatially resolved access to spin states for quantum technologies.",1712.03027v1
2017/12/28,Large intrinsic anomalous Hall effect in half-metallic ferromagnet Co3Sn2S2 with magnetic Weyl fermions,"The origin of anomalous Hall effect (AHE) in magnetic materials is one of the
most intriguing aspect in condensed matter physics and has been controversial
for a long time. Recent studies indicate that the intrinsic AHE is closely
related to the Berry curvature of occupied electronic states. In a magnetic
Weyl semimetal with broken time-reversal symmetry, there are significant
contributions on Berry curvature around Weyl nodes, which would lead to a large
intrinsic AHE. Here, we report the large intrinsic AHE in the half-metallic
ferromagnet Co3Sn2S2 single crystal. By systematically mapping out the
electronic structure of Co3Sn2S2 theoretically and experimentally, the large
intrinsic AHE should originate from the Weyl fermions near the Fermi energy.
Furthermore, the intrinsic anomalous Hall conductivity depends linearly on the
magnetization and this can be attributed to the sharp decrease of magnetization
and the change of topological characteristics.",1712.09947v1
2018/1/29,Current-induced spin-orbit torques in ferromagnetic and antiferromagnetic systems,"Spin-orbit coupling in inversion-asymmetric magnetic crystals and structures
has emerged as a powerful tool to generate complex magnetic textures,
interconvert charge and spin under applied current, and control magnetization
dynamics. Current-induced spin-orbit torques mediate the transfer of angular
momentum from the lattice to the spin system, leading to sustained magnetic
oscillations or switching of ferromagnetic as well as antiferromagnetic
structures. The manipulation of magnetic order, domain walls and skyrmions by
spin-orbit torques provides evidence of the microscopic interactions between
charge and spin in a variety of materials and opens novel strategies to design
spintronic devices with potentially high impact in data storage, nonvolatile
logic, and magnonic applications. This paper reviews recent progress in the
field of spin-orbitronics, focusing on theoretical models, material properties,
and experimental results obtained on bulk noncentrosymmetric conductors and
multilayer heterostructures, including metals, semiconductors, and topological
insulator systems. Relevant aspects for improving the understanding and
optimizing the efficiency of nonequilibrium spin-orbit phenomena in future
nanoscale devices are also discussed.",1801.09636v2
2018/2/16,"Role of typical elements in Nd$_{2}$Fe$_{14}$$X$ ($X$ = B, C, N, O, F)","The magnetic properties and structural stability of Nd$_{2}$Fe$_{14}X$ ($X$ =
B, C, N, O, F) are theoretically studied by first-principles calculations
focusing on the role of $X$. We find that B reduces the magnetic moment (per
formula unit) and magnetization (per volume) in Nd$_{2}$Fe$_{14}$B. The
crystal-field parameter $A_2^0 \langle r^2 \rangle$ of Nd is not enhanced
either, suggesting that B has minor roles in the uniaxial magnetocrystalline
anisotropy of Nd. These findings are in contrast to the long-held belief that B
works positively for the magnetic properties of Nd$_{2}$Fe$_{14}$B. As $X$
changes from B to C, N, O and F, both the magnetic properties and stability
vary significantly. The formation energies of Nd$_{2}$Fe$_{14}X$ and
$\alpha$-Fe relative to that of Nd$_{2}$Fe$_{17}X$ are negative for $X$ = B and
C, whereas they are positive when $X$ = N, O and F. This indicates that B plays
an important role in stabilizing the Nd$_{2}$Fe$_{14}$B phase.",1802.05817v1
2018/2/20,Comparison of the Magnetic properties of Mn3Fe2Si3O12 as a crystalline garnet and as a glass,"The crystalline garnet Mn3Fe2Si3O12 and an amorphous phase of the same
nominal composition are synthesized at high pressure. The magnetic properties
of the two forms are reported. Both phases order antiferromagnetically. The
crystalline phase exhibits a Curie-Weiss theta of -47.2 K, with a sharp
ordering transition at 12 K. The glassy phase exhibits a larger
antiferromagnetic Curie-Weiss theta, of -83.0 K, with a broad ordering
transition observed at 2.5 K. Both phases can be classified as magnetically
frustrated, although the amorphous phase shows a much higher degree of
frustration. The amorphous phase exhibits spin-glass behavior and is determined
to have an actual composition of Mn3Fe2Si3O13.",1802.07360v1
2018/2/23,Emulating topological chiral magnetic effects in artificial Weyl semimetals,"We realized highly tunable Weyl semimetal-bands and subsequently emulated the
topological chiral magnetic effects in superconducting quantum circuits.
Driving the superconducting quantum circuits with elaborately designed
microwave fields, we mapped the momentum space of a lattice to the parameter
space, realizing the Hamiltonian of a Weyl semimetal. By measuring the energy
spectrum, we directly imaged the Weyl points of cubic lattices, whose
topological winding numbers were further determined from the Berry curvature
measurement. In particular, we used an additional microwave field to produce a
momentum-dependent chemical potential, from which the chiral magnetic
topological current was extracted in the presence of an artificial magnetic
field. This pure topological current is proportional to the magnetic field,
which is in contrast to the famous Ampere's law, and may have significant
impacts on topological materials and quantum devices.",1802.08371v2
2018/2/28,Voigt effect-based wide-field magneto-optical microscope integrated in a pump-probe experimental setup,"In this work we describe an experimental setup for spatially-resolved
pump-probe experiment with integrated wide-field magneto-optical (MO)
microscope. The MO microscope can be used to study ferromagnetic materials with
both perpendicular-to-plane and in-plane magnetic anisotropy via polar Kerr and
Voigt effects, respectively. The functionality of the Voigt effect-based
microscope was tested using an in-plane magnetized ferromagnetic semiconductor
(Ga,Mn)As. It was revealed that the presence of mechanical defects in the
(Ga,Mn)As epilayer alters significantly the magnetic anisotropy in their
proximity. The importance of MO experiments with simultaneous temporal and
spatial resolutions was demonstrated using (Ga,Mn)As sample attached to a
piezoelectric actuator, which produces a voltage-controlled strain. We observed
a considerably different behavior in different parts of the sample that enabled
us to identify sample parts where the epilayer magnetic anisotropy was
significantly modified by a presence of the piezostressor and where it was not.
Finally, we discuss the possible applicability of our experimental setup for
the research of compensated antiferromagnets, where only MO effects even in
magnetic moments are present.",1802.10534v1
2018/3/3,"Dynamics in a one-dimensional ferrogel model: relaxation, pairing, shock-wave propagation","Ferrogels are smart soft materials, consisting of a polymeric network and
embedded magnetic particles. Novel phenomena, such as the variation of the
overall mechanical properties by external magnetic fields, emerge consequently.
However, the dynamic behavior of ferrogels remains largely unveiled. In this
paper, we consider a one-dimensional chain consisting of magnetic dipoles and
elastic springs between them as a simple model for ferrogels. The model is
evaluated by corresponding simulations. To probe the dynamics theoretically, we
investigate a continuum limit of the energy governing the system and the
corresponding equation of motion. We provide general classification scenarios
for the dynamics, elucidating the touching/detachment dynamics of the magnetic
particles along the chain. In particular, it is verified in certain cases that
the long-time relaxation corresponds to solutions of shock-wave propagation,
while formations of particle pairs underlie the initial stage of the dynamics.
We expect that these results will provide insight into the understanding of the
dynamics of more realistic models with randomness in parameters and
time-dependent magnetic fields.",1803.01225v1
2018/3/5,Measurement independent magnetocaloric effect in Mn-rich Mn-Fe-Ni-Sn(Sb/In) Heusler alloys,"We report a systematic study on the magneto-structural transition in Mn-rich
Fe-doped Mn-Fe-Ni-Sn(Sb/In) Heusler alloys by keeping the total valence
electron concentration (e/a ratio) fixed. The martensitic transition (MT)
temperature is found to shift by following a proportional relationship with the
e/a ratio of the magnetic elements alone. The magnetic entropy change across MT
for a selected sample (Mn49FeNi40Sn9In) has been estimated from three different
measurement methods (isofield magnetization (M) vs temperature (T), isothermal
M vs field (H) and heat capacity (HC) vs T). We observed that though the peak
value of magnetic entropy change changes with the measurement methods, the
broadened shape of the magnetic entropy change vs T curves and the
corresponding cooling power (~140 Jkg-1) remains invariant. The equivalent
adiabatic temperature change ~ -2.6 K has been obtained from indirect
measurements of temperature change. Moreover, an exchange bias field ~ 783 Oe
at 5 K and a magnetoresistance of -30% are also obtained in one of these
materials.",1803.01566v3
2018/3/20,All-optical nonequilibrium pathway to stabilizing magnetic Weyl semimetals in pyrochlore iridates,"Nonequilibrium many-body dynamics is becoming one of the central topics of
modern condensed matter physics. Floquet topological states were suggested to
emerge in photodressed band structures in the presence of periodic laser
driving. Here we propose a viable nonequilibrium route without requiring
coherent Floquet states to reach the elusive magnetic Weyl semimetallic phase
in pyrochlore iridates by ultrafast modification of the effective
electron-electron interaction with short laser pulses. Combining \textit{ab
initio} calculations for a time-dependent self-consistent reduced Hubbard $U$
controlled by laser intensity and nonequilibrium magnetism simulations for
quantum quenches, we find dynamically modified magnetic order giving rise to
transiently emerging Weyl cones that are probed by time- and angle-resolved
photoemission spectroscopy. Our work offers a unique and realistic pathway for
nonequilibrium materials engineering beyond Floquet physics to create and
sustain Weyl semimetals. This may lead to ultrafast, tens-of-femtoseconds
switching protocols for light-engineered Berry curvature in combination with
ultrafast magnetism.",1803.07447v2
2018/5/14,Unraveling the nature of magnetism of the 5$\boldsymbol{d^4}$ double perovskite Ba$_2$YIrO$_6$,"We report electron spin resonance (ESR) spectroscopy results on the double
perovskite Ba$_2$YIrO$_6$. On general grounds, this material is expected to be
nonmagnetic due to the strong coupling of the spin and orbital momenta of
Ir$^{5+}$ (5$d^4$) ions. However, controversial experimental reports on either
strong antiferromagnetism with static order at low temperatures or just a
weakly paramagnetic behavior have triggered a discussion on the breakdown of
the generally accepted scenario of the strongly spin-orbit coupled ground
states in the 5$d^4$ iridates and the emergence of a novel exotic magnetic
state. Our data evidence that the magnetism of the studied material is solely
due to a few percent of Ir$^{4+}$ and Ir$^{6+}$ magnetic defects while the
regular Ir$^{5+}$ sites remain nonmagnetic. Remarkably, the defect Ir$^{6+}$
species manifest magnetic correlations in the ESR spectra at $T\lesssim 20$ K
suggesting a long-range character of superexchange in the double prevoskites as
proposed by recent theories.",1805.05243v2
2018/5/23,Uncovering anisotropic magnetic phases via fast dimensionality analysis,"A quantitative geometric predictor for the dimensionality of magnetic
interactions is presented. This predictor is based on networks of superexchange
interactions and can be quickly calculated for crystalline compounds of
arbitrary chemistry, occupancy, or symmetry. The resulting data is useful for
classifying structural families of magnetic compounds. Starting with 42,520
compounds, we have classified and quantified compounds with $3d$ transition
metal cations. The predictor reveals trends in magnetic interactions that are
often not apparent from the space group of the compounds, such as triclinic or
monoclinic compounds that are strongly 2D. We present specific cases where the
predictor identifies compounds that should exhibit competition between 1D and
2D interactions, and how the predictor can be used to identify
sparsely-populated regions of chemical space with as-yet-unexplored topologies
of specific $3d$ magnetic cations. The predictor can be accessed for the full
list of compounds using a searchable web form, and further information on the
connectivity, symmetry, and valence of cation-anion and cation-cation
coordination can be freely exported.",1805.09433v1
2018/6/18,Magnetic properties of cobalt doped ZrO$_2$ nanoparticles: Evidence of Co segregation,"We synthesized pure and Co-doped (6.25 12.5 at.) ZrO$_2$ nanopowders in order
to study their magnetic properties.We analyzed magnetic behavior as a function
of the amount of Co and the oxygenation, which was controlled by low pressure
thermal treatments. As prepared pure and Co-doped samples are diamagnetic and
paramagnetic respectively. Ferromagnetism can be induced by performing low
pressure thermal treatments, which becomes stronger as the dwell time of the
thermal treatment is increased. This behavior can be reversed, recovering the
initial diamagnetic or paramagnetic behavior, by performing reoxidizing thermal
treatments. Also, a cumulative increase can be observed in the saturation of
the magnetization with the number of low pressure thermal treatments performed.
We believe that this phenomenon indicates that cobalt segregation induced by
the thermal treatments is the responsible for the magnetic properties of the
ZrO$_2$ Co system.",1806.06839v1
2018/6/28,Chemical- and hydrostatic-pressure effects on the Kitaev honeycomb material Na$_2$IrO$_3$,"The low-temperature magnetic properties of \tcr{polycrystalline}
Na$_2$IrO$_3$, a candidate material for the realization of a quantum
spin-liquid state, were investigated by means of muon-spin relaxation and
nuclear magnetic resonance methods under chemical and hydrostatic pressure. The
Li-for-Na chemical substitution promotes an inhomogeneous magnetic order,
whereas hydrostatic pressure (up to 3.9\,GPa) results in an enhancement of the
ordering temperature $T_\mathrm{N}$. In the first case, the inhomogeneous
magnetic order suggests either short- or long-range correlations of broadly
distributed $j=\,$\textonehalf\ Ir$^{4+}$ magnetic moments, reflecting local
disorder. The increase of $T_\mathrm{N}$ under applied pressure points at an
increased strength of three dimensional interactions arising from interlayer
compression.",1806.10766v4
2018/8/16,Dynamic multiferroicity of a ferroelectric quantum critical point,"Quantum matter hosts a large variety of phases, some coexisting, some
competing; when two or more orders occur together, they are often entangled and
cannot be separated. Dynamical multiferroicity, where fluctuations of electric
dipoles lead to magnetisation, is an example where the two orders are
impossible to disentangle. Here we demonstrate elevated magnetic response of a
ferroelectric near the ferroelectric quantum critical point (FE QCP) since
magnetic fluctuations are entangled with ferroelectric fluctuations. We thus
suggest that any ferroelectric quantum critical point is an \textit{inherent}
multiferroic quantum critical point. We calculate the magnetic susceptibility
near the FE QCP and find a region with enhanced magnetic signatures that
appears near the FE QCP, and controlled by the tuning parameter of the
ferroelectric phase. The effect is small but observable - we propose quantum
paraelectric strontium titanate as a candidate material where the magnitude of
the induced magnetic moments can be $\sim 5 \times 10^{-7} \mu_{B}$ per unit
cell near the FE QCP.",1808.05509v2
2018/8/25,Optically driven collective spin excitations and magnetization dynamics in the Néel-type skyrmion host GaV$_4$S$_8$,"GaV$_4$S$_8$ is a multiferroic semiconductor hosting magnetic cycloid (Cyc)
and N\'eel-type skyrmion lattice (SkL) phases with a broad region of thermal
and magnetic stability. Here, we use time-resolved magneto-optical Kerr
spectroscopy and micro-magnetic simulations to demonstrate the coherent
generation of collective spin excitations in the Cyc and SkL phases driven by
an optically-induced modulation of uniaxial anisotropy. Our results shed light
on spin-dynamics in anisotropic materials hosting skyrmions and pave a new
pathway for the optical control of their magnetic order.",1808.08476v1
2018/9/25,Two-dimensional parabolic Dirac system in the presence of non-magnetic and magnetic impurities,"We theoretically investigate the effect of the non-magnetic and magnetic
impurities to the 2D parabolic Dirac system. The induced charge density by the
charged impuri- ty is obtained by the linear response theory within the random
phase approximation. We also detailly calculate the RKKY interaction between
two magnetic impurities placed within the 2D sheet of the Dirac materials with
isotropic and anisotropic dis- persion. For the anisotropic dispersion, the
RKKY interaction is also anisotropic and related to the lattice parameters
which can be obtained throuh the DFT calculation or the experiments. The
fearures of the RKKY interaction also can be treated as a signature of the
topological phase transition as well as the change of Berry curvature. Our
results are also illuminating to the study of the static screening and the RKKY
interaction of the isotropic or anisotropic 3D Dirac or Weyl systems.",1809.09289v1
2018/9/29,Perpendicular magnetic anisotropy in bulk and thin-film CuMnAs for antiferromagnetic memory applications,"CuMnAs with perpendicular magnetic anisotropy is proposed as an active
material for antiferromagnetic memory. Information can be stored in the
antiferromagnetic domain state, while writing and readout can rely on the
existence of the surface magnetization. It is predicted, based on
first-principles calculations, that easy-axis anisotropy can be achieved in
bulk CuMnAs by substituting a few percent of As atoms by Ge, Si, Al, or B. This
effect is attributed to the changing occupation of certain electronic bands
near the Fermi level induced by the hole doping. The calculated temperature
dependence of the magnetic anisotropy does not exhibit any anomalies. Thin
CuMnAs(001) films are also predicted to have perpendicular magnetic anisotropy.",1810.00249v1
2018/10/31,Theory of chiral effects in magnetic textures with spin-orbit coupling,"We present a theoretical study of two-dimensional spatially and temporally
varying magnetic textures in the presence of spin-orbit coupling (SOC) of both
the Rashba and Dresselhaus types. We show that the effective gauge field due to
these SOCs, contributes to the dissipative and reactive spin torques in exactly
the same way as in electromagnetism. Our calculations reveal that Rashba
(Dresselhaus) SOC induces a chiral dissipation in interfacial (bulk) inversion
asymmetric magnetic materials. Furthermore, we show that in addition to chiral
dissipation $\alpha_c$, these SOCs also produce a chiral renormalization of the
gyromagnetic ratio $\tilde{\gamma}_c$, and show that the latter is
intrinsically linked to the former via a simple relation $\alpha_c =
(\tau/\tau_{\rm ex}) \tilde{\gamma}_c$, where $\tau_{\rm ex}$ and $\tau$ are
the exchange time and the electron relaxation time, respectively. Finally, we
propose a theoretical scheme based on the Scattering theory to calculate and
investigate the properties of damping in chiral magnets. Our findings should in
principle provide a guide for material engineering of effects related to chiral
dynamics in magnetic textures with SOC.",1810.13065v1
2018/11/4,Supervised learning of an opto-magnetic neural network with ultrashort laser pulses,"The explosive growth of data and its related energy consumption is pushing
the need to develop energy-efficient brain-inspired schemes and materials for
data processing and storage. Here, we demonstrate experimentally that Co/Pt
films can be used as artificial synapses by manipulating their magnetization
state using circularly-polarized ultrashort optical pulses at room temperature.
We also show an efficient implementation of supervised perceptron learning on
an opto-magnetic neural network, built from such magnetic synapses.
Importantly, we demonstrate that the optimization of synaptic weights can be
achieved using a global feedback mechanism, such that the learning does not
rely on external storage or additional optimization schemes. These results
suggest there is high potential for realizing artificial neural networks using
optically-controlled magnetization in technologically relevant materials, that
can learn not only fast but also energy-efficient.",1811.01375v2
2018/12/4,Optical excitation of single- and multi-mode magnetization precession in Galfenol nanolayers,"We demonstrate a variety of precessional responses of the magnetization to
ultrafast optical excitation in nanolayers of Galfenol (Fe,Ga), which is a
ferromagnetic material with large saturation magnetization and enhanced
magnetostriction. The particular properties of Galfenol, including cubic
magnetic anisotropy and weak damping, allow us to detect up to 6 magnon modes
in a 120-nm layer, and a single mode with effective damping ${\alpha}_{eff}$ =
0.005 and frequency up to 100 GHz in a 4-nm layer. This is the highest
frequency observed to date in time-resolved experiments with metallic
ferromagnets. We predict that detection of magnetization precession approaching
THz frequencies should be possible with Galfenol nanolayers.",1812.01237v1
2018/12/13,Current-induced nucleation and dynamics of skyrmions in a Co-based Heusler alloy,"We demonstrate room-temperature stabilization of dipolar magnetic skyrmions
with diameters in the range of $100$ nm in a single ultrathin layer of the
Heusler alloy Co$_2$FeAl (CFA) under moderate magnetic fields. Current-induced
skyrmion dynamics in microwires is studied with a scanning Nitrogen-Vacancy
magnetometer operating in the photoluminescence quenching mode. We first
demonstrate skyrmion nucleation by spin-orbit torque and show that its
efficiency can be significantly improved using tilted magnetic fields, an
effect which is not specific to Heusler alloys and could be advantageous for
future skyrmion-based devices. We then show that current-induced skyrmion
motion remains limited by strong pinning effects, even though CFA is a magnetic
material with a low magnetic damping parameter.",1812.05345v1
2018/12/31,Electric field switching of the uniaxial magnetic anisotropy of an antiferromagnet,"Electric field control of magnetic anisotropy in ferromagnets has been
intensively pursued in spintronics to achieve efficient memory and computing
devices with low energy consumption. Compared with ferromagnets,
antiferromagnets hold huge potential in high-density information storage for
their ultrafast spin dynamics and vanishingly small stray field. However, the
switching of magnetic anisotropy of antiferromagnets via electric field remains
elusive. Here we use ferroelastic strain from piezoelectric materials to switch
the uniaxial magnetic anisotropy and the N\'eel order reversibly in
antiferromagnetic Mn2Au films with an electric field of only a few kV/cm at
room temperature. Owing to the uniaxial magnetic anisotropy, a ratchet-like
switching behavior driven by the N\'eel spin-orbit torque is observed in the
Mn2Au, which can be reversed by electric fields.",1812.11868v1
2019/1/15,"Group theoretical analysis of structural instability, vacancy ordering and magnetic transitions in the system troilite (FeS) - pyrrhotite (Fe$_{1-x}$S)","A group-theoretical framework to describe vacancy ordering and magnetism in
the Fe$_{1-x}$S system is developed. This framework is used to determine the
sequence of crystal structures consistent with the observed magnetic structures
of troilite (FeS), and to determine the crystallographic nature of the
low-temperature Besnus transition in Fe$_{0.875}$S. We conclude that the Besnus
transition is a magnetically driven transition characterised by the rotation of
the moments out of the ac-plane, accompanied by small atomic displacements that
lower the symmetry to triclinic at low temperatures. Based on our phase
diagram, we predict related magnetically driven phase transitions at low
temperatures in all the commensurate superstructures of pyrrhotite. The exact
nature of the transition is determined by the symmetry of the vacancy ordered
state Based on this we predict spin-flop transitions in 3C and 5C pyrrhotite
and a transition akin to the Besnus transition in 6C pyrrhotite. Furthermore,
we clarify that 3C and 4C pyrrhotite carry a ferrimagnetic moment whereas 5C
and 6C are antiferromagnetic.",1901.04756v1
2019/1/17,Spin filtering in CrI$_3$ tunnel junctions,"The recently discovered magnetism of two-dimensional (2D) van der Waals
crystals have attracted a lot of attention. Among these materials is CrI$_3$ -
a magnetic semiconductor exhibiting transitions between antiferromagnetic and
ferromagnetic orderings under the influence of an applied magnetic field. Here,
using first-principles methods based on density functional theory, we explore
spin-dependent transport in tunnel junctions formed of fcc Cu (111) electrodes
and a CrI$_3$ tunnel barrier. We find about 100% spin polarization of the
tunneling current for a ferromagnetically-ordered four-monolayer CrI$_3$ and
tunneling magnetoresistance of about 3,000% associated with a change of
magnetic ordering in CrI$_3$. This behavior is understood in terms of the spin
and wave-vector dependent evanescent states in CrI$_3$ which control the
tunneling conductance. We find a sizable charge transfer from Cu to CrI$_3$
which adds new features to the mechanism of spin-filtering in CrI$_3$-based
tunnel junctions. Our results elucidate the mechanisms of spin filtering in
CrI3 tunnel junctions and provide important insights for the design of
magnetoresistive devices based on 2D magnetic crystals.",1901.05993v1
2019/1/21,Ferromagnetic Kondo lattice behavior in Ce11Pd4In9,"We report on the low-temperature physical properties of a novel compound
Ce$_{11}$Pd$_4$In$_9$ that crystallizes with the orthorhombic
Nd$_{11}$Pd$_4$In$_9$-type crystal structure (space group $Cmmm$). The compound
exhibits ferromagnetic ordering at $T_{\rm {C}}$ = 18.6 K and an order-order
transition at $T_{\rm {t}}$ $\sim$~1.6 K, as inferred from the low-temperature
magnetic susceptibility, heat capacity and electrical resistivity data. In the
paramagnetic region, the electrical transport in Ce$_{11}$Pd$_4$In$_9$ is
dominated by Kondo effect. Below $T_{\rm {C}}$, a distinct contribution due to
ferromagnetic spin waves dominates the electrical resistivity data, while at
the lowest temperatures, the electrical transport and thermodynamic properties
are governed by strong electron-electron correlations. The features observed
conjointly hint at strongly correlated ground state in Ce$_{11}$Pd$_4$In$_9$ .",1901.06888v1
2019/1/21,Non-collinear coupling across RuCo and RuFe alloys,"Spintronic applications, which rely on spin torques for operation, would
greatly benefit from a non-collinear alignment between magnetizations of
adjacent ferromagnetic layers for maximum performance and reliability. We
demonstrate that such an alignment can be created and controlled by coupling
two ferromagnetic layers across magnetic coupling layers. These coupling layers
consist of a non-magnetic material, Ru, alloyed with ferromagnetic elements of
Co or Fe. Changing the composition and thickness of the coupling layer enables
control of the relative angle between the magnetizations of ferromagnetic
layers between 0 and 180 degrees. The onset of the non-collinear alignment
between ferromagnetic layers coincide with the advent of magnetic order in the
coupling layer. This study will map the range of concentrations and thicknesses
of RuCo and RuFe coupling layers that give rise to non-collinearity between Co
layers.",1901.07055v1
2019/2/26,A new class of nonreciprocal spin waves on the edges of 2D antiferromagnetic honeycomb nanoribbons,"Antiferromagnetic two-dimensional (2D) materials are currently under
intensive theoretical and experimental investigations in view of their
potential applications in antiferromagnet-based magnonic and spintronic
devices. Recent experimental studies revealed the importance of magnetic
anisotropy and Dzyaloshinskii-Moriya interactions (DMI) on the ordered ground
state and the magnetic excitations in these materials. Here we present a robust
classical field theory approach to analyze the effect of magnetic anisotropy
and Dzyaloshinskii-Moriya interactions (DMI) on the edge and bulk spin waves in
2D antiferromagnetic nanoribbons. We predict the existence of a new class of
nonreciprocal edge spin waves characterized by opposite polarizations in
opposite directions. These novel edge spin waves are induced by the DMI and are
fundamentally different from conventional nonreciprocal spin waves for which
the polarization is independent of the propagation direction. Aside this
breakthrough in the field of antiferromagnetic spin waves, the study further
analysis the effect of the edges structure on the magnetic excitations. In
particular, we show that anisotropic bearded edges nanoribbons act as magnetic
topological insulators with exceptionally interesting potentials for
applications in magnonics.",1902.09704v3
2019/3/4,Thermoelectric microscopy of magnetic skyrmions,"The magnetic skyrmion is a nanoscale topological object characterized by the
winding of the magnetic moments, appearing in magnetic materials with broken
inversion symmetry. Because of its low current threshold for driving, the
skyrmions have been intensely studied toward novel storage applications by
using electron-beam, X-ray, and visible light microscopies. Here, we show that
the skyrmions can be imaged via thermoelectric signals of spin-caloritronic
phenomena in combination with focused heating. We applied a local temperature
gradient to a CoFeB/Ta/W multilayer film with scanning a heating position and,
by exploiting a Hall bar structure, mapped the magnitude as well as the
direction of the resultant thermoelectric current distributions, which link to
skyrmions' inner magnetic textures. This method also enables the observation of
skyrmion dynamics under driving current pulses, being a useful imaging
technique for the development of skyrmion devices.",1903.01037v2
2019/4/8,Magnetic anisotropy and entropy change in trigonal Cr$_{0.62}$Te,"We present a comprehensive investigation on anisotropic magnetic and
magnetocaloric properties of the quasi-two-dimensional weak itinerant
ferromagnet trigonal Cr$_{0.62}$Te single crystals. Magnetic-anisotropy-induced
satellite transition $T^*$ is observed at low fields applied parallel to the
$ab$ plane below $T_c$. The $T^*$ is featured by an anomalous magnetization
downturn, similar to that in structurally related CrI$_3$, and shows a
monotonous shift towards lower temperature with increasing field.
Magnetocrystalline anisotropy is also reflected in magnetic entropy change
$\Delta S_M(T,H)$ and relative cooling power RCP. Given the high $T_c$,
Cr$_{0.62}$Te crystals are materials of interest for nanofabrication in basic
science and applied technology.",1904.04247v3
2019/4/29,Room-temperature structural phase transition in the quasi-2D spin-1/2 Heisenberg antiferromagnet Cu(pz)$_2$(ClO$_4$)$_2$,"Cu(pz)$_2$(ClO$_4$)$_2$ (with pz denoting pyrazine C$_4$H$_4$N$_2$) is a
two-dimensional spin-1/2 square-lattice antiferromagnet with $T_{\mathrm{N}}$ =
4.24 K. Due to a persisting focus on the low-temperature magnetic properties,
its room-temperature structural and physical properties caught no attention up
to now. Here we report a study of the structural features of
Cu(pz)$_2$(ClO$_4$)$_2$ in the paramagnetic phase, up to 330 K. By employing
magnetization, specific heat, $^{35}$Cl nuclear magnetic resonance, and neutron
diffraction measurements, we provide evidence of a second-order phase
transition at $T^{\star}$ = 294 K, not reported before. The absence of a
magnetic ordering across $T^{\star}$ in the magnetization data, yet the
presence of a sizable anomaly in the specific heat, suggest a structural
order-to-disorder type transition. NMR and neutron-diffraction data corroborate
our conjecture, by revealing subtle angular distortions of the pyrazine rings
and of ClO$^-_4$ counteranion tetrahedra, shown to adopt a configuration of
higher symmetry above the transition temperature.",1904.12802v1
2019/6/3,Stability of edge magnetism against disorder in zigzag MoS$_2$ nanoribbons,"Molybdenum disulfide nanoribbons with zigzag edges show ferromagnetic and
metallic properties based on previous \emph{ab-initio} calculations. The
investigation of the role of disorder on the magnetic properties is, however,
still lacking due to the computational costs of these methods. In this work we
fill this gap by studying the magnetic and electronic properties of several
nanometer long MoS$_2$ zigzag nanoribbons using tight-binding and Hubbard
Hamiltonians. Our results reveal that proper tight-binding parameters for the
edge atoms are crucial to obtain quantitatively the metallic states and the
magnetic properties of MoS$_2$ nanoribbons. With the help of the fine-tuned
parameters, we perform large-scale calculations and predict the spin
domain-wall energy along the edges, which is found to be significantly lower
compared to that of the zigzag graphene nanoribbons. The tight-binding approach
allows us to address the effect of edge disorder on the magnetic properties.
Our results open the way for investigating electron-electron effects in
realistic-size nanoribbon devices in MoS$_2$ and also provide valuable
information for spintronic applications.",1906.00568v1
2019/6/3,Oxygen-vacancy induced magnetic phase transitions in multiferroic thin films,"Multiferroics in which giant ferroelectric polarization and magnetism coexist
are of tremendous potential for engineering disruptive applications in
information storage and energy conversion. Yet the functional properties of
multiferroics are thought to be affected detrimentally by the presence of point
defects, which may be abundant due to the volatile nature of some constituent
atoms and high temperatures involved in materials preparation. Here, we
demonstrate with theoretical methods that oxygen vacancies may enhance the
functionality of multiferroics by radically changing their magnetic
interactions in thin films. Specifically, oxygen vacancies may restore missing
magnetic super-exchange interactions in large axial ratio phases, leading to
full antiferromagnetic spin ordering, and induce the stabilization of
ferrimagnetic states with a significant net magnetization of 0.5 uB per formula
unit. Our theoretical study should help to clarify the origins of long-standing
controversies in bismuth ferrite and improve the design of technological
applications based on multiferroics.",1906.01117v1
2019/6/4,Magnetoresistance in Metallic Ferroelectrics,"Polar metals with ferroelectric-like displacements in metals have been
achieved recently, half century later than Anderson and Blount's prediction.
However, the genuine ferroelectricity with electrical dipolar switching has not
yet been attained experimentally in the conducting materials, especially the
ones possessing magnetic responses. Here we report the coexistence of
ferroelectricity and magnetoresistance (MR) in the metallic PbNb0.12Ti0.88O3
(PNTO) thin films. We found that the conducting and magnetic responses of PNTO
films are highly asymmetric. Negative MR up to 50% is observed under an
in-plane magnetic field; the MR switches to positive with the magnetic field
applied parallel to the surface normal. Such unique behavior is attributed to
the moving electron caused effective magnetic field which couples with the
spins of electrons, which form a dynamic multiferroic state in the metallic
PNTO. These findings break a path to multiferroic metal and offer a great
potential to the multi-functional devices.",1906.01257v1
2019/6/6,Complete optical valley polarization in Weyl semimetals in strong magnetic fields,"We present a theory of an optically induced valley polarization in an
interacting, time-reversal symmetric Weyl semimetal placed under strong
magnetic fields. Because the application of a magnetic field reduces the
symmetry of the crystal, the optical absorption intensity differs at Weyl nodes
that were equivalent by symmetry at zero field. At strong magnetic field, the
difference in the absorption intensity reaches 100% for a sizeable frequency
interval of the incident light. This complete valley polarization originates
from interband transitions involving the chiral Landau level, and can be
controlled by changing the directions of the magnetic field and the light
propagation. We identify the splitting of $0\to 1$ or $-1\to 0$ inter Landau
level transitions as an observable signature of the complete valley
polarization, and discuss its manifestation in the TaAs family of materials.",1906.02607v1
2019/6/21,Magnetic domains without domain walls: a unique effect of He+ ion bombardment in ferrimagnetic Co/Tb multilayers,"We show that it is possible to engineer magnetic multi-domain configurations
without domain walls in a prototypical rare earth/transition metal ferrimagnet
using keV He+ ion bombardment. We additionally shown that these patterns
display a particularly stable magnetic configuration due to a deep minimum in
the free energy of the system which is caused by flux closure and the
corresponding reduction of the magnetostatic part of the total free energy.
This is possible because light-ion bombardment differently affects an elements
relative contribution to the effective properties of the ferrimagnet. The
impact of bombardment is stronger for rare earth elements. Therefore, it is
possible to influence the relative contributions of the two magnetic subsystems
in a controlled manner. The selection of material system and the use of
light-ion bombardment open a route to engineer domain patterns in continuous
magnetic films much smaller than what is currently considered possible.",1906.09318v1
2019/7/1,"Structural, magnetostatic and magnetodynamic studies of Co/Mo-based uncompensated synthetic antiferromagnets","In this work, we comprehensively investigate and discuss the structural,
magnetostatic, dynamic, and magnetoresistive properties of epitaxial Co/Mo
superlattices. The magnetization of the Co sublayers is coupled
antiferromagnetically with a strength that depends on the thickness of the
nonmagnetic Mo spacer. The magnetization and magnetoresistance hysteresis loops
clearly reflect interlayer exchange coupling and the occurrence of uniaxial
magnetic anisotropy induced by the strained Co sublayers. Upon accounting for a
deviation of the sublayer thicknesses from the nominal value, theoretical
modeling, including both micromagnetic and macrospin approaches, precisely
reproduces experimental magnetic hysteresis loops, magnetoresistance curves,
and ferromagnetic resonance dispersion relations. The Mo spacer thickness as a
function of the interlayer magnetic coupling is determined as a fitting
parameter by modeling the experimental results.",1907.00592v2
2019/8/23,Magnon Pairs and Spin-Nematic Correlation in the Spin-Seebeck Effect,"Investigating exotic magnetic materials with spintronic techniques is
effective at advancing magnetism as well as spintronics. In this work, we
report unusual field-induced suppression of the spin-Seebeck effect (SSE) in a
quasi one-dimensional frustrated spin-$\frac{1}{2}$ magnet LiCuVO$_4$, known to
exhibit spin-nematic correlation in a wide range of external magnetic field
$B$. The suppression takes place above $|B| > 2$ T in spite of the $B$-linear
isothermal magnetization curves in the same $B$ range. The result can be
attributed to the growth of the spin-nematic correlation while increasing $B$.
The correlation stabilizes magnon pairs carrying spin-2, thereby suppressing
the interfacial spin injection of SSE by preventing the spin-1 exchange between
single magnons and conduction electrons at the interface. This interpretation
is supported by integrating thermodynamic measurements and theoretical analysis
on the SSE.",1908.08701v1
2019/9/12,Single pulse all-optical toggle switching of magnetization without Gd: The example of Mn2RuxGa,"Energy-efficient control of magnetization without the help of a magnetic
field is a key goal of spintronics. Purely heat-induced single-pulse
all-optical toggle switching has been demonstrated, but so far only in Gd based
amorphous ferrimagnet films. In this work, we demonstrate toggle switching in
the half-metallic compensated ferrimagnetic Heusler alloys Mn2RuxGa, which have
two crystallographically-inequivalent Mn sublattices. Moreover, we observe the
switching at room temperature in samples that are immune to external magnetic
fields in excess of 1 T, provided they exhibit compensation above room
temperature. Observations of the effect in compensated ferrimagnets without Gd
challenges our understanding of all-optical switching. The dynamic behavior
indicates that Mn2RuxGa switches in 2 ps or less. Our findings widen the basis
for fast optical switching of magnetization and break new ground for engineered
materials that can be used for nonvolatile ultrafast switches using ultrashort
pulses of light.",1909.05809v2
2019/10/1,A high-throughput and data-mining approach to predict new rare-earth free permanent magnets,"We present an application of a high-throughput search of new rare-earth free
permanent magnets focusing on 3d-5d transition metal compounds. The search
involved a part of the ICSD database (international crystallographic structural
database), together with tailored search criteria and electronic structure
calculations of magnetic properties. Our results suggest that it possible to
find candidates for rare-earth free permanent magnets using a
data-mining/data-filtering approach. The most promising candidates identified
here are Pt$_2$FeNi, Pt$_2$FeCu, and W$_2$FeB$_2$. We suggest these materials
to be a good platform for further investigations in the search of novel
rare-earth free permanent magnets.",1910.00548v1
2019/10/3,Shaping Magnetite Nanoparticles from First-principles,"Iron oxide magnetic nanoparticles (NPs) are stimuli-responsive materials at
the forefront of nanomedicine. Their realistic finite temperature simulations
are a formidable challenge for first-principles methods. Here, we use density
functional tight binding to open up the required time and length scales and
obtain global minimum structures of Fe3O4 NPs of realistic size (1400 atoms,
2.5 nm) and of different shapes, which we then refine with hybrid density
functional theory methods to accomplish proper electronic and magnetic
properties, which have never been accurately described in simulations. On this
basis, we develop a general empirical formula and prove its predictive power
for the evaluation of the total magnetic moment of Fe3O4 NPs. By converting the
total magnetic moment into the macroscopic saturation magnetization, we
rationalize the experimentally observed dependence with shape. We also reveal
interesting reconstruction mechanisms and unexpected patterns of charge
ordering.",1910.01704v2
2019/10/9,Long and short range magnetism in the frustrated double perovskite Ba2MnWO6,"The structural and magnetic properties of the face-centered cubic double
perovskite Ba2MnWO6 were investigated using neutron powder diffraction,
DC-magnetometry, muon spin relaxation and inelastic neutron scattering.
Ba2MnWO6 undergoes Type II long-range antiferromagnetic ordering at a Neel
temperature of 8(1) K with a frustration index, f = 8. Inelastic neutron
scattering was used to identify the magnetic coupling constants J1 and J2,
which were found to equal -0.080 meV and -0.076 meV respectively. This
indicated that both of the magnetic coupling constants were antiferromagnetic
with similar magnitudes, which is in contrast to other known 3d metal double
perovskites Ba2MWO6. Above the Neel temperature, muon spin relaxation
measurements and inelastic neutron scattering techniques identify a short-range
correlated magnetic state that is similar to that observed in the archetypical
face-centered cubic lattice antiferromagnet MnO.",1910.03963v1
2019/9/14,The internal energies of Heisenberg magnetic systems,"The internal energies, including transverse and longitudinal parts, of
quantum Heisenberg systems for arbitrary spin S are investigated by the
double-time Green's function method. The expressions for ferromagnetic (FM) and
antiferromagnetic (AFM) systems are derived when one component of magnetization
is considered with the higher order longitudinal correlation functions being
carefully treated. An unexpected result is that around the order and disorder
transition points the neighboring spins in a FM (AFM) system are more likely
longitudinally antiparallel (parallel) than parallel (antiparallel) to each
other for S<=3/2 in spite of the FM (AFM) exchange between the spins. This is
attributed to the strong quantum fluctuation of the systems with small S
values. We also present the expressions of the internal energies of FM systems
when the three-component of magnetizations are considered.",1910.10068v1
2019/10/25,Möbius Insulator and Higher-Order Topology in MnBi$_{2n}$Te$_{3n+1}$,"We propose MnBi$_{2n}$Te$_{3n+1}$ as a magnetically tunable platform for
realizing various symmetry-protected higher-order topology. Its canted
antiferromagnetic phase can host exotic topological surface states with a
M\""obius twist that are protected by nonsymmorphic symmetry. Moreover, opposite
surfaces hosting M\""obius fermions are connected by one-dimensional chiral
hinge modes, which offers the first material candidate of a higher-order
topological M\""obius insulator. We uncover a general mechanism to feasibly
induce this exotic physics by applying a small in-plane magnetic field to the
antiferromagnetic topological insulating phase of MnBi$_{2n}$Te$_{3n+1}$, as
well as other proposed axion insulators. For other magnetic configurations, two
classes of inversion-protected higher-order topological phases are ubiquitous
in this system, which both manifest gapped surfaces and gapless chiral hinge
modes. We systematically discuss their classification, microscopic mechanisms,
and experimental signatures. Remarkably, the magnetic-field-induced transition
between distinct chiral hinge mode configurations provides an effective
""topological magnetic switch"".",1910.11906v2
2019/10/30,Origin of Ising magnetism in Ca3Co2O6 unveiled by orbital imaging,"The one-dimensional cobaltate Ca3Co2O6 is an intriguing material having an
unconventional magnetic structure, displaying quantum tunneling phenomena in
its magnetization. Using a newly developed experimental method, s-core-level
non-resonant inelastic x-ray scattering (s-NIXS), we were able to image the
atomic Co 3d orbital that is responsible for the Ising magnetism in this
system. We show that we can directly observe that it is the complex d2 orbital
occupied by the sixth electron at the high-spin Co-trig{3+} (d6) sites that
generates this behavior. This is extremely rare in the research field of
transition metal compounds, and is only made possible by the delicately
balanced prismatic trigonal coordination. The ability to directly relate the
orbital occupation with the local crystal structure is essential to model the
magnetic properties of this system.",1910.13750v1
2019/10/30,Magneto-dielectric coupling and non-ergodic electrical behaviour in hexagonal Sr0.6Ba0.4MnO3 via local strain driven magnetic ordering,"The crystal structure of hexagonal-Sr0.6Ba0.4MnO3 allows various competing
superexchange interactions, leading to intriguing magnetic properties. Local
structural changes modify overlapping between Mn and oxygen ions with
temperature. Calculations based on our model spin-Hamiltonian reveal that the
dominant linear antiferromagnetic superexchange interaction between the
oxygen-linked Mn4+ ions results in short range correlations (SRC), manifesting
a smooth drop in magnetization below 325K. Dominance of superexchange
interaction changes its allegiance towards the non-linear oxygen-linked Mn-O-Mn
interactions, onsetting long-range correlations (LRC) below 225K. Below the
SRC-LRC crossover temperature, electrical response arising from the interacting
dipoles exhibits power-law divergent behaviour of relaxation time, upon
cooling. Non-ergodic character of the dipole-cluster glass state is examined
via the indispensable aging and rejuvenation effects, similar to the spin
glasses. Competitive-frustration among spin-exchange and local-strain is
reckoned as responsible for the electrical glass origin.",1910.14446v1
2019/11/18,Zero- to Ultralow-Field Nuclear Magnetic Resonance $J$-Spectroscopy with Commercial Atomic Magnetometers,"Zero- to ultralow-field nuclear magnetic resonance (ZULF NMR) is an
alternative spectroscopic method to high-field NMR, in which samples are
studied in the absence of a large magnetic field. Unfortunately, there is a
large barrier to entry for many groups, because operating the optical
magnetometers needed for signal detection requires some expertise in atomic
physics and optics. Commercially available magnetometers offer a solution to
this problem. Here we describe a simple ZULF NMR configuration employing
commercial magnetometers, and demonstrate sufficient functionality to measure
samples with nuclear spins prepolarized in a permanent magnet or initialized
using parahydrogen. This opens the possibility for other groups to use ZULF
NMR, which provides a means to study complex materials without magnetic
susceptibility-induced line broadening, and to observe samples through
conductive materials.",1911.07554v1
2019/12/16,Loop Currents in Two-leg Ladder Cuprates,"New phases with broken discrete Ising symmetries are uncovered in quantum
materials with strong electronic correlations. The two-leg ladder cuprate
\textbf{$Sr_{14-x}Ca_{x}Cu_{24}O_{41}$} hosts a very rich phase diagram where,
upon hole doping, the system exhibits a spin liquid state ending to an
intriguing ordered magnetic state at larger $Ca$ content. Using polarized
neutron diffraction, we report here the existence of short range magnetism in
this material for two $Ca$ contents, whose origin cannot be ascribed to Cu
spins. This magnetism develops exclusively within the two-leg ladders with a
diffraction pattern at forbidden Bragg scattering which is the hallmark of loop
current-like magnetism breaking both time-reversal and parity symmetries. Our
discovery shows local discrete symmetry breaking in a one dimensional spin
liquid system as theoretically predicted. It further suggests that a loop
current-like phase could trigger the long range magnetic order reported at
larger doping in two-leg ladder cuprates.",1912.07757v2
2019/12/17,Electric dipole moment as descriptor for interfacial Dzyaloshinskii-Moriya interaction,"Chiral magnets are of fundamental interest and have important technological
ramifications. The origin of chiral magnets lies in the Dzyaloshinskii-Moriya
interaction (DMI), an interaction whose experimental and theoretical
determination is laborious. We derive an expression that identifies the
electric dipole moment as descriptor for the systematic design of chiral
magnetic multilayers. Using density functional theory calculations, we
determine the DMI of (111)-oriented metallic ferromagnetic $Z$/Co/Pt
multilayers of ultrathin films. The non-magnetic layer $Z$ determines the DMI
at the Co-Pt interface. The results validate the electric and magnetic dipole
moments as excellent descriptors. We found a linear relation between the
electric dipole moment of Pt, the Allen electronegativity of $Z$, and the
contribution of Pt to the total DMI.",1912.08014v3
2020/3/2,Successive dielectric anomalies and magnetoelectric coupling in honeycomb Fe$_4$Nb$_2$O$_9$,"By combining single crystal x-ray and neutron diffraction, and the
magnetodielectric measurements on single crystal Fe4Nb2O9, we present the
magnetic structure and the symmetry-allowed magnetoelectric coupling in
Fe4Nb2O9. It undergoes an antiferromagnetic transition at TN=93 K, followed by
a displacive transition at TS=70 K. The temperature-dependent dielectric
constant of Fe4Nb2O9 is strongly anisotropic with the first anomaly at 93 K due
to the exchange striction as a result of the long range spin order, and the
second one at 70 K emanating from the structural phase transition primarily
driven by the O atomic displacements. Magneticfield induced magnetoelectric
coupling was observed in single crystal Fe4Nb2O9 and is compatible with the
solved magnetic structure that is characteristic of antiferromagnetically
arranged ferromagnetic chains in the honeycomb plane. We propose that such
magnetic symmetry should be immune to external magnetic fields to some extent
favored by the freedom of rotation of moments in the honeycomb plane, laying
out a promising system to control the magnetoelectric properties by magnetic
fields.",2003.01029v1
2020/4/9,First-Principles Calculation of Spin and Orbital Contributions to Magnetically Ordered Moments in Sr$_{2}$IrO$_{4}$,"We show how an accurate first-principles treatment of the
canted-antiferromagnetic ground state of Sr$_2$IrO$_4$, a prototypical $5d$
correlated spin-orbit coupled material, can be obtained without invoking any
free parameters such as the Hubbard U or tuning the spin-orbit coupling
strength. Our theoretically predicted iridium magnetic moment of 0.250 $\mu_B$,
canted by 12.6$^{\circ}$ off the a-axis, is in accord with experimental
results. By resolving the magnetic moments into their spin and orbital
components, we show that our theoretically obtained variation of the magnetic
scattering amplitude $<M_{m}>$ as a function of the polarization angle is
consistent with recent non-resonant magnetic x-ray scattering measurements. The
computed value of the band gap (55 meV) is also in line with the corresponding
experimental values. A comparison of the band structure to that of the cuprates
suggests the presence of incommensurate charge-density wave phases in
Sr$_{2}$IrO$_{4}$.",2004.04759v1
2020/5/6,Spontaneous skyrmionic lattice from anisotropic symmetric exchange in a Ni-halide monolayer,"Topological spin structures, such as magnetic skyrmions, hold great promises
for data storage applications, thanks to their inherent stability. In most
cases, skyrmions are stabilized by magnetic fields in non-centrosymmetric
systems displaying the chiral Dzyaloshinskii-Moriya exchange interaction, while
spontaneous skyrmion lattices have been reported in centrosymmetric itinerant
magnets with long-range interactions. Here, a spontaneous anti-biskyrmion
lattice with unique topology and chirality is predicted in the monolayer of a
semiconducting and centrosymmetric metal halide, NiI$_2$. Our first-principles
and Monte Carlo simulations reveal that the anisotropies of the short-range
symmetric exchange, when combined with magnetic frustration, can lead to an
emergent chiral interaction that is responsible for the predicted topological
spin structures. The proposed mechanism finds a prototypical manifestation in
two-dimensional magnets, thus broadening the class of materials that can host
spontaneous skyrmionic states.",2005.02714v1
2020/5/21,Strain and electric-field control of spin-spin interactions in monolayer CrI$_3$,"We investigate the impact of mechanical strains and a perpendicular electric
field on the electronic and magnetic ground-state properties of two-dimensional
monolayer CrI$_3$ using density functional theory. We propose a minimal spin
model Hamiltonian, consisting of symmetric isotropic exchange interactions,
magnetic anisotropy energy, and Dzyaloshinskii-Moriya (DM) interactions, to
capture most pertinent magnetic properties of the system. We compute the
mechanical strain and electric field dependence of various spin-spin
interactions. Our results show that both the amplitudes and signs of the
exchange interactions can be engineered by means of strain, while the electric
field affects only their amplitudes. However, strain and electric fields affect
both the directions and amplitudes of the DM vectors. The amplitude of the
magnetic anisotropy energy can also be substantially modified by an applied
strain. We show that in comparison with an electric field, strain can be more
efficiently used to manipulate the magnetic and electronic properties of the
system. Notably, such systematic tuning of the spin interactions is essential
for the engineering of room-temperature spintronic nanodevices.",2005.10520v1
2020/5/28,Observation of a random singlet state in a diluted Kitaev honeycomb material,"We report a $^{35}$Cl nuclear magnetic resonance (NMR) study of the diluted
Kitaev material $\alpha$-Ru$_{1-x}$Ir$_x$Cl$_3$ ($x=0.1$ and $0.2$) where
non-magnetic Ir$^{3+}$ dopants substitute Ru$^{3+}$ ions. Upon dilution, the
$^{35}$Cl spectra exhibit unusual large magnetic inhomogeneity, which sets in
at temperatures below the Kitaev exchange energy scale. At the same time, the
$^{35}$Cl spin-lattice relaxation rate $T_1^{-1}$ as a function of dilution and
magnetic field unravels a critical doping of $x_c\approx 0.22$, towards which
both the field-induced spin gap and the zero-field magnetic ordering are
simultaneously suppressed, while novel gapless low-energy spin excitations
dominate the relaxation process. These NMR findings point to the stabilization
of a random singlet phase in $\alpha$-Ru$_{1-x}$Ir$_x$Cl$_3$, arising from the
interplay of dilution and exchange frustration in the quantum limit.",2005.13836v2
2020/6/2,Nonreciprocal second harmonic generation in a magnetoelectric material,"Nonreciprocal devices that allow the light propagation in only one direction
are indispensable in photonic circuits and emerging quantum technologies.
Contemporary optical isolators and circulators, however, require large size or
strong magnetic fields because of the general weakness of magnetic light-matter
interactions, which hinders their integration into photonic circuits. Aiming at
stronger magneto-optical couplings, a promising approach is to utilize
nonlinear optical processes. Here, we demonstrate nonreciprocal magnetoelectric
second harmonic generation (SHG) in CuB2O4. SHG transmission changes by almost
100% in a magnetic-field reversal of just 10 mT. The observed nonreciprocity
results from an interference between the magnetic-dipole- and
electric-dipole-type SHG. Even though the former is usually notoriously smaller
than the latter, it is found that a resonantly enhanced
magnetic-dipole-transition has a comparable amplitude as non-resonant
electric-dipole-transition, leading to the near-perfect nonreciprocity. This
mechanism could form one of the fundamental bases of nonreciprocity in
multiferroics, which is transferable to a plethora of magnetoelectric systems
to realize future nonreciprocal and nonlinear-optical devices.",2006.01728v1
2020/6/26,Quantum oscillations with magnetic hysteresis observed in CeTe$_{3}$ thin films,"We have performed magnetotransport measurements in CeTe$_{3}$ thin films down
to $0.2~{\rm K}$. It is known that CeTe$_{3}$ has two magnetic transitions at
$T_{\rm N1} \approx 3~{\rm K}$ and $T_{\rm N2} \approx 1~{\rm K}$. A clear
Shubnikov-de-Haas (SdH) oscillation was observed at $4~{\rm K}$, demonstrating
the strong two-dimensional nature in this material. Below $T_{\rm N2}$, the SdH
oscillation has two frequencies, indicating that the Fermi surface could be
slightly modulated due to the second magnetic transition. We also observed a
magnetic hysteresis in the SdH oscillation below $T_{\rm N1}$. Especially,
there is a unique spike in the magnetoresistance at $B \approx 0.6~{\rm T}$
only when the magnetic field is swept from a high enough field (more than
$2~{\rm T}$) to zero field.",2006.14955v2
2020/7/20,Rare earth engineering in RMn$_6$Sn$_6$ topological kagome magnets,"Exploration of the topological quantum materials with electron correlation is
at the frontier of physics, as the strong interaction may give rise to new
topological phases and transitions. Here we report that a family of kagome
magnets RMn$_6$Sn$_6$ manifest the quantum transport properties analogical to
those in the quantum-limit Chern magnet TbMn$_6$Sn$_6$. The topological
transport in the family, including quantum oscillations with nontrivial Berry
phase and large anomalous Hall effect arising from Berry curvature field,
points to the existence of massive Dirac fermions. Our observation demonstrates
a close relationship between rare-earth magnetism and topological electron
structure, indicating the rare-earth elements can effectively engineer the
Chern quantum phase in kagome magnets.",2007.09913v3
2020/8/2,Thermal stability for domain wall mediated magnetization reversal in perpendicular STT MRAM cells with W insertion layers,"We present an analytical model for calculating energy barrier for the
magnetic field-driven domain wall-mediated magnetization reversal of a
magneto-resistive random access memory (MRAM) cell and apply it to study
thermal stability factor $\Delta$ for various thicknesses of W layers inserted
into the free layer (FL) as a function of the cell size and temperature. We
find that, by increasing W thickness, the effective perpendicular magnetic
anisotropy (PMA) energy density of the FL film monotonically increases, but at
the same time, $\Delta$ of the cell mainly decreases. Our analysis shows that,
in addition to saturation magnetization $M_s$ and exchange stiffness constant
$A_\mathrm{ex}$ of the FL film, the parameter that quantifies the $\Delta$ of
the cell is its coercive field $H_c$, rather than the net PMA field $H_k$ of
the FL film comprising the cell.",2008.00412v2
2020/8/6,"Magnetic, transport, and thermal properties of $δ$-phase UZr$_2$","Alloys of hexagonal $\delta$-phase UZr$_2$ have been synthesized and studied
by means of heat capacity, magnetic susceptibility, magnetization, electrical
resistivity, magnetoresistance, thermoelectric power, thermal conductivity
measurements, for the first time, at temperatures from 1.8 to 300 K and in
magnetic fields up to 8 T. The weak temperature dependence of the magnetic
susceptibility and the small value of both Seebeck (0.75 $\mu$V/K at room
temperature) and of the Sommerfeld coefficient (13.5 mJ mol$^{-1}$ K$^{-2}$)
point to 5$f$-electrons in this material having a delocalized nature. The
electrical resistivity and magnetoresistance indicate the presence of
significant electronic disorder in $\delta$-UZr$_2$, consistent with the
disorder in its crystal structure. Density functional theory calculations have
been performed and compared to experimental results.",2008.02746v1
2020/8/7,Voltage-controlled magnetic anisotropy in antiferromagnetic MgO-capped MnPt films,"The magnetic anisotropy in MgO-capped MnPt films and its voltage control are
studied using first-principles calculations. Sharp variation of the magnetic
anisotropy with film thickness, especially in the Pt-terminated film, suggests
that it may be widely tuned by adjusting the film thickness. In thick films the
linear voltage control coefficient is as large as 1.5 and $-0.6$ pJ/Vm for
Pt-terminated and Mn-terminated interfaces, respectively. The combination of a
widely tunable magnetic anisotropy energy and a large voltage-control
coefficient suggest that MgO-capped MnPt films can serve as a versatile
platform for magnetic memory and antiferromagnonic applications.",2008.03249v2
2020/8/13,Comparison of measured and simulated spin-wave mode spectra of magnetic nanostructures,"Motivated by the importance of magnetization dynamics in nanomagnets for the
development and optimization of magnetic devices and sensors, we measured and
modeled spin wave spectra in patterned elliptical nanomagnets. Ferromagnetic
resonance spectra for multiple nanomagnets of Ni80Fe20 , fabricated by
electron-beam lithography to have nominal short-axes of 200 nm or 100 nm, were
measured by use of heterodyne magneto-optical microwave microscopy. Scanning
electron microscope images taken of the same nanomagnets were used to define
element shapes for micromagnetic simulations. Measured spectra show significant
differences between nominally identical nanomagnets, which could be only
partially attributed to uncontrolled shape variations in the patterning
process, as evidence by the limited agreement between the measured and
simulated spectra. Agreement between measurements and simulations was improved
by including a zone of reduced magnetization and exchange at the edges of the
nanomagnets in the simulations. Our results show that the reduction of shape
variations between individual magnetic random-access memory elements can
potentially improve their performance. However, unambiguous determination of
materials parameters in nanomagnets based on analysis and modeling of spin wave
spectra remains problematic.",2008.05662v1
2020/10/31,Long-Range Magnetic Exchange Pathways in Complex Clusters from First-Principles,"This work builds a bridge between density functional theory (DFT) and model
interpretations of Anderson's superexchange theory by constructing a
$f$-$d$-$p$ model with DFT Wannier functions to enable a direct quantum
many-body solution within an embedding approach. When applied to long-range
magnetic interactions in a Mn-Ce magnetic molecule, we are able to obtain
numerical insights about double exchange and superexchange interactions. Direct
metal-metal charge transfer processes are generally weak in this molecule,
which leads to small contributions from double exchange interactions. For
long-range interactions, Mn-Ce charge transfer is not significant compared to
Ce-O charge transfer. The unusual superexchange between Mn atoms with different
valence states is identified as the dominant mechanism. This procedure opens a
path for quantitative understanding of different exchange interactions in
complex magnetic systems, including molecular magnets, transition metal organic
frameworks, and other solid materials.",2011.00385v1
2020/11/2,How correlations change the magnetic structure factor of the kagome Hubbard model,"The kagome Hubbard model (KHM) is a paradigmatic example of a frustrated
two-dimensional model. While its strongly correlated regime, described by a
Heisenberg model, is of topical interest due to its enigmatic prospective
spin-liquid ground state, the weakly and moderately correlated regimes remain
largely unexplored. Motivated by the rapidly growing number of metallic kagome
materials (e.g., Mn$_3$Sn, Fe$_3$Sn$_2$, FeSn, Co$_3$Sn$_2$S$_2$,
Gd$_3$Ru$_4$Al$_{12}$), we study the respective regimes of the KHM by means of
three complementary numerical methods: the dynamical mean-field theory (DMFT),
the dynamical vertex approximation (D$\Gamma$A), and determinant quantum Monte
Carlo (DQMC). In contrast to the archetypal square-lattice, we find no
tendencies towards magnetic ordering, as magnetic correlations remain
short-range. Nevertheless, the magnetic correlations undergo a remarkable
crossover as the system approaches the metal-to-insulator transition. The Mott
transition itself does however not affect the magnetic correlations. Our
equal-time and dynamical structure factors can be used as a reference for
inelastic neutron scattering experiments on the growing family of metallic
kagome materials.",2011.01085v1
2020/11/3,Unravelling the Local Crystallographic Structure of Ferromagnetic Ga$_y$Fe$_{4-y}$N Nanocrystals Embedded in GaN,"In the Fe-doped GaN phase-separated magnetic semiconductor GaFeN, the
presence of embedded Ga$_y$Fe$_{4-y}$N nanocrystals determines the magnetic
properties of the system. Here, through a combination of anomalous x-ray
diffraction and diffraction anomalous fine structure, the local structure of Ga
in self-assembled face-centered cubic (fcc) Ga$_y$Fe$_{4-y}$N nanocrystals
embedded in wurtzite GaN thin layers is investigated in order to shed light
onto the correlation between fabrication parameters, local structural
arrangement and overall magnetic properties of the material system. It is
found, that by adjusting the growth parameters and thus, the crystallographic
surroundings, the Ga atoms can be induced to incorporate into 3$c$ positions at
the faces of the fcc crystal lattice, reaching a maximum occupancy of 30\%. The
magnetic response of the embedded nanocrystals is ferromagnetic with Curie
temperature increasing from 450\,K to 500\,K with the Ga occupation. These
results demonstrate the outstanding potential of the employed experimental
protocol for unravelling the local structure of magnetic multi-phase systems,
even when embedded in a matrix containing the same element under investigation.",2011.01699v1
2020/12/9,Spin-lattice model for cubic crystals,"We present a methodology based on the N\'{e}el model to build a classical
spin-lattice Hamiltonian for cubic crystals capable of describing magnetic
properties induced by the spin-orbit coupling like magnetocrystalline
anisotropy and anisotropic magnetostriction, as well as exchange
magnetostriction. Taking advantage of the analytical solutions of the N\'{e}el
model, we derive theoretical expressions for the parameterization of the
exchange integrals and N\'{e}el dipole and quadrupole terms that link them to
the magnetic properties of the material. This approach allows to build accurate
spin-lattice models with the desire magnetoelastic properties. We also explore
a possible way to model the volume dependence of magnetic moment based on the
Landau energy. This new feature can allow to consider the effects of
hydrostatic pressure on the saturation magnetization. We apply this method to
develop a spin-lattice model for BCC Fe and FCC Ni, and we show that it
accurately reproduces the experimental elastic tensor, magnetocrystalline
anisotropy under pressure, anisotropic magnetostrictive coefficients, volume
magnetostriction and saturation magnetization under pressure at
zero-temperature. This work could constitute a step towards large-scale
modeling of magnetoelastic phenomena.",2012.05076v3
2020/12/11,Boron Content and the Superconducting Critical Temperature of Carbon-Based Materials,"In this paper, we present results on magnetization properties of boron
nitride-carbon (BN-C) and boron carbide-carbon (B4C-C) granular mixtures. The
temperature-dependent magnetization for field-cooled during cooling and
field-cooled during warming shows a kind of thermal hysteresis that is always
seen around a metamagnetic phase transition from an antiferromagnetic
martensite to a ferromagnetic austenite phase. The low-temperature
magnetization has an upward turn that can be attributed to superparamagnetism,
diamagnetic shielding, and trapped flux characteristic to high-temperature
superconducting materials. After subtracting the diamagnetic background, the
field-dependent magnetization loops M(B) are ferromagnetic-like, more
significant for the BN-C than for the B4C-C mixture. In addition, the
magnetization loops show the kink feature characteristic to granular
superconductivity. The irreversibility temperature for a B4C-C mixture having
37.5 wt% B is Tc = 76 K. Combining our data with previous results on B-doped
diamond and Q-carbon, we find that Tc increases linearly with the B
concentration.",2012.06624v1
2020/12/17,Anomaly-induced sound absorption in Weyl semimetals,"We develop a semiclassical theory of sound absorption in Weyl semimetals in
magnetic fields. We focus on the contribution to the absorption that stems from
the existence of Berry monopoles in the band structure of such materials, or,
equivalently, due to the chiral anomaly and chiral magnetic effect. Sound
absorption is shown to come primarily from the motion of Weyl nodes in energy
space, associated with the propagation of a sound wave. We argue that acoustic
magneto-chiral dichroism, which occurs when absorption of sound is different
for opposite propagation directions, and for opposite directions of the
magnetic field, can be a definitive probe of band topology. The part of the
monopole-related sound magnetoabsorption that is even in the magnetic field is
negative in time-reversal Weyl materials. The difference in the sign of the
effect as compared to the positive anomaly-related transport magnetoconductance
stems from the existence of valley electrochemical imbalances without magnetic
field in the sound propagation problem. In centrosymmetric Weyl semimetals with
few Weyl nodes, the magneto-absorption is negative at low frequencies, but can
change sign with increasing frequency.",2012.09895v2
2020/12/20,Tuning the Magnetic and Electronic Properties of Strontium Titanate by Carbon Doping,"The magnetic and electronic properties of strontium titanate with different
carbon dopant configurations are explored using first-principles calculations
with a generalized gradient approximation (GGA) and the GGA+U approach. Our
results show that the structural stability, electronic properties and magnetic
properties of C-doped SrTiO3 strongly depend on the distance between carbon
dopants. In both GGA and GGA+U calculations, the doping structure is mostly
stable with a nonmagnetic feature when the carbon dopants are nearest
neighbors, which can be ascribed to the formation of a C-C dimer pair
accompanied by stronger C-C and weaker C-Ti hybridizations as the C-C distance
becomes smaller. As the C-C distance increases, C-doped SrTiO3 changes from an
n-type nonmagnetic metal to ferromagnetic/antiferromagnetic half-metal and to
an antiferromagnetic/ferromagnetic semiconductor in GGA calculations, while it
changes from a nonmagnetic semiconductor to ferromagnetic half-metal and to an
antiferromagnetic semiconductor using the GGA+U method. Our work demonstrates
the possibility of tailoring the magnetic and electronic properties of C-doped
SrTiO3, which might provide some guidance to extend the applications of
strontium titanate as a magnetic or optoelectronic material.",2012.10963v1
2020/12/24,Dynamical correlation enhanced orbital magnetization in VI$_{3}$,"The effect of electronic correlations on the orbital magnetization in real
materials has not been explored beyond a static mean-field level. Based on the
dynamical mean-field theory, the effect of electronic correlations on the
orbital magnetization in layered ferromagnet VI$_3$ has been studied. A
comparison drawn with the results obtained from density functional theory
calculations robustly establishes the crucial role of dynamical correlations in
this case. In contrast to the density functional theory that leads to
negligible orbital magnetization in VI$_3$, in dynamical mean-field approach
the orbital magnetization is greatly enhanced. Further analysis show that this
enhancement is mainly due to the enhanced local circulations of electrons,
which can be attributed to a better description of the localization behavior of
correlated electrons in VI$_3$. The conclusion drawn in our study could be
applicable to a wide range of layered materials in this class.",2012.13151v1
2021/1/18,Oxygen doping and polaron magnetic coupling in Alq$_3$ films,"The understanding of the Physics underlying the performances of organic
spin-valve devices is still incomplete. According to some recent models, spin
transport takes place in an impurity band inside the fundamental gap of organic
semiconductors. This seems to be confirmed by recent experiments performed with
La$_{0.7}$Sr$_{0.3}$MnO$_3$/Alq$_3$/AlO$_x$/Co devices. The reported results
suggest a possible correlation between the magnetoresistance and the variable
oxygen doping in the Alq$_3$ spacer. In this paper we investigate by means of
first-principles calculations the electronic and magnetic properties of O$_2$
molecules and ions in Alq$_3$ films to establish whether oxygen plays any
important role for spin transport in
La$_{0.7}$Sr$_{0.3}$MnO$_3$/Alq$_3$/AlO$_x$/Co devices. The conclusion is that
it does not. In fact, we show that O$_2$ molecules do not form an impurity band
and there is no magnetic interaction between them. In contrast, we suggest that
spin-transport may be enabled by the direct exchange coupling between Alq$_3^-$
ions.",2101.07303v1
2021/2/1,"Electronic, magnetic and galvanomagnetic properties of Co-based Heusler alloys: possible states of a half-metallic ferromagnet and spin gapless semiconductor","Parameters of the energy gap and, consequently, electronic, magnetic and
galvanomagnetic properties in different X$_2$YZ Heusler alloys can vary quite
strongly. In particular, half-metallic ferromagnets (HMFs) and spin gapless
semiconductors (SGSs) with almost 100% spin polarization of charge carriers are
promising materials for spintronics. The changes in the electrical, magnetic
and galvanomagnetic properties of the Co$_2$YSi (Y = Ti, V, Cr, Mn, Fe) and
Co$_2$MnZ Heusler alloys (Z = Al, Si, Ga, Ge) in possible HMF and/or SGS states
were followed and their interconnection was established. Significant changes in
the values of the magnetization and residual resistivity were found. At the
same time, the correlations between the changes in these electronic and
magnetic characteristics depending on the number of valence electrons and spin
polarization are observed.",2102.00952v1
2021/3/4,Defect-Induced Magnetic Skyrmion in Two-Dimensional Chromium Tri-Iodide Monolayer,"Chromium iodide monolayers, which have different magnetic properties in
comparison to the bulk chromium iodide, have been shown to form skyrmionic
states in applied electromagnetic fields or in Janus-layer devices. In this
work, we demonstrate that spin-canted solutions can be induced into monolayer
chromium iodide by select substitution of iodide atoms with isovalent
impurities. Several concentrations and spatial configurations of halide
substitutional defects are selected to probe the coupling between the local
defect-induced geometric distortions and orientation of chromium magnetic
moments. This work provides atomic-level insight into how atomically precise
strain-engineering can be used to create and control complex magnetic patterns
in chromium iodide layers and lays out the foundation for investigating the
field- and geometric-dependent magnetic properties in similar two-dimensional
materials.",2103.03149v1
2021/3/9,Spin-Space Groups and Magnon Band Topology,"Band topology is both constrained and enriched by the presence of symmetry.
The importance of anti-unitary symmetries such as time reversal was recognized
early on leading to the classification of topological band structures based on
the ten-fold way. Since then, lattice point group and non-symmorphic symmetries
have been seen to lead to a vast range of possible topologically nontrivial
band structures many of which are realized in materials. In this paper we show
that band topology is further enriched in many physically realizable instances
where magnetic and lattice degrees of freedom are wholly or partially
decoupled. The appropriate symmetry groups to describe general magnetic systems
are the spin-space groups. Here we describe cases where spin-space groups are
essential to understand the band topology in magnetic materials. We then focus
on magnon band topology where the theory of spin-space groups has its simplest
realization. We consider magnetic Hamiltonians with various types of coupling
including Heisenberg and Kitaev couplings revealing a hierarchy of enhanced
magnetic symmetry groups depending on the nature of the lattice and the
couplings. We describe, in detail, the associated representation theory and
compatibility relations thus characterizing symmetry-enforced constraints on
the magnon bands revealing a proliferation of nodal points, lines, planes and
volumes.",2103.05656v1
2021/3/15,Nonlinear magnetoelectric effect in atomic vapor,"Magnetoelectric (ME) effect refers to the coupling between electric and
magnetic fields in a medium resulting in electric polarization induced by
magnetic fields and magnetization induced by electric fields. The linear ME
effect in certain magnetoelectric materials such as multiferroics has been of
great interest due to its application in the fabrication of spintronics
devices, memories, and magnetic sensors. However, the exclusive studies on the
nonlinear ME effect are mostly centered on the investigation of second-harmonic
generation in chiral materials. Here, we report the demonstration of nonlinear
wave mixing of optical electric fields and radio-frequency (rf) magnetic fields
in thermal atomic vapor, which is the consequence of the higher-order nonlinear
ME effect in the medium. The experimental results are explained by comparing
with density matrix calculations of the system. We also experimentally verify
the expected dependence of the generated field amplitudes on the rf field
magnitude as evidence of the magnetoelectric effect. This study can open up the
possibility for precision rf-magnetometry due to its advantage in terms of
larger dynamic range and arbitrary frequency resolution.",2103.08168v1
2021/3/21,Analytical Investigation of Magneto-Plasmons in Anisotropic Multi-layer Planar Waveguides Incorporating Magnetically Biased Graphene Sheets,"This article proposes a novel analytical model for the anisotropic
multi-layer structures containing magnetically biased graphene sheets. The
multi-layer structure is composed of various magnetic materials. An external
magnetic field is applied, normal to the structure surface. Each graphene
sheet, with an anisotropic conductivity tensor, has been sandwiched between two
adjacent magnetic materials. Our model is used to find the dispersion relation
of the structure. Now, obtaining plasmonic features of the structure, such as
the effective index and propagation loss is straightforward. Four exemplary
structural variants have been investigated to show the richness of the proposed
general structure regarding the related specific plasmonic wave phenomena and
effects. These aspects are essential to form our structural design platform to
propose novel plasmonic devices such as biosensors, modulators, absorbers,
transparent electrodes, and tunable metamaterials in THz frequencies. A very
good agreement between the analytical and full-wave simulation results is seen.",2103.11452v1
2021/4/8,Probing the interplay between lattice dynamics and short-range magnetic correlations in CuGeO3 with femtosecond RIXS,"Investigations of magnetically ordered phases on the femtosecond timescale
have provided significant insights into the influence of charge and lattice
degrees of freedom on the magnetic sub-system. However, short-range magnetic
correlations occurring in the absence of long-range order, for example in
spin-frustrated systems, are inaccessible to many ultrafast techniques. Here,
we show how time-resolved resonant inelastic X-ray scattering (trRIXS) is
capable of probing such short-ranged magnetic dynamics in a charge-transfer
insulator through the detection of a Zhang-Rice singlet exciton. Utilizing
trRIXS measurements at the O K-edge, and in combination with model
calculations, we probe the short-range spin-correlations in the frustrated spin
chain material CuGeO3 following photo-excitation, revealing a strong coupling
between the local lattice and spin sub-systems.",2104.03557v1
2021/4/13,Table-like magnetocaloric effect and enhanced refrigerant capacity in EuO1-δ thin films,"An approach to adjusting the conduction band population for tuning the
magnetic and magnetocaloric response of EuO1-{\delta} thin films through
control of oxygen vacancies ({\delta} = 0, 0.025, and 0.09) is presented. The
films each showed a paramagnetic to ferromagnetic transition around 65 K, with
an additional magnetic ordering transition at higher temperatures in the oxygen
deficient samples. All transitions are observed to be of second order. A
maximum magnetic entropy change of 6.4 J/kg K over a field change of 2 T with a
refrigerant capacity of 223 J/kg was found in the sample with {\delta} = 0, and
in all cases the refrigerant capacities of the thin films under study were
found to exceed that reported for bulk EuO. Adjusting the oxygen content was
shown to produce table-like magnetocaloric effects, desirable for ideal
Ericsson-cycle magnetic refrigeration. These films are thus excellent
candidates for small-scale magnetic cooling technology in the liquid nitrogen
temperature range.",2104.05948v1
2021/4/20,First-principles study of magnetic structures of triangular antiferromagnets NaYbS$_2$ and NaYbO$_2$,"We investigate the magnetic interactions in triangular rare-earth
delafossites materials NaYbO$_2$ and NaYbS$_2$ via first-principles
calculations. The calculated Curie-Weiss temperatures are in good agreement
with experiments. We perform classical Monte Carlo simulations of the two
compounds using the extracted exchange parameters. We find that if only the
nearest neighbor interactions are considered, the magnetic ground states of
NaYbO$_2$ and NaYbS$_2$ are a stripe and a planar 120\degree~ N\'{e}el state,
respectively. The simulated transition temperatures are much higher than the
lowest experimental temperatures, where no magnetic ordering was observed.
However, we show by adding suitable second neighbor interactions, the {\it
classical} magnetic ground state of NaYbO$_2$ becomes to the $Z_2$ vortex
phase, and the simulated specific heat $C_v$ are very similar to the
experimental observations, with no obvious phase transition down to the
extremely low temperature.",2104.09739v1
2021/5/12,Phase transitions of the ferroelectric $(\mathrm{ND}_4)_2\mathrm{FeCl}_5\cdot\mathrm{D}_2\mathrm{O}$ under a magnetic field,"Due to the strong coupling between magnetism and ferroelectricity,
$(\mathrm{ND}_4)_2\mathrm{FeCl}_5\cdot\mathrm{D}_2\mathrm{O}$ exhibits several
intriguing magnetic and electric phases. In this letter, we include high-order
onsite spin anisotropic interactions in a spin model that successfully captures
the ferroelectric phase transitions of
$(\mathrm{ND}_4)_2\mathrm{FeCl}_5\cdot\mathrm{D}_2\mathrm{O}$ under a magnetic
field and produces the large weights of high-order harmonic components in the
cycloid structure that are observed from neutron diffraction experiments.
Moreover, we predict a new ferroelectric phase sandwiched between the FE II and
FE III phases in a magnetic field. Our results emphasize the importance of the
high-order spin anisotropic interactions and provide a guideline to understand
multiferroic materials with rich phase diagrams.",2105.05906v1
2021/5/26,Rare-earth tuned magnetism and magnetocaloric effects in double perovskites $R_2$NiMnO$_6$,"We present a comprehensive experimental study of magnetization and
magnetocaloric effect (MCE) in double perovskite (DP) materials $R_2$NiMnO$_6$
with $R =$ Pr, Nd, Sm, Gd, Tb, and Dy. While a paramagnetic to ferromagnetic
transition, with T$_{\rm C}$ in the range $\sim 100 - 200~$K, is a common
feature that can be attributed to the ordering of Mn$^{4+}$ and Ni$^{2+}$
magnetic moments, qualitatively distinct behavior depending on the choice of
$R$ is observed at low temperatures. These low-temperature anomalies in
magnetization are also manifest in the change in magnetic entropy, $-\Delta
S_{M}$, whose sign depends on the choice of $R$. In order to understand these
results, we present theoretical analysis based on mean-field approximation and
Monte Carlo simulations on a minimal spin model. The model correctly captures
the key features of the experimental observations.",2105.12331v1
2021/6/3,Two-Dimensional Bipolar Magnetic Semiconductor with High Curie Temperature and Electrically Controllable Spin Polarization Realized in Exfoliated Cr(pyrazine)$_2$ Monolayer,"Exploring two-dimensional (2D) magnetic semiconductors with room temperature
magnetic ordering and electrically controllable spin polarization is a highly
desirable but challenging task for nanospintronics. Here, through first
principles calculations, we propose to realize such a material by exfoliating
the recently synthesized organometallic layered crystal
Li$_{0.7}$[Cr(pyz)$_2$]Cl$_{0.7}$0.25$\cdot$(THF) (pyz = pyrazine, THF =
tetrahydrofuran) [Science 370, 587 (2020)]. The feasibility of exfoliation is
confirmed by the rather low exfoliation energy of 0.27 J/m$^2$, even smaller
than that of graphite. In exfoliated Cr(pyz)$_2$ monolayer, each pyrazine ring
grabs one electron from the Cr atom to become a radical anion, then a strong
$d$-$p$ direct exchange magnetic interaction emerges between Cr cations and
pyrazine radicals, resulting in room temperature ferrimagnetism with a Curie
temperature of 342 K. Moreover, Cr(pyz)$_2$ monolayer is revealed to be an
intrinsic bipolar magnetic semiconductor where electrical doping can induce
half-metallic conduction with controllable spin-polarization direction.",2106.01582v1
2021/6/3,Resonant Nonlinear Hall Effect in Two-Dimensional Electron Systems,"We study the Hall conductivity of a two-dimensional electron gas under an
inhomogeneous magnetic field $B(x)$. First, we prove using the quantum kinetic
theory that an odd magnetic field can lead to a purely nonlinear Hall response.
Second, considering a real-space magnetic dipole consisting of a sign-changing
magnetic field and based on numerical semiclassical dynamics, we unveil a
parametric resonance involving the cyclotron ratio and a characteristic width
of $B(x)$, which can greatly enhance the Hall response. Different from previous
mechanisms that rely on the bulk Berry curvature dipole, here, the effect
largely stems from boundary states associated with the real-space magnetic
dipole. Our findings pave a new way to engineer current rectification and
higher harmonic generation in two-dimensional materials having or not crystal
inversion symmetry.",2106.02001v2
2021/6/4,Frustration enhanced by Kitaev exchange in a $\boldsymbol{\tilde{j}_{\text{eff}}=\frac12}$ triangular antiferromagnet,"Triangular Heisenberg antiferromagnets are prototypes of geometric
frustration, even if for nearest-neighbor interactions quantum fluctuations are
not usually strong enough to destroy magnetic ordering: stronger frustration is
required to stabilize a spin-liquid phase. On the basis of static magnetization
and electron spin resonance measurements, we demonstrate the emergence of
${\tilde{j}_{\text{eff}}=\frac12}$ moments in the triangular-lattice magnet
Na$_2$BaCo(PO$_4$)$_2$. These moments are subject to an extra source of
frustration that causes magnetic correlations to set in far above both the
magnetic ordering and Weiss temperatures. Corroborating the
$\tilde{j}_{\text{eff}}=\frac12$ ground state, theory identifies ferromagnetic
Kitaev exchange anisotropy as additional frustrating agent, altogether putting
forward Na$_2$BaCo(PO$_4$)$_2$ as a promising Kitaev spin-liquid material.",2106.02437v2
2021/6/19,Multiple energy-scales in vertex-frustrated mesospin systems,"The interplay between topology and energy-hierarchy plays a vital role in the
collective magnetic order in artificial ferroic systems. Here we investigate,
experimentally, the effect of having one or two activation energies of
interacting Ising-like magnetic islands -- mesospins -- in thermalized,
vertex-frustrated lattices. The thermally arrested magnetic states of the
elements were determined using synchrotron-based magnetic microscopy after
cooling the samples from temperatures above the Curie temperature of the
material. Statistical analysis of the correlations between mesospins across
several length-scales, reveals changes in the magnetic order, reflecting the
amount of ground state plaquettes realized for a vertex-frustrated lattice. We
show that the latter depends on the presence, or not, of different activation
energies.",2106.10510v3
2021/6/22,Quantum-confined charge transfer that enhances magnetic anisotropy in lanthanum M-type hexaferrites,"Iron-based hexaferrites are critical-element-free permanent magnet components
of magnetic devices. Of particular interest is electron-doped M-type
hexaferrite i.e., LaFe$_{12}$O$_{19}$ (LaM) in which extra electrons introduced
by lanthanum substitution of barium/strontium play a key role in uplifting the
magnetocrystalline anisotropy. We investigate the electronic structure of
lanthanum hexaferrite using a \textit{localized} density functional theory
which reproduces semiconducting behavior and identifies the origin of the very
large magnetocrystalline anisotropy. Localized charge transfer from lanthanum
to the iron at the crystal's $2a$ site produces a narrow $3d_{z^2}$ valence
band strongly locking the magnetization along the $c$ axis. The calculated
uniaxial magnetic anisotropy energies from fully self-consistent calculations
are nearly double the single-shot values, and agree well with available
experiments. The chemical similarity of lanthanum to other rare earths suggests
that LaM can host for other rare earths possessing non-trivial $4f$ electronic
states for, \textit{e.g.,} microwave-optical quantum transduction.",2106.11947v1
2021/7/8,Self-consistently renormailzed spin-wave theory of layered ferromagnets on honeycomb lattice,"We develop a self-consistently renormalized spin-wave theory, within a
mean-field approximation, for the two-dimensional Heisenberg ferromagnet with
perpendicular easy-axis anisotropy on the honeycomb lattice, as well as its
few-layer and bulk extensions. In this method, the magnetization dependence on
temperature is found as the solution of the self-consistency equation.
Furthermore, we account for the physical difference of surface and bulk layers
by treating the layers as separate sublattices. Thus, the method can be readily
generalized to study various magnetic phenomena in a broad range of systems,
including those comprising magnetically inequivalent sublattices. Using our
theory, we calculate the temperature-dependent magnetization for two
chromium-based layered van der Waals insulating magnets, Cr$_2$Ge$_2$Te$_6$ and
CrI$_3$, employing various sets of Heisenberg exchange and single-ion
anisotropy values reported for these materials in the existing literature. As
expected, we observe a strong dimensionality effect where the ordering
temperature is reduced and its sensitivity on the anisotropy is enhanced with
the decrease of dimensionality.",2107.04085v1
2021/7/12,Large anomalous Nernst effect in non-crystalline Gd-Fe ferrimagnetic alloy films for flexible thermoelectric applications,"The anomalous Nernst effect (ANE), a heat-charge conversion mechanism based
on a magnetic metal, has been extensively studied for application in thin
thermoelectric devices. The low magnetization and fabrication at room
temperature are important for flexible ANE thermoelectric devices on plastic
substrates. Therefore, we investigated the ANE in ferrimagnetic GdxFe100-x
films with low magnetization in this study by systematically varying the Gd
composition x. Although the Gd33Fe67 film with a Gd composition close to
magnetic compensation composition exhibited very low magnetization, an ANE
coefficient |S_ANE| of 2.13 uV/K was obtained, which is close to the highest
value reported thus far. Finally, we demonstrated the ANE in a Gd33Fe67 film
deposited on a flexible sheet. A sufficient ANE voltage was obtained while
maintaining the flexibility of the sample, indicating the potential application
of this material in thermoelectric devices exploiting the ANE of Gd-Fe films.",2107.05215v2
2021/7/21,Pinning and gyration dynamics of magnetic vortices revealed by correlative Lorentz and bright-field imaging,"Topological magnetic textures are of great interest in various scientific and
technological fields. To allow for precise control of nanoscale magnetism, it
is of great importance to understand the role of intrinsic defects in the host
material. Here, we use conventional and time-resolved Lorentz microscopy to
study the effect of grain size in polycrystalline permalloy films on the
pinning and gyration orbits of vortex cores inside magnetic nanoislands. To
assess static pinning, we use in-plane magnetic fields to shift the core across
the island while recording its position. This enables us to produce highly
accurate two-dimensional maps of pinning sites. Based on this technique, we can
generate a quantitative map of the pinning potential for the core, which we
identify as being governed by grain boundaries. Furthermore, we investigate the
effects of pinning on the dynamic behavior of the vortex core using
stroboscopic Lorentz microscopy, harnessing a new photoemission source that
accelerates image acquisition by about two orders of magnitude. We find
characteristic changes to the vortex gyration in the form of increased
dissipation and enhanced bistability in samples with larger grains.",2107.10208v1
2021/7/23,Carrier-induced ferromagnetism in 2D magnetically-doped semiconductor structures,"We show theoretically that the magnetic ions, randomly distributed in a
two-dimensional (2D) semiconductor system, can generate a ferromagnetic
long-range order via the RKKY interaction. The main physical reason is the
discrete (rather than continuous) symmetry of the 2D Ising model of the
spin-spin interaction mediated by the spin-orbit coupling of 2D free carriers,
which precludes the validity of the Mermin-Wagner theorem. Further, the
analysis clearly illustrates the crucial role of the molecular field
fluctuations as opposed to the mean field. The developed theoretical model
describes the desired magnetization and phase-transition temperature $T_c$ in
terms of a single parameter; namely, the chemical potential $\mu$. Our results
highlight a path way to reach the highest possible $T_c$ in a given material as
well as an opportunity to control the magnetic properties externally (e.g., via
a gate bias). Numerical estimations show that magnetic impurities such as
Mn$^{2+}$ with spins $S=5/2$ can realize ferromagnetism with $T_c$ close to
room temperature.",2107.11377v1
2021/9/2,Multifold enhancement in magnetization of atomically thin Cobalt Telluride,"Magnetism in semiconductor two-dimensional (2D) materials is gaining
popularity due to its potential application in memory devices, sensors,
spintronic and biomedical applications. Here, 2D Cobalt Telluride (CoTe) has
been synthesized from its bulk crystals using a simple and scalable
liquid-phase exfoliation method. The atomically thin CoTe shows over four
hundred times enhancement in its magnetic saturation values compared to the
bulk form. The UV-Vis absorption spectra reveal superior absorption in the high
energy region, suggesting a semiconducting nature. Furthermore, we explain
bandgap and origin of high magnetic behavior by density functional theory (DFT)
calculations. The 2D CoTe shows a larger magnetism compared to bulk CoTe due to
the reduced coordination number of the surface atoms, shape anisotropy and
surface charge effect.",2109.02783v1
2021/9/7,Inertial spin dynamics in epitaxial cobalt films,"We investigate the spin dynamics driven by terahertz magnetic fields in
epitaxial thin films of cobalt in its three crystalline phases. The terahertz
magnetic field generates a torque on the magnetization which causes it to
precess for about 1 ps, with a sub-picosecond temporal lag from the driving
force. Then, the magnetization undergoes natural damped THz oscillations at a
frequency characteristic of the crystalline phase. We describe the experimental
observations solving the inertial Landau-Lifshitz-Gilbert equation. Using the
results from the relativistic theory of magnetic inertia, we find that the
angular momentum relaxation time $\eta$ is the only material parameter needed
to describe all the experimental evidence. Our experiments suggest a
proportionality between $\eta$ and the strength of the magneto-crystalline
anisotropy.",2109.03076v2
2021/10/7,Ultrafast element- and depth-resolved magnetization dynamics probed by transverse magneto-optical Kerr effect spectroscopy in the soft x-ray range,"We report on time- and angle-resolved transverse magneto-optical Kerr effect
spectroscopy in the soft x-ray range that, by analysis via
polarization-dependent magnetic scattering simulations, allows us to determine
the spatio-temporal and element-specific evolution of femtosecond laser-induced
spin dynamics in nanostructured magnetic materials. In a ferrimagnetic GdFe
thin film system, we correlate a reshaping spectrum of the magneto-optical Kerr
signal to depth-dependent magnetization dynamics and disentangle contributions
due to non-equilibrium electron transport and nanoscale heat diffusion on their
intrinsic time scales. Our work provides a quantitative insight into
light-driven spin dynamics occurring at buried interfaces of complex magnetic
heterostructures, which can be tailored and functionalized for future
opto-spintronic devices.",2110.03599v2
2021/12/1,Giant topological Hall effect in centrosymmetric tetragonal Mn2-xZnxSb,"Topological magnetism typically appears in noncentrosymmetric compounds or
compounds with geometric frustration. Here we report the effective tuning of
magnetism in centrosymmetric tetragonal Mn2-xZnxSb by Zn substitution. The
magnetism is found to be closely coupled to the transport properties, giving
rise to to a very large topological hall effect is possibly associated with
topological magnetism. Our finding suggests Mn2-xZnxSb is a candidate material
for the centrosymmetric tetragonal topological magnetic system, offers
opportunities for studying and tuning spin textures and developing near room
temperature spin-based devices.",2112.00805v1
2022/1/5,Magnetic sensitivity distribution of Hall devices in antiferromagnetic switching experiments,"We analyze the complex impact of the local magnetic spin texture on the
transverse Hall-type voltage in device structures utilized to measure
magnetoresistance effects. We find a highly localized and asymmetric magnetic
sensitivity in the eight-terminal geometries that are frequently used in
current-induced switching experiments, for instance to probe antiferromagnetic
materials. Using current-induced switching of antiferromagnetic NiO/Pt as an
example, we estimate the change in the spin Hall magnetoresistance signal
associated with switching events based on the domain switching patterns
observed via direct imaging. This estimate correlates with the actual
electrical data after subtraction of a non-magnetic contribution. Here, the
consistency of the correlation across three measurement geometries with
fundamentally different switching patterns strongly indicates a magnetic origin
of the measured and analyzed electrical signals.",2201.01572v1
2022/1/12,Microscopic probe of magnetic polarons in antiferromagnetic Eu$_{5}$In$_{2}$Sb$_{6}$,"Colossal magnetoresistance (CMR) emerges from intertwined spin and charge
degrees of freedom in the form of ferromagnetic clusters also known as trapped
magnetic polarons. As a result, CMR is rarely observed in antiferromagnetic
materials. Here we use electron spin resonance (ESR) to reveal microscopic
evidence for the formation of magnetic polarons in antiferromagnetic
Eu$_{5}$In$_{2}$Sb$_{6}$. First, we observe a reduction of the Eu$^{2+}$ ESR
linewidth as a function of the applied magnetic field consistent with
ferromagnetic clusters that are antiferromagnetically coupled. Additionally,
the Eu$^{2+}$ lineshape changes markedly below T' ~ 200 K, a temperature scale
that coincides with the onset of CMR. The combination of these two effects
provide strong evidence that magnetic polarons grow in size below T' and start
influencing the macroscopic properties of the system.",2201.04464v1
2022/2/4,Vector vorticity of skyrmionic texture: an internal degree of freedom tunable by magnetic field,"Different from the skyrmion driven by the Dzyaloshinskii-Moriya interaction
in non-centrosymmetric materials, the skyrmionic texture in centrosymmetric
magnet may possess the extra internal degrees of freedom, which greatly enrich
its morphologies, imply the continuous deformation allowed by topological
protection, and enable flexible tunability and potential functionality. To
describe the internal degree of freedom to full extent, the conventional
integer-valued scalar vorticity is extended into a vector vorticity with
continuous rotation allowed. The further simplified vorticity angle, together
with helicity angle, represents the whole rotation freedom of spin space. The
centrosymmetric magnet with frustration provides a perfect platform for
realizing a controllable manipulation on these internal degrees of freedom,
where the magnetic field can be applied to tune vorticity continuously in both
crystal and isolated forms of skyrmionic texture, and the helicity can be
further controlled by electric field. Moreover, the simulation reveals the
distinctive dynamic effects related to the vorticity modulation, namely, a
straight motion can be generated by rotating magnetic field to tune vorticity,
and the vorticity can also be controlled to modulate the dynamics induced by
the spin polarized current.",2202.02091v1
2022/2/16,Emergence of Intergranular Tunneling Dominated Negative Magnetoresistance in Helimagnetic Manganese Phosphide Nanorod Thin Films,"Helical magnets are emerging as a novel class of materials for spintronics
and sensor applications; however, research on their charge and spin transport
properties in a thin film form is less explored. Herein, we report the
temperature and magnetic field dependent charge transport properties of a
highly crystalline MnP nanorod thin film over a wide temperature range (2-350
K). The MnP nanorod films of 100 nm thickness were grown on Si substrates at
500 oC using molecular beam epitaxy. The temperature dependent resistivity data
exhibits a metallic behavior over the entire measured temperature range.
However, large negative magnetoresistance of up to 12% is observed below 50 K
at which the system enters a stable helical (screw) magnetic state. In this
temperature regime, the MR(H,T) dependence seems to show a magnetic field
manipulated phase coexistence. The observed magnetoresistance is dominantly
governed by the intergranular spin dependent tunneling mechanism. These
findings pinpoint a correlation between the transport and magnetism in this
helimagnetic system.",2202.07915v1
2022/3/1,Excitations in the ordered and paramagnetic states of honeycomb magnet Na2Co2TeO6,"Na2Co2TeO6 is a proposed approximate Kitaev magnet, yet its actual magnetic
interactions are elusive due to a lack of knowledge on the full excitation
spectrum. Here, using inelastic neutron scattering and single crystals, we
determine the system's temperature-dependent magnetic excitations over the
entire Brillouin zone. Without committing to specific models, we unveil a
distinct signature of the third-nearest-neighbor coupling in the spin waves,
which signifies the associated distance as an emerging ""soft link"" in the
ordered state. The presence of at least six non-overlapping spin-wave branches
is at odds with all models proposed to date. Above the ordering temperature,
persisting dynamic correlations can be described by equal-time magnetic
structure factors of a hexagonal cluster, which reveal the leading
instabilities. Our result sets definitive constraint on theoretical models for
Na2Co2TeO6 and provides new insight for the materialization of the Kitaev
model.",2203.00282v1
2022/3/10,Ultrafast optically induced magnetic state transition in 2D antiferromagnets,"Manipulating spin in antiferromagnetic (AFM) materials has great potential in
AFM opto-spintronics. Laser pulses can induce a transient ferromagnetic (FM)
state in AFM metallic systems, but have never been proven in two-dimensional
(2D) AFM semiconductors and related van der Waals (vdW) heterostructures. Here,
using 2D vdW heterostructures of FM MnS2 and AFM MXenes as prototypes, we
investigated optically induced interlayer spin transfer dynamics based on the
real-time time-dependent density functional theory (rt-TDDFT). We observed that
laser pulses induce significant spin injection and the interfacial
atom-mediated spin transfer from MnS2 to Cr2CCl2. In particular, we first
demonstrated the transient FM state in semiconducting AFM/FM heterostructures
during photoexcited processes. Because the proximity magnetism breaks the
magnetic symmetry of Cr2CCl2 in heterostructures. Our results provide the
microscopic understanding for optically controlled interlayer spin dynamics in
2D magnetic heterostructures and open a new way to manipulate magnetic orders
in ultrafast opto-spintronics.",2203.05124v1
2022/3/25,"Comment on ""Hysteretic transition between states of a filled hexagonal magnetic dipole cluster""","In the paper ""Andrew D.P. Smith, Peter T. Haugen, Boyd F. Edwards: Hysteretic
transition between states of a filled hexagonal magnetic dipole cluster,
Journal of Magnetism and Magnetic Materials 549 (2022): 168991"" a hysteretic
transition between two stable arrangements of a cluster of seven dipoles is
presented. The relative strength of the center dipole in a hexagonal
arrangement serves as the bifurcation parameter. The authors clearly
demonstrate the existence of two instabilities accompanied by discontinuous
jumps of the dipole arrangement, but leave the question about the nature of
these instabilities unanswered. This comment clarifies the nature of the two
instabilities: the first one is a symmetry-breaking sub-critical bifurcation
with parabolic scaling of the magnetic potential energy difference between the
two branches, and the second one is a fold with its characteristic scaling in
the form of a semi-cubic parabola.",2203.13670v3
2022/3/30,Nonvolatile Electric Field Control of Thermal Magnons in the Absence of an Applied Magnetic Field,"Spin transport through magnetic insulators has been demonstrated in a variety
of materials and is an emerging pathway for next-generation spin-based
computing. To modulate spin transport in these systems, one typically applies a
sufficiently strong magnetic field to allow for deterministic control of
magnetic order. Here, we make use of the well-known multiferroic
magnetoelectric, BiFeO3, to demonstrate non-volatile, hysteretic,
electric-field control of thermally excited magnon current in the absence of an
applied magnetic field. These findings are an important step toward
magnon-based devices, where electric-field-only control is highly desirable.",2203.16519v2
2022/4/10,Universal quantum computation based on nanoscale skyrmion helicity qubits in frustrated magnets,"Skyrmions in frustrated magnets have the helicity degree of freedom, where
two different configurations of Bloch-type skyrmions are energetically favored
by the magnetic dipole-dipole interaction and characterized by opposite
helicities. A skyrmion must become a quantum-mechanical object when its radius
is of the order of nanometer. We construct a qubit based on the two-fold
degeneracy of the Bloch-type nanoscale skyrmions in frustrated magnets. It is
shown that the universal quantum computation is possible based on nanoscale
skyrmions in a multilayered system. We explicitly show how to construct the
$\pi /4$ phase-shift gate, the Hadamard gate, and the CNOT gate. The one-qubit
quantum gates are materialized by temporally controlling the electric field and
the spin current. The two-qubit gate is materialized with the use of the
Ising-type exchange coupling by controlling the distance between the skyrmion
centers in two adjacent layers. The merit of the present mechanism is that an
external magnetic field is not necessary. Our results may open a possible way
toward universal quantum computations based on nanoscale topological spin
textures.",2204.04589v1
2022/4/21,Temperature-dependent magnetism in Fe foams via spin-lattice dynamics,"Spin-lattice dynamics is used to study the magnetic properties of Fe foams.
The temperature dependence of the magnetization in foams is determined as a
function of the fraction of surface atoms in foams, nsurf. The Curie
temperature of foams decreases approximately linearly with nsurf, while the
critical exponent of the magnetization increases considerably more strongly. If
the data are plotted as a function of the fraction of surface atoms, reasonable
agreement with recent data on vacancy-filled Fe crystals and novel data on
void-filled crystals is observed for the critical . Critical temperature and
critical exponent also depend on the coordination of surface atoms. Although
the decrease we find is relatively small, it hints to the possibility of
improved usage of topology to taylor magnetic properties.",2204.10123v1
2022/4/26,Chirality-Induced Noncollinear Magnetization and Asymmetric Domain-Wall Propagation in Hydrogenated CoPd Thin Films,"Array-patterned CoPd-based heterostructures are created through e-beam
lithography and plasma pretreatment that induces oxidation with depth gradient
in the CoPd alloy films, breaking the central symmetry of the structure.
Effects on the magnetic properties of the follow-up hydrogenation of the thin
film are observed via magneto-optic Kerr effect microscopy. The system exhibits
strong vertical and lateral antiferromagnetic coupling in the perpendicular
component between the areas with and without plasma pretreatment, and
asymmetric domain-wall propagation in the plasma-pretreated areas during
magnetization reversal. These phenomenon exhibit evident magnetic chirality and
can be interpreted with the Ruderman-Kittel-Kasuya-Yosida coupling and the
Dzyaloshinskii-Moriya interaction (DMI). The sample processing demonstrated in
this study allows easy incorporation of lithography techniques that can define
areas with or without DMI to create intricate magnetic patterns on the sample,
which provides an avenue towards more sophisticate control of canted spin
textures in future spintronic devices.",2204.12428v1
2022/6/5,Two Types of 3D Quantum Hall Effects in Multilayer WTe$_2$,"Interplay between the topological surface states and bulk states gives rise
to diverse exotic transport phenomena in topological materials. The recently
proposed Weyl orbit in topological semimetals in the presence of magnetic field
is a remarkable example. This novel closed magnetic orbit consists of Fermi
arcs on two spatially separated sample surfaces which are connected by the bulk
chiral zero mode, which can contribute to transport. Here we report
Shubnikov-de Haas (SdH) oscillation and its evolution into quantum Hall effect
(QHE) in multilayered type-II Weyl semimetal WTe2. We observe both the
three-dimensional (3D) QHE from bulk states by parallelly stacking of confined
two-dimensional layers in the low magnetic field region and the 3D QHE in the
quantized surface transport due to Weyl orbits in the high magnetic field
region. Our study of the two types of novel QHEs controlled by magnetic field
and our demonstration of the crossover between quantized bulk and surface
transport provide an essential platform for the future quantized transport
studies in topological semimetals.",2206.02253v2
2022/6/8,SmI3: 4f5 honeycomb magnet with spin-orbital entangled Γ7 Kramers doublet,"We report magnetic properties of a 4f-honeycomb iodide SmI3 made up of
edge-shared network of SmI6 octahedra. High temperature magnetic susceptibility
indicates {\Gamma}7 Kramers doublet ground state of Sm3+ (4f5) ions stabilized
by the spin-orbit coupling and octahedral crystal electric field, which
interact with Sm-I-Sm bond angle nearly 90 degree. Magnetization measurements
down to 0.1 K detected antiferromagnetic correlations and an anomaly in the
magnetization curve before saturation without a sign of long-range order.
Relevance between SmI3 and the antiferromagnetic Kitaev material proposed in
the 4f-electron system is discussed.",2206.03628v1
2022/7/7,Unraveling Thermally Induced Spin reorientation of Strongly Disordered NdFe0.5Cr0.5O3 System,"Sophisticated spin instruments require high-precision spin control. In this
study, we accurately study the intrinsic magnetic properties of the strongly
disordered system NdFe0.5Cr0.5O3 through molecular field models combined with
ASD theory. The three constituent sub-magnetic phases of the system are
separated, and their magnetization contributions are calculated separately.
Fitting the angle of the A/B magnetic moment at a given temperature, the
reorientation temperature point and temperature dependence of different
magnetic phases are obtained. This research will provide a very good
theoretical support for studying complex disordered systems and applying
high-precision spin control and lay a foundation for the design of new
functional materials.",2207.03220v1
2022/8/9,First-principles Study of Non-Collinear Spin Fluctuations Using Self-adaptive Spin-constrained Method,"Spin fluctuations have a substantial influence on the electron and lattice
behaviors in magnetic materials, which, however, is difficult to be tracked
properly by prevalent first-principles methods. We propose a versatile
self-adaptive spin-constrained density functional theory formalism. Applying it
to the simulation of itinerant ferromagnetic Fe, we present the potential
energy surface comprising longitudinal and transverse variations of
magnetization. Moreover, this method enables us to identify the delicate
coupling between the magnetic moments and other degrees of freedom by following
energy variation. As manifestations, magnetic interaction, electronic band
structure, and phonon dispersion curves are illustrated for single-layered
CrI$_3$ with excited magnetic configuration. All the above information can be
obtained not only for spin fluctuations but also for non-collinear spin
configurations with arbitrarily modulations; thus, it holds promise for future
applications in condensed-matter physics research.",2208.04551v6
2022/8/25,Chiral Phonons with Giant Magnetic Moments in a Topological Crystalline Insulator,"We have studied the magnetic response of transverse optical phonons in
Pb$_{1-x}$Sn$_{x}$Te films. Polarization-dependent terahertz
magnetospectroscopy measurements revealed Zeeman splittings and diamagnetic
shifts, demonstrating that these phonon modes become chiral in magnetic fields.
Films in the topological crystalline insulator phase ($x > 0.32$) exhibited
magnetic moment values that are larger than those for topologically trivial
films ($x < 0.32$) by two orders of magnitude. Furthermore, the sign of the
effective $g$-factor was opposite in the two phases, which can be explained by
our theoretical model. These results strongly indicate the existence of
interplay between the magnetic properties of chiral phonons and the topology of
electronic band structure.",2208.12235v3
2022/8/28,Spontaneous spin-valley polarization in NbSe2 at a van der Waals interface,"A proximity effect at a van der Waals (vdW) interface enables creation of an
emergent quantum electronic ground state. Here we demonstrate that an
originally-superconducting two-dimensional (2D) NbSe2 forms a ferromagnetic
ground state with spontaneous spin polarization at a vdW interface with a 2D
ferromagnet V5Se8. We investigated the anomalous Hall effect (AHE) of the
NbSe2/V5Se8 magnetic vdW heterostructures, and found that the sign of the AHE
was reversed as the number of the V5Se8 layer was thinned down to the monolayer
limit. Interestingly, the AHE signal of those samples was enhanced with the
in-plane magnetic fields, suggesting an additional contribution to the AHE
signal other than magnetization. This unusual behavior is well reproduced by
band structure calculations, where the emergence of the Berry curvature along
the spin-degenerate nodal lines in 2D NbSe2 by the in-plane magnetization plays
a key role, unveiling a unique interplay between magnetism and Zeeman-type
spin-orbit interaction in a non-centrosymmetric 2D quantum material.",2208.13150v2
2022/9/23,Ballistic transport and spin dependent anomalous quantum tunnelling in Rashba-Zeeman and bilayer graphene hybrid structures,"In this work, we have studied the spin-dependent ballistic transport and
anomalous quantum tunnelling in Bilayer Graphene (BLG) hybrid connected to two
Rashba-Zeeman (RZ) leads under an external electric biasing. We investigated
the transmission and conductance for the proposed system using scattering
matrix formalism and Landauer - Buttiker formula considering a double
delta-like barrier under a set of experimentally viable parameters. We found
that the transmission characteristics are notably different for up and down
spin incoming electrons depending upon the strength of magnetization. Moreover,
the transmission of up and down spin electrons is found to be magnetization
orientation dependent. The maximum tunnelling and conductance can be achieved
by tuning biasing energy and magnetization strength and choosing a material
with suitable Rashba Spin-Orbit Coupling (RSOC). This astonishing property of
our system can be utilized in fabricating devices like spin filters. We found
the Fano factor of our system is 0.4 under strong magnetization conditions
while it reduces to 0.3 under low magnetization conditions. Moreover, we also
noticed that the transmission and conductance significantly depend on the
Rashba - Zeeman effect. So, considering a suitable RZ material, the tunnelling
of the electrons can be tuned and controlled.",2209.11573v1
2022/10/7,Enhanced Magnetism in Heterostructures with Transition-Metal Dichalcogenide Monolayers,"Two-dimensional materials and their heterostructures have opened up new
possibilities for magnetism at the nanoscale. In this study, we utilize
first-principles simulations to investigate the structural, electronic, and
magnetic properties of $\textrm{Fe}/\textrm{WSe}_2/\textrm{Pt}$ systems
containing pristine, defective, or doped $\textrm{WSe}_2$ monolayers. The
proximity effects of the ferromagnetic Fe layer are studied by considering
defective and vanadium-doped $\textrm{WSe}_2$ monolayers. All heterostructures
are found to be ferromagnetic, and the insertion of the transition-metal
dichalcogenide results in a redistribution of spin orientation and an increased
density of magnetic atoms due to the magnetized $\textrm{WSe}_2$. There is an
increase in the overall total density of states at the Fermi level due to
$\textrm{WSe}_2$; however, the transition-metal dichalcogenide may lose its
distinct semiconducting properties due to the stronger than van der Waals
coupling. Spin-resolved electronic structure properties are linked to larger
spin Seebeck coefficients found in heterostructures with $\textrm{WSe}_2$
monolayers.",2210.03817v1
2022/10/14,Higher-order magnetic anisotropy in soft-hard magnetic materials,"We have computationally studied the properties of higher-order magnetic
anisotropy constants in an L10/A1-FePt coreshell system which is characterized
by a strong second-order 2-ion Fe-Pt anisotropy component. We show that the
coreshell structure induces an unexpected fourth-order anisotropy constant K2
the magnitude of which varies non-monotonically with the core-size ratio R
reaching a peak at R = 0.50. Furthermore, we find that K2 scales with the
normalized magnetization by (M/Ms)^2.2 at temperatures below the Curie
temperature - a remarkable deviation from the established Callen-Callen theory
which instead predicts a scaling exponent of 10. We construct an analytic model
which demonstrates K2 arises from the canting of the core and shell
magnetization, and successfully reproduces and justifies the scaling exponent
obtained from numerical simulation.",2210.07875v1
2022/10/25,Tuning of topological properties in the strongly correlated antiferromagnet Mn$_3$Sn via Fe doping,"Magnetic topological materials, in which strong correlations between magnetic
and electronic properties of matter, give rise to various exotic phenomena such
as anomalous Hall effect (AHE), topological Hall effect (THE), and skyrmion
lattice. Here, we report on the electronic, magnetic, and topological
properties of Mn$_{3-\it{x}}$Fe$_{\it{x}}$Sn single crystals ($\it{x}$=0, 0.25,
and 0.35). Low temperature magnetic properties have been significantly changed
with Fe doping. Most importantly, we observe that large uniaxial
magnetocrystalline anisotropy that is induced by the Fe doping in combination
with competing magnetic interactions at low temperature produce nontrivial
spin-texture, leading to large topological Hall effect in the doped systems at
low temperatures. Our studies further show that the topological properties of
Mn$_{3-\it{x}}$Fe$_{\it{x}}$Sn are very sensitive to the Fe doping.",2210.14150v1
2022/11/7,Dynamic self-organisation and pattern formation by magnon-polarons,"Nonlinear dynamics can give rise, via the processes of self-organisation and
pattern formation, to the spontaneous manifestation of order in open and
complex systems far from equilibrium. Self-organising systems, transforming the
inflow of energy into information, are ubiquitously found in current topical
areas of science ranging from brainwave entrainment and neuromorphic computing
to energy-efficient data storage technologies. In the latter, magnetic
materials play a pivotal role combining very fast switching with permanent
retention of information. However, it has been shown that, at very short time
scales, magnetisation dynamics become chaotic due to internal instabilities,
resulting in incoherent spin-wave excitations that ultimately destroy magnetic
ordering. Here, contrary to all expectations, we show that such chaos gives
rise to a periodic pattern of reversed magnetic domains, with a feature size
far smaller than the spatial extent of the excitation. We explain this pattern
as a result of phase-synchronisation of magnon-polaron waves, driven by strong
coupling of magnetic and elastic modes. Our results reveal not only the
peculiar formation and evolution of magnon-polarons at short time-scales, but
also present a novel mechanism of magnetization reversal driven by coherent
packets of short-wavelength quasiparticles.",2211.03723v1
2022/11/10,First-principles study on Small Polaron and Li diffusion in layered LiCoO2,"Li-ion conductivity is one of the essential properties that determine the
performance of cathode materials for Li-ion batteries. Here, using the density
functional theory, we investigate the polaron stability and its effect on the
Li-ion diffusion in layered LiCoO2 with different magnetic orderings. The
localized Co4+ polaron appears in the magnetic configurations and sets the
Li-diffusion barrier of ~0.34 eV. The polaron also migrates in the opposite
direction to the Li-diffusion direction. On the other hand, the polaron does
not form in the non-magnetic structure, and the Li diffusion barrier without
the polaron is 0.21 eV. Although the existence of the polaron increases the
diffusion barrier, the magnetically ordered structures are more energetically
stable during the migration than the non-magnetic case. Thus, our work
advocates the hole polaron migration scenario for Li-ion diffusion. Moreover,
we demonstrate that the strong electron correlation of Co ions plays an
essential role in stabilizing the Co4+ polaron.",2211.05464v1
2022/11/25,Single-walled Ising nanotube with opposite sign of interactions using Wang-Landau algorithm,"The effect of opposite sign of interactions in a single-walled Ising nanotube
is investigated using the Wang-Landau algorithm. The thermodynamic observables
are calculated from the estimated density of states (DOS) with and without the
presence of an external magnetic field. Irrespective of the applied magnetic
field, a symmetric trend of DOS is observed for opposite sign of interactions
which is in contrast to the asymmetric trend for same sign of interactions.
Further, two types of anti-ferromagnetic (AFM) orderings, namely A-type and
C-type anti-ferromagnetic order, are observed for opposite sign of
interactions. These AFM spin orientations are switched to ferromagnetic (FM)
phase by increasing the applied magnetic field ($B$). However, the spin
ordering changes from the ordered AFM/FM phase to a disordered paramagnetic
phase by increasing the temperature. Phase diagram shows that these three
phases coexist around $B=2.0$. This study indicates that, by properly tuning
the magnetic properties, the single-walled nanotube can be used for fabrication
of new types of magnetic storage nano materials.",2211.13880v1
2022/11/26,Spontaneous superconducting diode effect in non-magnetic Nb/Ru/Sr$_2$RuO$_4$ topological junctions,"Non-reciprocal electronic transport in a material occurs if both time
reversal and inversion symmetries are broken. The superconducting diode effect
(SDE) is an exotic manifestation of this type of behavior where the critical
current for positive and negative currents are mismatched, as recently observed
in some non-centrosymmetric superconductors with a magnetic field. Here, we
demonstrate a SDE in non-magnetic Nb/Ru/Sr$_2$RuO$_4$ Josephson junctions
without applying an external magnetic field. The cooling history dependence of
the SDE suggests that time-reversal symmetry is intrinsically broken by the
superconducting phase of Sr$_2$RuO$_4$. Applied magnetic fields modify the SDE
dynamically by randomly changing the sign of the non-reciprocity. We propose a
model for such a topological junction with a conventional superconductor
surrounded by a chiral superconductor with broken time reversal symmetry.",2211.14626v2
2022/12/22,Topological kagome magnets and superconductors,"A kagome lattice naturally features Dirac fermions, flat bands and van Hove
singularities in its electronic structure. The Dirac fermions encode topology,
flat bands favour correlated phenomena such as magnetism, and van Hove
singularities can lead to instabilities towards long-range many-body orders,
altogether allowing for the realization and discovery of a series of
topological kagome magnets and superconductors with exotic properties. Recent
progress in exploring kagome materials has revealed rich emergent phenomena
resulting from the quantum interactions between geometry, topology, spin and
correlation. Here we review these key developments in this field, starting from
the fundamental concepts of a kagome lattice, to the realizations of Chern and
Weyl topological magnetism, to various flat-band many-body correlations, and
then to the puzzles of unconventional charge-density waves and
superconductivity. We highlight the connection between theoretical ideas and
experimental observations, and the bond between quantum interactions within
kagome magnets and kagome superconductors, as well as their relation to the
concepts in topological insulators, topological superconductors, Weyl
semimetals and high-temperature superconductors. These developments broadly
bridge topological quantum physics and correlated many-body physics in a wide
range of bulk materials and substantially advance the frontier of topological
quantum matter.",2212.11628v1
2023/1/18,Cavity-controlled magneto-optical properties of a strongly coupled van der Waals magnet,"Controlling the properties of quantum materials with light is of fundamental
and technological importance. While high-power lasers may achieve this goal,
more practical strategies aim to exploit the strong coupling of light and
matter in optical cavities, which has recently been shown to affect elemental
physical phenomena, like superconductivity, phase transitions, and topological
protection. Here we report the capacity of strong light-matter coupling to
modify and control the magneto-optical properties of magnets. Tuning the
hybridization of magnetic excitons and cavity photons allows us to realize
distinct optical signatures of external magnetic fields and magnons in the
archetypal van der Waals magnetic semiconductor CrSBr. These results highlight
novel directions for cavity-controlled magneto-optics and the manipulation of
quantum material properties by strong light-matter coupling.",2301.07593v1
2023/1/19,The unexpected magnetism in 2D group-IV-doped GaN for spintronic applications,"In this study, the structural and magnetic properties of group-IV-doped
monolayer GaN were systematically investigated by first-principles
calculations. Among all the group-IV dopants, only Ge and Sn atoms prefer to
substitute the Ga atom of monolayer GaN and form a buckling structure with a
magnetic moment of 1 $\mu_B$ per dopant. The N-rich growth conditions are more
desirable for such a substitution process than the Ga-rich grow conditions.
With a large diffusion barrier vertical to the monolayer GaN, both Ge and Sn
atoms tend to stay on the same side of monolayer GaN with an antiferromagnetic
coupling between them. When intrinsic vacancies exist in monolayer GaN, the
magnetic moments of group-IV dopants vanish due to the charge transferring from
the dopants to Ga or N vacancies. The precondition creation of Ga vacancies, a
plentiful supply of Ge or Sn dopants, and the N-rich conditions can be adopted
to maintain the magnetic properties of group-IV-doped monolayer GaN. These
theoretical results help to promote the applications of 2D GaN-based materials
in spintronics.",2301.07866v2
2023/3/9,Spin-order-dependent magneto-elastic coupling in two dimensional antiferromagnetic MnPSe$_3$ observed through Raman spectroscopy,"Layered antiferromagnetic materials have emerged as a novel subset of the
two-dimensional family providing a highly accessible regime with prospects for
layer-number-dependent magnetism. Furthermore, transition metal phosphorous
trichalcogenides, MPX3 (M = transition metal; X = chalcogen) provide a platform
for investigating fundamental interactions between magnetic and lattice degrees
of freedom providing new insights for developing fields of spintronics and
magnonics. Here, we use a combination of temperature dependent Raman
spectroscopy and density functional theory to explore
magnetic-ordering-dependent interactions between the manganese spin degree of
freedom and lattice vibrations of the non-magnetic sub-lattice via a
Kramers-Anderson super-exchange pathway in both bulk, and few-layer, manganese
phosphorous triselenide (MnPSe$_3$). We observe a nonlinear temperature
dependent shift of phonon modes predominantly associated with the non-magnetic
sub-lattice, revealing their non-trivial spin-phonon coupling below the
N{\'e}el temperature at 74 K, allowing us to extract mode-specific spin-phonon
coupling constants.",2303.05554v2
2023/4/8,Possible high-temperature magnetically topological material Mn$_{3}$Bi$_{2}$Te$_{6}$,"The Mn-Bi-Te family displaying magnetism and non-trivial topological
properties has received extensive attention. Here, we predict that the
antiferromagnetic structure of Mn$_{3}$Bi$_{2}$Te$_{6}$ with three MnTe layers
is energetically stable and the magnetic coupling strength of Mn-Mn is enhanced
four times compared with that in the single MnTe layer of MnBi$_{2}$Te$_{4}$.
The predicted N\'eel transition point is higher than 77 K, the liquid-nitrogen
temperature. The topological properties show that with the variation of the
MnTe layer from a single layer to three layers, the system transforms from a
nontrivial topological phase to a trivial topological phase. Interestingly, the
ferromagnetic state of Mn$_{3}$Bi$_{2}$Te$_{6}$ is a topological semimetal and
it exhibits a topological transition from trivial to nontrivial induced by the
magnetic transition. Our results enrich the Mn-Bi-Te family system, offer a new
platform for studying topological phase transitions, and pave a new way to
improve the working temperature of magnetically topological devices.",2304.03971v1
2023/5/5,X-ray Magnetic Circular Dichroism in Altermagnetic $α$-MnTe,"Altermagnetism is a recently identified magnetic symmetry class combining
characteristics of conventional collinear ferromagnets and antiferromagnets,
that were regarded as mutually exclusive, and enabling phenomena and
functionalities unparalleled in either of the two traditional elementary
magnetic classes. In this work we use symmetry and ab initio theory to explore
X-ray magnetic circular dichroism (XMCD) in the altermagnetic class. Our
results highlight the distinct phenomenology in altermagnets of this
time-reversal symmetry breaking response, and its potential utility for
element-specific spectroscopy and microscopy in altermagnets. As a
representative material for our XMCD study we choose $\alpha$-MnTe with the
compensated antiparallel magnetic order in which an anomalous Hall effect has
been already demonstrated both in theory and experiment. The predicted
magnitude of XMCD lies well within the resolution of existing experimental
techniques.",2305.03588v2
2023/5/29,Point Defects in Two-Dimensional RuCl3,"Defects are crucial in determining a variety of material properties
especially in low dimensions. In this work, we study point defects in monolayer
alpha-phase Ruthenium (III) chloride (alpha-RuCl3), a promising candidate to
realize quantum spin liquid with nearly degenerate magnetic states. Our
first-principles simulations reveal that Cl vacancies, Ru vacancies, and oxygen
substitutional defects are the most energetically stable point defects.
Besides, these point defects break the magnetic degeneracy: Cl vacancies and
oxygen substitutional defects energetically favor the zigzag-antiferromagnetic
configuration while Ru vacancies favor the ferromagnetic configuration,
shedding light on understanding the observed magnetic structures and further
defect engineering of magnetism in monolayer {\alpha}-RuCl3. We further
calculated their electronic structures and optical absorption spectra. The
polarization symmetry of optical responses provides a convenient signature to
identify the point defect types and long-range magnetic orders.",2305.18560v1
2023/5/23,Probabilistic Spin Wave Computing with quasistatic magnetic inputs,"Spin wave computing device where an algorithm can be encoded by recording a
corresponding magnetization pattern onto a hard magnetic material was
previously proposed1 and a particular implementation of a vector-matrix
algorithm was demonstrated. In the present article we analyze the conditions
allowing for implementation of complex algorithms which can combine multiple
additive, multiplicative and conditional operators including logic expressions.
Special attention is given to how the input data is provided. Rather than
relying on a set of independent sources of the RF field as is common with the
existing spin wave computing methods we demonstrate usability of more simple
solutions using adjustable external quasistatic magnetic fields. We also show
how for the given setup probabilistic switching of magnetic elements at
elevated temperatures can be used to convert deterministic algorithms into a
probabilistic form.",2306.07976v1
2023/6/14,Dy adatom on MgO(001) substrate: DFT+U(HIA) study,"The electronic structure and magnetism of individual Dy atom adsorbed on the
MgO(001) substrate is investigated using the combination of the density
functional theory with the Hubbard-I approximation to the Anderson impurity
model (DFT+U(HIA)). The divalent Dy$^{2+}$ adatom in $f^{10}$ configuration is
found. The calculated x-ray absorption (XAS) and magnetic circular dichroism
(XMCD) spectra are compared to the experimental data. Quantum tunneling between
degenerate $|{J=8.0, J_z= \pm 4.0}>$ states leads to formation of $|{J=8.0,
J_z= 0.0}>$ ground state with an in-plane orientation of the magnetic moment.
It explains absence of remanent magnetization in MgO adatom on the top of
Mg(001) substrate. Our studies can provide a viable route for further
investigation and prediction of the rare-earth single atom magnets.",2306.08415v1
2023/6/28,Noise-dependent bias in quantitative STEM-EMCD experiments revealed by bootstrapping,"Electron magnetic circular dichroism (EMCD) is a powerful technique for
estimating element-specific magnetic moments of materials on nanoscale with the
potential to reach atomic resolution in transmission electron microscopes.
However, the fundamentally weak EMCD signal strength complicates quantification
of magnetic moments, as this requires very high precision, especially in the
denominator of the sum rules. Here, we employ a statistical resampling
technique known as bootstrapping to an experimental EMCD dataset to produce an
empirical estimate of the noise dependent error distribution resulting from
application of EMCD sum rules to bcc iron in a 3 beam orientation. We observe
clear experimental evidence that noisy EMCD signals preferentially bias the
estimation of magnetic moments, further supporting this with error
distributions produced by Monte-Carlo simulations. Finally, we propose
guidelines for the recognition and minimization of this bias in the estimation
of magnetic moments.",2306.15866v2
2023/7/5,Low temperature spin Seebeck effect in non-magnetic vanadium dioxide,"The spin Seebeck effect (SSE) is sensitive to thermally driven magnetic
excitations in magnetic insulators. Vanadium dioxide in its insulating low
temperature phase is expected to lack magnetic degrees of freedom, as vanadium
atoms are thought to form singlets upon dimerization of the vanadium chains.
Instead, we find a paramagnetic SSE response in VO2 films that grows as the
temperature decreases below 50 K. The field and temperature dependent SSE
voltage is qualitatively consistent with a general model of paramagnetic SSE
response and inconsistent with triplet spin transport. The microscopic nature
of the magnetic excitations in VO2 requires further examination.",2307.02594v1
2023/7/10,Angular dependence of spin-orbit torque in monolayer $Fe_3GeTe_2$,"In ferromagnetic systems lacking inversion symmetry, an applied electric
field can control the ferromagnetic order parameters through the spin-orbit
torque. The prototypical example is a bilayer heterostructure composed of a
ferromagnet and a heavy metal that acts as a spin current source. In addition
to such bilayers, spin-orbit coupling can mediate spin-orbit torques in
ferromagnets that lack bulk inversion symmetry. A recently discovered example
is the two-dimensional monolayer ferromagnet $Fe_3GeTe_2$. In this work, we use
first-principles calculations to study the spin-orbit torque and ensuing
magnetic dynamics in this material. By expanding the torque versus
magnetization direction as a series of vector spherical harmonics, we find that
higher order terms (up to $\ell=4$) are significant and play important roles in
the magnetic dynamics. They give rise to deterministic, magnetic field-free
electrical switching of perpendicular magnetization.",2307.04900v2
2023/7/12,Giant non-volatile electric field control of proximity induced magnetism in the spin-orbit semimetal SrIrO3,"With its potential for drastically reduced operation power of information
processing devices, electric field control of magnetism has generated huge
research interest. Recently, novel perspectives offered by the inherently large
spin-orbit coupling of 5d transition metals have emerged. Here, we demonstrate
non-volatile electrical control of the proximity induced magnetism in SrIrO3
based back-gated heterostructures. We report up to a 700 % variation of the
anomalous Hall conductivity {\sigma}_AHE and Hall angle {\theta}_AHE as
function of the applied gate voltage Vg. In contrast, the Curie temperature TC
= 100K and magnetic anisotropy of the system remain essentially unaffected by
Vg indicating a robust ferromagnetic state in SrIrO3 which strongly hints to
gating-induced changes of the anomalous Berry curvature. The electric-field
induced ferroelectric-like state of SrTiO3 enables non-volatile switching
behavior of {\sigma}_AHE and {\theta}_AHE below 60 K. The large tunability of
this system, opens new avenues towards efficient electric-field manipulation of
magnetism.",2307.06064v2
2023/7/12,Strongly anisotropic magnetocaloric effect in a dipolar magnet LiGdF$_4$,"We report the detailed study of the magnetocaloric effect (MCE) in a
dipolar-Heisenberg magnet LiGdF$_4$ using magnetization measurements performed
on a single crystal sample. Entropy variation on isothermal demagnetization
from the magnetic field up to 3 T is determined in the temperature range 2-10 K
for two principal directions of the applied field (parallel and perpendicular
to the tetragonal $c$-axis of the crystal). The MCE is found to be highly
anisotropic, with the cooling efficiency being up to twice higher at
$H\parallel c$. The results are nicely interpreted in the frame of a
conventional molecular field approach taking into account considerable
anisotropy of the paramagnetic Curie-Weiss temperature. These results are
compared to earlier studies of MCE in powder samples of LiGdF$_4$ [T. Numazawa
et al., AIP Conf. Proc. 850, 1579 (2006)] as well as with analogous data for
other well known magnetocaloric materials. Our findings may open new
possibilities to enhance the efficiency of magnetic refrigeration in the liquid
helium-4 temperature range.",2307.06111v2
2023/7/25,Quantum dot detects Majorana modes of both chiralities,"A tunneling junction between normal electrode and a topological
superconducting wire, mediated by a quantum dot, is considered theoretically.
We show that the presence of the dot in the junction can be advantageous to
Majorana zero modes identification. Namely, we demonstrate that for the dot
strongly coupled to the wire, the Majorana mode from the upper chiral sub-band
""leaks"" into the dot, providing supplementary information on Majorana mode
formation. Thus, both the Zeeman-split dot sub-levels detect Majorana partners
of a Kramers pair, formed at the wire end. The characteristic three-peak
structures in both spin sectors of the spectral density of the dot, distinguish
from the trivial scenario of one Andreev resonance at Fermi energy produced
exclusively by the dot's spin sub-levels.",2307.13366v1
2023/8/17,Competing Lattice Instability and Magnetism on the Surface of Kagome Metals,"The kagome lattice is usually covered by surface atomic layers or buried
inside the bulk of kagome crystals and little is known about the kagome layer
on a surface. In this work, we reveal that the kagome layer in $R$V$_6$Sn$_6$
($R$ = Y and rare-earth elements) exhibits strong lattice instabilities when
exposed on the surface, despite that it is stable inside the bulk. V atoms
constitute a nonmagnetic kagome lattice and present $\sqrt 3 \times \sqrt 3$
and $2 \times 2$ surface charge orders (SCOs). We find that such SCOs compete
with magnetism when the kagome lattice is magnetic. In $R$Mn$_6$Sn$_6$, SCOs
are completely suppressed by the magnetism in the Mn kagome lattice while they
appear again if magnetism is turned off in simulations. Our work reveals
unexpected surface instability and intimate spin-lattice interaction in kagome
materials.",2308.08771v2
2023/8/17,Dielectric Screening and Electric Field Control of Ferromagnetism at the CaMnO$_3$/CaRuO$_3$ Interface,"Control of magnetism by an applied electric field is a desirable technique
for the functionalization of magnetic materials. Motivated by recent
experiments, we study the electric field control of the interfacial magnetism
of CaRuO$_3$/CaMnO$_3$ (CRO/CMO) (001), a prototype interface between a
non-magnetic metal and an antiferromagnetic insulator. Even without the
electric field, the interfacial CMO layer acquires a ferromagnetic moment due
to a spin-canted state, caused by the Anderson-Hasegawa double exchange (DEX)
between the Mn moments and the leaked electrons from the CRO side. An electric
field would alter the carrier density at the interface, leading to the
possibility of controlling the magnetism, since DEX is sensitive to the carrier
density. We study this effect quantitatively usingdensity-functional
calculations in the slab geometry. We find a text-book like dielectric
screening of the electric field, which introduces polarization charges at the
interfaces and the surfaces. The extra charge at the interface enhances the
ferromagnetism via the DEX interaction, while away from the interface the
original AFM state of the Mn layers remains unchanged. The effect could have
potential application in spintronics devices.",2308.09155v1
2023/8/21,"Magnetic phases of electron-doped, infinite-layer Sr$_{1-x}$La$_x$CuO$_2$ from first-principles density functional calculations","The magnetic phases of electron-doped, infinite-layer
$\mathrm{Sr}_{1-x}\mathrm{La}_{x}\mathrm{CuO}_2$ are elucidated by
first-principles density functional calculations. We describe the
antiferromagnetic parent state, metallic phase transition, as well as lattice
structure evolution due to electron doping and external pressure that are
consistent with experiments where comparison is possible. We investigate
low-energy states with multiple magnetic configurations and study their
specific heat coefficients, magnetic exchange coupling, as well as the density
of states at Fermi level. The latter quantity is used to suggest the effects of
magnetic fluctuations on the electronic structure of this strongly correlated
material.",2308.10659v3
2023/7/28,Room-temperature quantum oscillations of static magnetic susceptibility of silicon-carbide epitaxial layers grown on a silicon substrate by the method of the coordinated substitution of atoms,"The article presents the results of measurement and analysis of the field
dependences of the static magnetic susceptibility of thin epitaxial silicon
carbide films grown on the (110) surface of single-crystal silicon by the
method of the coordinated substitution of atoms. In weak magnetic fields, the
occurrence of two quantum effects at room temperature was experimentally found:
the hysteresis of the static magnetic susceptibility and, in the field
dependences, quantum Aharonov-Bohm oscillations of the static magnetic
susceptibility. The simultaneous occurrence of these effects is a consequence
of two- and one-particle interference of charge carriers (two-dimensional
holes) on microdefects consisting of dipole centers with negative correlation
energy (negative-U dipole centers).",2308.12971v1
2023/9/8,Equilibrium and Nonequilibrium phase transitions in continuous symmetric classical magnets,"The magnetism is an old problem of Physics. Most interesting part of the
research on magnetism is its thermodynamic behaviour. In this review, the
thermodynamic phase transitions, mainly in ferromagnetic model systems, are
discussed. The model system has a characteristic of continuous symmetry. In
this context, the classical XY and Heisenberg model are chosen for discussion.
With a historical survey of such phase transition observed in such models, the
results of the recent (over two decades) studies are collected and reviewed.
The equilibrium phase transition in such systems are discussed to highlight the
dependence of the critical temperatures on the anisotropy, dilution etc. On the
other hand, the nonequilibrium results of such systems driven by time dependent
magnetic field, are also reviewed. We believe, this review is a modern
documentation and collection of works in the field of theoretical magnetism
which may be extremely useful for the researcher working in this field.",2309.04127v1
2023/10/2,Magnetic properties of the quasi-one-dimensional S = 1 spin chain antiferromagnet BaNiTe2O7,"We report a quasi-one-dimensional S = 1 spin chain compound BaNiTe2O7. This
magnetic system has been investigated by magnetic susceptibility, specific
heat, and neutron powder diffraction. These results indicate that BaNiTe2O7
develops a short-range magnetic correlation around T ~ 22 K. With further
cooling, an antiferromagnetic phase transition is observed at TN ~ 5.4 K.
Neutron powder diffraction revealed antiferromagnetic noncollinear order with a
commensurate propagation vector k = (1/2, 1, 0). The refined magnetic moment
size of Ni2+ at 1.5 K is 1.84{\mu}B, and its noncollinear spin texture is
confirmed by first-principles calculations. Inelastic neutron-scattering
results and density functional theory calculations confirmed the
quasi-one-dimensional nature of the spin systems.",2310.00853v1
2023/10/17,Layer-Selective Non-Reciprocal Electric-Field Switching of Magnetism in van der Waals Heterostructure Multiferroics,"Multiferroic materials provide robust and efficient routes for the control of
magnetism by electric fields, which has been diligently sought after for a long
time. The two-dimensional (2D) vdW multiferroics is a more exciting endeavour.
To date, the nonvolatile manipulation of magnetism through ferroelectric
polarization still remains challenging in a 2D vdW heterostructure
multiferroic. Here, we report a van der Waals (vdW) heterostructure
multiferroic comprising atomically thin layered antiferromagnet (AFM) CrI3 and
ferroelectric (FE) {\alpha}-In2Se3. We demonstrate anomalously layer-selective
nonreciprocal and nonvolatile electric-field control of magnetization by the
ferroelectric polarization. The nonreciprocal electric control originates from
an intriguing antisymmetric enhancement of interlayer ferromagnetic coupling in
the opposite ferroelectric polarization configurations of {\alpha}-In2Se3,
which favor to selectively switch the spins in the second layer. Our work
provides numerous possibilities for creating diverse heterostructure
multiferroics at the limit of few atomic layers for multi-stage magnetic
memories and brain inspired in-memory computing.",2310.10911v1
2023/11/12,Scaling Theory of Magnetic Order and Microwave Absorption in Amorphous and Granular Ferromagnets,"Magnetic order and microwave absorption in amorphous ferromagnets and
materials sintered from nanoscale ferromagnetic grains are investigated
analytically and numerically within the random-anisotropy model. We show that a
scaling argument specific to static randomness allows one to make conclusions
about the behavior of a large system with a weak disorder by studying a smaller
system with a strong disorder. The breakdown of the scaling on increasing the
strength of the magnetic anisotropy and/or the size of the grain separates two
distinct regimes in magnetic ordering and frequency dependence of the absorbed
microwave power. Analytical results are confirmed by numerical experiments on
spin lattices containing up to ten million spins. Our findings should help
design materials with desired magnetic and microwave properties. The method can
be extended to other systems with quenched randomness.",2311.06843v1
2023/11/16,Persistent anisotropy of the spin cycloid in BiFeO3 through ferroelectric switching,"A key challenge in antiferromagnetic spintronics is the control of spin
configuration on nanometer scales applicable to solid-state technologies.
Bismuth ferrite (BiFeO3) is a multiferroic material that exhibits both
ferroelectricity and canted antiferromagnetism at room temperature, making it a
unique candidate in the development of electric-field controllable magnetic
devices. The magnetic moments in BiFeO3 are arranged into a spin cycloid,
resulting in unique magnetic properties which are tied to the ferroelectric
order. Previous understanding of this coupling has relied on average, mesoscale
measurements to infer behavior. Using nitrogen vacancy-based diamond
magnetometry, we show that the spin cycloid can be deterministically controlled
with an electric field. The energy landscape of the cycloid is shaped by both
the ferroelectric degree of freedom and strain-induced anisotropy, restricting
the magnetization changes to specific ferroelectric switching events. This
study provides understanding of the antiferromagnetic texture in BiFeO3 and
paves new avenues for designing magnetic textures and spintronic devices.",2311.10169v1
2023/11/30,Growth of high-quality CrI3 single crystals and engineering of its magnetic properties via V and Mn doping,"CrI3, as a soft van der Waals layered magnetic material, has been widely
concerned and explored for its magnetic complexity and tunability. In this
work, high quality and large size thin CrI3, V and Mn doped single crystals
were prepared by chemical vapor transfer method. A remarkable irreversible
Barkhausen effect was observed in CrI3 and CrMn0.06I3, which can be attributed
to the low dislocation density that facilitates movement of the domain walls.
In addition, the introduction of the doping element Mn allows higher saturation
magnetization intensity. Cr0.5V0.5I3 exhibits substantially increased
coercivity force and larger magnetocrystalline anisotropy compared to CrI3,
while kept similar Curie temperature and good environmental stability. The
first principles calculations suggest direct and narrowed band gaps in
Cr0.5V0.5I3 and VI3 comparing to CrI3. The smaller band gaps and good hard
magnetic property make Cr0.5V0.5I3 an alternative choice to future research of
spintronic devices.",2311.18360v1
2023/12/12,Topological magnon-polaron transport in a bilayer van der Waals magnet,"The stacking of intrinsically magnetic van der Waals materials provides a
fertile platform to explore tunable transport effects of magnons, presenting
significant prospects for spintronic applications. The possibility of having
topologically nontrivial magnons in these systems can further expand the scope
of exploration. In this work, we consider a bilayer system with intralayer
ferromagnetic exchange and a weak interlayer antiferromagnetic exchange, and
study the topological magnon-polaron excitations induced by magnetoelastic
couplings. Under an applied magnetic field, the system features a metamagnetic
transition, where the magnetic ground state changes from antiparallel layers to
parallel. We show that the metamagnetic transition is accompanied by a
transition of the topological structure of the magnon polarons, which results
in discernible changes in the topology induced transport effects. The
magnetic-field dependence of the thermal Hall conductivity and spin Nernst
coefficient is analyzed with linear response theories.",2312.07463v2
2023/12/29,Spin-orbit torques and magnetization switching in Gd/Fe multilayers generated by current injection in NiCu alloys,"Light transition metals have recently emerged as a sustainable material class
for efficient spin-charge interconversion. We report measurements of
current-induced spin-orbit torques generated by Ni$_{1-x}$Cu$_{x}$ alloys in
perpendicularly magnetized ferrimagnetic Gd/Fe multilayers. We show that the
spin-orbit torque efficiency of Ni$_{1-x}$Cu$_{x}$ increases with the Ni/Cu
atomic ratio, reaching values comparable to those of Pt for Ni$_{55}$Cu$_{45}$.
Furthermore, we demonstrate magnetization switching of a 20-nm-thick Gd/Fe
multilayer with a threshold current that decreases with increasing Ni
concentration, similar to the spin-orbit torque efficiency. Our findings show
that Ni$_{1-x}$Cu$_{x}$$-$based magnetic heterostructures allow for efficient
control of the magnetization by electric currents.",2312.17652v1
2023/12/31,Kagomerization of transition metal monolayers induced by two-dimensional hexagonal boron nitride,"The kagome lattice is an exciting solid state physics platform for the
emergence of nontrivial quantum states driven by electronic correlations:
topological effects, unconventional superconductivity, charge and spin density
waves, and unusual magnetic states such as quantum spin liquids. While kagome
lattices have been realized in complex multi-atomic bulk compounds, here we
demonstrate from first-principles a process that we dub kagomerization, in
which we fabricate a two-dimensional kagome lattice in monolayers of transition
metals utilizing a hexagonal boron nitride (h-BN) overlayer. Surprisingly, h-BN
induces a large rearrangement of the transition metal atoms supported on a
fcc(111) heavy-metal surface. This reconstruction is found to be rather generic
for this type of heterostructures and has a profound impact on the underlying
magnetic properties, ultimately stabilizing various topological magnetic
solitons such as skyrmions and bimerons. Our findings call for a
reconsideration of h-BN as merely a passive capping layer, showing its
potential for not only reconstructing the atomic structure of the underlying
material, e.g. through the kagomerization of magnetic films, but also enabling
electronic and magnetic phases that are highly sought for the next generation
of device technologies.",2401.00516v1
2024/1/5,Improved Magnetoelectric Properties of TbMnO3 by low-level Fe3+ Substitution,"The correlation between static magnetoelectric coupling and magnetic
structures was investigated in $TbMn_{0.98}Fe_{0.02}O_{3}$ with magnetic field
up to 8 T and down to 2 K. Neutron diffraction experiments reveal a substantial
increase in the temperature dependence of the incommensurate modulation vector
of the antiferromagnetic phase, responsible for the significant increase in
magnetoelectric coupling, i.e., stronger changes of ferroelectric polarization
with applied magnetic field than in other multiferroic materials. This shows
that even a small 2% substitution of $Mn^{3+}$ by $Fe^{3+}$ significantly
enhances the destabilization of the incommensurably modulated magnetic
cycloidal structure of $TbMnO_{3}$ in a magnetic field above 5 T.",2401.02802v1
2024/1/19,Excess heat capacity in magnetically ordered Ce heavy fermion metals,"We study the magnetic heat capacity of a series of magnetically ordered
Ce-based heavy fermion materials, which show an anomalous $T^3$ heat capacity
in excess of the phonon contribution in many materials. For compounds for which
magnon models have been worked out, we show that the local-moment magnon heat
capacity derived from the measured magnon spectra underestimates the
experimental specific heat. The excess heat capacity reveals increasing density
of states with increasing energy, akin to a pseudogap. We show that this
anomalous temperature-dependent term is not associated with proximity to a
quantum critical point (QCP), but is strongly correlated with $T_N$, indicating
the anomalous excitations are governed by the magnetic exchange interaction.
This insight may hold key information for understanding magnetically ordered
heavy fermions.",2401.10718v1
2024/1/19,Anti-Jahn-Teller disproportionation and prospects for spin-triplet superconductivity in d-element compounds,"We argue that the unusual properties of a wide class of materials based on
Jahn-Teller 3d and 4d ions with different crystal and electronic structures,
from quasi-two-dimensional unconventional superconductors (cuprates,
nickelates, ferropnictides/chalcogenides, ruthenate SrRuO4), manganites with
local superconductivity to 3D ferrates (CaSr)FeO3, nickelates RNiO3 and silver
oxide AgO with unusual charge and magnetic order can be explained within a
single scenario. The properties of these materials are related to the
instability of their highly symmetric Jahn-Teller ""progenitors"" with the ground
orbital E-state to charge transfer with anti-Jahn-Teller disproportionation and
the formation of a system of effective local composite spin-singlet or
spin-triplet, electronic or hole bosons moving in a non-magnetic or magnetic
lattice. These unusual systems are characterized by an extremely rich variety
of phase states from non-magnetic and magnetic insulators to unusual metallic
and superconducting states.",2401.11028v1
2024/1/21,3D Imaging of Magnetic Domains in Nd2Fe14B using Scanning Hard X-Ray Nanotomography,"Nanoscale structural and electronic heterogeneities are prevalent in
condensed matter physics. Investigating these heterogeneities in three
dimensions (3D) has become an important task for understanding their material
properties. To provide a tool to unravel the connection between nanoscale
heterogeneity and macroscopic emergent properties in magnetic materials,
scanning transmission X-ray microscopy (STXM) is combined with X-ray magnetic
circular dichroism (XMCD). A vector tomography algorithm has been developed to
reconstruct the full 3D magnetic vector field without any prior assumptions or
knowledge. 2D STXM projections of single crystalline \ndfeb\ pillars are
recorded for two different sample tilt angles while rotating around the
vertical tomographic axis using $120$ nm X-ray beams with left and right
circular polarization. Image alignment and iterative registration has been
implemented, based on the 2D STXM projections for the two tilts. Dichroic
projections obtained from difference images are used for the tomographic
reconstruction to obtain the 3D magnetization distribution at the nanoscale.",2401.11523v1
2024/1/31,Magnetically tunable electrokinetic instability and structuring of non-equilibrium nanoparticle gradients,"Inspired by emergent behaviors of living matter, there is increasing interest
in developing approaches to create dynamic patterns and structures in synthetic
materials with controllable complexity to enable functionalities that are not
possible in thermodynamic equilibrium. Here we show that electrophoretically
driven and maintained non-equilibrium gradients of magnetic nanoparticles in
non-polar solvent can undergo electrokinetic instabilities (EKI), leading to
various electrically controllable spatiotemporally patterned states. These
electrokinetic instabilities and patterns can be tuned with a magnetic field
via magnetostatic energy reduction mechanism to both increase and decrease the
pattern complexity. We reflect the experimental observations on the theoretical
electrokinetic and magnetostatic arguments. We further show that small amounts
of polar water in the otherwise non-polar system are critical enablers for the
electrophoretic mobility of the nanoparticles. Since functionalities of
magnetic nanoparticles are widely tunable, we foresee that the combination of
dissipative electrokinetic driving and magnetic energy reduction can lead to
novel functional dissipative materials.",2401.17956v1
2024/2/2,Two-dimensional 5d multiferroic W3Cl8: breathing Kagome lattice and tunable magneto-optical Kerr effect,"Owing to the strong spin-orbit coupling and the related fascinating physical
properties, heavy 5d transition-metals exhibit desirable application prospects.
However, up to now, the 5d magnetic materials are still very limited,
especially very rare for tungsten. In this work, we theoretically predict a
two-dimensional multiferroic W3Cl8 monolayer. Intrinsic 5d magnetism of
tungsten is activated by the W ions' fractional valence in a breathing Kagome
lattice of reduced effective dimension. A coplanar Y-type antiferromagnetism
composed by ferromagnetic W3 trimers is confirmed as the magnetic ground state.
The spontaneous ferroelectric polarization mainly originates from the ion
displacement induced by the breathing distortion of Kagome lattice. An
intrinsic magneto-optical Kerr effect with sizable Kerr angle can be observed
to detect this trimeric Y-type antiferromagnetism, and it depends strongly on
the detailed magnetic order. Thereby, we propose a general scheme for realizing
more 5d magnetism in two-dimensional multiferroic systems.",2402.01100v1
2024/3/14,Field-orientation-dependent magnetic phases in GdRu$_2$Si$_2$ probed with muon-spin spectroscopy,"Centrosymmetric GdRu$_2$Si$_2$ exhibits a variety of multi-Q magnetic states
as a function of temperature and applied magnetic field, including a square
skyrmion-lattice phase. The material's behavior is strongly dependent on the
direction of the applied field, with different phase diagrams resulting for
fields applied parallel or perpendicular to the crystallographic $c$ axis.
Here, we present the results of muon-spin relaxation ($\mu^+$SR) measurements
on single crystals of GdRu$_2$Si$_2$. Our analysis is based on the computation
of muon stopping sites and consideration of zero-point motion effects, allowing
direct comparison with the underlying spin textures in the material. Using
transverse-field $\mu^+$SR with fields applied along either the [001] or [100]
crystallographic directions, we distinguish between the magnetic phases in this
system via their distinct muon response, providing additional evidence for the
skyrmion and meron-lattice phases, while also suggesting the existence of
RKKY-driven muon hyperfine coupling. Zero-field $\mu^+$SR provides clear
evidence for a transition between two distinct magnetically-ordered phases at
39 K.",2403.09431v1
2024/3/15,Thermodynamic properties of a superconductor interfaced with an altermagnet,"Recently introduced magnetic materials called altermagnets (AM) feature zero
net magnetization but a momentum dependent magnetic exchange field, which can
have intriguing implications when combined with superconductivity. In our work,
we use the quasiclassical framework to study the effects of such a material on
a conventional superconductor (S) in an AM/S bilayer. We discuss the
superconducting phase diagram and heat capacity of AM/S while making a
comparison with a ferromagnet-superconductor bilayer. Furthermore, we examine
the density of states and analyze the system's response to an external magnetic
field. We illustrate the anisotropy of spin-susceptibility and magnetization of
AM/S by considering an external field in the in-plane and out-of-plane
direction, thereby facilitating the scope of experimental detection and
characterization of an AM in an AM/S hybrid system.",2403.10456v1
2024/3/16,Machine Learning Exchange Fields for Ab-initio Spin Dynamics,"We add the magnetic degrees of freedom to the widely used Gaussian
Approximation Potential of machine learning (ML) and present a model that
describes the potential energy surface of a crystal based on the atomic
coordinates as well as their noncollinear magnetic moments. Assuming an
adiabatic approximation for the spin directions and magnitudes, the ML model
depends solely on spin coordinates and orientation, resulting in computational
efffciency and enabling ab initio spin dynamics. Leveraging rotational
symmetries of magnetic interactions, the ML model can incorporate various
magnetic interactions, expanding into two-body, three-body terms, etc.,
following the spirit of cluster expansion. For simplicity, we implement the ML
model with a two-body form for the exchange interaction. Comparing total
energies and local fields predicted by the model for noncollinear spin
arrangements with explicit results of constrained noncollinear density
functional calculations for bcc Fe yields excellent results, within 1 meV/spin
for the total energy. Further optimization, including three-body and other
terms, is expected to encompass diverse magnetic interactions and enhance the
model's accuracy. This will extend the model's applicability to a wide range of
materials and facilitate the machine learning ab initio spin dynamics.",2403.10769v1
2024/3/26,Magnetic structure and properties of the honeycomb antiferromagnet [Na(OH$_2$)$_3$]Mn(NCS)$_3$,"We report the magnetic structure and properties of a thiocyanate-based
honeycomb magnet [Na(OH$_2$)$_3$]Mn(NCS)$_3$ which crystallises in the unusual
low-symmetry trigonal space group $P\overline{3}$. Magnetic measurements on
powder samples show this material is an antiferromagnet (ordering temperature
($T_\mathrm{N,mag} = 18.1(6)\,$)K) and can be described by nearest neighbour
antiferromagnetic interactions $J=-11.07(4)\,$K. A method for growing
neutron-diffraction sized single crystals (\textgreater10 mm$^3$) is
demonstrated. Low temperature neutron single crystal diffraction shows that the
compound adopts the collinear antiferromagnetic structure with
$T_\mathrm{N,neut}= 18.94(7)\,$K, magnetic space group $P \bar{3}'$. Low
temperature second-harmonic generation (SHG) measurements provide no evidence
of breaking of the centre of symmetry.",2403.17642v1
2005/7/30,GaMnAs grown on (311) GaAs substrates: modified Mn incorporation and new magnetic anisotropies,"We report the results of a detailed study of the structural, magnetic and
magnetotransport properties of as-grown and annealed Ga0.91Mn0.09As thin films
grown on (311)A and (311)B GaAs substrates. The high Curie temperature and hole
density of the (311)B material are comparable to those of GaMnAs grown on (001)
GaAs under the same growth conditions, while they are much lower for the (311)A
material. We find evidence that Mn incorporation is more efficient for (311)B
than for (001) and significantly less efficient for (311)A which is consistent
with the bonding on these surfaces. This indicates that growth on (311)B may be
a route to increased Curie temperatures in GaMnAs. A biaxial magnetic
anisotropy is observed for the (311) material with easy axes along the [010]
and [001] out-of-plane directions. An additional uniaxial in-plane anisotropy
is also observed with the easy axis along for the (311)A material, and along
for the (311)B material. This new observation may be of importance for the
resolution of the outstanding problem of the origin of uniaxial anisotropy in
(001) GaMnAs.",0508021v1
2016/10/5,Applicability of scaling behavior and power laws in the analysis of the magnetocaloric effect in second-order phase transition materials,"In recent years, universal scaling has gained renewed attention in the study
of magnetocaloric materials. It has been applied to a wide variety of pure
elements and compounds, ranging from rare earth-based materials to transition
metal alloys, from bulk crystalline samples to nanoparticles. It is therefore
necessary to quantify the limits within which the scaling laws would remain
applicable for magnetocaloric research. For this purpose, a threefold approach
has been followed: a) the magnetocaloric responses of a set of materials with
Curie temperatures ranging from 46 to 336 K have been modeled with a mean-field
Brillouin model, b) experimental data for Gd has been analyzed, and c) a
3D-Ising model ---which is beyond the mean-field approximation--- has been
studied. In this way we can demonstrate that the conclusions extracted in this
work are model-independent. It is found that universal scaling remains
applicable up to applied fields which provide a magnetic energy to the system
up to 8\% of the thermal energy at the Curie temperature. In this range, the
predicted deviations from scaling laws remain below the experimental error
margin of carefully performed experiments. Therefore, for materials whose Curie
temperature is close to room temperature, scaling laws at the Curie temperature
would be applicable for the magnetic field range available at conventional
magnetism laboratories ($\sim 10$ T), well above the fields which are usually
available for magnetocaloric devices.",1610.01550v1
2017/12/28,Nodal surface semimetals: Theory and material realization,"We theoretically study the three-dimensional topological semimetals with
nodal surfaces protected by crystalline symmetries. Different from the
well-known nodal-point and nodal-line semimetals, in these materials, the
conduction and valence bands cross on closed nodal surfaces in the Brillouin
zone. We propose different classes of nodal surfaces, both in the absence and
in the presence of spin-orbit coupling (SOC). In the absence of SOC, a class of
nodal surfaces can be protected by spacetime inversion symmetry and sublattice
symmetry and characterized by a $\mathbb{Z}_2$ index, while another class of
nodal surfaces are guaranteed by a combination of nonsymmorphic two-fold
screw-rotational symmetry and time-reversal symmetry. We show that the
inclusion of SOC will destroy the former class of nodal surfaces but may
preserve the latter provided that the inversion symmetry is broken. We further
generalize the result to magnetically ordered systems and show that protected
nodal surfaces can also exist in magnetic materials without and with SOC, given
that certain magnetic group symmetry requirements are satisfied. Several
concrete nodal-surface material examples are predicted via the first-principles
calculations. The possibility of multi-nodal-surface materials is discussed.",1712.09773v2
2018/6/29,Electronic correlation in the quasi-two-dimensional electride Y$_2$C,"Magnetic properties of the electride compound Y$_2$C were investigated by
muon spin rotation and magnetic susceptibility on two samples with different
form (poly- and single-crystalline), to examine the theoretically-predicted
Stoner ferromagnetism for the electride bands. There was no evidence of static
magnetic order in both samples even at temperatures down to 0.024 K. For the
poly-crystalline sample, the presence of a paramagnetic moment at Y sites was
inferred from the Curie-Weiss behavior of the muon Knight shift and
susceptibility, whereas no such tendency was observed in the single-crystalline
sample. These observations suggest that the electronic ground state of Y$_2$C
is at the limit between weak-to-strong electronic correlation, where onsite
Coulomb repulsion is sensitive to a local modulation of the electronic state or
a shift in the Fermi level due to the presence of defects/impurities.",1806.11260v2
2018/11/5,"Prediction of Weyl semimetal, AFM topological insulator, nodal line semimetal, and Chern insulator phases in Bi2MnSe4","Three dimensional materials with strong spin-orbit coupling and magnetic
interactions represent an opportunity to realize a variety of rare and
potentially useful topological phases. In this work, we use first principles
calculations to show that the recently synthesized material Bi2MnSe4 displays a
combination of band inversion and magnetic interactions, leading to several
topological phases. Bi2PbSe4, also studied, also displays band inversion and is
a topological insulator. In bulk form, the ferromagnetic phase of Bi2MnSe4 is
either a nodal line or Weyl semimetal, depending on the direction of the spins.
When the spins are arranged in a layered antiferromagnetic configuration, the
combination of time reversal plus a partial translation is a new symmetry, and
the material instead becomes an antiferromagnetic topological insulator.
However, the intrinsic TRS breaking at the surface of Bi2MnSe4 removes the
typical Dirac cone feature, allowing the observation of the half-integer
quantum anomalous Hall effect (AHC). Furthermore, we show that in thin film
form, for some thicknesses, Bi2MnSe4 becomes a Chern insulator with a band gap
of up to 58 meV. This combination of properties in a stoichiometric magnetic
material makes Bi2MnSe4 an excellent candidate for displaying robust
topological behavior.",1811.01863v1
2020/9/15,Strong spin-dephasing in a topological insulator - paramagnet heterostructure,"The interface between magnetic materials and topological insulators can drive
the formation of exotic phases of matter and enable functionality through
manipulation of the strong spin polarized transport. Here, we report that the
spin-momentum-locked transport in the topological insulator Bi$_2$Se$_3$ is
completely suppressed by scattering at a heterointerface with the
kagome-lattice paramagnet, Co$_7$Se$_8$.
Bi$_2$Se$_{3-}$Co$_7$Se$_{8-}$Bi$_2$Se$_3$ trilayer heterostructures were grown
using molecular beam epitaxy. Magnetotransport measurements revealed a
substantial suppression of the weak antilocalization effect for Co$_7$Se$_8$ at
thicknesses as thin as a monolayer, indicating a strong dephasing mechanism.
Bi$_{2-x}$Co$_x$Se$_3$ films, where Co is in a non-magnetic $3^+$ state, show
weak antilocalization that survives to $x = 0.5$, which, in comparison with the
heterostructures, suggests the unordered moments of the Co$^{2+}$ act as a far
stronger dephasing element. This work highlights several important points
regarding spin-polarized transport in topological insulator interfaces and how
magnetic materials can be integrated with topological materials to realize both
exotic phases as well as novel device functionality.",2009.06827v1
2021/12/8,"MnP films with desired magnetic, magnetocaloric and thermoelectric properties for a perspective magneto-thermo-electric cooling device","A perspective magneto-thermo-electric cooling device (MTECD) comprising a
central magnetocaloric (MC) material (e.g., Gd) sandwiched by two
thermoelectric (TE) materials (e.g., MnP) is proposed. The presence of the TE
materials in the MTECD guides the heat flow direction and enhances heat
pulsation. In this case, the usage of a ferromagnetic TE material that combines
large TE with small MC properties within a similar temperature region can
enhance the magnetic flux density and heat exchange efficiency. Here, we show
that MnP nanorod-structured films with desired magnetic, MC and TE properties
are very promising for use in MTECDs. The films were grown on Si substrates at
300, 400 and 500{\deg}C using molecular beam epitaxy. The 400 oC sample shows a
desired TE and MC combination. A large power factor of 24.06 {\mu}W m-1 K-2 is
achieved at room temperature. In this temperature region, the film exhibits a
small MC effect (-deltaSM ~0.64 J/kg K and deltaTad ~0.3 K at m0H = 2 T) but
ferromagnetism that gives rise to the enhanced MC effect of the central MC
material. These properties could enable the MTECD to operate at high frequency.",2112.04119v1
2023/5/25,Heesch Weyl Fermions in inadmissible chiral antiferromagnets,"Symmetry is a crucial factor in determining the topological properties of
materials. In nonmagnetic chiral crystals, the existence of the Kramers Weyl
fermions reveals the topological nature of the Kramers degeneracy at
time-reversal-invariant momenta (TRIMs). However, it is not clear whether Weyl
nodes can also be pinned at points of symmetry in magnetic materials where the
time-reversal is spontaneously broken. In this study, we introduce a new type
of Weyl fermions, called Heesch Weyl fermions (HWFs), which are stabilized and
pinned at points of symmetry by the Heesch groups in inadmissible chiral
antiferromagnets. The emergence of HWFs is fundamentally different from that of
Kramers Weyl fermions, as it does not rely on any anti-unitary symmetry
$\mathcal{A}$ that satisfies $\mathcal{A}^2=-1$. Importantly, the emergence of
HWFs is closely related to the antiferromagnetic order, as they are generally
obscured by nodal lines in the parent nonmagnetic state. Using group theory
analysis, we classify all the magnetic little co-groups of momenta where Heesch
Weyl nodes are enforced and pinned by symmetry. With the guidance of this
classification and first-principles calculations, we identify antiferromagnetic
(AFM) materials such as YMnO$_3$ and Mn$_3$IrGe as candidate hosts for the
AFM-order-induced HWFs.We also explore novel properties of Heesch Weyl
antiferromagnets, such as nonlinear anomalous Hall effects and axial movement
of Heesch Weyl nodes. Our findings shed new light on the role of symmetry in
determining and stabilizing topological properties in magnetic materials, and
open up new avenues for the design and exploration of topological materials.",2305.15876v1
2023/11/13,Ab initio amorphous spin Hamiltonian for the description of topological spin textures in FeGe,"Topological spin textures in magnetic materials such as skyrmions and
hopfions are interesting manifestations of geometric structures in real
materials, concurrently having potential applications as information carriers.
In the crystalline systems, the formation of these topological spin textures is
well understood as a result of the competition between interactions due to
symmetry breaking and frustration. However, in systems without translation
symmetry such as amorphous materials, a fundamental understanding of the
driving mechanisms of non-trivial spin structures is lacking owing to the
structural and interaction complexity in these systems. In this work, we use a
suite of first-principles-based calculations to propose an ab initio spin
Hamiltonian that accurately represents the diversity of structural and magnetic
properties in the exemplar amorphous FeGe. Monte Carlo simulations of our
amorphous Hamiltonian find emergent skyrmions that are driven by frustrated
geometric and magnetic exchange, consistent with those observed in experiment.
Moreover, we find that the diversity of local structural motifs results in a
large range of exchange interactions, far beyond those found in crystalline
materials. Finally, we observe the formation of large-scale emergent structures
in amorphous materials, far beyond the relevant interaction length-scale in the
systems, suggesting a new route to emergent correlated phases beyond the
crystalline limit.",2311.07725v1
2021/3/2,"Weyl, Dirac and high-fold chiral fermions in topological quantum materials","Quantum materials hosting Weyl fermions have opened a new era of research in
condensed matter physics. First proposed in 1929 in particle physics, Weyl
fermions have yet to be observed as elementary particles. In 2015, Weyl
fermions were detected as collective electronic excitations in the strong
spin-orbit coupled material tantalum arsenide, TaAs. This discovery was
followed by a flurry of experimental and theoretical explorations of Weyl
phenomena in materials. Weyl materials naturally lend themselves to the
exploration of the topological index associated with Weyl fermions and their
divergent Berry curvature field, as well as the topological bulk-boundary
correspondence giving rise to protected conducting surface states. Here, we
review the broader class of Weyl topological phenomena in materials, starting
with the observation of emergent Weyl fermions in the bulk and of Fermi arc
states on the surface of the TaAs family of crystals by photoemission
spectroscopy. We then discuss some of the exotic optical and magnetic responses
observed in these materials, as well as the progress in developing some of the
related chiral materials. We discuss the conceptual development of high-fold
chiral fermions, which generalize Weyl fermions, and we review the observation
of high-fold chiral fermion phases by taking the rhodium silicide, RhSi, family
of crystals as a prime example. Lastly, we discuss recent advances in Weyl-line
phases in magnetic topological materials. With this Review, we aim to provide
an introduction to the basic concepts underlying Weyl physics in condensed
matter, and to representative materials and their electronic structures and
topology as revealed by spectroscopic studies. We hope this work serves as a
guide for future theoretical and experimental explorations of chiral fermions
and related topological quantum systems with potentially enhanced
functionalities.",2103.01714v1
2005/1/5,Quantum criticality and universal scaling of a quantum antiferromagnet,"Quantum effects dominate the behaviour of many diverse materials. Of
particular current interest are those systems in the vicinity of a quantum
critical point (QCP). Their physical properties are predicted to reflect those
of the nearby QCP with universal features independent of the microscopic
details. The prototypical QCP is the Luttinger liquid (LL) which is of
relevance to many quasi-one-dimensional materials. The magnetic material KCuF3
realizes an array of weakly-coupled spin chains (or LLs) and thus lies close to
but not exactly at the Luttinger liquid quantum critical point. By using
inelastic neutron scattering we have collected a complete data set of the
magnetic correlations of KCuF3 as a function of momentum, energy, and
temperature. The LL description is found to be valid over an extensive range of
these parameters, and departures from this behaviour at high and low energies
and temperatures have been identified and explained.",0501069v1
2006/6/6,Brewster's angle for anisotropic material from the extinction theorem,"By the extinction theorem we explore the Brewster effect in the external and
internal reflections of electromagnetic wave associated with an anisotropic
material that is both dielectric and magnetic, including metamaterials. We
obtain Fresnel's coefficients and the condition of Brewster's angle, and give
microscopic explanations from the view point of molecular optics. The Brewster
angle is the incidence of angle at which the contribution of all electric and
magnetic dipoles in the anisotropic material to the reflection field becomes
zero. Distinct from isotropic media, the anisotropic material can exhibit
Brewster angle for both TE and TM waves due to the anisotropy of the material.",0606045v2
2007/10/3,"Effect of Ti4+ substitution on structural, transport and magnetic properties of La0.67Sr0.33Mn1-xTixO3","La$_{0.67}$Sr$_{0.33}$Mn$_{1-x}$Ti$_x$O$_{3}$ ($0 \le x \le 0.20$)
polycrystalline materials are prepared by employing lower annealing temperature
compared to the temperatures reported for the materials of the same
composition. The transport and magnetic properties of these materials are
significantly different from those compounds prepared at higher annealing
temperature. Samples with $x < 0.10$, show metal-insulator transition and those
with $x \ge 0.10$ exhibit insulating behavior over the entire temperature range
investigated. A gradual transition occurs from ferromagnetic-metallic state to
ferromagnetic-insulator state with increasing Ti substitution. Lattice
parameters and bond lengths of Mn and its near neighbours however do not change
appreciably with the dopant content $x$ in these materials. It is shown that
Ti$^{4+}$ doping in the low temperature annealed samples is inhomogeneous
resulting in isolated Mn rich regions that are connected by a variable range
hopping polaron.",0710.0715v1
2008/11/12,Disorder Effects in La substituted ferrimagnetic Ca2FeMoO6 double perovskite,"Ca2-xLaxFeMoO6 double perovskite with La concentration x = 0 to 0.6 was
synthesized using solid state sintering route. The standard techniques of XRD,
SEM and EDX were applied to characterize the material. Crystal structure of the
samples was stabilized in monoclinic phase with space group P2I/n and lattice
expansion was indicated with the increase of x. The increase of La
concentration gradually suppressed the coexisting minor secondary phase in the
material and simultaneously, EDX results indicated the accommodation of more Mo
atoms in the crystal structure. A significant modification in the surface
morphology of the material was noted from adhesive type surface for x = 0 to
brittle type surface with more grain boundary contributions for La doped
samples. We understand a significant change in magnetic properties (appearance
of cluster glass component, reduction of magnetic moment and indication of
higher TC) and in electrical properties (reduction of metallic character) in
terms of enhanced internal disorder in the material, introduced due to La
doping in double perovskite structure.",0811.1876v2
2010/2/2,First-principles design and subsequent synthesis of a material to search for the permanent electric dipole moment of the electron,"We describe the first-principles design and subsequent synthesis of a new
material with the specific functionalities required for a solid-state-based
search for the permanent electric dipole moment of the electron. We show
computationally that perovskite-structure europium barium titanate should
exhibit the required large and pressure-dependent ferroelectric polarization,
local magnetic moments, and absence of magnetic ordering even at liquid helium
temperature. Subsequent synthesis and characterization of
Eu$_{0.5}$Ba$_{0.5}$TiO$_3$ ceramics confirm the predicted desirable
properties.",1002.0376v2
2011/8/30,A simple construction for a cylindrical cloak via inverse homogenization,"An effective cylindrical cloak may be conceptualized as an assembly of
adjacent local neighbourhoods, each of which is made from a homogenized
composite material (HCM). The HCM is required to be a certain uniaxial
dielectric-magnetic material, characterized by positive-definite constitutive
dyadics. It can arise from the homogenization of remarkably simple component
materials, such as two isotropic dielectric-magnetic materials, randomly
distributed as oriented spheroidal particles. By carefully controlling the
spheroidal shape of the component particles, a high degree of HCM anisotropy
may be achieved, which is necessary for the cloaking effect to be realized. The
inverse Bruggeman formalism can provide estimates of the shape and constitutive
parameters for the component materials, as well as their volume fractions.",1108.5936v1
2014/7/24,Unambiguous separation of the inverse spin Hall and anomalous Nernst Effects within a ferromagnetic metal using the spin Seebeck effect,"The longitudinal spin Seebeck effect is measured on the ferromagnetic
insulator Fe$_3$O$_4$ with the ferromagnetic metal
Co$_{0.2}$Fe$_{0.6}$B$_{0.2}$ (CoFeB) as the spin detector. By using a
non-magnetic spacer material between the two materials (Ti), it is possible to
decouple the two ferromagnetic materials and directly observe pure spin flow
from Fe$_3$O$_4$ into CoFeB. It is shown, that in a single ferromagnetic metal
the inverse spin Hall effect (ISHE) and anomalous Nernst effect (ANE) can occur
simultaneously with opposite polarity. Using this and the large difference in
the coercive fields between the two magnets, it is possible to unambiguously
separate the contributions of the spin Seebeck effect from the ANE and observe
the degree to which each effect contributes to the total response. These
experiments show conclusively that the ISHE and ANE in CoFeB are separate
phenomena with different origins and can coexist in the same material with
opposite response to a thermal gradient.",1407.6758v1
2017/4/4,Model Hamiltonian and Time Reversal Breaking Topological Phases of Anti-ferromagnetic Half-Heusler Materials,"In this work, we construct a generalized Kane model with a new coupling term
between itinerant electron spins and local magnetic moments of
anti-ferromagnetic ordering in order to describe the low energy effective
physics in a large family of anti-ferromagnetic half-Heusler materials.
Topological properties of this generalized Kane model is studied and a large
variety of topological phases, including Dirac semimetal phase, Weyl semimetal
phase, nodal line semimetal phase, type-B triple point semimetal phase,
topological mirror (or glide) insulating phase and anti-ferromagnetic
topological insulating phase, are identified in different parameter regions of
our effective models. In particular, we find that the system is always driven
into the anti-ferromagnetic topological insulator phase once a bulk band gap is
open, irrespective of the magnetic moment direction, thus providing a robust
realization of anti-ferromagentic topological insulators. Furthermore, we
discuss the possible realization of these topological phases in realistic
anti-ferromagnetic half-Heusler materials. Our effective model provides a basis
for the future study of physical phenomena in this class of materials.",1704.01138v1
2017/12/25,Half-metallicity in honeycomb-kagome-lattice Mg3C2 monolayer with carrier doping,"To obtain high-performance spintronic devices with high integration density,
two-dimensional (2D) half-metallic materials are eagerly pursued all along.
Here, we propose a stable 2D material with a honeycomb-kagome lattice, i.e.,
the Mg3C2 monolayer, based on first-principles calculations. This monolayer is
an anti-ferromagnetic (AFM) semiconductor at its ground state. We further
demonstrate that a transition from AFM semiconductor to ferromagnetic
half-metal in this 2D material can be induced by carrier (electron or hole)
doping. This magnetic transition can be understood by the Stoner criterion. In
addition, the half-metallicity arises from the 2pz orbitals of the carbon (C)
atoms for the electron-doped system, but from the C 2px and 2py orbitals for
the case of hole doping. Our findings highlight a new promising material with
controllable magnetic and electronic properties toward 2D spintronic
applications.",1712.08985v2
2019/4/11,Study of soft/hard bimagnetic CoFe2/CoFe2O4 nanocomposite,"We report an experimental study of the bimagnetic nanocomposites
CoFe2/CoFe2O4.The precursor material, CoFe2O4 was prepared using the
conventional stoichiometric combustion method. The nanocomposite CoFe2/CoFe2O4
was obtained by total reduction of CoFe2O4 using a thermal treatment at 350oC
in H2 atmospheres following a partial oxidation in O2 atmospheres at 380oC
during 120; 30; 15, 10, and 5 min. The X-ray diffraction and Mossbauer
spectroscopy confirmed the formation the material CoFe2/CoFe2O4 The magnetic
hysteresis with different saturation magnetization confirms the formation of
the CoFe2/CoFe2O4 with different content of CoFe2O4. The high energy milling to
the precursor material increase the coercivity from 1.0 to 3.3 kOe, however the
same effect was not observed to the CoFe2/CoFe2O4 material.",1904.05984v1
2019/5/2,"Analysis, optimization, and characterization of magnetic photonic crystal structures and thin-film material layers","MPC (Magneto-Photonic Crystal) Optimisation is a feature-rich Windows
software application designed to enable researchers to analyze the optical and
magneto-optical spectral properties of multilayers containing gyrotropic
constituents. A set of computational algorithms aimed at enabling the design
optimization and optical or magneto-optical (MO) spectral analysis of 1D
magnetic photonic crystals (MPC) is reported, together with its Windows
software implementation. Relevant material property datasets (e.g., the optical
spectra of refractive index, absorption, and gyration) of several important
optical and MO materials are included, enabling easy reproduction of the
previously published results from the field of MPC-based Faraday rotator
development, and an effective demonstration-quality introduction of future
users to the multiple features of this package. We also report on the methods
and algorithms used to obtain the absorption coefficient spectral dispersion
datasets for new materials, for which the film thickness, transmission
spectrum, and refractive index dispersion function are known.",1905.00619v1
2019/8/16,Two-dimensional magnetic semiconductors with room Curie temperatures,"We propose two-dimensional (2D) Ising-type ferromagnetic semiconductors
TcSiTe3, TcGeSe3, and TcGeTe3 with high Curie temperatures around 200-0500 K.
Owing to large spin-orbit couplings, the large magnetocrystalline anisotropy
energy (MAE), large anomalous Hall conductivity, and large magneto-optical Kerr
effect were discovered in these intriguing 2D materials. By comparing all
possible 2D MGeTe3 materials (M = 3d, 4d, 5d transition metals), we found a
large orbital moment around 0.5 $\mu$B per atom and a large MAE for TcGeTe3.
The large orbital moments are revealed to be from the comparable crystal fields
and electron correlations in these Tc-based 2D materials. The microscopic
mechanism of the high Curie temperature is also addressed. Our findings reveal
the unique magnetic behaviors of 2D Tc-based materials and present a family of
2D ferromagnetic semiconductors with large MAE and Kerr rotation angles that
would have wide applications in designing spintronic devices.",1908.05836v2
2019/12/16,Magneto-optics of a Weyl semimetal beyond the conical band approximation: the case study of TaP,"Landau-level spectroscopy, the optical analysis of electrons in materials
subject to a strong magnetic field, is a versatile probe of the electronic band
structure and has been successfully used in the identification of novel states
of matter such as Dirac electrons, topological materials or Weyl semimetals.
The latter arise from a complex interplay between crystal symmetry, spin-orbit
interaction and inverse ordering of electronic bands. Here, we report on
unusual Landau-level transitions in the monopnictide TaP that decrease in
energy with increasing magnetic field. We show that these transitions arise
naturally at intermediate energies in time-reversal-invariant Weyl semimetals
where the Weyl nodes are formed by a partially gapped nodal-loop in the band
structure. We propose a simple theoretical model for electronic bands in these
Weyl materials that captures the collected magneto-optical data to great
extent.",1912.07327v2
2019/12/20,Van der Waals heterostructures for high-performance device applications: challenges and opportunities,"Discovery of two-dimensional materials with unique electronic, superior
optoelectronic or intrinsic magnetic order have triggered worldwide interests
among the fields of material science, condensed matter physics and device
physics. Vertically stacking of two-dimensional materials with distinct
electronic and optical as well as magnetic properties enables to create a large
variety of van der Waals heterostructures. The diverse properties of the
vertical heterostructures open up unprecedented opportunities for various kinds
of device applications, e.g. vertical field effect transistors, ultrasensitive
infrared photodetectors, spin-filtering devices and so on, which are
inaccessible in the conventional material heterostructures. Here, we review the
current status of vertical heterostructures device applications in vertical
transistors, infrared photodetectors and spintronic memory/transistors. The
relevant challenges for achieving high-performance devices are presented. We
also provide outlook on future development of vertical heterostructure devices
with integrated electronic and optoelectronic as well as spintronic
functinalities.",1912.10886v1
2020/2/12,Intrinsic anomalous Hall effect in Ni-substituted magnetic Weyl semimetal Co3Sn2S2,"Topological materials have recently attracted considerable attention among
materials scientists as their properties are predicted to be protected against
perturbations such as lattice distortion and chemical substitution. However,
any experimental proof of such robustness is still lacking. In this study, we
experimentally demonstrate that the topological properties of the ferromagnetic
kagome compound Co3Sn2S2 are preserved upon Ni substitution. We systematically
vary the Ni content in Co3Sn2S2 single crystals and study their magnetic and
anomalous transport properties. For the intermediate Ni substitution, we
observe a remarkable increase in the coercive field while still maintaining
significant anomalous Hall conductivity. The large anomalous Hall conductivity
of these compounds is intrinsic, consistent with first-principle calculations,
which proves its topological origin. Our results can guide further studies on
the chemical tuning of topological materials for better understanding.",2002.05062v1
2020/5/20,Detectability of Axion Dark Matter with Phonon Polaritons and Magnons,"Collective excitations in condensed matter systems, such as phonons and
magnons, have recently been proposed as novel detection channels for light dark
matter. We show that excitation of i) optical phonon polaritons in polar
materials in an ${\mathcal O}$(1 T) magnetic field (via the axion-photon
coupling), and ii) gapped magnons in magnetically ordered materials (via the
axion wind coupling to the electron spin), can cover the difficult-to-reach
${\mathcal O}$(1-100) meV mass window of QCD axion dark matter with less than a
kilogram-year exposure. Finding materials with a large number of optical phonon
or magnon modes that can couple to the axion field is crucial, suggesting a
program to search for a range of materials with different resonant energies and
excitation selection rules; we outline the rules and discuss a few candidate
targets, leaving a more exhaustive search for future work. Ongoing development
of single photon, phonon and magnon detectors will provide the key for
experimentally realizing the ideas presented here.",2005.10256v1
2020/5/21,Surface lattice resonance based magneto-plasmonic switch in NiFe patterned nano-structure,"In this work, a 2D magneto-plasmonic grating structure combining materials
with ferromagnetic and plasmonic properties is demonstrated. NiFe composite
ferromagnetic material, as an active medium with tunable physical properties,
and Au metal, as a plasmonic excitation layer, were the materials of choice.
Here, we have experimentally investigated the active control of the plasmonic
characteristics in Au/NiFe bilayer by the action of an external magnetic field,
as well as the switching effect of the system. The active plasmonic control,
can be achieved by the magnetization switching of the ferromagnetic material,
opening a new path in the development of active plasmonic devices. To our best
knowledge, this is the first demonstration of such a magneto-optical plasmonic
switch based on the coupling of plasmons with magneto-optical active materials,
in which the response time was estimated to be in the range of microseconds.",2005.10913v1
2020/8/17,Interaction between skyrmions and antiskyrmions in a coexisting phase of a Heusler material,"Coexisting phases of magnetic skyrmions and antiskyrmions have proposed to
exhibit a variety of fascinating properties, owing to interactions between
them. The recent discovery of the coexisting phase in a Heusler material could
offer a platform for skyrmion-antiskyrmion-based spintronics. Here we report
Lorentz electron microscopy experiments and micromagnetic simulations in a
similar Heusler material, Mn$_{1.3}$Pt$_{1.0}$Pd$_{0.1}$Sn. Around $B_c \sim$
420$\,$mT, we find a stochastic reversible transformation and a room
temperature coexisting phase of elliptical skyrmions and square-shaped
antiskyrmions. The closeness of the energy competition is sensitive to the
exchange stiffness constants and sample thickness. Furthermore, we reveal
isotropic long-range repulsive interaction between the skyrmions and
antiskyrmions regardless of their shapes and the skyrmion helicities, in stark
contrast to conventional thought of angle- and helicity-dependent short-range
pairwise interactions. The observed interaction possibly results from the
topological protection against the intrusion of magnetic flux density coming
from skyrmions (antiskyrmions) into antiskyrmions (skyrmions). Our results
provide new insight into interacting skyrmions and antiskyrmions and a guide
for developing skyrmion-antiskyrmion-based spintronics.",2008.07272v2
2020/11/3,Ferroic orders in two-dimensional transition/rare-earth metal halides,"Since the discovery of graphene, two-dimensional materials with atomic level
thickness have rapidly grown to be a prosperous field of physical science with
interdisciplinary interests, for their fascinating properties and broad
applications. Very recently, the experimental observation of ferromagnetism in
Cr$_2$Ge$_2$Te$_6$ bilayer and CrI$_3$ monolayer opened a door to pursuit
long-absent intrinsic magnetic orders in two-dimensional materials. Meanwhile,
the ferroelectricity was also experimentally found in SnTe monolayer and
CuInP$_2$S$_6$ few layers. The emergence of these ferroic orders in the
two-dimensional limit not only brings new challenges to our physical knowledge,
but also provides more functionalities for potential applications. Among
various two-dimensional ferroic ordered materials, transition/rare-earth metal
halides and their derivants are very common. In this Research Update, based on
transition/rare-earth metal halides, the physics of various ferroic orders in
two-dimensional will be illustrated. The potential applications based on their
magnetic and polar properties will also be discussed.",2011.01401v1
2020/11/27,Understanding doping of quantum materials,"Doping mobile carriers into ordinary semiconductors such as Si, GaAs, and ZnO
was the enabling step in the electronic and optoelectronic revolutions. The
recent emergence of a class of ""Quantum Materials"", where uniquely quantum
interactions between the components produce specific behaviors such as
topological insulation, unusual magnetism, superconductivity,
spin-orbit-induced and magnetically-induced spin splitting, polaron formation,
and transparency of electrical conductors, pointed attention to a range of
doping-related phenomena associated with chemical classes that differ from the
traditional semiconductors. These include wide-gap oxides, compounds containing
open-shell d electrons, and compounds made of heavy elements yet having
significant band gaps. The atomistic electronic structure theory of doping that
has been developed over the past two decades in the sub-field of semiconductor
physics has recently been extended and applied to quantum materials. The
present review focuses on explaining the main concepts needed for a basic
understanding of the doping phenomenology and indeed peculiarities in quantum
materials from the perspective of condensed matter theory, with the hope of
forging bridges to the chemists that have enabled the synthesis of some of the
most interesting compounds in this field.",2011.13521v1
2021/1/16,Magnetotransport in semiconductors and two-dimensional materials from first principles,"We demonstrate a first-principles method to study magnetotransport in
materials by solving the Boltzmann transport equation (BTE) in the presence of
an external magnetic field. Our approach employs ab initio electron-phonon
interactions and takes spin-orbit coupling into account. We apply our method to
various semiconductors (Si and GaAs) and two-dimensional (2D) materials
(graphene) as representative case studies. The magnetoresistance, Hall mobility
and Hall factor in Si and GaAs are in very good agreement with experiments. In
graphene, our method predicts a large magnetoresistance, consistent with
experiments. Analysis of the steady-state electron occupations in graphene
shows the dominant role of optical phonon scattering and the breaking of the
relaxation time approximation. Our work provides a detailed understanding of
the microscopic mechanisms governing magnetotransport coefficients,
establishing the BTE in a magnetic field as a broadly applicable
first-principles tool to investigate transport in semiconductors and 2D
materials.",2101.06457v2
2021/3/28,Electronic correlations in the normal state of kagome superconductor KV$_3$Sb$_5$,"Recently, intensive studies have revealed fascinating physics, such as charge
density wave and superconducting states, in the newly synthesized
kagome-lattice materials $A$V$_3$Sb$_5$ ($A$=K, Rb, Cs). Despite the rapid
progress, fundamental aspects like the magnetic properties and electronic
correlations in these materials have not been clearly understood yet. Here,
based on the density functional theory plus the single-site dynamical
mean-field theory calculations, we investigate the correlated electronic
structure and the magnetic properties of the KV$_3$Sb$_5$ family materials in
the normal state. We show that these materials are good metals with weak local
correlations. The obtained Pauli-like paramagnetism and the absence of local
moments are consistent with recent experiment. We reveal that the band
crossings around the Fermi level form three groups of nodal lines protected by
the spacetime inversion symmetry, each carrying a quantized $\pi$ Berry phase.
Our result suggests that the local correlation strength in these materials
appears to be too weak to generate unconventional superconductivity, and
non-local electronic correlation might be crucial in this kagome system.",2103.15078v2
2021/4/14,Nonlinear Hall effect with time-reversal symmetry: Theory and material realizations,"The appearance of a Hall conductance necessarily requires breaking of
time-reversal symmetry, either by an external magnetic field or by the internal
magnetization of a material. However, as a second response, Hall
dissipationless transverse currents can appear even in time-reversal symmetric
conditions in non-centrosymmetric materials. Moreover, this non-linear effect
has a quantum origin: it is related to the geometric properties of the
electronic wavefunctions and encoded in the dipole moment of the Berry
curvature. Here we review the general theory underpinning this effect and
discuss various material platforms where non-linear Hall transverse responses
have been theoretically proposed and experimentally verified. On the
theoretical front, the link between the non-linear Hall effect and the Berry
curvature dipole is discussed using Boltzmann transport theory. On the material
front, different platforms, including topological crystalline insulators,
transition metal dichalcogenides, graphene, and Weyl semimetals are reviewed.",2104.06690v2
2021/7/26,Engineering of Ferroic Orders in Thin Films by Anionic Substitution,"Multiferroics are a unique class of materials where magnetic and
ferroelectric orders coexist. The research on multiferroics contributes
significantly to the fundamental understanding of the strong correlations
between different material degrees of freedom and provides an energy-efficient
route toward the electrical control of magnetism. While multiple ABO3 oxide
perovskites have been identified as being multiferroic, their magnetoelectric
coupling strength is often weak, necessitating the material search in different
compounds. Here, we report the observation of room-temperature multiferroic
orders in multi-anion SrNbO3-xNx thin films. In these samples, the multi-anion
state enables the room-temperature ferromagnetic ordering of the Nb
d-electrons. Simultaneously, we find ferroelectric responses that originate
from the structural symmetry breaking associated with both the off-center
displacements of Nb and the geometric displacements of Sr, depending on the
relative O-N arrangements within the Nb-centered octahedra. Our findings not
only diversify the available multiferroic material pool but also demonstrate a
new multiferroism design strategy via multi-anion engineering.",2107.12509v1
2021/8/17,Polariton-drag enabled quantum geometric photocurrents in high symmetry materials,"Lowered symmetry enables access to a wide set of responses not typically
accessible in high symmetry materials. Prime examples are time-reversal
forbidden quantum geometric photocurrent responses (e.g., linear injection and
circular shift photocurrents) that are thought to vanish in non-magnetic
materials. Here we argue that polariton-drag processes enable to unblock such
quantum geometric photocurrents even in non-magnetic and centrosymmetric
materials. Strikingly, we uncover how a cooperative effect between finite q
irradiation and the Fermi surface position leads to a polariton selective
photoexcitation (PSP). PSP enables to directly address carriers within tight
momentum resolved windows of the Fermi surface to yield giant enhancements of
quantum geometric photocurrents. This selectivity enables to directly track
momentum resolved quantum geometric quantities along the Fermi surface
providing a new tool to interrogate the quantum geometry of high symmetry
materials.",2108.07823v2
2021/10/11,Flexoelectronic doping of the degenerate silicon and the correlated electron behavior,"In metal/degenerately doped silicon bilayer structure, the interfacial
flexoelectric effect due to strain gradient leads to charge carrier transfer
from metal layer to the silicon layer. This excess charge carrier concentration
is called flexoelectronic doping or flexoelectronic charge transfer, which
gives rise to an electronically polarized (order of magnitude larger than
ferroelectric materials) silicon layer. In the transport measurements, the
charge carrier concentration in silicon is found to increase by two orders of
magnitude due to flexoelectronic doping, which changes the Fermi level and the
Hall response. The flexoelectronic charge accumulation modifies the
electron-electron and the electron phonon coupling, which gives rise to Mott
metal-insulator transition and magnetism of phonons, respectively. The
coexistence of flexoelectronic polarization and magnetism gives rise to a new
class of materials called electronic multiferroics. By controlling the
flexoelectronic doping, material behavior can potentially be engineered for
quantum, spintronics and electronics applications in semiconductor materials.",2110.04938v2
2021/10/27,Nanocrystalline FeCr alloys synthesised by severe plastic deformation -- a potential material for exchange bias and enhanced magnetostriction,"This work gives insights into processing and characterisation of bulk
nanocrystalline FeCr materials. The investigated FeCr alloys, consisting of 30,
50 and 70 at.% ferromagnetic Fe and remaining anti-ferromagnetic Cr, are
processed by arc melting and subsequent severe plastic deformation by high
pressure torsion. The physical similarities between elemental Fe and Cr in
combination with the nanocrystalline structure of the as-deformed alloys,
necessitates advanced characterisation techniques for the as-deformed state:
In-situ annealing synchrotron X-ray diffraction measurements as well as
electron microscopy experiments are linked to magnetostrictive measurements and
reveal a single phase microstructure. Surprisingly, the nanocrystalline FeCr
alloys remain supersaturated solid solutions upon annealing above 500{\deg}C,
meaning a decomposition in a FeCr nanocomposite is suppressed. For the chosen
annealing conditions grain growth is faster than decomposition and enhanced
magnetostrictive values are found compared to materials in the as-deformed
state.",2110.14303v1
2021/11/23,Detecting triplet states in opto-electronic and photovoltaic materials and devices by transient optically detected magnetic resonance,"Triplet excited states in organic semiconductor materials and devices are
notoriously difficult to detect and study with established spectroscopic
methods. Yet, they are a crucial intermediate step in next-generation organic
light emitting diodes (OLED) that employ thermally activated delayed
fluorescence (TADF) to upconvert non-emissive triplets to emissive singlet
states. In organic photovoltaic (OPV) devices, however, triplets are an
efficiency-limiting exciton loss channel and are also involved in device
degradation. Here, we introduce an innovative spin-sensitive method to study
triplet states in both, optically excited organic semiconductor films, as well
as in electrically driven devices. The method of transient optically detected
magnetic resonance (trODMR) can be applied to all light-emitting materials
whose luminescence depends on paramagnetic spin states. It is thus an ideal
spectroscopic tool to distinguish different states involved and determine their
corresponding time scales. We unravel the role of intermediate excited spin
states in opto-electronic and photovoltaic materials and devices and reveal
fundamental differences in electrically and optically induced triplet states.",2111.12012v1
2022/2/11,Screening promising CsV3Sb5-like kagome materials from systematic first-principles evaluation,"CsV3Sb5 kagome lattice holds the promise for manifesting electron
correlation, topology and superconducting. However, by far only three
CsV3Sb5-like kagome materials have been experimentally spotted. In this work,
we enlarge this family of materials to 1386 compounds via element species
substitution, and the further screening process suggests that 28 promising
candidates have superior thermodynamic stability, hence they are highly likely
to be synthesized. Moreover, these compounds possess several identical
electronic structures, and can be categorized into five non-magnetic and three
magnetic groups accordingly. It is our hope that this work can greatly expand
the viable phase space of the CsV3Sb5-like materials for investigating or
tuning the novel quantum phenomena in kagome lattice.",2202.05645v1
2022/8/6,Defect control in the Heisenberg-Kitaev candidate material NaRuO$_2$,"The combination of geometric frustration, extended hopping, spin-orbit
coupling, and a disordered magnetic ground state make NaRuO$_{2}$ an attractive
Heisenberg-Kitaev candidate material. Historically, NaRuO$_2$ has been a
challenging material to produce, even in polycrystalline form. Here we present
synthetic efforts that identify a propensity for Na$_\text{Ru}$ defects to form
in NaRuO$_2$, revealing a full solid-solution between NaRuO$_{2}$ and
disordered Na$_2$RuO$_3$. We report the synthesis of alloys along the
Na$_{3+x}$Ru$_{3-x}$O$_6$ solid solution and characterize changes in the bulk
magnetization and electron transport as a function of Na-loading. Our results
highlight the importance of stoichiometry control in NaRuO$_{2}$ when
investigating and interpreting this material's physical properties.",2208.03428v2
2022/10/18,"Misfit Layered Compounds: Unique, Tunable Heterostructured Materials with Untapped Properties","Building on discoveries in graphene and two-dimensional (2D) transition metal
dichalcogenides, van der Waals (VdW) layered heterostructures - stacks of such
2D materials - are being extensively explored with resulting new discoveries of
novel electronic and magnetic properties in the ultrathin limit. Here we review
a class of naturally occurring heterostructures - so called misfits - that
combine disparate VdW layers with complex stacking. Exhibiting remarkable
structural complexity and diversity of phenomena, misfits provide a platform on
which to systematically explore the energetics and local bonding constraints of
heterostructures and how they can be used to engineer novel quantum fabrics,
electronic responsiveness, and magnetic phenomena. Like traditional classes of
layered materials, they are often exfoliatable and thus also incorporatable as
units in manually or robotically stacked heterostructures. Here we review the
known classes of misfit structures, the tools for their single crystal and thin
film synthesis, the physical properties they exhibit, and computational and
characterization tools that are unraveling their complexity. Directions for
future research are also discussed.",2210.10116v1
2022/12/16,Weyl excitations via helicon-phonon mixing in conducting materials,"Quasiparticles with Weyl dispersion can display an abundance of novel
topological, thermodynamic and transport phenomena, which is why novel Weyl
materials and platforms for Weyl physics are being intensively looked for in
electronic, magnetic, photonic and acoustic systems. We demonstrate that
conducting materials in magnetic fields generically host Weyl excitations due
to the hybridisation of phonons with helicons, collective neutral modes of
electrons interacting with electromagnetic waves propagating in the material.
Such Weyl excitations are, in general, created by the interactions of helicons
with longitudinal acoustic phonons. An additional type of Weyl excitation in
polar crystals comes from the interaction between helicons and longitudinal
optical phonons. Such excitations can be detected in X-ray and Raman scattering
experiments. The existence of the Weyl excitations involving optical phonons in
the bulk of the materials also leads to the formation of topologically
protected surface arc states that can be detected via surface plasmon
resonance.",2212.08213v3
2023/1/6,First-principles Investigation of Electrides Derived from Sodalites,"Recently, the electride materials, with excess anionic electrons confined in
their empty space, have received a growing attention due to their promising
applications in catalysis, nonlinear optics and spin-electronics. However, the
utilization of electride materials is limited by their thermal instability.
Here we introduce an alternative way to achieve the localized anionic electron
states via the removal of high symmetric Wyckoff sites of anions from the
existing sodalite compounds. Using four halide sodalites as the parental
structures, our simulation reveals that the materials after the removal of
anionic halide sites exhibit typical electride behaviors that are characterized
by the existence of localized electronic states near the Fermi level. Compared
to most previously studied electrides, these materials are expected to be more
thermally stable due to the complex structural framework and thus promising for
practical applications. Among them, Na$_4$(AlSiO$_4$)$_3$ manifests magnetic
electronic structure. We demonstrate that this magnetism originates from a
highly localized excess electron state surrounded by electronpositive alkaline
cations. Our results suggest Na$_4$(AlSiO$_4$)$_3$ could be a promising
spintronics component, thus encouraging further experimental study.",2301.02716v1
2023/5/30,Perpendicular in-plane negative magnetoresistance in ZrTe5,"The unique band structure in topological materials frequently results in
unusual magneto-transport phenomena, one of which is in-plane longitudinal
negative magnetoresistance (NMR) with the magnetic field aligned parallel to
the electrical current direction. This NMR is widely considered as a hallmark
of chiral anomaly in topological materials. Here we report the observation of
in-plane NMR in the topological material ZrTe5 when the in-plane magnetic field
is both parallel and perpendicular to the current direction, revealing an
unusual case of quantum transport beyond the chiral anomaly. We find that a
general theoretical model, which considers the combined effect of Berry
curvature and orbital moment, can quantitatively explain this in-plane NMR. Our
results provide new insights into the understanding of in-plane NMR in
topological materials.",2305.19009v1
2023/9/6,Composite (multi)ferroic order,"The formalism of composite and intertwined orders has been remarkably
successful in discussing the complex phase diagrams of strongly correlated
materials and high-$T_c$ superconductors. Here, we argue that composite orders
are also realized in ferroelectric and ferromagnetic materials if the lattice
anisotropy is taken into account. Such a composite order emerges above the
ferroic phase transition and its existence is fully determined by the easy axis
of the magnetization or polarization, respectively. In multiferroic materials,
where polarization and magnetization couple, composites of both orders are
possible. It turns out that the formalism of composite orders naturally
accounts for the magnetoelectric monopol, toroidal, and quadrupole orders. More
generally, composite orders might be relevant for explaining precursor
phenomena in incipient (multi)ferroic materials, as they arise at temperatures
above the ferroic phase transition and may contribute to the characterization
of currently hidden orders.",2309.03312v2
2023/9/23,Phonon chirality manipulation mechanism in TMD interlayer-sliding ferroelectrics,"As an ideal platform, both the theoretical prediction and first experimental
verification of chiral phonons are based on transition-metal dichalcogenide
materials. The manipulation of phonon chirality in these materials will have a
profound impact on the study of chiral phonons. In this work, we utilize the
sliding ferroelectric mechanism to study the phonon chirality manipulation
mechanism in transition-metal dichalcogenide materials. Based on
first-principles calculations, we study the different effects of interlayer
sliding on the phonon properties in bilayer and four-layer MoS$_2$ sliding
ferroelectrics. We find that sliding can regulate phonon chirality and Berry
curvature, which further affects the phonon angular momentum and magnetization
under a temperature gradient and the phonon Hall effect under a magnetic field.
Our work connects two emerging fields and opens up a new route to manipulate
phonon chirality in transition-metal dichalcogenide materials through the
sliding ferroelectric mechanism.",2309.13260v1
2023/10/26,Effects of Finite Material Size On Axion-magnon Conversion,"Magnetic materials are particularly favorable targets for detecting axions
interacting with electrons because the collective excitation of electron spins,
the magnon, can be excited through the axion-magnon conversion process. It is
often assumed that only the zero-momentum uniformly precessing magnetostatic
(Kittel) mode of the magnon is excited. This is justified if the de Broglie
wavelength of the axion is much longer than the size of the target magnetic
material. However, if the de Broglie wavelength is shorter, finite-momentum
magnon modes can also be excited. We systematically analyze the target material
size dependence of the axion-magnon conversion rate. We discuss the importance
of these effects in the detection of relativistic axions as well as in the
detection of axion dark matter of relatively heavy mass with large material
size.",2310.17704v2
2023/4/13,Probing magnetic ordering in air stable iron-rich van der Waals minerals,"In the rapidly expanding field of two-dimensional materials, magnetic
monolayers show great promise for the future applications in nanoelectronics,
data storage, and sensing. The research in intrinsically magnetic
two-dimensional materials mainly focuses on synthetic iodide and telluride
based compounds, which inherently suffer from the lack of ambient stability. So
far, naturally occurring layered magnetic materials have been vastly
overlooked. These minerals offer a unique opportunity to explore air-stable
complex layered systems with high concentration of local moment bearing ions.
We demonstrate magnetic ordering in iron-rich two-dimensional phyllosilicates,
focusing on mineral species of minnesotaite, annite, and biotite. These are
naturally occurring van der Waals magnetic materials which integrate local
moment baring ions of iron via magnesium/aluminium substitution in their
octahedral sites. Due to self-inherent capping by silicate/aluminate
tetrahedral groups, ultra-thin layers are air-stable. Chemical
characterization, quantitative elemental analysis, and iron oxidation states
were determined via Raman spectroscopy, wavelength disperse X-ray spectroscopy,
X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy.
Superconducting quantum interference device magnetometry measurements were
performed to examine the magnetic ordering. These layered materials exhibit
paramagnetic or superparamagnetic characteristics at room temperature. At low
temperature ferrimagnetic or antiferromagnetic ordering occurs, with the
critical ordering temperature of 38.7 K for minnesotaite, 36.1 K for annite,
and 4.9 K for biotite. In-field magnetic force microscopy on iron bearing
phyllosilicates confirmed the paramagnetic response at room temperature,
present down to monolayers.",2304.06533v1
2011/8/15,Polar octahedral rotations: a path to new multifunctional materials,"Perovskite ABO$_3$ oxides display an amazing variety of phenomena that can be
altered by subtle changes in the chemistry and internal structure, making them
a favorite class of materials to explore the rational design of novel
properties. Here we highlight a recent advance in which rotations of the BO$_6$
octahedra give rise to a novel form of ferroelectricity -- hybrid improper
ferroelectricity. Octahedral rotations also strongly influence other
structural, magnetic, orbital, and electronic degrees of freedom in perovskites
and related materials. Octahedral rotation-driven ferroelectricity consequently
has the potential to robustly control emergent phenomena with an applied
electric field. The concept of `functional' octahedral rotations is introduced
and the challenges for materials chemistry and the possibilities for new
rotation-driven phenomena in multifunctional materials are explored.",1108.2915v2
2016/2/11,Ferroelectricity in corundum derivatives,"The search for new ferroelectric (FE) materials holds promise for broadening
our understanding of FE mechanisms and extending the range of application of FE
materials. Here we investigate a class of ABO3 and A2BB'O6 materials that can
be derived from the X2O3 corundum structure by mixing two or three ordered
cations on the X site. Most such corundum derivatives have a polar structure,
but it is unclear whether the polarization is reversible, which is a
requirement for a FE material. In this paper, we propose a method to study the
FE reversal path of materials in the corundum derivative family. We first
categorize the corundum derivatives into four classes and show that only two of
these allow for the possibility of FE reversal. We then calculate the energy
profile and energy barrier of the FE reversal path using first-principles
density functional methods with a structural constraint. Furthermore, we
identify several empirical measures that can provide a rule of thumb for
estimating the energy barriers. Finally, the conditions under which the
magnetic ordering is compatible with ferroelectricity are determined. These
results lead us to predict several potentially new FE materials.",1602.03852v1
2016/3/10,Engineering charge ordering into multiferroicity,"Multiferroic materials have attracted great interests but are rare in nature.
In many transitional metal oxides, charge ordering and magnetic ordering
coexist, so that a method of engineering charge-ordered materials into
ferroelectric materials would lead to a large class of multiferroic materials.
We propose a strategy for designing new ferroelectric or even multiferroic
materials by inserting a spacing layer into each two layers of charge-ordered
materials and artificially making a superlattice. One example of the model
demonstrated here is the perovskite (LaFeO$_3$)$_2$/LaTiO$_3$ (111)
superlattice, in which the LaTiO$_3$ layer acts as the donor and the spacing
layer, and the LaFeO$_3$ layer is half doped and performs charge ordering. The
collaboration of the charge ordering and the spacing layer breaks the space
inversion symmetry, resulting in a large ferroelectric polarization. As the
charge ordering also leads to a ferrimagnetic structure, the
(LaFeO$_3$)$_2$/LaTiO$_3$ is multiferroic. It is expected that this work can
encourage the designing and experimentally implementation of a large class of
multiferroic structures with novel properties.",1603.03253v1
2016/4/20,Concepts of Ferrovalley Material and Anomalous Valley Hall Effect,"Valleytronics rooted in the valley degree of freedom is of both theoretical
and technological importance as it offers additional opportunities for
information storage and electronic, magnetic and optical switches. In analogy
to ferroelectric materials with spontaneous charge polarization in electronics,
as well as ferromagnetic materials with spontaneous spin polarization in
spintronics, here we introduce a new member of ferroic-family, i.e. a
ferrovalley material with spontaneous valley polarization. Combining a two-band
kp model with first-principles calculations, we show that 2H-VSe2 monolayer,
where the spin-orbit coupling coexists with the intrinsic exchange interaction
of transition-metal-d electrons, is such a room-temperature ferrovalley
material. We further predict that such system could demonstrate many
distinctive properties, for example, chirality-dependent optical band gap and
more interestingly, anomalous valley Hall effect. On account of the latter, a
series of functional devices based on ferrovalley materials, such as
valley-based nonvolatile random access memory, valley filter, are contemplated
for valleytronic applications.",1604.05833v3
2016/11/13,Topological Materials: Weyl Semimetals,"Topological insulators and topological semimetals are both new classes of
quantum materials, which are characterized by surface states induced by the
topology of the bulk band structure. Topological Dirac or Weyl semimetals show
linear dispersion round nodes, termed the Dirac or Weyl points, as the
three-dimensional analogue of graphene. We review the basic concepts and
compare these topological states of matter from the materials perspective with
a special focus on Weyl semimetals. The TaAs family is the ideal materials
class to introduce the signatures of Weyl points in a pedagogical way, from
Fermi arcs to the chiral magneto-transport properties, followed by the hunting
for the type-II Weyl semimetals in WTe2, MoTe2 and related compounds. Many
materials are members of big families and topological properties can be tuned.
As one example, we introduce the multifuntional topological materials, Heusler
compounds, in which both topological insulators and magnetic Weyl semimetals
can be found. Instead of a comprehensive review, this article is expected to
serve as a helpful introduction and summary by taking a snapshot of the quickly
expanding field.",1611.04182v2
2018/8/31,Engineering artificial topological phases via superlattices,"The search for new topological materials and states of matter is presently at
the forefront of quantum materials research. One powerful approach to novel
topological phases beyond the thermodynamic space is to combine different
topological/functional materials into a single materials platform in the form
of superlattices. However, despite some previous efforts, there has been a
significant gap between theories and experiments in this direction. Here, we
provide the first detailed set of experimentally-verifiable phase diagrams of
topological superlattices composed of archetypal topological insulator (TI),
Bi$_{2}$Se$_{3}$, and normal insulator (NI), In$_{2}$Se$_{3}$, by combining
molecular-level materials control, low-temperature magnetotransport
measurements, and field theoretical calculations. We show how the electronic
properties of topological superlattices evolve with unit-layer thicknesses and
utilize the weak antilocalization effect as a tool to gain quantitative
insights into the evolution of conducting channels within each set of
heterostructures. This orchestrated study opens the door to the possibility of
creating a variety of artificial-topological-phases by combining topological
materials with various other functional building blocks such as superconductors
and magnetic materials.",1808.10829v2
2019/3/15,Type-II Ising superconductivity in two-dimensional materials with strong spin-orbit coupling,"Recent discovery of Ising superconductivity protected against in-plane
magnetic field by spin-orbit coupling (SOC) has stimulated intensive research
interests. The effect, however, was only expected to appear in two-dimensional
(2D) noncentrosymmetric materials with spin-valley locking. In this work, we
proposed a new type of Ising superconductivity in 2D materials with $C_{nz}$
rotational symmetry ($n=3,4,6$). This mechanism, dubbed as type-II Ising
superconductivity, is applicable for centrosymmetric materials. Type-II Ising
superconductivity relies on the SOC-induced spin-orbital locking characterized
by Ising-type Zeeman-like fields displaying opposite signs for opposing
orbitals. We found that type-II Ising superconductivity are most prominent
around time-reversal invariant momenta and is not sensitive to inversion
symmetry breaking. By performing high-throughput first-principles calculations,
about one hundred candidate materials were identified. Our work significantly
enriches the physics and materials of Ising superconductor, opening new
opportunities for fundamental research and practical applications of 2D
materials.",1903.06660v3
2019/6/4,Two-dimensional topological materials discovery by symmetry-indicator method,"Two-dimensional (2D) topological materials (TMs) have attracted tremendous
attention due to the promise of revolutionary devices with non-dissipative
electric or spin currents. Unfortunately, the scarcity of 2D TMs holds back the
experimental realization of such devices. In this work, based on our recently
developed, highly efficient TM discovery algorithm using symmetry indicators,
we explore the possible 2D TMs in all non-magnetic compounds in four recently
proposed materials databases for possible 2D materials. We identify hundreds of
2D TM candidates, including 205 topological (crystalline) insulators and 299
topological semimetals. In particular, we highlight MoS, with a mirror Chern
number of -4, as a possible experimental platform for studying the
interaction-induced modification to the topological classification of
materials. Our results winnow out the topologically interesting 2D materials
from these databases and provide a TM gene pool which for further experimental
studies.",1906.01283v1
2020/5/27,Graph Neural Network for Hamiltonian-Based Material Property Prediction,"Development of next-generation electronic devices for applications call for
the discovery of quantum materials hosting novel electronic, magnetic, and
topological properties. Traditional electronic structure methods require
expensive computation time and memory consumption, thus a fast and accurate
prediction model is desired with increasing importance. Representing the
interactions among atomic orbitals in any material, a material Hamiltonian
provides all the essential elements that control the structure-property
correlations in inorganic compounds. Effective learning of material Hamiltonian
by developing machine learning methodologies therefore offers a transformative
approach to accelerate the discovery and design of quantum materials. With this
motivation, we present and compare several different graph convolution networks
that are able to predict the band gap for inorganic materials. The models are
developed to incorporate two different features: the information of each
orbital itself and the interaction between each other. The information of each
orbital includes the name, relative coordinates with respect to the center of
super cell and the atom number, while the interaction between orbitals are
represented by the Hamiltonian matrix. The results show that our model can get
a promising prediction accuracy with cross-validation.",2005.13352v1
2020/7/8,Anisotropic properties of monolayer 2D materials: an overview from the C2DB database,"We analyze the occurrence of in-plane anisotropy in the electronic, magnetic,
elastic and transport properties of more than one thousand 2D materials from
the C2DB database. We identify hundreds of anisotropic materials and classify
them according to their point group symmetry and degree of anisotropy. A
statistical analysis reveals that a lower point group symmetry and a larger
amount of different elements in the structure favour all types of anisotropies,
which could be relevant for future materials design approaches. Besides, we
identify novel compounds, predicted to be easily exfoliable from a parent bulk
compound, with anisotropies that largely outscore those of already known 2D
materials. Our findings provide a comprehensive reference for future studies of
anisotropic response in atomically-thin crystals and point to new previously
unexplored materials for the next generation of anisotropic 2D devices.",2007.04152v2
2020/9/24,Beyond Graphene: Low-Symmetry and Anisotropic 2D Materials,"Low-symmetry 2D materials---such as ReS$_2$ and ReSe$_2$ monolayers, black
phosphorus monolayers, group-IV monochalcogenide monolayers, borophene, among
others---have more complex atomistic structures than the honeycomb lattices of
graphene, hexagonal boron nitride, and transition metal dichalcogenides. The
reduced symmetries of these emerging materials give rise to inhomogeneous
electron, optical, valley, and spin responses, as well as entirely new
properties such as ferroelasticity, ferroelectricity, magnetism, spin-wave
phenomena, large nonlinear optical properties, photogalvanic effects, and
superconductivity. Novel electronic topological properties, nonlinear elastic
properties, and structural phase transformations can also take place due to low
symmetry. The ""Beyond Graphene: Low-Symmetry and Anisotropic 2D Materials""
Special Topic was assembled to highlight recent experimental and theoretical
research on these emerging materials.",2009.11584v1
2021/10/6,Strain Switching in van der Waals Heterostructures triggered by a Spin-Crossover Metal Organic Framework,"Van der Waals heterostructures (vdWHs) combine different layered materials
with properties of interest,1 such as two-dimensional (2D) semimetals,
semiconductors, magnets or superconductors. These heterostructures provide the
possibility of engineering new materials with emergent functionalities that are
not accessible in another way. Beyond inorganic 2D materials, layered molecular
materials remain still rather unexplored, with only few examples regarding
their isolation as atomically thin-layers. By a proper chemical design, the
physical properties of these systems can be tuned, as illustrated by the
so-called spin-crossover (SCO) compounds, in which a spin transition can be
induced by applying external stimuli like light, temperature, pressure or an
electric field. Here, we report on vdWHs formed by SCO layers and few-layers
graphene, being its properties modified by the strain concomitant to the spin
transition. These molecular/inorganic vdWHs represent the deterministic
incorporation of bistable molecular layers with other 2D materials of interest
in the emergent field of straintronics.",2110.02990v2
2022/4/1,Computational exfoliation of atomically thin 1D materials with application to Majorana bound states,"We introduce a computational database with calculated structural,
thermodynamic, electronic, magnetic, and optical properties of 820
one-dimensional materials. The materials are systematically selected and
exfoliated from experimental databases of crystal structures based on a
dimensionality scoring parameter. The database is furthermore expanded by
chemical element substitution in the materials. The materials are investigated
in both their bulk form and as isolated one-dimensional components. We discuss
the methodology behind the database, give an overview of some of the calculated
properties, and look at patterns and correlations in the data. The database is
furthermore applied in computational screening to identify materials, which
could exhibit Majorana bound states.",2204.00472v1
2022/7/12,Absorption $\textit{versus}$ Adsorption: High-Throughput Computation of Impurities in 2D Materials,"Doping of a two-dimensional (2D) material by impurity atoms occurs
\textit{via} two distinct mechanisms: absorption of the dopants by the 2D
crystal or adsorption on its surface. To distinguish the relevant mechanism, we
systematically dope 53 experimentally synthesized 2D monolayers by 65 different
chemical elements in both absorption and adsorption sites. The resulting 17,598
doped monolayer structures were generated using the newly developed ASE
\texttt{DefectBuilder} -- a Python tool to set up point defects in 2D and bulk
materials -- and subsequently relaxed by an automated high-throughput density
functional theory (DFT) workflow. We find that interstitial positions are
preferred for small dopants with partially filled valence electrons in host
materials with large lattice parameters. On the contrary, adatoms are favored
for dopants with a low number of valence electrons due to lower coordination of
adsorption sites compared to interstitials. The relaxed structures,
characterization parameters, defect formation energies, and magnetic moments
(spins) are available in an open database to help advance our understanding of
defects in 2D materials.",2207.05353v2
2023/8/4,Multimodal machine learning for materials science: composition-structure bimodal learning for experimentally measured properties,"The widespread application of multimodal machine learning models like GPT-4
has revolutionized various research fields including computer vision and
natural language processing. However, its implementation in materials
informatics remains underexplored, despite the presence of materials data
across diverse modalities, such as composition and structure. The effectiveness
of machine learning models trained on large calculated datasets depends on the
accuracy of calculations, while experimental datasets often have limited data
availability and incomplete information. This paper introduces a novel approach
to multimodal machine learning in materials science via composition-structure
bimodal learning. The proposed COmposition-Structure Bimodal Network (COSNet)
is designed to enhance learning and predictions of experimentally measured
materials properties that have incomplete structure information. Bimodal
learning significantly reduces prediction errors across distinct materials
properties including Li conductivity in solid electrolyte, band gap, refractive
index, dielectric constant, energy, and magnetic moment, surpassing
composition-only learning methods. Furthermore, we identified that data
augmentation based on modal availability plays a pivotal role in the success of
bimodal learning.",2309.04478v1
1996/11/26,Magnetic Oscillations and Maxwell Theory,"We explore the possibility of using the Kaluza-Klein geometry of Riemannian
Submersions to modify the classical Maxwell Theory. We further argue that the
resulting modification of Electromagnetism may be interesting in the context
of, among other topics, magnetic oscillations in metals.",9611205v1
1998/11/10,Coupling between electron-spin and ferromagnetic clusters,"We analyze the adiabatic magnetization of ferromagnetic clusters in an
intermediate coupling regime, where the anisotropic potential is comparable to
other energy scales. We find a non-monotonic behavior of the magnetic
susceptibility as a function of coupling with a peak. Coriolis coupling effects
are calculated for the first time; they reduce the susceptibility somewhat.",9811126v1
2000/10/26,Invalidation of the Kelvin Force in Ferrofluids,"Direct and unambiguous experimental evidence for the magnetic force density
being of the form $M\nabla B$ in a certain geometry - rather than being the
Kelvin force $M\nabla H$ - is provided for the first time. (M is the
magnetization, H the field, and B the flux density.)",0010412v1
2001/1/30,Magnetism of a tetrahedral cluster-chain,"Magnetic properties of a completely frustrated tetrahedral chain are briefly
summarized. Using exact diagonalization, and bond-operator theory results for
the ground-state phase diagram, the one-triplet excitations and the Raman
spectrum are given. The link to novel tellurate materials is clarified.",0101460v1
2002/6/12,Proposal for in situ Enhancement of Electron Spin Polarization in Semiconductors,"An extension of the original Overhauser effect to a more general
nonequilibrium state was proposed by G. Feher, and demonstrated by Clark and
Feher some forty years ago. It is suggested here that it might be possible to
produce excess electron spin polarization by allowing the role of the nuclei to
be played by other magnetic entities, such as paramagnetic impurities or
adjacent magnetically ordered structures.",0206215v1
2002/8/2,Phase diagram as a function of temperature and magnetic field for magnetic semiconductors,"Using an extension of the Nagaev model of phase separation (E.L. Nagaev, and
A.I. Podel'shchikov, Sov. Phys. JETP, 71 (1990) 1108), we calculate the phase
diagram for degenerate antiferromagnetic semiconductors in the T-H plane for
different current carrier densities. Both, wide-band semiconductors and
'double-exchange' materials, are investigated.",0208041v1
2002/8/21,Re-entrant spin glass and magnetoresistance in Co_{0.2}Zn_{0.8}Fe_{1.6}Ti_{0.4}O_4 spinel oxide,"We have investigated the static and dynamic response of magnetic clusters in
Co_{0.2}Zn_{0.8}Fe_{1.6}Ti_{0.4}O_4 spinel oxide, where a sequence of magnetic
phase transitions, i.e., paramagnetic (PM) to ferromagnetic at T_{C} $\leq$
270K and ferromagnetic to canted spin glass state at T_f$ $\leq$ 125K is
observed.",0208416v1
2002/12/27,On the Competition between Ferromagnetic and Antiferromagnetic States in Sr$_2$MnMoO$_6,"It is argued that the magnetic behavior of Sr$_2$MnMoO$_6$ is determined by
the existence of two total energy minima corresponding to the metallic
ferromagnetic and insulating antiferromagnetic states, which may be nearly
degenerate depending on the magnitude of the breathing distortion.",0212607v1
2003/1/10,An exact sampling scheme for Brownian motion in the presence of a magnetic field,"Langevin equation pertinent to diffusion limited aggregation of charged
particles in the presence of an external magnetic field is solved exactly. The
solution involves correlated random variables. A new scheme for exactly
sampling the components of the position and velocity is proposed.",0301136v1
2003/5/5,Persistent Spin Currents in Helimagnets,"We demonstrate that weak external magnetic fields generate dissipationless
spin currents in the ground state of systems with spiral magnetic order. Our
conclusions are based on phenomenological considerations and on microscopic
mean-field theory calculations for an illustrative toy model. We speculate on
possible applications of this effect in spintronic devices.",0305069v2
2003/8/15,Symmetry of Magnetically-Ordered Three-Dimensional Octagonal Quasicrystals,"The theory of magnetic symmetry in quasicrystals, described in a companion
paper [cond-mat/0304669], is used to enumerate all 3-dimensional octagonal spin
point groups and spin space-group types, and calculate the resulting selection
rules for neutron diffraction experiments.",0308322v1
2003/9/26,Vortex dynamics in dilute two dimensional Josephson junction arrays,"We have investigated the dynamics of vortices in a dilute two dimensional
Josephson junction array where a fraction of the superconducting islands is
missing. We have used the multiple trapping model to calculate the mobility of
vortices and the frequency dependence of the resistance and inductance of the
array.",0309620v1
2003/10/16,Electromagnetic radiation produced by avalanches in the magnetization reversal of Mn12-Acetate,"Electromagnetic radiation produced by avalanches in the magnetization
reversal of Mn12-Acetate has been measured. Short bursts of radiation have been
detected, with intensity significantly exceeding the intensity of the
black-body radiation from the sample. The model based upon superradiance from
inversely populated spin levels has been suggested.",0310385v1
2004/1/29,Intrinsic Josephson Effects in the Magnetic Superconductor RuSr2GdCu2O8,"We have measured interlayer current transport in small sized RuSr2GdCu2O8
single crystals. We find a clear intrinsic Josephson effect showing that the
material acts as a natural
superconductor-insulator-ferromagnet-insulator-superconductor superlattice. So
far, we detected no unconventional behavior due to the magnetism of the RuO2
layers.",0401606v1
2004/3/29,Correlation effects in Co/Cu and Fe/Cr magnetic multilayers,"The electronic structure of Co/Cu(001) and Fe/Cr(001) magnetic multilayers
has been investigated within the local density approximation combined with
dynamical mean field theory. Our calculation shows enhanced density of states
at the Fermi level, suggesting that electronic correlations might play an
important role in the transport properties of multilayers.",0403685v1
2004/4/7,Influence of point defects on magnetic vortex structures,"We employed micro-Hall magnetometry and micromagnetic simulations to
investigate magnetic vortex pinning at single point defects in individual
submicron-sized permalloy disks. Small ferromagnetic particles containing
artificial point defects can be fabricated by using an image reversal electron
beam lithography process. Corresponding micromagnetic calculations, modeling
the defects within the disks as holes, give reasonable agreement between
experimental and simulated pinning and depinning field values.",0404159v1
2004/4/8,Stoner-Wohlfart model applied to bicrystal magnetoresistance hysteresis,"We calculate numerically the magnetization direction as function of magnetic
field in the Stoner-Wohlfart theory and are able to reproduce the shape of the
low-field magnetoresistance hysteresis observed in manganite grain boundary
junctions. Moreover, we show that it is necessary to include biaxial
magnetocrystalline anisotropy to fully describe the grain boundary
magnetoresistance in La$_{0.7}$Sr$_{0.3}$MnO$_3$/SrTiO$_3$ bicrystal tunnel
junctions.",0404193v1
2004/6/24,Orbital ordering and magnetic structures in $\LMFO$ and $\LWFO$ double perovskites,"We analyzed the possible magnetic and orbital orderings of double
perovskites, using a simple extension of the double exchange model well suited
for these compounds. Orbital ordering is favored by the on site repulsion at
the Fe ions. We obtain a rich phase diagram, including ferri- and
antiferromagnetic phases, which can, in turn, be metallic or insulating,
depending on the existence of orbital order.",0406605v1
2005/3/1,Low Dimensional Lattice Diffusion in Solids Investigated by Nuclear Spin Echo Measurements,"Lattice diffusion and internal local magnetic field gradients in solids are
investigated by numerical simulation of nuclear mangetic resonance(NMR) spin
echo experiments. The Fourier-spectrum method is employed in order to solve the
Bloch-Torrey equation with arbitrary magnetic field gradients in one- and
two-dimensional lattice restrictions.",0503003v1
2005/5/10,Fluctuation-dissipation considerations and damping models for ferromagnetic materials,"The role of fluctuation-dissipation relations (theorems) for the
magnetization dynamics with Landau-Lifshitz-Gilbert and Bloch-Bloembergen
damping terms are discussed. We demonstrate that the use of the Callen-Welton
fluctuation-dissipation theorem that was proven for Hamiltonian systems can
give an inconsistent result for magnetic systems with dissipation.",0505259v1
2005/8/31,Planar Hall Effect MRAM,"We suggest a new type of magnetic random access memory (MRAM) that is based
on the phenomenon of the planar Hall effect (PHE) in magnetic films, and we
demonstrate this idea with manganite films. The PHE-MRAM is structurally
simpler than currently developed MRAM that is based on magnetoresistance tunnel
junctions (MTJ), with the tunnel junction structure being replaced by a single
layer film.",0508772v1
2005/11/16,"Crystal field and spin-fluctuations in heavy fermion metal CeAl3, YbRh2Si2 and UPd2Al3*","We have shown the existence of localized crystal-field states in conducting
magnetic materials coexisting with conduction electrons in CeAl3, UPd2Al3 and
YbRh2Si2. We point out that the magnetism is strongly correlated with the very
detailed local atomic-scale crystal structure.",0511397v1
2006/1/17,Spin wave instabilities and field induced transitions in heavy fermions,"We study phase transitions in heavy fermion systems due to spin-wave
instabilities. One motivation is to determine the changes in the spin-wave
parameters of a magnetically ordered heavy fermion system as it approaches a
quantum critical point (QCP) by applying pressure. The other more actual is to
provide an alternative approach, based on spin-wave instabilities, for the
magnetic field induced transitions recently observed in antiferromagnetic heavy
fermion materials.",0601385v1
2006/2/21,Magnetic-induced phonon anisotropy in ZnCr$_2$O$_4$ from first principles,"We have studied the influence of magnetic order on the optical phonons of the
geometrically frustrated spinel ZnCr$_2$O$_4$ from first-principles. By mapping
the first-principles phonon calculations onto a Heisenberg-like model, we
developed a method to calculate exchange derivatives and subsequently the
spin-phonon couping parameter from first-principles. All calculations were
performed within LSDA+U.",0602503v1
2006/3/9,Elastic domains in antiferromagnets,"We consider periodic domain structures which appear due to the magnetoelastic
interaction if the antiferromagnetic crystal is attached to an elastic
substrate. The peculiar behavior of such structures in an external magnetic
field is discussed. In particular, we find the magnetic field dependence of the
equilibrium period and the concentrations of different domains.",0603248v1
2006/8/1,Stability of magnetic configurations in nanorings,"The relative stability of the vortex, onion and ferromagnetic phases in
nanorings is examined as a function of the ring geometry. Total energy
calculations are carried out analytically, based on simple models for each
configuration. Results are summarized by phase diagrams, which might be used as
a guide to the production of rings with specific magnetic properties.",0608037v1
2006/11/9,Spin density wave formation in graphene facilitated by the in-plane magnetic field,"We suggest that by applying a magnetic field lying in the plane of graphene
layer one may facilitate an excitonic condensation of electron-hole pairs with
opposite spins and chiralities. The provided calculations yield a conservative
estimate for the transition temperature $T_c \sim 0.1 B$.",0611251v1
2007/3/4,Localized steady-state domain wall oscillators,"We predict a spatially localized magnetic domain wall oscillator upon the
application of an external magnetic field and a DC electric current. The
amplitude and frequency of the oscillator can be controlled by the field and/or
the current. The resulting oscillator could be used as an effective microwave
source for information storage application.",0703105v1
1997/3/5,Region of magnetic dominance near a rotating black hole,"This is a brief contribution in which a simplified criterion of the relevance
of the test-particle approximation describing motion of material near a
magnetized black hole is discussed. Application to processes of the dissipative
collimation of astronomical jets (as proposed by de Felice and Curir, 1992) is
mentioned.",9703014v1
2006/6/14,Negative index metamaterial combining magnetic resonators with metal films,"We present simulation results of a design for negative index materials that
uses magnetic resonators to provide negative permeability and metal film for
negative permittivity. We also discuss the possibility of using semicontinuous
metal films to achieve better manufacturability and enhanced impedance
matching.",0606129v1
2006/6/7,Limit to manipulation of qubits due to spontaneous symmetry breaking,"We consider a two-spin qubit that is subject to the orderparameter field of a
symmetry broken manipulation device. It is shown that the thin spectrum of the
manipulation device limits the coherence of the qubit.",0606058v1
2007/4/4,Reply to Comment of Kenzelmann and Harris,"In response to the comment of Kenzelmann and Harris I show how the continuum
theory of spiral multiferroics can be modified to describe general magnetic
orders and discuss why the microscopic mechanism of magnetically-induced
ferroelectricity usually makes such modifications unnecessary. This explains
why the simple model with a single vector order parameter successfully
describes thermodynamics and magnetoelectric properties of many spiral
multiferroics.",0704.0545v1
2007/6/3,Form factors in magnetic scattering of thermal neutrons,"This lecture addresses the concept of form factor in magnetic scattering of
thermal neutrons, analyzing its meaning, discussing its measurement by
polarized neutrons and detailing its computation for the ions by the spherical
tensor operator formalism.",0706.0335v1
2008/12/12,Magnetoelectric Effect for Novel Microwave Device Applications,"In a normally magnetized thin-film ferrite disk with magnetic-dipolar modes,
one can observe magnetoelectric oscillations. Such magnetoelectric properties
of an electrically small sample can be considered as very attractive phenomena
in microwaves. In this paper we discuss the question on novel microwave device
applications based on ferrite magnetoelectric particles.",0812.2343v2
2009/1/5,Smectic to nematic transition of magnetic texture in conical state,"Small-angle neutron scattering (SANS) profiles revealed the existence of
magnetic textures like liquid crystals in the low-temperature helical phase of
Fe0.7Co0.3Si, isomorphous of MnSi.",0901.0428v1
2009/10/28,Preparation of Cobalt Thin Films by Sputtering Systems and Its Magnetic Characterization,"Different thicknesses of cobalt thin films were growth by magnetron
sputtering deposition techniques. The films thicknesses were determinated with
X ray Photoelectron Spectroscopy (XPS) and Quartz Crystal Monitoring (QCM). XPS
is also used to determinate the films quality. The films magnetic properties
were determinated by Ferromagnetic Resonance (FMR) technique.",0910.5452v1
2009/11/12,Spin Resonance and dc Current Generation in a Quantum Wire,"We show that in a quantum wire the spin-orbit interaction leads to a narrow
spin resonance at low temperatures, even in the absence of an external magnetic
field. Resonance absorption by linearly polarized radiation gives a dc spin
current; resonance absorption by circularly polarized radiation gives a dc
electric current or magnetization.",0911.2433v1
2009/11/18,Thermal effects in the magnetic Casimir-Polder interaction,"We investigate the magnetic dipole coupling between a metallic surface and an
atom in a thermal state, ground state and excited hyperine state. This
interaction results in a repulsive correction and - unlike the electrical
dipole contribution - depends sensitively on the Ohmic dissipation in the
material.",0911.3483v1
2010/1/29,Cooper pairs under the action of disorder and strong magnetic field,"The zero temperature phase diagram of Cooper pairs exposed to disorder and
magnetic field is found to exhibit four distinct phases: a Bose and a Fermi
insulating, a metallic and a superconducting phase, respectively. The results
explain the giant negative magneto-resistance found experimentally in In-O,
TiN, Bi and high-$T_c$ materials.",1001.5431v2
2010/5/19,Observing Monopoles in a Magnetic Analog of Ice,"This is a nontechnical Perspective commentary on two recent neutron
scattering experiments (Science 326, 415 (2009) and Science 326, 411 (2009))
reporting evidence for the validity of a ""Coulomb phase"" description of the
low-temperature regime of frustrated spin ice magnetic materials as well as the
existence of topological defect (monopole-like) excitations in these systems.",1005.3557v1
2010/10/23,Effective Maxwell equations from time-dependent density functional theory,"The behavior of interacting electrons in a perfect crystal under macroscopic
external electric and magnetic fields is studied. Effective Maxwell equations
for the macroscopic electric and magnetic fields are derived starting from
time-dependent density functional theory. Effective permittivity and
permeability coefficients are obtained.",1010.4912v1
2010/12/22,Quasi-exact evaluation of the magnetic properties of a giant Keplerate molecule,"In this Letter we report how thermodynamic properties of a giant frustrated
magnetic Keplerate molecule of N=30 spins s=1/2 can be evaluated with the help
of the highly accurate finite-temperature Lanczos method. The comparison to
experimental data shows excellent agreement. Since this molecule is
structurally related to the archetypical kagome lattice antiferromagnet we
expect new detailed insight into properties of this important class of
frustrated materials.",1012.4980v1
2011/4/2,Use of a magnetic fluid for particle size analysis by a sedimentation method,"A new method of particle size analysis of micrometer-sized particles is
discussed. The improved method of sedimentation analysis with magnetic fluids
has the potential and versatility to characterize polydisperse systems.",1104.0318v1
2011/6/21,An FET-Based Unit Cell for an Active Magnetic Metamaterial,"A particle that can be used to create an active magnetic metamaterial has
been designed using an FET transistor loaded in its gate by a conducting ring
and in its source by a parallel resonance circuit. The design procedure is
discussed and the working principle is experimentally demonstrated in the RF
range.",1106.4144v1
2011/6/30,Radius and magnetic field from Synchrotron-self-absorbed radio and Inverse Compton X-ray observations of Supernovae,"Simple expressions for the radius and magnetic field of a system emitting
Synchrotron-self-absorbed radio and Inverse Compton X-rays are derived from
first principles which involve observable quantities only. These expressions
are useful for analyzing observations of Supernova blastwaves interacting with
dense circumstellar material at early times.",1106.6113v1
2011/9/7,Planar approximation for spin transfer systems with application to tilted polarizer devices,"Planar spin-transfer devices with dominating easy-plane anisotropy can be
described by an effective one-dimensional equation for the in-plane angle. Such
a description provides an intuitive qualitative understanding of the magnetic
dynamics. We give a detailed derivation of the effective planar equation and
use it to describe magnetic switching in devices with tilted polarizer.",1109.1331v1
2011/9/21,An Automated Ac Susceptibility Set up Fabricated Using a Closed-Cycle Helium Refrigerator,"We have described here the design and operation of an automated ac
susceptibility set up using a closed cycle helium refrigerator. This set up is
useful for measuring linear and nonlinear magnetic susceptibilities of various
magnetic materials. The working temperature range is 2 K to 300 K. The overall
sensitivity of the set up is found to be 10-3 emu.",1109.4597v1
2012/1/26,New Paradigms in Magnetic Recording,"The magnetic hard disc drive industry continues to face serious challenges in
its quest for ever decreasing bit size. This review summarizes recent advances
and promising new technology which have foundations in fundamental physical
principles. Some advantages of these new ideas are illustrated through
micromagnetic modeling and the numerous challenges associated with their
implementation are highlighted.",1201.5543v1
2012/7/3,Exchange engineering in 3d chains adsorbed on Cu$_2$N/Cu(001),"Covalent substrates can give rise to a variety of magnetic interaction
mechanisms among adsorbed transition metal atoms building atomic
nanostructures. We show this by calculating the ground state magnetic
configuration of monoatomic 3d chains deposited on a monolayer of Cu$_2$N grown
on Cu(001) as a function of $d$ filling and of adsorption sites of the one
dimensional nanostructures.",1207.0829v1
2012/8/14,The Nature of the magnetism-promoting hole state in the prototype magnetic semiconductor GaAs: Mn,"Recent experiments [1] suggest that the ferromagnetism (FM) in GaAs: Mn is
determined by the impurity band rather than holes in the valence band. We
discuss here the physical mechanism of FM mediated by the carriers in impurity
band, where the Mn d-level play a crucial role. The theory is based on the
first principle approach.",1208.2811v1
2013/1/17,Impact of growth conditions on the nature of magnetism and magnetotransport of $Sm_{0.55} Sr_{0.45} Mn O_3$ thin films,"The impact of growth conditions on the magnetic and electrical transport
properties of oriented polycrystalline Sm0.55Sr0.45MnO3 thin films prepared on
nearly lattice matching LSAT(100) single crystal substrates by nebulized spray
pyrolysis has been studied.",1301.4052v1
2014/2/14,Extremely high-resolution measurements of microwave magnetisation dynamics in magnetic thin films and nanostructures,"In this work we discuss the use of interferometric measurement technique to
study microwave magnetization dynamics on ferromagnetic nanostructures. We
demonstrate that in this way one can resolve features which are impossible to
resolve with broadband ferromagnetic resonance and traveling spin wave
spectroscopy otherwise.",1402.3459v1
2015/8/5,A Perfect Terahertz Metamaterial Absorber,"In this paper the design for an absorbing metamaterial with near unity
absorbance in terahertz region is presented. The absorber's unit cell structure
consists of two metamaterial resonators that couple to electric and magnetic
fields separately. The structure allows us to maximize absorption by varying
dielectric material and thickness and, hence the effective electrical
permittivity and magnetic permeability.",1508.01038v1
2015/10/15,"Modeling and Scaling of Hysteresis in Magnetic Materials. Frequency, Pick of Induction and Temperature Dependence","Recently introduced model of magnetic hysteresis was extended into set of the
following features: frequency, pick of induction and temperature of specimen.
Group theoretical classification of hysteresis loops' sets is presented. An
effect analogous to the Zeeman splitting has been revealed in the set of the
all hysteresis loops.",1510.06635v1
2016/5/17,Structural and magnetic study of PrMn$_{1-x}$Fe$_x$O$_3$ $(0 \leq x \leq 1)$ compounds,"The structural and magnetic study of PrMn1-xFexO3(0 <= x <= 1) substitutional
orthorhombical system, was performed on polycrystalline (x <= 0.5) as well as
on the single crystalline (0.5 <= x <= 1) samples.",1605.05128v2
2017/1/27,Application of Zeeman spatial beam-splitting in polarized neutron reflectometry,"Neutron Zeeman spatial beam-splitting is considered at reflection from
magnetically noncollinear films. Two applications of Zeeman beam-splitting
phenomenon in polarized neutron reflectometry are discussed. One is the
construction of polarizing devices with high polarizing efficiency. Another one
is the investigations of magnetically noncollinear films with low spin-flip
probability. Experimental results are presented for illustration.",1701.08199v1
2017/7/11,An inverse problem for Maxwell's equations with Lipschitz parameters,"We consider an inverse boundary value problem for Maxwell's equations, which
aims to recover the electromagnetic material properties of a body from
measurements on the boundary. We show that a Lipschitz continuous conductivity,
electric permittivity, and magnetic permeability are uniquely determined by
knowledge of all tangential electric and magnetic fields on the boundary of the
body at a fixed frequency.",1707.03299v2
2018/3/16,Larmor Frequency in Heterogeneous Media,"The Larmor frequency shift is found in porous media consisting of
NMR-reporting fluid filling a connected pore within an NMR-invisible matrix for
the case of fast diffusion in the fluid. The matrix material has a distinct
location-independent anisotropic magnetic susceptibility tensor that induces a
heterogeneous microscopic magnetic field when exposed to the strong main field
of an NMR device. Aside from the connectivity of the pore, the matrix geometry
is arbitrary.",1803.06198v1
2018/5/17,Large magneto-optical Kerr effect and imaging of magnetic octupole domains in an antiferromagnetic metal,"When a polarized light beam is incident upon the surface of a magnetic
material, the reflected light undergoes a polarization rotation. This
magneto-optical Kerr effect (MOKE) has been intensively studied in a variety of
ferro- and ferrimagnetic materials because it provides a powerful probe for
electronic and magnetic properties as well as for various applications
including magneto-optical recording. Recently, there has been a surge of
interest in antiferromagnets (AFMs) as prospective spintronic materials for
high-density and ultrafast memory devices, owing to their vanishingly small
stray field and orders of magnitude faster spin dynamics compared to their
ferromagnetic counterparts. In fact, the MOKE has proven useful for the study
and application of the antiferromagnetic (AF) state. Although limited to
insulators, certain types of AFMs are known to exhibit a large MOKE, as they
are weak ferromagnets due to canting of the otherwise collinear spin structure.
Here we report the first observation of a large MOKE signal in an AF metal at
room temperature. In particular, we find that despite a vanishingly small
magnetization of $M \sim$0.002 $\mu_{\rm B}$/Mn, the non-collinear AF metal
Mn$_3$Sn exhibits a large zero-field MOKE with a polar Kerr rotation angle of
20 milli-degrees, comparable to ferromagnetic metals. Our first-principles
calculations have clarified that ferroic ordering of magnetic octupoles in the
non-collinear Neel state may cause a large MOKE even in its fully compensated
AF state without spin magnetization. This large MOKE further allows imaging of
the magnetic octupole domains and their reversal induced by magnetic field. The
observation of a large MOKE in an AF metal should open new avenues for the
study of domain dynamics as well as spintronics using AFMs.",1805.06758v1
2018/6/22,Inverse problems for Maxwell's equations in a slab with partial boundary data,"We consider two inverse boundary value problems for the time-harmonic Maxwell
equations in an infinite slab. Assuming that tangential boundary data for the
electric and magnetic fields at a fixed frequency is available either on
subsets of one boundary hyperplane, or on subsets of different boundary
hyperplanes, we show that the electromagnetic material parameters, the
conductivity, electric permittivity, and magnetic permeability, are uniquely
determined by these partial measurements.",1806.08772v1
2018/7/29,Incommensurate atomic and magnetic modulations in the spin-frustrated β-NaMnO2 triangular lattice,"The layered {\beta}-NaMnO2, a promising Na-ion energy-storage material has
been investigated for its triangular lattice capability to promote complex
magnetic configurations that may release symmetry restrictions for the
coexistence of ferroelectric and magnetic orders. The complexity of the neutron
powder diffraction patterns underlines that the routinely adopted commensurate
structural models are inadequate. Instead, a single-phase superspace symmetry
description is necessary, demonstrating that the material crystallizes in a
compositionally modulated q= (0.077(1), 0, 0) structure. Here, Mn3+ Jahn-Teller
distorted MnO6 octahedra form corrugated layer stacking sequences of the
{\beta}-NaMnO2 type, which are interrupted by flat sheets of the {\alpha}-like
oxygen topology. Spontaneous long-range collinear antiferromagnetic order,
defined by the propagation vector k= (1/2, 1/2, 1/2), appears below TN1= 200 K.
Moreover, a second transition into a spatially modulated proper-screw magnetic
state (k+-q) is established at TN2= 95 K, with an antiferromagnetic order
parameter resembling that of a two-dimensional (2D) system. The evolution of
23Na NMR spin-lattice relaxation identifies a magnetically inhomogene-ous state
in the intermediate T-region (TN2 <T< TN1), while its strong suppression below
TN2 indicates that a spin-gap opens in the excitation spectrum. High-resolution
neutron inelastic scattering confirms that the magnetic dynamics are indeed
gapped ({\Delta}~5 meV) in the low-temperature magnetic phase, while
simulations on the basis of the single-mode approximation suggest that Mn-spins
residing on ad-jacent antiferromagnetic chains, establish sizable 2D
correlations. Our analysis points that novel struc-tural degrees of freedom
promote, cooperative magnetism and emerging dielectric properties in this
non-perovskite-type of manganite.",1807.10995v1
2018/8/15,Large magneto-optical effects and magnetic anisotropy energy in two-dimensional Cr$_2$Ge$_2$Te$_6$,"By performing systematic $ab$ $initio$ density functional calculations, here
we study two relativity-induced properties of atomically thin ferromagnetic
(FM) Cr$_2$Ge$_2$Te$_6$ films [monolayer (ML), bilayer (BL) and trilayer (TL)
as well as bulk], namely, magnetic anisotropy energy (MAE) and magneto-optical
(MO) effects. Competing contributions of both magneto-crystalline anisotropy
energy (C-MAE) and magnetic dipolar anisotropy energy (D-MAE) to the MAE, are
computed. Calculated MAEs of these materials are large, being in the order of
$\sim$0.1 meV/Cr. Interestingly, we find that the out-of-plane magnetic
anisotropy is preferred in all the systems except the ML where an in-plane
magnetization is favored because here the D-MAE is larger than the C-MAE.
Crucially, this explains why long-range FM order was observed in all the
few-layer Cr$_2$Ge$_2$Te$_6$ except the ML because the out-of-plane magnetic
anisotropy would open a spin-wave gap and thus suppress magnetic fluctuations
so that long-range FM order could be stabilized at finite temperature. In the
visible frequency range, large Kerr rotations up to $\sim$1.0 deg in these
materials are predicted and they are comparable to that observed in famous MO
materials such as PtMnSb and Y$_3$Fe$_5$O$_{12}$. Moreover, they are $\sim$100
times larger than that of 3$d$ transition metal MLs deposited on Au surfaces.
Faraday rotation angles in these 2D materials are also large, being up to
$\sim$120 deg/$\mu$m, and are thus comparable to the best-known MO
semiconductor Bi$_3$Fe$_5$O$_{12}$. These findings thus suggest that with large
MAE and MO effects, atomically thin Cr$_2$Ge$_2$Te$_6$ films would have
potential applications in novel magnetic, MO and spintronic nanodevices.",1808.05086v1
2019/4/27,Critical Behavior and Anisotropy in Single Crystal SrRuO$_3$,"The magnetization of single crystal SrRuO3 is studied as a function of
temperature along different crystallographic directions. The magnetocrystalline
anisotropy and behavior near the critical transition temperature are analyzed
in detail. The magnetization vs temperature is found to vary more like $T^2$
rather than $T^{3/2}$ expected for spin waves.",1904.12193v1
2019/5/2,Robust axion insulator and Chern insulator phases in a two-dimensional antiferromagnetic topological insulator,"The intricate interplay between nontrivial topology and magnetism in
two-dimensional (2D) materials has led to the emergence of many novel phenomena
and functionalities. An outstanding example is the quantum anomalous Hall (QAH)
effect, which was realized in magnetically doped topological insulators (TIs)
in the absence of magnetic field. Recently, the layered van der Waals compound
MnBi2Te4 has been theoretically predicted and experimentally verified to be a
TI with interlayer antiferromagnetic (AFM) order. It is a rare stoichiometric
material with coexisting topology and magnetism, thus represents a perfect
building block for complex topological-magnetic structures. Here we investigate
the quantum transport behaviors of both bulk crystal and exfoliated MnBi2Te4
flakes in a field effect transistor geometry. In the 6 septuple layers (SLs)
device tuned into the insulating regime, we observe a large longitudinal
resistance and zero Hall plateau, which are characteristic of the axion
insulator state. The robust axion insulator state occurs in zero magnetic
field, over a wide magnetic field range, and at relatively high temperatures.
Moreover, a moderate magnetic field drives a quantum phase transition from the
axion insulator phase to a Chern insulator phase with zero longitudinal
resistance and quantized Hall resistance h/e2 (h is the Plank constant and e is
the elemental charge). These results pave the road for using even-number-SL
MnBi2Te4 to realize the quantized topological magnetoelectric effect and axion
electrodynamics in condensed matter systems.",1905.00715v2
2019/5/14,Influence of transverse field on the spin-3/2 Blume-Capel model on rectangular lattice,"Transverse field effect on thermodynamic properties of the spin-3/2
Blume-Capel model on rectangular lattice in which the interactions in
perpendicular directions differ in signs is studied within the mean field
approximation. Phase diagrams in the (transverse field, temperature) plane are
constructed for various values of single-ion anisotropy.",1905.05852v1
2019/8/4,Experimental observation of coupled valley and spin Hall effect in p-doped WSe2 devices,"Giant spin Hall effect (GSHE) has been observed in heavy metal materials such
as Ta, Pt, and W, where spins are polarized in the surface plane and
perpendicular to the charge current direction. Spins generated in these
materials have successfully switched magnets with in-plane magnetic anisotropy
(IMA) and perpendicular magnetic anisotropy (PMA) through spin orbit torque
(SOT) mechanism. It is generally accepted that PMA magnets are preferred over
IMA magnets in data storage applications owing to their large thermal stability
even at ultra scaled dimensions. However, SOT switching of PMA magnets by
conventional GSHE materials requires either a small external magnetic field, a
local dipolar field, or introducing tilted anisotropy to break the symmetry
with respect to the magnetization. To deterministically switch a PMA without
any additional assistance, nonconventional GSHE materials that can generate
spins with polarization perpendicular to the surfaces are needed. Several
monolayer transition metal dichalcogenides (TMDs) have been predicted to
generate such out of plane spins due to their 2D nature and unique band
structures. Interestingly, opposite spins are locked to their respective
sub-band in each K valley of the TMD valence band with substantially large
energy splitting, which enables polarized spins to be accessible through
electrical gating and spatially separated by electric field through the valley
Hall effect (VHE). Therefore, spatial separation and accumulation of spins in
these 2D TMDs are uniquely referred to as coupled valley and spin Hall effect.
Here, we report an experiment of electrical generation of spin current with out
of plane polarization in monolayer WSe2 and detection of spin signals through a
nonlocal spin valve structure built on a lateral graphene spin diffusion
channel that partially overlaps with WSe2.",1908.01396v1
2020/4/24,"Antiferromagnetism in a nanocrystalline high entropy oxide (Co,Cu,Mg,Ni,Zn)O : Magnetic constituents and surface anisotropy leading to lattice distortion","For the first time, this study shows that distortion in a crystal structure
due to magnetic effect is possible in a lattice with extreme chemical disorder.
The multicomponent equimolar transition metal oxide (ME TMO),
(Co,Cu,Mg,Ni,Zn)O, which is a high entropy oxide, has been attracting a lot of
attention due to its unique application potential in many fields including
electrochemical energy storage. In the present investigation, nanocrystalline
ME TMO was synthesised by three bottom up methods. The presence of distortion
in the rocksalt crystal structure, revealed by X ray diffraction and Raman
spectroscopy, and correlated with magnetic measurements from SQUID and EPR
studies could be attributed to the additive effects of exchange striction (from
the magnetic constituents) and magnetic anisotropy (from the decreased
crystallite size). For the first time, iron has been doped into ME TMO, to show
that a higher amount of magnetic constituent increases the distortion in the
lattice. Nanocrystalline ME TMO also showed a core shell magnetic behavior
below the bifurcation temperature arising from the uncompensated or canted spin
at the surface. Neel temperature of the nanocrystalline ME TMO is reported for
first time to be as high as 700 K. This study helps unravel the structure and
magnetic properties of such high entropy materials, and augurs a definite scope
for better understanding of the factors influencing the crystal structure in
high entropy oxides.",2004.11684v1
2020/11/6,Extension of Hall-symbols of crystallographic space groups to magnetic space groups,"The Hall-symbols for describing unambiguously the generators of space groups
have been extended to describe whatever setting of the 1651 types of magnetic
space groups (Shubnikov groups). A computer program called MHALL has been
developed for parsing the Hall symbols, generate the full list of symmetry
operators and identify the transformation to the standard setting.",2011.03604v1
2020/12/4,Spin Wave Electromagnetic Nonlinear Interaction to Move RF Limiter Frequency Range to Higher Frequencies,"It is shown here that the usual operating frequencies for RF limiters, in the
nominal 5, 11 or 15 GHz center frequencies, can be lifted up into the much
higher frequencies of the 40 to 60 GHz range by a new formula developed from
fundamental spin wave electromagnetic interactions in magnetic material
characterized by a magnetization M.",2012.05687v1
2021/5/30,"Magnetic structure determination of rare-earth based, high moment, atomic laminates; potential parent materials for 2D magnets","We report muon spin rotation ($\mu$SR) and neutron diffraction on the
rare-earth based magnets (Mo$_{2/3}$RE$_{1/3}$)$_2$AlC, also predicted as
parent materials for 2D derivatives, where RE = Nd, Gd (only ($\mu$SR), Tb, Dy,
Ho and Er. By crossing information between the two techniques, we determine the
magnetic moment ($m$), structure, and dynamic properties of all compounds. We
find that only for RE = Nd and Gd the moments are frozen on a microsecond time
scale. Out of these two, the most promising compound for a potential 2D high
($m$) magnet is the Gd variant, since the parent crystals are pristine with $m
= 6.5 \pm 0.5 \mu_B$, N\'eel temperature of $29 \pm 1$ K, and the magnetic
anisotropy between in and out of plane coupling is smaller than $10^{-8}$. This
result suggests that magnetic ordering in the Gd variant is dominated by
in-plane magnetic interactions and should therefore remain stable if exfoliated
into 2D sheets.",2105.14555v2
2021/10/13,"A Combined First Principles Study of the Structural, Magnetic, and Phonon Properties of Monolayer CrI$_{3}$","The first magnetic 2D material discovered, monolayer (ML) CrI$_3$, is
particularly fascinating due to its ground state ferromagnetism. Yet, because
monolayer materials are difficult to probe experimentally, much remains
unresolved about ML CrI$_{3}$'s structural, electronic, and magnetic
properties. Here, we leverage Density Functional Theory (DFT) and high-accuracy
Diffusion Monte Carlo (DMC) simulations to predict lattice parameters, magnetic
moments, and spin-phonon and spin-lattice coupling of ML CrI$_{3}$. We exploit
a recently developed surrogate Hessian DMC line search technique to determine
CrI$_{3}$'s monolayer geometry with DMC accuracy, yielding lattice parameters
in good agreement with recently-published STM measurements - an accomplishment
given the $\sim 10$% variability in previous DFT-derived estimates depending
upon the functional. Strikingly, we find previous DFT predictions of ML
CrI$_3$'s magnetic spin moments are correct on average across a unit cell, but
miss critical local spatial fluctuations in the spin density revealed by more
accurate DMC. DMC predicts magnetic moments in ML CrI$_3$ are 3.62 $\mu_B$ per
chromium and -0.145 $\mu_B$ per iodine; both larger than previous DFT
predictions. The large disparate moments together with the large spin-orbit
coupling of CrI$_3$'s I-$\textit{p}$ orbital suggests a ligand
superexchange-dominated magnetic anisotropy in ML CrI$_3$, corroborating recent
observations of magnons in its 2D limit. We also find ML CrI$_3$ exhibits a
substantial spin-phonon coupling of $\sim$3.32 cm$^{-1}$. Our work thus
establishes many of ML CrI$_{3}$'s key properties, while also continuing to
demonstrate the pivotal role DMC can assume in the study of magnetic and other
2D materials.",2110.06731v1
2021/12/31,Demystifying magnetic resonance measurements of the true diffusion propagator,"In a recent work, a method for the magnetic resonance (MR) measurement of the
true diffusion propagator was introduced, which was subsequently implemented
and validated for free diffusion on a benchtop MR scanner. Here, we provide a
brief theoretical description of the method and discuss various experimental
regimes.",2112.15584v1
2022/1/12,Topological magnetic excitations,"Topological properties play an increasingly important role in future research
and technology. This also applies to the field of topological magnetic
excitations which has recently become a very active and broad field. In this
Perspective article, we give an insight into the current theoretical and
experimental investigations and try an outlook on future lines of research.",2201.12399v1
2022/6/4,Electronic and magnetic properties of the BaTiO$_{3}$/LaMnO$_{3}$ interface: a DFT study,"By means of ab initio calculations within the density functional theory (DFT)
electronic and magnetic properties of BaTiO3/LaMnO3 interface were
investigated. An impact of ferroelectric overlayer thickness onto the interface
properties was analysed through the spin-polarized density of states.",2206.01935v1
2022/8/12,Weyl nodal ring states and Landau quantization with very large magnetoresistance in square-net magnet EuGa$_4$,"Magnetic topological semimetals (TSMs) allow for an effective control of the
topological electronic states by tuning the spin configuration, and therefore
are promising materials for next-generation electronic and spintronic
applications. Of magnetic TSMs, Weyl nodal-line (NL) semimetals likely have the
most tunability, and yet they are the least experimentally studied so far due
to the scarcity of material candidates. Here, using a combination of
angle-resolved photoemission spectroscopy and quantum oscillation measurements,
together with density functional theory calculations, we identify the
square-net compound EuGa4 as a new magnetic Weyl nodal ring (NR) semimetal, in
which the line nodes form closed rings in the vicinity of the Fermi level.
Remarkably, the Weyl NR states show distinct Landau quantization with clear
spin splitting upon application of a magnetic field. At 2 K in a field of 14 T,
the transverse magnetoresistance of EuGa4 exceeds 200,000%, which is more than
two orders of magnitude larger than that of other known magnetic TSMs. High
field magnetoresistance measurements indicate no saturation up to 40 T. Our
theoretical model indicates that the nonsaturating MR naturally arises as a
consequence of the Weyl NR state. Our work thus point to the realization of
Weyl NR states in square-net magnetic materials, and opens new avenues for the
design of magnetic TSMs with very large magnetoresistance.",2208.06407v2
2022/10/13,Intertwined magnetism and charge density wave order in kagome FeGe,"Electron correlations often lead to emergent orders in quantum materials.
Kagome lattice materials are emerging as an exciting platform for realizing
quantum topology in the presence of electron correlations. This proposal stems
from the key signatures of electronic structures associated with its lattice
geometry: flat band induced by destructive interference of the electronic
wavefunctions, topological Dirac crossing, and a pair of van Hove singularities
(vHSs). A plethora of correlated electronic phases have been discovered amongst
kagome lattice materials, including magnetism, charge density wave (CDW),
nematicity, and superconductivity. These materials can be largely organized
into two types: those that host magnetism and those that host CDW order.
Recently, a CDW order has been discovered in the magnetic kagome FeGe,
providing a new platform for understanding the interplay between CDW and
magnetism. Here, utilizing angle-resolved photoemission spectroscopy, we
observe all three types of electronic signatures of the kagome lattice: flat
bands, Dirac crossings, and vHSs. From both the observation of a
temperature-dependent shift of the vHSs towards the Fermi level as well as
guidance via first-principle calculations, we identify the presence of the vHSs
near the Fermi level (EF) to be driven by the development of underlying
magnetic exchange splitting. Furthermore, we show spectral evidence for the CDW
order as gaps that open on the near-EF vHS bands, as well as evidence of
electron-phonon coupling from a kink on the vHS band together with phonon
hardening observed by inelastic neutron scattering. Our observation points to
the magnetic interaction-driven band modification resulting in the formation of
the CDW order, indicating an intertwined connection between the emergent
magnetism and vHS charge order in this moderately-correlated kagome metal.",2210.06653v1
2022/11/7,Quantum-classical approach to spin and charge pumping and the ensuing radiation in THz spintronics: Example of ultrafast-light-driven Weyl antiferromagnet Mn$_3$Sn,"The interaction of fs light pulses with magnetic materials has been intensely
studied for more than two decades in order to understand ultrafast
demagnetization in single magnetic layers or THz emission from their bilayers
with nonmagnetic spin-orbit (SO) materials. Here we develop a multiscale
quantum-classical formalism -- where conduction electrons are described by
quantum master equation of the Lindblad type; classical dynamics of local
magnetization is described by the Landau-Lifshitz-Gilbert (LLG) equation; and
incoming light is described by classical vector potential while outgoing
electromagnetic radiation is computed using Jefimenko equations for retarded
electric and magnetic fields -- and apply it a bilayer of antiferromagnetic
Weyl semimetal Mn$_3$Sn with noncollinear local magnetization in contact with
SO-coupled nonmagnetic material. Our QME+LLG+Jefimenko scheme makes it possible
to understand how fs light pulse generates directly spin and charge pumping and
electromagnetic radiation by the latter, including both odd and even high
harmonics (of the pulse center frequency) up to order $n \le 7$. The directly
pumped spin current then exert spin torque on local magnetization whose
dynamics, in turn, pumps additional spin and charge currents radiating in the
THz range. By switching on and off LLG dynamics and SO couplings, we unravel
which microscopic mechanism contribute the most to emitted THz radiation --
charge pumping by local magnetization of Mn$_3$Sn in the presence of its
intrinsic SO coupling is far more important than standardly assumed (for other
types of magnetic layers) spin pumping and subsequent spin-to-charge conversion
within the neighboring nonmagnetic SO-coupled material.",2211.03645v3
2023/2/13,"Structural, magnetic and elastic properties on stoichometric $Ni-Mn-Cu$ Heusler alloys","Heusler alloys with $Ni-Mn-Cu$ (all d-transition metal) composition have been
studied; equilibrium structures for different magnetic configurations are
found. Elastic constants and tetragonal distortion are analyzed. Distortion
effect on densities of electronic state peaks are characterized. For this
ternary family of alloys, we find that the one with the most interesting
properties and mechanical stability is $Ni_2MnCu$.",2302.06472v2
2023/3/8,Spontaneous topological Hall effect induced by non-coplanar antiferromagnetic order in intercalated van der Waals materials,"In ferromagnets, electric current generally induces transverse Hall voltage
in proportion to magnetization (anomalous Hall effect), and it is frequently
used for electrical readout of the up and down spin states. While these
properties are usually not expected in antiferromagnets, recent theoretical
studies predicted that non-coplanar antiferromagnetic order with finite scalar
spin chirality (i.e. solid angle spanned by neighboring spins) can often induce
large spontaneous Hall effect even without net magnetization or external
magnetic field. This phenomenon, i.e. spontaneous topological Hall effect, can
potentially be used for the efficient electrical readout of the
antiferromagnetic states, but its experimental verification has long been
elusive due to the lack of appropriate materials hosting such exotic magnetism.
Here, we report the discovery of all-in-all-out type non-coplanar
antiferromagnetic order in triangular lattice compounds CoTa3S6 and CoNb3S6, by
performing the detailed magnetic structure analysis based on polarized neutron
scattering experiments as well as systematic first-principles calculations.
These compounds are reported to host unconventionally large spontaneous Hall
effect despite their vanishingly small net magnetization, and our analysis
revealed that it can be well explained in terms of topological Hall effect,
which originates from the fictitious magnetic field associated with scalar spin
chirality in non-coplanar antiferromagnetic orders. The present results
indicate that the scalar spin chirality mechanism can offer a promising route
to realize giant spontaneous Hall response even in compensated
antiferromagnets, and highlight intercalated van der Waals magnets as an unique
quasi-two-dimensional material platform to enable various nontrivial manner of
electrical reading and possible writing of non-coplanar antiferromagnetic
domains.",2303.04879v1
2024/2/7,Oil removal from water oil emulsions using magnetic nanocomposite fibrous mats,"Herein we present the fabrication of hydrophobic and oleophilic poly(methyl
methacrylate) based nanocomposite fibrous mats with magnetic properties, and
their utilization for oil removal from stable water oil emulsions.",2402.04966v1
2009/5/2,Counterposition and negative phase velocity in uniformly moving dissipative materials,"The Lorentz transformations of electric and magnetic fields were implemented
to study (i) the refraction of linearly polarized plane waves into a half-space
occupied by a uniformly moving material, and (ii) the traversal of linearly
polarized Gaussian beams through a uniformly moving slab. Motion was taken to
occur tangentially to the interface(s) and in the plane of incidence. The
moving materials were assumed to be isotropic, homogeneous, dissipative
dielectric materials from the perspective of a co-moving observer. Two
different moving materials were considered: from the perspective of a co-moving
observer, material A supports planewave propagation with only positive phase
velocity, whereas material B supports planewave propagation with both positive
and negative phase velocity, depending on the polarization state. For both
materials A and B, the sense of the phase velocity and whether or not
counterposition occurred, as perceived by a nonco-moving observer, could be
altered by varying the observer's velocity. Furthermore, the lateral position
of a beam upon propagating through a uniformly moving slab made of material A,
as perceived by a nonco-moving observer, could be controlled by varying the
observer's velocity. In particular, at certain velocities, the transmitted beam
emerged from the slab laterally displaced in the direction opposite to the
direction of incident beam. The transmittances of a uniformly moving slab made
of material B were very small and the energy density of the transmitted beam
was largely concentrated in the direction normal to the slab, regardless of the
observer's velocity.",0905.0176v1
2023/11/8,AI-accelerated Discovery of Altermagnetic Materials,"Altermagnetism, a new magnetic phase, has been theoretically proposed and
experimentally verified to be distinct from ferromagnetism and
antiferromagnetism. Although altermagnets have been found to possess many
exotic physical properties, the very limited availability of known
altermagnetic materials (e.g., 14 confirmed materials) hinders the study of
such properties. Hence, discovering more types of altermagnetic materials is
crucial for a comprehensive understanding of altermagnetism and thus
facilitating new applications in the next-generation information technologies,
e.g., storage devices and high-sensitivity sensors. Here, we report 25 new
altermagnetic materials that cover metals, semiconductors, and insulators,
discovered by an AI search engine unifying symmetry analysis, graph neural
network pre-training, optimal transport theory, and first-principles electronic
structure calculation. The wide range of electronic structural characteristics
reveals that various novel physical properties manifest in these newly
discovered altermagnetic materials, e.g., anomalous Hall effect, anomalous Kerr
effect, and topological property. Noteworthy, we discovered 8 i-wave
altermagnetic materials for the first time. Overall, the AI search engine
performs much better than human experts and suggests a set of new altermagnetic
materials with unique properties, outlining its potential for accelerated
discovery of the materials with targeting properties.",2311.04418v2
2002/9/12,Some physical properties of lead iron niobate,"The results of the X-ray, microscopic, magnetic, and dielectric measurements
performed for PFN single crystals and ceramic samples are presented. The
influence of the technological conditions on selected physical properties of
the materials examined is shown.",0209289v1
2003/11/13,Effect of the orthorhombic distortion on the magneto-optical properties of SrRuO$_3$,"It is argued that the non-collinear orbital magnetism accompanying the
orthorhombic distortion is an important ingredient which should be taken into
consideration for making promising materials with the best magneto-optical
characteristics on the basis of SrRuO$_3$.",0311298v1
2004/4/7,Absence of room temperature ferromagnetism in bulk Mn-doped ZnO,"Structural and magnetic properties have been studied for polycrystalline
Zn_1-xMn_xO (x=0.02, 0.03, 0.05). Low-temperature (~500 oC) synthesis leaves
unreacted starting ZnO and manganese oxides. Contrary to a recent report, no
bulk ferromagnetism was observed for single-phase materials synthesized in air
at temperatures above 900 oC. Single-phase samples show paramagnetic
Curie-Weiss behavior.",0404186v1
2005/8/1,Induced transparency in EXAFS as cuprate superconductors go through Tc,"The increased transmission, observed in the EXAFS region of their X-ray
absorption spectra, as cuprate materials go through the superconducting
transition temperature Tc is correlated with an increase in Abrikosov Vortex
expulsion in zero magnetic field as the temperature T approaches Tc.",0508052v1
2006/2/3,Conserved geometric phase and group velocity,"In this paper we make use of the concept of conserved geometric phase and of
group velocity,in conjunction with the representation
theory\cite{Dirac,Dirac-letture}, in order to derive some relevant physical
quantities for the description of the dielectric and magnetic response of
crystalline materials. As an application of the model, we derive the expression
of the macroscopic dipole moment per unit volume, and the expression of the
current induced by a uniform static external electromagnetic field.",0602090v1
2006/9/20,Ferromagnetism and Superconductivity in Carbon-Based Systems,"In this article we shortly review previous and recently published
experimental results that provide evidence for intrinsic,
magnetic-impurity-free ferromagnetism and for high-temperature
superconductivity in carbon-based materials. The available data suggest that
the origin of those phenomena is related to structural disorder and the
presence of light elements like hydrogen, oxygen and/or sulfur.",0609497v1
1995/8/2,Spin-dependent resonant tunneling through semimetallic ErAs quantum wells,"Resonant tunneling through semimetallic ErAs quantum wells embedded in GaAs
structures with AlAs barriers was recently found to exhibit an intriguing
behavior in magnetic fields which is explained in terms of tunneling selection
rules and the spin-polarized band structure including spin-orbit coupling.",9508003v1
2006/7/12,Eleven shear surface waves guided by inclusions in magneto-electro-elastic materials,"Eleven pure shear surface waves are shown to exist in magneto-electro-elastic
materials, which contain different plane inclusions inside them. The plane
inclusions affect the electric and magnetic fields only, so that the medium
remains mechanically continuous across it. Expressions for velocities of
propagation of these 11 surface waves are obtained in explicit forms. It is
expected that these waves will have several applications in surface acoustic
wave devices.",0607113v1
2007/10/2,Nonlinear Optical Spectroscopy of Photonic Metamaterials,"We have obtained spectra of second-harmonic generation, third harmonic
generation, and four-wave mixing from a fishnet metamaterial around its
magnetic resonance. The resonant behaviors are distinctly different from those
for ordinary materials. They result from the fact that the resonance is
plasmonic, and its enhancement appears through the local field in the
nanostructure.",0710.0599v1
2009/6/30,Propagation and scattering of TE surface plasmon polaritons on interface between two dielectrics,"We study the TE polarized electromagnetic surface wave propagating along the
interface between materials with positive and negative magnetic permeability.
Contrary to the TM polarized surface wave, the TE surface wave exhibits almost
no radiation losses when scattered at semi-infinite dielectric interfaces.",0906.5498v1
2018/5/31,Observation of Meisser effect in Kapton Tapes,"Composed of organic compounds, Kapton tape is regularly used as a
non-conducting and non-magnetic material in cryogenic experiments. Here we
report the discovery of Meisser effect at transition temperature (Tc) of ~ 3.8
K and ~ 8.0 K in Kapton tapes. New organic superconducting materials may be
further explored in the tapes.",1805.12458v1
2019/3/1,Topology in abundance,"The topological classification of all known non-magnetic crystalline
compounds is now complete, revealing thousands of new candidate topological
materials waiting to be explored in the lab.",1903.00564v2
2023/1/9,Thermal Hall conductivity of $α$-RuCl$_3$,"Thermal Hall conductivity originating from topological magnons is observed in
the Kitaev candidate $\alpha$-RuCl$_3$ in broad intervals of temperature and
in-plane magnetic field, raising questions on the role of the Majorana mode in
heat conduction.",2301.03526v1
2012/5/18,Protostellar Accretion Flows Destabilized by Magnetic Flux Redistribution,"Magnetic flux redistribution lies at the heart of the problem of star
formation in dense cores of molecular clouds that are magnetized to a realistic
level. If all of the magnetic flux of a typical core were to be dragged into
the central star, the stellar field strength would be orders of magnitude
higher than the observed values. This well-known ""magnetic flux problem"" can in
principle be resolved through non-ideal MHD effects. Two dimensional
(axisymmetric) calculations have shown that ambipolar diffusion, in particular,
can transport magnetic flux outward relative to matter, allowing material to
enter the central object without dragging the field lines along. We show
through simulations that such axisymmetric protostellar accretion flows are
unstable in three dimensions to magnetic interchange instability in the
azimuthal direction. The instability is driven by the magnetic flux
redistributed from the matter that enters the central object. It typically
starts to develop during the transition from the prestellar phase of star
formation to the protostellar mass accretion phase. In the latter phase, the
magnetic flux is transported outward mainly through advection, by strongly
magnetized low-density regions that expand against the collapsing inflow. The
tussle between the gravity-driven infall and magnetically driven expansion
leads to a filamentary inner accretion flow, more disordered than previously
pictured. The efficient outward transport of magnetic flux by advection lowers
the field strength at small radii, making the magnetic braking less efficient
and the formation of rotationally supported disks easier in principle. However,
we find no evidence for such disks in any of our rotating collapse simulations.
We conclude that the inner protostellar accretion flow is shaped to a large
extent by this magnetic interchange instability. How disks form in such an
environment is unclear.",1205.4083v1
2017/4/6,Electronic structure and magnetic properties of magnetically dead layers in epitaxial CoFe2O4/Al2O3/Si(111) films studied by X-ray magnetic circular dichroism,"Epitaxial CoFe2O4/Al2O3 bilayers are expected to be highly efficient spin
injectors into Si owing to the spin filter effect of CoFe2O4. To exploit the
full potential of this system, understanding the microscopic origin of
magnetically dead layers at the CoFe2O4/Al2O3 interface is necessary. In this
paper, we study the crystallographic and electronic structures and the magnetic
properties of CoFe2O4(111) layers with various thicknesses (thickness d = 1.4,
2.3, 4, and 11 nm) in the epitaxial CoFe2O4(111)/Al2O3(111)/Si(111) structures
using soft X-ray absorption spectroscopy (XAS) and X-ray magnetic circular
dichroism (XMCD) combined with cluster-model calculation. The magnetization of
CoFe2O4 measured by XMCD gradually decreases with decreasing thickness d and
finally a magnetically dead layer is clearly detected at d = 1.4 nm. The
magnetically dead layer has frustration of magnetic interactions which is
revealed from comparison between the magnetizations at 300 and 6 K. From
analysis using configuration-interaction cluster-model calculation, the
decrease of d leads to a decrease in the inverse-to-normal spinel structure
ratio and also a decrease in the average valence of Fe at the octahedral sites.
These results strongly indicate that the magnetically dead layer at the
CoFe2O4/Al2O3 interface originates from various complex networks of
superexchange interactions through the change in the crystallographic and
electronic structures. Furthermore, from comparison of the magnetic properties
between d = 1.4 and 2.3 nm, it is found that ferrimagnetic order of the
magnetically dead layer at d = 1.4 nm is restored by the additional growth of
the 0.9-nm-thick CoFe2O4 layer on it.",1704.01712v1
2018/12/20,Magneto-optical imaging of stepwise magnetic domain disintegration at characteristic temperatures in EuB_6,"Prior to the onset of the ferromagnetic transition in semimetallic EuB_6,
unusual magnetic and electric behavior have been reported. Using a highly
sensitive magneto-optical imaging (MOI) technique, we visualize the behavior of
magnetic domains in a EuB_6 single crystal.The transformation from a
paramagnetic to a ferromagnetic state is shown to be non-Curie Weiss like and
proceeds via multiple breaks in the curvature of the temperature-dependent
local magnetization. From our experiments, we identify three characteristic
boundaries, T^*(H),T^*_c1(H) and T_c2(H),in a field - temperature magnetic
phase diagram.Using scaling and Modified Arrott plot analysis of isothermal
bulk magnetization data, we determine the critical exponents $\beta$ = 0.22
$\pm$ 0.01, $\gamma$ = 0.88 $\pm$ 0.05 and $\delta$= 5.0 $\pm$ 0.1 and a
critical transition temperature = 12.0 $\pm$ 0.2 K which is found to be equal
to T_c2. The critical exponents are close to those associated with the
universality class of tricritical mean field model. The absence of a model with
which the exponents correspond with directly, suggests the presence of large
critical fluctuations in this system. The critical fluctuations in this system
are sensitive to the applied magnetic field, which leads to field dependence of
boundaries in the magnetic phase diagram. With increasing T the magnetic
domains disintegrate into finger-like patterns before fragmenting into disjoint
magnetized puddles at T^*_c1 and ultimately disappearing at T*. At T^*_c1 we
observe a significant increase in the spatial inhomogeneity of the local
magnetic field distribution associated with the magnetic domain structure
disintegrating into smaller magnetized structures. We explain our results via
the formation of magnetic polaronic clusters and their coalescing into larger
domains.",1812.08564v1
2020/6/8,Field-induced oscillation of magnetization blocking in holmium metallacrown magnet,"Single-molecule magnets (SMMs) are promising elements for quantum
informatics. In the presence of strong magnetic anisotropy, they exhibit
magnetization blocking - a magnetic memory effect at the level of a single
molecule. Recent studies have shown that the SMM performance scales with the
height of magnetization blocking barrier. By employing molecular engineering
this can be significantly modified, remaining independent from other external
factors such as magnetic field. Taking advantage of hyperfine coupling of
electronic and nuclear spins further enhances their functionality, however, a
poor understanding of relaxation mechanisms in such SMMs limits the
exploitation of nuclear-spin molecular qubits. Here we report the opening
discovery of field-dependent oscillation of the magnetization blocking barrier
in a new holmium metallacrown magnet driven by the switch of relaxation
mechanisms involving hyperfine interaction. Single-crystal magnetic hysteresis
measurements combined with first-principles calculations reveal an activated
temperature dependence of magnetic relaxation dominated either by incoherent
quantum tunneling of magnetization at anti-crossing points of
exchange-hyperfine states or by Orbach-like processes at crossing points. We
demonstrate that these relaxation mechanisms can be consecutively switched on
and off by increasing the external field, which paves a way for manipulating
the magnetization dynamics of SMMs using hyperfine interaction.",2006.04401v1
2020/7/21,Non-equilibrium magnetic response of canonical spin glass and magnetic glass,"Time and history dependent magnetization has been observed in a wide variety
of materials, which are collectively termed as the glassy magnetic systems.
However, such systems showing similar non-equilibrium magnetic response can be
microscopically very different and they can be distinguished by carefully
looking into the details of the observed metastable magnetic behavior.
Canonical spin glass is the most well studied member of this class and has been
extensively investigated both experimentally and theoretically over the last
five decades. In canonical spin glasses, the low temperature magnetic state
obtained by cooling across the spin glass transition temperature in presence of
an applied magnetic field is known as the field cooled (FC) state. This FC
state in canonical spin glass is widely believed as an equilibrium state
arising out of a thermodynamic second order phase transition. Here, we show
that the FC state in canonical spin glass is not really an equilibrium state of
the system. We report careful dc magnetization and ac susceptibility
measurements on two canonical spin glass systems, AuMn (1.8%) and AgMn (1.1%).
The dc magnetization in the FC state shows clear temperature dependence. In
addition, the magnetization shows a distinct thermal hysteresis in the
temperature regime below the spin glass transition temperature. On the other
hand, the temperature dependence of ac susceptibility has clear frequency
dispersion below spin glass transition in the FC state prepared by cooling the
sample in the presence of a dc-bias field. We further distinguish the
metastable response of the FC state of canonical spin glass from the metastable
response the FC state in an entirely different class of glassy magnetic system
namely magnetic glass, where the non-equilibrium behavior is associated with
the kinetic-arrest of a first order magnetic phase transition.",2007.10597v1
2021/3/25,Distinct quantum anomalous Hall ground states induced by magnetic disorders,"The quantum anomalous Hall (QAH) effect in magnetic topological insulator
(TI) represents a new state of matter originated from the interplay between
topology and magnetism. The defining characteristics of the QAH ground state
are the quantized Hall resistivity ($\rho_{yx}$) and vanishing longitudinal
resistivity ($\rho_{xx}$) in the absence of external magnetic field. A
fundamental question concerning the QAH effect is whether it is merely a
zero-magnetic-field quantum Hall (QH) effect, or if it can host unique quantum
phases and phase transitions that are unavailable elsewhere. The most dramatic
departure of the QAH systems from other QH systems lies in the strong magnetic
disorders that induce spatially random magnetization. Because disorder and
magnetism play pivotal roles in the phase diagram of two-dimensional electron
systems, the high degree of magnetic disorders in QAH systems may create novel
phases and quantum critical phenomena. In this work, we perform systematic
transport studies of a series of magnetic TIs with varied strength of magnetic
disorders. We find that the ground state of QAH effect can be categorized into
two distinct classes: the QAH insulator and anomalous Hall (AH) insulator
phases, as the zero-magnetic-field counterparts of the QH liquid and Hall
insulator in the QH systems. In the low disorder limit of the QAH insulator
regime, we observe a universal quantized longitudinal resistance $\rho_{xx} =
h/e^{2}$ at the coercive field. In the AH insulator regime, we find that a
magnetic field can drive it to the QAH insulator phase through a quantum
critical point with distinct scaling behaviors from that in the QH phase
transition. We propose that the transmission between chiral edge states at
domain boundaries, tunable by disorder and magnetic fields, is the key for
determining the QAH ground state.",2103.13783v1
2023/9/23,Origin of spin-driven ferroelectricity and effect of external pressure on the complex magnetism of 6H-perovskite Ba3HoRu2O9,"The compound Ba3HoRu2O9 magnetically orders at 50 K (TN1) followed by another
complex magnetic ordering at 10 K (TN2). The 2nd magnetic phase transition was
characterized by the co-existence of two competing magnetic ground states
associated with two different magnetic wave vectors (K1=1/2 0 0 and K2=1/4 1/4
0). We have investigated the compound through time-of-flight neutron
diffraction, ac susceptibility, complex dielectric spectroscopy, and
magnetization under external pressure. We demonstrate that the non-colinear
structure involving two different magnetic ions, Ru(4d) and Ho(4f), breaks the
spatial inversion symmetry via inverse Dzyaloshinskii-Moriya (D-M) interaction
through strong4d-4f magnetic correlation, which shifts the oxygen atoms and
results in non-zero polarization. Such an observation of inverse D-M
interaction from two different magnetic spins ions which caused
ferroelectricity is rarely observed. The stronger spin-orbit coupling of
4d-orbital might play a major role in creating D-M interaction of non-collinear
spins. We have systematically studied the spin and dipolar dynamics, which
exhibit intriguing behavior with shorter coherence lengths of 2nd magnetic
phase associated with the K2-wave vector. The results manifest the development
of magnetoelectric domains instead of true long-range ordering which justifies
the experimentally obtained low value of ferroelectric polarization. Further,
we have investigated the effect of external pressure on this complex magnetism.
The result reveals an enhancement of ordering temperature by the application of
external pressure (1.6K/GPa). The external pressure might favor stabilizing the
ground state associated with 2nd magnetic phase. Our study shows an
unconventional mechanism of spin-driven ferroelectricity involving inverse D-M
interaction between Ru(4d) and Ho(4f) magnetic ions due to strong 4d-4f
cross-coupling.",2309.13465v3
2003/4/28,Diamagnetic Screening of the Magnetic Field in Accreting Neutron Stars II -- The effect of Polar Cap Widening,"Recently, we have proposed a model for the screening of the magnetic field of
an accreting neutron star by the accreted material flowing from the polar
regions towards the equator and sinking there underneath the surface (Choudhuri
& Konar). In this model it was assumed that the flow pattern remained
stationary over time. However, as the surface magnetic field weakens, the
accretion takes place over a wider region around the pole, making the flow more
radial and isotropic. In the present work, we extend this two-dimensional model
to include the time-dependence of the flow of the accreted material. The final
radial flow is found to be less efficient in screening the magnetic field
compared to the initial tangential flow. After an initial phase of rapid decay,
the magnetic field slowly reaches an asymptotic value when the accretion
becomes nearly isotropic and radial. Assuming the initial extent of the polar
cap to be $\sim 5^0$--$10^0$, a simple geometric argument suggests that the
magnetic field should decay by 3-4 orders of magnitude before stabilizing to an
asymptotic value, consistent with the magnetic fields observed in millisecond
pulsars.",0304490v1
1995/12/14,Analytical and computational study of magnetization switching in kinetic Ising systems with demagnetizing fields,"An important aspect of real ferromagnetic particles is the demagnetizing
field resulting from magnetostatic dipole-dipole interaction, which causes
large particles to break up into domains. Sufficiently small particles,
however, remain single-domain in equilibrium. This makes such small particles
of particular interest as materials for high-density magnetic recording media.
In this paper we use analytic arguments and Monte Carlo simulations to study
the effect of the demagnetizing field on the dynamics of magnetization
switching in two-dimensional, single-domain, kinetic Ising systems. For systems
in the ``Stochastic Region,'' where magnetization switching is on average
effected by the nucleation and growth of fewer than two well-defined critical
droplets, the simulation results can be explained by the dynamics of a simple
model in which the free energy is a function only of magnetization. In the
``Multi-Droplet Region,'' a generalization of Avrami's Law involving a
magnetization-dependent effective magnetic field gives good agreement with our
simulations.",9512110v1
2004/9/9,Nonlocal magnetization dynamics in ferromagnetic heterostructures,"Two complementary effects modify the GHz magnetization dynamics of nanoscale
heterostructures of ferromagnetic and normal materials relative to those of the
isolated magnetic constituents: On the one hand, a time-dependent ferromagnetic
magnetization pumps a spin angular-momentum flow into adjacent materials and,
on the other hand, spin angular momentum is transferred between ferromagnets by
an applied bias, causing mutual torques on the magnetizations. These phenomena
are manifestly nonlocal: they are governed by the entire spin-coherent region
that is limited in size by spin-flip relaxation processes. We review recent
progress in understanding the magnetization dynamics in ferromagnetic
heterostructures from first principles, focusing on the role of spin pumping in
layered structures. The main body of the theory is semiclassical and based on a
mean-field Stoner or spin-density--functional picture, but quantum-size effects
and the role of electron-electron correlations are also discussed. A growing
number of experiments support the theoretical predictions. The formalism should
be useful to understand the physics and to engineer the characteristics of
small devices such as magnetic random-access memory elements.",0409242v3
2008/4/26,Magnetically Regulated Star Formation in 3D: The Case of Taurus Molecular Cloud Complex,"We carry out three-dimensional MHD simulations of star formation in
turbulent, magnetized clouds, including ambipolar diffusion and feedback from
protostellar outflows. The calculations focus on relatively diffuse clouds
threaded by a strong magnetic field capable of resisting severe tangling by
turbulent motions and retarding global gravitational contraction in the
cross-field direction. They are motivated by observations of the Taurus
molecular cloud complex (and, to a lesser extent, Pipe Nebula), which shows an
ordered large-scale magnetic field, as well as elongated condensations that are
generally perpendicular to the large-scale field. We find that stars form in
earnest in such clouds when enough material has settled gravitationally along
the field lines that the mass-to-flux ratios of the condensations approach the
critical value. Only a small fraction (of order 1% or less) of the nearly
magnetically-critical, condensed material is turned into stars per local
free-fall time, however. The slow star formation takes place in condensations
that are moderately supersonic; it is regulated primarily by magnetic fields,
rather than turbulence. The quiescent condensations are surrounded by diffuse
halos that are much more turbulent, as observed in the Taurus complex. Strong
support for magnetic regulation of star formation in this complex comes from
the extremely slow conversion of the already condensed, relatively quiescent
C$^{18}$O gas into stars, at a rate two orders of magnitude below the maximum,
free-fall value. We analyze the properties of dense cores, including their mass
spectrum, which resembles the stellar initial mass function.",0804.4201v1
2008/7/23,A key role for unusual spin dynamics in ferropnictides,"The 2008 discovery of superconducting ferropnictides with Tc~26K-56K
introduced a new family of materials into the category of high Tc
superconductors. The ongoing project of understanding the superconducting
mechanism and pairing symmetry has already revealed a complicated and often
contradictory underlying picture of the structural and magnetic properties.
There is an almost unprecedented sensitivity of the calculated magnetism and
Fermi surface to structural details that prohibits correspondence with
experiment. Furthermore, experimental probes of the order parameter symmetry
are in surprisingly strong disagreement, even considering the relative
immaturity of the field. Here we outline all of the various and seemingly
contradictory evidences, both theoretical and experimental, and show that they
can be rectified if the system is assumed to be highly magnetic with a spin
density wave that is well-defined but with magnetic twin and anti-phase
boundaries that are dynamic on the time-scale of experiments. Under this
assumption, we find that our calculations can accurately reproduce even very
fine details of the structure, and a natural explanation for the temperature
separation of structural and magnetic transitions is provided. Thus, our theory
restores agreement between experiment and theory in crucial areas, making
further cooperative progress possible on both fronts. We believe that
fluctuating magnetic domains will be an essential component of unravelling the
interplay between magnetic interactions and superconductivity in these newest
high Tc superconductors.",0807.3737v1
2008/9/11,Magnetic monopole and string excitations in a two-dimensional spin ice,"We study the magnetic excitations of a square lattice spin-ice recently
produced in an artificial form, as an array of nanoscale magnets. Our analysis,
based upon the dipolar interaction between the nanomagnetic islands, correctly
reproduces the ground-state observed experimentally. In addition, we find
magnetic monopole-like excitations effectively interacting by means of the
usual Coulombic plus a linear confining potential, the latter being related to
a string-like excitation binding the monopoles pairs, what indicates that the
fractionalization of magnetic dipoles may not be so easy in two dimensions.
These findings contrast this material with the three-dimensional analogue,
where such monopoles experience only the Coulombic interaction. We discuss,
however, two entropic effects that affect the monopole interactions: firstly,
the string configurational entropy may loose the string tension and then, free
magnetic monopoles should also be found in lower dimensional spin ices;
secondly, in contrast to the string configurational entropy, an entropically
driven Coulomb force, which increases with temperature, has the opposite effect
of confining the magnetic defects.",0809.2105v2
2009/3/2,"Magnetic fields, stellar feedback, and the geometry of H II Regions","Magnetic pressure has long been known to dominate over gas pressure in atomic
and molecular regions of the interstellar medium. Here I review several recent
observational studies of the relationships between the H^+, H^0 and H_2 regions
in M42 (the Orion complex) and M17. A simple picture results. When stars form
they push back surrounding material, mainly through the outward momentum of
starlight acting on grains, and field lines are dragged with the gas due to
flux freezing. The magnetic field is compressed and the magnetic pressure
increases until it is able to resist further expansion and the system comes
into approximate magnetostatic equilibrium. Magnetic field lines can be
preferentially aligned perpendicular to the long axis of quiescent cloud before
stars form. After star formation and pushback occurs ionized gas will be
constrained to flow along field lines and escape from the system along
directions perpendicular to the long axis. The magnetic field may play other
roles in the physics of the H II region and associated PDR. Cosmic rays may be
enhanced along with the field and provide additional heating of atomic and
molecular material. Wave motions may be associated with the field and
contribute a component of turbulence to observed line profiles.",0903.0204v1
2009/7/22,Quantized spin wave modes in magnetic tunnel junction nanopillars,"We present an experimental and theoretical study of the magnetic field
dependence of the mode frequency of thermally excited spin waves in rectangular
shaped nanopillars of lateral sizes 60x100, 75x150, and 105x190 nm2, patterned
from MgO-based magnetic tunnel junctions. The spin wave frequencies were
measured using spectrally resolved electrical noise measurements. In all
spectra, several independent quantized spin wave modes have been observed and
could be identified as eigenexcitations of the free layer and of the synthetic
antiferromagnet of the junction. Using a theoretical approach based on the
diagonalization of the dynamical matrix of a system of three coupled, spatially
confined magnetic layers, we have modeled the spectra for the smallest pillar
and have extracted its material parameters. The magnetization and exchange
stiffness constant of the CoFeB free layer are thereby found to be
substantially reduced compared to the corresponding thin film values. Moreover,
we could infer that the pinning of the magnetization at the lateral boundaries
must be weak. Finally, the interlayer dipolar coupling between the free layer
and the synthetic antiferromagnet causes mode anticrossings with gap openings
up to 2 GHz. At low fields and in the larger pillars, there is clear evidence
for strong non-uniformities of the layer magnetizations. In particular, at zero
field the lowest mode is not the fundamental mode, but a mode most likely
localized near the layer edges.",0907.3792v2
2011/6/21,Miniature ceramic-anvil high-pressure cell for magnetic measurements in a commercial superconducting quantum interference device magnetometer,"A miniature opposed-anvil high-pressure cell has been developed for magnetic
measurement in a commercial superconducting quantum interference device (SQUID)
magnetometer. Non-magnetic anvils made of composite ceramic material were used
to generate high-pressure with a Cu-Be gasket. We have examined anvils with
different culet sizes (1.8, 1.6, 1.4, 1.2, 1.0, 0.8 and 0.6 mm). The pressure
generated at low temperature was determined by the pressure dependence of the
superconducting transition of lead (Pb). The maximum pressure $P_{max}$ depends
on the culet size of the anvil: the values of $P_{max}$ are 2.4 and 7.6 GPa for
1.8 and 0.6 mm culet anvils, respectively. We revealed that the composite
ceramic anvil has potential to generate high pressure above 5 GPa. The
background magnetization of the Cu-Be gasket is generally two orders of
magnitude smaller than the Ni-Cr-Al gasket for the indenter cell. The present
cell can be used not only with ferromagnetic and superconducting materials with
large magnetization but also with antiferromagnetic compounds with smaller
magnetization. The production cost of the present pressure cell is about one
tenth of that of a diamond anvil cell. The anvil alignment mechanism is not
necessary in the present pressure cell because of the strong fracture toughness
(6.5 MPa${\cdot}$m$^{1/2}$) of the composite ceramic anvil. The simplified
pressure cell is easy-to-use for researchers who are not familiar with high
pressure technology. Representative results on the magnetization of
superconducting MgB$_2$ and antiferromagnet CePd$_5$Al$_2$ are reported.",1106.4071v1
2011/7/1,Glass-like ordering and spatial inhomogeneity of magnetic structure in Ba3FeRu2O9 : The role of Fe/Ru-site disorder,"Several doped 6H hexagonal ruthenates, having the general formula Ba3MRu2O9,
have been studied over a significant period of time in order to understand the
unusual magnetism of ruthenium metal. However, among them, the M=Fe compound
appears different since it is observed that unlike others, the 3d Fe ions and
4d Ru ions can easily exchange their crystallographic positions and as a result
many possible magnetic interactions become realizable. The present study
involving several experimental methods on this compound establish that the
magnetic structure of Ba3FeRu2O9 is indeed very different from all other 6H
ruthenates. Local structural study reveals that the possible Fe/Ru-site
disorder further extends to create local chemical inhomogeneity, affecting the
high temperature magnetism of this material. There is a gradual decrease of
57Fe M\""ossbauer spectral intensity with decreasing temperature (below 100 K),
which reveals that there is a large spread in the magnetic ordering
temperatures, corresponding to many spatially inhomogeneous regions. However,
finally at about 25 K, the whole compound is found to take up a global
glass-like magnetic ordering.",1107.0121v1
2011/11/19,Griffiths phase-like behaviour and spin-phonon coupling in double perovskite Tb$_{2}$NiMnO$_{6}$,"The Griffiths phase-like features and the spin-phonon coupling effects
observed in Tb$_2$NiMnO$_6$ are reported. The double perovskite compound
crystallizes in monoclinic $P2_1/n$ space group and exhibits a magnetic phase
transition at $T_c \sim$ 111 K as an abrupt change in magnetization. A negative
deviation from ideal Curie-Weiss law exhibited by 1/$\chi(T)$ curves and
less-than-unity susceptibility exponents from the power-law analysis of inverse
susceptibility are reminiscent of Griffiths phase-like features. Arrott plots
derived from magnetization isotherms support the inhomogeneous nature of
magnetism in this material. The observed effects originate from
antiferromagnetic interactions which arise from inherent disorder in the
system. Raman scattering experiments display no magnetic-order-induced phonon
renormalization below $T_c$ in Tb$_2$NiMnO$_6$ which is different from the
results observed in other double perovskites and is correlated to the smaller
size of the rare earth. The temperature evolution of full-width-at-half-maximum
for the {\it stretching} mode at 645 cm$^{-1}$ presents an anomaly which
coincides with the magnetic transition temperature and signals a close
connection between magnetism and lattice in this material.",1111.4585v1
2012/10/10,Frustrated pentagonal Cairo lattice in the non-collinear antiferromagnet Bi4Fe5O13F,"The crystal and magnetic structures and underlying magnetic interactions of
Bi4Fe5O13F, a model system for studying the physics of the Cairo pentagonal
spin lattice, are investigated by transmission electron microscopy,
low-temperature synchrotron x-ray and neutron powder diffraction, thermodynamic
measurements, and density functional band-structure calculations. The crystal
structure of Bi4Fe5O13F contains infinite rutile-like chains of edge-sharing
FeO6 octahedra interconnected by the Fe2O7 groups of two corner-sharing FeO4
tetrahedra. The cavities between the chains are filled with the
fluorine-centered Bi4F tetrahedra. The Fe3+ cations form pentagonal units that
give rise to an unusual topology of frustrated exchange couplings and underlie
a sequence of the magnetic transitions at T1= 62 K, T2 = 71 K, and TN = 178 K.
Below T1, Bi4Fe5O13F forms a fully ordered non-collinear antiferromagnetic
structure, whereas the magnetic state between T1 and TN may be partially
disordered according to the sizable increase in the magnetic entropy at T1 and
T2. Therefore, Bi4Fe5O13F shows the evidence of intricate magnetic transitions
that were never anticipated for the pentagonal Cairo spin lattice.
Additionally, it manifests a sillimanite (Al2SiO5)-based homologous series of
compounds that feature the pentagonal magnetic lattice spaced by a variable
number of octahedral units along the rutile-type chains.",1210.2822v1
2013/4/11,Sign-reversal of the in-plane resistivity anisotropy in iron pnictides,"The concept of an electronically-driven breaking of the rotational symmetry
of a crystal, without involving magnetic order, has found experimental support
in several systems, from semiconductor heterostructures and ruthenates, to
cuprate and iron-pnictide superconductors. In the pnictide BaFe$_{2}$As$_{2}$,
such an ""electronic nematic state"" appears above the magnetic transition dome,
over a temperature range that can be controlled by external strain. Here, by
measuring the in-plane resistivity anisotropy, we probe the electronic
anisotropy of this material over the entire nematic/magnetic dome, whose end
points coincide with the optimal superconducting transition temperatures.
Counter-intuitively, we find that, unlike other materials, the resistivity
anisotropy in BaFe$_{2}$As$_{2}$ changes sign across the doping phase diagram,
even though the signs of the magnetic, nematic, and orthorhombic order
parameters are kept fixed. This behavior is explained by the Fermi surface
reconstruction in the magnetic phase and spin-fluctuation scattering in the
nematic phase. The unique behavior of the transport anisotropy unveils that the
primary role is played by magnetic scattering in the normal state transport
properties of the iron pnictides, suggesting a close connection between
magnetism, nematicity, and unconventional superconductivity.",1304.3490v1
2014/11/17,Experimental and theoretical investigations on magnetic and related properties of ErRuSi,"We report experimental and theoretical studies of magnetic and related
properties of ErRuSi compound. Various experimental techniques such as neutron
diffraction, magnetization, magneto-thermal, magneto-transport, optical have
been used to study the compound. Neutron diffraction shows ferromagnetic
ordering at low temperatures with moments aligned in ab plane. Neutron
diffraction and magnetization data show reduction in magnetic moment, which may
be due to crystalline electric field effects at low temperatures. The compound
shows good magnetocaloric properties with a low field adiabatic temperature
change of 4.7 K, which is larger than that of many proposed materials for
magnetic refrigeration at low temperatures. Magnetoresistance shows large
negative value at 8 K, which changes its sign and increases in magnitude, with
decrease in temperature and/or increase in field. The positive MR at low
temperatures attributed to the Lorentz force effect. The electronic structure
calculations accounting for electronic correlations of the 4f electrons of Er
reproduces the ferromagnetic ordering and effective magnetic moment. Interband
transitions between the Ru and Er d states and Er f states in one spin
projection are found to form the main features of the measured optical
conductivity in this compound.",1411.4391v1
2015/1/16,State of Co and Mn in half-metallic ferromagnet Co$_2$MnSi explored by magnetic circular dichroism in hard X-ray photoelectron emission and soft X-ray absorption spectroscopies,"The half-metallic Heusler compound Co$_2$MnSi is a very attractive material
for spintronic devices because it exhibits very high tunnelling
magnetoresistance ratios. This work reports on a spectroscopic investigation of
thin Co$_2$MnSi films as they are used as electrodes in magnetic tunnel
junctions. The investigated films exhibit a remanent in-plane magnetisation
with a magnetic moment of about 5~$\mu_B$ when saturated, as expected. The low
coercive field of only 4~mT indicates soft magnetic behaviour. Magnetic
dichroism in emission and absorption was measured at the Co and Mn $2p$ core
levels. The photoelectron spectra were excited by circularly polarised hard
X-rays with an energy of of 6~keV and taken from the remanently magnetised
film. The soft X-ray absorption spectra were taken in an induction field of
4~T. Both methods yielded large dichroism effects. An analysis reveals the
localised character of the electrons and magnetic moments attributed to the Mn
atoms, whereas the electrons related to the Co atoms contribute an itinerant
part to the total magnetic moment.",1501.03966v1
2015/3/11,Magnetic and magnetodielectric coupling anomalies in the Haldane spin-chain system Nd2BaNiO5,"We report the magnetic, heat-capacity, dielectric and magnetodielectric (MDE)
behaviour of a Haldane spin-chain compound containing light rare-earth ion,
Nd2BaNiO5, in detail, as a function of temperature (T) and magnetic field (H)
down to 2 K. In addition to the well-known long range antiferromagnetic order
setting in at (T_N=) 48 K as indicated in dc magnetization (M), we have
observed another magnetic transition near 10 K; this transition appears to be
of a glassy-type which vanishes with a marginal application of external
magnetic field (even H= 100 Oe). There are corresponding anomalies in
dielectric constant as well with variation of T. The isothermal M(H) curves at
2 and 5 K reveal the existence of a magnetic-field induced transition around 90
kOe; the isothermal H-dependent dielectric constant also tracks such a
metamagnetic transition. These results illustrate the MDE coupling in this
compound. Additionally, we observe a strong frequency dependence of a step in
T-dependent dielectric constant with this feature appearing around 25-30 K for
the lowest frequency of 1 kHz, far below T_N. This is attributed to interplay
between crystal-field effect and exchange interaction between Nd and Ni, which
establishes the sensitivity of dielectric measurements to detect such effects.
Interestingly enough, the observed dispersions of the T-dependent dielectric
constant curves is essentially H-independent in the entire T-range of
measurement, despite the existence of MDE coupling, which is in sharp contrast
with other heavy rare-earth members in this series.",1503.03307v1
2015/4/1,Multiferroicity and skyrmions carrying electric polarization in GaV4S8,"Skyrmions are whirl like topological spin objects with high potential for
future magnetic data storage. It is a fundamental question, relevant for both
basic research and application, if a ferroelectric (FE) polarization can be
associated with their magnetic texture and if these objects can be manipulated
by electric fields. Here, we study the interplay between magnetism and electric
polarization in the lacunar spinel GaV4S8, which undergoes a structural
transition associated with orbital ordering at 44 K and reveals a complex
magnetic phase diagram below 13 K, including a ferromagnetic (FM), cycloidal,
and N\'eel-type skyrmion lattice (SkL) phase. We found that the orbitally
ordered phase of GaV4S8 is FE with a sizable polarization of ~1 {\mu}C/cm2.
Moreover, we observed spin-driven excess polarizations in all magnetic phases
and, hence, GaV4S8 hosts three different multiferroic phases with coexisting
polar and magnetic order. These include the SkL phase where we predict a strong
spatial modulation of the FE polarization close to the skyrmion cores. By
taking into account the crystal symmetry and spin patterns of the magnetically
ordered phases, we identify the exchange striction as the main microscopic
mechanism behind the spin-driven FE polarization in each multiferroic phase.
Since GaV4S8 is unique among the known SkL host materials due to its polar
crystal structure and the observed strong magnetoelectric effect, this study is
an important step towards the non-dissipative electric-field control of
skyrmions.",1504.00309v2
2015/4/17,Twisted phase of the orbital-dominant ferromagnet SmN in a GdN/SmN heterostructure,"The strong spin-orbit interaction in the rare-earth elements ensures that
even within a ferromagnetic state there is a substantial orbital contribution
to the ferromagnetic moment, in contrast to more familiar transition metal
systems, where the orbital moment is usually quenched. The orbital-dominant
magnetization that is then possible within rare-earth systems facilitates the
fabrication of entirely new magnetic heterostructures, and here we report a
study of a particularly striking example comprising interfaces between GdN and
SmN. Our investigation reveals a twisted magnetization arising from the large
spin-only magnetic moment in GdN and the nearly zero, but orbital-dominant,
moment of SmN. The unusual twisted phase is driven by (i) the similar ferromag-
netic Gd-Gd, Sm-Sm and Gd-Sm exchange interactions, (ii) a SmN Zeeman
interaction 200 times weaker than that of GdN, and (iii) the orbital-dominant
SmN magnetic moment. The element specificity of X-ray magnetic circular
dichroism (XMCD) is used in seperate modes probing both bulk and surface
regions, revealing the depth profile of the twisting magnetization.",1504.04425v1
2015/5/14,"First-principles calculations of exchange interactions, spin waves, and temperature dependence of magnetization in inverse-Heusler-based spin gapless semiconductors","Employing first principles electronic structure calculations in conjunction
with the frozen-magnon method we calculate exchange interactions, spin-wave
dispersion, and spin-wave stiffness constants in inverse-Heusler-based spin
gapless semiconductor (SGS) compounds Mn$_2$CoAl, Ti$_2$MnAl, Cr$_2$ZnSi,
Ti$_2$CoSi and Ti$_2$VAs. We find that their magnetic behavior is similar to
the half-metallic ferromagnetic full-Heusler alloys, i.e., the intersublattice
exchange interactions play an essential role in the formation of the magnetic
ground state and in determining the Curie temperature, $T_\mathrm{c}$. All
compounds, except Ti$_2$CoSi possess a ferrimagnetic ground state. Due to the
finite energy gap in one spin channel, the exchange interactions decay sharply
with the distance, and hence magnetism of these SGSs can be described
considering only nearest and next-nearest neighbor exchange interactions. The
calculated spin-wave dispersion curves are typical for ferrimagnets and
ferromagnets. The spin-wave stiffness constants turn out to be larger than
those of the elementary 3$d$-ferromagnets. Calculated exchange parameters are
used as input to determine the temperature dependence of the magnetization and
$T_\mathrm{c}$ of the SGSs. We find that the $T_\mathrm{c}$ of all compounds is
much above the room temperature. The calculated magnetization curve for
Mn$_2$CoAl as well as the Curie temperature are in very good agreement with
available experimental data. The present study is expected to pave the way for
a deeper understanding of the magnetic properties of the inverse-Heusler-based
SGSs and enhance the interest in these materials for application in spintronic
and magnetoelectronic devices.",1505.03632v1
2015/6/9,Universal chiral-triggered magnetization switching in confined nanodots,"Spin orbit interactions are rapidly emerging as the key for enabling
efficient current-controlled spintronic devices. Much work has focused on the
role of spin-orbit coupling at heavy metal/ferromagnet interfaces in generating
current-induced spin-orbit torques. However, the strong influence of the
spin-orbit-derived Dzyaloshinskii-Moriya interaction (DMI) on spin textures in
these materials is now becoming apparent. Recent reports suggest DMI-stabilized
homochiral domain walls (DWs) can be driven with high efficiency by spin torque
from the spin Hall effect. However, the influence of the DMI on the
current-induced magnetization switching has not been explored nor is yet
well-understood, due in part to the difficulty of disentangling spin torques
and spin textures in nano-sized confined samples. Here we study the
magnetization reversal of perpendicular magnetized ultrathin dots, and show
that the switching mechanism is strongly influenced by the DMI, which promotes
a universal chiral non-uniform reversal, even for small samples at the
nanoscale. We show that ultrafast current-induced and field-induced
magnetization switching consists on local magnetization reversal with domain
wall nucleation followed by its propagation along the sample. These findings,
not seen in conventional materials, provide essential insights for
understanding and exploiting chiral magnetism for emerging spintronics
applications.",1506.02893v1
2015/9/1,Magnon-driven longitudinal spin Seebeck effect in F|N and N|F|N structures: role of asymmetric in-plane magnetic anisotropy,"The influence of an asymmetric in-plane magnetic anisotropy on the thermally
activated spin current is studied theoretically for two different systems; (i)
the system consisting of a ferromagnetic insulator in a direct contact with a
nonmagnetic metal, and the sandwich structure consisting of a ferromagnetic
insulating part sandwiched between two nonmagnetic metals. It is shown that
when the difference between the temperatures of the two nonmagnetic metals in a
structure is not large, the spin pumping currents from the magnetic part to the
nonmagnetic ones are equal in amplitude and have opposite directions, so only
the spin torque current contributes to the total spin current. The spin current
flows then from the nonmagnetic metal with the higher temperature to the
nonmagnetic metal having a lower temperature. Its amplitude varies linearly
with the difference in temperatures. In addition, we have found that if the
magnetic anisotropy is in the layer plane, then the spin current increases with
the magnon temperature, while in the case of an out-of-plane magnetic
anisotropy the spin current decreases when the magnon temperature enhances.
Enlarging the difference between the temperatures of the nonmagnetic metals,
the linear response becomes important, as confirmed by analytical expressions
inferred from the Fokker-Planck approach and by the results obtained upon a
full numerical integration of the stochastic Landau-Lifshitz-Gilbert equation.",1509.00376v1
2016/2/9,Measuring nanoscale magnetic write head fields using a hybrid quantum register,"The generation and control of nanoscale magnetic fields are of fundamental
interest in material science and a wide range of applications. Nanoscale
magnetic resonance imaging quantum spintronics for example require single spin
control with high precision and nanoscale spatial resolution using fast
switchable magnetic fields with large gradients. Yet, characterizing those
fields on nanometer length scales at high band width with arbitrary orientation
has not been possible so far. Here we demonstrate single electron and nuclear
spin coherent control using the magnetic field of a hard disc drive write head.
We use single electron spins for measuring fields with high spatial resolution
and single nuclear spins for large band width measurements. We are able to
derive field profiles from coherent spin Rabi oscillations close to GHz in
fields with gradients of up to 10 mT/nm and measure all components of a static
and dynamic magnetic field independent of its orientation. Our method paves the
way for precision measurement of the magnetic fields of nanoscale write heads
important for future miniaturization of the devices.",1602.02948v1
2016/2/20,Covalent bonds against magnetism in transition metal compounds,"Magnetism in transition metal compounds is usually considered starting from a
description of isolated ions, as exact as possible, and treating their
(exchange) interaction at a later stage. We show that this standard approach
may break down in many cases, especially in $4d$ and $5d$ compounds. We argue
that there is an important intersite effect -- an orbital-selective formation
of covalent metal-metal bonds, which leads to an ""exclusion"" of corresponding
electrons from the magnetic subsystem, and thus strongly affects magnetic
properties of the system. This effect is especially prominent for noninteger
electron number, when it results in suppression of the famous double exchange,
the main mechanism of ferromagnetism in transition metal compounds. We study
this novel mechanism analytically and numerically and show that it explains
magnetic properties of not only several $4d-5d$ materials, including
Nb$_2$O$_2$F$_3$ and Ba$_5$AlIr$_2$O$_{11}$, but can also be operative in $3d$
transition metal oxides, e.g. in CrO$_2$ under pressure. We also discuss the
role of spin-orbit coupling on the competition between covalency and magnetism.
Our results demonstrate that strong intersite coupling may invalidate the
standard single-site starting point for considering magnetism, and can lead to
a qualitatively new behaviour.",1602.06425v2
2016/6/6,Magnetocaloric effect and nature of magnetic transition in low dimensional DyCu2,"In this manuscript, we propose a method to prepare small flakes of DyCu2. On
top of that we also report on the magnetocaloric effect and nature of magnetic
transition of a strongly anisotropic DyCu2 in its low dimension. Magnetization
measurements were carried out in the temperature range of 5 to 100 K and up to
the maximum magnetic field strength of 50 kOe. Magnetic entropy change delta SM
is estimated using the well known Maxwells equations and is found to be 4.31 J
per kg K. Indeed, the delta SM peak broadened marginally compared with its bulk
DyCu2 and such a broadening can be attributed to significant increase in the
total grain boundary volume. As these small flakes consists larger delta SM
values at temperatures higher than the Neel temperature TN, one can use them as
a magnetic refrigerant material in a broad temperature range. We also plotted
the M2 vs H by M in order to find the nature of magnetic transition. Arrott
plots infer that indeed there exists nonlinearity in M2 vs H by M behavior and
such nonlinear behavior is ascribed to the random anisotropy or a random field
that is present in the system.",1606.01694v1
2016/8/5,Optical determination of the Neel vector in a CuMnAs thin-film antiferromagnet,"Recent breakthroughs in electrical detection and manipulation of
antiferromagnets have opened a new avenue in the research of non-volatile
spintronic devices. Antiparallel spin sublattices in antiferromagnets,
producing zero dipolar fields, lead to the insensitivity to magnetic field
perturbations, multi-level stability, ultra-fast spin dynamics and other
favorable characteristics which may find utility in fields ranging from
magnetic memories to optical signal processing. However, the absence of a net
magnetic moment and the ultra-short magnetization dynamics timescales make
antiferromagnets notoriously difficult to study by common magnetometers or
magnetic resonance techniques. In this paper we demonstrate the experimental
determination of the Neel vector in a thin film of antiferromagnetic CuMnAs
which is the prominent material used in the first realization of
antiferromagnetic memory chips. We employ a femtosecond pump-probe
magneto-optical experiment based on magnetic linear dichroism. This table-top
optical method is considerably more accessible than the traditionally employed
large scale facility techniques like neutron diffraction and X-ray magnetic
dichroism measurements. This optical technique allows an unambiguous direct
determination of the Neel vector orientation in thin antiferromagnetic films
utilized in devices directly from measured data without fitting to a
theoretical model.",1608.01941v1
2016/12/9,Discovery of ferromagnetism with large magnetic anisotropy in ZrMnP and HfMnP,"ZrMnP and HfMnP single crystals are grown by a self-flux growth technique and
structural as well as temperature dependent magnetic and transport properties
are studied. Both compounds have an orthorhombic crystal structure. ZrMnP and
HfMnP are ferromagnetic with Curie temperatures around $370$~K and $320$~K
respectively. The spontaneous magnetizations of ZrMnP and HfMnP are determined
to be $1.9$~$\mu_\textrm{B}$/f.u. and $2.1$~$\mu_\textrm{B}$/f.u. respectively
at $50$~K. The magnetocaloric effect of ZrMnP in term of entropy change
($\Delta S$) is estimated to be $-6.7$ kJm$^{-3}$K$^{-1}$ around $369$~K. The
easy axis of magnetization is [100] for both compounds, with a small anisotropy
relative to the [010] axis. At $50$~K, the anisotropy field along the [001]
axis is $\sim4.6$~T for ZrMnP and $\sim10$~T for HfMnP. Such large magnetic
anisotropy is remarkable considering the absence of rare-earth elements in
these compounds. The first principle calculation correctly predicts the
magnetization and hard axis orientation for both compounds, and predicts the
experimental HfMnP anisotropy field within 25 percent. More importantly, our
calculations suggest that the large magnetic anisotropy comes primarily from
the Mn atoms suggesting that similarly large anisotropies may be found in other
3d transition metal compounds.",1612.03166v1
2017/4/7,Site occupancies and their effects on the physical properties of spinel $Co\left(Cr_{1-x}Fe_{x} \right)_{2}O_{4}$: an {\it ab initio} study,"Recent experimental studies on Fe substituted spinel CoCr$_{2}$O$_{4}$ have
discovered multiple functional properties in the system such as temperature and
composition dependent magnetic compensation, tunable exchange bias and
magnetostriction. These properties are attributed to the renormalisation of the
inter-atomic magnetic exchange interactions arising due to the non-regular site
occupancies of the magnetic cations in the system. In this work, we perform
{\it ab initio} electronic structure calculations by DFT+U method and combine
with a generalised thermodynamic model to compute the site occupancy patterns
of the magnetic cations, the structural properties and the magnetic exchange
interactions of Co$\left(Cr_{1-x}Fe_{x} \right)_{2}$O$_{4}$ for the entire
composition range $0<x<1$. We find that the substituting Fe atoms prefer to
occupy the tetrahedral sites of the spinel structure for the entire range of
$x$, in agreement with the experimental inferences. Our results on the
variations of the structural parameters with compositions agree very well with
the experiments. By computing the variations of the various inter-atomic
magnetic exchange interactions, we provide a microscopic picture of the
evolution of a collinear structure from a non-collinear one due to substitution
of Fe in CoCr$_{2}$O$_{4}$. The computed results are analysed in terms of the
elements of the crystal field theory, and the features in the atoms and
orbital-projected densities of states. The results and analysis presented in
this work is the first comprehensive study on this system which would help
understanding the complexities associated with the site occupancies, the
electronic structures and the magnetic interactions in this multi-functional
material.",1704.02102v1
2017/4/21,Time- and spatially-resolved magnetization dynamics driven by spin-orbit torques,"Current-induced spin-orbit torques (SOTs) represent one of the most effective
ways to manipulate the magnetization in spintronic devices. The orthogonal
torque-magnetization geometry, the strong damping, and the large domain wall
velocities inherent to materials with strong spin-orbit coupling make SOTs
especially appealing for fast switching applications in nonvolatile memory and
logic units. So far, however, the timescale and evolution of the magnetization
during the switching process have remained undetected. Here, we report the
direct observation of SOT-driven magnetization dynamics in Pt/Co/AlO$_x$ dots
during current pulse injection. Time-resolved x-ray images with 25 nm spatial
and 100 ps temporal resolution reveal that switching is achieved within the
duration of a sub-ns current pulse by the fast nucleation of an inverted domain
at the edge of the dot and propagation of a tilted domain wall across the dot.
The nucleation point is deterministic and alternates between the four dot
quadrants depending on the sign of the magnetization, current, and external
field. Our measurements reveal how the magnetic symmetry is broken by the
concerted action of both damping-like and field-like SOT and show that
reproducible switching events can be obtained for over $10^{12}$ reversal
cycles.",1704.06402v1
2017/5/13,Revealing the magnetic proximity effect in EuS/Al bilayers through superconducting tunneling spectroscopy,"A ferromagnetic insulator attached to a superconductor is known to induce an
exchange splitting of the Bardeen-Cooper-Schrieffer (BCS) singularity by a
magnitude proportional to the magnetization, and penetrating into the
superconductor to a depth comparable with the superconducting coherence length.
We study this long-range magnetic proximity effect in EuS/Al bilayers and find
that the exchange splitting of the BCS peaks is present already in the
unpolarized state of the ferromagnetic insulator (EuS), and is being further
enhanced when magnetizing the sample by a magnetic field. The measurement data
taken at the lowest temperatures feature a high contrast which has allowed us
to relate the line shape of the split BCS conductance peaks to the
characteristic magnetic domain structure of the EuS layer in the unpolarized
state. These results pave the way to engineering triplet superconducting
correlations at domain walls in EuS/Al bilayers. Furthermore, the hard gap and
clear splitting observed in our tunneling spectroscopy measurements indicate
that EuS/Al bilayers are excellent candidates for substituting strong magnetic
fields in experiments studying Majorana bound states.",1705.04795v2
2017/7/24,Developing a Method to Determine Electrical Conductivity in Meteoritic Materials with Applications to Induction Heating Theory (2008 Student Thesis),"Magnetic induction was first proposed as a planetary heating mechanism by
Sonett and Colburn in 1968, in recent years this theory has lost favor as a
plausible source of heating in the early solar system. However, new models of
proto-planetary disk evolution suggest that magnetic fields play an important
role in solar system formation. In particular, the magneto-hydrodynamic
behavior of proto-planetary disks is believed to be responsible for the net
outward flow of angular momentum in the solar system. It is important to
re-evaluate the plausibility of magnetic induction based on the intense
magnetic field environments described by the most recent models of
proto-planetary disk evolution.
  In order to re-evaluate electromagnetic induction theory the electrical
conductivity of meteorites must be determined. To develop a technique capable
of making these measurements, a time-varying magnetic field was generated to
inductively heat metallic control samples. The thermal response of each sample,
which depends on electrical conductivity, was monitored until a thermal steady
state was achieved. The relationship between conductivity and thermal response
can be exploited to estimate the electrical conductivity of unknown samples.
After applying the technique to various metals it was recognized that this
method is not capable of making precise electrical conductivity measurements.
However, this method can constrain the product of the electrical conductivity
and the square of the magnetic permeability, or ${\sigma}{{\mu}^2}$, for
meteoritic and metallic samples alike. The results also illustrate that along
with electrical conductivity {\sigma}, the magnetic permeability {\mu} of a
substance has an important effect on induction heating phenomena for
paramagnetic ({\mu}/{\mu}0 > 1) and especially ferromagnetic materials
({\mu}/{\mu}0 >> 1).",1707.07648v1
2017/9/10,Dynamical Anisotropic Response of Black Phosphorus under Magnetic Field,"Black phosphorus (BP) has emerged as a promising material candidate for next
generation electronic and optoelectronic devices due to its high mobility,
tunable band gap and highly anisotropic properties. In this work, polarization
resolved ultrafast mid-infrared transient reflection spectroscopy measurements
are performed to study the dynamical anisotropic optical properties of BP under
magnetic fields up to 9 T. The relaxation dynamics of photoexcited carrier is
found to be insensitive to the applied magnetic field due to the broadening of
the Landau levels and large effective mass of carriers. While the anisotropic
optical response of BP decreases with increasing magnetic field, its
enhancement due to the excitation of hot carriers is similar to that without
magnetic field. These experimental results can be well interpreted by the
magneto-optical conductivity of the Landau levels of BP thin film, based on an
effective k*p Hamiltonian and linear response theory. These findings suggest
attractive possibilities of multi-dimensional controls of anisotropic response
(AR) of BP with light, electric and magnetic field, which further introduces BP
to the fantastic magnetic field sensitive applications.",1709.03079v1
2017/9/14,Magnetic field suppression of Andreev conductance at superconductor-graphene interfaces,"Studying the interplay between superconductivity and quantum magnetotransport
in two-dimensional materials has been a topic of interest in recent years.
Towards such a goal it is important to understand the impact of magnetic field
on the charge transport at the superconductor-normal channel (SN) interface.
Here we carried out a comprehensive study of Andreev conductance under weak
magnetic fields using diffusive superconductor- graphene Josephson weak links.
We observe that the Andreev conductance is suppressed even in magnetic fields
far below the upper critical field of the superconductor. The suppression of
Andreev conductance depends on and can be minimized by controlling the ramping
of the magnetic field. We identify that the key factor behind this suppression
is the reduction of the superconducting gap due to the piling of vortices on
the superconducting contacts. In devices where superconducting gap at the
superconductor-graphene interface is heavily reduced by proximity effect, the
enlarged vortex cores overlap quickly with increasing magnetic field, resulting
in a rapid decrease of the interfacial gap. However, in weak links with
relatively large effective superconducting gap the AR conductance persists up
to the upper critical field. Our results provide guidance to the study of
quantum material-superconductor systems in presence of magnetic field, where
'survival' of induced superconductivity is critical.",1709.04844v2
2017/9/28,Magnetization and Anisotropy of Cobalt Ferrite Thin Films,"The magnetization of thin films of cobalt ferrite frequently falls far below
the bulk value of 455 kAm-1, which corresponds to an inverse cation
distribution in the spinel structure with a significant orbital moment of about
0.6 muB that is associated with the octahedrally-coordinated Co2+ ions. The
orbital moment is responsible for the magnetostriction and magnetocrystalline
anisotropy, and its sensitivity to imposed strain. We have systematically
investigated the structure and magnetism of films produced by pulsed-laser
deposition on different substrates (TiO2, MgO, MgAl2O4, SrTiO3, LSAT, LaAlO3)
and as a function of temperature (500-700 C) and oxygen pressure (10-4 - 10
Pa). Magnetization at room-temperature ranges from 60 to 440 kAm-1, and
uniaxial substrate-induced anisotropy ranges from +220 kJm-3 for films on
deposited on MgO (100) to -2100 kJm-3 for films deposited on MgAl2O4 (100),
where the room-temperature anisotropy field reaches 14 T. No rearrangement of
high-spin Fe3+ and Co2+ cations on tetrahedral and octahedral sites can reduce
the magnetization below the bulk value, but a switch from Fe3+ and Co2+ to Fe2+
and low-spin Co3+ on octahedral sites will reduce the low-temperature
magnetization to 120 kAm-1, and a consequent reduction of Curie temperature can
bring the room-temperature value to near zero. Possible reasons for the
appearance of low-spin cobalt in the thin films are discussed.
  Keywords; Cobalt ferrite, thin films, pulsed-laser deposition, low-spin Co3+,
strain engineering of magnetization.",1709.09965v1
2017/10/5,"First-principles investigation of competing magnetic interactions in (Mn,Fe)Ru$_2$Sn Heusler solid solutions","Many Heusler compounds possess magnetic properties well-suited for
applications as spintronic materials. The pseudo-binary
Mn$_{0.5}$Fe$_{0.5}$Ru$_2$Sn, formed as a solid solution of two full Heuslers,
has recently been shown to exhibit exchange hardening suggestive of two
magnetic phases, despite existing as a \textit{single} chemical phase. We have
performed a first-principles study of the chemical and magnetic degrees of
freedom in the Mn$_{1-x}$Fe$_{x}$Ru$_2$Sn pseudo-binary to determine the origin
of the unique magnetic behavior responsible for exchange hardening within a
single phase. We find a transition from antiferromagnetic (AFM) to
ferromagnetic (FM) behavior upon replacement of Mn with Fe, consistent with
experimental results. The lowest energy orderings in Mn$_{1-x}$Fe$_{x}$Ru$_2$Sn
consist of chemically- and magnetically-uniform (111) planes, with Fe-rich
regions preferring FM ordering and Mn-rich regions preferring AFM ordering,
independent of the overall composition. Analysis of the electronic structure
suggests that the magnetic behavior of this alloy arises from a competition
between AFM-favoring Sn-mediated superexchange and FM-favoring RKKY exchange
mediated by spin-polarized conduction electrons. Changes in valency upon
replacement of Mn with Fe shifts the balance from superexchange-dominated
interactions to RKKY-dominated interactions.",1710.02089v1
2018/1/22,Role of quantum fluctuations on spin liquids and ordered phases in the Heisenberg model on the honeycomb lattice,"Motivated by the rich physics of honeycomb magnetic materials, we obtain the
phase diagram and analyze magnetic properties of the spin-1/2 and spin-1
J1-J2-J3 Heisenberg model on the honeycomb lattice. Based on the SU(2) and
SU(3) symmetry representations of the Schwinger boson approach, which treats
disordered spin liquids and magnetically ordered phases on an equal footing, we
obtain the complete phase diagrams in the (J2,J3)plane. This is achieved using
a fully unrestricted approach which does not assume any pre-defined Ansatze.
For S=1/2, we find a quantum spin liquid (QSL) stabilized between the N\'eel,
spiral and collinear antiferromagnetic phases in agreement with previous
theoretical work. However, by increasing S from 1/2 to 1, the QSL is quickly
destroyed due to the weakening of quantum fluctuations indicating that the
model already behaves as a quasi-classical system. The dynamical structure
factors and temperature dependence of the magnetic susceptibility are obtained
in order to characterize all phases in the phase diagrams. Moreover, motivated
by the relevance of the single-ion anisotropy, D, to various S=1 honeycomb
compounds, we have analyzed the destruction of magnetic order based on a SU(3)
representation of the Schwinger bosons. Our analysis provides a unified
understanding of the magnetic properties of honeycomb materials realizing the
J1-J2-J3 Heisenberg model from the strong quantum spin regime at S=1/2 to the
S=1 case. Neutron scattering and magnetic susceptibility experiments can be
used to test the destruction of the QSL phase when replacing S=1/2 by S=1
localized moments in certain honeycomb compounds.",1801.07042v1
2018/2/22,Magnetic properties of metal-organic coordination networks based on 3d transition metal atoms,"The magnetic anisotropy and exchange coupling between spins localized at the
positions of 3d transition metal atoms forming two-dimensional metal-organic
coordination networks (MOCNs) grown on the Au(111) metal surface are studied.
In particular, we consider MOCNs made of Ni or Mn metal centers linked by TCNQ
(7,7,8,8-tetracyanoquinodimethane) organic ligands, which form rectangular
networks with 1:1 stoichiometry. Based on the analysis of X-ray magnetic
circular dichroism (XMCD) data taken at T= 2.5 K, we find that Ni atoms in the
Ni-TCNQ MOCNs are coupled ferromagnetically and do not show any significant
magnetic anisotropy, while Mn atoms in the Mn-TCNQ MOCNs are coupled
antiferromagnetically and do show a weak magnetic anisotropy with
in-planemagnetization. We explain these observations using both
amodelHamiltonian based on mean-fieldWeiss theory and density functional theory
calculations that include spin-orbit coupling. Our main conclusion is that the
antiferromagnetic coupling between Mn spins and the in-plane magnetization of
the Mn spins can be explained neglecting effects due to the presence of the
Au(111) surface, while for Ni-TCNQ the metal surface plays a role in
determining the absence of magnetic anisotropy in the system.",1802.08243v1
2018/2/23,Using first-principles calculations to screen for fragile magnetism: Case study of LaCrGe3 and LaCrSb3,"In this paper, we present a coupled experimental/theoretical investigation of
pressure effect on the ferromagnetism of LaCrGe3 and LaCrSb3 compounds. The
magnetic, electronic, elastic and mechanical properties of LaCrGe3 and LaCrSb3
at ambient condition are studied by first-principles density functional theory
calculations. The pressure dependences of the magnetic properties of LaCrGe3
and LaCrSb3 are also investigated. The ferromagnetism in LaCrGe3 is rather
fragile with a ferro- to paramagnetic transition at a relatively small pressure
(around 7 GPa from our calculations, and 2 GPa in experiments). The key
parameter controlling the magnetic properties of LaCrGe3 is found to be the
proximity of the Cr DOS to the Fermi surface, a proximity that is strongly
correlated to the distance between Cr atoms along the c-axis, suggesting that
there would be a simple way to suppress magnetism in systems with one
dimensional arrangement of magnetic atoms. By contrast, the ferromagnetism in
LaCrSb3 is not fragile. Our calculation results are consistent with our
experimental results and demonstrate the feasibility of using first-principles
calculations to aid experimental explorations in screening for materials with
fragile magnetism.",1802.08398v1
2018/4/1,Evidence of large magnetic cooling power and double glass transition in Tb5Pd2,"We report a detailed dc magnetization, ac susceptibility and magnetocaloric
properties of a binary intermetallic compound Tb5Pd2. Our dc magnetization and
heat capacity results reveal absence of long range ordering in this compound.
Two distinct frequency dependent peaks (Tf1~60 K and Tf2~21 K) had been
observed in the ac-susceptibility. Analysis of these frequency dependent peaks
by Mydosh parameter, power and Vogel-Fulcher law reveals that around Tf1 the
compound is at the boundary of spin glass (SG) like-cluster glass (CG) like
state and it undergoes a cluster glass-like freezing below Tf2. Zero field
cooled memory effect and non-linear dc susceptibility also confirmed the
presence of two glassy transitions in this compound. The transformation from
SG/CG boundary to CG phase was also confirmed by the magnetic relaxation
measurement and Arrott plots study. Remarkably, a significant magnetic entropy
change was also observed in the temperature range of 60-120 K. Additionally a
large relative cooling power also observed in this compound. The observed value
is comparable to those of promising refrigerant material in this temperature
range and is quite notable as in this compound magnetic hysteresis was absent
in this temperature range. It was noted that in this compound short-range
interactions persist up to a higher temperature above Tf1 and this is
responsible for the observation of significant MCE over a wide temperature
range. Our studies suggest that this compound is an example of a glassy
magnetic compound which shows large magnetocaloric effect.",1804.00255v1
2018/8/30,Accelerating the calculation of dipolar interactions in particle based simulations with open boundary conditions by means of the P2NFFT method,"Magnetic gels are soft elastic materials consisting of magnetic particles
embedded in a polymer network. Their shape and elasticity can be controlled by
an external magnetic field, which gives rise to both, engineering and
biomedical applications. Computer simulations are a commonly used tool to study
these materials. A well-known bottleneck of these simulations is the demanding
calculation of dipolar interactions. Under periodic boundary conditions
established algorithms are available for doing this, however, at the expense of
restricting the way in which the gels can deform in an external magnetic field.
Moreover, the magnetic properties depend on the sample shape, ruling out
periodic boundary conditions entirely for some research questions. In this
article we will employ the recently developed dipolar variant of the P$^2$NFFT
method that is able to calculate dipolar interactions under open boundary
conditions with an $N \log N$ scaling in the number of particles, rather than
the expensive $N^2$ scaling of a direct summation of pair forces. The dipolar
P$^2$NFFT method has been implemented within the ScaFaCoS library. The
molecular dynamics software ESPResSo has been extended to make use of the
library.
  After a short summary of the method, we will discuss its value for studying
magnetic soft matter systems. A particular focus is put on developing a tuning
strategy to reach the best performance of the method at a predefined accuracy,
and lastly applying the method to a magnetic gel model. Here, adapting to the
gel's change in shape during the course of a simulation is of particular
interest.",1808.10341v1
2018/11/13,Interplay between Kitaev interaction and single ion anisotropy in ferromagnetic CrI$_3$ and CrGeTe$_3$ monolayers,"Magnetic anisotropy is crucially important for the stabilization of
two-dimensional (2D) magnetism, which is rare in nature but highly desirable in
spintronics and for advancing fundamental knowledge. Recent works on CrI$_3$
and CrGeTe$_3$ monolayers not only led to observations of the long-time-sought
2D ferromagnetism, but also revealed distinct magnetic anisotropy in the two
systems, namely Ising behavior for CrI$_3$ versus Heisenberg behavior for
CrGeTe$_3$. Such magnetic difference strongly contrasts with structural and
electronic similarities of these two materials, and understanding it at a
microscopic scale should be of large benefits. Here, first-principles
calculations are performed and analyzed to develop a simple Hamiltonian, to
investigate magnetic anisotropy of CrI$_3$ and CrGeTe$_3$ monolayers. The
anisotropic exchange coupling in both systems is surprisingly determined to be
of Kitaev-type. Moreover, the interplay between this Kitaev interaction and
single ion anisotropy (SIA) is found to naturally explain the different
magnetic behaviors of CrI$_3$ and CrGeTe$_3$. Finally, both the Kitaev
interaction and SIA are further found to be induced by spin-orbit coupling of
the heavy ligands (I of CrI$_3$ or Te of CrGeTe$_3$) rather than the commonly
believed 3d magnetic Cr ions.",1811.05413v1
2018/11/16,Parametrization of LSDA+$U$ for noncollinear magnetic configurations: Multipolar magnetism in UO$_2$,"To explore the formation of noncollinear magnetic configurations in materials
with strongly correlated electrons, we derive a noncollinear LSDA+$U$ model
involving only one parameter $U$, as opposed to the difference between the
Hubbard and Stoner parameters $U-J$. Computing $U$ in the constrained random
phase approximation, we investigate noncollinear magnetism of uranium dioxide
UO$_2$ and find that the spin-orbit coupling (SOC) stabilizes the 3$\textbf{k}$
ordered magnetic ground state. The estimated SOC strength in UO$_2$ is as large
as 0.73 eV per uranium atom, making spin and orbital degrees of freedom
virtually inseparable. Using a multipolar pseudospin Hamiltonian, we show how
octupolar and dipole-dipole exchange coupling help establish the 3$\textbf{k}$
magnetic ground state with canted ordering of uranium $f$-orbitals. The
cooperative Jahn-Teller effect does not appear to play a significant part in
stabilizing the noncollinear 3$\textbf{k}$ state, which has the lowest energy
even in an undistorted lattice. The choice of parameter $U$ in the LSDA+$U$
model has a notable quantitative effect on the predicted properties of UO$_2$,
in particular on the magnetic exchange interaction and, perhaps trivially, on
the band gap: The value of $U=3.46$ eV computed fully $ab$ $initio$ delivers
the band gap of 2.11~eV in good agreement with experiment, and a balanced
account of other pertinent energy scales.",1811.06864v2
2019/2/7,"Quadrupolar ordering and exotic magnetocaloric effect in RB4 (R = Dy, Ho)","The interplay of charge, spin, orbital and lattice degrees of freedom has
recently received great interest due to its potential to improve the
magnetocaloric effect (MCE) for the purpose of magnetic cooling applications.
Here we propose a new mechanism for a giant inverse MCE in rare-earth
tetraborides, especially for Ho1-xDyxB4 (x = 0.0, 0.5, and 1.0). For x = 0.0,
0.5, and 1.0, the maximum entropy changes of the giant inverse MCE are found to
be 22.7 J/kgK, 19.6 J/kgK, and 19.0 J/kgK with critical fields of 25 kOe, 40
kOe, and 50 kOe, respectively. It is remarkable that such a giant MCE is
realized, even when applying a low magnetic field, which enables a field-tuned
entropy change and brings about a significant advantage for several
applications. For all compounds, we have systematically studied how the entropy
changes as a function of the field and temperature and investigated their
correlation with consecutive double transitions, i.e., the magnetic dipolar
order at T = TN and the quadrupolar order at T = TQ (TQ < TN). We found that
the maximum entropy change occurs at T = TQ and the critical field associated
with the meta-magnetic transition, which is in good agreement with the
experimental data. Thus, we elucidate that this unique behaviour is attributed
to the strong coupling between magnetic dipoles and quadrupoles in the presence
of strong spin-orbit coupling and geometric frustration. Our work offers new
insights into both the academic interest of multipolar degrees of freedom in
magnetic materials and the discovery of giant MCE with various applications for
magnetic cooling systems.",1902.02576v1
2019/3/13,Thickness dependence of magnetization reversal and magnetostriction in FeGa thin films,"Among the magnetostrictive alloys the one formed of iron and gallium (called
""Galfenol"" from its U.S. Office of Naval Research discoverers in the late 90's)
is attractive for its low hysteresis, good tensile stress, good machinability
and its rare-earth free composition. One of its applications is its association
with a piezoelectric material to form a extrinsic multiferroic composite as an
alternative to the rare room temperature intrinsic multiferroics such as
BiFeO$_3$. This study focuses on thin Fe$_{0.81}$Ga$_{0.19}$ films of thickness
5, 10, 20 and 60 nm deposited by sputtering onto glass substrates.
Magnetization reversal study reveals a well-defined symmetry with two principal
directions independent of the thickness. The magnetic signature of this
magnetic anisotropy decreases with increasing FeGa thickness due to an increase
of the non-preferential polycrystalline arrangement, as revealed by
transmission electron microscopy (TEM) observations. Thus when magnetic field
is applied along these specific directions, magnetization reversal is mainly
coherent for the thinnest sample as seen from the transverse magnetization
cycles. Magnetostriction coefficient reaches 20 ppm for the 5 nm film and
decreases for thicker samples, where polycrystalline part with non-preferential
orientation prevails.",1903.05397v2
2019/3/13,Wide-field Magnetic Field and Temperature Imaging using Nanoscale Quantum Sensors,"The simultaneous imaging of magnetic fields and temperature (MT) is important
in a range of applications, including studies of carrier transport, solid-state
material dynamics, and semiconductor device characterization. Techniques exist
for separately measuring temperature (e.g., infrared (IR) microscopy,
micro-Raman spectroscopy, and thermo-reflectance microscopy) and magnetic
fields (e.g., scanning probe magnetic force microscopy and superconducting
quantum interference devices). However, these techniques cannot measure
magnetic fields and temperature simultaneously. Here, we use the exceptional
temperature and magnetic field sensitivity of nitrogen vacancy (NV) spins in
conformally-coated nanodiamonds to realize simultaneous wide-field MT imaging.
Our ""quantum conformally-attached thermo-magnetic"" (Q-CAT) imaging enables (i)
wide-field, high-frame-rate imaging (100 - 1000 Hz); (ii) high sensitivity; and
(iii) compatibility with standard microscopes. We apply this technique to study
the industrially important problem of characterizing multifinger gallium
nitride high-electron-mobility transistors (GaN HEMTs). We spatially and
temporally resolve the electric current distribution and resulting temperature
rise, elucidating functional device behavior at the microscopic level. The
general applicability of Q-CAT imaging serves as an important tool for
understanding complex MT phenomena in material science, device physics, and
related fields.",1903.05717v1
2019/4/1,Rotating magnetic field driven antiferromagnetic domain wall motion: Role of Dzyaloshinskii-Moriya interaction,"In this work, we study the rotating magnetic field driven domain wall (DW)
motion in antiferromagnetic nanowires, using the micromagnetic simulations of
the classical Heisenberg spin model. We show that in low frequency region, the
rotating field alone could efficiently drive the DW motion even in the absence
of Dzyaloshinskii-Moriya interaction (DMI). In this case, the DW rotates
synchronously with the magnetic field, and a stable precession torque is
available and drives the DW motion with a steady velocity. In large frequency
region, the DW only oscillates around its equilibrium position and cannot
propagate. The dependences of the velocity and critical frequency
differentiating the two motion modes on several parameters are investigated in
details, and the direction of the DW motion can be controlled by modulating the
initial phase of the field. Interestingly, a unidirectional DW motion is
predicted attributing to the bulk DMI, and the nonzero velocity for high
frequency is well explained. Thus, this work does provide useful information
for further antiferromagnetic spintronics applications.",1904.00870v2
2019/4/15,Topological Hall effect at above room temperature in heterostructures composed of a magnetic insulator and a heavy metal,"Non-volatile memory and computing technology rely on efficient read and write
of ultra-tiny information carriers that do not wear out. Magnetic skyrmions are
emerging as a potential carrier since they are topologically robust nanoscale
spin textures that can be manipulated with ultralow current density. To date,
most of skyrmions are reported in metallic films, which suffer from additional
Ohmic loss and thus high energy dissipation. Therefore, skyrmions in magnetic
insulators are of technological importance for low-power information processing
applications due to their low damping and the absence of Ohmic loss. Moreover,
they attract fundamental interest in studying various magnon-skyrmion
interactions11. Skyrmions have been observed in one insulating material
Cu2OSeO3 at cryogenic temperatures, where they are stabilized by bulk
Dzyaloshinskii-Moriya interaction. Here, we report the observation of magnetic
skyrmions that survive above room temperature in magnetic insulator/heavy metal
heterostructures, i.e., thulium iron garnet/platinum. The presence of these
skyrmions results from the Dzyaloshinskii-Moriya interaction at the interface
and is identified by the emergent topological Hall effect. Through tuning the
magnetic anisotropy via varying temperature, we observe skyrmions in a large
window of external magnetic field and enhanced stability of skyrmions in the
easy-plane anisotropy regime. Our results will help create a new platform for
insulating skyrmion-based room temperature low dissipation spintronic
applications.",1904.07107v1
2019/5/2,Strong magnetoelectric coupling in mixed ferrimagnetic-multiferroic phases of a double perovskite,"Exploring new magnetic materials is essential for finding advantageous
functional properties such as magnetoresistance, magnetocaloric effect,
spintronic functionality, and multiferroicity. Versatile classes of double
perovskite compounds have been recently investigated because of intriguing
physical properties arising from the proper combination of several magnetic
ions. In this study, it is observed that the dominant ferrimagnetic phase is
coexisted with a minor multiferroic phase in single-crystalline
double-perovskite Er2CoMnO6. The majority portion of the ferrimagnetic order is
activated by the long-range order of Er3+ moments below TEr = 10 K in addition
to the ferromagnetic order of Co2+ and Mn4+ moments arising at TC = 67 K,
characterized by compensated magnetization at TComp = 3.15 K. The inverted
magnetic hysteresis loop observed below TComp can be described by an extended
Stoner-Wohlfarth model. The additional multiferroic phase is identified by the
ferroelectric polarization of 0.9 uC/m2 at 2 K. The coexisting ferrimagnetic
and multiferroic phases appear to be strongly correlated in that metamagnetic
and ferroelectric transitions occur simultaneously. The results based on
intricate magnetic correlations and phases in Er2CoMnO6 enrich fundamental and
applied research on magnetic materials through the scope of distinct magnetic
characteristics in double perovskites.",1905.00595v1
2019/5/11,Giant Spin Seebeck Effect through an Interface Organic Semiconductor,"Interfacing an organic semiconductor C60 with a non-magnetic metallic thin
film (Cu or Pt) has created a novel heterostructure that is ferromagnetic at
ambient temperature, while its interface with a magnetic metal (Fe or Co) can
tune the anisotropic magnetic surface property of the material. Here, we
demonstrate that sandwiching C60 in between a magnetic insulator (Y3Fe5O12:
YIG) and a non-magnetic, strong spin-orbit metal (Pt) promotes highly efficient
spin current transport via the thermally driven spin Seebeck effect (SSE).
Experiments and first principles calculations consistently show that the
presence of C60 reduces significantly the conductivity mismatch between YIG and
Pt and the surface perpendicular magnetic anisotropy of YIG, giving rise to
enhanced spin mixing conductance across YIG/C60/Pt interfaces. As a result, a
600% increase in the SSE voltage (VLSSE) has been realized in YIG/C60/Pt
relative to YIG/Pt. Temperature-dependent SSE voltage measurements on
YIG/C60/Pt with varying C60 layer thicknesses also show an exponential increase
in VLSSE at low temperatures below 200 K, resembling the temperature evolution
of spin diffusion length of C60. Our study emphasizes the important roles of
the magnetic anisotropy and the spin diffusion length of the intermediate layer
in the SSE in YIG/C60/Pt structures, providing a new pathway for developing
novel spin-caloric materials.",1905.04555v1
2019/5/22,Magnetic order in single crystals of Na3Co2SbO6 with a honeycomb arrangement of 3d$^7$ Co$^{2+}$ ions,"We have synthesized single crystals of Na$_3$Co$_2$SbO$_6$ and characterized
the structure and magnetic order by measuring anisotropic magnetic properties,
heat capacity, x-ray and neutron single crystal diffraction. Magnetic
properties and specific heat of polycrystalline Na$_3$Co$_2$SbO$_6$ were also
measured for comparison. Na$_3$Co$_2$SbO$_6$ crystallizes in a monoclinic
structure (space group $C2/m$) with [Co$_2$SbO$_6$]$^{3-}$ layers separated by
Na$^+$ ions. The temperature dependence of magnetic susceptibility shows
significant anisotropic behavior in the whole temperature range 2\,K-350\,K
investigated in this work. An effective moment of about 5.5\,$\mu_B$/Co$^{2+}$
from a Curie-Weiss fitting of the magnetic susceptibility is larger than the
spin only value and signals significant orbital contribution.
Na$_3$Co$_2$SbO$_6$ single crystal undergoes a transition into a long-range
antiferromagnetically ordered state below $T_N$=5\,K. Neutron single crystal
diffraction confirmed the zigzag magnetic structure with a propagation vector
k\,=\,(0.5, 0.5, 0). The ordered moment is found to be 0.9\,$\mu_B$ at 4\,K and
align along the crystallographic \textit{b}-axis. Density functional theory
calculations suggest that the experimentally observed zigzag order is
energetically competing with the Neel order. It is also found that the
covalency between Co $d$ and O $p$ is quite strong and competes with the local
spin-orbit coupling, suggesting a $J_{eff}$=1/2 ground state may not be
realized in this compound.",1905.09365v1
2019/5/26,Pressure-controlled interlayer magnetism in atomically thin CrI3,"Stacking order can significantly influence the physical properties of
two-dimensional (2D) van der Waals materials. The recent isolation of
atomically thin magnetic materials opens the door for control and design of
magnetism via stacking order. Here we apply hydrostatic pressure up to 2 GPa to
modify the stacking order in a prototype van der Waals magnetic insulator CrI3.
We observe an irreversible interlayer antiferromagnetic (AF) to ferromagnetic
(FM) transition in atomically thin CrI3 by magnetic circular dichroism and
electron tunneling measurements. The effect is accompanied by a monoclinic to a
rhombohedral stacking order change characterized by polarized Raman
spectroscopy. Before the structural change, the interlayer AF coupling energy
can be tuned up by nearly 100% by pressure. Our experiment reveals interlayer
FM coupling, which is the established ground state in bulk CrI3, but never
observed in native exfoliated thin films. The observed correlation between the
magnetic ground state and the stacking order is in good agreement with first
principles calculations and suggests a route towards nanoscale magnetic
textures by moir\'e engineering.",1905.10905v1
2019/6/3,An XMCD study of magnetism and valence state in iron-substituted strontium titanate,"Room temperature ferromagnetism was characterized for thin films of
SrTi$_{0.6}$Fe$_{0.4}$O$_{3-{\delta}}$ grown by pulsed laser deposition on
SrTiO$_{3}$ and Si substrates under different oxygen pressures and after
annealing under oxygen and vacuum conditions. X-ray magnetic circular dichroism
demonstrated that the magnetization originated from Fe$^{2+}$ cations, whereas
Fe$^{3+}$ and Ti$^{4+}$ did not contribute. Films with the highest magnetic
moment (0.8 {\mu}B per Fe) had the highest measured Fe$^{2+}$:Fe${^3+}$ ratio
of 0.1 corresponding to the largest concentration of oxygen vacancies ({\delta}
= 0.19). Post-growth annealing treatments under oxidizing and reducing
conditions demonstrated quenching and partial recovery of magnetism
respectively, and a change in Fe valence states. The study elucidates the
microscopic origin of magnetism in highly Fe-substituted
SrTi$_{1-x}$Fe$_x$O$_{3-{\delta}}$ perovskite oxides and demonstrates that the
magnetic moment, which correlates with the relative content of Fe$^{2+}$ and
Fe$^{3+}$, can be controlled via the oxygen content, either during growth or by
post-growth annealing.",1906.00509v1
2019/6/21,"Anisotropic temperature-field phase diagram of single-crystalline $β$-Li$_2$IrO$_3$: magnetization, specific heat, and $^7$Li NMR study","Detailed magnetization, specific heat, and $^7$Li nuclear magnetic resonance
(NMR) measurements on single crystals of the hyperhoneycomb Kitaev magnet
$\beta$-Li$_2$IrO$_3$ are reported. At high temperatures, {\cred anisotropy of
the magnetization is reflected by the different Curie-Weiss temperatures for
different field directions}, in agreement with the combination of a
ferromagnetic Kitaev interaction ($K$) and a negative off-diagonal anisotropy
($\Gamma$) as two leading terms in the spin Hamiltonian. At low temperatures,
magnetic fields applied along $a$ or $c$ have only a weak effect on the system
and reduce the N\'eel temperature from 38 K at 0 T to about 35.5 K at 14 T,
with no field-induced transitions observed up to 58 T on a powder sample. In
contrast, the field applied along $b$ causes a drastic reduction in the $T_N$
that vanishes around $H_c=2.8$ T giving way to a crossover toward a quantum
paramagnetic state. $^7$Li NMR measurements in this field-induced state reveal
a gradual line broadening and a continuous evolution of the line shift with
temperature, suggesting the development of local magnetic fields. The
spin-lattice relaxation rate shows a peak around the crossover temperature 40 K
and follows power-law behavior below this temperature.",1906.09089v2
2019/7/2,Absence of ferromagnetism in VSe$_2$ caused by its charge density wave phase,"How magnetism emerges in low-dimensional materials such as transition metal
dichalcogenides at the monolayer limit is still an open question. Herein, we
present a comprehensive study of the magnetic properties of single crystal and
monolayer VSe$_{2}$, both experimentally and \emph{ab initio}. Magnetometry,
X-ray magnetic circular dichrosim (XMCD) and \emph{ab initio} calculations
demonstrate that the charge density wave in bulk stoichiometric VSe$_{2.0}$
causes a structural distortion with a strong reduction in the density of sates
at the Fermi level, prompting the system towards a non-magnetic state but on
the verge of a ferromagnetic instability. In the monolayer limit, the
structural rearrangement induces a Peierls distortion with the opening of an
energy gap at the Fermi level and the absence of magnetic order. Control
experiments on defect-induced VSe$_{2-\delta}$ single crystals show a breakdown
of magnetism, discarding vacancies as a possible origin of magnetic order in
VSe$_{2}$.",1907.02034v2
2019/7/17,Quasi 2-D magnetism in the Kagome layer compound FeSn,"Single crystals of the single Kagome layer compound FeSn are investigated
using x-ray and neutron scattering, magnetic susceptibility and magnetization,
heat capacity, resistivity, Hall, Seebeck, thermal expansion, thermal
conductivity measurements and density functional theory (DFT). FeSn is a planar
antiferromagnet below TN = 365 K and exhibits ferromagnetic magnetic order
within each Kagome layer. The in-plane magnetic susceptibility is sensitive to
synthesis conditions. Resistivity, Hall and Seebeck results indicate multiple
bands near the Fermi energy. The resistivity of FeSn is about 3 times lower for
current along the stacking direction than in the plane, suggesting that
transport and the bulk electronic structure of FeSn is not quasi 2D. FeSn is an
excellent metal with Rho(300K)/Rho(2K) values about 100 in both directions.
While the ordered state is antiferromagnetic, high temperature susceptibility
measurements indicate a ferromagnetic Curie-Weiss temperature of 173 K,
reflecting the strong in-plane ferromagnetic interactions. DFT calculations
show a 3D electronic structure with the Dirac nodal lines along the K-H
directions in the magnetic Brillouin zone about 0.3 eV below the Fermi energy,
with the Dirac dispersions at the K points gapped by spin-orbit coupling except
at the H point. The magnetism, however, is highly 2D with
Jin-plane/Jout-of-plane = 10. The predicted spin-wave spectrum is presented.",1907.07719v1
2019/11/21,Possible quantum paramagnetism in compressed Sr$_2$IrO$_4$,"The effect of compression on the magnetic ground state of Sr$_2$IrO$_4$ is
studied with x-ray resonant techniques in the diamond anvil cell. The weak
interlayer exchange coupling between square-planar 2D IrO$_2$ layers is readily
modified upon compression, with a crossover between magnetic structures around
7 GPa mimicking the effect of an applied magnetic field at ambient pressure.
Higher pressures drive an order-disorder magnetic phase transition with no
magnetic order detected above 17-20 GPa. The persistence of strong exchange
interactions between $\mathrm{J_{eff}}=1/2$ magnetic moments within the
insulating IrO$_2$ layers up to at least 35 GPa points to a highly frustrated
magnetic state in compressed Sr$_2$IrO$_4$ opening the door for realization of
novel quantum paramagnetic phases driven by extended $5d$ orbitals with
entangled spin and orbital degrees of freedom.",1911.09786v3
2020/1/20,Artificial double-helix for geometrical control of magnetic chirality,"Chirality plays a major role in nature, from particle physics to DNA, and its
control is much sought-after due to the scientific and technological
opportunities it unlocks. For magnetic materials, chiral interactions between
spins promote the formation of sophisticated swirling magnetic states such as
skyrmions, with rich topological properties and great potential for future
technologies. Currently, chiral magnetism requires either a restricted group of
natural materials or synthetic thin-film systems that exploit interfacial
effects. Here, using state-of-the-art nanofabrication and magnetic X-ray
microscopy, we demonstrate the imprinting of complex chiral spin states via
three-dimensional geometric effects at the nanoscale. By balancing dipolar and
exchange interactions in an artificial ferromagnetic double-helix
nanostructure, we create magnetic domains and domain walls with a well-defined
spin chirality, determined solely by the chiral geometry. We further
demonstrate the ability to create confined 3D spin textures and topological
defects by locally interfacing geometries of opposite chirality. The ability to
create chiral spin textures via 3D nano-patterning alone enables exquisite
control over the properties and location of complex topological magnetic
states, of great importance for the development of future metamaterials and
devices in which chirality provides enhanced functionality.",2001.07130v1
2020/1/23,Magnetic-field-induced robust zero Hall plateau state in MnBi$_2$Te$_4$ Chern insulator,"The intrinsic antiferromagnetic topological insulator MnBi2Te4 provides an
ideal platform for exploring exotic topological quantum phenomena. Recently,
the Chern insulator and axion insulator phases have been realized in few-layer
MnBi2Te4 devices at low magnetic field regime. However, the fate of MnBi2Te4 in
high magnetic field has never been explored in experiment. In this work, we
report transport studies of exfoliated MnBi2Te4 flakes in pulsed magnetic
fields up to 61.5 T. In the high-field limit, the Chern insulator phase with
Chern number C = -1 evolves into a robust zero Hall resistance plateau state.
Nonlocal transport measurements and theoretical calculations demonstrate that
the charge transport in the zero Hall plateau state is conducted by two
counter-propagating edge states that arise from the combined effects of Landau
levels and large Zeeman effect in strong magnetic fields. Our result
demonstrates the intricate interplay among intrinsic magnetic order, external
magnetic field, and nontrivial band topology in MnBi2Te4.",2001.08401v2
2020/4/2,Quantum transport evidence of Weyl fermions in an epitaxial ferromagnetic oxide,"Magnetic Weyl fermions, which occur in magnets, have novel transport
phenomena related to pairs of Weyl nodes, and they are, of both, scientific and
technological interest, with the potential for use in high-performance
electronics, spintronics and quantum computing. Although magnetic Weyl fermions
have been predicted to exist in various oxides, evidence for their existence in
oxide materials remains elusive. SrRuO3, a 4d ferromagnetic metal often used as
an epitaxial conducting layer in oxide heterostructures, provides a promising
opportunity to seek for the existence of magnetic Weyl fermions. Advanced oxide
thin film preparation techniques, driven by machine learning technologies, may
allow access to such topological matter. Here we show direct quantum transport
evidence of magnetic Weyl fermions in an epitaxial ferromagnetic oxide SrRuO3:
unsaturated linear positive magnetoresistance (MR), chiral-anomaly-induced
negative MR, Pi Berry phase accumulated along cyclotron orbits, light cyclotron
masses and high quantum mobility of about 10000 cm2/Vs. We employed
machine-learning-assisted molecular beam epitaxy (MBE) to synthesize SrRuO3
films whose quality is sufficiently high to probe their intrinsic quantum
transport properties. We also clarified the disorder dependence of the
transport of the magnetic Weyl fermions, and provided a brand-new diagram for
the Weyl transport, which gives a clear guideline for accessing the
topologically nontrivial transport phenomena. Our results establish SrRuO3 as a
magnetic Weyl semimetal and topological oxide electronics as a new research
field.",2004.00810v2
2020/4/15,Observation of domain wall bimerons in chiral magnets,"Topological defects embedded in or combined with domain walls have been
proposed in various systems, some of which are referred to as domain wall
skyrmions or domain wall bimerons. However, the experimental observation of
such topological defects remains an ongoing challenge. Here, using Lorentz
transmission electron microscopy, we report the experimental discovery of
domain wall bimerons in chiral magnet Co-Zn-Mn(110) thin films. By applying a
magnetic field, multidomain structures develop, and simultaneously, chained and
isolated bimerons arise as the localized state between the domains with the
opposite in-plane components of net magnetization. The multidomain formation is
attributed to magnetic anisotropy and dipolar interaction, and domain wall
bimerons are stabilized by the Dzyaloshinskii-Moriya interaction. In addition,
micromagnetic simulations show that domain wall bimerons appear for a wide
range of conditions in chiral magnets with cubic magnetic anisotropy. Our
results promote further study in various fields of physics.",2004.06976v2
2020/6/2,Stripe antiferromagnetic ground state of ideal triangular lattice KErSe$_2$,"Rare earth triangular lattice materials have been proposed as a good platform
for the investigation of frustrated magnetic ground states. KErSe$_2$ with the
delafossite structure, contains perfect two-dimensional Er$^{3+}$ triangular
layers separated by potassium ions, realizing this ideal configuration and
inviting study. Here we investigate the magnetism of KErSe$_2$ at miliKelvin
temperatures by heat capacity and neutron powder diffraction. Heat capacity
results reveal a magnetic transition at 0.2 K in zero applied field. This
long-range order is suppressed by an applied magnetic field of 0.5 T below 0.08
K. Neutron powder diffraction suggests that the zero-field magnetic structure
orders with $k=(\frac{1}{2},0,\frac{1}{2})$ in a stripe spin structure.
Unexpectedly, Er is found to have a reduced moment of 3.06(1) $\mu_B$/Er in the
ordered state and diffuse magnetic scattering, which originates at higher
temperatures, is found to persist in the ordered state potentially indicating
magnetic fluctuations. Neutron diffraction collected under an applied field
shows a metamagnetic transition at $\sim$ 0.5 T to ferromagnetic order with
$k$=(0,0,0) and two possible structures, which are likely dependent on the
applied field direction. First principle calculations show that the zero field
stripe spin structure can be explained by the first, second and third neighbor
couplings in the antiferromagnetic triangular lattice.",2006.01602v1
2020/7/25,Accessing new magnetic regimes by tuning the ligand spin-orbit coupling in van der Waals magnets,"Van der Waals (VdW) materials have opened new directions in the study of low
dimensional magnetism. A largely unexplored arena is the intrinsic tuning of
VdW magnets toward new ground-states. The chromium trihalides provided the
first such example with a change of inter-layer magnetic coupling emerging upon
exfoliation. Here, we take a different approach to engineer new ground-states,
not by exfoliation, but by tuning the spin-orbit coupling (SOC) of the
non-magnetic ligand atoms (Cl,Br,I). We synthesize a three-halide series,
CrCl$_{3-x-y}$Br$_{x}$I$_{y}$, and map their magnetic properties as a function
of Cl, Br, and I content. The resulting triangular phase diagrams unveil a
frustrated regime near CrCl$_{3}$. First-principles calculations confirm that
the frustration is driven by a competition between the chromium and halide
SOCs. Furthermore, we reveal a field-induced change of inter-layer coupling in
the bulk of CrCl$_{3-x-y}$Br$_{x}$I$_{y}$ crystals at the same field as in the
exfoliation experiments.",2007.12818v1
2020/9/14,Crossover from 2D ferromagnetic insulator to wide bandgap quantum anomalous Hall insulator in ultra-thin MnBi2Te4,"Intrinsic magnetic topological insulators offer low disorder and large
magnetic bandgaps for robust magnetic topological phases operating at higher
temperatures. By controlling the layer thickness, emergent phenomena such as
the Quantum Anomalous Hall (QAH) effect and axion insulator phases have been
realised. These observations occur at temperatures significantly lower than the
Neel temperature of bulk MnBi2Te4, and measurement of the magnetic energy gap
at the Dirac point in ultra-thin MnBi2Te4 has yet to be achieved. Critical to
achieving the promise of this system is a direct measurement of the
layer-dependent energy gap and verifying whether the gap is magnetic in the QAH
phase. Here we utilise temperature dependent angle-resolved photoemission
spectroscopy to study epitaxial ultra-thin MnBi2Te4. We directly observe a
layer dependent crossover from a 2D ferromagnetic insulator with a bandgap
greater than 780 meV in one septuple layer (1 SL) to a QAH insulator with a
large energy gap (>100 meV) at 8 K in 3 and 5 SL MnBi2Te4. The QAH gap is
confirmed to be magnetic in origin, as it abruptly diminishes with increasing
temperature above 8 K. The direct observation of a large magnetic energy gap in
the QAH phase of few-SL MnBi2Te4 is promising for further increasing the
operating temperature of QAH materials.",2009.06175v2
2020/9/21,Magneto-Elastic Coupling to Coherent Acoustic Phonon Modes in Ferrimagnetic Insulator GdTiO$_3$,"In this work we investigate single crystal GdTiO$_{3}$, a promising candidate
material for Floquet engineering and magnetic control, using ultrafast optical
pump-probe reflectivity and magneto-optical Kerr spectroscopy. GdTiO${}_{3}$ is
a Mott-Hubbard insulator with a ferrimagnetic and orbitally ordered ground
state (\textit{T${}_{C}$} = 32 K). We observe multiple signatures of the
magnetic phase transition in the photoinduced reflectivity signal, in response
to above band-gap 660 nm excitation. Magnetic dynamics measured via Kerr
spectroscopy reveal optical perturbation of the ferrimagnetic order on
spin-lattice coupling timescales, highlighting the competition between the
Gd${}^{3+}$ and Ti${}^{3+}$ magnetic sub-lattices. Furthermore, a strong
coherent oscillation is present in the reflection and Kerr dynamics,
attributable to an acoustic strain wave launched by the pump pulse. The
amplitude of this acoustic mode is highly dependent on the magnetic order of
the system, growing sharply in magnitude at \textit{T${}_{C}$}, indicative of
strong magneto-elastic coupling. The driving mechanism, involving
strain-induced modification of the magnetic exchange interaction, implies an
indirect method of coupling light to the magnetic degrees of freedom and
emphasizes the potential of GdTiO${}_{3}$ as a tunable quantum material.",2009.10222v1
2020/10/13,Evidence of the Berezinskii-Kosterlitz-Thouless Phase in a Frustrated Magnet,"The Berezinskii-Kosterlitz-Thouless (BKT) mechanism, building upon
proliferation of topological defects in 2D systems, is the first example of
phase transition beyond the Landau-Ginzburg paradigm of symmetry breaking. Such
a topological phase transition has long been sought yet undiscovered directly
in magnetic materials. Here, we pin down two transitions that bound a BKT phase
in an ideal 2D frustrated magnet TmMgGaO$_4$, via nuclear magnetic resonance
under in-plane magnetic fields, which do not disturb the low-energy electronic
states and allow BKT fluctuations to be detected sensitively. Moreover, by
applying out-of-plane fields, we find a critical scaling behaviour of the
magnetic susceptibility expected for the BKT transition. The experimental
findings can be explained by quantum Monte Carlo simulations applied on an
accurate triangular-lattice Ising model of the compound which hosts a BKT
phase. These results provide a concrete example for the BKT phase and offer an
ideal platform for future investigations on the BKT physics in magnetic
materials.",2010.06450v1
2020/11/2,Signatures of magnetostriction and spin-phonon coupling in magnetoelectric hexagonal 15R-BaMnO3,"Spin-phonon coupling, the interaction of spins with surrounding lattice is a
key parameter to understand the underlying physics of multiferroics and
engineer their magnetization dynamics. Elementary excitations in multiferroic
materials are strongly influenced by spin-phonon interaction, making Raman
spectroscopy a unique tool to probe these coupling(s). Recently, it has been
suggested that the dielectric and magnetic properties of 15R-type hexagonal
BaMnO3 are correlated through the spin-lattice coupling. Here, we report the
observation of an extensive renormalization of the Raman spectrum of 15R-BaMnO3
at 230 K, 280 K, and 330 K. Magnetic measurements reveal the presence of a
long-range and a short-range magnetic ordering in 15R-BaMnO3 at 230 K and 330
K, respectively. The Raman spectrum shows the appearance of new Raman modes in
the magnetically ordered phases. Furthermore, an additional Raman phonon
appears below ~ 280 K, possibly arising from a local lattice-distortion due to
the displacement of Mn-ions, that exhibits anomalous shift with temperature.
The origin of the observed renormalization and phonon anomalies in Raman
spectra are discussed based on the evidences from temperature- and
magnetic-field-dependent Raman spectra, temperature-dependent x-ray
diffraction, magnetization, and specific heat measurements. Our results
indicate the presence of magnetostriction and spin-phonon coupling in
15R-BaMnO3 thus suggesting that the optical phonons are strongly correlated to
its magnetoelectric properties.",2011.00757v1
2020/11/5,"Quantum rescaling, domain metastability and hybrid domain-walls in two-dimensional CrI3 magnets","Higher-order exchange interactions and quantum effects are widely known to
play an important role in describing the properties of low-dimensional magnetic
compounds. Here we identify the recently discovered two-dimensional (2D) van
der Waals (vdW) CrI3 as a quantum non-Heisenberg material with properties far
beyond an Ising magnet as initially assumed. We find that biquadratic exchange
interactions are essential to quantitatively describe the magnetism of CrI3 but
requiring quantum rescaling corrections to reproduce its thermal properties.
The quantum nature of the heat bath represented by discrete electron-spin and
phonon-spin scattering processes induced the formation of spin fluctuations in
the low temperature regime. These fluctuations induce the formation of
metastable magnetic domains evolving into a single macroscopic magnetization or
even a monodomain over surface areas of a few micrometers. Such domains display
hybrid characteristics of Neel and Bloch types with a narrow domain wall width
in the range of 3-5 nm. Similar behaviour is expected for the majority of 2D
vdW magnets where higher-order exchange interactions are appreciable.",2011.02732v1
2020/11/13,Magnetoelectric coupling and decoupling in multiferroic hexagonal YbFeO3 thin films,"The coupling between ferroelectric and magnetic orders in multiferroic
materials and the nature of magnetoelectric (ME) effects are enduring
experimental challenges. In this work, we have studied the response of
magnetization to ferroelectric switching in thin-film hexagonal YbFeO3, a
prototypical improper multiferroic. The bulk ME decoupling and potential
domain-wall ME coupling were revealed using x-ray magnetic circular dichroism
(XMCD) measurements with in-situ ferroelectric polarization switching. Our
Landau theory analysis suggests that the bulk ME-coupled ferroelectric
switching path has a higher energy barrier than that of the ME-decoupled path;
this extra barrier energy is also too high to be reduced by the magneto-static
energy in the process of breaking single magnetic domains into multi-domains.
In addition, the reduction of magnetization around the ferroelectric domain
walls predicted by the Landau theory may induce the domain-wall ME coupling in
which the magnetization is correlated with the density of ferroelectric domain
walls. These results provide important experimental evidence and theoretical
insights into the rich possibilities of ME couplings in hexagonal ferrites,
such as manipulating the magnetic states by an electric field.",2011.07154v1
2021/3/31,Crystal Growth and Anisotropic Magnetic Properties of Quasi-2D (Fe$_{1-x}$Ni$_{x}$)$_{2}$P$_{2}$S$_{6}$,"We report the crystal growth by chemical vapor transport together with a
thorough structural and magnetic characterization of the quasi-2D magnets
(Fe$_{1-x}$Ni$_x$)$_2$P$_2$S$_6$ with $x_\textrm{Ni} = \textrm{0, 0.3, 0.5,
0.7, 0.9 & 1}$. As-grown crystals exhibit a layered morphology with weak van
der Waals interactions between layers parallel to the crystallographic $ab$
plane of the monoclinic structure in the space group $C2/m$ (No. 12).
Magnetization measurements reveal an antiferromagnetic ground state for all
grown crystals. In the ordered state, the magnetization along different
crystallographic directions is in agreement with an Ising anisotropy for $0
\leq x \leq 0.9$ and only for Ni$_2$P$_2$S$_6$ a different behavior is observed
which is line with an anisotropic Heisenberg or XXZ model description. This
striking abrupt change of anisotropy at a critical Ni concentration is coupled
to a change in the width of the maximum in the magnetization around
$T_\textrm{max}$. Furthermore, all intermediate compounds $0 < x \leq 0.9$
exhibit an anisotropic magnetization already in the paramagnetic state similar
to the parent compound Fe$_2$P$_2$S$_6$.",2104.00066v1
2021/4/25,Topological quantum phase transition in the magnetic semimetal HoSb,"Magnetic topological semimetals, a novel state of quantum matter with
nontrivial band topology, have emerged as a new frontier in physics and
materials science. An external stimulus like temperature or magnetic field
could be expected to alter their spin states and thus the Fermi surface
anisotropies and topological features. Here, we perform the angular
magnetoresistance measurements and electronic band structure calculations to
reveal the evolution of HoSb's Fermi surface anisotropies and topological
nature in different magnetic states. The angular magnetoresistance results
manifest that its Fermi surface anisotropy is robust in the paramagnetic state
but is significantly modulated in the antiferromagnetic and ferromagnetic
states. More interestingly, a transition from the trivial (nontrivial) to
nontrivial (trivial) topological electronic phase is observed when HoSb
undergoes a magnetic transition from the paramagnetic (antiferromagnetic) to
antiferromagnetic (ferromagnetic) state induced by temperature (applied
magnetic field). Our studying suggests that HoSb provides an archetype platform
to study the correlations between magnetism and topological states of matter.",2104.12054v1
2021/5/13,Effect of magnetic anisotropy relaxation on laser-induced magnetization precession in thin galfenol films,"The rate and pathways of relaxation of a magnetic medium to its equilibrium
following excitation with intense and short laser pulses are the key
ingredients of ultrafast optical control of spins. Here we study experimentally
the evolution of the magnetization and magnetic anisotropy of thin films of a
ferromagnetic metal galfenol (Fe$_{0.81}$Ga$_{0.19}$) resulting from excitation
with a femtosecond laser pulse. From the temporal evolution of the hysteresis
loops we deduce that the magnetization $M_S$ and magnetic anisotropy parameters
$K$ recover within a nanosecond, and the ratio between $K$ and $M_S$ satisfies
the thermal equilibrium's power law in the whole time range spanning from a few
picoseconds to 3 nanoseconds. We further use the experimentally obtained
relaxation times of $M_S$ and $K$ to analyze the laser-induced precession and
demonstrate how they contribute to its frequency evolution at the nanosecond
timescale.",2105.06385v4
2021/6/24,Direct determination of the zero-field splitting for Fe$^{3+}$ ion in a synthetic polymorph of the oxalate mineral stepanovite NaMgFe(C$_2$O$_4$)$_3\cdot$9H$_2$O: a natural MOF,"We employed inelastic neutron scattering (INS), specific heat, and
magnetization analysis to study the magnetism in a synthetic polymorph of the
quasi-two-dimensional natural metal-organic framework material, stepanovite
NaMgFe(C$_2$O$_4$)$_3\cdot$9H$_2$O. No long-range magnetic order can be
observed down to 0.5 K. The INS spectra show two dispersionless excitations at
energy transfer 0.028(1) and 0.050(1) meV at base temperature, which are
derived from the magnetic transitions between zero-field splitting (ZFS) of $S$
= 5/2 ground state multiplets of Fe$^{3+}$ ion. Further analysis of the INS
results shows that the Fe$^{3+}$ ion has an easy-axis anisotropy with axial ZFS
parameter $D$ = $-$0.0128(5) meV and rhombic parameter $E$ = 0.0014(5) meV. The
upward behavior at zero field and Schottky-like peak under magnetic field of
the low-temperature magnetic specific heat further support the INS results. Our
results clearly reveal the magnetic ground and excited state of this
stepanovite polymorph.",2106.13182v1
2021/6/26,Magnetization dependent tunneling conductance of ferromagnetic barriers,"Recent experiments on van der Waals antiferrmagnets such as CrI3, CrCl3 and
MnPS3 have shown that using atomically thin layers as tunnel barriers and
measuring the temperature ($T$) and magnetic field ($H$) dependence of the
conductance allows their magnetic phase diagram to be mapped. In contrast,
barriers made of CrBr3 -- the sole van der Waals ferromagnet investigated in
this way -- were found to exhibit small and featureless magnetoconductance,
seemingly carrying little information about magnetism. Here we show that --
despite these early results -- the conductance of CrBr3 tunnel barriers does
provide detailed information about the magnetic state of atomically thin CrBr3
crystals for $T$ both above and below the Curie temperature ($T_C = 32$ K). Our
analysis establishes that the tunneling conductance depends on $H$ and $T$
exclusively through the magnetization $M(H,T)$, over the entire temperature
range investigated (2-50 K). The phenomenon is reproduced in detail by the
spin-dependent Fowler-Nordheim model for tunneling, and is a direct
manifestation of the spin splitting of the CrBr3 conduction band. These
findings demonstrate that the investigation of magnetism by tunneling
conductance measurements is not limited to antiferromagnets, but can also be
applied to ferromagnetic materials.",2106.13930v1
2021/7/16,Delicate Ferromagnetism in MnBi$_6$Te$_{10}$,"Tailoring magnetic orders in topological insulators is critical to the
realization of topological quantum phenomena. An outstanding challenge is to
find a material where atomic defects lead to tunable magnetic orders while
maintaining a nontrivial topology. Here, by combining magnetization
measurements, angle-resolved photoemission spectroscopy, and transmission
electron microscopy, we reveal disorder-enabled, tunable magnetic ground states
in MnBi$_6$Te$_{10}$. In the ferromagnetic phase, an energy gap of 15 meV is
resolved at the Dirac point on the MnBi$_2$Te$_4$ termination. In contrast,
antiferromagnetic MnBi$_6$Te$_{10}$ exhibits gapless topological surface states
on all terminations. Transmission electron microscopy and magnetization
measurements reveal substantial Mn vacancies and Mn migration in ferromagnetic
MnBi$_6$Te$_{10}$. We provide a conceptual framework where a cooperative
interplay of these defects drives a delicate change of overall magnetic ground
state energies, and leads to tunable magnetic topological orders. Our work
provides a clear pathway for nanoscale defect-engineering towards the
realization of topological quantum phases.",2107.08137v2
2021/9/18,Magnetoelectric effect in hydrogen harvesting: magnetic field as a trigger of catalytic reactions,"Magnetic fields have been regarded as an additional stimulus for electro- and
photocatalytic reactions, but not as a direct trigger for catalytic processes.
Multiferroic/magnetoelectric materials, whose electrical polarization and
surface charges can be magnetically altered, are especially suitable for
triggering and control of catalytic reactions solely with magnetic fields.
Here, we demonstrate that magnetic fields can be employed as an independent
input energy source for hydrogen harvesting by means of the magnetoelectric
effect. Composite multiferroic CoFe2O4-BiFeO3 core-shell nanoparticles act as
catalysts for the hydrogen evolution reaction (HER) that is triggered when an
alternating magnetic field is applied to an aqueous dispersion of the
magnetoelectric nanocatalysts. Based on density functional calculations, we
propose that the hydrogen evolution is driven by changes in the ferroelectric
polarization direction of BiFeO3 caused by the magnetoelectric coupling. We
believe our findings will open new avenues towards magnetically induced
renewable energy harvesting.",2109.08966v2
2021/10/21,Formation of a Solar Filament by Magnetic Reconnection and Associated Chromospheric Evaporation and Subsequent Coronal Condensation,"We present the first observation of a solar filament formed by magnetic
reconnection and associated chromospheric evaporation and subsequent coronal
condensation. Driven by shearing motion during flux emergence, a sequential
tether-cutting reconnection processes occurred and resulted in an M1.3 confined
flare accompany with the formation of a sigmoid structure. It is found that the
flare had a conjugate compact footpoint brightenings, which correspond to the
footpoints of the sigmoid. Furthermore, observational evidence of explosive
evaporation is well diagnosed at the conjugate footpoint brightenings in the
impulsive phase of the flare. After the flare, continuous cool condensations
formed at about the middle section of the sigmoid and then moved in opposite
directions along the sigmoid, eventually leading to the formation of the
filament. These observations suggest that magnetic reconnection not only can
form the magnetic field structure of the filament, but also heat their
chromospheric footpoints during their formation and drive chromospheric
evaporation. As a result, the heated chromospheric plasma may be evaporated
into the magnetic field structure of the filament, where the accumulated hot
plasma might suffer from thermal instability or thermal non-equilibrium,
causing catastrophic cooling and coronal condensation to form the cool dense
material of the filament. This observation lends strong support to the
evaporative-condensation model and highlights the crucial role of magnetic
reconnection in forming both the magnetic field structure and the cool dense
material of filaments.",2110.10951v1
2021/10/22,Incommensurate magnetic orders and topological Hall effect in the square-net centrosymmetric EuGa$_2$Al$_2$ system,"Neutron diffraction on the centrosymmetric square-net magnet EuGa$_2$Al$_2$
reveals multiple incommensurate magnetic states (AFM1,2,3) in zero field. In
applied field, a new magnetic phase (A) is identified from magnetization and
transport measurements, bounded by two of the $\mu_0H$~=~0 incommensurate
magnetic phases (AFM1,helical and AFM3, cycloidal) with different moment
orientations. Moreover, magneto-transport measurements indicate the presence of
a topological Hall effect, with maximum values centered in the A phase.
Together, these results render EuGa$_2$Al$_2$ a material with non-coplanar or
topological spin texture in applied field. X-ray diffraction reveals an
out-of-plane (OOP) charge density wave (CDW) below $T_{CDW} \sim$ 50 K while
the magnetic propagation vector lies in plane below $T_N$ = 19.5 K. Together
these data point to a new route to realizing in-plane non-collinear spin
textures through an OOP CDW. In turn, these non-collinear spin textures may be
unstable against the formation of topological spin textures in an applied
field.",2110.11935v4
2022/2/9,"Ferromagnetism induced by hybridization of Fe 3d orbitals with ligand InSb bands in n-type ferromagnetic semiconductor (In,Fe)Sb","Fe-doped III-V ferromagnetic semiconductor (FMS) (In,Fe)Sb is a promising
material for spintronic device applications because of the n-type carrier
conduction and the ferromagnetism with high Curie temperature (TC > 300 K). To
clarify the mechanism of the high-TC ferromagnetism, we have investigated the
electronic structure and magnetic properties of an (In,Fe)Sb thin film by
performing x-ray absorption spectroscopy (XAS) and x-ray magnetic circular
dichroism (XMCD) measurements at the Fe L2,3 edges. The magnetic-field
dependence of the XMCD spectra reveals that there are ferromagnetic-like Fe and
paramagnetic-like Fe components in the (In,Fe)Sb thin film. The XAS and XMCD
spectra of the ferromagnetic-like and paramagnetic-like Fe components resemble
those of other Fe-doped FMSs and extrinsic oxides, respectively. The finite
value of the ratio between the orbital and spin magnetic moments estimated by
applying the XMCD sum rules indicates that the valence state of the Fe ions
substituting for the In sites in (In,Fe)Sb is not purely ionic Fe3+, but
intermediate between Fe3+ and Fe2+. The qualitative correspondence between the
magnetic-field dependence of the visible-light magnetic circular dichroism
intensity and that of the XMCD intensity demonstrates that the Zeeman splitting
of the InSb band is proportional to the net magnetization of the doped Fe.
These results suggest that the ferromagnetism of (In,Fe)Sb originates from the
Fe 3d orbitals hybridized with the host InSb bands.",2202.04286v1
2022/3/15,Spin-polarized imaging of the antiferromagnetic structure and field-tunable bound states in kagome magnet FeSn,"Kagome metals are as an exciting playground for the explorations of novel
phenomena at the intersection of topology, electron correlations and magnetism.
The family of FeSn-based kagome magnets in particular attracted a lot of
attention for simplicity of the layered crystal structure and tunable
topological electronic band structure. Despite a significant progress in
understanding their bulk properties, surface electronic and magnetic structures
are yet to be fully explored in many of these systems. In this work, we focus
on a prototypical kagome metal FeSn. Using a combination of spin-averaged and
spin-polarized scanning tunneling microscopy, we provide the first atomic-scale
visualization of the layered antiferromagnetic structure at the surface of
FeSn. In contrast to the field-tunable electronic structure of cousin material
Fe3Sn2 that is a ferromagnet, we find that electronic density-of-states of FeSn
is robust to the application of external magnetic field. Interestingly, despite
the field-insensitive electronic band structure, FeSn exhibits bounds states
tied to specific impurities with large effective moments that strongly couple
to the magnetic field. Our experiments provide microscopic insights necessary
for theoretical modeling of FeSn and serve as a spring board for spin-polarized
measurements of topological magnets in general.",2203.08077v2
2022/5/1,"Existence of inter coupled structural, electronic and magnetic states in Sm$ _{2} $NiMnO$ _{6} $ double perovskite","Coupling between different interactions allows to control physical aspects in
multifunctional materials by perturbing any of the degrees of freedom. Here, we
aim to probe the correlation among structural, electronic and magnetic
observables of Sm$ _{2} $NiMnO$ _{6} $ ferromagnetic insulator double
perovskite. Our employed methodology includes thermal evolution of synchrotron
X-ray diffraction, near edge and extended edge hard X-ray absorption
spectroscopy and bulk magnetometry. The magnetic ordering in SNMO adopts two
transitions, at T$ _{C} $=159.6K due to ferromagnetic arrangement of Ni-Mn
sublattice and at T$ _{d} $=34.1K because of anti-parallel alignment of
polarized Sm paramagnetic moments with respect to Ni-Mn network. The global as
well as local crystal structure of SNMO undergoes isostructural transitions
across T$ _{C} $ and T$ _{d} $, observed by means of temperature dependent
variation in Ni/Mn-O, Ni-Mn bonding characters and super exchange angle in
Ni-O-Mn linkage. Hybridization between Ni, Mn 3\textit{d}, O 2\textit{p}
electronic states is also modified in the vicinity of magnetic transition. On
the other hand, the signature of Ni/Mn anti-site disorders are evidenced from
local structure and magnetization analysis. The change in crystal environments
governs the magnetic response by imposing alteration in metal - ligand orbital
overlap. Utilizing these complimentary probes we have found that structural,
electronic and magnetic states are inter-coupled in SNMO which makes it a
potential platform for technological usage.",2205.00537v1
2022/5/20,A feasibility analysis towards the simulation of hysteresis with spin-lattice dynamics,"We use spin-lattice dynamics simulations to study the possibility of modeling
the magnetic hysteresis behavior of a ferromagnetic material. The temporal
evolution of the magnetic and mechanical degrees of freedom is obtained through
a set of two coupled Langevin equations. Hysteresis loops are calculated for
different angles between the external field and the magnetocrystalline
anisotropy axes. The influence of several relevant parameters is studied,
including the field frequency, magnetic damping, magnetic anisotropy (magnitude
and type), magnetic exchange, and system size. The role played by a moving
lattice is also discussed. For a perfect bulk ferromagnetic system we find
that, at low temperatures, the exchange and lattice dynamics barely affect the
loops, while the field frequency and magnetic damping have a large effect on
it. The influence of the anisotropy magnitude and symmetry are found to follow
the expected behavior. We show that a careful choice of simulation parameters
allows for an excellent agreement between the spin-lattice dynamics
measurements and the paradigmatic Stoner-Wohlfarth model. Furthermore, we
extend this analysis to intermediate and high temperatures for the perfect bulk
system and for spherical nanoparticles, with and without defects, reaching
values close to the Curie temperature. In this temperature range, we find that
lattice dynamics has a greater role on the magnetic behavior, especially in the
evolution of the defective samples. The present study opens the possibility for
more accurate inclusion of lattice defects and thermal effects in hysteresis
simulations",2205.10418v3
2022/5/28,Helicity-independent all-optical switching of magnetization in ferrimagnetic alloys,"We review and discuss the process of single-shot helicity-independent
all-optical switching of magnetization by which a single suitably-ultrafast
excitation, under the right conditions, toggles magnetization from one stable
state to another. For almost a decade, this phenomenon was only consistently
observed in specific rare-earth-transition-metal ferrimagnetic alloys of
GdFeCo, but breakthrough experiments in recent years have revealed that the
same behavior can be achieved in a wide range of multi-sublattice magnets
including TbCo alloys doped with minute amounts of Gd, Gd/Co and Tb/Co
synthetic ferrimagnets, and the rare-earth-free Heusler alloy Mn$_2$Ru$_x$Ga.
Aiming to resolve the conditions that allow switching, a series of experiments
have shown that the process in the ferrimagnetic alloys GdFeCo and
Mn$_2$Ru$_x$Ga is highly sensitive to the pulse duration, starting temperature
and the alloy composition. We argue here that the switching displayed by these
two very different ferrimagnetic alloys can be generally understood within a
single phenomenological framework describing the flow of angular momentum
between the constituent sublattices and from the sublattices to the
environment. The conditions that facilitate switching stem from the properties
of these channels of angular momentum flow in combination with the size of the
angular momentum reservoirs. We conclude with providing an outlook in this
vibrant research field, with emphasis on the outstanding open questions
pertaining to the underlying physics along with noting the advances in
exploiting this switching process in technological applications.",2205.14342v1
2022/6/10,Topological spiral magnetism in the Weyl semimetal SmAlSi,"Weyl electrons are intensely studied due to novel charge transport phenomena
such as chiral anomaly, Fermi arcs, and photogalvanic effect. Recent
theoretical works suggest that Weyl electrons can also participate in magnetic
interactions, and the Weyl-mediated indirect exchange coupling between local
moments is proposed as a new mechanism of spiral magnetism that involves chiral
electrons. Despite reports of incommensurate and non-collinear magnetic
ordering in Weyl semimetals, an actual spiral order has remained hitherto
undetected. Here, we present evidence of Weyl-mediated spiral magnetism in
SmAlSi from neutron diffraction, transport, and thermodynamic data. We show
that the spiral order in SmAlSi results from the nesting between topologically
non-trivial Fermi pockets and weak magnetocrystalline anisotropy, unlike
related materials (Ce,Pr,Nd)AlSi, where a strong anisotropy prevents the spins
from freely rotating. We map the magnetic phase diagram of SmAlSi and reveal an
A-phase where topological magnetic excitations may exist. This is corroborated
by the observation of a topological Hall effect within the A-phase.",2206.05121v1
2022/6/13,The two-dimensional metallic triangular lattice antiferromagnet CeCd3P3,"Single crystals of $R$Cd$_{3}$P$_{3}$ ($R$ = La and Ce) have been
investigated by magnetization, electrical resistivity, Hall coefficient, and
specific heat. Magnetization measurements of CeCd$_{3}$P$_{3}$ demonstrate
clear quasi-2D magnetic behavior. Electrical resistivity and Hall coefficient
measurements suggest that $R$Cd$_{3}$P$_{3}$ compounds are low carrier density
metallic systems, in strong contrast to an earlier study of polycrystalline
material. Specific heat and electrical resistivity measurements of
CeCd$_{3}$P$_{3}$ reveal a high temperature (structural) phase transition at
$T_{s} = 127$~K and antiferromagnetic ordering below $T_{N} = 0.41$~K. Upon
applying magnetic field in the easy-plane ($H {\parallel} ab$) the magnetic
ordering temperature increases to 0.43~K at $H \sim 15$~kOe, demonstrating
partial lifting of the magnetic frustration. The large electronic specific heat
persists in an unusually wide range of temperature above $T_{N}$, due to the
frustrated spins. The observation of conventional metallic behavior in the
electrical resistivity suggests that the $f$-electrons in CeCd$_{3}$P$_{3}$
undergo negligible hybridization with the conduction electrons. Thus,
CeCd$_{3}$P$_{3}$ may be a model system for exploring the complex interplay
between magnetic frustration and RKKY physics on a low carrier density Ce
triangular lattice.",2206.06366v1
2022/6/29,Tailoring the switching efficiency of magnetic tunnel junctions by the fieldlike spin-orbit torque,"Current-induced spin-orbit torques provide a versatile tool for switching
magnetic devices. In perpendicular magnets, the dampinglike component of the
torque is the main driver of magnetization reversal. The degree to which the
fieldlike torque assists the switching is a matter of debate. Here we study the
switching of magnetic tunnel junctions with a CoFeB free layer and either W or
Ta underlayers, which have a ratio of fieldlike to dampinglike torque of 0.3
and 1, respectively. We show that the fieldlike torque can either assist or
hinder the switching of CoFeB when the static in-plane magnetic field required
to define the polarity of spin-orbit torque switching has a component
transverse to the current. In particular, the non-collinear alignment of the
field and current can be exploited to increase the switching efficiency and
reliability compared to the standard collinear alignment. By probing individual
switching events in real-time, we also show that the combination of transverse
magnetic field and fieldlike torque can accelerate or decelerate the reversal
onset. We validate our observations using micromagnetic simulations and
extrapolate the results to materials with different torque ratios. Finally, we
propose device geometries that leverage the fieldlike torque for density
increase in memory applications and synaptic weight generation.",2206.14587v2
2022/7/25,Spin-orbit torque switching of magnetic tunnel junctions for memory application,"Spin-orbit torques (SOT) provide a versatile tool to manipulate the
magnetization of diverse classes of materials and devices using electric
currents, leading to novel spintronic memory and computing approaches. In
parallel to spin transfer torques (STT), which have emerged as a leading
non-volatile memory technologie, SOT broaden the scope of current-induced
magnetic switching to applications that run close to the clock speed of the
central processing unit and unconventional computing architectures. In this
paper, we review the fundamental characteristics of SOT and their use to switch
magnetic tunnel junction (MTJ) devices, the elementary unit of the
magnetoresistive random access memory (MRAM). In the first part, we illustrate
the physical mechanisms that drive the SOT and magnetization reversal in
nanoscale structures. In the second part, we focus on the SOT-MTJ cell. We
discuss the anatomy of the MTJ in terms of materials and stack development,
summarize the figures of merit for SOT switching, review the field-free
operation of perpendicularly magnetized MTJs, and present options to combine
SOT, STT and voltage-gate assisted switching. In the third part, we consider
SOT-MRAMs in the perspective of circuit integration processes, introducing
considerations on scaling and performance, as well as macro-design
architectures. We thus bridge the fundamental description of SOT-driven
magnetization dynamics with an application-oriented perspective, including
device and system-level considerations, goals, and challenges.",2207.11974v1
2022/7/31,Possible coexistence of short-range resonating-valence-bond and long-range stripe correlations in the spatially anisotropic triangular-lattice quantum magnet Cu$_2$(OH)$_3$NO$_3$,"We show that short-range resonating-valence-bond correlations and long-range
order can coexist in the ground state (GS) of a frustrated spin system. Our
study comprises a comprehensive investigation of the quantum magnetism on the
structurally disorder-free single crystal of Cu$_2$(OH)$_3$NO$_3$, which
realizes the $s$ = 1/2 Heisenberg model on a spatially anisotropic triangular
lattice. Competing exchange interactions determined by fitting the
magnetization measured up to 55 T give rise to an exotic GS wavefunction with
coexistence of the dominant short-range resonating-valence-bond correlations
and weak long-range stripe order (ordered moment $M_0$ = $|\langle
s_i^z\rangle|$ $\sim$ 0.02). At low temperatures, a first-order spin-flop
transition is visible at $\sim$ 1-3 T. As the applied field further increases,
another two magnetic-field-induced quantum phase transitions are observed at
$\sim$ 14-19 and $\sim$ 46-52 T, respectively. Simulations of the Heisenberg
exchange model show semi-quantitative agreement with the magnetic-field
modulation of these unconventional phases, as well as the absence of visible
magnetic reflections in neutron diffraction, thus supporting the GS of the spin
system of Cu$_2$(OH)$_3$NO$_3$ may be approximate to a quantum spin liquid. Our
study establishes structurally disorder-free magnetic materials with spatially
anisotropic exchange interactions as a possible arena for spin liquids.",2208.00382v1
2022/10/4,Strain Coupled Domains in BaTiO3(111)-CoFeB Heterostructures,"Domain pattern transfer from ferroelectric to ferromagnetic materials is a
critical step for the electric field control of magnetism and has the potential
to provide new schemes for low-power data storage and computing devices. Here
we investigate domain coupling in BaTiO$_3$(111)/CoFeB heterostructures by
direct imaging in a wide-field Kerr microscope. The magnetic easy axis is found
to locally change direction as a result of the underlying ferroelectric domains
and their polarisation. By plotting the remanent magnetisation as a function of
angle in the plane of the CoFeB layer, we find that the magnetic easy axes in
adjacent domains are angled at 60$^\circ$ or 120$^\circ$, corresponding to the
angle of rotation of the polarisation from one ferroelectric domain to the
next, and that the magnetic domain walls may be charged or uncharged depending
on the magnetic field history. Micromagnetic simulations show that the
properties of the domain walls vary depending on the magnetoelastic easy axis
configuration and the charged or uncharged nature of the wall. The
configuration where the easy axis alternates by 60$^\circ$ and a charged wall
is initialised exhibits the largest change in domain wall width from 192 nm to
119 nm as a function of in-plane magnetic field. Domain wall width tuning
provides an additional degree of freedom for devices that seek to manipulate
magnetic domain walls using strain coupling to ferroelectrics.",2210.01511v1
2022/10/11,Influence of the high granularity calorimeter stainless steel absorbers onto the Compact Muon Solenoid inner magnetic field,"The Compact Muon Solenoid (CMS) detector is a general-purpose experimental
setup at the Large Hadron Collider (LHC) at CERN to investigate the production
of new particles in the proton-proton collisions at a centre of mass energy 13
TeV. The third run of the data taken is started in April 2022 and will continue
till the end of 2025. Then, during a long shutdown time, the existing CMS
hadron endcap calorimeter will be replaced with a new high granularity
calorimeter (HGCal) designed for the higher LHC luminosity. The HGCal contains
the stainless-steel absorber plates with a relative permeability limited by a
value of 1.05 from estimation of the electromagnetic forces acting on this
slightly magnetic material. To exclude the surprises with possible perturbation
of the inner magnetic flux density in the region of the charged particle
tracking system, an influence of this additional material onto the quality of
the magnetic field inside the inner tracker volume is investigated at this
limited value of the permeability of stainless steel . The three-dimensional
model of the CMS magnet is used for this purpose. The method of the magnetic
field double integrals characterizing the charged particle momentum resolution
the first time is applied to the CMS detector and the first time is described
in the journal publication. The results obtained with this method are presented
in detail and discussed.",2210.05719v1
2022/11/21,General time-reversal equivariant neural network potential for magnetic materials,"This study introduces time-reversal E(3)-equivariant neural network and
SpinGNN++ framework for constructing a comprehensive interatomic potential for
magnetic systems, encompassing spin-orbit coupling and noncollinear magnetic
moments. SpinGNN++ integrates multitask spin equivariant neural network with
explicit spin-lattice terms, including Heisenberg, Dzyaloshinskii-Moriya,
Kitaev, single-ion anisotropy, and biquadratic interactions, and employs
time-reversal equivariant neural network to learn high-order spin-lattice
interactions using time-reversal E(3)-equivariant convolutions. To validate
SpinGNN++, a complex magnetic model dataset is introduced as a benchmark and
employed to demonstrate its capabilities. SpinGNN++ provides accurate
descriptions of the complex spin-lattice coupling in monolayer CrI$_3$ and
CrTe$_2$, achieving sub-meV errors. Importantly, it facilitates large-scale
parallel spin-lattice dynamics, thereby enabling the exploration of associated
properties, including the magnetic ground state and phase transition.
Remarkably, SpinGNN++ identifies a new ferrimagnetic state as the ground
magnetic state for monolayer CrTe2, thereby enriching its phase diagram and
providing deeper insights into the distinct magnetic signals observed in
various experiments.",2211.11403v3
2022/12/15,Exploration of all-3d Heusler alloys for permanent magnets: an ab initio based high-throughput study,"Heusler alloys have attracted interest in various fields of functional
materials since their properties can quite easily be tuned by composition.
Here, we have investigated the relatively new class of all-3d Heusler alloys in
view of its potential as permanent magnets. To identify suitable candidates, we
performed a high-throughput study using an electronic structure database to
search for X$_2$YZ-type Heusler systems with tetragonal symmetry and high
magnetization. For the alloys which passed our selection filters, we have used
a combination of density functional theory calculations and spin dynamics
modelling to investigate their magnetic properties including the
magnetocrystalline anisotropy energy and exchange interactions. The candidates
which fulfilled all the search criteria served as input for the investigation
of the temperature dependence of the magnetization and determination of Curie
temperature. Based on our results, we suggest that Fe$_2$NiZn, Fe$_2$NiTi and
Ni$_2$CoFe are potential candidates for permanent magnets with large
out-of-plane magnetic anisotropy (1.23, 0.97 and 0.82 MJ/m$^3$ respectively)
and high Curie temperatures lying more than 200 K above the room temperature.
We further show that the magnitude and direction of anisotropy is very
sensitive to the strain by calculating the values of anisotropy energy for
several tetragonal phases. Thus, application of strain can be used to tune the
anisotropy in these compounds.",2212.07845v3
2023/3/12,Unusual magnetic hysteresis and transition between vortex to double pole states arising from interlayer coupling in diamond shaped nanostructures,"Controlling the magnetic ground states at the nanoscale is a long-standing
basic research problem and an important issue in magnetic storage technologies.
Here, we designed a nanostructured material that exhibits very unusual
hysteresis loops due to a transition between vortex and double pole states.
Arrays of 700 nm diamond-shape nanodots consisting of Py(30 nm)/Ru(tRu)/Py(30
nm) (Py, permalloy (Ni80Fe20)) trilayers were fabricated by interference
lithography and e-beam evaporation. We show that varying the Ru interlayer
spacer thickness (tRu) governs the interaction between the Py layers. We found
this interaction mainly mediated by two mechanisms: magnetostatic interaction
that favors antiparallel (antiferromagnetic, AFM) alignment of the Py layers
and exchange interaction that oscillates between ferromagnetic (FM) and AFM
couplings. For a certain range of Ru thicknesses, FM coupling dominates and
forms magnetic vortices in the upper and lower Py layers. For Ru thicknesses at
which AFM coupling dominates, the magnetic state in remanence is a double pole
structure. Our results showed that the interlayer exchange coupling interaction
remains finite even at 4 nm Ru thickness. The magnetic states in remanence,
observed by Magnetic Force Microscopy (MFM), are in good agreement with
corresponding hysteresis loops obtained by Magneto-Optic Kerr Effect (MOKE) and
micromagnetic simulations.",2303.06735v1
2023/3/15,Ultrafast Opto-magnetic Effects in the Extreme Ultraviolet Spectral Range,"Coherent light-matter interactions mediated by opto-magnetic phenomena like
the inverse Faraday effect (IFE) are expected to provide a non-thermal pathway
for ultrafast manipulation of magnetism on timescales as short as the
excitation pulse itself. As the IFE scales with the spin-orbit coupling
strength of the involved electronic states, photo-exciting the strongly
spin-orbit coupled core-level electrons in magnetic materials appears as an
appealing method to transiently generate large opto-magnetic moments. Here, we
investigate this scenario in a ferrimagnetic GdFeCo alloy by using intense and
circularly polarized pulses of extreme ultraviolet radiation. Our results
reveal ultrafast and strong helicity-dependent magnetic effects which are in
line with the characteristic fingerprints of an IFE, corroborated by ab initio
opto-magnetic IFE theory and atomistic spin dynamics simulations.",2303.08564v1
2023/4/24,Epitaxial monolayers of magnetic 2D semiconductor FeBr$_{2}$ grown on Au(111),"Magnetic two-dimensional (2D) semiconductors have attracted a lot of
attention because modern preparation techniques are capable of providing single
crystal films of these materials with precise control of thickness down to the
single-layer limit. It opens up a way to study rich variety of electronic and
magnetic phenomena with promising routes towards potential applications. We
have investigated the initial stages of epitaxial growth of the magnetic van
der Waals semiconductor FeBr\textsubscript{2} on a single-crystal Au(111)
substrate by means of low-temperature scanning tunneling microscopy, low-energy
electron diffraction, x-ray photoemission spectroscopy, low-energy electron
emission microscopy and x-ray photoemission electron microscopy. Magnetic
properties of the one- and two-layer thick films were measured via x-ray
absorption spectroscopy/x-ray magnetic circular dichroism. Our findings show a
striking difference in the magnetic behaviour of the single layer of
FeBr\textsubscript{2} and its bulk counterpart, which can be attributed to the
modifications in the crystal structure due to the interaction with the
substrate.",2304.11972v2
2023/5/24,Manipulation of magnetic solitons under the influence of DMI gradients,"Magnetic solitons are promising for applications due to their intrinsic
properties such as small size, topological stability, ultralow power
manipulation and potentially ultrafast operations. To date, research has
focused on the manipulation of skyrmions, domain walls, and vortices by applied
currents. The discovery of new methods to control magnetic parameters, such as
the interfacial Dzyaloshinskii-Moriya interaction (DMI) by strain, geometry
design, temperature gradients, and applied voltages promises new avenues for
energetically efficient manipulation of magnetic structures. The latter has
shown significant progress in 2d material-based technology. In this work, we
present a comprehensive study using numerical and analytical methods of the
stability and motion of different magnetic textures under the influence of DMI
gradients. Our results show that under the influence of linear DMI gradients,
N\'eel and Bloch-type skyrmions and radial vortex exhibit motion with finite
skyrmion Hall angle, while the circular vortex undergoes expulsion dynamics.
This work provides a deeper and crucial understanding of the stability and
gradient-driven dynamics of magnetic solitons, and paves the way for the design
of alternative low-power sources of magnetization manipulation in the emerging
field of 2d materials.",2305.15052v1
2023/5/30,Aging and passivation of magnetic properties in Co/Gd bilayers,"Synthetic ferrimagnets based on Co and Gd bear promise for directly bridging
the gap between volatile information in the photonic domain and non-volatile
information in the magnetic domain, without the need for any intermediary
electronic conversion. Specifically, these systems exhibit strong spin-orbit
torque effects, fast domain wall motion and single-pulse all-optical switching
of the magnetization. An important open challenge to bring these materials to
the brink of applications is to achieve long-term stability of their magnetic
properties. In this work, we address the time-evolution of the magnetic moment
and compensation temperature of magnetron sputter grown Pt/Co/Gd trilayers with
various capping layers. Over the course of three months, the net magnetic
moment and compensation temperature change significantly, which we attribute to
quenching of the Gd magnetization. We identify that intermixing of the capping
layer and Gd is primarily responsible for this effect, which can be alleviated
by choosing nitrides for capping as long as reduction of nitride to oxide is
properly addressed. In short, this work provides an overview of the relevant
aging effects that should be taken into account when designing synthetic
ferrimagnets based on Co and Gd for spintronic applications.",2305.18984v1
2023/6/26,"Spin-flop quasi metamagnetic, anisotropic magnetic, and electrical transport behavior of Ho substituted kagome magnet ErMn$_6$Sn$_6$","We report on the magnetic and electrical properties of a (Mn$_3$Sn)$_2$
triangular network kagome structured high quality Ho substituted ErMn$_6$Sn$_6$
single-crystal sample by magneto-transport measurements.
Er$_{0.5}$Ho$_{0.5}$Mn$_6$Sn$_6$ orders antiferromagnetically at N\'{e}el
temperature $T_\mathrm{N} \sim$ 350 K followed by a ferrimagnetic (FiM)
transition at $T_\mathrm{C} \sim$ 114 K and spin-orientation transition at
$T_\mathrm{t} \sim$ 20 K. The field-manifestations of these magnetic phases in
the \textit{ab}-basal plane and along the \textit{c}-axis are illustrated
through temperature-field \textit{T-H} phase diagrams. In
\textit{H}$\parallel$\textit{c}, narrow hysteresis between spin reorientation
and field-induced FiM phases below $T_\mathrm{t}$, enhanced/strengthened FiM
phase below $T_\mathrm{C}$ and stemming of FiM phase out of strongly coexisting
AFM and FiM phases below $T_\mathrm{N}$ through a non-meta-magnetic transition
are confirmed to arise from strong R-Mn sublattices interaction. In contrast,
\textit{H}$\parallel$\textit{ab}-plane, between $T_\mathrm{N}$ and
$T_\mathrm{C}$, individually contributing R-Mn sublattices with weak
antiferromagnetic interactions undergo a field-induced spin-flop
quasi-metamagnetic transition to FiM state. The temperature dependent
electrical resistivity suggests metallic nature with Fermi liquid behavior at
low temperatures. Essentially, the current study stimulates interest to
investigate the magnetic and electrical properties of mixed rare-earth layered
kagome magnetic metals for possible novel and exotic behavior.",2306.14417v1
2023/7/11,"Dzyaloshinskii-Moriya interactions, Néel skyrmions and V$_4$ magnetic clusters in multiferroic lacunar spinel GaV$_4$S$_8$","Using ab initio density functional theory with static mean-field
correlations, we calculate the Heisenberg and Dzyaloshinskii-Moriya
interactions (DMI) for an atomistic spin Hamiltonian for the lacunar spinel,
GaV$_4$S$_8$. The parameters describing these interactions are used in
atomistic spin dynamics and micromagnetic simulations. The magnetic properties
of the lacunar spinel GaV$_4$S$_8$, a material well-known from experiment to
host magnetic skyrmions of N\'eel character, are simulated with these ab initio
calculated parameters. The Dzyaloshinskii-Moriya contribution to the
micromagnetic energy is a sum of two Lifshitz invariants, supporting the
formation of N\'eel skyrmions and its symmetry agrees with what is usually
expected for $C_{3\nu}$-symmetric systems. The are several conclusions one may
draw from this work. One concerns the quantum nature of the magnetism, where we
show that the precise magnetic state of the V$_4$ cluster is crucial for
understanding quantitatively the magnetic phase diagram. In particular we
demonstrate that a distributed-moment state of each V$_4$ cluster explains well
a variety of properties of GaV$_4$S$_8$, such as the band gap, observed Curie
temperature and especially the stability of N\'eel skyrmions in the
experimentally relevant temperature and magnetic-field range. In addition, we
find that electronic correlations change visibly the calculated value of the
DMI.",2307.05733v1
2023/7/20,Magnetic properties and structural phase transition in ultrathin fcc Fe (111) and bcc Fe (111) films: first-principles study,"The aim of this work is to investigate the structural and magnetic
characteristics of Fe thin films with a triangular (hexagonal) lattice surfaces
(fcc (111) and bcc (111)). The properties of these structures have been
calculated using density functional theory (DFT) implemented in the
full-potential local-orbital(FPLO) code. The results indicate a structural
phase transition from fcc to bcc structure when the film thickness exceeds 23
Fe atomic monolayers. The considered fcc films prefer the low-spin
ferromagnetic state with an average magnetic moment of about 1.0 $\mu_{B}$ per
atom. This moment decreases with increasing film thickness until the critical
thickness, where, after the structural transition to the bcc phase, it reaches
a value close to that of bulk bcc Fe. Moreover, the values of the magnetic
anisotropy energy are positive (perpendicular magnetic anisotropy) for the
entire thickness range of films with fcc structure (in ferromagnetic low-spin
state) and systematically decrease with increasing film thickness. The
presented computational results explain the experimentally observed structural
transition and may help to select appropriate substrates with suitable lattice
parameters for the deposition of ultrathin Fe(111) films.",2307.11167v3
2023/7/28,Magnetic Antiskyrmions in Two-Dimensional van der Waals Magnets Engineered by Layer Stacking,"Magnetic skyrmions and antiskyrmions are topologically protected
quasiparticles exhibiting a whirling spin texture in real space. Antiskyrmions
offer some advantages over skyrmions as they are expected to have higher
stability and can be electrically driven with no transverse motion. However,
unlike the widely investigated skyrmions, antiskyrmions are rarely observed due
to the required anisotropic Dzyaloshinskii-Moriya interaction (DMI). Here we
propose to exploit the recently demonstrated van der Waals (vdW) assembly of
two-dimensional (2D) materials that breaks inversion symmetry and creates
conditions for anisotropic DMI. Using a 2D vdW magnet CrI${}_3$ as an example,
we demonstrate, based on density functional theory (DFT) calculations, that
this strategy is a promising platform to realize antiskyrmions. Polar layer
stacking of two centrosymmetric magnetic monolayers of CrI${}_3$ efficiently
lowers the symmetry, resulting in anisotropic DMI that supports antiskyrmions.
The DMI is reversible by switching the ferroelectric polarization inherited
from the polar layer stacking, offering the control of antiskyrmions by an
electric field. Furthermore, we find that the magnetocrystalline anisotropy and
DMI of CrI${}_3$ can be efficiently modulated by Mn doping, creating a
possibility to control the size of antiskyrmions. Using atomistic spin dynamics
simulations with the parameters obtained from our DFT calculations, we predict
the formation of antiskyrmions in a Cr${}_{0.88}$Mn${}_{0.12}$I${}_3$ bilayer
and switching their spin texture with polarization reversal. Our results open a
new direction to generate and control magnetic antiskyrmions in 2D vdW magnetic
systems.",2307.15769v1
2023/7/31,Bioinspired multi-asymmetric magnetized surfaces for tailoring energy-free liquid manipulation and 3-DOF solid transportation,"Through the utilization of smart materials and well-designed structures,
functional surfaces have been developed to enable small-scale liquid/solid
manipulation tasks, thereby facilitating crucial applications in the fields of
microfluidics, soft robotics, and biomedical engineering. However, the design
of functional systems with flexible, tunable, and multimodal liquid/solid
manipulation capabilities remains a challenging endeavor. Here, inspired by
asymmetric structural features in natural plants and metachrony in cross-scale
biological systems, I report a magnetic-responsive functional surface that can
achieve rich liquid operations under static magnetic fields, while also
enabling the transportation of solids with multiple degrees of freedom (DOFs)
under dynamic magnetic fields. The presence of curvature pillars on the
surface, combined with their magnetic-driven tilt/gradient arrangement, imparts
liquids with multi-directional spreading modes based on the asymmetry of
Laplace pressure. I elucidate the mechanisms governing these liquid spreading
modes and subsequently develop compelling liquid operations, such as adjustable
anti-gravity climbing, spontaneous modal shifts in liquid transport, and liquid
mixing. Furthermore, the dynamic metachronal motion of the magnetic pillars can
be harnessed for solid object transportation. I illustrate the
synchronous/asynchronous transport modes of the surface and propose a novel
strategy for achieving 3-DOF solid transportation by coordinating the
arrangement of objects and employing magnetic actuation strategies. This study
presents a new design concept for application-oriented manipulation surfaces,
which hold significant potential for extensive engineering applications.",2307.16740v2
2023/9/29,Muon Spin Relaxation Study of frustrated Tm$_3$Sb$_3$Mg$_2$O$_{14}$ with kagomé lattice,"The structure and magnetic properties of rare-earth ions Tm$^{3+}$ kagom\'{e}
lattice Tm$_3$Sb$_3$Mg$_2$O$_{14}$ are studied by X-ray diffraction, magnetic
susceptibility and muon spin relaxation ($\mu$SR) experiments. The existence of
a small amount of Tm/Mg site-mixing disorder is revealed. DC magnetic
susceptibility measurement shows that Tm$^{3+}$ magnetic moments are
antiferromagnetically correlated with a negative Curie-Weiss temperature of
-26.3 K. Neither long-range magnetic order nor spin-glass transition is
observed by DC and AC magnetic susceptibility, and confirmed by $\mu$SR
experiment down to 0.1 K. However, the emergence of short-range magnetic order
is indicated by the zero-field $\mu$SR experiments, and the absence of spin
dynamics at low temperatures is evidenced by the longitudinal-field $\mu$SR
technique. Compared with the results of Tm$_3$Sb$_3$Zn$_2$O$_{14}$, another
Tm-based kagom\'{e} lattice with much more site-mixing disorder, the gapless
spin liquid like behaviors in Tm$_3$Sb$_3$Zn$_2$O$_{14}$ can be induced by
disorder effect. Samples with perfect geometrical frustration are in urgent
demand to establish whether QSL exits in this kind of materials with rare-earth
kagom\'{e} lattice.",2309.16947v1
2023/10/17,Size-dependence and high temperature stability of radial vortex magnetic textures imprinted by superconductor stray fields,"Swirling spin textures, including topologically non-trivial states, such as
skyrmions, chiral domain walls, and magnetic vortices, have garnered
significant attention within the scientific community due to their appeal from
both fundamental and applied points of view. However, their creation,
controlled manipulation, and stability are typically constrained to certain
systems with specific crystallographic symmetries, bulk, or interface
interactions, and/or a precise stacking sequence of materials. Here, we make
use of the stray field of YBa2Cu3O7-{\delta} superconducting microstructures in
ferromagnet/superconductor hybrids to imprint magnetic radial vortices in
permalloy at temperatures below the superconducting transition temperature
(TC), a method easily extended to other ferromagnets with in-plane magnetic
anisotropy. We examine the size dependence and temperature stability of the
imprinted magnetic configurations. We show that above TC, magnetic domains
retain memory of the imprinted spin texture. Micromagnetic modelling coupled
with a SC field model reveals that the stabilization mechanism leading to this
memory effect is mediated by microstructural defects. Superconducting control
of swirling spin textures below and above the superconducting transition
temperature holds promising prospects for shaping spintronics based on magnetic
textures.",2310.11298v1
2023/10/24,Electric quadrupole second harmonic generation revealing dual magnetic orders in a magnetic Weyl semimetal,"Broken symmetries and electronic topology are nicely manifested together in
the second order nonlinear optical responses from topologically nontrivial
materials. While second order nonlinear optical effects from the electric
dipole (ED) contribution have been extensively explored in polar Weyl
semimetals (WSMs) with broken spatial inversion (SI) symmetry, they are rarely
studied in centrosymmetric magnetic WSMs with broken time reversal (TR)
symmetry due to complete suppression of the ED contribution. Here, we report
experimental demonstration of optical second harmonic generation (SHG) in a
magnetic WSM Co$_{3}$Sn$_{2}$S$_{2}$ from the electric quadrupole (EQ)
contribution. By tracking the temperature dependence of the rotation anisotropy
(RA) of SHG, we capture two magnetic phase transitions, with both the SHG
intensity increasing and its RA pattern rotating at $T_{C,1}$=175K and
$T_{C,2}$=120K subsequently. The fitted critical exponents for the SHG
intensity and RA orientation near $T_{C,1}$ and $T_{C,2}$ suggest that the
magnetic phase at $T_{C,1}$ is a 3D Ising-type out-of-plane ferromagnetism
while the other at $T_{C,2}$ is a 3D XY-type all-in-all-out in-plane
antiferromagnetism. Our results show the success of detection and exploration
of EQ SHG in a centrosymmetric magnetic WSM, and hence open the pathway towards
the future investigation of its tie to the band topology.",2310.15423v1
2024/2/6,Ultrafast terahertz field control of the emergent magnetic and electronic interactions at oxide interfaces,"Ultrafast electric-field control of emergent electronic and magnetic states
at oxide interfaces offers exciting prospects for the development of new
generations of energy-efficient devices. Here, we demonstrate that the
electronic structure and emergent ferromagnetic interfacial state in epitaxial
LaNiO3/CaMnO3 superlattices can be effectively controlled using intense
single-cycle THz electric-field pulses. We employ a combination of
polarization-dependent X-ray absorption spectroscopy with magnetic circular
dichroism and X-ray resonant magnetic reflectivity to measure a detailed
magneto-optical profile and thickness of the ferromagnetic interfacial layer.
Then, we use time-resolved and temperature-dependent magneto-optical Kerr
effect, along with transient optical reflectivity and transmissivity
measurements, to disentangle multiple correlated electronic and magnetic
processes driven by ultrafast high-field (~1 MV/cm) THz pulses. These processes
include an initial sub-picosecond electronic response, consistent with
non-equilibrium Joule heating; a rapid (~270 fs) demagnetization of the
ferromagnetic interfacial layer, driven by THz-field-induced nonequilibrium
spin-polarized currents; and subsequent multi-picosecond dynamics, possibly
indicative of a change in the magnetic state of the superlattice due to the
transfer of spin angular momentum to the lattice. Our findings shed light on
the intricate interplay of electronic and magnetic phenomena in this strongly
correlated material system, suggesting a promising avenue for efficient control
of two-dimensional ferromagnetic states at oxide interfaces using ultrafast
electric-field pulses.",2402.04302v1
2017/1/5,Effect of single-particle magnetostriction on the shear modulus of compliant magnetoactive elastomers,"The influence of an external magnetic field on the static shear strain and
the effective shear modulus of a magnetoactive elastomer (MAE) is studied
theoretically in the framework of a recently introduced approach to the
single-particle magnetostriction mechanism [V. M. Kalita et al, Phys. Rev. E
93, 062503 (2016)]. The planar problem of magnetostriction in an MAE with soft
magnetic inclusions in the form of a thin disk (platelet) having the magnetic
anisotropy in the plane of this disk is solved analytically. An external
magnetic field acts with torques on magnetic filler particles, creates
mechanical stresses in the vicinity of inclusions, induces shear strain and
increases the effective shear modulus of these composite materials. It is shown
that the largest effect of the magnetic field on the effective shear modulus
should be expected in MAEs with soft elastomer matrices, where the shear
modulus of the matrix is less than the magnetic anisotropy constant of
inclusions. It is derived that the effective shear modulus is non-linearly
dependent on the external magnetic field and approaches the saturation value in
magnetic fields exceeding the field of particle anisotropy. It is shown that
model calculations of the effective shear modulus correspond to a
phenomenological definition of effective elastic moduli and magnetoelastic
coupling constants. Obtained theoretical results compare well with known
experimental data. Determination of effective elastic coefficients in MAEs and
their dependence on magnetic field is discussed. The concentration dependence
of the effective shear modulus at higher filler concentrations has been
estimated using the method of Pad\'e approximants, which correctly predicts
that both the absolute and relative changes of the magnetic-field dependent
effective shear modulus will significantly increase with the growing
concentration of filler particles.",1701.01305v1
2017/2/13,Direct observation of enhanced magnetism in individual size- and shape-selected 3d transition metal nanoparticles,"Magnetic nanoparticles are important building blocks for future technologies
ranging from nano-medicine to spintronics. Many related applications require
nanoparticles with tailored magnetic properties. However, despite significant
efforts undertaken towards this goal, a broad and poorly-understood dispersion
of magnetic properties is reported, even within mono-disperse samples of the
canonical ferromagnetic 3d transition metals. We address this issue by
investigating the magnetism of a large number of size- and shape-selected,
individual nanoparticles of Fe, Co, and Ni using a unique set of complementary
characterization techniques. At room temperature only superparamagnetic
behavior is observed in our experiments for all Ni nanoparticles within the
investigated sizes, which range from 8 to 20 nm. However, Fe and Co
nanoparticles can exist in two distinct magnetic states at any size in this
range: (i) a superparamagnetic state as expected from the bulk and surface
anisotropies known for the respective materials and as observed for Ni; and
(ii) a state with unexpected stable magnetization at room temperature. This
striking state is assigned to significant modifications of the magnetic
properties arising from metastable lattice defects in the core of the
nanoparticles as concluded by calculations and atomic structural
characterization. Also related with the structural defects, we find that the
magnetic state of Fe and Co nanoparticles can be tuned by thermal treatment
enabling one to tailor their magnetic properties for applications. This work
demonstrates the importance of complementary single particle investigations for
a better understanding of nanoparticle magnetism and for full exploration of
their potential for applications.",1702.03710v1
2022/4/2,Canted Antiferromagnetic phases in the layered candidate Weyl material EuMnSb$_2$,"EuMnSb$_2$ is a candidate topological material which can be tuned towards a
Weyl semimetal, but there are differing reports for its antiferromagnetic (AFM)
phases. The coupling of bands dominated by pure Sb layers hosting topological
fermions to Mn and Eu magnetic states provides a potential path to tune the
topological properties. We present a detailed analysis of the magnetic
structure on three AFM phases based on single-crystal neutron diffraction,
magnetization, and heat capacity data as well as polycrystalline $^{151}$Eu
M\""ossbauer data. The Mn magnetic sublattice orders into a C-type AFM structure
below $323(1)$~K with the ordered Mn magnetic moment $\mu_{\text{Mn}}$ lying
perpendicular to the layers. AFM ordering of the Eu sublattice occurs below
$23(1)$~K with the ordered Eu magnetic moment $\mu_{\text{Eu}}$ canted away
from the layer normal and $\mu_{\text{Mn}}$ retaining its higher-temperature
order. $\mu_{\text{Eu}}$ is ferromagnetically aligned within each Eu layer but
exhibits a complicated AFM layer stacking. Both of these higher-temperature
phases are described by magnetic space group (MSG)
$Pn^{\prime}m^{\prime}a^{\prime}$ with the chemical and magnetic unit cells
having the same dimensions. Cooling below $=9(1)$~K reveals a third AFM phase
where $\mu_{\text{Mn}}$ remains unchanged but $\mu_{\text{Eu}}$ develops an
additional in-plane canting. This phase has MSG $P11\frac{2_1}{a^{\prime}}$. We
additionally find evidence of short-range magnetic correlations associated with
the Eu between $12~\text{K} \lesssim T \lesssim 30~\text{K}$. Using the
determined magnetic structures, we postulate the signs of nearest-neighbor
intralayer and interlayer exchange constants and the magnetic anisotropy within
a general Heisenberg-model. We then discuss implications of the various AFM
states in EuMnSb$_2$ and its topological properties.",2204.00761v2
2022/7/22,Neutron diffraction in MnSb2O6: Magnetic and structural domains in a helicoidal polar magnet with coupled chiralities,"MnSb$_{2}$O$_{6}$ is based on the structural chiral $P$321 space group #150
where the magnetic Mn$^{2+}$ moments ($S=5/2$, $L\approx 0$) order
antiferromagnetically at $T_\mathrm{N}=12$ K. Unlike the related iron based
langasite (Ba$_3$NbFe$_3$Si$_2$O$_{14}$) where the low temperature magnetism is
based on a proper helix characterized by a time-even pseudoscalar `magnetic'
chirality, the Mn$^{2+}$ ions in MnSb$_{2}$O$_{6}$ order with a cycloidal
structure at low temperatures, described instead by a time-even vector
`magnetic' polarity. A tilted cycloidal structure has been found [M. Kinoshita
et al. Phys. Rev. Lett. 117, 047201 (2016)] to facilitate ferroelectric
switching under an applied magnetic field. In this work, we apply polarized and
unpolarized neutron diffraction analyzing the magnetic and nuclear structures
in MnSb$_{2}$O$_{6}$ with the aim of understanding this magnetoelectric
coupling. We find no evidence for a helicoidal magnetic structure with one of
the spin envelope axes tilted away from the cycloidal $c$-axis. However, on
application of a magnetic field $\parallel$ $\vec{c}$ the spin rotation plane
can be tilted, giving rise to a cycloid-helix admixture that evolves towards a
distorted helix (zero cycloidal component) for fields great than $\approx$ 2 T.
We propose a mechanism for the previously reported ferroelectric switching
based on coupled structural and magnetic chiralities requiring only an
imbalance of structural chiral domains.",2207.10977v2
2022/11/15,Picosecond Spin-Orbit Torque Induced Coherent Magnetization Switching in a Ferromagnet,"Electrically controllable non-volatile magnetic memories show great potential
for the replacement of semiconductor-based technologies. Recently there has
been strong interest in spin-orbit torque (SOT) induced magnetization reversal
due to the device's increased lifetime and speed of operation. However, recent
SOT switching studies reveal an incubation delay in the ~ns range due to
stochasticity in the nucleation of a magnetic domain during reversal. Here, we
experimentally demonstrate ultrafast SOT-induced magnetization switching
dynamics of a ferromagnet with no incubation delay by avoiding the nucleation
process and driving the magnetization coherently. We employ an ultrafast
photo-conducting switch and a co-planar strip line to generate and guide ~ps
current pulses into the heavy metal/ferromagnet layer stack and induce
ultrafast SOT. We use magneto-optical probing to investigate the magnetization
switching dynamics with sub-picosecond time resolution. Depending on the
relative current pulse and in-plane magnetic field polarities, we observe
either an ultrafast demagnetization and subsequent recovery along with a
SOT-induced precessional oscillation, or ultrafast SOT switching. The
magnetization zero-crossing occurs in ~70 ps, which is approximately an order
of magnitude faster than previous studies. Complete switching needs ~250 ps and
is limited by the heat diffusion to the substrate. We use a macro-magnetic
simulation coupled with an ultrafast heating model to analyze the effect of
ultrafast thermal anisotropy torque and current-induced torque in the observed
dynamics. Good agreement between our experimental results and the macro-spin
model shows that the switching dynamics are coherent and present no noticeable
incubation delay. Our work suggests a potential pathway toward dramatically
increasing the writing speed of SOT magnetic random-access memory devices.",2211.08266v1
2010/7/12,Simple models for dynamic hysteresis loops calculation: Application to hyperthermia optimization,"To optimize the heating properties of magnetic nanoparticles (MNPs) in
magnetic hyperthermia applications, it is necessary to calculate the area of
their hysteresis loops in an alternating magnetic field. The three types of
theories suitable for describing the hysteresis loops of MNPs are presented and
compared to numerical simulations: equilibrium functions, Stoner-Wohlfarth
model based theories (SWMBTs) and linear response theory (LRT). Suitable
formulas to calculate the hysteresis area of major cycles are deduced from
SWMBTs and from numerical simulations; the domain of validity of the analytical
formula is explicitly studied. In the case of minor cycles, the hysteresis area
calculations are based on the LRT. A perfect agreement between LRT and
numerical simulations of hysteresis loops is obtained. The domain of validity
of the LRT is explicitly studied. Formulas to calculate the hysteresis area at
low field valid for any anisotropy of the MNP are proposed. Numerical
simulations of the magnetic field dependence of the area show it follows
power-laws with a large range of exponents. Then, analytical expressions
derived from LRT and SWMBTs are used for a theoretical study of magnetic
hyperthermia. It is shown that LRT is only pertinent for MNPs with strong
anisotropy and that SWMBTs should be used for weak anisotropy MNPs. The optimum
volume of MNPs for magnetic hyperthermia as function of material and
experimental parameters is derived. The maximum specific absorption rate (SAR)
achievable is calculated versus the MNP anisotropy. It is shown that an optimum
anisotropy increases the SAR and reduces the detrimental effects of size
distribution. The optimum anisotropy is simple to calculate and depends on the
magnetic field used in the hyperthermia experiments and on the MNP
magnetization only. The theoretical optimum parameters are compared to the one
of several magnetic materials.",1007.2009v2
2013/4/1,First-Principles Study of the Electronic and Magnetic Properties of Defects in Carbon Nanostructures,"Understanding the magnetic properties of graphenic nanostructures is
instrumental in future spintronics applications. These magnetic properties are
known to depend crucially on the presence of defects. Here we review our recent
theoretical studies using density functional calculations on two types of
defects in carbon nanostructures: Substitutional doping with transition metals,
and sp$^3$-type defects created by covalent functionalization with organic and
inorganic molecules. We focus on such defects because they can be used to
create and control magnetism in graphene-based materials. Our main results are
summarized as follows: i)Substitutional metal impurities are fully understood
using a model based on the hybridization between the $d$ states of the metal
atom and the defect levels associated with an unreconstructed D$_{3h}$ carbon
vacancy. We identify three different regimes, associated with the occupation of
distinct hybridization levels, which determine the magnetic properties obtained
with this type of doping; ii) A spin moment of 1.0 $\mu_B$ is always induced by
chemical functionalization when a molecule chemisorbs on a graphene layer via a
single C-C (or other weakly polar) covalent bond. The magnetic coupling between
adsorbates shows a key dependence on the sublattice adsorption site. This
effect is similar to that of H adsorption, however, with universal character;
iii) The spin moment of substitutional metal impurities can be controlled using
strain. In particular, we show that although Ni substitutionals are
non-magnetic in flat and unstrained graphene, the magnetism of these defects
can be activated by applying either uniaxial strain or curvature to the
graphene layer. All these results provide key information about formation and
control of defect-induced magnetism in graphene and related materials.",1304.0379v1
2015/2/20,Magnetic properties of (Fe$_{1-x}$Co$_x$)$_2$B alloys and the effect of doping by 5$d$ elements,"We have explored, computationally and experimentally, the magnetic properties
of \fecob{} alloys. Calculations provide a good agreement with experiment in
terms of the saturation magnetization and the magnetocrystalline anisotropy
energy with some difficulty in describing Co$_2$B, for which it is found that
both full potential effects and electron correlations treated within dynamical
mean field theory are of importance for a correct description. The material
exhibits a uniaxial magnetic anisotropy for a range of cobalt concentrations
between $x=0.1$ and $x=0.5$. A simple model for the temperature dependence of
magnetic anisotropy suggests that the complicated non-monotonous temperature
behaviour is mainly due to variations in the band structure as the exchange
splitting is reduced by temperature. Using density functional theory based
calculations we have explored the effect of substitutional doping the
transition metal sublattice by the whole range of 5$d$ transition metals and
found that doping by Re or W elements should significantly enhance the
magnetocrystalline anisotropy energy. Experimentally, W doping did not succeed
in enhancing the magnetic anisotropy due to formation of other phases. On the
other hand, doping by Ir and Re was successful and resulted in magnetic
anisotropies that are in agreement with theoretical predictions. In particular,
doping by 2.5~at.\% of Re on the Fe/Co site shows a magnetocrystalline
anisotropy energy which is increased by 50\% compared to its parent
(Fe$_{0.7}$Co$_{0.3}$)$_2$B compound, making this system interesting, for
example, in the context of permanent magnet replacement materials or in other
areas where a large magnetic anisotropy is of importance.",1502.05916v3
2017/6/28,The complete micromagnetic characterization of asymmetrically sandwiched ferromagnetic films,"The magnetic properties of ferromagnetic thin films down to the nanoscale are
ruled by the exchange stiffness, anisotropies and the effects of magnetic
fields. As surfaces break inversion symmetry, an additional effective chiral
exchange is omnipresent in any magnetic nanostructure. These so-called
Dzyaloshinskii-Moriya interactions (DMI) affect all inhomogeneous magnetic
states either subtly or spectacularly. E.g., DMIs cause a chirality selection
of the rotation sense and can fix the local rotation axis for the magnetization
in domain walls (DW). But, they can stabilize also entirely different twisted
magnetic structures. The chiral skyrmions a two-dimensional particle-like
topological soliton is the ultimately smallest of these objects, which
currently is targetted as a possible information carrier in novel spintronic
devices. Observation and quantification of the chiral exchange effects provide
for the salient point in understanding magnetic properties in ultrathin films
and other nanostructures. An easy and reliable method to determine the DMI
constant as materials parameter of asymmetric thin films is the crucial
problem. Here, we put forth an experimental approach for the determination of
the complete set of the micromagnetic parameters. Quasi-static Kerr microcopy
observations of DW creep motion and equilibrium sizes of circular magnetic
objects in combination with standard magnetometry are used to derive a
consistent set of these materials parameters in polycrystalline ultrathin film
systems, namely CrOx/Co/Pt stacks. The quantified micromagnetic model for these
films identifies the circular magnetic objects, as seen by the optical
microscopy, as ordinary bubble domains with homochiral walls. From
micromagnetic calculations, the chiral skyrmions stabilized by the DMI in these
films are shown to have diameters in the range 40-200nm, too small to be
observed by optical microscopy.",1706.09322v2
2019/8/19,Giant thermal magnetoconductivity in CrCl$_3$ and a general model for spin-phonon scattering,"Insulating quantum magnets lie at the forefront both of fundamental research
into quantum matter and of technological exploitation in the increasingly
applied field of spintronics. In this context, the magnetic thermal transport
is a particularly sensitive probe of the elementary spin and exotic topological
excitations in unconventional magnetic insulators. However, magnetic
contributions to heat conduction are invariably intertwined with lattice
contributions, and thus the issue of spin-phonon coupling in determining the
spin and thermal transport properties becomes more important with emergent
topological magnetic system. Here we report the observation of an anomalously
strong enhancement of the thermal conductivity, occurring at all relevant
temperatures, in the layered honeycomb material CrCl$_3$ in the presence of an
applied magnetic field. Away from the magnetically ordered phase at low
temperatures and small fields, there is no coherent spin contribution to the
heat conduction, and hence the effect must be caused by a strong suppression of
the phonon thermal conductivity due to magnetic fluctuations, which are in turn
suppressed by the field. We build an empirical model for the thermal
conductivity of CrCl$_3$ within a formalism assuming an independently
determined number of spin-flip processes and an efficiency of the phonon
scattering events they mediate. By extracting the intrinsic phonon thermal
conductivity we obtain a quantitative description at all fields and
temperatures and demonstrate that the scattering efficiency is entirely
independent of the field. In this way we use CrCl$_3$ as a model system to
understand the interactions between spin and phonon excitations in the context
of thermal transport. We anticipate that the completely general framework we
introduce will have broad implications for the interpretation of transport
phenomena in magnetic quantum materials.",1908.07004v2
2023/3/27,Magnetic properties of cobalt ultrathin film structures controlled by buffer layer roughness,"Growth optimization of multilayers is a topic of interest due to their unique
physical properties. Systems containing magnetic materials, such as
platinum-cobalt, have been studied because of their potential for technological
applications, e.g. spintronics, magnetic storage and magnetic sensors. Since
the magnetic properties of thin layers are strongly related to the growth
parameters, the fine tuning of these parameters is necessary to produce
multilayers with specific properties required in various applications. Here, an
efficient approach to tune the coercive field of Co ultrathin films in the
multilayer by varying the underlayer thickness is demonstrated. Using magnetron
sputtering, we prepared multilayer systems of Au(x)/Pt(5nm)/Co(0.7nm)/Au(5nm)
with various thicknesses of Au underlayer. The surface morphology of
Au(x)/Pt(5nm) stack on which Co layer was deposited was studied by atomic force
microscopy. We show the possibility to control the interfacial roughness by
changing the Au underlayer thickness due to its island-like growth mechanism
(Volmer-Weber mode). As the nominal thickness of Au increases, the islands grow
in larger lateral size, resulting in a higher overall roughness of the layer
surface. Magnetization measurements indicate a direct influence of the
underlayer roughness on the coercivity of the multilayers by promoting
additional magnetic anisotropy. With thickness of the Au layer up to 20 nm, we
can change the coercive field in the range from ~200 Oe to ~1100 Oe, while
remaining a nearly constant saturation magnetization. The use of Cu replacing
Au underlayer in the same multilayers was also investigated, demonstrating the
possibility of coercivity adjustment using different materials. The results are
important for applications where the magnetic properties of multilayer
structures based on Co thin films could be adjusted via buffer layer roughness
engineering.",2303.15141v1
2023/6/7,Flat band-engineered spin-density wave and the emergent multi-$k$ magnetic state in the topological kagome metal Mn$_{3}$Sn,"Magnetic kagome metals, in which topologically non-trivial band structures
and electronic correlation are intertwined, have recently emerged as an
exciting platform to explore exotic correlated topological phases, that are
usually not found in weakly interacting materials described within the
semi-classical picture of electrons. Here, via a comprehensive single-crystal
neutron diffraction and first-principles density functional theory study of the
archetypical topological kagome metal Mn$_3$Sn, which is also a magnetic Weyl
fermion material and a promising chiral magnet for antiferromagnetic
spintronics, we report the realisation of an emergent spin-density wave (SDW)
order, a hallmark correlated many-body phenomenon, that is engineered by the
Fermi surface nesting of topological flat bands. We further reveal that the
phase transition, from the well-known high-temperature coplanar and
non-collinear k = 0 inverse triangular antiferromagnetic order to a double-$k$
non-coplanar modulated incommensurate magnetic structure below $T_1$ = 280 K,
is primarily driven by the SDW instability. The double-$k$ nature of this
complex low-temperature magnetic order, which can be regarded as an intriguing
superposition of a longitudinal SDW with a modulation wavevector k$_L$ and a
transverse incommensurate helical magnetic order with a modulation wavevector
k$_T$, is unambiguously confirmed by our observation of the inter-modulation
high-order harmonics of the type of 2k$_L$+k$_T$. This discovery not only
solves a long-standing puzzle concerning the nature of the phase transition at
$T_1$, but also provides an extraordinary example on the intrinsic engineering
of correlated many-body phenomena in topological matter. The identified
multi-$k$ magnetic state can be further exploited for the engineering of the
new modes of magnetization and chirality switching in antiferromagnetic
spintronics.",2306.04312v1
2023/7/10,Near room-temperature intrinsic exchange bias in an Fe intercalated ZrSe2 spin glass,"Some magnetic systems display a shift in the center of their magnetic
hysteresis loop away from zero field, a phenomenon termed exchange bias.
Despite the extensive use of the exchange bias effect, particularly in magnetic
multilayers, for the design of spin-based memory/electronics devices, a
comprehensive mechanistic understanding of this effect remains a longstanding
problem. Recent work has shown that disorder-induced spin frustration might
play a key role in exchange bias, suggesting new materials design approaches
for spin-based electronic devices that harness this effect. Here, we design a
spin glass with strong spin frustration induced by magnetic disorder by
exploiting the distinctive structure of Fe intercalated ZrSe2, where Fe(II)
centers are shown to occupy both octahedral and tetrahedral interstitial sites
and to distribute between ZrSe2 layers without long-range structural order.
Notably, we observe behavior consistent with a magnetically frustrated, and
multi-degenerate ground state in these Fe0.17ZrSe2 single crystals, which
persists above room temperature. Moreover, this magnetic frustration leads to a
robust and tunable exchange bias up to 250 K. These results not only offer
important insights into the effects of magnetic disorder and frustration in
magnetic materials generally, but also highlight as design strategy the idea
that a large exchange bias can arise from an inhomogeneous microscopic
environment without discernible long-range magnetic order. In addition, these
results show that intercalated TMDs like Fe0.17ZrSe2 hold potential for
spintronics technologies that can achieve room temperature applications.",2307.05595v3
2024/1/2,A study of the magnetocaloric behavior of Dy-substituted YMn$_2$O$_5$ compounds,"In this paper, we report on the magnetic and magnetocaloric features of
Dy-substituted YMn$_2$O$_5$ (Y$_{1-x}$Dy$_x$Mn$_2$O$_5$) with $x=$ 0.6, 0.8,
and 1 series elaborated by sol-gel method. X-ray diffraction and Raman
measurements attest well the high quality of our polycrystalline samples that
crystallize in an orthorhombic structure with the Pbam space group. The Raman
phonon frequencies were carried out and compared with the lattice dynamics
calculations to identify the vibrational properties of all detected modes at
room temperature. As expected, our magnetic study reveals that the
magnetization was enhanced by the substitution of Y$^{3+}$ by Dy$^{3+}$. The
Dy-substituted YMn$_2$O$_5$ sets the N\'eel transition [TN (Mn)] in the
temperature range going from 40 to 45 K favoring the emergence of a transition
at a very low temperature due to the long-range ordering of the Dy3+ magnetic
moments below 13K [TN (Dy)]. Dual peaks in the magnetic entropy change curve
are also observed being in good agreement with magnetization data, which
enlarges the range of application of these materials. On the other hand, a
large magnetocaloric effect is observed close to 13 K which is mainly due the
ordering of Dy$^{3+}$ magnetic moments. Also, the incommensurate
antiferromagnetic transition of Mn magnetic moment taking place around 40 K
affects slightly the entropy change. Our refrigerant capacity (RC) findings are
higher compared to the average of RC for a, b, c axis of single crystal samples
as HoMn$_2$O$_5$ and TbMn$_2$O$_5$, which confirms that our polycrystalline
materials stand for promising magnetic refrigerant candidates that can be
invested in space technology, hydrogen and helium liquefaction at cryogenic
temperature.",2401.01431v1
2018/5/22,FMR-related phenomena in spintronic devices,"Spintronic devices, such as non-volatile magnetic random access memories and
logic devices, have attracted considerable attention as potential candidates
for future high efficient data storage and computing technology. In a heavy
metal or other emerging material with strong spin-orbit coupling (SOC), the
charge currents induce spin currents or spin accumulations via SOC. The
generated spin currents can exert spin-orbit torques (SOTs) on an adjacent
ferromagnet, which opens up a new way to realize magnetization dynamics and
switching of the ferromagnetic layer for spintronic devices. In the SOT scheme,
the charge-to-spin interconversion efficiency (SOT efficiency) is an important
figure of merit for applications. For the effective characterization of this
efficiency, the ferromagnetic resonance (FMR) based methods, such as the spin
transfer torque ferromagnetic resonance (ST-FMR) and the spin pumping, are
common utilized in addition to low frequency harmonic or dc measurements. In
this review, we focus on the ST-FMR measurements for the evaluation of the SOT
efficiency. We provide a brief summary of the different ST-FMR setups and data
analysis methods. We then discuss ST-FMR and SOT studies in various materials,
including heavy metals and alloys, topological insulators, two dimensional (2D)
materials, interfaces with strong Rashba effect, antiferromagnetic materials,
two dimensional electron gas (2DEG) in oxide materials and oxidized nonmagnetic
materials.",1805.08496v1
2020/8/19,Data-Driven Solvers for Strongly Nonlinear Material Response,"This work presents a data-driven magnetostatic finite-element solver that is
specifically well-suited to cope with strongly nonlinear material responses.
The data-driven computing framework is essentially a multiobjective
optimization procedure matching the material operation points as closely as
possible to given material data while obeying Maxwell's equations. Here, the
framework is extended with heterogeneous (local) weighting factors - one per
finite element - equilibrating the goal function locally according to the
material behavior. This modification allows the data-driven solver to cope with
unbalanced measurement data sets, i.e. data sets suffering from unbalanced
space filling. This occurs particularly in the case of strongly nonlinear
materials, which constitute problematic cases that hinder the efficiency and
accuracy of standard data-driven solvers with a homogeneous (global) weighting
factor. The local weighting factors are embedded in the distance-minimizing
data-driven algorithm used for noiseless data, likewise for the maximum entropy
data-driven algorithm used for noisy data. Numerical experiments based on a
quadrupole magnet model with a soft magnetic material show that the proposed
modification results in major improvements in terms of solution accuracy and
solver efficiency. For the case of noiseless data, local weighting factors
improve the convergence of the data-driven solver by orders of magnitude. When
noisy data are considered, the convergence rate of the data-driven solver is
doubled.",2008.08482v3
2022/6/10,Simulations of Frustrated Ising Hamiltonians with Quantum Approximate Optimization,"Novel magnetic materials are important for future technological advances.
Theoretical and numerical calculations of ground state properties are essential
in understanding these materials, however, computational complexity limits
conventional methods for studying these states. Here we investigate an
alternative approach to preparing materials ground states using the quantum
approximate optimization algorithm (QAOA) on near-term quantum computers. We
study classical Ising spin models on unit cells of square, Shastry-Sutherland,
and triangular lattices, with varying field amplitudes and couplings in the
material Hamiltonian. We find relationships between the theoretical QAOA
success probability and the structure of the ground state, indicating that only
a modest number of measurements ($\lesssim100$) are needed to find the ground
state of our nine-spin Hamiltonians, even for parameters leading to frustrated
magnetism. We further demonstrate the approach in calculations on a trapped-ion
quantum computer and succeed in recovering each ground state of the
Shastry-Sutherland unit cell with probabilities close to ideal theoretical
values. The results demonstrate the viability of QAOA for materials ground
state preparation in the frustrated Ising limit, giving important first steps
towards larger sizes and more complex Hamiltonians where quantum computational
advantage may prove essential in developing a systematic understanding of novel
materials.",2206.05343v2
2023/4/14,Recent advances in La2NiMnO6 Double Perovskites for various applications; Challenges and opportunities,"Double perovskites R2NiMnO6 (R= Rare earth element) (RNMO) are a significant
class of materials owing to their Multifunctional properties with structural
modifications. In particular, multifunctional double perovskite oxides
La2NiMnO6 (LNMO) which possess both electric and magnetic orderings, chemical
flexibility, versatility, and indispensable properties like high ferromagnetic
curie temperature, high absorption rates, dielectrics, etc. have drawn a lot of
attention due their rich physics and diverse applications in various
technology. This justifies the intense research in this class of materials, and
the keen interest they are subject to both the fundamental and practical side.
In view of the demands of this material in lead-free perovskite solar cells,
photocatalytic degradation of organic dyes, clean hydrogen production, electric
tuneable devices, Fuel cells, gas sensing, and Biomedical applications, there
is a need for an overview of all the literature so far, the ongoing research
and the future prospective. This review summarised all the Physical and
Structural Properties of LNMO such as electric, magnetic, catalytic, and
dielectric properties with their underlying mechanisms. This review article
provides insight into the scope of studies in LNMO material for exploring
unexposed properties in new material research and to identify areas of future
investigation of the materials in the double perovskite family.",2304.06951v1
2004/11/6,Surface Evidence of an Iron-Rich Solar Interior and a Neutron-Rich Solar Core,"Quantitative data on the solar wind, solar magnetic fields, solar eruptions,
solar neutrinos, and on the planetary material orbiting the Sun all indicate
the presence of an iron-rich solar interior and a neutron star at the core of
the Sun. Solar magnetic fields are deep-seated remnants from the core and/or
Bose-Einstein condensation of Fe-rich material into a rotating superconductor.
Neutron emission from the core triggers a series of reactions that produce
solar luminosity, the H carrier gas that maintains mass separation in the Sun,
and an outpouring of 3 E43 H+ ions per year in the solar wind.",0411163v1
1993/6/2,Toward a Unified Magnetic Phase Diagram of the Cuprate Superconductors,"We propose a unified magnetic phase diagram of cuprate superconductors. A new
feature of this phase diagram is a broad intermediate doping region of
quantum-critical, $z=1$, behavior, characterized by temperature independent
$T_1T/T_{\rm 2G}$ and linear $T_1T$, where the spin waves are not completely
absorbed by the electron-hole continuum. The spin gap in the moderately doped
materials is related to the suppression of the low-energy spectral weight in
the quantum disordered, $z=1$, regime. The crossover to the $z=2$ regime, where
$T_1T/T_{\rm 2G}^2 \simeq \mbox{const}$, occurs only in the fully doped
materials.",9306007v1
1995/12/22,Theory of Nuclear Magnetic Relaxation in Haldane Gap Materials: An Illustration of the Use of (1+1)-Dimensional Field Theory Techniques,"A comprehensive theory of nuclear magnetic relaxation is developed for
Haldane Gap materials using nonlinear sigma, boson and fermion models. We
include a thorough discussion of of the effects of interchain couplings,
nearest neighbour hyperfine couplings and crystal structure. We also introduce
a new theory of impurities corresponding to broken chain ends weakly coupled to
bulk magnons. The work is compared to recent experiments on NENP.",9512161v2
1997/7/17,Monte Carlo simulations of magnetovolume instabilities in anti-Invar systems,"We perform constant pressure Monte Carlo simulations of a spin-analogous
model which describes coupled spatial and magnetic degrees of freedom on an fcc
lattice. Our calculations qualitatively reproduce magnetovolume effects
observed in some rare earth manganese compounds, especially in the anti-Invar
material YMn2. These are a sudden collapse of the magnetic moment which is
connected with a huge volume change, and a largely enhanced thermal expansion
coefficient.",9707181v1
1998/9/5,Coexistence of the Electron Cooper Pair and Antiferromagnetic Short-Range Correlation in Copper Oxide Materials,"Within the fermion-spin theory, the physical properties of the electron
pairing state in the copper oxide materials are discussed. According to the
common form of the electron Cooper pair, it is shown that there is a
coexistence of the electron Cooper pair and magnetic short-range correlation,
and hence the antiferromagnetic short-range correlation can persist into the
superconducting state. Moreover, the mean-field results indicate that the
electron pairing state originating from the pure magnetic interaction in the
two-dimensional t-J model is the local state, and then does not reveal the true
superconducting ground-state.",9809098v2
1998/9/21,First Principles Investigation of Ferromagnetism and Ferroelectricity in Bismuth Manganite,"We present results of local spin density approximation (LSDA) pseudopotential
calculations for the perovskite structure oxide, bismuth manganite (BiMnO3).
The origin of the differences between bismuth manganite and other perovskite
manganites is determined by first calculating total energies and band
structures of the high symmetry cubic phase, then sequentially lowering the
magnetic and structural symmetry. Our results indicate that covalent bonding
between bismuth cations and oxygen anions stabilizes different magnetic and
structural phases compared with the rare earth manganites. This is consistent
with recent experimental results showing enhancement of charge ordering in
doped bismuth manganite.",9809282v1
1999/1/21,"Exchange interactions and magnetic properties of the layered vanadates CaV2O5, MgV2O5, CaV3O7 and CaV4O9","We have performed ab-initio calculations of exchange couplings in the layered
vanadates CaV2O5, MgV2O5, CaV3O7 and CaV4O9. The uniform susceptibility of the
Heisenberg model with these exchange couplings is then calculated by quantum
Monte Carlo method; it agrees well with the experimental measurements. Based on
our results we naturally explain the unusual magnetic properties of these
materials, especially the huge difference in spin gap between CaV2O5 and
MgV2O5, the unusual long range order in CaV3O7 and the ""plaquette resonating
valence bond (RVB)"" spin gap in CaV4O9.",9901214v1
1999/6/25,Structure and relevant dimension of the Heisenberg model and applications to spin rings,"For the diagonalization of the Hamilton matrix in the Heisenberg model
relevant dimensions are determined depending on the applicable symmetries.
Results are presented, both, by general formulae in closed form and by the
respective numbers for a variety of special systems. In the case of cyclic
symmetry, diagonalizations for Heisenberg spin rings are performed with the use
of so-called magnon states. Analytically solvable cases of small spin rings are
singled out and evaluated.",9906382v1
2000/3/20,Anomalous temperature dependence of magnetic quantum oscillations in CeBiPt,"Shubnikov--de Haas (SdH) and Hall-effect measurements of CeBiPt and LaBiPt
reveal the presence of simple and very small Fermi surfaces with hole-like
charge carriers for both semimetals. In the magnetic material, CeBiPt, we
observe a strong temperature dependence of the SdH frequency. This highly
unusual effect might be connected with an internal exchange field within the
material and a strongly spin-dependent scattering of the charge carriers.",0003329v1
2000/8/15,"Electronic structure, hyperfine interactions and disordering effects in iron nitride Fe4N","Iron nitride Fe4N is studied by full-potential LAPW method. Structure
parameters, electronic and magnetic properties as well as hyperfine interaction
parameters are obtained. We observe perfect agreement with experimental
results. Hypothetical Fe4N structure was also calculated to study the influence
of disordering effects on parameters of Moessbauer spectra. We performed
detailed analysis of EFG formation on Fe nuclei including magnetization
effects. We show that the formation of N-Fe-N local configuration is
energetically favourable in nitrogen austenites.",0008214v1
2001/1/25,Ferromagnetism in magnetically doped III-V semiconductors,"The origin of ferromagnetism in semimagnetic III-V materials is discussed.
The indirect exchange interaction caused by virtual electron excitations from
magnetic impurity level in the bandgap to the valence band can explain
ferromagnetism in GaAs(Mn) no matter samples are degenerated or not. Formation
of ferromagnetic clusters and percolation picture of phase transition describes
well all available experimental data and allows to predict the Mn-composition
dependence of transition temperature in wurtzite (Ga,In,Al)N epitaxial layers.",0101389v1
2001/8/11,Spin dynamics from time-dependent spin density-functional theory,"We derive the spin-wave dynamics of a magnetic material from the
time-dependent spin density functional theory in the linear response regime.
The equation of motion for the magnetization includes, besides the static spin
stiffness, a ""Berry curvature"" correction and a damping term. A gradient
expansion scheme based on the homogeneous spin-polarized electron gas is
proposed for the latter two quantities, and the first few coefficients of the
expansion are calculated to second order in the Coulomb interaction.",0108193v1
2001/9/13,Ferromagnetism of magnetic semiconductors--Zhang-Rice limit,"It is suggested that p-d hybridization contributes significantly to the hole
binding energy E_b of Mn acceptors in III-V compounds, leading in an extreme
case to the formation of Zhang-Rice-like small magnetic polarons. The model
explains both strong increase of E_b and evolution of Mn spin-resonance
spectrum with the magnitude of valence-band offsets. For such a structure of Mn
impurity in III-V materials, possible models accounting for the recently
determined Curie temperature of about 940 K in a compensated Ga(0.91)Mn(0.09)N
are discussed.",0109245v1
2001/11/12,Itinerant-electron Ferromagnetism in W(Nb)O3-d,"The crystal structure and the magnetic properties of the W1-xNbxO3-d,
(x<0.03) system have been investigated. In contrast to the orthorhombic
diamagnetic WO3, the material with x=0.01 is paramagnetic down to 5 K.
Introducing of 2.5 at. % of Nb into WO3 leads to a tetragonal structure and to
a weak itinerant ferromagnetic ordering below TC= 225 K. The saturation
magnetic moment at 5 K is 1.07*10-3 mB, whereas the paramagnetic effective
moment is 0.06 mB per mole. This high ratio indicates itinerant ferromagnetism
in W0.975Nb0.025O3-d.",0111210v1
2001/11/12,"The magnetic behavior of Li2MO3 (M=Mn, Ru and Ir) and Li2(Mn1-xRux)O3","The present study summerizes magnetic and Mossbauer measurements on ceramic
Li2MO3 M= Mn, Ru and Ir and the mixed Li2(Mn1-xRux)O3 materials, which show
many of the features reflecting to antiferromagnetic ordering or to existence
of paramagnetic states. Li2IrO3 and Li2RuO3 are paramagnetic down to 5 K.
Li2(Mn1-xRux)O3 compounds are antiferromagnetically ordered at TN = 48 K for
x=0. TN decreases as the Ru content increases and, for x=0.8, TN =34 K.",0111211v1
2001/11/21,Extraordinary magnetization behavior of single crystalline TbFe_4.4Al_7.6,"We report the observation of a field-induced transformation from the
easy-plane antiferromagnetic structure to the easy-axis ferrimagnetic structure
in a single crystal of TbFe_4.4Al_7.6 (tetragonal ThMn_12 structure) at 5 K.
Such a field-induced, irreversible transition has been identified for the first
time. This transition is accompanied by a giant orthorhombic distortion:
epsilon_aa = - epsilon_bb ~ 3.5x10^-4 that is associated with a magnetic
hardness (mu_0H_C ~ 3 T) that is unprecedented in this category of materials.",0111408v1
2002/4/14,Raman scattering through surfaces having biaxial symmetry,"Magnetic Raman scattering in two-leg spin ladder materials and the
relationship between the anisotropic exchange integrals are analyzed by P. J.
Freitas and R. R. P. Singh in Phys. Rev. B, {\bf 62}, 14113 (2000). The angular
dependence of the two-magnon scattering is shown to provide information for the
magnetic anisotropy in the Sr_14Cu_24O_41 and La_6Ca_8Cu_24O_41 compounds. We
point out that the experimental results of polarized Raman measurements at
arbitrary angles with respect to the crystal axes have to be corrected for the
light ellipticity induced inside the optically anisotropic crystals. We refer
quantitatively to the case of Sr_14Cu_24O_41 and discuss potential implications
for spectroscopic studies in other materials with strong anisotropy.",0204312v1
2002/5/8,Epitaxial Growth of an n-type Ferromagnetic Semiconductor CdCr2Se4 on GaAs(001) and GaP(001),"We report the epitaxial growth of CdCr2Se4, an n-type ferromagnetic
semiconductor, on both GaAs and GaP(001) substrates, and describe the
structural, magnetic and electronic properties. Magnetometry data confirm
ferromagnetic order with a Curie temperature of 130 K, as in the bulk material.
The magnetization exhibits hysteretic behavior with significant remanence, and
an in-plane easy axis with a coercive field of ~125 Oe. Temperature dependent
transport data show that the films are semiconducting in character and n-type
as grown, with room temperature carrier concentrations of n ~ 1 x 10^18 cm-3.",0205162v1
2002/10/8,Coulomb Correlations and Magnetic Anisotropy in ordered $L1_0$ CoPt and FePt alloys,"We present results of the magneto-crystalline anisotropy energy (MAE)
calculations for chemically ordered $L1_0$ CoPt and FePt alloys taking into
account the effects of strong electronic correlations and spin-orbit coupling.
The local spin density + Hubbard U approximation (LSDA+U) is shown to provide a
consistent picture of the magnetic ground state properties when intra-atomic
Coulomb correlations are included for both 3$d$ and 5$d$ elements. Our results
demonstrate significant and complex contribution of correlation effects to
large MAE of these material.",0210157v2
2003/1/22,Magnetic light scattering in low-dimensional quantum spin systems,"An overview of one- and two-dimensional quantum spin systems based on
transition-metal oxides and halides of current interest is given, such as
spin-Peierls, spin-dimer, geometrically frustrated and ladder systems. The most
significant and outstanding contributions of magnetic light scattering to the
understanding of these materials are discussed and compared to results of other
spectroscopies and thermodynamic measurements.",0301413v1
2003/4/8,Novel surface anisotropy term in the FMR spectra of amorphous microwires,"Some recent publications on ferromagnetic resonance in amorphous wires
mention presumably new kind of anisotropy, called there circumferential
anisotropy, as an explanation of various spectral features. In this paper we
argue that there is no special reason to speak of the new kind of anisotropy,
since the observed spectra can be well described in terms of more traditional
uniaxial and surface anisotropies alone.",0304195v1
2003/9/29,Nanometers-thick self-organized Fe stripes: bridging the gap between surfaces and magnetic materials,"We have fabricated 5nm-high Fe(110) stripes by self-organized (SO) growth on
a slightly vicinal R(110)/Al2O3(11-20) surface, with R=Mo, W. Remanence,
coercivity and domain patterns were observed at room temperature (RT). This
contrasts with conventional SO epitaxial systems, that are superparamagnetic or
even non-magnetic at RT due to their flatness. Our process should help to
overcome superparamagnetism without compromise on the lateral size if SO
systems are ever to be used in applications.",0309681v2
2003/10/23,Correlation between the Extraordinary Hall Effect and Resistivity,"We study the contribution of different types of scattering sources to the
extraordinary Hall effect. Scattering by magnetic nano-particles embedded in
normal-metal matrix, insulating impurities in magnetic matrix, surface
scattering and temperature dependent scattering are experimentally tested. Our
new data, as well as previously published results on a variety of materials,
are fairly interpreted by a simple modification of the skew scattering model.",0310551v1
2004/9/29,Large magnetoresistance at room-temperature in semiconducting polymer sandwich devices,"We report on the discovery of a large, room temperature magnetoresistance
(MR) effect in polyfluorene sandwich devices in weak magnetic fields. We
characterize this effect and discuss its dependence on voltage, temperature,
film thickness, electrode materials, and (unintentional) impurity
concentration. We usually observed negative MR, but positive MR can also be
achieved under high applied electric fields. The MR effect reaches up to 10% at
fields of 10mT at room temperature. The effect shows only a weak temperature
dependence and is independent of the sign and direction of the magnetic field.
We find that the effect is related to the hole current in the devices.",0409753v1
2004/11/2,Anisotropic electron g-factor in quantum dots with spin-orbit interaction,"g-factor tuning of electrons in quantum dots is studied as function of
in-plane and perpendicular magnetic fields for different confinements. Rashba
and Dresselhaus effects are considered, and comparison is made between wide-
and narrow-gap materials. The interplay between magnetic fields and intrinsic
spin-orbit coupling is analyzed, with two distinct phases found in the spectrum
for GaAs in perpendicular field. The anisotropy of the g-factor is reported,
and good agreement with available experimental findings is obtained.",0411071v1
2004/12/19,Oscillatory spin relaxation rates in quantum dots,"Phonon-induced spin relaxation rates in quantum dots are studied as function
of in-plane and perpendicular magnetic fields, temperature and electric field,
for different dot sizes. We consider Rashba and Dresselhaus spin-orbit mixing
in diferent materials, and show how Zeeman sublevels can relax via
piezoelectric and deformation potential coupling to acoustic phonons. We find
that strong lateral and vertical confinements may induce minima in the rates at
particular values of the magnetic field, where spin relaxation times can reach
even seconds. We obtain good agreement with experimental findings in GaAs
quantum dots.",0412520v1
2005/2/10,How to determine model Hamiltonians for strongly correlated materials,"The present paper reviews recent achievements on the ab initio determination
of effective model Hamiltonians aimed at the description of strongly correlated
materials. These models (Heisenberg, $t-J$, extended Hubbard, Kondo, etc) are
crucial to solid state physicists for the description and understanding of the
electronic remarkable properties such as magnetic orders, photo-induced
magnetism, transport properties, high $t\_c$ super conductivity, etc. We will
see how the association and the control of embedding techniques, fragment
spectroscopy, effective or intermediate Hamiltonian theories, provides a
systematic and well controlled method for the determination of trustworthy
models Hamiltonians.",0502268v1
2005/2/13,"Magnetic Field Dependence of CDW Phases in Per2M(mnt)2 (M=Pt, Au)","Recently the authors discovered that the suppression of the charge density
wave (CDW) ground states by high magnetic fields in the organic conductor
series Per2M(mnt)2 is followed by additional high field, CDW-like phases. The
purpose of this presentation is to review these compounds, to consider the
relevant parameters of the materials that describe the manner in which the CDW
ground state may undergo new field induced changes above the Pauli limit.",0502313v1
2005/5/3,Two-band second moment model for transition metals and alloys,"A semi-empirical formalism based on the second moment tight binding approach,
considering two bands is presented for deriving interatomic potentials for
magnetic d-band materials and transition metal alloys. It incorporates an
empirical local exchange interaction, which accounts for magnetic effects
without increasing the computing time required for force evaluation. The
consequences of applying a two-band picture to transition metal alloys and
transition metal impurities is examined, which combined with evidence from {\it
ab initio calculations} leads to some surprisingly simplifying conclusions.",0505060v1
2005/8/15,Electronic structure and anisotropic transport properties in hexagonal YPtIn and LuAgGe ternary compounds,"We present anisotropic, zero applied magnetic field, temperature dependent
resistivity measurements on hexagonal, non-magnetic, YPtIn and LuAgGe single
crystals. For these materials the in-plane resistivity, $\rho_{ab}$, is
significantly higher than the $c$ - axis one, $\rho_c$, with $\rho_{ab}/\rho_c
\approx 1.4$ for YPtIn and $\approx 4.2 - 4.7$ for LuAgGe. The connection
between the electronic structure and the anisotropic transport properties is
discussed using density functional calculations that link the observed
anisotropy with a specific shape of Fermi surface and anisotropy of the Fermi
velocities.",0508346v1
2005/9/1,Interlayer Aharonov-Bohm interference in tilted magnetic fields in quasi-one-dimensional layered conductors,"Different types of angular magnetoresistance oscillations in
quasi-one-dimensional layered materials, such as organic conductors (TMTSF)2X,
are explained in terms of Aharonov-Bohm interference in interlayer electron
tunneling. A two-parameter pattern of oscillations for generic orientations of
a magnetic field is visualized and compared with the experimental data.
Connections with angular magnetoresistance oscillations in other layered
materials are discussed.",0509039v2
2006/2/16,Disorder-Induced First Order Transition and Curie Temperature Lowering in Ferromagnatic Manganites,"We study the effect that size disorder in the cations surrounding manganese
ions has on the magnetic properties of manganites. This disorder is mimic with
a proper distribution of spatially disordered Manganese energies. Both, the
Curie temperature and the order of the transition are strongly affected by
disorder. For moderate disorder the Curie temperature decreases linearly with
the the variance of the distribution of the manganese site energies, and for a
disorder comparable to that present in real materials the transition becomes
first order. Our results provide a theoretical framework to understand disorder
effects on the magnetic behavior of manganites.",0602392v1
2006/2/24,Magnetocaloric effect in hexacyanochromate Prussian blue analogs,"We report on the magnetocaloric properties of two molecule-based
hexacyanochromate Prussian blue analogs, nominally CsNi[Cr(CN)_6](H_2O) and
Cr_3[Cr(CN)_6]_2x12(H_2O). The former orders ferromagnetically below Tc=90 K,
whereas the latter is a ferrimagnet below Tc=230 K. For both, we find
significantly large magnetic entropy changes DSm associated to the magnetic
phase transitions. Notably, our studies represent the first attempt to look at
molecule-based materials in terms of the magnetocaloric effect for temperatures
well above the liquid helium range.",0602589v1
2006/5/18,Intrinsic inhomogeneities and effects of resistive switching in doped manganites,"The effect of resistive switching in doped manganites being in the
ferromagnetic state has been studied using resistive and magneto-optic methods.
The visualization of magnetic structure of La0.75Sr0.25MnO3-x single crystals,
and its transformation under electric current proposed local superheating of
the material above the Curie temperature, which was supported by numerical
calculation. The obtained results suggest a significant role of
micrometer-scale inhomogeneity of manganites in phase separation, magnetic and
transport properties of the material.",0605457v1
2006/6/20,Orthorhombic to tetragonal phase transition and superconductivity in the Ba2Cu3O4Cl2 compound,"In this work we have investigated the orthorhombic to tetragonal phase
transition in the Ba2Cu3O4Cl2 compound. This transition was observed by X-ray
powder diffractometry carried out in samples heat treated between 700 and 750OC
and also in samples with Ba2ZnCu2O4Cl2 composition. Results of X-ray
diffractograms simulation confirm the phase transition. dc-Magnetization
measurements performed in SQUID showed the existence of diamagnetism signal.
The results suggest the existence of localized superconductivity and can
explain the different magnetic properties reported in literature for the
Ba2Cu3O4Cl2 compound.",0606524v1
2006/6/30,Quantum Spin Hall Effect and Enhanced Magnetic Response by Spin-Orbit Coupling,"We show that the spin Hall conductivity in insulators is related with a
magnetic susceptibility representing the strength of the spin-orbit coupling.
We use this relationship as a guiding principle to search real materials
showing quantum spin Hall effect. As a result, we theoretically predict that
bismuth will show the quantum spin Hall effect, both by calculating the helical
edge states, and by showing the non-triviality of the Z_2 topological number,
and propose possible experiments.",0607001v2
2006/7/24,A possibility of increasing spin injection efficiency in magnetic junctions,"Nonequilibrium electron spin polarization is calculated under spin injection
from one ferromagnet to another in magnetic junction. It is shown that the
nonequilibrium spin polarization can be comparable with equilibrium one if the
material parameters are chosen appropriately. This leads to lowering the
threshold current density necessary for the junction switching and opens a
perspective to creating THz laser based on the spin-polarized current
injection.",0607592v2
2006/10/19,Mesoscopic magnetism in dielectric photonic crystal meta materials: topology and inhomogeneous broadening,"We consider meta materials made from a two-dimensional dielectric rod-type
photonic crystal. The magnetic response is studied within the recently
developed homogenization theory and we in particular study the effects of
topology and inhomogeneous broadening. While topology itself mainly affects the
Mie resonance frequency we find that the dispersion in the topological radius R
of the dielectric rods may lead to significant inhomogeneous broadening and
suppression of the negative-mu phenomena for dR/R0 >> epsilon''/epsilon', with
epsilon=epsilon'+i*epsilon'' being the relative dielectric function of the
rods.",0610529v1
2007/1/22,Electronic structure and magnetism in the frustrated antiferromagnet LiCrO2,"LiCrO2 is a 2D triangular antiferromagnet, isostructural with the common
battery material LiCoO2 and a well-known Jahn-Teller antiferromagnet NaNiO2. As
opposed to the latter, LiCrO2 exibits antiferromagnetic exchange in Cr planes,
which has been ascribed to direct Cr-Cr d-d overlap. Using LDA and LDA+U first
principles calculations I confirm this conjecture and show that (a) direct d-d
overlap is indeed enhanced compared to isostructural Ni and Cr compounds, (b)
p-d charge transfer gap is also enhanced, thus suppressing the ferromagnetic
superexchange, (c) the calculated magnetic Hamiltonian maps well onto the
nearest neighbors Heisenberg exchange model and (d) interplanar inteaction is
antiferromagnetic.",0701520v1
2004/12/16,Theory of mesoscopic magnetism in meta-materials,"We provide a rigorous theoretical basis for the artificial magnetic activity
of meta-materials near resonances. Our approach is a renormalization-based
scheme that authorises a completely general theory. The major result is an
explicit expression of the effective permeability, in terms of resonant
frequencies. The theoretical results are checked numerically and we give
applications of our theory to Left-Handed Media and to the solution of the
Pokrovski-Efros paradox.",0412094v1
2007/4/5,Tri-layer superlattices: A route to magnetoelectric multiferroics?,"We explore computationally the formation of tri-layer superlattices as an
alternative approach for combining ferroelectricity with magnetism to form
magnetoelectric multiferroics. We find that the contribution to the
superlattice polarization from tri-layering is small compared to typical
polarizations in conventionalferroelectrics, and the switchable ferroelectric
component is negligible. In contrast, we show that epitaxial strain and
``negative pressure'' can yield large, switchable polarizations that are
compatible with the coexistence of magnetism, even in materials with no active
ferroelectric ions.",0704.0781v3
2007/6/5,Room-temperature ferromagnetism in nanoparticles of superconducting materials,"Nanoparticles of superconducting YBa2Cu3O7-delta (YBCO) (Tc = 91 K) exhibit
ferromagnetism at room temperature while the bulk YBCO, obtained by heating the
nanoparticles at high temperature (940 degree C), shows a linear magnetization
curve. Across the superconducting transition temperature, the magnetization
curve changes from that of a soft ferromagnet to a superconductor. Furthermore,
our experiments reveal that not only nanoparticles of metal oxides but also
metal nitrides such as NbN (Tc = 6 - 12 K) and delta-MoN (Tc ~ 6 K) exhibit
room-temperature ferromagnetism.",0706.0634v1
2007/12/30,Lecture Notes on Semiconductor Spintronics,"These informal lecture notes describe the progress in semiconductor
spintronics in a historic perspective as well as in a comparison to
achievements of spintronics of ferromagnetic metals. After outlining
motivations behind spintronic research, selected results of investigations on
three groups of materials are presented. These include non-magnetic
semiconductors, hybrid structures involving semiconductors and ferromagnetic
metals, and diluted magnetic semiconductors either in paramagnetic or
ferromagnetic phase. Particular attention is paid to the hole-controlled
ferromagnetic systems whose thermodynamic, micromagnetic, transport, and
optical properties are described in detail together with relevant theoretical
models.",0801.0145v1
2008/3/6,First-principles approach to lattice-mediated magnetoelectric effects,"We present a first-principles scheme for the computation of the
magnetoelectric response of magnetic insulators. The method focuses on the
lattice-mediated part of the magnetic response to an electric field, which we
argue can be expected to be the dominant contribution in materials displaying a
strong magnetoelectric coupling. We apply our method to Cr2O3, a relatively
simple and experimentally well studied magnetoelectric compound.",0803.0856v1
2008/5/21,Giant Magnetoelectric Effect in a Multiferroic Material with a High Ferroelectric Transition Temperature,"We present a unique example of giant magnetoelectric effect in a conventional
multiferroic HoMnO3, where polarization is very large (~56 mC/m2) and the
ferroelectric transition temperature is higher than the magnetic ordering
temperature by an order. We attribute the uniqueness of the giant
magnetoelectric effect to the ferroelectricity induced entirely by the
off-center displacement of rare earth ions with large magnetic moments. This
finding suggests a new avenue to design multiferroics with large polarization
and higher ferroelectric transition temperature as well as large
magnetoelectric effects.",0805.3289v1
2008/6/6,Conductive nanodots on the surface of irradiated CaF2,"CaF2(111) single crystal surfaces have been irradiated with swift heavy ions
under oblique angles resulting in chains of nanosized hillocks. In order to
characterize these nanodots with respect to their conductivity we have applied
non-contact atomic force microscopy using a magnetic tip. Measurements in UHV
as well as under ambient conditions reveal a clearly enhanced electromagnetic
interaction between the magnetic tip and the nanodots. The dissipated energy
per cycle is comparable to the value found for metals, indicating that the
interaction of the ion with the target material leads to the creation of
metallic Ca nanodots on the surface.",0806.1107v1
2008/6/10,Negative refraction in active and passive media: a discussion of various criteria,"There are three widely-used conditions for characterizing negative refraction
in isotropic dielectric-magnetic materials. Here we demonstrate that whilst all
the different conditions are equivalent for purely passive media, they are
distinct if active media are considered. Further, these criteria can also be
applied to negative refraction in acoustic materials, where we might replace
the dielectric permittivity $\epsilon$ with a bulk modulus $\kappa$, and the
magnetic permeability $\mu$ with the mass density $\rho$.",0806.1676v2
2008/7/4,"Short note on magnetic impurities in SmFeAsO$_{1-x}$F$_x$ (x=0, 0.07) compounds revealed by zero-field $^{75}$As NMR","We have performed zero-field $^{75}$As nuclear magnetic resonance study of
SmFeAsO$_{1-x}$F$_x$ (x=0, 0.07) polycrystals in a wide frequency range at
various temperatures. $^{75}$As resonance line was found at around 265 MHz
revealing the formation of the intermetallic FeAs clusters in the new layered
superconductors. We have also demonstrated that NMR is a sensitive tool for
probing the quality of these materials.",0807.0769v2
2008/7/16,Analytical solution of the equation of motion for a rigid domain wall in a magnetic material with perpendicular anisotropy,"This paper reports the solution of the equation of motion for a domain wall
in a magnetic material which exhibits high magneto-crystalline anisotropy.
Starting from the Landau-Lifschitz-Gilbert equation for field-induced motion,
we solve the equation to give an analytical expression, which specifies the
domain wall position as a function of time. Taking parameters from a Co/Pt
multilayer system, we find good quantitative agreement between calculated and
experimentally determined wall velocities, and show that high field uniform
wall motion occurs when wall rigidity is assumed.",0807.2604v3
2008/9/7,Magnetic properties of Co-doped TiO2 anatase nanopowders,"This letter reports on the magnetic properties of Ti1-xCoxO2 anatase phase
nanopowders with different Co contents. It is shown that oxygen vacancies play
a fundamental role in promoting the long-range ferromagnetic order in the
material studied, in addition to the transition-metal doping. Furthermore, the
results allow ruling out the premise of a strict connection between Co
clustering and the ferromagnetism observed in the Co:TiO2 anatase system.",0809.1256v2
2008/10/2,Superexchange-Driven Magnetoelectricity in Magnetic Vortices,"We demonstrate that magnetic vortices in which spins are coupled to polar
lattice distortions via superexchange exhibit an unusually large linear
magnetoelectric response. We show that the periodic arrays of vortices formed
by frustrated spins on Kagom\'e lattices provide a realization of this concept;
our {\it ab initio} calculations for such a model structure yield a
magnetoelectric coefficient that is 30 times larger than that of prototypical
single phase magnetoelectrics. Finally, we identify the design rules required
to obtain such a response in a practical material.",0810.0552v1
2008/10/28,Colossal magnetocapacitive effect in differently synthesized and doped CdCr2S4,"In the present work, we address the question of an impurity-related origin of
the colossal magnetocapacitive effect in the spinel system CdCr2S4. We
demonstrate that a strong variation in the dielectric constant below the
magnetic transition temperature or in external magnetic fields also arises in
crystals prepared without chlorine. This excludes that an inhomogeneous
distribution of chlorine impurities at the surface or in the bulk material
gives rise to the unusual effects in the spinel multiferroics. In addition, we
show that colossal magnetocapacitive effects can be also generated in
chlorine-free ceramic samples of CdCr2S4, doped with indium.",0810.5013v1
2008/11/20,Interlayer exchange coupling in Co2FeAl0.5Si0.5/Cr/Co2FeAl0.5Si0.5 trilayers,"Interlayer exchange couplings were examined for Co2FeAl0.5Si0.5(CFAS)/Cr/CFAS
trilayered films grown on MgO (001) single crystal and thermally oxidized Si
substrates. The films were (001) epitaxial on MgO and (110) textured
polycrystalline on SiO2. Strong exchange couplings were observed for the films
with the 1.5 nm thick Cr spacer layer. A 90 degree coupling is dominant in the
(001) epitaxial film. In contrast, an antiparallel coupling exists in the
polycrystalline one. The relationship of interlayer couplings with the
structure is discussed.",0811.3278v1
2008/12/23,Magnetically induced electronic ferroelectricity in half-doped manganites,"Using a joint approach of density functional theory and model calculations,
we demonstrate that a prototypical charge ordered half-doped manganite,
La$_{1/2}$Ca$_{1/2}$MnO$_3$ is multiferroic. The combination of a peculiar
charge-orbital ordering and a tendency to form spin dimers breaks inversion
symmetry, leads to a ferroelectric ground-state with a polarization up to
several $\mu C/cm^2$. The presence of improper ferroelectricity does not depend
on hotly debated structural details of this material: in the Zener-polaron
structure we find a similar dramatic ferroelectric response with a large
polarization of purely magnetic origin.",0812.4380v1
2009/3/26,Field theory for magnetic and lattice structure properties of Fe_{1+y}Te_{1-x}Se_x,"We study the magnetism and lattice distortion of Fe_{1+y}Te_{1-x}Se_x with a
general field theory formalism, motivated by recent neutron scattering
experiments. Besides the Ising nematic order parameter which can be naturally
defined in the 1111 and 122 materials, We show that the collinear order
observed in $\mathrm{Fe_{1+y}Te}$ materials is stabilized by an extra Ising
order parameter which doubles the generalized unit cell of the system. By
tuning this Ising order parameter, one can drive a transition between collinear
and noncollinear spin density wave orders, both of which are observed in the
FeTe family. The nature of the quantum and classical phase transitions are also
studied in this field theory formalism, with lattice strain tensor fluctuation
considered.",0903.4477v1
2009/4/18,Magnetic circular dichroism in GaMnAs: (no) evidence for an impurity band,"Magneto-optical properties of the ferromagnetic semiconductor GaMnAs are
studied in a material specific multi-band tight-binding approach. Two realistic
models are compared: one has no impurity band while the other shows an impurity
band for low Mn concentrations. The calculated magnetic circular dichroism
(MCD) is positive for both models proving that, unlike previously asserted, the
observed positive MCD signal is inconclusive as to the presence or absence of
an impurity band in GaMnAs. The positive MCD is due to the antiferromagnetic
p-d coupling and the transitions into the conduction band.",0904.2864v2
2009/5/3,Magnetic state electrical readout of Mn12 molecules,"We demonstrate that the different magnetic states of a Mn12 molecule can be
distinguished in a two-probe transport experiment from a complete knowledge of
the current-voltage curve. Our results, obtained with state-of-the-art
non-equilibrium transport methods combined with density functional theory,
demonstrate that spin configuration-specific negative differential resistances
(NDRs) appear in the I-V curves. These originate from the interplay between
electron localization and the re-hybridization of the molecular levels in an
external electric field and allow the detection of the molecule's spin-state.",0905.0281v1
2009/5/13,Hysteretic magnetoresistance in polymeric diodes,"We report on hysteretic organic magnetoresistance (OMAR) in polymeric diodes.
We found that magnitude and lineshape of OMAR depends strongly on the scan
speed of the magnetic field and on the time delay between two successive
measurements. The time-dependent OMAR phenomenon is universal for diodes made
with various polymers. However, the width and magnitude of OMAR varied with the
polymeric material. The suggestive reason for this hysteretic behavior are
trapped carriers, which in presence of a magnetic field changes the
ferromagnetic ground-state of the polymer leading to long spin relaxation time.
These experimental observations are significant for clarification of the OMAR
phenomenon.",0905.2025v1
2009/12/17,Interatomic forces for transition metals including magnetism,"}We present a formalism for extending the second moment tight-binding model,
incorporating ferro- and anti-ferromagn etic interaction terms which are needed
for the FeCr system. For antiferromagnetic and paramagnetic materials, an
explicit additional variable representing the spin is required. In a mean-field
approximation this spin can be eliminated, and the potential becomes explicitly
temperature dependent. For ferromagnetic interactions, this degree of freedom
can be eliminated, and the formalism reduces to the embedded atom method (EAM)
and we show the equivale nce of existing EAM potentials to ""magnetic""
potentials.",0912.3439v1
2010/2/22,Electrically Detected Magnetic Resonance Applied to the Study of Near Surface Electron Donors in Silicon,"Electrically detected magnetic resonance (EDMR) is applied to mm size devices
with implanted leads and a 50 micron square gap laid down on bulk phosphorus
doped silicon. Devices with a range of phosphorus concentrations and surface
types were prepared and measured to examine the interplay between donor and
charge trap states in producing EDMR signals.",1002.4071v1
2010/3/26,Structurally driven metamagnetism in MnP and related Pnma compounds,"We investigate the structural conditions for metamagnetism in MnP and related
materials using Density Functional Theory. A magnetic stability plot is
constructed taking into account the two shortest Mn-Mn distances. We find that
a particular Mn-Mn separation plays the dominant role in determining the change
from antiferromagnetic to ferromagnetic order in such systems. We establish a
good correlation between our calculations and structural and magnetic data from
the literature. Based on our approach it should be possible to find new
Mn-containing alloys that possess field-induced metamagnetism and associated
magnetocaloric effects.",1003.5193v2
2010/5/11,Size-dependent spin-reorientation transition in Nd2Fe14B nanoparticles,"Nd2Fe14B magnetic nanoparticles have been successfully produced using a
surfactant-assisted ball milling technique. The nanoparticles with different
size about 6, 20 and 300 nm were obtained by a size-selection process.
Spin-reorientation transition temperature of the NdFeB nanoparticles was then
determined by measuring the temperature dependence of DC and AC magnetic
susceptibility. It was found that the spin-reorientation transition temperature
(Tsr) of the nanoparticles is strongly size dependent, i.e., Tsr of the 300 nm
particles is lower than that of raw materials and a significant decrease was
observed in the 20 nm particles.",1005.1706v1
2010/5/25,Low-temperature nuclear and magnetic structures of La2O2Se2.Fe2O from X-ray and neutron diffraction measurements,"This paper describes the low temperature nuclear and magnetic structures of
La2O2Se2.Fe2O by analysis of X-ray and neutron diffraction data. The material
has been demonstrated to order antiferromagnetically at low temperatures, with
TN \approx 90 K a propagation vector of k = (1/2 0 1/2), resulting in a spin
arrangement similar to that in FeTe, despite there being no apparent lowering
in symmetry of the nuclear structure.",1005.4600v2
2010/6/30,Control of the structural and magnetic properties of perovskite oxide ultrathin films through the substrate symmetry effect,"Perovskite transition-metal oxides are networks of corner-sharing octahedra
whose tilts and distortions are known to affect their electronic and magnetic
properties. We report calculations on a model interfacial structure to avoid
chemical influences and show that the symmetry mismatch imposes an interfacial
layer with distortion modes that do not exist in either bulk material, creating
new interface properties driven by symmetry alone. Depending on the resistance
of the octahedra to deformation, the interface layer can be as small as one
unit cell or extend deep into the thin film.",1006.5758v1
2010/7/13,Magnetic-field control of the electric polarization in BiMnO3,"We present the microscopic theory of improper multiferroicity in BiMnO3,
which can be summarized as follows: (1) the ferroelectric polarization is
driven by the hidden antiferromagnetic order in the otherwise centrosymmetric
C2/c structure; (2) the relativistic spin-orbit interaction is responsible for
the canted spin ferromagnetism. Our analysis is supported by numerical
calculations of electronic polarization using Berry's phase formalism, which
was applied to the low-energy model of BiMnO3 derived from the first-principles
calculations. We explicitly show how the electric polarization can be
controlled by the magnetic field and argue that BiMnO3 is a rare and
potentially interesting material where ferroelectricity can indeed coexist and
interplay with the ferromagnetism.",1007.2039v1
2010/12/6,Electrodynamics of Nearly Ferroelectric Superconductors in the non-local Pippard limit,"We report the structure of the magnetic field and secular current in a Nearly
Ferroelectric Superconducting (NFE-SC) thin film. It was shown that unlike in
conventional superconducting films, the external radiation causes alternating
pattern of current strips. The strength of the innermost current torrents is
governed by the laser field intensity as well as resonance with the
ferroelectric component. The latter is modeled by secular reflection and random
scattering in the Pippard non-local limit. Our calculations suggest that
corresponding magnetic field pattern affects vortex formation in such material.",1012.1229v1
2010/12/20,Electromagnetic force density in dissipative isotropic media,"We derive an expression for the macroscopic force density that a narrow-band
electromagnetic field imposes on a dissipative isotropic medium. The result is
obtained by averaging the microscopic form for Lorentz force density. The
derived expression allows us to calculate realistic electromagnetic forces in a
wide range of materials that are described by complex-valued electric
permittivity and magnetic permeability. The three-dimensional energy-momentum
tensor in our expression reduces for lossless media to the so-called Helmholtz
tensor that has not been contradicted in any experiment so far. The momentum
density of the field does not coincide with any well-known expression, but for
non-magnetic materials it matches the Abraham expression.",1012.4258v1
2011/2/25,Electrotransport and magnetic properies of Cr-GaSb spintronic materials synthesized under high pressure,"Electrotarnsport and magnetic properties of new phases in the system Cr-GaSb
were studied. The samples were prepared by high-pressure (P=6-8 GPa)
high-temperature treatment and identified by x-ray diffraction and scanning
electron microscopy (SEM). One of the CrGa$_2$Sb$_2$ phases with an
orthorhombic structure $Iba2$ has a combination of ferromagnetic and
semiconductor properties and is potentially promising for spintronic
applications. Another high-temperature phase is paramagnetic and identified as
tetragonal $I4/mcm$.",1102.5236v1
2011/3/22,Ferroelectricity from spin supercurrents in LiCuVO4,"We have studied the magnetic structure of the ferroelectric frustrated
spin-1/2 chain material LiCuVO4 in applied electric and magnetic fields using
polarized neutrons. A symmetry and mean-field analysis of the data rules out
the presence of static Dzyaloshinskii-Moriya interaction, while exchange
striction is shown to be negligible by our specific-heat measurements. The
experimentally observed magnetoelectric coupling is in excellent agreement with
the predictions of a purely electronic mechanism based on spin supercurrents.",1103.4319v1
2011/4/1,Magnetism and Charge ordering in TMTTF$_2$-PF$_6$ organic crystals,"Using a combination of Density Functional Theory, mean-field analysis and
exact diagonalization calculations we reveal the emergence of a dimerized
charge ordered state in TMTTF$_2$-PF$_6$ organic crystal. The interplay between
charge and spin order leads to a rich phase diagram. Coexistence of charge
ordering with a structural dimerization results in a ferroelectric phase, which
has been observed experimentally. The tendency to the dimerization is
magnetically driven revealing TMTTF$_2$-PF$_6$ as a multiferroic material.",1104.0113v1
2011/5/6,Radio frequency readout of electrically detected magnetic resonance in phosphorus-doped silicon MOSFETs,"We demonstrate radio frequency (RF) readout of electrically detected magnetic
resonance in phosphorus-doped silicon metal-oxide field-effecttransistors
(MOSFETs), operated at liquid helium temperatures. For the first time, the Si:P
hyperfine lines have been observed using radio frequency reflectometry, which
is promising for high-bandwidth operation and possibly time-resolved detection
of spin resonance in donor-based semiconductor devices. Here we present the
effect of microwave (MW) power and MOSFET biasing conditions on the EDMR
signals.",1105.1235v1
2011/8/10,Magnetic nanowires generated via the waterborne desalting transition pathway,"We report a simple and versatile waterborne synthesis of magnetic nanowires
following the innovative concept of electrostatic ""desalting transition"".
Highly persistent superparamagnetic nanowires are generated from the controlled
assembly of oppositely charged nanoparticles and commercially available
polyelectrolytes. The wires have diameters around 200 nm and lengths comprised
between 1 {\mu}m and 1/2 mm, with either positive or negative charges on their
surface. Beyond, we show that this soft-chemistry assembly approach is a
general phenomenon independent of the feature of the macromolecular building
blocks, opening significant perspectives for the design of multifunctional
materials.",1108.2082v1
2011/11/28,Description of conductivity steps in polymer and other materials by functions of p-adic argument,"We study the quantum jumps of physical quantities in a strongly correlated
many electron systems based on a new p-adic functional integral approach. It is
shown that a description in terms of the p-adic numbers leads to the fractal
behavior and can describe the quantum jumps in the conductivity and
magnetization as a function of voltage and magnetic field in nanotechnology
devices and low-dimensional strongly correlated organic metals and other
materials.",1111.6476v1
2011/12/12,On the Verdet constant and Faraday rotation for graphene-like materials,"We present a rigorous and rather self-contained analysis of the Verdet
constant in graphene- like materials. We apply the gauge-invariant magnetic
perturbation theory to a nearest- neighbour tight-binding model and obtain a
relatively simple and exactly computable formula for the Verdet constant, at
all temperatures and all frequencies of sufficiently large absolute value.
Moreover, for the standard nearest neighbour tight-binding model of graphene we
show that the transverse component of the conductivity tensor has an asymptotic
Taylor expansion in the external magnetic field where all the coefficients of
even powers are zero.",1112.2613v2
2012/1/7,Phase Transitions in Systems with Finite Number of Atoms,"Properties of nanoparticles have been studied within the framework of Ising
model and the method of random-field interactions: the average magnetic moment
and position of critical points of the magnetic and the concentration phase
transitions depending on their size. It is shown that the Curie temperature is
inversely proportional to the size of the particle. Critical concentration of
the ordered state decreases with increasing of size of nanoparticles until the
percolation threshold of ""massive"" particles.",1201.1562v2
2012/1/28,Photoinduced helical metal and magnetization in two-dimensional electron systems with spin-orbit coupling,"Helical metals realized at the surfaces of topological insulators have
recently attracted wide attention due to their potential applications in
spintronics. In this paper we propose to realize helical metals through the
application of THz light on common two-dimensional semiconductors and discuss
their observable properties. We show that the application of circularly
polarized light enables coherent manipulation of magnetization. Moreover, for a
range of chemical potentials the system behaves as a helical metal, exhibiting
a large anomalous Hall conductivity and associated magnetoelectric effect.
Proposed dynamical engineering of material properties through light in
much-studied materials opens new perspectives for future applications.",1201.5997v1
2012/2/1,Spin state of negative charge-transfer material SrCoO3,"We employ the combination of the density functional and the dynamical
mean-field theory (LDA+DMFT) to investigate the electronic structure and
magnetic properties of SrCoO3, monocrystal of which were prepared recently. Our
calculations lead to a ferromagnetic metal in agreement with experiment. We
find that, contrary to some suggestions, the local moment in SrCoO3 does not
arise from intermediate spin state, but is a result of coherent superposition
of many different atomic states. We discuss how attribution of magnetic
response to different atomic states in solids with local moments can be
quantified.",1202.0110v2
2012/3/8,Origin of Magnetic Circular Dichroism in GaMnAs: Giant Zeeman Splitting versus Spin Dependent Density of States,"We present a unified interpretation of experimentally observed magnetic
circular dichroism (MCD) in the ferromagnetic semiconductor (Ga,Mn)As, based on
theoretical arguments, which demonstrates that MCD in this material arises
primarily from a difference in the density of spin-up and spin-down states in
the valence band brought about by the presence of the Mn impurity band, rather
than being primarily due to the Zeeman splitting of electronic states.",1203.1853v1
2012/4/15,The critical current density in type-II superconducting bulk materials,"The critical current density Jc in type-II conventional and high-Tc
superconducting bulk materials is investigated based on the quantum theory for
the vortex dynamics. It is shown that for a constant magnetic field, the
critical current density Jc decreases weakly with increasing temperature when
T<T_dp(depinning temperature); when T_dp< T <T_f (boundary fluctuation
temperature,Jc is power-law-decaying,and when T>T_f,Jc decays exponentially;
while for a constant temperature, Jc first decreases, then increases after
reaching a maximum, and finally decreases again as the magnetic field
increases. These results are in agreement with the experiments.",1204.3252v1
2012/7/2,Magneto-resistance in three-dimensional composites,"In this paper we study the magneto-resistance, i.e. the second-order term of
the resistivity perturbed by a low magnetic field, of a three-dimensional
composite material. Extending the two-dimensional periodic framework of [4], it
is proved through a H-convergence approach that the dissipation energy induced
by the effective magneto-resistance is greater or equal to the average of the
dissipation energy induced by the magneto-resistance in each phase of the
composite. This inequality validates for a composite material the Kohler law
which is known for a homogeneous conductor. The case of equality is shown to be
very sensitive to the magnetic fi eld orientation. We illustrate the result
with layered and columnar periodic structures.",1207.0468v1
2012/7/30,Strain engineering magnetic frustration in perovskite oxide thin films,"Our first-principles results show that geometric frustration can be induced
in thin films of multiferroic BiFeO3. We find that competing magnetic
interactions occur in the so-called super-tetragonal phase of this material,
which can be grown on strongly-compressive substrates. We show that the
frustration level can be tuned by appropriately choosing the substrate; in
fact, the three-dimensional spin order gets totally annihilated in a narrow
range of epitaxial strains. We argue that the effects revealed here are not
exclusive to BiFeO3, and predict that they also occur in multiferroic BiCoO3.",1207.6859v1
2012/9/4,Melting of hexagonal Skyrmion states in chiral magnets,"Skyrmions are spiral structures observed in thin films of certain magnetic
materials (10.1126/science.1120639). Of the phases allowed by the crystalline
symmetries of these materials(10.1103/PhysRevB.80.054416) only the hexagonally
packed phases (SC_h) has been observed. Here the melting of the $SC_h$ phase is
investigated using Monte Carlo simulations. In addition to the usual measure of
Skyrmion density chiral charge, a morphological measure is considered. In doing
so it is shown that the low temperature reduction in chiral charge is
associated with a change in Skyrmion profiles rather than Skyrmion destruction.
At higher temperatures the loss of six fold symmetry is associated with the
appearance of elongated Skyrmions that disrupt the hexagonal packing.",1209.0556v1
2012/9/25,Low-loss directional cloaks without superluminal velocity or magnetic response,"The possibility of making an optically large (many wavelengths in diameter)
object appear invisible has been a subject of many recent studies. Exact
invisibility scenarios for large (relative to the wavelength) objects involve
(meta)materials with superluminal phase velocity (refractive index less than
unity) and/or magnetic response. We introduce a new approximation applicable to
certain device geometries in the eikonal limit: piecewise-uniform scaling of
the refractive index. This transformation preserves the ray trajectories, but
leads to a uniform phase delay. We show how to take advantage of phase delays
to achieve a limited (directional and wavelength-dependent) form of
invisibility that does not require loss-ridden (meta)materials with
superluminal phase velocities.",1209.5627v1
2013/2/4,Disorder-induced cubic phase in Fe$_2$-based Heusler alloys,"Based on first-principles electronic structure calculations, we analyze the
chemical and magnetic mechanisms stabilizing the cubic phase in Fe$_2$-based
Heusler materials, which were previously predicted to be tetragonal when being
chemically ordered. In agreement with recent experimental data, we found that
these compounds crystallize within the so-called ""inverted"" cubic Heusler
structure perturbed by a certain portion of the intrinsic chemical disorder.
Understanding these mechanisms is a necessary step to guide towards the
successful future synthesis of the stable Fe$_2$-based tetragonal phases, which
are very promising candidates for the fabrication of rare-earth-free permanent
magnets.",1302.0713v1
2013/4/25,Superstripes : superconductivity in complex granular striped matter,"The role of phase separation and superstripes in high temperature
superconductors and related materials has been discussed at the meeting in
Erice, Italy, July 11 July 17, 2012. The focus was on the point where we are
after 25 years of research on the key role of complex structural, electronic,
and magnetic matter in the mechanism of high temperature superconductivity.",1304.6939v1
2013/7/11,Tuning the giant inverse magnetocaloric effect in Mn2-xCrxSb compounds,"Structural, magnetic and magnetocaloric properties of Mn2-xCrxSb compounds
have been studied. In these compounds a first order magnetic phase transition
from the ferrimagnetic to the antiferromagnetic state occurs with decreasing
temperature, giving rise to giant inverse magnetocaloric effects that can be
tuned over a wide temperature interval through changes in substitution
concentration. Entropy changes as high as 7.5 J/kgK have been observed, and a
composition independent entropy change is obtained for several different
concentrations/working temperatures, making these compounds suitable candidates
for a composite working material.",1307.3194v1
2013/9/14,Excellent magnetocaloric effect exhibited in the dense inorganic framework material Gd(OH)CO3,"The excellent magnetocaloric effect of a dense inorganic framework,
orthorhombic Gd(OH)CO3, is evaluated by isothermal magnetization and heat
capacity measurements. The large -{\Delta}Sm, both in gravimetric and
volumetric units, place it as a great candidate for cryogenic magnetic cooler.",1309.3653v1
2013/9/20,Magnetism and unusual Cu valency in quadruple perovskites,"We study a selection of Cu-containing magnetic quadruple perovskites
(CaCu$_{3}$Ti$_{4}$O$_{12}$, LaCu$_{3}$Fe$_{4}$O$_{12}$, and
YCu$_{3}$Co$_{4}$O$_{12}$) by ab initio calculations, and show that Cu is in an
effective divalent Cu(II)-like state or a trivalent Cu(III) state depending on
the choice of octahedral cation. Based on the electronic structure, we also
discuss the role of Mott and Zhang-Rice physics in this materials class.",1309.5186v1
2013/12/5,Magnetic properties of ferromagnetic Pu2Pt3Si5,"The structural, magnetic, and thermodynamic properties of a new plutonium
based compound, Pu2Pt3Si5, are reported. Single crystals produced by a Sn-flux
technique have been analyzed showing a ferromagnetic behavior at 58 K.
Pu2Pt3Si5 crystallizes in the U2Co3Si5-type orthorhombic Iabm structure (72)
with atomic parameters a = 9.9226(2) \AA, b = 11.4436(2) \AA and c = 6.0148(1)
\AA. The effective (\mu_eff ~0.74 \mu_B) and saturated (\mu_sat ~0.32 B/Pu)
moments as well as the Sommerfeld coefficient (\gamma_e ~2 mJ.mol-1.K-2/Pu)
could point towards 5f localization in this material.",1312.1576v1
2013/12/16,Physical properties of CeGe2-x (x = 0.24) single crystals,"We present data on the anisotropic magnetic properties, heat capacity and
transport properties of CeGe2-x (x = 0.24) single crystals. The electronic
coefficient of the heat capacity, gamma ~ 110 mJ/mol K^2, is enhanced; three
magnetic transitions, with critical temperatures of ~ 7 K, ~ 5 K, and ~ 4 K are
observed in thermodynamic and transport measurements. The ground state has a
small ferromagnetic component along the c - axis. Small applied field, below 10
kOe, is enough to bring the material to an apparent saturated paramagnetic
state (with no further metamagnetic transitions up to 55 kOe) with a reduced,
below 1 mu_B, saturated moment.",1312.4580v1
2014/2/9,Synthesis of Fe3O4@CoFe2O4@MnFe2O4 trimagnetic core/shell/shell nanoparticles,"We report the synthesis and characterization of original 'multishell'
magnetic nanoparticles made of a soft core (magnetite) covered with two
successive shells: a hard one (cobalt ferrite) and then a soft one (manganese
ferrite). Our results show that contrary to expectations from simple models in
which the coercivity of a bimagnetic core/shell nanoparticle depends simply on
the proportion of soft and hard phases within that particle, the addition of a
second shell made of a soft ferrite material enhances the coercivity. Taking
into account the interactions between the shells themselves and the core may
thus be necessary to understand the magnetic properties of such nanoparticles.",1402.1950v1
2014/5/28,Atomic scale electron vortices for nanoresearch,"Electron vortex beams were only recently discovered and their potential as a
probe for magnetism in materials was shown. Here we demonstrate a new method to
produce electron vortex beams with a diameter of less than 1.2 \AA. This unique
way to prepare free electrons to a state resembling atomic orbitals is
fascinating from a fundamental physics point of view and opens the road for
magnetic mapping with atomic resolution in an electron microscope.",1405.7247v1
2014/9/3,Current Induced Fingering Instability in Magnetic Domain Walls,"The shape instability of magnetic domain walls under current is investigated
in a ferromagnetic (Ga,Mn)(As,P) film with perpendicular anisotropy. Domain
wall motion is driven by the spin transfer torque mechanism. A current density
gradient is found either to stabilize domains with walls perpendicular to
current lines or to produce finger-like patterns, depending on the domain wall
motion direction. The instability mechanism is shown to result from the
non-adiabatic contribution of the spin transfer torque mechanism.",1409.1007v3
2014/9/18,Spin-transfer torque induced spin waves in antiferromagnetic insulators,"We explore the possibility of exciting spin waves in insulating
antiferromagnetic films by injecting spin current at the surface. We analyze
both magnetically compensated and uncompensated interfaces. We find that the
spin current induced spin-transfer torque can excite spin waves in insulating
antiferromagnetic materials and that the chirality of the excited spin wave is
determined by the polarization of the injected spin current. Furthermore, the
presence of magnetic surface anisotropy can greatly increase the accessibility
of these excitations.",1409.5460v2
2014/11/13,Ab initio Disordered Local Moment Approach for a Doped Rare-Earth Magnet,"Following the finite-temperature ab initio calculation framework based on the
relativistic disordered local moments, we computationally demonstrate the
possibility of doping-enhanced coercivity at high-temperatures, taking YCo$_5$
as a working material in order to extract the $3d$-electron part of the
electronic structure of the rare-earth permanent magnets. Alkaline-earth
dopants are shown to be the candidates to realize the proposed phenomenon.",1411.3451v1
2015/1/23,Negative Refraction Induced by Möbius Topology,"We theoretically show the negative refraction existing in M\""{o}bius
molecules. The negative refractive index is induced by the non-trivial topology
of the molecules. With the M\""{o}bius boundary condition, the effective
electromagnetic fields felt by the electron in a M\""{o}bius ring is spatially
inhomogeneous. In this regard, the $D_{N}$ symmetry is broken in M\""{o}bius
molecules and thus the magnetic response is induced through the effective
magnetic field. Our findings open up a new architecture for negative refractive
index materials based on the non-trivial topology of M\""{o}bius molecules.",1501.05729v2
2015/6/7,"Comment on: Synthesis, growth and characterization of a new metal organic Nlo material: Dibromo bis(L proline)Cd(II)","The title paper by Boopathi and Ramasamy reports a study on the crystal
growth and characterization of dibromobis (L-proline)Cd(II) (1). Many points of
criticism, concerning the crystal structure of (1) and the magnetic properties
of (1) dibromo bis(L-proline)Zn(II) (2) and diiodo bis(2-aminopyridine)Cd(II)
(3) are reported to show that compounds 1 to 3 are not soft magnets but instead
diamagnetic solids.",1506.02252v1
2015/6/30,Spin-wave localization in disordered magnets,"The effect of disorder on magnonic transport in low-dimensional magnetic
materials is studied in the framework of a classical spin model. Numerical
investigations give insight into scattering properties of the systems and show
the existence of Anderson localization in 1D and weak localization in 2D,
potentially affecting the functionality of magnonic devices.",1506.09045v2
2015/8/19,Compact AC Susceptometer for Fast Sample Characterization down to 0.1 K,"We report a new design of an AC magnetic susceptometer compatible with the
Physical Properties Measurement System (PPMS) by Quantum Design, as well as
with its adiabatic demagnetization refrigerator option. With the elaborate
compact design, the susceptometer allows simple and quick sample mounting
process. The high performance of the susceptometer down to 0.1 K is
demonstrated using several superconducting and magnetic materials. This
susceptometer provides a method to quickly investigate qualities of a large
number of samples in the wide temperature range between 0.1 and 300 K.",1508.04684v1
2015/12/15,Magnon Dirac materials,"We demonstrate how a Dirac-like magnon spectrum is generated for localized
magnetic moments forming a two-dimensional honeycomb lattice. The Dirac
crossing point is proven to be robust against magnon-magnon interactions, as
these only shift the spectrum. Local defects induce impurity resonances near
the Dirac point, as well as magnon Friedel oscillations. The energy of the
Dirac point is controlled by the exchange coupling, and thus a two-dimensional
array of magnetic dots is an experimentally feasible realization of Dirac
magnons with tunable dispersion.",1512.04902v2
2016/2/25,Gigantic directional asymmetry of luminescence in multiferroic CuB2O4,"We report direction dependent luminescence (DDL), i.e., the asymmetry in the
luminescence intensity between the opposite directions of the emission, in
multiferroic CuB2O4. Although it is well known that the optical constants can
change with the reversal of the propagation direction of light in multiferroic
materials, the largest asymmetry in the luminescence intensity was 0.5 % so
far. We have performed a measurement of photoluminescence with a He-Ne laser
irradiation (633 nm). The luminescence intensity changes by about 70 % with the
reversal of the magnetic field due to the interference between the electric
dipole and magnetic dipole transitions. We also demonstrate the imaging of the
canted antiferromagnetic domain structure of (Cu,Ni)B2O4 by using the large
DDL.",1602.08013v1
2016/3/30,Large linear magnetoresistance in a new Dirac material BaMnBi2,"We report the synthesis of high quality single crystals of BaMnBi2 and
investigate the transport properties of the samples. The Hall data reveals
electron-type carriers and a mobility mu(5K) =1500cm2/Vs. The temperature
dependence of magnetization displays behavior that is different from CaMnBi2 or
SrMnBi2 , which suggests the possible different magnetic structure of BaMnBi2.
Angle-dependent magnetoresistance reveals the quasi-two-dimensional Fermi
surface. A crossover from semiclassical MR-H2 dependence in low field to MR-H
dependence in high field is observed in transverse magnetoresistance. Our
results indicate the anisotropic Dirac fermion states in BaMnBi2.",1603.09117v1
2016/4/12,The disappearing momentum of the supercurrent in the superconductor to normal phase transformation,"A superconductor in a magnetic field has surface currents that prevent the
magnetic field from penetrating its interior. These currents carry kinetic
energy and mechanical momentum. When the temperature is raised and the system
becomes normal the currents disappear. Where do the kinetic energy and
mechanical momentum of the currents go, and how? Here we propose that the
answer to this question reveals a key necessary condition for materials to be
superconductors, that is not part of conventional BCS-London theory:
superconducting materials need to have hole carriers.",1604.03565v1
2016/4/21,Model for multi-shot all-thermal all-optical switching in ferromagnets,"All optical magnetic switching (AOS) is a recently observed rich and puzzling
phenomenon that offers promis- ing technological applications. However,
fundamental understanding of the underlying mechanisms remains elusive. Here we
present a new model for multi-shot helicity-dependent AOS in ferromagnetic
materials based on a purely heat-driven mechanism in the presence of Magnetic
Circular Dichroism (MCD). We predict that AOS should be possible with as little
as 0.5% of MCD, after a minimum number of laser shots. Finally, we re- produce
previous AOS results by simulating the sweeping of a laser beam on an FePtC
granular ferromagnetic film.",1604.06441v1
2016/5/23,Large magnetic anisotropy in Fe_{0.25}TaS_2,"We present a first-principles study of the large magneto-crystalline
anisotropy in the intercalated di-chalcogenide material \ce{Fe_{0.25}TaS_2},
investigated with the DFT+U approach. We verify a uniaxial magnetocrystalline
anisotropy energy(MAE) of 15meV/Fe. in the material. We further analyze the
dependence of MAE on the constituent elements and the effect of spin-orbit
coupling. Contrary to conventional intuition, we find a small contribution to
MAE due to strong spin-orbit coupling in the heavier element, Ta. We show that
the electronic configuration, crystal field environment and correlational
effects of the magnetic ion are more important.",1605.07141v1
2016/10/10,Modeling of Spatial Uncertainties in the Magnetic Reluctivity,"In this paper a computationally efficient approach is suggested for the
stochastic modeling of an inhomogeneous reluctivity of magnetic materials.
These materials can be part of electrical machines, such as a single phase
transformer (a benchmark example that is considered in this paper). The
approach is based on the Karhunen-Lo\`{e}ve expansion. The stochastic model is
further used to study the statistics of the self inductance of the primary coil
as a quantity of interest.",1610.02796v1
2017/1/23,Charge and spin transport on graphene grain boundaries in a quantizing magnetic field,"We study charge and spin transport along grain boundaries in single layer
graphene in the presence of a quantizing magnetic field. Transport states in a
grain boundary are produced by hybridization of Landau zero modes with
interfacial states. In selected energy regimes quantum Hall edge states can be
deflected either fully or partially into grain boundary states. The degree of
edge state deflection is studied in the nonlocal conductance and in the shot
noise. We also consider the possibility of grain boundaries as gate-switchable
spin filters, a functionality enabled by counterpropagating transport channels
laterally confined in the grain boundary.",1701.06490v1
2017/4/11,Ferromagnetic and insulating behavior of LaCoO3 films grown on a (001) SrTiO3 substrate. A simple ionic picture explained ab initio,"This paper shows that the oxygen vacancies observed experimentally in thin
films of LaCoO3 subject to tensile strain are thermodynamically stable
according to ab initio calculations. By using DFT calculations, we show that
oxygen vacancies on the order of 6 % forming chains perpendicular to the (001)
direction are more stable than the stoichiometric solution. These lead to
magnetic Co2+ ions surrounding the vacancies that couple ferromagnetically. The
remaining Co3+ cations in an octahedral environment are non magnetic. The gap
leading to a ferromagnetic insulating phase occurs naturally and we provide a
simple ionic picture to explain the resulting electronic structure.",1704.03240v1
2017/10/8,Hall effect spintronics for gas detection,"We present the concept of magnetic gas detection by the Extraordinary Hall
effect (EHE). The technique is compatible with the existing conductometric gas
detection technologies and allows simultaneous measurement of two independent
parameters: resistivity and magnetization affected by the target gas.
Feasibility of the approach is demonstrated by detecting low concentration
hydrogen using thin CoPd films as the sensor material. The Hall effect
sensitivity of the optimized samples exceeds 240% per 104 ppm at hydrogen
concentrations below 0.5% in the hydrogen/nitrogen atmosphere, which is more
than two orders of magnitude higher than the sensitivity of the conductance
detection.",1710.03700v1
2017/12/28,A three-dimensional magnetic topological phase,"We use photoemission spectroscopy to discover the first topological magnet in
three dimensions, the material Co$_2$MnGa.",1712.09992v1
2018/3/8,First-principles study of spin-wave dispersion in Sm(Fe$_{1-x}$Co$_{x}$)$_{12}$,"We present spin-wave dispersion in Sm(Fe$_{1-x}$Co$_x$)$_{12}$ calculated
based on first-principles. Anisotropy in the lowest branch of the spin-wave
dispersion around the $\Gamma$ point is discussed. Spin-waves propagate more
easily along $a^*$-axis than along $c^*$-axis, especially in SmFe$_{12}$. We
also compare values of the spin-wave stiffness with those obtained from an
experiment. The calculated values are in good agreement with the experimental
values.",1803.03165v3
2018/3/26,Measurement of the Hall effect at nanoscale with three probes,"The Hall effect and its varieties such as quantum, anomalous, and spin Hall
effects, provide indispensable tools for the characterization of electronic and
magnetic properties of materials, metrology, and spintronics. The conventional
four-probe Hall configuration is generally not amenable to measurements at
nanoscale, due to current shunting by the Hall electrodes. We demonstrate that
Hall measurements on the nanoscale can be facilitated by the three-probe Hall
configuration that avoids the shunting problem. We illustrate the efficiency of
the proposed approach with anomalous Hall effect-based measurements of
individual activation events during domain wall motion in magnetic films with
perpendicular anisotropy.",1803.09784v1
2018/6/20,Electronic transport in high magnetic fields of thin film MnSi,"We present a study of the magnetoresistivity of thin film MnSi in high
magnetic fields. We establish that the magnetoresistivity can be understood in
terms of spin fluctuation theory, allowing us to compare our data to studies of
bulk material. Despite of a close qualitative resemblance of bulk and thin film
data, there are clear quantitative differences. We propose that these reflect a
difference of the spin fluctuation spectra in thin film and bulk material MnSi.",1806.07710v2
2019/2/17,Redox-controlled epitaxy and magnetism of oxide heterointerfaces: EuO/SrTiO$_3$,"We demonstrate a novel route to prepare thin films of the ferromagnetic
insulator Europium monoxide. Key is a redox-controlled interface reaction
between metallic Eu and the substrate SrTiO$_3$ as the supplier of oxygen. The
process allows tuning the electronic, magnetic and structural properties of the
EuO films. Furthermore, we apply this technique to various oxidic substrates
and demonstrate the universality and limits of a redox-controlled EuO film
synthesis.",1902.06301v1
2019/12/23,Electronic and magnetic properties of structural defects in SrTiO$_3$(Co),"The synthesis conditions of SrTiO$_3$(Co) samples in which cobalt
predominantly enters the $A$ or $B$ sites of the perovskite $AB$O$_3$ structure
are found. EXAFS studies show that the Co impurity at the $A$ site is
off-center and is displaced from the site by 1.0 {\AA}. XANES studies reveal
two predominant oxidation states of Co: Co$^{2+}$ at the $A$ site and Co$^{3+}$
at the $B$ site. First-principles calculations of a number of possible
cobalt-containing structural defects reveal defects whose properties are
compatible with the experimentally observed Co oxidation state, its local
structure, magnetic, electrical, and optical properties.",1912.10711v1
2020/1/6,The optical tweezer of ferroelectric skyrmions,"Strong magneto-electric coupling in two-dimensional helical materials leads
to a peculiar type of topologically protected solutions -- skyrmions. Coupling
between the net ferroelectric polarization and magnetization allows control of
the magnetic texture with an external electric field. In this work we propose
the model of optical tweezer -- a particular configuration of an external
electric field and Gaussian laser beam that can trap or release the skyrmions
in a highly controlled manner. Functionality of such a tweezer is visualized by
micromagnetic simulations and model analysis.",2001.01614v1
2020/1/13,Structural and magnetic characterization of the elusive Jahn-Teller active NaCrF3,"We report the structural and magnetic characterization of the elusive Jahn-
Teller active compound NaCrF3.",2001.04144v3
2020/7/4,Synthesis of FeNi tetrataenite phase by means of chemical precipitation,"FeNi L10 (tetrataenite) phase has great perspectives for hard magnetic
materials production. In this paper it was synthesized in chemically
co-precipitated FeNi nanopowder by means of thermal treating included cycling
of oxidation and reduction processes at 320 {\deg}C. The presence of FeNi L10
phase in the samples was confirmed by magnetic measurements and DSC analysis.",2007.02177v2
2020/9/11,Low-Temperature Thermopower in CoSbS,"We report giant thermopower S = 2.5 mV/K in CoSbS single crystals, a material
that shows strong high-temperature thermoelectric performance when doped with
Ni or Se. Changes of low temperature thermopower induced by magnetic field
point to mechanism of electronic diffusion of carriers in the heavy valence
band. Intrinsic magnetic susceptibility is consistent with the Kondo-
Insulator-like accumulation of electronic states around the gap edges. This
suggests that giant thermopower stems from temperature-dependent
renormalization of the non-interacting bands and buildup of the electronic
correlations on cooling.",2009.05572v1
2020/11/7,Can the highly symmetric SU(4) spin-orbital model be realized in alpha-ZrCl3?,"We study physical properties of a potential candidate for the physical
realization of the SU(4) spin-orbital model - layered alpha-ZrCl3. Both DFT and
DFT+U+SOC calculations show that this material most probably dimerizes at
normal conditions. Therefore it is unlikely that symmetric SU(4) model can be
used for description of magnetic properties of alpha-ZrCl3 at low temperatures.
In the dimerized structure electrons occupy molecular orbitals formed by the xy
orbitals. One might expect a non-magnetic ground state in this case.
Interestingly the energy difference between various dimers packings is rather
small and thus dimers may start to flow over the lattice as they do in Li2RuO3.",2011.03707v1
2021/3/12,Incorporation of Si atoms into CrCoNiFe high-entropy alloy: a DFT study,"Density functional theory based computational study has been conducted in
order to investigate the effect of substitution of Cr and Co components by Si
on the structure, mechanical, electronic, and magnetic properties of the high
entropy alloy CrCoNiFe. It is found that the presence of a moderate
concentration of Si substitutes (up to 12.5 %) does not significantly reduce
the structural and mechanical stability of CrCoNiFe while it may modify its
electronic and magnetic properties. Based on that, Si is proposed as a cheap
and functional material for partial substitution of Cr or Co in CrCoNiFe.",2103.07322v1
2021/7/5,Magneto-optical effects in a high-$Q$ whispering-gallery-mode resonator with a large Verdet constant,"We have studied magneto-optical effects in an optical whispering-gallery-mode
resonator (WGMR) manufactured from a Faraday-rotator material with, to the best
of our knowledge, the record quality factor ($Q = 1.45\times10^8$) achieved for
such materials. We have experimentally measured the eigenfrequencies deviation
amplitude under the application of an external magnetic field and demonstrated
the polarization plane declination over the light path. An analytical model for
arbitrary magnetic field geometries in magneto-optic birefringent WRMRs has
been developed.",2107.02229v1
2021/7/16,Proposal for a micromagnetic standard problem: domain wall pinning at phase boundaries,"We propose a novel micromagnetic standard problem calculating the coercive
field for unpinning a domain wall at the interface of a multiphase magnet. This
problem is sensitive to discontinuities in material parameters for the exchange
interaction, the uniaxial anisotropy, and the spontaneous magnetization. We
derive an explicit treatment of jump conditions at material interfaces for the
exchange interaction in the finite-difference discretization. The micromagnetic
simulation results are compared with analytical solutions and show good
agreement. The proposed standard problem is well-suited to test the
implementation of both finite-difference and finite-element simulation codes.",2107.07855v1
2022/5/5,Negative refractive index in dielectric crystals containing stoichiometric rare-earth ions,"We investigate the prospect of achieving negative permittivity and
permeability at optical frequencies in a dielectric crystal containing
stoichiometric rare-earth ions. We derive the necessary transition linewidth,
ion density and electric and magnetic oscillator strengths using a simplified
model of non-interacting dipoles. We identify Erbium crystals in a magnetically
ordered phase as the most promising material to meet these conditions, and
describe initial optical measurements of two potential candidates, \ercl{} and
${}^7$\lierf{}, which display linewidths of 3~GHz and 250~MHz, respectively.
The properties of ${}^7$\lierf{} satisfied our criterion for negative
permeability.",2205.02739v1
2022/11/27,A Scheme to fabricate magnetic graphene-like cobalt nitride CoN4monolayer proposed by first-principles calculations,"We propose a scheme to fabricate the cobalt nitride CoN4 monolayer, a
magnetic graphene-like two-dimensional material, in which all Co and N atoms
are in a plane. Under the pressure above 40 GPa, the bulk CoN4 is stabilized in
a triclinic phase. With the pressure decreasing, the triclinic phase of CoN4 is
transformed into an orthorhombic phase, and the latter is a layered compound
with large interlayer spacing. At ambient condition, the weak interlayer
couplings are so small that single CoN4 layer can be exfoliated by the
mechanical method.",2211.14765v1
2022/12/15,Coreless vortices as direct signature of chiral $d$-wave superconductivity,"Chiral $d$-wave superconductivity has been proposed in a number of different
materials, but characteristic experimental fingerprints have been largely
lacking. We show that quadruply quantized coreless vortices are prone to form
and offer distinctive signatures of the chiral $d$-wave state in both the local
density of states and the total magnetic moment. Their dissimilarity in
positive versus negative magnetic fields further leads to additional
spontaneous symmetry breaking, producing clear evidence of time-reversal
symmetry breaking, chiral superconductivity, and the Chern number.",2212.08156v3
2023/4/7,Ising superconductivity: a first-principles perspective,"The recent discovery of Ising superconductivity has garnered a lot of
interest due in part to the resilience of these superconductors to large
in-plane magnetic fields. In this Perspective we explain the basic concepts
that define the behavior of Ising superconductors, provide an overview of the
electronic structure and magnetic properties with a focus on NbSe$_2$,
summarize key experimental observations that have been made in this class of
superconductors, highlight the role that defects and proximity-induced effects
at interfaces have on Ising superconductivity and finally discuss the prospects
for observing Ising superconductivity in bulk materials.",2304.03759v1
2023/5/24,Piezomagnetic Properties in Altermagnetic MnTe,"We examined the piezomagnetic effect in an antiferromagnet composed of MnTe,
which is a candidate material for altermagnetism with a high critical
temperature. We observed that the magnetization develops with the application
of stress and revealed that the piezomagnetic coefficient Q is
1.38$\times10^{-8}$ ${\mu}$B/MPa at 300 K. The poling-field dependence of
magnetization indicates that the antiferromagnetic domain can be controlled
using the piezomagnetic effect. We demonstrate that the piezomagnetic effect is
suitable for detecting and controlling the broken time reversal symmetry in
altermagnets.",2305.14786v2
2023/7/7,Anomalous Nernst effect in perpendicularly magnetised τ-MnAl thin films,"$\tau$-MnAl is interesting for spintronic applications as a ferromagnet with
perpendicular magnetic anisotropy due to its high uniaxial magnetocrystalline
anisotropy. Here we report on the anomalous Nernst effect of sputter deposited
$\tau$-MnAl thin films. We demonstrate a robust anomalous Nernst effect at
temperatures of 200 K and 300 K with a hysteresis similar to the anomalous Hall
effect and the magnetisation of the material. The anomalous Nernst coefficient
of (0.6$\pm$0.24) $\mu$V/K at 300 K is comparable to other perpendicular
magnetic anisotropy thin films. Therefore $\tau$-MnAl is a promising candidate
for spin-caloritronic research.",2307.03458v1
2023/8/23,Verification of Wiedemann-Franz law in silver with moderate residual resistivity ratio,"Electrical and thermal transport were studied in a vacuum-annealed
polycrystalline silver wire with residual resistivity ratio 200-400, in the
temperature range 0.1-1.2K and in magnetic fields up to 5T. Both at zero field
and at 5T the wire exhibits the Wiedemann-Franz law with the fundamental Lorenz
number, contrary to an earlier report [Gloos, K. et al, Cryogenics 30, 14
(1990)]. Our result demonstrates that silver is an excellent material for
thermal links in ultra-low-temperature experiments operating at high magnetic
fields.",2308.12349v1
2023/10/7,Flux trapping in hydrides not yet confirmed,"In Ref. [1], Minkov et al reported the time dependence of magnetic moment of
hydride materials under high pressure in a diamond anvil cell. Here we point
out that the straight lines interpolated with the measurement results give the
misleading impression that thermal flux creep in superconductors decays
linearly with time. To dispel this misconception, we correctly interpolated
logarithmic decay curves. Then, it has become apparent that there is no reason
to assume that the measured magnetic moment originates from flux trapping,
i.e., there is no reason to believe that persistent currents are circulating in
hydride materials under high pressure and that they are superconductors.",2310.06869v1
2023/10/30,"Magnetic Stability, Fermi Surface Topology, and Spin-Correlated Dielectric Response in Monolayer 1T-CrTe2","We have carried out density-functional theory (DFT) calculations to study the
magnetic stability of both ferromagnetic (FM) and anti-ferromagnetic (AFM)
states in monolayer 1T-CrTe2. Our results show that the AFM order is lower in
energy and thus is the ground state. By tuning the lattice parameters, the AFM
order can transition to the FM order, in good agreement with experimental
observation. We observe a commensurate SDW alongside the previously predicted
CDW, and attribute the AFM order to the SDW. This results in distinct hole and
electron Fermi pockets and a pronounced optical anisotropy, suggesting
quasi-one-dimensional behavior in this material.",2310.19735v1
2024/3/19,Ultrafast pseudomagnetic fields from electron-nuclear quantum geometry,"Recent experiments demonstrate precise control over coherently excited phonon
modes using high-intensity terahertz lasers, opening new pathways towards
dynamical, ultrafast design of magnetism in functional materials. In this work,
we put forward a coupling mechanism based on electron-nuclear quantum geometry.
This effect is rooted in the phase accumulation of the electronic wavefunction
under a circular evolution of nuclear coordinates. An excitation pulse then
induces a transient level splitting between electronic orbitals that carry
angular momentum. When converted to effective magnetic fields, values on the
order of tens of Teslas are easily reached.",2403.13070v1
2004/1/30,Neutrino Processes in Strong Magnetic Fields and Implications for Supernova Dynamics,"The processes of neutrino (antineutrino) absorption and electron (positron)
capture on nucleons provide the dominant mechanisms for heating and cooling the
material between the protoneutron star and the stalled shock in a core-collapse
supernova. Observations suggest that some neutron stars are born with magnetic
fields of at least 10^15 G while theoretical considerations give an upper limit
of 10^18 G for the protoneutron star magnetic fields. We calculate the rates
for the above neutrino processes in strong magnetic fields of 10^16 G. We find
that the main effect of such magnetic fields is to change the equations of
state through the phase space of electron and positron, which differs from the
classical case due to quantization of the motion of electron and positron
perpendicular to the magnetic field. As a result, the cooling rate can be
greatly reduced by magnetic fields of 10^16 G for typical conditions below the
stalled shock and a nonuniform protoneutron star magnetic field (e.g., a dipole
field) can introduce a large angular dependence of the cooling rate. In
addition, strong magnetic fields always lead to an angle-dependent heating rate
by polarizing the spin of nucleons. The implications of our results for the
neutrino-driven supernova mechanism are discussed.",0401634v2
1999/9/9,Micromagnetic simulations of thermally activated magnetization reversal of nanoscale magnets,"Numerical integration of a stochastic Landau-Lifshitz-Gilbert equation is
used to study dynamic processes in single-domain nanoscale magnets at nonzero
temperatures. Special attention is given to including thermal fluctuations as a
Langevin term, and the Fast Multipole Method is used to calculate dipole-dipole
interactions. It is feasible to simulate these dynamics on the nanosecond time
scale for spatial discretizations that involve on the order of 10000 nodes
using a desktop workstation. The nanoscale magnets considered here are single
pillars with large aspect ratio. Hysteresis-loop simulations are employed to
study the stable and metastable configurations of the magnetization. Each
pillar has magnetic end caps. In a time-dependent field the magnetization of
the pillars is observed to reverse via nucleation, propagation, and coalescence
of the end caps. In particular, the end caps propagate into the magnet and meet
near the middle. A relatively long-lived defect is formed when end caps with
opposite vorticity meet. Fluctuations are more important in the reversal of the
magnetization for fields weaker than the zero-temperature coercive field, where
the reversal is thermally activated. In this case, the process must be
described by its statistical properties, such as the distribution of switching
times, averaged over a large number of independent thermal histories.",9909136v2
2000/7/14,Interplay of spin and orbital ordering in the layered colossal magnetoresistance manganite La2-2xSr1+2xMn2O7 (0.5<=x<=1.0),"The crystallographic and magnetic phase diagram of the n=2 layered manganite
La2-2xSr1+2xMn2O7 in the region x=>0.5 has been studied using temperature
dependent neutron powder diffraction. The magnetic phase diagram reveals a
progression of ordered magnetic structures generally paralleling that of 3-D
perovskites with similar electronic doping: A (0.5<=x<=0.66) --> C
(0.75<=x<=0.90) --> G (0.90<=x<=1.0). However, the quasi-2-D structure
amplifies this progression to expose features of manganite physics uniquely
accessible in the layered systems: (a) a ""frustrated"" region between the A and
C regimes where no long-range magnetic order is observed; (b) magnetic
polytypism arising from weak inter-bilayer magnetic exchange in the Type-C
regime; and (c) a tetragonal to orthorhombic phase transition whose temperature
evolution directly measures ordering of d3y2-r2 orbitals in the a-b plane. This
orbital-ordering transition is precursory to Type-C magnetic ordering, where
ferromagnetic rods lie parallel to the b-axis. These observations support the
notion that eg orbital polarisation is the driving force behind magnetic spin
ordering. Finally, in the crossover region between Type-C and Type-G states, we
see some evidence for the development of local Type-C clusters embedded in a
Type-G framework, directly addressing proposals of similar short-range magnetic
ordering in highly-doped La1-xCaxMnO3 perovskites.",0007253v1
2004/7/28,Ab initio study of canted magnetism of finite atomic chains at surfaces,"By using ab initio methods on different levels we study the magnetic ground
state of (finite) atomic wires deposited on metallic surfaces. A
phenomenological model based on symmetry arguments suggests that the
magnetization of a ferromagnetic wire is aligned either normal to the wire and,
generally, tilted with respect to the surface normal or parallel to the wire.
  From a first principles point of view, this simple model can be best related
to the so--called magnetic force theorem calculations being often used to
explore magnetic anisotropy energies of bulk and surface systems. The second
theoretical approach we use to search for the canted magnetic ground state is
first principles adiabatic spin dynamics extended to the case of fully
relativistic electron scattering. First, for the case of two adjacent Fe atoms
an a Cu(111) surface we demonstrate that the reduction of the surface symmetry
can indeed lead to canted magnetism. The anisotropy constants and consequently
the ground state magnetization direction are very sensitive to the position of
the dimer with respect to the surface. We also performed calculations for a
seven--atom Co chain placed along a step edge of a Pt(111) surface. As far as
the ground state spin orientation is concerned we obtain excellent agreement
with experiment. Moreover, the magnetic ground state turns out to be slightly
noncollinear.",0407732v1
2004/10/21,Novel magnetic behavior of single crystalline Er2PdSi3,"We report the results of ac and dc magnetic susceptibility (chi) and
electrical resistivity (rho) measurements on the single crystals of Er2PdSi3,
crystallizing in an AlB2-derived hexagonal structure, for two orientations
H//[0001] and H//[2 -1 -1 0]. For H//[0001], there are apparently two magnetic
transitions as revealed by the ac chi data, one close to 7 K attributable to
antiferromagnetic ordering and the other around 2 K. However, for H // [2 -1 -1
0], we observe additional features above 7 K (near 11 and 23 K) in the plot of
low-field chi(T); also, there is no corresponding anomaly in the rho(T) plot.
In this respect, the magnetic behavior of this compound is novel, particularly
while compared with other members of this series. The features in ac chi
respond differently to the application of a small dc magnetic field for the two
directions. As far as low temperature (T= 1.8 and 5 K) isothermal magnetization
(M) behaviour is concerned, it exhibits meta-magnetic-like features around 2
kOe saturating at high fields for the former orientation, whereas for the
latter, there is no saturation even at 120 kOe. The sign of paramagnetic Curie
temperature is different for these two directions. Thus, there is a strong
anisotropy in the magnetic behavior. However, interestingly, the rho(T) plots
are found to be essentially isotropic, with the data revealing possible
formation of magnetic superzone formation below 7 K.",0410532v1
2006/6/5,On the Origin of the Metallic and Anisotropic Magnetic Properties of Na_xCoO_2 (x~~0.75),"Non-stoichiometric NaxCoO2 (0.5 < x < 1) consists of CoO2 layers made up of
edge-sharing CoO6 octahedra, and exhibits strongly anisotropic magnetic
susceptibilities as well as metallic properties. A modified Curie-Weiss law was
proposed for systems containing anisotropic magnetic ions to analyze the
magnetic susceptibilities of NaxCoO2 (x ~~ 0.75), and implications of this
analysis were explored. Our study shows that the lowspin Co4+ (S = 1/2) ions of
NaxCoO2 generated by the Na vacancies cause the anisotropic magnetic properties
of NaxCoO2, and suggests that the six nearest-neighbor Co3+ ions of each Co4+
ion adopt the intermediate-spin electron configuration thereby behaving
magnetically like low-spin Co4+ ions. The Weiss temperature of NaxCoO2 is more
negative along the direction of the lower g-factor (i.e., Theta_parallel <
Theta_perp < 0, and g_parallel < g_perp). The occurrence of intermediate-spin
Co3+ ions surrounding each Co4+ ion account for the apparently puzzling
magnetic properties of NaxCoO2 (x ~~ 0.75), i.e., the large negative Weiss
temperature, the three-dimensional antiferromagnetic ordering below ~22 K, and
the metallic properties. The picture of the magnetic structure derived from
neutron scattering studies below ~22 K are in apparent conflict with that
deduced from magnetic susceptibility measurements between ~50 - 300 K. These
conflicting pictures are resolved by noting that the spin exchange between Co3+
ions is more strongly antiferromagnetic than that between Co4+ and Co3+ ions.",0606103v1
2006/9/16,Correlation between magnetism and magnetocaloric effect in RCo2-based Laves phase compounds,"By virtue of the itinerant electron metamagnetism (IEM), the RCo2 compounds
with R=Er, Ho and Dy are found to show first order magnetic transition at their
ordering temperatures. The inherent instability of Co sublattice magnetism is
responsible for the occurrence of IEM, which leads to interesting magnetic and
related properties. The systematic studies of the variations in the magnetic
and magnetocaloric properties of the RCo2-based compounds show that the
magnetovolume effect plays a decisive role in determining the nature of
magnetic transitions and hence the magnetocaloric effect (MCE) in these
compound. It is found that the spin fluctuations arising due to the
magnetovolume effect reduce the strength of IEM in these compounds, which
subsequently lead to a reduction in the MCE. Most of the substitutions at the
Co site are found to result in a positive magnetovolume effect, leading to an
initial increase in the ordering temperature. Application of pressure, on the
other hand, causes a reduction in the ordering temperature due to the negative
magnetovolume effect. A comparative study of the magnetic and magnetocaloric
properties of RCo2 compounds under various substitutions and applied pressure
is presented. Analysis of the magnetization data using the Landau theory has
shown that there is a strong correlation between the Landau coefficient (B) and
the MCE. The variations seen in the order of magnetic transition and the MCE
values seem to support the recent model proposed by Khmelevskyi and Mohn for
the occurrence of IEM in RCo2 compounds.",0609401v1
2006/9/25,Metastable diamagnetism in Sm0.1Ca0.84Sr0.06MnO3 manganite,"Magnetic properties of polycrystalline Sm0.1Ca0.84Sr0.06MnO3 in pristine and
metastable states have been investigated in wide range of temperatures and
magnetic fields. It was found that below Curie temperature TC = 105 K the
pristine state exhibits phase separation comprising ferromagnetic and
antiferromagnetic phases. The metastable states with reduced magnetization were
obtained by successive number of quick coolings of the sample placed in
container with kerosene-oil mixture. By an increasing number of quick coolings
(> 6) the long time relaxation appeared at 10 K and the magnetization reversed
its sign and became strongly negative in wide temperature range, even under an
applied magnetic field of 15 kOe. The observed field and temperature
dependences of the magnetization in this state are reversed in comparison with
the ordinary ferromagnetic ones. Above TC, the observed diamagnetic
susceptibility of the reversed magnetization state at T = 120 K is ~ - 0.9 x
10-4 emu g-1 Oe-1. Only after some storage time at room temperature, the
abnormal magnetic state is erasable. It is suggested that the negative
magnetization observed results from a specific coupling of the nano/micro-size
ferromagnetic regions with a surrounding diamagnetic matrix formed, in a
puzzled way, by the repeating training (quick cooling) cycles.",0609626v1
2006/10/6,Spin-state ordering and magnetic structures in YBaCo2O5.5/5.44,"The antiferromagnetic - ferromagnetic phase transition in YBaCo2O5.50 and
YBaCo2O5.44 cobaltites with different types of oxygen-ion ordering in the
[YO0.5/0.44] layers has been studied by neutron powder diffraction. Using the
magnetic symmetry arguments in combination with group-theoretical analysis, the
crystal and magnetic structures above and below the phase transformation
temperature, Ti, were determined and successfully refined. In both cases, the
proposed models involve a spin-state ordering between diamagnetic (t2g6eg0, S =
0) and paramagnetic (t2g4eg2, S = 2) Co3+ ions with octahedral coordination.
Electronic ordering results in a nonzero spontaneous magnetic moment in the
high-temperature magnetic phases with isotropic negative exchange interactions.
In the case of YBaCo2O5.5, the phase transformation does not change Pmma
symmetry of the crystal structure. The wave vectors of magnetic structures
above and below Ti are k = 0 and k = c*/2, respectively. In the case of
YBaCo2O5.44, a crossover P4/nmm - I4/mmm was involved to solve the
low-temperature magnetic structure. The wave vectors in both high-temperature
and low-temperature magnetic phases are k = 0. Mechanisms of the phase
transformation in both compositions are discussed in the light of obtained
magnetic structures. The proposed spin configurations were compared with other
models reported in literature.",0610179v1
2004/6/18,Electrodynamics of a Magnet Moving through a Conducting Pipe,"The popular demonstration involving a permanent magnet falling through a
conducting pipe is treated as an axially symmetric boundary value problem.
Specifically, Maxwell's equations are solved for an axially symmetric magnet
moving coaxially inside an infinitely long, conducting cylindrical shell of
arbitrary thickness at nonrelativistic speeds. Analytic solutions for the
fields are developed and used to derive the resulting drag force acting on the
magnet in integral form. This treatment represents a significant improvement
over existing models which idealize the problem as a point dipole moving slowly
inside a pipe of negligible thickness. It also provides a rigorous study of
eddy currents under a broad range of conditions, and can be used for precision
magnetic braking applications. The case of a uniformly magnetized cylindrical
magnet is considered in detail, and a comprehensive analytical and numerical
study of the properties of the drag force is presented for this geometry.
Various limiting cases of interest involving the shape and speed of the magnet
and the full range of conductivity and magnetic behavior of the pipe material
are investigated and corresponding asymptotic formulas are developed.",0406085v2
2006/1/24,Trapping atoms on a transparent permanent-magnet atom chip,"We describe experiments on trapping of atoms in microscopic magneto-optical
traps on an optically transparent permanent-magnet atom chip. The chip is made
of magnetically hard ferrite-garnet material deposited on a dielectric
substrate. The confining magnetic fields are produced by miniature magnetized
patterns recorded in the film by magneto-optical techniques. We trap Rb atoms
on these structures by applying three crossed pairs of counter-propagating
laser beams in the conventional magneto-optical trapping (MOT) geometry. We
demonstrate the flexibility of the concept in creation and in-situ modification
of the trapping geometries through several experiments.",0601163v2
2007/10/29,Interplay of structure and spin-orbit strength in magnetism of metal-benzene sandwiches: from single molecules to infinite wires,"Based on first-principles density functional theory calculations we explore
electronic and magnetic properties of experimentally producible sandwiches and
infinite wires made of repeating benzene molecules and transition-metal atoms
of V, Nb, and Ta. We describe the bonding mechanism in the molecules and in
particular concentrate on the origin of magnetism in these structures. We find
that all the considered systems have sizable magnetic moments and ferromagnetic
spin-ordering, with the single exception of the V3-Bz4 molecule. By including
the spin-orbit coupling into our calculations we determine the easy and hard
axes of the magnetic moment, the strength of the uniaxial magnetic anisotropy
energy (MAE), relevant for the thermal stability of magnetic orientation, and
the change of the electronic structure with respect to the direction of the
magnetic moment, important for spin-transport properties. While for the V-based
compounds the values of the MAE are only of the order of 0.05-0.5 meV per metal
atom, increasing the spin-orbit strength by substituting V with heavier Nb and
Ta allows to achieve an increase in anisotropy values by one to two orders of
magnitude. The rigid stability of magnetism in these compounds together with
the strong ferromagnetic ordering makes them attractive candidates for
spin-polarized transport applications. For a Nb-benzene infinite wire the
occurrence of ballistic anisotropic magnetoresistance is demonstrated.",0710.5413v1
2007/12/6,Magnetohydrodynamic Simulations of Disk Galaxy Formation: the Magnetization of The Cold and Warm Medium,"Using magnetohydrodynamic (MHD) adaptive mesh refinement simulations, we
study the formation and early evolution of disk galaxies with a magnetized
interstellar medium. For a $10^{10}$ \msun halo with initial NFW dark matter
and gas profiles, we impose a uniform $10^{-9}$ G magnetic field and follow its
collapse, disk formation and evolution up to 1 Gyr. Comparing to a purely
hydrodynamic simulation with the same initial condition, we find that a
protogalactic field of this strength does not significantly influence the
global disk properties. At the same time, the initial magnetic fields are
quickly amplified by the differentially rotating turbulent disk. After the
initial rapid amplification lasting $\sim500$ Myr, subsequent field
amplification appears self-regulated. As a result, highly magnetized material
begin to form above and below the disk. Interestingly, the field strengths in
the self-regulated regime agrees well with the observed fields in the Milky Way
galaxy both in the warm and the cold HI phase and do not change appreciably
with time. Most of the cold phase shows a dispersion of order ten in the
magnetic field strength. The global azimuthal magnetic fields reverse at
different radii and the amplitude declines as a function of radius of the disk.
By comparing the estimated star formation rate (SFR) in hydrodynamic and MHD
simulations, we find that after the magnetic field strength saturates, magnetic
forces provide further support in the cold gas and lead to a decline of the
SFR.",0712.0872v1
2007/12/22,Twisted flux tube emergence from the convection zone to the corona,"3D numerical simulations of a horizontal magnetic flux tube emergence with
different twist are carried out in a computational domain spanning the upper
layers of the convection zone to the lower corona. We use the Oslo Staggered
Code to solve the full MHD equations with non-grey and non-LTE radiative
transfer and thermal conduction along the magnetic field lines. The emergence
of the magnetic flux tube input at the bottom boundary into a weakly magnetized
atmosphere is presented. The photospheric and chromospheric response is
described with magnetograms, synthetic images and velocity field distributions.
The emergence of a magnetic flux tube into such an atmosphere results in varied
atmospheric responses. In the photosphere the granular size increases when the
flux tube approaches from below. In the convective overshoot region some 200km
above the photosphere adiabatic expansion produces cooling, darker regions with
the structure of granulation cells. We also find collapsed granulation in the
boundaries of the rising flux tube. Once the flux tube has crossed the
photosphere, bright points related with concentrated magnetic field, vorticity,
high vertical velocities and heating by compressed material are found at
heights up to 500km above the photosphere. At greater heights in the magnetized
chromosphere, the rising flux tube produces a cool, magnetized bubble that
tends to expel the usual chromospheric oscillations. In addition the rising
flux tube dramatically increases the chromospheric scale height, pushing the
transition region and corona aside such that the chromosphere extends up to 6Mm
above the photosphere. The emergence of magnetic flux tubes through the
photosphere to the lower corona is a relatively slow process, taking of order 1
hour.",0712.3854v1
2008/2/29,Magnetic edge states in graphene in nonuniform magnetic fields,"We theoretically study electronic properties of a graphene sheet on xy plane
in a spatially nonuniform magnetic field, $B = B_0 \hat{z}$ in one domain and
$B = B_1 \hat{z}$ in the other domain, in the quantum Hall regime and in the
low-energy limit. We find that the magnetic edge states of the Dirac fermions,
formed along the boundary between the two domains, have features strongly
dependent on whether $B_0$ is parallel or antiparallel to $B_1$. In the
parallel case, when the Zeeman spin splitting can be ignored, the magnetic edge
states originating from the $n=0$ Landau levels of the two domains have
dispersionless energy levels, contrary to those from the $n \ne 0$ levels.
Here, $n$ is the graphene Landau-level index. They become dispersive as the
Zeeman splitting becomes finite or as an electrostatic step potential is
additionally applied. In the antiparallel case, the $n=0$ magnetic edge states
split into electron-like and hole-like current-carrying states. The energy gap
between the electron-like and hole-like states can be created by the Zeeman
splitting or by the step potential. These features are attributed to the fact
that the pseudo-spin of the magnetic edge states couples to the direction of
the magnetic field. We propose an Aharonov-Bohm interferometry setup in a
graphene ribbon for experimental study of the magnetic edge states.",0802.4360v1
2008/3/14,Hyper-domains in exchange bias micro-stripe pattern,"A combination of experimental techniques, e.g. vector-MOKE magnetometry, Kerr
microscopy and polarized neutron reflectometry, was applied to study the field
induced evolution of the magnetization distribution over a periodic pattern of
alternating exchange bias stripes. The lateral structure is imprinted into a
continuous ferromagnetic/antiferromagnetic exchange-bias bi-layer via laterally
selective exposure to He-ion irradiation in an applied field. This creates an
alternating frozen-in interfacial exchange bias field competing with the
external field in the course of the re-magnetization. It was found that in a
magnetic field applied at an angle with respect to the exchange bias axis
parallel to the stripes the re-magnetization process proceeds via a variety of
different stages. They include coherent rotation of magnetization towards the
exchange bias axis, precipitation of small random (ripple) domains, formation
of a stripe-like alternation of the magnetization, and development of a state
in which the magnetization forms large hyper-domains comprising a number of
stripes. Each of those magnetic states is quantitatively characterized via the
comprehensive analysis of data on specular and off-specular polarized neutron
reflectivity. The results are discussed within a phenomenological model
containing a few parameters which can readily be controlled by designing
systems with a desired configuration of magnetic moments of micro- and
nano-elements.",0803.2144v1
2008/8/22,Low-dimensional magnetism in the mixed Cr valence spin-chain compound Sr_4Cr_3O_9,"Sr_4Cr_3O_9 is the n = 2 member of a family of quasi-one-dimensional
compounds A_{n+2}T_{n+1}O_{3n+3} (A = Ca, Sr, or Ba, T = transition metal, and
n = 1 to \infty) having a crystal structure which consists of chains of n TO_6
octahedra alternated by one TO_6 trigonal prism running along the c-axis. The
chains are arranged on a triangular lattice in the ab-plane. We report the
synthesis, structure, magnetization M versus magnetic field H, magnetic
susceptibility \chi versus temperature T and specific heat C versus T
measurements on sintered and arc-melted polycrystalline samples of Sr_4Cr_3O_9.
The \chi data have a T dependence which is typical of low-dimensional magnetic
systems with dominant antiferromagnetic (AF) exchange interactions.
Specifically, \chi(T) shows a broad maximum at T_{max} \approx 200K for the
sintered pellet and T_{max}\approx 265K for the arc-melted sample, indicating
the onset of short-range magnetic order. Below T = 15K we observe 2 anomalies
in the \chi(T) data for both samples suggesting the onset of long-range
magnetic ordering. The corresponding anomalies in the C(T) data however are
weak indicating that only a small amount of the expected magnetic entropy is
recovered at the magnetic transitions and that strong short-range AF order
exists above these temperatures.",0808.3123v1
2008/9/25,"Experimental magnetic form factors in Co3V2O8: A combined study of ab initio calculations, magnetic Compton scattering and polarized neutron diffraction","We present a combination of ab initio calculations, magnetic Compton
scattering and polarized neutron experiments, which elucidate the density
distribution of unpaired electrons in the kagome staircase system Co3V2O8. Ab
initio wave functions were used to calculate the spin densities in real and
momentum space, which show good agreement with the respective experiments. It
has been found that the spin polarized orbitals are equally distributed between
the t2g and the eg levels for the spine (s) Co ions, while the eg orbitals of
the cross-tie (c) Co ions only represent 30% of the atomic spin density.
Furthermore, the results reveal that the magnetic moments of the cross-tie Co
ions, which are significantly smaller than those of the spine Co ions in the
zero-field ferromagnetic structure, do not saturate by applying an external
magnetic field of 2 T along the easy axis a, but that the increasing bulk
magnetization originates from induced magnetic moments on the O and V sites.
The refined individual magnetic moments are mu(Co_c)=1.54(4) mu_B,
mu(Co_s)=2.87(3) mu_B, mu(V)=0.41(4) mu_B, mu(O1)=0.05(5) mu_B, mu(O2)=0.35(5)
mu_B, and; mu(O3)=0.36(5) mu_B combining to the same macroscopic magnetization
value, which was previously only attributed to the Co ions.",0809.4404v2
2008/11/3,Compensation-dependent in-plane magnetization reversal processes in Ga1-xMnxP1-ySy,"We report the effect of dilute alloying of the anion sublattice with S on the
in-plane uniaxial magnetic anisotropy and magnetization reversal process in
Ga1-xMnxP as measured by both ferromagnetic resonance (FMR) and superconducting
quantum interference device (SQUID) magnetometry. At T=5K, raising the S
concentration increases the uniaxial magnetic anisotropy between in-plane <011>
directions while decreasing the magnitude of the (negative) cubic anisotropy
field. Simulation of the SQUID magnetometry indicates that the energy required
for the nucleation and growth of domain walls decreases with increasing y.
These combined effects have a marked influence on the shape of the
field-dependent magnetization curves; while the direction remains the easy axis
in the plane of the film, the field dependence of the magnetization develops
double hysteresis loops in the [011] direction as the S concentration increases
similar to those observed for perpendicular magnetization reversal in lightly
doped Ga1-xMnxAs. The incidence of double hysteresis loops is explained with a
simple model whereby magnetization reversal occurs by a combination of coherent
spin rotation and noncoherent spin switching, which is consistent with both FMR
and magnetometry experiments. The evolution of magnetic properties with S
concentration is attributed to compensation of Mn acceptors by S donors, which
results in a lowering of the concentration of holes that mediate
ferromagnetism.",0811.0385v1
2008/12/30,Covalent bonding and magnetism in cuprates,"The importance of covalent bonding for the magnetism of 3d metal complexes
was first noted by Pauling in 1931. His point became moot, however, with the
success of the ionic picture of Van Vleck, where ligands influence magnetic
electrons of 3d ions mainly through electrostatic fields. Anderson's theory of
spin superexchange later established that covalency is at the heart of
cooperative magnetism in insulators, but its energy scale was believed to be
small compared to other inter-ionic interactions and therefore it was
considered a small perturbation of the ionic picture. This assertion fails
dramatically in copper oxides, which came to prominence following the discovery
of high critical temperature superconductors (HTSC). Magnetic interactions in
cuprates are remarkably strong and are often considered the origin of the
unusually high superconducting transition temperature, Tc. Here we report a
detailed survey of magnetic excitations in the one-dimensional cuprate Sr2CuO3
using inelastic neutron scattering (INS). We show that although the
experimental dynamical spin structure factor is well described by the model
S=1/2 nearest-neighbour Heisenberg Hamiltonian typically used for cuprates, the
magnetic intensity is modified dramatically by strong hybridization of Cu 3d
states with O p states, showing that the ionic picture of localized 3d
Heisenberg spin magnetism is grossly inadequate. Our findings provide a natural
explanation for the puzzle of the missing INS magnetic intensity in cuprates
and have profound implications for understanding current and future
experimental data on these materials.",0812.5007v1
2009/2/2,Stray-fields based features observed for low and high magnetic fields in Ni$_{80}$Fe$_{20}$-Nb-Ni$_{80}$Fe$_{20}$ trilayers,"We report on the influence of stray fields for both low and high magnetic
fields applied parallel to trilayers consisting of a low-T Nb interlayer and
two outer Ni Fe layers having in-plane anisotropy. At low magnetic fields these
trilayers exhibit a pronounced magnetoresistance effect. Its dynamic transport
behavior is presented through detailed I-V characteristics. More importantly,
the detailed evolution of the longitudinal and transverse magnetic components
of the trilayers is presented from close to well below T . These data clearly
show that below T and for low magnetic fields the transport properties of the
Nb interlayer are influenced by transverse stray-fields that motivate
subsequent transverse magnetic coupling of the outer Ni Fe layers. By
generalizing this experimental finding we propose that the generic prerequisite
for the occurrence of intense magnetoresistance effects in relative trilayers
is that the coercive fields of the outer ferromagnetic layers should almost
coincide since the simultaneous occurrence of magnetic domains all over their
surface will promote a transverse magnetic coupling mediated by the
accompanying transverse stray fields. Finally, the trilayer's upper-critical
field exhibits a pronounced suppression for low magnetic fields indicative of a
behavior, while for high values the conventional behavior is recovered. A
similar process is observed in both Nb-Ni Fe bilayers and Nb single layers.
However, significant qualitative and quantitative differences exist between
these samples. Based on a mechanism that is motivated by longitudinal
stray-fields existing exclusively in the high-field regime we propose a
possible interpretation for this experimental finding.",0902.0314v1
2010/5/8,Non-Resonant X-ray Magnetic Scattering on Rare-Earth Iron Borates RFe$_3$(BO$_3$)$_4$,"Hard x-ray scattering (HXS) experiments with a photon energy of 100keV were
performed as a function of temperature and applied magnetic field on selected
compounds of the RFe$_3$(BO$_3$)$_4$ family. The results show the presence of
several unexpected diffraction features, in particular non-resonant magnetic
reflections in the magnetically ordered phase, and structural reflections that
violate the diffraction conditions for the low temperature phase $P3_121$ of
the rare-earth iron borates. The temperature and field dependence of the
magnetic superlattice reflections corroborate the magnetic structures of the
borate compounds obtained by neutron diffraction. The detailed analysis of the
intensity and scattering cross section of the magnetic reflection reveals
details of the magnetic structure of these materials such as the spin domain
structure of NdFe$_3$(BO$_3$)$_4$ and GdFe$_3$(BO$_3$)$_4$. Furthermore we find
that the correlation length of the magnetic domains is around 100 \AA{} for all
the compounds and that the Fe moments are rotated $53^\circ\pm3^\circ$ off from
the hexagonal basal plane in GdFe$_3$(BO$_3$)$_4$",1005.1333v2
2010/11/11,Competition between supersolid phases and magnetisation plateaux in the frustrated easy-axis antiferromagnet on a triangular lattice,"The majority of magnetic materials possess some degree of magnetic
anisotropy, either at the level of a single ion, or in the exchange
interactions between different magnetic ions. Where these exchange interactions
are also frustrated, the competition between them and anisotropy can stabilize
a wide variety of new phases in applied magnetic field. Motivated by the
hexagonal delafossite 2H-AgNiO 2, we study the Heisenberg antiferromagnet on a
layered triangular lattice with competing first- and second-neighbour
interactions and single-ion easy-axis anisotropy. Using a combination of
classical Monte Carlo simulation, mean-field analysis, and Landau theory, we
establish the magnetic phase diagram of this model as a function of temperature
and magnetic field for a fixed ratio of exchange interactions, but with values
of easy-axis anisotropy D extending from the Heisenberg (D =0) to the Ising
(D=&#8734) limits. We uncover a rich variety of different magnetic phases.
These include several phases which are magnetic supersolids (in the sense of
Matsuda and Tstuneto or Liu and Fisher), one of which may already have been
observed in AgNiO 2. We explore how this particular supersolid arises through
the closing of a gap in the spin-wave spectrum, and how it competes with rival
collinear phases as the easy-axis anisotropy is increased. The finite
temperature properties of this phase are found to be different from those of
any previously studied magnetic supersolid.",1011.2698v2
2011/7/21,Short-range spin order and frustrated magnetism in Mn2InSbO6 and Mn2ScSbO6,"The complex metal oxides Mn2ASbO6 (A=In, Sc) with a corundum-related
structure A3BO6 have been prepared as polycrystalline powders by a solid state
reaction route. The crystal structure and magnetic properties have been
investigated using a combination of X-ray and neutron powder diffraction,
electron microscopy, calorimetric and magnetic measurements. At room
temperature these compounds adopt a trigonal structure, space group R-3 with a
= 8.9313(1) {\AA}, c = 10.7071(2) {\AA} (for In) and a = 8.8836(1) {\AA}, c =
10.6168(2) {\AA} (for Sc) which persists down to 1.6 K. The Mn and A cations
were found to be randomly distributed over the A-sites. The overall behavior of
the magnetization of Mn2InSbO6 and Mn2ScSbO6 is quite similar. In spite of the
relatively large amount of Mn ions on the A-site, only short-ranged magnetism
is observed. Neutron diffraction patterns of Mn2InSbO6 showed no evidence of a
long-range magnetic ordering at 1.6 K, instead only a weak diffuse magnetic
peak was observed at low temperatures. The factors governing the observed
structural and magnetic properties of Mn2ASbO6 are discussed and compared with
those of other Mn-containing complex metal oxides with a corundum-related
structure. The influence of the A-cation sublattice on magnetic properties is
also considered.",1107.4206v1
2012/3/29,A critical analysis of vacancy-induced magnetism in mono and bilayer graphene,"The observation of intrinsic magnetic order in graphene and graphene-based
materials relies on the formation of magnetic moments and a sufficiently strong
mutual interaction. Vacancies are arguably considered the primary source of
magnetic moments. Here we present an in-depth density functional theory study
of the spin-resolved electronic structure of (monoatomic) vacancies in graphene
and bilayer graphene. We use two different methodologies: supercell
calculations with the SIESTA code and cluster-embedded calculations with the
ALACANT package. Our results are conclusive: The vacancy-induced extended $\pi$
magnetic moments, which present long-range interactions and are capable of
magnetic ordering, vanish at any experimentally relevant vacancy concentration.
This holds for $\sigma$-bond passivated and un-passivated reconstructed
vacancies, although, for the un-passivated ones, the disappearance of the $\pi$
magnetic moments is accompanied by a very large magnetic susceptibility. Only
for the unlikely case of a full $\sigma$-bond passivation, preventing the
reconstruction of the vacancy, a full value of 1$\mu_B$ for the $\pi$ extended
magnetic moment is recovered for both mono and bilayer cases. Our results put
on hold claims of vacancy-induced ferromagnetic or antiferromagnetic order in
graphene-based systems, while still leaving the door open to $\sigma$-type
paramagnetism.",1203.6485v1
2012/4/27,"Trends in the magnetic properties of Fe, Co and Ni clusters and monolayers on Ir(111), Pt(111) and Au(111)","We present a detailed theoretical investigation on the magnetic properties of
small single-layered Fe, Co and Ni clusters deposited on Ir(111), Pt(111) and
Au(111). For this a fully relativistic {\em ab-initio} scheme based on density
functional theory has been used. We analyse the element, size and geometry
specific variations of the atomic magnetic moments and their mutual exchange
interactions as well as the magnetic anisotropy energy in these systems. Our
results show that the atomic spin magnetic moments in the Fe and Co clusters
decrease almost linearly with coordination on all three substrates, while the
corresponding orbital magnetic moments appear to be much more sensitive to the
local atomic environment. The isotropic exchange interaction among the cluster
atoms is always very strong for Fe and Co exceeding the values for bulk bcc Fe
and hcp Co, whereas the anisotropic Dzyaloshinski-Moriya interaction is in
general one or two orders of magnitude smaller when compared to the isotropic
one. For the magnetic properties of Ni clusters the magnetic properties can
show quite a different behaviour and we find in this case a strong tendency
towards noncollinear magnetism.",1204.6230v1
2012/5/21,Magnetic structure of hexagonal YMnO3 and LuMnO3 from a microscopic point of view,"The aim of this work is to unravel a basic microscopic picture behind complex
magnetic properties of hexagonal manganites. For these purposes, we consider
two characteristic compounds: YMnO3 and LuMnO3, which form different magnetic
structures in the ground state. First, we establish an electronic low-energy
model, which describes the behavior of the Mn 3d bands of YMnO3 and LuMnO3, and
derive parameters of this model from the first-principles calculations. From
the solution of this model, we conclude that, despite strong frustration
effects in the hexagonal lattice, the relativistic spin-orbit interactions lift
the degeneracy of the magnetic ground state so that the experimentally observed
magnetic structures are successfully reproduced by the low-energy model. Then,
we analyze this result in terms of interatomic magnetic interactions, which
were computed using different approximations (starting from the model
Hamiltonian as well as directly from the first-principles electronic structure
calculations in the local-spin-density approximation). We argue that the main
reason why YMnO3 and LuMnO3 tend to form different magnetic structures is
related to the behavior of the single-ion anisotropy, which reflects the
directional dependence of the lattice distortion: namely, the expansion and
contraction of the Mn-trimers, which take place in YMnO3 and LuMnO3,
respectively. On the other hand, the magnetic coupling between the haxagonal
planes is controlled by the next-nearest-neighbor interactions, which are less
sensitive to the direction of the trimerization. Finally, using the Berry-phase
formalism, we evaluate the magnetic-state dependence of the ferroelectric
polarization, and discuss potential applications of the latter in
magnetoelectric switching phenomena.",1205.4478v1
2012/8/27,Microscopic mechanism for the 1/8 magnetization plateau in SrCu_2(BO_3)_2,"The frustrated quantum magnet SrCu_2(BO_3)_2 shows a remarkably rich phase
diagram in an external magnetic field including a sequence of magnetization
plateaux. The by far experimentally most studied and most prominent
magnetization plateau is the 1/8 plateau. Theoretically, one expects that this
material is well described by the Shastry-Sutherland model. But recent
microscopic calculations indicate that the 1/8 plateau is energetically not
favored. Here we report on a very simple microscopic mechanism which naturally
leads to a 1/8 plateau for realistic values of the magnetic exchange constants.
We show that the 1/8 plateau with a diamond unit cell benefits most compared to
other plateau structures from quantum fluctuations which to a large part are
induced by Dzyaloshinskii-Moriya interactions. Physically, such couplings
result in kinetic terms in an effective hardcore boson description leading to a
renormalization of the energy of the different plateaux structures which we
treat in this work on the mean-field level. The stability of the resulting
plateaux are discussed. Furthermore, our results indicate a series of stripe
structures above 1/8 and a stable magnetization plateau at 1/6. Most
qualitative aspects of our microscopic theory agree well with a recently
formulated phenomenological theory for the experimental data of SrCu_2(BO_3)_2.
Interestingly, our calculations point to a rather large ratio of the magnetic
couplings in the Shastry-Sutherland model such that non-perturbative effects
become essential for the understanding of the frustrated quantum magnet
SrCu_2(BO_3)_2.",1208.5379v1
2012/9/13,Magnetic phase transitions in single crystals of the chiral helimagnet Cr1/3NbS2,"The chiral helimagnet Cr1/3NbS2 has been investigated by magnetic, transport
and thermal properties measurements on single crystals and by first principles
electronic structure calculations. From the measured field and temperature
dependence of the magnetization for fields applied perpendicular to the c axis,
the magnetic phase diagram has been constructed in the vicinity of the phase
transitions. A transition from a paramagnetic to a magnetically ordered phase
occurs near 120 K. With increasing magnetic field and at temperatures below 120
K, this material undergoes transitions from a helimagnetic to a soliton-lattice
phase near 900 Oe, and then to a ferromagnetic phase near 1300 Oe. The
transitions are found to strongly affect the electrical transport. The
resistivity decreases sharply upon cooling near 120 K, and the spin
reorientation from the helimagnetic ground state to the commensurate
ferromagnetic state is evident in the magnetoresistance. At high fields a large
magnetoresistance (55 % at 140 kOe) is observed near the magnetic transition
temperature. Heat capacity and electronic structure calculations show the
density of states at the Fermi level is low in the magnetically ordered state.
Effects of spin fluctuations are likely important in understanding the behavior
of Cr1/3NbS2 near and above the magnetic ordering transitions.",1209.2783v1
2012/10/22,"Structure, magnetism and magnetic compensation behavior of Co50-xMn25Ga25+x and Co50-xMn25+xGa25 Heusler alloys","The structure, magnetism, magnetic compensation behavior, exchange
interaction and electronic structures of Co50-xMn25Ga25+x and Co50-xMn25+xGa25
(x=0-25) alloys have been systematically investigated by both experiments and
first-principles calculations. We found that all the samples exhibited body
centered cubic structures with a high degree of atomic ordering. With
increasing Ga content, the composition dependence of lattice parameters shows a
kink point at the middle composition in Co50-xMn25Ga25+x alloys, which can be
attributed to the enhanced covalent effect between the Ga and the transition
metals. Furthermore, a complicated magnetic competition has been revealed in
Co50-xMn25Ga25+x alloys, which causes the Curie temperature dramatically
decrease and results in a magnetic moment compensation behavior. In
Co50-xMn25+xGa25 alloys, however, with increasing Mn content, an additional
ferrimagnetic configuration was established in the native ferromagnetic matrix,
which causes the molecular moment monotonously decreases and the exchange
interaction enhances gradually. The electronic structure calculations indicate
that the Co50-xMn25+xGa25 alloys are likely to be in a coexistence state of the
itinerant and localized magnetism. Our study will be helpful to understand the
nature of magnetic ordering as well as to tune magnetic compensation and
electronic properties of Heusler alloys.",1210.5810v1
2013/1/9,The influence of structural disorder on magnetic domain formation in perpendicular anisotropy thin films,"Using a combination of resonant soft x-ray scattering, magnetometry, x-ray
reflectivity and microscopy techniques we have investigated the magnetic
properties and microstructure of a series of perpendicular anisotropy Co/Pt
multilayer films with respect to structural disorder tuned by varying the
sputtering deposition pressure. The observed magnetic changes in domain size,
shape and correlation length originate from structural and chemical variations
in the samples, such as chemical segregation and grain formation as well as
roughness at the surface and interfaces, which are all impacted by the
deposition pressure. For low pressure samples we find evidence of a random
""gas-like"" distribution of magnetic domains, while in the higher pressure
samples the domain structure exhibits only short range ""liquid-like"" positional
ordering. The structural and chemical disorder induced by the higher deposition
pressure first leads to an increase in the number of magnetic point defects
that limit free domain wall propagation. Then, as the sputtering pressure is
further increased, the domain wall energy density is lowered due to the
formation of local regions with reduced magnetic moment, and finally
magnetically void regions appear that confine the magnetic domains and
clusters, similar to segregated granular magnetic recording media.",1301.1737v2
2013/1/28,Magnetization dynamics in Co2$MnGe/Al2$O3$/Co tunnel junctions grown on different substrates,"We study static and dynamic magnetic properties of Co2MnGe (13 nm)/Al2O3 (3
nm)/Co (13 nm) tunnel magnetic junctions (TMJ), deposited on various single
crystalline substrates (a-plane sapphire, MgO(100), Si(111)). The results are
compared to the magnetic properties of Co and of Co$_{2}$MnGe single films
lying on sapphire substrates. X-rays diffraction always shows a (110)
orientation of the Co$_{2}$MnGe films. Structural observations obtained by high
resolution transmission electron microscopy confirmed the high quality of the
TMJ grown on sapphire. Our vibrating sample magnetometry measurements reveal
in-plane anisotropy only in samples grown on a sapphire substrate. Depending on
the substrate, the ferromagnetic resonance spectra of the TMJs, studied by the
microstrip technique, show one or two pseudo-uniform modes. In the case of MgO
and of Si substrates only one mode is observed: it is described by magnetic
parameters (g-factor, effective magnetization, in-plane magnetic anisotropy)
derived in the frame of a simple expression of the magnetic energy density;
these parameters are practically identical to those obtained for the Co single
film. With a sapphire substrate two modes are present: one of them does not
appreciably differ from the observed mode in the Co single film while the other
one is similar to the mode appearing in the Co$_{2}$MnGe single film: their
magnetic parameters can thus be determined independently, using a classical
model for the energy density in the absence of interlayer exchange coupling.",1301.6563v1
2013/3/18,"Absence of a static in-plane magnetic moment in the ""hidden-order"" phase of URu$_2$Si$_2$","We have carried out a careful magnetic neutron scattering study of the heavy
fermion compound \URuSi\ to probe the possible existence of a small magnetic
moment parallel to tetragonal basal plane in the ""hidden-order"" phase. This
small in-plane component of the magnetic moment on the uranium sites
$S_\parallel$ has been postulated by two recent models (rank-5
superspin/hastatic order) aiming to explain the hidden-order phase, in addition
to the well-known out-of-plane component $S_\perp ~ \approx~0.01-0.04
$\mu_B$/U. In order to separate $S_\parallel$ and $S_\perp$ we take advantage
of the condition that for magnetic neutron scattering only the components of
the magnetic structure that are perpendicular to the scattering vector $Q$
contribute to the magnetic scattering. We find no evidence for an in-plane
magnetic moment $S_\parallel$. Based on the statistics of our measurement, we
establish that the upper experimental limit for the size of any possible
in-plane component is $S^{\rm{max}}_\parallel ~ \leq~1\cdot 10^{-3} ~\mu_B$/U.",1303.4135v2
2013/10/11,"Chemical pressure effects on structural, dielectric and magnetic properties of solid solutions Mn3-xCoxTeO6","The effects of Co2+ doping on the structural, magnetic and dielectric
properties of the multiferroic frustrated antiferromagnet Mn3TeO6 have been
investigated. Ceramic samples of the solid solution series Mn3-xCoxTeO6 were
prepared by a solid-state reaction route. X-ray and neutron powder diffraction
and electron microscopy techniques were combined with calorimetric, dielectric
and magnetic measurements to investigate the dependence of the crystal
structure and physical properties on temperature and composition. It is shown
that the compounds with x up to 2.4 all adopt the trigonal corundum-related
structure of pure Mn3TeO6 (space group R-3) in the temperature range 5-295 K
and that the lattice parameters a and c and the unit-cell volume V decrease
linearly with increasing Co2+ concentration. The low- temperature magnetic
susceptibility and heat capacity data evidence the antiferromagnetic ordering
of all samples. The Neel temperature linearly increases with Co2+ concentration
x. Curie-Weiss fits of the high temperature susceptibility indicate that the
magnetic frustration decreases with x. The derived magnetic structure of
Mn3TeO6 can be described as an incommensurately modulated magnetic spin state
with k = [0, 0, kz] and an elliptical spin- spiral order of spins within the
chains of MnO6 octahedra. With increasing Co2+ concentration the propagation
vector kz changes from 0.453 (x = 0) to 0.516 (x = 2.4). The magnetic
anisotropy changes as well, leading to a reorientation of the spiral-basal
plane. A possible coexistence of long-range order of electrical dipoles and
magnetic moments in Mn3-xCoxTeO6 is discussed.",1310.3057v1
2014/3/21,Imaging superconducting vortex core and lattice with the scanning tunneling microscope,"The observation of vortices in superconductors was a major breakthrough in
developing the conceptual background for superconducting applications. Each
vortex carries a flux quantum, and the magnetic field radially decreases from
the center. Techniques used to make magnetic field maps, such as magnetic
decoration, give vortex lattice images in a variety of systems. However, strong
type II superconductors allow penetration of the magnetic field over large
distances, of order of the magnetic penetration depth \lambda.
Superconductivity survives up to magnetic fields where, for imaging purposes,
there is nearly no magnetic contrast. Static and dynamic properties of vortices
are largely unknown at such high magnetic fields. Reciprocal space studies
using neutron scattering give insight into the collective behavior. But the
microscopic details of vortex arrangements and their motion remain difficult to
obtain. Direct real space visualization can be made using scanning tunneling
microscopy and spectroscopy (STM/S). Instead of using magnetic contrast, the
electronic density of states describes spatial variations of the quasiparticle
and pair wavefunction properties. These are of order of the superconducting
coherence length \xi, which is much smaller than \lambda. In principle,
individual vortices can be imaged using STM up to the upper critical field
where vortex cores, of size \xi, overlap. In this review, we describe recent
advances in vortex imaging made with scanning tunneling microscopy and
spectroscopy. We introduce the technique and discuss vortex images which reveal
the influence of the Fermi surface distribution of the superconducting gap on
the internal structure of vortices, the collective behavior of the lattice in
different materials and conditions, and the observation of vortex lattice
melting.",1403.5514v1
2014/4/8,Nonhelical inverse transfer of a decaying turbulent magnetic field,"In the presence of magnetic helicity, inverse transfer from small to large
scales is well known in magnetohydrodynamic (MHD) turbulence and has
applications in astrophysics, cosmology, and fusion plasmas. Using high
resolution direct numerical simulations of magnetically dominated
self-similarly decaying MHD turbulence, we report a similar inverse transfer
even in the absence of magnetic helicity. We compute for the first time
spectral energy transfer rates to show that this inverse transfer is about half
as strong as with helicity, but in both cases the magnetic gain at large scales
results from velocity at similar scales interacting with smaller-scale magnetic
fields. This suggests that both inverse transfers are a consequence of a
universal mechanisms for magnetically dominated turbulence. Possible
explanations include inverse cascading of the mean squared vector potential
associated with local near two-dimensionality and the shallower $k^2$
subinertial range spectrum of kinetic energy forcing the magnetic field with a
$k^4$ subinertial range to attain larger-scale coherence. The inertial range
shows a clear $k^{-2}$ spectrum and is the first example of fully isotropic
magnetically dominated MHD turbulence exhibiting weak turbulence scaling.",1404.2238v3
2014/7/6,Scanning localized magnetic fields in a microfluidic device with a single nitrogen vacancy center,"Nitrogen vacancy (NV) color centers in diamond have emerged as highly
versatile optical emitters that exhibit room temperature spin properties. These
characteristics make NV centers ideal for magnetometry, which plays an
important role in chemical and biological sensing applications. The integration
of NV magnetometers with microfluidic systems could enable the study of
isolated chemical and biological samples in a fluid environment with high
spatial resolution. Here we demonstrate a method to perform localized
magnetometry with nanometer spatial precision using a single NV center in a
microfluidic device. We manipulate a magnetic particle within a liquid
environment using a combination of planar microfluidic flow control and
vertical magnetic actuation to achieve 3-dimensional manipulation. A diamond
nanocrystal containing a single NV center is deposited in the microfluidic
channels and acts as a local magnetic field probe. We map out the magnetic
field distribution of the magnetic particle by varying its position relative to
the diamond nanocrystal and performing optically resolved electron spin
resonance (ESR) measurements. We control the magnetic particle position with a
48 nm precision and attain a magnetic field sensitivity of 17.5
microTesla/Hz^1/2. These results open up the possibility for studying local
magnetic properties of biological and chemical systems with high sensitivity in
an integrated microfluidic platform.",1407.1452v2
2014/11/5,Room temperature magnetic order on zigzag edges of narrow graphene nanoribbons,"Magnetic order emerging in otherwise non-magnetic materials as carbon is a
paradigmatic example of a novel type of s-p electron magnetism predicted to be
of exceptional high-temperature stability. It has been demonstrated that atomic
scale structural defects of graphene can host unpaired spins. However, it is
still unclear under which conditions long-range magnetic order can emerge from
such defect-bound magnetic moments. Here we propose that in contrast to random
defect distributions, atomic scale engineering of graphene edges with specific
crystallographic orientation, comprising edge atoms only from one sub-lattice
of the bipartite graphene lattice, can give rise to a robust magnetic order. We
employ a nanofabrication technique based on Scanning Tunneling Microscopy to
define graphene nanoribbons with nanometer precision and well-defined
crystallographic edge orientations. While armchair ribbons display quantum
confinement gap, zigzag ribbons narrower than 7 nm reveal a bandgap of about
0.2 - 0.3 eV, which can be identified as a signature of interaction induced
spin ordering along their edges. Moreover, a semiconductor to metal transition
is revealed upon increasing the ribbon width, indicating the switching of the
magnetic coupling between opposite ribbon edges from antiferromagnetic to
ferromagnetic configuration. We found that the magnetic order on graphene edges
of controlled zigzag orientation can be stable even at room temperature,
raising hope for graphene-based spintronic devices operating under ambient
conditions.",1411.1196v1
2015/2/11,Anisotropic defect-induced ferromagnetism and transport in Gd-doped GaN two-dimensional electron gasses,"Here we report on the effect of rare earth Gd-doping on the magnetic
properties and magnetotransport of GaN two-dimensional electron gasses (2DEGs).
Samples are grown by plasma-assisted molecular beam epitaxy and consist of
AlN/GaN heterostructures where Gd is delta-doped within a polarization-induced
2DEG. Ferromagnetism is observed in these Gd-doped 2DEGs with a Curie
temperature above room temperature and an anisotropic spontaneous magnetization
preferring an out-of-plane (c-axis) orientation. At magnetic fields up to 50
kOe, the magnetization remains smaller for in-plane configuration than for
out-of-plane, which is indicative of exchange coupled spins locked along the
polar c-axis. The sample with the lowest Gd concentration (2.3 $\times$
$10^{14}$ cm$^{-2}$) exhibits a saturation magnetization of 41.1
$\mu_B/Gd^{3+}$ at 5 K revealing that the Gd ion spins (7 ${\mu}_B$) alone do
not account for the magnetization. Surprisingly, control samples grown without
any Gd display inconsistent magnetic properties; in some control samples weak
ferromagnetism is observed and in others paramagnetism. The ferromagnetic 2DEGs
do not exhibit the anomalous Hall effect; the Hall resistance varies
non-linearly with the magnetic field, but does not track the magnetization
indicating the lack of coupling between the ferromagnetic phase and the
conduction band electrons within the 2DEG.",1502.03478v2
2015/3/2,Spin-glass-like freezing of inner and outer surface layers in hollow γFe$_2$O$_3$ nanoparticles,"Disorder among surface spins largely dominates the magnetic response of
ultrafine magnetic particle systems. In this work, we examine time-dependent
magnetization in high-quality, monodisperse hollow maghemite nanoparticles with
a 14.8 $\pm$ 0.5 nm outer diameter and enhanced surface-to-volume ratio. The
nanoparticle ensemble exhibits spin-glass-like signatures in dc magnetic aging
and memory protocols and ac magnetic susceptibility. The dynamics of the system
slows near 50 K, and becomes frozen on experimental time scales below 20 K.
Remanence curves indicate the development of magnetic irreversibility
concurrent with the freezing of the spin dynamics. A strong exchange-bias
effect and its training behavior point to highly frustrated surface spins that
rearrange much more slowly than interior spins with bulk coordination. Monte
Carlo simulations of a hollow particle reproducing the experimental morphology
corroborated strongly disordered surface layers with complex energy landscapes
that underlie both glass-like dynamics and magnetic irreversibility. Calculated
hysteresis loops reveal that magnetic behavior is not identical at the inner
and outer surfaces, with spins at the outer surface layer of the 15 nm hollow
particles exhibiting a higher degree of frustration. Our study sheds light on
the origin of spin-glass-like phenomena and the role of surface spins in
magnetic hollow nanostructures.",1503.00602v2
2015/3/30,Implications of magnetic and magnetodielectric behavior of GdCrTiO5,"We have carried out dc magnetization (M), heat-capacity (C) and dielectric
studies down to 2K for the compound GdCrTiO5, crystallizing in orthorhombic
Pbam structure, in which well-known multiferroics RMn2O5 (R= Rare-earths) form.
The points of emphasis are: (i) The magnetic ordering temperature of Cr appears
to be suppressed compared to that in isostructural Nd counterpart, NdCrTiO5,
for which the Neel temperature is about 21 K. This finding on the Gd compound
suggests that Nd 4f orbital plays a role on the magnetism of Cr in contrast to
a proposal long ago. (ii) Dielectric constant does not exhibit any notable
feature below about 30 K in the absence of external magnetic field, but a peak
appears and gets stronger with the application of external magnetic fields,
supporting the existence of magnetodielectric coupling. (iii) The dielectric
anomalies appear even near 100 K, which can be attributed to short-range
magnetic-order. We also observe a gain in spectral weight below about 150 K in
Raman spectra in the frequency range 150 to 400 cm-1, which could be magnetic
in origin supporting short-range magnetic order. It is of interest to explore
whether geometrically frustration plays any role on the dielectric properties
of this family, as in the case of RMn2O5.",1503.08729v2
2015/7/27,Room temperature dielectric and magnetic properties of Gd and Ti co-doped BiFeO$_{3}$ ceramics,"Room temperature dielectric and magnetic properties of BiFeO$_3$ samples,
co-doped with magnetic Gd and non-magnetic Ti in place of Bi and Fe,
respectively, were reported. The nominal compositions of
Bi$_{0.9}$Gd$_{0.1}$Fe$_{1-x}$Ti$_x$O$_3$ (x = 0.00-0.25) ceramics were
synthesized by conventional solid state reaction technique. X-ray diffraction
patterns revealed that the substitution of Fe by Ti induces a phase transition
from rhombohedral to orthorhombic at x $>$ 0.20. Morphological studies
demonstrated that the average grain size was reduced from $\sim {~}$1.5 $\mu m$
to $\sim {~}$200 $nm$ with the increase in Ti content. Due to Ti substitution,
the dielectric constant was stable over a wide range of high frequencies (30
kHz to 20 MHz) by suppressing the dispersion at low frequencies. The dielectric
properties of the compounds are associated with their improved morphologies and
reduced leakage current densities probably due to the lower concentration of
oxygen vacancies in the compositions. Magnetic properties of
Bi$_{0.9}$Gd$_{0.1}$Fe$_{1-x}$Ti$_x$O$_3$ (x = 0.00-0.25) ceramics measured at
room temperature were enhanced with Ti substitution up to 20 $\%$ compared to
that of pure BiFeO$_3$ and Ti undoped Bi$_{0.9}$Gd$_{0.1}$FeO$_3$ samples. The
enhanced magnetic properties might be attributed to the substitution induced
suppression of spiral spin structure of BiFeO$_3$. An asymmetric shifts both in
the field and magnetization axes of magnetization versus magnetic field (M-H)
curves was observed. This indicates the presence of exchange bias effect in
these compounds notably at room temperature.",1507.07365v1
2015/10/5,Absence of magnetic proximity effects in magnetoresistive Pt/CoFe2O4 hybrid interfaces,"Ultra-thin Pt films grown on insulating ferrimagnetic CoFe2O4 (111) epitaxial
films display a magnetoresistance upon rotating the magnetization of the
magnetic layer. We report here X-ray magnetic circular dichroism (XMCD)
recorded at Pt-L2,3 and Pt-M3 edges. The results indicate that the Pt magnetic
moment, if any, is below the detection limit (< 0.001 {\mu}$_B$/Pt), thus
strongly favoring the view that the presence of CoFe2O4 does not induce the
formation of magnetic moments in Pt. Therefore, the observed magnetoresistance
cannot be attributed to some sort of proximity-induced magnetic moments at Pt
ions and subsequent magnetic-field dependent scattering. It thus follows that
either bulk (spin Hall and Inverse spin Hall Effects) or interface (Rashba)
spin-orbit related effects dominate the observed magnetoresistance.
Furthermore, comparison of bulk magnetization and XMCD data at (Fe,Co)-L2,3
edges suggests the presence of some spin disorder in the CoFe2O4 layer which
may be relevant for the observed anomalous non-saturating field-dependence of
spin Hall magnetoresistance.",1510.01080v4
2016/2/16,Fragile singlet ground state magnetism in pyrochlore osmates R2Os2O7 (R=Y and Ho),"The singlet ground state magnetism in pyrochlore osmates Y$_2$Os$_2$O$_7$ and
Ho$_2$Os$_2$O$_7$ is studied by DC and AC susceptibility, specific heat, and
neutron powder diffraction measurements. Despite the expected non-magnetic
singlet in the strong spin-orbit coupling (SOC) limit for Os$^{4+}$ ($5d^4$),
Y$_2$Os$_2$O$_7$ exhibits a spin-glass (SG) ground state below 4 K with weak
magnetism, suggesting possible proximity to a quantum phase transition between
the non-magnetic state in the strong SOC limit and the magnetic state in the
strong superexchange limit. Ho$_2$Os$_2$O$_7$ has the same structural
distortion as occurs in Y$_2$Os$_2$O$_7$. However, the Os sublattice in
Ho$_2$Os$_2$O$_7$ shows long-range magnetic ordering below 36\,K. The sharp
difference of the magnetic ground state between Y$_2$Os$_2$O$_7$ and
Ho$_2$Os$_2$O$_7$ signals the singlet ground state magnetism in
$R_2$Os$_2$O$_7$ is fragile and can be disturbed by the weak $4f-5d$
interactions.",1602.05121v1
2016/2/17,Antiferromagnetic Coupling between Surface and Bulk Magnetization and Anomalous Magnetic Transport in Electro-deposited Co Film,"We report an interesting magnetic behavior of a Co film (thickness ~ 350
{\AA}) grown on Si/Ti/Cu buffer layer by electro-deposition (ED) technique.
Using depth sensitive X-ray reflectivity and polarized neutron reflectivity
(PNR) we observed two layer structures for the Co film grown by ED with a
surface layer (thickness ~ 100 {\AA}) of reduced density (~ 68% of bulk)
compared to rest of the Co film (thickness ~ 250 {\AA}). The two layer
structure is consistent with the histogram profile obtained from atomic force
microscope (AFM) of the film. Interestingly, using PNR, we found that the
magnetization in the surface Co layer is inversely (antiferomagnetically)
coupled (negative magnetization for surface Co layer) with the rest of the Co
layer for the ED grown film. While we compare PNR result for a Co film of
similar layered structure grown by sputtering, the film showed a uniform
magnetization as expected. We also show that the depth dependent unusual
magnetic behavior of ED grown Co film may be responsible for anomalous
anisotropic magnetoresistance observed in low field in this film as compared to
the Co film grown by sputtering. Combining X-ray scattering, AFM,
superconducting quantum interface device magnetometry (SQUID), PNR and
magneto-transport measurements we attempted to correlate and compare the
structural, magnetic and morphological properties with magneto-transport of Co
films grown by ED and sputtering. The study indicates that the interesting
surface magnetic property and magneto-transport property of the ED film is
caused by its unique surface morphology.",1602.05297v1
2016/3/14,Lifshitz scaling effects on holographic paramagnetism/ferromagneism phase transition,"In the probe limit, we investigate holographic paramagnetism-ferromagnetism
phase transition in the four-dimensional (4D) and five-dimensional(5D) Lifshitz
black holes by means of numerical and semi-analytical methods, which is
realized by introducing a massive 2-form field coupled to the Maxwell field. We
find that the Lifshitz dynamical exponent $z$ contributes evidently to magnetic
moment and hysteresis loop of single magnetic domain quantitatively not
qualitatively. Concretely, in the case without external magnetic field, the
spontaneous magnetization and ferromagnetic phase transition happen when the
temperature gets low enough, and the critical exponent for the magnetic moment
is always $1/2$, which is in agreement with the result from mean field theory.
And the increasing $z$ enhances the phase transition and increases the DC
resistivity which behaves as the colossal magnetic resistance effect in some
materials. Furthermore, in the presence of the external magnetic field, the
magnetic susceptibility satisfies the Cure-Weiss law with a general $z$. But
the increase of $z$ will result in shortening the period of the external
magnetic field.",1603.04149v1
2016/5/17,"Magnetism of a rhombohedral-type pyrochlore-derived Kagome series, Mn2R3Sb3O14 (R= Rare-earths)","The results of magnetic investigations on a new series of compounds,
Mn2R3Sb3O14, containing 2-dimensional Kagome lattice of R ions and belonging to
pyrochlore series, are presented. Crystallographic features of light R members
(R= La, Pr and Nd) of this family, as established in the recent literature,
have been reported to be novel in many respects, in particular, the rhomohedral
nature of the structure which is rare among pyrochlores. It was also reported
that, as the R becomes heavier, beyond R= Sm, the fraction of well-known cubic
pyrochlore phase tends to gradually dominate. Here, we report that we are able
to form the Gd member in the rhombohedral form without noticeable admixture
from the cubic phase. With respect to magnetic behavior, our magnetization
measurements on the La member reveal that Mn exists in divalent state without
any evidence for long range magnetic ordering down to 2 K (that is, suppressed
magnetism), which is not so common for Mn based oxides, though
antiferromagnerism below 2 K is not ruled out. Nd and Gd members, are however,
found to show distinct features above 2 K in magnetic susceptibility and
heat-capacity, attributable to long-range magnetic ordering from respective
rare-earth sublattice. The experimental results with respect to magnetism are
found to be consistent with the results from ab initio band structure
calculations performed for the La case. The calculations imply that electron
correlation is important to describe insulating behavior.",1605.05027v1
2016/8/30,Magnetic properties of bilayer Sr$_3$Ir$_2$O$_7$: role of epitaxial strain and oxygen vacancies,"Using {\it ab initio} methods, we investigate the modification of the
magnetic properties of the $m=2$ member of the strontium iridates
Ruddlesden-Popper series Sr$_{m+1}$Ir$_{m}$O$_{3m+1}$, bilayer
Sr$_3$Ir$_2$O$_7$, induced by epitaxial strain and oxygen vacancies. Unlike the
single layer compound Sr$_2$IrO$_4$, which exhibits a robust in-plane magnetic
order, the energy difference between in-plane and out-of-plane magnetic
orderings in Sr$_3$Ir$_2$O$_7$ is much smaller and it is expected that small
external perturbations could induce magnetic transitions. Our results indicate
that epitaxial strain yields a spin-flop transition, that is driven by the
crossover between the intralayer $J_1$ and interlayer $J_2$ magnetic exchange
interactions upon compressive strain. While $J_1$ is essentially insensitive to
strain effects, the strength of $J_2$ changes by one order of magnitude for
tensile strains $\geq$ 3~\%. In addition, our study clarifies that the unusual
in-plane magnetic response observed in Sr$_3$Ir$_2$O$_7$ upon the application
of an external magnetic field originates from the canting of the local magnetic
moments due to oxygen vacancies, which tilt the octahedral networks - thereby
allowing for noncollinear spin configurations.",1608.08467v2
2016/9/10,Induced ferromagnetic moment at the interface between epitaxial SrRuO$_3$ film and Sr$_2$RuO$_4$ single crystal,"SrRuO$_3$ (SRO113) is an important material for device physics particularly
as one of the best metallic oxide electrodes for ferroelectric devices. This
oxide has moderate electron correlations with novel properties including
ferromagnetic ordering, which can be utilized in future to spintronics and
superconducting spintronics devices. Recently, we observed strongly enhanced
magnetization of SRO113 thin films grown on single crystals of the spin-triplet
superconductor Sr$_2$RuO$_4$ (SRO214). To clarify the origin of such an
enhancement, we conducted systematic investigations of magnetic properties of
SRO113 films deposited on a variety of oxide substrates. We carefully
subtracted the substrate contributions and found that the enhanced 2
magnetization occurs only for SRO113/SRO214 films. We further found that
neither strain nor metallicity of the substrate plays any significant roles in
the enhancement. The X-ray magnetic circular dichroism reveals that the
substrate-induced strain does not switch the Ru4+ state from the low-spin to
high-spin states. The film-thickness dependence of the magnetization of
SRO113/SRO214 films strongly suggest that the additional magnetization arises
due to the induction of magnetic moment into the SRO214 substrate over 20-nm
depth. Our results imply new magnetic functionality that can trigger studies
searching for yet unknown physical phenomena in magnetic ruthenates.",1609.03010v1
2016/9/21,Ultrafast Magnetization Reversal by Picosecond Electrical Pulses,"The field of spintronics involves the study of both spin and charge transport
in solid state devices with a view toward increasing their functionality and
efficiency. Alternatively, the field of ultrafast magnetism focuses on the use
of femtosecond laser pulses to excite electrons in magnetic materials, which
allows the magnetic order to be dramatically changed on unprecedented
sub-picosecond time-scales. Here, we unite these two distinct research
activities by using picosecond electrical pulses to rapidly excite electrons in
a magnetic metal. We are able to deterministically and repetitively reverse the
magnetization of a GdFeCo film with sub-10 picosecond electrical pulses. The
magnetization reverses in ~10ps, which is more than an order of magnitude
faster than any other electrically controlled magnetic switching. We attribute
the deterministic switching of the magnetization to ultrafast excitation of the
electrons, a fundamentally different mechanism from other current driven
switching mechanisms such as spin-transfer-torque (STT) or spin-orbit-torque
(SOT). The energy density required for switching is measured and the process is
found to be efficient, projecting to only 4 fJ needed to switch a (20 nm)^3
cell, which is comparable to other state-of-the-art STT-MRAM memory devices.
This discovery will launch a new field of research into picosecond spintronic
phenomena and devices.",1609.06392v2
2016/12/2,Magnetic Field Devices for Neutron Spin Transport and Manipulation in Precise Neutron Spin Rotation Mesurements,"The neutron spin is a critical degree of freedom for many precision
measurements using low-energy neutrons. Fundamental symmetries and interactions
can be studied using polarized neutrons. Parity-violation (PV) in the hadronic
weak interaction and the search for exotic forces that depend on the relative
spin and velocity, are two questions of fundamental physics that can be studied
via the neutron spin rotations that arise from the interaction of polarized
cold neutrons and unpolarized matter. The Neutron Spin Rotation (NSR)
collaboration developed a neutron polarimeter, capable of determining neutron
spin rotations of the order of $10^{-7}$ rad per meter of traversed material.
This paper describes two key components of the NSR apparatus, responsible for
the transport and manipulation of the spin of the neutrons before and after the
target region, which is surrounded by magnetic shielding and where residual
magnetic fields need to be below 100 \textmu G. These magnetic field devices,
called input and output coils, provide the magnetic field for adiabatic
transport of the neutron spin in the regions outside the magnetic shielding
while producing a sharp nonadiabatic transition of the neutron spin when
entering/exiting the low-magnetic-field region. In addition, the coils are self
contained, forcing the return magnetic flux into a compact region of space to
minimize fringe fields outside. The design of the input and output coil is
based on the magnetic scalar potential method.",1612.00880v1
2016/12/17,Magnetic resonance study of bulk and thin film EuTiO3,"Magnetic resonance spectra of EuTiO3 in both bulk and thin film form were
taken at temperatures from 3-350 K and microwave frequencies from 9.2-9.8 and
34 GHz. In the paramagnetic phase, magnetic resonance spectra are determined by
magnetic dipole and exchange interactions between Eu2+ spins. In the film, a
large contribution arises from the demagnetization field. From detailed
analysis of the linewidth and its temperature dependence, the parameters of
spin-spin interactions were determined: the exchange frequency is 15-15.5 GHz
and the estimated critical exponent of the spin correlation length is ~ 0.5. In
the bulk samples, the spectra exhibited a distinct minimum in the linewidth at
the N\'eel temperature, T_N = 5.5 K, while the resonance field practically does
not change even on cooling below T_N. This is indicative of a small magnetic
anisotropy ~ 320 G in the antiferromagnetic phase. In the film, the magnetic
resonance spectrum is split below T_N into several components due to excitation
of the magnetostatic modes, corresponding to a non-uniform precession of
magnetization. Moreover, the film was observed to degrade over two years. This
was manifested by an increase of defects and a change in the domain structure.
The saturated magnetization in the film, estimated from the magnetic resonance
spectrum, was about 900 emu/cm3 or 5.5 mu_B/unit cell at T = 3.5 K.",1612.05781v1
2017/1/7,Interface enhanced spin-orbit torques and current-induced magnetization switching of Pd/Co/AlO$_x$ layers,"Magnetic heterostructures that combine large spin-orbit torque efficiency,
perpendicular magnetic anisotropy, and low resistivity are key to develop
electrically-controlled memory and logic devices. Here we report on vector
measurements of the current-induced spin orbit torques and magnetization
switching in perpendicularly magnetized Pd/Co/AlO$_x$ layers as a function of
Pd thickness. We find sizeable damping-like (DL) and field-like (FL) torques,
of the order of 1~mT per $10^7$~A/cm$^2$, which have different thickness and
magnetization angle dependence. The analysis of the DL torque efficiency per
unit current density and electric field using drift-diffusion theory leads to
an effective spin Hall angle and spin diffusion length of Pd larger than 0.03
and 7~nm, respectively. The FL SOT includes a significant interface
contribution, is larger than estimated using drift-diffusion parameters, and is
further strongly enhanced upon rotation of the magnetization from the
out-of-plane to the in-plane direction. Finally, taking advantage of the large
spin-orbit torques in this system, we demonstrate bipolar magnetization
switching of Pd/Co/AlO$_x$ layers with similar current density as used for
Pt/Co layers with comparable perpendicular magnetic anisotropy.",1701.01843v1
2017/2/1,Absence of magnetism in the superconductor Ba2Ti2Fe2As4O: Insights from inelastic neutron scattering measurements and ab initio calculations of phonon spectra,"Ba2Ti2Fe2As4O is a self-doped superconductor exhibiting a Tc ~ 21.5 K and
containing, distinctively with respect to other Fe-based superconductors, not
only [Fe2As2] layers but also conducting [Ti2O] sheets. This compound exhibits
a transition at T* ~ 125 K which has tentatively been assigned in the
literature to a possible density-wave order. However, the nature of this
density wave (whether it is a charge- or spin-induced) is still under debate.
Magnetism in Ba2Ti2Fe2As4O has never been experimentally confirmed, which
raises the question whether this superconductor might be non-magnetic or
exhibiting a very weak magnetism. Here, we report evidence from inelastic
neutron scattering (INS) measurements and ab initio calculations of phonon
spectra pointing towards absence of magnetism in Ba2Ti2Fe2As4O. The INS
measurements did not reveal any noticeable change of the phonon spectra across
Tc, neither could magnetic effects be observed within the accessible (Q, E)
space, setting Ba2Ti2Fe2As4O as an unconventional superconductor. The effect of
magnetism on describing phonon spectra was further investigated by performing
ab initio calculations. In this context, non-magnetic calculations reproduced
well the measured phonon spectra. Therefore, our results indicate a
non-magnetic and unconventional character of the superconductor Ba2Ti2Fe2As4O.",1702.00479v2
2017/3/28,Local and collective magnetism of EuFe$_2$As$_2$,"We present an experimental study of the local and collective magnetism of
$\mathrm{EuFe_2As_2}$, that is isostructural with the high temperature
superconductor parent compound $\mathrm{BaFe_2As_2}$. In contrast to
$\mathrm{BaFe_2As_2}$, where only Fe spins order, $\mathrm{EuFe_2As_2}$ has an
additional magnetic transition below 20 K due to the ordering of the Eu$^{2+}$
spins ($J =7/2$, with $L=0$ and $S=7/2$) in an A-type antiferromagnetic texture
(ferromagnetic layers stacked antiferromagnetically). This may potentially
affect the FeAs layer and its local and correlated magnetism. Fe-K$_\beta$
x-ray emission experiments on $\mathrm{EuFe_2As_2}$ single crystals reveal a
local magnetic moment of 1.3$\pm0.15~\mu_B$ at 15 K that slightly increases to
1.45$\pm0.15~\mu_B$ at 300 K. Resonant inelastic x-ray scattering (RIXS)
experiments performed on the same crystals show dispersive broad (in energy)
magnetic excitations along $\mathrm{(0, 0)\rightarrow(1, 0)}$ and $\mathrm{(0,
0)\rightarrow(1, 1)}$ with a bandwidth on the order of 170-180 meV. These
results on local and collective magnetism are in line with other parent
compounds of the $\mathrm{AFe_2As_2}$ series ($A=$ Ba, Ca, and Sr), especially
the well characterized $\mathrm{BaFe_2As_2}$. Thus, our experiments lead us to
the conclusion that the effect of the high magnetic moment of Eu on the
magnitude of both Fe local magnetic moment and spin excitations is small and
confined to low energy excitations.",1703.09819v1
2017/4/6,Spin-coating of moderately concentrated superparamagnetic colloids in different magnetic field configurations,"Spin-coating technique is very fast, cheap, reproducible, simple and needs
less material to fabricate films of particulate systems/colloids. Their
thickness and uniformity may be controlled by means of external fields. We
apply magnetic fields during the spin-coating of a moderately concentrated
superparamagnetic colloid (made of silica coated magnetite particles). We study
the influence of different magnetic field configurations (homogeneous and
inhomogeneous) on the resulting spin-coated deposits and compare experimental
results under various conditions. Superparamagnetic colloids behave as,
non-Newtonian, magnetorheological fluids. Their viscosity vary significantly
under applied magnetic fields. We measure and compare the effect of uniform and
non-uniform magnetic fields on their relative effective viscosity, using the
spin-coated deposits and a previously existing model for simple colloids. The
mechanisms involved in the deposits formation under different experimental
conditions are also discussed. In particular, we show that the magnetophoretic
effect plays an important role in the spin-coating of magnetic colloids
subjected to non-uniform magnetic fields. We characterize an effective
magnetoviscosity in non-uniform magnetic fields that is largely influenced by
the magnetophoretic effect that enhances the flow of the magnetic fluid.",1704.01956v3
2017/4/26,Ising-type Magnetic Anisotropy in CePd$_2$As$_2$,"We investigated the anisotropic magnetic properties of CePd$_2$As$_2$ by
magnetic, thermal and electrical transport studies. X-ray diffraction confirmed
the tetragonal ThCr$_2$Si$_2$-type structure and the high-quality of the single
crystals. Magnetisation and magnetic susceptibility data taken along the
different crystallographic directions evidence a huge crystalline electric
field (CEF) induced Ising-type magneto-crystalline anisotropy with a large
$c$-axis moment and a small in-plane moment at low temperature. A detailed CEF
analysis based on the magnetic susceptibility data indicates an almost pure
$\langle\pm5/2 \rvert$ CEF ground-state doublet with the dominantly
$\langle\pm3/2 \rvert$ and the $\langle\pm1/2 \rvert$ doublets at 290 K and 330
K, respectively. At low temperature, we observe a uniaxial antiferromagnetic
(AFM) transition at $T_N=14.7$ K with the crystallographic $c$-direction being
the magnetic easy-axis. The magnetic entropy gain up to $T_N$ reaches almost
$R\ln2$ indicating localised $4f$-electron magnetism without significant
Kondo-type interactions. Below $T_N$, the application of a magnetic field along
the $c$-axis induces a metamagnetic transition from the AFM to a
field-polarised phase at $\mu_0H_{c0}=0.95$ T, exhibiting a text-book example
of a spin-flip transition as anticipated for an Ising-type AFM.",1704.08103v1
2017/5/8,The influence of magnetic order on the magnetoresistance anisotropy of Fe$_{1+δ-x}$Cu$_{x}$Te,"We performed resistance measurements on Fe$_{1+\delta-x}$Cu$_{x}$Te with
$x_{EDX}\leq 0.06$ in the presence of in-plane applied magnetic fields,
revealing a resistance anisotropy that can be induced at a temperature far
below the structural and magnetic zero-field transition temperatures. The
observed resistance anisotropy strongly depends on the field orientation with
respect to the crystallographic axes, as well as on the field-cooling history.
Our results imply a correlation between the observed features and the
low-temperature magnetic order. Hysteresis in the angle-dependence indicates a
strong pinning of the magnetic order within a temperature range that varies
with the Cu content. The resistance anisotropy vanishes at different
temperatures depending on whether an external magnetic field or a remnant field
is present: the closing temperature is higher in the presence of an external
field. For $x_{EDX} = 0.06$ the resistance anisotropy closes above the
structural transition, at the same temperature at which the zero-field
short-range magnetic order disappears and the sample becomes paramagnetic. Thus
we suggest that under an external magnetic field the resistance anisotropy
mirrors the magnetic order parameter. We discuss similarities to nematic order
observed in other iron pnictide materials.",1705.02849v1
2017/6/9,Negative spin Hall magnetoresistance of Pt on the bulk easy-plane antiferromagnet NiO,"We report on spin Hall magnetoresistance (SMR) measurements of Pt Hall bars
on the antiferromagnetic NiO(111) single crystal. An SMR with a sign opposite
of conventional SMR is observed over a wide range of temperatures as well as
magnetic fields stronger than 0.25T. The negative sign of the SMR can be
explained by the alignment of magnetic moments being almost perpendicular to
the external magnetic field within the easy plane (111) of the antiferromagnet.
This correlation of magnetic moment alignment and external magnetic field
direction is realized just by the easy-plane nature of the material without the
need of any exchange coupling to an additional ferromagnet. The SMR signal
strength decreases with increasing temperature, primarily due to the decrease
in N\'eel order by including fluctuations. An increasing magnetic field
increases the SMR signal strength as there are less domains and the magnetic
moments are more strongly manipulated at high magnetic fields. The SMR is
saturated at an applied magnetic field of $6$~T resulting in a spin-mixing
conductance of $\sim10^{18}~ \Omega^{-1}$m$^{-2}$, which is comparable to that
of Pt on insulating ferrimagnets such as yttrium iron garnet. An argon plasma
treatment doubles the spin-mixing conductance.",1706.03004v1
2017/6/12,Magnetic quantum phase transition in Cr-doped Bi2(SexTe1-x)3 driven by the Stark effect,"The interplay between magnetism and topology, as exemplified in the magnetic
skyrmion systems, has emerged as a rich playground for finding novel quantum
phenomena and applications in future information technology. Magnetic
topological insulators (TI) have attracted much recent attention, especially
after the experimental realization of quantum anomalous Hall effect. Future
applications of magnetic TI hinge on the accurate manipulation of magnetism and
topology by external perturbations, preferably with a gate electric field. In
this work, we investigate the magneto transport properties of Cr doped
Bi2(SexTe1-x)3 TI across the topological quantum critical point (QCP). We find
that the external gate voltage has negligible effect on the magnetic order for
samples far away from the topological QCP. But for the sample near the QCP, we
observe a ferromagnetic (FM) to paramagnetic (PM) phase transition driven by
the gate electric field. Theoretical calculations show that a perpendicular
electric field causes a shift of electronic energy levels due to the Stark
effect, which induces a topological quantum phase transition and consequently a
magnetic phase transition. The in situ electrical control of the topological
and magnetic properties of TI shed important new lights on future topological
electronic or spintronic device applications.",1706.03506v1
2017/6/23,Fabrication of highly dense isotropic Nd-Fe-B bonded magnets via extrusion-based additive manufacturing,"Isotropic bonded magnets with a high loading fraction of 70 vol.% Nd-Fe-B are
fabricated via an extrusion-based additive manufacturing, or 3D printing system
that enables rapid production of large parts for the first time. The density of
the printed magnet is 5.15 g/cm3. The room temperature magnetic properties are:
intrinsic coercivity Hci = 8.9 kOe (708.2 kA/m), remanence Br = 5.8 kG (0.58
Tesla), and energy product (BH)max = 7.3 MGOe (58.1 kJ/m3). The as-printed
magnets are then coated with two types of polymers, both of which improve the
thermal stability at 127 {\deg}C as revealed by flux aging loss measurements.
Tensile tests performed at 25 {\deg}C and 100 {\deg}C show that the ultimate
tensile stress (UTS) increases with increasing loading fraction of the magnet
powder, and decreases with increasing temperature. AC magnetic susceptibility
and resistivity measurements show that the 3D printed Nd-Fe-B bonded magnets
exhibit extremely low eddy current loss and high resistivity. Finally, we show
that through back electromotive force measurements that motors installed with
3D printed Nd-Fe-B magnets exhibit similar performance as compared to those
installed with sintered ferrites.",1706.07792v1
2017/7/27,Common Glass-Forming Spin-Liquid State in the Pyrochlore Magnets Dy$_2$Ti$_2$O$_7$ and Ho$_2$Ti$_2$O$_7$,"Despite a well-ordered pyrochlore crystal structure and strong magnetic
interactions between the Dy$^{3+}$ or Ho$^{3+}$ ions, no long range magnetic
order has been detected in the pyrochlore titanates Ho$_2$Ti$_2$O$_7$ and
Dy$_2$Ti$_2$O$_7$. To explore the actual magnetic phase formed by cooling these
materials, we measure their magnetization dynamics using toroidal,
boundary-free magnetization transport techniques. We find that the dynamical
magnetic susceptibility of both compounds has the same distinctive
phenomenology, that is indistinguishable in form from that of the dielectric
permittivity of dipolar glass-forming liquids. Moreover, Ho$_2$Ti$_2$O$_7$ and
Dy$_2$Ti$_2$O$_7$ both exhibit microscopic magnetic relaxation times that
increase along the super-Arrhenius trajectories analogous to those observed in
glass-forming dipolar liquids. Thus, upon cooling below about 2K,
Dy$_2$Ti$_2$O$_7$ and Ho$_2$Ti$_2$O$_7$ both appear to enter the same magnetic
state exhibiting the characteristics of a glass-forming spin-liquid.",1707.09014v3
2017/9/18,Direct-write of free-form 3D nanostructures with controlled magnetic frustration,"Building nanotechnological analogues of naturally occurring magnetic
structures has proven to be a powerful approach to studying topics like
geometry-induced magnetic frustration and to provide model systems for
statistical physics. Moreover, it practically allows to engineer novel physical
properties by realizing artificial lattice geometries that are not accessible
via natural crystallization or chemical synthesis. This has been accomplished
with great success in the field of two-dimensional artificial spin ice systems
with important branches reaching into the field of magnetic logic devices.
Although first proposals have been made to advance into three dimensions (3D),
established nanofabrication pathways based on electron beam lithography have
not been adapted to obtain free-form 3D nanostructures. Here we demonstrate the
direct-write fabrication of freestanding ferromagnetic 3D nano-architectures
with full control over the degree of magnetic frustration. By employing
micro-Hall sensing, we have determined the magnetic stray field generated by
our free-form structures in an externally applied magnetic field and we have
performed micromagnetic and macro-spin simulations to deduce the spatial
magnetization profiles in the structures and analyze their switching behavior.
Furthermore we show that the magnetic 3D elements can be combined with other 3D
elements of different chemical composition and intrinsic material properties.",1709.05847v1
2017/9/29,Tuning the antiferromagnetic helical pitch length and nanoscale domain size in Fe$_3$PO$_4$O$_3$ by magnetic dilution,"The insulating magnetic material Fe3PO4O3 features a non-centrosymmetric
lattice composed of Fe^{3+} triangular units. Frustration, due to competing
near neighbor ($J_1$) and next nearest neighbor ($J_2$) antiferromagnetic
interactions, was recently suggested to be the origin of an antiferromagnetic
helical ground state with unusual needle-like nanoscale magnetic domains in
Fe3PO4O3. Magnetic dilution is shown here to tune the ratio of these magnetic
interactions, thus providing deeper insight into this unconventional
antiferromagnet. Dilution of the Fe^{3+} lattice in Fe3PO4O3 was accomplished
by substituting non-magnetic Ga^{3+} to form the solid solution series
Fe_{3-x}Ga_xPO4O3 with $x = 0.012, 0.06, 0.25, 0.5, 1.0, 1.5$. Magnetic
susceptibility and neutron powder diffraction data from this series are
presented. A continuous decrease of the both the helical pitch length and the
domain size is observed with increasing dilution up to at least $x = 0.25$,
while for $x \ge 0.5$, the compounds lack long range magnetic order entirely.
The decrease in the helical pitch length with increasing $x$ can be
qualitatively understood by reduction of the ratio of $J_2/J_1$ in the
Heisenberg model, consistent with mean field considerations. Intriguingly, the
magnetic correlation length in the $ab$ plane remains nearly equal to the pitch
length for each value of $x \le 0.25$, showing that the two quantities are
intrinsically connected in this unusual antiferromagnet.",1710.00051v1
2017/12/20,Disentangling magnetic hardening and molecular spin chain contributions to exchange bias in ferromagnet/molecule bilayers,"We performed SQUID and FMR magnetometry experiments to clarify the
relationship between two reported magnetic exchange effects arising from
interfacial spin-polarized charge transfer within ferromagnetic metal
(FM)/molecule bilayers: the magnetic hardening effect, and
spinterface-stabilized molecular spin chains. To disentangle these effects,
both of which can affect the FM magnetization reversal, we tuned the metal
phthalocyanine molecule central site's magnetic moment to selectively enhance
or suppress the formation of spin chains within the molecular film. We find
that both effects are distinct, and additive. In the process, we 1) extended
the list of FM/molecule candidate pairs that are known to generate magnetic
exchange effects, 2) experimentally confirmed the predicted increase in
anisotropy upon molecular adsorption; and 3) showed that spin chains within the
molecular film can enhance magnetic exchange. This magnetic ordering within the
organic layer implies a structural ordering. Thus, by distengangling the
magnetic hardening and exchange bias contributions, our results confirm, as an
echo to progress regarding inorganic spintronic tunnelling, that the milestone
of spintronic tunnelling across structurally ordered organic barriers has been
reached through previous magnetotransport experiments. This paves the way for
solid-state devices studies that exploit the quantum physical properties of
spin chains, notably through external stimuli.",1712.07450v1
2018/2/17,Electric-field control of magnetism in few-layered van der Waals magnet,"Manipulating quantum state via electrostatic gating has been intriguing for
many model systems in nanoelectronics. When it comes to the question of
controlling the electron spins, more specifically, the magnetism of a system,
tuning with electric field has been proven to be elusive. Recently, magnetic
layered semiconductors have attracted much attention due to their emerging new
physical phenomena. However, challenges still remain in the demonstration of a
gate controllable magnetism based on them. Here, we show that, via ionic
gating, strong field effect can be observed in few-layered semiconducting
Cr$_{2}$Ge$_{2}$Te$_{6}$ devices. At different gate doping, micro-area Kerr
measurements in the studied devices demonstrate tunable magnetization loops
below the Curie temperature, which is tentatively attributed to the moment
re-balance in the spin-polarized band structure. Our findings of electric-field
controlled magnetism in van der Waals magnets pave the way for potential
applications in new generation magnetic memory storage, sensors, and
spintronics.",1802.06255v1
2018/2/20,Electrical Control of 2D Magnetism in Bilayer CrI3,"The challenge of controlling magnetism using electric fields raises
fundamental questions and addresses technological needs such as low-dissipation
magnetic memory. The recently reported two-dimensional (2D) magnets provide a
new system for studying this problem owing to their unique magnetic properties.
For instance, bilayer chromium triiodide (CrI3) behaves as a layered
antiferromagnet with a magnetic field-driven metamagnetic transition. Here, we
demonstrate electrostatic gate control of magnetism in CrI3 bilayers, probed by
magneto-optical Kerr effect (MOKE) microscopy. At fixed magnetic fields near
the metamagnetic transition, we realize voltage-controlled switching between
antiferromagnetic and ferromagnetic states. At zero magnetic field, we
demonstrate a time-reversal pair of layered antiferromagnetic states which
exhibit spin-layer locking, leading to a remarkable linear dependence of their
MOKE signals on gate voltage with opposite slopes. Our results pave the way for
exploring new magnetoelectric phenomena and van der Waals spintronics based on
2D materials.",1802.06979v2
2018/3/2,Broadband spectroscopy of thermodynamic magnetization fluctuations through a ferromagnetic spin-reorientation transition,"We use scanning optical magnetometry to study the broadband frequency spectra
of spontaneous magnetization fluctuations, or ""magnetization noise"", in an
archetypal ferromagnetic film that can be smoothly tuned through a spin
reorientation transition (SRT). The SRT is achieved by laterally varying the
magnetic anisotropy across an ultrathin Pt/Co/Pt trilayer, from the
perpendicular to in-plane direction, via graded Ar$^+$ irradiation. In regions
exhibiting perpendicular anisotropy, the power spectrum of the magnetization
noise, $S(\nu)$, exhibits a remarkably robust $\nu^{-3/2}$ power law over
frequencies $\nu$ from 1~kHz to 1~MHz. As the SRT region is traversed, however,
$S(\nu)$ spectra develop a steadily-increasing critical frequency, $\nu_0$,
below which the noise power is spectrally flat, indicating an evolving
low-frequency cutoff for magnetization fluctuations. The magnetization noise
depends strongly on applied in- and out-of-plane magnetic fields, revealing
local anisotropies and also a field-induced emergence of fluctuations in
otherwise stable ferromagnetic films. Finally, we demonstrate that higher-order
correlators can be computed from the noise. These results highlight broadband
spectroscopy of thermodynamic fluctuations as a powerful tool to characterize
the interplay between thermal and magnetic energy scales, and as a means of
characterizing phase transitions in ferromagnets.",1803.00962v1
2018/2/21,Optical Receiver with Helicity Dependent Switching of Magnetization,"In this work, we propose helicity-dependent switching (HDS) of magnetization
of Co/Pt for energy efficient optical receiver. Designing a low power optical
receiver for optical-to-electrical signal conversion has proven to be very
challenging. Current day receivers use a photodiode that produces a
photocurrent in response to input optical signals, and power hungry
trans-impedance amplifiers are required to amplify the small photocurrents.
Here, we propose light helicity induced switching of magnetization to overcome
the requirement of photodiodes and subsequent trans-impedance amplification by
sensing the change in magnetization with a magnetic tunnel junction (MTJ).
Magnetization switching of a thin ferromagnet layer using circularly polarized
laser pulses have recently been demonstrated which shows one-to-one
correspondence between light helicity and the magnetization state. We propose
to utilize this phenomena by using digital input dependent circularly polarized
laser pulses to directly switch the magnetization state of a thin Co/Pt
ferromagnet layer at the receiver. The Co/Pt layer is used as the free layer of
an MTJ, the resistance of which is modified by the laser pulses. With the
one-to-one dependence between input data and output magnetization state, the
MTJ resistance is directly converted to digital output signal. Our device to
circuit level simulation results indicate that, HDS based optical receiver
consumes only 0.124 pJ/bit energy, which is much lower than existing
techniques.",1803.07148v1
2018/7/1,Dynamic modeling of levitation of a superconducting bulk by coupled $H$-magnetic field and Arbitrary Lagrangian-Eulerian formulations,"Intrinsically stable magnetic levitation between superconductors and
permanent magnets can be exploited in a variety of applications of great
technical interest in the field of transportation (rail transportation), energy
(flywheels) and industry. In this contribution, we present a new model for the
calculation of levitation forces between superconducting bulks and permanent
magnet, based on the $H$-formulation of Maxwell's equations coupled with an
Arbitrary Lagrangian-Eulerian formulation. The model uses a moving mesh that
adapts at each time step based on the time-change of the distance between a
superconductor bulk and a permanent magnet. The model is validated against a
fixed mesh model (recently in turn validated against experiments) that uses an
analytical approach for calculating the magnetic field generated by the moving
permanent magnet. Then, it is used to analyze the magnetic field dynamics both
in field-cooled and zero-field-cooled conditions and successively used to test
different configurations of permanent magnets and to compare them in terms of
levitation forces. The easiness of implementation of this model and its
flexibility in handling different geometries, material properties, and
application scenarios make the model an attractive tool for the analysis and
optimization of magnetic levitation-based applications.",1807.00329v2
2018/11/23,Magnetic Interactions in BiFeO$_3$: a First-Principles Study,"First-principles calculations, in combination with the four-state energy
mapping method, are performed to extract the magnetic interaction parameters of
multiferroic BiFeO$_3$. Such parameters include the symmetric exchange (SE)
couplings and the Dzyaloshinskii-Moriya (DM) interactions up to second nearest
neighbors, as well as the single ion anisotropy (SIA). All magnetic parameters
are obtained not only for the $R3c$ structural ground state, but also for the
$R3m$ and $R\bar{3}c$ phases in order to determine the effects of
ferroelectricity and antiferrodistortion distortions, respectively, on these
magnetic parameters. In particular, two different second-nearest neighbor
couplings are identified and their origins are discussed in details. Moreover,
Monte-Carlo (MC) simulations using a magnetic Hamiltonian incorporating these
first-principles-derived interaction parameters are further performed. They
result (i) not only in the accurate prediction of the spin-canted G-type
antiferromagnetic structure and of the known magnetic cycloid propagating along
a $<$1$\bar{1}$0$>$ direction, as well as their unusual characteristics (such
as a weak magnetization and spin-density-waves, respectively); (ii) but also in
the finding of another cycloidal state of low-energy and that awaits to be
experimentally confirmed. Turning on and off the different magnetic interaction
parameters in the MC simulations also reveal the precise role of each of them
on magnetism.",1811.09574v1
2019/1/9,Observation of Interfacial Antiferromagnetic Coupling between Magnetic Topological Insulator and Antiferromagnetic Insulator,"Inducing magnetic orders in a topological insulator (TI) to break its time
reversal symmetry has been predicted to reveal many exotic topological quantum
phenomena. The manipulation of magnetic orders in a TI layer can play a key
role in harnessing these quantum phenomena towards technological applications.
Here we fabricated a thin magnetic TI film on an antiferromagnetic (AFM)
insulator Cr2O3 layer and found that the magnetic moments of the magnetic TI
layer and the surface spins of the Cr2O3 layers favor interfacial AFM coupling.
Field cooling studies show a crossover from negative to positive exchange bias
clarifying the competition between the interfacial AFM coupling energy and the
Zeeman energy in the AFM insulator layer. The interfacial exchange coupling
also enhances the Curie temperature of the magnetic TI layer. The unique
interfacial AFM alignment in magnetic TI on AFM insulator heterostructures
opens a new route toward manipulating the interplay between topological states
and magnetic orders in spin-engineered heterostructures, facilitating the
exploration of proof-of-concept TI-based spintronic and electronic devices with
multi-functionality and low power consumption.",1901.02905v1
2019/2/14,Anomalous Spin-Orbit Torques in Magnetic Single-Layer Films,"Spin-orbit interaction (SOI) couples charge and spin transport, enabling
electrical control of magnetization. A quintessential example of SOI-induced
transport is the anomalous Hall effect (AHE), first observed in 1880, in which
an electric current perpendicular to the magnetization in a magnetic film
generates charge accumulation on the surfaces. Here we report the observation
of a counterpart of the AHE that we term the anomalous spin-orbit torque
(ASOT), wherein an electric current parallel to the magnetization generates
opposite spin-orbit torques on the surfaces of the magnetic film. We interpret
the ASOT as due to a spin-Hall-like current generated with an efficiency of
0.053+/-0.003 in Ni80Fe20, comparable to the spin Hall angle of Pt. Similar
effects are also observed in other common ferromagnetic metals, including Co,
Ni, and Fe. First principles calculations corroborate the order of magnitude of
the measured values. This work suggests that a strong spin current with spin
polarization transverse to magnetization can exist in a ferromagnet, despite
spin dephasing. It challenges the current understanding of spin-orbit torque in
magnetic/nonmagnetic bilayers, in which the charge-spin conversion in the
magnetic layer has been largely neglected.",1902.05490v1
2019/2/14,Calculating temperature-dependent properties of Nd$_2$Fe$_{14}$B permanent magnets by atomistic spin model simulations,"Temperature-dependent magnetic properties of Nd$_2$Fe$_{14}$B permanent
magnets, i.e., saturation magnetization $M_\text{s}(T)$, effective magnetic
anisotropy constants $K_i^\text{eff}(T)$ ($i=1,2,3$), domain wall width
$\delta_w(T)$, and exchange stiffness constant $A_\text{e}(T)$, are calculated
by using \textit{ab-initio} informed atomistic spin model simulations. We
construct the atomistic spin model Hamiltonian for Nd$_2$Fe$_{14}$B by using
the Heisenberg exchange of Fe$-$Fe and Fe$-$Nd atomic pairs, the uniaxial
single-ion anisotropy of Fe atoms, and the crystal-field energy of Nd ions
which is approximately expanded into an energy formula featured by second,
fourth, and sixth-order phenomenological anisotropy constants. After applying a
temperature rescaling strategy, we show that the calculated Curie temperature,
spin-reorientation phenomenon, $M_\text{s}(T)$, $\delta_w(T)$, and
$K_i^\text{eff}(T)$ agree well with the experimental results. $A_\text{e}(T)$
is estimated through a general continuum description of the domain wall profile
by mapping atomistic magnetic moments to the macroscopic magnetization.
$A_\text{e}$ is found to decrease more slowly than $K_1^\text{eff}$ with
increasing temperature, and approximately scale with normalized magnetization
as $A_\text{e}(T) \sim m^{1.2}$. This work provokes a scale bridge between
\textit{ab-initio} calculations and temperature-dependent micromagnetic
simulations of Nd-Fe-B permanent magnets.",1902.05636v2
2019/4/25,Antisymmetric magnetoresistance and helical magnetic structure in compensated Gd/Co multilayer,"Using spin dependent specular and off-specular polarized neutron reflectivity
(PNR), we report the observation of a twisted helical magnetic structure with
planar 2{\pi} domain wall (DW) and highly correlated magnetic domains in a
Gd/Co multilayer. Specular PNR with polarization analysis reveals the formation
of planar 2{\pi}DWs below a compensation temperature (TComp), resulting to
positive exchange bias in this system. Off-specular PNR with spin polarization
showed development of magnetic inhomogenities (increase in magnetic roughness)
for central part (thickness ~ 25-30 {\AA}) of each Gd layer, where
magnetization is aligned perpendicular (in-plane) to an applied field. These
magnetic roughness are vertically correlated and results into Bragg sheet in
spin flip channel of Off-specular PNR data, which is contributing towards an
antisymmetric magnetoresistance at TComp in the system. The growth and
tunability of highly correlated magnetic inhomogeneities (roughness) and domain
structure around TComp in combination of twisted helical magnetic structure
with planar 2{\pi}DWs will be key for application in all-spin-based technology.",1904.11269v1
2019/5/3,"Contrasting the magnetism in La$_{2-x}$Sr$_x$FeCoO$_6$ ($x$ = 0, 1, 2) double perovskites: the role of electronic and cationic disorder","The magnetism of the double perovskite compounds \SLFCOx\ ($x$ = 0, 1, 2) are
contrasted using magnetization, neutron diffraction and electron paramagnetic
resonance with the support from density functional theory calculations. \LFCO\
is identified as a long-range ordered antiferromagnet displaying a near-room
temperature transition at $T_N$ = 270~K, accompanied by a low temperature
structural phase transition at $T_S$ = 200~K. The structural phase
transformation at $T_S$ occurs from $R\overline{3}c$ at 300~K to $Pnma$ at
200~K. The density functional theory calculations support an insulating
non-compensated AFM structure. The long-range ordered magnetism of \LFCO\
transforms to short-range glassy magnetism as La is replaced with Sr in the
other two compounds. The magnetism of \LFCO\ is differentiated from the
non-equilibrium glassy features of \SFCO\ and \SLFCO\ using the {\em
cooling-and-heating-in-unequal-fields} (CHUF) magnetization protocols. This
contransting magnetism in the \SLFCOx\ series is evidenced in electron
paramegnetic resonance studies. The electronic density-of-states estimated
using the density functional theory calculations contrast the insulating
feature of \LFCO\ from the metallic nature of \SFCO. From the present suite of
experimental and computational results on \SLFCOx, it emerges that the
electronic degrees of freedom, along with antisite disorder, play an important
role in controlling the magnetism observed in double perovskites.",1905.01038v1
2019/5/9,Domain wall pinning and hard magnetic phase in Co-doped bulk single crystalline Fe3GeTe2,"We report the effects of cobalt doping on the magnetic properties of
two-dimensional van der Waals ferromagnet Fe3GeTe2. Single crystals of
(Fe{1-x}Cox)3GeTe2 with x=0-0.78 were successfully synthesized and
characterized with x-ray diffraction, energy dispersive x-ray spectroscopy and
magnetization measurements. Both the Curie-Weiss temperature and ferromagnetic
(FM) ordered moment of Fe3GeTe2 are gradually suppressed upon Co doping. A kink
in zero-field-cooling low field M(T) curve which is previously explained as an
antiferromagnetic transition is observed for samples with x=0-0.58. Our
detailed magnetization measurements and theoretical calculations strongly
suggest that this kink is originated from the pinning of magnetic domain walls.
The domain pinning effects are suddenly enhanced when the doping concentration
of cobalt is around 50%, both the coercive field Hc and the magnetic remanence
to saturated magnetization ratio MR/MS are largely improved and a hard magnetic
phase emerges in bulk single crystal samples. The strong doping dependent
magnetic properties suggest more spintronic applications of Fe3GeTe2.",1905.03458v1
2019/5/13,Electronic structure of Fe and magnetism in the $3d/5d$ double perovskites Ca$_2$FeReO$_6$ and Ba$_2$FeReO$_6$,"The Fe electronic structure and magnetism in (i) monoclinic Ca$_2$FeReO$_6$
with a metal-insulator transition at $T_{MI} \sim 140$ K and (ii) quasi-cubic
half-metallic Ba$_2$FeReO$_6$ ceramic double perovskites are probed by soft
x-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD).
These materials show distinct Fe $L_{2,3}$ XAS and XMCD spectra, which are
primarily associated with their different average Fe oxidation states (close to
Fe$^{3+}$ for Ca$_2$FeReO$_6$ and intermediate between Fe$^{2+}$ and Fe$^{3+}$
for Ba$_2$FeReO$_6$) despite being related by an isoelectronic
(Ca$^{2+}$/Ba$^{2+}$) substitution. For Ca$_2$FeReO$_6$, the powder-averaged Fe
spin moment along the field direction ($B = 5$ T), as probed by the XMCD
experiment, is strongly reduced in comparison with the spontaneous Fe moment
previously obtained by neutron diffraction, consistent with a scenario where
the magnetic moments are constrained to remain within an easy plane. For $B=1$
T, the unsaturated XMCD signal is reduced below $T_{MI}$ consistent with a
magnetic transition to an easy-axis state that further reduces the
powder-averaged magnetization in the field direction. For Ba$_2$FeReO$_6$, the
field-aligned Fe spins are larger than for Ca$_2$FeReO$_6$ ($B=5$ T) and the
temperature dependence of the Fe magnetic moment is consistent with the
magnetic ordering transition at $T_C^{Ba} = 305$ K. Our results illustrate the
dramatic influence of the specific spin-orbital configuration of Re $5d$
electrons on the Fe $3d$ local magnetism of these Fe/Re double perovskites.",1905.04988v1
2019/5/20,Micromagnetic Modelling of the Heat Assisted Switching Process in high Anisotropy FePt Granular Thin Films,"The dynamic process of assisted magnetic switchins has been simulated to
investigate the associated physics. The model uses a Voronoi construction to
determine the physical structure of the nano granular thin film recording
media; and the Landau-Lifshitz-Bloch (LLB) equation is solved to evolve the
magnetic system in time. The reduction of the magnetization is determined over
a range of peak system temperatures and for a number of anisotropy values. The
results show that the HAMR process is not simply magnetization reversal over a
thermally reduced energy barrier. To achieve full magnetization reversal (for
all anisotropies investigated) an applied field strength of at least 6kOe is
required and the peak system temperature must reach at least the Curie point
(Tc). When heated to Tc the magnetization associated with each grain is
destroyed, which invokes the non-precessional linear reversal mode. Reversing
the magnetization through this linear reversal mode is favourable, as the
reversal time is two orders of magnitude smaller than that associated with
precession. Under these conditions, as the temperature decreases to ambient,
the magnetization recovers in the direction of the applied field, completing
the reversal process. Also the model produces results which are consistent with
the concept of thermal writability; when heating the media to Tc, the smaller
grains require a larger field strength to reverse the magnetization.",1905.08134v1
2019/6/29,Magnetocaloric properties of an inhomogeneous magnetic thin film of 7.6 nm La${}_{0.7}$Sr${}_{0.3}$MnO${}_{3}$ grown on SrTiO${}_{3.}$,"Magnetocaloric properties of an inhomogeneous magnetic system of a 7.6 nm
La${}_{0.7}$Sr${}_{0.3}$MnO${}_{3}$ consisting of superparamagnetic (SPM) with
blocking temperature ( $T_B$ = 240 K) and ferromagnetic (FM) phases ( $T_C$ =
290 K) is studied by dc magnetization measurements. Isothermal magnetization
versus applied magnetic field is carried out from 100 K to 320 K in magnetic
fields up to 4 kOe to determine changes in the magnetic entropy ($-\Delta S_M$)
and the relative cooling power (RCP). Due to the co-existence of SPM and FM
phases, there are two peaks in the temperature dependence of$-\Delta S_M$ in
different applied magnetic fields from 1.3 kOe to 4 kOe. The peaks are at 220 K
and 270 K which are close $T_B$ and $T_C$ of the film. The highest RCP occurs
at 270 K (which is in $T_B$ $\mathrm{<}$ $T$ $\mathrm{<}$ $T_C$) in H = 4 kOe
with the value of 0.19 (J/kg K). The $-\Delta S_M$ vs T data are fit to the
exponent power law, $-\Delta S_M=a H^n$ where it shows good fits for the whole
measured temperature range. This analysis reveals a deviation of n from $n$ =
2/3 which is likely due to the presence of SPM spin clusters in the dead layer
for $T$ $\mathrm{<}$ $T_C$. Results show that the thin film of
La${}_{0.7}$Sr${}_{0.3}$MnO${}_{3}$ can be a good candidate for magnetic
refrigeration devices with multiple RCP peaks in low and high temperatures.",1907.00125v1
2019/7/15,Nature of the magnetic moment of cobalt in ordered FeCo alloy,"The magnets are typically classified into Stoner and Heisenberg type,
depending on the itinerant or localized nature of the constituent magnetic
moments. In this work, we investigate theoretically the behaviour of the
magnetic moments of iron and cobalt in their B2-ordered alloy. The results
based on local spin density approximation (LSDA) for the density functional
theory (DFT) suggest that the Co magnetic moment strongly depends on the
directions of the surrounding magnetic moments, which usually indicates the
Stoner-type mechanism of magnetism. This is consistent with the disordered
local moment (DLM) picture of the paramagnetic state, where the magnetic moment
of cobalt gets substantially suppressed. We argue that this is due to the lack
of strong on-site electron correlations, which we take into account by
employing a combination of DFT and dynamical mean-field theory (DMFT). Within
LDA+DMFT, we find a substantial quasiparticle mass renormalization and a non
Fermi-liquid behaviour of Fe-$3d$ orbitals. The resulting spectral functions
are in very good agreement with measured spin-resolved photoemission spectra.
Our results suggest that local correlations play an essential role in
stabilizing a robust local moment on Co in the absence of magnetic order at
high temperatures.",1907.06613v5
2019/10/24,Bottom-up strategies for the assembling of magnetic systems using nanoclusters,"In the frame of the 20th Anniversary of the Journal of Nanoparticle Research
(JNR), our aim is to start from the historical context twenty, years ago and to
give some recent results and perspectives concerning nanomagnets prepared from
clusters preformed in the gas phase using the Low Energy Cluster Beam
Deposition (LECBD) technique. In this paper, we focus our attention on the
typical case of Co clusters embedded in various matrices to study interface
magnetic anisotropy and magnetic interactions as a function of volume
concentrations, and on still current and perspectives through two examples of
binary metallic 3d-5d TM (namely CoPt and FeAu) clusters assemblies to
illustrate size-related and nanoalloy phenomena on magnetic properties in
well-defined mass-selected clusters. The structural and magnetic properties of
these cluster assemblies were investigated using various experimental
techniques that include High Resolution Transmission Electron Microscopy
(HRTEM), Superconducting Quantum Interference Device (SQUID) magnetometry, as
well as synchrotron techniques such as Extended X-Ray Absorption Fine Structure
(EXAFS) and X-Ray Magnetic Circular Dichroism (XMCD). Depending on the chemical
nature of both NPs and matrix, we observe different magnetic responses compared
to their bulk counterparts. In particular, we show how finite size effects
(size reduction) enhance their magnetic moment and how specific relaxation in
nanoalloys can impact their magnetic anisotropy.",1910.11212v1
2019/10/25,Nature of hyperfine interactions in TbPc$_2$ single-molecule magnets: Multireference ab-initio study,"Lanthanide-based single-ion magnetic molecules can have large magnetic
hyperfine interactions as well as large magnetic anisotropy. Recent
experimental studies reported tunability of these properties by changes of
chemical environments or by application of external stimuli for device
applications. In order to provide insight onto the origin and mechanism of such
tunability, here we investigate the magnetic hyperfine and nuclear quadrupole
interactions for $^{159}$Tb nucleus in TbPc$_2$ (Pc=phthalocyanine)
single-molecule magnets using multireference ab-initio methods including
spin-orbit interaction. Since the electronic ground and first-excited
(quasi)doublets are well separated in energy, the microscopic Hamiltonian can
be mapped onto an effective Hamiltonian with an electronic pseudo-spin $S=1/2$.
From the ab-initio-calculated parameters, we find that the magnetic hyperfine
coupling is dominated by the interaction of the Tb nuclear spin with electronic
orbital angular momentum. The asymmetric $4f$-like electronic charge
distribution leads to a strong nuclear quadrupole interaction with significant
non-axial terms for the molecule with low symmetry. The ab-initio calculated
electronic-nuclear spectrum including the magnetic hyperfine and quadrupole
interactions is in excellent agreement with experiment. We further find that
the non-axial quadrupole interactions significantly influence the avoided level
crossings in magnetization dynamics and that the molecular distortions affect
mostly the Fermi contact terms as well as the non-axial quadrupole
interactions.",1910.11952v1
2019/11/1,Spin reorientation in FeCrAs revealed by single-crystal neutron diffraction,"The magnetic structure of the ""nonmetallic metal"" FeCrAs, a compound with the
characters of both metals and insulators, was examined as a function of
temperature using single-crystal neutron diffraction. The magnetic propagation
vector was found to be $\mathit{k}$ = (1/3, 1/3, 0), and the magnetic
reflections disppeared above $\mathit{T_{N}}$ = 116(1) K. In the ground state,
the Cr sublattice shows an in-plane spiral antiferromagnetic order. The moment
sizes of the Cr ions were found to be small, due to strong magnetic frustration
in the distorted Kagome lattice or the itinerant nature of the Cr magnetism,
and vary between 0.8 and 1.4 $\mu_{B}$ on different sites as expected for a
spin-density-wave (SDW) type order. The upper limit of the moment on the Fe
sublattice is estimated to be less than 0.1 $\mu_{B}$. With increasing
temperature up to 95 K, the Cr moments cant out of the $\mathit{ab}$ plane
gradually, with the in-plane components being suppressed and the out-of-plane
components increasing in contrast. This spin-reorientation of Cr moments can
explain the dip in the $\mathit{c}$-direction magnetic susceptibility and the
kink in the magnetic order parameter at $\mathit{T_{O}}$ ~ 100 K, a second
magnetic transition which was unexplained before. We have also discussed the
similarity between FeCrAs and the model itinerant magnet Cr, which exhibits
spin-flip transitions and SDW-type antiferromagnetism.",1911.00261v1
2019/11/27,Asymmetric modification of the magnetic proximity effect in Pt/Co/Pt trilayers by the insertion of a Ta buffer layer,"The magnetic proximity effect in top and bottom Pt layers induced by Co in
Ta/Pt/Co/Pt multilayers has been studied by interface sensitive, element
specific x-ray resonant magnetic reflectivity. The asymmetry ratio for
circularly polarized x-rays of left and right helicity has been measured at the
Pt $L_3$ absorption edge (11567 eV) with an in-plane magnetic field ($\pm158$
mT) to verify its magnetic origin. The proximity-induced magnetic moment in the
bottom Pt layer decreases with the thickness of the Ta buffer layer. Grazing
incidence x-ray diffraction has been carried out to show that the Ta buffer
layer induces the growth of Pt(011) rather than Pt(111) which in turn reduces
the induced moment. A detailed density functional theory study shows that an
adjacent Co layer induces more magnetic moment in Pt(111) than in Pt(011). The
manipulation of the magnetism in Pt by the insertion of a Ta buffer layer
provides a new way of controlling the magnetic proximity effect which is of
huge importance in spin-transport experiments across similar kind of
interfaces.",1911.12187v1
2019/11/28,Manipulating Spin Chirality of Magnetic Skyrmion Bubbles by In-Plane Re-versed Magnetic Fields in (Mn$_{1-x}$Ni$_x$)$_{65}$Ga$_{35}$ ($x = 0.45$) magnet,"Understanding the dynamics of the magnetic skyrmion, a particle-like
topologically stable spin texture, and its response dynamics to external fields
are indis-pensable for the applications in spintronic devices. In this letter,
the Lorentz transmis-sion electron microscopy (LTEM) was used to investigate
the spin chirality of the mag-netic skyrmion bubbles (SKBs) in the
centrosymmetric magnet MnNiGa at room tem-perature. The reversal of SKBs
excited by the in-plane magnetic field has been revealed. Moreover, the
collective behavior of interacting spin chirality can be manipulated by
reversing the directions of the magnetic fields on a wedge-shaped thin plate.
The dy-namic behavior of the bubbles at different position of the thin plate
has been explored with the micromagnetic simulation, indicating a non-uniform
and nontrivial dynamic magnetization on the surfaces and center of the thin
plate during the spin chirality re-versal. The results suggest that the
controllable symmetry breaking of the SKBs arising from thickness variation
provides an ability to manipulate the collective behavior of the spin chirality
with small external fields, leading to a promising application in nonvola-tile
spintronic devices for magnetic skyrmions.",1911.12497v1
2019/12/29,Gate-Tunable Graphene Hall Sensors with High Magnetic Field Sensitivity,"Solid-state magnetic field sensors are important to both modern electronics
and fundamental materials science. Many types of these sensors maintain high
sensitivity only in a limited range of temperature and background magnetic
field, but Hall-effect sensors are in principle able to operate over a broad
range of these conditions. Here, we fabricate and characterize micrometer-scale
graphene Hall sensors demonstrating high magnetic field sensitivity from
liquid-helium to room temperature and in background magnetic field up to
several Tesla. By tuning the charge carrier density with an electrostatic gate,
we optimize the magnetic field sensitivity for different working conditions.
From measurements of the Hall coefficient and the Hall voltage noise at 1 kHz,
we estimate an optimum magnetic field sensitivity of 80 nT Hz$^{-1/2}$ at 4.2
K, 700 nT Hz$^{-1/2}$ at room temperature, and 3 $\mu$T Hz$^{-1/2}$ in 3 T
background magnetic field at 4.2 K. Our devices perform competitively with the
best existing Hall sensor technologies at room temperature, outperform any Hall
sensors reported in the literature at 4.2 K, and demonstrate high sensitivity
for the first time in a few Tesla applied magnetic field.",1912.12678v1
2020/2/6,Exotic multiferroic properties of spinel structured $AB_2O_4$ compounds: A Monte Carlo Study,"Spinel structured compounds, $AB_2O_4$, are special because of their exotic
multiferroic properties. In $ACr_2O_4$ ($A$=$Co$, $Mn$,$Fe$), a switchable
polarization has been observed experimentally due to a non-collinear magnetic
spin order. In this article, we demonstrated the microscopic origin behind such
magnetic spin order, hysteresis, polarisation and the so-called magnetic
compensation effect in $ACr_2O_4$ ($A$=$Co$, $Mn$,$Fe$, $Ni$) using Monte Carlo
simulation. With a careful choice of the exchange interaction, we were able to
explain various experimental findings such as magnetization vs. temperature (T)
behavior, conical stability, unique magnetic ordering and polarization in a
representative compound $CoCr_2O_4$ which is the best known multiferroic
compound in the $AB_2O_4$ spinel family. We have also studied the effect of
$Fe$-substitution in $CoCr_2O_4$, with an onset of few exotic phenomena such as
magnetic compensation and sign reversible exchange bias effect. These effects
are investigated using an effective interactions mimicking the effect of
substitution. Two other compounds in this family, $CoMn_2O_4$ and $CoFe_2O_4$,
are also studied where no conical magnetic order and polarisation was observed,
as hence provide a distinct contrast. Here all calculations are done using the
polarisation calculated by the spin-current model. This model has certain
limitation and it works quite good for low temperature and low magnetic field.
But the model despite its limitation it can reproduce sign reversible exchange
bias and magnetic compensation like phenomena quite well.",2002.02180v1
2020/2/18,Evidence of itinerant holes for long-range magnetic order in tungsten diselenide semiconductor with vanadium dopants,"One primary concern in diluted magnetic semiconductors (DMSs) is how to
establish a long-range magnetic order with a low magnetic doping concentration
to maintain the gate tunability of the host semiconductor, as well as to
increase Curie temperature. Two-dimensional van der Waals semiconductors have
been recently investigated to demonstrate the magnetic order in DMSs; however,
a comprehensive understanding of the mechanism responsible for the gate-tunable
long-range magnetic order in DMSs has not been achieved yet. Here, we introduce
a monolayer tungsten diselenide (WSe2) semiconductor with V dopants to
demonstrate the long-range magnetic order through itinerant spin-polarized
holes. The V atoms are sparsely located in the host lattice by substituting W
atoms, which is confirmed by scanning tunneling microscopy and high-resolution
transmission electron microscopy. The V impurity states and the valence band
edge states are overlapped, which is congruent with density functional theory
calculations. The field-effect transistor characteristics reveal the itinerant
holes within the hybridized band; this clearly resembles the Zener model. Our
study gives an insight into the mechanism of the long-range magnetic order in
V-doped WSe2, which can also be used for other magnetically doped
semiconducting transition metal dichalcogenides.",2002.07333v1
2020/3/31,Magnetic properties of Co/Ni-based multilayers with Pd and Pt insertion layers,"In this study, the influence of Pd and Pt insertion layers in Co/Ni
multilayers (MLs) on their magnetic properties, e.g. magnetic anisotropies,
saturation magnetization, coercivity, magnetic domain size, and Curie
temperature, is investigated. We compare three series of [Co/Ni/X]N ML systems
(X = Pd, Pt, no insertion layer), varying the individual Co layer thickness as
well as the repetition number N. All three systems behave very similarly for
the different Co layer thicknesses. For all systems, a maximum effective
magnetic anisotropy was achieved for MLs with a Co layer thickness between 0.15
nm and 0.25 nm. The transition from an out-of-plane to an in-plane system
occurs at about 0.4 nm of Co. While [Co(0.2 nm)/Ni(0.4 nm)]N MLs change their
preferred easy magnetization axis from out-of-plane to in-plane after 6 bilayer
repetitions, insertion of Pd and Pt results in an extension of this transition
beyond 15 repetitions. The maximum effective magnetic anisotropy was more than
doubled from 105 kJ/m3 for [Co/Ni]3 to 275 and 186 kJ/m3 for Pt and Pd,
respectively. Furthermore, the insertion layers strongly reduce the initial
saturation magnetization of 1100 kA/m of Co/Ni MLs and lower the Curie
temperature from 720 to around 500 K",2003.14306v1
2020/6/18,Current-induced in-plane magnetization switching in biaxial ferrimagnetic insulator,"Ferrimagnetic insulators (FiMI) have been intensively used in microwave and
magneto-optical devices as well as spin caloritronics, where their
magnetization direction plays a fundamental role on the device performance. The
magnetization is generally switched by applying external magnetic fields. Here
we investigate current-induced spin-orbit torque (SOT) switching of the
magnetization in Y3Fe5O12 (YIG)/Pt bilayers with in-plane magnetic anisotropy,
where the switching is detected by spin Hall magnetoresistance. Reversible
switching is found at room temperature for a threshold current density of 10^7
A cm^-2. The YIG sublattices with antiparallel and unequal magnetic moments are
aligned parallel or antiparallel to the direction of current pulses, which is
consistent to the Neel order switching in antiferromagnetic system. It is
proposed that such a switching behavior may be triggered by the
antidamping-torque acting on the two antiparallel sublattices of FiMI. Our
finding not only broadens the magnetization switching by electrical means and
promotes the understanding of magnetization switching, but also paves the way
for all-electrically modulated microwave devices and spin caloritronics with
low power consumption.",2006.10313v1
2020/8/12,Metastable skyrmion lattices governed by magnetic disorder and anisotropy in $β$-Mn-type chiral magnets,"Magnetic skyrmions are vortex-like topological spin textures often observed
in structurally chiral magnets with Dzyaloshinskii-Moriya interaction. Among
them, Co-Zn-Mn alloys with a $\beta$-Mn-type chiral structure host skyrmions
above room temperature. In this system, it has recently been found that
skyrmions persist over a wide temperature and magnetic field region as a
long-lived metastable state, and that the skyrmion lattice transforms from a
triangular lattice to a square one. To obtain perspective on chiral magnetism
in Co-Zn-Mn alloys and clarify how various properties related to the skyrmion
vary with the composition, we performed systematic studies on
Co$_{10}$Zn$_{10}$, Co$_9$Zn$_9$Mn$_2$, Co$_8$Zn$_8$Mn$_4$ and
Co$_7$Zn$_7$Mn$_6$ in terms of magnetic susceptibility and small-angle neutron
scattering measurements. The robust metastable skyrmions with extremely long
lifetime are commonly observed in all the compounds. On the other hand,
preferred orientation of a helimagnetic propagation vector and its temperature
dependence dramatically change upon varying the Mn concentration. The
robustness of the metastable skyrmions in these materials is attributed to
topological nature of the skyrmions as affected by structural and magnetic
disorder. Magnetocrystalline anisotropy as well as magnetic disorder due to the
frustrated Mn spins play crucial roles in giving rise to the observed change in
helical states and corresponding skyrmion lattice form.",2008.05075v1
2020/10/7,Correlation of uniaxial magnetic anisotropy axes and principal resistivities in polycrystalline ferromagnetic films,"In the present study, we demonstrate the measurement of resistivity tensor
($\rho$) along the magnetic axes of a polycrystalline film of ferromagnetic
permalloy (Py). To this end, conventional Hall-bar and a more recent extended
van der Pauw methods were utilized for determining 2D $\rho$ in the film plane.
The samples were prepared by normal incidence sputter deposition within an
in-situ magnetic field to induce in-plane uniaxial magnetic anisotropy in the
film. Since $\rho$ might be affected by the internal magnetization of the film,
we performed measurements by rotation of a saturating magnetic field in the
film plane. Both methods indicate that the average resistivity is lower along
the easy axis of the film compared to the hard axis. Since X-ray diffraction
results indicated no dominating texture in the film, we concluded that there is
a correlation between uniaxial magnetic axes and principal resistivity axes.
This is an important finding that allows determining the direction of magnetic
anisotropy axes without magnetometry. The results also verify atomic or pair
ordering to be the origin of uniaxial magnetic anisotropy in the Py since
resistivity is sensitive to the level of order in solids. The extended van der
Pauw utilized here can be easily performed on the as-received samples which is
of practical interest.",2010.03554v3
2020/10/20,Pressure-induced huge increase of Curie temperature of the van der Waals ferromagnet VI3,"Evolution of magnetism in single crystals of the van der Waals compound VI3
in external pressure up to 7.3 GPa studied by measuring magnetization and ac
magnetic susceptibility is reported. Four magnetic phase transitions, at T1 =
54.5 K, T2 = 53 K, TC = 49.5 K, and TFM = 26 K, respectively have been observed
at ambient pressure. The first two have been attributed to the onset of
ferromagnetism in specific crystal-surface layers. The bulk ferromagnetism is
characterized by the magnetic ordering transition at Curie temperature TC and
the transition between two different ferromagnetic phases TFM, accompanied by a
structure transition from monoclinic to triclinic symmetry upon cooling. The
pressure effects on magnetic parameters were studied with three independent
techniques. TC was found to be almost unaffected by pressures up to 0.6 GPa
whereas TFM increases rapidly with increasing pressure and reaches TC at a
triple point at ~ 0.85 GPa. At higher pressures, only one magnetic phase
transition is observed moving to higher temperatures with increasing pressure
to reach 99 K at 7.3 GPa. In contrast, the low-temperature bulk magnetization
is dramatically reduced by applying pressure (by more than 50% at 2.5 GPa)
suggesting a possible pressure-induced reduction of vanadium magnetic moment.
We discussed these results in light of recent theoretical studies to analyze
exchange interactions and provide how to increase the Curie temperature of VI3.",2010.10319v1
2020/10/23,Current-induced orbital magnetization in systems without inversion symmetry,"In systems with time-reversal symmetry, the orbital magnetization is zero in
equilibrium. Recently, it has been proposed that the orbital magnetization can
be induced by an electric current in a helical crystal structure in the same
manner as that in a classical solenoid. In this paper, we extend this theory
and study the current-induced orbital magnetization in a broader class of
systems without inversion symmetry. First, we consider polar metals which have
no inversion symmetry. We find that the current-induced orbital magnetization
appears in a direction perpendicular to the electric current even without
spin-orbit coupling. Using the perturbation method, we physically clarify how
the current-induced orbital magnetization appears in polar metals. As an
example, we calculate the current-induced orbital magnetization in SnP, and
find that it might be sufficiently large for measurement. Next, we consider a
two-dimensional system without inversion symmetry. We establish a method to
calculate the current-induced orbital magnetization in the in-plane direction
by using real-space coordinates in the thickness direction. By applying this
theory to surfaces and interfaces of insulators, we find that an electric
current along surfaces and interfaces induces an orbital magnetization
perpendicular to the electric current.",2010.12159v1
2020/12/17,Superconducting Orbital Magnetoelectric Effect and its Evolution across the Superconductivity Normal Metal Phase Transition,"Superconducting magnetoelectric effect, which is the current-induced
magnetization in a superconductor, mainly focused on the spin magnetization in
previous studies, but ignore the effect of the orbital magnetic moments carried
by the paired Bloch electrons. In this work, we show that orbital magnetic
moments in superconductors can induce large orbital magnetization in the
presence of a current. We constructed a unified description for the
current-induced spin and orbital magnetization across the superconductivity
normal metal phase transition. We find that in a superconductor with uniform
pairing, the current-induced magnetization at a given current density is the
same as that in its normal metal state, while with the nonuniform
superconducting pairing, the current-induced magnetization exhibits an abrupt
change in magnitude near the superconductivity normal metal phase transition.
Importantly, our theory predicts the orbital magnetoelectric effect in
superconducting twisted bilayer graphene which has paired Bloch electrons with
large orbital magnetic moments and negligible spin-orbit coupling. We propose
that the measurement of the current-induced orbital magnetoelectric effect can
be used to detect the possible nonuniform pairings in twisted bilayer graphene
and other newly discovered superconductors with non-trivial Berry curvatures.",2012.09896v3
2021/1/21,Spin liquid behavior of a three-dimensional magnetic system Ba$_3$NiIr$_2$O$_9$ with $S$ = 1,"The quantum spin liquid (QSL) is an exotic phase of magnetic materials where
the spins continue to fluctuate without any symmetry breaking down to zero
temperature. Among the handful reports of QSL with spin $S\ge$1, examples with
magnetic ions on a three-dimensional magnetic lattice are extremely rare since
both larger spin and higher dimension tend to suppress quantum fluctuations. In
this work, we offer a new strategy to achieve 3-D QSL with high spin by
utilizing two types of transition metal ions, both are magnetically active but
located at crystallographically inequivalent positions. We design a 3-D
magnetic system Ba$_3$NiIr$_2$O$_9$ consisting of interconnected corner shared
NiO$_6$ octahedra and face shared Ir$_2$O$_9$ dimer, both having triangular
arrangements in \textit{a-b} plane. X-ray absorption spectroscopy measurements
confirm the presence of Ni$^{2+}$ ($S$=1). Our detailed thermodynamic and
magnetic measurements reveal that this compound is a realization of gapless QSL
state down to at least 100 mK. Ab-initio calculations find a strong magnetic
exchange between Ir and Ni sublattices and in-plane antiferromagnetic coupling
between the dimers, resulting in dynamically fluctuating magnetic moments on
both the Ir and Ni sublattice.",2101.08445v1
2021/5/2,High-energy magnetic excitations from heavy quasiparticles in CeCu$_2$Si$_2$,"Magnetic fluctuations is the leading candidate for pairing in cuprate,
iron-based and heavy fermion superconductors. This view is challenged by the
recent discovery of nodeless superconductivity in CeCu$_2$Si$_2$, and calls for
a detailed understanding of the corresponding magnetic fluctuations. Here, we
mapped out the magnetic excitations in \ys{superconducting (S-type)}
CeCu$_2$Si$_2$ using inelastic neutron scattering, finding a strongly
asymmetric dispersion for $E\lesssim1.5$~meV, which at higher energies evolve
into broad columnar magnetic excitations that extend to $E\gtrsim 5$ meV. While
low-energy magnetic excitations exhibit marked three-dimensional
characteristics, the high-energy magnetic excitations in CeCu$_2$Si$_2$ are
almost two-dimensional, reminiscent of paramagnons found in cuprate and
iron-based superconductors. By comparing our experimental findings with
calculations in the random-phase approximation,we find that the magnetic
excitations in CeCu$_2$Si$_2$ arise from quasiparticles associated with its
heavy electron band, which are also responsible for superconductivity. Our
results provide a basis for understanding magnetism and superconductivity in
CeCu$_2$Si$_2$, and demonstrate the utility of neutron scattering in probing
band renormalization in heavy fermion metals.",2105.00387v1
2021/6/27,Relaxation in Ordered Assembly of Magnetic Nanoparticles,"We study the relaxation characteristics in the two-dimensional ($l^{}_x
\times l^{}_y$) array of magnetic nanoparticles (MNPs) as a function of aspect
ratio $A^{}_r=l^{}_y/l^{}_x$, dipolar interaction strength $h^{}_d$ and
anisotropy axis orientation using computer simulation. The anisotropy axes of
all the MNPs are assumed to have the same direction, $\alpha$ being the
orientational angle. Irrespective of $\alpha$ and $A^{}_r$, the functional form
of the magnetization-decay curve is perfectly exponentially decaying with
$h^{}_d\leq0.2$. There exists a transition in relaxation behaviour at
$h^{}_d\approx0.4$; magnetization relaxes slowly for $\alpha\leq45^\circ$; it
relaxes rapildy with $\alpha>45^\circ$. Interestingly, it decays rapidly for
$h^{}_d>0.6$, irrespective of $\alpha$. It is because the dipolar interaction
promotes antiferromagnetic coupling in such cases. There is a strong effect of
$\alpha$ on the magnetic relaxation in the highly anisotropic system
($A^{}_r\geq25$). Interesting physics unfolds in the case of a huge aspect
ratio $A^{}_r=400$. There is a rapid decay of magnetization with $\alpha$, even
for weakly interacting MNPs. Remarkably, magnetization does not relax even with
a moderate value of $h^{}_d=0.4$ and $\alpha=0^\circ$ because of ferromagnetic
coupling dominance. Surprisingly, there is a complete magnetization reversal
from saturation (+1) to $-1$ state with $\alpha>60^\circ$. The dipolar field
and anisotropy axis tend to get aligned antiparallel to each other in such a
case. The effective N\'eel relaxation time $\tau^{}_N$ depends weakly on
$\alpha$ for small $h^{}_d$ and $A^{}_r\leq25.0$. For large $A^{}_r$, there is
a rapid fall in $\tau^{}_N$ as $\alpha$ is incremented from 0 to $90^\circ$.
These results benefit applications in data and energy storages where such
controlled magnetization alignment and desired structural anisotropy are
desirable.",2106.14271v1
2021/8/25,Magnetic properties of BiFeO$_3$-BaTiO$_3$ ceramics in the morphotropic phase boundary: a role of crystal structure and structural parameters,"A correlation between the crystal structure and magnetic properties of system
(1-x)BiFeO$_3$-(x)BaTiO$_3$ with compounds across the morphotropic phase
boundary was studied using X-ray and neutron diffraction, magnetometry, and
Mossbauer spectroscopy measurements. Increase in the dopants content leads to
the structural transition from the rhombohedral phase to the cubic phase via a
formation of the two-phase region (0.2 < x < 0.33), wherein the magnetic
structure changes from the modulated G-type antiferromagnetic to the collinear
antiferromagnetic via a stabilization of the non-collinear antiferromagnetic
phase with non-zero remanent magnetization. The value of magnetic moment
calculated per iron ion based on the Mossbauer and neutron diffraction data
decreases from m = 4.4 mB for the compound with x=0.25 to m=3.2 mB for the
compound with x=0.35 testifying a dominance of 3+ oxidation state of the iron
ions. Increase in the amount of the cubic phase leads to a reduction in the
remanent magnetization from 0.02 emu.g for the compounds with the dominant
rhombohedral phase (x < 0.27) down to about 0.001 emu/g for the compounds with
dominant cubic structure (x >= 0.27). Rapid decrease in the remanent
magnetization observed in the compounds across the phase coexistence region
points at no direct correlation between the type of structural distortion and
non-zero remanent magnetization, while the oxygen octahedra tilting is the key
factor determining the presence of non-zero remanent magnetization.",2108.11447v1
2021/9/15,Magnetic and structural properties of the intermetallic Ce(1-x)LaxCrGe3 series of compounds,"The Ce(1-x)LaxCrGe3 (x = 0, 0.19, 0.43, 0.58 and 1) intermetallic compound
system has been investigated by magnetization measurements and neutron
scattering techniques to determine the effect of La-doping on the magnetic
ordering and exchange interaction between Cr ions. The structural and magnetic
characterization in this series was first verified by X-ray diffraction and
bulk magnetization measurements. The samples exhibit the known hexagonal
perovskite structure (P63/mmc space group) and have a single magnetic phase
according to magnetization measurements. In this work, the ferromagnetic
ordering temperature for Cr evolves smoothly from a range of 68 K to 77 K for
CeCrGe3 to a range of 91 K to 96 K for LaCrGe3 as La replaces Ce. Magnetization
results indicate the formation of domain walls below the transition temperature
for all the Ce(1-x)LaxCrGe3 systems investigated. Neutron results indicate
ordered magnetic Cr moments aligned along the c axis for the x = 1 LaCrGe3
system, as well as for x = 0.19, 0.43, and 0.58, which contrasts with the x = 0
CeCrGe3 where the moments order in the ab plane.",2109.07366v1
2021/10/4,Large magnetodielectric coupling in the vicinity of metamagnetic transition in $6H-$perovskite Ba$_3$GdRu$_2$O$_9$,"The 6H-perovskites Ba$_3$RRu$_2$O$_9$ (R = rare earth element) demonstrate
the magnetodielectric (MD) coupling as a manifestation of $4d - 4f$ magnetic
interactions. Here, we have reported a detailed study of the structural,
magnetic, heat capacity, and MD properties of the 6H-perovskite
Ba$_3$GdRu$_2$O$_9$. The signature of long-range antiferromagnetic (AFM)
ordering $\sim$ 14.8 K ($T_N$) is evident from the magnetization and heat
capacity studies. The $T_N$ shifts towards the lower temperature side, apart
from splitting in two with the application of the magnetic field.
Field-dependent magnetization at 1.8 K shows three metamagnetic transitions
with the opening of small hysteresis in different regions. A new transition at
$T_1$ emerges after the onset of the first metamagnetic transition. Complex
magnetic behavior is observed in different magnetic field regions whereas these
field regions themselves vary with the temperature. Dielectric response
recorded at zero and 80 kOe field exhibits the development of MD coupling well
above $T_N$. The MD coupling ($\sim$ 4.5 \% at 10 K) is enhanced by 25 \% as
compared to the Dy counterpart. Effect of complex magnetic behavior is also
conveyed in the MD results where the maximum value of MD coupling is observed
in the vicinity of 10 K (onset of $T_1$) and near the second metamagnetic
transition. Our investigation suggests that both Gd and Ru moments align
simultaneously at $T_N$. Short-range magnetic correlations are possibly
responsible for MD coupling above $T_N$.",2110.01417v1
2021/11/29,Magnetic anisotropy and magnetic ordering of transition-metal phosphorus trisulfides,"Here, a magnetic model with an unprecedentedly large number of parameters was
determined from first-principles calculations for transition-metal phosphorus
trisulfides (TMPS$_3$'s), which reproduced the measured magnetic ground states
of bulk TMPS$_3$'s. Our Monte Carlo simulations for the critical temperature,
magnetic susceptibility, and specific heat of bulk and few-layer TMPS$_3$'s
agree well with available experimental data and show that the antiferromagnetic
order of FePS$_3$ and NiPS$_3$ persists down to monolayers. Remarkably, the
orbital polarization, which was neglected in recent first-principles studies,
dramatically enhances the magnetic anisotropy of FePS$_3$ by almost two orders
of magnitude. A recent Raman study [K. Kim et al., Nat. Commun. 10, 345 (2019)]
claimed that magnetic ordering is absent in monolayer NiPS$_3$ but
simultaneously reported a strong two-magnon continuum; we show that the
criterion used to judge magnetic ordering there is invalid in monolayer
NiPS$_3$, thus providing an understanding of the two seemingly contradictory
experimental results. The rich predictions on the magnetic susceptibility and
specific heat of few-layer FePS$_3$ and NiPS$_3$ await immediate experimental
verifications.",2111.14869v1
2021/12/4,Coexisting Ferromagnetic-antiferromagnetic Phase and Manipulation in Magnetic Topological Insulator MnBi4Te7,"Magnetic topological insulators (MTIs) have received a lot of attention due
to the existence of various quantum phenomena such as quantum anomalous Hall
effect (QAHE) and topological magnetoelectric effect, etc. The intrinsic
superlattice-like layered MTIs, MnBi2Te4/(Bi2Te3)n, have been extensively
investigated mainly through the transport measurements, while the direct
investigation of their superlattice-sensitive magnetic behaviors is relatively
rare. Here, we report a microscopic real-space investigation of magnetic phase
behaviors in MnBi4Te7 using cryogenic magnetic force microscopy (MFM). The
intrinsic robust A-type antiferromagnetic (AFM), and emerged surface spin-flop
(SSF), canted AFM (CAFM), ferromagnetic (FM)+CAFM, forced FM phases are
sequentially visualized via the increased external magnetic field, in agreement
with the metamagnetic behavior in the M-H curve. The temperature-dependent
magnetic phase evolution behaviors are further investigated to obtain the
complete H-T phase diagram of MnBi4Te7. The tentative local phase manipulation
via the stray field of the magnetic tip is demonstrated by transforming the AFM
to FM phase in its surface layers of MnBi4Te7. Our study the not only provide
key real-space ingredients for understanding their complicated magnetic,
electronic, and topological properties of these intrinsic MTIs, but also
suggest new directions for manipulating spin textures and locally controlling
their exotic properties.",2112.02320v1
2021/12/19,Optical signatures of periodic magnetization: the moiré Zeeman effect,"Detecting magnetic order at the nanoscale is of central interest for the
study of quantum magnetism in general, and the emerging field of moir\'e
magnets in particular. Here, we analyze the exciton band structure that arises
from a periodic modulation of the valley Zeeman effect. Despite long-range
electron-hole exchange interactions, we find a sizable splitting in the energy
of the bright circularly-polarized exciton Umklapp resonances, which serves as
a direct optical probe of magnetic order. We first analyze quantum moir\'e
magnets realized by periodic ordering of electron spins in Mott-Wigner states
of transition metal dichalcogenide (TMD) monolayers or twisted bilayers: we
show that spin-valley dependent exciton-electron interactions allow for probing
the spin-valley order of electrons and demonstrate that it is possible to
observe unique signatures of ferromagnetic order in a triangular lattice and
both ferromagnetic and N\'eel order in a honeycomb lattice. We then focus on
semiclassical moir\'e magnets realized in twisted bilayers of ferromagnetic
materials: we propose a detection scheme for moir\'e magnetism which is based
on inter-layer exchange coupling between spins in a moir\'e magnet and excitons
in a TMD monolayer.",2112.10276v2
2021/12/27,"Design, Dynamics, and Dissipation of a Torsional-Magnetic Spring Mechanism","We present an analytical and experimental study of torsional magnetic
mechanism where the restoring torque is due to magnetic field interactions
between rotating and fixed permanent magnets. The oscillator consists of a ball
bearing-supported permanent magnet, called the rotor, placed between two fixed
permanent magnets called the stators. Perturbing the rotor from its equilibrium
angle induces a restoring magnetic torque whose effect is modeled as a
torsional spring. This restoring effect is accompanied by dissipation
mechanisms arising from structural viscoelasticity, air and electromagnetic
damping, as well as friction in the ball bearings. To investigate the system
dynamics, we constructed an experimental setup capable of mechanical,
electrical and magnetic measurements. For various rotor-stator gaps in this
setup, we validated an analytical model that assumes viscous and dry (Coulomb)
damping during the rotor free response. Moreover, we forced the rotor by a
neighboring electromagnetic coil into high amplitude oscillations. We observed
unusual resonator nonlinearity: at large rotor-stator gaps, the oscillations
are softening; at reduced gaps, the oscillations stiffen-then-soften. The
developed reduced-order models capture the nonlinear effects of the
rotor-to-stator and the rotor-to-coil distances. These magnetic oscillators are
promising in low-frequency electromagnetic signal transmission and in designing
magneto-elastic metamaterials with tailorable nonlinearity.",2112.13806v1
2022/1/25,Collinear antiferromagnetic order in spin-$\frac52$ triangle lattice antiferromagnet Na$_3$Fe(PO$_4$)$_2$,"We set forth the structural and magnetic properties of the frustrated
spin-$5/2$ triangle lattice antiferromagnet Na$_3$Fe(PO$_4$)$_2$ examined via
x-ray diffraction, magnetization, heat capacity, and neutron diffraction
measurements on the polycrystalline sample. No structural distortion was
detected from the temperature-dependant x-ray diffraction down to 12.5 K,
except a systematic lattice contraction. The magnetic susceptibility at high
temperatures agrees well with the high-temperature series expansion for a
spin-$5/2$ isotropic triangular lattice antiferromagnet with an average
exchange coupling of $J/k_{\rm B} \simeq 1.8$ K rather than a one-dimensional
spin-$5/2$ chain model. This value of the exchange coupling is consistently
reproduced by the saturation field of the pulse field magnetization data. It
undergoes a magnetic long-range-order at $T_{\rm N} \simeq 10.4$ K. Neutron
diffraction experiments elucidate a collinear antiferromagnetic ordering below
$T_{\rm N}$ with the propagation vector $k = (1,0,0)$. An intermediate value of
frustration ratio ($f \simeq 3.6$) reflects moderate frustration in the
compound which is corroborated by a reduced ordered magnetic moment of $\sim
1.52$ $\mu_{\rm B}$ at 1.6 K, compared to its classical value ($5 \mu_{\rm
B}$). Magnetic isotherms exhibit a change of slope envisaging a field induced
spin-flop transition at $H_{\rm SF}\simeq3.2$ T. The magnetic field vs
temperature phase diagram clearly unfold three distinct phase regimes,
reminiscent of a frustrated magnet with in-plane (XY-type) anisotropy.",2201.10467v1
2022/3/15,Magnetically hidden state on the ground floor of the magnetic Devil's staircase,"We investigated the low-temperature and high-field thermodynamic and
ultrasonic properties of SrCu2(BO3)2, which exhibits various plateaux in its
magnetization curve above 27~T, called a magnetic Devil's staircase. The
results of the present study confirm that magnetic crystallization, the first
step of the staircase, occurs above 27~T as a 1st-order transition accompanied
by a sharp singularity in heat capacity $C_p$ and a kink in the elastic
constant. In addition, we observe a thermodynamic anomaly at lower fields
around 26~T, which has not been previously detected by any magnetic probes. At
low temperatures, this magnetically hidden state has a large entropy and does
not exhibit Schottky-type gapped behavior, which suggests the existence of
low-energy collective excitations. Based on our observations and theoretical
predictions, we propose that magnetic quadrupoles form a spin-nematic state
around 26~T as a hidden state on the ground floor of the magnetic Devil's
staircase.",2203.07607v2
2022/5/2,Three-dimensional skyrmionic cocoons in magnetic multilayers,"Three-dimensional (3D) topological spin textures emerge as promising
quasi-particles for encoding information in future spintronic devices. The
third dimension provides more malleability regarding their magnetic properties
as well as more flexibility for potential applications. However, the
stabilization and characterization of such quasi-particles in easily
implementable systems remain a work in progress. Here we observe a new type of
3D magnetic textures that we called skyrmionic cocoons that sits in the
interior of magnetic thin films multilayers and possesses a characteristic
ellipsoidal shape. Interestingly, these cocoons can coexist with more standard
`tubular' skyrmions going through all the multilayer as evidenced by the
existence of two very different contrasts in the MFM images recorded at room
temperature. The presence of these novel skyrmionic textures as well as the
understanding of their layer resolved chiral and topological properties have
been investigated by micromagnetic simulations. In order to experimentally
stabilize the combination of 3D skyrmion tubes and cocoons, we have elaborated
metallic multilayers in which the magnetic properties, notably the anisotropy,
of the magnetic films in the stacks is varied depending on their vertical
position. Finally, in complement to the magnetic imaging, we also measure the
magneto-resistive response of the multilayers as a function of the magnetic
field, and succeed to fit its evolution using the 3D micromagnetic simulations
as inputs for the magnetic configuration. The excellent agreement that is
reached brings additional evidence of the presence of skyrmionic cocoons that
hence can be electrically detected.",2205.01172v1
2022/5/27,Magnetic Ordering in GdAuAl$_4$Ge$_2$ and TbAuAl$_4$Ge$_2$: layered compounds with triangular lanthanide nets,"We report the synthesis of the entire $Ln$AuAl$_4$Ge$_2$ ($Ln$ = Y, Pr, Nd,
Sm, Gd, Tb, Dy, Ho, Er, and Tm) series and focus on the magnetic properties of
GdAuAl$_4$Ge$_2$ and TbAuAl$_4$Ge$_2$. Temperature and magnetic field dependent
magnetization, heat capacity, and electrical resistivity measurements reveal
that both compounds exhibit several magnetically ordered states at low
temperatures, with evidence for magnetic fluctuations extending into the
paramagnetic temperature region. For magnetic fields applied in the $ab$-plane
there are several ordered state regions that are associated with metamagnetic
phase transitions, consistent with there being multiple nearly degenerate
ground states. Despite Gd being an isotropic $S$-state ion and Tb having an
anisotropic $J$-state, there are similarities in the phase diagrams for the two
compounds, suggesting that factors such as the symmetry of the crystalline
lattice, which features well separated triangular planes of lanthanide ions, or
the Ruderman-Kittel-Kasuya-Yosida interaction as defined by the Fermi surface
topography control the magnetism. We also point out similarities to other
centrosymmetric compounds that host skyrmion lattices such as Gd$_2$PdSi$_3$,
and propose that the $Ln$AuAl$_4$Ge$_2$ family of compounds are of interest as
reservoirs for complex magnetism and electronic behaviors such as the
topological Hall effect.",2205.14063v1
2022/6/6,Topological magnetic dipoles and emergent field bundles in a ferromagnetic microstructure by X-ray magnetic vector tomography,"Advanced vector imaging techniques provide us with 3D maps of magnetization
fields in which topological concepts can be directly applied to describe
real-space experimental textures in non-ideal geometries. Here, the 3D
magnetization of a low symmetry permalloy microstructure is obtained by X-ray
vector magnetic tomography and analysed in detail in terms of topological
charges and emergent fields. A central asymmetric domain wall with a complex 3D
structure is observed in which magnetization chirality transitions are mediated
by Bloch points arranged in several dipoles and a triplet. The ideal spherical
symmetry of the emergent field of an isolated monopole is severely modified due
to shape effects of the permalloy microstructure. Emergent field lines
aggregate into bundles that either connect adjacent Bloch points within a
topological dipole or tend towards the surface. These bundles may present
different textures such as helical vortices or half merons, depending on
asymmetries and confinement, but are constrained by topological charge
conservation in a given sample volume. This precise description of the
singularities in realistic systems, enabled by the quantitative experimental
information on magnetization vector fields, can significantly improve our
understanding of topological constraints in 3D magnetic systems and provide
advancements in the design of magnetic devices.",2206.02499v1
2022/6/10,Computation of High Frequency Magnetoelastic Waves in Layered Materials,"The direct calculation of magnetoelastic wave dispersion in layered media is
presented using an efficient, accurate computational technique. The governing,
coupled equations for elasticity and magnetism, the Navier and Landau-Lifshitz
equations, respectively, are linearized to form a quadratic eigenvalue problem
that determines a complex web of wavenumber-frequency dispersion branches and
their corresponding mode profiles. Numerical discretization of the eigenvalue
problem via a spectral collocation method (SCM) is employed to determine the
complete dispersion maps for both a single, finite-thickness magnetic layer and
a finite magnetic-nonmagnetic double-layer. The SCM, previously used to study
elastic waves in non-magnetic media, is fast, accurate, and adaptable to a
variety of sample configurations and geometries. Emphasis is placed on the
extremely high frequency regimes being accessed in ultrafast magnetism
experiments. The dispersion maps and modes provide insight into how energy
propagates through the coupled system, including how energy can be transferred
between elastic- and magnetic-dominated waves as well as between different
layers. The numerical computations for a single layer are further understood by
a simplified analytical calculation in the high-frequency, exchange-dominated
regime where the resonance condition required for energy exchange (an
anticrossing) between quasi-elastic and quasi-magnetic dispersion branches is
determined. Nonresonant interactions are shown to be well approximated by the
dispersion of uncoupled elastic and magnetic waves. The methods and results
provide fundamental theoretical tools to model and understand current and
future magnetic devices powering spintronic innovation.",2206.05212v2
2022/6/17,Understanding the $sp$ magnetism in substitutional doped graphene,"Defect-induced magnetism in graphene has been predicted theoretically and
observed experimentally. However, there are open questions about the origin of
the magnetic behavior when substitutional impurities with $sp$ electrons are
considered. The aim of this work is to contribute to the understanding of
impurity-induced spin magnetism in doped graphene systems. Thus, the electronic
structure and spin magnetic moments for substitutional doped graphene with
impurities from groups IIIA (B, Al, and Ga) and VA (N, P, As, Sb, and Bi) of
the periodic table were obtained within the framework of density functional
theory. The nature of the magnetic ground state was determined from
calculations of the total energy as a function of the spin magnetic moment
using the fixed spin moment method. We show that the spontaneous magnetization
in the studied systems arises from an electronic instability by the presence of
a narrow impurity band at the Fermi level. Furthermore, we found that the
emergence of spin polarization requires the impurity to introduce an extra
electron to the graphene lattice and that the impurity-carbon hybridization is
close to the $sp^3$ geometry. These features reveal that the charge doping sign
and the hybridization degree play a fundamental role in the origin of $sp$
magnetism in substitutional doped graphene.",2206.08969v2
2022/7/1,Spectropolarimetry of Magnetic Chemically Peculiar Stars in the Orion OB1 Association,"We summarise the results of a spectropolarimetric survey of 56 chemically
peculiar (CP) stars in the association of Orion OB1. We uniformly collected the
observational material with the 6-m telescope BTA of the Special Astrophysical
Observatory in 2013-2021. We identify 14 new magnetic CP stars with a
longitudinal magnetic field exceeding approximately 500 G. The studied sample
contains 31 magnetic stars or 55% of the whole CP population in Orion OB1. We
show that the percentage of the magnetic CP stars and the field strength drops
sharply with age. The mean longitudinal magnetic field in the young subgroup
OB1b ($\log t=6.23$) is confidently almost three times stronger than in the
older subgroups OB1a ($\log t=7.05$) and OB1c ($\log t=6.66$). In the Orion
Nebula, a place with the youngest stellar population ($\log t < 6.0$), we
detect the magnetic field only in 20% of CP stars. Such occurrence drastically
differs from 83% of magnetic CP stars in the nearby subgroup OB1c. We consider
this effect an observational bias caused by a significant portion of a very
young population with the signatures of Herbig Ae/Be stars. The technique we
used for magnetic measurements, and the quality of available data do not allow
us to detect weak fields in the case of stars with a limited number of lines
and emissions in spectra.",2207.00337v1
2022/7/1,Evolution of magnetic phase in two dimensional van der Waals Mn$_{1-x}$Ni$_x$PS$_3$ single crystals,"Metal thio(seleno)phosphates MPX$_3$ have attracted considerable attentions
with wide spanned band gaps and rich magnetic properties. In this series, two
neighboring members MnPS$_3$ and NiPS$_3$ differ in magnetic atoms, magnetic
easy axes, spin anisotropy, as well as nearest-neighbor magnetic interactions.
The competition between these components may cause intriguing physical
phenomena. In this article, the evolution of magnetism of
Mn$_{1-x}$Ni$_x$PS$_3$ series is reported. Despite the incompatible
antiferromagnetic orders of two end members, the antiferromagnetism persists as
the ground state in the whole substitution region. The magnetic ordering
temperature $T_{\rm N}$ show nonmonotonic V-shape behavior, and the reentrant
spin glass phase at x=0.5 is observed. In addition, abnormal bifurcation of
$T_{\rm N}$ occurs at x=0.75, which may be due to the temperature-dependent
spin reorientation or phase separation. The evolution of magnetism is further
confirmed semi-quantitatively by our density functional theory calculations.
Our study indicates that exotic magnetism can be intrigued when multi-degrees
of freedom are involved in these low-dimensional systems, which call for more
in-depth microscopic studies in future.",2207.00382v1
2022/7/21,Imaging current control of magnetization in Fe$_3$GeTe$_2$ with a widefield nitrogen-vacancy microscope,"Van der Waals (vdW) magnets are appealing candidates for realising spintronic
devices that exploit current control of magnetization (e.g. switching or domain
wall motion), but so far experimental demonstrations have been sparse, in part
because of challenges associated with imaging the magnetization in these
systems. Widefield nitrogen-vacancy (NV) microscopy allows rapid, quantitative
magnetic imaging across entire vdW flakes, ideal for capturing changes in the
micromagnetic structure due to an electric current. Here we use a widefield NV
microscope to study the effect of current injection in thin flakes ($\sim10$nm)
of the vdW ferromagnet Fe$_3$GeTe$_2$ (FGT). We first observe current-reduced
coercivity on an individual domain level, where current injection in FGT causes
substantial reduction in the magnetic field required to locally reverse the
magnetisation. We then explore the possibility of current-induced domain-wall
motion, and provide preliminary evidence for such a motion under relatively low
current densities, suggesting the existence of strong current-induced torques
in our devices. Our results illustrate the applicability of widefield NV
microscopy to imaging spintronic phenomena in vdW magnets, highlight the
possibility of efficient magnetization control by direct current injection
without assistance from an adjacent conductor, and motivate further
investigations of the effect of currents in FGT and other vdW magnets.",2207.10329v2
2022/8/17,Magnetic domain scanning imaging using phase-sensitive THz-pulse detection,"In our study, we determine the alignment of magnetic domains in a CoFeB layer
using THz radiation. We generate THz-pulses by fs-laser-pulses in magnetized
CoFeB/Pt heterostructures, based on spin currents. An LT-GaAs Auston switch
detects the radiation phase-sensitively and allows to determine the
magnetization alignment. Our scanning technique with motorized stages with step
sizes in the sub-micrometer range, allows to image two dimensional magnetic
structures. Theoretically the resolution is restricted to half of the
wavelength if focusing optics in the far-field limit are used. By applying
near-field imaging, the spatial resolution is enhanced to the single digit
micrometer range. For this purpose, spintronic emitters in diverse geometric
shapes, e.g. circles, triangles, squares, and sizes are prepared to observe the
formation of magnetization patterns. The alignment of the emitted THz radiation
can be influenced by applying unidirectional external magnetic fields. We
demonstrate how magnetic domains with opposite alignment and different shapes
divided by domain walls are created by demagnetizing the patterns using minor
loops and imaged using phase sensitive THz radiation detection. For analysis,
the data is compared to Kerr microscope images. The possibility to combine this
method with THz range spectroscopic information of magnetic texture or
antiferromagnets in direct vicinity to the spintronic emitter, makes this
detection method interesting for much wider applications probing THz excitation
in spin systems with high resolution beyond the Abbe diffraction limit, limited
solely by the laser excitation area.",2208.08219v1
2022/9/19,Mapping time-dependent magnetic topologies of active stars,"Throughout the last decades, Zeeman-Doppler Imaging (ZDI) has been
intensively used to reconstruct large-scale magnetic topologies of active stars
from time series of circularly polarized (Stokes $V$) profiles. ZDI being based
on the assumption that the topology to be reconstructed is constant with time
(apart from being sheared by differential rotation), it fails at describing
stellar magnetic fields that evolve on timescales similar to the observing
period. We present a new approach, called TIMeS (for Time-dependent Imaging of
Magnetic Stars), to derive the time-dependent large-scale magnetic topologies
of active stars, from time series of high-resolution Stokes $V$ spectra. This
new method uses the combined concepts of sparse approximation and Gaussian
process regression to derive the simplest time-dependent magnetic topology
consistent with the data. Assuming a linear relation between the Stokes $V$
data and the reconstructed magnetic image, TIMeS is currently applicable to
cases in which the magnetic field is not too strong (with an upper limit
depending on $v\sin{i}$). We applied TIMeS to several simulated data sets to
investigate its ability to retrieve the poloidal and toroidal components of
large-scale magnetic topologies. We find that the proposed method works best in
conditions similar to those needed for ZDI, reconstructing reliable topologies
with minor discrepancies at very low latitudes whose contribution to the data
is small. We however note that TIMeS can fail at reconstructing the input
topology when the field evolves on a timescale much shorter than the stellar
rotation cycle",2209.09216v1
2022/9/21,Ferroaxial moment induced by vortex spin texture,"The nature of an electric ferro-axial moment characterizing a
time-reversal-even axial-vector quantity is theoretically investigated under
magnetic orderings. We clarify that a vortex spin texture results in the
emergence of the ferro-axial moment depending on the helicity. By introducing a
multipole description, we show that the ferro-axial nature appears when two
types of odd-parity magnetic multipoles become active under the vortex spin
texture: One is the magnetic monopole and the other is the magnetic toroidal
dipole. We present all the magnetic point groups to possess the ferro-axial
moment in the presence of the magnetic orderings with the magnetic monopole and
magnetic toroidal dipole. Moreover, we specifically consider a multi-orbital
model in a four-sublattice tetragonal system to demonstrate the ferro-axial
moment induced by the vortex spin texture. We show that the ferro-axial moment
is microscopically characterized by both the cluster-scale and atomic-scale
axial-vector quantities: The former is described by the vortex of the local
electric dipole and the latter is represented by the outer product of the local
orbital and spin angular momenta. Moreover, we find that the atomic-spin orbit
coupling and the hybridization between orbitals with different parity are key
ingredients to induce the ferro-axial moment. We also apply the result to a
magnetic skyrmion with a topologically-nontrivial spin texture and discuss
candidate materials.",2209.10657v2
2022/10/5,"Magnetic, structural and magnetocaloric properties of Y$_{0.9}$Gd$_{0.1}$Fe$_{2}$H$_{x}$ hydrides","At 300 K, Y$_{0.9}$Gd$_{0.1}$Fe$_{2}$H$_{x}$ hydrides crystallize
sequentially with increasing H concentration in various structures related to a
lowering of the cubic MgCu$_{2}$ type structure of the parent alloy: cubic C1,
monoclinic M1, cubic C2, monoclinic M2, cubic C3, orthorhombic O. Above 300 K,
they undergo a first-order transition at a T$_{O-D}$ temperature driven by
order-disorder of hydrogen atoms into interstitial sites. Their magnetic,
structural and magnetocaloric properties have been investigated through
magnetic measurements, and high-resolution synchrotron diffraction experiments.
The magnetization at 5 K decreases slightly from 4 to 3.8 ${\mu}_{B}$ for x = 3
to 3.9 H f.u., then with a larger slope for higher H content. A discontinuous
decrease of the magnetic transition temperature is observed: M1 and C2 hydrides
are ferrimagnetic with T$_{C}$ near 300 K, M2 hydride displays a sharp
ferromagnetic-antiferromagnetic transition at T$_{FM-AFM}$ =144 K, whereas C3
and O hydrides present only a sharp increase of the magnetization below 15 K
and a weak magnetization up to RT. Negative magnetic entropy variations
(${\Delta}$S$_{M}$) are measured near T$_{C}$ for the M1 and C2 phases, near
T$_{FM-AFM}$ for the M2 phase, whereas positive ${\Delta}$S$_{M}$ peaks due to
inverse MCE effect are found near T$_{O-D}$. A structural and magnetic phase
diagram is proposed.",2210.02262v1
2022/11/9,Engineering axion insulator phase in superlattices with inversion symmetry breaking,"We study theoretically the interplay between magnetism and topology in
three-dimensional HgTe/MnTe superlattices stacked along the (001) axis. Our
results show the evolution of the magnetic topological phases with respect to
the magnetic configurations. An axion insulator phase is observed for the
antiferromagnetic order with the out-of-plane N\'eel vector direction below a
critical thickness of MnTe, which is the ground state amongst all magnetic
configurations. Defining $T$ as the time-reversal symmetry, this axion
insulator phase is protected by a magnetic two-fold rotational symmetry
$C_2{\cdot}T$. The axion insulator phase evolves into a trivial insulator as we
increase the thickness of the magnetic layers. By switching the N\'eel vector
direction into the $ab$ plane, the system realizes different antiferromagnetic
topological insulators depending on the thickness of MnTe. These phases feature
gapless surface Dirac cones shifted away from high-symmetry points on surfaces
perpendicular to the N\'eel vector direction of the magnetic layers. In the
presence of ferromagnetism, the system realizes a magnetic Weyl semimetal and a
ferromagnetic semimetal for out-of-plane and in-plane magnetization directions,
respectively. We observe large anomalous Hall conductivity in the presence of
ferromagnetism in the three-dimensional superlattice.",2211.05152v2
2022/11/24,Unravelling the role of Sm 4f electrons in the magnetism of SmFeO$_3$,"Magnetic rare-earth orthoferrites $R$FeO$_3$ host a variety of functional
properties from multiferroicity and strong magnetostriction, to
spin-reorientation transitions and ultrafast light-driven manipulation of
magnetism, which can be exploited in spintronics and next-generation devices.
Among these systems, SmFeO$_3$ is attracting a particular interest for its rich
phase diagram and the high temperature Fe-spin magnetic transitions, which
combines with a very low temperature and as yet unclear Sm-spin ordering.
Various experiments suggest that the interaction between the Sm and Fe magnetic
moments (further supported by the magnetic anisotropy), is at the origin of the
complex cascade of transitions, but a conclusive and clear picture has not yet
been reached. In this work, by means of comprehensive first-principles
calculations, we unravel the role of the magnetic Sm ions in the Fe-spin
reorientation transition and in the detected anomalies in the lattice
vibrational spectrum, which are a signature of a relevant spin-phonon coupling.
By including both Sm-$f$ electrons and non-collinear magnetism, we find
frustrated and anisotropic Sm interactions, and a large magnetocrystalline
anisotropy mediated by the SOC of the Sm-$4f$ electrons, which drive the
complex magnetic properties and phase diagram of SmFeO$_3$.",2211.13528v1
2022/12/12,Robust superconductivity and fragile magnetism induced by the strong Cu impurity scattering in the high-pressure phase of FeSe,"Superconductivity in FeSe is strongly enhanced under applied pressure and it
is proposed to emerge from anomalously coupled structural and magnetic phases.
Small impurities inside the Fe plane can strongly disrupt the pair formation in
FeSe at ambient pressure and can also reveal the interplay between normal and
superconducting phases. Here, we investigate how an impurity inside the Fe
plane induced by the Cu substitution can alter the balance between competing
electronic phases of FeSe at high pressures. In the absence of an applied
magnetic field, at low pressures the nematic and superconducting phases are
suppressed by a similar factor. On the other hand, at high pressures, above 10
kbar, the superconductivity remains unaltered despite the lack of any signature
in transport associated to a magnetic phase in zero-magnetic field. However, by
applying a magnetic field, the resistivity displays an anomaly preceding the
activated behaviour in temperature, assigned to a magnetic anomaly. We find
that the high-pressure superconducting phase of FeSe is robust and remains
enhanced in the presence of Cu impurity, whereas the magnetic phase is not.
This could suggest that high-$T_{\rm c}$ superconductivity has a
sign-preserving order parameter in a presence of a rather glassy magnetic
phase.",2212.06128v1
2022/12/30,Exciton magnetic polaron in CdTe/Cd_{1-x}Mn_{x}Te semimagnetic quantum ring,"Magnetically doped nanostructures can significantly enhance the interaction
between the band carriers and the dopant atoms. Motivated by the demonstration
of the enhanced sp-d exchange interaction in quantum confined structures with
the increased stability of the exciton magnetic polaron (EMP), we report the
quantitative and qualitative analyses of the EMP formation in
CdTe/Cd_{1-x}Mn_{x}Te diluted magnetic quantum ring (QR). The QR with two
different configurations: (i) the non-magnetic ring (CdTe) embedded in the
semimagnetic Cd_{1-x}Mn_{x}Te matrix, and (ii) magnetically non-uniform quantum
structures embedded with Mn2+ ions both in the ring and in the barrier regimes,
have been investigated for various mole fractions of the Mn dopants. The larger
polaron binding energy (EMP) of 23meV is estimated for the 5% molar Mn contents
compared to the other quantum confined systems made of CdMnTe. The magnetic
field dependence of the MP energy and the corresponding polaron parameters like
exchange field, localization radius of the MP, and the degree of circular
polarization induced by the external applied magnetic field at T = 4.2K have
been derived. The obtained results are in excellent agreement with the trend of
the significant degradation of EMP in an external magnetic field, and with the
contradictory tendencies of EMP for the QR with configuration (i) and (ii), as
reported from the time-integrated measurements based on selective excitation
for the quantum systems made of CdMnTe and other DMS materials.",2212.14802v1
2023/1/15,Miniature Magnetic Nano islands in a Morphotropic Cobaltite Matrix,"High-density magnetic memories are key components in spintronics, quantum
computing, and energy-efficient electronics. Reduced dimensionality and
magnetic domain stability at the nanoscale are essential for the
miniaturization of magnetic storage units. Yet, inducing magnetic order, and
selectively tuning spin-orbital coupling at specific locations have remained
challenging. Here we demonstrate the construction of switchable magnetic
nano-islands in a nonmagnetic matrix based on cobaltite homo-structures. The
magnetic and electronic states are laterally modified by epitaxial strain,
which is regionally controlled by freestanding membranes. Atomically sharp
grain boundaries isolate the crosstalk between magnetically distinct regions.
The minimal size of magnetic nano-islands reaches 35 nm in diameter, enabling
an areal density of 400 Gbit per inch square. Besides providing an ideal
platform for precisely controlled read and write schemes, this methodology can
enable scalable and patterned memories on silicon and flexible substrates for
various applications.",2301.06017v1
2023/1/30,Simultaneous magnetic and electric Purcell enhancement in a hybrid metal-dielectric nanostructure,"Hybrid metal-dielectric structures, which combine the advantages of both
metal and dielectric materials, support high-confined but low-loss magnetic and
electric resonances under deliberate arrangements. However, their potential for
enhancing magnetic emission has not been explored. Here, we study the
simultaneous magnetic and electric Purcell enhancement supported by a hybrid
structure consisting of a dielectric nanoring and a silver nanorod Such a
structure enables low Ohmic loss and highly-confined field under the mode
hybridization of magnetic resonances on nanoring and electric resonances on
nanorod in the optical communication band. So, the 60-fold magnetic Purcell
enhancement and 45-fold electric Purcell enhancement can be achieved
simultaneously with $>95\%$ of the radiation transmitted to far field. The
position of emitter has a several-ten-nanometer tolerance for sufficiently
large Purcell enhancement, which brings convenience to experimental
fabrications. Moreover, an array formed by this hybrid nanostructure can
further enhance the magnetic Purcell factors. The findings provide a
possibility to selectively excite the magnetic and electric emission in
integrated photon circuits. It may also facilitate brighter magnetic emission
sources and light-emitting metasurfaces in a simpler arrangement.",2301.12703v1
2023/3/31,Optical markers of magnetic phase transition in CrSBr,"Here, we investigate the role of the interlayer magnetic ordering of CrSBr in
the framework of $\textit{ab initio}$ calculations and by using optical
spectroscopy techniques. These combined studies allow us to unambiguously
determine the nature of the optical transitions. In particular,
photoreflectance measurements, sensitive to the direct transitions, have been
carried out for the first time. We have demonstrated that optically induced
band-to-band transitions visible in optical measurement are remarkably well
assigned to the band structure by the momentum matrix elements and energy
differences for the magnetic ground state (A-AFM). In addition, our study
reveals significant differences in electronic properties for two different
interlayer magnetic phases. When the magnetic ordering of A-AFM to FM is
changed, the crucial modification of the band structure reflected in the
direct-to-indirect band gap transition and the significant splitting of the
conduction bands along the $\Gamma-Z$ direction are obtained. In addition,
Raman measurements demonstrate a splitting between the in-plane modes
$B^2_{2g}$/$B^2_{3g}$, which is temperature dependent and can be assigned to
different interlayer magnetic states, corroborated by the DFT+U study.
Moreover, the $B^2_{2g}$ mode has not been experimentally observed before.
Finally, our results point out the origin of interlayer magnetism, which can be
attributed to electronic rather than structural properties. Our results reveal
a new approach for tuning the optical and electronic properties of van der
Waals magnets by controlling the interlayer magnetic ordering in adjacent
layers.",2303.17926v1
2023/4/14,Fermi Surface and Lifshitz Transitions of a Ferromagnetic Superconductor under External Magnetic Fields,"Lifshitz transitions are being increasingly recognised as significant in a
wide variety of strongly correlated and topological materials, and
understanding the origin and influence of Lifshitz transitions is leading to
deeper understanding of key aspects of magnetic, transport or quantum critical
behavior. In the ferromagnetic superconductor UCoGe, a magnetic field applied
along the c-axis has been shown to induce a series of anomalies in both
transport and thermopower that may be caused by Lifshitz transitions. The need
to understand the subtleties of the relationship between magnetism,
superconductivity and a heavy electron Fermi surface in the ferromagnetic
superconductors makes it important to explore if and why a series of
magnetic-field-induced Lifshitz transitions occurs in UCoGe. Here we report
magnetic susceptibility measurements of UCoGe, performed at temperatures down
to 45 mK and magnetic fields (B ||c) up to 30 T. We observe a series of
clearly-defined features in the susceptibility, and multiple sets of strongly
field-dependent de Haas-van Alphen oscillations, from which we extract detailed
field-dependence of the quasiparticle properties. We complement our
experimental results with density functional theory bandstructure calculations,
and include a simple model of the influence of magnetic field on the calculated
Fermi surface. By comparing experimental and calculated results, we determine
the likely shape of the Fermi surface and identify candidate Lifshitz
transitions that could correspond to two of the features in susceptibility. We
connect these results to the development of magnetization in the system.",2304.07024v1
2023/4/16,Anomalous and Topological Hall Resistivity in Ta/CoFeB/MgO Magnetic Systems for Neuromorphic Computing Applications,"Topologically protected spin textures, such as magnetic skyrmions, have the
potential for dense data storage as well as energy-efficient computing due to
their small size and a low driving current. The evaluation of the writing and
reading of the skyrmion's magnetic and electrical characteristics is a key step
toward the implementation of these devices. In this paper, we present the
magnetic heterostructure Hall bar device and study the anomalous Hall and
topological Hall signals in the device. Using the combination of different
measurements like magnetometry at different temperatures, Hall effect
measurement from 2K to 300K, and magnetic force microscopy imaging, we
investigate the magnetic and electrical characteristics of the magnetic
structure. We measure the skyrmion topological resistivity at different
temperatures as a function of the magnetic field. The topological resistivity
is maximum around the zero magnetic field and it decreases to zero at the
saturating field. This is further supported by MFM imaging. Interestingly the
resistivity decreases linearly with the field, matching the behavior observed
in the corresponding micromagnetic simulations. We combine the experimental
results with micromagnetic simulations, thus propose a skyrmion-based synaptic
device and show spin-orbit torque-controlled potentiation/depression in the
device. The device performance as the synapse for neuromorphic computing is
further evaluated in a convolutional neural network CNN. The neural network is
trained and tested on the MNIST data set we show devices acting as synapses
achieving a recognition accuracy close to 90%, on par with the ideal
software-based weights which offer an accuracy of 92%.",2304.07742v1
2023/4/28,Persistent dynamic magnetic state in artificial honeycomb spin ice,"Topological magnetic charges, arising due to the non-vanishing magnetic flux
on spin ice vertices, serve as the origin of magnetic monopoles that traverse
the underlying lattice effortlessly. Unlike spin ice materials of atomic
origin, the dynamic state in artificial honeycomb spin ice is conventionally
described in terms of finite size domain wall kinetics that require magnetic
field or current application. Contrary to this common understanding, here we
show that thermally tunable artificial permalloy honeycomb lattice manifests a
perpetual dynamic state due to self-propelled magnetic charge defect relaxation
in the absence of any external tuning agent. Quantitative investigation of
magnetic charge defect dynamics using neutron spin echo spectroscopy reveals
sub-ns relaxation times that are comparable to monopole's relaxation in bulk
spin ices. Most importantly, the kinetic process remains unabated at low
temperature where thermal fluctuation is negligible. This suggests that dynamic
phenomena in honeycomb spin ice are mediated by quasi-particle type entities,
also confirmed by quantum Monte-Carlo simulations that replicate the kinetic
behavior. Our research unveils a new `macroscopic' magnetic particle that
shares many known traits of quantum particles, namely magnetic monopole and
magnon.",2305.00093v1
2023/5/1,Perpendicular magnetic anisotropy of an ultrathin Fe layer grown on NiO(001),"The magnetic anisotropy and magnetic interactions at the interface between Fe
and NiO(001) were investigated. Depending on the growth conditions of the
NiO(001) layers and the post-annealing temperature, the preferential
magnetization direction of the ultrathin Fe layer grown on a NiO(001) layer
changed from in-plane to a direction perpendicular to the film plane. The
lattice constant of the NiO(001) layers parallel to the growth direction
increased with O$_2$ flow rate, while that parallel to the in-plane were locked
onto the MgO(001) substrate regardless of the growth conditions of the NiO
layers. Moreover, perpendicular magnetization was observed only when the NiO
layer was grown with O$_2$ flow rates higher than 2.0 sccm corresponding to
oxygen-rich NiO. X-ray magnetic circular dichroism measurements revealed an
enhancement in anisotropic orbital magnetic moments similar to the origin of
perpendicular magnetic anisotropy at the Fe/MgO(001) interface. The interfacial
magnetic anisotropy energies were 0.93 and 1.02 mJ/m$^2$ at room temperature
and at 100 K, respectively, indicating less temperature dependence. In
contrast, the coercivity $H_c$ exhibited a significant temperature dependence.
Although no signature of exchange bias or unidirectional loop shift was
observed, $H_c$ was strongly dependent on the NiO layer thickness, indicating
that the exchange interaction at the interface between the ferromagnetic and
antiferromagnetic layers was not negligible, despite the NiO(001) being a
spin-compensated surface.",2305.00672v1
2023/5/19,Unraveling the magnetic structure of YbNiSn single crystal via crystal growth and neutron diffraction,"Neutron and x-ray diffraction experiments were performed on the ternary
intermetallic compound YbNiSn, formerly categorized as a ferromagnetic Kondo
compound. At zero field, an increase in scattering intensity was observed on
top of allowed and forbidden nuclear reflections below Tc, breaking the
reflection condition of the crystal symmetry Pnma. This indicates that the
magnetic structure of YbNiSn is antiferromagnetic-type, rather than the
previously proposed simple collinear ferromagnetic structure. Temperature
dependence of the scattering intensity of the 011 reflection confirmed the
magnetic ordering at 5.77(2) K. No incommensurate satellite reflection was
observed at 2.5 K. By applying external magnetic field of 1 T along the a axis,
the magnetic intensity at the nuclear-forbidden 001 position was suppressed,
while a slight enhancement at the nuclear-allowed 002 position was observed.
This suggests a spin-flip transition under the external magnetic field along
the a axis in YbNiSn. The proposed magnetic structures at zero field and 1 T
correspond to the magnetic space groups of Pn'm'a and Pnm'a', respectively. The
piezomagnetic effect and the switch between the two magnetic space groups by
the external stress, which could be detected by the anomalous Hall effect, are
proposed.",2305.11542v1
2023/6/10,The Central Role of Tilted Anisotropy for Field-Free Spin-Orbit Torque Switching of Perpendicular Magnetization,"The discovery of efficient magnetization switching activated by the spin Hall
effect (SHE)-induced spin-orbit torque (SOT) changed the course of magnetic
random-access memory (MRAM) research and development. However, for systems with
perpendicular magnetic anisotropy (PMA), the use of SOT is still hampered by
the necessity of a longitudinal magnetic field to break the magnetic symmetry
to achieve deterministic switching. In this work, we first demonstrate that a
robust and tunable field-free current-driven SOT switching of perpendicular
magnetization can be controlled by the growth protocol in Pt-based magnetic
heterostructures. It is further elucidated that such growth-dependent symmetry
breaking is originated from the laterally tilted magnetic anisotropy of the
ferromagnetic layer with PMA, which has been largely neglected in previous
studies and its critical role should be re-focused. We show by both experiments
and simulations that in a PMA system with tilted anisotropy, the deterministic
field-free switching possesses a conventional SHE-induced damping-like torque
feature and the resulting current-induced effective field has a non-linear
dependence on the applied current density, which could be potentially
misattributed to an unconventional SOT origin.",2306.06357v1
2023/6/21,Spin-orbit torques due to warped topological insulator surface states with an in-plane magnetization,"We investigate the extrinsic spin-orbit torque (SOT) on the surface of
topological insulators (TIs), which are characterized by two-dimensional warped
Dirac surface states, in the presence of an in-plane magnetization. The
interplay between extrinsic spin-orbit scattering and the in-plane
magnetization results in a net spin density leading to a SOT. Previous theory
suggested that the SOT could only be generated by an out-of-plane magnetic
field component, and any in-plane magnetic contribution could be gauged away.
However, we demonstrate theoretically that with an in-plane magnetization, the
SOT can be finite in TIs due to extrinsic spin-orbit scattering. In the case of
a TI model with a linear dispersion relation, the skew scattering term is zero,
and the extrinsic spin-orbit scattering influences the side-jump scattering,
leading to a finite SOT in TIs. However, when considering the warping term,
finite intrinsic and skew scattering terms will arise, in addition to
modifications to other scattering terms. We further show that the SOT depends
on the azimuthal angles of the magnetization and an external electric field. By
adjusting the extrinsic spin-orbit strength, Fermi energy, magnetization
strength and warping strength, the resulting SOTs can be maximized. These
findings shed light on the interplay between spin-orbit coupling and
magnetization in TIs, offering insights into the control and manipulation of
spin currents in these systems.",2306.12557v1
2023/7/12,Quasi-static magnetization dynamics in a compensated ferrimagnetic half-metal -- Mn$_2$Ru$_x$Ga,"Exploring anisotropy and diverse magnetization dynamics in specimens with
vanishing magnetic moments presents a significant challenge using traditional
magnetometry, as the low resolution of existing techniques hinders the ability
to obtain accurate results. In this study, we delve deeper into the examination
of magnetic anisotropy and quasi-static magnetization dynamics in \mrg\,(MRG)
thin films, as an example of a compensated ferrimagnetic half-metal, by
employing anomalous Hall effect measurements within a tetragonal crystal
lattice system. Our research proposes an innovative approach to accurately
determine the complete set of anisotropy constants of these MRG thin films. To
achieve this, we perform anomalous Hall voltage curve fitting, using torque
models under the macrospin approximation, which allow us to obtain out-of-plane
anisotropy constants $K_1=4.0\times10^4$ J m$^{-3}$ ($K_1/M=0.655$\,T) and
$K_2=2.54\times10^4$ J m$^{-3}$ ($K_2/M=0.416$\,T), along with a weaker
in-plane anisotropy constant $K_3=3.48\times10^3$ J m$^{-3}$
($K_3/M=0.057$\,T). By additionally employing first-order reversal curves
(FORC) and classical Preisach hysteresis (hysterons) models, we are able to
validate the efficacy of the macrospin model in capturing the magnetic behavior
of MRG thin films. Furthermore, our investigation substantiates that the
complex quasi-static magnetization dynamics of MRG thin films can be
effectively modelled using a combination of hysteronic and torque models. This
approach facilitates the exploration of both linear and non-linear quasi-static
magnetization dynamics, in the presence of external magnetic field and/or
current-induced effective fields, generated by the spin-orbit torque and spin
transfer torque mechanisms.",2307.06403v1
2023/8/9,1/3 plateau and 3/5 discontinuity in the magnetization and the magnetic phase diagram of hexagonal GdInO$_3$,"We report the high-pressure optical floating-zone growth of GdInO$_3$ single
crystals and show its magnetic phase diagram down to the mK-regime as
determined by magnetization measurements. The centered-honeycomb lattice
structure shows considerable magnetic frustration ($\lvert\Theta\rvert /T_{\rm
N}\simeq 5$) and develops long-range magnetic order below $T_{\rm N}$~=~2.1 K
from a short-range ordered paramagnetic phase. Concomitantly, a small net
magnetic moment evolves at $T_{\rm N}$ which points along the crystallographic
$c$ direction. Upon cooling, the net moment reorients at $T^{**}\simeq 1.7$ K
and $T^{*}\simeq 1$ K. A broad 1/3 plateau indicative of the up-up-down ($uud$)
spin configuration appears for $B||c$ but is absent for $B||ab$, thereby
suggesting easy axis anisotropy. At $T=0.4$ K, a jump in magnetization at
$\simeq 3/5$ of the saturation magnetization signals a discontinuous transition
to a high field phase and we find evidence for a possible tricritical point.
Small energy and field scales in the accessible regimes render GdInO$_3$ a
prime example to study the phase diagram of a semiclassical frustrated
hexagonal lattice in the presence of weak easy axis anisotropy of mainly
dipolar origin.",2308.04935v1
2023/10/28,"Local atomic and magnetic structure of multiferroic (Sr,Ba)(Mn,Ti)O$_3$","We present a detailed study of the local atomic and magnetic structure of the
type-I multiferroic perovskite system (Sr,Ba)(Mn,Ti)O$_3$ using x-ray and
neutron pair distribution function (PDF) analysis, polarized neutron
scattering, and muon spin relaxation ($\mu$SR) techniques. The atomic PDF
analysis reveals widespread nanoscale tetragonal distortions of the crystal
structure even in the paraelectric phase with average cubic symmetry,
corresponding to incipient ferroelectricity in the local structure. Magnetic
PDF analysis, polarized neutron scattering, and $\mu$SR likewise confirm the
presence of short-range antiferromagnetic correlations in the paramagnetic
state, which grow in magnitude as the temperature approaches the magnetic
transition. We show that these short-range magnetic correlations coincide with
a reduction of the tetragonal (i.e. ferroelectric) distortion in the average
structure, suggesting that short-range magnetism can play an important role in
magnetoelectric and/or magnetostructural phenomena even without genuine
long-range magnetic order. The reduction of the tetragonal distortion scales
linearly with the local magnetic order parameter, pointing to spontaneous
linear magnetoelectric coupling in this system. These findings provide greater
insight into the multiferroic properties of (Sr,Ba)(Mn,Ti)O$_3$ and demonstrate
the importance of investigating the local atomic and magnetic structure to gain
a deeper understanding of the intertwined degrees of freedom in multiferroics.",2310.18558v2
2023/11/16,Ultrafast all-optical toggle writing of magnetic bits without relying on heat,"While in accordance with Curie's principle, one would intuitively expect that
symmetry of the cause has to be found in the symmetry of the effect, ultrafast
excitation of matter is able to violate this principle. For instance, it is
believed that heating alone, obviously not having the symmetry of a magnetic
field, cannot result in a deterministic reversal of magnetization. However, if
the heating is induced by a femtosecond laser pulse and thus ultrafast, it does
facilitate toggle switching of magnetization between stable bit-states without
any magnetic field at all. Here we show that the regime of ultrafast toggle
switching can be also realized via a mechanism without relying on any heat. The
obvious mismatch between symmetries of the cause and the response can thus be
seen as a violation of Curie's principle. In particular, ultrafast laser
excitation of iron-garnet with linearly polarized light modifies magnetic
anisotropy and thus causes toggling magnetization between two stable bit
states. In contrast to the laser-heat-induced magnetization reversal, this new
regime of 'cold' toggle switching can be observed in ferrimagnets without the
compensation point and in an exceptionally broad temperature range. The control
of magnetic anisotropy required for the toggle switching is accompanied by
lower dissipations, than in the mechanism of laser-induced-heating, but the
dissipations and the switching-time are shown to be competing parameters.",2311.10173v2
2023/11/28,Disordered ground state in the spin-orbit coupled $J_{\rm eff}= 1/2$ cobalt-based metal-organic framework magnet with orthogonal spin dimers,"We present the magnetic properties of a strongly spin-orbit coupled quantum
dimer magnet based on Co$^{2+}$. The metal-organic framework compound
Co$_2$(BDC)$_2$(DPTTZ)$_2$$\cdot$DMF features Co$^{2+}$ dimers arranged nearly
orthogonal to each other, similar to the Shastry-Sutherland lattice. Our
assessment based on the magnetization and heat capacity experiments reveals
that the magnetic properties at low temperatures can be described by an
effective $J_{\rm eff} = 1/2$ Kramers doublet and the ground state is a singlet
with a tiny spin gap. Although the magnetic susceptibility could be analyzed in
terms of the interacting dimer model with an isotropic intradimer coupling
$J_0/k_{\rm B} \simeq 7.6$ K, this model fails to reproduce the shape of
magnetization isotherm and heat capacity data. A model of isolated spin dimers
with the anisotropic exchange couplings $J_{xy} \simeq 3.5$ K and $J_{z} \simeq
11$ K provides an adequate description to the magnetic susceptibility,
magnetization isotherm, and heat capacity data at low temperatures.
Interestingly, no field-induced quantum phase phase is detected down to 100~mK
around the critical field of gap closing, suggesting the absence of
Bose-Einstein condensation of triplons and establishing isolated dimers with a
negligible interdimer coupling.",2311.16890v1
2023/12/3,Raman fingerprints of spin-phonon coupling and magnetic transition in an organic molecule intercalated Cr2Ge2Te6,"The manipulation of spin-phonon coupling in both formations and explorations
of magnetism in two-dimensional van der Waals ferromagnetic semiconductors
facilitates unprecedented prospects for spintronics devices. The interlayer
engineering tunes spin-phonon coupling significantly and holds the promise for
controllable magnetism via organic cation intercalation. Here, we present
spectroscopic evidence to reveal the intercalation effect on intrinsic magnetic
and electronic transitions in quasi-two-dimensional Cr2Ge2Te6 using tetrabutyl
ammonium as the intercalant. The temperature-evolution of Raman modes E_g^3 and
A_g^1, along with the magnetization measurements, unambiguously captures the
enhancement of the ferromagnetic Curie temperature in the intercalated
heterostructure. Moreover, the E_g^4 mode highlighted the increased effect of
spin-phonon interaction in magnetic order-induced lattice distortion. Combined
with the first-principle calculations, we observed a substantial number of
electrons transferred from TBA+ to Cr through the interface. These results
provide the interplay between spin-phonon coupling and magnetic ordering in van
der Waals magnets where Raman fingerprints would be highly beneficial for
further understanding the manipulation of magnetism in layered
heterostructures.",2312.01270v1
2024/1/28,In-plane Antiferromagnetism in Ferromagnetic Kagome Semimetal Co3Sn2S2,"Co3Sn2S2 has been reported to be a Weyl semimetal with broken time-reversal
symmetry with c axis ferromagnetism (FM) below a Curie temperature of 177 K.
Despite the large interest in Co3Sn2S2, the magnetic structure is still under
debate and recent studies have challenged our understanding of the magnetic
phase diagram of Co3Sn2S2 by reporting unusual magnetic phases including the
presence of exchange bias. Understanding the magnetism of Co3Sn2S2 is important
since its electronic band structure including the much-celebrated flat bands
and Weyl nodes depend on the magnetic phase. In this work, using X-ray Magnetic
Circular Dichroism (XMCD), we establish that the magnetic moment in Co arises
from the spin, with negligible orbital moment. In addition, we detect an
in-plane AFM minority phase in the sea of a FM phase using spatially-resolved
angle-resolved photoemission spectroscopy ({\mu}-ARPES) combined with density
functional theory (DFT) calculation. Separately, we detect a sharp flat band
precisely at the Fermi level (EF) at some regions in the sample, which we
attribute to a surface state. The AFM phase survives even to the low
temperature of 6 K. This example of entirely different magnetic ground states
in a stoichiometric intermetallic invites further efforts to explore the
observed AFM phase and understand the origin and nature of the magnetic and
electronic inhomogeneity on the mesoscale and the interface between the AFM and
FM phases.",2401.15602v1
2024/2/21,Isotropic and anisotropic neutron star structure in 4D Einstein Gauss Bonnet Gravity,"With regard to the coupling constant and the strong magnetic field of neutron
stars, we have studied these stars in the 4D Einstein Gauss Bonnet (4D EGB)
gravity model in order to grasp a better understanding of these objects. In
this paper, we have shown that the neutron star properties are considerably
affected by the coupling constant and magnetic field. We have found that as a
consequence of the strong magnetic field and the coupling constant, the maximum
mass and radius of a neutron star are increasing functions of the coupling
constant, while Schwarzschild radius, compactness, surface gravitational
redshift, and Kretschmann scalar are decreasing functions. Additionally, our
study has shown that the physical properties of a magnetized neutron star are
greatly influenced not only by the strong magnetic field, but also by the
anisotropy. Moreover, we have shown that to obtain the hydrostatic equilibrium
configuration of the magnetized material, both the local anisotropy effect and
the anisotropy due to the magnetic field should be considered. Finally, we have
found that in the anisotropic magnetized neutron stars, the maximum mass and
radius do not always increase with increasing the internal magnetic field.",2402.14038v1
2024/2/22,Unexpected versatile electrical transport behaviors of ferromagnetic nickel films,"Perpendicular magnetic anisotropy (PMA) of magnets is paramount for
electrically controlled spintronics due to their intrinsic potentials for
higher memory density, scalability, thermal stability and endurance, surpassing
an in-plane magnetic anisotropy (IMA). Nickel film is a long-lived fundamental
element ferromagnet, yet its electrical transport behavior associated with
magnetism has not been comprehensively studied, hindering corresponding
spintronic applications exploiting nickel-based compounds. Here, we
systematically investigate the highly versatile magnetism and corresponding
transport behavior of nickel films. As the thickness reduces within the general
thickness regime of a magnet layer for a memory device, the hardness of nickel
films' ferromagnetic loop of anomalous Hall effect increases and then
decreases, reflecting the magnetic transitions from IMA to PMA and back to IMA.
Additionally, the square ferromagnetic loop changes from a hard to a soft one
at rising temperatures, indicating a shift from PMA to IMA. Furthermore, we
observe a butterfly magnetoresistance resulting from the anisotropic
magnetoresistance effect, which evolves in conjunction with the thickness and
temperature-dependent magnetic transformations as a complementary support. Our
findings unveil the rich magnetic dynamics and most importantly settle down the
most useful guiding information for current-driven spintronic applications
based on nickel film: The hysteresis loop is squarest for the ~8 nm-thick
nickel film, of highest hardness with Rxyr/Rxys~1 and minimum Hs-Hc, up to 125
K; otherwise, extra care should be taken for a different thickness or at a
higher temperature.",2402.14275v1
2024/3/3,Noncentrosymmetric Nowotny Chimney Ladder Ferromagnet Cr4Ge7 with a High Curie Temperature of ~ 207 K,"Noncentrosymmetric magnets usually host intriguing magnetic interactions
inherent the crystal structure with broken inversion symmetry, which can give
rise to rich magnetic behaviors. We report herein the high-pressure synthesis,
crystal structure, magnetizations and magnetic structure of a so-called Nowotny
chimney ladder compound Cr4Ge7. Our analysis on the powder neutron diffraction
data revises the crystal structure as a noncentrosymmetric space group (P-4c2,
No.116). It exhibits two magnetic orders within the temperature range of 2 -
400 K. The first order at ~ 207 K associated with a small magnetic moment of ~
0.75 miuB is assigned to a commensurate ferromagnetic structure with a
propagation vector k = (0, 0, 0). The weak itinerant ferromagnet nature should
be caused by the complex Cr spin orders from different Wyckoff positions. The
second order at ~ 18 K is assumed to arise from a competition between the
Dzyaloshinskii-Moria and Heisenberg interactions. The results provide an
excellent platform for study on intricate interactions between various magnetic
exchanges as well as for the exploration of high temperature exotic magnetic
properties which host potential applications in next-generation spintronics.",2403.01399v1
2024/3/6,The role of interfacial interactions and oxygen vacancies in tuning magnetic anisotropy in LaCrO$_{3}$/LaMnO$_{3}$ heterostructures,"The interplay of lattice, electronic, and spin degrees of freedom at
epitaxial complex oxide interfaces provides a route to tune their magnetic
ground states. Unraveling the competing contributions is critical for tuning
their functional properties. We investigate the relationship between magnetic
ordering and magnetic anisotropy and the lattice symmetry, oxygen content, and
film thickness in compressively strained LaMnO$_3$/LaCrO$_3$ superlattices.
Mn-O-Cr antiferromagnetic superexchange interactions across the heterointerface
resulting in a net ferrimagnetic magnetic structure. Bulk magnetometry
measurements reveal isotropic in-plane magnetism for as-grown oxygen-deficient
thinner thin samples due to equal fractions of orthorhombic a+a-c-, and a-a+c-
twin domains. As the superlattice thickness is increased, in-plane magnetic
anisotropy emerges as the fraction of the a+a-c- domain increases. On annealing
in oxygen, the suppression of oxygen vacancies results in a contraction of the
lattice volume, and an orthorhombic to rhombohedral transition leads to
isotropic magnetism independent of the film thickness. The complex interactions
are investigated using high-resolution synchrotron diffraction and X-ray
absorption spectroscopy. These results highlight the role of the evolution of
structural domains with film thickness, interfacial spin interactions, and
oxygen-vacancy-induced structural phase transitions in tuning the magnetic
properties of complex oxide heterostructures.",2403.03764v1
2024/4/4,Towards tailored magnetic anisotropy: A first-principles study of L1$_0$ FeNi ultrathin films,"In previous experiments, thin films of L1$\mathrm{_0}$ FeNi with different
surfaces, including (001), (110) and (111), were produced and studied. Each
surface defines a different alignment of the crystallographic tetragonal axis
with respect to the film's plane, resulting in different magnetic anisotropies.
In this study, we use density functional theory calculations to examine three
series of L1$\mathrm{_0}$ FeNi films with surfaces (001), (010), and (111), and
with thicknesses ranging from 0.5 to 3 nm (from 4 to 16 atomic monolayers). Our
results show that films (001) have perpendicular magnetic anisotropy, while
(010) favor in-plane magnetization, with a clear preference for the tetragonal
axis [001]. We propose calling this type of in-plane anisotropy fixed in plane.
A film with surface (111) and a thickness of four atomic monolayers has the
magnetization easy axis almost perpendicular to the plane of the film. As the
thickness of the (111) film increases, the direction of magnetization rotates
towards a tetragonal axis [001], positioned at an angle of about 45$^{o}$ to
the plane of the film. Furthermore, the magnetic moment of ultrathin films
increases by a maximum of 5%, and the most significant changes in spin and
orbital magnetic moments occur at a depth of about three near-surface atomic
monolayers. The presented results could be useful for experimental efforts to
synthesize ultrathin L1$\mathrm{_0}$ FeNi films with different surfaces.
Ultrathin L1$\mathrm{_0}$ FeNi films with varying magnetic anisotropies may
find applications in spintronic devices.",2404.03416v1
2018/2/22,Resonant torsion magnetometry in anisotropic quantum materials,"Unusual behavior of quantum materials commonly arises from their effective
low-dimensional physics, which reflects the underlying anisotropy in the spin
and charge degrees of freedom. Torque magnetometry is a highly sensitive
technique to directly quantify the anisotropy in quantum materials, such as the
layered high-T$_c$ superconductors, anisotropic quantum spin-liquids, and the
surface states of topological insulators. Here we introduce the magnetotropic
coefficient $k=\partial^2 F/\partial \theta^2$, the second derivative of the
free energy F with respect to the angle $\theta$ between the sample and the
applied magnetic field, and report a simple and effective method to
experimentally detect it. A sub-$\mu$g crystallite is placed at the tip of a
commercially available atomic force microscopy cantilever, and we show that $k$
can be quantitatively inferred from a shift in the resonant frequency under
magnetic field. While related to the magnetic torque $\tau=\partial F/\partial
\theta$, $k$ takes the role of torque susceptibility, and thus provides
distinct insights into anisotropic materials akin to the difference between
magnetization and magnetic susceptibility. The thermodynamic coefficient $k$ is
discontinuous at second-order phase transitions and subject to Ehrenfest
relations with the specific heat and magnetic susceptibility. We apply this
simple yet quantitative method on the exemplary cases of the Weyl-semimetal NbP
and the spin-liquid candidate RuCl$_3$, yet it is broadly applicable in quantum
materials research.",1802.08211v1
2020/7/7,Material systems for FM-/AFM-coupled skyrmions in Co/Pt-based multilayers,"By means of systematic first-principles calculations based on density
functional theory we search for suitable materials that can host
antiferromagnetically coupled skyrmions. We concentrate on fcc-stacked
(111)-oriented metallic $Z$/Co/Pt ($Z=4d$ series: Y$-$Pd, the noble metals: Cu,
Ag, Au, post noble metals: Zn and Cd) magnetic multilayers of films of
monatomic thickness. We present quantitative trends of magnetic properties:
Magnetic moments, interlayer exchange coupling, spin-stiffness,
Dzyaloshinskii-Moriya interaction, magnetic anisotropy, and the critical
temperature. We show that some of the $Z$ elements (Zn, Y, Zr, Nb, Tc, Ru, Rh,
and Cd) can induce antiferromagnetic interlayer coupling between the magnetic
Co layers, and that they influence the easy magnetization axis. Employing a
multiscale approach, we transfer the micromagnetic parameters determined from
$ab$ $initio$ to a micromagnetic energy functional and search for
one-dimensional spin-spiral solutions and two-dimensional skyrmions. We
determine the skyrmion radius by numerically solving the equation of the
skyrmion profile. We found an analytical expression for the skyrmion radius
that covers our numerical results and is valid for a large regime of
micromagnetic parameters. Based on this expression we have proposed a model
that allows to extrapolate from the $ab$ $initio$ results of monatomic films to
multilayers with Co films consisting of several atomic layers containing
$10\,$nm skyrmions. We found thickness regimes where tiny changes of the film
thickness may alter the skyrmion radius by orders of magnitude. We estimated
the skyrmion size as function of temperature and found that the size can easily
double going from cryogenic to room temperature. We suggest promising material
systems for ferromagnetically and antiferromagnetically coupled spin-spiral and
skyrmion systems.",2007.03487v2
2020/10/18,Current-induced spin torques on single GdFeCo magnetic layers,"Spintronics exploits spin-orbit coupling (SOC) to generate spin currents,
spin torques, and, in the absence of inversion symmetry, Rashba, and
Dzyaloshinskii-Moriya interactions (DMI). The widely used magnetic materials,
based on 3d metals such as Fe and Co, possess a small SOC. To circumvent this
shortcoming, the common practice has been to utilize the large SOC of
nonmagnetic layers of 5d heavy metals (HMs), such as Pt, to generate spin
currents by Spin Hall Effect (SHE) and, in turn, exert spin torques on the
magnetic layers. Here, we introduce a new class of material architectures,
excluding nonmagnetic 5d HMs, for high-performance spintronics operations. We
demonstrate very strong current-induced torques exerted on single GdFeCo layers
due to the combination of large SOC of the Gd 5d states, and inversion symmetry
breaking mainly engineered by interfaces. These ""self-torques"" are enhanced
around the magnetization compensation temperature (close to room temperature)
and can be tuned by adjusting the spin absorption outside the GdFeCo layer. In
other measurements, we determine the very large emission of spin current from
GdFeCo. This material platform opens new perspectives to exert ""self-torques""
on single magnetic layers as well as to generate spin currents from a magnetic
layer.",2010.09137v1
2022/4/10,Large Itinerant Electron Exchange Coupling in the Magnetic Topological Insulator MnBi2Te4,"Magnetism in topological materials creates phases exhibiting quantized
transport phenomena with applications in spintronics and quantum information.
The emergence of such phases relies on strong interaction between localized
spins and itinerant states comprising the topological bands, and the subsequent
formation of an exchange gap. However, this interaction has never been measured
in any intrinsic magnetic topological material. Using a multimodal approach,
this exchange interaction is measured in MnBi2Te4, the first realized intrinsic
magnetic topological insulator. Interrogating nonequilibrium spin dynamics,
itinerant bands are found to exhibit a strong exchange coupling to localized Mn
spins. Momentum-resolved ultrafast electron scattering and magneto-optic
measurements reveal that itinerant spins disorder via electron-phonon
scattering at picosecond timescales. Localized Mn spins, probed by resonant
X-ray scattering, disorder concurrently with itinerant spins, despite being
energetically decoupled from the initial excitation. Modeling the results using
atomistic simulations, the exchange coupling between localized and itinerant
spins is estimated to be >100 times larger than superexchange interactions.
This implies an exchange gap of >25 meV should occur in the topological surface
states. By directly quantifying local-itinerant exchange coupling, this work
validates the materials-by-design strategy of utilizing localized magnetic
order to create and manipulate magnetic topological phases, from static to
ultrafast timescales.",2204.04791v1
2023/8/4,Quench Risk Increase With Radiation Damage,"Superconducting magnets are often proposed to confine plasma in fusion
reactors. Superconducting material enables the magnets to carry current
densities that would melt materials with non-zero resistance. Quench occurs
when superconductivity is lost and the current starts to generate heat. Unless
prevented with a fast enough control system, the heat generated during a quench
can cause catastrophic damage to the coils. This work describes a less-studied
heating mechanism that increases the likelihood and aggressiveness of fusion
magnet quenches. Defects accumulate in the magnet structural material under
irradiation by the fusion process. The defects store energy in the material and
change thermal and normal state electrical properties. Wigner energy is
released when defects anneal. After a 0.9 mDPA neutron irradiation, a 10 K
disturbance from 20 K is predicted to release enough energy to result in a
final temperature of 40 K. Irradiation damage also reduces the quench time
constant by increasing normal state resistivity and thus Ohmic heating. The
continuous operation of a fusion reactor produces an increasingly unstable
thermodynamic system in superconducting magnets by changing electrical and
thermal properties with irradiation damage. The temperature margin between
operation and quench runaway reduces with irradiation. The next steps are to
include these observations in quench models and validate the predictions
experimentally. Implications of this work is felt by all fusion powerplant
projects planning to leverage superconducting magnets. Designs will recognize
this risk with more stringent specifications on quench control systems and
maximum duration of coil operation at cryogenic temperature between periodic
releases of Wigner energy to avoid catastrophic quench failures.",2308.03794v2
2023/8/25,High-susceptibility nanoparticles for micro-inductor core materials,"According to the laws of magnetism, the shape of magnetically soft objects
limits the effective susceptibility. For example, spherical soft magnets cannot
display an effective susceptibility larger than 3. Although true for
macroscopic multi-domain magnetic materials, we show that magnetic
nanoparticles in a single-domain state do not suffer from this limitation. This
is a consequence of the particle moment being forced to saturation by the
predominance of exchange forces, and only allowed to rotate coherently in
response to thermal and/or applied fields. We apply statistical mechanics to
determine the static and dynamic susceptibility of single-domain particles as a
function of size, temperature and material parameters. Our calculations reveal
that spherical single-domain particles with large saturation magnetisation and
small magneto-crystalline anisotropy, e.g. FeNi particles, can have very a
large susceptibility of 200 or more. We further show that susceptibility and
losses can be tuned by particle easy axis alignment with the applied field in
case of uniaxial anisotropy, but not for particles with cubic anisotropy. Our
model is validated experimentally by comparison with measurements on
nanocomposites containing spherical 11$\pm$3 nm $\gamma$-Fe$_2$O$_3$ particles
up to 45 vol% finely dispersed in a polymer matrix. In agreement with the
calculations for this specific material, the measured susceptibility of the
composites is up to 17 ($\gg$3) and depends linearly on the volume fraction of
particles. Based on these results, we predict that nanocomposites of 30 vol% of
superparamagnetic FeNi particles in an insulating non-magnetic matrix can have
a sufficiently large susceptibility to be used as micro-inductor core materials
in the MHz frequency range, while maintaining losses below state-of-the-art
ferrites.",2308.13407v2
2023/11/17,Structural and magnetic properties of molecular beam epitaxy (MnSb2Te4)x(Sb2Te3)1-x topological materials with exceedingly high Curie temperature,"Tuning magnetic properties of magnetic topological materials is of interest
to realize elusive physical phenomena such as quantum anomalous hall effect
(QAHE) at higher temperatures and design topological spintronic devices.
However, current topological materials exhibit Curie temperature (TC) values
far below room temperature. In recent years, significant progress has been made
to control and optimize TC, particularly through defect engineering of these
structures. Most recently we showed evidence of TC values up to 80K for
(MnSb2Te4)x(Sb2Te3)1-x, where x is greater than or equal to 0.7 and less than
or equal to 0.85, by controlling the compositions and Mn content in these
structures. Here we show further enhancement of the TC, as high as 100K, by
maintaining high Mn content and reducing the growth rate from 0.9 nm/min to 0.5
nm/min. Derivative curves reveal the presence of two TC components contributing
to the overall value and propose TC1 and TC2 have distinct origins: excess Mn
in SLs and Mn in Sb2-yMnyTe3QLs alloys, respectively. In pursuit of elucidating
the mechanisms promoting higher Curie temperature values in this system, we
show evidence of structural disorder where Mn is occupying not only Sb sites
but also Te sites, providing evidence of significant excess Mn and a new
crystal structure:(Mn1+ySb2-yTe4)x(Sb2-yMnyTe3)1-x. Our work shows progress in
understanding how to control magnetic defects to enhance desired magnetic
properties and the mechanism promoting these high TC in magnetic topological
materials such as (Mn1+ySb2-yTe4)x(Sb2-yMnyTe3)1-x.",2311.10891v1
2023/3/6,Experimental evidence for Berry curvature multipoles in antiferromagnets,"Berry curvature multipoles appearing in topological quantum materials have
recently attracted much attention. Their presence can manifest in novel
phenomena, such as nonlinear anomalous Hall effects (NLAHE). The notion of
Berry curvature multipoles extends our understanding of Berry curvature effects
on the material properties. Hence, research on this subject is of fundamental
importance and may also enable future applications in energy harvesting and
high-frequency technology. It was shown that a Berry curvature dipole can give
rise to a 2nd order NLAHE in materials of low crystalline symmetry. Here, we
demonstrate a fundamentally new mechanism for Berry curvature multipoles in
antiferromagnets that are supported by the underlying magnetic symmetries.
Carrying out electric transport measurements on the kagome antiferromagnet
FeSn, we observe a 3rd order NLAHE, which appears as a transverse voltage
response at the 3rd harmonic frequency when a longitudinal a.c. current drive
is applied. Interestingly, this NLAHE is strongest at and above room
temperature. We combine these measurements with a scaling law analysis, a
symmetry analysis, model calculations, first-principle calculations, and
magnetic Monte-Carlo simulations to show that the observed NLAHE is induced by
a Berry curvature quadrupole appearing in the spin-canted state of FeSn. At a
practical level, our study establishes NLAHE as a sensitive probe of
antiferromagnetic phase transitions in other materials, such as moir\'e
superlattices, two-dimensional van der Waal magnets, and quantum spin liquid
candidates, that remain poorly understood to date. More broadly, Berry
curvature multipole effects are predicted to exist for 90 magnetic point
groups. Hence, our work opens a new research area to study a variety of
topological magnetic materials through nonlinear measurement protocols.",2303.03274v3
2000/7/6,Band structure and atomic sum rules for x-ray dichroism,"Corrections to the atomic orbital sum rule for circular magnetic x-ray
dichroism in solids are derived using orthonormal LMTOs as a single-particle
basis for electron band states.",0007096v1
2004/1/28,Density Functional Calculations near Ferromagnetic Quantum Critical Points,"We discuss the application of the density functional theory in the local
density approximation (LDA) near a ferromagnetic quantum critical point. The
LDA fails to describe the critical fluctuations in this regime. This provides a
fingerprint of a materials near ferromagnetic quantum critical points:
overestimation of the tendency to magnetism in the local density approximation.
This is in contrast to the typical, but not universal, tendency of the LDA to
underestimate the tendency to magnetism in strongly Hubbard correlated
materials. We propose a method for correcting the local density calculations by
including critical spin fluctuations. This is based on (1) Landau expansion for
the free energy, evaluated within the LDA, (2) lowest order expansion of the
RPA susceptibility in LDA and (3) extraction of the amplitude of the relevant
(critical) fluctuations by applying the fluctuation-dissipation theorem to the
difference between a quantum-critical system and a reference system removed
from the quantum critical point. We illustrate some of the aspects of this by
the cases of Ni3Al and Ni3Ga, which are very similar metals on opposite sides
of a ferromagnetic quantum critical point. LDA calculations predict that Ni3Ga
is the more magnetic system, but we find that due to differences in the band
structure, fluctuation effects are larger in Ni3Ga, explaining the fact that
experimentally it is the less magnetic of the two materials.",0401563v1
2004/3/27,Optical properties of a spherical 2D electron gas in the presence of a uniform magnetic field,This paper was withdrawn by the authors.,0403663v3
2004/6/24,Comment on cond-mat/0406502 by V. Yukalov and E. Yukalova on Coherent Nuclear Radiation,"We show that the argument of Yukalov and Yukalova that dipole-dipole
interaction prevents a system of magnetic dipoles from exhibiting superradiance
unless assisted by a resonator is incorrect.",0406621v1
2005/9/13,Intrinsic magnetism of open boron nitride nanotubes,This paper has been withdrawn by the author due to the incomplete results.,0509312v2
2006/3/5,Spontaneous Skyrmion Ground States in Magnetic Metals,"Since the 1950s Heisenberg and others have attempted to explain the
appearance of countable particles in quantum field theory in terms of stable
localized field configurations. As an exception Skyrme's model succeeded to
describe nuclear particles as localized states, so-called 'skyrmions', within a
non-linear field theory. Skyrmions are a characteristic of non-linear continuum
models ranging from microscopic to cosmological scales. Skyrmionic states have
been found under non-equilibrium conditions, or when stabilised by external
fields or the proliferation of topological defects. Examples are Turing
patterns in classical liquids, spin textures in quantum Hall magnets, or the
blue phases in liquid crystals, respectively. However, it is believed that
skyrmions cannot form spontaneous ground states like ferromagnetic or
antiferromagnetic order in magnetic materials. Here, we show theoretically that
this assumption is wrong and that skyrmion textures may form spontaneously in
condensed matter systems with chiral interactions without the assistance of
external fields or the proliferation of defects. We show this within a
phenomenological continuum model, that is based on a few material-specific
parameters that may be determined from experiment. As a new condition not
considered before, we allow for softened amplitude variations of the
magnetisation - a key property of, for instance, metallic magnets. Our model
implies that spontaneous skyrmion lattice ground states may exist quite
generally in a large number of materials, notably at surfaces and in thin films
as well as in bulk compounds, where a lack of space inversion symmetry leads to
chiral interactions.",0603103v1
2006/3/14,"Theory of ferromagnetic (III,Mn)V semiconductors","The body of research on (III,Mn)V diluted magnetic semiconductors initiated
during the 1990's has concentrated on three major fronts: i) the microscopic
origins and fundamental physics of the ferromagnetism that occurs in these
systems, ii) the materials science of growth and defects and iii) the
development of spintronic devices with new functionalities. This article
reviews the current status of the field, concentrating on the first two, more
mature research directions. From the fundamental point of view, (Ga,Mn)As and
several other (III,Mn)V DMSs are now regarded as textbook examples of a rare
class of robust ferromagnets with dilute magnetic moments coupled by
delocalized charge carriers. Both local moments and itinerant holes are
provided by Mn, which makes the systems particularly favorable for realizing
this unusual ordered state. Advances in growth and post-growth treatment
techniques have played a central role in the field, often pushing the limits of
dilute Mn moment densities and the uniformity and purity of materials far
beyond those allowed by equilibrium thermodynamics. In (III,Mn)V compounds,
material quality and magnetic properties are intimately connected. In the
review we focus on the theoretical understanding of the origins of
ferromagnetism and basic structural, magnetic, magneto-transport, and
magneto-optical characteristics of simple (III,Mn)V epilayers, with the main
emphasis on (Ga,Mn)As. The conclusions we arrive at are based on an extensive
literature covering results of complementary ab initio and effective
Hamiltonian computational techniques, and on comparisons between theory and
experiment.",0603380v2
2007/5/10,"Influence of oxygen partial pressure on structural, transport and magnetic properties of Co doped TiO2 films","Thin films of Co-TiO2 are deposited on silicon and quartz substrates using
Pulse Laser Deposition (PLD) process at various oxygen partial pressures
ranging from 6.6 x 10-3 Pascals (Pa) to 53 Pa. Crystal structure, transport and
magnetic properties of reduced CoxTi(1-x)O2 (0 <x< 0.03) thin films are
investigated and are found to have a strong dependence on the oxygen partial
pressure. X-ray diffraction (XRD) data reveals the presence of mixed phase
material containing both anatase and rutile. However, these phases
intertransform with the change in the oxygen partial pressure in the chamber
during the growth of the films. X-ray Photoelectron Spectroscopy (XPS) shows no
Co or CoO related peaks for samples with Co concentration up to x=0.03.
However, the oxygen 1s peaks are asymmetric suggesting the presence of oxygen
vacancies. The transport and magnetic measurements show a clear dependence on
the concentration of oxygen vacancies. There is an enhancement in the
electrical conductivity and the magnetization as more vacancies are created in
the material. The resistivity as a function of temperature rho(T) follows the
polaronic behavior and the activation energies obtained, ~100 to 150meV, are
within the range that is typical for semiconducting materials.",0705.1527v1
2007/10/3,Flux line lattice state versus magnetism in electron-doped cuprate superconductor Sr_{1-x}La_{x}CuO_{2},"The microscopic details of flux line lattice state studied by muon spin
rotation is reported in an electron-doped high-$T_{\rm c}$ cuprate
superconductor, Sr$_{1-x}$La$_{x}$CuO$_{2}$ (SLCO, $x=0.10$--0.15). A clear
sign of phase separation between magnetic and non-magnetic phases is observed,
where the effective magnetic penetration depth [$\lambda\equiv\lambda(T,H)$] is
determined selectively for the latter phase. The extremely small value of
$\lambda(0,0)$ %versus $T_{\rm c}$ and corresponding large superfluid density
($n_s \propto \lambda^{-2}$) is consistent with presence of a large Fermi
surface with carrier density of $1+x$, which suggests the breakdown of the
""doped Mott insulator"" even at the ""optimal doping"" in SLCO. Moreover, a
relatively weak anisotropy in the superconducting order parameter is suggested
by the field dependence of $\lambda(0,H)$. These observations strongly suggest
that the superconductivity in SLCO is of a different class from hole-doped
cuprates.",0710.0773v4
2007/11/26,Coupling of magnetization and structural distortions in multiferroic BiFeO3 : an ab initio density functional theory study,"This paper has been withdrawn by the author due to a crucial citing error in
equation 4.",0711.3984v2
2010/3/31,Graphene and graphane: New stars of nanoscale electronics,"Discoveries of graphene and graphane possessing unique electronic and
magnetic properties offer a bright future for carbon based electronics, with
future prospects of superseding silicon in the semiconductor industry.",1003.6044v1
2010/6/1,Options for the Neutron Lifetime Measurements in Traps,"Different geometries for the neutron lifetime measurements by the method of
ultracold neutron storage in material traps and additional possibilities for
the neutron storage in the magnetic storage ring are considered.",1006.0175v1
2010/7/1,Antiferromagnetic I-Mn-V semiconductors,"After decades of research, the low Curie temperature of ferromagnetic
semiconductors remains the key problem in the development of magnetic
semiconductor spintronic technologies. Removing this roadblock might require a
change of the field's basic materials paradigm by looking beyond ferromagnets.
Recent studies of relativistic magnetic and magnetotransport anisotropy
effects, which in principle are equally well present in materials with
ferromagnetically and antiferromagnetically ordered spins, have inspired our
search for antiferromagnetic semiconductors suitable for high-temperature
spintronics. Since these are not found among the magnetic counterparts of
common III-V or II-VI semi- conductors, we turn the attention in this paper to
high N \'eel temperature I-II-V magnetic compounds whose electronic structure
has not been previously identified. Our combined experimental and theoretical
work on LiMnAs provides basic prerequisite for the systematic research of this
class of materials by demonstrating the feasibility to grow single crystals of
group-I alkali metal compounds by molecular beam epitaxy, by demonstrating the
semiconducting band structure of the I-Mn-V's, and by analyzing their
spin-orbit coupling characteristics favorable for spintronics.",1007.0177v1
2011/6/2,Relevance of the Heisenberg-Kitaev model for the honeycomb lattice iridates A_2IrO_3,"Combining thermodynamic measurements with theoretical density functional and
thermodynamic calculations we demonstrate that the honeycomb lattice iridates
A2IrO3 (A = Na, Li) are magnetically ordered Mott insulators where the
magnetism of the effective spin-orbital S = 1/2 moments can be captured by a
Heisenberg-Kitaev (HK) model with Heisenberg interactions beyond
nearest-neighbor exchange. Experimentally, we observe an increase of the
Curie-Weiss temperature from \theta = -125 K for Na2IrO3 to \theta = -33 K for
Li2IrO3, while the antiferromagnetic ordering temperature remains roughly the
same T_N = 15 K for both materials. Using finite-temperature functional
renormalization group calculations we show that this evolution of \theta, T_N,
the frustration parameter f = \theta/T_N, and the zig-zag magnetic ordering
structure suggested for both materials by density functional theory can be
captured within this extended HK model. Combining our experimental and
theoretical results, we estimate that Na2IrO3 is deep in the magnetically
ordered regime of the HK model (\alpha \approx 0.25), while Li2IrO3 appears to
be close to a spin-liquid regime (0.6 < \alpha < 0.7).",1106.0429v2
2013/6/4,Colloquium: Artificial spin ice: Designing and imaging magnetic frustration,"Frustration in the presence of competing interactions is ubiquitous in the
physical sciences and is a source of degeneracy and disorder, giving rise to
new and interesting physical phenomena. Perhaps nowhere does it occur more
simply than in correlated spin systems, where it has been studied in the most
detail. In the past few years, a new perspective has opened in the study of
frustration through the creation of artificial frustrated magnetic systems.
These materials consist of arrays of lithographically fabricated single-domain
ferromagnetic nanostructures that behave like giant Ising spins. The
nanostructures' interactions can be controlled through appropriate choices of
their geometric properties and arrangement on a (frustrated) lattice. The
degrees of freedom of the material can not only be directly tuned, but also
individually observed. Experimental studies have unearthed intriguing
connections to the out-of-equilibrium physics of disordered systems and
non-thermal granular materials, while revealing strong analogies to (spin) ice
materials and their fractionalized magnetic monopole excitations, lending the
enterprise a distinctly interdisciplinary flavor. The experimental results have
also been closely coupled to theoretical and computational analyses,
facilitated by connections to classic models of frustrated magnetism, whose
hitherto unobserved aspects have here found an experimental realization. We
review the considerable experimental and theoretical progress in this field,
including connections to other frustrated phenomena, and we outline future
vistas for progress in this rapidly expanding field.",1306.0825v4
2013/12/2,Hard x-ray emission spectroscopy: a powerful tool for the characterization of magnetic semiconductors,"This review aims to introduce the x-ray emission spectroscopy (XES) and
resonant inelastic x-ray scattering (RIXS) techniques to the materials
scientist working with magnetic semiconductors (e.g. semiconductors doped with
3d transition metals) for applications in the field of spin-electronics. We
focus our attention on the hard part of the x-ray spectrum (above 3 keV) in
order to demonstrate a powerful element- and orbital-selective characterization
tool in the study of bulk electronic structure. XES and RIXS are
photon-in/photon-out second order optical processes described by the
Kramers-Heisenberg formula. Nowadays, the availability of third generation
synchrotron radiation sources permits applying such techniques also to dilute
materials, opening the way for a detailed atomic characterization of
impurity-driven materials. We present the K{\beta} XES as a tool to study the
occupied valence states (directly, via valence-to-core transitions) and to
probe the local spin angular momentum (indirectly, via intra-atomic exchange
interaction). The spin sensitivity is employed, in turn, to study the
spin-polarized unoccupied states. Finally, the combination of RIXS with
magnetic circular dichroism (RIXS-MCD) extends the possibilities of standard
magnetic characterization tools.",1312.0399v2
2015/1/16,"Electronic correlations, magnetism and Hund's rule coupling in the ruthenium perovskites SrRuO$_3$ and CaRuO$_3$","A comparative density functional plus dynamical mean field theory study of
the pseudocubic ruthenate materials CaRuO$_3$ and SrRuO$_3$ is presented. Phase
diagrams are determined for both materials as a function of Hubbard repulsion
$U$ and Hund's rule coupling $J$. Metallic and insulating phases are found, as
are ferromagnetic and paramagnetic states. The locations of the relevant phase
boundaries are determined. Based on the computed phase diagrams, Mott-dominated
and Hund's dominated regimes of strong correlation are distinguished.
Comparison of calculated properties to experiments indicates that the actual
materials are in the Hund's coupling dominated region of the phase diagram so
can be characterized as Hund's metals, in common with other members of the
ruthenate family. Comparison of the phase diagrams for the two materials
reveals the role played by rotational and tilt (GdFeO$_3$-type) distortions of
the ideal perovskite structure. The presence of magnetism in SrRuO$_3$ and its
absence in CaRuO$_3$ despite the larger mass and larger tilt/rotational
distortion amplitude of CaRuO$_3$ can be understood in terms of density of
states effects in the presence of strong Hund's coupling. Comparison of the
calculated low-$T$ properties of CaRuO$_3$ to those of SrRuO$_3$ provides
insight into the effects of magnetic order on the properties of a Hund's metal.
The study provides a simultaneous description of magnetism and correlations and
explicates the roles played by band theory and Hubbard and Hund's interactions.",1501.03964v2
2015/1/29,Magnetocaloric effect in Gd3Ir compound,"Here we report magneto-thermal properties of Gd3Ir compounds using magnetic
and heat capacity data. We observed large isothermal entropy change, adiabatic
temperature change and relative cooling power are 4.1J/Kg, 4K and 437J/Kg on
50KOe respectively.",1501.07426v1
2015/3/1,Magnetic-dipolar-mode Fano resonances for microwave spectroscopy of high absorption matter,"Study of interaction between high absorption matter and microwave radiated
energy is a subject of great importance. Especially, this concerns microwave
spectroscopic characterization of biological liquids. Use of effective testing
methods to obtain information about physical properties of different liquids on
the molecular level is one of the most important problems in biophysics.
However, the standard methods based on the microwave resonant techniques are
not sufficiently suitable for biological liquids because the resonance peak in
a resonator with high-loss liquids is so broad that the material parameters
cannot be measured correctly. Although molecular vibrations of biomolecules may
have microwave frequencies, it is not thought that such resonant coupling is
significant due to their low energy compared with thermal energy and the
strongly dampening aqueous environment. This paper presents an innovative
microwave sensing technique for different types of lossy materials, including
biological liquids. The technique is based on the combination of the microwave
perturbation method and the Fano-resonance effects observed recently in
microwave structures with embedded magnetic-dipolar quantum dots. When
frequency of the magnetic-dipolar-mode (MDM) resonance is not equal to the
cavity resonance frequency, one gets Fano transmission intensity. With tuning,
by a bias magnetic field, the MDM resonance frequency to the cavity resonance
frequency, one observes a Lorentz line shape. Use of an extremely narrow
Lorentzian peak allows exact probing the resonant frequency of a cavity loaded
by a high-lossy-material sample. For different kinds of samples, one has
different frequencies of Lorentzian peaks. This gives a picture for precise
spectroscopic characterization of high absorption matter in microwaves.",1503.00286v1
2015/9/15,Search for New Superconductors: An Electro-Magnetic Phase Transition in an Iron Meteorite Inclusion at 117 K,"The discovery of superconductivity in pnictides and iron chalcogenides
inspires the search for new iron based superconducting phases. Iron-rich
meteorites present a unique opportunity for this search, because they contain a
broad range of compounds produced under extreme growth conditions. We
investigated a natural iron sulfide based materials (Troilite) inclusion with
its associated minerals in the iron meteorite Tlacotepec. Tlacotepec formed in
an asteroidal core under high pressure and at high temperature over millions of
years, while insoluble sulfur rich materials segregated into inclusions during
cooling along with included minerals. The search for superconductivity in these
heterogeneous materials requires a technique capable of detecting minute
amounts of a superconducting phase embedded in a non-superconducting matrix. We
used Magnetic Field Modulated Microwave Spectroscopy (MFMMS), a very sensitive,
selective, and non-destructive technique, to search for superconductivity in
heterogeneous systems. Here, we report the observation of an electro-magnetic
phase transition at 117 K that causes a MFMMS-response typical of a
superconductor. A pronounced and reproducible peak together with isothermal
magnetic field sweeps prove the appearance of a new electromagnetic phase below
117 K. This is very similar to the characteristic response due to flux trapping
in a granular superconductor with a short coherence length. Although the
compound responsible for the peak in the MFMMS-spectra was not identified, it
is possibly an iron sulfide based phase, or another material heterogeneously
distributed over the inclusion.",1509.04452v2
2016/4/29,Finite temperature elastic constants of paramagnetic materials within the disordered local moment picture from ab initio molecular dynamics calculations,"We present a theoretical scheme to calculate the elastic constants of
magnetic materials in the high-temperature paramagnetic state. Our approach is
based on a combination of disordered local moments picture and ab initio
molecular dynamics (DLM-MD). Moreover, we investigate a possibility to enhance
the efficiency of the simulations of elastic properties using recently
introduced method: symmetry imposed force constant temperature dependent
effective potential (SIFC-TDEP). We have chosen cubic paramagnetic CrN as a
model system. This is done due to its technological importance and its
demonstrated strong coupling between magnetic and lattice degrees of freedom.
We have studied the temperature dependent single-crystal and polycrystalline
elastic constants of paramagentic CrN up to 1200 K. The obtained results at T=
300 K agree well with the experimental values of polycrystalline elastic
constants as well as Poisson ratio at room temperature. We observe that the
Young's modulus is strongly dependent on temperature, decreasing by ~14% from
T=300 K to 1200 K. In addition we have studied the elastic anisotropy of CrN as
a function of temperature and we observe that CrN becomes substantially more
isotropic as the temperature increases. We demonstrate that the use of Birch
law may lead to substantial errors for calculations of temperature induced
changes of elastic moduli. The proposed methodology can be used for accurate
predictions of mechanical properties of magnetic materials at temperatures
above their magnetic order-disorder phase transition.",1604.08855v3
2016/8/16,Revealing frustrated local moment model for pressurized hyperhoneycomb iridate: paving a way toward quantum spin liquid,"There have been tremendous experimental and theoretical efforts toward
discovery of quantum spin liquid phase in honeycomb-based-lattice materials
with strong spin-orbit coupling. Here the bond-dependent Kitaev interaction
between local moments provides strong magnetic frustration and if it is the
only interaction present in the system, it will lead to an exactly solvable
quantum spin liquid ground state. In all of these materials, however, the
ground state is in a magnetically ordered phase due to additional interactions
between local moments. Recently, it has been reported that the magnetic order
in hyperhoneycomb material, $\beta$-Li$_2$IrO$_3$, is suppressed upon applying
hydrostatic pressure and the resulting state becomes a quantum paramagnet or
possibly a quantum spin liquid. Using ab-initio computations and strong
coupling expansion, we investigate the lattice structure and resulting local
moment model in pressurized $\beta$-Li$_2$IrO$_3$. Remarkably, the dominant
interaction under high pressure is not the Kitaev interaction nor further
neighbor interactions, but a different kind of bond-dependent interaction. This
leads to strong magnetic frustration and may provide a platform for discovery
of a new kind of quantum spin liquid ground state.",1608.04741v2
2016/8/18,Strain-induced Isostructural and Magnetic Phase Transitions in Monolayer MoN$_2$,"The change of bonding status, typically occurring only in chemical processes,
could dramatically alter the material properties. Here, we show that a tunable
breaking and forming of a diatomic bond can be achieved through physical means,
i.e., by a moderate biaxial strain, in the newly discovered MoN$_2$
two-dimensional (2D) material. Based on first-principles calculations, we
predict that as the lattice parameter is increased under strain, there exists
an isostructural phase transition at which the N-N distance has a sudden drop,
corresponding to the transition from a N-N nonbonding state to a N-N single
bond state. Remarkably, the bonding change also induces a magnetic phase
transition, during which the magnetic moments transfer from the N(2p)
sublattice to the Mo(4d) sublattice, meanwhile the type of magnetic coupling is
changed from ferromagnetic to anti-ferromagnetic. We provide a physical picture
for understanding these striking effects. The discovery is not only of great
scientific interest in exploring unusual phase transitions in low-dimensional
systems, but it also reveals the great potential of the 2D MoN$_2$ material in
the nanoscale mechanical, electronic, and spintronic applications.",1608.05164v2
2016/8/18,Ion Beam radiation and temperature effect on Co/Si and CoO/Co/Si thin films,"Co and CoO thin films were deposited by magnetron sputtering in the form of
multilayers. They were irradiated with Ar and Si ion beams of different
energies and fluences. The magnetic properties were investigated.",1608.05663v1
2016/9/1,Neutron tomography of magnetic Majorana fermions in a proximate quantum spin liquid,"Quantum matter provides an effective vacuum out of which arise emergent
particles not corresponding to any experimentally detected elementary particle.
Topological quantum materials in particular have become a focus of intense
research in part because of the remarkable possibility to realize Majorana
fermions, with their potential for new, decoherence-free quantum computing
architectures. In this paper we undertake a study on high-quality single
crystal of $\alpha-RuCl_3$ which has been identified as a material realizing a
proximate Kitaev state, a topological quantum state with magnetic Majorana
fermions. Four-dimensional tomographic reconstruction of dynamical correlations
measured using neutrons is uniquely powerful for probing such magnetic states.
We discover unusual signals, including an unprecedented column of scattering
over a large energy interval around the Brillouin zone center which is
remarkably stable with temperature. This is straightforwardly accounted for in
terms of the Majorana excitations present in Kitaev's topological quantum spin
liquid. Other, more delicate, features in the scattering can be transparently
associated with perturbations to an ideal model. This opens a window on
emergent magnetic Majorana fermions in correlated materials.",1609.00103v1
2018/7/31,Switchable geometric frustration in an artificial-spin-ice-superconductor hetero-system,"Geometric frustration emerges when local interaction energies in an ordered
lattice structure cannot be simultaneously minimized, resulting in a large
number of degenerate states. The numerous degenerate configurations may lead to
practical applications in microelectronics, such as data storage, memory and
logic. However, it is difficult to achieve extensive degeneracy, especially in
a two-dimensional system. Here, we showcase in-situ controllable geometric
frustration with massive degeneracy in a two-dimensional flux quantum system.
We create this in a superconducting thin film placed underneath a
reconfigurable artificial-spin-ice structure. The tunable magnetic charges in
the artificial-spin-ice strongly interact with the flux quanta in the
superconductor, enabling the switching between frustrated and crystallized flux
quanta states. The different states have measurable effects on the
superconducting critical current profile, which can be reconfigured by precise
selection of the spin ice magnetic state through application of an external
magnetic field. We demonstrate the applicability of these effects by realizing
a reprogrammable flux quanta diode. The tailoring of the energy landscape of
interacting 'particles' using artificial-spin-ices provides a new paradigm for
the design of geometric frustration, which allows us to control new
functionalities in other material systems, such as magnetic skyrmions,
electrons/holes in two-dimensional materials and topological insulators, as
well as colloids in soft materials.",1807.11650v1
2019/1/3,Colossal electromagnon excitation in the non-cycloidal phase of TbMnO3 under pressure,"The magnetoelectric coupling, i.e., cross-correlation between electric and
magnetic orders, is a very desirable property to combine functionalities of
materials for next-generation switchable devices. Multiferroics with
spin-driven ferroelectricity presents such a mutual interaction concomitant
with magneto- and electro-active excitations called electromagnons. TbMnO3 is a
paradigmatic material in which two electromagnons have been observed in the
cycloidal magnetic phase. However, their observation in TbMnO3 is restricted to
the cycloidal spin phase and magnetic ground states that can support the
electromagnon excitation are still under debate. Here, we show by performing
Raman spectroscopy measurements under pressure that the lower-energy
electromagnon (4 meV) disappears when the ground state enters from a cycloidal
phase to an antiferromagnetic phase (E-type). On the contrary, the
magnetoelectric activity of the higher-energy electromagnon (8 meV) increases
in intensity by one order of magnitude. Using microscopic model calculations,
we demonstrate that the lowerenergy electromagnon, observed in the cycloidal
phase, originates from a higher harmonic of the magnetic cycloid, and we
determine that the symmetric exchange-striction mechanism is at the origin of
the higher-energy electromagnon which survives even in the E-type phase. The
colossal enhancement of the electromagnon activity in TbMnO3 paves the way to
use multiferroics more efficiently for generation, conversion and control of
spin waves in magnonic devices.",1901.00919v1
2019/2/9,Antiferromagnetic phase transition in $Cr_{2}As$ via anisotropy of exchange interactions,"The electronic structure of anti-ferromagnetic $Cr_{2}As$ is investigated.
Anisotropy of exchange interactions between chrome sub-lattices is determined
($J^{X}(Cr_{I}-Cr_{II}) =4.77 meV,J^{Y}(Cr_{I}-Cr_{II}) =-6.36 meV$). The
behavior of exchange integrals from magnetic structure is analyzed.",1902.03337v1
2019/12/16,Dynamics of reconfigurable artificial spin ice: towards magnonic functional materials,"Over the past few years, the study of magnetization dynamics in artificial
spin ices has become a vibrant field of study. Artificial spin ices are
ensembles of geometrically arranged, interacting magnetic nanoislands, which
display frustration by design. These were initially created to mimic the
behavior in rare earth pyrochlore materials and to study emergent behavior and
frustration using two-dimensional magnetic measurement techniques. Recently, it
has become clear that it is possible to create artificial spin ices, which can
potentially be used as functional materials. In this Perspective, we review the
resonant behavior of spin ices (which is in the GHz frequency range), focusing
on their potential application as magnonic crystals. In magnonic crystals, spin
waves are functionalized for logic applications by means of band structure
engineering. While it has been established that artificial spin ices can
possess rich mode spectra, the applicability of spin ices to create magnonic
crystals hinges upon their reconfigurability. Consequently, we describe recent
work aiming to develop techniques and create geometries allowing full
reconfigurability of the spin ice magnetic state. We also discuss experimental,
theoretical, and numerical methods for determining the spectral response of
artificial spin ices, and give an outlook on new directions for reconfigurable
spin ices.",1912.07280v2
2019/12/27,Realizing spin-Hamiltonians in nanoscale active photonic lattices,"Spin models arise in the microscopic description of magnetic materials, where
the macroscopic characteristics are governed by exchange interactions among the
constituent magnetic moments. Recently, there has been a growing interest in
complex systems with spin Hamiltonians, largely due to the rich behaviors
exhibited by such interactions at the macroscale. Along these lines, it has
been shown that certain classes of optimization problems involving large
degrees of freedom can be effectively mapped into classical spin models. In
this vein, the respective extremum can be found by identifying the ground state
of the associated spin Hamiltonian. Here, we show both theoretically and
experimentally, that the cooperative interplay among vectorial electromagnetic
modes in coupled metallic nanolasers can be utilized as a means to emulate
certain types of spin-like systems. The ensuing spin exchange interactions are
in general anisotropic, in a way similar to that encountered in magnetic
materials involving spin-orbit coupling. For some topologies, we find that
these active nanophotonic structures are governed by a classical XY Hamiltonian
that exhibits two phases akin to those associated with ferromagnetic (FM) and
antiferromagnetic (AF) materials. In addition, we show that in certain
configurations, the electromagnetic field distribution can undergo geometrical
frustration, depending on the lattice shape and the transverse resonant modes
supported by the individual cavity elements. Our results could pave the way
towards a new scalable nanophotonic platform to study spin exchange
interactions, that can in turn be potentially exploited to investigate more
large-scale networks, emulate some magnetic materials, or to address a variety
of optimization problems.",1912.12075v1
2020/1/2,Magnetic proximity and nonreciprocal current switching in a monolayer WTe2 helical edge,"The integration of diverse electronic phenomena, such as magnetism and
nontrivial topology, into a single system is normally studied either by seeking
materials that contain both ingredients, or by layered growth of contrasting
materials. The ability to simply stack very different two dimensional (2D) van
der Waals materials in intimate contact permits a different approach. Here we
use this approach to couple the helical edges states in a 2D topological
insulator, monolayer WTe2, to a 2D layered antiferromagnet, CrI3. We find that
the edge conductance is sensitive to the magnetization state of the CrI3, and
the coupling can be understood in terms of an exchange field from the nearest
and next-nearest CrI3 layers that produces a gap in the helical edge. We also
find that the nonlinear edge conductance depends on the magnetization of the
nearest CrI3 layer relative to the current direction. At low temperatures this
produces an extraordinarily large nonreciprocal current that is switched by
changing the antiferromagnetic state of the CrI3.",2001.00634v1
2020/5/25,Temperature effect on the magnetic oscillations in 2D materials,"We study the magnetic oscillations (MO) in 2D materials with a buckled
honeycomb lattice, considering a perpendicular electric and magnetic field. At
zero temperature the MO consist of the sum of four sawtooth oscillations, with
two unique frequencies and phases. The values of these frequencies depend on
the Fermi energy and electric field, which in turn determine the condition for
a beating phenomenon in the MO. We analyse the temperature effect in the MO by
considering its local corrections over each magnetization peak, given by
Fermi-Dirac like functions. We show that the width of these functions is
related to the minimum temperature necessary to observe the spin and valley
properties in the MO. In particular, we find that in order to observe the spin
splitting, the width must be lower than the MO phase difference. Likewise, in
order to observe valley mixing effects, the width must be lower than the MO
period. We also show that at high temperatures, all the maxima and minima in
the MO are shift to a constant value, in which case we obtain a simple
expression for the MO and its envelope. The results obtained show unique
features in the MO in 2D materials, given by the interplay between the valley
and spin.",2005.12109v1
2020/6/4,Effects of uniaxial pressure on the spin ice Ho2Ti2O7,"The spin ice materials Ho2Ti2O7 and Dy2Ti2O7 are experimental and theoretical
exemplars of highly frustrated magnetic materials. However, the effects of an
applied uniaxial pressure are not well studied, and here we report
magnetization measurements of Ho2Ti2O7 under uniaxial pressure applied in the
[001], [111] and [110] crystalline directions. The basic features are captured
by an extension of the dipolar spin ice model. We find a good match between our
model and measurements with pressures applied along two of the three
directions, and extend the framework to discuss the influence of crystal
misalignment for the third direction. The parameters determined from the
magnetization measurements reproduce neutron scattering measurements we perform
under uniaxial pressure applied along the [110] crystalline direction. In the
detailed analysis we include the recently verified susceptibility dependence of
the demagnetizing factor. Our work demonstrates the application of a moderate
applied pressure to modify the magnetic interaction parameters. The knowledge
can be used to predict critical pressures needed to induce new phases and
transitions in frustrated materials, and in the case of Ho2Ti2O7 we expect a
transition to a ferromagnetic ground state for uniaxial pressures above 3.3
GPa.",2006.02756v2
2020/6/18,Tunable anomalous Hall transport in bulk and two-dimensional 1$T$-CrTe$_{2}$: A first-principles study,"Layered materials with robust magnetic ordering have been attracting
significant research interest. In recent experiments, a new layered material
1$T$-CrTe$_{2}$ has been synthesized and exhibits ferromagnetism above the room
temperature. Here, based on first-principles calculations, we investigate the
electronic, magnetic, and transport properties of 1$T$-CrTe$_{2}$, both in the
bulk and in the two-dimensional (2D) limit. We show that 1$T$-CrTe$_{2}$ can be
stable in the monolayer form, and has a low exfoliation energy. The monolayer
structure is an intrinsic ferromagnetic metal, which maintains a high Curie
temperature above the room temperature. Particularly, we reveal interesting
features in the anomalous Hall transport. We show that in the ground state,
both bulk and monolayer 1$T$-CrTe$_{2}$ possess vanishing anomalous Hall
effect, because the magnetization preserves one vertical mirror symmetry. The
anomalous Hall conductivity can be made sizable by tuning the magnetization
direction or by uniaxial strains that break the mirror symmetry. The
room-temperature 2D ferromagnetism and the tunable anomalous Hall effect make
the material a promising platform for nanoscale device applications.",2006.10795v2
2020/7/16,33% Giant Anomalous Hall Current Driven by both Intrinsic and Extrinsic Contributions in Magnetic Weyl Semimetal Co3Sn2S2,"Anomalous Hall effect (AHE) can be induced by intrinsic mechanism due to the
band Berry phase and extrinsic one arising from the impurity scattering. The
recently discovered magnetic Weyl semimetal Co3Sn2S2 exhibits a large intrinsic
anomalous Hall conductivity (AHC) and a giant anomalous Hall angle (AHA). The
predicted energy dependence of the AHC in this material exhibits a plateau at
1000 {\Omega}-1 cm-1 and an energy width of 100 meV just below EF, thereby
implying that the large intrinsic AHC will not significantly change against
small-scale energy disturbances such as slight p-doping. Here, we successfully
trigger the extrinsic contribution from alien-atom scattering in addition to
the intrinsic one of the pristine material by introducing a small amount of Fe
dopant to substitute Co in Co3Sn2S2. Our experimental results show that the AHC
and AHA can be prominently enhanced up to 1850 {\Omega}-1 cm-1 and 33%,
respectively, owing to the synergistic contributions from the intrinsic and
extrinsic mechanisms as distinguished by the TYJ model. In particular, the
tuned AHA holds a record value in low fields among known magnetic materials.
This study opens up a pathway to engineer giant AHE in magnetic Weyl
semimetals, thereby potentially advancing the topological
spintronics/Weyltronics.",2007.08268v1
2020/10/22,Multicaloric effects in Metamagnetic Heusler Ni-Mn-In under uniaxial stress and magnetic field,"The world's growing hunger for artificial cold on the one hand, and the ever
more stringent climate targets on the other, pose an enormous challenge to
mankind. Novel, efficient and environmentally friendly refrigeration
technologies based on solid-state refrigerants can offer a way out of the
problems arising from climate-damaging substances used in conventional
vapor-compressors. Multicaloric materials stand out because of their large
temperature changes which can be induced by the application of different
external stimuli such as a magnetic, electric, or a mechanical field. Despite
the high potential for applications and the interesting physics of this group
of materials, only few studies focus on their investigation by direct methods.
In this paper, we report on the advanced characterization of all relevant
physical quantities that determine the multicaloric effect of a Ni-Mn-In
Heusler compound. We have used a purpose-designed calorimeter to determine the
isothermal entropy and adiabatic temperature changes resulting from the
combined action of magnetic field and uniaxial stress on this metamagnetic
shape-memory alloy. From these results, we can conclude that the multicaloric
response of this alloy by appropriate changes of uniaxial stress and magnetic
field largely outperforms the caloric response of the alloy when subjected to
only a single stimulus. We anticipate that our findings can be applied to other
multicaloric materials, thus inspiring the development of refrigeration devices
based on the multicaloric effect.",2010.11511v1
2020/10/27,Adsorption-controlled growth of MnTe(Bi2Te3)n by molecular beam epitaxy exhibiting stoichiometry-controlled magnetism,"We report the growth of the intrinsic magnetic topological system
MnTe(Bi2Te3)n by molecular beam epitaxy. By mapping the temperature and the
Bi:Mn flux ratio, it is shown that there is a narrow growth window for the n=1
phase MnBi2Te4 with 2.0<Bi:Mn<2.6 at 225 {\deg}C. Here the films are
stoichiometric and excess Bi and Te is not incorporated. At higher flux ratios
(Bi:Mn>4.5) it is found that the n = 2 MnBi4Te7 phase is stabilized. Transport
measurements indicate that the MnBi2Te4 and MnBi4Te7 undergo magnetic
transitions around 25 K, and 10 K, respectively, consistent with
antiferromagnetic phases found in the bulk. Further, for Mn-rich conditions
(Bi:Mn<2), ferromagnetism emerges that exhibits a clear hysteretic state in the
Hall effect, which likely indicates Mn-doped MnBi2Te4. Understanding how to
grow ternary chalcogenide phases is the key to synthesizing new materials and
to interface magnetism and topology, which together are routes to realize and
control exotic quantum phenomena.",2010.14306v1
2020/11/27,d0 Ferromagnetism in Li-doped ZnO Compounds,"Recently, d0 ferromagnetic materials have been projected as one of the
promising novel materials for spintronics applications. In this work, we have
studied Li-doped ZnO compounds, i.e. Zn1-xLixO (x=0, 0.02, 0.04, and 0.06)
samples, prepared by the solid-state reaction route method. From the study of
crystal structure using X-ray diffraction (XRD) patterns, it is evident that
the prepared materials have been formed in a single-phase of the hexagonal
wurtzite structure. The refinement of the XRD patterns suggests that there are
very small changes in the lattice parameters upon Li-incorporation in ZnO. The
average crystallite size (SC), estimated from XRD patterns was found to be in
the range of 35-50 nm. The microstructural study by scanning electron
microscope reveals the uniform morphology of the grains of the order of 50-70
nm. The energy dispersive spectrum indicates that no unwanted ferromagnetic
impurities have crept into the final prepared samples. The measurement of the
temperature (T) variation of magnetization (M) with SQUID magnetometer
indicates that undoped ZnO exhibits diamagnetic property but all Li-doped
compounds exhibit room-temperature ferromagnetism and with a magnetic
irreversibility behavior between zero-field cooled and field cooled M-T data.
From the magnetization versus field measurements at 3 and 300 K, it is observed
that Li-doped samples exhibit ferromagnetic loops with ultra-soft coercivity
(~50 Oe) and with a maximum saturation magnetization of 0.10 emu/gm for x= 0.02
sample, which decreases with the increase in Li concentration.",2011.13713v1
2021/1/7,Reentrance of spin-driven ferroelectricity through rotational tunneling of ammonium,"Quantum effects fundamentally engender exotic physical phenomena in
macroscopic systems, which advance next-generation technological applications.
Rotational tunneling that represents the quantum phenomenon of the librational
motion of molecules is ubiquitous in hydrogen-contained materials. However, its
direct manifestation in realizing macroscopic physical properties is elusive.
Here we report an observation of reentrant ferroelectricity under low pressure
that is mediated by the rotational tunneling of ammonium ions in molecule-based
(NH$_4$)$_2$FeCl$_5 \cdot$H$_2$O. Applying a small pressure leads to a
transition from spin-driven ferroelectricity to paraelectricity coinciding with
the stabilization of a collinear magnetic phase. Such a transition is
attributed to the hydrogen bond fluctuations via the rotational tunneling of
ammonium groups as supported by theoretical calculations. Higher pressure lifts
the quantum fluctuations and leads to a reentrant ferroelectric phase
concomitant with another incommensurate magnetic phase. These results
demonstrate that the rotational tunneling emerges as a new route to control
magnetic-related properties in soft magnets, opening avenues for designing
multi-functional materials and realizing potential quantum control.",2101.02795v1
2021/3/29,Spin-group symmetry in magnetic materials with negligible spin-orbit coupling,"Symmetry formulated by group theory plays an essential role with respect to
the laws of nature, from fundamental particles to condensed matter systems.
Here, by combining symmetry analysis and tight-binding model calculations, we
elucidate that the crystallographic symmetries of a vast number of magnetic
materials with light elements, in which the neglect of relativistic spin-orbit
coupling (SOC) is an appropriate approximation, are considerably larger than
the conventional magnetic groups. Thus, a symmetry description that involves
partially-decoupled spin and spatial rotations, dubbed as spin group, is
required. Spin group permits more symmetry operations and thus more energy
degeneracies that are disallowed by the magnetic groups. One consequence of the
spin group is the new anti-unitary symmetries that protect SOC-free Z_2
topological phases with unprecedented surface node structures. Our work not
only manifests the physical reality of materials with weak SOC, but also shed
light on the understanding of all solids with and without SOC by a unified
group theory.",2103.15723v4
2021/11/9,Tunable intrinsic ferromagnetic topological phases in bulk van der Waals crystal MnSb6Te10,"Intrinsic ferromagnetism is a crucial ingredient to realize quantum anomalous
Hall effect in quasi two dimensional materials, thus the search of intrinsic
ferromagnetic topological materials is one of the most concerned issues in the
field of topological phases of matter. In this work, combining magnetotransport
measurements, first principles calculations, and angle-resolved photoemission
spectroscopy studies, we find that in MnSb6Te10, the n = 2 member of the
MnSb2Te4/(Sb2Te3)n family, the strong magnetic competition realizes a fragile
ferromagnetic ground state, which whereas easily enters into ferrimagnetic and
the Z_2 antiferromagnetic topological insulator phase with warming to higher
temperature. Interestingly, the system stays in an inversion-symmetry-protected
axion insulator phase in the ferromagnetic ground state as well as in the
external magnetic field driven spin-polarized FM phase and can be converted
into a Weyl semimetal with multiple Weyl nodes in the valence bands with hole
doping, which are manifested by the measured notable intrinsic anomalous Hall
effect. Our work thus provides an intrinsic magnetic topological material which
is highly tunable into versatile topological phases by temperature, magnetic
field, as well as carrier doping.",2111.04973v1
2021/11/15,Thickness dependent dark exciton emission in (PEA)2PbI4 nanoflake and its brightening by in-plane magnetic field,"Halide perovskite materials raised tremendous interest in recent years since
their cheap fabrication, superior performance in both solar cell and light
emitting diode (LED). Due to the existence of layered quantum well structure,
quasi two-dimensional(2D) halide perovskite has more intriguing spin related
physics than its 3D counterpart. For instance, the detection and brightening of
dark exciton (DX) in 2D halide perovskite attracts much attention since these
species can be used in opto-spintronic and quantum computing devices. Here, we
report the gradually brightened emission of the DX at 2.33 eV with the
thickness decreases in (PEA)2PbI4 single crystalline nanoflake, which hitherto
has not been reported. By coupling with in-plane (IP) magnetic field in Voigt
configuration, the DX emission can be sharply enhanced, while for the
out-of-plane (OP) magnetic field in Faraday configuration, the DX emission has
no noticeable change, which can be reconciled with the theory interpretation of
magnetic field dependent wave function mixing between the four exciton states
fi1, fi2, fi3- , fi3+. The emission of DX fi2 at 2.335 eV and the fine
splitting of all the four states are observed in static PL spectroscopy for the
first time. Our work thus clarifies the debating questions regarding to
previous research on DX behavior in 2D halide perovskite material and sheds
light on the road of realizing opto-spintronic or quantum computing devices
with these materials.",2111.07888v2
2023/5/1,Atomically-precise engineering of spin-orbit polarons in a kagome magnetic Weyl semimetal,"Atomically-precise engineering of defects in topological quantum materials,
which is essential for constructing new artificial quantum materials with
exotic properties and appealing for practical quantum applications, remains
challenging due to the hindrances in modifying complex lattice with atomic
precision. Here, we report the atomically-precise engineering of the
vacancy-localized spin-orbital polarons (SOP) in a kagome magnetic Weyl
semimetal Co3Sn2S2, using scanning tunneling microscope. We achieve the
step-by-step repairing of the selected vacancies, which results in the
formation of artificial sulfur vacancy with elaborate geometry. We find that
that the bound states localized around the vacancies experience a
symmetry-dependent energy shift towards Fermi level with increasing vacancy
size. Strikingly, as vacancy size increases, the localized magnetic moments of
SOPs are tunable and ultimately extended to the negative magnetic moments
resulting from spin-orbit coupling in the kagome flat band. These findings
establish a new platform for engineering atomic quantum states in topological
quantum materials, offering potential for kagome-lattice-based spintronics and
quantum technologies.",2305.00824v2
2012/7/13,"Extremely Large Magnetic Entropy Changes, Quantum Phases, Transitions and Diagram in Gd(OH)3 Single Crystal Nanowires - Quasi-1D Large Spin (S = -7/2) Chain Antiferromagnet","Systematically magnetic and magnetothermal measurements at temperatures down
to 2 K and magnetic fields up to 13.5 Tesla for Gd(OH)3 Single Crystal
Nanowires - Quasi-1D Large Spin (S = -7/2) Chain Antiferromagnet have been
conducted. We find that, (1) magnetic field enhances the thermal and local spin
fluctuations which suppress long-range spin ordering (LRO) within the measured
temperature range, and close to 0 K at the quantum critical point (QCP); (2)
possible field-induced exotic local spin-liquid-like, aligned-spin, and
spin-flip exotic paramagnetic phases, and transitions in the low temperature
and high field range have been observed, allowing us to identify a possible
quantum critical point; (3) there is extremely large, fully reversible MCE
(magnetic entropy change (-{\Delta}SM) = 27.8, 66, and 88 J / kg K, adiabatic
temperature change ({\Delta}Tad) = 6.7, 17.6, and 36.4 K at 2.55 K for field
changes of 2, 5, and 11 T, respectively in the continuum of quantum phase
transitions in this system; (4) moreover, careful experiments and analysis may
allow experimental determination and set up a quantum phase diagram of this
system. The magnetic-entropy change monotonically increases with decreasing
temperature, and it exceeds the magnetocaloric effect (MCE) in any other known
low temperature reversible MCE material by at least a factor of 3. The
extremely large magnetic entropy change may be attributed to the large amount
of weakly interacting spins that can be easily aligned at low-lying energy in
the quantum critical regime of our nanosized materials, since there is large
MCE in the local spin-liquid-like (low energy excitation and even gapless
state) range. These indicate that the material is a promising MCE candidate for
low temperature application, and possibly could make ultra-low temperatures
easily achievable for most laboratories and for space application as well.",1207.3239v1
2017/7/28,Origin of magnetic moments and presence of a resonating valence bond state in Ba$_2$YIrO$_6$,"While it was speculated that 5$d^4$ systems would possess non-magnetic
$J$~=~0 ground state due to strong Spin-Orbit Coupling (SOC), all such systems
have invariably shown presence of magnetic moments so far. A puzzling case is
that of Ba$_2$YIrO$_6$, which in spite of having a perfectly cubic structure
with largely separated Ir$^{5+}$ ($d^4$) ions, has consistently shown presence
of weak magnetic moments. Moreover, we clearly show from Muon Spin Relaxation
($\mu$SR) measurements that a change in the magnetic environment of the
implanted muons in Ba$_2$YIrO$_6$ occurs as temperature is lowered below 10~K.
This observation becomes counterintuitive, as the estimated value of SOC
obtained by fitting the RIXS spectrum of Ba$_2$YIrO$_6$ with an atomic $j-j$
model is found to be as high as 0.39~eV, meaning that the system within this
model is neither expected to possess moments nor exhibit temperature dependent
magnetic response. Therefore we argue that the atomic $j-j$ coupling
description is not sufficient to explain the ground state of such systems,
where despite having strong SOC, presence of hopping triggers delocalisation of
holes, resulting in spontaneous generation of magnetic moments. Our theoretical
calculations further indicate that these moments favour formation of
spin-orbital singlets in the case of Ba$_2$YIrO$_6$, which is manifested in
$\mu$SR experiments measured down to 60~mK.",1707.09304v2
2017/11/16,Pure phase BiFeO$_3$ thin films sputtered over Si: A new route towards high magnetization,"We have investigated the structural and magnetic properties of BiFeO$_3$
(BFO) thin films grown over (100)-oriented Si substrates by rf magnetron
sputtering in a new route under O$_2$ free low pressure Ar atmosphere.
Single-phase BFO films were deposited in a heated substrate and post-annealed
in situ. The new routed allows high deposition rate and produce polycrystalline
BFO pure phase, confirmed by high resolution X-ray diffraction. Scanning
electron and atomic force microscopy reveal very low surface roughness and mean
particle size of 33 nm. The BFO phase and composition were confirmed by
transmission electron microscopy and line scanning energy-dispersive X-ray
spectroscopy in transmission electron microscopy mode. The surface chemistry of
the thin film, analyzed by X-ray photoelectron spectroscopy, reveals the
presence of Fe$^{3+}$ and Fe$^{2+}$ in a 2:1 ratio, a strong indication that
the film contains oxygen vacancies. An hysteretic ferromagnetic behavior with
room temperature high saturation magnetization $\sim 165 \times 10^3$ A/m was
measured along the film perpendicular and parallel directions. Such high
magnetization, deriving from this new route, is explained in the scope of
oxygen vacancies, the break of the antiferromagnetic cycloidal order and the
increase of spin canting by change in the surface/volume ratio. Understanding
the magnetic behavior of a multiferroic thin films is a key for the development
of heterogeneous layered structures and multilayered devices and the production
of multiferroic materials over Si substrates opens new possibilities in the
development of materials that can be directly integrated into the existent
semiconductor and spintronic technologies.",1711.05873v3
2020/8/11,Ordered ground states of kagome magnets with generic exchange anisotropy,"There is a growing family of rare-earth kagome materials with dominant
nearest-neighbor interactions and strong spin orbit coupling. The low symmetry
of these materials makes theoretical description complicated, with six distinct
nearest-neighbor coupling parameters allowed. In this Article, we ask what
kinds of classical, ordered, ground states can be expected to occur in these
materials, assuming generic (i.e. non-fine-tuned) sets of exchange parameters.
We use symmetry analysis to show that there are only five distinct classical
ground state phases occurring for generic parameters. The five phases are: (i)
a coplanar, 2-fold degenerate, state with vanishing magnetization (${\sf
A_1}$), (ii) a noncoplanar, 2-fold degenerate, state with magnetization
perpendicular to the kagome plane (${\sf A_2}$), (iii) a coplanar, 6-fold
degenerate, state with magnetization lying within the kagome plane (${\sf
E}$-coplanar), (iv) a noncoplanar, 6-fold degenerate, state with magnetization
lying within a mirror plane of the lattice (${\sf E}$-noncoplanar$_{6}$), (v) a
noncoplanar, 12-fold degenerate, state with magnetization in an arbitrary
direction (${\sf E}$-noncoplanar$_{12}$). All five are translation invariant
(${\bf q}=0$) states. Having found the set of possible ground states, the
ground state phase diagram is obtained by comparing numerically optimized
energies for each possibility as a function of the coupling parameters. The
state ${\sf E}$ noncoplanar$_{12}$ is extremely rare, occupying $<1\%$ of the
full phase diagram, so for practical purposes there are four main ordered
states likely to occur in anisotropic kagome magnets with dominant nearest
neighbor interactions. These results can aid in interpreting recent experiments
on ``tripod kagome'' systems R$_3$A$_2$Sb$_3$O$_{14}$, as well as materials
closer to the isotropic limit such as Cr- and Fe- jarosites.",2008.04677v2
2021/8/26,Magnetoelastic anisotropy in Heusler-type Mn$_{2-δ}$CoGa$_{1+δ}$ films,"Perpendicular magnetization is essential for high-density memory application
using magnetic materials. High-spin polarization of conduction electrons is
also required for realizing large electric signals from spin-dependent
transport phenomena. Heusler alloy is a well-known material class showing the
half-metallic electronic structure. However, its cubic lattice nature favors
in-plane magnetization and thus minimizes the perpendicular magnetic anisotropy
(PMA), in general. This study focuses on an inverse-type Heusler alloy,
Mn$_{2-\delta}$CoGa$_{1+\delta}$ (MCG) with a small off-stoichiometry
($\delta$) , which is expected to be a half-metallic material. We observed
relatively large uniaxial magnetocrystalline anisotropy constant
($K_\mathrm{u}$) of the order of 10$^5$ J/m$^3$ at room temperature in MCG
films with a small tetragonal distortion of a few percent. A positive
correlation was confirmed between the $c/a$ ratio of lattice constants and
$K_\mathrm{u}$. Imaging of magnetic domains using Kerr microscopy clearly
demonstrated a change in the domain patterns along with $K_\mathrm{u}$. X-ray
magnetic circular dichroism (XMCD) was employed using synchrotron radiation
soft x-ray beam to get insight into the origin for PMA. Negligible angular
variation of orbital magnetic moment ($\Delta m_\mathrm{orb}$) evaluated using
the XMCD spectra suggested a minor role of the so-called Bruno's term to
$K_\mathrm{u}$. Our first principles calculation reasonably explained the small
$\Delta m_\mathrm{orb}$ and the positive correlation between the $c/a$ ratio
and $K_\mathrm{u}$. The origin of the magnetocrystalline anisotropy was
discussed based on the second-order perturbation theory in terms of the
spin--orbit coupling, claiming that the mixing of the occupied $\uparrow$- and
the unoccupied $\downarrow$-spin states is responsible for the PMA of the MCG
films.",2108.11547v2
2022/10/9,"Interplay of magnetism and band topology in Eu$_{1-x}$Ca$_x$Mg$_2$Bi$_2$ (x=0, 0.5) from first principles study","Recent discovery of the time reversal symmetry breaking magnetic Weyl
semimetals has created a huge surge of activities in the field of quantum
topological materials. In this work, we have studied systematically the ground
state magnetic order, electronic structure and the interplay between the
magnetic order and band topology in one such materials, EuMg$_2$Bi$_2$ (EMB)
and its Ca doped variant using first principles method within the framework of
density functional theory (DFT). The detailed investigation unravels the
existence of different topological phases in this single material which can be
tuned by an external probe such as magnetic field or chemical substitution. Our
DFT calculations including Coulomb correlation (U) and spin-orbit (SO)
interaction within GGA+U+SO approximation confirms that the magnetic ground
state of EMB is A-type Antiferromagnetic (A-AFM) with Eu magnetic moments
aligned along the crystallographic $a$ or $b$ direction. Although the ground
state of EMB is A-AFM, the Ferromagnetic (FM) state lies very close in energy.
We observe a single pair of Weyl points connecting valence and conduction band
very close to the Fermi level (FL) along $\Gamma$-A direction in the FM state
of EuMg$_2$Bi$_2$ with Eu moments aligned along crystallographic $c$ direction.
On doping 50\% Ca at Eu sites, we observe single pair of Weyl points moving
closer to the FL which is highly desirable for application purposes. Further we
observe that the separation between the Weyl points in the pair decreases in
doped compound compared to that in the parent compound which has direct
consequence on anomalous Hall conductivity (AHC). Our first principles
calculation of AHC shows high peak values exactly at these Weyl points and the
peak height decreases when we dope the system with Ca. Therefore, Ca doping can
be a good external handle to tune AHC in this system.",2210.04250v1
2022/10/26,Phase stability of Fe from first-principles: atomistic spin dynamics coupled with ab initio molecular dynamics simulations and thermodynamic integration,"The calculation of free energies from first principles in materials is a
formidable task which enables the prediction of phase stability with high
accuracy; these calculations are complicated in magnetic materials by the
interplay of electronic, magnetic, and vibrational degrees of freedom. In this
work, we show the feasibility and accuracy of the calculation of phase
stability in magnetic systems with ab initio methods and thermodynamic
integration by sampling the magnetic and vibrational phase space with coupled
atomistic spin dynamics-ab initio molecular dynamics (ASD-AIMD) simulations
[Stockem et al., PRL 121, 125902 (2018)], where energies and interatomic forces
are calculated with density functional theory (DFT). We employ the method to
calculate the phase stability of Fe at ambient pressure from 800 K up to 1800
K. The Gibbs free energy difference between fcc and bcc Fe at zero pressure as
a function of temperature is calculated carrying out thermodynamic integration
over temperature on the energies at the DFT level from ASD-AIMD, using a
reference free energy difference calculated in the paramagnetic state at
temperatures much higher than the magnetic transition temperatures with
thermodynamic integration over stress-strain variables with disordered local
moment (DLM)-AIMD simulations. We show the importance of the magnetic ordering
temperature of bcc Fe on the $\alpha$ to $\gamma$ structural transition
temperature, whereas the $\gamma$ to $\delta$ transition is well reproduced
independently of the exchange interactions. The Gibbs free energy difference
between the two structures is within 5 meV/atom from the CALPHAD estimate, and
both transition temperatures are reproduced within 150 K. The present work
paves the way to free energy calculations in magnetic materials from first
principles with accuracy in the order of 1 meV/atom.",2210.14718v2
2023/1/22,Stability of the In-Plane Room Temperature van der Waals Ferromagnet Chromium Ditelluride and Its Conversion to Chromium-Interleaved CrTe$_2$ Compounds,"Van der Waals magnetic materials are building blocks for novel kinds of
spintronic devices and playgrounds for exploring collective magnetic phenomena
down to the two-dimensional limit. Chromium-tellurium compounds are relevant in
this perspective. In particular, the 1$T$ phase of CrTe$_2$ has been argued to
have a Curie temperature above 300~K, a rare and desirable property in the
class of lamellar materials, making it a candidate for practical applications.
However, recent literature reveals a strong variability in the reported
properties, including magnetic ones. Using electron microscopy, diffraction and
spectroscopy techniques, together with local and macroscopic magnetometry
approaches, our work sheds new light on the structural, chemical and magnetic
properties of bulk 1$T$-CrTe$_2$ exfoliated in the form of flakes having a
thickness ranging from few to several tens of nanometers. We unambiguously
establish that 1$T$-CrTe$_2$ flakes are ferromagnetic above room temperature,
have an in-plane easy axis of magnetization, low coercivity, and we confirm
that their Raman spectroscopy signatures are two modes, $E_{2\text{g}}$
(103.5~cm$^{-1}$) and $A_{1\text{g}}$ (136.5~cm$^{-1}$). We also prove that
thermal annealing causes a phase transformation to monoclinic Cr$_5$Te$_8$ and,
to a lesser extent, to trigonal Cr$_5$Te$_8$. In sharp contrast with
1$T$-CrTe$_2$, none of these compounds have a Curie temperature above room
temperature, and they both have perpendicular magnetic anisotropy. Our findings
reconcile the apparently conflicting reports in the literature and open
opportunities for phase-engineered magnetic properties.",2301.09127v2
2023/1/31,Anisotropic Electron-Hole Excitation and Large Linear Dichroism in Two-Dimensional Ferromagnet CrSBr with In-Plane Magnetization,"The observation of magnetic ordering in atomically thin CrI$_3$ and
Cr$_2$Ge$_2$Te$_6$ monolayers has aroused intense interest in condensed matter
physics and material science. Studies of van de Waals two-dimensional (2D)
magnetic materials are of both fundamental importance and application interest.
In particular, exciton-enhanced magneto-optical properties revealed in CrI$_3$
and CrBr$_3$ monolayers have expanded the understanding of exciton physics in
2D materials. Unlike CrI$_3$ and CrBr$_3$ with out-of-plane magnetization,
CrSBr has an in-plane magnetic moment, therefore, providing a good opportunity
to study the magnetic linear dichroism and high-order magneto-optical effects.
Here, based on the many-body perturbation method within density-functional
theory, we have studied quasiparticle electronic structure, exciton, and
optical properties in CrSBr monolayer. Strongly bounded exciton has been
identified with the first bright exciton located at 1.35 eV, in good agreement
with an experiment of photoluminescence (Nat. Mater. \textbf{20}, 1657 (2021)).
Strong contrast in the optical absorption is found between the electric fields
lying along the in-plane two orthogonal directions. In accordance with a
typical and realistic experimental setup, we show that the rotation angle of
linear polarized light, either reflected or transmitted, could be comparable
with those revealed in black phosphorene. Such large linear dichroism arises
mainly from anisotropic in-plane crystal structure. The magnetic contribution
from the off-diagonal component of dielectric function to the linear dichroism
in CrSBr is negligible. Our findings not only have revealed excitonic effect on
the optical and magneto-optical properties in 2D ferromagnet CrSBr, but also
have shown its potential applications in 2D optics and optoelectronics.",2301.13342v2
2023/9/7,Charge transfer and asymmetric coupling of MoSe$_2$ valleys to the magnetic order of CrSBr,"Van der Waals (vdW) heterostructures composed of two-dimensional (2D)
transition metal dichalcogenides (TMD) and vdW magnetic materials offer an
intriguing platform to functionalize valley and excitonic properties in
non-magnetic TMDs. Here, we report magneto-photoluminescence (PL)
investigations of monolayer (ML) MoSe$_2$ on the layered A-type
antiferromagnetic (AFM) semiconductor CrSBr under different magnetic field
orientations. Our results reveal a clear influence of the CrSBr magnetic order
on the optical properties of MoSe$_2$, such as an anomalous linear-polarization
dependence, changes of the exciton/trion energies, a magnetic-field dependence
of the PL intensities, and a valley $g$-factor with signatures of an asymmetric
magnetic proximity interaction. Furthermore, first principles calculations
suggest that MoSe$_2$/CrSBr forms a broken-gap (type-III) band alignment,
facilitating charge transfer processes. The work establishes that
antiferromagnetic-nonmagnetic interfaces can be used to control the valley and
excitonic properties of TMDs, relevant for the development of opto-spintronics
devices.",2309.03766v1
2014/5/22,Dirac materials,"A wide range of materials, like d-wave superconductors, graphene, and
topological insulators, share a fundamental similarity: their low-energy
fermionic excitations behave as massless Dirac particles rather than fermions
obeying the usual Schrodinger Hamiltonian. This emergent behavior of Dirac
fermions in condensed matter systems defines the unifying framework for a class
of materials we call ""Dirac materials''. In order to establish this class of
materials, we illustrate how Dirac fermions emerge in multiple entirely
different condensed matter systems and we discuss how Dirac fermions have been
identified experimentally using electron spectroscopy techniques
(angle-resolved photoemission spectroscopy and scanning tunneling
spectroscopy). As a consequence of their common low-energy excitations, this
diverse set of materials shares a significant number of universal properties in
the low-energy (infrared) limit. We review these common properties including
nodal points in the excitation spectrum, density of states, specific heat,
transport, thermodynamic properties, impurity resonances, and magnetic field
responses, as well as discuss many-body interaction effects. We further review
how the emergence of Dirac excitations is controlled by specific symmetries of
the material, such as time-reversal, gauge, and spin-orbit symmetries, and how
by breaking these symmetries a finite Dirac mass is generated. We give examples
of how the interaction of Dirac fermions with their distinct real material
background leads to rich novel physics with common fingerprints such as the
suppression of back scattering and impurity-induced resonant states.",1405.5774v1
2018/5/18,Machine learning with force-field inspired descriptors for materials: fast screening and mapping energy landscape,"We present a complete set of chemo-structural descriptors to significantly
extend the applicability of machine-learning (ML) in material screening and
mapping energy landscape for multicomponent systems. These new descriptors
allow differentiating between structural prototypes, which is not possible
using the commonly used chemical-only descriptors. Specifically, we demonstrate
that the combination of pairwise radial, nearest neighbor, bond-angle,
dihedral-angle and core-charge distributions plays an important role in
predicting formation energies, bandgaps, static refractive indices, magnetic
properties, and modulus of elasticity for three-dimensional (3D) materials as
well as exfoliation energies of two-dimensional (2D) layered materials. The
training data consists of 24549 bulk and 616 monolayer materials taken from
JARVIS-DFT database. We obtained very accurate ML models using gradient
boosting algorithm. Then we use the trained models to discover exfoliable
2D-layered materials satisfying specific property requirements. Additionally,
we integrate our formation energy ML model with a genetic algorithm for
structure search to verify if the ML model reproduces the DFT convex hull. This
verification establishes a more stringent evaluation metric for the ML model
than what commonly used in data sciences. Our learnt model is publicly
available on the JARVIS-ML website (https://www.ctcms.nist.gov/jarvisml )
property predictions of generalized materials.",1805.07325v2
2018/11/20,"Machine learning, phase stability, and disorder with the Automatic Flow Framework for Materials Discovery","Traditional materials discovery approaches - relying primarily on laborious
experiments - have controlled the pace of technology. Instead, computational
approaches offer an accelerated path: high-throughput exploration and
characterization of virtual structures. These ventures, performed by automated
ab-initio frameworks, have rapidly expanded the volume of
programmatically-accessible data, cultivating opportunities for data-driven
approaches. Herein, a collection of robust characterization methods are
presented, implemented within the Automatic Flow Framework for Materials
Discovery (AFLOW), that leverages materials data for the prediction of phase
diagrams and properties of disordered materials. These methods directly address
the issue of materials synthesizability, bridging the gap between simulation
and experiment. Powering these predictions is the AFLOW.org repository for
inorganic crystals, the largest and most comprehensive database of its kind,
containing more than 2 million compounds with about 100 different properties
computed for each. As calculated with standardized parameter sets, the wealth
of data also presents a favorable learning environment. Machine learning
algorithms are employed for property prediction, descriptor development, design
rule discovery, and the identification of candidate functional materials. When
combined with physical models and intelligently formulated descriptors, the
data becomes a powerful tool, facilitating the discovery of new materials for
applications ranging from high-temperature superconductors to thermoelectrics.
These methods have been validated by the synthesis of two new permanent magnets
introduced herein - the first discovered by computational approaches.",1811.08464v1
2023/5/4,Magneto-active composites with locally tailored stiffness produced by laser powder bed fusion,"Additive manufacturing technologies enable the production of complex and
bioinspired shapes using magneto-responsive materials, which find diverse
applications in soft robotics. Particularly, the development of composites with
controlled gradients in mechanical properties offers new prospects for
advancements in magneto-active materials. However, achieving such composites
with gradients typically involves complex multi-material printing procedures.
In this study, a single-step laser powder bed fusion (LPBF) process is proposed
that enables precise local adjustments of the mechanical stiffness within
magneto-active composites. By utilizing distinct laser parameters in specific
regions of a composite containing thermoplastic polyurethane and atomized
magnetic powder derived from hard magnetic Nd-Fe-B, the stiffness of the
composite can be modified within the range of 2 to 22 MPa. Various
magneto-responsive actuators with locally tailored stiffness are fabricated and
their magnetic performance is investigated. The enhanced response exhibited by
actuators with locally adjusted mechanical properties in comparison to their
homogeneous counterparts with identical geometries is shown. As a demonstration
of a biomedical application, a magnetically responsive stent with localized
adjustment is presented with the ability to meet specific requirements in terms
of geometry and local stiffness based on an individual's anatomy and disease
condition. The proposed method presents an approach for creating functionally
graded materials using LPBF, not only for magneto-active materials but also for
several other structural and functional materials.",2305.02643v2
2006/6/16,Multiferroic tunnel junctions,"Multiferroics are singular materials that can display simultaneously electric
and magnetic orders. Some of them can be ferroelectric and ferromagnetic and,
for example, provide the unique opportunity of encoding information
independently in electric polarization and magnetization to obtain four
different logic states. However, schemes allowing a simple electrical readout
of these different states have not been demonstrated so far. In this article,
we show that this can be achieved if a multiferroic material is used as the
tunnel barrier in a magnetic tunnel junction. We demonstrate that thin films of
ferromagnetic-ferroelectric La0.1Bi0.9MnO3 (LBMO) retain both ferroic
properties down to a thickness of only 2 nm. We have used such films as
spin-filtering tunnel barriers the magnetization and electric polarization of
which can be switched independently. In that case, the tunnel current across
the structure is controlled by both the magnetic and ferroelectric
configuration of the barrier, which gives rise to four distinct resistance
states. This can be explained by the combination of spin filtering by the
ferromagnetic LBMO barrier and the partial charge screening of electrical
charges at the barrier/electrode interfaces due to ferroelectricity. We
anticipate our results to be a starting point for more studies on the interplay
between ferroelectricity and spin-dependent tunneling, and for the use of
nanometric multiferroic elements in prototype devices. On a wider perspective,
they may open the way towards novel reconfigurable logic spintronics
architectures and to electrically controlled readout in quantum computing
schemes using the spin-filter effect.",0606444v1
2009/6/17,The Kondo effect in ferromagnetic atomic contacts,"Iron, cobalt and nickel are archetypal ferromagnetic metals. In bulk,
electronic conduction in these materials takes place mainly through the $s$ and
$p$ electrons, whereas the magnetic moments are mostly in the narrow
$d$-electron bands, where they tend to align. This general picture may change
at the nanoscale because electrons at the surfaces of materials experience
interactions that differ from those in the bulk. Here we show direct evidence
for such changes: electronic transport in atomic-scale contacts of pure
ferromagnets (iron, cobalt and nickel), despite their strong bulk
ferromagnetism, unexpectedly reveal Kondo physics, that is, the screening of
local magnetic moments by the conduction electrons below a characteristic
temperature. The Kondo effect creates a sharp resonance at the Fermi energy,
affecting the electrical properties of the system;this appears as a Fano-Kondo
resonance in the conductance characteristics as observed in other artificial
nanostructures. The study of hundreds of contacts shows material-dependent
lognormal distributions of the resonance width that arise naturally from Kondo
theory. These resonances broaden and disappear with increasing temperature,
also as in standard Kondo systems. Our observations, supported by calculations,
imply that coordination changes can significantly modify magnetism at the
nanoscale. Therefore, in addition to standard micromagnetic physics, strong
electronic correlations along with atomic-scale geometry need to be considered
when investigating the magnetic properties of magnetic nanostructures.",0906.3135v1
2010/3/4,Spin glass like behavior in the novel layered material Na_2IrO_3,"We have synthesized the novel material Na_2IrO_3 and studied its structure,
transport, magnetic, and thermal properties using powder x-ray diffraction
(PXRD), electrical resistivity, isothermal magnetization M versus magnetic
field H, static \chi and dynamic \chi_ac magnetic susceptibility versus
temperature T, and heat capacity C versus T measurements. Na_2IrO_3
crystallizes in the monoclinic C2/c (No. 15) structure which is made up of Na
and NaIr_2O_6 layers alternately stacked along the c axis. From a Rietveld
refinement of the PXRD pattern we identify atomic disorder arising from a
mixing of Ir and Na sites within the NaIr_2O_6 layers. The \chi data in H = 1 T
shows Curie-Weiss behavior at high T > 100 K with an effective moment \mu_eff =
1.82(1) \mu_B indicating an effective spin S_eff = 1/2 on the Ir^{4+} moments.
A Weiss temperature \theta = - 62(1) K indicates substantial antiferromagnetic
interactions between these S_eff = 1/2, Ir^{4+} moments. The \chi data in low
field show a sharp cusp at T_g = 5.5 K and there is a bifurcation between
zero-field-cooled (ZFC) and field-cooled (FC) data below this T. The \chi_ac
data also show a sharp cusp at T_g = 5.5 K at a frequency f = 1 Hz which moves
to higher temperatures with increasing f. We did not observe any anomaly at T_g
in our C measurements and only a broad shoulder was observed at a much higher T
= 12 K. Our results indicate that in Na_2IrO_3, a spin-glass like state occurs
below the freezing temperature T_g = 5.5 K and this freezing most likely arises
either from structural disorder or geometrical magnetic frustration.",1003.0973v2
2011/4/4,Interplay between magnetism and superconductivity in iron-chalcogenide superconductors: crystal growth and characterizations,"In this review, we present a summary of the results on single crystal growth
of two types of iron-chalcogenide superconductors, Fe(1+y)Te(1-x)Se(x) (11),
and A(x)Fe(2-y)Se(2) (A= K, Rb, Cs, Tl, Tl/K, Tl/Rb), using Bridgman,
zone-melting, vapor self-transport, and flux techniques. The superconducting
and magnetic properties (the latter gained mainly from neutron scattering
measurements) of these materials are reviewed to demonstrate the connection
between magnetism and superconductivity. It will be shown that for the 11
system, while static magnetic order around the reciprocal lattice position
(0.5, 0) competes with superconductivity, spin excitations centered around
(0.5, 0.5) are closely coupled to the materials' superconductivity; this is
made evident by the strong correlation between the spectral weight around (0.5,
0.5) and the superconducting volume fraction. The observation of a spin
resonance below the superconducting temperature, Tc, and the magnetic-field
dependence of the resonance, emphasize the important role spin excitations play
in the superconductivity. Generally, these results illustrate the similarities
between the iron-based and cuprate superconductors. In A(x)Fe(2-y)Se(2),
superconductivity with Tc ~ 30 K borders an antiferromagnetic insulating phase;
this is closer to the behavior observed in the cuprates but differs from that
in other iron-based superconductors.",1104.0695v2
2011/8/2,Material laws and related uncommon phenomena in the electromagnetic response of type-II superconductors in longitudinal geometry,"Relying on our theoretical approach for the superconducting critical state
problem in 3D magnetic field configurations, we present an exhaustive analysis
of the electrodynamic response for the so-called longitudinal transport problem
in the slab geometry. A wide set of experimental conditions have been
considered, including modulation of the applied magnetic field either
perpendicular or parallel (longitudinal) to the transport current density. The
main objective of our work was to characterize the role of the macroscopic
material law that should properly account for the underlying mechanisms of flux
cutting and depinning. The intriguing occurrence of negative current patterns
and the enhancement of the transport current flow along the center of the
superconducting sample are reproduced as a straightforward consequence of the
magnetically induced internal anisotropy. Moreover, we show that related to a
maximal projection of the current density vector onto the local magnetic field,
a maximal transport current density occurs somewhere within the sample. The
elusive measurement of the flux cutting threshold (critical value of such
parallel component $J_{c ||}$) is suggested on the basis of local measurements
of the transport current density. Finally, we show that a high correlation
exists between the evolution of the transport current density and the
appearance of paramagnetic peak structures in terms of the applied longitudinal
magnetic field.",1108.0658v1
2012/7/31,Spin excitations in a single La$_2$CuO$_4$ layer,"The dynamics of S=1/2 quantum spins on a 2D square lattice lie at the heart
of the mystery of the cuprates
\cite{Hayden2004,Vignolle2007,Li2010,LeTacon2011,Coldea2001,Headings2010,Braicovich2010}.
In bulk cuprates such as \LCO{}, the presence of a weak interlayer coupling
stabilizes 3D N\'{e}el order up to high temperatures. In a truly 2D system
however, thermal spin fluctuations melt long range order at any finite
temperature \cite{Mermin1966}. Further, quantum spin fluctuations transfer
magnetic spectral weight out of a well-defined magnon excitation into a
magnetic continuum, the nature of which remains controversial
\cite{Sandvik2001,Ho2001,Christensen2007,Headings2010}. Here, we measure the
spin response of \emph{isolated one-unit-cell thick layers} of \LCO{}. We show
that coherent magnons persist even in a single layer of \LCO{} despite the loss
of magnetic order, with no evidence for resonating valence bond (RVB)-like spin
correlations \cite{Anderson1987,Hsu1990,Christensen2007}. Thus these
excitations are well described by linear spin wave theory (LSWT). We also
observe a high-energy magnetic continuum in the isotropic magnetic response.
This high-energy continuum is not well described by 2 magnon LSWT, or indeed
any existing theories.",1208.0018v1
2012/12/3,"A new look at the origin of the 6.67\,hr period X-ray pulsar 1E~161348-5055","The point X-ray source 1E 161348-5055 is observed to display pulsations with
the period 6.67 hr and |\dot{P}| \leq 1.6 x 10^{-9} s/s. It is associated with
the supernova remnant RCW\,103 and is widely believed to be a ~2000 yr old
neutron star. Observations give no evidence for the star to be a member of a
binary system. Nevertheless, it resembles an accretion-powered pulsar with the
magnetospheric radius ~3000 km and the mass-accretion rate ~ 10^{14} g/s. This
situation could be described in terms of accretion from a (residual) fossil
disk established from the material falling back towards the star after its
birth. However, current fall-back accretion scenarios encounter major
difficulties explaining an extremely long spin period of the young neutron
star. We show that the problems can be avoided if the accreting material is
magnetized. The star in this case is surrounded by a fossil magnetic slab in
which the material is confined by the magnetic field of the accretion flow
itself. We find that the surface magnetic field of the neutron star within this
scenario is ~10^{12} G and that a presence of > 10^{-7} M_\sun magnetic slab
would be sufficient to explain the origin and current state of the pulsar.",1212.0375v3
2013/3/21,Persistence of magnetic excitations in La2-xSrxCuO4 from the undoped insulator to the heavily overdoped non-superconducting metal,"One of the most intensely studied scenarios of high-temperature
superconductivity (HTS) postulates pairing by exchange of magnetic excitations
[1]. Indeed, such excitations have been observed up to around optimal doping in
the cuprates [2-7]. In the heavily overdoped regime neutron scattering
measurements indicate that magnetic excitations have effectively disappeared
[8-10], and this was argued to cause the demise of HTS with overdoping [1, 8,
10]. Here we use resonant inelastic x-ray scattering (RIXS), which is sensitive
to complementary parts of reciprocal space, to measure the evolution of the
magnetic excitations in La2-xSrxCuO4 across the entire phase diagram, from a
strongly correlated insulator (x = 0) to a non-superconducting metal (x =
0.40). For x = 0, well-defined magnon excitations are observed [11]. These
magnons broaden with doping, but they persist with a similar dispersion and
comparable intensity all the way to the non-superconducting, heavily overdoped
metallic phase. The destruction of HTS with overdoping is therefore caused
neither by the general disappearance nor by the overall softening of magnetic
excitations; other factor(s), such as the redistribution of spectral weight,
must be considered.",1303.5359v3
2013/8/9,Challenges and opportunities for applications of unconventional superconductors,"Since the discovery of high-$T_c$ cuprates the quest for new superconductors
has shifted toward more anisotropic, strongly correlated materials with lower
carrier densities and competing magnetic and charge density wave orders. While
these materials features enhance superconducting correlations, they also result
in serious problems for applications at liquid nitrogen (and higher)
temperatures and strong magnetic fields, so that such conventional
characteristics as the critical temperature $T_c$ and the upper critical field
$H_{c2}$ are no longer the main parameters of merit. This happens because of
strong fluctuations of the order parameter, thermally-activated hopping of
pinned vortices and electromagnetic granularity, as has been established after
extensive investigations of cuprates and Fe-based superconductors. In this
paper I give an overview of these mechanisms crucial for power and magnet
applications and discuss the materials restrictions which have to be satisfied
in order to make superconductors useful at high temperatures and magnetic
fields. These restrictions become more and more essential at higher
temperatures and magnetic fields, particularly for the yet-to-be-discovered
superconductors operating at room temperatures. In this case the performance of
superconductors will be limited by destructive fluctuations of the order
parameter so higher superfluid density and weaker electronic anisotropy which
reduce these fluctuations can become far more important than higher $T_c$.",1308.2016v1
2014/6/25,"Surface acoustic wave driven ferromagnetic resonance in (Ga,Mn)(As,P) epilayers","Interdigitated transducers were used to generate and detect surface acoustic
waves on a thin layer of (Ga,Mn)(As,P). The out-of-plane uniaxial magnetic
anisotropy of this dilute magnetic semiconductor is very sensitive to the
strain of the layer, making it an ideal test material for the dynamic control
of magnetization via magneto-striction. The time-domain measurement of the
amplitude and phase of the transmitted SAW during magnetic field sweeps
indicated a clear resonant behavior at a field close to the one calculated to
give a precession frequency equal to the SAW frequency. A resonance was
observed from 5K to 85K, just below the Curie temperature of the layer. A full
analytical treatment of the coupled magnetization/acoustic dynamics showed that
the magneto-strictive coupling modifies the elastic constants of the material
and accordingly the wave-vector solution to the elastic wave equation. The
shape and position of the resonance were well reproduced by the calculations,
in particular the fact that velocity (phase) variations resonated at lower
fields than the acoustic attenuation variations.",1406.6483v1
2015/5/11,Influence of Thermal Cycling on Giant Magnetocaloric Effect of Gd5Si1.3Ge2.7 Thin Film,"In the lifetime of a magnetic refrigerator the materials are subjected to
millions of thermal magnetic cycles, so it is of the utmost importance to
predict the behavior of such materials when subjected to related work
conditions. Thus, in this work we investigated the influence of thermal cycling
in the microstructure, magnetic phase transition and magnetic entropy change of
a Gd5Si1.3Ge2.7 thin film up to 1000 cycles. In a first stage, till 450 cycles,
the hysteresis area of the magnetization curves as a function of temperature
was found to decrease 16% with thermal cycling, due to an arresting of the
O(II) phase caused by internal strain. Nonetheless, after 1000 cycles there is
a clear loss of the magneto-structural transition. For all thermal cycles the
O(I) phase remains unchanged. Therefore, prolonged thermal cycling leads to a
strong reduction of the O(II) phase, attributed to an internal pressure
build-up, caused by the large number of expansion/compression cycles that the
O(II) phase undergoes across the magnetostructural transition.",1505.02575v1
2015/5/31,Residual stress induced stabilization of martensite phase and its effect on the magneto-structural transition in Mn rich Ni-Mn-In/Ga magnetic shape memory alloys,"The irreversibility of the martensite transition in magnetic shape memory
alloys (MSMAs) with respect to external magnetic field is one of the biggest
challenges that limits their application as giant caloric materials. This
transition is a magneto-structural transition that is accompanied with a steep
drop in magnetization (i.e., 'delta M') around the martensite start temperature
(Ms) due to the lower magnetization of the martensite phase. In this
communication, we show that 'delta M' around Ms in Mn rich Ni-Mn based MSMAs
gets suppressed by two orders of magnitude in crushed powders due to the
stabilization of the martensite phase at temperatures well above the Ms and the
austenite finish (Af) temperatures due to residual stresses. Analysis of the
intensities and the FWHM of the x-ray powder diffraction patterns reveals
stabilized martensite phase fractions as 97, 75 and 90% with corresponding
residual microstrains as 5.4, 5.6 and 3% in crushed powders of the three
different Mn rich Ni-Mn alloys, namely, Mn1.8Ni1.8In0.4, Mn1.75Ni1.25Ga and
Mn1.9Ni1.1Ga, respectively. Even after annealing at 773 K, the residual stress
stabilised martensite phase does not fully revert to the equilibrium cubic
austenite phase as the magneto-structural transition is only partially restored
with reduced value of 'delta M'. Our results have very significant bearing on
application of such alloys as inverse magnetocaloric and barocaloric materials.",1506.00266v1
2015/6/1,Development of Low Temperature and High Magnetic Field X-Ray Diffraction Facility,"The current progress of materials science regarding multifunctional materials
(MFM) has put forward the challenges to understand the microscopic origin of
their properties. Most of such MFMs have magneto-elastic correlations. To
investigate the underlying mechanism, it is therefore essential to investigate
the structural properties in the presence of magnetic field. Keeping this in
view low temperature and high magnetic field (LTHM) powder x-ray diffraction
(XRD), a unique state-of-art facility in India has been developed at CSR
Indore. This setup works on symmetric Bragg Brentano geometry using a parallel
incident x-ray beam from a rotating anode source working at 17 kW. Using this
one can do structural studies at non-ambient conditions i.e. at low-
temperatures (2-300 K) and high magnetic field (+8 to -8 T). The available
scattering angle ranges from 5{\deg} to 115{\deg} 2{\theta} with a resolution
better than 0.1{\deg}. The proper functioning of the setup has been checked
using Si sample. The effect of magnetic field on the structural properties has
been demonstrated on Pr0.5Sr0.5MnO3 sample. Clear effect of field induced phase
transition has been observed. Moreover, the effect of zero field cooled and
field cooled conditions is also observed.",1506.00365v1
2015/6/12,Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures,"Spin-transfer-torque magnetic random access memory (STT-MRAM) attracts
extensive attentions due to its non-volatility, high density and low power
consumption. The core device in STT-MRAM is CoFeB/MgO-based magnetic tunnel
junction (MTJ), which possesses a high tunnel magnetoresistance ratio as well
as a large value of perpendicular magnetic anisotropy (PMA). It has been
experimentally proven that a capping layer coating on CoFeB layer is essential
to obtain a strong PMA. However, the physical mechanism of such effect remains
unclear. In this paper, we investigate the origin of the PMA in
MgO/CoFe/metallic capping layer structures by using a first-principles
computation scheme. The trend of PMA variation with different capping materials
agrees well with experimental results. We find that interfacial PMA in the
three-layer structures comes from both the MgO/CoFe and CoFe/capping layer
interfaces, which can be analyzed separately. Furthermore, the PMAs in the
CoFe/capping layer interfaces are analyzed through resolving the magnetic
anisotropy energy by layer and orbital. The variation of PMA with different
capping materials is attributed to the different hybridizations of both d and p
orbitals via spin-orbital coupling. This work can significantly benefit the
research and development of nanoscale STT-MRAM.",1506.04078v4
2015/8/17,Magnetic Ordering Induced Giant Optical Property Change in Tetragonal BiFeO3,"Magnetic ordering, as one of the most important characteristics in magnetic
materials, could have significant influence on the band structure, spin
dependent transport, and other important properties of materials. Its
measurement, especially for the case of antiferromagnetic ordering, however, is
generally difficult to be achieved. Here we demonstrate the feasibility of
magnetic ordering detection using a noncontact and nondestructive optical
method. Taking the compressive strained tetragonal BiFeO3 (BFO) as an example
and combining density functional theory calculations with the minimal one-band
tight-binding models, we find that when BFO changes from C1-type
antiferromagnetic (AFM) phase to G-type AFM phase, the top of valance band
shifts from the Z point to {\Gamma} point, which makes the original direct band
gap become indirect. This can be explained by the two-center Slater-Koster
parameters using the Harrison approach. The impact of magnetic ordering on
energy band dispersion dramatically changes the optical properties of
tetragonal BFO. For the linear ones, the energy shift of the optical band gap
could be as large as 0.4 eV. As for the nonlinear ones, the change is even
larger. The second-harmonic generation coefficient d33 of G-AFM becomes more
than 13 times smaller than that of C1-type AFM case. Finally, we propose a
practical way to distin-guish the C1- and G-type AFM of BFO using the optical
method, which might be of great importance in next-generation information
storage technologies and widens the potential application of BFO to optical
switch.",1508.03919v1
2015/11/4,Minimum light transmission in graphene in the presence of a magnetic field,"We show that, on general theoretical grounds, transmission of light in
graphene always presents a non-vanishing minimum value independently of any
material and physical condition, the transmission coefficient being higher in
the presence of a substrate, and getting increasing when QED corrections higher
than alpha come into play. Explicit numerical calculations for typical cases
are carried out when an external magnetic field is applied to the sample,
showing that, in epitaxial graphene, a threshold effect exists leading to a non
trivial minimum transmission, for a non vanishing light frequency, only for
field values larger than a critical one, both in the large and in the
intermediate chemical potential regime. Such a threshold effect manifests even
in the maximum Faraday rotation polarization of light, which is substantially
controlled by the applied magnetic field. Instead, more transmission minima in
suspended graphene enters in the considered light frequency region for
increasing magnetic field, displaying an effective shift of frequency bands
where the sample gets more or less absorptive with a suitable tuning of the
external field. Two transition regions in different magnetic field ranges are
found, where the shift effect towards higher frequency values occurs both in
the transmission coefficient and in the Faraday rotation angle. Potential
technological application of the results presented are envisaged.",1511.01314v1
2015/12/8,A Two-Temperature Model of Magnetized Protostellar Outflows,"We explore kinematics and morphologies of molecular outflows driven by young
protostars using magnetohydrodynamic simulations in the context of the unified
wind model of Shang et al. The model explains the observed high-velocity jet
and low-velocity shell features. In this work we investigate how these
characteristics are affected by the underlying temperature and magnetic field
strength. We study the problem of a warm wind running into a cold ambient
toroid by using a tracer field that keeps track of the wind material. While an
isothermal equation of state is adopted, the effective temperature is
determined locally based on the wind mass fraction. In the unified wind model,
the density of the wind is cylindrically stratified and highly concentrated
toward the outflow axis. Our simulations show that for a sufficiently
magnetized wind, the jet identity can be well maintained even at high
temperatures. However, for a high temperature wind with low magnetization, the
thermal pressure of the wind gas can drive material away from the axis, making
the jet less collimated as it propagates. We also study the role of the
poloidal magnetic field of the toroid. It is shown that the wind-ambient
interface becomes more resistant to corrugation when the poloidal field is
present, and the poloidal field that bunches up within the toroid prevents the
swept-up material from being compressed into a thin layer. This suggests that
the ambient poloidal field may play a role in producing a smoother and thicker
swept-up shell structure in the molecular outflow.",1512.02609v1
2016/3/3,"Room-temperature magnetic topological semimetal state in half-metallic Heusler Co$_2$TiX (X=Si, Ge, or Sn)","Topological semimetals (TSMs) including Weyl semimetals and nodal-line
semimetals are expected to open the next frontier of condensed matter and
materials science. Although the first inversion breaking Weyl semimetal was
recently discovered in TaAs, its magnetic counterparts, i.e., the time-reversal
breaking Weyl and nodal line semimetals, remain elusive. They are predicted to
exhibit exotic properties distinct from the inversion breaking TSMs including
TaAs. In this paper, we identify the magnetic topological semimetal state in
the ferromagnetic half-metal compounds Co$_2$TiX (X=Si, Ge, or Sn) with Curie
temperatures higher than 350 K. Our first-principles band structure
calculations show that, in the absence of spin-orbit coupling, Co$_2$TiX
features three topological nodal lines. The inclusion of spin-orbit coupling
gives rise to Weyl nodes, whose momentum space locations can be controlled as a
function of the magnetization direction. Our results not only open the door for
the experimental realization of topological semimetal states in magnetic
materials at room temperatures, but also suggest potential applications such as
unusual anomalous Hall effects in engineered monolayers of the Co$_2$TiX
compounds at high temperatures.",1603.01255v3
2016/10/17,"Structural, magnetic, electric, dielectric, and thermodynamic properties of multiferroic GeV4S8","The lacunar spinel GeV4S8 undergoes orbital and ferroelectric ordering at the
Jahn-Teller transition around 30 K and exhibits antiferromagnetic order below
about 14 K. In addition to this orbitally driven ferroelectricity, lacunar
spinels are an interesting material class, as the vanadium ions form V4
clusters representing stable molecular entities with a common electron
distribution and a well-defined level scheme of molecular states resulting in a
unique spin state per V4 molecule. Here we report detailed x-ray, magnetic
susceptibility, electrical resistivity, heat capacity, thermal expansion, and
dielectric results to characterize the structural, electric, dielectric,
magnetic, and thermodynamic properties of this interesting material, which also
exhibits strong electronic correlations. From the magnetic susceptibility, we
determine a negative Curie-Weiss temperature, indicative for antiferromagnetic
exchange and a paramagnetic moment close to a spin S = 1 of the V4 molecular
clusters. The low-temperature heat capacity provides experimental evidence for
gapped magnon excitations. From the entropy release, we conclude about strong
correlations between magnetic order and lattice distortions. In addition, the
observed anomalies at the phase transitions also indicate strong coupling
between structural and electronic degrees of freedom. Utilizing dielectric
spectroscopy, we find the onset of significant dispersion effects at the polar
Jahn-Teller transition. The dispersion becomes fully suppressed again with the
onset of spin order. In addition, the temperature dependencies of dielectric
constant and specific heat possibly indicate a sequential appearance of orbital
and polar order.",1610.05244v1
2017/2/14,Can Magnetic Multilayers Propel Artificial Microswimmers Mimicking Sperm Cells?,"We formulate and solve the equations governing the dynamics of a microscopic
artificial swimmer composed of a head and of a tail made of a thin film of
permanent magnetic material. This is a variant of the model swimmer proposed by
Dreyfus et al. in 2005, whose tail is a filament obtained from the assembly of
super-paramagnetic beads. The swimmer is actuated by an oscillating magnetic
field, and its geometry is inspired by that of sperm cells. Using values for
the geometric and material parameters that are realistic for a magnetic
multilayer, we show that the model swimmer can reach swimming speeds exceeding
one body length per second, under reasonable values of the driving magnetic
field. This provides a proof of principle for the viability of the concept. In
addition, we discuss the possibility to steer the system along curved paths.
Finally, we compare the propulsion mechanism (swimming `gait') of our swimmer
with that of sperm cells. The main difference between the two is that, contrary
to its biological template, our artificial system does not rely on the
propagation of bending waves along the tail, at least for the range of material
and geometric parameters explored in this article.",1702.04278v1
2017/4/4,Van der Waals Engineering of Ferromagnetic Semiconductor Heterostructures for Spin and Valleytronics,"The integration of magnetic material with semiconductors has been fertile
ground for fundamental science as well as of great practical interest toward
the seamless integration of information processing and storage. Here we create
van der Waals heterostructures formed by an ultrathin ferromagnetic
semiconductor CrI3 and a monolayer of WSe2. We observe unprecedented control of
the spin and valley pseudospin in WSe2, where we detect a large magnetic
exchange field of nearly 13 T and rapid switching of the WSe2 valley splitting
and polarization via flipping of the CrI3 magnetization. The WSe2
photoluminescence intensity strongly depends on the relative alignment between
photo-excited spins in WSe2 and the CrI3 magnetization, due to ultrafast
spin-dependent charge hopping across the heterostructure interface. The
photoluminescence detection of valley pseudospin provides a simple and
sensitive method to probe the intriguing domain dynamics in the ultrathin
magnet, as well as the rich spin interactions within the heterostructure.",1704.00841v1
2017/4/17,Three Dimensional Polarimetric Neutron Tomography of Magnetic Fields,"Through the use of Time-of-Flight Three Dimensional Polarimetric Neutron
Tomography (ToF 3DPNT) we have for the first time successfully demonstrated a
technique capable of measuring and reconstructing three dimensional magnetic
field strengths and directions unobtrusively and non-destructively with the
potential to probe the interior of bulk samples which is not amenable
otherwise.
  Using a pioneering polarimetric set-up for ToF neutron instrumentation in
combination with a newly developed tailored reconstruction algorithm, the
magnetic field generated by a current carrying solenoid has been measured and
reconstructed, thereby providing the proof-of-principle of a technique able to
reveal hitherto unobtainable information on the magnetic fields in the bulk of
materials and devices, due to a high degree of penetration into many materials,
including metals, and the sensitivity of neutron polarisation to magnetic
fields. The technique puts the potential of the ToF time structure of pulsed
neutron sources to full use in order to optimise the recorded information
quality and reduce measurement time.",1704.04887v2
2017/4/21,Flux-closure domains in high aspect ratio electroless-deposited CoNiB nanotubes,"We report the imaging of magnetic domains in ferromagnetic CoNiB nanotubes
with very long aspect ratio, fabricated by electroless plating. While axial
magnetization is expected for long tubes made of soft magnetic materials, we
evidence series of azimuthal domains. We tentatively explain these by the
interplay of anisotropic strain and/or grain size, with magneto-elasticity
and/or anisotropic interfacial magnetic anisotropy. This material could be
interesting for dense data storage, as well as curvature-induced magnetic
phenomena such as the non-reciprocity of spin-wave propagation.",1704.06614v2
2017/4/27,Magnetic Domain-Wall Tilting due to Domain-Wall Speed Asymmetry,"Chiral magnetic materials provide a number of challenging issues such as the
highly efficient domain wall (DW) and skyrmion motions driven by electric
current, as of the operation principles of emerging spintronic devices. The DWs
in the chiral materials exhibit asymmetric DW speed variation under application
of in plane magnetic field. Here, we show that such DW speed asymmetry causes
the DW tilting during the motion along wire structure. It has been known that
the DW tilting can be induced by the direct Zeeman interaction of the DW
magnetization under application of in plane magnetic field. However, our
experimental observations manifests that there exists another dominant process
with the DW speed asymmetry caused by either the Dzyaloshinskii Moriya
interaction (DMI) or the chirality dependent DW speed variation. A theoretical
model based on the DW geometry reveals that the DW tilting is initiated by the
DW pinning at wire edges and then, the direction of the DW tilting is
determined by the DW speed asymmetry, as confirmed by a numerical simulation.
The present observation reveals the decisive role of the DW pinning with the DW
speed asymmetry, which determines the DW geometry and consequently, the
dynamics.",1704.08755v2
2017/10/2,Realization of the Axion Insulator State in Quantum Anomalous Hall Sandwich Heterostructures,"The 'magnetoelectric effect' arises from the coupling between magnetic and
electric properties in materials. The Z2 invariant of topological insulators
(TIs) leads to a quantized version of this phenomenon, known as the topological
magnetoelectric (TME) effect. This effect can be realized in a new topological
phase called an 'axion insulator' whose surface states are all gapped but the
interior still obeys time reversal symmetry. We demonstrate such a phase using
electrical transport measurements in a quantum anomalous Hall (QAH) sandwich
heterostructure, in which two compositionally different magnetic TI layers are
separated by an undoped TI layer. Magnetic force microscopy images of the same
sample reveal sequential magnetization reversals of the top and bottom layers
at different coercive fields, a consequence of the weak interlayer exchange
coupling due to the spacer. When the magnetization is antiparallel, both the
Hall resistance and Hall conductance show zero plateaus, accompanied by a large
longitudinal resistance and vanishing longitudinal conductance, indicating the
realization of an axion insulator state. Our findings thus show evidences for a
phase of matter distinct from the established QAH state and provide a promising
platform for the realization of the TME effect.",1710.00471v2
2018/4/20,Search for the magnetic monopole at a magnetoelectric surface,"We show, by solving Maxwell's equations, that an electric charge on the
surface of a slab of a linear magnetoelectric material generates an image
magnetic monopole below the surface provided that the magnetoelectric has a
diagonal component in its magnetoelectric response. The image monopole, in
turn, generates an ideal monopolar magnetic field outside of the slab. Using
realistic values of the electric- and magnetic- field susceptibilties, we
calculate the magnitude of the effect for the prototypical magnetoelectric
material Cr$_2$O$_3$. We use low energy muon spin rotation to measure the
strength of the magnetic field generated by charged muons as a function of
their distance from the surface of a Cr$_2$O$_3$ films, and show that the
results are consistent with the existence of the monopole. We discuss other
possible routes to detecting the monopolar field, and show that, while the
predicted monopolar field generated by Cr$_2$O$_3$ is above the detection limit
for standard magnetic force microscopy, detection of the field using this
technique is prevented by surface charging effects.",1804.07694v3
2018/7/10,Dynamic Response of Tunable Phononic Crystals and New Homogenization Approaches in Magnetoactive Composites,"This research investigates dynamic response of tunable periodic structures
and homogenization methods in magnetoelastic composites (MECs). The research on
tunable periodic structures is focused on the design, modeling and
understanding of wave propagation phenomena and the dynamic response of smart
phononic crystals. High amplitude wrinkle formation is employed to study a
one-dimensional phononic crystal slab consists of a thin film bonded to a thick
compliant substrate. Buckling induced surface instability generates a wrinkly
structure triggered by a compressive strain. It is demonstrated that surface
periodic pattern and the corresponding large deformation can control elastic
wave propagation in the low thickness composite slab. Simulation results show
that the periodic wrinkly structure can be used as a smart phononic crystal
which can switch band diagrams of the structure in a transformative manner. A
magnetoactive phononic crystal is proposed which its dynamic properties are
controlled by combined effects of large deformations and an applied magnetic
field. Finite deformations and magnetic induction influence phononic
characteristics of the periodic structure through geometrical pattern
transformation and material properties. A magnetoelastic energy function is
proposed to develop constitutive laws considering large deformations and
magnetic induction in the periodic structure. Analytical and finite element
methods are utilized to compute dispersion relation and band structure of the
phononic crystal for different cases of deformation and magnetic loadings. It
is demonstrated that magnetic induction not only controls the band diagram of
the structure but also has a strong effect on preferential directions of wave
propagation. Moreover, a thermally controlled phononic crystal is designed
using ligaments of bi-materials in the structure.",1810.05678v1
2018/11/1,Competition between static and dynamic magnetism in the Kitaev spin liquid material Cu2IrO3,"Anyonic excitations emerging from a Kitaev spin liquid can form a basis for
quantum computers. Searching for such excitations motivated intense research on
the honeycomb iridate materials. However, access to a spin liquid ground state
has been hindered by magnetic ordering. Cu2IrO3 is a new honeycomb iridate
without thermodynamic signatures of a long-range order. Here, we use muon spin
relaxation to uncover the magnetic ground state of Cu2IrO3. We find a
two-component depolarization with slow and fast relaxation rates corresponding
to distinct regions with dynamic and static magnetism, respectively. X-ray
absorption spectroscopy and first principles calculations identify a mixed
copper valence as the origin of this behavior. Our results suggest that a
minority of Cu2+ ions nucleate regions of static magnetism whereas the majority
of Cu+/Ir4+ on the honeycomb lattice give rise to a Kitaev spin liquid.",1811.00565v1
2018/11/29,"High Saturation Magnetization, Low Coercivity and Fine YIG Nanoparticles Prepared by Modifying Co-Precipitation Method","Nanoparticles with their specific properties newly have drawn a great deal of
attention of researchers [1-3]Yttrium iron Garnet magnetic nanoparticles
(YIG-NPs) are promising materials with novel applications in microwave,
spintronics, magnonics, and magneto-optical devices. However, achieving stable
and remarkable magnetic YIG-NPs has been remaining as a great challenge. In
this paper, synthesized YIG-NPs by modifying co-precipitation (MCP) method is
reported. Structural and magnetic properties of final products are compared to
those of the materials prepared by citrate-nitrate (CN) method. Smaller
crystals and particle size have been found by MCP method comparing to that of
synthesized by CN method. Using a relatively low annealing temperatures for
both sets of samples (~700 {\deg}C), the final YIG samples prepared by MCP
method show more structural purity than those made by CN method. Higher
saturation magnetization (Ms) and lower coercivity (Hc) are observed in MCP YIG
sample (23.23 emu/g 36 and 30.1 Oe) than the CN prepared YIG sample (16.43
emu/g and 44.95 Oe). The Curie temperature is measured to be 569 {\deg}C for
the MCP YIG sample determined from set of Ms measurement at different
temperatures ranging from 80-600 K. These findings lead to significant
improvement in quality of synthesized (synthetic methods) of YIG-NPs.",1811.12511v1
2018/12/6,Skyrmion phase and competing magnetic orders on a breathing kagome lattice,"Magnetic skyrmion textures are realized mainly in non-centrosymmetric, e.g.
chiral or polar, magnets. Extending the field to centrosymmetric bulk materials
is a rewarding challenge, where the released helicity / vorticity degree of
freedom and higher skyrmion density result in intriguing new properties and
enhanced functionality. We report here on the experimental observation of a
skyrmion lattice (SkL) phase with large topological Hall effect and an
incommensurate helical pitch as small as 2.8 nm in metallic Gd3Ru4Al12, which
materializes a breathing kagom\'e lattice of Gadolinium moments. The magnetic
structure of several ordered phases, including the SkL, is determined by
resonant x-ray diffraction as well as small angle neutron scattering. The SkL
and helical phases are also observed directly using Lorentz transmission
electron microscopy. Among several competing phases, the SkL is promoted over a
low-temperature transverse conical state by thermal fluctuations in an
intermediate range of magnetic fields.",1812.02553v2
2019/1/8,Double-Decker Filament Configuration Revealed by Mass Motions,"It is often envisaged that dense filament material lies in the dips of
magnetic field lines belonging to either a sheared arcade or a magnetic flux
rope. But it is also debated which configuration correctly depicts filaments'
magnetic structure, due to our incapacity to measure the coronal magnetic
field. In this paper, we address this issue by employing mass motions in an
active-region filament to diagnose its magnetic structure. The disturbance in
the filament was driven by a surge initiated at the filament's eastern end in
the NOAA active region 12685, which was observed by the 1-m New Vacuum Solar
Telescope (NVST) in the H$\alpha$ line center and line wing ($\pm0.4$~{\AA}).
Filament material predominately exhibits two kinds of motions, namely, rotation
about the spine and longitudinal oscillation along the spine. The former is
evidenced by antisymmetric Doppler shifts about the spine; the latter features
a dynamic barb with mass extending away from the H$\alpha$ spine until the
transversal edge of the EUV filament channel. The longitudinal oscillation in
the eastern section of the filament is distinct from that in the west, implying
that the underlying field lines have different lengths and curvature radii. The
composite motions of filament material suggest a double-decker host structure
with mixed signs of helicity, comprising a flux rope atop a sheared-arcade
system.",1901.02164v1
2019/1/10,Spin-wave Confinement and Coupling in Organic-Based Magnetic Nanostructures,"Vanadium tetracyanoethylene (V[TCNE]$_\text{x}$) is an organic-based
ferrimagnet that exhibits robust magnetic ordering (T$_\text{C}$ of over 600
K), high quality-factor (high-Q) microwave resonance (Q up to 3,500), and
compatibility with a wide variety of substrates and encapsulation technologies.
Here, we substantially expand the potential scope and impact of this emerging
material by demonstrating the ability to produce engineered nanostructures with
tailored magnetic anisotropy that serve as a platform for the exploration of
cavity magnonics, revealing strongly coupled quantum confined standing wave
modes that can be tuned into and out of resonance with an applied magnetic
field. Specifically, time-domain micromagnetic simulations of these
nanostructures faithfully reproduce the experimentally measured spectra,
including the quasi-uniform mode and higher-order spin-wave (magnon) modes.
Finally, when the two dominant magnon modes present in the spectra are brought
into resonance by varying the orientation of the in-plane magnetic field, we
observe anti-crossing behavior indicating strong coherent coupling between
these two magnon modes at room temperature. These results position
V[TCNE]$_\text{x}$ as a leading candidate for the development of coherent
magnonics, with potential applications ranging from microwave electronics to
quantum information.",1901.03286v2
2019/2/19,Micromagnetometry of two-dimensional ferromagnets,"The study of atomically thin ferromagnetic crystals has led to the discovery
of unusual magnetic behaviour and provided insight into the magnetic properties
of bulk materials. However, the experimental techniques that have been used to
explore ferromagnetism in such materials cannot probe the magnetic field
directly. Here, we show that ballistic Hall micromagnetometry can be used to
measure the magnetization of individual two-dimensional ferromagnets. Our
devices are made by van der Waals assembly in such a way that the investigated
ferromagnetic crystal is placed on top of a multi-terminal Hall bar made from
encapsulated graphene. We use the micromagnetometry technique to study
atomically thin chromium tribromide (CrBr3). We find that the material remains
ferromagnetic down to monolayer thickness and exhibits strong out-of-plane
anisotropy. We also find that the magnetic response of CrBr3 varies little with
the number of layers and its temperature dependence cannot be described by the
simple Ising model of two-dimensional ferromagnetism.",1902.06988v2
2019/2/25,Exchange Interactions Mediated by Non-Magnetic Cations in Double Perovskites,"Establishing the physical mechanism governing exchange interactions is
fundamental for exploring exotic phases such as the quantum spin liquids (QSLs)
in real materials. In this work, we address exchange interactions in
Sr2CuTe$_{1-x}$W$_{x}$O, a series of double perovskites that realize the
spin-1/2 square lattice and were suggested to harbor a QSL ground state arising
from random distribution of non-magnetic ions. Our {\it ab initio}
multi-reference configuration interaction calculations show that replacing Te
atoms with W atoms changes the dominant couplings from nearest to next-nearest
neighbor explained by the crucial role of unoccupied states of non-magnetic
ions in the super-superexchange mechanism. Combined with spin-wave theory
simulations, our calculated exchange couplings provide an excellent description
of the inelastic neutron scattering spectra of the end compounds, as well as
explain the magnetic excitations in Sr2CuTe$_{0.5}$W$_{0.5}$O as emerging from
the bond-disordered exchange couplings. Our results provide crucial
understanding of the role of non-magnetic cations in exchange interactions
paving the way to further exploration of QSL phases in bond-disordered
materials.",1902.09376v2
2019/4/30,Magnetism trends in doped Ce-Cu intermetallics in the vicinity of quantum criticality: realistic Kondo lattice models based on dynamical mean-field theory,"The quantum critical point (QCP) in the archetypical heavy-fermion compound
CeCu$_6$ doped by Au is described, accounting for the localized $4f$-electron
of Ce, using realistic electronic structure calculations combined with
dynamical mean-field theory (DMFT). Magnetism trends in
Ce(Cu$_{1-\epsilon}$Au$_\epsilon$)$_6$ are compared with those in Co-doped
CeCu$_{5}$, which resides on the non-ferromagnetic side of the composition
space of one of the earliest rare-earth permanent magnet compounds,
Ce(Co,Cu)$_5$. The construction of a realistic Doniach phase diagram shows that
the system crosses over a magnetic quantum critical point in the Kondo lattice
in $0.2<x<0.4$ of Ce(Cu$_{1-x}$Co$_x$)$_5$. Comparison between Au-doped
CeCu$_6$ and Co-doped CeCu$_5$ reveals that the swept region in the vicinity of
QCP for the latter thoroughly covers that of the former. The implications of
these trends on the coercivity of the bulk rare-earth permanent magnets are
discussed.",1904.13160v5
2019/5/10,Magnetic tunnel junctions with a B2-ordered CoFeCrAl equiatomic Heusler alloy,"The equiatomic quaternary Heusler alloy CoFeCrAl is a candidate material for
spin-gapless semiconductors (SGSs). However, to date, there have been no
experimental attempts at fabricating a junction device. This paper reports a
fully epitaxial (001)-oriented MgO barrier magnetic tunnel junction (MTJ) with
CoFeCrAl electrodes grown on a Cr buffer. X-ray and electron diffraction
measurements show that the (001) CoFeCrAl electrode films with atomically flat
surfaces have a $B2$-ordered phase. The saturation magnetization is 380
emu/cm$^3$, almost the same as the value given by the Slater--Pauling--like
rule, and the maximum tunnel magnetoresistance ratios at 300 K and 10 K are 87%
and 165%, respectively. Cross-sectional electron diffraction analysis shows
that the MTJs have MgO interfaces with fewer dislocations. The temperature- and
bias-voltage-dependence of the transport measurements indicates magnon-induced
inelastic electron tunneling overlapping with the coherent electron tunneling.
X-ray magnetic circular dichroism (XMCD) measurements show a ferromagnetic
arrangement of the Co and Fe magnetic moments of $B2$-ordered CoFeCrAl, in
contrast to the ferrimagnetic arrangement predicted for the $Y$-ordered state
possessing SGS characteristics. Ab-initio calculations taking account of the
Cr-Fe swap disorder qualitatively explain the XMCD results. Finally, the effect
of the Cr-Fe swap disorder on the ability for electronic states to allow
coherent electron tunneling is discussed.",1905.04070v1
2019/6/3,Very large Dzyaloshinskii-Moriya interaction in two-dimensional Janus manganese dichalcogenides and its application to realize skyrmion states,"The Dzyaloshinskii-Moriya interaction (DMI), which only exists in
noncentrosymmetric systems, is responsible for the formation of exotic chiral
magnetic states. The absence of DMI in most two-dimensional (2D) magnetic
materials is due to their intrinsic inversion symmetry. Here, using
first-principles calculations, we demonstrate that significant DMI can be
obtained in a series of Janus monolayers of manganese dichalcogenides MnXY in
which the difference between X and Y on the opposites sides of Mn breaks the
inversion symmetry. In particular, the DMI amplitudes of MnSeTe and MnSTe are
comparable to those of state-of-the-art ferromagnet/heavy metal (FM/HM)
heterostructures. In addition, by performing Monte Carlo simulations, we find
that at low temperatures the ground states of the MnSeTe and MnSTe monolayers
can transform from ferromagnetic states with worm-like magnetic domains into
the skyrmion states by applying external magnetic field. At increasing
temperature, the skyrmion states starts fluctuating above 50 K before an
evolution to a completely disordered structure at higher temperature. The
present results pave the way for new device concepts utilizing chiral magnetic
structures in specially designed 2D ferromagnetic materials.",1906.00648v3
2019/6/20,Predicting the Curie temperature of ferromagnets using machine learning,"The magnetic properties of a material are determined by a subtle balance
between the various interactions at play, a fact that makes the design of new
magnets a daunting task. High-throughput electronic structure theory may help
to explore the vast chemical space available and offers a design tool to the
experimental synthesis. This method efficiently predicts the elementary
magnetic properties of a compound and its thermodynamical stability, but it is
blind to information concerning the magnetic critical temperature. Here we
introduce a range of machine-learning models to predict the Curie temperature,
$T_\mathrm{C}$, of ferromagnets. The models are constructed by using
experimental data for about 2,500 known magnets and consider the chemical
composition of a compound as the only feature determining $T_\mathrm{C}$. Thus,
we are able to establish a one-to-one relation between the chemical composition
and the critical temperature. We show that the best model can predict
$T_\mathrm{C}$'s with an accuracy of about 50K. Most importantly our model is
able to extrapolate the predictions to regions of the chemical space, where
only a little fraction of the data was considered for training. This is
demonstrated by tracing the $T_\mathrm{C}$ of binary intermetallic alloys along
their composition space and for the Al-Co-Fe ternary system.",1906.08534v1
2019/11/1,Electric-Field Control of the Interlayer Exchange Coupling for Magnetization Switching,"We propose an electric-field-controlled mechanism for magnetization switching
assisted solely by the interlayer-exchange coupling (IEC) between the fixed and
the free magnets, which are separated by two oxide barriers sandwiching a
spacer material known for exhibiting large IEC. The basic idea relies on the
formation of a quantum-well (QW) within the spacer material and controlling the
transmission coefficient across the structure with an electric-field via the
resonant tunneling phenomena. Using non-equilibrium Green's function (NEGF)
method, we show that the structure can exhibit a bias-dependent oscillatory IEC
that can switch the free magnet to have either a parallel or an antiparallel
configuration with respect to the fixed magnet, depending on the sign of the
IEC. Such bi-directional switching can be achieved with the same voltage
polarity but different magnitudes. With proper choice of the spacer material,
the current in the structure can be significantly reduced. Due to the
conservative nature of the exerted torque by the IEC, the switching threshold
of the proposed mechanism is decoupled from the switching speed, while the
conventional spin-torque devices exhibit a trade-off due to the
non-conservative nature of the exerted torque.",1911.00183v1
2019/12/11,First Principles Heisenberg Models of 2D magnetic materials: The Importance of Quantum Corrections to the Exchange Coupling,"Magnetic materials are typically described in terms of the Heisenberg model,
which provides an accurate account of thermodynamic properties when combined
with first principles calculations. This approach is usually based on an energy
mapping between density functional theory and a classical Heisenberg model.
However, for two-dimensional systems the eigenenergies of the Heisenberg model
may differ significantly from the classical approximation, which leads to
modified expressions for exchange parameters. Here we demonstrate that density
functional theory yields local magnetic moments that are in accordance with
strongly correlated anti-ferromagnetic eigenstates of the Heisenberg
Hamiltonian. This implies that density functional theory provides a description
of these states that conforms with the quantum mechanical eigenstates of the
model. We then provide expressions for exchange parameters based on a proper
eigenstate mapping to the Heisenberg model and find that they are typically
reduced by 10 % compared to a classical analysis. Finally, we calculate the
corrections to critical temperature for magnetic ordering for a previously
predicted set of two-dimensional ferromagnetic insulators and find that the
inclusion of quantum effects may reduce the predictions of critical
temperatures by up to 7 %.",1912.05230v3
2020/1/17,"Magnetic, magnetoelastic and corrosion resistant properties of (Fe-Ni) based metallic glasses for structural health monitoring applications","We have performed a study of the magnetic, magnetoelastic, and corrosion
resistance properties of seven different composition magnetoelastic-resonant
platforms. For some applications, such as structural health monitoring, these
materials must have not only good magnetomechanical properties, but also a high
corrosion resistance. In the fabricated metallic glasses of composition
Fe(73-x)NixCr5Si10B12, the Fe/Ni ratio was varied (Fe + Ni = 73% at.) thus
changing the magnetic and magnetoelastic properties. A small amount of chromium
(Cr5) was added in order to achieve the desired good corrosion resistance. As
expected, all the studied properties change with the composition of the
samples. Alloys containing a higher amount of Ni than Fe do not show magnetic
behavior at room temperature, while iron-rich alloys have demonstrated not only
good magnetic properties, but also good magnetoelastic ones, with
magnetoelastic coupling coefficient as high as 0.41 for x=0 in the
Fe73Ni0Cr5Si10B12 (the sample containing only Fe but not Ni). Concerning
corrosion resistance, we have found a continuous degradation of these
properties as the Ni content increases in the composition. Thus, the corrosion
potential decreases monotonously from 46.74 mV for the x=0 composition,
Fe73Ni0Cr5Si10B12 to -239.47 mV for the x=73 composition Fe0Ni73Cr5Si10B12.",2001.06283v1
2020/3/2,Phase Sensitivity and Phase Noise of Cantilever-Type Magnetoelastic Sensors Based on the $Δ$E Effect,"Magnetoelastic sensors for the detection of low-frequency and low-amplitude
magnetic fields are in the focus of research since more than 30 years. In order
to minimize the limit of detection (LOD) of such sensor systems, it is of high
importance to understand and to be able to quantify the relevant noise sources.
In this contribution, cantilever-type electromechanic and magnetoelastic
resonators, respectively, are comprehensively investigated and mathematically
described not only with regard to their phase sensitivity but especially to the
extent of the sensor-intrinsic phase noise. Both measurements and calculations
reveal that the fundamental LOD is limited by additive phase noise due to
thermal-mechanical noise of the resonator, i.e. by thermally induced random
vibrations of the cantilever, and by thermal-electrical noise of the
piezoelectric material. However, due to losses in the magnetic material
parametric flicker phase noise arises, limiting the overall performance. In
particular it is shown that the LOD is virtually independent of the magnetic
sensitivity but is solely determined by the magnetic losses. Instead of the
sensitivity, the magnetic losses, represented by the material's effective
complex permeability, should be considered as the most important parameter for
the further improvement of such sensors in the future. This implication is not
only valid for magnetoelastic cantilevers but also applies to any type of
magnetoelastic resonator.",2003.01085v1
2020/3/23,Evolution of Griffiths Phase and Critical Behaviour of La1-xPbxMnO3+-y Solid Solutions,"Polycrystalline La1-xPbxMnO3+-y (x = 0.3, 0.35, 0.4) solid solutions were
prepared by solid state reaction method and their magnetic properties have been
investigated. Rietveld refinement of X-ray powder diffraction patterns showed
that all samples are single phase and crystallized with the rhombohedral
structure in the R-3c space group. A second order paramagnetic to ferromagnetic
phase transition was observed for all materials. The Griffiths phase (GP),
identified from the temperature dependence of the inverse susceptibility, was
suppressed by increasing magnetic field and showed a significant dependence on
A-site chemical substitution. The critical behaviour of the compounds was
investigated near to their Curie temperatures, using intrinsic magnetic field
data. The critical exponents (\b{eta}, {\gamma} and {\delta}) are close to the
mean-field approximation values for all three compounds. The observed
mean-field like behaviour is a consequence of the GP and the formation of
ferromagnetic clusters. Long-range ferromagnetic order is established as the
result of long-range interactions between ferromagnetic clusters. The
magnetocaloric effect was studied in terms of the isothermal entropy change.
Our study shows that the material with the lowest chemical substitution (x =
0.3) has the highest potential (among the three compounds) as magnetic
refrigerant, owing to its higher relative cooling power (258 J/kg at 5 T field)
and a magnetic phase transition near room temperature.",2003.10207v2
2020/3/25,Magnetic-field-induced FM-AFM metamagnetic transition and strong negative magnetoresistance in Mn$_{1/4}$NbS$_2$ under pressure,"Transition metal dichalcogenides (TMDC) stand out with their high chemical
stability and the possibility to incorporate a wide range of magnetic species
between the layers. The behavior of conduction electrons in such materials
intercalated by 3d-elements is closely related to their magnetic properties and
can be sensitively controlled by external magnetic fields. Here, we study the
magnetotransport properties of NbS$_2$ intercalated with Mn, Mn$_{1/4}$NbS$_2$,
demonstrating a complex behavior of the magnetoresistance and of the ordinary
and anomalous Hall resistivities. Application of pressure as tuning parameter
leads to the drastic changes of the magnetotransport properties of
Mn$_{1/4}$NbS$_2$ exhibiting large negative magnetoresistance up to $65 \%$ at
7.1 GPa. First-principles electronic structure calculations indicates
pressure-induced transition from ferromagnetic to antiferromagnetic state.
Theoretical calculations accounting for the finite temperature magnetic
properties of Mn$_{1/4}$NbS$_2$ suggest a field-induced metamagnetic
ferromagnetic-antiferromagnetic transition as an origin of the large negative
magentoresistance. These results inspire the development of materials for
spintronic applications based on intercalated TMDC with a well controllable
metamagnetic transition.",2003.11678v1
2020/3/26,Emergence of a nematic paramagnet via quantum order-by-disorder and pseudo-Goldstone modes in Kitaev magnets,"The appearance of nontrivial phases in Kitaev materials exposed to an
external magnetic field has recently been a subject of intensive studies. Here,
we elucidate the relation between the field-induced ground states of the
classical and quantum spin models proposed for such materials, by using the
infinite density matrix renormalization group (iDMRG) and the linear spin wave
theory (LSWT). We consider the $K \Gamma \Gamma'$ model, where $\Gamma$ and
$\Gamma'$ are off-diagonal spin exchanges on top of the dominant Kitaev
interaction $K$. Focusing on the magnetic field along the $[111]$ direction, we
explain the origin of the nematic paramagnet, which breaks the
lattice-rotational symmetry and exists in an extended window of magnetic field,
in the quantum model. This phenomenon can be understood as the effect of
quantum order-by-disorder in the frustrated ferromagnet with a continuous
manifold of degenerate ground states discovered in the corresponding classical
model. We compute the dynamical spin structure factors using a matrix operator
based time evolution and compare them with the predictions from LSWT. We, thus,
provide predictions for future inelastic neutron scattering experiments on
Kitaev materials in an external magnetic field along the $[111]$ direction. In
particular, the nematic paramagnet exhibits a characteristic pseudo-Goldstone
mode which results from the lifting of a continuous degeneracy via quantum
fluctuations.",2003.11876v2
2020/4/1,Physical properties and thermal stability of Fe5GeTe2 single crystals,"The magnetic and transport properties of Fe-deficient Fe5GeTe2 single
crystals (Fe5-xGeTe2 with x~0.3) were studied and the impact of thermal
processing was explored. Quenching crystals from the growth temperature has
been previously shown to produce a metastable state that undergoes a strongly
hysteretic first-order transition upon cooling below ~100K. The first-order
transition impacts the magnetic properties, yielding an enhancement in the
Curie temperature T_C from 270 to 310K. In the present work, T_HT ~550K has
been identified as the temperature above which metastable crystals are obtained
via quenching. Diffraction experiments reveal a structural change at this
temperature, and significant stacking disorder occurs when samples are slowly
cooled through this temperature range. The transport properties are
demonstrated to be similar regardless of the crystal's thermal history. The
scattering of charge carriers appears to be dominated by moments fluctuating on
the Fe(1) sublattice, which remain dynamic down to 100-120K. Maxima in the
magnetoresistance and anomalous Hall resistance are observed near 120K. The
Hall and Seebeck coefficients are also impacted by magnetic ordering on the
Fe(1) sublattice. The data suggest that both electrons and holes contribute to
conduction above 120K, but that electrons dominate at lower temperature when
all of the Fe sublattices are magnetically ordered. This study demonstrates a
strong coupling of the magnetism and transport properties in Fe5-xGeTe2 and
complements the previous results that demonstrated strong magnetoelastic
coupling as the Fe(1) moments order. The published version of this manuscript
is DOI:10.1103/PhysRevMaterials.3.104401 (2019)",2004.00494v1
2020/4/27,Soft and anisotropic local moments in 4$d$ and 5$d$ mixed-valence M$_2$O$_9$ dimers,"We investigate via exact diagonalization of finite clusters the electronic
structure and magnetism of M$_2$O$_9$ dimers in the mixed-valence hexagonal
perovskites A$_3$B'M$_2$O$_9$ for various different fillings of 4$d$ and 5$d$
transition-metal M ions. We find that the magnetic moments of such dimers are
determined by a subtle interplay of spin-orbit coupling, Hund's coupling, and
Coulomb repulsion, as well as the electron filling of the M ions. Most
importantly, the magnetic moments are anisotropic and temperature-dependent.
This behavior is a result of spin-orbit coupling, magnetic field effects, and
the existence of several nearly-degenerate electronic configurations whose
proximity allows occupation of excited states already at room temperature. This
analysis is consistent with experimental susceptibility measurements for a
variety of dimer-based materials. Furthermore, we perform a survey of
A$_3$B'M$_2$O$_9$ materials and propose ground-state phase diagrams for the
experimentally relevant M fillings of $d^{4.5}$, $d^{3.5}$ and $d^{2.5}$.
Finally, our results show that the usually applied Curie-Weiss law with a
constant magnetic moment cannot be used in these spin-orbit-coupled materials.",2004.13050v1
2020/4/28,Al-dependent electronic and magnetic properties of YCrO$_3$ with magnetocaloric application: an ab-initio and Monte-Carlo approach,"In this paper, a theoretical journey from electronic to magneto-caloric
effect has been shown through the magnetic properties of aluminium induced
yttrium chromate. The ground state electronic band structure and density of
states have been studied using first principle calculations under GGA+U
schemes. From the energy minimization, the ferromagnetic structure is more
stable than the antiferromagnetic one. The interaction constant as well as the
magnetic moment, have been determined from mean-field theory and DFT,
respectively. The Monte-Carlo simulation under Metropolis algorithm has been
employed to determine the critical temperature ($T_C$), which is nearly same as
the experimental value. The temperature-dependent magnetization shows that
these materials exhibit a paramagnetic to ferromagnetic phase transition at
~136 K, 130 K, 110 K, and 75 K respectively. The two inherent properties named
the isothermal entropy change ($\Delta S_M$) and the adiabatic temperature
change ($\Delta T_{ad}$) as a function of temperature for different applied
magnetic fields have been determined to measure the magnetocaloric efficiency
of these materials. The relative cooling power (RCP), which is calculated
around $T_C$, changes from 4.7 J/Kg to 2.5 J/Kg with the decreasing
Cr-concentration.",2004.13456v2
2020/5/28,Spectral signatures of the surface anomalous Hall effect in magnetic axion insulators,"The topological surface states of magnetic topological systems, such as Weyl
semimetals and axion insulators, are associated with unconventional transport
properties such as nonzero or half-quantized surface anomalous Hall effect.
Here we study the surface anomalous Hall effect and its spectral signatures in
different magnetic topological phases using both model Hamiltonian and
first-principles calculations. We demonstrate that by tailoring the
magnetization and interlayer electron hopping, a rich three-dimensional
topological phase diagram can be established, including three types of
topologically distinct insulating phases bridged by Weyl semimetals, and can be
directly mapped to realistic materials such as MnBi2Te4/(Bi2Te3)n systems.
Among them, we find that the surface anomalous Hall conductivity in the
axion-insulator phase is a well-localized quantity either saturated at or
oscillating around e2/2h, depending on the magnetic homogeneity. We also
discuss the resultant chiral hinge modes embedded inside the side surface bands
as the potential experimental signatures for transport measurements. Our study
is a significant step forward towards the direct realization of long-sought
axion insulators in realistic material systems.",2005.13943v4
2020/6/25,Effect of dilute magnetism in a topological insulator,"Three-dimensional topological insulators (TIs) have emerged as a unique state
of quantum matter and generated enormous interests in condensed matter physics.
The surfaces of a three dimensional (3D) TI are composed of a massless Dirac
cone, which is characterized by the Z2 topological invariant. Introduction of
magnetism on the surface of TI is essential to realize the quantum anomalous
Hall effect (QAHE) and other novel magneto-electric phenomena. Here, by using a
combination of first principles calculations, magneto-transport, angle-resolved
photoemission spectroscopy (ARPES), and time resolved ARPES (tr-ARPES), we
study the electronic properties of Gadolinium (Gd) doped Sb2Te3. Our study
shows that Gd doped Sb2Te3 is a spin-orbit-induced bulk band-gap material,
whose surface is characterized by a single topological surface state. We
further demonstrate that introducing diluted 4f-electron magnetism into the
Sb2Te3 topological insulator system by the Gd doping creates surface magnetism
in this system. Our results provide a new platform to investigate the
interaction between dilute magnetism and topology in doped topological
materials.",2006.14130v1
2020/7/15,Magnetic properties of $(Fe_{1-x}Mn_x)_2AlB_2$ and the impact of substitution on the magnetocaloric effect,"In this work, we investigate the magnetic structures of
$(Fe_{1-x}Mn_x)_2AlB_2$ solid-solution quaternaries in the $x = 0$ to $1$ range
using x-ray and neutron diffraction, magnetization measurements, and mean-field
theory calculations. While $Fe_2AlB_2$ and $Mn_2AlB_2$ are known to be
ferromagnetic (FM) and antiferromagnetic (AFM), respectively, herein we focused
on the magnetic structure of their solid solutions, which is not well
understood. The FM ground state of $Fe_2AlB_2$ becomes a canted AFM at $x
\approx 0.2$, with a monotonically diminishing FM component until $x \approx
0.5$. The FM transition temperature ($T_C$) decreases linearly with increasing
$x$. These changes in magnetic moments and structures are reflected in
anomalous expansions of the lattice parameters, indicating a magnetoelastic
coupling. Lastly, the magnetocaloric properties of the solid solutions were
explored. For $x = 0.2$ the isothermal entropy change is smaller by 30% than it
is for $Fe_2AlB_2$, while the relative cooling power is larger by 6%, due to
broadening of the temperature range of the transition.",2007.07647v3
2020/7/29,Reinvestigation of the intrinsic magnetic properties of (Fe$_{1-x}$Co$_x$)$_2$B alloys and crystallization behavior of ribbons,"New determination of the magnetic anisotropy from single crystals of
(Fe$_{1-x}$Co$_x$)$_2$B alloys are presented. The anomalous temperature
dependence of the anisotropy constant is discussed using the standard
Callen-Callen theory, which is shown to be insufficient to explain the
experimental results. A more material specific study using first-principles
calculations with disordered moments approach gives a much more consistent
interpretation of the experimental data. Since the intrinsic properties of the
alloys with $x=0.3-0.35$ are promising for permanent magnets applications,
initial investigation of the extrinsic properties are described, in particular
the crystallization of melt spun ribbons with Cu, Al, and Ti additions.
Previous attempts at developing a significant hysteresis have been unsuccessful
in this system. Our melt-spinning experiment indicates that this system shows
rapid crystallization.",2007.15113v1
2020/8/8,Tuning interchain ferromagnetic instability in A2Cr3As3 ternary arsenides by chemical pressure and uniaxial strain,"We analyze the effects of chemical pressure induced by alkali metal
substitution and uniaxial strain on magnetism in the A2Cr3As3 (A = Na, K, Rb,
Cs) family of ternary arsenides with quasi-one dimensional structure. Within
the framework of the density functional theory, we predict that the
non-magnetic phase is very close to a 3D collinear ferrimagnetic state, which
realizes in the regime of moderate correlations, such tendency being common to
all the members of the family with very small variations due to the different
interchain ferromagnetic coupling. We uncover that the stability of such
interchain ferromagnetic coupling has a non-monotonic behavior with increasing
the cation size, being critically related to the degree of structural
distortions which is parametrized by the Cr-As-Cr bonding angles along the
chain direction. In particular, we demonstrate that it is boosted in the case
of the Rb, in agreement with recent experiments. We also show that uniaxial
strain is a viable tool to tune the non-magnetic phase towards an interchain
ferromagnetic instability. The modifcation of the shape of the Cr triangles
within the unit cell favors the formation of a net magnetization within the
chain and of a ferromagnetic coupling among the chains. This study can provide
relevant insights about the interplay between superconductivity and magnetism
in this class of materials.",2008.03552v4
2020/9/23,Robust metastable skyrmions with tunable size in the chiral magnet FePtMo$_3$N,"Synthesis of new materials that can host magnetic skyrmions and their
thorough experimental and theoretical characterization are essential for future
technological applications. The $\beta$-Mn-type compound FePtMo$_3$N is one
such novel material that belongs to the chiral space group $P4_132$, where the
antisymmetric Dzyaloshinkii-Moriya interaction is allowed due to the absence of
inversion symmetry. We report the results of small-angle neutron scattering
(SANS) measurements of FePtMo$_3$N and demonstrate that its magnetic ground
state is a long-period spin helix with a Curie temperature of 222~K. The
magnetic field-induced redistribution of the SANS intensity showed that the
helical structure transforms to a lattice of skyrmions at $\sim$13~mT at
temperatures just below $T_{\text C}$. Our key observation is that the skyrmion
state in FePtMo$_3$N is robust against field cooling down to the lowest
temperatures. Moreover, once the metastable state is prepared by field cooling,
the skyrmion lattice exists even in zero field. Furthermore, we show that the
skyrmion size in FePtMo$_3$N exhibits high sensitivity to the sample
temperature and can be continuously tuned between 120 and 210~nm. This offers
new prospects in the control of topological properties of chiral magnets.",2009.11283v1
2020/10/29,Domain wall dynamics in antiferromagnetically-coupled double-lattice systems,"In ferromagnetic materials, the rich dynamics of magnetic domain walls (DWs)
under magnetic field or current have been successfully described using the
well-known q-{\phi} analytical model. We demonstrate here that this simple
unidimensional model holds for multiple-sublattice materials such as
ferrimagnetic alloys or synthetic antiferromagnets (SAF) by using effective
parameters, and is in excellent agreement with double-lattice micromagnetic
simulations. We obtain analytical laws for the DW velocity and internal
precession angle as a function of net magnetisation for different driving
forces (magnetic field, spin transfer and spin-orbit torques) and different
propagation regimes in ferrimagnetic alloys and SAFs. The model predicts that
several distinctive dynamical features occur near or at the magnetic and the
angular compensation points when the net magnetization or the net angular
momentum of the system vanishes, and we discuss the experimental observations
that have been reported for some of them. Using a higher degree-of-freedom
analytical model that accounts for inter-sublattice distortions, we give
analytical expressions for these distortions that agree with the micromagnetic
simulations. This model shows that the DW velocity and precession rate are
independent of the strength of the inter-sublattice exchange coupling, and
justifies the use of the simpler effective parameters model.",2010.15443v1
2020/11/20,Designer spin order in diradical nanographenes,"The magnetic properties of carbon materials are at present the focus of an
intense research effort in physics, chemistry and materials science due to
their potential applications in spintronics and quantum computations. Although
the presence of spins in open-shell nanographenes has been recently confirmed,
the ability to control magnetic coupling sign has remained elusive, but the
most desirable. Here, we demonstrate an effective approach of engineering
magnetic ground states in atomically precise open-shell bipartite/nonbipartite
nanographenes using combined scanning probe techniques and mean-field Hubbard
model calculations. The magnetic coupling sign between two spins has been
controlled via breaking bipartite lattice symmetry of nanographenes. In
addition, the exchange-interaction strength between two spins has been widely
tuned by finely tailoring their spin density overlap, realizing a large
exchange-interaction strength of 42 meV. Our demonstrated method provides ample
opportunities for designer above-room-temperature magnetic phases and
functionalities in graphene nanomaterials.",2011.10224v1
2020/12/4,Anomalous Hall and Nernst effects in ferrimagnetic Mn$_4$N films: possible interpretation and prospect for enhancement,"Ferrimagnetic Mn$_4$N is a promising material for heat flux sensors based on
the anomalous Nernst effect (ANE) because of its sizable uniaxial magnetic
anisotropy ($K_{\rm u}$) and low saturation magnetization ($M_{\rm s}$). We
experimentally and theoretically investigated the ANE and anomalous Hall effect
in sputter-deposited Mn$_4$N films. It was revealed that the observed negative
anomalous Hall conductivity ($\sigma_{xy}$) could be explained by two different
coexisting magnetic structures, that is, a dominant magnetic structure with
high $K_{\rm u}$ contaminated by another structure with negligible $K_{\rm u}$
owing to an imperfect degree of order of nitrogen. The observed transverse
thermoelectric power ($S_{\rm ANE}$) of $+0.5\, \mu{\rm V/K}$ at $300\, {\rm
K}$ gave a transverse thermoelectric coefficient ($\alpha_{xy}$) of $+0.34\,
{\rm A/(m \cdot K)}$, which was smaller than the value predicted from
first-principles calculation. The interpretation for $\alpha_{xy}$ based on the
first-principles calculations led us to conclude that the realization of single
magnetic structure with high $K_{\rm u}$ and optimal adjustment of the Fermi
level are promising approaches to enhance $S_{\rm ANE}$ in Mn$_4$N through the
sign reversal of $\sigma_{xy}$ and the enlargement of $\alpha_{xy}$ up to a
theoretical value of $1.77\, {\rm A/(m \cdot K)}$.",2012.02510v2
2020/12/17,Magnetic reversal and pinning in a perpendicular zero moment half-metal,"Compensated ferrimagnets are promising materials for fast spintronic
applications based on domain wall motion as they combine the favourable
properties of ferromagnets and antiferromagnets. They inherit from
antiferromagnets immunity to external fields, fast spin dynamics and rapid
domain wall motion. From ferromagnets they inherit straightforward ways to read
out the magnetic state, especially in compensated half metals, where electrons
flow in only one spin channel. Here, we investigate domain structure in
compensated half-metallic Mn2Ru0.5Ga films and assess their potential in domain
wall motion-based spin-electronic devices. Our focus is on understanding and
reducing domain wall pinning in unpatterned epitaxial thin films. Two modes of
magnetic reversal, driven by nucleation or domain wall motion, are identified
for different thin film deposition temperatures $(T_{dep})$. The magnetic
aftereffect is analysed to extract activation volumes $(V^*)$, activation
energies $(E_A)$, and their variation $({\Delta}E_A)$. The latter is decisive
for the magnetic reversal regime, where domain wall motion dominated reversal
(weak pinning) is found for ${\Delta}E_A<0.2$ eV and nucleation dominated
reversal (strong pinning) for ${\Delta}E_A>0.5$ eV. A minimum ${\Delta}E_A=28$
meV is found for $T_{dep}=290{\deg}$C. Prominent pinning sites are visualized
by analysing virgin domain patterns after thermal demagnetization. In the
sample investigated they have spacings of order 300 nm, which gives an upper
limit of the track-width of spin-torque domain-wall motion-based devices.",2012.09515v1
2021/3/26,Microwave resonances of magnetic skyrmions in thin film multilayers,"Non-collinear magnets exhibit a rich array of dynamic properties at microwave
frequencies. They can host nanometre-scale topological textures known as
skyrmions, whose spin resonances are expected to be highly sensitive to their
local magnetic environment. Here, we report a magnetic resonance study of an
[Ir/Fe/Co/Pt] multilayer hosting N\'eel skyrmions at room temperature.
Experiments reveal two distinct resonances of the skyrmion phase during
in-plane ac excitation, with frequencies between 6-12 GHz. Complementary
micromagnetic simulations indicate that the net magnetic dipole moment rotates
counterclockwise (CCW) during both resonances. The magnon probability
distribution for the lower-frequency resonance is localised within isolated
skyrmions, unlike the higher-frequency mode which principally originates from
areas between skyrmions. However, the properties of both modes depend
sensitively on the out-of-plane dipolar coupling, which is controlled via the
ferromagnetic layer spacing in our heterostructures. The gyrations of stable
isolated skyrmions reported in this room temperature study encourage the
development of new material platforms and applications based on skyrmion
resonances. Moreover, our material architecture enables the resonance spectra
to be tuned, thus extending the functionality of such applications over a
broadband frequency range.",2103.14524v1
2021/6/9,Intriguing Magnetoelectric Effect in Two-dimensional Ferromagnetic/Perovskite Oxide Ferroelectric Heterostructure,"Two-dimensional (2D) magnets have broad application prospects in the
spintronics, but how to effectively control them with a small electric field is
still an issue. Here we propose that 2D magnets can be efficiently controlled
in a multiferroic heterostructure composed of 2D magnetic material and
perovskite oxide ferroelectric (POF) whose dielectric polarization is easily
flipped under a small electric field. We illustrate the feasibility of such
strategy in the bilayer CrI3/BiFeO3(001) heterostructure by using the
first-principles calculations. Different from the traditional POF multiferroic
heterostructures which have strong interface interactions, we find that the
interface interaction between CrI3 and BiFeO3(001) is van der Waals type.
Whereas, the heterostructure has particular strong magnetoelectric coupling
where the bilayer CrI3 can be efficiently switched between ferromagnetic and
antiferromagnetic types by the polarized states of BiFeO3(001). We also
discover the competing effect between electron doping and the additional
electric field on the interlayer exchange coupling interaction of CrI3, which
is responsible to the magnetic phase transition. Our results provide a new
avenue for the tuning of 2D magnets with a small electric field.",2106.04998v2
2021/8/6,Angular dependence of hump-shape Hall Effects for distinguishing between Karplus-Luttinger and Geometrical Origins,"Among various magnetic thin film heterostructures in solid state Physics, two
contrasting mechanisms of the hump-shaped Hall Effects remain ambiguous and
debated, namely the overlap of two opposite-signed Karplus-Luttinger Hall-loops
associated with inhomogeneous collinear magnetic bubbles with perpendicular
anisotropy, or the Geometrical/Topological Hall Effect associated with magnetic
skyrmions. Their similarity in topology imposes difficulty in discrimination
via magnetic imaging. Here, this ambiguity is overcome by the divergence
exponent of angle-dependent hump peak fields via magnetic field rotation
characterization on several heterostructures. Their difference in sensitivity
to in-plane fields reveals that the former mechanism involves higher uniaxial
anisotropy than the latter, departing from the pure skyrmion regime described
by Ginzburg-Landau framework of triple-q spin-wave superposition. Various
materials can be collapsed into a single curve of divergence exponent versus
domain wall energy, bridging the crossover of the two aforementioned
mechanisms.",2108.03086v5
2021/11/13,Sensitive electronic correlation effects on electronic properties in ferrovalley material Janus FeClF monolayer,"The electronic correlation may have essential influence on electronic
structures in some materials with special structure and localized orbital
distribution. In this work, taking Janus monolayer FeClF as a concrete example,
the correlation effects on its electronic structures are investigated by using
generalized gradient approximation plus $U$ (GGA+$U$) approach. For
perpendicular magnetic anisotropy (PMA), the increasing electron correlation
effect can induce the ferrovalley (FV) to half-valley-metal (HVM) to quantum
anomalous Hall (QAH) to HVM to FV transitions. For QAH state, there are a unit
Chern number and a chiral edge state connecting the conduction and valence
bands. The HVM state is at the boundary of the QAH phase, whose carriers are
intrinsically 100\% valley polarized. With the in-plane magnetic anisotropy, no
special QAH states and prominent valley polarization are observed. However, for
both out-of-plane and in-plane magnetic anisotropy, sign-reversible Berry
curvature can be observed with increasing $U$. It is found that these
phenomenons are related with the change of $d_{xy}$/$d_{x^2-y^2}$ and $d_{z^2}$
orbital distributions and different magnetocrystalline directions. It is also
found that the magnetic anisotropy energy (MAE) and Curie temperature strongly
depend on the $U$. With PMA, taking typical $U=$2.5 eV, the electron valley
polarization can be observed with valley splitting of 109 meV, which can be
switched by reversing the magnetization direction. The analysis and results can
be readily extended to other nine members of monolayer FeXY (X/Y=F, Cl, Br and
I) due to sharing the same Fe-dominated low-energy states and electronic
correlations with FeClF monolayer.",2111.07110v1
2021/11/15,Microscopic origin of multiferroic order in monolayer NiI$_2$,"The discovery of multiferroic behavior in monolayer NiI$_2$ provides a new
symmetry-broken state in van der Waals monolayers, featuring the simultaneous
emergence of helimagnetic order and ferroelectric order at a critical
temperature of $T=21$ K. However, the microscopic origin of multiferroic order
in NiI$_2$ monolayer has not been established, and in particular, the role of
non-colinear magnetism and spin-orbit coupling in this compound remains an open
problem. Here we reveal the origin of the two-dimensional multiferroicity in
NiI$_2$ using first-principles electronic structure methods. We show that the
helimagnetic state appears as a consequence of the long-range magnetic exchange
interactions, featuring sizable magnetic moments in the iodine atoms. We
demonstrate that the electronic density reconstruction accounting for the
ferroelectric order emerges from the interplay of non-collinear magnetism and
spin-orbit coupling. We demonstrate that the ferroelectric order is controlled
by the iodine spin-orbit coupling, and leads to an associated
electronically-driven distortion in the lattice. Our results establish the
microscopic origin of the multiferroic behavior in monolayer NiI$_2$, putting
forward the coexistence of helical magnetic order and ligand spin-orbit
coupling as driving forces for multiferroic behavior in two-dimensional
materials.",2111.07909v2
2021/12/21,CrSbSe3: a pseudo one-dimensional ferromagnetic semiconductor,"Low-dimensional magnetic materials have attracted much attention due to their
novel properties and high potential for spintronic applications. In this work,
we study the electronic structure and magnetic properties of the pseudo
one-dimensional compound CrSbSe$_3$, using density functional calculations,
superexchange model analyses, and Monte Carlo simulations. We find that
CrSbSe$_3$ is a ferromagnetic (FM) semiconductor with a band gap of about 0.65
eV. The FM couplings within each zig-zag spin chain are due to the Cr-Se-Cr
superexchange with the near-90$^\circ$ bonds, and the inter-chain FM couplings
are one order of magnitude weaker. By inclusion of the spin-orbit coupling
(SOC) effects, our calculations reproduce the experimental observation of the
easy magnetization $a$ axis and the hard $b$ axis (the spin-chain direction),
with the calculated moderate magnetic anisotropy of 0.19 meV/Cr. Moreover, we
identify the nearly equal contributions from the single ion anisotropy of Cr,
and from the exchange anisotropy due to the strong SOC of the heavy elements Sb
and Se and their couplings with Cr. Using the parameters of the magnetic
coupling and anisotropy from the above calculations, our Monte Carlo
simulations yield the Curie temperature $T_{\rm{C}}$ of 108 K.",2112.10937v1
2022/1/10,A Perspective on Electrical Generation of Spin Current for Magnetic Random Access Memories,"Spin currents are used to write information in magnetic random access memory
(MRAM) devices by switching the magnetization direction of one of the
ferromagnetic electrodes of a magnetic tunnel junction (MTJ) nanopillar.
Different physical mechanisms of conversion of charge current to spin current
can be used in 2-terminal and 3-terminal device geometries. In 2-terminal
devices, charge-to-spin conversion occurs by spin filtering in the MTJ's
ferromagnetic electrodes and present day MRAM devices operate near the
theoretically expected maximum charge-to-spin conversion efficiency. In
3-terminal devices, spin-orbit interactions in a channel material can also be
used to generate large spin currents. In this perspective article, we discuss
charge-to-spin conversion processes that can satisfy the requirements of MRAM
technology. We emphasize the need to develop channel materials with larger
charge-to-spin conversion efficiency -- that can equal or exceed that produced
by spin filtering -- and spin currents with a spin polarization component
perpendicular to the channel interface. This would enable high-performance
devices based on sub-20 nm diameter perpendicularly magnetized MTJ nanopillars
without need of a symmetry breaking field. We also discuss MRAM characteristics
essential for CMOS integration. Finally, we identify critical research needs
for charge-to-spin conversion measurements and metrics that can be used to
optimize device channel materials and interface properties prior to full MTJ
nanopillar device fabrication and characterization.",2201.03671v1
2022/1/14,Enhancement of supercurrent through ferromagnetic materials by interface engineering,"Josephson junctions containing ferromagnetic materials exhibit interesting
physics and show promise as circuit elements for superconducting logic and
memory. For memory applications, the properties of the junction should be
controllable by changing the magnetic configuration inside the junction. To
achieve good magnetic switching properties, one should choose a soft magnetic
material such as NiFe (permalloy); however, NiFe exhibits poor supercurrent
transmission in Josephson junctions. In this work we put thin layers of Ni on
either side of the NiFe and characterize the magnetic behavior and supercurrent
transmission properties of the Ni/NiFe/Ni trilayers as a function of Ni and
NiFe thicknesses. Using a Ni thickness of 0.4 nm, we find that the magnetic
switching behavior of the trilayers is not severely degraded relative to plain
NiFe, while the maximum supercurrent in the $\pi$-state of the trilayer
Josephson junctions is increased by a factor of four relative to that of NiFe
junctions. We speculate that the supercurrent enhancement is due to the
different spin-dependent transport properties of the Cu/Ni and Cu/NiFe
interfaces.",2201.05444v4
2022/4/29,Site-specific electronic and magnetic excitations of the skyrmion material Cu$_2$OSeO$_3$,"The manifestation of skyrmions in the Mott-insulator Cu$_2$OSeO$_3$
originates from a delicate balance between magnetic and electronic energy
scales. As a result of these intertwined couplings, the two
symmetry-inequivalent magnetic ions, Cu-I and Cu-II, bond into a spin S=1
entangled tetrahedron. However, conceptualizing the unconventional properties
of this material and the energy of the competing interactions is a challenging
task due the complexity of this system. Here we combine X-ray Absorption
Spectroscopy and Resonant Inelastic X-ray Scattering to uncover the electronic
and magnetic excitations of Cu$_2$OSeO$_3$ with site-specificity. We quantify
the energies of the 3d crystal-field splitting for both Cu-I and Cu-II,
fundamental to optimize model Hamiltonians. Additionally, we unveil a
site-specific magnetic mode, indicating that individual spin character is
preserved within the entangled-tetrahedron picture. Our results thus provide
experimental constraint for validating theories that describe the interactions
of Cu$_2$OSeO$_3$, highlighting the site-selective capabilities of resonant
spectroscopies",2204.14209v1
2022/5/13,Rare-earth monopnoctides -- family of antiferromagnets hosting magnetic Fermi arcs,"Since the discovery of topological insulators a lot of research effort has
been devoted to magnetic topological materials, in which non-trivial spin
properties can be controlled by magnetic fields, culminating in a wealth of
fundamental phenomena and possible applications. The main focus was on
ferromagnetic materials that can host Weyl fermions and therefore spin textured
Fermi arcs. The recent discovery of Fermi arcs and new magnetic bands splitting
in antiferromagnet (AFM) NdBi has opened up new avenues for exploration. Here
we show that these uncharted effects are not restricted to this specific
compound, but rather emerge in CeBi, NdBi, and NdSb when they undergo
paramagnetic to AFM transition. Our data show that the Fermi arcs in NdSb have
2-fold symmetry, leading to strong anisotropy that may enhance effects of spin
textures on transport properties. Our findings thus demonstrate that the RBi
and RSb series are materials that host magnetic Fermi arcs and may be a
potential platform for modern spintronics.",2205.06693v1
2022/9/14,Tuning magnetoelectricity in a mixed-anisotropy antiferromagnet,"Control of magnetization and electric polarization is attractive in relation
to tailoring materials for data storage and devices such as sensors or
antennae. In magnetoelectric materials, these degrees of freedom are closely
coupled, allowing polarization to be controlled by a magnetic field, and
magnetization by an electric field, but the magnitude of the effect remains a
challenge in the case of single-phase magnetoelectrics for application. We
demonstrate that the magnetoelectric properties of the mixed-anisotropy
antiferromagnet LiNi$_{1-x}$Fe$_x$PO$_4$ are profoundly affected by replacing a
fraction of the Ni$^{2+}$ ions with Fe$^{2+}$ on the transition metal site.
This introduces random site-dependent single-ion anisotropy energies and causes
a lowering of the magnetic symmetry of the system. In turn, magnetoelectric
couplings that are symmetry-forbidden in the parent compounds, LiNiPO$_4$ and
LiFePO$_4$, are unlocked and the dominant coupling is enhanced by two orders of
magnitude. Our results demonstrate the potential of mixed-anisotropy magnets
for tuning magnetoelectric properties.",2209.06702v1
2022/9/29,Site-specific atomic substitution in a giant magnetocaloric Fe$_2$P-type system,"Giant magnetocaloric (GMC) materials constitute a requirement for near room
temperature magnetic refrigeration. (Fe,Mn)$_2$(P,Si) is a GMC compound with
strong magnetoelastic coupling. The main hindrance towards application of this
material is a comparably large temperature hysteresis, which can be reduced by
metal site substitution with a nonmagnetic element. However, the
(Fe,Mn)$_2$(P,Si) compound has two equally populated metal sites, the
tetrahedrally coordinated $3f$ and the pyramidally coordinated $3g$ sites. The
magnetic and magnetocaloric properties of such compounds are highly sensitive
to the site specific occupancy of the magnetic atoms. Here we have attempted to
study separately the effect of $3f$ and $3g$ site substitution with equal
amounts of vanadium. Using formation energy calculations, the site preference
of vanadium and its influence on the magnetic phase formation are described. A
large difference in the isothermal entropy change (as high as 44\%) with
substitution in the $3f$ and $3g$ sites is observed. The role of the lattice
parameter change with temperature and the strength of the magnetoelastic
coupling on the magnetic properties are highlighted.",2209.14962v1
2022/10/25,Topological phase transitions and Berry-phase hysteresis in exchange-coupled nanomagnets,"Topological phase in magnetic materials yields a quantized contribution to
the Hall effect known as the topological Hall effect, which is often caused by
skyrmions, with each skyrmion creating a magnetic flux quantum h/e. The control
and understanding of topological properties in nanostructured materials is the
subject of immense interest for both fundamental science and technological
applications, especially in spintronics. In this work, the electron-transport
properties and spin structure of exchange-coupled cobalt nanoparticles with an
average particle size of 13.7 nm are studied experimentally and theoretically.
Magnetic and Hall-effect measurements identify topological phase transitions in
the exchange-coupled cobalt nanoparticles and were used to discover a
qualitatively new type of hysteresis in the topological Hall effect namely,
Berry-phase hysteresis. Micromagnetic simulations reveal the origin of the
topological Hall effect namely, the chiral domains, with domain-wall chirality
quantified by an integer skyrmion number. These spin structures are different
from the skyrmions formed due to Dzyaloshinskii Moriya interactions in B20
crystals and multilayered thin films, and caused by cooperative magnetization
reversal in the exchange-coupled cobalt nanoparticles. An analytical model is
developed to explain the underlying physics of Berry-phase hysteresis, which is
strikingly different from the iconic magnetic hysteresis and constitutes one
aspect of 21st-century reshaping of our view on nature at the borderline of
physics, chemistry, mathematics, and materials science.",2210.14291v1
2022/11/16,Spin-Reorientation-Driven Linear Magnetoelectric Effect in Topological Antiferromagnet Cu$_3$TeO$_6$,"The search for new materials for energy-efficient electronic devices has
gained unprecedented importance. Among the various classes of magnetic
materials driving this search are antiferromagnets, magnetoelectrics, and
systems with topological spin excitations. Cu$_3$TeO$_6$ is a material that
belongs to all three of these classes. Combining static electric polarization
and magnetic torque measurements with phenomenological simulations we
demonstrate that magnetic-field-induced spin reorientation needs to be taken
into account to understand the linear magnetoelectric (ME) effect in
Cu$_3$TeO$_6$. Our calculations reveal that the magnetic field pushes the
system from the nonpolar ground state to the polar magnetic structures.
However, nonpolar structures only weakly differing from the obtained polar ones
exist due to the weak effect that the field-induced breaking of some symmetries
has on the calculated structures. Among those symmetries is the $PT$
($\overline{1}'$) symmetry, preserved for Dirac points found in Cu$_3$TeO$_6$.
Our findings establish Cu$_3$TeO$_6$ as a promising playground to study the
interplay of spintronics-related phenomena.",2211.08902v2
2023/1/18,Emergence of field-induced memory effect in spin ices,"Out-of-equilibrium investigation of strongly correlated materials deciphers
the hidden equilibrium properties. Herein, we have investigated the
out-of-equilibrium magnetic properties of polycrystalline Dy2Ti2O7 and Ho2Ti2O7
spin ices. The experimental results show the emergence of magnetic
field-induced anomalous hysteresis observed only in temperature/magnetic
field-dependent ac susceptibility measurements. The observed memory effect
(anomalous thermomagnetic hysteresis) strongly depends on the driving thermal
and non-thermal variables. Contrary, in the absence of the magnetic field,
dipolar interaction induced Ising paramagnetic to spin ice crossover develops a
liquid-gas transition type hysteresis below 4 K. Unlike field-induced
hysteresis, it shows weak dependency on thermal and non-thermal variables. Due
to the non-colinear spin structure, the applied dc bias magnetic field produces
quench disorder sites in the cooperative Ising spin matrix and suppresses the
spin-phonon coupling. These quench disorders create dynamic spin correlations
governed by quantum fluctuations, having slow spin relaxation and quick decay
times, which additionally contribute to ac susceptibility. The initial
conditions and measurement protocol decide the magnitude and sign of this
dynamical term contributing to ac susceptibility. It has been suggested that
such kind of out-of-equilibrium properties emerge by the cumulative effect of
geometric frustration, disorder, quantum fluctuations, and the cooperative
nature of spin dynamics of these materials.",2301.07741v1
2023/3/1,"The ""Sign problem"" of the 3rd order anomalous Hall effect in topological magnetic materials","The anomalous Hall effect (AHE), which provides a bridgeway between the
geometry of quantum wavefunctions and transport measurements, has been a key
focus of intensive studies. In addition to the well-studied linear AHE,
governed by the electronic Berry curvature, nonlinear AHE originated from
higher-order Berry-curvature multipoles has also been observed in recent
studies. Inspired by the 3rd order AHE and its room temperature sign switching
in kagome antiferromagnet FeSn [S. Sankar, R. Liu, X. Gao, et al, to be
published (2023)], we investigate the generic sign structure of Berry-curvature
induced 3rd order AHE in topological magnetic material. We find that in
contrast to the linear Hall coefficient, whose sign is determined by the broken
time-reversal symmetry, the sign of the 3rd order Hall coefficient is dictated
by the interplay between time-reversal symmetry breaking, magnetic order, and
spin-orbit couplings. Our calculations give a possible solution for the ""sign
problem"" of the 3rd order AHE response in the phase space spanned by the in-
and out-of-plane magnetization, the spin-orbital coupling strength and chemical
potential. We further propose realistic experiment setups to systematically
reveal the sign structure in the 3rd order AHE response via continuously
rotating the magnetic field directions.",2303.00819v2
2023/3/8,Spin-valve nature and giant coercivity of a ferrimagnetic spin semimetal Mn$_2$IrGa,"Spin semimetals are amongst the most recently discovered new class of
spintronic materials, which exhibit a band gap in one spin channel and
semimetallic feature in the other, thus facilitating tunable spin transport.
Here, we report Mn$_2$IrGa to be a candidate material for spin semimetal along
with giant coercivity and spin-valve characteristics using a combined
experimental and theoretical study. The alloy crystallizes in an inverse
Heusler structure (without any martensitic transition) with a para- to
ferri-magnetic transition at $T_\mathrm{C} \sim$ 243 K. It shows a giant
coercive field of about 8.5 kOe (at 2 K). The negative temperature coefficient,
relatively low magnitude and weak temperture dependance of electrical
resistivity suggest the semimetallic character of the alloy. This is further
supported by our specific heat measurement. Magnetoresistance (MR) confirms an
irreversible nature (with its magnitude $\sim$1\%) along with a change of sign
across the magnetic transition indicating the potentiality of Mn$_2$IrGa in
magnetic switching applications. In addition, asymmetric nature of MR in the
positive and negative field cycles is indicative of spin-valve characteristics.
Our ab-initio calculations confirm the inverse Heusler structure with
ferrimagnetic ordering to be the lowest energy state, with a saturation
magnetization of 2 $\mu_\mathrm{B}$. $<100>$ is found to be the easy magnetic
axis with considerable magneto-crystalline anisotropy energy. A large positive
Berry flux at/around $\Gamma$ point gives rise to an appreciable anomalous Hall
conductivity ($\sim$-180 S/cm).",2303.04649v2
2023/3/20,NiSi: New venue for antiferromagnetic spintronics,"Envisaging antiferromagnetic spintronics pivots on two key criteria of high
transition temperature and tuning of underlying magnetic order using
straightforward application of magnetic field or electric current. Here, we
show that NiSi metal can provide suitable new platform in this quest. First,
our study unveils high temperature antiferromagnetism in single crystal NiSi
with $T_{N} \geq 700$ K. Antiferromagnetic order in NiSi is accompanied by the
non-centrosymmetric magnetic character with small ferromagnetic component in
a-c plane. Second, we find that NiSi manifests distinct magnetic and electronic
hysteresis responses to field applications due to the disparity in two moment
directions. While magnetic hysteresis is characterized by one-step switching
between ferromagnetic states of uncompensated moment, electronic behavior is
ascribed to metamagnetic switching phenomena between non-collinear spin
configurations. Importantly, the switching behaviors persist to high
temperature. The properties underscore the importance of NiSi in the pursuit of
antiferromagnetic spintronics.",2303.11387v1
2023/4/11,Additive manufacturing of Ni-Mn-Sn shape memory Heusler alloy -- Microstructure and magnetic properties from powder to printed parts,"Ni-Mn-based Heusler alloys like Ni-Mn-Sn show an elastocaloric as well as
magnetocaloric effect during the magneto-structural phase transition, making
this material interesting for solid-state cooling application. Material
processing by additive manufacturing can overcome difficulties related to
machinability of the alloys, caused by their intrinsic brittleness. Since the
magnetic properties and transition temperature are highly sensitive to the
chemical composition, it is essential to understand and monitoring these
properties over the entire processing chain. In the present work the
microstructural and magnetic properties from gas-atomized powder to
post-processed Ni-Mn-Sn alloy are investigated. Direct energy deposition was
used for processing, promoting the evolution of a polycrystalline
microstructure being characterized by elongated grains along the building
direction. A complete and sharp martensitic transformation can be achieved
after applying a subsequent heat treatment at 1173 K for 24 h. The
Mn-evaporation of 1.3 at. % and the formation of Mn-oxide during DED-processing
lead to an increase of the transition temperature of 45 K and a decrease of
magnetization, clearly pointing at the necessity of controlling the
composition, oxygen partial pressure and magnetic properties over the entire
processing chain.",2304.05383v1
2023/4/25,Spin-liquid-like state in a square lattice antiferromagnet,"Collective behavior of spins, frustration-induced strong quantum fluctuations
and subtle interplay between competing degrees of freedom in quantum materials
can lead to correlated quantum states with fractional excitations that are
essential ingredients for establishing paradigmatic models and have immense
potential for quantum technologies. Quenched randomness is a new paradigm in
elucidating the emergence of spin-liquidlike states in geometrically frustrated
magnets. Herein, we report magnetization, specific heat, electron spin
resonance, and muon spin resonance studies on a 3d-electron-based square
lattice antiferromagnet Sr3CuTa2O9. In this material, S = 1/2 Cu2+
nearest-neighbor ions constitute a two-dimensional square lattice. The negative
value of Curie-Weiss temperature, obtained from the Curie-Weiss fit of
high-temperature magnetic susceptibility data indicates the presence of
antiferromagnetic interaction between Cu2+ moments. Specific heat data show the
absence of long-range magnetic ordering down to 64 mK despite a reasonably
strong exchange interaction between Cu2+ spins as reflected from a Curie-Weiss
temperature of -27 K. The power-law behavior and the data collapse of specific
heat and magnetization data evince the emergence of a random-singlet state in
Sr3CuTa2O9. The power-law-like spin auto-correlation function and the data
collapse of muon polarization asymmetry with longitudinal field dependence of
t/({\mu}0H){\gamma} further support credence to the presence of a
randomness-induced liquid-like state. Our results suggest that randomness
induced by disorder is a viable route to realize quantum spin liquid-like state
in this square lattice antiferromagnet.",2304.13116v1
2023/6/29,High-throughput design of all-d-metal Heusler alloys for magnetocaloric applications,"Due to their versatile composition and customizable properties, A$_2$BC
Heusler alloys have found applications in magnetic refrigeration, magnetic
shape memory effects, permanent magnets, and spintronic devices. The discovery
of all-$d$-metal Heusler alloys with improved mechanical properties compared to
those containing main group elements, presents an opportunity to engineer
Heuslers alloys for energy-related applications. Using high-throughput density
functional theory calculations, we screened magnetic all-$d$-metal Heusler
compounds and identified 686 (meta)stable compounds. Our detailed analysis
revealed that the inverse Heusler structure is preferred when the
electronegativity difference between the A and B/C atoms is small, contrary to
conventional Heusler alloys. Additionally, our calculations of Pugh ratios and
Cauchy pressures demonstrated that ductile and metallic bonding are widespread
in all-$d$-metal Heuslers, supporting their enhanced mechanical behaviour. We
identified 49 compounds with a double-well energy surface based on Bain path
calculations and magnetic ground states, indicating their potential as
candidates for magnetocaloric and shape memory applications. Furthermore, by
calculating the free energies, we propose that 11 compounds exhibit structural
phase transitions, and propose isostructural substitution to enhance the
magnetocaloric effect.",2306.17092v1
2023/7/20,Triple-Well Charge Density Wave Transition Driven by Cooperation between Peierls-like Effect and Antiferromagnetic Order in FeGe,"Kagome materials provide a promising platform to explore intriguing
correlated phenomena including magnetism, charge density wave (CDW), and
nontrivial band topology. Recently, a CDW order was observed in
antiferromagnetic kagome metal FeGe, sparking enormous research interests in
intertwining physics of CDW and magnetism. Two of the core questions are (i)
what are the driving forces of the CDW transition in FeGe and (ii) whether
magnetism play a critical role in the transition. Such questions are critical
as conventional mechanisms of van Hove singularities and Fermi surface nesting
fail to explain the stable pristine phase, as well as the role of magnetism.
Here, supported by density functional theory and tight-binding models, we
unravel the triple-well CDW energy landscape of FeGe, indicating that both the
pristine and CDW phases are locally stable. We point out that an entire
downward shift of Ge band, instead of the previously proposed Fe bands,
competes with the lattice distortion energy, driving the triple-well CDW
transition. It is indeed a cooperation between the Peierls-like effect and the
Fermi energy pinning phenomenon, which is distinct from the conventional
Peierls effect that drives a double-well transition. Moreover, we demonstrate
that the antiferromagnetic order also plays a critical role in driving the CDW
transition, through weakening the Fe-Ge hybridization by exchange splitting and
lowering the position of Ge-bands with respect to the Fermi energy. Our work
thus not only deepens the understanding of the CDW mechanism in FeGe, but also
indicates an intertwined connection between the emergent magnetism and CDW in
kagome materials.",2307.10565v2
2023/8/15,Phases and magnetism at the microscale in compounds containing nominal Pb10-xCux(PO4)6O,"Achieving superconductivity at room temperature could lead to substantial
advancements in industry and technology. Recently, a compound known as Cu-doped
lead-apatite, Pb10-xCux(PO4)6O (0.9 < x < 1.1), referred to as ""LK-99"", has
been reported to exhibit unusual electrical and magnetic behaviors that appear
to resemble a superconducting transition above room temperature. In this work
we collected multiphase samples containing the nominal Pb10-xCux(PO4)6O phase
(no superconductivity observed in our measured samples), synthesized by three
independent groups, and studied their chemical, magnetic, and electrical
properties at the microscale to overcome difficulties in bulk measurements.
Through the utilization of optical, scanning electron, atomic force, and
scanning diamond nitrogen-vacancy microscopy techniques, we are able to
establish a link between local magnetic properties and specific microscale
chemical phases. Our findings indicate that while the Pb10-xCux(PO4)6O phase
seems to have a mixed magnetism contribution, a significant fraction of the
diamagnetic response can be attributed to Cu-rich regions (e.g., Cu2S derived
from a reagent used in the synthesis). Additionally, our electrical
measurements reveal the phenomenon of current path switch and a change in
resistance states of Cu2S. This provides a potential explanation for the
electrical behavior observed in compounds related to Pb10-xCux(PO4)6O.",2308.07800v3
2023/8/22,Dynamics of K$_2$Ni$_2$(SO$_4$)$_3$ governed by proximity to a 3D spin liquid model,"Quantum spin liquids (QSLs) have become a key area of research in magnetism
due to their remarkable properties, such as long-range entanglement, fractional
excitations, pinch-point singularities, and topologically protected phenomena.
In recent years, the search for QSLs has expanded into the three-dimensional
world, where promising features have been found in materials that form
pyrochlore and hyper-kagome lattices, despite the suppression of quantum
fluctuations due to high dimensionality. One such material is the $S = 1$
K$_2$Ni$_2$(SO$_4$)$_3$ compound, which belongs to the langbeinite family
consisting of two interconnected trillium lattices. Although magnetically
ordered, K$_2$Ni$_2$(SO$_4$)$_3$ has been found to exhibit a highly dynamical
and correlated state which can be driven into a pure quantum spin liquid under
magnetic fields of only $B \simeq 4$~T. In this article, we combine inelastic
neutron scattering measurements with pseudo-fermion functional renormalization
group (PFFRG) and classical Monte Carlo (cMC) calculations to study the
magnetic properties of K$_2$Ni$_2$(SO$_4$)$_3$, revealing a high level of
agreement between the experiment and theory. We further reveal the origin of
the dynamical state in K$_2$Ni$_2$(SO$_4$)$_3$ by studying a larger set of
exchange parameters, uncovering an `island of liquidity' around a focal point
given by a magnetic network composed of tetrahedra on a trillium lattice.",2308.11746v1
2023/8/17,Ferromagnetic and insulating behavior in both half magnetic levitation and non-levitation LK-99 like samples,"Finding materials exhibiting superconductivity at room temperature has long
been one of the ultimate goals in physics and material science. Recently,
room-temperature superconducting properties have been claimed in a copper
substituted lead phosphate apatite (Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O, or called
LK-99) [1-3]. Using a similar approach, we have prepared LK-99 like samples and
confirmed the half-levitation behaviors in some small specimens under the
influence of a magnet at room temperature. To examine the magnetic properties
of our samples, we have performed systematic magnetization measurements on the
as-grown LK-99-like samples, including the half-levitated and non-levitated
samples. The magnetization measurements show the coexistence of
soft-ferromagnetic and diamagnetic signals in both half-levitated and
non-levitated samples. The electrical transport measurements on the as-grown
LK-99-like samples including both half-levitated and non-levitated samples show
an insulating behavior characterized by the increasing resistivity with the
decreasing temperature.",2308.11768v2
2023/9/24,Approaching Ferrite-Based Exchange-Coupled Nanocomposites as Permanent Magnets,"During the past decade, CoFe2O4 (hard)/Co-Fe alloy (soft) magnetic
nanocomposites have been routinely prepared by partial reduction of CoFe2O4
nanoparticles. Monoxide (i.e., FeO or CoO) has often been detected as a
byproduct of the reduction, although it remains unclear whether the formation
of this phase occurs during the reduction itself or at a later stage. Here, a
novel reaction cell was designed to monitor the reduction in situ using
synchrotron powder X-ray diffraction (PXRD). Sequential Rietveld refinements of
the in situ data yielded time-resolved information on the sample composition
and confirmed that the monoxide is generated as an intermediate phase. The
macroscopic magnetic properties of samples at different reduction stages were
measured by means of vibrating sample magnetometry (VSM), revealing a magnetic
softening with increasing soft phase content, which was too pronounced to be
exclusively explained by the introduction of soft material in the system. The
elemental compositions of the constituent phases were obtained from joint
Rietveld refinements of ex situ high-resolution PXRD and neutron powder
diffraction (NPD) data. It was found that the alloy has a tendency to emerge in
a Co-rich form, inducing a Co deficiency on the remaining spinel phase, which
can explain the early softening of the magnetic material.",2309.13729v1
2023/12/30,Strain induced electronic and magnetic transition in S = 3/2 antiferromagnetic spin chain compound LaCrS3,"Exploring the physics of low-dimensional spin systems and their
pressure-driven electronic and magnetic transitions are thriving research field
in modern condensed matter physics. In this context, recently antiferromagnetic
Cr-based compounds such as CrI3, CrBr3, CrGeTe3 have been investigated
experimentally and theoretically for their possible spintronics applications.
Motivated by the fundamental and industrial importance of these materials, we
theoretically studied the electronic and magnetic properties of a relatively
less explored Cr-based chalcogenide, namely LaCrS3 where 2D layers of magnetic
Cr3+ ions form a rectangular lattice. We employed density functional theory +
Hubbard U approach in conjunction with constrained random-phase approximation
(cRPA) where the later was used to estimate the strength of U. Our findings at
ambient pressure show that the system exhibits semiconducting antiferromagnetic
ground state with a gap of 0.5 eV and large Cr moments that corresponds to
nominal S=3/2 spin-state. The 1st nearest neighbor (NN) interatomic exchange
coupling (J1) is found to be strongly antiferromagnetic (AFM), while 2nd NN
couplings are relatively weaker ferromagnetic (FM), making this system a
candidate for 1D non-frustrated antiferromagnetic spin-chain family of
materials. Based on orbital resolved interactions, we demonstrated the reason
behind two different types of interactions among 1st and 2nd NN despite their
very similar bond lengths. We observe a significant spin-orbit coupling effect,
giving rise to a finite magneto crystalline anisotropy, and
Dzyaloshinskii-Moriya (DM) interaction. Further, we found that by applying
uniaxial tensile strain along crystallographic a and b-axis, LaCrS3 exhibits a
magnetic transition to a semi-conducting FM ground state, while compression
gives rise to the realization of novel gapless semiconducting antiferromagnetic
ground state.",2401.00239v1
2024/1/9,"Monolayer Fe$_{3}$GaX$_{2}$ (X=I, Br, Sb): high-temperature two-dimensional magnets and a novel partially ordered spin state","We systematically investigated the effects of charge doping and strain on
monolayer Fe$_3$GaTe$_2$, and proposed three new novel two-dimensional magnetic
materials: monolayer Fe$_3$GaX$_2$ (X=I, Br, Sb). We found that both strain and
charge doping can tune the magnetic interactions, and the tuning by charge
doping is more significant. Differential charge analysis revealed that the
doped charges predominantly accumulate around Te atoms. Based on this insight,
we introduced Fe$_{3}$GaI$_{2}$, Fe$_{3}$GaBr$_{2}$, and Fe$_{3}$GaSb$_{2}$
monolayers. The Fe$_{3}$GaI$_{2}$ and Fe$_{3}$GaBr$_{2}$ monolayers contain I
and Br atoms rather than Te atoms, emulate electron-doped Fe$_{3}$GaTe$_{2}$
monolayer, resulting in notably high T$_c$ values of 867 K and 844 K,
respectively. In contrast, the Fe$_3$GaSb$_2$ monolayer mimics hole-doped
Fe$_{3}$GaTe$_{2}$ monolayer, presents a mix of FM and antiferromagnetic
interactions, manifesting a distinctive partially ordered magnetic state. Our
study demonstrates that substitution atoms based on the charge-doping effect
offer a promising approach for predicting new magnetic materials. The proposed
Fe$_{3}$GaI$_{2}$, Fe$_{3}$GaBr$_{2}$, and Fe$_{3}$GaSb$_{2}$ monolayers hold
great potential for spintronics applications, and may stimulate the pursuit of
new types of spin liquid.",2401.04399v1
2013/3/25,"Polaron-like vortices, dissociation transition and self induced pinning in magnetic superconductors","In magnetic superconductors vortices polarize spins nonuniformly and
repolarize them when moving. At a low spin relaxation rate and at low bias
currents vortices carrying magnetic polarization clouds become polaron-like and
their velocities are determined by the effective drag coefficient which is
significantly bigger than the Bardeen-Stephen (BS) one. As current increases,
vortices release polarization clouds and the velocity as well as the voltage in
the I-V characteristics jump to values corresponding to the BS drag coefficient
at a critical current $J_c$. The nonuniform components of the magnetic field
and magnetization drop as velocity increases resulting in weaker polarization
and {\it discontinuous} dynamic dissociation depinning transition.
Experimentally the jump shows up as a depinning transition and the
corresponding current at the jump is the depinning current. As current
decreases, on the way back, vortices are retrapped by polarization clouds at
the current $J_r<J_c$. As a result, polaronic effect suppresses dissipation and
enhances critical current. Borocarbides (RE)Ni$_2$B$_2$C with a short
penetration length and highly polarizable rare earth spins seem to be optimal
systems for a detailed study of vortex polaron formation by measuring I-V
characteristics. We propose also to use superconductor-magnet multilayer
structure to study polaronic mechanism of pinning with the goal to achieve high
critical currents. The magnetic layers should have large magnetic
susceptibility to enhance the coupling between vortices and magnetization in
magnetic layers while the relaxation of the magnetization should be slow. For
Nb and proper magnet multilayer structure, we estimate the critical current
density $J_c\sim 10^{9}\ \rm{A/m^2}$ at magnetic field $B\approx 1$ T.",1303.6184v1
2013/4/11,Magnetic Anisotropy of Single Mn Acceptors in GaAs in an External Magnetic Field,"We investigate the effect of an external magnetic field on the physical
properties of the acceptor hole states associated with single Mn acceptors
placed near the (110) surface of GaAs. Crosssectional scanning tunneling
microscopy images of the acceptor local density of states (LDOS) show that the
strongly anisotropic hole wavefunction is not significantly affected by a
magnetic field up to 6 T. These experimental results are supported by
theoretical calculations based on a tightbinding model of Mn acceptors in GaAs.
For Mn acceptors on the (110) surface and the subsurfaces immediately
underneath, we find that an applied magnetic field modifies significantly the
magnetic anisotropy landscape. However the acceptor hole wavefunction is
strongly localized around the Mn and the LDOS is quite independent of the
direction of the Mn magnetic moment. On the other hand, for Mn acceptors placed
on deeper layers below the surface, the acceptor hole wavefunction is more
delocalized and the corresponding LDOS is much more sensitive on the direction
of the Mn magnetic moment. However the magnetic anisotropy energy for these
magnetic impurities is large (up to 15 meV), and a magnetic field of 10 T can
hardly change the landscape and rotate the direction of the Mn magnetic moment
away from its easy axis. We predict that substantially larger magnetic fields
are required to observe a significant field-dependence of the tunneling current
for impurities located several layers below the GaAs surface.",1304.3303v2
2017/6/25,"Magnetic anisotropy of $L1_0$-ordered FePt thin films studied by Fe and Pt $L_{2,3}$-edges x-ray magnetic circular dichroism","The strong perpendicular magnetic anisotropy of $L{\rm1_0}$-ordered FePt has
been the subject of extensive studies for a long time. However, it is not known
which element, Fe or Pt, mainly contributes to the magnetic anisotropy energy
(MAE). We have investigated the anisotropy of the orbital magnetic moments of
Fe 3$d$ and Pt 5$d$ electrons in $L{\rm1_0}$-ordered FePt thin films by Fe and
Pt $L_{2,3}$-edge x-ray magnetic circular dichroism (XMCD) measurements for
samples with various degrees of long-range chemical order $S$. Fe
$L_{2,3}$-edge XMCD showed that the orbital magnetic moment was larger when the
magnetic field was applied perpendicular to the film than parallel to it, and
that the anisotropy of the orbital magnetic moment increased with $S$. Pt
$L_{2,3}$-edge XMCD also showed that the orbital magnetic moment was smaller
when the magnetic field was applied perpendicular to the film than parallel to
it, opposite to the Fe $L_{2,3}$-edge XMCD results although the anisotropy of
the orbital magnetic moment increases with $S$ like the Fe edge. These results
are qualitatively consistent with the first-principles calculation by Solovyev
${\it et\ al.}$ [Phys. Rev. B $\bf{52}$, 13419 (1995).], which also predicts
the dominant contributions of Pt 5$d$ to the magnetic anisotropy energy rather
than Fe 3$d$ due to the strong spin-orbit coupling and the small spin splitting
of the Pt 5$d$ bands in $L{\rm1_0}$-ordered FePt.",1706.08183v1
2019/11/4,Signatures of low-dimensional magnetism and short-range magnetic order in Co-based trirutiles,"Features of low dimensional magnetism resulting from a square-net arrangement
of Co atoms in trirutile CoTa$_2$O$_6$ is studied in the present work by means
of density functional theory and is compared with the experimental results of
specific heat and neutron diffraction. The small total energy differences
between the ferromagnetic (FM) and antiferromagnetic (AFM) configuration of
CoTa$_2$O$_6$ shows that competing magnetic ground states exist, with the
possibility of transition from FM to AFM phase at low temperature. Our
calculation further suggests the semi-conducting behavior for CoTa$_2$O$_6$
with a band gap of $\sim$0.41 eV. The calculated magnetic anisotropy energy is
$\sim$2.5 meV with its easy axis along the [100] (in-plane) direction. Studying
the evolution of magnetism in Co$_{1-x}$Mg$_x$Ta$_2$O$_6$ (x = 0, 0.1, 0.3,
0.5, 0.7 and 1). it is found that the sharp AFM transition exhibited by
CoTa$_2$O$_6$ at $T_N$ = 6.2 K in its heat capacity vanishes with Mg-dilution,
indicating the obvious effect of weakening the superexchange pathways of Co.
The current specific heat study reveals the robust nature of $T_N$ for
CoTa$_2$O$_6$ in applied magnetic fields. Clear indication of short-range
magnetism is obtained from the magnetic entropy, however, diffuse components
are absent in neutron diffraction data. At $T_N$, CoTa$_2$O$_6$ enters a
long-range ordered magnetic state which can be described using a propagation
vector, (1/4, 1/4, 0). Upon Mg-dilution at $x \geq$0.1, the long-range ordered
magnetism is destroyed. The present results should motivate an investigation of
magnetic excitations in this low-dimensional anisotropic magnet.",1911.01036v1
2020/2/6,Complex Magnetic Order in a Decorated Spin Chain System Rb$_2$Mn$_3$(MoO$_4$)$_3$(OH)$_2$,"Macroscopic magnetic properties and microscopic magnetic structure of
Rb$_2$Mn$_3$(MoO$_4$)$_3$(OH)$_2$ (space group $Pnma$) are investigated by
magnetization, heat capacity and single-crystal neutron diffraction
measurements. The compound's crystal structure contains bond-alternating
[Mn$_3$O$_{11}$]$^{\infty}$ chains along the $b$-axis, formed by isosceles
triangles of Mn ions occupying two crystallographically nonequivalent sites
(Mn1 site on the base and Mn2 site on the vertex). These chains are only weakly
linked to each other by nonmagnetic oxyanions. Both SQUID magnetometry and
neutron diffraction experiments show two successive magnetic transitions as a
function of temperature. On cooling, it transitions from a paramagnetic phase
into an incommensurate phase below 4.5~K with a magnetic wavevector near ${\bf
k}_{1} = (0,~0.46,~0)$. An additional commensurate antiferromagnetically
ordered component arises with ${\bf k}_{2} = (0,~0,~0)$, forming a complex
magnetic structure below 3.5~K with two different propagation vectors of
different stars. On further cooling, the incommensurate wavevector undergoes a
lock-in transition below 2.3~K. The experimental results suggest that the
magnetic superspace group is $Pnma.1'(0b0)s0ss$ for the single-${\bf k}$
incommensurate phase and is $Pn'ma(0b0)00s$ for the 2-${\bf k}$ magnetic phase.
We propose a simplified magnetic structure model taking into account the major
ordered contributions, where the commensurate ${\bf k}_{2}$ defines the
ordering of the $c$-axis component of Mn1 magnetic moment, while the
incommensurate ${\bf k}_{1}$ describes the ordering of the $ab$-plane
components of both Mn1 and Mn2 moments into elliptical cycloids",2002.02429v1
2020/5/26,"Outflows, cores and magnetic field orientations in W43-MM1 as seen by ALMA","It has been proposed that the magnetic field, pervasive in the ISM, plays an
important role in the process of massive star formation. To better understand
its impact at the pre and protostellar stages, high-angular resolution
observations of polarized dust emission toward a large sample of massive dense
cores are needed. To this end, we used the Atacama Large Millimeter Array in
Band 6 (1.3 mm) in full polarization mode to map the polarized emission from
dust grains at a physical scale of $\sim$2700 au in the massive protocluster
W43-MM1. We used these data to measure the orientation of the magnetic field at
the core scale. Then, we examined the relative orientations of the core-scale
magnetic field, of the protostellar outflows determined from CO molecular line
emission, and of the major axis of the dense cores determined from 2D Gaussian
fit in the continuum emission. We found that the orientation of the dense cores
is not random with respect to the magnetic field. Instead, the dense cores are
compatible with being oriented 20-50$^\deg$ with respect to the magnetic field.
The outflows could be oriented 50-70$^\deg$ with respect to the magnetic field,
or randomly oriented with respect to the magnetic field, similar to current
results in low-mass star-forming regions. In conclusion, the observed alignment
of the position angle of the cores with respect to the magnetic field lines
shows that the magnetic field is well coupled with the dense material; however,
the 20-50$^\deg$ preferential orientation contradicts the predictions of the
magnetically-controlled core-collapse models. The potential correlation of the
outflow directions with respect to the magnetic field suggests that, in some
cases, the magnetic field is strong enough to control the angular momentum
distribution from the core scale down to the inner part of the circumstellar
disks where outflows are triggered.",2005.12921v2
2020/9/17,Enhanced magnetocaloric effect and magnetic phase diagrams of single-crystal GdCrO$_3$,"The crystalline structure, magnetism, and magnetocaloric effect of a
GdCrO$_3$ single crystal grown with the laser-diode-heated floating-zone
technique have been studied. The GdCrO$_3$ single crystal crystallizes into an
orthorhombic structure with the space group $Pmnb$ at room temperature. Upon
cooling, under a magnetic field of 0.1 T, it undergoes a magnetic phase
transition at $T_{\textrm{N-Cr}} =$ 169.28(2) K with Cr$^{3+}$ ions forming a
canted antiferromagnetic (AFM) structure, accompanied by a weak ferromagnetism.
Subsequently, a spin reorientation takes place at $T_{\textrm{SR}} =$ 5.18(2) K
due to Gd$^{3+}$-Cr$^{3+}$ magnetic couplings. Finally, the long-range AFM
order of Gd$^{3+}$ ions establishes at $T_{\textrm{N-Gd}} =$ 2.10(2) K. Taking
into account the temperature-(in)dependent components of Cr$^{3+}$ moments, we
obtained an ideal model for describing the paramagnetic behavior of Gd$^{3+}$
ions within 30--140 K. We observed a magnetic reversal (positive $\rightarrow$
negative $\rightarrow$ positive) at 50 Oe with a minimum centering around 162
K. In the studied temperature range of 1.8-300 K, there exists a strong
competition between magnetic susceptibilities of Gd$^{3+}$ and Cr$^{3+}$ ions,
leading to puzzling magnetic phenomena. We have built the
magnetic-field-dependent phase diagrams of $T_{\textrm{N-Gd}}$,
$T_{\textrm{SR}}$, and $T_{\textrm{N-Cr}}$, shedding light on the nature of the
intriguing magnetism. Moreover, we calculated the magnetic entropy change and
obtained a maximum value at 6 K and ${\Delta}{\mu}_0H$ = 14 T, i.e.,
-${\Delta}S_{\textrm{M}} \approx$ 57.5 J/kg K. Among all RCrO$_3$ (R = $4f^n$
rare earths, $n =$ 7-14) compounds, the single-crystal GdCrO$_3$ compound
exhibits the highest magnetic entropy change, as well as an enhanced adiabatic
temperature, creating a prominent magnetocaloric effect for potential
application in magnetic refrigeration.",2009.08028v2
2020/11/11,Destruction of long-range magnetic order in an external magnetic field and the associated spin dynamics in Cu2GaBO5 and Cu2AlBO5 ludwigites,"The quantum spin systems Cu$_2$M'BO$_5$ (M' = Al, Ga) with the ludwigite
crystal structure consist of a structurally ordered Cu$^{2+}$ sublattice in the
form of three-leg ladders, interpenetrated by a structurally disordered
sublattice with a statistically random site occupation by magnetic Cu$^{2+}$
and nonmagnetic Ga$^{3+}$ or Al$^{3+}$ ions. A microscopic analysis based on
density-functional-theory calculations for Cu$_2$GaBO$_5$ reveals a frustrated
quasi-two-dimensional spin model featuring five inequivalent antiferromagnetic
exchanges. A broad low-temperature $^{11}$B nuclear magnetic resonance points
to a considerable spin disorder in the system. In zero magnetic field,
antiferromagnetic order sets in below $T_\text{N}$ $\approx$ 4.1 K and ~2.4 K
for the Ga and Al compounds, respectively. From neutron diffraction, we find
that the magnetic propagation vector in Cu$_2$GaBO$_5$ is commensurate and lies
on the Brillouin-zone boundary in the (H0L) plane, $\mathbf{q}_\text{m}$ =
(0.45 0 -0.7), corresponding to a complex noncollinear long-range ordered
structure with a large magnetic unit cell. Muon spin relaxation is monotonic,
consisting of a fast static component typical for complex noncollinear spin
systems and a slow dynamic component originating from the relaxation on
low-energy spin fluctuations. Gapless spin dynamics in the form of a diffuse
quasielastic peak is also evidenced by inelastic neutron scattering. Most
remarkably, application of a magnetic field above 1 T destroys the static
long-range order, which is manifested in the gradual broadening of the magnetic
Bragg peaks. We argue that such a crossover from a magnetically long-range
ordered state to a spin-glass regime may result from orphan spins on the
structurally disordered magnetic sublattice, which are polarized in magnetic
field and thus act as a tuning knob for field-controlled magnetic disorder.",2011.05819v1
2023/3/21,Robust intralayer antiferromagnetism and tricriticality in a van der Waals compound: VBr3 case,"We studied magnetic states and phase transitions in the van der Waals
antiferromagnet VBr3 by specific heat and magnetization measurements of single
crystals in high magnetic fields and by ab initio density functional theory
calculations focused on exchange interactions. The magnetization behavior
resembles Ising antiferromagnets with magnetic moments kept in the out-of-plane
direction by strong uniaxial magnetocrystalline anisotropy. The out-of-plane
magnetic field induces a spin-flip metamagnetic transition, which is of
first-order type at low temperatures while at higher temperatures the
transition becomes continuous. The first-order and continuous transition
segments in the field-temperature phase diagram meet at a tricritical point at
= 12 K. The magnetization response to the in-plane field manifests a continuous
spin-flop transition, which at 2 K terminates at a field mu0Hc = 27 T that can
serve as an estimate of the anisotropy field in VBr3. The magnetization curves
above the metamagnetic transition saturate at the same value of magnetic moment
musat = 1.2 muB/f.u., which is much smaller than the spin-only (S = 1) moment
of the V3+ ion. The reduced moment can be explained by the existence of a
significant orbital magnetic moment antiparallel to the spin. The orbital
moment is a key ingredient of a mechanism responsible for the observed large
anisotropy. The exact energy evaluation of possible magnetic orders
unambiguously shows that the magnetic ground state of VBr3 is the intralayer
zigzag antiferromagnetic order that renders the antiferromagnetic ground state
significantly more stable against the spin-flip transition than the other
options. The calculations also predict that a minimal distortion of the Br ion
sublattice causes a radical change of the orbital occupation in the ground
state, connected with the formation of the orbital moment and the stability of
magnetic order.",2303.11794v2
2023/8/31,Beyond domain alignment: Revealing the effect of intrinsic magnetic order on electrochemical water splitting,"To reach a long term viable green hydrogen economy, rational design of active
oxygen evolution reaction (OER) catalysts is critical. An important hurdle in
this reaction originates from the fact that the reactants are singlet
molecules, whereas the oxygen molecule has a triplet ground state with parallel
spin alignment, implying that magnetic order in the catalyst is essential.
Accordingly, multiple experimentalists reported a positive effect of external
magnetic fields on OER activity of ferromagnetic catalysts. However, it remains
a challenge to investigate the influence of the intrinsic magnetic order on
catalytic activity. Here, we tuned the intrinsic magnetic order of epitaxial
La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ thin film model catalysts from ferro- to
paramagnetic by changing the temperature in-situ during water electrolysis.
Using this strategy, we show that ferromagnetic ordering below the Curie
temperature enhances OER activity. Moreover, we show a slight current density
enhancement upon application of an external magnetic field and find that the
dependence of magnetic field direction correlates with the magnetic anisotropy
in the catalyst film. Our work thus suggests that both the intrinsic magnetic
order in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ films and magnetic domain alignment
increase their catalytic activity. We observe no long-range magnetic order at
the catalytic surface, implying that the OER enhancement is connected to the
magnetic order of the bulk catalyst. Combining the effects found with existing
literature, we propose a unifying picture for the spin-polarized enhancement in
magnetic oxide catalysts.",2308.16654v1
2004/3/29,Stress effect on magnetoimpedance (MI) in amorphous wires at GHz frequencies and application to stress-tunable microwave composite materials,"The effect of tensile stress on magnetoimpedance (MI) in CoMnSiB amorphous
wires at microwave frequencies (0.5-3 GHz) is investigated both experimentally
and theoretically. In the presence of the dc bias magnetic field of the order
of the anisotropy field, the impedance shows very large and sensitive change
when the wire is subjected to a tensile stress: 100% and 60% per 180 MPa for
frequencies 500 MHz and 2.5 GHz, respectively. It is demonstrated that this
behavior owes mainly to the directional change in the equilibrium magnetization
caused by the applied stress and field, which agrees well with the theoretical
results for the surface impedance. This stress effect on MI is proposed to use
for creating microwave stress-tunable composite materials containing short
magnetic wires. The analysis of the dielectric response from such materials
shows that depending on the stress level in the material, the dispersion of the
effective permittivity can be of a resonant or relaxation type with a
considerable change in its values (up to 100% at 600 MPa). This media can be
used for structural stress monitoring by microwave contrast imaging.",0403708v3
2006/2/21,Alignment of Carbon Nanotube Additives for Improved Performance of Magnesium Diboride Superconductors,"The rapid progress on MgB2 superconductor since its discovery[1] has made
this material a strong competitor to low and high temperature superconductors
(HTS) for applications with a great potential to catch the niche market such as
in magnetic resonant imaging (MRI). Thanks to the lack of weak links and the
two-gap superconductivity of MgB2 [2,3] a number of additives have been
successfully used to enhance the critical current density, Jc and the upper
critical field, Hc2.[4-12] Carbon nanotubes (CNTs) have unusually electrical,
mechanical and thermal properties[13-16] and hence is an ideal component to
fabricate composites for improving their performance. To take advantages of the
extraordinary properties of CNTs it is important to align CNTs in the
composites. Here we report a method of alignment of CNTs in the CNT/MgB2
superconductor composite wires through a readily scalable drawing technique.
The aligned CNT doped MgB2 wires show an enhancement in magnetic Jc(H) by more
than an order of magnitude in high magnetic fields, compared to the undoped
ones. The CNTs have also significantly enhanced the heat transfer and
dissipation. CNTs have been used mainly in structural materials, but here the
advantage of their use in functional composites is shown and this has wider
ramifications for other functional materials.",0602484v1
2006/2/27,Ferromagnetic Wires Composite Media with Tunable Scattering Spectra at Microwaves,"We demonstrate composite media with ferromagnetic wires that exhibit a
frequency region at the microwave regime with scattering spectra strongly
dependent on an external magnetic field or stress. These tunable composite
materials have recently been proposed theoretically; however, no direct
experimental verification has been reported. We used composite materials with
predominantly oriented CoFeCrSiB glass-coated amorphous wires having large
magnetoimpedance at GHz frequencies. The free space measurements of reflection
and transmission coefficients were conducted in the frequency range 1-8 GHz in
the presence of an external static magnetic field or stress applied to the
whole sample. In general, the transmission spectra show greater changes in the
range of 10dB for a relatively small magnetic field of few Oe or stress of 0.1
MPa. The obtained results are quantitatively consistent with the analytical
expressions predicted by the effective medium arguments. The incident
electromagnetic wave induces an electrical dipole moment in each wire, the
aggregate of which forms the effective dipole response of the whole composite
structure in the radiative near or far field region. The field and stress
dependences of the effective response arise from a field or tensile stress
sensitivity of the ac surface impedance of a ferromagnetic wire. In the
vicinity of the antenna resonance the variations in the magneto-impedance of
the wire inclusions result in large changes of the total effective response. A
number of applications of proposed materials is discussed including the field
tunable microwave surfaces and the self-sensing media for the remote
non-destructive evaluation of structural materials.",0602644v2
2010/12/9,Unified picture for diluted magnetic semiconductors,"For already a decade the field of diluted magnetic semiconductors (DMS) is
one of the hottest. In spite of the great success of material specific Density
Functional Theory (DFT) to provide accurately critical Curie temperatures
($T_{C}$) in various III-V based materials, the ultimate search for a unifying
model/theory was still an open issue. Many crucial questions were still without
answer, as for example: Why, after one decade, does GaMnAs still exhibit the
highest $T_{C}$? Is there any intrinsic limitations or any hope to reach room
temperature? How to explain in a unique theory the proximity of GaMnAs to the
metal-insulator transition, and the change from RKKY couplings in II-VI
materials to the double exchange regime in GaMnN? The aim of the present work
is to provide this missing theory. We will show that the key parameter is the
position of the Mn level acceptor and that GaMnAs has the highest $T_{C}$ among
III-V DMS. Our theory (i) provides an overall understanding, (ii) is
quantitatively consistent with existing DFT based studies, (iii) able to
explain both transport and magnetic properties in a broad variety of DMS and
(iv) reproduces the $T_{C}$ obtained from first principle studies for many
materials including both GaMnN and GaMnAs. The model also reproduces accurately
recent experimental data of the optical conductivity of GaMnAs and predicts
those of other materials.",1012.1983v1
2015/6/30,Nanoscale $β$-Nuclear Magnetic Resonance Depth Imaging of Topological Insulators,"Considerable evidence suggests that variations in the properties of
topological insulators (TIs) at the nanoscale and at interfaces can strongly
affect the physics of topological materials. Therefore, a detailed
understanding of surface states and interface coupling is crucial to the search
for and applications of new topological phases of matter. Currently, no methods
can provide depth profiling near surfaces or at interfaces of topologically
inequivalent materials. Such a method could advance the study of interactions.
Herein we present a non-invasive depth-profiling technique based on $\beta$-NMR
spectroscopy of radioactive $^8$Li$^+$ ions that can provide ""one-dimensional
imaging"" in films of fixed thickness and generates nanoscale views of the
electronic wavefunctions and magnetic order at topological surfaces and
interfaces. By mapping the $^8$Li nuclear resonance near the surface and 10 nm
deep into the bulk of pure and Cr-doped bismuth antimony telluride films, we
provide signatures related to the TI properties and their topological
non-trivial characteristics that affect the electron-nuclear hyperfine field,
the metallic shift and magnetic order. These nanoscale variations in
$\beta$-NMR parameters reflect the unconventional properties of the topological
materials under study, and understanding the role of heterogeneities is
expected to lead to the discovery of novel phenomena involving quantum
materials.",1506.08940v1
2016/2/24,The emergence of giant multicaloric phenomena near room temperature,"Caloric responses (temperature changes) can be induced in solid-state
materials by applying external stimuli such as stress, pressure, and electric
and magnetic fields. The magnetic-field-stimulated response is called the
magnetocaloric effect, and materials that exhibit this property have long been
sought for applications in room temperature magnetic cooling due to their
potentially superior efficiency and low impact on the environment. Other
solid-state caloric phenomena are less developed, but are likewise under
intense investigation. Here we introduce a new material that not only displays
giant barocaloric (hydrostatic-pressure-induced) properties, but also a large
magnetocaloric response near room temperature. It is unprecedented that two
caloric effects of such extreme magnitude occur in the same material and at the
same temperature. These effects originate from a magnetostructural transition
and a magneto-volume (magnetostriction) effect where the volume change is large
enough to force the system from a localized ordered state into an itinerant
paramagnetic state.",1602.07584v1
2018/6/21,Quantum Transport and Band Structure Evolution under High Magnetic Field in Few-Layer Tellurene,"Quantum Hall effect (QHE) is a macroscopic manifestation of quantized states
which only occurs in confined two-dimensional electron gas (2DEG) systems.
Experimentally, QHE is hosted in high mobility 2DEG with large external
magnetic field at low temperature. Two-dimensional van der Waals materials,
such as graphene and black phosphorus, are considered interesting material
systems to study quantum transport, because it could unveil unique host
material properties due to its easy accessibility of monolayer or few-layer
thin films at 2D quantum limit. Here for the first time, we report direct
observation of QHE in a novel low-dimensional material system:
tellurene.High-quality 2D tellurene thin films were acquired from recently
reported hydrothermal method with high hole mobility of nearly 3,000 cm2/Vs at
low temperatures, which allows the observation of well-developed
Shubnikov-de-Haas (SdH) oscillations and QHE. A four-fold degeneracy of Landau
levels in SdH oscillations and QHE was revealed. Quantum oscillations were
investigated under different gate biases, tilted magnetic fields and various
temperatures, and the results manifest the inherent information of the
electronic structure of Te. Anomalies in both temperature-dependent oscillation
amplitudes and transport characteristics were observed which are ascribed to
the interplay between Zeeman effect and spin-orbit coupling as depicted by the
density functional theory (DFT) calculations.",1806.08229v1
2018/11/21,Strong Rashba-Edelstein Effect-Induced Spin-Orbit Torques in Monolayer Transition-Metal Dichalcogenide/Ferromagnet Bilayers,"The electronic and optoelectronic properties of two dimensional materials
have been extensively explored in graphene and layered transition metal
dichalcogenides (TMDs). Spintronics in these two-dimensional materials could
provide novel opportunities for future electronics, for example, efficient
generation of spin current, which should enable the efficient manipulation of
magnetic elements. So far, the quantitative determination of charge current
induced spin current and spin-orbit torques (SOTs) on the magnetic layer
adjacent to two-dimensional materials is still lacking. Here, we report a large
SOT generated by current-induced spin accumulation through the Rashba-Edelstein
effect in the composites of monolayer TMD (MoS$_2$ or WSe$_2$)/CoFeB bilayer.
The effective spin conductivity corresponding to the SOT turns out to be almost
temperature-independent. Our results suggest that the charge-spin conversion in
the chemical vapor deposition-grown large-scale monolayer TMDs could
potentially lead to high energy efficiency for magnetization reversal and
convenient device integration for future spintronics based on two-dimensional
materials.",1811.08583v1
2019/1/3,Can Injection Model Replenish the Filaments in Weak Magnetic Environment?,"We observed an H$\alpha$ surge occurred in the active region NOAA 12401 on
2015 August 17, and discuss its trigger mechanism, kinematic and thermal
properties. It is suggested that this surge is caused by a chromospheric
reconnection which ejects cool and dense material with the transverse velocity
about 21-28 km s$^{-1}$ and the initial doppler velocity of 12 km s$^{-1}$.
This surge is similar to the injection of newly formed filament materials from
their footpoints, except that the surge here occurred in a relatively weak
magnetic environment of ~100 G. Thus we discuss the possibility of filament
material replenishment via the erupting mass in such a weak magnetic field,
which is often associated with quiescent filaments. It is found that the local
plasma can be heated up to about 1.3 times of original temperature, which
results in an acceleration about -0.017 km s$^{-2}$. It can lift the dense
material up to 10 Mm and higher with a inclination angle smaller than
50$^{\circ}$, namely typical height of active region filaments. But it can
hardly inject the material up to those filaments higher than 25 Mm, namely some
quiescent filaments. Thus we think injection model does not work well in the
formation of quiescent filaments.",1901.00659v1
2019/1/8,High entropy oxides: An emerging prospect for magnetic rare earth - transition metal perovskites,"It has been shown that oxide ceramics containing multiple transition and/or
rare-earth elements in equimolar ratios have a strong tendency to crystallize
in simple single phase structures, stabilized by the high configurational
entropy. In analogy to the metallic alloy systems, these oxides are denoted
high entropy oxides (HEOs). The HEO concept allows to access hitherto uncharted
areas in the multi-element phase diagram. Among the already realized structures
there is the highly complex class of rare earth - transition element
perovskites. This fascinating class of materials generated by applying the
innovative concept of high entropy stabilization provides a new and manyfold
research space with promise of discoveries of unprecedented properties and
phenomena. The present study provides a first investigation of the magnetic
properties of selected compounds of this novel class of materials.
Comprehensive studies by DC and AC magnetometry are combined with element
specific spectroscopy in order to understand the interplay between magnetic
exchange and the high degree of chemical disorder in the systems. We observe a
predominant antiferromagnetic behavior in the single phase materials, combined
with a small ferromagnetic contribution possibly stemming from small
ferromagnetic clusters or configurations in the antiferromagnetic matrix. In
the long term perspective it is proposed to screen the properties of this
family of compounds with high throughput methods, including combined
experimental and theoretical approaches.",1901.02395v2
2019/3/3,Non-Kitaev spin liquids in Kitaev materials,"We point out that the Kitaev materials may not necessarily support Kitaev
spin liquid. It is well-known that having a Kitaev term in the spin interaction
is not the sufficient condition for the Kitaev spin liquid ground state. Many
other spin liquids may be stabilized by the competing spin interactions of the
systems. We thus explore the possibilities of non-Kitaev spin liquids in the
honeycomb Kitaev materials. We carry out a systematic classification of gapped
$\mathbb{Z}_2$ spin liquids using the Schwinger boson representation for the
spin variables. The presence of strong spin-orbit coupling in the Kitaev
materials brings new ingredients into the projective symmetry group
classification of the non-Kitaev spin liquid. We predict the spectroscopic
properties of these gapped non-Kitaev spin liquids. Moreover, among the gapped
spin liquids that we discover, we identify the spin liquid whose spinon
condensation leads to the magnetic Bragg peak structure of the zig-zag magnetic
order that was observed in Na$_2$IrO$_3$ and $\alpha$-RuCl$_3$. We further
discuss the possibility of gapped $\mathbb{Z}_2$ spin liquid and the deconfined
quantum criticality from the zig-zag magnetic order to spin dimerization in
pressurized $\alpha$-RuCl$_3$.",1903.00895v2
2019/6/25,A neutron scattering measurement of crystalline-electric fields in magnesium rare-earth selenide spinels,"The symmetry of local moments plays a defining role in the nature of exotic
grounds states stabilized in frustrated magnetic materials. We present
inelastic neutron scattering (INS) measurements of the crystal electric field
(CEF) excitations in the family of compounds MgRE$_2$Se$_4$ (RE $\in$ $\{$Ho,
Tm, Er and Yb$\}$). These compounds form in the spinel structure, with the rare
earth ions comprising a highly frustrated pyrochlore sublattice. Within the
symmetry constraints of this lattice, we fit both the energies and intensities
of observed modes in the INS spectra to determine the most likely CEF
Hamiltonian for each material and comment on the ground state wavefunctions in
the local electron picture. In this way, we experimentally confirm
MgTm$_2$Se$_4$ has a non-magnetic ground state, and MgYb$_2$Se$_4$ has
effective $S=\frac{1}{2}$ spins with $g_\parallel = 5.188(79)$ and $g_\perp =
0.923(85)~\mu_B$. The spectrum of MgHo$_2$Se$_4$ indicates a ground state
doublet containing Ising spins with $g_\parallel = 2.72(46)$, though low-lying
CEF levels are also seen at thermally accessible energies $\delta_E =
0.591(36)$, 0.945(30) and 2.88(7)~meV, which can complicate interpretation.
These results are used to comment on measured magnetization data of all
compounds, and are compared to published results on the material
MgEr$_2$Se$_4$.",1906.10767v2
2019/9/9,Ferroelectric nonlinear anomalous Hall effect in few-layer WTe$_2$,"Under broken time reversal symmetry such as in the presence of external
magnetic field or internal magnetization, a transverse voltage can be
established in materials perpendicular to both longitudinal current and applied
magnetic field, known as classical Hall effect. However, this symmetry
constraint can be relaxed in the nonlinear regime, thereby enabling nonlinear
anomalous Hall current in time-reversal invariant materials - an underexplored
realm with exciting new opportunities beyond classical linear Hall effect.
Here, using group theory and first-principles theory, we demonstrate a
remarkable ferroelectric nonlinear anomalous Hall effect in time-reversal
invariant few-layer WTe$_2$ where nonlinear anomalous Hall current switches in
odd-layer WTe$_2$ while remaining invariant in even-layer WTe$_2$ upon
ferroelectric transition. This even-odd oscillation of ferroelectric nonlinear
anomalous Hall effect was found to originate from the absence and presence of
Berry curvature dipole reversal and shift dipole reversal due to distinct
ferroelectric transformation in even and odd-layer WTe$_2$. Our work not only
treats Berry curvature dipole and shift dipole on an equal footing to account
for intraband and interband contributions to nonlinear anomalous Hall effect,
but also establishes Berry curvature dipole and shift dipole as new order
parameters for noncentrosymmetric materials. The present findings, therefore,
suggest that ferroelectric metals and Weyl semimetals may offer unprecedented
opportunities for the development of nonlinear quantum electronics.",1909.03610v1
2020/2/12,Artificial Multiferroics and Enhanced Magnetoelectric Effect in van der Waals Heterostructures,"Multiferroic materials with coupled ferroelectric and ferromagnetic
properties are important for multifunctional devices due to their potential
ability of controlling magnetism via electric field, and vice versa. The recent
discoveries of two-dimensional ferromagnetic and ferroelectric materials have
ignited tremendous research interest and aroused hope to search for
two-dimensional multiferroics. However, intrinsic two-dimensional multiferroic
materials and, particularly, those with strong magnetoelectric couplings are
still rare to date. In this paper, using first-principles simulations, we
propose artificial two-dimensional multiferroics via a van der Waals
heterostructure formed by ferromagnetic bilayer chromium triiodide (CrI3) and
ferroelectric monolayer Sc2CO2. In addition to the coexistence of
ferromagnetism and ferroelectricity, our calculations show that, by switching
the electric polarization of Sc2CO2, we can tune the interlayer magnetic
couplings of bilayer CrI3 between ferromagnetic and antiferromagnetic states.
We further reveal that such a strong magnetoelectric effect is from a dramatic
change of the band alignment induced by the strong build-in electric
polarization in Sc2CO2 and the subsequent change of the interlayer magnetic
coupling of bilayer CrI3. These artificial multiferroics and enhanced
magnetoelectric effect give rise to realizing multifunctional nanoelectronics
by van der Waals heterostructures.",2002.05213v1
2020/3/26,Two-Dimensional Materials for Energy-Efficient Spin-Orbit Torque Devices,"Spin-orbit torques (SOTs), which rely on spin current generation from charge
current in a nonmagnetic material, promise an energy-efficient scheme for
manipulating magnetization in magnetic devices. A critical topic for spintronic
devices using SOTs is to enhance the charge to spin conversion efficiency.
Besides, the current-induced spin polarization is usually limited to in-plane,
whereas out-of-plane spin polarization could be favored for efficient
perpendicular magnetization switching. Recent advances in utilizing two
important classes of van der Waals materials$-$topological insulators and
transition-metal dichalcogenides$-$as spin sources to generate SOT shed light
on addressing these challenges. Topological insulators such as bismuth selenide
have shown a giant SOT efficiency, which is larger than those from
three-dimensional heavy metals by at least one order of magnitude.
Transition-metal dichalcogenides such as tungsten telluride have shown a
current-induced out-of-plane spin polarization, which is allowed by the reduced
symmetry. In this review, we use symmetry arguments to predict and analyze SOTs
in van der Waal material-based heterostructures. We summarize the recent
progress of SOT studies based on topological insulators and transition-metal
dichalcogenides and show how these results are in line with the symmetry
arguments. At last, we identify unsolved issues in the current studies and
suggest three potential research directions in this field.",2003.11966v2
2020/5/19,Imaging and spectral study on the null point of a fan-spine structure during a solar flare,"Using the multi-instrument observations, we make the first simultaneous
imaging and spectral study on the null point of a fan-spine magnetic topology
during a solar flare. When magnetic reconnection occurs at the null point, the
fan-spine configuration brightens in the (extreme-)ultraviolet channels. In the
H$\alpha$ images, the fan-spine structure is partly filled and outlined by the
bi-directional material flows ejected from the reconnection site. The
extrapolated coronal magnetic field confirms the existence of the fan-spine
topology. Before and after the flare peak, the total velocity of the outflows
is estimated to be about 60 km s$^{-1}$. During the flare, the Si IV line
profile at the reconnection region is enhanced both in the blue-wing and
red-wing. At the flare peak time, the total velocity of the outflows is found
to be 144 km s$^{-1}$. Superposed on the Si IV profile, there are several deep
absorption lines with the blueshift of several tens of km s$^{-1}$. The reason
is inferred to be that the bright reconnection region observed in Si IV channel
is located under the cooler material appearing as dark features in the
H$\alpha$ line. The blueshifted absorption lines indicate the movement of the
cooler material toward the observer. The depth of the absorption lines also
depends on the amount of cooler material. These results imply that this kind of
spectral profiles can be used as a tool to diagnose the properties of cooler
material above reconnection site.",2005.09613v1
2021/1/29,Reservoir Computing with Magnetic Thin Films,"Advances in artificial intelligence are driven by technologies inspired by
the brain, but these technologies are orders of magnitude less powerful and
energy efficient than biological systems. Inspired by the nonlinear dynamics of
neural networks, new unconventional computing hardware has emerged with the
potential to exploit natural phenomena and gain efficiency, in a similar manner
to biological systems. Physical reservoir computing demonstrates this with a
variety of unconventional systems, from optical-based to memristive systems.
Reservoir computers provide a nonlinear projection of the task input into a
high-dimensional feature space by exploiting the system's internal dynamics. A
trained readout layer then combines features to perform tasks, such as pattern
recognition and time-series analysis. Despite progress, achieving
state-of-the-art performance without external signal processing to the
reservoir remains challenging. Here we perform an initial exploration of three
magnetic materials in thin-film geometries via microscale simulation. Our
results reveal that basic spin properties of magnetic films generate the
required nonlinear dynamics and memory to solve machine learning tasks
(although there would be practical challenges in exploiting these particular
materials in physical implementations). The method of exploration can be
applied to other materials, so this work opens up the possibility of testing
different materials, from relatively simple (alloys) to significantly complex
(antiferromagnetic reservoirs).",2101.12700v2
2021/8/1,Observation of multiple nodal-lines in SmSbTe,"Having been a ground for various topological fermionic phases, the family of
ZrSiS-type 111 materials has been under experimental and theoretical
investigations. Within this family of materials, the subfamily LnSbTe (Ln =
lanthanide elements) is gaining interests in recent times as the strong
correlation effects and magnetism arising from the 4f electrons of the
lanthanides can provide an important platform to study the linking between
topology, magnetism, and correlation. In this paper, we report the systematic
study of the electronic structure of SmSbTe - a member of the LnSbTe subfamily
- by utilizing angle-resolved photoemission spectroscopy in conjunction with
first-principles calculations, transport, and magnetic measurements. Our
experimental results identify multiple Dirac nodes forming the nodal-lines
along the G- X and Z- R directions in the bulk Brillouin zone (BZ) as predicted
by our theoretical calculations. A surface Dirac-like state that arises from
the square net plane of the Sb atoms is also observed at the X point of the
surface BZ. Our study highlights SmSbTe as a promising candidate to understand
the topological electronic structure of LnSbTe materials.",2108.00489v1
2021/8/27,An overview of the structural correlation of magnetic and electrical properties of Pr2NiMnO6 Double perovskite,"Double perovskites R2NiMnO6 (R= Rare earth element) (RNMO) are a significant
class of materials owing to their varied tunability of the magnetic and
electrical properties with the structural modifications. Pr2NiMnO6 (PNMO) is
one of the least explored members of this series, which shows spin-phonon
coupling, magnetocaloric effect, and electrochemical performance for various
applications such as spintronics, magnetocaloric refrigerant, and solid oxide
fuel cells. Most of the studies in PNMO are limited to the application domain
and focus on the comparative study with different rare earth elements. Detailed
structural studies like neutron diffraction are sparse in PNMO samples which
will give a perception to the ordering in the compound that strongly depends on
the physical and chemical properties. This review article goes through the
various aspects of PNMO materials that have been reported till now and showcase
the octahedral distortions and corresponding structural changes and the
exchange interactions, which in turn correlates with the magnetic and
electrical properties. The comparison study of PNMO with other members of the
RNMO family and the relevance of PNMO over other members is also tried to
showcase through this article. Hope this article provides an insight into the
scope of studies in PNMO material for exploring unexposed properties of the
materials in the double perovskite family.",2108.12498v1
2022/7/2,Emergence of strong room-temperature ferroelectricity and multiferroicity in 2D-Ti$_3$C$_2$T$_x$ free-standing MXene film,"Two-dimensional (2D) multiferroics are key candidate materials towards
advancement of smart technology. Here, we employed a simple synthesis approach
to address the long-awaited dream of developing ferroelectric and multiferroic
2D materials, specially in the new class of materials called MXenes. The etched
Ti$_3$C$_2$T$_x$ MXene was first synthesized after HF-treatment followed by
delamination process for successful synthesis of free-standing Ti$_3$C$_2$T$_x$
film. The free-standing film was then exposed to air at room-temperature as
well as heated at different temperature to form TiO$_2$ layer derived from the
Ti$_3$C$_2$T$_x$ MXene itself. TiO$_2$ is reported to be an incipient
ferroelectric that assumes a ferroelectric phase in composite form. The
structural and morphological analysis confirmed successful synthesis of
free-standing film and the Raman spectroscopy revealed the formation of
different phases of TiO$_2$. The ferroelectric measurement showed a clear
polarization hysteresis loop at room-temperature. Also, the magnetic hysteresis
was observed in the film indicating a possibility of coupling between
ferroelectric and ferromagnetic phases at room-temperature. The magnetoelectric
coupling test was also performed that showed a clear, switchable spontaneous
polarization under applied magnetic field. This is the first report on
existence of ferroelectric phase and multiferroic coupling in 2D free-standing
MXene film at room-temperature which opens-up possibility of 2D materials-based
electric and magnetic data storage applications at room-temperature.",2207.00893v1
2022/10/24,Ab-initio calculation of the Hubbard $U$ and Hund exchange $J$ in local moment magnets: The case of Mn-based full Heusler compounds,"Mn-based full Heusler compounds possess well-defined local atomic Mn moments,
and thus the correlation effects between localized d electrons are expected to
play an important role in determining the electronic and magnetic properties of
these materials. Employing ab-initio calculations in conjunction with the
constrained random-phase approximation (cRPA) method, we calculate the strength
of the effective on-site Coulomb interaction parameters (Hubbard U and Hund
exchange J) in the case of X2MnZ full Heusler compounds with X being one of Ni,
Pd or Cu, and Z being one of In, Sn, Sb or Te. We show that the Z element (or
sp element) in Heusler compounds significantly reduces the strength of the
Hubbard U parameter for Mn 3d electrons compared to the elementary bulk Mn. On
the contrary, the effect of the sp-atom on the strength of the U parameter of
Ni, Cu or Pd valence d electrons is not so substantial with respect to the
elementary bulk values. The U values for all transition metal atoms decrease
with increasing sp electron number in the In-Sn-Sb-Te sequence. Our cRPA
calculations reveal that despite their well-defined local magnetic moments, the
Mn-based full Heusler alloys fall into the category of the weakly correlated
materials.",2210.13061v1
2023/10/17,Extremely large anomalous Hall conductivity and unusual axial diamagnetism in a quasi-1D Dirac material La$_3$MgBi$_5$,"Anomalous Hall effect (AHE), one of the most important electronic transport
phenomena, generally appears in ferromagnetic materials but is rare in
materials without magnetic elements. Here, we present a study of
La$_3$MgBi$_5$, whose band structure carries multitype Dirac fermions. Although
magnetic elements are absent in La$_3$MgBi$_5$, clear signals of AHE can be
observed. In particular, the anomalous Hall conductivity is extremely large,
reaching 42,356 $\Omega^{-1}$ cm$^{-1}$ with an anomalous Hall angle of 8.8 %,
the largest one that has been observed in the current AHE systems. The AHE is
suggested to originate from the combination of skew scattering and Berry
curvature. Another unique property discovered in La$_3$MgBi$_5$ is the axial
diamagnetism. The diamagnetism is significantly enhanced and dominates the
magnetization in the axial directions, which is the result of restricted motion
of the Dirac fermion at Fermi level. Our findings not only establish
La$_3$MgBi$_5$ as a suitable platform to study AHE and quantum transport, but
also indicate the great potential of 315-type Bi-based materials for exploring
novel physical properties.",2310.11378v1
2024/3/20,Tailoring Physical Properties of Crystals through Synthetic Temperature Control: A Case Study for new Polymorphic NbFeTe2 phases,"Growth parameters play a significant role in the crystal quality and physical
properties of layered materials. Here we present a case study on a van der
Waals magnetic NbFeTe2 material. Two different types of polymorphic NbFeTe2
phases, synthesized at different temperatures, display significantly different
behaviors in crystal symmetry, electronic structure, electrical transport, and
magnetism. While the phase synthesized at low temperature showing behavior
consistent with previous reports, the new phase synthesized at high
temperature, has completely different physical properties, such as metallic
resistivity, long-range ferromagnetic order, anomalous Hall effect, negative
magnetoresistance, and distinct electronic structures. Neutron diffraction
reveals out-of-plane ferromagnetism below 70K, consistent with the electrical
transport and magnetic susceptibility studies. Our work suggests that simply
tuning synthetic parameters in a controlled manner could be an effective route
to alter the physical properties of existing materials potentially unlocking
new states of matter, or even discovering new materials.",2403.13596v1
1998/3/10,Hard Simulation Problems in the Modeling of Magnetic Materials: Parallelization and Langevin Micromagnetics,"We present recent results on two attempts at understanding and utilizing
large-scale simulations of magnetic materials. In the first study we consider
massively parallel implementations on a Cray T3E of the n-fold way algorithm
for magnetization switching in kinetic Ising models. We find an intricate
relationship between the average time increment and the size of the spin blocks
on each processor. This narrows the regime of efficient implementation. The
second study concerns incorporating noise into micromagnetic calculations using
Langevin methods. This allows measurement of quantities such as the probability
that the system has not switched within a given time. Preliminary results are
reported for arrays of single-domain nanoscale pillars.",9803118v1
1999/1/11,Negative magnetoresistance in La(0.6)Y(0.1)Ca(0.3)MnO(3): Evidence for charge localization governed by the Curie-Weiss law,"Colossal negative magnetoresistance \Delta \rho (T,B) observed in
La(0.6)Y(0.1)Ca(0.3)MnO(3) at B=1T shows a nearly perfect symmetry around
T_0=160K suggesting a universal field-induced transport mechanism in this
material. Attributing this symmetry to strong magnetic fluctuations (triggered
by the Y substitution and further enhanced by magnetic field, both above and
below the field-dependent Curie temperature T_C(B)=T_0), the data are
interpreted in terms of the nonthermal spin hopping and magnetization M
dependent charge carrier localization scenario leading to \Delta \rho (T,B)=
-\rho_s(1-exp(-\gamma M^2)) with M(T,B)=CB/|T-T_C|^n. The separate fits through
all the data points above and below T_C yield C^{+}\simeq C^{-} and n^{+}\simeq
n^{-}\simeq 1. The obtained results corroborate the importance of fluctuation
effects in this material recently found (cond-mat/9812219) to dominate its
magneto-thermopower behavior far beyond T_C.",9901081v1
1999/7/6,Dipolar random field Ising model: an application to garnet films,"The dipolar-random field Ising model (DRFIM) recently introduced displays a
behaviour that can be connected to the magnetization of bidimensional magnetic
media. Epitaxial magnetic garnet films seem to be the ideal test material for
such a model. In this work the results of the measurements performed on garnet
samples are presented, as well as the comparisons with simulation results
obtained by the DRFIM. The results prove that a variety of hysteresis loops are
well described by the DRFIM. This capability does not derive from the fine
tuning of a great number of parameters, but by the interplay of exchange and
dipolar interactions.",9907075v1
1999/10/22,Carrier density change in Colossal Magnetoresistive Pyrochlore Tl2Mn2O7,"Hall resistivity and magneto-thermopower have been measured for colossal
magnetoresistive Tl2Mn2O7 over wide temperature and magnetic-field ranges.
These measurements revealed that a small number of free electron-like carriers
is responsible for the magneto-transport properties. In contrast to perovskite
CMR materials, the anomalous Hall coefficient is negligible even in the
ferromagnetic state due to negligibly small skew scattering. The characteristic
feature in Tl2Mn2O7 is that the carrier density changes with temperature and
the magnetic field. The carrier density increases around TC as the temperature
is lowered or as the magnetic field is increased, which explains the CMR of
this material. The conduction-band-edge shift, which is caused by the strong
s-d interaction between localized Mn moments and s-like conduction electrons,
is a possible mechanism for the carrier density change.",9910345v1
2002/5/30,Effects of the Magnetic Field on the Relaxation of Small Particle Systems,"We study the effect of a magnetic field on the thermal relaxation of
non-interacting small monodomain particle systems particles with a distribution
of anisotropy constants and random easy-axes directions. Numerical calculations
of the relaxation curves for different distribution widths, and under different
magnetic fields $H$ and temperatures $T$, have been performed in the framework
of a two-state approximation. We show how the obtained data can be analyzed in
terms of an modified $Tln(t/\tau_0)$ scaling from which the field dependence of
the mean relaxing energy barriers can be extracted, a microscopic information
which is not easily obtainable by other methods.",0205652v1
2002/10/15,Theoretical models of ferromagnetic III-V semiconductors,"Recent materials research has advanced the maximum ferromagnetic transition
temperature in semiconductors containing magnetic elements toward room
temperature. Reaching this goal would make information technology applications
of these materials likely. In this article we briefly review the status of work
over the past five years which has attempted to achieve a theoretical
understanding of these complex magnetic systems. The basic microscopic origins
of ferromagnetism in the (III,Mn)V compounds that have the highest transition
temperatures appear to be well understood, and efficient computation methods
have been developed which are able to model their magnetic, transport, and
optical properties. However many questions remain.",0210318v1
2003/2/17,Structural Aspects of Magnetic Coupling in CaCu3Mn4O12 and CaCu3Ti4O12,"Two perovskite-derived materials, CaCu3Mn4O12 and CaCu3Ti4O12, have drawn
much recent interest due to their magnetoresistive, dielectric, and
magnetoelectronic characteristics. Here we present initial theoretical insights
into each of these points, based on first principles, density functional based
calculations. Our results predict CCMO to have a spin-asymmetric energy gap,
which leads to distinct temperature- and magnetic field-dependent changes in
properties, and helps to account for its observed negative magnetoresistivity.
We have studied CCTO primarily to gain insight into the exchange coupling in
both these compounds, where the conventional superexchange coupling vanishes by
symmetry for both nearest and next nearest Cu-Cu neighbors, a consequence of
the structure. In CCTO, it is necessary to go to 5th Cu-Cu neighbors to obtain
a (superexchange) coupling that can provide the coupling necessary to give
three dimensional order. Non-superexchange mechanisms may be necessary to
describe the magnetic coupling in this structural class.",0302343v1
2003/3/20,"Towards a Fully Ab-Initio Description of the Diluted Magnetic Semiconductor $Ga_{1-x}Mn_{x}As$. Ferromagnetism, Electronic Structure, and Optical Response","There are two competing views of itinerant ferromagnetism, the first viewing
ferromagnetism as resulting from the indirect coupling between local moments
via the itinerant carrier dynamics, the so-called RKKY mechanism, while in the
alternative picture, ferromagnetism results from the spin polarization of
itinerant carriers by the strong atomic Hund interaction - the so-called double
exchange (DE) scenario. Which view describes the ferromagnetism in diluted
magnetic semiconductors, materials with promise for spintronic applications, is
still unclear. Here, we describe the detailed physical response of the
prototype material $Ga_{1-x}Mn_{x}As$ using a combination of first-principles
bandstructure with methods based on dynamical mean field theory to incorporate
strong, dynamical correlations {\it and} intrinsic as well as extrinsic
disorder in one single theoretical picture. We show how ferromagnetism is
driven by DE, in agreement with very recent observations, along with a good
quantitative description of the details of the electronic structure, as probed
by scanning tunnelling microscopy (STM) and optical conductivity. Our results
show how ferromagnetism can be driven by DE even in diluted magnetic
semiconductors with small carrier concentration.",0303427v1
2003/6/18,Nitrides as spintronic materials,"A report of progress in spintronics-related works involving group III
nitrides is given emphasizing contradictory opinions concerning basics
characteristics of these materials. The actual position of magnetic impurities
in the GaN lattice as well as a possible role of magnetic precipitates is
discussed. The question whether the hole introduce by the Mn impurities is
localized tightly on the Mn d-levels or rather on the hybridized p-d bonding
states is addressed. The nature of spin-spin interactions and magnetic phases,
as provided by theoretical and experimental findings, is outlined, and possible
origins of the high temperature ferromagnetism observed in (Ga,Mn)N are
presented. Experimental studies aiming at evaluating characteristic times of
spin coherence and dephasing in GaN are described.",0306483v1
2003/8/22,Low Temperature Spin Freezing in Dy2Ti2O7 Spin Ice,"We report a study of the low temperature bulk magnetic properties of the spin
ice compound Dy2Ti2O7 with particular attention to the (T < 4 K) spin freezing
transition. While this transition is superficially similar to that in a spin
glass, there are important qualitative differences from spin glass behavior:
the freezing temperature increases slightly with applied magnetic field, and
the distribution of spin relaxation times remains extremely narrow down to the
lowest temperatures. Furthermore, the characteristic spin relaxation time
increases faster than exponentially down to the lowest temperatures studied.
These results indicate that spin-freezing in spin ice materials represents a
novel form of magnetic glassiness associated with the unusual nature of
geometrical frustration in these materials.",0308458v1
2004/1/26,Specific Heat of Sr4Ru3O10,"We have measured the specific heat of single crystals of the triple-layer
Ruddlesden-Popper material, Sr4Ru3O10, grown both in an image furnace and by
flux-growth. The flux grown sample has a sharp mean-field-like anomaly at the
onset of magnetic order, Tc = 102 K, but a much broader anomaly, indicative of
residual heterogeneity, is observed for the image furnace sample. Even for the
flux grown sample, however, the anomaly is at least an order of magnitude
smaller than one would expect for complete ordering of the spins. Neither
sample exhibits an anomaly at Tm ~ 50 K, where magnetic measurements suggest
that basal plane antiferromagnetism sets in. Anomalous behavior (e.g.
consistent with a term in the specific heat ~ T^3/2 as would be observed for a
three-dimensional ferromagnet with weak exchange) is observed at low
temperatures for both samples, indicative of the unusual magnetic order in this
material.",0401510v1
2004/7/13,Magnetism in BEDT-TTF materials,"Strong commensurate antiferromagnetism proximate to superconductivity is
found in some members of the kappa-(ET) family, while a spin gap (SG) is found
in the theta-(ET). Both kappa- and theta-(ET) materials have frustrated
triangular lattice structures. We show from calculations of spin-spin
correlations within the effective half-filled band triangular lattice proposed
for the kappa-ET, as well as for the real lattice, that long range AFM order is
not obtained as a consequence of this frustration. We argue that some other
mechanism reduces the magnetic frustration in these systems. We show that the
low temperature magnetic states in these materials can only be understood if
the effects of the {\it cooperative} charge and bond ordering transitions
occurring at higher temperatures in these systems are taken into account. In
the kappa-ET, this co-operative transition leads to unequal hole populations on
the ET dimers that form the triangular lattice.",0407334v2
2004/12/13,Space-Time Parity Violation and Magnetoelectric Interactions in Antiferromagnets,"The properties of antiferromagnetic materials with violated space-time parity
are considered. Particular attention is given to the bismuth ferrite BiFeO3
ferroelectric magnet. This material is distinguished from other
antiferromagnets in that the inversion center is absent in its crystal and
magnetic structures. This circumstance gives rise to the diversified and
unusual properties, namely, to the appearance of a spatially modulated spin
structure and to the unique possibility of the linear magnetoelectric effect
coexisting with a weak ferromagnetic moment. The magnetic-induced phase
transitions accompanied by the suppression of the modulated spin structure and
appearance of a number of new and unusual effects are considered. These are the
linear magnetoelectric effect and the appearance of a toroidal moment and a
weak ferromagnetic moment of the magnetoelectric nature.",0412318v1
2005/9/5,Magnetoelectric Coupling in epsilon-Fe2O3,"Nanoparticles of the ferrimagnetic epsilon-Fe2O3 oxide have been synthesized
by sol-gel method. Here, we report on the measurements of the dielectric
permittivity as a function of temperature, frequency and magnetic field. It is
found that, coinciding with the transition from collinear ferrimagnetic
ordering to an incommensurate magnetic state occurring at about 100 K, there is
an abrupt change (about 30 %) of permittivity suggesting the existence of a
magnetoelectric coupling in this material. Indeed, magnetic field dependent
measurements at 100 K have revealed an increase of the permittivity by about
0.3 % in 6 T. Prospective advantages of epsilon-Fe2O3 as multiferroic material
are discussed.",0509104v1
2006/3/22,Neutron scattering from a coordination polymer quantum paramagnet,"Inelastic neutron scattering measurements are reported for a powder sample of
the spin-1/2 quantum paramagnet $\rm Cu(Quinoxaline)Br_2$. Magnetic neutron
scattering is identified above an energy gap of 1.9 meV. Analysis of the sharp
spectral maximum at the onset indicates that the material is magnetically
quasi-one-dimensional. Consideration of the wave vector dependence of the
scattering and polymeric structure further identifies the material as a
two-legged spin-1/2 ladder. Detailed comparison of the data to various models
of magnetism in this material based on the single mode approximation and the
continuous unitary transformation are presented. The latter theory provides an
excellent account of the data with leg exchange $J_{\parallel}=2.0$ meV and
rung exchange $J_{\perp}=3.3$ meV.",0603592v2
2007/8/1,Phase diagram and magnetocaloric effect of CoMnGe_{1-x}Sn_{x} alloys,"We propose the phase diagram of a new pseudo-ternary compound,
CoMnGe_{1-x}Sn_{x}, in the range x less than or equal to 0.1. Our phase diagram
is a result of magnetic and calometric measurements. We demonstrate the
appearance of a hysteretic magnetostructural phase transition in the range
x=0.04 to x=0.055, similar to that observed in CoMnGe under hydrostatic
pressure. From magnetisation measurements, we show that the isothermal entropy
change associated with the magnetostructural transition can be as high as 4.5
J/(K kg) in a field of 1 Tesla. However, the large thermal hysteresis in this
transition (~20 K) will limit its straightforward use in a magnetocaloric
device.",0708.0204v1
2007/9/27,Neel to Spin-Glass-like Phase Transition versus Dilution in Geometrically Frustrated ZnCr_{2-2x}Ga_{2x}O_4,"ZnCr2O4 undergoes a first order spin-Peierls-like phase transition at 12.5 K
from a cubic spin liquid phase to a tetragonal Neel state. Using powder
diffraction and single crystal polarized neutron scattering, we determined the
complex spin structure of the Neel phase. This phase consisted of several
magnetic domains with different characteristic wave vectors. This indicates
that the tetragonal phase of ZnCr2O4 is very close to a critical point
surrounded by many different Neel states. We have also studied, using elastic
and inelastic neutron scattering techniques, the effect of nonmagnetic dilution
on magnetic correlations in ZnCr_{2-2x}Ga_{2x}O_4 (x=0.05 and 0.3). For x=0.05,
the magnetic correlations do not change qualitatively from those in the pure
material, except that the phase transition becomes second order. For x= 0.3,
the spin-spin correlations become short range. Interestingly, the spatial
correlations of the frozen spins in the x=0.3 material are the same as those of
the fluctuating moments in the pure and the weakly diluted materials.",0709.4475v1
2008/6/22,"Electronic structures of ternary iron arsenides AFe$_2$As$_2$ (A=Ba, Ca, or Sr)","We have studied the electronic and magnetic structures of the ternary iron
arsenides AFe$_2$As$_2$ (A = Ba, Ca, or Sr) using the first-principles density
functional theory. The ground states of these compounds are in a collinear
antiferromagnetic order, resulting from the interplay between the nearest and
the next-nearest neighbor superexchange antiferromagnetic interactions bridged
by As $4p$ orbitals. The correction from the spin-orbit interaction to the band
structure is small. The pressure can reduce dramatically the magnetic moment
and diminish the collinear antiferromagnetic order. Based on the calculations,
we propose that the low energy dynamics of these materials is described
effectively by a $t-J_H-J_1-J_2$-type model.",0806.3526v3
2009/7/9,Plasmon polaritons in photonic superlattices containing a left-handed material,"We analyze one-dimensional photonic superlattices which alternate layers of
air and a left-handed material. We assume Drude-type dispersive responses for
the dielectric permittivity and magnetic permeability of the left-handed
material. Maxwell's equations and the transfer-matrix technique are used to
derive the dispersion relation for the propagation of obliquely incident
optical fields. The photonic dispersion indicates that the growth-direction
component of the electric (or magnetic) field leads to the propagation of
electric (or magnetic) plasmon polaritons, for either TE or TM configurations.
Furthermore, we show that if the plasma frequency is chosen within the photonic
$<n(\omega)>=0$ zeroth-order bandgap, the coupling of light with plasmons
weakens considerably. As light propagation is forbidden in that particular
frequency region, the plasmon-polariton mode reduces to a pure plasmon mode.",0907.1644v1
2009/9/7,Magnetic excitations in Kondo liquid: Superconductivity and Hidden Magnetic Quantum Critical Fluctuations,"We report Knight shift experiments on the superconducting heavy electron
material CeCoIn$_5$ that allow one to track with some precision the behavior of
the heavy electron Kondo liquid in the superconducting state with results in
agreement with BCS theory. An analysis of the $^{115}$In nuclear quadrupole
resonance (NQR) spin-lattice relaxation rate $T_1^{-1}$ measurements under
pressure reveals the presence of 2d magnetic quantum critical fluctuations in
the heavy electron component that are a promising candidate for the pairing
mechanism in this material. Our results are consistent with an
antiferromagnetic quantum critical point (QCP) located at slightly negative
pressure in CeCoIn$_5$ and provide additional evidence for significant
similarities between the heavy electron materials and the high $T_c$ cuprates.",0909.1341v1
2009/9/24,Magnetization reversals in a disk-shaped small magnet with an interface,"We consider a nanodisk possessing two coupled materials with different
ferromagnetic exchange constant. The common border line of the two media passes
at the disk center dividing the system exactly in two similar half-disks. The
vortex core motion crossing the interface is investigated with a simple
description based on a two-dimensional model which mimics a very thin real
material with such a line defect. The main result of this study is that,
depending on the magnetic coupling which connects the media, the vortex core
can be dramatically and repeatedly flipped from up to down and vice versa by
the interface. This phenomenon produces burst-like emission of spin waves each
time the switching process takes place.",0909.4519v1
2010/4/27,Integral equation method for the electromagnetic wave propagation in stratified anisotropic dielectric-magnetic materials,"We investigate the propagation of electromagnetic waves in stratified
anisotropic dielectric-magnetic materials using the integral equation method
(IEM). Based on the superposition principle, we use Hertz vector formulations
of radiated fields to study the interaction of wave with matter. We derive in a
new way the dispersion relation, Snell's law and reflection/transmission
coefficients by self-consistent analyses. Moreover, we find two new forms of
the generalized extinction theorem. Applying the IEM, we investigate the wave
propagation through a slab and disclose the underlying physics which are
further verified by numerical simulations. The results lead to a unified
framework of the IEM for the propagation of wave incident either from a medium
or vacuum in stratified dielectric-magnetic materials.",1004.4695v2
2010/6/1,Magnetic and humidity sensing properties of nanostructured Cu[x]Co[1-x]Fe2O4 synthesized by auto combustion technique,"Magnetic nanomaterials (23-43 nm) of Cu$_x$Co$_{1-x}$Fe$_2$O$_4$\ (x = 0.0,
0.5 and 1.0) were synthesized by auto combustion method. The crystallite sizes
of these materials were calculated from X-ray diffraction peaks. The band
observed in Fourier transform infrared spectrum near 575 cm$^{-1}$ in these
samples confirm the presence of ferrite phase. Conductivity measurement shows
the thermal hysteresis and demonstrates the knee points at 475$^o$C, 525$^o$C
and 500$^o$C for copper ferrite, cobalt ferrite and copper-cobalt mixed ferrite
respectively. The hystersis M-H loops for these materials were traced using the
Vibrating Sample Magnetometer (VSM) and indicate a significant increase in the
saturation magnetization (M$_s$) and remanence (M$_r$) due to the substitution
of Cu$^{2+}$ ions in cobalt ferrite, while the intrinsic coercivity (H$_c$) was
decreasing. Among these ferrites, copper ferrite exhibits highest sensitivity
for humidity.",1006.0083v1
2010/11/10,Extraordinary Magnetooptics in Plasmonic Crystals,"Plasmonics has been attracting considerable interest as it allows
localization of light at nanoscale dimensions. A breakthrough in integrated
nanophotonics can be obtained by fabricating plasmonic functional materials.
Such systems may show a rich variety of novel phenomena and also have huge
application potential. In particular magnetooptical materials are appealing as
they may provide ultrafast control of laser light and surface plasmons via an
external magnetic field. Here we demonstrate a new magnetooptical material: a
one-dimensional plasmonic crystal formed by a periodically perforated noble
metal film on top of a ferromagnetic dielectric film. It provides giant Faraday
and Kerr effects as proved by the observation of enhancement of the transverse
Kerr effect near Ebbesen's extraordinary transmission peaks by three orders of
magnitude. Surface plasmon polaritons play a decisive role in this enhancement,
as the Kerr effect depends sensitively on their properties. The plasmonic
crystal can be operated in transmission, so that it may be implemented in
devices for telecommunication, plasmonic circuitry, magnetic field sensing and
all-optical magnetic data storage.",1011.2320v1
2010/11/25,Model for domain wall avalanches in ferromagnetic thin films,"The Barkhausen jumps or avalanches in magnetic domain-walls motion between
succesive pinned configurations, due the competition among magnetic external
driving force and substrum quenched disorder, appear in bulk materials and thin
films. We introduce a model based in rules for the domain wall evolution of
ferromagnetic media with exchange or short-range interactions, that include
disorder and driving force effects. We simulate in 2-dimensions with Monte
Carlo dynamics, calculate numerically distributions of sizes and durations of
the jumps and find power-law critical behavior. The avalanche-size exponent is
in excellent agreement with experimental results for thin films and is close to
predictions of the other models, such as like random-field and random-bond
disorder, or functional renormalization group. The model allows us to review
current issues in the study of avalanches motion of the magnetic domain walls
in thin films with ferromagnetic interactions and opens a new approach to
describe these materials with dipolar or long-range interactions.",1011.5643v3
2011/1/10,A story of high-temperature ferromagnetism in semiconductors,"The comprehensive search for multifunctional materials has resulted in the
discovery of semiconductors and oxides showing ferromagnetic features
persisting to room temperature. In this tutorial review the methods of
synthesis of these materials, as well as the application of element-specific
nano-analytic tools, particularly involving synchrotron radiation and electron
microscopy, are described and shown to reveal the presence of nano-scale phase
separations. Various means to control the aggregation of magnetic cations are
discussed together with the mechanisms accounting for ferromagnetism of either
condensed or diluted magnetic semiconductors. Finally, the question of whether
high temperature ferromagnetism is possible in semiconductors not containing
magnetic ions is touched upon.",1101.1981v1
2011/6/14,Magnetism of Edge Modified Nano Graphene,"In order to study a magnetic principle of carbon based materials, multiple
spin state of zigzag edge modified graphene molecules are analyzed by the first
principle density functional theory to select suitable modification element.
Radical carbon modified C64H17 shows that the highest spin state is most
stable, which arises from two up-spin's tetrahedral molecular orbital
configuration at zigzag edge. In contrast, oxygen modified C59O5H17 show the
lowest spin state to be most stable due to four spins cancellation at oxygen
site. Boron modified C59B5H22 have no {\pi}-molecular orbit at boron site to
bring stable molecular spin state to be the lowest one. Whereas, C59N5H2 have
two {\pi}-electrons, where spins cancel each other to give the stable lowest
spin state. Silicon modified C59Si5H27 and Phosphorus modified C59P5H22 show
curved molecular geometry due to a large atom insertion at zigzag site, which
also bring complex spin distribution. Radical carbon and dihydrogenated carbon
modification are promising candidates for designing carbon-based magnetic
materials.",1106.2589v1
2011/7/7,Local antiferromagnetic exchange and collaborative Fermi surface as key ingredients of high temperature superconductors,"Cuprates, ferropnictides and ferrochalcogenides are three classes of
unconventional high-temperature superconductors, who share similar phase
diagrams in which superconductivity develops after a magnetic order is
suppressed, suggesting a strong interplay between superconductivity and
magnetism, although the exact picture of this interplay remains elusive. Here
we show that there is a direct bridge connecting antiferromagnetic exchange
interactions determined in the parent compounds of these materials to the
superconducting gap functions observed in the corresponding superconducting
materials. High superconducting transition temperature is achieved when the
Fermi surface topology matches the form factor of the pairing symmetry favored
by local magnetic exchange interactions. Our result offers a principle guide to
search for new high temperature superconductors.",1107.1334v1
2011/8/25,Driving Force of Ultrafast Magnetization Dynamics,"Irradiating a ferromagnetic material with an ultrashort laser pulse leads to
demagnetization on a femtosecond timescale. We implement Elliott-Yafet type
spin-flip scattering, mediated by electron-electron and electron-phonon
collisions, into the framework of a spin-resolved Boltzmann equation.
Considering three mutually coupled reservoirs, (i) spin-up electrons, (ii)
spin-down electrons and (iii) phonons, we trace non-equilibrium electron
distributions during and after laser excitation. We identify the driving force
for ultrafast magnetization dynamics as the equilibration of temperatures and
chemical potentials between the electronic subsystems. This principle can be
used to easily predict the maximum quenching of magnetization upon ultrashort
laser irradiation in any material, as we show for the example of
3d-ferromagnetic nickel.",1108.5170v1
2011/11/22,"RbFe2+Fe3+F6: Synthesis, Structure, and Characterization of a New Charge-Ordered Magnetically Frustrated Pyrochlore-Related Mixed-Metal Fluoride","A new charge-ordered magnetically frustrated mixed-metal fluoride with a
pyrochlore-related structure has been synthesized and characterized. The
material, RbFe2F6 (RbFe2+Fe3+F6) was synthesized through mild hydrothermal
conditions. The material exhibits a three-dimensional pyrochlore-related
structure consisting of corner-shared Fe2+F6 and Fe3+F6 octahedra. In addition
to single crystal diffraction data, neutron powder diffraction and magnetometry
measurements were carried out. Magnetic data clearly reveal strong
antiferromagnetic interactions (a Curie-Weiss temperature of -270 K) but
sufficient frustration to prevent ordering until 16 K. No structural phase
transformation is detected from the variable temperature neutron diffraction
data. Infrared, UV -vis, thermogravimetric, and differential thermal analysis
measurements were also performed. First-principles density functional theory
(DFT) electronic structure calculations were also done. Crystal data: RbFe2F6,
orthorhombic, space group Pnma (No. 62), a = 7.0177(6) {\AA}, b = 7.4499(6)
{\AA}, c = 10.1765(8) {\AA}, V = 532.04(8) {\AA}3, Z = 4.",1111.5230v1
2012/2/7,Magnetically driven metal-insulator transition in NaOsO3,"The metal-insulator transition (MIT) is one of the most dramatic
manifestations of electron correlations in materials. Various mechanisms
producing MITs have been extensively considered, including the Mott (electron
localization via Coulomb repulsion), Anderson (localization via disorder) and
Peierls (localization via distortion of a periodic 1D lattice). One additional
route to a MIT proposed by Slater, in which long-range magnetic order in a
three dimensional system drives the MIT, has received relatively little
attention. Using neutron and X-ray scattering we show that the MIT in NaOsO3 is
coincident with the onset of long-range commensurate three dimensional magnetic
order. Whilst candidate materials have been suggested, our experimental
methodology allows the first definitive demonstration of the long predicted
Slater MIT. We discuss our results in the light of recent reports of a Mott
spin-orbit insulating state in other 5d oxides.",1202.1482v1
2012/6/21,Neutron Diffraction Study of anomalous negative thermal expansion in non-superconducting PrFe1-xRuxAsO,"Neutron powder diffraction has been used to investigate the structural and
magnetic behavior of the isoelectronically doped Fe pnictide material
PrFe1-xRuxAsO. Substitution of Ru for Fe suppresses the structural and magnetic
phase transitions that occur in the undoped compound PrFeAsO. Contrary to the
behavior usually observed in 1111 pnictide materials, the suppression of both
the structural and magnetic transitions does not result in the emergence of
superconductivity or any other new ground state. Interestingly, PrFeAsO itself
shows an unusual negative thermal expansion (NTE) along the c-axis, from 60K
down to at least 4K; this does not occur in superconducting samples such as
those formed by doping with fluorine on the oxygen site. We find that NTE is
present for all concentrations of PrFe1-xRuxAsO with x ranging from 0.05 to
0.75. These results suggest that the absence of superconductivity in these
materials could be related to the presence of NTE.",1206.4994v2
2012/6/28,The Landau-Lifshitz-Bloch equation for ferrimagnetic materials,"We derive the Landau-Lifshitz-Bloch (LLB) equation for a two-component
magnetic system valid up to the Curie temperature. As an example, we consider
disordered GdFeCo ferrimagnet where the ultrafast optically induced
magnetization switching under the action of heat alone has been recently
reported. The two-component LLB equation contains the longitudinal relaxation
terms responding to the exchange fields from the proper and the neighboring
sublattices. We show that the sign of the longitudinal relaxation rate at high
temperatures can change depending on the dynamical magnetization value and a
dynamical polarisation of one material by another can occur. We discuss the
differences between the LLB and the Baryakhtar equation, recently used to
explain the ultrafast switching in ferrimagnets. The two-component LLB equation
forms basis for the largescale micromagnetic modeling of nanostructures at high
temperatures and ultrashort timescales.",1206.6672v1
2012/7/4,"A variable temperature study of the crystal and magnetic structures of the giant magnetoresistant materials LnMnAsO (Ln = La, Nd)","A variable temperature neutron and synchrotron diffraction study have been
performed on the giant magnetoresistant oxypnictides LnMnAsO (Ln = La, Nd). The
low temperature magnetic structures have been studied and results show a spin
reorientation of the Mn2+ spins below TN (Nd) for NdMnAsO. The Mn2+ spins
rotate from alignment along c to alignment into the basal plane and the Mn2+
and Nd3+ moments refine to 3.54(4) \mu B and 1.93(4) \mu B respectively at 2 K.
In contrast there is no change in magnetic structure with temperature for
LaMnAsO. There is no evidence of a structural transition down to 2 K, however
discontinuities in the cell volume, Ln-O and Mn-As bond lengths are detected at
\sim 150 K for both materials. This temperature coincides with the electronic
transition previously reported and suggests a coupling between electronic and
lattice degrees of freedom.",1207.0961v1
2012/8/7,Bipolar Magnetic Semiconductors: A New Class of Spintronics Materials,"Electrical control of spin polarization is very desirable in spintronics,
since electric field can be easily applied locally in contrast with magnetic
field. Here, we propose a new concept of bipolar magnetic semiconductor (BMS)
in which completely spin-polarized currents with reversible spin polarization
can be created and controlled simply by applying a gate voltage. This is a
result of the unique electronic structure of BMS, where the valence and
conduction bands possess opposite spin polarization when approaching the Fermi
level. Our band structure and spin-polarized electronic transport calculations
on semi-hydrogenated single-walled carbon nanotubes confirm the existence of
BMS materials and demonstrate the electrical control of spin-polarization in
them.",1208.1355v1
2012/9/6,Magnetothermoelectric properties of Bi2Se3,"We present a study of entropy transport in Bi2Se3 at low temperatures and
high magnetic fields. In the zero-temperature limit, the magnitude of the
Seebeck coefficient quantitatively tracks the Fermi temperature of the 3D Fermi
surface at \Gamma-point as the carrier concentration changes by two orders of
magnitude (10$^{17}$ to 10$^{19}$cm$^{-3}$). In high magnetic fields, the
Nernst response displays giant quantum oscillations indicating that this
feature is not exclusive to compensated semi-metals. A comprehensive analysis
of the Landau Level spectrum firmly establishes a large $g$-factor in this
material and a substantial decrease of the Fermi energy with increasing
magnetic field across the quantum limit. Thus, the presence of bulk carriers
significantly affects the spectrum of the intensively debated surface states in
Bi2Se3 and related materials.",1209.1312v2
2012/12/19,Realizing a High Magnetic Moment in Gd/Cr/FeCo: The Role of the Rare Earth,"The search for materials or systems exhibiting a high magnetic saturation has
been of longstanding importance. It has been suggested that increased
saturation could be achieved by coupling a transition metal via a spacer to a
rare earth. We report Gd/Cr/Fe70Co30 multilayer stacks and find reduced yet
modulating magnetic moment as a function of Cr thickness. Through a micro
structural analysis the lowered moment is indicated by the nucleation of the
ultrathin Gd films into an fcc phase. We discuss the possible solution in terms
of quasi-perfect lattice match seed material to promote growth of hcp Gd.",1212.4859v1
2013/1/23,Data Storage: Review of Heusler Compounds,"In the recent decade, the family of Heusler compounds has attracted
tremendous scientific and technological interest in the field of spintronics.
This is essentially due to their exceptional magnetic properties, which qualify
them as promising functional materials in various data-storage devices, such as
giant-magnetoresistance spin valves, magnetic tunnel junctions, and
spin-transfer torque devices. In this article, we provide a comprehensive
review on the applications of the Heusler family in magnetic data storage. In
addition to their important roles in the performance improvement of these
devices, we also try to point out the challenges as well as possible solutions,
of the current Heusler-based devices. We hope that this review would spark
further investigation efforts into efficient incorporation of this eminent
family of materials into data storage applications by fully arousing their
intrinsic potential.",1301.5455v2
2013/2/11,Phase stability of chromium based compensated ferrimagnets with inverse Heusler structure,"Chromium based inverse Heusler compounds of the type Cr2YZ (Y=Co, Fe; Z=Al,
Ga, In, Si, Ge, Sn) have been proposed as fully compensated half-metallic
ferrimagnets. Such materials are of large interest for spintronics because they
combine small magnetic moment with high spin polarization over a wide
temperature range. We assess their thermodynamic stability by their formation
enthalpies obtained from density functional theory calculations. All compounds
under investigation are unstable. Cr2FeSi and Cr2CoAl are stable with respect
to the elemental constituents, but decompose into binary phases. Cr2FeGe,
Cr2CoGa, Cr2FeSn and Cr2CoIn are found to be unstable with respect to their
elemental constituents. We identify possible binary decompositions.",1302.2487v2
2013/6/13,Speed limit of FePt spin dynamics on femtosecond timescales,"Magnetization manipulation is becoming an indispensable tool for both basic
and applied research. Theory predicts two types of ultrafast demagnetization
dynamics classified as type I and type II. In type II materials, a second
slower process takes place after the initial fast drop of magnetization. In
this letter we investigate this behavior for FePt recording materials with
perpendicular anisotropy. The magnetization dynamics have been simulated using
a thermal micromagnetic model based on the Landau-Lifshitz-Bloch equation. We
identify a transition to type II behavior and relate it to the electron
temperatures reached by the laser heating. This slowing down is a fundamental
limit to reconding speeds in heat assisted reversal.",1306.3112v1
2013/7/4,"Oxypnictide SmFeAs(O,F) superconductor: a candidate for high-field magnet applications","The recently discovered oxypnictide superconductor SmFeAs(O,F) is the most
attractive material among the Fe-based superconductors due to its highest
transition temperature of 56 K and potential for high-field performance. In
order to exploit this new material for superconducting applications, the
knowledge and understanding of its electro-magnetic properties are needed.
Recent success in fabricating epitaxial SmFeAs(O,F) thin films opens a great
opportunity to explore their transport properties. Here we report on a high
critical current density of over 10^5 A/cm^2 at 45 T and 4.2 K for both main
field orientations, feature favourable for high-field magnet applications.
Additionally, by investigating the pinning properties, we observed a
dimensional crossover between the superconducting coherence length and the FeAs
interlayer distance at 30-40 K, indicative of a possible intrinsic Josephson
junction in SmFeAs(O,F) at low temperatures that can be employed in electronics
applications such as a terahertz radiation source and a superconducting Qubit.",1307.1282v1
2013/8/12,Coercivity weighted Langevin magnetisation; A new approach to interpret superparamagnetic and nonsuperparamagnetic behaviour in single domain magnetic nanoparticles,"Superparamagnetism (SPM) is an attractive material property often appearing
in nanoscaled single domain (SD) configurations. However, not all SD particles
are superparamagnetic, which depends on a few parameters including material
type, temperature, measurement time and magneto crystalline anisotropy. The
non-linear magnetisation response of magnetic particles can be interpreted by
classical Langevin approach but its applicability is limited to pure SD-SPM
behaviour. The classical Langevin equation lacks parameters to account for
possible remanence and coercivity in SD regime, resultantly, the SD-nonSPM
possibility is left untreated. To solve this issue, we propose a new model by
including SD coercivity parameters in classical Langevin equations. The new
model 1) combines steady or time varying magnetisation dynamics and temperature
or particle size dependent coercivity and 2) helps to calculate coercivity
compensated magnetisations and susceptibilities directly. The model covers full
spectrum of SD diameters and defines the switching between superparamagnetic
and non-superparamagnetic states more precisely.",1308.2517v2
2013/11/7,Quantum Spin Ice: A Search for Gapless Quantum Spin Liquids in Pyrochlore Magnets,"The spin ice materials, including Ho2Ti2O7 and Dy2Ti2O7, are rare earth
pyrochlore magnets which, at low temperatures, enter a constrained paramagnetic
state with an emergent gauge freedom. Remarkably, the spin ices provide one of
very few experimentally realised examples of fractionalization because their
elementary excitations can be regarded as magnetic monopoles and, over some
temperature range, the spin ice materials are best described as liquids of
these emergent charges. In the presence of quantum fluctuations, one can
obtain, in principle, a quantum spin liquid descended from the classical spin
ice state characterised by emergent photon-like excitations. Whereas in
classical spin ices the excitations are akin to electrostatic charges, in the
quantum spin liquid these charges interact through a dynamic and emergent
electromagnetic field. In this review, we describe the latest developments in
the study of such a quantum spin ice, focussing on the spin liquid
phenomenology and the kinds of materials where such a phase might be found.",1311.1817v1
2014/2/24,Creation of bielectron of Dirac cone: the tachyon solution in magnetic field,"Schr\""odinger equation for pair of two massless Dirac particles when magnetic
field is applied in Landau gauge is solved exactly. In this case the separation
of center of mass and relative motion is obtained. Landau quantization
$\epsilon=\pm\,B\sqrt{l}$ for pair of two Majorana fermions coupled via a
Coulomb potential from massless chiral Dirac equation in cylindric coordinate
is found. The root ambiguity in energy spectrum leads into Landau quantization
for bielectron, when the states in which the one simultaneously exists are
allowed. The tachyon solution with imaginary energy in Cooper problem
($\epsilon^{2}<0$) is found. The continuum symmetry of Dirac equation allows
perfect pairing between electron Fermi spheres when magnetic field is applied
in Landau gauge creating a Cooper pair.",1402.5794v4
2014/4/18,Quantum critical behavior in heavy electron materials,"Quantum critical behavior in heavy electron materials is typically brought
about by changes in pressure or magnetic field. In this communication, we
develop a simple unified model for the combined influence of pressure and
magnetic field on the effectiveness of the hybridization that plays a central
role in the two-fluid description of heavy electron emergence. We show that it
leads to quantum critical and delocalization lines that accord well with those
measured for CeCoIn5, yields a quantitative explanation of the field and
pressure induced changes in antiferromagnetic ordering and quantum critical
behavior measured for YbRh2Si2, and provides a valuable framework for
describing the role of magnetic fields in bringing about quantum critical
behavior in other heavy electron materials.",1404.4672v2
2014/4/24,Effects of loss factors on zero permeability and zero permittivity gaps in 1D photonic crystal containing DNG materials,"The effects of electric and magnetic loss factors on zero-mu and zero-epsilon
gaps in a one-dimensional lossy photonic crystal composed of double-negative
and double-positive materials are theoretically investigated by employing the
characteristic matrix method. This study contradicts the previous reports as it
indicates that by applying the inevitable factors of electric and magnetic
losses to the double-negative material, the zero-mu and zero-epsilon gaps
appear simultaneously in the transmission spectrum, being independent of the
incidence angle and polarizations. Moreover, the results show that these gaps
appear not only for an oblique incidence but also in the case of normal
incidence, and their appearance at the normal incidence is directly related to
the magnetic and electric loss factors. Besides, the results indicate that as
the loss factors and angle of incidence increase, the width of both gaps also
increases.",1404.6203v1
2014/6/14,Emergence of magnetism and controlling factors of superconductivity in Li/Na-ammonia co-intercalated FeSe1-zTez,"The discovery of superconductivity in alkali-ammonia co-intercalated FeSe has
generated intensive interest because of their highest Tc (~ 45 K) among
iron-chalcogenide superconductors with bulk form. Here, we report the phase
diagrams of two series of Li/Na-ammonia co-intercalated FeSe1-zTez. When
superconductivity is suppressed by Te doping, the magnetic ordering states are
emergent. Moreover, a novel phase Lix(NH3)yFe2-{\delta}Te2 with possible
antiferromagnetism is discovered. This strongly indicates the intimate relation
between superconductivity and magnetism in these materials, like in other
iron-based superconductors. On the other hand, comparative structure analysis
with FeSe1-zTez suggests that although there is remarkable similarity in phase
diagrams for both iron-chalcogenide and iron-pnictide superconductors, the
different types of anions with different charges lead to the dissimilar
controlling factors in superconductivity for both classes of materials. This
opens up an opportunity to tune the superconductivity in iron-chalcogenide
superconductors in more ways than just one.",1406.3733v2
2014/6/19,Anomalous thermospin effect in the low-buckled Dirac materials,"A strong spin Nernst effect with nontrivial dependences on the carrier
concentration and electric field applied is expected in silicene and other
low-buckled Dirac materials. These Dirac materials can be considered as being
made of two independent electron subsystems of the two-component gapped Dirac
fermions. For each subsystem the gap breaks a time-reversal symmetry and thus
plays a role of an effective magnetic field. Accordingly, the standard Kubo
formalism has to be altered by including the effective magnetization in order
to satisfy the third law of thermodynamics. We explicitly demonstrate this by
calculating the magnetization and showing how the correct thermoelectric
coefficient emerges.",1406.5148v2
2014/6/27,Spin-phonon coupling in BaFe12O19 M-type hexaferrite,"The spin-phonon coupling in magnetic materials is due to the modulation of
the exchange integral by lattice vibrations. BaFe12O19 M-type hexaferrite,
which is the most used magnetic material as permanent magnet, transforms into
ferromagnet at high temperatures, but no spin-phonon coupling was previously
observed at this transition. In this letter, we investigated the
temperature-dependent Raman spectra of polycrystalline BaFe12O19 M-type
hexaferrite from room temperature up to 780 K to probe spin-phonon coupling at
the ferrimagnetic transition. An anomaly was observed in the position of the
phonon attributed to the Fe(4)O6 octahedra, evidencing the presence of a
spin-phonon coupling in BaM in the ferrimagnetic transition at 720 K. The
results also confirmed the spin-phonon coupling is different for each phonon
even when they couple with the same spin configuration.",1406.7334v2
2014/7/11,A 4-fold-symmetry hexagonal ruthenium for magnetic heterostructures exhibiting enhanced perpendicular magnetic anisotropy and tunnel magnetoresistance,"An unusual crystallographic orientation of hexagonal Ru with a 4-fold
symmetry emerging in epitaxial MgO/Ru/Co2FeAl/MgO heterostructures is reported,
in which an approximately Ru(02-23) growth attributes to the lattice matching
among MgO, Ru, and Co2FeAl. Perpendicular magnetic anisotropy of the
Co2FeAl/MgO interface is substantially enhanced as compared with those with a
Cr(001) layer. The MTJs incorporating this structure gave rise to the largest
tunnel magnetoresistance for perpendicular MTJs using low damping Heusler
alloys. The 4-fold-symmetry hexagonal Ru arises from an epitaxial growth with
an unprecedentedly high crystal index, opening a unique pathway for the
development of perpendicular anisotropy films of cubic and tetragonal
ferromagnetic alloys.",1407.3160v2
2014/7/29,Motion of domain walls and the dynamics of kinks in the magnetic Peierls potential,"We study the dynamics of magnetic domain walls in the Peierls potential due
to the discreteness of the crystal lattice. The propagation of a narrow domain
wall (comparable to the lattice parameter) under the effect of a magnetic field
proceeds through the formation of kinks in its profile. We predict that,
despite the discreteness of the system, such kinks can behave like sine-Gordon
solitons in thin films of materials such as yttrium iron garnets, and we derive
general conditions for other materials. In our simulations we also observe
long-lived breathers. We provide analytical expressions for the effective mass
and limiting velocity of the kink in excellent agreement with our numerical
results.",1407.7754v1
2014/8/20,First observation of flux avalanches in a-MoSi superconducting thin films,"We have observed the occurrence of dendritic flux avalanches in an amorphous
film of Mo$_{84}$Si$_{16}$. These events are understood to have a
thermomagnetic origin and involve the abrupt penetration of bursts of magnetic
flux taking place within a limited window of temperatures and magnetic fields.
While dc-magnetometry allows one to determine the threshold fields for the
occurrence of the thermomagnetic instabilities, magneto-optical imaging reveals
the spatial distribution of magnetic flux throughout the sample. Conducting
appropriate experiments, typical for this goal, avalanches were confirmed to be
a characteristic of this material, ruling out the otherwise admissible
possibility of an experimental artifact or a feature related to defects in the
film. After the present observation, a-MoSi can be included in the gallery of
superconducting materials exhibiting flux avalanches when in the form of thin
films, a characteristic that must be carefully taken into consideration when
one plans to employ films of those materials in applications.",1408.4650v1
2015/1/22,Anatomy of Dzyaloshinskii-Moriya Interaction at Co/Pt Interfaces,"The Dzyaloshinskii-Moriya Interaction (DMI) between spins is induced by
spin-orbit coupling in magnetic materials lacking inversion symmetry. DMI is
recognized to play a crucial role at the interface between ferromagnetic (FM)
and heavy nonmagnetic (NM) metals to create topological textures called
magnetic skyrmions which are very attractive for ultra-dense information
storage and spintronic devices. DMI also plays an essential role for fast
domain wall (DW) dynamics driven by spin-orbit torques. Here, we present first
principles calculations which clarify the main features and microscopic
mechanisms of DMI in Co/Pt bilayers. DMI is found to be predominantly located
at the interfacial Co layer, originating from spin-orbit energy provided by the
adjacent NM layer. Furthermore, no direct correlation is found between DMI and
proximity induced magnetism in Pt. These results clarify underlying mechanisms
of DMI at FM/NM bilayers and should help optimizing material combinations for
skyrmion- and DW-based storage and memory devices.",1501.05511v1
2015/2/9,A theory of finite deformation magneto-viscoelasticity,"This paper deals with the mathematical modelling of large strain
magneto-viscoelastic deformations. Energy dissipation is assumed to occur both
due to the mechanical viscoelastic effects as well as the resistance offered by
the material to magnetisation. Existence of internal damping mechanisms in the
body is considered by decomposing the deformation gradient and the magnetic
induction into `elastic' and `viscous' parts. Constitutive laws for material
behaviour and evolution equations for the non-equilibrium fields are derived
that agree with the laws of thermodynamics. To illustrate the theory the
problems of stress relaxation, magnetic field relaxation, time dependent
magnetic induction and strain are formulated and solved for a specific form of
the constitutive law. The results, that show the effect of several modelling
parameters on the deformation and magnetisation process, are illustrated
graphically.",1502.02482v1
2015/3/6,Design of a Mott Multiferroic from a Non-Magnetic Polar Metal,"We examine the electronic properties of newly discovered ""ferroelectric""
metal LiOsO$_3$ combining density-functional and dynamical mean-field theories.
We show that the material is close to a Mott transition and that electronic
correlations can be tuned to engineer a Mott multiferroic state in 1/1
superlattice of LiOsO$_3$ and LiNbO$_3$. We use electronic structure
calculations to predict that the (LiOsO$_3$)$_1$/(LiNbO$_3$)$_1$ superlattice
is a type-I multiferroic material with a ferrolectric polarization of
41.2~$\mu$C cm$^{-2}$, Curie temperature of 927\,K, and N\'eel temperature of
671\,K. Our results support a route towards high-temperature multiferroics,
\emph{i.e.}, driving non-magnetic \emph{polar metals} into correlated
insulating magnetic states.",1503.01948v1
2015/3/13,Magneto-optics in transition metal diselenide monolayers,"We perform photoluminescence experiments at 4K on two different transition
metal diselenide monolayers, namely MoSe2 and WSe2 in magnetic fields $B_z$ up
to 9T applied perpendicular to the sample plane. In MoSe2 monolayers the valley
polarization of the neutral and the charged exciton (trion) can be tuned by the
magnetic field, independent of the excitation laser polarization. In the
investigated WSe2 monolayer sample the evolution of the trion valley
polarization depends both on the applied magnetic field and the excitation
laser helicity, while the neutral exciton valley polarization depends only on
the latter. Remarkably we observe a reversal of the sign of the trion
polarization between WSe2 and MoSe2. For both systems we observe a clear Zeeman
splitting for the neutral exciton and the trion of about $\pm2$meV at
$B_z\mp9$T. The extracted Land\'{e}-factors for both exciton complexes in both
materials are $g\approx -4$.",1503.04105v1
2015/4/7,Fractal butterflies in buckled graphene-like materials,"We study theoretically the properties of buckled graphene-like materials,
such as silicene and germanene, in a strong perpendicular magnetic field and a
periodic potential. We analyze how the spin-orbit interaction and the
perpendicular electric field influences the energy spectra of these systems.
When the magnetic flux through a unit cell of the periodic potential measured
in magnetic flux quantum is a rational number, ? = p/q, then in each Landau
level the energy spectra have a band structure, which is characterized by the
corresponding gaps. We study the dependence of those gaps on the parameters of
the buckled graphene-like materials. Although some gaps have weak dependence on
the magnitude of the spin-orbit coupling and the external electric field, there
are gaps that show strong nonomonotic dependence on these parameters. For ? =
1/2, the spin-orbit interaction also opens up a gap at one of the Landau
levels. The magnitude of the gap increases with spin-orbit coupling and
decreases with the applied electric field.",1504.01749v1
2015/6/15,Chiral plasmons without magnetic field,"Plasmons, the collective oscillations of interacting electrons, possess
emergent properties that dramatically alter the optical response of metals. We
predict the existence of a new class of plasmons -- chiral Berry plasmons
(CBPs) -- for a wide range of two-dimensional metallic systems including gapped
Dirac materials. As we show, in these materials the interplay between Berry
curvature and electron-electron interactions yields chiral plasmonic modes at
zero magnetic field. The CBP modes are confined to system boundaries, even in
the absence of topological edge states, with chirality manifested in split
energy dispersions for oppositely directed plasmon waves. We unveil a rich CBP
phenomenology and propose setups for realizing them, including in anomalous
Hall metals and optically-pumped 2D Dirac materials. Realization of CBPs will
offer a new paradigm for magnetic field-free, sub-wavelength optical
non-reciprocity, in the mid IR-THz range, with tunable splittings as large as
tens of THz, as well as sensitive all-optical diagnostics of topological bands.",1506.04743v2
2015/6/28,Shielding superconductors with thin films,"Determining the optimal arrangement of superconducting layers to withstand
large amplitude AC magnetic fields is important for certain applications such
as superconducting radiofrequency cavities. In this paper, we evaluate the
shielding potential of the superconducting film/insulating film/superconductor
(SIS') structure, a configuration that could provide benefits in screening
large AC magnetic fields. After establishing that for high frequency magnetic
fields, flux penetration must be avoided, the superheating field of the
structure is calculated in the London limit both numerically and, for thin
films, analytically. For intermediate film thicknesses and realistic material
parameters we also solve numerically the Ginzburg-Landau equations. It is shown
that a small enhancement of the superheating field is possible, on the order of
a few percent, for the SIS' structure relative to a bulk superconductor of the
film material, if the materials and thicknesses are chosen appropriately.",1506.08428v1
2015/8/6,Odd-parity magnetoresistance in pyrochlore iridate thin films with broken time-reversal symmetry,"A new class of materials termed topological insulators have been intensively
investigated due to their unique Dirac surface state carrying dissipationless
edge spin currents. Recently, it has been theoretically proposed that the three
dimensional analogue of this type of band structure, the Weyl Semimetal phase,
is materialized in pyrochlore oxides with strong spin-orbit coupling,
accompanied by all-in-all-out spin ordering. Here, we report on the fabrication
and magnetotransport of Eu2Ir2O7 single crystalline thin films. We reveal that
one of the two degenerate all-in-all-out domain structures, which are connected
by time-reversal operation, can be selectively formed by the polarity of the
cooling magnetic field. Once formed, the domain is robust against an oppositely
polarised magnetic field, as evidenced by an unusual odd field dependent term
in the magnetoresistance and an anomalous term in the Hall resistance. Our
findings pave the way for exploring the predicted novel quantum transport
phenomenon at the surfaces/interfaces or magnetic domain walls of pyrochlore
iridates.",1508.01318v1
2015/8/6,The many faces of quantum kagome materials: Interplay of further-neighbour exchange and Dzyaloshinskii-Moriya interaction,"The field of frustrated magnetism has been enriched significantly by the
discovery of various kagome lattice compounds. These materials exhibit a great
variety of macroscopic behaviours ranging from magnetic orders to quantum spin
liquids. Using large-scale exact diagonalization, we construct the phase
diagram of the $S=1/2$ $J_1$-$J_2$ kagome Heisenberg model with $z$-axis
Dzyaloshinskii-Moriya interaction $D_z$. We show that this model can
systematically account for many of the experimentally observed phases. Small
$J_2$ and $D_z$ can stabilize respectively a gapped and a gapless spin liquid.
When $J_2$ or $D_z$ is substantial, the ground state develops a $\mathbf{Q}=0$,
$120^\textrm{o}$ antiferromagnetic order. The critical strengths for inducing
magnetic transition are $D^c_z \sim 0.1\, J_1$ at $J_2=0$, and $J^c_2\sim 0.4\,
J_1$ at $D_z=0$. The previously reported values of $D_z$ and $J_2$ for
herbertsmithite [ZnCu$_3$(OH)$_6$Cl$_2$] place the compound in close proximity
to a quantum critical point.",1508.01523v1
2015/6/3,Stable room-temperature ferromagnetic phase at the FeRh(100) surface,"Interfaces and low dimensionality are sources of strong modifications of
electronic, structural, and magnetic properties of materials. FeRh alloys are
an excellent example because of the first-order phase transition taking place
at $\sim$400 K from an antiferromagnetic phase at room temperature to a high
temperature ferromagnetic one. It is accompanied by a resistance change and
volume expansion of about 1\%. We have investigated the electronic and magnetic
properties of FeRh(100) epitaxially grown on MgO by combining spectroscopies
characterized by different probing depths, namely X-ray magnetic circular
dichroism and photoelectron spectroscopy. We thus reveal that the symmetry
breaking induced at the Rh-terminated surface stabilizes a surface
ferromagnetic layer involving five planes of Fe and Rh atoms in the nominally
antiferromagnetic phase at room temperature. First-principles calculations
provide a microscopic description of the structural relaxation and the electron
spin-density distribution that fully support the experimental findings.",1508.01777v1
2015/9/15,Successive magnetic field-induced transitions and colossal magnetoelectric effect in Ni$_{3}$TeO$_{6}$,"We report the discovery of a metamagnetic phase transition in a polar
antiferromagnet Ni$_3$TeO$_6$ that occurs at 52 T. The new phase transition
accompanies a colossal magnetoelectric effect, with a magnetic-field-induced
polarization change of 0.3 $\mu$C/cm$^2$, a value that is 4 times larger than
for the spin-flop transition at 9 T in the same material, and also comparable
to the largest magnetically-induced polarization changes observed to date. Via
density-functional calculations we construct a full microscopic model that
describes the data. We model the spin structures in all fields and clarify the
physics behind the 52 T transition. The high-field transition involves a
competition between multiple different exchange interactions which drives the
polarization change through the exchange-striction mechanism. The resultant
spin structure is rather counter-intuitive and complex, thus providing new
insights on design principles for materials with strong magnetoelectric
coupling.",1509.04715v1
2015/11/1,Reciprocal spin Hall effects in conductors with strong spin-orbit coupling: a review,"Spin Hall effect and its inverse provide essential means to convert charge to
spin currents and vice versa, which serve as a primary function for spintronic
phenomena such as the spin-torque ferromagnetic resonance and the spin Seebeck
effect. These effects can oscillate magnetization or detect a thermally
generated spin splitting in the chemical potential. Importantly this conversion
process occurs via the spin-orbit interaction, and requires neither magnetic
materials nor external magnetic fields. However, the spin Hall angle, i.e., the
conversion yield between the charge and spin currents, depends severely on the
experimental methods. Here we discuss the spin Hall angle and the spin
diffusion length for a variety of materials including pure metals such as Pt
and Ta, alloys and oxides determined by the spin absorption method in a lateral
spin valve structure.",1511.00332v1
2015/11/5,Interface control of electronic transport across the magnetic phase transition in SrRuO_3/SrTiO_3 heterointerface,"The emerging material class of complex-oxides, where manipulation of physical
properties lead to new functionalities at their heterointerfaces, is expected
to open new frontiers in Spintronics. For example, SrRuO_3 is a promising
material where external stimuli like strain, temperature and structural
distortions control the stability of electronic and magnetic states, across its
magnetic phase transition, useful for Spintronics. Despite this, not much has
been studied to understand such correlations in SrRuO_3. Here we explore the
influence of electron-lattice correlation to electron-transport, at interfaces
between SrRuO_3 and Nb:SrTiO_3 across its ferromagnetic transition, using a
nanoscale transport probe and first-principles calculations. We find that the
geometrical reconstructions at the interface and hence modifications in
electronic structures dominate the transmission across its ferromagnetic
transition, eventually flipping the charge-transport length-scale in SrRuO_3.
This approach can be easily extended to other devices where competing ground
states can lead to different functional properties across their
heterointerfaces.",1511.01933v1
2015/11/30,Strong charge and spin fluctuations in La$_2$O$_3$Fe$_2$Se$_2$,"The electronic structure and magnetic properties of the strongly correlated
material La$_2$O$_3$Fe$_2$Se$_2$ are studied by using both the density function
theory plus $U$ (DFT+$U$) method and the DFT plus Gutzwiller (DFT+G)
variational method. The ground-state magnetic structure of this material
obtained with DFT+$U$ is consistent with recent experiments, but its band gap
is significantly overestimated by DFT+$U$, even with a small Hubbard $U$ value.
In contrast, the DFT+G method yields a band gap of 0.1 - 0.2 eV, in excellent
agreement with experiment. Detailed analysis shows that the electronic and
magnetic properties of of La$_2$O$_3$Fe$_2$Se$_2$ are strongly affected by
charge and spin fluctuations which are missing in the DFT+$U$ method.",1511.09195v1
2015/12/11,Time reversal symmetry breaking superconductivity in topological materials,"Fascinating phenomena have been known to arise from the Dirac theory of
relativistic quantum mechanics, which describes high energy particles having
linear dispersion relations. Electrons in solids usually have non-relativistic
dispersion relations but their quantum excitations can mimic relativistic
effects. In topological insulators, electrons have both a linear dispersion
relation, the Dirac behavior, on the surface and a non-relativistic energy
dispersion in the bulk. Topological phases of matter have attracted much
interest, particularly broken-symmetry phases in topological insulator
materials. Here, we report by Nb doping that the topological insulator Bi2Se3
can be turned into a bulk type-II superconductor while the Dirac surface
dispersion in the normal state is preserved. A macroscopic magnetic ordering
appears below the superconducting critical temperature of 3.2 K indicating a
spontaneous spin rotation symmetry breaking of the Nb magnetic moments. Even
though such a magnetic order may appear at the edge of the superconductor, it
is mediated by superconductivity and presents a novel phase of matter which
gives rise to a zero-field Hall effect.",1512.03519v1
2015/12/11,Possible ferrimagnetism and ferroelectricity of half-substituted rare-earth titanate: a first-principles study on Y$_{0.5}$La$_{0.5}$TiO$_3$,"Titanates with the perovskite structure, including ferroelectrics (e.g.,
BaTiO$_3$) and ferromagnetic ones (e.g., YTiO$_3$), are important functional
materials. Recent theoretical studies predicted multiferroic states in strained
EuTiO$_3$ and titanate superlattices, the former of which has already been
experimental confirmed. Here, a first-principles calculation is performed to
investigate the structural, magnetic, and electronic properties of Y
half-substituted LaTiO3. Our results reveal that the magnetism of
Y$_{0.5}$La$_{0.5}$TiO$_3$ sensitively depends on its structural details
because of the inherent phase competition. The lowest energy state is the
ferromagnetic state, resulting in 0.25 $\mu_{\rm B}$/Ti. Furthermore, some
configurations of Y$_{0.5}$La$_{0.5}$TiO$_3$ exhibit hybrid improper
polarizations, which can be significantly affected by magnetism, resulting in
the multiferroic properties. Because of the quenching disorder of substitution,
the real Y$_{0.5}$La$_{0.5}$TiO3 material with random A-site ions may exhibit
interesting relaxor behaviors.",1512.03616v1
2015/12/19,Thermo-magnetic properties of the magnetocaloric layered materials based upon FeMnAsP: a Green function-method approach,"The compounds FeMnAsxP1-x are very promising as far as commercial
applications of the magnetocaloric effect are concerned. However, the
theoretical literature on magnetocaloric materials still adopts simple
molecular-field models in the description of important properties like the
entropy variation that accompanies applied isothermal magnetic field cycling,
for instance. We apply a Green function theoretical treatment for such
analysis. The advantages of such approach are well-known since the details of
the crystal structure are incorporated in the model, as well as a precise
description of correlations between spins of the transition metal ions can be
obtained. For the sake of simplcity we adopt a simple one-exchange parameter
Heisenberg model, and the observed first-order phase transitions are reproduced
by the introduction of a biquadratic term in the hamiltonian. Good agreement
with experimental magnetocaloric data for FeMnAsxP1-x compounds is obtained, as
well as an agreement with the magnetic field dependence for these properties
predicted from the Landau theory of continuous phase transitions.",1512.08503v1
2016/3/29,Coherent Charge and Spin Density Waves in Underdoped HgBa$_{2}$CuO$_{4+δ}$,"Various forms of spin and charge ordering have been identified in a wide
range of cuprate superconducting materials, but whether these behaviors are
ubiquitous phenomena is not established. In this work we focus on one of the
simplest compounds, HgBa$_{2}$CuO$_{4+\delta}$ (Hg1201), a superconductor with
a high transition temperature, 97 K, having only a single layer and tetragonal
structure, in contrast to one of the most extensively studied materials,
YBa$_{2}$Cu$_{3}$O$_{6+y}$ (Y123). Using nuclear magnetic resonance we have
discovered a coherent spatial modulation of both spin and charge that is
temperature and magnetic field independent, in competition with
superconductivity similar to other cuprates. However, there is no evidence for
the magnetic field and temperature induced charge order observed in Y123.
Electronic instabilities are a common feature of cuprates as in the present
work on Hg1201, but their manifestations are not universal.",1603.08839v1
2016/4/4,Reversibly switchable electromagnetic device with leakage-free electrolyte,"Electrical control of oxygen off-stoichiometry of transition-metal oxides at
room temperature is a desired strategy to simultaneously switch the electrical
conductance and magnetism of the device. Although the use of the
electrochemical redox reaction of transition-metal oxides is the most
reasonable way to achieve the aforementioned switch, such a device has not been
realized because of the lack of a leakage-free liquid electrolyte. Here, we
demonstrate an electromagnetic device that can reversibly switch a
transition-metal oxide from an insulator/non-magnet to a metal/magnet (Tc=275
K) using a newly developed 'leakage-free electrolyte', incorporated in an
amorphous NaTaO3 nanopillar array film. Reversible switching occurs
electrically, obeying Faraday's laws of electrolysis, under a DC voltage of
+(-)3 V within 2-3 s at RT. The present electromagnetic device does not have
the drawback of liquid leakage, and the leakage-free electrolyte provides a
novel design concept for practical electromagnetic devices using
transition-metal oxides.",1604.00824v1
2016/7/2,Transition Metal and Vacancy Defect Complexes in Phosphorene: A Spintronic Perspective,"Inducing magnetic moment in otherwise nonmagnetic two-dimensional
semiconducting materials is the key first step to design spintronic materials.
Here, we study the absorption of transition-metals on pristine and defected
single-layer phosphorene, within density functional theory. We predict that
increased transition-metal diffusivity on pristine phosphorene would hinder any
possibility of controlled magnetism, and thus any application. In contrast, the
point-defects will anchor metals, and exponentially reduce the diffusivity.
Similar to other two-dimensional materials, metals bind strongly on both
pristine and defected phosphorene, and we provide a microscopic description of
bonding, which explain the qualitative trend with increasing number of valence
electrons. We further argue that the divacancy complex is imperative in any
practical purpose due to their increased thermodynamic stability over
monovacancy. For most cases, the defect-transition metal complexes retain the
intrinsic semiconduction properties, and also induce a local magnetic moment
with large exchange-splitting and spin-flip energies, which are necessary for
spintronic applications. Specifically, the V/Mn/Fe absorbed at the divacancy
have tremendous promise in this regard. Further, we provide a simple
microscopic model to describe the local moment formation in these transition
metal and defect complexes.",1607.00521v1
2016/11/23,"Electron interactions, spin-orbit coupling, intersite correlations in pyrochlore iridates","We perform combined density functional and dynamical mean-field calculations
to study the pyrochlore iridates Lu$_2$Ir$_2$O$_7$, Y$_2$Ir$_2$O$_7$ and
Eu$_2$Ir$_2$O$_7$. Both single-site and cluster dynamical mean-field
calculations are performed and spin-orbit coupling is included. Paramagnetic
metallic phases, antiferromagnetic metallic phases with tilted Weyl cones and
antiferromagnetic insulating phases are found. The magnetic phases display
all-in/all-out magnetic ordering, consistent with previous studies. Unusually
for electronically three dimensional materials, the single-site dynamical
mean-field approximation fails to reproduce qualitative material trends,
predicting in particular that the paramagnetic phase properties of
Y$_2$Ir$_2$O$_7$ and Eu$_2$Ir$_2$O$_7$ are almost identical, although in
experiments the Y compound has a much higher resistance than the Eu compound.
This qualitative failure is attributed to the importance of intersite magnetic
correlations in the physics of these materials.",1611.07997v2
2017/1/12,Nondestructive Measurement of Orbital Angular Momentum for an Electron Beam,"Free electrons with a helical phase front, referred to as ""twisted""
electrons, possess an orbital angular momentum (OAM) and, hence, a quantized
magnetic dipole moment along their propagation direction. This intrinsic
magnetic moment can be used to probe material properties. Twisted electrons
thus have numerous potential applications in materials science. Measuring this
quantity often relies on a series of projective measurements that subsequently
change the OAM carried by the electrons. In this Letter, we propose a
nondestructive way of measuring an electron beam's OAM through the interaction
of this associated magnetic dipole with a conductive loop. Such an interaction
results in the generation of induced currents within the loop, which are found
to be directly proportional to the electron's OAM value. Moreover, the electron
experiences no OAM variations and only minimal energy losses upon the
measurement, and, hence, the nondestructive nature of the proposed technique.",1701.03199v1
2017/2/9,GHz-Band Integrated Magnetic Inductors,"The demand on mobile electronics to continue to shrink in size while increase
in efficiency drives the demand on the internal passive components to do the
same. Power amplifiers require inductors with small form factors, high quality
factors, and high operating frequency in the single-digit GHz range. This work
explores the use of magnetic materials to satisfy the needs of power amplifier
inductor applications. This paper discusses the optimization choices regarding
material selection, device design, and fabrication methodology. The inductors
achieved here present the best performance to date for an integrated magnetic
core inductor at high frequencies with a 1 nH inductance and peak quality
factor of 4 at ~3 GHz. Such compact inductors show potential for efficiently
meeting the need of mobile electronics in the future.",1702.03009v1
2017/2/15,Stability of Weyl points in magnetic half-metallic Heusler compounds,"We employ {\it ab-initio} fully-relativistic electronic structure
calculations to study the stability of the Weyl points in the momentum space
within the class of the half-metallic ferromagnetic full Heusler materials, by
focusing on Co$_2$TiAl as a well-established prototype compound. Here we show
that both the number of the Weyl points together with their $k$-space
coordinates can be controlled by the orientation of the magnetization. This
alternative degree of freedom, which is absent in other topological materials
(e.g. in Weyl semimetals), introduces novel functionalities, specific for the
class of half-metallic ferromagnets. Of special interest are Weyl points which
are preserved irrespectively of any arbitrary rotation of the magnetization
axis.",1702.04558v1
2017/2/21,"Back hopping in spin-transfer-torque devices, possible origin and counter measures","The effect of undesirable high-frequency free-layer switching in magnetic
multilayer systems, referred to as back hopping, is investigated by means of
the spin-diffusion model. A possible origin of the back-hopping effect is found
to be the destabilization of the pinned layer which leads to perpetual
switching of both layers. The influence of different material parameters on the
critical switching currents for the free and pinned layer is obtained by
micromagnetic simulations. It is found that the choice of a free-layer material
with low polarization $\beta$ and saturation magnetization $M_s$, and a
pinned-layer material with high $\beta$ and $M_s$ leads to a low free-layer
critical current and a high pinned-layer critical current and hence reduces the
likelihood of back hopping. While back hopping was observed in various types of
devices, there are only few experiments that exhibit this effect in
perpendicularly magnetized systems. However, our simulations suggest, that this
is likely to change due to loss of pinned-layer anisotropy when decreasing
device sizes.",1702.06604v3
2017/3/7,Successive field-induced transitions in BiFeO$_{3}$ around room temperature,"The effects of high magnetic fields applied perpendicular to the spontaneous
ferroelectric polarization on single crystals of BiFeO$_3$ were investigated
through magnetization, magnetostriction, and neutron diffraction measurements.
The magnetostriction measurements revealed lattice distortion of $2\times
10^{-5}$, during the reorientation process of the cycloidal spin order by
applied magnetic fields. Furthermore, anomalous changes in magnetostriction and
electric polarization at a larger field demonstrate an intermediate phase
between cycloidal and canted antiferromagnetic states, where a large
magnetoelectric effect was observed. Neutron diffraction measurements clarified
that incommensurate spin modulation along [110] direction in the cycloidal
phase becomes commensurate in the intermediate phase. Theoretical calculations
based on the standard spin Hamiltonian of this material suggest an
antiferromagnetic cone-type spin order in the intermediate phase.",1703.02306v1
2017/3/27,Anomalous Hall effect and topological defects in antiferromagnetic Weyl semimetals: Mn$_3$Sn/Ge,"We theoretically study the interplay between bulk Weyl electrons and magnetic
topological defects, including magnetic domains, domain walls, and
$\mathbb{Z}_6$ vortex lines, in the antiferromagnetic Weyl semimetals \mnsn\
and Mn$_3$Ge with negative vector chirality. We argue that these materials
possess a hierarchy of energies scales which allows a description of the spin
structure and spin dynamics using a XY model with $\mathbb{Z}_6$ anisotropy. We
propose a dynamical equation of motion for the XY order parameter, which
implies the presence of $\mathbb{Z}_6$ vortex lines, the double-domain pattern
in the presence of magnetic fields, and the ability to control domains with
current. We also introduce a minimal electronic model which allows efficient
calculation of the electronic structure in the antiferromagnetic configuration,
unveiling Fermi arcs at domain walls, and sharp quasi-bound states at
$\mathbb{Z}_6$ vortices. Moreover, we have shown how these materials may allow
electronic-based imaging of antiferromagnetic microstructure, and propose a
possible device based on domain-dependent anomalous Hall effect.",1703.08910v1
2017/4/4,Magnetic and dielectric order in the kagome-like francisite Cu$_3$Bi(SeO$_3$)$_2$O$_2$Cl,"We report a single-crystal neutron diffraction and inelastic neutron
scattering study on the spin 1/2 cuprate Cu$_3$Bi(SeO$_3$)$_2$O$_2$Cl,
complemented by dielectric and electric polarization measurements. The study
clarifies a number of open issues concerning this complex material, whose
frustrated interactions on a kagome-like lattice, combined with
Dzyaloshinskii-Moriya interactions, are expected to stabilize an exotic canted
antiferromagnetic order. In particular, we determine the nature of the
structural transition occurring at 115 K, the magnetic structure below 25 K
resolved in the updated space group, and the microscopic ingredients at the
origin of this magnetic arrangement. This was achieved by an analysis of the
measured gapped spin waves, which signifies the need of an unexpected and
significant anisotropic exchange beyond the proposed Dzyaloshinskii-Moriya
interactions. Finally, we discuss the mutliferroic properties of this material
with respect to the space group symmetries.",1704.00915v1
2017/4/21,Time resolved measurements of the switching trajectory of Pt/Co elements induced by spin-orbit torques,"We report the experimental observation of spin-orbit torque induced switching
of perpendicularly magnetized Pt/Co elements in a time resolved stroboscopic
experiment based on high resolution Kerr microscopy. Magnetization dynamics is
induced by injecting sub-nanosecond current pulses into the bilayer while
simultaneously applying static in-plane magnetic bias fields. Highly
reproducible homogeneous switching on time scales of several tens of
nanoseconds is observed. Our findings can be corroborated using micromagnetic
modelling only when including a field-like torque term as well as the
Dzyaloshinskii-Moriya interaction mediated by finite temperature.",1704.06418v1
2017/5/30,"Spin-transport, spin-torque and memory in antiferromagnetic devices: Part of a collection of reviews on antiferromagnetic spintronics","Ferromagnets are key materials for sensing and memory applications. In
contrast, antiferromagnets that represent the more common form of magnetically
ordered materials, have so far found less practical application beyond their
use for establishing reference magnetic orientations via exchange bias. This
might change in the future due to the recent progress in materials research and
discoveries of antiferromagnetic spintronic phenomena suitable for device
applications. Experimental demonstrations of the electrical switching and
electrical detection of the N\'eel order open a route towards memory devices
based on antiferromagnets. Apart from the radiation and magnetic-field
hardness, memory cells fabricated in antiferromagnets are inherently multilevel
which could be used for neuromorphic computing. Switching speeds attainable in
antiferromagnets far exceed those of the ferromagnetic and semiconductor memory
technologies. Here we review the recent progress in electronic spin-transport
and spin-torque phenomena in antiferromagnets that are dominantly of the
relativistic quantum mechanics origin. We discuss their utility in pure
antiferromagnetic or hybrid ferromagnetic/antiferromagnetic memory devices",1705.10675v1
2017/6/3,Large spontaneous exchange bias in a weak ferromagnet Pb6Ni9(TeO6)5,"We report the magnetic and dielectric behavior of Pb6Ni9(TeO6)5, a new
compound comprising the honeycomb-like layers of S=1 spins, through detailed
structural, magnetic and dielectric investigation. An antiferromagnetic-type
transition at 25 K (TN) with weak-ferromagnetic behavior is revealed.
Interestingly, a large value of coercive field of 1.32 T at 2 K is observed.
The isothermal magnetization after zero-field-cooled condition, it exhibits the
presence of large spontaneous exchange bias (SEB) with a magnitude of 0.19 T at
2 K; which is rare in single bulk materials, especially without external
doping. The value of |HEB| further enhances to 0.24 T under 16 T field-cooled
condition, confirming the presence of large exchange bias in the material. In
addition, the dielectric constant shows an anomaly at the onset of TN,
indicating the presence of magnetodielectric coupling.",1706.00903v1
2017/6/26,Magnetic Proximity Effect in Pt/CoFe2O4 Bilayers,"We observe the magnetic proximity effect (MPE) in Pt/CoFe2O4 bilayers grown
by molecular beam epitaxy. This is revealed through angle-dependent
magnetoresistance measurements at 5 K, which isolate the contributions of
induced ferromagnetism (i.e. anisotropic magnetoresistance) and spin Hall
effect (i.e. spin Hall magnetoresistance) in the Pt layer. The observation of
induced ferromagnetism in Pt via AMR is further supported by density functional
theory calculations and various control measurements including insertion of a
Cu spacer layer to suppress the induced ferromagnetism. In addition, anomalous
Hall effect measurements show an out-of-plane magnetic hysteresis loop of the
induced ferromagnetic phase with larger coercivity and larger remanence than
the bulk CoFe2O4. By demonstrating MPE in Pt/CoFe2O4, these results establish
the spinel ferrite family as a promising material for MPE and spin manipulation
via proximity exchange fields.",1706.08473v1
2017/7/10,Broadband suppression of backscattering at optical frequencies using low permittivity dielectric spheres,"The exact suppression of backscattering from rotationally symmetric objects
requires dual symmetric materials where ${\epsilon_r} = {\mu_r}$. This prevents
their design at many frequency bands, including the optical one, because
magnetic materials are not available. Electromagnetically small non-magnetic
spheres of large permittivity offer an alternative. They can be tailored to
exhibit balanced electric and magnetic dipole polarizabilities, which result in
approximate zero backscattering. In this case, the effect is inherently
narrowband. Here, we put forward a different alternative that allows broadband
functionality: Electromagnetically large spheres made from low permittivity
materials. The effect occurs in a parameter regime that approaches the trivial
${\epsilon_r} \to {\mu_r} =1$ case, where approximate duality is met in a
weakly wavelength dependence fashion. Despite the low permittivity, the overall
scattering response of the spheres is still significant. Radiation patterns
from these spheres are shown to be highly directive across an octave spanning
band. The effect is analytically and numerically shown using the Mie
coefficients.",1707.02775v1
2017/8/30,Phase-Encoded Hyperpolarized Nanodiamond for Magnetic Resonance Imaging,"Surface-functionalized nanomaterials can act as theranostic agents that
detect disease and track biological processes using hyperpolarized magnetic
resonance imaging (MRI). Candidate materials are sparse however, requiring
spinful nuclei with long spin-lattice relaxation (T1) and spin-dephasing times
(T2), together with a reservoir of electrons to impart hyperpolarization. Here,
we demonstrate the versatility of the nanodiamond material system for
hyperpolarized 13C MRI, making use of its intrinsic paramagnetic defect
centers, hours-long nuclear T1 times, and T2 times suitable for spatially
resolving millimeter-scale structures. Combining these properties, we enable a
new imaging modality that exploits the phase-contrast between spins encoded
with a hyperpolarization that is aligned, or anti-aligned with the external
magnetic field. The use of phase-encoded hyperpolarization allows nanodiamonds
to be tagged and distinguished in an MRI based on their spin-orientation alone,
and could permit the action of specific bio-functionalized complexes to be
directly compared and imaged.",1709.01851v1
2017/9/27,The influence of superparamagnetism on exchange anisotropy at CoO/[Co/Pd] interfaces,"Magnetic systems exhibiting exchange bias effect are being considered as
materials for applications in data storage devices, sensors and biomedicine. As
the size of new mag- netic devices is being continuously reduced, the influence
of thermally induced instabilities in magnetic order has to be taken into
account during their fabrication process. In this study we show the influence
of superparamagnetism on magnetic properties of exchange-biased [CoO/Co/Pd]10
multilayer. We find that the process of progressive thermal blocking of the
superparamagnetic clusters causes an unusually fast rise of the exchange
anisotropy field and coercivity, and promotes the easy axis switching to
out-of-plane direction.",1709.09399v1
2017/11/5,Magnetoelectric properties of the layered room-temperature antiferromagnets BaMn2P2 and BaMn2As2,"Properties of two ThCr2Si2-type materials are discussed within the context of
their established structural and magnetic symmetries. Both materials develop
collinear, G-type antiferromagnetic order above room temperature, and magnetic
ions occupy acentric sites in centrosymmetric structures. We refute a previous
conjecture that BaMn2As2 is an example of a magnetoelectric material with
hexadecapole order by exposing flaws in supporting arguments, principally, an
omission of discrete symmetries enforced by the symmetry of sites used by Mn
ions and, also, improper classifications of the primary and secondary
order-parameters. Implications for future experiments designed to improve our
understanding of BaMn2P2 and BaMn2As2 magnetoelectric properties, using neutron
and x-ray diffraction, are examined. Patterns of Bragg spots caused by
conventional magnetic dipoles and magnetoelectric (Dirac) multipoles are
predicted to be distinct, which raises the intriguing possibility of a unique
and comprehensive examination of the magnetoelectric state by diffraction. A
roto-inversion operation in Mn site symmetry is ultimately responsible for the
distinguishing features.",1711.01571v1
2017/12/4,Accurate analysis for harmonic Hall voltage measurement for spin-orbit torques,"An accurate method is developed to extract the spin-orbit effective fields
through analysis of the results of harmonic Hall voltage measurements by
deriving detailed analytical equations, in which both the z-component of the
applied magnetic field and the second-order perpendicular magnetic anisotropy
are taken into account. The method is tested by analyzing the results of a
macrospin simulation. The spin-orbit effective fields extracted from the
analysis are found to be in excellent agreement with the input spin-orbit
effective fields used for the macrospin simulation over the entire range of the
polar magnetization angle and a wide range (0-2) of the ratio of the planar to
the anomalous Hall voltage considered in this study. The accuracy of the
proposed method is demonstrated more clearly via a systematic study involving a
comparison of its results with those of the conventional analytical method.",1712.00902v1
2017/12/22,Magnetoresistance in YBi and LuBi semimetals due to nearly perfect carrier compensation,"Monobismuthides of yttrium and lutetium are shown as new representatives of
materials which exhibit extreme magnetoresistance and magnetic-field-induced
resistivity plateau. At low temperatures and in magnetic field of 9T the
magnetoresistance attains the order of magnitude of 10,000% and 1,000%, on YBi
and LuBi, respectively. Our thorough examination of electron transport
properties of both compounds show that observed features are the consequence of
nearly perfect carrier compensation rather than of possible nontrivial topology
of electronic states. The field-induced plateau of electrical resistivity can
be explained with Kohler scaling. Anisotropic multi-band model of electronic
transport describes very well the magnetic field dependence of electrical
resistivity and Hall resistivity. Data obtained from the Shubnikov-de Haas
oscillations analysis also confirm that Fermi surface of each compound contains
almost equal amounts of holes and electrons. First-principle calculations of
electronic band structure are in a very good agreement with the experimental
data.",1712.08433v3
2017/12/22,Magnetically Ordered Insulators for Advanced Spintronics,"Magnetically ordered, electrically insulating materials pave the way towards
novel spintronic devices. In these materials the flow of magnetic excitations
such as magnons results in pure spin currents. These spin currents can be
driven by gradients of the spin chemical potential and/or temperature such that
they can play the same role in novel spintronic devices as charge currents in
traditional electronic circuits. Connecting spin current based and charge
current based devices requires spin to charge interconversion. This has been
achieved by the spin Hall effect with an efficiency of several 10%. The recent
progress in materials development and understanding of pure spin current
physics opens up a plethora of novel device concepts and opportunities for
fundamental studies.",1712.08517v1
2018/1/19,"Superconductivity in potassium-doped 2,2$'$-bipyridine","Organic compounds are always promising candidates of superconductors with
high transition temperatures. We examine this proposal by choosing
2,2$'$-bipyridine solely composed by C, H, and N atoms. The presence of
Meissner effect with a transition temperature of 7.2 K in this material upon
potassium doping is demonstrated by the $dc$ magnetic susceptibility
measurements. The real part of the $ac$ susceptibility exhibits the same
transition temperature as that in $dc$ magnetization, and a sharp peak appeared
in the imaginary part indicates the formation of the weakly linked
superconducting vortex current. The occurence of superconductivity is further
supported by the resistance drop at the transition together with its
suppression by the applied magnetic fields. The superconducting phase is
identified to be K$_3$-2,2$'$-bipyridine from the analysis of Raman scattering
spectra. This work not only opens an encouraging window for finding
superconductivity after optoelectronics in 2,2$'$-bipyridine-based materials
but also offers an example to realize superconductivity from conducting
polymers and their derivatives.",1801.06320v2
2018/2/3,Hybrid Nodal Loop Metal: Unconventional Magnetoresponse and Material Realization,"A nodal loop is formed by band crossing along a one-dimensional closed
manifold, with each point on the loop a linear nodal point in the transverse
dimensions and can be classified as type-I or type-II depending on the band
dispersion. Here, we propose a class of nodal loops composed of both type-I and
type-II points, which are hence termed as hybrid nodal loops. Based on
firstprinciples calculations, we predict the realization of such loops in the
existing electride material Ca2As. For a hybrid loop, the Fermi surface
consists of coexisting electron and hole pockets that touch at isolated points
for an extended range of Fermi energies, without the need for fine-tuning. This
leads to unconventional magnetic responses, including the zero-field magnetic
breakdown and the momentum space Klein tunneling observable in the magnetic
quantum oscillations, as well as the peculiar anisotropy in the cyclotron
resonance.",1802.00905v1
2018/2/4,Pressure-tuned magnetic interactions in honeycomb Kitaev materials,"A range of honeycomb-lattice compounds has been proposed and investigated in
the search for a topological Kitaev spin liquid. However, sizable Heisenberg
interactions and additional symmetry-allowed exchange anisotropies in the
magnetic Hamiltonian of these potential Kitaev materials push them away from
the pure Kitaev spin-liquid state. Particularly the Kitaev-to-Heisenberg
coupling ratio is essential in this respect. With the help of advanced
quantum-chemistry methods, we explore how the magnetic coupling ratios depend
on pressure in several honeycomb compounds (Na$_2$IrO$_3$,
$\beta$-Li$_2$IrO$_3$, and $\alpha$-RuCl$_3$). We find that the Heisenberg and
Kitaev terms are affected differently by uniform pressure or strain: the Kitaev
component increases more rapidly than the Heisenberg counterpart. This provides
a scenario where applying pressure or strain can stabilize a spin liquid in
such materials.",1802.01051v1
2018/3/13,Spin wave localization and guiding by magnon band structure engineering in yttrium iron garnet,"In spintronics the propagation of spin-wave excitations in magnetically
ordered materials can also be used to transport and process information. One of
the most popular materials in this regard is the ferrimagnetic insulator
yttrium-iron-garnet due its exceptionally small spin-wave damping parameter.
While the small relaxation rate allows for large propagation length of magnetic
excitations, it also leads to non-locality of the magnetic properties. By
imaging spin waves their band structure is mapped. In doing so wave vector
selection is shown to suppress dispersion effects to a large extent allowing
for local measurements of spin relaxation. Moreover we demonstrate even higher
control of magnon propagation by employing the wave vector selectivity near an
avoided crossing of different spin-wave modes where the group velocity
approaches zero. Here local engineering of the dispersion allows constructing
magnonic waveguides and at the same time reveals the local relaxation
properties.",1803.04943v3
2018/3/16,Revealing weak spin-orbit coupling effects on charge carriers in a $π$-conjugated polymer,"We measure electrically detected magnetic resonance (EDMR) on organic
light-emitting diodes (OLEDs) made of the polymer
poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) at room
temperature and high magnetic fields, where spectral broadening of the
resonance due to spin-orbit coupling (SOC) exceeds that due to the local
hyperfine fields. Density-functional-theory calculations on an open-shell model
of the material reveal g-tensors of charge-carrier spins in the lowest
unoccupied (electron) and highest occupied (hole) molecular orbitals. These
tensors are used for simulations of magnetic resonance line-shapes. Besides
providing the first quantification and direct observation of SOC effects on
charge-carrier states in these weakly SO-coupled hydrocarbons, this procedure
demonstrates that spin-related phenomena in these materials are fundamentally
monomolecular in nature.",1803.06052v1
2018/5/7,Mixed topological semimetals driven by orbital complexity in two-dimensional ferromagnets,"The concepts of Weyl fermions and topological semimetals emerging in
three-dimensional momentum space are extensively explored owing to the vast
variety of exotic properties that they give rise to. On the other hand, very
little is known about semimetallic states emerging in two-dimensional magnetic
materials, which present the foundation for both present and future information
technology. Here, we demonstrate that including the magnetization direction
into the topological analysis allows for a natural classification of
topological semimetallic states that manifest in two-dimensional ferromagnets
as a result of the interplay between spin-orbit and exchange interactions. We
explore the emergence and stability of such mixed topological semimetals in
realistic materials, and point out the perspectives of mixed topological states
for current-induced orbital magnetism and current-induced domain wall motion.
Our findings pave the way to understanding, engineering and utilizing
topological semimetallic states in two-dimensional spin-orbit ferromagnets.",1805.02549v3
2018/5/8,A Geometrically Frustrated Trimer-Based Mott Insulator,"The crystal structure of Ba4NbRu3O12 is based on triangular planes of
elongated Ru3O12 trimers oriented perpendicular to the plane. We report that it
is semiconducting, that its Weiss temperature and effective magnetic moment are
-155 K and 2.59 {\mu}B/f.u. respectively, and that magnetic susceptibility and
specific heat data indicate that it exhibits magnetic ordering near 4 K. The
presence of a high density of low energy states is evidenced by a substantial
Sommerfeld-like T-linear term (gamma = 31(2) mJ/mole-K^2) in the specific heat.
Electronic structure calculations reveal that the electronic states at the
Fermi Energy reside on the Ru3O12 trimers and that the calculated density of
electronic states is high and continuous around the Fermi Energy - in other
words density functional theory calculates the material to be a metal. Our
results imply that Ba4NbRu3O12 is a geometrically frustrated trimer-based Mott
insulator.",1805.03124v1
2018/6/3,From Claringbullite to a new spin liquid candidate Cu$_3$Zn(OH)$_6$FCl,"The search for quantum spin liquid (QSL) materials has attracted significant
attention in the field of condensed matter physics in recent years, but until
now only a handful of them are considered as candidates hosting QSL ground
state. Owning to their geometrically frustrated structure, Kagome materials are
ideal system to realize QSL. In this study, we synthesized the kagome
structured material Claringbullite (Cu$_4$(OH)$_6$FCl) and then performed Zn
doping to form Cu$_3$Zn(OH)$_6$FCl. Comprehensive measurements reveal that
doping Zn$^{2+}$ ions transforms magnetically ordered Cu$_4$(OH)$_6$FCl into a
non-magnetic QSL candidate Cu$_3$Zn(OH)$_6$FCl. Therefore, the successful
syntheses of Cu$_4$(OH)$_6$FCl and Cu$_3$Zn(OH)$_6$FCl not only provide a new
platform for the study of QSL but also a novel pathway of investigating the
transition between QSL and magnetically ordered systems.",1806.00803v2
2018/7/12,Bond ordering and phase transitions in Na$_{2}$IrO$_{3}$ under high pressure,"The Kitaev model of spin-1/2 on a honeycomb lattice supports degenerate
topological ground states and may be useful in topological quantum computation.
Na$_{2}$IrO$_{3}$ with honeycomb lattice of Ir ions have been extensively
studied as candidates for the realization of the this model, due to the
effective $J_{\text{eff}}=1/2$ low-energy excitations produced by spin-orbit
and crystal-field effect. As the eventual realization of Kitaev model has
remained evasive, it is highly desirable and challenging to tune the candidate
materials toward such end. It is well known external pressure often leads to
dramatic changes to the geometric and electronic structure of materials. In
this work, the high pressure phase diagram of Na$_{2}$IrO$_{3}$ is examined by
first-principles calculations. It is found that Na$_{2}$IrO$_{3}$ undergoes a
sequence of structural and magnetic phase transitions, from the magnetically
ordered phase with space group $C2/m$ to two bond-ordered non-magnetic phases.
The low-energy excitations in these high-pressure phases can be well described
by the $J_{\text{eff}}=1/2$ states.",1807.04413v1
2018/7/12,Origin of skyrmion lattice phase splitting in Zn-substituted Cu$_{2}$OSeO$_{3}$,"We present an investigation into the structural and magnetic properties of
Zn-substituted Cu$_{2}$OSeO$_{3}$, a system in which the skyrmion lattice (SkL)
phase in the magnetic field-temperature phase diagram was previously seen to
split as a function of increasing Zn concentration. We find that splitting of
the SkL is only observed in polycrystalline samples and reflects the occurrence
of several coexisting phases with different Zn content, each distinguished by
different magnetic behaviour. No such multiphase behaviour is observed in
single crystal samples.",1807.04641v1
2018/7/30,Investigating the magnetic ground state of the skyrmion host material Cu$_{2}$OSeO$_{3}$ using long-wavelength neutron diffraction,"We present long-wavelength neutron diffraction data measured on both single
crystal and polycrystalline samples of the skyrmion host material
Cu$_{2}$OSeO$_{3}$. We observe magnetic satellites around the $(0\bar{1}1)$
diffraction peak not accessible to other techniques, and distinguish helical
from conical spin textures in reciprocal space. We confirm successive
transitions from helical to conical to field polarised ordered spin textures as
the external magnetic field is increased. The formation of a skyrmion lattice
with propagation vectors perpendicular to the field direction is observed in a
region of the field-temperature phase diagram that is consistent with previous
reports. Our measurements show that not only the field-polarised phase but also
the helical ground state are made up of ferrimagnetic clusters instead of
individual spins. These clusters are distorted Cu tetrahedra, where the spin on
one Cu ion is anti-aligned with the spin on the three other Cu ions.",1807.11333v1
2018/8/11,Walker solution for Dzyaloshinskii domain wall in ultrathin ferromagnetic films,"We analyze the electric current and magnetic field driven domain wall motion
in perpendicularly magnetized ultrathin ferromagnetic films in the presence of
interfacial Dzyaloshinskii-Moriya interaction and both out-of-plane and
in-plane uniaxial anisotropies. We obtain exact analytical Walker-type
solutions in the form of one-dimensional domain walls moving with constant
velocity due to both spin-transfer torques and out-of-plane magnetic field.
These solutions are embedded into a larger family of propagating solutions
found numerically. Within the considered model, we find the dependencies of the
domain wall velocity on the material parameters and demonstrate that adding
in-plane anisotropy may produce domain walls moving with velocities in excess
of 500 m/s in realistic materials under moderate fields and currents.",1808.03772v2
2018/8/28,Negative-pressure-induced helimagnetism in ferromagnetic cubic perovskites Sr$_{1-x}$Ba$_{x}$CoO$_{3}$,"Helimagnetic materials are identified as promising for novel spintronic
applications. Since helical spin order is manifested as a compromise of
competing magnetic exchange interactions, its emergence is limited by unique
constraints imposed by the crystalline lattice and the interaction geometries,
as exemplified by the multiferroic perovskite manganites with large
orthorhombic distortion. Here we show that a simple cubic perovskite SrCoO$_3$
with room-temperature ferromagnetism has the potential to host helimagnetic
order upon isotropic lattice expansion. Increasing the Ba content $x$ in
Sr$_{1-x}$Ba$_x$CoO$_3$ continuously expands the cubic lattice, eventually
suppressing the ferromagnetic order near $x$=0.4, where helimagnetic
correlations are observed as incommensurate diffuse magnetic scattering by
neutron diffraction measurements. The emergence of helimagnetism is
semi-quantitatively reproduced by first-principles calculations, leading to the
conjecture that a simple cubic lattice with strong $d$-$p$ hybridisation can
exhibit a variety of novel magnetic phases originating from competing exchange
interactions.",1808.09423v1
2018/10/11,Observation of planar Hall effect in the magnetic Weyl semimetal Co$_{3}$Sn$_{2}$S$_{2}$,"We report detailed magneto-transport measurements on single crystals of the
magnetic Weyl semi-metal Co$_{3}$Sn$_{2}$S$_{2}$. Recently a large anomalous
Hall effect and chiral anomaly have been observed in this material which have
been suggested to be related to the large Berry curvature between the Weyl
points (Liu et al., Nature Physics (2018).). Another effect expected to result
from the topological band structure of magnetic Weyl materials is the planar
Hall effect (PHE). In this work we report observation of this intrinsic effect
in single crystals of Co$_{3}$Sn$_{2}$S$_{2}$. Crucially, the PHE is observed
for temperature $T \leq 74$~K which is much smaller than the ferromagnetic
ordering temperature $T_c = 175$~K\@. Together with the large anomalous Hall
conductivity, this further demonstrates the Topological character of
Co$_3$Sn$_2$S$_2$.",1810.04867v2
2018/10/15,Realizing Magnetoelectric Coupling with Hydroxide as a Knob,"Materials with a coexistence of magnetic and ferroelectric order (i.e.,
multiferroics) provide an efficient route for the control of magnetism by
electric fields. Unfortunately, a long-sought room temperature multiferroic
with strongly coupled ferroelectric and ferromagnetic (or ferrimagnetic)
orderings is still lacking. Here, we propose that hydrogen intercalation in
antiferromagnetic transition metal oxides is a promising way to realize
multiferroics with strong magnetoelectric coupling. Taking brownmillerite
SrCoO2.5 as an example, we show that hydrogen intercalated SrCoO2.5 displays
strong ferrimagnetism and large electric polarization in which the hydroxide
acts as a new knob to simultaneously control the magnetization and polarization
at room temperature. We expect that ion intercalation will become a general way
to design magnetoelectric and spintronic functional materials.",1810.06357v1
2018/12/5,Single spin sensing of domain wall structure and dynamics in a thin film skyrmion host,"Skyrmions are nanoscale magnetic structures with features promising for
future low-power memory or logic devices. In this work, we demonstrate novel
scanning techniques based on nitrogen vacancy center magnetometry that
simultaneously probe both the magnetic dynamics and structure of room
temperature skyrmion bubbles in a thin film system Ta/CoFeB/MgO. We confirm the
handedness of the Dzyaloshinskii-Moriya interaction in this material and
extract the helicity angle of the skyrmion bubbles. Our measurements also show
that the skyrmion bubbles in this material change size in discrete steps,
dependent on the local pinning environment, with their average size determined
dynamically as their domain walls hop between pinning sites. In addition, an
increase in magnetic field noise is observed near all skyrmion bubble domain
walls. These measurements highlight the importance of interactions between
internal degrees of freedom of skyrmion bubble domain walls and pinning sites
in thin film systems. Our observations have relevance for future devices based
on skyrmion bubbles where pinning interactions will determine important aspects
of current-driven motion.",1812.01764v1
2018/12/17,The Doping effect of Chalcogen on the Two-Dimensional Ferromagnetic Material Chromium Tribromide,"Recently the discovery of magnetic order in two-dimensional monolayer
chromium trihalides opens the new research field in two-dimensional materials.
We use first-principles calculations to systematically examine the doping
effect of chalcogen on CrBr3. In the case of S-doping, four stable
configurations, Cr2Br5S, Cr2Br4S2-A, Cr2Br4S2-B and Cr2Br3S3-A, are predicted
to be ferromagnetic semiconductors. It is found that the new bands appearing in
the original bandgap are made up of S-p and Cr-d-egorbits, lead to the obvious
reduce of bandgap and the enhanced optical absorption in the visible range. Due
to the decrease of valence electron after chalcogen doping, the magnetic moment
also decreases with the increase of S atoms, and the character of ferromagnetic
semiconductor is always hold in a wide range of strain. The results shown that
monolayer CrBr3with chalcogen doping supply a effectual way to control the
magnetism and extend the optoelectronic applications.",1812.06567v1
2019/1/9,Anisotropic magnetic entropy change in Cr$_2$X$_2$Te$_6$ (X = Si and Ge),"Intrinsic, two-dimensional (2D) ferromagnetic semiconductors are an important
class of materials for spintronics applications. Cr$_2$X$_2$Te$_6$ (X = Si and
Ge) semiconductors show 2D Ising-like ferromagnetism, which is preserved in
few-layer devices. The maximum magnetic entropy change associated with the
critical properties around the ferromagnetic transition for Cr$_2$Si$_2$Te$_6$
$-\Delta S_M^{max} \sim$ 5.05 J kg$^{-1}$ K$^{-1}$ is much larger than $-\Delta
S_M^{max} \sim$ 2.64 J kg$^{-1}$ K$^{-1}$ for Cr$_2$Ge$_2$Te$_6$ with an
out-of-plane field change of 5 T. The rescaled $-\Delta S_M(T,H)$ curves
collapse onto a universal curve independent of temperature and field for both
materials. This indicates similar critical behavior and 2D Ising magnetism,
confirming the magnetocrystalline anisotropy that could preserve the long-range
ferromagnetism in few-layers of Cr$_2$X$_2$Te$_6$.",1901.02876v1
2019/1/11,Tunability of Magnetic Anisotropy of Co on Two-Dimensional Materials by Tetrahedral Bonding,"Pairing of $\pi$ electronic state structures with functional or metallic
atoms makes them possible to engineer physical and chemical properties. Herein,
we predict the reorientation of magnetization of Co on hexagonal BN (h-BN) and
graphene multilayers. The driving mechanism is the formation of the tetrahedral
bonding between sp$^3$ and d orbitals at the interface. More specifically, the
intrinsic $\pi$-bonding of h-BN and graphene is transformed to sp$^3$ as a
result of strong hybridization with metallic $d_{z^2}$ orbital. The different
features of these two tetrahedral bondings, sp$^2$ and sp$^3$, are well
manifested in charge density and density of states in the vicinity of the
interface, along with associated band structure near the $\bar{K}$ valley. Our
findings provide a novel approach to tailoring magnetism by means of degree of
the interlayer hybrid bonds in 2D layered materials.",1901.03490v1
2019/4/1,Towards mechanomagnetics in elastic crystals: insights from [Cu(acac)$_2$],"We predict that the magnetic properties of \cuacac, an elastically flexible
crystal, change dramatically when the crystal is bent. We find that unbent
\cuacac\ is an almost perfect Tomonaga-Luttinger liquid. Broken-symmetry
density functional calculations reveal that the magnetic exchange interactions
along the chains is an order of magnitude larger than the interchain exchange.
The geometrically frustrated interchain interactions cannot magnetically order
the material at any experimentally accessible temperature. The ordering
temperature ($T_N$), calculated from the chain random phase approximation,
increases by approximately 24 orders of magnitude when the material is bent. We
demonstrate that geometric frustration both suppresses $T_N$ and enhances the
sensitivity of $T_N$ to bending. In \cuacac, $T_N$ is extremely sensitive to
bending, but remains too low for practical applications, even when bent.
Partially frustrated materials could achieve the balance of high $T_N$ and good
sensitivity to bending required for practical applications of mechanomagnetic
elastic crystals.",1904.00571v2
2019/4/5,Simultaneous inverse design of materials and parameters of core-shell nanoparticle via deep-learning: Demonstration of dipole resonance engineering,"Recent introduction of data-driven approaches based on deep-learning
technology has revolutionized the field of nanophotonics by allowing efficient
inverse design methods. In this paper, simultaneous inverse design of materials
and structure parameters of core-shell nanoparticle is achieved for the first
time using deep-learning of a neural network. A neural network to learn
correlation between extinction spectra of electric and magnetic dipoles and
core-shell nanoparticle designs, which include material information and shell
thicknesses, is developed and trained. We demonstrate deep-learning-assisted
inverse design of core-shell nanoparticle for 1) spectral tuning electric
dipole resonances, 2) finding spectrally isolated pure magnetic dipole
resonances, and 3) finding spectrally overlapped electric dipole and magnetic
dipole resonances. Our finding paves the way of the rapid development of
nanophotonics by allowing a practical utilization of a deep-learning technology
for nanophotonic inverse design.",1904.02848v1
2019/7/16,Quantum tunneling devices incorporating two-dimensional magnetic semiconductors,"Research in two-dimensional (2D) materials has experienced rapid growth in
the past few years. In particular, various layered compounds exhibiting quantum
phenomena, such as superconductivity and magnetism, have been isolated in
atomically thin form, often in spite of their chemical instability. The nature
of the 2D phases can be different than their bulk counterparts, making such
systems attractive for fundamental studies. Owing to their high crystallinity
and absence of dangling bonds, devices and heterostructures incorporating these
materials may also show performance exceeding that of traditional films. In
this roadmap article, we focus on a few recent developments in spin-based
quantum devices utilizing the 2D magnetic semiconductor, CrI$_3$.",1907.07087v1
2019/7/25,Order out of a Coulomb phase and Higgs transtion: frustrated transverse interactions of Nd2Zr2O7,"The pyrochlore material Nd$_2$Zr$_2$O$_7$ with an ""all-in-all-out"" (AIAO)
magnetic order shows novel quantum moment fragmentation with gapped flat
dynamical spin ice modes. The parameterized spin Hamiltonian with a dominant
frustrated ferromagnetic transverse term reveals a proximity to a U(1) spin
liquid. Here we study magnetic excitations of Nd$_2$Zr$_2$O$_7$ above the
ordering temperature ($T_\text{N}$) using high-energy-resolution inelastic
neutron scattering. We find strong spin ice correlations at zero energy with
the disappearance of gapped magnon excitations of the AIAO order. It seems that
the gap to the dynamical spin ice closes above $T_\text{N}$ and the system
enters a quantum spin ice state competing with and suppressing the AIAO order.
Classical Monte Carlo, molecular dynamics and quantum boson calculations
support the existence of a Coulombic phase above $T_\text{N}$. Our findings
relate the magnetic ordering of Nd$_2$Zr$_2$O$_7$ with the Higgs mechanism and
provide explanations for several previously reported experimental features.",1907.11056v1
2019/9/6,Unveiling multiferroic proximity effect in graphene,"We demonstrate that electronic and magnetic properties of graphene can be
tuned via proximity of multiferroic substrate. Our first-principles
calculations performed both with and without spin-orbit coupling clearly show
that by contacting graphene with bismuth ferrite BiFeO$_3$ (BFO) film, the
spin-dependent electronic structure of graphene is strongly impacted both by
the magnetic order and by electric polarization in the underlying BFO. Based on
extracted Hamiltonian parameters obtained from the graphene band structure, we
propose a concept of six-resistance device based on exploring multiferroic
proximity effect giving rise to significant proximity electro- (PER), magneto-
(PMR), and multiferroic (PMER) resistance effects. This finding paves a way
towards multiferroic control of magnetic properties in two dimensional
materials.",1909.02844v1
2019/9/16,Advanced Materials and Device Architectures for Magnetooptical Spatial Light Modulators,"Faraday and Kerr rotations are magnetooptical (MO) effects used for rotating
the polarization of light in transmission and reflection from a magnetized
medium, respectively. MO effects combined with intrinsically fast magnetization
reversal, which can go down to a few tens of femtoseconds or less, can be
applied in magnetooptical spatial light modulators (MOSLMs) promising for
nonvolatile, ultrafast, and high-resolution spatial modulation of light. With
the recent progress in low-power switching of magnetic and MO materials, MOSLMs
may lead to major breakthroughs and benefit beyond state-of-the-art holography,
data storage, optical communications, heads-up displays, virtual and augmented
reality devices, and solid-state light detection and ranging (LIDAR). In this
study, the recent developments in the growth, processing, and engineering of
advanced materials with high MO figures of merit for practical MOSLM devices
are reviewed. The challenges with MOSLM functionalities including the intrinsic
weakness of MO effect and large power requirement for switching are assessed.
The suggested solutions are evaluated, different driving systems are
investigated, and resulting device architectures are benchmarked. Finally, the
research opportunities on MOSLMs for achieving integrated, high-contrast, and
low-power devices are presented.",1909.07494v2
2019/9/24,Thermal cycling memory in phase separated manganites,"We have studied the irreversibility of the magnetization induced by thermal
cycles in La0.5Ca0.5MnO3 manganites, which present a low temperature state
characterized by the coexistence of phases. The effect is evidenced by a
decrease of the magnetization after cycling the sample between 300 and 50 K. We
developed a phenomenological model that allows us to correlate the value of the
magnetization with the number of cycles performed. The experimental results
show excellent agreement with our model, suggesting that this material could be
used for the development of a device to monitor thermal changes. The effect of
thermal cycling is towards an increase of the amount of the non ferromagnetic
phase in the compounds and it might be directly related with the strain at the
contact surface among the coexisting phases.",1909.11165v1
2019/11/8,Magnetic and Electronic Properties of Single-Crystalline BaCoSO,"Doped BaCoSO was recently predicted to be a high-temperature superconductor
in a new class based on Co and Ni. Using a Co-S self flux method, we
synthesized single crystals of the antiferromagnetic insulator BaCoSO. Our
magnetic and specific heat measurements and neutron diffraction provide details
of its magnetic anisotropy and order. Its band gap was determined to be about
1.3 eV by our measurements of its photoemission spectrum and infrared optical
conductivity. Our results can pave the way to exploring the predicted
superconductivity in this Co-based material.",1911.03076v1
2019/12/4,Light-driven ultrafast phonomagnetism,"Exciting atomic oscillations with light is a powerful technique to control
the electronic properties of materials, leading to remarkable phenomena such as
light-induced superconductivity and ultrafast insulator to metal transitions.
Here we show that light-driven lattice vibrations can be utilised to encode
efficiently spin information in a magnetic medium. Intense mid-infrared
electric field pulses, tuned to resonance with a vibrational normal mode of
antiferromagnetic DyFeO3, drive the emergence of long-living weak ferromagnetic
order. Light-driven phonon displacements promptly lower the energy barrier
separating competing magnetic states, allowing the alignment of spins to occur
within a few picoseconds, via non-equilibrium dynamics of the magnetic energy
landscape.",1912.01938v1
2019/12/9,Theory of magnetostriction for multipolar quantum spin ice in pyrochlore materials,"Multipolar magnetism is an emerging field of quantum materials research. The
building blocks of multipolar phenomena are magnetic ions with a non-Kramers
doublet, where the orbital and spin degrees of freedom are inextricably
intertwined, leading to unusual spin-orbital entangled states. The detection of
such subtle forms of matter has, however, been difficult due to a limited
number of appropriate experimental tools. In this work, motivated by a recent
magnetostriction experiment on Pr$_2$Zr$_2$O$_7$, we theoretically investigate
how multipolar quantum spin ice, an elusive three dimensional quantum spin
liquid, and other multipolar ordered phases in the pyrochlore materials can be
detected using magnetostriction. We provide theoretical results based on
classical and/or quantum studies of non-Kramers and Kramers magnetic ions, and
contrast the behaviors of distinct phases in both systems. Our work paves an
important avenue for future identification of exotic ground states in
multipolar systems.",1912.04291v2
2019/12/13,Epitaxial growth and antiferromagnetism of Sn-substituted perovskite iridate SrIr$_{0.8}$Sn$_{0.2}$O$_3$,"5d iridates have shown vast emergent phenomena due to a strong interplay
among its lattice, charge and spin degrees of freedom, because of which the
potential in spintronic application of the thin-film form is highly leveraged.
Here we have epitaxially stabilized perovskite SrIr$_{0.8}$Sn$_{0.2}$O$_3$ on
[001] SrTiO$_3$ substrates through pulsed laser deposition and systematically
characterized the structural, electronic and magnetic properties. Physical
properties measurements unravel an insulating ground state with a weak
ferromagnetism in the compressively strained epitaxial film. The octahedral
rotation pattern is identified by synchrotron x-ray diffraction, resolving a
mix of $a^+b^-c^-$ and $a^-b^+c^-$ domains. X-ray magnetic resonant scattering
directly demonstrates a G-type antiferromagnetic structure of the magnetic
order and the spin canting nature of the weak ferromagnetism.",1912.06735v1
2020/1/6,Role of anti-phase boundaries in the formation of magnetic domains in magnetite thin films,"Anti-phase boundaries (APBs) are structural defects which have been shown to
be responsible for the anomalous magnetic behaviour observed in different
nanostructures. Understanding their properties is crucial in order to use them
to tune the properties of magnetic materials by growing APBs in a controlled
way since their density strongly depends on the synthesis method. With this
aim, in this work we investigate their influence on magnetite (Fe$_3$O$_4$)
thin films by considering an atomistic spin model, focusing our study on the
role that the exchange interactions play across the APB interface. We conclude
that the main atypical features reported experimentally in this material are
well described by the model we propose here, confirming the new exchange
interactions created in the APB as the responsible for this deviation from bulk
properties.",2001.01766v1
2020/1/20,Antiferromagnetic quantum spin Hall states in iron halogenide,"It is widely known that quantum spin Hall (QSH) insulator can be viewed as
two copies of quantum anomalous Hall (QAH) insulator with opposite local
magnetic moments. However, nearly every QSH insulator discovered so far is a
nonmagnetic semiconductor. Due to the vanishing local magnetic moment of each
copy, the QAH states only conceptually exist in these QSH insulators. In this
work, we show a realistic construction of QSH states with finite local magnetic
moment by staking bilayer QAH insulators. Our explicit construction benefits
from an effective QAH model with a large topological gap and is further
supported by a class of two-dimensional ferromagnetic materials. Our work not
only validates the conceptual relationship of QSH and QAH but also provides an
ideal material platform for realizing antiferromagnetic QSH state which is
highly tunable between QAH and QSH states as a function of the number of
layers.",2001.07110v1
2020/2/7,Interplay of Magnetism and Topological Superconductivity in Bilayer Kagome Metals,"The binary intermetallic materials, $M_3$Sn$_2$ ($M$ = 3d transition metal)
present a new class of strongly correlated systems that naturally allows for
the interplay of magnetism and metallicity. Using first principles calculations
we confirm that bulk Fe$_3$Sn$_2$ is a ferromagnetic metal, and show that $M$ =
Ni and Cu are paramagnetic metals with non-trivial band structures. Focusing on
Fe$_3$Sn$_2$ to understand the effect of enhanced correlations in an
experimentally relevant atomistically thin single kagome-bilayer, our ab-initio
results show that dimensional confinement naturally exposes the flatness of
band structure associated with the bilayer kagome geometry in a resultant
ferromagnetic Chern metal. We use a multistage minimal modeling of the magnetic
bands progressively closer to the Fermi energy. This effectively captures the
physics of the Chern metal with a non-zero anomalous Hall response over a
material relevant parameter regime along with a possible superconducting
instability of the spin-polarised band resulting in a topological
superconductor.",2002.02953v3
2020/3/8,Field-induced spin reorientation in the antiferromagnetic Dirac material EuMnBi$_2$ revealed by neutron and resonant x-ray diffraction,"Field-dependent magnetic structure of a layered Dirac material EuMnBi$_2$ was
investigated in detail by the single crystal neutron diffraction and the
resonant x-ray magnetic diffraction techniques. On the basis of the reflection
conditions in the antiferromagnetic phase at zero field, the Eu moments were
found to be ordered ferromagnetically within the $ab$ plane and stacked
antiferromagnetically along the $c$ axis in the sequence of up-up-down-down.
Upon the spin-flop transition under the magnetic field parallel to the $c$
axis, the Eu moments are reoriented from the $c$ to the $a$ or $b$ directions
forming two kinds of spin-flop domains, whereas the antiferromagnetic structure
of the Mn sublattice remains intact as revealed by the quantitative analysis of
the change in the neutron diffraction intensities. The present study provides a
concrete basis to discuss the dominant role of the Eu sublattice on the
enhanced two-dimensionality of the Dirac fermion transport in EuMnBi$_2$.",2003.03719v1
2020/3/9,X-ray circular dichroism versus orbital magnetization,"The x-ray magnetic circular dichroism (XMCD) sum rule yields an extremely
useful ground-state observable, which provides a quantitative measure of
spontaneous time-reversal symmetry breaking (T-breaking) in a given material. I
derive here its explicit expression within band-structure theory, in the
general case: trivial insulators, topological insulators, and metals. Orbital
magnetization provides a different measure of T-breaking in the electronic
ground state. The two observables belong to the class of ""geometrical""
observables; both are local and admit a ""density"" in coordinate space. In both
of them one could include/exclude selected groups of bands, in order to acquire
element-specific information about the T-breaking material. Only in the case of
an isolated flat band the contributions to the two observables coincide.
Finally, I provide the corresponding geometrical formula-in a different Hilbert
space-for a many-body interacting system.",2003.04256v1
2020/4/8,Nonreciprocal thermal transport in a multiferroic helimagnet,"Breaking of spatial inversion symmetry (SIS) induces unique phenomena in
condensed matter. Besides the classic examples such as natural optical activity
and piezoelectricity, the spin-orbit interaction further enriches the effect of
SIS breaking, as exemplified by the Rashba effect. In particular, by combining
this symmetry with magnetic fields or another type of time-reversal symmetry
(TRS) breaking, noncentrosymmetric materials can be made to exhibit
nonreciprocal responses, which are responses that differ for rightward and
leftward stimuli. For example, resistivity becomes directionally dependent;
that is to say, rectification appears in noncentrosymmetric materials in a
magnetic field. However, the effect of SIS breaking on thermal transport
remains to be elucidated. Here we show nonreciprocal thermal transport in the
multiferroic helimagnet TbMnO3. The longitudinal thermal conductivity depends
on whether the thermal current is parallel or antiparallel to the vector
product of the electric polarization and magnetization. This phenomenon is
thermal rectification that is controllable with external fields in a uniform
crystal. This discovery may pave the way to thermal diodes with controllability
and scalability.",2004.03801v1
2020/8/17,Giant Magnetic-Field-Induced Strain in Ni2MnGa-based polycrystal,"Ferromagnetic Ni2MnGa-based alloys play an important role in technological
fields, such as smart actuators, magnetic refrigeration and robotics. The
possibility of obtaining large non-contact deformation induced by an external
perturbation is one of its key strengths for applications. However, the search
for materials with low cost, practical fabrication procedures and large signal
output under small perturbing fields still poses challenges. In the present
study we demonstrate that by judicial choice of substitution on the Mn site, an
abrupt magnetostructural transition from a paramagnetic austenite phase to a
ferromagnetic martensite one can be tuned to close to room temperature
achieving large and reproducible strains. The required magnetic field to induce
the strain varies from small values, as low as 0.25 T for 297.4 K and 1.6% of
strain, to 8 T for 305 K and 2.6% of strain. Our findings point to encouraging
possibilities for application of shape memory alloys in relatively inexpensive,
scalable polycrystalline materials.",2008.07569v1
2020/8/23,Butterfly-shaped magnetoresistance in triangular-lattice antiferromagnet Ag$_2$CrO$_2$,"Spintronic devices using antiferromagnets (AFMs) are promising candidates for
future applications. Recently, many interesting physical properties have been
reported with AFM-based devices. Here we report a butterfly-shaped
magnetoresistance (MR) in a micrometer-sized triangular-lattice antiferromagnet
Ag$_2$CrO$_2$. The material consists of two-dimensional triangular-lattice
CrO$_2$ layers with antiferromagnetically coupled $S$ = 3/2 spins and Ag$_2$
layers with high electrical conductivity. The butterfly-shaped MR appears only
when the magnetic field is applied perpendicularly to the CrO$_2$ plane with
the maximum MR ratio ($\approx$ 15%) at the magnetic ordering temperature.
These features are distinct from those observed in conventional magnetic
materials. We propose a theoretical model where fluctuations of partially
disordered spins with the Ising anisotropy play an essential role in the
butterfly-shaped MR in Ag$_2$CrO$_2$.",2008.09945v1
2020/8/28,Optical Magnetic Lens: towards actively tunable terahertz optics,"As we read this text, our eyes dynamically adjust the focal length to keep
the line image in focus on the retina. Similarly, in many optics applications
the focal length must be dynamically tunable. In the quest for compactness and
tunability, flat lenses based on metasurfaces were introduced. However, their
dynamic tunability is still limited because their functionality mostly relies
upon fixed geometry. In contrast, we put forward an original concept of a
tunable Optical Magnetic Lens (OML) that focuses photon beams using a
subwavelength-thin layer of a magneto-optical material in a non-uniform
magnetic field. We applied the OML concept to a wide range of materials and
found out that the effect of OML is present in a broad frequency range from
microwaves to visible light. For terahertz light, OML can allow 50% relative
tunability of the focal length on the picosecond time scale, which is of
practical interest for ultrafast shaping of electron beams in microscopy. The
OML based on magneto-optical natural bulk and 2D materials may find broad use
in technologies such as 3D optical microscopy and acceleration of charged
particle beams by THz beams.",2008.12640v1
2020/10/19,Theory of Spoof Magnetic Localized Surface Plasmons Beyond Effective Medium Approximations,"A homogeneous negative permeability sphere can support magnetic localized
surface plasmons (MLSPs). Generally, negative permeability materials are
metamaterial (MM) structures exhibiting very deep subwavelength spatial scales,
whose effects may be detrimental in the near-field for those applications based
on effective medium approximations. We suggest to overcome this fundamental
limitation by demonstrating analytically that the electromagnetic spatial
distribution, associated to a MLSP resonance and excited by a near-field
source, can be accurately reproduced outside the sphere by substituting the
negative permeability sphere with a homogeneous high-index dielectric one with
the same radius. Considering that a large class of ferroelectric materials
shows ultra-high dielectric constant and low-losses at low frequency (up to
GHz), our spoof MLSPs theory could be a key tool for realizing high performance
subwavelength magnetic photonic devices in the radiofrequency and microwave
regions.",2010.09281v2
2020/10/20,Topological correspondence between magnetic space group representations,"The past years have seen rapid progress in the classification of topological
materials. These diagnostical methods are increasingly getting explored in the
pertinent context of magnetic structures. We report on a general class of
electronic configurations within a set of anti-ferromagnetic-compatible space
groups that are necessarily topological. Interestingly, we find a systematic
correspondence between these anti-ferromagnetic phases to necessarily
nontrivial topological ferro/ferrimagnetic counterparts that are readily
obtained through physically motivated perturbations. Addressing the exhaustive
list of magnetic space groups in which this mechanism occurs, we also verify
its presence on planes in 3D systems that were deemed trivial in existing
classification schemes. This leads to the formulation of the concept of
subdimensional topologies, featuring non-triviality within part of the system
that coexists with stable Weyl points away from these planes, thereby
uncovering novel topological materials in the full 3D sense that have readily
observable features in their bulk and surface spectrum.",2010.10536v3
2020/11/2,Tunable chiral symmetry breaking in symmetric Weyl materials,"Asymmetric Weyl semimetals, which possess an inherently chiral structure,
have different energies and dispersion relations for left- and right-handed
fermions. They exhibit certain effects not found in symmetric Weyl semimetals,
such as the quantized circular photogalvanic effect and the helical magnetic
effect. In this work, we derive the conditions required for breaking chiral
symmetry by applying an external field in symmetric Weyl semimetals. We
explicitly demonstrate that in certain materials with the $T_d$ point group,
magnetic fields along low symmetry directions break the symmetry between left-
and right-handed fermions; the symmetry breaking can be tuned by changing the
direction and magnitude of the magnetic field. In some cases, we find an
imbalance between the number of type I left- and right-handed Weyl cones (which
is compensated by the number of type II cones of each chirality.)",2011.00970v3
2020/11/24,"Structural, dielectric and magnetic studies of (0-3) type multiferroic (1-x) BaTi0.8Sn0.2O3-(x) La0.5Ca0.5MnO3 (0 <x< 1) composite ceramics","Multiferroic composites with the composition (1-x) BaTi0.8Sn0.2O3 - (x)
La0.5Ca0.5MnO3 (x =0, 0.3, 0.5, 0.7, 0.9 and 1) were prepared by sol-gel
techniques. Rietveld refinements of the composites with 0-3 and 3-0 type
connectivities exhibit the formation of pure phases and confirm the fraction of
the composite samples. It was found that the composites grain size decreases
slightly with increasing the La0.5Ca0.5MnO3 content. Magnetic measurements of
the composite ceramics exhibit a gradual increase in saturation and remanent
magnetization with increasing La0.5Ca0.5MnO3 content. Dielectric data
demonstrate that the composite materials show high values of the dielectric
constant in comparison with the parent compound BaTi0.8Sn0.2O3 (BTSO). In
addition, an attempt is made to measure the magnetoelectric coupling
coefficient and to explain the negative permittivity and losses occurring in
these materials at a certain frequency and temperature conditions.",2011.12270v1
2020/12/2,Bloch-type photonic skyrmions in optical chiral multilayers,"Magnetic skyrmions are topological quasiparticles in magnetic field. Until
recently, as one of their photonic counterparts, N\'eel-type photonic skyrmion
is discovered in surface plasmon polaritons. The deep-subwavelength features of
the photonic skyrmions suggest their potentials in quantum technologies and
data storage. So far, the Bloch-type photonic skyrmion has yet to be
demonstrated in this brand new research field. Here, by exploiting the quantum
spin Hall effect of a plasmonic optical vortex in multilayered structure, we
predict the existence of photonic twisted-N\'eel- and Bloch-type skyrmions in
chiral materials. Their chirality-dependent features can be considered as
additional degrees-of-freedom for future chiral sensing, information processing
and storage technologies. In particular, our findings enlarge the family of
photonic skyrmions and reveal a remarkable resemblance of the feature of chiral
materials in two seemingly distant fields: photonic skyrmions and magnetic
skyrmions.",2012.01015v2
2021/1/22,Quasi-isotropic orbital magnetoresistance in lightly doped SrTiO$_{3}$,"A magnetic field parallel to an electrical current does not produce a Lorentz
force on the charge carriers. Therefore, orbital longitudinal magnetoresistance
is unexpected. Here we report on the observation of a large and non saturating
magnetoresistance in lightly doped SrTiO$_{3-x}$ independent of the relative
orientation of current and magnetic field. We show that this quasi-isotropic
magnetoresistance can be explained if the carrier mobility along all
orientations smoothly decreases with magnetic field. This anomalous regime is
restricted to low concentrations when the dipolar correlation length is longer
than the distance between carriers. We identify cyclotron motion of electrons
in a potential landscape tailored by polar domains as the cradle of
quasi-isotropic orbital magnetoresistance. The result emerges as a challenge to
theory and may be a generic feature of lightly-doped quantum paralectric
materials.",2101.09062v1
2021/2/2,Topological Aspects of Antiferromagnets,"The long fascination antiferromagnetic materials have exerted on the
scientific community over about a century has been entirely renewed recently
with the discovery of several unexpected phenomena including various classes of
anomalous spin and charge Hall effects and unconventional magnonic transport,
but also homochiral magnetic entities such as skyrmions. With these
breakthroughs, antiferromagnets standout as a rich playground for the
investigation of novel topological behaviors, and as promising candidate
materials for disruptive low-power microelectronic applications. Remarkably,
the newly discovered phenomena are all related to the topology of the magnetic,
electronic or magnonic ground state of the antiferromagnets. This review
exposes how non-trivial topology emerges at different levels in
antiferromagnets and explores the novel mechanisms that have been discovered
recently. We also discuss how novel classes of quantum magnets could enrich the
currently expanding field of antiferromagnetic spintronics and how spin
transport can in turn favor a better understanding of exotic quantum
excitations.",2102.01632v3
2021/2/18,Tunable magnetism in ferroelectric α-In2Se3 by hole-doping,"Two-dimensional (2D) multiferroics attract intensive investigations because
of underlying science and their potential applications. Although many 2D
systems have been observed/predicted to be ferroelectric or ferromagnetic, 2D
materials with both ferroic properties are still scarce. By using
first-principles calculations, we predict that hole-doping can induce robust
ferromagnetism in 2D ferroelectric {\alpha}-In2Se3 due to its unique flat band
structure, and the Curie temperature (TC) can be much higher than room
temperature. Moreover, the doping concentration, strain, and number of layers
can effectively modulate the magnetic moment and the TC of the material.
Interestingly, strong magnetoelectric coupling is found at the surface of hole
doped multilayer {\alpha}-In2Se3, which allows non-volatile electric control of
magnetization. Our work provides a feasible approach for designing/searching 2D
multiferroics with great potential in future device applications, such as
memory devices and sensors.",2102.09135v1
2021/3/11,Partial Meissner effect measurement by a superconducting magnetic flux lens,"Magnetic flux trapping in the Meissner transition of superconducting radio
frequency cavities can substantially increase dissipation which impacts
cryogenic costs and necessitates expensive magnetic shielding. Recent findings
point at the material preparation and the cool down dynamics at the vortex
state as the main ways to counteract flux trapping. Most of the related
measurements are performed on the cavity, with risk of results being impacted
by the cool down specifics of each facility. We demonstrate an alternative
experiment in which flux expulsion is quantified from sheet material, with
samples conduction cooled in a stand-alone instrument designed to collimate
expelled flux at controlled cool down conditions. A series of tests reliably
and reproducibly relate the amount of expelled flux to the cooling rate, the
velocity of the superconducting front and the spatial temperature gradient. The
results are in line with tests performed on bare cavities and show that
expulsion of trapped flux improves with the spatial temperature gradient,
independent on the cooling rate. Our concept offers means to control the
dynamics of the Meissner effect and can be used for material qualification
prior to cavity fabrication.",2103.06697v1
2021/3/18,Two-dimensional multiferroic metal with voltage-tunable magnetization and metallicity,"We design a multiferroic metal that combines seemingly incompatible
ferromagnetism, ferroelectricity, and metallicity by hole doping a
two-dimensional (2D) ferroelectric with high density of states near the Fermi
level. The strong magnetoelectric effect is demonstrated in hole-doped and
arsenic-doped monolayer {\alpha}-In2Se3 using first-principles calculations.
Taking advantage of the oppositely charged surfaces created by an out-of-plane
polarization, the 2D magnetization and metallicity can be electrically switched
on and off in an asymmetrically doped monolayer. The substitutional arsenic
defect pair exhibits an intriguing electric field-tunable charge
disproportionation process accompanied with an on-off switch of local magnetic
moments. The charge ordering process can be controlled by tuning the relative
strength of on-site Coulomb repulsion and defect dipole-polarization coupling
via strain engineering. Our design principle relying on no transition metal
broadens the materials design space for 2D multiferroic metals.",2103.10238v3
2021/3/30,Room-temperature optically detected magnetic resonance of single defects in hexagonal boron nitride,"Optically addressable spins in materials are important platforms for quantum
technologies, such as repeaters and sensors. Identification of such systems in
two-dimensional (2d) layered materials offers advantages over their bulk
counterparts, as their reduced dimensionality enables more feasible on-chip
integration into devices. Here, we report optically detected magnetic resonance
(ODMR) from previously identified carbon-related defects in 2d hexagonal boron
nitride (hBN). We show that single-defect ODMR contrast can be as strong as 6%
and displays a magnetic-field dependence with both positive or negative sign
per defect. This bipolarity can shed light into low contrast reported recently
for ensemble ODMR measurements for these defects. Further, the ODMR lineshape
comprises a doublet resonance, suggesting either low zero-field splitting or
hyperfine coupling. Our results offer a promising route towards realising a
room-temperature spin-photon quantum interface in hexagonal boron nitride.",2103.16494v1
2021/5/7,Polarization-dependent mode coupling in hyperbolic nanospheres,"Hyperbolic materials offer a much wider freedom in designing optical
properties of nanostructures than ones with isotropic and elliptical
dispersion, both metallic or dielectric. Here, we present a detailed
theoretical and numerical study of the unique optical properties of spherical
nanoantennas composed of such materials. Hyperbolic nanospheres exhibit a rich
modal structure that, depending on the polarization and direction of incident
light, can exhibit either a full plasmonic-like response with multiple electric
resonances, a single, dominant electric dipole or one with mixed magnetic and
electric modes with an atypical reversed modal order. We derive resonance
conditions for observing these resonances in the dipolar approximation and
offer insight into how the modal response evolves with the size, material
composition, and illumination. Specifically, the origin of the magnetic dipole
mode lies in the hyperbolic dispersion and its existence is determined by two
diagonal permittivity components of different sign. Our analysis shows that the
origin of this unusual behavior stems from complex coupling between electric
and magnetic multipoles, which leads to very strongly scattering or absorbing
modes. These observations assert that hyperbolic nanoantennas offer a promising
route towards novel light-matter interaction regimes.",2105.03474v2
2021/5/12,Stimuli-responsive twist actuators made from soft elastic composite materials -- linking mesoscopic and macroscopic descriptions,"Very recently, the construction of twist actuators from magnetorheological
gels and elastomers has been suggested. These materials consist of magnetizable
colloidal particles embedded in a soft elastic polymeric environment. The twist
actuation is enabled by a net chirality of the internal particle arrangement.
Upon magnetization by a homogeneous external magnetic field, the systems
feature an overall torsional deformation around the magnetization direction.
Starting from a discrete minimal mesoscopic model set-up we work towards a
macroscopic characterization. The two scales are linked by identifying
expressions for the macroscopic system parameters as functions of the
mesoscopic model parameters. In this way, the observed behavior of a
macroscopic system can in principle be mapped to and illustratively be
understood from an appropriate mesoscopic picture. Our results apply equally
well to corresponding soft electrorheological gels and elastomers.",2105.05628v1
2021/6/10,Broadband resonant calibration-free complex permittivity retrieval of liquid solutions,"Material susceptibilities govern interactions between electromagnetic waves
and matter and are of a crucial importance for basic understanding of natural
phenomena and for tailoring practical applications. Here we present a new
calibration-free method for relative complex permittivity retrieval, which
allows using accessible and cheap apparatus and simplifies the measurement
process. The method combines advantages of resonant and non-resonant
techniques, allowing to extract parameters of liquids and solids in a broad
frequency range, where material's loss tangent is less than 0.5. The essence of
the method is based on exciting magnetic dipole resonance in a spherical sample
with variable dimensions. Size-dependent resonant frequencies and quality
factors of magnetic dipolar modes are mapped on real and imaginary parts of
permittivity by employing Mie theory. Samples are comprised of liquid
solutions, enclosed in stretchable covers, which allows changing the dimensions
continuously. This approach allows tuning magnetic dipolar resonance over a
wide frequency range, effectively making resonance retrieval method broadband.
The technique can be extended to powder and solid materials, depending on their
physical parameters, such as granularity and processability.",2106.09458v2
2021/7/20,Strong bulk spin-orbit torques quantified in the van der Waals ferromagnet Fe3GeTe2,"The recent emergence of magnetic van der Waals materials allows for the
investigation of current induced magnetization manipulation in two dimensional
materials. Uniquely, Fe3GeTe2 has a crystalline structure that allows for the
presence of bulk spin-orbit torques (SOTs), that we quantify in a Fe3GeTe2
flake. From the symmetry of the measured torques, we identify the current
induced effective fields using harmonic analysis and find dominant bulk SOTs,
which arise from the symmetry in the crystal structure. Our results show that
Fe3GeTe2 uniquely can exhibit bulk SOTs in addition to the conventional
interfacial SOTs enabling magnetization manipulation even in thick single
layers without the need for complex multilayer engineering.",2107.09420v1
2021/7/25,Long-range anisotropic Heisenberg ferromagnets and electrically tunable ordering,"Recent realizations of intrinsic magnetic order in truly two-dimensional
materials have opened new avenues in the fundamental knowledge and spintronic
applications. Here we develop an anisotropic Heisenberg model with relativistic
exchange interactions that are obtained from the first-principles calculations.
We demonstrate the crucial importance of magnetic interactions beyond the
first-neighbour to qualitatively and quantitatively reproduce the experimental
results. Once we ascertain the predictive capacity of the model for chromium
trihalides and CrGeTe$_3$, we investigate the feasibility of tuning the
magnetic ordering by electrical means in these materials. A remarkable
five-fold increase in the ferromagnetic Curie temperature is predicted in
monolayer CrI$_3$ within experimentally obtainable hole density. The elusive
microscopic mechanism behind the doping-dependent Curie temperature is
illustrated. Further, in the present context, the effects of biaxial strain and
chemical doping are also addressed. The results should trigger further
experimental attention to test the present conclusions.",2107.11739v1
2021/7/28,Superexchange dominates in magnetic topological insulators,"It has been suggested that the enlarged spin susceptibility in topological
insulators, described by Van Vleck's formalism, accounts for the ferromagnetism
of bismuth-antimony topological chalcogenides doped with transition metal
impurities. In contrast, earlier studies of HgTe and related topological
systems pointed out that the interband analog of the
Ruderman-Kittel-Kasuya-Yosida interaction (the Bloembergen-Rowland mechanism)
leads to antiferromagnetic coupling between pairs of localized spins. Here, we
critically revisit these two approaches, show their shortcomings, and elucidate
why the magnitude of the interband contribution is small even in topological
systems. From the proposed theoretical approach and our computational studies
of magnetism in Mn-doped HgTe and CdTe, we conclude that, in the absence of
band carriers, the superexchange dominates, and its sign depends on the
coordination and charge state of magnetic impurities rather than on the
topological class of the host material.",2107.13388v2
2021/9/1,Magnonic Proximity Effect in Insulating Ferro- and Antiferromagnetic Trilayers,"The design of spin-transport based devices such as magnon transistors or spin
valves will require multilayer systems composed of different magnetic materials
with different physical properties. Such layered structures can show various
interface effects, one class of which being proximity effects, where a certain
physical phenomenon that occurs in the one layers leaks into another one. In
this work a magnetic proximity effect is studied in trilayers of different
ferro- and antiferromagnetic materials within an atomistic spin model. We find
the magnetic order in the central layer - with lower critical temperature -
enhanced, even for the case of an antiferromagnet surrounded by ferromagnets.
We further characterize this proximity effect via the magnon spectra which are
specifically altered, especially for the case of the antiferromagnet in the
central layer.",2109.00286v1
2021/9/16,Quadratic magnetoelectric effect during field cooling in sputter grown Cr$_2$O$_3$ films,"Cr$_2$O$_3$ is the archetypal magnetoelectric (ME) material, which has a
linear coupling between electric and magnetic polarizations. Quadratic ME
effects are forbidden for the magnetic point group of Cr$_2$O$_3$, due to
space-time inversion symmetry. In Cr$_2$O$_3$ films grown by sputtering, we
find a signature of a quadratic ME effect that is not found in bulk single
crystals. We use Raman spectroscopy and magetization measurements to deduce the
removal of space-time symmetry, and corroborate the emergence of the quadratic
ME effect. We propose that meta-stable site-selective trace dopants remove the
space, time, and space-time inversion symmetries from the original magnetic
point group of bulk Cr$_2$O$_3$. We include the quadratic ME effect in a model
describing the switching process during ME field cooling, and estimate the
effective quadratic susceptibility value. The quadratic magnetoelectric effect
in a uniaxial antiferromagnet is promising for multifunctional
antiferromagnetic and magnetoelectric devices that can incorporate optical,
strain-induced, and multiferroic effects.",2109.07677v1
2021/9/18,Strain Tunable Intrinsic Ferromagnetic in 2D Square CrBr$_2$,"Two-dimensional (2D) intrinsic magnetic materials with high Curie temperature
(Tc) coexisting with 100% spin-polarization are highly desirable for realizing
promising spintronic devices. In the present work, the intrinsic magnetism of
monolayer square CrBr2 is predicted by using first-principles calculations. The
monolayer CrBr2 is an intrinsic ferromagnetic (FM) half-metal with the
half-metallic gap of 1.58 eV. Monte Carlo simulations based on the Heisenberg
model estimates Tc as 212 K. Furthermore, the large compressive strain makes
CrBr2 undergo ferromagnetic-antiferromagnetic phase transition, when the
biaxial tensile strain larger than 9.3% leads to the emergence of
semiconducting electronic structures. Our results show that the intrinsic
half-metal with a high Tc and controllable magnetic properties endow monolayer
square CrBr2 a potential material for spintronic applications.",2109.08808v1
2021/10/26,Spin-phonon coupling in Sr and Ti incorporated 9R-BaMnO3,"Materials having strong coupling between different degrees of freedom such as
spin, lattice, orbital, and charge are of immense interest due to their
potential device applications. Here, we have stabilized the 9R phase of BaMnO3,
by Sr (Ti) doping in the Ba (Mn) site using solid-state route at ambient
pressure, which otherwise requires high-pressure conditions to syntheize.
Crsyatl structure, phonon spectra, and their evolution with temperature are
investigated using x-ray diffraction and Raman spectroscopic techniques.
Temperature-dependent magnetization data reveal an antiferromagnetic transition
at around (TN =) 262 K and 200 K for Ba0.9Sr0.1MnO3 and BaMn0.9Ti0.1O3,
respectively. No structural phase transition or lattice instabilities are
observed in the measured temperature range (80 - 400 K) for both the compounds.
We have observed anomalous behaviour of four different phonon modes involving
Mn or O-vibrations at low temperatures which have been attributed to
spin-phonon coupling.",2110.13737v1
2021/11/29,Tailoring High-Frequency Magnonics in Monolayer Chromium Trihalides,"Monolayer chromium trihalides, the archetypal two dimensional (2D) magnetic
materials, are readily suggested as a promising platform for high frequency
magnonics. Here we detail the spin wave properties of monolayer CrBr$_3$ and
CrI$_3$, using spin dynamics simulations parametrized from the first
principles. We reveal that spin wave dispersion can be tuned in a broad range
of frequencies by strain, paving the way towards flexo magnonic applications.
We further show that ever present halide vacancies in these monolayers host
sufficiently strong Dzyaloshinskii Moriya interaction to scatter spin waves,
which promotes design of spin-wave guides by defect engineering. Finally we
discuss the spectra of spin-waves propagating across a moir\'e periodic
modulation of magnetic parameters in a van der Waals heterobilayer, and show
that the nanoscale moir\'e periodicities in such samples are ideal for
realization of a magnonic crystal in the terahertz frequency range. Recalling
the additional tunability of magnetic 2D materials by electronic gating, our
results situate these systems among the front-runners for prospective high
frequency magnonic applications.",2111.14305v1
2022/1/28,Antiferromagnetic fluctuations and orbital-selective Mott transition in the van der Waals ferromagnet Fe3-xGeTe2,"Fe3-xGeTe2 is a layered magnetic van der Waals material of interest for both
fundamental and applied research. Despite the observation of intriguing
physical properties, open questions exist even on the basic features related to
magnetism: is it a simple ferromagnet or are there antiferromagnetic regimes
and are the moments local or itinerant. Here, we demonstrate that
antiferromagnetic spin fluctuations coexist with the ferromagnetism through
comprehensive elastic and inelastic neutron scattering and thermodynamic
measurements. Our realistic dynamical mean-field theory calculations reveal
that the competing magnetic fluctuations are driven by an orbital selective
Mott transition, where only the plane-perpendicular a1g orbital of the Fe(3d)
manifold remains itinerant. Our results highlight the multi-orbital character
in Fe3-xGeTe2 that supports a rare coexistence of local and itinerant physics
within this material.",2201.12375v2
2022/6/2,Diagonal and off-diagonal thermal conduction with resonant phonon scattering in $Ni_3TeO_6$,"The coupling between phonon and magnon is ubiquitous in magnetic materials
and plays a crucial role in many aspects of magnetic properties, most notably
in spintronics. Yet, this academically and technologically interesting problem
still poses a severe challenge to a general understanding of the issue in
certain materials. We report that Ni3TeO6 exhibits clear evidence of
significant magnon-phonon coupling in both longitudinal thermal conductivity
($\kappa_{xx}$) and thermal Hall coefficient ($\kappa_{xy}$). The
Debye-Callaway model, a phenomenological description for phonon heat
conduction, can explain the measured magnetic field dependence of
$\kappa_{xx}(H)$: phonon scattering from spin fluctuation in the paramagnetic
phase and additional scattering due to magnon-phonon coupling in the collinear
antiferromagnetic phase. We further suggest that a similar approach could be
applied to understand the finite $\kappa_{xy}$ values in $Ni_3TeO_6$.",2206.00837v2
2022/6/9,Reconfigurable Reservoir Computing in a Magnetic Metamaterial,"In-materia reservoir computing (RC) leverages the intrinsic physical
responses of functional materials to perform complex computational tasks.
Magnetic metamaterials are exciting candidates for RC due to their huge state
space, nonlinear emergent dynamics, and non-volatile memory. However, to be
suitable for a broad range of tasks, the material system is required to exhibit
a broad range of properties, and isolating these behaviours experimentally can
often prove difficult. By using an electrically accessible device consisting of
an array of interconnected magnetic nanorings -- a system shown to exhibit
complex emergent dynamics -- here we show how reconfiguring the reservoir
architecture allows exploitation of different aspects the system's dynamical
behaviours. This is evidenced through state-of-the-art performance in diverse
benchmark tasks with very different computational requirements, highlighting
the additional computational configurability that can be obtained by altering
the input/output architecture around the material system.",2206.04446v3
2022/9/1,Magneto-optical Kerr effect and magnetoelasticity in weak ferromagnetic RuF$_4$ monolayer,"Considerable research interest has been attracted to noncollinear magnetic
structures for their intriguing physics and promising applications. In this
work, based on relativistic density functional theory, we reveal the
interesting magnetic order and relevant properties in monolayer RuF$_4$, which
can be exfoliated from its bulk phase. Although the spins on Ru ions are almost
antiferromagnetically aligned between nearest-neighbors, weak ferromagnetism is
generated because of the antisymmetric Dzyaloshinskii-Moriya interaction as
well as the single-ion anisotropy. A prominent magneto-optical Kerr effect can
be observed for this antiferromagnet, similar to those of regular strong
ferromagnets. In addition, a uniaxial strain can induce a ferroelastic
switching together with the in-plane rotation of spin direction, giving rise to
a strong intrinsic magnetoelasticity. Our work not only suggests an alternative
direction for two-dimensional magnetic materials, but also provides hints to
future devices based on antiferromagnetic magnetoelastic or magneto-optical
materials.",2209.00178v1
2022/9/18,Strong Dzyaloshinskii-Moriya Interaction in Monolayer CrI$_3$ on Metal Substrates,"Dzyaloshinskii-Moriya interaction (DMI) is the primary mechanism for
realizing real-space chiral spin textures, which are regarded as key components
for the next-generation spintronics. However, DMI arises from a perturbation
term of the spin-orbit interaction and is usually weak in pristine magnetic
semiconductors. To date, large DMI and the resulting skyrmions are only
realized in a few materials under stringent conditions. Using first-principles
calculations, we demonstrate that significant DMI occurs between
nearest-neighbor Cr atoms in two-dimensional (2D) magnetic semiconductor
CrI$_3$ on Au or Cu substrates. This exceptionally strong DMI is generated by
the interfacial charge transfer and weak chemical interactions between chromium
halides and metal substrates, which break the spatial inversion symmetry. These
findings highlight the significance of substrate effects in 2D magnets and
expand the inventory of feasible materials with strong DMI.",2209.08444v1
2022/11/6,Hierarchies of Hofstadter butterflies in 2D covalent-organic frameworks,"The Hofstadter butterfly is one of the first and most fascinating examples of
the fractal and self-similar quantum nature of free electrons in a lattice
pierced by a perpendicular magnetic field. However, the direct experimental
verification of this effect on single-layer materials is still missing as very
strong and inaccessible magnetic fields are necessary. For this reason, its
indirect experimental verification has only been realized in artificial
periodic 2D systems, like moir\'e lattices. The only recently synthesized 2D
covalent-organic frameworks might circumvent this limitation: Due to their
large pore structures, magnetic fields needed to detect most features of the
Hofstadter butterfly are indeed accessible with today's technology. This work
opens the door to making this exotic and theoretical issue from the 70s
measurable and might solve the quest for the experimental verification of the
Hofstadter butterfly in single-layer materials. Moreover, the intrinsic
hierarchy of different pore sizes in a 2D covalent-organic framework adds
additional complexity and beauty to the original butterflies and leads to a
directly accessible playground for new physical observations.",2211.03215v1
2022/12/26,Optimal design of nanomagnets for on-chip field gradients,"The generation of localized magnetic field gradients by on-chip nanomagnets
is important for a variety of technological applications, in particular for
spin qubits. To advance beyond the empirical design of these nanomagnets, we
propose a systematic and general approach based on the micromagnetic
formulation of an optimal field gradient source. We study the different field
configurations that can be realized and find out quantitatively the most
suitable ferromagnetic layer geometries. Using micromagnetic simulations, we
then investigate the minimum requirements for reaching magnetic saturation in
these nanomagnets. In terms of either longitudinal or transverse field
gradient, the results provide an optimal solution for uniform, saturated
nanomagnets, where the magnetic material can be selected according to the
strength of the external fields that can be used.",2212.13156v1
2023/2/14,MICROSTRUCTURE OF Glidcop AL-60,"Glidcop is an oxide-particle-dispersion strengthened copper composite that
has a combination of high mechanical strength and high electrical conductivity.
It has been used as a conductor for 100 T ultrahigh field pulsed magnets by the
National High Magnetic Field Laboratory, USA. In the quest for even higher
field pulsed magnets, material development is crucial. Since the mechanical
properties of a material are often determined by its micro-structure, full
characterization of the microstructure of Glidcop is necessary. In this work,
we studied the microstructure of Glidcop AL-60 using both transmission electron
microscopy (TEM) and scanning transmission electron microscopy (STEM). We
identified both alpha-Al2O3 and cubic eta-Al2O3 nanoparticles in AL-60 and
investigated their size and density distribution. The small alumina particles
eta-Al2O3 nanoparticles with typical size of 5 to 30 nm are of triangular
shape. They have had well defined crystal orientation relation-ship with the Cu
matrix. We observed dislocations pinned by the alumina nanoparticles in
cold-drawn wires. We believed that dislocation bypassing alumina particles via
Orowan looping was the main strengthening mechanism. We observed microcracks
near large particles, demonstrating the detrimental effect of large particles
in AL-60.",2302.08978v1
2023/3/5,Electrical detection of antiferromagnetic dynamics in Gd-Co thin films by using a 154-GHz gyrotron irradiation,"THz magnetization dynamics is a key property of antiferromagnets as well as
ferrimagnets that could harness the THz forefront and spintronics. While most
of the present THz measurement techniques are for bulk materials whose
sensitivities rely on the volume of the material, measurement techniques
suitable for thin films are quite limited. In this study, we explored and
demonstrated electrical detection of the antiferromagnetic dynamics in
ferrimagnetic Gd-Co thin films by using a 154 GHz gyrotron, a high-power
electromagnetic wave source. Captured resonant modes allow us to characterize
the peculiar magnetization dynamics of the Gd-Co around the net angular
momentum compensation. As the gyrotron frequency is scalable up to THz, our
demonstration can be an important milestone toward the THz measurements for
antiferro- and ferri- magnetic thin films.",2303.02639v1
2023/3/7,Charting the Skyrmion Free-Energy Landscape,"Chiral magnets feature a rich phase diagram with a variety of thermodynamical
phases. These include helical and conical spin arrangements and topologically
charged objects such as (anti)skyrmions. Crucially, due to hysteresis effects,
the thermodynamical phases can co-exist at any given temperature and external
magnetic field, typically leading to metastability of, e.g., the material's
topological phase. In this work, we use Monte Carlo simulations to study these
effects. We compute the relative free energies of co-existing states, enabling
us to determine the ground state at all values of the external parameters. We
also introduce a method to estimate the activation energy, i.e. the height of
the energy barrier that separates the topological phase from the ground state.
This allows us to address the skyrmion lifetime, which is relevant for
technological applications. Finally, we prescribe predicting the system's
evolution through any path in the space of external parameters. This can serve
as a guideline to prepare the magnetic material in any desired phase or even
trigger a phase transition in an experimental setup.",2303.04099v1
2023/3/15,Acoustically driven magnon-phonon coupling in a layered antiferromagnet,"Harnessing the causal relationships between mechanical and magnetic
properties of van der Waals materials presents a wealth of untapped opportunity
for scientific and technological advancement, from precision sensing to novel
memories. This can, however, only be exploited if the means exist to
efficiently interface with the magnetoelastic interaction. Here, we demonstrate
acoustically-driven spin-wave resonance in a crystalline antiferromagnet,
chromium trichloride, via surface acoustic wave irradiation. The resulting
magnon-phonon coupling is found to depend strongly on sample temperature and
external magnetic field orientation, and displays a high sensitivity to
extremely weak magnetic anisotropy fields in the few~mT range. Our work
demonstrates a natural pairing between power-efficient strain-wave technology
and the excellent mechanical properties of van der Waals materials,
representing a foothold towards widespread future adoption of dynamic
magneto-acoustics.",2303.08305v1
2023/4/20,Control of conductivity in Fe-rich cobalt-ferrite thin films with perpendicular magnetic anisotropy,"We fabricated two types of cobalt-ferrite (001) thin films, insulative
Fe-rich cobalt-ferrite CoxFe3-xO4+{\delta} (I-CFO) and conductive Fe-rich
cobalt-ferrite CoyFe3-yO4 (C-CFO), with perpendicular magnetic anisotropy (PMA)
on MgO (001) substrates. Although the stoichiometric cobalt-ferrite is known as
an insulating material, it is found that the conductivity of Fe-rich
cobalt-ferrites can be controlled by changing the source materials and
deposition conditions in the pulsed laser deposition technique. The I-CFO and
C-CFO films exhibit PMA through the in-plane lattice distortion. We
investigated the Fe-ion-specific valence states in both I-CFO and C-CFO films
by M\""ossbauer spectroscopy and X-ray magnetic circular dichroism, and found
that the difference in conductivity corresponds to the abundance ratio of Fe2+
state at the octahedral B-site (Oh) in the inverse spinel structure.
Furthermore, first-principles calculations reproduce the changes in the density
of states at the Fermi level depending on the cation vacancies at the B-site,
which explains the difference in the conductivity between I-CFO and C-CFO.",2304.10048v1
2023/5/16,Unconventional anomalous Hall effect in epitaxially stabilized orthorhombic Ru$^{3+}$ perovskite thin films,"Complex oxides are mesmerizing material systems to realize multiple physical
properties and functionalities by integrating different elements in a single
compound. However, owing to the chemical instability, not all the combinations
of elements can be materialized despite the intriguing potential expected from
their magnetic and electronic properties. In this study, we demonstrate an
epitaxial stabilization of orthorhombic Ru$^{3+}$ perovskite oxides: LaRuO$_3$
and NdRuO$_3$, and their magnetotransport properties that reflect the
difference between non-magnetic La$^{3+}$ and magnetic Nd$^{3+}$. Above all, an
unconventional anomalous Hall effect accompanied by an inflection point in
magnetoresistance is observed around 1.3 T below 1 K for NdRuO$_3$, which is
ascribed to topological Hall effect possibly due to a non-coplanar spin texture
on Nd$^{3+}$ sublattice. These studies not only serve a new testbed for the
interplay between spin-orbit coupling and Coulomb interaction but also open a
new avenue to explore topological emergent phenomena in well-studied perovskite
oxides.",2305.09201v1
2023/5/27,Giant spontaneous magnetostriction in MnTe driven by a novel magnetostructural coupling mechanism,"We present a comprehensive x-ray scattering study of spontaneous
magnetostriction in hexagonal MnTe, an antiferromagnetic semiconductor with a
Neel temperature of $T_{\mathrm{N}} = 307$ K. We observe the largest
spontaneous magnetovolume effect known for an antiferromagnet, reaching a
volume contraction of $|\Delta V/V| > 7 \times 10^{-3}$. This can be justified
semiquantitatively by considering bulk material properties, the spatial
dependence of the superexchange interaction, and the geometrical arrangement of
magnetic moments in MnTe. The highly unusual linear scaling of the
magnetovolume effect with the short-range magnetic correlations, beginning in
the paramagnetic state well above $T_{\mathrm{N}}$, points to a novel physical
mechanism, which we explain in terms of a trilinear coupling of the elastic
strain with superposed distinct domains of the antiferromagnetic order
parameter. This novel mechanism for coupling lattice strain to robust
short-range magnetic order casts new light on magnetostrictive phenomena and
also provides a template by which the exceptional magnetostrictive properties
of MnTe might be realized in a wide range of other functional materials.",2305.17549v1
2023/6/27,Phase transitions associated with magnetic-field induced topological orbital momenta in a non-collinear antiferromagnet,"Resistivity measurements are widely exploited to uncover electronic
excitations and phase transitions in metallic solids. While single crystals are
preferably studied to explore crystalline anisotropies, these usually cancel
out in polycrystalline materials. Here we show that in polycrystalline
Mn3Zn0.5Ge0.5N with non-collinear antiferromagnetic order, changes in the
diagonal and, rather unexpected, off-diagonal components of the resistivity
tensor occur at low temperatures indicating subtle transitions between magnetic
phases of different symmetry. This is supported by neutron scattering and
explained within a phenomenological model which suggests that the phase
transitions in magnetic field are associated with field induced topological
orbital momenta. The fact that we observe transitions between spin phases in a
polycrystal, where effects of crystalline anisotropy are cancelled suggests
that they are only controlled by exchange interactions. The observation of an
off-diagonal resistivity extends the possibilities for realising
antiferromagnetic spintronics with polycrystalline materials.",2306.15332v1
2023/7/25,Spin waves in bilayers of transition-metal dichalcogenides,"Van der Waals magnetic materials are currently of great interest as materials
for applications in future ultrathin nanoelectronics and nanospintronics. Due
to weak coupling between individual monolayers, these materials can be easily
obtained in the monolayer and bilayer forms. The latter are of specific
interest as they may be considered as natural two-dimensional spin valves. In
this paper, we study theoretically spin waves in bilayers of transition metal
dichalcogenides. The considerations are carried within the general spin wave
theory based on effective spin Hamiltonian and Hollstein-Primakoff-Bogolubov
transformation. The spin Hamiltonian includes intra-layer as well as
inter-layer nearest-neighbour exchange interactions, easy-plane anisotropy, and
additionally a weak in-plane easy-axis anisotropy. The bilayer systems consist
of two ferromagnetic (in-plane magnetization) monolayers that are coupled
either ferromagnetically or antiferromagnetically. In the latter case, we
analyse the spin wave spectra in all magnetic phases, i.e. in the
antiferromagnetic, spin-flop, and ferromagnetic ones.",2307.13414v2
2023/7/25,Magnetotransport and Berry phase Tuning in Gd-doped Bi2Se3 Topological Insulator Single Crystals,"The Berry phase is an important concept in solids, correlated to the band
topology, axion electrodynamics and potential applications of topological
materials. Here, we investigate the magnetotransport and Berry phase of rare
earth element Gd doped Bi2Se3 (Gd_Bi2Se3) topological insulator at low
temperatures and high magnetic fields. Gd_Bi2Se3 single crystals show
Shubnikov-de Haas (SdH) oscillations with nontrivial Berry phase while Bi2Se3
single crystals show zero Berry phase in SdH oscillations. The temperature
dependent magnetization curves can be well fitted with the Curie-Weiss law in
3-300 K region, indicating no magnetic ordering in Gd_Bi2Se3 crystals.
Moreover, Gd doping has limited influence on the quantum oscillation parameters
(e.g., frequency of oscillations, the area of the Fermi surface, effective
electron mass, Fermi wave vectors etc.), but has an impact on the Hall
mobility, carrier density, and band topology. Our results demonstrate that Gd
doping can tune the Berry phase of topological insulators effectively, which
may pave a way for the future realization of many predicted exotic transport
phenomena of topological origin.",2307.13847v1
2023/8/17,Characterization of the Magnetocaloric Effect in RMn6Sn6 including High Entropy Alloys,"We present a comprehensive study of the magnetocaloric effect (MCE) in a
family of kagome magnets with formula RMn6Sn6 (R=Tb, Ho, Er, and Lu). These
materials have a small rare-earth content and tunable magnetic ordering, hence
they provide a venue to study the fundamentals of the MCE. We examine the
effect of different types of order (ferrimagnetic and antiferromagnetic) and
the presence of a metamagnetic transition on the MCE. We extend the study to
high-entropy rare-earth alloys of the family. Our results suggest several
guidelines for enhancing the MCE in tunable magnetic materials with a small
rare-earth content.",2308.09161v2
2023/9/3,Crystallographic Disorder and Strong Magnetic Anisotropy in Dy3.1Pt2.0Sb3.8,"We report the crystal growth and characterization of a rare-earth-containing
material, Dy3.00(1)Pt2Sb4.48(2). This compound possesses a similar structure to
the previously reported Y3Pt4Ge6, but lacks two layers of Pt atoms.
Crystallographic disorder was found in Dy3.00(1)Pt2Sb4.48(2). Additionally, the
Dy-Dy framework was found to have both square net and triangular lattices.
Dy3.00(1)Pt2Sb4.48(2)8 was determined to be antiferromagnetically ordered
around ~15 K while a competing antiferromagnetic sublattice also exists at
lower temperature. Strong magnetic anisotropy was observed and several
metamagnetic transitions were seen in the hysteresis loops. Furthermore, the
Curie-Weiss fitting revealed unusually small effective moment of Dy, which is
far below the expected value of Dy3+ (10.65 muB). This material might provide a
new platform to study the relation between crystallographic disorder and
magnetism.",2309.01177v2
2023/9/5,Strain Engineering of Magneto-optical Properties in C$_3$B/C$_3$N van der Waals Heterostructure,"Carbon-based bilayer van der Waals (vdW) materials are attracting much
attention due to their predicted interesting physical properties. Here, we
theoretically investigate electronic and optical properties of C$_3$B/C$_3$N
vdW heterostructure (HTS) under external magnetic field and mechanical strain.
The tight-binding model of the system is constructed to include the
strain-induced modification of the hopping interactions. The influence of a
uniform perpendicular magnetic field is included by using the Peierls
substitution method. We observe the intriguing electronic and optical
characteristics of the HTS under mechanical strain, covering the band
inversion, alteration of band gap and optical gap, distortion of band-edge
states, as well as significant enhancement of optical absorption. Furthermore,
the interplay between external magnetic field and biaxial strain leads to
exotic features of quantization and optical spectra. This work provides
important information for the comprehension of the engineering of materials by
external effects. Our study suggests that C$_3$B/C$_3$N vdW HTS is a promising
candidate for next-generation electronic and optoelectronic devices.",2309.02535v1
2023/9/6,Magnetic order in the $S_{\mathrm{eff}}$ = 1/2 triangular-lattice compound NdCd$_3$P$_3$,"We present and characterize a new member of the $R$Cd$_3$P$_3$ ($R$= rare
earth) family of materials, NdCd$_3$P$_3$, which possesses Nd$^{3+}$ cations
arranged on well-separated triangular lattice layers. Magnetic susceptibility
and heat capacity measurements demonstrate a likely $S_{\mathrm{eff}}$ = 1/2
ground state, and also reveal the formation of long-range antiferromagnetic
order at $T_{N} = 0.34$ K. Via measurements of magnetization, heat capacity,
and electrical resistivity, we characterize the electronic properties of
NdCd$_3$P$_3$ and compare results to density functional theory calculations.",2309.03332v1
2023/9/18,Nonlinear dynamics and magneto-elasticity of nanodrums near the phase transition,"Nanomechanical resonances of two-dimensional (2D) materials are sensitive
probes for condensed-matter physics, offering new insights into magnetic and
electronic phase transitions. Despite extensive research, the influence of the
spin dynamics near a second-order phase transition on the nonlinear dynamics of
2D membranes has remained largely unexplored. Here, we investigate nonlinear
magneto-mechanical coupling to antiferromagnetic order in suspended
FePS$_3$-based heterostructure membranes. By monitoring the motion of these
membranes as a function of temperature, we observe characteristic features in
both nonlinear stiffness and damping close to the N\'{e}el temperature
$T_{\rm{N}}$. We account for these experimental observations with an analytical
magnetostriction model in which these nonlinearities emerge from a coupling
between mechanical and magnetic oscillations, demonstrating that
magneto-elasticity can lead to nonlinear damping. Our findings thus provide
insights into the thermodynamics and magneto-mechanical energy dissipation
mechanisms in nanomechanical resonators due to the material's phase change and
magnetic order relaxation.",2309.09672v1
2023/10/9,Magnetocaloric effect of nanostructured La0.6Sr0.4CoO3,"In this study, we investigate the magnetic and magnetocaloric properties of
nanostructured La0.6Sr0.4CoO3 (LSC) samples synthesized under confinement
conditions within porous templates. Using this method, we obtained
de-agglomerated nanoparticles, which provide us with the feasibility of
applying them in nanoparticle films that can be tailored to intricate
geometries. We specifically explored the impact of pore size of the template on
key parameters including saturation magnetization (MS), Curie temperature (TC),
maximum entropy change ({\Delta}S), and relative cooling power (RCP). Our
findings reveal enhancements in those quantities, that are likely to be related
with the nanostructure of the samples, indicating the potential of
nanostructured LSC as an active material for magnetic refrigeration devices.
Our alternative approach of synthesizing magnetocaloric materials under
confinement conditions presents an exciting prospect for future research and
development in the field.",2310.05722v1
2023/11/15,Dimensional reduction from magnetic field in moiré superlattices,"Moir\'e materials provide a highly tunable platform in which novel electronic
phenomena can emerge. We study strained moir\'e materials in a uniform magnetic
field and predict highly anisotropic electrical conductivity which switches
easy-axis as magnetic field or strain is varied. The dramatic anisotropy
reflects one-dimensional localization (dimensional reduction) of the electron
wavefunctions along a crystal axis due to quantum interference effects. This
can be understood in an effective one-dimensional quasiperiodic
Aubry-Andr\'e-like models, or in a complementary semiclassical picture. This
phenomenon should be observable in strained moir\'e materials at realistic
fields and low strain disorder, as well as unstrained systems with anisotropic
Fermi surfaces.",2311.09323v1
2023/11/19,Unraveling oscillations at ferro(para)magnetic and non-collinear antiferromagnetic interfaces,"Here, we show that the ferro(para)magnetic and non-collinear
antiferromagnetic interfaces contribute to oscillating signals observed in the
magnetoresistance. We associate the effect with the fact that the spins on the
surface of IrMn3 produce instability in the surface magnetoresistance of the
material, which is sensitive to the magnetic field. We carried out experiments
using bilayers of IrMn3 under permalloy (Py) and IrMn3 under platinum (Pt). The
oscillations were intensely evident at the Py/IrMn3 interface and less explicit
at the Pt/IrMn3 interface. We carried out the experiments using pulsed current,
with a square pulse width of 1{\mu}s and amplitudes of 20 {\mu}A to 20 mA. The
oscillating signals are proportional to the crystallographic direction of the
material, the ferromagnetism of the material adjacent to IrMn3, and sensitive
to the amplitude of the pulsed current. We believe that observation is a way of
transmitting encoded information through magnetoresistance.",2311.11401v1
2023/12/13,Spontaneous time-reversal symmetry breaking by disorder in superconductors,"A growing number of superconducting materials display evidence for
spontaneous time-reversal symmetry breaking (TRSB) below their critical
transition temperatures. Precisely what this implies for the nature of the
superconducting ground state of such materials, however, is often not
straightforward to infer. We review the experimental status and survey
different mechanisms for the generation of signatures of TRSB in
superconductors. In cases where a TRSB complex combination of two
superconducting order parameter components is realized, defects, dislocations
and sample edges may generate superflow patterns that can be picked up by
magnetic probes. However, even single-component condensates that do not break
time-reversal symmetry in their pure bulk phases can also support signatures of
magnetism inside the superconducting state. This includes, for example, the
generation of localized orbital current patterns or spin-polarization near
atomic-scale impurities, twin boundaries and other defects. Signals of TRSB may
also arise from a superconductivity-enhanced Ruderman-Kittel-Kasuya-Yosida
exchange coupling between magnetic impurity moments present in the normal
state. We discuss the relevance of these different mechanisms for TRSB in light
of recent experiments on superconducting materials of current interest.",2312.08099v1
2024/1/21,Entangled-Beam Reflectometry and Goos-Hänchen Shift,"We introduce the technique of Entangled-Beam Reflectometry for extracting
spatially correlated (magnetic or non-magnetic) information from material
surfaces or thin films. Our amplitude- and phase-sensitive technique exploits
the coherent nature of an incoming entangled probe beam, of matter or light
waves, undergoing reflection from the surface. Such reflection encodes the
surface spatial structure into the probe's geometric and phase-derived
Goos-H\""anchen shifts, which can then be measured to unveil the structure. We
investigate the way these shifts depend on the wave packet widths, and
illustrate our technique in the case of in-plane periodic (non-)magnetic
structures by utilizing spin-path mode-entangled neutron beams.",2401.11586v1
2024/1/25,Universal collective Larmor-Silin mode emerging in magnetized correlated Dirac fermions,"Employing large-scale quantum Monte Carlo simulations, we find in magnetized
interacting Dirac fermion model, there emerges a new and universal collective
Larmor-Silin spin wave mode in the transverse dynamical spin susceptibility.
Such mode purely originates from the interaction among Dirac fermions and
distinguishes itself from the usual particle-hole continuum with finite
lifetime and clear dispersion, both at small and large momenta in a large
portion of the Brillouin zone. Our unbiased numerical results offer the dynamic
signature of this new collective excitations in interacting Dirac fermion
systems, and provide experimental guidance for inelastic neutron scattering,
electron spin resonance and other spectroscopic approaches in the investigation
of such universal collective modes in quantum Moire materials, topological
insulators and quantum spin liquid materials under magnetic field, with
quintessential interaction nature beyond the commonly assumed noninteracting
Dirac fermion or spinon approximations.",2401.14358v2
2024/3/7,Spin-Phonon interaction in quasi 2D- Cr$_2Te_3$,"Spin-phonon interaction plays an important role in 2D magnetic materials and
motivates the development of next-generation spin- and charge-dependent
microelectronic devices. Understanding the spin-phonon interaction by tuning
the growth parameter of single crystal Cr$_2Te_3$, a robust quasi-2D room
temperature magnetic material, is crucial for spintronic devices. The synthesis
of single crystal 2D Cr$_2Te_3$ flakes on a Si substrate from co-deposited thin
film by plasma annealing techniques is a significant achievement. The
temperature dependence and polarization-resolved Raman spectroscopy with
support of density functional theory classified lattice symmetry operations
were used to identify the phonon modes to investigate the spin/electron-phonon
interactions in Cr$_2Te_3$. The mean-field theory model in single crystal
Cr$_2Te_3$ is employed to quantify the spin-phonon interaction and correlate
with in-plane and out-of-plane magnetic behavior. The observation of a positive
correlation between phonon mode frequency and spin-phonon interaction strength
in single crystal Cr$_2Te_3$ can be a potential candidate for spintronic
applications.",2403.04426v1
2024/3/13,Geometric and electronic properties of two kinds of CrO2 magnetic monolayers: D3d and D2h phases,"Due to the high magnetic coupling strength between the Cr elements, the bulk
phase CrO2 is one of several ferromagnetic oxides known to have the highest
Curie temperature. When the dimensionality of the material is reduced from 3D
to 2D, the 2D CrO2 system material is expected to maintain a high Curie
temperature. In this work, we predict two new phases of CrO2 monolayer (D3d and
D2h) by using first-principles calculations. We have found that the Curie
temperature of 2D CrO2 is much lower than that of its bulk phase, but still
remains as high as 191K, which is comparable to that of Fe2Cr2Ge6. In addition,
1L D3d-CrO2 is in the ferromagnetic state, while 1L D2h-CrO2 is in the
antiferromagnetic state. Also, the different geometric structure affects its
electrical properties: the 1L D3d-CrO2 is a half-metal while 1L D2h-CrO2 is a
semiconductor. Our studies have shown that there is a wealth of electrical and
magnetic properties in CrO2.",2403.08357v1
2024/3/22,All van der Waals three-terminal SOT-MRAM realized by topological ferromagnet Fe3GeTe2,"Magnetic van der Waals (vdW) materials have attracted massive attention
because of their academic interest and application potential for the past few
years. Its main advantage is the intrinsic two-dimensionality, enabling much
smaller devices of novel concepts. One particular exciting direction lies in
the current-driven spin-orbit torque (SOT). Here, we, for the first time,
realize an all vdW three-terminal SOT memory, employing the unique physics
principle of gigantic intrinsic SOT of Fe3GeTe2 (FGT) and the well-known
industry-adopted tunnelling magnetoresistance (TMR) effect. We designed the
device operation procedure and fabricated the FGT/h-BN/FGT vdW heterostructure
as a proof of concept. This device exhibits a classical TMR effect and
unambiguously demonstrates the conception by precise performance as expected:
the magnetic information of the top-FGT is written by current-driven SOT and
read out by TMR separately. The writing and reading current paths are
physically decoupled, enhancing the design and optimization flexibility
substantially and further strengthening the device's endurance naturally. Our
work would prompt more expansive use of vdW magnets for spintronic
applications.",2403.15020v1
2024/3/26,Large topological Hall effect arising from spin reorientation in kagome magnet Fe3Ge,"Materials systems with spin chirality can provide ultra-high-density,
ultra-fast, and ultralow-power information carriers for digital transformation.
These material systems include magnetic skyrmions, chiral domain walls, spin
reorientation,and so on. The topological Hall effect (THE) has been identified
as the most convenient and effective tool for detecting the presence of spin
chirality in these systems. The research on the THE that may arise from spin
reorientation and specifically in Fe3Ge with spin reorientation remains an
unexplored area, so we study the THE in Fe3Ge Conduct systematic research.
X-Ray Diffraction (XRD) results indicate that our Fe3Ge ribbon sample has a
D019 structure. First-principles calculations and magnetic and electrical
testing confirm spin reorientation in the Fe3Ge ribbon sample at 350 K.The Hall
resistivity test results are consistent with our expectations, indicating the
presence of the THE in the Fe3Ge ribbon sample. The topological Hall
resistivity reaches a maximum value of 0.69 m{\Omega} cm at 400 K. For the
first time, a detailed experimental study of the THE in Fe3Ge with spin
reorientation has been conducted, introducing a new member to the family of
THE.",2403.17354v1
2006/3/23,Cosmological Magnetic Field: a fossil of density perturbations in the early universe,"The origin of the substantial magnetic fields that are found in galaxies and
on even larger scales, such as in clusters of galaxies, is yet unclear. If the
second-order couplings between photons and electrons are considered, then
cosmological density fluctuations, which explain the large scale structure of
the universe, can also produce magnetic fields on cosmological scales before
the epoch of recombination. By evaluating the power spectrum of these
cosmological magnetic fields on a range of scales, we show here that magnetic
fields of 10^{-18.1} gauss are generated at a 1 megaparsec scale and can be
even stronger at smaller scales (10^{-14.1} gauss at 10 kiloparsecpc). These
fields are large enough to seed magnetic fields in galaxies and may therefore
have affected primordial star formation in the early universe.",0603631v1
2007/1/11,Magnetic Field Spectrum at Cosmological Recombination,"A generation of magnetic fields from cosmological density perturbations is
investigated. In the primordial plasma before cosmological recombination, all
of the materials except dark matter in the universe exist in the form of
photons, electrons, and protons (and a small number of light elements). Due to
the different scattering nature of photons off electrons and protons, electric
currents and electric fields are inevitably induced, and thus magnetic fields
are generated. We present a detailed formalism of the generation of
cosmological magnetic fields based on the framework of the well-established
cosmological perturbation theory following our previous works. We numerically
obtain the power spectrum of magnetic fields for a wide range of scales, from
$k\sim 10^{-5}$ Mpc$^{-1}$ up to $k\sim 2\times 10^{4}$ Mpc$^{-1}$ and provide
its analytic interpretation. Implications of these cosmologically generated
magnetic fields are discussed.",0701329v1
1996/7/30,A quantum model for the magnetic multi-valued recording,"We have proposed a quantum model for the magnetic multi-valued recording in
this paper. The hysteresis loops of the two-dimensional systems with randomly
distributed magnetic atoms have been studied by the quantum theory developed
previously. The method has been proved to be exact in this case. We find that
the single-ion anisotropies and the densities of the magnetic atoms are mainly
responsible for the hysterisis loops. Only if the magnetic atoms contained by
the systems are of different (not uniform) anistropies and their density is
low, there may be more sharp steps in the hysteresis loops. Such materials can
be used as the recording media for the so-called magnetic multi-valued
recording. Our result explained the experimental results qualitativly.",9607221v1
1998/1/8,An experimental measurement of the staggered magnetization curve for a Haldane spin chain,"Long-range magnetic ordering in R_2 Ba Ni O_5 (R=magnetic rare earth)
quasi-1-dimensional mixed-spin antiferromagnets is described by a simple
mean-field model that is based on the intrinsic staggered magnetization
function of isolated Haldane spin chains for the Ni-subsystem, and single-ion
magnetization functions for the rare earth ions. The model is applied to new
experimental results obtained in powder diffraction experiments on Nd_2 Ba Ni
O_5 and Nd Y Ba Ni O_5, and to previously published diffraction data for Er_2
Ba Ni O_5. From this analysis we extract the bare staggered magnetization curve
for Haldane spin chains in these compounds.",9801068v2
1998/12/1,Simulation of Magnetization Switching in Biaxial Single-Domain Ferromagnetic Particles,"The magnetization switching dynamics of biaxial single-domain homogeneous
ferromagnetic particles, in which the two easy axes are perpendicular to each
other, is simulated using a 4-state clock model. A zero-field mapping of the
statics between the symmetric 4-state clock model and two decoupled Ising
models is extended to non-zero field statics and to the dynamics. This
significantly simplifies the analysis of the simulation results. We measure the
magnetization switching time of the model and analyze the results using droplet
theory. The switching dynamics in the asymmetric model is more complicated. If
the easy axis is perpendicular to the stable magnetization direction, the
system can switch its magnetization via two different channels, one very fast
and the other very slow. A maximum value for the switching field as a function
of system size is obtained. The asymmetry affects the switching fields
differently, depending on whether the switching involves one single droplet or
many droplets of spins in the stable magnetization configuration. The angular
dependence of the switching field in symmetric and asymmetric models is also
studied.",9812010v1
1999/4/14,Magnetic clusters formation in Li_{1-x}Ni_{1+x}O_2 compounds : experiments and numerical simulations,"The magnetic properties of Li_{1-x}Ni_{1+x}O_2 compounds with x ranging
between 0.02 and 0.2 are investigated. Magnetization and ac susceptibility
measured at temperatures between 2 K and 300 K reveal a high sensitivity to x,
the excess Nickel concentration. We introduce a percolation model describing
the formation of Ni clusters and use an Ising model to simulate their magnetic
properties. Numerical results, obtained by a Monte-Carlo technique, are
compared to the experimental data. We show the existence of a critical
concentration, x_c = 0.136, locating the Ni percolation threshold. The system
is superparamagnetic for x<x_c, while it is ferrimagnetic for x>x_c. The 180
Ni-O-Ni inter-plane super-exchange coupling J_\perp \simeq -110K is confirmed
to be the predominant magnetic interaction. From the low temperature behavior,
we find a clear indication of a 90 Ni-O-Ni intra-plane antiferromagnetic
interaction $J_\parallel \simeq -1.5K$ which implies magnetic frustration.",9904194v1
1999/10/7,Magnetic remanence of Josephson junction arrays,"In this work we study the magnetic remanence exhibited by Josephson junction
arrays in response to an excitation with an AC magnetic field. The effect,
predicted by numerical simulations to occur in a range of temperatures, is
clearly seen in our tridimensional disordered arrays. We also discuss the
influence of the critical current distribution on the temperature interval
within which the array develops a magnetic remanence. This effect can be used
to determine the critical current distribution of an array.",9910118v1
2000/2/17,"Silence of magnetic layers to magnetoresistive process and electronic separation at low temperatures in (La, Sm)Mn$_2$Ge$_2$","A closer look at the temperature (T) dependence of magnetoresistance (MR) of
two polycrystalline magnetic compounds, LaMn$_2$Ge$_2$ and SmMn$_2$Ge$_2$,
previously reported by us, is made. A common feature for both these compounds
is that the low temperature MR is positive (say, below, 30 K) in spite of the
fact that both are ferromagnetic at such low temperatures; in addition, MR as a
function of magnetic field (H) does not track magnetization (M) in the sense
that M saturates at low fields, while MR varies linearly with H. These
observations suggest that the magnetic layers interestingly do not dominate low
temperature magnetotransport process. Interestingly enough, as the T is
increased, say around 100 K, these magnetic layers dominate MR process as
evidenced by the tracking of M and MR in SmMn$_2$Ge$_2$. These results tempts
us to propose that there is an unusual ""electronic separation"" for MR process
as the T is lowered in this class of compounds.",0002275v1
2000/2/24,The local magnetic moments and hyperfine magnetic fields in disordered metal-metalloid alloys,"The local magnetic moments and hyperfine magnetic fields (HFF) in the ordered
alloys Fe_{15}Sn and Fe_{15}Si are calculated with the first-principles
full-potential linear augmented plane wave (FP LAPW) method. The results are
compared with the experimental data on Fe-M (M=Si, Sn) disordered alloys at
small metalloid concentration. The relaxation of the lattice around the
impurity and its influence on the quantities under consideration are studied.
The mechanism of the local magnetic moment formation is described. It is proved
that the main distinction between these alloys is connected with the different
lattice parameters. Three contributions to the HFF are discussed: the
contributions of the core and valence electron polarization to the
Fermi-contact part, and the contibution from the orbital magnetic moment.",0002371v1
2000/3/14,"Magnetic and electrical resistance behaviour of the oxides, Ca$_{3-x}$Y$_x$LiRuO$_6$ (x= 0.0, 0.5 and 1.0)","We have investigated the magnetic and electrical resistance behaviour of
  Ca$_{3-x}$Y$_x$LiRuO$_6$. The parent compound exhibits magnetic ordering from
Ru sublattice at a rather high temperature, 113 K. Though the paramagnetic
  Curie temperature ($\theta$$_p$) is negative indicative of antiferromagnetic
ordering, the large magnitude (-250 K) of $\theta$$_p$ reveals complex nature
of the magnetism in this compound. Ru ions appear to be in the pentavalent
state. We note that the N\'eel temperature undergoes only a marginal reduction
by Y substitution. All these compositions are found to be insulators and thus
the electron doping does not result in metallicity. Thus the overall magnetic
and transport behaviour are found to be essentially insensitive to Y
substitution for Ca, a finding which may favour the idea of
quasi-one-dimensional magnetism in these compounds.",0003227v1
2000/5/30,Effects of arbitrarily directed field on spin phase oscillations in biaxial molecular magnets,"Quantum phase interference and spin-parity effects are studied in biaxial
molecular magnets in a magnetic field at an arbitrarily directed angle. The
calculations of the ground-state tunnel splitting are performed on the basis of
the instanton technique in the spin-coherent-state path-integral
representation, and complemented by exactly numerical diagonalization. Both the
Wentzel-Kramers-Brillouin exponent and the preexponential factor are obtained
for the entire region of the direction of the field. Our results show that the
tunnel splitting oscillates with the field for the small field angle, while for
the large field angle the oscillation is completely suppressed. This distinct
angular dependence, together with the dependence of the tunnel splitting on the
field strengh, provide an independent test for spin-parity effects in biaxial
molecular magnets. The analytical results for the molecular Fe$_{8}$ magnet,
are found to be in good areement with the numerical simulations, which suggests
that even the molecular magnet with total spin S=10 is large enough to be
treated as a giant spin system.",0005527v1
2000/11/13,Magnetization reversal triggered by spin injection in magnetic nanowires,"It is shown that a pulsed current driven through Ni nanowires provokes an
irreversible magnetization reversal at a field distant from the spontaneous
switching field $H_{sw}$ by $\Delta H$ of as much as 40 % of $H_{sw}$. The
state of the magnetization is assessed by magnetoresistive measurements carried
out on single, isolated nanowires. The reversible part of the magnetization
follows that of a uniform rotation. The switching occurs between the two states
accessible otherwise by normal field ramping. $\Delta H$ is studied as a
function of the angle between the applied field and the wire, and also of the
direction of the pulsed current. The results are interpreted in terms of
spin-flip transfer from the spin-polarized current to the magnetization, while
the switching is approximated by a curling reversal mode.",0011228v1
2000/12/15,Evolution and stability of a magnetic vortex in small cylindrical ferromagnetic particle under applied field,"The energy of a displaced magnetic vortex in a cylindrical particle made of
isotropic ferromagnetic material (magnetic dot) is calculated taking into
account the magnetic dipolar and the exchange interactions. Under the
simplifying assumption of small dot thickness the closed-form expressions for
the dot energy is written in a non-perturbative way as a function of the
coordinate of the vortex center. Then, the process of losing the stability of
the vortex under the influence of the externally applied magnetic field is
considered. The field destabilizing the vortex as well as the field when the
vortex energy is equal to the energy of a uniformly magnetized state are
calculated and presented as a function of dot geometry. The results (containing
no adjustable parameters) are compared to the recent experiment and are in good
agreement.",0012299v1
2001/2/2,Ab-initio study of disorder effects on the electronic and magnetic structures of Sr$_2$FeMoO$_6$,"We have investigated the electronic structure of ordered and disordered
Sr$_2$FeMoO$_6$ using {\it ab-initio} band structure methods. The effect of
disorder was simulated within super-cell calculations to realize several
configurations with mis-site disorders. It is found that such disorder effects
destroy the half-metallic ferro-magnetic state of the ordered compound. It also
leads to a substantial reduction of the magnetic moments at the Fe sites in the
disordered configurations. Most interestingly, it is found for the disordered
configurations, that the magnetic coupling within the Fe sub-lattice as well as
that within the Mo sub-lattice always remain ferro-magnetic, while the two
sub-lattices couple anti-ferromagnetically, in close analogy to the magnetic
structure of the ordered compound, but in contrast to recent suggestions.",0102024v1
2001/2/21,"Coordination and chemical effects on the structural, electronic and magnetic properties in Mn pnictides","Simple structures of MnX binary compounds, namely hexagonal NiAs and
zincblende, are studied as a function of the anion (X = Sb, As, P) by means of
the all-electron FLAPW method within local spin density and generalized
gradient approximations. An accurate analysis of the structural, electronic and
magnetic properties reveals that the cubic structure greatly favours the
magnetic alignment in these compounds leading to high magnetic moments and
nearly half-metallic behaviour for MnSb and MnAs. The effect of the anion
chemical species is related to both its size and the possible hybridization
with the Mn $d$ states; both contributions are seen to hinder the magnitude of
the magnetic moment for small and light anions. Our results are in very good
agreement with experiment - where available - and show that the generalized
gradient approximation is essential to correctly recover both the equilibrium
volume and magnetic moment.",0102376v1
2001/6/8,Magnetic Field scaling of Relaxation curves in Small Particle Systems,"We study the effects of the magnetic field on the relaxation of the
magnetization of small monodomain non-interacting particles with random
orientations and distribution of anisotropy constants. Starting from a master
equation, we build up an expression for the time dependence of the
magnetization which takes into account thermal activation only over barriers
separating energy minima, which, in our model, can be computed exactly from
analytical expressions. Numerical calculations of the relaxation curves for
different distribution widths, and under different magnetic fields H and
temperatures T, have been performed. We show how a $\svar$ scaling of the
curves, at different T and for a given H, can be carried out after proper
normalization of the data to the equilibrium magnetization. The resulting
master curves are shown to be closely related to what we call effective energy
barrier distributions, which, in our model, can be computed exactly from
analytical expressions. The concept of effective distribution serves us as a
basis for finding a scaling variable to scale relaxation curves at different H
and a given T, thus showing that the field dependence of energy barriers can be
also extracted from relaxation measurements.",0106167v2
2001/6/20,Ferrohydrodynamics: testing a new magnetization equation,"A new magnetization equation recently derived from irreversible
thermodynamics is employed to the calculation of an increase of ferrofluid
viscosity in a magnetic field. Results of the calculations are compared with
those obtained on the basis of two well-known magnetization equations. One of
the two was obtained phenomenologically, another one was derived
microscopically from the Fokker-Planck equation. It is shown that the new
magnetization equation yields a quite satisfactory description of
magnetiviscosity in the entire region of magnetic field strength and the flow
vorticity. This equation turns out to be valid -- like the microscopically
derived equation but unlike the former phenomenological equation -- even far
from equilibrium, and so it should be recommended for further applications.",0106415v1
2001/10/23,Effect of local Coulomb interactions on the electronic structure and exchange interactions in Mn12 magnetic molecules,"We have studied the effect of local Coulomb interactions on the electronic
structure of the molecular magnet Mn12-acetate within the LDA+U approach. The
account of the on-site repulsion results in a finite energy gap and an integer
value of the molecule's magnetic moment, both quantities being in a good
agreement with the experimental results. The resulting magnetic moments and
charge states of non-equivalent manganese ions agree very well with
experiments. The calculated values of the intramolecular exchange parameters
depend on the molecule's spin configuration, differing by 25-30% between the
ferrimagnetic ground state and the completely ferromagnetic configurations. The
values of the ground-state exchange coupling parameters are in reasonable
agreement with the recent data on the magnetization jumps in megagauss magnetic
fields. Simple estimates show that the obtained exchange parameters can be
applied, at least qualitatively, to the description of the spin excitations in
Mn12-acetate.",0110488v1
2001/11/7,Study of Magnetic Excitation in Singlet-Ground-State Magnets CsFeCl$_3$ and RbFeCl$_3$ by Nuclear Magnetic Relaxation,"The temperature dependences of spin-lattice relaxation time $T_1$ of
$^{133}$Cs in CsFeCl$_3$ and $^{87}$Rb in RbFeCl$_3$ were measured in the
temperature range between 1.5 K and 22 K, at various fields up to 7 T applied
parallel (or perpendicular) to the c-axis, and the analysis was made on the
basis of the DCEFA. The mechanism of the nuclear magnetic relaxation is
interpreted in terms of the magnetic fluctuations which are characterized by
the singlet ground state system. In the field region where the phase transition
occurs, $T_1^{-1}$ exhibited the tendency of divergence near $T_{\rm N}$, and
this feature was ascribed to the transverse spin fluctuation associated with
the mode softening at the $K$-point. It was found that the damping constant of
the soft mode is remarkably affected by the occurrence of the magnetic ordering
at lower temperature, and increases largely in the field region where the phase
transition occurs.",0111097v2
2002/1/27,Optical detection of magnetic data using magnetooptic indicators with in-plane magnetization,"We investigate detection of magnetic data using magnetooptical indicators
with in-plane magnetization. A simple model for the magnetooptical detection
system is presented. We find that the signal to noise ratio changes strongly
with the bit size, the polarization noise and the distance between the magnetic
carrier and the indicator. In particular, it is found that within our model a
signal to noise ratio of 30 is possible for a bit size of 200 nm. We also
estimate the resolution of the system, and find that a spot size of $\sim 200$
nm can be obtained using a suitably designed solid immersion lens. Finally, we
discuss detection of several magnetic tracks simultaneously.",0201493v1
2002/3/11,High TC ferromagnetism in diluted magnetic semiconducting GaN:Mn films,"Wurtzite GaN:Mn films on sapphire substrates were successfully grown by use
of the molecular beam epitaxy (MBE) system. The film has an extremely high
Curie temperature of around 940 K, although the Mn concentration is only about
3 ~ 5 %. Magnetization measurements were carried out in magnetic fields
parallel to the film surface up to 7 T. The magnetization process shows the
coexistence of ferromagnetic and paramagnetic contributions at low
temperatures, while the typical ferromagnetic magnetization process is mainly
observed at high temperatures because of the decrease of the paramagnetic
contributions. The observed transport characteristics show a close relation
between the magnetism and the impurity conduction. The double exchange
mechanism of the Mn-impurity band is one of the possible models for the high-TC
ferromagnetism in GaN:Mn.",0203223v1
2002/4/23,Field-induced gap in the spin-1/2 antiferromagnetic Heisenberg chain: A density matrix renormalization group study,"We study the spin-1/2 antiferromagnetic Heisenberg chain in both uniform and
(perpendicular) staggered magnetic fields using the density-matrix
renormalization-group method. This model has been shown earlier to describe the
physics of the copper benzoate materials in magnetic field. In the present
work, we extend the study to more general case for a systematic investigation
of the field-induced gap and related properties of the spin-1/2
antiferromagnetic Heisenberg chain. In particular, we explore the high magnetic
field regime where interesting behaviors in the field-induced gap,
magnetization, and spin correlation functions are found. Careful examination of
the low energy properties and magnetization reveals interesting competing
effects of the staggered and uniform fields. The incommensurate behavior in the
spin correlation functions is demonstrated and discussed in detail. The present
work reproduces earlier results in good agreement with experimental data on
copper benzoate and predicts new interesting field-induced features at very
high magnetic field.",0204489v1
2002/4/29,Positive and Perpendicular Exchange Bias CoO/Co Bilayers,"We have carried out detailed experimental studies of the exchange bias effect
of a series of CoO/Co(111) textured bilayers with different Co layer thickness,
using the magneto-optical Kerr effect, SQUID magnetometry, polarized neutron
reflectivity, x-ray diffraction, and atomic force microscopy. All samples
exhibit a pronounced asymmetry of the magnetic hysteresis at the first
magnetization reversal as compared to the second reversal. Polarized neutron
reflectivity measurements show that the first reversal occurs via nucleation
and domain wall motion, while the second reversal is characterized by
magnetization rotation. Off-specular diffuse spin-flip scattering indicates the
existence of interfacial magnetic domains. All samples feature a small positive
exchange bias just below the blocking temperature, followed by a dominating
negative exchange bias field with decreasing temperature. For very thin
Co-films the coexistence of ferromagnetic domains with parallel and
perpendicular magnetization directions leads to a peculiar shape of the
hysteresis with an extended plateau like region of almost zero magnetization.",0204607v2
2002/5/28,Thermomagnetic history effects in SmMn$_2$Ge$_2$,"The intermetallic compound SmMn$_2$Ge$_2$, displaying multiple magnetic phase
transitions, is being investigated in detail for its magnetization behavior
near the 145 K first order ferromagnetic to antiferromagnetic transition
occuring on cooling, in particular for thermomagnetic history effects in the
magnetization data. The most unusual finding is that the thermomagnetic
irreversibility, [= M$^{FCW}$(T)-M$^{ZFC}$(T)] at 135 K is higher in
intermediate magnetic field strengths. By studying the response of the sample
(i.e., thermomagnetic irreversibility and thermal hysteresis) to different
histories of application of magnetic field and temperature, we demonstrate how
the supercooling and superheating of the metastable magnetic phases across the
first order transition at 145 K contribute to overall thermomagnetic
irreversibility.",0205577v1
2002/5/31,Pressure Induced Change in the Magnetic Modulation of CeRhIn5,"We report the results of a high pressure neutron diffraction study of the
heavy fermion compound CeRhIn5 down to 1.8 K. CeRhIn5 is known to order
magnetically below 3.8 K with an incommensurate structure. The application of
hydrostatic pressure up to 8.6 kbar produces no change in the magnetic wave
vector qm. At 10 kbar of pressure however, a sudden change in the magnetic
structure occurs. Although the magnetic transition temperature remains the
same, qm increases from (0.5, 0.5, 0.298) to (0.5, 0.5, 0.396). This change in
the magnetic modulation may be the outcome of a change in the electronic
character of this material at 10 kbar.",0205667v2
2002/7/22,Exact results of the one-dimensional tranverse Ising model in an external longitudinal magnetic field,"Magnetic properties of the 1D mixed spin-1/2 and spin-S (S >1/2) transverse
Ising model in the presence of an external longitudinal magnetic field are
calculated exactly by the use of the generalised decoration-iteration mapping
transformation. By assuming that only the spin-S atoms do interact with the
transverse field the exact results for the Gibbs free energy, longitudinal
magnetization, transverse magnetization, entropy and specific heat have been
derived and discussed in detail. In addition to the standard temperature
variations of the transverse magnetization, another two non-trivial thermal
dependences have been found. The results support the concept that the spin
reorientation from the longitudinal towards the transverse field direction
takes place in the narrow temperature region.",0207518v1
2002/9/10,Magnetic Properties of a-Si films doped with rare-earth elements,"Amorphous silicon films doped with Y, La, Gd, Er, and Lu rare-earth elements
(a-Si:RE) have been prepared by co-sputtering and studied by means of electron
spin resonance (ESR), dc-magnetization, ion beam analysis, optical
transmission, and Raman spectroscopy. For comparison the magnetic properties of
laser-crystallized and hydrogenated a-Si:RE films were also studied. It was
found that the rare-earth species are incorporated in the a-Si:RE films in the
RE3+ form and that the RE-doping depletes the neutral dangling bonds (D0)
density. The reduction of D0 density is significantly larger for the magnetic
REs (Gd3+ and Er3+) than for the non-magnetic ones (Y3+, La3+, Lu3+). These
results are interpreted in terms of a strong exchange-like interaction, J RE-DB
SRE SDB, between the spin of the magnetic REs and that of the D0. All our
Gd-doped Si films showed basically the same broad ESR Gd3+ resonance (DHpp ~
850 Oe) at g ~ 2.01, suggesting the formation of a rather stable RE-Si complex
in these films.",0209240v1
2002/9/14,Field - Induced Spin Phase Transitions in the Cobalt Valence Tautomers,"Magnetic properties of the Co valence tautomers are considered in wide range
of magnetic field and temperature. Particularly, a model of the first order
structural phase transition accompanied by a magnetic moment jump is proposed.
The phase diagrams of the phase transition on a B-T plane (B is magnetic field
and T is temperature) are calculated for four ligand types. Dependence of the
critical magnetic field on physical characteristics known from experiments
(transition temperature at the absense of magnetic field, entropy change per
formula unit, energy difference between two phases) is found. The phase diagram
is parametrized for comparison with other phase transitions of this kind.",0209337v1
2002/11/18,Neutron Scattering Studies of Pyrochlore Compound Nd2Mo2O7 in Magnetic Field,"Neutron diffraction studies have been carried out in the applied magnetic
field H(//[011]) on a single crystal of pyrochlore ferromagnet Nd2Mo2O7, whose
Hall resistivity(r_H) has been reported to have quite unusual magnetic field
(H)- and temperature (T)- dependences. The intensities of the observed magnetic
reflections have been reproduced at 1.6 K as a function of H, by considering
the change of the magnetic structure with H, where effects of the exchange
fields at the Mo and Nd sites induced by the Mo-Mo and Mo-Nd exchange
interactions and the single ion anisotropies of Mo- and Nd- moments are
considered. From the H-dependent magnetic structure, the H-dependence of r_H
has been calculated by using the chiral order mechanism. By comparing the
result with the H-dependence of the observed r_H, it is found that the chiral
order mechanism does not work well in the present system.",0211369v1
2003/1/13,Magnetic-field effects in defect-controlled ferromagnetic Ga_{1-x}Mn_xAs semiconductors,"We have studied the magnetic-field and concentration dependences of the
magnetizations of the hole and Mn subsystems in diluted ferromagnetic
semiconductor Ga_{1-x}Mn_xAs. A mean-field approximation to the hole-mediated
interaction is used, in which the hole concentration p(x) is parametrized in
terms of a fitting (of the hole effective mass and hole/local moment coupling)
to experimental data on the Tc critical temperature. The dependence of the
magnetizations with x, for a given temperature, presents a sharply peaked
structure, with maxima increasing with applied magnetic field, which indicates
that application to diluted-magnetic-semiconductor devices would require
quality-control of the Mn-doping composition. We also compare various
experimental data for Tc(x) and p(x) on different Ga_{1-x}Mn_xAs samples and
stress the need of further detailed experimental work to assure that the
experimental measurements are reproducible.",0301184v1
2003/1/14,Magnetic phase diagram for a non-extensive system: Experimental connection with manganites,"In the present paper we make a thorough analysis of a classical spin system,
within the framework of Tsallis nonextensive statistics. From the analysis of
the generalized Gibbs free energy, within the mean-field approximation, a
para-ferromagnetic phase diagram, which exhibits first and second order phase
transitions, is built. The features of the generalized, and classical, magnetic
moment are mainly determined by the values of $q$, the non-extensive parameter.
The model is successfully applied to the case of
La$_{0.60}$Y$_{0.07}$Ca$_{0.33}$MnO$_3$ manganite. The temperature and magnetic
field dependence of the experimental magnetization on this manganite are
faithfully reproduced. The agreement between rather ""exotic"" magnetic
properties of manganites and the predictions of the $q$-statistics, comes to
support our early claim that these materials are magnetically nonextensive
objects.",0301239v2
2003/2/17,Magnetization dynamics with a spin-transfer torque,"The magnetization reversal and dynamics of a spin valve pillar, whose lateral
size is 64$\times$64 nm$^2$, are studied by using micromagnetic simulation in
the presence of spin transfer torque. Spin torques display both characteristics
of magnetic damping (or anti-damping) and of an effective magnetic field. For a
steady-state current, both M-I and M-H hysteresis loops show unique features,
including multiple jumps, unusual plateaus and precessional states. These
states originate from the competition between the energy dissipation due to
Gilbert damping and the energy accumulation due to the spin torque supplied by
the spin current. The magnetic energy oscillates as a function of time even for
a steady-state current. For a pulsed current, the minimum width and amplitude
of the spin torque for achieving current-driven magnetization reversal are
quantitatively determined. The spin torque also shows very interesting thermal
activation that is fundamentally different from an ordinary damping effect.",0302337v1
2003/2/21,Ab initio study of Curie temperatures of diluted III-V magnetic semiconductors,"The electronic structure of diluted (Ga,Mn)As magnetic semiconductors in the
presence of As-antisites and magnetic disorder is studied within the framework
of the local spin density approximation. Both the chemical and magnetic
disorders are treated using the coherent potential approximation. A ground
state with partial disorder in the local moments and with a reduced total
magnetic moment appears in the presence of As-antisites. We first estimate the
Curie temperature T_c from total energy differences between the ferromagnetic
and the paramagnetic state by identifying these with the corresponding energy
difference in a classical Heisenberg model. A more systematic approach within
the framework of the mean-field approximation to estimate T_c consists in an
evaluation of the effective exchange fields acting on the magnetic moment at a
given site. The presence of As-antisites strongly reduces the Curie
temperature. The results indicate that the effect of impurities on the
electronic structure cannot be neglected and influences the Curie temperature
non-negligibly. A comparison of the calculated Curie temperatures to existing
experimental data indicates an increase of the donor concentration with the
increase of the Mn-content.",0302441v1
2003/3/6,Electronic and magnetic properties of multishell Co nanowires coated with Cu,"The structural, electronic, and magnetic properties of ultrathin Cu-coated Co
nanowires have been studied by using empirical genetic algorithm simulations
and a tight-binding $spd$ model Hamiltonian in the unrestricted Hartree-Hock
approximation. For some specific stoichiometric compositions, Cu atoms occupy
the surface, while Co atoms prefer to stay in the interior, forming the perfect
coated multishell structures. The outer Cu layers lead to substantial
variations of the magnetic moment of interior Co atoms, depending on the
structure and thickness of Cu layers. In particular, single Co atom row in the
center of nanowire is found to be nonmagnetic when coated with two Cu layers.
All the other Co nanowires in the coated Cu shell are still magnetic but the
magnetic moments are reduced as compared with Co nanowires without Cu coating.
The interaction between Cu and Co atoms induces nonzero magnetic moment for Cu
atoms.",0303097v1
2003/4/27,Magnetism and Superconductivity in RuM1.5Ce0.5Sr2Cu2O10 (M=Eu and Y),"RuY1.5Ce0.5Sr2Cu2O10, is not superconducting (SC) and orders magnetically at
TM =152 K. The Ru moment at 5K is 0.75 mB. Ferromagnetic hysteresis loops are
observed below Tirr= 100 K. At 100 K, the remanent magnetization (Mrem) and the
coercive field (HC) become zero. Surprisingly, at Tirr <T< TM a reappearance of
antiferromagnetic (AFM) hysteresis loops are observed with a peak at 120 K for
both Mrem and HC. The paramagnetic constants are: Peff =2.06 mB (greater than
the 1.73 mB expected for low spin Ru5+) and q= 136 K which agrees well with TM.
Substitution of Zn (2.5% atm.) for Cu in RuEu1.5Ce0.5Sr2Cu2O10 (TC=38 K),
suppresses TC but does not affect the magnetic features such as: TM and Tirr,
Mrem and HC. This indicates that both SC and magnetic states are practically
decoupled. We argue that the magnetic structure of this system becomes (i) AFM
ordered at TM. (ii) Due to the tilting of the RuO6 octahedra away from the
crystallographic c axis, at Tirr < TM, weak-ferromagnetic (W-FM) order is
induced by the canting of the Ru moments. (iii) At TC (TM/TC~4), the specific
materials (M=Eu, Gd) become SC. Below TC, both SC and W-FM states coexist.",0304607v1
2003/5/9,X-ray resonant magnetic scattering from structurally and magnetically rough interfaces in multilayered systems II. Diffuse scattering,"The theoretical formulation of x-ray resonant magnetic scattering from rough
surfaces and interfaces is given for the diffuse (off-specular) scattering, and
general expressions are derived in both the Born approximation (BA) and the
distorted-wave Born approximation (DWBA) for both single and multiple
interfaces. We also give in the BA the expression for off-specular magnetic
scattering from magnetic domains. For this purpose, structural and magnetic
interfaces are defined in terms of roughness parameters related to their
height-height correlation functions and the correlations between them. The
results are generalized to the case of multiple interfaces, as in the case of
thin films or multilayers. Theoretical calculations for each of the cases are
illustrated as numerical examples and compared with experimental data of
mangetic diffuse scattering from a Gd/Fe multilayer.",0305221v1
2003/5/15,Ferromagnetism and Metamagnetism in Copper-doped Germanium Clathrate,"Cu-doped type-I germanium clathrate can exhibit dilute magnetism, including
ferromagnetism, antiferromagnetism, and metamagnetic transitions up to 90 K.
63Cu NMR measurements confirm that these transitions are due to a dilute
composition of magnetic defects coupled by conduction electrons, behavior
similar to that of magnetic semiconductors. Magnetic measurements indicate
localized magnetic moments, attributed to clusters of magnetic ions, with
competition between ferromagnetic and antiferromagnetic exchange, and also
indications of glassy behavior in the ferromagnetic phase. NMR Knight shifts
and relaxation times show that the conduction band is metallic with a large
Korringa ratio. Comparison to a mean-field theory for the ordering behavior
gives a good accounting for the ferromagnetic transition.",0305369v1
2003/5/18,A disordered RKKY lattice mean field theory for ferromagnetism in diluted magnetic semiconductors,"We develop a lattice mean field theory for ferromagnetic ordering in diluted
magnetic semiconductors by taking into account the spatial fluctuations
associated with random disorder in the magnetic impurity locations and the
finite mean free path associated with low carrier mobilities. Assuming a
carrier-mediated indirect RKKY exchange interaction among the magnetic
impurities, we find substantial deviation from the extensively used continuum
Zener model Weiss mean-field predictions. Our theory allows accurate analytic
predictions for Tc, and provides simple explanations for a number of observed
anomalies including the non-Brillouin function magnetization curves, the
suppressed low-temperature magnetization saturation, and the dependence of Tc
on conductivity.",0305413v1
2003/6/23,Anisotropic magnetoresistive and magnetic properties of La_{0.5}Sr_{0.5}CoO_{3-δ} film,"The magnetic and transport properties of La_{0.5}Sr_{0.5}CoO_{3-\delta} film
grown on a LaAlO_3 substrate by pulsed-laser deposition are studied. The
properties are found to be influenced by the magnetic anisotropy and
inhomogeneity. Magnetoresistance anisotropy is determined by the shape
anisotropy of the magnetization and the strain-induced magnetic anisotropy due
to the film-substrate lattice interaction. Indications of the
temperature-driven spin reorientation transition from an out-of plane orderded
state at low temperatures to an in-plane ordered state at high temperatures as
a result of competition between the mentioned sources of magnetic anisotropy
are found.",0306565v1
2003/7/21,Does a surface spin-flop occur in antiferromagnetically coupled multilayers? Magnetic states and reorientation transitions in antiferromagnetic superlattices,"Equilibrium spin configurations and their stability limits have been
calculated for models of magnetic superlattices with a finite number of thin
ferromagnetic layers coupled antiferromagnetically through (non-magnetic)
spacers as Fe/Cr and Co/Ru multilayers. Depending on values of applied magnetic
field and unaxial anisotropy, the system assumes collinear(antiferromagnetic,
ferromagnetic, various ""ferrimagnetic"") phases, or spatially inhomogeneous
(symmetric spin-flop phase and asymmetric, canted and twisted, phases)via
series of field induced continuous and discontinuous transitions. Contrary to
semi-infinite systems a surface phase transition, so-called ""surface
spin-flop"", does not occur in the models with a finite number of layers. It is
shown that ""discrete jumps"" observed in some Fe/Cr superlattices and
interpreted as ""surface spin-flop"" transition are first-order ""volume""
transitions between different canted phases. Depending on the system several of
these collinear and canted phases can exist as metastable states in broad
ranges of the magnetic fields, which may cause severe hysteresis effects. The
results explain magnetization processes in recent experiments on
antiferromagnetic Fe/Cr superlattices.",0307494v1
2003/7/25,Dynamics of a magnetic moment induced by a spin-polarized current,"Effects of an incoming spin-polarized current on a magnetic moment are
explored. We found that the spin torque occurs only when the incoming spin
changes as a function of time inside of the magnetic film. This implies that
some modifications are necessary in a phenomenological model where the
coefficient of the spin torque term is a constant, and the coefficient is
determined by dynamics instead of geometrical details. The precession of the
magnetization reversal depends on the incoming energy of electrons in the
spin-polarized current. If the incoming energy is smaller than the interaction
energy, the magnetization does not precess while reversing its direction. We
also found that the relaxation time associated with the reversal depends on the
incoming energy. The coupling between an incoming spin and a magnetic moment
can be estimated by measuring the relaxation time.",0307633v1
2003/8/6,Tuning the properties of magnetic CdMnTe quantum dots,"We show that CdMnTe self-assembled quantum dots can be formed by depositing a
submonolayer of Mn ions over a ZnTe surface prior to deposition of the CdTe dot
layer. Single dot emission lines and strongly polarized quantum dot
photoluminescence in an applied magnetic field confirm the presence of Mn in
individual quantum dots. The width of PL lines of the single CdMnTe dots is 3
meV due to magnetic moment fluctuations of the Mn ions. After rapid thermal
annealing, the emission lines of individual magnetic quantum dots narrow
significantly to 0.25 meV showing that effect of magnetic fluctuations is
strongly reduced most probably due to an increase in the average quantum dot
size. These results suggest a way to tune the spin properties of magnetic
quantum dots.",0308112v1
2003/8/28,External control of the direction of magnetization in ferromagnetic InMnAs/GaSb heterostructures,"In this paper, we demonstrate external control over the magnetization
direction in ferromagnetic (FM) In_{1-x}Mn_{x}As/GaSb heterostructures. FM
ordering with T_C as high as 50 K is confirmed by SQUID magnetization,
anomalous Hall effect (AHE), and magneto-optical Kerr effect (MOKE)
measurements. Even though tensile strain is known to favor an easy axis normal
to the layer plane, at low temperatures we observe that the magnetization
direction in several samples is intermediate between the normal and in-plane
axes. As the temperature increases, however, the easy axis rotates to the
direction normal to the plane. We further demonstrate that the easy
magnetization axis can be controlled by incident light through a bolometric
effect, which induces a pronounced increase in the amplitude of the AHE. A
mean-field-theory model for the carrier-mediated ferromagnetism reproduces the
tendency for dramatic reorientations of the magnetization axis, but not the
specific sensitivity to small temperature variations.",0308605v1
2003/9/12,Anisotropy of exchange stiffness and its effect on the properties of magnets,"Using the spin-spiral formulation of the tight-binding linear muffin-tin
orbital method, the principal components of the exchange stiffness tensor are
calculated for typical hard magnets including tetragonal CoPt-type and
hexagonal YCo5 alloys. The exchange stiffness is strongly anisotropic in all
studied alloys. This anisotropy makes the domain wall surface tension
anisotropic. Competition between this anisotropic surface tension and
magnetostatic energy controls the formation and dynamics of nanoscale domain
structures in hard magnets. Anisotropic domain wall bending is described in
detail from the general point of view and with application to cellular Sm-Co
magnets. It is shown that the repulsive cell-boundary pinning mechanism in
these magnets is feasible only due to the anisotropic exchange stiffness if
suitably oriented initial pinning centers are available. In polytwinned
CoPt-type magnets the exchange stiffness anisotropy controls the orientation of
macrodomain wall segments. These segments may reorient both statically during
microstructural coarsening and dynamically during the macrodomain wall
splitting in external field. Reorientation of segments may facilitate their
pinning at antiphase boundaries.",0309321v1
2003/11/22,Influence of a Uniform Current on Collective Magnetization Dynamics in a Ferromagnetic Metal,"We discuss the influence of a uniform current, $\vec{j} $, on the
magnetization dynamics of a ferromagnetic metal. We find that the magnon energy
$\epsilon(\vec{q})$ has a current-induced contribution proportional to
$\vec{q}\cdot \vec{\cal J}$, where $\vec{\cal J}$ is the spin-current, and
predict that collective dynamics will be more strongly damped at finite ${\vec
j}$. We obtain similar results for models with and without local moment
participation in the magnetic order. For transition metal ferromagnets, we
estimate that the uniform magnetic state will be destabilized for $j \gtrsim
10^{9} {\rm A} {\rm cm}^{-2}$. We discuss the relationship of this effect to
the spin-torque effects that alter magnetization dynamics in inhomogeneous
magnetic systems.",0311522v1
2003/12/10,Second-order transverse magnetic anisotropy induced by disorders in the single-molecule magnet Mn12,"For the single-molecule magnet Mn12, Cornia et al. recently proposed that
solvent molecules may cause the quantum tunneling that requires a lower
symmetry than S4. However, magnetic quantum tunneling and electron paramagnetic
resonance experiments suggested that the proposed theory may not correspond to
the measurements. In this regard, we consider positional disorder induced by
the solvent molecules and orientational disorder by the methyl groups of a Mn12
molecule. We calculate, within density-functional theory, the second-order
transverse magnetic anisotropy parameter E and an easy-axis tilting angle
induced by the positional disorder and the E value by the orientational
disorder. We also calculate the local magnetic anisotropy and the local easy
axis for each inequivalent Mn site in different environments to investigate
their effects on the global E value. We find that the hydrogen bonding between
a Mn12 molecule and the solvent molecule is crucial to obtain a substantial E
value and that the E value increases upon geometry relaxations. Our
calculations on relaxed geometries show that the largest calculated E value is
0.016 K and that the largest tilting angle is 0.5 degrees. Our largest E value
is comparable to experimental results but larger than Cornia et al.'s.",0312261v1
2003/12/18,Magnetic Studies of Polycrystalline and Single-Crystal NaxCoO2,"We have investigated the preparation and bulk magnetic properties of NaxCoO2
in the range 0.5<x<0.95, including those for single crystals grown by the
floating-zone method in an image furnace. To characterize the samples and
ascertain their quality we performed x-ray powder diffraction, electron-probe
microanalysis (EPMA) and magnetization measurements. Based on our findings we
are able to report conditions for the preparation of single-phase
polycrystalline and single-crystal samples in the range 0.65<x<0.95. For lower
concentration samples, however, i.e. x<0.65, residual Co3O4 impurities above
the detectable limit remained, and conditions to eliminate this have still to
be identified. Investigations of the anisotropic magnetization of NaxCoO2
single crystals show: (i) transitions at ~320 K, ~275K and ~22 K present for
all Na doping levels investigated, (ii) a strong increase in magnetization
below ~8 K, (iii) a crossover in sense for the anisotropy around 8-10 K, and
(iv) a hysteresis in the magnetization for certain Na doping levels at
temperatures below ~15 K. Notably, neither of the high temperature anomalies
(275 K, 320 K) could be observed in the powder samples.",0312493v1
2003/12/18,Current induced magnetization dynamics in current perpendicular to the plane spin valves,"We observe magnetization dynamics induced by spin momentum transfer in the
noise spectra of current perpendicular to the plane giant magnetoresistance
spin valves. The dynamics are observable only for those combinations of current
direction and magnetic configuration in which spin transfer acts to reorient
the free layer magnetization away from the direction set by the net magnetic
field. Detailed measurements as a function of magnetic configuration reveal an
evolution of the noise spectra, going from a spectrum with a well-defined noise
peak when the free layer is roughly collinear with the pinned layer to a
spectrum dominated by 1/f noise when the free layer is in an orthogonal
configuration. Finally, the amplitude of the corresponding resistance noise
increases rapidly with increasing current until it saturates at a value that is
a substantial fraction of the magnetoresistance between parallel and
antiparallel states.",0312504v2
2004/3/8,Absence of ferromagnetism in Co and Mn substituted polycrystalline ZnO,"We discuss the properties of semiconducting bulk ZnO when substituted with
the magnetic transition metal ions Mn and Co, with substituent fraction ranging
from $x$ = 0.02 to $x$ = 0.15. The magnetic properties were measured as a
function of magnetic field and temperature and we find no evidence for magnetic
ordering in these systems down to $T$ = 2 K. The magnetization can be fit by
the sum of a Curie-Weiss term with a Weiss temperature of $\Theta\gg$100 K and
a Curie term. We attribute this behavior to contributions from both \textit{t}M
ions with \textit{t}M nearest neighbors and from isolated spins. This
particular functional form for the susceptibility is used to explain why no
ordering is observed in \textit{t}M substituted ZnO samples despite the large
values of the Weiss temperature. We also discuss in detail the methods we used
to minimize any impurity contributions to the magnetic signal.",0403196v2
2004/4/22,Non-collinear magnetic structures: a possible cause for current induced switching,"Current induced switching in Co/Cu/Co trilayers is described in terms of
ab-initio determined magnetic twisting energies and corresponding sheet
resistances. In viewing the twisting energy as an energy flux the
characteristic time thereof is evaluated by means of the
Landau-Lifshitz-Gilbert equation using ab-initio parameters. The obtained
switching times are in very good agreement with available experimental data. In
terms of the calculated currents, scalar quantities since a classical Ohm's law
is applied, critical currents needed to switch magnetic configurations from
parallel to antiparallel and vice versa can unambiguously be defined. It is
found that the magnetoresistance viewed as a function of the current is
essentially determined by the twisting energy as a function of the relative
angle between the orientations of the magnetization in the magnetic slabs,
which in turn can also explain in particular cases the fact that after having
switched off the current the system remains in the switched magnetic
configuration. For all ab-initio type calculations the fully relativistic
Screened Korringa-Kohn-Rostoker method and the corresponding Kubo-Greenwood
equation in the context of density functional theory are applied.",0404534v1
2004/4/26,"Comparative study of specific heat measurements in LaMnO3, La1.35Sr1.65Mn2O7, La1.5Sr0.5NiO4 and La1.5Sr0.5CoO4","We present the temperature dependence of the specific heat, without external
magnetic field and with H= 9 T, for LaMnO3, La1.35Sr1.65Mn2O7, La1.5Sr0.5NiO4
and La1.5Sr0.5CoO4 single crystals. We found that spin-wave excitations in the
ferromagnetic and bilayer-structure La1.35Sr1.65Mn2O7 were suppressed by the 9
T magnetic field. On the other hand, the external magnetic field had no effect
in the specific heat of the other three antiferromagnetic samples. Also, the
electronic part of the interactions were removed at very low temperatures in
the La1.5Sr0.5NiO4 single crystal, even with a zero applied magnetic field.
Below 4 K, we found that the specific heat data for La1.35Sr1.65Mn2O7 and
La1.5Sr0.5NiO4 crystals could be fitted to an exponential decay law. Detailed
magnetization measurements in this low temperature interval showed the
existence of a peak close to 2 K. Both results, magnetizations and specific
heat suggest the existence of an anisotropy gap in the energy spectrum of
La1.35Sr1.65Mn2O7 and La1.5Sr0.5NiO4 compounds.",0404596v1
2004/6/24,Thermal Effects on the Magnetic Field Dependence of Spin Transfer Induced Magnetization Reversal,"We have developed a self-aligned, high-yield process to fabricate CPP
(current perpendicular to the plane) magnetic sensors of sub 100 nm dimensions.
A pinned synthetic antiferromagnet (SAF) is used as the reference layer which
minimizes dipole coupling to the free layer and field induced rotation of the
reference layer. We find that the critical currents for spin transfer induced
magnetization reversal of the free layer vary dramatically with relatively
small changes the in-plane magnetic field, in contrast to theoretical
predictions based on stability analysis of the Gilbert equations of
magnetization dynamics including Slonczewski-type spin-torque terms. The
discrepancy is believed due to thermal fluctuations over the time scale of the
measurements. Once thermal fluctuations are taken into account, we find good
quantitative agreement between our experimental results and numerical
simulations.",0406574v1
2004/7/14,Ferromagnetic resonance study of free hole contribution to magnetization and magnetic anisotropy in modulation-doped Ga$_{1 - x}$Mn$_{x}$As/Ga$_{1 - y}$Al$_{y}$As:Be,"Ferromagnetic resonance (FMR) is used to study magnetic anisotropy of GaMnAs
in a series of Ga$_{1 - x}$Mn$_{x}$As/Ga$_{1 - y}$Al$_{y}$As heterostructures
modulation-doped by Be. The FMR experiments provide a direct measure of cubic
and uniaxial magnetic anisotropy fields, and their dependence on the doping
level. It is found that the increase in doping -- in addition to rising the
Curie temperature of the Ga$_{1 - x}$Mn$_{x}$As layers -- also leads to a very
significant increase of their uniaxial anisotropy field. The FMR measurements
further show that the effective $g$-factor of Ga$_{1 - x}$Mn$_{x}$As is also
strongly affected by the doping. This in turn provides a direct measure of the
contribution from the free hole magnetization to the magnetization of Ga$_{1 -
x}$Mn$_{x}$As system as a whole.",0407371v1
2004/8/6,Relevance of a magnetic moment distribution and scaling law methods to study the magnetic behavior of antiferromagnetic nanoparticles,"In antiferromagnetic nanoparticles magnetization the linear component,
$\chi_{AF}$H superposed to the saturation one usually complicates the fit of
experimental data. We present a method based on scaling laws to determine the
variation of $\chi_{AF}$ with temperature and to find the temperature
dependence of the average magnetic moment $<\mu>$, without any assumption on
both the magnetization dependence on field or the moment distribution function,
whose relevance can also be estimated. We have applied this method to ferritin
and found that $<\mu>$ decreases with increasing temperature and that a
distribution function cannot be ignored. The fit with Langevin magnetization
law and lognormal moment distribution functions yielded parameters close to
those estimated with the scaling method. We also show that in general if the
distribution is ignored, and a single particle moment $\mu_p$ is used, $\mu_p$
presents an artificial systematic increase with temperature. This calls the
attention to the necessity of evaluating the effect of a size distribution
before concluding about the physical nature of the parameters variation.",0408134v1
2004/8/16,Large Magneto-Dielectric Effects in Orthorhombic HoMnO3 and YMnO3,"We have found a remarkable increase (up to 60 %) of the dielectric constant
with the onset of magnetic order at 42 K in the metastable orthorhombic
structures of YMnO3 and HoMnO3 that proves the existence of a strong
magneto-dielectric coupling in the compounds. Magnetic, dielectric, and
thermodynamic properties show distinct anomalies at the onset of the
incommensurate magnetic order and thermal hysteresis effects are observed
around the lock-in transition temperature at which the incommensurate magnetic
order locks into a temperature independent wave vector. The orders of Mn3+
spins and Ho3+ moments both contribute to the magneto-dielectric coupling. A
large magneto-dielectric effect was observed in HoMnO3 at low temperature where
the dielectric constant can be tuned by an external magnetic field resulting in
a decrease of up to 8 % at 7 Tesla. By comparing data for YMnO3 and HoMnO3 the
contributions to the coupling between the dielectric response and Mn and Ho
magnetic orders are separated.",0408365v2
2004/8/17,Vortex state oscillations in soft magnetic cylindrical dots,"We have studied magnetic vortex oscillations in soft sub-micron cylindrical
dots with variable thickness and diameter by an analytical approach and
micromagnetic simulations. We have considered two kinds of modes of the vortex
magnetization oscillations: 1) low-frequency translation mode, corresponding to
the movement of the vortex as a whole near its equilibrium position; 2)
high-frequency vortex modes, which correspond to radially symmetric
oscillations of the vortex magnetization, mainly outside the vortex core. The
vortex translational eigenmode was calculated numerically in frequency and time
domains for different dot aspect ratios. To describe the discrete set of vortex
high-frequency modes we applied the linearized equation of motion of dynamic
magnetization over the vortex ground state. We considered only radially
symmetric magnetization oscillations modes. The eigenfrequencies of both kinds
of excitation modes are determined by magnetostatic interactions. They are
proportional to the thickness/diameter ratio and lie in the GHz range for
typical dot sizes.",0408388v1
2004/9/10,"Effects of Capping on the (Ga,Mn)As Magnetic Depth Profile","Annealing can increase the Curie temperature and net magnetization in
uncapped (Ga,Mn)As films, effects that are suppressed when the films are capped
with GaAs. Previous polarized neutron reflectometry (PNR) studies of uncapped
(Ga,Mn)As revealed a pronounced magnetization gradient that was reduced after
annealing. We have extended this study to (Ga,Mn)As capped with GaAs. We
observe no increase in Curie temperature or net magnetization upon annealing.
Furthermore, PNR measurements indicate that annealing produces minimal
differences in the depth-dependent magnetization, as both as-grown and annealed
films feature a significant magnetization gradient. These results suggest that
the GaAs cap inhibits redistribution of interstitial Mn impurities during
annealing.",0409270v2
2004/10/25,Absence of magnetic moments in plutonium,"Many theories published in the last decade propose that either ordered or
disordered local moments are present in elemental plutonium at low
temperatures. We present new experimental data and review previous experimental
results. None of the experiments provide any evidence for ordered or disordered
magnetic moments (either static or dynamic) in plutonium at low temperatures,
in either the alpha- or delta-phases. The experiments presented and discussed
are magnetic susceptibility,electrical resistivity, NMR, specific heat, and
both elastic and inelastic neutronscattering. Many recent calculations
correctly predict experimentally observed atomic volumes, including that of
delta-Pu. These calculations achieve observed densities by the localization of
electrons, which then give rise to magnetic moments. However, localized
magnetic moments have never been observed experimentally in Pu. A theory is
needed that is in agreement with all the experimental observations. Two
theories are discussed that might provide understanding of the ensemble of
unusual properties of Pu, including the absence of experimental evidence for
localized magnetic moments; an issue that has persisted for over 50 years.",0410634v1
2004/11/17,Electronic Transport Spectroscopy of Carbon Nanotubes in a Magnetic Field,"We report magnetic field spectroscopy measurements in carbon nanotube quantum
dots exhibiting four-fold shell structure in the energy level spectrum. The
magnetic field induces a large splitting between the two orbital states of each
shell, demonstrating their opposite magnetic moment and determining transitions
in the spin and orbital configuration of the quantum dot ground state. We use
inelastic cotunneling spectroscopy to accurately resolve the spin and orbital
contributions to the magnetic moment. A small coupling is found between
orbitals with opposite magnetic moment leading to anticrossing behavior at zero
field.",0411440v1
2004/12/10,Linear and Circularly Polarized Light to Study Anisotropy and Resonant Scattering in Magnetic Thin Films,"The remarkable polarization properties of the synchrotron light have lead to
the advent of modern synchrotron-related spectroscopic studies with angular
and/or magnetic selectivity. We give here an overview of the prominent aspect
of the polarization of the light delivered by a bending magnet, and some
dichroic properties in X-ray Absorption Spectroscopy (XAS). We report then two
studies developed at the Brazilian Synchrotron Light Laboratory (LNLS),
exemplifying the profit gained using linear and circular polarization of the
X-ray for the study of magnetic thin films and multilayers. Angle-resolved XAS
was used in strained manganite thin films to certify a model of local
distortion limited within the $MnO_{6}$ polyhedron. A pioneer experience of
X-ray magnetic scattering at grazing incidence associated with dispersive XAS
in a $Co/Gd$ multilayer draws new perspectives for magnetic studies in thin
films and multilayers in atmospheric conditions in the hard X-ray range.",0412280v1
2005/1/24,"Magnetic and Transport Properties of Ternary Indides of type R2CoIn8 (R = Ce, Pr and Dy)","We have synthesized and investigated the magnetic and transport properties of
a series of compounds, R2CoIn8 (R = rare earth). Compounds form in single phase
with a tetragonal structure (space group P4/mmm, no. 162). The Ce compound
shows heavy fermion behavior. The magnetic susceptibility of Pr2CoIn8 shows a
marked deviation from the Curie-Weiss behavior at low temperatures, which is
attributed to the crystalline electric field effects. Heat capacity and
magnetization measurements show that Dy2CoIn8 undergoes a magnetic transition
at 17 K and a second transition near 5 K, the latter of which may be due to
spin reorientation. Magnetization of this compound shows two metamagnetic
transitions approximately at 3.6 T and 8.3 T.",0501553v1
2005/2/10,Ultra fast bit addressing in a magnetic memory matrix with crossed wire write line geometry,"An ultra fast bit addressing scheme for magnetic random access memories
(MRAM) in a crossed wire geometry is proposed. In the addressing scheme a word
of cells is programmed simultaneously by sub nanosecond field pulses making use
of the magnetization precession of the free layer. Single spin simulations of
the free layer dynamics show that the pulse parameters for programming an
arbitrary word of the array can be chosen such that the magnetization of the
cells to be written performs either a half or a full precessional turn during
application of the programming pulse depending on the initial and final
magnetization orientation of the addressed cells. Such bit addressing scheme
leads to a suppression of the magnetization ringing in all cells of the memory
array thereby allowing ultra high MRAM write clock rates above 1 GHz.",0502263v1
2005/3/15,Adjustable spin torque in magnetic tunnel junctions with two fixed layers,"We have fabricated nanoscale magnetic tunnel junctions (MTJs) with an
additional fixed magnetic layer added above the magnetic free layer of a
standard MTJ structure. This acts as a second source of spin-polarized
electrons that, depending on the relative alignment of the two fixed layers,
either augments or diminishes the net spin-torque exerted on the free layer.
The compound structure allows a quantitative comparison of spin-torque from
tunneling electrons and from electrons passing through metallic spacer layers,
as well as analysis of Joule selfheating effects. This has significance for
current-switched magnetic random access memory (MRAM), where spin torque is
exploited, and for magnetic sensing, where spin torque is detrimental.",0503376v1
2005/3/16,Magnetically driven ferroelectric order in Ni$_3$V$_2$O$_8$,"We show that for Ni$_3$V$_2$O$_8$ long-range ferroelectric and incommensurate
magnetic order appear simultaneously in a single phase transition. The
temperature and magnetic field dependence of the spontaneous polarization show
a strong coupling between magnetic and ferroelectric orders. We determine the
magnetic symmetry of this system by constraining the data to be consistent with
Landau theory for continuous phase transitions. This phenomenological theory
explains our observation the spontaneous polarization is restricted to lie
along the crystal b axis and predicts that the magnitude should be proportional
to a magnetic order parameter.",0503385v1
2005/3/29,Anisotropic pinned/biased magnetization in $SrRuO_3/SrMnO_3$ superlattices,"The exchange coupling at the interfaces of magnetic superlattices consisting
of ferromagnetic $SrRuO_3$ and antiferromagnetic $SrMnO_3$ grown on (001)
oriented $SrTiO_3$ is studied with in-plane and out-of-plane orientations, with
respect to the substrate plane, of the cooling magnetic field. The
magnetization of the in-plane, field cooled hysteresis loop is lower than the
corresponding in-plane zero-field-cooled hysteresis loop. The out-of-plane
field cooled hysteresis loop is shifted, from the origin, along the graphical
magnetization axis. We attribute this irreversible rotation of the moment to
the pinning/biasing of spin in the $SrRuO_3$ layer in the vicinity of
interfaces by the antiferromagnetic $SrMnO_3$ layer.",0503672v1
2005/4/19,High temperature magnetic ordering in La2RuO5,"Magnetic susceptibility, heat capacity and electrical resistivity
measurements have been carried out on a new ruthenate, La2RuO5 (monoclinic,
space group P21/c) which reveal that this compound is a magnetic semiconductor
with a high magnetic ordering temperature of 170K. The entropy associated with
the magnetic transition is 8.3 J/mole-K -close to that expected for the low
spin (S=1) state of Ru4+ ions. The low temperatures specific heat coefficient g
is found to be nearly zero consistent with the semiconducting nature of the
compound. The magnetic ordering temperature of La2RuO5 is comparable to the
highest known Curie temperature of another ruthenate, namely, metallic SrRuO3,
and in both these compounds the nominal charge state of Ru is 4+.",0504489v1
2005/5/8,Unusual Exchange Bias Associated with Phase Separation in Perovskite Cobaltites,"We report the observation of unusual exchange bias phenomena in the doped
perovskite cobaltites La_{1-x}Sr_{x}CoO_{3} (x = 0.15, 0.18, and 0.30) in which
a spontaneous phase separation into ferromagnetic clusters embedded in a
non-ferromagnetic matrix occurs. When the La_{1-x}Sr_{x}CoO_{3} samples are
cooled in a static magnetic field through a freezing temperature, the
magnetization hysteresis loops exhibit exchange bias, i.e., the loops shift to
the negative field and the magnetization becomes asymmetric. Moreover, exchange
bias disappears when the measuring magnetic field is high enough. These results
suggest that the intrinsic phase inhomogeniety in a spontaneously
phase-separated system may induce an interfacial exchange anisotropy after a
field cooling. The diminution of exchange bias in high magnetic fields is
ascribed to the propagation of ferromagnetic regions with increasing magnetic
field.",0505189v1
2005/5/29,A Unified Theoretical Description of the Thermodynamical Properties of Spin Crossover with Magnetic Interactions,"After the discovery of the phenomena of light-induced excited spin state
trapping (LIESST), the functional properties of metal complexes have been
studied intensively. Among them, cooperative phenomena involving low spin-high
spin (spin-crossover) transition and magnetic ordering have attracted
interests, and it has become necessary to formulate a unified description of
both phenomena. In this work, we propose a model in which they can be treated
simultaneously by extending the Wajnflasz-Pick model including a magnetic
interaction. We found that this new model is equivalent to
Blume-Emery-Griffiths (BEG) Hamiltonian with degenerate levels. This model
provides a unified description of the thermodynamic properties associated with
various types of systems, such as spin-crossover (SC) solids and Prussian blue
analogues (PBA). Here, the high spin fraction and the magnetization are the
order parameters describing the cooperative phenomena of the model. We present
several typical temperature dependences of the order parameters and we
determine the phase diagram of the system using the mean-field theory and Monte
Carlo simulations. We found that the magnetic interaction drives the SC
transition leading to re-entrant magnetic and first-order SC transitions.",0505701v1
2005/7/2,First-principles effective-mass Hamiltonian for semiconductor nanostructures in a magnetic field,"A multi-band effective-mass Hamiltonian is derived for lattice-matched
semiconductor nanostructures in a slowly varying external magnetic field. The
theory is derived from the first-principles magnetic-field coupling Hamiltonian
of Pickard and Mauri, which is applicable to nonlocal norm-conserving
pseudopotentials in the local density approximation to density functional
theory. The pseudopotential of the nanostructure is treated as a perturbation
of a bulk reference crystal, with linear and quadratic response terms included
in k.p perturbation theory. The resulting Hamiltonian contains several
interface terms that have not been included in previous work on nanostructures
in a magnetic field. The derivation provides the first direct analytical
expressions showing how the coupling of the nonlocal potential to the magnetic
field influences the effective magnetic dipole moment of the electron.",0507044v1
2005/7/19,Short-range effects and magnetization reversal in Co$_{80}$Fe$_{20}$ thin films: a MOKE magnetometry/domain imaging and AMR study,"A MOKE magnetometry unit simultaneously sensitive to both in-plane
magnetization components, based on an intensity differential detection method,
allows us to observe the uniaxial anisotropy impressed during CoFe-deposition
and to discriminate the magnetization processes under a magnetic field parallel
and perpendicular to such axes. Our MOKE imaging unit, using a CCD camera for
Kerr effect domain visualization provides direct evidence on the dominant
M-processes, namely domain wall motion and moment rotation. Further magnetic
information was obtained by AMR measurements due to the dependence of the
electrical resistivity on the short-range spin disorder and also on the angle
between the electrical current direction (I) and the spontaneous magnetization
($\emph{\textbf{M}}_{S}$).",0507441v2
2005/7/26,55Mn NMR and magnetization studies of La0.67Sr0.33MnO3 thin films,"55Mn nuclear magnetic resonance and magnetization studies of the series of
La0.67Sr0.33MnO3 thin films have been performed at low temperature. Two
distinct lines were observed, at 322 MHz and 380 MHz, corresponding to two
different phases, the former located at the interface, with localized charges,
and the latter corresponding to the film bulk, with itinerant carriers (as it
was also found in Ca manganite films). The spin-echo amplitude was measured as
a function of a dc magnetic field applied either in the film plane or
perpendicular to it. The field dependence of both the main NMR signal intensity
and frequency shift is quite consistent with that calculated in a simple single
domain model. The best fit to the model shows that magnetization rotation
processes play a dominant role when the applied field exceeds the effective
anisotropy field. Distinctly different magnetic anisotropies are deduced from
the interface NMR signal.",0507598v1
2005/8/10,Magnetic bistability and controllable reversal of asymmetric ferromagnetic nanorings,"Magnetization reversals through the formation of vortex state and the
rotation of onion state are two processes with comparable probabilities for
symmetric magnetic nanorings with radius of about 50 nanometers. This magnetic
bistability is the manifestation of the competition between the exchange energy
and the magnetostatic energy in nanomagnets. The relative probability of the
two processes in symmetric nanorings is dictated by the ring geometry and can
not be altered. In this work, we report the magnetic behavior of a novel type
of nanorings -- asymmetric nanorings. By tuning the asymmetry we can control
the fraction of the vortex formation process from about 40% to nearly 100% by
utilizing the direction of the external magnetic field. The observed results
have been accounted for by the dependence of the domain wall energy on the
local cross section area of nanoring for which we have provided theoretical
calculations.",0508249v1
2005/8/11,Magnetization self-organization in a single-domain ferromagnet subject to a spin current,"The Landau-Lifshitz equation for the magnetization dynamics of a
single-domain magnetic system is solved using the methods of self-organization.
The description takes into account the torque due to spin transfer. The
potential energy of the system includes the uniaxial and easy-plane
anisotropies, and the Zeeman energy due to an external magnetic field. The
equilibrium and stationary states are investigated as a function of the spin
current and external magnetic field. The presented bifurcation diagram allows
to determine the margins of a neutral stability mode of the equilibrium and
stationary states for different values of the easy-plane anisotropy constant.
Using the power spectral density method, the trajectory tracing, Hausdorff
dimension, and maximum Lyapunov exponent, the dynamics of the phase states in
an external magnetic field is demonstrated. The analytical transcendent
equations for switching between different equilibrium states are also obtained,
proving the importance of phase averaging.",0508280v1
2005/8/18,"Coupling of Magnetic Order, Ferroelectricity, and Lattice Strain in Multiferroic Rare Earth Manganites","Multiferroic rare earth manganites attracted recent attention because of the
coexistence of different types of magnetic and ferroelectric orders resulting
in complex phase diagrams and a wealth of physical phenomena. The coupling and
mutual interference of the different orders and the large magnetoelectric
effect observed in several compounds are of fundamental interest and bear the
potential for future applications in which the dielectric (magnetic) properties
can be modified by the onset of a magnetic (dielectric) transition or the
application of a magnetic (electric) field. The physical mechanisms of the
magnetoelectric effect and the origin of ferroelectric order at magnetic
transitions have yet to be explored. We discuss multiferroic phenomena in the
hexagonal HoMnO3 and show that the strong magneto-dielectric coupling is
intimately related to the lattice strain induced by unusually large spin-phonon
correlations.",0508422v1
2005/8/26,Magneto-optical study of magnetization reversal asymmetry in exchange bias,"The asymmetric magnetization reversal in exchange biased Fe/MnF$_{2}$
involves coherent (Stoner-Wohlfarth) magnetization rotation into an
intermediate, stable state perpendicular to the applied field. We provide here
experimentally tested analytical conditions for the unambiguous observation of
both longitudinal and transverse magnetization components using the
magneto-optical Kerr effect. This provides a fast and powerful probe of
coherent magnetization reversal as well as its chirality. Surprisingly, the
sign and asymmetry of the transverse magnetization component of Fe/MnF$_{2}$
change with the angle between cooling and measurement fields.",0508635v2
2005/9/5,Magnetic and electronic transport percolation in epitaxial GeMn films,"Electronic transport and magnetic properties of Ge1-xMnx/Ge(100) films are
investigated as a function of Mn dilution. Depending on x, characteristic
temperatures separate different regimes in both properties. Resistivity
exhibits an insulator-like behavior in the whole temperature range and, below
about 80 K, two distinct activation energies are observed. At a higher
temperature value, TR, resistivity experiences a sudden reduction. Hall
coefficient shows a strong contribution from the anomalous Hall effect and, at
TR, a sign inversion, from positive to negative, is recorded. The magnetic
properties, inferred from magneto-optical Kerr effect, evidence a progressive
decrease of the ferromagnetic long range order as the temperature is raised,
with a Curie temperature TC not far from TR. The transport and magnetic results
are qualitatively consistent with a percolation mechanism due to bound magnetic
polarons in a GeMn diluted magnetic semiconductor, with localized holes [A.
Kaminski and S. Das Sarma, Phys. Rev. B 68, 235210 (2003)].",0509111v1
2005/9/8,Field sweep rate dependence of the coercive field of single-molecule magnets: a classical approach with applications to the quantum regime,"A method, based on the Neel-Brown model of thermally activated magnetization
reversal of a magnetic single-domain particle, is proposed to study the field
sweep rate dependence of the coercive field of single-molecule magnets (SMMs).
The application to Mn12 and Mn84 SMMs allows the determination of the important
parameters that characterize the magnetic properties: the energy barrier, the
magnetic anisotropy constant, the spin, tau_0, and the crossover temperature
from the classical to the quantum regime. The method may be particularly
valuable for large SMMs that do not show quantum tunneling steps in the
hysteresis loops.",0509193v2
2005/9/14,Evolution of magnetism of Cr nanoclusters on a Au(111) surface,"We have carried out collinear and non-collinear electronic structure
calculations to investigate the structural, electronic and magnetic properties
of isolated Cr atoms, dimers and compact trimers. We find that the Cr monomer
prefers to adsrob on the fcc hollow site with a binding energy of 3.13 eV and a
magnetic moment of of 3.93 $\mu_B$. The calculated Kondo temperature of 0.7 K
for the monomer is consistent with the lack of a Kondo peak in scanning
tunneling microscopy (STM) experiments at 7 K. The compact Cr dimer orders
antiferromagnetically and its bond length contracts to 1.72 $\AA$ close to the
value for the free-standing Cr dimer. The very low magnetic moment of 0.005
$\mu_B$ for the Cr atoms in the dimer is due to the strong $d-d$ hybridization
between the Cr adatoms. Thus, these calculations reveal that the absence of the
Kondo effect observed in STM experiments is due to the small local moments
rather than the Kondo quenching of the local moments suggested experimentally.
The Cr compact trimer exhibits non-collinear co-planar magnetism with vanishing
net magnetic moment in agreement with experiment.",0509384v1
2005/9/15,Asymmetric magnetization reversal in the exchange bias system Fe/FeF_2 studied by MOKE,"The asymmetry of the magnetization reversal process in exchange biased
Fe/FeF$_2$ has been studied by magneto-optical Kerr effect. Qualitatively
different transverse magnetization loops are observed for different directions
of the cooling and the measuring field. These loops can be simulated by a
simple calculation of the total energy density which includes the relevant
magnetic anisotropies and coherent magnetization rotation only. Asymmetric
magnetization reversal is shown to originate from the unidirectional anisotropy
and may be observed if the external measuring field is not collinear with
either the exchange bias or the easy axis of the antiferromagnetic epitaxial
FeF$_2$(110) layer.",0509419v2
2005/9/27,Effect of electric/magnetic field on pinned/biased moments at the interfaces of magnetic superlattices,"We have observed the pinned/biased moments in the superlattices consisting of
ferromagnetic (FM) SrRuO3 (SRO) and antiferromagnetic (AFM) SrMnO3
(SMO)bilayer. The alternate stacking of SRO and SMO leading to a low field
positive magnetoresistance with enhanced hysteretic field dependent
magnetoresistance under the application of the out-of-plane magnetic field. We
attribute these effects to the observed biased/pinned magnetic moments in the
SRO layer in the vicinity of the interfaces. In addition, the biased/pinned
moments can be oriented under the application of either the out-of-plane
magnetic field or a combination of out-of-plane magnetic field and in-plane
electric field. These results will bring new insights in the understanding of
the coupling at the AFM/FM interface which can be useful for creating new
exotic phenomena at the interfaces of the multilayer.",0509676v1
2005/10/29,First-principles approach to Non-Collinear Magnetism: towards Spin-dynamics,"A description of non-collinear magnetism in the framework of spin-density
functional theory is presented for the exact exchange energy functional which
depends explicitly on two-component spinor orbitals. The equations for the
effective Kohn-Sham scalar potential and magnetic field are derived within the
optimized effective potential (OEP) framework. With the example of a
magnetically frustrated Cr monolayer it is shown that the resulting
magnetization density exhibits much more non-collinear structure than standard
calculations. Furthermore, a time-dependent generalization of the non-collinear
OEP method is well suited for an ab-initio description of spin dynamics. We
also show that the magnetic moments of solids Fe, Co and Ni are well
reproduced.",0510800v3
2005/11/4,Synchronized Magnetization Oscillations in F/N/F Nanopillars,"Current-induced magnetization dynamics in a trilayer structure composed of
two ferromagnetic free layers and a nonmagnetic spacer is examined. Both free
layers are treated as a monodomain magnetic body with an uniform agnetization.
The dynamics of the two magnetizations is modeled by modified
Landau-Lifshitz-Gilbert equations with spin-transfer torque terms. By solving
the equations simultaneously, we discuss their various solutions in detail. We
show that there exists the synchronous motion of two magnetizations among the
various solutions; the magnetizations are resonantly coupled via spin-transfer
torques and perform precessional motions with the same period. The condition to
excite the synchronous motion depends on the difference between the intrinsic
frequencies of the two ferromagnetic free layers as well as the magnitude of
current.",0511095v1
2005/11/16,Giant magnetoimpedance in composite wires with insulator layer between non-magnetic core and soft magnetic shell,"A method for calculation of the magnetoimpedance in composite wires having an
insulator layer between non-magnetic core and soft magnetic shell is described.
It is assumed that the magnetic shell has a helical anisotropy and the driving
current flows through the core only. The distribution of eddy currents and
expressions for the impedance are found by means of a solution of Maxwell
equations taking into account the magnetization dynamics within the shell
governed by the Landau-Lifshitz equation. The effect of the insulator layer on
the magnetoimpedance is analyzed.",0511386v1
2006/1/2,The effect of externally applied pressure on the magnetic behavior of Cu2Te2O5(BrxCl{1-x})2,"The effect of externally applied pressure on the magnetic behavior of
Cu2Te2O5(BrxCl{1-x})2 with x = 0, 0.73 and 1, is investigated by a combination
of magnetic susceptibility, neutron diffraction and neutron inelastic
scattering measurements. The magnetic transition temperatures of the x = 0 and
0.73 compositions are observed to increase linearly with increasing pressure at
a rate of 0.23(2) K/kbar and 0.04(1) K/kbar respectively. However, the bromide
shows contrasting behavior with a large suppression of the transition
temperature under pressure, at a rate of -0.95(9) K/kbar. In neutron inelastic
scattering measurements of Cu2Te2O5Br2 under pressure only a small change to
the ambient pressure magnetic excitations were observed. A peak in the density
of states was seen to shift from ~5 meV in ambient pressure to ~6 meV under an
applied pressure of 11.3 kbar, which was associated with an increase in the
overall magnetic coupling strength.",0601023v1
2006/1/10,Engineering of spin-lattice relaxation dynamics by digital growth of diluted magnetic semiconductor CdMnTe,"The technological concept of ""digital alloying"" offered by molecular-beam
epitaxy is demonstrated to be a very effective tool for tailoring static and
dynamic magnetic properties of diluted magnetic semiconductors. Compared to
common ""disordered alloys"" with the same Mn concentration, the spin-lattice
relaxation dynamics of magnetic Mn ions has been accelerated by an order of
magnitude in (Cd,Mn)Te digital alloys, without any noticeable change in the
giant Zeeman spin splitting of excitonic states, i.e. without effect on the
static magnetization. The strong sensitivity of the magnetization dynamics to
clustering of the Mn ions opens a new degree of freedom for spin engineering.",0601194v1
2006/1/30,"Magnetism of two-dimensional defects in Pd: stacking faults, twin boundaries and surfaces","Careful first-principles density functional calculations reveal the
importance of hexagonal versus cubic stacking of closed packed planes of Pd as
far as local magnetic properties are concerned. We find that, contrary to the
stable face centered cubic phase, which is paramagnetic, the hexagonal
close-packed phase of Pd is ferromagnetic with a magnetic moment of 0.35
$\mu_{B}$/atom. Our results show that two-dimensional defects with local hcp
stacking, like twin boundaries and stacking faults, in the otherwise fcc Pd
structure, increase the magnetic susceptibility. The (111) surface also
increases the magnetic susceptibility and it becomes ferromagnetic in
combination with an individual stacking fault or twin boundary close to it. On
the contrary, we find that the (100) surface decreases the tendency to
ferromagnetism. The results are consistent with the magnetic moment recently
observed in small Pd nanoparticles, with a large surface area and a high
concentration of two-dimensional stacking defects.",0601658v1
2006/1/30,Multiple transfer of angular momentum quanta from a spin-polarized hole to magnetic ions in ZnMnSe/ZnBeSe quantum wells,"The magnetization kinetics in (Zn,Mn)Se/(Zn,Be)Se quantum wells has been
studied on a ps-time scale after pulsed laser excitation. The magnetization
induced by an external magnetic field is reduced by up to 30% during ~100 ps
due to spin and energy transfer from photocarriers to Mn spin system. The giant
Zeeman splitting leads to a complete spin polarization of the carriers,
resulting in a strong suppression of flip-flop processes between carriers and
magnetic ions. Therefore a multiple angular momentum transfer from each
spin-polarized hole to the Mn ions becomes the dominant mechanism in the
magnetization dynamics. A model based on spin-momentum coupling in the valence
band is suggested for explaining this transfer.",0601661v1
2006/3/8,Anomalous impurity effect on magnetization in frustrated one-dimensional ferro- and ferrimagnets,"Significant decrease of spontaneous magnetization in frustrated
one-dimensional ferro- and ferrimagnets due to non-magnetic impurities is
predicted. Using the density-matrix renormalization group method and the exact
diagonalization method, we confirm that the total spin can vanish due to a
single impurity in finite chains. Introducing the picture of magnetic domain
inversion, we numerically investigate the impurity-density dependence of
magnetization. In particular, we show that even with an infinitesimal density
of impurities the magnetization in the ground state is reduced by about 40%
from that of the corresponding pure system. Conditions for the materials which
may show this anomalous impurity effect are formulated.",0603193v1
2006/3/22,Structural and magnetic instabilities of layered magnetic systems,"We present a study of the magnetic order and the structural stability of
two-dimensional quantum spin systems in the presence of spin-lattice coupling.
For a square lattice it is shown that the plaquette formation is the most
favourable form of static two-dimensional dimerization. We also demonstrate
that such distortions may coexist with long range magnetic order, in contrast
to the one-dimensional case. Similarly, the coupling to Einstein phonons is
found to reduce, but not to eliminate the staggered magnetic moment. In
addition, we consider the renormalization of the square lattice phonon spectrum
due to spin-phonon coupling in the adiabatic approximation. Towards low
temperatures significant softening mainly of zone boundary phonons is found,
especially around the $(\pi,0)$ point of the Brillouin zone. This result is
compatible with the tendency to plaquette formation in the static limit. We
also point out the importance of a ""magnetic pressure"" on the lattice due to
spin-phonon coupling. At low temperatures, this results in a tendency towards
shear instabilities of the lattice.",0603576v1
2006/5/9,"Superexchange in Dilute Magnetic Dielectrics: Application to (Ti,Co)O_2","We extend the model of ferromagnetic superexchange in dilute magnetic
semiconductors to the ferromagnetically ordered highly insulating compounds
(dilute magnetic dielectrics). The intrinsic ferromagnetism without free
carriers is observed in oxygen-deficient films of anatase TiO_2 doped with
transition metal impurities in cation sublattice. We suppose that ferromagnetic
order arises due to superexchange between complexes [oxygen vacancies +
magnetic impurities], which are stabilized by charge transfer from vacancies to
impurities. The Hund rule controls the superexchange via empty vacancy related
levels so that it becomes possible only for the parallel orientation of
impurity magnetic moments. The percolation threshold for magnetic ordering is
determined by the radius of vacancy levels, but the exchange mechanism does not
require free carriers. The crucial role of the non-stoichiometry in formation
of the ferromagnetism makes the Curie temperatures extremely sensitive to the
methods of sample preparation.",0605242v1
2006/6/2,Temperature and magnetic field dependences of the elastic constants of Ni-Mn-Al magnetic Heusler alloys,"We report on measurements of the adiabatic second order elastic constants of
the off-stoichiometric Ni$_{54}$Mn$_{23}$Al$_{23}$ single crystalline Heusler
alloy. The variation in the temperature dependence of the elastic constants has
been investigated across the magnetic transition and over a broad temperature
range. Anomalies in the temperature behaviour of the elastic constants have
been found in the vicinity of the magnetic phase transition. Measurements under
applied magnetic field, both isothermal and variable temperature, show that the
value of the elastic constants depends on magnetic order, thus giving evidence
for magnetoelastic coupling in this alloy system.",0606065v1
2006/6/20,Magnetic Percolation and the Phase Diagram of the Disordered RKKY model,"We consider ferromagnetism in spatially randomly located magnetic moments, as
in a diluted magnetic semiconductor, coupled via the carrier-mediated indirect
exchange RKKY interaction. We obtain via Monte Carlo the magnetic phase diagram
as a function of the impurity moment density $n_{i}$ and the relative carrier
concentration $n_{c}/n_{i}$. As evidenced by the diverging correlation length
and magnetic susceptibility, the boundary between ferromagnetic (FM) and
non-ferromagnetic (NF) phases constitutes a line of zero temperature critical
points which can be viewed as a magnetic percolation transition. In the dilute
limit, we find that bulk ferromagnetism vanishes for $n_{c}/n_{i}>.1$. We also
incorporate the local antiferromagnetic direct superexchange interaction
between nearest neighbor impurities, and examine the impact of a damping factor
in the RKKY range function.",0606532v2
2006/6/27,Theoretical limit of the minimal magnetization switching field and the optimal field pulse for Stoner particles,"The theoretical limit of the minimal magnetization switching field and the
optimal field pulse design for uniaxial Stoner particles are investigated. Two
results are obtained. One is the existence of a theoretical limit of the
smallest magnetic field out of all possible designs. It is shown that the limit
is proportional to the damping constant in the weak damping regime and
approaches the Stoner-Wohlfarth (SW) limit at large damping. For a realistic
damping constant, this limit is more than ten times smaller than that of
so-called precessional magnetization reversal under a non-collinear static
field. The other is on the optimal field pulse design: If the magnitude of a
magnetic field does not change, but its direction can vary during a reversal
process, there is an optimal design that gives the shortest switching time. The
switching time depends on the field magnitude, damping constant, and magnetic
anisotropy. However, the optimal pulse shape depends only on the damping
constant.",0606681v1
2006/7/11,The effect of hole-doping on the magnetic properties of Nd1-xTiO3,"The magnetic properties of the hole(x)-doped Mott-Hubbard, antiferromagnetic
insulator, NdTiO3, have been investigated in Nd1-xTiO3. For the materials in
0.010(6) < x < 0.112(4), correlation between the structural and magnetic
properties is discussed with respect to the Ti - O - Ti angles and the Ti - O
bond distances. For 0.010(6) < x < 0.071(10), long-range magnetic order is
observed through low temperature neutron diffraction and heat capacity. Neel
ordering temperatures of 88.2 K and 61.9 K are determined, respectively, for x
= 0.019(6) and x = 0.064(10). From high resolution neutron diffraction, the
Pnma magnetic structure is assigned, unambiguously, as GxCy on Ti3+ and Cy2 on
Nd3+. The Ti3+ ordered moment decreases gradually from 0.45(8) uB for x =
0.019(6) to 0.31(7) uB for x = 0.071(10), but vanishes abruptly for higher x.
Antiferromagnetic short-range order exists for 0.074(9) < x < 0.098(10) as
determined by neutron diffraction and the field-dependence of the
susceptibility. This is the first observation of short-range order for any
hole-doped titanate system. For 29(4)% hole-doping in Nd1-xTiO3, x > 0.098(10),
all magnetic ordering is destroyed.",0607286v1
2006/8/1,Non-collinear long-range magnetic ordering in HgCr2S4,"The low-temperature magnetic structure of \HG has been studied by
high-resolution powder neutron diffraction. Long-range incommensurate magnetic
order sets in at T$_N\sim$22K with propagation vector
\textbf{k}=(0,0,$\sim$0.18). On cooling below T$_N$, the propagation vector
increases and saturates at the commensurate value \textbf{k}=(0,0,0.25). The
magnetic structure below T$_N$ consists of ferromagnetic layers in the
\textit{ab}-plane stacked in a spiral arrangement along the \textit{c}-axis.
Symmetry analysis using corepresentations theory reveals a point group symmetry
in the ordered magnetic phase of 422 (D$_4$), which is incompatible with
macroscopic ferroelectricity. This finding indicates that the spontaneous
electric polarization observed experimentally cannot be coupled to the magnetic
order parameter.",0608031v2
2006/8/3,Monte Carlo simulation of the irreversible growth of magnetic thin films,"The growth of magnetic films with ferromagnetic interactions between
nearest-neighbor spins is studied in $(d+1)-$dimensional rectangular geometries
for $d = 1,2$. Magnetic films are grown irreversibly by adding spins at the
boundaries of the growing interface. The orientation of the added spins depends
on both the energetic interaction with already deposited spins and the
temperature, through a Boltzmann factor. At low temperatures thin films, of
thickness $L$, are constituted by a sequence of well ordered magnetic domains.
Spins belonging to each domain, of average length $l_{D} \gg L$, have mostly
the same orientation, but consecutive domains have opposite magnetization. Such
kind of ``spontaneous magnetization reversal'' during the growth process has a
short characteristic length $l_{R}$, such that $l_{D} \gg l_{R} \sim L$. At
higher temperatures, a transition between ordered and disordered states is also
observed. The emerging behavior is compared to that of the equilibrium Ising
model.",0608075v1
2006/8/11,Electronic states in a magnetic quantum-dot molecule: phase transitions and spontaneous symmetry breaking,"We show that a double quantum-dot system made of diluted magnetic
semiconductor behaves unlike usual molecules. In a semiconductor double quantum
dot or in a diatomic molecule, the ground state of a single carrier is
described by a symmetric orbital. In a magnetic material molecule, new ground
states with broken symmetry can appear due the competition between the
tunnelling and magnetic polaron energy. With decreasing temperature, the ground
state changes from the normal symmetric state to a state with spontaneously
broken symmetry. Interestingly, the symmetry of a magnetic molecule is
recovered at very low temperatures. A magnetic double quantum dot with
broken-symmetry phases can be used a voltage-controlled nanoscale memory cell.",0608284v1
2006/8/14,Simultaneous Antiferromagnetic Fe3+ and Nd3+ Ordering in NdFe3(11BO3)4,"By means of magnetic susceptibility and specific heat measurements, x-ray and
unpolarised neutron diffraction investigations on powder and single-crystal
samples, simultaneous long-range antiferromagnetic Fe and Nd ordering in
NdFe3(11BO3)4 with R 3 2 chemical structure has been found at temperatures
below TN = 30.5(5) K down to 1.6 K. At temperatures down to 20 K to the
propagation vector is khex = [0,0,3/2] and becomes slightly incommensurate at
lower temperatures. Symmetry analysis yields magnetic spiral configurations
with the magnetic moments oriented parallel to hexagonal basal plane according
to the irreducible representations tau_3 in the commensurate case. This is in
agreement with the easy directions of magnetisation perpendicular to the c-axis
as determined by magnetic susceptibility measurements. At 1.6 K the magnetic Fe
moment amounts to 4.9 muB close to the free ion moment of Fe3+. The magnetic
Nd3+ moment saturates presumably due to crystal-field effects at 2.7 muB.",0608304v1
2006/8/21,New sensor for thermodynamic measurement of magnetization reversal in magnetic nanomaterials,"A sensor for thermal and thermodynamic measurements of small magnetic systems
have been designed and built. It is based on a 5&mu;m-thick suspended polymer
membrane, which has a very low heat capacity (&asymp; 10-6 J/K at nitrogen
temperature), and on which a heater and a highly sensitive thermometer are
deposited. The sensor properties have been characterized as a function of
temperature and frequency. Energy exchanges as small as 1 picojoule (10-12
Joule) were detected in the 40K- 300K temperature range. Such values correspond
to those required for measuring the thermal signatures occurring during
magnetization reversal in very thin samples (typically 10 nm thick), which
would be deposited on the membrane. It is expected that this method will
constitute a powerful tool in view of analyzing magnetization reversal
processes in magnetic nanosystems, e.g. exhibiting the exchange-spring and
exchange-bias phenomena.",0608457v1
2006/8/31,Magnetic phase diagram of the semi-Heusler alloys from first-principles,"The magnetic phase diagram of the Mn-based semi-Heusler alloys is determined
at T=0 using first-principles calculations in conjunction with the
frozen-magnon approximation. We show that the magnetism in these systems
strongly depends on the number of conduction electrons, their spin polarization
and the position of the unoccupied Mn 3d states with respect to Fermi energy.
Various magnetic phases are obtained depending on these characteristics. The
conditions leading to diverse magnetic behavior are identified. We find that in
the case of a large conduction electron spin polarization and the unoccupied Mn
3d states lying far above the Fermi level, an RKKY-like ferromagnetic
interaction is dominating. On the other hand, the antiferromagnetic
superexchange becomes important in the presence of large peaks of the
unoccupied Mn 3d states lying close to the Fermi energy. The overall magnetic
behavior depends on the competition of these two exchange mechanisms. The
obtained results are in very good agreement with the available experimental
data.",0609001v1
2006/10/12,Impact of rare earth magnetic moment on ordering of Ru in Sr2RuREO6 (RE = Gd and Eu),"We report synthesis and magnetization of Sr2RuREO6 (RE/Ru-211O6) with RE = Gd
and Eu. Both Gd,Eu/Ru-211O6 are formed in distorted perovskite-type single
phase with monoclinic P21/n space group. Magnetization (M/T) measurements
exhibited antiferromagnetic ordering of Ru moments for both Gd and Eu compounds
at TN of around 30 K due to super-exchange Ru-O-O-Ru interaction. Interestingly
enough, detailed M/H plots of Gd/Ru-211O6 exhibited, the development of a
ferromagnetic (FM) component at 20 K. Further at below 10 K, the FM component
disappears and rather an spin freezing field (HSF) of around 1000 Oe is seen at
5 K. In case of Eu/Ru-211O6, the basic antiferromagnetic ordering of Ru moments
remains invariant down to 5 K, and the appearance of FM component is not seen.
It seems that the high magnetic moment of 8mB for Gd3+ influences the AFM
ordering of Ru in case of Gd/Ru-211O6.",0610325v1
2006/10/31,Carbon-doped ZnO: A New Class of Room Temperature Dilute Magnetic Semiconductor,"We report magnetism in carbon doped ZnO. Our first-principles calculations
based on density functional theory predicted that carbon substitution for
oxygen in ZnO results in a magnetic moment of 1.78 $\mu_B$ per carbon. The
theoretical prediction was confirmed experimentally. C-doped ZnO films
deposited by pulsed laser deposition with various carbon concentrations showed
ferromagnetism with Curie temperatures higher than 400 K, and the measured
magnetic moment based on the content of carbide in the films ($1.5 - 3.0 \mu_B$
per carbon) is in agreement with the theoretical prediction. The magnetism is
due to bonding coupling between Zn ions and doped C atoms. Results of
magneto-resistance and abnormal Hall effect show that the doped films are
$n$-type semiconductors with intrinsic ferromagnetism. The carbon doped ZnO
could be a promising room temperature dilute magnetic semiconductor (DMS) and
our work demonstrates possiblity of produing DMS with non-metal doping.",0610870v1
2006/11/30,Crystalline Ni nanoparticles as the origin of ferromagnetism in Ni implanted ZnO crystals,"We report the structural and magnetic properties of ZnO single crystals
implanted at 623 K with up to 10 at. % of Ni. As revealed by X-ray diffraction,
crystalline fcc-Ni nanoparticles were formed inside ZnO. The magnetic behavior
(magnetization with field reversal and with different temperature protocol) of
all samples is well explained by a magnetic Ni-nanoparticle system. Although
the formation of Ni:ZnO based diluted magnetic semiconductor cannot be ruled
out, the major contribution to the magnetic properties stems from crystalline
nanoparticles synthesized under these implantation conditions.",0611770v1
2006/12/2,Magnetization and EPR studies of the single molecule magnet Ni$_4$ with integrated sensors,"Integrated magnetic sensors that allow simultaneous EPR and magnetization
measurements have been developed to study single molecule magnets. A high
frequency microstrip resonator has been integrated with a micro-Hall effect
magnetometer. EPR spectroscopy is used to determine the energy splitting
between the low lying spin-states of a Ni$_4$ single crystal, with an S=4
ground state, as a function of applied fields, both longitudinal and transverse
to the easy axis at 0.4 K. Concurrent magnetization measurements show changes
in spin-population associated with microwave absorption. Such studies enable
determination of the energy relaxation time of the spin system.",0612060v1
2007/1/11,Magnetic Phase Control in Monolayer Films by Substrate Tuning,"We propose to tailor exchange interactions in magnetic monolayer films by
tuning the adjacent non-magnetic substrate. As an example, we demonstrate a
ferromagnetic-antiferromagnetic phase transition for one monolayer Fe on a
Ta(x)W(1-x)(001) surface as a function of the Ta concentration. At the critical
Ta concentration, the nearest-neighbor exchange interaction is small and the
magnetic phase space is dramatically broadened. Complex magnetic order such as
spin-spirals, multiple-Q, or even disordered local moment states can occur,
offering the possibility to store information in terms of ferromagnetic dots in
an otherwise zero-magnetization state matrix.",0701241v2
2007/2/5,Existence of two electronic states in Sr4Ru3O10 at low temperatures,"We report measurements on in-plane resistivity, thermopower, and
magnetization as a function of temperature and magnetic fields on single
crystalline Sr4Ru3O10 grown by the floating zone method. As the temperature was
lowered to below around 30 K, the in-plane and c-axis resistivities and the
thermopower were found to exhibit a step feature accompanied by hysteresis
behavior when the in-plane field was swept up and down from below 10 kOe to
above 20 kOe. The sharp increase in the thermopower with increasing in-plane
magnetic field at low temperatures has not been observed previously in layered
transition metal oxides. Comparing with magnetization data, we propose that the
step feature marks the transition between the two different electronic states
in Sr4Ru3O10. We propose that the alignment of domains by the in-plane magnetic
field is responsible to the emergence of the new electronic states in high
applied in-plane magnetic field.",0702093v1
2007/2/26,Anomalous magnetic phase diagram in low-carrier two-band systems and possible application to CeOs4Sb12,"Magnetic properties under the external field are investigated in low-carrier
two-band systems, which may explain the nontrivial phase boundary found in
temperature vs. magnetic field diagram discovered in some materials, such as
filled-skutterudite compound CeOs$_{4}$Sb$_{12}$. Analysis is made both for the
periodic Anderson model with the small-dispersive $f$ band and the simplified
two parabolic band model in the vicinity of the Fermi level. The magnetic
susceptibilities are calculated by using the random phase approximation. It is
shown that the maximum value of the magnetic susceptibility perpendicular to
the external field is enhanced and yields the anomalous phase boundary. By
applying the magnetic field, the phase boundary shifts to higher temperature
region in the insulating state with a small band gap. On the other hand, the
similar phase boundary also appears in the semi-metallic states, in which the
structure of the density of states in the vicinity of the Fermi level and the
finite temperature effect are essential.",0702587v1
2004/7/25,Nonlinear ac responses of electro-magnetorheological fluids,"We apply a Langevin model to investigate the nonlinear ac responses of
electro-magnetorheological (ERMR) fluids under the application of two crossed
dc magnetic (z axis) and electric (x axis) fields and a probing ac sinusoidal
magnetic field. We focus on the influence of the magnetic fields which can
yield nonlinear behaviors inside the system due to the particles with a
permanent magnetic dipole moment.
  Based on a perturbation approach, we extract the harmonics of the magnetic
field and orientational magnetization analytically. To this end, we find that
the harmonics are sensitive to the degree of anisotropy of the structure as
well as the field frequency. Thus, it is possible to real-time monitor the
structure transformation of ERMR fluids by detecting the nonlinear ac
responses.",0407132v2
2006/3/15,Magneto-Dielectric Substrates in Antenna Miniaturization: Potential and Limitations,"In the present paper we discuss antenna miniaturization using
magneto-dielectric substrates. Recent results found in the literature reveal
that advantages over conventional dielectric substrates can only be achieved if
natural magnetic inclusions are embedded into the substrate. This observation
is revised and the physical background is clarified. We present a detailed
discussion concerning magnetic materials available in the microwave regime and
containing natural magnetic constituents. The effects of magnetic dispersion
and loss are studied: constraints on the microwave permeability are used to
estimate the effect of magnetic substrates on the achievable impedance
bandwidth. Microwave composites filled with thin ferromagnetic films are
considered as a prospective antenna substrate. We calculate the impedance
bandwidth for a $\lambda/2$-patch antenna loaded with the proposed substrate,
and challenge the results against those obtained with conventional dielectric
substrates. It is shown that the radiation quality factor is strongly minimized
with the proposed substrate even in the presence of realistic losses. Estimates
for the radiation efficiency are given as a function of the magnetic loss
factor.",0603116v1
2007/4/26,Change in the room temperature magnetic property of ZnO upon Mn doping,"We present in this paper the changes in the room temperature magnetic
property of ZnO on Mn doping prepared using solvo-thermal process. The zero
field cooled (ZFC) and field cooled (FC) magnetisation of undoped ZnO showed
bifurcation and magnetic hysteresis at room temperature. Upon Mn doping the
magnetic hysteresis at room temperature and the bifurcation in ZFC-FC
magnetization vanishes. The results seem to indicate that undoped ZnO is
ferromagnetic while on the other hand the Mn doped ZnO is not a ferromagnetic
system. We observe that on addition of Mn atoms the system shows
antiferromagnetism with very giant magnetic moments.",0704.3541v3
2007/5/2,Spin-polarized transport in II-VI magnetic resonant tunneling devices,"We investigate electronic transport through II-VI semiconductor resonant
tunneling structures containing diluted magnetic impurities. Due to the
exchange interaction between the conduction electrons and the impurities, there
arises a giant Zeeman splitting in the presence of a moderately low magnetic
field. As a consequence, when the quantum well is magnetically doped the
current-voltage characteristics shows two peaks corresponding to transport for
each spin channel. This behavior is experimentally observed and can be
reproduced with a simple tunneling model. The model thus allows to analyze
other configurations. First, we further increase the magnetic field, which
leads to a spin polarization of the electronic current injected from the leads,
thus giving rise to a relative change in the current amplitude. We demonstrate
that the spin polarization in the emitter can be determined from such a change.
Furthermore, in the case of a magnetically doped injector our model shows a
large increase in peak amplitude and a shift of the resonance to higher
voltages as the external field increases. We find that this effect arises from
a combination of giant Zeeman splitting, 3-D incident distribution and broad
resonance linewidth.",0705.0237v1
2007/8/10,Dynamic Origin of Vortex Core Switching in Soft Magnetic Nanodots,"The magnetic vortex with the in-plane curling magnetization and the
out-of-plane magnetization at the core is a unique ground state in nanoscale
magnetic elements. This kind of magnetic vortex can be used as a memory unit
for information storage, through its downward or upward core-orientation and,
thus, controllable core switching deserves some special attention. Our
analytical and micromagnetic calculations reveal that the origin of the vortex
core reversal is a gyrotropic field. This field is induced by vortex dynamic
motion and is proportional to the velocity of the moving vortex. Our
calculations elucidate the physical origin of the vortex core dynamic reversal
and offer a key to effective manipulation of the vortex-core orientation.",0708.1359v1
2007/8/16,"Definitive Evidence of Interlayer Coupling Between (Ga,Mn)As Layers Separated by a Nonmagnetic Spacer","We have used polarized neutron reflectometry to study the structural and
magnetic properties of the individual layers in a series of
(Al,Be,Ga)As/(Ga,Mn)As/GaAs/(Ga,Mn)As multilayer samples. Structurally, we
observe that the samples are virtually identical except for the GaAs spacer
thickness (which varies from 3-12 nm), and confirm that the spacers contain
little or no Mn. Magnetically, we observe that for the sample with the thickest
spacer layer, modulation doping by the(Al,Be,Ga)As results in (Ga,Mn)As layers
with very different temperature dependent magnetizations. However, as the
spacer layer thickness is reduced, the temperature dependent magnetizations of
the top an bottom (Ga,Mn)As layers become progressively more similar - a trend
we find to be independent of the crystallographic direction along which spins
are magnetized. These results definitively show that (Ga,Mn)As layers can
couple across a non-magnetic spacer, and that such coupling depends on spacer
thickness.",0708.2289v2
2007/9/14,Bound magnetic polarons in the very dilute regime,"We study bound magnetic polarons (BMP) in a very diluted magnetic
semiconductor CdMnTe by means of site selective spectroscopy. In zero magnetic
field we detect a broad and asymmetric band with a characteristic spectral
width of about 5 meV. When external magnetic fields are applied a new line
appears in the emission spectrum. Remarkably, the spectral width of this line
is reduced greatly down to 0.24 meV. We attribute such unusual behavior to the
formation of BMP, effected by sizable fluctuations of local magnetic moments.
The modifications of the optical spectra have been simulated by the Monte-Carlo
method and calculated within an approach considering the nearest Mn ion. A
quantitative agreement with the experiment is achieved without use of fitting
parameters. It is demonstrated that the low-energy part of the emission spectra
originates from the energetic relaxation of a complex consisting of a hole and
its nearest Mn ion. It is also shown that the contribution to the narrow line
arises from the remote Mn ions.",0709.2314v1
2007/9/17,X-Ray Analysis of Oxygen-induced Perpendicular Magnetic Anisotropy in Pt/Co/AlOx trilayer,"X-ray spectroscopy measurements have been performed on a series of Pt/Co/AlOx
trilayers to investigate the role of Co oxidation in the perpendicular magnetic
anisotropy of the Co/AlOx interface. It is observed that high temperature
annealing modifies the magnetic properties of the Co layer, inducing an
enhancement of the perpendicular magnetic anisotropy. The microscopic
structural properties are analyzed via X-ray Absorption Spectroscopy, X-ray
Magnetic Circular Dichroism and X-ray Photoelectron Spectroscopy measurements.
It is shown that annealing enhances the amount of interfacial oxide, which may
be at the origin of a strong perpendicular magnetic anisotropy.",0709.2581v2
2007/9/21,Magnetism of NiMn2O4-Fe3O4 Spinel Interfaces,"We investigate the magnetic properties of the isostructural spinel-spinel
interface of NiMn2O4(NMO)-Fe3O4. Although the magnetic transition temperature
of the NMO film is preserved, both bulk and interface sensitive measurements
demonstrate that the interface exhibits strong interfacial magnetic coupling up
to room temperature. While NMO thin films have a ferrimagnetic transition
temperature of 60K, both NiFe2O4 and MnFe2O4 are ferrimagnetic at room
temperature. Our experimental results suggest that these magnetic properties
arise from a thin interdiffused region of (Fe,Mn,Ni)3O4 at the interface
leading to Mn and Ni magnetic properties similar to MnFe2O4 and NiFe2O4.",0709.3518v2
2007/10/11,Dielectric Susceptibility and Heat Capacity of Ultra-Cold Glasses in Magnetic Field,"Recent experiments demonstrated unexpected, even intriguing properties of
certain glassy materials in magnetic field at low temperatures. We have studied
the magnetic field dependence of the static dielectric susceptibility and the
heat capacity of glasses at low temperatures. We present a theory in which we
consider the coupling of the tunnelling motion to nuclear quadrupoles in order
to evaluate the static dielectric susceptibility. In the limit of weak magnetic
field we find the resonant part of the susceptibility increasing like $B^2$
while for the large magnetic field it behaves as 1/B. In the same manner we
consider the coupling of the tunnelling motion to nuclear quadrupoles and
angular momentum of tunnelling particles in order to find the heat capacity.
Our results show the Schotky peak for the angular momentum part, and $B^2$
dependence for nuclear quadrupoles part of heat capacity, respectively. We
discuss whether or not this approach can provide a suitable explanation for
such magnetic properties.",0710.2222v1
2007/10/24,Criterion of multi-switching stability for magnetic nanoparticles,"We present a procedure to study the switching and the stability of an array
of magnetic nanoparticles in the dynamical regime. The procedure leads to the
criterion of multi-switching stability to be satisfied in order to have stable
switching. The criterion is used to compare various magnetic-field-induced
switching schemes, either present in the literature or suggested in the present
work. In particular, we perform micromagnetic simulations to study the
magnetization trajectories and the stability of the magnetization after
switching for nanoparticles of elliptical shape. We evaluate the stability of
the switching as a function of the thickness of the particles and the rise and
fall times of the magnetic pulses, both at zero and room temperature.
Furthermore, we investigate the role of the dipolar interaction and its
influence on the various switching schemes. We find that the criterion of
multi-switching stability can be satisfied at room temperature and in the
presence of dipolar interactions for pulses shaped according to CMOS
specifications, for switching rates in the GHz regime.",0710.4480v1
2007/10/26,Transport and magnetic properties in YBaCo2O5.45: Focus on the high-temperature transition,"The electronic transport properties and the magnetic susceptibility were
measured in detail in $YBaCo_2O_{5.45}$. Close to the so-called metal-insulator
transition, strong effects of resistance relaxation, a clear thermal hysteresis
and a sudden increase of the resistance noise are observed. This is likely due
to the first order character of the transition and to the underlying phases
coexistence. Despite these out of equilibrium features, a positive and linear
magneto-resistance is also observed, possibly linked to the heterogeneity of
the state. From a magnetic point of view, the paramagnetic to ordered magnetic
state transition is observed using non linear susceptibilty. This transition
shows the characteristics of a continuous transition, and time dependent
effects can be linked with the dynamics of magnetic domains in presence of
disorder. Thus, when focusing on the order of the transitions, the electronic
one and the magnetic one can not be directly associated.",0710.5008v1
2007/11/1,Two magnetic regimes in doped ZnO corresponding to a dilute magnetic semiconductor and a dilute magnetic insulator,"Films of ZnO doped with magnetic ions, Mn and Co and, in some cases, with Al
have been fabricated with a very wide range of carrier densities. Ferromagnetic
behaviour is observed in both insulating and metallic films, but not when the
carrier density is intermediate. Insulating films exhibit variable range
hopping at low temperatures and are ferromagnetic at room temperature due to
the interaction of the localised spins with static localised states. The
magnetism is quenched when carriers in the localised states become mobile. In
the metallic (degenerate semiconductor) range, robust ferromagnetism reappears
together with very strong magneto-optic signals and room temperature anomalous
Hall data. This demonstrates the polarisation of the conduction bands and
indicates that, when ZnO is doped into the metallic regime, it behaves as a
genuine magnetic semiconductor.",0711.0172v2
2007/11/2,Magnetism without magnetic impurities in oxides ZrO2 and TiO2,"We perform a theoretical study of the magnetism induced in transition metal
dioxides ZrO2 and TiO2 by substitution of the cation by a vacancy or an
impurity from the groups 1A or 2A of the periodic table, where the impurity is
either K or Ca. In the present study both supercell and embedded cluster
methods are used. It is demonstrated that the vacancy and the K-impurity leads
to a robust induced magnetic moment on the surrounding O-atoms for both the
cubic ZrO2 and rutile TiO2 host crystals. On the other hand it is shown that
Ca-impurity leads to a non magnetic state. The native O-vacancy does not induce
a magnetic moment in the host dioxide crystal.",0711.0280v1
2007/11/12,Enhancing Domain Wall Speed in Nanowires with Transverse Magnetic Fields,"Dynamic micromagnetic simulation studies have been completed to observe the
motion of a domain wall in a magnetic nanowire in an effort to increase the
field-driven domain wall speed. Previous studies have shown that the wire
dimensions place a cap on the maximum speed attainable by a domain wall when
driven by a magnetic field placed along the direction of the nanowire. Here we
present data showing a significant increase in the maximum speed of a domain
wall due to the addition of a magnetic field placed perpendicular to the
longitudinal driving field. The results are expressed in terms of the relative
alignment of the transverse field direction with respect to the direction of
the magnetic moments within the domain wall. In particular, when the transverse
field is parallel to the magnetic moments within the domain wall, the velocity
of the wall varies linearly with the strength of the transverse field
increasing by up to 20%. Further examination of the domain wall structure shows
that the length of the domain wall also depends linearly on the strength of the
transverse field. We present a simple model to correlate the effects.",0711.1864v1
2007/12/4,Microwave excitations associated with a wavy angular dependence of the spin transfer torque : model and experiments,"The spin transfer torque (STT) can lead to steady precession of magnetization
without any external applied field in magnetic spin valve where the magnetic
layer have very different spin diffusion length. This effect is associated with
an unusual angular dependence of the STT, called ""wavy"" (WAD-STT), predicted in
the frame of diffusive models of spin transfer. In this article, we present a
complete experimental characterization of the magnetization dynamics in the
presence of a WAD-STT. The results are compared to the prediction of the
magnetization dynamics obtained by single domain magnetic simulations
(macrospin approximation). The macrospin simulations well reproduced the main
static and dynamical experimental features (phase diagram, R(I) curves,
dependence of frequency with current and field) and suggest that the dynamical
excitations observed experimentally are associated with a large angle
out-of-plane precession mode. The present work validates the diffusive models
of the spin transfer and underlines the role of the spin accumulation and the
spin relaxation effects on the STT.",0712.0548v1
2007/12/18,Observation of electromagnon excitations in the BiFe0$_3$ spiral magnet,"Recently, oxide multiferroics have attracted much attention due to their
large magnetoelectric effect which allows the tuning of magnetic properties
with electric field and vice versa and open new venues for future spintronic
applications such as multiple-state memory devices with dual magnetic and
electric control. BiFeO$_3$ (BFO) belongs to this new class of materials and
shows both ferroelectric and antiferromagnetic orders at room temperature with
a large electric polarizationassociated with a cycloidal spiral magnetic
ordering. The incommensurate magnetic order induces magnon zone folding and
allows investigations by optical probes of unusual spin waves which couples to
optical phonons, the so called ""`electromagnons""'. Here, we unravel for the
first time the electromagnon spectra of BFO by means low energy inelastic light
scattering technique. We show the existence of two species of electromagnons
corresponding to spin wave excitations in and out of the cycloidal plane. The
present observations present an unique opportunity to study the interplay
between ferroelectric and magnetic orders.",0712.3044v1
2008/1/8,Nature of magnetic coupling between Mn ions in as-grown Ga$_{1-x}$Mn$_{x}$As studied by x-ray magnetic circular dichroism,"The magnetic properties of as-grown Ga$_{1-x}$Mn$_{x}$As have been
investigated by the systematic measurements of temperature and magnetic field
dependent soft x-ray magnetic circular dichroism (XMCD). The {\it intrinsic}
XMCD intensity at high temperatures obeys the Curie-Weiss law, but residual
spin magnetic moment appears already around 100 K, significantly above Curie
temperature ($T_C$), suggesting that short-range ferromagnetic correlations are
developed above $T_C$. The present results also suggest that antiferromagnetic
interaction between the substitutional and interstitial Mn (Mn$_{int}$) ions
exists and that the amount of the Mn$_{int}$ affects $T_C$.",0801.1155v2
2008/1/9,Magnetic coupling in highly-ordered NiO/Fe3O4(110): Ultrasharp magnetic interfaces vs. long-range magnetoelastic interactions,"We present a laterally resolved X-ray magnetic dichroism study of the
magnetic proximity effect in a highly ordered oxide system, i.e. NiO films on
Fe3O4(110). We found that the magnetic interface shows an ultrasharp
electronic, magnetic and structural transition from the ferrimagnet to the
antiferromagnet. The monolayer which forms the interface reconstructs to
NiFe2O4 and exhibits an enhanced Fe and Ni orbital moment, possibly caused by
bonding anisotropy or electronic interaction between Fe and Ni cations. The
absence of spin-flop coupling for this crystallographic orientation can be
explained by a structurally uncompensated interface and additional
magnetoelastic effects.",0801.1468v1
2008/1/13,3d-electron induced magnetic phase transition in half-metallic semi-Heusler alloys,"We study the effect of the non-magnetic 3\textit{d} atoms on the magnetic
properties of the half-metallic (HM) semi-Heusler alloys Co$_{1-x}$Cu$_{x}$MnSb
and Ni$_{1-x}$Cu$_{x}$MnSb ($0 \leq x \leq 1$) using first-principles
calculations. We determine the magnetic phase diagram of both systems at zero
temperature and obtain a phase transition from a ferromagnetic to an
antiferromagnetic state. For low Cu concentrations the ferromagnetic RKKY-like
exchange mechanism is dominating, while the antiferromagnetic superexchange
coupling becomes important for larger Cu content leading to the observed
magnetic phase transition. A strong dependence of the magnetism in both systems
on the position of the Fermi level within the HM gap is obtained. Obtained
results are in good agreement with the available experimental data.",0801.1968v1
2008/1/17,Magnetic structure at zigzag edges of graphene bilayer ribbons,"We study the edge magnetization of bilayer graphene ribbons with zigzag
edges. The presence of flat edge-state bands at the Fermi energy of undoped
bilayer, which gives rise to a strong peak in the density of states, makes
bilayer ribbons magnetic at the edges even for very small on-site electronic
repulsion. Working with the Hubbard model in the Hartree Fock approximation we
show that the magnetic structure in bilayer ribbons with zigzag edges is
ferromagnetic along the edge, involving sites of the two layers, and
antiferromagnetic between opposite edges. It is also shown that this magnetic
structure is a consequence of the nature of the edge states present in bilayer
ribbons with zigzag edges. Analogously to the monolayer case, edge site
magnetization as large as $m \approx0.2 \mu_{B}$ (per lattice site) even at
small on-site Hubbard repulsion $U \approx 0.3 {eV}$ is realized in nanometer
wide bilayer ribbons.",0801.2788v1
2008/2/15,Magnetic properties of Ag(2)VOP(2)O(7): an unexpected spin dimer system,"Magnetic properties of the silver vanadium phosphate Ag(2)VOP(2)O(7) are
studied by means of magnetic susceptibility measurements and electronic
structure calculations. In spite of the layered crystal structure suggesting 1D
or 2D magnetic behavior, this compound can be understood as a spin dimer
system. The fit of the magnetic susceptibility indicates an intradimer
interaction of about 30 K in perfect agreement with the computational results.
Our study emphasizes the possible pitfalls in interpreting experimental data on
structural basis only and points out the importance of microscopic models for
the understanding of the magnetic properties of vanadium phosphates.",0802.2293v1
2008/2/21,First principles calculation of spin-interactions and magnetic ground states of Cr trimers on Au(111),"We present calculations of the magnetic ground states of Cr trimers in
different geometries on top of a Au(111) surface. By using a least square fit
method based on a fully relativistic embedded-cluster Green's function method
first we determined the parameters of a classical vector-spin model consisting
of second and fourth order interactions. The newly developed method requires no
symmetry constraints, therefore, it is throughout applicable for small
nanoparticles of arbitrary geometry. The magnetic ground states were then found
by solving the Landau-Lifshitz-Gilbert equations. In all considered cases the
configurational energy of the Cr trimers is dominated by large
antiferromagnetic nearest neighbor interactions, whilst biquadratic
spin-interactions have the second largest contributions to the energy. We find
that an equilateral Cr trimer exhibits a frustrated 120$^\circ$ N\'eel type of
ground state with a small out-of-plane component of the magnetization and we
show that the Dzyaloshinsky-Moriya interactions determine the chirality of the
magnetic ground state. In cases of a linear chain and an isosceles trimer
collinear antiferromagnetic ground states are obtained with a magnetization
lying parallel to the surface.",0802.3113v1
2008/3/10,3D-xy critical properties of YBa2Cu4O8 and magnetic field induced 3D to 1D crossover,"We present reversible magnetization data of a YBa2Cu4O8 single crystal and
analyze the evidence for 3D-xy critical behavior and a magnetic field induced
3D to 1D crossover. Remarkable consistency with these phenomena is observed in
agreement with a magnetic field induced finite size effect, whereupon the
correlation length transverse to the applied magnetic field cannot grow beyond
the limiting magnetic length scale L_H. By applying the appropriate scaling
form we obtain the zero-field critical temperature, the 3D to 1D crossover, the
vortex melting line and the universal ratios of the related scaling variables.
Accordingly there is no continuous phase transition in the (H,T)-plane along
the H_c2-lines as predicted by the mean-field treatment.",0803.1384v2
2008/3/27,Hyperfine Fields in an Ag/Fe Multilayer Film Investigated with 8Li beta-Detected Nuclear Magnetic Resonance,"Low energy $\beta$-detected nuclear magnetic resonance ($\beta$-NMR) was used
to investigate the spatial dependence of the hyperfine magnetic fields induced
by Fe in the nonmagnetic Ag of an Au(40 \AA)/Ag(200 \AA)/Fe(140 \AA) (001)
magnetic multilayer (MML) grown on GaAs. The resonance lineshape in the Ag
layer shows dramatic broadening compared to intrinsic Ag. This broadening is
attributed to large induced magnetic fields in this layer by the magnetic Fe
layer. We find that the induced hyperfine field in the Ag follows a power law
decay away from the Ag/Fe interface with power $-1.93(8)$, and a field
extrapolated to $0.23(5)$ T at the interface.",0803.3874v1
2008/3/28,Edge State Magnetism of Single Layer Graphene Nanostructures,"We study edge state magnetism in graphene nanostructures using a mean field
theory of the Hubbard model. We investigate how the magnetism of the zigzag
edges of graphene is affected by the presence of other types of terminating
edges and defects. By a detailed study of both regular shapes, such as
polygonal nanodots and nanoribbons, and irregular shapes, we conclude that the
magnetism in zigzag edges is very robust. Our calculations show that the zigzag
edges that are longer than three to four repeat units are always magnetic,
irrespective of other edges, regular or irregular. We, therefore, clearly
demonstrate that the edge irregularities and defects of the bounding edges of
graphene nanostructures does not destroy the edge state magnetism.",0803.4080v2
2008/5/20,Crystal chemistry aspects of the magnetically induced ferroelectricity in TbMn2O5 and BiMn2O5,"The origin of magnetic frustration was stated and the ions whose shift is
accompanied by emerging magnetic ordering and ferroelectricity in TbMn2O5 and
BiMn2O5 were determined on the basis of calculation of magnetic coupling
parameters by using the structural data. The displacements accompanying the
magnetic ordering are not polar, they just induce changes of bond valence
(charge disordering) of Mn1 and Mn2, thus creating instability of the crystal
structure. To approximate again the bond valence to the initial value (charge
ordering) under magnetic ordering conditions is possible only due to polar
displacement of Mn2 (or O1) and O4 ions along the b axis that is the cause of
ferroelectric transition.",0805.3053v3
2008/5/21,Non-equilibrium thermodynamic study of magnetization dynamics in the presence of spin-transfer torque,"The dynamics of magnetization in the presence of spin-transfer torque was
studied. We derived the equation for the motion of magnetization in the
presence of a spin current by using the local equilibrium assumption in
non-equilibrium thermodynamics. We show that, in the resultant equation, the
ratio of the Gilbert damping constant, $\alpha$, and the coefficient, $\beta$,
of the current-induced torque, called non-adiabatic torque, depends on the
relaxation time of the fluctuating field $\tau_{c}$. The equality
$\alpha=\beta$ holds when $\tau_c$ is very short compared to the time scale of
magnetization dynamics. We apply our theory to current-induced magnetization
reversal in magnetic multilayers and show that the switching time is a
decreasing function of $\tau_{c}$.",0805.3306v1
2008/6/18,A frequency-adjustable electromagnet for hyperthermia measurements on magnetic nanoparticles,"We describe a low-cost and simple setup for hyperthermia measurements on
colloidal solutions of magnetic nanoparticles (ferrofluids) with a
frequency-adjustable magnetic field in the range 5-500 kHz produced by an
electromagnet. By optimizing the general conception and each component (nature
of the wires, design of the electromagnet), a highly efficient setup is
obtained. For instance, in a useful gap of 1.1 cm, a magnetic field of 4.8 mT
is generated at 100 kHz and 500 kHz with an output power of 3.4 W and 75 W,
respectively. A maximum magnetic field of 30 mT is obtained at 100 kHz. The
temperature of the colloidal solution is measured using optical fiber sensors.
To remove contributions due to heating of the electromagnet, a differential
measurement is used. In this configuration the sensitivity is better than 1.5
mW at 100 kHz and 19.3 mT. This setup allows one to measure weak heating powers
on highly diluted colloidal solutions. The hyperthermia characteristics of a
solution of Fe nanoparticles are described, where both the magnetic field and
the frequency dependence of heating power have been measured.",0806.3005v1
2008/6/23,Magnetic field induced transitions in multiferroic TbMnO3 probed by resonant and non-resonant X-ray diffraction,"Multiferroic TbMnO3 is investigated using x-ray diffraction in high magnetic
fields. Measurements on first and second harmonic structural reflections due to
modulations induced by the Mn and Tb magnetic order are presented as function
of temperature and field oriented along the a and b-directions of the crystal.
The relation to changes in ordering of the rare earth moments in applied field
is discussed. Observations below T_N(Tb) without and with applied magnetic
field point to a strong interaction of the rare earth order, the Mn moments and
the lattice. Also, the incommensurate to commensurate transition of the wave
vector at the critical fields is discussed with respect to the Tb and Mn
magnetic order and a phase diagram on basis of these observations for magnetic
fields H||a and H||b is presented. The observations point to a complicated and
delicate magneto-elastic interaction as function of temperature and field.",0806.3623v2
2008/8/19,Magnetization and spin dynamics of a Cr-based magnetic cluster: Cr$_{7}$Ni,"We study the magnetization and the spin dynamics of the Cr$_7$Ni ring-shaped
magnetic cluster. Measurements of the magnetization at high pulsed fields and
low temperature are compared to calculations and show that the spin Hamiltonian
approach provides a good description of Cr$_7$Ni magnetic molecule. In
addition, the phonon-induced relaxation dynamics of molecular observables has
been investigated. By assuming the spin-phonon coupling to take place through
the modulation of the local crystal fields, it is possible to evaluate the
decay of fluctuations of two generic molecular observables. The nuclear
spin-lattice relaxation rate $1/T_1$ directly probes such fluctuations, and
allows to determine the magnetoelastic coupling strength.",0808.2621v1
2008/10/15,Magnetic susceptibility and magnetization fluctuation measurements of mixed Gadolinium-Yttrium Iron Garnets,"We study the magnetic properties of Gadolinium-Yttrium Iron Garnet
($\text{Gd}_{x}\text{Y}_{3-x}\text{Fe}_5\text{0}_{12}$, $x=3,1.8$) ferrite
ceramics. The complex initial permeability is measured in the temperature range
2 K to 295 K at frequency of 1 kHz, and in the frequency range 100 Hz to 200
MHz at temperatures 4 K, 77 K, and 295 K. The magnetic viscosity-induced
imaginary part of the permeability is observed at low frequencies. Measurements
of the magnetization noise are made at 4 K. Using the fluctuation-dissipation
theorem, we find that the observed magnetization fluctuations are consistent
with our measurements of the low-frequency imaginary part of permeability. We
discuss some implications for proposed precision measurements as well as other
possible applications.",0810.2770v1
2008/10/16,Magnetic ordering above room temperature in the sigma-phase of Fe66V34,"Magnetic properties of four sigma-phase Fe_(100-x)V_x samples with
34.4<x<55.1 were investigated by Mossbauer spectroscopy and magnetic
measurements in the temperature interval 5-300 K. Four magnetic quantities viz.
hyperfine field, Curie temperature, magnetic moment and susceptibility were
determined. The sample containing 34.4 at% V was revealed to exhibit the
largest values found up to now for the sigma-phase for average hyperfine field,
B = 12.1 T, average magnetic moment per Fe atom, m = 0.89 mB, and Curie
temperature, TC = 315.5 K. The quantities were shown to be strongly correlated
with each other. In particular, TC is linearly correlated with m with a slope
of 406.5 K/mB, as well as B is so correlated with m yielding 14.3 T/mB for the
hyperfine coupling constant.",0810.2908v1
2008/12/4,Exchange bias and its phase reversal in the zero magnetization admixed rare earth intermetallics,"Exchange bias effect is an important attribute in several device
applications. Traditionally, it is discussed as a form of exchange anisotropy
at the interface between the ferromagnetic/antiferromagnetic layers of two
distinct systems. We report here on the magnetically ordered alloys possessing
the feature of unidirectional anisotropy, which reverses its sign across a
characteristic temperature. These are admixed rare earth intermetallics,
comprising two dissimilar rare earth (RE) ions, belonging to the two different
halves of the 4f-series and imbibing the notion of ferromagnetic coupling
between the spins of all 4f-rare earth ions and that of the conduction
electrons. Magnetic moments of dissimilar RE ions in such admixed alloys,
however, get antiferromagnetically coupled and they display magnetic
compensation feature such that the field induced reversal in the orientation of
the magnetic moments of dissimilar rare earth ions happens across the
compensation temperature (Tcomp). Above a threshold field, the conduction
electron polarization also reverses its sign across Tcomp, this is argued to
correlate with the observed phase reversal in the exchange bias field.",0812.0929v1
2008/12/12,Magnetic tunnel junctions with ferroelectric barriers: Prediction of four resistance states from first-principles,"Magnetic tunnel junctions (MTJs), composed of two ferromagnetic electrodes
separated by a thin insulating barrier layer, are currently used in spintronic
devices, such as magnetic sensors and magnetic random access memories.
Recently, driven by demonstrations of ferroelectricity at the nanoscale,
thin-film ferroelectric barriers were proposed to extend the functionality of
MTJs. Due to the sensitivity of conductance to the magnetization alignment of
the electrodes (tunnelling magnetoresistance) and the polarization orientation
in the ferroelectric barrier (tunnelling electroresistance), these multiferroic
tunnel junctions (MFTJs) may serve as four-state resistance devices. Based on
first-principles calculations we demonstrate four resistance states in
SrRuO3/BaTiO3/SrRuO3 MFTJs with asymmetric interfaces. We find that the
resistance of such a MFTJ is significantly changed when the electric
polarization of the barrier is reversed and/or when the magnetizations of the
electrodes are switched from parallel to antiparallel. These results reveal the
exciting prospects of MFTJs for application as multifunctional spintronic
devices.",0812.2393v1
2009/1/15,Spin injection in Silicon at zero magnetic field,"In this letter, we show efficient electrical spin injection into a SiGe based
\textit{p-i-n} light emitting diode from the remanent state of a
perpendicularly magnetized ferromagnetic contact. Electron spin injection is
carried out through an alumina tunnel barrier from a Co/Pt thin film exhibiting
a strong out-of-plane anisotropy. The electrons spin polarization is then
analysed through the circular polarization of emitted light. All the light
polarization measurements are performed without an external applied magnetic
field \textit{i.e.} in remanent magnetic states. The light polarization as a
function of the magnetic field closely traces the out-of-plane magnetization of
the Co/Pt injector. We could achieve a circular polarization degree of the
emitted light of 3 % at 5 K. Moreover this light polarization remains almost
constant at least up to 200 K.",0901.2183v1
2009/1/27,Broadband Ferromagnetic Resonance Linewidth Measurement of Magnetic Tunnel Junction Multilayers,"The broadband ferromagnetic resonance (FMR) linewidth of the free layer of
magnetic tunnel junctions is used as a simple diagnostic of the quality of the
magnetic structure. The FMR linewidth increases near the field regions of free
layer reversal and pinned layer reversal, and this increase correlates with an
increase in magnetic hysteresis in unpatterned films, low frequency noise in
patterned devices, and previous observations of magnetic domain ripple by use
of Lorentz microscopy. Postannealing changes the free layer FMR linewidth
indicating that considerable magnetic disorder, originating in the
exchange-biased pinned layer, is transferred to the free layer.",0901.4196v1
2009/2/8,Magnetic and magnetoelectric studies in pure and cation doped BiFeO3,"We report magnetic and magnetoelectric studies on BiFeO3 and divalent cation
(A) suvtitute Bi0.7A0.3FeO3 (A = Sr,Ba, and Sr0.5Ba0.5). It is shown that the
rapid increase of magnetization at the Neel temperature (TN = 642 K) is
suppressed in the co-doped compound A = Sr0.5Ba0.5. All the divalent subtituted
compounds show enhanced magnetization and hysteresis loop. Both longitudinal
and transverse magnetoelectric coefficients were measured using the dynamical
lock-in technique. The co-doped compound shows the highest magnetoelectric
coefficient at room temperature although it is not the compound with the
highest saturation magnetization. It is found that as the size of the A-site
cation increses, the transverse magnetoelectric coeffient increases and exceeds
the longitudinal magnetoelectric coefficient. It is suggested that changes in
magnetic domain structure and magnetostriction are possible reasons for the
observed changes in the magnetoelectric coefficients.",0902.1283v1
2009/2/9,Field-induced staggered magnetic moment in the quasi-two-dimensional organic Mott insulator $κ$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Cl,"We investigated the magnetism under a magnetic field in the
quasi-two-dimensional organic Mott insulator
$\kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Cl through magnetization and
$^{13}$C-NMR measurements. We found that in the nominally paramagnetic phase
(i.e., above N\'eel temperature) the field-induced local moments have a
staggered component perpendicular to the applied field. As a result, the
antiferromagnetic transition well defined at a zero field becomes crossover
under a finite field. This unconventional behavior is qualitatively reproduced
by the molecular-field calculation for Hamiltonian including the exchange,
Dzyaloshinsky-Moriya (DM), and Zeeman interactions. This calculation also
explains other unconventional magnetic features in
$\kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Cl reported in the literature. The
present results highlight the importance of the DM interaction in field-induced
magnetism in a nominally paramagnetic phase, especially in low-dimensional spin
systems.",0902.1431v1
2009/2/9,Magnetization reversal via internal spin waves in magnetic nanoparticles,"By numerically solving the equations of motion for atomic spins we show that
internal spin-wave processes in large enough magnetic particles, initially in
unstable states, lead to complete magnetization reversal and thermalization.
The particle's magnetization strongly decreases in the middle of reversal and
then recovers. We identify two main scenarios, exponential and linear spin-wave
instabilities. For the latter, the longitudinal and transverse relaxation rates
have been obtained analytically. Orientation dependence of these rates leads to
a nonexponential relaxation of the particle's magnetization at long times.",0902.1492v1
2009/2/19,Training Induced Positive Exchange Bias in NiFe/IrMn Bilayers,"Positive exchange bias has been observed in the
Ni$_{81}$Fe$_{19}$/Ir$_{20}$Mn$_{80}$ bilayer system via soft x-ray resonant
magnetic scattering. After field cooling of the system through the blocking
temperature of the antiferromagnet, an initial conventional negative exchange
bias is removed after training i. e. successive magnetization reversals,
resulting in a positive exchange bias for a temperature range down to 30 K
below the blocking temperature (450 K). This new manifestation of magnetic
training is discussed in terms of metastable magnetic disorder at the
magnetically frustrated interface during magnetization reversal.",0902.3427v3
2009/2/25,Magnetic and magnetoelectric excitations in TbMnO$_3$,"Magnetic and magnetoelectric excitations in the multiferroic TbMnO_3 have
been investigated at terahertz frequencies. Using different experimental
geometries we can clearly separate the electro-active excitations
(electromagnons) from the magneto-active modes, i.e. antiferromagnetic
resonances (AFMR). Two AFMR resonances were found to coincide with
electromagnons. This indicates that both excitations belong to the same mode
and the electromagnons can be excited by magnetic ac-field as well. In external
magnetic fields and at low temperatures distinct fine structure of the
electromagnons appears. In spite of the 90^o rotation of the magnetic
structure, the electromagnons are observable for electric ac-fields parallel to
the a-axis only. Contrary to simple expectations, the response along the c-axis
remains purely magnetic in nature.",0902.4382v1
2009/3/5,Signature of magnetic monopole and Dirac string dynamics in spin ice,"Magnetic monopoles have eluded experimental detection since their prediction
nearly a century ago by Dirac. Recently it has been shown that classical
analogues of these enigmatic particles occur as excitations out of the
topological ground state of a model magnetic system, dipolar spin ice. These
quasi-particle excitations do not require a modification of Maxwell's
equations, but they do interact via Coulombs law and are of magnetic origin. In
this paper we present an experimentally measurable signature of monopole
dynamics and show that magnetic relaxation measurements in the spin ice
material $Dy_{2}Ti_{2}O_{7}$ can be interpreted entirely in terms of the
diffusive motion of monopoles in the grand canonical ensemble, constrained by a
network of ""Dirac strings"" filling the quasi-particle vacuum. In a magnetic
field the topology of the network prevents charge flow in the steady state, but
there is a monopole density gradient near the surface of an open system.",0903.1074v3
2009/3/13,Why magnetism in CeO$_{1-x}$F$_x$FeAs and LaO$_{1-x}$F$_x$FeAs is different,"Using state-of-the-art first-principles calculations we study the magnetic
behaviour of CeOFeAs. We find the Ce layer moments oriented perpendicular to
those of the Fe layers. An analysis of incommensurate magnetic structures
reveals that the Ce-Ce magnetic coupling is rather weak with, however, a strong
Fe-Ce coupling. Comparison of the origin of the tetragonal to orthorhombic
structural distortion in CeOFeAs and LaOFeAs show marked differences; in
CeOFeAs the distortion is stabilized by a lowering of spectral weight at the
Fermi level, while in LaOFeAs by a reduction in magnetic frustration. Finally,
we investigate the impact of electron doping upon CeOFeAs and show that while
the ground state Fe moment remains largely unchanged by doping, the stability
of magnetic order goes to zero at a doping that corresponds well to the
vanishing of the N\'eel temperature.",0903.2356v1
2009/4/11,"Magnetic behavior of nano crystals of a spin-chain system, Ca3Co2O6: Absence of multiple steps in the low temperature isothermal magnetization","We report that the major features in the temperature dependence of dc and ac
magnetization of a well-known spin-chain compound, Ca3Co2O6, which has been
known to exhibit two complex magnetic transitions due to geometrical
frustration (one near 24 K and the other near 10 K), are found to be
qualitatively unaffected in its nano form synthesized by high-energy
ball-milling. However, the multiple steps in isothermal magnetization - a topic
of current interest in low-dimensional systems - known for the bulk form well
below 10 K is absent in the nano particles. We believe that this finding will
be useful to the understanding of the 'step' magnetization behavior of such
spin-chain systems.",0904.1813v1
2009/5/5,Photoinduced magnetization change in multiferroic YbFe2O4,"We have studied the influence of laser illumination on the magnetization in
multiferroic YbFe2O4 single crystals. A photoinduced magnetization change has
been confirmed in both ab plane and c axis direction. The temperature
dependence of the photoinduced magnetization reduction excludes laser heating
as the cause. In terms of the breakdown of charge order driven by laser
illumination, the photoinduced magnetization change provides a strong evidence
for the spin-charge coupling in YbFe2O4. This photomagnetic effect based on
charge-order-induced multiferroicity could be used for non-thermal optical
control of magnetization.",0905.0569v1
2009/6/9,Unified nonequilibrium dynamical theory for exchange bias and training effects,"We investigate the exchange bias and training effects in the FM/AF
heterostructures using a unified Monte Carlo dynamical approach. This real
dynamical method has been proved reliable and effective in simulating dynamical
magnetization of nanoscale magnetic systems. The magnetization of the
uncompensated AF layer is still open after the first field cycling is finished.
Our simulated results show obvious shift of hysteresis loops (exchange bias)
and cycling dependence of exchange bias (training effect) when the temperature
is below 45 K. The exchange bias fields decrease with decreasing the cooling
rate or increasing the temperature and the number of the field cycling. With
the simulations, we show the exchange bias can be manipulated by controlling
the cooling rate, the distributive width of the anisotropy energy, or the
magnetic coupling constants. Essentially, these two effects can be explained on
the basis of the microscopical coexistence of both reversible and irreversible
moment reversals of the AF domains. Our simulated results are useful to really
understand the magnetization dynamics of such magnetic heterostructures. This
unified nonequilibrium dynamical method should be applicable to other exchange
bias systems.",0906.1753v1
2009/6/16,Stoner ferromagnetic phase of a graphene in the presence of an in-plane magnetic field,"We study the effects of an in-plane magnetic field on the ground state
properties of both gapless and gapped graphene sheets within Random Phase
Approximation. The critical magnetic field which leads to a fully spin
polarized phase increases by decreasing the carrier density at zero gap
indicating that no spontaneous magnetic phase transition occurs. However, at
large energy gap values it decreases by decreasing the density. We find a
continuous quantum magnetic phase transition (Stoner phase) for Dirac fermions
in a doped graphene sheet. Novel in-plane magnetic field dependence of the
charge and spin susceptibilities are uncovered.",0906.2882v2
2009/6/17,"Microscopic mechanism of the non-crystalline anisotropic magnetoresistance in (Ga,Mn)As","Starting with a microscopic model based on the Kohn-Luttinger Hamiltonian and
kinetic p-d exchange combined with Boltzmann formula for conductivity we
identify the scattering from magnetic Mn combined with the strong spin-orbit
interaction of the GaAs valence band as the dominant mechanism of the
anisotropic magnetoresistance (AMR) in (Ga,Mn)As. This fact allows to construct
a simple analytical model of the AMR consisting of two heavy-hole bands whose
charge carriers are scattered on the impurity potential of the Mn atoms. The
model predicts the correct sign of the AMR (resistivity parallel to
magnetization is smaller than perpendicular to magnetization) and identifies
its origin arising from the destructive interference between electric and
magnetic part of the scattering potential of magnetic ionized Mn acceptors when
the carriers move parallel to the magnetization.",0906.3151v1
2009/6/20,Persistent current in a mesoscopic cylinder: effects of radial magnetic field,"In this work, we study persistent current in a mesoscopic cylinder subjected
to both longitudinal and transverse magnetic fluxes. A simple tight-binding
model is used to describe the system, where all the calculations are performed
exactly within the non-interacting electron picture. The current $I$ is
investigated numerically concerning its dependence on total number of electrons
$N_e$, system size $N$, longitudinal magnetic flux $\phi_l$ and transverse
magnetic flux $\phi_t$. Quite interestingly we observe that typical current
amplitude oscillates as a function of the transverse magnetic flux, associated
with the energy-flux characteristics, showing $N \phi_0$ flux-quantum
periodicity, where $N$ and $\phi_0$ $(=ch/e)$ correspond to the system size and
the elementary flux-quantum respectively. This analysis may provide a new
aspect of persistent current for multi-channel cylindrical systems in the
presence of radial magnetic field $B_r$, associated with the flux $\phi_t$.",0906.3795v1
2009/6/26,Magnetic behavior of nanocrystalline ErCo2,"We have investigated the magnetic behavior of the nanocrystalline form of a
well-known Laves phase compound, ErCo2 - the bulk form of which has been known
to undergo an interesting first-order ferrimagnetic ordering near 32 K -
synthesized by high-energy ball-milling. It is found that, in these
nanocrystallites, Co exhibits ferromagnetic order at room temperature as
inferred from the magnetization data. However, the magnetic transition
temperature for Er sublattice remains essentially unaffected as though the
(Er)4f-Co(3d) coupling is weak on Er magnetism. The net magnetic moment as
measured at high fields, sat at 120 kOe, is significantly reduced with respect
to that for the bulk in the ferrimagnetically ordered state and possible
reasons are outlined. We have also compared the magnetocaloric behavior for the
bulk and the nano particles.",0906.4889v1
2009/7/23,Large specific absorption rates in the magnetic hyperthermia properties of metallic iron nanocubes,"We report on the magnetic hyperthermia properties of chemically synthesized
ferromagnetic 11 and 16 nm Fe(0) nanoparticles of cubic shape displaying the
saturation magnetization of bulk iron. The specific absorption rate measured on
16 nm nanocubes is 1690+-160 W/g at 300 kHz and 66 mT. This corresponds to
specific losses-per-cycle of 5.6 mJ/g, largely exceeding the ones reported in
other systems. A way to quantify the degree of optimization of any system with
respect to hyperthermia applications is proposed. Applied here, this method
shows that our nanoparticles are not fully optimized, probably due to the
strong influence of magnetic interactions on their magnetic response. Once
protected from oxidation and further optimized, such nano-objects could
constitute efficient magnetic cores for biomedical applications requiring very
large heating power.",0907.4063v3
2009/8/20,MnSi$_{1.7}$ nanoparticles embedded in Si: Superparamagnetism with a collective behavior,"The doping of Mn in Si is attracting research attentions due to the
possibility to fabricate Si-based diluted magnetic semiconductors. However, the
low solubility of Mn in Si favors the precipitation of Mn ions even at
non-equilibrium growth conditions. MnSi$_{1.7}$ nanoparticles are the common
precipitates, which show exotic magnetic properties in comparison with the
MnSi$_{1.7}$ bulk phase. In this paper we present the static and dynamic
magnetic properties of MnSi$_{1.7}$ nanoparticles. Using the Preisach model, we
derive the magnetic parameters, such as the magnetization of individual
particles, the distribution of coercive fields and the inter-particle
interaction field. Time-dependent magnetization measurements reveal a
spin-glass behavior of the system.",0908.2906v3
2009/9/25,Proximal magnetometry of monolayers of single molecule magnets on gold using polarized muons,"The magnetic properties of a monolayer of Fe4 single molecule magnets grafted
onto a Au (111) thin film have been investigated using low energy muon spin
rotation. The properties of the monolayer are compared to bulk Fe4. We find
that the magnetic properties in the monolayer are consistent with those
measured in the bulk, strongly indicating that the single molecule magnet
nature of Fe4 is preserved in a monolayer. However, differences in the
temperature dependencies point to a small difference in their energy scale. We
attribute this to a ~60% increase in the intramolecular magnetic interactions
in the monolayer.",0909.4634v1
2009/10/20,"Sharp fall of electrical resistance for a small application of magnetic field on a metastable form of a compound, Tb5Si3, under pressure","We report an unusual sensitivity of electrical resistivity (rho) to an
application of a small magnetic field in an intermetallic compound, Tb5Si3,
under pressure. In this compound, there is a magnetic field-induced first-order
magnetic transition at 1.8 K. Under pressure, there is a metastable magnetic
phase after reducing the field to zero. This metastable phase is relatively of
higher rho and interestingly a small magnetic field (less than 2 kOe) in the
reverse direction results in a sharp fall of rho to restore virgin state rho.
The present finding could be relevant to spintronic applications.",0910.3794v1
2009/10/24,Measuring the magnetization of three monolayer thick Co islands and films by X-ray dichroism,"Co islands and films are characterized by x-ray magnetic circular dichroism
photoemission electron microscopy (XMCD-PEEM). The spatial resolution
capabilties of the technique together with atomic growth control permit
obtaining perfectly flat triangular islands with a given thickness (3 ML), very
close to an abrupt spin-reorientation transition. The magnetic domain
configurations are found to depend on island size: while small islands can be
magnetized in a single-domain state, larger islands show more complex patterns.
Furthermore, the magnetization pattern of the larger islands presents a common
chirality. By means of dichroic spectro-microscopy at the Co L absorption
edges, an experimental estimate of the ratio of the spin- and orbital magnetic
moment for three monolayer thick films is obtained.",0910.4687v1
2009/11/1,Asymmetric hysteresis of Néel caps in flux-closure magnetic dots,"We investigated with XMCD-PEEM magnetic imaging the magnetization reversal
processes of N\'eel caps inside Bloch walls in self-assembled, micron-sized
Fe(110) dots with flux-closure magnetic state. In most cases the
magnetic-dependent processes are symmetric in field, as expected. However, some
dots show pronounced asymmetric behaviors. Micromagnetic simulations suggest
that the geometrical features (and their asymmetry) of the dots strongly affect
the switching mechanism of the N\'eel caps.",0911.0204v1
2009/11/3,Competing magnetic interactions in exchange bias modulated films,"The magnetization reversal in stripe-like exchange bias patterned $\rm
Ni_{81}Fe_{19}/IrMn$ thin films was investigated by complementary inductive and
high resolution magneto optical magnetometry, magneto optical Kerr microscopy,
and polarized neutron reflectometry to clarify the effects of competing
interfacial exchange bias and lateral interface contributions. Structures of
varying ferromagnetic layer thickness and stripe period were analyzed
systematically at the frozen-in domain state of oppositely aligned stripe
magnetization. For all samples the mean magnetization of the magnetic hybrid
structures was found to be aligned nearly orthogonally with respect to the
stripe axis and the set exchange bias direction. Due to the interaction of
interfacial coupling, exchange, and magneto-static energy contributions, the
opening angle of neighboring stripe magnetizations increases with decreasing
ferromagnetic layer thickness and increasing stripe period. The experimental
observations are in agreement with an earlier proposed model for designing
micro-patterned exchange bias films.",0911.0559v1
2009/11/22,Electronic structure and magnetic properties of Ni0.2Cd0.3Fe2.5-xAlxO4 (x = 0.0 - 0.4) ferrite nanoparticles,"Structural, magnetic and electronic structural properties of
Ni0.2Cd0.3Fe2.5-xAlxO4 ferrites nanoparticles have been studied x-ray
diffraction (XRD), transmission electron microscopy (TEM), dc magnetization,
and near edge x-ray absorption fine structure spectroscopy (NEXAFS)
measurements. Nanoparticles of Ni0.2Cd0.3Fe2.5-xAlxO4 (x = 0.0 - 0.4) ferrite
were synthesized using sol-gel method. The XRD and TEM measurements show that
all samples have single phase nature with cubic structure and have
nanocrystalline behavior. From the XRD and TEM analysis, it is observed that
particle size increases with Al doping. DC magnetization measurements infer
that magnetic moment decreases whereas blocking temperature increases with
increase in Al doping. It is observed that the magnetic moment decreases with
Al doping which may be due to the dilution of the sublattice by the doping of
Al ions. The NEXAFS measurements performed at room temperature indicates that
Fe exist in mixed valence state.",0911.4227v1
2009/11/30,Absence of localized-spin magnetism in the narrow-gap semiconductor FeSb2,"We report inelastic neutron scattering measurements aimed at investigating
the origin of the temperature-induced paramagnetism in the narrow-gap
semiconductor FeSb2. We find that inelastic response for energies up to 60 meV
and at temperatures 4.2 K, 300 K and 550 K is essentially consistent with the
scattering by lattice phonon excitations. We observe no evidence for a
well-defined magnetic peak corresponding to the excitation from the
non-magnetic S = 0 singlet ground state to a state of magnetic multiplet in the
localized spin picture. Our data establish the quantitative limit of S_{eff}^2
< 0.25 on the fluctuating local spin. However, a broad magnetic scattering
continuum in the 15 meV to 35 meV energy range is not ruled out by our data.
Our findings make description in terms of the localized Fe spins unlikely and
suggest that paramagnetic susceptibility of itinerant electrons is at the
origin of the temperature-induced magnetism in FeSb2.",0911.5699v3
2009/12/1,A common magnetic origin for the Invar effects in fcc iron-based ferromagnets,"Using first-principles calculations, in conjunction with Ising magnetism, we
undertake a theoretical study to elucidate the origin of the experimentally
observed Invar effects in disordered fcc iron-based ferromagnets. First, we
show that our theory can account for the Invar effects in iron-nickel alloys,
the anomalies being driven by the magnetic contributions to the average free
energies. Second, we present evidence indicating that the relationship between
thermal expansion and magnetism is essentially the same in all the studied
alloys, including those which display the Invar effect and those which do not.
Hence we propose that magnetism plays a crucial role in determining whether a
system exhibits normal thermal expansion, the Invar effect, or something else.
The crucial determining factor is the rate at which the relative orientation of
the local magnetic moments of nearest-neighbor iron atoms fluctuates as the
system is heated.",0912.0215v4
2010/1/5,Magnetic frustration in an iron based Cairo pentagonal lattice,"The Fe3+ lattice in the Bi2Fe4O9 compound is found to materialize the first
analogue of a magnetic pentagonal lattice. Due to its odd number of bonds per
elemental brick, this lattice, subject to first neighbor antiferromagnetic
interactions, is prone to geometric frustration. The Bi2Fe4O9 magnetic
properties have been investigated by macroscopic magnetic measurements and
neutron diffraction. The observed non-collinear magnetic arrangement is related
to the one stabilized on a perfect tiling as obtained from a mean field
analysis with direct space magnetic configurations calculations. The
peculiarity of this structure arises from the complex connectivity of the
pentagonal lattice, a novel feature compared to the well-known case of
triangle-based lattices.",1001.0710v1
2010/1/8,Low-magnetic-field control of dielectric constant at room temperature realized in Ba0.5Sr1.5Zn2Fe12O22,"We show that room temperature resistivity of Ba0.5Sr1.5Zn2Fe12O22 single
crystals increases by more than three orders of magnitude upon being subjected
to optimized heat treatments. The increase in the resistivity allows the
determination of magnetic field (H)-induced ferroelectric phase boundaries up
to 310 K through the measurements of dielectric constant at a frequency of 10
MHz. Between 280 and 310 K, the dielectric constant curve shows a peak centered
at zero magnetic field and thereafter decreases monotonically up to 0.1 T,
exhibiting a magnetodielectric effect of 1.1%. This effect is ascribed to the
realization of magnetic field-induced ferroelectricity at an H value of less
than 0.1 T near room temperature. Comparison between electric and magnetic
phase diagrams in wide temperature- and field-windows suggests that the
magnetic field for inducing ferroelectricity has decreased near its helical
spin ordering temperature around 315 K due to the reduction of spin anisotropy
in Ba0.5Sr1.5Zn2Fe12O22.",1001.1319v1
2010/1/14,Alfven node-free vibrations of white dwarf in the model of solid star with toroidal magnetic field,"In the context of the white dwarf asteroseismology, we investigate
vibrational properties of a non-convective solid star with an axisymmetric
purely toroidal intrinsic magnetic field of two different shapes. Focus is laid
on regime of node-free global Lorentz-force-driven vibrations about symmetry
axis at which material displacements have one and the same form as those for
nodeless spheroidal and torsional vibrations restored by Hooke's force of
elastic shear stresses. Particular attention is given to the even-parity
poloidal Alfven modes whose frequency spectra are computed in analytic form
showing how the purely toroidal magnetic fields completely buried beneath the
star surface can manifest itself in seismic vibrations of non-magnetic white
dwarfs. The obtained spectral formulae are discussed in juxtaposition with
those for Alfven modes in the solid star model with the poloidal, homogeneous
internal and dipolar external, magnetic field whose inferences are relevant to
Alfven vibrations in magnetic white dwarfs.",1001.2424v2
2010/1/15,On Using Magnetic and optical methods to determine the size and characteristics of nanoparticles embedded in oxide semiconductors,"Films of oxides doped with transition metals are frequently believed to have
magnetic inclusions. Magnetic methods to determine the amount of nanophases and
their magnetic characteristics are described. The amount of the sample that is
paramagnetic may also be measured. Optical methods are described and shown to
be very powerful to determine which defects are also magnetic.",1001.2674v1
2010/1/27,"Coupled structural and magnetic properties of ferric fluoride nanostructures: part II, a Monte-Carlo Heisenberg study","We present a numerical study of the magnetic structure of nanostructured iron
fluoride, using the Monte-Carlo-Metropolis simulated annealing technique and a
classical Heisenberg Hamiltonian with a superexchange angle dependence. The
parameters are adjusted on experimental results, and the atomic structure and
topology taken from a previous atomistic model of grain boundaries in the same
system. We find perfect antiferromagnetic crystalline grains and a disordered
magnetic configuration (speromagnetic like) at the grain boundary, in agreement
with experimental findings. Both the lowest magnetic energy and the rate of
magnetic frustration are found to be dependent on the relative disorientation
of crystalline grains, i.e. on the cationic topology. By simulating hysteresis
loops, we find that the magnetization rotation is not spatially uniform. We
conclude on possible extensions of the model.",1001.4959v1
2010/1/28,Magnetic phase stability of monolayers: Fe on Ta(x)W(1-x) (001) random alloy as a case study,"We present a new approach to study the magnetic phase stability of magnetic
overlayers on nonmagnetic substrates. The exchange integrals among magnetic
atoms in the overlayer are estimated in the framework of the adiabatic
approximation and used to construct the effective classical two-dimensional
Heisenberg Hamiltonian. Its stability is then studied with respect to a large
number of collinear and non-collinear magnetic arrangements which include, as
special cases, not only ferromagnetic and various antiferromagnetic
configurations, but also possible incommensurate spin-spiral structures. This
allows us to investigate a broader class of systems than a conventional total
energy search based on few, subjectively chosen configurations. As a case study
we consider the Fe-monolayer on the random nonmagnetic bcc-Ta(x)W(1-x) (001)
surface which was studied recently by a conventional approach. We have found a
crossover of the ground state of the Fe monolayer from the ferromagnet on the
Ta surface to the c(2x2) antiferromagnet on the W surface and that at the
composition with about 20 % of Ta an incommensurate magnetic configuration
might exist.",1001.5126v1
2010/2/5,XYZ-polarisation analysis of diffuse magnetic neutron scattering from single crystals,"Studies of diffuse magnetic scattering largely benefit from the use of a
multi-detector covering wide scattering angles. Therefore, the different
contributions to the diffuse scattering that originate from magnetic, nuclear
coherent, and nuclear spin-incoherent scattering can be separated by the
so-called XYZ-polarization analysis. In the past this method has been
successfully applied to the analysis of diffuse scattering by polycrystalline
samples of magnetic disordered materials. Single crystal studies that exploit
the vector properties of spin correlations are of particular interest for
furthering our understanding of frustration effects in magnetism. Based on the
symmetry properties of polarised scattering a suitable extension of the
conventional XYZ method has been derived, which allows for the complete
separation and the analysis of features of diffuse magnetic scattering from
single crystals.",1002.1228v2
2010/2/5,Direct observation of Oersted-field-induced magnetization dynamics in magnetic nanostripes,"We have used time-resolved x-ray photoemission electron microscopy to
investigate the magnetization dynamics induced by nanosecond current pulses in
NiFe/Cu/Co nanostripes. A large tilt of the NiFe magnetization in the direction
transverse to the stripe is observed during the pulses. We show that this
effect cannot be quantitatively understood from the amplitude of the Oersted
field and the shape anisotropy. High frequency oscillations observed at the
onset of the pulses are attributed to precessional motion of the NiFe
magnetization about the effective field. We discuss the possible origins of the
large magnetization tilt and the potential implications of the static and
dynamic effects of the Oersted field on current-induced domain wall motion in
such stripes.",1002.1302v3
2010/3/9,Effect of induced shape anisotropy on magnetic properties of ferromagnetic cobalt nanocubes,"We report on the synthesis of ferromagnetic cobalt nanocubes of various sizes
using thermal pyrolysis method and the effect of shape anisotropy on the static
and dynamic magnetic properties were studied. Shape anisotropy of approximately
10 % was introduced in nanocubes by making nanodiscs using a linear chain amine
surfactant during synthesis process. It has been observed that, ferromagnetism
persisted above room temperature and a sharp drop in magnetic moment at low
temperatures in zero-field cooled magnetization may be associated with the spin
disorder due to the effective anisotropy present in the system. Dynamic
magnetic properties were studied using RF transverse susceptibility
measurements at different temperatures and the singularities due to anisotropy
fields were probed at low temperatures. Symmetrically located broad peaks are
observed in the frozen state at the effective anisotropy fields and the peak
structure is strongly affected by shape anisotropy and temperature.
Irrespective of size the shape anisotropy gave rise to higher coercive fields
and larger transverse susceptibility ratio at all temperatures. The role of
shape anisotropy and the size of the particles on the observed magnetic
behaviour were discussed.",1003.1855v1
2010/3/19,Magnetic ordering and magnetodielectric phenomena in CoSeO$_4$,"CoSeO$_4$ has a structure consisting of edge-sharing chains of Co$^{2+}$
octahedra which are held together by SeO$_4^{2-}$ tetrahedra via shared oxygen
atoms at the edges of the octahedra. DC magnetization measurements indicate a
transition to an ordered state below 30 K. Powder neutron diffraction
refinements suggest an ordered state with two unique antiferrromagnetic chains
within the unit cell. Isothermal magnetization measurements indicate a
temperature-dependent field-induced magnetic transition below the ordering
temperature. From neutron diffraction, we find this corresponds to a
realignment of spins from the canted configuration towards the c-axis. The
dielectric constant shows a change in slope at the magnetic ordering
temperature as well as a quadratic dependence on the external magnetic field.",1003.3702v1
2010/4/21,"Effect of pressure on the magnetic, transport, and thermal-transport properties of the electron-doped manganite CaMn$_{1-x}$Sb$_{x}$O$_{3}$","We have demonstrated the effect of hydrostatic pressure on magnetic and
transport properties, and thermal transport properties in electron-doped
manganites CaMn$_{1-x}$Sb$_{x}$O$_{3}$. The substitution of Sb$^{5+}$ ion for
Mn $^{4+}$site of the parent matrix causes one-electron doping with the
chemical formula CaMn$^{4+}_{1-2x}$Mn$^{3+}_{x}$Sb$^{5+}_{x}$O$_{3}$
accompanied by a monotonous increase in unit cell volume as a function of $x$.
Upon increasing the doping level of Sb, the magnitudes of both electrical
resistivity and negative Seebeck coefficient are suppressed at high
temperatures, indicating the electron doping. Anomalous diamagnetic behaviors
at $x=0.05$ and 0.08 are clearly observed in field cooled dc magnetization. The
effect of hydrostatic pressure on dc magnetization is in contrast to the
chemical pressure effect due to Sb doping. The dynamical effect of ac magnetic
susceptibility measurement points to the formation of the magnetically
frustrated clusters such as FM clusters embedded in canted AFM matrix.",1004.3669v3
2010/5/20,Temperature and magnetic field induced structural transformation in Si doped CeFe2: in-field x-ray diffraction study,"Using x-ray powder diffraction technique at various temperatures and applied
magnetic fields, we have studied the magnetostructural properties of
Ce(Fe0.95Si0.05)2. The x-ray diffraction data establish quantitative
relationships between bulk magnetization and the evolution of structurally
distinct phases with magnetic field and temperature, and confirm the distinct
features of first order phase transition like supercooling and superheating,
metastability, and phase co-existence of different structural polymorphs. We
observe the lattice volume mismatch across the structural phase transition,
which appears to be the cause for the step behavior of the magnetization
isotherms at low temperatures. The present study shows that the lattice
distortion has to be treated explicitly, like spin, along with the effects of
lattice-spin coupling to account for the magnetization behavior of this system.
This structure template can resolve the issue of kinetics in this material as
observed in different time scale measurements and with different experimental
protocols.",1005.3662v1
2010/6/18,Magnetic anisotropy in thin films of Prussian blue analogues,"The magnetic anisotropy of thin (~ 200 nm) and thick (~ 2 $\mu$m) films and
of polycrystalline (diameters ~ 60 nm) powders of the Prussian blue analogue
Rb$_{0.7}$Ni$_{4.0}$[Cr(CN)$_6$]$_{2.9} \cdot n$H$_2$O, a ferromagnetic
material with $T_c \sim 70$ K, have been investigated by magnetization, ESR at
50 GHz and 116 GHz, and variable-temperature x-ray diffraction (XRD). The
origin of the anisotropic magnetic response cannot be attributed to the direct
influence of the solid support, but the film growth protocol that preserves an
organized two-dimensional film is important. In addition, the anisotropy does
not arise from an anisotropic g-tensor nor from magneto-lattice variations
above and below $T_c$. By considering effects due to magnetic domains and
demagnetization factors, the analysis provides reasonable descriptions of the
low and high field data, thereby identifying the origin of the magnetic
anisotropy.",1006.3801v2
2010/6/21,Magnetoelectric effects in an organo-metallic quantum magnet,"We observe a bilinear magnetic field-induced electric polarization of 50 $\mu
C/m^2$ in single crystals of NiCl$_2$-4SC(NH$_2$)$_2$ (DTN). DTN forms a
tetragonal structure that breaks inversion symmetry, with the highly polar
thiourea molecules all tilted in the same direction along the c-axis.
Application of a magnetic field between 2 and 12 T induces canted
antiferromagnetism of the Ni spins and the resulting magnetization closely
tracks the electric polarization. We speculate that the Ni magnetic forces
acting on the soft organic lattice can create significant distortions and
modify the angles of the thiourea molecules, thereby creating a magnetoelectric
effect. This is an example of how magnetoelectric effects can be constructed in
organo-metallic single crystals by combining magnetic ions with electrically
polar organic elements.",1006.4122v1
2010/7/15,Stability of edge states and edge magnetism in graphene nanoribbons,"We critically discuss the stability of edge states and edge magnetism in
zigzag edge graphene nanoribbons (ZGNRs). We point out that magnetic edge
states might not exist in real systems, and show that there are at least three
very natural mechanisms - edge reconstruction, edge passivation, and edge
closure - which dramatically reduce the effect of edge states in ZGNRs or even
totally eliminate them. Even if systems with magnetic edge states could be
made, the intrinsic magnetism would not be stable at room temperature. Charge
doping and the presence of edge defects further destabilize the intrinsic
magnetism of such systems.",1007.2602v3
2010/7/27,Spin-ordering and magnetoelastic coupling in the extended Kagome system YBaCo4O7,"Low temperature magnetic and structural behavior of the extended Kagome
system YBaCo4O7 has been studied by single crystal neutron diffraction and
high-resolution powder X-ray diffraction. Long-range magnetic ordering
associated with a structural transition from orthorhombic Pbn2_1 to monoclinic
P2_1 symmetry has been found at T_1 ~ 100 K. The interplay between the
structural and magnetic degrees of freedom testifies that the degeneracy of the
magnetic ground state, present in the orthorhombic phase, is lifted through a
strong magnetoelastic coupling, as observed in other frustrated systems. At T_2
~ 60 K, an additional magnetic transition is observed, though iso-symmetric.
Models for the magnetic structures below T_1 and T_2 are presented, based on
refinements using a large number of independent reflections. The results
obtained are compared with previous single crystal and powder diffraction
studies on this and related compositions.",1007.4683v1
2010/7/27,Magnetic interaction at an interface between manganite and other transition metal oxides,"A general consideration is presented for the magnetic interaction at an
interface between a perovskite manganite and other transition metal oxides. The
latter is specified by the electron number $n$ in the $d_{3z^2-r^2}$ level as
$(d_{3z^2-r^2})^n$. Based on the molecular orbitals formed at the interface and
the generalized Hund's rule, the sign of the magnetic interaction is rather
uniquely determined. The exception is when the $d_{3z^2-r^2}$ orbital is
stabilized in the interfacial manganite layer neighboring to a
$(d_{3z^2-r^2})^1$ or $(d_{3z^2-r^2})^2$ system. In this case, the magnetic
interaction is sensitive to the occupancy of the Mn $d_{3z^2-r2}$ orbital. It
is also shown that the magnetic interaction between the interfacial Mn layer
and the bulk region can be changed. Manganite-based heterostructures thus show
a rich magnetic behavior. We also present how to generalize the argument
including $t_{2g}$ orbitals.",1007.4763v1
2010/8/2,Domain wall magnetism in thin films of orthorhombic manganites,"Thin films of orthorhombic TbMnO3, as well as other orthorhombic manganites,
epitaxially grown on cubic SrTiO3 substrates display an induced magnetic moment
that is absent in the bulk (antiferromagnetic) counterpart. Here we show that
there is a clear correlation between the domain microstructure and the induced
magnetic moment in TbMnO3 films on SrTiO3. In addition, the distinct dependence
of the magnetization with the film thickness is not consistent with domain
magnetism and indicates that the domain walls, rather than the domains, are the
origin of the net magnetic moment. Since the orientation of the domain walls
can be designed by the film-substrate relationship and its density can be tuned
with the film thickness, these results represent a significant step forward
towards the design of devices based on domain wall functionality.",1008.0315v4
2010/9/10,Electronic and magnetic properties of superlattices of graphene/graphane nanoribbons with different edge hydrogenation,"Zigzag graphene nanoribbons patterned on graphane are studied using
spin-polarized ab initio calculations. We found that the electronic and
magnetic properties of the graphene/graphane superlattice strongly depends on
the degree of hydrogenation at the interfaces between the two materials. When
both zigzag interfaces are fully hydrogenated, the superlattice behaves like a
freestanding zigzag graphene nanoribbon, and the magnetic ground state is
antiferromagnetic. When one of the interfaces is half hydrogenated, the
magnetic ground state becomes ferromagnetic, and the system is very close to
being a half metal with possible spintronics applications whereas the magnetic
ground state of the superlattice with both interfaces half hydrogenated is
again antiferromagnetic. In this last case, both edges of the graphane
nanoribbon also contribute to the total magnetization of the system. All the
spin-polarized ground states are semiconducting, independent of the degree of
hydrogenation of the interfaces. The ab initio results are supplemented by a
simple tight-binding analysis that captures the main qualitative features. Our
ab initio results show that patterned hydrogenation of graphene is a promising
way to obtain stable graphene nanoribbons with interesting technological
applications.",1009.2026v2
2010/9/10,Electric Field Controlled Magnetic Anisotropy in a Single Molecule,"We have measured quantum transport through an individual Fe$_4$
single-molecule magnet embedded in a three-terminal device geometry. The
characteristic zero-field splittings of adjacent charge states and their
magnetic field evolution are observed in inelastic tunneling spectroscopy. We
demonstrate that the molecule retains its magnetic properties, and moreover,
that the magnetic anisotropy is significantly enhanced by reversible electron
addition / subtraction controlled with the gate voltage. Single-molecule
magnetism can thus be electrically controlled.",1009.2027v1
2010/9/13,Fingerprinting the magnetic behavior of antiferromagnetic nanostructures using remanent magnetization curves,"Antiferromagnetic (AF) nanostructures from Co3O4, CoO and Cr2O3 were prepared
by the nanocasting method and were characterized magnetometrically. The field
and temperature dependent magnetization data suggests that the nanostructures
consist of a core-shell structure. The core behaves as a regular
antiferromagnet and the shell as a two-dimensional diluted antiferromagnet in a
field (2d DAFF) as previously shown on Co3O4 nanowires [Benitez et al., Phys.
Rev. Lett. 101, 097206 (2008)]. Here we present a more general picture on three
different material systems, i.e. Co3O4, CoO and Cr2O3. In particular we
consider the thermoremanent (TRM) and the isothermoremanent (IRM) magnetization
curves as ""fingerprints"" in order to identify the irreversible magnetization
contribution originating from the shells. The TRM/IRM fingerprints are compared
to those of superparamagnetic systems, superspin glasses and 3d DAFFs. We
demonstrate that TRM/IRM vs. H plots are generally useful fingerprints to
identify irreversible magnetization contributions encountered in particular in
nanomagnets.",1009.2324v1
2010/9/28,The Dielectric Response of La0.5Ca0.5-xSrxMnO3 (0.1 <= x <= 0.4) Manganites with Different Magnetic Ground States,"The dielectric behavior of half doped manganites La0.5Ca0.5-xSrxMnO3 (0.1
\leq \times \leq 0.4) with varying magnetic ground states has been studied. The
real part of relative permittivity as a function of temperature
{\epsilon}^'(T), exhibits a maximum around the ferromagnetic (TC) and charge
ordering transition (TCO) temperatures accompanied with high dielectric losses.
The activation energies obtained for x = 0.1 and 0.3 samples below TCO are the
same ~ 0.12eV, whereas the relaxation time constant varies in the range 2.8
\times 10-9 s - 6.03 \times 10-11 s. In contrast to samples having x \leq 0.3,
for x = 0.4 doping the dielectric permittivity exhibits a strong temperature
dependence in the vicinity of magnetic phase transitions. This behavior may be
correlated with the presence of competing magnetic interactions (magnetic
polarons) close to the magnetic transitions.",1009.5460v1
2010/10/6,Itinerant Nature of Atom-Magnetization Excitation by Tunneling Electrons,"We have performed single-atom magnetization curve (SAMC) measurements and
inelastic scanning tunneling spectroscopy (ISTS) on individual Fe atoms on a
Cu(111) surface. The SAMCs show a broad distribution of magnetic moments with
$\unit[3.5]{\mu_{\rm B}}$ being the mean value. ISTS reveals a magnetization
excitation with a lifetime of $\unit[200]{fsec}$ which decreases by a factor of
two upon application of a magnetic field of $\unit[12]{T}$. The experimental
observations are quantitatively explained by the decay of the magnetization
excitation into Stoner modes of the itinerant electron system as shown by newly
developed theoretical modeling.",1010.1284v2
2010/10/15,Magneto-transport in impurity-doped few-layer graphene spin valve,"Using Keldysh nonequilibrium Green's function method we study the
spin-dependent transport through impurity-doped few layer graphene sandwiched
between two magnetic leads with an arbitrary mutual orientations of the
magnetizations. We find for parallel electrodes magnetizations that the
differential conductance possesses two resonant peaks as the applied bias
increases. These peaks are traced back to a buildup of a magnetic moment on the
impurity due to the electrodes spin polarization. For a large mutual angle of
the electrodes magnetization directions, the two resonant peaks approach each
others and merge into a single peak for antiparallel orientation of the
electrodes magnetizations. We point out that the tunneling magnetoresistance
(TMR) may change sign for relatively small changes in the values of the
polarization parameters. Furthermore, we inspect the behaviour of the
differential conductance and TMR upon varying the temperature.",1010.3145v1
2010/11/11,Structural and magnetic properties of Co-Mn-Sb thin films,"Thin Co-Mn-Sb films of different compositions were investigated and utilized
as electrodes in alumina based magnetic tunnel junctions with CoFe counter
electrode. The preparation conditions were optimized with respect to magnetic
and structural properties. The Co-Mn-Sb/Al-O interface was analyzed by X-ray
absorption spectroscopy and magnetic circular dichroism with particular focus
on the element-specific magnetic moments. Co-Mn-Sb crystallizes in different
complex cubic structures depending on its composition. The magnetic moments of
Co and Mn are ferromagnetically coupled in all cases. A tunnel magneto
resistance ratio of up to 24 % at 13K was found and indicates that Co-Mn-Sb is
not a ferromagnetic half-metal. These results are compared to recent works on
the structure and predictions of the electronic properties.",1011.2663v1
2010/11/17,Confirmation of room-temperature long range magnetic order in GaN:Mn,"We propose a method for nano-scale characterization of long range magnetic
order in diluted magnetic systems to clarify the origins of the room
temperature ferromagnetism. The GaN:Mn thin films are grown by metal-organic
chemical vapor deposition with the concentration of Ga-substitutional Mn up to
3.8%. Atomic force microscope (AFM) and magnetic force microscope (MFM)
characterizations are performed on etched artificial microstructures and
natural dislocation pits. Numerical simulations and theoretical analysis on the
AFM and MFM data have confirmed the formation of long range magnetic order and
ruled out the possibility that nano-clusters contributed to the ferromagnetism.
We suggest that delocalized electrons might play a role in the establishment of
this long range magnetic order.",1011.3937v1
2010/11/30,Magnetic and multiferroic phases of single-crystalline Mn$_{0.85}$Co$_{0.15}$WO$_4$,"The magnetic and multiferroic phase diagram of Mn$_{0.85}$Co$_{0.15}$WO$_4$
single crystals is investigated by means of magnetic, heat capacity,
dielectric, polarization, and neutron scattering experiments. Three magnetic
phase transitions are detected through distinct anomalies in all physical
quantities. The ferroelectric polarization is observed only along the b-axis
below 10 K but not along the a-axis as recently suggested. The magnetic phases
studied by neutron scattering are very complex. Up to four different magnetic
structures, partially coexisting at certain temperature ranges, have been
identified. Upon decreasing temperature two commensurate phases (AF4, AF1) are
followed by an incommensurate phase (AF5) and a second incommensurate phase
(AF2) is detected as a minor phase. The ferroelectric polarization is possibly
associated with both (AF2 and AF5) phases.",1011.6643v1
2010/11/30,Robust Ferroelectric State in Multiferroic Mn$_{1-x}$Zn$_x$WO$_4$,"We report the remarkably robust ferroelectric state in the multiferroic
compound Mn$_{1-x}$Zn$_x$WO$_4$. The substitution of the magnetic Mn$^{2+}$
with nonmagnetic Zn$^{2+}$ reduces the magnetic exchange and provides control
of the various magnetic and multiferroic states of MnWO$_4$. Only 5 % of Zn
substitution results in a complete suppression of the frustrated collinear
(paraelectric) low temperature phase. The helical magnetic and ferroelectric
phase develops as the ground state. The multiferroic state is stable up to a
high level of substitution of more than 50 %. The magnetic, thermodynamic, and
dielectric properties as well as the ferroelectric polarization of single
crystals of Mn$_{1-x}$Zn$_x$WO$_4$ are studied for different substitutions up
to x=0.5. The magnetic phases have been identified in single crystal neutron
scattering experiments. The ferroelectric polarization scales with the neutron
intensity of the incommensurate peak of the helical phase.",1011.6645v2
2010/12/6,Ab-initio description of the magnetic shape anisotropy due to the Breit interaction,"A quantum-mechanical description of the magnetic shape anisotropy, that is
usually ascribed to the classical magnetic dipole-dipole interaction, has been
developed. This is achieved by including the Breit-interaction, that can be
seen as an electronic current-current interaction in addition to the
conventional Coulomb interaction, within fully relativistic band structure
calculations. The major sources of the magnetic anisotropy, spin-orbit coupling
and the Breit-interaction, are treated coherently this way. This seems to be
especially important for layered systems for which often both sources
contribute with opposite sign to the magnetic anisotropy energy. Applications
to layered transition metal systems are presented to demonstrate the
implications of this new approach in treating the magnetic shape anisotropy.",1012.1115v1
2010/12/9,The magnetocaloric and barocaloric effects in Gd5Si2Ge2 compound,"The caloric effect in Gd5Si2Ge2 compound is studied experimentally and
theoretically. The first-order phase transition is sensitive to both magnetic
field and pressure. It indicates that the influences of magnetic field and
pressure on the phase transition are virtually equivalent. Moreover, the
theoretical analyses reveal that the total entropy change is almost definite at
a certain Curie temperature whether the applied external field is magnetic
field or pressure. On the basis of theoretical analyses, the entropy change
simultaneously induced by magnetic field and hydrostatic pressure can be
obtained experimentally. As for Gd5Si2Ge2 compound, the entropy change curve is
broadened dramatically, and the refrigerant capacity is improved from 284.7 to
447.0 J/kg. Additionally, the required magnetic field in magnetic refrigeration
technique may be reduced by the application of hydrostatic pressure.",1012.2102v2
2010/12/17,Structural and magnetic properties of Co2MnSi thin films,"Co2MnSi (CMS) films of different thicknesses (20, 50 and 100 nm) were grown
by radio frequency (RF) sputtering on a-plane sapphire substrates. Our X-rays
diffraction study shows that, in all the samples, the cubic <110> CSM axis is
normal to the substrate and that there exist well defined preferential in-plane
orientations. Static and dynamic magnetic properties were investigated using
vibrating sample magnetometry (VSM) and micro-strip line ferromagnetic
resonance (MS-FMR), respectively. From the resonance measurements versus the
direction and the amplitude of an applied magnetic field we derive most of the
magnetic parameters: magnetization, gyromagnetic factor, exchange stiffness
coefficient and magnetic anisotropy terms. The in-plane anisotropy can be
described as resulting from the superposition of two terms showing a two-fold
and a four-fold symmetry without necessarily identical principal axes. The
observed behavior of the hysteresis loops is in agreement with this complex
form of the in-plane anisotropy",1012.3837v2
2011/1/6,Landau Level Physics in a Quantum Well: new singular features in magnetization and violations of de Haas - van Alphen periodicities,"Analytical calculations based on a Landau Level (LL) picture are reported for
an interface (with a finite-width Quantum Well (QW)) and for a fully
three-dimensional charged quantum electronic system in an external magnetic
field. They lead to a sequence of previously unnoticed singular features in
global magnetization and magnetic susceptibility that lead to nontrivial
corrections to the standard de Haas - van Alphen periods. Additional features
due to Zeeman splitting are also reported (such as new energy minima that
originate from the interplay of QW, Zeeman and LL Physics) that are possibly
useful for the design of quantum devices. A corresponding calculation in a
Composite Fermion picture leads to new predictions on magnetic response
properties of a fully-interacting electron liquid in a finite-width interface.",1101.1307v1
2011/1/13,Frustrated couplings between alternating spin-1/2 chains in AgVOAsO4,"We report on the crystal structure and magnetic behavior of the spin-1/2
compound AgVOAsO4. Magnetic susceptibility, high-field magnetization, and
electron spin resonance measurements identify AgVOAsO4 as a gapped quantum
magnet with a spin gap Delta ~ 13 K and a saturation field H_s ~ 48.5 T.
Extensive band structure calculations establish the microscopic magnetic model
of spin chains with alternating exchange couplings J ~ 40 K and J' ~ 26 K.
However, the precise evaluation of the spin gap emphasizes the role of
interchain couplings which are frustrated due to the peculiar crystal structure
of the compound. The unusual spin model and the low energy scale of the
exchange couplings make AgVOAsO4 a promising candidate for an experimental
investigation of Bose-Einstein condensation and other exotic ground states in
high magnetic fields.",1101.2546v2
2011/1/28,First detection of a magnetic field in the fast rotating runaway Oe star zeta Ophiuchi,"The star zeta Ophiuchi is one of the brightest massive stars in the northern
hemisphere and was intensively studied in various wavelength domains. The
currently available observational material suggests that certain observed
phenomena are related to the presence of a magnetic field. We acquired
spectropolarimetric observations of zeta Oph with FORS1 mounted on the 8-m
Kueyen telescope of the VLT to investigate if a magnetic field is indeed
present in this star. Using all available absorption lines, we detect a mean
longitudinal magnetic field B_z_all = 141+-45G, confirming the magnetic nature
of this star. We review the X-ray properties of zeta Oph with the aim to
understand whether the X-ray emission of zeta Oph is dominated by magnetic or
by wind instability processes.",1101.5500v1
2011/3/6,"Basic design and engineering of normal-conducting, iron-dominated electromagnets","The intention of this course is to provide guidance and tools necessary to
carry out an analytical design of a simple accelerator magnet. Basic concepts
and magnet types will be explained as well as important aspects which should be
considered before starting the actual design phase. The central part of this
course is dedicated to describing how to develop a basic magnet design.
Subjects like the layout of the magnetic circuit, the excitation coils, and the
cooling circuits will be discussed. A short introduction to materials for the
yoke and coil construction and a brief summary about cost estimates for magnets
will complete this topic.",1103.1119v1
2011/3/7,Vectorial Control of Magnetization by Light,"Coherent light-matter interactions have recently extended their applications
to the ultrafast control of magnetization in solids. An important but
unrealized technique is the manipulation of magnetization vector motion to make
it follow an arbitrarily designed multi-dimensional trajectory. Furthermore,
for its realization, the phase and amplitude of degenerate modes need to be
steered independently. A promising method is to employ Raman-type nonlinear
optical processes induced by femtosecond laser pulses, where magnetic
oscillations are induced impulsively with a controlled initial phase and an
azimuthal angle that follows well defined selection rules determined by the
materials' symmetries. Here, we emphasize the fact that temporal variation of
the polarization angle of the laser pulses enables us to distinguish between
the two degenerate modes. A full manipulation of two-dimensional magnetic
oscillations is demonstrated in antiferromagnetic NiO by employing a pair of
polarization-twisted optical pulses. These results have lead to a new concept
of vectorial control of magnetization by light.",1103.1239v1
2011/3/9,Magnetization and magnon excitation energies of the magnetic semiconductors EuTe and EuO on the basis of the renormalized spin wave theory,"We present analytic expressions for the temperature dependent magnetization
and magnon dispersion relation of the antiferromagnetic (AFM) EuTe and the
ferromagnetic (FM) EuO. These bulk semiconductors represent concentrated spin
systems for which the interaction between magnons has to be taken into account.
We do this using the renormalized spin wave theory. A higher order Green's
function according to Tjablikov is used for their description. As a result, we
obtain a modified Bloch- T3/2 law, for low temperatures and high magnetic
fields. A full analytic expression is given for the sublattice magnetization of
the AFM EuTe (B0=0), with a N\'eel temperature of TN = 9.81 K. The
magnetization curves {\sigma}N(T) of EuO (for 0 \leq T \leq 0.68TC) and
{\sigma}R(T) (for 0.82TC < T < TC) agree well with experiment. The spin wave
excitation energy perfectly matches experimental data from inelastic neutron
scattering. In the case of EuTe the magnon excitation energies exhibit a
characteristic maximum. For q = 0, an energy gap Eg occurs in the spin wave
spectrum, a consequence of the AFM exchange interaction J2(T). Such energy gaps
exist in the spectrum of magnon excitation energies only in systems with AFM
interactions.",1103.1831v1
2011/3/19,Magnetic properties and energy absorption of CoFe2O4 nanoparticles for magnetic hyperthermia,"We have studied the magnetic and power absorption properties of three samples
of CoFe2O4 nanoparticles with sizes from 5 to 12 nm prepared by thermal
decomposition of Fe (acac)3 and Co(acac)2 at high temperatures. The blocking
temperatures TB estimated from magnetization M(T) curves spanned the range 180
< TB < 320 K, reflecting the large magnetocrystalline anisotropy of these
nanoparticles. Accordingly, high coercive fields HC \approx 1.4 - 1.7 T were
observed at low temperatures. Specific Power Absorption (SPA) experiments
carried out in ac magnetic fields indicated that, besides particle volume, the
effective magnetic anisotropy is a key parameter determining the absorption
efficiency. SPA values as high as 98 W/g were obtained for nanoparticles with
average size of \approx12 nm.",1103.3786v1
2011/3/31,Bulk and Surface Magnetization of Co atoms in Rutile Ti_[1-x]Co_xO_[2-delta] Thin Films Revealed by X-Ray Magnetic Circular Dichroism,"We have studied magnetism in Ti_[1-x]Co_xO_[2-\delta] thin films with various
x and \delta by soft x-ray magnetic circular dichroism (XMCD) measurements at
the Co L_[2,3] absorption edges. The estimated ferromagnetic moment by XMCD was
0.15-0.24 \mu\beta/Co in the surface, while in the bulk it was 0.82-2.25
\mu\beta/Co, which is in the same range as the saturation magnetization of
1.0-1.5 \mu\beta/Co. Theseresults suggest that the intrinsic origin of the
erromagnetism. The smaller moment of Co atom at surface is an indication of a
magnetically dead layer of a few nm thick at the surface of the thin films.",1103.6092v2
2011/4/11,Collinear to Anti-collinear Quantum Phase Transition by Vacancies,"We study static vacancies in the collinear magnetic phase of a frustrated
Heisenberg $J_1$-$J_2$ model. It is found that vacancies can rapidly suppress
the collinear antiferromagnetic state (CAFM)and generate a new magnetic phase,
an anti-collinear magnetic phase (A-CAFM), due to magnetic frustration. We
investigate the quantum phase transition between these two states by studying a
variety of vacancy superlattices. We argue that the anti-collinear magnetic
phase can exist in iron-based superconductors in the absence of any preceding
structural transitions and an observation of this novel phase will
unambiguously resolve the relation between the magnetic and structural
transitions in these materials.",1104.1848v2
2011/4/15,Temperature-dependent properties of the magnetic order in single-crystal BiFeO3,"We report neutron diffraction and magnetization studies of the magnetic order
in multiferroic BiFeO3. In ferroelectric monodomain single crystals, there are
three magnetic cycloidal domains with propagation vectors equivalent by
crystallographic symmetry. The cycloid period slowly grows with increasing
temperature. The magnetic domain populations do not change with temperature
except in the close vicinity of the N{\P}eel temperature, at which, in
addition, a small jump in magneti- zation is observed. No evidence for the
spin-reorientation transitions proposed in previous Raman and dielectric
studies is found. The magnetic cycloid is slightly anharmonic for T=5 K. The
an- harmonicity is much smaller than previously reported in NMR studies. At
room temperature, a circular cycloid is observed, within errors. We argue that
the observed anharmonicity provides important clues for understanding
electromagnons in BiFeO3.",1104.3109v1
2011/5/30,Chiral orbital current and anomalous magnetic moment in gapped graphene,"We present a low-energy effective-mass theory to describe chiral orbital
current and anomalous magnetic moment in graphenes with band gap and related
materials. We show that a Bloch electron generally contains an anomalous
current density due to inter-band matrix elements, which describes a chiral
current circulation associated with magnetic moment. In gapped graphenes, the
chiral current is opposite between different valleys, and corresponding
magnetic moment accounts for valley splitting of Landau levels. In gapped
bilayer graphene, in particular, the valley-dependent magnetic moment is
responsible for divergence of paramagnetic susceptibility at the band bottom,
and full valley polarization is achieved in relatively small magnetic field
range. The formulation also applies to the gapped surface states of
three-dimensional topological insulator, where the anomalous current is related
to the magneto-electric response in spatially-modulated potential.",1105.5919v2
2011/6/1,Enhancement of magnetic anisotropy barrier in long range interacting spin systems,"Magnetic materials are usually characterized by anisotropy energy barriers
which dictate the time scale of the magnetization decay and consequently the
magnetic stability of the sample. Here we present a unified description, which
includes coherent rotation and nucleation, for the magnetization decay in
generic anisotropic spin systems. In particular, we show that, in presence of
long range exchange interaction, the anisotropy energy barrier grows as the
volume of the particle for on site anisotropy, while it grows even faster than
the volume for exchange anisotropy, with an anisotropy energy barrier
proportional to $V^{2-\alpha/d}$, where $V$ is the particle volume, $\alpha
\leq d $ is the range of interaction and $d$ is the embedding dimension. These
results shows a relevant enhancement of the anisotropy energy barrier w.r.t.
the short range case, where the anisotropy energy barrier grows as the particle
cross sectional area for large particle size or large particle aspect ratio.",1106.0148v2
2011/6/6,Engineering the magnetic properties of the Mn$_{13}$ cluster by doping,"With a goal to produce giant magnetic moment in Mn$_{13}$ cluster which will
be useful for practical applications, we have considered the structure and
magnetic properties of pure Mn$_{13}$ cluster and substitutionally doped it
with X = Ti, V, Cr, Fe, Co, Ni atom to produce Mn$_{12}$X clusters. We find
that Ti and V substitutions in Mn$_{13}$ cluster are the most promising in
terms of gaining substantial binding energy as well as achieving higher
magnetic moment through ferromagnetic alignment of atom-centered magnetic
moments. This has been demonstrated in terms of energetics and electronic
properties of the clusters. For comparison, we have also studied the effect of
N-capping of Mn$_{13}$ cluster, predicted in the earlier work [Phys. Rev. Lett.
{\bf 89}, 185504 (2002)] as a means to produce stable giant magnetic moment in
Mn clusters upto cluster size of 5 Mn atoms.",1106.0968v1
2011/6/7,Asymmetric magnetic dots: A way to control magnetic properties,"We have used Monte Carlo simulations to investigate the magnetic properties
of asymmetric dots as a function of their geometry. The asymmetry of round dots
is produced by cutting off a fraction of the dot and is characterized by an
asymmetry parameter $\alpha$. This shape asymmetry has interesting effects on
the coercivity ($H_{c}$), remanence ($M_{r}$), and barrier for vortex and C-
state formation. The dependences of $H_{c}$ and $M_{r}$ are non monotonic as a
function of $\alpha$ with a well defined minima in these parameters. The vortex
enters the most asymmetric part and exits through the symmetric portion of the
dot. With increasing $\alpha $ the vortex formation starts with a C-state which
persists for longer fields and the barrier for vortex exit diminishes with
increasing asymmetry, thus providing control over the magnetic chirality. This
implies interesting, naively-unexpected, magnetic behavior as a function of
geometry and magnetic field.",1106.1403v1
2011/6/9,Quantitative model for anisotropy and reorientation thickness of the magnetic moment in thin epitaxially strained metal films,"A quantitative mathematical model for the critical thickness of strained
epitaxial metal films is presented, at which the magnetic moment experiences a
reorientation from in-plane to perpendicular magnetic anisotropy. The model is
based on the minimum of the magnetic anisotropy energy with respect to the
orientation of the magnetic moment of the film. Magnetic anisotropy energies
are taken as the sum of shape anisotropy, magnetocrystalline anisotropy and
magnetoelastic anisotropy, the two latter ones being present as constant
surface and variable volume contributions. Other than anisotropy materials
constants, readily available from literature, only information about the strain
in the films for the determination of the magnetoelastic anisotropy energy is
required. Application of the epitaxial Bain path allows to express the strain
in the film in terms of substrate lattice constant and film lattice parameter,
and thus to obtain an approximate closed expression for the reorientation
thickness in terms of lattice mismatch. The model can predict the critical spin
reorientation transition thickness with surprising accuracy.",1106.1917v1
2011/6/12,Critical Behavior of AC Antiferromagnetic and Ferromagnetic Susceptibilities of a Spin-1/2 Metamagnetic Ising System,"In this study, the temperature variations of the equilibrium and the
non-equilibrium antiferromagnetic and ferromagnetic susceptibilities of a
metamagnetic system are examined near the critical point. The kinetic equations
describing the time dependencies of the total and staggered magnetizations are
derived by utilizing linear response theory. In order to obtain dynamic
magnetic relaxation behavior of the system, the stationary solutions of the
kinetic equations in existence of sinusoidal staggered and physical external
magnetic fields are performed. In addition, the static and dynamical mean field
critical exponents are calculated in order to formulate the critical behavior
of antiferromagnetic and ferromagnetic magnetic response of a metamagnetic
system. Finally, a comparison of the findings of this study with previous
theoretical and experimental studies is represented and it is shown that a good
agreement is found with our results.",1106.2306v1
2011/6/12,Magnetism in Closed-shell Quantum Dots: Emergence of Magnetic Bipolarons,"Similar to atoms and nuclei, semiconductor quantum dots exhibit formation of
shells. Predictions of magnetic behavior of the dots are often based on the
shell occupancies. Thus, closed-shell quantum dots are assumed to be inherently
nonmagnetic. Here, we propose a possibility of magnetism in such dots doped
with magnetic impurities. On the example of the system of two interacting
fermions, the simplest embodiment of the closed-shell structure, we demonstrate
the emergence of a novel broken-symmetry ground state that is neither
spin-singlet nor spin-triplet. We propose experimental tests of our predictions
and the magnetic-dot structures to perform them.",1106.2346v1
2011/6/23,Enhancement of magnetism of Fe by Cr and V,"Enhancement of magnetism of Fe that occurs by alloying with Cr or V is
discussed on the basis of first-principles electronic structure calculation.
The d states of Fe next to Cr(V) are pushed down to the lower energy side
compared to those of pure Fe due to the hybridization with Cr(V) d states,
which leads a Co-like electronic structure for the Fe atom. This enhances
magnetic moments of other Fe atoms and also the exchange couplings among them.
The same mechanism works as well for the magnetism of Fe/Cr heterostructures.
The idea is extended to design of a new type of antiferromagnets with high
N\'eel temperature. Such heterostructures could be used to increase a magnetic
anisotropy of permanent magnets.",1106.4630v1
2011/6/23,"Dynamics of a magnetic dimer with exchange, dipolar and Dzyalozhinski-Moriya interaction","We investigate the dynamics of a magnetic system consisting of two magnetic
moments coupled by either exchange, dipole-dipole, or Dzyalozhinski-Moriya
interaction. We compare the switching mechanisms and switching rates as induced
by the three couplings. For each coupling and each configuration of the two
anisotropy axes, we describe the switching modes and, using the kinetic theory
of Langer, we provide (semi-)analytical expressions for the switching rate. We
then compare the three interactions with regard to their efficiency in the
reversal of the net magnetic moment of the dimer. We also investigate how the
energy barriers vary with the coupling. For the dipole-dipole interaction we
find that the energy barrier may either increase or decrease with the coupling
depending on whether the latter is weak or strong. Finally, upon comparing the
various switching rates, we find that the dipole-dipole coupling leads to the
slowest magnetic dimer, as far as the switching of its net magnetic moment is
concerned.",1106.4713v2
2011/6/27,Crystal Structure and Magnetic Properties of the New Zn1.5Co1.5B7O13Br Boracite,"New Zn1.5Co1.5B7O13Br boracite crystals were grown by chemical transport
reactions in quartz ampoules, at a temperature of 1173 K. The crystal structure
was characterized by X-ray diffraction. The crystals present an orthorhombic
structure with space group Pca21, (No. 29). The determined cell parameters
were: a = 8.5705(3){\AA}, b = 8.5629(3) {\AA}, and c = 12.1198(4){\AA}, and
cell volume, V = 889.45(5) {\AA}3 with Z = 4. Magnetic properties in single
crystals of the new boracite, were determined. The Susceptibility-Temperature
(X -T) behavior at different magnetic intensities was studied. The inverse of
the magnetic susceptibility X-1(T) shows a Curie-Weiss characteristic with spin
s = 3/2 and a small orbital contribution, l. At low temperatures, below 10 K,
X(T) shows irreversibility that is strongly dependent on the applied magnetic
field. This boracite is ferrimagnetic up to a maximum temperature of about 16
K, as shows the coercive field. The reduction of the irreversibility by the
influence of the magnetic field, may be related to a metamagnetic phase
transition.",1106.5446v1
2011/6/29,Hysteretic magnetoresistance and thermal bistability in a magnetic two-dimensional hole system,"Colossal negative magnetoresistance and the associated field-induced
insulator-to-metal transition, the most characteristic features of magnetic
semiconductors, are observed in n-type rare earth oxides and chalcogenides,
p-type manganites, n-type and p-type diluted magnetic semiconductors (DMS) as
well as in quantum wells of n-type DMS. Here, we report on magnetostransport
studies of Mn modulation-doped InAs quantum wells, which reveal a magnetic
field driven and bias voltage dependent insulator-to-metal transition with
abrupt and hysteretic changes of resistance over several orders of magnitude.
These phenomena coexist with the quantised Hall effect in high magnetic fields.
We show that the exchange coupling between a hole and the parent Mn acceptor
produces a magnetic anisotropy barrier that shifts the spin relaxation time of
the bound hole to a 100 s range in compressively strained quantum wells. This
bistability of the individual Mn acceptors explains the hysteretic behaviour
while opening prospects for information storing and processing. At high bias
voltage another bistability, caused by the overheating of electrons10, gives
rise to abrupt resistance jumps.",1106.5832v1
2011/8/21,Complex magnetism and magnetic field-driven electrical polarization in Co$_3$TeO$_6$,"The magnetic and electrical properties of Co$_3$TeO$_6$ single-crystals with
corundum related structure reveal a magnetic-field induced polarization below
21 K. A sharp peak in the specific heat at \approx 18 K indicates a
reconstructive-type first-order phase transition. From second-harmonic
generation (SHG) measurements breaking of inversion symmetry is evident and the
point-group symmetry was determined as m. The temperature and magnetic-field
dependence of the magnetic and electrical polarizations are discussed in the
light of the SHG results.",1108.4186v1
2011/8/22,Kondo screening and Magnetism at Interfaces,"The nature of magnetic order and transport properties near surfaces is a
topic of great current interest. Here we model metal-insulator interfaces with
a multi-layer system governed by a tight-binding Hamiltonian in which the
interaction is non-zero on one set of adjacent planes and zero on another. As
the interface hybridization is tuned, magnetic and metallic properties undergo
an evolution that reflects the competition between anti-ferromagnetism and
(Kondo) singlet formation in a scenario similar to that occurring in
heavy-fermion materials. For a few-layer system at intermediate hybridization,
a Kondo insulating phase results where magnetic order and conductivity are
suppressed in all layers. As more insulating layers are added, magnetic order
is restored in all correlated layers except that at the interface. Residual
signs of Kondo physics are however evident in the bulk as a substantial
reduction of the order parameter in the 2-3 layers immediately adjacent to the
interfacial one. We find no signature of long range magnetic order in the
metallic",1108.4239v2
2011/9/3,Low-temperature heat transport of the layered spin-dimer compound Ba_3Mn_2O_8,"We report the study on the low-temperature heat transport of Ba_3Mn_2O_8
single crystal, a layered spin-dimer compound exhibiting the
magnetic-field-induced magnetic order or the magnon Bose-Einstein condensation.
The thermal conductivities (\kappa) along both the ab plane and the c axis show
nearly isotropic dependence on magnetic field, that is, \kappa is strongly
suppressed with increasing field, particularly at the critical fields of
magnetic phase transitions. These results indicate that the magnetic
excitations play a role of scattering phonons and the scattering effect is
enhanced when the magnetic field closes the gap in the spin spectrum. In
addition, the magnons in the BEC state of this materials do not show notable
ability of carrying heat.",1109.0587v1
2011/9/23,Magnetic Core-Shell Structure and Proximity Effect in 7 nm Single-Crystal Co3O4 Nanowires,"We present a study of magnetic properties of single-crystal Co3O4 nanowires
with diameter about 7 nm. The nanowires expose (111) planes composed of plenty
of Co3+ cations and exhibit two N\'eel temperatures at 56 K (TN of wire cores)
and 73 K (TN of wire shells), which are far above TN = 40 K of bulk Co3O4. This
novel bahavior is attributed to symmetry breaking of surface Co3+ cations and
magnetic proximity effect. The nanowire shells show macroscopic residual
magnetic moments. Cooling in a magnetic field, a fraction of the residual
moments are tightly pinned to the antiferromagnetic lattice, which results in
an obvious horizontal and vertical shift of hysteresis loop. Our experiment
demonstrates that the exchange bias field HE and the pinned magnetic moments
Mpin follow a simple expression HE = aMpin with a a constant.",1109.4989v1
2011/10/4,Zero and finite temperature mean field study of magnetic field induced electric polarization in Ba2CoGe2O7,"We investigate the spin-induced polarization in the multiferroic compound
Ba2CuGe2O7 using variarional and finite temperature mean field approaches. The
compound is described by a spin-3/2 Heisenberg model extended with easy plane
anisotropy and Dzyaloshinskii-Moriya (DM) interaction. Applying magnetic field
parallel to the [110] axis, three phases can be distinguished: (i) At high
magnetic field we find a partially magnetized phase with spins parallel to the
fields and uniform polarization; (ii) Below a critical field the ground state
is a twofold degenerate canted antiferromagnet, where the degeneracy can be
lifted by a finite DM interaction; (iii) At zero field a U(1) symmetry breaking
phase takes place, exhibiting a Goldstone-mode. To reproduce the magnetization
and polarization measurements reported in Murakawa et al. [Phys. Rev. Lett.
105, 137202 (2010)], we introduce an additional term in the Hamiltonian that
couples the polarizations on neighboring tetrahedra. This results in the
appearance of a canted ferrimagnetic phase for h < 1 T, characterized by a
finite staggered polarization, as well as by a finite magnetization along the
[-1,1,0] axis that leads to torque anomalies.",1110.0788v1
2011/10/13,Femtoscale magnetically induced lattice distortions in multiferroic TbMnO3,"Magneto-electric multiferroics exemplified by TbMnO3 possess both magnetic
and ferroelectric long-range order. The magnetic order is mostly understood,
whereas the nature of the ferroelectricity has remained more elusive. Competing
models proposed to explain the ferroelectricity are associated respectively
with charge transfer and ionic displacements. Exploiting the magneto-electric
coupling, we use an electric field to produce a single magnetic domain state,
and a magnetic field to induce ionic displacements. Under these conditions,
interference charge-magnetic X-ray scattering arises, encoding the amplitude
and phase of the displacements. When combined with a theoretical analysis, our
data allow us to resolve the ionic displacements at the femtoscale, and show
that such displacements make a significant contribution to the zero-field
ferroelectric moment.",1110.2875v1
2011/10/31,Temperature-dependent multi-k magnetic structure in multiferroic Co3TeO6,"A complex magnetic order of the multiferroic compound Co3TeO6 has been
revealed by neutron powder diffraction studies on ceramics and crushed single
crystals. The compound adopts a monoclinic structure (s.g. C2/c) in the studied
temperature range 2 K - 300 K but exhibits successive antiferromagnetic
transitions at low temperature. Incommensurate antiferromagnetic order with the
propagation vector k1 = (0, 0.485, 0.055) sets in at 26 K. A transition to a
second antiferromagnetic structure with k2 = (0, 0, 0) takes place at 21.1 K.
Moreover, a transition to a commensurate antiferromagnetic structure with k3 =
(0, 0.5, 0.25) occurs at 17.4 K. The magnetic structures have been determined
by neutron powder diffraction using group theory analysis as a preliminary
tool. Different coordinations of the Co2+ ions involved in the low-symmetry
C2/c structure of Co3TeO6 render the exchange-interaction network very complex
by itself. The observed magnetic phase transformations are interpreted as an
evidence of competing magnetic interactions. The temperature dependent changes
in the magnetic structure, derived from refinements of high-resolution neutron
data, are discussed and possible mechanisms connected with the spin
reorientations are described.",1110.6776v1
2011/11/30,B-T phase diagram of CoCr2O4 in magnetic fields up to 14 T,"We have measured the magnetization and specific heat of multiferroic CoCr2O4
in magnetic fields up to 14 T. The high-field magnetization measurements
indicate a new phase transition at T* = 5 - 6 K. The phase between T* and the
lock-in transition at 15 K is characterized by magnetic irreversibility. At
higher magnetic fields, the irreversibility increases. Specific-heat
measurements confirm the transition at T*, and also show irreversible behavior.
We construct a field-temperature phase diagram of CoCr2O4.",1111.7239v1
2011/12/8,Photovoltaic Effect on Molecule Coupled Ferromagnetic Films of a Magnetic Tunnel Junction,"Economical solar energy conversion to electricity can be boosted by the
discovery of fundamentally new photovoltaic mechanism, and a suitable system to
realize it with commonly available materials like iron (Fe) and nickel (Ni).
This paper reports the observation of photovoltaic effect on a molecular
spintronics device, composed of magnetic tunnel junction (MTJ) and
organometallic molecular clusters (OMCs). A prefabricated MTJ with exposed side
edges, after enabling the bridging of OMC channels between its two
ferromagnetic films, exhibited following phenomenon (i) dramatic increase in
exchange coupling, (ii) 3-6 orders current suppression and (iii) photovoltaic
effect. This paper focuses on the photovoltaic effect. Control experiments on
isolated ferromagnetic films suggested that OMCs neither affected the magnetic
properties nor produced any photovoltaic effect; photovoltaic effect was only
observed on the ferromagnetic films serving as magnetic electrodes in a MTJ.
Present paper invites further investigation of the similar photovoltaic effect
on other combinations of MTJs and promising magnetic molecules, like single
molecular magnets, organometallic clusters and porphyrins. This research can
lead to mass producible and economical spin photovoltaic devices.",1112.1879v2
2012/1/2,Magnetodielectric behavior in La2CoMnO6 nanoparticles,"We have investigated magnetic, dielectric and magnetodielectric properties of
La2CoMnO6 nanoparticles prepared by sol-gel method. Magnetization measurements
revealed two distinct ferromagnetic transitions at 218 K and 135 K that can be
assigned to ordered and disordered magnetic phases of the La2CoMnO6
nanoparticles. Two dielectric relaxations culminating around the magnetic
transitions were observed with a maximum magnetodielectric response reaching
10% and 8% at the respective relaxation peaks measured at 100 kHz under 5T
magnetic field. The dc electrical resistivity followed an insulating behavior
and showed a negative magnetoresistance; there was no noticeable anomaly in
resistivity or magnetoresistance near the magnetic ordering temperatures.
Complex impedance analysis revealed a clear intrinsic contribution to the
magnetodielectric response; however, extrinsic contribution due to
Maxwell-Wagner effect combined with magnetoresistance property dominated the
magnetodielectric effect at high temperatures.",1201.0448v1
2012/1/13,Intermediate state switching dynamics in magnetic double layer nanopillars grown by molecular beam epitaxy,"We observe a stable intermediate resistance switching state in the current
perpendicular to plane geometry for all Co/Cu/Co double layer nanopillar
junctions grown by molecular beam epitaxy. This novel state has a resistance
between the resistances of the parallel and antiparallel alignment of both
Co-layer magnetizations. The state, which originates from an additional
in-plane magnetic easy axis, can be reached by spin transfer torque switching
or by an external magnetic field. In addition to spin torque-induced coherent
small-angle spin wave modes we observe a broad microwave emission spectrum. The
latter is attributed to incoherent magnetic excitations that lead to a
switching between the intermediate state and the parallel or antiparallel
alignment of both ferromagnetic layers. We conclude that the additional
magnetic easy axis suppresses a stable trajectory of coherent large-angle
precession, which is not observed in our samples.",1201.2752v1
2012/1/22,Magnetic order and the electronic ground state in the pyrochlore iridate Nd2Ir2O7,"We report a combined muon spin relaxation/rotation, bulk magnetization,
neutron scattering, and transport study of the electronic properties of the
pyrochlore iridate Nd2Ir2O7. We observe the onset of strongly hysteretic
behavior in the temperature dependent magnetization below 120 K, and an abrupt
increase in the temperature dependent resistivity below 8 K. Zero field muon
spin relaxation measurements show that the hysteretic magnetization is driven
by a transition to a magnetically disordered state, and that below 8 K a
complex magnetically ordered ground state sets in, as evidenced by the onset of
heavily damped spontaneous muon precession. Our measurements point toward the
absence of a true metal-to-insulator phase transition in this material and
suggest that Nd2Ir2O7 lies either within or on the metallic side of the
boundary of the Dirac semimetal regime within its topological phase diagram.",1201.4606v2
2012/2/28,Magnetization study to probe the effect of N2+ irradiation on Fe/Co bilayers,"Fe/Co bilayers were made using ion beam sputtering and then were subjected to
nitrogen-ion irradiation to explore the influence of irradiation on their
magnetic properties. Magnetization studies of Fe/Co bilayers along with their
irradiated counterparts were then performed. The magnetization and coercivity
of the as-deposited sample exhibited a two-fold uniaxial symmetry while the
behavior for high temperature irradiated sample depicts a small shift in the
two fold behavior. The magnetization data measured with the magnetic field
perpendicular to the plane of the film exhibited a hysteresis in both the case
of the irradiated sample as well as as-deposited sample. A small increase in
coercivity for the irradiated sample was observed which is due to various
reasons including formation of FeCo solid solution due to ion irradiation at
the interface.",1202.6137v1
2012/3/18,Hydrogen-induced reversible spin-reorientation transition and magnetic stripe domain phase in bilayer Co on Ru(0001),"Imaging the change in the magnetization vector in real time by spin-polarized
low-energy electron microscopy, we observed a hydrogen-induced, reversible
spin-reorientation transition in a cobalt bilayer on Ru(0001). Initially,
hydrogen sorption reduces the size of out-of-plane magnetic domains and leads
to the formation of a magnetic stripe domain pattern, which can be understood
as a consequence of reducing the out-of-plane magnetic anisotropy. Further
hydrogen sorption induces a transition to an in-plane easy-axis. Desorbing the
hydrogen by heating the film to 400 K recovers the original out-of-plane
magnetization. By means of ab-initio calculations we determine that the origin
of the transition is the local effect of the hybridization of the hydrogen
orbital and the orbitals of the Co atoms bonded to the absorbed hydrogen.",1203.3945v1
2012/3/30,Structural domain and spin ordering induced glassy magnetic phase in single layered manganite Pr$_{0.22}$Sr$_{1.78}$MnO$_4$,"The single layered manganite Pr$_{0.22}$Sr$_{1.78}$MnO$_4$ undergoes
structural transition from high temperature tetragonal phase to low temperature
orthorhombic phase below room temperature. The orthorhombic phase was reported
to have two structural variants with slightly different lattice parameters and
Mn-3$d$ levels show orbital ordering within both the variants, albeit having
mutually perpendicular ordering axis. In addition to orbital ordering, the
orthorhombic variants also order antiferromagnetically with different N\'eel
temperatures. Our magnetic investigation on the polycrystalline sample of
Pr$_{0.22}$Sr$_{1.78}$MnO$_4$ shows large thermal hysteresis indicating the
first order nature of the tetragonal to orthorhombic transition. We observe
magnetic memory, large relaxation, frequency dependent ac susceptbility and
aging effects at low temperature, which indicate spin glass like magnetic
ground state in the sample. The glassy magnetic state presumably arises from
the interfacial frustration of orthorhombic domains with orbital and spin
orderings playing crucial role toward the competing magnetic interactions.",1203.6761v1
2012/5/7,Gamma-irradiation influence on the initial magnetic conductivity of based on the system Fe-Si-B amorphous and nanocrystalline alloys,"The dependence of initial magnetic permeability {\mu}i of based on the
Fe-Si-B amorphous and nanocrystalline alloys on the {\gamma}-irradiation dose
was investigated by the method of inductance factor determination. It was
determined that the alloying of amorphous Fe-Si-B alloys by nickel and
molybdenum increases the radiation sensitivity of the {\mu}i. Initial magnetic
permeability of nanocrystalline magnetic alloys is less sensitive to the action
of {\gamma}-irradiation as compared with the alloyed amorphous alloys. Has been
suggested that radiation influence on the initial magnetic permeability are
caused by creation of non-magnetic incorporation in structure of amorphous
alloys as well as amorphous matrix of nanocrystalline alloys.",1205.1354v1
2012/5/17,Effect of electron doping on the magnetic correlations in the bilayered brownmillerite compound Ca_{2.5-x}La_{x}Sr_{0.5}GaMn_{2}O_{8}: a neutron diffraction study,"The effect of electron doping on the magnetic properties of the
Brownmillerite-type bilayered compounds has been investigated by neutron powder
diffraction in La substituted Ca2.5-xLaxSr0.5GaMn2O8 compounds (x = 0.05 and
0.1), in comparison with the undoped compound (x = 0). In all compounds, a
long-range three dimensional collinear antiferromagnetic (AFM) structure is
found below the N\'eel temperature TN of respective compound, whereas, well
above TN, three dimensional short-range magnetic ordering is observed. In the
intermediate temperature range just above TN, a strong effect of electron
doping (La substitution) on the magnetic correlations has been observed. Here,
a short-range AFM correlation with possible dimensionality of three has been
found for substituted compounds (x = 0.05 and 0.1) as compared to the reported
two dimensional long-range AFM ordering in the parent compound. With increasing
the electron doping, a decrease in TN is also observed. The short-range
magnetic correlations set in over a large temperature range above TN. A
magnetic phase diagram in the x-T plane is proposed from these results.",1205.3872v1
2012/5/28,Doping-induced metallicity and coexistence of magnetic subsystems in {K$_{2}$Fe$_{4+x}$Se$_{5}$},"Electronic structure calculations are used to analyze the electronic and
magnetic properties in {K$_{2}$Fe$_{4+x}$Se$_{5}$}. Fe atoms can be divided
into two distinct groups. The $x{=}0$ (parent) compound forms an insulating,
collinear, local moment phase with high N{\'{e}}el temperature. We show that
large biquadratic exchange coupling and exchange-elastic interactions stabilize
the magnetic order. For $x{>}0$ the additional Fe atoms fill vacancy sites.
They form impurity bands for small $x$, which broaden as $x$ increases. They
determine the states at the Fermi level and may be viewed as a magnetic
subsystem separate from the host. Spin fluctuations are prevalent because
magnetic interactions between the `defect' and the `parent' atoms are
relatively weak, while chemical fluctuations are prevalent for low $x$.
Fluctuations of either type leads to the formation of a weakly metallic state.
The unusual coexistence of the two magnetic subsystems offers a new perspective
as to how superconductivity and strong antiferromagnetism can coexist. We argue
that spin fluctuations of the impurity subsystem share common features with the
Fe-pnictide superconductors.",1205.6159v1
2012/6/4,muSR Investigation of magnetically ordered states in A-site ordered perovskite manganites RBaMn2O6 (R = Y and La),"The magnetically ordered states of the A-site ordered perovskite manganites
LaBaMn2O6 and YBaMn2O6 have been investigated by muon spin relaxation in zero
external magnetic field. Our data reveal striking differences in the nature of
the magnetically ordered state of these materials. For LaBaMn2O6, the muSR
time-spectra in the ferromagnetic state below ~ 330 K reveal a strongly
inhomogeneous phase, reminiscent of a Griffiths phase. Within this magnetically
inhomogeneous phase, an antiferromagnetic state develops below 150 K, which
displays well defined static internal magnetic fields, but reaches only 30% of
the volume fraction at low temperatures. A broad distribution of muSR
relaxation rates is inferred down to the lowest temperatures. This behavior is
similar to the A-site disordered La0.5Ba0.5MnO3. On the other hand, for
YBaMn2O6, the muSR time spectra for both (i) the charge and orbital ordered and
(ii) the paramagnetic phases reveal rather homogeneous states, namely, an
exponential relaxation in the paramagnetic state and well defined muon spin
oscillation in the antiferromagnetic state.",1206.0515v2
2012/6/20,Vibrating-coil magnetometry of the spin liquid properties of Tb2Ti2O7,"We have explored the spin liquid state in Tb2Ti2O7 with vibrating coil
magnetometry down to 0.04 K under magnetic fields up to 5 T. We observe
magnetic history dependence below $T < 0.2$K reminiscent of the classical spin
ice systems Ho2Ti2O7 and Dy2Ti2O7. The magnetic phase diagram inferred from the
magnetization is essentially isotropic, without evidence of magnetization
plateaux as anticipated for so-called quantum spin ice, predicted theoretically
for [111] when quantum fluctuations renormalize the interactions. Instead, the
magnetization for $T \ll T*$ agrees semi-quantitatively with the predictions of
""all-in/all-out"" (AIAO) antiferromagnetism. Taken together this suggests that
the spin liquid state in Tb2Ti2O7 is akin to an incipient AIAO-antiferromagnet.",1206.4521v1
2012/6/20,Magnetic transitions and magnetodielectric effect in the antiferromagnet SrNdFeO$_4$,"We investigated the magnetic phase diagram of single crystals of
SrNdFeO$_{4}$ by measuring the magnetic properties, the specific heat and the
dielectric permittivity. The system has two magnetically active ions, Fe$^{3+}$
and Nd$^{3+}$. The Fe$^{3+}$ spins are antiferromagnetically ordered below 360
K with the moments lying in the ab-plane, and undergo a reorientation
transition at about 35-37 K to an antiferromagnetic order with the moments
along the c-axis. A short-range, antiferromagnetic ordering of Nd$^{3+}$ along
the c-axis was attributed to the reorientation of Fe$^{3+}$ followed by a
long-range ordering at lower temperature [S. Oyama {\it et al.} J. Phys.:
Condens. Matter. {\bf 16}, 1823 (2004)]. At low temperatures and magnetic
fields above 8 T, the Nd$^{3+}$ moments are completely spin-polarized. The
dielectric permittivity also shows anomalies associated with spin configuration
changes, indicating that this compound has considerable coupling between spin
and lattice. A possible magnetic structure is proposed to explain the results.",1206.4597v1
2012/6/24,Low-Temperature Low-Field Phases of the Pyrochlore Quantum Magnet Tb$_2$Ti$_2$O$_7$,"By means of ac magnetic-susceptibility measurements, we find evidence for a
new magnetic phase of Tb$_2$Ti$_2$O$_7$ below about 140 mK in zero magnetic
field. In magnetic fields parallel to [111], this phase---exhibiting frequency-
and amplitude-dependent susceptibility and an extremely slow spin
dynamics---extends to about 70 mT, at which it gives way to another phase. The
field dependence of the susceptibility of this second phase, which extends to
about 0.6 T, indicates the presence of a weak magnetization plateau below 50
mK, as has been predicted by a single-tetrahedron four-spin model, giving
support to the underlying proposal that the disordered low-field ground state
of Tb$_2$Ti$_2$O$_7$ is a quantum spin ice.",1206.5541v3
2012/7/20,"Magnetic, magnetocaloric and magnetotransport properties of RSn_{1+x}Ge_{1-x} compounds (R=Gd, Tb, Er; x=0.1)","We have studied the magnetic, magnetocaloric and magnetotransport properties
of RSn1+xGe1-x(R=Gd, Tb, Er; x=0.1) series by means of magnetization, heat
capacity and resistivity measurements. It has been found that all the compounds
crystallize in the orthorhombic crystal structure described by the
centrosymmetric space group Cmcm (No. 63). The magnetic susceptibility and heat
capacity data suggest that all the compounds are antiferromagnetic. Large
negative values of {\theta}p in case of GdSn1.1Ge0.9 and TbSn1.1Ge0.9 indicate
that strong antiferromagnetic interactions are involved, which is also
reflected in the magnetization isotherms. On the other hand ErSn1.1Ge0.9 shows
weak antiferromagnetic interaction. The heat capacity data have been analyzed
by fitting the temperature dependence and the values of {\theta}D and {\gamma}
have been estimated. Among these three compounds, ErSn1.1Ge0.9 shows
considerable magnetic entropy change of 9.5 J/kg K and an adiabatic temperature
change of 3.2 K for a field of 50 kOe. The resistivity data in different
temperature regimes have been analyzed and the dominant contributions have been
identified. All the compounds show small but positive magnetoresistance.",1207.4971v1
2012/7/24,Exploiting magnetic properties of Fe doping in zirconia,"In this study we explore, both from theoretical and experimental side, the
effect of Fe doping in ZrO2 (ZrO2:Fe). By means of first principles simulation
we study the magnetization density and the magnetic interaction between Fe
atoms. We also consider how this is affected by the presence of oxygen
vacancies and compare our findings with models based on impurity band and
carrier mediated magnetic interaction. Experimentally thin films (~ 20 nm) of
ZrO2:Fe at high doping concentration are grown by atomic layer deposition. We
provide experimental evidence that Fe is uniformly distributed in the ZrO2 by
transmission electron microscopy and energy dispersive X-ray mapping, while
X-ray diffraction evidences the presence of the fluorite crystal structure.
Alternating gradient force magnetometer measurements show magnetic signal at
room temperature, however with low magnetic moment per atom. Results from
experimental measures and theoretical simulations are compared.",1207.5692v2
2012/7/24,Colossal non-saturating linear magnetoresistance in two-dimensional electron systems at a GaAs/AlGaAs heterointerface,"Engineering devices with a large electrical response to magnetic field is of
fundamental importance for a range of applications such as magnetic field
sensing and magnetic read-heads. We show that a colossal non-saturating linear
magnetoresistance (NLMR) arises in two-dimensional electron systems hosted in a
GaAs/AlGaAs heterostructure in the strongly insulating regime. When operated at
high source-drain bias, the magnetoresistance of our devices increases almost
linearly with magnetic field reaching nearly 10,000% at 8 Tesla, thus
surpassing many known non-magnetic materials that exhibit giant NLMR. The
temperature dependence and mobility analysis indicate that the NLMR has a
purely classical origin, driven by nanoscale inhomogeneities. A large NLMR
combined with small device dimensions makes these systems a new and attractive
candidate for on-chip magnetic field sensing.",1207.5709v2
2012/7/27,Tunable magnetic states in h-BN sheets,"Magnetism in 2D atomic sheets has attracted considerable interest as its
existence could allow the development of electronic and spintronic devices. The
existence of magnetism is not sufficient for devices, however, as states must
be addressable and modifiable through the application of an external drive. We
show that defects in hexagonal boron nitride present a strong interplay between
the the N-N distance in the edge and the magnetic moments of the defects. By
stress-induced geometry modifications, we change the ground state magnetic
moment of the defects. This control is made possible by the triangular shape of
the defects as well as the strong spin localisation in the magnetic state.",1207.6457v3
2012/8/3,Magneto-orbital helices and multiferroicity,"Orbitally ordered states evolving coincidentally with structural distortions
and magnetic ordering provide a novel route to controlling electronic and
magnetic properties of materials through external fields. We report an
unprecedented magneto-orbital helix in CaMn7O12, found to give rise to the
largest magnetically induced ferroelectric polarisation measured to date.
Characterisation of the structural modulation using x-ray diffraction, and
analysis of magnetic exchange shows that orbital order is crucial in
stabilising a chiral magnetic structure, thus allowing for electric
polarisation. Additionally, the presence of a global structural rotation
enables the coupling between this polarisation and magnetic helicity required
for multiferrocitiy. These novel principles open up the possibility of
discovering new high-temperature multiferroics.",1208.0775v1
2012/8/7,Observation of Coherent Helimagnons and Gilbert damping in an Itinerant Magnet,"We study the magnetic excitations of itinerant helimagnets by applying
time-resolved optical spectroscopy to Fe0.8Co0.2Si. Optically excited
oscillations of the magnetization in the helical state are found to disperse to
lower frequency as the applied magnetic field is increased; the fingerprint of
collective modes unique to helimagnets, known as helimagnons. The use of
time-resolved spectroscopy allows us to address the fundamental magnetic
relaxation processes by directly measuring the Gilbert damping, revealing the
versatility of spin dynamics in chiral magnets. (*These authors contributed
equally to this work)",1208.1462v1
2012/8/8,"Preparation, structural, dielectric and magnetic properties of LaFeO3-PbTiO3 solid solutions","Solid solutions of (1-x)LaFeO3-(x)PbTiO3 (0<x<1) have been prepared by
conventional solid-state reaction. These complex perovskites have been studied
by means of X-ray (XRPD) and neutron powder (NPD) diffraction, complemented
with dielectric, magnetic, heat capacity and M\""ossbauer measurements. Complete
solubility in the perovskite series was demonstrated. The NPD and XRPD patterns
were successfully refined as orthorhombic (x \leq 0.7) and tetragonal (x \geq
0.8). A composition-driven phase transformation occurs within the interval
0.7<x<0.8. The samples with x<0.5 showed evidence of long-range magnetic
ordering with an G-type antiferromagnetic arrangement of the magnetic moments
of the Fe3+ cations in the B-site with propagation vector k = (0,0,0). Based on
the obtained experimental data, a combined structural and magnetic phase
diagram has been constructed. The factors governing the structural, dielectric
and magnetic properties of (1-x) LaFeO3 - (x)PbTiO3 solid solutions are
discussed, as well as their possible multiferroicity.",1208.1577v2
2012/8/10,Effects of charge doping and constrained magnetization on the electronic structure of an FeSe monolayer,"The electronic structural properties in the presence of constrained
magnetization and a charged background are studied for a monolayer of FeSe in
non-magnetic, checkerboard-, and striped-antiferromagnetic (AFM) spin
configurations. First principles techniques based on the pseudopotential
density functional approach and the local spin density approximation are
utilized. Our findings show that the experimentally observed shape of the Fermi
surface is best described by the checkerboard AFM spin pattern. To explore the
underlying pairing mechanism, we study the evolution of the non-magnetic to the
AFM-ordered structures under constrained magnetization. We estimate the
strength of electronic coupling to magnetic excitations involving an increase
in local moment and, separately, a partial moment transfer from one Fe atom to
another. We also show that the charge doping in the FeSe can lead to an
increase in the density of states at the Fermi level and possibly produce
higher superconducting transition temperatures.",1208.2260v2
2012/8/30,Weak ferromagnetism and internal magnetoelectric effect in LiFeP$_2$O$_7$,"The magnetic, thermodynamic, and pyroelectric properties of LiFeP$_2$O$_7$
single crystals are investigated with emphasis on the magnetoelectric
interaction of the electrical polarization with the magnetic order parameter.
The magnetic order below T$_N\simeq$ 27 K is found to be a canted
antiferromagnet with a weak ferromagnetic component along the $b-$axis. A sharp
peak of the pyroelectric current at T$_N$ proves the strong internal
magnetoelectric interaction resulting in a sizable polarization decrease at the
onset of magnetic order. The magnetoelectric effect in external magnetic fields
combines a linear and a quadratic field dependence below T$_N$. Thermal
expansion data show a large uniaxial magnetoelastic response and prove the
existence of strong spin lattice coupling. LiFeP$_2$O$_7$ is a polar compound
with a strong interaction of the magnetic order parameter with the electric
polarization and the lattice.",1208.6182v1
2012/9/12,Giant magnetocaloric effect in magnetically frustrated EuHo$_2$O$_4$ and EuDy$_2$O$_4$ compounds,"We have investigated the magnetic and magnetocaloric properties of
EuHo$_2$O$_4$ and EuDy$_2$O$_4$ by magnetization and heat capacity measurements
down to 2 K. These compounds undergo a field-induced antiferromagnetic to
ferromagnetic transition and exhibit a huge entropy change. For a field change
of 0-8 T, the maximum magnetic entropy and adiabatic temperature changes are 30
(25) J kg$^{-1}$ K$^{-1}$ and 12.7 (16) K, respectively and the corresponding
value of refrigerant capacity is 540 (415) J kg$^{-1}$ for EuHo$_2$O$_4$
(EuDy$_2$O$_4$). These magnetocaloric parameters also remain large down to
lowest temperature measured and are even larger than that for some of the
potential magnetic refrigerants reported in the same temperature range for a
moderate field change. Moreover, these materials are highly insulating and
exhibit no thermal and field hysteresis, fulfilling the necessary conditions
for a good magnetic refrigerant in the low-temperature region.",1209.2513v1
2012/9/25,Dense matter is strong magnetic fields,"Compact stars having strong magnetic fields (magnetars) have been
observationally determined to have surface magnetic fields of order of
10^14-10^15 G, the implied internal field strength being several orders larger.
We study the equation of state and composition of hypernuclear matter and quark
matter - two forms of dense matter in strong magnetic fields. We find that the
magnetic field has substantial influence on the properties of hypernuclear
matter and quark matter for magnetic field B \ge 10^17 G and B \ge 10^18 G
respectively. In particular the matter properties become anisotropic. Moreover,
above a critical field B_cr, both hypernuclear and quark matter show
instability, although the values of B_cr are different for two kinds of matter.",1209.5611v3
2012/10/23,Geometric-phase interference in a Mn_{12} single-molecule magnet with four-fold rotational symmetry,"We study the magnetic relaxation rate Gamma of the single-molecule magnet
Mn_{12}-tBuAc as a function of magnetic field component H_T transverse to the
molecule's easy axis. When the spin is near a magnetic quantum tunneling
resonance, we find that Gamma increases abruptly at certain values of H_T.
These increases are observed just beyond values of H_T at which a
geometric-phase interference effect suppresses tunneling between two excited
energy levels. The effect is washed out by rotating H_T away from the spin's
hard axis, thereby suppressing the interference effect. Detailed numerical
calculations of Gamma using the known spin Hamiltonian accurately reproduce the
observed behavior. These results are the first experimental evidence for
geometric-phase interference in a single-molecule magnet with true four-fold
symmetry.",1210.6105v2
2012/10/24,Alternating domains with uniaxial and biaxial magnetic anisotropy in epitaxial Fe films on BaTiO3,"We report on domain formation and magnetization reversal in epitaxial Fe
films on ferroelectric BaTiO3 substrates with ferroelastic a-c stripe domains.
The Fe films exhibit biaxial magnetic anisotropy on top of c domains with
out-of-plane polarization, whereas the in-plane lattice elongation of a domains
induces uniaxial magnetoelastic anisotropy via inverse magnetostriction. The
strong modulation of magnetic anisotropy symmetry results in full imprinting of
the a-c domain pattern in the Fe films. Exchange and magnetostatic interactions
between neighboring magnetic stripes further influence magnetization reversal
and pattern formation within the a and c domains.",1210.6533v2
2013/1/7,Improved magnetization in sputtered dysprosium thin films,"50nm thick nanogranular polycrystalline dysprosium thin films have been
prepared via ultra-high vacuum DC sputtering on SiO2 and Si wafers. The maximum
in-plane spontaneous magnetization at T = 4K was found to be MS4K = 3.28T for
samples deposited on wafers heated to 350C with a Neel point of TN = 173K and a
ferromagnetic transition at TC = 80K, measured via zero field cooled field
cooled magnetization measurements, close to single crystal values. The slightly
reduced magnetization is explained in the light of a metastable face centered
cubic crystal phase which occurred at the seed interface and granularity
related effects, that are still noticeably influential despite an in-plane
magnetic easy axis. As deposited samples showed reduced magnetization of MS4K =
2.26T, however their ferromagnetic transition shifted to a much higher
temperature of TC = 172K and the antiferromagnetic phase was completely
suppressed probably as a result of strain.",1301.1212v1
2013/1/10,"Magnetization precession induced by quasi-transverse picosecond strain pulses in (311) ferromagnetic (Ga,Mn)As","Quasi-longitudinal and quasi-transverse picosecond strain pulses injected
into a ferromagnetic (311) (Ga,Mn)As film induce dynamical shear strain in the
film, thereby modulating the magnetic anisotropy and inducing resonant
precession of the magnetization at a frequency ~10 GHz. The modulation of the
out-of-plane magnetization component by the quasitransverse strain reaches
amplitudes as large as 10% of the equilibrium magnetization. Our theoretical
analysis is in good agreement with the observed results, thus providing a
strategy for ultrafast magnetization control in ferromagnetic films by strain
pulses.",1301.2188v1
2013/1/17,Low field anisotropic colossal magnetoresistance in $Sm_{0.53} Sr_{0.47} Mn O_3$ thin films,"SSMO5347 thin films (thicknesses ~200 nm) were deposited by on-axis dc
magnetron sputtering on the single crystal LSAT (001) substrates. These films
are oriented along the out of plane c-direction. The ferromagnetic and
insulator-metal transition occurs at 96 K and 91 K, respectively. The
magnetization easy axis is observed to lie in the plane of the film while the
magnetic hard axis is found to be along the normal to this. The
magnetotransport of the SSMO films, which was measured as a function of angle
(theta) between the magnetic field (H) and plane of the film, shows colossal
anisotropy. Magnetoresistance (MR) decreases drastically as theta increases
from 0 degree (H//easy axis) to 90 degree (H//hard axis). The out-of-plane
anisotropic MR (AMR) is as high as 88 % at H=3.6 kOe and 78 K. The colossal
anisotropy has been explained in terms of the magnetic anisotropies at play and
the magnetic domain motion in applied magnetic field.",1301.4048v1
2013/1/23,Electric-field-induced magnetization changes in Co/Al2O3 granular multilayers,"We study experimentally the effect of electric field on the magnetization of
Co/Al2O3 granular multilayers. We observe two distinct regimes: (a) low-field
regime when the net magnetization of the system changes in a reversible way
with the applied electric field and (b) high-field regime when the
magnetization decreases irreversibly. The former is attributed to the changes
in the relative 3d-orbital occupation of the minority and majority bands in the
Co granules. A theoretical model has been developed to explain the electric
field induced changes in the band structure of the granular system and hence
the magnetic moment. The latter result may be understood assuming the electric
field induces oxygen migration from Al2O3 to the Co granules, since an increase
in oxidation state of the Co granules is shown, through ab-initio calculations,
to give rise to a reduced magnetization of the system.",1301.5396v1
2013/2/4,"Parimagnetism in RCo$_2$ series (R=Dy, Ho, and Tm)","X-ray circular magnetic dichroism (XMCD), longitudinal ($\chi_{ac}$) and
transverse (TS) ac magnetic susceptibility have been measured in several
members of the $R$Co$_2$ series ($R$ = Dy, Ho, and Tm) as a function of
temperature and applied magnetic field. We show that parimagnetism is a general
behavior along the $R$Co$_2$ ferrimagnetic series ($R$ being a heavy rare earth
ion). XMCD results evidence the presence of two compensation temperatures,
defining two different parimagnetic configurations, which is a fully unexpected
result. The inverse $\chi_{ac}$ curve exhibits a deviation from Curie-Weiss
behavior which is recovered under applied magnetic field. The large excess of
polarizability above the critical temperature proves the existence of an
enhanced effective moment due to the presence of short range magnetic
correlations, which are also observed in TS measurements. The combination of TS
and XMCD measurements allows to depict new magnetic phase diagrams for the
$R$Co$_2$ series. A new scenario allowing to understand the observed
phenomenology as a Griffiths phase-like behavior is proposed, where the
amorphous $R$Co$_2$ represents the undiluted system case.",1302.0775v1
2013/2/16,Magnetic state of pyrochlore Cd2Os2O7 emerging from strong competition of ligand distortions and longer-range crystalline anisotropy,"By many-body quantum-chemical calculations, we investigate the role of two
structural effects - local ligand distortions and the anisotropic Cd-ion
coordination - on the magnetic state of Cd2Os2O7, a spin S=3/2 pyrochlore. We
find that these effects strongly compete, rendering the magnetic interactions
and ordering crucially depend on these geometrical features. Without trigonal
distortions a large easy-plane magnetic anisotropy develops. Their presence,
however, reverses the sign of the zero-field splitting and causes a large
easy-axis anisotropy (D = -6.8 meV), which in conjunction with the
antiferromagnetic exchange interaction (J = 6.4 meV) stabilizes an
all-in/all-out magnetic order. The competition uncovered here is a generic
feature of pyrochlore magnets.",1302.3989v1
2013/3/14,Magnetic hysteresis loop as a probe to distinguish single layer from many layer graphitic structure,"In this report we have pointed out that magnetic hysteresis loop can be used
as a probe to distinguish a single layer from a many layer graphitic structure.
Chemically we have synthesized graphitic oxide (GO) and reduced graphitic oxide
(RGO) for this investigation. We observe ferromagnetic like hysteresis loops
for both GO and RGO below a certain applied critical magnetic field and above
this critical field we observe cross-over of the positive magnetization to
negative magnetization leading to diamagnetic behaviour. This cross-over is
more dominant for the case of many layer graphitic structure. Upon annealing of
GO in air the critical cross-over field decreases and the magnetization
increases for multilayer graphitic structure. Possible reasons for all these
observations and phenomena is presented here.",1303.3433v1
2013/3/18,Determination of the magnetization profile of Co/Mg periodic multilayers by magneto-optic Kerr effect and X-ray magnetic resonant reflectivity,"The resonant magnetic reflectivity of Co/Mg multilayers around the Co L2,3
absorption edge is simulated then measured on a specifically designed sample.
The dichroic signal is obtained when making the difference between the two
reflectivities measured with the magnetic field applied in two opposite
directions parallel to the sample surface. The simulations show that the
existence of magnetic dead layers at the interfaces between the Co and Mg
layers leads to an important increase of the dichroic signal measured in the
vicinity of the third Bragg peak that otherwise should be negligible. The
measurements are in agreement with the model introducing 0.25 nm thick dead
layers. This is attributed to the Co atoms in contact with the Mg layers and
thus we conclude that the Co-Mg interfaces are abrupt from the magnetic point
of view.",1303.4380v1
2013/3/19,X-ray absorption spectroscopy and magnetic circular dichroism studies of L1_0-Mn-Ga thin films,"Tetragonally distorted \(\rm{Mn}_{3-x}\rm{Ga}_x\) thin films with \(0.1< x <
2\) show a strong perpendicular magnetic anisotropy and low magnetization and
thus have the potential to serve as electrodes in spin transfer torque magnetic
random access memory. Because a direct capping of these films with MgO is
problematic due to oxide formation, we examined the influence of a CoFeB
interlayer, and of two different deposition methods for the MgO barrier on the
formation of interfacial MnO for \(\rm{Mn}_{62}\rm{Ga}_{38}\) by element
specific X-ray absorption spectroscopy (XAS) and magnetic circular dichroism
(XMCD). A highly textured L1\(_0\) crystal structure of the Mn-Ga films was
verified by X-ray diffraction (XRD) measurements. For samples with e-beam
evaporated MgO barrier no evidence for MnO was found, whereas in samples with
magnetron sputtered MgO MnO was detected, even for the thickest interlayer
thickness. Both XAS and XMCD measurements showed an increasing interfacial MnO
amount with decreasing CoFeB interlayer thickness. Additional element specific
full hysteresis loops determined an out-of-plane magnetization axis for the Mn
and Co, respectively.",1303.4648v2
2013/3/25,Optical generation of intense ultrashort magnetic pulses at the nanoscale,"Generating, controlling, and sensing strong magnetic fields at ever shorter
time and length scales is important for both fundamental solid-state physics
and technological applications such as magnetic data recording. Here, we
propose a scheme for producing strong ultrashort magnetic pulses localized at
the nanoscale. We show that a bimetallic nanoring illuminated by femtosecond
laser pulses responds with transient thermoelectric currents of picosecond
duration, which in turn induce Tesla-scale magnetic fields in the ring cavity.
Our method provides a practical way of generating intense nanoscale magnetic
fields with great potential for materials characterization, terahertz radiation
generation, and data storage applications.",1303.6072v1
2013/3/28,Spin Torque on Magnetic Textures Coupled to the Surface of a Three-Dimensional Topological Insulator,"We investigate theoretically the spin torque and magnetization dynamic in a
thin ferromagnetic (FM) layer with spatially varying magnetization. The FM
layer is deposited on the surface of a topological insulator (TI). In the limit
of the adiabatic relaxation of electron spin along the magnetization, the
interaction between the exchange interaction and the Rashba-like surface
texture of a TI yields a topological gauge field. Under the gauge field and an
applied current, spin torque is induced according to the direction of the
current. We derived the corresponding effective anisotropy field and hence the
modified Landau-Lifshitz-Gilbert equation, which describes the spin torque and
the magnetization dynamic. In addition, we study the effective field for
exemplary magnetic textures, such as domain wall, skyrmion, and vortex
configurations. The estimated strength of the effective field is comparable to
the switching fields of typical FM materials, and hence can significantly
influence the dynamics of the FM layer.",1303.7031v1
2013/4/8,Reentrant cluster glass behavior in La2CoMnO6 nanoparticles,"Magnetic study on La2CoMnO6 nanoparticles revealed multiple magnetic
transitions at 218 K, 135 K and below 38 K and the nature of the low
temperature transition was unclear [J Appl Phys 111, 024102 2012]. Presence of
mixed valance states of Co and Mn has been confirmed from the XPS measurement
and its presence along with antisite disorder affects in reducing the
saturation magnetization of the nanoparticles. The zero field cooled and field
cooled bifurcation in dc magnetization, relaxation in zero field cooled
magnetization and large enhancement in coercive field below the glassy
temperature has been discussed. Frequency dependence of ac susceptibility using
power law has revealed cluster glass behavior. Further, the dc field
superimposed on ac susceptibility and absence of memory effect in ac
susceptibility has suggested the existence of non interacting clusters
comprising of competing interactions below 38 K. Competing magnetic
interactions due to the presence of mixed valances and antisite disorder found
to establish a reentered cluster glassy state in the nanoparticles.",1304.2267v1
2013/4/19,Boundaries for efficient use of electron vortex beams to measure magnetic properties,"Development of experimental techniques for characterization of magnetic
properties at high spatial resolution is essential for progress in
miniaturization of magnetic devices, for example, in data storage media.
Inelastic scattering of electron vortex beams (EVB) was recently reported to
contain atom-specific magnetic information. We have developed a theoretical
description of inelastic scattering of EVB on crystals and performed
simulations for EVB of different diameters. We show that use of an EVB wider
than an interatomic distance does not provide any advantage over an ordinary
convergent beam without angular momentum. On the other hand, in the atomic
resolution limit, electron energy loss spectra measured by EVB are strongly
sensitive to the spin and orbital magnetic moments of studied matter, when
channeling through or very close to the atomic columns. Our results demonstrate
the boundaries for efficient use of EVB in measurement of magnetic properties.",1304.5461v3
2013/4/23,Magnetic force microscopy study of the switching field distribution of low density arrays of single domain magnetic nanowires,"In the present work, we report on the in situ magnetic force microscopy (MFM)
study of the magnetization reversal in two-dimensional arrays of ferromagnetic
Ni80Fe20 and Co55Fe45 nanowires(NW) with different diameters (40, 50, 70 and
100 nm) deposited inside low porosity (P<1%) nanoporous polycarbonate
membranes. In such arrays, the nanowires are sufficiently isolated from each
other so that long range dipolar interactions can be neglected. The MFM
experiments performed for different magnetization states at the same spot of
the samples are analysed to determine the switching field distribution (SFD).
The magnetization curves obtained from the MFM images are relatively square
shaped. The SFD widths are narrower compared to those obtained for high density
arrays. The weak broadening of the curves may be ascribed to the NW intrinsic
SFD. The influence of diameter and composition of the ferromagnetic NW is also
investigated.",1304.6441v1
2013/4/24,Observation of an inter-sublattice exchange magnon in CoCr$_2$O$_4$ and analysis of magnetic ordering,"We report on an investigation of optical properties of multiferroic
CoCr$_{2}$O$_{4}$ at terahertz frequencies in magnetic fields up to 30 T. Below
the ferrimagnetic transition (94 K), the terahertz response of
CoCr$_{2}$O$_{4}$ is dominated by a magnon mode, which shows a steep
magnetic-field dependence. We ascribe this mode to an exchange resonance
between two magnetic sublattices with different $g$-factors. In the framework
of a simple two-sublattice model (the sublattices are formed by Co$^{2+}$ and
Cr$^{3+}$ ions), we find the inter-sublattice coupling constant, $\lambda = -
(18 \pm 1)$ K, and trace the magnetization for each sublattice as a function of
field. We show that the Curie temperature of the Cr$^{3+}$ sublattice,
$\Theta_{2}$ = $(49 \pm 2)$ K, coincides with the temperature range, where
anomalies of the dielectric and magnetic properties of CoCr$_{2}$O$_{4}$ have
been reported in literature.",1304.6525v1
2013/5/2,Coupled Spin and Pseudo-magnetic Field in Graphene Nanoribbons,"Pseudo-magnetic field becomes an experimental reality after the observation
of zero-field Landau level-like quantization in strained graphene, but it is
not expected that the time-reversal symmetric pseudo-magnetic fields will have
any effect on the spin degree of freedom of the charge carriers. Here, we
demonstrate that spin-orbit coupling (SOC) could act as a bridge between
pseudo-magnetic field and spin. In quantum spin Hall (QSH) states, the
direction of the spin of edge states is tied to their direction of motion
because of the SOC. The pseudo-magnetic field affects the clockwise and
counter-clock-wise edge currents of the QSH states, and consequently lifts the
degenerate edge states of opposite spin orientation. Because of opposite signs
of the pseudo-magnetic field in two valleys of graphene, the one-dimensional
charge carriers at the two opposite edges have different group velocities, and
in some special cases the edge states can only propagate at one edge of the
nanoribbon and the group velocity at the other edge becomes zero.",1305.0335v2
2013/5/6,Spatially homogeneous ferromagnetism below the enhanced Curie temperature in EuO_{1-x} thin films,"We have used low energy implanted muons as a volume sensitive probe of the
magnetic properties of EuO_{1-x} thin films. We find that static and
homogeneous magnetic order persists up to the elevated T_C in the doped samples
and the muon signal displays the double dome feature also observed in the
sample magnetization. Our results appear incompatible with either the magnetic
phase separation or bound magnetic polaron descriptions previously suggested to
explain the elevated T_C, but are compatible with an RKKY-like interaction
mediating magnetic interactions above 69 K.",1305.1341v2
2013/6/6,Giant exchange bias in a single-phase magnet with two magnetic sublattices,"Exchange bias phenomenon is generally ascribed to the exchange coupling at
the interfaces between ferromagnetic and antiferromagnetic layers. Here, we
propose a bulk form of exchange bias in a single-phase magnet where the
coupling between two magnetic sublattices induces a significant shift of the
coercive field after a field cooling. Our experiments in a complicated magnet
YbFe2O4 demonstrate a giant exchange bias at low temperature when the coupling
between the Yb3+ and Fe2+/Fe3+ sublattices take places. The cooling magnetic
field dependence and the training effect of exchange bias are consistent with
our model. In strong contrast to conventional interfacial exchange bias, this
bulk form of exchange bias can be huge, reaching the order of a few Tesla.",1306.1370v1
2013/6/7,Thermal Photons From Magnetized Bare Strange Stars,"A plasma made out of strange-quark matter (SQM) and electrons, has a rather
high plasma frequency (>20 MeV). Thus, a compact star made of such material all
the way up to its surface, i.e., a bare strange star, would be unable to
radiate away its thermal emission.
  We use the MIT-bag model and assume that SQM is the ground state of nuclear
matter at high density. We investigate whether the presence of a magnetic field
will allow propagation of radiation at frequencies below the SQM plasma
frequencies. Hence, we study the presence of gyrofrequencies in a SQM plasma
permeated by a strong magnetic field (B > 10^{12} G). We find that small
regions in the frequency spectrum allow radiation propagation due to the
presence of the magnetic fields. It is likely that narrow bands of radiation
would likely be observable from magnetized bare strange stars .",1306.1828v1
2013/6/10,Direct proof of unique magnetic and superconducting phases in superoxygenated high-Tc cuprates,"We present a combined magnetic neutron scattering and muon spin rotation
study of the nature of the magnetic and superconducting phases in
electronically phase separated La(2-x)Sr(x)CuO(4+y), x = 0.04, 065, 0.09. For
all samples, we find long-range modulated magnetic order below T_N ~ T_c = 39
K. In sharp contrast wit oxygen-stoichiometric La(2-x)Sr(x)CuO(4), we find that
the magnetic propagation vector as well as the ordered magnetic moment is
independent of Sr content and consistent with that of the 'striped' cuprates.
Our study provides direct proof that superoxygenation in La(2-x)Sr(x)CuO(4+y)
allows the spin stripe ordered phase to emerge and phase separate from
superconducting regions with the hallmarks of optimally doped
oxygen-stoichiometric La(2-x)Sr(x)CuO(4).",1306.2155v2
2013/6/13,"Investigation of the quaternary Fe2-xCoxMnSi alloys by structural, magnetic, resistivity and spin polarization measurements","Effects of the Co substitution have been observed on the structural, magnetic
and magneto-transport properties of Fe2-xCoxMnSi alloy. Curie temperature (TC)
and saturation magnetization (MS) of these alloys increased linearly with the
Co substitution. Competitive magnetic interaction between ferromagnetic (FM)
and anti-ferromagnetic (AFM) phases exists in Fe2-xCoxMnSi for x less than 0.2,
AFM phase is completely disappears for x greater than or equal to 0.2. The
value of Rhodes-Wohlfarth ratio pc/ps is greater than one for these alloys
which is the characteristics of iterant magnetism present in the system.
M\""ossbauer spectroscopic measurements have been done to investigate the atomic
disorder and local magnetic moment for some x values. Resistivity measurements
also confirm the stability of ferromagnetism with the concentration of Co and
also show a sign of half metallicity. Resistivity shows semiconducting
behaviour for x = 0.4 which is interesting in view of spin gapless
semiconductors.",1306.3086v3
2013/6/18,"Modification in structural, dielectric and magnetic properties of La and Nd co-substituted epitaxial BiFeO3 thin films","The influence of La and Nd co-substitution on the structural and magnetic
properties of BiFeO3 (BFO) thin films was examined. Epitaxial thin films of
pure and, La and Nd co-doped BFO on the SrRuO3 buffered single crystal SrTiO3
(001) substrate were deposited using pulsed laser deposition. The structural
change in co doped La and Nd BFO thin films which was caused by the changes of
force constant in the crystal lattice induced by ionic radii mismatch was
investigated. Raman spectroscopy studies manifest the structural change in
doped BFO films from rhombohedral to monoclinic distorted phase which is
induced by the co substitution of La and Nd. Room temperature magnetic
hysteresis curves indicated that saturation magnetization is enhanced in the
doped film with saturation magnetization of ~20 emu/cm3. The dielectric and
magnetic properties are effectively improved in BLNFO films compared to pure
BFO thin films.",1306.4214v1
2013/7/9,Strain-controlled nonvolatile magnetization switching,"We investigate different approaches towards a nonvolatile switching of the
remanent magnetization in single-crystalline ferromagnets at room temperature
via elastic strain using ferromagnetic thin film/piezoelectric actuator
hybrids. The piezoelectric actuator induces a voltage-controllable strain along
different crystalline directions of the ferromagnetic thin film, resulting in
modifications of its magnetization by converse magnetoelastic effects. We
quantify the magnetization changes in the hybrids via ferromagnetic resonance
spectroscopy and superconducting quantum interference device magnetometry.
These measurements demonstrate a significant strain-induced change of the
magnetization, limited by an inefficient strain transfer and domain formation
in the particular system studied. To overcome these obstacles, we address
practicable engineering concepts and use a model to demonstrate that a
strain-controlled, nonvolatile magnetization switching should be possible in
appropriately engineered ferromagnetic/piezoelectric actuator hybrids.",1307.2433v1
2013/7/18,Correlation between defect and magnetism of Ar9+ implanted and un-implanted Zn0.95Mn0.05O thin films suitable for electronic application,"Sol-gel derived thin films of Zn0.95Mn0.05O have been implanted with Ar9+
ions with doses viz. 5x10e14 ions/cm2 (low), 1x10e15 ions/cm2 (intermediate)
and 1x10e16 ions/cm2 (high). Structural, morphological, optical and magnetic
properties of the films have been investigated. Structural study confirmed
single phase, wurtzite structure of the films. The absence of impurity phase
has been confirmed from several measurements. Ion implantation induces a large
concentration of point defects into the films as identified from optical study.
All films exhibit well above room temperature (RT) intrinsic ferromagnetism
(FM) as evidenced from field and temperature dependent magnetization
measurements. The magnetization attains the maximum value for high dose of Ar9+
ion implanted film. It shows RT saturation magnetization (MS) value of
0.69emu/gm. The observed FM has been correlated with proportion of intrinsic
defects, such as, zinc and oxygen vacancies and the values of MS. Defect
induced formation of bound magnetic polaron actually controls the FM. The
utility of these films in transparent spin electronic device has also been
exhibited.",1307.4895v1
2013/7/31,Arrays of carbon nanoscrolls as deep-subwavelength magnetic metamaterials,"We demonstrate theoretically that an array of carbon nanoscrolls acts as a
hyperbolic magnetic metamaterial in the THz regime with genuine subwavelength
operation corresponding to wavelength-to-structure ratio of about 200. Due to
the low sheet resistance of graphene, the electromagnetic losses in an array of
carbon nanoscrolls are almost negligible offering a very sharp magnetic
resonance of extreme positive and negative values of the effective magnetic
permeability. The latter property leads to superior imaging properties for
arrays of carbon nanoscrolls which can operate as magnetic endoscopes in the
THz where magnetic materials are scarce. Our optical modelling is supplemented
with ab initio density-functional calculations of the self-winding of a single
layer of graphene onto a carbon nanotube so as to form a carbon nanoscroll. The
latter process is viewed as a means to realize ordered arrays of carbon
nanoscrolls in the laboratory based on arrays of aligned carbon nanotubes which
are nowadays routinely fabricated.",1307.8368v1
2013/8/24,Emerging magnetism and electronic phase separation at titanate interfaces,"The emergence of magnetism in otherwise nonmagnetic compounds and its
underlying mechanisms have become the subject of intense research. Here we
demonstrate that the nonmagnetic oxygen vacancies are responsible for an
unconventional magnetic state common for titanate interfaces and surfaces.
Using an effective multiorbital modelling, we find that the presence of
localized vacancies leads to an interplay of ferromagnetic order in the
itinerant t2g band and complex magnetic oscillations in the
orbitally-reconstructed eg-band, which can be tuned by gate fields at oxide
interfaces. The magnetic phase diagram includes highly fragmented regions of
stable and phase-separated magnetic states forming beyond nonzero critical
defect concentrations.",1308.5319v1
2013/8/27,Creating Magnetic Fields in excess of 1000 T by Misoriented Stacking in a Graphene Bilayer,"It is well established that some kinds of lattice deformations in graphene
monolayer, which change electron hopping in sublattice and affect in-plane
motion of electrons, may induce out-of-plane pseudo-magnetic fields as large as
100 T. Here, we demonstrate that stacking misorientation in graphene bilayers
mimics the effect of huge in-plane pseudo-magnetic fields greater than 1000 T
on the interlayer hopping of electrons. As well as addressing the similarity
between the effect of in-plane pseudo-magnetic fields and twisting on the
electronic band structure of Bernal graphene bilayer, we point out that
in-plane magnetic fields (or twisting) could modify the low-energy pseudospin
texture of the graphene bilayer (the pseudospin winding number is reduced from
2 to 1), thereby changing the chiralities of quasiparticles from that of spin 1
to spin 1/2. Our results illustrate the possibility of controllably
manipulating electronic properties of Bernal graphene bilayer by introducing
the in-plane magnetic field or twisting.",1308.5763v2
2013/8/27,Experimental realization of magnetic energy concentration and transmission at a distance by metamaterials,"Controlling electromagnetic energy is essential for an efficient and
sustainable society. A key requirement is concentrating magnetic energy in a
desired volume of space in order to either extract the energy to produce work
or store it. Metamaterials have opened new possibilities for controlling
electromagnetic energy. Recently, a superconductor-ferromagnetic metamaterial
that allows unprecedented concentration and amplification of magnetic energy,
and also its transmission at distance through free space, has been devised
theoretically. Here we design and build an actual version of the
superconductor-ferromagnetic metamaterial and experimentally confirm these
properties. We show that also a ferromagnetic metamaterial, without
superconducting parts, can achieve concentration and transmission of energy
with only a slight decrease in the performance. Transmission of magnetic energy
at a distance by magnetic metamaterials may provide new ways of enhancing
wireless power transmission, where efficiency depends critically on the
magnetic coupling strength between source and receiver.",1308.5878v1
2013/9/5,3d-4f spin interaction induced giant magnetocaloric effect in zircon-type DyCrO4 and HoCrO4 compounds,"We have investigated the influence of 3d-4f spin interaction on magnetic and
magnetocaloric properties of DyCrO$_4$ and HoCrO$_4$ compounds by magnetization
and heat capacity measurements. Both the compounds exhibit complicated magnetic
properties and huge magnetic entropy change around the ferromagnetic transition
due to the strong competition between ferromagnetic and antiferromagnetic
superexchange interactions. For a field change of 8 T, the maximum values of
magnetic entropy change ($\Delta S_{M}^{max}$), adiabatic temperature change
($\Delta T_{ad}$), and refrigerant capacity (RC) reach 29 J kg$^{-1}$ K$^{-1}$,
8 K, and 583 J kg$^{-1}$, respectively for DyCrO$_4$ whereas the corresponding
values for HoCrO$_4$ are 31 J kg$^{-1}$ K$^{-1}$, 12 K, and 622 J kg$^{-1}$.
$\Delta S_{M}^{max}$, $\Delta T_{ad}$, and RC are also quite large for a
moderate field change. The large values of magnetocaloric parameters suggest
that the zircon-type DyCrO$_4$ and HoCrO$_4$ could be the potential magnetic
refrigerant materials for liquefaction of hydrogen.",1309.1242v1
2013/9/16,Magnetic control of the valley degree of freedom of massive Dirac fermions with application to transition metal dichalcogenides,"We study the valley-dependent magnetic and transport properties of massive
Dirac fermions in multivalley systems such as the transition metal
dichalcogenides. The asymmetry of the zeroth Landau level between valleys and
the enhanced magnetic susceptibility can be attributed to the different orbital
magnetic moment tied with each valley. This allows the valley polarization to
be controlled by tuning the external magnetic field and the doping level. As a
result of this magnetic field induced valley polarization, there exists an
extra contribution to the ordinary Hall effect. All these effects can be
captured by a low energy effective theory with a valley-orbit coupling term.",1309.3814v1
2013/9/16,Magnetic Phase Transition in the Low Dimensional Compound BaMn2Si2O7,"The structural and magnetic properties of BaMn2Si2O7 have been investigated.
The magnetic susceptibility and specific heat, measured using single crystals,
suggest that the quasi-one-dimensional magnetism originating from the loosely
coupled Mn2+ chain carrying S=5/2 is present at high temperatures, which is
similar to the other quasi-one-dimensional barium silicates, BaM2Si2O7 (M: Cu
and Co). The Neel temperature (TN=26 K) is high compared to the magnetic
interaction along the chain (J = -6 K). The neutron powder diffraction study
has revealed that the magnetic structure is long-ranged with antiferromagnetic
arrangement along the chain (c) direction and ferromagnetic arrangement along
the a and b axes. The detailed structural analysis suggests that the interchain
interaction via Mn-O-Mn bond along the a axis is relatively large, which makes
the system behave more two-dimensionally in the ac plane and enhances TN.",1309.4005v2
2013/10/1,Temperature and Field Dependence of Magnetic Domains in La$_{1.2}$Sr$_{1.8}$Mn$_2$O$_7$,"Colossal magnetoresistance and field-induced ferromagnetism are well
documented in manganite compounds. Since domain wall resistance contributes to
magnetoresistance, data on the temperature and magnetic field dependence of the
ferromagnetic domain structure are required for a full understanding of the
magnetoresistive effect. Here we show, using cryogenic Magnetic Force
Microscopy, domain structures for the layered manganite
La$_{1.2}$Sr$_{1.8}$Mn$_2$O$_7$ as a function of temperature and magnetic
field. Domain walls are suppressed close to the Curie temperature T$_C$, and
appear either via the application of a c-axis magnetic field, or by decreasing
the temperature further. At temperatures well below T$_C$, new domain walls,
stable at zero field, can be formed by the application of a c-axis field.
Magnetic structures are seen also at temperatures above T$_C$: these features
are attributed to inclusions of additional Ruddleston-Popper manganite phases.
Low-temperature domain walls are nucleated by these ferromagnetic inclusions.",1310.0258v5
2013/10/7,Double magnetic resonance and spin anisotropy in Fe-based superconductors due to static and fluctuating antiferromagnetic orders,"Motivated by recent neutron scattering experiments in Fe-based
superconductors, we study how the magnetic resonance in the superconducting
state is affected by the simultaneous presence of either static or fluctuating
magnetic orders using the random phase approximation. We find that for the
underdoped materials with coexisting superconducting and antiferromagnetic
orders, spin rotational symmetry is explicitly broken at the ordering momentum
$Q_1 = (\pi,0)$. Only the longitudinal susceptibility exhibits the resonance
mode, whereas a spin-wave Goldstone mode develops in the transverse component.
Meanwhile, at the frustrated momentum $Q_2 = (0,\pi)$, the susceptibility
becomes isotropic in spin space and the magnetic resonance exists for both
components. Furthermore, the resonance energies at $Q_1$ and $Q_2$ have
distinct scales, which provides a natural explanation for the recently observed
double resonance peaks. In addition, we show that near optimal doping the
existence of strong magnetic fluctuations, which are modeled here via a
Gaussian mode, can still induce the spin anisotropy in the magnetic
susceptibility.",1310.1657v2
2013/10/13,Jahn-Teller distortion induced magnetic phase transition in cubic BaFeO$_{3}$,"Using density functional theory (DFT) with local density approximation (LDA)
and generalized gradient approximation (GGA) correlation functionals, the
electronic and magnetic structures of cubic BaFeO$_{3}$ in the ferromagnetic
(FM) and antiferromagnetic (AFM) states are studied. Our LDA/GGA and
LDA$+U$/GGA$+U$ results show that cubic BFO has a FM ground state, in agreement
with recent experimental works. Two types of Jahn-Teller (JT) distortions,
denoted as JT1 and JT2, are considered. We find FM to ferrimagnetic (FIM) and
FM to AFM magnetic phase transitionn in the JT1 and JT2 type of distortions,
respectively. Larger strains are required for the FM-AFM transition as compared
to the FM-FIM. DFT$+U$ calculations also show that the magnetic moments
dramatically decrease at large strains due to strong overlapping between the Fe
and O atoms. The origins of these transitions is discussed in terms of a
competition between double exchange and superexchange interactions. Oxygen and
Fe displacements are therefore responsible for the magnetic phase transitions
and the reduction of the magnetic moments.",1310.3502v1
2013/10/31,Novel dielectric anomalies due to spin-chains above and below Neel temperature in Ca3Co2O6,"We bring out novel dielectric behavior of a spin-chain compound, Ca3Co2O6,
undergoing Neel order at (T_N=) 24 K. It is found that the virgin curve in the
plot of isothermal dielectric constant versus magnetic-field lies outside the
'butterfly-shaped' envelope curve well below T_N (e.g., 2.6 K), with a
signature of a partial arrest of the high-field magnetoelectric ME) phase in
zero-field after travelling through magnetic-field-induced magnetic
transitions. This behavior is in contrast to that observed in the isothermal
magnetization data. Thus, this work brings out a novel case for
'phase-coexistence phenomenon' due to ME coupling. Another strange finding is
that there is a weak, but a broad, peak in dielectric constant around 85 - 115
K well above T_N, attributable to incipient spin-chain magnetic ordering. This
finding should inspire further work to study ME coupling on artificial
assemblies of magnetic chains, also keeping in mind miniaturization required
for possible applications.",1310.8548v1
2013/11/4,Magnetic interactions in the Martensitic phase of Mn rich Ni-Mn-In shape memory alloys,"The magnetic properties of Mn$_{2}$Ni$_{(1+x)}$In$_{(1-x)}$ ($x$ = 0.5, 0.6,
0.7) and Mn$_{(2-y)}$Ni$_{(1.6+y)}$In$_{0.4}$ ($y$ = -0.08, -0.04, 0.04, 0.08)
shape memory alloys have been studied. Magnetic interactions in the martensitic
phase of these alloys are found to be quite similar to those in
Ni$_2$Mn$_{(1+x)}$In$_{(1-x)}$ type alloys. Doping of Ni for In not only
induces martensitic instability in Mn$_2$NiIn type alloys but also affects
magnetic properties due to a site occupancy disorder. Excess Ni preferentially
occupies X sites forcing Mn to the Z sites of X$_2$YZ Heusler composition
resulting in a transition from ferromagnetic ground state to a state dominated
by ferromagnetic Mn(Y) - Mn(Y) and antiferromagnetic Mn(Y)-Mn(Z) interactions.
These changes in magnetic ground state manifest themselves in observation of
exchange bias effect even in zero field cooled condition and virgin
magnetization curve lying outside the hysteresis loop.",1311.0579v1
2013/11/8,Novel magnetic state in $d^4$ Mott insulators,"We show that the interplay of strong Hubbard interaction $U$ and spin-orbit
coupling $\lambda$ in systems with $d^4$ electronic configuration leads to
several unusual magnetic phases. Most notably, we find that competition between
superexchange and spin-orbit coupling leads to a phase transition from a
non-magnetic state predicted by atomic physics to a novel magnetic state in the
large $U$ limit. We show that the local moment changes dramatically across this
phase transition, challenging the conventional wisdom that local moments are
robust against small perturbations in a Mott insulator. The Hund's coupling
plays an important role in determining the nature of the magnetism. We identify
candidate materials and present predictions for Resonant X-ray Scattering (RXS)
signatures of the unusual magnetism in $d^4$ Mott insulators.",1311.2823v2
2013/11/14,Structural variations and magnetic properties of the quantum antiferromagnets Cs2CuCl4-xBrx,"Depending on the crystal growth conditions, an orthorhombic (O-type) or a
tetragonal (T-type) structure can be found in the solid solution Cs2CuCl4-xBrx
(0 < x < 4). Here we present measurements of the temperature-dependent magnetic
susceptibility and isothermal magnetization on the T-type compounds x = 1.6 and
1.8 and compare these results with the magnetic properties recently derived for
the O-type variant by Cong et al., Phys. Rev. B 83, 064425 (2011). The systems
were found to exhibit quite dissimilar magnetic properties which can be
assigned to differences in the Cu coordination in these two structural
variants. Whereas the tetragonal compounds can be classified as quasi-2D
ferromagnets, characterized by ferromagnetic layers with a weak
antiferromagnetic inter-layer coupling, the orthorhombic materials, notably the
border compounds x = 0 and 4, are model systems for frustrated 2D Heisenberg
antiferromagnets",1311.3351v1
2013/12/3,Depth dependent magnetization profiles of hybrid exchange springs,"We report on the magnetization depth profile of a hybrid exchange spring
system in which a Co/Pd multilayer with perpendicular anisotropy is coupled to
a CoFeB thin film with in-plane anisotropy. The competition between these two
orthogonal anisotropies promotes a strong depth dependence of the magnetization
orientation. The angle of the magnetization vector is sensitive both to the
strength of the individual anisotropies and to the local exchange constant, and
is thus tunable by changing the thickness of the CoFeB layer and by
substituting Ni for Pd in one layer of the Co/Pd stack. The resulting magnetic
depth profiles are directly probed by element specific x-ray magnetic circular
dichroism (XMCD) of the Co, Fe, and Ni layers located at different average
depths. The experimental results are corroborated by micromagnetic simulations.",1312.0878v1
2013/12/22,Dynamical Skyrmion State in a Spin Current Nano-Oscillator with Perpendicular Magnetic Anisotropy,"We study the spectral characteristics of spin current nano-oscillators based
on the Pt/[Co/Ni] magnetic multilayer with perpendicular magnetic anisotropy.
By varying the applied magnetic field and current, both localized and
propagating spin wave modes of the oscillation are achieved. At small fields,
we observe an abrupt onset of the modulation sidebands. We use micromagnetic
simulations to identify this state as a dynamical magnetic skyrmion stabilized
in the active device region by spin current injection, whose current-induced
dynamics is accompanied by the gyrotropic motion of the core due to the skew
deflection. Our results demonstrate a practical route for controllable skyrmion
manipulation by spin current in magnetic thin films.",1312.6343v2
2013/12/27,Ground-state magnetic phase diagram of bow-tie graphene nanoflakes in external magnetic field,"The magnetic phase diagram of a ground state is studied theoretically for
graphene nanoflakes of bow-tie shape and various size in external in-plane
magnetic field. The tight-binding Hamiltonian supplemented with Hubbard term is
used to model the electronic structure of the systems in question. The
existence of the antiferromagnetic phase with magnetic moments localized at the
sides of the bow-tie is found for low field and a field-induced spin-flip
transition to ferromagnetic state is predicted to occur in charge-undoped
structures. For small nanoflake doped with a single charge carrier the
low-field phase is ferrimagnetic and a metamagnetic transition to ferromagnetic
ordering can be forced by the field. The critical field is found to decrease
with increasing size of the nanoflake. The influence of diagonal and
off-diagonal disorder on the mentioned magnetic properties is studied. The
effect of off-diagonal disorder is found to be more important than this of
diagonal disorder, leading to significantly widened distribution of critical
fields for disordered population of nanoflakes.",1312.7298v1
2013/12/30,Transient coherence of an EIT media under strong phase modulation,"A strong phase modulated coupling field leads to an amplitude modulation of a
probe field in an electromagnetically induced transparency process. Time vs.
detuning plots for different modulation frequencies reveals a transition
between an adiabatic regime where a series of smooth pulses are created with a
global phase dependent upon the detuning, and a non-adiabatic regime where a
strong transient oscillating response is added to these pulses. In the extreme
non-adiabatic regime, where the modulation frequency is higher than the
transient decay time, a coherent interference pattern is revealed. Adding a
magnetic field lifts the hyperfine level degeneracy, resulting in a separation
of the original pulse to three pulses. Every pulse has now a different phase
dependent upon the magnetic field causing an interference effect between the
different magnetic level transients. We explore the dynamics of the magnetic
and non magnetic cases and show its resemblance to the Landau-Zener theory. We
also show that combining the global phase of the pulses with the transient
interference allows for a wide magnetic sensing range without loosing the
sensitivity of a single EIT line.",1312.7708v1
2014/2/12,Magnetic anisotropy of thin sputtered MgB2 films on MgO substrates in high magnetic fields,"We investigated the magnetic anisotropy ratio of thin sputtered
polycrystalline MgB2 films on MgO substrates. Using high magnetic field
measurements, we estimated an anisotropy ratio of 1.35 for T=0 K with an upper
critical field of 31.74 T in the parallel case and 23.5 T in the perpendicular
case. Direct measurements of a magnetic-field sweep at 4.2 K show a linear
behavior, confirmed by a linear fit for magnetic fields perpendicular to the
film plane. Furthermore, we observed a change of up to 12% of the anisotropy
ratio in dependence of the film thickness.",1402.2901v1
2014/2/27,Switchable Magnetic Bottles and Field Gradients for Particle Traps,"Versatile methods for the manipulation of individual quantum systems, such as
confined particles, have become central elements in current developments in
precision spectroscopy, frequency standards, quantum information processing,
quantum simulation, and alike. For atomic and some subatomic particles, both
neutral and charged, a precise control of magnetic fields is essen- tial. In
this paper, we discuss possibilities for the creation of specific magnetic
field configurations which find appli- cation in these areas. In particular, we
pursue the idea of a magnetic bottle which can be switched on and off by
transition between the normal and the superconducting phase of a suitable
material in cryogenic environments, for example in trap experiments in moderate
magnetic fields. Methods for a fine-tuning of the magnetic field and its linear
and quadratic components in a trap are presented together with possible
applications.",1402.6822v1
2014/3/4,Magnetic fluctuation from oxygen deficiency centers on the SiO$_2$ surface,"The magnetic stability of oxygen deficiency centers on the surface of
{\alpha}-quartz is investigated with first- principles calculations to
understand their role in contributing to magnetic flux noise in superconducting
qubits (SQs) and superconducting quantum interference devices (SQUIDs)
fabricated on amorphous silica substrates. Magnetic defects on the substrate
are likely responsible for some of the 1/f noise that plagues these systems.
Dangling-bonds associated with three-coordinated Si atoms allow electron
density transfer between spin up and down channels, resulting in low energy
magnetic states. Such under-coordinated Si defects are common in both
stoichiometric and oxygen deficient silica and quartz and are a probable source
of magnetic flux fluctuations in SQs and SQUIDs.",1403.0685v1
2014/3/28,First-principle prediction of Martensitic transformation and magnetic properties of Heusler-type Pt2-xMn1+xGa alloys,"The electronic structure, magnetism and phase stability of Pt2-xMn1+xGa(x=0,
0.25, 0.5, 0.75, 1) alloys are studied by first-principle calculations. The
calculations reveal that a potential magnetic martensitic transformation can be
expected in all the series. In addition, a large magnetic-field-induced strain
is likely to appear in Pt2-xMn1+xGa(x=0, 0.25, 0.75, 1) alloys. The electronic
structure calculations indicate that the tetragonal phase is stabilized upon
the distortion because of the pseudogap formation at the Fermi Level. The
magnetic structure is also investigated and the total magnetic moment of the
tetragonal phase is a little larger than that of the cubic austenite phase in
all the series.",1403.7318v3
2014/3/30,Scattering of electron vortex beams on a magnetic crystal: towards atomic resolution magnetic measurements,"Use of electron vortex beams (EVB), that is convergent electron beams
carrying an orbital angular momentum (OAM), is a novel development in the field
of transmission electron microscopy. They should allow measurement of
element-specific magnetic properties of thin crystals using electron magnetic
circular dichroism (EMCD)---a phenomenon similar to the x-ray magnetic circular
dichroism. Recently it has been shown computationally that EVBs can detect
magnetic signal in a scanning mode only at atomic resolution. In this follow-up
work we explore in detail the elastic and inelastic scattering properties of
EVBs on crystals, as a function of beam diameter, initial OAM, acceleration
voltage and beam displacement from an atomic column. We suggest that for a 10
nm layer of bcc iron oriented along (001) zone axis an optimal configuration
for a detection of EMCD is an EVB with OAM of $1\hbar$ and a diameter of 1.6
\AA, acceleration voltage 200 keV and an annular detector with inner and outer
diameters of $G$ and $5G$, respectively, where $\mathbf{G}=(100)$.",1403.7730v1
2014/4/14,Impurity induced enhancement of perpendicular magnetic anisotropy in Fe/MgO tunnel junctions,"Using first-principles calculations, we investigated the impact of chromium
(Cr) and vanadium (V) impurities on the magnetic anisotropy and spin
polarization in Fe/MgO magnetic tunnel junctions. It is demonstrated using
layer resolved anisotropy calculation technique, that while the impurity near
the interface has a drastic effect in decreasing the perpendicular magnetic
anisotropy (PMA), its position within the bulk allows maintaining high surface
PMA. Moreover, the effective magnetic anisotropy has a strong tendency to go
from in-plane to out-of-plane character as a function of Cr and V concentration
favoring out-of-plane magnetization direction for ~1.5 nm thick Fe layers at
impurity concentrations above 20 %. At the same time, spin polarization is not
affected and even enhanced in most situations favoring an increase of tunnel
magnetoresistance (TMR) values.",1404.3523v1
2014/4/17,Large and robust electrical spin injection into GaAs at zero magnetic field using an ultrathin CoFeB/MgO injector,"We demonstrate a large electrical spin injection into GaAs at zero magnetic
field thanks to an ultrathin perpendicularly magnetized CoFeB contact of a few
atomic planes (1.2 nm). The spin-polarization of electrons injected into GaAs
was examined by the circular polarization of electroluminescence from a Spin
Light Emitting Diode with embedded InGaAs/GaAs quantum wells. The
electroluminescence polarization as a function of the magnetic field closely
traces the out-of-plane magnetization of the CoFeB/MgO injector. A circular
polarization degree of the emitted light as large as 20% at 25 K is achieved at
zero magnetic field. Moreover the electroluminescence circular polarization is
still about 8% at room temperature.",1404.4527v1
2014/4/17,Evolution of Magnetism in the $Na_{3-d}Na_{1-x}Mg_xIr_2O_6$ Series of Honeycomb Iridates,"The structural and magnetic properties of a new series of iridium-based
honeycomb lattices with the formula Na3-delta(Na1-xMgx)Ir2O6 (x = 0 to 1) are
reported. As x and delta are increased, the honeycomb lattice contracts and the
strength of the antiferromagnetic interactions decreases systematically due to
a reduction in Ir-O-Ir bond angles. Samples with imperfect stoichiometry
exhibit disordered magnetic freezing at temperatures Tf between 3.4 K and 5 K.
This glassy magnetism likely arises due to the presence of non-magnetic Ir3+,
which are distributed randomly throughout the lattice, with a possible
additional contribution from stacking faults. Together, these results
demonstrate that chemical defects and non-stoichiometry have a significant
effect on the magnetism of compounds in the A2IrO3 materials family.",1404.4579v1
2014/4/26,"Fe clusters (Fe$_n$, n=1-6) chemisorbed on vacancy defects in graphene: Stability, spin-dipole moment and magnetic anisotropy","In this work, we have studied the chemical and magnetic interactions of
Fe$_n$ ; n=1-6 clusters with vacancy defects (monovacancy to correlated
vacancies with six missing C atoms) in a graphene sheet by ab-initio density
functional calculations combined with Hubbard U corrections for correlated Fe-
d electrons. It is found that the vacancy formation energies are lowered in the
presence of Fe, indicating an easier destruction of the graphene sheet. Due to
strong chemical interactions between Fe clusters and vacancies, a complex
distribution of magnetic moments appear on the distorted Fe clusters which
results in reduced averaged magnetic moments compared to the free clusters. In
addition to that, we have calculated spin-dipole moments and magnetic
anisotropy energies. The calculated spin-dipole moments arising from
anisotropic spin density distributions, vary between positive and negative
values, yielding increased or decreased effective moments. Depending on the
cluster geometry, the easy axis of magnetization of the Fe clusters shows
in-plane or out-of-plane behavior.",1404.6641v2
2014/4/26,Electric field control of magnetic properties and magneto-transport in composite multiferroics,"We study magnetic state and electron transport properties of composite
multiferroic system consisting of a granular ferromagnetic thin film placed
above the ferroelectric substrate. Ferroelectricity and magnetism in this case
are coupled by the long-range Coulomb interaction. We show that magnetic state
and magneto-transport strongly depend on temperature, external electric field,
and electric polarization of the substrate. Ferromagnetic order exists at
finite temperature range around ferroelectric Curie point. Outside the region
the film is in the superparamagnetic state. We demonstrate that magnetic phase
transition can be driven by an electric field and magneto-resistance effect has
two maxima associated with two magnetic phase transitions appearing in the
vicinity of the ferroelectric phase transition. We show that positions of these
maxima can be shifted by the external electric field and that the magnitude of
the magneto-resistance effect depends on the mutual orientation of external
electric field and polarization of the substrate.",1404.6671v2
2014/5/2,Spin-orbit torque-driven magnetization switching and thermal effects studied in Ta\CoFeB\MgO nanowires,"We demonstrate magnetization switching in out-of-plane magnetized
Ta\CoFeB\MgO nanowires by current pulse injection along the nanowires, both
with and without a constant and uniform magnetic field collinear to the current
direction. We deduce that an effective torque arising from spin-orbit effects
in the multilayer drives the switching mechanism. While the generation of a
component of the magnetization along the current direction is crucial for the
switching to occur, we observe that even without a longitudinal field thermally
generated magnetization fluctuations can lead to switching. Analysis using a
generalized N\'eel-Brown model enables key parameters of the thermally induced
spin-orbit torques switching process to be estimated, such as the attempt
frequency and the effective energy barrier.",1405.0452v1
2014/6/17,Exchange bias in phase-segregated Nd2/3Ca1/3MnO3 as a function of temperature and cooling magnetic fields,"Exchange bias (EB) phenomena have been observed in Nd2/3Ca1/3MnO3 colossal
magnetoresistance perovskite below the Curie temperature $T_{C}$ = 70 K and
attributed to an antiferromagnetic (AFM) - ferromagnetic (FM) spontaneous phase
segregated state of this compound. Field cooled magnetic hysteresis loops
exhibit shifts toward negative direction of the magnetic field axis. The values
of exchange field $H_{EB}$ and coercivity $H_{C}$ are found to be strongly
dependent of temperature and strength of the cooling magnetic field $H_{cool}$.
These effects are attributed to evolution of the FM phase content and a size of
FM clusters. A contribution to the total magnetization of the system due to the
FM phase has been evaluated. The exchange bias effect decreases with increasing
temperature up to $T_{C}$ and vanishes above this temperature with
disappearance of FM phase. Relaxation of a non-equilibrium magnetic state of
the compound manifests itself through a training effect also observed while
studying EB in Nd2/3Ca1/3MnO3.",1406.4404v1
2014/6/26,Magnetic force microscopy investigation of arrays of nickel nanowires and nanotubes,"The magnetic properties of arrays of nanowires (NWs) and nanotubes (NTs), 150
nm in diameter, electrodeposited inside nanoporous polycarbonate membranes are
investigated. The comparison of the nanoscopic magnetic force microscopy (MFM)
imaging and the macroscopic behavior as measured by alternating gradient force
magnetometry (AGFM) is made. It is shown that MFM is a complementary technique
that provides an understanding of the magnetization reversal characteristics at
the microscopic scale of individual nanostructures. The local hysteresis loops
have been extracted by MFM measurements. The influence of the shape of such
elongated nanostructures on the dipolar coupling and consequently on the
squareness of the hysteresis curves is demonstrated. It is shown that the
nanowires exhibit stronger magnetic interactions than nanotubes. The
non-uniformity of the magnetization states is also revealed by combining the
MFM and AGFM measurements.",1406.6886v1
2014/6/28,Effects of Strain and Buffer Layer on Interfacial Magnetization in Sr$_2$CrReO$_6$ Films Determined by Polarized Neutron Reflectometry,"We have determined the depth-resolved magnetization structures of a series of
highly ordered Sr$_{2}$CrReO$_{6}$ (SCRO) ferrimagnetic epitaxial films via
combined studies of x-ray reflectometry, polarized neutron reflectometry and
SQUID magnetometry. The SCRO films deposited directly on
(LaAlO$_3$)$_{0.3}$(Sr$_2$AlTaO$_6$)$_{0.7}$ or SrTiO$_{3}$ substrates show
reduced magnetization of similar width near the interfaces with the substrates,
despite having different degrees of strain. When the SCRO film is deposited on
a Sr$_{2}$CrNbO$_{6}$ (SCNO) double perovskite buffer layer, the width the
interfacial region with reduced magnetization is reduced, agreeing with an
improved Cr/Re ordering. However, the relative reduction of the magnetization
averaged over the interfacial regions are comparable among the three samples.
Interestingly, we found that the magnetization suppression region is wider than
the Cr/Re antisite disorder region at the interface between SCRO and SCNO.",1406.7351v2
2014/6/30,Hyperfine field assessment of the magnetic structure of ZrZn2,"Time differential perturbed angular gamma-gamma-correlation (TDPAC) method on
111Cd nuclei probes inserted in ZrZn1.9 is used to measure the magnetic
hyperfine fields (MHF) at Zr and Zn sites and the electric field gradient (EFG)
Vzz at Zn sites as a function of temperature at various pressures and as a
function of pressure at the temperature 4 K. Our data indicate that the local
magnetic moment of Zr in the magnetically ordered state is substantially larger
than its value obtained from the macroscopic measurements and that there is
also an induced magnetic moment at the Zn site. We conclude that ZrZn2 is not a
simple ferromagnet and discuss a possible type of its magnetic ordering.",1406.7719v1
2014/7/9,"Molecular magnetism and crystal field effects in the Kondo system Ce$_3$Pd$_{20}$(Si,Ge)$_6$ with two Ce sublattices","The unusual electronic and magnetic properties of the systems
Ce$_3$Pd$_{20}$T$_6$ (T = Ge, Si) with two non-equivalent Ce positions are
discussed. The logarithmic growth of resistance for both the systems confirms
the presence of the Kondo effect in the two respective temperature ranges. The
two-scale behavior is explained by consecutive splitting of Ce ion levels in
the crystal field. The effects of the frustration caused by the coexistence of
the different positions of cerium are treated, which may also significantly
enhance the observed values of specific heat. A model of ""molecular magnetism""
with Ce2 cubes is developed.",1407.2366v1
2014/7/15,Non-coplanar and counter-rotating incommensurate magnetic order stabilized by Kitaev interactions in $γ$-Li2IrO3,"Materials that realize Kitaev spin models with bond-dependent anisotropic
interactions have long been searched for, as the resulting frustration effects
are predicted to stabilize novel forms of magnetic order or quantum spin
liquids. Here we explore the magnetism of $\gamma$-Li$_2$IrO$_3$, which has the
topology of a 3D Kitaev lattice of inter-connected Ir honeycombs. Using
resonant magnetic x-ray diffraction we find a complex, yet highly-symmetric
incommensurate magnetic structure with non-coplanar and counter-rotating Ir
moments. We propose a minimal Kitaev-Heisenberg Hamiltonian that naturally
accounts for all key features of the observed magnetic structure. Our results
provide strong evidence that $\gamma$-Li$_2$IrO$_3$ realizes a spin Hamiltonian
with dominant Kitaev interactions.",1407.3954v1
2014/7/15,Sub-diffraction sub-100 ps all-optical magnetic switching by passive wavefront shaping,"The recently discovered magnetization reversal driven solely by a femtosecond
laser pulse has been shown to be a promising way to record information at
record breaking speeds. Seeking to improve the recording density has raised
intriguing fundamental question about the feasibility to combine the ultrafast
temporal with sub-wavelength spatial resolution of magnetic recording. Here we
report about the first experimental demonstration of sub-diffraction and
sub-100 ps all-optical magnetic switching. Using computational methods we
reveal the feasibility of sub-diffraction magnetic switching even for an
unfocused incoming laser pulse. This effect is achieved via structuring the
sample such that the laser pulse experiences a passive wavefront shaping as it
couples and propagates inside the magnetic structure. Time-resolved studies
with the help of photo-emission electron microscopy clearly reveal that the
sub-wavelength switching with the help of the passive wave-front shaping can be
pushed into sub-100 ps regime.",1407.4010v1
2014/7/17,Normal and inverse magnetocaloric effect in magnetic multilayers with antiferromagnetic interlayer coupling,"The thermodynamics of a spin-1/2 magnetic multilayer system with
antiferromagnetic interplanar couplings is studied using the Pair Approximation
method. The special attention is paid to magnetocaloric properties, quantified
by isothermal entropy change. The multilayer consists of two kinds of magnetic
planes, one of which is diluted. The intraplanar couplings in both planes have
arbitrary anisotropy ranging between Ising and isotropic Heisenberg
interactions. The phase diagram related to the occurrence of magnetic
compensation phenomenon is constructed and discussed. Then the isothermal
entropy change is discussed as a function of interaction parameters, magnetic
component concentration and external magnetic field amplitude. The ranges of
normal and inverse magnetocaloric effect are found and related to the presence
or absence of compensation.",1407.4848v2
2014/8/7,Ferromagnetic resonance of a magnetic dimer with dipolar coupling,"We develop a general formalism for analyzing the ferromagnetic resonance
characteristics of a magnetic dimer consisting of two magnetic elements (in a
horizontal or vertical configuration) coupled by dipolar interaction, taking
account of their finite-size and aspect ratio. We study the effect on the
resonance frequency and resonance field of the applied magnetic field (in
amplitude and direction), the inter-element coupling, and the uniaxial
anisotropy in various configurations. We obtain analytical expressions for the
resonance frequency in various regimes of the interlayer coupling. We
(numerically) investigate the behavior of the resonance field in the
corresponding regimes. The critical value of the applied magnetic field at
which the resonance frequency vanishes may be an increasing or a decreasing
function of the dimer's coupling, depending on the anisotropy configuration. It
is also a function of the nanomagnets aspect ratio in the case of in-plane
anisotropy. This and several other results of this work, when compared with
experiments using the standard ferromagnetic resonance with fixed frequency, or
the network analyzer with varying frequency and applied magnetic field, provide
a useful means for characterizing the effective anisotropy and coupling within
systems of stacked or assembled nanomagnets.",1408.1594v1
2014/9/3,Tuning the magnetic exchange via a control of orbital hybridization in Cr2(Te1-xWx)O6,"We report the complex magnetic phase diagram and electronic structure of
Cr2(Te1-xWx)O6 systems. While compounds with different x values possess the
same crystal structure, they display different magnetic structures below and
above xc = 0.7, where both the transition temperature TN and sublattice
magnetization (Ms) reach a minimum. Unlike many known cases where magnetic
interactions are controlled either by injection of charge carriers or by
structural distortion induced via chemical doping, in the present case it is
achieved by tuning the orbital hybridization between Cr 3d and O 2p orbitals
through W 5d states. The result is supported by ab-initio electronic structure
calculations. Through this concept, we introduce a new approach to tune
magnetic and electronic properties via chemical doping.",1409.1243v1
2014/9/9,Magnetization in AIIIBV semiconductor heterostructures with the depletion layer of manganese,"The magnetic moment and magnetization in GaAs/Ga$_{0.84}$In$_{0.16}$As/GaAs
heterostructures with Mn deluted in GaAs cover layers and with atomically
controlled Mn $\delta$-layer thicknesses near GaInAs-quantum well ($\sim$3 nm)
in temperature range T=(1.8-300)K in magnetic field up to 50 kOe have been
investigated. The mass magnetization all of the samples of
GaAs/Ga$_{0.84}$In$_{0.16}$As/GaAs with Mn increases with the increasing of the
magnetic field that pointed out on the presence of low-dimensional
ferromagnetism in the manganese depletion layer of GaAs based structures. It
has been estimated the manganese content threshold at which the ferromagnetic
ordering was found.",1409.2598v1
2014/9/19,Magnetic Bubblecade Memory,"Unidirectional motion of magnetic domain walls is the key concept underlying
next-generation domain-wall-mediated memory and logic devices. Such motion has
been achieved either by injecting large electric currents into nanowires or by
employing domain-wall tension induced by sophisticated structural modulation.
Herein, we demonstrate a new scheme without any current injection or structural
modulation. This scheme utilizes the recently discovered chiral domain walls,
which exhibit asymmetry in their speed with respect to magnetic fields. Because
of this asymmetry, an alternating magnetic field results in the coherent motion
of the domain walls in one direction. Such coherent unidirectional motion is
achieved even for an array of magnetic bubble domains, enabling the design of a
new device prototype-magnetic bubblecade memory-with two-dimensional
data-storage capability.",1409.5610v2
2014/9/25,Tuning the Band Structures of a 1D Width-Modulated Magnonic Crystal by a Transverse Magnetic Field,"Theoretical studies, based on three independent techniques, of the band
structure of a one-dimensional width-modulated magnonic crystal under a
transverse magnetic field are reported. The band diagram is found to display
distinct behaviors when the transverse field is either larger or smaller than a
critical value. The widths and center positions of bandgaps exhibit unusual
non-monotonic and large field-tunability through tilting the direction of
magnetization. Some bandgaps can be dynamically switched on and off by simply
tuning the strength of such a static field. Finally, the impact of the lowered
symmetry of the magnetic ground state on the spin-wave excitation efficiency of
an oscillating magnetic field is discussed. Our finding reveals that the
magnetization direction plays an important role in tailoring magnonic band
structures and hence in the design of dynamic spin-wave switches.",1409.7183v1
2014/10/6,Defect-induced magnetism in graphite through neutron irradiation,"We have investigated the variation in the magnetization of highly ordered
pyrolytic graphite (HOPG) after neutron irradiation, which introduces defects
in the bulk sample and consequently gives rise to a large magnetic signal. We
observe strong paramagnetism in HOPG, increasing with the neutron fluence. We
correlate the induced paramagnetism with structural defects by comparison with
density-functional theory calculations. In addition to the in-plane vacancies,
the trans-planar defects also contribute to the magnetization. The lack of any
magnetic order between the local moments is possibly due to the absence of
hydrogen/nitrogen chemisorption, or the magnetic order cannot be established at
all in the bulk form.",1410.1308v3
2014/10/16,"Understanding the Magnetic Puzzles of Double Perovskites A2FeOsO6 (A=Ca, Sr)","Double perovskites Sr2FeOsO6 and Ca2FeOsO6 show puzzling magnetic properties,
the former a low-temperature antiferromagnet while the later a high-temperature
insulating ferrimagnet. Here, in order to understand the underlying mechanism,
we have investigated the frustrated magnetism of A2FeOsO6 by employing density
functional theory and maximally-localized Wannier functions. We find that
lattice distortion enhances the antiferromagnetic nearest-neighboring Fe-O-Os
interaction but weakens the antiferromagnetic interactions through the
Os-O-O-Os and Fe-O-Os-O-Fe paths, which is responsible for the magnetic
transition from the low-temperature antiferromagnetism to the high-temperature
ferrimagnetism with the decrease of the radius of the A2+ ions. We also discuss
the 5d3-3d5 superexchange and propose such superexchange is intrinsically
antiferromagnetic instead of the expected ferromagnetic. Our work illustrate
that the magnetic frustration can be effectively relieved by lattice
distortion, which provides another dimension to tune the complex magnetism in
other 3d-5d (4d) double perovskites.",1410.4280v1
2014/10/23,Surface aligned magnetic moments and hysteresis of an endohedral single-molecule magnet on a metal,"The interaction between the endohedral unit in the single-molecule magnet
Dy$_2$ScN@C$_{80}$ and a rhodium (111) substrate leads to alignment of the Dy
4$f$ orbitals. The resulting orientation of the Dy$_2$ScN plane parallel to the
surface is inferred from comparison of the angular anisotropy of x-ray
absorption spectra and multiplet calculations in the corresponding ligand
field. The x-ray magnetic circular dichroism (XMCD) is also angle dependent and
signals strong magnetocrystalline anisotropy. This directly relates geometric
and magnetic structure. Element specific magnetization curves from different
coverages exhibit hysteresis at a sample temperature of $\sim4$ K. From the
measured hysteresis curves we estimate the zero field remanence life-time
during x-ray exposure of a sub-monolayer to be about 30 seconds.",1410.6272v2
2014/10/24,Investigation of the crystal and magnetic structures of the trigonal multiferroic iron-boracite Fe3B7O13(OH),"We have investigated the crystal and magnetic structures of the trigonal
iron-boracite Fe3B7O13X with X = OH by neutron diffraction. Neutron diffraction
enables us to locate the hydrogen atom of the hydroxyl group and determine the
magnetic ground state of this member of the multiferroic boracite family. No
evidence was found for a monoclinic distortion in the magnetic ordered state.
The magnetic symmetry allows for magnetoelectric and ferroelectric properties.
The N/'eel tempera- ture TN of 4.86(4) K confirms the general trends within the
boracites that TN decreases from X = I > Br > Cl > OH. Surprisingly while
Fe3B7O13OH exhibits the largest frustration with $|\theta/T_N| = 5.6$ within
the Fe3B7O13X series, no reduction of the magnetic moment is found using
neutron diffraction.",1410.6602v1
2014/10/24,Nondiagonal Graphene Conductivity in the Presence of In-Plane Magnetic Fields,"We study the electron/hole transport in puddle-disordered and rough graphene
samples which are subject to in-plane magnetic fields. Previous treatments,
mostly devoted to regimes where the electron/hole scattering wavelengths are
larger than the surface height correlation length, are based on the use of
transport equations with appropriate forms for the collision term. We point out
in this work, as a counterpoint, that classical Lorentz force effects, which
are expected to hold when the Fermi level is far enough away from the charge
neutral point, can be heuristically assessed through disordered Boltzmann
equations that contain magnetic-field dependent material derivatives, and keep
the zero magnetic-field structure of the collision term. It turns out that the
electric conductivity tensor gets a peculiar nondiagonal component, induced by
the in-plane magnetic field that crosses the rough topography of the graphene
sheet, even if the projected random transverse magnetic field vanishes in the
mean. Numerical estimates of the transverse conductivities suggest that they
are suitable of observation under conditions which are within the reach of
up-to-date experimental methods.",1410.6706v2
2014/11/17,Domain formation in magnetic polymer composites: an approach via stochastic homogenization,"We study the magnetic energy of magnetic polymer composite materials as the
average distance between magnetic particles vanishes. We model the position of
these particles in the polymeric matrix as a stochastic lattice scaled by a
small parameter $\varepsilon$ and the magnets as classical $\pm 1$ spin
variables interacting via an Ising type energy. Under surface scaling of the
energy we prove, in terms of $\Gamma$-convergence that, up to subsequences, the
(continuum) $\Gamma$-limit of these energies is finite on the set of
Caccioppoli partitions representing the magnetic Weiss domains where it has a
local integral structure. Assuming stationarity of the stochastic lattice, we
can make use of ergodic theory to further show that the $\Gamma$-limit exists
and that the integrand is given by an asymptotic homogenization formula which
becomes deterministic if the lattice is ergodic.",1411.4463v2
2014/11/23,Studying the Magnetic Properties of CoSi Single Crystals,"The magnetic properties of CoSi single crystals have been measured in a range
of temperatures $T = 5.5 - 450$ K and magnetic field strengths $H \leq 11$ kOe.
A comparison of the results for crystals grown in various laboratories allowed
the temperature dependence of magnetic susceptibility $\chi(T) = M(T)/H$ to be
determined for a hypothetical ""ideal"" (free of magnetic impurities and defects)
CoSi crystal. The susceptibility of this ideal crystal in the entire
temperature range exhibits a diamagnetic character. The $\chi(T)$ value
significantly increases in absolute value with decreasing temperature and
exhibits saturation at the lowest temperatures studied. For real CoSi crystals
of four types, paramagnetic contributions to the susceptibility have been
evaluated and nonlinear (with respect to the field) contributions to the
magnetization have been separated and taken into account in the calculations of
$\chi(T)$.",1411.6242v1
2014/11/24,Localized magnetic plasmons in all-dielectric mu<0 metastructures,"Metamaterials are known to exhibit a variety of electromagnetic properties
non-existing in nature. We show that an all-dielectric (non-magnetic) system
consisting of deep subwavelength, high permittivity resonant spheres possess
effective negative magnetic permeability (dielectric permittivity being
positive and small). Due to the symmetry of the electromagnetic wave equations
in classical electrodynamics, localized ""magnetic"" plasmon resonances can be
excited in a metasphere made of such metamaterial. This is theoretically
demonstrated by the coupled-dipole approximation and numerically for real
spheres, in full agreement with the exact analytical solution for the
scattering process by the same metasphere with effective material properties
predicted by effective medium theory. The emergence of this phenomenon as a
function of structural order within the metastructures is also studied.
Universal conditions enabling effective negative magnetic permeability relate
subwavelength sphere permittivity and size with critical filling fraction. Our
proposal paves the way towards (all-dielectric) magnetic plasmonics, with a
wealth of fascinating applications.",1411.6548v2
2014/11/27,Frustrated diamond-chain quantum $XXZ$ Heisenberg antiferromagnet in a magnetic field,"We consider the antiferromagnetic spin-1/2 $XXZ$ Heisenberg model on a
frustrated diamond-chain lattice in a $z$- or $x$-aligned external magnetic
field. We use the strong-coupling approach to elaborate an effective
description in the low-temperature strong-field regime. The obtained effective
models are spin-1/2 $XY$ chains which are exactly solvable through the
Jordan-Wigner fermionization. We perform exact-diagonalization studies of the
magnetization curves to test the quality of the effective description. The
results may have relevance for the description of the azurite spin-chain
compound.",1411.7515v1
2014/12/1,All-optical magnetization switching in ferrimagnetic alloys: deterministic vs thermally activated dynamics,"Using photo-emission electron microscopy with X-ray magnetic circular
dichroism as a contrast mechanism, new insights into the all-optical
magnetization switching (AOS) phenomenon in GdFe based rare-earth transition
metal ferrimagnetic alloys are provided. From a sequence of static images taken
after single linearly polarized laser pulse excitation, the repeatability of
AOS can be measured with a correlation coefficient. It is found that low
coercivity enables thermally activated domain wall motion, limiting in turn the
repeatability of the switching. Time-resolved measurement of the magnetization
dynamics reveal that while AOS occurs below and above the magnetization
compensation temperature $T_\text{M}$, it is not observed in GdFe samples where
$T_\text{M}$ is absent. Finally, AOS is experimentally demonstrated against an
applied magnetic field of up to 180 mT.",1412.0396v1
2014/12/1,Resistivity minimum in strongly phase separated manganite thin films: impact of intrinsic and extrinsic perturbations,"The origin of the resistivity minimum observed in strongly phase separated
manganites has been investigated in single crystalline thin films of LPCMO
(x~0.42, y~0.40). The antiferromagnetic/charge ordered insulator
(AFM/COI)-ferromagnetic metal (FMM) phase transition, coupled with the colossal
hysteresis between the field cool cooled and field cooled warming magnetization
demonstrates strongly phase separated nature, which gives rise to
non-equilibrium magnetic liquid state that freezes into a magnetic glass. The
thermal cycling and magnetic field dependence of the resistivity unambiguously
shows that the pronounced resistivity minimum observed during warming is a
consequence non-equilibrium states resulting from the magnetic frustration
created by the delicate coexistence of the FMM and AFM/COI phases. The
non-equilibrium states and hence the resistivity minimum is extremely sensitive
to the relative fraction of the coexisting phases and can be tuned by intrinsic
and extrinsic perturbations like the defect density, thermal cycling and
magnetic field.",1412.0418v1
2014/12/8,Anapoles and other magneto-electric multipoles in BaFe2Se3,"We submit that the magnetic space-group Cac (#9.41) is consistent with the
established magnetic structure of BaFe2Se3, with magnetic dipole moments in a
motif that uses two ladders [Caron J M et al 2011 Phys. Rev. B 84 180409(R)].
The corresponding crystal class m1' allows axial and polar dipoles and forbids
bulk ferromagnetism. The compound supports magneto-electric multipoles,
including a magnetic charge (monopole) and an anapole (magnetic toroidal
dipole) visible in the Bragg diffraction of x-rays and neutrons. Our
comprehensive simulation of neutron Bragg diffraction by BaFe2Se3 exploits
expressions of a general nature that can be of use with other magnetic
materials. Electric toroidal moments are also allowed in BaFe2Se3. A discussion
of our findings for resonant x-ray Bragg diffraction illustrates the benefit of
a common platform for neutron and x-ray diffraction.",1412.2536v1
2014/12/10,Spin-dependent Seebeck effect and spin caloritronics in magnetic graphene,"We investigate the spin-dependent thermoelectric effects in magnetic graphene
in both diffusive and ballistic regimes. Employing the Boltzmann and Landauer
formalisms we calculate the spin and charge Seebeck coefficients (thermopower)
in magnetic graphene varying the spin splitting, temperature, and doping of the
junction. It is found that while in normal graphene the temperature gradient
drive a charge current, in the case of magnetic graphene a significant spin
current is also established. In particular we show that in the undoped magnetic
graphene in which different spin carriers belong to conduction and valence
bands, a pure spin current is driven by the temperature gradient. In addition
it is revealed that profound thermoelectric effects can be achieved at
intermediate easily accessible temperatures when the thermal energy is
comparable with Fermi energy $k_BT\lesssim \mu$. By further investigation of
the spin-dependent Seebeck effect and a significantly large figure of merit for
spin thermopower $\mathcal{Z}_{\rm sp}T$, we suggest magnetic graphene as a
promising material for spin-caloritronics studies and applications.",1412.3318v2
2014/12/15,High pressure neutron scattering of the magnetoelastic Ni-Cr Prussian blue analogue,"This paper summarizes 0 GPa to 0.6 GPa neutron diffraction measurements of a
nickel hexacyanochromate coordination polymer (NiCrPB) that has the
face-centered cubic, Prussian blue structure. Deuterated powders of NiCrPB
contain ~100 nm sided cubic particles. The application of a large magnetic
field shows the ambient pressure, saturated magnetic structure. Pressures of
less than 1 GPa have previously been shown to decrease the magnetic
susceptibility by as much as half, and we find modifications to the nuclear
crystal structure at these pressures that we quantify. Bridging cyanide
molecules isomerize their coordination direction under pressure to change the
local ligand field and introduce inhomogeneities in the local (magnetic)
anisotropy that act as pinning sites for magnetic domains, thereby reducing the
low field magnetic susceptibility.",1412.4712v1
2015/1/11,Magnetic Order Driven Topological Transition in the Haldane-Hubbard Model,"In this letter we study the Haldane model with on-site repulsive interactions
at half-filling. We show that the mean-field Hamiltonian with magnetic order
effectively modifies parameters in the Haldane Hamiltonian, such as sublattice
energy difference and phase in next nearest hopping. As interaction increases,
increasing of magnetic order corresponds to varying these parameters and
consequently, drives topological transitions. At the mean-field level, one
scenario is that the magnetic order continuously increases, and inevitably, the
fermion gap closes at the topological transition point with nonzero magnetic
order. Beyond the mean-field, interaction between fermions mediated by
spin-wave fluctuations can further open up the gap, rendering a first-order
transition. Another scenario is a first-order transition at mean-field level
across which a canted magnetic order develops discontinuously, avoiding the
fermion gap closing. We find that both scenarios exist in the phase diagram of
the Haldane-Hubbard model. Our predication is relevant to recent experimental
realization of the Haldane model in cold atom system.",1501.02455v2
2015/1/30,Phase diagram and optimal switching induced by spin Hall effect in a perpendicular magnetic layer,"In a ferromagnet/heavy-metal bilayer device with strong spin Hall effect an
in-plane current excites magnetic dynamics through spin torque. We analyze
bilayers with perpendicular magnetization and calculate three-dimensional phase
diagrams describing switching by external magnetic field at a fixed current. We
then concentrate on the case of a field applied in the plane formed by the film
normal and the current direction. Here we analytically study the evolution of
both the conventional ""up""/""down"" magnetic equilibria and the additional
equilibria created by the spin torque. Expressions for the stability regions of
all equilibria are derived, and the nature of switching at each critical
boundary is discussed. The qualitative picture obtained this way predicts
complex hysteresis patterns that should occur in bilayers. By analyzing the
phase portraits of the system we show that when the spin torque induced
equilibrium exists, switching between ""up"" and ""down"" states proceeds through
it as an intermediate state. Using numeric simulations we analyze the switching
time and compare it to that of a conventional spin torque device with collinear
magnetizations of the polarizer and the free layer.",1501.07787v1
2015/2/20,Competing magnetic double-Q phases and superconductivity-induced re-entrance of C2 magnetic stripe order in iron pnictides,"We perform a microscopic theoretical study of the generic properties of
competing magnetic phases in iron pnictides. As a function of electron filling
and temperature, the magnetic stripe (single-Q) order forms a dome, but
competing non-collinear and non-uniform double-Q phases exist at the foot of
the dome in agreement with recent experiments. We compute and compare the
electronic properties of the different magnetic phases, investigate the role of
competing superconductivity, and show how disorder may stabilize double-Q
order. Superconductivity is shown to compete more strongly with double-Q
magnetic phases, which can lead to re-entrance of the C2 (single-Q) order in
agreement with recent thermal expansion measurements on K-doped Ba-122
crystals.",1502.05859v2
2015/2/27,Néel-type Skyrmion Lattice with Confined Orientation in the Polar Magnetic Semiconductor GaV$_4$S$_8$,"Following the early prediction of the skyrmion lattice (SkL) - a periodic
array of spin vortices - it has been observed recently in various magnetic
crystals mostly with chiral structure. Although non-chiral but polar crystals
with C$_{nv}$ symmetry were identifed as ideal SkL hosts in pioneering
theoretical studies this archetype of SkL has remained experimentally
unexplored. Here, we report the discovery of a SkL in the polar magnetic
semiconductor GaV$_4$S$_8$ with rhombohedral (C$_{3v}$) symmetry and easy axis
anisotropy. The SkL exists over an unusually broad temperature range compared
with other bulk crystals and the orientation of the vortices is not controlled
by the external magnetic feld but instead confned to the magnetic easy axis.
Supporting theory attributes these unique features to a new non-chiral or
N\'eel-type of SkL describable as a superposition of spin cycloids in contrast
to the Bloch-type SkL in chiral magnets described in terms of spin helices.",1502.08049v1
2015/3/9,Magnetic Cluster Expansion model for random and ordered magnetic face-centered cubic Fe-Ni-Cr alloys,"A Magnetic Cluster Expansion (MCE) model for ternary face-centered cubic
Fe-Ni-Cr alloys has been developed using DFT data spanning binary and ternary
alloy configurations. Using this MCE model Hamiltonian, we perform Monte Carlo
simulations and explore magnetic structures of alloys over the entire range of
alloy compositions, considering both random and ordered alloy structures. In
random alloys, the removal of magnetic collinearity constraint reduces the
total magnetic moment but does not affect the predicted range of compositions
where the alloys adopt low temperature ferromagnetic configurations. During
alloying of ordered fcc Fe-Ni compounds with Cr, chromium atoms tend to replace
nickel rather than iron atoms. Replacement of Ni by Cr in alloys with high iron
content increases the Curie temperature of the alloys. This can be explained by
strong antiferromagnetic Fe-Cr coupling, similar to that found in bcc Fe-Cr
solutions, where the Curie temperature increase, predicted by simulations as a
function of Cr concentration, is confirmed by experimental observations.",1503.02481v1
2015/3/17,Magnetic rotational spectroscopy for probing rheology of nanoliter droplets and thin films,"In-situ characterization of minute amounts of complex fluids is a challenge.
Magnetic Rotational Spectroscopy (MRS) with submicron probes offers flexibility
and accuracy providing desired spatial and temporal resolution in
characterization of nanoliter droplets and thin films when other methods fall
short. MRS analyzes distinct features of the in-plane rotation of a magnetic
probe, when its magnetic moment makes full revolution following an external
rotating magnetic field. The probe demonstrates a distinguishable movement
which changes from rotation to tumbling to trembling as the frequency of
rotation of the driving magnetic field changes. In practice, MRS has been used
in analysis of gelation of thin polymer films, ceramic precursors, and
nanoliter droplets of insect biofluids. MRS is a young field, but it has many
potential applications requiring rheological characterization of scarcely
available, chemically reacting complex fluids.",1503.05229v1
2015/3/21,Localized magnetic states in three dimensional Dirac solids,"Formation of localized magnetic states in a metallic host is a classic
problem ofcondensed matter physics formalized by P. W. Anderson within the so
called single impurity Anderson model (SIAM). The general picture in a host of
a simple one-band metal is that a large Hubbard $U$ in the impurity orbital is
pre-requisite for the formation of localized magnetic states. In recent years
three dimensional (3D) Dirac solids have emerged the hallmark of which is
strong spin-orbit interaction. In this work we show that such a strong
spin-orbit interaction allows to form localized magnetic states even with small
values of Hubbard $U$. This opens up the fascinating possibility of forming
magnetic states with $s$ or $p$ orbital impurities -- different from
traditional paradigms of $d$ or $f$ orbital based magnetic moments.",1503.06355v1
2015/4/8,Proximity effect between a topological insulator and a magnetic insulator with large perpendicular anisotropy,"We report that thin films of a prototype topological insulator,
Bi$_{2}$Se$_{3}$, can be epitaxially grown onto the (0001) surface of
BaFe$_{12}$O$_{19}$(BaM), a magnetic insulator with high Curie temperature and
large perpendicular anisotropy. In the Bi$_2$Se$_3$ thin films grown on
non-magnetic substrates, classic weak antilocalization (WAL) is manifested as
cusp-shaped positive magnetoresistance (MR) in perpendicular magnetic fields
and parabola-shaped positive MR in parallel fields, whereas in
Bi$_{2}$Se$_{3}$/BaM heterostructures the low field MR is parabola-shaped,
which is positive in perpendicular fields and negative in parallel fields. The
magnetic field and temperature dependence of the MR is explained as a
consequence of the suppression of WAL due to strong magnetic interactions at
the Bi$_{2}$Se$_{3}$/BaM interface.",1504.01922v1
2015/4/15,Control of the magnetic phase coexistence in NdFe$_3$(BO$_3$)$_4$ by electric fields,"We present a resonant x-ray diffraction study of the magnetic order in
NdFe$_3$(BO$_3$)$_4$ and its coupling to applied electric fields. Our
high-resolution measurements reveal A coexistence of two different magnetic
phases, which can be triggered effectively by external electric fields. More in
detail, the volume fraction of the collinear magnetic phase is found to
strongly increase at the expense of helically ordered regions when an electric
field is applied. These results confirm that the collinear magnetic phase is
responsible for the ferroelectric polarization of NdFe$_3$(BO$_3$)$_4$ and,
more importantly, demonstrate that magnetic phase coexistence provides an
alternative route towards materials with a strong magnetoelectric response.",1504.03848v1
2015/4/22,Structures and magnetic properties of Co-Zr-B magnets studied by first-principles calculations,"The structures and magnetic properties of the Co-Zr-B alloys near the Co5Zr
composition were studied using adaptive genetic algorithm and first-principles
calculations to guide further experimental effort on optimizing their magnetic
performances. Through extensive structural searches, we constructed the contour
maps of the energetics and magnetic moments of the Co-Zr-B magnet alloys as a
function of composition. We found that the Co-Zr-B system exhibits the same
structural motif as the ""Co11Zr2"" polymorphs, which plays a key role in
achieving high coercivity. Boron atoms can either substitute selective cobalt
atoms or occupy the interstitial sites. First-principles calculation shows that
the magnetocrystalline anisotropy energies can be significantly improved
through proper boron doping.",1504.05829v1
2015/4/21,Uniaxial anisotropy and low-temperature antiferromagnetism of Mn2BO4 single crystal,"The Mn2BO4 single crystals have been grown using the flux technique. The
careful study crystal structure and magnetic properties have been carried out.
The antiferromagnet transition at TN = 26 K has been traced through the dc
magnetization and specific heat temperature dependences. The magnetic uniaxial
anisotropy has been detected with easy axis of magnetization lying in ab-plane.
A reduction of the effective magnetic moment value is assigned to the
non-quenched orbital moment of Jahn-Teller Mn3+ ions. Based on the
superexchange interactions calculations the magnetic behavior is discussed.",1504.05870v1
2015/4/23,Spin-Reorientation and Weak Ferromagnetism in Antiferromagnetic TbMn_{0.5}Fe_{0.5}O_3,"Orthorhombic single crystals of TbMn0.5Fe0.5O3 are found to exhibit
spin-reorientation, magnetization reversal and weak ferromagnetism. Strong
anisotropy effects are evident in the temperature dependent magnetization
measurements along the three crystallographic axes a, b and c. A broad magnetic
transition is visible at T_N (Fe/Mn) = 286 K due to paramagnetic to AxGyCz
ordering. A sharp transition is observed at T_SR (Fe/Mn) = 28 K, which is
pronounced along c axis in the form of a sharp jump in magnetization where the
spins reorient to GxAyFz configuration. The negative magnetization observed
below TSR Fe/Mn along c axis is explained in terms of domain wall pinning. A
component of weak ferromagnetism is observed in field-scans along c-axis but
below 28 K. Field-induced steps-like transitions are observed in hysteresis
measurement along b axis below 28 K. It is noted that no sign of Tb-order is
discernible down to 2 K. TbMn0.5Fe0.5O3 could be highlighted as a potential
candidate to evaluate its magneto-dielectric effects across the magnetic
transitions.",1504.06060v1
2015/4/27,Probing the magnetic moment of FePt micromagnets prepared by Focused Ion Beam milling,"We investigate the degradation of the magnetic moment of a 300 nm thick FePt
film induced by Focused Ion Beam (FIB) milling. A $1~\mu \mathrm{m} \times
8~\mu \mathrm{m}$ rod is milled out of a film by a FIB process and is attached
to a cantilever by electron beam induced deposition. Its magnetic moment is
determined by frequency-shift cantilever magnetometry. We find that the
magnetic moment of the rod is $\mu = 1.1 \pm 0.1 \times 10 ^{-12}
\mathrm{Am}^2$, which implies that 70% of the magnetic moment is preserved
during the FIB milling process. This result has important implications for atom
trapping and magnetic resonance force microscopy (MRFM), that are addressed in
this paper.",1504.07104v2
2015/5/15,Multiple magnetic transitions in the spin-$\frac12$ chain antiferromagnet SrCuTe2O6,"Using thermodynamic measurements and density-functional band-structure
calculations, we explore magnetic behavior of SrCuTe2O6. Despite being a
structural sibling of a three-dimensional frustrated system PbCuTe2O6, this
spin-1/2 quantum magnet shows remarkably different low-temperature behavior.
Above 7 K, magnetic susceptibility of SrCuTe2O6 follows the spin-chain model
with the antiferromagnetic intrachain coupling of J = 49.3 K. We ascribe this
quasi-one-dimensional behavior to the leading third-neighbor coupling that
involves a weakly bent Cu--O......O--Cu superexchange pathway with a short
O.....O contact of 2.79 \AA. Below 5 K, SrCuTe2O6 undergoes two consecutive
magnetic transitions that may be triggered by the frustrated nature of
interchain couplings. Field dependence of the magnetic transitions (phase
diagram) is reported.",1505.04037v2
2015/5/23,Exciton splitting in semiconducting carbon nanotubes in ultrahigh magnetic fields above 300 T,"In high magnetic fields, the exciton absorption spectrum of a semiconducting
single-walled carbon nanotube splits as a result of Aharonov-Bohm magnetic
flux. A magnetic field of 370 T, generated by the electro-magnetic flux
compression destructive pulsed magnet-coil technique, was applied to
single-chirality semiconducting carbon nanotubes. Using streak spectroscopy, we
demonstrated the separation of the independent band-edge exciton states at the
K and K' points of the Brillouin zone after the mixing of the dark and bright
states above 150 T. These results enable a quantitative discussion of the whole
picture of the Aharonov-Bohm effect in single-walled carbon nanotubes.",1505.06305v1
2015/5/29,Time-resolved imaging of pulse-induced magnetization reversal with a microwave assist field,"The reversal of the magnetization under the influence of a field pulse has
been previously predicted to be an incoherent process with several competing
phenomena such as domain wall relaxation, spin wave-mediated instability
regions, and vortex-core mediated reversal dynamics. However, there has been no
study on the direct observation of the switching process with the aid of a
microwave signal input. We report a time-resolved imaging study of
magnetization reversal in patterned magnetic structures under the influence of
a field pulse with microwave assistance. The microwave frequency is varied to
demonstrate the effect of resonant microwave-assisted switching. We observe
that the switching process is dominated by spin wave dynamics generated as a
result of magnetic instabilities in the structures, and identify the
frequencies that are most dominant in magnetization reversal.",1505.07936v1
2015/6/21,Magnetic and magnetotransport behavior of RFe5Al7 (R= Gd and Dy): Observation of re-entrant inverse-magnetocaloric phenomenon and asymmetric magnetoresistance behavior,"We have compared and contrasted magnetic, magnetocaloric and magnetoresistive
properties of Gd and Dy members of the rare-earth (R) series RFe5Al7,
crystallizing in ThMn12 structure, known to order antiferromagnetically. Among
other observations, we would like to emphasize on the following novel findings:
(i) There are multiple sign-crossovers in the temperature (T) dependence of
isothermal entropy change (DeltaS) in the case of Dy compound; in addition to
nil DeltaS at the magnetic compensation point known for two-magnetic-sublattice
systems, there is an additional sign-crossover at low temperatures, as though
there is a re-entrant inverse magnetocaloric phenomenon. Corresponding sign
reversals could also be observed in the magnetoresistance data. (ii) The plots
of magnetoresistance versus magnetic field are found to be highly asymmetric
with the reversal of the direction of magnetic-field (H) well below TN for both
compounds, similar to that known for an antiferromagnetic tunnel junctions. We
attribute these to subtle changes in spin orientations of R and Fe moments
induced by T and H.",1506.06373v1
2015/7/9,Temperature evolution of superparamagnetic clusters in single-crystal La0.85Sr0.15CoO3 from nonlinear magnetic ac response and neutron depolarization,"The representative measurements of the second harmonic in ac magnetization
complemented by neutron depolarization have been performed for single-crystal
La0.85Sr0.15CoO3 in the temperature range 97 K < T < 230 K, where occurrence of
a small fraction (~ 0.001) of nanoscale ferromagnetic clusters (FMC) has been
found. Magnetic, geometrical and dynamical parameters of the FMC system have
been evaluated in the temperature range T < 140 K, where superparamagnetic
regime installs, by means of the formalism involving the Fokker-Planck equation
(FPE). With lowering the temperature, the amount of clusters fraction, the
cluster size and magnetic moment along with its diffusion relaxation time
strongly increase, each in its own temperature interval. Below 130 K, FMC
contribute essentially to the total linear magnetic susceptibility. The damping
factor of the order 0.1 proves the importance of precession in thermal
relaxation of the cluster magnetic moment. The FMC are a precursor of
long-range ferromagnetic correlations seen below 100 K with neutron-scattering
techniques. The employed technique supplemented with FPE-based data-treatment
formalism is a novel method for studying superparamagnetic systems.",1507.02593v2
2015/7/28,Phenomenology of chiral damping in noncentrosymmetric magnets,"A phenomenology of magnetic chiral damping is proposed in the context of
magnetic materials lacking inversion symmetry breaking. We show that the
magnetic damping tensor adopts a general form that accounts for a component
linear in magnetization gradient in the form of Lifshitz invariants. We propose
different microscopic mechanisms that can produce such a damping in
ferromagnetic metals, among which spin pumping in the presence of anomalous
Hall effect and an effective ""$s$-$d$"" Dzyaloshinskii-Moriya antisymmetric
exchange. The implication of this chiral damping in terms of domain wall motion
is investigated in the flow and creep regimes. These predictions have major
importance in the context of field- and current-driven texture motion in
noncentrosymmetric (ferro-, ferri-, antiferro-)magnets, not limited to metals.",1507.07762v1
2015/8/3,Static magnetic proximity effect in Pt/Ni$_{1-x}$Fe$_x$ bilayers investigated by x-ray resonant magnetic reflectivity,"We present x-ray resonant magnetic reflectivity (XRMR) as a very sensitive
tool to detect proximity induced interface spin polarization in Pt/Fe,
Pt/Ni$_{33}$Fe$_{67}$, Pt/Ni$_{81}$Fe$_{19}$ (permalloy), and Pt/Ni bilayers.
We demonstrate that a detailed analysis of the reflected x-ray intensity gives
insight in the spatial distribution of the spin polarization of a non-magnetic
metal across the interface to a ferromagnetic layer. The evaluation of the
experimental results with simulations based on optical data from ab initio
calculations provides the induced magnetic moment per Pt atom in the spin
polarized volume adjacent to the ferromagnet. We find the largest spin
polarization in Pt/Fe and a much smaller magnetic proximity effect in Pt/Ni.
Additional XRMR experiments with varying photon energy are in good agreement
with the theoretical predictions for the energy dependence of the magnetooptic
parameters and allow identifying the optical dispersion $\delta$ and absorption
$\beta$ across the Pt L3-absorption edge.",1508.00379v1
2015/8/10,Field dependent magnetization of BiFeO3 in ultrathin La0.7Sr0.3MnO3/BiFeO3 superlattice,"We report the observation of field-induced magnetization of BiFeO3 (BFO) in
an ultrathin BFO/La0.7Sr0.3MnO3 (LSMO) superlattice using polarized neutron
reflectivity (PNR). Our PNR results indicate parallel alignment of
magnetization across BFO/LSMO interfaces. The study showed an increase in
average magnetization on increasing applied magnetic field at 10K. We observed
a saturation magnetization of 110 \pm 15 kA/m (~0.8 {\mu}B/Fe) for ultrathin
BFO layer (~2 unit cell) sandwiched between ultrathin LSMO layers (~ 2 unit
cell), which is much higher than the canted moment (0.03 {\mu}B/Fe) in the bulk
BFO. The macroscopic VSM results on superlattice clearly indicate
superparamagnetic behavior typically observed in nanoparticles of manganites.",1508.02218v1
2015/8/17,Magnetization dynamics driven by angle-dependent spin-orbit spin transfer torque,"Spin-orbit spin transfer torque allows an efficient control of magnetization
by an in-plane current. Recent experiments found that the spin-orbit torque has
strong dependence on the magnetization angle [Garello et al., Nature
Nanotechnol. 8, 587 (2013); Qiu et al., Sci. Rep. 4, 4491 (2014)]. We
theoretically investigate magnetization switching and domain wall motion in a
perpendicularly magnetized layer, induced by angle-dependent spin-orbit torque.
We obtain analytic expressions of the switching current and domain wall
velocity, in agreement with numerical results. Based on the expressions, we
find that the spin-orbit torque increasing with the polar angle of
magnetization is beneficial for both switching and domain wall motion. Our
result will serve as a guideline to design and interpret switching and domain
wall experiments based on spin-orbit torque.",1508.04067v2
2015/8/25,Ground-state properties of the triangular-lattice Heisenberg antiferromagnet with arbitrary spin quantum number $s$,"We apply the coupled cluster method to high orders of approximation and exact
diagonalizations to study the ground-state properties of the triangular-lattice
spin-$s$ Heisenberg antiferromagnet. We calculate the fundamental ground-state
quantities, namely, the energy $e_0$, the sublattice magnetization $M_{\rm
sub}$, the in-plane spin stiffness $\rho_s$ and the in-plane magnetic
susceptibility $\chi$ for spin quantum numbers $s=1/2, 1, \ldots, s_{\rm max}$,
where $s_{\rm max}=9/2$ for $e_0$ and $M_{\rm sub}$, $s_{\rm max}=4$ for
$\rho_s$ and $s_{\rm max}=3$ for $\chi$. We use the data for $s \ge 3/2$ to
estimate the leading quantum corrections to the classical values of $e_0$,
$M_{\rm sub}$, $\rho_s$, and $\chi$. In addition, we study the magnetization
process, the width of the 1/3 plateau as well as the sublattice magnetizations
in the plateau state as a function of the spin quantum number $s$.",1508.06254v1
2015/8/26,Non-circular skyrmion and its anisotropic response in thin films of chiral magnets under tilted magnetic field,"We study the equilibrium and dynamical properties of skyrmions in thin films
of chiral magnets with oblique magnetic field. The shape of an individual
skyrmion is non-circular and the skyrmion density decreases with the tilt angle
from the normal of films. As a result, the interaction between two skyrmions
depends on the relative angle between them in addition to their separation. The
triangular lattice of skyrmions under a perpendicular magnetic field is
distorted into a centered rectangular lattice for a tilted magnetic field. For
a low skyrmion density, skyrmions form a chain like structure. The dynamical
response of the non-circular skyrmions depends on the direction of external
currents.",1508.06361v1
2015/8/31,Surface functionalization enhanced magnetism in SnO_2 nanoparticles and its correlation to photoluminescence properties,"High value of magnetic moment 0.08 emu/g at room temperature for SnO_2
nanoparticles (NPs) was observed. Surface functionalization with
octadecyltrichlorosilane (OTS) enhanced the saturation magnetic moment of NPs
to an anomalously high value of 0.187 emu/g by altering the electronic
configuration on NPs surface. Surface functionalization also suppressed
photoluminescence (PL) peaks arising from oxygen defects around 2 eV and caused
an increase in the intensities of two peaks near violet region (2.6 - 3 eV). PL
studies under uniform external magnetic field enriched understanding of the
role of OTS. Both OTS and external magnetic field significantly modulated the
luminescence spectra, by altering the surface electronic structure of NPs.
Extra spins on the surface of SnO2 NPs created by the surface functionalization
process and their influence on resultant magnetic moment and luminescence
properties are discussed in details.",1508.07791v1
2015/9/6,Electrical control of magnetism in oxides,"This review article aims at illustrating the recent progresses in the
electrical control of magnetism in oxides with profound physics and enormous
potential applications. In the first part, we provide a comprehensive summary
of the electrical control of magnetism in the classic multiferroic
heterostructures and clarify their various mechanisms lying behind. The second
part focuses on the novel route of electric double layer gating for driving a
significantly electronic phase transition in magnetic oxides by a small
voltage. The electric field applied on the ordinary dielectric oxide in the
third part is used to control the magnetic phenomenon originated from the
charge transfer and orbital reconstruction at the interface between dissimilar
correlated oxides. At last, we analyze the challenges in electrical control of
magnetism in oxides, both on mechanism and practical application, which would
inspire more in-depth researches and advance the development in this field.",1509.01795v1
2015/9/15,Magnetic structure driven by monoclinic distortions in the double perovskite Sr2YRuO6,"The monoclinic double-perovskite Sr2YRuO6 has recently gained a renewed
interest in order to get a deeper insight into the exotic magnetic ground
states associated with geometric frustration. Striking discrepancies between
the spin order derived from the neutron diffraction refinements and the
macroscopic magnetic and thermal responses is a major challenge that must be
addressed. In this work, detailed neutron diffraction measurements as a
function of temperature yield a completely different interpretation of the
patterns. We show that at low temperatures a spin structure of the K2NiF4-type
is an accessible configuration for the magnetic ground state. In the
neighborhood of the magnetic transition this configuration evolves into a
canted super-structure. The deduced temperature dependence of the canting angle
exhibits two closely spaced peaks, which are in excellent agreement with the
double peaks in the magnetic contribution to the specific heat and in the
thermal expansion coefficient. We explain these features in terms of
reorientation of the net ferromagnetic moment of the noncollinear spin state,
due to the local breaking of the inversion symmetry promoted by the monoclinic
distortions, with structural changes acting as the driving force.",1509.04377v1
2015/9/16,Charge-Induced Spin Torque in Anomalous Hall Ferromagnets,"We demonstrate that spin-orbit coupled electrons in a magnetically doped
system exert a spin torque on the local magnetization, without a flowing
current, when the chemical potential is modulated in a magnetic field. The spin
torque is proportional to the anomalous Hall conductivity, and its effective
field strength may overcome the Zeeman field. Using this effect, the direction
of the local magnetization is switched by gate control in a thin film. This
charge-induced spin torque is essentially an equilibrium effect, in contrast to
the conventional current-induced spin-orbit torque, and, thus, devices using
this operating principle possibly have higher efficiency than the conventional
ones. In addition to a comprehensive phenomenological derivation, we present a
physical understanding based on a model of a Dirac-Weyl semimetal, possibly
realized in a magnetically doped topological insulator. The effect might be
realized also in nanoscale transition materials, complex oxide ferromagnets,
and dilute magnetic semiconductors.",1509.04799v1
2015/9/26,Spin relaxation near a ferromagnetic transition,"We study spin relaxation in dilute magnetic semiconductors near a
ferromagnetic transition, where spin fluctuations become strong. An enhancement
in the scattering rate of itinerant carriers from the spin fluctuations of
localized impurities leads to a change in the dominant spin relaxation
mechanism from Dyakonov-Perel to spin flips in scattering. On the ferromagnetic
side of the transition, we show that due to the presence of two magnetic
components -- the itinerant carriers and the magnetic impurities -- with
different gyromagnetic ratios, the relaxation rate of the total magnetization
can be quite different from the relaxation rate of the spin. Following a
disturbance of the equilibrium magnetization, the spin is initially
redistributed between the two components to restore the equilibrium
magnetization. It is only on a longer time scale, controlled by the spin-orbit
interaction, that the total spin itself relaxes to its equilibrium state.",1509.07926v1
2015/10/21,Titanium Nitride as a Seed Layer for Heusler Compounds,"Titanium nitride (TiN) shows low resistivity at room temperature, high
thermal stability and thus has the potential to serve as seed layer in magnetic
tunnel junctions. High quality TiN thin films with regard to the
crystallographic and electrical properties were grown and characterized by
X-ray diffraction and 4-terminal transport measurements. Element specific X-ray
absorption spectroscopy revealed pure TiN in the bulk. To investigate the
influence of a TiN seed layer on a ferro(i)magnetic bottom electrode, an
out-of-plane magnetized Mn2.45Ga as well as in- and out-of-plane magnetized
Co2FeAl thin films were deposited on a TiN buffer, respectively. The magnetic
properties were investigated using a superconducting quantum interference
device (SQUID) and anomalous Hall effect (AHE) for Mn2.45Ga. Magneto optical
Kerr effect (MOKE) measurements were carried out to investigate the magnetic
properties of Co2FeAl. TiN buffered Mn2.45Ga thin films showed higher
coercivity and squareness ratio compared to unbuffered samples. The Heusler
compound Co2FeAl showed already good crystallinity when grown at room
temperature.",1510.06256v3
2015/11/6,"Structural, magnetic and electrical properties of sputter deposited Mn-Fe-Ga thin films","We investigated structural, magnetic and electrical properties of sputter
deposited Mn-Fe-Ga compounds. The crystallinity of the Mn-Fe-Ga thin films was
confirmed using x-ray diffraction. X-ray reflection and atomic force microscopy
measurements were utilized to investigate the surface properties, roughness,
thickness and density of the deposited Mn-Fe-Ga. Depending on the
stoichiometry, as well as the used substrates (SrTiO3 (001) and MgO (001)) or
buffer layer (TiN) the Mn-Fe-Ga crystallizes in the cubic or the tetragonally
distorted phase. Anomalous Hall effect and alternating gradient magnetometry
measurements confirmed strong perpendicular magnetocrystalline anisotropy. Low
saturation magnetization and hard magnetic behavior was reached by tuning the
composition. Temperature dependent anomalous Hall effect measurements in a
closed cycle He-cryostat showed a slight increase in coercivity with decreasing
temperature (300K to 2K). TiN buffered Mn2.7Fe0.3Ga revealed sharper switching
of the magnetization compared to the unbuffered layers.",1511.02097v2
2015/11/8,Quantum phase transitions and decoupling of magnetic sublattices in the quasi-two-dimensional Ising magnet Co3V2O8 in a transverse magnetic field,"The application of a magnetic field transverse to the easy axis, Ising
direction in the quasi-two-dimensional Kagome staircase magnet, Co3V2O8,
induces three quantum phase transitions at low temperatures, ultimately
producing a novel high field polarized state, with two distinct sublattices.
New time-of-flight neutron scattering techniques, accompanied by large angular
access, high magnetic field infrastructure allow the mapping of a sequence of
ferromagnetic and incommensurate phases and their accompanying spin
excitations. At least one of the transitions to incommensurate phases at \mu
0Hc1~6.25 T and \mu 0Hc2~7 T is discontinuous, while the final quantum critical
point at \mu 0Hc3~13 T is continuous.",1511.02483v1
2015/11/30,The QUAX proposal: a search of galactic axion with magnetic materials,"Aim of the QUAX (QUaerere AXion) proposal is to exploit the interaction of
cosmological axions with the spin of electrons in a magnetized sample. Their
effect is equivalent to the application of an oscillating rf field with
frequency and amplitude which are fixed by axion mass and coupling constant,
respectively. The rf receiver module of the QUAX detector consists of
magnetized samples with the Larmor resonance frequency tuned to the axion mass
by a polarizing static magnetic field. The interaction of electrons with the
axion-equivalent rf field produces oscillations in the total magnetization of
the samples. To amplify such a tiny field, a pump field at the same frequency
is applied in a direction orthogonal to the polarizing field. The induced
oscillatory magnetization along the polarizing field is measured by a SQUID
amplifier operated at its quantum noise level.",1511.09461v1
2015/12/17,A self-consistent spin-diffusion model for micromagnetics,"We propose a three-dimensional micromagnetic model that dynamically solves
the Landau-Lifshitz-Gilbert equation coupled to the full spin-diffusion
equation. In contrast to previous methods, we solve for the magnetization
dynamics and the electric potential in a self-consistent fashion. This
treatment allows for an accurate description of magnetization dependent
resistance changes. Moreover, the presented algorithm describes both spin
accumulation due to smooth magnetization transitions and due to material
interfaces as in multilayer structures. The model and its finite-element
implementation are validated by current driven motion of a magnetic vortex
structure. In a second experiment, the resistivity of a magnetic multilayer
structure in dependence of the tilting angle of the magnetization in the
different layers is investigated. Both examples show good agreement with
reference simulations and experiments respectively.",1512.05519v4
2015/12/19,Verification of Anderson superexchange in MnO via magnetic pair distribution function analysis and \textit{ab initio} theory,"We present temperature-dependent atomic and magnetic pair distribution
function (PDF) analysis of neutron total scattering measurements of
antiferromagnetic MnO, an archetypal strongly correlated transition-metal
oxide. The known antiferromagnetic ground-state structure fits the
low-temperature data closely with refined parameters that agree with
conventional techniques, confirming the reliability of the newly developed
magnetic PDF method. The measurements performed in the paramagnetic phase
reveal significant short-range magnetic correlations on a $\sim$1~nm length
scale that differ substantially from the low-temperature long-range spin
arrangement. \textit{Ab initio} calculations using a self-interaction-corrected
local spin density approximation of density functional theory predict magnetic
interactions dominated by Anderson superexchange and reproduce the measured
short-range magnetic correlations to a high degree of accuracy. Further
calculations simulating an additional contribution from a direct exchange
interaction show much worse agreement with the data. The Anderson superexchange
model for MnO is thus verified by experiment and confirmed by \textit{ab
initio} theory.",1512.06270v2
2015/12/22,(C$_{4}$H$_{12}$N$_{2}$)[CoCl$_{4}$] -tetrahedrally coordinated Co$^{2+}$ without the orbital degeneracy,"We report on the synthesis, crystal structure, and magnetic properties of a
previously unreported Co$^{2+}$ $S={3 \over 2}$ compound,
(C$_{4}$H$_{12}$N$_{2}$)[CoCl$_{4}$], based upon a tetrahedral crystalline
environment. The $S={3 \over 2}$ magnetic ground state of Co$^{2+}$, measured
with magnetization, implies an absence of spin-orbit coupling and orbital
degeneracy. This contrasts with compounds based upon an octrahedral and even
known tetrahedral Co$^{2+}$ based systems where a sizable spin-orbit coupling
is measured. The compound is characterized with single crystal x-ray
diffraction, magnetic susceptibility, infrared, and ultraviolet/visible
spectroscopy. Magnetic susceptibility measurements find no magnetic ordering
above 2 K. The results are also compared with the previously known monoclinic
hydrated analogue.",1512.07124v1
2016/1/6,Dynamic response of an artificial square spin ice,"Magnetization dynamics in an artificial square spin-ice lattice made of
Ni80Fe20 with magnetic field applied in the lattice plane is investigated by
broadband ferromagnetic resonance spectroscopy. The experimentally observed
dispersion shows a rich spectrum of modes corresponding to different
magnetization states. These magnetization states are determined by exchange and
dipolar interaction between individual islands, as is confirmed by a
semianalytical model. In the low field regime below 400 Oe a hysteretic
behavior in the mode spectrum is found. Micromagnetic simulations reveal that
the origin of the observed spectra is due to the initialization of different
magnetization states of individual nanomagnets. Our results indicate that it
might be possible to determine the spin-ice state by resonance experiments and
are a first step towards the understanding of artificial geometrically
frustrated magnetic systems in the high-frequency regime.",1601.01219v1
2016/1/9,Switching the magnetization of magnetostrictive nanomagnets from single-domain to non-volatile vortex states with a surface acoustic wave,"We report manipulation of the magnetic states of elliptical cobalt
magnetostrictive nanomagnets (of nominal dimensions ~ 340 nm x 270 nm x 12 nm)
delineated on bulk 128{\deg} Y-cut lithium niobate with Surface Acoustic Waves
(SAWs) launched from interdigitated electrodes. Isolated nanomagnets that are
initially magnetized to a single domain state with magnetization pointing along
the major axis of the ellipse are driven into a vortex state by surface
acoustic waves that modulate the stress anisotropy of these nanomagnets. The
nanomagnets remain in the vortex state until they are reset by a strong
magnetic field to the initial single domain state, making the vortex state
non-volatile. This phenomenon is modeled and explained using a micromagnetic
framework and could lead to the development of extremely energy efficient
magnetization switching methodologies.",1601.02081v1
2016/1/12,Non-locally sensing the magnetic states of nanoscale antiferromagnets with an atomic spin sensor,"The ability to sense the magnetic state of individual magnetic nano-objects
is a key capability for powerful applications ranging from readout of
ultra-dense magnetic memory to the measurement of spins in complex structures
with nanometer precision. Magnetic nano-objects require extremely sensitive
sensors and detection methods. Here we create an atomic spin sensor consisting
of three Fe atoms and show that it can detect nanoscale antiferromagnets
through minute surface-mediated magnetic interaction. Coupling, even to an
object with no net spin and having vanishing dipolar stray field, modifies the
transition matrix element between two spin states of the Fe-atom-based spin
sensor that changes the sensor's spin relaxation time. The sensor can detect
nanoscale antiferromagnets at up to three nanometers distance and achieves an
energy resolution of 10 micro-electronvolts surpassing the thermal limit of
conventional scanning probe spectroscopy. This scheme permits simultaneous
sensing of multiple antiferromagnets with a single spin sensor integrated onto
the surface.",1601.02723v2
2016/1/15,Evolutions of Neutron Stars and their Magnetic Fields,"Estimations of magnetic fields of neutron stars, observed as radio and X-ray
pulsars, are discussed. It is shown, that theoretical and observational values
for different types of radiopulsars are in good correspondence. Radiopulsars in
close binaries and millisecond pulsars, which have passed the stage of disk
accretion (recycled radiopulsars), have magnetic fields 2-4 orders of magnitude
smaller than ordinary single pulsars. Most probably, the magnetic field of the
neutron star was screened by the infalling material. Several screening models
are considered. Formation of single recycled pulsars loosing its companion is
discussed. Magnetic fields of some X-ray pulsars are estimated from the
cyclotron line energy. In the case of Her X-1 this estimation exceeds
considerably the value of its magnetic field obtained from long term
observational data related to the beam structure evolution. Another
interpretation of the cyclotron feature, based on the relativistic dipole
radiation mechanism, could remove this discrepancy. Observational data about
soft gamma repeaters and their interpretation as magnetars are critically
analyzed.",1601.04006v1
2016/2/4,Quadrupole order in the frustrated pyrochlore magnet Tb$_2$Ti$_2$O$_7$,"We have studied the hidden long-range order (LRO) of the frustrated
pyrochlore magnet Tb$_2$Ti$_2$O$_7$ by means of specific-heat experiments and
Monte-Carlo (MC) simulations, which has been discussed as the LRO of quadrupole
moments inherent to the non-Kramers ion of Tb$^{3+}$. We have found that the
sharp specific-heat peak is collapsed into a broad hump by magnetic fields
above 0.3 T for $H//[001]$. This result, qualitatively reproduced by MC
simulations, suggests that a field-induced magnetic state overcomes the
quadrupolar LRO state, as a similar case of a classical spin ice. The present
results support the interpretation that Tb$_{2+x}$Ti$_{2-x}$O$_{7+y}$ is a
unique material in the boundary between the quadrupolar ($x \geq x_c =
-0.0025$) and spin-liquid ($x \leq x_c$) states, where the magnetic field along
the [001] axis is a tuning parameter which induces the magnetic ordered state.",1602.01806v1
2016/2/12,Derivation of the magnetic Euler-Heisenberg energy,"In quantum field theory, the vacuum is a fluctuating medium which behaves as
a nonlinear polarizable material. In this article, we perform the first
rigorous derivation of the magnetic Euler-Heisenberg effective energy, a
nonlinear functional that describes the effective fluctuations of the quantum
vacuum in a classical magnetic field. We start from a classical magnetic field
in interaction with a quan-tized Dirac field in its ground state, and we study
a limit in which the classical magnetic field is slowly varying. After a change
of scales, this is equivalent to a semi-classical limit $\hbar\to0$, with a
strong magnetic field of order $1/\hbar$. In this regime, we prove that the
energy of Dirac's polarized vacuum converges to the Euler-Heisenberg
functional. The model has ultraviolet divergences, which we regularize using
the Pauli-Villars method. We also discuss how to remove the regularization of
the Euler-Heisenberg effective Lagrangian, using charge renormaliza-tion,
perturbatively to any order of the coupling constant.",1602.04047v3
2016/2/15,Electrical Switching of Magnetization in Films of alpha-Iron with Naturally Hydroxidized Surface,"Control of the magnetization vector in ferromagnetic films and
heterostructures by using electric tools instead of external magnetic fields
can lead to low-power memory devices. We observe the robust changes in
magnetization states of a thin (about 30 nm) film of alpha-Fe covered by the
naturally formed layer ( about 6 nm in thickness) of iron ohyhydroxides (FeOOH)
under discharging a capacitor through the film. Strikingly, the magnetization
vector is switchable by the discharge even with no any biasing field at room
temperatures. In this electrically induced magnetization switching (EIMS) we
reveal the key role of the FeOOH layer. We demonstrate experimental evidences
that not the discharge current itself but the electric field (of the order of
10 kV/m) generated by this current is responsible for EIMS. The results
reported here provide a plausible explanation of the observed phenomenon in
terms of electric-field-induced weak ferromagnetism in the FeOOH layer and its
coupling with the underlying alpha-Fe.",1602.04590v1
2016/2/25,Static Magnetic Proximity Effect in Pt Layers on Sputter-Deposited NiFe2O4 and on Fe of Various Thicknesses Investigated by XRMR,"The longitudinal spin Seebeck effect is detected in sputter-deposited NiFe2O4
films using Pt as a spin detector and compared to previously investigated
NiFe2O4 films prepared by chemical vapor deposition. Anomalous Nernst effects
induced by the magnetic proximity effect in Pt can be excluded for the
sputter-deposited NiFe2O4 films down to a certain limit, since x-ray resonant
magnetic reflectivity measurements show no magnetic response down to a limit of
0.04 {\mu}B per Pt atom comparable to the case of the chemicallydeposited
NiFe2O4 films. These differently prepared films have various thicknesses.
Therefore, we further studied Pt/Fe reference samples with various Fe
thicknesses and could confirm that the magnetic proximity effect is only
induced by the interface properties of the magnetic material.",1602.07895v1
2016/3/14,The magnetic ground state of Sr2IrO4 and implications for second-harmonic generation,"The currently accepted magnetic ground state of Sr2IrO4 (the -++- state)
preserves inversion symmetry. This is at odds, though, with recent experiments
that indicate a magnetoelectric ground state, leading to the speculation that
orbital currents or more exotic magnetic multipoles might exist in this
material. Here, we analyze various magnetic configurations and demonstrate that
two of them, the magnetoelectric -+-+ state and the non-magnetoelectric ++++
state, can explain these recent second-harmonic generation (SHG) experiments,
obviating the need to invoke orbital currents. The SHG-probed magnetic order
parameter has the symmetry of a parity-breaking multipole in the -+-+ state and
of a parity-preserving multipole in the ++++ state. We speculate that either
might have been created by the laser pump used in the experiments. An
alternative is that the observed magnetic SHG signal is a surface effect. We
suggest experiments that could be performed to test these various
possibilities, and also address the important issue of the suppression of the
RXS intensity at the L2 edge.",1603.04311v3
2016/3/18,"Structural and Magnetic Characterization of Large Area, Free-Standing Thin Films of Magnetic Ion Intercalated Dichalcogenides Mn0.25TaS2 and Fe0.25TaS2","Free-standing thin films of magnetic ion intercalated transition metal
dichalcogenides are produced using ultramicrotoming techniques. Films of
thicknesses ranging from 30nm to 250nm were achieved and characterized using
transmission electron diffraction and X-ray magnetic circular dichroism.
Diffraction measurements visualize the long range crystallographic ordering of
the intercalated ions, while the dichroism measurements directly assess the
orbital contributions to the total magnetic moment. We thus verify the
unquenched orbital moment in Fe0.25TaS2 and measure the fully quenched orbital
contribution in Mn0.25TaS2. Such films can be used in a wide variety of
ultrafast X-ray and electron techniques that benefit from transmission
geometries, and allow measurements of ultrafast structural, electronic, and
magnetization dynamics in space and time.",1603.05921v1
2016/3/31,"Influence of the different strains components on the uniaxial magnetic anisotropy constants for (Ga,Mn)As bulk system: a First-Principles Study","We present a computational study of the magnetic anisotropy energy for a
given concentration of the Mn ions in the GaAs host, in the framework of the
density functional theory. We focus on the influence of a different kind of
strains on the uniaxial magnetic anisotropy constants $K_1$ and $K_2$, which
reflect the magnetic anisotropy energy out- and in- (001) plane, respectively.
We have shown that the general trends for the applied biaxial strain on
anisotropy constants are consistent with the experimental data. We have
predicted the critical strains, for which the magnetization vector changes its
direction. Our results have shown that it is not possible to modify
considerably the uniaxial magnetic anisotropy constants, exposing (Ga,Mn)As to
hydrostatic pressure of a magnitude reasonable from experimental point of view.",1603.09546v3
2016/4/10,Voltage-dependent spin flip in magnetically-substituted graphene nanoribbons: Toward the realization of graphene-based spintronic devices,"We examine the possibility of using graphene nanoribbons (GNRs) with directly
substituted chromium atoms as spintronic device. Using density functional
theory, we simulate a voltage bias across a constructed GNR in a device setup,
where a magnetic dimer has been substituted into the lattice. Through this
first principles approach, we calculate the electronic and magnetic properties
as a function of Hubbard U, voltage, and magnetic configuration. By calculating
of the total energy of each magnetic configuration, we determine that initial
antiferromagnetic ground state flips to a ferromagnetic state with applied
bias. Mapping this transition point to the calculated conductance for the
system reveals that there is a distinct change in conductance through the GNR,
which indicates the possibility of a spin valve. We also show that this
corresponds to a distinct change in the induced magnetization within the
graphene.",1604.02741v1
2016/5/11,Possible magnetism based on orbital motion of protons in ice,"A peak anomaly is observed in the magnetic susceptibility as a function of
temperature in solid H2O near Tp=60 K. At external magnetic fields below 2 kOe,
Tp becomes positive in the temperature range between 45 and 66 K. The magnetic
field dependence of the susceptibility in the same temperature range exhibits
an inverted ferromagnetic hysteretic loop superimposed on top of the
diamagnetic signature of ice at fields below 600 Oe. We suggest that a fraction
of protons that are capable of undergoing correlated tunneling in a hexagonal
path without disrupting the stoichiometry of the lattice create an induced
magnetic field opposite to the induced magnetic field created by the electrons
upon application of an external field which counters the overall diamagnetism
of the material.",1605.03383v1
2016/5/25,Chirality-induced magnon transport in AA-stacked bilayer honeycomb chiral magnets,"In this Letter, we study the magnetic transport in AA-stacked bilayer
honeycomb chiral magnets coupled either ferromagnetically or
antiferromagnetically. For both couplings, we observe chirality-induced gaps,
chiral protected edge states, magnon Hall and magnon spin Nernst effects of
magnetic spin excitations. For ferromagnetically coupled layers, thermal Hall
and spin Nernst conductivities do not change sign as function of magnetic field
or temperature similar to single-layer honeycomb ferromagnetic insulator. In
contrast, for antiferromagnetically coupled layers, we observe a sign change in
the thermal Hall and spin Nernst conductivities as the magnetic field is
reversed. We discuss possible experimental accessible honeycomb bilayer quantum
materials in which these effects can be observed.",1605.07971v5
2016/5/26,Handling magnetic anisotropy and dynamic magnetic response of ferromagnetic multilayers in flexible substrates,"We investigate the dynamic magnetic response of ferromagnetic flexible
NiFe/Ta and FeCuNbSiB/Ta multilayers under external stress. We explore the
possibility of handling magnetic anisotropy and dynamic magnetic response of
flexible magnetostrictive nanostructures. We quantify the sensitivity of the
multilayers under external stress by calculating the ratio $|\Delta
\textrm{MI}|/|\Delta \bar{\sigma}|$ and show that considerable values can be
reached by tuning the magnetic field, frequency, magnetostriction constant, and
external stress. The results reveal possibilities of application of flexible
magnetostrictive multilayers under external stress and place them as very
attractive candidates as element sensor for the development of sensitive smart
touch sensors.",1605.08193v2
2016/5/27,Edge states and skyrmion dynamics in nanostripes of frustrated magnets,"Magnetic skyrmions are particle-like topological excitations recently
discovered in chiral magnets. Their small size, topological protection and the
ease with which they can be manipulated by electric currents generated much
interest in using skyrmions for information storage and processing. Recently,
it was suggested that skyrmions with additional degrees of freedom can exist in
magnetically frustrated materials. Here, we show that dynamics of skyrmions and
antiskyrmions in nanostripes of frustrated magnets is strongly affected by
complex spin states formed at the stripe edges. These states create multiple
edge channels which guide the skyrmion motion. Non-trivial topology of edge
states gives rise to complex current-induced dynamics, such as emission of
skyrmion-antiskyrmion pairs. The edge state topology can be controlled with an
electric current through the exchange of skyrmions and antiskyrmions between
the edges of a magnetic nanostructure. These results can lead to conceptually
new electronic devices.",1605.08645v1
2016/6/6,Tracking local magnetic dynamics via high-energy charge excitations in a relativistic Mott insulator,"We use time- and energy-resolved optical spectroscopy to investigate the
coupling of electron-hole excitations to the magnetic environment in the
relativistic Mott insulator Na$_2$IrO$_3$. We show that, on the picosecond
timescale, the photoinjected electron-hole pairs delocalize on the hexagons of
the Ir lattice via the formation of quasi-molecular orbital (QMO) excitations
and the exchange of energy with the short-range-ordered zig-zag magnetic
background. The possibility of mapping the magnetic dynamics, which is
characterized by typical frequencies in the THz range, onto high-energy (1-2
eV) charge excitations provides a new platform to investigate, and possibly
control, the dynamics of magnetic interactions in correlated materials with
strong spin-orbit coupling, even in the presence of complex magnetic phases.",1606.01667v2
2016/6/10,Effect of Gd/Nd doping on the magnetic properties of PrMnO3,"A study on temperature dependent magnetic properties of single phase
orthorhombic perovskites system associated with space group Pbnm compounds
Pr1-x(Gd/Nd)xMnO3 (x=0.3, 0.5, 0.7) was carried out. A magnetization reversal
is observed below the Neel temperature (TN), in DC magnetization measurements
(at 50 Oe) in the doped compounds. This may be due to the antiparallel coupling
between the two magnetic sublattices (|Pr+Gd/Nd | and Mn). With lowering of
temperature, the |Pr+ Gd/Nd|) ions begin to polarize under the negative
internal field due to canted moment of Mn moments. The hysteresis plot taken at
50K shows a ferrimagnetic characteristic and the presence of spin canting of
ions in the magnetic sublattices. Arrott plot indicates field induced second
order paramagnetic to ferrimagnetic (PM-FiM) phase transition in this system.",1606.03274v1
2016/6/18,Temperature and magnetic field dependence of the internal and lattice structures of skyrmions by off-axis electron holography,"The internal and lattice structures of magnetic skyrmions in B20-type FeGe
are investigated using off-axis electron holography. The temperature, magnetic
field and angular dependence of the magnetic moments of individual skyrmions
are analyzed. Whereas the internal skyrmion shape is found to vary with
magnetic field, the inter-skyrmion distance remains almost unchanged in the
lattice phase. The amplitude of the local magnetic moment is found to depend on
temperature, while the skyrmion shape does not. Deviations from a circular to a
hexagonal skyrmion structure are observed in the lattice phase.",1606.05723v1
2016/6/22,Photo-enhanced magnetization in Fe-doped ZnO nanowires,"An emerging branch of electronics, the optospintronics, would be highly
boosted if the control of magnetic order by light is implemented in magnetic
semiconductors nanostructures being compatible with the actual technology. Here
we show that the ferromagnetic magnetization of low Fe-doped ZnO nanowires
prepared by carbothermal process is enhanced under illumination up to
temperatures slightly below room temperature. This enhancement is related to
the existence of an oxygen vacancy V$_{\rm O}$ in the neighbouring of an
antiferromagnetic superexchange Fe$^{3+}$-Fe$^{3+}$ pair. Under illumination
the V$_{\rm O}$ is ionized to V$_{\rm O}^+$ giving an electron to a close
Fe$^{3+}$ ion from the antiferromagnetic pair. This light excited electron
transition allows the transition of Fe$^{3+}$ to Fe$^{2+}$ forming stable
ferromagnetic double exchange pairs, increasing the total magnetization. The
results here presented indicate an efficient way to influence the magnetic
properties of ZnO based nanostructures by light illumination at high
temperatures.",1606.06955v1
2016/6/23,Spin-Hall nano-oscillator with oblique magnetization and Dzyaloshinskii-Moriya interaction as generator of skyrmions and nonreciprocal spin-waves,"Spin-Hall oscillators are promising sources of spin-wave signals for
magnonics applications, and can serve as building blocks for magnonic logic in
ultralow power computation devices. Here, we analytically and micromagnetically
study magnetization dynamics excited in a Spin-Hall oscillator with oblique
magnetization when the spin-Hall effect and interfacial Dzyaloshinskii-Moriya
interaction act simultaneously. Our key results are (i) excitation of
nonreciprocal spin-waves propagating perpendicularly to the in-plane projection
of the static magnetization, (ii) skyrmions generation by pure spin-current,
(iii) excitation of a new spin-wave mode with a spiral spatial profile
originating from a gyrotropic rotation of a dynamical skyrmion. These results
demonstrate that Spin-Hall oscillators can be used as generators of magnetic
skyrmions and different types of propagating spin-waves for magnetic data
storage and signal processing applications.",1606.07280v1
2016/6/23,Electromagnon dispersion probed by inelastic x-ray scattering,"Inelastic x-ray scattering with meV energy resolution (IXS) is an ideal tool
to measure collective excitations in solids and liquids. In non-resonant
scattering condition, the cross section is strongly dominated by lattice
vibrations (phonons). However, it is possible to probe additional degrees of
freedom such as magnetic fluctuations that are strongly coupled to the phonons.
The IXS spectrum of the coupled system will contain not only the phonon
dispersion (majority component) but also the so far undetected magnetic
correlation function (minority component). Here we report the discovery of
strong magnon-phonon coupling in LiCrO$_2$ that enables the measurement of
magnetic correlations throughout the Brillouin-zone via IXS. We found
electromagnon excitations and electric dipole active two-magnon excitations in
the magnetically ordered phase and paraelectromagnons in the paramagnetic phase
of LiCrO$_2$. We predict that the numerous group of (frustrated) magnets with
dominant direct exchange and non-collinear magnetism shows similarly strong
coupling and surprisingly large and measurable IXS cross section for magnons
and multi-magnon processes.",1606.07321v1
2016/6/28,Termination control of magnetic coupling at a complex oxide interface,"Atomically flat interfaces between ternary oxides have chemically different
variants, depending on the terminating lattice planes of both oxides.
Electronic properties change with the interface termination which affects, for
instance, charge accumulation and magnetic interactions at the interface.
Well-defined terminations have yet rarely been achieved for oxides of ABO3 type
(with metals A, B). Here, we report on a strategy of thin film growth and
interface characterization applied to fabricate the La0.7Sr0.3MnO3-SrRuO3
interface with controlled termination. Ultra-strong antiferromagnetic coupling
between the ferromagnets occurs at the MnO2-SrO interface, but not for the
other termination, in agreement with density functional calculations. X-ray
magnetic circular dichroism measurements reveal coupled reversal of Mn and Ru
magnetic moments at the MnO2-SrO interface. Our results demonstrate termination
control of magnetic coupling across a complex oxide interface and provide a
pathway for theoretical and experimental explorations of novel electronic
interface states with engineered magnetic properties.",1606.08687v1
2016/6/28,Magnetization switching of FePt nanoparticle recording medium by femtosecond laser pulses,"Manipulation of magnetization with ultrashort laser pulses is promising for
information storage device applications. The dynamic of the magnetization
response depends on the energy transfer from the photons to the spins during
the initial laser excitation. A material of special interest for magnetic
storage is FePt nanoparticles , on which optical writing with optical angular
momentum was demonstrated recently by Lambert et al., although the mechanism
remained unclear. Here we investigate experimentally and theoretically the
all-optical switching of FePt nanoparticles. We show that the magnetization
switching is a stochastic process. We develop a complete multiscale model which
allows us to optimize the number of laser shots needed to write the
magnetization of high anisotropy FePt nanoparticles in our experiments. We
conclude that only angular momentum induced optically by the inverse Faraday
effect will provide switching with one single femtosecond laser pulse.",1606.08723v1
2016/8/1,Magnetic relaxation phenomena in the Chiral Magnet Fe$_{1-x}$Co$_x$Si: An ac susceptibility study,"We present a systematic study of the ac susceptibility of the chiral magnet
Fe$_{1-x}$Co$_x$Si with $x$ = 0.30 covering four orders of magnitude in
frequencies from 0.1 Hz to 1 kHz, with particular emphasis to the pronounced
history dependence. Characteristic relaxation times ranging from a few
milliseconds to tens of seconds are observed around the skyrmion lattice
A-phase, the helical-to-conical transition and in a region above $T_C$. The
distribution of relaxation frequencies around the A-phase is broad, asymmetric
and originates from multiple coexisting relaxation processes. The pronounced
dependence of the magnetic phase diagram on the magnetic history and cooling
rates as well as the asymmetric frequency dependence and slow dynamics suggest
more complicated physical phenomena in Fe$_{0.7}$Co$_{0.3}$Si than in other
chiral magnets.",1608.00404v2
2016/8/11,Interplay between conducting and magnetic systems in the antiferromagnetic organic superconductor $κ$-(BETS)$_2$FeBr$_4$,"The mutual influence of the conduction electron system provided by organic
donor layers and magnetic system localized in insulating layers of the
molecular charge transfer salt $\kappa$-(BETS)$_2$FeBr$_4$ has been studied. It
is demonstrated that besides the high-field re-entrant superconducting state,
the interaction between the two systems plays important role for the low-field
superconductivity. The coupling of normal-state charge carriers to the magnetic
system is reflected in magnetic quantum oscillations and can be evaluated based
on the angle-dependent beating behaviour of the oscillations. On the other
hand, the conduction electrons have their impact on the magnetic system, which
is revealed through the pressure-induced changes of the magnetic phase diagram
of the material.",1608.03490v1
2016/8/12,Ultrafast inhomogeneous magnetization dynamics analyzed by interface-sensitive nonlinear magneto-optics,"We analyze laser-induced ultrafast, spatially inhomogeneous magnetization
dynamics of epitaxial Co/Cu(001) films in a 0.4-10 nm thickness range with
time-resolved magnetization-induced second harmonic generation, which probes
femtosecond spin dynamics at the vacuum/Co and Co/Cu interfaces. The
interference of these two contributions makes the overall signal particularly
sensitive to differences in the transient magnetization redistribution between
the two interfaces, i.e. ultrafast magnetization profiles in the ferromagnetic
film. We find in films of up to 3 nm thickness a stronger demagnetization at
the surface, because the film thickness is smaller than the effective mean free
path of the spin current mediating the demagnetization, i.e. the difference
between the mean free paths of the majority and minority carriers. For film
thicknesses larger than 3 nm, the magnetization profile reverses, since
majority spins can escape into the conducting substrate only from the
interface-near region.",1608.03842v1
2016/8/19,Progressive magnetic softening of ferromagnetic layers in multilayer ferromagnet-nonmagnet systems and the role of granularity,"We report a study of the structural and magnetic behavior of the topmost
magnetic layer in a ferromagnet-nonmagnet (Co-Au) multilayer system. Glancing
angle X-ray diffraction measurements performed on a series of multilayers
showed a gradually increasing degree of amorphization of the topmost magnetic
layer with increasing number of bilayers. Concurrently, the magnetic hardness
and magneto-crystalline anisotropy of the top Co layer were found to decrease,
as observed by magneto-optical Kerr effect measurements. This magnetic
softening has been discussed in the light of Herzer's random anisotropy model.
Micromagnetic simulations of the multilayer system also corroborated these
observations.",1608.05568v5
2016/9/13,Formation of new phase inclusions in the system of quasi-equilibrium magnons of high density,"The paper studies the spatial variation of the magnetization in a
nonconducting magnetic sample with an excess number of magnons in comparison to
the equilibrium. The phenomenon is considered using the Landau-Lifshits
equation with additional terms describing the longitudinal relaxation of the
magnetization, the magnon diffusion and the magnon creation by external
pumping. The free energy of the system is presented in the mean field
approximation. It is shown that, if the pumping exceeds some critical value,
regions of the new phase arise where the magnetic moments are oriented opposite
to the magnetization of the magnetic sample. The phenomenon is similar to the
appearance of droplets of the condensed phase in the supersaturated vapor. The
appearance of the new phase either in the form of a single domain or a
periodical lattice is demonstrated. The studied process is a competitor to the
process of the Bose-Einstein condensation of magnons.",1609.04768v1
2016/9/23,Calculations of Magnetic properties of metals through the magnetic-field-containing relativistic tight-binding approximation method,"Magnetic properties of metals are investigated through electronic structure
calculations based on the recently-proposed magnetic-field-containing
relativistic tight-binding approximation (MFRTB) method [Phys. Rev. B
\textbf{91}, 075122 (2015)]. It is found that electronic energy bands for the
metal immersed in the uniform magnetic field have a cluster structure in which
multiple energy bands lie within a small energy width. Each cluster corresponds
to the energy level that is derived on the basis of the semiclassical
approximation. While the cluster is responsible for the de Haas-van Alphen
(dHvA) oscillations, constituent energy bands of the cluster cause additional
oscillation peaks of the magnetization. Also, the energy width of the cluster
leads to the reduction of the amplitude of the dHvA oscillations, which can be
observed as the pseudo Dingle temperature and/or the overestimation of the
curvature of the Fermi surface.",1609.07194v1
2016/9/26,Effect of Negative Pressure on the Prototypical Itinerant Magnet MnSi,"The evolution of the magnetic and charge transport properties of itinerant
magnetic metal MnSi with the substitution of Al and Ga on the Si site is
investigated. We observe an increase in unit cell volume indicating that both
Al and Ga substitutions create negative chemical pressure. There are
substantial increases in the Curie temperature and the ordered moment
demonstrating that the substitutions give the magnetism a more local character.
The substitutions also increase the range of temperature and field where the
skyrmion phase is stable due to a change in the character of the magnetism. In
contrast to the behavior of pure MnSi and expectations for the intrinsic
anomalous Hall effect, we find a significant temperature dependence to the
magnitude and sign of anomalous Hall conductivity constant in Al or Ga
substituted samples. This temperature dependence likely reflects changes in the
spin-orbit coupling strength with temperature, which may have significant
consequences on the helical and skyrmion states. Overall, we observe a
continuous evolution of magnetic and charge transport properties through
positive to negative pressure",1609.08181v2
2016/9/29,"On the rich magnetic phase diagram of (Ni, Co)-Mn-Sn Heusler alloys","We put a spotlight on the exceptional magnetic properties of the metamagnetic
Heusler alloy (Ni,Co)-Mn-Sn by means of first principles simulations.
  In the energy landscape we find a multitude of local minima, which belong to
different ferrimagnetic states and are close in total magnetization and energy.
All these magnetic states correspond to the local high spin state of the Mn
atoms with different spin alignments and are related to the magnetic properties
of Mn. Compared to pure Mn, the magneto-volume coupling is reduced by Ni, Co,
and Sn atoms in the lattice and no local low-spin Mn states appear. For the
cubic phase we find a ferromagnetic ground state whereas the global energy
minimum is a tetragonal state with complicated spin structure and vanishing
magnetization which so far has been overlooked in simulations.",1609.09399v1
2016/10/2,Nearest-neighbour antiferromagnetic interaction as a limiting factor for critical temperature in model DMS system,"In numerous diluted magnetic semiconductor (DMS) systems, the competition
takes place between the short-range antiferromagnetic (AF) superexchange
interactions and the long-range Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling
mediated by the charge carriers. Such a situation strongly influences the
critical temperature, the maximization of which constitutes a challenging task
in DMS physics and technology. The aim of the paper is to discuss theoretically
the limiting effect of AF interactions between nearest-neighbour magnetic ions
on the stability of inhomogeneous ferromagnetic state in a model diluted
magnetic system reflecting some crucial features of DMS.
  The modified molecular field-based model is constructed to account for the
magnetic inhomogeneity. The behavior of the system is studied as a function of
the ratio of superexchange integral to effective ferromagnetic coupling
integral, including the possibility of clustering/anticlustering tendency for
the magnetic ions. The ground state of the system is analysed. The critical
temperature is found to change non-monotonically with the concentration of
magnetic ions and decrease severely for larger concentrations. The behavior of
the system significantly differs from the predictions of the usual homogeneous
mean-field model. Brief comparison with selected experimental results for
(Zn,Mn)Te is provided.",1610.00310v1
2016/10/3,Magnetic microscopy and simulation of strain-mediated control of magnetization in Ni/PMN-PT nanostructures,"Strain-mediated thin film multiferroics comprising
piezoelectric/ferromagnetic heterostructures enable the electrical manipulation
of magnetization with much greater efficiency than other methods; however, the
investigation of nanostructures fabricated from these materials is limited.
Here we characterize ferromagnetic Ni nanostructures grown on a ferroelectric
PMN-PT substrate using scanning electron microscopy with polarization analysis
(SEMPA) and micromagnetic simulations. The magnetization of the Ni
nanostructures can be controlled with a combination of sample geometry and
applied electric field, which strains the ferroelectric substrate and changes
the magnetization via magnetoelastic coupling. We evaluate two types of
simulations of ferromagnetic nanostructures on strained ferroelectric
substrates: conventional micromagnetic simulations including a simple uniaxial
strain, and coupled micromagnetic-elastodynamic simulations. Both simulations
qualitatively capture the response of the magnetization changes produced by the
applied strain, with the coupled solution providing more accurate
representation.",1610.00746v1
2016/10/6,Chiral magnetic effect and Maxwell-Chern-Simons electrodynamics in Weyl semimetals,"The Weyl semimetal, due to a non-zero energy difference in the pair of Weyl
nodes shows chiral magnetic effect(CME). This leads to a flow of
dissipationless electric current along an applied magnetic field. Such a chiral
magnetic effect in Weyl semimetals has been studied using the laws of classical
electrodynamics. It has been shown that the CME in a such a semimetal changes
the properties namely, frequency dependent skin depth, capacitive transport,
plasma frequency etc. in an unconventional way as compared to the conventional
metals. In the low frequency regime, the properties are controlled by a natural
length scale due to CME called the chiral magnetic length. Further, unlike the
conventional metals, the plasma frequency in this case is shown to be strongly
magnetic field-dependent. Since the plasma frequency lies below the optical
frequency, the Weyl semimetals will look transparent. Such new and novel
observations might help in exploiting these class of materials in potential
applications which could completely change the future technology.",1610.01864v2
2016/10/14,Nambu mechanics for stochastic magnetization dynamics,"The Landau-Lifshitz-Gilbert (LLG) equation describes the dynamics of a damped
magnetization vector that can be understood as a generalization of Larmor spin
precession. The LLG equation cannot be deduced from the Hamiltonian framework,
by introducing a coupling to a usual bath, but requires the introduction of
additional constraints. It is shown that these constraints can be formulated
elegantly and consistently in the framework of dissipative Nambu mechanics.
This has many consequences for both the variational principle and for
topological aspects of hidden symmetries that control conserved quantities. We
particularly study how the damping terms of dissipative Nambu mechanics affect
the consistent interaction of magnetic systems with stochastic reservoirs and
derive a master equation for the magnetization. The proposals are supported by
numerical studies using symplectic integrators that preserve the topological
structure of Nambu equations. These results are compared to computations
performed by direct sampling of the stochastic equations and by using closure
assumptions for the moment equations, deduced from the master equation.",1610.04598v2
2016/10/26,Theory of magnetic ordering in the heavy rare earths: ab-initio electronic origin of pair- and four- spin interactions,"We describe an ab-initio disordered local moment theory for long period
magnetic phases and investigate the temperature and magnetic field dependence
of the magnetic states in the heavy rare earth elements (HRE), namely
paramagnetic, conical and helical anti-ferromagnetic(HAFM), fan and
ferromagnetic (FM) states. We obtain a generic HRE magnetic phase diagram which
is consequent on the response of the common HRE valence electronic structure to
f-electron magnetic moment ordering. The theory directly links the first order
HAFM-FM transition to the loss of Fermi surface nesting as well as providing a
template for analysing the other phases and exposing where f-electron
correlation effects are particularly intricate. Gadolinium, for a range of
hexagonal, close-packed lattice constants, c and a, is the prototype and
applications to other HREs are made straightforwardly by scaling the pair and
quartic local moment interactions with de Gennes factors and choosing
appropriate lanthanide contracted c and $a$ values.",1610.08304v1
2016/7/17,Effect of stress induced anisotropy and applied magnetic field on second order perturbed energy of thin ferromagnetic films,"All the simulations were carried out for sc(001) film with three (N=3)
layers. The effect of applied magnetic field and stress induced anisotropy on
energy of ultra-thin ferromagnetic films has been investigated using Heisenberg
Hamiltonian with second order perturbation. The energy becomes minimums at
certain values of angles, applied magnetic field and stress, by indicating that
film can be easily oriented in theses certain directions by applying particular
applied magnetic field or stress. For example, when applied magnetic field
perpendicular to film plane is 3.6, the film can be easily oriented along 0.97
and 2.65 radians directions. When in plane applied magnetic field is 3, energy
minimums can be detected at 1 and 2.6 radians. When applied stress is 2.7, film
can be easily oriented in 2.8 direction.",1611.02229v1
2016/11/9,Voltage control of magnetic anisotropy in epitaxial Ru/Co2FeAl/MgO heterostructures,"Voltage control of magnetic anisotropy (VCMA) in magnetic heterostructures is
a key technology for achieving energy-efficiency electronic devices with
ultralow power consumption. Here, we report the first demonstration of the VCMA
effect in novel epitaxial Ru/Co2FeAl(CFA)/MgO heterostructures with interfacial
perpendicular magnetic anisotropy (PMA). Perpendicularly magnetized tunnel
junctions with the structure of Ru/CFA/MgO were fabricated and exhibited an
effective voltage control on switching fields for the CFA free layer. A large
VCMA coefficient of 108 (139) fJ/Vm for the CFA film was achieved at room
temperature (4 K). The interfacial stability in the heterostructure was
confirmed by repeating measurements. Temperature dependences of both the
interfacial PMA and the VCMA effect were also investigated. It is found that
the temperature dependences follow power laws of the saturation magnetization
with an exponent of ~2. The significant VCMA effect observed in this work
indicates that the Ru/CFA/MgO heterostructure could be one of the promising
candidates for spintronic devices with voltage control.",1611.02827v1
2016/11/23,Absence of magnetic thermal conductivity in the quantum spin liquid candidate YbMgGaO4,"We present the ultra-low-temperature specific heat and thermal conductivity
measurements on the single crystals of YbMgGaO$_4$, which was recently argued
to be a promising candidate for quantum spin liquid (QSL). In the zero magnetic
field, a large magnetic contribution of specific heat is observed, and exhibits
a power-law temperature dependence ($C_m \sim T^{0.74}$). On the contrary, we
do not observed any significant contribution of thermal conductivity from
magnetic excitations. In magnetic fields $H \ge$ 6 T, the exponential
$T$-dependence of $C_m$ and the enhanced thermal conductivity indicate a magnon
gap of the fully-polarized state. The absence of magnetic thermal conductivity
at the zero field in this QSL candidate puts a strong constraint on the
theories of its ground state.",1611.07683v1
2016/12/5,Magnetism in f electron superlattices,"We analyze antiferromagnetism in $f$ electron superlattices. We show that the
competition between the Kondo effect and the RKKY interaction in $f$ electron
materials is modified by the superlattice structure. Thus, the quantum critical
point which separates the magnetic phase and the Fermi liquid phase depends on
the structure of the $f$ electron superlattice. The competition between the
Kondo effect and the RKKY interaction is also reflected in the magnetic
interlayer coupling between different $f$ electron layers. We demonstrate that
in the case of weak Kondo effect the magnetic interlayer coupling behaves
similar to other magnetic heterostructures without Kondo effect. However, close
to the quantum phase transition, the dependence of the interlayer coupling on
the distance between the $f$ electron layers is modified by the Kondo effect.
Another remarkable effect, which is characteristic for $f$ electron
superlattice, is that the magnetic interlayer coupling does vanish stepwise
depending on the distance between different $f$ electron layers. As a
consequence, the quantum critical point depends also stepwise on this distance.",1612.01266v1
2016/12/11,Surface magnetism of cool stars,"Magnetic fields are essential ingredients of many physical processes in the
interiors and envelopes of cool stars. Yet their direct detection and
characterisation is notoriously difficult, requiring high-quality observations
and advanced analysis techniques. Significant progress has been recently
achieved by several types of direct magnetic field studies on the surfaces of
cool active stars. In particular, complementary techniques of the field
topology mapping with polarisation data and total magnetic flux measurements
from intensity spectra have been systematically applied to different classes of
active stars leading to interesting and occasionally controversial results. In
this paper we summarise the current status of direct magnetic field studies of
cool stars, and investigations of surface inhomogeneities caused by the field,
based on the material presented at the Cool Stars 19 splinter session.",1612.03388v1
2016/12/19,"New radical cation salt $κ$-(BETS)$_2$Co$_{0.13}$Mn$_{0.87}$[N(CN)$_2$]$_3$ with two magnetic metals: synthesis, structure, conductivity and magnetic peculiarities","A new metallic radical cation salt
$\kappa$-(BETS)$_2$Co$_{0.13}$Mn$_{0.87}$[N(CN)$_2$]$_3$, where BETS is
bis(ethylenedithio)tetraselenafulvalene, C$_{10}$S$_4$Se$_4$H$_8$, has been
synthesized. In this salt, a part of Mn$^{2+}$ ions are replaced by Co$^{2+}$
which acts as a magnetic dopant with a different effective magnetic moment.
Crystal structure, band structure, conducting and magnetic properties of the
salt have been studied. Below 30 K the material undergoes a metal-insulator
transition, which is suppressed by applying a pressure of ~0.5kbar, leading to
a superconducting ground state. While the structural and conducting properties
are very similar to those of the parent salt
$\kappa$-(BETS)$_2$Mn[N(CN)$_2$]$_3$, magnetic properties associated with
localized moments in the anion layer are found to be surprisingly different.",1612.06188v2
2016/12/21,Magnetic order in 4-layered Aurivillius Phases,"We determine the viability of 4-layered Aurivillius phases to exhibit
long-range magnetic order above room temperature. We use Monte Carlo
simulations to calculate transition temperatures for an effective Heisenberg
model containing a minimal set of required couplings. The magnitude of the
corresponding coupling constants has been determined previously from electronic
structure calculations for $\mathrm{Bi_5FeTi_3O_{15}}$, for which we obtain a
transition temperature far below room temperature. We analyze the role of
further neighbor interactions within our Heisenberg model, in particular that
of the second-nearest-neighbor coupling within the perovskite-like layers of
the Aurivillius structure, as well as that of the weak inter-layer coupling, in
order to identify the main bottleneck for achieving higher magnetic transition
temperatures. Based on our findings, we show that the most promising strategy
to obtain magnetic order at higher temperatures is to increase the
concentration of magnetic cations within the perovskite-like layers, and we
propose candidate compounds where magnetic order could be achieved above room
temperature.",1612.07343v1
2016/12/30,Nuclear magnetic resonance signature of the spin-nematic phase in LiCuVO$_{4}$ at high magnetic fields,"We report a 51V nuclear magnetic resonance investigation of the frustrated
spin-1/2 chain compound LiCuVO4, performed in pulsed magnetic fields and
focused on high-field phases up to 55 T. For the crystal orientations H // c
and H // b we find a narrow field region just below the magnetic saturation
where the local magnetization remains uniform and homogeneous, while its value
is field dependent. This behavior is the first microscopic signature of the
spin-nematic state, breaking spin-rotation symmetry without generating any
transverse dipolar order, and is consistent with theoretical predictions for
the LiCuVO4 compound.",1612.09483v3
2017/1/4,Suppression of magnetic excitations near the surface of the topological Kondo insulator SmB6,"We present a detailed investigation of the temperature and depth dependence
of the magnetic properties of 3D topological Kondo insulator SmB6 , in
particular near its surface. We find that local magnetic field fluctuations
detected in the bulk are suppressed rapidly with decreasing depths,
disappearing almost completely at the surface. We attribute the magnetic
excitations to spin excitons in bulk SmB6 , which produce local magnetic fields
of about ~1.8 mT fluctuating on a time scale of ~60 ns. We find that the
excitonic fluctuations are suppressed when approaching the surface on a length
scale of 40-90 nm, accompanied by a small enhancement in static magnetic
fields. We associate this length scale to the size of the excitonic state.",1701.00955v1
2017/1/4,Magnetic Properties of Transition-Metal Adsorbed ot-Phosphorus Monolayer: A First-principles and Monte Carlo Study,"Using the first-principles and Monte Carlo methods, here we systematically
study magnetic properties of monolayer octagonal-tetragonal phosphorus with 3d
transition-metal (TM) adatoms. Different from the puckered hexagonal black
phosphorus monolayer (phosphorene or $\alpha$-P), the octagonal-tetragonal
phase of 2D phosphorus (named as ot-P or $\epsilon$-P in this article) is
buckled with octagon-tetragon structure. Our calculations show that all TMs,
except the closed-shell Zn atom, are able to strongly bind onto monolayer
$ot$-P with significant binding energies. Local magnetic moments (up to 6
$\mu$B) on adatoms of Sc, Ti, V, Cr, Mn, Fe and Co originate from the exchange
and crystal-field splitting of TM 3d orbitals. The magnetic coupling between
localized magnetic states of adatoms is dependent on adatomic distances and
directions. Lastly, the uniformly magnetic order is investigated to screening
two-dimensional dilute ferromagnets with high Curie temperature for
applications of spintronics. It is found that ot-P with V atoms homogeneously
adsorbed at the centre of octagons with a concentration of 5% has the most
stable ferromagnetic ground state. Its Curie temperature is estimated to be 173
K using the Monte Carlo method.",1701.01105v2
2017/1/23,Understanding stability diagram of perpendicular magnetic tunnel junctions,"Perpendicular magnetic tunnel junctions (MTJ) with a bottom pinned reference
layer and a composite free layer (FL) are investigated. Different thicknesses
of the FL were tested to obtain an optimal balance between tunneling
magnetoresistance (TMR) ratio and perpendicular magnetic anisotropy. After
annealing at 400 $^\circ$C, the TMR ratio for 1.5 nm thick CoFeB sublayer
reached 180 % at room temperature and 280 % at 20 K with an MgO tunnel barrier
thickness corresponding to the resistance area product RA = 10
Ohm$\mathrm{\mu}$m$^2$. The voltage vs. magnetic field stability diagrams
measured in pillar-shaped MTJs with 130 nm diameter indicate the competition
between spin transfer torque (STT), voltage controlled magnetic anisotropy
(VCMA) and temperature effects in the switching process. An extended stability
phase diagram model that takes into account all three parameters and the
effective damping measured independently using broadband ferromagnetic
resonance technique enabled the determination of both STT and VCMA coefficients
that are responsible for the FL magnetization switching.",1701.06411v1
2017/2/7,Ferromagnetism in chiral multilayer 2D semimetals,"We calculate the temperature dependent long-range magnetic coupling in the
presence of dilute concentrations of random magnetic impurities in chiral
multilayer two-dimensional semimetals, i.e., undoped intrinsic multilayer
graphene. Assuming a carrier-mediated indirect RKKY exchange interaction among
the well-separated magnetic impurities with the itinerant carriers mediating
the magnetic interaction between the impurities, we investigate the magnetic
properties of intrinsic multilayer graphene using an effective chiral
Hamiltonian model. We find that due to the enhanced density of states in the
rhombohedral stacking sequence of graphene layers, the magnetic ordering of
multilayer graphene is ferromagnetic in the continuum limit. The ferromagnetic
transition temperature is calculated using a finite-temperature self-consistent
field approximation and found to be within the experimentally accessible range
for reasonable values of the impurity-carrier coupling.",1702.01859v1
2017/2/13,Voltage-driven charge-mediated fast 180 degree magnetization switching in nanoheterostructure at room temperature,"Voltage-driven 180$^\circ$ magnetization switching without electric current
provides the possibility for revolutionizing the spintronics. We demonstrated
the voltage-driven charge-mediated 180$^\circ$ magnetization switching at room
temperature by combining first-principles calculations and
temperature-dependent magnetization dynamics simulation. The electric field
($E$) induced interface charge is found to allow a giant modulation of the
magnetic anisotropy ($K$) of the nanomagnet. Particularly $K$ is revealed to
vary linearly with respect to $E$ and the epitaxial strain. Magnetization
dynamics simulations using the so-obtained $K$ show that both in-plane and
perpendicular 180$^\circ$ switching can be achieved by $E$ pulses. The
temperature effect renders the 180$^\circ$ switching as probability events.
Statistical analysis indicates a fast (around 4 ns) and low-error-probability
180$^\circ$ switching achievable at room temperature by controlling the
magnitude of $E$ and the pulse width. The study inspires the rational design of
miniaturized nanoscale spintronic devices where thermal fluctuation has a great
impact.",1702.03670v2
2017/2/16,Effect of laser induced orbital momentum on magnetization switching,"The observed magnetization switching by circularly polarized ultrafast laser
pulses has been attributed to the inverse Faraday effect in which the induced
non-equilibrium orbital momentum serves as an effective magnetic filed via
spin-orbit coupling for magnetization rotation and switching. We critically
examine this scenario by explicitly calculating the magnitude of the induced
orbital momentum for generic itinerant band. We show that the calculated
induced angular momentum is not large enough for reversing the magnetization in
one laser pulse with the order of 100 femtosecond duration. Instead, we propose
that each laser pulse is capable to expand a reverse domain a few nano-meters
and it takes multiple pulses to complete the magnetization reversal process via
domain wall motion.",1702.04823v3
2017/2/24,Out-of-plane easy-axis in thin films of diluted magnetic semiconductor Ba1-xKx(Zn1-yMny)2As2,"Single-phased, single-oriented thin films of Mn-doped ZnAs-based diluted
magnetic semiconductor (DMS) Ba1-xKx(Zn1-yMny)2As2 (x = 0.03, 0.08; y = 0.15)
have been deposited on Si, SrTiO3, LaAlO3, (La,Sr)(Al,Ta)O3, and MgAl2O4
substrates, respectively. Utilizing a combined synthesis and characterization
system excluding the air and further optimizing the deposition parameters,
high-quality thin films could be obtained and be measured showing that they can
keep inactive-in-air up to more than 90 hours characterized by electrical
transport measurements. In comparison with films of x = 0.03 which possess
relatively higher resistivity, weaker magnetic performances, and larger energy
gap, thin films of x = 0.08 show better electrical and magnetic performances.
Strong magnetic anisotropy was found in films of x = 0.08 grown on
(La,Sr)(Al,Ta)O3 substrate with their magnetic polarization aligned almost
solely on the film growth direction.",1702.07506v1
2017/2/28,Superconducting spin valves controlled by spiral re-orientation in B20-family magnets,"We propose a superconducting spin-triplet valve, which consists of a
superconductor and an itinerant magnetic material, with the magnet showing an
intrinsic non-collinear order characterized by a wave vector that may be
aligned in a few equivalent preferred directions under control of a weak
external magnetic field. Re-orienting the spiral direction allows one to
controllably modify long-range spin-triplet superconducting correlations,
leading to spin-valve switching behavior. Our results indicate that the
spin-valve effect may be noticeable. This bilayer may be used as a magnetic
memory element for cryogenic nanoelectronics. It has the following advantages
in comparison to superconducting spin valves proposed previously: (i) it
contains only one magnetic layer, which may be more easily fabricated and
controlled, (ii) its ground states are separated by a potential barrier, which
solves the ""half-select"" problem of the addressed switch of memory elements.",1702.08828v2
2017/3/15,Anisotropic super-paramagnetism in cobalt implanted rutile-TiO2 single crystals,"We study the magnetic properties of single crystals of rutile TiO2 implanted
with cobalt for various fluences. The temperature variation of zero field
cooled(ZFC) and field cooled (FC) magnetization shows a much higher blocking
temperature (TB) along [1-10]. Similarly the scaling of magnetization isotherms
above TB is seen only when the field is parallel to [1-10] direction. With
field along this direction, the magnetization shows near saturation at a much
smaller field compared to that of[001] direction. The Co nanoclusters possess
an ""easy"" and ""hard axis"" of magnetization coupled by the magneto crystalline
anisotropy of secondary phases of cobalt with TiO2. In addition, at T=2 K we
observe a crossover in the magnetization vs field isotherms between the two
field directions in the samples which has been attributed to the anisotropic
paramagnetism arising from cobalt present in 2+ ionic state with S = 3/2.",1703.04965v1
2017/3/21,Enhancing the Spectral Hardening of Cosmic TeV Photons by Mixing with Axionlike Particles in the Magnetized Cosmic Web,"Large-scale extragalactic magnetic fields may induce conversions between
very-high-energy photons and axionlike particles (ALPs), thereby shielding the
photons from absorption on the extragalactic background light. However, in
simplified ""cell"" models, used so far to represent extragalactic magnetic
fields, this mechanism would be strongly suppressed by current astrophysical
bounds. Here we consider a recent model of extragalactic magnetic fields
obtained from large-scale cosmological simulations. Such simulated magnetic
fields would have large enhancement in the filaments of matter. As a result,
photon-ALP conversions would produce a significant spectral hardening for
cosmic TeV photons. This effect would be probed with the upcoming Cherenkov
Telescope Array detector. This possible detection would give a unique chance to
perform a tomography of the magnetized cosmic web with ALPs.",1703.07314v2
2017/4/5,The magnetic and electronic properties of Oxyselenides - influence of transition metal ions and lanthanides,"Magnetic oxyselenides have been the topic of research for several decades
being first of interest in the context of photoconductivity and
thermoelectricity owing to their intrinsic semiconducting properties and
ability to tune the energy gap through metal ion substitution. More recently,
interest in the oxyselenides has experienced a resurgence owing to the possible
relation to strongly correlated phenomena given the fact that many oxyslenides
share a similar structure to unconventional superconducting pnictides and
chalcogenides. The two dimensional nature of many oxyselenide systems also
draws an analogy to cuprate physics where a strong interplay between
unconventional electronic phases and localised magnetism has been studied for
several decades. It is therefore timely to review the physics of the
oxyselenides in the context of the broader field of strongly correlated
magnetism and electronic phenomena. Here we review the current status and
progress in this area of research with the focus on the influence of
lanthanides and transition metal ions on the intertwined magnetic and
electronic properties of oxyselenides. The emphasis of the review is on the
magnetic properties and comparisons are made with iron based pnictide and
chalcogenide systems.",1704.01441v1
2017/4/11,Models of Star-Planet Magnetic Interaction,"Magnetic interactions between a planet and its environment are known to lead
to phenomena such as aurorae and shocks in the solar system. The large number
of close-in exoplanets that were discovered triggered a renewed interest in
magnetic interactions in star-planet systems. Multiple other magnetic effects
were then unveiled, such as planet inflation or heating, planet migration,
planetary material escape, and even modification of the host star properties.
We review here the recent efforts in modelling and understanding magnetic
interactions between stars and planets in the context of compact systems. We
first provide simple estimates of the effects of magnetic interactions and then
detail analytical and numerical models for different representative scenarii.
We finally lay out a series of future developments that are needed today to
better understand and constrain these fascinating interactions.",1704.03254v1
2017/5/3,Relation between Kitaev magnetism and structure in $α$-RuCl$_3$,"Raman scattering has been employed to investigate lattice and magnetic
excitations of the honeycomb Kitaev material $\alpha$-RuCl$_3$ and its
Heisenberg counterpart CrCl$_3$. Our phonon Raman spectra give evidence for a
first-order structural transition from a monoclinic to a rhombohedral structure
for both compounds. Significantly, only $\alpha$-RuCl$_3$ features a large
thermal hysteresis, consistent with the formation of a wide phase of
coexistence. In the related temperature interval of $70-170$ K, we observe a
hysteretic behavior of magnetic excitations as well. The stronger magnetic
response in the rhombohedral compared to the monoclinic phase evidences a
coupling between the crystallographic structure and low-energy magnetic
response. Our results demonstrate that the Kitaev magnetism concomitant with
fractionalized excitations is susceptible to small variations of bonding
geometry.",1705.01312v1
2017/5/22,Interaction between magnetic moments and itinerant carriers in d0 ferromagnetic SiC,"Elucidating the interaction between magnetic moments and itinerant carriers
is an important step to spintronic applications. Here, we investigate magnetic
and transport properties in d0 ferromagnetic SiC single crystals prepared by
postimplantation pulsed laser annealing. Magnetic moments are contributed by
the p states of carbon atoms, but their magnetic circular dichroism is
different from that in semi-insulating SiC samples. The anomalous Hall effect
and negative magnetoresistance indicate the influence of d0 spin order on free
carriers. The ferromagnetism is relatively weak in N-implanted SiC compared
with that in Al-implanted SiC after annealing. The results suggest that d0
magnetic moments and itinerant carriers can interact with each other, which
will facilitate the development of SiC spintronic devices with d0
ferromagnetism.",1705.07793v1
2017/6/1,GdPtPb: A non collinear antiferromagnet with distorted Kagomé lattice,"In the spirit of searching for Gd-based, frustrated, rare earth magnets, we
have found antiferomagnetism (AF) in GdPtPb which crystallizes in the
ZrNiAl-type structure that has a distorted Kagom\'e lattice of Gd-triangles.
Single crystals were grown and investigated using structural, magnetic,
transport and thermodynamic measurements. GdPtPb orders antiferromagnetically
at 15.5 K arguably with a planar, non-collinear structure. The high temperature
magnetic susceptibility data reveal an ""anti-frustration"" behavior having a
frustration parameter, $|f|$ = $|\Theta|$/ $T_N$ = 0.25, which can be explained
by mean field theory (MFT) within a two sub-lattice model. Study of the
magnetic phase diagram down to $T$ = 1.8 K reveals a change of magnetic
structure through a metamagnetic transition at around 20 kOe and the
disappearance of the AF ordering near 140 kOe. In total, our work indicates
that, GdPtPb can serve as an example of a planar, non collinear, AF with a
distorted Kagom\'e magnetic sub-lattice.",1706.00449v1
2017/6/5,Quantum control of topological defects in magnetic systems,"Energy-efficient classical information processing and storage based on
topological defects in magnetic systems have been studied over past decade. In
this work, we introduce a class of macroscopic quantum devices in which a
quantum state is stored in a topological defect of a magnetic insulator. We
propose non-invasive methods to coherently control and readout the quantum
state using ac magnetic fields and magnetic force microscopy, respectively.
This macroscopic quantum spintronic device realizes the magnetic analog of the
three-level rf-SQUID qubit and is built fully out of electrical insulators with
no mobile electrons, thus eliminating decoherence due to the coupling of the
quantum variable to an electronic continuum and energy dissipation due to Joule
heating. For a domain wall sizes of $10-100$~nm and reasonable material
parameters, we estimate qubit operating temperatures in the range of $0.1-1$~K,
a decoherence time of about $0.01-1$~$\mu$s, and the number of Rabi flops
within the coherence time scale in the range of $10^{2}-10^{4}$.",1706.01526v2
2017/6/6,Quantitative characterization of spin-orbit torques in Pt/Co/Pt /Co/Ta/BTO heterostructure on the magnetization azimuthal angle dependence,"Substantial understanding of spin-orbit interactions in heavy-metal
(HM)/ferromagnet (FM) heterostructures is crucial in developing spin-orbit
torque (SOT) spintronics devices utilizing spin Hall and Rashba effects. Though
the study of SOT effective fields dependence on the out-of-plane magnetization
angle has been relatively extensive, the understanding of in-plane
magnetization angle dependence remains unknown. Here, we analytically propose a
method to compute the SOT effective fields as a function of the in-plane
magnetization angle using harmonic Hall technique in perpendicular magnetic
anisotropy (PMA) structures. Two different samples with PMA,
Pt/Co/Pt/Co/Ta/BaTiO3 (BTO) test sample and Pt/Co/Pt/Co/Ta reference sample are
studied using the derived formula. Our measurements reveal that only the
dampinglike field of the test sample with BTO capping layer exhibits an
in-plane magnetization angle dependence while no angular dependence is found in
the reference sample. The presence of the BTO layer in the test sample, which
gives rise to a Rashba effect at the interface, is ascribed as the source of
the angular dependence of the the dampinglike field.",1706.01622v1
2017/6/14,Broadband conversion of microwaves into propagating spin waves in patterned magnetic structures,"We have used time-resolved scanning Kerr microscopy (TRSKM) and micromagnetic
simulations to demonstrate that, when driven by spatially uniform microwave
field, the edges of patterned magnetic samples represent both efficient and
highly tunable sources of propagating spin waves. The excitation is due to the
local enhancement of the resonance frequency induced by the non-uniform dynamic
demagnetizing field generated by precessing magnetization aligned with the
edges. Our findings represent a crucial step forward in the design of nanoscale
spin-wave sources for magnonic architectures, and are also highly relevant to
the understanding and interpretation of magnetization dynamics driven by
spatially-uniform magnetic fields in patterned magnetic samples.",1706.04409v2
2017/6/16,Manifestation of higher-order inter-granular exchange in magnetic recording media,"Exchange coupling between magnetic grains is essential for maintaining the
stability of stored information in magnetic recording media. Using an atomistic
spin model, we have investigated the coupling between neighbouring magnetic
grains where magnetic impurity atoms have migrated into the non-magnetic grain
boundary. We find that when the impurity density is low a biquadratic term in
addition to the bilinear term is required to properly describe the
inter-granular exchange coupling. The temperature dependence both terms is
found to follow a power law behaviour with the biquadratic exchange constant
decaying faster than the bilinear. For increasing grain boundary thickness the
inter-granular exchange is lower and decays faster with temperature. Further
simulations of a grain at a bit boundary show an unexpected energy minimum for
in-plane magnetisation which can only be reproduced using a biquadratic
exchange term.",1706.05188v1
2017/6/23,Detection of induced paramagnetic moments in Pt on Y$_3$Fe$_5$O$_{12}$ via x-ray magnetic circular dichroism,"Magnetic moments in an ultra-thin Pt film on a ferrimagnetic insulator
Y$_3$Fe$_5$O$_{12}$ (YIG) have been investigated at high magnetic fields and
low temperatures by means of X-ray magnetic circular dichroism (XMCD). We
observed an XMCD signal due to the magnetic moments in a Pt film at the Pt
$L_{3}$- and $L_{2}$-edges. By means of the element-specific magnetometry, we
found that the XMCD signal at the Pt $L_{3}$-edge gradually increases with
increasing the magnetic field even when the field is much greater than the
saturation field of YIG. Importantly, the observed XMCD intensity was found to
be much greater than the intensity expected from the Pauli paramagnetism of Pt
when the Pt film is attached to YIG. These results imply the emergence of
induced paramagnetic moments in Pt on YIG and explain the characteristics of
the unconventional Hall effect in Pt/YIG systems.",1706.07559v1
2017/6/26,Observation of two types of anyons in the Kitaev honeycomb magnet,"Quantum spin liquid is a disordered magnetic state with fractional spin
excitations. Its clearest example is found in an exactly solved Kitaev
honeycomb model where a spin flip fractionalizes into two types of anyons,
quasiparticles that are neither fermions nor bosons: a pair of gauge fluxes and
a Majorana fermion. Here we demonstrate this kind of fractionalization in the
Kitaev paramagnetic state of the honeycomb magnet $\alpha$-RuCl$_3$. The
spin-excitation gap measured by nuclear magnetic resonance consists of the
predicted Majorana fermion contribution following the cube of the applied
magnetic field, and a finite zero-field contribution matching the predicted
size of the gauge-flux gap. The observed fractionalization into gapped anyons
survives in a broad range of temperatures and magnetic fields despite
inevitable non-Kitaev interactions between the spins, which are predicted to
drive the system towards a gapless ground state. The gapped character of both
anyons is crucial for their potential application in topological quantum
computing.",1706.08455v2
2017/6/28,Electric control of the edge magnetization in zigzag stanene nanoribbon,"There has been tremendous interest in manipulating electron and hole-spin
states in low-dimensional structures for electronic and spintronic
applications. We study the edge magnetic coupling and anisotropy in zigzag
stanene nanoribbons, by first-principles calculations. Taking into account
considerable spin-orbit coupling and ferromagnetism at each edge, zigzag
stanene nanoribbon is insulating and its band gap depends on the inter-edge
magnetic coupling and the magnetization direction. Especially for nanoribbon
edges with out-of-plane antiferromagnetic coupling, two non-degenerate valleys
of edge states emerge and the spin degeneracy is tunable by a transverse
electric field, which give full play to spin and valley degrees of freedom.
More importantly, both the magnetic order and anisotropy can be selectively
controlled by electron and hole doping, demonstrating a readily accessible
gate-induced modulation of magnetism. These intriguing features offer a
practical avenue for designing energy-efficient devices based on multiple
degrees of freedom of electron and magneto-electric couplings.",1706.09098v1
2017/7/9,Magneto-optical Kerr effect of a Ni_{2.00}Mn_{1.16}Ga_{0.84} single crystal across austenite and intermartensite transitions,"We carried out magneto-optical Kerr effect (MOKE) and magnetization
measurements on a single crystal of Ni2.00Mn1.16Ga0.84 in a longitudinal
geometry. While there had been reports of polar geometry measurements so far,
we show that - against earlier predictions - surface magnetic states of the
martensite and the austenite can be also probed efficiently via longitudinal
MOKE. A single variant magnetic state, which occurs at room temperature, is
characterized by ferromagnetic hysteresis loops similar to standard
ferromagnets. Temperature dependencies of Kerr rotation were found to be
linearly proportional to magnetization for martensitic phases. After passing
through an inter martensitic structural transition at around 260 K in zero
magnetic field, the coercive fields are more than doubled in comparison with
the room temperature values. On the other hand, at higher temperatures above
338 K where an austenite structure is formed, the MOKE signals are dominated by
quadratic contributions and the magnitude of Kerr rotation drops due to changes
in the electronic and magnetic domains structure. After the sample is cooled
across the austenite-martensite transition again, we observed a multiple beam
reflected by the sample due to different types of structural domains present on
its surface.",1707.02619v1
2017/7/23,A core-shell-surface layer model to explain the size dependence of effective magnetic anisotropy in magnetic nanoparticles,"The particle size (D) dependence of the effective magnetic anisotropy Keff of
magnetic nanoparticles (NPs) usually shows Keff increasing with decreasing D.
This dependence is often interpreted using the Eq.: Keff = Kb + (6Ks/D) where
Kb and Ks are the anisotropy constants of the spins in the bulk-like core and
surface layer, respectively. Here, we show that this model is inadequate to
explain the observed size-dependency of Keff for smaller nanoparticles with D <
5 nm. Instead the results in NPs of maghemite ({\gamma}-Fe2O3), NiO and Ni are
best described by an extension of the above model leading to the variation
given by Keff = Kb + (6Ks/D) +Ksh{[1-(2d/D)]^(-3) -1}, where the last term is
due to the spins in a shell of thickness d with anisotropy Ksh. The validation
of this core-shell-surface layer (CSSL) model for three different magnetic NPs
systems viz. ferrimagnetic {\gamma}-Fe2O3, ferromagnetic Ni and
antiferromagnetic NiO suggests its possible applicability for all magnetic
nanoparticles.",1707.07241v1
2017/8/2,Strongly exchange-coupled and surface-state-modulated magnetization dynamics in Bi2Se3/YIG heterostructures,"We report strong interfacial exchange coupling in Bi2Se3/yttrium iron garnet
(YIG) bilayers manifested as large in-plane interfacial magnetic anisotropy
(IMA) and enhancement of damping probed by ferromagnetic resonance (FMR). The
IMA and spin mixing conductance reached a maximum when Bi2Se3 was around 6
quintuple-layer (QL) thick. The unconventional Bi2Se3 thickness dependence of
the IMA and spin mixing conductance are correlated with the evolution of
surface band structure of Bi2Se3, indicating that topological surface states
play an important role in the magnetization dynamics of YIG.
Temperature-dependent FMR of Bi2Se3/YIG revealed signatures of magnetic
proximity effect of $T_c$ as high as 180 K, and an effective field parallel to
the YIG magnetization direction at low temperature. Our study sheds light on
the effects of topological insulators on magnetization dynamics, essential for
development of TI-based spintronic devices.",1708.00593v1
2017/8/5,Third order perturbed Heisenberg Hamiltonian of sc ferromagnetic films with fifty spin layers,"Magnetic energy of simple cubic structured ferromagnetic films with 10 to 50
spin layers was determined using third order perturbed Heisenberg Hamiltonian.
By plotting 3-D plot of energy versus angle and stress induced anisotropy, the
values of stress induced anisotropy corresponding to energy minimums and
maximums were determined. By plotting the graphs of energy versus angle at
these different stress induced anisotropy values, the easy and hard directions
were determined. Magnetic easy and hard directions are related to energy
minimums and maximums of the curve. Similar graphs were plotted for spin
exchange interaction to determine the easy and hard directions. Graphs of
energy versus angle were plotted by keeping all the magnetic energy parameters
at constant values for each number of spin layers to determine the variation of
magnetic easy directions, hard direction and corresponding energies with the
number of spin layers. The magnetic easy axis gradually rotates from out of
plane to in plane direction as the number of spin layers is increased. In
addition, the magnetic anisotropy energy increases with the number of spin
layers.",1708.02996v1
2017/8/14,Ultralow-temperature thermal conductivity of the Kitaev honeycomb magnet $α$-RuCl$_3$ across the field-induced phase transition,"Recently, there have been increasingly hot debates on whether there exists a
quantum spin liquid in the Kitaev honeycomb magnet $\alpha$-RuCl$_3$ in high
magnetic field. To investigate this issue, we perform the ultralow-temperature
thermal conductivity measurements on the single crystals of $\alpha$-RuCl$_3$
down to 80 mK and up to 9 T. Our experiments clearly show a field-induced phase
transition occurring at $H_c$ $\approx$ 7.5 T, above which the zigzag magnetic
order is completely suppressed. The minimum of thermal conductivity at 7.5 T is
attributed to the strong scattering of phonons by the magnetic fluctuations.
Most importantly, above 7.5 T, we do not observe any significant contribution
of thermal conductivity from gapless magnetic excitations, which puts a strong
constraint on the nature of the high-field phase of $\alpha$-RuCl$_3$.",1708.04090v2
2017/9/19,Spin Seebeck effect in a polar antiferromagnet $α$-Cu$_{2}$V$_{2}$O$_{7}$,"We have studied the longitudinal spin Seebeck effect in a polar
antiferromagnet $\alpha$-Cu$_{2}$V$_{2}$O$_{7}$ in contact with a Pt film.
Below the antiferromagnetic transition temperature of
$\alpha$-Cu$_{2}$V$_{2}$O$_{7}$, spin Seebeck voltages whose magnetic field
dependence is similar to that reported in antiferromagnetic MnF$_{2}$$\mid$Pt
bilayers are observed. Though a small weak-ferromagnetic moment appears owing
to the Dzyaloshinskii-Moriya interaction in $\alpha$-Cu$_{2}$V$_{2}$O$_{7}$,
the magnetic field dependence of spin Seebeck voltages is found to be
irrelevant to the weak ferromagnetic moments. The dependences of the spin
Seebeck voltages on magnetic fields and temperature are analyzed by a magnon
spin current theory. The numerical calculation of spin Seebeck voltages using
magnetic parameters of $\alpha$-Cu$_{2}$V$_{2}$O$_{7}$ determined by previous
neutron scattering studies reveals that the magnetic-field and temperature
dependences of the spin Seebeck voltages for
$\alpha$-Cu$_{2}$V$_{2}$O$_{7}$$\mid$Pt are governed by the changes in magnon
lifetimes with magnetic fields and temperature.",1709.06330v1
2017/9/23,Skyrmion formation in a bulk chiral magnet at zero magnetic field and above room temperature,"We report that in a $\beta$-Mn-type chiral magnet Co$_9$Zn$_9$Mn$_2$,
skyrmions are realized as a metastable state over a wide temperature range,
including room temperature, via field-cooling through the thermodynamic
equilibrium skyrmion phase that exists below a transition temperature
$T_\mathrm{c}$ $\sim$ 400 K. The once-created metastable skyrmions survive at
zero magnetic field both at and above room temperature. Such robust skyrmions
in a wide temperature and magnetic field region demonstrate the key role of
topology, and provide a significant step toward technological applications of
skyrmions in bulk chiral magnets.",1709.08047v1
2017/10/2,Reciprocal space mapping of magnetic order in thick epitaxial MnSi films,"We report grazing incidence small angle neutron scattering (GISANS) and
complementary off-specular neutron reflectometry (OSR) of the magnetic order in
a single-crystalline epitaxial MnSi film on Si(111) in the thick film limit.
Providing a means of direct reciprocal space mapping, GISANS and OSR reveal a
magnetic modulation perpendicular to the films under magnetic fields parallel
and perpendicular to the film, where additional polarized neutron reflectometry
(PNR) and magnetization measurements are in excellent agreement with the
literature. Regardless of field orientation, our data does not suggest the
presence of more complex spin textures, notably the formation of skyrmions.
This observation establishes a distinct difference with bulk samples of MnSi of
similar thickness under perpendicular field, in which a skyrmion lattice
dominates the phase diagram. Extended x-ray absorption fine structure
measurements suggest that small shifts of the Si positions within the
unstrained unit cell control the magnetic state, representing the main
difference between the films and thin bulk samples.",1710.00544v1
2017/10/12,Frustrated two dimensional quantum magnets,"We overview physical effects of exchange frustration and quantum spin
fluctuations in (quasi-) two dimensional (2D) quantum magnets ($S=1/2$) with
square, rectangular and triangular structure. Our discussion is based on the
$J_1$-$J_2$ type frustrated exchange model and its generalizations. These
models are closely related and allow to tune between different phases,
magnetically ordered as well as more exotic nonmagnetic quantum phases by
changing only one or two control parameters. We survey ground state properties
like magnetization, saturation fields, ordered moment and structure factor in
the full phase diagram as obtained from numerical exact diagonalization
computations and analytical linear spin wave theory. We also review finite
temperature properties like susceptibility, specific heat and magnetocaloric
effect using the finite temperature Lanczos method. This method is powerful to
determine the exchange parameters and g-factors from experimental results. We
focus mostly on the observable physical frustration effects in magnetic phases
where plenty of quasi-2D material examples exist to identify the influence of
quantum fluctuations on magnetism.",1710.04399v1
2017/10/27,Nuclear Magnetic Resonance in Noncollinear Antiferromagnet Mn3Al2Ge3O12,"The 55Mn nuclear magnetic resonance spectrum of noncollinear 12-sublattice
antiferromagnet Mn3Al2Ge3O12 has been studied in the frequency range of 200 -
640 MHz in the external magnetic field H || [001]} at T=1.2 K. Three absorption
lines have been observed in fields less than the field of the reorientation
transition Hc at the polarization h||H of the rf field. Two lines have been
observed at H > Hc and h_|_H. The spectral parameters indicate that the
magnetic structure of manganese garnet differs slightly from the exchange
triangular 120-degree structure. The anisotropy of the spin reduction and (or)
weak antiferromagnetism that are allowed by the crystal symmetry lead to the
difference of approximately 3% in the magnetization of sublattices in the field
H < Hc. When the spin plane rotates from the orientation perpendicular to the
C3 axis to the orientation perpendicular to the C4 axis, all magnetic moments
of the electronic subsystem decrease by approximately 2% from the average value
in the zero field.",1710.10048v1
2017/10/28,Edge magnetism impact on electrical conductance and thermoelectric properties of graphenelike nanoribbons,"Edge states in narrow quasi two-dimensional nanostructures determine, to a
large extent, their electric, thermoelectric and magnetic properties.
Non-magnetic edge states may quite often lead to topological insulator type
behavior. However another scenario develops when the zigzag edges are magnetic
and the time reversal symmetry is broken. In this work we report on the
electronic band structure modifications, electrical conductance and
thermoelectric properties of narrow zigzag nanoribbons with spontaneously
magnetized edges. Theoretical studies based on the Kane-Mele- Hubbard
tight-binding model show that for silicene, germanene and stanene both the
Seebeck coefficient and the thermoelectric power factor are strongly enhanced
for energies close to the charge neutrality point. Perpendicular gate voltage
lifts the spin degeneracy of energy bands in the ground state with antiparallel
magnetized zigzag edges and makes the electrical conductance significantly
spin-polarized. Simultaneously the gate voltage worsens the thermoelectric
performance. Estimated room-temperature figures of merit for the aforementioned
nanoribbons can exceed a value of 3 if phonon thermal conductances are
adequately reduced.",1710.10502v1
2017/12/6,Dynamic quantum kagome ice,"The search for two dimensional quantum spin liquids, exotic magnetic states
with an entangled ground state remaining disordered down to zero temperature,
has been a great challenge in frustrated magnetism during the last decades.
Recently, fractionalized excitations, called spinons, emerging from these
states, have been evidenced in kagome and triangular antiferromagnets. In
contrast, quantum ferromagnetic spin liquids in two dimensions, namely quantum
kagome ices, have been less investigated, yet their classical counterparts
exhibit amazing properties, magnetic monopole crystals as well as magnetic
fragmentation. Here we show that, by applying a magnetic field on the
pyrochlore oxide Nd$_2$Zr$_2$O$_7$, which has been shown to develop three
dimensional quantum magnetic fragmentation in zero field, we are able to reduce
the dimension of the system and to create a dynamic kagome ice state. Our
results open the way to the observation of the quantum kagome ice state which
was recently investigated theoretically.",1712.02418v2
2017/12/7,Revealing the correlation between real-space structure and chiral magnetic order at the atomic scale,"We image simultaneously the geometric, electronic and magnetic structure of a
buckled iron bilayer film that exhibits chiral magnetic order. We achieve this
by combining spin-polarized scanning tunneling microscopy and magnetic exchange
force microscopy (SPEX), to independently characterize the geometric as well as
the electronic and magnetic structure of non-flat surfaces. This new SPEX
imaging technique reveals the geometric height corrugation of the
reconstruction lines resulting from strong strain relaxation in the bilayer,
enabling the decomposition of the real-space from the eletronic structure at
the atomic level, and the correlation with the resultant spin spiral ground
state. By additionally utilizing adatom manipulation, we reveal the chiral
magnetic ground state of portions of the unit cell that were not previously
imaged with SP-STM alone. Using density functional theory (DFT), we investigate
the structural and electronic properties of the reconstructed bilayer and
identify the favorable stoichiometry regime in agreement with our experimental
result.",1712.02717v2
2018/1/2,"Magnetization pinning in modulated nanowires: from topological protection to the ""corkscrew"" mechanism","Diameter-modulated nanowires offer an important paradigm to design the
magnetization response of 3D magnetic nanostructures by engineering the domain
wall pinning. With the aim to understand its nature and to control the process,
we analyze the magnetization response in FeCo modulated polycrystalline
two-segment nanowires varying the minor diameter. Our modelling indicates a
very complex behavior with a strong dependence on the disorder distribution and
an important role of topologically non-trivial magnetization structures. We
demonstrate that modulated nanowires with a small diameter difference are
characterized by an increased coercive field in comparison to the straight ones
which is explained by a formation of topologically protected walls formed by
two 3D skyrmions with opposite chiralities. For a large diameter difference we
report the occurrence of a novel pinning type called here the ""corkscrew"": the
magnetization of the large diameter segment forms a skyrmion tube with a core
position in a helical modulation along the nanowire. This structure is pinned
at the constriction and in order to penetrate the narrow segments the
vortex/skyrmion core size should be reduced.",1801.00643v1
2018/1/23,Correlation between Magnetic Properties and Depinning Field in Field-Driven Domain Wall Dynamics in GdFeCo Ferrimagnets,"The influence of temperature on the magnetic-field-driven domain wall (DW)
motion is investigated in GdFeCo ferrimagnets with perpendicular magnetic
anisotropy (PMA). We find that the depinning field strongly depends on
temperature. Moreover, it is also found that the saturation magnetization
exhibits a similar dependence on temperature to that of depinning field. From
the creep-scaling criticality, a simple relation between the depinning field
and the properties of PMA is clearly identified theoretically as well as
experimentally. Our findings open a way for a better understanding how the
magnetic properties influence on the depinning field in magnetic system and
would be valuably extended to depinning studies in other system.",1801.07436v1
2018/1/30,Field-induced magnetic phase transitions and memory effect in bilayer ruthenate Ca$_3$Ru$_2$O$_7$ with Fe substitution,"Bilayer ruthenate Ca$_3$(Ru$_{1-x}$Fe$_x$)$_2$O$_7$ ($x$ = 0.05) exhibits an
incommensurate magnetic soliton lattice driven by the Dzyaloshinskii-Moriya
interaction. Here we report complex field-induced magnetic phase transitions
and memory effect in this system via single-crystal neutron diffraction and
magnetotransport measurements. We observe first-order
incommensurate-to-commensurate magnetic transitions upon applying the magnetic
field both along and perpendicular to the propagation axis of the
incommensurate spin structure. Furthermore, we find that the metastable states
formed upon decreasing the magnetic field depend on the temperature and the
applied field orientation. We suggest that the observed field-induced
metastability may be ascribable to the quenched kinetics at low temperature.",1801.10200v1
2018/1/31,Coupled magnetic and ferroelectric states in the distorted honeycomb system Fe$_{4}$Ta$_{2}$O$_{9}$,"We report on the magnetic, thermodynamic, dielectric, and pyroelectric
measurements on the hitherto unreported Fe${_4}$Ta${_2}$O${_9}$. This system is
seen to exhibit a series of magnetic transitions, many of which are coupled to
the emergence of ferroelectric order, making Fe${_4}$Ta${_2}$O${_9}$ the only
genuine multiferroic in its material class. We suggest that the observed
properties arise as a consequence of an effective reduction in the
dimensionality of the magnetic lattice, with the magnetically active
Fe${^{2+}}$ ions preferentially occupying a quasi 2D buckled honeycomb
structure. The low temperature $H$-$T$ phase diagram of Fe${_4}$Ta${_2}$O${_9}$
reveals a rich variety of coupled magnetic and ferroelectric phases, in
similarity with that observed in the distorted Kagome systems.",1801.10427v1
2018/2/19,Temperature Dependent Magnetism in Artificial Honeycomb Lattice of Connected Elements,"Artificial magnetic honeycomb lattices are expected to exhibit a broad and
tunable range of novel magnetic phenomena that would be difficult to achieve in
natural materials, such as long-range spin ice, entropy-driven magnetic
charge-ordered state and spin-order due to the spin chirality. Eventually, the
spin correlation is expected to develop into a unique spin solid state density
ground state, manifested by the distribution of the pairs of vortex states of
opposite chirality. Here we report the creation of a new artificial permalloy
honeycomb lattice of ultra-small connecting bonds, with a typical size of
$\simeq$ 12 nm. Detail magnetic and neutron scattering measurements on the
newly fabricated honeycomb lattice demonstrate the evolution of magnetic
correlation as a function of temperature. At low enough temperature, neutron
scattering measurements and micromagnetic simulation suggest the development of
loop state of vortex configuration in this system.",1802.06631v1
2018/2/22,Power law analysis for temperature dependence of magnetocrystalline anisotropy constants of Nd$_2$Fe$_{14}$B magnets,"Phenomenological analysis for the temperature dependence of the
magnetocrystalline anisotropy (MA) in rare earth magnets is presented. We
define phenomenological power laws applicable to compound magnets using the
Zener theory, apply these laws to the magnetocrystalline anisotropy constants
(MACs) of Nd$_2$Fe$_{14}$B magnets. The results indicate that the MACs obey the
power law well, and a general understanding for the temperature-dependent MA in
rare earth magnets is obtained through the analysis. Furthermore, to examine
the validity of the power law, we discuss the temperature dependence of the
MACs in Dy$_2$Fe$_{14}$B and Y$_2$Fe$_{14}$B magnets as examples wherein it is
difficult to interpret the MA using the power law.",1802.07959v2
2018/3/1,Calculating the Magnetic Anisotropy of Rare-Earth-Transition-Metal Ferrimagnets,"Magnetocrystalline anisotropy, the microscopic origin of permanent magnetism,
is often explained in terms of ferromagnets. However, the best performing
permanent magnets based on rare earths and transition metals (RE-TM) are in
fact ferrimagnets, consisting of a number of magnetic sublattices. Here we show
how a naive calculation of the magnetocrystalline anisotropy of the classic
RE-TM ferrimagnet GdCo$_5$ gives numbers which are too large at 0 K and exhibit
the wrong temperature dependence. We solve this problem by introducing a
first-principles approach to calculate temperature-dependent magnetization vs.
field (FPMVB) curves, mirroring the experiments actually used to determine the
anisotropy. We pair our calculations with measurements on a recently-grown
single crystal of GdCo$_5$, and find excellent agreement. The FPMVB approach
demonstrates a new level of sophistication in the use of first-principles
calculations to understand RE-TM magnets.",1803.00235v1
2018/3/18,An experimental and Ab-initio study of Electronic and Magnetic properties of FeGa3,"Electronic structure of FeGa3 has been studied using experiments and
ab-initio calculations. Magnetization measurements show that FeGa3 is
inherently diamagnetic in nature. Our studies indicate that the previously
reported magnetic moment on the Fe atoms in FeGa3 is not an intrinsic property
of FeGa3, but is primarily due to the presence of disorder, defects, grain
boundaries etc that break the symmetry about the Fe dimers. Analysis of the
results obtained from magnetic measurements, photoelectron spectroscopy, Fe
K-edge X-ray absorption near edge spectroscopy and ab-initio calculations
clearly indicates that, the effects of on-site Coulomb repulsion between the Fe
3d electrons do not play any role in determining the electronic and magnetic
properties of FeGa3. Detailed analysis of results of single crystal and
poycrystalline FeGa3, helps to resolve the discrepancy in the electronic and
magnetic properties in FeGa3 existing in the literature, consistently.",1803.06605v1
2018/4/5,Scalable Magnetic Field SLAM in 3D Using Gaussian Process Maps,"We present a method for scalable and fully 3D magnetic field simultaneous
localisation and mapping (SLAM) using local anomalies in the magnetic field as
a source of position information. These anomalies are due to the presence of
ferromagnetic material in the structure of buildings and in objects such as
furniture. We represent the magnetic field map using a Gaussian process model
and take well-known physical properties of the magnetic field into account. We
build local maps using three-dimensional hexagonal block tiling. To make our
approach computationally tractable we use reduced-rank Gaussian process
regression in combination with a Rao-Blackwellised particle filter. We show
that it is possible to obtain accurate position and orientation estimates using
measurements from a smartphone, and that our approach provides a scalable
magnetic field SLAM algorithm in terms of both computational complexity and map
storage.",1804.01926v2
2018/4/5,Observation of transition from semiconducting to metallic ground state in high-quality single crystalline FeSi,"We report anomalous physical properties of single-crystalline FeSi over a
wide temperature range 1.8-400 K. X-ray diffraction, specific heat, and
magnetization measurements indicate that the FeSi crystals synthesized in this
study are of high quality with a very low concentration of magnetic impurities
($\sim$0.01$\%$). The electrical resistivity $\rho$($T$) can be described by
activated behavior with an energy gap $\Delta$ = 57 meV between 67 K and 150 K.
At temperatures below 67 K, $\rho$($T$) is significantly lower than an
extrapolation of the activated behavior, and the Hall coefficient and
magneto-resistivity undergo a sign change in this region. At $\sim$19 K, a
transition from semiconducting to metallic-like behavior is observed with
deceasing temperature. Whereas the transition temperature is very robust in a
magnetic field, the magnitude of the resistivity below $\sim$30 K is very
sensitive to magnetic field. There is no indication of a bulk phase transition
or onset of magnetic order in the vicinity of either 67 K or 19 K from specific
heat and magnetic susceptibility measurements. These measurements provide
evidence for a conducting surface state in FeSi at low temperatures.",1804.02036v1
2018/4/16,Structural and magnetic properties of CeZnAl$_3$ single crystals,"We have synthesized single crystals of CeZnAl$_3$, which is a new member of
the family of the Ce-based intermetallics Ce$TX_3$ ($T$ = transition metal,
$X$= Si, Ge, Al), crystallizing in the non-centrosymmetric tetragonal
BaNiSn$_3$-type structure. Magnetization, specific heat and resistivity
measurements all show that CeZnAl$_3$ orders magnetically below around 4.4 K.
Furthermore, magnetization measurements exhibit a hysteresis loop at low
temperatures and fields, indicating the presence of a ferromagnetic component
in the magnetic state. This points to a different nature of the magnetism in
CeZnAl$_3$ compared to the other isostructural Ce$T$Al$_3$ compounds.
Resistivity measurements under pressures up to 1.8 GPa show a moderate
suppression of the ordering temperature with pressure, suggesting that
measurements to higher pressures are required to look for quantum critical
behavior.",1804.05477v1
2018/4/27,Tunable Electronic Structure and Magnetic Coupling in Strained Two-Dimensional Semiconductor MnPSe3,"The electronic structures and magnetic properties of strained monolayer
MnPSe3 are investigated systematically by first-principles calculations. It is
found that the magnetic ground state (GS) of monolayer MnPSe3 can be
significantly affected by biaxial strain engineering, while the semiconducting
characteristics are well preserved. Owing to the sensitivity of the magnetic
coupling towards the structural deformation, a biaxial tensile strain about 13%
can lead to an antiferromagnetic-ferromagnetic (AFM-FM) transition. The
underlying physical mechanism of strain-dependent magnetic stability is mainly
attributed to the competition effect of direct AFM interaction and indirect FM
superexchange interaction between the nearest-neighbor (NN) two Mn atoms. In
addition, we find that FM MnPSe3 is an intrinsic half semiconductor with a
large spin exchange splitting in conduction bands, which is crucial for the
spin-polarized carrier injection and detection. The sensitive interdependence
among external stimuli, electronic structure and magnetic coupling suggests
that monolayer MnPSe3 can be a promising candidate in spintronics.",1804.10399v1
2018/5/5,Selection Rules for All-Optical Magnetic Recording in Iron Garnet,"Finding an electronic transition a subtle excitation of which can launch
dramatic changes of electric, optical or magnetic properties of media is one of
the long-standing dreams in the field of photo-induced phase transitions [1-5].
Therefore the discovery of the magnetization switching only by a femtosecond
laser pulse [6-10] triggered intense discussions about mechanisms responsible
for these laser-induced changes. Here we report the experimentally revealed
selection rules on polarization and wavelengths of ultrafast photo-magnetic
recording in Co-doped garnet film and identify the workspace of the parameters
(magnetic damping, wavelength and polarization of light) allowing this effect.
The all-optical magnetic switching under both single pulse and multiple-pulse
sequences can be achieved at room temperature, in narrow spectral ranges with
light polarized either along <110> or <100> crystallographic axes of the
garnet. The revealed selection rules indicate that the excitations responsible
for the coupling of light to spins are d-electron transitions in octahedral and
tetrahedral Co-sublattices, respectively.",1805.02021v1
2018/5/13,Steady and dynamic magnetic phase transitions in interacting quantum dots arrays coupled with leads,"We apply the Hubbard model, non-equilibrium Green's function (NEGF) theory,
exact diagonalization (ED) and the hierarchical equations of motion (HEOM)
method to investigate abundant magnetic phase transitions in the 1D interacting
quantum dots arrays (QDA) sandwiched by non-interaction leads. The spin
polarization phase transitions are firstly studied with a mean-field
approximation. The many-body calculation of the ED method is then used to
verify such transitions. We find with the weak device-leading couplings, the
anti-ferromagnetic (AF) state only exists in the uniform odd-numbered QDA or
the staggered-hopping QDA systems. With increasing the coupling strength or the
bias potentials, there exists the magnetism-to non-magnetism phase transition.
With the spin-resolved HEOM method we also investigate the detailed dynamic
phase transition process of these lead-QDA-lead systems.",1805.04939v1
2018/5/22,Spin-orbit torque in completely compensated synthetic antiferromagnet,"Synthetic antiferromagnets (SAF) have been proposed to replace ferromagnets
in magnetic memory devices to reduce the stray field, increase the storage
density and improve the thermal stability. Here we investigate the spin-orbit
torque in a perpendicularly magnetized Pt/[Co/Pd]/Ru/[Co/Pd] SAF structure,
which exhibits completely compensated magnetization and an exchange coupling
field up to 2100 Oe. The magnetizations of two Co/Pd layers can be switched
between two antiparallel states simultaneously by spin-orbit torque. The
magnetization switching can be read out due to much stronger spin-orbit
coupling at bottom Pt/[Co/Pd] interface compared to its upper counterpart
without Pt. Both experimental and theoretical analyses unravel that the torque
efficiency of antiferromagnetic coupled stacks is significantly higher than the
ferromagnetic counterpart, making the critical switching current of SAF
comparable to the conventional single ferromagnet. Besides adding an important
dimension to spin-orbit torque, the efficient switching of completely
compensated SAF might advance magnetic memory devices with high density, high
speed and low power consumption.",1805.08486v2
2018/6/6,Attractive interaction between superconducting vortices in tilted magnetic fields,"Many practical applications of high T$_c$ superconductors involve layered
materials and magnetic fields applied on an arbitrary direction with respect to
the layers. When the anisotropy is very large, Cooper pair currents can
circulate either within or perpendicular to the layers. Thus, tilted magnetic
fields lead to intertwined lattices of Josephson and Abrikosov vortices, with
quantized circulation across and within layers, respectively. Transport in such
intertwined lattices has been studied in detail, but direct observation and
manipulation of vortices remains challenging. Here we present magnetic force
microscopy experiments in tilted magnetic fields in the extremely quasi-two
dimensional superconductor $Bi_{2}Sr_{2}CaCu_{2}O_{8}$. We trigger Abrikosov
vortex motion in between Josephson vortices, and find that Josephson vortices
in different layers can be brought on top of each other. Our measurements
suggest that intertwined lattices in tilted magnetic fields can be
intrinsically easy to manipulate thanks to the mutual interaction between
Abrikosov and Josephson vortices.",1806.02021v2
2018/6/7,Magnetic domain walls as broadband spin wave and elastic magnetisation wave emitters,"We report on the direct observation of spin wave and elastic wave emission
from magnetic domain walls in ferromagnetic thin films. Driven by alternating
homogeneous magnetic fields the magnetic domain walls act as coherent
magnetisation wave sources. Directional and low damped elastic waves below and
above the ferromagnetic resonance are excited. The wave vector of the
magnetoelastically induced acoustic shear waves is linearly tuned by varying
the excitation frequency. Domain wall emitted magnetostatic surface spin waves
occur at higher frequencies, which characteristics are confirmed by
micromagnetic simulations. The distinct modes of magnetisation wave excitation
from micromagnetic objects are a general physical phenomenon relevant for
dynamic magnetisation processes in structured magnetic films. Magnetic domain
walls can act as reconfigurable antennas for spin wave and elastic wave
generation with control of the wave orientation.",1806.02646v1
2018/6/11,Unconventional superconductivity and an ambient-pressure magnetic quantum critical point in single-crystal LaNiC$_2$,"Superconductivity in noncentrosymmetric LaNiC$_2$ is expected to be induced
by electron--phonon interactions due to its lack of magnetic instabilities. The
non-Bardeen-Cooper-Schrieffer (BCS) behaviors found in this material call into
question the long-standing idea that relates unconventional superconductivity
with magnetic interactions. Here we report magnetic penetration-depth
measurements in a high-purity single crystal of LaNiC$_2$ at pressures up to
2.5 GPa and temperatures down to 0.04 K. At ambient pressure and below 0.5$T_c$
the penetration depth goes as $T^4$ for the in-plane and $T^2$ for the
out-of-plane component, firmly implying the existence of point nodes in the
energy gap and the unconventional character of this superconductor. The present
study also provides first evidence of magnetism in LaNiC$_2$ by unraveling a
pressure-induced antiferromagnetic phase inside the superconducting state at
temperatures below 0.5 K, with a quantum critical point around ambient
pressure. The results presented here maintain a solid base for the notion that
unconventional superconductivity only arises near magnetic order or
fluctuations.",1806.03818v1
2018/6/27,Site-selective Probe of Magnetic Excitations in Rare-earth Nickelates using Resonant Inelastic X-ray Scattering,"We have used high-resolution resonant inelastic x-ray scattering (RIXS) to
study a thin film of NdNiO$_3$, a compound whose unusual spin- and bond-ordered
electronic ground state has been of long-standing interest. Below the magnetic
ordering temperature, we observe well-defined collective magnon excitations
along different high-symmetry directions in momentum space. The magnetic
spectra depend strongly on the incident photon energy, which we attribute to
RIXS coupling to different local electronic configurations of the expanded and
compressed NiO$_6$ octahedra in the bond-ordered state. Both the noncollinear
magnetic ground state and the observed site-dependent magnon excitations are
well described by a model that assumes strong competition between the
antiferromagnetic superexchange and ferromagnetic double-exchange interactions.
Our study provides direct insight into the magnetic dynamics and exchange
interactions of the rare-earth nickelates, and demonstrates that RIXS can serve
as a site-selective probe of magnetism in these and other materials.",1806.10499v1
2018/7/10,Modeling Molecular Magnets with Large Exchange and On-Site Anisotropies,"Spins in molecular magnets can experience both anisotropic exchange
interactions and on-site magnetic anisotropy. In this paper we study the effect
of exchange anisotropy on the molecular magnetic anisotropy both with and
without on-site anisotropy. When both the anisotropies are small, we find that
the axial anisotropy parameter $D_M$ in the effective spin Hamiltonian is the
sum of the individual contributions due to exchange and on-site anisotropies.
We find that even for axial anisotropy of about $15\%$, the low energy spectrum
does not correspond to a single parent spin manifold but has intruders states
arising from other parent spin. In this case, the low energy spectrum can not
be described by an effective Hamiltonian spanning the parent spin space. We
study the magnetic susceptibility, specific heat as a function of temperature
and magnetization as a function of applied field to characterize the system in
this limit. We find that there is synergy between the two anisotropies,
particularly for large systems with higher site spins.",1807.03500v1
2018/7/19,Measurement of the angle dependence of magnetostriction in pulsed magnetic fields using a piezoelectric strain gauge,"We present a high resolution method for measuring magnetostriction in
millisecond pulsed magnetic fields at cryogenic temperatures with a sensitivity
of $1.11\times10^{-11}/\sqrt{\rm Hz}$. The sample is bonded to a thin
piezoelectric plate, such that when the sample's length changes, it strains the
piezoelectric and induces a voltage change. This method is more sensitive than
a fiber-Bragg grating method. It measures two axes simultaneously instead of
one. The gauge is small and versatile, functioning in DC and millisecond pulsed
magnetic fields. We demonstrate its use by measuring the magnetostriction of
Ca$_3$Co$_{1.03}$Mn$_{0.97}$O$_6$ single crystals in pulsed magnetic fields. By
comparing our data to new and previously published results from a fiber-Bragg
grating magnetostriction setup, we confirm that this method detects
magnetostriction effects. We also demonstrate the small size and versatility of
this technique by measuring angle dependence with respect to the applied
magnetic field in a rotator probe in 65 T millisecond pulsed magnetic fields.",1807.07192v1
2018/8/6,"Thermally induced gaplessness and Fermi arcs in a ""s-wave"" magnetic superconductor","An electron system with pre-existing local moments and an effective
electron-electron attraction can exhibit simultaneous magnetic and
superconducting order. Increasing the magnetic coupling weakens pairing and the
ground state loses superconductivity at a critical coupling. In the vicinity of
the critical coupling magnetic order dramatically modifies the quasiparticle
dispersion in the superconductor, creating low energy spectral weight and
significant gap anisotropy in the notional 's-wave' state. Using a Monte Carlo
approach to the Hubbard-Kondo lattice problem we establish a thermal phase
diagram, for varying magnetic coupling, that corresponds qualitatively to the
borocarbide superconductors. In addition to the superconducting and magnetic
transition temperatures, we identify two new thermal scales in this nominal
s-wave system. These are associated, respectively, with crossover from gapped
to gapless superconductivity, and from an anisotropic (nodal) 'Fermi surface'
at low temperature, through a Fermi arc regime, to an isotropic Fermi surface
at high temperature. Some of the spectral effects are already visible in the Ho
and Er based borocarbides, others can be readily tested.",1808.02012v1
2018/8/21,Pseudo Jahn-Teller Effect and Magnetoelastic Coupling in Spin-Orbit Mott Insulators,"The consequences of the Jahn-Teller (JT) orbital-lattice coupling for
magnetism of pseudospin J_{eff}=1/2 and J_{eff}=0 compounds are addressed. In
the former case, represented by Sr_2IrO_4, this coupling generates, through the
so-called pseudo-JT effect, orthorhombic deformations of a crystal concomitant
with magnetic ordering. The orthorhombicity axis is tied to the magnetization
and rotates with it under magnetic field. The theory resolves a number of
puzzles in Sr_2IrO_4 such as the origin of in-plane magnetic anisotropy and
magnon gaps, metamagnetic transition, etc. In J_{eff}=0 systems, the pseudo-JT
effect leads to spin-nematic transition well above magnetic ordering, which may
explain the origin of `orbital order' in Ca_2RuO_4",1808.06919v2
2018/8/27,Dynamics of the antiferromagnetic skyrmion induced by a magnetic anisotropy gradient,"The dynamics of antiferromagnets is a current hot topic in condensed matter
physics and spintronics. However, the dynamics of insulating antiferromagnets
cannot be excited by an electric current, which is a method usually used to
manipulate ferromagnetic metals. Here, we propose to use the voltage-controlled
magnetic anisotropy gradient as an excitation source to manipulate insulating
antiferromagnetic textures. We analytically and numerically study the dynamics
of an antiferromagnetic skyrmion driven by a magnetic anisotropy gradient. Our
analytical calculations demonstrate that such a magnetic anisotropy gradient
can effectively drive an antiferromagnetic skyrmion towards the area of lower
magnetic anisotropy. The micromagnetic simulations are in good agreement with
our analytical solution. Furthermore, the magnetic anisotropy gradient induced
velocity of an antiferromagnetic skyrmion is compared with that of a
ferromagnetic skyrmion. Our results are useful for the understanding of
antiferromagnetic skyrmion dynamics and may open a new way for the design of
antiferromagnetic spintronic devices.",1808.08664v2
2018/9/13,Magnetic anisotropy of ferromagnetic metals in low-symmetry systems,"We have constructed an analytic formula to treat the perpendicular magnetic
anisotropy energy in ferromagnetic metals with low symmetry, such as C4V and
C3V. We find that the anisotropy energy is proportional to a part of the
expectation values of the orbital angular momentum and magnetic dipole
operator. Although the result is similar to the model proposed by Laan [J.
Phys.: Condens. Matter 10, 3239 (1998)], we have derived a concrete expression
for the spin-flip virtual excitation process term, which can be dominant in
atoms with small magnetic moments and/or small exchange splitting. Pt monatomic
layer with proximity-induced spin polarization grown on Fe is an example of
this. Other multilayer systems such as Co/Pd and Co/Ni and bilayer systems such
as Fe(CoB)/MgO can be discussed similarly. Moreover, the relation between
perpendicular magnetic anisotropy energy and measurable physical parameters is
discussed based on X-ray magnetic circular dichroism spectroscopy.",1809.04749v4
2018/9/25,Single-crystal neutron diffraction study of hexagonal YbMnO$_3$ multiferroic under magnetic field,"We report single-crystal neutron diffraction study of the magnetic structure
of the multiferroic compound YbMnO$_3$, a member of the hexagonal manganite
family, in zero-field and under a magnetic field applied along the $c$-axis. We
propose a scenario for the zero-field magnetic ordering and for the
field-induced magnetic reorientation of the Mn and of the two Yb on distinct
crystallographic sites, compatible with the macroscopic measurements, as well
as with previous powder neutron diffraction experiment and results from other
techniques (optical second harmonic generation, M\""ossbauer spectroscopy). Our
study should contribute in settling some debated issues about the magnetic
properties of this material, as part of a broader investigation of the entire
hexagonal RMnO$_3$ (R = Dy, Ho, Er, Tm, Yb, Lu, Y) family.",1809.09370v1
2018/9/30,Direct observation of magnetic domain evolution in the vicinity of Verwey transition in Fe3O4 thin films,"We report a direct observation of magnetic domain evolution near the Verwey
transition (TV) in Fe3O4 films. We found the stripe domains in the
Fe3O4/Mg2TiO4 film while the irregular domains in the Fe3O4/MgO film and the
similar characters of magnetic domains in the vicinity of TV for both samples:
the bigger domain size and the higher contrast of the phase signal below TV and
the more disordered domain images at TV. Remarkably, the magnetic behaviors can
be well understood and the domain-wall energy and the demagnetizing energy can
be calculated from the magnetic domains near TV in the Fe3O4/Mg2TiO4 film. Our
work presents a demonstration of the low temperature magnetic domains and gives
a new perspective to understand the Verwey transition in Fe3O4 thin films.",1810.00340v1
2018/10/5,Ultrafast demagnetization of Pt magnetic moment in L1${}_0$-FePt probed by hard x-ray free electron laser,"We demonstrate ultrafast magnetization dynamics in a 5d transition metal
using circularly-polarized x-ray free electron laser in the hard x-ray region.
A decay time of light-induced demagnetization of L1${}_0$-FePt was determined
to be $\tau_\textrm{Pt} = 0.6\ \textrm{ps}$ using time-resolved x-ray magnetic
circular dichroism at the Pt L${}_3$ edge, whereas magneto-optical Kerr
measurements indicated the decay time for total magnetization as
$\tau_\textrm{total} = 0.1\ \textrm{ps}$. A transient magnetic state with the
photo-modulated magnetic coupling between the 3d and 5d elements is firstly
demonstrated.",1810.02551v1
2018/10/9,Cluster magnetism of Ba4NbMn3O12: localized electrons or molecular orbitals?,"Recently synthesised Ba4NbMn3O12 belong to cluster magnets - systems with
tightly bound groups of magnetism ions, in this case Mn3 trimers. Often such
magnetic clusters can be described by molecular orbitals (MO), however strong
electron correlations may invalidate this description. To understand the
electronic and magnetic state of Ba4NbMn3O12 we carried out ab initio
calculations and show that this system is better described not in MO picture,
but as a system with electrons localized on the Mn ions, with strong
intra-cluster and weaker inter-cluster exchange. The calculated spin of the Mn3
trimer is S=2, in agreement with the experiment. The predicted magnetic
structure of Ba4NbMn3O12 is that of ferromagnetic layers of Mn3 trimers,
stacked antiferromagnetically.",1810.03915v2
2018/10/12,Two-step gap opening across the quantum critical point in a Kitaev honeycomb magnet,"Quantum spin liquid involves fractionalized quasipariticles such as spinons
and visons. They are expressed as itinerant Majorana fermions and $Z_2$ fluxes
in the Kitaev model with bond-dependent exchange interactions on a honeycomb
spin lattice. The observation has recently attracted attention for a candidate
material $\alpha$-RuCl$_3$, showing spin liquid behaviour induced by a magnetic
field. Since the observable spin excitation is inherently composed of the two
quasiparticles, which further admix each other by setting in the magnetic field
as well as non-Kitaev interactions, their individual identification remains
challenging. Here we report an emergent low-lying spin excitation through
nuclear magnetic and quadrupole resonance measurements down to $\sim 0.4$ K
corresponding to $1/500$ of the exchange energy under the finely tuned magnetic
field across the quantum critical point. We determined the critical behaviour
of low-lying excitations and found evolution of two kinds of the spin gap at
high fields. The two excitations exhibit repulsive magnetic field dependence,
suggesting anti-crossing due to the hybridization between fractionalized
quasiparticles.",1810.05379v1
2018/10/17,Role of Tin and Carbon in the magnetic interactions in Mn$_3$SnC,"In this paper we attempt to understand the role of tin and carbon in magnetic
interactions in Mn$_3$SnC. Mn$_3$SnC exhibits a time dependent magnetic
configuration and a complex magnetic ground state with both ferromagnetic and
antiferromagnetic orders. Such a magnetic state is attributed to presence of
distorted Mn$_6$C octahedra with long and short Mn--Mn bonds. Our studies show
that C deficiency increases the tensile strain on the Mn$_6$C octahedra which
elongates Mn--Mn bonds and strengthens ferromagnetic interactions while Sn
deficiency tends to ease out the strain resulting in shorter as well as longer
Mn--Mn bond distances in comparison with stoichiometric Mn$_3$SnC. Such a
variation strengthens both, ferromagnetic and antiferromagnetic interactions.
Thus the structural strain caused by both Sn and C is responsible for complex
magnetic ground state of Mn$_3$SnC.",1810.07482v1
2018/10/23,Absence of a multiglass state in some transition metal doped quantum paraelectrics,"We critically investigate the purported existence of a multiglass state in
the quantum paraelectrics SrTiO${_3}$ and KTaO${_3}$ doped with magnetic 3d
transition metals. We observe that the transition metals have limited
solubility in these hosts, and that traces of impurity magnetic oxides persist
even in the most well processed specimens. Our dielectric measurements indicate
that the polar nano-regions formed as a consequence of doping appear to lack
co-operativity, and the associated relaxation process exhibits a thermally
activated Arrhenius form. At lower temperatures, the dielectric susceptibility
could be fit using the Barrett's formalism, indicating that the
quantum-paraelectric nature of the host lattices are unaltered by the doping of
magnetic transition metal oxides. All these doped quantum paraelectrics exhibit
a crossover from the high temperature Curie-Weiss regime to one dominated by
quantum fluctuations, as evidenced by a $T{^2}$ dependence of the temperature
dependent dielectric susceptibility. The temperature dependence of the magnetic
susceptibility indicate that magnetic signatures observed in some of the
specimens could be solely ascribed to the presence of impurity oxides
corresponding to the magnetic dopants used. Hence, the doped quantum
paraelectrics appear to remain intrinsically paramagnetic down to the lowest
measured temperatures, ruling out the presence of a multiglass state.",1810.09822v1
2018/11/5,Magnetic and defect probes of the SmB$_6$ surface state,"The impact of non-magnetic and magnetic impurities on topological insulators
is a central problem concerning their fundamental physics and possible novel
spintronics and quantum computing applications. SmB$_6$, predicted to be a
topological Kondo insulator, is considered a benchmark material. Using a
spin-polarized tip in scanning tunneling spectroscopy destroys the signature
peak of the topological surface state, revealing its spin texture. Further,
combining local STS with macroscopic transport measurements on SmB$_6$
containing different substitutions enables us to investigate the effect of
impurities. The surface states around impurities are locally suppressed with
different length scales depending on their magnetic properties and, for
sufficiently high impurity level, globally destroyed. Our study points directly
to the topological nature of SmB$_6$, and unveils, microscopically and
macroscopically, how impurities -- magnetic or non-magnetic -- affect
topological surface states.",1811.01642v1
2018/11/6,Tunable magnetism of a single-carbon vacancy in graphene,"Removing a single-carbon vacancy introduces (quasi-)localized states for both
and electrons in graphene. Interactions between the localized dangling bond and
quasilocalized electrons of a single-carbon vacancy in graphene are predicted
to control its magnetism. However, experimentally confirming this prediction
through manipulating the interactions between the and electrons remains an
outstanding challenge. Here we report the manipulation of magnetism of
individual single-carbon vacancy in graphene by using a scanning tunnelling
microscopy (STM) tip. Our spin-polarized STM measurements, complemented by
density functional theory calculations, indicate that interactions between the
localized and quasilocalized electrons could split the electrons into two
states with opposite spins even when they are well above the Fermi level. Via
the STM tip, we successfully manipulate both the magnitude and direction of
magnetic moment of the electrons with respect to that of the electrons. Three
different magnetic states of the single-carbon vacancy, exhibiting magnetic
moments of about 1.6, 0.5, and 0 respectively, are realized in our experiment.",1811.02277v1
2018/11/20,NMR shifts in $^3$He in aerogel induced by demagnetizing fields,"Magnetic materials generate demagnetizing field that depends on geometry of
the sample and results in a shift of magnetic resonance frequency. This
phenomenon should occur in porous nanostructures as well, e.g., in globally
anisotropic aerogels. Here we report results of nuclear magnetic resonance
(NMR) experiments with liquid $^3$He confined in anisotropic aerogels with
different types of anisotropy (nematic and planar aerogels). Strands of
aerogels in pure $^3$He are covered by a few atomic layers of paramagnetic
solid $^3$He which magnetization follows the Curie-Weiss law. We have found
that in our samples the NMR shift in solid $^3$He is clearly seen at ultralow
temperatures and depends on value and orientation of the magnetic field. The
obtained results are well described by a model of a system of non-interacting
paramagnetic cylinders. The shift is proportional to the magnetization of solid
$^3$He and may complicate NMR experiments with superfluid $^3$He in aerogel.",1811.08208v1
2018/11/27,Fast flux control of 3D transmon qubits using a magnetic hose,"Fast magnetic flux control is a crucial ingredient for circuit quantum
electrodynamics (cQED) systems. So far it has been a challenge to implement
this technology with the high coherence 3D cQED architecture. In this paper we
control the magnetic field inside a superconducting waveguide cavity using a
magnetic hose, which allows fast flux control of 3D transmon qubits on time
scales < 100 ns. The hose is designed as an effective microwave filter to not
compromise the energy relaxation time of the qubit. The magnetic hose is a
promising tool for fast magnetic flux control in various platforms intended for
quantum information processing and quantum optics.",1811.10875v2
2018/11/24,Study of the magnetic properties of the compound M_n B_i using the Monte Carlo simulations,"The aim of this paper is to investigate the magnetic properties of the M_n
B_i magnetic systems by using the Monte Carlo simulation. Indeed, we analyzed
the effect of the number of layers on the magnetic properties of the compound
M_n B_i. The magnetization, the binder cumulant, the Curie temperature and the
hysteresis cycle are also calculated in this work. We used the free boundary
conditions to simulate the properties of the studied system, and we presented
the effect of multilayer numbers on the magnetic properties of M_n B_i films.
Meanwhile, there are clear indications that coercive field increases
drastically with the increases multilayer numbers is consistent with the
experimental facts.",1811.11290v2
2018/12/5,Controlling stability of Bose-Einstein condensation of interacting magnons in an antiferromagnet by an external magnetic field,"We propose a mechanism for destabilizing or stabilizing Bose-Einstein
condensation (BEC) of interacting magnons in an antiferromagnet. We study how
the interaction between magnons affects the magnon BEC in a two-sublattice
antiferromagnet without and with an external magnetic field. We show that in
the absence of the magnetic field the magnon BEC is destabilized by the
attractive interband interaction, which is larger than the repulsive intraband
interaction. We also show that in the presence of the magnetic field the magnon
BEC is stabilized only if the magnetic field is large enough to make the
intraband interaction larger than the interband interaction. Our results
provide the first step for understanding the interaction effects on the magnon
BEC in antiferromagnets and may open interaction physics of multicomponent BEC
of magnons in magnets.",1812.01787v2
2018/12/10,Optical second harmonic generation from interfaces between heavy and ferromagnetic metals,"Surfaces and interfaces of magnetic nanostructures can reveal rather
interesting and unusual properties that differ substantially from those of
bulky materials. Here we apply the surface-sensitive method of optical second
harmonic generation (SHG) for the studies of magnetization induced effects that
appear in the nonlinear reflection from interfaces between ferromagnetic (Co)
and heavy metals (Pt, Ta, W, Au, Ag, Cu). We demonstrate the appearance of
magnetization induced variation in the p-polarized SHG intensity in the
geometry of the longitudinal magneto-optical Kerr effect that is forbidden for
homogeneous magnetic structures. This confirms the existence of chiral magnetic
states at heavy metal/ferromagnet interfaces that appear due to the
surface-induced Dzyaloshinskii-Moriya interaction. The related nonlinear
chiroptical effect in the SHG intensity is proportional to the dc
flexo-electric polarization that is shown to exist for chiral magnetic states
at the considered interfaces.",1812.03922v2
2018/12/14,Analytic Expression for Magnetic Activation Energy,"We theoretically investigate the magnetic activation energy of permanent
magnets. Practically, it is widely used in a phenomenological form as
$\mathcal{F}_\mathrm{B}(H_\mathrm{ext})=\mathcal{F}_\mathrm{B}^0\left(1-H_\mathrm{ext}/H_0\right)^n,$
where $\mathcal{F}_\mathrm{B}^0$ is the activation energy in the absence of an
external magnetic field $H_\mathrm{ext}$, $n$ is a real parameter, and $H_0$ is
defined by the equation $\mathcal{F}_\mathrm{B}(H_0)=0$. We derive the general
and direct expressions for these phenomenological parameters under the
restriction of uniform rotation of magnetization and on the basis of the
perturbative theory with respect to $H_\mathrm{ext}$. Further,we apply our
results to Nd$_2$Fe$_{14}$B magnets and confirm the validity of the proposed
method by comparing with the Monte Carlo calculations.",1812.05766v2
2018/12/15,Novel magnetic field tuning of quantum spin excitations in a weakly coupled $S=$1/2 Heisenberg spin chain as seen from NMR,"We report our NMR study of the spin excitations in the quasi-one dimensional
(1D) $S=1/2$ quantum magnet CH$_3$NH$_3$Cu(HCOO)$_3$ lying in the 1D-3D
dimensional crossover regime with Dzyaloshinskii-Moriya(DM) interactions. Above
$T_N$, the spinon excitation is observed from the constant $1/T_1$ at low
temperatures contributed from the staggered spin susceptibility. At low
temperatures well below $T_N$, the $1/T_1$ begins to flatten out under weak
magnetic fields. With the increasing field intensity, $1/T_1$ tends to show a
power-law temperature dependence gradually, with the index increasing from zero
to $\sim3$, and finally $\sim5$, which are the respective typical
characteristic for the dominating two-magnon Raman process and three-magnon
scattering contributions to the nuclear relaxation in a conventional 3D magnet.
A possible physical mechanism for this novel magnetic field tuning of quantum
spin excitations related with the enhanced effective staggered field created by
the DM interactions under magnetic field is discussed.",1812.06261v2
2018/12/29,Magnetocaloric effect as a signature of quantum level-crossing for a spin-gapped system,"Recent research dealing with magnetocaloric effect (MCE) study of
antiferromagnetic (AFM) low dimensional spin systems have revealed a number of
fascinating ground-state crossover characteristics upon application of external
magnetic field. Herein, through MCE investigation we have explored
field-induced quantum level-crossing characteristics of one such spin system:
NH4CuPO4.H2O (NCP), an AFM spin 1/2 dimer. Experimental magnetization and
specific heat data are presented and the data have been employed to evaluate
entropy, magnetic energy and magnetocaloric properties. We witness a sign
change in magnetic Grueneisen parameter across the level-crossing field B_C. An
adiabatic cooling is observed at low temperature by tracing the isentropic
curves in temperature-magnetic field plane. Energy-level crossover
characteristics in NCP interpreted through MCE analysis are well consistent
with the observations made from magnetization and specific heat data.",1812.11298v2
2018/12/29,Magnetization flip in Fe-Cr-Ga system,"A systematic investigation about the structure and magnetism of Fe75-xCr25Gax
(11<x<33) and Fe50Cr50-yGay (0<y<33) series has been carried out in this work.
It shows that the parent Fe50Cr25Ga25 phase has higher tolerance for Ga
replacing Cr than replacing Fe atoms. An abrupt flip of Curie temperature and
magnetization in the Fe50Cr50-yGay (0<y<33) series was observed at the
composition of Fe50Cr25Ga25. We proposed an explanation concerning anti-sites
occupation and magnetic structure transition in this series. The induced
structure is proved energetically favorable from first-principles calculations.
This work can help us to understand the dependences between the crystal
structure and magnetism in Fe-based Heusler compounds, and provides a method to
deduce the atomic configurations based on the evolution of magnetism.",1812.11304v1
2019/1/7,Strain-tunable magnetic and electronic properties of monolayer CrI3,"Two-dimensional CrI3 has attracted much attention as it is reported to be a
ferromagnetic semiconductor with the Curie temperature around 45K. By
performing first-principles calculations, we find that the magnetic ground
state of CrI3 is variable under biaxial strain. Our theoretical investigations
show that the ground state of monolayer CrI3 is ferromagnetic under
compression, but becomes antiferromagnetic under tension. Particularly, the
transition occurs under a feasible in-plane strain around 1.8%. Accompanied by
the transition of the magnetic ground state, it undergoes a transition from
magnetic-metal to half-metal to half-semiconductor to spin-relevant
semiconductor when strain varies from -15% to 10%. We attribute these
transitions to the variation of the d-orbitals of Cr atoms and the p-orbitals
of I atoms. Generally, we report a series of magnetic and electronic phase
transition in strained CrI3, which will help both theoretical and experimental
researchers for further understanding of the tunable electronic and magnetic
properties of CrI3 and their analogous.",1901.01745v1
2019/1/17,Direct Assembly of Magnetic Janus Particles at a Droplet Interface,"Self-assembly of nanoparticles at fluid-fluid interfaces is a promising route
to fabricate functional materials from the bottom-up. However, directing and
controlling particles into highly tunable and predictable structures -- while
essential -- is a challenge. We present a liquid interface assisted approach to
fabricate nanoparticle structures with tunable properties. To demonstrate its
feasibility, we study magnetic Janus particles adsorbed at the interface of a
spherical droplet placed on a substrate. With an external magnetic field turned
on, a single particle moves to the location where its position vector relative
to the droplet centre is parallel to the direction of the applied field.
Multiple magnetic Janus particles arrange into reconfigurable hexagonal lattice
structures and can be directed to assemble at desirable locations on the
droplet interface by simply varying the magnetic field direction. We develop an
interface energy model to explain our observations, finding excellent
agreement. Finally, we demonstrate that the external magnetic field allows
\revisedtext{one} to tune the particle deposition pattern obtained when the
droplet evaporates. Our results have implications for the fabrication of varied
nanostructures on substrates for use in nanodevices, organic electronics, or
advanced display, printing and coating applications.",1901.05724v1
2019/1/23,Field-induced instability of the quantum-spin-liquid ground state in the $J_{\rm eff}=\frac{1}{2}$ triangular-lattice compound NaYbO$_2$,"Polycrystalline samples of NaYbO$_2$ are investigated by bulk magnetization
and specific-heat measurements, as well as by nuclear magnetic resonance (NMR)
and electron spin resonance (ESR) as local probes. No signatures of long-range
magnetic order are found down to 0.3~K, evidencing a highly frustrated
spin-liquid-like ground state in zero field. Above 2\,T, signatures of magnetic
order are observed in thermodynamic measurements, suggesting the possibility of
a field-induced quantum phase transition. The $^{23}$Na NMR relaxation rates
reveal the absence of magnetic order and persistent fluctuations down to 0.3~K
at very low fields and confirm the bulk magnetic order above 2~T. The $H$-$T$
phase diagram is obtained and discussed along with the existing theoretical
concepts for layered spin-$\frac{1}{2}$ triangular-lattice antiferromagnets",1901.07760v2
2019/1/29,"Optimal uni-axial ferromagnetism in (La,Ce)$_2$Fe$_{14}$B for permanent magnets","Prospects for light-rare-earth-based permanent magnet compound
R$_{2}$Fe$_{14}$B (R=La$_{1-x}$Ce$_{x}$ with $0 \le x\le 1$) are inspected from
first principles referring to the latest experimental data. Ce-rich 2:14:1
compounds come with good structure stability, reasonably good combination of
magnetization and magnetic anisotropy, while a drawback lies in the low Curie
temperature that is only 120~K above the room temperature at the
Ce$_2$Fe$_{14}$B limit. Best compromise is inspected on the basis of ab initio
data for (La$_{1-x}$Ce$_{x}$)$_2$Fe$_{14}$B referring to the magnetic
properties of the champion magnet compound Nd$_{2}$Fe$_{14}$B and prerequisite
conditions imposed by practical utility.",1901.10119v1
2019/2/6,"(Fe,Sn)4N alloy as a model spin-glass system with short-range competing interactions on a nonfrustrated simple cubic lattice","The origin of the spin-glass state in (Fe,Sn)4N alloys is studied on the
basis of a Heisenberg Hamiltonian with parameters derived from first principles
within the magnetic force theorem applied in the framework of the disordered
local moments method and local spin-density approximation. We show that in the
alloy concentration range where the spin-glass state is stable only one Fe
sublattice is intrinsically magnetic and the interatomic exchange magnetic
interactions are essentially short ranged due to effects of chemical and
magnetic disorder. The magnetic Fe atoms with well-localized spin moments are
randomly distributed over the nongeometrically frustrated simple cubic lattice.
The magnetic frustration, which generally is believed to be an essential
ingredient of the spin-glass state formation condition, may occur only due to
the competition of the two nearest-neighbor interactions. We thus argue that
(Fe,Sn)4N is a rare example of a spin-glass system where the mechanism of
spin-glass state formation might be studied in the framework of the minimal
random-site model on a simple cubic lattice with competing interactions, while
the effects of the geometrical frustration can be excluded.",1902.02230v1
2019/2/8,Machine learning as an improved estimator for magnetization curve and spin gap,"The magnetization process is a very important probe to study magnetic
materials, particularly in search of spin-liquid states in quantum spin
systems. Regrettably, however, progress of the theoretical analysis has been
unsatisfactory, mostly because it is hard to obtain sufficient numerical data
to support the theory. Here we propose a machine-learning algorithm that
produces the magnetization curve and the spin gap well out of poor numerical
data. The plateau magnetization, its critical field and the critical exponent
are estimated accurately. One of the hyperparameters identifies by its score
whether the spin gap in the thermodynamic limit is zero or finite. After
checking the validity for exactly solvable one-dimensional models we apply our
algorithm to the kagome antiferromagnet. The magnetization curve that we obtain
from the exact-diagonalization data with 36 spins is consistent with the DMRG
results with 132 spins. We estimate the spin gap in the thermodynamic limit at
a very small but finite value.",1902.02941v2
2019/2/14,Breakdown of the Hebel-Slichter effect in superconducting graphene due to the emergence of Yu-Shiba-Rusinov states at magnetic resonant scatterers,"Employing analytical methods and quantum transport simulations we investigate
the relaxation of quasiparticle spins in graphene proximitized by an $s$-wave
superconductor in the presence of resonant magnetic and spin-orbit active
impurities. Off resonance, the relaxation increases with decreasing temperature
when electrons scatter off magnetic impurities---the Hebel-Slichter
effect---and decreases when impurities have spin-orbit coupling. This distinct
temperature~dependence (not present in the normal state) uniquely discriminates
between the two scattering mechanisms. However, we show that the Hebel-Slichter
picture breaks down at resonances. The emergence of Yu-Shiba-Rusinov bound
states within the superconducting gap redistributes the spectral weight away
from magnetic resonances. The result is opposite to the Hebel-Slichter
expectation: the spin relaxation decreases with decreasing temperature. Our
findings hold for generic $s$-wave superconductors with resonant magnetic
impurities, but also, as we show, for resonant magnetic Josephson junctions.",1902.05474v2
2019/2/19,Spin-wave mediated interactions for Majority Computation using Skyrmions and Spin-torque Nano-oscillators,"Recent progress in all-electrical nucleation, detection and manipulation of
magnetic skyrmions has unlocked the tremendous potential of skyrmion-based
spintronic devices. Here, we show via micromagnetic simulations that the stable
magnetic oscillations of STNO radiate spin waves (SWs) that can be scattered in
the presence of skyrmions in the near vicinity. Interference between SWs
emitted by the STNO and SWs scattered by the skyrmion gives rise to interesting
dynamics that leads to amplification or attenuation of STNO's magnetic
oscillations. In the presence of strong Dzyaloshinskii-Moriya interaction
(DMI), the amplified magnetic oscillations evolve into a new skyrmion. These
interactions between skyrmions and STNOs are found to be identical for both
Neel-type and Bloch-type skyrmions, and are not observed between domain walls
and STNOs. These findings offer a novel perspective in processing information
using single skyrmions and we propose a 3-bit majority gate for logic
applications.",1902.06925v2
2019/2/21,Neutron scattering study of commensurate magnetic ordering in single crystal CeSb$_2$,"Temperature and field-dependent magnetization $M(H,T)$ measurements and
neutron scattering study of a single crystal CeSb$_2$ are presented. Several
anomalies in the magnetization curves have been confirmed at low magnetic
field, i.e., 15.6 K, 12 K, and 9.8 K. These three transitions are all
metamagnetic transitions (MMT), which shift to lower temperatures as the
magnetic field increases. The anomaly at 15.6 K has been suggested as
paramagnetic (PM) to ferromagnetic (FM) phase transition. The anomaly located
at around 12 K is antiferromagnetic-like transition, and this turning point
will clearly split into two when the magnetic field $H\geq0.2$ T. Neutron
scattering study reveals that the low temperature ground state of CeSb$_2$
orders antiferromagnetically with commensurate propagation wave vectors
$\textbf{k}=(-1,\pm1/6,0)$ and $\textbf{k}=(\pm1/6,-1,0)$, with N\'eel
temperature $T_N\sim9.8$ K. This transition is of first-order, as shown in the
hysteresis loop observed by the field cooled cooling (FCC) and field cooled
warming (FCW) processes.",1902.08000v1
2019/2/24,Decoupling of the Kinetic and Magnetic Energy Cascades in MHD Turbulence,"Magnetic and kinetic energy in ideal incompressible MHD are not global
invariants and, therefore, it had been justified to discuss only the cascade of
their sum, total energy. We provide a physical argument based on scale-locality
of the cascade, along with compelling evidence that at high Reynolds numbers,
magnetic and kinetic energy budgets statistically decouple beyond a
transitional ""conversion"" range. This arises because magnetic field-line
stretching is a large-scale process which vanishes on average at intermediate
and small scales within the inertial-inductive range, thereby allowing each of
mean kinetic and magnetic energy to cascade conservatively and at an equal
rate. One consequence is that the turbulent magnetic Prandtl number is unity
over the ""decoupled range"" of scales.",1902.08983v1
2019/2/25,Anisotropic magnetotransport and magnetic phase diagrams of the antiferromagnetic heavy-fermion superconductor Ce$_3$PdIn$_{11}$,"We report the results of our detailed magnetotransport studies on single
crystals of the antiferromagnetic heavy-fermion superconductor
Ce$_3$PdIn$_{11}$. Electrical resistivity measurements, carried out in
different magnetic field orientations with respect to the crystallographic
axes, were mainly aimed to amass further insight about the magnetically ordered
state. The results manifest a clear metamagnetic transitions in the ordered
phase when the applied field is parallel to the tetragonal $c$ axis, while no
similar features are seen for the transverse direction, i.e., with the field
confined within the $ab$ plane. This finding elucidates the fact that the $c$
axis is the easy magnetic direction in this system. Based on the electrical
transport and heat capacity data obtained for Ce$_3$PdIn$_{11}$, magnetic field
-- temperature phase diagrams were constructed, which elucidate fairly
enigmatic behaviors in this material featuring the existence of both second-
and first-order magnetic phase transitions.",1902.09270v1
2019/2/26,The Enhanced Ferromagnetism of Single-Layer CrX3 (X=Br and I) by Van der Waals Engineering,"The recent experimental discovery of intrinsic ferromagnetism in single-layer
CrI3 opens a new avenue to low-dimensional spintronics. However, the low Curie
temperature Tc=45 K is still a large obstacle to its realistic device
application. In this work, we demonstrate that the Tc and magnetic moment of
CrX3(X=Br, I) can be enhanced simultaneously by coupling them to buckled
two-dimensional Mene (M=Si, Ge) to form magnetic van der Waals (vdW)
heterostructures. Our first-principles calculations reveal that n-doping of
CrX3, induced by a significant spin-dependent interlayer charge transfer from
Mene, is responsible for its drastic enhancement of Tc and magnetic moment.
Furthermore, the diversified electronic properties including halfmetallicity
and semi-conductivity with configuration dependent energy gap are also
predicted in this novel vdW heterostructure, implying their broad potential
applications in spintronics. Our study suggests that the vdW engineering may be
an efficient way to tune the magnetic properties of 2D magnets, and the
Mene_CrX3 magnetic vdW heterostructures are wonderful candidates in spintronics
and nanoelectronics device.",1902.09893v1
2019/2/27,Multipole expansion for magnetic structures: A generation scheme for symmetry-adapted orthonormal basis set in crystallographic point group,"We propose a systematic method to generate a complete orthonormal basis set
of multipole expansion for magnetic structures in arbitrary crystal structure.
The key idea is the introduction of a virtual atomic cluster of a target
crystal, on which we can clearly define the magnetic configurations
corresponding to symmetry-adapted multipole moments. The magnetic
configurations are then mapped onto the crystal so as to preserve the magnetic
point group of the multipole moments, leading to the magnetic structures
classified according to the irreducible representations of crystallographic
point group. We apply the present scheme to pyrhochlore and hexagonal ABO3
crystal structures, and demonstrate that the multipole expansion is useful to
investigate the macroscopic responses of antiferromagnets.",1902.10819v1
2019/3/6,Magnetism study on a frustration-free spatially anisotropic $S$ = 1 square lattice antiferromagnet Ni[SC(NH$_2$)$_2$]$_6$Br$_2$,"Magnetism of the $S$ = 1 Heisenberg antiferromagnets on the spatially
anisotropic square lattice has been scarcely explored. Here we report a study
of the magnetism, specific heat, and thermal conductivity on
Ni[SC(NH$_2$)$_2$]$_6$Br$_2$ (DHN) single crystals. Ni$^{2+}$ ions feature an
$S$ = 1 rectangular lattice in the $bc$ plane, which can be viewed as an
unfrustrated spatially anisotropic square lattice. A long-range
antiferromagnetic order is developed at $T \rm_N =$ 2.23 K. Below $T\rm_N$, an
upturn is observed in the $b$-axis magnetic susceptibility and the resultant
minimum might be an indication for the $XY$ anisotropy in the ordered state. A
gapped spin-wave dispersion is confirmed from the temperature dependence of the
magnetic specific heat. Anisotropic temperature-field phase diagrams are mapped
out and possible magnetic structures are proposed.",1903.02296v1
2019/3/16,Predicted electric field induced surface magnetization of vortex phase of superconductors,"We predict a new effect in condensed matter surface magnetization of the
vortex phase of a superconductor induced by electric field. The magnetized
superconductor should be one of the plates of a plane capacitor on which a
voltage has to be applied. Applying alternating voltage to the capacitor,
electrostatic induction leads to oscillations of the magnetic moment which has
to be measured by electromotive force inducted in a detector coil. The derived
explicit formula for the magnetization contains the effective mass of Cooper
pairs and a systematic investigation of the predicted magnetization will lead
to a creation of an effective Cooper pair mass spectroscopy. For cleaved
superconductors this effective mass is a property of the bulk material.",1903.06940v5
2019/3/19,Study of magnetization reversal in Neel and Bloch regime of Ni and Py stripes using Kerr microscopy,"We present a systematic study of the magnetization reversal of nickel and
permalloy micro-stripes with Neel and Bloch domain walls using Kerr microscopy.
Magnetic field driven domain propagation was observed from higher width to
lower width stripes for magnetic fields applied along the length of
micro-stripes. Stripe like domains were observed with nucleation starting in
lower width region followed by their propagation to higher width regions for
magnetic fields applied along the width of micro-stripes. The comparison of
magnetization reversal in Bloch and N\'eel domain wall regime showed higher
domain wall density in Bloch regime for both nickel and permalloy stripes.",1903.08106v3
2019/3/21,Room temperature and low-field resonant enhancement of spin Seebeck effect in partially compensated magnets,"Resonant enhancement of spin Seebeck effect (SSE) due to phonons was recently
discovered in Y3Fe5O12 (YIG). This effect is explained by hybridization between
the magnon and phonon dispersions. However, this effect was observed at low
temperatures and high magnetic fields, limiting the scope for applications.
Here we report observation of phonon-resonant enhancement of SSE at room
temperature and low magnetic field. We observed in Lu2BiFe4GaO12 and
enhancement 700 % greater than that in a YIG film and at very low magnetic
fields around 10-1 T, almost one order of magnitude lower than that of YIG. The
result can be explained by the change in the magnon dispersion induced by
magnetic compensation due to the presence of non-magnetic ion substitutions.
Our study provides a way to tune the magnon response in a crystal by chemical
doping with potential applications for spintronic devices.",1903.09007v1
2019/3/26,"Magnetic and magnetoelectric properties of $A$FeF$_5$ ($A$ = Ca, Sr) spin-chain compounds","Fluorides in general are characterized by big variety of crystal structures,
whereas those containing transition metals also often show sizable magnetic
properties. The tendency of fluorine to form linear chain structures in many
cases results in low-dimensional magnetism. Despite the plethora of magnetic
phenomena in fluorides, their magnetoelectric properties are less studied than
those of oxides. In the present work we theoretically study the magnetic and
magnetoelectric properties of spin-chain compounds CaFeF$_5$ and SrFeF$_5$. The
density functional theory is employed for determination of magnetic exchange
constants, which are then used in Monte Carlo calculations. The symmetry
analysis reveals that CaFeF$_5$ does not show magnetoelectric properties,
whereas SrFeF$_5$ is a multiferroic.",1903.10828v2
2019/4/2,Magnetoelectric domains and their switching mechanism in a Y-type hexaferrite,"By employing resonant X-ray microdiffraction, we image the magnetisation and
magnetic polarity domains of the Y-type hexaferrite
Ba$_{0.5}$Sr$_{1.5}$Mg$_2$Fe$_{12}$O$_{22}$. We show that the magnetic polarity
domain structure can be controlled by both magnetic and electric fields, and
that full inversion of these domains can be achieved simply by reversal of an
applied magnetic field in the absence of an electric field bias. Furthermore,
we demonstrate that the diffraction intensity measured in different X-ray
polarisation channels cannot be reproduced by the accepted model for the polar
magnetic structure, known as the 2-fan transverse conical (TC) model. We
propose a modification to this model, which achieves good quantitative
agreement with all of our data. We show that the deviations from the TC model
are large, and may be the result of an internal magnetic chirality, most likely
inherited from the parent helical (non-polar) phase.",1904.01278v2
2019/4/5,Common universal behaviors of magnetic domain walls driven by spin-polarized electrical current and magnetic field,"We explore universal behaviors of magnetic domain wall driven by the
spin-transfer of an electrical current, in a ferromagnetic (Ga,Mn)(As,P) thin
film with perpendicular magnetic anisotropy. For a current direction transverse
to domain wall, the dynamics of the thermally activated creep regime and the
depinning transition are found to be compatible with a self-consistent
universal description of magnetic field induced domain wall dynamics. This
common universal behavior, characteristic of the so-called quenched
Edwards-Wilkinson universality class, is confirmed by a complementary and
independent analysis of domain wall roughness. However, the tilting of domain
walls and the formation of facets is produced by the directionality of
interaction with the current, which acts as a magnetic field only in the
direction transverse to domain wall.",1904.03047v2
2019/4/10,Magnetization-polarization cross-control near room temperature in hexaferrite single crystals,"Mutual control of the electricity and magnetism in terms of magnetic (H) and
electric (E) fields, the magnetoelectric (ME) effect, offers versatile low
power-consumption alternatives to current data storage, logic gate, and
spintronic devices. Despite its importance, E-field control over magnetization
(M) with significant magnitude was observed only at low temperatures. Here we
have successfully stabilized a simultaneously ferrimagnetic and ferroelectric
phase in a Y-type hexaferrite single crystal up to T=450K and demonstrated the
reversal of large non-volatile M by E field close to room temperature.
Manipulation of the magnetic domains by E field is directly visualized at room
temperature by using magnetic force microscopy. The present achievement
provides an important step towards the application of bulk ME multiferroics.",1904.05017v1
2019/4/12,Spin excitations of magnetoelectric LiNiPO$_4$ in multiple magnetic phases,"Spin excitations of magnetoelectric LiNiPO$_4$ are studied by infrared
absorption spectroscopy in the THz spectral range as a function of magnetic
field through various commensurate and incommensurate magnetically ordered
phases up to 33\,T. Six spin resonances and a strong two-magnon continuum are
observed in zero magnetic field. Our systematic polarization study reveals that
some of the excitations are usual magnetic-dipole active magnon modes, while
others are either electromagnons, electric-dipole active, or magnetoelectric,
both electric- and magnetic-dipole active spin excitations. Field-induced
shifts of the modes for all three orientations of the field along the
orthorhombic axes allow us to refine the values of the relevant exchange
couplings, single-ion anisotropies, and the Dzyaloshinskii-Moriya interaction
on the level of a four-sublattice mean-field spin model. This model also
reproduces the spectral shape of the two-magnon absorption continuum, found to
be electric-dipole active in the experiment.",1904.06106v1
2019/5/8,Electric field control of magnetism in Si3N4 gated Pt/Co/Pt heterostructures,"In this work we show the presence of a magnetoelectric coupling in
silicon-nitride gated Pt/Co/Pt heterostructures using X-ray photoemission
electron microscopy (XPEEM). We observe a change in magnetic anisotropy in the
form of domain wall nucleation and a change in the rate of domain wall
fluctuation as a function of the applied electric field to the sample. We also
observe the coexistence of in-plane and out of plane magnetization in Pt/Co/Pt
heterostructures in a region around the spin reorientation transition whose
formation is attributed to substrate surface roughness comparable to the film
thickness; with such domain configuration, we find that the in-plane
magnetization is more sensitive to the applied electric field than out of plane
magnetization. Although we find an effective magnetoelectric coupling in our
system, the presence of charge defects in the silicon nitride membranes hampers
a systematic electrostatic control of the magnetization.",1905.03082v1
2019/5/29,Kramers Weyl Semimetals as Quantum Solenoids and Their Applications in Spin-Orbit Torque Devices,"Kramers Weyl semimetals are Weyl semimetals that have Weyl points pinned at
the time reversal invariant momenta. Recently it has been discovered that all
chiral crystals host Weyl points at time reversal invariant momenta, so metals
with chiral lattice symmetry all belong to the category of Kramers Weyl
semimetals. In this work, we show that due to the chiral lattice symmetry,
Kramers Weyl semimetals have the unique longitudinal magnetoelectric effect in
which the charge current induced spin and orbital magnetization is parallel to
the direction of the current. This feature allows Kramers Weyl semimetals to
act as nanoscale quantum solenoids with both orbital and spin magnetization. As
the moving electrons of Kramers Weyl semimetal can generate longitudinal
magnetization, Kramers Weyl semimetals can be used for new designs of
spin-orbit torque devices with all electric control of magnetization switching
for magnets with perpendicular magnetic anisotropy.",1905.12575v4
2019/6/1,Magnetic Skyrmion Annihilation by Quantum Mechanical Tunneling,"Magnetic skyrmions are nano-scale magnetic states that could be used in
various spintronics devices. A central issue is the mechanism and rate of
various possible annihilation processes and the lifetime of metastable
skyrmions. While most studies have focused on classical over-the-barrier
mechanism for annihilation, it is also possible that quantum mechanical
tunneling through the energy barrier takes place. Calculations of the lifetime
of magnetic skyrmions in a two-dimensional lattice are presented and the rate
of tunneling compared with the classical annihilation rate. A remarkably strong
variation in the crossover temperature and the lifetime of the skyrmion is
found as a function of the values of parameters in the extended Heisenberg
Hamiltonian, i.e. the out-of-plane anisotropy, Dzyaloshinskii-Moriya
interaction (DMI) and applied magnetic field. Materials parameters and
conditions are identified where the onset of tunneling could be observed on a
laboratory time scale. In particular, it is predicted that skyrmion tunneling
could be observed in the PdFe/Ir(111) system when an external magnetic field on
the order of 6 T is applied.",1906.00196v2
2019/6/8,Direct observation of van der Waals stacking dependent interlayer magnetism,"Controlling the crystal structure is a powerful approach for manipulating the
fundamental properties of solids. Unique to two-dimensional (2D) van der Waals
materials, the control can be achieved by modifying the stacking order through
rotation and translation between the layers. Here, we report the first
observation of stacking dependent interlayer magnetism in the 2D magnetic
semiconductor, chromium tribromide (CrBr3), enabled by the successful growth of
its monolayer and bilayer through molecular beam epitaxy. Using in situ
spin-polarized scanning tunneling microscopy and spectroscopy, we directly
correlated the atomic lattice structure with observed magnetic order. We
demonstrated that while individual CrBr3 monolayer is ferromagnetic, the
interlayer coupling in bilayer depends strongly on the stacking order and can
be either ferromagnetic or antiferromagnetic. Our observations provide direct
experimental evidence for exploring the stacking dependent layered magnetism,
and pave the way for manipulating 2D magnetism with unique layer twist angle
control.",1906.03383v1
2019/6/20,Purely magnetic logic based on polarized spin waves,"Spin wave, the precession of magnetic order in magnetic materials, is a
collective excitation that carries spin angular momentum. Similar to the
acoustic or optical waves, the spin wave also possesses the polarization degree
of freedom. Although such polarization degrees of freedom are frozen in
ferromagnets, they are fully unlocked in antiferromagnets or ferrimagnets. Here
we introduce the concept of magnetic gating and demonstrate a spin wave analog
of the Datta-Das spin transistor in antiferromagnet. Utilizing the interplay
between polarized spin wave and the antiferromagnetic domain walls, we propose
a universal logic gate of pure magnetic nature, which realizes all Boolean
operations in one single magnetic structure. We further construct a full
functional 4-bit Arithmetic Logic Unit using only sixteen spin wave universal
logic gates, operating in a weaving fashion as a Jacquard loom machine. The
spin wave-based architecture proposed here also sets a model for the future
energy efficient non-volatile computing, the distributed processing-in-memory
computing, and the evolvable neuromorphic computing.",1906.08702v1
2019/7/1,Spin currents driven by the Higgs mode in magnetic superconductors,"Higgs mode in superconducting materials describes slowly-decaying
oscillations of the order parameter amplitude. We demonstrate that in magnetic
superconductors with built-in spin-splitting field Higgs mode is strongly
coupled to the spin degrees of freedom allowing for the generation of
time-dependent spin currents.
  Converting such spin currents to electric signals by spin-filtering elements
provides a tool for the second-harmonic generation and the electrical detection
of the Higgs mode generated by the external irradiation. The non-adiabatic spin
torques generated by these spin currents allow for the magnetic detection of
the Higgs mode by measuring the precession of magnetic moment in the adjacent
ferromagnet. We discuss also the reciprocal effect which is the generation of
the Higgs mode by the magnetic precession. Coupling the collective modes in
superconductors to light and magnetic dynamics opens the new direction of
superconducting optospintronics.",1907.00539v1
2019/7/8,Tailored Morphologies in 2D Ferronematic Wells,"We focus on a dilute uniform suspension of magnetic nanoparticles in a
nematic-filled micron-sized shallow well with tangent boundary conditions, as a
paradigm system with two coupled order parameters. This system exhibits
spontaneous magnetization without magnetic fields. We numerically obtain the
stable nematic and associated magnetization morphologies, induced purely by the
geometry, boundary conditions and the coupling between the magnetic
nanoparticles and the host nematic medium. Our most striking observations
pertain to domain walls in the magnetization profile whose location can be
manipulated by the coupling and material properties, and stable interior and
boundary nematic defects, whose location and multiplicity can be tailored by
the coupling too. These novel morphologies are not accessible in uncoupled
systems and can be used for new multistable systems with singularities and
stable interfaces.",1907.03833v2
2019/7/9,"Magnetization reversal, giant exchange bias effect and magnetoresistance in oxygen vacancy ordered Sr$_{4}$Fe$_{3}$CoO$_{11}$","We report the structural, magnetic, exchange bias and magnetotransport effect
in Sr$_{4}$Fe$_{3}$CoO$_{11}$. The material crystallizes in the orthorhombic
$\textit{Cmmm}$ space group. It shows antiferromagnetic (G-type) transition
(T$_{N}$ = 255 K) along with interesting temperature induced magnetization
reversal (T$_{Comp.}$= 47 K measured at 100 Oe). The magnetic reversal can be
elucidated considering the increased magnetocrystalline anisotropy with Co
substitution. Magnetoresistance measurements shows an interesting crossover
from negative to positive side at $\sim$ 100 K. The negative magnetoresistance
reaches 80 $\%$ at 25 K in 7 T magnetic field. Giant exchange bias effect is
observed below T$_{N}$ under field cooling condition. The origin of the
negative magnetoresistance and giant exchange bias in this sample can be
attributed to the magnetic frustration.",1907.03986v1
2019/8/18,Magnetic Entropy in a Non-Collinear Weak Ferromagnetic YCrO3,"We carried out temperature and field dependent magnetic measurements to
understand the evolution of magnetic non-collinearity near antiferromagnetic
phase in conjunction with the evolution of magnetic entropy near phase
transition. We observed the maximum change in entropy just before magnetic
ordering of Cr3+ in YCrO3 with the maximum change in magnetic entropy of -0.38
Jkg-1K-1 at 8 Tesla external field. The data is linear in higher fields 3 T - 8
T , whereas it showed deviations in the lower field region. The maximum entropy
change fits well with mean field approximation at higher fields, while the
observed deviation in lower field substantiates the onset of weak
ferromagnetism in YCrO3.",1908.06454v1
2019/8/19,Magnetic Proximity Effect in a van der Waals Moiré Superlattice,"We investigate the magnetic proximity effect in van der Waals heterostructure
formed by a monolayer semiconductor stacked on a 2D ferromagnet, where the
lattice mismatch and twisting between the layers typically lead to the
formation of moir\'e pattern. We find that the magnetic proximity effect
arising from the spin dependent interlayer coupling depends sensitively on the
interlayer atomic registry. Consequently, in the moir\'e pattern, the spatial
variation of the atomic registry leads to a lateral modulation of magnetic
proximity field. Such moir\'e modulated magnetic proximity effect manifests as
a miniband spin splitting that strongly depends on the moir\'e periodicity
which can be mechanically tuned by a relative twisting and/or strain between
the layers. We also show, because of the moir\'e modulation on the interlayer
distance, a perpendicular electric field can be used to control the miniband
spin splitting. Our results suggest potential nanodevices where the moir\'e
modulated magnetic proximity effect can lead to unique spin controllability.",1908.06740v1
2019/8/21,Magnetic field induced quantum phases in a tensor network study of Kitaev magnets,"Recent discovery of the half quantized thermal Hall conductivity in
$\alpha$-RuCl$_3$, a candidate material for the Kitaev spin liquid, suggests
the presence of a highly entangled quantum state in external magnetic fields.
This field induced phase appears between the low field zig-zag magnetic order
and the high field polarized state. Motivated by this experiment, we study
possible field induced quantum phases in theoretical models of the Kitaev
magnets, using the two dimensional tensor network approach or infinite tensor
product states. We find various quantum ground states in addition to the chiral
Kitaev spin liquid occupying a small area in the phase diagram. They form a
band of emergent quantum phases in an intermediate window of external magnetic
fields, somewhat reminiscent of the experiment. We discuss the implications of
these results in view of the experiment and previous theoretical studies.",1908.07671v2
2019/9/19,Imaging three-dimensional magnetic systems with X-rays,"Recent progress in nanofabrication and additive manufacturing have
facilitated the building of nanometer-scale three-dimensional structures, that
promise to lead to an emergence of new functionalities within a number of
fields, compared to state-of-the-art two dimensional systems. In magnetism, the
move to three-dimensional systems offers the possibility for novel magnetic
properties not available in planar systems, as well as enhanced performance,
both of which are key for the development of new technological applications. In
this review paper we will focus our attention on three-dimensional magnetic
systems and how their magnetic configuration can be retrieved using X-ray
magnetic nanotomography.",1909.08956v3
2019/9/27,Orientation Dependent Interaction and Self-assembly of Cubic Magnetic Colloids in a Nematic Liquid Crystal,"Spherical microparticles dispersed in nematic liquid crystals have been
extensively investigated in the past years. Here, we report experimental
studies on the elastic deformation, colloidal interaction and self-assembly of
hematite microcubes with homeotropic surface anchoring in a nematic liquid
crystal. We demonstrate that the colloidal interaction and self-assembly of
cubic colloids are orientation dependent. In a notable departure from the
conventional microspheres, the microcubes stabilise diverse structures, such as
bent chains, branches, kinks and closed-loops. The microcubes reorient under
rotating external magnetic field, thereby experiencing an elastic torque in the
medium, which allows us to measure the magnetic moment through competition
between elastic and magnetic torques. Our findings envisage that the faceted
magnetic colloids in liquid crystals are potential for developing new
functional magnetic materials with specific morphologies.",1909.12528v1
2019/10/16,Anisotropic superexchange through nonmagnetic anions with spin-orbit coupling,"Anisotropic superexchange interaction is one of the most important
interactions in realizing exotic quantum magnetism, which is traditionally
regarded to originate from magnetic ions and has no relation with the
nonmagnetic ions. In our work, by studying a multi-orbital Hubbard model with
spin-orbit coupling on both magnetic cations and nonmagnetic anions, we
analytically demonstrate that the spin-orbit coupling on nonmagnetic anions
alone can induce antisymmetric Dzyaloshinskii-Moriya interaction, symmetric
anisotropic exchange and single ion anisotropy on the magnetic ions and thus it
actually contributes to anisotropic superexchange on an equal footing as that
of magnetic ions. Our results promise one more route to realize versatile
exotic phases in condensed matter systems, long-range orders in low dimensional
materials and switchable single molecule magnetic devices for recording and
manipulating quantum information through nonmagnetic anions.",1910.07118v3
2019/11/10,Pressure-driven switching of magnetism in layered CrCl3,"Layered transition-metal compounds with controllable magnetic behaviors
provide many fascinating opportunities for the fabrication of high-performance
magneto-electric and spintronic devices. The tuning of their electronic and
magnetic properties is usually limited to the change of layer thickness,
electrostatic doping, and the control of electric and magnetic fields. However,
pressure has been rarely exploited as a control parameter for tailoring their
magneto-electric properties. Here, we report a unique pressure-driven
isostructural phase transition in layered CrCl3 accompanied by a simultaneous
switching of magnetism from a ferromagnetic to an antiferromagnetic ordering.
Our experiments, in combination with ab initio calculations, demonstrate that
such a magnetic transformation hinders the band-gap collapse under pressure,
leading to an anomalous semiconductor-to-semiconductor transition. Our findings
not only reveal high potential of CrCl3 in electronic and spintronic
applications under ambient and extreme conditions but also establish the basis
for exploring unusual phase transitions in layered transition-metal compounds.",1911.03846v1
2019/11/18,Chemical synthesis and magnetic properties of monodisperse cobalt ferrite nanoparticles,"In this work, a successful synthesis of magnetic cobalt ferrite (CoFe2O4)
nanoparticles is presented. The synthesized CoFe2O4 nanoparticles have a
spherical shape and highly monodisperse in the selected solvent. The effect of
different reaction conditions such as temperature, reaction time and varying
capping agents on the phase and morphology is studied. Scanning transmission
electron microscopy showed that the size of these nanoparticles can be
controlled by varying reaction conditions. Both X-ray diffraction and energy
dispersive X-ray spectroscopy corroborate the formation of CoFe2O4 spinel
structure with cubic symmetry. Due to optimized reaction parameters, each
nanoparticle was shown to be a single magnetic domain with diameter ranges from
6 to 16 nm. Finally, the magnetic investigations showed that the obtained
nanoparticles are superparamagnetic with a small coercivity value of about 315
Oe and a saturation magnetization of 58 emu/g at room temperature. These
results make the cobalt ferrite nanoparticles promising for advanced magnetic
nanodevices and biomagnetic applications.",1911.07496v1
2019/12/19,Origin of Magnetic Ordering in a Structurally-Perfect Quantum Kagome Antiferromagnet,"The ground state of the simple Heisenberg nearest-neighbor quantum kagome
antiferromagnetic model is a magnetically disordered spin liquid, yet various
perturbations may lead to fundamentally different states. Here we disclose the
origin of magnetic ordering in the structurally-perfect kagome material
YCu$_3$(OH)$_6$Cl$_3$, which is free of the widespread impurity problem. {\it
Ab-initio} calculations and modeling of its magnetic susceptibility reveal
that, similar to the archetypal case of herbertsmithite, the nearest-neighbor
exchange is by far the dominant isotropic interaction. Dzyaloshinskii-Moriya
(DM) magnetic anisotropy deduced from electron spin resonance and specific-heat
measurements is, however, significantly larger than in herbertsmithite. By
enhancing spin correlations within kagome planes, this anisotropy is essential
for magnetic ordering. Our study isolates the effect of DM anisotropy from
other perturbations and unambiguously confirms the theoretical phase diagram.",1912.09047v2
2019/12/23,Successive incommensurate spin orderings and excitations in multiferroic SrMnGe2O6,"Anisotropic multiferroic properties of SrMnGe2O6 pyroxene single crystals
were systematically investigated by means of magnetization, heat capacity,
pyroelectric current measurement and elastic and inelastic neutron scattering
experiments. Single crystal neutron diffraction allows us to unambiguously
reveal the presence of two incommensurate magnetic orderings: a non-polar
amplitude-modulated collinear sinusoidal magnetic structure emerges at
TN1=4.36(2)K followed by a polar elliptical cycloidal spin structure below
TN2=4.05(2)K. Pyroelectric current measurements on single crystal confirm the
appearance of a spontaneous polarization within the (ac) plane below TN2
associated with the latter magnetic symmetry through extended
Dzyaloshinsky-Moriya mechanism. The magnetic phase diagram was calculated
considering the three isotropic exchange couplings relevant in this system. The
magnetic excitations spectra of SrMnGe2O6 measured by inelastic neutron
scattering were successfully modeled using a set of exchange interactions
consistent with this phase diagram.",1912.10935v2
2020/1/10,Unidirectional tilt of domain walls in equilibrium in biaxial stripes with Dzyaloshinskii-Moriya interaction,"The orientation of a chiral magnetic domain wall in a racetrack determines
its dynamical properties. In equilibrium, magnetic domain walls are expected to
be oriented perpendicular to the stripe axis. We demonstrate the appearance of
a unidirectional domain wall tilt in out-of-plane magnetized stripes with
biaxial anisotropy and Dzyaloshinskii--Moriya interaction (DMI). The tilt is a
result of the interplay between the in-plane easy-axis anisotropy and DMI. We
show that the additional anisotropy and DMI prefer different domain wall
structure: anisotropy links the magnetization azimuthal angle inside the domain
wall with the anisotropy direction in contrast to DMI, which prefers the
magnetization perpendicular to the domain wall plane. Their balance with the
energy gain due to domain wall extension defines the equilibrium magnetization
the domain wall tilting. We demonstrate that the Walker field and the
corresponding Walker velocity of the domain wall can be enhanced in the system
supporting tilted walls.",2001.03408v1
2020/1/17,Inducing Magnetic Phase Transitions in Monolayer CrI$_3$ via Lattice Deformations,"Atomically thin films of layered chromium triiodide (CrI$_3$) have recently
been regarded as suitable candidates to a wide spectrum of technologically
relevant applications, mainly owing to the opportunity they offer to achieve a
reversible transition between coexisting in-plane ferro- and out-of-plane
antiferro-magnetic orders. However, no routes for inducing such a transition
have been designed down to the single-layer limit. Here, we address the
magnetic response of monolayer CrI$_3$ to in-plane lattice deformations through
a combination of isotropic Heisenberg spin Hamiltonians and first-principles
calculations. Depending on the magnitude and orientation of the lattice strain
exerted, we unveil a series of direction-dependent parallel-to-antiparallel
spins crossovers, which yield the emergence of ferromagnetic, N\'eel
antiferromagnetic, zigzag and stripy antiferromagnetic ground states.
Additionally, we identify a critical point in the magnetic phase diagram
whereby the exchange couplings vanish and the magnetism is quenched. Our work
establishes guidelines for extensively tailoring the spin interactions in
monolayer CrI$_3$ via strain engineering, and further expands the magnetically
ordered phases which can be hosted in a two-dimensional crystal.",2001.06198v1
2020/1/26,Effect of metal dopant on structural and magnetic properties of ZnO nanoparticles,"Zn1-xRxO (R = Li, Mg, Cr, Mn, Fe and Cd) were obtained by using
co-precipitation synthesis technique with constant weight percent of 3% from R
ions. The phase composition, crystal structure, morphology, Density Functional
Theory (DFT), and, magnetic properties were examined to comprehend the
influence of Zn2+ partial substitution with R ions. X-ray diffraction shows
that the ZnO lattice parameters were slightly affected by R doping and the
doped sample crystallinity is enhanced. Our results show that introducing Cr,
Mn and Fe along with Mg into ZnO induces a clear magnetic moment without any
apparent distortion in the structural morphology. The spatial configuration of
dopant atoms is determined from first-principles calculations, giving a better
understanding of the position of the dopant atom responsible for the magnetism.
The magnetic moments obtained from our calculations are 3.67, 5.0, and 4.33
{\mu}B per dopant atom for Cr, Mn, and Fe, respectively, which agree with the
experimental values. While Cr and Fe tend to form clusters, Mn has more
propensity to remain evenly distributed within the system, avoiding
cluster-derived magnetism.",2001.09489v3
2020/2/6,Domain structure dynamics in the ferromagnetic Kagome-lattice Weyl semimetal Co$_3$Sn$_2$S$_2$,"Co$_3$Sn$_2$S$_2$, a Weyl semimetal that consists of layers of Kagome
lattices, transitions from a high-temperature paramagnetic phase to a
low-temperature ferromagnetic phase below 177 K. The phase transition occurs
through an intermediate non-trivial magnetic phase, the so-called ""A""-phase
just below the Curie temperature. The ""A""-phase was earlier linked with a
competing anti-ferromagnetic phase, a spin-glass phase and certain indirect
measurements indicated the possibility of magnetic Skyrmions in this phase. We
have imaged the magnetic domain structure in a single crystal of
Co$_3$Sn$_2$S$_2$ at different temperatures, magnetic fields and field-angles
by magnetic force microscopy. At low temperatures, we observed stripe domains
indicating presence of uniaxial anisotropy. Above 130 K, the domain walls
become mobile and they tend to align relatively easily when the magnetic field
is increased along the $c$-axis than in the $a-b$ plane. Our detailed study of
field-dependent domain dynamics reveal that the anomalous nature of the phase
transition just below $T_c$ is dominantly governed by domain wall motion.",2002.02494v1
2020/2/13,Development of the magnetism in the solid solution of the candidate Weyl semimetals Ce$_x$Pr$_{1-x}$AlGe,"We investigate the macroscopic and microscopic physical properties of the
solid solution of Ce$_{1-x}$Pr$_{x}$AlGe. The series tunes from CeAlGe with its
multi-$\vec{k}$ structure and a major Moment in the ab-plane, to PrAlGe with an
easy-c-axis ferromagnetic ground state co-existing with a low density of
nanoscale textured magnetic Domain walls. Using AC-, DC-susceptiblity,
resistivity, specific heat, muon spin relaxation/rotation and neutron
scattering we analyze the magnetic ground state of the series. We provide
further evidence supporting our previous claim for spin-glass like properties
in pure PrAlGe. With introduction of Pr to CeAlGe the finite magnetic field
required to stabilize the topological multi-$\vec{k}$ magnetic phase for $x=0$
becomes suppressed. The crossover between the two end-member ground states
occurs in the vicinity of $x=0.3$, a region where we further anticipate the
field-induced topological magnetic phase for $x < 0.3$ to become the zero field
ground state.",2002.05745v1
2020/2/19,Ground State Phase Diagrams and Magnetic Properties of the Double Perovskite Pb2FeReO6,"The Half-Metallic Ferromagnetic behavior of some double perovskites attracts
much interest. In this work, we studied the magnetic behavior of the double
perovskite Pb2FeReO6. The magnetic atoms are Fe and Re and have the spins S=5/2
and {\sigma}=1, respectively. In a first step, we provide a theoretical study
of the ground state phase diagrams .In fact, we present and discuss the stable
configurations from the all 6x3=18 possible configurations. Secondly, the
magnetic properties of this compound when varying different physical parameters
is carried out. Besides, we used Monte Carlo simulations (MCS), under the
Metropolis algorithm to provide the magnetic behavior of the studied system as
a function of the temperature, the crystal field, the exchange coupling
interactions and the external magnetic field. In addition, we studied and
discussed the critical temperature of the double perovskite Pb2FeReO6. To
complete our study, we presented and analyzed the hysteresis loops for specific
values of physical parameters.",2002.08122v1
2020/2/21,Determination of spin-orbit torque efficiencies in heterostructures with in-plane magnetic anisotropy,"It has been shown that the spin Hall effect from heavy transition metals can
generate sufficient spin-orbit torque and further produce current-induced
magnetization switching in the adjacent ferromagnetic layer. However, if the
ferromagnetic layer has in-plane magnetic anisotropy, probing such switching
phenomenon typically relies on tunneling magnetoresistance measurement of
nano-sized magnetic tunnel junctions, differential planar Hall voltage
measurement, or Kerr imaging approaches. We show that in magnetic
heterostructures with spin Hall metals, there exist current-induced in-plane
spin Hall effective fields and unidirectional magnetoresistance that will
modify their anisotropic magnetoresistance behavior. We also demonstrate that
by analyzing the response of anisotropic magnetoresistance under such
influences, one can directly and electrically probe magnetization switching
driven by the spin-orbit torque, even in micron-sized devices. This pump-probe
method allows for efficient and direct determination of key parameters from
spin-orbit torque switching events without lengthy device fabrication
processes.",2002.09104v1
2020/3/1,Magnetic Properties of an Effective Spin-$\frac{1}{2}$ Triangular-Lattice Compound LiYbS$_2$,"Here, we report the synthesis and magnetic properties of a Yb-based
triangular-lattice compound LiYbS$_2$. At low temperatures, it features an
effective spin-$\frac{1}{2}$ state due to the combined effect of crystal
electric field and spin orbit coupling. Magnetic susceptibility measurements
and $^7$Li nuclear magnetic resonance experiments reveal the absence of
magnetic long range ordering down to 2~K, which suggests a possible quantum
spin liquid ground state. A dominant antiferromagnetic nearest neighbour
exchange interaction $J/k_{\rm B}\simeq$ 5.3~K could be extracted form the
magnetic susceptibility. The NMR linewidth analysis yields the coupling
constant between the Li nuclei and Yb$^{3+}$ ions which was found to be purely
dipolar in nature.",2003.00566v1
2020/3/4,Tailoring the opto-electronic response of graphene nanoflakes by size and shape optimization,"The long spin-diffusion length, spin-lifetimes and excellent optical
absorption coefficient of graphene provide an excellent platform for building
opto-electronic devices as well as spin-based logic in a nanometer regime. In
this study, by employing density functional theory and its time-dependent
version, we provide a detailed analysis of how the size and shape of graphene
nanoflakes can be used to alter their magnetic structure and optical
properties. As the edges of zigzag graphene nanoribbons are known to align
anti-ferromagnetically and armchair nanoribbons are typically non-magnetic, a
combination of both in a nanoflake geometry can be used to optimize the
ground-state magnetic structure and tailor the exchange coupling decisive for
ferro- or anti-ferromagnetic edge magnetism, thereby offering the possibility
to optimize the external fields needed to switch magnetic ordering. Most
importantly, we show that the magnetic state alters the optical response of the
flake leading to the possibility of opto-spintronic applications.",2003.02010v1
2020/3/5,Reexaming the ground state and magnetic properties of curium dioxide,"The ground state electronic structure and magnetic behaviors of curium
dioxide (CmO$_{2}$) are controversial. In general, the formal valence of Cm
ions in CmO$_{2}$ should be tetravalent. It implies a $5f^{6.0}$ electronic
configuration and a non-magnetic ground state. However, it is in sharp contrast
with the large magnetic moment measured by painstaking experiments. In order to
clarify this contradiction, we tried to study the ground state electronic
structure of CmO$_{2}$ by means of a combination of density functional theory
and dynamical mean-field theory. We find that CmO$_{2}$ is a wide-gap charge
transfer insulator with strong 5$f$ valence state fluctuation. It belongs to a
mixed-valence compound indeed. The predominant electronic configurations for Cm
ions are $5f^{6.0}$ and $5f^{7.0}$. The resulting magnetic moment agrees quite
well with the experimental value. Therefore, the magnetic puzzle in CmO$_{2}$
can be appropriately explained by the mixed-valence scenario.",2003.02716v2
2020/3/6,Frustrated Magnetism in Triangular Lattice TlYbS$_2$ Crystals Grown via Molten Flux,"The triangular lattice compound TlYbS$_2$ was prepared as large single
crystals via a molten flux growth technique using sodium chloride. Anisotropic
magnetic susceptibility measurements down to 0.4 K indicate a complete absence
of long-range magnetic order. Despite this lack of long-range order,
short-range antiferromagnetic interactions are evidenced through broad
transitions, suggesting frustrated behavior. Variable magnetic field
measurements reveal metamagnetic behavior at temperatures less than 2 K.
Complex low temperature field-tunable magnetic behavior, in addition to no
observable long-range order down to 0.4 K, suggest that TlYbS$_2$ is a
frustrated magnet and a possible quantum spin liquid candidate.",2003.03321v1
2020/2/14,Origins of Slow Magnetic Relaxation in Single-Molecule Magnets,"Exponential and power law temperature dependences are widely used to fit
experimental data of magnetic relaxation time in single molecular magnets. We
derived a theory to show how these rules arise from the underling relaxation
mechanisms and to clarify the conditions for their occurrence. The theory
solves the puzzle of lower-than-expected Orbach barriers found in recent
experiments, and elucidates it as a result of the Raman process in disguise.
Our results highlight the importance of reducing the rate of direct tunneling
between the ground state doublet so as to achieve long time coherence in
magnetic molecules. To this end, large spin and small transverse magnetic
anisotropy can reduce magnitude of the transition operator, and rigid ligands
may weaken the spin-phonon coupling in that they raise the energy of
vibrational modes and better screen the acoustic phonons.",2003.13392v2
2020/3/31,Spin-torque switching mechanisms of perpendicular magnetic tunnel junctions nanopillars,"Understanding the magnetization dynamics induced by spin transfer torques in
perpendicularly magnetized magnetic tunnel junction nanopillars and its
dependence on material parameters is critical to optimizing device performance.
Here we present a micromagnetic study of spin-torque switching in a disk-shaped
element as a function of the free layer's exchange constant and disk diameter.
The switching is shown to generally occur by 1) growth of the magnetization
precession amplitude in the element center; 2) an instability in which the
reversing region moves to the disk edge, forming a magnetic domain wall; and 3)
the motion of the domain wall across the element. For large diameters and small
exchange, step 1 leads to a droplet with a fully reversed core that experiences
a drift instability (step 2). While in the opposite case (small diameters and
large exchange), the central region of the disk is not fully reversed before
step 2 occurs. The origin of the micromagnetic structure is shown to be the
disk's non-uniform demagnetization field. Faster, more coherence and energy
efficient switching occur with larger exchange and smaller disk diameters,
showing routes to increase device performance.",2003.13875v1
2020/4/9,Magnetic field-dependent resistance crossover and logarithmic to non-saturating magnetoresistance in topological insulator Bi$_2$Te$_3$,"We report a metal-insulator like transition in single crystalline 3D
topological insulator Bi2Te3 at a temperature of 230K in presence of an
external magnetic field applied normal to the surface. This transition becomes
more prominent at larger magnetic field strength with the residual resistance
value increasing linearly with the magnetic field. At low temperature, the
magnetic field dependence of the magnetoresistance shows a transition from
logarithmic to linear behavior and the onset magnetic field value for this
transition decreases with increasing temperature. The logarithmic
magnetoresistance indicates the weak anti-localization of the surface Dirac
electrons while the high temperature behavior originates from the bulk carriers
due to intrinsic impurities. At even higher temperatures beyond~230 K, a
completely classical Lorentz model type quadratic behavior of the
magnetoresistance is observed. We also show that the experimentally observed
anomalies at ~230K in the magneto-transport properties do not originate from
any stacking fault in Bi2Te3.",2004.04375v2
2020/4/9,Hysteresis-free magnetization reversal of exchange-coupled bilayers with finite magnetic anisotropy,"Exchange-coupled structures consisting of ferromagnetic and ferrimagnetic
layers become technologically more and more important. We show experimentally
the occurrence of completely reversible, hysteresis-free minor loops of [Co(0.2
nm)/Ni(0.4 nm)/Pt(0.6 nm)]$_N$ multilayers exchange-coupled to a 20 nm thick
ferrimagnetic Tb$_{28}$Co$_{14}$Fe$_{58}$ layer, acting as hard magnetic
pinning layer. Furthermore, we present detailed theoretical investigations by
means of micromagnetic simulations and most important a purely analytical
derivation for the condition of the occurrence of full reversibility in
magnetization reversal. Hysteresis-free loops always occur if a domain wall is
formed during the reversal of the ferromagnetic layer and generates an
intrinsic hard-axis bias field that overcomes the magnetic anisotropy field of
the ferromagnetic layer. The derived condition further reveals that the
magnetic anisotropy and the bulk exchange of both layers, as well as the
exchange coupling strength and the thickness of the ferromagnetic layer play an
important role for its reversibility.",2004.04419v1
2020/4/14,High-intensity pulsed ion beam treatment of amorphous iron-based metal alloy,"Abstract The results of intense pulsed ion beam (IPIB) treatment of the soft
magnetic amorphous alloy of a FINEMET-type are presented. Foil produced from
the alloy was irradiated with short (about 100 ns) pulses of carbon ions and
protons with energy of up to 300 keV and an energy density of up to 7 J/cm2.
X-ray diffraction, M\""ossbauer spectroscopy and magnetic measurements were used
to investigate structural and magnetic properties of irradiated foils. It is
shown that the foil remains intact after the treatment, and the crystal
structure still amorphous. Spontaneous magnetization vector is found to lie
almost along perpendicular to the foil plane after irradiation, whereas for the
initial amorphous foil it belongs to the plane. The magnetic properties of the
foil undergo changes: the coercive force decreases, the saturation induction
increases slightly, and the magnetization curve has shallower slope.",2004.06410v1
2020/5/4,Second-harmonic voltage responce for the magnetic Weyl semimetal Co$_3$Sn$_2$S$_2$,"We experimentally investigate longitudinal and transverse second-harmonic
voltage response to ac electrical current for a magnetic Weyl semimetal
Co$_3$Sn$_2$S$_2$. In contrast to the previously observed Berry-curvature
induced non-linear Hall effect for non-magnetic Weyl and Dirac semimetals, the
second-harmonic transverse voltage demonstrates sophisticated interplay of
different effects for Co$_3$Sn$_2$S$_2$. In high magnetic fields, it is of
Seebeck-like square-B law, while the low-field behavior is found to be linear
and sensitive to the direction of sample magnetization. The latter can be
expected both for the non-linear Hall effect and for the surface state
contribution to the Seebeck effect in Weyl semimetals. Thus, thermoelectric
effects are significant in Co$_3$Sn$_2$S$_2$, unlike non-magnetic Weyl and
Dirac materials.",2005.01298v1
2020/5/12,Impact of the lattice on magnetic properties and possible spin nematicity in the S=1 triangular antiferromagnet NiGa$_2$S$_4$,"NiGa$_2$S$_4$ is a triangular lattice S=1 system with strong
two-dimensionality of the lattice, actively discussed as a candidate to host
spin-nematic order brought about by strong quadrupole coupling. Using Raman
scattering spectroscopy we identify a phonon of E$_g$ symmetry which can
modulate magnetic exchange $J_1$ and produce quadrupole coupling. Additionally,
our Raman scattering results demonstrate a loss of local inversion symmetry on
cooling, which we associate with sulfur vacancies. This will lead to disordered
Dzyaloshinskii-Moriya interactions, which can prevent long range magnetic
order. Using magnetic Raman scattering response we identify 160~K as a
temperature of an upturn of magnetic correlations. The temperature below 160~K,
but above 50~K where antiferromagnetic magnetic start to increase, is a
candidate for spin-nematic regime.",2005.06073v1
2020/5/13,Spin current injection at magnetic insulator/superconductor interfaces,"Opposite to the common idea of a magnetic order requirement to obtain spin
current propagation, materials with no magnetic ordering have also been
revealed to be efficient spin conductors. In this work, we investigate the spin
current injection at the interface between a magnetic insulator and a
superconductor. We are mainly interested in the paramagnetic
insulator/superconductor interface however, our model also describes the
ferromagnetic phase. We used the Schwinger bosonic formalism to describe the
magnetic insulator and standard BCS theory was applied to treat the
superconductor layer. In the normal-metal limit, our results are in agreement
with the expected ones. For example, we found the correct spin current behavior
$I\approx T^{3/2}$ at low temperature. In addition, our model shows a
pronounced peak in the spin current injection at temperatures close to the
superconductor transition temperature due to the superconducting quasiparticle
coherence. The role of magnetic fields in the spin current injection is also
investigated.",2005.06435v3
2020/5/19,Magnetic hard-direction ordering in anisotropic Kondo systems,"We present a generic mechanism that explains why many Kondo materials show
magnetic ordering along directions that are not favoured by the crystal-field
anisotropy. Using a renormalization-group (RG) analysis of single impurity
Kondo models with single-ion anisotropy, we demonstrate that strong
fluctuations above the Kondo temperature drive a moment re-orientation over a
wide range of parameters, e.g. for different spin values $S$ and number of
Kondo channels $N$. In tetragonal systems this can happen for both easy-plane
or easy axis anisotropy. The characteristic crossing of magnetic
susceptibilities is not an artefact of the weak-coupling RG treatment but can
be reproduced in brute-force perturbation theory. Employing numerical
renormalization group (NRG), we show that for an under-screened moment ($S=1$,
$N=1$) with easy-plane anisotropy, a crossing of magnetic susceptibilities can
also occur in the strong-coupling regime (below the Kondo temperature). This
suggests that collective magnetic ordering of such under-screened moments would
develop along the magnetic hard axis.",2005.09533v3
2020/5/19,Nonconventional magnetic phenomena in neodymium thin film,"Neodymium is a remarkable active component in numerous magnetic alloys that
are used in various applications. However, the application of bare neodymium
thin film is limited due to the lack of information about its electrical and
magnetic properties. We report synergistic study of Nd thin film using
experimental and theoretical techniques of polarized neutron reflectometry,
magnetoresistance measurement and density functional theory. Unlike bulk Nd,
thin film specimen is a very poor electrical conductor. Also, as grown thin
film on silicon substrate does not exhibit any magnetism in zero field.
However, moderate inplane field application of $H$ = 1.2 T tends to induce weak
magnetism in the system at low temperature of $T$ $<$ 18 K, which coincides
with an unusual cross-over behavior in magnetoresistance. The study provides
important insight in the physical characteristics of Nd thin film that are
atypical for a magnetic system.",2005.09729v1
2020/5/21,Cooperative Ru(4d)-Ho(4f) magnetic orderings and phase coexistence in the 6H-perovskite multiferroic Ba3HoRu2O9,"We report cooperative magnetic orderings in a 6H-perovskite multiferroic
system, Ba3HoRu2O9, via comprehensive neutron powder diffraction measurements.
This system undergoes long-range antiferromagnetic ordering at TN1 ~ 50 K with
a propagation wave vector of K1 = (0.5 0 0), a transition temperature much
higher than the previously reported one at ~10 K (TN2). Both Ru and Ho-moments
order simultaneously below TN1, followed by spin-reorientations at lower
temperatures, demonstrating strong Ru(4d)-Ho(4f) magnetic correlation. Below
TN1 another magnetic phase with a propagation wave vector K2 = (0.25 0.25 0)
emerges and coexists with the one associated with K1, which is rarely observed
and suggests complex magnetism due to phase competition in the magnetic ground
state. We argue that the exchange-striction arising from the up-up-down-down
spin structure associated with K2-wave vector below TN2 may be responsible for
the small ferroelectric polarization reported previously in this compound.",2005.10861v2
2020/5/22,Zero-point quantum swing of magnetic couples,"Quantum fluctuations are ubiquitous in physics. Ranging from conventional
examples like the harmonic oscillator to intricate theories on the origin of
the universe, they alter virtually all aspects of matter -- including
superconductivity, phase transitions and nanoscale processes. As a rule of
thumb, the smaller the object, the larger their impact. This poses a serious
challenge to modern nanotechnology, which aims total control via atom-by-atom
engineered devices. In magnetic nanostructures, high stability of the magnetic
signal is crucial when targeting realistic applications in information
technology, e.g. miniaturized bits. Here, we demonstrate that zero-point
spin-fluctuations are paramount in determining the fundamental magnetic
exchange interactions that dictate the nature and stability of the magnetic
state. Hinging on the fluctuation-dissipation theorem, we establish that
quantum fluctuations correctly account for the large overestimation of the
interactions as obtained from conventional static first-principles frameworks,
filling in a crucial gap between theory and experiment [1,2]. Our analysis
further reveals that zero-point spin-fluctuations tend to promote the
non-collinearity and stability of chiral magnetic textures such as skyrmions --
a counter-intuitive quantum effect that inspires practical guidelines for
designing disruptive nanodevices.",2005.11206v1
2020/5/28,Nonequilibrium quasistationary spin disordered state in the Kitaev-Heisenberg magnet $α$-RuCl$_3$,"Excitation by light pulses enables the manipulation of phases of quantum
condensed matter. Here, we photoexcite high-energy holon-doublon pairs as a way
to alter the magnetic free energy landscape of the Kitaev-Heisenberg magnet
$\alpha$-RuCl$_3$, with the aim to dynamically stabilize a proximate spin
liquid phase. The holon-doublon pair recombination through multimagnon emission
is tracked through the time-evolution of the magnetic linear dichroism
originating from the competing zigzag spin ordered ground state. A small
holon-doublon density suffices to reach a spin disordered state. The phase
transition is described within a dynamic Ginzburg-Landau framework,
corroborating the quasistationary nature of the transient spin disordered
phase. Our work provides insight into the coupling between the electronic and
magnetic degrees of freedom in $\alpha$-RuCl$_3$ and suggests a new route to
reach a proximate spin liquid phase in Kitaev-Heisenberg magnets.",2005.14189v1
2020/5/29,Plasma-induced magnetic patterning of FePd thin films without and with exchange bias,"We demonstrate control of magnetic domain structures in continuous FePd thin
films by patterning their surfaces with plasma treatment. The Fe-oxide layer
formed on the surface upon ambient exposure of the FePd alloy thin film grown
on an Al$_2$O$_3$(0001) substrate was patterned into microstructures by e-beam
lithography followed by O$_2$- or Ar-plasma treatment. Microscopic pinning of
magnetic domain walls in the thin films is then observed by magneto-optic Kerr
effect microscopy, with the magnetic field needed to reverse the magnetization
of the plasma-treated areas being larger than that for the untreated areas. An
intriguing competition between the uniaxial anisotropy and the exchange bias is
also observed in the system. This study demonstrates that patterning of the
film surface with plasma treatment can be an easy and efficient method for
sophisticated engineering of magnetic structures in thin films, and therefore
has potential application in developing future data-storage and spintronic
devices.",2005.14497v1
2020/6/11,"Thermal Expansion and Volume Magnetostriction in Breathing Pyrochlore Magnets LiACr$_4$X$_8$ (A = Ga, In, X = O, S)","We report thermal expansion and magnetostriction in breathing pyrochlore
magnets LiACr$_4$X$_8$ (A = Ga, In, X = O, S) measured by a dilatometric method
on sintered samples. All four of these compounds showed a large volume
contraction associated with antiferromagnetic order with decreasing
temperature. Above the Ne\'el temperature, LiGaCr4S8 showed negative thermal
expansion, LiInCr4O8 showed positive thermal expansion with concave-downward
temperature dependence, and LiInCr4S8 showed positive forced volume
magnetostriction. All these phenomena are likely caused by the complex
structure-magnetism correlation within the breathing pyrochlore structure with
J and J'. These results suggested that breathing pyrochlore magnets are
promising for the realization of various volumetric phenomena related to their
magnetism not only in the magnetically-ordered phase but also in the
paramagnetic phase.",2006.06187v1
2020/6/13,Data-driven determination of the spin Hamiltonian parameters and their uncertainties: The case of the zigzag-chain compound KCu$_4$P$_3$O$_{12}$,"We propose a data-driven technique to estimate the spin Hamiltonian,
including uncertainty, from multiple physical quantities. Using our technique,
an effective model of KCu$_4$P$_3$O$_{12}$ is determined from the
experimentally observed magnetic susceptibility and magnetization curves with
various temperatures under high magnetic fields. An effective model, which is
the quantum Heisenberg model on a zigzag chain with eight spins having $J_1=
-8.54 \pm 0.51 \{\rm meV}$, $J_2 = -2.67 \pm 1.13 \{\rm meV}$, $J_3 = -3.90 \pm
0.15 \{\rm meV}$, and $J_4 = 6.24 \pm 0.95 \{\rm meV}$, describes these
measured results well. These uncertainties are successfully determined by the
noise estimation. The relations among the estimated magnetic interactions or
physical quantities are also discussed. The obtained effective model is useful
to predict hard-to-measure properties such as spin gap, spin configuration at
the ground state, magnetic specific heat, and magnetic entropy.",2006.07523v1
2020/7/8,Magnetization around mix jets entering inertial confinement fusion fuel,"Engineering features are known to cause jets of ablator material to enter the
fuel hot-spot in inertial confinement fusion implosions. The Biermann battery
mechanism wraps them in self-generated magnetic field. We show that higher-Z
jets have an additional thermoelectric magnetic source term that is not present
for hydrogen jets, verified here through a kinetic simulation. It has similar
magnitude to the Biermann term. We then include this in an extended
magneto-hydrodynamics approach to post-process an xRAGE radiation-hydrodynamic
implosion simulation. The simulation includes an accurate model for the capsule
fill tube, producing a dense carbon jet that becomes wrapped in a 4000T
magnetic field. A simple spherical carbon mix model shows that this insulates
the electron heat conduction enough to cause contraction of the jet to an
optically thick equilibrium. The denser magnetized jet hydrodynamics could
change its core penetration and therefore the final mix mass, which is known to
be well correlated with fusion yield degradation. Fully exploring this will
require self-consistent magneto-hydrodynamic simulations. Experimental
signatures of this self-magnetization may emerge in the high energy neutron
spectrum.",2007.04293v1
2020/8/4,Two-step magnetic ordering into a canted state in ferrimagnetic monoclinic Mn$_3$As$_2$,"We report the magnetic structure of room-temperature-stable, monoclinic
Mn$_3$As$_2$ at 3 K and 250 K using neutron powder diffraction measurements.
From magnetometry data, the Curie temperature of Mn$_3$As$_2$ was confirmed to
be around 270 K. Calorimetry analysis showed the presence of another transition
at 225 K. At 270 K, Mn$_3$As$_2$ undergoes a $k = 0$ ferrimagnetic ordering in
the magnetic space group $C2/m$ (#12.58) with Mn moments pointing along $b$.
Below 225 K, there is a canting of Mn moments in the $ac$ plane which produces
a multi-$k$ non-collinear magnetic structure in space group $C2/c$ (#15.85).
The components of Mn moments along $b$ follow $k=0$ ordering and the components
along $a$ and $c$ have $k = [0 0 \frac{1}{2}]$ propagation vector. The change
in the magnetic ground state with temperature provides a deeper insight into
the factors that govern magnetic ordering in Mn-As compounds.",2008.01776v2
2020/9/17,Magnetic and electronic properties of a topological nodal line semimetal candidate: HoSbTe,"We report the experimental and theoretical studies of a magnetic topological
nodal line semimetal candidate HoSbTe. Single crystals of HoSbTe are grown from
Sb flux, crystallizing in a tetragonal layered structure (space group: P4/nmm,
no.129), in which the Ho-Te bilayer is separated by the square-net Sb layer.
The magnetization and specific heat present distinct anomalies at 4 K related
to an antiferromagnetic (AFM) phase transition. Meanwhile, with applying
magnetic field perpendicular and parallel to the crystallographic c axis, an
obvious magnetic anisotropy is observed. Electrical resistivity undergoes a
bad-metal-like state below 200 K and reveals a plateau at about 8 K followed by
a drop due to the AFM transition. In addition, with the first-principle
calculations of band structure, we find that HoSbTe is a topological nodal line
semimetal or a weak topological insulator with or without taking the spin-orbit
coupling into account, providing a platform to investigate the interplay
between magnetic and topological fermionic properties.",2009.08036v1
2020/9/25,Low Energy Magneto-optics of Tb$_{2}$Ti$_{2}$O$_{7}$ in [111] Magnetic Field,"The pyrochlore magnet Tb$_{2}$Ti$_{2}$O$_{7}$ shows a lack of magnetic order
to low temperatures and is considered to be a quantum spin liquid candidate. We
perform time-domain THz spectroscopy on high quality Tb$_{2}$Ti$_{2}$O$_{7}$
crystal and study the low energy excitations as a function of [111] magnetic
field with high energy resolution. The low energy crystal field excitations
change their energies anomalously under magnetic field. Despite several sharp
field dependent changes, we show that the material's spectrum can be described
not by a phase transitions, but by field dependent hybridization between the
low energy crystal field levels. We highlight the strong coupling between spin
and lattice degrees of freedom in Tb$_{2}$Ti$_{2}$O$_{7}$ as evidenced by the
magnetic field tunable crystal field environment. Calculations based on single
ion physics with field induced symmetry reduction of the crystal field
environment can reproduce our data.",2009.12354v1
2020/11/2,Magnetic detwinning and biquadratic magnetic interaction in EuFe2As2 revealed by 153Eu NMR,"In the nematic state of iron-based superconductors, twin formation often
obscures the intrinsic, anisotropic, in-plane physical properties.Relatively
high in-plane external magnetic fields $H_{\rm ext}$ greater than the typical
lab-scale magnetic fields 10--15 T are usually required to completely detwin a
sample. However, recently a very small in-plane $H_{\rm ext} \sim$ 0.1 T was
found to be sufficient for detwinning the nematic domains in EuFe$_2$As$_2$. To
explain this behavior, a microscopic theory based on biquadratic magnetic
interactions between the Eu and Fe spins has been proposed. Here, using
$^{153}$Eu nuclear magnetic resonance (NMR) measurements below the Eu$^{2+}$
ordering temperature, we show experimental evidence of the detwinning under
small in-plane $H_{\rm ext}$. Our NMR study also reveals the evolution of the
angles between the Eu and Fe spins during the detwinning process, which
provides the first experimental evidence for the existence of biquadratic
coupling in the system.",2011.01145v1
2020/11/3,Gravito-magnetic resonance in the field of a gravitational wave,"Using the construction of the Fermi frame, the field of a gravitational wave
can be described in terms of gravito-electromagnetic fields that are transverse
to the propagation direction and orthogonal to each other. In particular, the
gravito-magnetic field acts on spinning particles and we show that, due to the
action of the gravitational wave field, a new phenomenon, that we call
gravito-magnetic resonance, may appear. We give both a classical and a quantum
description of this phenomenon and suggest that it can be used as the basis for
a new type of gravitational wave detectors. Our results highlight the
effectiveness of collective spin excitations, e.g. spin waves in magnetized
materials, in detecting high frequency gravitational waves. Here we suggest
that, when gravitational waves induce a precession of the electron spin, power
is released in the ferromagnetic resonant mode endowed with quadrupole symmetry
of a magnetized sphere. This offers a possible path to the detection of the
gravito-magnetic effects of a gravitational wave.",2011.01663v1
2020/11/16,Topologically stable bimerons and skyrmions in vanadium dichalcogenide Janus monolayers,"We investigate the magnetic phase diagram of 1T-vanadium dichalcogenide
monolayers in Janus configuration (VSeTe, VSSe, and VSTe) from first
principles. The magnetic exchange, magnetocrystalline anisotropy and
Dzyaloshinskii-Moriya interaction (DMI) are computed using density functional
theory calculations, while the temperature- and field-dependent magnetic phase
diagram is simulated using large-scale atomistic spin modeling in the presence
of thermal fluctuations. The boundaries between magnetic ordered phases and
paramagnetic phases are determined by cross-analyzing the average topological
charge with the magnetic susceptibility and its derivatives. We find that in
such Janus monolayers, DMI is large enough to stabilize non-trivial chiral
textures. In VSeTe monolayer, an asymmetrical bimeron lattice state is
stabilized for in-plane field configuration whereas skyrmion lattice is formed
for out-of-plane field configuration. In VSSe monolayer, a skyrmion lattice is
stabilized for out-of-plane field configuration. This study demonstrates that
non-centrosymmetric van der Waals magnetic monolayers can support topological
textures close to room temperature.",2011.07813v1
2020/11/17,Single-shot dynamics of spin-orbit torque and spin transfer torque switching in three-terminal magnetic tunnel junctions,"Current-induced spin-transfer torques (STT) and spin-orbit torques (SOT)
enable the electrical switching of magnetic tunnel junctions (MTJs) in
nonvolatile magnetic random access memories. In order to develop faster memory
devices, an improvement of the timescales underlying the current driven
magnetization dynamics is required. Here we report all-electrical time-resolved
measurements of magnetization reversal driven by SOT in a three-terminal MTJ
device. Single-shot measurements of the MTJ resistance during current injection
reveal that SOT switching involves a stochastic two-step process consisting of
a domain nucleation time and propagation time, which have different genesis,
timescales, and statistical distributions compared to STT switching. We further
show that the combination of SOT, STT, and voltage control of magnetic
anisotropy (VCMA) leads to reproducible sub-ns switching with a spread of the
cumulative switching time smaller than 0.2 ns. Our measurements unravel the
combined impact of SOT, STT, and VCMA in determining the switching speed and
efficiency of MTJ devices.",2011.08709v1
2020/11/22,Built-in Electric-Field-Control of Magnetic Coupling in van der Waals semiconductors,"Electrical control of magnetism in a two-dimensional (2D) semiconductor is of
great interest for emerging nanoscale low-dissipation spintronic devices. Here,
we propose a general approach of tuning magnetic coupling and anisotropy of a
van der Waals (vdW) 2D magnetic semiconductor via a built-in electric field
generated by the adsorption of superatomic ions. Using first-principles
calculations, we predict a significant enhancement of ferromagnetic (FM)
coupling and a great change of magnetic anisotropy in 2D semiconductors when
they are sandwiched between superatomic cations and anions. The magnetic
coupling is directly affected by the built-in electric field, which lifts the
energy levels of mediated ligands' orbitals and enhances the super-exchange
interactions. These findings will be of interest for ionic gating controlled
ferromagnets and magnetoelectronics based on vdW 2D semiconductors.",2011.10923v1
2020/12/11,Slow Spin Relaxation in Single Endohedral Fullerene Molecules,"Well-protected magnetization, tunable quantum states and long coherence time
are desired for the use of magnetic molecules in spintronics and quantum
information technologies. In this work, endohedral fullerene molecules M@C28
with different transition metal cores were explored through systematic
first-principles calculations and spin dynamics analyses. Many of them have
stable magnetization, giant magnetic anisotropy energy and bias-tunable
structure. In particular, some of them may have coherence time up to several
milliseconds for their quantum spin states at high temperature (~10K) after
full consideration of spin-vibration couplings. These results suggest that
these M@C28 provide a rich pool for the development of single-molecule magnets,
magnetic molecular junctions, and molecular qubits.",2012.06141v2
2020/12/18,Breaking Space Inversion-Symmetry to Obtain Asymmetric Spin-Wave Excitation in Systems with Nonuniform Magnetic Exchange,"We report on the consequences of non-uniform exchange in magnetic systems.
The quantum mechanical exchange interaction between spins is responsible for
the phenomenon of magnetic order, and is generally considered to be uniform
across bulk magnetic systems. Partly inspired by the Dzyaloshinskii-Moriya
interaction--also known as antisymmetric exchange--we use a linearly varying
exchange interaction along a magnetic strip as a route to spatial inversion
symmetry-breaking. We find that, in addition to asymmetric modes and
localization, spatially-varying exchange can be used to design nonreciprocal
magnetic signal excitation at frequencies that are tunable. Moreover, our work
predicts nonreciprocity to occur across a vast range of frequencies up to
hundreds of GHz. Such spin wave engineering is a key area of ongoing research
in the fields of magnonics and spintronics, which are expected to enable the
next generation of communication technology. Analogous nonreciprocity is
expected to occur in other wave systems with gradient properties.",2012.10381v2
2021/2/4,Classical Spin Liquid State in the $S=\frac{5}{2}$ Heisenberg Kagomé Antiferromagnet Li$_9$Fe$_3$(P$_2$O$_7$)$_3$(PO$_4$)$_2$,"We investigate the low temperature magnetic properties of a $S=\frac{5}{2}$
Heisenberg kagom\'e antiferromagnet, the layered monodiphosphate
Li$_9$Fe$_3$(P$_2$O$_7$)$_3$(PO$_4$)$_2$, using magnetization measurements and
$^{31}$P nuclear magnetic resonance. An antiferromagnetic-type order sets in at
$T_{\rm N}=1.3$ K and a characteristic magnetization plateau is observed at 1/3
of the saturation magnetization below $T^* \sim 5$ K. A moderate $^{31}$P NMR
line broadening reveals the development of anisotropic short-range correlations
within the plateau phase concomitantly with a gapless spin-lattice relaxation
time $T_1 \sim k_B T / \hbar S$, which both point to the presence of a
semiclassical nematic spin liquid state predicted for the Heisenberg kagom\'e
antiferromagnetic model or to the persistence of the zero-energy modes of the
kagome lattice under large magnetic fields.",2102.02882v2
2021/2/5,Symmetry-Driven Spin-Wave Gap Modulation in Nanolayered SrRuO3/SrTiO3 Heterostructures: Implications for Spintronic Applications,"A strong correlation between magnetic interaction and topological symmetries
leads to unconventional magneto-transport behavior. Weyl fermions induce
topologically protected spin-momentum locking, which is closely related to
spin-wave gap formation in magnetic crystals. Ferromagnetic SrRuO3, regarded as
a strong candidate for Weyl semimetal, inherently possesses a nonzero spin-wave
gap owing to its strong magnetic anisotropy. In this paper, we propose a method
to control the spin-wave dynamics by nanolayer designing of the SrRuO3/SrTiO3
superlattices. In particular, the six-unit-cell-thick SrRuO3 layers within the
superlattices undergo a phase transition in crystalline symmetry from
orthorhombic to tetragonal, as the thickness of the SrTiO3 layers is modulated
with atomic-scale precision. Consequently, the magnetic anisotropy, anomalous
Hall conductivity, and spin-wave gap could be systematically manipulated. Such
customization of magnetic anisotropy via nanoscale heterostructuring offers a
novel control knob to tailor the magnon excitation energy for future spintronic
applications, including magnon waveguides and filters. Our nanolayer approach
unveils the important correlation between the tunable lattice degrees of
freedom and spin dynamics in topologically non-trivial magnetic materials.",2102.03008v1
2021/2/22,Robust formation of nanoscale magnetic skyrmions in easy-plane thin film multilayers with low damping,"We experimentally demonstrate the formation of room-temperature skyrmions
with radii of about 25\,nm in easy-plane anisotropy multilayers with
interfacial Dzyaloshinskii-Moriya interaction (DMI). We detect the formation of
individual magnetic skyrmions by magnetic force microscopy and find that the
skyrmions are stable in out-of-plane fields up to about 200 mT. We determine
the interlayer exchange coupling as well as the strength of the interfacial
DMI. Additionally, we investigate the dynamic microwave spin excitations by
broadband magnetic resonance spectroscopy. From the uniform Kittel mode we
determine the magnetic anisotropy and low damping $\alpha_{\mathrm{G}} < 0.04$.
We also find clear magnetic resonance signatures in the non-uniform (skyrmion)
state. Our findings demonstrate that skyrmions in easy-plane multilayers are
promising for spin-dynamical applications.",2102.11117v1
2021/2/23,High magnetic field induced crossover from the Kondo to Fermi liquid behavior in 1$T$-VTe$_{2}$ single crystals,"The magnetic and magnetotransport properties of metallic 1$T$-VTe$_{2}$
single crystals were investigated at temperatures from 1.3 to 300 K and in
magnetic fields up to 35 T. Upon applying a high magnetic field, it is found
that the electrical resistivity displays a crossover from the logarithmic
divergence of the single-impurity Kondo effect to the Fermi liquid behavior at
low temperatures. The Brillouin scale of the negative magnetoresistivity above
the Kondo temperature $T_{\rm{K}}$ = 12 K indicates that the Kondo features
originate from intercalated V ions, with $S$ = 1/2. Both magnetic
susceptibility and Hall effect show an anomaly around $T_{\rm{K}}$. By using
the modified Hamann expression we successfully describe the
temperature-dependent resistivity under various magnetic fields, which shows
the characteristic peak below $T_{\rm{K}}$ due to the splitting of the Kondo
resonance.",2102.11444v1
2021/2/24,Koopmans' theorem as the mechanism of nearly gapless surface states in self-doped magnetic topological insulators,"The magnetization-induced gap at the surface state is widely believed as the
kernel of magnetic topological insulators (MTIs) because of its relevance to
various topological phenomena, such as the quantum anomalous Hall effect and
the axion insulator phase. However, if the magnetic gap exists in an intrinsic
MTI, such as MnBi$_{2}$Te$_{4}$, still remains elusive, with significant
discrepancies between theoretical predictions and various experimental
observations. Here, including the previously overlooked self-doping in real
MTIs, we find that in general a doped MTI prefers a ground state with a gapless
surface state. We use a simple model based on Koopmans' theorem to elucidate
the mechanism and further demonstrated it in self-doped
MnBi$_{2}$Te$_{4}$/(Bi$_{2}$Te$_{3}$)$_{n}$ family through first-principles
calculations. Our work shed light on the design principles of MTIs with
magnetic gaps by revealing the critical role of doping effects in understanding
the delicate interplay between magnetism and topology.",2102.12104v1
2021/3/6,Resolving Discrepancies in Spin-Torque Ferromagnetic Resonance Measurements: Lineshape vs. Linewidth Analyses,"When spin-orbit torques are measured using spin-torque ferromagnetic
resonance (ST-FMR), two alternative ways of analyzing the results to extract
the torque efficiencies -- lineshape analysis and analysis of the change in
linewidth versus DC current -- often give inconsistent results. We identify a
source for these inconsistencies. We show that fits of ST-FMR data to the
standard analysis framework leave significant residuals that we identify as due
to (i) current-induced excitations of a small volume of magnetic material with
magnetic damping much larger than the bulk of the magnetic layer, that we
speculate is associated with the heavy-metal/magnet interface and (ii)
oscillations of the sample magnetization at the modulation frequency due to
heating. The dependence of the residual signals on DC current can interfere
with an accurate extraction of spin-torque efficiencies by the linewidth
method. We show that the discrepancies between the two types of analysis can be
largely eliminated by extrapolating the window of magnetic fields used in the
linewidth fits to small values so as to minimize the influence of the residual
signals.",2103.04172v1
2021/3/8,Magnetic field driven novel phase transitions in EuTiO$_3$,"The influence of an external static magnetic field (up to 480 mT)on the
structural properties of EuTiO$_3$ (ETO) polycrystalline samples was examined
by powder XRD at the Elettra synchrotron facilities in the temperature range
100-300K. While the cubic to tetragonal structural phase transition temperature
in this magnetic field range remains almost unaffected, significant lattice
effects appear at two characteristic temperatures (~200K and 250K), which
becomes more pronounced at a critical threshold magnetic field. At ~200K a
change in the sign of the magnetostriction is detected attributed to a
modification of the local magnetic properties from intrinsic ferromagnetism to
intrinsic antiferromagnetism. These data are a clear indication that strong
spin-lattice interactions govern also the high temperature phase of ETO and
trigger the appearance of magnetic domain formation and novel phase transitions",2103.04742v2
2021/3/11,"Perpendicular magnetic anisotropy at Fe/Au(111) interface studied by Mössbauer, x-ray absorption, and photoemission spectroscopies","The origin of the interfacial perpendicular magnetic anisotropy (PMA) induced
in the ultrathin Fe layer on the Au(111) surface was examined using
synchrotron-radiation-based M\""{o}ssbauer spectroscopy (MS), X-ray magnetic
circular dichroism (XMCD), and angle-resolved photoemission spectroscopy
(ARPES). To probe the detailed interfacial electronic structure of orbital
hybridization between the Fe 3$d$ and Au 6$p$ bands, we detected the
interfacial proximity effect, which modulates the valence-band electronic
structure of Fe, resulting in PMA. MS and XMCD measurements were used to detect
the interfacial magnetic structure and anisotropy in orbital magnetic moments,
respectively. $In$-$situ$ ARPES also confirms the initial growth of Fe on large
spin-orbit coupled surface Shockley states under Au(111) modulated electronic
states in the vicinity of the Fermi level. This suggests that PMA in the
Fe/Au(111) interface originates from the cooperation effects among the spin,
orbital magnetic moments in Fe, and large spin-orbit coupling in Au. These
findings pave the way to develop interfacial PMA using $p$-$d$ hybridization
with a large spin-orbit interaction.",2103.06572v1
2021/3/24,Large Magnetic Moment in Flexoelectronic Silicon at Room Temperature,"Time-dependent rotational electric polarizations have been proposed to
generate temporally varying magnetic moments, for example, through a
combination of ferroelectric polarization and optical phonons. This phenomenon
has been called dynamical multiferroicity, but explicit experimental
demonstrations have been elusive to date. Here, we report the detection of a
temporal magnetic moment as high as 1.2 mu_B/atom in charge-doped thin film of
silicon under flexural strain. We demonstrate that the magnetic moment is
generated by a combination of electric polarization arising from a
flexoelectronic charge separation along the strain gradient and the deformation
potential of phonons. The effect can be controlled by adjusting the external
strain gradient, doping concentration and dopant, and can be regarded as a
dynamical multiferroic effect involving flexoelectronics polarization instead
of ferroelectricity. The discovery of a large magnetic moment in silicon may
enable the use of non-magnetic and non-ferroelectric semiconductors in various
multiferroic and spintronic applications.",2103.12907v1
2021/4/5,Competing ferromagnetic and antiferromagnetic interactions drive the magnetocaloric tunability in Gd55Co30NixAl15-x microwires,"We have employed Gd55Co30NixAl15-x (x = 10, 5 and 0) amorphous microwires as
a model system to unravel the impact of multiple magnetic interactions on the
magnetism and the magnetocaloric behavior in Gd-alloy microwire systems. Our
study shows that in addition to the RKKY ferromagnetic (FM) interaction
(Gd-Gd), antiferromagnetic (AFM) interactions (Gd-Co, Gd-Ni) coexist and
contribute to the magnetic and magnetocaloric response of the system. The
dilution effect of Al element on the FM Gd-Gd interaction is responsible for
the decrease of the Curie temperature (TC), whereas the increase of the
saturation magnetization (MS) is originated from the reduced AFM Gd-Ni
interaction. A thorough analysis of critical exponents suggests that the
presence of the AFM interactions hinders the system to exhibit a long-range FM
order below the TC. Adjusting these interactions is shown to preserve the large
refrigerant capacity (RC) while tuning the TC over a wide temperature range,
which is desirable for active magnetic refrigeration.",2104.01790v1
2021/4/11,Experimental and theoretical demonstration of negative magnetization induced by particle size reduction in nano-form Gd$_{1-x}$Ca$_x$MnO$_3$,"We report a pervasive phenomenon of gradual emergence of negative
magnetization in typical $R_{1-x}D_x$MnO$_3$ orthorhombic perovskite manganites
in nano form (with $R^{3+}$ being a trivalent high-magnetic-moment ion from the
heavier rare-earth elements Gd, Tb, Dy and $D^{2+}$ refers to divalent alkaline
elements Sr, Ca, etc.), while the bulk form manifests no negative
magnetization. Extensive magnetization studies have been carried out in
Gd$_{1-x}$Ca$_x$MnO$_3$ manganites around half doping. We demonstrate
experimentally that particle size reduction in nano-form manganites enhances
the propensity of the system to exhibit negative magnetization and provide a
theoretical explanation for the phenomenon. To test the universality of our
findings, we have extended the measurement to Dy$_{0.6}$Ca$_{0.4}$MnO$_3$ and
obtained similar results.",2104.04933v1
2021/4/12,Strongly anisotropic spin dynamics in magnetic topological insulators,"The recent discovery of magnetic topological insulators has opened new
avenues to explore exotic states of matter that can emerge from the interplay
between topological electronic states and magnetic degrees of freedom, be it
ordered or strongly fluctuating. Motivated by the effects that the dynamics of
the magnetic moments can have on the topological surface states, we investigate
the magnetic fluctuations across the
(MnBi$_{\text{2}}$Te$_{\text{4}}$)(Bi$_{\text{2}}$Te$_{\text{3}}$)$_{\text{n}}$
family. Our paramagnetic electron spin resonance experiments reveal contrasting
Mn spin dynamics in different compounds, which manifests in a strongly
anisotropic Mn spin relaxation in MnBi$_{\text{2}}$Te$_{\text{4}}$ while being
almost isotropic in MnBi$_{\text{4}}$Te$_{\text{7}}$. Our density-functional
calculations explain these striking observations in terms of the sensitivity of
the local electronic structure to the Mn spin-orientation, and indicate that
the anisotropy of the magnetic fluctuations can be controlled by the carrier
density, which may directly affect the electronic topological surface states.",2104.05659v1
2021/4/13,Physics of star-planet magnetic interactions,"Magnetic interactions between a planet and its environment are known to lead
to aurorae and shocks in the solar system. The large number of close-in
exoplanets that have been discovered so far triggered a renewed interest in
understanding magnetic interactions in other star-planet systems. Multiple
magnetic effects were then unveiled, such as planet inflation or heating,
planet migration, planetary material escape, and even some modifications of the
host star apparent activity. Our goal here is to lay out the basic physical
principles underlying star-planet magnetic interactions. We first briefly
review the hot exoplanets' population as we know it. We then move to a general
description of star-planet magnetic interactions, and finally focus on the
fundamental concept of Alfv\'en wings and its implication for exosystems.",2104.05968v2
2021/5/26,Exotic spintronic properties of transition-metal monolayers on graphyne,"The recent discovery of two-dimensional (2D) magnetic materials which are
compound of transition metal (TM) with other elements, has opened new avenues
for basic research on low-dimensional magnetism and potential applications in
spintronics. To further explore new 2D magnets of pure TM is thus of an
interesting topic. Based on the first-principles calculations, here we propose
a strategy of obtaining monolayer TM magnets, i.e., depositing TM atoms on
graphyne (Gy) which has proper hexagonal hollow geometry. We find that TM
monolayer with perfect hexagonal geometry can be formed on Gy. The TM monolayer
exhibits a wealth of physical properties in dependence of TM species, such as
ferromagnetic and antiferromagnetic ground states, as well as intriguing
semimetal and half-metal characteristics. We also find that the half-metal
characteristics makes the monolayer TM have great potential applications in the
horizontal magnetic tunnel junction (MTJ) devices, where the tunneling
magnetoresistance can reach as high as 850000%. Our results provide a new
framework for obtaining 2D magnets with outstanding spintronic properties.",2105.12515v2
2021/6/17,Magnetic dynamos in white dwarfs -- II. Relating magnetism and pollution,"We investigate whether the recently suggested rotation and crystallization
driven dynamo can explain the apparent increase of magnetism in old metal
polluted white dwarfs. We find that the effective temperature distribution of
polluted magnetic white dwarfs is in agreement with most/all of them having a
crystallizing core and increased rotational velocities are expected due to
accretion of planetary material which is evidenced by the metal absorption
lines. We conclude that a rotation and crystallization driven dynamo offers not
only an explanation for the different occurrence rates of strongly magnetic
white dwarfs in close binaries, but also for the high incidence of weaker
magnetic fields in old metal polluted white dwarfs.",2106.09727v1
2021/7/1,Van der Waals Magnet based Spin-Valve Devices at Room Temperature,"The discovery of van der Waals (vdW) magnets opened up a new paradigm for
condensed matter physics and spintronic technologies. However, the operations
of active spintronic devices with vdW magnets are so far limited to cryogenic
temperatures, inhibiting its broader practical applications. Here, for the
first time, we demonstrate room temperature spin-valve devices using vdW
itinerant ferromagnet Fe5GeTe2 in heterostructures with graphene. The tunnel
spin polarization of the Fe5GeTe2/graphene vdW interface is detected to be
significantly large ~ 45 % and negative at room temperature. Lateral spin-valve
device design enables electrical control of spin signal and realization of
basic building blocks for device application such as efficient spin injection,
transport, precession, and detection functionalities. Furthermore, measurements
with different magnetic orientations provide unique insights into the magnetic
anisotropy of Fe5GeTe2 and its relation with spin polarization and dynamics in
the heterostructure. These findings open opportunities for the applications of
vdW magnet-based all-2D spintronic devices and integrated spin circuits at
ambient temperatures.",2107.00310v1
2021/7/15,Wide-field magneto-optical microscope to access quantitative magnetization dynamics with femtosecond temporal and sub-micrometer spatial resolution,"We introduce a wide-field magneto-optical microscope to probe magnetization
dynamics with femtosecond temporal and sub-micrometer spatial resolution. We
carefully calibrate the non-linear dependency between the magnetization of the
sample and the detected light intensity by determining the absolute values of
the magneto-optical polarization rotation. With that, an analytical transfer
function is defined to directly map the recorded intensity to the corresponding
magnetization, which results in significantly reduced acquisition times and
relaxed computational requirements. The performance of the instrument is
characterized by probing the magnetic all-optical switching dynamics of GdFe in
a pump-probe experiment. The high spatial resolution of the microscope allows
for accurately subdividing the laser-excited area into different
fluence-regions in order to capture the strongly non-linear magnetization
dynamics as a function of the optical pump intensity in a single measurement.",2107.07375v2
2021/7/21,Spin orbit torque switching of antiferromagnet through the Neel reorientation in rare-earth ferrite,"We suggest coherent switching of canted antiferromagnetic (AFM) spins using
spin-orbit torque (SOT) in small magnet. The magnetic system of orthoferrite
features biaxial easy anisotropy and the Dzyaloshinskii Moriya interaction,
which is perpendicular to the easy axes and therefore creates weak
magnetization (m). A damping-like component of the SOT induces N\'eel
reorientation along one of the easy axes and then exerts torque on m, leading
to tilting of the N\'eel order l. The torque on the magnetization becomes
stronger due to coupling with the induced Oersted field or the field-like
component of the SOT, enhancing the tilting of l. Therefore, l is found to
experience deterministic switching after the SOT is turned off. Based upon both
numerical and analytical analysis of the coherent switching, XOR logic gates
are also found to be implemented in a single magnetic layer. In addition, we
investigate how magnetic parameters affect the critical reorientation angle and
current density in a simple layered structure of platinum and a canted AFM. Our
findings are expected to provide an alternative spin-switching mechanism for
ultrafast applications such as spin logic and electronic devices.",2107.10156v1
2021/8/5,Triaxial magnetic anisotropy in the two-dimensional ferromagnetic semiconductor CrSBr,"Two-dimensional (2D) ferromagnets have recently drawn extensive attention,
and here we study the electronic structure and magnetic properties of the bulk
and monolayer of CrSBr, using first-principles calculations and Monte Carlo
simulations. Our results show that bulk CrSBr is a magnetic semiconductor and
has the easy magnetization b-axis, hard c-axis, and intermediate a-axis. Thus,
the experimental triaxial magnetic anisotropy (MA) is well reproduced here, and
it is identified to be the joint effects of spin-orbit coupling (SOC) and
magnetic dipole-dipole interaction. We find that bulk CrSBr has a strong
ferromagnetic (FM) intralayer coupling but a marginal interlayer one. We also
study CrSBr monolayer in detail and find that the intralayer FM exchange
persists and the shape anisotropy has a more pronounced contribution to the MA.
Using the parameters of the FM exchange and the triaxial MA, our Monte Carlo
simulations show that CrSBr monolayer has Curie temperature Tc = 175 K.
Moreover, we find that a uniaxial tensile (compressive) strain along the a (b)
axis would further increase the Tc.",2108.02418v2
2021/8/6,Helical spin order in EuFe2As2 and EuRbFe4As4 single crystals,"In this work, fabrication and characterization of magnetic properties of
EuFe2As2 and EuRbFe4As4 single crystals is reported. Magnetization measurements
of samples with well defined thin film geometry and crystal orientation
demonstrate a striking similarity in ferromagnetic properties of Eu subsystems
in these two compounds. Measurements with magnetic field applied along ab
crystal planes reveal meta-magnetic transition in both compounds. Numerical
studies employing the Jz1-Jz2 Heisenberg model suggest that the ground state of
the magnetic order in Eu subsystem for both compounds is the helical spin order
with the helical angle about 2pi/5, while the meta-magnetic transition is the
helix-to-fan first order phase transition.",2108.03184v1
2021/8/20,Probing anisotropy in epitaxial Fe/Pt bilayers by spin-orbit torque ferromagnetic resonance,"We report the generation and detection of spin-orbit torque ferromagnetic
resonance (STFMR) in micropatterned epitaxial Fe/Pt bilayers grown by molecular
beam epitaxy. The magnetic field dependent measurements at an in-plane magnetic
field angle of 45 degrees with respect to the microwave-current direction
reveal the presence of two distinct voltage peaks indicative of a strong
magnetic anisotropy. We show that STFMR can be employed to probe the underlying
magnetic properties including the anisotropies in the Fe layer. We compare our
STFMR results with broadband ferromagnetic resonance spectroscopy of the
unpatterned bilayer thin films. The experimental STFMR measurements are
interpreted using an analytical formalism and further confirmed using
micromagnetic modeling, which shed light on the field-dependent magnetization
alignment in the microstructures responsible for the STFMR rectification. Our
results demonstrate a simple and efficient method for determining magnetic
anisotropies in microstructures by means of rf spectroscopy.",2108.09132v1
2021/8/31,Onset of superconductor-insulator transition in an ultrathin NbN film under in-plane magnetic field studied by terahertz spectroscopy,"Optical conductivity of a moderately disordered superconducting NbN film was
investigated by terahertz time-domain spectroscopy in external magnetic field
applied along the film plane. The film thickness of about 5 nm was comparable
with the coherence length, so vortices should not form. This was confirmed by
the fact that no marked difference between the spectra with terahertz electric
field set perpendicular and parallel to the external magnetic field was
observed. Simultaneous use of Maxwell-Garnett effective medium theory and the
model of optical conductivity by Herman and Hlubina proved to correctly
reproduce the terahertz spectra obtained experimentally in a magnetic field of
up to 7 T. This let us conclude that the magnetic field tends to suppress the
superconductivity, resulting in an inhomogeneous state where superconducting
domains are enclosed within a normal-state matrix. The scattering rate due to
pair-breaking effects was found to linearly increase with magnetic field.",2108.13698v1
2021/9/3,Magnetization Plateaus of a Double Fullerene Core/Shell Like-Nanostructure in an External Magnetic Field: Monte Carlo Study,"This paper concerns the investigation of the critical (HC) and the saturation
(HS) magnetic fields behavior of the studied system as a function of different
physical parameters. The Monte Carlo method has been used to study the magnetic
properties of a ferrimagnetic behavior of a double fullerene X60 core/shell
like-nanostructure, where the symbol X can be assigned to any magnetic atom.
Based on the Ising model, we focus our study on a system formed by a double
sphere core/shell. The two spheres are containing the spins: $\sigma=\pm 1/2$
in the core are surrounded by the spin $S=\pm 1, 0$ in the shell. Many types of
magnetization curves have been found, depending on the competitions among the
exchange couplings, the crystal fields and the temperature.",2109.01453v1
2021/9/9,Identification of object composition with Magnetic Inductive Tomography,"The inductive response of an object to an oscillating magnetic field reveals
information about its electrical conductivity and magnetic permeability. Here
we introduce a technique that uses measurements of the angular, frequency and
spatial dependence of the inductive signal to determine object composition.
Identification is performed by referencing an object's inductive response to
that of materials with mutually exclusive properties such as copper (high
electric conductivity, negligible magnetic permeability) and ferrite
(negligible electric conductivity, high magnetic permeability). The technique
uses a sensor with anisotropic sensitivity to discriminate between the
different characters of the eddy current and magnetisation driven object
responses. Experimental validation of the method is performed through Magnetic
Induction Tomography measurement with a radio-frequency atomic magnetometer.
Possible applications of the technique in security screening devices are
discussed.",2109.04074v1
2021/9/10,Magnetic-Field-Dependent Stimulated Emission from Nitrogen-Vacancy Centres in Diamond,"Negatively charged nitrogen-vacancy centres in diamond are promising quantum
magnetic field sensors. Laser threshold magnetometry has been a theoretical
approach for the improvement of NV-centre ensemble sensitivity via increased
signal strength and magnetic field contrast. In this work we experimentally
demonstrate laser threshold magnetometry. We use a macroscopic high-finesse
laser cavity containing a highly NV-doped and low absorbing diamond gain medium
that is pumped at 532nm and resonantly seeded at 710nm. This enables
amplification of the signal power by stimulated emission of 64%. We show the
magnetic-field dependency of the amplification and thus, demonstrate
magnetic-field dependent stimulated emission from an NV-centre ensemble. This
emission shows a record contrast of 33% and a maximum output power in the mW
regime. These advantages of coherent read-out of NV-centres pave the way for
novel cavity and laser applications of quantum defects as well as diamond NV
magnetic field sensors with significantly improved sensitivity for the health,
research and mining sectors.",2109.05060v1
2021/9/14,Quantum magnetism of ferromagnetic spin dimers in $α$-KVOPO$_4$,"Magnetism of the spin-$\frac12$ $\alpha$-KVOPO$_4$ is studied by
thermodynamic measurements, $^{31}$P nuclear magnetic resonance (NMR), neutron
diffraction, and density-functional band-structure calculations. Ferromagnetic
Curie-Weiss temperature of $\theta_{\rm CW}\simeq 15.9$ K and the saturation
field of $\mu_0H_s\simeq 11.3$ T suggest the predominant ferromagnetic coupling
augmented by a weaker antiferromagnetic exchange that leads to a short-range
order below 5 K and the long-range antiferromagnetic order below $T_{\rm
N}\simeq 2.7$ K in zero field. Magnetic structure with the propagation vector
$\mathbf k=(0,\frac12,0)$ and the ordered magnetic moment of 0.58 $\mu_B$ at
1.5 K exposes a non-trivial spin lattice where strong ferromagnetic dimers are
coupled antiferromagnetically. The reduction in the ordered magnetic moment
with respect to the classical value (1 $\mu_{\rm B}$) indicates sizable quantum
fluctuations in this setting, despite the predominance of ferromagnetic
exchange. We interpret this tendency toward ferromagnetism as arising from the
effective orbital order in the folded chains of the VO$_6$ octahedra.",2109.06840v1
2021/9/24,Partial Charge Transfer and Absence of Induced Magnetization in EuS(111)/Bi$_2$Se$_3$ Heterostructures,"Heterostructures made from topological and magnetic insulators promise to
form excellent platforms for new electronic and spintronic functionalities
mediated by interfacial effects. We report the results of a first-principles
density functional theory study of the geometric, electronic structure, and
magnetic properties of EuS(111)/Bi$_2$Se$_3$ interface, including van der Waals
and relativistic spin-orbit effects. In contrast to previous theoretical
studies, we find no appreciable magnetic anisotropy in such a heterostructure.
We also do not see additional induced magnetization at the interface or the
magnetic proximity effect on the topological states. This is due to the
localized nature of Eu moments, and because of a partial charge transfer of
$\sim$0.5 electron from Eu to Se. The formation of the surface dipole shifts
the Dirac cone about 0.4~eV below the chemical potential, and the associated
electrostatic screening moves the topological state from the first to the
second quintuple layer of Bi$_2$Se$_3$.",2109.11991v1
2021/10/6,Magnon Interference Tunneling Spectroscopy as a Probe of 2D Magnetism,"Probing two-dimensional single-layer quantum magnets remains a significant
challenge. In this letter, we propose exploiting tunneling spectroscopy in the
presence of magnetic impurities to obtain information about the magnon
dispersion relations in analogy to quasiparticle interference in non-magnetic
materials. We show this technique can be used to establish the dispersion
relations even for frustrated magnets, where the presence of an impurity
generally leads to a nontrivial spin texture. Finally, we consider the problem
of establishing Chern magnon bands in 2D magnets showing how tuneable
impurities allow probing the nature of the surface states.",2110.02662v1
2021/10/26,"Structure and magnetic studies of geometrically frustrated disordered pyrochlores A$_{2}$Zr$_{2}$O$_{7}$: (A = Eu, Gd, Er)","The spin ice system Dy$_{2}$Ti$_{2}$O$_{7}$ exhibits strong
frequency-dependent spin-freezing at $\sim$ 16 K temperature. Although it has
been a matter of discussion for years, the origin of this unusual spin freezing
is still unknown. The replacement of Ti with isovalent Zr leads to the dynamic
magnetic ground state at low temperatures in Dy$_{2}$Zr$_{2}$O$_{7}$ and
prevents the formation of high-temperature spin freezing. Interestingly the
high-temperature spin freezing re-emerges in the presence of the magnetic
field. In this direction, we have studied a series of disordered pyrochlore
oxides A$_{2}$Zr$_{2}$O$_{7}$ (A = Eu, Gd, Er) and compared their crystal
structure, magnetic, and heat capacity behavior with that of
Dy$_{2}$Zr$_{2}$O$_{7}$ and Ho$_{2}$Zr$_{2}$O$_{7}$ systems. Our study shows
that depending on the disordered parameter, the spin-freezing behavior can be
retained by slowing down the spin dynamic with a suitable choice of the
magnetic field. We observe that unlike titanates, modification at the rare
earth site does not make considerable change in the magnetic ground state of
these zirconates compounds.",2110.13573v1
2021/10/27,Magnetoconductivity of a metal with closed Fermi surface reconstructed by a biaxial density wave,"We investigate quantum dynamics and kinetics of a 2D conductor with closed
Fermi surface reconstructed by a biaxial density wave, in which electrons move
along a two-dimensional periodic net of semiclassical trajectories coupled by
the magnetic breakdown tunnelling under a strong magnetic field. We derive a
quasi-particle dispersion law and magnetoconductivity tensor. The
quasi-particle spectrum is found to be the alternating series of
two-dimensional magnetic energy bands with gaps between them. The longitudinal
magnetoconductivity shows giant oscillations with change of magnetic field,
while the Hall coefficient changes sign and is absent in a wide range of the
magnetic fields in between. Preliminary estimations show that the suggested
magnetoconductivity mechanism may be the origin of such behaviour of the Hall
coefficient vs. magnetic field, as observed in experiments in materials with
analogous topology of the Fermi surface, such as the high-Tc superconducting
cuprates.",2110.14265v1
2021/10/27,Planar magnetic texture on the surface of a topological insulator,"We study the planar magnetic textures in an insulating magnetic film coupled
to the Dirac surface state of a topological insulator. It is shown that the
radial vortex with winding number $w=\pm1$ leads to the confinement of Dirac
states, where an exact mapping to the Schr\""{o}dinger equation of a
two-dimensional hydrogen atom is found. The fully spin polarized zero energy
bound state resembles the zeroth Landau level of Dirac electrons in a uniform
out-of-plane magnetic field. Interestingly, when the hybrid system is proximity
coupled to an $s$-wave superconductor, the existence of Majorana zero modes at
Abrikosov vortex depends only on the relative value of the magnetic exchange
coupling and the pairing strength. We conclude with a brief discussion on the
physical realization with such magnetic textures.",2110.14352v1
2021/10/31,Revealing the Intrinsic Magnetism of Non-Magnetic Glasses,"Ordinary multi-component silicate glasses belong to a class of amorphous
insulators normally displaying no special form of magnetism, save for the
Larmor dominant diamagnetism from the constituent atoms' core electrons and the
extrinsic Langevin paramagnetism due to the ubiquitous Fe-group dilute
paramagnetic impurities. Here we show that the macroscopic magnetisation of
three case-study glass types measured in a SQUID-magnetometer cannot be
explained solely by means of the Larmor-Langevin contributions. In particular,
we reveal a novel {\em intrinsic} contribution to the bulk magnetisation due to
the amorphous structure itself, a contribution that is peculiar both in its
temperature and magnetic-field dependence and represents the first true
magnetic effect in nominally non-magnetic glasses. The only theoretical
interpretation we know of for such an effect and which can consistently explain
the experimental data demands the re-thinking of the atomic organisation of
glasses at the nanometric scale.",2111.00614v1
2021/11/6,Complex magnetic phase diagram in noncentrosymmetric EuPtAs,"We report the observation of multiple magnetic transitions in single crystals
of EuPtAs using magnetization, transport, and thermodynamic measurements.
EuPtAs crystallizes in the noncentrosymmetric tetragonal LaPtSi-type structure
(space group I41md) and undergoes a second-order antiferromagnetic transition
at 14.8 K, which is followed by a first-order transition at about 7.5 K. Both
transitions are suppressed by magnetic fields applied parallel and
perpendicular to the c axis, and multiple field-induced transitions are
observed for both field directions, leading to complex temperature-field
diagrams with a dome-like magnetic phase for fields parallel to the c axis.
Moreover, the dependence of the low temperature resistivity on the application
of a training field, but the lack of remanent magnetization, suggests the
presence of multiple antiferromagnetic domains in zero-field.",2111.03879v1
2021/11/17,Chiral Coupling between Magnetic Layers with Orthogonal Magnetization,"We report on the occurrence of strong interlayer Dzyaloshinskii-Moriya
interaction (DMI) between an in-plane magnetized Co layer and a perpendicularly
magnetized TbFe layer through a Pt spacer. The DMI causes a chiral coupling
that favors one-handed orthogonal magnetic configurations of Co and TbFe, which
we reveal through Hall effect and magnetoresistance measurements. The DMI
coupling mediated by Pt causes effective magnetic fields on either layer of up
to 10-15 mT, which decrease monotonously with increasing Pt thickness. Ru, Ta,
and Ti spacers mediate a significantly smaller coupling compared to Pt,
highlighting the essential role of Pt in inducing the interlayer DMI. These
results are relevant to understand and maximize the interlayer coupling induced
by the DMI as well as to design spintronic devices with chiral spin textures.",2111.09197v1
2021/11/20,Giant Dzyaloshinskii-Moriya interaction and ratchet motion of bimeronic excitations in two-dimensional magnets,"Topological magnetic excitations rooted in Dzyaloshinskii-Moriya interaction
(DMI) are promising information carriers for next-generation memory and
spintronic devices. The recently discovered two-dimensional (2D) magnets
provide fertile new platforms for revealing rich physical phenomena with
atomic-scale precision, as exemplified by the enhanced DMI associated with an
effective electric field that breaks the inversion symmetry. Here we use
first-principles calculations to establish a conceptually difierent
compositional engineering approach to induce giant DMI in a representative
CrMnI$_6$ 2D magnet, and the underlying mechanism is rooted in the spontaneous
inversion symmetry breaking in the bipartite system. Using atomistic magnetics
simulations, we further reveal that bimeronic excitations can emerge upon
cooling a spin random state or perturbing a ferromagnetic state. Strikingly,
the bimeron can exhibit unidirectional soliton-like propagation, and such a
ratchet phenomenon is highly desirable for racetrack memories. These findings
may prove instrumental in developing novel devices for quantum information
based on 2D magnets.",2111.10505v1
2021/11/24,Manipulation of magnetic skyrmions in continuous Ir/Co/Pt multilayers,"We show that magnetic skyrmions can be stabilized at room temperature in
continuous Ir/Co/Pt multilayers on SiO2/Si substrate without prior application
of electric current or magnetic field. While decreasing the Co thickness,
tuning of the magnetic anisotropy gives rise to a transition from worm-like
domain patterns to long and separate stripes. The skyrmions are clearly imaged
in both states using Magnetic Force Microscopy. The density of skyrmions can be
significantly enhanced after applying the in-plane field procedure. In
addition, we have investigated the phase diagram of a sample deposited in the
same run, but onto a SiNx membrane using Lorentz transmission electron
microscopy. Interestingly, this sample shows a different behaviour as function
of magnetic field hinting to the influence of strain on the phase diagram of
skyrmions in thin film multilayers. Our results provide means to manipulate
skyrmion, further allowing for optimized engineering of skyrmion-based devices.",2111.12634v1
2021/12/21,Magnetically tunable Shubnikov-de Hass oscillations in MnBi2Te4,"Shubnikov-de Hass oscillations are directly observed in undoped
antiferromagnetic topological insulator MnBi2Te4. With increasing magnetic
fields, the oscillation period decreases gradually in the magnetic transition
from canted antiferromagnetism to ferromagnetism and then saturates in high
magnetic fields, indicating the field-induced evolution of the band structure.
From the analysis of the high-field oscillations, a nontrivial Berry phase and
a small effective mass are extracted, in agreement with the predicted Weyl
semimetal phase in ferromagnetic MnBi2Te4. Furthermore, rotating the
magnetization of MnBi2Te4 can lead to a splitting of the high-field
oscillations, which suggests the enhanced asymmetry of the Weyl cones in tilted
fields. Therefore, the observation of these magnetically tunable quantum
oscillations clearly demonstrates the indispensable role of field in tuning the
band structure or physical properties of MnBi2Te4.",2112.10962v1
2021/12/29,Nonreciprocal optics and magnetotransport in Weyl metals as signatures of band topology,"We consider effects of spatial dispersion in noncentrosymmetric time-reversal
invariant Weyl metals in the presence of a static magnetic field. In
particular, we study currents that are linear in both the spatial derivatives
of an applied electric field, and the static magnetic field, which are
responsible for the phenomenon of gyrotropic birefringence. We show that the
chiral anomaly and the chiral magnetic effect make the leading contribution to
this class of phenomena in metals. We apply the obtained results to the problem
of electromagnetic wave transmission through a thin slab of a Weyl semimetal,
and show that the transmission coefficient contains a component that is odd in
the applied static magnetic field. As such, it can be easily distinguished from
conventional Ohmic magnetotransport effects, which are quadratic in the applied
magnetic field. The relative magnitude of the effect can reach a few percent in
Weyl materials subject to magnetic fields of 0.1Tesla, while the effect is
several orders of magnitude smaller in metals without Berry monopoles. We
conclude that the nonreciprocal optical and magnetotransport effects can be a
robust probe of band topology in metals.",2112.14756v1
2021/12/31,Anisotropic melting of frustrated Ising antiferromagnets,"Magnetic frustrations and dimensionality play an important role in
determining the nature of the magnetic long-range order and how it melts at
temperatures above the ordering transition $T_N$. In this work, we use
large-scale Monte Carlo simulations to study these phenomena in a class of
frustrated Ising spin models in two spatial dimensions. We find that the
melting of the magnetic long-range order into an isotropic gas-like paramagnet
proceeds via an intermediate stage where the classical spins remain
anisotropically correlated. This correlated paramagnet exists in a temperature
range $T_N < T < T^\ast$, whose width increases as magnetic frustrations grow.
This intermediate phase is typically characterized by short-range correlations,
however the two-dimensional nature of the model allows for an additional exotic
feature -- formation of an incommensurate liquid-like phase with algebraically
decaying spin correlations. The two-stage melting of magnetic order is generic
and pertinent to many frustrated quasi-2D magnets with large (essentially
classical) spins.",2112.15514v1
2022/1/3,Operation of a Continuous Flow Liquid Helium Magnetic Microscopy Cryostat as a Closed Cycle System,"We demonstrate successful operation of a continuous flow liquid helium
magnetic cryostat (Oxford Instruments, Microstat MO) in closed cycle operation
using a modular cryocooling system (ColdEdge Technologies, Stinger). For the
system operation, we have developed a custom gas handling manifold and we show
that despite the lower cooling power of the cryocooler with respect to the
nominal cryostat cooling power requirements, the magnetic cryostat can be
operated in a stable manner. We provide the design of the gas handling
manifold, and a detailed analysis of the system performance in terms of cooling
times, magnetic field ramping rates and vibrations at the sample. Base
temperature can be reached within 10 hours while the superconducting magnet can
be energized at a ramping rate of 0.5 T/min. Vibrations are measured
interferometrically and show amplitudes with a root mean square on the order of
5 nm permitting the use of the system for sensitive magnetic microscopy
experiments.",2201.00647v1
2022/1/6,Large Magnetic-Field-Induced Strain at the Spin-Reorientation Transition in the A-Site Ordered Spinel Oxide LiFeCr4O8,"Sintered samples of a spinel oxide LiFeCr4O8, where Cr3+ and Fe3+ ions have
localized moments, were found to show a large magnetic-field-induced volume
increase approaching 500 ppm by applying a magnetic field of 9 T. This large
volume increase appeared only at around 30 K. At 30 K, a spin-reorientation
transition from ferrimagnetic to conical order occurs, giving rise to this
large volume increase. The coexistence of ferrimagnetic and conical phases at
this transition was found to be important, suggesting that such a large
magnetic-field-induced volume change can be realized at various magnetic
transitions in localized magnets with strong spin-lattice coupling.",2201.01897v1
2022/1/12,Magnetic domain wall pinning in cobalt ferrite microstructures,"A detailed correlative structural, magnetic and chemical analysis of
non-stoichiometric cobalt ferrite micrometric crystals was performed by x-ray
magnetic circular dichroism combined with photoemission microscopy, low energy
electron microscopy, and atomic force microscopy. The vector magnetization at
the nanoscale is obtained from magnetic images at different x-ray incidence
angles and compared with micromagnetic simulations, revealing the presence of
defects which pin the magnetic domain walls. A comparison of different types of
defects and the domain walls location suggests that the main source of pinning
in these microcrystals are linear structural defects induced in the spinel by
the substrate steps underneath the islands.",2201.04384v1
2022/1/27,Simultaneous measurement of the exchange parameter and saturation magnetization using propagating spin waves,"The exchange interaction in ferromagnetic ultra-thin films is a critical
parameter in magnetization-based storage and logic devices, yet the accurate
measurement of it remains a challenge. While a variety of approaches are
currently used to determine the exchange parameter, each has its limitations,
and good agreement among them has not been achieved. To date, neutron
scattering, magnetometry, Brillouin light scattering, spin-torque ferromagnetic
resonance spectroscopy, and Kerr microscopy have all been used to determine the
exchange parameter. Here we present a novel method that exploits the wavevector
selectivity of Brillouin light scattering to measure the spin wave dispersion
in both the backward volume and Damon-Eshbach orientations. The exchange,
saturation magnetization, and magnetic thickness are then determined by a
simultaneous fit of both dispersion branches with general spin wave theory
without any prior knowledge of the thickness of a magnetic ""dead layer"". In
this work, we demonstrate the strength of this technique for ultrathin metallic
films, typical of those commonly used in industrial applications for magnetic
random-access memory.",2201.11270v1
2022/1/31,Anomalous Nernst effect in La0.5Ca0.5Coo3,"We report the occurrence of the anomalous Nernst effect (ANE) in
polycrystalline perovskite La0.5Ca0.5CoO3. The sample is ferromagnetic below TC
= 147 K and resistivity shows non-metallic behavior above and below the TC with
only a small negative magnetoresistance (~2%) around TC. Field dependence of
magnetization at 10 K shows large hysteresis with a coercive field of 6 kOe but
a small magnetization ~ 0.64 Bohr magneton/Co even in a field of 50 kOe, which
indicates the presence of magnetically heterogeneous ground state consisting of
ferromagnetic and non-ferromagnetic phases. The field dependence of the Nernst
thermopower (Sxy) at low temperatures shows complete saturation but the
magnetization does not. This indicates that the ANE in La0.5Ca0.5CoO3 depends
only on the transport properties of the ferromagnetic phase, while it is not
affected by the non-ferromagnetic phase. Due to the higher value of remnant
Sxy, the magnetized polycrystalline sample exhibits ANE in absence of an
external magnetic field.",2201.12982v1
2022/2/1,Magnetic structures and electronic properties of cubic-pyrochlore ruthenates from first principles,"The magnetic ground states of $R_2$Ru$_2$O$_7$ and $A_2$Ru$_2$O$_7$ with $R=$
Pr, Gd, Ho, and Er, as well as $A=$ Ca, Cd are predicted devising a combination
of the cluster-multipole (CMP) theory and spin-density-functional theory
(SDFT). The strong electronic correlation effects are estimated by the
constrained-random-phase approximation (cRPA) and taken into account within the
dynamical-mean-field theory (DMFT). The target compounds feature $d$-orbital
magnetism on Ru$^{4+}$ and Ru$^{5+}$ ions for $R$ and $A$, respectively, as
well as $f$-orbital magnetism on the $R$ site, which leads to an intriguing
interplay of magnetic interactions in a strongly correlated system. We find
CMP+SDFT is capable of describing the magnetic ground states in these
compounds. The cRPA captures a difference in the screening strength between
$R_2$Ru$_2$O$_7$ and $A_2$Ru$_2$O$_7$ compounds, which leads to a qualitative
and quantitative understanding of the electronic properties within DMFT.",2202.00277v1
2022/2/8,"Spin-Phonon Relaxation in Magnetic Molecules: Theory, Predictions and Insights","Magnetic molecules have played a central role in the development of magnetism
and coordination chemistry and their study keeps leading innovation in
cutting-edge scientific fields such as magnetic resonance, magnetism,
spintronics, and quantum technologies. Crucially, a long spin lifetime well
above cryogenic temperature is a stringent requirement for all these
applications. In this chapter we review the foundations of spin relaxation
theory and provide a detailed overview of first-principles strategies applied
to the problem of spin-phonon relaxation in magnetic molecules. Firstly, we
present a rigorous formalism of spin-phonon relaxation based on open quantum
systems theory. These results are then used to derive classical
phenomenological relations based on the Debye model. Finally, we provide a
prescription of how to map the relaxation formalism onto existing electronic
structure methods to obtain a quantitative picture of spin-phonon relaxation.
Examples from the literature, including both transition metals and lanthanides
compounds, will be discussed in order to illustrate how Direct, Orbach and
Raman relaxation mechanisms can affect spin dynamics for this class of
compounds.",2202.03776v1
2022/3/24,Emergence of electric-field-tunable interfacial ferromagnetism in 2D antiferromagnet heterostructures,"Van der Waals (vdW) magnet heterostructures have emerged as new platforms to
explore exotic magnetic orders and quantum phenomena. Here, we study
heterostructures of layered antiferromagnets, CrI3 and CrCl3, with
perpendicular and in-plane magnetic anisotropy, respectively. Using
magneto-optical Kerr effect microscopy, we demonstrate out-of-plane magnetic
order in the CrCl3 layer proximal to CrI3, with ferromagnetic interfacial
coupling between the two. Such an interlayer exchange field leads to higher
critical temperature than that of either CrI3 or CrCl3 alone. We further
demonstrate significant electric-field control of the coercivity, attributed to
the naturally broken structural inversion symmetry of the heterostructure
allowing unprecedented direct coupling between electric field and interfacial
magnetism. These findings illustrate the opportunity to explore exotic magnetic
phases and engineer spintronic devices in vdW heterostructures.",2203.13051v1
2022/4/10,Tunable Magnetic Scattering and Ferroelectric Switching at the LaAlO$_3$/EuTiO$_3$/Sr$_{0.99}$Ca$_{0.01}$TiO$_3$ Interface,"Ferroelectric and ferromagnetic orders rarely coexist, and magnetoelectric
coupling is even more scarce. A possible avenue for combining these orders is
by interface design, where orders formed at the constituent materials can
overlap and interact. Using a combination of magneto-transport and scanning
SQUID measurements, we explore the interactions between ferroelectricity,
magnetism, and the 2D electron system (2DES) formed at the novel
LaAlO$_3$/EuTiO$_3$/Sr$_{0.99}$Ca$_{0.01}$TiO$_3$ heterostructure. We find that
the electrons at the interface experience magnetic scattering appearing along
with a diverging Curie-Weiss-type behaviour in the EuTiO$_3$ layer. The 2DES is
also affected by the switchable ferroelectric polarization at the
Sr$_{0.99}$Ca$_{0.01}$TiO$_3$ bulk. While the 2DES interacts with both
magnetism and ferroelectricity, we show that the presence of the conducting
electrons has no effect on magnetization in the EuTiO$_3$ layer. Our results
provide a first step towards realizing a new multiferroic system where
magnetism and ferroelectricity can interact via an intermediate conducting
layer.",2204.04657v1
2022/4/15,Spin Conductivity Based on Magnetic Toroidal Quadrupole Hidden in Antiferromagnets,"We report our theoretical results on spin conductivity in antiferromagnets by
focusing on the role of the magnetic toroidal quadrupole (MTQ) in electron
systems. The MTQ is characterized as a time-reversal-odd rank-2 polar tensor
degree of freedom in electrons, which is distinct from conventional rank-1
magnetic and magnetic toroidal dipoles. Based on a microscopic $sd$ model
analysis for a tetragonal system under both collinear and noncollinear
antiferromagnetic orderings, we clarify that the MTQ becomes a source of an
extrinsic spin conductivity even with neither a uniform magnetization nor
spin-orbit coupling. We also list all the magnetic point groups to accommodate
the MTQs as a primary order parameter as well as the candidate
antiferromagnetic materials.",2204.07326v1
2022/5/16,Magnetic neutron scattering from spherical nanoparticles with Neel surface anisotropy: Analytical treatment,"The magnetization profile and the related magnetic small-angle neutron
scattering cross section of a single spherical nanoparticle with Neel surface
anisotropy is analytically investigated. We employ a Hamiltonian that comprises
the isotropic exchange interaction, an external magnetic field, a uniaxial
magnetocrystalline anisotropy in the core of the particle, and the Neel
anisotropy at the surface. Using a perturbation approach, the determination of
the magnetization profile can be reduced to a Helmholtz equation with Neumann
boundary condition, whose solution is represented by an infinite series in
terms of spherical harmonics and spherical Bessel functions. From the resulting
infinite series expansion, we analytically calculate the Fourier transform,
which is algebraically related to the magnetic small-angle neutron scattering
cross section. The approximate analytical solution is compared to the numerical
solution using the Landau-Lifshitz equation, which accounts for the full
nonlinearity of the problem.",2205.07549v1
2022/5/24,Magnetism between magnetic adatoms on monolayer NbSe$_2$,"In this work, we report on an $ab-initio$ computational study of the
electronic and magnetic properties of transition metal adatoms on a monolayer
of NbSe$_2$. We demonstrate that Cr, Mn, Fe and Co prefer all to sit above the
Nb atom, where the $d$ states experience a substantial hybridization. The
inter-atomic exchange coupling is shown to have an oscillatory nature
accompanied by an exponential decay, in accordance with what theory predicts
for a damped Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. Our results
indicate that the qualitative features of the magnetic coupling for the four
investigated adatoms can be connected to the fine details of their Fermi
surface. In particular, the oscillations of the exchange in Fe and Co are found
to be related to a single nesting vector, connecting large electrons and hole
pockets. Most interestingly, this behavior is found to be unaffected by changes
induced on the height of the impurity, which makes the magnetism robust to
external perturbations. Considering that NbSe$_2$ is a superconductor down to a
single layer, our research might open the path for further research into the
interplay between magnetic and superconducting characteristics, which could
lead to novel superconductivity engineering.",2205.11932v1
2022/5/24,Metabolic Reactions Studied by Zero- and Low-Field Nuclear Magnetic Resonance,"State-of-the-art magnetic resonance imaging uses hyperpolarized molecules to
track metabolism in vivo, but large superconducting magnets are required, and
the strong magnetic fields largely preclude measurement in the presence of
conductive materials and magnify problems of magnetic susceptibility
inhomogeneity. Operating at zero and low field circumvents these limitations,
but until now has not been possible due to limited sensitivity. We show that
zero- and low-field nuclear magnetic resonance can be used for probing two
important metabolic reactions: the conversion of hyperpolarized fumarate to
malate and pyruvate to lactate. This work paves the way to a heretofore
unexplored class of biomedical imaging applications.",2205.12380v1
2022/5/31,Anisotropy driven response of skyrmion lattice in MnSc$_2$S$_4$ to applied magnetic fields,"We theoretically and experimentally study the stability of the unconventional
fractional antiferromagnetic skyrmion lattice (AF-SkL) in Mn$_2$S$_4$ spinel
under magnetic fields applied along the $[$1-10$]$ crystal direction. By
performing numerical Monte Carlo simulations for the minimal effective spin
model that we proposed in Ref. [S. Gao, et al., Nature 586, 37-41 (2020)], we
show that the skyrmion lattice is aligned within the equivalent and symmetric
$[$1-11$]$ or $[$1-11$]$ planes, which are equally inclined to the applied
magnetic field. We attribute this behavior to the magnetic anisotropy of the
host material. Neutron single crystal diffraction presents a very good
agreement with the predictions of the effective model. It reveals that the
topological spin texture gets destabilized at low temperatures and moderate
magnetic fields and is replaced by a conical phase for B// $[$1-10$]$. The
present study elucidates the central role of the magnetic anisotropy in the
stabilization of antiferromagnetic skyrmionic states.",2205.15787v1
2022/6/8,"Emerging Two-Dimensional Magnetism in Nonmagnetic Electrides Hf2X (X = S, Se, Te)","Recent experimental discoveries of two-dimensional (2D) magnets have
triggered intense research activities to search for atomically thin magnetic
systems. Using first-principles calculations, we predict the emergence of 2D
magnetism in the monolayers (MLs), few layers, and surfaces of nonmagnetic
layered electrides Hf2X (X = S, Se, Te) consisting of three-atom-thick Hf-X-Hf
stacks. It is revealed that each bulk Hf2X hosts a novel quantum state of Dirac
nodal lines with a high density of states arising from Hf-5d cationic and
interlayer anionic electrons around -0.9 eV below the Fermi level EF. However,
for the MLs, few layers, and surfaces of Hf2X, such hybridized states are
shifted toward EF to generate van Hove singularities, leading to a Stoner
instability. The resulting surface ferromagnetism gives rise to strongly
spin-polarized topological surface states at Hf2X(001), demonstrating that
anionic electrons, 2D magnetism, and band topology are entangled with each
other. Our findings will open new perspectives for the discovery of 2D magnets
via exploiting surface effects in nonmagnetic layered electrides.",2206.03689v1
2022/7/5,Determinants of local chemical environments and magnetic moments of high-entropy alloys,"High-entropy alloys (HEAs) such as CrMnFeCoNi exhibit unconventional
mechanical properties due to their compositional disorder. However, it remains
a formidable challenge to estimate the local chemical-environment and magnetic
effects of HEAs. Herein we identify the state-associated cohesive energy and
band filling originated from the tight-binding and Friedel models as
descriptors to quantify the site-to-site chemical bonding and magnetic moments
of HEAs. We find that the s-state cohesive energy is indispensable in
determining the bonding-strength trend of CrMnFeCoNi that differs from the
bonding characteristics of precious and refractory HEAs, while the s-band
filling is effective in determining the magnetic moments. This unusual behavior
stems from the unique chemical and magnetic nature of Cr atoms and is
essentially due to the localized and transferred itinerant electrons. Our study
establishes a fundamental physical picture of chemical bonding and magnetic
interactions of HEAs and provides a rational guidance for designing advanced
structural alloys.",2207.01891v1
2022/7/16,Magnetization Switching of Single Magnetite Nanoparticles Monitored Optically,"Magnetic nanomaterials record information as fast as picoseconds in computer
memories but retain it for millions of years in ancient rocks. This exceedingly
broad range of times is covered by hopping over a potential energy barrier
through temperature, ultrafast optical excitation for demagnetization or
magnetization manipulation, mechanical stress, or microwaves. As switching
depends on nanoparticle size, shape, orientation, and material properties, only
single-nanoparticle studies can eliminate ensemble heterogeneity. Here, we push
the sensitivity of photothermal magnetic circular dichroism down to individual
20-nm magnetite nanoparticles. Single-particle magnetization curves display
superparamagnetic to ferromagnetic behaviors, depending on size, shape, and
orientation. Some nanoparticles undergo thermally activated switching on time
scales of milliseconds to minutes. Surprisingly, the switching barrier appears
to vary in time, leading to dynamical heterogeneity. Our observations will help
to identify and eventually control the nanoscale parameters influencing the
switching of magnetic nanoparticles, an important step for applications in many
fields.",2207.07866v2
2022/7/16,Observation of magnetism induced topological edge state in antiferromagnetic topological insulator MnBi4Te7,"Breaking time reversal symmetry in a topological insulator may lead to
quantum anomalous Hall effect and axion insulator phase. MnBi4Te7 is a recently
discovered antiferromagnetic topological insulator with TN ~12.5 K, which is
constituted of alternatively stacked magnetic layer (MnBi2Te4) and non-magnetic
layer (Bi2Te3). By means of scanning tunneling spectroscopy, we clearly observe
the electronic state present at a step edge of a magnetic MnBi2Te4 layer but
absent at non-magnetic Bi2Te3 layers at 4.5 K. Furthermore, we find that as the
temperature rises above TN, the edge state vanishes, while the point defect
induced state persists upon temperature increasing. These results confirm the
observation of magnetism induced edge states. Our analysis based on an axion
insulator theory reveals that the nontrivial topological nature of the observed
edge state.",2207.07942v1
2022/7/18,Nutational switching in ferromagnets and antiferromagnets,"It was demonstrated recently that on ultrashort time scales magnetization
dynamics does not only exhibit precession but also nutation. Here, we
investigate how nutation can contribute to spin switching leading towards
ultrafast data writing. We use analytic theory and atomistic spin simulations
to discuss the behavior of ferromagnets and antiferromagnets in high-frequency
magnetic fields. In ferromagnets, linearly polarized fields align the
magnetization perpendicular to the external field, enabling $90^{\circ}$
switching. For circularly polarized fields in the $xy$ plane, the magnetization
tilts to the $z$ direction. During this tilting, it rotates around the $z$
axis, allowing $180^{\circ}$ switching. In antiferromagnets, external fields
with frequencies higher than the nutation frequency align the order parameter
parallel to the field direction, while for lower frequencies it is oriented
perpendicular to the field. The switching frequency increases with the magnetic
field strength, and it deviates from the Larmor frequency, making it possible
to outpace precessional switching in high magnetic fields.",2207.08566v1
2022/8/11,Magnetic-field-induced ab-plane rotation of the Eu magnetic moments in trigonal EuMg2Bi2 and EuMg2Sb2 single crystals below their Neel temperatures,"The thermodynamic and electronic-transport properties of trigonal EuMg2Bi2 in
ab-plane magnetic fields Hx and the A-type antiferromagnetic structure have
recently been reported. At a temperature of 1.8 K < TN, the Eu magnetic moments
with spin S = 7/2 remain locked in the ab plane up to and above the ab-plane
critical field Hxc = 27.5 kOe at which the Eu moments become parallel to Hx.
Here additional measurements at low fields are reported that reveal a new
spin-reorientation transition at a field Hc1 = 465 Oe where the Eu moments
remain in the ab plane but become perpendicular to Hx. At higher fields, the
moments cant towards the field resulting in M proportional to Hx up to Hxc.
Similar results are reported from measurements of the magnetic properties of
EuMg2Sb2 single crystals, where Hc1 = 220 Oe is found. Theory is formulated
that models the low-field magnetic behavior of both materials, and the
associated anisotropies are calculated. The ab-plane trigonal anisotropy in
EuMg2Sb2 is found to be significantly smaller than in EuMg2Bi2.",2208.06020v1
2022/8/15,The origin of enhanced interfacial perpendicular magnetic anisotropy in LiF-inserted Fe/MgO interface,"The Fe/MgO interface is an essential ingredient in spintronics as it shows
giant tunneling magnetoresistance and strong perpendicular magnetic anisotropy
(PMA). A recent study demonstrated that the insertion of an ultra-thin LiF
layer between the Fe and MgO layers enhances PMA significantly. In this study,
we perform x-ray magnetic circular dichroism measurements on Fe/LiF/MgO
multilayers to reveal the origin of the PMA enhancement. We find that the LiF
insertion increases the orbital-magnetic-moment anisotropy and thus the
magnetic anisotropy energy. We attribute the origin of this
orbital-magnetic-moment-anisotropy enhancement to the stronger electron
localization and electron-electron correlation or the better interface quality
with fewer defects.",2208.07007v1
2022/8/19,Phononic-crystal cavity magnomechanics,"Establishing a way to control magnetic dynamics and elementary excitations
(magnons) is crucial to fundamental physics and the search for novel phenomena
and functions in magnetic solid-state systems. Electromagnetic waves have been
developed as means of driving and sensing in magnonic and spintronics devices
used in magnetic spectroscopy, non-volatile memory, and information processors.
However, their millimeter-scale wavelengths and undesired cross-talk have
limited operation efficiency and made individual control of densely integrated
magnetic systems difficult. Here, we utilize acoustic waves (phonons) to
control magnetic dynamics in a miniaturized phononic crystal micro-cavity and
waveguide architecture. We demonstrate acoustic pumping of localized
ferromagnetic magnons, where their back-action allows dynamic and
mode-dependent modulation of phononic cavity resonances. The phononic crystal
platform enables spatial driving, control and read-out of tiny magnetic states
and provides a means of tuning acoustic vibrations with magnons. This
alternative technology enhances the usefulness of magnons and phonons for
advanced sensing, communications and computation architectures that perform
transduction, processing, and storage of classical and quantum information.",2208.09105v1
2022/8/19,Modulation of magnetic property of double-perovskite La2MnCoO6 films by controlling B-antisite disorder,"The predicted physical properties of double perovskites have usually been
compromised by their intrinsic B-antisite (AS) disorder effect, but the
relationship between them is still unclear for the La2MnCoO6 (LMCO) system.
This study focuses on controlling the AS disorder and quantitatively reveals
correlations with magnetic and electronic states in epitaxial LMCO films grown
on (111) SrTiO3 substrates. The AS fraction was precisely controlled by tuning
the growth conditions as evaluated from saturation magnetization and x-ray
reflection profiles. The saturation magnetization at 5 K decreased linearly
from 6 uB per formula unit by 50% as the AS fraction increased from 0
(perfectly ordered) to 0.5 (fully disordered). The x-ray absorption
spectroscopy revealed that valence states of Mn and Co were 4+ (3d^3) and 2+
(3d^7), respectively, regardless of AS fraction. A local-spin-moment model is
proposed to explain the net magnetizations with and without AS disorder and
Mn/Co valence states, suggesting that only the rearrangement of local spin
moment of Co at the antisite plays a key role in tuning the magnetism in this
LMCO system.",2208.09166v1
2022/8/22,Ultrafast Spin Dynamics and Photoinduced Insulator-to-Metal Transition in $α$-$RuCl_3$,"Laser-induced ultrafast demagnetization is a phenomenon of utmost interest
and attracts significant attention because it enables potential applications in
ultrafast optoelectronics and spintronics. As a spin-orbit coupling assisted
magnetic insulator, $\alpha$-$RuCl_3$ provides an attractive platform to
explore the physics of electronic correlations and related unconventional
magnetism. Using time-dependent density functional theory, we explore the
ultrafast laser-induced dynamics of the electronic and magnetic structures in
$\alpha$-$RuCl_3$. Our study unveils that laser pulses can introduce ultrafast
demagnetizations in $\alpha$-$RuCl_3$, accompanied by an out-of-equilibrium
insulator-to-metal transition in a few tens of femtoseconds. The spin response
significantly depends on the laser wavelength and polarization on account of
the electron correlations, band renormalizations and charge redistributions.
These findings provide physical insights into the coupling between the
electronic and magnetic degrees of freedom in $\alpha$-$RuCl_3$ and shed light
on suppressing the long-range magnetic orders and reaching a proximate spin
liquid phase for two-dimensional magnets on an ultrafast timescale.",2208.10222v1
2022/9/6,Current-driven magnetization dynamics and their correlation with magnetization configurations in perpendicularly magnetized tunnel junctions,"We study spin-transfer-torque driven magnetization dynamics of a
perpendicular magnetic tunnel junction (MTJ) nanopillar. Based on the
combination of spin-torque ferromagnetic resonance and microwave spectroscopy
techniques, we demonstrate that the free layer (FL) and the weak pinned
reference layer (RL) exhibit distinct dynamic behaviors with opposite frequency
vs. field dispersion relations. The FL can support a single coherent spin-wave
(SW) mode for both parallel and antiparallel configurations, while the RL
exhibits spin-wave excitation only for the antiparallel state. These two SW
modes corresponding to the FL and RL coexist at an antiparallel state and
exhibit a crossover phenomenon of oscillation frequency with increasing the
external magnetic field, which could be helpful in the mutual synchronization
of auto-oscillations for SW-based neuromorphic computing.",2209.02271v1
2022/9/9,Control of magnetic states and spin interactions in bilayer CrCl$_{3}$ with strain and electric fields: an ab initio study,"Using ab initio density functional theory (DFT), we demonstrated the
possibility of controlling the magnetic ground-state properties of bilayer
CrCl$_{3}$ by means of mechanical strains and electric fields. In principle, we
investigated the influence of these two fields on parameters describing the
spin Hamiltonian of the system. The obtained results show that biaxial strains
change the magnetic ground state between ferromagnetic (FM) and
antiferromagnetic (AFM) phases. The mechanical strain also affects the
direction and amplitude of the uniaxial magnetic anisotropy (MAE). Importantly,
the direction and amplitude of the Dzyaloshinskii-Moriya vectors are also
highly tunable under external strain and electric fields. The competition
between nearest neighbor interaction, MAE, and Dzyaloshinskii-Moriya
interactions can lead to the stabilization of various exotic spin textures and
novel magnetic excitations. The high tunability of magnetic properties by
external fields makes bilayer CrCl$_{3}$ a promising candidate for application
in the emerging field of two-dimensional quantum spintronics and magnonics.",2209.04527v2
2022/9/18,Magnetism and topology in Tb-based icosahedral quasicrystal,"Quasicrystal (QC) possesses a unique lattice structure with rotational
symmetry forbidden in conventional crystals. The electric property is far from
complete understanding and it has been a long-standing issue whether the
magnetic long-range order is realized in the QC. The main difficulty was lack
of microscopic theory to analyze the effect of the crystalline electric field
(CEF) at the rare-earth atom in QCs. Here we show the full microscopic analysis
of the CEF in Tb-based QCs. We find that magnetic anisotropy arising from the
CEF plays a key role in realizing unique magnetic textures on the icosahedron
whose vertices Tb atoms are located at. Our analysis suggests that the
long-range order of the hedgehog characterized by the topological charge of one
is stabilized in the Tb-based QC. We also find that the whirling-moment state
is characterized by unusually large topological charge of three. The magnetic
textures as well as the topological states are shown to be switched by
controlling compositions of the non-rare-earth elements in the ternary
compounds. Our model is useful to understand the magnetism as well as the
topological property in the rare-earth-based QCs and approximant crystals.",2209.08488v1
2022/9/18,Magnetically confined wind shock,"Many stars across all classes possess strong enough magnetic fields to
influence dynamical flow of material off the stellar surface. For the case of
massive stars (O and B types), about 10\% of them harbour strong, globally
ordered (mostly dipolar) magnetic fields. The trapping and channeling of their
stellar winds in closed magnetic loops leads to {\it magnetically confined wind
shocks} (MCWS), with pre-shock flow speeds that are some fraction of the wind
terminal speed that can be a few thousand km s$^{-1}$. These shocks generate
hot plasma, a source of X-rays. In the last decade, several developments took
place, notably the determination of the hot plasma properties for a large
sample of objects using \xmm\ and \ch, as well as fully self-consistent MHD
modelling and the identification of shock retreat effects in weak winds. In
addition, these objects are often sources of H$\alpha$ emission which is
controlled by either sufficiently high mass loss rate or centrifugal breakout.
Here we review the theoretical aspects of such magnetic massive star wind
dynamics.",2209.08540v1
2022/10/20,Strong variation of spin-orbit torques with relative spin relaxation rates in ferrimagnets,"Spin-orbit torques (SOTs) have been widely understood as an interfacial
transfer of spin that is independent of the bulk properties of the magnetic
layer. Here, we report that SOTs acting on ferrimagnetic FexTb1-x layers
decrease and vanish upon approaching the magnetic compensation point because
the rate of spin transfer to the magnetization becomes slower than the rate of
spin relaxation into the crystal lattice due to spin-orbit scattering. These
results indicate that the relative rates of competing spin relaxation processes
within magnetic layers play a critical role in determining the strength of
SOTs, which provides a unified understanding for the diverse and even seemingly
puzzling SOT phenomena in ferromagnetic and compensated systems. Our work
indicates that spin-orbit scattering within the magnet should be minimized for
efficient SOT devices. We also find that the interfacial spin-mixing
conductance of interfaces of ferrimagnetic alloys (such as FexTb1-x) is as
large as that of 3d ferromagnets and insensitive to the degree of magnetic
compensation.",2210.11042v1
2022/10/24,Reduction of energy cost of magnetization switching in a biaxial nanoparticle by use of internal dynamics,"A solution to energy-efficient magnetization switching in a nanoparticle with
biaxial anisotropy is presented. Optimal control paths minimizing the energy
cost of magnetization reversal are calculated numerically as functions of the
switching time and materials properties, and used to derive energy-efficient
switching pulses of external magnetic field. Hard-axis anisotropy reduces the
minimum energy cost of magnetization switching due to the internal torque in
the desired switching direction. Analytical estimates quantifying this effect
are obtained based on the perturbation theory. The optimal switching time
providing a tradeoff between fast switching and energy efficiency is obtained.
The energy cost of switching and the energy barrier between the stable states
can be controlled independently in a biaxial nanomagnet. This provides a
solution to the dilemma between energy-efficient writability and good thermal
stability of magnetic memory elements.",2210.13514v2
2022/10/27,Magnetic Solitons due to interfacial chiral interactions,"We study solitons in a zig-zag lattice of magnetic dipoles. The lattice
comprises two sublattices of parallel chains with magnetic dipoles at their
vertices. Due to orthogonal easy planes of rotation for dipoles belonging to
different sublattices, the total dipolar energy of this system is separable
into a sum of symmetric and chiral long-ranged interactions between the magnets
where the last takes the form of Dzyaloshinskii-Moriya coupling. For a specific
range of values of the offset between sublattices, the dipoles realize an
equilibrium magnetic state in the lattice plane, consisting of one chain
settled in an antiferromagnetic parallel configuration and the other in a
collinear ferromagnetic fashion. If the offset grows beyond this value, the
internal Dzyaloshinskii-Moriya field stabilizes two Bloch domain walls at the
edges of the antiferromagnetic chain. The dynamics of these solitons is studied
by deriving the long-wavelength lagrangian density for the easy axis
antiferromagnet. We find that the chiral couplings between sublattices give
rise to an effective magnetic field that stabilizes the solitons in the
antiferromagnet. When the chains displace respect to each other, an emergent
Lorentz force accelerates the domain walls along the lattice.",2210.15716v2
2022/11/6,Triclinic BiFeO3: A room-temperature multiferroic phase with enhanced magnetism and resistivity,"The magnetic and transport properties of BiFeO3/La2NiMnO6 (BFO/LNMO)
composite have been investigated both experimentally and theoretically. Unlike
the normal rhombohedral (R3c) phase, BFO in the composites is crystallized in
the triclinic phase (P1). Interestingly, the composites demonstrate a
significant enhancement in the magnetization, magnetoelectric coupling and show
higher resistivity than that of the regular BFO (R3c). As LNMO has its Curie
temperature at 280 K, the room temperature and above room temperature magnetic
contribution in the composites is expected to be from the triclinic BFO phase.
Experimentally observed enhancement in magnetization is validated using
classical Monte Carlo simulation and density functional theory (DFT)
calculations. The calculations reveal higher magnetic moments in triclinic BFO
as compared to the rhombohedral BFO. Overall, this study reveals triclinic BFO
as the promising room temperature multiferroic phase which is helpful to
optimize the multiferroicity of BFO and achieve wider applications in future.",2211.03123v3
2022/11/20,Magnetic dynamo caused by axions in neutron stars,"The coupling between axions and photons modifies Maxwell's equations,
introducing a dynamo term in the magnetic induction equation. In neutron stars,
for critical values of the axion decay constant and axion mass, the magnetic
dynamo mechanism increases the total magnetic energy of the star. We show that
this generates substantial internal heating due to enhanced dissipation of
crustal electric currents. These mechanisms would lead magnetized neutron stars
to increase their magnetic energy and thermal luminosity by several orders of
magnitude, in contrast to observations of thermally-emitting neutron stars. To
prevent the activation of the dynamo, bounds on the allowed axion parameter
space can be derived.",2211.10863v1
2022/11/23,Anatomy of spin wave driven magnetic texture motion via magnonic torques,"The interplay between spin wave and magnetic texture represents the
information exchange between the fast and slow dynamical parts of magnetic
systems. Here we formulate a set of magnonic torques acting on background
magnetic texture, by extracting time-invariant information from the fast
precessing spin waves. Under the frame of magnonic torques, we use theoretical
formulations and micromagnetic simulations to investigate the spin wave driven
domain wall motion in two typical symmetry-breaking situations: the rotational
symmetry broken by the Dzyaloshinkii-Moriya interaction, and the translational
symmetry broken by magnetic damping. The torque-based microscopic analyses
provide compact yet quantitative tools to reinterpret the magnetic texture
dynamics induced by spin wave, beyond the conventional framework of global
momentum conservation.",2211.12958v1
2022/12/16,Magnetic Properties of Multifunctional $^7$LiFePO$_4$ under Hydrostatic Pressure,"LiFePO$_4$ (LFPO) is an archetypical and well-known cathode material for
rechargeable Li-ion batteries. However, its quasi-one-dimensional (Q1D)
structure along with the Fe ions, LFPO also displays interesting
low-temperature magnetic properties. Our team has previously utilized the muon
spin rotation ($\mu^+$SR) technique to investigate both magnetic spin order as
well as Li-ion diffusion in LFPO. In this initial study we extend our
investigation and make use of high-pressure $\mu^+$SR to investigate effects on
the low-$T$ magnetic order. Contrary to theoretical predictions we find that
the magnetic ordering temperature as well as the ordered magnetic moment
increase at high pressure (compressive strain).",2212.08439v1
2022/12/22,Lattice constants and magnetism of L10-ordered FePt under high pressure,"We studied the relationship between the lattice constant and magnetism of
L10-ordered FePt under high pressure by means of first-principles calculations
and synchrotron x-ray measurements. Based on our calculations, we found that
the c/a ratio shows an anomaly at ~ 20 GPa and that the Pt magnetic moment is
sharply suppressed at ~ 60 GPa. As for the c/a, we experimentally verified the
anomaly at ~ 20 GPa by powder x-ray diffraction. We also measured the x-ray
magnetic circular dichroism at the Pt L edge up to ~ 20 GPa. Any significant
change of the Pt magnetic moment was not observed, in agreement with the
calculations. These results thus indicate the possibility that novel magnetic
states can be created in L10-ordered FePt by lattice deformation under high
pressure.",2212.12065v1
2023/1/19,Maple Leaf Antiferromagnet in a Magnetic Field,"We analyze the quantum antiferromagnet on the maple leaf lattice in the
presence of a magnetic field. Starting from its exact dimer ground state and
for a magnetic field strength of the order of the local dimer spin exchange
coupling, we perform a strong coupling expansion and extract an effective
hardcore boson model. The interplay of effective many-body interactions,
suppressed single-particle dynamics, and correlated hopping gives way to an
intriguing series of superfluid to insulator transitions which correspond to
magnetization plateaux in terms of the maple leaf spin degrees of freedom.
While we find plateaux at intermediate magnetization to be dominated by bosonic
density wave order, we conjecture plateau formation from multi-boson bound
states due to correlated hopping for lower magnetization.",2301.08264v2
2023/1/27,Solid-state lithium-ion supercapacitor for voltage control of skyrmions,"Ionic control of magnetism gives rise to high magneto-electric coupling
efficiencies at low voltages, which is essential for low-power magnetism-based
non-conventional computing technologies. However, for on-chip applications,
magneto-ionic devices typically suffer from slow kinetics, poor cyclability,
impractical liquid architectures or strong ambient effects. As a route to
overcoming these problems, we demonstrate an LiPON-based solid-state ionic
supercapacitor with a magnetic Pt/Co$_{40}$Fe$_{40}$B$_{20}$/Pt thin-film
electrode which enables voltage control of a magnetic skyrmion state. Skyrmion
nucleation and annihilation are caused by Li ion accumulation and depletion at
the magnetic interface under an applied voltage. The skyrmion density can be
controlled through dc applied fields or through voltage pulses. The skyrmions
are nucleated by single 60-$\mu$s voltage pulses and devices are cycled 750,000
times without loss of electrical performance. Our results demonstrate a simple
and robust approach to ionic control of magnetism in spin-based devices.",2301.11585v1
2023/2/2,Designing layered 2D skyrmion lattices in moiré magnetic hetero-structures,"Skyrmions are promising for the next generation of spintronic and magnonic
devices, but their zero-field stability and controlled nucleation through
chiral interactions remain challenging. In this theoretical study, we explore
the potential of moir\'e magnetic heterostructures to generate ordered skyrmion
lattices from the stacking-dependent magnetism in 2D magnets. We consider
heterostructures formed by twisting ultrathin CrBr_3 films on top of CrI_3
substrates, assuming a moderate interfacial Dzyaloshinskii-Moriya interaction.
At large moir\'e periodicity and appropriate substrate thickness, a moir\'e
skyrmion lattice emerges in the interfacial CrBr_3 layer due to the weaker
exchange interactions in CrBr_3 compared to CrI_3. This lattice is then
projected to the remaining layers of the CrBr_3 film via emergent chiral
interlayer fields. By varying the pristine stacking configurations within the
ultrathin CrBr_3 film, we realize layered ferromagnetic and antiferromagnetic
skyrmion lattices without the need for a permanent magnetic field. Our findings
suggest the possibility of creating colorful skyrmion lattices in moir\'e
magnetic heterostructures, enabling further exploration of their fundamental
properties and technological relevance.",2302.01074v2
2023/2/7,Magnetic Ball Chain Robots for Endoluminal Interventions,"This paper introduces a novel class of hyperredundant robots comprised of
chains of permanently magnetized spheres enclosed in a cylindrical polymer
skin. With their shape controlled using an externally-applied magnetic field,
the spherical joints of these robots enable them to bend to very small radii of
curvature. These robots can be used as steerable tips for endoluminal
instruments. A kinematic model is derived based on minimizing magnetic and
elastic potential energy. Simulation is used to demonstrate the enhanced
steerability of these robots in comparison to magnetic soft continuum robots
designed using either distributed or lumped magnetic material. Experiments are
included to validate the model and to demonstrate the steering capability of
ball chain robots in bifurcating channels.",2302.03728v1
2023/2/10,Photocarrier Transport of Ferroelectric Photovoltaic Thin Films Detected by the Magnetic Dynamics of Adjacent Ferromagnetic Layers,"We have observed photocarrier transport behaviors in
BiFeO$_3$/La$_{1-x}$Sr$_x$MnO$_3$~(BFO/LSMO) heterostructures by using
time-resolved synchrotron x-ray magnetic circular dichroism in reflectivity.
The magnetization of LSMO layers was used as a probe of photo-induced carrier
dynamics in the photovoltaic BFO layers. During the photo-induced
demagnetization process, the decay time of LSMO~($x$=0.2) magnetization
strongly depends on the ferroelectric polarization direction of the BFO layer.
The variation of decay time should be attributed to the different sign of
accumulated photocarriers at the BFO/LSMO interface induced by the photovoltaic
effect of the BFO layer. The photocarriers can reach the BFO/LSMO interface and
influence the magnetization distribution in the LSMO layers within the
timescale of $\sim$100~ps. Our results provide a novel strategy to investigate
carrier dynamics and mechanisms of optical control of magnetization in thin
film heterostructures.",2302.05000v1
2023/2/15,A strain-controlled magnetostrictive pseudo spin valve,"Electric-field control of magnetism via inverse magnetostrictive effect is an
efficient path towards improving energy-efficient storage and sensing devices
based on giant magnetoresistance effect. In this letter, we report on lateral
electric-field driven strain-mediated modulation of magnetic properties in
Co$/$Cu$/$Py pseudo spin valve grown on ferroelectric PMN-PT substrate. We show
a decrease of the giant magnetoresistance ratio of the pseudo spin valve with
increasing electric field, which is attributed to the deviation of the Co layer
magnetization from the initial direction due to strain-induced magnetoelastic
anisotropy contribution. Additionally, we demonstrate that strain-induced
magnetic anisotropy effectively shifts the switching field of the
magnetostrictive Co layer, while keeping the switching field of the nearly
zero-magnetostrictive Py layer unaffected due to its negligible
magnetostriction constant. We argue that magnetostrictively optimized magnetic
films in properly engineered multilayered structures can offer a path to
enhancing the selective magnetic switching in spintronic devices.",2302.07620v1
2023/2/26,Emergence of net magnetization by magnetic-field-biased diffusion in antiferromagnetic L1$_0$ NiMn,"NiMn is a collinear antiferromagnet with high magneto crystalline anisotropy
($K_2=-9.7\times10^5\;\text{J m}^{-3}$). Through magnetic annealing of NiMn
with excess Ni, strongly pinned magnetic moments emerge due to an imbalance in
the distribution of Ni in the antiferromagnetic Mn-sublattices. The results are
explained with a model of magnetic-field-biased diffusion, supported by ab
initio calculations. Another observation is the oxidation of Mn at the surface,
causing an enrichment of Ni in the sub-surface region. This leads to an
additional ferromagnetic response appearing in the magnetization measurements,
which can be removed by surface polishing.",2302.13387v1
2023/3/20,"Magnetization, dielectric and thermal studies in the double perovskite polycrystalline compound Tm2CoMnO6","We report here a comprehensive study on structural, magnetic, caloric and
electronic properties of the monoclinic phase of double perovskite compound
Tm2CoMnO6 (TCMO) in its polycrysttaline format. Magnetic measurements confirm
the presence of thermal hysteresis in magnetization indicates towards a first
order magnetic transition at its critical point (Tc). Our study finds the
metamagnetic jump in isothermal M(H) at 2 K that signifies the rare earth spin
allignement in loop cycling above a certain critical field. This jump is only
present at very low T that dies out as the T raises. M(H) measurements at
different temperature stipulate that Co2+ and Mn4+ do not order completely
inspite of strong ferromagnetic correlation that is against the previous study
on TCMO. The concurrence of structral, magnetic and dielectric anomaly at Tc
suggest its possible magnetostructural copuling. We found a high dielectric
constant (2700) in TCMO and the Maxwell-Wagner electrial loss spectrum analysis
hints towards a long range hopping mechanism. Sizeable magnetocaloric effect in
terms of entropy change across the transition temperatures has been obtained
from heat capacity data that clearly corroborates its intrinsic behaviour.",2303.10907v2
2023/3/28,Analysis of ultrafast magnetization switching dynamics in exchange-coupled ferromagnet-ferrimagnet heterostructures,"Magnetization switching in ferromagnets has so far been limited to the
current-induced spin-orbit-torque effects. Recent observation of
helicity-independent all-optical magnetization switching in exchange-coupled
ferromagnet ferrimagnet heterostructures expanded the range and applicability
of such ultrafast heat-driven magnetization switching. Here we report the
element-resolved switching dynamics of such an exchange-coupled system, using a
modified microscopic three-temperature model. We have studied the effect of i)
the Curie temperature of the ferromagnet, ii) ferrimagnet composition, iii) the
long-range RKKY exchange-coupling strength, and iv) the absorbed optical energy
on the element-specific time-resolved magnetization dynamics. The phase-space
of magnetization illustrates how the RKKY coupling strength and the absorbed
optical energy influence the switching time. Our analysis demonstrates that the
threshold switching energy depends on the composition of the ferrimagnet and
the switching time depends on the Curie temperature of the ferromagnet as well
as RKKY coupling strength. This simulation anticipates new insights into
developing faster and more energy-efficient spintronics devices.",2303.16294v1
2023/4/28,Multilayer metamaterials with mixed ferromagnetic domain core and antiferromagnetic domain wall structure,"Magnetic nano-objects possess great potential for more efficient data
processing, storage and neuromorphic type of applications. Using high
perpendicular magnetic anisotropy synthetic antiferromagnets in the form of
multilayer-based metamaterials we purposely reduce the antiferromagnetic (AF)
interlayer exchange energy below the out-of-plane demagnetization energy, which
controls the magnetic domain formation. As we show via macroscopic magnetometry
as well as microscopic Lorentz transmission electron microscopy, in this
unusual magnetic energy regime, it becomes possible to stabilize nanometer
scale stripe and bubble textures consisting of ferromagnetic (FM) out-of-plane
domain cores separated by AF in-plane Bloch-type domain walls. This unique
coexistence of mixed FM/AF order on the nanometer scale opens so far unexplored
perspectives in the architecture of magnetic domain landscapes as well as the
design and functionality of individual magnetic textures, such as bubble
domains with alternating chirality.",2304.14775v1
2023/5/6,Field-Free Spin-Orbit Torque driven Switching of Perpendicular Magnetic Tunnel Junction through Bending Current,"Current-induced spin-orbit torques (SOTs) enable fast and efficient
manipulation of the magnetic state of magnetic tunnel junctions (MTJs), making
it attractive for memory, in-memory computing, and logic applications. However,
the requirement of the external magnetic field to achieve deterministic
switching in perpendicular magnetized SOT-MTJs limits its implementation for
practical applications. Here, we introduce a field-free switching (FFS)
solution for the SOT-MTJ device by shaping the SOT channel to create a ""bend""
in the SOT current. The resulting bend in the charge current creates a
spatially non-uniform spin current, which translates into inhomogeneous SOT on
an adjacent magnetic free layer enabling deterministic switching. We
demonstrate FFS experimentally on scaled SOT-MTJs at nanosecond time scales.
This proposed scheme is scalable, material-agnostic, and readily compatible
with wafer-scale manufacturing, thus creating a pathway for developing purely
current-driven SOT systems.",2305.03961v1
2023/5/17,Quantum disordered ground state in the spin-orbit coupled Jeff = 1/2 distorted honeycomb magnet BiYbGeO5,"We delineate quantum magnetism in the strongly spin-orbit coupled, distorted
honeycomb-lattice antiferromagnet BiYbGeO$_{5}$. Our magnetization and heat
capacity measurements reveal that its low-temperature behavior is well
described by an effective $J_{\rm eff}=1/2$ Kramers doublet of Yb$^{3+}$. The
ground state is nonmagnetic with a tiny spin gap. Temperature-dependent
magnetic susceptibility, magnetization isotherm, and heat capacity could be
modeled well assuming isolated spin dimers with anisotropic exchange
interactions $J_{\rm Z} \simeq 2.6$~K and $J_{\rm XY} \simeq 1.3$~K. Heat
capacity measurements backed by muon spin relaxation suggest the absence of
magnetic long-range order down to at least 80\,mK both in zero field and in
applied fields. This sets BiYbGeO$_5$ apart from Yb$_2$Si$_2$O$_7$ with its
unusual regime of magnon Bose-Einstein condensation and suggests negligible
interdimer couplings, despite only a weak structural deformation of the
honeycomb lattice.",2305.10221v1
2023/5/25,Origin of magnetic anisotropy in $La_{(1\-x)}Sr_{x}MnO_{3}$,"Here, we report the origin of magnetic anisotropy in Sr-doped infinite layer
manganites $La_{(1\-x)}Sr_{x}MnO_{3}$ (0.125 \leq x \leq 0.400). Magnetic
anisotropy is responsible for the large difference in the temperature
dependence of field-cooled and zero-field-cooled magnetization. Translational
symmetry breaking in the context of spins around the boundary between the
ferromagnetic (FM) antiferromagnetic (AFM) region leads to FM-AFM interaction
and results in magnetic anisotropy (exchange anisotropy). Here, we propose that
FM-AFM interaction around the boundary between FM clusters or domains in the
AFM background or between AFM clusters or domains in the ferromagnetic
background is responsible for doping-dependent nonmonotonic behavior and the
origin of magnetic anisotropy.",2305.16493v1
2023/6/1,Structural Trends and Itinerant Magnetism of the New Cage-structured Compound HfMn$_{2}$Zn$_{20}$,"A new cage-structured compound - HfMn$_{2}$Zn$_{20}$ - belonging to the
AB$_{2}$C$_{20}$ (A, B = transition or rare earth metals, and C = Al, Zn, or
Cd) family of structures has been synthesized via the self-flux method. The new
compound crystallizes in the space group Fd-3m with lattice parameter a =
14.0543(2) \r{A} (Z = 8) and exhibits non-stoichiometry due to Mn/Zn mixing on
the Mn-site and an underoccupied Hf-site. The structure refines to
Hf$_{0.93}$Mn$_{1.63}$Zn$_{20.37}$ and follows lattice size trends when
compared to other HfM$_{2}$Zn$_{20}$ (M = Fe, Co, and Ni) structures. The
magnetic measurements show that this compound displays a modified Curie-Weiss
behavior with a transition temperature around 22 K. The magnetization shows no
saturation, a small magnetic moment, and near negligible hysteresis, all signs
of the itinerant magnetism. The Rhodes-Wohlfarth ratio and the spin fluctuation
parameters ratio both confirm the itinerant nature of the magnetism in
HfMn$_{2}$Zn$_{20}$.",2306.01146v3
2023/6/17,Coherent two-dimensional THz magnetic resonance spectroscopies for molecular magnets: Analysis of Dzyaloshinskii-Moriya interaction,"To investigate the novel quantum dynamic behaviors of magnetic materials that
arise from complex spin-spin interactions, it is necessary to probe the
magnetic response at a speed greater than the spin-relaxation and dephasing
processes. Recently developed two-dimensional (2D) terahertz magnetic resonance
(THz-MR) spectroscopy techniques use the magnetic components of laser pulses,
and this allows investigation of the details of the ultrafast dynamics of spin
systems. For such investigations, quantum treatment -- not only of the spin
system itself but also of the environment surrounding the spin system -- is
important. In our method, based on the theory of multidimensional optical
spectroscopy, we formulate nonlinear THz-MR spectra using an approach based on
the numerically rigorous hierarchical equations of motion. We conduct numerical
calculations of both linear (1D) and 2D THz-MR spectra for a linear chiral spin
chain. The pitch and direction of chirality (clockwise or anticlockwise) are
determined by the strength and sign of the Dzyaloshinskii-Moriya interaction
(DMI). We show that not only the strength but also the sign of the DMI can be
evaluated through the use of 2D THz-MR spectroscopic measurements, while 1D
measurements allow us to determine only the strength.",2306.10222v1
2023/7/14,Observation and control of hybrid spin-wave-Meissner-current transport modes,"Superconductors are materials with zero electrical resistivity and the
ability to expel magnetic fields known as the Meissner effect. Their
dissipationless diamagnetic response is central to magnetic levitation and
circuits such as quantum interference devices. Here, we use superconducting
diamagnetism to shape the magnetic environment governing the transport of spin
waves - collective spin excitations in magnets that are promising on-chip
signal carriers - in a thin-film magnet. Using diamond-based magnetic imaging,
we observe hybridized spin-wave-Meissner-current transport modes with strongly
altered, temperature-tunable wavelengths. We extract the temperature-dependent
London penetration depth from the wavelength shifts and realize local control
of spin-wave refraction using a focused laser. Our results demonstrate the
versatility of superconductor-manipulated spin-wave transport and have
potential applications in spin-wave gratings, filters, crystals and cavities.",2307.07581v1
2023/7/20,Quantitative investigation of the short-range magnetic correlations in candidate quantum spin liquid NaYbO$_2$,"We present a neutron diffraction study of NaYbO$_2$, a candidate quantum spin
liquid compound hosting a geometrically frustrated triangular lattice of
magnetic Yb$^{3+}$ ions. We observe diffuse magnetic scattering that persists
to at least 20 K, demonstrating the presence of short-range magnetic
correlations in this system up to a relatively high energy scale. Using reverse
Monte Carlo and magnetic pair distribution function analysis, we confirm the
predominant antiferromagnetic nature of these correlations and show that the
diffuse scattering data can be well described by noninteracting layers of XY
spins on the triangular lattice. We rule out Ising spins and
short-range-ordered stripe or 120$^{\circ}$ phases as candidate ground states
of NaYbO$_2$. These results are consistent with a possible QSL ground state in
NaYbO$_2$ and showcase the benefit of combined reciprocal- and real-space
analysis of materials with short-range magnetic correlations.",2307.10582v2
2023/7/26,Highly Tunable Perpendicular Magnetic Anisotropy and Anisotropic Magnetoresistance in Ru-doped La0.67Sr0.33MnO3 Epitaxial Films,"As a prototypical half-metallic ferromagnet, La0.67Sr0.33MnO3 (LSMO) has been
extensively studied due to its versatile physical properties and great
potential in spintronic applications. However, the weak perpendicular magnetic
anisotropy (PMA) limits the controllability and detection of magnetism in LSMO,
thus hindering the realization of oxide-based spintronic devices with low
energy consumption and high integration level. Motivated by this challenge, we
develop an experimental approach to enhance the PMA of LSMO epitaxial films. By
cooperatively introducing 4d Ru doping and a moderate compressive strain, the
maximum uniaxial magnetic anisotropy in Ru-doped LSMO can reach 3.0 to 1E5 J/m3
at 10 K. Furthermore, we find a significant anisotropic magnetoresistance
effect in these Ru-doped LSMO films, which is dominated by the strong PMA. Our
findings offer an effective pathway to harness and detect the orientations of
magnetic moments in LSMO films, thus promoting the feasibility of oxide-based
spintronic devices, such as spin valves and magnetic tunnel junctions.",2307.13881v1
2023/8/11,"Goodenough-Kanamori-Anderson rules in 2D magnet: A chemical trend in MCl2 with M=V, Mn, and Ni","Density-functional-theory calculations were performed to investigate the
magnetism in a series of triangular-lattice monolayer MCl2 (M=V, Mn, and Ni).
The magnetic stability manifests a distinct chemical trend; VCl2 and MnCl2 show
the antiferromagnetic ground states and NiCl2 shows the ferromagnetic ground
state. The microscopic mechanism behind the magnetic interaction is explained
by the so-called Goodenough-Kanamori-Anderson rules and by the virtual-hopping
process through the hopping integrals between the 3d-orbital maximally
localized Wannier functions. Our result highlights the role of the direct
exchange interaction and the superexchange interaction in the magnetic
stabilization in two-dimensional magnets.",2308.06068v1
2023/8/22,Enhancements of Electron-Atom Collisions due to Pauli Repulsion in Neutron-Star Magnetic Fields,"Neutron star surfaces and atmospheres are unique environments that sustain
the largest-known magnetic fields in the universe. Our knowledge of neutron
star material properties, including the composition and equation of state,
remains highly unconstrained. Electron-atom collisions are integral to
theoretical thermal conduction and spectral emission models that describe
neutron star surfaces. The theory of scattering in magnetic fields was
developed in the 1970s, but focused only on bare nuclei scattering. In this
work, we present a quantum treatment of atom-electron collisions in magnetic
fields; of significant importance is the inclusion of Pauli repulsion arising
from two interacting electrons. We find strange behaviors not seen in
collisions without a magnetic field. In high magnetic fields, Pauli repulsion
can lead to orders of magnitude enhancements of collision cross sections.
Additionally, the elastic collision cross sections that involve the ground
state become comparable to those involving excited states, and states with
large orbits have the largest contribution to the collisions. We anticipate
significant changes to transport properties and spectral line broadening in
neutron star surfaces and atmospheres, which will aid in spectral diagnostics
of these extreme environments.",2308.11667v1
2023/9/6,Numerical analysis of voltage-controlled magnetization switching operation in magnetic-topological-insulator-based devices,"We theoretically investigate influences of electronic circuit delay, noise
and temperature on write-error-rate (WER) in voltage-controlled magnetization
switching operation of a magnetic-topological-insulator-based (MTI) device by
means of the micromagnetic simulation. This device realizes magnetization
switching via spin-orbit torque(SOT) and voltage-controlled magnetic anisotropy
(VCMA) which originate from 2D-Dirac electronic structure. We reveal that the
device operation is extremely robust against circuit delay and signal-to-noise
ratio. We demonstrate that the WER on the order of approximately $10^{-4}$ or
below is achieved around room temperature due to steep change in VCMA. Also, we
show that the larger SOT improves thermal stability factor. This study provides
a next perspective for developing voltage-driven spintronic devices with
ultra-low power consumption.",2309.03043v1
2023/9/8,Chiral magneto-phonons with tunable topology in anisotropic quantum magnets,"We propose a mechanism to obtain chiral phonon-like excitations from the
bond-dependent magnetoelastic couplings in the absence of out-of-plane
magnetization and magnetic fields. We provide a systematic way to understand
the hybrid excitation by its phononic analog, and thus we dub it
magneto-phonon. We recognize that the system is equivalent to the class D of
topological phonons, and show the tunable chirality and topology by an in-plane
magnetic field in the example of a triangular lattice ferromagnet. As a
possible experimental probe, we evaluate the phonon magnetization and the
thermal Hall conductivity. Our study gives a new perspective on tunable
topological and chiral excitations without Dzyaloshinskii-Moriya or Raman spin
interactions, which suggests possible applications of spintronics and phononics
in various anisotropic magnets and/or Kitaev materials.",2309.04064v2
2023/9/18,Tunable Tesla-scale magnetic attosecond pulses through ring-current gating,"Coherent control over electron dynamics in atoms and molecules using
high-intensity circularly-polarized laser pulses gives rise to current loops,
resulting in the emission of magnetic fields. We propose and demonstrate with
ab-initio calculations ``current-gating"" schemes to generate direct or
alternating-current magnetic pulses in the infrared spectral region, with
highly tunable waveform and frequency, and showing femtosecond-to-attosecond
pulse duration. In optimal conditions, the magnetic pulse can be highly
isolated from the driving laser and exhibits a high flux density ($\sim1$ Tesla
at few hundred nanometers from the source, with a pulse duration of 787
attoseconds) for application in forefront experiments of ultrafast
spectroscopy. Our work paves the way toward the generation of attosecond
magnetic fields to probe ultrafast magnetization, chiral responses, and spin
dynamics.",2309.09654v1
2023/9/27,Investigation of magnetic properties of $4f$-adatoms on graphene,"Rare-earth (RE) atoms on top of 2D materials represent an interesting
platform with the prospect of tailoring the magnetic anisotropy for practical
applications. Here, we investigate the ground state and magnetic properties of
selected $4f$-atoms deposited on a graphene substrate in the framework of the
DFT+$U$ approach. The inherent strong spin-orbit interaction in conjunction
with crystal field effects acting on the localized $4f$-shells results in a
substantial magnetic anisotropy energy (tens of meVs), whose angular dependence
is dictated by the $C_{6v}$ symmetry of the graphene substrate. We obtain the
crystal field parameters and investigate spin-flip events via quantum tunneling
of magnetization in the view of achieving a protected quantum-spin behavior.
Remarkably, the large spin and orbital moments of the open $4f$-shells (Dy, Ho
and Tm) generate a strong magneto-elastic coupling which provides more
flexibility to control the magnetic state via the application of external
strain.",2309.15513v1
2023/9/24,Effect of organic solvent on the cold sintering processing of SrFe12O19 platelet-based permanent magnets,"In this work we have investigated the effect of the solvent during the
processing of SrFe12O19 platelet-based permanent magnets by cold sintering
process (CSP) plus a post-thermal treatment. Several organic solvents: glacial
acetic acid, oleic acid and oleylamine have been analyzed, optimizing the CSP
temperatures at 190-270 {\deg}C, under pressures of 375-670 MPa and 6-50 wt% of
solvent. Modifications in the morphological and structural properties are
identified depending on the solvent, which impacts on the magnetic response.
Independently of the solvent, the mechanical integrity of ferrite magnets
obtained by CSP is improved by a post-annealing at 1100 {\deg}C for 2 h,
resulting in relative densities around 92 % with an average grain size of 1
{\mu}m and a fraction of SrFe12O19 phase > 91 %. Hc > 2.1 kOe and MS of 73
emu/g are obtained in the final sintered ceramic magnets, exhibiting the
highest HC value of 2.8 kOe for the magnet sintered using glacial acetic acid.",2309.15859v1
2023/10/4,Magnetic field induces giant nonlinear optical response in Weyl semimetals,"We study the second-order optical response of Weyl semimetals in the presence
of a magnetic field. We consider an idealized model of a perfectly linear Weyl
node and use the Kubo formula at zero temperature to calculate the intrinsic
contribution to photocurrent and second harmonic generation conductivity
components. We obtain exact analytical expressions applicable at arbitrary
values of frequency, chemical potential, and magnetic field. Our results show
that finite magnetic field significantly enhances the nonlinear optical
response in semimetals, while magnetic resonances lead to divergences in
nonlinear conductivity. In realistic systems, these singularities are
regularized by a finite scattering rate, but result in pronounced peaks which
can be detected experimentally, provided the system is clean and interactions
are weak. We also perform a semiclassical calculation that complements and
confirms our microscopic results at small magnetic fields and frequencies.",2310.02578v2
2023/10/4,Structure transition and zigzag magnetic order in Ir/Rh-substituted honeycomb lattice RuCl3,"We report magnetization and neutron diffraction studies on crystal and
magnetic structures of Ir- and Rh-substituted honeycomb lattice
$\alpha$-RuCl$_3$. The iridium or rhodium atoms are distributed at the Ru site
with little structural modification. Both systems undergo a room-temperature
monoclinic $C2/m$ to low-temperature trigonal $R\bar{3}$ phase transformation
with a large recoverable hysteresis. At low temperature, a zigzag spin order is
observed with the same characteristic wavevector $(0,0.5,1)$ as in the parent
$\alpha$-RuCl$_3$. Detailed magnetic structure refinement reveals an ordered
moment of $\rm 0.32(5) \mu_B/Ru$ and a upper boundary of canting angle of
$15(4)^\circ$ away from the basal plane at 5~K for the 10\% Ir-substituted
$\alpha$-RuCl$_3$, which is different from the 0.45-0.73~$\rm \mu_B/Ru$ and
$32^\circ$-$48^\circ$ canting angle reported in the parent compound
$\alpha$-RuCl$_3$. The observation of unchanged RuCl$_6$ local octahedral
environment, reduced magnetic moment size and canting angle highlights the
potential to study quantum spin liquid behavior through non-magnetic ion
doping.",2310.02965v1
2023/10/16,Emergent spin-gapped magnetization plateaus in a spin-1/2 perfect kagome antiferromagnet,"The two-dimensional (2D) spin-1/2 kagome Heisenberg antiferromagnet is
believed to host quantum spin liquid (QSL) states with no magnetic order, but
its ground state remains largely elusive. An important outstanding question
concerns the presence or absence of the 1/9 magnetization plateau, where exotic
quantum states, including topological ones, are expected to emerge. Here we
report the magnetization of a recently discovered kagome QSL candidate
YCu$_3$(OH)$_{6.5}$Br$_{2.5}$ up to 57 T. Above 50 T, a clear magnetization
plateau at 1/3 of the saturation moment of Cu$^{2+}$ ions is observed,
supporting that this material provides an ideal platform for the kagome
Heisenberg antiferromagnet. Remarkably, we found another magnetization plateau
around 20 T, which is attributed to the 1/9 plateau. The temperature dependence
of this plateau reveals the distinct spin gap, whose magnitude estimated by the
plateau width is approximately 10% of the exchange interaction. The observation
of 1/9 and 1/3 plateaus highlights the emergence of novel states in quantum
spin systems.",2310.10069v1
2023/10/22,Critical behavior and magnetocaloric effect in Tsai-type 2/1 and 1/1 quasicrystal approximants,"Stable Tsai-type quinary 1/1 and 2/1 approximant crystals (ACs) with chemical
compositions Au56.25Al10Cu7In13Tb13.75 and Au55.5Al10Cu7In13Tb14.5,
respectively, exhibiting ferromagnetic (FM) long-range orders were successfully
synthesized and studied for their magnetic properties and magnetocaloric
effect. The 1/1 and 2/1 ACs primarily differ in their long-range atomic
arrangement and rare earth (RE) distribution, with the latter approaching
quasiperiodic order while still preserving periodicity. Analyses based on the
scaling principle and Kouvel-Fisher (KF) relations suggested mean-field-like
behavior near Curie temperatures in both compounds. From magnetization
measurements and the Maxwell equation, a magnetic entropy change of -4.3 and
-4.1 J/K mol Tb were derived under a magnetic field change of 7 T for the 1/1
and 2/1 ACs, respectively. The results indicated a prominent role of
intra-cluster magnetic interactions on critical behavior and magnetic entropy
of the Tsai-type compounds.",2310.14292v1
2023/10/30,Role of Brownian motion and Néel relaxations in Mossbauer spectra of magnetic liquids,"The absorption cross section of M\""{o}ssbauer radiation in magnetic liquids
is calculated, taking into consideration both translational and rotational
Brownian motion of magnetic nanoparticles. Stochastic reversals of their
magnetization are also regarded in the absence of external magnetic field. The
role of Brownian motion in ferrofluids is considered in the framework of the
diffusion theory, while for the magnetorheological fluids with large
nanoparticles it is done in the framework of the Langevin's approach. For
rotation we derived the equation analogous to Langevin's equation and gave the
corresponding correlation function. In both cases the equations for rotation
are solved in the approximation of small rotations during lifetime of the
excited state of M\""{o}ssbauer nuclei. The influence of magnetization
relaxations is studied with the aid of the Blume-Tjon model.",2310.19599v1
2023/11/6,2D Magnetic Heterostructures: Spintronics and Quantum Future,"The discovery of two-dimensional (2D) magnetism within atomically thin
structures derived from layered crystals has opened up a new realm for
exploring magnetic heterostructures. This emerging field provides a
foundational platform for investigating unique physical properties and
exquisite phenomena at the nanometer and molecular/atomic scales. By
engineering 2D interfaces using physical methods and selecting interlayer
interactions, we unlock the potential for extraordinary exchange dynamics. This
potential extends to high-performance and high-density magnetic memory
applications, as well as future advancements in neuromorphic and quantum
computing. This review delves into recent advances in 2D magnets, elucidates
the mechanisms behind 2D interfaces, and highlights the development of 2D
devices for spintronics and quantum information. Particular focus is placed on
2D magnetic heterostructures with topological properties, promising for a
resilient and low-error information system. Finally, we discuss the trends of
2D heterostructures for future electronics, considering the challenges and
opportunities from physics, material synthesis, and technological prospective.",2311.03505v1
2023/11/27,What are the emergent fermions and gauge fields in magnetized kagome spin liquid?,"Inspired by the recent quantum oscillation measurement on the kagom\'{e}
lattice antiferromagnet in finite magnetic fields, we raise the question about
the physical contents of the emergent fermions and the gauge fields if the U(1)
spin liquid is relevant for the finite-field kagom\'{e} lattice
antiferromagnet. Clearly, the magnetic field is non-perturbative in this
regime, and the finite-field state has no direct relation with the U(1) Dirac
spin liquid proposal at zero field. Based on the dual vortex theory, we here
propose that, the $S^z$ magnetization is the emergent U(1) gauge flux, and the
fermionized dual vortex is the emergent fermion. In this formalism, the
magnetic field polarizes the spin component along the field direction that
modulates the U(1) flux for the fermionized vortices and generates the quantum
oscillation. Within the mean-field theory, we further discuss gauge field
correlation, vortex-antivortex continuum and thermal Hall effect. We expect
this work to provide a bit insight for the magnetized kagom\'{e} spin liquids.",2311.15911v1
2023/12/4,Negative Magnetization and Magnetic Ordering of Rare Earth and Transition Metal Sublattices in NdFe0.5Cr0.5O3,"We investigate the effect of alloying at the 3d transition metal site of a
rare-earth-transition metal oxide, by considering NdFe0.5Cr0.5O3 alloy with two
equal and random distribution of 3d ions, Cr and Fe, interacting with an early
4f rare earth ion, Nd. Employing temperature- and field-dependent magnetization
measurements, temperature-dependent x-ray diffraction, neutron powder
diffraction, and Raman spectroscopy, we characterize its structural and
magnetic properties. Our study reveals bipolar magnetic switching (arising from
negative magnetization) and magnetocaloric effect which underline the potential
of the studied alloy in device application. The neutron diffraction study shows
the absence of spin reorientation transition over the entire temperature range
of 1.5-320 K, although both parent compounds exhibit spin orientation
transition. We discuss the microscopic origin of this curious behavior. The
neutron diffraction results also reveal the ordering of Nd spins at an
unusually high temperature of about 40 K, which is corroborated by Raman
measurements.",2312.01595v1
2023/12/4,Nuclear and magnetic structure of an epitaxial La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ film using diffraction methods,"We use a combination of transmission electron microscopy, X-Ray and neutron
diffraction, SQUID magnetometry and symmetry analysis to determine the nuclear
and magnetic structure of an epitaxial LSMO film, deposited on a Si substrate.
The film undergoes a magnetic ordering transition at 260K. At 300K, in the
paramagnetic phase, the manganite film has a $I4/m$ space group. In the
magnetic phase, SQUID and neutron diffraction results lead us to assign a
ferromagnetic spin-order to the film, associated to magnetic moments with a
slightly out-of-plane component, namely $(3.5, 0, 0.3)\,\mu_B$. Symmetry
analysis further shows that only the $P\bar 1'$ group is compatible with such a
magnetic ordering.",2312.01931v1
2023/12/15,A study on the kinetic arrest of magnetic phases in nanostructured Nd0.6Sr0.4MnO3 thin films,"The Nd0.6Sr0.4MnO3 manganite system exhibits a phase transition from
paramagnetic insulating (PMI) to ferromagnetic metallic (FMM) state around its
Curie temperature TC = 270 K (bulk). The morphology-driven changes in the
kinetically arrested magnetic phases in NSMO thin films with granular and a
crossed-nano-rod-type morphology are studied. At low temperatures, the
manganite thin films possess a magnetic glassy state arising from the
coexistence of the high-temperature PMI phase and the low-temperature FMM
phase. The extent of kinetic arrest and its relaxation was studied using the
""cooling and heating in unequal field (CHUF)"" protocol in magnetic and
magneto-transport investigations. The sample with rod morphology showed a large
extent of phase coexistence compared to the granular sample. Further, with a
field-cooling protocol, time-evolution studies were carried out to understand
the relaxation of arrested magnetic phases across these morphologically
distinct thin films. The results on the devitrification of the arrested
magnetic state are interpreted from the point of view of homogeneous and
heterogeneous nucleation of the FM phase in the PM matrix with respect to
temperature.",2312.09700v2
2024/1/26,Efficient Control of Magnetization Dynamics Via W/CuO$_\text{x}$ Interface,"Magnetization dynamics, which determine the speed of magnetization switching
and spin information propagation, play a central role in modern spintronics.
Gaining its control will satisfy the different needs of various spintronic
devices. In this work, we demonstrate that the surface oxidized Cu
(CuO$_\text{x}$) can be employed for the tunability of magnetization dynamics
of ferromagnet (FM)/heavy metal (HM) bilayer system. The capping CuO$_\text{x}$
layer in CoFeB/W/CuO$_\text{x}$ trilayer reduces the magnetic damping value in
comparison with the CoFeB/W bilayer. The magnetic damping even becomes lower
than that of the CoFeB/CuO$_\text{x}$ by ~ 16% inferring the stabilization of
anti-damping phenomena. Further, the reduction in damping is accompanied by a
very small reduction in the spin pumping-induced output DC voltage in the
CoFeB/W/CuO$_\text{x}$ trilayer. The simultaneous observation of anti-damping
and spin-to-charge conversion can be attributed to the orbital Rashba effect
observed at the HM/CuO$_\text{x}$ interface. Our experimental findings
illustrate that the cost-effective CuO$_\text{x}$ can be employed as an
integral part of modern spintronics devices owing to its rich underneath
spin-orbital physics.",2401.14708v1
2024/1/30,"Magneto-synthesis effect on magnetic order, phonons, and magnons in single-crystal Sr$_2$IrO$_4$","It was shown earlier that applying a magnetic field during the growth of
Sr$_2$IrO$_4$, also known as ""field-alteration"", induces significant changes to
its structural, magnetic, and transport properties. However, the microscopic
nature of these changes is enigmatic. In this study, we employed resonant
elastic and inelastic x-ray scattering, as well as Raman scattering, to
investigate samples from two batches of Sr$_2$IrO$_4$ grown in magnetic fields
of different strengths. Our findings reveal that samples grown in a weaker
magnetic field have similar magnetic order to non-altered samples, whereas
those grown in a stronger field show a different stacking of weak in-plane
ferromagnetic moments. Additionally, we observed significant softening and
broadening of select Raman-active phonons in the field altered samples, with a
stronger effect in the samples grown in the stronger field. We discuss insights
that our results provide into the microscopic nature of field-alteration in
Sr$_2$IrO$_4$.",2401.17407v1
2024/2/12,Photoinduced Topological Phase Transitions in a Kitaev kagome magnet,"Based on the magnetic Floquet-Bloch theory, we investigate topological
natures of Floquet magnons in a laser-irradiated kagome magnet exhibiting
Heisenberg, Kitaev and Dzyaloshinskii Moriya interactions in the presence of an
external magnetic field applied along directions of [111]. In a strong magnetic
field perpendicular to the lattice plane [111] direction, the system is in the
fully polarized paramagnetic phase and the magnon band carries an asymmetric
Chern number throughout the region of the phase diagram. Our results show that
periodically driven intrinsic topological magnetic materials can be manipulated
into different topological phases with different thermal conductivities and
Berry curvature signatures by adjusting the light intensity throughout the
phase diagram region.",2402.07731v1
2024/2/26,Oscillatory Hall effect from magnetoelectronic coupling in flexoelectronic silicon,"The magnetoelectronic coupling can be defined as cross-domain coupling
between electronic and magnetic properties, where modulation in magnetic
properties changes the electronic properties. In this letter, an explicit
experimental evidence of magnetoelectronic coupling is presented, which is
uncovered from oscillatory Hall effect response in Hall measurement. The strain
gradient in a MgO (1.8 nm)/p-Si (~400 nm) freestanding sample leads to transfer
of electrons (~5X10^18 cm^-3) from valence to conduction band due to
flexoelectronic charge separation in the p-Si layer. The resulting
flexoelectronic polarization gives rise to temporal magnetic moment from
dynamical multiferroicity. The external magnetic field changes the net temporal
magnetic moment, which causes modulations in charge carrier concentration and
oscillatory Hall effect. The period of oscillatory Hall response is 1.12 T,
which is attributed to the magnitude of temporal magnetic moment. The discovery
of oscillatory Hall effect adds a new member to the family of Hall effects.",2402.16330v1
2024/2/27,Skyrmion Generation in a Plasmonic Nanoantenna through the Inverse Faraday Effect,"Skyrmions are topological structures characterized by a winding vectorial
configuration that provides a quantized topological charge. In magnetic
materials, skyrmions are localized spin textures that exhibit unique stability
and mobility properties, making them highly relevant to the burgeoning field of
spintronics. In optics, these structures open new frontiers in manipulating and
controlling light at the nanoscale. The convergence of optics and magnetics
holds therefore immense potential for manipulating magnetic processes at
ultrafast timescales. Here, we explore the possibility of generating skyrmionic
topological structures within the magnetic field induced by the inverse Faraday
effect in a plasmonic nanostructure. Our investigation reveals that a gold
nanoring, featuring a dark mode, can generate counter-propagating photocurrents
between its inner and outer segments, thereby enabling the magnetization of
gold and supporting a skyrmionic vectorial distribution. We elucidate that
these photocurrents arise from the localized control of light polarization,
facilitating their counter-propagative motion. The generation of skyrmions
through the inverse Faraday effect at the nanoscale presents a pathway towards
directly integrating this topology into magnetic layers. This advancement holds
promise for ultrafast timescales, offering direct applications in ultrafast
data writing and processing.",2402.17426v1
2024/3/6,Competing magnetic correlations and uniaxial anisotropy in (Fe$_{1-x}$Mn$_{x}$)$_2$AlB$_2$ single crystals,"We have succeeded for the first time in synthesizing single crystals of
nanolaminated borides (Fe$_{1-x}$Mn$_{x}$)$_2$AlB$_2$ in the entire Fe-Mn
composition range using the Al self-flux method, and have established $T$-$x$,
$H$-$T$ and three-dimensional $H$-$T$-$x$ magnetic phase diagrams from the
results of magnetization measurements. The ferromagnetic correlation of
Fe$_2$AlB$_2$ is weakened with the Mn substitution, whereas the
antiferromagnetic correlation of Mn$_2$AlB$_2$ is enhanced with the Fe up to
$x=0.65$. The spin direction in the magnetic ordered states changes from the
$a$ to the $b$ axis with increasing Mn concentration and temperature. At $x$ =
0.31-0.46, there are three magnetic phases; ferromagnetic, antiferromganetic,
and intermediate phases in between. At $x$ = 0.65 and 0.74, a spin-flop-like
metamagnetic transition was observed at a finite field parallel to the spin
direction. These observations indicate that in (Fe$_{1-x}$Mn$_{x}$)$_2$AlB$_2$
the ferromagnetic and antiferromagnetic correlations coexist and the uniaxial
magnetic anisotropy competes between the $a$ and $b$ axes.",2403.03415v1
2024/3/7,Resonant Quantum Magnetodielectric Effect in Multiferroic Metal-Organic Framework [CH3NH3]Co(HCOO)3,"We report the observation of both resonant quantum tunneling of magnetization
(RQTM) and resonant quantum magnetodielectric (RQMD) effect in the perovskite
multiferroic metal-organic framework [CH3NH3]Co(HCOO)3. An intrinsic magnetic
phase separation emerges at low temperatures due to hydrogen-bond-modified long
range super-exchange interaction, leading to the coexistence of canted
antiferromagnetic order and single-ion magnet. Subsequently, a stair-shaped
magnetic hysteresis loop along the [101] direction characterizing the RQTM
appears below the magnetic blocking temperature. More interestingly, the
magnetic field dependence of dielectric permittivity exhibits pronounced
negative peaks at the critical fields corresponding to the RQTM, a phenomenon
termed the RQMD effect which enables electrical detection of the RQTM. These
intriguing properties make the multiferroic metal-organic framework a promising
candidate for solid-state quantum computing.",2403.04244v1
2024/3/5,A first-principles study and mesoscopic modeling of two-dimensional spin and orbital fluctuations in FeSe,"We calculated the structural, electronic and magnetic properties of FeSe
within density-functional theory at the generalized gradient approximation
level. First, we studied how the bandwidth of the d-bands at the Fermi energy
are renormalized by adding simple corrections: Hubbard U, Hunds J and by
introducing long-range magnetic orders. We found that introducing either a
striped or a staggered dimer antiferromagnetic order brings the bandwidths --
which are starkly overestimated at the generalized gradient approximation level
-- closer to those experimentally observed. Second, for the ferromagnetic, the
striped, checkerboard and the staggered dimer antiferromagnetic order, we
investigate the change in magnetic formation energy with local magnetic moment
of Fe at a pressure up to 6 GPa. The bilinear and biquadratic exchange energies
are derived from the Heisenberg model and noncollinear first-principles
calculations, respectively. We found a non-trivial behavior of the
spin-exchange parameters on the magnetization, and we put forward a
field-theory model that rationalizes these results in terms of two-dimensional
spin and orbital fluctuations. The character of these fluctuations can be
either that of a standard density wave or a topological vortex. Topological
vortexes can result in mesoscopic magnetization structures.",2403.04802v1
2024/3/25,Intrinsic Dipole Hall effect in tMoTe$_2$ moiré: magnetoelectricity and contact-free signature of topological transitions,"We discover an intrinsic dipole Hall effect in a variety of magnetic
insulating states at integer fillings of twisted MoTe$_2$ moir\'e superlattice,
including topologically trivial and nontrivial ferro-, antiferro-, and
ferri-magnetic configurations. The dipole Hall current, in linear response to
in-plane electric field, generates an in-plane orbital magnetization
$M_{\parallel}$ along the field, through which an AC field can drive
magnetization oscillation up to THz range. Upon the continuous topological
phase transitions from trivial to quantum anomalous Hall states in both
ferromagnetic and antiferromagnetic configurations, the dipole Hall current and
$M_{\parallel}$ have an abrupt sign change, enabling contact free detection of
the transitions through the magnetic stray field. In configurations where the
linear response is forbidden by symmetry, the dipole Hall current and
$M_{\parallel}$ appear as a crossed nonlinear response to both in-plane and
out-of-plane electric fields. These magnetoelectric phenomena showcase novel
functionalities of insulators from the interplay between magnetism, topology
and electrical polarization.",2403.16586v1
2024/3/27,Ferroelastic control of magnetic domain structure: direct imaging by Magnetic Force Microscopy,"Pyrrhotite, Fe$_7$S$_8$, provides an example of exceptionally strong
magnetoelastic coupling through pinning of ferromagnetic domains by
ferroelastic twins. Using direct imaging of both magnetic and ferroelastic
domains by magnetic force microscopy (MFM), the mechanism by which this
coupling controls local magnetic switching behaviour of regions on the
pyrrhotite surface is revealed, and leads to quantitative fitting of field
dependent MFM phase shifts with bulk magnetometry data. It is shown that
characteristic inflection points in the magnetometry data along certain
direction, in particular $[\overline 120]^*_h$ of the hexagonal parent
structure, are in fact caused by ferroelastic pinning of the magnetic moments.",2403.18747v1
2024/3/31,Sign-reversal Anomalous Hall effect driven by a magnetic transition in Cr$_{7-δ}$Te$_8$,"The search for exotic spin configurations and related novel transport
properties continues to be fueled by the promise of new electronic states and
outstanding candidate components for spintronic applications. In layered
Cr$_{7-\delta}$Te$_8$, the applied field drives a before unreported magnetic
transition revealed by the alternating current magnetic susceptibility
measurements around room temperature. This observed magnetic transition results
in a sign change for the anomalous Hall effect which exhibits non-monotonous
temperature dependence. The prominent topological Hall effect (THE) with a
large value of 1$\mu \Omega \cdot cm$ has been observed without breaking the
inversion symmetry for Cr$_{7-\delta}$Te$_8$. This robust THE can persist up to
room temperature attributed to the nonzero fluctuation-driven scalar spin
chirality. The complicated interactions of long-range and short-range magnetic
orders lead to rich exotic magnetic states with related novel transport
properties in Cr$_{7-\delta}$Te$_8$.",2404.00659v1
2024/4/2,Field-induced spin polarization in lightly Cr-substituted layered antiferromagnet NiPS3,"Tuning magnetic properties in layered magnets is an important route to
realize novel phenomenon related to two-dimensional (2D) magnetism. Recently,
tuning antiferromagnetic (AFM) properties through substitution and
intercalation techniques have been widely studied in MPX3 compounds.
Interesting phenomena, such as diverse AFM structures and even the signatures
of ferrimagnetism, have been reported. However, long-range ferromagnetic (FM)
ordering has remained elusive. In this work, we explored the magnetic
properties of the previously unreported Cr-substituted NiPS3. We found that Cr
substitution is extremely efficient in controlling spin orientation in NiPS3.
Our study reveals a field-induced spin polarization in lightly (9%)
Cr-substituted NiPS3, which is likely attributed to the attenuation of AFM
interactions and magnetic anisotropy due to Cr doping. Our work provides a
possible strategy to achieve FM phase in AFM MPX3, which could be useful for
investigating 2D magnetism as well as potential device applications.",2404.02091v1
2011/6/14,Nonideal MHD Effects and Magnetic Braking Catastrophe in Protostellar Disk Formation,"Dense, star-forming, cores of molecular clouds are observed to be
significantly magnetized. A realistic magnetic field of moderate strength has
been shown to suppress, through catastrophic magnetic braking, the formation of
a rotationally supported disk during the protostellar accretion phase of
low-mass star formation in the ideal MHD limit. We address, through 2D
(axisymmetric) simulations, the question of whether realistic levels of
nonideal effects, computed with a simplified chemical network including dust
grains, can weaken the magnetic braking enough to enable a rotationally
supported disk to form. We find that ambipolar diffusion, the dominant nonideal
MHD effect over most of the density range relevant to disk formation, does not
enable disk formation, at least in 2D. The reason is that ambipolar diffusion
allows the magnetic flux that would be dragged into the central stellar object
in the ideal MHD limit to pile up instead in a small circumstellar region,
where the magnetic field strength (and thus the braking efficiency) is greatly
enhanced. We also find that, on the scale of tens of AU or more, a realistic
level of Ohmic dissipation does not weaken the magnetic braking enough for a
rotationally supported disk to form, either by itself or in combination with
ambipolar diffusion. The Hall effect, the least explored of these three
nonideal MHD effects, can spin up the material close to the central object to a
significant, supersonic rotation speed, even when the core is initially
non-rotating, although the spun-up material remains too sub-Keplerian to form a
rotationally supported disk. The problem of catastrophic magnetic braking that
prevents disk formation in dense cores magnetized to realistic levels remains
unresolved. Possible resolutions of this problem are discussed.",1106.2620v1
2014/10/17,Ferromagnetic resonance in $ε$-Co magnetic composites,"We investigate the electromagnetic properties of assemblies of nanoscale
$\epsilon$-cobalt crystals with size range between 5 nm to 35 nm, embedded in a
polystyrene (PS) matrix, at microwave (1-12 GHz) frequencies. We investigate
the samples by transmission electron microscopy (TEM) imaging, demonstrating
that the particles aggregate and form chains and clusters. By using a broadband
coaxial-line method, we extract the magnetic permeability in the frequency
range from 1 to 12 GHz, and we study the shift of the ferromagnetic resonance
with respect to an externally applied magnetic field. We find that the
zero-magnetic field ferromagnetic resonant peak shifts towards higher
frequencies at finite magnetic fields, and the magnitude of complex
permeability is reduced. At fields larger than 2.5 kOe the resonant frequency
changes linearly with the applied magnetic field, demonstrating the transition
to a state in which the nanoparticles become dynamically decoupled. In this
regime, the particles inside clusters can be treated as non-interacting, and
the peak position can be predicted from Kittel's ferromagnetic resonance theory
for non-interacting uniaxial spherical particles combined with the
Landau-Lifshitz-Gilbert (LLG) equation. In contrast, at low magnetic fields
this magnetic order breaks down and the resonant frequency in zero magnetic
field reaches a saturation value reflecting the interparticle interactions as
resulting from aggregation. Our results show that the electromagnetic
properties of these composite materials can be tuned by external magnetic
fields and by changes in the aggregation structure.",1410.4789v2
2020/5/27,High-resolution tunneling spin transport characteristics of topologically distinct magnetic skyrmionic textures from theoretical calculations,"High-resolution tunneling electron spin transport properties (longitudinal
spin current (LSC) and spin transfer torque (STT) maps) of topologically
distinct real-space magnetic skyrmionic textures are reported by employing a
3D-WKB combined scalar charge and vector spin transport theory in the framework
of spin-polarized scanning tunneling microscopy (SP-STM). For our theoretical
investigation metastable skyrmionic spin structures with various topological
charges ($Q=-3,-2,-1,0,1,2$) in the (Pt$_{0.95}$Ir$_{0.05}$)/Fe/Pd(111)
ultrathin magnetic film are considered. Using an out-of-plane magnetized SP-STM
tip it is found that the maps of the LSC vectors acting on the spins of the
magnetic textures and all STT vector components exhibit the same topology as
the skyrmionic objects. In contrast, an in-plane magnetized tip generally does
not result in spin transport vector maps that are topologically equivalent to
the underlying spin structure, except for the LSC vectors acting on the spins
of the skyrmionic textures at a specific relation between the spin
polarizations of the sample and the tip. The magnitudes of the spin transport
vector quantities exhibit close relations to charge current SP-STM images
irrespectively of the skyrmionic topologies. Moreover, we find that the STT
efficiency (torque/current ratio) acting on the spins of the skyrmions can
reach large values up to $\sim$25 meV/$\mu$A ($\sim$0.97 $h/e$) above the rim
of the magnetic objects, but it considerably varies between large and small
values depending on the lateral position of the SP-STM tip above the
topological spin textures. A simple expression for the STT efficiency is
introduced to explain its variation. Our calculated spin transport vectors can
be used for the investigation of spin-polarized tunneling-current-induced spin
dynamics of topologically distinct surface magnetic skyrmionic textures.",2005.13266v2
2021/1/14,Intriguing magnetism of the topological kagome magnet TbMn_6Sn_6,"Magnetic topological phases of quantum matter are an emerging frontier in
physics and material science. Along these lines, several kagome magnets have
appeared as the most promising platforms. Here, we explore magnetic
correlations in the transition-metal-based kagome magnet TbMn$_{6}$Sn$_{6}$
using muon spin rotation, combined with local field analysis and neutron
diffraction. Our results show that the system exhibits an out-of-plane
ferrimagnetic structure $P6/mm'm'$ (comprised by Tb and Mn moments) with slow
magnetic fluctuations below $T_{\rm C2}$~=~320~K. These fluctuations exhibit a
slowing down below $T_{\rm C1}^{*}$~${\simeq}$~120~K, and we see the formation
of static patches with ideal out-of-plane order below $T_{\rm
C1}$~${\simeq}$~20~K which grow in a volume with decreasing temperature. The
appearance of the static patches has a similar onset to the interesting
phenomenon such as spin-polarized Dirac dispersion with a large Chern gap and
topological edge states. We further show that the temperature evolution of the
anomalous Hall conductivity (AHC) is strongly influenced by the low temperature
magnetic crossover. Our presented experimental results show that the onset of
the topological electronic properties tied to the Dirac band is promoted only
by true static out-of-plane ferrimagnetic order in TbMn$_{6}$Sn$_{6}$ and is
washed out by the slow magnetic fluctuations above $T_{\rm
C1}$~${\simeq}$~20~K. Remarkably, hydrostatic pressure of 2.1 GPa stabilises
static out-of-plane topological ferrimagnetic ground state in the whole volume
of the sample. Therefore the exciting perspective arises of a magnetic system
in which the topological response can be controlled, and thus explored, over a
wide range of parameters.",2101.05763v2
2021/4/6,Modulating Curie Temperature and Magnetic Anisotropy in Nanoscale Layered Cr_{2}Te_{3} Films: Implications for Room-Temperature Spintronics,"Nanoscale layered ferromagnets have demonstrated fascinating two-dimensional
magnetism down to atomic layers, providing a peculiar playground of spin orders
for investigating fundamental physics and spintronic applications. However,
strategy for growing films with designed magnetic properties is not well
established yet. Herein, we present a versatile method to control the Curie
temperature (T_{C}) and magnetic anisotropy during growth of ultrathin
Cr_{2}Te_{3} films. We demonstrate increase of the TC from 165 K to 310 K in
sync with magnetic anisotropy switching from an out-of-plane orientation to an
in-plane one, respectively, via controlling the Te source flux during film
growth, leading to different c-lattice parameters while preserving the
stoichiometries and thicknesses of the films. We attributed this modulation of
magnetic anisotropy to the switching of the orbital magnetic moment, using
X-ray magnetic circular dichroism analysis. We also inferred that different
c-lattice constants might be responsible for the magnetic anisotropy change,
supported by theoretical calculations. These findings emphasize the potential
of ultrathin Cr_{2}Te_{3} films as candidates for developing room-temperature
spintronics applications and similar growth strategies could be applicable to
fabricate other nanoscale layered magnetic compounds.",2104.02224v1
2021/6/2,Highly tunable magnetic phases in transition metal dichalcogenide Fe$_{1/3+δ}$NbS$_2$,"Layered transition metal dichalcogenides (TMDCs) host a plethora of
interesting physical phenomena ranging from charge order to superconductivity.
By introducing magnetic ions into 2H-NbS$_2$, the material forms a family of
magnetic intercalated TMDCs T$_x$NbS$_2$ (T = 3d transition metal). Recently,
Fe$_{1/3+\delta}$NbS$_2$ has been found to possess intriguing resistance
switching and magnetic memory effects coupled to the N\'{e}el temperature of
T$_N \sim 45$ K [1,2]. We present comprehensive single crystal neutron
diffraction measurements on under-intercalated ($\delta \sim -0.01$),
stoichiometric, and over-intercalated ($\delta \sim 0.01$) samples. Magnetic
defects are usually considered to suppress magnetic correlations and,
concomitantly, transition temperatures. Instead, we observe highly tunable
magnetic long-ranged states as the Fe concentration is varied from
under-intercalated to over-intercalated, that is from Fe vacancies to Fe
interstitials. The under- and over- intercalated samples reveal distinct
antiferromagnetic stripe and zig-zag orders, associated with wave vectors $k_1$
= (0.5, 0, 0) and $k_2$ = (0.25, 0.5, 0), respectively. The stoichiometric
sample shows two successive magnetic phase transitions for these two wave
vectors with an unusual rise-and-fall feature in the intensities connected to
$k_1$. We ascribe this sensitive tunability to the competing next nearest
neighbor exchange interactions and the oscillatory nature of the
Ruderman-Kittel-Kasuya-Yosida (RKKY) mechanism. We discuss experimental
observations that relate to the observed intriguing switching resistance
behaviors. Our discovery of a magnetic defect tuning of the magnetic structure
in bulk crystals Fe$_{1/3+\delta}$NbS$_2$ provides a possible new avenue to
implement controllable antiferromagnetic spintronic devices.",2106.01341v1
2022/4/20,"The first- and second-order magneto-optical effects and intrinsically anomalous transport in 2D van der Waals layered magnets CrXY (X = S, Se, Te; Y = Cl, Br, I)","Recently, the two-dimensional magnetic semiconductor CrSBr has attracted
considerable attention due to its excellent air-stable property and high
magnetic critical temperature. Here, we systematically investigate the
electronic structure, magnetocrystalline anisotropy energy, first-order
magneto-optical effects (Kerr and Faraday effects) and second-order
magneto-optical effects (Schafer-Hubert and Voigt effects) as well as
intrinsically anomalous transport properties (anomalous Hall, anomalous Nernst,
and anomalous thermal Hall effects) of two-dimensional van der Waals layered
magnets CrXY (X = S, Se, Te; Y = Cl, Br, I) by using the first-principles
calculations. Our results show that monolayer and bilayer CrXY (X = S, Se) are
narrow band gap semiconductors, whereas monolayer and bilayer CrTeY are
multi-band metals. The magnetic ground states of bilayer CrXY and the easy
magnetization axis of monolayer and bilayer CrXY are confirmed by the
magnetocrystalline anisotropy energy calculations. Utilizing magnetic group
theory analysis, the first-order magneto-optical effects as well as anomalous
Hall, anomalous Nernst, and anomalous thermal Hall effects are identified to
exist in ferromagnetic state with out-of-plane magnetization. The second-order
magneto-optical effects are not restricted by the above symmetry requirements,
and therefore can arise in ferromagnetic and antiferromagnetic states with
in-plane magnetization. The calculated results are compared with the available
theoretical and experimental data of other two-dimensional magnets and some
conventional ferromagnets. The present work reveals that monolayer and bilayer
CrXY with superior magneto-optical responses and anomalous transport properties
provide an excellent material platform for the promising applications of
magneto-optical devices, spintronics, and spin caloritronics.",2204.09223v2
2023/3/17,Diffusive Excitonic Bands from Frustrated Triangular Sublattice in a Singlet-Ground-State System,"Magnetic order in most materials occurs when magnetic ions with finite
moments in a crystalline lattice arrange in a particular pattern below the
ordering temperature determined by exchange interactions between the ions.
However, when the crystal electric field (CEF) effect results in a spin-singlet
ground state on individual magnetic sites, the collective ground state of the
system can either remain non-magnetic, or more intriguingly, the exchange
interactions between neighboring ions, provided they are sufficiently strong,
can admix the excited CEF levels, resulting in a magnetically ordered ground
state. The collective magnetic excitations in such a state are so-called spin
excitons that describe the CEF transitions propagating through the lattice. In
most cases, spin excitons originating from CEF levels of a localized single ion
are dispersion-less in momentum (reciprocal) space and well-defined in both the
magnetically ordered and paramagnetic states. Here we use thermodynamic and
neutron scattering experiments to study stoichiometric Ni2Mo3O8 without site
disorder, where Ni2+ ions form a bipartite honeycomb lattice comprised of two
triangular lattices, with ions subject to the tetrahedral and octahedral
crystalline environment, respectively. We find that in both types of ions, the
CEF excitations have nonmagnetic singlet ground states, yet the material has
long-range magnetic order. Furthermore, CEF spin excitons from the
triangular-lattice arrangement of tetrahedral sites form, in both the
antiferromagnetic and paramagnetic states, a dispersive diffusive pattern
around the Brillouin zone boundary in reciprocal space. The present work thus
demonstrates that spin excitons in an ideal triangular lattice magnet can have
dispersive excitations, irrespective of the existence of static magnetic order,
and this phenomenon is most likely due to spin entanglement and geometric
frustrations.",2303.10241v1
2005/12/15,Recent progress in first-principles studies of magnetoelectric multiferroics,"Materials that combine magnetic and ferroelectric properties have generated
increasing interest over the last few years, due to both their diverse
properties and their potential utility in new types of magnetoelectric device
applications. In this review we discuss recent progress in the study of such
magnetoelectric multiferroics which has been achieved using computational
first-principles methods based on density functional theory. In particular, we
show how first-principles methods have been successfully used to explain
various properties of multiferroic materials and to predict novel effects and
new systems that exhibit multiferroic properties.",0512330v1
2009/5/13,Correlation between Organic Magnetoresistance (OMAR) and Ferromagnetic ordering,"We report observation of ferromagnetic (FM) ordering in organic
semiconductors, namely regio-regular poly (3-hexyl thiophene) (RRP3HT) and
1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methanofullerene (PCBM), in the
temperature range of 5-300 K in addition to magnetoresistance (OMAR) observed
in the diodes made from the same materials. Particle induced x-ray emission
spectroscopy confirms the presence of dilute magnetic impurities in the
materials mainly as residues from the synthesis process. However, upon blending
these two materials with FM signal, the FM ordering is suppressed by a huge
paramagnetic (PM) signal indicating ground state charge transfer formation in
the blend. Together with the magneto-transport studies, these results indicate
that OMAR response is observed in a device only when the corresponding active
materials are FM. In the diodes with P3HT:PCBM complex, that as a blend shows
PM response, OMAR vanishes almost completely. We propose that ferromagnetism in
the active material can have important correlation with the OMAR response in
the diodes.",0905.2021v1
2010/1/21,Defects in Heavy-Fermion Materials: Unveiling Strong Correlations in Real Space,"Complexity in materials often arises from competing interactions at the
atomic length scale. One such example are the strongly correlated heavy-fermion
materials where the competition between Kondo screening and antiferromagnetic
ordering is believed to be the origin of their puzzling non-Fermi-liquid
properties. Insight into such complex physical behavior in strongly correlated
electron systems can be gained by impurity doping. Here, we develop a
microscopic theoretical framework to demonstrate that defects implanted in
heavy-fermion materials provide an opportunity for unveiling competing
interactions and their correlations in real space. Defect-induced perturbations
in the electronic and magnetic correlations possess characteristically
different spatial patterns that can be visualized via their spectroscopic
signatures in the local density of states or non-local spin susceptibility.
These real space patterns provide insight into the complex electronic structure
of heavy-fermion materials, the light or heavy character of the perturbed
states, and the hybridization between them. The strongly correlated nature of
these materials also manifests itself in highly non-linear quantum interference
effects between defects that can drive the system through a first-order phase
transition to a novel inhomogeneous ground state.",1001.3875v1
2011/5/31,Octahedral rotation-induced ferroelectricity in cation ordered perovskites,"Increasing demands for electric field-tunable electric, magnetic, and orbital
(EMO) materials has renewed interests in ferroelectricity and its coupling to
EMO properties in complex perovskite oxides. The historic design strategy to
achieve a spontaneous polarization involves the incorporation of second-order
Jahn-Teller (SOJT) active cations. The challenge, however, is that this
mechanism is limited to specific chemistries and the polar distortions that
arise are largely decoupled from EMO properties, limiting their use as
field-tunable multifunctional technology materials. Here we report the
crystal-chemistry criteria which circumvents those restrictions and enables the
rational design of new materials displaying octahedral rotation-induced
ferroelectricity - an innovative route to realize electric polarization without
the need for SOJT cations - from non-polar building blocks. The strategy
exploits the centric octahedral rotation patterns, which strongly couple to EMO
properties, and cation ordering commonly observed in non-polar $AB$O$_3$
perovskites. By uniting switchable electric polarizations to the connectivity
of the transition-metal oxygen octahedra, electric-field control over materials
properties is possible.",1106.0049v3
2014/5/14,An Investigation of Machine Learning Methods Applied to Structure Prediction in Condensed Matter,"Materials characterization remains a significant, time-consuming undertaking.
Generally speaking, spectroscopic techniques are used in conjunction with
empirical and ab-initio calculations in order to elucidate structure. These
experimental and computational methods typically require significant human
input and interpretation, particularly with regards to novel materials.
Recently, the application of data mining and machine learning to problems in
material science have shown great promise in reducing this overhead. In the
work presented here, several aspects of machine learning are explored with
regards to characterizing a model material, titania, using solid-state Nuclear
Magnetic Resonance (NMR). Specifically, a large dataset is generated,
corresponding to NMR $^{47}$Ti spectra, using ab-initio calculations for
generated TiO$_2$ structures. Principal Components Analysis (PCA) reveals that
input spectra may be compressed by more than 90%, before being used for
subsequent machine learning. Two key methods are used to learn the complex
mapping between structural details and input NMR spectra, demonstrating
excellent accuracy when presented with test sample spectra. This work compares
Support Vector Regression (SVR) and Artificial Neural Networks (ANNs), as one
step towards the construction of an expert system for solid state materials
characterization.",1405.3564v1
2014/8/8,"Quantum size effects in layered VX2 (X=S, Se, Te) materials: Manifestation of metal to semimetal or semiconductor transition","Most of the 2D transition metal dichalcogenides (TMDC) are nonmagnetic in
pristine form. However, 2D pristine VX2 (X=S, Se, Te) materials are found to be
ferromagnetic. Using spin polarized density functional theory (DFT)
calculations, we have studied the electronic, magnetic and surface properties
of this class of materials in both trigonal prismatic 2H- and octahedral
1T-phase. Our calculations reveal that they exhibit materially different
properties in those two polymorphs. Most importantly, detailed investigation of
electronic structure explored the quantum size effect in 2H-phase of these
materials thereby leading to metal to semimetal (2H-VS2) or semiconductor
(2H-VSe2, 2H-VTe2) transition when downsizing from bilayer to corresponding
monolayer.",1408.1777v1
2016/9/6,"Structure, ferromagnetic, dielectric and electronic features of the LaBiFe2O6 material","In this paper the synthesis and study of the structural, morphological,
electrical, magnetic and electronic properties of the LaBiFe2O6 novel material
are reported. The material was produced using the standard ceramic method. The
Rietveld analysis of experimental data of x-ray diffraction showed that it
synthesizes in an orthorhombic perovskite structure (Pnma, #62 space group).
Two types of grain, micro and submicrometric, with the LaBiFe2O6 stoichiometry
were identified by scanning electron microscopy and X-ray dispersive
spectroscopy. Results of electrical polarization and dielectric constant
ferroelectric suggest the occurrence of response of the material at room
temperature. A T=300 K the material is ferromagnetic and exhibits an anomaly at
T=258 K, which is attributed to anisotropy effects, suggesting the occurrence
of biferroic behaviour. Results of diffuse reflectance suggest a semiconductor
behaviour with energy gap Eg=2,17 eV, which is in agreement with calculations
of band structure and density of states for one spin orientation, while for the
other spin configuration calculations suggest a conductor feature.",1609.01752v2
2017/9/18,Topological Hyperbolic and Dirac Plasmons,"In this chapter, criteria for existence of propagating optical modes which
are transversely bound at the interface of two materials are studied. In
particular, quite general cases are considered, where the materials involved
are assumed to be anisotropic, but also demonstrating magneto-electric effects.
Moreover, surface states of two-dimensional materials like topological
insulators and graphene are also modeled via consideration of a conductivity
sheet existing at the interface. A characteristic equation for obtaining the
propagation constant of generalized interface modes is presented. Furthermore,
optical modes sustained by a thin film of anisotropic materials with
magneto-electric effect and topological surface states are also investigated.
It is shown that interface modes supported by such a system are hybrid in
nature, and can be further decomposed into the well-known classes of transverse
magnetic and electric modes, only at the absence of magneto-electric effect.
Although the formulations driven here are mathematically abstract, they can be
used to investigate polaritons in van der Waal materials, hyperbolic materials,
and topological insulators.",1709.05810v1
2017/12/11,Predicting the Spin Seebeck Voltage in Spin-polarized Materials: A Quantum Mechanical Transport Model Approach,"The spin Seebeck effect has recently been demonstrated as a viable method of
direct energy conversion that has potential to outperform energy conversion
from the conventional Seebeck effect. In this study, a computational transport
model is developed and validated that predicts the spin Seebeck voltage in
spin-polarized materials using material parameter obtain from first principle
ground state density functional calculations. The transport model developed is
based on a 1D effective mass description coupled with a microscopic inverse
spin Hall relationship. The model can predict both the spin current and voltage
generated in a non-magnetic material placed on top of a ferromagnetic material
in a transverse spin Seebeck configuration. The model is validated and verified
with available experimental data of La:YIG. Future applications of this model
include the high-throughput exploration of new spin-based thermoelectric
materials.",1712.04074v1
2017/12/20,Non-Superconducting Non-Abelian Statistics in One-Dimensional Topological Insulators,"Topological materials are of great interest for applications in quantum
computing, providing intrinsic robustness against environmental noises. A
popular direction is to look for Majorana modes in integrated systems
interfaced with superconducting materials. However, is superconductivity
necessary for materials to exhibits non-abelian statistics? Here we predict
with strong theoretical and numerical evidences that there exist topologically
phases in a class of one-dimensional single crystals, which contain large
bandgaps and are within experimental reach. Specifically, the nontrivial Zak
phases are associated with gapless boundary states, which provides the
non-Abelian statistics required for constructing topologically-protected
quantum gates, even without superconductivity and magnetic field. Another
anomalous feature of these materials is that the electric polarization is
quantized and a transverse field induces a longitudinal polarization. This
novel material property provides an experimentally-accessible mechanism for
braiding the non-Abelian anyons.",1712.07696v3
2018/4/30,New iron-based multiferroics with improper ferroelectricity,"In this contribution to the special issue on magnetoelectrics and their
applications, we focus on some single phase multiferroics theoretically
predicted and/or experimentally discovered by the authors in recent years. In
these materials, iron is the common core element. However, these materials are
conceptually different from the mostly-studied BiFeO$_3$, since their
ferroelectricity is improper. Our reviewed materials are not simply repeating
one magnetoelectric mechanism, but cover multiple branches of improper
ferroelectricity, including the magnetism-driven ferroelectrics, geometric
ferroelectric, as well as electronic ferroelectric driven by charge ordering.
In this sense, these iron-based improper ferroelectrics can be an encyclopaedic
playground to explore the comprehensive physics of multiferroics and
magnetoelectricity. Furthermore, the unique characteristics of iron's $3d$
orbitals make some of their magnetoelectric properties quite prominent,
comparing with the extensively-studied Mn-based improper multiferroics. In
addition, these materials establish the crossover between multiferroics and
other fields of functional materials, which enlarges the application scope of
multiferroics.",1804.11125v1
2018/7/2,Coevolutionary search for optimal materials in the space of all possible compounds,"Over the past decade, evolutionary algorithms, data mining, and other methods
showed great success in solving the main problem of theoretical
crystallography: finding the stable structure for a given chemical composition.
Here we develop a method that addresses the central problem of computational
materials science: the prediction of material(s), among all possible
combinations of all elements, that possess the best combination of target
properties. This nonempirical method combines our new coevolutionary approach
with the carefully restructured ""Mendelevian"" chemical space, energy filtering,
and Pareto optimization to ensure that the predicted materials have optimal
properties and a high chance to be synthesizable. The first calculations,
presented here, illustrate the power of this approach. In particular, we find
that diamond (and its polytypes, including lonsdaleite) are the hardest
possible materials and that bcc-Fe has the highest zero-temperature
magnetization among all possible compounds.",1807.00854v2
2018/9/24,Mathematical analysis of transmission properties of electromagnetic meta-materials,"We study time-harmonic Maxwell's equations in meta-materials that use either
perfect conductors or high-contrast materials. Based on known effective
equations for perfectly conducting inclusions, we calculate the transmission
and reflection coefficients for four different geometries. For high-contrast
materials and essentially two-dimensional geometries, we analyze parallel
electric and parallel magnetic fields and discuss their potential to exhibit
transmission through a sample of meta-material. For a numerical study, one
often needs a method that is adapted to heterogeneous media; we consider here a
Heterogeneous Multiscale Method for high contrast materials. The qualitative
transmission properties, as predicted by the analysis, are confirmed with
numerical experiments. The numerical results also underline the applicability
of the multiscale method.",1809.08824v1
2019/7/23,Transport in two-dimensional topological materials: recent developments in experiment and theory,"We review theoretical and experimental highlights in transport in
two-dimensional materials focussing on key developments over the last five
years. Topological insulators are finding applications in magnetic devices,
while Hall transport in doped samples and the general issue of topological
protection remain controversial. In transition metal dichalcogenides
valley-dependent electrical and optical phenomena continue to stimulate
state-of-the-art experiments. In Weyl semimetals the properties of Fermi arcs
are being actively investigated. A new field, expected to grow in the near
future, focuses on the non-linear electrical and optical responses of
topological materials, where fundamental questions are once more being asked
about the intertwining roles of the Berry curvature and disorder scattering. In
topological superconductors the quest for chiral superconductivity, Majorana
fermions and topological quantum computing is continuing apace.",1907.10058v1
2020/2/11,The role of delocalized chemical bonding in square-net-based topological semimetals,"Principles that predict reactions or properties of materials define the
discipline of chemistry. In this work we derive chemical rules, based on atomic
distances and chemical bond character, which predict topological materials in
compounds that feature the structural motif of a square-net. Using these rules
we identify over 300 potential new topological materials. We show that simple
chemical heuristics can be a powerful tool to characterize topological matter.
In contrast to previous database-driven materials categorization our approach
allows us to identify candidates that are alloys, solid-solutions, or compounds
with statistical vacancies. While previous material searches relied on density
functional theory, our approach is not limited by this method and could also be
used to discover magnetic and statistically-disordered topological semimetals.",2002.04611v1
2020/2/20,"Generalized Electron Hydrodynamics, Vorticity Coupling, and Hall Viscosity in Crystals","Theoretical and experimental studies have revealed that electrons in
condensed matter can behave hydrodynamically, exhibiting fluid phenomena such
as Stokes flow and vortices. Unlike classical fluids, preferred directions
inside crystals lift isotropic restrictions, necessitating a generalized
treatment of electron hydrodynamics. We explore electron fluid behaviors
arising from the most general viscosity tensors in two and three dimensions,
constrained only by thermodynamics and crystal symmetries. Hexagonal 2D
materials such as graphene support flows indistinguishable from those of an
isotropic fluid. By contrast 3D materials including Weyl semimetals, exhibit
significant deviations from isotropy. Breaking time-reversal symmetry, for
example in magnetic topological materials, introduces a non-dissipative Hall
component to the viscosity tensor. While this vanishes by isotropy in 3D,
anisotropic materials can exhibit nonzero Hall viscosity components. We show
that in 3D anisotropic materials the electronic fluid stress can couple to the
vorticity without breaking time-reversal symmetry. Our work demonstrates the
anomalous landscape for electron hydrodynamics in systems beyond graphene, and
presents experimental geometries to quantify the effects of electronic
viscosity.",2002.08976v1
2020/6/8,Materials loss measurements using superconducting microwave resonators,"The performance of superconducting circuits for quantum computing is limited
by materials losses. In particular, coherence times are typically bounded by
two-level system (TLS) losses at single photon powers and millikelvin
temperatures. The identification of low loss fabrication techniques, materials,
and thin film dielectrics is critical to achieving scalable architectures for
superconducting quantum computing. Superconducting microwave resonators provide
a convenient qubit proxy for assessing performance and studying TLS loss and
other mechanisms relevant to superconducting circuits such as non-equilibrium
quasiparticles and magnetic flux vortices. In this review article, we provide
an overview of considerations for designing accurate resonator experiments to
characterize loss, including applicable types of loss, cryogenic setup, device
design, and methods for extracting material and interface losses, summarizing
techniques that have been evolving for over two decades. Results from
measurements of a wide variety of materials and processes are also summarized.
Lastly, we present recommendations for the reporting of loss data from
superconducting microwave resonators to facilitate materials comparisons across
the field.",2006.04718v2
2020/7/31,Quantum Phases and Spin Liquid Properties of 1T-TaS2,"Quantum materials exhibiting magnetic frustration are connected to diverse
phenomena including high-Tc superconductivity, topological order and quantum
spin liquids (QSLs). A QSL is a quantum phase (QP) related to a
quantum-entangled fluid-like state of matter. Previous experiments on QSL
candidate materials are usually interpreted in terms of a single QP, although
theories indicate that many distinct QPs are closely competing in typical
frustrated spin models. Here we report on combined temperature-dependent muon
spin relaxation and specific heat measurements for the triangular-lattice QSL
candidate material 1T-TaS2 that provide evidence for competing QPs. The
measured properties are assigned to arrays of individual QSL layers within the
layered charge density wave structure of 1T-TaS2 and their characteristic
parameters can be interpreted as those of distinct Z2 QSL phases. The present
results reveal that a QSL description can extend beyond the lowest
temperatures, offering a new perspective in the search for novel quantum
materials.",2007.15905v2
2020/8/6,Redox-Governed Charge Doping Dictated by Interfacial Diffusion in Two-Dimensional Materials,"Controlling extra charge carriers is pivotal in manipulating electronic,
optical, and magnetic properties of various two-dimensional (2D) materials.
Nonetheless, the ubiquitous hole doping of 2D materials in the air and acids
has been controversial in its mechanistic details. Here we show their common
origin is an electrochemical reaction driven by redox couples of oxygen and
water molecules. Using real-time photoluminescence imaging of WS2 and Raman
spectroscopy of graphene, we capture molecular diffusion through the 2D
nanoscopic space between 2D materials and hydrophilic substrates, and show that
the latter accommodate water molecules also serving as a hydrating solvent. We
also demonstrate that HCl-induced doping is governed by dissolved O2 and pH in
accordance with the Nernst equation. The nanoscopic electrochemistry anatomized
in this work sets an ambient limit to material properties, which is universal
to not only 2D but also other forms of materials.",2008.02498v1
2021/5/3,A Snapshot Review -- Fluctuations in Quantum Materials: From Skyrmions to Superconductivity,"By measuring a linear response function directly, such as the dynamic
susceptibility, one can understand fundamental material properties. However, a
fresh perspective can be offered by studying fluctuations. This can be related
back to the dynamic susceptibility through the fluctuation-dissipation theorem,
which relates the fluctuations in a system to its response, an alternate route
to access the physics of a material. Here, we describe a new x-ray tool for
material characterization that will offer an opportunity to uncover new physics
in quantum materials using this theorem. We provide details of the method and
discuss the requisite analysis techniques in order to capitalize on the
potential to explore an uncharted region of phase space. This is followed by
recent results on a topological chiral magnet, together with a discussion of
current work in progress. We provide a perspective on future measurements
planned for work in unconventional superconductivity.",2105.00673v1
2021/5/15,Energy conversion from heat to electricity by highly reversible phase-transforming ferroelectrics,"Searching for performant multiferroic materials attracts general research
interests in energy science as they have been increasingly exploited as the
conversion media among thermal, electric, magnetic and mechanical energies by
using their temperature-dependent ferroic properties. Here we report a material
development strategy that guides us to discover a reversible phase-transforming
ferroelectric material exhibiting enduring energy harvesting from small
temperature differences. The material satisfies the crystallographic
compatibility condition between polar and nonpolar phases, which shows only
2.5C thermal hysteresis and high figure of merit. It stably generates 15uA
electricity in consecutive thermodynamic cycles in absence of any bias fields.
We demonstrate our device to consistently generate 6uA/cm2 current density near
100C over 540 complete phase transformation cycles without any electric and
functional degradation. The energy conversion device can light up a LED
directly without attaching an external power source. This promising material
candidate brings the low-grade waste heat harvesting closer to a practical
realization, e.g. small temperature fluctuations around the water boiling point
can be considered as a clean energy source.",2105.07201v2
2021/8/11,Electronic properties of the Rutile-type dioxide SnO2 material doped by sulfur element: DFT study,"In this work, we study the effect of doping the Rutile-type dioxide SnO2
material by the non-metal Sulfur (S) atoms on the electronic properties. In
fact, we have used the ab-initio method applied on the basis of the Density
Functional Theory (DFT) using the Quantum Espresso code. Through the density of
states and the band structure calculations for different concentrations have
been deduced. When doping the SnO2 material with 6% of Sulfur (S), we found a
perfect symmetry between up and down spin states in the total DOS confirming
the non-magnetic behavior of this material doped SnO2 with 6% of Sulfur. It is
also worth to note that the SnO2 material doped with 6% of Sulfur, exhibits a
semiconductor of the P-type. Moreover the band gap decreases when increasing
the concentration of doping the SnO2 by Sulfur. Our results are in good
agreement with the existing literature both experimental and theoretical.",2108.05156v1
2021/12/17,Systematic electronic structure in the cuprate parent state from quantum many-body simulations,"The quantitative description of correlated electron materials remains a
modern computational challenge. We demonstrate a numerical strategy to simulate
correlated materials at the fully ab initio level beyond the solution of
effective low-energy models, and apply it to gain a detailed microscopic
understanding across a family of cuprate superconducting materials in their
parent undoped states. We uncover microscopic trends in the electron
correlations and reveal the link between the material composition and magnetic
energy scales via a many-body picture of excitation processes involving the
buffer layers. Our work illustrates a path towards a quantitative and reliable
understanding of more complex states of correlated materials at the ab initio
many-body level.",2112.09735v3
2022/12/19,CompuMat: A Computational Composite Material for Tangible Interaction,"This paper introduces a computational composite material comprising layers
for actuation, computation and energy storage. Key to its design is inexpensive
materials assembled from traditionally available fabrication machines to
support the rapid exploration of applications from computational composites.
The actuation layer is a soft magnetic sheet that is programmed to either bond,
repel, or remain agnostic to other areas of the sheet. The computation layer is
a flexible PCB made from copper-clad kapton engraved by a fiber laser, powered
by a third energy-storage layer comprised of 0.4mm-thin lithium polymer
batteries. We present the material layup and an accompanying digital
fabrication process enabling users to rapidly prototype their own untethered,
interactive and tangible prototypes. The material is low-profile, inexpensive,
and fully untethered, capable of being used for a variety of applications in
HCI and robotics including structural origami and proprioception.",2212.09859v1
2023/1/26,Unraveling the effects of inter-site Hubbard interactions in spinel Li-ion cathode materials,"Accurate first-principles predictions of the structural, electronic,
magnetic, and electrochemical properties of cathode materials can be key in the
design of novel efficient Li-ion batteries. Spinel-type cathode materials
Li$_x$Mn$_2$O$_4$ and Li$_x$Mn$_{1.5}$Ni$_{0.5}$O$_4$ are promising candidates
for Li-ion battery technologies, but they present serious challenges when it
comes to their first-principles modeling. Here, we use density-functional
theory with extended Hubbard functionals - DFT+$U$+$V$ with on-site $U$ and
inter-site $V$ Hubbard interactions - to study the properties of these
transition-metal oxides. The Hubbard parameters are computed from
first-principles using density-functional perturbation theory. We show that
while $U$ is crucial to obtain the right trends in properties of these
materials, $V$ is essential for a quantitative description of the structural
and electronic properties, as well as the Li-intercalation voltages. This work
paves the way for reliable first-principles studies of other families of
cathode materials without relying on empirical fitting or calibration
procedures.",2301.11143v2
2023/12/26,Targeted materials discovery using Bayesian algorithm execution,"Rapid discovery and synthesis of new materials requires intelligent data
acquisition strategies to navigate large design spaces. A popular strategy is
Bayesian optimization, which aims to find candidates that maximize material
properties; however, materials design often requires finding specific subsets
of the design space which meet more complex or specialized goals. We present a
framework that captures experimental goals through straightforward user-defined
filtering algorithms. These algorithms are automatically translated into one of
three intelligent, parameter-free, sequential data acquisition strategies
(SwitchBAX, InfoBAX, and MeanBAX). Our framework is tailored for typical
discrete search spaces involving multiple measured physical properties and
short time-horizon decision making. We evaluate this approach on datasets for
TiO$_2$ nanoparticle synthesis and magnetic materials characterization, and
show that our methods are significantly more efficient than state-of-the-art
approaches.",2312.16078v1
2024/3/8,Anisotropic effects in two-dimensional materials,"Among a huge variety of known two-dimensional materials, some of them have
anisotropic crystal structures; examples include so different systems as a
few-layer black phoshphorus (phosphorene), beryllium nitride BeN$_4$, van der
Waals magnet CrSBr, rhenium dichalgogenides ReX$_2$. As a consequence, their
optical and electronic properties turn out to be highly anisotropic as well. In
some cases, the anisotropy results not just in a smooth renormalization of
observable properties in comparison with the isotropic case but in the
appearance of dramatically new physics. The examples are hyperbolic plasmons
and excitons, strongly anisotropic ordering of adatoms at the surface of
two-dimensional or van der Waals materials, essential change of transport and
superconducting properties. Here, we present a systematic review of electronic
structure, transport and optical properties of several representative groups of
anisotropic two-dimensional materials including semiconductors, anisotropic
Dirac and semi-Dirac materials, as well as superconductors.",2403.05374v1
2023/3/21,"AlphaMat: A Material Informatics Hub Connecting Data, Features, Models and Applications","The development of modern civil industry, energy and information technology
is inseparable from the rapid explorations of new materials, which are hampered
by months to years of painstaking attempts, resulting in only a small fraction
of materials being determined in a vast chemical space. Artificial intelligence
(AI)-based methods are promising to address this gap, but face many challenges
such as data scarcity and inaccurate material descriptor coding. Here, we
develop an AI platform, AlphaMat, that connects materials and applications.
AlphaMat is not limited by the data scale (from 101 to 106) and can design
structural and component descriptors that are effective for docking with
various AI models. With prediction time of milliseconds and high accuracy,
AlphaMat exhibits strong powers to model at least 12 common attributes
(formation energy, band gap, ionic conductivity, magnetism, phonon property,
bulk modulus, dielectric constant, adsorption energy, etc.), resulting in an
unexplored material database with over 117,000 entries. We further demonstrate
the ability of AlphaMat to mine and design materials, which successfully
discover thousands of new materials in photonics, batteries, catalysts, and
capacitors from the largest inorganic compound databases that cover all
elements in periodic table. This work proposes the first material informatics
hub that does not require users to have strong programming knowledge to build
AI models to design materials. Users can either directly retrieve our database
or easily build AI models through AlphaMat to discover and design the required
materials. AlphaMat can shorten the cycle of database construction and material
discovery by at least decades, and its effective use will facilitate the
applications of AI technology in material science and lead scientific and
technological progress to a new height.",2303.11651v1
2013/12/13,Micromagnetics of shape anisotropy based permanent magnets,"In the search for rare-earth free permanent magnets, various ideas related to
shape anisotropy are being pursued. In this work we assess the limits of shape
contributions to the reversal stability using micromagnetic simulations. In a
first series of tests we altered the aspect ratio of single phase prolate
spheroids from 1 to 16. Starting with a sphere of radius $4.3$ times the
exchange length $ L_{\mathrm{ex}}$ we kept the total magnetic volume constant
as the aspect ratio was modified. For a ferromagnet with zero
magnetocrystalline anisotropy the maximum coercive field reached up to $0.5$
times the magnetization $M_{\mathrm{s}}$. Therefore, in materials with moderate
uniaxial magnetocrystalline anisotropy, the addition of shape anisotropy could
even double the coercive field. Interestingly due to non-uniform magnetization
reversal there is no significant increase of the coercive field for an aspect
ratio greater than 5. A similar limit of the maximum aspect ratio was observed
in cylinders. The coercive field depends on the wire diameter. By decreasing
the wire diameter from $8.7 L_{\mathrm{ex}}$ to $2.2 L_{\mathrm{ex}}$ the
coercive field increased by 40%. In the cylinders nucleation of a reversed
domain starts at the corners at the end. Smoothing the edges can improve the
coercive field by about 10%.
  In further simulations we compacted soft magnetic cylinders into a bulk-like
arrangement. Misalignment and magnetostatic interactions cause a spread of $0.1
M_{\mathrm{s}}$ in the switching fields of the rods. Comparing the volume
averaged hysteresis loops computed for isolated rods and the hysteresis loop
computed for interacting rods, we conclude that magnetostatic interactions
reduce the coercive field by up to 20%.",1312.3791v3
2016/6/14,On the multiferroic skyrmion-host GaV4S8,"The lacunar spinel GaV4S8 exhibits orbital ordering at 44 K and shows a
complex magnetic phase diagram below 12.7 K, which includes ferromagnetic and
cycloidal spin order. At low but finite external magnetic fields, N\'eel-type
skyrmions are formed in this material. Skyrmions are whirl-like spin vortices
that have received great theoretical interest because of their non-trivial spin
topology and that are also considered as basic entities for new data-storage
technologies. Interestingly, we found that the orbitally ordered phase shows
sizable ferroelectric polarization and that excess spin-driven polarizations
appear in all magnetic phases, including the skyrmion-lattice phase. Hence,
GaV4S8 shows simultaneous magnetic and polar order and belongs to the class of
multiferroics, materials that attracted enormous attention in recent years.
Here, we summarize the existing experimental information on the magnetic,
electronic, and dielectric properties of GaV4S8. By performing detailed
magnetic susceptibility, resistivity, specific heat, and dielectric
experiments, we complement the low-temperature phase diagram. Specifically, we
show that the low-temperature and low-field ground state of GaV4S8 seems to
have a more complex spin configuration than purely collinear ferromagnetic spin
order. In addition, at the structural Jahn-Teller transition the magnetic
exchange interaction changes from antiferromagnetic to ferromagnetic. We also
provide experimental evidence that the vanadium V4 clusters in GaV4S8 can be
regarded as molecular units with spin 1/2. However, at high temperatures
deviations in the susceptibility show up, indicating that either the magnetic
moments of the vanadium atoms fluctuate independently or excited states of the
V4 molecule become relevant.",1606.04511v1
2017/1/26,Seed Layer Impact on Structural and Magnetic Properties of [Co/Ni] Multilayers with Perpendicular Magnetic Anisotropy,"[Co/Ni] multilayers with perpendicular magnetic anisotropy (PMA) have been
researched and applied in various spintronic applications. Typically the seed
layer material is studied to provide the desired face-centered cubic
(\textit{fcc}) texture to the [Co/Ni] to obtain PMA. The integration of [Co/Ni]
in back-end-of-line (BEOL) processes also requires the PMA to survive
post-annealing. In this paper, the impact of NiCr, Pt, Ru, and Ta seed layers
on the structural and magnetic properties of [Co(0.3 nm)/Ni(0.6 nm)]
multilayers is investigated before and after annealing. The multilayers were
deposited \textit{in-situ} on different seeds via physical vapor deposition at
room temperature. The as-deposited [Co/Ni] films show the required
\textit{fcc}(111) texture on all seeds, but PMA is only observed on Pt and Ru.
In-plane magnetic anisotropy (IMA) is obtained on NiCr and Ta seeds, which is
attributed to strain-induced PMA loss. PMA is maintained on all seeds after
post-annealing up to 400$^{\circ}$C. The largest effective perpendicular
anisotropy energy ($K_U^{\mathrm{eff}}\approx 2\times10^5$J/m$^3$) after
annealing is achieved on NiCr seed. The evolution of PMA upon annealing cannot
be explained by further crystallization during annealing or strain-induced PMA,
nor can the observed magnetization loss and the increased damping after
annealing. Here we identify the diffusion of the non-magnetic materials from
the seed into [Co/Ni] as the major driver of the changes in the magnetic
properties. By selecting the seed and post-annealing temperature, the [Co/Ni]
can be tuned in a broad range for both PMA and damping.",1701.07713v1
2018/5/16,"Single Crystal Permanent Magnet: Extraordinary Magnetic Behavior in the ta, Cu and Fe Substituted CeCo5 System","To reduce material and processing costs of commercial permanent magnets and
to attempt to fill the empty niche of energy products, 10 - 20 MGOe, between
low-flux (ferrites, alnico) and high-flux (Nd2Fe14B- and SmCo5-type) magnets,
we report synthesis, structure, magnetic properties and modeling of Ta, Cu and
Fe substituted CeCo5. Using a self-flux technique, we grew single crystals of I
- Ce15.1Ta1.0Co74.4Cu9.5, II - Ce16.3Ta0.6Co68.9Cu14.2, III -
Ce15.7Ta0.6Co67.8Cu15.9, IV - Ce16.3Ta0.3Co61.7Cu21.7 and V -
Ce14.3Ta1.0Co62.0Fe12.3Cu10.4. X-ray diffraction analysis (XRD) showed that
these materials retain a CaCu5 substructure and incorporate small amounts of Ta
in the form of \dumb-bells"", filling the 2e crystallographic sites within the
1D hexagonal channel with the 1a Ce site, whereas Co, Cu and Fe are
statistically distributed among the 2c and 3g crystallographic sites. Scanning
electron microscopy, energy dispersive X-ray spectroscopy (SEM-EDS) and
scanning transmission electron microscopy (STEM) examinations provided strong
evidence of the single-phase nature of the as-grown crystals, even though they
readily exhibited significant magnetic coercivitie of ~1.6 - ~1.8 kOe caused by
Co-enriched, nano-sized, structural defects and faults that can serve as
pinning sites. Formation of the ""composite crystal"" during the heat treatment
creates a 3D array of extended defects within a primarily single grain single
crystal, which greatly improves its magnetic characteristics. Possible causes
of the formation of the ""composite crystal"" may be associated with Ta atoms
leaving matrix interstices at lower temperatures and/or matrix degradation
induced by decreased miscibility at lower temperatures. Fe strongly improves
both the Curie temperature and magnetization of the system resulting in
(BH)max:~13 MGOe at room temperature.",1805.06545v1
2018/9/12,Electromagnetic fields induced by an electric charge near a Weyl semimetal,"Weyl semimetals (WSM) are a new class of topological materials that exhibit a
bulk Hall effect due to time-reversal symmetry breaking, as well as a chiral
magnetic effect due to inversion symmetry breaking. These unusual
electromagnetic responses can be characterized by an axion term $\theta
\textbf{E} \cdot \textbf{B}$ with space and time dependent axion angle $\theta
(\textbf{r} ,t)$. In this paper we compute the electromagnetic fields produced
by an electric charge near to a topological Weyl semimetal with two Weyl nodes
in the bulk Brillouin zone. We find that, as in ordinary metals and
dielectrics, outside the WSM the electric field is mainly determined by the
optical properties of the material. The magnetic field is, on the contrary, of
topological origin in nature due to the magnetoelectric effect of topological
phases. We show that the magnetic field exhibits a particularly interesting
behavior above the WSM: the field lines begin at the surface and then end at
the surface (but not at the same point). This behavior is quite different from
that produced by an electric charge near the surface of a topological
insulator, where the magnetic field above the surface is generated by an image
magnetic monopole beneath the surface, in which case, the magnetic field lines
are straight rays. The unconventional behavior of the magnetic field is an
experimentally observable signature of the anomalous Hall effect in the bulk of
the WSM. We discuss a simple candidate material for testing our predictions, as
well as two experimental setups which must be sensitive to the effects of the
induced magnetic field.",1809.04210v2
2018/10/7,"Role of Spin, Phonon and Plasmon Dynamics on Ferromagnetism in Cr doped 3C-SiC","The defect induced magnetism has initiated a lot of interest in field of
spintronics. In this regard, SiC is a promising material because of its unique
properties under extreme conditions. Hence it will be very much interesting to
investigate the interaction between defects and itinerant carrier in doped SiC
for spintronics application. We report the structural stability and magnetic
interaction in Cr doped 3C-SiC synthesized by Thermal Plasma Technique. The EPR
spectrum of undoped 3C-SiC shows a sharp resonance line corresponding to
$g=2.00$ associated with the defects present in the system. Anomalous
temperature evolution tendency of the relative intensity of EPR spectra can be
attributed to magnetically correlated defects in the host matrix. For the first
time we report the detailed quantitative analysis of X-band and Q-band EPR
study in Cr doped 3C-SiC which reveals that Cr can be in multivalent state. The
non monotonous variation of Longitudinal Mode (LO) of the Raman spectra has
been explained based on the interaction between carriers and surface plasmon
using Longitudinal optical plasmon coupling model (LOPC). The carrier density
calculated by using LOPC fit with experimental data varies from
$1.8\times10^{15}$ to $4.2\times10^{17}$ cm$^{-3}$. Room temperature magnetic
measurements exhibit ferromagnetic behavior with non-zero coercivity for all
the samples up to 7 T field. We, for the first time, show the Curie temperature
to be above 760 K. Quantitative analysis of magnetic interaction validates the
applicability of Bound Magnetic Polaron Model (BMP) which probably arises from
the exchange interaction of Cr$^{3+}$ ions with related (Si, C) defects. The
polaron density estimated from the BMP fit agrees well with the carrier density
obtained from the line shape fitting of Raman spectra.",1810.03146v3
2019/12/24,Quantum versus Classical Spin Fragmentation in Dipolar Kagome Ice Ho3Mg2Sb3O14,"A promising route to realize entangled magnetic states combines geometrical
frustration with quantum-tunneling effects. Spin-ice materials are canonical
examples of frustration, and Ising spins in a transverse magnetic field are the
simplest many-body model of quantum tunneling. Here, we show that the tripod
kagome lattice material Ho${_3}$Mg${_2}$Sb${_3}$O${_{14}}$ unites an ice-like
magnetic degeneracy with quantum-tunneling terms generated by an intrinsic
splitting of the Ho$^{3+}$ ground-state doublet, which is further coupled to a
nuclear spin bath. Using neutron scattering and thermodynamic experiments, we
observe a symmetry-breaking transition at $T^{\ast}\approx0.32$ K to a
remarkable state with three peculiarities: a concurrent recovery of magnetic
entropy associated with the strongly coupled electronic and nuclear degrees of
freedom; a fragmentation of the spin into periodic and ice-like components; and
persistent inelastic magnetic excitations down to $T\approx0.12$ K. These
observations deviate from expectations of classical spin fragmentation on a
kagome lattice, but can be understood within a model of dipolar kagome ice
under a homogeneous transverse magnetic field, which we survey with exact
diagonalization on small clusters and mean-field calculations. In
Ho${_3}$Mg${_2}$Sb${_3}$O${_{14}}$, hyperfine interactions dramatically alter
the single-ion and collective properties, and suppress possible quantum
correlations, rendering the fragmentation with predominantly single-ion quantum
fluctuations. Our results highlight the crucial role played by hyperfine
interactions in frustrated quantum magnets, and motivate further investigations
of the role of quantum fluctuations on partially-ordered magnetic states.",1912.11229v2
2020/2/26,Spin-orbit quantum impurity in a topological kagome magnet,"Quantum states induced by single-atomic-impurities are the current frontier
of material and information science. Recently the spin-orbit coupled correlated
kagome magnets are emerging as a new class of topological quantum materials,
although the effect of single-atomic impurities remains unexplored. Here we use
state-of-the-art scanning tunneling microscopy/spectroscopy (STM/S) to study
the atomic indium impurity in a topological kagome magnet Co3Sn2S2, which is
designed to support the spin-orbit quantum state. We find each impurity
features a strongly localized bound state. Our systematic
magnetization-polarized tunneling probe reveals its spin-down polarized nature
with an unusual moment of -5uB, indicative of additional orbital magnetization.
As the separation between two impurities progressively shrinks, their
respective bound states interact and form quantized molecular orbital states.
The molecular orbital of three neighboring impurities further exhibits an
intriguing splitting owing to the combination of geometry, magnetism, and
spin-orbit coupling, analogous to the splitting of the topological Weyl fermion
line12,19. Our work demonstrates the quantum-level interplay between magnetism
and spin-orbit coupling at an individual atomic impurity, which provides
insights into the emergent impurity behavior in a topological kagome magnet and
the potential of spin-orbit quantum impurities for information science.",2002.11783v1
2021/3/24,Magnetism and Spin Dynamics in Room-Temperature van der Waals Magnet Fe$_5$GeTe$_2$,"Two-dimensional (2D) van der Waals (vdWs) materials have gathered a lot of
attention recently. However, the majority of these materials have Curie
temperatures that are well below room temperature, making it challenging to
incorporate them into device applications. In this work, we synthesized a
room-temperature vdW magnetic crystal Fe$_5$GeTe$_2$ with a Curie temperature
T$_c = 332$ K, and studied its magnetic properties by vibrating sample
magnetometry (VSM) and broadband ferromagnetic resonance (FMR) spectroscopy.
The experiments were performed with external magnetic fields applied along the
c-axis (H$\parallel$c) and the ab-plane (H$\parallel$ab), with temperatures
ranging from 300 K to 10 K. We have found a sizable Land\'e g-factor difference
between the H$\parallel$c and H$\parallel$ab cases. In both cases, the Land\'e
g-factor values deviated from g = 2. This indicates contribution of orbital
angular momentum to the magnetic moment. The FMR measurements reveal that
Fe$_5$GeTe$_2$ has a damping constant comparable to Permalloy. With reducing
temperature, the linewidth was broadened. Together with the VSM data, our
measurements indicate that Fe$_5$GeTe$_2$ transitions from ferromagnetic to
ferrimagnetic at lower temperatures. Our experiments highlight key information
regarding the magnetic state and spin scattering processes in Fe$_5$GeTe$_2$,
which promote the understanding of magnetism in Fe$_5$GeTe$_2$, leading to
implementations of Fe$_5$GeTe$_2$ based room-temperature spintronic devices.",2103.13433v2
2021/10/6,Antiferromagnetic VdW Phase at the Interface of Sputtered Topological Insulator/Ferromagnet-Bi2Te3/Ni80Fe20 Heterostructures,"Magnetic ordering in topological insulators (TI) is crucial for breaking
time-reversal symmetry (TRS) and thereby opening a gap in the topological
surface states (TSSs) [1-6], which is the key for realizing useful topological
properties such as the quantum anomalous Hall (QAH) effect, axion insulator
state and the topological magnetoelectric effect. Combining TIs with magnetic
materials can be expected to yield interfaces [26-28] with unique topological
and magnetic phases but such interfaces largely remain unexplored. Here, we
report the discovery of a novel antiferromagnetic (AFM) Van der Waals (VdW)
phase at the interface of a sputtered c-axis oriented TI/FM (Bi2Te3/Ni80Fe20)
heterostructure due to the formation of a Ni-intercalated Bi2Te3 VdW
interfacial layer. The TI/FM heterostructure is shown to possess a significant
spontaneous exchange bias and the presence of an AFM order at the interface via
measurements of the hysteresis loop as well as the observation of compensated
magnetic moments at the interface using polarized neutron reflectometry (PNR).
An in-depth analysis of the structural and chemical properties of the
interfacial AFM phase was carried out using selected area electron diffraction
(SAED), electron energy loss spectroscopy (EELS), and X-ray photoelectron
spectroscopy (XPS). These studies show evidence of solid-state reaction between
the intercalated Ni atoms and Bi2Te3 layers and of the formation of
topologically nontrivial magnetic VdW compounds. The N\'eel temperature of the
interfacial AFM phase is 63 K, which is higher than that of typical magnetic
topological insulators [53]. Our study shows how industrial
CMOS-process-compatible sputtered TI/FM heterostructures can provide a novel
materials platform for exploring the emergence of interfacial topological
magnetic phases and high-temperature topological magnetic states.",2110.02845v2
2023/4/4,Synthesis and Anisotropic Magnetic Properties of LiCrTe$_2$ Single Crystals with a Triangular-Lattice Antiferromagnetic Structure,"We report on the synthesis of LiCrTe$_2$ single crystals and on their
anisotropic magnetic properties. We have obtained these single crystals by
employing a Te/Li-flux synthesis method. We find LiCrTe$_2$ to crystallize in a
TlCdS$_2$ -type structure with cell parameters of $a$ = 3.9512(5) \r{A} and $c$
= 6.6196(7) \r{A} at $T$ = 175 K. The content of lithium in these crystals was
determined to be near stoichiometric by means of neutron diffraction. We find a
pronounced magnetic transition at $T^{\rm ab}_{\rm N}$ = 144 K and $T^{\rm
c}_{\rm N}$ = 148 K, respectively. These transition temperatures are
substantially higher than earlier reports on polycrystalline samples. We have
performed neutron powder diffraction measurements that reveal that the
long-range low-temperature magnetic structure of single crystalline LiCrTe$_2$
is an A-type antiferromagnetic (AFM) structure. Our DFT calculations are in
good agreement with these experimental observations. We find the system to be
easy axis with moments oriented along the $c$-direction experimentally as well
as in our calculations. Thereby, the magnetic Hamiltonian can be written as $H
= H_{\rm Heisenberg} + \sum_i K_c (S_i^z)^2$ with $K_c=-0.34K$ (where
$|S^z|=\frac{3}{2}$). We find LiCrTe$_2$ to be highly anisotropic, with a
pronounced metamagnetic transition for $H \perp ab$ with a critical field of
$\mu H_{MM}$(5 K) $\approx$ 2.5 T. Using detailed orientation-dependent
magnetization measurements, we have determined the magnetic phase diagram of
this material. Our findings suggest that LiCrTe$_2$ is a promising material for
exploring the interplay between crystal structure and magnetism, and could have
potential applications in spin-based 2D devices.",2304.01767v1
2024/3/4,Molecular intercalation in the van der Waals antiferromagnets FePS3 and NiPS3,"We have performed electrochemical treatment of the van der Waals
antiferromagnetic materials FePS$_3$ and NiPS$_3$ with the ionic liquid
EMIM-BF$_4$, achieving significant molecular intercalation. Mass analysis of
the intercalated compounds, EMIM$_x$-FePS$_3$ and EMIM$_x$-NiPS$_3$, indicated
respective intercalation levels, $x$, of approximately 27\% and 37\%, and X-ray
diffraction measurements demonstrated a massive (over 50\%) enhancement of the
$c$-axis lattice parameters. To investigate the consequences of these changes
for the magnetic properties, we performed magnetic susceptibility and $^{31}$P
nuclear magnetic resonance (NMR) studies of both systems. For
EMIM$_x$-FePS$_3$, intercalation reduces the magnetic ordering temperature from
$T_N = 120$~K to 78~K, and we find a spin gap in the antiferromagnetic phase
that drops from 45~K to 30~K. For EMIM$_x$-NiPS$_3$, the ordering temperature
is almost unaffected (changing from 148~K to 145~K), but a change towards
nearly isotropic spin fluctuations suggests an alteration of the magnetic
Hamiltonian. Such relatively modest changes, given that the huge extension of
the $c$ axes is expected to cause a very strong suppression any interlayer
interactions, point unequivocally to the conclusion that the magnetic
properties of both parent compounds are determined solely by two-dimensional
(2D), intralayer physics. The changes in transition temperatures and
low-temperature spin dynamics in both compounds therefore indicate that
intercalation also results in a significant modulation of the intralayer
magnetic interactions, which we propose is due to charge doping and
localization on the P sites. Our study offers chemical intercalation with ionic
liquids as an effective method to control not only the interlayer but also the
intralayer interactions in quasi-2D magnetic materials.",2403.01714v1
1992/9/5,Aspects of Spin Dynamics in the Cuprate Superconductors,"One of the interesting aspects of the CuO superconductors is that
superconductivity is happening so close to the antiferromagnetic state. The
nuclear magnetic resonance and the recent neutron scattering experiments
clearly indicate that magnetic correlations persist in to the heavily doped
regime. In this paper we will discuss some of the details of the coupling of
the nuclear magnetic spin to the conduction electron spins. Furthermore we will
show that a simple band structure can explain the recent neutron scattering
data in the \LaSrCuO material for the optimal concentration of $x\approx 0.15$
if the lifetime effects are included.",9209005v1
1995/9/29,Surprises on the Way from 1D to 2D Quantum Magnets: the Novel Ladder Materials,"One way of making the transition between the quasi-long range order in a
chain of S=1/2 spins coupled antiferromagnetically and the true long range
order that occurs in a plane, is by assembling chains to make ladders of
increasing width. Surprisingly this crossover between one and two dimensions is
not at all smooth. Ladders with an even number of legs have purely short range
magnetic order and a finite energy gap to all magnetic excitations. Predictions
of this novel groundstate have now been verified experimentally. Holes doped
into these ladders are predicted to pair, and possibly superconduct.",9509181v1
1995/11/12,The Magnetic Behavior of the t-J Model,"Using the spin-hole coherent state representation, and taking the long range
antiferromagnetic N\'{e}el order as the background of the spin degree part, we
have studied the magnetic behavior of the t-J model in the usual slave boson
and slave fermion treatment of the single occupation constraint, and shown that
we can qualitatively explain the anomalous magnetic and transport properties of
the normal state of the cuprate superconducting materials by the t-J model.",9511053v1
1996/6/14,Nonlinear transverse magnetic moment in anisotropic superconductors,"We consider the nonlinear transverse magnetic moment that arises in the
Meissner state of superconductors with strongly anisotropic order parameter. We
compute this magnetic moment as a function of applied field and geometry,
assuming d-wave pairing, for realistic samples, finite in all three dimensions,
of high temperature superconducting materials. Return currents, shape effects
and the anisotropy of the penetration depth are all included. We numerically
solve the nonlinear Maxwell-London equations for a finite system. The effect,
which is a probe of the order parameter symmetry in the bulk of the sample,
should be readily measurable if pairing is in a d-wave state. Failure to
observe it would set a lower bound to the s-wave component.",9606102v1
1996/11/6,Incommensurate nodes in the energy spectrum of weakly coupled antiferromagnetic Heisenberg ladders,"Heisenberg ladders are investigated using the bond-mean-field theory
[M.Azzouz, Phys. Rev. B 48, 6136 (1993)]. The zero inter-ladder coupling energy
gap, the uniform spin susceptibility and the nuclear magnetic resonance
spin-relaxation rate are calculated as a function of temperature and magnetic
field. For weakly coupled ladders, the energy spectrum vanishes at
incommensurate wavevectors giving rise to nodes. As a consequence, the spin
susceptibility becomes linear at low temperature. Our results for the single
ladder successfully compare to experiments on SrCu_2O_3 and (VO)_2P_2O_7
materials and new predictions concerning the coupling to the magnetic field are
made.",9611049v1
1997/3/24,Incommensurate magnetism in cuprate materials,"In the low doping region an incommensurate magnetic phase is observed in
LSCO. By means of the composite operator method we show that the single-band 2D
Hubbard model describes the experimental situation. In the higher doping
region, where experiments are not available, the incommensurability is
depressed owing to the van Hove singularity near the Fermi level. A
proportionality between the incommensurability amplitude and the critical
temperature is predicted, suggesting a close relation between superconductivity
and incommensurate magnetism.",9703207v1
1997/3/25,Phase Diagram of the S = 1/2 Frustrated Coupled Ladder System,"We present a theoretical study of the magnetic phase diagram of the
frustrated coupled ladder structure realized recently in several materials.
This system displays a nondegenerate spin-gap state in the dimer limit and an
infinitely degenerate spin-gap state in the regime of weakly-coupled zig-zag
chains. Between these we demonstrate the existence of gapless, magnetically
ordered regions whose order is antiferromagnetic close to the honeycomb lattice
limit, and incommensurate along the chains when all three magnetic interactions
compete.",9703214v1
1997/5/19,Nucleation Theory of Magnetization Switching in Nanoscale Ferromagnets,"A nucleation picture of magnetization switching in single-domain
ferromagnetic nanoparticles with high local anisotropy is discussed. Relevant
aspects of nucleation theory are presented, stressing the effects of the
particle size on the switching dynamics. The theory is illustrated by Monte
Carlo simulations and compared with experiments on single particles.",9705189v1
1997/9/17,Transport Coefficients of InSb in a Strong Magnetic Field,"Improvement of a superconducting magnet system makes induction of a strong
magnetic field easier. This fact gives us a possibility of energy conversion by
the Nernst effect. As the first step to study the Nernst element, we measured
the conductivity, the Hall coefficient, the thermoelectric power and the Nernst
coefficient of the InSb, which is one of candidates of the Nernst elements.
  From this experiment, it is concluded that the Nernst coefficient is smaller
than the theoretical values. On the other hand, the conductivity, the Hall
coefficient ant the thermoelectric power has the values expected by the theory.",9709188v1
1997/12/17,Computation of the Nonlinear Magnetic Response of a Three Dimensional Anisotropic Superconductor,"Many problems in computational magnetics involve computation of fields which
decay within a skin depth $\delta$, much smaller than the sample size $d$. We
discuss here a novel perturbation method which exploits the smallness of
$\epsilon \equiv \delta / d$ and the asymptotic behavior of the solution in the
exterior and interior of a sample. To illustrate this procedure we consider the
computation of the magnetic dipole and quadrupole moments of an anisotropic,
unconventional, three dimensional superconductor. The method significantly
reduces the required numerical work and can be implemented in different
numerical algorithms.",9712210v1
1998/4/1,Magnetic Reversal on Vicinal Surfaces,"We present a theoretical study of in-plane magnetization reversal for vicinal
ultrathin films using a one-dimensional micromagnetic model with
nearest-neighbor exchange, four-fold anisotropy at all sites, and two-fold
anisotropy at step edges. A detailed ""phase diagram"" is presented that catalogs
the possible shapes of hysteresis loops and reversal mechanisms as a function
of step anisotropy strength and vicinal terrace length. The steps generically
nucleate magnetization reversal and pin the motion of domain walls. No sharp
transition separates the cases of reversal by coherent rotation and reversal by
depinning of a ninety degree domain wall from the steps. Comparison to
experiment is made when appropriate.",9804009v1
1998/7/13,Magnetoresistance of Epitaxial Fe Wires with Varied Domain Wall Structure,"The low temperature negative domain wall (DW) contribution to the resistivity
observed in expitaxial Fe microstructures has been investigated as a function
of film thickness. The DW spin structure changes from Bloch to Neel-like with
decreasing film thickness. Results suggest that an interplay between orbital
effects in the internal magnetic fields near DWs and thin film surface
scattering are at the origin of the observed negative wall contribution.",9807183v1
1998/9/5,Electronic and magnetic states in doped LaCoO_3,"The electronic and magnetic states in doped perovskite cobaltites, (La,
Sr)CoO_3, are studied in the numerically exact diagonalization method on
Co_2O_{11} clusters. For realistic parameter values, it is shown that a high
spin state and an intermediate spin state coexist in one-hole doped clusters
due to strong p-d mixing. The magnetic states in the doped cobaltites obtained
in the calculation explain various experimental results.",9809099v1
1998/9/9,Magnetic Properties Of Ni-Mo Single Crystal Alloys: Theory and Experiment,"The magnetization of Ni_{1-x}Mo_{x} single crystals with x=4,6,8 and 10 % by
weight have been measured at 4.2K using a vibrating sample magnetometer and a
Superconducting Quantum Interference Device (SQUID). The magnetization of the
alloy at these low concentrations and at 0 K have been theoretically determined
by using the tight-binding linearized muffin-tin orbital method coupled with
augmented space recursion. The theoretical data are compared with the
experiment.",9809137v1
1998/9/30,Thickness dependent magnetotransport in ultra-thin manganite films,"To understand the near-interface magnetism in manganites, uniform, ultra-thin
films of La_{0.67}Sr_{0.33}MnO_3 were grown epitaxially on single crystal (001)
LaAlO_3 and (110) NdGaO_3 substrates. The temperature and magnetic field
dependent film resistance is used to probe the film's structural and magnetic
properties. A surface and/or interface related dead-layer is inferred from the
thickness dependent resistance and magnetoresistance. The total thickness of
the dead layer is estimated to be $\sim 30 \AA$ for films on NdGaO_3 and $\sim
50 \AA$ for films on LaAlO_3.",9809414v1
1998/12/28,The Kronig-Penney-Ising picture of the colossal magnetoresistance,"From general arguments, it is shown that a magnetic Kronig-Penney model based
on the thermodynamics of an Ising model can be used for describing the Colossal
Magnetoresistance (CMR) phenomenon. The model considers a tunneling-like
transmission process of hopping electrons through a dynamic lattice
characterized by evolving magnetic clusters. In this model, correlations
between the magnetic states are considered to be more relevant than the lattice
strain effects for obtaining the CMR features. Physical arguments lead to the
theoretical description of the intrinsic temperature and field dependences of
the CMR observed in typical manganite materials.",9812406v1
1999/3/2,Influence of magnetic fields on the spin reorientation transition in ultra-thin films,"The dependence of the spin reorientation transition in ultra-thin
ferromagnetic films on external magnetic fields is studied. For different
orientations of the applied field with respect to the film, phase diagrams are
calculated within a mean field theory for the classical Heisenberg model. In
particular we find that the spin reorientation transition present in this model
is not suppressed completely by an applied field, as the magnetization
component perpendicular to the field may show spontaneous order in a certain
temperature interval.",9903040v1
1999/3/11,Breakdown of the resistor model of CPP-GMR in magnetic multilayered nanostructures,"We study the effect on CPP GMR of changing the order of the layers in a
multilayer. Using a tight-binding simple cubic two band model (s-d),
magneto-transport properties are calculated in the zero-temperature, zero-bias
limit, within the Landauer-Buttiker formalism. We demonstrate that for layers
of different thicknesses formed from a single magnetic metal and multilayers
formed from two magnetic metals, the GMR ratio and its dependence on disorder
is sensitive to the order of the layers. This effect disappears in the limit of
large disorder, where the results of the widely-used Boltzmann approach to
transport are restored.",9903190v1
1999/6/29,Magnetic susceptibility of diluted pyrochlore and SCGO antiferromagnets,"We investigate the magnetic susceptibility of the classical Heisenberg
antiferromagnet with nearest-neighbour interactions on the geometrically
frustrated pyrochlore lattice, for a pure system and in the presence of
dilution with nonmagnetic ions. Using the fact that the correlation length in
this system for small dilution is always short, we obtain an approximate but
accurate expression for the magnetic susceptibility at all temperatures. We
extend this theory to the compound SrCr_{9-9x}Ga_{3+9x}O_{19} (SCGO) and
provide an explanation of the phenomenological model recently proposed by
Schiffer and Daruka [Phys. Rev. B56, 13712 (1997)].",9906421v1
1999/7/31,"Characterisation, Raman, Magnetic and Resistivity measurements in polycrystalline samples of LaMnO3 doped with Cd","We report a study of polycrystalline samples of the family La1-xCdxMnO3+dwith
different percentage of Mn4+ ions. X-rays diffraction, Iodometric titration,
Raman, Magnetic and Electrical Resistivity measurements provide a general
characterisation of the physical properties. Results are qualitatively similar
to the ones found in Ca doped manganese perovskites.
  Key words: Cd, manganese perovskites, magnetoresistance, Raman, magnetic,
resistivity",9908006v2
1999/8/3,The Fermi surfaces of Metallic Alloys and the Oscillatory Magnetic Coupling between Magnetic Layers separated by such Alloy Spacers,"We review the theory of oscillatory magnetic coupling in Metallic Multilayers
across alloy spacers. We illustrate the relationship between the frequencies of
the oscillations and the extremal caliper vectors of the Fermi surface of the
spacer by explicit calculations for Cu$_{(1-x)}$Ni$_x$, Cr$_{(1-x)}$V$_x$ and
Cr$_{(1-x)}$Mo$_x$ alloys. We argue the measurement of the frequencies of such
oscillations can be an extremely useful and cheap probe of the Fermi surface of
random alloys.",9908035v1
1999/9/28,"Magnetotransport properties of (Ga,Mn)As investigated at low temperature and high magnetic field","Magnetotransport properties of ferromagnetic semiconductor (Ga,Mn)As have
been investigated. Measurements at low temperature (50 mK) and high magnetic
field (<= 27 T) have been employed in order to determine the hole concentration
p = 3.5x10^20 cm ^-3 of a metallic (Ga0.947Mn0.053)As layer. The analysis of
the temperature and magnetic field dependencies of the resistivity in the
paramagnetic region was performed with the use of the above value of p, which
gave the magnitude of p-d exchange energy |N0beta | ~ 1.5 eV.",9909393v1
1999/10/24,Phase transitions in Ising magnetic films and superlattices,"Within the framework of mean field theory, we examine the phase transitions
in Ising magnetic films and superlattices. By transfer matrix method, we derive
two general nonlinear equations for phase transition temperatures of Ising
magnetic films and superlattices, respectively. The equations can be applied to
the films and superlattices with arbitrary exchange interaction constants and
arbitrary layer number. Numerical results for phase transition temperatures as
a function of exchange interaction constants are presented.",9910378v1
1999/10/25,Heavy Fermion Behaviors in LiV_{2}O_{4},"Experiments of various types on the metallic transition metal oxide compound
LiV_{2}O_{4} with the fcc normal-spinel structure are reviewed. The
low-temperature T < 10 K data consistently indicate heavy fermion (HF)
behaviors characteristic of those of the heaviest-mass f-electron HF compounds.
A crossover is observed above about 50 K in the magnetic susceptibility, ^{7}Li
spin-lattice relaxation rate and neutron magnetic scattering function to a
magnetic state variously described as an antiferromagnetically-coupled
local-moment metal or, at the opposite extreme, as an itinerant
nearly-ferromagnetic metal. Recent theoretical investigations to understand
these properties of LiV_{2}O_{4} are discussed.",9910404v1
1999/12/29,Systematic Study of Magnetic Interactions in Insulating Cuprates,"The magnetic interactions in one-dimensional, two-dimensional (2D) and ladder
cuprates are evaluated systematically by using small Cu-O clusters. We find
that the superexchange interaction J between nearest neighbor Cu spins strongly
depends on Cu-O structure through the Madelung potential, and in 2D and ladder
cuprates there is a four-spin interaction Jcyc, with magnitude of 10% of J. We
show that Jcyc has a strong influence on the magnetic excitation in the
high-energy region of 2D cuprates.",9912480v2
2000/1/31,Ferromagnetism below the Stoner limit in La-doped SrB_6,"Spin-polarized band calculations for LaSr_7B_{48} show a weak ferro-magnetic
state. This is despite a low density-of-states (DOS) and a low Stoner factor.
The reason for the magnetic state is found to be associated with a gain in
potential energy in addition to the exchange energy, as a spin-splitting is
imposed. An impurity like La DOS is essential for this effect. It makes a
correction to the Stoner factor, and provides an explanation of the recently
observed weak ferro-magnetism in doped hexaborides.",0001437v1
2000/2/12,Quantum Tunneling of Magnetization in Molecular Complexes with Large Spins. Effect of the Environment,"We review the present state of theory and experiments on the quantum
tunneling of magnetization in mesoscopic spin systems. Most attention is paid
to the relaxation of magnetization in the molecular complexes Mn12 and Fe8. The
role of the thermostat (phonons, nuclear spins, dipolar fields) is studied.",0002180v1
2000/4/11,Can half metallic zincblende MnAs be grown?,"In this paper we investigate theoretically the ground state NiAs-type
structure of MnAs and we compare the magnetic and structural properties with an
hypothetical zincblende structure. A zincblende structure can be obtained, in
principle, from the diluted magnetic semiconductor Ga$_{1-x}$Mn$_x$As in the
limit $x=1$. Using density functional calculations within the local
spin-density approximation (LSDA), we show that the zincblende structure,
although showing half metallic behavior which is very attractive for
spintronics, can not be stabilized at equilibrium. We perform a tight-binding
analysis of the Mn-As bond in the tetrahedral coordination to investigate the
nature of the bonding in diluted magnetic semiconductors.",0004184v1
2000/5/2,Two-Dimensional Modeling of Soft Ferromagnetic Films,"We examine the response of a soft ferromagnetic film to an in-plane applied
magnetic field. Our theory, based on asymptotic analysis of the micromagnetic
energy in the thin-film limit, proceeds in two steps: first we determine the
magnetic charge density by solving a convex variational problem; then we
construct an associated magnetization field using a robust numerical method.
Experimental results show good agreement with the theory. Our analysis is
consistent with prior work by van den Berg and by Bryant and Suhl, but it goes
much further; in particular it applies even for large fields which penetrate
the sample.",0005057v1
2000/6/10,Metamagnetism in one dimensional systems with edge sharing CuO polihedra,"We study a Heisenberg chain with nearest-neighbor (NN) J1 and next-NN J2
exchange interactions with anisotropies Delta_1 and Delta_2 respectively. We
investigate by analytical and numerical methods the region of parameters for
which there is a jump in the magnetization M as a function of magnetic field B.
Some materials with edge sharing CuO polihedra are candidates to show an abrupt
change in M(B).",0006178v1
2000/10/23,Nuclear Magnetic Relaxation in Sc Metal,"The nuclear magnetic relaxation in scandium metal is investigated at liquid
helium temeprature for both single crystal and powder samples. The obtained
temperature and field dependence of the Korringa constant are described by the
means of the spin uctuation theory. It is shown that one of the reason for the
high field decreasing of the relaxation rate is the quenching of spin
uctuations. The other possible reason is the magnetic impurity influence. The
reasons of the existing variations of the Korringa constant are discussed. The
possible sources of non-single exponential relaxation are investigated.",0010351v1
2000/10/26,Magnetic-history-dependent nanostructural and resistivity changes in Pr0.5Ca0.5Mn0.98Cr0.02O3,"We show that nanostructure and resistivity of Pr0.5Ca0.5Mn0.98Cr0.02O3 are
sensitive to whether the sample is zero-field-cooled (ZFC) of field-cooled (FC)
either in the 'self magnetic field (H = 2 T)' of the electron microscope or
under the external magnetic field of 2 T. FC resistivity at H = 2 T is lower
than ZFC values below 140 K. The average value of the chare-orbital modulation
vector (q = 0.44) of the FC crystallites is lower than that of the ZFC
cystallites (q = 0.48) and the FC crystallites exhibit numerous defects like
discommensuration, dislocations and regios with loss of superstructures
compared to the ZFC crystallites.",0010427v1
2000/11/20,Effects of Disorder on Ferromagnetism in Diluted Magnetic Semiconductors,"We present results of a numerical mean field treatment of interacting spins
and carriers in doped diluted magnetic semiconductors, which takes into account
the positional disorder present in these alloy systems. Disorder is found to
enhance the ferromagnetic transition temperature significantly for metallic
densities not too far from the metal-insulator transition. Concurrently, the
ferromagnetic phase is found to have very unusual temperature dependence of the
magnetization as well as specific heat as a result of disorder. Unusual spin
and charge transport is implied.",0011319v2
2000/12/11,Realization of an ultra-high magnetic field on a nano-scale,"In tunnel junctions of which at least one side is a ferromagnet, very large
magnetic polarization change ($\approx 0.1 \mu_B$) and splitting of the spin up
and spin down Fermi energy ($\approx 0.1 eV$) can be created under steady state
finite current conditions (bias voltage $\approx$ 1 volt). This is {\bf much
higher} than can be created by the highest magnetic field on earth. We
illustrate this with a specific calculation of a recently observed very large
Hall effect in the Al side of a Co-I-Al tunnel junction. Other recent
experiments that support this idea are discussed.",0012186v1
2001/3/5,"Theory of Magnetic Properties and Spin-Wave Dispersion for Ferromagnetic (Ga,Mn)As","We present a microscopic theory of the long-wavelength magnetic properties of
the ferromagnetic diluted magnetic semiconductor (Ga,Mn)As. Details of the host
semiconductor band structure, described by a six-band Kohn-Luttinger
Hamiltonian, are taken into account. We relate our quantum-mechanical
calculation to the classical micromagnetic energy functional and determine
anisotropy energies and exchange constants. We find that the exchange constant
is substantially enhanced compared to the case of a parabolic heavy-hole-band
model.",0103116v2
2001/5/4,Magnetism of a tetrahedral cluster spin-chain,"We discuss the magnetic properties of a dimerized and completely frustrated
tetrahedral spin-1/2 chain. Using a combination of exact diagonalization and
bond-operator theory the quantum phase diagram is shown to incorporate a
singlet-product, a dimer, and a Haldane phase. In addition we consider one-,
and two-triplet excitations in the dimer phase and evaluate the magnetic Raman
cross section which is found to be strongly renormalized by the presence of a
two-triplet bound state. The link to a novel tellurate materials is clarified.",0105096v1
2001/5/9,Spin tunneling via dislocations in Mn-12 acetate crystals,"We show that dislocations should be the main source of spin tunneling in
Mn-12 crystals. Long-range strains caused by dislocations produce broad
distribution of relaxation times that has been seen in many experiments. When
the external magnetic field is applied along the c-axis of the crystal, local
rotations of the magnetic anisotropy axis due to dislocations result in the
effective local transverse magnetic field that unfreezes odd tunneling
resonances. Scaling law is derived that provides universal description of spin
tunneling for all resonances.",0105195v1
2001/5/14,Thermal and Dynamic Effects in Langevin Simulation of Hysteresis in Nanoscale Pillars,"Dynamic quantities related to hysteresis have been measured in micromagnetic
simulations of single-domain nanoscale magnets at nonzero temperature. The
hysteresis-loop area and magnetization-field correlation display the
characteristics of resonance, and the resonance frequency is found to be
temperature dependent. The period-averaged magnetization displays symmetry
breaking at high frequencies.",0105279v1
2001/5/23,Field-Induced Magnetic Order in Quantum Spin Liquids,"We study magnetic field-induced three-dimensional ordering transitions in
low-dimensional quantum spin liquids, such as weakly coupled, antiferromagnetic
spin-1/2 Heisenberg dimers and ladders. Using stochastic series expansion
quantum Monte Carlo simulations, thermodynamic response functions are obtained
down to ultra-low temperatures. We extract the critical scaling exponents which
dictate the power-law dependence of the transition temperature on the applied
magnetic field. These are compared with recent experiments on candidate
materials and with predictions for the Bose-Einstein condensation of magnons
obtained in mean-field theory.",0105464v1
2001/6/18,Vortex avalanches and magnetic flux fragmentation in superconductors,"We report results of numerical simulations of non isothermal dendritic flux
penetration in type-II superconductors. We propose a generic mechanism of
dynamic branching of a propagating hotspot of a flux flow/normal state
triggered by a local heat pulse. The branching occurs when the flux hotspot
reflects from inhomogeneities or the boundary on which magnetization currents
either vanish, or change direction. Then the hotspot undergoes a cascade of
successive splittings, giving rise to a dissipative dendritic-type flux
structure. This dynamic state eventually cools down, turning into a frozen
multi-filamentary pattern of magnetization currents.",0106353v1
2001/6/26,Fragility of the spin-glass-like collective state to a magnetic field in an interacting Fe-C nanoparticle system,"The effect of applied magnetic fields on the collective nonequilibrium
dynamics of a strongly interacting Fe-C nanoparticle system has been
investigated. It is experimentally shown that the magnetic aging diminishes to
finally disappear for fields of moderate strength. The field needed to remove
the observable aging behavior increases with decreasing temperature. The same
qualitative behavior is observed in an amorphous metallic spin glass
(Fe_{0.15}Ni_{0.85})_{75}P_{16}B_6Al_3.",0106530v1
2001/7/5,Heisenberg exchange parameters of molecular magnets from the high-temperature susceptibility expansion,"We provide exact analytical expressions for the magnetic susceptibility
function in the high temperature expansion for finite Heisenberg spin systems
with an arbitrary coupling matrix, arbitrary single-spin quantum number, and
arbitrary number of spins. The results can be used to determine unknown
exchange parameters from zero-field magnetic susceptibility measurements
without diagonalizing the system Hamiltonian. We demonstrate the possibility of
reconstructing the exchange parameters from simulated data for two specific
model systems. We examine the accuracy and stability of the proposed method.",0107111v1
2001/7/12,Theory of Angular Magnetoresistance in CPP spin valves,"The resistance of CPP spin valve is a continuous function of the angle
$\theta $ between the magnetizations of both ferromagnets. We use the cicuit
theory for non-collinear magnetoelectronics to compute the angular
magnetoresistance of CPP spin valves taking the spin accumulation in the
ferromagnetic layers into account.",0107250v1
2001/7/26,Layer-dependent magnetization at the surface of a band-ferromagnet,"The temperature-dependence of the magnetization near the surface of a
band-ferromagnet is measured with monolayer resolution. The simultaneous
application of novel highly surface-sensitive techniques enables one to deduce
the layer-dependent magnetization curves at a Fe(100) surface. Analysis of data
is based on a simple mean-field approach. Implications for modern theories of
itinerant-electron ferromagnetism are discussed.",0107545v1
2001/8/1,Correlation between magnetic and transport properties of phase separated La$_{0.5}$Ca$_{0.5}$MnO$_{3}$,"The effect of low magnetic fields on the magnetic and electrical transport
properties of polycrystalline samples of the phase separated compound
La$_{0.5}$Ca$_{0.5}$MnO$_{3}$ is studied. The results are interpreted in the
framework of the field induced ferromagnetic fraction enlargement mechanism. A
fraction expansion coefficient af, which relates the ferromagnetic fraction f
with the applied field H, was obtained. A phenomenological model to understand
the enlargement mechanism is worked out.",0108026v2
2001/8/8,Edge-state effects on the magneto-polarizability of nanographite layers,"The possibility for carbon materials such as activated carbon fibers or
graphite ribbons, to support edge-states could change drastically their
magnetic properties. The purpose of this work is to propose a novel way to
identify the existence of those states by considering the behaviour of the
static electric polarizability under a perpendicular magnetic field. The
edge-sates are shown to induce a quadratic dependence on magnetic field
detectable experimentally nowaday.",0108135v1
2001/9/4,Quantum phase interference (Berry phase) in single-molecule magnets of Mn12,"Magnetization measurements of a molecular clusters Mn12 with a spin ground
state of S = 10 show resonance tunneling at avoided energy level crossings. The
observed oscillations of the tunnel probability as a function of the magnetic
field applied along the hard anisotropy axis are due to topological quantum
phase interference of two tunnel paths of opposite windings. Mn12 is therefore
the second molecular clusters presenting quantum phase interference.",0109066v1
2001/10/1,Exchange-correlation effects in magnetic-field-induced superconductivity,"Motivated by recent experiments on the organic superconductor
$\lambda-(BETS)_2FeCl_4$ we study the Jaccarino-Peter effect (JPE), the
earliest example of magnetic-field-induced superconductivity, from the point of
view of current-density-functional theory. It is found that both Meissner
(diamagnetic) and Pauli (paramagnetic) pair breaking are suppressed by an
exchange-correlation contribution to the vector potential, arising at the sites
of the magnetic ions. This explains a number of otherwise puzzling experimental
observations, and sheds new light on earlier theories of the JPE.",0110040v1
2002/1/14,Spin polarization contrast observed in GaAs by force-detected nuclear magnetic resonance,"We applied the recently developed technique of force-detected nuclear
magnetic resonance (NMR) to observe 71Ga, 69Ga, and 75As in GaAs. The nuclear
spin-lattice relaxation time is 21$\pm$5 min for 69Ga at $\sim 5$ K and 4.6
Tesla. We have exploited this long relaxation time to first create and then
observe spatially varying nuclear spin polarization within the sample,
demonstrating a new form of contrast for magnetic resonance force microscopy
(MRFM). Such nuclear spin contrast could be used to indirectly image electron
spin polarization in GaAs-based spintronic devices.",0201216v1
2002/1/23,Mechanical detection of FMR spectrum in a normally magnetized YIG disk,"The ferromagnetic resonance spectrum of a normally magnetized YIG disk, with
thickness of 4.75$\mu$m and radius of 80$\mu$m, is measured at room temperature
both by magnetic resonance force microscopy and by standard detection of the
microwave susceptibility. The comparison indicates that MRFM represents one of
the most potent means of obtaining the \emph{complete} FMR spectra of
micron-size samples. In the weak coupling regime, the measured data can be
quantitatively understood within the framework of the Damon and Eshbach model.",0201409v1
2002/1/25,Magnetic Order in Transition Metal Oxides with Orbital Degrees of Freedom,"We investigate the frustrated magnetic interactions in cubic transition metal
oxides with orbital degeneracy. The $e_g$ orbitals order easier and their
ordering explains the $A$-type antiferromagnetic phase in KCuF$_3$ and
LaMnO$_3$. In $t_{2g}$ systems the magnetic order changes at a transition from
an orbital liquid to orbital ordered states. The fluctuations of $t_{2g}$
orbitals play a prominent role in LaVO$_3$ and YVO$_3$, where they compete with
the Jahn-Teller effect and trigger the C-type antiferromagnetic order.",0201455v1
2002/3/7,Ferromagnetism in Oriented Graphite Samples,"We have studied the magnetization of various, well characterized samples of
highly oriented pyrolitic graphite (HOPG), Kish graphite and natural graphite
to investigate the recently reported ferromagnetic-like signal and its possible
relation to ferromagnetic impurities. The magnetization results obtained for
HOPG samples for applied fields parallel to the graphene layers - to minimize
the diamagnetic background - show no correlation with the magnetic impurity
concentration. Our overall results suggest an intrinsic origin for the
ferromagnetism found in graphite. We discuss possible origins of the
ferromagnetic signal.",0203153v1
2002/3/18,Relaxation of Shallow Donor Electron Spin due to Interaction with Nuclear Spin Bath,"We study the low-temperature dynamics of a shallow donor, e.g., $^{31}$P,
impurity electron spin in silicon, interacting with the bath of nuclear spins
of the $^{29}$Si isotope. For small applied magnetic fields, the electron spin
relaxation is controlled by the steady state distribution of the nuclear spins.
We calculate the relaxation times $T_1$ and $T_2$ as functions of the external
magnetic field, and conclude that nuclear spins play an important role in the
donor electron spin decoherence in Si:P at low magnetic fields.",0203362v1
2002/3/26,"Atomistic, microstructural and micromagnetic aspects of the multiscale modelling of hysteretic phenomena","We formulated a technique which combines the first-principles, micromagnetic
and microstructural calculations and allows us to study the nature of
hysteretic phenomena in hard magnets. Two distinct sources of coercivity in
polytwinned CoPt type magnets, domain wall pinning at antiphase boundaries and
splitting at twin boundaries, are illustrated for a realistic microstructure.
Methodology of multiscale modelling of hysteretic phenomena in nanoscale
magnets is discussed.",0203544v1
2002/6/24,"Boltzmann theory of engineered anisotropic magnetoresistance in (Ga,Mn)As","We report on a theoretical study of dc transport coefficients in (Ga,Mn)As
diluted magnetic semiconductor ferromagnets that accounts for quasiparticle
scattering from ionized Mn$^{2+}$ acceptors with a local moment $S=5/2$ and
from non-magnetic compensating defects. In metallic samples Boltzmann transport
theory with Golden rule scattering rates accounts for the principle trends of
the measured difference between resistances for magnetizations parallel and
perpendicular to the current. We predict that the sign and magnitude of the
anisotropic magnetoresistance can be changed by strain engineering or by
altering chemical composition.",0206416v1
2002/8/19,Manganese nanoclusters and nanowires on GaAs surfaces,"We have computed the local magnetic moments of manganese and neighboring
arsenic for various cluster configurations on the (001) surface of GaAs bulk
crystal using a cluster of 512 atoms. We obtained for manganese a substantial
local magnetic moment of 3.66 Bohr magnetons for all cases considered. The
induced magnetic moment of arsenic is less than that of manganese by two orders
of magnitude and falls off drastically beyond nearest neighbor distance. A
small amount of charge is transferred from the manganese to arsenic. The
possibility of a spin polarized wire channel on the arsenic layer below the
surface is suggested.",0208370v1
2002/8/23,Even-odd effects in magnetoresistance of ferromagnetic domain walls,"Difference in density of states for the spin's majority and minority bands in
a ferromagnet changes the electrostatic potential along the domains,
introducing the discontinuities of the potential at domain boundaries. The
value of discontinuity oscillates with number of domains. Discontinuity depends
on the positions of domain walls, their motion or collapse of domain walls in
applied magnetic field. Large values of magnetoresistance are explained in
terms of spin-accumulation. We suggest a new type of domain walls in nanowires
of itinerant ferromagnets, in which the magnetization vector changes without
rotation. Absence of transverse magnetization components allows considerable
spin accumulation assuming the spin relaxation length, L_S, is large enough.",0208463v1
2002/9/3,"Defect correlations, metal-insulator transition, and magnetic order in ferromagnetic semiconductors","Diluted ferromagnetic III-V semiconductors typically show a high degree of
compensation. Compensation is connected to the presence of comparable densities
of charged defects of either sign. This naturally leads to the development of
strong correlations between defect positions during growth and annealing. We
show that these correlations are required to understand the experimentally
observed transport and magnetic properties as well as the persistence of the
energy gap upon doping with magnetic ions.",0209055v1
2002/9/13,Disorder induced critical phenomena in magnetically glassy Cu-Al-Mn alloys,"Measurements of magnetic hysteresis loops in Cu-Al-Mn alloys of different Mn
content at low temperatures are presented. The loops are smooth and continuous
above a certain temperature, but exhibit a magnetization discontinuity below
that temperature. Scaling analysis suggest that this system displays a disorder
induced phase transition line. Measurements allow to determine the critical
exponents $\beta=0.03\pm 0.01$ and $\beta \delta = 0.4 \pm 0.1$ in agreement
with those reported recently [Berger et al., Phys. Rev. Lett. {\bf 85}, 4176
(2000)]",0209323v1
2002/9/24,Giant entropy change at the co-occurrence of structural and magnetic transitions in the Ni2.19Mn0.81Ga Heusler alloy,"In this paper we report the existence of a giant magnetocaloric effect (MCE)
in a intermetallic compound non-containing rare-earth. This effect is
associated with the concomitant occurrence of a structural and a magnetic
transition. The result has been compared with that obtained in a parent
compound in which magnetic and structural transition occur separately.",0209564v2
2002/9/25,High magnetic field-induced insulating phase in an organic conductor,"We report electrical transport, skin depth, and magnetocaloric measurements
in the tau-series of organic conductors at very high magnetic fields. Above 36
T these materials show a magnetic field induced first order phase transition
from a metallic to an insulating state. The transition, which is a bulk
thermodynamic phenomenon, does not follow the conventional prescription for
field induced phase transitions in organic conductors.",0209592v1
2002/9/30,Temperature dependence of the upper critical field of high-Tc superconductors from isothermal magnetization data. Application to polycrystalline samples and ceramics,"Using a recently developed scaling procedure that allows to establish the
temperature dependence of the normalized upper critical field from measurements
of the equilibrium isothermal magnetization, we analyze experimental data
obtained on polycrystalline and ceramic samples. We show that the scaling
procedure works quite well in all cases that we have considered. This provides
a very strong evidence that the temperature dependencies of the normalized
upper critical field are independent of the orientation of an applied magnetic
field with respect to the crystallographic axes of these materials.",0209684v2
2002/10/2,Local Magnetic Susceptibility of the Positive Muon in the Quasi 1D S=1/2 Antiferromagnet KCuF$_3$,"We report muon spin rotation measurements of the local magnetic
susceptibility around a positive muon in the paramagnetic state of the quasi
one-dimensional spin 1/2 antiferromagnet KCuF$_3$. Signals from two distinct
sites are resolved which have a temperature dependent frequency shift which is
different than the magnetic susceptibility. This difference is attributed to a
muon induced perturbation of the spin 1/2 chain.",0210060v1
2002/10/16,Quantum dynamics of crystals of molecular nanomagnets inside a resonant cavity,"It is shown that crystals of molecular nanomagnets exhibit enhanced magnetic
relaxation when placed inside a resonant cavity. Strong dependence of the
magnetization curve on the geometry of the cavity has been observed, providing
evidence of the coherent microwave radiation by the crystals. A similar
dependence has been found for a crystal placed between Fabry-Perot
superconducting mirrors. These observations open the possibility of building a
nanomagnetic microwave laser pumped by the magnetic field.",0210340v1
2002/10/21,Magnetization of small lead particles,"The magnetization of an ensemble of isolated lead grains of sizes ranging
from below 6 nm to 1000 nm is measured. A sharp disappearance of Meissner
effect with lowering of the grain size is observed for the smaller grains. This
is a direct observation by magnetization measurement of the occurrence of a
critical particle size for superconductivity, which is consistent with
Anderson's criterion.",0210459v1
2002/11/1,Exploring dynamical magnetism with time-dependent density-functional theory: from spin fluctuations to Gilbert damping,"We use time-dependent spin-density-functional theory to study dynamical
magnetic phenomena. First, we recall that the local-spin-density approximation
(LSDA) fails to account correctly for magnetic fluctuations in the paramagnetic
state of iron and other itinerant ferromagnets. Next, we construct a
gradient-dependent density functional that does not suffer from this problem of
the LSDA. This functional is then used to derive, for the first time, the
phenomenological Gilbert equation of micromagnetics directly from
time-dependent density-functional theory. Limitations and extensions of Gilbert
damping are discussed on this basis, and some comparisons with phenomenological
theories and experiments are made.",0211021v1
2002/11/6,Symmetry Violation in a Superconducting Film with a Square Array of Ferromagnetic Dots,"We study the equilibrium state of a superconducting film covered with a
regular square array of perpendicularly magnetized magnetic dots. The dots
induce vortices in the film directly under them and antivortices between the
dots. We show that the symmetry of the dot array is spontaneously violated by
the vortices. The positions of the vortices and the antivortices depend on the
magnetization and the size of the dots.",0211117v1
2002/11/12,Electronic structure and magnetic anisotropy of the [Co_4(hmp)_4(CH_3OH)_4Cl_4] molecule,"Accurate density-functional based calculations have been performed on the
Co_4(hmp)_4(CH_3OH)_4Cl_4 molecular magnet where hmp is deprotonated
hydroxymethyl pyridine. In addition to the experimentally observed staggered
geometry, we identify two isomers, referred to as eclipsed and
half-staggered/half-eclipsed, that are reasonably low in energy. Our
calculations show that the magnetic anisotropy is strongly dependent on the
pyridine-pyridine separation and that the three structures exhibit easy axis,
easy plane and triaxial behavior. Other effects such as partial reprotonation
of the hmp is considered.",0211221v1
2002/12/3,Thermal stability of coupled ferromagnetic and superparamagnetic particles,"We consider a single-domain ferromagnetic particle with uniaxial anisotropy
coupled to a single-domain soft ferromagnetic particle (superparamagnetic
particle). The problem of thermally agitated magnetization reversal in this
case can be reduced to the random magnetization dynamics of the first particle
with an effectively larger anisotropy field. The magnetic external field is
also altered in a manner that depends on the sign of the coupling and can be
either enhanced or suppressed.",0212041v1
2003/1/8,Evidence for a large magnetic heat current in insulating cuprates,"The in-plane thermal conductivity $k$ of the two-dimensional
antiferromagnetic monolayer cuprate Sr$_2$CuO$_2$Cl$_2$ is studied. Analysis of
the unusual temperature dependence of $k$ reveals that at low temperatures the
heat is carried by phonons, whereas at high temperatures magnetic excitations
contribute significantly. Comparison with other insulating layered cuprates
suggests that a large magnetic contribution to the thermal conductivity is an
intrinsic property of these materials.",0301093v1
2003/1/29,Existence of the magnetization plateau in a class of exactly solvable Ising-Heisenberg chains,"The mapping transformation technique is applied to obtain exact results for
the spin-1/2 and spin-S (S=1/2,1) Ising-Heisenberg antiferromagnetic chain in
the presence of an external magnetic field. Within this scheme, a field-induced
first-order metamagnetic transition resulting in multiplateau magnetization
curves, is investigated in detail. It is found that the scenario of the plateau
formation depends fundamentally on the ratio between Ising and Heisenbrg
interaction constants, as well as on the anisotropy strength of the XXZ
Heisenberg interaction.",0301557v2
2003/2/12,Epitaxial Growth of the Diluted Magnetic Semiconductors CryGe1-y and CryMnxGe1-x-y,"We report the epitaxial growth of CryGe1-y and CryMnxGe1-x-y(001) thin films
on GaAs(001), describe the structural and transport properties, and compare the
measured magnetic properties with those predicted by theory. The samples are
strongly p-type, and hole densities increase with Cr concentration. The
CryGe1-y system remains paramagnetic for the growth conditions and low Cr
concentrations employed (y < 0.04), consistent with density functional theory
predictions. Addition of Cr into the ferromagnetic semiconductor MnxGe1-x host
systematically reduces the Curie temperature and total magnetization.",0302231v1
2003/3/4,Field-tuned quantum tunneling in a supramolecule dimer $[Mn_4]_2$,"Field-tuned quantum tunneling in two single-molecule magnets coupled
antiferromagnetically and formed a supramolecule dimer is studied. We obtain
step-like magnetization curves by means of the numerically exact solution of
the time-dependent Schr\H{o}dinger equation. The steps in magnetization curves
show the phenomenon of quantum resonant tunneling quantitatively. The effects
of the sweeping rate of applied field is discussed. These results obtained from
quantum dynamical evolution well agree with the recent experiment[W.Wernsdorfer
et al. Nature 416(2002)406].",0303048v1
2003/3/18,Diluted Magnetic Semiconductor at Finite Temperature,"We studied the diluted magnetic semiconductor by the self-consistent Green's
function approach, which treats the spin-wave kinematics appropriately at
finite temperatures. The critical temperature can be obtained by a simple
formula in a wide range of parameter space. In addition, the magnetization
curve versus temperature is concave, which is dramatically different from the
usual convex shape. Finally, we discuss the possibility of generalizing the
current theory to include the realistic band structure, electronic correlations
and disorders in a systematic way.",0303328v3
2003/4/28,Experimental study of MnCl3(C12H8N2) - an S = 2 Heisenberg antiferromagnetic chain,"The thermodynamic and magnetic properties of MnCl3(C12H8N2), have been
studied down to 2 K. The material is an S = 2 antiferromagnetic linear chain
that undergoes long-range ordering to a canted antiferromagnetic state at 23 K.
The comparison of magnetic data from polycrystalline samples with the results
of specific heat measurements using a pressed pellet of powder reveals the
importance of the length of the chains in the sample in relation to the
magnetic correlation length.",0304644v1
2003/5/6,High Magnetic Field Sensor Using LaSb2,"The magnetotransport properties of single crystals of the highly anisotropic
layered metal LaSb2 are reported in magnetic fields up to 45 T with fields
oriented both parallel and perpendicular to the layers. Below 10 K the
perpendicular magnetoresistance of LaSb2} becomes temperature independent and
is characterized by a 100-fold linear increase in resistance between 0 and 45 T
with no evidence of quantum oscillations down to 50 mK. The Hall resistivity is
hole-like and gives a high field carrier density of n ~ 3x10^20 cm^-3. The
feasibility of using LaSb2 for magnetic field sensors is discussed.",0305116v1
2003/5/16,Correlation Functions of the Magnetization in Thin Films,"We calculate the correlation functions of uniform magnetization in thin
ferromagnetic films for small deviations from equilibrium, by using a
functional formalism. To take account of dissipation and fluctuations
consistently, the magnetization is coupled to a bosonic heat bath. The
correlation functions show strong dependence on the nature of the coupling
between the bath and the system. Depending on what coupling we choose, we show
how the recent results $(\text{J. Appl. Phys. 90, 5768 (2001); Phys. Rev. B 65,
172417 (2002)}) $ obtained by macroscopic methods can be related to the
microscopic treatment adopted here.",0305400v1
2003/6/18,Experimental measurements of multiple stable trapped domain wall states induced in nanofabricated elements,"The presence of a domain wall trapped by a sub-micron notch is probed in two
ways: through electronic transport measurements and by Magnetic Force
Microscopy (MFM). We observe complex magnetic features which are consistent
with numerical simulations predicting the existence of multiple magnetic
configurations stabilized by the notch structure.",0306486v1
2003/6/20,Magnetic properties of GaMnAs single layers and GaInMnAs superlattices investigated at low temperature and high magnetic field,"Magnetotransport properties of GaMnAs single layers and InGaMnAs/InGaAs
superlattice structures were investigated at temperatures from 4 K to 300 K and
magnetic fields up to 23 T to study the influence of carriers confinement
through different structures. Both single layers and superlattice structures
show paramagnetic-to-ferromagnetic phase transition. In GaMnAs/InGaAs
superlattice beside the Curie temperature (Tc ~ 40 K), a new phase transition
is observed close to 13 K.",0306534v1
2003/7/30,Magnetism in Atomic-Sized Palladium Contacts and Nanowires,"We have investigated Pd nanowires theoretically, and found that, unlike
either metallic or free atomic Pd, they exhibit Hund's rule magnetism. In long,
monoatomic wires, we find a spin moment of 0.7 Bohr magnetons per atom, whereas
for short, monoatomic wires between bulk leads, the predicted moment is about
0.3 Bohr magnetons per wire atom. In contrast, a coaxial (6,1) wire was found
to be nonmagnetic. The origin of the wire magnetism is analyzed.",0307737v1
2003/8/16,Frequency Dependence of Superconducting Cavity Q and Magnetic Breakdown Field,"A theoretical explanation is given to account for the unexpected observation
that L- and S-band Nb superconducting cavities were found to have lower Q and
lower magnetic breakdown field than those of the higher X-band frequencies.
Both effects can be related to the trapping of magnetic flux in the cavity
walls. The frequency dependence arises from the frequency dependence of the
resistivity of oscillating fluxoids. Calculations based on this model are in
agreement with experimental observations.",0308324v1
2003/10/6,"Ferromagnetism in (In,Mn)As alloy thin films grown by metalorganic vapor phase epitaxy","Ferromagnetic properties of In1-xMnxAs thin films were investigated. Room
temperature ferromagnetic order was observed in nominally single-phase films
with x = 0.01-0.10. Magnetization measurements indicated that these In1-xMnxAs
samples had a Curie temperature of 333 K. The Curie temperature was independent
of Mn concentration. The temperature dependent magnetization along with the
magnitude of the saturation magnetization and microstructural data indicate
that the source of the high-temperature ferromagnetism in single-phase films is
not attributable to MnAs nanoprecipitates. The high transition temperature is
attributed to the presence of near neighbor Mn pairs.",0310104v1
2003/10/31,Conversion of dislocation oscillation waves to spin ones in the vicinity of OPT temperatures,"Dislocation waves in magnetic crystals in the vicinity of orientation phase
transition (OPT) temperatures are considered in a frame of the field theory of
the defects. The singularities of the dislocation flows, elastic deformations
and magnetization occur if the magnetic subsystem is inhomogeneous and the
dispersion of the media is not taken into account. Media dispersion causes a
regularity of these parameters and a conversion of the spin wave to the
dislocation wave.",0310762v1
2003/11/13,Noncollinear magnetism in distorted perovskite compounds,"Using results of the band structure calculations in the local-spin-density
approximation we demonstrate how the crystal distortions affect the magnetic
structure of orthorhombically distorted perovskites leading to a non-collinear
spin arrangement. Our results suggest that the non-collinearity of the spin
magnetic moments, being generally small in La$M$O$_3$ series with $M$=Cr-Fe, is
large in SrRuO$_3$.",0311297v1
2003/11/21,Trapped field in a superconducting disk magnetized with low swept-down rate of applied field,"We have proposed a systematic theoretic framework to calculate the trapped
magnetic field and temperature distributions in a superconducting disk (SD)
magnetized by a field-cooling process. Our calculations are based on the
critical state model with temperature and field-dependent critical current
density, and the heat conduction equation with account of the heat produced by
flux motion. We distinguish the normal state region from the superconducting
state region. Our calculated results are in good agreement with the recently
experimental results reported by different groups, and the deviation is well
explained.",0311499v1
2003/12/14,Theory of spin waves in diluted-magnetic-semiconductor quantum wells,"We present a theory of collective spin excitations in
diluted-magnetic-semiconductor quantum wells in which local magnetic moments
are coupled via a quasi-two-dimensional gas of electrons or holes. In the case
of a ferromagnetic state with partly spin-polarized electrons, we find that the
Goldstone collective mode has anomalous $k^4$ dispersion and that for symmetric
quantum wells odd parity modes do not disperse at all. We discuss the gap in
the collective excitation spectrum which appears when spin-orbit interactions
are included.",0312347v2
2003/12/18,Controlled normal and inverse magnetoresistance and current-driven magnetization switching in magnetic nanopillars,"Combining pairs of ferromagnetic metals with different signs of scattering
anisotropies, let us independently invert the magnetoresistance and the
direction of current-driven switching in
ferromagnetic/non-magnetic/ferromagnetic metal nanopillars. We show all four
combinations of normal and inverse behaviors, at both room temperature and
4.2K. In all cases studied, the direction of switching is set by the net
scattering anisotropy of the fixed (polarizing) ferromagnet. We provide simple
arguments for what we see.",0312475v1
2004/2/4,Ferromagnetism mediated by few electrons in a semimagnetic quantum dot,"A (II,Mn)VI diluted magnetic semiconductor quantum dot with an integer number
of electrons controlled with a gate voltage is considered. We show that a
single conduction band electron is able to induce a spontaneous collective
magnetization of the Mn spins, overcoming the short range antiferromagnetic
interactions. The carrier mediated ferromagnetism in the dot survives at
temperatures above 1 Kelvin, two orders of magnitude larger than the Curie
temperature for the same material in bulk. The magnetic behavior of the dot
depends dramatically on the parity of the number of injected electrons.",0402140v2
2004/2/16,Numerical simulations of two dimensional magnetic domain patterns,"I show that a model for the interaction of magnetic domains that includes a
short range ferromagnetic and a long range dipolar anti-ferromagnetic
interaction reproduces very well many characteristic features of
two-dimensional magnetic domain patterns. In particular bubble and stripe
phases are obtained, along with polygonal and labyrinthine morphologies. In
addition, two puzzling phenomena, namely the so called `memory effect' and the
`topological melting' observed experimentally are also qualitatively described.
Very similar phenomenology is found in the case in which the model is changed
to be represented by the Swift-Hohenberg equation driven by an external
orienting field.",0402406v2
2004/2/16,On calculation of effective galvanomagnetic characteristics of inhomogeneous metals. Exact solution for the longitudinal effective conductivity of polycrystals of metals in high magnetic fields,"In the framework of the perturbation theory an expression suitable for
calculation of the effective conductivity of 3-D inhomogeneous metals in
uniform magnetic field $H$ is derived. For polycrystals of metals with closed
Fermi surfaces in high magnetic fields the perturbation series defining the
longitudinal and the hall elements of the perturbation series can be summed
allowing us to obtain the exact expression for the leading terms of all these
elements of the effective conductivity tensor.",0402426v1
2004/2/26,"Zinc-blende CaP, CaAs and CaSb as half-metals: A new route to magnetism in calcium compounds","Existence of ferromagnetism in bulk calcium compounds is discovered
theoretically. First-principles calculations of calcium phosphide, calcium
arsenide and calcium antimonide in the zinc-blende structure have been
performed to show the half-metallic ground state in each optimized stable
structure. Magnetism comes from spin-polarization of electrons in
  $p$-orbitals of P, As or Sb and $d$-orbitals of calcium atoms. The
half-metallicity is analogous to the half-metallic zinc-blende compounds, {\it
e.g.} CrAs or CrSb, but the predicted compounds become ferromagnetic without
transition metals. In (In$_{1-x}$Ca$_x$)Sb, the magnetism remains to be stable
in a range of the doping rate ($x>0.8$).",0402641v1
2004/2/28,Resonant Spin Hall Conductance in Two-Dimensional Electron Systems with Rashba Interaction in a Perpendicular Magnetic Field,"We study transport properties of a two-dimensional electron system with
Rashba spin-orbit coupling in a perpendicular magnetic field. The spin orbit
coupling competes with Zeeman splitting to introduce additional degeneracies
between different Landau levels at certain magnetic fields. This degeneracy, if
occuring at the Fermi level, gives rise to a resonant spin Hall conductance,
whose height is divergent as 1/T and whose weight is divergent as $-\ln T$ at
low temperatures. The Hall conductance is unaffected by the Rashba coupling.",0403005v1
2004/3/1,Raman scattering on phonon-plasmon coupled modes in magnetic fields,"Raman scattering on phonon--plasmon coupled modes in high magnetic fields is
considered theoretically. The calculations of the dielectric function were
performed in the long-wave approximation for the semiclassical and
ultra-quantum magnetic fields taking into account the electron damping and
intrinsic lifetime of optical phonons. The Raman scattering has resonances at
the frequencies of coupled modes as well as at multiples of the cyclotron
frequency. The dependence of the Raman cross section on the carrier
concentration is analyzed.",0403044v1
2004/3/1,Co-occurrence of Superparamagnetism and Anomalous Hall Effect in Highly Reduced Cobalt Doped Rutile TiO2 Films,"We report a detailed magnetic and structural analysis of highly reduced Co
doped rutile TiO2 films displaying an anomalous Hall effect (AHE). The
temperature and field dependence of magnetization, and transmission electron
microscopy clearly establish the presence of nano-sized superparamagnetic
cobalt clusters of 8-10 nm size in the films at the interface. The
co-occurrence of superparamagnetism and AHE raises questions regarding the use
of the AHE as a test of the intrinsic nature of ferromagnetism in diluted
magnetic semiconductors.",0403056v1
2004/3/24,Direct evidence for ferromagnetic spin polarization in gold nanoparticles,"We report the first direct observation of ferromagnetic spin polarization of
Au nanoparticles with a mean diameter of 1.9 nm using X-ray magnetic circular
dichroism (XMCD). Owing to the element selectivity of XMCD, only the gold
magnetization is explored. Magnetization of gold atoms estimated by XMCD shows
a good agreement with the results obtained by conventional magnetometry. This
result is evidence of intrinsic spin polarization in nano-sized gold.",0403600v1
2004/4/1,Temperature dependence of spin-transfer-induced switching of nanomagnets,"We measure the temperature, magnetic-field, and current dependence for the
switching of nanomagnets by a spin-polarized current. Depending on current
bias, switching can occur between either two static magnetic states or a static
state and a current-driven precessional mode. In both cases, the switching is
thermally activated and governed by the sample temperature, not a higher
effective magnetic temperature. The activation barriers for switching between
static states depend linearly on current, with a weaker dependence for dynamic
to static switching.",0404003v1
2004/5/1,Comment on 'Pulsed field studies of the magnetization reversal in molecular nanomagnets',"In a recent paper, cond-mat/0404041, J. Vanacken et al. reported experimental
studies of crystals of Mn12-ac molecular nanomagnets in pulsed magnetic fields
with sweep rates up to 4000 T/s. Steps in the magnetization curve were
observed. The data were explained by collective dipolar relaxation. We give
here an alternative explanation that is based on thermal avalanches triggered
by defect molecules (faster relaxing species). These species are always present
in Mn12-ac molecular nanomagnets. We propose a simple method to test this
interpretation. Note that we do not question the possibility of collective
effects that are bassed on spin--spin interactions.",0405014v2
2004/5/20,Ferromagnetic and random spin ordering in diluted magnetic semiconductors,"In a diluted magnetic semiconductor system, the exchange interaction between
magnetic impurities has two independent components: a direct antiferromagnetic
interaction and a ferromagnetic interaction mediated by charge carriers.
Depending on the system parameters, the ground state of the system may be
ordered either ferromagnetically or randomly. In this paper we use percolation
theory to find the ferromagnetic transition temperature and the location of the
quantum critical point separating the ferromagnetic phase and a valence bond
glass phase.",0405467v2
2004/5/26,The steady state in noncollinear magnetic multilayers,"There are at least two different putative steady state solutions for current
across noncollinear magnetic multilayers; one has a discontinuity in the spin
current at the interface the other is continuous. We compare the resistance of
the two and find the solution with the continuous spin currents is lower. By
using the entropic principle we can state that this solution is a better
estimate of the resistance for a noncollinear magnetic",0405624v1
2004/5/26,Current induced spin flip scattering at interfaces in noncollinear magnetic multilayers,"We show that when one drives a charge current across noncollinear magnetic
layers the two electron Coulomb scattering creates a spin flip potential at
interfaces. This scattering is found when the interface potential is updated
due to the spin accumulation attendant to charge flow, and it contributes in
linear response to the current. With this scattering there is an injection of
transverse spin distributions in a layer that propagate, and that in the steady
state lead to spin currents transverse to the magnetization.",0405626v1
2004/5/27,Angular-dependence of magnetization switching for a multi-domain dot: experiment and simulation,"We have measured the in-plane angular variation of nucleation and
annihilation fields of a multi-domain magnetic single dot with a microsquid.
The dots are Fe/Mo(110) self-assembled in UHV, with sub-micron size and a
hexagonal shape. The angular variations were quantitatively reproduced by
micromagnetic simulations. Discontinuities in the variations are observed, and
shown to result from bifurcations related to the interplay of the non-uniform
magnetization state with the shape of the dot.",0405651v1
2004/6/21,Large negative magnetoresistance in thiospinel CuCrZrS4,"We report on large negative magnetoresistance observed in ferromagnetic
thiospinel compound CuCrZrS$_{4}$. Electrical resistivity increased with
decreasing temperature according to the form proportional to
$\textrm{exp}(T_{0}/T)^{1/2} $, derived from variable range hopping with strong
electron-electron interaction. Resistivity under magnetic fields was expressed
by the same form with the characteristic temperature T0 decreasing with
increasing magnetic field. Magnetoresistance ratio $\rho (T,0)/\rho(T,H)$ is
1.5 at 100 K for H=90 kOe and increases divergently with decreasing temperature
reaching 80 at 16 K. Results of magnetization measurements are also presented.
Possible mechanism of the large magnetoresistance is discussed.",0406459v1
2004/6/21,"Magnetic susceptibility, exchange interactions and spin-wave spectra in the local spin density approximation","Starting from exact expression for the dynamical spin susceptibility in the
time-dependent density functional theory a controversial issue about exchange
interaction parameters and spin-wave excitation spectra of itinerant electron
ferromagnets is reconsidered. It is shown that the original expressions for
exchange integrals based on the magnetic force theorem (J. Phys. F14 L125
(1984)) are optimal for the calculations of the magnon spectrum whereas static
response function is better described by the ``renormalized'' magnetic force
theorem by P. Bruno (Phys. Rev. Lett. 90, 087205 (2003)). This conclusion is
confirmed by the {\it ab initio} calculations for Fe and Ni.",0406488v1
2004/7/1,Magnetic tunneling junctions with the Heusler compound Co_2Cr_{0.6}Fe_{0.4}Al,"The Heusler alloy is used as an electrode of magnetic tunneling junctions.
The junctions are deposited by magnetron dc sputtering using shadow mask
techniques with AlO_{x} as a barrier and cobalt as counter electrode.
Measurements of the magnetoresistive differential conductivity in a temperature
range between 4K and 300K are shown. An analysis of the barrier properties
applying the Simmons model to the bias dependent junction conductivity is
performed. VSM measurements were carried out to examine the magnetic properties
of the samples.",0407034v1
2004/7/27,Selective optical manipulation of the spin state of a single magnetic impurity in a semiconductor quantum dot,"We consider the optical properties of a single magnetic impurity in a
self-assembled quantum dot. We show that using the resonant pumping one can
address and manipulate selectively individual spin states of a magnetic
impurity. The mechanisms of resonant optical polarization of a single impurity
in a quantum dot involve anisotropic exchange interactions and are different to
those in diluted semiconductors. A Mn impurity can act as qubit. The limiting
factors for the qubit manipulation are the electron-hole exchange interaction
and finite temperature.",0407705v1
2004/7/27,Dynamical Mean Field Theory of Temperature and Field Dependent Band Shifts in Magnetically Coupled Semimetals: Applocation to EuB6,"A model for semimetals such as $EuB_6$, in which band overlaps are controlled
by magnetic order, is presented and is solved in the dynamical mean field
approximation. First order phase boundaries are computed by evaluating free
energies of different states. The phase diagram is determined. A specific and
physically reasonable choice of parameters is found to approximately reproduce
the available data on $EuB_6$. For this material, predictions are made for the
location of a metamagnetic transition and its associated endpoint, and a change
in the order of the magnetic transition.",0407706v1
2004/7/28,Large quantum nonlinear dynamic susceptibility of single-molecule magnets,"The nonlinear dynamical response of Mn$_{12}$ single-molecule magnets is
experimentally found to be very large, quite insensitive to the spin-lattice
coupling constant, and displaying peaks reversed with respect to classical
superparamagnets. It is shown that these features are caused by the strong
field dependence of the relaxation rate due to the detuning of energy levels
between which tunneling takes place. The nonlinear susceptibility technique,
previously overlooked, is thus proposed as a privileged probe to ascertain the
occurrence of quantum effects in mesoscopic magnetic systems.",0407738v1
2004/8/9,Spin Diffusion and Relaxation in a Nonuniform Magnetic Field,"We consider a quasiclassical model that allows us to simulate the process of
spin diffusion and relaxation in the presence of a highly nonuniform magnetic
field. The energy of the slow relaxing spins flows to the fast relaxing spins
due to the dipole-dipole interaction between the spins. The magnetic field
gradient suppresses spin diffusion and increases the overall relaxation time in
the system. The results of our numerical simulations are in a good agreement
with the available experimental data.",0408192v2
2004/8/11,Free energies in the presence of electric and magnetic fields,"We discuss different free energies for materials in static electric and
magnetic fields. We explain what the corresponding Hamiltonians are, and
describe which choice gives rise to which result for the free energy change,
dF, in the thermodynamic identity. We also discuss which Hamiltonian is the
most appropriate for calculations using statistical mechanics, as well as the
relationship between the various free energies and the ""Landau function"", which
has to be minimized to determine the equilibrium polarization or magnetization,
and is central to Landau's theory of second order phase transitions.",0408259v1
2004/9/10,Airy-function electron localization in the oxide superlattices,"Oxide superlattices and microstructures hold the promise for creating a new
class of devices with unprecedented functionalities. Density-functional studies
of the recently fabricated superlattices of lattice-matched perovskite
titanates (SrTiO3)n/(LaTiO3)m reveal a classic wedge-shaped potential
originating from the Coulomb potential of a charged sheet of La atoms. The
potential in turn confines the electrons in the vicinity of the sheet, leading
to an Airy-function localization of the electron states. Magnetism is
suppressed for structures with a single LaTiO3 monolayer, while the bulk
antiferromagnetism is recovered in the structures with a thicker LaTiO3, with a
narrow transition region separating the magnetic LaTiO3 and the non-magnetic
SrTiO3.",0409281v1
2004/9/24,Minimal field requirement in precessional magnetization switching,"We investigate the minimal field strength in precessional magnetization
switching using the Landau-Lifshitz-Gilbert equation in under-critically damped
systems. It is shown that precessional switching occurs when localized
trajectories in phase space become unlocalized upon application of field
pulses. By studying the evolution of the phase space, we obtain the analytical
expression of the critical switching field in the limit of small damping for a
magnetic object with biaxial anisotropy. We also calculate the switching times
for the zero damping situation. We show that applying field along the medium
axis is good for both small field and fast switching times.",0409671v1
2004/10/1,"Mixed magnetic phases in (Ga,Mn)As epilayers","Two different ferromagnetic-paramagnetic transitions are detected in
(Ga,Mn)As/GaAs(001) epilayers from ac susceptibility measurements: transition
at a higher temperature results from (Ga,Mn)As cluster phases with [110]
uniaxial anisotropy and that at a lower temperature is associated with a
ferromagnetic (Ga,Mn)As matrix with <100> cubic anisotropy. A change in the
magnetic easy axis from [100] to [110] with increasing temperature can be
explained by the reduced contribution of <100> cubic anisotropy to the magnetic
properties above the transition temperature of the (Ga,Mn)As matrix.",0410022v1
2004/10/4,Effects of Antiferromagnetic Spin Rotation on Anisotropy of Ferromagnetic/Antiferromagnetic Bilayers,"In epitaxial (111) oriented Ni$_{80}$Fe$_{20}$/Fe$_{50}$Mn$_{50}$ bilayers,
we separate two distinct behaviors: unidirectional anisotropy (exchange bias)
in thick Fe$_{50}$Mn$_{50}$, and enhanced coercivity in thin
Fe$_{50}$Mn$_{50}$. By measuring the magnetization response to a rotating
magnetic field, we quantitatively determine the relevant anisotropies, and
demonstrate that the enhanced coercivity is related to the rotatable magnetic
anisotropy of Fe$_{50}$Mn$_{50}$. We also demonstrate the consequences of the
anisotropy changes with temperature.",0410091v1
2004/10/12,Evidence for magnetic clusters in BaCoO$_3$,"Magnetic properties of the transition metal oxide BaCoO$_3$ are analyzed on
the basis of the experimental and theoretical literature available via ab inito
calculations. These can be explained by assuming the material to be formed by
noninteracting ferromagnetic clusters of about 1.2 nm in diameter separated by
about 3 diameters. Above about 50 K, the so-called blocking temperature,
superparamagnetic behavior of the magnetic clusters occurs and, above 250 K,
paramagnetism sets in.",0410303v1
2004/10/20,Spin-Transfer Torque and Electron-Magnon Scattering,"According to the spin-torque model, current-driven magnetic dynamics in
ferromagnetic multilayers is determined by the transfer of electron spin
perpendicular to the layers' magnetizations. By separating the largest
contributions to the magnetic dynamics, we demonstrate that the dominant effect
of spin-torque is rather due to the electron spin parallel to the field. We
show that this effect can be equivalently described as stimulated
current-driven excitation of spin-waves, and discuss four specifically
quantum-mechanical aspects of spin-transfer, not described by the spin-torque.",0410520v1
2004/11/18,Quantum Limit in a Parallel Magnetic Field in Layered Conductors,"We show that electron wave functions in a quasi-two-dimensional conductor in
a parallel magnetic field are always localized on conducting layers. Wave
functions and electron spectrum in a quantum limit, where the ""sizes"" of
quasi-classical electron orbits are of the order of nano-scale distances
between the layers, are determined. AC infrared measurements to investigate
Fermi surfaces and to test Fermi liquid theory in Q2D organic and high-Tc
materials in high magnetic fields, H = 10-45 T, are suggested.",0411496v1
2004/11/23,Coexistence of Antiferromagnetism and Triplet Superconductivity,"The authors discuss the possibility of coexistence of antiferromagnetism and
triplet superconductivity as a particular example of a broad class of systems
where the interplay of magnetism and superconductivity is important. This paper
focuses on the case of quasi-one-dimensional metals, where it is known
experimentally that antiferromagnetism is in close proximity to triplet
superconductivity in the temperature versus pressure phase diagram. Over a
narrow range of pressures, the authors propose an intermediate non-uniform
phase consisting of alternating insulating antiferromagnetic and triplet
superonducting stripes.",0411582v1
2005/3/8,Quantum phase interference and spin parity in Mn12 single-molecule magnets,"Magnetization measurements of Mn12 molecular nanomagnets with spin ground
states of S = 10 and S = 19/2 showresonance tunneling at avoided energy level
crossings. The observed oscillations of the tunnel probability as a function of
the magnetic field applied along the hard anisotropy axis are due to
topological quantum phase interference of two tunnel paths of opposite
windings. Spin-parity dependent tunneling is established by comparing the
quantum phase interference of integer and half-integer spin systems.",0503193v1
2005/3/29,Dipole-exchange spin waves in Fibonacci magnetic multilayers,"A microscopic model is employed to calculate the spectrum of spin waves in
quasiperiodic magnetic multilayers in the dipole-exchange regime. Results are
presented for structures in which thin ferromagnetic films are separated by
non-magnetic spacers following a Fibonacci sequence and extend previous
magnetostatic calculations. The results show the splitting of the frequency
bands and the mode mixing caused by the dipolar interaction between the films
as a function of spacer thickness, as well as the fractal aspect of the
spectrum induced by the non-periodic aspect of the structure.",0503683v1
2005/4/8,Temperature dependent asymmetry of the nonlocal spin-injection resistance: evidence for spin non-conserving interface scattering,"We report nonlocal spin injection and detection experiments on mesoscopic
Co-Al2O3-Cu spin valves. We have observed a temperature dependent asymmetry in
the nonlocal resistance between parallel and antiparallel configurations of the
magnetic injector and detector. This strongly supports the existence of a
nonequilibrium resistance that depends on the relative orientation of the
detector magnetization and the nonequilibrium magnetization in the normal metal
providing evidence for increasing interface spin scattering with temperature.",0504201v2
2005/5/11,"Annealing-induced changes of the magnetic anisotropy of (Ga,Mn)As epilayers","The dependence of the magnetic anisotropy of As-capped (Ga,Mn)As epilayers on
the annealing parameters - temperature and time - has been investigated. A
uniaxial magnetic anisotropy is evidenced, whose orientation with respect to
the crystallographic axes changes upon annealing from [-110] for the as-grown
samples to [110] for the annealed samples. Both cubic an uniaxial anisotropies
are tightly linked to the concentration of charge carriers, the magnitude of
which is controlled by the annealing process.",0505278v1
2005/5/20,A rotating cavity for high-field angle-dependent microwave spectroscopy of low-dimensional conductors and magnets,"The cavity perturbation technique is an extremely powerful method for
measuring the electrodynamic response of a material in the millimeter- and
sub-millimeter spectral range (10 GHz to 1 THz), particularly in the case of
high-field/frequency magnetic resonance spectroscopy. However, the application
of such techniques within the limited space of a high-field magnet presents
significant technical challenges. We describe a 7.62 mm x 7.62 mm (diameter x
length) rotating cylindrical cavity which overcomes these problems.",0505513v1
2005/6/1,"Crystal field states in conducting magnetic materials: NdAl2, UPd2Al3 and YbRh2Si2","The existence of CEF states and the magnetism in conducting compounds NdAl2,
UPd2Al3 and YbRh2Si2 is discussed. We point out that in metallic compounds
localized crystal-field states coexist with conduction electrons. These
compounds are physical realization of an anisotropic spin liquid, which in case
of the atomic-like configuration with an odd number of f electrons, is unstable
with respect to spin fluctuations for T->0K. YbRh2Si2 is discussed as a
compound with the Kramers doublet ground state with a very low magnetic
ordering temperature being a reason for the quantum critical point phenomena at
low T.",0506021v1
2005/6/13,Magnetism via superconductivity in SF proximity structures,"We consider the proximity effects in hybrid superconductor (S) - ferromagnet
(F) structures drawing attention to the induced ferromagnetism of the S metal.
The analysis is based on a quasiclassical theory of proximity effect for metals
in the dirty limit conditions. It is shown that, below the superconducting
critical temperature, ferromagnetic correlations extend a distance of order of
the superconducting coherence length \xi_{S} into the superconductor, being
dependent on the S/F interface parameters. We argue that the properties of
mesoscopic SF hybrids may drastically depend upon the magnetic proximity
effect, and recent experiments lend support to the model of SF structures where
the superconducting and magnetic parameters are tightly coupled.",0506277v1
2005/7/7,"Reorientation Transition in Single-Domain (Ga,Mn)As","We demonstrate that the interplay of in-plane biaxial and uniaxial anisotropy
fields in (Ga,Mn)As results in a magnetization reorientation transition and an
anisotropic AC susceptibility which is fully consistent with a simple single
domain model. The uniaxial and biaxial anisotropy constants vary respectively
as the square and fourth power of the spontaneous magnetization across the
whole temperature range up to T_C. The weakening of the anisotropy at the
transition may be of technological importance for applications involving
thermally-assisted magnetization switching.",0507187v1
2005/7/26,Butterfly hysteresis curve is a signature of adiabatic Landau-Zener transition,"We stress that the so-called butterfly hysteresis curves observed in
dynamical magnetization measurements on systems of low-spin magnetic molecules
such as V-15 and V-6 are a signature of adiabatic Landau-Zener transitions
rather than that of a phonon bottleneck. We investigate the magnetization
dynamics analytically with the help of a simple relaxation theory in the basis
of the adabatic energy levels of the spin 1/2, to a qualitative accordance with
experimental observations. In particular, reversible behavior is found near
zero field, the corresponding susceptibility being bounded by the equilibrium
and adiabatic susceptibilities from below and above, respectively.",0507618v1
2005/8/18,Field- and pressure-induced phases in Sr$_{4}$Ru$_{3}$O$_{10}$: A spectroscopic investigation,"We have investigated the magnetic-field- and pressure-induced structural and
magnetic phases of the triple-layer ruthenate - Sr$_{4}$Ru$_{3}$O$_{10}$.
Magnetic-field-induced changes in the phonon spectra reveal dramatic
spin-reorientation transitions and strong magneto-elastic coupling in this
material. Additionally, pressure-dependent Raman measurements at different
temperatures reveal an anomalous negative Gruneisen-parameter associated with
the B$_{1g}$ mode ($\sim$ 380 cm$^{-1}$) at low temperatures (T $<$ 75K), which
can be explained consistently with the field dependent Raman data.",0508438v2
2005/9/15,Spectroscopy of phonons and spin torques in magnetic point contacts,"Phonon spectroscopy is used to investigate the mechanism of current-induced
spin torques in nonmagnetic/ferromagnetic (N/F) point contacts. Magnetization
excitations observed in the magneto-conductance of the point contacts are
pronounced for diffusive and thermal contacts, where the electrons experience
significant scattering in the contact region. We find no magnetic excitations
in highly ballistic contacts. Our results show that impurity scattering at the
N/F interface is the origin of the new single-interface spin torque effect.",0509396v1
2005/9/15,Reduction of the ordered magnetic moment in YMnO3 with hydrostatic pressure,"YMnO3 exhibits a ferroelectric transition at high temperature (~ 900 K) and
magnetic ordering at T_N ~ 70 K where the dielectric constant shows an anomaly
indicative of the magneto-dielectric effect. Here we report powder neutron
diffraction experiments in this compound that show that the magnetic moment at
saturation is reduced by application of hydrostatic pressure. Our results yield
further insight about the nature of the spin-lattice interaction in ferroic
materials.",0509413v1
2005/9/22,Current-induced motion of a domain wall in magnetic nanowires,"The dynamics of current-induced motion of a magnetic domain wall in a
quasi-one-dimensional ferromagnet with both easy-axis and easy-plane
anisotropy, is studied. We pay a special attention to the case of a sharp
domain wall, and calculate the spin torque created by the electric current. The
torque has two components, one of which is acting as a driving force for the
motion of the domain wall while the other distorts its shape, forcing thus the
magnetic moments to deviate from the easy plane.",0509574v1
2005/10/11,Negative Giant Longitudinal Magnetoresistance in NiMnSb/InSb: An interface effect,"We report on the electrical and magneto-transport properties of the contact
formed between polycrystalline NiMnSb thin films grown using pulsed laser
deposition (PLD) and n-type degenerate InSb (100) substrates. A negative giant
magnetoresistance (GMR) effect is observed when the external magnetic field is
parallel to the surface of the film and to the current direction. We attribute
the observed phenomenon to magnetic precipitates formed during the magnetic
film deposition and confined to a narrow layer at the interface. The effect of
these precipitates on the magnetoresistance depends on the thermal processing
of the system.",0510284v1
2005/10/21,Magnetic Vortex Core Dynamics in a Ferromagnetic Dot,"We report direct imaging by means of x-ray photoemission electron microscopy
of the dynamics of magnetic vortices confined in micron-size circular Permalloy
dots that are 30 nm thick. The vortex core positions oscillate on a 10-ns
timescale in a self-induced magnetostatic potential well after the in-plane
magnetic field is turned off. The measured oscillation frequencies as a
function of the aspect ratio (thickness/radius) of the dots are in agreement
with theoretical calculations presented for the same geometry.",0510595v1
2005/11/7,Exact-Exchange Spin-Current Density-Functional Theory,"A spin-current density-functional theory (SCDFT) is introduced, which takes
into account currents of the spin-density and thus currents of the
magnetization in addition to the electron density, the non-collinear
spin-density, and the density current, which are considered in standard current
spin-density-functional theory. An exact exchange Kohn-Sham formalism based on
SCDFT is presented, which represents a general framework for the treatment of
magnetic and spin properties. As illustration an oxygen atom in a magnetic
field is treated with the new approach.",0511156v2
2005/11/22,Spatial Imaging and Mechanical Control of Spin Coherence in Strained GaAs Epilayers,"The effect of uniaxial tensile strain on spin coherence in n-type GaAs
epilayers is probed using time-resolved Kerr rotation, photoluminescence, and
optically-detected nuclear magnetic resonance spectroscopies. The bandgap,
electron spin lifetime, electron g-factor, and nuclear quadrupole splitting are
simultaneously imaged over millimeter scale areas of the epilayers for
continuously varying values of strain. All-optical nuclear magnetic resonance
techniques allow access to the strain induced nuclear quadrupolar resonance
splitting in field regimes not easily addressable using conventional
optically-detected nuclear magnetic resonance.",0511562v1
2005/12/19,Ti substituted La(0.67)Ca(0.33)MnO(3) ortho-perovskites: Dominant role of local structure on the electrical transport and magnetic properties,"We discuss the effects of local structure on the electrical transport and
magnetic properties of La(0.67)Ca(0.33)Mn(1-x)Ti(x)O(3) system.Based on the
intercomparison of the structure, transport and magnetic properties of the Mn
site substituted La(0.67)Ca(0.33)MnO(3) with isovalent diamagnetic and
paramagnetic ions, we argue that local structural effects have a decisive role
to play, compared to the local spin coupling effects, in the
ferromagnetic-metallic ground state of the CMR manganites",0512436v1
2005/12/28,Mn and Fe Impurities in MgB_{2},"Based on first principles calculations, we show that $Mn$ impurities are
magnetic in $MgB_{2}$ due to exchange-splitting of $d_{3z^2-1}$ band and they
substantially modify $B$ $p_{\sigma}$ and $p_{\pi}$ bands through
hybridization. Thus, $Mn$ impurities could act as strong magnetic scattering
centers leading to pair-breaking effects in $MgB_{2}$. In contrast, we find
$Fe$ impurities in $MgB_{2}$ to be nearly non-magnetic.",0512675v3
2006/1/15,Self-Induced Quasistationary Magnetic Fields,"The interaction of electromagnetic radiation with temporally dispersive
magnetic solids of small dimensions may show very special resonant behaviors.
The internal fields of such samples are characterized by
magnetostatic-potential scalar wave functions. The oscillating modes have the
energy orthogonality properties and unusual pseudo-electric (gauge) fields.
Because of a phase factor, that makes the states single valued, a persistent
magnetic current exists. This leads to appearance of an eigen-electric moment
of a small disk sample. One of the intriguing features of the mode fields is
dynamical symmetry breaking.",0601319v1
2006/1/16,Nature of the intensification of a cyclotron resonance in potassium in a normal magnetic field,"The cyclotron-resonance peak which has been observed [G. A. Baraff et al.,
Phys. Rev. Lett. 22, 590 (1969) ] in potassium in a magnetic field directed
perpendicular to the surface may be due to an effect of zero-curvature points
of the Fermi surface on the cyclotron orbit of effective electrons.",0601354v1
2006/1/17,Microwave Response and Spin Waves in Superconducting Ferromagnets,"Excitation of spin waves is considered in a superconducting ferromagnetic
slab with the equilibrium magnetization both perpendicular and parallel to the
surface. The surface impedance is calculated and its behavior near propagation
thresholds is analyzed. Influence of non-zero magnetic induction at the surface
is considered in various cases. The results provide a basis for investigation
of materials with coexisting superconductivity and magnetism by microwave
response measurements.",0601386v2
2006/1/19,A significant influence of the substrate on the magnetic anisotropy of monatomic nanowires,"The magnetic anisotropy energy of Fe and Co monatomic nanowires both
free-standing and at the step edge of a Pt surface is investigated within the
framework of the density-functional theory and local-spin-density (LSDA)
approximation. Various types of the analysis of the calculated data reveal that
the spin-orbit interaction of the Pt atoms and the hybridization between the
electronic states have an important impact on the direction of the easy axis
and on the magnitude of the magnetic anisotropy, both by a direct contribution
localized at the Pt atoms and by an indirect contribution due to the
modification of the Co-localized part via hybridization effects.",0601445v1
2006/1/26,Tunable conductance of magnetic nanowires with structured domain walls,"We show that in a magnetic nanowire with double magnetic domain walls,
quantum interference results in spin-split quasistationary states localized
mainly between the domain walls. Spin-flip-assisted transmission through the
domain structure increases strongly when these size-quantized states are tuned
on resonance with the Fermi energy, e.g. upon varying the distance between the
domain walls which results in resonance-type peaks of the wire conductance.
This novel phenomena is shown to be utilizable to manipulate the spin density
in the domain vicinity. The domain walls parameters are readily controllable
and the predicted effect is hence exploitable in spintronic devices.",0601620v1
2006/2/4,Spin-transfer-driven ferromagnetic resonance of individual nanomagnets,"We demonstrate a technique that enables ferromagnetic resonance (FMR)
measurements of the normal modes for magnetic excitations in individual
nanoscale ferromagnets, smaller in volume by a factor of 1000 than can be
probed by other methods. The measured peak shapes indicate two regimes of
response: simple FMR and phase locking. Studies of the resonance frequencies,
amplitudes, and linewidths as a function of microwave power, DC current, and
magnetic field provide detailed new information about the exchange, damping,
and spin-transfer torques that govern the dynamics in magnetic nanostructures.",0602105v1
2006/2/6,Magnetic ordering in Gd2Sn2O7: the archetypal Heisenberg pyrochlore antiferromagnet,"Low-temperature powder neutron diffraction measurements are performed in the
ordered magnetic state of the pyrochlore antiferromagnet Gd2Sn2O7. Symmetry
analysis of the diffraction data indicates that this compound has the ground
state predicted theoretically for a Heisenberg pyrochlore antiferromagnet with
dipolar interactions. The difference in magnetic structures of Gd2Sn2O7 and of
nominally analogous Gd2Ti2O7 is found to be determined by a specific type of
third-neighbor superexchange interaction on the pyrochlore lattice between
spins across empty hexagons.",0602138v1
2006/2/27,Asymmetric Heat Flow in Mesoscopic Magnetic System,"The characteristics of heat flow in a coupled magnetic system are studied.
The coupled system is composed of a gapped chain and a gapless chain. The
system size is assumed to be quite small so that the mean free path is
comparable to it. When the parameter set of the temperatures of reservoirs is
exchanged, the characteristics of heat flow are studied with the Keldysh Green
function technique. The asymmetry of current is found in the presence of a
local equilibrium process at the contact between the magnetic systems. The
present setup is realistic and such an effect will be observed in real
experiments. We also discuss the simple phenomenological explanation to obtain
the asymmetry.",0602621v1
2006/3/1,Orbital ordering and enhanced magnetic frustration of strained BiMnO3 thin films,"Epitaxial thin films of multiferroic perovskite BiMnO3 were synthesized on
SrTiO3 substrates, and orbital ordering and magnetic properties of the thin
films were investigated. The ordering of the Mn^{3+} e_g orbitals at a wave
vector (1/4 1/4 1/4) was detected by Mn K-edge resonant x-ray scattering. This
peculiar orbital order inherently contains magnetic frustration. While bulk
BiMnO3 is known to exhibit simple ferromagnetism, the frustration enhanced by
in-plane compressive strains in the films brings about cluster-glass-like
properties.",0603020v1
2006/3/1,"Structural Anomalies at the Magnetic and Ferroelectric Transitions in $RMn_2O_5$ (R=Tb, Dy, Ho)","Strong anomalies of the thermal expansion coefficients at the magnetic and
ferroelectric transitions have been detected in multiferroic $RMn_2O_5$. Their
correlation with anomalies of the specific heat and the dielectric constant is
discussed. The results provide evidence for the magnetic origin of the
ferroelectricity mediated by strong spin-lattice coupling in the compounds.
Neutron scattering data for $HoMn_2O_5$ indicate a spin reorientation at the
two low-temperature phase transitions.",0603032v1
2006/3/7,Theory of carrier mediated ferromagnetism in dilute magnetic oxides,"We analyze the origin of ferromagnetism as a result of carrier mediation in
diluted magnetic oxide semiconductors in the light of the experimental evidence
reported in the literature. We propose that a combination of percolation of
magnetic polarons at lower temperature and Ruderman-Kittel-Kasuya-Yosida
ferromagnetism at higher temperature may be the reason for the very high
critical temperatures measured (up to ~700 K).",0603182v2
2006/4/5,Valley Polarization in Si(100) at Zero Magnetic Field,"The valley splitting, which lifts the degeneracy of the lowest two valley
states in a SiO$_2$/(100)Si/SiO$_2$ quantum well is examined through transport
measurements. We demonstrate that the valley splitting can be observed directly
as a step in the conductance defining a boundary between valley-unpolarized and
polarized regions. This persists to well above liquid helium temperature and
shows no dependence on magnetic field, indicating that single-particle valley
splitting and valley-polarization exist in (100) silicon even at zero magnetic
field.",0604118v2
2006/4/5,Anisotropy of Magnetization Reversal and Magnetoresistance in Square Arrays of Permalloy Nano-Rings,"Magnetization reversal mechanisms and impact of magnetization direction are
studied in square arrays of interconnected circular permalloy nanorings using
MOKE, local imaging, numerical simulations and transport techniques.",0604132v1
2006/5/12,Large domain wall resistance in self-organised manganite film,"The electrical resistance of magnetic domain walls in ferromagnetic metallic
manganites can be enhanced to 10-12 Ohm.m2 by patterning nanoconstrictions [J.
Appl. Phys. 89, 6955 (2001)]. We show equally large enhancements in a phase
separated La0.60Ca0.40MnO3 manganite film without recourse to nanopatterning.
The domain walls were measured in the current-perpendicular-to-the-plane (CPP)
geometry between ferromagnetic metallic La0.70Ca0.30MnO3 electrodes patterned
like magnetic tunnel junctions.",0605341v2
2006/5/24,CVD of CrO2 Thin Films: Influence of the Deposition Parameters on their Structural and Magnetic Properties,"This work reports on the synthesis of CrO2 thin films by atmospheric pressure
CVD using chromium trioxide (CrO3) and oxygen. Highly oriented (100) CrO2 films
containing highly oriented (0001) Cr2O3 were grown onto Al2O3(0001) substrates.
Films display a sharp magnetic transition at 375 K and a saturation
magnetization of 1.92 Bohr magnetons per f.u., close to the bulk value of 2
Bohr magnetons per f.u. for the CrO2.
  Keywords: Chromium dioxide (CrO2), Atmospheric pressure CVD, Spintronics.",0605600v1
2006/5/29,Extraordinary magnetooptical effects and transmission through the metal-dielectric plasmonic systems,"We report on significant enhancement of the magnetooptical effects in
gyrotropic systems of a metallic film perforated by subwavelength hole arrays
and a uniform dielectric film magnetized perpendicular to its plane.
Calculations, based on a rigorous coupled-wave analysis, demonstrate the
Faraday and Kerr effect spectra having several resonance peaks in the near
infrared range, some of them coinciding with transmittance peaks. Qualitative
analysis revealed that magnetic polaritons being coupled magnetic-film
waveguiding modes with surface plasmons play a crucial role in the observed
effect.",0605702v1
2006/5/31,"Spin injection from perpendicular magnetized ferromagnetic $δ$-MnGa into (Al,Ga)As heterostructures","Electrical spin injection from ferromagnetic $\delta$-MnGa into an (Al,Ga)As
p-i-n light emitting diode (LED) is demonstrated. The $\delta$-MnGa layers show
strong perpendicular magnetocrystalline anisotropy, enabling detection of spin
injection at remanence without an applied magnetic field. The bias and
temperature dependence of the spin injection are found to be qualitatively
similar to Fe-based spin LED devices. A Hanle effect is observed and
demonstrates complete depolarization of spins in the semiconductor in a
transverse magnetic field.",0606013v1
2006/6/2,Electronic structure of Diluted Magnetic Semiconductors $Ga_{1-x}Mn_{x}N$ and $Ga_{1-x}Cr_{x}N$,"We have undertaken a study of diluted magnetic semiconductors
$Ga_{1-x}Mn_{x}N$ and $Ga_{1-x}Cr_{x}N$ with $x=0.0625, 0.125$, using the all
electron linearized augmented plane wave method (LAPW) for different
configurations of Mn as well as Cr. We study four possible configurations of
the impurity in the wurtzite GaN structure to predict energetically most
favorable structure within the 32 atom supercell and conclude that the
near-neighbor configuration has the lowest energy. We have also analyzed the
ferro-magnetic as well as anti-ferromagnetic configurations of the impurity
atoms. The density of states as well as bandstructure indicate half metallic
state for all the systems. $T_c$ has also been estimated for the above systems.",0606061v1
2006/6/21,Quantum Dynamics of Spin Wave Propagation Through Domain Walls,"Through numerical solution of the time-dependent Schrodinger equation, we
demonstrate that magnetic chains with uniaxial anisotropy support stable
structures, separating ferromagnetic domains of opposite magnetization. These
structures, domain walls in a quantum system, are shown to remain stable if
they interact with a spin wave. We find that a domain wall transmits the
longitudinal component of the spin excitations only. Our results suggests that
continuous, classical spin models described by LLG equation cannot be used to
describe spin wave-domain wall interaction in microscopic magnetic systems.",0606549v1
2006/6/25,Quantum chaos and fluctuations in isolated nuclear spin systems,"Using numerical simulations we investigate dynamical quantum chaos in
isolated nuclear spin systems. We determine the structure of quantum states,
investigate the validity of the Curie law for magnetic susceptibility and find
the spectrum of magnetic noise. The spectrum is the same for positive and
negative temperatures. The study is motivated by recent interest in
condensed-matter experiments for searches of fundamental parity- and
time-reversal-invariance violations. In these experiments nuclear spins are
cooled down to microkelvin temperatures and are completely decoupled from their
surroundings. A limitation on statistical sensitivity of the experiments arises
from the magnetic noise.",0606635v1
2006/6/27,Magnetic Susceptibility of the Double-Exchange Model in the RKKY Limit,"The magnetic susceptibility and Edwards-Anderson order parameter q of the
spin-glass-like (SGL) phase of the double-exchange model are evaluated in the
weak-coupling or RKKY limit. Dynamical mean-field theory is used to show that
q=M(T/Tsg)^2, where M is the classical Brillouin function and Tsg is the SGL
transition temperature. The correlation length of the SGL phase is determined
by a correlation parameter Q that maximizes Tsg and minimizes the free energy.
The magnetic susceptibility has a cusp at Tsg and reaches a nonzero value as T
goes to zero.",0606699v1
2006/6/29,Optical Aharonov-Bohm effect in stacked type-II quantum dots,"Excitons in vertically stacked type-II quantum dots experience the
topological magnetic phase and demonstrate the Aharonov-Bohm oscillations in
the emission intensity. Photoluminescence of vertically stacked ZnTe/ZnSe
quantum dots is measured in magnetic fields up to 31 T. The Aharonov-Bohm
oscillations are found in the magnetic-field dependence of emission intensity.
The positions of the peaks of the emission intensity are in a good agreement
with numerical simulations of excitons in stacked quantum dots.",0606752v1
2006/7/3,Orbital contribution to the magnetic properties of nanowires: Is the orbital polarization ansatz justified?,"We show that considerable orbital magnetic moments and magneto-crystalline
anisotropy energies are obtained for a Fe monatomic wire described in a
tight-binding method with intra-atomic electronic interactions treated in a
full Hartree Fock (HF) decoupling scheme. Even-though the use of the orbital
polarization ansatz with simplified Hamiltonians leads to fairly good results
when the spin magnetization is saturated this is not the case of unsaturated
systems. We conclude that the full HF scheme is necessary to investigate low
dimensional systems.",0607047v2
2006/7/4,Dynamics of Pinned Magnetic Vortices,"We observe the dynamics of a single magnetic vortex in the presence of a
random array of pinning sites. At low excitation amplitudes, the vortex core
gyrates about its equilibrium position with a frequency that is characteristic
of a single pinning site. At high amplitudes, the frequency of gyration is
determined by the magnetostatic energy of the entire vortex, which is confined
in a micron-scale disk. We observe a sharp transition between these two
amplitude regimes that is due to depinning of the vortex core from a local
defect. The distribution of pinning sites is determined by mapping fluctuations
in the frequency as the vortex core is displaced by a static in-plane magnetic
field.",0607095v1
2006/7/7,Softening of Spin-Wave Stiffness near the Ferromagnetic Phase Transition in Diluted Magnetic Semiconductors,"Employing the self-consistent Green's function approach, we studied the
temperature dependence of the spin-wave stiffness in diluted magnetic
semiconductors. Note that the Green's function approach includes the spatial
and temperature fluctuations simultaneously which was not possible within
conventional Weiss mean-field theory. It is rather interesting that we found
the stiffness becomes dramatically softened as the critical temperature is
approached, which seems to explain the mysterious sharp drop of magnetization
curves in samples within diffusive regime.",0607201v1
2006/7/19,Direct evidence of random field effect on magnetic ordering of La_(0.5)Gd_(0.2)Sr_(0.3)MnO_(3) manganite system,"We report direct experimental evidence of the effect of quenched random field
on magnetic ordering of La_(0.5)Gd_(0.2)Sr_(0.3)MnO_(3) manganites system. We
demonstrate magnetic measurements providing serious evidence to support that
quenched random field of Gd divides the system in finite size clusters which
undergo cluster-glass like freezing. The size or concentration of these
clusters is found to be closely related to the effect of random field, which in
turn is a function of applied field.",0607486v1
2006/8/1,Ferroelectricity in the Magnetic E-Phase of Orthorhombic Perovskites,"We show that the symmetry of the spin zigzag chain E phase of the
orthorhombic perovskite manganites and nickelates allows for the existence of a
finite ferroelectric polarization. The proposed microscopic mechanism is
independent of spin-orbit coupling. We predict that the polarization induced by
the E-type magnetic order can potentially be enhanced by up to two orders of
magnitude with respect to that in the spiral magnetic phases of TbMnO3 and
similar multiferroic compounds.",0608025v2
2006/8/8,Ferroelectricity in perovskite $HoMnO_3$ and $YMnO_3$,"Ferroelectricity is observed in orthorhombic $HoMnO_3$ and $YMnO_3$ at the
magnetic lock-in transitions into an E-type structure or an incommensurate
phase with a temperature independent wave vector, respectively. In $HoMnO_3$
the ferroelectric polarization strongly depends on the external magnetic field
indicating the involvement of the rare earth moment order in this compound. The
results are discussed within the framework of recent theoretical models, in
particular the double exchange driven polar displacements predicted for E-type
magnetic structures.",0608195v2
2006/8/10,Spin Dynamics of a Magnetic Antivortex,"We report on a study of the dynamics of a magnetic antivortex in a submicron,
asteroid shaped, permalloy ferromagnet using micromagnetic simulations. As with
vortex states in disk and square geometries, a gyrotropic mode was found in
which a shifted antivortex core orbits about the center of the asteroid. Pulsed
magnetic fields were used to generate azimuthal or radial spin wave modes,
depending on the field orientation. The degeneracy of low frequency azimuthal
mode frequencies is lifted by gyrotropic motion of the antivortex core, and
restored by inserting a hole in the center of the particle to suppress this
motion. We briefly compare the dynamics of the vortex state of the asteroid to
the antivortex. The size dependence of the antivortex modes is reported.",0608245v1
2006/8/22,Clustering induced suppression of ferromagnetism in diluted magnets,"Ferromagnetism in diluted magnets in the compensated regime p << x is shown
to be suppressed by the formation of impurity spin clusters. The majority bulk
spin couplings are shown to be considerably weakened by the preferential
accumulation of holes in spin clusters, resulting in low-energy magnon
softening and enhanced low-temperature decay of magnetic order. A locally
self-consistent magnon renormalization analysis of spin dynamics shows that
although strong intra-cluster correlations tend to prolong global order, T_c is
still reduced compared to the ordered case.",0608474v2
2006/8/25,Large Nonlinear Kerr Angle in non-Centrosymmetric Fe/AlGaAs (001)Heterostructure,"A large nonlinear magneto-optical effect is observed in a non-centrosymmetric
Fe/AlGaAs (001) heterostructure. This effect is a direct consequence of
interference between second-harmonic optical waves of magnetic and
crystallographic origin, generated at ferromagnetic Fe interface and bulk
AlGaAs, respectively. The longitudinal nonlinear Kerr rotation is measured to
be 1.6 degrees along the [1-10] hard axis, about two orders of magnitude
stronger than the linear equivalent. The rotational second-harmonic signal
shows large magnetic contrast along all the in-plane directions, demonstrating
a high sensitivity to the magnetization of an anisotropic interface in the
longitudinal geometry.",0608572v1
2006/8/28,Stripeless incommensurate magnetism in a doped strongly correlated oxide,"We studied the nano-scale structure of the short-range incommensurate
magnetic order in La1.5Sr0.5CoO4 by elastic neutron scattering. We find that
magnetic diffuse scattering is isotropic in the a-b plane, in contrast with the
naive expectation based on the popular stripe model. Indeed, charge segregation
into lines favoring certain lattice direction(s) would facilitate linear
stacking faults in an otherwise robust antiferromagnetism of un-doped material,
leading to anisotropic disorder, with a characteristic symmetry pattern present
in the neutron scattering data.",0608575v3
2006/9/13,Interface Magnetoresistance in Manganite-Titanate Heterojunctions,"We have found that the current- voltage characteristics of
La0.7Sr0.3MnO3(-delta)/Nb:SrTiO3 rectifying junctions are quantitatively
well-described by (thermally-assisted) tunneling with an effectively
temperature-independent Schottky barrier under no magnetic field, while those
of the oxygen deficient junction remarkably deviate from such a simple behavior
as magnetic field is applied. These results indicate a new form of
magnetoresistance arising from magnetic field changes of the interface band
diagram via the strong electron-spin coupling in manganites.",0609315v1
2006/10/17,Unconventional relaxation in antiferromagnetic CoRh$_2$O$_4$ nanoparticles,"Magnetic relaxation in antiferromagnetic CoRh$_2$O$_4$ nanoparticles is
investigated at 2 K by cooling the sample from a temperature (70 K) well above
the antiferromagnetic ordering temperature at 27 K, following zero field cooled
(ZFC) and field cooled (FC) process. In ZFC process, the sample at 2 K is
subsequently followed by magnetic field on and off sequences, whereas in FC
process the cooling field is made off during measurement of remanent
magnetization as a function of time. The experiments suggest an unconventional
relaxation behaviour in the system, as an effect of increasing surface exchange
anisotropy with decreasing the size of antiferromagnetic nanoparticles.",0610450v1
2006/10/19,Heat capacity and magnetocaloric effect in polycrystalline Gd1-xSmxMn2Si2,"We report the magnetocaloric effect in terms of isothermal magnetic entropy
change as well as adiabatic temperature change, calculated using the heat
capacity data. Using the zero field heat capacity data, the magnetic
contribution to the heat capacity has been estimated. The variations in the
magnetocaloric behavior have been explained on the basis of the magnetic
structure of these compounds. The refrigerant capacities have also been
calculated for these compounds.",0610551v1
2006/10/24,Exchange interaction of magnetic impurities in graphene,"The indirect exchange interaction between magnetic impurities localized in a
graphene plane is considered theoretically, with the influence of intrinsic
spin-orbit interaction taken into account. Such an interaction gives rise to an
energy gap at the Fermi level, which makes the usual RKKY model not applicable.
The results show that the effective indirect exchange interaction is described
by a range function which decays exponentially with the distance between
magnetic moments. The interaction is also shown to depend on whether the two
localized moments belong to the same sublattice or are located in two different
sublattices.",0610658v1
2006/11/6,Unusual field and temperature dependence of Hall effect in graphene,"We calculate the classic Hall conductivity and mobility of the undoped and
doped (or in the gate voltage) graphene as a function of temperature, magnetic
field, and carrier concentration. Carrier collisions with defects and acoustic
phonons are taken into account. The Hall resistivity varies almost linearly
with temperature. The magnetic field dependence of resistivity and mobility is
anomalous in weak magnetic fields. There is the square root contribution from
the field in the resistivity. The Hall mobility diverges logarithmically with
the field for low doping.",0611147v2
2006/11/8,Reversal modes in magnetic nanotubes,"The magnetic switching of ferromagnetic nanotubes is investigated as a
function of their geometry. Two independent methods are used: Numerical
simulations and analytical calculations. It is found that for long tubes the
reversal of magnetization is achieved by two mechanism: The propagation of a
transverse or a vortex domain wall depending on the internal and external radii
of the tube.",0611234v1
2006/11/28,A detailed analysis of dipolar interactions and analytical approximations in arrays of magnetic nanowires,"The investigation of the role of interactions in magnetic wire arrays is
complex and often subject to strong simplifications. In this paper we obtained
analytical expressions for the magnetostatic interactions between wires and
investigate the range of validity of dipole-dipole, first order and second
order approximations. We also analyze the extension of the interwire
magnetostatic interactions in a sample and found that the number of wires
required to reach energy convergence in the array strongly depends on the
relative magnetic orientation between the wires.",0611728v1
2006/12/14,Magnetic order of FeMn alloy on the W(001) surface,"We investigate theoretically the ground state of the FeMn binary alloy
monolayer on the W(001) surface, the stability of different magnetic
configurations (ferro/antiferromagnetic, disordered local moments, etc.) and
estimate concentrations at which a transition occurs between different magnetic
orders. The tight-binding linear muffin-tin orbital method combined with the
coherent potential approximation is used to treat the surface alloy
appropriately. We discuss the role of disorder on the phase transitions in
surface alloys composed from two different 3d transition metals.",0612366v1
2007/1/1,Magnetic-field symmetries of mesoscopic nonlinear conductance,"We examine contributions to the dc-current of mesoscopic samples which are
non-linear in applied voltage. In the presence of a magnetic field, the current
can be decomposed into components which are odd (antisymmetric) and even
(symmetric) under flux reversal. For a two-terminal chaotic cavity, these
components turn out to be very sensitive to the strength of the Coulomb
interaction and the asymmetry of the contact conductances. For both two- and
multi-terminal quantum dots we discuss correlations of current non-linearity in
voltage measured at different magnetic fields and temperatures.",0701024v1
2007/2/2,Current-induced magnetic vortex core switching in a Permalloy nanodisk,"We report on the switching of a magnetic vortex core in a sub-micron
Permalloy disk, induced by a short current pulse applied in the film plane.
Micromagnetic simulations including the adiabatic and non-adiabatic spin-torque
terms are used to investigate the current-driven magnetization dynamics. We
predict that a core reversal can be triggered by current bursts a tenth of a
nanosecond long. The vortex core reversal process is found to be the same as
when an external field pulse is applied. The control of a vortex core's
orientation using current pulses introduces the technologically relevant
possibility to address individual nanomagnets within dense arrays.",0702048v1
2007/2/6,Magnetic structure and phase diagram in a spin-chain system: Ca$_3$Co$_2$O$_6$,"The low-temperature structure of the frustrated spin-chain compound
Ca$_3$Co$_2$O$_6$ is determined by the ground state of the 2D Ising model on
the triangular lattice. At high-temperatures it transforms to the honeycomb
magnetic structure. It is shown that the crossover between the two magnetic
structures at 12 K arises from the entropy accumulated in the disordered
chains. This interpretation is in an agreement with the experimental data.
General rules for for the phase diagram of frustrated Ising chain compounds are
formulated.",0702155v1
2007/2/20,Temperature Hysteresis of Magnetization in Lanthanum Manganite,"We propose an explanation for the experimentally observed temperature
hysteresis of magnetization in single crystals of lanthanum manganite
(La0.8Sr0.2MnO3). The phenomenon is interpreted within the framework of a
double-exchange model with allowance for the interaction of the magnetic
subsystem with a bistable mode of the tilting-rotational oscillations in the
correlated sublattice of MnO6 octahedra.",0702459v1
2007/2/26,Impurity Conduction and Magnetic Polarons in Antiferromagnetic Oxides,"Low-temperature transport and magnetization measurements for the
antiferromagnets SrMnO(3) and CaMnO(3) identify an impurity band of mobile
states separated by energy E from electrons bound in Coulombic potentials. Very
weak electric fields are sufficient to excite bound electrons to the impurity
band, increasing the mobile carrier concentration by more than three orders of
magnitude. The data argue against the formation of self-trapped magnetic
polarons (MPs) predicted by theory, and rather imply that bound MPs become
stable only for kT<<E.",0702608v1
2007/3/2,Chiral spin pairing in helical magnets,"The Ginzburg-Landau Hamiltonian for incommensurate frustrated classical spin
systems is analyzed. The coupling to phonons through the Dzyaloshinskii-Moriya
interaction and/or the four-spin exchange interaction of the Coulomb origin
under the egde-sharing network of magnetic and ligand ions drive chiral spin
piarings, introducing two successive second-order phase transitions upon
cooling. First, a vector spin-chiral order appears with an either parity,
leaving an O(2) chiral spin liquid. Then, the O(2) symmetry is broken by the
spin ordering into a helical magnetic state. Possible candidate materials are
also discussed.",0703064v2
2007/3/11,Hole states in wide band-gap diluted magnetic semiconductors and oxides,"Puzzling disagreement between photoemission and optical findings in
magnetically doped GaN and ZnO is explained within a generalized alloy theory.
The obtained results show that the strong coupling between valence-band holes
and localized spins gives rise to a mid-gap Zhang-Rice-like state, to a sign
reversal of the apparent p-d exchange integral, and to an increase of the
band-gap with the magnetic ion concentration.",0703278v1
2007/3/12,Enhanced magneto-transport at high bias in quasi-magnetic tunnel junctions with EuS spin-filter barriers,"In quasi-magnetic tunnel junctions (QMTJs) with a EuS spin filter tunnel
barrier between Al and Co electrodes, we observed large magnetoresistance (MR).
The bias dependence shows an abrupt increase of MR ratio in high bias voltage,
which is contrary to conventional magnetic tunnel junctions (MTJs). This
behavior can be understood as due to Fowler-Nordheim tunneling through the
fully spin-polarized EuS conduction band. The I-V characteristics and bias
dependence of MR calculated using tunneling theory shows excellent agreement
with experiment.",0703289v1
2007/3/29,Thermo-reversible permanent magnets in the quasi-binary GdCo5-xCux system,"Ferrimagnetic GdCo5-xCux alloys exhibiting the effect of Gd- and
3d-sublattice magnetization compensation at defined temperatures were studied
with respect to their use as thermo-reversible permanent magnets (PM). Coercive
fields &#61549;0Hc in the range 0.3 to 1.6 T were measured for annealed single
crystals with x = 1 - 2.2 having compensation points in the vicinity of room
temperature. Two applications of such a thermo-reversible PM, namely a
thermally controlled actuator and a contactless temperature sensor, are
demonstrated.",0703775v1
2007/3/20,Electromagnetic wormholes and virtual magnetic monopoles,"We describe new configurations of electromagnetic (EM) material parameters,
the electric permittivity $\epsilon$ and magnetic permeability $\mu$, that
allow one to construct from metamaterials objects that function as invisible
tunnels. These allow EM wave propagation between two points, but the tunnels
and the regions they enclose are not detectable to EM observations. Such
devices function as wormholes with respect to Maxwell's equations and
effectively change the topology of space vis-a-vis EM wave propagation. We
suggest several applications, including devices behaving as virtual magnetic
monopoles.",0703059v1
2007/4/10,Superconductor strip in a closed magnetic environment: exact analytic representation of the critical state,"An exact analytic representation of the critical state of a current-carrying
type-II superconductor strip located inside a cylindrical magnetic cavity of
high permeability is derived. The obtained results show that, when the cavity
radius is small, penetration of magnetic flux fronts is strongly reduced as
compared to the situation in an isolated strip. From our generic representation
it is possible to establish current profiles in closed cavities of various
other geometries too by means of conformal mapping of the basic configuration
addressed.",0704.1227v1
2007/4/23,Ferroelectricity driven by the non-centrosymmetric magnetic ordering in multiferroic TbMn_2O_5: a first-principles study,"The ground state structural, electronic and magnetic properties of
multiferroic TbMn$_2$O$_5$ are investigated via first-principles calculations.
We show that the ferroelectricity in TbMn$_2$O$_5$ is driven by the
non-centrosymmetric magnetic ordering, without invoking the spin-orbit coupling
and non-collinear spins. The {\it intrinsic} electric polarization in this
compound is calculated to be 1187 $nC\cdot$ cm$^{-2}$, an order of magnitude
larger than previously thought.",0704.2908v2
2007/4/25,Pressure induced magnetic ordering in Yb2Pd2Sn with two quantum critical points,"Pressure induced long range antiferromagnetic order is discovered in Yb2Pd2Sn
by measuring the electrical resistivity under pressure up to 5.0 GPa. Magnetic
ordering is observed above about 1.0 GPa, being the lowest pressure in
Yb-intermetallics showing pressure induced magnetic ordering, Unexpectedly,
ordering disappears above about 4.0 GPa, giving rise to the first observation
of the appearance of two quantum critical points persisting in a broad range of
pressure within a single material.",0704.3307v2
2007/5/2,Magneto-elastic waves in crystals of magnetic molecules,"We study magneto-elastic effects in crystals of magnetic molecules. Coupled
equations of motion for spins and sound are derived and the possibility of
strong resonant magneto-acoustic coupling is demonstrated. Dispersion laws for
interacting linear sound and spin excitations are obtained for bulk and surface
acoustic waves. We show that ultrasound can generate inverse population of spin
levels. Alternatively, the decay of the inverse population of spin levels can
generate ultrasound. Possibility of solitary waves of the magnetization
accompanied by the elastic twists is demonstrated.",0705.0371v1
2007/5/10,Magnetically Induced Field Effect in Carbon Nanotube Devices,"Three-terminal devices with conduction channels formed by quasi-metallic
carbon nanotubes (CNT) are shown to operate as nanotube-based field-effect
transistors under strong magnetic fields. The off-state conductance of the
devices varies exponentially with the magnetic flux intensity. We extract the
quasi-metallic CNT chirality as well as the characteristics of the Schottky
barriers formed at the metal-nanotube contacts from temperature-dependent
magnetoconductance measurements.",0705.1493v1
2007/5/14,On the Enhanced Reverse Beta Processes in Graphene-Iron Composite Nanostructures at High Temperatures in Strong Magnetic Field,"Strong dense many-spin interactions have been proposed to organize novel
orbital dynamics (the Little Effect) for novel chemical and catalytic
phenomena. The recent determinations of the relativistic and quantum Hall
effects of carriers in graphene under strong magnetic confinement have
substantiated the Little Effect. Moreover such nonclassical phenomena under the
stronger magnetic confinement of ferro-nanocatalysts are here shown to organize
reverse beta processes and possibly pycnonuclear reactions under high
temperature and high-pressure conditions. Such processes have implications for
reverse beta reactions and nuclear reactions within the interior of the earth
and new technologies for carbon nanotube-ferrometal and nanographene-ferrometal
composites.",0705.1909v1
2007/6/12,Magnetic fingerprint in a ferromagnetic wire: Spin torque diode effect and induction of the DC voltage spectrum inherent in the wire under application for RF current,"We report the rectifying effect of a constant-wave radio frequency (RF)
current by a magnetic domain wall (DW) on a single-layered ferromagnetic wire.
A direct-current (DC) voltage is generated by the spin torque diode effect,
which is a consequence of magnetoresistance oscillation due to the resonant
spin wave excitation induced by the spin-polarized RF current. The DC voltage
spectrum strongly depends on the internal spin structure in the DW, which
corresponds to the magnetic fingerprint of the spin structure in the
ferromagnetic wire.",0706.1733v1
2007/6/14,"Magnetic patterning of (Ga,Mn)As by hydrogen passivation","We present an original method to magnetically pattern thin layers of
(Ga,Mn)As. It relies on local hydrogen passivation to significantly lower the
hole density, and thereby locally suppress the carrier-mediated ferromagnetic
phase. The sample surface is thus maintained continuous, and the minimal
structure size is of about 200 nm. In micron-sized ferromagnetic dots
fabricated by hydrogen passivation on perpendicularly magnetized layers, the
switching fields can be maintained closer to the continuous film coercivity,
compared to dots made by usual dry etch techniques.",0706.2138v1
2007/6/16,Experimental Evidence for Two-Dimensional Magnetic Order in Proton Bombarded Graphite,"We have prepared magnetic graphite samples bombarded by protons at low
temperatures and low fluences to attenuate the large thermal annealing produced
during irradiation. An overall optimization of sample handling allowed us to
find Curie temperatures $ T_c \gtrsim 350$ K at the used fluences. The
magnetization versus temperature shows unequivocally a linear dependence, which
can be interpreted as due to excitations of spin waves in a two dimensional
Heisenberg model with a weak uniaxial anisotropy.",0706.2442v1
2007/6/27,Molecular dynamics simulations of the dipolar-induced formation of magnetic nanochains and nanorings,"Iron, cobalt and nickel nanoparticles, grown in the gas phase, are known to
arrange in chains and bracelet-like rings due to the long-range dipolar
interaction between the ferromagnetic (or super-paramagnetic) particles. We
investigate the dynamics and thermodynamics of such magnetic dipolar
nanoparticles for low densities using molecular dynamics simulations and
analyze the influence of temperature and external magnetic fields on two- and
three-dimensional systems. The obtained phase diagrams can be understood by
using simple energetic arguments.",0706.3920v1
2007/7/5,Anomalous exchange coupling in transition-metal-oxide based superlattices with antiferromagnetic spacer layers,"A direct correlation is seen between the coercive field (HC) and the
magnetic-field-dependent resistivity (MR) in SrMnO3/SrRuO3 superlattices of
perpendicular magnetic anisotropy. The magnetoresistance shows a sharp jump at
Hc for in-plane current and the out-of-plane magnetic field. Both HC and
high-field MR also oscillate with the thickness of the SrMnO3 spacer layers
separating the metallic ruthenate. Since the spacer in these superlattices has
no mobile carriers to facilitate an oscillatory coupling, we attribute the
observed behavior to the spin-polarized quantum tunneling of electrons between
the ferromagnetic layers and antiferromagnetically ordered t2g spins of SrMnO3.",0707.0768v1
2007/8/1,"First principles investigations of the electronic, magnetic and chemical bonding properties of CeTSn (T=Rh,Ru)","The electronic structures of CeRhSn and CeRuSn are self-consistently
calculated within density functional theory using the local spin density
approximation for exchange and correlation. In agreement with experimental
findings, the analyses of the electronic structures and of the chemical bonding
properties point to the absence of magnetization within the mixed valent Rh
based system while a finite magnetic moment is observed for trivalent cerium
within the Ru-based stannide, which contains both trivalent and intermediate
valent Ce.",0708.0188v1
2007/8/6,Multiferroic nature of charge-ordered rare earth manganites,"Charge-ordered rare earth manganites Nd0.5Ca0.5MnO3, La0.25Nd0.25Ca0.5MnO3,
Pr0.7Ca0.3MnO3 and Pr0.6Ca0.4MnO3 are found to exhibit dielectric constant
anomalies around the charge-ordering or the magnetic transition temperatures.
Magnetic fields have a marked effect on the dielectric properties, indicating
the presence of coupling between the magnetic and electrical order parameters.
The observation of magnetoferroelectricity in these manganites is in accord
with the recent theoretical predictions of Khomskii and coworkers.",0708.0746v1
2007/8/14,"Random telegraph noise from magnetic nanoclusters in the ferromagnetic semiconductor (Ga,Mn)As","Measurements of the low frequency electrical noise in the ferromagnetic
semiconductor (Ga,Mn)As reveal an enhanced integrated noise at low temperature.
For moderate localization, we find a 1/f normalized power spectrum density over
the entire range of temperatures studied (4.2K < T < 70K). However, for
stronger localization and a high density of Mn interstitials, we observe
Lorentzian noise spectra accompanied by random telegraph noise. Magnetic field
dependence and annealing studies suggest that interstitial Mn defects couple
with substitutional Mn atoms to form nanoscale magnetic clusters characterized
by a net moment of about 20 Bohr magnetons whose fluctuations modulate hole
transport.",0708.1895v1
2007/9/2,Nonresonant microwave absorption in epitaxial La-Sr-Mn-O films and its relation to colossal magnetoresistance,"We study magnetic-field-dependent nonresonant microwave absorption and
dispersion in thin La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ films and show that it
originates from the colossal magnetoresistance. We develop the model for
magnetoresistance of a thin ferromagnetic film in oblique magnetic field. The
model accounts fairly well for our experimental findings, as well as for
results of other researchers. We demonstrate that nonresonant microwave
absorption is a powerful technique that allows contactless measurement of
magnetic properties of thin films, including magnetoresistance, anisotropy
field and coercive field.",0709.0094v1
2007/12/4,Magnetostructure of MnAs on GaAs revisited,"The ferromagnetic to nonferromagnetic (&#945;-&#946;) phase transition in
epitaxial MnAs layers on GaAs(100) is studied by x-ray magnetic circular
dichroism and x-ray magnetic linear dichroism photoemission electron microscopy
in order to elucidate the nature of the controversial nonferromagnetic state of
&#946;-MnAs. In the coexistence region of the two phases the &#946; phase shows
a clear XMLD signal characteristic of antiferromagnetism. The nature and the
possible causes of the elusiveness of this magnetic state are discussed.",0712.0564v1
2007/12/12,Large magnetocaloric effect in Gd4Co3,"We report a large entropy change (DeltaS) below 300 K, peaking near TC= 220
K, due to isothermal change of magnetic field, for Gd4Co3, with a refrigeration
capacity higher than that of Gd. Notably, the isothermal magnetization is
nonhysteretic - an important criterion for magnetic refrigeration without loss.
DeltaS behavior is also compared with that of magnetoresistance.",0712.1999v2
2007/12/13,Bose-Einstein Condensation in Magnetic Insulators,"The elementary excitations in antiferromagnets are magnons, quasiparticles
with integer spin and Bose statistics. In an experiment their density is
controlled efficiently by an applied magnetic field and can be made finite to
cause the formation of a Bose-Einstein condensate (BEC). Studies of magnon
condensation in a growing number of magnetic materials provide a unique window
into an exciting world of quantum phase transitions (QPT) and exotic quantum
states.",0712.2250v1
2008/1/7,Origin of the Structural and Magnetic Anomaly of the Layered Compound SrFeO2: A Density Functional Investigation,"The structural and magnetic anomaly of the layered compound SrFeO$_{2}$ were
examined by first principles density functional calculations and Monte Carlo
simulations. The down-spin Fe 3$d$ electron occupies the $d_{z^2}$ level rather
than the degenerate ($d_{xz}$, $d_{yz}$) levels, which explains the absence of
Jahn-Teller instability, the easy ab-plane magnetic anisotropy and the observed
three-dimensional (0.5, 0.5, 0.5) antiferromagnetic order. Monte Carlo
simulations show that the strong inter-layer spin exchange is essential for the
high N\'eel temperature.",0801.1137v2
2008/1/9,Anisotropy in the magnetic and electrical transport properties of Fe1-xCrxSb2,"We have investigated anisotropy in magnetic and electrical transport
properties of Fe1-xCrxSb2 (0<= x <=1) single crystals. The magnetic ground
state of the system evolves from paramagnetic to antiferromagnetic with gradual
substitution of Fe with Cr. Anisotropy in electrical transport diminishes with
increased Cr substitution and fades away by x=0.5. We find that the variable
range hopping (VRH) conduction mechanism dominates at low temperatures for
0.4<= x <=0.75.",0801.1351v2
2008/1/9,Colossal Positive Magnetoresistance in a Doped Nearly Magnetic Semiconductor,"We report on a positive colossal magnetoresistance (MR) induced by
metallization of FeSb$_{2}$, a nearly magnetic or ""Kondo"" semiconductor with 3d
ions. We discuss contribution of orbital MR and quantum interference to
enhanced magnetic field response of electrical resistivity.",0801.1354v1
2008/1/11,Weak Ferromagnetism in Fe1-xCoxSb2,"Weak ferromagnetism in Fe1-xCoxSb2 is studied by magnetization and Mossbauer
measurements. A small spontaneous magnetic moment of the order of 10^-3 uB
appears along the b-axis for 0.2<= x <= 0.4. Based on the structural analysis,
we argue against extrinsic sources of weak ferromagnetism. We discuss our
results in the framework of the nearly magnetic electronic structure of the
parent compound FeSb2.",0801.1688v1
2008/1/15,Broadband ferromagnetic resonance of Ni81Fe19 wires using a rectifying effect,"The broadband ferromagnetic resonance measurement using the rectifying effect
of Ni81Fe19 wire has been investigated. One wire is deposited on the center
strip line of the coplanar waveguide (CPW) and the other one deposited between
two strip lines of CPW. The method is based on the detection of the
magnetoresistance oscillation due to the magnetization dynamics induced by the
radio frequency field. The magnetic field dependences of the resonance
frequency and the rectification spectrum are presented and analytically
interpreted on the standpoint of a uniform magnetization precession model.",0801.2203v1
2008/2/4,Ground state and thermal transitions in Field Induced spin-Supersolid Phase,"We use a quantum Monte Carlo method to study the ground state and
thermodynamic phase transitions of the spin supersolid phase in the S=1
Heisenberg model with uniaxial anisotropy. The thermal melting of the
supersolid phase shows unqiue signatures in experimentally measurable
observables. This Hamiltonian is a particular case of a more general and
ubiquitous model that describes the low energy spectrum of a class of {\it
isotropic} and {\it frustrated} spin systems. We also discuss some alternative
realizations of spin supersolid states in real magnets.",0802.0458v1
2008/2/5,Spin-valve effect and magnetoresistivity in single crystalline Ca3Ru2O7,"The laminar perovskite Ca3Ru2O7 naturally forms ferromagnetic double-layers
of alternating moment directions, as in the spin-valve superlattices. The
mechanism of huge magnetoresistive effect in the material has been
controversial due to a lack of clear understanding of various magnetic phases
and phase-transitions. In this neutron diffraction study in a magnetic field,
we identify four different magnetic phases in Ca3Ru2O7 and determine all
first-order and second-order phase transitions between them. The spin-valve
mechanism then readily explains the dominant magnetoresistive effect in
Ca3Ru2O7.",0802.0713v1
2008/2/6,Self-organized plane arrays of metallic magnetic elements,"We studied the dynamic magnetic properties of plane periodical arrays of
circular permalloy nano-dots fabricated using a self-organized mask formed by
polysterene nanospheres on the surface of a Permalloy film. Conventional
(microwave cavity) and broadband coplanar-line ferromagnetic resonance setups
were used for the measurements. We found several well resolved resonance peaks.
This result shows that the self-organized mask fabrication technique is able to
produce high-quality samples with small dispersion of geometrical and magnetic
parameters.",0802.0731v1
2008/2/12,Dynamical Coupling Between Ferromagnets Due to Spin Transfer Torque,"We use a combination of analytic calculations and numerical simulations to
demonstrate that electrical current flowing through a magnetic bilayer induces
dynamical coupling between the layers. The coupling originates from the
dependence of the spin transfer torque exerted on the layers on the relative
orientations of their magnetic moments. We demonstrate that such coupling
modifies the behaviors of both layers, significantly affecting the the
stability of the current-induced dynamical regimes and the efficiency of
current-induced magnetic reversal.",0802.1560v1
2008/2/25,Tunnel barrier enhanced voltage signals generated by magnetization precession of a single ferromagnetic layer,"We report the electrical detection of magnetization dynamics in an
Al/AlOx/Ni80Fe20/Cu tunnel junction, where a Ni80Fe20 ferromagnetic layer is
brought into precession under the ferromagnetic resonance (FMR) conditions. The
dc voltage generated across the junction by the precessing ferromagnet is
enhanced about an order of magnitude compared to the voltage signal observed
when the contacts in this type of multilayered structure are ohmic. We discuss
the relation of this phenomenon to magnetic spin pumping and speculate on other
possible underlying mechanisms responsible for the enhanced electrical signal.",0802.3646v1
2008/3/3,Laser-induced Precession of Magnetization in GaMnAs,"We report on the photo-induced precession of the ferromagnetically coupled Mn
spins in (Ga,Mn)As, which is observed even with no external magnetic field
applied. We concentrate on various experimental aspects of the time-resolved
magneto-optical Kerr effect (TR-MOKE) technique that can be used to clarify the
origin of the detected signals. We show that the measured data typically
consist of several different contributions, among which only the oscillatory
signal is directly connected with the ferromagnetic order in the sample.",0803.0320v1
2008/3/4,LaFeAsO$_{1-x}$F$_x$: A low carrier density superconductor near itinerant magnetism,"Density functional studies of 26K superconducting LaFeAs(O,F) are reported.
We find a low carrier density, high density of states, $N(E_F)$ and modest
phonon frequencies relative to $T_c$. The high $N(E_F)$ leads to proximity to
itinerant magnetism, with competing ferromagnetic and antiferromagnetic
fluctuations and the balance between these controlled by doping level. Thus
LaFeAs(O,F) is in a unique class of high $T_c$ superconductors: high $N(E_F)$
ionic metals near magnetism.",0803.0429v2
2008/3/7,Neutron scattering study of Kondo lattice antiferromagnet YbNiSi3,"The Kondo lattice antiferromagnet YbNiSi3 was investigated by neutron
scattering. The magnetic structure of YbNiSi3 was determined by neutron
diffraction on a single-crystalline sample. Inelastic scattering experiments
were also performed on a pulverized sample to study the crystalline electric
field (CEF) excitations. Two broad CEF excitations were observed, from which
the CEF parameters were determined. The temperature dependence of the magnetic
susceptibility chi and the magnetic specific heat Cmag were calculated using
the determined CEF model, and compared with previous results.",0803.1084v1
2008/3/11,Substantial magneto-electric coupling near room temperature in Bi2Fe4O9,"We report remarkable multiferroic effects in polycrystalline Bi2Fe4O9.
High-resolution X-ray diffraction shows that this compound has orthorhombic
structure. Magnetic measurements confirm an antiferromagnetic transition around
260 K. A pronounced inverse S-shape anomaly in the loss tangent of dielectric
measurement is observed near the Neel temperature. This feature shifts with the
application of magnetic field. These anomalies are indicative of substantial
coupling between the electric and magnetic orders in this compound.",0803.1539v1
2008/3/13,Magnetic Boron Nitride Nanoribbons with Tunable Electronic Properties,"We present theoretical evidence, based on total-energy first-principles
calculations, of the existence of spin-polarized states well localized at and
extended along the edges of bare zigzag boron nitride nanoribbons. Our
calculations predict that all the magnetic configurations studied in this work
are thermally accessible at room temperature and present an energy gap. In
particular, we show that the high spin state, with a magnetic moment of 1
$\mu_B$ at each edge atom, presents a rich spectrum of electronic behaviors as
it can be controlled by applying an external electric field in order to obtain
metallic $\leftrightarrow$ semiconducting $\leftrightarrow$ half-metallic
transitions.",0803.2024v1
2008/3/20,Interplay between magnetic and lattice excitations in BiFeO$_3$,"We have performed Raman scattering investigations on the high energy magnetic
excitations in a BiFeO$_3$ single crystal as a function of both temperature and
laser excitation energy. A strong feature observed at 1250 cm$^{-1}$ in the
Raman spectra has been previously assigned to two phonon overtone. We show here
that its unusual frequency shift with the excitation energy and its asymmetric
temperature dependent Fano lineshape reveal a strong coupling to magnetic
excitations. In the same energy range, we have also identified the two-magnon
excitation with a temperature dependence very similar to $\alpha$-Fe$_2$O$_3$
hematite.",0803.3015v1
2008/4/3,Density-functional description of superconducting and magnetic proximity effects across a tunneling barrier,"A density-functional formalism for superconductivity {\em and} magnetism is
presented. The resulting relations unify previously derived Kohn-Sham equations
for superconductors and for non-collinear magnetism. The formalism, which
discriminates Cooper pair singlets from triplets, is applied to two quantum
liquids coupled by tunneling through a barrier. An exact expression is derived,
relating the eigenstates and eigenvalues of the Kohn-Sham equations,
unperturbed by tunneling, on one side of the barrier to the proximity-induced
ordering potential on the other.",0804.0562v2
2008/4/24,Current-induced domain wall motion in a nanowire with perpendicular magnetic anisotropy,"We study theoretically the current-induced magnetic domain wall motion in a
metallic nanowire with perpendicular magnetic anisotropy. The anisotropy can
reduce the critical current density of the domain wall motion. We explain the
reduction mechanism and identify the maximal reduction conditions. This result
facilitates both fundamental studies and device applications of the current-
induced domain wall motion.",0804.3864v1
2008/5/5,Magnetoelectric oscillations in quasi-2D ferrite disk particles,"In this paper we show that magnetic-dipolar-mode (MDM) oscillations of a
quasi-2D ferrite disk are characterized by unique symmetry features with
topological phases resulting in appearance of the magnetoelectric (ME)
properties. The entire ferrite disk can be characterized as a pair of two,
electric and magnetic, coupled eigen moments. However, there is no a ""glued
pair"" of two dipoles. An external electromagnetic field in the near-field
region ""views"" such a ME particle, as a system with a normally oriented eigen
electric moment and an in-plane rotating eigen magnetic dipole moment.",0805.0518v1
2008/5/8,Theory of huge tunneling magnetoresistance in graphene,"We investigate theoretically the spin-independent tunneling magnetoresistance
effect in a graphene monolayer modulated by two parallel ferromagnets deposited
on a dielectric layer. For the parallel magnetization configuration, Klein
tunneling can be observed in the transmission spectrum, but at specific oblique
incident angles. For the antiparallel magnetization configuration, the
transmission can be blocked by the magnetic-electric barrier provided by the
ferromagnets. Such a transmission discrepancy results in a tremendous
magnetoresistance ratio and can be tuned by the inclusion of an electric
barrier.",0805.1105v1
2008/5/24,Role of charge carriers for ferromagnetism in cobalt-doped rutile TiO2,"Electric and magnetic properties of a high temperature ferromagnetic oxide
semiconductor, cobalt-doped rutile TiO2, are summarized. The cobalt-doped
rutile TiO2 epitaxial thin films with different electron densities and cobalt
contents were grown on r-sapphire substrates with laser molecular beam epitaxy.
Results of magnetization, magnetic circular dichroism, and anomalous Hall
effect measurements were examined for samples with systematically varied
electron densities and cobalt contents. The samples with high electron
densities and cobalt contents show the high temperature ferromagnetism,
suggesting that charge carriers induce the ferromagnetism.",0805.3748v1
2008/6/2,Effect of magnetic field and temperature on the ferroelectric loop in MnWO4,"The ferroelectric properties of MnWO4 single crystal have been investigated.
Despite a relatively low remanent polarization, we show that the sample is
ferroelectric. The shape of the ferroelectric loop of MnWO4 strongly depends on
magnetic field and temperature. While its dependence does not directly
correlate with the magnetocapacitance effect before the paraelectric
transition, the effect of magnetic field on the ferroelectric polarization loop
supports magnetoelectric coupling.",0806.0117v1
2008/6/4,Magnetization dynamics in optically excited nanostructured nickel films,"In this work, Laser-induced magnetization dynamics of nanostructured nickel
films is investigated. The influence of the nanosize is discussed considering
the time-scale of hundreds of femtoseconds as well as the GHz regime. While no
nanosize effect is observed on the short time-scale, the excited magnetic mode
in the GHz regime can be identified by comparison with micromagnetic
simulations. The thickness dependence reveals insight on the dipole interaction
between single nickel structures. Also, transient reflectivity changes are
discussed.",0806.0711v1
2008/6/4,Electric Field Induced Transformation of Magnetic Domain Structure in Magnetoelectric Iron Garnet Films,"The room temperature magnetoelectric effect was observed in epitaxial iron
garnet films that appeared as magnetic domain wall motion induced by electric
field. The films grown on gadolinium-gallium garnet substrates with various
crystallographic orientations were examined. The effect was observed in (210)
and (110) films and was not observed in (111) films. Dynamic observation of the
domain wall motion in 400 V voltage pulses gave the value of domain wall
velocity in the range 30-50 m/s. The same velocity was achieved in magnetic
field pulse about 50 Oe.",0806.0811v1
2008/6/12,Magnetic behavior of nanocrystalline LaMn2Ge2,"The compound, LaMn2Ge2, crystallizing in ThCr2Si2-type tetragonal crystal
structure, has been known to undergo ferromagnetic order below (T_C=) 326 K. In
this article, we report the magnetic behavior of nanocrystalline form of this
compound, obtained by high-energy ball-milling. T_C of this compound is reduced
maginally for the nanoform, whereas there is a significant reduction of the
magnitude of the saturation magnetic moment with increasing milling time. The
coercive field however increases with decreasing particle size. Thus, this work
provides a route to tune these parameters by reducing the particle size in this
ternary family.",0806.2030v1
2008/6/17,Structural and angular dependence of coercivity and magnetic remanence of electrochemical ferromagnetic nanowires,"A novel method for controlling nanowire magnetic properties and growth from
filling time profile is presented.
  The wires are grown with an electrodeposition method (""Template synthesis"")
with a wide selection of pore diameters. We show that stray-fields presence in
ferromagnetic nanowires are entirely dependent on the nanowire diameter.
Besides a crossover effect in the reversal mechanism is observed with change in
diameter. In this work, theory and experiment agree and confirm that according
to the variety of hysteresis loop measured, about four ranges of values of pore
diameter control the orientation of nanowire magnetization easy axis with
respect to the geometrical axis.",0806.2826v1
2008/6/19,Magnetic Excitation in Artificially Designed Oxygen Molecule Magnet,"We performed inelastic neutron scattering experiment to study magnetic
excitation of O$_2$ molecules adsorbed in microporous compound. The
dispersionless excitation with characteristic intensity modulation is observed
at $\hbar \omega = 7.8$ meV at low temperature. The neutron cross section is
explained by spin dimer model with intradimer distance of 3.1 \AA . Anomalous
behaviour in the temperature dependence is discussed in the context of enhanced
magnetoelasticity in the soft framework of O$_2$ molecule.",0806.3117v1
2008/7/18,Current-induced dynamics of spiral magnet,"We study the dynamics of the spiral magnet under the charge current by
solving the Landau-Lifshitz-Gilbert equation numerically. In the steady state,
the current ${\vec j}$ induces (i) the parallel shift of the spiral pattern
with velocity $v=(\beta/\alpha)j$ ($\alpha$, $\beta$: the Gilbert damping
coefficients), (ii) the uniform magnetization $M$ parallel or anti-parallel to
the current depending on the chirality of the spiral and the ratio $\beta /
\alpha $, and (iii) the change in the wavenumber $k$ of the spiral. These are
analyzed by the continuum effective theory using the scaling argument, and the
various nonequilibrium phenomena such as the chaotic behavior and
current-induced annealing are also discussed.",0807.2901v1
2008/7/19,Structure and Magnetism of HoBaCo2O5+delta Layered Cobaltites with 0.02<delta<0.22,"In this paper we have studied, by means of high-resolution neutron powder
diffraction and magnetic susceptibility, the structural and magnetic features
of selected samples of the HoBaCo2O5+delta layered cobaltite in the low oxygen
content range (0.02<delta<0.22). The results shows a strong antiferromagnetic
contribution at room temperature coupled to an intermediate spin state of the
Co3+ ions.",0807.3071v1
2008/7/24,Surface magnetic phase transition of the double-exchange ferromagnet: Schwinger-boson mean-field study,"The surface magnetic phase transition of a double-exchange model for metallic
manganites is studied using a Schwinger-boson mean-field method. About three
unit-cells wide surface layers are identified. The magnetic moment in these
layers decreases more rapidly than that in the bulk when the temperature is
increased. This behavior is consistent with experimental observations. We also
discuss the implication of this behavior on the tunneling magnetoresistance
effect using manganites and possible improvement of the magnetoresistance
effect near the bulk Curie temperature.",0807.3949v2
2008/7/27,Magnetic-dipolar and electromagnetic vortices in quasi-2D ferrite disks,"Magnetic-dipolar-mode (MDM) oscillations in a quasi-2D ferrite disk show
unique dynamical symmetry properties resulting in appearance of topologically
distinct structures. Based on the magnetostatic (MS) spectral problem
solutions, in this paper we give an evidence for eigen MS power-flow-density
vortices in a ferrite disk. Due to these circular eigen power flows, the MDMs
are characterized by MS energy eigen states. It becomes evident that the reason
of stability of the vortex configurations in saturated ferrite samples is
completely different from the nature of stability in magnetically soft
cylindrical dots. We found a clear correspondence between analytically derived
MDM vortex states and numerically modeled electromagnetic vortices in quasi-2D
ferrite disks.",0807.4281v1
2008/7/28,Anomalous training effect of perpendicular exchange bias in Pt/Co/Pt/IrMn multilayers,"A new characteristic is observed in the training effect of perpendicular
exchange bias. For Pt/Co/Pt/IrMn multilayers with perpendicular magnetic
anisotropy, the magnetization reversal process is accompanied by pinned domain
wall motion and the asymmetry of hysteresis loop is always equal to zero during
subsequent measurements. It is interesting to find that the exchange field
decreases greatly as a function of the cycling number while the coercivity
almost does not change. It is clearly demonstrated that the training effect of
perpendicular exchange bias strongly depends on the magnetization reversal
mechanism of the ferromagnetic layer.",0807.4357v1
2008/7/31,Scattering Theory of Gilbert Damping,"The magnetization dynamics of a single domain ferromagnet in contact with a
thermal bath is studied by scattering theory. We recover the
Landau-Liftshitz-Gilbert equation and express the effective fields and Gilbert
damping tensor in terms of the scattering matrix. Dissipation of magnetic
energy equals energy current pumped out of the system by the time-dependent
magnetization, with separable spin-relaxation induced bulk and spin-pumping
generated interface contributions. In linear response, our scattering theory
for the Gilbert damping tensor is equivalent with the Kubo formalism.",0807.5009v1
2008/8/1,Asymmetric Magnetization Reversal in a Single Exchange-Biased Micro Bar,"The asymmetric magnetization reversal is studied in a single exchange-biased
microbar of 1.5 x 13 micrometer with anisotropic magnetoresistance and magnetic
force microscopy. The particle has a moment of less than 10^-9 emu and is not
accessible with standard magnetometry. The asymmetric hysteresis loop of
CoFe/CrMnPt shows a repeatable rotation process, followed by an irreversible
nucleation process that is marked by jumps in the magnetoresistance. The
induced unidirectional anisotropy enhances the rotation process in one branch
of the hysteresis loop, followed by a sped up nucleation process. Imprinted
ferromagnetic domain patterns left behind by the antiferromagnet are observed
after the nucleation process occurred but before complete saturation is
reached.",0808.0057v1
2008/8/9,Transport and Magnetic Properties of FexVse2 (x = 0 - 0.33),"We present our results of the effect of Fe intercalation on the structural,
transport and magnetic properties of 1T-VSe2. Intercalation of iron, suppresses
the 110K charge density wave (CDW) transition of the 1T-VSe2. For the higher
concentration of iron, formation of a new kind of first order transition at
160K takes place, which go on stronger for the 33% Fe intercalation.
Thermopower of the FexVSe2 compounds (x = 0 - 0.33), however do not show any
anomaly around the transition. The intercalation of Fe does not trigger any
magnetism in the weak paramagnetic 1T-VSe2, and Fe is the low spin state of
Fe3+.",0808.1333v1
2008/8/20,"Anharmonic effect on lattice distortion, orbital ordering and magnetic properties in Cs2AgF4","We develop the cluster self-consistent field method incorporating both
electronic and lattice degrees of freedom to study the origin of ferromagnetism
in Cs$_{2}$AgF$_{4}$. After self-consistently determining the harmonic and
anharmonic Jahn-Teller distortions, we show that the anharmonic distortion
stabilizes the staggered x$^{2}$-z$^{2}$/y$^{2}$-z$^{2}$ orbital and
ferromagnetic ground state, rather than the antiferromagnetic one. The
amplitudes of lattice distortions, Q$_{2}$ and Q$_{3}$, the magnetic coupling
strengthes, J$_{x,y}$, and the magnetic moment, are in good agreement with the
experimental observation.",0808.2759v1
2008/8/21,Switching magnetic vortex core by a single nanosecond current pulse,"In a ferromagnetic nanodisk, the magnetization tends to swirl around in the
plane of the disk and can point either up or down at the center of this
magnetic vortex. This binary state can be useful for information storage. It is
demonstrated that a single nanosecond current pulse can switch the core
polarity. This method also provides the precise control of the core direction,
which constitutes fundamental technology for realizing a vortex core memory.",0808.2858v1
2008/8/30,Control of Domain Wall Position by Electrical Current in Structured Co/Ni Wire with Perpendicular Magnetic Anisotropy,"We report the direct observation of the current-driven domain wall (DW)
motion by magnetic force microscopy in a structured Co/Ni wire with
perpendicular magnetic anisotropy. The wire has notches to define the DW
position. It is demonstrated that single current pulses can precisely control
the DW position from notch to notch with high DW velocity of 40 m/s.",0809.0047v1
2008/9/12,Geometric dephasing-limited Hanle effect in long-distance lateral silicon spin transport devices,"Evidence of spin precession and dephasing (""Hanle effect"") induced by an
external magnetic field is the only unequivocal proof of spin-polarized
conduction electron transport in semiconductor devices. However, when spin
dephasing is very strong, Hanle effect in a uniaxial magnetic field can be
impossible to measure. Using a Silicon device with lateral injector-detector
separation over 2 millimeters, and geometrically-induced dephasing making spin
transport completely incoherent, we show experimentally and theoretically that
Hanle effect can still be measured using a two-axis magnetic field.",0809.2225v1
2008/9/16,Effect of the Dielectric-Constant Mismatch and Magnetic Field on the Binding Energy of Hydrogenic Impurities in a Spherical Quantum Dot,"Within the effective mass approximation and variational method the effect of
dielectric constant mismatch between the size-quantized semiconductor sphere,
coating and surrounding environment on impurity binding energy in both the
absence and presence of a magnetic field is considered. The dependences of the
binding energy of a hydrogenic on-center impurity on the sphere and coating
radii, alloy concentration, dielectric-constant mismatch, and magnetic field
intensity are found for the GaAs-Ga_(1-x)Al_(x)As-AlAs (or vacuum) system.",0809.2662v1
2008/9/26,Domain wall displacement in Py square ring for single nanometric magnetic bead detection,"A new approach based on the domain wall displacement in confined
ferromagnetic nanostructures for attracting and sensing a single nanometric
magnetic particles is presented. We modeled and experimentally demonstrated the
viability of the approach using an anisotropic magnetoresistance device made by
a micron-size square ring of Permalloy designed for application in magnetic
storage. This detection concept can be suitable to biomolecular recognition,
and in particular to single molecule detection.",0809.4649v1
2008/10/5,Electric Field Driven Magnetic Domain Wall Motion in Iron Garnet Film,"The dynamic observation of domain wall motion induced by electric field in
magnetoelectric iron garnet film is reported. Measurements in 800 kV/cm
electric field pulses gave the domain wall velocity ~45 m/s. Similar velocity
was achieved in magnetic field pulse about 50 Oe. Reversible and irreversible
micromagnetic structure transformation is demonstrated. These effects are
promising for applications in spintronics and magnetic memory.",0810.0850v1
2008/10/5,Current-Induced Dynamics in Almost Symmetric Magnetic Nanopillars,"Magnetic nanodevices usually include a free layer whose configuration can be
changed by spin-polarized current via the spin transfer effect, and a fixed
reference layer. Here, we demonstrate that the roles of the free and the
reference layers interchange over a small range of their relative thicknesses.
Precession of both layers can be induced by spin transfer in symmetric devices,
but the dynamics of one of the layers is rapidly suppressed in asymmetric
devices. We interpret our results in terms of the dynamical coupling between
magnetic layers due to spin transfer.",0810.0863v1
2008/10/8,Character of magnetic instabilities in CaFe2As2,"The density functional non-interacting susceptibility has been analyzed in
different phases of CaFe2As2 and compared with similar data for pure d-metals.
The conditions for the ""no local moment"" itinerant state with large
frustrations are found for the ""collapsed"" phase (corresponding to
superconducting phase). This itineracy determines the instability versus the
incommensurate magnetic order for the narrow region of wave vectors. For the
ambient pressure phase, the local moments on Fe atoms with much less frustrated
antiferromagnetic interactions are stabilized and a magnetic short or long
range order for all wave vectors is developed.",0810.1445v1
2008/10/17,Magnetic Phase Diagram of FeAs based superconductors,"The recently discovered high-temperature superconductivity in doped
quaternary iron oxypnictides correlates experimentally with a magnetic
instability. We have used first-principles calculations to determine a magnetic
phase diagram of ReO$_{1-\delta}$FeAs (Re=La--Dy) as a function of the doping
$\delta$, of the FeAs in-plane lattice constant $a$, and of the distance
between the Fe and As planes, that is qualitatively consistent with recent
experimental findings on the doping, internal (chemical) and external pressure
dependence. The existence of a tricritical point (TCP) in the phase diagram
suggests new ways of enhancing $T_c$.",0810.3246v1
2008/10/23,Perfectly elastic collisions as origin of quantum states of superconductivity and magnetic order,"One of the most interesting properties of solid materials is the ability to
form different collective quantum states, such as superconductivity and
magnetic order. This paper presents a model of perfectly elastic collisions
(p.e.c.) as the universal origin of these collective quantum states. The superb
agreement between calculated values and experimental data for critical
temperatures, moreover, the explanation of the isotope effect in
superconductivity and magnetic order confirms that this model successfully
describes these two quantum states.",0810.4265v1
2008/10/27,Alternating current driven instability in magnetic junctions,"An effect is considered of alternating (high-frequency) current on the
spin-valve type magnetic junction configuration. The stability with respect to
small fluctuations is investigated in the macrospin approximation. When the
current frequency is close to the eigenfrequency (precession frequency) of the
free layer, parametric resonance occurs. Both collinear configurations,
antiparallel and parallel ones, can become unstable under resonance conditions.
The antiparallel configuration can become unstable under non-resonant
conditions, also. The threshold current density amplitude is of the order of
the dc current density switching the magnetic junction.",0810.4753v1
2008/10/30,Direct Evidence for Multiferroic Magnetoelectric Coupling in 0.9BiFeO3-0.1BaTiO3,"Magnetic, dielectric and calorimetric studies on 0.9BiFeO3-0.1BaTiO3 indicate
strong magnetoelectric coupling. XRD studies reveal a very remarkable change in
the rhombohedral distortion angle and a significant shift in the atomic
positions at the magnetic Tc due to an isostructural phase transition. The
calculated polarization using Rietveld refined atomic positions scales linearly
with magnetization. Our results provide the first unambiguous evidence for
magnetoelectric coupling of intrinsic multiferroic origin in a BiFeO3 based
system.",0810.5418v1
2008/11/1,Room Temperature Ferromagnetic Semiconductor Rutile Ti1-xCoxO2-δ Epitaxial Thin Films Grown by Sputtering Method,"Room temperature ferromagnetic semiconductor rutile Ti1-xCoxO2-\delta (101)
epitaxial thin films were grown on r-sapphire substrates by a dc sputtering
method. Ferromagnetic magnetization, magnetic circular dichroism, and anomalous
Hall effect were clearly observed at room temperature in sputter-grown films
for the first time. The magnetization value is nearly as large as 3\mu B/Co
that is consistent with the high spin state Co2+ in this compound recently
established by spectroscopic methods. Consequently, its originally large
magneto-optical response is further enhanced.",0811.0073v1
2008/11/14,Almeida-Thouless Line in BiFeO3: Is Bismuth Ferrite a mean field spin glass?,"Low-temperature magnetic properties of epitaxial BiFeO3 thin films grown on
(111)-SrTiO3 substrates have been studied. ZFC and FC magnetization curves show
a large discrepency beginning at a characteristic temperature Tf that is
dependent on the magnetic-field strengh. Tf(H) varies according to the well
known de Aleimda-Thouless line (varies in Hexp(2/3)) suggesting an acentric
long rnage spin-glass behavior and mean field system.",0811.2347v1
2008/11/26,Anomalous Ferromagnetism in TbMnO3 Thin Films,"Magnetometry, x-ray, and neutron scattering have been used to study the
structural and magnetic properties of a TbMnO3 thin film grown on a [001]
SrTiO3 substrate by pulsed laser deposition. Although bulk TbMnO3 is a low
temperature antiferromagnet, magnetometry measurements indicate the presence of
low temperature ferromagnetism. Depth profiling by x-ray and polarized neutron
reflectometry reveals a net sample magnetization that is commensurate with the
film thickness, indicating that the observed ferromagnetism is not due to an
altered surface phase (such as Mn3O4), or external impurities that might give
rise to an artificial magnetic signal. Instead, these results show that the
ferromagnetism is an intrinsic property of the TbMnO3 film.",0811.4430v1
2008/12/5,A new scheme to calculate the exchange tensor and its application to diluted magnetic semiconductors,"A new scheme to calculate the exchange tensor
$\underline{\underline{J}}_{ij}$ describing in a phenomenological way the
anisotropic exchange coupling of two moments in a magnetically ordered system
is presented. The ab-initio approach is based on spin-polarised relativistic
multiple-scattering theory within the framework of spin-density functional
theory. The scheme is applied to ferromagnetic CrTe as well as the diluted
magnetic semiconductor (DMS) system Ga$_{1-x}$Mn$_{x}$As. In the later case the
results show that there is a noticeable anisotropy in the exchange coupling
present, although not as pronounced as suggested in recent theoretical
investigations.",0812.1145v1
2008/12/24,Tuning magnetic frustration of nanomagnets in triangular-lattice geometry,"We study the configuration of magnetic moments on triangular lattices of
single-domain ferromagnetic islands, examining the consequences of
magnetostatic interactions in this frustrated geometry. By varying the
island-island distance along one direction, we are able to tune the ratio of
different interactions between neighboring islands, resulting in a
corresponding variation in the local correlations between the island moments.
Unlike other artificial frustrated magnets, this lattice geometry displays
regions of ordered moment orientation, possibly resulting from a higher degree
of anisotropy leading to a reduced level of frustration.",0812.4468v1
2009/1/7,Electrically Controlled Magnetic Memory and Programmable Logic based on Graphene/Ferromagnet Hybrid Structures,"It has been shown that the combining of the electrical effect on the exchange
bias field with giant magneto-resistance effect of the graphene/ferromagnet
hybrid structures reveals a new non-volatile magnetic random access memory
device conception. In such device an electric bias realizes the writing bits
instead a magnetic field of remote word line with high energy consumption.
Interplay of two graphene mediated exchange bias fields applied to different
sides of free ferromagnet results in programable logic operations that depends
on specific realization of the structure.",0901.0926v1
2009/1/13,Spin-glass state and long-range magnetic order in Pb(Fe1/2Nb1/2)O3,"We have investigated the magnetic ground-state of the multiferroic relaxor
ferroelectric \pfn with $\mu$SR spectroscopy and neutron scattering. We find
that a transition to a partially disordered phase occurs below T=20 K that
coexists with long-range antiferromagnetic ordering. The disordered phase
resembles a spin-glass. No clustering of magnetic ions could be evidenced by
$\mu$SR so that the coexistence appears homogeneous in the sample.",0901.1816v2
2009/1/19,Magnetism in Mn delta-doped cubic GaN: density-functional theory studies,"The magnetism in 12.5% and 25% Mn delta-doped cubic GaN has been investigated
using the density-functional theory calculations. The results show that the
single-layer delta-doping and half-delta-doping structures show robust ground
state half-metallic ferromagnetism (HMF), and the double-layer delta-doping
structure shows robust ground state antiferromagnetism (AFM) with large
spin-flip energy of 479.0 meV per Mn-Mn pair. The delta-doping structures show
enhanced two-dimensional magnetism. We discuss the origin of the HMF using a
simple crystal field model. Finally, we discuss the antiferromagnet/ferromagnet
heterostructure based on Mn doped GaN.",0901.2820v1
2009/1/26,Room temperature ferromagnetism in Cr-doped hydrogenated amorphous Si films,"Ferromagnetism above room temperature was observed in Cr-doped hydrogenated
amorphous silicon films deposited by rf magnetron-sputtering. Structure
analysis reveals that films are amorphous without any detectable precipitates
up to the solubility limit 16 atomic percentages of Cr. Experimental results
suggest that hydrogenation has a dramatic influence on magnetic properties,
electrical conductivity and carrier concentration in the thin films. Pronounced
anomalous Hall effect and magnetization curve both suggest the origin of the
ferromagnetism may arises from percolation of magnetic polarons.",0901.4123v1
2009/2/13,Charge pumping and the colored thermal voltage noise in spin valves,"Spin pumping by a moving magnetization gives rise to an electric voltage over
a spin valve. Thermal fluctuations of the magnetization manifest themselves as
increased thermal voltage noise with absorption lines at the ferromagnetic
resonance frequency and/or zero frequency. The effect depends on the
magnetization configuration and can be of the same order of magnitude as the
Johnson-Nyquist thermal noise. Measuring colored voltage noise is an
alternative to ferromagnetic resonance experiments for nano-scale ferromagnetic
circuits.",0902.2389v2
2009/3/17,Electronic transport in ferromagnetic conductors with inhomogeneous magnetic order parameter -- domain-wall resistance,"We microscopically derive transport equations for the conduction electrons in
ferromagnetic materials with an inhomogeneous magnetization profile. Our
quantum kinetic approach includes elastic scattering and anisotropic spin-flip
scattering at magnetic impurities. In the diffusive limit, we calculate the
resistance through a domain wall and find that the domain-wall resistance can
be positive or negative. In the limit of long domain walls we derive analytical
expressions and compare them with existing works, which used less general
models or different theoretical frameworks.",0903.3033v2
2009/3/31,Electronic properties of hexagonal tungsten monocarbide WC with 3d impurities from first-principles calculations,"First principles FLAPW- GGA calculations have been performed to predict the
structural, electronic, cohesive and magnetic properties for hexagonal WC doped
with all 3d metals. The optimized lattice parameters, density of states,
cohesive and formation energies have been obtained and analyzed for ternary
solid solutions with nominal compositions W0.875M0.125C (where M = Sc, Ti, ...,
Ni, Cu). In addition, the magnetic properties of these solid solutions have
been examined, and magnetization has been established for W0.875Co0.125C.",0903.5387v1
2009/3/31,"Structural, electronic and magnetic properties of ether carbides (Fe3W3C, Fe6W6C, Co3W3C and Co6W6C) from first principles calculations","First-principles FLAPW-GGA calculations have been performed with the purpose
to determine the peculiarities of the structural, electronic, magnetic
properties and stability for a family of related ether carbides M3W3C and M6W6C
(where M= Fe and Co). The geometries of all phases were optimized and their
structural parameters, theoretical density, cohesive and formation energies,
total and partial densities of states, atomic magnetic moments have been
obtained and analyzed in comparison with available theoretical and experimental
data.",0903.5390v1
2009/3/31,Re-analysing the phase sequence in Eu0.8Y0.2MnO3,"To clarify the controversy concerning the ferroelectricity of the lower
temperature magnetic phases of Eu0.8Y0.2MnO3, hence its multiferroic character,
we have studied in detail the temperature dependence of the electric
polarization. The existence of a spontaneous polarization in 30K < T < 22K,
provides clear evidence for the ferroelectric character of the re-entrant
magnetic phase, stable in that temperature range. Both lower temperature
magnetic phases allow easily-induced electric polarization, which actually mask
any spontaneous polarization.",0903.5471v1
2009/5/1,Finite electric field effects in the large perpendicular magnetic anisotropy surface Pt/Fe/Pt(001),"We have investigated crystalline magnetic anisotropy in the electric field
(EF) for the Fe-Pt surface which have a large perpendicular anisotropy, by
means of the first-principles approach. The anisotropy is reduced linearly with
respect to the inward EF, associated with the induced spin density around the
Fe layer. Although the magnetic anisotropy energy (MAE) density reveals the
large variation around the atoms, the intrinsic contribution to the MAE is
found to mainly come from the Fe layer.",0905.0060v1
2009/5/10,The high temperature Jahn-Teller transition in LaMn7O12,"A first order structural Jahn-Teller transition at T_{JT} = 650 K has been
recently reported for the quadruple perovskite LaMn7O12 . We have carried out
magnetization and transport measurements below and above T_{JT} in order to
investigate the effect of the transition. Electrical conduction turns out to be
polaronic, changing from non-adiabatic to adiabatic through the transition.
Magnetic behavior can be described by non-interacting Mn3+ ions below T_{JT},
while above T_{JT} it is of questionable interpretation. The effect of thermal
cycling on as grown samples of different purity degree also allowed us to
clarify the intrinsic magnetic response of LaMn7O12 at lower temperatures.",0905.1500v1
2009/5/14,Single-Spin Microscope with Sub-Nanoscale Resolution Based on Optically Detected Magnetic Resonance,"We summarize our new scanning magnetic 3-D imaging system. This scanning
system uses optically detected magnetic resonance in a single nitrogen vacancy
center in a diamond nanocrystal. The theoretical analysis and the first
experimental demonstrations have proved that this method has single spin
sensitivity and a sub-nanoscale spatial resolution at room temperature.",0905.2361v1
2009/5/18,Charge and spin Hall effect in graphene with magnetic impurities,"We point out the existence of finite charge and spin Hall conductivities of
graphene in the presence of a spin orbit interaction (SOI) and localized
magnetic impurities. The SOI in graphene results in different transverse forces
on the two spin channels yielding the spin Hall current. The magnetic
scatterers act as spin-dependent barriers, and in combination with the SOI
effect lead to a charge imbalance at the boundaries. As indicated here, the
charge and spin Hall effects should be observable in graphene by changing the
chemical potential close to the gap.",0905.2785v2
2009/5/19,First-principles theory of magnetically induced ferroelectricity in TbMnO3,"We study the polarization induced via spin-orbit interaction by a magnetic
cycloidal order in orthorhombic TbMnO3 using first-principle methods. The case
of magnetic spiral lying in the b-c plane is analyzed, in which the pure
electronic contribution to the polarization is shown to be small. We focus our
attention on the lattice-mediated contribution, and study it's dependence on
the Coulomb interaction parameter U in the LDA+U method and on the wave-vector
of the spin spiral. The role of the spin-orbit interaction on different sites
is also analyzed.",0905.3033v1
2009/5/21,Current oscillations in a superlattice under non-quantizing electric and magnetic fields,"We calculate the current density in a semiconductor superlattice with
parabolic miniband under crossed non-quantizing electric and magnetic fields.
The Corbino disk geometry is considered. The current-voltage curve contains
oscillations with period proportional to the magnetic field. The possibility is
shown of the negative absolute conductivity. The Ampere-Gauss characteristics
also contain overshoots under high enough electric fields. In all cases, the
peaks smear with temperature rising.",0905.3457v2
2009/6/12,Six-fold configurational anisotropy and magnetic reversal in nanoscale Permalloy triangles,"Six-fold configurational anisotropy was studied in Permalloy triangles, in
which the shape symmetry order yields two energetically non-degenerate
micromagnetic configurations of the spins, the so-called ""Y"" and ""buckle""
states. A twelve pointed switching astroid was measured using magneto-optical
experiments and successfully reproduced numerically, with different polar
quadrants identified as specific magnetic transitions, thereby giving a
comprehensive view of the magnetic reversal in these structures. A detailed
analysis highlighted the necessity to include the physical rounding of the
structures in the simulations to account for the instability of the Y state.",0906.2322v1
2009/6/22,Pinning and switching of magnetic moments in bilayer graphene,"We examine the magnetic properties of the localized states induced by lattice
vacancies in bilayer graphene with an unrestricted Hartree-Fock calculation. We
show that with realistic values of the parameters and for experimentally
accessible gate voltages we can have a magnetic switching between an
unpolarized and a fully polarized system.",0906.4126v1
2009/6/23,Multiferroic oxides-based flash-memory and spin-field-effect transistor,"We propose a modified spin-field-effect transistor fabricated in a two
dimensional electron gas (2DEG) formed at the surface of multiferroic oxides
with a transverse helical magnetic order. The topology of the oxide local
magnetic moments induces a resonant momentum-dependent effective spin-orbit
interaction acting on 2DEG. We show that spin polarization dephasing is
strongly suppressed which is crucial for functionality. The carrier spin
precession phase depend linearly on the magnetic spiral helicity. The latter is
electrically controllable by virtue of the magento-electric effect. We also
suggest a flash-memory device based on this structure.",0906.4210v1
2009/6/29,Influence of Demagnetization Effect on Giant Magneto Impedance of soft Ferromagnetic Metal,"The large change in electromagnetic impedance in ferromagnetic state of soft
magnetic metals in presence of biasing magnetic field is associated with change
in screening of electromagnetic field. The screening depends on the
permeability of the metal. Apart from dependence on intrinsic properties of
metal the permeability depends on size of the sample. It is observed that the
decrease in MI in amorphous ferromagnetic ribbon of Fe40Ni40B20 alloy is large
for long sample whereas corresponding change is small for short one with same
biasing field. As intrinsic magnetic properties and bias field are same and the
demagnetization factor increases with reduction of length of the sample the
reduction of MI effect is associated with demagnetization field.",0906.5203v1
2009/6/29,Clamping of ferroelectric and ferromagnetic domain walls in conical spiral magnets,"We study the structure of domain walls in multiferroic magnets with the
conical spiral ordering. We formulate a simple spin model which has a conical
spiral ground state in absence of magnetic anisotropies. We find a transition
from the regime where ferromagnetic and ferroelectric domain walls are clamped
to the regime where they are decoupled and derive a continuum model describing
rotation of the spiral plane at the domain wall. The importance of these
results for the switching phenomena observed in CoCr2O4 is discussed.",0906.5298v1
2009/6/30,Photoinduced magnetism in the ferromagnetic semiconductors,"We study the enhancement of the magnetic transition temperature $T_c$ due to
incident light in ferromagnetic semiconductors such as EuS. The photoexcited
carriers mediate an extra ferromagnetic interaction due to the coupling with
the localized magnetic moments. The Hamiltonian consists of a Heisenberg model
for the localized moments and an interaction term between the photoexcited
carriers and the localized moments. The model predicts a small enhancement of
the transition temperature in semi-quantitative agreement with the experiments.",0906.5514v1
2009/6/30,Theory of vortex states in magnetic nanodisks with induced Dzyaloshinskii-Moriya interactions,"Vortex states in magnetic nanodisks are essentially affected by
surface/interface induced Dzyaloshinskii-Moriya interactions. Within a
micromagnetic approach we calculate the equilibrium sizes and shape of the
vortices as functions of magnetic field, the material and geometrical
parameters of nanodisks. It was found that the Dzyaloshinskii-Moriya coupling
can considerably increase sizes of vortices with ""right"" chirality and suppress
vortices with opposite chirality. This allows to form a bistable system of
homochiral vortices as a basic element for storage applications.",0906.5552v2
2009/7/8,Spherical neutron polarimetry study of hysteresis in multiferroic MnWO4,"The electric-field dependence of the magnetic structure of multiferroic MnWO4
has been investigated using spherical neutron polarimetry as a function of
temperature. The application of an electric field drives the magnetic structure
to a single chiral domain. The magnitude of the field required to do this is
shown to increase with temperature. The link between the magnetic order and
electric polarization is further demonstrated.",0907.1361v1
2009/7/16,Long-lived spin memory in Mn-doped GaAs: Time resolved study,"We study the electron spin dynamics in p-type GaAs doped with magnetic Mn
acceptors by means of time-resolved pump-probe and photoluminescence
techniques. Measurements in transverse magnetic fields show a long spin
relaxation time of 20 ns that can be uniquely related to electrons. Application
of weak longitudinal magnetic fields above 100 mT extends the spin relaxation
times up to microseconds which is explained by suppression of the
Bir-Aronov-Pikus spin relaxation for the electron on the Mn acceptor.",0907.2851v1
2009/7/21,Memristive switching of MgO based magnetic tunnel junctions,"Here we demonstrate that both, tunnel magneto resistance (TMR) and resistive
switching (RS), can be observed simultaneously in nano-scale magnetic tunnel
junctions. The devices show bipolar RS of 6 % and TMR ratios of about 100 %.
For each magnetic state, multiple resistive sates are created depending on the
bias history which provides a method for multi-bit data storage and logic. The
electronic transport measurements are discussed in the framework of a
memristive system. Differently prepared MgO barriers are compared to gain
insight into the switching mechanism.",0907.3684v1
2009/8/10,Phase diagram of an anisotropic frustrated ferromagnetic spin-1/2 chain in a magnetic field: a density matrix renormalization group study,"We study the phase diagram of a frustrated spin-1/2 ferromagnetic chain with
anisotropic exchange interactions in an external magnetic field, using the
density matrix renormalization group method. We show that an easy-axis
anisotropy enhances the tendency towards multimagnon bound states, while an
easy-plane anisotropy favors chirally ordered phases. In particular, a moderate
easy-plane anisotropy gives rise to a quantum phase transition at intermediate
magnetization. We argue that this transition is related to the finite-field
phase transition experimentally observed in the spin-1/2 compound LiCuVO_4.",0908.1281v2
2009/8/20,Quantum Transport in a Biphenyl Molecule: Effects of Magnetic Flux,"Electron transport properties of a biphenyl molecule are studied based on the
Green's function formalism. The molecule is sandwiched between two metallic
electrodes, where each benzene ring is threaded by a magnetic flux $\phi$. The
results are focused on the effects of the molecule to electrode coupling
strength and the magnetic flux $\phi$. Our numerical study shows that, for a
fixed molecular coupling, the current amplitude across the bridge can be {\em
regulated} significantly just by tuning the flux $\phi$. This aspect may be
utilized in designing nano-scale electronic circuits.",0908.2884v1
2009/8/25,Electronic shells of Dirac fermions in graphene quantum rings in a magnetic field,"We present results of tight binding calculations demonstrating existence of
degenerate electronic shells of Dirac Fermions in narrow, charge neutral
graphene quantum rings. We predict removal of degeneracy with finite magnetic
field. We show, using a combination of tight binding and configuration
interaction methods, that by filling a graphene ring with additional electrons
this carbon based structure with half-filled shell acquires a finite magnetic
moment.",0908.3693v1
2009/8/26,Local magnetism and magnetoelectric effect in HoMnO3 studied with muon-spin relaxation,"We present the results of muon-spin relaxation (muSR) measurements on the
hexagonal manganite HoMnO3. Features in the temperature-dependent relaxation
rate, lambda, correlate with the magnetic transitions at 76 K, 38 K and 34 K.
The highest temperature transition, associated with the ordering of Mn3+
moments has the largest effect on lambda. The application of a static electric
field of E=10^4 Vm^-1 below T=50 K causes a small reduction in lambda which is
suggestive of coupling between ferroelectric and magnetic domain walls in the
ordered state of the material.",0908.3782v1
2009/8/31,Microwave screening by conduction currents in thin magnetic films: application in stripline broadband FMR,"Ferromagnetic resonance in conducting magnetic bilayers was studied using
microstrip transducers. It was found that excitation or suppression of standing
spin waves could be achieved through enhanced inhomogeneity of eddy currents in
the bilayer caused by finite thickness. This effect is observable in films with
thicknesses below the magnetic skin depth and can be used to study standing
spin wave modes in heterostructures.",0908.4443v2
2009/11/8,Nonequilibrium dynamical ferromagnetism of interacting Single-Molecule Magnets,"We propose a nonequilibrium Monte Carlo (MC) approach to explore
nonequilibrium dynamical ferromagnetism of interacting single molecule magnets
(SMMs). Both quantum spin tunneling and thermally activated spin reversal are
successfully implemented in the same MC simulation framework. Applied to a
typical example, this simulation method satisfactorily reproduces experimental
magnetization curves with experimental parameters. Our results show that both
quantum and classical effects are essential to determine the hysteresis
behaviors. This method is effective and reliable to gain deep insights into
SMMs.",0911.1539v1
2009/11/10,Direct and inverse measurement of thin films magnetostriction,"Two techniques of measurements of thin film magnetostriction are compared:
direct, when changes of the substrate curvature caused by the film
magnetization are controlled, and inverse (""indirect""), when the modification
of the magnetic anisotropy induced by the substrate deformation (usually
bending) is measured. We demonstrate how both the elastic strength of the
substrate and the effective magneto-mechanical coupling between the substrate
deformation and magnetic anisotropy of the film depend on different conditions
of bending. Equations to be used for magnetostriction value determination in
typical cases are given and critical parameters for the corresponding
approximations are identified.",0911.1914v1
2009/11/20,Transport Currents and Persistent Currents in Solids: Orbital Magnetism and Hall Effect of Dirac Electrons,"Features of electronic currents in solids are truly diverse depending on
circumstances, e.g. non-equilibrium transport currents leading to dissipation
and persistent currents flowing in equilibrium. Differences between these
currents may be clear in many cases, while there are some where they are not.
Results of theoretical studies on the latter cases will be introduced briefly
focusing on the inter-band effects of magnetic fields in orbital magnetisms and
Hall effects of Dirac electrons.",0911.3956v1
2009/12/12,Induction in a von Karman flow driven by ferromagnetic impellers,"We study magnetohydrodynamics in a von K\'arm\'an flow driven by the rotation
of impellers made of material with varying electrical conductivity and magnetic
permeability. Gallium is the working fluid and magnetic Reynolds numbers of
order unity are achieved. We find that specific induction effects arise when
the impeller's electric and magnetic characteristics differ from that of the
fluid. Implications in regards to the VKS dynamo are discussed.",0912.2429v1
2009/12/29,Temperature oscillations of magnetization observed in nanofluid ferromagnetic graphite,"We report on unusual magnetic properties observed in the nanofluid
room-temperature ferromagnetic graphite (with an average particle size of
l=10nm). More precisely, the measured magnetization exhibits a low-temperature
anomaly (attributed to manifestation of finite size effects below the quantum
temperature) as well as pronounced temperature oscillations above T=50K
(attributed to manifestation of the hard-sphere type pair correlations between
ferromagnetic particles in the nanofluid).",0912.5350v1
2009/12/30,Work Function of Strongly Magnetized Neutron Star Crustal Matter and the Associated Magneto-Sphere,"Following an extremely interesting idea \cite{R1}, published long ago, the
work function at the outer crust region of a strongly magnetized neutron star
is obtained using relativistic version of Thomas-Fermi type model. In the
present scenario, the work function becomes anisotropic; the longitudinal part
is an increasing function of magnetic field strength, whereas the transverse
part diverges. An approximate estimate of the electron density in the
magnetosphere due to field emission and photo emission current, from the polar
cap region are obtained.",0912.5446v1
2010/1/30,Thermoelectrically Controlled Spin-Switch,"The search for novel spintronic devices brings about new ways to control
switching in magnetic thin-films. In this work we experimentally demonstrate a
device based on thermoelectrically controlled exchange coupling. The read out
signal from a giant magnetoresistance element is controlled by exchange
coupling through a weakly ferromagnetic Ni-Cu alloy. This exchange coupling is
shown to vary strongly with changes in temperature, and both internal Joule
heating and external heating is used to demonstrate magnetic switching. The
device shows no degradation upon thermal cycling. Ways to further optimize the
device performance are discussed. Our experimental results show a new way to
thermoelectrically control magnetic switching in multilayers.",1002.0089v1
2010/2/26,Electronic Ferroelectricity in a Dimer Mott Insulator,"Motivated from recent experiments in kappa-(BEDT-TTF)_2Cu_2(CN)_3, dielectric
and magnetic properties in a dimer-Mott insulator are studied. We derive the
effective Hamiltonian where the number of electron per dimer is taken to be
one. Charge and magnetic structures in finite temperature are obtained by using
the mean-field and Monte-Carlo methods. Magnetic and ferroelectric phases are
exclusive with each other. Dielectric fluctuation is remarkable near a phase
boundary between dimer-Mott phase and ferroelectric phase. Implications of the
present results for kappa-(BEDT-TTF)_2Cu_2(CN)_3 are discussed.",1002.4971v1
2010/3/10,Fe and N self-diffusion in non-magnetic Fe:N,"Fe and N self-diffusion in non-magnetic FeN has been studied using neutron
reflectivity. The isotope labelled multilayers, FeN/57Fe:N and Fe:N/Fe:15N were
prepared using magnetron sputtering. It was remarkable to observe that N
diffusion was slower compared to Fe while the atomic size of Fe is larger
compared to N. An attempt has been made to understand the diffusion of Fe and N
in non-magnetic Fe:N.",1003.2069v1
2010/3/28,Giant magnetic broadening of ferromagnetic resonance in a GMR Co/Ag/Co/Gd quadlayer,"Both magnetic-resonance damping and the giant magnetoresistance effect have
been predicted to be strongly affected by the local density of states in thin
ferromagnetic films. We employ the antiferromagnetic coupling between Co and Gd
to provide a spontaneous change from parallel to antiparallel alignment of two
Co films. A sharp increase in magnetic damping accompanies the change from
parallel to antiparallel alignment, analogous to resistivity changes in giant
magnetoresistance.",1003.5344v1
2010/4/23,Anisotropic Nature of Work Function in Strong Quantizing Magnetic Field,"Following an extremely interesting idea \cite{R1}, published long ago, the
work function associated with the emission of ultra-relativistic electrons from
magnetically deformed metallic crystal of astrophysical relevance is obtained
using relativistic version of Thomas-Fermi type model. In the present scenario,
surprisingly, the work function becomes anisotropic; the longitudinal part is
an increasing function of magnetic field strength, whereas the transverse part
diverges.",1004.4102v2
2010/4/29,Effects of a Conducting Sphere Moving Through a Gradient Magnetic Field,"We examine several conducting spheres moving through a magnetic field
gradient. An analytical approximation is derived and an experiment is conducted
to verify the analytical solution. The experiment is simulated as well to
produce a numerical result. Both the low and high magnetic Reynolds number
regimes are studied. Deformation of the sphere is noted in the high Reynolds
number case. It is suggested that this deformation effect could be useful for
designing or enhancing present protection systems against space debris.",1004.5412v1
2010/6/9,Interaction of iron clusters (Fe_n; n <= 6) with a divacancy in graphene,"In this work, we have studied the chemical and magnetic interactions of Fe_n;
n <= 6, clusters with a divacancy site in a graphene sheet by ab-initio density
functional calculations. Our results show significant chemical interactions
between the cluster and graphene. As a result, a complex distribution of
magnetic moments appear on the distorted Fe clusters in presence of graphene
and results in a lower average magnetic moments compared to the free clusters.
The presence of cluster also prevents the formation of 5-8-5 ringed structure
known to exhibit in a graphene sheet having a divacancy defect. The clusters
induce electronic states primarily of d-character near the Fermi level.",1006.1910v1
2010/7/2,Limits on intrinsic magnetism in graphene,"We have studied magnetization of graphene nanocrystals obtained by sonic
exfoliation of graphite. No ferromagnetism is detected at any temperature down
to 2 K. Neither do we find strong paramagnetism expected due to the massive
amount of edge defects. Rather, graphene is strongly diamagnetic, similar to
graphite. Our nanocrystals exhibit only a weak paramagnetic contribution
noticeable below 50K. The measurements yield a single species of defects
responsible for the paramagnetism, with approximately one magnetic moment per
typical graphene crystallite.",1007.0423v2
2010/7/6,Hybrid Improper Ferroelectricity: A Mechanism for Controllable Magnetization-Polarization Coupling,"First-principles calculations are presented for the layered perovskite
Ca$_3$Mn$_2$O$_7$. The results reveal a rich set of coupled structural,
magnetic and polar domains in which oxygen octahedron rotations induce
ferroelectricity, magnetoelectricity and weak-ferromagnetism. The key point is
that the rotation distortion is a combination of two non-polar modes with
different symmetries. We use the term ""hybrid"" improper ferroelectricity to
describe this phenomenon and discuss how control over magnetism is achieved
through these functional antiferrodistortive octahedron rotations.",1007.1003v2
2010/7/13,Ratchet propagation of a magnetic domain wall in a single magnetic wire with quantum interference,"Quantum interference incorporating spatially asymmetric potential profiles is
realized experimentally to manipulate a magnetic domain wall (DW) into a single
multilayered wire whose spacer has a thickness gradient for generating
asymmetrical interlayer exchange coupling from side to side. We demonstrate
experimentally how to guide a DW in a micron-scale ferromagnetic wire without
reflection symmetry of the interlayer exchange coupling. This is the ratcheting
of a DW in a form of ratchet potential using quantum interference. The
experimental results can be described well by numerical simulations considering
spatially asymmetric potential profiles due to quantum interference.",1007.2166v1
2010/7/20,Spin and Valley Splittings in Multilayered Massless Dirac Fermion System,"The inter-layer magnetoresistance in a multilayered massless Dirac fermion
system, $\alpha$-(BEDT-TTF)$_2$I$_3$, under hydrostatic pressure was
investigated. We succeeded in detecting the zero-mode (n=0) Landau level and
its spin splitting in the magnetic field normal to the 2D plane. We
demonstrated that the effective Coulomb interaction in the magnetic field
intensifies the spin splitting of zero-mode Landau carriers. At temperatures
below 2K, magnetic fields above several Tesla break the twofold valley
degeneracy.",1007.3342v2
2010/8/24,"Complete symmetry analyses of the surface-induced piezomagnetic, piezoelectric and linear magnetoelectric effects","The impact of the surface on the magnetic symmetry is studied. It is shown
how symmetry breaking transforms the ""seeding"" 90 bulk magnetic classes, which
include 66 piezomagnetic classes and 58 magnetoelectric classes, into the 21
surface-induced magnetic classes, which all are piezomagnetic, piezoelectric
and 19 of them are linear magnetoelectric. So, the new piezomagnetic,
piezoelectric properties and linear magnetoelectric coupling should appear in
nanomaterials, which are absent in the bulk.",1008.4070v1
2010/9/8,Observation of tunable exchange bias in Sr$_2$YbRuO$_6$,"The double perovskite compound, Sr$_{2}$YbRuO$_{6}$, displays reversal in the
orientation of magnetic moments along with negative magnetization due to an
underlying magnetic compensation phenomenon. The exchange bias (EB) field below
the compensation temperature could be the usual negative or the positive
depending on the initial cooling field. This EB attribute has the potential of
getting tuned in a preselected manner, as the positive EB field is seen to
crossover from positive to negative value above $T_{\mathrm{comp}}$.",1009.1554v1
2010/9/24,Parametric excitation of a magnetic nanocontact by a microwave field,"We demonstrate that magnetic oscillations of a current-biased magnetic
nanocontact can be parametrically excited by a microwave field applied at twice
the resonant frequency of the oscillation. The threshold microwave amplitude
for the onset of the oscillation decreases with increasing bias current, and
vanishes at the transition to the auto-oscillation regime. The parametrically
excited oscillation mode is the same as the one in the auto-oscillation regime,
enabling studies of both the passive and the active dynamics of the oscillator.
Theoretical analysis shows that measurements of parametric excitation provide
quantitative information about the relaxation rate, the spin transfer
efficiency, and the nonlinearity of the nanomagnetic system.",1009.4837v1
2010/9/28,Ferromagnetic Behavior of High Purity ZnO nanoparticles,"ZnO nanoparticles with Wurtzite structure were prepared by chemical methods
at low temperature in aqueous solution. Nanoparticles are in the range from
about 10 to 30 nm. Ferromagnetic properties were observed from 2 K to room
temperature and above. Magnetization vs temperature, M(T) and isothermal
measurements M(H) were determined. The coercive field clearly shows
ferromagnetism above room temperature. The chemical synthesis, structural
defects in the bulk related to oxygen vacancies are the main factors for the
observed magnetic behavior.
  PACS numbers: 61.46.Hk Nanocrystals, 75.50.Pp Magnetic semiconductors,
81.05.Dz II-VI semiconductors",1009.5641v1
2010/10/1,"Mapping the magnetic exchange interactions from first principles: Anisotropy anomaly and application to Fe, Ni, and Co","Mapping the magnetic exchange interactions from model Hamiltonian to density
functional theory is a crucial step in multi-scale modeling calculations.
Considering the usual magnetic force theorem but with arbitrary rotational
angles of the spin moments, a spurious anisotropy in the standard mapping
procedure is shown to occur provided by bilinear-like contributions of high
order spin interactions. The evaluation of this anisotropy gives a hint on the
strength of non-bilinear terms characterizing the system under investigation.",1010.0273v2
2010/10/12,Coherent spin-current oscillations in transverse magnetic fields,"We address the coherence of the dynamics of spin-currents with components
transverse to an external magnetic field for the spin-1/2 Heisenberg chain. We
study current autocorrelations at finite temperatures and the real-time
dynamics of currents at zero temperature. Besides a coherent Larmor
oscillation, we find an additional collective oscillation at higher
frequencies, emerging as a coherent many-magnon effect at low temperatures.
Using numerical and analytical methods, we analyze the oscillation frequency
and decay time of this coherent current-mode versus temperature and magnetic
field.",1010.2351v2
2010/10/21,The effect of Dzyaloshinskii-Moriya interactions on the phase diagram and magnetic excitations of SrCu2(BO3)2,"The orthogonal dimer structure in the SrCu2(BO3)2 spin-1/2 magnet provides a
realization of the Shastry-Sutherland model. Using a dimer-product variational
wave function, we map out the phase diagram of the Shastry-Sutherland model
including anisotropies. Based on the variational solution, we construct a
bond-wave approach to obtain the excitation spectra as a function of magnetic
field. The characteristic features of the experimentally measured neutron and
ESR spectra are reproduced, like the anisotropy induced zero field splittings
and the persistent gap at higher fields.",1010.4476v2
2010/11/1,Optical control of magnetization of micron-size domains in antiferromagnetic NiO single crystals,"We propose Raman-induced collinear difference-frequency generation (DFG) as a
method to manipulate dynamical magnetization. When a fundamental beam
propagates along a threefold rotational axis, this coherent second-order
optical process is permitted by angular momentum conservation through the
rotational analogue of the Umklapp process. As a demonstration, we
experimentally obtained polarization properties of collinear magnetic DFG along
a [111] axis of a single crystal of antiferromagnetic NiO with micro
multidomain structure, which excellently agreed with the theoretical
prediction.",1011.0327v1
2010/12/2,Hybrid metal-dielectric ring resonators for optical magnetic metamaterials down to ultraviolet range,"In this paper, we derive a model from Maxwell equations for the magnetic
resonance of split-ring resonators. Using this model we revisit the scaling of
split-ring resonators. Inspired by our model, we propose a new type of
split-hybrid metal-dielectric ring resonator, of which the ring is made
composed of moderately high index dielectric material (e.g. SiC, TiO2, ZnS)
(for the major portion), while and metal (e.g. Ag) fills the gap. Such a new
magnetic metamaterial is able to overcome the saturation problem of split-ring
resonatorssaturation-free and therefore is able to operate at short wavelength
down to ultraviolet range.",1012.0400v2
2010/12/23,On the derivation of the magnetocaloric properties in ferrimagnetic spinel Mn3O4,"Large magnetocaloric effect has been observed in Mn3O4 around its
ferrimagnetic transition at TN = 42.75 K. Field-induced isothermal entropy
changes (\DeltaS) were derived from both magnetic and calorimetric techniques.
The maximum |\DeltaS| and adiabatic temperature change ({\Delta}Tad) at TN are
11 J kg-1 K-1 and 1.9 K, respectively, for a magnetic field change of 20 kOe.
Moreover, it is found that the complex magnetic phase transitions taking place
below TN produce additional -but smaller- features on \DeltaS(T).",1012.5161v1
2011/1/21,Cr doped III-V nitrides: potential candidates for spintronics,"Studies of Cr-doped III-V nitrides, dilute magnetic alloys, in the
zinc-blende crystal structure are presented. The objective of the work is to
investigate half-metallicity in Al(0.75)Cr(0.25)N, Ga(0.75)Cr(0.25)N and
In(0.75)Cr(0.25)N for their possible application in the spin based electronic
devices. The calculated spin polarized band structures, electronic properties
and magnetic properties of these compounds reveal that Al0.75Cr0.25N and
Ga0.75Cr0.25N are half-metallic dilute magnetic semiconductors while
In0.75Cr0.25N is metallic in nature. The present theoretical predictions
provide evidence that some Cr doped III-V nitrides can be used in spintronics
devices.",1101.4059v1
2011/2/4,Anisotropy in transport and magnetic properties of K0.64Fe1.44Se2,"We report a study of anisotropy in transport and magnetic properties of
K0.64Fe1.44Se2.00 single crystals. The anisotropy in resistivity is up to one
order of magnitude between 1.8 K and 300 K. Magnetic susceptibility exhibits
weak temperature dependence in the normal state with decrease in temperature
with no significant anomalies. The lower critical fields Hc1 of
K0.64Fe1.44Se2.00 are only about 3 Oe and the anisotropy of Hc1,c/Hc1,ab is
about 1. The critical currents for H||ab and H||c are about 10-10^3 A/cm2,
smaller than in iron pnictides and in FeTe_{1-x}Se_{x} and nearly isotropic.",1102.1010v3
2011/2/11,Oscillations of the Nernst coefficient in bismuth,"We calculate the magnetic-field dependence (oscillations) of the Nernst
coefficient in bismuth at low temperatures for the case when the magnetic field
is directed along the trigonal axis of the crystal. In the calculations we take
into account the scattering of the electrons and holes in bismuth on impurities
and the dependence of this scattering on the magnetic field. The results of
these calculations are compared with the experimental data recently published.",1102.2328v1
2011/2/11,Magnetic dipolar ordering and quantum phase transition in Fe8 molecular magnet,"We show that a crystal of mesoscopic Fe8 single molecule magnets is an
experimental realization of the Quantum Ising Phase Transition (QIPT) model in
a transverse field, with dipolar interactions. Quantum annealing has enabled us
to explore the QIPT at thermodynamical equilibrium. The phase diagram and
critical exponents we obtain are compared to expectations for the mean-field
QIPT Universality class.",1102.2447v1
2011/2/18,Perpendicular magnetic anisotropy of full-Heusler films in Pt/Co2FeAl/MgO trilayers,"We report on perpendicular magnetic anisotropy (PMA) in a Pt/Co2FeAl/MgO
sandwiched structure with a thick Co2FeAl layer of 2-2.5 nm. The PMA is
thermally stable that the anisotropy energy density Ku is 1.3{\times}106
erg/cm3 for the structure with 2 nm Co2FeAl after annealing at 350 oC. The
thicknesses of Co2FeAl and MgO layers greatly affect the PMA. Our results
provide an effective way to realize relative thick perpendicularly magnetized
Heusler alloy films.",1102.3802v1
2011/3/11,Magnetic Properties of Pr0.7Ca0.3MnO3/SrRuO3 Superlattices,"High-quality Pr0.7Ca0.3MnO3/SrRuO3 superlattices were fabricated by pulsed
laser deposition and were investigated by high-resolution transmission electron
microscopy and SQUID magnetometry. Superlattices with orthorhombic and
tetragonal SrRuO3 layers were investigated. The superlattices grew coherently;
in the growth direction Pr0.7Ca0.3MnO3 layers were terminated by MnO2- and
SrRuO3 layers by RuO2-planes. All superlattices showed antiferromagnetic
interlayer coupling in low magnetic fields. The coupling strength was
significantly higher for orthorhombic than for tetragonal symmetry of the
SrRuO3 layers. The strong interlayer exchange coupling in the superlattice with
orthorhombic SrRuO3 layers led to a magnetization reversal mechanism with a
partially inverted hysteresis loop.",1103.2299v1
2011/3/24,Effect of nonadiabatic spin transfer torque on domain wall resonance frequency and mass,"The dynamics of a magnetic domain wall in a semi circular nanowire loop is
studied by an analytical model and micromagnetic simulations. We find a damped
sinusoidal oscillation of the domain wall for small displacement angles around
its equilibrium position under an external magnetic field in the absence of
currents. By studying the effect of current induced nonadiabatic spin transfer
torque on the magnetic domain wall resonance frequency and mass, a red shift is
found in the resonance frequency and domain wall mass increases by increasing
the ratio of nonadiabatic spin torque to adiabatic contribution above 1.",1103.4670v1
2011/4/2,Role of Ni-Mn hybridization in magnetism of martensitic state of Ni-Mn-In shape memory alloys,"Extended X-ray Absorption Fine Structure (EXAFS) studies on
Ni$_{50}$Mn$_{25+x}$In$_{25-x}$ have been carried out at Ni and Mn K edge as a
function of temperature. Thermal evolution of nearest neighbor Ni-Mn and Mn-Mn
bond distances in the martensitic phase give a clear evidence of a close
relation between structural and magnetic degrees of freedom in these alloys. In
particular, the study highlights the role of Ni 3d - Mn 3d hybridization in the
magnetism of martensitic phase of these alloys.",1104.0297v1
2011/4/12,A simple model for calculating magnetic nanowire domain wall fringing fields,"We present a new approach to calculating magnetic fringing fields from
head-to-head type domain walls in planar magnetic nanowires. In contrast to
calculations based on micromagnetically simulated structures the descriptions
of the fields are for the most part analytic and thus significantly less time
and resource intensive. The models presented begin with an intuitive picture of
domain walls, which is built upon in a phenomenological manner. Comparisons
with fields calculated using micromagnetic methods show good quantitative
agreement.",1104.2249v2
2011/5/13,"Effects of Annealing Conditions on the Microstructure and Magnetic Properties of the Perovskite Manganite, La0.75Sr0.25MnO3","The effects of annealing conditions upon the microstructure and the magnetic
properties of the colossal magnetoresistive manganite La0.75Sr0.25MnO3 have
been investigated. Increasing the annealing temperature and time of annealing
is seen to increase the size of crystallites within the samples. The
spontaneous magnetic moment per formula unit and the Curie temperature, as
obtained from Arrott plot analysis, are observed to depend upon the average
size of crystallites.",1105.2700v1
2011/5/16,Magnetic imaging of shipwrecks,"The ferromagnetic material in a shipwreck on the seabed causes a modification
to the earth's magnetic field which can be measured at the surface. Proton
magnetometer measurements at the surface are used to locate wrecks. Here I
discuss how to interpret such data to explore the shape and orientation of the
shipwreck on the seabed. I give details of how to model shipwrecks and deduce
the magnetic signal that results. I also discuss how to analyse data in a more
general way. As examples, I present and analyse data on the shipwrecks of
YSTROOM and BOUBOULINA (ex COLONEL LAMB).",1105.3136v1
2011/5/24,Aharonov-Bohm Exciton Absorption Splitting in Chiral Specific Single-Walled Carbon Nanotubes in Magnetic Fields of up to 78 T,"The Ajiki-Ando (A-A) splitting of single-walled carbon nanotubes(SWNT)
originating from the Aharanov-Bohm effect was observed in chiral specific SWNTs
by the magneto-absorption measurements conducted at magnetic fields of up to 78
T. The absorption spectra from each chirality showed clear A-A splitting of the
$E_{11}$ optical excitonic transitions. The parameters of both the dark-bright
exciton energy splitting and the rate of A-A splitting in a magnetic field were
determined for the first time from the well-resolved absorption spectra.",1105.4711v1
2011/5/31,An Automated Home Made Low Cost Vibrating Sample Magnetometer,"The design and operation of a homemade low cost vibrating sample magnetometer
is described here. The sensitivity of this instrument is better than 10-2 emu
and found to be very efficient for the measurement of magnetization of most of
the ferromagnetic and other magnetic materials as a function of temperature
down to 77 K and magnetic field upto 800 Oe. Both M(H) and M(T) data
acquisition are fully automated employing computer and Labview software",1105.6313v1
2011/6/6,Rise and fall of defect induced ferromagnetism in SiC single crystals,"6H-SiC (silicon carbide) single crystals containing VSi-VC divacancies are
investigated with respect to magnetic and structural properties. We found that
an initial increase of structural disorder leads to pronounced ferromagnetic
properties at room temperature. Further introduction of disorder lowers the
saturation magnetization and is accompanied with the onset of lattice
amorphization. Close to the threshold of full amorphization, also divacancy
clusters are formed and the saturation magnetization nearly drops to zero.",1106.0966v1
2011/6/13,Magnetostatic interactions between magnetic nanotubes,"The investigation of interactions between magnetic nanotubes is complex and
often involves substantial simplifications. In this letter an analytical
expression for the magnetostatic interaction, taking into account the geometry
of the tubes, has been obtained. This expression allows for the definition of a
critical vertical separation for relative magnetization between nanotubes and
can be used for tailoring barcode-type nanostructures with prospective
applications such as biological separation and transport.",1106.2372v1
2011/6/13,On the theory of indirect exchange in EuO,"We present the calculations of the Curie temperature and magnetization of
doped EuO both in the absence and in the presence of external magnetic field.
The calculations were performed both for the free electrons model and for the
model with finite electron band width. Both models give similar results for the
magnetization, close to Brillouin function.",1106.2465v3
2011/6/16,Evidence of defect-induced ferromagnetism in ZnFe$_{2}$O$_{4}$ thin films,"X-ray absorption near-edge and grazing incidence X-ray fluorescence
spectroscopy are employed to investigate the electronic structure of
ZnFe$_{2}$O$_{4}$ thin films. The spectroscopy techniques are used to determine
the non-equilibrium cation site occupancy as a function of depth and oxygen
pressure during deposition and its effects on the magnetic properties. It is
found that low deposition pressures below 10$^{-3}$ mbar cause iron
superoccupation of tetrahedral sites without Zn$^{2+}$ inversion, resulting in
an ordered magnetic phase with high room temperature magnetic moment.",1106.3128v1
2011/6/22,Electric spectroscopy of vortex states and dynamics in magnetic disks,"Spin-polarized radio frequency (RF) currents and RF-Oersted fields resonantly
excite a magnetic vortex core confined in a micron-scale soft magnetic disk. In
this study, we measured the rectifying voltage spectra caused by the
anisotropic magnetoresistance oscillation due to the gyration of the vortex
with different polarity and chirality. The measured spectra are presented such
that we can determine the vortex properties and strength of the spin torques
and Oersted field accurately and directly through analytical calculation.",1106.4516v2
2011/7/3,Terahertz magnetoelectric response via electromagnons in magnetic oxides,"Terahertz magnetic resonance driven by the light electric field, now referred
to as electromagnon, has stimulated interest due to its strong candidate for
future spin-electronics. One unique characteristic of electromagnons is the
terahertz magnetochromism, a color change by external magnetic field, as
recently demonstrated in the hexaferrite. By taking perovskite manganites and
hexaferrite as model cases, the current understating of the electromagnon
activity is discussed in terms of the symmetric exchange mechanism.",1107.0428v1
2011/7/16,Inverse magnetocaloric effect in ferromagnetic Sm0.6-xLaxSr0.4MnO3 due to 4f-3d exchange interaction,"We report magnetic and magnetocaloric properties of Sm0.6-xLaxSr0.4MnO3 (x =
0-0.6). A rapid increase around TC and an anomalous peak at a temperature
T*<<TC occur in magnetization which lead to normal and inverse magnetocaloric
effects (MCE), respectively. While TC increases with increasing x (TC=118 K for
x=0 and TC=363 K for x=0.6), T* increases from 30 K (x=0) to 120 K (x=0.4) and
then decreases to 105 K (x=0.5). The \DeltaSm reaches +1.07 Jkg-1K-1 at 10 K
and -4 Jkg-1K-1 around TC in x=0.4 for \Delta H=5T. The inverse MCE is
attributed to antiferromagnetic coupling between Sm-4f and Mn-3d magnetic
moments.",1107.3233v1
2011/8/1,Double-k phase of the Dzyaloshinskii-Moriya helimagnet Ba2CuGe2O7,"Neutron diffraction is used to re-investigate the magnetic phase diagram of
the noncentrosymmetric tetragonal antiferromagnet Ba2CuGe2O7. A novel
incommensurate double-k magnetic phase is detected near the
commensurate-incommensurate phase transition. This phase is stable only for
magnetic field closely aligned with the 4-fold symmetry axis. The results
emphasize the inadequacy of existing theoretical models for this unique
material, and points to additional terms in the Hamiltonian or lattice effects.",1108.0432v1
2011/8/4,Tight-binding description of Landau levels of graphite in tilted magnetic fields,"The electronic structure of Bernal-stacked graphite subject to tilted
magnetic fields is studied theoretically. The minimal nearest-neighbor
tight-binding model with the Peierls substitution is employed to describe the
structure of Landau levels. We show that while the orbital effect of the
in-plane component of the magnetic field is negligible for massive Dirac
fermions in the vicinity of the K point of the graphite Brillouin zone, at the
H point it leads to the experimentally observable splitting of Landau levels,
which grows approximately linearly with the in-plane field intensity.",1108.1072v2
2011/9/9,Incommensurate spin-density wave in two-dimensional Hubbard model,"We consider the magnetic phase diagram of the two-dimensional Hubbard model
on a square lattice. We take into account both spiral and collinear
incommensurate magnetic states. The possibility of phase separation of spiral
magnetic phases is taken into consideration as well. Our study shows that all
the listed phases appear to be the ground state at certain parameters of the
model. Relation of the obtained results to real materials, e.g. Cu-based
high-temperature superconductors, is discussed.",1109.2033v2
2011/9/27,Ferroelectric charge order stabilized by antiferromagnetism in multiferroic LuFe2O4,"Neutron diffraction measurements on multiferroic LuFe2O4 show changes in the
antiferromagnetic (AFM) structure characterized by wavevector q = (1/3 1/3 1/2)
as a function of electric field cooling procedures. The increase of intensity
from all magnetic domains and the decrease in the 2D magnetic order observed
below the Neel temperature are indicative of increased ferroelectric charge
order. The AFM order changes the dynamics of the CO state, and stabilizes it.
It is determined that the increase in electric polarization observed at the
magnetic ordering temperature is due to a transition from paramagnetic 2D
charge order to AFM 3D charge order.",1109.5762v1
2011/10/17,Downtrack response of differential reader for high density magnetic recording,"The downtrack responses of a differential reader to various magnetic patterns
have been investigated micromagnetically. The differential signals can well
discriminate the ""0"" and ""1"" readback bits and the waveforms obtained resemble
the counterparts for longitudinal media or for perpendicular media after
differentiation. Pulse shapes are found Gaussian. With decreasing head media
spacing, free layer thickness, and gap length, PW50 roughly linearly decreases
and the maximum signal exponentially increases. These properties, together with
small inter-symbol interference, are essential for future high density magnetic
recording.",1110.3576v1
2011/11/7,Monte Carlo Study of Magnetic Resistivity in Semiconducting MnTe,"We investigate in this paper properties of the spin resistivity in the
magnetic semiconducting MnTe of NiAs structure. MnTe is a crossroad
semiconductor with a large band gap. It is an antiferromagnet with the N\'eel
temperature around 310K. Due to this high N\'eel temperature, there are many
applications using its magnetic properties. The method we use here is the Monte
Carlo simulation in which we take into account the interaction between
itinerant spins and lattice Mn spins. Our results show a very good agreement
with experiments on the shape of the spin resistivity near the N\'eel
temperature.",1111.1507v1
2011/11/23,Rashba spin torque in an ultrathin ferromagnetic metal layer,"In a two-dimensional ferromagnetic metal layer lacking inversion symmetry,
the itinerant electrons mediate the interaction between the Rashba spin-orbit
interaction and the ferromagnetic order parameter, leading to a Rashba spin
torque exerted on the magnetization. Using Keldysh technique, in the presence
of both magnetism and a spin-orbit coupling, we derive a spin diffusion
equation that provides a coherent description to the diffusive spin dynamics.
The characteristics of the spin torque and its implication on magnetization
dynamics are discussed in the limits of large and weak spin-orbit coupling.",1111.5466v1
2011/11/25,Magnetism in Transition metal doped Cubic SiC,"We report here our study on SiC doped with transition metals using first
principle density functional theory calculations. We have considered cubic SiC
with 3d transition metals as substitutional impurities for Si and C site
separately. Cubic SiC doped with Cr, Mn, show ferromagnetism whereas with Sc,
Ti, V and Co show site dependency of magnetic properties. Rests of the
impurities are found to be non-magnetic.",1111.5905v1
2011/12/12,Temperature dependence of microwave voltage emission associated to spin-transfer induced vortex oscillation in magnetic tunnel junction,"The temperature dependence of a vortex-based nano-oscillator induced by spin
transfer torque (STVO) in magnetic tunnel junctions (MTJ) is considered. We
obtain emitted signals with large output power and good signal coherence. Due
to the reduced non-linearities compared to the uniform magnetization case, we
first observe a linear decrease of linewidth with decreasing temperature.
However, this expected behavior no longer applies at lower temperature and a
bottom limit of the linewidth is measured.",1112.2643v1
2011/12/13,Exact cloaking of uniform magnetic fields with a superconductor-magnetic bilayer,"The experimental realization of cloaks for electromagnetic fields has been
possible only in reduced schemes because of extreme material conditions
required in exact cloaks. Here we analytically demonstrate that a simple
arrangement of two concentric homogeneous and isotropic layers with different
permeabilities can keep a uniform externally applied magnetic field
unperturbed. If the inner layer is superconducting, the device prevents
exterior fields from entering an enclosed region, which represents a case for
an exact cloaking of uniform fields. When the applied field is inhomogeneous
the cloaking property is reduced but may be optimized by changing the thickness
of the layers.",1112.2847v1
2011/12/28,Spectral signatures of magnetic Bloch oscillations in one-dimensional easy-axis ferromagnets,"Domain walls in a one-dimensional gapped easy-axis ferromagnet can exhibit
Bloch oscillations in an applied magnetic field. We investigate how exchange
couplings modify this behavior within an approximation based on noninteracting
domain-wall bound states. In particular, we obtain analytical results for the
spectrum and the dynamic structure factor, and show where in momentum space to
expect equidistant energy levels, the Wannier-Zeeman ladder, which is the
spectral signature of magnetic Bloch oscillations. We compare our results to
previous calculations employing a single domain-wall approximation, and make
predictions relevant for the material $CoCl2\cdot2H2O$.",1112.6195v2
2012/1/17,Spin wave excitation in magnetic insulators by spin-transfer torque,"We study the excitation of spin waves in magnetic insulators by the
current-induced spin-transfer torque. We predict preferential excitation of
surface spin waves induced by an easy-axis surface anisotropy with critical
current inversely proportional to the penetration depth and surface anisotropy.
The surface modes strongly reduce the critical current and enhance the
excitation power of the current-induced magnetization dynamics.",1201.3442v1
2012/1/18,Ginzburg-Landau slopes of the anisotropic upper critical magnetic field and band parameters in the superconductor (TMTSF)2ClO4,"We theoretically determine the Ginzburg-Landau slopes of the anisotropic
upper critical magnetic field in a quasi-one-dimensional superconductor and
correct the previous works on this issue. By using the experimentally measured
values of the Ginzburg-Landau slopes in the superconductor (TMTSF)$_2$ClO$_4$,
we determine band parameters of its electron spectrum. Our main result is that
the so-called quantum dimensional crossover has to happen in this material in
magnetic fields, $H = 3-8 \ T$, which are much lower than the previously
assumed. We discuss how this fact influences metallic and superconducting
properties of the (TMTSF)$_2$ClO$_4$.",1201.3882v1
2012/1/23,Micromagnetic Simulations for Spin Transfer Torque in Magnetic Multilayers,"We investigate the spin transfer torque (STT) in the magnetic multilayer
structures with micromagnetic simulations. We implement the STT contribution
for the magnetic multilayer structures in addition to the
Landau-Lifshitz-Gilbert (LLG) micromagnetic simulators. Not only the Sloncewski
STT term, the zero, first, and second order field- like terms are also
considered, and the effects of the Oersted field by the current are addressed.
We determine the switching current densities of the free layer with the
exchange biased synthetic ferrimagnetic reference layers for various cases.",1201.4707v1
2012/1/27,Dynamics of Successive Minor Hysteresis Loops,"Cumulative growth of successive minor hysteresis loops in Co/Pd multilayers
with perpendicular anisotropy was studied in the context of time dependent
magnetization reversal dynamics. We show that in disordered ferromagnets, where
magnetization reversal involves nucleation, domains' expansion and
annihilation, differences between the time dependencies of these processes are
responsible for accumulation of nuclei for rapid domain expansion, for the
asymmetry of forward and backward magnetization reversals and for the
respective cumulative growth of hysteresis loops. Loops stop changing and
become macroscopically reproducible when populations of upward and downward
nucleation domains balance each other and the respective upward and downward
reversal times stabilize.",1201.5791v1
2012/2/1,"Confined one-way mode at magnetic domain wall for broadband high-efficiency one-way waveguide, splitter and bender","We find the one-way mode can be well-confined at the magnetic domain wall by
the photonic bandgap of gyromagnetic bulk material. Utilizing the well-confined
one-way mode at the domain wall, we demonstrate the photonic one-way waveguide,
splitter and bender can be realized with simple structures, which are predicted
to be high-efficiency, broadband, frequency-independent, reflection-free,
crosstalk-proof and robustness against disorder. Additionally, we find that the
splitter and bender in our proposal can be transformed into each other with
magnetic control, which may have great potential applications in all photonic
integrated circuit.",1202.0081v1
2012/3/23,Magnetic dispersion and anisotropy in multiferroic BiFeO3,"We have determined the full magnetic dispersion relations of multiferroic
BiFeO3. In particular, two excitation gaps originating from magnetic
anisotropies have been clearly observed. The direct observation of the gaps
enables us to accurately determine the Dzyaloshinskii-Moriya (DM) interaction
and the single ion anisotropy. The DM interaction supports a strong
magneto-electric coupling in this compound.",1203.5294v3
2012/4/7,Electric field formulation for thin film magnetization problems,"We derive a variational formulation for thin film magnetization problems in
type-II superconductors written in terms of two variables, the electric field
and the magnetization function. A numerical method, based on this formulation,
makes it possible to accurately compute all variables of interest, including
the electric field, for any value of the power in the power law current-voltage
relation characterizing the superconducting material. For high power values we
obtain a good approximation to the critical state model solution. Numerical
simulation results are presented for simply and multiply connected films, and
also for an inhomogeneous film.",1204.1609v1
2012/4/22,A Transfer Matrix Approach to Electron Transport in Graphene through Arbitrary Electric and Magnetic Potential Barriers,"A transfer matrix method is presented for solving the scattering problem for
the quasi one-dimensional massless Dirac equation applied to graphene in the
presence of an arbitrary inhomogeneous electric and perpendicular magnetic
field. It is shown that parabolic cylindrical functions, which have previously
been used in literature, become inaccurate at high incident energies and low
magnetic fields. A series expansion technique is presented to circumvent this
problem. An alternate method using asymptotic expressions is also discussed and
the relative merits of the two methods are compared.",1204.4868v1
2012/4/26,Unexpected resonant response in [Fe(001)/Cr(001)]_(10) /MgO(001) multilayers in magnetic field,"We observed unexpected resonant response in [Fe/Cr]_(10) multilayers
epitaxially grown on MgO(100) substrates which exists only when both ac current
and dc magnetic field are simultaneously applied. The magnitude of the
resonances is determined by the multilayer magnetization proving their
intrinsic character. The reduction of interface epitaxy leads to non-linear
dependence of the magnitude of resonances on the alternating current density.
We speculate that the existence of the interface transition zone could
facilitate the subatomic vibrations in thin metallic films and multilayers
grown on bulk insulating substrates.",1204.5942v1
2012/5/8,Ligand effects on the electronic structure and magnetism of magnetite surfaces,"We address the effect of functionalization on the electronic and magnetic
properties of magnetite surface as an indicator of the same properties in
nanoparticles too big for a direct ab-initio approach. Using well-established
methods and references (namely LDA+U on magnetite surfaces) we could verify the
validity of our approach, and using two typical ligands, dopamine and citrate,
namely pi and sigma electron donors, we could predict that those ligands would
induce a different change in the electronic properties of the systems, but in
both cases an enhancement of magnetization.",1205.1842v1
2012/5/12,Ultrafast Time-Resolved Faraday Rotation in EuO Thin Films,"We have investigated the ultrafast spin dynamics in EuO thin films by
time-resolved Faraday rotation spectroscopy. The photoinduced magnetization is
found to be increased in a transient manner, accompanied with subsequent
demagnetization. The dynamical magnetization enhancement showed a maximum
slightly below the Curie temperature with prolonged tails toward both lower and
higher temperatures and dominates the demagnetization counterpart at 55 K. The
magnetization enhancement component decays in ~1 ns. The realization of the
transient collective ordering is attributable to the enhancement of the f-d
exchange interaction.",1205.2818v2
2012/6/27,"Electronic, magnetic properties and correlation effects in the layered quaternary iron oxyselenide Na2Fe2Se2O from first principles","By means of the first-principle calculations, we have investigated
electronic, magnetic properties and correlation effects for the newly
discovered layered oxyselenide Na2Fe2Se2O. Our results reveal that the electron
correlations in the Fe 3d bands promote a transition of Na2Fe2Se2O from
magnetic metallic or half-metallic states to the antiferromagnetic
Mott-insulating state. In addition, the bonding picture in Na2Fe2Se2O is
described as an anisotropic mixture of ionic and covalent contributions.",1206.6182v1
2012/6/30,Thermodynamically stable equal-module exchange magnetic classes,"It is shown that within the framework of application of the general scheme of
the Landau theory of phase transitions to the magnetic crystals the equilibrium
and stable equal-module exchange structures automatically appears in addition
to the other magnetic states. No additional conditions such as the existence of
the Andreev-Marchenko spin scalar are needed. Furthermore, they are not
constrained by the dimensionality of irreducible representation as it typically
takes place for the Andreev-Marchenko-type structures.",1207.0050v1
2012/7/4,Evidence for Intra-Unit-Cell magnetic order in Bi2Sr2CaCu2O8+d,"Polarized elastic neutron scattering measurements have been performed in the
bilayer copper oxide system Bi2Sr2CaCu2O8+d, providing evidence for an intra
unit cell (IUC) magnetic order inside the pseudo-gap state. That shows time
reversal symmetry breaking in that state as already reported in Bi2Sr2CaCu2O8+d
through dichroism in circularly polarized photoemission experiments. The
magnetic order displays the same characteristic features as the one previously
reported for monolayer HgBa2CuO4+d and bilayer YBa2Cu3O6+x, demonstrating that
this genuine phase is ubiquitous of the pseudo-gap of high temperature copper
oxide materials.",1207.1038v1
2012/7/17,Ultrafast dynamical path for the switching of a ferrimagnet after femtosecond heating,"Ultrafast laser-induced magnetic switching in rare earth, transition metal
ferrimagnetic alloys has recently been reported to occur by ultrafast heating
alone. Using atomistic simulations and a ferrimagnetic Landau-Lifshitz-Bloch
formalism, we demonstrate that for switching to occur it is necessary that
angular momentum is transferred from the longitudinal to transverse
magnetization components. This dynamical path leads to magnetization switching
and subsequent ultrafast precession caused by the inter-sublattice exchange
field on the nanoscale.",1207.4092v2
2012/7/19,Magnetic field enhanced structural instability in EuTiO_{3},"EuTiO_{3} undergoes a structural phase transition from cubic to tetragonal at
T_S = 282 K which is not accompanied by any long range magnetic order. However,
it is related to the oxygen ocathedra rotation driven by a zone boundary
acoustic mode softening. Here we show that this displacive second order
structural phase transition can be shifted to higher temperatures by the
application of an external magnetic field (increased by 4 K for mu_{0}H = 9 T).
This observed field dependence is in agreement with theoretical predictions
based on a coupled spin-anharmonic-phonon interaction model.",1207.4698v1
2012/8/11,Planar arrays of magnetic nanocrystals embedded in GaN,"Single planar arrays of Ga(x)Fe(4-x)N magnetic nanocrystals embedded in GaN
have been fabricated in an epitaxial process. The phase of the nanocrystals and
their epitaxial relationship with the host matrix are studied $via$
high-resolution transmission electron microscopy and high-resolution x-ray
diffraction. By changing the growth parameters and mode, the crystallographic
phase and chemical composition of the nanocrystals can be varied on demand. In
view of the different magnetic properties of the various phases, applications
in room-temperature ferromagnetic as well as antiferromagnetic spintronic
devices are envisaged.",1208.2356v1
2012/9/26,Ferromagnetic InMnAs on InAs Prepared by Ion Implantation and Pulsed Laser Annealing,"Ferromagnetic InMnAs has been prepared by Mn ion implantation and pulsed
laser annealing. The InMnAs layer reveals a saturated magnetization of 2.6
mu_B/Mn at 5 K and a perpendicular magnetic anisotropy. The Curie temperature
is determined to be 46 K, which is higher than those in previous reports with
similar Mn concentrations. Ferromagnetism is further evidenced by the large
magnetic circular dichroism.",1209.5865v1
2012/10/5,Two Models Relevant to the Interaction of a Point Charge and a Magnetic Moment,"An understanding of the interaction of a point charge and a magnetic moment
is crucial for understanding the experiments involving electromagnetic momentum
carried by permeable materials as well as the experimentally-observed
Aharonov-Bohm and Aharonov-Casher phase shifts. Here we present two simple
models for a magnetic moment which have vastly different interactions with a
distant point charge. It is suggested that a satisfactory theoretical
understanding of the interaction is still lacking and that the ""hidden
momentum"" interpretation has been introduced into the textbook literature
prematurely.",1210.1777v1
2012/10/21,Quadratic-in-magnetization permittivity and conductivity tensor in cubic crystals,"We present diagonal and off-diagonal elements of the permittivity and
conductivity tensor up to the second order in magnetization for cubic crystals.
We express all tensor elements as a function of a general sample orientation,
for arbitrary magnetization direction and for (001), (011) and (111) surface
orientations. Finally, we discuss, how to extract values of quadratic elements
G of the second order permittivity tensors for different sample surface
orientations from both experiment and ab-initio calculations.",1210.5737v2
2012/11/1,Spin Seebeck effect in antiferromagnets and compensated ferrimagnets,"We theoretically investigate the spin Seebeck effect (SSE) in
antiferromagnets and ferrimagnets, and show that the SSE vanishes in
antiferromagnets but survives in ferrimagnets even at the magnetization
compensation point despite the absence of its saturation magnetization. The
non-vanishing SSE in ferrimagnets stems from two non-degenerate magnons. We
demonstrate that the magnitude of the SSE in ferrimagnets is unchanged across
the magnetization compensation point.",1211.0123v1
2012/11/6,Angular dependence of the Hall effect of lsmo films,"We find that the Hall effect resistivity ($\rho_{xy}$) of thin films of
\lsmo\ varies as a function of the angle $\theta$ between the applied magnetic
field and the film normal as $\rho_{xy}=a\cos \theta + b\cos 3\theta$, where
$|b|$ increases with increasing temperature and decreases with increasing
magnetic field. We find that the angular dependence of the longitudinal
resistivity and the magnetization cannot fully explain the surprising term $b$,
suggesting it is a manifestation of an intrinsic transport property.",1211.1160v1
2012/11/6,Defect-mediated spin relaxation and dephasing in graphene,"A principal motivation to develop graphene for future devices has been its
promise for quantum spintronics. Hyperfine and spin-orbit interactions are
expected to be negligible in single-layer graphene. Spin transport experiments,
on the other hand, show that graphene's spin relaxation is orders of magnitude
faster than predicted. We present a quantum interference measurement that
disentangles sources of magnetic and non-magnetic decoherence in graphene.
Magnetic defects are shown to be the primary cause of spin relaxation, while
spin-orbit interaction is undetectably small.",1211.1417v1
2012/11/15,Optical energy optimization at the nanoscale by near-field interference,"Employing plasmonic antennas for subdiffraction focusing of light on
recording media requires to take into account the complete structure of the
medium, including dielectric cover layers. We find, with finite difference time
domain simulations, that optical energy transfer to the magnetic recording
layer is most efficient for an off-resonant antenna. Furthermore, we show that
the focal spot in the magnetic film is well below the diffraction limit, making
nanoscale all-optical magnetic data recording achievable.",1211.3532v1
2012/11/16,Parallel-leaky capacitance equivalent circuit model for MgO magnetic tunnel junctions,"The capacitance of MgO based magnetic tunnel junctions (MTJs) has been
observed to be magnetic field dependent. We propose an equivalent circuit for
the MTJs with a parallel-leaky capacitance (Cl) across the series combination
of geometric and interfacial capacitance. The analysis of junctions with
different tunneling magnetoresistance values suggests higher Cl for low TMR
junctions. Using Cole-Cole plots the capacitive nature of MTJs is manifested.
Fitting with Maxwell-Wagner capacitance model validates the RC parallel network
model for MTJs and the extracted field dependent parameters match with the
experimental values.",1211.3808v1
2012/11/18,Controlling the Spin Torque Efficiency with Ferroelectric Barriers,"Non-equilibrium spin-dependent transport in magnetic tunnel junctions
comprising a ferroelectric barrier is theoretically investigated. The exact
solutions of the free electron Schr\""odinger equation for electron tunneling in
the presence of interfacial screening are obtained by combining Bessel and Airy
functions. We demonstrate that the spin transfer torque efficiency, and more
generally the bias-dependence of tunneling magneto- and electroresistance, can
be controlled by switching the ferroelectric polarization of the barrier. This
effect provides a supplementary way to electrically control the current-driven
dynamic states of the magnetization and related magnetic noise in spin transfer
devices.",1211.4196v1
2012/11/30,Ab initio study of magnetic anisotropy in cobalt doped zinc oxide with electron-filling,"Based on first-principles calculation, it has been predicted that the
magnetic anisotropy energy (MAE) in Co-doped ZnO (Co:ZnO) depends on
electron-filling. Results show that the charge neutral Co:ZnO presents a ""easy
plane"" magnetic state. While modifying the total number of electrons, the easy
axis rotates from in-plane to out-of-plane. The alternation of the MAE is
considered to be the change of the ground state of Co ion, resulting from the
relocating of electrons on Co d-orbitals with electron-filling.",1211.7287v2
2012/12/4,"Drastic changes in electronic, magnetic, mechanical and bonding properties from Zr2CoH5 to Mg2CoH5","Despite similarities in formulae and local structures of Zr2CoH5 and Mg2CoH5,
they are shown from ab initio calculations to present contrasted electronic,
magnetic, mechanical and bonding properties due to the environment of cobalt
with hydrogen characterized by negatively charged CoHx entities (x = 4, 5
resp.) and to the chemical nature of Zr versus Mg. Zr2CoH5 is found more
cohesive, harder and less ductile than Mg2CoH5. High density of states at the
Fermi level arises from out-of-plane non-bonding Co-dz2 in Zr2CoH5 which is
found metallic ferromagnet in the ground state, in contrast with non magnetic
and insulating Mg2CoH5.",1212.0698v1
2012/12/17,Anomalous Hall Effect in perpendicularly magnetized Mn(_{3-x})Ga thin films,"Mn$_{3-x}$Ga (x = 0.1, 0.4, 0.7) thin films on MgO and SrTiO$_3$ substrates
were investigated with magnetic anisotropy perpendicular to the film plane. An
anomalous Hall-effect was observed for the tetragonal distorted lattice in the
crystallographic D0$_{22}$ phase. The Hall resistivity $\varrho_{xy}$ was
measured in a temperature range from 20 to 330 K. The determined skew
scattering and side jump coefficients are discussed with regard to the film
composition and used substrate and compared to the crystallographic and
magnetic properties.",1212.4019v1
2012/12/18,The reversal of magnetization driven by the Dzyaloshinskii-Moriya interaction(DMI) in perovskite Bi2FeMnO6,"Ab initio calculations show that the coupling between
antiferrodistortive(AFD) distortions and magnetization in perovskite Bi2FeMnO6
is prohibited to make magnetization rotate as on-site Coulomb interaction($U$)
is larger than 2.7 eV, where anomalies in antiferromagnetic(AFM) vectors and
band gap varying with on-site Coulomb interaction can be observed. This
coupling is attributed to the antisymmetric Dzyaloshinskii-Moriya
interaction(DMI) driven by the eg-eg states AFM interaction and charge
redistribution with respect to different AFD distortions.",1212.4350v1
2013/1/4,Ferromagnetic bubble clusters in Y$_{0.67}$Ca$_{0.33}$MnO$_3$ thin films,"We studied the ferromagnetic topology in a Y$_{0.67}$Ca$_{0.33}$MnO$_3$ thin
film with a combination of magnetic force microscopy and magnetization
measurements. Our results show that the spin-glass like behavior, reported
previously for this system, could be attributed to frustrated interfaces of the
ferromagnetic clusters embedded in a non-ferromagnetic matrix. We found
temperature dependent changes of the magnetic topology at low temperatures,
which suggests a non-static Mn$^{3+}$/Mn$^{4+}$ ratio.",1301.0678v1
2013/1/17,Imaging the antiferromagnetic to ferromagnetic first order phase transition of FeRh,"The antiferromagnetic (AFM) to ferromagnetic (FM) first order phase
transition of an epitaxial FeRh thin-film has been studied with x-ray magnetic
circular dichroism using photoemission electron microscopy. The FM phase is
magnetized in-plane due to shape anisotropy, but the magnetocrystalline
anisotropy is negligible and there is no preferred in-plane magnetization
direction. When heating through the AFM to FM phase transition the nucleation
of the FM phase occurs at many independent nucleation sites with random domain
orientation. The domains subsequently align to form the final FM domain
structure. We observe no pinning of the FM domain structure.",1301.4164v1
2013/1/22,"Structural, magnetic, and nanoscale switching properties of BiFeO3 thin films grown by pulsed electron deposition","We report the epitaxial growth of BiFeO3 by pulsed electron deposition and
the resulting crystal quality, magnetic and nanoscale switching properties.
X-ray diffraction shows high quality single phase, epitaxial (001) oriented
films grown on SrTiO3 (001) substrates. Both field and temperature dependent
magnetic properties reveal an antiferromagnetic behavior of the films. For the
film with a SrRuO3 bottom electrode, an exchange-enhancement effect between
antiferromagnetic BiFeO3 and ferromagnetic SrRuO3 was observed at low
temperature. The piezoelectric force microscopy and switching spectroscopy
measurements demonstrate the local domain switching process and suggest that
the BiFeO3 films are high quality ferroelectrics.",1301.5237v1
2013/1/31,Electric-field switching magnetization and spin transfer in ultrathin BiFeO3 film,"First-principles density-functional theory calculations show switching
magnetization by 90 degree can be achieved in ultrathin BFO film by applying
external electric-field. Up-spin carriers appear to the surface with positive
field while down-spin ones to the negative field surface, arising from the
redistribution of Fe-t2g orbital. The half-metallic behavior of Fe-3d states in
the surface of R phase film makes it a promising candidate for AFM/FM bilayer
heterostructure possessing electric-field tunable FM magnetization reversal and
opens a new way towards designing spintronic multiferroics. The interface
exchange-bias effect in this BFO/FM bilayer is mainly driven by the Fe-t2g
orbital reconstruction, as well as spin transferring and rearrangement.",1301.7559v1
2013/2/6,Quantum Monte Carlo study of low dimensional magnetic system,"Monte Carlo simulations are performed for the S = 1/2 XY and ferro- and
antiferromagnetic Heisenberg model in two dimensions using the loop algorithm.
Thermodynamic properties of all these models are investigated in wide
temperature range. The energy, specific heat, susceptibility and other
parameters are given as function of temperature and the Trotter number. The
comparison of calculated thermodynamic quantities with theoretical and with
experimental data are given. It is shown that our results are in good agreement
with them.",1302.1279v1
2013/2/15,Magnetoelectric Effect driven by Magnetic Domain Modification in LuFe2O4,"Magneto-capacitance effect was investigated using the impedance spectroscopy
on single crystals of LuFe2O4. The intrinsic impedance response could be
separated from the interfacial response and showed a clear hysteresis loop
below TFerri ~ 240 K under the magnetic field. The neutron diffraction
experiment under the magnetic field proves the origin of dielectric property
related to the motion of nano-sized ferromagnetic domain boundary. These
results imply that the modification of the microscopic domain structure is
responsible for the magnetoelectric effect in LuFe2O4.",1302.3661v1
2013/3/27,Magnetism driven ferroelectricity above liquid nitrogen temperature in Y2CoMnO6,"We report multiferroic behavior in double perovskite Y2CoMnO6 with
ferroelectric transition temperature Tc = 80K. The origin of ferroelectricity
is associated with magnetic ordering of Co2+ and Mn4+ moments in a
up-up-down-down arrangement. The saturation polarization and magnetization are
estimated to be 65 uC/m2 and 6.2 Bohr magneton/f.u. respectively. The
magnetoelectric coupling parameter, on the other hand, is small as a 5 Tesla
field suppresses the electric polarization by only ~8%. This is corroborated
with observed hysteretic behaviour at 5K that remains unsaturated even upto 7
Tesla. A model based on exchange-striction is proposed to explain the observed
high temperature ferroelectricity.",1303.6921v1
2013/4/30,Is magnetic chiral dichroism feasible with electron vortices?,"We discuss the feasibility of detecting magnetic transitions with focused
electron vortex probes, suggested by selection rules for the magnetic quantum
number. We theoretically estimate the dichroic signal strength in the L$_{2,3}$
edge of the ferromagnetic d metals. It is shown that under realistic
conditions, the dichroic signal is undetectable for nanoparticles larger than
~1 nm. This is confirmed by a key experiment with nanometer sized vortices.",1304.7976v3
2013/5/7,Spin Wave Excitation in Magnetic Insulator Thin Films by Spin-Transfer Torque,"We describe excitation of dipole-exchange spin waves in insulating magnetic
thin films by spin current injection at the surface of the film. An easy-axis
magnetic surface anisotropy can induce a non-chiral surface spin wave mode with
penetration depth inversely proportional to the strength of the surface
anisotropy, which strongly reduces the critical current and enhances the
excitation power. The importance of the interface spin wave modes on the
excitation spectrum is reduced by spin pumping, which depends on the quality of
the interface as expressed by the spin mixing conductance.",1305.1364v2
2013/5/22,Electric control of the magnetization in BiFeO$_3$/LaFeO$_3$ superlattices,"First-principles techniques are used to investigate the behavior of
BiFeO$_{3}$/LaFeO$_{3}$ perovskite oxide superlattices epitaxially grown on a
(001)-SrTiO$_3$ substrate. The calculations show that 1/1 superlattices exhibit
a $Pmc2_1$ ground state combining a trilinear coupling of one polar and two
oxygen rotational lattice modes, and weak ferromagnetism. The microscopic
mechanism allowing one to manipulate the magnetization with an electric field
in such systems is presented and its dependence on strain and chemical
substitution is discussed. BiFeO$_{3}$/LaFeO$_{3}$ artificial superlattices
appear to be good candidates to achieve electric switching of magnetization at
room temperature.",1305.5093v1
2013/5/23,Absolute cross-section normalization of magnetic neutron scattering data,"We discuss various methods to obtain the resolution volume for neutron
scattering experiments, in order to perform absolute normalization on inelastic
magnetic neutron scattering data. Examples from previous experiments are given.
We also try to provide clear definitions of a number of physical quantities
which are commonly used to describe neutron magnetic scattering results,
including the dynamic spin correlation function and the imaginary part of the
dynamic susceptibility. Formulas that can be used for general purposes are
provided and the advantages of the different normalization processes are
discussed.",1305.5521v1
2013/6/14,Magnetic moment suppression in Ba3CoRu2O9: hybridization effect,"An unusual orbital state was recently proposed to explain the magnetic and
transport properties of Ba$_3$CoRu$_2$O$_9$ [Phys. Rev. B. {\bf 85}, 041201
(2012)]. We show that this state contradicts to the first Hund's rule and does
not realize in the system under consideration because of a too small
crystal-field splitting in the $t_{2g}$ shell. A strong suppression of the
local magnetic moment in Ba$_3$CoRu$_2$O$_9$ is attributed to a strong
hybridization between the Ru 4$d$ and O 2$p$ states.",1306.3333v1
2013/7/2,Size Dependence of Domain Pattern Transfer in Multiferroic Heterostructures,"Magnetoelectric coupling in multiferroic heterostructures can produce large
lateral modulations of magnetic anisotropy enabling the imprinting of
ferroelectric domains into ferromagnetic films. Exchange and magnetostatic
interactions within ferromagnetic films oppose the formation of such domains.
Using micromagnetic simulations and a 1-D model, we demonstrate that competing
energies lead to the breakdown of domain pattern transfer below a critical
domain width. Moreover, rotation of the magnetic field results in abrupt
transitions between two scaling regimes with different magnetic anisotropy.",1307.0605v2
2013/7/11,Ultra-Low-Intensity Magneto-Optical and Mechanical Effects in Metal Nanocolloids,"We theoretically and numerically investigate the linear and nonlinear
magneto-optical contributions to the refractive index of metal nanospheres. The
analysis is in good agreement with the experimental extinction spectra of gold
nanocolloid solutions, with threshold magnetic fields less than 1 mT when
illuminated with light intensities less than 1 W/cm^2. Plasmonic current loops
and vortex power flows provide a new framework for the dynamical interaction
between material magnetization, light polarization and nano-surfaces. The
photo-induced magneto-optical interaction of non-magnetic metal nanocolloids
imparts significant, non-negligible torque forces in nanofluids.",1307.3188v1
2013/7/18,Spin correlated dielectric memory and rejuvenation in relaxor ferroelectric CuCrS2,"CuCrS2, a Heisenberg antiferromagnet with layered edge sharing triangular
lattice, exhibits a spiral magnetic order. Dielectric (E) and polarization
studies show magnetoelectric (ME) coupling at Neel temperature (T_N=38 K) where
simultaneous dielectric and magnetic long range order occur. The compound shows
a diffused ferroelectric (FE) transition and slow relaxation dynamics above
T_N, indicative of relaxor FE behavior. Interestingly, memory effect and
magnetic field induced rejuvenation are also observed in E, establishing
cooperative glassy dynamics and ME coupling even above T_N. We discuss the role
of geometrical frustration and metal ligand hybridization for these unusual
properties.",1307.4859v1
2013/7/18,Analog of Fishtail Anomaly in Plastically Deformed Graphene,"By introducing a strain rate generated pseudo-electric field, we discuss a
magnetic response of a plastically deformed graphene. Our results demonstrate
the appearance of dislocation induced paramagnetic moment in a zero applied
magnetic field. More interestingly, it is shown that in the presence of the
magnetoplastic effect, the resulting magnetization exhibits typical features of
the so-called fishtail anomaly (previously observed in superconductors). The
estimates of the model parameters suggest quite an optimistic possibility to
experimentally realize the predicted phenomena in plastically deformed
graphene.",1307.4946v1
2013/7/22,Analytical expression for the harmonic Hall voltages in evaluating spin orbit torques,"Solid understanding of current induced torques is key to the development of
current and voltage controlled magnetization dynamics in ultrathin magnetic
heterostructures. A versatile technique is needed to evaluate such torques in
various systems. Here we examine the adiabatic (low frequency) harmonic Hall
voltage measurement that has been recently developed to study current induced
effective field that originate from the spin orbit effects. We analytically
derive a form that can be used to evaluate the harmonic Hall voltages and
extract relevant parameters in two representative systems, i.e. out of plane
and in-plane magnetized systems. Contributions from the anomalous Hall and
planar Hall effects are considered.",1307.5603v1
2013/7/26,NMR investigation of the Knight shift anomaly in CeIrIn5 at high magnetic fields,"We report nuclear magnetic resonance Knight shift data in the heavy fermion
material CeIrIn5 at fields up to 30 T. The Knight shift of the In displays a
strong anomaly, and we analyze the results using two different interpretations.
We find that the Kondo lattice coherence temperature and the effective mass of
the heavy electrons remains largely unaffected by the magnetic field, despite
the fact that the Zeeman energy is on the order of the coherence temperature.",1307.7114v1
2013/7/26,Orientation Dependence of the Critical Magnetic Field for Multiferroic BiFeO$_3$,"Multiferroic BiFeO3 undergoes a transition from a distorted spiral phase to a
G-type antiferromagnet above a critical field H_c that depends on the
orientation m of the field. We show that H_c(m) has a maximum when oriented
along a cubic diagonal parallel to the electric polarization P and a minimum in
the equatorial plane normal to P when two magnetic domains with the highest
critical fields are degenerate. The measured critical field along a cubic axis
is about 19 T but H_c is predicted to vary by as much as 2.5 T above and below
this value. The orientational dependence of H_c(m) is more complex than
indicated by earlier work, which did not consider the competition between
magnetic domains.",1307.7155v1
2013/8/9,High TMR ratio in Co2FeSi and Fe2CoSi based magnetic tunnel junctions,"Magnetic tunnel junctions with Fe1+xCo2-xSi (0 < x < 1) electrodes and MgO
barrier were prepared on MgO substrates by magnetron co-sputtering. Maximum
tunnel magnetoresistance (TMR) ratios of 262 % at 15 K and 159 % at room
temperature were observed for x=0.75. Correlations of the annealing temperature
dependent atomic ordering and TMR amplitude are discussed. The high TMR for an
intermediate stoichiometry is ascribed to the adjustment of the Fermi energy
within a minority spin pseudo gap.",1308.2072v1
2013/8/21,Thermal transport due to quantum interference in magnetic tunnel junctions,"We study the thermal transport in magnetic tunnel junctions. Thermal
gradients across the tunneling barrier appear around the Fowler-Nordheim
tunneling regime, due to the current-induced heat caused by quantum
interference. Both thermovoltage and thermal temperature follow a linear
response with the applied current, which is an evidence for a thermoelectric
effect. By increasing the barrier transparency, the dynamics of thermoelectric
properties is observed with the current. Accordingly, a large range of the
Seebeck coefficient, 10 - 1000 {\mu}V/K, has been obtained in magnetic tunnel
junctions.",1308.4483v1
2013/8/26,Anomalous Nernst Effects of [CoSiB/Pt] Multilayer Films,"We report a measurement for the anomalous Nernst effects induced by a
temperature gradient in [CoSiB/Pt] multilayer films with perpendicular magnetic
anisotropy. The Nernst voltage shows a characteristic hysteresis which reflects
the magnetization of the film as in the case of the anomalous Hall effects.
With a local heating geometry, we also measure the dependence of the anomalous
Nernst voltage on the distance d from the heating element. It is roughly
proportional to 1/d^1.3, which can be conjectured from the expected temperature
gradient along the sample from the heat equation.",1308.5485v1
2013/9/10,Spin rectification induced by dynamical Hanle effect,"Dynamic response of spin accumulation to a time-dependent magnetic field has
been investigated in a ferromagnetic/nonmagnetic bilayer under ferromagnetic
resonance. In this system, magnetization precession driven by a microwave
generates direct-current (dc) and alternate-current (ac) spin accumulation in
the nonmagnetic layer by the spin pumping. The ac spin accumulation is coupled
with the microwave magnetic field through a dynamical Hanle spin precession,
giving rise to rectified spin accumulation comparable with the dc spin
accumulation directly generated by the spin pumping.",1309.2365v1
2013/9/12,Structural control of magnetic anisotropy in a strain driven multiferroic EuTiO3 thin film,"Octahedral distortion plays a key role in engineering the physical properties
of heterostructures composed of perovskite oxides. We observe a strong in-plane
uniaxial magnetic anisotropy in a strain-enabled multiferroic EuTiO3 thin film
epitaxially grown on a (110)o DyScO3 substrate. First principles calculations
show that the magnetic anisotropy is closely correlated with the uniaxial TiO6
octahedral tilting and the ferroelectric polarization of the film, indicating
potential strong magnetoelectric coupling in the strain-engineered multiferroic
system.",1309.3185v1
2013/9/25,Bulk modulus of the nanoparticle system in concentrated magnetic fluids and local field-induced structural anisotropy,"In the present study we probe the bulk modulus and the structure of
concentrated magnetic fluids by Small Angle X-ray Scattering. The
electrostatically stabilized nanoparticles experience a repulsive interparticle
potential modulated by dipolar magnetic interactions. On the interparticle
distance lengthscale, we show that nanoparticles are trapped under-field in
oblate cages formed by their first neighbours. We propose a theoretical model
of magnetostriction for the field-induced deformation of the cage. This model
captures the anisotropic features of the experimentally observed scattering
pattern on the local scale in these strongly interacting colloidal dispersions.",1309.6523v1
2013/9/25,Magnetic and transport properties of Mn2CoAl oriented thin films,"The structure, magnetic and transport properties of thin films of the Heusler
ferrimagnet Mn_{2}CoAl have been investigated for properties related to spin
gapless semiconductors. Oriented films were grown by molecular beam epitaxy on
GaAs substrates and the structure was found to transform from tetragonal to
cubic for increasing annealing temperature. The anomalous Hall resistivity is
found to be proportional to the square of the longitudinal resistivity and
magnetization expected for a topological Berry curvature origin. A delicate
balance of the spin-polarized carrier type when coupled with voltage
gate-tuning could significantly impact advanced electronic devices.",1309.6660v1
2013/10/8,Theory of magnetic oscillations in Weyl semimetals,"Weyl semimetals are a new class of Dirac material that posses bulk energy
nodes in three dimensions. In this paper, we study a Weyl semimetal subject to
an applied magnetic field. We derive expressions for the density of states,
electronic specific heat, and the quantum oscillations of the magnetization, DC
conductivity, and thermal conductivity. We find phase shifts in the quantum
oscillations that distinguish the Weyl semimetal from conventional three
dimensional Schr\""odinger Fermions.",1310.2223v3
2013/11/10,Electronic Structure of Magnetic Semiconductor CdCr_2Te_4: A Possible Spin-Dependent Symmetry Filter,"We present a theoretical investigation of the electronic and magnetic
structure of spinel CdCr_2Te_4 using density functional theory, its extensions
via onsite Hubbard U interactions, and a screened-hybrid-functional exchange
potential. We find that the ground state is semiconducting within the latter
approach, and within this magnetic-semiconducting system we compute the complex
band structure, finding a slowly decaying evanescent $\tilde{\Delta}_1$ state
possibly suitable for realizing a spin-dependent symmetry filter effect.",1311.2265v1
2013/12/3,Dynamical properties of three terminal magnetic tunnel junctions: spintronics meets spin-orbitronics,"This letter introduces a micromagnetic model able to characterize the
magnetization dynamics in three terminal magnetic tunnel junctions, where the
effects of spin-transfer torque and spin-orbit torque are taken into account.
Our results predict that the possibility to separate electrically those two
torque sources is very promising from a technological point of view for both
next generation of nanoscale spintronic oscillators and microwave detectors. A
scalable synchronization scheme based on the parallel connection of those three
terminal devices is also proposed.",1312.0806v1
2013/12/15,Novel magnetic arrangement and structural phase transition induced by spin-lattice coupling in multiferroics,"Using an effective Hamiltonian of mutiferroic BiFeO$_3$ (BFO) as a toy model,
we explore the effect of the coefficient, C, characterizing the strength of the
spin-current interaction, on physical properties. We observe that for larger C
values and below a critical temperature, the magnetic moments organize
themselves in a novel cycloid which propagates along a low-symmetry direction
and is associated with a structural phase transition from polar rhombohedral to
a polar triclinic state. We emphasize that both of these magnetic and
structural transitions are results of a remarkable self-organization of
different solutions of the spin-current model.",1312.4161v1
2013/12/23,Radial modulation enhances critical fields in 2d superconductors,"The 1964 reports of Fulde, Ferrell, Larkin, and Ovchinnikov (FFLO or LOFF) on
paramagnetic enhancement of superconductivity suggested that superconductivity
can persist at applied magnetic fields above both its orbital and paramagnetic
limits. By forming spatially alternating superconducting and paramagnetic
regions, the increase in local magnetic field in the paramagnetic region allows
a reduction in field inside the superconductor. We present an FFLO phase
diagram model for layered organic superconductors and confirm it with high
magnetic field data from four materials. Our work suggests that paramagnetic
and superconducting regions form as radially alternating rings about each
vortex rather than plane waves, as FFLO is usually described.",1312.6448v1
2014/1/24,A fast pneumatic sample-shuttle with attenuated shocks,"We describe a home-built pneumatic shuttle suitable for the fast displacement
of samples in the vicinity of a highly sensitive atomic magnetometer. The
samples are magnetized at 1 T using a Halbach assembly of magnets. The device
enables the remote detection of free induction decay in ultra-low-field and
zero-field NMR experiments, in relaxometric measurements and in other
applications involving the displacement of magnetized samples within time
intervals as short as a few tens of milliseconds. Other possible applications
of fast sample shuttling exist in radiological studies, where samples have to
be irradiated and then analyzed in a 'cold' environment.",1401.6454v1
2014/1/30,Magnetoresistance Induced by Rare Strong Scatterers in a High Mobility 2DEG,"We observe a strong negative magnetoresistance at non-quantizing magnetic
fields in a high-mobility two-dimensional electron gas (2DEG). This strong
negative magnetoresistance consists of a narrow peak around zero magnetic field
and a huge magnetoresistance at larger fields. The peak shows parabolic
magnetic field dependence and is attributed to the interplay of smooth disorder
and rare strong scatterers. We identify the rare strong scatterers as
macroscopic defects in the material and determine their density from the peak
curvature.",1401.7940v3
2014/2/14,Thermodynamically self-consistent non-stochastic micromagnetic model for the ferromagnetic state,"In this work, a self-consistent thermodynamic approach to micromagnetism is
presented. The magnetic degrees of freedom are modeled using the
Landau-Lifshitz-Baryakhtar theory, that separates the different contributions
to the magnetic damping, and thereby allows them to be coupled to the electron
and phonon systems in a self-consistent way. We show that this model can
quantitatively reproduce ultrafast magnetization dynamics in Nickel.",1402.3487v3
2014/2/17,"Comment on ""Theoretical design of molecular nanomagnets for magnetic refrigeration"" [Appl. Phys. Lett. 103, 202410 (2013)]","Garlatti et al. [Appl. Phys. Lett. 103, 202410 (2013)] report theoretical
simulations aimed at showing that the best molecular nanomagnets for magnetic
refrigeration between T = 10 K and sub-Kelvin region are those made of strongly
ferromagnetically-coupled magnetic ions. This Comment revises such conclusion
based on results that, apparently, contrast with the established belief in this
research field.",1402.4074v2
2014/2/17,Photon Polarization Precession Spectroscopy for High-Resolution Studies of Spinwaves,"A new type of spectroscopy for high-resolution studies of spin waves that
relies on resonant scattering of hard x-rays is introduced. The energy transfer
in the scattering process is encoded in the precession of the polarization
vector of the scattered photons. Thus, the energy resolution of such a
spectroscopy is independent of the bandwidth of the probing radiation. The
measured quantity resembles the intermediate scattering function of the
magnetic excitations in the sample. At pulsed x-ray sources, especially x-ray
lasers, the proposed technique allows to take single-shot spectra of the
magnetic dynamics. The method opens new avenues to study low-energy
non-equilibrium magnetic processes in a pump-probe setup.",1402.4795v1
2014/3/4,Ultrafast switching of the electric polarization and magnetic chirality in BiFeO3 by an electric field,"Using a first-principles-based effective Hamiltonians within molecular
dynamics simulations, we discover that applying an electric field that is
opposite to the initial direction of the polarization results in a switching of
both the polarization and the magnetic chirality vector of multiferroic BiFeO3
at an ultrafast pace (namely of the order of picoseconds). We discuss the
origin of such a double ultrafast switching, which is found to involve original
intermediate magnetic states and may hold promise for designing various
devices.",1403.0671v1
2014/3/10,Mean-field solution of the Hubbard model: the magnetic phase diagram,"The present paper is based on our graduate lectures in condensed-matter
physics. We found that the mean-field solution of the Hubbard model is an
excellent tool to stimulate students' reflections towards the treatment of
realistic magnetic interactions. We show by detailed analytical and numerical
calculations how to find the mean-field solution of the model on a square
lattice. We then interpret the physical implications of the ground-state
magnetic phase diagram in terms of the electron density and the ratio between
the Coulomb repulsion and the electron-structure bandwidth.",1403.2259v1
2014/3/21,Field induced large magnetocaloric effect and magnetoresistance in ErNiSi,"Large magnetocaloric effect (MCE) and magnetoresistance (MR) together with
negligible hysteresis loss has been observed in ErNiSi compound, which
undergoes metamagnetic transition at low temperatures. Magnetization, heat
capacity and resistivity measurements confirm the metamagnetic transition. The
maximum value of isothermal entropy change and MR for a field change of 50 kOe
are found to be 19.1 J/kg K and -34 %. Large MCE with negligible magnetic
hysteresis loss could make this material promising for low temperature magnetic
refrigeration.",1403.5396v1
2014/4/4,Thermally assisted domain wall nucleation in perpendicular anisotropy trilayer nanowires,"We study thermally assisted domain wall generation in perpendicular magnetic
anisotropy CoFeB trilayer nanowires by the effect of Joule heating. The
anomalous Hall effect is utilized to detect magnetization reversal in order to
study the domain wall generation. We observe a statistical distribution in the
switching process which is consistent with the thermal activation process. Our
results show that the proposed method provides an efficient way for generating
domain walls in perpendicular magnetic nanowires at predefined locations.",1404.1135v1
2014/4/22,Rapid Scanning Terahertz Time-Domain Magnetospectroscopy with a Table-Top Repetitive Pulsed Magnet,"We have performed terahertz time-domain magnetospectroscopy by combining a
rapid scanning terahertz time-domain spectrometer based on the electronically
coupled optical sampling method with a table-top mini-coil pulsed magnet
capable of producing magnetic fields up to 30 T. We demonstrate the capability
of this system by measuring coherent cyclotron resonance oscillations in a
high-mobility two-dimensional electron gas in GaAs and interference-induced
terahertz transmittance modifications in a magnetoplasma in lightly doped
n-InSb.",1404.5592v1
2014/5/22,Improvement of magnetic hardness at finite temperatures: ab initio disordered local moment approach for YCo$_5$,"Temperature dependence of the magnetocrystalline anisotropy energy and
magnetization of the prototypical rare-earth magnet YCo$_5$ is calculated from
first principles, utilizing the relativistic disordered local moment approach.
We discuss a strategy to enhance the finite-temperature anisotropy field by
hole doping, paving the way for an improvement of the coercivity near room
temperature or higher.",1405.5673v2
2014/5/30,The role of thermal disorder for magnetism and the $α- γ$ transition in Cerium; Results from density-functional theory,"The electronic structures of fcc Ce are calculated for large supercells with
varying disorder by use of density-functional theory. Thermal disorder induces
fluctuations of the amplitude of the magnetic moments and an increase the
average moments in the high-volume phase. The ferro-magnetic solutions move
towards lower volume than in calculations for the perfectly ordered lattice.
Therefore, disorder contributes via entropy to the stabilization of the
$\gamma$ phase at high $T$, and it is important for an understanding of the
$\alpha-\gamma$ transition. Core level spectroscopy would be a mean to detect
disorder through the spread of Madelung shifts and local exchange splittings.",1405.7884v1
2014/6/10,Influence of Ta insertions on the magnetic properties of MgO/CoFeB/MgO films probed by ferromagnetic resonance,"We show by vector network analyzer ferromagnetic resonance measurements that
low Gilbert damping {\alpha} down to 0.006 can be achieved in perpendicularly
magnetized MgO/CoFeB/MgO thin films with ultra-thin insertions of Ta in the
CoFeB layer. While increasing the number of Ta insertions allows thicker CoFeB
layers to remain perpendicular, the effective areal magnetic anisotropy does
not improve with more insertions, and also comes with an increase in {\alpha}.",1406.2491v2
2014/6/17,Structural Changes Related to the Magnetic Transitions in Hexagonal InMnO3,"Two magnetic ordering transitions are found in InMnO3, the paramagnetic to
antiferromagnetic transition near ~118 K and a lower possible spin rotation
transition near ~42 K. Multiple length scale structural measurements reveal
enhanced local distortion found to be connected with tilting of the MnO5
polyhedra as temperature is reduced. Strong coupling is observed between the
lattice and the spin manifested as changes in the structure near both of the
magnetic ordering temperatures (at ~42 K and ~ 118 K). External parameters such
as pressure are expected to modify the coupling.",1406.4405v1
2014/7/3,Imprinting skyrmions in thin films by ferromagnetic and superconducting templates,"Magnetic skyrmions are promising candidates as information carriers in a new
generation of memories. How to generate and stabilize skyrmions is essential
for their successful application to technology. Here we theoretically
demonstrate that arrays of skyrmions can be imprinted in ultrathin
ferromagnetic films in large numbers by bringing a magnetic nanostructured
template close to the film. Two kind of templates, allowed by present-day
nanotechnologies, are studied: arrays of ferromagnetic nanorods and
superconducting vortices. Skyrmions are generated when exposing magnetic films
to the template fields for short times and remain stable after removing the
template.",1407.0928v1
2014/7/16,Electronic and magnetic properties of the graphene/Eu/Ni(111) hybrid system,"The electronic and magnetic properties of the graphene/Eu/Ni(111)
intercalation-like system are studied in the framework of the GGA+U approach
with dispersive interactions taken into account. Intercalation of monoatomic Eu
layer underneath graphene on Ni(111) leads to the drastic changes of the
electronic structure of graphene compared to free-standing graphene as well as
graphene/Ni(111). The strong influence of the spin-polarised Eu 4f states,
crossing the graphene-derived $\pi$ states, on magnetic properties of graphene
and on spin-filtering properties of the graphene/Eu/Ni(111) trilayer is
discussed.",1407.4389v1
2014/7/21,Josephson junction with a magnetic vortex,"We have studied Josephson tunneling through a circularly polarized micron or
submicron-size disk of a soft ferromagnetic material. Such a disk contains a
vortex that exhibits rich classical dynamics and has recently been proposed as
a tool to study quantum dynamics of the nanoscale vortex core. The change in
the Josephson current that is related to a tiny displacement of the vortex core
has been computed analytically and plotted numerically for permalloy disks used
in experiments. It is shown that a Josephson junction with a magnetic disk in
the vortex state can be an interesting physical system that may be used to
measure the nanoscale motion of the magnetic vortex.",1407.5419v1
2014/8/18,Self-resonant Coil for Contactless Electrical Conductivity Measurement under Pulsed Ultra-high Magnetic Fields,"In this study, we develop experimental apparatus for contactless electrical
conductivity measurements under pulsed high magnetic fields over 100 T using a
self-resonant-type high-frequency circuit. The resonant power spectra were
numerically analyzed, and the conducted simulations showed that the apparatus
is optimal for electrical conductivity measurements of materials with high
electrical conductivity. The newly developed instruments were applied to a
high-temperature cuprate superconductor La$_{2-x}$Sr$_x$CuO$_4$ to show
conductivity changes in magnetic fields up to 102 T with a good signal-to-noise
ratio. The upper critical field was determined with high accuracy.",1408.3905v1
2014/9/14,Tunable Magnetism and Half-Metallicity in Hole-doped Monolayer GaSe,"We find, through first-principles calculations, that hole doping induces a
ferromagnetic phase transition in monolayer GaSe. Upon increasing hole density,
the average spin magnetic moment per carrier increases and reaches a plateau
near 1.0 $\mu_{\rm{B}}$/carrier in a range of $3\times
10^{13}$/cm$^{2}$-$1\times 10^{14}$/cm$^{2}$ with the system in a half-metal
state before the moment starts to descend abruptly. The predicted magnetism
originates from an exchange splitting of electronic states at the top of the
valence band where the density of states exhibits a sharp van Hove singularity
in this quasi-two-dimensional system.",1409.4112v1
2014/9/17,"Electronic structure, spin excitations, and orbital ordering in a three-orbital model for iron pnictides","A three-orbital itinerant-electron model involving d_{xz}, d_{yz} and d_{xy}
Fe 3d orbitals is proposed for iron pnictides towards understanding the (\pi,0)
ordered magnetism and magnetic excitations in these materials. It is shown that
this model at half filling yields a gapped (\pi,0) magnetic state with high
degree of robustness and stability, and simultaneously reproduces several
experimentally observed features such as the electronic structure, spin
excitations, as well as the ferro orbital order between the d_{xz} and d_{yz}
orbitals.",1409.4984v2
2014/9/22,Vibrational and magnetic properties of crystalline CuTe2O5,"In the present work we have performed an ab initio calculation of vibrational
properties of CuTe2O5 by means of density functional theory method. One has
compared calculated values with known experimental data on Raman and infrared
spectroscopy in order to verify the obtained results. Lattice contribution to
the heat capacity, obtained from the ab initio simulations was added to
magnetic contribution calculated from the simple spin hamiltonian model in
order to obtain total heat capacity. Obtained result are in good agreement to
the experimental data. Thus, the DFT methods could complement the experimental
and theoretical studying of low-dimensional magnetic systems such as CuTe2O5.",1409.6133v1
2014/9/28,Magnetoresistance due to Broken C4 Symmetry in Cubic B20 Chiral Magnets,"The B20 chiral magnets with broken inversion symmetry and C4 rotation
symmetry have attracted much attention. The broken inversion symmetry leads to
the Dzyaloshinskii-Moriya that gives rise to the helical and Skyrmion states.
We report the unusual magnetoresistance (MR) of B20 chiral magnet
Fe0.85Co0.15Si that directly reveals the broken C4 rotation symmetry. We
present a microscopic theory, a minimal theory with two spin-orbit terms, that
satisfies all the symmetry requirements and accounts for the transport
experiments.",1409.7867v1
2014/10/14,Magnetic-field-driven localization of light in a cold-atom gas,"We discover a transition from extended to localized quasi-modes for light in
a gas of immobile two-level atoms in a magnetic field. The transition takes
place either upon increasing the number density of atoms in a strong field or
upon increasing the field at a high enough density. It has many characteristic
features of a disorder-driven (Anderson) transition but is strongly influenced
by near-field interactions between atoms and the anisotropy of the atomic
medium induced by the magnetic field.",1410.3634v2
2014/10/14,Skyrmion-like states in multilayer exchange coupled ferromagnetic nanostructures with distinct anisotropy directions,"We report the experimental observation of magnetic skyrmion-like states in
patterned ferromagnetic nanostructures consisting of perpendicular magnetized
Co/Pt multilayer film exchange coupled with Co nanodisks in vortex state. The
magnetic force microscopy and micromagnetic simulations show that depending on
the magnitude of Co/Pt perpendicular anisotropy in these systems two different
modes of skyrmion formation are realized.",1410.4174v1
2014/10/21,Magnetic switching dynamics in a ferrimagnetic two sub-lattice model including ultrafast exchange scattering,"We study the heat-induced magnetization dynamics in a toy model of a
ferrimagnetic alloy, which includes localized spins antiferromagnetically
coupled to an itinerant carrier system with a Stoner gap. We determine the
one-particle spin-density matrix including exchange scattering between
localized and itinerant bands as well as scattering with phonons. While a
transient ferromagnetic-like state can always be achieved by a sufficiently
strong excitation, this transient ferromagnetic-like state only leads to
magnetization switching for model parameters that also yield a compensation
point in the equilibrium M(T) curve.",1410.5745v2
2014/12/11,Possible origin of nonlinear magnetic anisotropy variation in electric field effect in a double interface system,"We investigated the effect of an electric field on the interface magnetic
anisotropy of a thin MgO/Fe/MgO layer using density functional theory. The
perpendicular magnetic anisotropy energy (MAE) increases not only under
electron depletion but also under some electron accumulation conditions,
showing a strong correlation with the number of electrons on the interface Fe
atom. The reverse variation in the MAE under the electric field is ascribed to
novel features on the charged interface, such as electron leakage. We discuss
the origin of the variation in terms of the electronic structures.",1412.3577v1
2014/12/18,Coherent elastic excitation of spin waves,"We model the injection of elastic waves into a ferromagnetic film (F) by a
non-magnetic transducer (N). We compare the configurations in which the
magnetization is normal and parallel to the wave propagation. The lack of axial
symmetry in the former results in the emergence of evanescent interface states.
We compute the energy-flux transmission across the N$|$F interface and
sound-induced magnetization dynamics in the ferromagnet. We predict efficient
acoustically induced pumping of spin current into a metal contact attached to
F.",1412.5820v2
2015/1/8,Theoretical evaluation on the temperature dependence of magnetic anisotropy constants of Nd2Fe14B - Effects of exchange field and crystal field strength -,"To identify the possible mechanism of coercivity (Hc) degradation of Nd-Fe-B
sintered magnets, we study the roles of the exchange field acting on the 4f
electrons in Nd ions and theoretically investigate how the variation of the
exchange field affects the values of the magnetic anisotropy constants K1 and
K2. We find that, with decreasing exchange field strength, both values decrease
as a result of the lower asphericity of the 4f electron cloud, indicating that
the local anisotropy constants might become small around the grain boundaries
where the exchange fields are decreased owing to the smaller coordination
number.",1501.01782v1
2015/1/28,Superconductivity for Magnets,"The present state of development of a series of industrial superconductors is
reviewed in consideration of their future applications in high field
accelerator magnets, with particular attention on the material aspect. The
discussion is centred on Nb3Sn and MgB2, which are industrially available in a
round wire configuration in kilometre lengths and are already envisaged for use
in the LHC Upgrade (HL-LHC). The two systems Bi-2212 and R.E.123 may be used in
magnets with even higher fields in future accelerators: they are briefly
described.",1501.07146v1
2015/2/17,Magnetotransport in disordered two-dimensional topological insulators: signatures of charge puddles,"In this numerical study we investigate the influence and interplay of
disorder, spin-orbit coupling and magnetic field on the edge-transport in
HgTe/CdTe quantum wells in the framework of coherent elastic scattering. We
show that the edge states remain unaffected by the combined effect of moderate
disorder and a weak magnetic field at realistic spin-orbit coupling strengths.
Agreement with the experimentally observed linear magnetic field dependence for
the conductance of long samples is obtained when considering the existence of
charge puddles.",1502.04919v1
2015/3/9,Magnetic spheres in microwave cavities,"We apply Mie scattering theory to study the interaction of magnetic spheres
with microwaves in cavities beyond the magnetostatic and rotating wave
approximations. We demonstrate that both strong and ultra-strong coupling can
be realized for a stand alone magnetic spheres made from yttrium iron garnet
(YIG), acting as an efficient microwave antenna. The eigenmodes of YIG spheres
with radii of the order mm's display distinct higher angular momentum character
that has been observed in experiments.",1503.02419v2
2015/3/11,Electron-beam evaporated cobalt films on molecular beam epitaxy prepared GaAs(001),"We have deposited Co films on the GaAs(001) surface by using an e-beam
evaporation method. The thicknesses of the Co films are measured by using x-ray
reflectivity and Rutherford backscattering. The magnetic properties of the
films have been measured using superconducting quantum interference device. The
magnetization of the films was found to decrease with increasing film
thickness. The slight degradation of magnetic properties is attributed to
increasing roughness on the Co surface or the Co/GaAs interface during the Co
deposition.",1503.03458v1
2015/4/2,Direct Observation of Large Amplitude Spin Excitations Localized in a Spin-Transfer Nanocontact,"We report the direct observation of large amplitude spin-excitations
localized in a spin-transfer nanocontact using scanning transmission x-ray
microscopy. Experiments were conducted using a nanocontact to an ultrathin
ferromagnetic multilayer with perpendicular magnetic anisotropy. Element
resolved x-ray magnetic circular dichroism images show an abrupt onset of spin
excitations at a threshold current that are localized beneath the nanocontact,
with average spin precession cone angles of 25{\deg} at the contact center. The
results strongly suggest that we have observed a localized magnetic soliton.",1504.00488v1
2015/4/6,Local structure surrounding V sites in Co doped ZnV2O4,"Co doped ZnV2O4 has been investigated by Synchrotron X-ray diffraction,
Magnetization measurement and Extended X-ray absorption fine structure (EXAFS)
analysis. With Co doping in the Zn site the system moves towards the itinerant
electron limit. From Synchrotron and magnetization measurement it is observed
that there is an effect in bond lengths and lattice parameters around the
magnetic transition temperature. The EXAFS study indicates that Co ion exists
in the High spin state in Co doped ZnV2O4.",1504.01232v1
2015/4/17,Magnetism of Ta Dichalcogenide Monolayers Tuned by Strain and Hydrogenation,"The effects of strain and hydrogenation on the electronic and magnetic
properties of monolayers of Ta based dichalcogenides (TaX2; X = S, Se, Te) are
investigated using density-functional theo-ry. We predict a complex scenario of
strain-dependent magnetic phase transitions involving par-amagnetic,
ferromagnetic, and modulated antiferromagnetic states. Covering one of the two
chalcogenide surfaces with hydrogen switches the antiferromagnetic/nonmagnetic
TaX2 mono-layers to a semiconductor. Our research opens new pathways towards
the manipulation of mag-netic properties for future optoelectronics and
spintronics applications.",1504.04602v1
2015/5/21,General Formalism for Magnetic Anisotropy Constants,"Direct expressions for the magnetic anisotropy constants are given at a
finite temperature from microscopic viewpoints. In the present derivation, it
is assumed that the Hamiltonian is a linear function with respect to the
magnetization direction. We discuss in detail the first-order constant $K_1$
and show that the results reproduce previous results. We also apply our method
to Nd$_2$Fe$_{14}$B compounds and demonstrate that the temperature dependencies
of the magnetocrystalline anisotropy constants $K_1$, $K_2$, and $K_3$ are
successfully computed.",1505.05686v1
2015/5/27,Excitation of magnetic precession in bismuth iron garnet via a polarization-independent impulsive photomagnetic effect,"A polarization-independent, nonthermal optical effect on the magnetization in
bismuth iron garnet is found, in addition to the circular
polarization-dependent inverse Faraday effect and the linear
polarization-dependent photoinduced magnetic anisotropy. Its impulsive
character is demonstrated by the field dependence of the amplitude of the
resulting precession, which cannot be explained by a long-living photo or
heat-induced anisotropy.",1505.07447v1
2015/6/11,An operational definition of the 100 second blocking temperature T$_{\mathrm{B}100}$ for single molecule magnets,"An important figure of merit for the performance of single-molecule magnets
(SMMs) is the 100 s blocking temperature T$_{\mathrm{B}100}$. It is the
temperature at which the remanence or zero field relaxation time is 100
seconds. If there is more than one relaxation process of the magnetisation, the
determination of the relaxation times may, however, become ambiguous. Here we
propose an operational definition for the zero-field magnetic relaxation times
from which T$_{\mathrm{B}100}$ may be determined. This definition allows for a
direct comparison of the performance of different samples independent of the
details of the relaxation processes involved in the demagnetization.",1506.03657v1
2015/6/18,Spin Hall Effect measurement techniques,"Spin Hall Effect is relativistic quantum mechanical effect which enables
non-magnetic materials show magnetic phenomena without the application of a
magnetic field. With spin Hall Effect, one can realize spintronics devices
operating purely on electrical and optical means and eliminate the use of
ferromagnets which have associated fringe fields. In this review article, we
present the experimental developments and current understanding of the Spin
Hall Effect Phenomena. We discuss various experiments as well as device
structures which employ electrical, optical or both techniques to demonstrate
Spin Hall effect. Most of these devices structures are simple and easy to
fabricate in modern laboratories.",1506.05606v3
2015/7/14,Thermodynamic evidence for the Bose glass transition in twinned YBa$_2$Cu$_3$O$_{7-δ}$ crystals,"We used a micromechanical torsional oscillator to measure the magnetic
response of a twinned YBa$_2$Cu$_3$O$_{7-\delta}$ single crystal disk near the
Bose glass transition. We observe an anomaly in the temperature dependence of
the magnetization consistent with the appearance of a magnetic shielding
perpendicular to the correlated pinning of the twin boundaries. This effect is
related to the thermodynamic transition from the vortex liquid phase to a Bose
glass state.",1507.04022v1
2015/7/19,Spin-transfer-torque efficiency enhanced by edge-damage of perpendicular magnetic random access memories,"We numerically investigate the effect of magnetic and electrical damages at
the edge of a perpendicular magnetic random access memory (MRAM) cell on the
spin-transfer-torque (STT) efficiency that is defined by the ratio of thermal
stability factor to switching current. We find that the switching mode of an
edge-damaged cell is different from that of an undamaged cell, which results in
a sizable reduction in the switching current. Together with a marginal
reduction of the thermal stability factor of an edge-damaged cell, this feature
makes the STT efficiency large. Our results suggest that a precise edge control
is viable for the optimization of STT-MRAM.",1507.05276v1
2015/7/21,Electric field controlled magnetization and transport properties of La0.7Ca0.3MnO3 ultrathin film,"We have investigated the effect of electric field control on the
magnetization and the transport properties in La0.7Ca0.3MnO3 (LCMO) ultrathin
film (~10 nm) by using it as the semiconductor channel material of a
prototypical field effect device and SiO2 as dielectric gate. A large
electroresistance (ER) of ~78% at Vg = -8 V is found in LCMO at 200 K. The
direct magnetization measurements confirm the formation of a large
ferromagnetic phase with the increase in the applied gate voltage at 200 K.",1507.05767v1
2015/7/31,Influence of longitudinal electric field on the oscillating magnetocaloric effect of graphenes,"The present effort explores the influence of a longitudinal applied electric
field on the magnetocaloric properties of graphenes. The magnetic entropy
change $\Delta S(T,\Delta B,E)$ has two contributions: $S_{cos}(T,B,E)$ with an
oscillating character on $m$, inversely proportional to the magnetic field; and
$S_{per}(T,B,E)$ with a periodic character also on $m$. In comparison to the
case without electric field, the maximum value of the magnetic entropy change
either increases or decreases due to an applied electric field, depending on
the value of $m$; and, in addition, the temperature in which the maximum
entropy change occurs decreases due to the electric field.",1507.08899v1
2015/8/7,The Lifshitz-Matsubara sum formula for the Casimir pressure between magnetic metallic mirrors,"We examine the conditions of validity for the Lifshitz-Matsubara sum formula
for the Casimir pressure between magnetic metallic plane mirrors. As in the
previously studied case of non-magnetic materials (Guerout et al, Phys. Rev. E
90 042125), we recover the usual expression for the lossy model of optical
response, but not for the lossless plasma model. We also show that the modes
associated with the Foucault currents play a crucial role in the limit of
vanishing losses, in contrast to expectations.",1508.01659v2
2015/9/9,Strong orientational coupling of block copolymer microdomains to smectic layering revealed by magnetic field alignment,"We elucidate the roles of the isotropic-nematic (I-N) and nematic-smectic A
(N-SmA) transitions in magnetic field directed self-assembly of a liquid
crystalline block copolymer (BCP), using \textit{in situ} x-ray scattering.
Cooling into the nematic from the disordered melt yields poorly ordered and
weakly aligned BCP microdomains. Continued cooling into the SmA however results
in an abrupt increase in BCP orientational order with microdomain alignment
tightly coupled to the translational order parameter of the smectic layers.
These results underscore the significance of the N-SmA transition in generating
highly aligned states under magnetic fields in these hierarchically ordered
materials.",1509.02961v1
2015/9/14,Spin Transport in Antiferromagnetic Insulators Mediated by Magnetic Correlations,"We report a systematic study of spin transport in antiferromagnetic (AF)
insulators having a wide range of ordering temperatures. Spin current is
dynamically injected from Y3Fe5O12 (YIG) into various AF insulators in
Pt/insulator/YIG trilayers. Robust, long-distance spin transport in the AF
insulators is observed, which shows strong correlation with the AF ordering
temperatures. We find a striking linear relationship between the spin decay
length in the AFs and the damping enhancement in YIG, suggesting the critical
role of magnetic correlations in the AF insulators as well as at the AF/YIG
interfaces for spin transport in magnetic insulators.",1509.04336v1
2015/11/5,Force law in material media and quantum phases,"We show that the known expressions for the force on a point-like dipole are
incompatible with the relativistic transformation of force, and in this respect
we apply the Lagrangian approach to the derivation of the correct equation for
force on a small electric/magnetic dipole. The obtained expression for the
generalized momentum of a moving dipole predicts two novel quantum effects with
non-topological and non-dynamic phases, when an electric dipole is moving in an
electric field, and when a magnetic dipole is moving in a magnetic field,
correspondingly. The implications of the obtained results are discussed.",1511.04341v1
2015/11/23,Extension of structure integration to magnetic system,"We extend our previously developed method, ""structure integration"", to
evaluate free energy directly for magnetic large systems on given lattice. The
present method express the density of states(DOS) as the parameters independent
of system but depend on lattice, and replace the DOS unknown a priori as that
known a priori. Through two-dimensional square lattice Ising model, we find
that the present method can evaluate magnetic free energy efficiently and
accurately above critical temperature without iterative method like Monte Carlo
simulation.",1511.07239v2
2015/12/24,Polaritons dispersion in a composite ferrite-semiconductor structure near gyrotropic-nihility state,"In the context of polaritons in a ferrite-semiconductor structure which is
influenced by an external static magnetic field, the gyrotropic-nihility can be
identified from the dispersion equation related to bulk polaritons as a
particular extreme state, at which the longitudinal component of the
corresponding constitutive tensor and bulk constant simultaneously acquire
zero. Near the frequency of the gyrotropic-nihility state, the conditions of
branches merging of bulk polaritons, as well as an anomalous dispersion of bulk
and surface polaritons are found and discussed.",1512.07870v2
2016/1/4,Photovoltaic Chiral Magnetic Effect,"We theoretically predict a generation of a current in Weyl semimetals by
applying circularly polarized light. The electric field of the light can drive
an effective magnetic field of order of ten Tesla. For lower frequency light, a
non-equilibrium spin distribution is formed near the Fermi surface. Due to the
spin-momentum locking, a giant electric current proportional to the effective
magnetic field is induced. On the other hand, higher frequency light realizes a
quasi-static Floquet state with no induced electric current. We discuss
relevant materials and estimate order of magnitude of the induced current.",1601.00379v1
2016/1/8,Magnetism in La$_{0.7}$Sr$_{0.3}$Mn$_{1-x}$Co$_x$O$_3$ ($0 \leq x \leq 1$),"We study the structural and magnetic properties of
La$_{0.7}$Sr$_{0.3}$Mn$_{1-x}$Co$_x$O$_3$ ($0 \leq x \leq 1$). Rietveld
refinement of X-ray Diffraction (XRD) pattern suggests phase purity of the
polycrystalline samples with R$\bar{3}$c space group. Interplay of
Ferromagnetic (FM) and Antiferromagnetic (AFM) interaction upon Co substitution
at Mn site in La$_{0.7}$Sr$_{0.3}$MnO$_3$ is evident from magnetic
measurements. There is an optimal cobalt substitution at which the coercive
field is maximum.",1601.01793v1
2016/1/13,Anisotropic Paramagnetic Meissner Effect by Spin-Orbit Coupling,"Conventional $s$-wave superconductors repel external magnetic flux. However,
a recent experiment [A. Di Bernardo et al., Phys. Rev. X \textbf{5}, 041021
(2015)] has tailored the electromagnetic response of superconducting
correlations via adjacent magnetic materials. We consider another route to
alter the Meissner effect where spin-orbit interactions induce an anisotropic
Meissner response that changes sign depending on the field orientation. The
tunable electromagnetic response opens new paths in the utilization of hybrid
systems comprised of magnets and superconductors.",1601.03404v2
2016/1/25,"Theory of electron spin resonance in bulk topological insulators Bi2Se3, Bi2Te3 and Sb2Te3","We report a theoretical study of electron spin resonance in bulk topological
insulators, such as Bi2Se3, Bi2Te3 and Sb2Te3. Using the effective four-band
model, we find the electron energy spectrum in a static magnetic field and
determine the response to electric and magnetic dipole perturbations,
represented by oscillating electric and magnetic fields perpendicular to the
static field. We determine the associated selection rules and calculate the
absorption spectra. This enables us to separate the effective orbital and spin
degrees of freedom and to determine the effective g-factors for electrons and
holes.",1601.06507v1
2016/2/18,Metallic Nickel Silicides: Experiments and Theory for NiSi and First Principles Calculations for Other Phases,"We report detailed experimental investigation of the transport and magnetic
properties of orthorhombic NiSi along with first principles studies of this
phase and related nickel silicides. Neutron scattering shows no evidence for
magnetism, in agreement with first principles calculations. Comparison of first
principles results and experimental results from our measurements and
literature show a weak electron phonon coupling. We discuss transport and other
properties of NiSi and find behavior characteristic of a weak correlated metal
far from magnetism. Trends among the nickel silicides as a function of nickel
content are discussed.",1602.05840v1
2016/3/13,Perpendicular magnetic anisotropy in Co$_2$Fe$_{0.4}$Mn$_{0.6}$Si,"We report perpendicular magnetic anisotropy (PMA) in the half-metallic
ferromagnetic Heusler alloy Co$_2$Fe$_{0.4}$Mn$_{0.6}$Si (CFMS) in a
MgO/CFMS/Pd trilayer stack. PMA is found for CFMS thicknesses between 1 and 2
nm, with a magnetic anisotropy energy density of $K_U = 1.5\times 10^6$
erg/cm$^3$ for t$_{\tiny \textrm{CFMS}} = 1.5$ nm. Both the MgO and Pd layer
are necessary to induce the PMA. We measure a tunable anomalous Hall effect,
where its sign and magnitude vary with both the CFMS and Pd thickness.",1603.04072v1
2016/4/13,Tunable Weyl fermions and Fermi arcs in magnetized topological crystalline insulators,"Based on $k\cdot p$ analysis and realistic tight-binding calculations, we
find that time-reversal-breaking Weyl semimetals can be realized in
magnetically-doped (Mn, Eu, Cr etc.) Sn$_{1-x}$Pb$_x$(Te,Se) class of
topological crystalline insulators. All the Weyl points are well separated in
momentum space and possess nearly the same energy due to high crystalline
symmetry. Moreover, both the Weyl points and Fermi arcs are highly tunable by
varying Pb/Sn composition, pressure, magnetization, temperature, surface
potential etc., opening up the possibility of manipulating Weyl points and
rewiring the Fermi arcs.",1604.03947v1
2016/4/18,How to reveal metastable skyrmionic spin structures by spin-polarized scanning tunneling microscopy,"We predict the occurrence of metastable skyrmionic spin structures such as
antiskyrmions and higher-order skyrmions in ultra-thin transition-metal films
at surfaces using Monte Carlo simulations based on a spin Hamiltonian
parametrized from density functional theory calculations. We show that such
spin structures will appear with a similar contrast in spin-polarized scanning
tunneling microscopy (SP-STM) images. Both skyrmions and antiskyrmions display
a circular shape for out-of-plane magnetized tips and a two-lobe butterfly
contrast for in-plane tips. An unambiguous distinction can be achieved by
rotating the tip magnetization direction without requiring the information of
all components of the magnetization.",1604.05030v1
2016/5/27,Effect of Dzyaloshinski-Moriya interaction on spin-polarized neutron scattering,"For magnetic materials containing many lattice imperfections (e.g.,
nanocrystalline magnets), the relativistic Dzyaloshinski-Moriya (DM)
interaction may result in nonuniform spin textures due to the lack of inversion
symmetry at interfaces. Within the framework of the continuum theory of
micromagnetics, we explore the impact of the DM interaction on the elastic
magnetic small-angle neutron scattering (SANS) cross section of bulk
ferromagnets. It is shown that the DM interaction gives rise to a
polarization-dependent asymmetric term in the spin-flip SANS cross section.
Analysis of this feature may provide a means to determine the DM constant.",1605.08586v1
2016/7/20,New Approach to Metal-Insulator Phase Transition Kinetics in Magnetic Field,"The metal--insulator phase transition is considered on the basis of
Ginzburg-Landau type equations with two different order parameters. An
inclusion of magnetic field in this picture is an important step for
understanding of behavior of the metal--insulator phase transition kinetics.
The magnetic field leads to various singularities of the surface tension and
results in drastic variations of the phase transition kinetics. The strongest
singularity is due to Landau diamagnetism and determines anomalous features of
MI transition kinetics. This singularity supports the well known experimental
fact that almost all semimetals behave like diamagnetic materials.",1607.06027v1
2016/8/8,Temperature dependence of the spin Hall angle and switching current in the nc-W(O)/CoFeB/MgO system with perpendicular magnetic anisotropy,"We investigated the temperature dependence of the switching current for a
perpendicularly magnetized CoFeB film deposited on a nanocrystalline tungsten
film with large oxygen content: nc-W(O). The spin Hall angle
$|\Theta_\mathrm{SH}| \approx 0.22$ is independent of temperature, whereas the
switching current increases strongly at low temperature. We show that the
nc-W(O) is insensitive to annealing. It thus can be a good choice for the
integration of spin Hall driven writing of information in magnetic memory or
logic devices that require a high-temperature annealing process during
fabrication.",1608.02528v1
2016/9/19,Large Unidirectional Magnetoresistance in a Magnetic Topological Insulator,"We report current-direction dependent or unidirectional magnetoresistance
(UMR) in magnetic/nonmagnetic topological insulator (TI) heterostructures,
Cr$_x$(Bi$_{1-y}$Sb$_y$)$_{2-x}$Te$_3$/(Bi$_{1-y}$Sb$_y$)$_2$Te$_3$, that is
several orders of magnitude larger than in other reported systems. From the
magnetic field and temperature dependence, the UMR is identified to originate
from the asymmetric scattering of electrons by magnons. In particular, the
large magnitude of UMR is an outcome of spin-momentum locking and a small Fermi
wavenumber at the surface of TI. In fact, the UMR is maximized around the Dirac
point with the minimal Fermi wavenumber.",1609.05906v1
2016/9/30,"A historical introduction to the symmetries of magnetic structures: Part 1. Early quantum theory, neutron powder diffraction and the colored space groups","This paper introduces the historical development of the symmetries for
describing magnetic structures culminating in the derivation of the black and
white and colored space groups. Beginning from the Langevin model of the Curie
law, it aims to show the challenges that magnetic ordering presented and how
different symmetry frameworks were developed to meet them. As well as
explaining core ideas, later papers will show how the different schemes are
connected. With these goals in mind, the maths related is kept to the minimum
required for clarity.",1609.09666v1
2016/10/7,Ballistic Anisotropic Magnetoresistance in Core Shell Nanowires and Rolled-up Nanotubes,"In ferromagnetic nanostructures, the ballistic anisotropic magnetoresistance
(BAMR) is a change in the ballistic conductance with the direction of
magnetization due to spin-orbit interaction. Very recently, a directional
dependent ballistic conductance has been predicted to occur in a number of
newly synthesized nonmagnetic semiconducting nanostructures subject to
externally applied magnetic fields, without necessitating spin-orbit coupling.
In this article, we review past works on the prediction of this BAMR effect in
core-shell nanowires and rolled-up nanotubes. This is complemented by new
results we establish for the transport properties of tubular nanosystems
subject to external magnetic fields.",1610.02337v1
2016/10/26,Classical spin liquid instability driven by off-diagonal exchange in strong spin-orbit magnets,"We show that the off-diagonal exchange anisotropy drives Mott insulators with
strong spin-orbit coupling to a classical spin liquid regime, characterized by
an infinite number of ground states and Ising variables living on closed or
open strings. Depending on the sign of the anisotropy, quantum fluctuations
either fail to lift the degeneracy down to very low temperatures, or select
non-collinear magnetic states with unconventional spin correlations. The
results apply to all 2D and 3D tri-coordinated materials with bond-directional
anisotropy, and provide a consistent interpretation of the suppression of the
x-ray magnetic circular dichroism signal reported recently for
$\beta$-Li$_2$IrO$_3$ under pressure.",1610.08463v1
2016/12/8,"First-principles study on the magnetic properties of ordered Nd$_{6}$(Fe,Ga)$_{14}$ alloys","We studied the stable magnetic structure of ordered Nd$_{6}$Fe$_{14-x}$Ga$_x$
($x = 0, 1)$ alloys, which appears in the grain-boundary (GB) phase of Nd-Fe-B
permanent magnets, using first-principles techniques. Slight Ga doping ($x =
1$) was shown to contribute to the stabilization of an anti-ferromagnetic (AF)
state, whereas the non-doped case ($x = 0$) was revealed to favor ferromagnetic
state rather than AF state with a slight energy difference.",1612.02633v3
2016/12/22,Ab initio Study of Effect of Co Substitution on the Magnetic Properties of Ni and Pt-based Heusler Alloys,"Using density functional theory based calculations, we have carried out
in-depth studies of effect of Co substitution on the magnetic properties of Ni
and Pt-based shape memory alloys. We show the systematic variation of the total
magnetic moment, as a function of Co doping. A detailed analysis of evolution
of Heisenberg exchange coupling parameters as a function of Co doping has been
presented here. The strength of RKKY type of exchange interaction is found to
decay with the increase of Co doping.",1612.07518v1
2017/2/15,Pressure-induced insulator-metal transition in EuMnO3,"We study the influence of external pressure on the electronic and magnetic
structure of EuMnO3 from first-principles calculations. We find a
pressure-induced insulator-metal transition at which the magnetic order changes
from A-type antiferromagnetic to ferromagnetic with a strong interplay with
Jahn-Teller distortions. In addition, we find that the non-centrosymmetric
E*-type antiferromagnetic order can become nearly degenerate with the
ferromagnetic ground state in the high-pressure metallic state. This situation
can be exploited to promote a magnetically-driven realization of a
non-centrosymmetric (ferroelectric) metal.",1702.04607v2
2017/3/17,Electrical detection of magnetic states in crossed nanowires using the topological Hall effect,"We used micromagnetic simulations to investigate the spatial distributions of
the effective magnetic fields induced by spin chirality in crossed nanowires
with three characteristic magnetic structures: a radiated-shape, an antivortex,
and a uniform-like states. Our results indicate that, unlike the anomalous Hall
effect, the topological Hall effect (which is related to the spin chirality)
depends on both the polarity and the vorticity. Therefore, measuring the
topological Hall effect can detect both the polarity and the vorticity
simultaneously in crossed nanowires. This approach may be suitable for use as
an elemental technique in the quest for a next-generation multi-value memory.",1703.06051v1
2017/4/20,Current-induced effective magnetic field in a half-metallic oxide La0.67Sr0.33MnO3,"We investigated current-induced effective magnetic field Heff in
half-metallic oxide La0.67Sr0.33MnO3 (LSMO) films with various thicknesses by
using the planar Hall effect. Applying in-plane current to the LSMO films
exerted an in-plane Heff orthogonal to the current direction on magnetization.
The Heff magnitude increased with increasing current magnitude, and the
direction reversed when the applied current switched to opposite sign. Assuming
that a 6.5-u.c. insulating layer is created in the LSMO, the values of Heff
observed in devices with three different LSMO thicknesses were almost scaled
with current density, evaluated from the effective LSMO thickness excluding the
insulating layer, suggesting that Heff is induced in the LSMO bulk.",1704.05989v1
2017/4/28,Superconducting States for Semi-Dirac Fermions at Zero and Finite Magnetic Fields,"We address the superconducting singlet state of anisotropic Dirac fermions
that disperse linearly in one direction and parabolically in the other. For
systems that have uniaxial anisotropy, we show that the electromagnetic
response to an external magnetic flux is extremely anisotropic near the quantum
critical point of the superconducting order. In the quantum critical regime and
above a critical magnetic field, we show that the superconductor may form a
novel exotic smectic state, with a stripe pattern of flux domains.",1704.08780v3
2017/5/17,Spin-polaron formation and magnetic state diagram in La doped $CaMnO_3$,"$La_xCa_{1-x}MnO_3$ (LCMO) has been studied in the framework of density
functional theory (DFT) using Hubbard-U correction. We show that the formation
of spin-polarons of different configurations is possible in the G-type
antiferromagentic phase. We also show that the spin-polaron (SP) solutions are
stabilized due to an interplay of magnetic and lattice effects at lower La
concentrations and mostly due to the lattice contribution at larger
concentrations. Our results indicate that the development of SPs is unfavorable
in the C- and A-type antiferromagnetic phases. The theoretically obtained
magnetic state diagram is in good agreement with previously reported
experimental results",1705.06081v2
2017/7/24,Magnetic properties of quasi one-dimensional vanadium-benzene nanowire affected by gas molecules: a first-principle study,"Magnetic properties of quasi one-dimensional vanadium-benzene nanowires
(VBNW) are investigated theoretically with the absorption of gas molecules-NO
and NO2. With the increase adsorption of NO on VBNW, the phase transition from
half metal to ferromagnetic metal and last to paramagnetic semiconductor can be
observed. With the increase of NO2 on VBNW, half metallic property can be
enhanced at first and decreased later. Thus, the electronic and magnetic
properties of VBNW can be sensitive and selective to NO and NO2, revealing the
potential applications in spintronic sensors of these two kinds of molecules.",1707.07423v1
2017/8/8,Reinvestigation on large perpendicular magnetic anisotropy in Fe/MgO interface from first-principles approach,"We investigated electronic structure and magnetic anisotropy in the Fe/MgO
interface of magnetic metal and dielectric insulator under the Cr layer of
small electronegativity, by means of the first-principles density functional
approach. The result indicates that the interface resonance state gets occupied
unlike a typical rigid band picture as the number of Fe layers decreases,
finding large perpendicular anisotropies in the oscillating behavior for
thickness dependence. We discuss scenarios of the two dimensional van Hove
singularity associated with flat band dispersions, and also the accuracies of
anisotropy energy in comparison with the available experimental data.",1708.02400v1
2017/8/28,Evidence for field induced proximity type behavior in ferromagnetic nanofluid,"We report some unusual magnetic properties observed in CoFe2O4 based
ferrofluid (with an average particle size of D = 6 nm). More precisely, in
addition to the low-field ferromagnetic (FM) phase transition with an intrinsic
Curie temperature T_Cb=350K, a second phase transition with an extrinsic Curie
temperature T_Cw = 266K emerges at higher (saturating) magnetic field. The
transitions meet at the crossover point T_cr = 210 K. The origin of the second
transition is attributed to magnetic field induced proximity type interaction
between FM particles through non-FM layers.",1708.08373v1
2017/9/8,Room temperature ferromagnetism in transparent and conducting Mn-doped $SnO_{2}$ thin films,"The magnetization as a function of magnetic field showed hysteretic behavior
at room temperature. According to the temperature dependence of the
magnetization, the Curie temperature $(T_{C})$ is higher than 350 K.
Ferromagnetic Mn-doped tin oxide thin films exhibited low electrical
resistivity and high optical transmittance in the visible region (400-800 nm).
The coexistence of ferromagnetism, high visible transparency and high
electrical conductivity in the Mn-doped $SnO_{2}$ films is expected to be a
desirable trait for spintronics devices.",1709.05930v1
2017/10/19,Tailoring symmetric metallic and magnetic edge states of nanoribbon in semiconductive monolayer PtS2,"Fabrication of atomic scale of metallic wire remains challenging. In present
work, a nanoribbon with two parallel symmetric metallic and magnetic edges was
designed from semiconductive monolayer PtS2 by employing first-principles
calculations based on density functional theory. Edge energy, bonding charge
density, band structure and simulated STM of possible edges states of PtS2 were
systematically studied. It was found that Pt-terminated edge nanoribbons were
the relatively stable metallic and magnetic edge tailored from a noble
transition metal dichalcogenides PtS2. The nanoribbon with two atomic metallic
wires may have promising application as nano power transmission lines, which at
least two lines are needed.",1710.07008v1
2017/11/30,Spin glass transition in a thin-film NiO/Permalloy bilayer,"We experimentally study magnetization aging in a thin-film NiO/Permalloy
bilayer. Aging characteristics are nearly independent of temperature below the
exchange bias blocking temperature, but rapidly vary above it. The dependence
on the magnetic history qualitatively changes across this temperature. The
observed behaviors are consistent with the spin glass transition at the
exchange bias blocking temperature, with significant implications for magnetism
and magnetoelectronic phenomena in antiferromagnet/ferromagnet bilayers.",1711.11544v1
2018/3/8,Relativistic quantum dynamics of twisted electron beams in arbitrary electric and magnetic fields,"General relativistic quantum dynamics of twisted (vortex) Dirac particles is
constructed. The Hamiltonian and equations of motion in the Foldy-Wouthuysen
representation are derived for a twisted relativistic electron in arbitrary
electric and magnetic fields. A critical experiment for a verification of the
results is proposed. The new important effect of a radiative orbital
polarization of a twisted electron beam in a magnetic field resulting in a
nonzero average projection of the intrinsic orbital angular momentum on the
field direction is predicted.",1803.07410v2
2018/5/15,Atomic-scale detection of magnetic impurity interactions in bulk semiconductors,"We demonstrate on the basis of ab initio simulations how passivated
semiconductor surfaces can be exploited to study bulklike interaction
properties and wave functions of magnetic impurities on the atomic scale with
conventional and spin-polarized scanning tunneling microscopy. By applying our
approach to the case of $3d$ transition metal impurities close to the
H/Si$(111)$ surface, we show exemplarily that their wave functions in Si are
less extended than for Mn in GaAs, thus obstructing ferromagnetism in Si.
Finally, we discuss possible applications of this method to other dilute
magnetic semiconductors.",1805.05745v1
2018/5/21,Magnetic skyrmions as host of neutrino mass spectroscopy,"Large magneto-electric effect in multi-ferroics and topological protection
against decays of excited magnetic skyrmions are an ideal setting for detecting
radiative emission of neutrino pair (RENP). We propose a new RENP scheme using
multi-ferroic magnetic skyrmion condensates in order to determine the absolute
neutrino mass including the mass hierarchy patterns, the type of neutrino mass
(Majorana vs Dirac), one of CP violation parameters, and to detect relic 1.9 K
cosmic neutrino. We critically examine the possibility of feasible experiments,
and show what are required as good targets for neutrino physics.",1805.07890v2
2018/6/8,Supersymmetric quantum electronic states in graphene under uniaxial strain,"We study uniaxially strained graphene under the influence of non-uniform
magnetic fields perpendicular to the material sample with a coordinate
independent strain tensor. For that purpose, we solve the Dirac equation with
anisotropic Fermi velocity and explore the conditions upon which such an
equation possesses a supersymmetric structure in the quantum mechanical sense
through examples. Working in a Laudau-like gauge, wave functions and energy
eigenvalues are found analytically in terms of the magnetic field intensity,
the anisotropy scales and other relevant parameters that shape the magnetic
field profiles.",1806.03382v1
2018/7/4,Control of multiferroic order by magnetic field in frustrated helimagnet MnI$_2$. Theory,"We provide a theoretical description of frustrated multiferroic $\rm MnI_2$
with a spiral magnetic ordering in magnetic field $\bf h$. We demonstrate that
subtle interplay of exchange coupling, dipolar forces, hexagonal anisotropy,
and the Zeeman energy account for the main experimental findings observed
recently in this material (Kurumaji, et al., Phys.\ Rev.\ Lett.\ {\bf 106},
167206 (2011)). We describe qualitatively the non-trivial evolution of electric
polarization $\bf P$ upon $\bf h$ rotation, changing $\bf P$ direction upon $h$
increasing, and disappearance of ferroelectricity at $h>h_c$, where $h_c$ is
smaller than the saturation field.",1807.01693v2
2018/7/5,Coulomb blockade-tuned indirect exchange in ferromagnetic nanostructures,"We develop a theory of the reversible switching of the magnetic state of the
ferromagnet-insulator-normal metalferromagnet (FINF) nanostructure. The
switching is controlled by tuning the Coulomb blockade strength via the gate
voltage on the normal metal granule. The proposed mechanism allows for
realizing the switching without passing a dissipative current through the
structure.",1807.02051v1
2018/7/15,Carbonate-Bridged Dinuclear and Trinuclear Dysprosium(III) Single-Molecule Magnets,"In 2016, we reported a single-ion magnet [Dy(bbpen)Br] with an energy barrier
over 1000 K. Here a dimeric [Dy2(mu-CO3)(bbpen)2(H2O)].H2O.CH3OH (1) and a
trimeric [Dy3(mu3-CO3)(bppen)3](CF3SO3).H2O (2) single-molecule magnets (SMMs)
were obtained through replacing the Br- anion with the carbonate bridge. Their
effective relaxation barriers at zero dc field are decrease to 51 K and 422 K,
respectively, which are consist with their structural modifications.",1807.05539v1
2018/7/26,Emission of coherent propagating magnons by insulator-based spin-orbit torque oscillators,"We experimentally demonstrate generation of coherent propagating magnons in
ultra-thin magnetic-insulator films by spin-orbit torque induced by dc electric
current. We show that this challenging task can be accomplished by utilizing
magnetic-insulator films with large perpendicular magnetic anisotropy. We
demonstrate simple and flexible spin-orbit torque devices, which can be used as
highly efficient nanoscale sources of coherent propagating magnons for
insulator-based spintronic applications.",1807.09976v1
2018/8/3,Modulated Continuous Wave Control for Energy-efficient Electron-nuclear Spin Coupling,"We develop energy efficient, continuous microwave schemes to couple electron
and nuclear spins, using phase or amplitude modulation to bridge their
frequency difference. These controls have promising applications in biological
systems, where microwave power should be limited, as well as in situations with
high Larmor frequencies due to large magnetic fields and nuclear magnetic
moments. These include nanoscale NMR where high magnetic fields achieves
enhanced thermal nuclear polarisation and larger chemical shifts. Our controls
are also suitable for quantum information processors and nuclear polarisation
schemes.",1808.01209v2
2018/8/8,Quantum magnetization fluctuations via spin shot noise,"Recent measurements in current-driven spin valves demonstrate magnetization
fluctuations that deviate from semiclassical predictions. We posit that the
origin of this deviation is spin shot noise. On this basis, our theory predicts
that magnetization fluctuations asymmetrically increase in biased junctions
irrespective of the current direction. At low temperatures, the fluctuations
are proportional to the bias, but at different rates for opposite current
directions. Quantum effects control fluctuations even at higher temperatures.
Our results are in semiquantitative agreement with recent experiments and are
in contradiction to semiclassical theories of spin-transfer torque.",1808.02907v2
2018/9/25,Anomalous Transport Behavior in Quantum Magnets,"Transport behavior characterized by a low-temperature electrical resistivity
that displays a power-law behavior $\rho(T\to 0) \propto T^s$ with an exponent
$s<2$, is commonly observed in magnetic materials in both the magnetic and
nonmagnetic phases. We give a pedagogical overview of this phenomenon that
summarizes both the experimental situation and the state of its theoretical
understanding. We also put it in context by drawing parallels with unusual
power-law transport behavior in other systems.",1809.09675v1
2018/11/1,A Single-Crystal Neutron Diffraction Study on Magnetic Structure of CsCo2Se2,"The magnetic structure of CsCo2Se2 was investigated using single-crystal
neutron diffraction technique. An antiferromagnetic transition with the
propagation vector (0,0,1) was observed at T_N = 78 K. The Co magnetic moment
0.772(6) {\mu}_B at 10 K pointing in the basal plane couples ferromagnetically
in the plane which stacks antiferromagnetically along the c direction. Tuning
and suppressing the interplane antiferromagnetic interaction may be crucial to
induce the material to a superconducting state.",1811.00243v1
2018/11/2,Noncollinear spin density of an adatom on a magnetic surface,"We show that an individual adatom on a magnetic surface can exhibit a
noncollinear spin density. Using density functional theory we study Co and Ir
adatoms on a Mn monolayer on the W(110) surface which possesses a noncollinear
canted spin structure. Due to hybridization with the nearest and next-nearest
Mn atoms of the monolayer the spin direction of the underlying substrate is
encoded into the orbitals of the adatom. This explains recent scanning
tunneling microscopy experiments showing a spin sensitive shape asymmetry of
adatoms [Serrate \emph{et al.}, Phys. Rev. B \textbf{93}, 125424 (2016)] which
confirms the intra-atomic noncollinear magnetism of the adatoms.",1811.00865v1
2018/11/8,"Evidence of enhanced magnetism in cool, polluted white dwarfs","We report the discovery of a new, polluted, magnetic white dwarf in the
Luyten survey of high-proper motion stars. High-dispersion spectra of NLTT 7547
reveal a complex heavy element line spectrum in a cool (~5 200 K)
hydrogen-dominated atmosphere showing the effect of a surface averaged field of
163 kG, consistent with a 240 kG centred dipole, although the actual field
structure remains uncertain. The abundance pattern shows the effect of accreted
material with a distinct magnesium-rich flavour. Combined with earlier
identifications, this discovery supports a correlation between the incidence of
magnetism in cool white dwarfs and their contamination by heavy elements.",1811.03210v1
2018/12/8,Magnetic properties of nanowires with ferromagnetic core and antiferromagnetic shell,"We present a Monte Carlo study of the magnetic properties of thin cylindrical
nanowires composed of a ferromagnetic core and an antiferromagnetic shell
implementing a classical spin Hamiltonian. We address systematically the impact
of interface exchange coupling on the loop characteristics and the
magnetization reversal mechanism. We study the effect of shell
polycrystallinity on the characteristic fields of the isothermal hysteresis
loop (coercivity, exchange-bias). We demonstrate that coupling to a
polycrystalline antiferromagnetic shell increases the critical core diameter
for transition from transverse to vortex domain walls.",1812.03339v1
2018/12/17,Symmetry and polarity of the voltage-controlled magnetic anisotropy studied by the Anomalous Hall effect,"The voltage-controlled magnetic anisotropy (VCMA) effect in FeB and FeB/W
films was measured by four independent methods. All measurements are consistent
and show the same tendency. The coercive field, Hall angle, anisotropy field,
the magnetization switching time and retention time linearly decrease when the
gate voltage increases and they linearly increase when the gate voltage
decreases.",1812.07077v1
2018/12/18,Magnetic excitations in frustrated fcc type-III antiferromagnet MnS$_2$,"Spin wave dispersion in the frustrated fcc type-III antiferromagnet MnS$_2$
has been determined by inelastic neutron scattering using a triple-axis
spectrometer. Existence of multiple spin wave branches, with significant
separation between high-energy and low-energy modes highlighting the intrinsic
magnetic frustration effect on the fcc lattice, is explained in terms of a spin
wave analysis carried out for the antiferromagnetic Heisenberg model for this
$S=5/2$ system with nearest and next-nearest-neighbor exchange interactions.
Comparison of the calculated dispersion with spin wave measurement also reveals
small suppression of magnetic frustration resulting from reduced exchange
interaction between frustrated spins, possibly arising from anisotropic
deformation of the cubic structure.",1812.07267v1
2018/12/28,Site preference of dopant elements in Nd2Fe14B,"Ab initio calculations of formation energy and mixing energy for
(Nd,R)2(Fe,Co)14B [R = rare-earth elements other than Nd] are presented to
address the site preference of dopants and the corresponding magnetic
properties. Contrasting trends between magnetic calculations and non-magnetic
calculations are discussed in conjunction with the nature of localized moments
in the metallic ferromagnetism at high temperatures. Implications on the
optimal heat treatment temperature to maximize the intrinsic properties are
discussed referring to the experimental Curie temperature.",1812.10945v1
2019/1/3,A magnetic tight-binding model : surface properties of transition metals and cobalt nanoparticules,"The magnetic and surface properties of some transition metals have been
investigated through the tight-binding approximation including Coulomb
correlations. These surface properties are derived from a charge neutrality
rule restricted to the d-band leading to a charge distribution including sp
surface states in agreement with a Linear Muffin-Tin Orbital (LMTO)
calculation. This new approach describes the local magnetism, surface energies
and work functions without recourse to the total energy. Our investigation
focuses on fcc cobalt, bcc iron, fcc nickel and fcc platinum surfaces with an
exploration of fcc cobalt nanoparticles.",1901.00841v4
2019/1/25,Polarized neutron reflectometry study from iron oxide nanoparticles monolayer,"We report on the polarized neutron reflectometry investigation of monolayer
of magnetic iron oxide nanoparticles assembled by the Langmuir-Schaefer method.
After deposition onto a solid substrate the polarized neutron reflectometry
measurements in the external magnetic field were carried out. Thickness,
density, roughness and in-depth resolved magnetization profile of the resulted
layer were obtained from accurate fitting routine.",1901.08819v1
2019/3/5,Electronic structure and magnetism of transition metal dihalides: bulk to monolayer,"Based on first-principles calculations, the evolution of the electronic and
magnetic properties of transition metal dihalides MX$_2$ (M= V, Mn, Fe, Co, Ni;
X = Cl, Br, I) is analyzed from the bulk to the monolayer limit. A variety of
magnetic ground states is obtained as a result of the competition between
direct exchange and superexchange. The results predict that FeX$_2$, NiX$_2$,
CoCl$_2$ and CoBr$_2$ monolayers are ferromagnetic insulators with sizable
magnetocrystalline anisotropies. This makes them ideal candidates for robust
ferromagnetism at the single layer level. Our results also highlight the
importance of spin-orbit coupling to obtain the correct ground state.",1903.01789v1
2019/3/21,Magnetic Skyrmions in Atomic Thin CrI$_3$ Monolayer,"In this letter, we report the visualization of topologically protected spin
textures, in the form of magnetic skyrmions, in recently discovered
monoatomic-thin two-dimensional CrI$_3$. By combining density functional theory
and atomistic spin dynamic simulation, we demonstrate that an application of
out-of-plane electric field to CrI$_3$ lattice favors the formation of sub-10
nm skyrmions at 0 K temperature. The spin texture arises due to a strong
correlation between magneto-crystalline anisotropy, Dzyaloshinskii-Moriya
interaction and the vertical electric field, whose shape and size could be
tuned with the magnetic field. Such finding will open new avenues for
atomic-scale quantum engineering and precision sensing.",1903.08797v1
2019/7/3,Dynamic magnetic features of a mixed ferro-ferrimagnetic ternary alloy in the form of AB$_p$C$_{1-p}$,"Dynamic magnetic features of a mixed ferro-ferrimagnetic ternary alloy in the
form of AB$_p$C$_{1-p}$, especially. The effect of Hamiltonian parameters on
the dynamic magnetic features of the system are investigated. For this aim, an
AB$_p$C$_{1-p}$ ternary alloy system was simulated within the mean-field
approximation based on a Glauber type stochastic dynamic and for simplicity, A,
B and C ions as SA = 1/2, SB = 1 and SC = 3/2, were chosen respectively. It was
found that in our dynamic system the critical temperature was always dependent
on the concentration ratio of the ternary alloy.",1907.01850v1
2019/7/5,Single-particle versus collective effects in assemblies of nanomagnets: screening,"We discuss experimentally realizable situations in which surface effects may
""screen out"" the dipolar interactions in an assembly of nanomagnets, which then
behaves as a noninteracting system. We consider three examples of physical
observables, equilibrium magnetization, ac susceptibility and ferromagnetic
resonance spectrum, to illustrate this screening effect. For this purpose, we
summarize the formalism that accounts for both the intrinsic features of the
nanomagnets and their collective effects within an assembly the condition for
screening.",1907.02720v1
2019/7/11,Conduction of surface electrons in a topological insulator with spatially random magnetization,"Using the Green functions method we study transport properties of surface
electrons in topological insulators in the presence of a correlated random
exchange field. Such an exchange field may be due to random magnetization with
correlated fluctuations. We determine the relaxation time due to scattering
from the magnetization fluctuations and from other structural defects. Then we
calculate the longitudinal charge conductivity taking into account the
contribution due to vertex correction.",1907.05313v1
2019/8/22,"Thermally activated magnetization reversal in a FeCoB nanomagnet. High-precision measurement method of coercive field, delta, retention time and size of nucleation domain","Features of thermally-activated magnetization switching have been studied in
a FeCoB nanomagnet using the N\'eel model. A method of a high-precision
measurement of the coercive field, retention time, {\Delta} and the size of the
switching nucleation domain has been proposed and experimentally demonstrated
using a Hall-probe setup. A high measurement precision, repeatability and
reliability are the features of the proposed method. The dependency of the
parameters of thermally-activated magnetization switching on the gate voltage
and the bias current were studied.",1908.08435v2
2019/8/30,Generation and imaging of magnetoacoustic waves over millimetre distances,"Using hybrid piezoelectric/magnetic systems we have generated large amplitude
magnetization waves mediated by magneto-elasticity with up to 25 degrees
variation in the magnetization orientation. We present direct imaging and
quantification of both standing and propagating acoustomagnetic waves with
different wavelengths, over large distances up to several millimeters in a
nickel thin film.",1908.11674v2
2019/9/3,Magnon Accumulation in Chirally Coupled Magnets,"We report strong chiral coupling between magnons and photons in microwave
waveguides that contain chains of small magnets on special lines. Large magnon
accumulations at one edge of the chain emerge when exciting the magnets by a
phased antenna array. This mechanism holds the promise of new functionalities
in non-linear and quantum magnonics.",1909.00953v1
2019/9/10,Analog of the Intertype Superconductivity in Nanostructured Materials,"Magnetization hysteresis loops of tin samples with an inverted opal structure
are presented. The sample formed by tin particles with the size of 70 and 128
nm is found to be a type-I superconductor. The tin sample formed by 80 and 42
nm particles demonstrates an analog of intertype superconductivity: features of
both type-I and II superconductors are observed on the magnetization isothermal
curves. Behaviors of the irreversible and reversible magnetization support
coexistence of type-I and II superconducting nanoparticles in this sample.",1909.04271v1
2019/9/10,Effect of interfacial Dzyaloshinskii-Moriya interaction on polarized neutrons reflection,"The antisymmetric Dzyaloshinskii-Moriya interaction (DMI) in
noncentrosymmetric systems leads to various nonuniform chiral magnetic
textures. Polarized neutron scattering is a powerful method for investigation
such chiral distributions. The most used technique is a small-angle neutrons
scattering (SANS). Multilayered magnetic films with the interface induced DMI
(iDMI) can't be investigated by SANS because of their small volume. The
appropriate technique is a polarized neutron reflectometry. Within the
framework of the continuum theory of micromagnetics, we explore the impact of
the iDMI on the polarized neutrons reflection from multilayers with random
magnetic anisotropy. It is shown that the iDMI gives rise to a
polarization-dependent asymmetric term in the reflection.",1909.04345v1
2019/9/19,Magnetization dynamics of the compensated ferrimagnet $Mn_{2}Ru_{x}Ga$,"Here we study both static and time-resolved dynamic magnetic properties of
the compensated ferrimagnet from room temperature down to 10K, thus crossing
the magnetic compensation temperature $T_{M}$. The behaviour is analysed with a
model of a simple collinear ferrimagnet with uniaxial anisotropy and
site-specific gyromagnetic ratios. We find a maximum zero-applied-field
resonance frequency of $\sim$160GHz and a low intrinsic Gilbert damping
$\alpha$$\sim$0.02, making it a very attractive candidate for various
spintronic applications.",1909.09085v1
2019/11/4,Sum rules in zone axis STEM-orbital angular momentum resolved electron magnetic chiral dichroism,"In this work we derive sum rules for orbital angular momentum(OAM) resolved
electron magnetic chiral dichroism (EMCD) which enable the evaluation of the
strength of spin and orbital components of the atomic magnetic moments in a
crystalline sample. We also demonstrate through numerical simulations that
these rules appear to be only slightly dependent from the dynamical diffraction
of the electron beam in the sample, making possible their application without
the need of additional dynamical diffraction calculations.",1911.02006v1
2019/12/5,Micromagnetic Modeling of the Magnetization Behavior of NiMnGa FMSMAs,"The model calculations of the magnetization curves for the internally twinned
NiMnGa ferromagnetic shape memory alloy are performed at the different volume
fractions of twin variants. The method is based on the direct minimization of
our new micromagnetic free energy model of FMSMAs taking into account both the
magnetic anisotropy energy and the magnetostatic energy contributions
associated with the laminated twin microstructure. The effect of the
magnetostatic energy is discussed in comparison with some early models, where
the magnetostatic energy was completely ignored.",1912.02495v1
2020/1/27,Bidirectional switching assisted by interlayer exchange coupling in asymmetric magnetic tunnel junctions,"We study the combined effects of spin transfer torque, voltage modulation of
interlayer exchange coupling and magnetic anisotropy on the switching behavior
of perpendicular magnetic tunnel junctions (p-MTJs). In asymmetric p-MTJs, a
linear-in-voltage dependence of interlayer exchange coupling enables the
effective perpendicular anisotropy barrier to be lowered for both voltage
polarities. This mechanism is shown to reduce the critical switching current
and effective activation energy. Finally, we analyze the possibility of having
switching via interlayer exchange coupling only.",2001.10024v1
2020/2/8,Atomic diffusion in alpha-iron across the Curie point: an effcient and transferable ab-initio-based modelling approach,"An accurate prediction of atomic diffusion in Fe alloys is challenging due to
thermal magnetic excitations and magnetic transitions. We propose an effcient
approach to address these properties via Monte Carlo simulation, using
ab-initio based effective interaction models. The temperature evolution of
self- and Cu diffusion coeffcients in alpha-iron are successfully predicted,
particularly the diffusion acceleration around the Curie point, which requires
a quantum treatment of spins. We point out a dominance of magnetic disorder
over chemical effects on diffusion in the very dilute systems.",2002.03126v2
2020/2/28,Scattering Signatures of Bond-Dependent Magnetic Interactions,"Bond-dependent magnetic interactions can generate exotic phases such as
Kitaev spin-liquid states. Experimentally determining the values of
bond-dependent interactions is a challenging but crucial problem. Here, I show
that each symmetry-allowed nearest-neighbor interaction on triangular and
honeycomb lattices has a distinct signature in paramagnetic neutron-diffraction
data, and that such data contain sufficient information to determine the spin
Hamiltonian unambiguously via unconstrained fits. Moreover, I show that
bond-dependent interactions can often be extracted from powder-averaged data.
These results facilitate experimental determination of spin Hamiltonians for
materials that do not show conventional magnetic ordering.",2002.12894v2
2020/4/1,Packing fraction related distortion of Mn$_6$C octahedra and its effect on the first order magnetic transition in Mn based antiperovskites,"In this paper, we attempt to understand the cause of magnetostructural
transformation in Mn-based antiperovskites by calculating EXAFS at the K edges
of constituent metal atoms in three antiperovskite compounds, Mn$_3$GaC,
Mn$_3$SnC and Mn$_3$InC. These three compounds have very different magnetic
ground states despite the similar cubic structure. Our calculations show that
the distortions of Mn$_6$C octahedra, which are responsible for the first-order
magnetic transition to antiferromagnetic state, depends on the packing fraction
of the lattice.",2004.00258v1
2020/4/4,Energy and momentum conservation in spin transfer,"We utilize simulations of spin-polarized electron scattering by a chain of
localized quantum spins to show that energy and linear momentum conservation
laws impose strong constraints on the properties of magnetic excitations
induced by spin transfer. In turn, electron's orbital and spin dynamics depends
on the dynamical characteristics of the local spins. Our results suggest the
possibility to achieve precise control of spin transfer-driven magnetization
dynamics by tailoring the spectral characteristics of the magnetic systems and
the driving electrons.",2004.01957v1
2020/4/8,Persistent magnetization at neutrino pair emission,"Measurement of parity violating magnetization is proposed as a means to
determine neutrino properties such as Majorana/Dirac distinction and absolute
neutrino masses. The process we use is radiative neutrino pair emission from a
collective and coherent body of lanthanoid ions doped in host crystals. A
vector-component of electron spin flip parallel to photon direction emitted
from ion excited state generates this type of magnetization which is stored for
a long time in crystals till spin relaxation time.",2004.03812v1
2020/6/14,Ideal memristor based on viscous magnetization dynamics driven by spin torque,"We show that ideal memristors - devices whose resistance is proportional to
the charge that flows through them - can be realized using spin torque-driven
viscous magnetization dynamics. The latter can be accomplished in the spin
liquid state of thin-film heterostructures with frustrated exchange, where
memristive response is tunable by proximity to the glass transition, while
current-induced Joule heating facilitates nonvolatile operation and
second-order memristive functionality beneficial for neuromorphic applications.
Ideal memristive behaviors can be achieved in other systems characterized by
viscous dynamics of physical, electronic, or magnetic degrees of freedom.",2006.07996v1
2020/6/30,Supersymmetric spin-phonon coupling prevents odd integer spins from quantum tunneling,"Quantum tunneling of the magnetization is a phenomenon that impedes the use
of small anisotropic spin systems for storage purposes even at the lowest
temperatures. Phonons, usually considered for temperature dependent relaxation
of magnetization over the anisotropy barrier, also contribute to magnetization
tunneling for integer spin quantum numbers. Here we demonstrate that certain
spin-phonon Hamiltonians are unexpectedly robust against the opening of a
tunneling gap, even for strong spin-phonon coupling. The key to understanding
this phenomenon is provided by an underlying supersymmetry that involves both
spin and phonon degrees of freedom.",2006.16575v2
2020/7/15,Magnetic-Field Dependence of Novel Gap Behavior Related to the Quantum-Size Effect,"$^{195}$Pt-NMR measurements of Pt nanoparticles with a mean diameter of 4.0
nm were performed in a high magnetic field of approximately $\mu_0 H = 23.3$ T
to investigate the low-temperature electronic state of the nanoparticles. The
characteristic temperature $T^*$, below which the nuclear spin-lattice
relaxation rate $1/T_1$ deviates from the relaxation rate of the bulk, shows a
magnetic-field dependence. This dependence supports the theoretical prediction
of the appearance of discrete energy levels.",2007.07688v1
2020/9/3,TB2J: a python package for computing magnetic interaction parameters,"We present TB2J, a Python package for the automatic computation of magnetic
interactions, including exchange and Dzyaloshinskii-Moriya interactions,
between atoms of magnetic crystals from the results of density functional
calculations. The program is based on the Green's function method with the
local rigid spin rotation treated as a perturbation. As input,the package uses
the output of either Wannier90, which is interfaced with many density
functional theory packages,or of codes based on localized orbitals. A minimal
user input is needed, which allows for easy integration into high-throughput
workflows. The package is open source under BSD 2-Clause license, available at
https://github.com/mailhexu/TB2J.",2009.01910v2
2020/9/15,Zero-field magnetic ground state of EuMg$_2$Bi$_2$,"Layered trigonal EuMg$_2$Bi$_2$ is reported to be a topological semimetal
that hosts multiple Dirac points that may be gapped or split by the onset of
magnetic order. Here, we report zero-field single-crystal neutron-diffraction
and bulk magnetic susceptibility measurements versus temperature $\chi(T)$ of
EuMg$_2$Bi$_2$ that show the intraplane ordering is ferromagnetic (Eu$^{2+},\,
S= 7/2$) with the moments aligned in the $ab$-plane while adjacent layers are
aligned antiferromagnetically (i.e., A-type antiferromagnetism) below the
N\'eel temperature.",2009.06880v1
2020/10/27,Thermodynamic approach to electric quadrupole moments,"Higher-rank electric/magnetic multipole moments are attracting attention
these days as candidate order parameters for exotic material phases. However,
quantum-mechanical formulation of those multipole moments is still an ongoing
issue. In this paper, we propose a thermodynamic definition of electric
quadrupole moments as a measure of symmetry breaking, following previous
studies of orbital magnetic dipole moments and magnetic quadrupole moments. The
obtained formulas are illustrated with a model of orbital-ordered nematic
phases of iron-based superconductors.",2010.13999v1
2021/1/8,A Hopfield neural network in magnetic films with natural learning,"Macroscopic spin ensembles possess brain-like features such as non-linearity,
plasticity, stochasticity, selfoscillations, and memory effects, and therefore
offer opportunities for neuromorphic computing by spintronics devices. Here we
propose a physical realization of artificial neural networks based on magnetic
textures, which can update their weights intrinsically via built-in physical
feedback utilizing the plasticity and large number of degrees of freedom of the
magnetic domain patterns and without resource-demanding external computations.
We demonstrate the idea by simulating the operation of a 4-node Hopfield neural
network for pattern recognition.",2101.03016v1
2021/3/15,Magnetically switchable spin wave retarder with $90^\circ$ antiferromagnetic domain wall,"Polarization, denoting the precession direction with respect to the
background magnetization, is an intrinsic degree of freedom of spin wave. Using
magnetic textures to control the spin wave polarization is fundamental and
indispensable toward reprogrammable polarization-based magnonics. Here, we show
that due to the intrinsic cubic anisotropy, a $90^\circ$ antiferromagnetic
domain wall naturally acts as a spin wave retarder (wave-plate). Moreover, for
a $90^\circ$ domain wall pair developed by introducing a second domain in a
homogenous antiferromagnetic wire, the sign of retarding effect can be flipped
by simply switching the direction of the intermediate domain.",2103.08342v2
2021/4/4,Magnetic skyrmion braids,"Filamentary textures can take the form of braided, rope-like superstructures
in nonlinear media such as plasmas and superfluids. The formation of similar
superstructures in solids has been predicted, for example from flux lines in
superconductors. However, their observation has proved challenging. Here, we
use electron microscopy and numerical methods to reveal braided superstructures
of magnetic skyrmions in thin crystals of B20-type FeGe. Their discovery opens
the door to applications of rich topological landscapes of geometric braids in
magnetic solids.",2104.01682v1
2021/4/4,General structure of a gauge boson propagator and pressure of deconfined QCD matter in a weakly magnetized medium,"We have systematically constructed the general structure of the gauge boson
self-energy and the effective propagator in presence of a nontrivial background
like hot magnetized material medium. Based on this as well as the general
structure of fermion propagator in weakly magnetized medium we have calculated
pressure of deconfined QCD matter within HTL approximation.",2104.01684v1
2021/5/28,"Role of symmetry mismatch, charge transfer and low dimensionality in the magnetic order of CaMnO$_3$/SrTiO$_3$ ultrathin heterostructures","By means of ab initio calculations, we study the effect of charge transfer
and symmetry mismatch on the magnetic and electronic properties of CaMnO$_3$
ultrathin films, epitaxially grown on SrTiO$_3$ (001). We find that the
interplay of these degrees of freedom, together with the low dimensionality and
the strain imposed by the substrate, changes the bulk occupancy of the Mn e_$g$
orbitals, which determines the magnetic configuration of the ultrathin CMO
films. A transition from an insulating G-type to a metallic A-type
antiferromagnetic configuration is stabilized.",2105.13788v1
2021/6/3,Ultrafast Electron Dynamics in Magnetic Thin Films,"In past decades, ultrafast spin dynamics in magnetic systems have been
associated with heat deposition from high energy laser pulses, limiting the
selective access to spin order. Here we use a long wavelength terahertz pump
optical probe setup to measure structural features in the ultrafast time scale.
We find that complete demagnetisation is possible with <6 THz pulses. This
occurs concurrently with longitudinal acoustic phonons and an electronic
response, followed by the magnetic response. The required fluence for full
demagnetisation is low, ruling out the necessity of a high power light source.",2106.01828v1
2021/6/11,"Multiscale modeling of cancellous bone considering full coupling of mechanical, electrical and magnetic effects","Modeling of cancellous bone has important applications in the detection and
treatment of fatigue fractures and diseases like osteoporosis. In this paper,
we present a fully coupled multiscale approach considering mechanical,
electrical and magnetic effects by using the multiscale finite element method
and a two-phase material model on the microscale. We show numerical results for
both scales, including calculations for a femur bone, comparing a healthy bone
to ones affected by different stages of osteoporosis. Here, the magnetic field
strength resulting from a small mechanical impact decreases drastically for
later stages of the disease, confirming experimental research.",2106.06343v1
2021/6/24,Magnonics vs. Ferronics,"Magnons are the elementary excitations of the magnetic order that carry spin,
momentum, and energy. Here we compare the magnon with the ferron, i.e. the
elementary excitation of the electric dipolar order that transports
polarization and heat in ferroelectrics.",2106.12775v1
2021/7/7,Fluctuation theorem for spin transport at insulating ferromagnetic junctions,"General relations for nonequilibrium spin transport at a magnetic junction
between a normal metal and a ferromagnetic insulator are derived from the
quantum fluctuation theorem. They include the extended Onsager relations
between the spin conductance and the spin-current noise that hold for
nonequilibrium states driven by an external current. These relations, that are
valid for a general setup of spin Hall magnetoresistance, provide a
comprehensive viewpoint for understanding of unidirectional spin Hall
magnetoresistance in insulating ferromagnetic junctions.",2107.03001v3
2021/7/2,MagTense: a micromagnetic framework using the analytical demagnetization tensor,"We present the open source micromagnetic framework, MagTense, which utilizes
a novel discretization approach of rectangular cuboid or tetrahedron geometry
""tiles"" to analytically calculate the demagnetization field. Each tile is
assumed to be uniformly magnetized, and from this assumption only, the
demagnetization field can be analytically calculated. Using this novel approach
we calculate the solution to the mmag standard micromagnetic problems 2, 3 and
4 and find that the MagTense framework accurately predicts the solution to each
of these. Finally, we show that simulation time can be significantly improved
by performing the dense demagnetization tensor matrix multiplications using
NVIDIA CUDA.",2107.05364v1
2021/9/18,Berry curvature induced nonlinear magnetoresistivity in two dimensional systems,"The band geometric properties of quantum materials play an elemental role in
the linear and nonlinear transport of electrons. In this paper, we propose that
the interplay of the Berry curvature, the orbital magnetic moment and the
Lorentz force can induce a finite nonlinear resistivity in two dimensional
systems in presence of a perpendicular magnetic field. The induced nonlinear
magnetoresistivity scales linearly with the magnetic field and is purely
quantum mechanical in origin. This novel transport signature can be used as an
additional experimental probe for the geometric quantities in intrinsically
time reversal symmetric systems.",2109.08979v2
2022/5/4,The Faraday effect in magnetoplasmonic nanostructures with spatial modulation of magnetization,"The magneto-optical Faraday effect in the magnetoplasmonic nanostructures
with nonuniform, periodically modulated spatial distribution of the
magnetization is considered. It is shown that in such nanostructures the
Faraday effect can experience the resonant enhancement in the spectral range of
the plasmonic and waveguide optical modes excitation. It happens both for $s$
and $p$-polarized light. Such an effect can serve for the spectrally selective
detection of the short spin waves in the magnetic materials.",2205.02020v1
2022/5/12,MagneticKP: A package for quickly constructing $\boldsymbol{k}\cdot\boldsymbol{p}$ models of magnetic and non-magnetic crystals,"We propose an efficient algorithm to construct $\boldsymbol{k}\cdot
\boldsymbol{p}$ effective Hamiltonians, which is much faster than the
previously proposed algorithms. This algorithm is implemented in MagneticKP
package. The package applies to both single-valued (spinless) and double-valued
(spinful) cases, and it works for both magnetic and nonmagnetic systems. By
interfacing with SpaceGroupIrep or MSGCorep packages, it can directly output
the $\boldsymbol{k}\cdot \boldsymbol{p}$ Hamiltonian around arbitrary momentum
and expanded to arbitrary order in $k$.",2205.05830v1
2022/6/9,Chiral magnetic skyrmions across length scales,"The profile and energy of chiral skyrmions, found in magnetic materials with
the Dzyaloshinskii-Moriya interaction, can be approximated by formulae obtained
through asymptotic analysis in the limits of small and large skyrmion radius.
Using fitting techniques, we modify these formulae so that their validity
extends to almost the entire range of skyrmion radii. Such formulae are
obtained for skyrmions that are stabilised in the presence of an external field
or easy-axis anisotropy or a combination of these. We further study the effect
of the magnetostatic field on the skyrmion profile. We compare the profile of
magnetic bubbles, stabilized without the chiral Dzyaloshinskii-Moriya
interaction to that of a chiral skyrmion.",2206.04761v1
2022/6/15,Twisted light affects ultrafast demagnetization,"Irradiation with an ultrashort laser pulse can completely destroy the
magnetic order of ferromagnetic thin films on the femtosecond timescale. This
phenomenon holds great potential for ultrafast spintronics and information
processing and is an active field of research. It is still an open question if
the angular momentum of light can support this effect. While it has been shown
that the spin of light only has a negligible influence, we experimentally
demonstrate the influence of ultrashort laser pulses with orbital angular
momentum (OAM) on the magnetization dynamics of a thin nickel film. Our results
reveal that the photonic OAM affects the demagnetization behavior within the
first hundreds of femtoseconds depending on the handedness of the OAM with
respect to the direction of the sample magnetization.",2206.07502v1
2022/6/23,Non-linear anomalous Hall effect of two-dimensional spin-3/2 heavy holes,"We identify a sizable non-linear anomalous Hall effect in the electrical
response of spin-3/2 heavy holes in zincblende semiconductor nanostructures.
The response is driven by a quadrupole interaction with the electric field
enabled by Td-symmetry. This interaction, until recently believed to be
negligible, reflects inversion symmetry breaking and in two dimensions results
in an electric-field dependent correction to the in-plane g-factor. The effect
can be observed in state-of-the-art heterostructures, either via magnetic
doping or by using a vector magnet, where even for small perpendicular magnetic
fields it is comparable in magnitude to topological materials.",2206.11916v1
2022/7/7,Tunable anomalous Hall and Nernst effects in MM'X compounds,"Based on first-principles calculations, the anomalous Hall (AHC) and
anomalous Nernst conductivities (ANC) of the XMnP (X=Ti, Zr, Hf) compounds were
evaluated, and the possibility to tailor such properties by changing the
magnetization directions was also investigated. We observed that nodal lines
and small gap areas consist the dominant contributions to AHC and ANC, where
the significant variations in AHC and ANC when altering the magnetization
direction originate from the whole Brillouin zone. Our studies gave a promising
clue on engineering magnetic intermetallic compounds for tunable transverse
thermoelectric applications.",2207.03320v1
2022/8/19,Toroidal Scattering and Nonreciprocal Transport by Magnetic Impurities,"We propose the second-order response of metals in an electric field induced
by magnetic impurities which locally break inversion symmetry. The impurities
with toroidal moments scatter conduction electrons in the presence of the
spin-orbit coupling, leading to nonreciprocal response. This mechanism is
ubiquitous when a magnetic impurity is placed off an inversion center such as
an interstitial site and a surface of a two-dimensional system.",2208.09167v2
2022/9/22,Barkhausen noise from formation of 360$^{\circ}$ domain walls in disordered permalloy thin films,"Barkhausen noise in disordered ferromagnets is typically understood to
originate primarily from jerky field-driven motion of domain walls. We study
the magnetization reversal process in disordered permalloy thin films using
micromagnetic simulations, and find that the magnetization reversal process
consists of gradual formation of immobile 360$^{\circ}$ domain walls via a
sequence of localized magnetization rotation events. The density of
360$^{\circ}$ domain walls formed within the sample as well as the statistical
properties of the Barkhausen jumps are controlled by the disorder strength.",2209.10847v2
2022/10/3,Probing domain wall dynamics in magnetic Weyl semimetals via the non-linear anomalous Hall effect,"The magnetic textures of Weyl semimetals are embedded into their topological
structure and interact dynamically with it. Here, we examine electric
field-induced structural phase transitions in domain walls mediated by the spin
transfer torque, and their footprint in charge transport. Remarkably, domain
wall dynamics lead to a transient, local, non-linear anomalous Hall effect and
non-linear anomalous drift current, which serve as direct probes of the
magnetization dynamics and of the domain wall location. We discuss experimental
observation in state-of-the-art samples.",2210.01150v1
2022/10/26,Linearized frequency domain Landau-Lifshitz-Gilbert equation formulation,"We present a general finite element linearized Landau-Lifshitz-Gilbert
equation (LLGE) solver for magnetic systems under weak time-harmonic excitation
field. The linearized LLGE is obtained by assuming a small deviation around the
equilibrium state of the magnetic system. Inserting such expansion into LLGE
and keeping only first order terms gives the linearized LLGE, which gives a
frequency domain solution for the complex magnetization amplitudes under an
external time-harmonic applied field of a given frequency. We solve the linear
system with an iterative solver using generalized minimal residual method. We
construct a preconditioner matrix to effectively solve the linear system. The
validity, effectiveness, speed, and scalability of the linear solver are
demonstrated via numerical examples.",2210.14525v1
2022/12/2,Interplay between spin wave and magnetic vortex,"In this paper, the interplay between spin wave and magnetic vortex is
studied. We find three types of magnon scatterings: skew scattering, symmetric
side deflection and back reflection, which associate with respectively magnetic
topology, energy density distribution and linear momentum transfer torque
within vortex. The vortex core exhibits two translational modes: the intrinsic
circular mode and a coercive elliptical mode, which can be excited based on
permanent and periodic magnon spin-transfer torque effects of spin wave.
Lastly, we propose a vortex-based spin wave valve in which via inhomogeneity
modulation we access arbitrary control of the phase shift.",2212.01172v1
2023/3/14,Magnetic and Structural Properties of 5d Osmate Double Perovskites Probed by Nuclear Magnetic Resonance,"The combined effect of electronic correlation and strong
spin-orbit-coupling(SOC) can give rise to a variety of exotic quantum phases.
Double perovskites provide a simple structure to study the spin-orbit-lattice
entangled states. In this thesis, focusing on the 5d osmate double perovskite
system, we conduct a combination of work including theoretical model
simulation, first-principle calculation, and nuclear magnetic resonance
experiments to understand the fundamental physical properties of this material
system.",2303.07573v1
2023/5/21,An Alternative Derivation of the Landau-Lifshitz-Gilbert Equation for Saturated Ferromagnets,"The Landau-Lifshitz-Gilbert equation for rigid and saturated ferromagnets is
derived using a two-continuum model constructed by H.F. Tiersten for elastic
and saturated ferromagnets. The relevant basic laws of physics are applied
systematically to the two continua or their combination. The exchange
interaction is introduced into the model through surface distributed magnetic
couples. This leads to a continuum theory with magnetization gradients in the
stored energy density. The saturation condition of the magnetization functions
as constraints on the energy density and has implications in the constitutive
relations.",2305.18232v1
2023/6/19,Vison manipulation with local magnetic fields,"Quantum spin liquids hosting non-abelian anyons have recently experienced
renewed interest following the discovery of a variety of materials proximate to
these quantum phases. Their anyonic excitations have potential for application
to topological quantum computation, but designing logical operations with
reduced poisoning requires developing protocols to faithfully create, move and
read-out such quasiparticles. In this paper, we present one such protocol for
manipulating $Z_2$ fluxes (``visons'') of ferromagnetic and antiferromagnetic
Kitaev models perturbed by a small uniform magnetic field. Our design employs a
local driving magnetic field and can achieve high probabilities of generating
and displacing flux pairs of both the $A_z$ and $B$ phases of the model.",2306.11092v1
2023/7/31,Phase diagram of a ferromagnetic semiconductor. The origin of superparamagnetism,"We study the theoretical model of a ferromagnetic semiconductor as a system
of randomly distributed Ising spins with a long-range exchange interaction.
Using the density-of-states approach, we analytically obtain the magnetic
susceptibility and heat capacity over a wide range of temperatures and magnetic
fields. It is shown that the finite system of spins in magnetic field less than
a certain critical field is in a superparamagnetic state due to thermodynamic
fluctuations. The complex phase structure of a ferromagnetic semiconductor is
discussed.",2307.16538v2
2023/8/3,Successful growth and room temperature ambient-pressure magnetic levitation of LK-99,"Recently, Sukbae Lee et al. reported inspiring experimental findings on the
atmospheric superconductivity of a modified lead apatite crystal (LK-99) at
room temperature (10.6111/JKCGCT.2023.33.2.061, arXiv: 2307.12008, arXiv:
2307.12037). They claimed that the synthesized LK-99 materials exhibit the
Meissner levitation phenomenon of superconductors and have a superconducting
transition temperature (Tc) higher than 400 K. Here, for the first time, we
successfully verify and synthesize the LK-99 crystals which can be magnetically
levitated with larger levitated angle than Sukbae Lee's sample at room
temperature. It is expected to realize the true potential of room temperature,
non-contact superconducting magnetic levitation in near future.",2308.01516v1
2023/8/30,Experimental setup for synchronized surface and magnetic loss studies of grain oriented FeSi steel sheets,"We present technical details on an experimental setup that allows to measure
magnetic losses in electrical steel sheets and the movement of magnetic domains
on the sample surface simultaneously. The setup is suitable to investigate
grain oriented electrical sheets in the polarization range 0.05 T to 2.3 T and
at excitation frequencies between 50 Hz and 4 kHz. The screened surface area is
13 mm x 18 mm.",2308.16344v1
2023/9/22,Using superconductivity to control magnetism: a facet of superconducting spintronics,"Magnets are used in electronics to store and read information. A magnetic
moment is rotated to a desired direction, so that information can later be
retrieved by reading this orientation. Controlling the moment via electric
currents causes resistive losses and heating, a major bottleneck in advancing
computing technologies. Superconducting spintronics can resolve this using the
unique features of superconductors.",2309.12836v1
2023/10/2,Stuffed Rare Earth Garnets,"We report the synthesis and magnetic characterization of stuffed rare earth
gallium garnets, RE3+xGa5-xO12 (RE=Lu, Yb, Er, Dy, Gd), for x up to 0.5. The
excess rare earth ions partly fill the octahedral sites normally fully occupied
by Ga3+, forming disordered pairs of corner-shared face-sharing magnetic
tetrahedra. The Curie-Weiss constants and observed effective moments per rare
earth are smaller than are seen for the unstuffed gallium garnets. No
significant change in the field-dependent magnetization is observed but missing
entropy is seen when integrating the low-temperature heat capacity to 0.5 K.",2310.01606v1
2023/12/3,Thermally Averaged Magnetic Anisotropy Tensors via Machine Learning Based on Gaussian Moments,"We propose a machine learning method to model molecular tensorial quantities,
namely the magnetic anisotropy tensor, based on the Gaussian-moment
neural-network approach. We demonstrate that the proposed methodology can
achieve an accuracy of 0.3--0.4 cm$^{-1}$ and has excellent generalization
capability for out-of-sample configurations. Moreover, in combination with
machine-learned interatomic potential energies based on Gaussian moments, our
approach can be applied to study the dynamic behavior of magnetic anisotropy
tensors and provide a unique insight into spin-phonon relaxation.",2312.01415v1
2023/12/22,Hyperbolic Spin Waves in Magnetic Polar Metals,"We demonstrate the emergence of collective spin modes with hyperbolic
dispersion in three-dimensional spin-orbit coupled polar metals magnetized by
intrinsic ordering or applied fields. These particle-hole bound states exist
for arbitrarily weak repulsive interactions; they are optically accessible and
can be used to generate pure spin current when magnetization is tilted away
from the polar axis. We suggest material hosts for these excitations and
discuss their potential relevance to nanoscale spintronic and polaritonic
applications.",2312.14377v2
2023/11/30,Spin-Dependent Capture Mechanism for Magnetic Field Effects on Interface Recombination Current in Semiconductor Devices,"Electrically detected magnetic resonance (EDMR) and near-zero field
magnetoresistance (NZFMR) are techniques that probe defect states at dielectric
interfaces critical for metal-oxide-semiconductor (MOS) electronic devices such
as the Si/SiO$_2$ MOS field effect transistor (MOSFET). A comprehensive theory,
adapted from the trap-assisted recombination theory of Shockley, Read, and
Hall, is introduced to include the spin-dependent recombination effects that
provide the mechanism for magnetic field sensitivity.",2312.14933v1
2024/1/2,Possible Meissner effect near room temperature in copper-substituted lead apatite,"With copper-substituted lead apatite below room temperature, we observe
diamagnetic dc magnetization under magnetic field of 25 Oe with remarkable
bifurcation between zero-field-cooling and field-cooling measurements, and
under 200 Oe it changes to be paramagnetism. A glassy memory effect is found
during cooling. Typical hysteresis loops for superconductors are detected below
250 K, along with an asymmetry between forward and backward sweep of magnetic
field. Our experiment suggests at room temperature the Meissner effect is
possibly present in this material.",2401.00999v1
2024/1/9,Co-doping Er plus V or Er plus Nb into CaWO4,"Er3+ plus V5+, and Er3+ plus Nb5+ co-doped CaWO4, formulas Ca1-xErxW1-xMxO4,
were synthesized in air by a conventional solid-state method. A color change
from white to pink was observed in the final products. An equal fraction of
dopants was employed to obtain charge neutrality, and the limits of the
solubility for our conditions are lower than x=0.15. The magnetic
susceptibility data shows that that the magnetic coupling becomes increasingly
antiferromagnetic with increasing Er3+content. The Curie-Weiss fit and
isothermal magnetization imply that different degrees of spin-orbit coupling
appear to be present in the two doping systems. No transitions were observed in
the heat capacity data above 0.4 K.",2401.04790v1
2024/2/26,Efficient calculation of magnetocrystalline anisotropy energy using symmetry-adapted Wannier functions,"Magnetocrystalline anisotropy, a crucial factor in magnetic properties and
applications like magnetoresistive random-access memory, often requires
extensive $k$-point mesh in first-principles calculations. In this study, we
develop a Wannier orbital tight-binding model incorporating crystal and spin
symmetries and utilize time-reversal symmetry to divide magnetization
components. This model enables efficient computation of magnetocrystalline
anisotropy. Applying this method to $\mathrm{L1_0}$ $\mathrm{FePt}$ and
$\mathrm{FeNi}$, we calculate the dependence of the anisotropic energy on
$k$-point mesh size, chemical potential, spin-orbit interaction, and
magnetization direction. The results validate the practicality of the models to
the energy order of $10~[\mathrm{\mu eV}/f.u.]$.",2402.16331v1
2023/12/6,MatterGen: a generative model for inorganic materials design,"The design of functional materials with desired properties is essential in
driving technological advances in areas like energy storage, catalysis, and
carbon capture. Generative models provide a new paradigm for materials design
by directly generating entirely novel materials given desired property
constraints. Despite recent progress, current generative models have low
success rate in proposing stable crystals, or can only satisfy a very limited
set of property constraints. Here, we present MatterGen, a model that generates
stable, diverse inorganic materials across the periodic table and can further
be fine-tuned to steer the generation towards a broad range of property
constraints. To enable this, we introduce a new diffusion-based generative
process that produces crystalline structures by gradually refining atom types,
coordinates, and the periodic lattice. We further introduce adapter modules to
enable fine-tuning towards any given property constraints with a labeled
dataset. Compared to prior generative models, structures produced by MatterGen
are more than twice as likely to be novel and stable, and more than 15 times
closer to the local energy minimum. After fine-tuning, MatterGen successfully
generates stable, novel materials with desired chemistry, symmetry, as well as
mechanical, electronic and magnetic properties. Finally, we demonstrate
multi-property materials design capabilities by proposing structures that have
both high magnetic density and a chemical composition with low supply-chain
risk. We believe that the quality of generated materials and the breadth of
MatterGen's capabilities represent a major advancement towards creating a
universal generative model for materials design.",2312.03687v2
2001/6/6,New circumstellar magnetic field diagnostics,"In this paper I will discuss new magnetic field diagnostics and
instrumentation for an area of astrophysics where magnetic field observations
have been difficult - circumstellar material. Such diagnostics would be
particularly relevant to star formation and evolution. Stellar photosphere
diagnostics include the Zeeman effect and atomic scattering diagnostics like
the Hanle Effect and atomic alignment. The Zeeman Effect is in general not
sensitive enough for the field strengths expected for circumstellar material,
and it is easily defeated by Doppler broadening in a dynamic envelope. Atomic
scattering diagnostics, pioneered recently for the Sun, are promising, but have
never been applied outside the Sun. For the study of unresolved envelopes, the
Hanle Effect may be applicable particularly in the ultraviolet. A medium
resolution UV spectropolarimeter, for instance, would serve for such studies.
Atomic alignment effects could utilize a ground-based, high signal-to-noise
spectropolarimeter, with profile information from high spectral resolution. I
will briefly mention several instrumentation development efforts in these
directions.",0106114v1
2006/8/4,Enhanced density and magnetic fields in interstellar OH masers,"Aims: We have observed the 6030 and 6035 MHz transitions of OH in high-mass
star-forming regions to obtain magnetic field estimates in both maser emission
and absorption.
  Methods: Observations were taken with the Effelsberg 100 m telescope.
  Results: Our observations are consistent with previous results, although we
do detect a new 6030 MHz maser feature near -70 km/s in the vicinity of W3(OH).
In absorption we obtain a possible estimate of -1.1 +/- 0.3 mG for the average
line-of-sight component of the magnetic field in the absorbing OH gas in K3-50
and submilligauss upper limits for the line-of-sight field strength in DR 21
and W3.
  Conclusions: These results indicate that the magnetic field strength in the
vicinity of OH masers is higher than that of the surrounding, non-masing
material, which in turn suggests that the density of masing OH regions is
higher than that of their surroundings.",0608121v1
1995/12/3,Non-collinear magnetism in Al-Mn topologically disordered systems,"We have performed the first ab-initio calculations of a possible complex
non-collinear magnetic structure in aluminium-rich Al-Mn liquids within the
real-space tight-binding LMTO method. In our previous work we predicted the
existence of large magnetic moments in Al-Mn liquids [A.M. Bratkovsky, A.V.
Smirnov, D. N. Manh, and A. Pasturel, \prb {\bf 52}, 3056 (1995)] which has
been very recently confirmed experimentally. Our present calculations show that
there is a strong tendency for the moments on Mn to have a non-collinear
(random) order retaining their large value of about 3~$\mu_B$. The d-electrons
on Mn demonstrate a pronounced non-rigid band behaviour which cannot be
reproduced within a simple Stoner picture. The origin of the magnetism in these
systems is a topological disorder which drives the moments formation and
frustrates their directions in the liquid phase.",9512013v1
1998/8/28,Ferromagnetic resonance force microscopy on microscopic cobalt single layer films,"We report mechanical detection of ferromagnetic resonance signals from
microscopic Co single layer thin films using a magnetic resonance force
microscope (MRFM). Variations in the magnetic anisotropy field and the
inhomogeneity of were clearly observed in the FMR spectra of microscopic Co
thin films 500 and 1000 angstrom thick and 40 X 200 micron^2 in lateral extent.
This demonstrates the important potential that MRFM detection of FMR holds for
microscopic characterization of spatial distribution of magnetic properties in
magnetic layered materials and devices.",9808326v1
1998/12/31,Anisotropic spin freezing in the S=1/2 zigzag ladder compound SrCuO2,"Using magnetic neutron scattering we characterize an unusual low temperature
phase in orthorhombic SrCuO2. The material contains zigzag spin ladders formed
by pairs of S=1/2 chains (J=180 meV) coupled through a weak frustrated
interaction |J'|<0.1J. At T<Tc1=5.0(4)K an elastic peak develops in a gapless
magnetic excitation spectrum indicating spin freezing on a time scale larger
than 200 picoseconds. While the frozen state has long range commensurate
antiferromagnetic order along the chains with the correlation length exceeding
200 lattice periods along the c-axis and a substantial correlation length of
60(25) spacings along the a-axis perpendicular to the zigzag plane, only 2
lattice units are correlated along the b-axis which is the direction of the
frustrated interactions. The frozen magnetic moment of each Cu ion is very
small, 0.033(7) Bohr magneton even at T=0.35K, and has unusual temperature
dependence with a cusp at Tc2=1.5K reminiscent of a phase transition. We argue
that slow dynamics of stripe-like cooperative magnetic defects in tetragonal
a-c planes yield this anisotropic frozen state.",9812440v3
1999/11/1,"First Principles Study of Structural, Electronic and Magnetic Interplay in Ferroelectromagnetic Yttrium Manganite","We present results of local spin density approximation pseudopotential
calculations for the ferroelectromagnet, yttrium manganite (YMnO3). The origin
of the differences between ferroelectric and non-ferroelectric perovskite
manganites is determined by comparing the calculated properties of yttrium
manganite in its ferroelectric hexagonal and non-ferroelectric orthorhombic
phases. In addition, orthorhombic YMnO3 is compared with the prototypical
non-ferroelectric manganite, lanthanum manganite. We show that, while the
octahedral crystal field splitting of the cubic perovskite structure causes a
centro-symmetric Jahn-Teller distortion around the Mn3+ ion, the markedly
different splitting in hexagonal perovskites creates an electronic
configuration consistent with ferroelectric distortion. We explain the nature
of the distortion, and show that a local magnetic moment on the Mn3+ ion is a
requirement for it to occur.",9910524v2
2000/7/10,Reentrant spin glass transition in La$_{0.96-y}$Nd$_{y}$K$_{0.04}$MnO$_3$: origin and effects on the colossal magnetoresistivity,"Magnetic, electric and structural properties of
La$_{0.96-y}$Nd$_y$K$_{0.04}$MnO$_{3+\delta}$ with 0$\leq y \leq$0.4 have been
studied experimentally. A disordered magnetic state is formed as La is
substituted by Nd, reflecting the competition between ferromagnetic (FM) double
exchange and antiferromagnetic superexchange interactions. Key structural
parameters are identified and correlated with changes in magnetic and electric
properties. By application of a large magnetic field, spin disorder scattering
is removed, creating a new magnetoresistance peak at a temperature lower than
the first near-$T_c$ peak. Time dependent zero-field-cooled magnetisation
measurements have been performed for $y$=0.4 around this temperature. A
reentrant spin glass (RSG) transition is evidenced, with low field ageing
properties in both the RSG and FM phases, similar to those observed in
archetypal spin glass materials.",0007154v1
2000/9/6,Mixing of magnetic and phononic excitations in incommensurate Spin-Peierls systems,"We analyze the excitation spectra of a spin-phonon coupled chain in the
presence of a soliton. This is taken as a microscopic model of a Spin-Peierls
material placed in a high magnetic field. We show, by using a semiclassical
approximation in the bosonized representation of the spins that a trapped
magnetic state obtained in the adiabatic approximation is destroyed by
dynamical phonons. Low energy states are phonons trapped by the soliton. When
the magnetic gap is smaller than the phonon frequencies the only low energy
state is a mixed magneto-phonon state with the energy of the gap. We emphasize
that our results are relevant for the Raman spectra of the inorganic
Spin-Peierls material CuGeO$_3$.",0009091v1
2000/12/7,Superconductivity on the threshold of magnetism in CePd2Si2 and CeIn3,"The magnetic ordering temperature of some rare earth based heavy fermion
compounds is strongly pressure-dependent and can be completely suppressed at a
critical pressure, p$_c$, making way for novel correlated electron states close
to this quantum critical point. We have studied the clean heavy fermion
antiferromagnets CePd$_2$Si$_2$ and CeIn$_3$ in a series of resistivity
measurements at high pressures up to 3.2 GPa and down to temperatures in the mK
region. In both materials, superconductivity appears in a small window of a few
tenths of a GPa on either side of p$_c$. We present detailed measurements of
the superconducting and magnetic temperature-pressure phase diagram, which
indicate that superconductivity in these materials is enhanced, rather than
suppressed, by the closeness to magnetic order.",0012118v1
2001/2/5,Theory of Thermal Remagnetization of Permanent Magnets,"A self-consistent mean-field theory explaining the thermal remagnetization
(TR) of polycrystalline permanent magnets is given. The influence of the
environment of a grain is treated by an inclusion approximation, relating the
field inside the grain to the local field outside by means of an internal
demagnetization factor $n$. For the switching fields and the fluctuations of
the local fields around the mean field Gaussian distributions of widths
$\sigmas$ and $\sigmaf$ resp. are assumed. The isothermal hysteresis curve, the
recoil curves, and the TR in dependence on the model parameters $n$, $\sigmas$,
and $\sigmaf$ are calculated. Furthermore, the influence of the initial
temperature and the strong dependence of the TR on the demagnetization factor
of the sample are studied, and it is shown that for reasonable parameter sets
TR effects up to 100 % are possible. The theoretical results correspond well
with the experimental situation.",0102056v1
2001/2/27,A new class of magnetic materials: Sr2FeMoO6 and related compounds,"Ordered double perovskite oxides of the general formula, A2BB'O6, have been
known for several decades to have interesting electronic and magnetic
properties. However, a recent report of a spectacular negative
magnetoresistance effect in a specific member of this family, namely Sr2FeMoO6,
has brought this class of compounds under intense scrutiny. It is now believed
that the origin of magnetism in this class of compounds is based on a novel
kinetically-driven mechanism. This new mechanism is also likely to be
responsible for the unusually high temperature ferromagnetism in several other
systems, such as dilute magnetic semiconductors, as well as in various
half-metallic ferromagnetic systems, such as Heussler alloys.",0102502v1
2001/4/6,Dependence of the flux creep activation energy on current density and magnetic field for MgB2 superconductor,"Systematic ac susceptibility measurements have been performed on a MgB$_2$
bulk sample. We demonstrate that the flux creep activation energy is a
nonlinear function of the current density $U(j)\propto j^{-0.2}$, indicating a
nonlogarithmic relaxation of the current density in this material. The
dependence of the activation energy on the magnetic field is determined to be a
power law $U(B)\propto B^{-1.33}$, showing a steep decline in the activation
energy with the magnetic field, which accounts for the steep drop in the
critical current density with magnetic field that is observed in MgB$_2$. The
irreversibility field is also found to be rather low, therefore, the pinning
properties of this new material will need to be enhanced for practical
applications.",0104112v1
2001/4/20,Superconducting Bulk Magnets: Very High Trapped Fields and Cracking,"Improved trapped fields are reported for bulk melt-textured YBa2Cu3O7-x
(YBCO) material in the temperature range between 20 K and 50 K. Trapped fields
up to 12.2 T were obtained at 22 K on the surface of single YBCO disks (with Ag
and Zn additions). In YBCO mini-magnets, maximum trapped fields of 16 T (at 24
K) and of 11.2 T (at 47 K) were achieved using (Zn + Ag) and Zn additions,
respectively. In all cases, the YBCO disks were encapsulated in steel tubes in
order to reinforce the material against the large tensile stress acting during
the magnetizing process and to avoid cracking. We observed cracking not only
during the magnetizing process, but also as a consequence of flux jumps due to
thermomagnetic instabilities in the temperature range betweeen 20 K and 30 K.",0104396v1
2001/7/5,ZrZn2: geometrical enhancement of the local DOS and quantum design of magnetic instabilities,"The recent discovery of coexisting ferromagnetism and superconductivity in
ZrZn2, and the fact that they are simultaneously suppressed on applying
pressure suggest the possibility of a pairing mechanism which is mediated by
exchange interactions and connected with the proximity to a magnetic quantum
critical point. On the basis of first principles, full potential calculations
we study the conditions that, for ZrZn2, determine the proximity to this
magnetic instability. More specifically, we discuss the role played by the
geometrical arrangement of the lattice, the hybridization and the presence of
disorder, in addition to the widely used method of applying external pressures.
These circumstances influence the width of the relevant Zr d bands whose
narrowing, due to the reduction of the effective number of neighbours or to an
increase of the cell volume, causes an enhancement of the density of states at
the Fermi level. Finally, we highlight some general features that may aid the
design of other materials close to a magnetic instability.",0107125v4
2001/7/20,The onset of magnetic order in fcc-Fe films on Cu(100),"On the basis of a first-principles electronic structure theory of finite
temperature metallic magnetism in layered materials, we investigate the onset
of magnetic order in thin (2-8 layers) fcc-Fe films on Cu(100) substrates. The
nature of this ordering is altered when the systems are capped with copper.
Indeed we find an oscillatory dependence of the Curie temperatures as a
function of Cu-cap thickness, in excellent agreement with experimental data.
The thermally induced spin-fluctuations are treated within a mean-field
disordered local moment (DLM) picture and give rise to layer-dependent `local
exchange splittings' in the electronic structure even in the paramagnetic
phase. These features determine the magnetic intra- and interlayer interactions
which are strongly influenced by the presence and extent of the Cu cap.",0107436v1
2001/11/15,Universal Temperature Behavior of Remanent Magnetization Observed in Low-Tc and High-Tc Josephson Junction Arrays,"A comparative study of the magnetic remanence exhibited by tridimensional
Josephson junction arrays in response to an excitation with an AC magnetic
field is presented. The observed temperature behavior of the remanence curves
for disordered arrays fabricated from three different materials (Nb,
YBa_2Cu_3O_7 and La_{1.85}Sr_{0.15}CuO_4) is found to follow the same universal
law (based on the explicit temperature expressions for the activation energy
and the inductance-dominated contribution to the magnetization of the array
within the framework of the phase-slip model) regardless of the origin of the
superconducting electrodes of the junctions which form the array.",0111271v1
2002/3/23,Clustering transitions in vibro-fluidized magnetized granular materials,"We study the effects of long range interactions on the phases observed in
cohesive granular materials. At high vibration amplitudes, a gas of magnetized
particles is observed with velocity distributions similar to non-magnetized
particles. Below a transition temperature compact clusters are observed to form
and coexist with single particles. The cluster growth rate is consistent with a
classical nucleation process. However, the temperature of the particles in the
clusters is significantly lower than the surrounding gas, indicating a
breakdown of equipartition. If the system is quenched to low temperatures, a
meta-stable network of connected chains self-assemble due to the anisotropic
nature of magnetic interactions between particles.",0203488v2
2002/8/6,Pressure dependence of the magnetization in the ferromagnetic superconductor UGe_2,"The recent discovery that superconductivity occurs in several clean itinerant
ferromagnets close to low temperature magnetic instabilities naturally invites
an interpretation based on a proximity to quantum criticality. Here we report
measurements of the pressure dependence of the low temperature magnetisation in
one of these materials, UGe_2. Our results show that both of the magnetic
transitions observed in this material as a function of pressure are first order
transitions and do not therefore correspond to quantum critical points. Further
we find that the known pressure dependence of the superconducting transition is
not reflected in the pressure dependence of the static susceptibility. This
demonstrates that the spectrum of excitations giving superconductivity is not
that normally associated with a proximity to quantum criticality in weak
itinerant ferromagnets. In contrast our data suggest that instead the pairing
spectrum might be related to a sharp spike in the electronic density of states
that also drives one of the magnetic transitions.",0208115v1
2002/8/28,Low frequency 1/f noise in doped manganite grain-boundary junctions,"We have performed a systematic analysis of the low frequency 1/f-noise in
single grain boundary junctions in the colossal magnetoresistance material
La_{2/3}Ca_{1/3}MnO_{3-delta}. The grain boundary junctions were formed in
epitaxial La_{2/3}Ca_{1/3}MnO_{3-delta} films deposited on SrTiO_3 bicrystal
substrates and show a large tunneling magnetoresistance of up to 300% at 4.2 K
as well as ideal, rectangular shaped resistance versus applied magnetic field
curves. Below the Curie temperature T_C the measured 1/f noise is dominated by
the grain boundary. The dependence of the noise on bias current, temperature
and applied magnetic field gives clear evidence that the large amount of low
frequency noise is caused by localized sites with fluctuating magnetic moments
in a heavily disordered grain boundary region. At 4.2 K additional temporally
unstable Lorentzian components show up in the noise spectra that are most
likely caused by fluctuating clusters of interacting magnetic moments. Noise
due to fluctuating domains in the junction electrodes is found to play no
significant role.",0208556v1
2002/9/27,Effect of a magnetic field on long-range magnetic order in stage-4 and stage-6 superconducting La2CuO(4+y),"We have measured the enhancement of the static incommensurate spin-density
wave (SDW) order by an applied magnetic field in stage-4 and stage-6 samples of
superconducting La2CuO(4+y). We show that the stage-6 La2CuO(4+y) (Tc=32 K)
forms static long-range SDW order with the same wave-vector as that in the
previously studied stage-4 material. We have measured the field dependence of
the SDW magnetic Bragg peaks in both stage-4 and stage-6 materials at fields up
to 14.5 T. A recent model of competing SDW order and superconductivity
describes these data well.",0209648v2
2003/4/4,The easy axis of the magnetic response of the conduction electrons of yttrium and rare earths,"We describe a scheme for first-principles calculations of the static,
paramagnetic, spin susceptibility of metals with relativistic effects such as
spin-orbit coupling included. This gives the direction for an applied modulated
magnetic field to maximise its response. This easy axis depends on the
modulation's wave-vector q. For h.c.p. yttrium we find the peak response at a
q= (0,0,0.57)pi/c, coincident with a Fermi surface nesting vector, to have an
easy axis perpendicular to q. This is consistent with the {\it helical}
anti-ferromagnetic order found in many dilute rare earth-Yalloys. Conversely,
the easy axis for the response to a uniform magnetic field lies along the
c-axis. The conduction electrons' role in the canting of magnetic moments in
Gd-Y alloys and other rare earth materials is mooted.",0304112v1
2003/9/24,Magnetic susceptibilities of diluted magnetic semiconductors and anomalous Hall-voltage noise,"The carrier spin and impurity spin densities in diluted magnetic
semiconductors are considered using a semiclassical approach. Equations of
motions for the spin densities and the carrier spin current density in the
paramagnetic phase are derived, exhibiting their coupled diffusive dynamics.
The dynamical spin susceptibilities are obtained from these equations. The
theory holds for p-type and n-type semiconductors doped with magnetic ions of
arbitrary spin quantum number. Spin-orbit coupling in the valence band is shown
to lead to anisotropic spin diffusion and to a suppression of the Curie
temperature in p-type materials. As an application we derive the Hall-voltage
noise in the paramagnetic phase. This quantity is critically enhanced close to
the Curie temperature due to the contribution from the anomalous Hall effect.",0309547v1
2003/10/13,Aharonov-Bohm effect in higher genus materials,"Flux periodicity of conducting electrons on a closed surface with genus two
$g=2$ (double torus) are investigated theoretically. We examine flux
periodicity of the ground-state energy and of the wave functions as a function
of applied magnetic field. A fundamental flux period of the ground-state energy
is twice a fundamental unit of magnetic flux for uniformly applied magnetic
field, which is shown to be valid for a simple ladder geometry and carbon
double torus. Flux periodicity of the wave functions in a double torus is
complicate as compared with a simple torus ($g=1$), and an adiabatic addition
of magnetic fluxes does not provide a good quantum number for the energy
eigenstates. The results are extended to higher genus materials and the
implications of the results are discussed.",0310292v1
2004/5/27,"Magnetic behavior of Co ions in the exotic spin-chain compound,Ca3Co2O6, from 59Co NMR studies","We have performed field-swept 59Co NMR measurements on the 'exotic'
spin-chain material, Ca3Co2O6, crystallizing in K4CdCl6-type rhombohedral
structure, believed to exhibit two magnetic transition temperatures (around 24
and 12 K). This is the first NMR investigation of this family of compounds. We
are able to detect the NMR signal below about 15 K, which is a conclusive proof
for the existence of non-magnetic Co ions (Co3+ - low-spin 3d6, in addition to
magnetic Co ions) at least in a narrow temperature range around 10 K, thereby
resolving a controversy on this issue in the literature. In addition, we find
that the spin-lattice and spin-spin relaxation times undergo a dramatic
increase below about 12 K, with a profound influence on the intensity of the
NMR signal as a function of temperature, providing a microscopic evidence for
the existence of 12K-transition. The spectral features present quite an
interesting situation.",0405642v2
2004/6/30,Weak ferromagnetism and magnetoelectric coupling in bismuth ferrite,"We analyze the coupling between the ferroelectric and magnetic order
parameters in the magnetoelectric multiferroic BiFeO_3 using density functional
theory within the local spin density approximation and the LSDA+U method. We
show that weak ferromagnetism of the Dzyaloshinskii-Moriya type occurs in this
material, and we analyze the coupling between the resulting magnetization and
the structural distortions. We explore the possibility of
electric-field-induced magnetization reversal and show that, although it is
unlikely to be realized in BiFeO_3, it is not in general impossible. Finally we
outline the conditions that must be fulfilled to achieve switching of the
magnetization using an electric field.",0407003v1
2004/7/6,"High pressure effects on the electrical resistivity behavior of the Kondo lattice, YbPd2Si2","We report the influence of external pressure (P= up to 8 GPa) on the
temperature dependence of electrical resistivity of a Yb-based Kondo lattice,
YbPd2Si2, which does not undergo magnetic ordering under ambient pressure
condition. There are qualitative changes in the temperature dependence of
electrical resistivity due to the application of external pressure. While the
resistivity is found to vary quadratically below 15 K (down to 45 mK)
characteristic of Fermi-liquids, a drop is observed below 0.5 K for P= 1 GPa.
Since the resistance values do not attain zero, we are attempted to attribute
this drop to magnetic ordering, rather than to superconductivity. The
temperature at which this fall occurs goes through a peak as a function of P (8
K for2 GPa and about 5 K at higher pressures). mimicking Doniach's magnetic
phase diagram. We conclude that this is one of the few Yb-based stoichiometric
materials, in which one can travers from valence fluctuation to magnetic
ordering by the application of external pressure.",0407125v1
2004/7/29,Electronic features around Fermi level correlating to occurrence of magnetism or superconductivity in Laves-phase intermetallic compounds,"Based on density functional calculations, the relationship between magnetism
or superconductivity and electronic states around Fermi level were derived, and
the location of the Fermi level in nonmagnetic ""form"" of Laves-phase compounds
is very sensitive to determine the presence of nonmagnetism, or ferromagnetism,
or antiferromagnetism, or superconductivity. The Fermi level at the nonbonding
and antibonding regions corresponds for the nonmagnetism and magnetism,
respectively, whereas at bonding region with responsibility for
superconductivity. This rules will be very useful and convenient to search the
new magnetic and superconductive materials.",0407753v1
2004/9/14,Growth and magnetic properties of MnO2&#8722;delta nanowire microspheres,"We report the synthesis of MnO2&#8722;delta microspheres using hydrothermal
and conventional chemical reaction methods. The microspheres of
MnO2&#8722;delta consist of nanowires having a diameter of 20-50 nm and a
length of 2-8 micro m. The value of the oxygen vacancy delta estimated from the
x-ray photoelectron spectrum (XPS) is 0.3. The magnetization versus temperature
curve indicates a magnetic transition at about 13 K. It is found that a
parasitic ferromagnetic component is imposed on the antiferromagnetic structure
of MnO2&#8722;delta, which might result from distortion of the lattice
structure due to oxygen vacancies. The magnetic transition temperature TN is
about 10 K lower than that of the bulk MnO2 single crystal.",0409345v1
2004/10/19,Ferromagnetism makes a doped semiconductor less shiny,"Magnetic semiconductors have attracted interest because of the question of
how a magnetic metal can be derived from a paramagnetic insulator. Here our
approach is to carrier dope insulating FeSi and we show that the magnetic
half-metal which emerges has unprecedented optical properties, unlike those of
other low carrier density magnetic metals. All traces of the semiconducting gap
of FeSi are obliterated and the material is unique in being less reflective in
the ferromagnetic than in the paramagnetic state, corresponding to larger
rather than smaller electron scattering in the ordered phase.",0410481v1
2004/11/24,Binding energy of shallow donors in a quantum well in the presence of a tilted magnetic field,"We present results of variational calculations of the binding energy of a
neutral donor in a quantum well in the presence of a magnetic field tilted
relative to the QW plane. Assuming that the donor is located in the center of
the QW, we perform calculations for parameters typical of a II-VI wide-gap
semiconductor heterostructure, using as an example the case of a rectangular
CdTe quantum well with CdMgTe barriers. We present the dependence of the
binding energy of a neutral donor on the tilt angle and on the magnitude of the
applied magnetic filed. As a key result, we show that measurement of the
binding energy of a donor at two angles of the magnetic field with respect to
the quantum well plane can be used to unambiguously determined the conduction
band offset of the materials building up heterostructure.",0411619v1
2005/1/19,Magnetism and Transport in YbMn2Sb2,"A new ternary intermetallic compound, namely, YbMn2Sb2, has been synthesized
and its magnetic and electrical transport properties have been studied in the
temperature range of 2 to 300 K. This compound crystallizes in a trigonal,
La2O2S type structure (space group P3bm1, No. 164) and is found to be
ferromagnetically ordered at room temperature. The magnetism is attributed to
the ordering of Mn sublattice. M5 xray absorption spectrum of YbMn2Sb2 obtained
at room temperature suggests that the valency of Yb in this compound is close
to 2. Electrical resistivity of this compound is metal like and a positive
magnetoresistance of 13 percent is observed at 5 K in an applied field of 9T.
Key words Rare earth intermetallics and alloys, Magnetic properties, Xray
absorption spectroscopy, Electrical transport.",0501450v1
2005/2/15,Influence of strain and oxygen vacancies on the magnetoelectric properties of multiferroic bismuth ferrite,"The dependencies on strain and oxygen vacancies of the ferroelectric
polarization and the weak ferromagnetic magnetization in the multiferroic
material bismuth ferrite, BiFeO_3, are investigated using first principles
density functional theory calculations. The electric polarization is found to
be rather independent of strain, in striking contrast to most conventional
perovskite ferroelectrics. It is also not significantly affected by oxygen
vacancies, or by the combined presence of strain and oxygen vacancies. The
magnetization is also unaffected by strain, however the incorporation of oxygen
vacancies can alter the magnetization slightly, and also leads to the formation
of Fe^{2+}. These results are discussed in light of recent experiments on
epitaxial films of BiFeO_3 which reported a strong thickness dependence of both
magnetization and polarization.",0502364v1
2005/3/17,Relaxor ferroelectricity and colossal magnetocapacitive coupling in ferromagnetic CdCr2S4,"Multiferroic materials, which reveal magnetic and electric order, are in the
focus of recent solid state research. Especially the simultaneous occurrence of
ferroelectricity and ferromagnetism, combined with an intimate coupling of
magnetization and polarization via magneto-capacitive effects, could pave the
way for a new generation of electronic devices. Here we present measurements on
a simple cubic spinel with unusual properties: It shows ferromagnetic order and
simultaneously relaxor ferroelectricity, i.e. a ferroelectric cluster state,
reached by a smeared-out phase transition, both with sizable ordering
temperatures and moments. Close to the ferromagnetic ordering temperature the
magneto-capacitive coupling, characterized by a variation of the dielectric
constant in an external magnetic field, reaches colossal values of nearly 500%.
We attribute the relaxor properties to geometric frustration, which is well
known for magnetic moments, but here is found to impede long-range order of the
structural degrees of freedom.",0503434v1
2005/4/18,Geometrical Magnetic Frustration in Rare Earth Chalcogenide Spinels,"We have characterized the magnetic and structural properties of the CdLn2Se4
(Ln = Dy, Ho), and CdLn2S4 (Ln = Ho, Er, Tm, Yb) spinels. We observe all
compounds to be normal spinels, possessing a geometrically frustrated
sublattice of lanthanide atoms with no observable structural disorder. Fits to
the high temperature magnetic susceptibilities indicate these materials to have
effective antiferromagnetic interactions, with Curie-Weiss temperatures theta ~
-10 K, except CdYb2S4 for which theta ~ -40 K. The absence of magnetic long
range order or glassiness above T = 1.8 K strongly suggests that these
materials are a new venue in which to study the effects of strong geometrical
frustration, potentially as rich in new physical phenomena as that of the
pyrochlore oxides.",0504422v2
2005/6/14,Magnetocapacitance effect in perovskite-superlattice based multiferroics,"We report the structural and magnetoelectrical properties of
La$_{0.7}$Ca$_{0.3}$MnO$_3$/BaTiO$_3$ perovskite superlattices grown on
(001)-oriented SrTiO$_3$ by the pulsed laser deposition technique. Magnetic
hysteresis loops together with temperature dependent magnetic properties
exhibit well-defined coercivity and magnetic transition temperature (T$_C$)
\symbol{126}140 K. $DC$ electrical studies of films show that the
magnetoresistance (MR) is dependent on the BaTiO$_3$ thickness and negative
$MR$ as high as 30% at 100K are observed. The $AC$ electrical studies reveal
that the impedance and capacitance in these films vary with the applied
magnetic field due to the magnetoelectrical coupling in these structures - a
key feature of multiferroics. A negative magnetocapacitance value in the film
as high as 3% per tesla at 1kHz and 100K is demonstrated, opening the route for
designing novel functional materials.",0506305v1
2005/8/15,"First principles study of the multiferroics BiFeO$_{3}$, Bi$_{2}$FeCrO$_{6}$, and BiCrO$_{3}$: Structure, polarization, and magnetic ordering temperature","We present results of an {\it ab initio} density functional theory study of
three bismuth-based multiferroics, BiFeO$_{3}$, Bi$_{2}$FeCrO$_{6}$, and
BiCrO$_{3}$. We disuss differences in the crystal and electronic structure of
the three systems, and we show that the application of the LDA+$U$ method is
essential to obtain realistic structural parameters for Bi$_{2}$FeCrO$_{6}$. We
calculate the magnetic nearest neighbor coupling constants for all three
systems and show how Anderson's theory of superexchange can be applied to
explain the signs and relative magnitudes of these coupling constants. From the
coupling constants we then obtain a mean-field approximation for the magnetic
ordering temperatures. Guided by our comparison of these three systems, we
discuss the possibilities for designing a multiferroic material with large
magnetization above room temperature.",0508362v2
2005/9/20,Induced Magnetic Order by Ion Irradiation of Carbon-Based Structures,"In this chapter we review the magnetic effects produced by proton irradiation
on graphite, disordered carbon and fullerene films. The advantage of proton
irradiation is twofold: it enables us to make an impurity analysis
simultaneously to the implantation of hydrogen. In this chapter we will review
the main effects obtained after proton irradiation in different carbon-based
structures. This chapter is organized as follows. In section 2 we provide the
main characteristics of our irradiation facility. In this section we show an
example of element analysis obtained in one of the graphite samples used for
the irradiation studies. The irradiation effects are reviewed in section 3.
This section is divided in two main subsections that describe the effects in
oriented graphite and carbon-based thin films. In section 4 we discuss some of
the effects observed after annealing the sample at high temperatures in vacuum
or after leaving it at room temperature for a long period of time.",0509519v1
2005/11/12,Universal properties of modulated antiferromagnetic systems,"Magnetism and superconductivity are physical phenomena whose foundations are
rooted in quantum mechanics and whose technological applications do not cease
to surprise us. In this article we describe a class of magnetic materials, we
call modulated antiferromagnetic systems (MAS), that has a prominent
representative in the copper-oxide high-temperature superconductors. The class,
however, is not exclusive to these superconductors. Indeed, several materials
that belong to that class are insulators. The magnetic spectral weight of MAS
displays the following universal properties: a local intensity maximum
(resonance peak) at the commensurate antiferromagnetic wave vector; peaks at
the nearly-antiferromagnetic wave vectors for excitation energies well below
the resonance, and at wave vectors rotated by 45 degrees for energies above
resonance. Moreover, we predict an observable rotation by 45 degrees of the
peaks immediately below the resonance. All these universal signatures,
condensed in a twisted hour-glass-like spectrum, are merely consequences of the
unique topological characteristics of the single-particle magnetic dispersion
relation. We thus provide a unifying scenario that explains the phenomenology
that has been observed in inelastic neutron scattering experiments of the
high-temperature superconductors.",0511303v1
2006/4/26,"Preparation, characterization and magnetic studies of Bi_0.5 X_0.5(X=Ca,Sr)MnO_3 nanoparticles","Nanoparticles (dia ~ 5 - 7 nm) of Bi_0.5 X_0.5(X=Ca,Sr)MnO_3 are prepared by
polymer assisted sol-gel method and characterized by various physico-chemical
techniques. X-ray diffraction gives evidence for single phasic nature of the
materials as well as their structures. Mono dispersed to a large extent,
isolated nanoparticles are seen in the transmission electron micrographs. High
resolution electron microscopy shows the crystalline nature of the
nanoparticles. Superconducting quantum interferometer based magnetic
measurements from 10 K to 300 K show that these nanomanganites retain the
charge ordering (CO) nature unlike Pr and Nd based nanomanganites. The CO in Bi
based manganites is thus found to be very robust consistent with the
observation that magnetic field of the order of 130 T are necessary to melt the
CO in these compounds. These results are supported by electron magnetic
resonance measurements.",0604584v1
2006/6/9,The magnetotransport properties of La0.7Sr0.3MnO3/BaTiO3 superlattices grown by pulsed laser deposition technique,"We have investigated the magnetotransport properties of La0.7Sr0.3MnO3/BaTiO3
superlattices, grown on SrTiO3 substrate by pulsed laser deposition technique,
both with current-in-plane and current-perpendicular-to-the-plane directions.
Several features indicate the presence of magnetic inhomogeneities at the
interfaces which is independent of BaTiO3 layer thickness variation. First, the
magnetic property in the superlattices decreases. Second, a hysteresis in
magnetoresistance due to the relaxation of the resistive state is observed.
Third, a threshold under an applied magnetic field in the magnetoresistance is
seen. Such behaviors are in agreement with the phase separation scenario which
could be the possible reason for these magnetic inhomogeneities at the
interfaces. On the contrary, the magnetoresistance with the
current-perpendicular-to-the-plane direction is mostly attributed to the
tunneling effect along with the ordering of the spin at the interface. This
study confirms the importance of the interfaces in superlattices that can be
used to control novel physical properties in oxide materials.",0606232v1
2006/9/2,Spin Accumulation in the Electron Transport with Rashba Interaction,"The non-equilibrium transportation of two-dimensional electrons through a
narrow channel is investigated under the influence of the Rashba interaction.
By introducing suitable lifetime in the Green's function, the average spin
values can be calculated from the ballistic regime to the diffusive regime. It
is shown that the spin accumulation is a combined effect of the spin current
and disorders. In the diffusive regime, disorders offer a mechanism to stop the
spin current and generate the spin accumulation. In the ballistic regime, spins
are more spread out and do not have definite signs. Further consideration
indicates that the inclusion of ferromagnetic spin-spin interaction increases
the spin accumulation near the edge.",0609035v1
2006/10/30,"Nucleation of magnetisation reversal, from nanoparticles to bulk materials","We review models for the nucleation of magnetisation reversal, i.e. the
formation of a region of reversed magnetisation in an initially magnetically
saturated system. For small particles models for collective reversal, either
uniform (Stoner-Wohlfarth model) or non-uniform like curling, provide good
agreement between theory and experiment. For microscopic objects and thin
films, we consider two models, uniform (Stoner-Wohlfarth) reversal inside a
nucleation volume and a droplet model, where the free energy of an inverse
bubble is calculated taking into account volume energy (Zeeman energy) and
surface tension (domain wall energy). In macroscopic systems, inhomogeneities
in magnetic properties cause a distribution of energy barriers for nucleation,
which strongly influences effects of temperature and applied field on
magnetisation reversal. For these systems, macroscopic material parameters like
exchange interaction, spontaneous magnetisation and magnetic anisotropy can
give an indication of the magnetic coercivity, but exact values for nucleation
fields are, in general, hard to predict.",0610840v2
2006/11/30,Spin-subband populations and spin polarization of quasi two-dimensional carriers under in-plane magnetic field,"Under an in-plane magnetic field, the density of states of quasi
two-dimensional carriers deviates from the occasionally stereotypic step-like
form both quantitatively and qualitatively. For the first time, we study how
this affects the spin-subband populations and the spin-polarization as
functions of the temperature, T, and the in-plane magnetic field, B, for narrow
to wide dilute-magnetic-semiconductor quantum wells. We examine a wide range of
material and structural parameters, focusing on the quantum well width, the
magnitude of the spin-spin exchange interaction, and the sheet carrier
concentration. Generally, increasing T, the carrier spin-splitting, U,
decreases, augmenting the influence of the minority-spin carriers. Increasing
B, U increases and accordingly carriers populate majority-spin subbands while
they abandon minority-spin subbands. Furthermore, in line with the density of
states modification, all energetically higher subbands become gradually
depopulated. We also indicate the ranges where the system is completely
spin-polarized.",0611784v3
2007/5/30,Epitaxial thin films of multiferroic Bi2FeCrO6 with B-site cationic order,"Epitaxial thin films of Bi2FeCrO6 have been synthesized by pulsed laser
deposition on SrRuO3 on (100)- and (111)-oriented SrTiO3 substrates. Detailed
X-ray diffraction and cross-section transmission electron microscopy analysis
revealed a double perovskite crystal structure of the Bi2FeCrO6 epitaxial films
very similar to that of BiFeO3 along with a particularly noteworthy Fe3+/Cr3+
cation ordering along the [111] direction. The films contain no detectable
magnetic iron oxide impurities and have the correct cationic average
stoichiometry throughout their thickness. They however exhibit a slight
modulation in the Fe and Cr compositions forming complementary stripe patterns,
suggesting minor local excess or depletion of Fe and Cr. The epitaxial BFCO
films exhibit good ferroelectric and piezoelectric properties, in addition to
magnetic properties at room temperature, as well as an unexpected
crystallographic orientation dependence of their room temperature magnetic
properties. Our results qualitatively confirm the predictions made using the
ab-initio calculations: the double-perovskite structure of Bi2FeCrO6 films
exhibit a Fe3+/Cr3+ cation ordering and good multiferroic properties, along
with the unpredicted existence of magnetic ordering at room temperature.",0705.4390v1
2007/8/16,"Room-temperature magnetocaloric effect in La0.7Sr0.3Mn1-xM'xO3 (M'=Al, Ti)","Magnetic entropy and adiabatic temperature changes in and above the
room-temperature region has been measured for La0.7Sr0.3Mn1-xM'xO3 (M' = Al,
Ti) by means of magnetization and heat capacity measurements in magnetic fields
up to 6 T. The magnetocaloric effect becomes largest at the ferromagnetic
ordering temperature Tc that is tuned to ~300 K by the substitution of Al or Ti
for Mn. While the substitution of Al for Mn drastically reduces the entropy
change, it extends considerably the working temperature span and improves the
relative cooling power. The magnetocaloric effect seems to be only lightly
affected by Ti substitution. Although manganites have been considered potential
for magnetic refrigerants, the magnetocaloric effect in these materials is
limited due to the existence of short-range ferromagnetic correlations above
Tc.",0708.2168v1
2007/9/6,Magneto-optical behaviour of EuIn_2P_2,"We report results of a magneto-optical investigation of the Zintl-phase
compound EuIn$_2$P$_2$. The compound orders magnetically at $T_C$=24 K and
exhibits concomitant large magnetoresistance effects. For $T\le$50 K and
increasing magnetic fields we observe a transfer of spectral weight in
$\sigma_1(\omega)$ from energies above 1 eV into the low-energy metallic
component as well as into a mid-infrared signal centered at about 600
cm$^{-1}$. This latter absorption is reminiscent to what has been seen in a
large variety of so-called Kondo materials and ascribed to excitations across
the hybridization gap. The observed gain of Drude weight upon increasing
magnetic field suggests an enhancement of the itinerant charge-carrier
concentration due to the increasing magnetization, a phenomenon that was
previously observed in other compounds which exhibit colossal magnetoresistive
effects.",0709.0791v1
2007/9/12,Magnetic properties of the Haldane-gap material NENB,"Results of magnetization and high-field ESR studies of the new spin-1
Haldane-chain material [Ni(C2H8N2)2NO2](BF4) (NENB) are reported. A definite
signature of the Haldane state in NENB was obtained. From the analysis of the
frequency-field dependence of magnetic excitations in NENB, the
spin-Hamiltonian parameters were calculated, yielding Delta = 17.4 K,
g_parallel = 2.14, D = 7.5 K, and |E| = 0.7 K for the Haldane gap, g factor and
the crystal-field anisotropy constants, respectively. The presence of
fractional S = 1/2 chain-end states, revealed by ESR and magnetization
measurements, is found to be responsible for spin-glass freezing effects. In
addition, extra states in the excitation spectrum of NENB have been observed in
the vicinity of the Haldane gap, which origin is discussed.",0709.1779v1
2007/9/24,Spin phonon induced colinear order and magnetization plateaus in triangular and kagome antiferromagnets. Applications to CuFeO_2,"Coupling between spin and lattice degrees of freedom are important in
geometrically frustrated magnets where they can lead to degeneracy lifting and
novel orders. We show that moderate spin-lattice couplings in triangular and
Kagome antiferromagnets can induce complex colinear magnetic orders. When
classical Heisenberg spins on the triangular lattice are coupled to Einstein
phonons, a rich variety of phases emerge, including the experimentally observed
four sublattice state and the five sublattice 1/5th plateau state seen in the
magneto-electric material CuFeO$_2$. In addition we predict magnetization
plateaus at 1/3, 3/7, 1/2, 3/5 and 5/7 at these couplings. Strong spin-lattice
couplings induce a striped colinear state, seen in $\alpha$-NaFeO$_2$ and
MnBr$_2$. On the Kagome lattice, moderate spin-lattice couplings induce
colinear order, but an extensive degeneracy remains.",0709.3546v1
2007/11/26,Absorption suppression in photonic crystals,"We study electromagnetic properties of periodic composite structures, such as
photonic crystals, involving lossy components. We show that in many cases a
properly designed periodic structure can dramatically suppress the losses
associated with the absorptive component, while preserving or even enhancing
its useful functionality. As an example, we consider magnetic photonic
crystals, in which the lossy magnetic component provides nonreciprocal Faraday
rotation. We show that the electromagnetic losses in the composite structure
can be reduced by up to two orders of magnitude, compared to those of the
uniform magnetic sample made of the same lossy magnetic material. Importantly,
the dramatic absorption reduction is not a resonance effect and occurs over a
broad frequency range covering a significant portion of photonic frequency
band.",0711.4041v4
2008/1/15,Fundamentals of half-metallic Full-Heusler alloys,"Intermetallic Heusler alloys are amongst the most attractive half-metallic
systems due to the high Curie temperatures and the structural similarity to the
binary semiconductors. In this review we present an overview of the basic
electronic and magnetic properties of the half-metallic full-Heusler alloys
like Co$_2$MnGe. Ab-initio results suggest that the electronic and magnetic
properties in these compounds are intrinsically related to the appearance of
the minority-spin gap. The total spin magnetic moment in the unit cell, $M_t$,
scales linearly with the number of the valence electrons, $Z_t$, such that
$M_t=Z_t-24$ for the full-Heusler alloys opening the way to engineer new
half-metallic alloys with the desired magnetic properties. Moreover we present
analytical results on the disorder in Co$_2$Cr(Mn)Al(Si) alloys, which is
susceptible to destroy the perfect half-metallicity of the bulk compounds and
thus degrade the performance of devices. Finally we discuss the appearance of
the half-metallic ferrimagnetism due to the creation of Cr(Mn) antisites in
these compounds and the Co-doping in Mn$_2$VAl(Si) alloys which leads to the
fully-compensated half-metallic ferrimagnetism.",0801.2252v1
2008/3/17,Pushing the detection limit of Magnetic Circular Dichroism to 2 nm,"Magnetic Circular Dichroism (MCD) is a standard technique for the study of
magnetic properties of materials in synchrotron beamlines. We present here a
new scattering geometry in the Transmission Electron Microscope through which
MCD can be observed with unprecedented spatial resolution. A convergent
electron beam is used to scan a multilayer Fe/Au sample and record energy loss
spectra. Differences in the spectra induced by the magnetic moments of the Fe
atoms can be resolved with a resolution of 2 nm. This is a breakthrough
achievement when compared both to the previous EMCD resolution (200 nm) or the
best XMCD experiments (approx. 20 nm), with an improvement of two and one order
of magnitude, respectively.",0803.2415v1
2008/4/17,Interface magnetism in Fe2O3/FeTiO3-heterostructures,"To resolve the microscopic origin of magnetism in the Fe2O3/FeTiO3-system, we
have performed density functional theory calculations taking into account
on-site Coulomb repulsion. By varying systematically the concentration,
distribution and charge state of Ti in a hematite host, we compile a phase
diagram of the stability with respect to the end members and find a clear
preference to form layered arrangements as opposed to solid solutions. The
charge mismatch at the interface is accommodated through Ti4+ and a
disproportionation in the Fe contact layer into Fe2+, Fe3+, leading to
uncompensated moments in the contact layer and giving first theoretical
evidence for the lamellar magnetism hypothesis. This interface magnetism is
associated with impurity levels in the band gap showing halfmetallic behavior
and making Fe2O3/FeTiO3 heterostructures prospective materials for spintronics
applications.",0804.2870v1
2008/4/22,Memory Effect in the Photoinduced Femtosecond Rotation of Magnetization in the Ferromagnetic Semiconductor GaMnAs,"We report a femtosecond response in photoinduced magnetization rotation in
the ferromagnetic semiconductor GaMnAs, which allows for detection of a
four-state magnetic memory at the femtosecond time scale. The temporal profile
of this cooperative magnetization rotation exhibits a discontinuity that
reveals two distinct temporal regimes, marked by the transition from a highly
non-equilibrium, carrier-mediated regime within the first 200 fs, to a thermal,
lattice-heating picosecond regime.",0804.3456v1
2008/7/11,Quantitative magnetic information from reciprocal space maps in transmission electron microscopy,"One of the most challenging issues in the characterization of magnetic
materials is to obtain quantitative analysis on the nanometer scale. Here we
describe how electron magnetic circular dichroism (EMCD) measurements using the
transmission electron microscope (TEM) can be used for that purpose, utilizing
reciprocal space maps. Applying the EMCD sum rules, an orbital to spin moment
ratio of $m_L/m_S=0.08 \pm 0.01$ is obtained for Fe, which is consistent with
the commonly accepted value. Hence, we establish EMCD as a quantitative element
specific technique for magnetic studies, using a widely available instrument
with superior spatial resolution.",0807.1805v2
2008/10/2,Magnetic Modulation in Mechanical Alloyed Cr1.4fe0.6o3 Oxide,"We have synthesized Cr1.4Fe0.6O3 compound through mechanical alloying of
Cr2O3 and Fe2O3 powders and subsequent thermal annealing. The XRD spectrum, SEM
picture and microanalysis of EDAX spectrum have been used to understand the
structural evolution in the alloyed compound. The alloyed samples are matching
to rhombohedral structure with R3C space group. The observation of a modulated
magnetic order confirmed a systematic diffusion of Fe atoms into the Cr sites
of lattice structure. A field induced magnetic behaviour is seen in the field
dependence of magnetization data of the annealed samples. The behaviour is
significantly different from the mechanical alloyed samples. The experimental
results provided the indications of considering the present material as a
potential candidate for opto-electronic applications.",0810.0439v1
2008/12/18,On the transition to the normal phase for superconductors surrounded by normal conductors,"For a cylindrical superconductor surrounded by a normal material, we discuss
transition to the normal phase of stable, locally stable and critical
configurations. Associated with those phase transitions, we define critical
magnetic fields and we provide a sufficient condition for which those critical
fields coincide. In particular, when the conductivity ratio of the
superconducting and the normal material is large, we show that the
aforementioned critical magnetic fields coincide, thereby proving that the
transition to the normal phase is sharp. One key-ingredient in the paper is the
analysis of an elliptic boundary value problem involving `transmission'
boundary conditions. Another key-ingredient involves a monotonicity result
(with respect to the magnetic field strength) of the first eigenvalue of a
magnetic Schroedinger operator with discontinuous coefficients.",0812.3580v1
2009/2/13,From magnetism to one-dimensional spin liquid in the anisotropic triangular lattice,"We investigate the anisotropic triangular lattice that interpolates from
decoupled one-dimensional chains to the isotropic triangular lattice and has
been suggested to be relevant for various quasi-two-dimensional materials, such
as Cs$_2$CuCl$_4$ or $\kappa$-(ET)$_2$Cu$_2$(CN)$_3$, an organic material that
shows intriguing magnetic properties. We obtain an excellent accuracy by means
of a novel representation for the resonating valence bond wave function with
both singlet and triplet pairing. This approach allows us to establish that the
magnetic order is rapidly destroyed away from the pure triangular lattice and
incommensurate spin correlations are short range. A non-magnetic spin liquid
naturally emerges in a wide range of the phase diagram, with strong
one-dimensional character. The relevance of the triplet pairing for
$\kappa$-(ET)$_2$Cu$_2$(CN)$_3$ is also discussed.",0902.2338v1
2009/2/16,Locking electron spins into magnetic resonance by electron-nuclear feedback,"The main obstacle to coherent control of two-level quantum systems is their
coupling to an uncontrolled environment. For electron spins in III-V quantum
dots, the random environment is mostly given by the nuclear spins in the
quantum dot host material; they collectively act on the electron spin through
the hyperfine interaction, much like a random magnetic field. Here we show that
the same hyperfine interaction can be harnessed such that partial control of
the normally uncontrolled environment becomes possible. In particular, we
observe that the electron spin resonance frequency remains locked to the
frequency of an applied microwave magnetic field, even when the external
magnetic field or the excitation frequency are changed. The nuclear field
thereby adjusts itself such that the electron spin resonance condition remains
satisfied. General theoretical arguments indicate that this spin resonance
locking is accompanied by a significant reduction of the randomness in the
nuclear field.",0902.2659v1
2009/3/30,Pressure Evolution of a Field Induced Fermi Surface Reconstruction and of the Neel Critical Field in CeIn3,"We report high-pressure skin depth measurements on the heavy fermion material
CeIn3 in magnetic fields up to 64 T using a self-resonant tank circuit based on
a tunnel diode oscillator. At ambient pressure, an anomaly in the skin depth is
seen at 45 T. The field where this anomaly occurs decreases with applied
pressure until approximately 1.0 GPa, where it begins to increase before
merging with the antiferromagnetic phase boundary. Possible origins for this
transport anomaly are explored in terms of a Fermi surface reconstruction. The
critical magnetic field at which the Neel ordered phase is suppressed is also
mapped as a function of pressure and extrapolates to the previous ambient
pressure measurements at high magnetic fields and high pressure measurements at
zero magnetic field.",0903.5270v1
2009/4/22,Theory of Thermal Hall Effect in Quantum Magnets,"We present a theory of the thermal Hall effect in insulating quantum magnets,
where the heat current is totally carried by charge-neutral objects such as
magnons and spinons. Two distinct types of thermal Hall responses are
identified. For ordered magnets, the intrinsic thermal Hall effect for magnons
arises when certain conditions are satisfied for the lattice geometry and the
underlying magnetic order. The other type is allowed in a spin liquid which is
a novel quantum state since there is no order even at zero temperature. For
this case, the deconfined spinons contribute to the thermal Hall response due
to Lorentz force. These results offer a clear experimental method to prove the
existence of the deconfined spinons via a thermal transport phenomenon.",0904.3427v3
2009/4/30,The alignment of the polarization of HAe/Be stars with the interstellar magnetic field,"We present a study of the correlation between the direction of the symmetry
axis of the circumstellar material around intermediate mass young stellar
objects and that of the interstellar magnetic field. We use CCD polarimetric
data on 100 Herbig Ae/Be stars. A large number of them shows intrinsic
polarization, which indicates that their circumstellar envelopes are not
spherical. The interstellar magnetic field direction is estimated from the
polarization of field stars. There is an alignment between the position angle
of the Herbig Ae/Be star polarization and that of the field stars for the most
polarized objects. This may be an evidence that the ambient interstellar
magnetic field plays a role in shaping the circumstellar material around young
stars of intermediate mass and/or in defining their angular momentum axis.",0904.4812v2
2009/5/21,Long-range Ni/Mn structural order in epitaxial double perovskite La2NiMnO6 thin films,"We report and compare the structural, magnetic, and optical properties of
ordered La2NiMnO6 thin films and its disordered LaNi0.5Mn0.5O3 counterpart. An
x-ray diffraction study reveals that the B-site Ni/Mn ordering induces
additional XRD reflections as the crystal symmetry is transformed from a
pseudocubic perovskite unit cell in the disordered phase to a monoclinic form
with larger lattice parameters for the ordered phase. Polarized Raman
spectroscopy studies reveal that the ordered samples are characterized by
additional phonon excitations that are absent in the disordered phase. The
appearance of these additional phonon excitations is interpreted as the
clearest signature of Brillouin zone folding as a result of the long-range
Ni/Mn ordering in La2NiMnO6. Both ordered and disordered materials display a
single ferromagnetic-to-paramagnetic transition. The ordered films display also
a saturation magnetization close to 4.8 mB/f.u. and a transition temperature
(FM-TC) around 270 K, while the disordered ones have only a 3.7 mB/f.u.
saturation magnetization and a FM-TC around 138 K. The differences in their
magnetic behaviours are understood based on the distinct local electronic
configurations of their Ni/Mn cations.",0905.3550v1
2009/7/2,Exploring the spin-1/2 frustrated square lattice model with high-field magnetization measurements,"We report on high-field magnetization measurements for a number of layered
vanadium phosphates that were recently recognized as spin-1/2 frustrated square
lattice compounds with ferromagnetic nearest-neighbor couplings (J_1) and
antiferromagnetic next-nearest-neighbor couplings (J_2). The saturation fields
of the materials lie in the range from 4 to 24 T and show excellent agreement
with the previous estimates of the exchange couplings deduced from low-field
thermodynamic measurements. The consistency of the high-field data with the
regular frustrated square lattice model provides experimental evidence for a
weak impact of spatial anisotropy on the nearest-neighbor couplings in layered
vanadium phosphates. The variation of the J_2/J_1 ratio within the compound
family facilitates the experimental access to the evolution of the
magnetization curve upon the change of the frustration magnitude. Our results
support the recent theoretical prediction by Thalmeier et al. [Phys. Rev. B,
77, 104441 (2008)] and give evidence for the enhanced bending of the
magnetization curves due to the increasing frustration of the underlying spin
system.",0907.0391v1
2009/7/15,Multiferroicity in rare-earth nickelates RNiO3,"We show that charge ordered rare-earth nickelates of the type RNiO3 (R= Ho,
Lu, Pr and Nd) are multiferroic with very large magnetically induced
ferroelectric (FE) polarizations. This we determine from first principles
electronic structure calculations. The emerging FE polarization is directly
tied to the long-standing puzzle of which kind of magnetic ordering is present
in this class of materials: its direction and size indicate the type of
ground-state spin configuration that is realized. Vice versa, the small energy
differences between the different magnetic orderings suggest that a chosen
magnetic ordering can be stabilized by cooling the system in presence of an
electric field.",0907.2704v1
2009/8/27,Reciprocal and real space maps for EMCD experiments,"Electron magnetic chiral dichroism (EMCD) is an emerging tool for
quantitative measurements of magnetic properties using the transmission
electron microscope (TEM), with the possibility of nanometer resolution. The
geometrical conditions, data treatment and electron gun settings are found to
influence the EMCD signal. In this article, particular care is taken to obtain
a reliable quantitative measurement of the ratio of orbital to spin magnetic
moment using energy filtered diffraction patterns. For this purpose, we
describe a method for data treatment, normalization and selection of mirror
axis. The experimental results are supported by theoretical simulations based
on dynamical diffraction and density functional theory. Special settings of the
electron gun, so called telefocus mode, enable a higher intensity of the
electron beam, as well as a reduction of the influence from artifacts on the
signal. Using these settings, we demonstrate the principle of acquiring real
space maps of the EMCD signal. This enables advanced characterization of
magnetic materials with superior spatial resolution.",0908.3963v1
2009/11/24,Low temperature study of field induced antiferro-ferromagnetic transition in Pd doped FeRh,"The first order antiferromagnetic (AFM) to ferromagnetic (FM) transition in
the functional material Fe49(Rh0.93Pd0.07)51 has been studied at low
temperatures and high magnetic fields. We have addressed the non-monotonic
variation of lower critical field required for FM to AFM transition. It is
shown that critically slow dynamics of the transition dominates below 50 K. At
low temperature and high magnetic field, state of the system depends on the
measurement history resulting in tunable coexistence of AFM and FM phases. By
following cooling and heating in unequal magnetic field (CHUF) protocol it is
shown that equilibrium state at 6 Tesla magnetic field is AFM state. Glass like
FM state at 6 T (obtained after cooling in 8 T) shows reentrant transition with
increasing temperature; viz. devitrification to AFM state followed by melting
to FM state.",0911.4552v1
2009/12/14,Optical characterization of Bi$_2$Se$_3$ in a magnetic field: infrared evidence for magnetoelectric coupling in a topological insulator material,"We present an infrared magneto-optical study of the highly thermoelectric
narrow-gap semiconductor Bi$_2$Se$_3$. Far-infrared and mid-infrared (IR)
reflectance and transmission measurements have been performed in magnetic
fields oriented both parallel and perpendicular to the trigonal $c$ axis of
this layered material, and supplemented with UV-visible ellipsometry to obtain
the optical conductivity $\sigma_1(\omega)$. With lowering of temperature we
observe narrowing of the Drude conductivity due to reduced quasiparticle
scattering, as well as the increase in the absorption edge due to direct
electronic transitions. Magnetic fields $H \parallel c$ dramatically
renormalize and asymmetrically broaden the strongest far-IR optical phonon,
indicating interaction of the phonon with the continuum free-carrier spectrum
and significant magnetoelectric coupling. For the perpendicular field
orientation, electronic absorption is enhanced, and the plasma edge is slightly
shifted to higher energies. In both cases the direct transition energy is
softened in magnetic field.",0912.2769v2
2009/12/29,Ni3TeO6 - a collinear antiferromagnet with ferromagnetic honeycomb planes,"We report a comprehensive study of magnetic properties of Ni3TeO6. The system
crystallizes in a noncentrosymmetric rhombohedral lattice, space group R3.
There are three differently coordinated Ni atoms in the unit cell. Two of them
form an almost planar honeycomb lattice, while the third one is placed between
the layers. Magnetization and specific heat measurements revealed a single
magnetic ordering at TN = 52 K. Below TN the susceptibility with the magnetic
field parallel to the c-axis drops towards zero while the perpendicular
susceptibility remains constant, a characteristic of antiferromagnetic
materials. Neutron diffraction confirmed that the system is antiferromagnet
below TN with ferromagnetic ab-planes stacked antiferromagnetically along the
c-axis. All Ni moments are in the S = 1 spin state and point along the c-axis.",0912.5268v1
2010/1/18,The missing atom as a source of carbon magnetism,"Atomic vacancies have a strong impact in the mechanical, electronic and
magnetic properties of graphene-like materials. By artificially generating
isolated vacancies on a graphite surface and measuring their local density of
states on the atomic scale, we have shown how single vacancies modify the
electronic properties of this graphene-like system. Our scanning tunneling
microscopy experiments, complemented by tight binding calculations, reveal the
presence of a sharp electronic resonance at the Fermi energy around each single
graphite vacancy, which can be associated with the formation of local magnetic
moments and implies a dramatic reduction of the charge carriers' mobility.
While vacancies in single layer graphene naturally lead to magnetic couplings
of arbitrary sign, our results show the possibility of inducing a macroscopic
ferrimagnetic state in multilayered graphene samples just by randomly removing
single C atoms.",1001.3081v2
2010/2/4,Neutron scattering and muSR investigations of the spin liquid state with quenched disorder in LuCuGaO4,"LuCuGaO4 has magnetic Cu2+ and diamagnetic Ga3+ ions distributed on a
triangular bilayer and is suggested to undergo a spin-glass transition with T_g
approximately 0.4 K. Using muSR and neutron scattering measurements, we show
that at low temperature the spins form a short-range correlated state with spin
fluctuations detectable over a wide range of timescales: at 0.05 K magnetic
fluctuations can be detected in both the muSR time window and also extending
beyond 7 meV in the inelastic neutron scattering response, indicating magnetic
fluctuations spanning timescales between 1E-5 and 1E-10 seconds. The dynamical
susceptibility scales according to the form \chi''(\omega)T^\alpha, with
\alpha=1, throughout the measured temperature range (0.05 - 50 K). These
effects are associated with quantum fluctuations and some degree of structural
disorder in ostensibly quite different materials, including certain heavy
fermion alloys, kagome spin liquids, quantum spin glasses, and valence bond
glasses. We therefore suggest LuCuGaO4 is an interesting model compound for the
further examination of disorder and quantum magnetism.",1002.0975v2
2010/2/23,Growth model investigation of Vanadium-Benzene Polymer,"Electronic and magnetic properties of VnBzn+1 sandwich clusters are
investigated using density functional theory. Growth model is applied to
investigate the property change of Vanadium-Benzene sandwich clusters. Our
results show that, for n<8, all V ions tend to put their spin in ferromagnetic
state, and that the magnetic moments of VnBzn+1 increase linearly with n.
Finite-size effects induce a nonmonotonous behavior of the VnBzn+1 magnetic
properties. In the case of n=8, the electronic properties of VnBzn+1 has the
same characteristics with the counterpart of Vanadium-Benzene infinite wire,
hence, the critical length of VnBzn+1 is defined eight. Furthermore, our
results demonstrate that Vanadium-Benzene infinite wire is a proper material
for spin polarized transport and has a high stability in the presence of
external electronic and magnetic fields.",1002.4323v1
2010/3/30,Electric Field Effect on Magnetization and Magnetocrystalline Anisotropy at the Fe/MgO(001) Interface,"Density-functional calculations are performed to explore magnetoelectric
effects originating from the influence of an external electric field on
magnetic properties of the Fe/MgO(001) interface. It is shown that the effect
on the interface magnetization and magnetocrystalline anisotropy can be
substantially enhanced if the electric field is applied across a dielectric
material with a large dielectric constant. In particular, we predict an
enhancement of the interface magnetoelectric susceptibility by a factor of the
dielectric constant of MgO over that of the free standing Fe (001) surface. We
also predict a significant effect of electric field on the interface
magnetocrystalline anisotropy due to the change in the relative occupancy of
the 3d-orbitals of Fe atoms at the Fe/MgO interface. These results may be
interesting for technological applications such as electrically controlled
magnetic data storage.",1003.5870v1
2010/5/4,Competition between Ferrimagnetism and Magnetic Frustration in Zinc Substituted YBaFe4O7,"The substitution of zinc for iron in YBaFe4O7 has allowed the oxide series
YBaFe4-xZnxO7, with 0.40 < x < 1.50, belonging to the ""114"" structural family
to be synthesized. These oxides crystallize in the hexagonal symmetry (P63mc),
as opposed to the cubic symmetry (F-43m) of YBaFe4O7. Importantly, the d.c.
magnetization shows that the zinc substitution induces ferrimagnetism, in
contrast to the spin glass behaviour of YBaFe4O7. Moreover, a.c. susceptibility
measurements demonstrate that concomitantly these oxides exhibit a spin glass
or a cluster glass behaviour, which increases at the expense of ferrimagnetism,
as the zinc content is increased. This competition between ferrimagnetism and
magnetic frustration is interpreted in terms of lifting of the geometric
frustration, inducing the magnetic ordering, and of cationic disordering, which
favours the glassy state.",1005.0480v1
2010/7/22,Microscopic model of (CuCl)LaNb2O7: coupled spin dimers replace a frustrated square lattice,"We present a microscopic model of the spin-gap quantum magnet (CuCl)LaNb2O7
that was previously suggested as a realization of the spin-1/2 frustrated
square lattice. Taking advantage of the precise atomic positions from recent
crystal structure refinement, we evaluate individual exchange integrals and
construct a minimum model that naturally explains all the available
experimental data. Surprisingly, the deviation from tetragonal symmetry leads
to the formation of spin dimers between fourth neighbors due to a Cu-Cl-Cl-Cu
pathway with a leading antiferromagnetic exchange J4 ~ 25 K. The total
interdimer exchange amounts to 12 - 15 K. Our model is in agreement with
inelastic neutron scattering results and is further confirmed by quantum
Monte-Carlo simulations of the magnetic susceptibility and the high-field
magnetization. Our results establish (CuCl)LaNb2O7 as a non-frustrated system
of coupled spin dimers with predominant antiferromagnetic interactions and
provide a general perspective for related materials with unusual
low-temperature magnetic properties.",1007.3883v2
2010/8/17,Nonlinear Near-Field Microwave Microscope For RF Defect Localization in Superconductors,"Niobium-based Superconducting Radio Frequency (SRF) cavity performance is
sensitive to localized defects that give rise to quenches at high accelerating
gradients. In order to identify these material defects on bulk Nb surfaces at
their operating frequency and temperature, it is important to develop a new
kind of wide bandwidth microwave microscopy with localized and strong RF
magnetic fields. By taking advantage of write head technology widely used in
the magnetic recording industry, one can obtain ~200 mT RF magnetic fields,
which is on the order of the thermodynamic critical field of Nb, on submicron
length scales on the surface of the superconductor. We have successfully
induced the nonlinear Meissner effect via this magnetic write head probe on a
variety of superconductors. This design should have a high spatial resolution
and is a promising candidate to find localized defects on bulk Nb surfaces and
thin film coatings of interest for accelerator applications.",1008.2948v1
2010/9/23,Ferromagnetic order in aged Co-doped TiO2 anatase nanopowders,"Oxide based diluted magnetic semiconductor (DMS) materials have been a
subject of increasing interest due to reports of room temperature
ferromagnetism in several systems and their potential use in the development of
spintronic devices. However, concerns on the stability of the magnetic
properties of different DMS systems have been raised. Their magnetic moment is
often unstable, vanishing with a characteristic decay time of weeks or months,
which precludes the development of real applications. This paper reports on the
ferromagnetic properties of two-year-aged Ti1-xCoxO2-{\delta} reduced anatase
nanopowders with different Co contents (0.03<x<0.10). Aged samples retain
rather high values of magnetization, remanence and coercivity which provide
strong evidence for a quite preserved long-range ferromagnetic order. In what
concern Co segregation, some degree of metastability of the diluted Co doped
anatase structure could be inferred in the case of the sample with the higher
Co content.",1009.4671v1
2010/10/26,The magnetic and crystal structure of azurite Cu$_3$(CO$_3$)$_2$(OH)$_2$ as determined by neutron diffraction,"Here we present neutron diffraction results on the mineral azurite. We have
found that the crystal structure of azurite can be described in the space group
$P2_1$ which is the next lower symmetric group of $P2_1/c$ as found in earlier
work. This small change in symmetry does not greatly influence the lattice
parameters or atomic fractional coordinates which are presented here for single
crystal diffraction refinements. The ordered magnetic moment structure of this
material has been determined and is comprised of two inequivalent magnetic
moments on copper sites of magnitude 0.68(1) and 0.25(1) $\mu_{B}$. This result
is discussed in terms of the anisotropic exchange and Dzyaloshinskii-Moriya
interactions. It is found that the system is likely governed by one-dimensional
behaviour despite the long-range ordered ground state. We also highlight the
significance of strain in this material which is strongly coupled to the
magnetism.",1010.5340v2
2011/1/4,The Sensitivity of the Magnetic Properties of the ZnCr2O4 and MgCr2O4 Spinels to Non-stoichiometry,"We report that small amounts of metal atom non-stoichiometry are possible in
the ZnCr2O4 and MgCr2O4 spinels. The non-stoichiometry, though less than 2%,
significantly impacts TN and the nature of the magnetic correlations above TN.
The Zn1+xCr2-xO4 spinel is particularly sensitive. While stoichiometric ZnCr2O4
displays antiferromagnetic short range correlations in the susceptibility above
TN, ferromagnetic correlations are observed in non-stoichiometric, hole doped
Zn1+xCr2-xO4. The Mg1+xCr2-xO4 spinels are less profoundly affected by
non-stoichiometry, though significant changes are also observed. We contrast
the magnetic properties of Zn1+xCr2-xO4 and Mg1+xCr2-xO4 (x=0, 0.02, 0.04) with
those of materials with the equivalent amounts of isovalent non-magnetic Ga3+
substituted on the Cr3+ site to separate the effects of static site disorder
and hole doping.",1101.0753v1
2011/3/7,Stable magnetostructural coupling with tunable magnetoresponsive effects in hexagonal phase-transition ferromagnets,"The magnetostructural coupling between the structural and the magnetic
transition plays a crucial role in magnetoresponsive effects in a
martensitic-transition system. A combination of various magnetoresponsive
effects based on this coupling may facilitate the multifunctional applications
of a host material. Here, we demonstrate a possibility to obtain a stable
magnetostructural coupling in a broad temperature window from 350 to 70 K,
showing tunable magnetoresponsive effects, based on simultaneous manipulation
of the phase stability and the magnetic structure by suitable chemical
substitution of iron in MnNiGe. The resultant MnNiGe:Fe exhibits a
magnetic-field-induced martensitic transition from paramagnetic austenite to
ferromagnetic martensite, featuring (i) a large volume increase, (ii) a
distinct magnetization change, (iii) small thermal hysteresis and (iv) a giant
negative magnetocaloric effect. The results indicate that stable
magnetostructural coupling is accessible in hexagonal phase-transition systems
to attain the magnetoresponsive effects with broad tunability.",1103.1313v2
2011/4/8,Neutron scattering study of magnetic phase separation in nanocrystalline La$_{5/8}$Ca$_{3/8}$MnO$_3$,"We demonstrate that magnetic phase separation and competing spin order in the
colossal magnetoresistive (CMR) manganites can be directly explored via tuning
strain in bulk samples of nanocrystalline La$_{1-x}$Ca$_x$MnO$_3$. Our results
show that strain can be reversibly frozen into the lattice in order to
stabilize coexisting antiferromagnetic domains within the nominally
ferromagnetic metallic state of La$_{5/8}$Ca$_{3/8}$MnO$_3$. The measurement of
tunable phase separation via magnetic neutron powder diffraction presents a
direct route of exploring the correlated spin properties of phase separated
charge/magnetic order in highly strained CMR materials and opens a potential
avenue for realizing intergrain spin tunnel junction networks with enhanced CMR
behavior in a chemically homogeneous material.",1104.1571v2
2011/4/13,From topological insulators to superconductors and Confinement,"Topological matter in 3D is characterized by the presence of a topological BF
term in its long-distance effective action. We show that, in 3D, there is
another marginal term that must be added to the action in order to fully
determine the physical content of the model. The quantum phase structure is
governed by three parameters that drive the condensation of topological
defects: the BF coupling, the electric permittivity and the magnetic
permeability of the material. For intermediate levels of electric permittivity
and magnetic permeability the material is a topological insulator. We predict,
however, new states of matter when these parameters cross critical values: a
topological superconductor when electric permittivity is increased and magnetic
permeability is lowered and a charge confinement phase in the opposite case of
low electric permittivity and high magnetic permeability. Synthetic topological
matter may be fabricated as 3D arrays of Josephson junctions.",1104.2485v3
2011/5/24,Structural and Magnetic Characteristics of MnAs Nanoclusters Embedded in Be-doped GaAs,"We describe a systematic study of the synthesis, microstructure and
magnetization of hybrid ferromagnet-semiconductor nanomaterials comprised of
MnAs nanoclusters embedded in a p-doped GaAs matrix. These samples are created
during the in situ annealing of Be-doped (Ga,Mn)As heterostructures grown by
molecular beam epitaxy. Transmission electron microscopy and magnetometry
studies reveal two distinct classes of nanoclustered samples whose structural
and magnetic properties depend on the Mn content of the initial (Ga,Mn)As
layer. For Mn content in the range 5% - 7.5%, annealing creates a
superparamagnetic material with a uniform distribution of small clusters
(diameter around 6 nm) and with a low blocking temperature (T_B approximately
10 K). While transmission electron microscopy cannot definitively identify the
composition and crystalline phase of these small clusters, our experimental
data suggest that they may be comprised of either zinc-blende MnAs or Mn-rich
regions of (Ga,Mn)As. At higher Mn content (> 8 %), we find that annealing
results in an inhomogeneous distribution of both small clusters as well as much
larger NiAs-phase MnAs clusters (diameter around 25 nm). These samples also
exhibit supermagnetism, albeit with substantially larger magnetic moments and
coercive fields, and blocking temperatures well above room temperature.",1105.4669v1
2011/7/8,Spin-polarized Mn$^{2+}$ emission from Manganese-doped colloidal nanocrystals,"We report magneto-photoluminescence studies of strongly quantum-confined
""0-D"" diluted magnetic semiconductors (DMS), realized in Mn$^{2+}$-doped
ZnSe/CdSe core/shell colloidal nanocrystals. In marked contrast to their 3-D
(bulk), 2-D (quantum well), 1-D (quantum wire), and 0-D (self-assembled quantum
dot) DMS counterparts, the ubiquitous yellow emission band from internal
\emph{d-d} ($^4T_1 \rightarrow ^6A_1$) transitions of the Mn$^{2+}$ ions in
these nanocrystals is \emph{not} suppressed in applied magnetic fields and
\emph{does} become circularly polarized. This polarization tracks the Mn$^{2+}$
magnetization, and is accompanied by a sizable energy splitting between right-
and left-circular emission components that scales with the exciton-Mn
\emph{sp-d} coupling strength (which, in turn, is tunable with nanocrystal
size). These data highlight the influence of strong quantum confinement on both
the excitation and the emission mechanisms of magnetic ions in DMS
nano-materials.",1107.1674v1
2011/7/17,Spin current induced magnetization oscillations in a paramagnetic disc,"When electron spins are injected uniformly into a paramagnetic disc, they can
precess along the demagnetizing field induced by the resulting magnetic moment.
Normally this precession damps out by virtue of the spin relaxation which is
present in paramagnetic materials. We propose a new mechanism to excite a
steady-state form of this dynamics by injecting a constant spin current into
this paramagnetic disc. We show that the rotating magnetic field generated by
the eddy currents provide a torque which makes this possible. Unlike the
ferromagnetic equivalent, the spin-torque-oscillator, the oscillation frequency
is fixed and determined by the dimensions and intrinsic parameters of the
paramagnet. The system possesses an intrinsic threshold for spin injection
which needs to be overcome before steady-state precession is possible. The
additional application of a magnetic field lowers this threshold. We discuss
the feasibility of this effect in modern materials. Transient analysis using
pump-probe techniques should give insight in the physical processes which
accompany this effect.",1107.3288v1
2011/8/19,Quantum Anomalous Hall Effect in Magnetic Topological Insulator GdBiTe3,"The quantum anomalous Hall (QAH) state is a two-dimensional bulk insulator
with a non-zero Chern number in absence of external magnetic fields. Protected
gapless chiral edge states enable dissipationless current transport in
electronic devices. Doping topological insulators with random magnetic
impurities could realize the QAH state, but magnetic order is difficult to
establish experimentally in the bulk insulating limit. Here we predict that the
single quintuple layer of GdBiTe3 film could be a stoichiometric QAH insulator
based on ab-initio calculations, which explicitly demonstrate ferromagnetic
order and chiral edge states inside the bulk gap. We further investigate the
topological quantum phase transition by tuning the lattice constant and
interactions. A simple low-energy effective model is presented to capture the
salient physical feature of this topological material.",1108.4857v1
2011/8/25,Spin Accumulation at Ferromagnet/Non-magnetic Material Interfaces,"Many proposed and realized spintronic devices involve spin injection and
accumulation at an interface between a ferromagnet and a non-magnetic material.
We examine the electric field, voltage profile, charge distribution, spin
fluxes, and spin accumulation at such an interface. We include the effects of
both screening and spin scattering. We also include both the spin-dependent
chemical potentials {\mu}_{\uparrow,\downarrow} and the effective magnetic
field H* that is zero in equilibrium. For a Co/Cu interface, we find that the
spin accumulation in the copper is an order of magnitude larger when both
chemical potential and effective magnetic field are included. We also show that
screening contributes to the spin accumulation in the ferromagnet; this
contribution can be significant.",1108.4969v2
2011/10/10,Magnetic order and frustrated dynamics in Li(Ni0.8Co0.1Mn0.1)O2: a study by μ+SR and SQUID magnetometry,"Recently, the mixed transition metal oxides of the form Li(Ni1-y-zCoyMnz)O2,
have become the center of attention as promising candidates for novel battery
material. These materials have also revealed very interesting magnetic
properties due to the alternate stacking of planes of metal oxides on a 2D
triangular lattice and the Li-layers. The title compound,
Li(Ni0.8Co0.1Mn0.1)O2, has been investigated by both magnetometry and
measurements and {\mu}+SR. We find the evolution of localized magnetic moments
with decreasing temperature below 70 K. The magnetic ground state (T = 2 K) is,
however, shown to be a frustrated system in 3D, followed by a transition into a
possible 2D spinglass above 22 K. With further increasing temperature the
compound show the presence of remaining correlations with increasing effective
dimensionality all the way up to the ferrimagnetic transition at TC = 70 K.",1110.2071v1
2011/11/25,Growth and electronic and magnetic structure of iron oxide films on Pt(111),"Ultrathin (111)-oriented polar iron oxide films were grown on a Pt(111)
single crystal either by the reactive deposition of iron or oxidation of
metallic iron monolayers. These films were characterized using low energy
electron diffraction, scanning tunneling microscopy and conversion electron
Mossbauer spectroscopy. The reactive deposition of Fe led to the island growth
of Fe3O4, in which the electronic and magnetic properties of the bulk material
were modulated by superparamagnetic size effects for thicknesses below 2 nm,
revealing specific surface and interface features. In contrast, the oxide films
with FeO stoichiometry, which could be stabilized as thick as 4 nm under
special preparation conditions, had electronic and magnetic properties that
were very different from their bulk counterpart, w\""ustite. Unusual long range
magnetic order appeared at room temperature for thicknesses between three and
ten monolayers, the appearance of which requires severe structural modification
from the rock-salt structure.",1111.5938v2
2012/1/12,Effect of Interface Induced Exchange Fields on Cuprate-Manganite Spin Switches,"We examine the anomalous inverse spin switch behavior in
La$_{0.7}$Ca$_{0.3}$MnO$_3$ (LCMO)/YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO)/LCMO
trilayers by combined transport studies and polarized neutron reflectometry.
Measuring magnetization profiles and magnetoresistance in an in-plane rotating
magnetic field, we prove that, contrary to many accepted theoretical scenarios,
the relative orientation between the two LCMO's magnetizations is not
sufficient to determine the magnetoresistance. Rather the field dependence of
magnetoresistance is explained by the interplay between the applied magnetic
field and the (exponential tail of the) induced exchange field in YBCO, the
latter originating from the electronic reconstruction at the LCMO/YBCO
interfaces.",1201.2707v2
2012/3/6,Robustness and stability of half-metallic ferromagnetism in alkaline-earth metal mononitrides against doping and deformation,"We employ ab-initio electronic structure calculations and study the magnetic
properties of CaN and SrN compounds crystallizing in the rocksalt structure.
These alkaline-earth metal mononitrides are found to be half-metallic with a
total spin magnetic moment per formula unit of 1.0 $\mu_B$. The Curie
temperature is estimated to be 480 K for CaN and 415 K for SrN well-above the
room temperature. Upon small degrees of doping with holes or electrons, the
rigid-band model suggests that the magnetic properties are little affected.
Finally we studied for these alloys the effect of deformation taking into
account tetragonalization keeping constant the unit cell volume which models
the growth on various substrates. Even large degrees of deformation only
marginally affect the electronic and magnetic properties of CaN and SrN in the
rocksalt structure. Finally, we show that this stands also for the zincblende
structure. Our results suggest that alkaline-earth metal mononitrides are
promising materials for magnetoelectronic applications.",1203.1106v2
2012/3/8,Magnetism and Antiferroelectricity in MgB$_6$,"We report on a density functional theory study demonstrating the coexistence
of weak ferromagnetism and antiferroelectricity in boron-deficient MgB6. A
boron vacancy produces an almost one dimensional extended molecular orbital,
which is responsible for the magnetic moment formation. Then, long-range
magnetic order can emerge from the overlap of such orbitals above percolation
threshold. Although there is a finite density of states at the Fermi level, the
localized nature of the charge density causes an inefficient electron
screening. We find that the Mg ions can displace from the center of their cubic
cage, thus generating electrical dipoles. In the ground state these order in an
antiferroelectric configuration. If proved experimentally, this will be the
first material without d or f electrons displaying the coexistence of magnetic
and electric order.",1203.1836v1
2012/3/14,Temperature dependence of in-plane correlation lengths in exchange biased Co/FeF2,"We have measured resonant soft x-ray diffuse magnetic scattering as a
function of temperature in a positively exchange biased Co/FeF2 bilayer and
analyzed the data in the distorted wave Born approximation to obtain in-plane
charge and magnetic correlation lengths associated with the Co and FeF2 layers
and estimate interfacial roughness. Tuning to the Fe and Co L3 edges reveals
significantly different temperature trends in these quantities in the
antiferromagnetic and ferromagnetic layers, respectively. While the magnetic
correlation length of the uncompensated interfacial spins in FeF2 layer
increase as temperature decreases, these quantities remain unchanged in the Co
layer. Our results indicate that uncompensated Fe spins order within a range of
few hundred nanometers in otherwise randomly distributed uncompensated magnetic
moments, giving rise to spin clusters in the antiferromagnet whose size
increase as the temperature decrease.",1203.3231v1
2012/4/18,Landau theory of topological defects in multiferroic hexagonal manganites,"Topological defects in ordered states with spontaneously broken symmetry
often have unusual physical properties, such as fractional electric charge or a
quantised magnetic field-flux, originating from their non-trivial topology.
Coupled topological defects in systems with several coexisting orders give rise
to unconventional functionalities, such as the electric-field control of
magnetisation in multiferroics resulting from the coupling between the
ferroelectric and ferromagnetic domain walls. Hexagonal manganites provide an
extra degree of freedom: In these materials, both ferroelectricity and
magnetism are coupled to an additional, non-ferroelectric structural order
parameter. Here we present a theoretical study of topological defects in
hexagonal manganites based on Landau theory with parameters determined from
first-principles calculations. We explain the observed flip of electric
polarisation at the boundaries of structural domains, the origin of the
observed discrete vortices, and the clamping between ferroelectric and
antiferromagnetic domain walls. We show that structural vortices induce
magnetic ones and that, consistent with a recent experimental report,
ferroelectric domain walls can carry a magnetic moment.",1204.4126v1
2012/5/17,Tailoring Magnetic Doping in the Topological Insulator Bi2Se3,"We theoretically investigate the possibility of establishing ferromagnetism
in the topological insulator Bi2Se3 via magnetic doping of 3d transition metal
elements. The formation energies, charge states, band structures, and magnetic
properties of doped Bi2Se3 are studied using first-principles calculations
within density functional theory. Our results show that Bi substitutional sites
are energetically more favorable than interstitial sites for single impurities.
Detailed electronic structure analysis reveals that Cr and Fe doped materials
are still insulating in the bulk but the intrinsic band gap of Bi2Se3 is
substantially reduced due to the strong hybridization between the d states of
the dopants and the p states of the neighboring Se atoms. The calculated
magnetic coupling suggests that Cr doped Bi2Se3 is possible to be both
ferromagnetic and insulating, while Fe doped Bi2Se3 tends to be weakly
antiferromagnetic.",1205.3936v2
2012/5/26,New Perspective on the Reciprocity Theorem of Classical Electrodynamics,"We provide a simple physical proof of the reciprocity theorem of classical
electrodynamics in the general case of material media that contain linearly
polarizable as well as linearly magnetizable substances. The excitation source
is taken to be a point-dipole, either electric or magnetic, and the monitored
field at the observation point can be electric or magnetic, regardless of the
nature of the source dipole. The electric and magnetic susceptibility tensors
of the material system may vary from point to point in space, but they cannot
be functions of time. In the case of spatially non-dispersive media, the only
other constraint on the local susceptibility tensors is that they be symmetric
at each and every point. The proof is readily extended to media that exhibit
spatial dispersion: For reciprocity to hold, the electric susceptibility tensor
Chi_E_mn that relates the complex-valued magnitude of the electric dipole at
location r_m to the strength of the electric field at r_n must be the transpose
of Chi_E_nm. Similarly, the necessary and sufficient condition for the magnetic
susceptibility tensor is Chi_M_mn = Chi^T_M_nm.",1205.5894v1
2012/9/8,Critical role of next-nearest-neighbor interlayer interaction in magnetic behavior of magnetic/nonmagnetic multilayers,"We report magnetoresistance data in magnetic semiconductor multilayers, which
exhibit a clear step-wise behavior as a function of external field. We
attribute this highly non-trivial step-wise behavior to next-nearest-neighbor
interlayer exchange coupling. Our microscopic calculation suggests that this
next-nearest-neighbor coupling can be as large as 24% of the nearest-neighbor
coupling. It is argued that such unusually long-range interaction is made
possible by the quasi-one-dimensional nature of the system and by the long
Fermi wavelength characteristic of magnetic semiconductors.",1209.1703v1
2012/9/28,Phase separation at the magnetic-superconducting transition in La$_{0.7}$Y$_{0.3}$FeAsO$_{1-x}$F$_{x}$,"In this paper we report a detailed $\mu^{+}$SR and {}$^{19}$F-NMR study of
the La$_{0.7}$Y$_{0.3}$FeAsO$_{1-x}$F$_{x}$ class of materials. Here, the
diamagnetic La$_{1-y}$Y$_{y}$ substitution increases chemical pressure and,
accordingly, sizeably enhances the optimal superconducting transition
temperature. We investigate the magnetic-superconducting phase transition by
keeping the Y content constant ($y = 0.3$) and by varying the F content in the
range $0.025 \leq x \leq 0.15$. Our results show how magnetism and
superconductivity coexist for $x = 0.065$. Such coexistence is due to
segregation of the two phases in macroscopic regions, resembling what was
observed in LaFeAsO$_{1-x}$F$_{x}$ materials under applied hydrostatic
pressure. This scenario is qualitatively different from the nanoscopic
coexistence of the two order parameters observed when La is fully substituted
by magnetic rare-earth ions like Sm or Ce.",1209.6512v1
2012/11/23,Field-induced quantum soliton lattice in a frustrated two-leg spin-1/2 ladder,"The field-induced quantum phase transitions (QPT) of the spin ladder material
Bi(Cu(1-x)Znx)2PO6 have been investigated via 31P nuclear magnetic resonance
(NMR) on single-crystal samples with x = 0 and x = 0.01. Measurements at
temperatures between 0.25 K and 20 K in magnetic fields up to 31 T served to
establish the nature of the various phases. In BiCu2PO6, an incommensurate (IC)
magnetic order develops above a critical field mu0*H(c1) ~ 21 T; the field and
temperature dependences of the NMR lines and the resulting model for the spin
structure are discussed. Supported by results of Density-Matrix Renormalization
Group (DMRG) calculations it is argued that the observed field-induced IC order
involves the formation of a magnetic-soliton lattice. An additional QPT is
predicted to occur at H > H(c1). For x = 0.01, this IC order is found to be
stable against site disorder, although with a renormalized critical field.",1211.5522v1
2012/12/2,Manipulating the magnetic anisotropy of cobalt doped titanium dioxide by carrier accumulation,"Based on first-principles calculations, we predict that the magnetic
anisotropy energy (MAE) of Co-doped TiO$_2$ sensitively depends on carrier
accumulation. This magnetoelectric phenomenon provides a promising route to
directly manipulate the magnetization direction of diluted magnetic
semiconductor by external electric-fields. We calculate the band structures and
reveal the origin of carrier-dependent MAE in k-space. In fact, the carrier
accumulation shifts the Fermi energy and regulates the competing contributions
to MAE. The first-principles calculations provide a straightforward way to
design spintronics materials with electrically controllable spin direction.",1212.0175v3
2012/12/3,Role of covalent hybridization in martensitic structure and magnetic properties of shape memory alloys: the case of Ni50Mn5+xGa35-xCu10,"We have investigated the impact of covalent hybridization on martensitic
structure and magnetic properties of Ni50Mn5+xGa35-xCu10 shape memory alloys.
We found that the lattice distortion ((c-a)/a) of L10 martensite monotonously
changes with the substitution of Mn for Ga atoms and shows a kink behavior at
Ga(at.%)= 25 due to the weakened covalent effect between main-group and
transition-metal atoms. Moreover, owing to the competition between covalence
hybridization and magnetic ordering of introduced Mn atoms, the molecular
magnetic moment and Curie temperature coincidently show maximums at Ga(at.%)=25
as well. These behaviors are closely associated with corresponding changes of
the strength of covalent hybridization. The results therefore suggest that
careful control of the concentration of main-group atoms in Heusler alloys can
serve as an additional general tuning parameter for searching new
multifunctional materials.",1212.0302v1
2012/12/13,Magnetic properties changes of MnAs thin films irradiated with highly charged ions,"We present the first investigation on the effect of highly charged ion
bombardment on a manganese arsenide thin film. The MnAs films, 150 nm thick,
are irradiated with 90 keV Ne$^{9+}$ ions with a dose varying from
$1.6\times10^{12}$ to $1.6\times10^{15}$ ions/cm$^2$. The structural and
magnetic properties of the film after irradiation are investigated using
different techniques, namely, X-ray diffraction, magneto-optic Kerr effect and
magnetic force microscope. Preliminary results are presented. From the study of
the lattice spacing, we measure a change on the film structure that depends on
the received dose, similarly to previous studies with other materials.
Investigations on the surface show a strong modification of its magnetic
properties.",1212.3288v1
2013/1/2,Spin-orbital locked magnetic excitations in a half-metallic double perovskite Ba2FeReO6,"We present a powder inelastic neutron scattering study of magnetic
excitations in Ba$_2$FeReO$_6$, a member of the double perovskite family of
materials which exhibit half-metallic behavior and high Curie temperatures. We
find clear evidence of two well-defined dispersing magnetic modes in its low
temperature ferrimagnetic state. We develop a local moment model, which
incorporates the interaction of Fe spins with spin-orbit locked magnetic
moments on Re, and show that this captures our experimental observations. Our
study further opens up double perovskites as model systems to explore the
interplay of strong correlations and spin-orbit coupling in 5d transition metal
oxides.",1301.0327v1
2013/1/9,Electrically tunable transverse magnetic focusing in graphene,"Electrons in a periodic lattice can propagate without scattering for
macroscopic distances despite the presence of the non-uniform Coulomb potential
due to the nuclei. Such ballistic motion of electrons allows the use of a
transverse magnetic field to focus electrons. This phenomenon, known as
transverse magnetic focusing (TMF), has been used to study the Fermi surface of
metals and semiconductor heterostructures, as well as to investigate Andreev
reflection, spin-orbit interaction, and to detect composite fermions. Here we
report on the experimental observation of transverse magnetic focusing in high
mobility mono-, bi-, and tri-layer graphene devices. The ability to tune the
graphene carrier density enables us for the first time to investigate TMF
continuously from the hole to the electron regime and analyze the resulting
focusing fan. Moreover, by applying a transverse electric field to tri-layer
graphene, we use TMF as a ballistic electron spectroscopy method to investigate
controlled changes in the electronic structure of a material. Finally, we
demonstrate that TMF survives in graphene up to 300 K, by far the highest
temperature reported for any system, opening the door to novel room temperature
applications based on electron-optics.",1301.1969v1
2013/2/11,Terahertz spectroscopy of spin waves in multiferroic BiFeO$_3$ in high magnetic fields,"We have studied the magnetic field dependence of far-infrared active magnetic
modes in a single ferroelectric domain \BFO/ crystal at low temperature. The
modes soften close to the critical field of 18.8\,T along the [001]
(pseudocubic) axis, where the cycloidal structure changes to the homogeneous
canted antiferromagnetic state and a new strong mode with linear field
dependence appears that persists at least up to 31\,T. A microscopic model that
includes two \DM/ interactions and easy-axis anisotropy describes closely both
the zero-field spectroscopic modes as well as their splitting and evolution in
a magnetic field. The good agreement of theory with experiment suggests that
the proposed model provides the foundation for future technological
applications of this multiferroic material.",1302.2491v2
2013/2/19,Magnetoelectric susceptibility tensor of multiferroic TbMnO3 with cycloidal antiferromagnetic structure in external field,"Magnetoelectric, dielectric and magnetic susceptibility tensors of
multiferroic TbMnO3 with cycloidal antiferromagnetic structure in external
electric and magnetic fields have been investigated with taking into account
dynamics of spin, electro-dipole and acoustic subsystems. All components of
tensors depend on values of external electric and magnetic fields. The
possibility of control of electrodynamic properties of multiferroic TbMnO3 with
cycloidal antiferromagnetic structure by external electric and magnetic fields
has been shown. The resonant interaction of spin, electro-dipole,
electromagnetic and acoustic waves in such material is observed.",1302.4515v1
2013/3/11,Magnetic control of spin-orbit fields: a first-principles study of Fe/GaAs junctions,"The microscopic structure of spin-orbit fields for the technologically
important Fe/GaAs interface is uncovered from first principles. A symmetry
based method allows to obtain the spin-orbit fields---both their magnitude and
orientation---for a generic Bloch state, from the electronic band structure for
any in-plane magnetization orientation. It is demonstrated that the spin-orbit
fields depend not only on the electric field across the interface, but also
surprisingly strongly on the Fe magnetization orientation, opening prospects
for their magnetic control. These results give important clues in searching for
spin-orbit transport and optical phenomena in ferromagnetic/nonmagnetic
systems.",1303.2510v1
2013/4/7,Thermodynamic properties of a diluted Heisenberg ferromagnet with interaction anisotropy -- magnetocaloric point of view,"The thermodynamics of a site-diluted ferromagnetic Heisenberg model for spin
$S=1/2$ with interaction anisotropy in spin space is investigated. The study is
aimed at presenting the magnetocaloric properties of such a model, including
the entropy and temperature changes in magnetization/demagnetization processes,
generalized Gr\""uneisen ratio as well as the quantities characterizing the
efficiency of magnetic cooling cycles. The results are obtained using Pair
Approximation (PA) method and extensively compared with the Molecular Field
Approximation (MFA) calculations. The importance of interaction anisotropy and
site-dilution is discussed. The inadequacy of the MFA approach (even on the
qualitative level) is found for selected quantities, while PA provides the
results which are consistent with the experimentally observed behaviour.",1304.2034v1
2013/4/20,Antiferromagnetic Exchange Interactions in Ni$_{2}$Mn$_{1.4}$In$_{0.6}$ ferromagnetic Heusler alloy,"Magnetism in Ni-Mn-Z (Z = Ga,In,Sn,Sb) Heusler alloys has so far been
predominantly attributed to Rudermann-Kittel-Kasuya-Yoshida type interactions
between Mn atoms. We investigate magnetic interactions in one such alloy,
Ni$_{2}$Mn$_{1.4}$In$_{0.6}$ and attempt to explain the origin of
antiferromagnetic (AFM) interactions that coexist with ferromagnetic ones.
Through the combination of x-ray absorption spectroscopy and x-ray magnetic
circular dichroism (XMCD), we find that Ni plays an important role along with
Mn in the overall magnetism. A significant hybridization that develops between
Mn and Ni orbitals results in a small antiferromagnetic moment at Ni sites. The
shift in the XMCD hysteresis loops in the martensitic phase suggests that
antiferromagnetism results from superexchange like interactions between Mn
atoms mediated by Ni.",1304.5580v1
2013/4/26,Strong magnon softening in tetragonal FeCo compounds,"Magnons play an important role in fast precessional magnetization reversal
processes serving as a heat bath for dissipation of the Zeeman energy and thus
being responsible for the relaxation of magnetization. Employing \emph{ab
initio} many-body perturbation theory we studied the magnon spectra of the
tetragonal FeCo compounds considering three different experimental $c/a$
ratios, $c/a=$1.13, 1.18, and 1.24 corresponding to FeCo grown on Pd, Ir, and
Rh, respectively. We find that for all three cases the short-wave-length
magnons are strongly damped and tetragonal distortion gives rise to a
significant magnon softening. The magnon stiffness constant $D$ decreases
almost by a factor of two from FeCo/Pd to FeCo/Rh. The combination of soft
magnons together with the giant magnetic anisotropy energy suggests FeCo/Rh to
be a promising material for perpendicular magnetic recording applications.",1304.7091v1
2013/5/21,Contrasting behavior of the structural and magnetic properties in Mn- and Fe-doped In$_2$O$_3$ films,"We have observed room temperature ferromagnetism (FM) in In$_2$O$_3$ thin
films doped with either 5 at.% Mn or Fe, prepared by pulsed laser deposition
(PLD) at substrate temperatures ranging from 300 to 600$\,^{\circ}{\rm C}$. The
dependence of saturation magnetization on grain size was investigated for both
types of In$_2$O$_3$ films. It is revealed that, for the Mn-doped films, the
magnetization was largest with small grains, indicating the importance of grain
boundaries. In contrast, for Fe-doped films, the largest magnetization was
observed with large grains.",1305.4831v1
2013/7/3,Asymmetric Magnetic Domain-Wall Motion by the Dzyaloshinskii-Moriya Interaction,"We demonstrate here that ultrathin ferromagnetic Pt/Co/Pt films with
perpendicular magnetic anisotropy exhibit a sizeable Dzyaloshinskii-Moriya
interaction (DMI) effect. Such a DMI effect modifies the domain-wall (DW)
energy density and consequently, results in an asymmetric DW expansion driven
by an out-of-plane magnetic field under an in-plane magnetic field bias. From
an analysis of the asymmetry, the DMI effect is estimated to be strong enough
for the DW to remain in the N\'eel-type configuration in contrast to the
general expectations of these materials. Our findings emphasize the critical
role of the DMI effect on the DW dynamics as the underlying physics of the
asymmetries that are often observed in spin-transfer-related phenomena.",1307.0984v1
2013/7/20,Magnetic properties of Sn/1-x/Cr/x/Te diluted magnetic semiconductors,"We present the studies of Sn/1-x/Cr/x/Te semimagnetic semiconductors with
chemical composition x ranging from 0.004 to 0.012. The structural
characterization indicates that even at low average Cr-content x < ?0.012, the
aggregation into micrometer size clusters appears in our samples. The magnetic
properties are affected by the presence of clusters. In all our samples we
observe the transition into the ordered state at temperatures between 130 and
140 K. The analysis of both static and dynamic magnetic susceptibility data
indicates that the spin-glass-like state is observed in our samples. The
addition of Cr to the alloy seems to shift the spin-glass-like transition from
130 K for x = 0.004 to 140 K for x = 0.012.",1307.5464v1
2013/9/9,Origin of the unusual strong suppression of low frequency antiferromagnetic fluctuations in underdoped HgBa$_2$CuO$_{4+δ}$,"Generally strong charge and magnetic inhomogeneities are observed in NQR/NMR
experiments on underdoped cuprates. It is not the case for the underdoped
HgBa$_2$CuO$_{4+\delta}$, the most symmetric and highest T$_c$ single layer
cuprate, whose magnetic inhomogeneity is strongly suppressed. Also neutron
scattering experiments reveal a unique pair of weakly dispersive magnetic modes
in this material. We propose that these special properties stem from the
symmetric positioning of the O-dopants between adjacent CuO$_2$ layers that
lead to a strong superexchange interaction between a pair of hole spins. In
this Letter we present a theoretical model, which gives a consistent
explanation to the anomalous magnetic properties of this material.",1309.2119v2
2013/9/10,Thin films of the spin ice compound Ho2Ti2O7,"The pyrochlore compounds Ho2Ti2O7 and Dy2Ti2O7 show an exotic form of
magnetism called the spin ice state, resulting from the interplay between
geometrical frustration and ferromagnetic coupling. A fascinating feature of
this state is the appearance of magnetic monopoles as emergent excitations
above the degenerate ground state. Over the past years, strong effort has been
devoted to the investigation of these monopoles and other properties of the
spin ice state in bulk crystals. A tantalising prospect is to incorporate spin
ice materials into devices for spintronics and devices that can manipulate the
magnetic monopoles. This would require the availability of spin ice thin films.
Here, we report the fabrication of Ho2Ti2O7 thin films using pulsed laser
deposition. These films not only show a high crystalline quality, but also
exhibit the hallmarks of a spin ice: a pronounced magnetic anisotropy and an
intermediate plateau in the magnetisation along the [111] crystal direction.",1309.2441v1
2013/9/22,Controlling electron propagation on a topological insulator surface via proximity interactions,"The possibility of electron beam guiding is theoretically explored on the
surface of a topological insulator through the proximity interaction with a
magnetic material. The electronic band modification induced by the exchange
coupling at the interface defines the path of electron propagation in analogy
to the optical fiber for photons. Numerical simulations indicate the guiding
efficiency much higher than that in the ""waveguide"" formed by an electrostatic
potential barrier such as p-n junctions. Further, the results illustrate
effective flux control and beam steering that can be realized by altering the
magnetization/spin texture of the adjacent magnetic materials. Specifically,
the feasibility to switch on/off and make a large-angle turn is demonstrated
under realistic conditions. Potential implementation to logic and interconnect
applications is also examined in connection with electrically controlled
magnetization switching.",1309.5590v1
2013/10/9,Single-Walled Carbon Nanotube Sample Purification,"Removal of impurities and aggregates from as-grown single walled-carbon
nanotube (SWCNT) materials remains an important challenge in nanotube research
and applications. We report a simple but effective purification method that
uses permanent magnets to remove nanotube aggregates, as well as residual
metallic catalyst, from surfactant-coated aqueous SWCNT suspensions. Samples
have been characterized by optical absorption, fluorescence and Raman
spectroscopies; AFM and near-IR fluorescence microscopies; and TGA. We found
that magnetic purification gives samples with reduced absorption backgrounds
and high fluorescence efficiencies comparable to those prepared by
ultracentrifugation. Nanotubes in magnetically processed HiPco samples are at
least 80% individualized. We propose that SWCNT aggregates are preferentially
removed because they contain disproportionate amounts of ferromagnetic catalyst
particles. As compared to ultracentrifugation, magnetic processing offers major
advantages in cost, simplicity, energy consumption, and scalability.",1310.2653v2
2013/10/16,Dynamics of skyrmions in chiral magnets: dynamic phase transitions and equation of motion,"We study the dynamics of skyrmions in a metallic chiral magnet. First we show
that skyrmions can be created dynamically by destabilizing the ferromagnetic
background state through a spin polarized current. We then treat skyrmions as
rigid particles and derive the corresponding equation of motion. The dynamics
of skyrmions is dominated by the Magnus force, which accounts for the weak
pinning of skyrmions observed in experiments. Finally we discuss the quantum
motion of skyrmions.",1310.4255v2
2013/10/16,Domain wall motion in magnetic nanowires: An asymptotic approach,"We develop a systematic asymptotic description for domain wall motion in
one-dimensional magnetic nanowires under the influence of small applied
magnetic fields and currents and small material anisotropy. The magnetization
dynamics, as governed by the Landau--Lifshitz--Gilbert equation, is
investigated via a perturbation expansion. We compute leading-order behaviour,
propagation velocities, and first-order corrections of both travelling waves
and oscillatory solutions, and find bifurcations between these two types of
solutions. This treatment provides a sound mathematical foundation for numerous
results in the literature obtained through more ad hoc arguments.",1310.4442v1
2013/11/14,Living on the edge : ground-state selection in quantum spin-ice pyrochlores,"The search for new quantum phases, especially in frustrated magnets, is
central to modern condensed matter physics. One of the most promising places to
look is in rare-earth pyrochlore magnets with highly-anisotropic exchange
interactions, materials closely related to the spin ices Ho2Ti2O7 and Dy2Ti2O7.
Here we establish a general theory of magnetic order in these materials. We
find that many of their most interesting properties can be traced back to the
accidental degeneracies where phases with different symmetry meet. These
include the ordered ground state selection by fluctuations in Er2Ti2O7, the
dimensional-reduction observed in Yb2Ti2O7, and the absence of magnetic order
in Er2Sn2O7.",1311.3501v2
2013/12/11,Cs2NaAl1-xCrxF6: A family of compounds presenting magnetocaloric effect,"In this paper we explore the magnetocaloric effect (MCE) of chromium-doped
elpasolite Cs$_2$NaAl$_{1-x}$Cr$_x$F$_6$ (x = 0.01 and 0.62) single crystals.
Our magnetization and heat capacity data show the magnetocaloric potentials to
be comparable to those of garnets, perovskites and other fluorides, producing
magnetic entropy changes of 0.5 J/kg$\cdot$K (x = 0.01) and 11 J/kg$\cdot$K (x
= 0.62), and corresponding adiabatic temperature changes of 4 K and 8 K,
respectively. These values are for a magnetic field change of 5 T at a
temperature around 3 K. A clear Schottky anomaly below 10 K, which becomes more
apparent when an external magnetic field is applied, was observed and related
to the splitting of the Cr$^{3+}$ energy levels. These results hint at a new
family of materials with potential wide use in cryorefrigeration.",1312.3014v2
2013/12/11,Electric current generation in distorted graphene,"Graphene-like materials can be effectively described by Quantum
Electrodynamics in (2+1)-dimensions. In a pristine state, these systems exhibit
a symmetry between the nonequivalent Dirac points in the honeycomb lattice.
Realistic samples which include distortions and crystalline anisotropies are
considered through mass gaps of topological and dynamical nature. In this work
we show that the incorporation of an in-plane uniform external magnetic field
on this pseudochiral asymmetric configuration generates a non-dissipative
electric current aligned with the magnetic field: The pseudo chiral magnetic
effect. This scenario resembles the chiral magnetic effect in Quantum
Chromodynamics.",1312.3274v3
2014/1/8,Evidence for Magneto-Levitation Accretion in Long-Period X-ray Pulsars,"Study of observed spin evolution of long-period X-ray pulsars challenges
quasi-spherical and Keplerian disk accretion scenarios. It suggests that the
magnetospheric radius of the neutron stars is substantially smaller than Alfven
radius and the spin-down torque applied to the star from accreting material
significantly exceeds the value predicted by the theory. We show that these
problems can be avoided if the fossil magnetic field of the accretion flow
itself is incorporated into the accretion model. The initially spherical flow
in this case decelerates by its own magnetic field and converts into a
non-Keplerian disk (magnetic slab) in which the material is confined by its
intrinsic magnetic field (""levitates"") and slowly moves towards the star on a
diffusion timescale. Parameters of pulsars expected within this
magneto-levitation accretion scenario are evaluated.",1401.1654v1
2014/2/12,Fine-Tuning of Magnetic Interactions in Organic Spin Ladders,"We have succeeded in synthesizing two types of new organic radical crystals
3-I-V [= 3- (3-iodophenyl)-1,5-diphenylverdazyl] and 3-Br-4-F-V [=
3-(3-bromo-4-fluorophenyl)-1,5- diphenylverdazyl]. Their crystal strucutures
are found to be isomorphous to that of previously reported spin ladder
3-Cl-4-F-V. Through the quantitative analysis of their molecular arrangements
and magnetic properties, we confirm that these materials form ferromagnetic
chain-based spin ladders with slightly modulated magnetic interactions. These
results present the first quantitative demonstration of the fine-tuning of
magnetic interactions in the molecular- based materials.",1402.2743v1
2014/2/21,Insights into the High Temperature Superconducting Cuprates from Resonant Inelastic X-ray Scattering,"Recent improvements in instrumentation have established resonant inelastic
x-ray scattering (RIXS) as a valuable new probe of the magnetic excitations in
the cuprates. This article introduces RIXS, focusing on the Cu $L_3$ resonance,
and reviews recent experiments using this technique. These are discussed in
light of other experimental probes such as inelastic neutron scattering and
Raman scattering. The success of these studies has motivated the development of
several new RIXS spectrometers at synchrotrons around the world that promise,
among other improvements, 5-10 times better energy resolution. We finish by
outlining several key areas which hold promise for further important
discoveries in this emerging field.",1402.5423v3
2014/2/26,Determination of magnetic form factors for organic charge transfer salts: a first principles investigation,"Organic charge transfer salts show a variety of complex phases ranging from
antiferromagnetic long-range order, spin liquid, bad metal or even
superconductivity. A powerful method to investigate magnetism is spin-polarized
inelastic neutron scattering. However, such measurements have often been
hindered in the past by the small size of available crystals as well as by the
fact that the spin in these materials is distributed over molecular rather than
atomic orbitals and good estimates for the magnetic form factors are missing.
By considering Wannier functions obtained from density functional theory
calculations, we derive magnetic form factors for a number of representative
organic molecules. Compared to Cu2+, the form factors |F(q)|2 fall off more
rapidly as function of q reflecting the fact that the spin density is very
extended in real space. Form factors |F(q)|2 for TMTTF, BEDT-TTF and
(BEDT-TTF)2 have anisotropic and nonmonotonic structure.",1402.6599v1
2014/4/3,Magnetic Field Tunable Small-scale Mechanical Properties of Nickel Single Crystals Measured by Nanoindentation Technique,"Nano- and micromagnetic materials have been extensively employed in
micro-functional devices. However, measuring small-scale mechanical and
magnetomechanical properties is challenging, which restricts the design of new
products and the performance of smart devices. A new magnetomechanical
nanoindentation technique is developed and tested on a nickel single crystal in
the absence and presence of a saturated magnetic field. Small-scale parameters
such as Young's modulus, indentation hardness, and plastic index are dependent
on the applied magnetic field, which differ greatly from their macroscale
counterparts. Possible mechanisms that induced 31% increase in modulus and 7%
reduction in hardness (i.e., the flexomagnetic effect and the interaction
between dislocations andmagnetic field, respectively) are analyzed and
discussed. Results could be useful in the microminiaturization of applications,
such as tunable mechanical resonators and magnetic field sensors.",1404.0884v1
2014/5/23,Interface deformations affect the orientation transition of magnetic ellipsoidal particles adsorbed at fluid-fluid interfaces,"Manufacturing new soft materials with specific optical, mechanical and
magnetic properties is a significant challenge. Assembling and manipulating
colloidal particles at fluid interfaces is a promising way to make such
materials. We use lattice-Boltzmann simulations to investigate the response of
magnetic ellipsoidal particles adsorbed at liquid-liquid interfaces to external
magnetic fields. We provide further evidence for the first-order orientation
phase transition predicted by Bresme and Faraudo [Journal of Physics: Condensed
Matter 19 (2007), 375110]. We show that capillary interface deformations around
the ellipsoidal particle significantly affect the tilt-angle of the particle
for a given dipole-field strength, altering the properties of the orientation
transition. We propose scaling laws governing this transition, and suggest how
to use these deformations to facilitate particle assembly at fluid-fluid
interfaces.",1405.6097v2
2014/5/26,Structural and Magnetic Dynamics in the Magnetic Shape Memory Alloy Ni$_2$MnGa,"Magnetic shape memory Heusler alloys are multiferroics stabilized by the
correlations between electronic, magnetic and structural order. To study these
correlations we use time resolved x-ray diffraction and magneto-optical Kerr
effect experiments to measure the laser induced dynamics in a Heusler alloy
Ni$_2$MnGa film and reveal a set of timescales intrinsic to the system. We
observe a coherent phonon which we identify as the amplitudon of the modulated
structure and an ultrafast phase transition leading to a quenching of the
incommensurate modulation within 300~fs with a recovery time of a few ps. The
thermally driven martensitic transition to the high temperature cubic phase
proceeds via nucleation within a few ps and domain growth limited by the speed
of sound. The demagnetization time is 320~fs, which is comparable to the
quenching of the structural modulation.",1405.6534v1
2014/6/4,Hall effect of triplons in a dimerized quantum magnet,"The celebrated Shastry Sutherland model has a gapped dimer singlet ground
state. The material SrCu$_2$(BO$_3$)$_2$ serves as a good realization of this
model, upto small anisotropies arising from Dzyaloshinskii-Moriya (DM)
interactions. The DM interactions admix a triplet component into the singlet
ground state and give rise to weakly dispersing triplon bands. We show that an
applied magnetic field splits the triplon modes and opens band gaps.
Surprisingly, we are left with topological bands with Chern numbers $\pm 2$.
SrCu$_2$(BO$_3$)$_2$ thus supports topologically protected triplonic edge modes
and is a magnetic analogue of the integer quantum Hall effect. At a critical
value of the magnetic field set by the strength of DM interactions, the three
triplon bands touch once again in a spin-1 generalization of a Dirac cone, and
lose their topological character. We predict a strong thermal Hall signature in
the topological regime.",1406.1163v2
2014/6/5,Magnetic properties of epitaxial Fe$_3$O$_4$ films with various crystal orientations and TMR effect in room temperature,"Fe$_3$O$_4$ is a ferrimagnetic spinel ferrite that exhibits electric
conductivity at room temperature (RT). Although the material has been predicted
to be a half metal according to ab-initio calculations, magnetic tunnel
junctions (MTJs) with Fe$_3$O$_4$ electrodes have demonstrated a small tunnel
magnetoresistance effect. Not even the sign of the TMR ratio has been
experimentally established. Here, we report on the magnetic properties of
epitaxial Fe$_3$O$_4$ films with various crystal orientations. The films
exhibited apparent crystal orientation dependence on hysteresis curves. In
particular, Fe$_3$O$_4$(110) films exhibited in-plane uniaxial magnetic
anisotropy. With respect to the squareness of hysteresis, Fe$_3$O$_4$ (111)
demonstrated the largest squareness. Furthermore, we fabricated MTJs with
Fe$_3$O$_4$(110) electrodes, and obtained an TMR effect of -12\% at RT. The
negative TMR ratio corresponded to the negative spin polarization of
Fe$_3$O$_4$ predicted from band calculations.",1406.1296v1
2014/7/8,Heat transport and electron cooling in ballistic normal-metal/spin-filter/superconductor junctions,"We investigate electron cooling based on a clean
normal-metal/spin-filter/superconductor junction. Due to the suppression of the
Andreev reflection by the spin-filter effect, the cooling power of the system
is found to be extremely higher than that for conventional
normal-metal/nonmagnetic-insulator/superconductor coolers. Therefore we can
extract large amount of heat from normal metals. Our results strongly indicate
the practical usefulness of the spin-filter effect for cooling detectors,
sensors, and quantum bits.",1407.1977v2
2014/10/10,"Moment evolution across the ferromagnetic phase transition of giant magnetocaloric (Mn,Fe)2(P,Si,B) compounds","A strong electronic reconstruction resulting in a quenching of the Fe
magnetic moments has recently been predicted to be at the origin of the giant
magnetocaloric effect displayed by Fe2Pbased materials. To verify this
scenario, X-ray Magnetic Circular Dichroism experiments have been carried out
at the L edges of Mn and Fe for two typical compositions of the
(Mn,Fe)2(P,Si,B) system. The dichroic absorption spectra of Mn and Fe have been
measured element specific in the vicinity of the first-order ferromagnetic
transition. The experimental spectra are compared with first-principle
calculations and charge-transfer multiplet simulations in order to derive the
magnetic moments. Even though signatures of a metamagnetic behaviour are
observed either as a function of the temperature or the magnetic field, the
similarity of the Mn and Fe moment evolution suggests that the quenching of the
Fe moment is weaker than previously predicted.",1410.2802v2
2014/10/29,"Spin transport and spin-caloric effects in (Cr,Zn)Te half-metallic nanostructures: Effect of spin disorder at elevated temperatures from first principles","An important contribution to the thermoelectric and spin-caloric transport
properties in magnetic materials at elevated temperatures is the formation of a
spin-disordered state due to local moment fluctuations. This effect has not
been largely investigated so far. We focus on various magnetic nanostructures
of CrTe in the form of thin layers or nanowires embedded in ZnTe matrix,
motivated by the miniaturization of spintronics devices and by recent
suggestions that magnetic nanostructures can lead to extraordinary
thermoelectric effects due to quantum confinement. The electronic structure of
the studied systems is calculated within the multiple scattering screened
Korringa-Kohn-Rostoker Green function (KKR-GF) framework. The Monte Carlo
method is used to simulate the magnetization in the temperature induced spin
disorder. The transport properties are evaluated from the transmission
probability obtained using the Baranger-Stone approach within the KKR-GF
framework. We find qualitative and quantitative changes in the thermoelectric
and spin-caloric coefficients when spin-disorder is included in the
calculation. Furthermore, we show that substitutional impurities in CrTe
nanowires could considerably enhance the Seebeck coefficient and the
thermoelectric figure of merit.",1410.8057v1
2014/10/31,Antiferromagnetic dichroism and Davydov splitting of 3d-excitons in a complex multisublattice magnetoelectric CuB2O4,"The space and time symmetry breaking at magnetic phase transitions in
multiferroics results in a number of strongly pronounced optical effects. Our
high-resolution spectroscopic study of 3d- excitons in a complex
multi-sublattice magnetoelectric CuB2O4 demonstrates that, among those, a large
antiferromagnetic linear dichroism is observed which is highly
sublattice-sensitive to subtle changes in the spin subsystems. We prove that
the discovered linear dichroism is related microscopically to the magnetic
Davydov splitting of the exciton states. We announce a novel magnetic phase
transition and argue that an elliptical spiral structure rather than a simple
circular helix is realized in the incommensurate phase, these findings being
overlooked in previous studies by optical and other techniques. We claim that
this spectroscopic method can be effectively applied to other materials for
revealing hidden features of magnetic structures and phase transitions.",1410.8727v1
2014/11/6,Magnetic Structure and Ordering of Multiferroic Hexagonal LuFeO3,"We report on the magnetic structure and ordering of hexagonal LuFeO3 films
grown by molecular-beam epitaxy (MBE) on YSZ (111) and Al2O3 (0001) substrates.
Using a set of complementary probes including neutron diffraction, we find that
the system magnetically orders into a ferromagnetically-canted
antiferromagnetic state via a single transition between 138-155 K, while a
paraelectric to ferroelectric transition occurs above 1000 K. The symmetry of
the magnetic structure in the ferroelectric state implies that this material is
a strong candidate for linear magnetoelectric coupling and control of the
ferromagnetic moment directly by an electric field.",1411.1694v1
2014/11/26,Electrical manipulation of orbital occupancy and magnetic anisotropy in manganites,"Electrical manipulation of lattice, charge, and spin has been realized
respectively by the piezoelectric effect, field-effect transistor, and electric
field control of ferromagnetism, bringing about dramatic promotions both in
fundamental research and industrial production. However, it is generally
accepted that the orbital of materials are impossible to be altered once they
have been made. Here we use electric-field to dynamically tune the electronic
phase transition in (La,Sr)MnO3 films with different Mn^4+/(Mn^3+ + Mn^4+)
ratios. The orbital occupancy and corresponding magnetic anisotropy of these
thin films are manipulated by gate voltage in a reversible and quantitative
manner. Positive gate voltage increases the proportion of occupancy of the
orbital and magnetic anisotropy that were initially favored by strain
(irrespective of tensile and compressive), while negative gate voltage reduces
the concomitant preferential orbital occupancy and magnetic anisotropy. Besides
its fundamental significance in orbital physics, our findings might advance the
process towards practical oxide-electronics based on orbital.",1411.7128v1
2015/1/20,"Structural, electronic, and magnetic properties of tris(8-hydroxyquinoline)iron(III) molecules and its magnetic coupling with ferromagnetic surface: first-principles study","Using first-principles calculations, we have systematically investigated the
structural, electronic, and magnetic properties of facial (fac-) and meridional
(mer-) tris(8-hydroxyquinoline)iron(III) (Feq3) molecules and their interaction
with ferromagnetic substrate. Our calculation results show that for the
isolated Feq3, mer-Feq3 is more stable than the fac-Feq3; and both Feq3 isomers
have a high spin-state of 5 {\mu}B as the ground state when an on-site
Hubbard-U term is included to treat the highly localized Fe 3d electrons; while
the standard DFT calculations produce a low spin-state of 1 {\mu}B. These
magnetic behaviors can be understood by the octahedral ligand field splitting
theory. Furthermore, we found that fac-Feq3 has a stronger bonding to the Co
surface than mer-Feq3 and an anti-ferromagnetic coupling was discovered between
Fe and Co substrate, originating from the superexchange coupling between Fe and
Co mediated by the interface oxygen and nitrogen atoms. These findings suggest
that Feq3 molecular films may serve as a promising spin-filter material in
spintronic devices.",1501.04926v1
2015/1/30,Tunable Dipolar Capillary Deformations for Magnetic Janus Particles at Fluid-Fluid Interfaces,"Janus particles have attracted significant interest as building blocks for
complex materials in recent years. Furthermore, capillary interactions have
been identified as a promising tool for directed self-assembly of particles at
fluid-fluid interfaces. In this paper, we develop theoretical models describing
the behaviour of magnetic Janus particles adsorbed at fluid-fluid interfaces
interacting with an external magnetic field. Using numerical simulations, we
test the models predictions and show that the magnetic Janus particles deform
the interface in a dipolar manner. We suggest how to utilise the resulting
dipolar capillary interactions to assemble particles at a fluid-fluid
interface, and further demonstrate that the strength of these interactions can
be tuned by altering the external field strength, opening up the possibility to
create novel, reconfigurable materials.",1501.07707v2
2015/2/14,Barkhausen noise in the Random Field Ising Magnet Nd$_2$Fe$_{14}$B,"With sintered needles aligned and a magnetic field applied transverse to its
easy axis, the rare-earth ferromagnet Nd$_2$Fe$_{14}$B becomes a
room-temperature realization of the Random Field Ising Model. The transverse
field tunes the pinning potential of the magnetic domains in a continuous
fashion. We study the magnetic domain reversal and avalanche dynamics between
liquid helium and room temperatures at a series of transverse fields using a
Barkhausen noise technique. The avalanche size and energy distributions follow
power-law behavior with a cutoff dependent on the pinning strength dialed in by
the transverse field, consistent with theoretical predictions for Barkhausen
avalanches in disordered materials. A scaling analysis reveals two regimes of
behavior: one at low temperature and high transverse field, where the dynamics
are governed by the randomness, and the second at high temperature and low
transverse field where thermal fluctuations dominate the dynamics.",1502.04234v1
2015/2/20,Magnetic and Dielectric Properties of Multiferroic BiFeO3 Nanoparticles Synthesized by a Novel Citrate Combustion Method,"Single phase BiFeO3 nanoparticles have been successfully synthesized for the
first time by a novel citrate combustion method without using any solvent. Well
mixed metal nitrates along with citric acid which is used as fuel combust to
give BiFeO3 nanoparticles after annealing. These particles are single phase in
nature and crystallize in the rhombohedral distorted perovskite structure
(space group-R3c) which has been confirmed by the Rietveld refinement of the
room temperature powder x-ray diffraction data. Nearly spherical particles of
average particle size 47 nm have been seen from transmission electron
micrograph. Room temperature magnetic hysteresis measurement shows weak
ferromagnetism though the magnetization does not saturate upto 1.75 T applied
field. The coercive field value is calculated to be 180 Oe which is 3 times
higher than that prepared by solvent free combustion method using Glycine. 57Fe
M\""ossbauer spectrum can be fitted with a sextet corresponding to single
magnetic state of hyperfine field about 49.5 T corresponding to Fe3+ state of
the iron atom. The dielectric relaxation and ac conductivity as a function of
frequency have been discussed. High dielectric permittivity has not been found
in these nanoparticles like other reported BiFeO3 ceramics.",1502.05797v1
2015/3/3,Parity-time symmetry from stacking purely dielectric and magnetic slabs,"We show that Parity-time symmetry in matching electric permittivity to
magnetic permeability can be established by considering an effective Parity
operator involving both mirror symmetry and coupling between electric and
magnetic fields. This approach extends the discussion of Parity-time symmetry
to the situation with more than one material potential. We show that the band
structure of a one-dimensional photonic crystal with alternating purely
dielectric and purely magnetic slabs can undergo a phase transition between
propagation modes and evanescent modes when the balanced gain/loss parameter is
varied. The cross-matching between different material potentials also allows
exceptional points of the constitutive matrix to appear in the long wavelength
limit where they can be used to construct ultrathin metamaterials with
unidirectional reflection.",1503.00902v1
2015/3/29,Edge-channel interferometer at the graphene quantum Hall pn junction,"We demonstrate a quantum Hall edge-channel interferometer in a high-quality
graphene pn junction under a high magnetic field. The co-propagating p and n
quantum Hall edge channels traveling along the pn interface functions as a
built-in Aharanov-Bohm-type interferometer, the interferences in which are
sensitive to both the external magnetic field and the carrier concentration.
The trajectories of peak and dip in the observed resistance oscillation are
well reproduced by our numerical calculation that assumes magnetic flux
quantization in the area enclosed by the co-propagating edge channels. Coherent
nature of the co-propagating edge channels are confirmed by the
checkerboard-like pattern in the dc-bias and magnetic-field dependences of the
resistance oscillations.",1503.08385v1
2015/4/9,The origin of nematic order in FeSe,"The origin of the 90 K nematic transition in the chalcogenide FeSe, which
displays no magnetic order down to T=0, remains a major puzzle for a unifying
theory for the iron-based superconductors. We analyze this problem in light of
recent experimental data which reveal very small Fermi pockets in this
material. We show that the smallness of the Fermi energy leads to a
near-degeneracy between magnetic fluctuations and fluctuations in the
charge-current density-wave channel. While the two fluctuation modes cooperate
to promote the same preemptive Ising-nematic order, they compete for primary
order. We argue that this explains why in FeSe the nematic order emerges when
the magnetic correlation length is smaller than in other Fe-based materials,
and why no magnetism is observed. We discuss how pressure lifts this
near-degeneracy, resulting in a non-monotonic dependence of the nematic
transition with pressure, in agreement with experiments.",1504.02315v1
2015/4/10,Variation of magnetic properties of Sr$_2$FeMoO$_6$ due to oxygen vacancies,"Oxygen vacancies can be of utmost importance for improving or deteriorating
physical properties of oxide materials. Here, we studied from first-principles
the electronic and magnetic properties of oxygen vacancies in the double
perovskite Sr$_2$FeMoO$_6$ (SFMO). We show that oxygen vacancies can increase
the Curie temperature in SFMO, although the total magnetic moment is reduced at
the same time. We found also that the experimentally observed valence change of
the Fe ions from $3+$ to $2+$ in the x-ray magnetic circular dichroism (XMCD)
measurements is better explained by oxygen vacancies than by the assumed mixed
valence state. The agreement of the calculated x-ray absorption spectra and
XMCD results with experimental data is considerably improved by inclusion of
oxygen vacancies.",1504.02629v6
2015/4/17,Magnetocaloric Effect of Gadolinium at Adiabatic and Quasi-Isothermal Conditions in High Magnetic Fields,"High cooling power of magnetocaloric refrigeration can be achieved only at
large amounts of heat, which can be transferred in one cycle from cold end to
hot end at quasi-isothermal conditions. The simple experimental method for
direct measurement of the transferred heat from material with magnetocaloric
effect (MCE) to massive nonmagnetic block at quasi-isothermal conditions was
proposed. The vacuum calorimeter was designed for the simultaneous measurements
of MCE both at adiabatic conditions (deltaT) and quasi-isothermal conditions
(deltaQ) in the magnetic fields of Bitter coil magnet. This calorimeter was
tested on samples of pure polycrystalline Gd with direct MCE. The maximal
obtained values were deltaT = 17.7 K and deltaQ = 5900 J/kg at initial
temperature 20 0C in magnetic field 140 kOe.",1504.04634v1
2015/6/4,Energy and material efficient non-circular bore Bitter magnets,"There exist a number of experiments/applications where the second dimension
of the bore of Bitter magnets is not fully utilized. Using an analytical
solution for elliptical bore coils, we show that reducing one of the dimensions
of the bore can lead to considerable decrease in consumed power and/or coil
material. The results of additional numerical computation show that a 20%
higher magnetic field can be achieved for an elliptical bore and racetrack bore
coils with 1:10 ratio of the transverse dimensions of the bore than for a
circular bore coil with the same larger transverse dimension of the bore,
consumed power, and disk area.",1506.01599v6
2015/6/5,Magnetic Structure of the Quasi-One-Dimensional La3OsO7 as Determined by Neutron Powder Diffraction,"Insulating 5d3 La3OsO7 and hole doped La2.8Ca0.2OsO7 materials featuring well
separated pseudo-one-dimensional zig-zag chains of corner-sharing OsO6
octahedra have been synthesized and their magnetic and electrical transport
properties characterized. Long range magnetic order between the
antiferromagnetic chains is determined with a propagation vector k = 1/2, 1/2,
0 and TN = 45 and 53 K for the parent and doped materials. An Os5+ moment of
1.7(1) {\mu}B for La3OsO7 and 1.2(2) {\mu}B for La2.8Ca0.2OsO7 is refined. The
long range magnetic structure is compared to the few currently known for
isostructural Ln3MO7 compounds.",1506.02052v2
2015/6/11,Magnetism in tetragonal manganese-rich Heusler compounds,"A comprehensive study of the total energy of manganese-rich Heusler compounds
using density functional theory is presented. Starting from a large set of
cubic parent systems, the response to tetragonal distortions is studied in
detail. We single out the systems that remain cubic from those that most likely
become tetragonal. The driving force of the tetragonal distortion and its
effect on the magnetic properties, especially where they deviate from the
Slater--Pauling rule, as well as the trends in the Curie temperatures, are
highlighted. By means of partial densities of states, the electronic structural
changes reveal the microscopic origin of the observed trends. We focus our
attention on the magnetocrystalline anisotropy and find astonishingly high
values for tetragonal Heusler compounds containing heavy transition metals
accompanied by low magnetic moments, which indicates that these materials are
promising candidates for spin-transfer torque magnetization-switching
applications.",1506.03735v1
2015/6/18,Separating read and write units in multiferroic devices,"Strain-mediated multiferroic composites, i.e., piezoelectric-magnetostrictive
heterostructures, hold profound promise for energy-efficient computing in
beyond Moore's law era. While reading a bit of information stored in the
magnetostrictive nanomagnets using a magnetic tunnel junction (MTJ), a material
selection issue crops up since magnetostrictive materials in general cannot be
utilized as the free layer of the MTJ. This is an important issue since we need
to achieve a high magnetoresistance for technological applications. We show
here that magnetically coupling the magnetostrictive nanomagnet and the free
layer e.g., utilizing the magnetic dipole coupling between them can circumvent
this issue. By solving stochastic Landau-Lifshitz-Gilbert equation of
magnetization dynamics in the presence of room-temperature thermal
fluctuations, we show that such design can eventually lead to a superior
energy-delay product.",1506.07865v1
2015/7/7,Spectrum for non-magnetic Mott insulators from power functional within Reduced Density Matrix Functional Theory,"A fully first principles theory capable of treating strongly correlated
solids remains the outstanding challenge of modern day materials science. This
is exemplified by the transition metal oxides, prototypical Mott insulators,
that remain insulating even in the absence of long range magnetic order.
Capturing the non-magnetic insulating state of these materials presents a
difficult challenge for any modern electronic structure theory. In this paper
we demonstrate that reduced density matrix functional theory, in conjunction
with the power functional, can successfully treat the non-magnetic insulating
state of the transition metal oxides NiO and MnO. We show that the electronic
spectrum retains a gap even in the absence of spin order. We further discuss
the detailed way in which RDMFT performs for Mott insulators and band
insulators, finding that for the latter occupation number minimization alone is
required, but for the former full minimization over both occupation numbers and
natural orbitals is essential.",1507.01754v1
2015/7/24,Magnetic torque anomaly in the quantum limit of the Weyl semi-metal NbAs,"Electrons in materials with linear dispersion behave as massless Weyl- or
Dirac-quasiparticles, and continue to intrigue physicists due to their close
resemblance to elusive ultra-relativistic particles as well as their potential
for future electronics. Yet the experimental signatures of Weyl-fermions are
often subtle and indirect, in particular if they coexist with conventional,
massive quasiparticles. Here we report a large anomaly in the magnetic torque
of the Weyl semi-metal NbAs upon entering the ""quantum limit"" state in high
magnetic fields, where topological corrections to the energy spectrum become
dominant. The quantum limit torque displays a striking change in sign,
signaling a reversal of the magnetic anisotropy that can be directly attributed
to the topological properties of the Weyl semi-metal. Our results establish
that anomalous quantum limit torque measurements provide a simple experimental
method to identify Weyl- and Dirac- semi-metals.",1507.06981v1
2015/7/30,"First principle investigations of the structural, electronic and magnetic properties of the new zirconium based full-Heusler compounds, Zr2MnZ (Z = Al, Ga and In)","The crystal structure, electronic and magnetic properties of the new
full-Heusler compounds Zr2MnZ (Z=Al, Ga, In), were studied within the Density
Functional Theory (DFT) framework. The materials exhibit unique properties that
connect the spin gapless semiconducting character with the completely
compensated ferrimagnetism. In magnetic configurations, Zr2MnZ (Z=Al, Ga, In)
crystallize in inverse Heusler structure, are stable against decomposition and
have zero magnetic moment per formula unit properties, in agreement with
Slater-Pauling rule. The Zr2MnAl compound presents spin gapless semiconducting
properties with a energy band gap of 0.41 eV in the majority spin channel and a
zero band gap in the minority spin channel. By substituting Ga or In elements,
for Al in Zr2MnAl, semiconducting pseudo band gaps are formed in the majority
spin channels due to the different neighborhood around the manganese atoms,
which decreases the energy of Mn's triple degenerated anti-bonding states.",1507.08605v2
2015/8/4,Magnetically induced phonon splitting in ACr$_2$O$_4$ spinels from first principles,"We study the magnetically-induced phonon splitting in cubic ACr$_2$O$_4$
(A=Mg, Zn, Cd, Hg) spinels from first principles, and demonstrate that the sign
of the splitting, which is experimentally observed to be opposite in
CdCr$_2$O$_4$ compared to ZnCr$_2$O$_4$ and MgCr$_2$O$_4$, is determined solely
by the particular magnetic ordering pattern observed in these compounds. We
further show that this interaction between magnetism and phonon frequencies can
be fully described by the previously proposed spin-phonon coupling model that
includes only the nearest neighbor exchange. Finally, using this model with
materials specific parameters calculated from first principles, we provide
additional insights into the physics of spin-phonon coupling in this intriguing
family of compounds.",1508.00834v1
2015/8/4,Acoustic signatures of the phases and phase transitions in Yb$_2$Ti$_2$O$_7$,"We report on measurements of the sound velocity and attenuation in a single
crystal of the candidate quantum- spin-ice material Yb$_2$Ti$_2$O$_7$ as a
function of temperature and magnetic field. The acoustic modes couple to the
spins magneto-elastically and, hence, carry information about the spin
correlations that sheds light on the intricate magnetic phase diagram of
Yb$_2$Ti$_2$O$_7$ and the nature of spin dynamics in the material.
Particularly, we find a pronounced thermal hysteresis in the acoustic data with
a concomitant peak in the specific heat indicating a possible first-order phase
transition at about $0.17$ K. At low temperatures, the acoustic response to
magnetic field saturates hinting at the development of magnetic order.
Furthermore, mean-field calculations suggest that Yb$_2$Ti$_2$O$_7$ undergoes a
first-order phase transition from a cooperative paramagnetic phase to a
ferromagnet below $T\approx 0.17$ K.",1508.00925v1
2015/9/2,Effect of Chemical Pressure on High Temperature Ferrimagnetic Double Perovskites Sr2CrOsO6 and Ca2CrOsO6,"The ordered double perovskites Sr2CrOsO6 and Ca2CrOsO6 have been synthesized
and characterized with neutron powder diffraction, electrical transport
measurements, and high field magnetization experiments. Sr2CrOsO6 and Ca2CrOsO6
crystallize with R-3 and P21/n space group symmetry, respectively. Both
materials are found to be ferrimagnetic insulators with saturation
magnetizations near 0.2 {\mu}B. Sr2CrOsO6 orders at 660 K, showing
non-monotonic magnetization temperature dependence, while Ca2CrOsO6 orders at
490 K and does not show non-monotonic behavior. Evidence for a theoretically
predicted canted magnetic structure in Sr2CrOsO6 is sought and not found.",1509.00901v1
2015/9/4,Origin of lowered magnetic moments in epitaxially strained thin films of multiferroic Bi$_2$FeCrO$_6$,"We have investigated the effect of epitaxial strain on the magnetic
properties and $B$-site cation ordering in multiferroic Bi$_2$FeCrO$_6$ (001)
thin films using a density-functional theory approach. We find that in thin
films with rock-salt ordering of Fe and Cr the ground state is characterised by
C-type anti-ferromagnetic (AFM) order. This is in contrast to the bulk form of
the material which was predicted to be a ferrimagnet with G-type AFM order.
Furthermore, the cation ordered thin-films undergo a transition with epitaxial
strain from C to A-type AFM order. Other magnetic orders appear as thermally
accessible excited states. We also find that $B$-site cation disordered
structures are more stable in coherent epitaxial strains thereby explaining the
lowered magnetic moments observed in these samples at room temperature. Strain
varies both the sign as well as strength of the Fe-Cr superexchange coupling
resulting in a very interesting phase diagram for Bi$_2$FeCrO$_6$ thin films.",1509.01563v2
2015/9/16,Structural and magnetic properties of a new and ordered quaternary alloy MnNiCuSb (SG: F-43m),"We have synthesized a new crystallographically ordered quaternary Heusler
alloy, MnNiCuSb. The crystal structure of the alloy has been determined by
Rietveld refinement of the powder x-ray diffraction data. This alloy
crystallizes in the LiMgPdSb type structure with F-43m space group. MnNiCuSb is
a ferromagnet with a high TC ~ 690K and magnetic moment of 3.85MuB/f.u. Besides
this we have also studied two other off-stoichiometric compositions; one Cu
rich and the other Ni rich (MnNi0.9Cu1.1Sb and MnNi1.1Cu0.9Sb) which are also
ferromagnets. It must be stressed that MnNiCuSb is one of the very few known,
non-Fe containing quaternary Heusler alloys with 1: 1: 1: 1 composition.",1509.04833v1
2015/9/17,A spin wave diode,"A diode, a device allowing unidirectional signal transmission, is a
fundamental element of logic structures and lies in the heart of modern
information systems. Spin wave or magnon, representing a collective
quasi-particle excitation of the magnetic order in magnetic materials, is a
promising candidate of information carrier for the next generation
energy-saving technologies. Here we propose a scalable and reprogrammable pure
spin wave logic hardware architecture using domain walls and surface anisotropy
stripes as waveguides on a single magnetic wafer. We demonstrate theoretically
the design principle of the simplest logic component, a spin wave diode,
utilizing the chiral bound states in a magnetic domain wall with
Dzyaloshiskii-Moriya interaction, and confirm its performance through
micromagnetic simulations. Our findings open a new vista for realizing
different types of pure spin wave logic components and finally achieving an
energy-efficient and hardware-reprogrammable spin wave computer.",1509.05095v1
2015/10/23,Laser-induced THz magnetization precession for a tetragonal Heusler-like nearly compensated ferrimagnet,"Laser-induced magnetization precessional dynamics was investigated in
epitaxial films of Mn$_3$Ge, which is a tetragonal Heusler-like nearly
compensated ferrimagnet. The ferromagnetic resonance (FMR) mode was observed,
the precession frequency for which exceeded 0.5 THz and originated from the
large magnetic anisotropy field of approximately 200 kOe for this ferrimagnet.
The effective damping constant was approximately 0.03. The corresponding
effective Landau-Lifshitz constant of approximately 60 Mrad/s and is comparable
to those of the similar Mn-Ga materials. The physical mechanisms for the
Gilbert damping and for the laser-induced excitation of the FMR mode were also
discussed in terms of the spin-orbit-induced damping and the laser-induced
ultrafast modulation of the magnetic anisotropy, respectively.",1510.06793v1
2015/11/4,S=1/2 quantum critical spin ladders produced by orbital ordering in Ba2CuTeO6,"The ordered hexagonal perovskite Ba2CuTeO6 hosts weakly coupled S=1/2 spin
ladders produced by an orbital ordering of Cu2+. The magnetic susceptibility
chi(T) of Ba2CuTeO6 is well described by that expected for isolated spin
ladders with exchange coupling of J~86 K but shows a deviation from the
expected thermally activated behavior at low temperatures below T*~25 K. An
anomaly in chi(T), indicative of magnetic ordering, is observed at T_mag=16 K.
No clear signature of long-range ordering, however, is captured in NMR,
specific heat or neutron diffraction measurements at and below T_mag. The
marginal magnetic transition, indicative of strong quantum fluctuations, is
evidence that Ba2CuTeO6 is in very close proximity to a quantum critical point
between a magnetically ordered phase and a gapped spin liquid controlled by
inter-ladder couplings.",1511.01477v1
2015/11/15,Noncollinear and noncoplanar magnetic order in the extended Hubbard model on anisotropic triangular lattice,"Motivated by the importance of non-collinear and non-coplanar magnetic phases
in determining various electrical properties of magnetic materials, we
investigate the phase diagrams of the extended Hubbard model on anisotropic
triangular lattice. We make use of a mean-field scheme that treats collinear,
non-collinear and non-coplanar phases on equal footing. In addition to the
ferromagnetic and 120{\deg} antiferromagnetic phases, we find the
four-sublattice flux, the 3Q non-coplanar and the non-collinear charge-ordered
states to be stable at specific values of filling fraction $n$. Inter-site
Coulomb repulsion leads to intriguing spin-charge ordered phases. Most notable
of these are the collinear and non-collinear magnetic states at $n=2/3$, which
occur together with a pinball-liquid-like charge order. Our results demonstrate
that the elementary single-orbital extended Hubbard model on a triangular
lattice hosts unconventional spin-charge ordered phases, which have been
reported in more complex and material-specific electronic Hamiltonians relevant
to layered triangular systems.",1511.04733v1
2015/11/27,Realization of Stable Ferromagnetic Order in Topological Insulator: Codoping Enhanced Magnetism in 4f Transition Metal Doped Bi2Se3,"The realization of long range and insulating ferromagnetic states in
topological insulator (TI) has been a pressing issue since its discovery. Only
recently, such state was achieved in Cr-doped Bi2-xSbxTe3, leading to the
discovery of quantum anomalous Hall effect (QAHE). However, the effect is only
observed at extremely low temperatures mainly due to the limited magnetism. To
fully understand the mechanism of the ferromagnetic ordering whereby improving
the ferromagnetism, we investigated 4f transition metal-doped Bi2Se3, using
density-functional-theory approaches. We found that Eu and Sm prefer the Bi
substitutional sites with large magnetic moments to ensure stable long-range
ferromagnetic states. Additionally, codoping can be a novel strategy to
preserve the insulating property of the host material as well as improving the
incorporation of magnetic dopants. Our findings thus offer the critical step in
facilitating the realization of QAHE in TI systems.",1511.08646v1
2015/11/28,Extremely large magnetoresistance in few-layer graphene/boron-nitride heterostructures,"Understanding magnetoresistance, the change in electrical resistance upon an
external magnetic field, at the atomic level is of great interest both
fundamentally and technologically. Graphene and other two-dimensional layered
materials provide an unprecedented opportunity to explore magnetoresistance at
its nascent stage of structural formation. Here, we report an extremely large
local magnetoresistance of ~ 2,000% at 400 K and a non-local magnetoresistance
of > 90,000% in 9 T at 300 K in few-layer graphene/boron-nitride
heterostructures. The local magnetoresistance is understood to arise from large
differential transport parameters, such as the carrier mobility, across various
layers of few-layer graphene upon a normal magnetic field, whereas the
non-local magnetoresistance is due to the magnetic field induced
Ettingshausen-Nernst effect. Non-local magnetoresistance suggests the
possibility of a graphene based gate tunable thermal switch. In addition, our
results demonstrate that graphene heterostructures may be promising for
magnetic field sensing applications.",1511.08867v1
2015/12/2,Orbital magnetic susceptibility of graphene and MoS2,"We calculate the orbital magnetic susceptibility $\chi_{\mathrm{orb}}$ for an
8-band tight-binding model of gapless and gapped graphene using Green's
functions. Analogously, we study $\chi_{\mathrm{orb}}$ for a $\mathrm{MoS_2}$
12-band model. For both materials, we unravel the character of the processes
involved in the magnetic response by looking at the contribution at each point
of the Brillouin zone. By this, a clear distinction between intra- and
interband excitations is generally possible and we are able to predict
qualitative features of $\chi_{\mathrm{orb}}$ only through the knowledge of the
band structure. The study is complemented by comparing the magnetic response
with that of 2-band lattice Hamiltonians which reduce to the Dirac and
Bernevig-Hughes-Zhang (BHZ) models in the continuum limit.",1512.00669v2
2015/12/10,Magnetic hyperbolic optical metamaterials,"Strongly anisotropic media where the principal components of electric
permittivity or magnetic permeability tensors have opposite signs are termed as
hyperbolic media. Such media support propagating electromagnetic waves with
extremely large wavevectors exhibiting unique optical properties. However in
all artificial and natural optical materials studied to date, the hyperbolic
dispersion originates solely from the electric response. This restricts
material functionality to one polarization of light and inhibits free-space
impedance matching. Such restrictions can be overcome in media having
components of opposite signs for both electric and magnetic tensors. Here we
present the experimental demonstration of the magnetic hyperbolic dispersion in
three-dimensional metamaterials. We measure metamaterial isofrequecy contours
and reveal the topological phase transition between the elliptic and hyperbolic
dispersion. In the hyperbolic regime, we demonstrate the strong enhancement of
thermal emission, which becomes directional, coherent and polarized. Our
findings show the possibilities for realizing efficient impedance-matched
hyperbolic media for unpolarized light.",1512.03125v2
2015/12/20,Piezo Voltage Controlled Planar Hall Effect Devices,"The electrical control of the magnetization switching in ferromagnets is
highly desired for future spintronic applications. Here we report on hybrid
piezoelectric (PZT) /ferromagnetic (Co2FeAl) devices in which the planar Hall
voltage in the ferromagnetic layer is tuned solely by piezo voltages. The
change of planar Hall voltage is associated with magnetization switching
through 90 in the plane under piezo voltages. Room temperature magnetic NOT and
NOR gates are demonstrated based on the piezo voltage controlled Co2FeAl planar
Hall effect devices without the external magnetic field. Our demonstration may
lead to the realization of both information storage and processing using
ferromagnetic materials.",1512.06374v2
2016/1/12,Magnetic phase diagram of the helimagnetic spinel compound ZnCr2Se4 revisited by small-angle neutron scattering,"We performed small-angle neutron scattering (SANS) measurements on the
helimagnetic spinel compound ZnCr2Se4. The ground state of this material is a
multi-domain spin-spiral phase, which undergoes domain selection in a magnetic
field and reportedly exhibits a transition to a proposed spin-nematic phase at
higher fields. We observed a continuous change in the magnetic structure as a
function of field and temperature, as well as a weak discontinuous jump in the
spiral pitch across the domain-selection transition upon increasing field. From
our SANS results we have established the absence of any long-range magnetic
order in the high-field (spin-nematic) phase. We also found that all the
observed phase transitions are surprisingly isotropic with respect to the field
direction.",1601.03005v1
2016/2/19,Magnetic anisotropy of large floating-zone-grown single-crystals of SrRuO3,"SrRuO3 is a highly interesting material due to its anomalous-metal properties
related with ferromagnetism and its relevance as conductive perovskite layer or
substrate in heterostructure devices. We have used optical floating zone
technique in an infrared image furnace to grow large single crystals of SrRuO3
with volumes attaining several hundred mm3. Crystals obtained for optimized
growth parameters exhibit a high ferromagnetic Curie temperature of 165 K and a
low-temperature magnetization of 1.6 muB at a magnetic field of 6 T. The high
quality of the crystals is further documented by large residual resistance
ratios of 75 and by crystal structure and chemical analyzes. With these
crystals the magnetic anisotropy could be determined.",1602.06171v2
2016/2/23,Experimental Investigation of Temperature-Dependent Gilbert Damping in Permalloy Thin Films,"The Gilbert damping of ferromagnetic materials is arguably the most important
but least understood phenomenological parameter that dictates real-time
magnetization dynamics. Understanding the physical origin of the Gilbert
damping is highly relevant to developing future fast switching spintronics
devices such as magnetic sensors and magnetic random access memory. Here, we
report an experimental study of temperature-dependent Gilbert damping in
permalloy (Py) thin films of varying thicknesses by ferromagnetic resonance.
From the thickness dependence, two independent contributions to the Gilbert
damping are identified, namely bulk damping and surface damping. Of particular
interest, bulk damping decreases monotonically as the temperature decreases,
while surface damping shows an enhancement peak at the temperature of ~50 K.
These results provide an important insight to the physical origin of the
Gilbert damping in ultrathin magnetic films.",1602.07325v1
2016/2/26,Water dispersible CoFe2O4 nanoparticles with improved colloidal stability for biomedical applications,"Single phase cobalt ferrite (CoFe2O4, CFO) nanoparticles of a controlled size
(~ 6 nm) exhibiting superparamagnetic properties have been synthesized by
hydrothermal technique using oleic acid (OA) as surfactant. The oleic acid
coated CFO nanoparticles are stable in non-polar organic media, such as hexane
but are not well dispersible in water. The surface of these snanoparticles has
been further modified by citric acid using ligand exchange process, which makes
CFO nanoparticles more stable colloidal solution in water. Citric acid coated
CFO nanoparticles exhibits high dispersibility in water, high zeta potential,
very low coercivity and moderate saturation magnetization. Biocompatibility of
these CFO nanoparticles is demonstrated through cytotoxicity test in L929 cell
line.",1602.08415v1
2016/3/11,Separating hyperfine from spin-orbit interactions in organic semiconductors by multi-octave magnetic resonance using coplanar waveguide microresonators,"Separating the influence of hyperfine from spin-orbit interactions in
spin-dependent carrier recombination and dissociation processes necessitates
magnetic resonance spectroscopy over a wide range of frequencies. We have
designed compact and versatile coplanar waveguide resonators for
continuous-wave electrically detected magnetic resonance, and tested these on
organic light-emitting diodes. By exploiting both the fundamental and
higher-harmonic modes of the resonators we cover almost five octaves in
resonance frequency within a single setup. The measurements with a common
pi-conjugated polymer as the active material reveal small but non-negligible
effects of spin-orbit interactions, which give rise to a broadening of the
magnetic resonance spectrum with increasing frequency.",1603.03807v1
2016/3/15,Colossal Magnetocapacitance Effect and Multiferroism of Polycrystalline La0.2Pb0.7Fe12O19,"The mutual control of the electric and magnetic properties of a multiferroic
solid is of fundamental and great technological importance. We report here on
the colossal magnetoelectric coupling effect of polycrystalline
La0.2Pb0.7Fe12O19. A large classic ferroelectric hysteresis loop with full
saturation and a strong magnetic hysteresis loop were observed simultaneously
in polycrystalline La0.2Pb0.7Fe12O19 due to the coexistence of an off-centered
FeO6 octahedron in its unit cell and electron spins in the partially filled 3d
orbits of the Fe3+ ions. The coupling voltage and capacity demonstrate giant
oscillations, along with magnetic field; the maximum magnetocapacitance ratio
exceeds 1.9E5 at 80 Hz. The substitution of La ions with Pb ions progressively
stabilized the conical spin structure, which gave rise to the spin-current
induced capacity oscillations upon magnetic field.",1603.04508v1
2016/4/20,Magnetoresistance and Shubnikov-de Hass oscillation in YSb,"YSb crystals are grown and the transport properties under magnetic field are
measured. The resistivity exhibits metallic behavior under zero magnetic field
and the low temperature resistivity shows a clear upturn once a moderate
magnetic field is applied. The upturn is greatly enhanced by increasing
magnetic field, finally resulting in a metal-to-insulator-like transition. With
temperature further decreased, a resistivity plateau emerges after the
insulator-like regime. At low temperature (2.5 K) and high field (14 T), the
transverse magnetoresistance (MR) is quite large (3.47 $\times 10^4\%$ ). In
addition, Shubnikov-de Haas (SdH) oscillation has also been observed in YSb.
Periodic behavior of the oscillation amplitude reveals the related information
about Fermi surface and two major oscillation frequencies can be obtained from
the FFT spectra of the oscillations. The trivial Berry phase extracted from SdH
oscillation, band structure revealed by angle-resolved photoemission
spectroscopy (ARPES) and first-principles calculations demonstrate that YSb is
a topologically trivial material.",1604.05912v2
2016/5/4,Emergent Order in the Kagome Ising Magnet Dy3Mg2Sb3O14,"The kagome lattice -- a two-dimensional (2D) arrangement of corner-sharing
triangles -- is at the forefront of the search for exotic states generated by
magnetic frustration. Such states have been observed experimentally for
Heisenberg and planar spins. In contrast, frustration of Ising spins on the
kagome lattice has previously been restricted to nano-fabricated systems and
spin-ice materials under applied magnetic field. Here, we show that the layered
Ising magnet Dy3Mg2Sb3O14 hosts an emergent order predicted theoretically for
individual kagome layers of in-plane Ising spins. Neutron-scattering and bulk
thermomagnetic measurements, supported by Monte Carlo simulations, reveal a
phase transition at T* = 0.3 K from a disordered spin-ice like regime to an
""emergent charge ordered"" state in which emergent charge degrees of freedom
exhibit three-dimensional order while spins remain partially disordered. Our
results establish Dy3Mg2Sb3O14 as a tuneable system to study interacting
emergent charges arising from kagome Ising frustration.",1605.01423v1
2016/5/7,Order-by-disorder effects in antiferromagnets on face-centered cubic lattice,"We discuss the role of quantum fluctuations in Heisenberg antiferromagnets on
face-centered cubic lattice with small dipolar interaction in which the
next-nearest-neighbor exchange coupling dominates over the nearest-neighbor
one. It is well known that a collinear magnetic structure which contains (111)
ferromagnetic planes arranged antiferromagnetically along one of the space
diagonals of the cube is stabilized in this model via order-by-disorder
mechanism. On the mean-field level, the dipolar interaction forces spins to lie
within (111) planes. By considering 1/S - corrections to the ground state
energy, we demonstrate that quantum fluctuations lead to an anisotropy within
(111) planes favoring three equivalent directions for the staggered
magnetization (e.g., $[11\overline{2}]$, $[1\overline{2}1]$, and
$[\overline{2}11]$ directions for (111) plane). Such in-plane anisotropy was
obtained experimentally in related materials MnO, $\alpha$-MnS, $\alpha$-MnSe,
EuTe, and EuSe. We find that the order-by-disorder mechanism can contribute
significantly to the value of the in-plane anisotropy in EuTe. Magnon spectrum
is also derived in the first order in 1/S.",1605.02208v2
2016/7/18,Engineering the polar magneto-optical Kerr effect in strongly strained L10-MnAl films,"We report the engineering of the polar magnetooptical (MO) Kerr effect in
perpendicularly magnetized L10-MnAl epitaxial films with remarkably tuned
magnetization, strain, and structural disorder by varying substrate temperature
(Ts) during molecular-beam epitaxy growth. The Kerr rotation was enhanced by a
factor of up to 5 with Ts increasing from 150 to 350 oC as a direct consequence
of the improvement of the magnetization. A similar remarkable tuning effect was
also observed on the Kerr ellipticity and the magnitude of the complex Kerr
angle, while the phase of the complex Kerr angle appears to be independent of
the magnetization. The combination of the good semiconductor compatibility, the
moderate coercivity of 0.3-8.2 kOe, the tunable polar MO Kerr effect of up to
~0.034o, and giant spin procession frequencies of up to ~180 GHz makes L10-MnAl
films a very interesting MO material. Our results give insights on both the
microscopic mechanisms of the MO Kerr effect in L10-MnAl alloys and their
scientific and technological application potential in the emerging spintronics
and ultrafast MO modulators.",1607.04938v4
2016/7/20,Realizing the $XY$ Hamiltonian in polariton simulators,"Several platforms are currently being explored for simulating physical
systems whose complexity increases faster than polynomially with the number of
particles or degrees of freedom in the system. Defects and vacancies in
semiconductors or dielectric materials, magnetic impurities embedded in solid
helium \cite{lemeshko13}, atoms in optical lattices, photons, trapped ions and
superconducting q-bits are among the candidates for predicting the behaviour of
spin glasses, spin-liquids, and classical magnetism among other phenomena with
practical technological applications. Here we investigate the potential of
polariton graphs as an efficient simulator for finding the global minimum of
the $XY$ Hamiltonian. By imprinting polariton condensate lattices of bespoke
geometries we show that we can simulate a large variety of systems undergoing
the U(1) symmetry breaking transitions. We realise various magnetic phases,
such as ferromagnetic, anti-ferromagnetic, and frustrated spin configurations
on unit cells of various lattices: square, triangular, linear and a disordered
graph. Our results provide a route to study unconventional superfluids,
spin-liquids, Berezinskii-Kosterlitz-Thouless phase transition, classical
magnetism among the many systems that are described by the $XY$ Hamiltonian.",1607.06065v1
2016/8/8,"Magnetothermoelectric effects in graphene and their dependence on scatterer concentration, magnetic field and band gap","Using a semiclassical Boltzmann transport equation (BTE) approach, we derive
analytical expressions for electric and thermoelectric transport coefficients
of graphene in the presence and absence of a magnetic field. Scattering due to
acoustic phonons, charged impurities and vacancies are considered in the model.
Seebeck ($S_{xx}$) and Nernst ($N$) coefficients have been evaluated as
functions of carrier density, temperature, scatterer concentration, magnetic
field and induced band gap, and the results are compared with experimental
data. $S_{xx}$ is an odd function of Fermi energy while $N$ is an even
function, as observed in experiments. The peaks of both coefficients are found
to increase with decreasing scatterer concentration and increasing temperature.
Furthermore, opening a band gap decreases $N$ but increases $S_{xx}$. Applying
a magnetic field introduces an asymmetry in the variation of $S_{xx}$ with
Fermi energy across the Dirac point. The formalism is more accurate and
computationally efficient than the conventional Green's function approach used
to model transport coefficients and can be used to explore transport properties
of other exotic materials.",1608.02310v1
2016/9/25,Coexistence of bulk and surface polaritons in a~magnetic-semiconductor superlattice influenced by a transverse magnetic field,"It is demonstrated that the effect of coexistence of bulk and surface
polaritons within the same frequency band and wavevector space can be achieved
in a magnetic-semiconductor superlattice providing a conscious choice of
characteristic resonant frequencies and material fractions of the structure's
underlying components as well as geometry of the external static magnetic
field. The study is based on the effective medium theory which is involved to
calculate dispersion characteristics of the long-wavelength electromagnetic
modes of ordinary and extraordinary bulk polaritons and hybrid EH and HE
surface polaritons derived via averaged expressions with respect to the
effective constitutive parameters of the superlattice.",1609.07744v2
2016/9/24,Optical manipulation of a magnon-photon hybrid system,"We demonstrate an all-optical method for manipulating the magnetization in a
1-mm YIG (yttrium-iron-garnet) sphere placed in a $\sim0.17\,$T uniform
magnetic field. An harmonic of the frequency comb delivered by a multi-GHz
infrared laser source is tuned to the Larmor frequency of the YIG sphere to
drive magnetization oscillations, which in turn give rise to a radiation field
used to thoroughly investigate the phenomenon. The radiation damping issue that
occurs at high frequency and in the presence of highly magnetizated materials,
has been overcome by exploiting magnon-photon strong coupling regime in
microwave cavities. Our findings demonstrate an effective technique for
ultrafast control of the magnetization vector in optomagnetic materials via
polarization rotation and intensity modulation of an incident laser beam. We
eventually get a second-order susceptibility value of $\sim10^{-7}$ cm$^2$/MW
for single crystal YIG.",1609.08147v1
2016/10/17,Designing compensated magnetic states in tetragonal Mn3Ge-based alloys,"Magnetic compensated state attracted much interests due to the observed large
exchange bias and large coercivity, and its potential applications in the
antiferromagnetic spintronics with merit of no stray field. In this work, by ab
initio calculations with KKR-CPA for the treatment of random substitution, we
obtain the complete compensated states in the Ni (Pd, Pt) doped Mn3Ge-based
D022-type tetragonal Heusler alloys. We find the total moment change is
asymmetric across the compensation point (at ~ x = 0.3) in Mn3-xYxGe (Y = Ni,
Pd, Pt), which is highly conforming to that experimentally observed in Mn3Ga.
In addition, an uncommon discontinuous jump is observed across the critical
zero-moment point, indicating that some non-trivial properties can emerge at
this point. Further electronic analysis for the three compensation compositions
reveals large spin polarizations, together with the high Curie temperature of
the host Mn3Ge, making them promising candidates for spin transfer torque
applications.",1610.04971v1
2016/10/18,Magnetic properties of low-moment ferrimagnetic Heusler Cr2CoGa thin films grown by molecular beam epitaxy,"Recently, theorists have predicted many materials with a low magnetic moment
and large spin-polarization for spintronic applications. These compounds are
predicted to form in the inverse Heusler structure, however, many of these
compounds have been found to phase segregate. In this study, ordered Cr2CoGa
thin films were synthesized without phase segregation using molecular beam
epitaxy. The present as-grown films exhibit a low magnetic moment from
antiferromagnetically coupled Cr and Co atoms as measured with SQUID
magnetometry and soft X-ray magnetic circular dichroism. Electrical
measurements demonstrated a thermally-activated semiconductor-like resistivity
with an activation energy of 87 meV. These results confirm spin gapless
semiconducting behavior, which makes these thin films well positioned for
future devices.",1610.05808v1
2016/11/3,Magnetic avalanches in granular ferromagnets: Thermal activated collective behavior,"We present a numerical study on the thermal activated avalanche dynamics in
granular materials composed of ferromagnetic clusters embedded in a
non-magnetic matrix. A microscopic dynamical simulation based on the
reaction-diffusion process is developed to modeling the magnetization process
of such systems. The large-scale simulations presented here explicitly
demonstrate inter-granular collective behavior induced by thermal activation of
spin tunneling. In particular, we observe an intriguing criticality controlled
by the rate of energy dissipation. We show that thermal activated avalanches
can be understood in the framework of continuum percolation and the emergent
dissipation induced criticality is in the universality class of
three-dimensional percolation transition. Implications of these results to the
phase-separated states of colossal magnetoresistance materials and other
artificial granular magnetic systems are also~discussed.",1611.01098v1
2016/11/8,Thermal and Magnetic Properties of Nanostructured Ferrimagnetic Composites with Graphene - Graphite Fillers,"We report the results of an experimental study of thermal and magnetic
properties of nanostructured ferrimagnetic iron oxide composites with graphene
and graphite fillers synthesized via the current activated pressure assisted
densification. The thermal conductivity was measured using the laser-flash and
transient plane source techniques. It was demonstrated that addition of 5 wt. %
of equal mixture of graphene and graphite flakes to the composite results in a
factor of x2.6 enhancement of the thermal conductivity without significant
degradation of the saturation magnetization. The microscopy and spectroscopic
characterization reveal that sp2 carbon fillers preserve their crystal
structure and morphology during the composite processing. The strong increase
in the thermal conductivity was attributed to the excellent phonon heat
conduction properties of graphene and graphite. The results are important for
energy and electronic applications of the nanostructured permanent magnets.",1611.02359v1
2016/11/24,Defect-induced magnetism in SiC probed by nuclear magnetic resonance,"We give evidence for intrinsic, defect-induced bulk paramagnetism in SiC by
means of $^{13}$C and $^{29}$Si nuclear magnetic resonance (NMR) spectroscopy.
The temperature dependence of the internal dipole-field distribution, probed by
the spin part of the NMR Knight shift and the spectral linewidth, follows a
Curie law and scales very well with the macroscopic DC susceptibility. In order
to quantitatively analyze the NMR spectra, a microscopic model based on
dipole-dipole interactions was developed. The very good agreement between these
simulations and the NMR data establishes a direct relation between the
frequency distribution of the spectral intensity and the corresponding
real-space volumes of nuclear spins. The presented approach by NMR can be
applied to a variety of similar materials and, thus, opens a new avenue for the
microscopic exploration and exploitation of diluted bulk magnetism in
semiconductors.",1611.08186v2
2016/11/26,First order reversal curves and intrinsic parameter determination for magnetic materials; limitations of hysteron-based approaches in correlated systems,"The generic problem of extracting information on intrinsic particle
properties from the whole class of interacting magnetic fine particle systems
is a long standing and difficult inverse problem. As an example, the Switching
Field Distribution (SFD) is an important quantity in the characterization of
magnetic systems, and its determination in many technological applications,
such as recording media, is especially challenging. Techniques such as the
first order reversal curve (FORC) methods, were developed to extract the SFD
from macroscopic measurements. However, all methods rely on separating the
contributions to the measurements of the intrinsic SFD and the extrinsic
effects of magnetostatic and exchange interactions. We investigate the
underlying physics of the FORC method by applying it to the output predictions
of a kinetic Monte-Carlo model with known input parameters. We show that the
FORC method is valid only in cases of weak spatial correlation of the
magnetization and suggest a more general approach.",1611.08762v1
2016/11/29,Magneto-optical switching in microcavities based on a TGG defect sandwiched between periodic and disordered one-dimensional photonic structures,"The employment of magneto-optical materials to fabricate photonic crystals
gives the unique opportunity to achieve optical tuning by applying a magnetic
field. In this study we have simulated the transmission spectrum of a
microcavity in which the Bragg reflectors are made with silica (SiO2) and
yttria (Y2O3) and the defect layer is made with TGG (Tb3Ga5O12). We show that
the application of an external magnetic field results in a tuning of the defect
mode of the microcavity. In the simulations we have considered the wavelength
dependence of the refractive indexes and the Verdet constants of the materials.
A tuning of the defect mode of about 22 nm with a magnetic field of 5 T, at low
temperature (8 K), is demonstrated. Furthermore, we discuss the possibility to
tune a microcavity with disordered photonic structures as reflectors. In the
presence of the magnetic field such microcavity shows a shift of resonances in
a broad range of wavelengths. This study presents a method of contactless
optical tuning.",1611.09740v3
2016/12/7,Intrinsic Ferromagnetism in the Diluted Magnetic Semiconductor Co:TiO$_2$,"Here we present a study of magnetism in \CTO\ anatase films grown by pulsed
laser deposition under a variety of oxygen partial pressures and deposition
rates. Energy-dispersive spectrometry and transition electron microscopy
analyses indicate that a high deposition rate leads to a homogeneous
microstructure, while very low rate or postannealing results in cobalt
clustering. Depth resolved low-energy muon spin rotation experiments show that
films grown at a low oxygen partial pressure ($\approx 10^{-6}$ torr) with a
uniform structure are fully magnetic, indicating intrinsic ferromagnetism.
First principles calculations identify the beneficial role of low oxygen
partial pressure in the realization of uniform carrier-mediated ferromagnetism.
This work demonstrates that Co:TiO$_2$ is an intrinsic diluted magnetic
semiconductor.",1612.02235v1
2016/12/12,Anomalous thermal conductivity and magnetic torque response in the honeycomb magnet $α$-RuCl$_3$,"We report on the unusual behavior of the in-plane thermal conductivity
($\kappa$) and torque ($\tau$) response in the Kitaev-Heisenberg material
$\alpha$-RuCl$_3$. $\kappa$ shows a striking enhancement with linear growth
beyond H = 7 T, where magnetic order disappears, while $\tau$ for both of the
in-plane symmetry directions shows an anomaly at the same field. The
temperature- and field-dependence of $\kappa$ are far more complex than
conventional phonon and magnon contributions, and require us to invoke the
presence of unconventional spin excitations whose properties are characteristic
of a field-induced spin-liquid phase related to the enigmatic physics of the
Kitaev model in an applied magnetic field",1612.03881v3
2016/12/13,Noninteger-spin magnonic excitations in untextured magnets,"Interactions are responsible for intriguing physics, e.g. emergence of exotic
ground states and excitations, in a wide range of systems. Here we
theoretically demonstrate that dipole-dipole interaction leads to bosonic
eigen-excitations with average spin ranging from zero to above $\hbar$ in
magnets with uniformly magnetized ground states. These exotic excitations can
be interpreted as quantum coherent conglomerates of spin $\hbar$ magnons, the
eigen-excitations when the dipolar interactions are disregarded. We further
find that the eigenmodes in an easy-axis antiferromagnet are spin-zero
quasiparticles instead of the widely believed spin $\pm \hbar$ magnons. The
latter re-emerge when the symmetry is broken by a sufficiently large applied
magnetic field. The average spin greater than $\hbar$ is accompanied by vacuum
fluctuations and may be considered to be a weak form of frustration.",1612.04163v2
2016/12/16,Chiral magnetic superconductivity,"Materials with charged chiral quasiparticles in external parallel electric
and magnetic fields can support an electric current that grows linearly in
time, corresponding to diverging DC conductivity. From experimental viewpoint,
this ""Chiral Magnetic Superconductivity"" (CMS) is thus analogous to
conventional superconductivity. However the underlying physics is entirely
different -- the CMS does not require a condensate of Cooper pairs breaking the
gauge degeneracy, and is thus not accompanied by Meissner effect. Instead, it
owes its existence to the (temperature-independent) quantum chiral anomaly and
the conservation of chirality. As a result, this phenomenon can be expected to
survive to much higher temperatures. Even though the chirality of
quasiparticles is not strictly conserved in real materials, the chiral magnetic
superconductivity should still exhibit itself in AC measurements at frequencies
larger than the chirality-flipping rate, and in microstructures of Dirac and
Weyl semimetals with thickness below the mean chirality-flipping length that is
about 1-100 $\mu$m. In nuclear physics, the CMS should contribute to the
charge-dependent elliptic flow in heavy ion collisions.",1612.05677v1
2017/1/10,Capturing ultrafast magnetic dynamics by time-resolved soft x-ray magnetic circular dichroism,"Experiments of time-resolved x-ray magnetic circular dichroism (Tr-XMCD) and
resonant x-ray scattering at a beamline BL07LSU in SPring-8 with a
time-resolution of under 50 ps are presented. A micro-channel plate is utilized
for the Tr-XMCD measurements at nearly normal incidence both in the partial
electron and total fluorescence yield (PEY and TFY) modes at the L2,3
absorption edges of the 3d transition-metals in the soft x-ray region. The
ultrafast photo-induced demagnetization within 50 ps is observed on the
dynamics of a magnetic material of FePt thin film, having a distinct threshold
of the photon density. The spectrum in the PEY mode is less-distorted both at
the L2,3 edges compared with that in the TFY mode and has the potential to
apply the sum rule analysis for XMCD spectra in pump-probed experiments.",1701.03156v2
2017/1/18,Single crystal growth and anisotropic magnetic properties of Li$_2$Sr[Li$_{1-x}$Fe$_x$N]$_2$,"Up to now, investigation of physical properties of ternary and higher
nitridometalates was severely hampered by challenges concerning phase purity
and crystal size. Employing a modified lithium flux technique, we are now able
to prepare sufficiently large single crystals of the highly air and moisture
sensitive nitridoferrate $\rm Li_2Sr[Li_{1-x}Fe_xN]_2$ for anisotropic
magnetization measurements. The magnetic properties are most remarkable: large
anisotropy and coercivity fields of 7 Tesla at $T = 2$ K indicate a significant
orbital contribution to the magnetic moment of iron. Altogether, the novel
growth method opens a route towards interesting phases in the comparatively
recent research field of nitridometalates and should be applicable to various
other materials.",1701.05127v2
2017/1/19,Low temperature magnetic structure of CeRhIn$_5$ by neutron diffraction on absorption-optimized samples,"Two aspects of the ambient pressure magnetic structure of heavy fermion
material CeRhIn$_5$ have remained under some debate since its discovery:
whether the structure is indeed an incommensurate helix or a spin density wave,
and what is the precise magnitude of the ordered magnetic moment. By using a
single crystal sample optimized for hot neutrons to minimize neutron absorption
by Rh and In, here we report an ordered moment of $m=0.54(2)~\mu_B$. In
addition, by using spherical neutron polarimetry measurements on a similar
single crystal sample, we have confirmed the helical nature of the magnetic
structure, and identified a single chiral domain.",1701.05488v2
2017/2/2,Microscopic theory of magnetic detwinning in iron-based superconductors with large-spin rare earths,"Detwinning of magnetic (nematic) domains in Fe-based superconductors has so
far only been obtained through mechanical straining, which considerably
perturbs the ground state of these materials. The recently discovered
non-mechanical detwinning in EuFe$_{2}$As$_{2}$ by ultra-low magnetic fields
offers an entirely different, non-perturbing way to achieve the same goal.
However, this way seemed risky due to the lack of a microscopic understanding
of the magnetically driven detwinning. Specifically, the following issues
remained unexplained: (i) ultra-low value of the first detwinning field of
$\sim$0.1$\,$T, two orders of magnitude below that of BaFe$_{2}$As$_{2}$, (ii)
reversal of the preferential domain orientation at $\sim$1$\,$T, and
restoration of the low-field orientation above 10$-$15$\,$T. In this paper, we
present, using published as well as newly measured data, a full theory that
quantitatively explains all the observations. The key ingredient of this theory
is a biquadratic coupling between Fe and Eu spins, analogous to the Fe-Fe
biquadratic coupling that drives the nematic transition in this family of
materials.",1702.00649v2
2017/2/8,Investigation of the complex magnetism in the breathing pyrochlore LiIn(Cr$_{1-x}$Rh$_x$)$_4$O$_8$,"We have performed a detailed investigation of the new `breathing' pyrochlore
compound LiInCr$_4$O$_8$ through Rh substitution with measurements of magnetic
susceptibility, specific heat, and x-ray powder diffraction. The
antiferromagnetic phase of LiInCr$_4$O$_8$ is found to be slowly suppressed
with increasing Rh, up to the critical concentration of $x$ = 0.1 where the
antiferromagnetic phase is still observed with the peak in specific heat $T_p$
= 12.5 K, slightly lower than $T_p$ = 14.3 K for the $x$ = 0 compound. From the
measurements of magnetization we also uncover evidence that substitution
increases the amount of frustration. Comparisons are made with the
LiGa$_y$In$_{1-y}$Cr$_4$O$_8$ system as well as other frustrated
pyrochlore-related materials and find comparable amounts of frustration. The
results of this work shows that engineered breathing pyrochlores presents an
important method to further understand the complex magnetism in frustrated
systems.",1702.02538v1
2017/2/20,Effect of annealing on the magnetic properties of zinc ferrite thin films,"We report on the magnetic properties of zinc ferrite thin film deposited on
SrTiO$_3$ single crystal using pulsed laser deposition. X-ray diffraction
result indicates the highly oriented single phase growth of the film along with
the presence of the strain. In comparison to the bulk antiferromagnetic order,
the as-deposited film has been found to exhibit ferrimagnetic ordering with a
coercive field of 1140~Oe at 5~K. A broad maximum, at $\approx$105~K, observed
in zero-field cooled magnetization curve indicates the wide grain size
distribution for the as-deposited film. Reduction in magnetization and blocking
temperature has been observed after annealing in both argon as well as oxygen
atmospheres, where the variation was found to be dependent on the annealing
temperature.",1702.06033v1
2017/3/3,Discovery of Magnetic Antiskyrmions Beyond Room Temperature in Tetragonal Heusler Materials,"Skyrmions, topologically stable spin textures, are of great interest for new
generations of spintronic devices. In general, the stabilization of skyrmions
has been achieved in systems with broken inversion symmetry, where the
asymmetric Dzyaloshinskii-Moriya interaction (DMI) modifies the uniform
magnetic state to a swirling state. Depending on the crystal symmetries, two
distinct types of skyrmions, Bloch and N\'eel types, have been observed
experimentally. Here, we present, the experimental manifestation of a special
type of spin-swirling, namely antiskyrmions, in a family of acentric tetragonal
Heusler compounds with D2d crystal symmetry. A spiral magnetic ground-state,
which propagates in the tetragonal basal plane, is transformed into a skyrmion
lattice-state under magnetic fields applied along the tetragonal axis over a
wide temperature interval. Direct imaging by Lorentz Transmission Electron
Microscopy (LTEM) shows field stabilized antiskyrmion lattices and isolated
antiskyrmions between 100 K and 400 K, and zero-field metastable antiskyrmions
at low temperatures.",1703.01017v1
2017/3/3,Magnetic field induced polarization enhancement in monolayers of tungsten dichalcogenides: Effects of temperature,"Optical orientation of localized/bound excitons is shown to be effectively
enhanced by the application of magnetic fields as low as 20 mT in monolayer
WS$_2$. At low temperatures, the evolution of the polarization degree of
different emission lines of monolayer WS$_2$ with increasing magnetic fields is
analyzed and compared to similar results obtained on a WSe$_2$ monolayer. We
study the temperature dependence of this effect up to $T=60$ K for both
materials, focusing on the dynamics of the valley pseudospin relaxation. A rate
equation model is used to analyze our data and from the analysis of the width
of the polarization deep in magnetic field we conclude that the competition
between the dark exciton pseudospin relaxation and the decay of the dark
exciton population into the localized states are rather different in these two
materials which are representative of the two extreme cases for the ratio of
relaxation rate and depolarization rate.",1703.01129v1
2017/3/7,Electrically controlled terahertz magneto-optical phenomena in continuous and patterned graphene,"The magnetic circular dichroism and the Faraday rotation are the fundamental
phenomena of great practical importance arising from the breaking of the time
reversal symmetry by a magnetic field. In most materials the strength and the
sign of these effects can be only controlled by the field value and its
orientation. Furthermore, the terahertz range is lacking materials having the
ability to affect the polarisation state of the light in a non-reciprocal
manner. Here we demonstrate, using broadband terahertz magneto-electro-optical
spectroscopy, that in graphene both the magnetic circular dichroism and the
Faraday rotation can be modulated in intensity, tuned in frequency and,
importantly, inverted using only electrostatic doping at a fixed magnetic
field. In addition, we observe strong magneto-plasmonic resonances in a
patterned array of graphene antidots, which potentially allows exploiting these
magneto-optical phenomena in a broad THz range.",1703.02449v1
2017/3/14,A Novel Spin-Orbit Torque due to Conduction Electrons,"The anomalous Hall effect is mainly used to probe the magnetization
orientation in ferromagnetic materials. A less explored aspect is the torque
acting back on magnetization, an effect that can be important at high currents.
The spin-orbit coupling of the conduction electrons causes spin-up and
spin-down electrons to scatter to opposite sides when a charge current flows in
the sample. This is equivalent to a spin current with orientation and flow
perpendicular to the driving charge current, leading to a non-equilibrium spin
accumulation that exerts a torque on the bulk magnetization through the s-d
exchange interaction. The symmetry of this toque is that of an uniaxial
anisotropy along the driving current. The large screening currents generated
with laser pulses in all-optical magnetic switching experiments make for
practical uses of this torque.",1703.04724v2
2017/4/3,Magnetoelectric Phase Diagrams of Multiferroic GdMn2O5,"Electric and magnetic properties of multiferroic GdMn2O5 in external magnetic
fields were investigated to map out the magnetoelectric phases in this
material. Due to strong magnetoelectric coupling, the dielectric permittivity
is highly sensitive to phase boundaries in GdMn2O5, which allowed to construct
the field-temperature phase diagrams. Several phase transitions are observed
which are strongly field-dependent with respect to field orientation and
strength. The phase diagram for a magnetic field along the crystallographic
a-axis corresponds well to a polarization step, as induced by 90 degree
rotation of Gd magnetic moments. Our results support the model of two
ferroelectric sublattices, Mn-Mn and Gd-Mn with strong R-Mn (4f-3d) interaction
for the polarization in RMn2O5.",1704.00659v1
2017/4/19,Antiferromagnetic Topological Nodal Line Semimetals,"We study three-dimensional nodal line semimetals (NLSMs) with magnetic
ordering and strong spin-orbit interaction. Two distinct classes of magnetic
NLSMs are proposed. The first class is band-inversion NLSM where the accidental
line node is induced by band inversion and locally protected by glide mirror
plane and the combined time-reversal and inversion symmetries. This can be
viewed as a trivial stacking of the two-dimensional antiferromagnetic Dirac
semimetals. The second class is essential NLSM where the nodal features are
filling-enforced by specific magnetic symmetry group. We further provide two
concrete tight-binding models for magnetic NLSMs which belong to these two
different classes, respectively. We conclude with a brief discussion on the
possible material venues and the experimental implications for such phases.",1704.05608v1
2017/4/25,Cryomodule Test Stand Reduced-Magnetic Support Design At Fermilab,"In a partnership with SLAC National Accelerator Laboratory (SLAC) and
Jefferson Lab, Fermilab will assemble and test 17 of the 35 total 1.3 GHz
cryomodules for the Linac Coherent Light Source II (LCLS-II) Project. These
devices will be tested at Fermilab's Cryomodule Test Facility (CMTF) within the
Cryomodule Test Stand (CMTS-1) cave. The problem of magnetic pollution became
one of major issues during design stage of the LCLS-II cryomodule as the
average quality factor of the accelerating cavities is specified to be $2.7
\times 10^{10}$. One of the possible ways to mitigate the effect of stray
magnetic fields and to keep it below the goal of 5 mGauss involves the
application of low permeable materials. Initial permeability and magnetic
measurement studies regarding the use of 316L stainless steel material
indicated that cold work (machining) and heat affected zones from welding would
be acceptable.",1704.07877v1
2017/4/27,Chirality-induced Antisymmetry in Magnetic Domain-Wall Speed,"In chiral magnetic materials, numerous intriguing phenomena such as built in
chiral magnetic domain walls (DWs) and skyrmions are generated by the
Dzyaloshinskii Moriya interaction (DMI). The DMI also results in asymmetric DW
speed under in plane magnetic field, which provides a useful scheme to measure
the DMI strengths. However, recent findings of additional asymmetries such as
chiral damping have disenabled unambiguous DMI determination and the underlying
mechanism of overall asymmetries becomes under debate. By extracting the
DMI-induced symmetric contribution, here we experimentally investigated the
nature of the additional asymmetry. The results revealed that the additional
asymmetry has a truly antisymmetric nature with the typical behavior governed
by the DW chirality. In addition, the antisymmetric contribution changes the DW
speed more than 100 times, which cannot be solely explained by the chiral
damping scenario. By calibrating such antisymmetric contributions, experimental
inaccuracies can be largely removed, enabling again the DMI measurement scheme.",1704.08751v1
2017/4/28,Observation of Spin-Orbit Effects with Spin Rotation Symmetry,"The spin-orbit interaction enables interconversion between a charge current
and a spin current. It is usually believed that in a nonmagnetic metal (NM) or
at a NM/ferromagnetic metal (FM) bilayer interface, the symmetry of spin-orbit
effects (SOE) requires that the spin current, charge current and spin
orientation are all orthogonal to each other. Here we show the observation of a
SOE near the NM/FM interface that exhibits a very different symmetry from the
conventional spin Hall effect, insofar as the spin polarization is further
rotated about the magnetization. These results imply that a perpendicularly
polarized spin current can be generated with an in-plane charge current simply
by use of a FM/NM bilayer with magnetization collinear to the charge current.
The ability to generate a spin current with arbitrary polarization using
typical magnetic materials will greatly benefit the development of magnetic
memories.",1704.08998v1
2017/5/9,Low spin wave damping in the insulating chiral magnet Cu$_{2}$OSeO$_{3}$,"Chiral magnets with topologically nontrivial spin order such as Skyrmions
have generated enormous interest in both fundamental and applied sciences. We
report broadband microwave spectroscopy performed on the insulating chiral
ferrimagnet Cu$_{2}$OSeO$_{3}$. For the damping of magnetization dynamics we
find a remarkably small Gilbert damping parameter of about $1\times10^{-4}$ at
5 K. This value is only a factor of 4 larger than the one reported for the best
insulating ferrimagnet yttrium iron garnet. We detect a series of sharp
resonances and attribute them to confined spin waves in the mm-sized samples.
Considering the small damping, insulating chiral magnets turn out to be
promising candidates when exploring non-collinear spin structures for high
frequency applications.",1705.03416v1
2017/5/12,"Growth, Crystal Structure and Magnetic Characterization of Zn-Stabilized CePtIn4","The growth and characterization of CePtIn4, stabilized by 10% Zn substitution
for In, is reported. The new material is orthorhombic, space group Cmcm (No.
63), with lattice parameters a = 4.51751(4) {\AA}, b = 16.7570(2) {\AA}, and c
= 7.36682(8) {\AA}, and the refined crystal composition has 10% of Zn
substituted for In, i.e. the crystals are CePt(In3.6Zn0.1)4. Crystals were
grown using a self-flux method: only growths containing Zn yielded CePtIn4
crystals, while Ce3Pt4In13 crystals formed when Zn was not present. Anisotropic
temperature-dependent magnetic susceptibilities for single crystals show that
Zn-stabilized CePtIn4 orders magnetically at ~1.9 K. High-temperature
Curie-Weiss fits indicate an effective moment of ~2.30 muB/ Ce and a
directionally averaged Weiss-temperature of approximately - 9 K. Specific heat
data shows a peak consistent with the ordering temperature seen in the magnetic
susceptibility data. Zn-stabilized CePtIn4 is metallic and displays no
superconducting transition down to 0.14 K.",1705.04634v1
2017/5/29,"Contributions of Co and Fe orbitals to Perpendicular Magnetic Anisotropy of MgO/CoFeB Bilayers with Spin-Orbit-Torque-Related (Ta, W, IrMn, and Ti) Underlayers","We study the perpendicular magnetic anisotropy (PMA) of the CoFeB/MgO
bilayers in contact with W, Ta, IrMn and Ti which has been suggested as the
spin-orbit-torque-related underlayers. The saturation magnetization of the
CoFeB depends on the underlayer materials due to formation of a dead-layer,
affecting PMA strength of each film. The x-ray magnetic circular dichroism
measurement reveals that the interfacial intermixing suppresses only the
perpendicular orbital moment of Fe, while the intermixing simultaneously
suppresses both the perpendicular and in-plane orbital moments of Co.",1705.10064v1
2017/6/14,"Dirac's ""magnetic monopole"" in pyrochlore ice U(1) spin liquids: Spectrum and classification","We study the U(1) quantum spin liquid on the pyrochlore spin ice systems. For
the non-Kramers doublets such as Pr$^{3+}$ and Tb$^{3+}$, we point out that the
inelastic neutron scattering not only detects the low-energy gauge photon, but
also contains the continuum of the ""magnetic monopole"" excitations. Unlike the
spinons, these ""magnetic monopoles"" are purely of quantum origin and have no
classical analogue. We further point out that the ""magnetic monopole""
experiences a background dual ""$\pi$"" flux due to the spin-1/2 nature of the
local moment when the ""monopole"" hops on the dual diamond lattice. We then
predict that the ""monopole"" continuum has an enhanced spectral periodicity.
This prediction can be examined among the existing data on the non-Kramers
doublet spin liquid candidate materials like Pr$_2$TM$_2$O$_7$ and
Tb$_2$TM$_2$O$_7$ (with TM = ""transition metal""). The application to the
Kramers doublet systems and numerical simulation is further discussed. Finally,
we present a general classification of distinct symmetry enriched U(1) quantum
spin liquids based on the translation symmetry fractionalization patterns of
""monopoles"" and ""spinons"".",1706.04333v2
2017/6/21,Spin pumping and shot noise in ferrimagnets: bridging ferro- and antiferromagnets,"A combination of novel technological and fundamental physics prospects has
sparked a huge interest in pure spin transport in magnets, starting with
ferromagnets and spreading to antiferro- and ferrimagnets. We present a
theoretical study of spin transport across a ferrimagnet$|$non-magnetic
conductor interface, when a magnetic eigenmode is driven into a coherent state.
The obtained spin current expression includes intra- as well as
cross-sublattice terms, both of which are essential for a quantitative
understanding of spin-pumping. The dc current is found to be sensitive to the
asymmetry in interfacial coupling between the two sublattice magnetizations and
the mobile electrons, especially for antiferromagnets. We further find that the
concomitant shot noise provides a useful tool for probing the quasiparticle
spin and interfacial coupling.",1706.07118v2
2017/6/22,Spatially modulated magnetic structure of EuS due to the tetragonal domain structure of SrTiO$_3$,"The combination of ferromagnets with topological superconductors or
insulators allows for new phases of matter that support excitations such as
chiral edge modes and Majorana fermions. EuS, a wide-band-gap ferromagnetic
insulator with a Curie temperature around 16 K, and SrTiO$_3$ (STO), an
important substrate for engineering heterostructures, may support these phases.
We present scanning superconducting quantum interference device (SQUID)
measurements of EuS grown epitaxially on STO that reveal micron-scale
variations in ferromagnetism and paramagnetism. These variations are oriented
along the STO crystal axes and only change their configuration upon thermal
cycling above the STO cubic-to-tetragonal structural transition temperature at
105 K, indicating that the observed magnetic features are due to coupling
between EuS and the STO tetragonal structure. We speculate that the STO
tetragonal distortions may strain the EuS, altering the magnetic anisotropy on
a micron-scale. This result demonstrates that local variation in the induced
magnetic order from EuS grown on STO needs to be considered when engineering
new phases of matter that require spatially homogeneous exchange.",1706.07374v1
2017/7/6,Strong angular dependent transmission ratio due to interplay between spin waves and the domain wall in perpendicular magnetic anisotropy materials,"Spin waves (SW) can induce rich domain wall (DW) motion in a
perpendicular-magnetic anisotropy nanostrip. In-plane magnetization tilt angle
resulting from the fluctuation of the effective field of the magnetization
response in the DW region plays an essential role in the dynamics of SW
interacting with a DW. We performed simulation and found that the transmission
ratio of the propagating SW across the DW depends strongly on the tilt angle in
the low-frequency regime. The material parameters and the geometrical
configuration can be fine-tuned for practical devices.",1707.01617v1
2017/7/19,Experimental evidence for topological surface states wrapping around bulk SnTe crystal,"We demonstrate that the metallic topological surface states wrap on all sides
the 3D topological crystalline insulator SnTe. This is achieved by studying
oscillatory quantum magneto-transport and magnetization at tilted magnetic
fields which enables us to observe simultaneous contributions from neighbouring
sample sides. Taking into account pinning of the Fermi energy by the SnTe
reservoir we successfully describe theoretically the de Haas-van Alphen
oscillations of magnetization. The determined \pi-Berry phase of surface states
confirms their Dirac fermion character. We independently observe oscillatory
contributions of magneto-transport and magnetization originating from the bulk
SnTe reservoir of high hole density. It is concluded that the bulk and surface
Landau states exist in parallel. Our main result that the bulk reservoir is
surrounded on all sides by the topological surface states has an universal
character.",1707.05999v1
2017/8/30,Magnetic order induces symmetry breaking in the single crystalline orthorhombic CuMnAs semimetal,"Recently, orthorhombic CuMnAs has been proposed to be a magnetic material
where topological fermions exist around the Fermi level. Here we report the
magnetic structure of the orthorhombic Cu0.95MnAs and Cu0.98Mn0.96As single
crystals. While Cu0.95MnAs is a commensurate antiferromagnet (C-AFM) below 360
K with a propagation vector of k = 0, Cu0.98Mn0.96As undergoes a second-order
paramagnetic to incommensurate antiferromagnetic (IC-AFM) phase transition at
320 K with k = (0.1,0,0), followed by a second-order IC-AFM to C-AFM phase
transition at 230 K. In the C-AFM state, the Mn spins order parallel to the
b-axis but antiparallel to their nearest-neighbors with the easy axis along the
b axis. This magnetic order breaks Ry gliding and S2z rotational symmetries,
the two crucial for symmetry analysis, resulting in finite band gaps at the
crossing point and the disappearance of the massless topological fermions.
However, the spin-polarized surface states and signature induced by non-trivial
topology still can be observed in this system, which makes orthorhombic CuMnAs
promising in antiferromagnetic spintronics.",1708.09340v1
2017/9/6,Characterizing spin transport: detection of spin accumulation via magnetic stray field,"Spin transport in electric conductors is largely determined by two material
parameters - spin diffusion length and spin Hall angle. In metals, these are
typically determined indirectly by probing magnetoresistance in magnet/metal
heterostructures, assuming knowledge of the interfacial properties. We suggest
profiling the charge current induced spin Hall spin accumulation in metals, via
detection of the magnetic stray field generated by the associated static
magnetization, as a direct means of determining spin transport parameters. We
evaluate the spatial profile of the stray field as well as the Oersted field
generated by the charge current. We thus demonstrate that such a charge current
induced spin accumulation is well within the detection limit of contemporary
technology. Measuring the stray fields may enable direct access to spin-related
properties of metals paving the way for a better and consistent understanding
of spin transport therein.",1709.01820v1
2017/10/2,Multi-scale modelling of current-induced switching in magnetic tunnel junctions using ab initio spin transfer torques,"There exists a significant challenge in developing efficient magnetic tunnel
junctions with low write currents for non-volatile memory devices. With the aim
of analysing potential materials for efficient current-operated magnetic
junctions we have developed a multi-scale methodology combining the ab initio
calculations of spin-transfer torque with large-scale time-dependent
simulations using atomistic spin dynamics. In this work we introduce our
multi-scale approach including a discussion on a number of possible mapping
schemes the ab initio spin torques into the spin dynamics. We demonstrate this
methodology on a prototype Co/MgO/Co/Cu tunnel junction showing that the spin
torques are primarily acting at the interface between the Co free layer and
MgO. Using spin dynamics we then calculate the reversal switching times for the
free layer and the critical voltages and currents required for such switching.
Our work provides an efficient, accurate and versatile framework for designing
novel current-operated magnetic devices, where all the materials details are
take into account.",1710.00574v1
2017/10/16,Quantum oscillations and Dirac-Landau levels in Weyl superconductors,"When magnetic field is applied to metals and semimetals quantum oscillations
appear as individual Landau levels cross the Fermi level. Quantum oscillations
generally do not occur in superconductors (SC) because magnetic field is either
expelled from the sample interior or, if strong enough, drives the material
into the normal state. In addition, elementary excitations of a superconductor
-- Bogoliubov quasiparticles -- do not carry a well defined electric charge and
therefore do not couple in a simple way to the applied magnetic field. We
predict here that in Weyl superconductors certain types of elastic strain have
the ability to induce chiral pseudo-magnetic field which can reorganize the
electronic states into Dirac-Landau levels with linear band crossings at low
energy. The resulting quantum oscillations in the quasiparticle density of
states and thermal conductivity can be experimentally observed under a bending
deformation of a thin film Weyl SC and provide new insights into this
fascinating family of materials.",1710.05497v2
2017/10/23,Magnetic anisotropy in antiferromagnetic hexagonal MnTe,"Antiferromagnetic hexagonal MnTe is a promising material for spintronic
devices relying on the control of antiferromagnetic domain orientations. Here
we report on neutron diffraction, magnetotransport, and magnetometry
experiments on semiconducting epitaxial MnTe thin films together with density
functional theory (DFT) calculations of the magnetic anisotropies.
  The easy axes of the magnetic moments within the hexagonal basal plane are
determined to be along $\left<1\bar100\right>$ directions. The spin-flop
transition and concomitant repopulation of domains in strong magnetic fields is
observed.
  Using epitaxially induced strain the onset of the spin-flop transition
changes from $\sim2$~T to $\sim0.5$~T for films grown on InP and SrF$_2$
substrates, respectively.",1710.08523v2
2017/11/5,Aharonov-Casher effect and quantum transport in graphene based nano rings: A self-consistent Born approximation,"In this study, Rashba coupling induced Aharonov-Casher effect in a graphene
based nano ring is investigated theoretically. The graphene based nano ring is
considered as a central device connected to semi-infinite graphene nano
ribbons. In the presence of the Rashba spin-orbit interaction, two armchair
shaped edge nano ribbons are considered as semi-infinite leads. The
non-equilibrium Green's function approach is utilized to obtain the quantum
transport characteristics of the system. The relaxation and dephasing
mechanisms within the self-consistent Born approximation is scrutinized. The
Lopez-Sancho method is also applied to obtain the self-energy of the leads. We
unveil that the non-equilibrium current of the system possesses measurable
Aharonov-Casher oscillations with respect to the Rashba coupling strength. In
addition, we have observed the same oscillations in dilute impurity regimes in
which amplitude of the oscillations is shown to be suppressed as a result of
the relaxations.",1711.01633v1
2017/11/16,Magnetic properties of Ruddlesden-Popper phases Sr$_{3-x}$Y$_{x}$(Fe$_{1.25}$Ni$_{0.75}$)O$_{7-δ}$: A combined experimental and theoretical investigation,"We present a comprehensive study of the magnetic properties of
Sr$_{3-x}$Y$_{x}$(Fe$_{1.25}$Ni$_{0.75}$)O$_{7-\delta}$ ($0 \leq x \leq 0.75$).
Experimentally, the magnetic properties are investigated using superconducting
quantum interference device (SQUID) magnetometry and neutron powder diffraction
(NPD). This is complemented by the theoretical study based on density
functional theory as well as the Heisenberg exchange parameters. Experimental
results show an increase in the N\'eel temperature ($T_N$) with the increase of
Y concentrations and O occupancy. The NPD data reveals all samples are
antiferromagnetically ordered at low temperatures, which has been confirmed by
our theoretical simulations for the selected samples. Our first-principles
calculations suggest that the 3D magnetic order is stabilized due to finite
inter-layer exchange couplings. The latter give rise to a finite inter-layer
spin correlations which disappear above the $T_N$.",1711.06037v2
2017/11/16,Anisotropic magnetic properties of the ferromagnetic semiconductor CrSbSe$_3$,"Single crystals of CrSbSe$_3$, a structurally pseudo-one-dimensional
ferromagnetic semiconductor, were grown using a high-temperature solution
growth technique and were characterized by x-ray diffraction, anisotropic,
temperature- and field-dependent magnetization, temperature-dependent
resistivity and optical absorption measurements. A band gap of 0.7 eV was
determined from both resistivity and optical measurements. At high
temperatures, CrSbSe$_3$ is paramagnetic and isotropic with a Curie-Weiss
temperature of $\sim$145 K and an effective moment of $\sim$4.1 $\mu_B$/Cr. A
ferromagnetic transition occurs at $T_c$ = 71 K. The $a$-axis, perpendicular to
the chains in the structure, is the magnetic easy axis, while the chain axis
direction, along $b$, is the hard axis. Magnetic isotherms measured around
$T_c$ do not follow the behavior predicted by simple mean field critical
exponents for a second order phase transition. A tentative set of critical
exponents is estimated based on a modified Arrott plot analysis, giving
$\beta\sim$0.25, $\gamma\sim$1.38 and $\delta\sim$6.6.",1711.06342v1
2017/11/22,Structural properties of Fe/Cu magnetic multilayers: a Monte Carlo approach,"Using atomistic Monte Carlo simulations, we investigated the impact of the
interface on the structural properties of iron and copper (Fe/Cu) magnetic
multilayers grown by Vorono\""i diagram. Interest in magnetic multilayers has
recently emerged as they are shown to be promising candidates for magnetic
storage media, magneto-resistive sensors, and personalized medical treatment.
As these artificial materials show large differences in properties compared to
conventional ones, many experimental and theoretical works have been dedicated
on shedding light on these differences and tremendous results have emerged.
However, little is known how the interfaces influence the structure of the
layers around them. By a numerical approach, we show that the structure of each
layer depends on its thickness and the interface morphology. The Fe and Cu
layers can adopt either the body-centered-cubic (bcc) or face-centered-cubic
(fcc) structure, while the interface can assume amorphous, bcc, fcc, or a
mixture of bcc and fcc structures depending on the layer thicknesses. These
results are in good agreement with the experiments. They could be helpful in
understanding effects such as giant magneto-resistance from the structural
viewpoint.",1711.08508v1
2017/11/24,Thermodynamic model of a solid with RKKY interaction and magnetoelastic coupling,"Thermodynamic description of a model system with magnetoelastic coupling is
presented. The elastic, vibrational, electronic and magnetic energy
contributions are taken into account. The long-range RKKY interaction is
considered together with the nearest-neighbour direct exchange. The generalized
Gibbs potential and the set of equations of state are derived, from which all
thermodynamic functions are self-consistently obtained. Thermodynamic
properties are calculated numerically for FCC structure for arbitrary external
pressure, magnetic field and temperature, and widely discussed. In particular,
for some parameters of interaction potential and electron concentration
corresponding to antiferromagnetic phase, the existence of negative thermal
expansion coefficient is predicted.",1711.09152v2
2017/11/27,Extreme magnetoresistance induced by Zeeman effect-driven electron-hole compensation and topological protection in MoSi$_2$,"The magnetoresistance is the magnetic field induced change of electrical
resistivity of a material. Recent studies have revealed extremely large
magnetoresistance in several non-magnetic semimetals, which has been explained
on the basis of either electron-hole compensation or the Fermi surface
topology, or the combination of both. Here, we present a single crystal study
on MoSi$_2$, which exhibits extremely large magnetoresistance, approaching
almost 10$^7$ % at 2 K and 14 T magnetic field. It is found that the
electron-hole compensation level in MoSi$_2$ evolves with magnetic field, which
is resulted from strong Zeeman effect, and found beneficial in boosting the
large non-saturating magnetoresistance. The non-trivial Berry phase in the de
Haas-van Alphen oscillations and the moderate suppression of backward
scattering of the charge carriers lend support for the topological nature of
this semimetal. The ultra-large carrier mobility of the topologically protected
charge carriers reinforces the magnetoresistance of MoSi2 to an unprecedented
large value.",1711.09646v1
2017/11/30,Interacting Fields and Flows: Magnetic Hot Jupiters,"We present Magnetohydrodynamic (MHD) simulations of the magnetic interactions
between a solar type star and short period hot Jupiter exoplanets, using the
publicly available MHD code PLUTO. It has been predicted that emission due to
magnetic interactions such as the electron cyclotron maser instability (ECMI)
will be observable. In our simulations, a planetary outflow, due to UV
evaporation of the exoplanets atmosphere, results in the build-up of
circumplanetary material. We predict the ECMI emission and determine that the
emission is prevented from escaping from the system. This is due to the
evaporated material leading to a high plasma frequency in the vicinity of the
planet, which inhibits the ECMI process.",1711.11282v1
2017/12/19,Advances in the Physics of Magnetic Skyrmions and Perspective for Technology,"Magnetic skyrmions are small swirling topological defects in the
magnetization texture stabilized by the protection due to their topology. In
most cases they are induced by chiral interactions between atomic spins
existing in non-centrosymmetric magnetic compounds or in thin films in which
inversion symmetry is broken by the presence of an interface. The skyrmions can
be extremely small with diameters in the nanometer range and, importantly, they
behave as particles that can be moved, created or annihilated, making them
suitable for abacus-type applications in information storage, logic or
neuro-inspired technologies. Up to the last years skyrmions were observed only
at low temperature (and in most cases under large applied fields) but important
efforts of research has been recently devoted to find thin film and
multilayered structures in which skyrmions are stabilized above room
temperature and manipulated by current. This article focuses on these recent
advances on the route to devices prototypes.",1712.07236v1
2017/12/31,"Magnetic and Structural Properties of the Iron Oxychalcogenides La$_{2}$O$_{2}$Fe$_{2}$O$M_{2}$ ($M$= S, Se)","We present the results of structural and magnetic phase comparisons of the
iron oxychalcogenides La$_{2}$O$_{2}$Fe$_{2}$O$M$$_{2}$ ($M$ = S, Se). Elastic
neutron scattering reveals that $M$ = S and Se have similar nuclear structures
at room and low temperatures. We find that both materials obtain
antiferromagnetic ordering at a Neel temperature $T_{N}$ 90.1 $\pm$ 0.16 K and
107.2 $\pm$ 0.06 K for $M$= Se and S, respectively. The magnetic arrangements
of $M$ = S, Se are obtained through Rietveld refinement. We find the order
parameter exponent $\beta$ to be 0.129 $\pm$ 0.006 for $M$ = Se and 0.133 $\pm$
0.007 for $M$ = S. Each of these values is near the Ising symmetry value of
1/8. This suggests that although lattice and electronic structural
modifications result from chalcogen exchange, the nature of the magnetic
interactions is similar in these materials.",1801.00342v2
2018/1/11,Preconditioned nonlinear conjugate gradient method for micromagnetic energy minimization,"Fast computation of demagnetization curves is essential for the computational
design of soft magnetic sensors or permanent magnet materials. We show that a
sparse preconditioner for a nonlinear conjugate gradient energy minimizer can
lead to a speed up by a factor of 3 and 7 for computing hysteresis in soft
magnetic and hard magnetic materials, respectively. As a preconditioner an
approximation of the Hessian of the Lagrangian is used, which only takes local
field terms into account. Preconditioning requires a few additional sparse
matrix vector multiplications per iteration of the nonlinear conjugate gradient
method, which is used for minimizing the energy for a given external field. The
time to solution for computing the demagnetization curve scales almost linearly
with problem size.",1801.03690v1
2018/1/18,A unified formulation of dichroic signals using the Borrmann effect and twisted photon beams,"Dichroic signals derived from the Borrmann effect and a twisted photon beam
with topological charge l = 1 are formulated with an effective wavevector. The
unification applies for non-magnetic and magnetic materials. Electronic degrees
of freedom associated with an ion are encapsulated in multipoles previously
used to interpret conventional dichroism and Bragg diffraction enhanced by an
atomic resonance. A dichroic signal exploiting the Borrmann effect with a
linearly polarized beam presents charge-like multipoles that include a
hexadecapole. A difference between dichroic signals obtained with a twisted
beam carrying spin polarization (circular polarization) and opposite winding
numbers presents charge-like atomic multipoles, whereas a twisted beam carrying
linear polarization alone presents magnetic (time-odd) multipoles. Charge-like
multipoles include a quadrupole, and magnetic multipoles include a dipole and
an octupole. We discuss the practicalities and relative merits of spectroscopy
exploiting the two remarkably closely-related processes.",1801.06012v3
2018/2/1,Negative thermal expansion and magnetoelastic coupling in the breathing pyrochlore lattice material LiGaCr4S8,"The physical properties of the spinel LiGaCr4S8 have been studied with
neutron diffraction, X-ray diffraction, magnetic susceptibility and heat
capacity measurements. The neutron diffraction and synchrotron X-ray
diffraction data reveal negative thermal expansion (NTE) below 111(4) K. The
magnetic susceptibility deviates from Curie-Weiss behavior with the onset of
NTE. At low temperature a broad peak in the magnetic susceptibility at 10.3(3)
K is accompanied by the return of normal thermal expansion. First principles
calculations find a strong coupling between the lattice and the simulated
magnetic ground state. These results indicate strong magnetoelastic coupling in
LiGaCr4S8.",1802.00158v2
2018/2/7,"Structure, magnetic and transport properties of epitaxial thin films of equiatomic CoFeMnGe quaternary Heusler alloy","Future spintronics requires the realization of thin film of half-metallic
ferromagnets having high Curie temperature and 100\% spin polarization at the
Fermi level for potential spintronics applications. In this paper, we report
the epitaxial thin films growth of half-metallic CoFeMnGe Heusler alloy on MgO
(001) substrate using pulsed laser deposition system, along with the study of
structural, magnetic and transport properties. The magnetic property
measurements of the thin film suggest a soft ferromagnetic state at room
temperature with an in-plane magnetic anisotropy and a Curie temperature well
above the room temperature. Anisotropic magnetoresistance (AMR) ratio and
temperature dependent electrical resistivity measurements of the thin film
indicate the compound to be half-metallic in nature and therefore suitable for
the fabrications of spintronics devices.",1802.02413v1
2018/2/9,Antiferromagnetic ground state in the MnGa$_4$ intermetallic compound,"Magnetism of the binary intermetallic compound MnGa$_4$ is re-investigated.
Band-structure calculations predict antiferromagnetic behavior in contrast to
Pauli paramagnetism reported previously. Magnetic susceptibility measurements
on single crystals indeed reveal an antiferromagnetic transition at $T_N=393$
K. Neutron powder diffraction and $^{69,71}$Ga nuclear quadrupole resonance
spectroscopy show collinear antiferromagnetic order with magnetic moments
alligned along the [111] direction of the cubic unit cell. The magnetic moment
of 0.80(3)$\mu_B$ at 1.5 K extracted from the neutron data is in good agreement
with the band-structure results.",1802.03256v2
2018/2/11,Correlation between Superconductivity and Magnetic Fluctuations in Fe(Se1-xSx) Revealed by 77Se NMR,"We present $^{77}$Se-NMR measurements on FeSe$_{1-x}$S$_x$ samples with
sulfur content $x=0,9,15$ and $29\%$. Twinned nematic domains are observed in
the NMR spectrum for all samples except $x=29\%$. The NMR spin-lattice
relaxation rate shows that magnetic fluctuations are initially enhanced between
$x=0\%$ and $x=9\%$, but are strongly suppressed for higher $x$ values. The
observed behavior of the magnetic fluctuations parallels the superconducting
transition temperature $T_c$ in these materials, providing strong evidence for
the primary importance of magnetic fluctuations for superconductivity, despite
the presence of nematic quantum criticality in this system.",1802.03776v1
2018/2/16,Carrier driven antiferromagnetism and exchange-bias in SrRuO3/CaRuO3 heterostructures,"Oxide heterostructures exhibit a rich variety of magnetic and transport
properties which arise due to contact at an interface. This can lead to
surprising effects that are very different from the bulk properties of the
materials involved. We report the magnetic properties of bilayers of SrRuO3, a
well known ferromagnet, and CaRuO3, which is nominally a paramagnet. We find
intriguing features that are consistent with CaRuO3 developing dual magnetic
character, with both a net moment as well as antiferromagnetic order. We argue
the ordered SrRuO3 layer induces an undulating polarization profile in the
conduction electrons of CaRuO3, by a mechanism akin to Friedel oscillations. At
low temperatures, this oscillating polarization is inherited by rigid local
moments within CaRuO3, leading to a robust exchange bias. We present ab initio
simulations in support of this picture. Our results demonstrate a new ordering
mechanism and throw light on the magnetic character of CaRuO3 .",1802.05869v1
2018/3/4,Spin Hall effects without spin currents in magnetic insulators,"The spin Hall effect (SHE) is normally discussed in terms of a spin current,
which is ill-defined in strongly spin-orbit-coupled systems because of spin
non-conservation. In this work we propose an alternative view of SHE phenomena
by relating them to a spin analog of charge polarization induced by an electric
field. The spin density polarization is most conveniently defined in
insulators, which can have a SHE if they break time-reversal symmetry, i.e. if
they are magnetic. The reciprocal of this SHE is a counterpart of the inverse
SHE (ISHE), and is manifested in magnetic insulators as a charge polarization
induced by a Zeeman field gradient. We use a modified Kane-Mele model to
illustrate the magnetic spin Hall effect, and to discuss its bulk-boundary
relationship.",1803.01294v2
2018/5/7,Revealing Controllable Anisotropic Magnetoresistance in Spin Orbit Coupled Antiferromagnet Sr2IrO4,"Antiferromagnetic spintronics actively introduces new principles of magnetic
memory, in which the most fundamental spin-dependent phenomena, i.e.
anisotropic magnetoresistance effects, are governed by an antiferromagnet
instead of a ferromagnet. A general scenario of the antiferromagnetic
anisotropic magnetoresistance effects mainly stems from the magnetocrystalline
anisotropy related to spin-orbit coupling. Here we demonstrate magnetic field
driven contour rotation of the fourfold anisotropic magnetoresistance in bare
antiferromagnetic Sr2IrO4/SrTiO3 (001) thin films hosting a strong spin-orbit
coupling induced Jeff=1/2 Mott state. Concurrently, an intriguing minimal in
the magnetoresistance emerges. Through first principles calculations, the
band-gap engineering due to rotation of the Ir isospins is revealed to be
responsible for these emergent phenomena, different from the traditional
scenario where relatively more conductive state was obtained usually when
magnetic field was applied along the magnetic easy axis. Our findings
demonstrate a new efficient route, i.e. via the novel Jeff=1/2 state, to
realize controllable anisotropic magnetoresistance in antiferromagnetic
materials.",1805.02394v1
2018/5/15,Spin direction controlled electronic band structure in two dimensional ferromagnetic CrI3,"Manipulating physical properties using the spin degree of freedom constitutes
a major part of modern condensed matter physics and is very important for
spintronics devices. Using the newly discovered two dimensional van der Waals
ferromagnetic CrI3 as a prototypic material, we theoretically demonstrated a
giant magneto band-structure (GMB) effect whereby a change of magnetization
direction significantly modifies the electronic band structure. Our density
functional theory calculations and model analysis reveal that rotating the
magnetic moment of CrI3 from out-of-plane to in-plane causes a
direct-to-indirect bandgap transition, inducing a magnetic field controlled
photoluminescence. Moreover, our results show a significant change of Fermi
surface with different magnetization directions, giving rise to giant
anisotropic magnetoresistance. Additionally, the spin reorientation is found to
modify the topological states. Given that a variety of properties are
determined by band structures, our predicted GMB effect in CrI3 opens a new
paradigm for spintronics applications.",1805.05675v1
2018/5/16,Magnetic properties of single crystalline itinerant ferromagnet AlFe2B2,"Single crystals of AlFe$_{2}$B$_{2}$ have been grown using the self flux
growth method and then measured the structural properties, temperature and
field dependent magnetization, and temperature dependent electrical resistivity
at ambient as well as high pressure. The Curie temperature of AlFe$_{2}$B$_{2}$
is determined to be $274$~K. The measured saturation magnetization and the
effective moment for paramagnetic Fe-ion indicate the itinerant nature of the
magnetism with a Rhode-Wohlfarth ratio $ \frac{M_{C}}{M_{sat}}\approx 1.14$.
Temperature dependent resistivity measurements under hydrostatic pressure shows
that transition temperature \textit{T$_C$} is suppressed down to 255 K for $p =
2.24$~GPa pressure with a suppression rate of $\sim -8.9$~K/GPa. The anisotropy
fields and magnetocrystalline anisotropy constants are in reasonable agreement
with density functional theory calculations.",1805.06373v1
2018/6/1,Dirac-Surface-State Modulated Spin Dynamics in a Ferrimagnetic Insulator at Room Temperature,"This work demonstrates dramatically modified spin dynamics of magnetic
insulator (MI) by the spin-momentum locked Dirac surface states of the adjacent
topological insulator (TI) which can be harnessed for spintronic applications.
As the Bi-concentration x is systematically tuned in 5 nm thick (BixSb1-x)2Te3
TI film, the weight of the surface relative to bulk states peaks at x = 0.32
when the chemical potential approaches the Dirac point. At this concentration,
the Gilbert damping constant of the precessing magnetization in 10 nm thick
Y3Fe5O12 MI film in the MI/TI heterostructures is enhanced by an order of
magnitude, the largest among all concentrations. In addition, the MI acquires
additional strong magnetic anisotropy that favors the in-plane orientation with
similar Bi-concentration dependence. These extraordinary effects of the Dirac
surface states distinguish TI from other materials such as heavy metals in
modulating spin dynamics of the neighboring magnetic layer.",1806.00151v1
2018/6/11,Quantum Spin Fragmentation in Kagome Ice Ho3Mg2Sb3O14,"A promising route to realize entangled magnetic states combines geometrical
frustration with quantum-tunneling effects. Spin-ice materials are canonical
examples of frustration, and Ising spins in a transverse magnetic field are the
simplest many-body model of quantum tunneling. Here, we show that the tripod
kagome lattice material Ho3Mg2Sb3O14 unites an ice-like magnetic degeneracy
with quantum-tunneling terms generated by an intrinsic splitting of the Ho3+
ground-state doublet, realizing a frustrated transverse Ising model. Using
neutron scattering and thermodynamic experiments, we observe a
symmetry-breaking transition at T*~0.32 K to a remarkable quantum state with
three peculiarities: a continuous magnetic excitation spectrum down to T~0.12K;
a macroscopic degeneracy of ice-like states; and a fragmentation of the spin
into periodic and aperiodic components strongly affected by quantum
fluctuations. Our results establish that Ho3Mg2Sb3O14 realizes a
spin-fragmented state on the kagome lattice, with intrinsic quantum dynamics
generated by a homogeneous transverse field.",1806.04081v1
2018/6/26,Influence of an anomalous temperature-dependence of the phase coherence length on the conductivity of magnetic topological insulators,"Magnetotransport constitutes a useful probe to understand the interplay
between electronic band topology and magnetism in spintronics devices based on
topological materials. A recent theory of Lu and Shen [Phys. Rev. Lett. 112,
146601 (2014)] on magnetically doped topological insulators predicts that
quantum corrections $\Delta\kappa$ to the temperature-dependence of the
conductivity can change sign during the Curie transition. This phenomenon has
been attributed to a suppression of the Berry phase of the topological surface
states at the Fermi level, caused by a magnetic energy gap. Here, we
demonstrate experimentally that $\Delta\kappa$ can reverse its sign even when
the Berry phase at the Fermi level remains unchanged, provided that the
inelastic scattering length decreases with temperature below the Curie
transition.",1806.10014v1
2018/7/24,Giant Electrostatic Modification of Magnetism via Electrolyte-Gate-Induced Cluster Percolation in La$_{1-x}$Sr$_x$CoO$_{3-δ}$,"Electrical control of magnetism is a long-standing goal in physics and
technology, recently developed electrolyte gating techniques providing a
promising route to realization. Validating a recent theoretical prediction,
here we demonstrate large enhancement of electrostatic modulation of
ferromagnetic order in ion-gel-gated ultrathin
La$_{0.5}$Sr$_{0.5}$CoO$_{3-\delta}$ by thickness-tuning to the brink of a
magnetic percolation transition. Application of only 3-4 V then drives a
transition from a short-range-ordered insulator to a robust long-range
ferromagnetic metal, realizing giant electrostatic Curie temperature modulation
over a 150 K window. In operando polarized neutron reflectometry confirms
gate-controlled ferromagnetism, also demonstrating unusually deep penetration
of induced magnetization, in further agreement with theory.",1807.09364v1
2018/7/31,Combined cluster and atomic displacement expansion for solid solutions and magnetism,"Finite temperature disordered solid solutions and magnetic materials are
difficult to study directly using first principles calculations, due to the
large unit cells and many independent samples that are required. In this work,
we develop a combined cluster expansion and atomic displacement expansion,
which we fit to first principles energies, forces, and stresses. We then use
the expansion to calculate thermodynamic quantities at nearly first principles
levels of accuracy. We demonstrate that by treating all the relevant degrees of
freedom explicitly, we can achieve improved convergence properties as compared
to a simple cluster expansion, and our model naturally includes both
configurational and vibrational entropy. In addition, we can treat coupling
between structural and chemical or magnetic degrees of freedom. As examples, we
use our expansion to calculate properties of Si$_{1-x}$Ge$_x$, magnetic MnO, Al
with vacancies, and Ba$_x$Sr$_{1-x}$TiO$_3$.",1808.00090v2
2018/8/2,Spontaneous formation and relaxation of spin domains in antiferromagnetic spin-1 quasi-condensates,"Quantum systems of many interacting particles at low temperatures generally
organize themselves into ordered phases of matter, whose nature and symmetries
are captured by an order parameter. In the simplest cases, this order parameter
is spatially uniform. For example, a system of localized spins with
ferromagnetic interactions align themselves to a common direction and build up
a macroscopic magnetization on large distances. However, non-uniform situations
also exist in nature, for instance in antiferromagnetism where the
magnetization alternates in space. The situation becomes even richer when the
spin-carrying particles are mobile, for instance in the so-called stripe phases
emerging for itinerant electrons in strongly-correlated materials.
Understanding such inhomogeneously ordered states is of central importance in
many-body physics. In this work, we study experimentally the magnetic ordering
of itinerant spin-1 bosons in inhomegeneous spin domains at nano-Kelvin
temperatures. We demonstrate that spin domains form spontaneously after a phase
separation transition, \textit{i.e.} in the absence of external magnetic force,
purely because of the antiferromagnetic interactions between the atoms.
Furthermore, we explore how the equilibrium domain configuration emerges from
an initial state prepared far-from-equilibrium.",1808.01015v1
2018/8/30,Influence of spin glass-like magnetic relaxation on the zero-field-cooled exchange bias effect,"The zero-field-cooled exchange bias (ZEB) effect is a remarkable phenomenon
recently reported for some reentrant spin glass-like compounds. In this work,
the time-evolution of magnetization is thoroughly investigated for two ZEB
materials in order to figure out the role played by the spin glass-like phase
on such effect. La$_{1.5}$Sr$_{0.5}$CoMnO$_{6}$ and
La$_{1.5}$Ca$_{0.5}$CoMnO$_{6}$ were chosen as representative samples of ZEB
systems, since the former compound presents the largest ZEB reported so far,
while the second has a much smaller effect, despite being
structurally/chemically similar. Comprehensive magnetic measurements were
carried on both samples, and the results are discussed in terms of the amount
and time-evolution of the spin glass-like phase under the influence of a
varying field. We also propose a phenomenological model, based on the pinning
of spin glass-like moments and on the dynamics of their magnetic relaxation, to
explain the asymmetry observed in the hysteresis loops. The good agreement
between the simulated and experimental results confirms our hypothesis that the
spin glass-like phase is key to the ZEB effect.",1808.10305v1
2018/9/7,Integrating all-optical switching with spintronics,"All-optical switching (AOS) of magnetic materials describes the reversal of
the magnetization using short (femtosecond) laser pulses, and has been observed
in a variety of materials. In the past decade it received extensive attention
due to its high potential for fast and energy-efficient data writing in future
spintronic memory applications. Unfortunately, the AOS mechanism in the
ferromagnetic multilayers commonly used in spintronics needs multiple pulses
for the magnetization reversal, losing its speed and energy efficiency. Here,
we experimentally demonstrate `on-the-fly' single-pulse AOS in combination with
spin Hall effect (SHE) driven motion of magnetic domains in Pt/Co/Gd
synthetic-ferrimagnetic racetracks. Moreover, using field-driven-SHE-assisted
domain wall (DW) motion measurements, both the SHE efficiency in the racetrack
is determined and the chirality of the optically written DW's is verified. Our
experiments demonstrate that Pt/Co/Gd racetracks facilitate both single-pulse
AOS as well as efficient SHE induced domain wall motion, which might ultimately
pave the way towards integrated photonic memory devices.",1809.02347v1
2018/9/24,Observation of the nonlinear anomalous Hall effect in 2D WTe2,"The Hall effect occurs only in systems with broken time-reversal symmetry,
such as solids under an external magnetic field in the ordinary Hall effect and
magnetic materials in the anomalous Hall effect (AHE). Here we show a new Hall
effect in a nonmagnetic material under zero magnetic field, in which the Hall
voltage depends quadratically on the longitudinal current. We observe the
effect (referred to as nonlinear AHE) in two-dimensional Td-WTe2, a semimetal
with broken inversion symmetry and only one mirror line in the crystal plane.
Our angle-resolved electrical measurements reveal that the Hall voltage changes
sign when the bias current reverses direction; it maximizes (vanishes) when the
bias current is perpendicular (parallel) to the mirror line. The observed
effect can be understood as an AHE induced by the bias current which generates
an out-of-plane magnetization. The temperature dependence of the Hall
conductivity further suggests that both intrinsic Berry curvature dipole and
extrinsic spin-dependent scatterings contribute to the observed nonlinear AHE.
Our results open the possibility of exploring the intrinsic Berry curvature
effect in nonlinear electrical transport in solids .",1809.08744v2
2018/9/27,"$\mathrm{Fe}_{1-x}\mathrm{Ni}_x$ Alloy Nanoparticles Encapsulated inside Carbon Nanotubes: Controlled Synthesis, Structure and Magnetic Properties","In the present work, different synthesis procedures have been demonstrated to
fill carbon nanotubes (CNTs) with $\mathrm{Fe}_{1-x}\mathrm{Ni}_x$ alloy
nanoparticles (x = 0.33, 0.5). CNTs act as templates for the encapsulation of
magnetic nanoparticles, and provide a protective shield against oxidation as
well as prevent nanoparticles agglomeration. By variation of the reaction
parameters, the purity of the samples, degree of filling, the composition and
size of filling nanoparticles have been tailored and therefore the magnetic
properties. The samples were analyzed by scanning electron microscopy (SEM),
transmission electron microscopy (TEM), Bright-field (BF) TEM tomography, X-ray
powder diffraction, superconducting quantum interference device (SQUID) and
thermogravimetric analysis (TGA). The Fe1-xNix-filled CNTs show a huge
enhancement in the coercive fields compared to the corresponding bulk
materials, which make them excellent candidates for several applications such
as magnetic storage devices.",1809.10500v1
2018/10/5,Zero-field dynamics stabilized by in-plane shape anisotropy in MgO-based spin-torque oscillators,"Here we demonstrate numerically that shape anisotropy in MgO-based
spin-torque nano-oscillators consisting of an out-of-plane magnetized free
layer and an in-plane polarizer is necessary to stabilize out-of-plane
magnetization precession without the need of external magnetic fields. As the
in-plane anisotropy is increased, a gradual tilting of the magnetization
towards the in-plane easy direction is introduced, favouring zero-field
dynamics over static in-plane states. Above a critical value, zero-field
dynamics are no longer observed. The optimum ratio of in-plane shape to
out-of-plane uniaxial anisotropy, for which large angle out-of-plane zero-field
dynamics occur within the widest current range, is reported.",1811.00106v1
2018/11/8,Sensitivity enhancement for a light axion dark matter search with magnetic material,"The sensitivity of experimental searches for axion dark matter coupled to
photons is typically proportional to the strength of the applied static
magnetic field. We demonstrate how a permeable material can be used to enhance
the magnitude of this static magnetic field, and therefore improve the
sensitivity of such searches in the low frequency lumped-circuit limit. Using
gadolinium iron garnet toroids at temperature 4.2 K results in a factor of 4
enhancement compared to an air-core toroidal design. The enhancement is limited
by magnetic saturation. Correlation of signals from three such toroids allows
efficient rejection of systematics due to electromagnetic interference. The
sensitivity of a centimeter-scale axion dark matter search based on this
approach is on the order of $g_{a\gamma\gamma}\approx10^{-9}$ GeV$^{-1}$ after
8 hours of data collection for axion masses near $10^{-10}$ eV. This approach
may substantially extend the sensitivity reach of large-volume lumped element
axion dark matter searches.",1811.03231v1
2018/11/26,Engineering Large Anisotropic Magnetoresistance in La0.7Sr0.3MnO3 Films at Room Temperature,"The magnetoresistance (MR) effect is widely employed in technologies that
pervade our world from magnetic reading heads to sensors. Diverse contributions
to MR, such as anisotropic, giant, tunnel, colossal, and spin-Hall, are
revealed in materials depending on the specific system and measuring
configuration. Half-metallic manganites hold promise for spintronic
applications but the complexity of competing interactions has not permitted the
understanding and control of their magnetotransport properties to enable the
realization of their technological potential. Here we report on the ability to
induce a dominant switchable magnetoresistance in La0.7Sr0.3MnO3 epitaxial
films, at room temperature (RT). By engineering an extrinsic magnetic
anisotropy, we show a large enhancement of anisotropic magnetoresistance (AMR)
which leads to, at RT, signal changes much larger than the other contributions
such as the colossal magnetoresistance (CMR). The dominant extrinsic AMR
exhibits large variation in the resistance in low field region, showing high
sensitivity to applied low magnetic fields. These findings have a strong impact
on the real applications of manganite based devices for the high-resolution low
field magnetic sensors or spintronics.",1811.10301v1
2018/11/29,Control of magnetism in bilayer CrI$_{3}$ by an external electric field,"Recently intrinsic ferromagnetism in two-dimensional(2D) van der Waals
materials was discovered [1, 2, 3]. A monolayer of Chromiun triiodide(CrI3) is
ferromagnetic while a bilayer structure was reported to be anti-ferro magnetic,
moreover an external electric field changes its magnetic phase [4]. We have
studied the two found in nature stackings of CrI3 bilayers and found that
indeed the magnetic phase of one of them can be tuned by an external electric
field while the other remains ferromagnetic. We simulate those results with ab
initio calculations and explain them with a simple model based on a rigid shift
of the bands associated with different spins. The model can be applied to
similar van der Waal stacked insulating bilayer anti-ferromagnets.",1811.11910v1
2018/11/30,Magnetic and mechanical effects of Mn substitutions in AlFe2B2,"The mechanical and magnetic properties of the newly discovered MAB-phase
class of materials based upon AlFe2B2 were investigated. The samples were
synthesised from stoichiometric amounts of all constituent elements. X-ray
diffraction shows that the main phase is orthorhombic with an elongated b-axis,
similar to AlFe2B2. The low hardness and visual inspection of the samples after
deformation indicate that these compounds are deformed via a delamination
process. When substituting iron in AlFe2B2 with manganese, the magnetism in the
system goes from being ferro- to antiferromagnetic via a disordered
ferrimagnetic phase exhibited by AlFeMnB2. Density functional theory
calculations indicate a weakening of the magnetic interactions among the
transitions metal ions as iron is substituted by manganese in AlFe2B2. The
Mn-Mn exchange interactions in AlMn2 B2 are found to be very small.",1811.12720v1
2018/11/30,Influence of Landau levels in the phonon dispersion of Weyl semimetals,"Weyl semimetals display unusual electronic transport properties when placed
under magnetic fields. Here, we investigate how magnetic fields alter the
dynamics of long wavelength lattice vibrations in these materials. To that end,
we develop a theory for the phonon dispersion, which incorporates contributions
from chiral and nonchiral Landau levels, electron-phonon interactions,
electron-electron interactions, and disorder. We predict (i) a
magnetic-field-induced hybridization between optical phonons and plasmons, (ii)
avoided crossings between pseudoscalar optical phonons and electronic
excitations originating from nonchiral Landau levels, (iii) a sharp dependence
of the sound velocity on the relative angle between the sound propagation and
the magnetic field. We compare our results to recent theoretical studies on the
signatures of the chiral anomaly in phonon dynamics.",1811.12899v2
2018/12/4,Nematic superconductivity in doped Bi2Se3 topological superconductors,"Nematic superconductivity is a novel class of superconductivity characterized
by spontaneous rotational-symmetry breaking in the superconducting gap
amplitude and/or Cooper-pair spins with respect to the underlying lattice
symmetry. Doped Bi2Se3 superconductors, such as CuxBi2Se3, SrxBi2Se3, and
NbxBi2Se3, are considered as candidates for nematic superconductors, in
addition to the anticipated topological superconductivity. Recently, various
bulk probes, such as nuclear magnetic resonance, specific heat,
magnetotransport, magnetic torque, and magnetization, have consistently
revealed two-fold symmetric behavior in their in-plane magnetic-field-direction
dependence, although the underlying crystal lattice possesses three-fold
rotational symmetry. More recently, nematic superconductivity is directly
visualized using scanning tunneling microscopy and spectroscopy. In this short
review, we summarize the current researches on the nematic behavior in
superconducting doped Bi2Se3 systems, and discuss issues and perspectives.",1812.01378v2
2018/12/13,Engineering chiral edge states in 2D topological insulator/ferromagnetic insulator heterostructures,"Chiral edge state (CES) at zero magnetic field has already been realized in
the magnetically doped topological insulator (TI). However, this scheme
strongly relies on material breakthroughs, and in fact, most of the TIs cannot
be driven into a Chern insulator in this way. Here, we propose to achieve the
CESs in 2D TI/ferromagnetic insulator/TI sandwiched structures through
spin-selective coupling between the helical edge states of the two TIs. Due to
this coupling, the edge states of one spin channel are gapped and those of the
other spin channel remain almost gapless, so that the helical edge states of
each isolated TI are changed into the CESs. Such CESs can be hopefully achieved
in all TI materials, which are immune to magnetic-disorder-induced
backscattering. We propose to implement our scheme in the van der Waals
heterostructures between monolayer 1T'-WTe$_2$ and bilayer CrI$_3$. The
electrical control of magnetism in bilayer CrI$_3$ switches the transport
direction of the CESs, which can realize a low-consumption transistor.",1812.05280v2
2019/1/8,Magnetic Skyrmion Lattice by Fourier Transform Method,"We demonstrate a fast numerical method of theoretical studies of skyrmion
lattice or spiral order in magnetic materials with Dzyaloshinsky-Moriya
interaction. The method is based on the Fourier expansion of the magnetization
combined with a minimization of the free energy functional of the magnetic
material in Fourier space, yielding the optimal configuration of the system for
any given set of parameters. We employ a Lagrange multiplier technique in order
to satisfy micromagnetic constraints. We apply this method to a system that
exhibits, depending on the parameter choice, ferromagnetic, skyrmion lattice,
or spiral (helical) order. Known critical fields corresponding to the
helical-skyrmion as well as the skyrmion-ferromagnet phase transitions are
reproduced with high precision. Using this numerical method we predict new
types of excited (metastable) states of the skyrmion lattice, which may be
stabilized by coupling the skyrmion lattice with a superconducting vortex
lattice. The method can be readily adapted to other micromagnetic systems.",1901.02459v2
2019/1/29,Low-impedance superconducting microwave resonators for strong coupling to small magnetic mode volumes,"Recent experiments on strongly coupled microwave and ferromagnetic resonance
modes have focused on large volume bulk crystals such as yttrium iron garnet,
typically of millimeter-scale dimensions. We extend these experiments to lower
volumes of magnetic material by exploiting low-impedance lumped-element
microwave resonators. The low impedance equates to a smaller magnetic mode
volume, which allows us to couple to a smaller number of spins in the
ferromagnet. Compared to previous experiments, we reduce the number of
participating spins by two orders of magnitude, while maintaining the strength
of the coupling rate. Strongly coupled devices with small volumes of magnetic
material may allow the use of spin orbit torques, which require high current
densities incompatible with existing structures.",1901.10395v1
2019/1/30,Tuning the Magnetic Ordering Temperature of Hexagonal Ferrites by Structural Distortion Control,"To tune the magnetic properties of hexagonal ferrites, a family of
magnetoelectric multiferroic materials, by atomic-scale structural engineering,
we studied the effect of structural distortion on the magnetic ordering
temperature (TN). Using the symmetry analysis, we show that unlike most
antiferromagnetic rare-earth transition-metal perovskites, a larger structural
distortion leads to a higher TN in hexagonal ferrites and manganites, because
the K3 structural distortion induces the three-dimensional magnetic ordering,
which is forbidden in the undistorted structure by symmetry. We also revealed a
near-linear relation between TN and the tolerance factor and a power-law
relation between TN and the K3 distortion amplitude. Following the analysis, a
record-high TN (185 K) among hexagonal ferrites was predicted in hexagonal
ScFeO3 and experimentally verified in epitaxially stabilized films. These
results add to the paradigm of spin-lattice coupling in antiferromagnetic
oxides and suggests further tunability of hexagonal ferrites if more lattice
distortion can be achieved.",1901.11118v1
2019/2/6,Accelerating spin-space sampling by auxiliary spin-dynamics and temperature-dependent spin-cluster expansion,"Atomistic simulations of thermodynamic properties of magnetic materials rely
on an accurate modelling of magnetic interactions and an efficient sampling of
the high-dimensional spin space. Recent years have seen significant progress
with a clear trend from model systems to material specific simulations that are
usually based on electronic-structure methods. Here we develop a Hamiltonian
Monte Carlo framework that makes use of auxiliary spin-dynamics and an
auxiliary effective model, the temperature-dependent spin-cluster expansion, in
order to efficiently sample the spin space. Our method does not require a
specific form of the model and is suitable for simulations based on
electronic-structure methods. We demonstrate fast warm-up and a reasonably
small dynamical critical exponent of our sampler for the classical Heisenberg
model. We further present an application of our method to the magnetic phase
transition in bcc iron using magnetic bond-order potentials.",1902.02116v1
2019/2/10,Spin dynamics of anisotropic azimuthal modes in heterogeneous magnetic nanodisks,"It is well known that azimuthal spin wave modes of magnetic vortex state in
permalloy nanodisks have circular symmetry. Intuitively, magnetic materials
having magnetocrystalline anisotropy is not compatible with the circular
symmetry of the azimuthal modes. In this article, however, we report cubic
azimuthal modes in heterogeneous nanodisks consisting of a permalloy core and a
Fe shell. The fourfold symmetry of azimuthal modes is due to the exchange, and
magneto-static, interactions between the permalloy core and the Fe shell. In
comparison to results of circular azimuthal mode, the vortex switching occurs
considerably faster under the excitation of cubic azimuthal mode. The gyration
path of vortex core turns into square under the influence of induced cubic
anisotropy in the Py region. We find out periodic oscillation of the vortex
core size and the gyration speed as well. Our findings may offer a new route
for spintronic applications using heterogeneous magnetic nanostructures.",1902.03536v1
2019/2/20,Photoinduced Floquet topological magnons in Kitaev magnets,"We study periodically driven pure Kitaev model and ferromagnetic phase of the
Kitaev-Heisenberg model on the honeycomb lattice by off-resonant linearly and
circularly-polarized lights at zero magnetic field. Using a combination of
linear spin wave and Floquet theories, we show that the effective
time-independent Hamiltonians in the off-resonant regime map onto the
corresponding anisotropic static spin model, plus a tunable photoinduced
magnetic field along the $[111]$ direction, which precipitates Floquet
topological magnons and chiral magnon edge modes. They are tunable by the light
amplitude and polarization. Similarly, we show that the thermal Hall effect
induced by the Berry curvature of the Floquet topological magnons can also be
tuned by the laser field. Our results pave the way for ultrafast manipulation
of topological magnons in irradiated Kitaev magnets, and could play a pivotal
role in the investigation of ultrafast magnon spin current generation in Kitaev
materials.",1902.07716v2
2019/3/12,Superconductivity behavior in epitaxial TiN films points at surface magnetic disorder,"We analyze the evolution of the normal and superconducting electronic
properties in epitaxial TiN films, characterized by high Ioffe-Regel parameter
values, as a function of the film thickness. As the film thickness decreases,
we observe an increase of in the residual resistivity, which becomes dominated
by diffusive surface scattering for $d\leq20\,$nm. At the same time, a
substantial thickness-dependent reduction of the superconducting critical
temperature is observed compared to the bulk TiN value. In such a high quality
material films, this effect can be explained by a weak magnetic disorder
residing in the surface layer with a characteristic magnetic defect density of
$\sim10^{12}\,\mathrm{cm}^{-2}$. Our results suggest that surface magnetic
disorder is generally present in oxidized TiN films.",1903.05009v3
2019/3/14,High-pressure optical floating-zone growth of Li2FeSiO4 single crystals,"We report the growth of mm-sized Pmnb-Li2FeSiO4 single crystals by means of
the optical floating-zone method at high argon pressure and describe the
conditions required for a stable growth process. The crystal structure is
determined and refined by single-crystal X-ray diffraction. The lattice
constants amount to a = 6.27837(3) A, b = 10.62901(6) A and c = 5.03099(3) A at
100 K. In addition, we present high-resolution neutron powder diffraction data
that suggest that the slight Li-Fe site exchange seems to be intrinsic to this
material. High quality of the crystal is confirmed by very sharp anomalies in
the static magnetic susceptibility and in the specific heat associated with the
onset of long-range antiferromagnetic order at TN = 17.0(5) K and pronounced
magnetic anisotropy for the three crystallographic axes. Furthermore, magnetic
susceptibility excludes the presence of sizable amounts of magnetic impurity
phases.",1903.05884v1
2019/3/28,Magnetic-Resonance-Induced Pseudo-electric Field and Giant Current Response in Axion Insulators,"A quantized version of the magnetoelectric effect, known as the topological
magnetoelectric effect, can exist in a time-reversal invariant topological
insulator with all its surface states gapped out by magnetism. This topological
phase, called the axion insulator phase, has been theoretically proposed but is
still lack of conclusive experimental evidence due to the small signal of
topological magnetoelectric effect. In this work, we propose that the dynamical
in-plane magnetization in an axion insulator can generate a ""pseudo-electric
field"", which acts on the surface state of topological insulator films and
leads to the non-zero response current. Strikingly, we find that the current at
magnetic resonance (either ferromagnetic or anti-ferromagnetic) is larger than
that of topological magnetoelectric effect by several orders of magnitude, and
thereby serves as a feasible smoking gun to confirm the axion insulator phase
in the candidate materials.",1903.12068v2
2019/4/9,Manipulation of Magnetic Skyrmions by Superconducting Vortices in Ferromagnet-Superconductor Heterostructures,"Dynamics of magnetic skyrmions in hybrid ferromagnetic films harbors novel
physical phenomena and holds promise for technological applications. In this
work, we discuss the behavior of magnetic skyrmions when coupled to
superconducting vortices in a ferromagnet-superconductor heterostructure. We
use numerical simulations and analytic arguments to reveal broader
possibilities for manipulating the skyrmion-vortex dynamic correlations in the
hybrid system, that are not possible in its separated constituents. We explore
the thresholds of particular dynamic phases, and quantify the phase diagram as
a function of the relevant material parameters, applied current and induced
magnetic torques. Finally, we demonstrate the broad and precise tunability of
the skyrmion Hall-angle in presence of vortices, with respect to currents
applied to either or both the superconductor and the ferromagnet within the
heterostructure.",1904.04537v3
2019/5/17,Colossal infrared and terahertz magneto-optical activity in a two-dimensional Dirac material,"When two-dimensional electron gases (2DEGs) are exposed to magnetic field,
they resonantly absorb electromagnetic radiation via electronic transitions
between Landau levels (LLs). In 2DEGs with a Dirac spectrum, such as graphene,
theory predicts an exceptionally high infrared magneto-absorption, even at zero
doping. However, the measured LL magneto-optical effects in graphene have been
much weaker than expected because of imperfections in the samples available so
far for such experiments. Here we measure magneto-transmission and Faraday
rotation in high-mobility encapsulated monolayer graphene using a custom
designed setup for magneto-infrared microspectroscopy. Our results show a
strongly enhanced magneto-optical activity in the infrared and terahertz ranges
characterized by a maximum allowed (50%) absorption of light, a 100% magnetic
circular dichroism as well as a record high Faraday rotation. Considering that
sizeable effects have been already observed at routinely achievable magnetic
fields, our findings demonstrate a new potential of magnetic tuning in 2D Dirac
materials for long-wavelength optoelectronics and plasmonics.",1905.07159v1
2019/5/29,Rational design principles of quantum anomalous Hall effect from superlattice-like magnetic topological insulators,"As one of paradigmatic phenomena in condensed matter physics, the quantum
anomalous Hall effect (QAHE) in stoichiometric Chern insulators has drawn great
interest for years. By using model Hamiltonian analysis and first-principle
calculations, we establish a topological phase diagram and map on it with
different two-dimensional configurations, which is taken from the
recently-grown magnetic topological insulators MnBi4Te7 and MnBi6Te10 with
superlattice-like stacking patterns. These configurations manifest various
topological phases, including quantum spin Hall effect with and without
time-reversal symmetry, as well as QAHE. We then provide design principles to
trigger QAHE by tuning experimentally accessible knobs, such as slab thickness
and magnetization. Our work reveals that superlattice-like magnetic topological
insulators with tunable exchange interaction serve as an ideal platform to
realize the long-sought QAHE in pristine compounds, paving a new avenue within
the area of topological materials.",1905.12208v1
2019/6/6,Defect-induced magnetism and Yu-Shiba-Rusinov states in twisted bilayer graphene,"Atomic defects have a significant impact in the low-energy properties of
graphene systems. By means of first-principles calculations and tight-binding
models we provide evidence that chemical impurities modify both the normal and
the superconducting states of twisted bilayer graphene. A single hydrogen atom
attached to the bilayer surface yields a triple-point crossing, whereas
self-doping and three-fold symmetry-breaking are created by a vacant site. Both
types of defects lead to time-reversal symmetry-breaking and the creation of
local magnetic moments. Hydrogen-induced magnetism is found to exist also at
the doping levels where superconductivity appears in magic angle graphene
superlattices. As a result, the coexistence of superconducting order and
defect-induced magnetism yields in-gap Yu-Shiba-Rusinov excitations in magic
angle twisted bilayer graphene.",1906.02711v1
2019/6/11,Proximity magnetoresistance in graphene induced by magnetic insulators,"We demonstrate the existence of Giant proximity magnetoresistance (PMR)
effect in a graphene spin valve where spin polarization is induced by a nearby
magnetic insulator. PMR calculations were performed for yttrium iron garnet
(YIG), cobalt ferrite (CFO), and two europium chalcogenides EuO and EuS. We
find a significant PMR (up to 100%) values defined as a relative change of
graphene conductance with respect to parallel and antiparallel alignment of two
proximity induced magnetic regions within graphene. Namely, for high Curie
temperature (Tc) CFO and YIG insulators which are particularly important for
applications, we obtain 22% and 77% at room temperature, respectively. For low
Tc chalcogenides, EuO and EuS, the PMR is 100% in both cases. Furthermore, the
PMR is robust with respect to system dimensions and edge type termination. Our
findings show that it is possible to induce spin polarized currents in graphene
with no direct injection through magnetic materials.",1906.04469v1
2019/6/17,Local Photothermal Control of Phase Transitions for On-demand Room-temperature Rewritable Magnetic Patterning,"The ability to make controlled patterns of magnetic structures within a
nonmagnetic background is essential for several types of existing and proposed
technologies. Such patterns provide the foundation of magnetic memory and logic
devices, allow the creation of artificial spin-ice lattices and enable the
study of magnon propagation. Here, we report a novel approach for magnetic
patterning that allows repeated creation and erasure of arbitrary shapes of
thin-film ferromagnetic structures. This strategy is enabled by epitaxial
Fe$_{0.52}$Rh$_{0.48}$ thin films designed so that both ferromagnetic and
antiferromagnetic phases are bistable at room temperature. Starting with the
film in a uniform antiferromagnetic state, we demonstrate the ability to write
arbitrary patterns of the ferromagnetic phase by local heating with a focused
laser. If desired, the results can then be erased by cooling with a
thermoelectric cooler and the material repeatedly re-patterned.",1906.07239v1
2019/6/18,Analytical computation of the demagnetizing energy of thin film domain walls,"Due to its non-local nature, calculating the demagnetizing field remains the
biggest challenge in understanding domain structures in ferromagnetic
materials. Analytical descriptions of demagnetizing effects typically
approximate domain walls as uniformly magnetized ellipsoids, neglecting both
the smooth rotation of magnetization from one domain to the other and the
interaction between the two domains. Here, instead of the demagnetizing field,
we compute analytically the demagnetizing energy of a straight domain wall
described by the classical $\tanh$ magnetization profile in a thin film with
perpendicular magnetic anisotropy. We then use our expression for the
demagnetizing energy to derive an improved version of the 1D model of
field-driven domain wall motion, resulting in accurate expressions for
important properties of the domain wall such as the domain wall width and the
Walker breakdown field. We verify the accuracy of our analytical results by
micromagnetic simulations.",1906.07475v2
2019/6/20,Lower Critical Field Measurement System based on Third-Harmonic Method for Superconducting RF Materials,"We develop a lower critical field (Hc1) measurement system using the
third-harmonic response of an applied AC magnetic field from a solenoid coil
positioned above a superconducting sample. Parameter Hc1 is measured via
detection of the third-harmonic component, which drastically changes when a
vortex begins to penetrate the superconductor with temperature increase. The
magnetic field locally applied to one side of the sample mimics the magnetic
field within superconducting radio-frequency (SRF) cavities and prevents edge
effects of the superconducting sample. With this approach, our measurement
system can potentially characterize surface-engineered SRF materials such as
Superconductor-Insulator-Superconductor multilayer structure (S-I-S structure).
As a validation test, we measure the temperature dependence of Hc1 of two
high-RRR bulk Nb samples and obtain results consistent with the literature. We
also confirm that our system can apply magnetic fields of at least 120 mT at
4-5 K without any problem of heat generation of the coil. This field value is
higher than those reported in previous works and makes it possible to more
accurately estimate Hc1 at lower temperatures.",1906.08468v1
2019/6/21,Goos-Hänchen effect of spin waves at heterochiral interfaces,"We theoretically investigate the Goos-H\""{a}nchen (GH) effect of spin-wave
beams reflected from the interface between two ferromagnetic films with
different Dzyaloshinskii-Moriya interactions (DMIs). The formula of the GH
shift as functions of the incident angle and material parameters is derived
analytically. We show that the GH effect occurs only when spin waves are
totally reflected at the interface and vanishes otherwise. We further explore
the GH shift of spin waves by narrow DMI strips of different widths. It is
found that the induced shift is independent of the strip width down to $10$ nm,
offering a novel approach to measure the DMI strength of ultra-narrow magnetic
strips which is out the scope of current technology. Full micromagnetic
simulations compare well with our theoretical findings. Strong distortion of
edge magnetizations for narrower strips however generates a width dependence of
the GH shift. The results presented in this work are helpful for understanding
the GH effect in chiral magnets and for quantifying the DMI parameter in
magnetic strips of sub-$50$ nm scales.",1906.08999v2
2019/6/26,Concentration tuned tetragonal strain in alloys: application to magnetic anisotropy of FeNi$_{1-x}$Co$_x$,"We explore an opportunity to induce and control tetragonal distortion in
materials. The idea involves formation of a binary alloy from parent compounds
having body-centered and face-centered symmetries. The concept is illustrated
in the case of FeNi$_{1-x}$Co$_x$ magnetic alloy formed by substitutional
doping of the L1$_0$ FeNi magnet with Co. Using electronic structure
calculations we demonstrate that the tetragonal strain in this system can be
controlled by concentration and it reaches maximum for $x=0.5$. This finding is
then applied to create a large magnetocrystalline anisotropy (MAE) in
FeNi$_{1-x}$Co$_x$ system by considering an interplay of the tetragonal
distortion with electronic concentration and chemical anisotropy. In
particular, we identify a new ordered FeNi$_{0.5}$Co$_{0.5}$ system with MAE
larger by a factor 4.5 from the L1$_0$ FeNi magnet.",1906.11329v1
2019/7/4,Dynamics of the magnetoelastic phase transition and adiabatic temperature change in Mn1.3Fe0.7P0.5Si0.55,"The adiabatic temperature change DTad of a Mn1.3Fe0.7P0.5Si0.55 Fe2P-type
alloy was measured under different magnetic field-sweep rates from 0.93 Ts-1 to
2870 Ts-1. We find a field-sweep-rate independent magnetocaloric effect due to
a partial alignment of magnetic moments in the paramagnetic region overlapping
with the magnetocaloric effect of the first-order phase transition.
Additionally, the first-order phase transition is not completed even in fields
up to 20 T leading to a non-saturating behavior of DTad. Measurements in
different pulsed fields reveal that the first-order phase transition cannot
follow the fast field changes as previously assumed, resulting in a distinct
field-dependent hysteresis in DTad.",1907.02307v1
2019/7/7,Rotating magnetocaloric effect in the ferromagnetic Weyl semi-metal Co$_{3}$Sn$_{2}$S$_{2}$,"The rotating magnetocaloric effect (RMCE) is a recent interest in magnetic
refrigeration technique in which the cooling effect is attained by rotating the
anisotropic magnetocaloric material from one orientation to the other in a
fixed magnetic field. In this work, we report the anisotropic magnetocaloric
properties of single crystals of the ferromagnetic Weyl semimetal
Co$_{3}$Sn$_{2}$S$_{2}$ for magnetic field $H\parallel c$ axis and $H\parallel
ab$ plane. We observed a significant (factor of $2$) difference between the
magnetocaloric effect measured in both orientations. The rotating
magnetocaloric effect has been extracted by taking the difference of the
magnetic entropy change ($\Delta S_{M}$) for fields applied in the two
crystallographic orientations. In a scaling analysis of $\Delta S_{M}$, the
rescaled $\Delta S_{M}(T,H)$ vs reduced temperature $\theta$ curves collapse
onto a single universal curve, indicating that the transition from paramagnetic
to ferromagnetic phase at 174~K is a second order transition. Furthermore,
using the power law dependence of $\Delta S_{M}$ and relative cooling power
RCP, the critical exponents $\beta$ and $\gamma$ are calculated, which are
consistent with the recent critical behavior study on this compound
\cite{Yan2018}.",1907.03317v1
2019/7/12,Oxygen-vacancy tuning of magnetism in SrTi$_{0.75}$Fe$_{0.125}$Co$_{0.125}$O$_{3-δ}$ perovskite,"We use density functional theory to calculate the structure, band-gap and
magnetic properties of oxygen-deficient
SrTi$_{1-x-y}$Fe$_x$Co$_y$O$_{3-\delta}$ with x = y = 0.125 and ${\delta}$ =
(0,0.125,0.25). The valence and the high or low spin-states of the Co and Fe
ions, as well as the lattice distortion and the band-gap, depend on the oxygen
deficiency, the locations of the vacancies, and on the direction of the Fe-Co
axis. A charge redistribution that resembles a self-regulatory response lies
behind the valence spin-state changes. Ferromagnetism dominates, and both the
magnetization and the band gap are greatest at ${\delta}$ = 0.125. This
qualitatively mimics the previously reported magnetization measured for
SrTiFeO$_{3-\delta}$, which was maximum at an intermediate deposition pressure
of oxygen.",1907.05961v1
2019/7/23,Magnetic semimetals and quantized anomalous Hall effect in EuB6,"Exploration of the novel relationship between magnetic order and topological
semimetals has received enormous interest in a wide range of both fundamental
and applied research. Here we predict that soft ferromagnetic (FM) material
EuB6 can achieve multiple topological semimetal phases by simply tuning the
direction of the magnetic moment. Explicitly, EuB6 is a topological nodal-line
semimetal when the moment is aligned along the [001] direction, and it evolves
into a Weyl semimetal with three pairs of Weyl nodes by rotating the moment to
the [111] direction. Interestingly, we identify a novel semimetal phase
featuring the coexistence of a nodal line and Weyl nodes with the moment in the
[110] direction. Topological surface states and anomalous Hall conductivity,
which is sensitive to the magnetic order, have been computed and are expected
to be experimentally observable. Large-Chern-number quantum anomalous Hall
effect can be realized in its [111]-oriented quantum-well structure.",1907.10051v1
2019/9/7,Designing rare-earth free permanent magnets in Heusler alloys via interstitial doping,"Based on high-throughput density functional theory calculations, we
investigated the effects of light interstitial H, B, C, and N atoms on the
magnetic properties of cubic Heusler alloys, with the aim to design new
rare-earth free permanent magnets. It is observed that the interstitial atoms
induce significant tetragonal distortions, leading to 32 candidates with large
($>$ 0.4 MJ/m$^3$) uniaxial magneto-crystalline anisotropy energies (MAEs) and
10 cases with large in-plane MAEs. Detailed analysis following the the
perturbation theory and chemical bonding reveals the strong MAE originates from
the local crystalline distortions and thus the changes of the chemical bonding
around the interstitials. This provides a valuable way to tailor the MAEs to
obtain competitive permanent magnets, filling the gap between high performance
Sm-Co/Nd-Fe-B and widely used ferrite/AlNiCo materials.",1909.03275v1
2019/9/18,Large negative magnetoresistance in the new antiferromagnetic rare-earth dichalcogenide EuTe$_2$,"We report the synthesis and characterization of a rare-earth dichalcogenide
EuTe$_2$. An antiferromagnetic transition was found at T$_M$ = 11 K. The
antiferromagnetic order can be tuned by an applied magnetic field to access a
first-order spin flop transition and a spin flip transition. These transitions
are associated with a giant negative magnetoresistance with a value of nearly
100\%. Heat capacity measurements reveal strong electronic correlations and a
reduced magnetic entropy. Furthermore, density functional theory calculations
demonstrate that the electrons near the Fermi surface mainly originate from the
Te 5$p$ orbitals and the magnetism is dominated by localized electrons from the
Eu 4$f$ orbitals. These results suggest that both the RKKY and Kondo
interactions between the local moments and itinerant electrons play crucial
roles in the magnetism and large negative magnetoresistance of EuTe$_2$.",1909.08340v1
2019/9/27,Thermally driven two-magnet nano-oscillator with large spin-charge conversion,"Next-generation spintronic applications require material properties that can
be hardly met by one material candidate. Here we demonstrate that by combining
insulating and metallic magnets, enhanced spin-charge conversion and
energy-efficient thermal spin currents can be realized. We develop a nanowire
device consisting of an yttrium iron garnet and permalloy bi-layer. An
interfacial temperature gradient drives the nanowire magnetization into
auto-oscillations at gigahertz frequencies. Interfacial spin coupling and
magnetoresistance of the permalloy layer translate spin dynamics into sizable
microwave signals. The results show prospect for energy-efficient spintronic
devices and present an experimental realization of magnon condensation in a
heterogeneous magnetic system.",1909.12445v1
2019/10/4,Intrinsic 2D Ferromagnetism in V5Se8 Epitaxial Thin Films,"The discoveries of intrinsic ferromagnetism in atomically-thin van der Waals
crystals have opened up a new research field enabling fundamental studies on
magnetism at two-dimensional (2D) limit as well as development of magnetic van
der Waals heterostructures. To date, a variety of 2D ferromagnetism has been
explored mainly by mechanically exfoliating 'originally ferromagnetic (FM)' van
der Waals crystals, while bottom-up approach by thin film growth technique has
demonstrated emergent 2D ferromagnetism in a variety of 'originally non-FM' van
der Waals materials. Here we demonstrate that V5Se8 epitaxial thin films grown
by molecular-beam epitaxy (MBE) exhibit emergent 2D ferromagnetism with
intrinsic spin polarization of the V 3d electrons despite that the bulk
counterpart is 'originally antiferromagnetic (AFM)'. Moreover,
thickness-dependence measurements reveal that this newly-developed 2D
ferromagnet could be classified as an itinerant 2D Heisenberg ferromagnet with
weak magnetic anisotropy, broadening a lineup of 2D magnets to those
potentially beneficial for future spintronics applications.",1910.01959v1
2019/10/24,Electron spin resonance in spiral antiferromagnet linarite: theory and experiment,"We present combined experimental and theoretical investigation of the
low-frequency ESR dynamics in the ordered phases of magnetic mineral linarite.
This material consists of weakly coupled spin-1/2 chains of copper ions with
frustrated ferro- and antiferromagnetic interactions. In zero magnetic field,
linarite orders into a spiral structure and exhibits a peculiar magnetic phase
diagram sensitive to the field orientation. The resonance frequencies and their
field dependence are analyzed combining microscopic and macroscopic theoretical
approaches and precise values of magnetic anisotropy constants are obtained. We
conclude that possible realization of exotic multipolar quantum states in this
material is greatly influenced by the biaxial anisotropy.",1910.11056v1
2019/10/24,Spin waves in ferromagnetic thin films,"A spin wave is the disturbance of intrinsic spin order in magnetic materials.
In this paper, a spin wave in the Landau-Lifshitz-Gilbert equation is obtained
based on the assumption that the spin wave maintains its shape while it
propagates at a constant velocity. Our main findings include: (1) in the
absence of Gilbert damping, the spin wave propagates at a constant velocity
with the increment proportional to the strength of the magnetic field; (2) in
the absence of magnetic field, at a given time the spin wave converges
exponentially fast to its initial profile as the damping parameter goes to zero
and in the long time the relaxation dynamics of the spin wave converges
exponentially fast to the easy-axis direction with the exponent proportional to
the damping parameter; (3) in the presence of both Gilbert damping and magnetic
field, the spin wave converges to the easy-axis direction exponentially fast at
a small timescale while propagates at a constant velocity beyond that. These
provides a comprehensive understanding of spin waves in ferromagnetic
materials.",1910.11200v1
2019/11/1,Tuning interfacial Dzyaloshinskii-Moriya interactions in thin amorphous ferrimagnetic alloys,"Skyrmions can be stabilized in magnetic systems with broken inversion
symmetry and chiral interactions, such as Dzyaloshinskii-Moriya interactions
(DMI). Further, compensation of magnetic moments in ferrimagnetic materials can
significantly reduce magnetic dipolar interactions, which tend to favor large
skyrmions. Tuning DMI is essential to control skyrmion properties, with
symmetry breaking at interfaces offering the greatest flexibility. However, in
contrast to the ferromagnet case, few studies have investigated interfacial DMI
in ferrimagnets. Here we present a systematic study of DMI in ferrimagnetic
CoGd films by Brillouin light scattering. We demonstrate the ability to control
DMI by the CoGd cap layer composition, the stack symmetry and the ferrimagnetic
layer thickness. The DMI thickness dependence confirms its interfacial nature.
In addition, magnetic force microscopy reveals the ability to tune DMI in a
range that stabilizes sub-100 nm skyrmions at room temperature in zero field.
Our work opens new paths for controlling interfacial DMI in ferrimagnets to
nucleate and manipulate skyrmions.",1911.00607v1
2019/11/21,Strain-induced phase transition in CrI$_{3}$ bilayers,"A monolayer of CrI$_3$ is a two-dimensional crystal that in its equilibrium
configuration is a ferromagnetic semiconductor, however, two coupled layers can
be ferromagnetic or antiferromagnetic depending on the stacking. We study the
magnetic phase diagram upon the strain of the antiferromagnetically coupled
bilayer with C2/m symmetry. We found that strain may be an efficient tool to
tune the magnetic phase of the structure. A tensile strain stabilizes the
antiferromagnetic phase, while a compressive strain turns the system
ferromagnetic. We understood that behavior by looking at the relative
displacement between layers due to the strain. We also study the evolution of
the magnetic anisotropy, the magnetic exchange coupling between Cr atoms, and
how the Curie temperature is affected by the strain.",1911.09734v4
2019/11/26,Exciton-Polariton Topological Insulator with an Array of Magnetic Dots,"Recently there have been several proposals on exciton-polariton topological
insulators, most requiring strong external magnetic fields induced by bulky
superconducting coils. We propose an alternate design for a polariton
topological insulator, where excitons are in a proximity of an additional layer
of a ferromagnetic material with a predefined magnetic moment located between
the pillars of the cavity. Our design supports a variety of topological phases
and transitions between Chern numbers $\pm 2$ and $\pm 1$ by varying either the
magnetic moment of the ferromagnetic material or the spin-orbit coupling
between different spin projections, thus enabling compact polariton devices
harnessing switchable topological edge modes.",1911.11385v1
2019/11/26,Enhanced anisotropy and study of magnetization reversal in Co/C60 bilayer thin film,"The interface between organic semiconductor [OSC]/ferromagnetic [FM] material
can exhibit ferromagnetism due to their orbital hybridization. Charge/spin
transfer may occur from FM to OSC layer leading to the formation of
`spinterface' i.e. the interface exhibiting a finite magnetic moment. In this
work, the magnetic properties of Co/C$_{60}$ bilayer thin film have been
studied to probe the interface between Co and C$_{60}$ layer. Polarized neutron
reflectivity [PNR] measurement indicates that the thickness and moment of the
spinterface are $\sim$ 2 $\pm$ 0.18 nm and 0.8 $\pm$ 0.2 $\mu_B$/cage,
respectively. The comparison of the magnetization reversal between the
Co/C$_{60}$ bilayer and the parent single layer Co thin film reveals that
spinterface modifies the domain microstructure. Further, the anisotropy of the
bilayer system shows a significant enhancement ($\sim$ two times) in comparison
to its single layer counterpart which is probably due to an additional
interfacial anisotropy arising from the orbital hybridization at the
Co/C$_{60}$ interface.",1911.11873v1
2019/12/31,Ferromagnetic kinetic exchange interaction in magnetic insulators,"The superexchange theory predicts dominant antiferromagnetic kinetic
interaction when the orbitals accommodating magnetic electrons are covalently
bonded through diamagnetic bridging atoms/groups. Here we show that explicit
consideration of magnetic and (leading) bridging orbitals, together with the
electron transfer between the former, reveals a strong ferromagnetic kinetic
exchange contribution. First principle calculations show that it is comparable
in strength with antiferromagnetic superexchange in a number of magnetic
materials with diamagnetic metal bridges. In particular, it is responsible for
a very large ferromagnetic coupling ($-10$ meV) between the iron ions in a
Fe$^{3+}$-Co$^{3+}$-Fe$^{3+}$ complex.",1912.13274v3
2020/1/4,Observation of spin-motive force in ferrimagnetic GdFeCo alloy films,"Non-uniform magnetic structures produce emergent electromagnetic phenomena
such as the topological Hall effect and the spin-motive force (SMF). The
experimental reports on the SMF, however, are very few and the relationship
between the SMF and material parameters is still unclear. In this study, we
investigated the SMF in ferrimagnetic GdFeCo alloy films using the
spin-torque-induced ferromagnetic resonance method and clarified the
relationship. The amplitude of the detected SMF becomes larger than that of the
transition metal alloy FeCo by the Gd doping and reaches the maximum near a Gd
composition of the boundary between in-plane and perpendicularly magnetized
films. According to the analytical calculation, the enhancement is related to
the trajectory of the magnetization precession. Moreover, we find that the SMF
induced by the magnetic resonance is inversely proportional to the square of
the damping constant.",2001.01042v2
2020/1/7,Half-integer quantized anomalous thermal Hall effect in the Kitaev material $α$-RuCl$_3$,"Heat transport mediated by Majorana edge modes in a magnetic insulator leads
to a half-integer thermal quantum Hall conductance, which has recently been
reported for the two-dimensional honeycomb material $\alpha$-RuCl$_3$. While
the conventional electronic Hall effect requires a perpendicular magnetic
field, we find that this is not the case in $\alpha$-RuCl$_3$. Strikingly, the
thermal Hall plateau appears even for a magnetic field with no out-of-plane
components. The field-angular variation of the quantized thermal Hall
conductance has the same sign structure of the topological Chern number, which
is either $\pm$1, as the Majorana band structure of the pure Kitaev spin
liquid. This observation of a half-integer anomalous thermal Hall effect firmly
establishes that the Kitaev interaction is primarily responsible and that the
non-Abelian topological order associated with fractionalization of the local
magnetic moments persists even in the presence of non-Kitaev interactions in
$\alpha$-RuCl$_3$.",2001.01899v1
2020/1/9,"High temperature thermal cycling effect on the irreversible responses of lattice structure, magnetic properties and electrical conductivity in Co$_{2.75}$Fe$_{0.25}$O$_{4+δ}$ spinel oxide","We report high temperature synchrotron X-ray diffraction (SXRD), dc
magnetization and current-voltage (I-V) characteristics for the samples of
Co$_{2.75}$Fe$_{0.25}$O$_4$ ferrite. The material was prepared by chemical
reaction of the Fe and Co nitrate solutions at pH = 11 and subsequent annealing
at temperatures 200 0C, 500 0C and 900 0C. The measurements were performed by
cycling the temperature from 300 K to high temperature (warming mode) and
return back to 300 K (cooling mode). The SXRD patterns indicated a fine
bi-phased cubic spinel structure in the highly Co rich spinel oxide.
Magnetization curves showed intrinsic ferrimagnetic features and defect induced
additional ferromagnetic phase at higher temperatures. Electrical conductivity
showed thermal hysteresis loop between warming and cooling modes of temperature
variation. The samples exhibited new information on the irreversibility
phenomena of lattice structure, magnetization and electrical conductivity on
cycling the measurement temperatures.",2001.02829v2
2020/1/24,Anisotropic magnetoresistance in spin-orbit semimetal SrIrO3,"SrIrO3, the three-dimensional member of the Ruddlesden-Popper iridates, is a
paramagnetic semimetal characterised by a the delicate interplay between
spin-orbit coupling and Coulomb repulsion. In this work, we study the
anisotropic magnetoresistance (AMR) of SrIrO3 thin films, which is closely
linked to spin-orbit coupling and probes correlations between electronic
transport, magnetic order and orbital states. We show that the low-temperature
negative magnetoresistance is anisotropic with respect to the magnetic field
orientation, and its angular dependence reveals the appearance of a fourfold
symmetric component above a critical magnetic field. We show that this AMR
component is of magnetocrystalline origin, and attribute the observed
transition to a field-induced magnetic state in SrIrO3.",2001.08939v1
2020/2/10,Measurement of the Spin-Forbidden Dark Excitons in MoS2 and MoSe2 monolayers,"Excitons with binding energies of a few hundreds of meV control the optical
properties of transition metal dichalcogenide monolayers. Knowledge of the fine
structure of these excitons is therefore essential to understand the
optoelectronic properties of these 2D materials. Here we measure the exciton
fine structure of MoS2 and MoSe2 monolayers encapsulated in boron nitride by
magneto-photoluminescence spectroscopy in magnetic fields up to 30 T. The
experiments performed in transverse magnetic field reveal a brightening of the
spin-forbidden dark excitons in MoS2 monolayer: we find that the dark excitons
appear at 14 meV below the bright ones. Measurements performed in tilted
magnetic field provide a conceivable description of the neutral exciton fine
structure. The experimental results are in agreement with a model taking into
account the effect of the exchange interaction on both the bright and dark
exciton states as well as the interaction with the magnetic field.",2002.03877v1
2020/2/12,Meron-Like Topological Spin Defects in Monolayer CrCl3,"Noncollinear spin textures in low-dimensional magnetic systems have been
studied for decades because of their extraordinary properties and promising
applications derived from the chirality and topological nature. However,
material realizations of topological spin states are still limited. Employing
first-principles and Monte Carlo simulations, we propose that monolayer
chromium trichloride (CrCl3) can be a promising candidate for observing the
vortex/antivortex type of topological defects, so-called merons. The numbers of
vortices and antivortices are found to be the same, maintaining an overall
integer topological unit. By perturbing with external magnetic fields, we show
the robustness of these meron pairs and reveal a rich phase space to tune the
hybridization between the ferromagnetic order and meron-like defects. The
signatures of topological excitations under external magnetic field also
provide crucial information for experimental justifications. Our study predicts
that two-dimensional magnets with weak spin-orbit coupling can be a promising
family for realizing meron-like spin textures.",2002.05208v2
2020/2/17,"Structural, electronic, and magnetic properties of Vanadium-based Janus dichalcogenide monolayers: A first-principles study","The structural, electronic, and magnetic properties of VSSe, VSeTe, VSTe
monolayers in both 2H and 1T phases are investigated via first-principles
calculations. The 2H phase is energetically favorable in VSSe and VSeTe,
whereas the 1T phase is lower in energy in VSTe. For V-based Janus monolayers
in the 2H phase, calculations of the magnetic anisotropy show an easy-plane for
the magnetic moment. As such, they should not exhibit a ferromagnetic phase
transition, but instead, a Berezinskii-Kosterlitz-Thouless (BKT) transition. A
classical XY model with nearest-neighbor coupling estimates critical
temperatures (T$_{BKT}$) ranging from 106 K for VSSe to 46 K for VSTe.",2002.07104v3
2020/2/26,Topological Properties of SnSe/EuS and SnTe/CaTe Interfaces,"We use density functional theory calculations to study the electronic
structure of epitaxial (111) interfaces of the topological crystalline
insulators SnSe and SnTe with the magnetic insulator EuS and the non-magnetic
insulator CaTe, respectively. We consider both interface slab models with a
vacuum region and periodic heterostructures without vacuum. We find that gaps
of 21 meV at the $\Gamma$ point and 9 meV at the M point arise in the
topological state at the SnSe/EuS interface, due to the magnetic proximity
effect, which breaks the time reversal symmetry. The surface state at $\Gamma$
is shifted below the Fermi level by 88 meV and the surface state at M is
shifted above the Fermi level by 47 meV, owing to band bending at the
interface. By comparison, the topological state at the interface of SnTe/CaTe
is unperturbed by the presence of non-magnetic CaTe.",2002.11488v3
2020/3/26,Bipolar spin Hall nano-oscillators,"We demonstrate a novel type of spin Hall nano-oscillator (SHNO) that allows
for efficient tuning of magnetic auto-oscillations over an extended range of
gigahertz frequencies, using bipolar direct currents at constant magnetic
fields. This is achieved by stacking two distinct ferromagnetic layers with a
platinum interlayer. In this device, the orientation of the spin polarised
electrons accumulated at the top and bottom interfaces of the platinum layer is
switched upon changing the polarity of the direct current. As a result, the
effective anti-damping required to drive large amplitude auto-oscillations can
appear either at the top or bottom magnetic layer. Tuning of the
auto-oscillation frequencies by several gigahertz can be obtained by combining
two materials with sufficiently different saturation magnetization. Here we
show that the combination of NiFe and CoFeB can result in 3 GHz shifts in the
auto-oscillation frequencies. Bipolar SHNOs as such may bring enhanced
synchronisation capabilities to neuromorphic computing applications.",2003.11776v1
2020/3/31,Nonlinear localized excitations in a topological ferromagnetic honeycomb lattice,"We theoretically investigate nonlinear localized excitations in a Heisenberg
honeycomb ferromagnet with a second neighbour Dzialozinskii-Moriya interaction,
which has been proved to possess the topological band structure. Using the
time-dependent variational principle, we obtain the equation of motion for the
system in the Glauber coherent-state representation. By means of the
semidiscrete multiple-scale method, different types of nonlinear localized
excitations are gotten.Our results show that both two-dimensional discrete
breathers and bulk gap solitons may occur in the Heisenberg honeycomb
ferromagnet.",2003.14268v3
2020/4/16,Magnetic domain wall substructures in Pt/Co/Ni/Ir multi-layers,"We examine the substructures of magnetic domain walls (DWs) in
[Pt/(Co/Ni)$_M$/Ir]$_N$ multi-layers using a combination of micromagnetic
theory and Lorentz transmission electron microscopy (LTEM). Thermal stability
calculations of Q=$\pm$1 substructures (2-$\pi$ vertical Bloch lines (VBLs) and
DW skyrmions) were performed using a geodesic nudged elastic band (GNEB) model,
which supports their metastability at room temperature. Experimental variation
in strength of the interfacial Dzyaloshinskii-Moriya interaction (DMI) and film
thickness reveals conditions under which these substructures are present and
enables the formation of a magnetic phase diagram. Reduced thickness is found
to favor Q=$\pm$1 substructures likely due to the suppression of hybrid DWs.
The results from this study provide an important framework for examining 1-D DW
substructures in chiral magnetic materials.",2004.07888v2
2020/4/17,Detection of the Chiral Spin Structure in Ferromagnetic SrRuO$_3$ Thin Film,"A SrRuO$_3$ (SRO) thin film and its heterostructure have brought much
attention because of the recently demonstrated fascinating properties, such as
topological Hall effect and skyrmions. Critical to the understanding of those
SRO properties is the study of the spin configuration. Here, we conduct
resonant soft x-ray scattering (RSXS) at oxygen K-edge to investigate the spin
configuration of a 4 unit-cell SRO film that was grown epitaxially on a single
crystal SrTiO$_3$. The RSXS signal under a magnetic field (~0.4 Tesla) clearly
shows a magnetic dichroism pattern around the specular reflection. Model
calculations on the RSXS signal demonstrate that the magnetic dichroism pattern
originates from a N\'eel-type chiral spin structure in this SRO thin film. We
believe that the observed spin structure of the SRO system is a critical piece
of information for understanding its intriguing magnetic and transport
properties.",2004.08092v1
2020/5/9,Self-consistent T-matrix approach to gap renormalization in quantum magnets with bond disorder,"Based on the self-consistent T-matrix approximation (SCTMA), analytical
theory of density of states (DOS) in three-dimensional quantum magnets with the
bond disorder is proposed. It successfully describes DOS in both cases of
resonant and non-resonant scattering which appearance is governed by the ratio
of scattering length and the average distance between impurities. Corrections
to the quasiparticles band gap in these cases are shown to be $\propto c^{2/3}$
and $\propto c$, respectively. Moreover, the theory yields a semi-circle form
of DOS for the bound states inside the gap which results in highly nontrivial
DOS in the intermediate parameters region between two limiting cases when the
band DOS and the semi-circle are overlapped. Long-wavelength excitations are
discussed. In the resonant regime their damping is almost constant $\propto
c^{2/3}$, which according to Ioffe-Regel criterion means their localization.
Applicability of the theory is illustrated by a quantitative description of the
recent experimental data on spin-dimer system Ba$_{3-x}$Sr$_x$Cr$_2$O$_8$.",2005.04438v2
2020/5/20,Electronic and magnetic properties of the Jahn-Teller active fluoride $\mathrm{NaCrF_{3}}$ from first-principles calculations,"In perovskite-type compounds, the interplay of cooperative Jahn-Teller
effect, electronic correlations and orbital degree of freedom leads to
intriguing properties. $\mathrm{NaCrF_{3}}$ is a newly synthesized Jahn-Teller
active fluoroperovskite where the $\mathrm{CrF_{6}^{4-}}$ octahedrons are
considerably distorted. Based on the first-principles calculation, we analyze
its electronic structure and magnetic properties. Our numerical results show
that the $\mathrm{Cr^{2+}}$ ions adopt the high-spin
$t_{2g\uparrow}^{3}e_{g\uparrow}^{1}$ configuration with $G$-type orbital
ordering. We also estimate the magnetic exchange couplings and find that the
in-plane and interplanar nearest-neighbor interactions are ferromagnetic and
antiferromagnetic, respectively. The ground state of this material is $A$-type
antiferromagnetic, in agreement with the experiments. Reasonable Curie-Weiss
and $\mathrm{N\acute{e}el}$ temperatures compared to the experiments are given
by mean-field approximation theory. Our results give a complete explanation of
its electronic structure, magnetic and orbital order, and help to further
comprehend the behaviors of Jahn-Teller active perovskite-type fluoride.",2005.10162v1
2020/6/9,Back-hopping in Spin-Transfer-Torque switching of perpendicularly magnetized tunnel junctions,"We analyse the phenomenon of back-hopping in spin-torque induced switching of
the magnetization in perpendicularly magnetized tunnel junctions. The analysis
is based on single-shot time-resolved conductance measurements of the
pulse-induced back-hopping. Studying several material variants reveals that the
back-hopping is a feature of the nominally fixed system of the tunnel junction.
The back-hopping is found to proceed by two sequential switching events that
lead to a final state P' of conductance close to --but distinct from-- that of
the conventional parallel state. The P' state does not exist at remanence. It
generally relaxes to the conventional antiparallel state if the current is
removed. The P' state involves a switching of the sole spin-polarizing part of
the fixed layers. The analysis of literature indicates that back-hopping occurs
only when the spin-polarizing layer is too weakly coupled to the rest of the
fixed system, which justifies a posteriori the mitigation strategies of
back-hopping that were implemented empirically in spin-transfer-torque magnetic
random access memories.",2006.05108v1
2020/6/23,Canted antiferromagnetism in high purity $\mathrm{NaFeF_3}$ prepared by a novel wet-chemical synthesis method,"We report a novel synthesis method for, and structural and magnetic
characterization of the fluoroperovskite $\mathrm{NaFeF_3}$. We have developed
a wet-chemical method that allows preparation of large volumes of air-sensitive
fluoroperovskites with high purity. $\mathrm{NaFeF_3}$ has a N\'eel temperature
($T_N$) of 90 K and a Weiss constant ($\theta$) of -124 K, corresponding to
dominant antiferromagnetic interactions. Below $T_N$, a slight difference is
observed between zero-field and field cooled samples, indicating spin-canting
and weak ferromagnetism. AC magnetometry confirms that weak ferromagnetism is
inherent to $\mathrm{NaFeF_3}$ and not due to impurities. From powder neutron
diffraction data, we describe the magnetic structure precisely as a weakly
canted G-type (magnetic space group $Pn'ma'$). A ferromagnetic component is
allowed in $Pn'ma'$, however, this component may be absent in zero magnetic
fields and is too small to be confirmed on the basis of powder neutron
diffraction data.",2006.12891v2
2020/7/12,"Magnetocaloric effect in Ni2(Mn,Cu)Ga0.84Al0.16 Heusler alloys","Polycrystalline Heusler compounds Ni2Mn0.75Cu0.25Ga0.84Al0.16 with a
martensitic transition between ferromagnetic phases and
Ni2Mn0.70Cu0.30Ga0.84Al0.16 with a magnetostructural transformation were
investigated by magnetization and thermal measurements, both as a function of
temperature and magnetic field. The compound Ni2Mn0.75Cu0.25Ga0.84Al0.16
presents a large magnetocaloric effect among magnetically aligned structures
and its causes are explored. In addition, Ni2Mn0.70Cu0.30Ga0.84Al0.16 shows
very high, although irreversible, entropy and adiabatic temperature change at
room temperature under a magnetic field change 0-1 T. Improved refrigerant
capacity is also a highlight of the 30% Cu material when compared to similar
Ni2MnGa-based alloys.",2007.05899v2
2020/7/12,"Large magnetic anisotropy energy and robust half-metallic ferromagnetism in 2D MnXSe$_4$ (X = As, Sb)","In recent years, intrinsic two-dimensional (2D) magnetism aroused great
interest because of its potential application in spintronic devices. However,
low Curie temperature (\emph{T}$_c$) and magnetic anisotropy energy (MAE) limit
its application prospects. Here, using first-principles calculations based on
density-functional theory (DFT), we predicted a series of stable MnXSe$_4$
(X=As, Sb) single-layer. The MAE of single-layer MnAsSe$_4$ and MnSbSe$_4$ was
648.76 and 808.95 ${\mu}$eV per Mn atom, respectively. Monte Carlo (MC)
simulations suggested the \emph{T}$_c$ of single-layer MnAsSe$_4$ and
MnSbSe$_4$ was 174 and 250 K, respectively. The energy band calculation with
hybrid Heyd-Scuseria-Ernzerhof (HSE06) function indicated the MnXSe$_4$ (X =
As, Sb) were ferromagnetic (FM) half-metallic. Also it had 100\%
spin-polarization ratio at the Fermi level. For MnAsSe$_4$ and MnSbSe$_4$, the
spin-gap were 1.59 and 1.48 eV, respectively. These excellent magnetic
properties render MnXSe$_4$ (X = As, Sb) promising candidate materials for 2D
spintronic applications.",2007.05951v1
2020/7/15,Analysis of Magnetoacoustic Quadrupole Resonance and Application to Probe Quadrupole Degrees of Freedom in Quantum Magnets,"Motivated by the recent progress of high-frequency ultrasonic measurements,
we propose a theory of magnetoacoustic resonance as a microscopic probe for
quadrupole degrees of freedom hidden in magnetic materials. A local strain
driven by an acoustic wave couples to electronic states of a magnetic ion
through various quadrupole-strain couplings, and this provides a periodically
time-dependent oscillating field. As a typical two-level system with the
quadrupole, we consider a non-Kramers doublet and investigate single- and
multiphonon-mediated transition processes on the basis of the Floquet theory.
An analytic form of the transition probability is derived within the weak
coupling theory, which helps us analyze the magnetoacoustic quadrupole
resonance. We apply the theory to realistic non-Kramers doublet systems for the
f2 configuration in Oh and D4h symmetries, and discuss how to identify the
relevant quadrupole by controlling the quadrupole-strain coupling with an
applied magnetic field in ultrasonic measurements.",2007.07503v2
2020/7/28,Chiral Spin Spirals at the Surface of the van der Waals Ferromagnet Fe$_3$GeTe$_2$,"Topologically protected magnetic structures provide a robust platform for low
power consumption devices for computation and data storage. Examples of these
structures are skyrmions, chiral domain walls, and spin spirals. Here we use
scanning electron microscopy with polarization analysis to unveil the presence
of chiral counterclockwise N\'eel spin spirals at the surface of a bulk van der
Waals ferromagnet Fe$_3$GeTe$_2$ (FGT), at zero magnetic field. These N\'eel
spin spirals survive up to FGT's Curie temperature $T_\mathrm{C}= 220
\mathrm{~K}$, with little change in the periodicity $p=300 \mathrm{~nm}$ of the
spin spiral throughout the studied temperature range. The formation of a spin
spiral showing counterclockwise rotation strongly suggests the presence of a
positive Dzyaloshinskii-Moriya interaction in FGT, which provides the first
steps towards the understanding of the magnetic structure of FGT. Our results
additionally pave the way for chiral magnetism in van der Waals materials and
their heterostructures.",2007.14113v1
2020/7/28,Large Tunable Anomalous Hall Effect in the Kagom$\acute{e}$ Antiferromagnet U$_3$Ru$_4$Al$_{12}$,"The Berry curvature in magnetic systems is attracting interest due to the
potential tunability of topological features via the magnetic structure.
$f$-electrons, with their large spin-orbit coupling, abundance of non-collinear
magnetic structures and high electronic tunability, are attractive candidates
to search for tunable topological properties. In this study, we measure
anomalous Hall effect (AHE) in the distorted kagom$\acute{e}$ heavy fermion
antiferromagnet U$_3$Ru$_4$Al$_{12}$. A large intrinsic AHE in high fields
reveals the presence of a large Berry curvature. Moreover, the fields required
to obtain the large Berry curvature are significantly different between $B
\parallel a$ and $B \parallel a^*$, providing a mechanism to control the
topological response in this system. Theoretical calculations illustrate that
this sensitivity may be due to the heavy fermion character of the electronic
structure. These results shed light on the Berry curvature of a strongly
correlated band structure in magnetically frustrated heavy fermion materials,
but also emphasize 5$f$-electrons as an ideal playground for studying
field-tuned topological states.",2007.14378v1
2020/7/29,The spontaneous exchange bias effect on La$_{1.5}$Ba$_{0.5}$CoMnO$_{6}$,"La$_{1.5}$Ba$_{0.5}$CoMnO$_{6}$ is a re-entrant cluster glass material
exhibiting a robust negative exchange bias (EB) effect even after being cooled
from an unmagnetized state down to low temperature in zero magnetic field. Here
we thoroughly investigate this phenomena by performing magnetization as a
function of applied field [$M(H)$] measurements at several different
temperatures and maximum applied magnetic fields ($H_m$). The spontaneous EB
(SEB) effect is observed below 20 K, and shows a maximum value for $H_m$ = 75
kOe. The effect is greatly enhanced when the $M(H)$ curves are measured after
the system is cooled in the presence of a magnetic field. The asymmetry of the
$M(H)$ curves here investigated can be well described by a recently proposed
model based on the unconventional relaxation of the SG-like moments during the
hysteresis cycle.",2007.14976v1
2020/7/30,Structure and magnetism of a new hexagonal polymorph of Ba$_3$Tb(BO$_3$)$_3$ with a quasi-2D triangular lattice,"This article reports the structural and magnetic characterisation of a new
hexagonal ($P6_3cm$) low-temperature phase of Ba$_3$Tb(BO$_3$)$_3$,
isostructural with the heavier lanthanide borates with formula
Ba$_3$Ln(BO$_3$)$_3$ (Ln = Dy-Lu). The crystal structure contains a
quasi-two-dimensional (2D) triangular lattice of Tb$^{3+}$ ions and is
predicted to display unusual magnetic behaviour as a result of the low
dimensionality. Magnetic susceptibility $\chi(T)$ shows antiferromagnetic
interactions ($\theta_{CW} = -7.15$ K) and no sharp ordering transition at $T
\geq 2$ K, but analysis of $\chi'(T)$, isothermal magnetisation and heat
capacity suggests the possibility of short-range ordering at $T \approx 10$ K.
The material exhibits an inverse magnetocaloric effect at $T < 4$ K.",2007.15453v2
2020/8/3,Experimental evidence of hidden spin polarization in silicon by using strain gradient,"The centrosymmetric materials with hidden spin polarization are considered to
be the promising candidates for realization of energy efficient spintronics
systems and devices. However, the control of hidden spin polarization and
resulting transport behavior is not well understood. We hypothesized that
inhomogeneous strain can be the external knob to study and control hidden spin
polarization. In this work, we demonstrate a strain gradient mediated symmetry
breaking to discover the hidden spin polarization in centrosymmetric Si
lattice. The hidden spin polarization gives rise to magnetocrystalline
anisotropy and local magnetic moment along <111> directions in the Si. The
local magnetic moment gives rise to spin-acoustic phonon coupling, which is the
underlying cause of observed spin-Hall effect in both n-Si and p-Si. Discovery
of hidden magnetic moment in Si not only challenges the fundamental
understanding of the origin of the magnetism but also presents a giant leap in
realization of spintronics systems.",2008.01033v3
2020/8/11,Role of chemical pressure on the electronic and magnetic properties of spin-1/2 kagome mineral averievite,"We investigate the electronic and magnetic properties of the kagome mineral
averievite (CsCl)Cu$_5$V$_2$O$_{10}$ and its phosphate analog
(CsCl)Cu$_5$P$_2$O$_{10}$ using first-principles calculations. The crystal
structure of these compounds features Cu$^{2+}$ kagome layers sandwiched
between Cu$^{2+}$-P$^{5+}$/Cu$^{2+}$-V$^{5+}$ honeycomb planes, with pyrochlore
slabs made of corner-sharing Cu-tetrahedra being formed. The induced chemical
pressure effect upon substitution of V by P causes significant changes in the
structure and magnetic properties. Even though the in-plane antiferromagnetic
(AFM) coupling (J$_1$) within the kagome layer is similar in the two materials,
the inter-plane AFM coupling (J$_2$) between kagome and honeycomb layers is
five times larger in the P-variant increasing the degree of magnetic
frustration in the constituting Cu-tetrahedra.",2008.04966v1
2020/8/24,Emergent helical texture of electric dipoles,"Long-range ordering of magnetic dipoles in bulk materials gives rise to a
broad range of magnetic structures, from simple collinear ferromagnets and
antiferromagnets, to complex magnetic helicoidal textures stabilized by
competing exchange interactions. In contrast, in the context of dipolar order
in dielectric crystals, only parallel (ferroelectric) and antiparallel
(antiferroelectric) collinear alignments of electric dipoles are typically
considered. Here, we report an observation of incommensurate helical ordering
of electric dipoles by light hole-doping of the quadruple perovskite BiMn7O12.
In analogy with magnetism, the electric dipole helicoidal texture is also
stabilized by competing instabilities. Specifically, orbital ordering and lone
electron pair stereochemical activity compete, giving rise to phase transitions
from a non-chiral cubic structure, to an incommensurate electric dipole and
orbital helix, via an intermediate density wave.",2008.10517v1
2020/8/31,Room-temperature giant magnetotranstance effect in single-phase multiferroics,"Single-phase multiferroic materials are usually considered useless because of
the weak magnetoelectric effects, low operating temperature, and small electric
polarization induced by magnetic orders. As a result, current studies on
applications of the magnetoelectric effects are mainly focusing on multiferroic
heterostructures and composites. Here we report a room-temperature giant effect
in response to external magnetic fields in single-phase multiferroics. A low
magnetic field of 1000 Oe applied on the spin-driven multiferroic hexaferrites
BaSrCo2Fe11AlO22 and Ba0.9Sr1.1Co2Fe11AlO22 is able to cause a huge change in
the linear magnetoelectric coefficient by several orders, leading to a giant
magnetotranstance (GMT) effect at room temperature. The GMT effect is
comparable to the well-known giant magnetoresistance (GMR) effect in magnetic
multilayers, and thus opens up a door toward practical applications for
single-phase multiferroics.",2008.13410v1
2020/9/6,Strain-tunable magnetism and nodal loops in monolayer MnB,"Designing two-dimensional (2D) materials with magnetic and topological
properties has continuously attracted intense interest in fundamental science
and potential applications. Here, on the basis of first-principles
calculations, we predict the coexistence of antiferromagnetism and Dirac nodal
loop (NL) in the monolayer MnB, where the band crossing points are very close
to the Fermi Level. Remarkably, a moderate strain can induce an
antiferromagnetic to ferromagnetic phase transition, driving the monolayer MnB
to a ferromagnetic metal with Weyl NLs. Such a type of topological quantum
phase transition has not been observed before. In addition, the
symmetry-protected properties of the two types of NLs as well as the magnetic
critical temperatures are investigated. The controllable magnetic and
topological order in monolayer MnB offers a unique platform for exploring
topological quantum phase transitions and realizing nanospintronic devices.",2009.02688v1
2020/9/9,"Structural, Elastic, Electronic and Magnetic Properties of MnNbZ (Z=As, Sb) and FeNbZ (Z=Sn, Pb) Semi-Heusler Alloys","The study of structural, electronic, magnetic, and elastic properties of new
series of semi-Heusler alloys MnNbZ (Z=As, Sb) and FeNbZ (Z=Sn, Pb) has been
performed by density functional theory. The magnetic phase and hence the
structural stability of the alloys were considered wherein ferromagnetic state
is found to stable. The half-metallic states are observed from the density of
states and band structure calculations. The total magnetic moments found for
all studied compounds are 1 $\mu_B$/f.u., which obey Slating-Pauling rule for
semi-Heusler with ferromagnetic behavior. The calculated elastic constant
C$_{ij}$, cohesive energy, and formation energy confirmed that these materials
are mechanically stable. Among the four system, MnNbAs is found to have the
highest ductility while the remaining systems are found to be brittle in
nature. These properties confirmed that among others, MnNbAs is one of the
novel candidate for spintronic devices applications.",2009.04123v1
2020/9/16,Dynamical mass generation for ferromagnetic skyrmions in two dimensions,"Magnetic skyrmions are topological magnetization textures that are
characterized by the homotopy group of two dimensional spheres. Despite years
of intensive research on skyrmions, the fundamental problem of the inertia of a
skyrmion in driven motion remains unresolved. By properly taking into account a
direct coupling between skyrmion motion and the correspondingly excited
magnons, we identify a dynamical mass for the skyrmion in motion. The direct
coupling between skyrmion motion and magnons can be employed to engineer
skyrmion dynamics with magnons through ingenious material and geometry design.",2009.07486v4
2020/9/25,Magnetoactive elastomer based on superparamagnetic nanoparticles with Curie point close to room temperature,"A magnetoactive elastomer (MAE) consisting of single-domain La0.8Ag0.2Mn1.2O3
nanoparticles with a Curie temperature close to room temperature (TC = 308 K)
in a silicone matrix has been prepared and comprehensively studied. It has been
found that at room temperature and above, MAE particles are magnetized
superparamagnetically with a low coercivity below 10 Oe, and the influence of
magnetic anisotropy on the appearance of a torque is justified. A coupling
between magnetization and magnetoelasticity has been also established. The
mechanisms of the appearance of magnetoelasticity, including the effect of MAE
rearrangement and MAE compression by magnetized particles, have been revealed.
It has been found that the magnetoelastic properties of MAE have critical
features near TC. The magnetoelastic properties of MAE disappear at T > TC and
are restored at T < TC. This makes it possible to use MAE at room temperature
as a smart material for devices with self-regulating magnetoelastic properties.",2009.12048v1
2020/9/29,High-pressure induced magnetic phase transition in half-metallic $\textbf{KBeO}_\textbf{3}$ perovskite,"In this paper, we present the study of the structural, mechanical,
magneto-electronic and thermodynamic properties of the perovskite KBeO$_3$. The
calculations were performed by the full potential augmented plane wave method,
implemented in the WIEN2k code which is based on density functional theory,
using generalized gradient approximation. The computed formation energy and
elastic constants indicate the synthesizability and mechanical stability of
KBeO$_3$. Moreover, our results showed that the latter is a half-metallic
material with half-metallic gap of 0.67 eV and an integer magnetic moment of
3$\mu_{\text{B}}$ per unit cell. In addition, KBeO$_3$ maintains the
half-metallic character under the pressure up to about 97 GPa corresponding to
the predicted magnetic-phase transition pressure from ferromagnetic to
non-magnetic state. The volume ratio $V/V_{0}$, bulk modulus, heat capacity,
thermal expansion and the Debye temperature are analyzed using the
quasi-harmonic Debye model.",2009.14107v1
2020/10/5,"Properties of amorphous CoZr(RE) (RE=Gd, Sm, Dy) films with various uniaxial anisotropies, prepared by a new process","If a DC magnetic field is applied parallel to the plane of amorphous CoZr(RE)
thin films during sputter depositing, a uniaxial anisotropy is formed the
direction of which depends upon the choice of RE substituted and its
concentration. When RE = Gd a perpendicular anisotropy K, forms over a large
concentration range, a spin reorientation process being at the origin of the
process. A well-defined K, is developed also in CoFeZrGd and CoZrGdSm films.
CoZrGdDy films exhibit simultaneously a perpendicular and an in-plane uniaxial
anisotropy. The related magnetization process and domain structures are quite
peculiar.",2010.01831v1
2020/11/3,Driving spin chirality by electron dynamics in laser-excited antiferromagnets,"Optical generation of complex spin textures is one of the most exciting
challenges of modern spintronics. Here, we uncover a distinct physical
mechanism for imprinting spin chirality into collinear magnets with short laser
pulses. By simultaneously treating the laser-ignited evolution of electronic
structure and magnetic order, we show that their intertwined dynamics can
result in an emergence of quasi-stable chiral states. We find that laser-driven
chirality does not require any auxiliary external fields or intrinsic
spin-orbit interaction to exist, and it can survive on the time scale of
nanoseconds even in the presence of thermal fluctuations, which makes the
uncovered mechanism relevant for understanding various optical experiments on
magnetic materials. Our findings open a new perspective at the interaction of
complex chiral magnetism with light.",2011.01670v3
2020/11/20,Neutron scattering by magnetic octupoles of a quantum liquid,"Neutron scattering is a powerful tool to study magnetic structures and
dynamics, benefiting from a precisely established theoretical framework. The
neutron dipole moment interacts with electrons in materials via their magnetic
field, which can have spin and orbital origins. Yet in most experimentally
studied cases the individual degrees of freedom are well described within the
dipole approximation, sometimes accompanied by further terms of a multipolar
expansion that usually act as minor corrections to the dipole form factor. Here
we report a unique example of neutrons diffracted mainly by magnetic octupoles.
This unusual situation arises in a quantum spin ice where the electronic
wavefunction becomes essentially octupolar under the effect of correlations.
The discovery of such a new type of quantum spin liquid that comes with a
specific experimental signature in neutron scattering is remarkable, because
these topical states of matter are notoriously difficult to detect.",2011.10418v1
2020/11/23,Unconventional Hall effect and its variation with Co-doping in van der Waals Fe3GeTe2,"Two-dimensional (2D) van der Waals (vdW) magnetic materials have attracted a
lot of attention owing to the stabilization of long-range magnetic order down
to atomic dimensions, and the prospect of novel spintronic devices with unique
functionalities. The clarification of the magnetoresistive properties and its
correlation to the underlying magnetic configurations is essential for 2D
vdW-based spintronic devices. Here, the effect of Co-doping on the magnetic and
magnetotransport properties of Fe3GeTe2 have been investigated.
Magnetotransport measurements reveal an unusual Hall effect behavior whose
strength was considerably modified by Co-doping and attributed to arise from
the underlying complicated spin textures. The present results provide a clue to
tailoring of the underlying interactions necessary for the realization of a
variety of unconventional spin textures for 2D vdW FM-based spintronics.",2011.11269v2
2020/11/26,3D Nanomagnetism in Low Density Interconnected Nanowire Networks,"Free-standing, interconnected metallic nanowire networks with density as low
as 40 mg/cm^{3} have been achieved over cm-scale areas, using electrodeposition
into polycarbonate membranes that have been ion-tracked at multiple angles.
Networks of interconnected magnetic nanowires further provide an exciting
platform to explore 3-dimensional nanomagnetism, where their structure,
topology and frustration may be used as additional degrees of freedom to tailor
the materials properties. New magnetization reversal mechanisms in cobalt
networks are captured by the first-order reversal curve method, which
demonstrate the evolution from strong demagnetizing dipolar interactions to
intersections-mediated domain wall pinning and propagation, and eventually to
shape-anisotropy dominated magnetization reversal. These findings open up new
possibilities for 3-dimensional integrated magnetic devices for memory, complex
computation, and neuromorphics.",2011.13468v2
2020/11/27,d0 Ferromagnetism in Mg-doped Rutile TiO2 Nanoparticles,"In a quest of enriching the area of d0 magnetism in oxide materials, we have
undertaken to study Mg-doped TiO2 compounds. The Ti1-xMgxO2 (x=0, 0.02, 0.04
and 0.06) nanoparticles were prepared by solid-state reaction route. The X-ray
diffractions (XRD) patterns of these samples indicate single phase of
tetragonal rutile-structure of TiO2. The refinement of the XRD patterns reveals
no change in the crystallographic lattice parameters in comparison to pure TiO2
upon Mg doping and it indicates that Mg2+ ions do not enter core grains and
form core/shell structure. SEM observations reveal the uniform morphology with
nanometric grains in the range of 150-200 nm. The measurement of magnetic
properties of these compounds indicates that pure TiO2 and Ti0.98Mg0.02
compounds exhibit paramagnetic behavior and Ti0.96Mg0.04 compound exhibits
ferromagnetic (FM) phase superimposed with the dominating paramagnetic phase.
However, Ti0.94Mg0.06 compound exhibits ferromagnetic to paramagnetic
transition with FM transition temperature of 180.2 K. The measurements of zero
field and field cooled magnetization data indicate low temperature magnetic
irreversibility for x=0.06 sample and it was attributed to the competing AFM
(core) and the FM (shell) interactions. The measurement of hysteresis curves at
various temperatures indicates domain wall pinning and an exchange-bias
behavior.",2011.13718v1
2020/12/2,Magneto-active elastic shells with tunable buckling strength,"Shell buckling is central in many biological structures and advanced
functional materials, even if, traditionally, this elastic instability has been
regarded as a catastrophic phenomenon to be avoided for engineering structures.
Either way, predicting critical buckling conditions remains a long-standing
challenge. The subcritical nature of shell buckling imparts extreme sensitivity
to material and geometric imperfections. Consequently, measured critical loads
are inevitably lower than classic theoretical predictions. Here, we present a
robust mechanism to dynamically tune the buckling strength of shells,
exploiting the coupling between mechanics and magnetism. Our experiments on
pressurized spherical shells made of a magnetorheological elastomer demonstrate
the tunability of their buckling pressure via magnetic actuation. We develop a
theoretical model for thin magnetic elastic shells, which rationalizes the
underlying mechanism, in excellent agreement with experiments. A dimensionless
magneto-elastic buckling number is recognized as the key governing parameter,
combining the geometrical, mechanical, and magnetic properties of the system.",2012.01163v2
2020/12/17,Magnetic equivalent of electric superradiance: radiative damping in yttrium-iron-garnet films,"A dense system of independent oscillators, connected only by their
interaction with the same cavity excitation mode, will radiate coherently,
which effect is termed superradiance. In several cases, especially if the
density of oscillators is high, the superradiance may dominate the intrinsic
relaxation processes. This limit can be achieved, e.g., with cyclotron
resonance in two-dimensional electron gases. In those experiments, the
cyclotron resonance is coupled to the electric field of light, while the
oscillator density can be easily controlled by varying the gate voltage.
However, in the case of magnetic oscillators, to achieve the dominance of
superradiance is more tricky, as material parameters limit the oscillator
density, and the magnetic coupling to the light wave is rather small. Here we
present quasi-optical magnetic resonance experiments on thin films of yttrium
iron garnet. Due to the simplicity of experimental geometry, the intrinsic
damping and the superradiance can be easily separated in the transmission
spectra. We show that with increasing film thickness, the losses due to
coherent radiation prevail the system's internal broadening.",2012.09440v1
2020/12/20,Reconstructing phase-resolved hysteresis loops from first-order reversal curves,"The first order reversal curve (FORC) method is a magnetometry based
technique used to capture nanoscale magnetic phase separation and interactions
with macroscopic measurements using minor hysteresis loop analysis. This makes
the FORC technique a powerful tool in the analysis of complex systems which
cannot be effectively probed using localized techniques. However, recovering
quantitative details about the identified phases which can be compared to
traditionally measured metrics remains an enigmatic challenge. We demonstrate a
technique to reconstruct phase-resolved magnetic hysteresis loops by
selectively integrating the measured FORC distribution. From these minor loops,
the traditional metrics - including the coercivity and saturation field, and
the remanent and saturation magnetization - can be determined. In order to
perform this analysis, special consideration must be paid to the accurate
quantitative management of the so-called reversible features. This technique is
demonstrated on three representative materials systems, high anisotropy FeCuPt
thin-films, Fe nanodots, and SmCo/Fe exchange spring magnet films, and shows
excellent agreement with the direct measured major loop, as well as the phase
separated loops.",2012.11041v1
2020/12/23,On bifurcation behavior of hard magnetic soft cantilevers,"Hard magnetic materials belong to a novel class of soft active materials with
the capability of quick, large, and complex deformation via applying an
external actuation. They have an extensive range of potential applications in
soft robots, biomedical devices, and stretchable electronics, etc. Recently,
investigation on the experimental and theoretical nonlinear mechanics of hard
magnetic soft cantilevers has received notable considerations. In the available
analyses, the most attention was paid to the non-bifurcation-type nonlinear
mechanics of the system, and bifurcation was considered for a specific case. In
the current study, the general trend of bifurcation-type nonlinear mechanics of
hard magnetic soft cantilevers is introduced and the effective parameters on
the occurrence of bifurcation are identified. Additionally, new trajectories
due to the bifurcation and the corresponding workspace are presented.
Eventually, a comprehensive comparative study between the new trajectories and
workspace with those reported in the prior studies is carried out.",2012.12673v1
2020/12/31,Detection of magnetic gap in the topological surface states of MnBi2Te4,"Recently, intrinsic antiferromagnetic topological insulator MnBi2Te4 has
drawn intense research interest and leads to plenty of significant progress in
physics and materials science by hosting quantum anomalous Hall effect, axion
insulator state, and other quantum phases. An essential ingredient to realize
these quantum states is the magnetic gap in the topological surface states
induced by the out-of-plane ferromagnetism on the surface of MnBi2Te4. However,
the experimental observations of the surface gap remain controversial. Here, we
report the observation of the surface gap via the point contact tunneling
spectroscopy. In agreement with theoretical calculations, the gap size is
around 50 meV, which vanishes as the sample becomes paramagnetic with
increasing temperature. The magnetoresistance hysteresis is detected through
the point contact junction on the sample surface with an out-of-plane magnetic
field, substantiating the surface ferromagnetism. Furthermore, the non-zero
transport spin polarization coming from the ferromagnetism is determined by the
point contact Andreev reflection spectroscopy. Combining these results, the
magnetism-induced gap in topological surface states of MnBi2Te4 is revealed.",2012.15591v1
2020/12/31,Topological solitons and bulk polarization switch in collinear type II multiferroics,"We introduce a microscopic model for collinear multiferroics capable to
reproduce, as a consequence of magnetic frustration and easy-axis anisotropy,
the so-called ""uudd"" (or antiphase) magnetic ordering observed in several type
II multiferroic materials. The crucial role of lattice distortions in the
multiferroic character of these materials is entered into the model via an
indirect magnetoelectric coupling, mediated by elastic degrees of freedom
through a pantograph mechanism. Long range dipolar interactions set electric
dipoles in the antiferroelectric order. We investigate this model by means of
extensive DMRG computations and complementary analytical methods. We show that
a lattice dimerization induces a spontaneous Z2 ferrielectric bulk
polarization, with a sharp switch off produced by a magnetic field above a
critical value. The topological character of the magnetic excitations makes
this mechanism robust.",2012.15711v1
2021/1/2,Proper and improper chiral magnetic interactions,"Atomistic spin models are of great value for predicting and understanding the
magnetic properties of real materials, and extensions of the existing models
open routes to new physics and potential applications. The
Dzyaloshinskii-Moriya interaction is the prototype for chiral magnetic
interactions, and several recent works have uncovered or proposed various types
of generalized chiral interactions. However, in some cases the proposed
interactions or their interpretation do not comply with basic principles such
as being independent of the magnetic configuration from which they are
evaluated, or even obeying time-reversal invariance. In this letter, we present
a simple explanation for the origin of these puzzling findings, and point out
how to resolve them.",2101.00463v2
2021/1/14,Magnetic field-induced thermal emission tuning of InSb-based metamaterials in the terahertz frequency regime,"This work theoretically and analytically demonstrates the magnetic
field-induced spectral radiative properties of photonic metamaterials
incorporating both Indium Antimonide (InSb) and Tungsten (W) in the terahertz
(THz) frequency regime. We have varied multiple factors of the nanostructures,
including composite materials, layer thicknesses and surface grating fill
factors, which impact the light-matter interactions and in turn modify the
thermal emission of the metamaterials. We have proposed and validated a method
for determining the spectral properties of InSb under an applied direct current
(DC) magnetic field, and have employed this method to analyze how these
properties can be dynamically tuned by modulating the magnitude of the field.
For the first time, we have designed an InSb-W metamaterial exhibiting unity
narrowband emission which can serve as an emitter for wavelengths around 55
$\mu$m (approximately 5.5 THz). Additionally, the narrowband emission of this
metamaterial can be magnetically tuned in both bandwidth and peak wavelength
with a normal emissivity close to unity.",2101.05852v2
2021/1/16,Universal Critical Exponents of the Magnetic Domain Wall Depinning Transition,"Magnetic field driven domain wall dynamics in a ferrimagnetic GdFeCo thin
film with perpendicular magnetic anisotropy is studied using low temperature
magneto-optical Kerr microscopy. Measurements performed in a practically
athermal condition allow for the direct experimental determination of the
velocity ($ \beta = 0.30 \pm 0.03 $) and correlation length ($ \nu = 1.3 \pm
0.3 $) exponents of the depinning transition. The whole family of exponents
characterizing the transition is deduced, providing evidence that the depinning
of magnetic domain walls is better described by the quenched Edwards-Wilkinson
universality class.",2101.06555v3
2021/1/25,Raman Spectroscopy and Aging of the Low-Loss Ferrimagnet Vanadium Tetracyanoethylene,"Vanadium tetracyanoethylene (V[TCNE]$_{x}$, $x\approx 2$) is an organic-based
ferrimagnet with a high magnetic ordering temperature $\mathrm{T_C>600 ~K}$,
low magnetic damping, and growth compatibility with a wide variety of
substrates. However, similar to other organic-based materials, it is sensitive
to air. Although encapsulation of V[TCNE]$_{x}$ with glass and epoxy extends
the film lifetime from an hour to a few weeks, what is limiting its lifetime
remains poorly understood. Here we characterize encapsulated V[TCNE]$_{x}$
films using confocal microscopy, Raman spectroscopy, ferromagnetic resonance
and SQUID magnetometry. We identify the relevant features in the Raman spectra
in agreement with \textit{ab initio} theory, reproducing $\mathrm{C=C,C\equiv
N}$ vibrational modes. We correlate changes in the effective dynamic
magnetization with changes in Raman intensity and in photoluminescence. Based
on changes in Raman spectra, we hypothesize possible structural changes and
aging mechanisms in V[TCNE]$_x$. These findings enable a local optical probe of
V[TCNE]$_{x}$ film quality, which is invaluable in experiments where assessing
film quality with local magnetic characterization is not possible.",2101.10240v1
2021/2/3,Evolutionary search for cobalt-rich compounds in the yttrium-cobalt-boron system,"Modern high-performance permanent magnets are made from alloys of rare earth
and transition metal elements, and large magnetization is achieved in the
alloys with high concentration of transition metals. We applied evolutionary
search scheme based on first-principles calculations to the Y-Co-B system and
predicted 37 cobalt-rich compounds with high probability of being stable.
Focusing on remarkably cobalt-rich compounds, YCo$_{16}$ and YCo$_{20}$, we
found that, although they are metastable phases, the phase stability is
increased with increase of temperature due to the contribution of vibrational
entropy. The magnetization and Curie temperature are higher by 0.22 T and 204 K
in YCo$_{16}$ and by 0.29 T and 204 K in YCo$_{20}$ than those of
Y$_{2}$Co$_{17}$ which has been well studied as strong magnetic compounds.",2102.02097v1
2021/2/8,Anomalous sound attenuation in Weyl semimetals in magnetic and pseudomagnetic fields,"We evaluate the sound attenuation in a Weyl semimetal subject to a magnetic
field or a pseudomagnetic field associated with a strain. Due to the interplay
of intra- and inter-node scattering processes as well as screening, the fields
generically reduce the sound absorption. A nontrivial dependence on the
relative direction of the magnetic field and the sound wave vector, i.e., the
magnetic sound dichroism, can occur in materials with nonsymmetric Weyl nodes
(e.g., different Fermi velocities and/or relaxation times). It is found that
the sound dichroism in Weyl materials can also be activated by an external
strain-induced pseudomagnetic field. In view of the dependence on the field
direction, the dichroism may lead to a weak enhancement of the sound
attenuation compared with its value at vanishing fields.",2102.04510v3
2021/3/1,"Li$_2$Sr[MnN]$_2$: a magnetically ordered, metallic nitride","Li$_2$Sr[MnN]$_2$ single crystals were successfully grown out of Li rich
flux. The crystal structure was determined by single crystal X-ray diffraction
and revealed almost linear $-$N$-$Mn$-$N$-$Mn$-$ chains as central structural
motif. Tetragonal columns of this air and moisture sensitive nitridomanganate
were employed for electrical transport, heat capacity, and anisotropic
magnetization measurements. Both the electronic and magnetic properties are
most remarkable, in particular the linear increase of the magnetic
susceptibility with temperature that is reminiscent of underdoped cuprate and
Fe-based superconductors. Clear indications for antiferromagnetic ordering at
$T_{\rm N} = 290$ K were obtained. Metallic transport behavior is
experimentally observed in accordance with electronic band structure
calculations.",2103.00952v1
2021/3/2,Anisotropic Multi-layer Elliptical Waveguides Incorporating Graphene Layers: A Novel Analytical Model,"This article aims to propose a novel analytical model for anisotropic
multi-layer elliptical structures incorporating graphene layers. The
multi-layer structure is formed of various magnetic materials. An external
magnetic bias has been applied in the axial direction. A graphene layer, with
isotropic surface conductivity, has been sandwiched between two adjacent
anisotropic materials. A novel matrix representation has been derived to find
the propagation parameters of the multi-layer structure. Two exemplary
important cases of the proposed general structure, as waveguides, have been
investigated to show, first the validity of our proposed analytical model, and
second, the richness of the general structure. The analytical and simulation
results show an excellent agreement. A very large value of the figure of merit
(FOM), e.g. FOM=110, is achieved for the second structure for the chemical
potential and external magnetic bias of 0.9 ev and 1T, respectively. Our
general structure and its analytical model can be exploited to design
innovative THz devices such as absorbers, couplers, and cloaks.",2103.01925v1
2021/3/16,Machine learning prediction of magnetic properties of Fe-based metallic glasses considering local structures,"Magnetism prediction is of great significance for Fe-based metallic glasses
(FeMGs), which have shown great commercial value. Theories or models
established based on condensed matter physics exhibit several exceptions and
limited accuracy. In this work, machine learning (ML) models learned from a
large amount of experimental data were trained based on eXtreme gradient
boosting (XGBoost), artificial neural networks (ANN), and random forest to
predict the magnetic properties of FeMGs. The XGBoost and ANN models exhibited
comparably excellent predictive performance, with R^2 >= 0.903, mean absolute
percentage error (MAPE) <= 6.17, and root mean squared error (RMSE) <= 0.098.
The trained ML models aggregate the influence of 13 factors, which is difficult
to achieve in traditional physical models. The influence of local structure,
which was represented by the experimental parameter of the supercooled liquid
region, presented a significant impact on the predictive performance of ML
models. The developed ML-based method here can predict the magnetic properties
of FeMGs by considering multiple factors simultaneously, including complex
local structures.",2103.12543v1
2021/3/24,Effective strain manipulation of the antiferromagnetic state of polycrystalline NiO,"As a candidate material for applications such as magnetic memory,
polycrystalline antiferromagnets offer the same robustness to external magnetic
fields, THz spin dynamics, and lack of stray field as their single crystalline
counterparts, but without the limitation of epitaxial growth and lattice
matched substrates. Here, we first report the detection of the average Neel
vector orientiation in polycrystalline NiO via spin Hall magnetoresistance
(SMR). Secondly, by applying strain through a piezo-electric substrate, we
reduce the critical magnetic field required to reach a saturation of the SMR
signal, indicating a change of the anisotropy. Our results are consistent with
polycrystalline NiO exhibiting a positive sign of the in-plane
magnetostriction. This method of anisotropy-tuning offers an energy efficient,
on-chip alternative to manipulate a polycrystalline antiferromagnets magnetic
state.",2103.13105v1
2021/3/25,Emergent ferromagnetism with Fermi-liquid behavior in proton intercalated CaRuO3,"The evolution between Fermi liquid and non-Fermi-liquid states in correlated
electron systems has been a central subject in condensed matter physics because
of the coupled intriguing magnetic and electronic states. An effective pathway
to explore the nature of non-Fermi liquid behavior is to approach its phase
boundary. Here we report a crossover from non-Fermi liquid to Fermi-liquid
state in metallic CaRuO3 through ionic liquid gating induced protonation with
electric field. This electronic transition subsequently triggers a reversible
magnetic transition with the emergence of an exotic ferromagnetic state from
this paramagnetic compound. Our theoretical analysis reveals that hydrogen
incorporation plays a critical role in both the electronic and magnetic phase
transitions via structural distortion and electron doping. These observations
not only help understand the correlated magnetic and electronic transitions in
perovskite ruthenate systems, but also provide novel pathways to design
electronic phases in correlated materials.",2103.13545v1
2021/3/30,Integer vs. half-integer spin on an approximate honeycomb lattice,"Recent interest in honeycomb lattice materials has focused on their potential
to host quantum spin liquid (QSL) states. Variations in bond angles and spin
allow a range of interesting behaviors on this lattice, from the predicted QSL
ground state of the Kitaev model to exotic magnetic orders. Here we report the
physical properties of two compounds with rare earths on an approximate
honeycomb lattice. The isostructural compounds Nd$_2$S$_5$Sn (J =
$\frac{9}{2}$) and Pr$_2$S$_5$Sn (J = 4) permit a direct comparison of
half-integer versus integer spins on this lattice. We find strikingly different
magnetic properties for the two compounds. Nd$_2$S$_5$Sn orders
antiferromagnetically at T$_N$ $\approx$ 2.5 K, and undergoes several magnetic
transitions to other ordered states under applied field. Pr$_2$S$_5$Sn displays
no magnetic ordering transition above T = 0.41 K, and may be proximate to a
spin liquid state.",2103.16684v1
2021/4/2,Spin glass state in layered compound MnSb2Te4,"As a sister compound and isostructural of MnBi2Te4, the high quality MnSb2Te4
single crystals are grown via solid-state reaction where prolonged annealing
and narrow temperature window play critical roles on account of its thermal
metastability. X-ray diffraction analysis on MnSb2Te4 single crystals reveals
pronounced cation intermixing, 28.9(7)% Sb antisite defects on the Mn (3a) site
and 19.3(6)% Mn antisite defects on the Sb (6c) site, compared with MnBi2Te4.
Unlike antiferromagnetic (AFM) nature MnBi2Te4, MnSb2Te4 contains magnetic and
antiferromagnetic competition and exhibits a spin glass (SG) state below 24 K.
Its magnetic hysteresis, anisotropy, and relaxation process are investigated in
detail with DC and AC magnetization measurements. Moreover, anomalous Hall
effect as a p-type conductor is demonstrated through transport measurements.
This work grants MnSb2Te4 a possible access to the future exploration of exotic
quantum physics by removing the odd/even layer number restraint in intrinsic
AFM MnBi2Te4-family materials as a result of the crossover between its
magnetism and potential topology in the Sb-Te layer.",2104.00898v1
2021/4/6,B12C2N Interstitial Boron subcarbonitride with peculiar magnetic properties: First principles investigations,"The subcarbides B12C3 and B13C2 known for their abrasive properties, can be
structurally considered as carbon inserted rhombohedral alpha-B12 and expressed
as B12{C-C-C} and B12(C-B-C). Using density functional theory DFT computations,
the substitution of the central atom in the linear triatomic interstitials by N
leads to an original new boron subcarbonitride B12C2N or B12(C-N-C) identified
as slightly more cohesive than the two subcarbides. While B12C3 is insulating
with a E(Gap) close to 0.2 eV, and B13C2 a weak metal with small density of
state DOS at the Fermi level, B12C2N ground state is a half-metallic
ferromagnet with M= 1 BM. From the equation of state, the magnetization is
found unchanged over a broad volume range around equilibrium. Total and
magnetic charge density projections, in accordance with charge transfer
calculations, show the charge envelopes to be concentrated on (C:N:C) and the
magnetic charge having the shape of a torus centered on N. The triatomic
interstitials interact through terminal carbons specifically with one of the
two boron substructures of alpha-B12 forming 3B1-C-N-C-3B1-like complex.
Further syntheses and experimental characterizations are expected to extend the
field of investigation of such an original class of materials.",2104.02315v1
2021/4/13,Peierls transition driven ferroelasticity in two-dimensional $d$-$f$ hybrid magnet,"For broad nanoscale applications, it is crucial to implement more functional
properties, especially those ferroic orders, into two-dimensional materials.
Here GdI$_3$ is theoretically identified as a honeycomb antiferromagnet with
large $4f$ magnetic moment. The intercalation of metal atoms can dope electrons
into Gd's $5d$-orbitals, which alters its magnetic state and lead to Peierls
transition. Due to the strong electron-phonon coupling, the Peierls transition
induces prominent ferroelasticity, making it a multiferroic system. The strain
from undirectional stretching can be self-relaxed via resizing of triple
ferroelastic domains, which can protect the magnet aganist mechnical breaking
in flexible applications.",2104.05945v1
2021/5/6,Tuning magnetic and optical properties through strain in epitaxial LaCrO3 thin films,"We report on the effect of epitaxial strain on magnetic and optical
properties of perovskite LaCrO3 (LCO) single crystal thin films. Epitaxial LCO
thin films are grown by pulsed laser deposition on proper choice of substrates
to impose different strain states. A combined experimental and theoretical
approach is used to demonstrate the direct correlation between lattice-strain
and functional properties. The magnetization results show that the lattice
anisotropy plays a critical role in controlling the magnetic behavior of LCO
films. The strain induced tetragonality in the film lattice strongly affects
the optical transitions and charge transfer gap in LCO. This study opens new
possibilities to tailoring the functional properties of LCO and related
materials by strain engineering in epitaxial growth.",2105.02941v1
2021/5/9,Planar topological Hall effect in a hexagonal ferromagnetic Fe5Sn3 single crystal,"The planar topological Hall effect (PTHE), appeared when the magnetic field
tended to be along the current, is believed to result from the real-space Berry
curvature of the spin spiral structure and has been experimentally observed in
skyrmion-hosting materials. In this paper, we report an experimental
observation of the PTHE in a hexagonal ferromagnetic Fe5Sn3 single crystal.
With a current along the c axis of Fe5Sn3, the transverse resistivity curves
exhibited obvious peaks near the saturation field as the magnetic field rotated
to the current and appeared more obvious with increasing temperature, which was
related to the noncoplanar spin structure in Fe5Sn3. This spin structure
induced nonzero scalar spin chirality, which acted as fictitious magnetic
fields to conduction electrons and contributed the additional transverse
signal. These findings deepen the understanding of the interaction between
conduction electrons and complex magnetic structures and are instructive for
the design of next-generation spintronic devices.",2105.03898v1
2021/5/13,Frustrated network of indirect exchange paths between tetrahedrally coordinated Co in Ba2CoO4,"We present a detailed study of the electronic and magnetic interactions of
Ba2CoO4, structurally very uncommon because of the isolated CoO4 distorted
tetrahedral coordination. We show the presence of Co(d)-O(p) hybridized states
characterized by spin polarized oxygen atoms, with their magnetic moments
parallel to that on Co. The calculated isotropic exchange interaction
parameters, which include the contributions from ligand spins, demonstrate the
presence of a 3D network of magnetic couplings, that are partially frustrated
in the identified magnetic ground state. Our results indicate that the dominant
indirect exchange mechanism responsible for this ground state is mediated by O
atoms along the Co-O...O-Co path.",2105.06437v2
2021/5/28,Exceptional sign changes of the non-local spin Seebeck effect in antiferromagnetic hematite,"Low power spintronic devices based on the propagation of pure magnonic spin
currents in antiferromagnetic insulator materials offer several distinct
advantages over ferromagnetic components including higher frequency magnons and
a stability against disturbing external magnetic fields. In this work, we make
use of the insulating antiferromagnetic phase of iron oxide, the mineral
hematite $\alpha$-Fe$_2$O$_3$ to investigate the long distance transport of
thermally generated magnonic spin currents. We report on the excitation of
magnons generated by the spin Seebeck effect, transported both parallel and
perpendicular to the antiferromagnetic easy-axis under an applied magnetic
field. Making use of an atomistic hematite toy model, we calculate the
transport characteristics from the deviation of the antiferromagnetic ordering
from equilibrium under an applied field. We resolve the role of the magnetic
order parameters in the transport, and experimentally we find significant
thermal spin transport without the need for a net magnetization.",2105.13653v1
2021/5/30,Quartic asymmetric exchange for two-dimensional ferromagnets with trigonal prismatic symmetry,"We suggest a possible origin of noncollinear magnetic textures in
ferromagnets (FMs) with the $D_{3h}$ point group symmetry. The suggested
mechanism is different from the Dzyaloshinskii-Moriya interaction (DMI) and its
straightforward generalizations. The considered symmetry class is important
because a large fraction of all single-layer intrinsic FMs should belong to it.
In particular, so does a monolayer Fe$_3$GeTe$_2$. At the same time, DMI
vanishes identically in materials described by this point group, in the
continuous limit. We use symmetry analysis to identify the only possible
contribution to the free energy density in two dimensions that is of the fourth
order with respect to the local magnetization direction and linear with respect
to its spatial derivatives. This contribution predicts long-range conical
magnetic spirals with both the average magnetization and the average chirality
dependent on the spiral propagation direction. We relate the predicted spirals
to a recent experiment on Fe$_3$GeTe$_2$. Finally, we demonstrate that, for
easy-plane materials, the same mechanism may stabilize bimerons.",2105.14495v3
2021/5/31,Predicting Intrinsic Antiferromagnetic and Ferroelastic MnF4 monolayer with Controllable Magnetization,"Two-dimensional (2D) multiferroic materials with controllable magnetism have
promising prospects in miniaturized quantum device applications, such as
high-density data storage and spintronic devices. Here, using first-principles
calculations, we propose a coexistence of antiferromagnetism and
ferroelasticity in multiferroic $MnF_{4}$ monolayer. The $MnF_{4}$ monolayer is
found to be an intrinsic wide-gap semiconductor with large spin polarization ~3
$\mu_{B}$/Mn, in which the antiferromagnetic order originates from the
cooperation and competition of the direct exchange and super exchange.
$MnF_{4}$ monolayer is also characterized by strongly uniaxial magnetic
anisotropic behavior, that can be manipulated by the reversible ferroelastic
strain and carrier doping. Remarkably, the carrier doping not only leads to an
antiferromagnetic to ferromagnetic phase transformation, bult also could switch
the easy magnetization axis between the in-plane and out-of-plane directions.
In addition, the N\'eel temperature was evaluated to be about 140 K from the
Monte Carlo simulations based on the Heisenberg model. The combination of
antiferromagnetic and ferroelastic properties in $MnF_{4}$ monolayer provides a
promising platform for studying the magnetoelastic effects, and brings about
new concepts for next-generation nonvolatile memory and multi-stage storage.",2105.14757v1
2021/6/4,Topological superconducting domain walls in magnetic Weyl semimetals,"Recent experimental breakthrough in magnetic Weyl semimetals have inspired
exploration on the novel effects of various magnetic structures in these
materials. Here we focus on a domain wall structure which connects two uniform
domains with different magnetization directions. We study the topological
superconducting state in presence of an s-wave superconducting pairing
potential. By tuning the chemical potential, we can reach a topological state,
where a chiral Majorana mode or zero-energy Majorana bound state is localized
at the edges of the domain walls. This property allows a convenient braiding
operation of Majorana modes by controlling the dynamics of domain walls.",2106.02215v1
2021/6/7,Voltage-control of damping constant in magnetic-insulator/topological-insulator bilayers,"The magnetic damping constant is a critical parameter for magnetization
dynamics and the efficiency of memory devices and magnon transport. Therefore,
its manipulation by electric fields is crucial in spintronics. Here, we
theoretically demonstrate the voltage-control of magnetic damping in ferro- and
ferrimagnetic-insulator (FI)/topological-insulator (TI) bilayers. Assuming a
capacitor-like setup, we formulate an effective dissipation torque induced by
spin-charge pumping at the FI/TI interface as a function of an applied voltage.
By using realistic material parameters, we find that the effective damping for
a FI with 10nm thickness can be tuned by one order of magnitude under the
voltage with 0.25V. Also, we provide perspectives on the voltage-induced
modulation of the magnon spin transport on proximity-coupled FIs.",2106.03332v1
2021/6/28,On the use of magnetic particles to enhance the flow of vibrated grains through narrow apertures,"The flow of grains through narrow apertures posses an extraordinary
challenge: clogging. Strategies to alleviate the effect of clogging, such as
the use of external vibration, are always part of the design of machinery for
the handling of bulk materials. It has recently been shown that one way to
reduce clogging is to use a small fraction of small particles as an additive.
Besides, several works reported that self-repelling magnetic grains can flow
through narrow apertures with little clogging, which suggest these are
excellent candidates as ""lubricating"" additives for other granular materials.
In this work, we study the effect of adding self-repelling magnetic particles
to a sample of grains in two-dimensions. We find that, in contrast with
intuition, the added magnetic grains not necessarily aid the flow of the
original species.",2106.14864v1
2021/7/9,Magnetic structures and phase transitions of A-site Ordered Double-Perovskite SmBaMn2O6,"Magnetic structures and the relationship between spin and charge-orbital
orderings of an A-site ordered double-perovskite manganite SmBaMn2O6, an
anticipated multiferroic material, were investigated by means of neutron
diffraction. The spin arrangement in MnO2 planes perpendicular to the c axis is
revealed to be the same as that in the A-site disordered half-doped manganites
CE-type but the stacking pattern is found to be different displaying a unique
twofold period. The temperature dependence of the superlattice magnetic and
nuclear reflections clarifies that the antiferromagnetic spin ordering occurs
at a temperature slightly lower than the temperature at which a rearrangement
of the charge-orbital orderings occurs. The result evidences that the
rearrangement leads the spin ordering. The intensities of the magnetic
reflections are found to change across Tf = 10 K, suggesting a spin-flop by 90
[deg.] while keeping the Mn spin ordering pattern unchanged.",2107.04179v2
2021/7/13,Exploration of trivial and non-trivial electronic phases and of collinear and non-collinear magnetic phases in low-spin d$^5$ perovskites,"The $4d$ and $5d$ transition metal oxides have become important members of
the emerging quantum materials family due to competition between onsite Coulomb
repulsion ($U$) and spin-orbit coupling (SOC). Specifically, the systems with
$d^5$ electronic configuration in an octahedral environment are found to be
capable of posessing invariant semimetallic state and perturbations can lead to
diverse magnetic phases. In this work, by formulating a multi-band Hubbard
model and performing SOC tunable DFT+$U$ calculations on a prototype SrIrO$_3$
and extending the analysis to other iso-structural and isovalent compounds, we
present eight possible electronic and magnetic configurations in the $U$-SOC
phase diagram that can be observed in the family of low-spin $d^5$ perovskites.
They include the protected Dirac semimetal state, metal and insulator regimes,
collinear and noncollinear spin ordering. The latter is explained through
connecting hopping interactions to the rotation and tilting of the octahedra as
observed in GdFeO$_3$. Presence of several soft phase boundaries makes the
family of $d^5$ perovskites an ideal platform to study electronic and magnetic
phase transitions under external stimuli.",2107.06016v2
2021/7/17,Magnetic anisotropy and critical behavior of the quaternary van der Waals ferromagnetic material $\bf CrGe_δSi_{1-δ}Te_3$,"Recently, two-dimensional ferromagnetism in the family of Chromium compounds
$\rm CrXTe_3 (X=Si, Ge)$ has attracted a broad research interest. Despite the
structural similarity in $\rm CrTe_6$ octahedra, the size effect of inserted Ge
or Si dimer contributes to significant differences in magnetism. Here, we
report a new quaternary van der Waals ferromagnetic material $\rm
CrGe_{\delta}Si_{1-\delta}Te_3$ synthesized by flux method. Ge substitution in
Si site results in the lattice expansion, further increasing the Curie
temperature and reducing the magnetic anisotropy. The critical behavior of $\rm
Cr_{0.96}Ge_{0.17}Si_{0.82}Te_3$ has been studied by specific heat as well as
magnetization measurements. And the extracted critical exponents are
self-consistent and well-obeying the scaling laws, which are closer to the 2D
Ising model with interaction decaying as $J(r)\approx r^{-3.44}$.",2107.08222v1
2021/7/19,Broadband circularly polarized thermal radiation from magnetic Weyl semimetals,"We numerically demonstrate that a planar slab made of magnetic Weyl semimetal
(a class of topological materials) can emit high-purity circularly polarized
(CP) thermal radiation over a broad mid- and long-wave infrared wavelength
range for a significant portion of its emission solid angle. This effect
fundamentally arises from the strong infrared gyrotropy or nonreciprocity of
these materials which primarily depends on the momentum separation between Weyl
nodes in the band structure. We clarify the dependence of this effect on the
underlying physical parameters and highlight that the spectral bandwidth of CP
thermal emission increases with increasing momentum separation between the Weyl
nodes. We also demonstrate using recently developed thermal discrete dipole
approximation (TDDA) computational method that finite-size bodies of magnetic
Weyl semimetals can emit spectrally broadband CP thermal light, albeit over
smaller portion of the emission solid angle compared to the planar slabs. Our
work identifies unique fundamental and technological prospects of magnetic Weyl
semimetals for engineering thermal radiation and designing efficient CP light
sources.",2107.09185v1
2021/7/20,Superconductivity in disordered locally noncentrosymmetric materials: an application to CeRh$_2$As$_2$,"Layered three-dimensional centrosymmetric crystals can exhibit
characteristics of noncentrosymmetric materials. This happens when each
individual layer alone lacks inversion, but, when combined, inversion symmetry
is restored; hence the designation: locally noncentrosymmertic superconductors
(LNCSs). In LNCSs, the effects of impurities and subdominant magnetic field
induced pairing channels remain unexplored. Using a minimal model, we examine
all pairing channels and show that there is always a subdominant
superconducting instability that is favored at high magnetic fields, which can
substantially alter the magnetic field -- temperature phase diagram. Also, we
find that the phase diagram responds to disorder in a non-monotonic way, which
can be subjected to experimental verification. We apply these ideas to the
recently unveiled two-phase superconducting phase diagram of CeRh$_2$As$_2$. We
identify the two phases as singlet-triplet mixed even- and odd-parity states at
low and a high fields, respectively. Furthermore, we predict the presence of
two superconducting phases also for in-plane magnetic fields in cleaner
samples, since a high-field phase could have been so far hindered by impurity
effects.",2107.09723v1
2021/8/8,Exchange scaling of ultrafast angular momentum transfer in 4$\it{f}$ antiferromagnets,"Ultrafast manipulation of the magnetic state of matter bears great potential
for future information technologies. While demagnetisation in ferromagnets is
governed by dissipation of angular momentum, materials with multiple spin
sublattices, e.g. antiferromagnets, can allow direct angular momentum transfer
between opposing spins, promising faster functionality. In lanthanides,
4$\it{f}$ magnetic exchange is mediated indirectly through the conduction
electrons (the Ruderman-Kittel-Kasuya-Yosida interaction, RKKY), and the effect
of such conditions on direct spin transfer processes is largely unexplored.
Here, we investigate ultrafast magnetization dynamics in 4f antiferromagnets,
and systematically vary the 4$\it{f}$ occupation, thereby altering the
magnitude of RKKY. By combining time-resolved soft x-ray diffraction with
ab-initio calculations, we find that the rate of direct transfer between
opposing moments is directly determined by the magnitude of RKKY. Given the
high sensitivity of RKKY to the conduction electrons, our results offer a novel
approach for fine-tuning the speed of magnetic devices.",2108.03714v1
2021/8/11,Optical excitation and probing of the antiferromagnetic modes with non-uniform in-depth distribution in birefringent antiferromagnetic crystals,"Optical pump-probe setups are commonly used for excitation and investigation
of the spin dynamics in various types of magnetic materials. However, usually
the spatially homogeneous excitation is considered. In the present study we
describe an approach for optical excitation of the nonuniform THz spin dynamics
and for probing its spatial distribution inside a magnetic crystal. We propose
to illuminate a crystal with laser pulses of properly adjusted polarization to
benefit from a strong optical birefringence inherent to the crystal. It results
in an unusual behavior of the effective magnetic field generated by the pulses
due to the inverse Faraday effect and the peculiar sign-changing dependence of
the direct Faraday effect inside the crystal. The study is performed exemplary
for yttrium orthoferrite crystal although the proposed approach is applicable
for various magnetic materials with optical anisotropy.",2108.05443v2
2021/8/16,Frustration-induced diffusive scattering anomaly and dimension change in $\rm FeGe_2$,"Magnetic frustration, arising from the competition of exchange interactions,
has received great attention because of its relevance to exotic quantum
phenomena in materials. In the current work, we report an unusual
checkerboard-shaped scattering anomaly in $\rm FeGe_2$, far from the known
incommensurate magnetic satellite peaks, for the first time by inelastic
neutron scattering. More surprisingly, such phenomenon appears as spin dynamics
at low temperature, but it becomes prominent above N\'eel transition as elastic
scattering. A new model Hamiltonian that includes an intraplane next-nearest
neighbor was proposed and attributes such anomaly to the near-perfect magnetic
frustration and the emergence of unexpected two-dimensional magnetic order in
the quasi-one-dimensional $\rm FeGe_2$.",2108.06882v2
2021/9/4,Inverse Faraday effect in Mott insulators,"The inverse Faraday effect (IFE), where a static magnetization is induced by
circularly polarized light, offers a promising route to ultrafast control of
spin states. Here we study the IFE in Mott insulators using the Floquet theory.
We find two distinct IFE behavior governed by the inversion symmetry. In the
Mott insulators with inversion symmetry, we find that the effective magnetic
field induced by the IFE couples ferromagnetically to the neighboring spins.
While for the Mott insulators without inversion symmetry, the effective
magnetic field due to IFE couples antiferromagnetically to the neighboring
spins. We apply the theory to the spin-orbit coupled single- and multi-orbital
Hubbard model that is relevant for the Kitaev quantum spin liquid material and
demonstrate that the magnetic interactions can be tuned by light.",2109.01940v4
2021/10/14,Higher-order Oscillatory Planar Hall Effect in Topological Kagome Metal,"Exploration of exotic transport behavior for quantum materials is of great
interest and importance for revealing exotic orders to bring new physics. In
this Letter, we report the observation of exotic prominent planar Hall effect
(PHE) and planar anisotropic magnetoresistivity (PAMR) in strange kagome metal
KV$_3$Sb$_5$. The PHE and PAMR, which are driven by an in-plane magnetic field
and display sharp difference from other Hall effects driven by an out-of-plane
magnetic field or magnetization, exhibit exotic higher-order oscillations in
sharp contrast to those following empirical rule only allowing twofold
symmetrical oscillations. These higher-order oscillations exhibit strong field
and temperature dependence and vanish around charge density wave (CDW)
transition. The unique transport properties suggest a significant interplay of
the lattice, magnetic and electronic structure in KV$_3$Sb$_5$. This interplay
can couple the hidden anisotropy and transport electrons leading to the novel
PHE and PAMR in contrast to other materials.",2110.07538v2
2021/10/15,Tellurite glass rods with nanodiamonds as photonic magnetic field and temperature sensors,"We present the results of work on a hybrid material composed of a tellurite
glass rod doped with nanodiamonds containing nitrogen-vacancy-nitrogen and
paramagnetic nitrogen-vacancy color centers. The reported results include
details on tellurite glass and cane fabrication, confocal and wide-field
imaging of the nanodiamond distribution in their volume, as well as on the
spectroscopic characterization of their fluorescence and Optically Detected
Magnetic Resonance measurements of magnetic fields and temperatures. Magnetic
fields up to 50 G were examined with a sensitivity of 10$^{-5}$ T Hz$^{-1/2}$
whereas temperature measurements were simultaneously performed with a
sensitivity of 74 kHz K$^{-1}$ within the 8 Kelvin range at room temperature.
In that way, we demonstrate the suitability of such systems for fiber magneto-
and thermometry with a reasonable performance already in the form of glass
rods. At the same time, the rods constitute an interesting starting point for
further processing into photonic components such as microstructured fibers or
fiber tapers for the realization of specialized sensing modalities.",2110.08132v1
2021/10/17,Semiclassical Boltzmann magnetotransport theory in anisotropic systems with a nonvanishing Berry curvature,"Understanding the transport behavior of an electronic system under the
influence of a magnetic field remains a key subject in condensed matter
physics. Particularly in topological materials, their nonvanishing Berry
curvature can lead to many interesting phenomena in magnetotransport owing to
the coupling between the magnetic field and Berry curvature. By fully
incorporating both the field-driven anisotropy and inherent anisotropy in the
band dispersion, we study the semiclassical Boltzmann magnetotransport theory
in topological materials with a nonvanishing Berry curvature. We show that as a
solution to the Boltzmann transport equation the effective mean-free-path
vector is given by the integral equation, including the effective velocity
arising from the coupling between the magnetic field, Berry curvature and
mobility. We also calculate the conductivity of Weyl semimetals with an
isotropic energy dispersion, and find that the coupling between the magnetic
field and Berry curvature induces anisotropy in the relaxation time, showing a
substantial deviation from the result obtained assuming a constant relaxation
time.",2110.08816v3
2021/10/20,Spin Fluctuations Yield zT Enhancement in Ferromagnets,"Thermal fluctuation of local magnetization in magnetic metals intercoupled
with charge carriers and phonons offers a path to enhance thermoelectric
performance. The thermopower enhancement by spin fluctuations (SF) has been
observed before. However, the crucial evidence for enhancing
thermoelectric-figure-of-merit (zT) by SF has not been reported until now. Here
we report evidence for such enhancement in the ferromagnetic CrTe. The SF leads
to nearly 80% zT enhancement in ferromagnetic CrTe near and below TC~335 K. The
ferromagnetism in CrTe is originated from the collective electronic and
localized magnetic moments. The field-dependent transport properties
demonstrate the profound impact of SF on the electrons and phonons. The SF
simultaneously enhances the thermopower and reduces the thermal conductivity.
Under an external magnetic field, the enhancement in thermopower is suppressed,
and the thermal conductivity is enhanced, evidencing the existence of a strong
SF near and below TC. The anomalous thermoelectric transport properties are
analyzed based on theoretical models, and a good agreement with experimental
data is found. Furthermore, the detailed analysis proves an insignificant
impact from spin-wave contribution to the transport properties. This study
contributes to the fundamental understanding of spin fluctuation for designing
high-performance spin-driven thermoelectric materials.",2110.10798v1
2021/10/27,Staggered Pseudo Magnetic Field in Twisted Transition Metal Dichalcogenides: Physical Origin and Experimental Consequences,"Strong magnetic fields profoundly affect the quantum physics of charged
particles, as seen for example by the integer and fractionally quantized Hall
effects, and the fractal `Hofstadter butterfly' spectrum of electrons in the
presence of a periodic potential and a magnetic field. Intrinsic physics can
lead to effects equivalent to those produced by an externally applied magnetic
field. Examples include the `staggered flux' phases emerging in some theories
of quantum spin liquids and the Chern insulator behavior of twisted bilayer
graphene when valley symmetry is broken. In this paper we show that when two
layers of the transition metal dichalcogenide material WSe2 are stacked at a
small relative twist angle to form a Moire bilayer, the resulting low energy
physics can be understood in terms of electrons moving in a strong and tunable
staggered flux. We predict experimental consequences including sign reversals
of the Hall coefficient on application of an interlayer potential and spin
currents appearing at sample edges and interfaces.",2110.14570v1
2021/10/28,The dynamic chirality flips of Skyrmion bubbles,"Magnetic skyrmion, a topological magnetic domain with complex non-coplanar
spin texture, appears a disk-like structure in two dimensions. Exploring
three-dimensional spin texture and related chirality switching has drawn
enormous interests from the perspective of fundamental research. Here, the
three-dimensional magnetic moment of the skyrmion bubbles in centrosymmetric
Mn-Ni-Ga were reconstructed with the vector field tomography approach via
Lorentz transmission electron microscopy. The type of the bubbles was
determined from investigating the magnetic vectors in entire space. We found
that the bubbles switched their chirality easily but still keep the polarity to
remain the singularity of the bubbles within the material. Our results offer
valuable insights into the fundamental mechanisms underlying the spin chirality
flips dynamics of skyrmion bubbles.",2110.14898v1
2021/10/28,Curved Magnetism in CrI$_3$,"Curved magnets attract considerable interest for their unusually rich phase
diagram, often encompassing exotic (e.g., topological or chiral) spin states.
Micromagnetic simulations are playing a central role in the theoretical
understanding of such phenomena; their predictive power, however, rests on the
availability of reliable model parameters to describe a given material or
nanostructure. Here we demonstrate how non-collinear-spin polarized
density-functional theory can be used to determine the flexomagnetic coupling
coefficients in real systems. By focusing on monolayer CrI$_3$, we find a
crossover as a function of curvature between a magnetization normal to the
surface to a cycloidal state, which we rationalize in terms of effective
anisotropy and Dzyaloshinskii-Moriya contributions to the magnetic energy. Our
results reveal an unexpectedly large impact of spin-orbit interactions on the
curvature-induced anisotropy, which we discuss in the context of existing
phenomenological models.",2110.15088v3
2021/11/9,Double frustration and magneto-electro-elastic excitations in collinear multiferroic materials,"We discuss a model scenario for multiferroic systems of type II (collinear
spins) where the electric dipolar order competes with a frustrated magnetic
order in determining the elastic distortions of the lattice ion positions. High
magnetic frustration due to second neighbors exchange and small spin easy-axis
anisotropy lead to the appearance of the so called quantum magnetic plateau
states. Increasing the magnetic field above the plateau border produces
composite excitations, where fractionalized spin tertions arise together with
spontaneous dipolar flips (in the form of domain walls) and enhanced localized
elastic distortions. This peculiar magneto-electric effect may be described by
magneto-electric-elastic (MEE) quasiparticles that could be detected by X-ray
and neutron diffraction techniques. Our results are supported by extensive DMRG
computations on the spin sector and self-consistent equations for the lattice
distortions.",2111.04896v1
2021/11/9,Role of electronic excitation on the anomalous magnetism of elemental Copper,"Magnetic susceptibility of elemental copper (Cu) shows an anomalous rise at
low temperatures superimposed on the expected atypical diamagnetic response.
Such temperature dependent susceptibility, which is also known as the Curie
tail, can not be explained on the basis of Larmor diamagnetic and Pauli
paramagnetic contributions expected in Cu. Using valence band resonant
photoemission spectroscopy results and density functional theory calculations,
we show the magnetic anomaly appears due to presence of holes in Cu 3d band,
which originates from thermally excited electronic configuration. Our study
therefore highlights that the Curie tail, which is generally overlooked
presuming it either due to paramagnetic impurities or defects, can in fact be
intrinsic to a material, and even simple systems like elemental Cu is
susceptible to electronic excitations giving rise to anomalous magnetic state.",2111.05056v1
2021/12/1,Electric Field Control of Magnetism of Mn dimer supported on Carbon-doped-h-BN surface,"Using density functional theory we show that the interaction between two Mn
atoms can be tuned from anti-ferromagnetic (AFM) to ferromagnetic (FM) state by
creating charge disproportion between the two on a 2D surface. The non-metallic
planar heterostructures, the 2D surface, in our work is designed by doping
carbon hexagon rings in a hexagonal boron nitride (h-BN) sheet. In addition, we
show that an external electric field can be used to control the charge
disproportion and hence the magnetism. In fact, our calculations demonstrate
that the magnetic states of the dimer can be switched from AFM to FM or vice
versa in an external electric field. The origin of this magnetic switching is
explained using the charge transfer from (or to) the Mn dimer to (or from) the
2D material. The switching between anti-ferromagnetic to ferromagnetic states
can be useful for future spintronic applications.",2112.00638v1
2021/12/12,Thermal Hall Effect in the Kitaev-Heisenberg System with Spin-Phonon Coupling,"We investigate the thermal Hall effect in a Kitaev-Heisenberg system, a model
for Kitaev candidate $\alpha$-RuCl$_3$, in the presence of the coupling between
spin and phonon arising from chlorine atoms' vibration. We observe that the
coupling modifies the relative stability between different magnetic states
under a magnetic field, especially stabilizing a canted zigzag
antiferromagnetic state. Remarkably, the spin-phonon interaction has distinct
effects on the thermal Hall conductivity in different magnetically ordered
states. For the canted zigzag state, which is relevant to
$\alpha\text{-RuCl}_3$, the spin-phonon interaction enhances the energy gap
that is induced by a magnetic field and suppresses the thermal Hall
conductivity at low temperatures. Importantly, we find that the spin-phonon
interaction destabilizes the quantized thermal Hall effect in the spin-liquid
state. Our results demonstrate a crucial role of phonon degrees of freedom to
the thermal Hall effect in Kitaev materials.",2112.06107v2
2022/1/11,Perpendicular magnetic tunnel junctions with multi-interface free layer,"Future generations of magnetic random access memory demand magnetic tunnel
junctions that can provide simultaneously high magnetoresistance, strong
retention, low switching energy and small cell size below 10nm. Here we study
perpendicular magnetic tunnel junctions with composite free layers where
multiple ferromagnet/nonmagnet interfaces can contribute to the thermal
stability. Different nonmagnetic materials (MgO, Ta, Mo) have been employed as
the coupling layers in these multi-interface free layers. The evolution of
junction properties under different annealing conditions is investigated. A
strong dependence of tunneling magnetoresistance on the thickness of the first
CoFeB layer has been observed. In junctions where Mo and MgO are used as
coupling layers, large tunneling magnetoresistance above 200% has been achieved
after 400{\deg}C annealing.",2201.03798v1
2022/1/11,Graphene Lattices with Embedded Transition-Metal Atoms and Tunable Magnetic Anisotropy Energy: Implications for Spintronic Devices,"Doping of the graphene lattice with transition metal atoms resulting in high
magnetic anisotropy energy (MAE) is an important goal of materials research
owing to its potential application in spintronics. In this article, by using
spin-polarized density functional theory including spin-orbit coupling, we
examined magnetic properties of graphene with vacancy defects, both bare and
nitrogen-decorated, and doped by Cr, Mn and Fe transition metal single atom
(TM-SA) and two different TM atoms simultaneously. [...] The computational
findings are supplemented by an atomic-resolution characterization of an
incidental Mn impurity bonded to four carbon atoms, whose localized spin
matches expectations as measured using core-level electron energy-loss
spectroscopy. Conducting TM-doped graphene with robust magnetic features offers
prospects for the design of graphene-based spintronic devices.",2201.03867v1
2022/1/18,Terahertz electron paramagnetic resonance generalized spectroscopic ellipsometry: The magnetic response of the nitrogen defect in 4H-SiC,"We report on terahertz (THz) electron paramagnetic resonance generalized
spectroscopic ellipsometry (THz-EPR-GSE). Measurements of the field and
frequency dependencies of the magnetic response due to the spin transitions
associated with the nitrogen defect in 4H-SiC are shown as an example.
THz-EPR-GSE dispenses with the need of a cavity, permits independently scanning
field and frequency parameters, and does not require field or frequency
modulation. We investigate spin transitions of hexagonal ($h$) and cubic ($k$)
coordinated nitrogen including coupling with its nuclear spin (I=1), and we
propose a model approach for the magnetic susceptibility to account for the
spin transitions. From the THz-EPR-GSE measurements we can fully determine the
polarization properties of the spin transitions and we obtain $g$ and hyperfine
splitting parameters using magnetic field and frequency dependent Lorentzian
oscillator lineshape functions. We propose frequency-scanning THz-EPR-GSE as a
new and versatile method to study properties of spins in solid state materials.",2201.06695v1
2022/1/20,Spin valve effect in two-dimensional VSe$_2$ system,"Vanadium based dichalcogenides, VSe$_2$, are two-dimensional materials in
which magnetic Vanadium atoms are arranged in a hexagonal lattice and are
coupled ferromagnetically within the plane. However, adjacent atomic planes are
coupled antiferromagnetically. This provides new and interesting opportunities
for application in spintronics and data storage and processing technologies. A
spin valve magnetoresistance may be achieved when magnetic moments of both
atomic planes are driven to parallel alignment by an external magnetic field.
The resistance change associated with the transition from antiparallel to the
parallel configuration is qualitatively similar to that observed in
artificially layered metallic magnetic structures. Detailed electronic
structure of VSe$_2$ was obtained from DFT calculations. Then, the ballistic
spin-valve magnetoresistance was determined within the Landauer formalism. In
addition, we also analyze thermal and thermoelectric properties. Both phases of
VSe$_2$, denoted as H and T, are considered.",2201.08420v1
2022/2/11,Unusual electrical and magnetic properties in layered EuZn2As2,"Eu-based compounds often exhibit unusual magnetism, which is critical for
nontrivial topological properties seen in materials such as EuCd2As2. We
investigate the structure and physical properties of EuZn2As2 through
measurements of the electrical resistivity, Hall effect, magnetization, and
neutron diffraction. Our data show that EuZn2As2 orders antiferromagnetically
with an A-type spin configuration below TN = 19 K. Surprisingly, there is
strong evidence for dominant ferromagnetic fluctuations above TN, as reflected
by positive Curie-Weiss temperature and extremely large negative
magnetoresistance (MR) between TN and Tfl {\guillemotright} 200 K. Furthermore,
the angle dependence of the MRab indicates field-induced spin reorientation
from the ab-plane to a direction approximately 45{\deg} from the ab plane.
Compared to EuCd2As2, the doubled TN and Tfl make EuZn2As2 a better platform
for exploring topological properties in both magnetic fluctuation (TN < T <
Tfl) and ordered (T < TN) regimes.",2202.05884v1
2022/2/14,Magnetic orderings from spin-orbit coupled electrons on kagome lattice,"We investigate magnetic orderings on kagome lattice numerically from the
tight-binding Hamiltonian of electrons, governed by the filling factor and
spin-orbit coupling (SOC) of electrons. We find that even a simple kagome
lattice model can host both ferromagnetic and noncollinear antiferromagnetic
orderings depending on the electron filling, reflecting gap structures in the
Dirac and flat bands characteristic to the kagome lattice. Kane--Mele- or
Rashba-type SOC tends to stabilize noncollinear orderings, such as magnetic
spirals and 120-degree antiferromagnetic orderings, due to the effective
Dzyaloshinskii--Moriya interaction from SOC. The obtained phase structure helps
qualitative understanding of magnetic orderings in various kagome-layered
materials with Weyl or Dirac electrons.",2202.06665v1
2022/2/21,Exploration of the spin-phonon coupling in the noncollinear antiferromagnetic antiperovskite Mn$_3$NiN,"Antiferromagnetic antiperovskites, of the form Mn$_3B$N ($B$ = Ni, Cu, Zn,
Sn, Ir, and Pt), have shown an outstanding behavior in which, giant negative
thermal expansion and chiral magnetic structures are intertwined. As such,
aiming to shed light on the magnetostructural behavior, related to the magnetic
ordering and structure of this type of materials, we studied by theoretical
first-principles calculations the spin-phonon coupling in the Manganese-based
antiperovskite Mn$_3$NiN, as a prototype in the Mn$_3B$N family. We found a
strong spin-lattice coupling by means of the understanding of the
phonon-dispersion curves obtained when including the chiral noncollinear
magnetic structure. To do so, we highlight the importance of the
exchange-correlation scheme selected and its influence on the electronic,
structural, and vibrational degrees of freedom. Finally, we found two unstable
vibrational modes at the $M$- and $R$-points when the magnetic ordering is
switched to ferromagnetic from the chiral $\Gamma_{4g}$ and $\Gamma_{5g}$. The
latter coupling was observed as a key signature of the strong spin-lattice
interaction.",2202.10544v1
2022/2/22,Magnetic properties of equiatomic CrMnFeCoNi,"Magnetic, specific heat, and structural properties of the equiatomic Cantor
alloy system are reported for temperatures between 5 kelvin and 300 kelvin, and
up to fields of 70 kilo-oersted. Magnetization measurements performed on
as-cast, annealed, and cold-worked samples reveal a strong processing history
dependence and that high-temperature annealing after cold-working does not
restore the alloy to a pristine state. Measurements on known precipitates show
that the two transitions, detected at 43 kelvin and 85 kelvin, are intrinsic to
the Cantor alloy and not the result of an impurity phase. Experimental and ab
initio density functional theory (DFT) computational results suggest that these
transitions are a weak ferrimagnetic transition and a spin-glass-like
transition, respectively, and magnetic and specific heat measurements provide
evidence of significant Stoner enhancement and electron-electron interactions
within the material.",2202.11073v1
2022/2/23,Ferroelectric control of magnetic skyrmions in two-dimensional van der Waals heterostructures,"Magnetic skyrmions are chiral nanoscale spin textures which are usually
induced by Dzyaloshinskii-Moriya interaction (DMI). Recently, magnetic
skyrmions have been observed in two-dimensional (2D) van der Waals (vdW)
ferromagnetic materials, such as Fe$_{3}$GeTe$_{2}$. The electric control of
skyrmions is important for their potential application in low-power memory
technologies. Here, we predict that DMI and magnetic skyrmions in a
Fe$_{3}$GeTe$_{2}$ monolayer can be controlled by ferroelectric polarization of
an adjacent 2D vdW ferroelectric In$_{2}$Se$_{3}$. Based on density functional
theory and atomistic spin-dynamics modeling, we find that the interfacial
symmetry breaking produces a sizable DMI in a
Fe$_{3}$GeTe$_{2}$/In$_{2}$Se$_{3}$ vdW heterostructure. We show that the
magnitude of DMI can be controlled by ferroe-lectric polarization reversal,
leading to creation and annihilation of skyrmions. Furthermore, we find that
the sign of DMI in a In$_{2}$Se$_{3}$/Fe$_{3}$GeTe$_{2}$/In$_{2}$Se$_{3}$
heterostructure changes with ferroelectric switching reversing the skyrmion
chirality. The predicted electrically controlled skyrmion formation may be
interesting for spintronic applications.",2202.11348v2
2022/3/3,Electron correlations and charge density wave in the topological kagome metal FeGe,"Charge order in kagome metals is of extensive current interest. Recently, a
charge density wave was discovered in the magnetic binary kagome metal FeGe. In
analogy to its predecessor, the non-magnetic $A$V$_3$Sb$_5$ ($A$=K, Cs, Rb),
the in-plane ordering occurs at the $M$ point. In contrast, however, the system
manifestly shows effects of substantial correlations. Here we identify the
topological bands crossing the Fermi energy (E$_F$) in FeGe and characterize
the correlation-induced renormalization of these bands. We then derive a charge
order from an effective model comprising topological kagome `flat' bands in the
presence of a magnetic order. We demonstrate edge states as well as excess
out-of-plane magnetic moment associated with the charge order; both are
fingerprints of non-trivial band topology and consistent with recent
experimental observations. Our results point to FeGe as an ideal platform to
realize and elucidate correlated topological physics.",2203.01930v1
2022/3/11,Magnetic anisotropy energies and metal-insulator transitions in monolayers of $α$-RuCl$_3$ and OsCl$_3$ on graphene,"Transition metal thriclorides, with $4d$ or $5d$ electrons, are materials at
the forefront of recent studies about the interplay of spin-orbit coupling and
strong Coulomb interactions. Within our first-principles calculations
(DFT+$U$+SOC) we study the effects of graphene on the electronic and magnetic
properties of the monolayers of $\alpha$-RuCl$_3$ and OsCl$_3$. Despite the
spatially inhomogeneous $n$-type doping induced by graphene, we show that the
occupancy of the upper Hubbard bands of MLs of \rucl and OsCl$_3$ can be tuned
through external electric fields, and allows the control of (i) metal-insulator
transitions, and (ii) the magnetic easy-axis and anisotropy energies. Our
findings point towards the tunning of electronic and magnetic properties of
transition metal thriclorides monolayers by using graphene and external
electronic fields.",2203.06052v1
2022/3/23,Dipolar Magnetic Interactions and A-type Antiferromagnetic Order in the Zintl Phase Insulator EuZn2P2,"Zintl phases, containing strongly covalently bonded frameworks with separate
ionically bonded ions, have emerged as a critical materials family in which to
couple magnetism and strong spin-orbit coupling to drive diverse topological
phases of matter. Here we report the single-crystal synthesis, magnetic,
thermodynamic, transport, and theoretical properties of the Zintl compound
EuZn2P2 that crystallizes in the anti-La2O3 P-3m1 structure, containing
triangular layers of Eu2+ ions. In-plane resistivity measurements reveal
insulating behavior with an estimated bandgap of Eg=0.11eV. Comparing Eu
magnetic ordering temperatures across trigonal EuM2X2 (M=divalent metal,
X=pnictide) shows that EuZn2P2 exhibits the highest ordering temperature, with
variations in TN correlating with changes in expected dipolar interaction
strengths within and between layers and independent of the magnitude of
electrical conductivity. These results provide experimental validation of the
cytochemical intuition that the cation Eu2+ layers and the anionic (M2X2)2-
framework can be treated as electronically distinct subunits, enabling further
predictive materials design.",2203.12739v1
2022/3/27,Making a case for femto- phono- magnetism with FePt,"In the field of femtomagnetism magnetic matter is controlled by ultrafast
laser pulses; here we show that coupling phonon excitations of the nuclei to
spin and charge leads to femto-phono-magnetism, a powerful route to control
magnetic order at ultrafast times. With state-of-the-art theoretical
simulations of coupled spin-, charge-, and lattice-dynamics we identify strong
non-adiabatic spin-phonon coupled modes that dominate early time spin dynamics.
Activating these phonon modes we show leads to an additional (up to 40\% extra)
loss of moment in FePt occurring within 40 femtoseconds of the pump laser
pulse. Underpinning this enhanced ultrafast loss of spin moment we identify a
physical mechanism in which minority spin-current drives an enhanced inter-site
minority charge transfer, in turn promoting increased on-site spin flips. Our
finding demonstrates that the nuclear system, often assumed to play only the
role of an energy sink aiding long time re-magnetisation of the spin system,
can play a profound role in controlling femtosecond spin-dynamics in materials.",2203.14234v1
2022/4/9,What is measured when measuring a thermoelectric coefficient?,"A thermal gradient generates an electric field in any solid hosting mobile
electrons. In presence of a finite magnetic field (or Berry curvature) this
electric field has a transverse component. These are known as Seebeck and
Nernst coefficients. As Callen argued, back in 1948, the Seebeck effect
quantifies the entropy carried by a flow of charged particles in absence of
thermal gradient. Similarly, the Nernst conductivity, $\alpha_{xy}$, quantifies
the entropy carried by a flow of magnetic flux in absence of thermal gradient.
The present paper summarizes a picture in which the rough amplitude of the
thermoelectric response is given by fundamental units and material-dependent
length scales. Therefore, knowledge of material-dependent length scales allows
predicting the amplitude of the signal measured by experiments. Specifically,
the Nernst conductivity scales with the square of the mean-free-path in metals.
Its anomalous component in magnets scales with the square of the fictitious
magnetic length. Ephemeral Cooper pairs in the normal state of a superconductor
generate a signal, which scales with the square of the superconducting
coherence length and smoothly evolves to the signal produced by mobile vortices
below the critical temperature.",2204.04429v1
2022/4/27,"Infrared study of the layered, magnetic insulator Mn(Bi$_{0.07}$Sb$_{0.93}$)$_2$Te$_4$ at low temperatures","Topological insulators with intrinsic magnetic ordering, potentially hosting
rare quantum effects, recently attracted extensive attention. MnBi$_2$Te$_4$ is
the first established example. The Sb-doped variant
Mn(Bi$_{1-x}$Sb$_x$)$_2$Te$_4$ shows a great variety of electronic properties
depending on the Sb content~$x$, such as shifts in the Fermi level and the Neel
temperature $T_{\mathrm N}$, and the change of the free charge carrier type
from $n$- to $p$-type at high Sb substitution ratios. Here, we investigate the
effect of magnetic ordering on the bulk electronic structure of
Mn(Bi$_{1-x}$Sb$_x$)$_2$Te$_4$ with high Sb content $x=0.93$ by
temperature-dependent reflectivity measurements over a broad frequency range.
We observe anomalies in the optical response across $T_{\mathrm N}$ when the
antiferromagnetic order sets, which suggests a coupling between the magnetic
ordering and the electronic structure of the material.",2204.12843v1
2022/6/1,Spectral Recognition of Magnetic Nanoparticles with Artificial Neural Networks,"Ferromagnetic resonance (FMR) spectroscopy is a powerful method for
quantifying internal magnetic anisotropy fields in nanoparticles, which is
important in a wide range of biomedical and storage applications. The
interpretation of FMR spectra, however, can only be achieved with the use of an
appropriate model, and no inverse methods are available to extract internal
fields from FMR spectra. Here, we present the use of artificial neural networks
for spectral recognition, i.e., to identify the internal magnetic anisotropy
field from the FMR spectrum. We trained two different types of networks, a
convolutional neural network and a multi-layer perceptron, by feeding the
networks pre-computed FMR spectra labeled with the corresponding anisotropy
fields. Testing of the trained networks with unseen spectra showed that they
successfully predict the correct anisotropy fields and, surprisingly, the
networks performed well for data that was beyond their training range. These
results show the promise of using artificial neural networks for accelerated
high-throughput analysis of magnetic materials and nanostructures; for example
they could serve in automatizing and optimizing exploration missions where
nanomagnetic signals are often used as proxies.",2206.00166v1
2022/6/15,Magnetic Bloch Theorem and Reentrant Flat Bands in Twisted Bilayer Graphene at $2π$ Flux,"Bloch's theorem is the centerpiece of topological band theory, which itself
has defined an era of quantum materials research. However, Bloch's theorem is
broken by a perpendicular magnetic field, making it difficult to study
topological systems in strong flux. For the first time, moir\'e materials have
made this problem experimentally relevant, and its solution is the focus of
this work. We construct gauge-invariant irreps of the magnetic translation
group at $2\pi$ flux on infinite boundary conditions, allowing us to give
analytical expressions in terms of the Siegel theta function for the magnetic
Bloch Hamiltonian, non-Abelian Wilson loop, and many-body form factors. We
illustrate our formalism using a simple square lattice model and the
Bistritzer-MacDonald Hamiltonian of twisted bilayer graphene, obtaining
reentrant ground states at $2\pi$ flux under the Coulomb interaction.",2206.07717v3
2022/6/17,Large non-reciprocal charge transport in Pt2MnGe up to room temperature,"Non-reciprocal charge transport that is strongly associated with the
structural or magnetic chirality of the quantum materials system is one of the
most exotic properties of condensed matter physics. Here, using magnetic alloys
film Pt2MnGe, we have realized the large non-reciprocal charge transport up to
room temperature, which roots in the organic combination of chirality dependent
carrier scattering and special magnetic configurations. In this framework, the
conduction electrons are scattered asymmetrically by the emerging non-zero
vector spin chirality under in-plane magnetic field, resulting in robust
non-reciprocal response. More astonishingly, the vector spin chirality in
Pt2MnGe film can be reversed by a spin-polarized current through spin Hall
effect in a junction with Pt layer. Our work resolves the general limitation of
non-reciprocal charge transport to cryogenic temperatures, and paves the way
for extending its applications in the emerging field of chiral spintronics.",2206.08498v1
2022/7/8,Unraveling the nature of thermally induced spin reorientation in NdFe1-xCrxO3,"Understanding spin control mechanisms is an important part of condensed
matter physics and the theoretical basis for designing spintronic devices. In
this letter, based on four-sublattices molecular field theory, we propose that
the underlying NdFe1-xCrxO3 magnetic mechanism is driven by spin reorientation
sensitive to temperature. The actual coupling angular momentum, angle between
the Nd3+ and Cr3+/Fe3+ moments at the given temperature is realized via the
Nd3+ magnetic moment projection onto the Cr3+/Fe3+ plane. As the temperature
increases, the angle between the moment of Nd3+ and the moment of Cr3+/Fe3+
decreases monotonically. In this work, the magnetic mechanism of NdFe1-xCrxO3
(x=0.1, 0.9), the close relationship between A/B angle and temperature are
presented, which laid a theoretical foundation for the design of new
multifunctional magnetic materials.",2207.03646v1
2022/7/22,Frustrated magnetic interactions in FeSe,"The structurally simplest high-temperature superconductor FeSe exhibits an
intriguing superconducting nematic paramagnetic phase with unusual spin
excitation spectra that are different from typical spin waves; thus,
determining its effective magnetic exchange interactions is challenging. Here
we report neutron scattering measurements of spin fluctuations of FeSe in the
tetragonal paramagnetic phase. We show that the equal-time magnetic structure
factor, $\mathcal{S}(\textbf{Q})$, can be effectively modeled using the
self-consistent Gaussian approximation calculation with highly frustrated
nearest-neighbor ($J_{1}$) and next-nearest-neighbor ($J_{2}$) exchange
couplings, and very weak further neighbor exchange interaction. Our results
elucidate the frustrated magnetism in FeSe, which provides a natural
explanation for the highly tunable superconductivity and nematicity in FeSe and
related materials.",2207.10981v1
2022/7/26,$\textit{Ab initio}$ description of magnetic properties of spin-glass pyrochlore NaSrMn$_{2}$F$_{7}$,"In this study, I have investigated the magnetic and critical properties of
manganese pyrochlore fluoride NaSrMn$_{2}$F$_{7}$, which exhibits a glass
transition at T$_\text{f}$$=$2.5 (K) due to charge disorder. A DFT+$U$+SOC
framework is used in this paper to derive spin-Hamiltonian terms, including
isotropic and anisotropic exchange interactions. An optimized geometry reveals
a local distortion of the F-Mn-F angle along the $ < $111$ > $ direction
(95.48$^{\circ}$ and 84.51$^{\circ}$), which is considered a weak bond disorder
($\delta J$). In spite of the complex structure of this material, first
principle calculations show that its magnetic properties are only controlled by
the nearest neighbor's Heisenberg exchange interaction, and other interactions
do not affect spin arrangements in the ground state. Thus, this material is
considered a suitable candidate for studying electron correlation in spin
glasses. Using a replica-exchange framework, Monte Carlo simulations indicate
that no phase transition is observed when magnetic susceptibility changes with
temperature. Based on $\delta J$ and the spin Hamiltonian, 2.6 (K) is obtained
as the phase transition temperature.",2207.12968v3
2022/7/27,Selectively controlled ferromagnets by electric fields in van der Waals ferromagnetic heterojunctions,"Charge transfer plays a key role at the interfaces of heterostructures, which
can affect electronic structures and ultimately the physical properties of the
materials. However, charge transfer is difficult to manipulate externally once
the interface formed. Here, we report electrically tunable charge transfer in
Fe3GeTe2/Cr2Ge2Te6/Fe3GeTe2 all-magnetic van der Waals heterostructures, which
can be exploited to selectively modify the magnetic properties of the top or
bottom Fe3GeTe2 electrodes. The directional charge transfer from metallic
Fe3GeTe2 to semiconducting Cr2Ge2Te6 remarkably modifies magnetic anisotropy
energy of Fe3GeTe2, leading to the dramatically suppressed coercivity. The
electrically selective control of ferromagnets demonstrated in this study could
stimulate the development of spintronic devices based on van der Waals magnets.",2207.13338v1
2022/8/1,Two-Dimensional Organic-Inorganic Room-Temperature Multiferroic,"Organic-inorganic multiferroics are promising for the next generation of
electronic devices. To date, dozens of organic-inorganic multiferroics have
been reported; however, most of them show magnetic Curie temperature much lower
than room temperature, which drastically hampers their application. Here, by
performing first-principle calculations and building effective model
Hamiltonians, we reveal a molecular orbital-mediated magnetic coupling
mechanism in two-dimensional Cr(pyz)2 (pyz=pyrazine), and the role that the
valence state of the molecule plays in determining the magnetic coupling type
between metal ions. Based on these, we demonstrate that a two-dimensional
organic-inorganic room-temperature multiferroic, Cr(h-fpyz)2 (h-fpyz=
half-fluoropyrazine), can be rationally designed by introducing
ferroelectricity in Cr(pyz)2 while keeping the valence state of the molecule
unchanged. Our work not only reveals the origin of magnetic coupling in 2D
organic-inorganic systems, but also provides a way to design room temperature
multiferroic materials rationally.",2208.00591v1
2022/8/18,Short-range Crystalline Order-Tuned Conductivity in Cr$_2$Si$_2$Te$_6$ van der Waals Magnetic Crystals,"Two-dimensional magnetic materials (2DMM) are significant for studies on the
nature of 2D long range magnetic order but also for future spintronic devices.
Of particular interest are 2DMM where spins can be manipulated by electrical
conduction. Whereas Cr$_2$Si$_2$Te$_6$ exhibits magnetic order in few-layer
crystals, its large band gap inhibits electronic conduction. Here we show that
the defect-induced short-range crystal order in Cr$_2$Si$_2$Te$_6$ on the
length scale below 0.6 nm induces substantially reduced band gap and robust
semiconducting behavior down to 2 K that turns to metallic above 10 GPa. Our
results will be helpful to design conducting state in 2DMM and call for
spin-resolved measurement of the electronic structure in exfoliated ultrathin
crystals.",2208.08648v1
2022/8/22,Nonlinear transport due to magnetic-field-induced flat bands in the nodal-line semimetal ZrTe5,"The Dirac material ZrTe$_5$ at very low carrier density was recently found to
be a nodal-line semimetal, where ultra-flat bands are expected to emerge in
magnetic fields parallel to the nodal-line plane. Here we report that in very
low carrier-density samples of ZrTe$_5$, when the current and the magnetic
field are both along the crystallographic $a$ axis, the current-voltage
characteristics presents a pronounced nonlinearity which tends to saturate in
the ultra quantum limit. The magnetic-field dependence of the nonlinear
coefficient is well explained by the Boltzmann theory for flat-band transport,
and we argue that this nonlinear transport is likely due to the combined effect
of flat bands and charge puddles, the latter appear due to very low carrier
densities.",2208.10314v3
2022/9/2,Magnetic phase diagram and possible Kitaev-like behavior of honeycomb-lattice antimonate Na3Co2SbO6,"Recent theoretical studies have suggested that Kitaev physics and such
effects as formation of a mysterious spin-liquid state can be expected not only
in RuCl3 and iridates, but also in conventional $3d$ transition metal
compounds. Using DC and AC magnetometry, thermodynamic and $^{23}$Na nuclear
magnetic resonance measurements (NMR) we studied such a candidate material
Na3Co2SbO6. A full phase diagram of Na3Co2SbO6 in a wide range of magnetic
fields and temperatures is presented. The results demonstrate transformation of
the antiferromagnetic structure under the external magnetic field, gradual
development of the saturation phase, as well as evidence of gapped behavior in
certain parts of the phase diagram",2209.00846v2
2022/9/13,Topological magnons in Kitaev magnets with finite Dzyaloshinskii-Moriya interaction at high field,"There have been intensive studies on Kitaev materials for the sake of the
realization of exotic states such as quantum spin liquid and topological
orders. In realistic materials, the Kitaev interaction may coexist with the
Dzyaloshinskii-Moriya interaction (DMI), and it is a challenge to distinguish
their magnitudes separately. Here, we study the topological magnon excitations
and related thermal Hall conductivity of kagome magnet exhibiting Heisenberg,
Kitaev and DM interactions exposed to a magnetic field. In a strong magnetic
field perpendicular to the plane of the lattice ([111] direction) that bring
the system into the fully polarized paramagnetic phase, we find that the magnon
bands carry nontrivial Chern numbers in the full region of the phase diagram.
Furthermore, there are phase transitions relate two topological phases with
opposite Chern numbers, which lead to the sign changes of the thermal Hall
conductivity. In the phase with negative thermal conductivity, the Kitaev
interaction is relatively large and the width of the phase increases with the
strength of DMI. Hence the study here will contribute to the understanding of
related compounds.",2209.05813v1
2022/9/22,Spin wave study of magnetic perpendicular surface anisotropy in single crystalline MgO$\text{/}$Fe$\text{/}$MgO films,"Broadband ferromagnetic resonance is measured in single crystalline Fe films
of varying thickness sandwiched between MgO layers. An exhaustive magnetic
characterization of the films (exchange constant, cubic, uniaxial and surface
anisotropies) is enabled by the study of the uniform and the first
perpendicular standing spin wave modes as a function of applied magnetic field
and film thickness. Additional measurements of non-reciprocal spin wave
propagation allow us to separate each of the two interface contributions to the
total surface anisotropy. The results are consistent with the model of a
quasi-bulk film interior and two magnetically different top and bottom
interfaces, a difference ascribed to different oxidation states.",2209.10906v2
2022/10/7,"Anisotropic magnetic properties and tunable conductivity in two-dimensional layered NaCrX2 (X=Te,Se,S) single crystals","Monolayer NaCrX2 (X=Te,Se,S) were theoretically proposed to be
two-dimensional intrinsic ferromagnetic semiconductors while their physical
properties have not been thoroughly investigated in bulk single crystals. We
report the single-crystal growth, structural, magnetic and electronic transport
properties of NaCr(Te1-xSex)2 (0 6 x 6 1) and NaCrS2. For NaCr(Te1-xSex)2, the
strong perpendicular magnetic anisotropy of NaCrTe2 can be gradually tuned to
be a nearly isotropic one by Se-doping. Meanwhile, a systematic change in the
conductivity with increasing x is observed, displaying a doping-induced
metal-insulator-like transition. Under magnetic field larger than 30 koe, both
NaCrTe2 and NaCrSe2 can be polarized to a ferromagnetic state. While for
NaCrS2, robust antiferromagnetism is observed up to 70 kOe and two
field-induced metamagnetic transitions are identified along H||ab. These
intriguing properties together with the potential to be exfoliated down to
few-layer thickness make NaCrX2 (X=Te,Se,S) promising for exploring spintronic
applications.",2210.03420v1
2022/10/25,Observation of Giant Orbital Magnetic Moments and Paramagnetic Shift in Artificial Relativistic Atoms and Molecules,"Massless Dirac fermions have been observed in various materials such as
graphene and topological insulators in recent years, thus offering a
solid-state platform to study relativistic quantum phenomena. Single quantum
dots (QDs) and coupled QDs formed with massless Dirac fermions can be viewed as
artificial relativistic atoms and molecules, respectively. Such structures
offer a unique platform to study atomic and molecular physics in the
ultra-relativistic regime. Here, we use a scanning tunneling microscope to
create and probe single and coupled electrostatically defined graphene QDs to
unravel the unique magnetic field responses of artificial relativistic
nanostructures. Giant orbital Zeeman splitting and orbital magnetic moment are
observed in single graphene QDs. While for coupled graphene QDs, Aharonov Bohm
oscillations and strong Van Vleck paramagnetic shift are observed. Such
properties of artificial relativistic atoms and molecules can be leveraged for
novel magnetic field sensing modalities.",2210.14256v1
2022/10/27,Electron-phonon mediated spin-flip as driving mechanism for ultrafast magnetization dynamics in 3$d$ ferromagnets,"Despite intense experimental effort, theoretical proposals and modeling
approaches, a lack of consensus exists about the intrinsic mechanisms driving
ultrafast magnetization dynamics in 3$d$ ferromagnets. In this work, we find
evidence of electron-phonon mediated spin-flip as the driving mechanism for the
ultrafast magnetization dynamics in all three 3$d$ ferromagnets; nickel, iron
and cobalt. We use a microscopic three temperature model with parameters
calculated from first-principles, which has been validated by direct comparison
to the electron and lattice dynamics extracted from previous experiments. By
direct comparison to the experimentally measured magnetization dynamics for
different laser fluence, we determine the spin-flip probability of each
material. In contrast to previous findings but in agreement to ab-initio
predictions, we find that relatively small values of the spin-flip probability
enable ultrafast demagnetization in all three 3$d$ ferromagnets.",2210.15269v1
2022/11/1,Strongly nonlinear antiferromagnetic dynamics in high magnetic fields,"Antiferromagnetic (AFM) materials possess a well-recognized potential for
ultrafast data processing thanks to their intrinsic ultrafast spin dynamics,
absence of stray fields, and large spin transport effects. The very same
properties, however, make their manipulation difficult, requiring frequencies
in THz range and magnetic fields of tens of Teslas. Switching of AFM order
implies going into the nonlinear regime, a largely unexplored territory. Here
we use THz light from a free electron laser to drive antiferromagnetic NiO into
a highly nonlinear regime and steer it out of nonlinearity with magnetic field
from a 33-Tesla Bitter magnet. This demonstration of large-amplitude dynamics
represents a crucial step towards ultrafast resonant switching of AFM order.",2211.00353v1
2022/11/11,Small-angle neutron scattering of long-wavelength magnetic modulations in reduced sample dimensions,"Magnetic small-angle neutron scattering (SANS) is ideally suited to provide
direct, reciprocal-space information of long-wavelength magnetic modulations,
such as helicoids, solitons, merons, or skyrmions. SANS of such structures in
thin films or micro-structured bulk materials is strongly limited by the tiny
scattering volume vis a vis the prohibitively large background scattering by
the substrate and support structures. Considering near-surface scattering
closely above the critical angle of reflection, where unwanted signal
contributions due to substrate or support structures becomes very small, we
establish equivalent scattering patterns of the helical, conical, skyrmion
lattice, and fluctuation-disordered phases in a polished bulk sample of MnSi
between conventional transmission and near-surface SANS geometries. This
motivates the prediction of a complete repository of scattering patterns
expected for thin films in the near-surface SANS geometry for each orientation
of the magnetic order with respect to the scattering plane.",2211.06006v1
2022/11/30,Strain driven antiferromagnetic exchange interaction in SrMnO$_3$ probed by phase shifted Spin Hall magnetoresistance,"Multiferroics have found renewed interest in topological magnetism and for
logic-in-memory applications. Among them, SrMnO$_{3}$, possessing strong
magnetoelectric coupling is gaining attention for the design of coexisting
magnetic and polar orders upon straining. Here we demonstrate antiferromagnetic
exchange interactions in strained SMO thin films extracted from a new feature
in the phase response of Spin Hall magnetoresistance, which has not been
explored in earlier works, such as in magnetic insulators. We explain our
findings with a model that incorporates magnetic anisotropy along [110]
direction, corroborates with DFT studies and is consistent with the direction
of ferroelectric polarization in SrMnO$_{3}$. The fundamental insights obtained
from our studies establishes the potential of this material in
magnetoelectrically coupled devices for different logic and memory
applications.",2211.16888v1
2022/12/6,Dynamics of hybrid magnetic skyrmion driven by spin-orbit torque in ferrimagnets,"Magnetic skyrmions are magnetic textures with topological protection, which
are expected to be information carriers in future spintronic devices. In this
work, we propose a scheme to implement hybrid magnetic skyrmions (HMS) in
ferrimagnets, and we study theoretically and numerically the dynamics of the
HMS driven by spin-orbit torque. It is revealed that the skyrmion Hall effect
depends on the skyrmion helicity and the net angular momentum ({\delta}s),
allowing the effective modulation of the HMS motion through tuning
Dzyaloshinskii-Moriya interaction and {\delta}s. Thus, the Hall effect can be
suppressed through selecting suitable materials to better control the HMS
motion. Moreover, Magnus force for finite {\delta}s suppresses the transverse
motion and enhances the longitudinal propagation, resulting in the HMS dynamics
in ferrimagnets faster than that in antiferromagnets.",2212.02807v1
2022/12/30,Unique determination of localized basis in molecular spin,"Localized basis plays an important role in comprehending the magnetic
dynamics in molecular spins from a physics perspective. Nonetheless, the
uniqueness and rigor of its determination have received limited attention. In
this study, we propose a new determination of the localized basis applicable to
both non-Kramers and Kramers molecular spin systems, leveraging the
time-reversal symmetry of the spin Hamiltonian and the molecular spin's main
magnetic axis. By introducing this, we establish a distinct and practical means
of determining the localized basis, enabling the association of a molecular
spin wave function with either an ""up"" or ""down"" magnetic moment orientation in
molecular spins. This finding facilitates a comprehensive interpretation of
magnetic dynamics and simplifies the construction of theoretical models for
materials analysis.",2212.14639v3
2023/1/6,"Spin Transport in Magnetically Ordered Systems: Ferromagnets, Antiferromagnets and Frustrated Systems","In this review, we outline the important results on the resistivity
encountered by an electron in magnetically ordered materials. The mechanism of
the collision between the electron and the lattice spins is shown. Experiments
on the spin resistivity in various magnetic materials as well as theoretical
background are recalled. We focus on our works since 15 years using principally
Monte Carlo simulations. In these works, we have studied the spin resistivity
in various kinds of magnetic systems ranging from ferromagnets and
antiferromagnets to frustrated spin systems. It is found that the spin
resistivity shows a broad peak at the transition temperature in systems with a
second-order phase transition, while it undergoes a discontinuous jump at the
transition temperature of a first-order transition. New results on the
hexagonal-close-packed (HCP) antiferromagnet are also shown in extended details
for the Ising case in both the frustrated and non-frustrated parameter regions.",2301.02689v1
2023/1/8,Spin glass behavior in amorphous Cr2Ge2Te6 phase-change alloy,"The layered crystal structure of Cr2Ge2Te6 shows ferromagnetic ordering at
the two-dimensional limit, which holds promise for spintronic applications.
However, external voltage pulses can trigger amorphization of the material in
nanoscale electronic devices, and it is unclear whether the loss of structural
ordering leads to a change in magnetic properties. Here, we demonstrate that
Cr2Ge2Te6 preserves the spin-polarized nature in the amorphous phase, but
undergoes a magnetic transition to a spin glass state below 20 K.
Quantum-mechanical computations reveal the microscopic origin of this
transition in spin configuration: it is due to strong distortions of the
Cr-Te-Cr bonds, connecting chromium-centered octahedra, and to the overall
increase in disorder upon amorphization. The tunable magnetic properties of
Cr2Ge2Te6 could be exploited for multifunctional, magnetic phase-change devices
that switch between crystalline and amorphous states.",2301.02974v2
2023/2/7,Sputtered terbium iron garnet films with perpendicular magnetic anisotropy for spintronic applications,"We report the structural, magnetic, and interfacial spin transport properties
of epitaxial terbium iron garnet (TbIG) ultrathin films deposited by magnetron
sputtering. High crystallinity was achieved by growing the films on gadolinium
gallium garnet (GGG) substrates either at high temperature, or at room
temperature followed by thermal annealing, above 750 {\deg}C in both cases. The
films display large perpendicular magnetic anisotropy (PMA) induced by
compressive strain, and tunable structural and magnetic properties through
growth conditions or the substrate lattice parameter choice. The ferrimagnetic
compensation temperature (TM) of selected TbIG films was measured through
temperature-dependent anomalous Hall effect (AHE) in Pt/TbIG heterostructures.
In the studied films, TM was found to be between 190-225 K, i.e., approximately
25-60 K lower than the bulk value, which is attributed to the combined action
of Tb deficiency and oxygen vacancies in the garnet lattice evidenced by x-ray
photoelectron spectroscopy measurements. Sputtered TbIG ultrathin films with
large PMA and highly tunable properties reported here can provide a suitable
material platform for a wide range of spintronic experiments and device
applications.",2302.03758v1
2023/2/9,Single-shot laser-induced switching of an exchange biased antiferromagnet,"Ultrafast manipulation of magnetic order has challenged our understanding the
fundamental and dynamic properties of magnetic materials. So far single shot
magnetic switching has been limited to ferrimagnetic alloys and multilayers. In
ferromagnetic (FM)/antiferromagnetic (AFM) bilayers, exchange bias (He) arises
from the interfacial exchange coupling between the two layers and reflects the
microscopic orientation of the antiferromagnet. Here we demonstrate the
possibility of single shot switching of the antiferromagnet (change of the sign
and amplitude of He) with a single femtosecond laser pulse in IrMn/CoGd
bilayers. We demonstrate the switching for a wide range of fluences for
different layer thicknesses and compositions. Atomistic simulations predict
ultrafast switching and recovery of the AFM magnetization on a timescale of 2
ps. These results provide the fastest and the most energy-efficient method to
set the exchange bias and pave the way to potential applications for ultrafast
spintronic devices.",2302.04510v1
2023/2/10,Generalized method of image dyons for quasi-two dimensional slabs with ordinary-topological insulator interfaces,"Electrostatic charges near the interface bewteen topological (TI) and
ordinary (OI) insulators induce magnetic fields in the medium that can be
described through the so-called method of image dyons (electric charge -
magnetic monopole pairs), the magnetoelectric extension of the method of image
charges in classical electrostatics. Here, we provide the expressions for the
image dyons and ensuing magnetoelectric potentials in a system comprised by two
planar-parallel OI-TI interfaces conforming a finite-width slab. The obtained
formulae extend earlier work in that they account for all different
combinations of materials forming the slab and its surroundings, including
asymmetric systems, as well as all possible combinations of external
magnetization orientations on the interfaces. The equations are susceptible of
implementation in simple computational codes, to be solved recurrently, in
order to model magnetoelectric fields in topological quantum wells, thin films,
or layers of two-dimensional materials. We exemplify this by calculating the
magnetic fields induced by a point charge in nanometer-thick quantum wells, by
means of a Mathematica code made available in repositories.",2302.05180v1
2023/2/21,Aluminium substituted yttrium iron garnet thin films with reduced Curie temperature,"Magnetic garnets such as yttrium iron garnet (Y$_3$Fe$_5$O$_{12}$, YIG) are
widely used in spintronic and magnonic devices. Their magnetic and
magneto-optical properties can be modified over a wide range by tailoring their
chemical composition. Here, we report the successful growth of Al-substituted
yttrium iron garnet (YAlIG) thin films via radio frequency sputtering in
combination with an ex situ annealing step. Upon selecting appropriate process
parameters, we obtain highly crystalline YAlIG films with different Al$^{3+}$
substitution levels on both, single crystalline Y$_3$Al$_5$O$_{12}$ (YAG) and
Gd$_3$Ga$_5$O$_{12}$ (GGG) substrates. With increasing Al$^{3+}$ substitution
levels, we observe a reduction of the saturation magnetisation as well as a
systematic decrease of the magnetic ordering temperature to values well below
room temperature. YAlIG thin films thus provide an interesting material
platform for spintronic and magnonic experiments in different magnetic phases.",2302.10517v2
2023/2/25,Magnonic Hall Effect and Magnonic Holography of Hopfions,"Hopfions are localized and topologically non-trivial magnetic configurations
that have received considerable attention in recent years. Through a
micromagnetic approach, we analyze the scattering of spin waves by magnetic
hopfions. We show that the spin waves experience an emergent electromagnetic
field related to the topological properties of the hopfion. We find that spin
waves propagating along the hopfion symmetry axis are deflected by the magnetic
texture, which acts as a convergent or divergent lens, depending on the spin
wave propagation direction. The effect differs for spin waves propagating along
the plane perpendicular to the symmetry axis. In the last case, they respond
with a skew scattering and a closely related Aharonov-Bohm effect. This allows
probing the existence of a magnetic hopfion by magnonic holography.",2302.13190v1
2023/3/13,Antiskyrmionic ferroelectric medium,"Typical magnetic skyrmion is a string of inverted magnetization within a
ferromagnet, protected by a sleeve of a vortex-like spin texture, such that its
cross-section carries a positive integer topological charge. Some magnets form
antiskyrmions, the antiparticle strings which carry a negative topological
charge instead. Here we demonstrate that topologically equivalent but purely
electric antiskyrmion can exist in a ferroelectric material as well. In
particular, our computer experiments reveal that the archetype ferroelectric,
barium titanate, can host antiskyrmions. The polarization pattern around their
cores reminds ring windings of decorative knots rather than the typical
magnetic antiskyrmion texture. We show that the antiskyrmion of barium titanate
has just 2-3 nm in diameter, a hexagonal cross-section, and an exotic
topological charge of minus two. We deduce that formation of antiskyrmions is
favored by a fortunate combination of the moderate anisotropy of the anharmonic
electric susceptibility and the characteristic anisotropy of the polarization
correlations in barium titanate crystals.",2303.07389v2
2023/3/24,Machine learning-based spin structure detection,"One of the most important magnetic spin structure is the topologically
stabilised skyrmion quasi-particle. Its interesting physical properties make
them candidates for memory and efficient neuromorphic computation schemes. For
the device operation, detection of the position, shape, and size of skyrmions
is required and magnetic imaging is typically employed. A frequently used
technique is magneto-optical Kerr microscopy where depending on the samples
material composition, temperature, material growing procedures, etc., the
measurements suffer from noise, low-contrast, intensity gradients, or other
optical artifacts. Conventional image analysis packages require manual
treatment, and a more automatic solution is required. We report a convolutional
neural network specifically designed for segmentation problems to detect the
position and shape of skyrmions in our measurements. The network is tuned using
selected techniques to optimize predictions and in particular the number of
detected classes is found to govern the performance. The results of this study
shows that a well-trained network is a viable method of automating data
pre-processing in magnetic microscopy. The approach is easily extendable to
other spin structures and other magnetic imaging methods.",2303.16905v1
2023/4/2,Hydrostatic pressure effects in the Kitaev quantum magnet $α$-RuCl$_3$: A single-crystal neutron diffraction study,"We report a comprehensive single-crystal neutron diffraction investigation of
the Kitaev quantum magnet $\alpha$-RuCl$_{3}$ under hydrostatic pressure.
Utilizing a He-gas pressure cell, we successfully applied an ideal hydrostatic
pressure in situ at low temperatures, which allows to effectively eliminate any
possible influences from the structural transition occurring between 200 K and
50 K under ambient conditions. Our experiments reveal a gradual suppression of
the ziagzag antiferromagnetic order as hydrostatic pressure increases.
Furthermore, a reversible pressure-induced structural transition occurs at a
critical pressure of $P_d$ = 0.15 GPa at 30 K, as evidenced by the absence of
magnetic order and non-uniform changes in lattice constants. The decrease in
magnetic transition temperature is discussed in relation to a pressure-induced
change in the trigonal distortion of the Ru-Cl octahedra in this compound. Our
findings emphasize the significance of the trigonal distortion in Kitaev
materials, and provide a new perspective on the role of hydrostatic pressures
in the realization of the Kitaev quantum spin liquid state in
$\alpha$-RuCl$_{3}$.",2304.00632v1
2023/4/6,"Local magnetic and geometric structure in Mn-doped La(Fe,Si)13","Magnetic cooling has the potential to replace conventional gas compression
refrigeration. Materials such as La(Fe,Si)$_{13}$ exhibit a sizeable
first-order magnetocaloric effect, and it is possible to tailor the phase
transition towards room temperature by Mn-H-doping, resulting in a large
temperature range for operation. Within this work, we discuss variations of the
electronic and lattice structure in La(Fe,Si)$_{13}$ with increasing Mn content
utilizing X-ray magnetic circular dichroism (XMCD) and extended X-ray
absorption fine structure spectroscopy (EXAFS). While XMCD shows a decrease of
the magnetic polarization at the Fe K edge, low-temperature EXAFS measurements
indicate increased positional disorder in the La environment that is otherwise
absent for Fe and Mn. First-principles calculations link the positional
disorder to an enlarged Mn-Si distance -- explaining the increased positional
disorder in the La surrounding.",2304.03065v1
2023/4/8,A surrogate model for data-driven magnetic stray field calculations,"In this contribution we propose a data-driven surrogate model for the
prediction of magnetic stray fields in two-dimensional random
micro-heterogeneous materials. Since data driven models require thousands of
training data sets, FEM simulations appear to be too time consuming. Hence, a
stochastic model based on Brownian motion, which utilizes an efficient
evaluation of stochastic transition matrices, is applied for the training data
generation. For the encoding of the microstructure and the optimization of the
surrogate model, two architectures are compared, i.e. the so-called UResNet
model and the Fourier Convolutional neural network (FCNN). Here we analyze two
FCNNs, one based on the discrete cosine transformation and one based on the
complex-valued discrete Fourier transformation. Finally, we compare the
magnetic stray fields for independent microstructures (not used in the training
set) with results from the FE$^2$ method, a numerical homogenization scheme, to
demonstrate the efficiency of the proposed surrogate model.",2304.03982v1
2023/4/25,Simulations of Magnetization Reversal in FM/AFM Bilayers With THz Frequency Pulses,"It is widely known that antiferromagnets (AFMs) display a high frequency
response in the terahertz (THz) range, which opens up the possibility for
ultrafast control of their magnetization for next generation data storage and
processing applications. However, because the magnetization of the different
sublattices cancel, their state is notoriously difficult to read. One way to
overcome this is to couple AFMs to ferromagnets - whose state is trivially read
via magneto-resistance sensors. Here we present conditions, using theoretical
modelling, that it is possible to switch the magnetization of an AFM/FM bilayer
using THz frequency pulses with moderate field amplitude and short durations,
achievable in experiments. Consistent switching is observed in the phase
diagrams for an order of magnitude increase in the interface coupling and a
tripling in the thickness of the FM layer. We demonstrate a range of reversal
paths that arise due to the combination of precession in the materials and the
THz-induced fields. Our analysis demonstrates that the AFM drives the switching
and results in a much higher frequency dynamics in the FM due to the exchange
coupling at the interface. The switching is shown to be robust over a broad
range of temperatures relevant for device applications.",2304.12969v1
2023/5/4,Quantum Enhanced Probes of Magnetic Circular Dichroism,"Magneto-optical microscopies, including optical measurements of magnetic
circular dichroism, are increasingly ubiquitous tools for probing spin-orbit
coupling, charge-carrier g-factors, and chiral excitations in matter, but the
minimum detectable signal in classical magnetic circular dichroism measurements
is fundamentally limited by the shot-noise limit of the optical readout field.
Here, we use a two-mode squeezed light source to improve the minimum detectable
signal in magnetic circular dichroism measurements by 3 dB compared with
state-of-the-art classical measurements, even with relatively lossy samples
like terbium gallium garnet. We also identify additional opportunities for
improvement in quantum-enhanced magneto-optical microscopies, and we
demonstrate the importance of these approaches for environmentally sensitive
materials and for low temperature measurements where increased optical power
can introduce unacceptable thermal perturbations.",2305.02904v1
2023/5/4,Quantifying the magnetic interactions governing chiral spin textures using deep neural networks,"The interplay of magnetic interactions in chiral multilayer films gives rise
to nanoscale topological spin textures, which form attractive elements for
next-generation computing. Quantifying these interactions requires several
specialized, time-consuming, and resource-intensive experimental techniques.
Imaging of ambient domain configurations presents a promising avenue for
high-throughput extraction of the parent magnetic interactions. Here we present
a machine learning-based approach to determine the key interactions --
symmetric exchange, chiral exchange, and anisotropy -- governing chiral domain
phenomenology in multilayers. Our convolutional neural network model, trained
and validated on over 10,000 domain images, achieved $R^2 > 0.85$ in predicting
the parameters and independently learned physical interdependencies between
them. When applied to microscopy data acquired across samples, our
model-predicted parameter trends are consistent with independent experimental
measurements. These results establish ML-driven techniques as valuable,
high-throughput complements to conventional determination of magnetic
interactions, and serve to accelerate materials and device development for
nanoscale electronics.",2305.02954v1
2023/5/5,Andreev reflection at the altermagnet-superconductor interface,"Altermagnets are a new class of magnetic materials, which exhibit large spin
splitting, but due to the combined spin and real space group symmetry
protection maintain zero net macroscopic magnetization. Such a characteristic
may prove them to be superior in applications in superconducting
heterostructures and thus here we investigate the Andreev reflection at the
altermagnet/superconductor interface. We compare and contrast altermagnets to
other magnetic materials, revealing qualitative differences in the behavior of
altermagnetic junction depending on the Fermi surface orientation. We study the
resonant states arising in setups with strong tunneling barriers and show that
sensitivity to non-magnetic disorder is also dependent on the orientation. Our
results provide a building block for altermagnetic superconducting
heterostructures such as Josephson $\pi$ junctions with superior properties.",2305.03856v2
2023/5/18,Magnetic catalysis in weakly interacting hyperbolic Dirac materials,"Due to linearly vanishing density of states, emergent massless Dirac
quasiparticle resulting from the free fermion motion on a family of
two-dimensional half-filled bipartite hyperbolic lattices feature dynamic mass
generation through quantum phase transitions only for sufficiently strong
finite-range Coulomb repulsion. As such, strong nearest-neighbor Coulomb
repulsion ($V$) is conducive to the nucleation of a charge-density-wave (CDW)
order with a staggered pattern of average fermionic density between two
sublattices of bipartite hyperbolic lattices. Considering a collection of
spinless fermions (for simplicity), here we show that application of strong
external magnetic fields by virtue of producing a \emph{finite} density of
states near the zero energy triggers the condensation of the CDW order even for
\emph{infinitesimal} $V$. The proposed magnetic catalysis mechanism is
operative for uniform as well as inhomogeneous (bell-shaped) magnetic fields.
We present scaling of the CDW order with the total flux enclosed by hyperbolic
Dirac materials for a wide range of (especially subcritical) $V$.",2305.11174v1
2023/5/20,Magnetic States of Graphene Proximitized Kitaev Materials,"Single layer $\alpha$-ruthenium trichloride ($\rm\alpha-RuCl_3$) has been
proposed as a potential quantum spin liquid. Graphene/$\rm RuCl_3$
heterobilayers have been extensively studied with a focus on the large
interlayer electron transfer that dopes both materials. Here we examine the
interplay between the competing magnetic state of $\rm RuCl_3$ layer and
graphene electronic properties. We perform self-consistent Hartree-Fock
calculations on a Hubbard-Kanamori model of the $4d^5$ $t_{2g}$ electrons of
$\rm\alpha-RuCl_3$ and confirm that out-of-plane ferromagnetic and zigzag
antiferromagnetic states are energetically competitive. We show that the
influence of hybridization between graphene and $\rm\alpha-RuCl_3$ bands is
strongly sensitive to the magnetic configuration of $\rm RuCl_3$ and the
relative orientations of the two layers. We argue that strong hybridization
leads to graphene magneto-resistance and that it may tilt the balance between
closely competing magnetic states. Our analysis can be applied to any van der
Waals heterobilayer system with weak interlayer hybridization and allows for
arbitrary lattice constant mismatch and relative orientation.",2305.12116v2
2023/5/30,Ferromagnetic interlayer coupling in CrSBr crystals irradiated by ions,"Layered magnetic materials are becoming a major platform for future
spin-based applications. Particularly the air-stable van der Waals compound
CrSBr is attracting considerable interest due to its prominent
magneto-transport and magneto-optical properties. In this work, we observe a
transition from antiferromagnetic to ferromagnetic behavior in CrSBr crystals
exposed to high-energy, non-magnetic ions. Already at moderate fluences, ion
irradiation induces a remanent magnetization with hysteresis adapting to the
easy-axis anisotropy of the pristine magnetic order up to a critical
temperature of 110 K. Structure analysis of the irradiated crystals in
conjunction with density functional theory calculations suggest that the
displacement of constituent atoms due to collisions with ions and the formation
of interstitials favors ferromagnetic order between the layers.",2305.18791v2
2023/7/31,Evidence of Pseudogravitational Distortions of the Fermi Surface Geometry in the Antiferromagnetic Metal FeRh,"The confluence between high-energy physics and condensed matter has produced
groundbreaking results via unexpected connections between the two traditionally
disparate areas. In this work, we elucidate additional connectivity between
high-energy and condensed matter physics by examining the interplay between
spin-orbit interactions and local symmetry-breaking magnetic order in the
magnetotransport of thin-film magnetic semimetal FeRh. We show that the change
in sign of the normalized longitudinal magnetoresistance observed as a function
of increasing in-plane magnetic field results from changes in the Fermi surface
morphology. We demonstrate that the geometric distortions in the Fermi surface
morphology are more clearly understood via the presence of pseudogravitational
fields in the low-energy theory. The pseudogravitational connection provides
additional insights into the origins of a ubiquitous phenomenon observed in
many common magnetic materials and points to an alternative methodology for
understanding phenomena in locally-ordered materials with strong spin-orbit
interactions.",2308.00192v1
2023/8/2,Light Driven Spontaneous Phonon Chirality and Magnetization in Paramagnets,"Spin-phonon coupling enables the mutual manipulation of phonon and spin
degrees of freedom in solids. In this study, we reveal the inherent
nonlinearity within this coupling. Using a paramagnet as an illustration, we
demonstrate the nonlinearity by unveiling spontaneous symmetry breaking under a
periodic drive. The drive originates from linearly polarized light, respecting
a mirror reflection symmetry of the system. However, this symmetry is
spontaneously broken in the steady state, manifested in the emergence of
coherent chiral phonons accompanied by a nonzero magnetization. We establish an
analytical self-consistent equation to find the parameter regime where
spontaneous symmetry breaking occurs. Furthermore, we estimate realistic
parameters and discuss potential materials that could exhibit this behavior.
Our findings shed light on the exploration of nonlinear phenomena in magnetic
materials and present possibilities for on-demand control of magnetization.",2308.00933v1
2023/8/9,Physics-aware differentiable design of magnetically actuated kirigami for shape morphing,"Shape morphing that transforms morphologies in response to stimuli is crucial
for future multifunctional systems. While kirigami holds great promise in
enhancing shape-morphing, existing designs primarily focus on kinematics and
overlook the underlying physics. This study introduces a differentiable inverse
design framework that considers the physical interplay between geometry,
materials, and stimuli of active kirigami, made by soft material embedded with
magnetic particles, to realize target shape-morphing upon magnetic excitation.
We achieve this by combining differentiable kinematics and energy models into a
constrained optimization, simultaneously designing the cuts and magnetization
orientations to ensure kinematic and physical feasibility. Complex kirigami
designs are obtained automatically with unparallel efficiency, which can be
remotely controlled to morph into intricate target shapes and even multiple
states. The proposed framework can be extended to accommodate various active
systems, bridging geometry and physics to push the frontiers in shape-morphing
applications, like flexible electronics and minimally invasive surgery.",2308.05054v1
2023/8/22,Skyrmion motion in magnetic anisotropy gradients: Acceleration caused by deformation,"Magnetic skyrmions are nano-sized topologically non-trivial spin textures
that can be moved by external stimuli such as spin currents and internal
stimuli such as spatial gradients of a material parameter. Since the total
energy of a skyrmion depends linearly on most of these parameters, like the
perpendicular magnetic anisotropy, the exchange constant, or the
Dzyaloshinskii-Moriya interaction strength, a skyrmion will move uniformly in a
weak parameter gradient. In this paper, we show that the linear behavior
changes once the gradients are strong enough so that the magnetic profile of a
skyrmion is significantly altered throughout the propagation. In that case, the
skyrmion experiences acceleration and moves along a curved trajectory.
Furthermore, we show that when spin-orbit torques and material parameter
gradients trigger a skyrmion motion, it can move on a straight path along the
current or gradient direction. We discuss the significance of suppressing the
skyrmion Hall effect for spintronic and neuromorphic applications of skyrmions.
Lastly, we extend our discussion and compare it to a gradient generated by the
Dzyaloshinskii-Moriya interaction.",2308.11361v1
2023/8/29,Self-biased magnetoelectric Ni/LiNbO3/Ni for body embedded electronic energy harvesters,"In this study, we present the fabrication and characterization of
Ni/LiNbO3/Ni trilayers using RF sputtering. These trilayers exhibit thick Ni
layers (10 microns) and excellent adherence to the substrate, enabling high
magnetoelectric coefficients. By engineering the magnetic anisotropy of Nickel
through anisotropic thermal residual stress induced during fabrication, and by
selecting a carefully chosen cut angle for the LiNbO3 substrate, we achieved a
self-biased behavior. We demonstrate that these trilayers can power medical
implant devices remotely using a small AC magnetic field excitation, thereby
eliminating the need for a DC magnetic field and bulky magnetic field sources.
The results highlight the potential of these trilayers for the wireless and
non-invasive powering of medical implants. This work contributes to the
advancement of magnetoelectric materials and their applications in healthcare
technology.",2308.15428v1
2023/9/19,Multiple Magnetoelectric Plateaux in Polar Magnet Fe$_2$Mo$_3$O$_8$,"The magnetization and electric polarization of a polar antiferromagnet
Fe$_2$Mo$_3$O$_8$ are studied up to 66 T for spin-saturation magnetic fields
applied along the polar axis. The magnetization process at 1.4 K exhibited
multistep structures below the saturation field of 65 T. The electric
polarization along the polar axis exhibits a similar multistep behavior with a
total change of 1.2 $\rm{\mu}C/cm^{2}$. A combined triangular-lattice
antiferromagnetic model with strong Ising-type spin anisotropy reproduces this
multistep magnetoelectric (ME) effect. The exchange striction mechanism
explains the remarkable ME response in the two sub-lattice type-I multiferroic
materials. These results and interpretation demonstrate a method for realizing
multistage magnetoelectric effects in hybrid spin systems.",2309.10583v1
2023/10/2,The Co$^{2+}$-Ir$^{5+}$ orbital hybridization in LaCaCoIrO$_6$ double perovskite,"Here, we report on the structural, electronic, and magnetic properties of a
polycrystalline sample of the LaCaCoIrO$_6$ double-perovskite investigated by
means of synchrotron x-ray powder diffraction, x-ray absorption spectroscopy,
and x-ray magnetic circular dichroism at the Co and Ir $L_{2,3}$ edges,
magnetometry, and electrical transport. Our results indicate a configuration of
nearly Co$^{2+}$/Ir$^{5+}$ configuration for the transition-metal ions, with
spin canting within the Co antiferromagnetic superstructure responsible for the
ferromagnetic-like behavior observed below 100 K. The highly insulating
character of LaCaCoIrO$_6$ and its positive magnetoresistance further suggest
that this antiferromagnetic superexchange interaction occurs through an
indirect hybridization between the Co $e_g$ orbitals",2310.01114v1
2023/10/10,Fragility of the magnetic order in the prototypical altermagnet RuO$_2$,"Altermagnetism is a topic that has lately been gaining attention and the
RuO$_2$ compound is among one of the most studied altermagnetic candidates.
However, the survey of available literature on RuO$_2$ properties suggests that
there is no consensus about the magnetism of this material. By performing
density functional theory calculations, we show that the electronic properties
of stoichiometric RuO$_2$ are described in terms of a smaller Hubbard $U$
within DFT+$U$ than the value required to have magnetism. We further argue that
Ru vacancies can actually aid the formation of a magnetic state in RuO$_2$.
This in turn suggests that a characterization of the amount of Ru vacancies in
experimental samples might help the resolution of the controversy between the
different experimental results.",2310.06909v2
2023/10/8,PT-symmetry enabled spintronic thermal diode and logic gates,"Devices for performing computation and logic operations with low-energy
consumption are of key importance for environmentally friendly data-processing
and information technology. Here, we present a design for magnetic elements
that use excess heat to perform logic operations. The basic information channel
is coupled non-conductive magnetic stripes with a normal metal spacer. The
thermal information signal is embodied in magnetic excitations and it can be
transported, locally enhanced, and controllably steered by virtue of charge
current pulses in the spacer. Functionality of essential thermal logic gates is
demonstrated by material-specific simulations. The operation principle takes
advantage of the special material architecture with a balanced gain/loss
mechanism for magnetic excitation which renders the circuit parity-time
symmetric with exceptional points tunable by the current strength in the
spacer. Heat flow at these points can be enhanced, be non-reciprocal, or may
oscillate between the information channels enabling so controlled thermal diode
and thermal gate operations. The findings point to a new route for exploiting
heat for useful work on the nanoscale.",2310.09958v1
2023/10/18,Theory of moiré magnetism in twisted bilayer $α$-RuCl$_3$,"Twisted heterostructures of van der Waals materials have received much
attention for their many remarkable properties. Here, we present a
comprehensive theory of the long-range ordered magnetic phases of twisted
bilayer $\alpha$-RuCl$_3$ via a combination of first-principles calculations
and atomistic simulations. While a monolayer exhibits zigzag antiferromagnetic
order with three possible ordering wave vectors, a rich phase diagram is
obtained for moir\'e superlattices as a function of interlayer exchange and
twist angle. For large twist angles, each layer spontaneously picks a single
zigzag ordering wave vector, whereas, for small twist angles, the ground state
involves a combination of all three wave vectors in a complex hexagonal domain
structure. This multi-domain order minimizes the interlayer energy while
enduring the energy cost due to the domain wall formation. Our results indicate
that magnetic frustration due to stacking-dependent interlayer exchange in
moir\'e superlattices can be used to tune the magnetic ground state and enhance
quantum fluctuations in $\alpha$-RuCl$_3$.",2310.12211v1
2023/10/20,Surface-symmetry-driven Dzyaloshinskii--Moriya interaction and canted ferrimagnetism in collinear magnetoelectric antiferromagnet Cr$_2$O$_3$,"Antiferromagnets are normally thought of as materials with compensated
magnetic sublattices. This adds to their technological advantages but
complicates readout of the antiferromagnetic state. We demonstrate
theoretically the existence of a Dzyaloshinskii-Moriya interaction (DMI) which
is determined by the magnetic symmetry classes of Cr$_2$O$_3$ surfaces with an
in-plane magnetic easy axis. The DMI explains a previously predicted
out-of-plane magnetization at the nominally compensated surfaces of chromia,
leading to a surface-localized canted ferrimagnetism. This is in agreement with
magnetotransport measurements and with density functional theory predictions
which further allow us to quantify the strength of DMI. The temperature
dependence of the transversal resistance for these planes shows distinct
behavior in comparison with that of the Cr$_2$O$_3$ $c$ plane, which we
attribute to the influence of DMI. Our work provides a framework to analyze
surface-driven phenomena in antiferromagnets, and motivates the use of
nominally compensated chromia surfaces for antiferomagnetic spintronics and
magnonics.",2310.13438v1
2023/10/31,Phase-Modulated Elastic Properties of Two-Dimensional Magnetic FeTe: Hexagonal and Tetragonal Polymorphs,"Two-dimensional (2D) layered magnets, such as iron chalcogenides, have
emerged these years as a new family of unconventional superconductor and
provided the key insights to understand the phonon-electron interaction and
pairing mechanism. Their mechanical properties are of strategic importance for
the potential applications in spintronics and optoelectronics. However, there
is still lack of efficient approach to tune the elastic modulus despite the
extensive studies. Herein, we report the modulated elastic modulus of 2D
magnetic FeTe and its thickness-dependence via phase engineering. The grown 2D
FeTe by chemical vapor deposition can present various polymorphs, i.e.
tetragonal FeTe (t-FeTe, antiferromagnetic) and hexagonal FeTe (h-FeTe,
ferromagnetic). The measured Young's modulus of t-FeTe by nanoindentation
method showed an obvious thickness-dependence, from 290.9+-9.2 to 113.0+-8.7
GPa when the thicknesses increased from 13.2 to 42.5 nm, respectively. In
comparison, the elastic modulus of h-FeTe remains unchanged. Our results could
shed light on the efficient modulation of mechanical properties of 2D magnetic
materials and pave the avenues for their practical applications in nanodevices.",2310.20167v1
2023/11/1,Towards Ultimate Memory with Single-Molecule Multiferroics,"The demand for high-density storage is urgent in the current era of data
explosion. Recently, several single-molecule (-atom) magnets/ferroelectrics
have been reported to be promising candidates for high-density storage. As
another promising candidate, single-molecule multiferroics are not only small
but also possess ferroelectric and magnetic orderings, which can sometimes be
strongly coupled and used as data storages to realize the combination of
electric writing and magnetic reading. However, they have been rarely proposed,
and never been experimentally reported. Here, by building Hamiltonian models,
we propose a new model of single-molecule multiferroic in which electric
dipoles and magnetic moments are parallel and can rotate with the rotation of
the single molecule. Furthermore, with performing spin-lattice dynamics
simulations, we reveal the conditions (e.g., large enough single-ion anisotropy
and appropriate electric field) under which the new single-molecule
multiferroic can arise. Based on this model, as well as first-principles
calculations, a realistic example Co(NH3)4N@SWCNT is constructed and
numerically confirmed to demonstrate the feasibility of the new single-molecule
multiferroic model. Our work not only sheds light on the discovery of
single-molecule multiferroics but also provides a new guideline to design
multifunctional materials for ultimate memory devices.",2311.00255v1
2023/11/20,One-ninth magnetization plateau stabilized by spin entanglement in a kagome antiferromagnet,"The spin-1/2 antiferromagnetic Heisenberg model on a Kagome lattice is
geometrically frustrated, which is expected to promote the formation of
many-body quantum entangled states. The most sought-after among these is the
quantum spin liquid phase, but magnetic analogs of liquid, solid, and
supersolid phases may also occur, producing fractional plateaus in the
magnetization. Here, we investigate the experimental realization of these
predicted phases in the Kagome material YCu3(OD)6+xBr3-x (x=0.5). By combining
thermodynamic and Raman spectroscopic techniques, we provide evidence for
fractionalized spinon excitations and observe the emergence of a 1/9
magnetization plateau. These observations establish YCu3(OD)6+xBr3-x as a model
material for exploring the 1/9 plateau phase.",2311.11619v1
2023/11/20,Spinon heat transport in the three-dimensional quantum magnet PbCuTe$_2$O$_6$,"Quantum spin liquids (QSL) are novel phases of matter which remain quantum
disordered even at the lowest temperature. They are characterized by emergent
gauge fields and fractionalized quasiparticles. Here we show that the
sub-Kelvin thermal transport of the three-dimensional $S=1/2$ hyper-hyperkagome
quantum magnet PbCuTe$_2$O$_6$ is governed by a sizeable charge-neutral
fermionic contribution which is compatible with the itinerant fractionalized
excitations of a spinon Fermi surface. We demonstrate that this hallmark
feature of the QSL state is remarkably robust against sample crystallinity,
large magnetic field, and field-induced magnetic order, ruling out the
imitation of QSL features by extrinsic effects. Our findings thus reveal the
characteristic low-energy features of PbCuTe$_2$O$_6$ which qualify this
compound as a true QSL material.",2311.12221v1
2023/11/21,"Probing of Excitonic Transitions in All Inorganic Perovskite Quantum Dots (CsPbX$_3$: X= Cl, Br, I) by Magnetic Circular Dichroism Spectroscopy","Higher-order electronic transitions of all inorganic lead halide perovskite
quantum dots (QDs) (CsPbX$_3$: X = Cl, Br, I) are hardly detected by
traditional spectroscopic techniques due to the condensed electronic level of
QDs. This work assigned the various excitonic transitions in undoped CsPbX$_3$
QDs through a high-resolution absorption spectroscopic technique - magnetic
circular dichroism (MCD). Moreover, we investigated the nature of these
transitions through sensitive Zeeman responses to the electronic states, likely
involving the interaction of spins with the applied external magnetic field.
The study unveiled multiple excitonic transitions in the QDs, showing unusual
temperature dependence and shedding light on the role of spin-orbit
interactions in the presence of a magnetic field. This study offers a
comprehensive insight into excitonic transitions, and the potential
manipulation of their spin through thermal means holds the promise of advancing
electronic and photonic devices based on these materials.",2311.12567v1
2023/12/1,Incommensurate Spiral Spin Order in CaMn$_2$Bi$_2$ observed via High Pressure Neutron Diffraction,"High pressure neutron diffraction is employed to investigate the magnetic
behavior of CaMn$_2$Bi$_2$ in extreme conditions. In contrast to
antiferromagnetic ordering on Mn atoms reported at ambient pressure, our
results reveal that at high pressure, incommensurate spiral spin order emerges
due to the interplay between magnetism on the Mn atoms and strong spin-orbit
coupling on the Bi atoms: sinusoidal spin order is observed at pressures as
high as 7.4 GPa. Competing antiferromagnetic order is observed at different
temperatures in the partially frustrated lattice. This research provides a
unique toolbox for conducting experimental magnetic and spin dynamics studies
on magnetic quantum materials via high pressure neutron diffraction.",2312.00397v1
2023/12/11,"Impersonating a Superconductor: High-Pressure BaCoO$_3$, an Insulating Ferromagnet","We report the high-pressure synthesis (6 GPa, 1200 $^{\circ}$C) and ambient
pressure characterization of hexagonal HP-BaCoO$_3$. The material (with the 2H
crystal structure) has a short intrachain Co-Co distance of about 2.07
$\text{\r{A}}$. Our magnetization investigation revealed robust diamagnetic
behavior below approximately 130 K when exposed to weak applied magnetic fields
(10 Oe) and a distinct half-levitation phenomenon below that temperature, such
as is often observed for superconductors. Its field-dependent magnetization
profile, however, unveils the characteristics of ferromagnetism, marked by a
substantial magnetic retentivity of 0.22(1) ${\mu}_B$/Co at a temperature of 2
K. Electrical resistivity measurements indicate that HP-BaCoO$_3$ is a
ferromagnetic insulator, not a superconductor.",2312.14955v1
2024/1/11,Magnetic control of Weyl nodes and wave packets in three-dimensional warped semimetals,"We investigate the topological phase transitions driven by band warping and a
transverse magnetic field, for three-dimensional Weyl semimetals. First, we use
the Chern number as a mathematical tool to derive the topological phase
diagram. Next, we associate each of the topological sectors to a given angular
momentum state of a rotating wave packet. Then we show how the position of the
Weyl nodes can be manipulated by a transverse external magnetic field that
ultimately quenches the wave packet rotation, first partially and then
completely, thus resulting in a sequence of field-induced topological phase
transitions. Finally, we calculate the current-induced magnetization and the
anomalous Hall conductivity of a prototypical warped Weyl material. Both
observables reflect the topological transitions associated with the wave packet
rotation and can help to identify the elusive 3D quantum anomalous Hall effect
in three-dimensional, warped Weyl materials.",2401.06282v1
2024/1/27,Interplay of altermagnetism and weak ferromagnetism in two-dimensional RuF$_4$,"Gaining growing attention in spintronics is a class of magnets displaying
zero net magnetization and spin-split electronic bands called altermagnets.
Here, by combining density functional theory and symmetry analysis, we show
that RuF$_4$ monolayer is a two-dimensional $d$-wave altermagnet. Spin-orbit
coupling leads to pronounced spin splitting of the electronic bands at the
$\Gamma$ point by $\sim 100$ meV and turns the RuF$_4$ into a weak ferromagnet
due to non trivial spin-momentum locking that cants the Ru magnetic moments.
The net magnetic moment scales linearly with the spin-orbit coupling strength.
Using group theory we derive an effective spin Hamiltonian capturing the
spin-splitting and spin-momentum locking of the electronic bands.
Disentanglement of the altermagnetic and spin-orbit coupling induced spin
splitting uncovers to which extent the altermagnetic properties are affected by
the spin-orbit coupling. Our results move the spotlight to the non trivial
spin-momentum locking and weak ferromagnetism in the two-dimensional
altermagnets relevant for novel venues in this emerging field of material
science research.",2401.15424v1
2024/2/22,Non-relativistic spin splitting in compensated magnets that are not altermagnets,"The non-relativistic spin-splitting (NRSS) of electronic bands in
""altermagnets"" has sparked renewed interest in antiferromagnets (AFMs) that
have no net magnetization. However, altermagnets with collinear and compensated
magnetism are not the only type of NRSS AFMs. In this study, we identify the
symmetry conditions and characteristic signatures of a distinct group of NRSS
AFMs that go beyond the description of altermagnets. These compounds exhibit a
broken spin-degeneracy among the spin-polarized bands at the $\Gamma$ point in
the absence of spin-orbit coupling (SOC). We use density functional theory
calculations to validate these models in ternary magnetic nitrides,
specifically MnXN$_2$ (X = Si, Ge, Sn), and their cation ordered variants. By
removing the previous NRSS constraint on $\Gamma$, these compounds may
facilitate the generation of spin currents without cancellation arising from
the alternating spin polarizations. Our findings expand the scope of NRSS
eligible materials.",2402.14321v1
2024/2/26,"Synthesis, structural and magnetic characterizations of Li$_4$Cu$_{1-x}$Ni$_x$TeO$_6$ ( $x$ = 0, 0.1, 0.2, 0.5, and 1)","We investigated the effect of Ni doping in a recently proposed quantum spin
liquid (QSL) candidate Li$_4$CuTeO$_6$. We performed a comprehensive study on
the structural and magnetic properties. We find that the anti-site disorder
between Li$^+$ and Cu$^{2+}$ persists until 50\% Ni doping in which Ni and Cu
occupy different crystallographic sites. As a result, while Cu sits in both
triangular and honeycomb layers in Li$_4$CuTeO$_6$, Ni forms only honeycomb
layer in Li$_4$NiTeO$_6$ and Li$_4$Cu$_{0.5}$Ni$_{0.5}$TeO$_6$. Our magnetic
susceptibility measurements show that the Weiss temperature decreases from
-145.68 K in Li$_4$CuTeO$_6$ to -6.15 K in Li$_4$NiTeO$_6$ as Ni doping
increases, and find no hint of magnetic ordering or freezing down to 1.8 K. Our
analysis implies the existence of abundant low energy excitations in these
materials.",2402.16768v1
2024/2/13,Broadband transverse susceptibility in multiferroic Y-type hexaferrite Ba$_{0.5}$Sr$_{1.5}$Co$_2$Fe$_{12}$O${22}$,"Single phase multiferroics in which ordered magnetic and ferroelectricity
coexist, are of great interest for new multifunctional devices, and among them
Y-type hexaferrites are good candidates. Transverse susceptibility
measurements, which have been proved to be a versatile tool to study singular
properties of bulk and nanoparticle magnetic systems, have been carried out
with a broadband system on polycrystalline Y type hexaferrites with composition
Ba$_{0.5}$Sr$_{1.5}$Co$_2$Fe$_{12}$O${22}$, optimal to exhibit multiferroic
properties. In the temperature range 80-350 K transverse susceptibility
measurements with DC fields up to $\pm$5000 Oe reveal different behaviour
depending on the sintering temperature. The thermal evolution of the anisotropy
field peak exhibit four regions with different slopes: positive in 80-130 K,
negative in 130-200 K, constant in 200-280 K and negative in 280-350 K, which
can be considered a signature of spin transitions in this compound.",2402.16879v1
2024/3/12,Anomalous Shiba spectrum and superconductivity induced magnetic interactions in materials with topological band inversion,"We study the Shiba states in materials with bulk band inversion such as
iron-based topological superconductors or doped topological insulators. We show
that the structure of the Shiba state spectrum depends on the doping level
relative to the chemical potential at which the band-inversion occurs.
Moreover, we demonstrate that the transition from ferro-magnetic to
antiferromagnetic coupling and vice versa, which is caused by the coupling of
magnetic impurities through the overlap of Shiba states, is highly dependent on
the doping level. Additionally, topological edge states may have a substantial
impact on the Shiba states, leading to a decrease in Shiba state energies and
the creation of new states when the magnetic impurity approaches the boundary.",2403.08028v1
2024/3/18,Uncovering the lowest thickness limit for room-temperature ferromagnetism of Cr$_{1.6}$Te$_{2}$,"Half-metallic ferromagnetic transition metal dichalcogenides have emerged as
important building blocks for scalable magnonics and memory applications.
Downscaling such systems to the ultra-thin limit is critical to integrate them
into technology. Here, we achieved layer-by-layer control over the transition
metal dichalcogenide Cr$_{1.6}$Te$_{2}$ by using pulsed laser deposition, and
we uncovered the minimum critical thickness above which room temperature
magnetic order is maintained. The electronic and magnetic structure is explored
experimentally and theoretically and it is shown that the films exhibit strong
in-plane magnetic anisotropy as a consequence of large spin-orbit effects. Our
study establishes Cr$_{1.6}$Te$_{2}$ as a platform material, viable for
ferromagnetic nanoscale devices and magnetic-memory architectures.",2403.11977v1
2024/3/20,Magneto-Ionic Vortices: Voltage-Reconfigurable Swirling-Spin Analog-Memory Nanomagnets,"Rapid progress in information technologies has spurred the need for
innovative memory concepts, for which advanced data-processing methods and
tailor-made materials are required. Here we introduce a previously unexplored
nanoscale magnetic object: an analog magnetic vortex controlled by
electric-field-induced ion motion, termed magneto-ionic vortex or ""vortion"".
This state arises from paramagnetic FeCoN through voltage gating and gradual
N3-ion extraction within patterned nanodots. Unlike traditional vortex states,
vortions offer comprehensive analog adjustment of key properties such as
magnetization amplitude, nucleation/annihilation fields, or coercivity using
voltage as an energy-efficient tuning knob. This manipulation occurs
post-synthesis, obviating the need for energy-demanding methods like laser
pulses or spin-torque currents. By leveraging an overlooked aspect of
N3-magneto-ionics -- planar ion migration within nanodots -- precise control of
the magnetic layer's thickness is achieved, which enables reversible
transitions among paramagnetic, single-domain, and vortion states, offering
future prospects for analog computing, multi-state data storage, or
brain-inspired devices.",2403.13722v1
2024/3/22,Exciton-activated effective phonon magnetic moment in monolayer MoS2,"Optical excitation of chiral phonons plays a vital role in studying the
phonon-driven magnetic phenomena in solids. Transition metal dichalcogenides
host chiral phonons at high symmetry points of the Brillouin zone, providing an
ideal platform to explore the interplay between chiral phonons and valley
degree of freedom. Here, we investigate the helicity-resolved magneto-Raman
response of monolayer MoS2 and identify a doubly degenerate
Brillouin-zone-center chiral phonon mode at ~270 cm-1. Our wavelength- and
temperature-dependent measurements show that this chiral phonon is activated
through the resonant excitation of A exciton. Under an out-of-plane magnetic
field, the chiral phonon exhibits giant Zeeman splitting, which corresponds to
an effective magnetic moment of 2.5mu_B. Moreover, we carry out theoretical
calculations based on the Morphic effects in nonmagnetic crystals, which
reproduce the linear Zeeman splitting and Raman cross-section of the chiral
phonon. Our study provides important insights into lifting the chiral phonon
degeneracy in an achiral covalent material, paving a new route to excite and
control chiral phonons.",2403.15347v1
2024/3/23,Magnetic parity violation and parity-time-reversal-symmetric magnets,"Parity-time-reversal symmetry ($\mathcal{PT}$ symmetry), a symmetry for the
combined operations of space inversion ($\mathcal{P}$) and time reversal
($\mathcal{T}$), is a fundamental concept of physics and characterizes the
functionality of materials as well as $\mathcal{P}$ and $\mathcal{T}$
symmetries. In particular, the $\mathcal{PT}$-symmetric systems can be found in
the centrosymmetric crystals undergoing the parity-violating magnetic order
which we call the odd-parity magnetic multipole order. While this spontaneous
order leaves $\mathcal{PT}$ symmetry intact, the simultaneous violation of
$\mathcal{P}$ and $\mathcal{T}$ symmetries gives rise to various emergent
responses that are qualitatively different from those allowed by the
nonmagnetic $\mathcal{P}$-symmetry breaking or by the ferromagnetic order. In
this review, we introduce candidates hosting the intriguing spontaneous order
and overview the characteristic physical responses. Various off-diagonal and/or
nonreciprocal responses are identified, which are closely related to the
unusual electronic structures such as hidden spin-momentum locking and
asymmetric band dispersion.",2403.15680v1
2024/4/3,High-throughput calculations of antiferromagnets hosting anomalous transport phenomena,"We develop a high-throughput computational scheme based on cluster multipole
theory to identify new functional antiferromagnets. This approach is applied to
228 magnetic compounds listed in the AtomWork-Adv database, known for their
elevated N\'eel temperatures. We conduct systematic investigations of both
stable and metastable magnetic configurations of these materials. Our findings
reveal that 34 of these compounds exhibit antiferromagnetic structures with
zero propagation vectors and magnetic symmetries identical to conventional
ferromagnets, rendering them potentially invaluable for spintronics
applications. By cross-referencing our predictions with the existing MAGNDATA
database and published literature, we verify the reliability of our findings
for 26 out of 28 compounds with partially or fully elucidated magnetic
structures in the experiments. These results not only affirm the reliability of
our scheme but also point to its potential for broader applicability in the
ongoing quest for the discovery of new functional magnets.13",2404.02437v1
2023/3/6,Epitaxial van der Waals heterostructures of Cr2Te3 on 2D materials,"Achieving large-scale growth of two-dimensional (2D) ferromagnetic materials
with high Curie temperature (TC) and perpendicular magnetic anisotropy (PMA) is
highly desirable for the development of ultra-compact magnetic sensors and
magnetic memories. In this context, van der Waals (vdW) Cr2Te3 appears as a
promising candidate. Bulk Cr2Te3 exhibits strong PMA and a TC of 180 K.
Moreover, both PMA and TC might be adjusted in ultrathin films by engineering
composition, strain, or applying an electric field. In this work, we
demonstrate the molecular beam epitaxy (MBE) growth of vdW heterostructures of
five-monolayer quasi-freestanding Cr2Te3 on three classes of 2D materials:
graphene (semimetal), WSe2 (semiconductor) and Bi2Te3 (topological insulator).
By combining structural and chemical analysis down to the atomic level with ab
initio calculations, we confirm the single crystalline character of Cr2Te3
films on the 2D materials with sharp vdW interfaces. They all exhibit PMA and
TC close to the bulk Cr2Te3 value of 180 K. Ab initio calculations confirm this
PMA and show how its strength depends on strain. Finally, Hall measurements
reveal a strong anomalous Hall effect, which changes sign at a given
temperature. We theoretically explain this effect by a sign change of the Berry
phase close to the Fermi level. This transition temperature depends on the 2D
material in proximity, notably as a consequence of charge transfer. MBE-grown
Cr2Te3/2D material bilayers constitute model systems for the further
development of spintronic devices combining PMA, large spin-orbit coupling and
sharp vdW interface.",2303.03076v1
2023/5/19,"DFT + U Study of structural, electronic, optical and magnetic properties of LiFePO4 Cathode materials for Lithium-Ion batteries","In this study, we have employed a DFT+U calculation using quantum-espresso
(QE) code to investigate the structural, electronic, optical, and magnetic
properties of LiFePO$\rm_{4}$ cathode material for Li-ion batteries. Crystals
of LiFePO$\rm_{4}$ and related materials have recently received a lot of
attention due to their very promising use as cathodes in rechargeable
lithium-ion batteries. The structural optimization was performed and the
equilibrium parameters such as the lattice constants, and the bulk modulus are
calculated using QE code and found to be a=4.76 {\AA}, b=6.00 {\AA}, c=10.28
{\AA}, B=90.2 GPa, respectively. The projected density of states (PDOS) for the
LiFePO$\rm_{4}$ material is remarkably similar to experimental results in
literature showing the transition metal $3d$ states forming narrow bands above
the O $2p$ band. The results of the various spin configurations suggested that
the ferromagnetic configuration can serve as a useful approximation for
studying the general features of these systems. In the absence of Li, the
majority spin transition metal $3d$ states are well-hybridized with the O 2p
band in FePO$\rm_{4}$. The result obtained with a DFT + U showed that LiFePO4
is direct band gap materials with a band gap of 3.82 eV, which is within the
range of the experimental values. The PDOS analyses show qualitative
information about the crystal field splitting and bond hybridization and help
rationalize the understanding of the structural, electronic, optical, and
magnetic properties of the LiFePO$\rm_{4}$ as a novel cathode material. On the
basis of the predicted optical absorbance, reflection, refractive index, and
energy loss function, LiFePO$\rm_{4}$ is demonstrated to be viable and
cost-effective, which is very suitable as a cathode material for Li-ion
battery.",2305.11459v1
2004/10/8,How to realize a negative refractive index material at the atomic level in an optical frequency range,"The theoretical mechanism for realizing the negative refractive index with
{\it electromagnetically induced transparency} (EIT) is studied. It is shown
that in a three-level dense atomic gas, there is a frequency band in which the
EIT medium will exhibit simultaneously negative electric permittivity and
magnetic permeability in the optical frequency range, and the atomic gas thus
becomes a left-handed material. The expressions for the electric permittivity
and the magnetic permeability for the probe frequency is presented. One of the
remarkable features of the present novel scheme is such that the obtained EIT
left-handed material is {\it isotropic} and may therefore have some potentially
important applications in the development of new techniques in quantum optics.",0410211v1
2007/1/14,Sr1.5Ba0.5Zn2Fe12O22 Hexaferrites Ferromagnetic Resonance and Nonlinear Excitation for Magneto-Electric Devices,"A magneto electric (ME) effect was reported [1] for the insulator material of
helimagnetic hexaferrite of Sr1.5Ba0.5Zn2Fe12O22. In this study we are
interested in investigating this materials ferromagnetic resonance to define
its internal anisotropy fields. By using a vibrating sample magnetometer (VSM)
and ferromagnetic resonance (FMR) analysis we realized that this helical
hexaferrite has about -0.5 kOe exchange anisotropy field of HE. Also, by using
an alternative free energy model we derived this materials Polder tensor and
its ferromagnetic resonance condition. Meanwhile, we were able to show a
potential magneto electric coupling by nonlinear excitation of planar helical
hexaferrite, in which a magnetic nonlinear excitation is integrated into
dielectric permittivity.
  Index Terms, Ferrites, ferromagnetic resonances, and magnetic nonlinear
excitations.",0701309v2
2007/2/5,Demagnetization Protocols for Frustrated Interacting Nanomagnet Arrays,"We report a study of demagnetization protocols for frustrated arrays of
interacting single domain permalloy nanomagnets by rotating the arrays in a
changing magnetic field. The most effective demagnetization is achieved by not
only stepping the field strength down while the sample is rotating, but by
combining each field step with an alternation in the field direction. By
contrast, linearly decreasing the field strength or stepping the field down
without alternating the field direction leaves the arrays with a larger
remanent magnetic moment. These results suggest that non-monotonic variations
in field magnitude around and below the coercive field are important for the
demagnetization process.",0702084v1
2005/8/31,Classification of dispersion equations for homogeneous dielectric-magnetic uniaxial materials,"The geometric representation at a fixed frequency of the wavevector (or
dispersion) surface $\omega(\vec k)$ for lossless, homogeneous
dielectric--magnetic uniaxial materials is explored, when the elements of the
relative permittivity and permeability tensors of the material can have any
sign. Electromagnetic plane waves propagating inside the material can exhibit
dispersion surfaces in the form of ellipsoids of revolution, hyperboloids of
one sheet, or hyperboloids of two sheets. Furthermore, depending on the
relative orientation of the optic axis, the intersections of these surfaces
with fixed planes of propagation can be circles, ellipses, hyperbolas, or
straight lines. The obtained understanding is used to study the reflection and
refraction of electromagnetic plane waves due to a planar interface with an
isotropic medium.",0508235v1
2007/12/8,Magnetic Moment Collapse-Driven Mott Transition in MnO,"The metal-insulator transition in correlated electron systems, where electron
states transform from itinerant to localized, has been one of the central
themes of condensed matter physics for more than half a century. The
persistence of this question has been a consequence both of the intricacy of
the fundamental issues and the growing recognition of the complexities that
arise in real materials, even when strong repulsive interactions play the
primary role. The initial concept of Mott was based on the relative importance
of kinetic hopping (measured by the bandwidth) and on-site repulsion of
electrons. Real materials, however, have many additional degrees of freedom
that, as is recently attracting note, give rise to a rich variety of scenarios
for a ``Mott transition.'' Here we report results for the classic correlated
insulator MnO which reproduce a simultaneous moment collapse, volume collapse,
and metallization transition near the observed pressure, and identify the
mechanism as collapse of the magnetic moment due to increase of crystal field
splitting, rather than to variation in the bandwidth.",0712.1262v1
2008/7/14,Intrinsic peculiarities of real material realizations of a spin-1/2 kagome lattice,"Spin-1/2 magnets with kagome geometry, being for years a generic object of
theoretical investigations, have few real material realizations. Recently, a
DFT-based microscopic model for two such materials, kapellasite Cu3Zn(OH)6Cl2
and haydeeite Cu3Mg(OH)6Cl2, was presented [O. Janson, J. Richter and H.
Rosner, arXiv:0806.1592]. Here, we focus on the intrinsic properties of real
spin-1/2 kagome materials having influence on the magnetic ground state and the
low-temperature excitations. We find that the values of exchange integrals are
strongly dependent on O--H distance inside the hydroxyl groups, present in most
spin-1/2 kagome compounds up to date. Besides the original kagome model,
considering only the nearest neighbour exchange, we emphasize the crucial role
of the exchange along the diagonals of the kagome lattice.",0807.2005v1
2009/1/14,Magnetic influence on classical dispersion,"We discuss the Lorentz model for dispersion and absorption of radiation in
dilute, linear and isotropic materials. Initially, with the purpose of making
the paper as self-contained as possible, we reproduce the usual calculations
concerning the interaction between the charged material oscillators and the
electric field of the incident radiation, obtaining the main behavior of the
reactive and dissipative electromagnetic properties of the materials.
Thereafter, we also include the magnetic contribution of the Lorentz force to
the equation of motion of the oscillators up to first order in $v/c$, which
leads to some interesting results, like the approximately linear dependence of
the refraction index with the radiation intensity and the appearance of a
second region of anomalous dispersion around half the natural frequencies of
the material.",0901.1922v1
2009/4/13,Magnetically tunable dielectric materials,"The coupling between localized spins and phonons can lead to shifts in the
dielectric constant of insulating materials at magnetic ordering transitions.
Studies on isostructural SeCuO3 (ferromagnetic) and TeCuO3 (antiferromagnetic)
illustrate how the q-dependent spin-spin correlation function couples to phonon
frequencies leading to a shift in the dielectric constant. A model is discussed
for this spin-phonon coupling. The magnetodielectric coupling in multiferroic
materials can be very large at a ferroelectric transition temperature. This
coupling is investigated in the recently identified multiferroic Ni3V2O8.",0904.1974v1
2010/5/18,Strength of Correlations in electron and hole doped cuprates,"High temperature superconductivity was achieved by introducing holes in a
parent compound consisting of copper oxide layers separated by spacer layers.
It is possible to dope some of the parent compounds with electrons, and their
physical properties are bearing some similarities but also significant
differences from the hole doped counterparts. Here, we use a recently developed
first principles method, to study the electron doped cuprates and elucidate the
deep physical reasons why their behavior is so different than the hole doped
materials. We find that electron doped compounds are Slater insulators, e.g. a
material where the insulating behavior is the result of the presence of
magnetic long range order. This is in sharp contrast with the hole doped
materials, where the parent compound is a Mott charge transfer insulator,
namely a material which is insulating due to the strong electronic correlations
but not due to the magnetic order.",1005.3095v1
2010/5/24,The Puzzle of High Temperature Superconductivity in Layered Iron Pnictides and Chalcogenides,"The response of the worldwide scientific community to the discovery in 2008
of superconductivity at Tc = 26 K in the Fe-based compound LaFeAsO_{1-x}F_x has
been very enthusiastic. In short order, other Fe-based superconductors with the
same or related crystal structures were discovered with Tc up to 56 K. Many
experiments were carried out and theories formulated to try to understand the
basic properties of these new materials and the mechanism for Tc. In this
selective critical review of the experimental literature, we distill some of
this extensive body of work, and discuss relationships between different types
of experiments on these materials with reference to theoretical concepts and
models. The experimental normal-state properties are emphasized, and within
these the electronic and magnetic properties because of the likelihood of an
electronic/magnetic mechanism for superconductivity in these materials.",1005.4392v2
2010/8/19,Electronic and magnetic properties of SrTiO3/LaAlO3 interfaces from first principles,"A number of intriguing properties emerge upon the formation of the epitaxial
interface between the insulating oxides LaAlO3 and SrTiO3. These properties,
which include a quasi two-dimensional conducting electron gas, low temperature
superconductivity, and magnetism, are not present in the bulk materials,
generating a great deal of interest in the fundamental physics of their
origins. While it is generally accepted that the novel behavior arises as a
result of a combination of electronic and atomic reconstructions and
growth-induced defects, the complex interplay between these effects remains
unclear. In this report, we review the progress that has been made towards
unraveling the complete picture of the SrTiO3/LaAlO3 interface, focusing
primarily on present ab initio theoretical work and its relation to the
experimental data. In the process, we highlight some key unresolved issues and
discuss how they might be addressed by future experimental and theoretical
studies.",1008.3379v1
2011/9/9,Towards an experimental realization of affinely transformed linearized QED vacuum via inverse homogenization,"Within the framework of quantum electrodynamics (QED), vacuum is a nonlinear
medium which can be linearized for a rapidly time-varying electromagnetic field
with a small amplitude subjected to a magnetostatic field. The linearized QED
vacuum is a uniaxial dielectric-magnetic medium for which the degree of
anisotropy is exceedingly small. By implementing an affine transformation of
the spatial coordinates, the degree of anisotropy may become sufficiently large
as to be readily perceivable. The inverse Bruggeman formalism can be
implemented to specify a homogenized composite material (HCM) which is
electromagnetically equivalent to the affinely transformed QED vacuum. This HCM
can arise from remarkably simple component materials; for example, two
isotropic dielectric materials and two isotropic magnetic materials, randomly
distributed as oriented spheroidal particles.",1109.2125v1
2011/10/12,Charge self-consistent dynamical mean-field theory based on the full-potential linear muffin-tin orbital method: methodology and applications,"Full charge self-consistence (CSC) over the electron density has been
implemented into the local density approximation plus dynamical mean-field
theory (LDA+DMFT) scheme based on a full-potential linear muffin-tin orbital
method (FP-LMTO). Computational details on the construction of the electron
density from the density matrix are provided. The method is tested on the
prototypical charge-transfer insulator NiO using a simple static Hartree-Fock
approximation as impurity solver. The spectral and ground state properties of
bcc Fe are then addressed, by means of the spin-polarized T-matrix fluctuation
exchange solver (SPTF). Finally the permanent magnet SmCo$_5$ is studied using
multiple impurity solvers, SPTF and Hubbard I, as the strength of the local
Coulomb interaction on the Sm and Co sites are drastically different. The
developed CSC-DMFT method is shown to in general improve on materials
properties like magnetic moments, electronic structure and the materials
density.",1110.2606v1
2012/5/7,Thermodynamics of Ferrotoroidic Materials: Toroidocaloric Effect,"The three primary ferroics, namely ferromagnets, ferroelectrics and
ferroelastics exhibit corresponding large (or even giant)
magnetocaloric,electrocaloric and elastocaloric effects when a phase transition
is induced by the application of an appropriate external field. Recently the
suite of primary ferroics has been extended to include ferrotoroidic materials
in which there is an ordering of toroidic moments in the form of magnetic
vortex-like structures, examples being LiCo(PO_4)_3 and Ba_2CoGe_2O_7. In the
present work we formulate the thermodynamics of ferrotoroidic materials. Within
a Landau free energy framework we calculate the toroidocaloric effect by
quantifying isothermal entropy change (or adiabatic temperature change) in the
presence of an applied toroidic field when usual magnetization and polarization
may also be present simultaneously. We also obtain a nonlinear
Clausius-Clapeyron relation for phase coexistence.",1205.1392v1
2012/9/11,Domain wall motion governed by the spin Hall effect,"Perpendicularly magnetized materials have attracted tremendous interest due
to their high anisotropy, which results in extremely narrow, nano-sized domain
walls. As a result, the recently studied current-induced domain wall motion
(CIDWM) in these materials promises to enable a novel class of data, memory,
and logic devices. In this letter, we propose the spin Hall effect as a
radically new mechanism for CIDWM. We are able to carefully tune the net spin
Hall current in depinning experiments on Pt/Co/Pt nanowires, offering unique
control over CIDWM. Furthermore, we determine that the depinning efficiency is
intimately related to the internal structure of the domain wall, which we
control by small fields along the nanowire. This new manifestation of CIDWM
offers a very attractive new degree of freedom for manipulating domain wall
motion by charge currents, and sheds light on the existence of contradicting
reports on CIDWM in perpendicularly magnetized materials.",1209.2320v1
2012/11/29,Experimental Demonstration Of Scanned Spin-Precession Microscopy,"Progress in spintronics has been aided by characterization tools tailored to
certain archetypical materials. New device structures and materials will
require characterization tools that are material independent, provide
sufficient resolution to image locally-varying spin properties and enable
subsurface imaging. Here we report the demonstration of a novel spin-microscopy
tool based on the variation of a global spin-precession signal in response to
the localized magnetic field of a scanned probe. We map the local spin density
in optically pumped GaAs from this spatially-averaged signal with a resolution
of 5.5 microns. This methodology is also applicable to other spin properties
and its resolution can be improved. It can extend spin microscopy to device
structures not accessible by other techniques, such as buried interfaces and
non-optically active materials, due to the universal nature of magnetic
interactions between the spins and the probe.",1211.7118v1
2013/2/6,On Magnetoacoustic Waves in Finitely Deformed Elastic Solids,"In this paper, in the context of the quasi-magnetostatic approximation, we
examine incremental motions superimposed on a static finite deformation of a
magnetoelastic material in the presence of an applied magnetic field. Explicit
expressions are obtained for the associated magnetoacoustic (or magnetoelastic
moduli) tensors in the case of an incompressible isotropic magnetoelastic
material, and these are then used to study the propagation of incremental plane
waves. The propagation condition is derived in terms of a generalized acoustic
tensor and the results are illustrated by obtaining explicit formulas in two
special cases: first, when the material is undeformed but subject to a uniform
bias field and second for a prototype model of magnetoelastic interactions in
the finite deformation regime. The results provide a basis for the experimental
determination of the material parameters of a magneto-sensitive elastomer from
measurements of the speed of incremental waves for different pre-strains, bias
magnetic fields, and directions of propagation.",1302.1285v1
2013/2/20,Magnetostrictive thin films for microwave spintronics,"Multiferroic composite materials, consisting of coupled ferromagnetic and
piezoelectric phases, are of great importance in the drive towards creating
faster, smaller and more energy efficient devices for information and
communications technologies. Such devices require thin ferromagnetic films with
large magnetostriction and narrow microwave resonance linewidths. Both
properties are often degraded, compared to bulk materials, due to structural
imperfections and interface effects in the thin films. We report the
development of single crystal thin films of Galfenol (Fe81Ga19) with
magnetostriction as large as the best reported values for bulk material. This
allows the magnetic anisotropy and microwave resonant frequency to be tuned by
voltage-induced strain, with a larger magnetoelectric response and a narrower
linewidth than any previously reported Galfenol thin films. The combination of
these properties make the single crystal thin films excellent candidates for
developing tunable devices for magnetic information storage, processing and
microwave communications.",1302.5097v1
2013/2/23,Electric Levitation Using Epsilon-Near-Zero Metamaterials,"Levitation of objects with action at a distance has always been intriguing to
humans. Several ways to achieve this, such as aerodynamic, acoustic, or
electromagnetic methods, including radiation pressure, stable potential wells,
and quantum Casimir-Lifshitz forces, exist. A fascinating approach for
levitation is that of magnets over superconductors based on the Meissner effect
-the expulsion of the magnetic field by a superconductor. With the advent of
metamaterials -designed structures with electromagnetic properties that may not
be found in nature- we ask whether a material may be conceived exhibiting
similar field expulsion, but involving the electric field. We show how a
special subcategory of metamaterials, called epsilon-near-zero materials,
exhibits such electric classic analog to the Meissner effect, exerting a
repulsion on nearby sources. Repulsive forces using anisotropic and chiral
metamaterials have been investigated, but our proposal uses a different
mechanism based on field expulsion, and is very robust to both losses and
material dispersion.",1302.5827v2
2014/5/19,Multiferroic Iron Oxide Thin Films at Room-Temperature,"In spite of being highly relevant for the development of a new generation of
information storage devices, not many single-phase materials displaying
magnetic and ferroelectric orders above room temperature are known. Moreover,
these uncommon materials typically display insignificant values of the remanent
moment in one of the ferroic orders or are complex multicomponent oxides which
will be very challenging to integrate in devices. Here we report on the
strategy to stabilize the metastable epsilon-Fe2O3 in thin film form, and we
show that besides its already known ferrimagnetic nature, the films are also
ferroelectric at 300 K with a remanent polarization of 1 microC/cm2. The film
polarization shows long retention times and can be switched under small applied
voltages. These characteristics make of epsilon-Fe2O3 the first single-ion
transition-metal oxide which is ferro(ferri)magnetic and ferroelectric at room
temperature. The simple composition of this new multiferroic oxide and the
discovery of a robust path for its thin film growth may boost the exploitation
of epsilon-Fe2O3 in novel devices.",1405.4909v1
2014/4/29,Materials Bound by Non-Chemical Forces: External Fields and the Quantum Vacuum,"We discuss materials which owe their stability to external fields. These
include: 1) external electric or magnetic fields, and 2) quantum vacuum
fluctuations in these fields induced by suitable boundary conditions (the
Casimir effect). Instances of the first case include the floating water bridge
and ferrofluids in magnetic fields. An example of the second case is taken from
biology where the Casimir effect provides an explanation of the formation of
stacked aggregations or ""rouleaux"" by negatively charged red blood cells. We
show how the interplay between electrical and Casimir forces can be used to
drive self-assembly of nano-structured materials, and could be generalized both
as a probe of Casimir forces and as a means of manufacturing nanoscale
structures. Interestingly, all the cases discussed involve the generation of
the somewhat exotic negative pressures. We note that very little is known about
the phase diagrams of most materials in the presence of external fields other
than those represented by the macroscopic scalar quantities of pressure and
temperature. Many new and unusual states of matter may yet be undiscovered.",1407.4483v1
2014/8/8,Orbital-driven nematicity in FeSe,"A very fundamental and unconventional characteristic of superconductivity in
iron-based materials is that it occurs in the vicinity of {\it two} other
instabilities. Apart from a tendency towards magnetic order, these Fe-based
systems have a propensity for nematic ordering: a lowering of the rotational
symmetry while time-reversal invariance is preserved. Setting the stage for
superconductivity, it is heavily debated whether the nematic symmetry breaking
is driven by lattice, orbital or spin degrees of freedom. Here we report a very
clear splitting of NMR resonance lines in FeSe at $T_{nem}$ = 91K, far above
superconducting $T_c$ of 9.3 K. The splitting occurs for magnetic fields
perpendicular to the Fe-planes and has the temperature dependence of a
Landau-type order-parameter. Spin-lattice relaxation rates are not affected at
$T_{nem}$, which unequivocally establishes orbital degrees of freedom as
driving the nematic order. We demonstrate that superconductivity competes with
the emerging nematicity.",1408.1875v3
2014/9/20,Notes on Constraints for the Observation of Polar Kerr Effect in Complex Materials,"While Kerr effect has been used extensively for the study of magnetic
materials, it is only recently that its has shown to be a powerful tool for the
study of more complex quantum matter. Since such materials tend to exhibit a
wealth of new phases and broken symmetries, it is important to understand the
general constraints on the possibility of observing a finite Kerr effect. In
this paper we reviewed the consequences of reciprocity on the scattering of
electromagnetic waves. In particular we concentrate on the possible detection
of Kerr effect from chiral media with and without time-reversal symmetry
breaking. We show that a finite Kerr effect is possible only if reciprocity is
broken. Introducing the utilization of the Sagnac interferometer as a detector
for breakdown of reciprocity via the detection of a finite Kerr effect, we
argue that in the linear regime, a finite detection is possible only if
reciprocity is broken. We then discuss possible Kerr effect detection for
materials with natural optical activity, magnetism, and chiral
superconductivity.",1409.5866v1
2015/1/9,Giant spin-phonon-electronic coupling in a 5d oxide,"Enhanced coupling of material properties offers new fundamental insights and
routes to multifunctional devices. In this context 5d oxides provide new
paradigms of cooperative interactions driving novel emergent behavior. This is
exemplified in 5d osmates that host a metal-insulator transition (MIT) driven
by magnetic order. Here we consider the most robust case, the 5d perovskite
NaOsO3, and reveal a giant coupling between spin and phonon through a frequency
shift of {\Delta}{\omega}=40 cm-1, the largest measured in any material. We
identify the dominant octahedral breathing mode and show isosymmetry with spin
ordering which induces dynamic charge disproportionation that sheds new light
on the MIT. The occurrence of the dramatic spin-phonon-electronic coupling in
NaOsO3 is due to a property common to all 5d materials: the large spatial
extent of the 5d ion. This allows magnetism to couple to phonons on an
unprecedented scale and consequently offers multiple new routes to enhanced
coupled phenomena.",1501.02290v1
2015/4/29,Gate-Tunable Tunneling Resistance in Graphene/Topological Insulator Vertical Junctions,"Graphene-based vertical heterostructures, particularly stacks incorporated
with other layered materials, are promising for nanoelectronics. The stacking
of two model Dirac materials, graphene and topological insulator, can
considerably enlarge the family of van der Waals heterostructures. Despite well
understanding of the two individual materials, the electron transport
properties of a combined vertical heterojunction are still unknown. Here we
show the experimental realization of a vertical heterojunction between Bi2Se3
nanoplate and monolayer graphene. At low temperatures, the electron transport
through the vertical heterojunction is dominated by the tunneling process,
which can be effectively tuned by gate voltage to alter the density of states
near the Fermi surface. In the presence of a magnetic field, quantum
oscillations are observed due to the quantized Landau levels in both graphene
and the two-dimensional surface states of Bi2Se3. Furthermore, we observe an
exotic gate-tunable tunneling resistance under high magnetic field, which
displays resistance maxima when the underlying graphene becomes a quantum Hall
insulator.",1504.07780v3
2015/9/2,A negative index meta-material for Maxwell's equations,"We derive the homogenization limit for time harmonic Maxwell's equations in a
periodic geometry with periodicity length $\eta>0$. The considered
meta-material has a singular sub-structure: the permittivity coefficient in the
inclusions scales like $\eta^{-2}$ and a part of the substructure
(corresponding to wires in the related experiments) occupies only a volume
fraction of order $\eta^2$; the fact that the wires are connected across the
periodicity cells leads to contributions in the effective system. In the limit
$\eta\to 0$, we obtain a standard Maxwell system with a frequency dependent
effective permeability $\mu^{\mathrm{eff}}(\omega)$ and a frequency independent
effective permittivity $\varepsilon^{\mathrm{eff}}$. Our formulas for these
coefficients show that both coefficients can have a negative real part, the
meta-material can act like a negative index material. The magnetic activity
$\mu^{\mathrm{eff}}\neq 1$ is obtained through dielectric resonances as in
previous publications. The wires are thin enough to be magnetically invisible,
but, due to their connectedness property, they contribute to the effective
permittivity. This contribution can be negative due to a negative permittivity
in the wires.",1509.00708v1
2015/10/19,What Makes Effective Gating Possible in Two-Dimensional Heterostructures?,"Electrostatic gating provides a way to obtain key functionalities in modern
electronic devices and to qualitatively alter materials properties. While
electrostatic description of such gating gives guidance for related doping
effects, inherent quantum properties of gating provide opportunities for
intriguing modification of materials and unexplored devices. Using
first-principles calculations for Co/bilayer graphene, Co/BN, and Co/benzene,
as well as a simple physical model, we show that magnetic heterostructures with
two-dimensional layered materials can manifest tunable magnetic proximity
effects. van der Waals bonding is identified as a requirement for large
electronic structure changes by gating. In particular, the magnitude and sign
of spin polarization in physisorbed graphene can be controlled by gating, which
is important for spintronic devices.",1510.05404v1
2016/1/18,Large magnetoresistance in LaBi: origin of field-induced resistivity upturn and plateau in compensated semimetals,"The discovery of non-magnetic extreme magnetoresistance (XMR) materials has
induced great interests because the XMR phenomenon challenges our understanding
of how a magnetic field can alter electron transport in semimetals. Among XMR
materials, the LaSb shows XMR and field-induced exotic behaviors but it seems
to lack the essentials for these properties. Here, we study the
magnetotransport properties and electronic structure of LaBi, isostructural to
LaSb. LaBi exhibits large MR as in LaSb, which can be ascribed to the nearly
compensated electron and hole with rather high mobilities. More importantly,
our analysis suggests that the XMR as well as field-induced resistivity upturn
and plateau observed in LaSb and LaBi can be well explained by the two-band
model with the compensation situation. We present the critical conditions
leading to these field-induced properties. It will contribute to understanding
the XMR phenomenon and explore novel XMR materials.",1601.04618v2
2016/4/19,Observation of spin Seebeck contribution to the transverse thermopower in Ni-Pt and MnBi-Au bulk nanocomposites,"Transverse thermoelectric devices produce electric fields perpendicular to an
incident heat flux. Classically, this process is driven by the Nernst effect in
bulk solids, wherein a magnetic field generates a Lorentz force on thermally
excited electrons. The spin Seebeck effect (SSE) also produces
magnetization-dependent transverse electric fields. SSE is traditionally
observed in thin metallic films deposited on electrically insulating
ferromagnets, but the films' high resistance limits thermoelectric conversion
efficiency. Combining Nernst and SSE in bulk materials would enable devices
with simultaneously large transverse thermopower and low electrical resistance.
Here we demonstrate experimentally this is possible in composites of conducting
ferromagnets (Ni or MnBi) containing metallic nanoparticles with strong
spin-orbit interactions (Pt or Au). These materials display positive shifts in
transverse thermopower attributable to inverse spin Hall electric fields in the
nanoparticles. This more than doubles the power output of the Ni-Pt materials,
establishing proof-of-principle that SSE persists in bulk nanocomposites.",1604.05626v3
2016/7/31,"X-ray powder diffraction of high-absorption materials at the XRD1 beamline off the best conditions: Application to (Gd,Nd)5Si4 compounds","Representative compounds of the new family of magnetic materials Gd5-xNdxSi4
were analyzed by X-ray diffraction at the XRD1 beamline at LNLS. To reduce
X-ray absorption, thin layers of the powder samples were mounted outside the
capillaries and measured in Debye-Scherrer geometry as usual. The X-ray
diffraction analyses and the magnetometry results indicate that the behavior of
the magnetic transition temperature as a function of Nd content may be directly
related to the average of the four smallest interatomic distances between
different rare earth sites of the majority phase of each compound. The quality
and consistency of the results show that the XRD1 beamline is able to perform
satisfactory X-ray diffraction experiments on high-absorption materials even
off the best conditions.",1608.00565v2
2016/9/16,Interface Engineering in La0.67Sr0.33MnO3-SrTiO3 Heterostructures,"Interface engineering is an extremely useful tool for systematically
investigating materials and the various ways materials interact with each
other. We describe different interface engineering strategies designed to
reveal the origin of the electric and magnetic dead-layer at La0.67Sr0.33MnO3
interfaces. La0.67Sr0.33MnO3 is a key example of a strongly correlated
peroskite oxide material in which a subtle balance of competing interactions
gives rise to a ferromagnetic metallic groundstate. This balance, however, is
easily disrupted at interfaces. We systematically vary the dopant profile, the
disorder and the oxygen octahedra rotations at the interface to investigate
which mechanism is responsible for the dead layer. We find that the magnetic
dead layer can be completely eliminated by compositional interface engineering
such that the polar discontinuity at the interface is removed. This, however,
leaves the electrical dead-layer largely intact. We find that deformations in
the oxygen octahedra network at the interface are the dominant cause for the
electrical dead layer.",1609.04976v1
2016/11/9,Possible Weyl fermions in the magnetic Kondo system CeSb,"Materials where the electronic bands have unusual topologies allow for the
realization of novel physics and have a wide range of potential applications.
When two electronic bands with linear dispersions intersect at a point, the
excitations could be described as Weyl fermions which are massless particles
with a particular chirality. Here we report evidence for the presence of Weyl
fermions in the ferromagnetic state of the low-carrier density, strongly
correlated Kondo lattice system CeSb, from electronic structure calculations
and angle-dependent magnetoresistance measurements. When the applied magnetic
field is parallel to the electric current, a pronounced negative
magnetoresistance is observed within the ferromagnetic state, which is
destroyed upon slightly rotating the field away. These results give evidence
for CeSb belonging to a new class of Kondo lattice materials with Weyl fermions
in the ferromagnetic state.",1611.02927v2
2016/12/13,Chemical bonding and electronic-structure in MAX phases as viewed by X-ray spectroscopy and density functional theory,"This is a critical review of MAX-phase carbides and nitrides from an
electronic-structure and chemical bonding perspective. This large group of
nanolaminated materials is of great scientific and technological interest and
exhibit a combination of metallic and ceramic features. These properties are
related to the special crystal structure and bonding characteristics with
alternating strong M-C bonds in high-density MC slabs, and relatively weak M-A
bonds between the slabs. Here, we review the trend and relationship between the
chemical bonding, conductivity, elastic and magnetic properties of the MAX
phases in comparison to the parent binary MX compounds with the underlying
electronic structure probed by polarized X-ray spectroscopy. Spectroscopic
studies constitute important tests of the results of state-of-the-art
electronic structure density functional theory that is extensively discussed
and are generally consistent. By replacing the elements on the M, A, or X-sites
in the crystal structure, the corresponding changes in the conductivity,
elasticity, magnetism and other materials properties makes it possible to
tailor the characteristics of this class of materials by controlling the
strengths of their chemical bonds.",1612.04398v1
2016/12/19,Dynamical Multiferroicity,"An appealing mechanism for inducing multiferroicity in materials is the
generation of electric polarization by a spatially varying magnetization that
is coupled to the lattice through the spin-orbit interaction. Here we describe
the reciprocal effect, in which a time-dependent electric polarization induces
magnetization even in materials with no existing spin structure. We develop a
formalism for this dynamical multiferroic effect in the case for which the
polarization derives from optical phonons, and compute the strength of the
phonon Zeeman effect, which is the solid-state equivalent of the
well-established vibrational Zeeman effect in molecules, using density
functional theory. We further show that a recently observed behavior -- the
resonant excitation of a magnon by optically driven phonons -- is described by
the formalism. Finally, we discuss examples of scenarios that are not driven by
lattice dynamics and interpret the excitation of Dzyaloshinskii-Moriya-type
electromagnons and the inverse Faraday effect from the viewpoint of dynamical
multiferroicity.",1612.06331v2
2017/2/16,Anomalous Nonlocal Resistance and Spin-charge Conversion Mechanisms in Two-Dimensional Metals,"We uncover two anomalous features in the nonlocal transport behavior of
two-dimensional metallic materials with spin-orbit coupling. Firstly, the
nonlocal resistance can have negative values and oscillate with distance, even
in the absence of a magnetic field. Secondly, the oscillations of the nonlocal
resistance under an applied in-plane magnetic field (Hanle effect) can be
asymmetric under field reversal. Both features are produced by direct
magnetoelectric coupling, which is possible in materials with broken inversion
symmetry but was not included in previous spin diffusion theories of nonlocal
transport. These effects can be used to identify the relative contributions of
different spin-charge conversion mechanisms. They should be observable in
adatom-functionalized graphene, and may provide the reason for discrepancies in
recent nonlocal transport experiments on graphene.",1702.04955v3
2017/3/10,Highly crystalline 2D superconductors,"Recent technological advances in controlling materials have developed methods
to produce idealized two-dimensional (2D) electron systems such as
heterogeneous interfaces, molecular-beam-epitaxy (MBE) grown atomic layers,
exfoliated thin flakes and field-effect devices. These 2D electron systems are
highly-crystalline with less disorder in common, some of which indeed show
sheet resistance more than one order of magnitude lower even in atomic layers
or single layers than that of conventional amorphous/granular thin films. Here,
we present a review on the recent developments of highly-crystalline 2D
superconductors and a series of unprecedented physical properties discovered in
these systems. In particular, we highlight the quantum metallic state (or
possible metallic ground state), the quantum Griffiths phase in out-of-plane
magnetic fields, and the superconducting state maintained in anomalously large
in-plane magnetic fields, which were observed in exfoliated 2D materials,
MBE-grown atomic-layer thin films and electric-double-layer (ion-gated)
interfaces. These phenomena are discussed on the basis of weakened disorder
and/or broken spatial inversion symmetry. These novel aspects suggest that
highly-crystalline 2D systems are promising platforms for exploring new quantum
physics and superconductors.",1703.03541v1
2017/5/23,"Unexpected 3+ valence of iron in FeO$_2$, a geologically important material lying ""in between"" oxides and peroxides","Recent discovery of pyrite FeO$_2$, which can be an important ingredient of
the Earth's lower mantle and which in particular may serve as an extra source
of water in the Earth's interior, opens new perspectives for geophysics and
geochemistry, but this is also an extremely interesting material from physical
point of view. We found that in contrast to naive expectations Fe is nearly 3+
in this material, which strongly affects its magnetic properties and makes it
qualitatively different from well known sulfide analogue - FeS$_2$. Doping,
which is most likely to occur in the Earth's mantle, makes FeO$_2$ much more
magnetic. In addition we show that unique electronic structure places FeO$_2$
""in between"" the usual dioxides and peroxides making this system interesting
both for physics and solid state chemistry.",1705.08085v2
2017/6/20,"Room Temperature Magnetoresistance and Exchange Bias in ""314 - type"" Oxygen-Vacancy Ordered SrCo$_{0.85}$Fe$_{0.15}$O$_{2.62}$","Herein, we report the magneto-transport and exchange bias effect in a ""314 -
type"" oxygen - vacancy ordered material with composition
SrCo$_{0.85}$Fe$_{0.15}$O$_{2.62}$. This material exhibits a ferrimagnetic
transition above room temperature, at 315 K. The negative magnetoresistance
starts to appear from room temperature (-1.3 $\%$ at 295 K in 70 kOe) and
reaches a sizable value of 58 $\%$ at 4 K in 70 kOe. Large exchange bias effect
is observed below 315 K when the sample is cooled in the presence of a magnetic
field. The coexistence of nearly compensated and ferrimagnetic regions in the
layered structure originate magnetoresistance and exchange bias in this sample.
The appearance of a sizable magnetoresistance and giant exchange bias effect,
especially near room temperature indicates that ""314-type"" cobaltates are a
promising class of material systems for the exploration of materials with
potential applications as magnetic sensors or in the area of spintronics.",1706.06264v2
2017/8/7,Small Fermi Surfaces and Strong Correlation Effects in Dirac Materials with Holography,"Recent discovery of transport anomaly in graphene demonstrated that a system
known to be weakly interacting may become strongly correlated if system
parameter(s) can be tuned such that fermi surface is sufficiently small. We
study the strong correlation effects in the transport coefficients of Dirac
materials doped with magnetic impurity under the magnetic field using
holographic method. The experimental data of magneto-conductivity are well fit
by our theory, however, not much data are available for other transports of
Dirac material in such regime. Therefore, our results on heat
transport,thermo-electric power and Nernst coefficients are left as predictions
of holographic theory for generic Dirac materials in the vicinity of charge
neutral point with possible surface gap. We give detailed look over each
magneto-transport observable and 3Dplots to guide future experiments.",1708.02257v2
2017/11/21,Multiferroic Quantum Criticality,"The zero-temperature limit of a continuous phase transition is marked by a
quantum critical point, which can generate exotic physics that extends to
elevated temperatures. Magnetic quantum criticality is now well known, and has
been explored in systems ranging from heavy fermion metals to quantum Ising
materials. Ferroelectric quantum critical behaviour has also been recently
established, motivating a flurry of research investigating its consequences.
Here, we introduce the concept of multiferroic quantum criticality, in which
both magnetic and ferroelectric quantum criticality occur in the same system.
We develop the phenomenology of multiferroic quantum critical behaviour,
describe the associated experimental signatures, and propose material systems
and schemes to realize it.",1711.07989v2
2018/9/21,Exchange Bias in the [CoO/Co/Pd]10 Antidot Large Area Arrays,"Magnetic nanostructures revealing exchange bias effect have gained a lot of
interest in recent years due to their possible applications in modern devices
with various functionalities. In this paper, we present our studies on
patterned [CoO/Co/Pd]10 multilayer where ferromagnetic material is in a form of
clusters, instead of being a continuous layer. The system was patterned using
nanosphere lithography technique which resulted in creation of an assembly of
well-ordered antidots or islands over a large substrate area. We found that the
overall hysteresis loop of the films consists of hard and soft components. The
hard component hysteresis loop exhibits a large exchange bias field up to -11
kOe. The patterning process causes a slight increase of the exchange field as
the antidot radius rises. We also found that the material on edges of the
structures gives rise to a soft unbiased magnetization component.",1809.07996v1
2019/4/9,Observation of Giant Quantized Phonon Modes in Graphene via Tunneling Spectra,"Phonons, the fundamental vibrational modes of a crystal lattice, play a
crucial role in determining electronic properties of materials through
electron-phonon interaction. However, it has proved difficult to directly probe
the phonon modes of materials in electrical measurements. Here, we report the
observation of giant quantized phonon peaks of the K and K out-of-plane phonon
in graphene monolayer in magnetic fields via tunneling spectra, which are
usually used to measure local electronic properties of materials. A
perpendicular magnetic field quantizes massless Dirac fermions in graphene into
discrete Landau levels (LLs). We demonstrate that emission or absorption of
phonons of quasiparticles in the LLs of graphene generates a new sequence of
discrete states: the quantized phonon modes. In our tunneling spectra, the
intensity of the observed phonon peaks is about 50 times larger than that of
the LLs because that the K and K out-of-plane phonon opens an inelastic
tunneling channel. We also show that it is possible to switch on off the
quantized phonon modes at nanoscale by controlling interactions between
graphene and the supporting substrate.",1904.04425v1
2019/4/23,Tailored tunnel magnetoresistance response in three ultrathin chromium trihalides,"Materials that demonstrate large magnetoresistance have attracted significant
interest for many decades. Recently, extremely large tunnel magnetoresistance
(TMR) has been reported by several groups across ultrathin CrI$_3$ by
exploiting the weak antiferromagnetic coupling between adjacent layers. Here,
we report a comparative study of TMR in all three chromium trihalides (CrX$_3$,
X= Cl, Br, or I) in the two-dimensional limit. As the materials exhibit
different transition temperatures and interlayer magnetic ordering in the
ground state, tunneling measurements allow for an easy determination of the
field-temperature phase diagram for the three systems. By changing sample
thickness and biasing conditions, we then demonstrate how to maximize and
further tailor the TMR response at different temperatures for each material. In
particular, near the magnetic transition temperature, TMR is non-saturating up
to the highest fields measured for all three compounds owing to the large,
field-induced exchange coupling.",1904.10476v2
2019/5/18,"The New Nitrides: Layered, Ferroelectric, Magnetic, Metallic and Superconducting Nitrides to Boost the GaN Photonics and Electronics Eco-System","The nitride semiconductor materials GaN, AlN, and InN, and their alloys and
heterostructures have been investigated extensively in the last 3 decades,
leading to several technologically successful photonic and electronic devices.
Just over the past few years, a number of new nitride materials have emerged
with exciting photonic, electronic, and magnetic properties. Some examples are
2D and layered hBN and the III-V diamond analog cBN, the transition metal
nitrides ScN, YN, and their alloys (e.g. ferroelectric ScAlN), piezomagnetic
GaMnN, ferrimagnetic Mn4N, and epitaxial superconductor/semiconductor NbN/GaN
heterojunctions. This article reviews the fascinating and emerging physics and
science of these new nitride materials. It also discusses their potential
applications in future generations of devices that take advantage of the
photonic and electronic devices eco-system based on transistors, light-emitting
diodes, and lasers that have already been created by the nitride
semiconductors.",1905.07627v1
2019/5/27,Thermal Hall signatures of non-Kitaev spin liquids in honeycomb Kitaev materials,"Motivated by the recent surge of field-driven phenomena discussed for Kitaev
materials, in particular the experimental observation of a finite thermal Hall
effect and theoretical proposals for the emergence of additional spin liquid
phases beyond the conventional Kitaev spin liquid, we develop a theoretical
understanding of the thermal Hall effect in honeycomb Kitaev materials in
magnetic fields. Our focus is on gapless U(1) spin liquids with a spinon Fermi
surface, which have been shown to arise as field-induced phases. We demonstrate
that in the presence of symmetry-allowed, second-neighbor Dzyaloshinskii-Moriya
interactions these spin liquids give rise to a finite, non-quantized, thermal
Hall conductance in a magnetic field. The microscopic origin of this thermal
Hall effect can be traced back to an interplay of Dzyaloshinskii-Moriya
interaction and Zeeman coupling, which generates an internal U(1) gauge flux
that twists the motion of the emergent spinons. We argue that such a
non-quantized thermal Hall effect is a generic response in Kitaev models for a
range of couplings.",1905.11321v1
2019/7/9,Magnetic instabilities in doped Fe$_2YZ$ full-Heusler thermoelectric compounds,"Thermoelectricity is a promising avenue for harvesting energy but large-scale
applications are still hampered by the lack of highly-efficient low-cost
materials. Recently, Fe$_2YZ$ Heusler compounds were predicted theoretically to
be interesting candidates with large thermoelectric power factor. Here, we show
that under doping conditions compatible with thermoelectric applications, these
materials are prone to an unexpected magnetic instability detrimental to their
thermoelectric performance. We rationalize the physics at the origin of this
instability, provide guidelines for avoiding it and discuss its impact on the
thermoelectric power factor. Doing so, we also point out the shortcomings of
the rigid band approximation commonly used in high-throughput theoretical
searches of new thermoelectrics.",1907.04267v2
2019/7/31,Perspective: Heusler interfaces -- opportunities beyond spintronics?,"Heusler compounds, in both cubic and hexagonal polymorphs, exhibit a
remarkable range of electronic, magnetic, elastic, and topological properties,
rivaling that of the transition metal oxides. To date, research on these
quantum materials has focused primarily on bulk magnetic and thermoelectric
properties or on applications in spintronics. More broadly, however, Heuslers
provide a platform for discovery and manipulation of emergent properties at
well-defined crystalline interfaces. Here, motivated by advances in the
epitaxial growth of layered Heusler heterostructures, I present a vision for
Heusler interfaces, focusing on the frontiers and challenges that lie beyond
spintronics. The ability to grow these materials epitaxially on technologically
important semiconductor substrates, such as GaAs, Ge, and Si, provides a direct
path for their integration with modern electronics. Further advances will
require new methods to control the stoichiometry and defects to ""electronic
grade"" quality, and to control the interface abruptness and ordering at the
atomic scale.",1908.00101v1
2019/8/1,"Theory of surface-induced multiferroicity in magnetic materials, thin films and multilayers","We present a theoretical study of the onset of electric polarization close to
a surface in magnetic materials and in thin films and multilayers. We consider
two different paths that lead to the onset of multiferroic behavior at the
boundary in materials that are bulk collinear ferromagnets or antiferromagnets.
These two paths are distinguished by the presence or absence of a surface
induced Dzyaloshinskii-Moriya interaction which can be taken into account
through Lifshitz invariants in the free energy of the system. Experimental
consequences are discussed in the light of the developed theory.",1908.00602v2
2019/8/10,"Multielemental single-atom-thick A layers in nanolaminated V2(Sn, A)C (A=Fe, Co, Ni, Mn) for tailoring magnetic properties","Tailoring of individual single-atom-thick layers in nanolaminated materials
offers atomic-level control over material properties. Nonetheless, multielement
alloying in individual atomic layers in nanolaminates is largely unexplored.
Here, we report a series of inherently nanolaminated V2(A'xSn1-x)C (A'=Fe, Co,
Ni and Mn, and combinations thereof, with x=1/3) synthesized by an alloy-guided
reaction. The simultaneous occupancy of the four magnetic elements and Sn, the
individual single-atom-thick A layers in the compound constitute
high-entropy-alloy analogues, two-dimensional in the sense that the alloying
exclusively occurs in the A layers. V2(A'xSn1-x)C exhibit distinct
ferromagnetic behavior that can be compositionally tailored from the
multielement A-layer alloying. This two-dimensional alloying provides a
structural-design route with expanded chemical space for discovering materials
and exploit properties.",1908.03709v1
2019/9/13,SOS: Symmetry Operational Similarity,"Symmetry often governs condensed matter physics. The act of breaking symmetry
spontaneously leads to phase transitions, and various observables or observable
physical phenomena can be directly associated with broken symmetries. Examples
include ferroelectric polarization, ferromagnetic magnetization, optical
activities (including Faraday and magneto-optic Kerr rotations), second
harmonic generation, photogalvanic effects, nonreciprocity, various
Hall-effect-type transport properties, and multiferroicity. Herein, we propose
that observable physical phenomena can occur when specimen constituents (i.e.,
lattice distortions or spin arrangements, in external fields or other
environments, etc.) and measuring probes/quantities (i.e., propagating light,
electrons or other particles in various polarization states, including vortex
beams of light and electrons, bulk polarization or magnetization, etc.) share
symmetry operational similarity (SOS) in relation to broken symmetries. In
addition, quasi-equilibrium electronic transport processes such as diode-type
transport effects, linear or circular photogalvanic effects, Hall-effect-type
transport properties ((planar) Hall, Ettingshausen, Nernst, thermal Hall, spin
Hall, and spin Nernst effects) can be understood in terms of symmetry
operational systematics. The power of the SOS approach lies in providing simple
and physically transparent views of otherwise unintuitive phenomena in complex
materials. In turn, this approach can be leveraged to identify new materials
that exhibit potentially desired properties as well as new phenomena in known
materials.",1909.06267v1
2019/10/30,Large anomalous Nernst effect in a van der Waals ferromagnet Fe$_3$GeTe$_2$,"Anomalous Nernst effect, a result of charge current driven by temperature
gradient, provides a probe of the topological nature of materials due to its
sensitivity to the Berry curvature near the Fermi level. Fe3GeTe2, one
important member of the recently discovered two-dimensional van der Waals
magnetic materials, offers a unique platform for anomalous Nernst effect
because of its metallic and topological nature. Here, we report the observation
of large anomalous Nernst effect in Fe3GeTe2. The anomalous Hall angle and
anomalous Nernst angle are about 0.07 and 0.09 respectively, far larger than
those in common ferromagnets. By utilizing the Mott relation, these large
angles indicate a large Berry curvature near the Fermi level, consistent with
the recent proposal for Fe3GeTe2 as a topological nodal line semimetal
candidate. Our work provides evidence of Fe3GeTe2 as a topological ferromagnet,
and demonstrates the feasibility of using two-dimensional magnetic materials
and their band topology for spin caloritronics applications.",1910.13617v1
2020/1/7,Molecular beam epitaxy of the magnetic kagome metal FeSn on LaAlO3 (111),"Materials with a layered Kagome lattice are expected to give rise to novel
physics arising from band structures with topological properties, spin liquid
behavior and the formation of skyrmions. Until now, most work on Kagome
materials has been performed on bulk samples due to difficulties in thin film
synthesis. Here, by using molecular beam epitaxy, layered Kagome-structured
FeSn films are synthesized on (111) oriented LaAlO3 substrate. Both in-situ and
ex-situ characterizations indicate these films are highly crystalline and
c-axis oriented, with atomically smooth surfaces. However, the films grow as
disconnected islands, with lateral dimensions on the micron scale. By
patterning Pt electrodes using a focused electron beam, longitudinal and
transverse resistance of single islands have been measured in magnetic fields.
Our work opens a pathway for exploring mesoscale transport properties in thin
films of Kagome materials and related devices.",2001.01820v2
2020/4/1,Topological and Thermoelectric Properties of Double Antiperovskite Pnictides,"Doubling the perovskite cell (double perovskite) has been found to open new
possibilities for engineering functional materials, magnetic materials in
particular. This route should be applicable to the antiperovskite (aPV) class.
In the pnictide based double aPV (2aPV) class introduced here magnetism is very
rare, and we address them as new topological materials, possibly with
thermoelectric interest. We have found that the 2aPV supercell provides a
systematically larger band gap that can serve to inhibit bulk conductivity, and
also large spin-orbit coupling (SOC) for band inversion. We present examples
from a broad study of double antiperovskites focusing on the X$_6$AA$'$B$_2$
configuration, where X is the alkaline earth element and A and B are the group
5A pnictogens. We find that an ""extended s"" state at the valence band minimum,
described alternatively as a cation valence state or a modulated interstitial
planewave state, plays a crucial role in both topological and thermoelectric
properties. Several of these compounds may house topological phases, while
transport calculations indicate they may also find themselves useful in
thermoelectric applications.",2004.00717v1
2020/10/25,Multifunctional Oxides for Topological Magnetic Textures by Design,"Several challenges in designing an operational Skyrmion racetrack memory are
well-known. Among those challenges, a few contradictions can be identified if
researchers were to rely only on metallic materials. Hence, expanding the
exploration on Skyrmion Physics into oxide materials is essential to bridge the
contradicting gap. In this topical review, we first briefly revise the theories
and criteria involved in stabilizing and manipulating Skymions, followed by
studying the behaviors of dipolar-stabilized magnetic bubbles. Next, we explore
the properties of multiferroic Skyrmions with magnetoelectric coupling, which
can only be stabilized in Cu$_2$OSeO$_3$ thus far, as well as the rare bulk
N\'eel-type Skyrmions in some polar materials. As an interlude section, we
review the theory of Anomalous (AHE) and Topological Hall Effect (THE), before
going through the recent progress of THE in oxide thin films. The debate about
an alternative interpretation is also discussed. Finally, this review ends with
future outlooks about the promising strategies of using interfacial
charge-transfer and (111)-orientation of perovskites to benefit the field of
Skyrmion research.",2010.13012v1
2020/11/16,"First-principles study of the electronic, magnetic, and crystal structure of perovskite molybdates","The molybdate oxides SrMoO$_3$, PbMoO$_3$, and LaMoO$_3$ are a class of
metallic perovskites that exhibit interesting properties including high
mobility, and unusual resistivity behavior. We use first-principles methods
based on density functional theory to explore the electronic, crystal, and
magnetic structure of these materials. In order to account for the electron
correlations in the partially-filled Mo $4d$ shell, a local Hubbard $U$
interaction is included. The value of $U$ is estimated via the constrained
random-phase approximation approach, and the dependence of the results on the
choice of $U$ are explored. For all materials, GGA+$U$ predicts a metal with an
orthorhombic, antiferromagnetic structure. For LaMoO$_3$, the $Pnma$ space
group is the most stable, while for SrMoO$_3$ and PbMoO$_3$, the $Imma$ and
$Pnma$ structures are close in energy. The $R_4^+$ octahedral rotations for
SrMoO$_3$ and PbMoO$_3$ are found to be overestimated compared to the
experimental low-temperature structure.",2011.08323v2
2020/11/24,Uniaxial Néel Vector Control in Perovskite Oxide Thin Films by Anisotropic Strain Engineering,"Antiferromagnetic thin films typically exhibit a multi-domain state, and
control of the antiferromagnetic N\'eel vector is challenging as
antiferromagnetic materials are robust to magnetic perturbations. By relying on
anisotropic in-plane strain engineering of epitaxial thin films of the
prototypical antiferromagnetic material LaFeO3, uniaxial N\'eel vector control
is demonstrated. Orthorhombic (011)- and (101)-oriented DyScO3, GdScO3 and
NdGaO3 substrates are used to engineer different anisotropic in-plane strain
states. The anisotropic in-plane strain stabilises structurally monodomain
monoclinic LaFeO3 thin films. The uniaxial N\'eel vector is found along the
tensile strained b axis, contrary to bulk LaFeO3 having the N\'eel vector along
the shorter a axis, and no magnetic domains are found. Hence, anisotropic
strain engineering is a viable tool for designing unique functional responses,
further enabling antiferromagnetic materials for mesoscopic device technology.",2011.12056v1
2021/3/31,Spontaneous valley polarization in 2D organometallic lattice,"2D ferrovalley materials that exhibit spontaneous valley polarization are
both fundamentally intriguing and practically appealing to be used in
valleytronic devices. Usually, the research on 2D ferrovalley materials is
mainly focused on inorganic systems, severely suffering from in-plane
magnetization. Here, we alternatively show by kp model analysis and
high-throughput first-principles calculations that ideal spontaneous valley
polarization is present in 2D organometallic lattice. We explore the design
principle for organic 2D ferrovalley materials composed of (quasi-)planer
molecules and transition-metal atoms in hexagonal lattice, and identify twelve
promising candidates. These systems have a ferromagnetic or antiferromagnetic
semiconducting state, and importantly they exhibit robust out-of-plane
magnetization. The interplay between spin and valley, together with strong
spin-orbit coupling of transition-metal atoms, guarantee the spontaneous valley
polarization in these systems, facilitating the anomalous valley Hall effect.
Our findings significantly broaden the scientific and technological impact of
ferrovalley physics.",2103.16741v1
2021/3/31,Casimir forces in the flatland: interplay between photo-induced phase transitions and quantum Hall physics,"We investigate how photo-induced topological phase transitions and the
magnetic-field-induced quantum Hall effect simultaneously influence the Casimir
force between two parallel sheets of staggered two-dimensional (2D) materials
of the graphene family. We show that the interplay between these two effects
enables on-demand switching of the force between attractive and repulsive
regimes while keeping its quantized characteristics. We also show that doping
these 2D materials below their first Landau level allows one to probe the
photoinduced topology in the Casimir force without the difficulties imposed by
a circularly polarized laser. We demonstrate that the magnetic field has a huge
impact on the thermal Casimir effect for dissipationless materials, where the
quantized aspect of the energy levels leads to a strong repulsion that could be
measured even at room temperature.",2103.16743v1
2021/7/22,Nearly room temperature ferromagnetism in pressure-induced correlated metallic state of van der Waals insulator CrGeTe$_3$,"A complex interplay of different energy scales involving Coulomb repulsion,
spin-orbit coupling and Hund's coupling energy in two-dimensional (2D) van der
Waals (vdW) material produces novel emerging physical state. For instance,
ferromagnetism in vdW charge transfer insulator CrGeTe$_3$, that provides a
promising platform to simultaneously manipulate the magnetic and electrical
properties for potential device implementation using few layers thick
materials. Here, we show a continuous tuning of magnetic and electrical
properties of CrGeTe$_3$ single crystal using pressure. With application of
pressure, CrGeTe$_3$ transforms from a FM insulator with Curie temperature,
$T_{\rm{C}} \sim $ 66 K at ambient condition to a correlated 2D Fermi metal
with $T_{\rm{C}}$ exceeding $\sim$ 250 K. Notably, absence of an accompanying
structural distortion across the insulator-metal transition (IMT) suggests that
the pressure induced modification of electronic ground states are driven by
electronic correlation furnishing a rare example of bandwidth-controlled IMT in
a vdW material.",2107.10573v1
2021/8/9,The role of spin-lattice coupling for ultrafast magnetization changes in rare earth metals,"By comparing femtosecond laser-pulse-induced spin dynamics in the surface
state of the rare earth metals Gd and Tb we show that the spin polarization of
the valence states in both materials decays with significantly different time
constants of 15\,ps and 400\,fs, respectively. The distinct spin polarization
dynamics in Gd and Tb are opposed by similar exchange splitting dynamics in the
two materials. The different time scales observed in our experiment can be
attributed to weak and strong $4f$ spin to lattice coupling in Gd and Tb
suggesting an intimate coupling of spin polarization and 4f magnetic moment.
While in Gd the lattice mainly acts as a heat sink, it contributes
significantly to ultrafast demagnetization of Tb. This helps explain why all
optical switching is observed in FeGd -- but rarely in FeTb-based compounds.",2108.04380v2
2021/8/11,Aspects of wave propagation in a nonlinear medium: birefringence and the second-order magnetoelectric coefficients,"Magnetoelectric materials have the interesting property of exhibiting
polarization induced by a magnetic field or magnetization induced by an
electric field. As a consequence, a multitude of effects can be produced by
means of controllable external fields. A method for deriving phase velocities
and its corresponding polarization vectors for light rays in nonlinear optical
materials in a nondispersive regime is here revisited and used to study wave
propagation in a certain class of second-order magnetoelectric media. In
particular, the birefringence effect is theoretically examined and it is shown
that it can be used as a tool to obtain most of the second-order
magnetoelectric coefficients $\beta_{ijk}$ of a material having an isotropic
linear sector. Estimates of the effect are presented. Some optical properties
of nonlinear materials presenting a natural optic axis are also discussed.",2108.05220v2
2021/8/19,On-the-fly Autonomous Control of Neutron Diffraction via Physics-Informed Bayesian Active Learning,"Neutron scattering is a unique and versatile characterization technique for
probing the magnetic structure and dynamics of materials. However, instruments
at neutron scattering facilities in the world is limited, and instruments at
such facilities are perennially oversubscribed. We demonstrate a significant
reduction in experimental time required for neutron diffraction experiments by
implementation of autonomous navigation of measurement parameter space through
machine learning. Prior scientific knowledge and Bayesian active learning are
used to dynamically steer the sequence of measurements. We developed the
autonomous neutron diffraction explorer (ANDiE) and used it to determine the
magnetic order of MnO and Fe1.09Te. ANDiE can determine the Neel temperature of
the materials with 5-fold enhancement in efficiency and correctly identify the
transition dynamics via physics-informed Bayesian inference. ANDiE's active
learning approach is broadly applicable to a variety of neutron-based
experiments and can open the door for neutron scattering as a tool of
accelerated materials discovery.",2108.08918v2
2021/10/12,Large positive magnetoresistance in photocarrier doping potassium tantalites in the extreme quantum limit,"We report on a high-field magnetotransport study of KTaO3 single crystals.
This material is a promising candidate to study in the extreme quantum limit
(EQL). By photocarrier doping with 360 nm light, we have observed a significant
positive, non-saturating, and linear magnetoresistance at low temperatures
accompanied by a vanishing Hall coefficient. When cooled down to 10 K and
subjected to a magnetic field of 12 T, the value of magnetoresistance of KTaO3
(100) is increased by as much as 433%. Such behavior can be attributed to all
electrons occupying only the lowest Landau level in the EQL. In this state, a
quantum magnetoresistance is produced. This result provides novel insights into
the next generation of magnetic devices based on complex materials and adds a
new family of materials with positive magnetoresistance.",2110.05791v1
2021/12/27,Wide Field Imaging of van der Waals Ferromagnet Fe3GeTe2 by Spin Defects in Hexagonal Boron Nitride,"Emergent color centers with accessible spins hosted by van der Waals
materials have attracted substantial interest in recent years due to their
significant potential for implementing transformative quantum sensing
technologies. Hexagonal boron nitride (hBN) is naturally relevant in this
context due to its remarkable ease of integration into devices consisting of
low-dimensional materials. Taking advantage of boron vacancy spin defects in
hBN, we report nanoscale quantum imaging of low-dimensional ferromagnetism
sustained in Fe3GeTe2/hBN van der Waals heterostructures. Exploiting spin
relaxometry methods, we have further observed spatially varying magnetic
fluctuations in the exfoliated Fe3GeTe2 flake, whose magnitude reaches a peak
value around the Curie temperature. Our results demonstrate the capability of
spin defects in hBN of investigating local magnetic properties of layered
materials in an accessible and precise way, which can be extended readily to a
broad range of miniaturized van der Waals heterostructure systems.",2112.13570v1
2022/1/12,"Weyl-type nodal chains in X2MnO4 (X= Li, Na)","Recently, magnetic topological semimetals have received a lot of attention
due to their potential applications in the field of spintronics. By using
first-principles calculations, we propose that two ferromagnetic spinel
materials of X2MnO4 (X=Li, Na) have Weyl-type nodal chains around the Fermi
level. Their stabilities are validated by cohesive energies, phonon
dispersions, and elastic constants. The nodal chains are composed of two types
of nodal loops, which are protected by the glide operation Mz, the mirror
operation M101 and their equivalent. The drumhead surface states are observed
on the (001) surface and they exhibit nontrivial topological features. In
addition, under different electron correlations and lattice strains, the
semimetal states of these two materials are well kept. Our work provides two
promising candidates for exploring the combination of magnetic materials and
topological semimetal states.",2201.04306v1
2022/1/19,Observation of short-period helical spin order and magnetic transition in a non-chiral centrosymmetric helimagnet,"The search for materials exhibiting nanoscale spiral order continues to be
fuelled by the promise of emergent inductors. Although such spin textures have
been reported in many materials, most of them exhibit long periods or are
limited to operate far below room temperature. Here, we present the real-space
observation of an ordered helical spin order with a period of 3.2 nm in a
non-chiral centrosymmetric helimagnet MnCoSi at room temperature via
multi-angle and multi-azimuth approach of Lorentz transmission electron
microscopy (TEM). A magnetic transition from the ordered helical spin order to
a cycloidal spin order below 228 K is clearly revealed by in situ neutron
powder diffraction and Lorentz TEM, which is closely correlated with
temperature-induced variation in magneto-crystalline anisotropy. These results
reveal the origin of spiral ordered spin textures in non-chiral centrosymmetric
helimagnet, which can serve as a new strategy for searching materials with
nanoscale spin order with potential applications in emergent electromagnetism.",2201.09675v1
2022/3/3,First-principles calculations of the surface states of doped and alloyed topological materials via band unfolding method,"One of the most remarkable characteristics of topological materials is that
they have special surface states, which are determined by the topological
properties of their bulk materials. The angle resolved photoemission
spectroscopy (ARPES) is a powerful tool to explore the surface states, which
allows to further investigate the topological phase transitions. However, it is
very difficult to compare the first-principle calculated band structures to the
ARPES results,when the systems are doped or alloyed, because the band
structures are heavily folded.We develop an efficient band unfolding method
based on numerical atomic orbitals (NAOs). We apply this method to study the
surface states of the non-magnetically and magnetically doped topological
insulators Bi$_2$Se$_3$ and the topological crystalline insulators
Pb$_{1-x}$Sn$_{x}$Te.",2203.01569v1
2022/3/31,High-temperature ferromagnetism in two-dimensional material MnSn originated from interlayer coupling,"MnSn monolayer synthesized recently is a novel two-dimensional ferromagnetic
material with a hexagonal lattice, in which three Mn atom come together to form
a trimer, making it remarkably different from other magnetic two-dimensional
materials. Most impressively, there happens a sharp increase of Curie
temperature from 54 K to 225 K when the number of layers increase from 1 to 3.
However, no quantitative explanation is reported in previous studies. Herein,
by means of first-principle calculations method and Monte carlo method, we
demonstrate that strong interlayer ferromagnetic coupling is the essential role
in enhancing its critical temperature, which act as a magnetic field to
stabilize the ferromagnetism in the MnSn multilayers.",2203.17126v1
2022/7/28,Antiferromagnetic Order in the Rare Earth Halide Perovskites CsEuBr$_3$ and CsEuCl$_3$,"Bulk CsEuBr$_3$ and CsEuCl$_3$ are experimentally shown to be magnetic
semiconductors that order antiferromagnetically at Neel temperatures of 2.0 K
and 1.0 K respectively. Given that nanoparticles and thin films of CsEuCl$_3$
have been reported to order ferromagnetically at a similar temperature, our
observation of antiferromagnetic ordering in CsEuBr$_3$ and CsEuCl$_3$ expands
the possible applications of halide perovskites to now include spintronic
devices where both ferromagnetic and antiferromagnetic devices can be
fabricated from a single material. The conclusion that CsEuCl$_3$ can be used
as a switchable magnetic material is also supported by our density-functional
theory calculations.",2207.14330v2
2022/10/11,Electrodynamics in geometric algebra,"We consider the electrodynamics of electric charges and currents in vacuum
and then generalise our results to the description of a dielectric and magnetic
material medium : first in spatial algebra (SA) and then in space-time algebra
(STA). Introducing a polarisation multivector $\tilde{P} =
\boldsymbol{\tilde{p}} -\,\frac{1}{c}\,\boldsymbol{\tilde{M}}$ and an auxiliary
electromagnetic field multivector $G = \varepsilon_0\,F + \tilde{P}$, we
express the Maxwell equation in the material medium in SA. Introducing a bound
current vector $\tilde{J} = J -\,c\,\nabla\cdot\tilde{P}$ in space-time, the
Maxwell equation is then expressed in STA. The wave equation in the material
medium is obtained by taking the gradient of the Maxwell equation. For a
uniform electromagnetic medium consisting of induced electric and magnetic
dipoles, the stress-energy momentum vector is written as
$\dot{T}\left(\dot{\nabla}\right) = \frac{1}{c}\,J \cdot F = f$ where $f$ is
the electromagnetic force density vector in space-time. Finally, the Maxwell
equation in the material medium can be written in STA as a wave equation for
the potential vector $A$.",2210.05601v1
2023/1/12,Optical fingerprints of the electronic band reconstruction in van der Waals magnetic materials,"We report a broadband study of the charge dynamics in the van der Waals (vdW)
magnetic materials 2H-$M_x$TaS$_2$ ($M$ = Mn and Co), which span the onset of
both long-range antiferromagnetic (AFM) and ferromagnetic (FM) order, depending
on the intercalation $M$ and its concentration $x$. We discover a spectral
weight ($SW$) shift from high to low energy scales for FM compositions, while
reversely $SW$ is removed from low towards high spectral energies for AFM
compounds. This maps the related reconstruction of the electronic band
structure along the crossover from the FM to AFM order, which restores an
occupation balance in the density of states between spin majority and minority
bands of the intercalated 3$d$ elements.",2301.04898v1
2023/1/24,"Theory of electric, magnetic, and toroidal polarizations in crystalline solids with applications to hexagonal lonsdaleite and cubic diamond","Multipolar order in bulk crystalline solids is characterized by multipole
densities -- denoted as polarizations in this work -- that cannot be cleanly
defined using the concepts of classical electromagnetism. Here we use group
theory to overcome this difficulty and present a systematic study of electric,
magnetic and toroidal multipolar order in crystalline solids. Based on our
symmetry analysis, we identify five categories of polarized matter, each of
which is characterized by distinct features in the electronic band structure.
For example, Rashba spin splitting in electropolar bulk materials like wurtzite
represents the electric dipolarization in these materials. We also develop a
general formalism of indicators for individual multipole densities that provide
a physical interpretation and quantification of multipolar order. Our work
clarifies the relation between patterns of localized multipoles and macroscopic
multipole densities they give rise to. To illustrate the general theory, we
discuss its application to polarized variants of hexagonal lonsdaleite and
cubic diamond structures. Our work provides a general framework for classifying
and expanding current understanding of multipolar order in complex materials.",2301.09842v2
2023/3/5,Indirect Exchange Interaction Leads to Large Lattice Contribution to Magnetocaloric Entropy Change,"Materials with a large magnetocaloric response are highly desirable for
magnetic cooling applications. It is suggested that a strong spin-lattice
coupling tends to generate a large magnetocaloric effect, but no microscopic
mechanism has been proposed. In this work, we use spin lattice dynamics
simulation to examine the lattice contribution to the magnetocaloric entropy
change in bcc iron (Fe) and hcp gadolinium (Gd) with exchange interaction
parameters determined from ab initio calculations. We find that indirect
Ruderman Kittel Kasuya Yosida (RKKY) exchange interaction in hcp Gd leads to
longer range spin lattice coupling and more strongly influences the low
frequency long wavelength phonons. This results in a higher lattice
contribution towards the total magnetocaloric entropy change as compared to bcc
Fe with short range direct exchange interactions. Our analysis provides a
framework for understanding the magnetocaloric effect in magnetic materials
with strong spin lattice couplings. Our finding suggests that long range
indirect RKKY type exchange gives rise to a larger lattice contribution to the
magnetocaloric entropy change and is, thus, beneficial for magnetocaloric
materials.",2303.02565v1
2023/6/15,First-Principles Study of Large Gyrotropy in MnBi for Infrared Thermal Photonics,"Nonreciprocal gyrotropic materials have attracted significant interest
recently in material physics, nanophotonics, and topological physics. Most of
the well-known nonreciprocal materials, however, only show nonreciprocity under
a strong external magnetic field and within a small segment of the
electromagnetic spectrum. Here, through first-principles density functional
theory calculations, we show that due to strong spin-orbit coupling
manganese-bismuth (MnBi) exhibits nonreciprocity without any external magnetic
field and a large gyrotropy in a broadband long-wavelength infrared regime
(LWIR). Further, we design a multi-layer structure based on MnBi to obtain a
maximum degree of spin-polarized thermal emission at 7 $\mu$m. The connection
established here between large gyrotropy and the spin-polarized thermal
emission points to a potential use of MnBi to develop spin-controlled thermal
photonics platforms.",2306.09233v1
2023/6/16,"Spin Textures in Synthetic Antiferromagnets: Challenges, Opportunities, and Future","Spin textures such as magnetic domain walls and skyrmions have the potential
to revolutionize electronic devices by encoding information bits. Although
recent advancements in ferromagnetic films have led to promising device
prototypes, their widespread implementation has been hindered by the
material-related drawbacks. Antiferromagnetic spin textures, however, offer a
solution to many of these limitations, paving the way for faster, smaller, more
energy-efficient, and more robust electronics. The functionality of synthetic
antiferromagnets, comprised of two or more magnetic layers separated by
spacers, may be easily manipulated by making use of different materials as well
as interface engineering. In this Perspective article, we examine the
challenges and opportunities presented by spin textures in synthetic
antiferromagnets and propose possible directions and prospects for future
research in this burgeoning field.",2306.09565v1
2023/6/19,"Magnetoelectric energy in electrodynamics: Magnetoelectricity, bi(an)isotropy, and magnetoelectric meta-atoms","In materials with an intrinsic magnetoelectric (ME) effect, the energy
density comprises the polarization, magnetization and ME energy densities.
These three components of energy define local (subwavelength) characteristics
of electromagnetic (EM) responses in multiferroic materials. In a subwavelength
domain, coupling between the electric and magnetic dipole oscillations forms
the ME field structures which are characterized by the violation of both
spatial and temporal symmetry. Unlike multiferroics, bi(an)isotropic
metamaterials are associated with an EM response characterized only by spatial
symmetry breaking. This also applies to chiral materials. Since no intrinsic
magnetoelectricity is assumed in such structures, any concepts about the stored
ME energy are not applicable. This clearly points to the effect of nonlocality.
That is why the basic concepts of bi(an)isotropy can only be analyzed by the EM
far field characteristics. In this paper, we argue that in the implementation
of local (subwavelength) ME meta atoms and systems for near field probing of
chirality, the concept on ME energy is crucial. Real ME energy can occur when
ME fields in a singular subwavelength domain are characterized by a violation
of both the symmetry of time reversal and spatial reflection.",2306.10906v1
2023/7/5,Phenomenology of bond and flux orders in kagome metals,"Despite much experimental and theoretical work, the nature of the charge
order in the kagome metals belonging to the family of materials AV$_3$Sb$_5$
(A=Cs,Rb,K) remains controversial. A crucial ingredient for the identification
of the ordering in these materials is their response to external perturbations,
such as strain or magnetic fields. To this end, we provide a comprehensive
symmetry classification of the possible charge orders in kagome materials with
a $2\times2$ increase of the unit cell. Motivated by the experimental reports
of time-reversal-symmetry breaking and rotational anisotropy, we consider the
interdependence of flux and bond orders. Deriving the relevant Landau free
energy for possible orders, we study the effect of symmetry-breaking
perturbations such as strain and magnetic fields. Our results, thus, provide a
roadmap for future tests of these intricate orders.",2307.02528v1
2023/7/6,Emergence of half-metallic ferromagnetism in transition metal substituted Na$_{0.5}$Bi$_{0.5}$TiO$_3$,"The multifunctional materials with prominent properties such as electrical,
ferroelectric, magnetic, optical and magneto-optical are of keen interest to
several practical implications. In the roadmap of designing such materials, in
the present work, using density functional theory based first-principles
calculations, we have investigated the functional properties of transition
metal substituted-NBT. Our calculations predict the emergence of half-metallic
ferromagnetism in the system. A nonzero magnetic moment of 1.49 $\mu_{\rm
B}/{\rm f.u.}$ is obtained for 25\% concentration of Ni. Our data on optical
properties for pure NBT is in excellent agreement with available theory and
experiments. For Ni-NBT, we observed a diverging nature of static dielectric
constant, which could be attributed to the induced metallic character in the
material. Our simulations on MOKE predict a significant Kerr signal of
0.7$^\circ$ for 6.25\% Ni-concentration.",2307.02859v1
2023/7/10,Porous CrO$_2$: a ferromagnetic half-metallic member in sparse hollandite oxide family,"A stable polymorph of CrO$_2$ is predicted using PBE+U method. The porous
material is isostructural with $\alpha$-MnO$_2$ making it the second transition
metal oxide in sparse hollandite group of materials. However, unlike the
anti-ferromagnetic semiconducting character of the $\alpha$-MnO$_2$, it is
found to be a ferromagnetic half-metal. At Fermi level, the hole pocket has
ample contribution from O-2$p$ orbital, though, the electron pocket is mostly
contributed by Cr-3$d_{xy}$ and Cr-3d$_{x^2-y^2}$. A combination of negative
charge transfer through orbital mixing and extended anti-bonding state near
Fermi level is responsible for the half-metallic ferromagnetic character of the
structure. A comparative study of rutile and hollandite CrO$_2$ and hollandite
MnO$_2$ structures delineate the interplay between structural, electronic and
magnetic properties. The material shows a robust magnetic character under
hydrothermal pressure, as well as, the band topology is conserved under
uniaxial strain. Moderate magneto-crystalline anisotropy is observed and it
shows a correspondence with the anisotropy of elastic constants.",2307.04584v1
2023/7/11,Flux Expulsion and Material Properties of Niobium Explored in 644-650 MHz Cavities,"Upcoming projects requiring high-Q ~650 MHz medium-to-high-${\beta}$
elliptical cavities drive a need to understand magnetic RF loss mechanisms and
mitigations in greater detail. High-temperature annealing and fast-cooldowns
have proven effective techniques for promoting magnetic flux expulsion in
cavities, however the extent of their effectiveness has been observed to vary
between niobium material lot and vendor. We explore the fast-cooldown method,
and high-temperature annealing (900{\deg}C) in 644-650 MHz cavities fabricated
from two different niobium vendors: Tokyo-Denkai, and Ningxia. which promote
flux-expulsion efficiency. Using EBSD and PPMS methods, we aim to trace cavity
flux expulsion efficiency to specific, measurable properties of the bulk
niobium material, which, if identified, can lead to methods by which the flux
expulsion properties of Nb material can be predicted prior to cavity
fabrication, and can enable fine-tuning of cavity temperature treatments.",2307.05813v1
2023/9/12,Wurtzite vs rock-salt MnSe epitaxy: electronic and altermagnetic properties,"Newly discovered altermagnets are magnetic materials exhibiting both
compensated magnetic order, similar to antiferromagnets, and simultaneous
non-relativistic spin-splitting of the bands, akin to ferromagnets. This
characteristic arises from the specific symmetry operations that connect the
spin sublattices. In this report, we show with ab initio calculations that the
semiconductive MnSe exhibits altermagnetic spin-splitting in the wurtzite phase
as well as a critical temperature well above room temperature. It is the first
material from such space group identified to possess altermagnetic properties.
Furthermore, we demonstrate experimentally through structural characterization
techniques that it is possible to obtain thin films of both the intriguing
wurtzite phase of MnSe and the more common rock-salt MnSe using molecular beam
epitaxy on GaAs substrates. The choice of buffer layers plays a crucial role in
determining the resulting phase and consequently extends the array of materials
available for the physics of altermagnetism.",2309.06422v2
2023/10/18,Dissipationless Nonlinearity in Quantum Material Josephson Diodes,"Dissipationless nonlinearities for three-wave mixing are a key component of
many superconducting quantum devices, such as amplifiers and bosonic qubits. So
far, such third-order nonlinearities have been primarily achieved with circuits
of concatenated Josephson tunnel junctions. In this work, we theoretically
develop an alternative approach to realize third-order nonlinearities from
gate-tunable and intrinsically symmetry-broken quantum material Josephson
junctions. We illustrate this approach on two examples, an Andreev
interferometer and a magnetic Josephson junction. Our results show that both
setups enable Kerr-free three-wave mixing for a broad range of frequencies, an
attribute that is highly desirable for amplifier applications. Moreover, we
also find that the magnetic junction constitutes a paradigmatic example for
three-wave mixing in a minimal single-junction device without the need for any
external biases. We hope that our work will guide the search of dissipationless
nonlinearities in quantum material superconducting devices and inspire new ways
of characterizing symmetry-breaking in quantum materials with microwave
techniques.",2310.12198v1
2023/11/15,Thermal Magnetoelectrics in all Inorganic Quasi-Two-Dimensional Halide Perovskites,"From lithium-ion batteries to high-temperature superconductors, oxide
materials have been widely used in electronic devices. However, demands of
future technologies require materials beyond oxides, as anion chemistries
distinct from oxygen can expand the palette of mechanisms and phenomena, to
achieve superior functionalities. Examples include nitride-based wide bandgap
semiconductors and halide perovskite solar cells, with MAPbBr3 being a
representation revolutionizing photovoltaics research. Here, we demonstrate
magnetoelectric behaviour in quasi-two-dimensional halides (K,Rb)3Mn2Cl7
through simultaneous thermal control of electric and magnetic polarizations by
exploiting a polar-to-antipolar displacive transition. Additionally, our
calculations indicate a possible polarization switching path including a strong
magnetoelectric coupling, indicating halides can be excellent platforms to
design future multiferroic and ferroelectric devices. We expect our findings to
broaden the exploration of multiferroics to non-oxide materials and open access
to novel mechanisms, beyond conventional electric/magnetic control, for
coupling ferroic orders.",2311.09324v1
2023/11/20,Orbital Kerr effect and terahertz detection via the nonlinear Hall effect,"We investigate the optical response induced by a d.c. current flowing in a
nonmagnetic material that lacks inversion symmetry. In this class of materials,
the flowing current experiences a nonlinear Hall effect and induces a
nonequilibrium orbital magnetization, even in the absence of spin-orbit
coupling. As a result, an orbital-driven Kerr effect arises that can be used to
probe not only the orbital magnetization, but also the nonlinear Hall effect.
In addition, in the long wavelength limit, the nonlinear Hall effect leads to a
rectification current that can be used to detect terahertz radiation. We apply
the theory to selected model systems, such as WTe$_2$ bilayer, as well as to
realistic materials, i.e., bulk Te and metallic superlattices. The
nonequilibrium orbital Kerr efficiencies obtained in these systems are
comparable to the largest values reported experimentally in GaAs and MoS$_2$,
exceeding the values reported in metals and suggesting a large terahertz
current responsivity.",2311.11889v1
2024/2/22,Observation of Surface State Suppression in Magnetic Weyl Semimetal NdAlSi,"Understanding and mastering the control of surface states in topological
materials are crucial steps for the development of future electronic devices
and technologies that leverage the unique properties of these materials. Here,
using angle-resolved photoemission spectroscopy, we provide a good case study
of this by visualizing the electronic structure of a magnetic Weyl semimetal on
both flat and uneven surfaces. Our observations reveal that the preparation of
an uneven sample surface can effectively suppress all surface states in the
Weyl semimetal NdAlSi, including topological surface Fermi arcs. This results
in the observation of pure bulk states devoid of any Fermi energy shift. This
discovery not only opens up a new avenue to directly study the pure bulk states
of a Weyl semimetal using low photon energies in ARPES but also provides key
insights into the control of the surface states in topological materials.",2402.14447v1
2024/3/1,Spin-gapped metals: A novel class of materials -- the case of semi-Heusler compounds,"Gapped metals, a recently discovered new class of materials, possess a band
gap slightly above or below the Fermi level. These materials are intrinsic p-
or n-type semiconductors eliminating the need for extrinsic doping. Inspired by
this concept, we propose the so-called ""spin-gapped metals"" exhibiting
intrinsic p- or n-type behavior for each spin channel independently. Their
properties would be similar to the dilute magnetic semiconductors eliminating
the requirement for transition metal doping. Here, we demonstrate this novel
concept in semi-Heusler compounds using first principles electronic band
structure calculations. We comprehensively analyze their electronic and
magnetic properties, paving the way for novel technological applications of
Heusler compounds.",2403.00936v1
2024/3/8,Superconductivity of the New Medium-Entropy Alloy V4Ti2W with a Body-Centered Cubic Structure,"Medium- and high-entropy alloy (MEA and HEA) superconductors have attracted
considerable interest since their discovery. This paper reports the
superconducting properties of ternary tungsten-containing MEA V4Ti2W for the
first time. V4Ti2W is a type II superconductor with a body-centered cubic (BCC)
structure. Experimental results of resistivity, magnetization, and heat
capacity indicate that the superconducting transition temperature of the MEA
V4Ti2W is roughly 5.0 K. The critical magnetic fields at the upper and lower
ends are 9.93(2) T and 40.7(3) mT, respectively. Interestingly, few BCC MEA
superconductors with VEC greater than 4.8 have been found. The addition of
tungsten leads to a VEC of 4.83 e/a for V4Ti2W, which is rarely higher than the
4.8 value. Adding tungsten element expands the variety of MEA alloys, which may
improve the microstructure and mechanical properties of materials and even
superconducting properties. This material could potentially offer a new
platform for the investigation of innovative MEA and HEA superconductors.",2403.05115v1
1999/4/19,"Dynamic transverse susceptibility in Au-Fe-Au ""nano-onions""","A precision radio-frequency (RF) transverse modulation technique based on a
resonant tunnel diode oscillator (TDO) has been used to study the dynamic
susceptibility in novel ring-shaped single domain Fe nanoparticles synthesized
using reverse-micelle chemistry. Hysteresis loops measured using a SQUID
magnetometer indicate a large coercivity (Hc = 400Oe) below the blocking
temperature (TB ~52K). The dynamic susceptibility shows remarkable consistency
with the M-H data and exhibits peaks at characteristic anisotropy fields.
Overall, these RF experiments are well suited to probe the magnetic anisotropy
in nanophase materials.",9904267v1
2000/12/8,Averaging rheological quantities in descriptions of soft glassy materials,"Many mean-field models have been introduced to describe the mechanical
behavior of glassy materials. They often rely on averages performed over
distributions of elements or states. We here underline that averaging is a more
intricate procedure in mechanics than in more classical situations such as
phase transitions in magnetic systems. This leads us to modify the predictions
of the recently proposed SGR model for soft glassy materials, for which we
suggest that the viscosity should diverge at the glass transition temperature
$T_g$ with an exponential form $\eta \sim \exp(\frac{A}{T-T_g})$.",0012134v1
2000/12/19,Material-specific spin filtering in ferromagnet/superconductor ballistic nanojunctions,"We study spin-dependent electronic transport across
ferromagnet/superconductor ballistic junctions modeled using tight-binding
Hamiltonians with s, p and d orbitals and material-specific parameters. We show
that by accurately modeling the band structure of the bulk materials, one can
reproduce the measured differential conductance of Cu/Pb nanocontacts. In
contrast the differential conductance of Co/Pb contacts can only be reproduced
if an enhanced magnetic moment is present at the interface.",0012352v1
2003/2/7,"Lattice constant in diluted magnetic semiconductors (Ga,Mn)As","We use the density-functional calculations to investigate the compositional
dependence of the lattice constant of (Ga,Mn)As containing various native
defects. The lattice constant of perfect mixed crystals does not depend much on
the concentration of Mn. The lattice parameter increases if some Mn atoms
occupy interstitial positions. The same happens if As antisite defects are
present. A quantitative agreement with the observed compositional dependence is
obtained for materials close to a complete compensation due to these two
donors. The increase of the lattice constant of (Ga,Mn)As is correlated with
the degree of compensation: the materials with low compensation should have
lattice constants close to the lattice constant of GaAs crystal.",0302150v1
2003/4/22,Orbital ordering in charge transfer insulators,"We discuss a new mechanism of orbital ordering, which in charge transfer
insulators is more important than the usual exchange interactions and which can
make the very type of the ground state of a charge transfer insulator, i.e. its
orbital and magnetic ordering, different from that of a Mott-Hubbard insulator.
This purely electronic mechanism allows us to explain why orbitals in
Jahn-Teller materials typically order at higher temperatures than spins, and to
understand the type of orbital ordering in a number of materials, e.g.
K_2CuF_4, without invoking the electron-lattice interaction.",0304494v1
2005/3/3,Gigantic Enhancement of Magneto-Chiral Effect in Photonic Crystals,"We theoretically propose a method to enhance dramatically a
magneto-chiral(MC) effect by using the photonic crystals composed of a
multiferroic material. The MC effect, the directional birefringence even for
unpolarized light, is so small that it has been difficult to observe
experimentally. Two kinds of periodic structures are investigated; (a) a
multilayer and (b) a stripe composed of a magneto-chiral material and air. In
both cases, the difference in reflectivity between different magnetization
directions is enhanced by a factor of hundreds compared with a bulk material.",0503066v3
2005/7/1,Incorporation of cobalt into ZnO nanoclusters,"The structural, optical and magnetic properties of nanostructured ZnO films
co-doped with cobalt and aluminium have been studied. The nanocrystalline
films, with cluster sizes in range 50 - 100 nm, were deposited by pulsed laser
ablation in a mixed atmosphere of oxygen and helium. The nanocrystallites have
the wurtzite structure and are highly oriented with the c-axis perpendicular to
the substrate. Both optical and electron spin resonance (ESR) spectroscopy
results show the substitutional incorporation of Co$^{2+}$ ions on the Zn site
inside the ZnO nanoclusters. The temperature dependence of the ESR spectra
follows Curie law corresponding to a paramagnetic material.",0507030v1
2006/4/25,Spin Precession and Avalanches,"In many magnetic materials, spin dynamics at short times are dominated by
precessional motion as damping is relatively small. In the limit of no damping
and no thermal noise, we show that for a large enough initial instability, an
avalanche can transition to an ergodic phase where the state is equivalent to
one at finite temperature, often above that for ferromagnetic ordering. This
dynamical nucleation phenomenon is analyzed theoretically. For small finite
damping the high temperature growth front becomes spread out over a large
region. The implications for real materials are discussed.",0604563v1
2006/11/2,Thermal conductivity via magnetic excitations in spin-chain materials,"We discuss the recent progress and the current status of experimental
investigations of spin-mediated energy transport in spin-chain and spin-ladder
materials with antiferromagnetic coupling. We briefly outline the central
results of theoretical studies on the subject but focus mainly on recent
experimental results that were obtained on materials which may be regarded as
adequate physical realizations of the idealized theoretical model systems. Some
open questions and unsettled issues are also addressed.",0611052v1
2006/11/3,Scanning probe imaging of coexistent ferromagnetism and ferroelectricity at room temperature,"Room temperature coexistence of ferromagnetism and ferroelectricity in a thin
film of a novel material of nominal composition PbTi0.5Fe0.5O3-d is probed by
standard ferroelectric and ferromagnetic hysteresis loop measurements and by
scanning probe microscopy of various kinds. Both magnetic domains and
ferroelectric domains are observed in the same spatial region of the material,
implying phase coexistence in this system. For both order parameters, sample
morphology strongly affects roughness of the domain walls.",0611084v1
2007/9/24,External Control of a Metal-Insulator Transition in GaMnAs Wires,"Quantum transport in disordered ferromagnetic (III,Mn)V semiconductors is
studied theoretically. Mesoscopic wires exhibit an Anderson disorder-induced
metal-insulator transition that can be controlled by a weak external magnetic
field. This metal-insulator transition should also occur in other materials
with large anisotropic magneto resistance effects. The transition can be useful
for studies of zero-temperature quantum critical phase transitions and
fundamental material properties.",0709.3847v2
2007/10/5,Supplementary material to Heavy electrons and the symplectic symmetry of spin,"This online material provides the technical detail for ``Heavy electrons and
the symplectic symmetry of spin"",(arXiv 0710.1122). Three parts. Part I -
symplectic spins, their properties and gauge symmetries. Part II - derivation
of two-chanel model for tetragonal heavy electron systems with the view to
application to PuCoGa5 and NpPd_5Al_2, symplectic-N mean field theory and
computation of NMR relaxation rate. Part III - brief discussion of the
application to frustrated magnetism in the J1-J2 model, mainly used to test the
method.",0710.1128v2
2008/7/15,Phenomenological Landau analysis of predicted magnetoelectric fluorides: KMnFeF$_{6}$ and Ba$_{2}$Ni$_{7}$F$_{18}$,"Recently, we predicted based on symmetry considerations that KMnFeF$_{6}$ and
Ba$_{2}$Ni$_{7}$F$_{18}$ are likely magnetoelectric multiferroic materials. In
this contribution, we investigate with Landau theory and crystal structure
considerations the polarization and the linear magnetoelectric effect in these
materials. Based on these two examples, we show that any magnetoferroelectric
will display additional electrical polarization below its magnetic ordering
temperature. This additional electrical polarization is not related to the
linear magnetoelectric effect. Its magnitude depends on the dielectric
susceptibility.",0807.2399v1
2009/3/7,Impurity effects in multiferroic compounds,"We investigate the effect of impurities in multiferroic materials using an
equation of motion approach for the spin dynamics of the host multiferroic
compound. We model the impurities as a two-level system and focus on the regime
where the impurity spins relax slowly. When the impurity strength is weak the
host spins oscillate with no decay and the electric polarization is not
affected. However as the impurity strength is increased the host spin
components get damped and the electrion polarization is suppressed. Since
polarization in multiferroic materials is driven by magnetic ordering we
conclude that the presence of impurities is detrimental to multiferroicity.",0903.1319v1
2009/3/16,Superconductivity: Exotic Commonalities in Phase and Mode,"Recent muon and neutron experiments on the new FeAs-based superconductors
revealed phase diagrams characterized by first-order evolution from
antiferromagnetic to superconducting states, and an inelastic magnetic
resonance mode whose energy scales as $\sim 4 k_{B}T_{c}$. These features
exhibit striking commonalities with cuprate, backyball, organic, and
heavy-fermion superconductors as well as superfluid $^{4}$He.",0903.2758v1
2009/7/6,Thermal entanglement witness for materials with variable local spin lengths,"We show that the thermal entanglement in a spin system using only magnetic
susceptibility measurements is restricted to the insulator materials. We
develop a generalization of the thermal entanglement witness that allows us to
get information about the system entanglement with variable local spin lengths
that can be used experimentally in conductor or insulator materials. As an
application, we study thermal entanglement for the half-filled Hubbard model
for linear, square and cubic clusters. We note that it is the itinerancy of
electrons that favors the entanglement. Our results suggest a weak dependence
between entanglement and external spin freedom degrees.",0907.1068v1
2009/7/13,Universal Electromagnetic Waves in Dielectric,"The dielectric susceptibility of a wide class of dielectric materials
follows, over extended frequency ranges, a fractional power-law frequency
dependence that is called the ""universal"" response. The electromagnetic fields
in such dielectric media are described by fractional differential equations
with time derivatives of non-integer order. An exact solution of the fractional
equations for a magnetic field is derived. The electromagnetic fields in the
dielectric materials demonstrate fractional damping. The typical features of
""universal"" electromagnetic waves in dielectric are common to a wide class of
materials, regardless of the type of physical structure, chemical composition,
or of the nature of the polarizing species, whether dipoles, electrons or ions.",0907.2163v1
2009/7/30,Magnetoelectric response of multiferroic BiFeO3 and related materials,"We present a first-principles scheme for computing the magnetoelectric
response of multiferroics. We apply our method to BiFeO3 (BFO) and related
compounds in which Fe is substituted by other magnetic species. We show that
under certain relevant conditions -- i.e., in absence of incommensurate spin
modulation, as in BFO thin films and some BFO-based solid solutions -- these
materials display a large linear magnetoelectric response. Our calculations
reveal the atomistic origin of the coupling and allow us to identify the most
promising strategies to enhance it.",0907.5281v1
2010/6/23,Multiferroic BiFeO3-BiMnO3 Nanocheckerboard From First Principles,"We present a first principles study of an unusual heterostructure, an
atomic-scale checkerboard of BiFeO3-BiMnO3, and compare its properties to the
two bulk constituent materials, BiFeO3 and BiMnO3. The ""nanocheckerboard"" is
found to have a multiferroic ground state with the desired properties of each
constituent: polar and ferrimagnetic due to BiFeO3 and BiMnO3, respectively.
The effect of B-site cation ordering on magnetic ordering in the BiFeO3-BiMnO3
system is studied. The checkerboard geometry is seen to give rise to a a novel
magnetostructural effect that is neither present in the bulk constituent
materials, nor in the layered BiFeO3-BiMnO3 superlattice.",1006.4648v1
2011/11/4,Spintronics in semiconductors,"For the last years spin effects in semiconductors have been of great interest
not only in the context of solid state physics, but also for their potential
usage in technology. In this paper we give a short review of spintronic
materials, in which electron spin as an additional degree of freedom is
exploited. Afterwards, we discuss the properties of classic, non-magnetic
semiconductors, where the efforts are put on enriching the traditional
semiconductor technology engaging the electrical effects of spin effects.
Various phenomena and scientific state of the art is highlighted.",1111.1032v1
2011/12/31,Brief review on iron-based superconductors: are there clues for unconventional superconductivity?,"Study of superconductivity in layered iron-based materials was initiated in
2006 by Hosono's group, and boosted in 2008 by the superconducting transition
temperature, Tc, of 26 K in LaFeAsO1-xFx. Since then, enormous researches have
been done on the materials, with Tc reaching as high as 55 K. Here, we review
briefly experimental and theoretical results on atomic and electronic
structures and magnetic and superconducting properties of FeAs-based
superconductors and related compounds. We seek for clues for unconventional
superconductivity in the materials.",1201.0237v1
2012/12/11,Optical isolation with epsilon-near-zero metamaterials,"We suggest a principle for isolation of circularly polarized waves in
magnetically active extreme-parameter metamaterials. Using theoretical analysis
and numerical simulations, we show that metamaterials with extreme parameters,
such as epsilon-near-zero materials (ENZ), when merged with magneto-optical
materials, become transparent for forward circularly polarized waves of a given
handedness and opaque for backward propagating waves of the same handedness. We
theoretically study two possible implementations of such hybrid materials: (1)
the case of metal-dielectric stacks; and (2) rectangular waveguide near its
cut-off frequency. We prove that these structures can be utilized as compact
isolators for circularly polarized waves.",1212.2292v1
2013/4/1,Evolution of the domain topology in a ferroelectric,"Topological materials, including topological insulators, magnets with
Skyrmions and ferroelectrics with topological vortices, have recently attracted
phenomenal attention in the materials science community. Complex patterns of
ferroelectric domains in hexagonal REMnO3 (RE: rare earths) turn out to be
associated with the macroscopic emergence of Z2xZ3 symmetry. The results of our
depth profiling of crystals with a self-poling tendency near surfaces reveal
that the partial dislocation (i.e., wall-wall) interaction, not the interaction
between vortices and antivortices, is primarily responsible for topological
condensation through the macroscopic breaking of the Z2-symmetry.",1304.0275v1
2013/11/29,Electronic Structure Trends of Möbius Graphene Nanoribbons from Minimal-Cell Simulations,"Investigating topological effects in materials requires often the modeling of
material systems as a whole. Such modeling restricts system sizes, and makes it
hard to extract systematic trends. Here, we investigate the effect of M\""obius
topology in the electronic structures of armchair graphene nanoribbons. Using
density-functional tight-binding method and minimum-cell simulations through
revised periodic boundary conditions, we extract electronic trends merely by
changing cells' symmetry operations and respective quantum number samplings. It
turns out that for a minimum cell calculation, once geometric and magnetic
contributions are ignored, the effect of the global topology is unexpectedly
short-ranged.",1311.7494v1
2014/11/16,Replica-exchange Wang-Landau sampling: Pushing the limits of Monte Carlo simulations in materials sciences,"We describe the study of thermodynamics of materials using replica-exchange
Wang-Landau (REWL) sampling, a generic framework for massively parallel
implementations of the Wang-Landau Monte Carlo method. To evaluate the
performance and scalability of the method, we investigate the magnetic phase
transition in body-centered cubic (bcc) iron using the classical Heisenberg
model parametrized with first principles calculations. We demonstrate that our
framework leads to a significant speedup without compromising the accuracy and
precision and facilitates the study of much larger systems than is possible
with its serial counterpart.",1411.4212v1
2015/1/28,Hidden antiferromagnetism on the light-irradiated surface of bulk SrTiO3 and at the LaAlO3_SrTiO3 interfaces,"We study properties of electrons on illuminated surfaces of SrTiO3 with
titanium dxz_dyz and dxy bands for their spectrum. Recently A. F.
Santander-Syro et al [Nature Materials, 13, 1085 (2014)] found that the dxy
bands actually comprise two chiral branches with the Kramers degeneracy at the
zone center lifted in absence of a magnetic moment. From symmetry analysis of
instabilities possible in the Fermi liquid with exchange interactions we
identified the metallic in-layer state with the concrete antiferromagnetic
phase and discuss if the same state materializes at conducting LaAlO3_SrTiO3
interfaces.",1501.07231v2
2015/3/10,Graphene Spintronics,"The isolation of graphene has triggered an avalanche of studies into the
spin-dependent physical properties of this material, as well as graphene-based
spintronic devices. Here we review the experimental and theoretical
state-of-art concerning spin injection and transport, defect-induced magnetic
moments, spin-orbit coupling and spin relaxation in graphene. Future research
in graphene spintronics will need to address the development of applications
such as spin transistors and spin logic devices, as well as exotic physical
properties including topological states and proximity-induced phenomena in
graphene and other 2D materials.",1503.02743v1
2015/6/30,Equalizing the near and far electromagnetic fields around particles made of different materials,"We demonstrate that the electromagnetic fields scattered by particles made of
different materials can be equalized. Emphasize is placed first in metallic
nanoparticles that host localized surface plasmons and it is shown that their
electromagnetic fields can be identically reproduced with dielectric particles.
We derive the explicit formulas relating the different constitutive parameters
that yield identical electromagnetic responses. This method provides the
dielectric permittivities of spherical particles that reproduce the strong near
electric field intensities observed around metallic particles featuring
localized surface plasmon resonances in optics or near infrared frequencies. We
also demonstrate the ability of homogenous dielectric particles to host the
magnetic resonances predicted for exotic materials with negative permeability.",1506.09180v1
2015/12/8,"Rebuttal of ""The multicaloric effect in multiferroic materials""","The paper refutes the model and claims published in the Solid State
Communications [1] as well as elsewhere. The theoretical approach proposed in
""The multicaloric effect in multiferroic materials"" by Melvin M.~Vopson has a
number of inaccuracies and mistakes. The Author of [1] does not pay necessary
attention to the range of applicability of the derived equations and confuses
the dependent and independent variables. The resulting equations for
electrically and magnetically induced multicaloric effects are incorrect and
cannot be used for measurement interpretation.",1602.04238v1
2016/2/24,Application of the Maximum relative Entropy method to the physics of ferromagnetic materials,"It is known that the Maximum relative Entropy (MrE) method can be used to
both update and approximate probability distributions functions in statistical
inference problems. In this manuscript, we apply the MrE method to infer
magnetic properties of ferromagnetic materials. In addition to comparing our
approach to more traditional methodologies based upon the Ising model and Mean
Field Theory, we also test the effectiveness of the MrE method on
conventionally unexplored ferromagnetic materials with defects.",1603.00068v2
2017/9/26,Spintronic Functionalities in Multiferroic Oxide-based Heterostructures,"The list of materials systems displaying both electric and magnetic long
range order is short. Oxides, however, concentrate numerous examples of
multiferroicity with, in some cases, a large magnetoelectric coupling. As a
result, a fruitful research field has emerged contemporaneously with the
consolidation of spintronic. The synergy between multiferroics and spintronics
was meant to be inevitable and hence the characterization of spintronic
functionalities in multiferroic materials is rather abundant. The aim of the
present chapter is to review the oxide heterostructures where magnetoelectric
coupling is demonstrated by means of spintronic functionalities (i.e.
magnetoresistance, anisotropic magnetoresistance, giant magnetoresistance or
tunnel magnetoresistance).",1709.08918v1
2017/11/1,Optical two-photon nonlinear waves in two-dimensional materials,"A theory of an optical two-photon breather in a graphene monolayer (or
graphene-like two-dimensional material) is constructed. The system of the
material equations for two-photon transitions and the wave equation for
transverse magnetic polarized modes of the surface plasmon polaritons are shown
to reduce to the nonlinear Schr\""odinger equation with damping. Explicit
analytical expressions for a surface small intensity two-photon breather
(0$\pi$ pulse) of self-induced transparency are obtained. It is shown that the
optical conductivity of graphene reduces the amplitude of the surface
two-photon nonlinear wave during the propagation. The one-photon and two-photon
breathers in graphene are compared and have obtained that the differences
between their parameters are significant.",1711.00343v1
2017/12/16,"Photo-Hall, photorefractive and photomagnetoelectric effects in tungsten bronzes and related tetragonal ferroelectrics","We present an extensive study of the electric, magnetic and elastic responses
of tetragonal ferroelectrics under illumination, using a new theory
intertwining material and wave symmetries. Optical rectification,
photomagnetic, photovoltaic and phototoroidal vector responses are worked out
as functions of the wave vector and wave polarization directions. Second-order
response tensors associated with photoelastic, photomagnetoelectric,
photorefractive effects and photoconductivity are described. We discuss in
detail the photo-Hall and a new non-linear optical effect in tungsten bronzes.
Finally, we compare the properties of tetragonal materials with those of
hexagonal, orthorhombic and trigonal ferroelectrics previously reported in the
literature.",1712.05977v3
2018/3/28,Raman Spectrum of CrI$_3$: an ab-initio study,"We study the Raman spectrum of CrI$_3$, a material that exhibits magnetism in
a single-layer. We employ first-principles calculations within density
functional theory to determine the effects of polarization, strain, and
incident angle on the phonon spectra of the 3D bulk and the single-layer 2D
structure, for both the high- and low-temperature crystal structures. Our
results are in good agreement with existing experimental measurements and serve
as a guide for additional investigations to elucidate the physics of this
interesting material.",1803.10825v1
2018/4/14,Tuning effective hyperfine fields in PEDOT:PSS thin films by doping,"Using electrically detected magnetic resonance spectroscopy, we demonstrate
that doping the conducting polymer
poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) with
ethylene glycol allows for the control of effective local charge carrier
hyperfine fields through motional narrowing. These results suggest that doping
of organic semiconductors could enable the tuning of macroscopic material
properties dependent on hyperfine fields such as magnetoresistance, the
magneto-optical responses and spin-diffusion.",1804.05139v1
2018/5/7,Probing dynamics in quantum materials with femtosecond x-rays,"Optical pulses are routinely used to drive dynamical changes in the
properties of solids. In quantum materials, many new phenomena have been
discovered, including ultrafast transitions between electronic phases,
switching of ferroic orders and nonequilibrium emergent behaviors such as
photo-induced superconductivity. Understanding the underlying non-equilibrium
physics requires detailed measurements of multiple microscopic degrees of
freedom at ultrafast time resolution. Femtosecond x-rays are key to this
endeavor, as they can access the dynamics of structural, electronic and
magnetic degrees of freedom. Here, we cover a series of representative
experimental studies in which ultrashort x-ray pulses from free electron lasers
have been used, opening up new horizons for materials research.",1805.02376v1
2018/6/2,Topologically induced transparency in a two-phase metamaterial,"It is theoretically and numerically demonstrated that a mixture of two
topologically distinct material phases is characterized by an anomalous
""transparency window"" in a spectral range wherein the individual material
phases are strongly reflecting. In particular, it is shown that a metamaterial
formed by a metallic wire grid embedded in a magnetized plasma may support the
propagation of waves with long wavelengths, notwithstanding the components,
when taken separately, completely block the electromagnetic radiation. The
effect is explained in terms of the topological properties of the
magnetoplasmon. Furthermore, it is highlighted that some naturally available
materials may be regarded as a mixture of two topologically distinct phases,
and hence may be as well characterized by a similar anomalous transparency
effect.",1806.00625v1
2019/11/8,Homogenization of quasiperiodic structures and two-scale cut-and-projection convergence,"Quasiperiodic arrangements of the constitutive materials in composites result
in effective properties with very unusual electromagnetic and elastic
properties. The paper discusses the cut-and-projection method that is used to
characterize effective properties of quasiperiodic materials. Characterization
of cut-and-projection convergence limits of partial differential operators is
presented, and correctors are established. We provide the proofs of the results
announced in (Wellander et al., 2018) and give further examples. Applications
to problems of interest in physics include electrostatic, elastostatic and
quasistatic magnetic cases.",1911.03560v1
2019/12/5,Spin pumping into a spin glass material,"Spin pumping is a recently established means for generating a pure spin
current, whereby spins are pumped from a magnet into the adjacent target
material under the ferromagnetic resonance condition. We theoretically
investigate the spin pumping from an insulating ferromagnet into spin glass
materials. Combining a dynamic theory of spin glasses with the linear-response
formulation of the spin pumping, we calculate temperature dependence of the
spin pumping near the spin glass transition. The analysis predicts that a
characteristic peak appears in the spin pumping signal, reflecting that the
spin fluctuations slow down upon the onset of spin freezing.",1912.02337v2
2020/1/20,Filling-enforced Dirac loops and their evolutions under various perturbations,"Based on symmetry analysis, we propose that filling-enforced Dirac loops
(FEDLs) in non-magnetic systems exist and only exist in only five space groups
(SGs), namely, SG.57, SG.60, SG.61, SG.62 and SG.205. %, respectively.
  We explore all possible configurations of the FEDLs in these space groups,
and classify them accordingly. Furthermore, we study the evolutions of the
FEDLs under various types of symmetry-breaking perturbations, such as an
applied strain or an external field. The results show that FEDL materials can
serve as parent materials of both topological semimetals hosting nodal
points/loops, and topological insulators/topological crystalline insulators. By
means of first-principles calculations, many materials possessing FEDLs are
predicted.",2001.07107v1
2020/3/3,Heat flux sensing by anomalous Nernst effect in Fe-Al thin films on a flexible substrate,"We performed a numerical analysis of the material parameters required for
realizing a heat flux sensor exploiting the anomalous Nernst effect (ANE). The
results showed the importance of high thermopower of ANE ($S_{\text{ANE}}$) and
small saturation magnetization. This motivated us to investigate the effect of
Al substitution of Fe on ANE and found $S_{\text{ANE}} =$ 3.4 $\mu$V/K in
Fe$_{81}$Al$_{19}$ because of the dominant intrinsic mechanism. Using this
material, we made a prototype ANE-based heat flux sensor on a thin flexible
polyimide sheet and demonstrated accurate sensing with it. This study gives
important information for enhancing sensor sensitivity.",2003.01459v1
2020/3/9,Floquet engineering correlated materials with unpolarized light,"Floquet engineering is a powerful tool that drives materials with periodic
light. Traditionally, the light is monochromatic, with amplitude, frequency,
and polarization varied. We introduce Floquet engineering via unpolarized light
built from quasi-monochromatic light, and show how it can modify strongly
correlated systems, while preserving the original symmetries. Different types
of unpolarized light can realize different strongly correlated phases As an
example, we treat insulating magnetic materials on a triangular lattice and
show how unpolarized light can induce a Dirac spin liquid.",2003.04272v4
2020/5/9,Epitaxial Growth and Band Structure of Antiferromagnetic Mott Insulator CeOI,"The van der Waals material CeOI is predicted to be a layered
antiferromagnetic Mott insulator by DFT+U calculation. We successfully grow the
CeOI films down to monolayer on graphene/6H-SiC(0001) substrate by using
molecular beam epitaxy. Films are studied by {\it in-situ} scanning tunneling
microscopy and spectroscopy, which shows a band gap of 4.4 eV. A metallic phase
with composition unidentified also exists. This rare earth oxyhalide adds a new
member to the two-dimensional magnetic materials.",2005.04359v1
2020/5/11,Perspective on Metallic Antiferromagnets,"Antiferromagnet materials have recently gained renewed interest due to their
possible use in spintronics technologies, where spin transport is the
foundation of their functionalities. In that respect metallic antiferromagnets
are of particular interest, since they enable complex interplays between
electronic charge transport, spin, optical, and magnetization dynamics. Here we
review phenomena where the metallic conductivity provides unique perspectives
for the practical use and fundamental properties of antiferromagnetic
materials.",2005.05247v1
2020/6/13,Photonic crystals as metamaterials,"The visionary work of Veselago had inspired intensive research efforts over
the last decade, towards the realization of man-made structures with
unprecedented electromagnetic (EM) properties. These structures, known as
metamaterials, are typically periodic metallic-based resonant structures
demonstrating effective constitutive parameters beyond the possibilities of
natural material. For example they can exhibit optical magnetism or
simultaneously negative effective permeability and permittivity which implies
the existence of a negative refractive index. However, also periodic dielectric
and polar material, known as photonic crystals, can exhibit EM capabilities
beyond natural materials. This paper reviews the conditions and manifestations
of metamaterial capabilities of photonic crystal systems.",2006.07536v1
2020/11/19,Edge photogalvanic effect caused by optical alignment of carrier momenta in 2D Dirac materials,"We show that the inter-band absorption of radiation in a 2D Dirac material
leads to a direct electric current flowing at sample edges. The photocurrent
originates from the momentum alignment of electrons and holes and is controlled
by the radiation polarization. We develop a microscopic theory of such an edge
photogalvanic effect and calculate the photocurrent for gapped and gapless 2D
Dirac materials, also in the presence of a static magnetic field which
introduces additional imbalance between the electron and hole currents.
Further, we show that the photocurrent can be considerably multiplied in a
ratchet-like structure with an array of narrow strips.",2011.10070v1
2020/12/24,Unconventional superconductivity near a flat band in organic and organometallic materials,"We study electron correlation driven superconductivity on a decorated
honeycomb lattice (DHL), which has a low-energy flat band. On doping, we find
singlet superconductivity with extended-s, extended-d and f-wave symmetry
mediated by magnetic exchange. f-wave singlet pairing is enabled by the lattice
decoration. The critical temperature is predicted to be significantly higher
than on similar lattices lacking flat bands. We discuss how high-temperature
superconductivity could be realized in the DHL materials such as Rb3TT. 2 H2O
and Mo3S7(dmit)3.",2012.13211v1
2021/1/28,Prediction of new low-energy phases of BiFeO$_3$ with large unit cell and complex tilts beyond Glazer notation,"Bismuth ferrite is one of the most widely studied multiferroic materials
because of its large ferroelectric polarisation coexisting with magnetic order
at room temperature. Using density functional theory (DFT), we identify several
previously unknown polar and non-polar structures within the low-energy phase
space of perovskite-structure bismuth ferrite, BiFeO$_3$. Of particular
interest is a series of non-centrosymmetric structures with polarisation along
one lattice vector, combined with anti-polar distortions, reminiscent of
ferroelectric domains, along a perpendicular direction. We discuss possible
routes to stabilising the new phases using biaxial heteroepitaxial strain or
interfacial electrostatic control in heterostructures.",2101.12114v1
2021/8/31,Magnetoresistance and Scaling Laws in Type-II Weyl Semimetal WP_2,"Topological materials with extremely large magnetoresistance exhibit a
prognostic feature of resistivity turn-on behaviour. This occurs when the
temperature dependence of resistivity changes from metallic to semiconducting
characteristics on application of external magnetic field above a threshold
value. Here, we study the magneto-transport properties of type-II Weyl
Semimetal WP2. We find that semi-classical theories of magnetoresistance are
consistent with our data without the need to invoke topological surface states.
Our findings in this work provides an alternative basis to understand the
temperature dependence of magnetoresistance in topological materials.",2108.13981v1
2021/12/31,Searching for new ferromagnetism precursors in two-dimensional model materials in frame of local force theorem,"In this work we conduct a numerical search of non-trivial mechanisms, leading
to new tendencies towards long-range ferromagnetic ordering in two-dimensional
materials. For this purpose we employ an original variant of pairwise
infinitesimal spin rotations technique to establish the magnetic transition
temperature as the rigid function of basic crystal's parameters. It favored the
numerical optimization of this function using modified genetic algorithm,
designed to harvest local extrema. It resulted in revealing the moderate
metallicity, accompanied by essential orbital anisotropy, as the prime
configuration, which provides the most favoring conditions to ferromagnetic
ordering, related to double-exchange and superexchange mechanisms.",2112.15374v1
2022/1/13,Understanding the Stability for LiNi0.5Mn0.5O2 as a Co-free positive electrode material,"For understanding the stability of Co-free positive electrode material,
LiNi0.5Mn0.5O2 was synthesized with different addition amount of lithium during
calcination. The valence states of transition metal in the prepared samples
were determined by combining accurate stoichiometry analysis via ICP, magnetic
moment measurement via SQUID, and element valence analysis via XPS with Ar ion
etching. Unexpectedly, the transition metals, Ni and Mn, at interior and
surface of LiNi0.5Mn0.5O2 particles show different electrochemical properties.
This answer lingering questions of Li de-intercalation mechanism in
LiNi0.5Mn0.5O2.",2201.04772v2
2022/2/17,Tutorial: Macroscopic QED and vacuum forces,"This tutorial introduces the theory of macroscopic QED, where a Hamiltonian
is found that represents the electromagnetic field interacting with a
dispersive, dissipative material. Using a one dimensional theory as motivation,
we build up the more cumbersome three dimensional theory. Then considering the
extension of this theory to moving materials, where the material response
changes due to both the Doppler effect and the mixing of electric and magnetic
responses, it is shown that one gets the theory of quantum electromagnetic
forces for free. We finish by applying macroscopic QED to reproduce Pendry's
expression for the quantum friction force between sliding plates.",2202.08762v1
2022/6/16,Ferroelectricity going 2D,"The discoveries of magnetism and ferroelectricity in 2D van der Waals (vdW)
materials have brought important functionalities to the 2D materials family,
and may trigger a revolution in next generation nanoelectronics and
spintronics. In this perspective article, we briefly review the recent progress
in the field of 2D ferroelectrics, focusing on the mechanisms that drive
spontaneous polarizations in 2D systems, unique properties brought about by the
reduced lattice dimensionality, and promising applications of 2D
ferroelectrics. At the end, we provide an outlook for challenges that need to
be addressed and our view on possible future research directions.",2206.07938v1
2022/8/15,A General Lattice and Basis Formalism Enabling Efficient and Discretized Exploration of Crystallographic Phase Space,"Three-dimensional lattices are fundamental to solid-state physics. The
description of a lattice with an atomic basis constitutes the necessary
information to predict solid phase properties and evolution. Here, we present a
new algorithm for systematically exploring crystallographic phase space.
Coupled with ab-initio techniques, such as density functional theory, this
algorithm offers a new approach for exploring and tuning materials behavior,
with a broad range of potential applications: polar and magnetic transitions,
martensitic phase transformations, and generally materials stability.",2208.07404v1
2022/9/11,Orbital correlations in ultrathin films of late transition metals,"We develop a two-orbital Hubbard model of electron correlations in ultrathin
(111)-oriented fcc films of late transition metals such as Co and Ni. Our model
indicates that the Mott-Hund's interaction results in ferromagnetic
nearest-neighbor orbital correlations. Frustration associated with the mismatch
between orbital and crystal symmetries prevents orbital ordering, resulting in
the orbital liquid state. This state can be manifested in phenomena involving
spin-orbit coupling, such as magnetic anisotropy.",2209.04949v3
2023/2/4,"Comment on ""Axion-matter coupling in multiferroics""","A previous publication [H. S. Roising et al., Phys. Rev. Research 3, 033236
(2021)] involving the current authors pointed out a coupling between dark
matter axions and ferroic orders in multiferroics. In this comment we argue
that using this coupling for dark matter sensing is likely not feasible for the
material class we considered, with present-day technologies and level of
materials synthesis. The proposed effect (for QCD axions) is small and is
overwhelmed by thermal noise. This finding means that likely materials for the
proposed detection scheme would need to be found with significantly lower
magnetic ordering temperatures.",2302.02174v1
2023/4/27,An algorithm for exact analytical solutions for tilted anisotropic Dirac materials,"In this article, we obtain the exact solutions for bound states of tilted
anisotropic Dirac materials under the action of external electric and magnetic
fields with translational symmetry. In order to solve the eigenvalue equation
that arises from the effective Hamiltonian of these materials, we describe an
algorithm that allow us to decouple the differential equations that are
obtained for the spinor components.",2305.00913v2
2023/7/17,Visualization of out-of-plane spin generation in mirror symmetry broken Co,"Generating out-of-plane spins in sputtered materials holds immense potential
for achieving field-free spin-orbit torque switching in practical applications
and mass production. In this work, we present the detection of out-of-plane
spins from single-layer ferromagnetic Co layers, which are visualized through
helicity-dependent photomapping techniques. Our experiments have shown that
out-of-plane spin generation is dependent on the magnetization direction,
current density, and Co thickness. Our findings indicate that amorphous
sputtered Co can be a promising candidate as an out-of-plane spin source
material for industrial massive production.",2307.08273v1
2023/9/7,Electric Analog of Magnons in Order-Disorder Ferroelectrics,"We analyze the ``ferron"" excitations in order-disorder ferroelectrics by a
microscopic pseudo-spin model. We demonstrate that analogous to magnons, the
quanta of spin waves in magnetic materials, ferrons carry both static and
oscillating electric dipole moments, exhibit a Stark effect, and may be
parametrically excited by THz radiation. The anti-crossing gap of the
ferron-photon hybrid depends strongly on propagation direction and an applied
static electric field. We predict ferron diffusion lengths that can reach
centimeters, which implies efficient transport of electric polarization by
temperature gradients. These properties suggest that ferroelectric materials
may be useful for information technology beyond data storage applications.",2309.03691v1
2023/12/7,Oxidation tuning of ferroic transitions in Gd$_2$C monolayer,"Tuning of ferroic phases provides great opportunities for material
functionalities, especially in two-dimensional materials. Here, a $4f$
rare-earth carbide Gd$_2$C monolayer is predicted to be ferromagnetic metal
with large magnetization, inherited from its bulk property. Based on
first-principles calculations, we propose a strategy that the surface
passivation can effectively tune its ferroicity, namely switching among
ferromagnetic, antiferromagnetic, and ferroelectric phases. Metal-insulator
transition also occurs accompanying these ferroic transitions. Our calculation
also suggests that the magneto-optic Kerr effect and second harmonic generation
are effective methods to monitor these phase transitions.",2312.04011v1
2024/3/27,Phase-space representation of coherent states generated through SUSY QM for tilted anisotropic Dirac materials,"In this paper, we examine the electron interaction within tilted anisotropic
Dirac materials when subjected to external electric and magnetic fields
possessing translational symmetry. Specifically, we focus on a distinct
non-zero electric field magnitude, enabling the separation of the differential
equation system inherent in the eigenvalue problem. Subsequently, employing
supersymmetric quantum mechanics facilitates the determination of eigenstates
and eigenvalues corresponding to the Hamiltonian operator. To delve into a
semi-classical analysis of the system, we identify a set of coherent states.
Finally, we assess the characteristics of these states using fidelity and the
phase-space representation through the Wigner function.",2403.19048v1
2024/4/2,Real-space Calculation of Orbital Hall Responses in Disordered Materials,"We developed an efficient numerical approach to compute the different
components of the orbital Hall responses in disordered materials from the Berry
phase theory of magnetization. We propose a theoretical framework based on the
Chebyshev expansion of Green's functions and the position operator for systems
under arbitrary boundary conditions. The capability of this scheme is
illustrated by computing the orbital Hall conductivity for gapped graphene and
Haldane model in the presence of nonperturbative disorder effects. This
methodology opens the door to realistic simulations of orbital Hall responses
in arbitrary complex models of disordered materials.",2404.01739v1
1998/10/19,The effects of magnetic fields in cold clouds in cooling flows,"Large masses of absorbing material are inferred to exist in cooling flows in
clusters of galaxies from the excess X-ray absorption in the spectra of some
X-ray clusters. The absorbing material is probably in the form of cold clouds
pressure-confined by the surrounding, hot, X-ray emitting gas. The cold clouds
could remain relatively static until they are destroyed by evaporation or
ablation, or give rise to star formation. If the final fate of the clouds is
stars, the IMF of the stars formed over the whole cooling flow region ($r \sim
100$ kpc) should be biased to low masses, to avoid a very luminous, blue halo
for the central galaxy of the cooling flow. However, there is evidence for
bright star formation in the innermost (r < 10 kpc) regions of some cooling
flows, and, therefore, the biasing of the IMF towards low masses should not
occur or be less important at smaller radii. The consideration of magnetic
fields may shed light on these two points. If magnetic fields are present, the
magnetic critical mass should be considered, besides the Jeans mass, in
establishing a natural mass scale for star formation. When this new mass scale
is taken into account, we obtain the right variation of the biasing of the IMF
with the radius in addition to inhibition of high-mass star formation at large
radii. We also demonstrate that magnetic reconnection is a efficient than
ambipolar diffusion in removing magnetic fields in cold clouds.",9810280v1
2005/3/14,Gravitational Radiation from an Accreting Millisecond Pulsar with a Magnetically Confined Mountain,"The amplitude of the gravitational radiation from an accreting neutron star
undergoing polar magnetic burial is calculated. During accretion, the magnetic
field of a neutron star is compressed into a narrow belt at the magnetic
equator by material spreading equatorward from the polar cap. In turn, the
compressed field confines the accreted material in a polar mountain which is
misaligned with the rotation axis in general, producing gravitational waves.
The equilibrium hydromagnetic structure of the polar mountain, and its
associated mass quadrupole moment, are computed as functions of the accreted
mass, M_a, by solving a Grad-Shafranov boundary value problem. The orientation-
and polarization-averaged gravitational wave strain, h_c ~ 6e-24 for a 0.6 kHz
source at 1 kpc with M_a > 10^-5 M_Sun, exceeds previous estimates that failed
to treat equatorward spreading and flux freezing self-consistently. It is
concluded that an accreting millisecond pulsar emits a persistent, sinusoidal
gravitational wave signal at levels detectable, in principle, by long baseline
interferometers after phase-coherent integration, provided that the polar
mountain is hydromagnetically stable. Magnetic burial also reduces the magnetic
dipole moment, mu, monotonically, implying a novel, observationally testable
scaling h_c(mu). The implications for the rotational evolution of (accreting)
X-ray and (isolated) radio millisecond pulsars are explored.",0503287v1
2002/12/2,On the effect of heterovalent substitutions in ruthenocuprates,"We discuss the properties of superconducting derivatives of the RuSr2GdCu2O8
(1212-type) ruthenocuprate, for which heterovalent doping has been achieved
through partial substitution of Cu ions into the RuO2 planes
(Ru1-xSr2GdCu2+xO8-d, 0<x<0.75, Tcmax=72 K for x=0.3-0.4) and Ce ions into the
Gd sites (RuSr2Gd1-yCeyCu2O8, 0<y<0.1). The measurements of XANES, thermopower,
and magnetization under external pressure reveal an underdoped character of all
compounds. Muon spin rotation experiments indicate the presence of magnetic
order at low temperatures (Tm=14-2 K for x=0.1-0.4). Properties of these two
series lead us to the qualitative phase diagram for differently doped 1212-type
ruthenocuprates. The difference in temperature of magnetic ordering found for
superconducting and non-superconducting RuSr2GdCu2O8 is discussed in the
context of the properties of substituted compounds. The high pressure oxygen
conditions required for synthesis of Ru1-xSr2RECu2+xO8-d, have been extended to
synthesis of a Ru1-xSr2Eu2-yCeyCu2+xO10-d series. The Cu->Ru doping achieved in
these phases is found to decrease the temperature for magnetic ordering as well
the volume fraction of the magnetic phase.",0212018v2
2005/10/8,Design of magnetic materials: Co$_2$Cr$_{1-x}$Fe$_{x}$Al,"Doped Heusler compounds Co$_2$Cr$_{1-x}$Fe$_{x}$Al with varying Cr to Fe
ratio $x$ were investigated experimentally and theoretically. The electronic
structure of the ordered, doped Heusler compound Co$_2$Cr$_{1-x}$Fe$_{x}$Al
($x=n/4, n=0,1,2,3,4)$ was calculated using different types of band structure
calculations. The ordered compounds turned out to be ferromagnetic with small
Al magnetic moment being aligned anti-parallel to the 3d transition metal
moments. All compounds show a gap around the Fermi-energy in the minority
bands. The pure compounds exhibit an indirect minority gap, whereas the
ordered, doped compounds exhibit a direct gap. Magnetic circular dichroism
(MCD) in X-ray absorption spectra was measured at the $L_{2,3}$ edges of Co,
Fe, and Cr of the pure compounds and the $x=0.4$ alloy in order to determine
element specific magnetic moments. Calculations and measurements show an
increase of the magnetic moments with increasing iron content. The
experimentally observed reduction of the magnetic moment of Cr can be explained
by Co-Cr site-disorder. The presence of the gap in the minority bands of
Co$_2$CrAl can be attributed to the occurrence of pure Co$_2$ and mixed CrAl
(001)-planes in the $L2_1$ structure. It is retained in structures with
different order of the CrAl planes but vanishes in the $X$-structure with
alternating CoCr and CoAl planes.",0510203v1
2001/4/30,Measurement of the Relativistic Potential Difference Across a Rotating Dielectric Cylinder,"According to the Special Theory of Relativity, a rotating magnetic dielectric
cylinder in an axial magnetic field should exhibit a contribution to the radial
electric potential that is associated with the motion of the material's
magnetic dipoles. In 1913 Wilson and Wilson reported a measurement of the
potential difference across a magnetic dielectric constructed from wax and
steel balls. Their measurement has long been regarded as a verification of this
prediction. In 1995 Pelligrini and Swift questioned the theoretical basis of
experiment. In particular, they pointed out that it is not obvious that a
rotating medium may be treated as if each point in the medium is locally
inertial. They calculated the effect in the rotating frame and predicted a
potential different from both Wilson's theory and experiment. Subsequent
analysis of the experiment suggests that Wilson's experiment does not
distinguish between the two predictions due to the fact that their composite
steel-wax cylinder is conductive in the regions of magnetization. We report
measurements of the radial voltage difference across various rotating
dielectric cylinders, including a homogeneous magnetic material (YIG), to
unambiguously test the competing calculations. Our results are compatible with
the traditional treatment of the effect using a co-moving locally inertial
reference frame, and are incompatible with the predictions based on the model
of Pelligrini and Swift.",0104101v1
2007/10/18,"Growth, Structure and Properties of BiFeO3-BiCrO3 Films obtained by Dual Cross Beam PLD","The properties of epitaxial Bi2FeCrO6 thin films, recently synthesized by
pulsed laser deposition, have partially confirmed the theoretical predictions
(i.e. a magnetic moment of 2 muB per formula unit and a polarization of ~80
microC/cm2 at 0K). The existence of magnetic ordering at room temperature for
this material is an unexpected but very promising result that needs to be
further investigated. Since magnetism is assumed to arise from the exchange
interaction between the Fe and Cr cations, the magnetic behaviour is strongly
dependent on both their ordering and the distance between them. We present here
the successful synthesis of epitaxial Bi2FexCryO6 (BFCO x/y) films grown on
SrTiO3 substrates using dual crossed beam pulsed laser deposition. The crystal
structure of the films has different types of (111)-oriented superstructures
depending on the deposition conditions. The multiferroic character of BFCO
(x/y) films is proven by the presence of both ferroelectric and magnetic
hysteresis at room temperature. The oxidation state of Fe and Cr ions in the
films is shown to be 3+ only and the difference in macroscopic magnetization
with Fe/Cr ratio composition could only be due to ordering of the Cr3+ and Fe3+
cations therefore to the modification of the exchange interaction between them.",0710.3424v1
2009/10/24,Monte Carlo Study of the Spin Transport in Magnetic Materials,"The resistivity in magnetic materials has been theoretically shown to depend
on the spin-spin correlation function which in turn depends on the
magnetic-field, the density of conduction electron, the magnetic ordering
stability, etc. However, these theories involved a lot of approximations, so
their validity remained to be confirmed. The purpose of this work is to show by
extensive Monte Carlo (MC) simulation the resistivity of the spin current from
low-$T$ ordered phase to high-$T$ paramagnetic phase in a ferromagnetic film.
We take into account the interaction between the itinerant spins and the
localized lattice spins as well as the interaction between itinerant spins
themselves. We show that the resistivity undergoes an anomalous behavior at the
magnetic phase transition in agreement with previous theories in spite of their
numerous approximations. The origin of the resistivity peak near the phase
transition in ferromagnets is interpreted here as stemming from the existence
of magnetic domains in the critical region. This interpretation is shown to be
in consistence with previous theoretical pictures. Resistivity in a simple
cubic antiferromagnet is also shown. The absence of a peak in this case is
explained.",0910.4619v3
2010/1/8,On the exclusion of intra-cluster plasma from AGN-blown bubbles,"Simple arguments suggest that magnetic fields should be aligned tangentially
to the surface of an AGN-blown bubble. If this is the case, charged particles
from the fully ionised intra-cluster medium (ICM) will be prevented,
ordinarily, from crossing the boundary by the Lorentz force. However, recent
observations indicate that thermal material may occupy up to 50% of the volume
of some bubbles. Given the effect of the Lorentz force, the thermal content
must then be attributed to one, or a combination, of the following processes:
i) the entrainment of thermal gas into the AGN outflow that inflated the
bubble; ii) rapid diffusion across the magnetic field lines at the ICM/bubble
interface; iii) magnetic reconnection events which transfer thermal material
across the ICM/bubble boundary. Unless the AGN outflow behaves as a magnetic
tower jet, entrainment may be significant and could explain the observed
thermal content of bubbles. Alternatively, the cross-field diffusion
coefficient required for the ICM to fill a typical bubble is roughly 10^16 cm^2
s^-1, which is anomalously high compared to predictions from turbulent
diffusion models. Finally, the mass transfer rate due to magnetic reconnection
is uncertain, but significant for plausible reconnection rates. We conclude
that entrainment into the outflow and mass transfer due to magnetic
reconnection events are probably the most significant sources of thermal
content in AGN-blown bubbles.",1001.1356v1
2010/1/28,Magnetic Doping and Kondo Effect in Bi2Se3 Nanoribbons,"A simple surface band structure and a large bulk band gap have allowed Bi2Se3
to become a reference material for the newly discovered three-dimensional
topological insulators, which exhibit topologically-protected conducting
surface states that reside inside the bulk band gap. Studying topological
insulators such as Bi2Se3 in nanostructures is advantageous because of the high
surface-to-volume ratio, which enhances effects from the surface states;
recently reported Aharonov-Bohm oscillation in topological insulator
nanoribbons by some of us is a good example. Theoretically, introducing
magnetic impurities in topological insulators is predicted to open a small gap
in the surface states by breaking time-reversal symmetry. Here, we present
synthesis of magnetically-doped Bi2Se3 nanoribbons by vapor-liquid-solid growth
using magnetic metal thin films as catalysts. Although the doping concentration
is less than ~ 2%, low-temperature transport measurements of the Fe-doped
Bi2Se3 nanoribbon devices show a clear Kondo effect at temperatures below 30 K,
confirming the presence of magnetic impurities in the Bi2Se3 nanoribbons. The
capability to dope topological insulator nanostructures magnetically opens up
exciting opportunities for spintronics.",1001.5239v1
2010/10/4,Defects induced ferromagnetism in Mn doped ZnO,"Single phase Mn doped (2 at %) ZnO samples have been synthesized by
solid-state reaction technique. Before the final sintering at 500 C, the mixed
powders have been milled for different milling periods (6, 24, 48 and 96
hours). The grain sizes of the samples are very close to each other (~ 32 \pm 4
nm). However, the defective state of the samples is different from each other
as manifested from the variation of magnetic properties and electrical
resistivity with milling time. All the samples have been found to be
ferromagnetic with clear hysteresis loops at room temperature. The maximum
value for saturation magnetization (0.11 {\mu}_B / Mn atom) was achieved for 96
hours milled sample. Electrical resistivity has been found to increase with
increasing milling time. The most resistive sample bears the largest saturation
magnetization. Variation of average positron lifetime with milling time bears a
close similarity with that of the saturation magnetization. This indicates the
key role played by open volume vacancy defects, presumably zinc vacancies near
grain surfaces, in inducing ferromagnetic order in Mn doped ZnO. To attain
optimum defect configuration favorable for ferromagnetism in this kind of
samples proper choice of milling period and annealing conditions is required.",1010.0547v1
2011/3/22,Dipolar Interactions between Iron-Oxide Nanoparticles in Frozen Ferrofluids and Ferronematics,"We present a detailed study of the magnetic behavior of iron-oxide
(gamma-Fe2O3 and Fe3O4) nanoparticles constituents of ferrofluids (FF's) with
average particle sizes <d> = 2.5 and 10 nm. The particles were dispersed in the
frozen liquid carrier (pure FF) and in a frozen lyotropic liquid crystalline
matrix in the nematic phase or ferronematic (FN) (ferrolyomesophase). Both FF
and FN phases displayed superparamagnetic (SPM) behaviour at room temperature,
with blocking temperatures T_B ~ 10 and 100 K for <d> = 2.5 and 10 nm,
respectively. Dynamic ac susceptibility measurements showed a thermally
activated N\'eel-Brown dependence of the blocking temperature with applied
frequency. Our results show that dipolar interactions are small, but
non-negligible, as compared to the single-particle energy barriers from
magnetic anisotropy. From the fit of ac susceptibility we calculated the
effective magnetic anisotropy constant K_{eff} for 2.5 nm maghemite particles.
Although interparticle interactions present in highly diluted samples do not
appreciably modify the dynamic magnetic behavior of isolated particles, the
calculated magnetic anisotropy were abut one order of magnitude larger that the
bulk materials, suggesting the existence of large surface anisotropy. Using the
thermally activated model to fit the dynamic data yielded effective energy
barriers Ea = 3.5x10^{-21} J. From these data, we obtained K_{eff} = 422 kJ/m^3
for the single-particle effective magnetic anisotropy.",1103.4403v1
2011/4/29,Constraints on Cold Magnetized Shocks in Gamma-Ray Bursts,"We consider a model in which the ultra-relativistic jet in a gamma-ray burst
(GRB) is cold and magnetically accelerated. We assume that the energy flux in
the outflowing material is partially thermalized via internal shocks or a
reverse shock, and we estimate the maximum amount of radiation that could be
produced in such magnetized shocks. We compare this estimate with the available
observational data on prompt gamma-ray emission in GRBs. We find that, even
with highly optimistic assumptions, the magnetized jet model is radiatively too
inefficient to be consistent with observations. One way out is to assume that
much of the magnetic energy in the post-shock, or even pre-shock, jet material
is converted to particle thermal energy by some unspecified process, and then
radiated. This can increase the radiative efficiency sufficiently to fit
observations. Alternatively, jet acceleration may be driven by thermal pressure
rather than magnetic fields. In this case, which corresponds to the traditional
fireball model, sufficient prompt GRB emission could be produced either from
shocks at a large radius or from the jet photosphere closer to the center.",1105.0003v2
2011/11/21,Magnetic Field Effect on Crossover Temperature from Non-Fermi Liquid to Fermi Liquid Behavior in f^2-Impurity Systems with Crystalline-Electric-Field Singlet State Competing with Kondo-Yosida Singlet State,"We investigate the magnetic field dependence of the physical properties of
f^2-configuration systems with a crystalline-electric field (CEF) singlet
ground state, which gives rise to a non- Fermi liquid (NFL) fixed point due to
the competition between the Kondo-Yosida singlet and CEF singlet states. On the
basis of the numerical renormalization group method, we find that the magnetic
field breaks this NFL fixed point via two mechanisms: one causing the
polarization of f-electrons and the other giving the ""channel"" anisotropy.
These two mechanisms induce a difference in the magnetic field dependence of
the characteristic temperature T_F^{*}(H), the crossover temperature from NFL
to Fermi-liquid behavior. While the polarization of f-electrons gives
T_F^{*}(H) \propto H^x (x\sim2.0), the ""channel"" anisotropy gives the
H-independent T_F^{*}(H). These two mechanisms cross over continuously at
approximately the crossover magnetic field H_c, where an anomalous H-dependence
of T_F^{*}(H) appears. Such T_F^{*}(H) well reproduces the NFL behaviors
observed in Th_{1-x}U_xRu_2Si_2. We also find that the H-dependence of the
resistivity and the magnetic susceptibility are in good agreement with the
experimental results of this material. These results suggest that the NFL
behaviors observed in Th_{1-x}U_xRu_2Si_2 can be understood if this material is
located in the CEF singlet side near the critical phase boundary between the
two singlet states.",1111.4718v2
2012/2/17,"Landau theory for the phase diagram of the multiferroic Mn$_{1-x}$(Fe,Zn,Mg)$_{x}$WO$_{4}$","We present a theoretical analysis of the temperature-magnetic
field-concentration phase diagram of the multiferroic Mn$_{1-x}$M$_{x}$WO$_{4}$
(M=Fe, Zn, Mg), which exhibits three ordered phases, with collinear and
non-collinear incommensurate and with a commensurate magnetic order. The middle
phase is also ferroelectric. The analysis uses a semi-phenomenological Landau
theory, based on a Heisenberg Hamiltonian with a single-ion anisotropy. With a
small number of adjustable parameters, the Landau theory gives an excellent fit
to all three transition lines, as well as the magnetic and the ferroelectric
order parameters. The fit of the magnetic and ferroelectric order parameters is
further improved by including the effect of fluctuations near the transitions.
We demonstrate the highly frustrated nature of these materials and suggest a
simple explanation for the dramatic effects of doping with different magnetic
ions at the Mn sites. The model enables an examination of different sets of
exchange couplings that were proposed by a number of groups. Small
discrepancies are probably a consequence of small errors in the experimental
magnetic parameters. In addition, using the Ginzburg criterion we estimate the
temperature range in which fluctuations of the order parameters become
important.",1202.3881v1
2012/9/29,Emergence and Frustration of Magnetic Order with Variable-Range Interactions in a Trapped Ion Quantum Simulator,"Frustration, or the competition between interacting components of a network,
is often responsible for the complexity of many body systems, from social and
neural networks to protein folding and magnetism. In quantum magnetic systems,
frustration arises naturally from competing spin-spin interactions given by the
geometry of the spin lattice or by the presence of long-range antiferromagnetic
couplings. Frustrated magnetism is a hallmark of poorly understood systems such
as quantum spin liquids, spin glasses and spin ices, whose ground states are
massively degenerate and can carry high degrees of quantum entanglement. The
controlled study of frustrated magnetism in materials is hampered by short
dynamical time scales and the presence of impurities, while numerical modeling
is generally intractable when dealing with dynamics beyond N~30 particles.
Alternatively, a quantum simulator can be exploited to directly engineer
prescribed frustrated interactions between controlled quantum systems, and
several small-scale experiments have moved in this direction. In this article,
we perform a quantum simulation of a long-range antiferromagnetic quantum Ising
model with a transverse field, on a crystal of up to N = 16 trapped Yb+ atoms.
We directly control the amount of frustration by continuously tuning the range
of interaction and directly measure spin correlation functions and their
dynamics through spatially-resolved spin detection. We find a pronounced
dependence of the magnetic order on the amount of frustration, and extract
signatures of quantum coherence in the resulting phases.",1210.0142v1
2012/10/22,Electronic structure and magnetic and optical properties of double perovskite Bi2FeCrO6 from first-principles investigation,"Double perovskite Bi$_2$FeCrO$_6$, related with BiFeO$_3$, is very
interesting because strong ferroelectricity and high magnetic Curie temperature
beyond room temperature are observed in it. However, existing
density-functional-theory (DFT) studies, using pseudo-potentials, produce
metallic ground state under the local density approximation (LDA) and need
LDA+U method to yield needed nonmetallic ground state, resulting in low
magnetic Curie temperature (below 130 K). Here, we optimize its crystal
structure and then investigate its electronic structure and magnetic and
optical properties by combining the full-potential augmented plane wave method
with Monte Carlo simulation. Our optimized structure is a robust ferrimagnetic
semiconductor. This nonmetallic phase is formed due to crystal field splitting
and spin exchange splitting, in contrast to Mott-Hubbard states in previous DFT
studies. Spin exchange constants and optical properties are calculated. Our ab
initio magnetic Curie temperature is 450 K, much higher than previous DFT-based
value and consistent with experimental results. Our study and analysis reveals
that the main magnetic mechanism is an antiferromagnetic superexchange between
Fe and Cr over the intermediate O atom. These results are useful to
understanding such perovskite materials and exploring their potential
applications.",1210.5981v2
2012/11/26,Thermodynamic properties of the Yb2Ti2O7 pyrochlore as a function of temperature and magnetic field: validation of a quantum spin ice exchange Hamiltonian,"The thermodynamic properties of the pyrochlore Yb2Ti2O7 material are
calculated using the numericallinked-cluster (NLC) calculation method for an
effective anisotropic-exchange spin-1/2 Hamiltonian with parameters recently
determined by fitting the neutron scattering spin wave data obtained at high
magnetic field h. Magnetization, M(T,h), as a function of temperature T and for
different magnetic fields h applied along the three high symmetry directions
[100], [110] and [111], are compared with experimental measurements on the
material for temperature T>1.8K. The excellent agreement between experimentally
measured and calculated M(T,h) over the entire temperature and magnetic field
range considered provides strong quantitative validation of the effective
Hamiltonian. It also confirms that fitting the high-field neutron spin wave
spectra in the polarized paramagnetic state is an excellent method for
determining the microscopic exchange constants of rare-earth insulating magnets
that are described by an effective spin-1/2 Hamiltonian. Finally, we present
results which demonstrate that a recent analysis of the polarized neutron
scattering intensity of Yb2Ti2O7 using a random phase approximation (RPA)
method [Chang et al., Nature Communications {3}, 992 (2012)] does not provide a
good description of M(T,h) for $T\lesssim 10$ K, that is in the entire
temperature regime where correlations become non-negligible.",1211.5934v1
2013/1/15,Interplay of 4f-3d Magnetism and Ferroelectricity in DyFeO3,"DyFeO3 exhibits a weak ferromagnetism (TNFe ~ 645 K) that disappears below a
spin-reorientation (Morin) transition at TSRFe ~ 50 K. It is also known that
applied magnetic field induces ferroelectricity at the magnetic ordering
temperature of Dy-ions (TNDy ~ 4.5 K). Here, we show that the ferroelectricity
exists in the weak ferromagnetic state (TSRFe < T < TN,C) without applying
magnetic field, indicating the crucial role of weak ferromagnetism in inducing
ferroelectricity. 57Fe M\""ossbauer studies show that hyperfine field (Bhf)
deviates from mean field-like behaviour that is observed in the weak
ferromagnetic state and decreases below the onset of spin-reorientation
transition (80 K), implying that the Bhf above TSR had additional contribution
from Dy-ions due to induced magnetization by the weak ferromagnetic moment of
Fe-sublattice and below TSR, this contribution decreases due to collinear
ordering of Fe-sublattice. These results clearly demonstrate the presence of
magnetic interactions between Dy(4f) and Fe(3d) and their correlation with
ferroelectricity in the weak ferromagnetic state of DyFeO3.",1301.3263v1
2013/1/21,Galactic Spiral Patterns and Dynamo Action II: Asymptotic Solutions,"The exploration of mean-field galactic dynamos affected by a galactic spiral
pattern, begun in Chamandy et al. (2013, hereafter Paper I) with numerical
simulations, is continued here with an asymptotic solution. The mean-field
dynamo model used generalizes the standard theory to include the delayed
response of the mean electromotive force to variations of the mean magnetic
field and turbulence parameters (the temporal non-locality, or {\tau} effect).
The effect of the spiral pattern on the dynamo considered is the enhancement of
the {\alpha}-effect in spiral-shaped regions (which may overlap the gaseous
spiral arms or be located in the interarm regions). The axisymmetric and
enslaved non-axisymmetric modes of the mean magnetic field are studied
semi-analytically to clarify and strengthen the numerical results. Good
qualitative agreement is obtained between the asymptotic solution and numerical
solutions of Paper I for a global, rigidly rotating material spiral (density
wave). At all galactocentric distances except for the co-rotation radius, we
find magnetic arms displaced in azimuth from the {\alpha}-arms, so that the
ridges of magnetic field strength are more tightly wound than the
{\alpha}-arms. Moreover, the effect of a finite dynamo relaxation time {\tau}
(related to the turbulence correlation time) is to phase-shift the magnetic
arms in the direction opposite to the galactic rotation even at the co-rotation
radius. This mechanism can be used to explain the phase shifts between magnetic
and material arms observed in some spiral galaxies.",1301.4761v2
2013/11/12,Superconductivity and unusual magnetic behavior in amorphous carbon,"Traces of superconductivity (SC) at elevated temperatures (up to 65 K) were
observed by magnetic measurements in three different inhomogeneous sulfur doped
amorphous carbon (a-C) systems: (a) in commercial and (b) synthesized powders
and (c) in a-C thin films. (a) Studies performed on commercial (a-C) powder
which contains 0.21% of sulfur, revealed traces of non-percolated
superconducting phases below Tc = 65 K. The SC volume fraction is enhanced by
the sulfur doping. (b) a-C powder obtained by pyrolytic decomposition of
sucrose did not show any sign for SC above 5 K. This powder was mixed with
sulfur and synthesized at 400 C (a-CS). The inhomogeneous products obtained,
show traces of SC phases at TC= 17 and 42 K. (c) Non-superconducting composite
a-C-W thin films were grown by electron-beam induced deposition. SC emerged at
Tc = 34.4 K only after heat treatment with sulfur. Other parts of the pyrolytic
a-CS powder, show unusual magnetic features. (i) Pronounced irreversible peaks
around 55-75 K appear in the first zero-field-cooled (ZFC) sweep only. Their
origin is not known. (ii) Unexpectedly these peaks are totally suppressed in
the second ZFC runs measured a few minutes later. (iii) Around the peak
position the field-cooled (FC) curves cross the ZFC plots (ZFC>FC). These
peculiar magnetic observations also ascribed to a-CS powder prepared from the
commercial a-C powder and are connected to each other. All SC and magnetic
phenomena observed are intrinsic properties of the sulfur doped a-C materials.
It is proposed that the a-CS systems behave similarly to well known high TC
curates and/or pnictides in which SC emerges from magnetic states.",1311.2767v1
2014/1/14,Spin Fluctuations and Frustrated Magnetism in the Multiferroic FeVO$_4$,"We report $^{51}$V nuclear magnetic resonance (NMR) studies on single
crystals of the multiferroic material FeVO$_4$. The high-temperature Knight
shift shows Curie-Weiss behavior, $^{51}K = a/(T + \theta)$, with a large Weiss
constant $\theta \approx$ 116 K. However, the $^{51}$V spectrum shows no
ordering near these temperatures, splitting instead into two peaks below 65 K,
which suggests only short-ranged magnetic order on the NMR time scale. Two
magnetic transitions are identified from peaks in the spin-lattice relaxation
rate, $1/^{51}T_1$, at temperatures $T_{N1} \approx$ 19 K and $T_{N2} \approx$
13 K, which are lower than the estimates obtained from polycrystalline samples.
In the low-temperature incommensurate spiral state, the maximum ordered moment
is estimated as 1.95${\mu}_B$/Fe, or 1/3 of the local moment. Strong low-energy
spin fluctuations are also indicated by the unconventional power-law
temperature dependence $1/^{51}T_1 \propto T^2$. The large Weiss constant,
short-range magnetic correlations far above $T_{N1}$, small ordered moment,
significant low-energy spin fluctuations, and incommensurate ordered phases all
provide explicit evidence for strong magnetic frustration in FeVO$_4$.",1401.3053v2
2014/1/23,"Magnetization, magnetostriction, and their relationship in Invar Fe$_{1-x}A_{x}$ ($A={\rm Pt},{\rm Ni}$)","A method is proposed for investigating the spontaneous magnetization, the
spontaneous volume magnetostriction, and their relationship in disordered
face-centered-cubic Fe$_{0.72}$Pt$_{0.28}$ and Fe$_{0.65}$Ni$_{0.35}$ in the
temperature interval $0 \leq T/T_{\rm C} < 1$. It relies on the disordered
local moment formalism and the observation that the reduced magnetization in
each of the investigated materials is accurately described by an equation of
the form $M(T)/M(0) = [ 1 -s (T/T_{\rm C})^{3/2}- (1-s)(T/T_{\rm C})^{p}
]^{q}$. The present approach yields interesting results. The alloys at zero
Kelvin share several physical properties: the volume in a partially disordered
local moment state shrinks as the fraction of Fe moments which point down
increases in the interval $0 < x^{{\rm Fe}\downarrow} < 1/2$, following closely
$V(0) - 4 [V(0)-V(1/2)] x^{{\rm Fe}\downarrow} (1-x^{{\rm Fe}\downarrow})$,
while the magnetization collapses, following closely $M(0) - 2 M(0) x^{{\rm
Fe}\downarrow}$; the volume in the homogeneous ferromagnetic state greatly
exceeds that in the disordered local moment state; $x^{{\rm Fe}\downarrow}(0)$
is close to zero. These common properties can account for a variety of
intriguing phenomena displayed by both alloys, including the anomaly in the
magnetostriction at zero Kelvin and, more surprisingly perhaps, the scaling
between the reduced magnetostriction and the reduced magnetization squared
below the Curie temperature. However, the thermal evolution of the fraction of
Fe moments which point down depends strongly on the alloy under consideration.
This, in turn, can explain the observed marked difference in the temperature
dependence of the reduced magnetization between the two alloys.",1401.6089v2
2014/2/27,Enhanced Stability of Skyrmions in Two-Dimensional Chiral Magnets with Rashba Spin-Orbit Coupling,"Recent developments have led to an explosion of activity on skyrmions in
three-dimensional (3D) chiral magnets. Experiments have directly probed these
topological spin textures, revealed their nontrivial properties, and led to
suggestions for novel applications. However, in 3D the skyrmion crystal phase
is observed only in a narrow region of the temperature-field phase diagram. We
show here, using a general analysis based on symmetry, that skyrmions are much
more readily stabilized in two-dimensional (2D) systems with Rashba spin-orbit
coupling. This enhanced stability arises from the competition between field and
easy-plane magnetic anisotropy and results in a nontrivial structure in the
topological charge density in the core of the skyrmions. We further show that,
in a variety of microscopic models for magnetic exchange, the required
easy-plane anisotropy naturally arises from the same spin-orbit coupling that
is responsible for the chiral Dzyaloshinskii-Moriya interactions. Our results
are of particular interest for 2D materials like thin films, surfaces, and
oxide interfaces, where broken surface-inversion symmetry and Rashba spin-orbit
coupling naturally lead to chiral exchange and easy-plane compass anisotropy.
Our theory gives a clear direction for experimental studies of 2D magnetic
materials to stabilize skyrmions over a large range of magnetic fields down to
T=0.",1402.7082v2
2014/11/15,Spin-transfer-torque through antiferromagnetic IrMn,"Spin-transfer-torque, a transfer of angular momentum between the electron
spin and the local magnetic moments, is a promising and key mechanism to
control ferromagnetic materials in modern spintronic devices . However, much
less attention has been paid to the same effect in antiferromagnets. For the
sake of investigating how the spin current interacts with the magnetic moments
in antiferromagnets, we perform spin-torque ferromagnetic resonance
measurements on Co20Fe60B20 4nm/Ir25Mn75 tIrMn nm/Pt 4 nm multilayers under a
spin Hall effect of Pt. The effective magnetic damping in Co20Fe60B20 is
modified by the spin current injected from the Pt layer via the IrMn layer. The
results indicate that the spin current interacts with IrMn magnetic moments and
exerts the anti-damping torque on the magnetic moments of Co20Fe60B20 through
the IrMn. It is also found that the reduction of the exchange bias in the
IrMn/Pt interface degrades the anti-damping torque exerted on the Co20Fe60B20
layer, suggesting the transmission of the spin torque becomes less efficient as
the interface exchange coupling degrades. Our work infers that the magnetic
moments in IrMn can be manipulated by spin torque similarly to the one in a
ferromagnetic layer.",1411.4100v4
2015/1/21,"The electronic and magnetic structure of p-element (C,N) doped rutile-TiO$_{2}$; A hybrid DFT study","We study the electronic and magnetic structure of carbon and nitrogen
impurities and interstitials in rutile TiO${_2}$. To this end we perform
\textit{ab-initio} calculations of a 48-atom supercell employing the VASP code.
In order to obtain a realistic description of the electronic and magnetic
structure, exchange and correlation are treated with the HSE06 hybrid
functional. Both, atomic positions and cell dimensions are fully relaxed.
Substitutional carbon and nitrogen are found to have a magnetic moment of 2 and
1$\mu{_B}$, respectively, with a tendency for anti-ferromagnetic long range
order. For C/N on interstitial sites we find that carbon is non-magnetic while
nitrogen always possesses a magnetic moment of 1$\mu{_B}$. We find that these
interstitial positions are on a saddle point of the total energy. The stable
configuration is reached when both carbon and nitrogen form a C-O and N-O dimer
with a bond length close to the double bond for CO and NO. This result is in
agreement with earlier experimental investigations detecting such N-O entities
from XPS measurements. The frequencies of the symmetric stretching mode are
calculated for these dimers, which could provide a means for experimental
verification. For all configurations investigated both C and N states are found
inside the TiO${_2}$ gap. These new electronic states are discussed with
respect to tuning doped TiO${_2}$ for the application in photocatalysis",1501.05233v1
2015/1/23,Tensile strain-induced softening of iron at high temperature,"In weakly ferromagnetic materials, already small changes in the atomic
configuration triggered by temperature or chemistry can alter the magnetic
interactions responsible for the non-random atomic-spin orientation. Different
magnetic states, in turn, can give rise to substantially different macroscopic
properties. A classical example is iron, which exhibits a great variety of
properties as one gradually removes the magnetic long-range order by raising
the temperature towards and beyond its Curie point of
$T_{\text{C}}^{0}=1043$\,K. Using first-principles theory, here we demonstrate
that uniaxial tensile strain can also destabilize the magnetic order in iron
and eventually lead to a ferromagnetic to paramagnetic transition at
temperatures far below $T_{\text{C}}^{0}$. In consequence, the intrinsic
strength of the ideal single-crystal body-centered cubic iron dramatically
weakens above a critical temperature of $\sim 500$\,K. The discovered
strain-induced magneto-mechanical softening provides a plausible atomic-level
mechanism behind the observed drop of the measured strength of Fe whiskers
around $300-500$\,K. Alloying additions which have the capability to partially
restore the magnetic order in the strained Fe lattice, push the critical
temperature for the strength-softening scenario towards the magnetic transition
temperature of the undeformed lattice. This can result in a surprisingly large
alloying-driven strengthening effect at high temperature as illustrated here in
the case of Fe-Co alloy.",1501.05774v2
2015/3/3,Tunable room-temperature ferromagnet using an iron-oxide and graphene oxide nanocomposite,"Magnetic materials have found wide application ranging from electronics and
memories to medicine. Essential to these advances is the control of the
magnetic order. To date, most room-temperature applications have a fixed
magnetic moment whose orientation is manipulated for functionality. Here we
demonstrate an iron-oxide and graphene oxide nanocomposite based device that
acts as a tunable ferromagnet at room temperature. Not only can we tune its
transition temperature in a wide range of temperatures around room temperature,
but the magnetization can also be tuned from zero to 0.011 A.m$^2$/kg through
an initialization process with two readily accessible knobs (magnetic field and
electric current), after which the system retains its magnetic properties
semi-permanently until the next initialization process. We construct a
theoretical model to illustrate that this tunability originates from an
indirect exchange interaction mediated by spin-imbalanced electrons inside the
nanocomposite.",1503.00960v1
2015/4/14,Direct Evidence for Dominant Bond-directional Interactions in a Honeycomb Lattice Iridate Na2IrO3,"Heisenberg interactions are ubiquitous in magnetic materials and have been
prevailing in modeling and designing quantum magnets. Bond-directional
interactions offer a novel alternative to Heisenberg exchange and provide the
building blocks of the Kitaev model, which has a quantum spin liquid (QSL) as
its exact ground state. Honeycomb iridates, A2IrO3 (A=Na,Li), offer potential
realizations of the Kitaev model, and their reported magnetic behaviors may be
interpreted within the Kitaev framework. However, the extent of their relevance
to the Kitaev model remains unclear, as evidence for bond-directional
interactions remains indirect or conjectural. Here, we present direct evidence
for dominant bond-directional interactions in antiferromagnetic Na2IrO3 and
show that they lead to strong magnetic frustration. Diffuse magnetic x-ray
scattering reveals broken spin-rotational symmetry even above Neel temperature,
with the three spin components exhibiting nano-scale correlations along
distinct crystallographic directions. This spin-space and real-space
entanglement directly manifests the bond-directional interactions, provides the
missing link to Kitaev physics in honeycomb iridates, and establishes a new
design strategy toward frustrated magnetism.",1504.03618v1
2016/1/10,Room temperature chiral magnetic skyrmion in ultrathin magnetic nanostructures,"Magnetic skyrmions are chiral spin structures with a whirling configuration.
Their topological properties, nanometer size and the fact that they can be
moved by small current densities have opened a new paradigm for the
manipulation of magnetisation at the nanoscale. To date, chiral skyrmion
structures have been experimentally demonstrated only in bulk materials and in
epitaxial ultrathin films and under external magnetic field or at low
temperature. Here, we report on the observation of stable skyrmions in
sputtered ultrathin Pt/Co/MgO nanostructures, at room temperature and zero
applied magnetic field. We use high lateral resolution X-ray magnetic circular
dichroism microscopy to image their chiral N\'eel internal structure which we
explain as due to the large strength of the Dzyaloshinskii-Moriya interaction
as revealed by spin wave spectroscopy measurements. Our results are
substantiated by micromagnetic simulations and numerical models, which allow
the identification of the physical mechanisms governing the size and stability
of the skyrmions.",1601.02278v1
2016/2/7,Hexagonal phase stabilization and magnetic orders of multiferroic Lu$_{1-x}$Sc$_x$FeO$_3$,"Hexagonal LuFeO$_3$ has drawn a lot of research attention due to its
contentious room-temperature multiferroicity. Due to the unstability of
hexagonal phase in the bulk form, most experimental studies focused on
LuFeO$_3$ thin films which can be stabilized by strain using proper substrates.
Here we report on the hexagonal phase stabilization, magnetism, and
magnetoelectric coupling of bulk LuFeO$_3$ by partial Sc-substitution of Lu.
First, our first-principles calculations show that the hexagonal structure can
be stabilized by partial Sc substitution, while the multiferroic properties
including the noncollinear magnetic order and geometric ferroelectricity remain
robustly unaffected. Therefore, Lu$_{1-x}$Sc$_x$FeO$_3$ can act as a platform
to check the multiferroicity of LuFeO$_3$ and related materials in the bulk
form. Second, the magnetic characterizations on bulk Lu$_{1-x}$Sc$_x$FeO$_3$
demonstrate a magnetic anomaly (probable antiferromagnetic ordering) above room
temperature, $\sim425-445$ K, followed by magnetic transitions in low
temperatures ($\sim167-172$ K). In addition, a magnetoelectric response is
observed in the low temperature region. Our study provides useful information
on the multiferroic physics of hexagonal $R$FeO$_3$ and related systems.",1602.02365v1
2016/3/31,"Theory of multiple--phase competition in pyrochlore magnets with anisotropic exchange, with application to Yb2Ti2O7, Er2Ti2O7 and Er2Sn2O7","The family of magnetic rare-earth pyrochlore oxides R2M2O7 plays host to a
diverse array of exotic phenomena, driven by the interplay between geometrical
frustration and spin-orbit interaction, which leads to anisotropy in both
magnetic moments and their interactions. In this article we establish a
general, symmetry--based theory of pyrochlore magnets with anisotropic exchange
interactions. Starting from a very general model of nearest-neighbour exchange
between Kramers ions, we find four distinct classical ordered states, all with
q=0, competing with a variety of spin-liquids and unconventional forms of
magnetic order. The finite-temperature phase diagram of this model is
determined by Monte Carlo simulation, supported by classical spin-wave
calculations. We pay particular attention to the region of parameter space
relevant to the widely studied materials Er2Ti2O7, Yb2Ti2O7, and Er2Sn2O7. We
find that many of the most interesting properties of these materials can be
traced back to the ""accidental"" degeneracies where phases with different
symmetries meet. These include the ordered ground state selection by
fluctuations in Er2Ti2O7, the dimensional-reduction observed in Yb2Ti2O7, and
the lack of reported magnetic order in Er2Sn2O7. We also discuss the
application of this theory to other pyrochlore oxides.",1603.09466v2
2016/5/6,Optically probing symmetry breaking in the chiral magnet Cu2OSeO3,"We report on the linear optical properties of the chiral magnet Cu2OSeO3,
specifically associated with the absence of inversion symmetry, the chiral
crystallographic structure, and magnetic order. Through spectroscopic
ellipsometry, we observe local crystal-field excitations below the
charge-transfer gap. These crystal-field excitations are optically allowed due
to the lack of inversion symmetry at the Cu sites. Optical polarization
rotation measurements were used to study the structural chirality and magnetic
order. The temperature dependence of the natural optical rotation, originating
in the chiral crystal structure, provides evidence for a finite
magneto-electric effect in the helimagnetic phase. We find a large
magneto-optical susceptibility on the order of V(540nm)~10^4 rad/(T*m) in the
helimagnetic phase and a maximum Faraday rotation of ~165deg/mm in the
ferrimagnetic phase. The large value of V can be explained by considering spin
cluster formation and the relative ease of domain reorientation in this
metamagnetic material. The magneto-optical activity allows us to map the
magnetic phase diagram, including the skyrmion lattice phase. In addition to
this, we probe and discuss the nature of the various magnetic phase transitions
in Cu2OSeO3.",1605.01900v1
2016/5/9,Control of spin-orbit torques through crystal symmetry in WTe2/ferromagnet bilayers,"Recent discoveries regarding current-induced spin-orbit torques produced by
heavy-metal/ferromagnet and topological-insulator/ferromagnet bilayers provide
the potential for dramatically-improved efficiency in the manipulation of
magnetic devices. However, in experiments performed to date, spin-orbit torques
have an important limitation -- the component of torque that can compensate
magnetic damping is required by symmetry to lie within the device plane. This
means that spin-orbit torques can drive the most current-efficient type of
magnetic reversal (antidamping switching) only for magnetic devices with
in-plane anisotropy, not the devices with perpendicular magnetic anisotropy
that are needed for high-density applications. Here we show experimentally that
this state of affairs is not fundamental, but rather one can change the allowed
symmetries of spin-orbit torques in spin-source/ferromagnet bilayer devices by
using a spin source material with low crystalline symmetry. We use WTe2, a
transition-metal dichalcogenide whose surface crystal structure has only one
mirror plane and no two-fold rotational invariance. Consistent with these
symmetries, we generate an out-of-plane antidamping torque when current is
applied along a low-symmetry axis of WTe2/Permalloy bilayers, but not when
current is applied along a high-symmetry axis. Controlling S-O torques by
crystal symmetries in multilayer samples provides a new strategy for optimizing
future magnetic technologies.",1605.02712v1
2016/5/17,Magnetic properties of perovskites La$_{0.7}$Sr$_{0.3}$Mn$_{0.7}^{3+}$Mn$_{0.3-x}^{4+}$Ti$_x$O$_3$:Monte Carlo simulation versus experiments,"This work presents a Monte Carlo study of the phase transition in the
perovskites La$_{0.7}$Sr$_{0.3}$Mn$_{0.7}^{3+}$Mn$_{0.3-x}^{4+}$Ti$_x$O$_3$
($x$= 0.1, 0.2, and 0.25). We take into accountnearest-neighbor (NN)
interactions between magnetic ions Mn$^{3+}$($S=2$) and Mn$^{4+}$($S=3/2$)
using a spin model describing a strong anisotropy on the $z$ axis. We have
calculated the uniform and staggered magnetizations as well as the
Edwards-Anderson order parameter as functions of temperature, with and without
an applied magnetic field. Fitting the experimental Curie temperature at $x=0$,
we estimated values of various exchange interactions in the system. The
dominant one is that between Mn$^{3+}$ and Mn$^{4+}$ which is at the origin of
the ferromagnetic ordering. Effects of the very small interaction $J\_2$
between NN Mn$^{3+}$ is analyzed: we show that it can cause an
antiferromagnetic phase above $T\_c$ which disappears at smaller $J\_2$ or at
Mn$^{3+}$ concentrations smaller than 0.55. Our results show a good agreement
with experiments on the magnetizations for substitution concentration $x=0.1$,
0.2 and 0.3. We also studied the applied-field effect on the magnetization and
our obtained results are compared with experiments performed at $x=10\%$.",1605.05107v1
2016/7/11,Additive interfacial chiral interaction in multilayers for stabilization of small individual skyrmion at room temperature,"Facing the ever-growing demand for data storage will most probably require a
new paradigm. Nanoscale magnetic skyrmions are anticipated to solve this issue
as they are arguably the smallest spin textures in magnetic thin films in
nature. We designed cobalt-based multilayered thin films where the cobalt layer
is sandwiched between two heavy metals providing additive interfacial
Dzyaloshinskii-Moriya interactions, which reach a value close to 2 mJ m-2 in
the case of the Ir|Co|Pt asymmetric multilayers. Using a
magnetization-sensitive scanning x-ray transmission microscopy technique, we
imaged small magnetic domains at very low field in these multilayers. The study
of their behavior in perpendicular magnetic field allows us to conclude that
they are actually magnetic skyrmions stabilized by the large
Dzyaloshinskii-Moriya interaction. This discovery of stable sub-100 nm
individual skyrmions at room temperature in a technologically relevant material
opens the way for device applications in a near future.",1607.02958v1
2016/7/12,Thermodynamic transport theory of spin waves in ferromagnetic insulators,"We use the Boltzmann transport theory in the relaxation time approximation to
describe the thermal transport of spin waves in a ferromagnet. By treating spin
waves as magnon excitations we are able to compute analytically and numerically
the coefficients of the constitutive thermo-magnetic transport equations. As a
main result, we find that the absolute thermo-magnetic power coefficient
$\epsilon_M$, relating the gradient of the potential of the magnetization
current and the gradient of the temperature, in the limit of low temperature
and low field, is a constant $\epsilon_M = -0.6419 \, k_B/\mu_B$. The theory
correctly describes the low-temperature and magnetic-field dependencies of spin
Seebeck experiments. Furthermore, the theory predicts that in the limit of very
low temperatures the spin Peltier coefficient $\Pi_M$, relating the heat and
the magnetization currents, tends to a finite value which depends on the
amplitude of the magnetic field. This indicates the possibility to exploit the
spin Peltier effect as an efficient cooling mechanism in cryogenics.",1607.03301v3
2016/8/21,Manipulating antiferromagnets with magnetic fields: ratchet motion of multiple domain walls induced by asymmetric field pulses,"Future applications of antiferromagnets (AFs) in many spintronics devices
rely on the precise manipulation of domain walls. The conventional approach
using static magnetic fields is inefficient due to the low susceptibility of
AFs. Recently proposed electrical manipulation with spin-orbit torques is
restricted to metals with a specific crystal structure.
  Here we propose an alternative, broadly applicable approach: using asymmetric
magnetic field pulses to induce controlled ratchet motion of AF domain walls.
  The efficiency of this approach is based on three peculiarities of AF
dynamics. First, a time-dependent magnetic field couples with an AF order
parameter stronger than a static magnetic field, which leads to higher mobility
of the domain walls. Second, the rate of change of the magnetic field couples
with the spatial variation of the AF order parameter inside the domain and this
enables synchronous motion of multiple domain walls with the same structure.
Third, tailored asymmetric field pulses in combination with static friction can
prevent backward motion of domain walls and thus lead to the desired controlled
ratchet effect.
  The proposed use of an external field, rather than internal spin-orbit
torques, avoids any restrictions on size, conductivity, and crystal structure
of the AF material.
  We believe that our approach paves a way for the development of new AF-based
devices based on controlled motion of AF domain walls.",1608.05967v1
2016/9/26,Mechanical force involved multiple fields switching of both local ferroelectric and magnetic domain in a Bi5Ti3FeO15 thin film,"Multiferroics have received intense attention due to their great application
potential in multi-state information storage devices and new types of sensors.
Coupling among ferroic orders such as ferroelectricity, (anti-)ferromagnetism,
ferroelasticity, etc. will enable dynamic interaction between these ordering
parameters. Direct visualization of such coupling behaviour in single phase
multiferroic materials is highly desirable for both applications and
fundamental study. Manipulation of both ferroelectric and magnetic domains of
Bi5Ti3FeO15 thin film using electric field and external mechanical force is
reported, which confirms the magnetoelectric coupling in Bi5Ti3FeO15, indicates
the electric and magnetic orders are coupled through ferroelasticity. Due to
the anisotropic relaxation of ferroelastic strain, the back-switching of
out-of-plane electric domains is not as obvious as in-plane. An inevitable
destabilization of the coupling between elastic and magnetic ordering happens
because of the elastic strain relaxation, which result in a subsequent decay of
magnetic domain switching. Mechanical force applied on the surface of
Bi5Ti3FeO15 film generates by an AFM tip will effectively drive a transition of
the local ferroelastic strain state, reverse both the polarization and
magnetization in a way similar to an electric field. Current work provides a
framework for exploring cross-coupling among multiple orders and potential for
developing novel nanoscale functional devices.",1609.07831v1
2017/1/30,Antiferromagnetism in the van der Waals layered spin-lozenge semiconductor CrTe3,"The crystallographic, magnetic, and transport properties of the van der Waals
bonded, layered compound CrTe3 have been investigated on single crystal and
polycrystalline materials. The crystal structure contains layers made up of
lozenge shaped Cr_4 tetramers. Electrical resistivity measurements show the
crystals to be semiconducting, with a temperature dependence consistent with a
band gap of 0.3eV. The magnetic susceptibility exhibits a broad maximum near
300K characteristic of low dimensional magnetic systems. Weak anomalies are
observed in the susceptibility and heat capacity near 55K, and single crystal
neutron diffraction reveals the onset of long range antiferromagnetic order at
this temperature. Strongly dispersive spin-waves are observed in the ordered
state. Significant magneto-elastic coupling is indicated by the anomalous
temperature dependence of the lattice parameters and is apparent in structural
optimization in van der Waals density functional theory calculations for
different magnetic configurations. The cleavability of the compound is apparent
from its handling and is confirmed by first principles calculations, which
predict a cleavage energy 0.5J/m^2, similar to graphite. Based on these
results, CrTe3 is identified as a promising compound for studies of low
dimensional magnetism in bulk crystals as well as magnetic order in monolayer
materials and van der Waals heterostructures.",1701.08621v2
2017/3/21,Annealing stability of magnetic tunnel junctions based on dual MgO free layers and [Co/Ni] based thin synthetic antiferromagnet fixed system,"We study the annealing stability of bottom-pinned perpendicularly magnetized
magnetic tunnel junctions based on dual MgO free layers and thin fixed systems
comprising a hard [Co/Ni] multilayer antiferromagnetically coupled to thin a Co
reference layer and a FeCoB polarizing layer. Using conventional magnetometry
and advanced broadband ferromagnetic resonance, we identify the properties of
each sub-unit of the magnetic tunnel junction and demonstrate that this
material option can ensure a satisfactory resilience to the 400$^\circ$C
thermal annealing needed in solid-state magnetic memory applications. The dual
MgO free layer possesses an anneal-robust 0.4 T effective anisotropy and
suffers only a minor increase of its Gilbert damping from 0.007 to 0.010 for
the toughest annealing conditions. Within the fixed system, the ferro-coupler
and texture-breaking TaFeCoB layer keeps an interlayer exchange above 0.8
mJ/m$^2$, while the Ru antiferrocoupler layer within the synthetic
antiferromagnet maintains a coupling above -0.5 mJ/m$^2$. These two strong
couplings maintain the overall functionality of the tunnel junction upon the
toughest annealing despite the gradual degradation of the thin Co layer
anisotropy that may reduce the operation margin in spin torque memory
applications. Based on these findings, we propose further optimization routes
for the next generation magnetic tunnel junctions.",1703.07154v1
2017/5/1,Cycloidal magnetism driven ferroelectricity in double tungstate LiFe(WO$_4$)$_2$,"Tungstates $A$WO$_4$ with the wolframite structure characterized by the
$A$O$_6$ octahedral zigzag chains along the $c$-axis, can be magnetic if
$A$=Mn, Fe, Co, Cu, Ni. Among them, MnWO$_4$ is a unique member with a cycloid
Mn$^{2+}$ spin order developed at low temperature, leading to an interesting
type-II multiferroic behavior. However, so far no other multiferroic material
in the tungstate family has been found. In this work, we present the synthesis
and the systematic study of the double tungstate LiFe(WO$_4$)$_2$. Experimental
characterizations including structural, thermodynamic, magnetic, neutron powder
diffraction, and pyroelectric measurements, unambiguously confirm that
LiFe(WO$_4$)$_2$ is the secondly found multiferroic system in the tungstate
family. The cycloidal magnetism driven ferroelectricity is also verified by
density functional theory calculations. Although here the magnetic couplings
between Fe ions are indirect, namely via the so-called super-super-exchanges,
the temperatures of magnetic and ferroelectric transitions are surprisingly
much higher than those of MnWO$_4$.",1705.00476v1
2017/5/3,Linearly polarized GHz magnetization dynamics of spin helix modes in the ferrimagnetic insulator Cu$_{2}$OSeO$_{3}$,"Linear dichroism -- the polarization dependent absorption of electromagnetic
waves -- is routinely exploited in applications as diverse as structure
determination of DNA or polarization filters in optical technologies. Here
filamentary absorbers with a large length-to-width ratio are a prerequisite.
For magnetization dynamics in the few GHz frequency regime strictly linear
dichroism was not observed for more than eight decades. Here, we show that the
bulk chiral magnet Cu$_{2}$OSeO$_{3}$ exhibits linearly polarized magnetization
dynamics at an unexpectedly small frequency of about 2 GHz. Unlike optical
filters that are assembled from filamentary absorbers, the magnet provides
linear polarization as a bulk material for an extremely wide range of
length-to-width ratios. In addition, the polarization plane of a given mode can
be switched by 90$^\circ$ via a tiny variation in width. Our findings shed a
new light on magnetization dynamics in that ferrimagnetic ordering combined
with anisotropic exchange interaction offers strictly linear polarization and
cross-polarized modes for a broad spectrum of sample shapes. The discovery
allows for novel design rules and optimization of microwave-to-magnon
transduction in emerging microwave technologies.",1705.01582v1
2017/6/29,Reconfigurable topological spin wave beamsplitters and interferometers,"Conventional magnonic devices use three classes of magnetostatic waves that
require detailed manipulation of magnetization structure that makes the design
and the device/circuitry scalability difficult tasks. Here, we demonstrate that
devices based on topological exchange spin waves do not suffer from the problem
with additional nice features of nano-scale wavelength and high frequency. Two
results are reported. 1) A perpendicular ferromagnet on a honeycomb lattice is
generically a topological magnetic material in the sense that topologically
protected chiral edge spin waves exist in the band gap as long as spin-orbit
induced nearest-neighbor pseudodipolar interaction (and/or next-nearest
neighbor Dzyaloshinskii-Moriya interaction) is present. 2) As a proof of
concept, spin wave beamsplitters and spin wave interferometers are designed by
using domain walls to manipulate the propagation of topologically protected
chiral spin waves. Since magnetic domain walls can be controlled by magnetic
fields or electric current/fields, one can essentially draw, erase and redraw
different spin wave devices and circuitry on the same magnetic plate so that
the proposed devices are reconfigurable and tunable. Devices made from magnetic
topological materials are robust against both internal and external
perturbations such as the spin wave frequency variation and device geometry as
well as defects.",1706.09548v2
2017/8/10,Magnetic anisotropy of the alkali iridate Na$_{2}$IrO$_{3}$ at high magnetic fields: evidence for strong ferromagnetic Kitaev correlations,"The magnetic field response of the Mott-insulating honeycomb iridate
Na$_{2}$IrO$_{3}$ is investigated using torque magnetometry measurements in
magnetic fields up to 60 tesla. A peak-dip structure is observed in the torque
response at magnetic fields corresponding to an energy scale close to the
zigzag ordering ($\approx 15~K$) temperature. Using exact diagonalization
calculations, we show that such a distinctive signature in the torque response
constrains the effective spin models for these classes of Kitaev materials to
ones with dominant ferromagnetic Kitaev interactions, while alternative models
with dominant antiferromagnetic Kitaev interactions are excluded. We further
show that at high magnetic fields, long range spin correlation functions decay
rapidly, signaling a transition to a long-sought-after field-induced quantum
spin liquid beyond the peak-dip structure. Kitaev systems are thus revealed to
be excellent candidates for field-induced quantum spin liquids, similar physics
having been suggested in another Kitaev material $\alpha-$RuCl$_{3}$.",1708.03235v5
2017/10/12,Magnetic monolayer Li$_{2}$N: Density Functional Theory Calculations,"Density functional theory (DFT) calculations are used to investigate the
electronic and magnetic structures of a two-dimensional (2D) monolayer
Li$_{2}$N. It is shown that bulk Li$_{3}$N is a non-magnetic semiconductor. The
non-spinpolarized DFT calculations show that $p$ electrons of N in 2D Li$_{2}$N
form a narrow band at the Fermi energy $E_{\rm{F}}$ due to a low coordination
number, and the density of states at the Fermi energy ($g(E_{\rm{F}}$)) is
increased as compared with bulk Li$_{3}$N. The large $g(E_{\rm{F}}$) shows
instability towards magnetism in Stoner's mean field model. The spin-polarized
calculations reveal that 2D Li$_{2}$N is magnetic without intrinsic or impurity
defects. The magnetic moment of 1.0\,$\mu_{\rm{B}}$ in 2D Li$_{2}$N is mainly
contributed by the $p_{z}$ electrons of N, and the band structure shows
half-metallic behavior. {Dynamic instability in planar Li$_{2}$N monolayer is
observed, but a buckled Li$_{2}$N monolayer is found to be dynamically stable.}
The ferromagnetic (FM) and antiferromagnetic (AFM) coupling between the N atoms
is also investigated to access the exchange field strength. {We found that
planar (buckled) 2D Li$_{2}$N is a ferromagnetic material with Curie
temperature $T_{c}$ of 161 (572) K.}",1710.04440v1
2018/1/28,Hierarchies of Length Scale Based Typology in Anisotropic Multiband Superconductor,"Since Ginzburg and Landau's seminal work in 1950 superconducting states have
been classified by the hierarchy of the fundamental length scales of the
theory; the magnetic field penetration lengths and coherence lengths. In the
simplest single-component case they form a dimensionless ratio \kappa. As
pointed out by Ginzburg in 1952, in general the ratio depends on the direction
of the applied magnetic field due to material anisotropies. Single component
materials can therefore display type-1 superconductivity when the field is
applied in one direction and type-2 when the field is applied in a different
direction. In this paper we expand the above length scale analysis to
anisotropic multi-component superconductors, that can have multiple coherence
lengths as well as multiple magnetic field penetration lengths, leading to
unconvential length scale hierarchies. We demonstrate that the anisotropies in
multi-band superconductors cannot in general be rescaled, leading to new
regimes with various mixed hierarchies in different directions. For example, a
regime is possible, where for a field applied in a certain direction coherence
lengths are smaller than the magnetic field penetration lengths in one of the
perpendicular directions, where as the penetration lengths are lager in the
another direction. We demonstrate a new regime, where vortices form stripes in
the direction where coherence lengths exceed the magnetic field penetration
length and vortex cores overlap, while the vortex stripes repel each other in
the orthogonal direction where the magnetic field penetration length exceeds
the coherence lengths.",1801.09274v2
2018/3/7,Spheroidal and conical shapes of ferrofluid-filled capsules in magnetic fields,"We investigate the deformation of soft spherical elastic capsules filled with
a ferrofluid in external uniform magnetic fields at fixed volume by a
combination of numerical and analytical approaches. We develop a numerical
iterative solution strategy based on nonlinear elastic shape equations to
calculate the stretched capsule shape numerically and a coupled finite element
and boundary element method to solve the corresponding magnetostatic problem,
and employ analytical linear response theory, approximative energy
minimization, and slender-body theory. The observed deformation behavior is
qualitatively similar to the deformation of ferrofluid droplets in uniform
magnetic fields. Homogeneous magnetic fields elongate the capsule, and a
discontinuous shape transition from a spheroidal shape to a conical shape takes
place at a critical field strength. We investigate how capsule elasticity
modifies this hysteretic shape transition. We show that conical capsule shapes
are possible but involve diverging stretch factors at the tips, which gives
rise to rupture for real capsule materials. In a slender-body approximation we
find that the critical susceptibility above which conical shapes occur for
ferrofluid capsules is the same as for droplets. At small fields capsules
remain spheroidal, and we characterize the deformation of spheroidal capsules
both analytically and numerically. Finally, we determine whether wrinkling of a
spheroidal capsule occurs during elongation in a magnetic field and how it
modifies the stretching behavior. We find the nontrivial dependence between the
extent of the wrinkled region and capsule elongation. Our results can be
helpful in order to quantitatively determine capsule or ferrofluid material
properties from magnetic deformation experiments. All results also apply to
elastic capsules filled with a dielectric liquid in an external uniform
electric field.",1803.02607v2
2018/3/7,Magnetoresistance in Hybrid Pt/CoFe2O4 Bilayers Controlled by Competing Spin Accumulation and Interfacial Chemical Reconstruction,"Pure spin currents hold promises for an energy-friendlier spintronics. They
can be generated by a flow of charge along a non-magnetic metal having a large
spin-orbit coupling. It produces a spin accumulation at its surfaces,
controllable by the magnetization of an adjacent ferromagnetic layer.
Paramagnetic metals typically used are close to a ferromagnetic instability and
thus magnetic proximity effects can contribute to the observed
angular-dependent magnetoresistance (ADMR). As interface phenomena govern the
spin conductance across the metal/ferromagnetic-insulator heterostructures,
unraveling these distinct contributions is pivotal to full understanding of
spin current conductance. We report here x-ray absorption and magnetic circular
dichroism (XMCD) at Pt-M and (Co,Fe)-L absorption edges and atomically-resolved
energy loss electron spectroscopy (EELS) data of Pt/CoFe2O4 bilayers where
CoFe2O4 layers have been capped by Pt grown at different temperatures. It turns
out that the ADMR differs dramatically, being either dominated by spin Hall
magnetoresistance (SMR) associated to spin Hall effect or anisotropic
magnetoresistance (AMR). The XMCD and EELS data indicate that the Pt layer
grown at room temperature does not display any magnetic moment, whereas when
grown at higher temperature it is magnetic due to interfacial Pt-(Co,Fe)
alloying. These results allow disentangling spin accumulation from interfacial
chemical reconstructions and for tailoring the angular dependent
magnetoresistance.",1803.02611v1
2018/3/7,Magnetically-defined topological edge plasmons in edgeless electron gas,"Topological materials bear gapped excitations in bulk yet protected gapless
excitations at boundaries. Magnetoplasmons (MPs), as high-frequency density
excitations of two-dimensional electron gas (2DEG) in a perpendicular magnetic
field, embody a prototype of band topology for bosons. The
time-reversal-breaking magnetic field opens a topological gap for bulk MPs up
to the cyclotron frequency; topologically-protected edge magnetoplasmons (EMPs)
bridge the bulk gap and propagate unidirectionally along system's boundaries.
However, all the EMPs known to date adhere to physical edges where the electron
density terminates abruptly. This restriction has made device application
extremely difficult. Here we demonstrate a new class of topological edge
plasmons -- domain-boundary magnetoplasmons (DBMPs), within a uniform edgeless
2DEG. Such DBMPs arise at the domain boundaries of an engineered sign-changing
magnetic field and are protected by the difference of gap Chern numbers (+/-1)
across the magnetic domains. They propagate unidirectionally along the domain
boundaries and are immune to domain defects. Moreover, they exhibit wide
tunability in the microwave frequency range under an applied magnetic field or
gate voltage. Our study opens a new direction to realize high-speed
reconfigurable topological devices.",1803.02913v1
2018/4/11,Interplay between structure and magnetism in the low-dimensional spin system $K(C_8H_{16}O_4)_2CuCl_3{*}H_2O$,"Materials based on a crown ether complex together with magnetic ions,
especially Cu(II), can be used to synthesize new low dimesional quantum spin
systems. We have prepared the new crown ether complex
Di-\mu-chloro-bis(12-crown-4)-aquqdichloro-copper(II)-potassium,
$K(C_8H_{16}O_4)_2CuCl_3{*}H_2O$ (1), determined its structure, and analyzed
its magnetic properties. Complex (1) has a monoclinic structure and
crystallizes in space group $P2_1/n$ with the lattice parameters of
$a=9.5976(5)\r{A}$, $b=11.9814\r{A}, c=21.8713\r{A}$ and
$\beta=100.945(4)\deg$. The magnetic properties of this compound have been
investigated in the temperature range 1.8 K - 300 K. The magnetic
susceptibility shows a maximum at 23 K, but no 3-D long range magnetic order
down to 1.8 K. The S=1/2 Cu(II) ions form antiferromagnetically coupled dimers
with Cu-Cl distances of $2.2554(8)\r{A}$ and $4.683(6)\r{A}$, and a Cu-Cl-Cu
angle of $115.12(2)\deg$ with $2J_{dimer}=-2.96meV (-23.78 cm^{-1})$. The
influence of $H_2O$ on the Cl-Cu-Cl exchange path is analyzed. Our results show
that the values of the singlet-triplet splitting are increasing considering
$H_2O$ molecules in the bridging interaction. This is supported by Density
functional theory (DFT) calculations of coupling constants with Perdew and Wang
(PWC), Perdew, Burke and Ernzenrhof (PBE) and strongly constrained and
appropriately normed (SCAN) exchange-correlation function show excellent
agreement for the studied compound.",1804.03849v2
2018/4/21,The effect of adding magnetic oxide as grain boundary for HAMR,"Grain-to-grain Curie temperature (Tc) variation in the media reduces
signal-to-noise ratio due to its contribution in transition jitter noise,
especially when average grain size is pushing down to increase the area storage
capacity. A thermally insulating magnetic grain boundary may suppress such
grain-to-grain Tc variation, especially at small grain size. Here we present an
experimental study on the effect of adding thermally-insulating magnetic oxide,
in particular BaFexOy, as part of the grain boundary materials in granular
FePt-C HAMR media. It is found that the BaFexOy is chemically inert to FePt and
the chemical ordering of FePt-BaFexOy-C media are similar to that of FePt-C
meida. By tuning the volume fraction of BaFexOy and C, well-separated FePt
grains (average grain size = 6.8 nm) surrounded by BaFexOy shell with
perpendicular Hc above 35 kOe can be obtained. Transmission electron microscopy
study with chemical analysis shows that the magnetic oxide appears to be
crystalline and surround the FePt grains with immediate full enclosure.
Magnetic measurements indicate an effective increase of magnetic grain size at
temperatures below FePt Curie temperature. Pulsed laser pump-probe measurement
indicates a measurable reduction of Curie temperature variation for the
FePt-BaFexOy-C media with carefully comparison with the reference FePt-C media.",1804.07892v1
2018/5/4,Heat transport of cuprate-based low-dimensional quantum magnets with strong exchange coupling,"Transport properties provide important access to a solid's quasiparticles,
such as quasiparticle density, mobility, and scattering. The transport of heat
can be particularly revealing because, in principle, all types of excitations
in a solid may contribute. Heat transport is well understood for phonons and
electrons, but relatively little is known about heat transported by magnetic
excitations. However, during the last about two decades, the magnetic heat
transport attracted increasing attention after the discovery of large and
unusual signatures of it in low-dimensional quantum magnetic cuprate materials.
Today it constitutes an important probe to otherwise often elusive, topological
quasiparticles in a broader class of quantum magnets. This review summarizes
the experimental foundation of this research, i.e. the state of the art for the
magnetic heat transport in the mentioned cuprate materials which host
prototypical low-dimensional antiferromagnetic $S=1/2$ Heisenberg models. These
comprise, in particular, the two-dimensional square lattice, and
one-dimensional spin chain and two-leg ladder spin models. It is shown, how
studying the heat transport provides direct access to the thermal occupation
and the scattering of the already quite exotic quasiparticles of these models
which range from spin-1 spin wave and triplon excitations to fractionalized
spin-1/2 spinons. Remarkable transport properties of these quasiparticles have
been revealed: the spin-heat transport often is highly efficient and in some
cases even ballistic, in agreement with theoretical predictions.",1805.01746v2
2018/5/4,Selective measurements of intertwined multipolar orders: non-Kramers doublets on a triangular lattice,"Motivated by the rapid experimental progress on the spin-orbit-coupled Mott
insulators, we propose and study a generic spin model that describes the
interaction between the non-Kramers doublets on a triangular lattice and is
relevant for triangular lattice rare-earth magnets. We predict that the system
supports both pure quadrupolar orders and intertwined multipolar orders in the
phase diagram. Besides the multipolar orders, we explore the magnetic
excitations to reveal the dynamic properties of the systems. Due to the
peculiar properties of the non-Kramers doublets and the selective coupling to
the magnetic field, we further study the magnetization process of the system in
the magnetic field. We point out the selective measurements of the static and
dynamic properties of the intertwined multipolarness in the neutron scattering,
NMR and $\mu$SR probes and predict the experimental consequences. The relevance
to the existing materials such as TmMgGaO$_{4}$, Pr-based and Tb-based magnets,
and many ternary chalcogenides is discussed. Our results illustrate the rich
physics and the promising direction in the interplay between strong
spin-orbit-entangled multipole moments and the geometrical frustration.",1805.01865v3
2018/5/17,L10 Fe-Pd Synthetic Antiferromagnet through an fcc Ru Spacer Utilized for Perpendicular Magnetic Tunnel Junctions,"Magnetic materials that possess large bulk perpendicular magnetic anisotropy
(PMA) are essential for the development of magnetic tunnel junctions (MTJs)
used in future spintronic memory and logic devices. The addition of an
antiferromagnetic layer to these MTJs was recently predicted to facilitate
ultra-fast magnetization switching. Here, we report a demonstration of a bulk
perpendicular synthetic antiferromagnetic (P-SAFM) structure comprised of a
(001) textured FePd/Ru/FePd trilayer with a face-centered-cubic (fcc) phase Ru
spacer. The L10 FePd P-SAFM structure shows a large bulk PMA (~10.2 Merg/cc)
and strong antiferromagnetic coupling (~2.60 erg/cm2). Full perpendicular
magnetic tunnel junctions (P-MTJs) with a L10 FePd P-SAFM layer are then
fabricated. Tunneling magnetoresistance ratios of up to ~25% (~60%) are
observed at room temperature (5K) after post-annealing at 350 C. Exhibiting
high thermal stabilities and large Ku, the bulk P-MTJs with an L10 FePd P-SAFM
layer could pave a way for next-generation ultrahigh-density and
ultra-low-energy spintronic applications.",1805.06942v1
2018/6/4,Magnetic oscillations in silicene,"In this work the magnetic oscillations (MO) in pristine silicene at $T=0$ K
are studied. Considering a constant electron density we obtain analytical
expressions for the ground state internal energy and magnetization, under a
perpendicular electric and magnetic field, taking in consideration the Zeeman
effect. It is found that the MO are sawtooth-like, depending on the change in
the last occupied energy level. This leads us to a classification of the MO
peaks in terms of the Landau level (LL), valley or spin changes. Using this
classification we analyze the MO for different values of the electric field
$E_{z}$. When $E_{z}=0$, the energy levels have a valley degeneracy and the MO
peaks occur only whenever the last energy level changes its LL and/or spin.
When $E_{z}\neq0$, the valley degeneracy is broken and new MO peaks appear,
associated with the valley change in the last energy level. By analyzing the MO
peaks amplitude it is possible to extract information about the Fermi velocity
and the spin-orbit interaction strength. Finally we analyze the MO frequencies,
which can also be associated with the change of LL, valley or spin in the last
energy level.",1806.01415v1
2018/6/6,General Relativistic Razor-Thin Disks with Magnetically Polarized Matter,"The origin of magnetic fields in the universe still remains unknown and
constitutes one of the most intriguing questions in astronomy and astrophysics.
Their significance is enormous since they have a strong influence on many
astrophysical phenomena. In regards of this motivation, theoretical models of
galactic disks with sources of magnetic field may contribute to understand the
physics behind them. Inspired by this, we present a new family of analytical
models for thin disks composed by magnetized material. The solutions are
axially symmetric, conformastatic and are obtained by solving the
Einstein-Maxwell Field Equations for continuum media without the test field
approximation, and assuming that the sources are razor-thin disk of
magnetically polarized matter. We find analytical expressions for the surface
energy density, the pressure, the polarization vector, the electromagnetic
fields, the mass and the rotational velocity for circular orbits, for two
particular solutions. In each case, the energy-momentum tensor agrees with the
energy conditions and also the convergence of the mass for all the solutions is
proved. Since the solutions are well-behaved, they may be used to model
astrophysical thin disks, and also may contribute as initial data in numerical
simulations. In addition, the process to obtain the solutions is described in
detail, which may be used as a guide to find solutions with magnetized material
in General Relativity.",1806.02280v1
2018/7/26,"Quantum Magnetism, Spin Waves, and Light","Both magnetic materials and light have always played a predominant role in
information technologies, and continue to do so as we move into the realm of
quantum technologies. In this course we review the basics of magnetism and
quantum mechanics, before going into more advanced subjects. Magnetism is
intrinsically quantum mechanical in nature, and magnetic ordering can only be
explained by use of quantum theory. We will go over the interactions and the
resulting Hamiltonian that governs magnetic phenomena, and discuss its
elementary excitations, denominated magnons. After that we will study
magneto-optical effects and derive the classical Faraday effect. We will then
move on to the quantization of the electric field and the basics of optical
cavities. This will allow us to understand a topic of current research
denominated Cavity Optomagnonics. These notes were written as the accompanying
material to the course I taught in the Summer Semester 2018 at the
Friedrich-Alexander University in Erlangen. The course is intended for Master
or advanced Bachelor students. Basic knowledge of quantum mechanics,
electromagnetism, and solid state at the Bachelor level is assumed. Each
section is followed by a couple of simple exercises which should serve as to
""fill in the blanks"" of what has been derived, plus specific references to
bibliography, and a couple of check-points for the main concepts developed. The
figures are pictures of the blackboard taken during the lecture.",1807.10626v2
2018/10/17,Critical behavior and magnetocaloric effect in ferromagnetic nano-crystalline Pr$_2$CoMnO$_6$,"To understand the nature of magnetic phase transition in nano-crystalline
Pr$_2$CoMnO$_6$, in present study we have investigated the critical behavior
and magnetocaloric effect. To estimate the critical exponents, various methods
have been adopted like; the modified Arrott plots (MAP), the Kouvel-Fisher
method (KF) and the critical isotherm analysis. This material shows a second
order type a paramagnetic (PM) to ferromagnetic (FM) phase transition around
160 K. The critical exponents obtained from modified Arrott plots are $\beta$ =
0.531, $\gamma$ = 0.935 and $T_c$ = 160 K. Kouvel-Fisher method gives the
exponents as $\beta$ = 0.533$\pm$0.001 with $T_c$ = 160.72$\pm$0.03 K and
$\gamma$ = 0.932$\pm$0.003 with $T_c$ = 160.15$\pm$0.05 K. The third exponent
$\delta$ = 2.763$\pm$0.005 obtained from critical isothermal is in agreement
with Wisdom scaling rule. The estimated critical exponents do not exactly match
with any established universality class, however, the deduced exponent values
suggest that spin interaction in the present material is close to mean-field
model which suggests the existence of long-range ferromagnetic order in
nano-crystalline Pr$_2$CoMnO$_6$. The reliability of critical exponents is
checked by universal scaling hypothesis on magnetic data across T$_c$. We have
calculated the magnetic entropy change from magnetic data and found maximum
value of -$\Delta$S = 2.05 (J kg$^{-1}$ K$^{-1}$) for 50 kOe at 180 K.
Moreover, field dependent change in magnetic entropy obeys scaling and also
indicates that the magnetic interaction is close to mean-field type.",1810.07602v1
2018/10/31,Transverse Magneto-Optical Kerr Effect at Narrow Optical Resonances,"Magneto-optical spectroscopy based on the transverse magneto-optical Kerr
effect (TMOKE) is a sensitive method for investigation of magnetically-ordered
media. However, in magnetic materials the optical transitions are usually
characterized by spectrally broad resonances with widths considerably exceeding
the Zeeman splitting in the magnetic field. Here we investigate experimentally
and theoretically the TMOKE in the vicinity of relatively narrow optical
resonances provided by confined quantum systems. For experimental demonstration
we use the exciton resonance in a (Cd,Mn)Te diluted magnetic semiconductor
quantum well, where the strong exchange interaction with magnetic ions enables
the giant Zeeman splitting of exciton spin states $\Delta$ in magnetic fields
of a few Tesla. In the weak coupling regime, when the splitting $\Delta$ is
smaller than the spectral broadening of the optical transitions $\Gamma$, the
TMOKE magnitude grows linearly with the increase of the Zeeman splitting and
its spectrum has an S-shape, which remains virtually unchanged in this range.
In the strong coupling regime ($\Delta>\Gamma$) the TMOKE magnitude saturates,
while its spectrum is strongly modified resulting in the appearance of two
separate peaks. The TMOKE is sensitive not only to the sample surface but can
be used to probe the confined electronic states in depth if the upper layer is
sufficiently transparent. Our results demonstrate that TMOKE of spectrally
narrow resonances serves as a versatile tool for probing the charge and spin
structure of electronic states in various confined quantum systems and can be
used for spin tomography in combination with the conventional polar Kerr
effect.",1810.13344v1
2018/11/19,Magnetic Excitations in Non-Collinear Antiferromagnetic Weyl Semimetal $\mathsf{Mn_{3}Sn}$,"$\mathsf{Mn_{3}Sn}$ has recently attracted considerable attention as a
magnetic Weyl semimetal exhibiting concomitant transport anomalies at room
temperature. The topology of the electronic bands, their relation to the
magnetic ground state and their nonzero Berry curvature lie at the heart of the
problem. The examination of the full magnetic Hamiltonian reveals otherwise
hidden aspects of these unusual physical properties. Here, we report the full
spin wave spectra of $\mathsf{Mn_{3}Sn}$ measured over a wide momentum - energy
range by the inelastic neutron scattering technique. Using a linear spin wave
theory, we determine a suitable magnetic Hamiltonian which not only explains
the experimental results but also stabilizes the low-temperature helical phase,
consistent with our DFT calculations. The effect of this helical ordering on
topological band structures is further examined using a tight-binding method,
which confirms the elimination of Weyl points in the helical phase. Our work
provides a rare example of the intimate coupling between the electronic and
spin degrees of freedom for a magnetic Weyl semimetal system.",1811.07549v1
2018/12/2,Direct detection of induced magnetic moment and efficient spin-to-charge conversion in graphene/ferromagnetic structures,"This article shows that the spin-to-charge current conversion in single-layer
graphene (SLG) by means of the inverse Rashba-Edelstein effect (IREE) is made
possible with the integration of this remarkable 2D-material with the unique
ferrimagnetic insulator yttrium iron garnet (YIG = $Y_{3}Fe_{5}O_{12}$) as well
as with the ferromagnetic metal permalloy (Py = $Ni_{81}Sb_{19}$). By means of
X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD)
techniques, we show that the carbon atoms of the SLG acquires an induced
magnetic moment due to the proximity effect with the magnetic layer. The spin
currents are generated in the magnetic layer by spin pumping from microwave
driven ferromagnetic resonance and are detected by a dc voltage along the
graphene layer, at room temperature. The spin-to-charge current conversion,
occurring at the graphene layer, is explained by the extrinsic spin-orbit
interaction (SOI) induced by the proximity effect with the ferromagnetic layer.
The results obtained for the SLG/YIG and SLG/Py systems confirm very similar
values for the IREE parameter, which are larger than the values reported in
previous studies for SLG. We also report systematic investigations of the
electronic and magnetic properties of the SLG/YIG by means of scanning
tunneling microscopy (STM).",1812.00455v1
2018/12/24,Non-Reciprocal Spin Pumping in Asymmetric Magnetic Trilayers,"In magnetic trilayer systems, spin pumping is generally addressed as a
reciprocal mechanism characterized by one unique spin mixing conductance common
to both interfaces. However, this assumption is questionable in cases where
different types of interfaces are present in the material. Here, we present a
general theory for analyzing spin pumping in cases with more than one unique
interface. The theory is applied to analyze layer-resolved ferromagnetic
resonance experiments on the trilayer system
Ni$_{20}$Fe$_{80}$/Ru/Fe$_{49}$Co$_{49}$V$_2$ where the Ru spacer thickness is
varied to tune the indirect exchange coupling. The results show that the spin
pumping in trilayer systems with dissimilar magnetic layers is non-reciprocal,
with a surprisingly large difference between spin-pumping induced damping of
different interfaces. Our findings have importance on dynamics of spintronic
devices based on magnetic multilayer materials.",1812.09978v1
2019/2/27,Deterministic field-free skyrmion nucleation at a nano-engineered injector device,"Magnetic skyrmions are topological solitons that exhibit an increased
stability against annihilation, and can be displaced with low current
densities, making them a promising candidate as an information carrier. In
order to demonstrate a viable skyrmion-based memory device, it is necessary to
reliably and reproducibly nucleate, displace, detect, and delete the magnetic
skyrmions. While the skyrmion displacement and detection have both been
investigated in detail, much less attention has been dedicated to the study of
the sub-ns dynamics of the skyrmion nucleation process. Only limited studies on
the statics and above-ns dynamics have been performed, leaving still many open
questions on the dynamics of the nucleation process. Furthermore, the vast
majority of the presently existing studies focus on the nucleation from random
natural pinning sites, or from patterned constrictions in the magnetic material
itself, which limit the functionality of the skyrmion-based device. Those
limitations can be overcome by the fabrication of a dedicated injector device
on top of the magnetic material. In this study, we investigate the nucleation
of magnetic skyrmions from a dedicated nano-engineered injector, demonstrating
the reliable magnetic skyrmion nucleation at the remnant state. The sub-ns
dynamics of the skyrmion nucleation process were also investigated, allowing us
to shine light on the physical processes driving the nucleation.",1902.10435v1